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May 28

Cat physiology

Do cats enjoy chilled water in their bowl? My observation is that they do not, even on hot days. Is there a reason for this? Thanks. Viriditas (talk) 02:26, 28 May 2009 (UTC)

Maybe it is a matter of taste. Try putting identical amounts of room temp and refrigerated water in bowls, and check an hour later how much is left in each. Repeat the next day to make sure. Then try intermediate temps to find the ideal. Maybe someone can make sure that cats are not somehow harmed by cold water. Edison (talk) 03:37, 28 May 2009 (UTC)

Googling for 'cat cold water' finds stuff like this, with some cats demanding ice water from their human slaves. If you see evidence to the contrary then a matter of taste it must be. 62.78.198.48 (talk) 08:01, 28 May 2009 (UTC)

Water from the fridge usually has less oxygen in it than agitated water. If you keep it in a jug, shake the jug before pouring the water. On the other hand some cats prefer mud-puddle water to both tap and bottled water. They usually prefer their food an drink at room temp. Very cold food can upset their stomachs. That is why you shouldn't store cat food in the fridge. (..and don't reheat it in the microwave because that can harden cartilage and collagen pieces in the food and also upset their stomach.) Most of the time, all that will happen is that they'll throw up. They do that without much sign of later discomfort. (Also in case of hairballs.) Cleanup in aisle 2 :-) 71.236.24.129 (talk) 08:00, 28 May 2009 (UTC)

Cats are not as different to dogs as they like us to think. Hot dogs use their tongues for cooling. Cuddlyable3 (talk) 10:16, 28 May 2009 (UTC)

Tongues? Man, they really do put gross stuff in hot dogs. — DanielLC 14:52, 28 May 2009 (UTC)

• Even when our cat has a bowl full of water, he calls us to open up the kitchen door to allow him to go outside and drink rain water. (That cat is full of surprises...) - Mgm|^(talk) 09:57, 29 May 2009 (UTC)

I'm wondering how many cats the OP has observed. My experience with cats and dogs is that they are, like humans, individuals. The soup that my father calls too hot, my friend calls just right; my father once ridiculed me when I said that I didn't think lukewarm water was as thirst-quenching as cold water. It probably isn't any different with pets. They have food preferences (Precious my hot dog loves salmon, Obi my cool dog shares apples with me, and Houdini the dog of my heart utterly adored bananas), so why not temperature preferences as well? As long as what you're giving your cat isn't reheated or so cold as to cause stomach upset, as mentioned above, there's no reason you shouldn't indulge your pet's individuality as long as it's convenient for you. —Preceding unsigned comment added by 66.215.227.218 (talk) 22:34, 29 May 2009 (UTC)

Incubation Period

What is the incubation period of a common sore throat? Isaiasnaruto (talk) 03:26, 28 May 2009 (UTC)

Acute pharyngitis lists a variety of causes for throat inflammation. Any specific one you are interested in? Check out the articles referenced there in case they already have an answer. 62.78.198.48 (talk) 07:56, 28 May 2009 (UTC)

Depends on the pathogen; see Acute pharyngitis and common cold. The latter article gives an incubation period of 2-5 days for a viral infection of the upper respiratory tract. --Dr Dima (talk) 07:55, 28 May 2009 (UTC)

Sound ever transverse?

Our article on sound suggests that sound waves can be transverse when moving through solid media. However, some of my real-life sources inform me this is incorrect. Some clarification would be immensely helpful. —Anonymous Dissident^Talk 08:14, 28 May 2009 (UTC)

I assume your link is to transverse wave. Sound waves always need some kind of elastic media to travel in. There is no error in the Sound article about waves being transverse or longitudinal. I added to the Sound article information that transverse waves are at right angle to the direction of propagation. I hope that helps to clarify. Cuddlyable3 (talk) 10:07, 28 May 2009 (UTC)

(ec):Transverse or shear sound waves are possible in elastic solids. For example, in an earthquake the first seismic waves to arrive are the compressional (known as primary) P-waves followed by the slower transverse (known as secondary) S-waves. S-waves, however, do not pass through liquids and this property has allowed them to be used to show that the earth's Outer core is in a liquid state. Mikenorton (talk) 10:14, 28 May 2009 (UTC)

Yes, I agree. However, there can exist a transverse wave in a gas when the gas (plasma) is at least partially ionized and a magnetic field is present. It is called Alfvén wave. It is not a sound in the conventional sense, though. An ion sound wave (more generally, a magnetosonic wave) can also exist under the same conditions, but it is longitudinal rather than transverse. See Waves in plasma and follow the links for more details. --Dr Dima (talk) 18:02, 28 May 2009 (UTC)

Maximum optical zoom

Is there a limitation for the optical zooming, assuming vacuum case? And what is the maximum practical optical zoom ever made (For examples for telescope and camera purposes)? The reason I ask this question is because of some very high resolution imaging satellites. Thanks again for your help in advance --Email4mobile (talk) 10:15, 28 May 2009 (UTC).

To begin with, you seem to be making the common mistake of misusing the word zoom. The focal length of a lens is (among other things) what determines how large the things you're photographing will appear in the photograph. With a short focal length, or a "wide-angle lens", you might take in a whole landscape. With a long focal length lens, which is often a telephoto lens, you can fill the frame with a small songbird from some distance away.

A zoom lens is simply a lens that can change its focal length. You can have zoom lenses that are entirely wide-angle. Telescopes and earth-imaging satellites are not generally "zoom" optical systems. I think you want to know about upper limits on focal lengths, or the ability to resolve fine detail.

As you increase the focal length of an optical system, you also need to increase the diameter of the lens or mirror to maintain a reasonable f-number, or else you will end up with a very faint image. Increasing the diameter gets harder and harder the bigger you get; first there's the obvious expense of manufacturing a big lens or mirror, but there are also the engineering challenges of getting the lens or mirror to support its own weight without bending (which would ruin the optical quality), or the costs of launching all that weight in the case of orbiting telescopes or imaging satellites.

Furthermore, even if you increase the focal length and diameter, your ability to resolve fine detail when looking at space from the ground, or looking at the ground from space, is limited by atmospheric seeing. Have you ever seen some wavy distortion when you look over a hot grill? A similar phenomenon limits the images from telescopes. Looking up from the ground, your angular resolution is not likely to be much better than 1 arcsecond no matter how big your telescope, unless you use advanced technologies like adaptive optics. Looking down from space, the same phenomenon limits resolution on the ground to about 5 cm. -- Coneslayer (talk) 11:48, 28 May 2009 (UTC)

You do not need adaptive optics: lucky imaging works just as well. Combining several images of the same thing would also improve image quality: this is often used in digital photography, I forget the names of the techniques. Using just ultra-violet could improve resolution more. So if things like this could improve the resolution by - complete guess - ten times, then you are down to a resolution of .5cm. I suppose you would see faces at this resolution, perhaps identify people. The article about the 5cm resolution was written in 1966 - technology will have improved since then. 78.146.211.210 (talk) 23:40, 29 May 2009 (UTC)

Fisrt I'd like to thank you very much for correcting my wrong information about optical zoom; and second awfull thanks for all the valuable explanation summerized in your text :) Coneslayer --Email4mobile (talk) 12:00, 28 May 2009 (UTC).

No problem... it's a complicated subject, and I glossed over a lot in the above discussion. You could spend all day reading the articles I linked to, and the related articles they link to. Feel free to stop back with follow-up questions. -- Coneslayer (talk) 12:15, 28 May 2009 (UTC)

Military satellites are known to be able to resolve down to 10cm - it is believed that they are able to recognise individual human faces, and there were claims in the 1970's that a satellite from that era could read license plates on cars...which I think means we're down to a centimeter or so. However, the very best stuff is classified - so the best we KNOW they can do is 10cm...which is about what you get on Google Maps in their high res city centers (although in that case the high-rez pictures come from Aerial photography - not satellites). SteveBaker (talk) 14:02, 28 May 2009 (UTC)

A limit comes from diffraction on the aperture. The larger your front lens is, the better is the limit resolution. Assuming a circular aperture (diameter $d$) and looking at objects close to the optical main axis, the Rayleigh's criterion (see the same link; its use is subjective and the limit is not rigid) says that from distance $\ell$ the smallest resolvable object can be $1.220{\tfrac {\lambda \ell }{d}}$ wide. $\lambda$ is the wavelength, thus, you can see sharper in blue than in red. With your eye's $d\approx 0.5\,\mathrm {cm}$ and green $\lambda \approx 530\,\mathrm {nm}$, from $\ell =10\,\mathrm {m}$ you can resolve two points up to $1.3\,\mathrm {mm}$ apart (try it, I have!). From a satellite's $\ell \approx 300\,\mathrm {km}$ and with a reasonable $d\approx 1\,\mathrm {m}$ (the same $\lambda$), we get $19.4\,\mathrm {cm}$, which really is about the resolution of the Google Earth satellite images: the better ones have already likely been taken from airplanes. — Pt _(T) 14:25, 28 May 2009 (UTC)

I would expect even the 20cm ones have been taken from planes. 20cm resolution from satellites is achievable, but it's not easy. --Tango (talk) 17:04, 28 May 2009 (UTC)

Respondents have assumed the OP is asking about the limit of a fixed telephoto lens. However zooming means changing the focal length of a lens while keeping the scene in focus. A limit to the ratio of a zoom lens is the increasing complexity of its design. Here is The World's First Triple Digit Zoom Lens Cuddlyable3 (talk) 10:32, 29 May 2009 (UTC)

the op might find the article superlens interesting.just-emery (talk) 17:09, 31 May 2009 (UTC)

Live Google Maps

With the current technology, is it possible to have a live Google Maps kind of thing, where we can zoom in on any part of planet earth to see people walking, birds flying, river flowing, traffic moving and sharks swimming? Is there any such service already in existence? I guess not, at least to such extreme level of precision. If not, when can we expect such thing (if ever) and how difficult is it to get there in comparison to where we are today. Thanks - DSachan (talk) 12:27, 28 May 2009 (UTC)

No, it isn't possible. The true-color images we see in Google Earth come from the imagery of a finite number of satellites, and (as I was surprised to learn) aerial photography. In order to have a "Live" Google Earth, you would need millions, if not billions, of satellites, all sending immense amounts of data per second, to be integrated and stitched in short enough time to be considered "live". I'm not sure that this will even be possible, never mind practical or worth the tremendous cost, for more than 100 years.

Now, if you're willing to sacrifice some spatial resolution, in a way we already have what you speak of: the GOES satellites send imagery at a resolution of a few kilometers every 15 minutes, and together have coverage of the entire planet (though the resolution declines as you approach the poles). I see no reason why in the near future we couldn't have near-real-time views at this spatial resolution, although I'm not sure anyone would be able to justify the cost.-RunningOnBrains^{(talk page)} 12:47, 28 May 2009 (UTC)

(edit conflict) Not now, and not likely. Imagery satellites are typically in orbits where they only pass over a particular point on the earth for a brief period, typically every few days. They cannot provide persistent motion imagery, nor image a particular location whenever you want. I was surprised to see in Satellite_imagery#Moving_images that a company planned to put an imaging satellite in geosynchronous orbit to provide ongoing live video; note, however, that because of the high orbit, the resolution would be very poor (250 meters). That's not good enough to see the kinds of things you're asking about. -- Coneslayer (talk) 12:52, 28 May 2009 (UTC)

Also - satellite photography has to be done on a more or less cloudless day - and if you want it to look any good, sometime close to midday. But the highest resolution commercial satellites produce really terrible spatial resolution - 5 meters, I believe. You can buy imagery from the Russian military at perhaps 1 meter accuracy. US military satellites can reach 10cm or better...but that imagery isn't for sale! There is a 'gentlemans agreement' amongst satellite photography sources not to sell better than 1 meter accuracy data to anyone other than government agencies because of the obvious privacy issues. (They chose that number because it makes recognition of individual humans impossible).

Aerial photography is therefore the only way to get high resolution imagery - and it's expensive.

So certainly, we're nowhere near even close to being able to do this. But even if we were - consider the bandwidth requirements. Most of the high res stuff in Google maps is about 10cm resolution. The surface of the earth covers 510,072,000 square kilometers - even if we ignore the oceans, that's still 148,940,000 square kilometers. At 10cm resolution, that's 14,894,000,000,000,000 pixels. About 8,000 of the largest hard drives you can buy. If we updated it every second, that's something like 24,000 terabytes per second! There is no known transmission medium that could possibly get even a tiny fraction of that from satellite down to the earth! This is so far away from being possible! Consider satellite TV - they typically have about 1.6 Gbits/second (per satellite) of down-stream bandwidth. It would take about a quarter of a million satellites of that kind of performance to transmit the data down to us...for the land alone. If you wanted to do the oceans too - you'd need a million satellites!

No! SteveBaker (talk) 13:56, 28 May 2009 (UTC)

FYI, you can buy commercial satellite imagery from US companies with sub-meter resolution these days. -- Coneslayer (talk) 14:00, 28 May 2009 (UTC)

You would need to make it on-demand - the satellites only transmit the data that is wanted at that moment (that would increase latency slightly, but not too much). The bandwidth isn't really a problem, it's the sheer number of satellites you would need to have constant global coverage. You could use fewer satellites by having them higher, but that would lower the resolution. Getting 10cm resolution from a geostationary satellite, for example, would require technology well beyond current level - you're probably talking decades until we can manage that. --Tango (talk) 14:06, 28 May 2009 (UTC)

Maybe what you want are webcams. Start with Webcampedia. You can certainly see all that stuff on webcams (including "sharkcam").--Shantavira|^{feed me} 14:22, 28 May 2009 (UTC)

Really what you want is to have access to security cameras, then in a place like Britain you could check on people all day long and with the need be secure against terrorism we'll hopefully soon have cameras and microphones inside the houses too, except for politicians of course because what they do is so sensitive. We could start with a law that all webcams are permanently accessible to the security forces at lease though you really need other people like for instance schools to be able to use them to make certain people are applying from the appropriate area. The more eyes are watching the less chance they have to get away with their crimes. RIPA details the advances Britain has made along these lines. Dmcq (talk) 15:33, 28 May 2009 (UTC)

Telescreen springs to mind. Smartse (talk) 17:11, 28 May 2009 (UTC)

See Talking CCTV - what a disgrace we have these in Britain! 78.147.139.18 (talk) 23:18, 28 May 2009 (UTC)

"If you have nothing to hide, then why worry?". Double plus good! Fribbler (talk) 15:58, 28 May 2009 (UTC)

You joke, but I remember a news story a year or two ago about a town (in the UK, I believe) that started broadcasting its CCTV on a local TV channel (so, CCTV is a misnomer, I guess!) so residents could help spot crimes as they occurring and inform the police. I don't know how successful it was or if the scheme is still running and can't find it now. --Tango (talk) 16:14, 28 May 2009 (UTC)

What?!? have you got a link? Smartse (talk) 17:11, 28 May 2009 (UTC)

As I said, I can't find it now. I'll have another look, though... --Tango (talk) 17:23, 28 May 2009 (UTC)

Here's the original news story,[1] and an update with comments.[2] Apparently the pilot scheme in Shoreditch has finished but a second phase is in the planning. Mikenorton (talk) 17:42, 28 May 2009 (UTC)

I think its dreadful that in some northern UK town - Middlesborough? - they have a tannoy system where the security droids can bark out commands at the public. I'm surprised that nobodies rioted about that yet, they would do in the south. Its truely 1984. Spy satellites - a few years ago I remember reading something about them. Many or most of them see in the ultraviolet, because that has least distortion through the atmosphere, as far as I recall. They can see fag packets. Most observation satellites see in various wavelengths and create false-colour images. True-colour visual wavelength images may be in the minority. I expect the cleverest satellites could use astronomy techniques in reverse, such as lucky imaging. 78.147.139.18 (talk) 23:09, 28 May 2009 (UTC)

The technology is available to "populate" Google Map-type images with computer generated moving vehicles and people. You can even be one of them, see Second life. Cuddlyable3 (talk) 10:19, 29 May 2009 (UTC)

Does heat contribute to production or increase in PCB's (Polychlorinated Biphenyls)

Can intense heat cause production of, or, an increase in the amount of Polychlorinated Biphenyls (PCBs) in new Non-PCB transformer oil over time?209.26.182.3 (talk) 14:52, 28 May 2009 (UTC)

Seems unlikely, but the chemists on the board can weigh in on the possiblity of PCB being created from the heating of mineral oil or silicone coolant. If a transformer once had PCB contaminated oil in it, but was flushed until it tested PCB-free, I supposed that operation at high temperature could free up a bit more PCB from the windings. There was a time when utilities allowed PCB to contaminate mineral oil cooled transformers by the common use of tanks and filter presses, so there were so many parts per billion of PCB found in equipment which did not start out with PCB or "Askarel" (trade-name). High temperatures reportedly caused PCB to turn to dioxin, which was supposed to be worse than PCB. Edison (talk) 19:06, 28 May 2009 (UTC)

No. As far as I know, no commonly-used transformer oil type (mineral, silicone, or fluorocarbon) contains any chlorine. It is therefore impossible for any chemcal reaction involving the oil to generate a polychlorinated biphenyl. TenOfAllTrades(talk) 19:23, 28 May 2009 (UTC)

What is needed to heal Humanity's ills?

Say by some great miracle, all religious/tribal/political countries/factions/groups in the world agreed to a 5 year truce with each other. Meaning, no violence, retaliation, nothing. What can humankind do during this time of peace to get reduce of world hunger, make education and healthcare more available to everyone? For instance, what should the US do first in this opportunity? I always thought that if everyone was well fed, had access to healthcare and all types of education, this world would be a very different place meaning less violence and more social awareness and a reduction of the human population. --Reticuli88 (talk) 16:35, 28 May 2009 (UTC)

Of course, from where do you get food, health care, or education? Those things require people to do work in order to provide people with them. Farmers need to grow food; truckers need to transport goods around, teachers have to, well, teach. So how do you recompense those people? Plus, if people receive food, shelter, education, and healthcare for absolutely no cost at all, then what is the motivation to work? Why should I be a teacher if I don't need any money to buy my own food and put my own kids through college? Why be a farmer if I have no motivation because I am so well taken care of I have no reason to work hard? See? Sometimes its not all that easy. --Jayron32.talk.contribs 16:53, 28 May 2009 (UTC)

Teachers and farmers are not doing it for the money. The motivation for work, real work, not digging ditches and cleaning toilets, comes from within. The concept that people are motivated to work hard because there is a carrot dangling in front of them doesn't address the fundamental problem. People like Abraham Maslow have addressed some aspects of this motivation, and John Neulinger proposed creating a society that was based not on work as we know it, but on work redefined as leisure, where leisure is pursued for its intrinsic reward. But the question proposed by the editor is flawed, since fear and "violence" from "religious/tribal/political countries/factions/groups" is encouraged at every level of society, and governments want their citizens to have as many people as possible to increase the tax base. We know that the higher the population density the more social and ecological problems result, from crime to mental illness, to pollution and resource extraction. In a world where people are treated as "consumers" (a recent invention of the last century) and where accumulating wealth is the highest human value, scarcity will be the result. The kind of "peace" that Reticuli88 talks about is an important issue for psychology. See also inner peace. Viriditas (talk) 21:00, 28 May 2009 (UTC)

Some teachers and farmers are not doing it for the money. At least, its easy for them to say that when they are recieving a living wage AND still have real pressures to do SOMETHING for work. The neat thing is that someone did the experiment and we actually have data on this. See Kolkhoz for what happened when farmer's WERE'NT doing it for the money any more. Strangely enough, the stopped farming really well, and an entire nation starved. People in collective (that is, on average) will only work as hard as they have to and no more. Individual, anecdotal examples exist of a person working harder just for the sheer joy of it. But in the bulk, people don't do that. --Jayron32.talk.contribs 00:37, 29 May 2009 (UTC)

Most teachers are not doing it for the money. They do it because they are interested in education and they tend to be "idealistic and altruistic" about why they teach.(Goodlad 2004:171-173) As for farmers in the modern world, "economic considerations now make it difficult for farmers to earn a living at farming, because farm costs have been rising much faster than farm income." For farmers in the United States, "the lifestyle was highly valued by older generations", and "people used to expect no more of a farm than to produce enough to feed themselves."(Diamond 2006:57-60) So it wasn't about money, it was about feeling good about your work and being able to be self-sufficient and raise your family. This is true for any profession. Why do mathematicians work hard at math? For the money? Of course not. They do it because they love it. Viriditas (talk) 03:21, 29 May 2009 (UTC)

You appear to be asking for a discussion about what might happen if some other rather impossible event were to occur. This is not a discussion forum. This is a reference desk. If you have a question that might possibly be something that has been studied and reported on in a respectable resource, please ask. If all you want is a discussion, please use one of the thousands of discussion forums available on the Internet. -- kainaw™ 17:02, 28 May 2009 (UTC)

Absolutely. We can refer you to a variety of philosophical, economic, and political theories, but this is not the place for a long and drawn-out discussion. Maybe you can start with utopia. That article is a great introduction and is full of links to numerous theories spanning the gamut from communism to fascism, feminism to individualism to mass annihilation. Personally, my favorite quote regarding utopia comes from an unlikely source, "The Khmer Rouge leadership boasted over the state-controlled radio that only one or two million people were needed to build the new agrarian communist utopia. As for the others, as their proverb put it, "To keep you is no benefit, to destroy you is no loss."" (Let me be clear - I don't condone this statement or the genocidal actions it represents - but I feel that it succinctly summarizes the problem that one man's utopia is not necessarily the same as the next). For virtually every atrocity historians can attribute to human activity, somebody thought it was a good idea. Nimur (talk) 17:11, 28 May 2009 (UTC)

It seems unlikely that poverty and crime would disappear with the end of war and conflict, even places that have known peace for many decades (Sweden?) have crime and poverty. In many places people do have free access to education and healthcare, but are still afflicted by the problems you mention to some degree (although hunger has been stamped out even among the poor among most of the industrialized world). I think historically urbanisation has reduced human birth rates much more effectively than eliminating war or reducing poverty. I think it should also be remembered that the well being of the world's people is improving, as described in this TED talk. To me, rather than an end to wars what the world really needs is good government. I would define that as largely transparent with as little corruption as possible, and being responsive to the populace without pandering to short sighted populism that is a problem even in the first world (like in, say, California). In my opinion a mostly free economic system is also paramount, as well as means for people to improve their status in society and better themselves, education as the great equaliser and all that. But while I think a world without wars is possible, a world without violence and theft is not, they seem to me inseperable from the human condition. TastyCakes (talk) 17:04, 28 May 2009 (UTC)

I agree with TastyCakes, corruption is the main thing to get rid of. If you achieve that, then I think hunger would all but disappear. Growing enough food to support the current world population isn't difficult, the problem is getting it where it is needed. Getting rid of hunger and poverty isn't likely to reduce violence, though. While some people are violent because they need to be to get the essentials to live, most people do it for reasons of power. There is always going to be a finite amount of power available so people will always fight over it (at all scales of existence - domestic violence is to do with power in a family, gangs fighting in the streets is about power in a particular sector of society, civil wars are about power in a country, regular wars are about power in a region, or even the world). --Tango (talk) 17:13, 28 May 2009 (UTC)

How is this a science question? Seems like a forum topic anyway - i don't think anyone in the world could answer this, let alone the reference desk.YobMod 17:16, 28 May 2009 (UTC)

That's a strange answer. Many people have attempted to answer this question, particularly in the fields of psychology and engineering. Buckminster Fuller, Paolo Soleri, and K. Eric Drexler come to mind, but the list is much larger than that. Futures studies addresses these types of questions, and Reticuli88 should be pointed in that direction. Viriditas (talk) 20:38, 28 May 2009 (UTC)

That some people who have approached philosophical questions happen to have had scientific backgrounds does not make the question about science. All we have is speculation - where are the testable hypotheses? The consequences of an impossible situation can not be scientifically explored. Eg, Stevebaker's reply after this suggests people reproduce more after a war. It may be true , but with only one example and absolutely no controlled studies, it is not a scientific answer (not that he claimed it to be, except by putting it on the science ref desk). I predict that world-peace would inspire an hysterical epidemic of religiosity, resulting in a huge drop in birth-rate as people prepare for the Rapture. The fact that i have 2 degrees in sciences does not make that a scientific prediction.YobMod 12:53, 29 May 2009 (UTC)

Let's try to find some generalities that might apply to this hypothetical situation: When wars end - people make more babies. The present 'baby boomer' generation are the consequences of the end of the second world war. So I'd expect one consequence of the end of all of these conflicts would be a jump in world population. That's really not a good thing. SteveBaker (talk) 21:52, 28 May 2009 (UTC)

I suspect if there really were a five year truce, many people would use this period to, well, stockpile weapons, train armies, and spy on their enemies. Otherwise, when the five years are up, they're going to get trampled by their enemies who have been busy doing the same. Dcoetzee 21:59, 28 May 2009 (UTC)

As to why Dcoetzee's answer is probably the best one, see Game theory. There are four outcomes here: Both nations disarm, Nation A does and Nation B does not; Nation A does not and Nation B does, and no one disarms. This is a classic Nash equilibrium whereby the best possible outcome (all countries disarm) cannot be reached because two of the three other outcomes (one country disarming while the other does not) is so catastrophic for the peacenik nation that the fourth option (both countries stockpile weapons) is the only stable equilibrium. Its a classic case of the prisoner's dilemma. See also Balance of terror for the classic application of the prisoner's dilemma to military strategy. --Jayron32.talk.contribs 00:31, 29 May 2009 (UTC)

The problem is that this is NOT a prisoner's dilemma situation. At worst, it's a "Continuously iterated prisoner's dilemma" - the same test happens over and over and you can learn from what happened in previous rounds. At best, it's not a prisoner's dilemma at all - because the players can communicate. That radically shifts the results. SteveBaker (talk) 01:54, 29 May 2009 (UTC)

Except that the communication is meaningless. You can TELL the other nation you want to reduce your armaments together, but do you TRUST your enemy? If you don't trust what they tell you, its just as good as not talking at all. And the net result is ultimately the same; the payoff matrix for the "Do we build weapons or not" game is identical to the prisoner's dilemma payoff matrix, and you ultimately always end up with the same equilibrium result. Both look like this:

	Disarm	Stockpile Weapons
Disarm	WIN BIG/WIN BIG	WIN BIG/LOSE BIGGER
Stockpile Weapons	LOSE BIGGER/WIN BIG	WIN A LITTLE/WIN A LITTLE

See Peace war game, which discusses (with refs) exactly what I was talking about. --Jayron32.talk.contribs 02:03, 29 May 2009 (UTC)

NO!!!!!! it's not like that! You've completely failed to understand what the prisoner's dilemma teaches us.

In the true prisoner's dilemma you have no information about how the other person is behaving right now or is likely to behave in the future. So you have no information on which to make your decision. It's also an all-or-nothing thing. In the disarmament scenario - you can slowly ramp down your arms production and watch to make sure that the other guy does the same thing - every round of defense-funding decision-making becomes another game of prisoner's dilemma. Hence it's an ITERATED version - and game theory predicts utterly different conclusions under those situations (read the article AGAIN!). In an iterated system, your chart looks like this:

	Reduce armaments by 1%	Increase armambents by 1%
Reduce armaments by 1%	Win a modest amount/Win a tiny amount	Win a tiny amount/Lose a tiny amount
Increase armaments by 1%	Lose a tiny amount/Win a tiny amount	Lose a tiny amount/Lose a tiny amount

You can even look back at how the other guy has been doing in the past. If he rearms a bit when he says that he won't - you can arm yourself a little more as 'punishment' in the next round. In this "iterated" prisoner's dilemma, there is a clear strategy that always works - as demonstrated by a very famous computer simulation/game (which you can find out about in the article). "Tit for Tat". You start out as "Mr Nice Guy" - but if/when the other guy screws you over - you punish him on the following round - then you go back to being Mr Nice Guy. That stategy is utterly unbeatable over the longer term when there is no communication between players other than the game results. But even more than that - if you have communication, you can try to make it clear the rules by which you are playing - with openness in your processes (everyone can see your military expenditure budget BEFORE that gets turned into weapons manufacture) - then it becomes clear that you are playing Mr Nice Guy - and your opponents can benefit by doing the same.

So this is NOT the classic Prisoner's Dilemma - unless you play the game like North Korea currently is (which is closer to the classical version of the game - and has results that are probably going to play out very soon). North Korea's government see this as a one-off event because their stability is at risk and they know that if they screw up - the could be deposed and there is no second chance...their insular policies and closed borders mean that there is none of the information flow needed for a communicative/iterative version of Prisoner's Dilemma - and the consequences are exactly as game theory predicts.

When people cooperate and are open - you get things like the de-escalation towards the end of the cold war. But that only happens if you talk to each other and regard it as an iterated game and not a one-off. That requires a stable political system - and explains why stable/open governments spend less time at war than unstable/closed governments.

SteveBaker (talk) 14:47, 29 May 2009 (UTC)

This reminds me of that Jack Handy quote:

I can picture in my mind a world without war, a world without hate. And I can picture us attacking that world, because they'd never expect it.[3]. TastyCakes (talk) 20:18, 29 May 2009 (UTC)

"An excess of virtue is to be feared more than an excess of vice because only the latter is subject to the moderation of conscience." I devoutly hope not to see the so-called great miracle that the OP anticipates would give an opportunity to impose a US-centric one-size-fits-all ideology on everyone. But a "reduction of the human population" can be done in many ways, few of them nice. Cuddlyable3 (talk) 10:08, 29 May 2009 (UTC)

Well there you have it, I think the consensus is we should have a big war or preferably a plague that decimates us. Perhaps I'll build a huge robot that goes WARNING!!! WARNING!!! CRUSH!!! KILL!!! DESTROY!!! as it goes about its work. Dmcq (talk) 15:13, 29 May 2009 (UTC)

Would it have red glowing eyes? I think it should. SteveBaker (talk) 22:15, 29 May 2009 (UTC)

The trouble, Reticuli88, is that just about any good-hearted person basically knows what we would all have to do to cut the nonsense and play nice (and basically, it consists of everyone, well, deciding to cut the nonsense and play nice) - but getting everyone to implement the solution all at once? Impossible. - AJ —Preceding unsigned comment added by 66.215.227.218 (talk) 22:15, 29 May 2009 (UTC)

Robert LeFevre (i think) pointed out the difference between negative rights and positive rights thus: If everyone suddenly resolved to refrain from force and fraud, negative rights would immediately be satisfied (except for human error); but even that miracle is not enough to fulfill positive rights, even if we agree on what those rights are, because no one knows enough about what other people need.

If this were a discussion forum, which it isn't, I'd assert that most of the world's poverty and deprivation is caused by states' active prevention of economic activity. Religious and tribal antagonisms are usually only a pretext for the political class to consolidate their control and exploitation. —Tamfang (talk) 19:14, 3 June 2009 (UTC)

Cerebral Hemispheric Dominance

Is this article correct? I thought that it's a myth. —Preceding unsigned comment added by 194.90.167.67 (talk) 18:22, 28 May 2009 (UTC)

Well, it does read like an essay and not like an encyclopedia article. I'll give it a thorough look through later. Livewireo (talk) 18:30, 28 May 2009 (UTC)

And its been written almost entirely by one editor who has only made edits to the article. Livewireo (talk) 18:34, 28 May 2009 (UTC)

Would a redirect to Lateralization of brain function be more appropriate here? It would seem that the two articles cover much the same topic, and the Lateralization of brain function article is much better written... --Jayron32.talk.contribs 02:10, 29 May 2009 (UTC)

You're going to throw away an entire article that someone went to great trouble to write simply because of the writing style. Talk about judging a book by its cover. Further, laterization and dominance are 2 different subjects. I'm sure that volumes could be written on dominance but if it redirects to a completely different article then it will get relegated to a mere paragraph or two, Wikipedia is merging too many articles and is becoming much less useful because of it. just-emery (talk) 17:16, 31 May 2009 (UTC)

Beware the labor theory of value; no matter how much trouble someone spends on writing twaddle, it remains twaddle. Besides, it appears that Julie.summey has spent only two hours on Wikipedia, so she might well not notice if it's undone. —Tamfang (talk) 22:19, 3 June 2009 (UTC)

If you disagree with the article then why not help edit it? Also the article has a discussion page for the editers to discuss questions like this.just-emery (talk) 17:30, 31 May 2009 (UTC)

Motor Oil

My car's owners manual recommends using 10W-30 grade. I have a case of 10W-40 which I would like to blend with another grade so the mix is approximate to 10W-30. Can I do this? What other grade do I need to buy, and what proportions do I need to use? —Preceding unsigned comment added by 75.36.216.34 (talk) 18:46, 28 May 2009 (UTC)

With very rare exception, it is always best to follow the owner's manual's reccommendation. Is it possible to simply return the oil to the place of pruchase and exchange it for the correct weight? That would easier and less costly than buying more oil and then having to mix the two. cheers, 10draftsdeep (talk) 19:01, 28 May 2009 (UTC)

In general, you can't just mix different grades of commercial motor oils and expect them to work appropriately. We have information on the grades of motor oil at Motor oil#Grades. One difficulty you'd face in mixing oils is that oils with designations such as 10W-30 or 10-W40 are multi-grade oils, meaning that they have special additives which allow them to perform like different oil grades at different temperatures. Matching the exact performance characteristics at differing temperatures would thus be very difficult. Even matching a single weight oil wouldn't be trivial, as the number designations are based on the kinematic viscosity of the oil, which isn't going to be linearly additive (that is, mixing equal part 10 weight oil and 30 weight oil is not going to get you the equivalent of 20 weight oil), especially when potential non-newtonian fluid behavior is taken into account. Leave motor-oil mixing to the professionals, who have proper test lab facilities. -- 128.104.112.106 (talk) 19:37, 28 May 2009 (UTC)

All of that is technically correct, as it should be in an encyclopedia. That said, though, the odds of negative consequences from tossing one quart of 10W40 into your engine now and then are "slim to nil".

10W40 will be slightly more viscous when hot. If you have an old enough engine, where you're actually burning through a quart of oil periodically, then a bit more viscosity is not a bad thing. At the other end of the calendar, the 10W components are "close enough" for winter use.

So, it's a case of theory vs practice. Theoretically, don't do it. Practically, it don't make much difference.

--DaHorsesMouth (talk) 20:31, 28 May 2009 (UTC)

Drain the old oil and do a proper full oil change using, if you want, your supply of 10W-40. Your engine will thank you. That is better than experimenting blindly with a mix of two oils that become increasingly different in viscosity as the engine heats, and they might not even stay blended. Change the oil filter too.Cuddlyable3 (talk) 09:54, 29 May 2009 (UTC)

I have mixed different oil viscosities several times, with no perceptible harm to my engine. Oil grades cover a range of viscosities... some 10W30 oils are a bit thicker/thinner than others. Your engine will not grenade if you are a little bit off in your mixing skills. That said, the simplest solution would be to return the oil for the proper grade if possible. If not, adding a quart or two of 10W40 to each oil change should be quite safe. 75.157.28.248 (talk) 20:15, 29 May 2009 (UTC)

Poor TV picture improves a lot when VCR on

I live in an area with a low signal strength. I have a 20db (as far as I recall) signal amplifier between the tv and the aerials coaxil cable. Even so, sometimes the image becomes very hazy and difficult to see - it looks exactly as I would expect from a low signal strength. But when I press the appropriate button on my remote, the TV takes the aerial input via a VCR, and the picture becomes perfect, crystal clear! So the signal goes aerial - 20db amplifier - VCR - scart lead - tv. Yes, I still have and use a VCR.

My question is - is this simply due to the VCR adding some extra amplification to the 20db amplifier? Or could there be some other reason? Could I get the same result by buying an even more powerful signal amplifier, or by putting two in series? I assume that although the signal is weak, the signal/noise ratio must be good. It is several times cheaper to buy a new amplifier than upgrade the tv aerial. A subsidary question is why the signal seems to be much worse for several minutes at a time, and then improve again? 78.147.151.201 (talk) 21:25, 28 May 2009 (UTC)

Does your aerial go into your VCR or tv first? I would expect that whichever is the system that gets the 'mains' aerial would be the one that gets the best reception. Also are you definitely taking the signal from the best location? I know where I am I can get a couple of different signals - my strongest one being from Emley Moor. It may be that you should check that to make-sure as well. Perhaps your VCR has better decoding/system than your tv? My old digi-box is much worse than my new one, even though the aerial hasn't changed. ny156uk (talk) 22:57, 28 May 2009 (UTC)

The aerial goes into the VCR first, and then there is another short coaxil cable from the VCR to the TV, as well as a scart cable that is in use when the VCR is on. But you still get a picture when the VCR is turned off. I thought the aerial signal just went straight though the VCR without being changed in any way. The aerial is definately pointed at the nearest and best transmitter, which is some way away. I have not bought a digital radio because the signal is not good enough, and the tv signal is not good enough for digital tv either. 78.147.139.18 (talk) 23:37, 28 May 2009 (UTC)

So you have the coax from the aerial going through a splitter with one output going to your TV and the other going to your VCR? I'm betting a poor quality splitter. It's pretty common for cheap splitters to give a better signal to one output than to the other. Especially the old fashioned T shaped ones. APL (talk) 01:11, 29 May 2009 (UTC)

No, the signal goes to the VCR, then through the VCR to the TV. I imagine there is merely a plain connection between the in and out coaxial sockets. It still functions when the VCR is off. The same thing happened when I used other VCRs. 84.13.164.142 (talk) 09:10, 29 May 2009 (UTC)

Not to be picky on this, but do you live in an area that is undergoing mandatory transfer to Digital TV? In the U.S. for example, all over-the-air analog televison will cease on June 12, 2009. I believe the UK and Canada have 2-3 more years; but it may be something to think on as analog TV becomes less and less availible. --Jayron32.talk.contribs 00:22, 29 May 2009 (UTC)

See also Digital television transition. --Jayron32.talk.contribs 00:23, 29 May 2009 (UTC)

I am well aware that this area will convert to digital tv in the future. But that does not have any bearing on the current problem. As I mentioned, the TV signal is currently too weak to allow recieving digital tv. I think the signal strength is going to be increased when the digital switchover occurs in this region, so hopefully I will be able to get it then. TV is not very important to me. 84.13.164.142 (talk) 09:34, 29 May 2009 (UTC)

Geolocate puts this poster in Liverpool. (Which brings to mind a different question: Does the UK still have television police? I recall years ago seeing a story where authorities were tossing televisions out of second-story windows if the owner didn't have the proper paperwork.) -- Tcncv (talk) 01:22, 29 May 2009 (UTC)

Well - you're exaggerating wildly...but the essentials are true. In the UK, the free (and advert-free) BBC television and radio stations (probably the highest quality broadcast anywhere in the world) are funded by the "Television License" - effectively a tax. If you have a television - you have to buy a license. I forget how much it is - but we're talking over 100 pounds a year. It's not funded from central government taxation because the BBC is required to be independant from the government in order that they may criticize them and hold politicians feet to the fire without being concerned about having their funding withdrawn. Hence, lots of people don't pay the license fee.

In order to enforce the system, there are 'Television detector vans' that drive around to houses that don't have TV licenses and they use a directional antenna to pick up secondary radio waves created in the process of decoding the TV signal. They can detect to a fair degree of accuracy where the TV is in the house. Armed with this information, they can come to your door and demand to see your TV license - and if you don't have one, you get fined. I suppose it's possible that they might be empowered to confiscate your TV if you continually break the law - but that's not a common thing. No - they certainly don't toss your TV out of second floor windows!! And no, they aren't police officers - they are tax collectors.

Americans are frequently horrified at this concept. But I should explain that the process is essentially no different from the car taxes you pay in the USA for the privilege of driving on the public roads. If you get stopped for not having your car tax paid up to date - you get fined...same deal if you get caught operating a TV without a license in the UK. It's arguably unfair that you pay the same car tax whether you drive 100 miles a year in a tiny MINI Cooper or 100,000 miles a year in a honking great SUV. It's arguably unfair that you pay the same TV license no matter how much you watch the BBC...but that's life. Having experienced US "free" television - I can tell you that the TV license is an absolute bargin. SteveBaker (talk) 01:42, 29 May 2009 (UTC)

Well, there's a difference, though. When you're driving on public roads, you are, not to belabor the point, driving on the public roads. You're taking up space that could be used by other drivers. When you're just sitting in your private space, intercepting the EM radiation that the government shoots through you whether you like it or not, it's hard to argue that you're putting any burden on that resource. --Trovatore (talk) 03:08, 29 May 2009 (UTC)

As with many things American, SteveBaker, "your mileage may vary" as the expression goes. In Michigan, your classic MINI (pre-1983) would have a license fee based on weight but your new one would have been charged based on MSRP price. I don't know of any states that charge by mileage yet although I have heard of such proposals. Rmhermen (talk) 05:54, 29 May 2009 (UTC)

...but if everyone use that as an argument then a much greater burden is placed upon the people that are willing to pay. It's more about fairness than about whether you are using a finite resource. --antilived^{T | C | G} 03:58, 29 May 2009 (UTC)

Not being allowed to listen to electromagnetic radiation that someone sends through your residence is a bit like not being allowed to listen to a loud argument by the couple living in the next apartment, or not being allowed to read a flyer thrust through your mail slot. If they don't want you to enjoy the broadcast, they should not send it into your property. (Just a Yank view of things.) Edison (talk) 04:42, 29 May 2009 (UTC)

Edison - If the BBC encoded the signal and charged you a monthly/annual fee for use of a decoder/their decoding algorithm would that be better? Essentially that's what pay satellite tv companies such as Sky tv do. Seems that the bbc method is better in my view (though obvious sky is through satellites but they work to receive signals in much the same way). ny156uk (talk) 07:39, 29 May 2009 (UTC)

In my opinion, yes, the encryption option is much better. For one thing, if you wanted to use your TV only to watch private stations, and not the BBC at all, you could do that and not pay for the BBC. (There are private TV stations in Britain, right? I haven't been there in a couple decades and I don't think I watched any TV while I was there, but I thought I had heard that by now there were private stations. If not, well, you could watch Dutch or French TV.) --Trovatore (talk) 10:13, 29 May 2009 (UTC)

The worst thing about the current BBC license system is that if you do not watch tv, do not have any tv in the house, do not watch it on the internet either, and thus are not required to pay the license fee, then you still get frequently and truely harrassed by many threatening letters commanding you with threats to buy a liscense. The letters really are upsetting and even when you tell the licensing people that you do not have a license, then the threatening and hysterical letters keep on coming. 84.13.164.142 (talk) 09:16, 29 May 2009 (UTC)

Yes, we Americans have the pleasure of watching 12–15 minutes of commercials every hour. I actually think there are advantages to the British system. Several shows are rebroadcast on our PBS stations or are picked up on some of our cable networks. I especially like the science and technology coverage. Most of the best are of British origin. And it is refreshing to see a comedy that is based on wit rather than the slapstick, and dramas that don't feel compelled to lead with some sexually suggestive scenario as if there were no other way to get the audiences attention. Of course I realize that what we see is a non-representative fraction of British broadcasting. I'm sure you have your trashy shows too. But in general, I can see there are advantages to the pay system – more emphasis on quality that there would be in the pursuit of the advertising dollar. (POV alert!) We on the other hand have Lost – a drag-u-drama with no apparent plot, that seems made up from week to week, but for some reason has a huge loyal following. (Diving for cover now.)

Oh, and I do clearly remember seeing a television tossed from a window, bouncing off a porch (?) roof, and crashing to the sidewalk below. Likely part of some high publicity enforcement back in the 70's. They had the electronic detection trucks then too. -- Tcncv (talk) 05:27, 29 May 2009 (UTC)

Getting back to the original questions... 84.13.164.142 (talk) 09:10, 29 May 2009 (UTC)

The OP's TV takes its signal at its aerial connector when the VCR is off and at its SCART connector when the VCR is on. Possibly the tuner or i.f. signal amplifier stages in the TV (which are bypassed by a SCART input) are failing. Older TVs with mechanical tuners, and the dual-standard 405/625 TVs once sold in the UK, are plagued by unreliable switch contacts. Cuddlyable3 (talk) 09:45, 29 May 2009 (UTC)

The TV is a year or two old. 405 transittion ended decades ago, so a TV capable of recieving 405 would be a musuem piece. 84.13.164.142 (talk) 09:47, 29 May 2009 (UTC)

Tuner - that's an interesting point. Could it be that the VCRs tuner is more tuned in than the TVs tuner is? That the problems are caused by the Tvs tuning drifting off? When listening exclusively to one channel only on FM radio, the tuner often seems to need adjusting. Perhaps the tuning is affected by day or night. 84.13.164.142 (talk) 12:15, 29 May 2009 (UTC)

Problem probably solved. The coxial cable socket on the Durabrand tv seems to have a loose connection with the internal circiutry, and I can reproduce the bad picture if I wriggle it around. So I will take the back off and see if I can tighten something up without electrocuting myself from the capacitors. 78.146.211.210 (talk) 21:05, 29 May 2009 (UTC)

Coaxial aerial sockets are a weak point on many TVs. They are often held by solder to a printed circuit board and the solder joint fails because of mechanical stress. Cuddlyable3 (talk) 18:40, 30 May 2009 (UTC)

determining diet via feces

It is my understanding that biologists can determine an animal's diet via examining it's feces (I'm sure it is a bit more complicated than that). What I'm wondering is if scientists can tell if an animal is a herbivore, carnivore or omnivore by examining fossilized feces? In other words can we tell what the diet of a dinosaur was based on it's fossilized poop? —Preceding unsigned comment added by 69.77.185.91 (talk) 21:27, 28 May 2009 (UTC)

Not exactly the answer to your question, but in Germany there's a plan to identify a specific dog by the DNA in his droppings. Who'da thunk it? --DaHorsesMouth (talk) 22:30, 28 May 2009 (UTC)

One could certainly can make some good inferences about diet, as long as its possible to match the poop with the pooper. Inevitably, we have an article about fossilized poop, better known as coprolite, or see this article for more details. Rockpocket 00:06, 29 May 2009 (UTC)

See Scatology. It works for whales and elephants. Can't remember reading of a dinosaur study. Rockpocket objection that you wouldn't be able to determine the origin probably has a lot to do with that. Teeth usually are a pretty good indicator. They do sometimes mix up scavengers and hunters though. 71.236.24.129 (talk) 02:08, 29 May 2009 (UTC)

The movie The Last Emperor contains a delightful scene where learned dieticians inpect the feces of the youthful emperor Puyi and conclude that his intake of honey should be increased. Cuddlyable3 (talk) 09:29, 29 May 2009 (UTC)

In order to make determinations about an animal's diet by examining its feces, it's usually necessary to do some poking and prodding. (Well, if you've been eating a lot of corn . . . never mind.) Since a coprolite (like any fossil) is, regardless of what it used to be, currently a rock (however interesting), that would be difficult. I suppose you could slice it up and examine the inside, but I doubt that we know enough about what plant and animal materials of various kinds look like after they've been through digestion AND fossilization to get anything useful out of it. - AJ —Preceding unsigned comment added by 66.215.227.218 (talk) 22:08, 29 May 2009 (UTC)

I think the point is that certain parts of animal tissue (such as fur, skin, teeth etc) and plant material (seeds) do not get digested. So you can identify those in the coprolite then you can determine what type of diet the animal that deposited it had. I imagine a tooth or seed is quite recognizable, even when fossilized, if you know what you are looking for. Rockpocket 21:15, 30 May 2009 (UTC)

Mix rice varieties to reduce clumping?

I have some red rice and some white Basmati rice. Both tend to stick together in clumps when cooked separately. Will they clump less if cooked as a mixture? NeonMerlin 22:32, 28 May 2009 (UTC)

Are you rinsing the rice through before you cook it? Basmati rice normally isn't 'sticky' (at least not in my experience of cooking with it). Not sure how much impact mixing rice will have but rinsing through before with cold-water and then after with boiling water (and fluffing up with a fork) are the things i'd recommend (though i'm by no means a rice expert). ny156uk (talk) 22:47, 28 May 2009 (UTC)

I'd second ny156uk's assessment. Rice does not have any gluten per se, but the starches like amylopectin that adhere to the outside of the kernel can undergo some gluten-like polymerization which will lead to the "stickiness". Glutinous rice (aka Sushi rice) is known for its high amylopectin content and takes advantage of this. Rinsing the rice in cold water prior to cooking should reduce this in rice varieties for which this is not a desirable property. Mixing the rices will have no effect on this, as each rice likely produces amylopectin and will stick to each other just as well as it will stick to itself. Just rinse well, and you should be fine. --Jayron32.talk.contribs 00:17, 29 May 2009 (UTC)

Note that Sushi rice is not the same thing at glutinous rice. Also there are ways you can cook the rice to reduce the clumping effect, although I consider such rice to be disgusting so don't know how to do it personally Nil Einne (talk) 08:54, 29 May 2009 (UTC)

You can usually vary the amount of stickiness by just changing the amount of water you put in, and generally less sticky rice require less water too. --antilived^{T | C | G} 03:25, 30 May 2009 (UTC)

two questions about force, motion , and displacement

1st question:

If you can push a 165 pound weight 1 foot in a straight line, with x amount of force, how much further will it be displaced if pushed at the perfect arc angle (such as is used by cannons for optimum range) with the same amount of force. dont need an exact just a general answer (2feet/ 3feet/ 4 feet etc) general guess?

2nd question:

Does anyone know the power to displacement equasion in its most basic form, using to example above again if X force moves 165 pounds 1 foot, how far will double the amount of force be able to move it, twice the distance, triple the distance? again just basic guesses would be fine, just need a general idea.

Thanks for your help I dont know much about these type of things.

Rob —Preceding unsigned comment added by 79.68.137.18 (talk) 23:05, 28 May 2009 (UTC)

The question is unclear. What do you mean by "pushing in a straight line"? Sitting on the ground? Accelerated at shoulder level parallel to the ground? Also, "force" is of limited interest - you need energy (force times distance) for this calculation (although you can do some simple substitutions and use time). If you use the usual abstractions (a spherical cow of uniform density on a flat planet with no air resistance and a uniform gravity field), and use the same angle to the ground (45 degrees for optimal range in that case), I think twice the energy will give you twice the range. But it's 2 am here, so my thinking may be of limited value. --Stephan Schulz (talk) 00:02, 29 May 2009 (UTC)

Ok what i meant was put simply, when i push my brother directly forward in the chest he moves 1 foot, if i push upwards and forwards he moves further. I wanted to know why this was?

So it is double the energy, double the distance of displacement then?

Rob —Preceding unsigned comment added by 79.68.137.18 (talk) 00:13, 29 May 2009 (UTC)

Well, in that case its a very hard problem. Your brother is actively resisting being pushed. I suspect if you push him from a different angle, you may throw him more off-balance. It is doubtful if you can transfer enough energy to actually make him go ballistic (except in the figurative sense). --Stephan Schulz (talk) 00:32, 29 May 2009 (UTC)

There are so many layers of confusion here. We have to start by answering the basic, underlying principles...and that means Sir Isaac Newton. Newtons' laws of motion say that when an object is in motion - it will keep moving at the same speed - in the same direction until some other force acts upon it. So if you push your 165lb weight - it can only stop moving (ever!) if some other force acts on it. Out in deep space, the smallest, gentlest nudge would send your 165lb weight off on an infinite journey. But in our common experience, things stop moving because of friction, gravity and air resistance. So the only reason your 165lb weight stops AT ALL is because of some combination of those three things. So the first part of your first question doesn't contain enough information for us. We need to know why it stopped - what OTHER force than the one you used to get it moving caused it to stop so quickly.

Now - if you'd told us that (and let's suppose it's just friction with the floor) - we have to move on to the object moving in a curve. Again - that nice Mr Newton had something to say here - objects move in a straight line - unless acted on by some other force. So now, for your weight to move in a curve - there needs to be some other force. If you fire a cannonball up at (say) a 45 degree angle - then gravity is what bends the path into a curve - as air resistance slows it down. But if you simply push a weight across the floor - friction slows it down - but nothing bends the motion into a curve. So answering your question requires some indication of what bends that straight line motion into an arc.

Worse still - a force has to operate over some distance. When you push something with your hands - you have to actually make your hands move forwards for a while as you exert force on the object. Force times distance is Energy...and (as is increasingly irritating here on the science desk) lots of people confuse force and energy.

Now for the second part of your question: Power is yet a different thing from force and energy. Power is the rate at which energy can be delivered. So the amount of power you need depends on how fast you need to move your object. If you expend some amount of energy very quickly, you need more power than if you expend it slowly. A sports car can get up to 60mph faster than a rusted out VW bug because it's engine produces more power - but the amount of energy the two cars need to get up to 60mph is roughly the same.

So we can't answer either part of your question because they simply don't mean anything without understanding all of the forces involved, the time these things take to happen and so forth.

SteveBaker (talk) 01:24, 29 May 2009 (UTC)

Well i personally think the first question at least can be answered with some meaning. In all common sense, we can assume the damping force to be friction, the force which causes curved motion to be gravity, the angle of projection to be 45 degrees, the coefficient of friction to be some unknown, say k, and no air resistance. I think i also need another constant, the e value, for when the body bounces off the ground, we need to know how much energy is lost in the collision. So with all these assumptions and the knowledge of the two constants e and k, this becomes a pretty well defined problem, and e and k shouldn't be so hard to find anyway, provided the OP tells us what is the body and what surface he is using, and some clever guesswork. Of course, if he is pushing his brother, e is 0 and k...hmm... you have to take a guess...So now the problem can easily be approached... see projectile motion.. we just plug in the formula for maximum range..., and when you push the object along the ground you can also calculate the distance it moves, using energy conservation. But i think i forgot the biggest assumption we should make... that when we push the body, we just give an impulse... that is a force for a very short amount of time essentially giving it a constant kinetic energy... You might think this is just crap... too much approximations, but i think its not so bad, it should give you a reasonable idea of the number we are looking for... Will get back to you after doing the calculation bit...provided someone tells me what i can choose k...Rkr1991 (talk) 04:47, 29 May 2009 (UTC)

By invoking a coefficient of friction k are you supposing that the OPs brother slides 1 to 4 feet? If so, how can the brother move further when pushed at an "optimum cannon" angle ?Cuddlyable3 (talk) 09:21, 29 May 2009 (UTC)

Yes, i suppose that the OP does something (like pushing or striking) his brother to give him some kinetic energy, with which he slides along for some distance. See, when he is launched at an angle, he will fall at the same angle (provided the floor is flat. Now, he can either bounce up and do another projectile motion, or since he has some horizontal component of velocity, slide along for some more distance. This depends on the coefficient of restitution, which is zero if the body in question is the OP's brother. SO for the brother problem, we just take the horizontal component of velocity and its like the sliding part all over again, we just add the result to the range. If, however, the object is something like a ball, where the value of e is not zero. then we must make an infinite sum of the ranges caused by repeated bouncing. If the collision is perfectly elastic, then the distance traveled is, of course, infinity, which can never happen. SO for the brother problem i need to know what friction coefficient i can take, to give a decent figure. Rkr1991 (talk) 10:41, 29 May 2009 (UTC)

Hmmm this is getting too complicated for me, I just wanted a simple explanation for why when you push something both up and forward at the same time (i used the analogy of a cannon since they are never fired strait when they want to hit something far away, they are fired both up and forward), it is moved further than if you just pushed it strait on, I know for a fact that I can push something further this way, I just wanted to know why.

Also wanted to know if, under the same conditions, double the amount of force applied to an object makes it move twice as far, or more than twice.

Thanks again, also please bare in mind that I know little of physics, hence why I am asking here.

Rob —Preceding unsigned comment added by 79.68.137.18 (talk) 10:47, 29 May 2009 (UTC)

Well, if i assume you are applying a constant force for a short period of time while pushing (just ignore it, its for the geeks) then double the force means the distance goes up by square root of 2 times, that is, force is proportional to the square of the distance, not the distance. The energy you give is proportional to the distance, that is, if you double the energy you give, the object moves twice the distance. If you want to compare it with throwing it, then please hold on, i'll get back to you with just a number as soon as i can find a suitable value of k to assume, cause i have no idea. Rkr1991 (talk) 11:04, 29 May 2009 (UTC)

Thank you, so if you double the force you double the distance, put basically. now I just need to know why pushing something up and forward moves it further than just pushing forward.

Rob —Preceding unsigned comment added by 79.68.137.18 (talk) 11:12, 29 May 2009 (UTC)

Well, if you push something up and away, you also reduce the weight on the ground and hence the amount of friction. But in the case of your brother (not, I hope, an inanimate object), he will not really slide significantly on normal floors. If you push him, he will be off-balance. To recover, he will typically take a step to move his legs under his center of mass again. So this is at least partially an active movement. If you push him up and away, you may cause his center of gravity to rise, so he will be more off balance before he can recover. With an living, acting object that presumably never fully leaves the ground its really very hard to determine exactly what happens. --Stephan Schulz (talk) 11:20, 29 May 2009 (UTC)

Okay Rob, a simple explanation for why pushing something both up and forward at the same time moves that thing further than just pushing forward. Let's use your cannon example.

If a cannon fires a cannonball straight forward, that ball keeps going forward until it hits the ground, then it stops (let's ignore rolling for now!). If the cannon fires a cannonball straight up, it goes straight up slower and slower until it starts coming down again, hits the ground and stops. If a cannon fires a cannonball both up and forward, the cannon ball will go forward until it hits the ground and stops, but it will also go up until it starts coming down again. This 'going up' keeps it away from the ground for longer, so takes longer before it hits the ground. This means it can go further forwards before hitting the ground.

If you want to get slightly more complicated, you can think about what angle gets you furthest.

When it comes to you pushing your brother, it's likely that other things are involved, like what muscles you use to push straight forwards compared to pushing up and forwards. I know that if I push something up and forwards, my legs are more involved than if I just push forwards, and I can push back against the ground more (rather than just relying on my own weight). Think about how you position yourself, what parts of your body you're using, what way you're bending, etc. 80.41.31.27 (talk) 11:27, 29 May 2009 (UTC)

It was confusing to hear about pushing your brother if you really want to discuss firing a cannon. When a cannon is fired at an angle the speed of the ball leaving the muzzle has two parts: the horizontal velocity and the vertical velocity. The vertical velocity is initially upwards but gravity will turn it around and the ball will hit the ground at the same velocity but going downwards. The vertical velocity is what determines the time the ball is in the air. The horizontal velocity is constant (air friction modifies it slightly but you specified a vacuum) as long as the ball flies. The distance the ball flies is the product of its horizontal velocity and time in the air. For simplicity assume the ball hits something at the same height as the cannon and that it doesn't bounce or roll any further after the impact.

Consider 3 cases. 1) The cannon is aimed horizontally. Result: the ball has no vertical velocity so it drops "like a stone" i.e. the time for it to hit the ground is short. The horizontal velocity has no time to take it more than a short distance. You have already observed this. 2) The cannon is aimed straight up. Result: the ball has lots of vertical velocity and stays up in the air for a long time. But the horizontal velocity is zero so the ball doesn't go anywhere. Duck and cover or protect your head with a helmet! 3) The cannon is aimed at an angle somewhere between horizontal and vertical. Result: the ball has both horizontal and vertical velocities and can go far. There is an article about calculating how far. In short the distance the ball flies is proportional to the square of its speed leaving the cannon. So if you double the speed of the ball it flies 2x2 = 4 times as far. Cuddlyable3 (talk) 11:33, 29 May 2009 (UTC)

Thank you both for the simple explanation, I asked about my borther being pushed and trajectories, because I saw a video of dummies getting throw backwards by a shockwave from an explosion, (as i understand it like a really innifecient cannonball) and noticed that the dummies that where thrown up and away were thrown really far. And was wondering if the angle had anything to do with this. Thanks for your answers they really helped.

Rob —Preceding unsigned comment added by 79.68.137.18 (talk) 12:18, 29 May 2009 (UTC)

Fog and cloud

Clouds form on dust etc particles, fog also. So is there any difference between fog and cloud (apart from the height) ? If so, what is it? —Preceding unsigned comment added by 79.75.108.190 (talk) 23:56, 28 May 2009 (UTC)

See our article on Fog: "Fog is a cloud bank that is in contact with the ground. A cloud may be considered partly fog; for example, the part of a cloud that is suspended in the air above the ground is not considered fog, whereas the part of the cloud that comes in contact with higher ground is considered fog. Fog is distinguished from mist only by its density, as expressed in the resulting decrease in visibility: Fog reduces visibility to less than 1 km, whereas mist reduces visibility to no less than 2 km." Rockpocket 00:00, 29 May 2009 (UTC)

Yes, this is just conventional terminology. In some cases, precise standard definitions apply (for example, in weather statistics or aviation forecasts); in most common usage, the distinction is sort of ... cloudy. Nimur (talk) 14:57, 29 May 2009 (UTC)

May 29

Time quickens?

Thank you for always answering my questions.

Does time ever quicken in special relativity? Lorenz transformations shows transformation of coordinates in a reference frame S to another reference frame S'. The time is transformed from t for S to t' for S' as follows.

$t'=\gamma (t-{\frac {vx}{c^{2}}})$

where v is the velocity of S' and x seems to be the distance of the event in the direction of x-axis for S. If v and x have the same sign, that is, if the origin of S' approaches the event (The origins of S nad S' are at the same point at time 0), t' will be less than $\gamma t$, and if, for example, x =vt, t' will be even less than t ( if t is positive).

By Relativistic aberration,

$\cos \theta _{o}={\frac {\cos \theta _{s}-{\frac {v}{c}}}{1-{\frac {v}{c}}\cos \theta _{s}}}$

where v is the velocity of the source, $\theta _{o}$ is the observed direction of the light ( It seems to be from the observer to the source), and $\theta _{s}$ is the direction of emission of the light (It seems to be from the source to the observer), if the light is emitted at an angle $90^{\circ }$ or $-90^{\circ }$, the light is observed as coming form $\theta _{o}$ where $\cos \theta _{o}=-{\frac {v}{c}}$, that is, from the hemisphere at opposite side to v. If two plane sources are at both side of the observer parallel to each other and to the axis of v, and if the source is approaching the observer, at the time the wavefront is supposed to be in head to head if at rest, they seem to have already crossed each other in the direction opposite to v.

Does time quicken? Like sushi (talk) 04:52, 29 May 2009 (UTC)

Special relativity applies to observers who are moving at a constant velocity relative to one another (and where the effects of gravity are either uniform or negligible). Each observer sees time passing more slowly for the other observer - this is a symmetric observational effect. If the observers want to compare the actual duration that they each experience between two events, they will have to both become stationary in the same frame of reference, so that they have a common definition of simultaneity (see relativity of simultaneity). To achieve this, one or the other (or both) will have to accelerate, which takes us out of the realm of special relativity and into general relativity. In general relativity, there are asymmetric time dilation effects due to non-uniform gravitational fields or, equivalently, relative accelerations. So when the two observers compare the actual duration that they have experienced between events, one observer may find that they have experienced a longer duration than the other. Informally, we can say that time has passed "more quickly" for one observer than for the other. See time dilation and twin paradox for more details. Gandalf61 (talk) 12:50, 29 May 2009 (UTC)

Gandalf, your explanation is essentially correct, except at the moment when you said "will have to accelerate, which takes us out of the realm of special relativity and into general relativity." Special relativity can deal with accelerated objects within flat Minkowsky space-time. See Rindler coordinates. Dauto (talk) 14:33, 29 May 2009 (UTC)

Looking at a moving image of relativity of simultaneity, it seems like, if the relative inertial motion is resolved, that is, if the two observers become stationary to each other, the effect of special relativistic time dilation vanishes. To achieve this, accelaration is needed, but if the accelarations are symmetric, and general relativistic time dilations are the same, observers can see the resoluion of special relativistic time dilation between them? And if so, is the resolution attributed to accelaration? (Then, for an observer, the other's accelaration must look differently from his, even though they are the same.)

Like sushi (talk) 14:49, 29 May 2009 (UTC)

If the accelerations are the same, both observers will experience the same amount of time lapse. Note that there is no need to use general relativity to understand that problem since it is assumed that the two observers are moving within flat space-time. Dauto (talk) 15:15, 29 May 2009 (UTC)

I know this is a "standard" view of special relativity that's taught in classrooms, but I strongly recommend ignoring it, I think it will just confuse you. The emphasis on disagreeing observers is backwards. There's only one world, and a bunch of equivalent descriptions of it in terms of different coordinates, and the Lorentz transformation is just a translation between different coordinate systems. It's the same as

x' = cos θ (x + y tan θ)

y' = cos θ (y − x tan θ)

for converting between different Cartesian coordinate systems that are at a relative angle of θ. I've deliberately written that in an unusual way to emphasize the similarity to the Lorentz transformation as it's usually written. With y = ct, v/c = tan θ and γ = cos θ, the analogy is very close. The coordinates (x,t) describe an event, i.e. something happening at a given place and time. The Lorentz transformation turns that into (x',t') which is the location of the same event with respect to a different coordinate system.

When you write down just the t' part of the Lorentz transform, it's the same as writing down just the y' part of the Cartesian rotation. That's likely to get you into trouble, because the y' coordinate is nearly meaningless without its corresponding x'. You could say that it describes the "horizontal" line through the point represented by (x',y'), but "horizontal" in this sense is a coordinate-dependent concept. In different coordinates you would have gotten a different line, and your choice of coordinates was arbitrary, so this line is meaningless. It's very tempting to imagine that t has independent meaning, because it does in Newtonian physics, but in relativity you'll frequently get into trouble it you treat it as though it does.

Okay, think of a line with evenly spaced dots on it, and a rotation of that line:

       *
       |
       |          *
       *         /
       |        *
       |       /
       *      *

I did the best I could in ASCII—the line segments are supposed to be the same length and the * spacing is supposed to be the same in both. The point is that the stars on the diagonal line are "more compressed in the vertical direction" than the stars on the vertical line. The rotation has compressed the dots, if you like, though it's a strange notion of compression that's tied specifically to the y or y' coordinate. A rotation won't always compress the dots, sometimes it will uncompress them. For example, if you take the diagonal line and rotate it the same amount counterclockwise, you'll get the vertical line again. This is the geometric meaning of your observation that the Lorentz transformation sometimes makes t' larger than t and sometimes smaller. There is no "quickening of time" exactly in special relativity, just as no rotation can increase the y-coordinate spacing of the dots beyond the vertical case, but there are rotations that increase the spacing.

So obviously this vertical dot compression doesn't really mean anything—the two lines are the same, our definition of "vertical" is arbitrary. But can we make the compression mean something? Yes, if we're willing to bend one of the lines and make a triangle, like this:

       *
       |\
       | *
       *  >
       | *
       |/
       *

That looks awful, but I hope the point is clear: "because of the compression", if you like, there are three star spacings' worth of distance from bottom to top on the bent line, only two on the straight line. Is this a paradox? After all, the compression was a meaningless coordinate artifact a moment ago. It's not a paradox because this is really a different setup, and it's not even clear it ought to have the same name. Before we had two symmetrical lines, now we have an asymmetrical arrangement, and it's the asymmetry that determines which path is longer.

Moving along to your intersecting wavefronts. This requires at least two spatial dimensions and one time dimension, which makes it harder to visualize. Let's say that, with respect to some arbitrary inertial frame S with coordinates (x,y,t), your wavefronts are moving straight up (in the +y direction) and straight down (in the −y direction) and intersect all along the x axis at t = 0. The events where the wave fronts appear are then given by y = ±ct (+ for the upward-moving one, − for the downward). If you now replace t by a third Cartesian coordinate, z, and plot y = ±cz for some constant c, the result is an "extruded X", like this:

      \\\\\/////////////     ^ z
       \\\/////////////      |
    ... \///////////// ...   |___\ x
        /\\\\\\\\\\\\\           /
       ///\\\\\\\\\\\\\
      /////\\\\\\\\\\\\\

with the x and z axes as shown and the y axis pointing into the page. Now, rotate this shape clockwise in the plane of the page by a small angle so that the part to the right tilts down. First, the crossing of the wavefronts (i.e. the former x axis) no longer happens "at the same time" (i.e. at the same z coordinate). Points farther to the right are now at lower values of z or at "earlier times". Second, this is hard to visualize, but if you take slices of the figure in the xy plane, representing the wavefronts "at a given instant", they are no longer parallel. Rather, they are both inclined to the left by an amount that depends on how much you rotated the figure. That's aberration.

This analogy can only be taken so far. Many things end up with the wrong sign (in special relativity there are fewer clock ticks along the non-straight path, not more). And there's no analogue to the speed of light or the distinction between past and future in Euclidean geometry. But the analogy is still very helpful for understanding what the Lorentz transformation and "observers" are really about. People talk it up to be a subtle, even mystical thing, but it really, really isn't. When people talk about "observers" they are talking about planar slices through the world, and, just as in Cartesian geometry, those slices have no special meaning. You can slice a cube one way and get squares, or a different way and get equilateral triangles and hexagons, but it's just a cube any way you slice it. There is a tendency to do far too much slicing in relativity because people don't want to let go of the Newtonian world where there really was such a thing as "the state of the universe at a given moment". To really understand relativity you need to give up the idea that, in the tilted extruded X, the wavefront crossing events happen "at different times" just because they have different z (or t) coordinates. That's a Newtonian idea and it will lead you astray. -- BenRG (talk) 18:36, 29 May 2009 (UTC)

I don't know if I have understood what you (Mr. or Ms.BenRG) say, but I think I do understand that two events which occur at the same place at rest will always be observed to occur with larger time interval if in relative motion. Now it might have been better to ask if an event can be observed at an earlier time in relative motion than at rest. And I think the answer is "yes"?.

(Additionally, I have been suspecting that, if an event occurs later in relative motion than at rest, the event which has already been observed could be something not yet has occured at the time. But this is solved, if I admit that c is the ultimate speed.)

Thank you.Like sushi (talk) 04:09, 30 May 2009 (UTC)

The point is that light relative to you will always travel the same speed- c. This is a product of Maxwells law and special relativity. Maxwells law say the speed of light is c (using energy density equations). Special relativity say all physical laws apply in intertial reference frames, so the speed of light is always c in an inertial reference frame. Imagine a man walking 5 m/s north on a train going 10 m/s. His speed relative to you, an observer on the ground, is 15 m/s. However a light pulse emitted on a train going .5 c relative to you, again on the ground, is still only c (Michelson Morley experiment, neutral pions prove for waves, particles). So, imagine a train with 2 mirrors. One is on the roof of the train, one on the floor. These mirrors are seperate by a distance c*t (where t is the amount of time the light takes to travel between the mirrors). Imagine a photocell on the top mirror. Every time a blip of light hits the top mirror a photocell on it records the time. The blip is than bounced to the floor and then bounced back to the top, striking the photocell again. But now imagine the train is moving with some velocity v. As the light pulse is traveling from the bottom of the train to the top, the top mirror has moved some distance v*t, where t is the time it takes the light pulse to reach the top of the train. So, the light doesn't only travel c*t, the distance between the mirrors. It also has a horizontal component of displacement right?. The vertical component is c*t, the horizontal is v*t, and you get a triangle. But to you, an observer on the ground, light cannot move faster than c. So it takes longer than a second for the light pulse to hit the top mirror. It happens say every 1.0001 seconds (thats a hella fast train). Time seems to have slowed down to the guy on the train. To the guy on the train the same thing happens to you. However, for the Fitzgerald contractions only the reference frame of the guy on the ground is correct.

  ----------MIRROR-----                     ----------MIRROR----- 
                                                   /
.          | light pulse                          /
                                                /
                                              /
  ----------MIRROR-----             ----------MIRROR-----   

train at rest moving train, so the top mirror moves a bit to the left as the light pulse travels.

24.171.145.63 (talk) 20:28, 30 May 2009 (UTC)

At the end of the explanation above 24.171.145.63 said "However, for the Fitzgerald contractions only the reference frame of the guy on the ground is correct." That is not correct. Both observers see each other's rulers suffer Fitzgerald contraction and they both see their own ruler suffer no contraction. Both are correct. Dauto (talk) 00:31, 31 May 2009 (UTC)

What I meant is that if the train stamped a mark on the track every time its clock said 1 second, these marks would be a certain distance x apart. But since its second is longer on the train than a guy who is at rest, the marks are really more than x meters apart. The guy at rest can take out a ruler and measure the distance and he will get more then x, not x. 24.171.145.63 (talk) 03:18, 31 May 2009 (UTC)

That is correct. On the other hand, it is also correct that if the track stamps a mark on the train every second, it will be the guy on the train that will end up measuring a distance larger than x. Dauto (talk) 04:39, 2 June 2009 (UTC)

TV signal splitters for coaxial cables

What do these actually do? Mine are encased in plastic and I cannot see what any circuity inside them is, if they have any. Does it make any difference which sockets of the Y you put the input and output cables?

I am running three tvs off one aerial. Sometimes all three tvs may be on at once. The aerial signal goes through an amplifier and then is split into a TV and cable2. Cable2 goes to another part of the house, then it is split into a tv and cable3. Cable3 feeds another tv. It is not possible to provide seperate cables, but as I imagine the TV aerial sockets are all joined up in parallel rather than in series, then it should not make any difference. Is there any way of doing this better while not going to the expense of more or better aerials please, or drilling new cables through walls and floors? 84.13.164.142 (talk) 10:11, 29 May 2009 (UTC)

The key consideration with splitters is that each split reduces signal quality. Based on the architecture you describe, TV 1 is getting a better signal than TV 2 and TV 3. As a result, you should consider putting your best / most-watched TV on the TV 1 line (or switching the splitters such that the best TV becomes the TV 1 line). In my personal experience, though, TVs are rarely affected by this sort of thing -- at least with normal numbers of splitters. More critical is something like a cable modem, which should always be placed as close to the incoming signal as possible. — Lomn 15:19, 29 May 2009 (UTC)

We have a splitter article, from which it's pretty obvious the thing is a hybrid coil. From that article, you can learn that that the inner electrical component is really just a small transformer. Impdendence-balancing is pretty important for high-quality RF signal handling. While 1→2 splitters are common, there are also 1→3 and others. For your configuration, that would let you do it all at once instead of a second split on one output of the first split (see Lomn's comments for why). DMacks (talk) 15:28, 29 May 2009 (UTC)

According to the article, a hybrid coil is a kind of transformer. These splitters are small and very light, so I very much doubt they have a tranformer in them. Perhaps they have no electronics at all. 78.146.211.210 (talk) 21:00, 29 May 2009 (UTC)

Transformers needn't be large nor heavy. A power transformer usually is because it needs to handle a lot of current, be insulated against a large voltage, and/or it has an iron metal core. But for low-voltage high-frequency RF applications you can have an air core and just a few windings. DMacks (talk) 21:53, 29 May 2009 (UTC)

A power splitter can also use resistors only. This is likely what you have inside the case. Resistive splitters, however, will always give unwanted extra attenuation to your signal whereas transformer splitters do not suffer this problem. Resistors are cheaper than transformers.--ThrobbingTrousers (talk) 02:58, 4 June 2009 (UTC)

Why are cockroaches such a pest in the US but not in the UK?

While coackroaches seem to be a common pest in the US, I've never heard of any cockroach problems in the UK. Yet in the UK we have far milder winters than in places like New York, so they would find it easier to survive the cold, and we also have central heating. Is it simply that cockroaches are not a native species in the UK? 84.13.164.142 (talk) 10:58, 29 May 2009 (UTC)

I have had cockroach issues in Glasgow (so they do exist), but you're right that they seem to be pretty mild in the UK. I'm curious too as to why; my auntie in Germany had some pretty horrific cockroach infestations, which really doesn't have a greatly different climate to Scotland. 87.114.167.162 (talk) 11:02, 29 May 2009 (UTC)

I don't know where your auntie in Germany is, but Frankfurt is about 5 C hotter in summer[4][5] which is not an insignificant difference. Most sources[6] say cockroaches are originally tropical, and Glasgow is much colder and further north (even if you take into account house heating). —Preceding unsigned comment added by Maltelauridsbrigge (talk • contribs) 11:25, 29 May 2009 (UTC)

My experience - mild winters make for a reasonably nice summer. When we get a hard cold freeze that doesn't thaw until Spring, the cockroach problem is much worse. Our exterminator claims that this is because the eggs and larvae and such can survive being frozen quickly, but not being slowly frozen. Where I live (at least for the next week or so), the problem is compounded by the addition of palmetto bugs (flying cockroaches). I've fogged the trees that overhang my house and it is rather scary how many palmetto bugs fall out - hundreds of them. So, we have cockroaches on the ground and palmetto bugs in the trees and almost nothing to keep their populations in check. -- kainaw™ 12:21, 29 May 2009 (UTC)

It is also because America is a land of opportunities.

Because New York is in the US. —Preceding unsigned comment added by Wikivanda199 (talk • contribs) 15:54, 29 May 2009 (UTC)

I don't know about the UK, but when apartments in New York don't have roaches, it's often because they have mice who are eating the roaches. 207.241.239.70 (talk) 04:32, 30 May 2009 (UTC)

Automatic train control

Building a computer/sensor system which could replace a human driver for a car or an airplane is exceedingly difficult and probably not possible today (especially not if operational safety is taken into account), although we are actively working on getting there. However, at first glance, I would have thought trains would be a lot more feasible. Several subway/metro systems in the world (eg Toulouse Metro) already do this. However, from the list of driverless trains, it looks like this has never been implemented for long-distance mainline trains (ie beyond a metro system serving a city). Is there a reason for this? Is there something that make automatic control of long-distance trains more difficult / less feasible than for metro systems? Thanks! — QuantumEleven 11:06, 29 May 2009 (UTC)

I think small, closed systems like the Toulouse Metro and the Docklands Light Railway are workable because the automatic controller totally "owns" the system - it knows where all the trains are (and the system is heavily instrumented to support that). Most existing long-distance train networks are a lot more ad-hoc (a lot more like the road) with a variety of trains, tracks, signalling systems, and vexing things like level crossings. I'm sure if you built a new, modern, fully grade-separated long distance railway then an automatic system would be quite workable. 87.114.167.162 (talk) 12:50, 29 May 2009 (UTC)

(ec) I'd say that the anon above me has hit the major points. I'll also add that there are challenges associated with the time and distance to an engineer in the event of a problem. For existing systems, you can have a couple of guys with pagers at head office downtown who can be anywhere in the metro system in under an hour. A train with some sort of impending mechanical failure can often coast as far as the next station to disembark its passengers.

Long-distance routes typically have stations which are much more widely separated than those of a city metro/subway/light rail system. It is possible to strand passengers in the 'middle of nowhere', potentially between multiple working tracks. Head office can't send help for hours, so you need to have widely dispersed response teams. The line remains blocked until the train receives assistance; this can have a ripple effect on all rail service across a country. It's sometimes remarkably useful to have a 'man on the scene'. TenOfAllTrades(talk) 13:24, 29 May 2009 (UTC)

It is probably cheaper to hire people to run the trains then it would be to install the hardware and develop the software to run such a system on the current rail networks. 65.121.141.34 (talk) 13:09, 29 May 2009 (UTC)

Plus there's a comfort factor in knowing there's a person up front "in control" even if they're really not, or if the computers do a better job overall anyway. Ask an A-380 or 777 pilot who's doing most of the flying up front, for example. Arakunem^Talk 13:28, 29 May 2009 (UTC)

Yep - on a typical transatlantic flight, the pilot actually flies the plane for less than three minutes. However, if you lose both engines in a freak bird-strike accident and have to land on a handy river...you probably want a pilot on board. This could probably be solved by having a handful of well-qualified pilots stading by on the ground who could take over and fly the plane by remote control at short-notice in the event of an emergency...but the public might find that hard to swallow. SteveBaker (talk) 14:16, 29 May 2009 (UTC)

Aye, there's the rub. That darn pattern recognition in humans is still hard to beat when it comes to picking a nice soft landing spot out of an urban jungle. :) Of course with trains, your options are much simpler: Go, Go faster, Go slower, Stop. Arakunem^Talk 14:20, 29 May 2009 (UTC)

I used to think that too. I used to design flight simulators for a living - so I know a lot about what pilots have to do. But one time we had a shot at building train simulators too (we actually delivered a bunch of them to Burlington Northern Railroads). That was quite an eye-opener. While it's true that you pretty much have just the one control - what you do with it is pretty tricky. It's such a high-skilled job that the average train driver in the US earns more than the average airline pilot - which surprised me quite a bit too! There are many subtleties with driving a train that are not at all obvious to the layperson.

For example - suppose you have a long train and a series of hills to go up and down. One's natural instinct is to gun the throttle to get up the hill and sit on the brakes on the way back down again - but often, as the locomotive crests the top of the hill - the majority of the train has not yet reached the bottom of the hill - so you often actually need more power rather than less - as you reach the bottom of the hill and start going up the next one - you tend to want to apply more power - but with the rest of the train stretching back a few miles behind you, most of the weight is still rolling downhill and you may well be applying the brakes whilst simultaneously heading up a steep hill!

Also, when your train is going around a curve, it has a tendancy to want to straighten out (like pulling on the ends of a piece of string) - which would derail the cars in the middle of the train - so keeping your the tensions in the couplings between cars fairly slack (which means no acceleration) is important when going around curves.

When you stop, it's essential not to come to a nice slow, gentle stop - you actually want to stomp on the brakes fairly abruptly...what that does is to cause all of the slack in the couplings to be taken out as each carriage runs into the one in front with a nice thump. If you don't do that - so that all of the couplings are stretched out tight - then when you try to accelerate away, the locomotive has to overcome the static friction and accelerate all 100 or so carriages at once...which it probably can't do. If the couplings are all squashed up - then the engine only has to start one carriage moving at a time - which is much easier. If you see a train backing up and then starting off rolling forwards - that's a sure sign that the driver screwed up and stopped too gently!

Then, locomotive drivers are responsible for keeping a lookout for things around the track that need maintenance or are in a dangerous state - this requires them to be alert throughout the entire trip - even if they are going 100 miles across a dead flat desert at a constant speed. There are loads more things like that. It's surprising how much complexity there is in such a seemingly simple system. Even though it's essentially a one-dimensional system - it's a lot tougher than driving a car OR flying a plane. SteveBaker (talk) 22:11, 29 May 2009 (UTC)

(Steve, I've taken the liberty of putting paragraph breaks into your item above. Please try to use normal length paragraphs.)

The issues Steve discusses about controlling a train are real, but most of them -- all except the last paragraph -- relate to long freight trains. Automatic driving of that sort of train, if it was ever going to happen, might well involve sensors placed along the train to provide feedback on the speed of different cars and the tension of the couplings -- sensors which, of course, ordinary freight cars today don't have.

On the other hand, passenger trains are shorter and have a higher power-to-weight ratio, which means those driving issues basically don't arise. My guess is that if we ever saw automatically driven trains on a long-distance railway, it'd be a totally isolated line without level crossings and with only one kind of train -- a description that best fits some of the high-speed passenger train lines built since in the late 20th century. Further, these lines already have cab signaling systems; it'd "just" be a matter of taking the human out of the loop.

On a number of subways and similar urban transit systems today, driving a train normally consists of pushing a "go" button when people have finished boarding at each stop. The human driver can take over if necessary (and on some systems is encouraged to do so for part of the day, to keep in practice), but usually doesn't. On the Docklands Light Railway in London, they go one step further: there is a human on board who can drive the train, but normally he's riding with the passengers, checking tickets and giving information. That's the way I'd expect an automated long-distance railway to do it: the same person who normally works as a conductor is also able to drive the train if the automatic system fails. Then there would be just two issues: (1) getting the consent of the crew members and their unions to such an arrangement, and (2) the hazard of operating a train with nobody looking out the front. But either or both of those might still be a "showstopper".

Also, I said above the the new high-speed lines are totally isolated, but that's only true of some of them (e.g. the Shinkansen in Japan, with a different track gauge from their other railways). The TGV trains in France and ICEs in Germany mostly spend only part of their time on the high-speed lines; if you travel from Nice to Paris, for example, until you reach Marseille you're on a conventional railway and your top speed is maybe half the TGV's limit of 186 mph. If automatic driving was introduced on the high-speed line, the train would still have to carry a human driver on the less isolated, mixed-traffic line from Nice to Marseille. --Anonymous, 05:04 UTC, May 30, 2009.

Feel free to criticise my overly long paragraphs - but I should point out that you should not edit other people's posts - it's a HUGE no-no around here. K'thnks. SteveBaker (talk) 15:52, 30 May 2009 (UTC)

"Except to fix formatting errors that interfere with readability". I had to break up the long wikitext line for technical reasons anyway, and I decided that the long paragraph was interfering with readability. I admit it's a marginal call, but the main reason for the rule is to not be deceptive and I announced what I'd done. --Anon, 16:40, May 30.

I would think that pilots only actually flying the aircraft for 3 minutes on TA flights would be a bad idea, because then when there is an actual emergency the computers can not handle, the pilot will be out of practice and will not perform optimally. 65.121.141.34 (talk) 14:42, 29 May 2009 (UTC)

Eh, I doubt this is as relevant as you consider it. What does the pilot need to practice? Takeoffs and landings in adverse conditions. What is all but 3 minutes of a TA flight? Stable level operation. Pilots need to keep sharp, yes, but they'll do that better in a good sim that provides emergency conditions than by doing nothing at 35000 feet. — Lomn 15:11, 29 May 2009 (UTC)

What keeps them sharp is definitely the simulator time. The landing on the Hudson river was fairly impressive - but the guy would have trained hard at looking for suitable landing spots in busy areas after unexpected engine failures - and would have also trained for water landings - it was really just a matter of putting the two things together. And even with all that training, there was one critical switch that they forgot to throw (it's right there in the landing-over-water procedures manual) that would have made the plane sink more slowly and given people more time to get off. Airline pilots don't spend a lot of time in the simulator - but when they do - they get all of the problems thrown at them at once. You're on approach...it's night - and it's foggy - and at the last minute you're switched to a parallel runway and...oh...your undercarriage didn't come down...and wouldn't you know it - there is another plane converging on your position - and your left engine is only producing half power...GO!!! SteveBaker (talk) 22:11, 29 May 2009 (UTC)

"Forgot" isn't exactly the right word. There was a checklist for the procedure and they were following it, but the failure happened at such a low altitude that there wasn't enough time to complete it. The "ditch button" was one of the things they didn't get to. (It would be interesting to see a copy of that checklist. I wonder if it's available somewhere.) --Anonymous, 05:10 UTC, May 30, 2009.

Yes - technically, what went wrong was that the co-pilot continued to attempt to restart the engines long after the airspeed was too low for that to stand even a chance to work. Hence he left it too late to start the procedures for ditching in water. Theoretically it is the Captains' responsibility to start or end these procedures - so he should have told the Copilot to abandon his efforts to start the engines earlier. However, he was pretty busy - and it's entirely understandable. All things considered, he did it pretty much by the book. SteveBaker (talk) 15:52, 30 May 2009 (UTC)

This is a recorded message from the computer flying the aircraft. Good day ladies and gentlemen and thank you for flying AutoAirways' new automatic airplane. Our pilotless system is perfectly safe because it is impossible for an error to occur-KLIKK for an error to occur-KLIKK for an error to occur-KLIKK for an error to... Cuddlyable3 (talk) 12:00, 30 May 2009 (UTC)

If pilots only fly a plane for 3 minutes, what do they do the rest of the time? Read a book? Play I spy? Sleep in their chairs? 78.151.147.255 (talk) 00:14, 3 June 2009 (UTC)

relay setting calculation for spaj 140 c

Can any one give me an example for relay setting calculation of abb spaj 140 c relay?????????? —Preceding unsigned comment added by Parthi2020 (talk • contribs) 11:48, 29 May 2009 (UTC)

Protective relaying takes a year or 2 of study,after getting an electrical engineering degree, and cannot be conveyed in a few words. Have you studied a standard text such as "Protective relaying theory and applications" by Walter Elmore, ABB, (2004) which sells for $100? It has examples such as you seek. The setting should be sensitive and selective, both terms of art. It should trip for faults but generally not for heavy loads. It should be able to carry normal and emergency loads, with tap settings and current transformer taps correctly chosen. This is one of the simpler applications, protecting a radial feeder. I have not used this particular relay. The manufacturer's brochure shows it to be a flexible relay capable of acting as device 50, 50N, 51, 51N, and 50 breaker protection. Do you know what these mean? You could take a simple example, and set it to trip for a fault on the feeder it protects, based on the calculated fault current, such that the backup protection does not operate. It should trip for the lowest current phase to phase or phase to ground fault, at the remote end of the feeder, perhaps "buried in" the remote transformer (so that you do not leave a bit of feeder unprotected at the remote end). It should not trip before downstream fuses or other devices have a chance to clear faults downstream from them: that is coordination. If used as a 50, the operating time would be substantially constant, like a CO-6 relay. This would allow fast clearing, and might be used on an undergrounfd feeder. The 51 application would mean the operating time decreases as the amount of fault current increases, like a CO-7 relay, or a GE IAC-51. Edison (talk) 14:35, 29 May 2009 (UTC)

My protection coordination course was only two hours instead of two years, but shouldn't the relay be set to trip before any downstream fuses, to give it a chance to clear a line-to-line fault? I seem to remember basing the relay settings on the time-current curves of downstream fuses—the strategy was to have the relay re-close twice, then stay closed long enough to blow the fuse, and finally trip and stay open.—eric 15:42, 29 May 2009 (UTC)

There are many strategies for fault clearing. What does Elmore say? Edison (talk) 20:16, 30 May 2009 (UTC)

Pork

I heard that Americans extensively use Pork in their daily diet,but there is a common belief that Pig is a host to many disease causing agents like the Tapeworm!!!!!It is also said that these agents may be destroyed by high temperatures but the ova doesn't get destroyed even at such temperatures.But lot of people still eat it without any fear of infection!!!!What makes them still consume Pork extensively???? —Preceding unsigned comment added by 59.165.84.9 (talk) 14:29, 29 May 2009 (UTC)

Tapeworms such as Taenia solium are not transmitted by eating cooked pork. Only the ingestion of uncooked pork, or contaminated human vomit and faeces transmit the worms. Once proper hygiene standards are adhered to, there's little to worry about. Same as any meat, really. Fribbler (talk) 14:35, 29 May 2009 (UTC)

Taste and price? Bacon is immense, and it's not particularly expensive. Pork chops are great and not baldy priced either. Sausages are commonly pork as well. Essentially the taste, price and availability of the meat are major factors on how much of it is eaten (though the amount that sells will have impacts on price and availability too of course). Also my understanding is that Pigs can survive in quite a lot of environments thus making them a good animal to farm which helps too. 194.221.133.226 (talk) 14:33, 29 May 2009 (UTC)

Americans and many other humans also smoke, which is proven to be bad for you. Just because it might be harmful, does not stop everyone from participating in said activity. Also, I have been eating pork for many years, and have never gotten a tapeworm to my knowledge, so I can infer that the risk of eating properly prepared pork to be low enough to justify the reward. mmmmmmmmmm bacon. 65.121.141.34 (talk) 14:39, 29 May 2009 (UTC)

I think, larvae remain alive only when the pork is undercooked and not all pigs harbor tapeworm larvae. Also FYI, pork is one of the world's most commonly consumed meats. So, it is not just USA but the other part of the world also consumes it including Europe, China or India. [7] - DSachan (talk) 14:41, 29 May 2009 (UTC)

Tapeworms and trichina are rare in pork in the United States, and we usually eat our pork fully cooked, which further reduces the risk. On the other hand, outbreaks of Escherichia coli O157:H7 from beef occur with some frequency, and a high percentage of chickens are contaminated with salmonella. Your statement that "there is a common belief that Pig is a host to many disease causing agents" probably reflects more on your own culture than either the beliefs or reality of US food production. -- Coneslayer (talk) 14:46, 29 May 2009 (UTC)

Chill dudes!!!!Even I like Pork but my muslim friend abused it so much that even I started feeling lethargic towards it....He also said that even if Pigs are reared in most hygienic environments they will not forget their inherent practice of eating each others faecal matter!!!!That was the reason I posted this question...actually I wanted to ask whether Pig is really a fit to be eaten animal or not??? —Preceding unsigned comment added by 59.165.84.9 (talk) 17:22, 29 May 2009 (UTC)

Religious taboos are generally not scientifically based; religious taboos established over a millennium ago are even less likely to be scientifically based. --jpgordon^∇∆∇∆ 18:16, 29 May 2009 (UTC)

Plenty of the answers have shown that pigs are clearly a hygienic enough animal to eat. They are widely eaten around the world, and according to this site (http://www.gan.ca/animals/pigs.en.html) and many others they are reasonable clean and intelligent animals (that is clean in a hygiene senese, not religious). ny156uk (talk) 17:57, 29 May 2009 (UTC)

In terms of hygiene, cows routinely get just as dirty as pigs when they are in feed lots. And chickens will be scavenge their own dead. 65.121.141.34 (talk) 18:31, 29 May 2009 (UTC)

Indeed, there is nothing particularly unique about pigs vis-a-vis other animals in terms of how hygenic eating it is. Swine and cattle and poultry and sheep and any animal can be kept under clean or dirty conditions; the meat can be properly handled or it can be contaminated by improper butchering techiniques. In terms of the risk of disease from pork vs. other meats, there is no difference at all. If you eat beer or lamb or chicken or turkey then these are no more or less risky to eat than pork is. --Jayron32.talk.contribs 20:19, 29 May 2009 (UTC)

Unless you drive too soon afterwards. 65.121.141.34 (talk) 20:22, 29 May 2009 (UTC)

Just skimming this makes me so glad I'm a vegetarian! I don't advocate eating any sentient being, but strictly sticking to the scientific nitty-gritty, the greatest risk with any kind of meat comes not from the kind of animal it's from, but from the conditions in which the animal lived and died and how the body was handled after death. If the environment was reasonably clean and the meat was properly handled at the right temperature with clean instruments, contamination is unlikely. The more the situation deviates from this ideal, the greater the risk there is that the end result will be unsuitable for consumption. - AJ —Preceding unsigned comment added by 66.215.227.218 (talk) 21:57, 29 May 2009 (UTC)

A comment to the vegetarian: Humanity has eaten meat for ten thousands of years, even before we could be considered "humanity". Obviously this works nicely even in very unclean environments and with animals that were far from living a sterile life, so "unsuitable for consumption" is a very...cultural expression. Today our nice big brain with all the cultural ideas in it may find it "unsuitable", but our ancestors certainly ate what meat they could get, and lived fine with it. Sure, they sometimes got sick, but our immunesystem is really capable of handling most of the insults that nature has thrown at us. I don't say you should eat every meat under every circumstance, but, believe it or not, not many (biological) things you can eat will kill you. This is really only western luxury thinking. --TheMaster17 (talk) 22:26, 29 May 2009 (UTC)

Somewhat of a side-issue, but I should point out that "humans have done it for 1000s of years so it must be ok/healthy enough" is not really a valid argument. The human life expectancy for most of its history has been ~30 years, and almost doubled in the 20th century after public health improvements were introduced. So during those 1000s of years of early history,

• many people did die of what we would now consider to be avoidable causes (food poisoning and various gastrointestinal diseases),
• the short lifetimes meant most people didn't live long enough to develop and subsequently die from chronic conditions like cancer, heart disease, diabetes etc; and so we cannot assess (based on historical evidence) if their habits and lifestyles increased the risk of developing such conditions.

Again, I am not arguing against your conclusion (that eating meat is not necessarily unhealthy); just your justification for it. Abecedare (talk) 01:01, 30 May 2009 (UTC)

The low average age in history (and in most countries with a low average today) is largely because of having a high number of infant deaths (see Infant mortality and Life expectancy. If you lived passed your adolescence you were likely to live to a similar age to people today. A simple wander around any old graveyard and you'll find examples of people living well into their 70s and 80s. I've no idea whether people died of food-poisoning etc. it would seem reasonable that they contributed to early-death but I doubt their contribution was notable - especially in comparison to infant mortality and child-birth. ny156uk (talk) 08:37, 30 May 2009 (UTC)

I totally agree with Ny156uk. And I have a counter argument for Avecedare: If the contribution would have been notable, there would have been selective pressure to correct this. So we would have adapted, and today's population would still be more tolerant. Evolution is a wonderful thing: It takes care that most organisms that survive are totally capable to cope with every thing that they encounter on a regular basis. And as far as we know, bacteria were here before us, so we always had to adapt to them. And our ancestors were also omnivore for a time long enough that our body is really adapted to this (teeth, digestion etc.). There may be short and individual perturbations of the balance with bacteria (this is why some of us still get ill), but on larger scales they are corrected. --TheMaster17 (talk) 11:07, 30 May 2009 (UTC)

Regardless of whether you're actually likely to get intestinal parasites from eating cooked pork or not, there's also the possibility that these worms are in fact good for you. See http://news.bbc.co.uk/1/hi/health/7856095.stm 213.122.2.54 (talk) 19:09, 30 May 2009 (UTC)

beer freezing

Water freezes at 32F. What temperature will a can of beer freeze? I understand that the alcoholic content would make a significant difference and lower the freezing point, but would a 5% alchohol content lower the freezing point by 1 degree, or more on the order of 10 degrees? Would this be overridden by the higher pressure found inside the can? I know, a lot of questions, but I don't have the equipment to test this observationally. 65.121.141.34 (talk) 14:33, 29 May 2009 (UTC)

American-style lager#Ice beer suggests that the water in the beer will freeze separately, see fractional freezing. SpinningSpark 14:44, 29 May 2009 (UTC)

In countries with a very cold climate, I think freezing is used as an informal way to concentrate alcohol to produce a kind of spirit, instead of distillation. 84.13.52.104 (talk) 15:15, 29 May 2009 (UTC)

Dude, 65 said a can of beer, not a vat. —Preceding unsigned comment added by Wikivanda199 (talk • contribs) 15:48, 29 May 2009 (UTC)

Dude, what does that's got to do with anything? Dauto (talk) 16:41, 29 May 2009 (UTC)

He might have a point. Fractional freezing might be effected by pressure. And I assume that the can is pressurized and the vat is not? 65.121.141.34 (talk) 19:00, 29 May 2009 (UTC)

Coming back to the original question: Ethanol freezes at -174F, so the answer has to lie somewhere between 32F and -174F :-) I think we need a theoretical chemist here who can give a melting point formula for solutions. I have no clue if the relationship is linear. If this was the case, the freezing point would be lowered by 5% of 32F-(-174F)=5% of 206F which is roughly 10F, so it would freeze at 22F (without fractionated freezing, which would be irrelevant if the whole can freezes and is melted again (without taking out frozen solid). Hmm, but this is all considering normal pressure. I can't remember my physics lessons concerning pressure and melting point any more. Chemists? Physicists? Anyone? --TheMaster17 (talk) 23:09, 29 May 2009 (UTC)

It's certainly not a linear relationship. Due to the phenomenon called freezing point depression, the freezing point of a solution (in this case, water and ethanol) can be lower than the freezing point of either of the two substances alone. The freezing point of water is 0°C and the freezing point of ethylene glycol is −13°C, but when mixed in the proper ratio (as in automobile antifreeze) the freezing point can be lowered to about −50°C. See, for example, [8]. (I failed to find a good explanation of this in a Wikipedia article, though.) —Bkell (talk) 02:50, 30 May 2009 (UTC)

So the answer is: We don't know? Because there are at least three phenomenons involved: Mixing, freezing point depression and fractional freezing? So there is no "rule of thumb" for even water and ethanol? --TheMaster17 (talk) 10:50, 30 May 2009 (UTC)

No precise answer, but i can tell you that 4.7% alc. beer freezes in a typical household freezer (-18°C). But this can force the bubbles out, causing the container to explode, so the beer splatters all over the place before freezing.YobMod 11:11, 31 May 2009 (UTC)

Best solvent for a blocked printer head?

My colour cartridge printer head is partly blocked. This comment here http://www.pcguide.com/vb/showthread.php?t=49543 suggests other solvents: "Since it's dried hard you need a more powerful solvent than plain water cold or hot. Try Windex. If that does'nt work use straight household amonia. Clorox Bleach will remove the ink no matter how hard it is. Don't bleach too long or it will dissolve other parts of the cartrige as well. Heat will help, but I would not exceed 180 deg F."

What would be the best solvent for dissolving dried ink without dissolving the plastic-and-copper ink cartridge? I have a number of solvents available: water, white sprit, nail varnish remover, bleach, RugDoctor Traffic Cleaner which I think contains glycol - the same chemical used as a solvent in gloss paint. Would anything be better than water?

I am from the UK, so what would the UK equivalent of Windex be? Is ammonia available here - I've never seen any for sale? And is "Clorox Bleach" just the same as "bleach"? The cartridge is an HP78. Thanks. 84.13.52.104 (talk) 15:28, 29 May 2009 (UTC)

Windex in the US is a window cleaner and is usually blue. I would imagine the standard window cleaner in the UK will be chemically the same. 65.121.141.34 (talk) 16:32, 29 May 2009 (UTC)

Clorox bleach is just bleach. Windex is a window cleaner with ammonia in it; there are probably equivalents over there? --98.217.14.211 (talk) 17:39, 29 May 2009 (UTC)

Don't mix bleach and ammonia, though; bad things can result. —Bkell (talk) 03:00, 30 May 2009 (UTC)

Ethanol? Propanol? --Russoc4 (talk) 17:44, 29 May 2009 (UTC)

Ultrasonic cleaning using water is worth trying instead of chemicals. Cuddlyable3 (talk) 11:26, 30 May 2009 (UTC)

Unfortunately I do not have an ultrasonic cleaner. I am surprised that bleach is recommended, as it is not a solvent, but perhaps bleaching the ink colour chemicals helps. 78.147.249.77 (talk) 15:53, 30 May 2009 (UTC)

Bleach (sodium hypochlorite), especially undiluted bleach, is a reasonably powerful oxidizer. This is why it works for bleaching - the colored molecules are oxidized to a colorless form. However the oxidation reaction is not limited to dye molecules, and a large number of molecules can be oxidized. This is why sodium hypochlorite is sometimes used as a drain cleaner - oxidizing molecules tends to break them into smaller pieces which may be easier to dissolve/mechanically dislodge. Using bleach is somewhat of a scorched earth tactic, though, as in its undiluted form it is quite reactive and is slightly dangerous (especially, as mentioned above, with ammonia). If you wanted to use an oxidizer, I might start with a gentler one such as hydrogen peroxide. But before I did any of that, I'd see what the manufacturer recommends to be done for clogged print heads. If it's from a company like HP, where the print head is part of the cartridge itself, you might be best served just buying a new one. -- 128.104.112.106 (talk) 17:15, 30 May 2009 (UTC)

This webpage http://www.northlight-images.co.uk/article_pages/inkjet_cleaning.html recommends using a houshold bathroom spray cleaner, which contains bleach. I like to refill my cartridges, and now have some old ones to play with, so I will try bleach. I do not have any hydrogen peroxide, unless it is easy to buy. 78.144.254.133 (talk) 20:31, 30 May 2009 (UTC)

Try standing the head in a bath of Whey overnight. (Should be available at your grocery store or health food store.) Then rinse in water and pad onto a folded pad of paper towels. If you are in the UK you may be able to find a solvent for drafting pens marketed by the German company Rotring. That should also work. 71.236.26.74 (talk) 07:23, 1 June 2009 (UTC)

Sleep

How much amount of sleep is really necessary for a man in his 20's????Will 5 hours of sleep in night suffice??? —Preceding unsigned comment added by 59.165.84.9 (talk) 17:25, 29 May 2009 (UTC)

You should check out the article sleep. See optimal amount of sleep for adults. 152.16.223.48 (talk) 17:33, 29 May 2009 (UTC)

Old proverb: six hours for a woman, seven for a man and eight for a fool. SpinningSpark 20:01, 29 May 2009 (UTC)

What does that make the French, with their nine hour average?[9] Clarityfiend (talk) 23:10, 29 May 2009 (UTC)

No comment. --Tango (talk) 23:50, 29 May 2009 (UTC)

Yeah, but you got that number from the Daily Mail. Here is a 2006 survey by the Institut National de Sommeil et de Vigilance which comes up with an average of 7.5 hours. An average is not a very reliable figure anyway, since sleep patterns vary a lot with age, and different countries have different age profiles. --Heron (talk) 09:38, 30 May 2009 (UTC)

Twelve for a parrot, FWIW. Plus a long nap in the afternoon. Alright for some, isn't it? ;) --Kurt Shaped Box (talk) 10:04, 30 May 2009 (UTC)

Carnivores that naturally hunt for their food - Dogs, cats, lions, etc - often sleep for over 20 hours a day. If they don't need to hunt for food - they can simply sleep and conserve energy. How much sleep they need - is a different matter though. SteveBaker (talk) 15:11, 30 May 2009 (UTC)

I've heard it proposed that sleep is evolution's way of keeping us out of trouble when we don't need to be doing anything useful. --Tango (talk) 21:14, 30 May 2009 (UTC)

That does not even start to explain the dreadful consequences the following day of sleep deprivation during the night. It is much more likely the other way round, that we sleep overnight because that is a convenient time to do it. Disconnecting our brain and senses from the environment can be a dangerous thing to do when there are predators about, yet all animals do this despite it being unecessary merely to conserve energy. There simply have to be further reasons for sleep, many of which are discussed in the article, and I find it telling that bears waking from hibernation immediately have a need for sleep because they are suffering from sleep deprivation. SpinningSpark 09:17, 31 May 2009 (UTC)

There are all sorts of bizarre things about the way other animals sleep. Dolphins sleep with one half of their brain at a time - so they are never totally unconscious - which is just as well because they need to keep swimming to the surface in order to breathe. There was a hilarious piece of research I read recently that said that some roosting birds can do the same half-brain-at-a-time sleeping trick - but when they are perched in a row - only the birds on the ends of the row have half their brains awake...which suggests that they need to keep half their brain awake in order to keep one eye functioning to look out for danger - while the birds in the middle of the row can sleep with both hemispheres! SteveBaker (talk) 18:32, 1 June 2009 (UTC)

I read something similar recently about sleeping gulls (it may even have been based on the same research). When they're all flocked on a field or a car park, or wherever and dozing in the sun, it's only the ones in the centre of the congregation that sleep with both sides of the brain. I'll bet that it's the larger, stronger more dominant ones that always get to sit right in the middle. --Kurt Shaped Box (talk) 19:45, 1 June 2009 (UTC)

Fetus affected by anesthesia?

If a pregnant woman is put under general anesthesia, will the fetus be anesthetized as well, or would the placenta filter out too much of the anesthetic to make a difference? —Preceding unsigned comment added by 66.215.227.218 (talk) 21:48, 29 May 2009 (UTC)

This article suggests that the answer is ... maybe. --Sean 00:22, 30 May 2009 (UTC)

Thanks. I've since found another article that says that the fetus would be anesthetized under general anesthesia . . . at least they don't seem to get the same stress reactions and reflex responses that would seem to indicate pain during medical procedures. Of course, since the fetus can't report pain in the same way you or I would, it's hard to know for sure. —Preceding unsigned comment added by 66.215.227.218 (talk) 18:48, 30 May 2009 (UTC)

There is a remarkable phenomenon in newborns called the breast crawl (no article yet, but see [10]). When the mother is given analgesics (such as pethidine) around birth, the baby performs very poorly in breast crawling, suggesting analgesics effect the bably also. Indeed one study has found that blood plasma half life of pethidine is 3.0-4.5 hours in the mother, but as long as 13-23 hours in the infant, suggesting the impact on a fetus may actually be potentiated. Rockpocket 21:09, 30 May 2009 (UTC)

Could this rocket put a person into space?

The Skylark (rocket) can lift 440 pounds to 357 miles. Could it in theory be used to put a person into space for a brief time? Would there be so much of a problem with re-entry heating if it was not moving at an orbital speed but just going straight up and straight down? In any case, does the final stage of the rocket burn up or not as it falls to earth? 78.146.211.210 (talk) 23:14, 29 May 2009 (UTC)

I would think the payload's volume would be too small to make this feasible... But it's not given so I don't know. Clearly the available space for life support would be minimal, and I think heat shielding alone is likely to make 440 lbs too little. TastyCakes (talk) 23:24, 29 May 2009 (UTC)

Even if you could fit in the life support (not a great deal needed for just a few minutes) and heat shield (not much needed for a sub-orbital craft compared to a Space Shuttle or similar), you would need some impressive parachutes and they aren't light. --Tango (talk) 23:44, 29 May 2009 (UTC)

Taking the Project Mercury capsules as a baseline, the article says their launch weight was 4,265 lb. However, nearly half of this is fuel for the retro-engine burn to get the thing out of orbit - this would not be needed in the case of a straight-up-straight-down flight. The landing weight was 2,241 lb. A good deal of this would be engines, also not needed, and also the remains of the heatshield can be subtracted and most of the life-support. After taking all that off you might just about be getting into the right ballpark of 440 lb, but it is probably right on the limit of what can be achieved. But remember, space actually starts a lot lower than 357 miles, it is 62.1 miles by one definition. Skylark could easily achieve a manned mission to this height since payload is much greater for a lower altitude mission. SpinningSpark 01:14, 30 May 2009 (UTC)

Of course, being in space is not the same as being in orbit. A significantly larger rocket is needed to reach an altitude and stay there (in other words, to change the necessary angular momentum for an orbit that does not re-intersect the ground). Further, orbital altitudes are necessarily much higher than the ~100 km "boundary of space" definition, because atmospheric drag will decay very low orbits at a dramatic pace. Low earth orbits are typically as high as 300-500 km. Nimur (talk) 15:09, 30 May 2009 (UTC)

Wear a space suit, and a lightweight bag full of foam plus a personal parachute would suffice for reentry from orbit, let alone from a suborbital flight. See MOOSE. Edison (talk) 20:08, 30 May 2009 (UTC)

A space suit isn't light, that lightweight foam is only lightweight relative to a conventional heat shield and the parachute you would need to land all that weight at a safe speed wouldn't be light either (unless you could someone bail out of the bag and suit at just the right moment so the parachute only have to slow you down). You're not going to fit all that, and a person, into 440lbs. --Tango (talk) 20:32, 30 May 2009 (UTC)

Skylark is only 17 inches in diameter. Even if you envision a small person standing straight up the whole time it is hard to see how one could launch a person and the hardware required to get them back through reentry while using such a small rocket. Dragons flight (talk) 22:33, 30 May 2009 (UTC)

I would give it a shot, personally speaking. Sometimes the payload is larger in diameter than the rest of the rocket. Edison (talk) 02:05, 31 May 2009 (UTC)

pH change at river mouth?

I was just wondering, at the mouth of a river, would the pH change with water depth?

I know that the water containing the lower salt concentrations would remain floating up the top (usually the river water)and that the ocean water (containg more salt ions) would remain down the bottom. but does the pH vary with water depth at the mouth of the river where this water seperation occurs? if so, why?

thanks —Preceding unsigned comment added by 122.108.206.219 (talk) 23:45, 29 May 2009 (UTC)

Lots of salts alter the pH of water, so pH would also change with different amounts of different sorts of salts. It would be impossible to predict how pH will change with depth, but I would expect that in any body of water, there will be some variance in pH at different locations, whether its in the deep ocean, a fresh-water lake, or a brackish estuary like you describe. --Jayron32.talk.contribs 00:47, 31 May 2009 (UTC)

May 30

Plumeria

I've posted a query on its Talk page about Plumeria's otherwise New World origins including one Asian locale. --Thanks, Deborahjay (talk) 05:09, 30 May 2009 (UTC)

Trees of the World (Russell et.al.) describes the genus as distributed in Southern Mexico, Panama, and the Caribbean. It is also mentioned ibid. that the "the trees are found growing in temple grounds of Buddhists, Hindus, and even [sic] Muslims". I think is is therefore safe to assume Plumeria to be introduced in Southern India rather than being native there. I'll keep looking for a more definitive ref though. Best regards, --Dr Dima (talk) 05:31, 30 May 2009 (UTC)

Carnivores' flesh indigestible for humans?

Over the decades, I've collected the following impressions I'd like confirmed or disabused:

• Fox meat is indigestible for humans; legendary example: fur trappers lost in a blizzard would starve to death beside their plentiful catch of foxes or similar animals.
• Humans lack the necessary enzymes to digest certain proteins found in carnivore flesh.
• The above does not apply to the flesh of omnivores (e.g. dogs, humans).

Any science to back this up or otherwise? And where might I have searched such info? (Afterthought: probably someplace like The Straight Dope, but since I'm a Ref Desk Regular, I naturally posted here.) -- Thanks, Deborahjay (talk) 05:33, 30 May 2009 (UTC)

Dog meat is definitely edible. Bear meat is edible, too; there is a sort of salami-like product made with bear meat that used to be sold in Russia, I forgot what it's called. --Dr Dima (talk) 05:37, 30 May 2009 (UTC)

The Bear page does state: "Bears have been hunted since prehistoric times for their meat and fur". But while I understand they kill and eat animals, I thought they were omnivores (perhaps based on cartoons viewed in my childhood?). -- Deborahjay (talk) 05:46, 30 May 2009 (UTC)

Yes, you are right, both brown bears and domestic dogs may be considered ominvores (even though wolves and polar bears are obligate carnivores AFAIK, and they are so close genetically that the dog-wolf and brown-polar bear hybrids are fertile). However, cats are carnivores, and cat meat can be eaten, too. --Dr Dima (talk) 06:06, 30 May 2009 (UTC)

This forum is of the consensus that fox may not be particularly tasty (depending on what it dined on last), but is edible; one person even provided a recipe ("boil slightly, then fry"). There's another recipe for "pan boiled fox" here, with a claim that the person has tasted it. Clarityfiend (talk) 05:44, 30 May 2009 (UTC)

We also have an article on cat meat (a.k.a roof rabbit). --Dr Dima (talk) 05:50, 30 May 2009 (UTC)

And from the Brits (who should know their foxes): fox pasta. That article also says that "the Thais eat a lot of fox." Clarityfiend (talk) 05:54, 30 May 2009 (UTC)

OP's interjection: The cat meat page includes a telltale line: "Because cats are carnivorous, consumption of cat meat is not permissible under Jewish or Islamic dietary laws." Given my longtime albeit sketchy exposure to the Laws of Kashrut, this may be the source of my having extrapolated "don't consume" to "can't digest". The bacteria-and-toxin warning is effectively alarming, though. -- Deborahjay (talk) 06:05, 30 May 2009 (UTC)

AFAIK, carnivore meat can be eaten under pikuach nefesh conditions. If cat meat was deadly, it would not have been allowed under any conditions, I think. --Dr Dima (talk) 06:09, 30 May 2009 (UTC)

There was the analysis once of the cause of death of a human fossil as having been eating the organs of a large feline (source?).Julzes (talk) 06:49, 30 May 2009 (UTC)

Big cats don't take kindly to humans trying to eat them alive. --Kurt Shaped Box (talk) 09:41, 30 May 2009 (UTC)

It might have had something to do with eating the liver. In many carnivores the liver can be poisonous with too much vitamin A. Dmcq (talk) 10:00, 30 May 2009 (UTC)

For which we have an article, of course. Vimescarrot (talk) 10:11, 30 May 2009 (UTC)

Yes, I believe skeletal analysis concluded that this woman probably ate a lion's liver.Julzes (talk) 18:30, 30 May 2009 (UTC)

Have you ever heard that whale intestines are considered bad food, for some reason? Apparently (according to to TV), not even the scavengers will touch them. --Kurt Shaped Box (talk) 10:09, 30 May 2009 (UTC)

The standard explanation given to me is that it's inadvisable to eat carnivore flesh because they're higher up the food chain, thus will have more concentraded toxins (pesticides, herbicides, among any other, more natural, toxins). Vimescarrot (talk) 10:13, 30 May 2009 (UTC)

Another reason that's often been cited whenever the question of why people don't eat <carnivorous animal in question> has been raised here is that carnivore meat (supposedly) picks up the taste of whatever the animal has been feeding on. Which usually means that it's unpleasant on the palette. --Kurt Shaped Box (talk) 10:19, 30 May 2009 (UTC)

I would say that is a superstition. Most animals digest their food completely, breaking it down to basic molecules, then use these as nutrition for their cells. No "taste" can be transported from the stomach to the muscles in this way. This goes more into the spiritual direction "you are what you eat", the superstition that you take up spiritual parts of the animals/plants you eat. Biological nonsense. There are a few exceptions to this, but as far as I know these organisms enrich "by purpose" only certain contents of their food (e.g. toxins) they could not build themself. I would expect most mammal meat is perfectly digestible by humans, as the composition of mammals is mainly the same. Even other animals should pose no problem to our digestion, with the important exception of toxins that some have evolved to deposit in certain parts of their bodies, sometimes even in their flesh. And concerning the enzymes: What our digestion does is to cut down proteins/fats to very small pieces, than take them up. So it is basically unimportant what it was before, because afterwards it is just "basic chemistry stuff" that is then reused. It is a bit more complicated with sugars and other contents, but as we are talking about meat, which is mostly protein and fat, we are perfectly evolved to digest what may be in there. And as a remark: this is about digestion, not taste, and not about contamination if the meat is from carrion. --TheMaster17 (talk) 10:44, 30 May 2009 (UTC)

Actually it is partially true (just to be clear I was referring to Vimescarrot and KSB when I said it's partially true). Stuff like mercury, PCBs etc can't be digested... See also biomagnification and perhaps bioaccumulation. It's a far greater problem now then it used to be of course. This is of course in regard to toxins, not so much taste, although diet can definitely influence taste albeit not in such a simplistic way Nil Einne (talk) 11:36, 30 May 2009 (UTC)

This is not true at all, there are multiple examples of the animal's diet effecting taste and/or texture of the meat. Our cattle feeding article states there is a big difference in the taste between corn-fed and grass-fed cattle citing a study by Colorado State University. Corn-fed chicken is well known to be tastier and has a yellow colour, here's a recipe from a TV station saying so. The effect is scientifically objective enough that it can be tested for as this supermarket found to its cost when it tried to cheat. Atlantic salmon do not have the same taste as farmed salmon, even the red colour comes from their diet of krill, farmed salmon are either artificially coloured or dyes are added to their feed. SpinningSpark 13:55, 30 May 2009 (UTC)

I just want to point out that we do eat carnivores—lots of the fishes we eat are apparently purely carnivores. --98.217.14.211 (talk) 12:20, 30 May 2009 (UTC)

My (= OP's) intent was mammalian carnivores, though you're right, I did leave that unspecified. For the record (if I recall correctly), the Laws of Kashrut forbid eating scavengers and avian raptors, among other and better-known prohibitions. -- Deborahjay (talk) 12:59, 30 May 2009 (UTC)

I'm pretty sure if they'd had access to them, the Chinese would have given it a try, as per their saying "if its back faces the sky, you can eat it"[11]. TastyCakes (talk) 15:00, 30 May 2009 (UTC)

I once read in one of those SAS Survival Handbooks that you can eat at least some bits of just about everything that crawls, walks or flies, provided you know how to prepare it. In addition to the livers of several species and the skins of several more, you apparently shouldn't eat the heads of rats or venomous snakes (the latter seems obvious). --Kurt Shaped Box (talk) 16:29, 30 May 2009 (UTC)

I read the same handbook - you missed out "swims". Basically, the flesh of all animals is edible. You need to be a little careful with internal organs, but if you stick to flesh you are safe (at least, if you cook it, but even raw the risks are generally pretty small, the only diseases you need to worry about are those than can infect both the animal you are eating and you, and that's not many for most animals). --Tango (talk) 17:18, 30 May 2009 (UTC)

I don't know about 'swims' - there's plenty of odd things at sea. Would you be able to eat a stinging jellyfish, for example? --Kurt Shaped Box (talk) 17:34, 30 May 2009 (UTC)

Perhaps the handbook didn't count jellyfish as swimming, they generally just float around. At least some jellyfish are eaten, though: Jellyfish#Culinary uses. --Tango (talk) 17:49, 30 May 2009 (UTC)

Here's a quote from the survival instructions that live in my survival tin (which, usefully, lives on a shelf in my room...): "If it walks, crawls, creeps, flies or swims - it can be eaten. Avoid, however, oddly shaped fish, especially those with spines or horns or box shaped bodies." I believe the flesh of even those fish it says to avoid is edible, but it is just risky because you might accidentally eat a poisonous internal organ. --Tango (talk) 17:54, 30 May 2009 (UTC)

Poison... Poison... Tasty fish!. --Kurt Shaped Box (talk) 17:56, 30 May 2009 (UTC)

The reason those fur trappers died - despite stuffing themselves full of fox meat was because those kinds of animals are very lean - without enough fat content in your diet, you don't last long. See our article rabbit starvation. SteveBaker (talk) 15:07, 30 May 2009 (UTC)

Crocodile and alligator both taste pretty good and are easily digested. Rockpocket 20:56, 30 May 2009 (UTC)

We eat fish, and most fish we eat are strictly carnivorous. So are seals andf various other sea animals. Plus there's alot of scavenging bottom feeders like crab that we eat, and they dont eat any vegitation. Carnivourous snakes and frogs also eaten. Domestic dogs are a popular food in Thailand, although they are fed an omnivorous diet. 209.148.195.177 (talk) 11:06, 31 May 2009 (UTC)

What I've heard is that eating the liver of a predator can be fatal because they concentrate vitamin A at extremely high levels, but I don't think predator meat in general is inedible, although most of the muscule tissue must be so tough that you'd have to boil the hell out of it to make it chewable. Looie496 (talk) 18:09, 31 May 2009 (UTC)

Body pressure and atmoshperic pressure

what is the pressure inside an human body?How does it balance atmospheric pressure? —Preceding unsigned comment added by Mukildev (talk • contribs) 05:40, 30 May 2009 (UTC)

The most part of the inside of a human body is solid and will therefore be at atmospheric pressure. However there are some places within the body that are occupied by air but they are connected to the atmosphere to equalise changes in pressure. The middle ear is connected by the Eustachian tube, the digestive tract has an aperture at each end and cranial sinuses have external apertures. The lungs will have varying pressure depending on whether the person is inhaling or exhaling, but in any case they are open to the atmosphere. Richard Avery (talk) 09:18, 30 May 2009 (UTC)

However, Blood pressure is considerably higher. -Arch dude (talk) 10:11, 30 May 2009 (UTC)

Is that the reason for arterial spurt (wut, no arti-cool?), as a matter of interest? --Kurt Shaped Box (talk) 10:23, 30 May 2009 (UTC)

Roughly, yes. The reason it spurts is because of the varying pressure, due to the heart beating. If it were just constant high pressure it would spray out at a constant rate. --Tango (talk) 11:40, 30 May 2009 (UTC)

Thanks. Yes, that makes sense. --Kurt Shaped Box (talk) 16:31, 30 May 2009 (UTC)

• Pressures below atmospheric pressure often exist in the human body. Transpulmonary pressure has a red link for pleural pressure but says, "pleural pressure is always negative and relatively large". I do not think that is entirely true since pleural pressure is often said to be positive during forced expiration. See this and this. The page for transpulmonary pressure should link to pleural cavity. Breathing has a big ugly red link to negative pressure breathing. Interstitial fluid pressure is often negative due to lymphatic function, see. --JWSurf (talk) 00:49, 31 May 2009 (UTC)

Numerical Schrodinger solutions

Is this assumption that I'm making correct? If its not could anyone explain why? In an empirical method for the determination of electronic structure, the Schrodinger equation is written in terms of parameters chosen to agree with the experimental quantities. So, in density functional methods, can the schrodinger equation be solved numerically? Without needing parameters that appeal to experimental measurements? I appreciate thats a strange way of writing what I mean.....144.32.155.203 (talk) 14:05, 30 May 2009 (UTC)

You are asking too many questions at once... I think the best for you would be to read Density functional theory to understand what it is, and to read Hartree-Fock method and related methods to understand what the alternatives are. The simplest density-functional method is Thomas-Fermi model - it is really simple and intuitive. There are many good introductory-level quantum mechanics textbooks that cover both Thomas-Fermi and Hartree-Fock. Once you understand that, the rest will hopefully be easier. If you have any specific questions after you've done that - please don't hesitate to ask. As for "the Schrodinger equation is written in terms of parameters chosen to agree with the experimental quantities" - can you please be more specific? --Dr Dima (talk) 21:45, 30 May 2009 (UTC)

Is burnt food bad for you?

Someone claims that burnt food creates harmful free radicals inside the body. Does burnt food cause any harm, radically or otherwise? Vimescarrot (talk) 19:00, 30 May 2009 (UTC)

I think it does, but then so does pretty much everything else. BBQs are particularly nasty for carcinogens, I believe, but I still love them! Unless somebody gives you statistics regarding how many years eating burnt toast will, on average, take off your life, treat claims of it being harmful with a pinch of salt. The mechanism they describe is probably true - burnt food probably does contain free radicals and free radicals are harmful, but the human body has ways of dealing with harmful things, including free radicals (and, even better, free radicals give you an excuse to drink red wine, because apparently it contains anti-oxidants which deal with the free radicals!). --Tango (talk) 19:13, 30 May 2009 (UTC)

I should probably give you some links - Free radical#Free radicals in biology would be a good place to start if you want to find out more - lots of great links in there. --Tango (talk) 19:14, 30 May 2009 (UTC)

Wouldn't the pinch of salt also kill you? 213.122.2.54 (talk) 19:26, 30 May 2009 (UTC)

I would be less worried about free radicals per se than about polycyclic aromatic hydrocarbons, which tend to form when organic material is exposed to high temperatures. Benzo(a)pyrene in particular (should be benzo[a]pyrene but for technical reasons I think you can't wikilink that) is a nasty carcinogen. --Trovatore (talk) 20:06, 30 May 2009 (UTC)

Yes burnt food definately is, particularly burnt meat. Its not just the free radicals, but other seriously carcinogenic chemicals. Acrylamide is widespread in baked or fried food, and I wonder if it is doing us harm without it being detected due to its ubiquity, in the same way that lead did with the Romans without them being aware of its dangers because it was in everything. 78.144.254.133 (talk) 20:17, 30 May 2009 (UTC)

It's something I have wondered about, this is conjecture but my guess is people have evolved some defences against the stuff in burnt food and we're probably much more resistant to these chemicals than other animals. Anyway a possible investigation for someone. Dmcq (talk) 20:58, 30 May 2009 (UTC)

(Proto-)Humans have been cooking food (Control of fire by early humans) long enough for evolution to have built up a defence to it, so that's a highly plausible conjecture. --Tango (talk) 21:11, 30 May 2009 (UTC)

Actually I'd be much more interested if we haven't built any defences against them. I haven't the foggiest what that would mean. Dmcq (talk) 21:36, 30 May 2009 (UTC)

I guess it would mean either that the problem of defending against these carcinogens biologically is an obstructively complex one compared to others solved by human evolution over the same time period, or else that the carcinogens don't kill significant numbers of people until old age, at which point throughout most of the time period in question we'd be dead anyway (or too old to breed would also do the trick, if there is such a thing). 213.122.49.104 (talk) 22:01, 30 May 2009 (UTC)

Or that burnt food doesn't offer a significantly greater risk than the numerous other causes of free radicals, so all animals already have the defences necessary. --Tango (talk) 00:29, 31 May 2009 (UTC)

Tango, keep up. It's not free radicals. It's polycyclic aromatic hydrocarbons.

Anyway, according to our article, there are specific defenses against benzo[a]pyrene, which after all occurs all over the place, not just in your barbecue but anywhere organic matter burns. --Trovatore (talk) 00:46, 31 May 2009 (UTC)

I'm surprised no one has pointed this out yet, but in addition to the polycyclic aromatic hydrocarbons and carcinogens and such, burned food tastes really nasty. - Sticking to Chocolate —Preceding unsigned comment added by 66.215.227.218 (talk) 21:42, 30 May 2009 (UTC)

Burnt chocolate is the worst - don't melt chocolate in a microwave, take the extra couple of minutes to do it properly over a bowl of hot water! --Tango (talk) 00:29, 31 May 2009 (UTC)

Burnt food is awesome. If my mother tells me my food is cooked, I tell her to leave it in for another ten minutes...which is why I asked this question. Vimescarrot (talk) 00:50, 31 May 2009 (UTC)

I don't care for burned food in general, but there are a few exceptions. Sharp cheddar cheese is very nice cooked to a slightly brown crust. When I make a pasta sauce from red bell peppers, I find that it comes out sweeter if I sautée them with the garlic and hot pepper until there are black spots on the skin of a few of them, before I put in the wine and veggie juice (which brings down the temperature). A similar principle applies to eggplant. --Trovatore (talk) 01:57, 31 May 2009 (UTC)

I'm actually very fond myself of the crusty edges at the corners of pans - someone actually made a maze-like baking pan in which everything would come out with crusty edges, and I so want to get one! But actual BURNT food - nah! I suppose it depends what you call "burnt." What I call toast, my brother calls "warm bread." What my brother calls toast, I call "charcoal." Each to his or her own, I suppose. - Sticking to Crusty Chocolate Brownies and Warm Bread —Preceding unsigned comment added by 66.215.227.218 (talk) 04:25, 31 May 2009 (UTC)

Thanks Trovatore for the Benzo(a)pyrene reference. So all mammals can deal with burnt food to some extent. The enzymes to do this are part of the very wide ranging Cytochrome P450 family and seemingly mice have more than twice as many genes for this family as people. Sounds like mice should thrive on welsh rarebit and the burnt edges of pie dishes. :) Dmcq (talk) 08:20, 31 May 2009 (UTC)

I think it's also worth emphasizing that protective measures selected during evolution might not be expected to prevent complications like cancer after childbearing years. This is a simplification, but not a worse simplification than the notion that it's safer to eat carcinogens because we have some protections against them. --Scray (talk) 14:30, 31 May 2009 (UTC)

It depends on the kind of food. Burnt fat gives barbecued meat a lot of its flavor, and burnt sugar, if not too badly burnt, is caramel. Burnt protein, though, is nasty. I too have heard that burnt fat can be carcinogenic, but don't know a source for the facts. Looie496 (talk) 18:04, 31 May 2009 (UTC)

It is I believe a scientific fact that a proportion of cancers are caused by the wrong kind of diet. If evolution has not protected us against that, or many other lethal illnesses such as heart disease or (formerly) diabetes, why should it protect us against burnt food? 89.240.58.231 (talk) 18:47, 31 May 2009 (UTC)

Perhaps because those wrong kinds of diets have only been around for a few tens to a few thousands of years, giving natural selection insufficient time to adapt populations to them, whereas diets incorporating burnt meat have been around for at least several hundred thousand years, as Dmcq and Tango suggested. Remember also that evolution mostly works by people with the less adaptive genes dying before they reproduce, hence naturally selecting in favour of the ones who have better adaptive genes: diseases that mostly affect people over, say, 40 are not very succeptible to natural selection, as .104 and Scray indicated. 87.81.230.195 (talk) 19:07, 31 May 2009 (UTC)

See Charcoal biscuit for beneficial use of "burnt" substances in your food. Eating soil by the shovel load is really bad for you. But a bit of certain kinds of clay can be quite healthy (surprise, surprise:-) You should remember that cooking food gets rid of a couple of nasty pathogens and parasites. Natural selection isn't going to help solve this puzzle as others above have indicated. Ultimately you are going to die of some form of cancer ... if you don't die of something else first. 71.236.26.74 (talk) 07:11, 1 June 2009 (UTC)

Storage capacity of the human brain, in gigabytes?

Remember the 1995 movie "Johnny Mnemonic," about the guy with the 160-GB data transport device implanted in his head? (Neither do I; I changed the channel after the first 15 minutes.) But today, something (OK, it was the fact that I found my keychain in the washer after doing my laundry, with my 512-MB thumb drive attached) made me think about how just a few decades ago, even the experts would never have thought that ordinary folk would need half a gig of storage capacity for personal use, let alone that it could fit in the pocket of a pair of shorts. And that brought back what I thought when I was trying to watch "Johnny Mnemonic": 160 GB may have been huge back in 1995 (as they implied), but even today the most amazing computers can't do what the human brain has been doing much better all along. Arguably the human brain is (and probably always will be) the most sophisticated computer yet devised: both the brain and computers as we know them require a sophisticated network of components devoted to specific tasks, relay information via electrical impulses, and process new messages/stored information via symbolic coding of sorts (be it "110=green pixel" or "your-cheating-ex's-perfume=adrenalin=angry"). What I'm wondering is, if the human brain were a computer, made of the materials and with the technology we have, what would its specs and storage capacity be? Has anyone ever calculated this? (P.S. Don't lose that protective cap that goes over the end of your thumb drive. Turns out, it's waterproof.) - AJ —Preceding unsigned comment added by 66.215.227.218 (talk) 21:30, 30 May 2009 (UTC)

This article makes a reasonable estimation. In summary, it proposes the brain is like a 168,0000 MHz Pentium computer by scaling up from an estimate of the processing power of the retina, which can transmit ten one-million-point images per second. This is likely a huge underestimation because the brain does a much more complex job, in terms of parallel processing, than a retina. But it is probably a reasonable minimum value. In terms of memory, they propose the average brain could hold about 100 million megabytes, based on total synapse estimation. This doesn't account for neuroplasticity, however, and how that modifies storage capacity is difficult to estimate (since we don't really understand it biologically yet). Rockpocket 21:46, 30 May 2009 (UTC)

The problem is, we don't really know how the brain works. We have some idea, but it does not make a comparison to a digital computer any easier. Problem #1: the brain uses a wide varety of coding strategies (population, rate, combinatorial, spike timing, etc...) while the digital computer uses only two (parallel binary and sequential binary). Problem #2: data processing in brain is not synchronous. Problem #3: for a data flow within the digital computer, Shannon information is well defined; for the "data" flow within the brain, it is not (for example, the more precisely you specify the spike timing the more "information" you find). Problem #4: the state of the digital computer is uniquely defined at any given moment, and there are only 2^(number of the gates) possible states. Not so for the brain, unless you count every sub-unit of every ion channel as a separate gate. And so on... --Dr Dima (talk) 22:02, 30 May 2009 (UTC)

Both you and the article say "168,0000 Mhz". Do you mean 168,000 Mhz or do you mean 1.680.000 Mhz? The figure I get from the numbers given in the article is 16,800,000 Mhz. 89.240.58.231 (talk) 18:58, 31 May 2009 (UTC)

I mean what the article said, since that was where I cut and pasted it from. I didn't do the calculation myself. Looking at it again, it is a very weird way or writing it though, so I guess your calculation might be correct and they made a typo. Rockpocket 03:30, 1 June 2009 (UTC)

Thanks, Rockpocket - that was an excellent article! Unfortuantely, it was outdated by about 10 years, making it hard to compare the human brain with the latest in computer technology, since I don't know what the very latest and greatest human creations are capable of. Still, I have no doubt the human brain is still the clear winner when it comes to sheer capacity, if not always speed. Still, artificial intelligence is a very interesting field - it's always interesting to see how AI and psychology have taken from and built off of each other. Even the old dualistic talk of the "ghost in the machine" acknowledged that there had, in fact, to be a machine for the ghost to operate - and whether there's any spiritual dimension to our consciousness or not, everything that we are and do does in fact exist in the brain in some way. On the other hand, as a big fan of The Sims and its sequels, it's funny and a tad ironic to dive into the programs' inner workings and see how some of the most apparently natural humanlike behavior is brought about through the most mechanical and artificial ways . . . Dr Dima, you raise some excellent points. I'm very aware that we don't understand exactly how the brain works - a fact which brings me endless wonder (and frustration!). I don't claim that the computer and the brain are exactly parallel - only that there are enough similarities to make the comparison, and my question, compelling. As for the possibility for counting every sub-unit of every ion channel as a separate gate . . . Data storage, even by computers, need not be digital. There is such a thing as a "trit," or trinary bit, with three possible states, so the brain may have any number of possible states. . . . Obviously the state of the brain is "uniquely defined at any given moment" in some way - the way my brain now is the result of its unique chemical composition, history, and recent input, and were those exact data to be duplicated in your brain, or in my brain at some future time, you or my future self would experience this precise moment I'm having now. Strong emotional flashback memories, or even recurring dreams, demonstrate the abilty of the brain to reproduce at least partially a previous state. Furthermore, what's to say that there *aren't* a finite number of brain states? After all, there are definitely a finite number of computer states, but their capacity is great enough that no two computers (not counting networks, etc.) are in exactly the same state. As a writer, I type things all the time that have never been typed before. Sometimes I even share my writing with friends - and if I've been successful, my choice of words will stir up in them the same things I was feeling when I sat down to write - experiencing a few of the same cognitive patterns. Yes, it's *very* complicated, and I realize that I can't expect a definitive answer to this question. But it's sure fun to think about, and to explore the parallels and divergences while we're at it. - AJ —Preceding unsigned comment added by 66.215.227.218 (talk) 22:42, 30 May 2009 (UTC)

For a discussion, see Technological singularity and related articles. For the "latest" computers, see Supercomputer. -Arch dude (talk) 01:26, 31 May 2009 (UTC)

Thank you! Unfortunately, the specs for the supercomputers are given in FLOPS instead of MIPS, but at least after searching around a bit I was able to compare the human brain to my own desktop PC. (Of course, I'm really going to feel stupid now next time it gets the better of me, which still happens once in a while!) - AJ, Clearly the Better Machine —Preceding unsigned comment added by 66.215.227.218 (talk) 04:44, 31 May 2009 (UTC)

Most of the computers we used are based on a Von Neumann architecture. This is the sort of thing that looks so obvious to anyone who uses computers that it's hard to remember why it was so ground-breaking—you keep the memory in one area, the input/output in another, have another part for doing the logics, have another part for taking care of the operations, etc. It's a great way to design a piece of hardware—each component can be relatively independent of each other, so when your hard drive crashes you just put in a new one, and all is well. But as far as I can tell it's a lousy model of the human brain (which is not it's fault—it wasn't trying to be one). While it's clear that our brain has specialized sub-organs for handling different types of "processing" (language centers are particularly conspicuous in this regard—if you suffer damage to them, you suddenly can't do certain types of language operations), it seems fairly clear that all parts of the brain are suffused with some aspects of all of the other components, and the divisions between these sub-organs appear somewhat fluid.

I sort of see digital computers and wetware processing as apples and oranges. There are a few ways in which they can interface but they aren't the same architecture. They have superficial similarities—like a dolphin and a tuna fish do—but they operate on quite different means. I think the computer metaphor probably does more harm in understanding how the brain works than it does good. (But I'm not an expert at this, just someone who has read a few books here and there.) --98.217.14.211 (talk) 14:24, 31 May 2009 (UTC)

It is tricky to think in terms of the brain as a piece of electronics because they work very differently. The brain has relatively few cells and an awful lot of 'wiring'. Each cell has thousands of connections out to other cells. Cells (and the connections between them) work VERY slowly compared to the logic gates in a computer...a million times slower. In a computer, the nearest thing to a "cell" might be a logic gate (AND,OR,NOT,XOR,etc) - it takes a couple of gates to make a memory bit and thousands of gates to make (say) a 32 bit floating point addition unit. But the computer has much, much less wiring. Most gates have only two or three wires going to them...and they are a few million times faster than a cell. Furthermore - in the computer, only a fraction of the gates inside the CPU are switching at any given moment - and barely a handful of the memory bits are switching on each clock cycle. By contrast, most of the cells in the brain are firing all the time.

Comparing a large, slow, vastly-interconnected, highly active "biological machine" with a small, fast, minimally-connected, rarely-switching one is very difficult - the comparisons just don't make sense numerically.

However, we can do this: With a digital computer, we can write software that emulates a brain...'neural network' software can simulate what happens at the neuron level in the brain. So we could ask how much of a 'brain' could a modern computer simulate? I did some calculations here a while back that suggested that the speed of neural network software running on a PC is about a factor of a billion short of a real brain...that's actually not very much. I believe (on that basis) that if Moore's law continues at it's present rate (doubling the performance of computers every year) then in about 25 to 30 years - with a warehouse-full of a few million bucks worth of electronics (something like Google's massive computer farm) - I think we could build a complete simulation of a human brain - accurate and functional.

But using a computer to simulate a brain is a severe mis-use of it's resources. If you try to do the reverse and use a brain to simulate a computer (something I often have to do when I'm debugging a computer program by following it through line-by-line) - I'd be lucky (even with support of pencil and paper) to run one line of software per second. That makes my brain a few billion times slower than a real computer - with a few billion times less 'fast RAM'.

So if a modern PC is a billion times 'less' than a brain when simulating a brain. And my brain is a billion times 'less' than a PC when simulating a PC...what can we truly say about their comparable performance? You could argue that by some bizarre kind of averaging - they are about the same. But that's not right. So what about some actual experiments?

I like to do this one. Imagine somewhere in your home where you have a shelf - maybe in the garage, full of paint cans and such. Now - imagine that the bracket holding the shelf up at one end were to fail - what would happen? I'm sure you can imagine the rapid sliding of everything off one end - a big pile of stuff on the floor - some of the lids came off of the paint cans - so there is a spreading puddle of paint - maybe colors mixing and flowing together. You did this "calculation" in a fraction of a second. The results are horribly inaccurate - you don't know the precise positions of the paint cans or exactly where the paint will be distributed...but you know the important parts of the answer AMAZINGLY quickly. Doing that same thing inside a computer would take weeks of CPU time. The results would be much more accurate (but not perfectly so) - but the essential useful data (did it make a horrible mess?) is still there.

So in doing that kind of calculation, our brains are vastly more efficient than computers.

On the other hand - the time it would take you to divide two hundred-digit numbers in your head - and get a result accurate to two hundred digits - is similarly wildly different from the time the PC would take to do the same thing. Even 'savants' who can actually do this kind of thing take a long time.

This is a measure of how the differences between the design of (and demands upon) brains and computers is so different that we really can't come up with a scale of comparison...not numerically, not functionally.

SteveBaker (talk) 17:59, 31 May 2009 (UTC)

light acting like a solid

Hi

I read somewhere about someone producing light that could act like a matter to some degree, I know that it doesn't mean we are gona make green lantern rings or something, but is this true, and if it is how does it work and to what extent, just quantum size or perhaps a new kind of optical levitation for micro chips.

Thank you

Rob —Preceding unsigned comment added by 79.68.182.166 (talk) 23:03, 30 May 2009 (UTC)

The Z boson possibly? SpinningSpark 01:59, 31 May 2009 (UTC)

Preempting my reply with the caveat that I don't really fully understand quantum mechanics myself, I was under the impression that the idea behind wave–particle duality was that all light (energy) showed matter-like properties, and vice versa. Rockpocket 02:05, 31 May 2009 (UTC)

It can behave like a particle (photon) but not like solid matter the way I think you are getting at. -RunningOnBrains^{(talk page)} 02:20, 31 May 2009 (UTC)

As I understand things, since photons have energy, they also have mass and momentum. When photons are absorbed by or reflect off of other objects, those objects react. See radiation pressure and solar sail. -- Tcncv (talk) 04:51, 31 May 2009 (UTC)

Photons do not under any circumstances have mass. They have energy, they have momentum, and they can behave like a particle, but they are explicitly and exactly zero mass. Nimur (talk) 18:36, 31 May 2009 (UTC)

Wikipedia article: Lene_Hau claims she changed light to matter which I believe is an oversimplifaction of her experiments with Bose–Einstein condensate --Digrpat (talk) 04:41, 31 May 2009 (UTC)

Judging from the paper abstract and the Scientific American article, what they did is transfer a qubit from a photon to some sort of matter substrate and then to another photon. That sounds like it might be useful for quantum computing, but it doesn't make the light act like matter. -- BenRG (talk) 10:27, 31 May 2009 (UTC)

Perhaps I should have expanded on my answer a little, the Z boson, like the photon of light, is a boson that mediates a force. Like the photon it carries no charges. The difference is that the mass of the photon is zero while that of the Z boson is very large. For that reason, the Z boson is sometimes described, rather inaccurately, as "heavy light". SpinningSpark 09:56, 31 May 2009 (UTC)

To be completely clear - the photon has no REST mass - but moving at the speed of light, it does indeed have mass (as it must because it has energy and E=mc²). But the line between 'light' and 'matter' is a fuzzy one. We can regard photons as particles - and we can regard electrons, neutrons and protons as waves. We can (if we choose) regard a 1972 VW bug as a wave! But in terms of shining a laser beam and somehow making it 'hard' so you could hit it without your hand going right through it - no. There is no way for that to happen. However, the same thing is true for a beam of alpha radiation (helium nucleii) or beta radiation (electrons). The idea of "hard light" that the authors of StarTrek talk about in the holodeck of the starship Enterprise is pure fiction. SteveBaker (talk) 17:34, 31 May 2009 (UTC)

To be clear, what Steve is calling "mass" is "relativistic mass", which isn't a concept used much in modern physics. It's a useful way of getting your head round this kind of stuff, but isn't actually useful for doing anything. "mass" in modern terminology means "rest mass". The key thing which stops light being "hard" isn't that it isn't matter (it is, for sufficient intents and purposes), it's that there are no bonds between photons. Solid matter is lots of particles bonded together, a beam of light is just lots of particles. (Star Trek holodecks use "force fields" to make things hard, the term "hard light" appears in Red Dwarf in reference to holograms, though, perhaps you were thinking of that?) --Tango (talk) 17:52, 31 May 2009 (UTC)

The reason that this concept is not much used in modern physics is because it misrepresents the equation (E=mc^2), and encourages its use in situations that do not apply. Making a clear distinction between mass and energy is important to correctly understand that they are interchangeable, (via nuclear processes, for example), but they are not equivalent in every circumstance. (Matter can be converted back and forth to energy, but it is not the same thing as energy - the key difference being the presence or absence of mass. This dramatically affects the physical processes which can and do occur). Nimur (talk) 18:44, 31 May 2009 (UTC)

Thank you for clarifying. I should not have used the unqualified term mass when I meant relativistic mass, which itself is a questionable concept. I would have been better to relate energy directly to momentum. -- Tcncv (talk) 18:33, 31 May 2009 (UTC)

May 31

Determining the Concentration of a Solution

Hello. I want to find the concentration of a copper(II) sulfate solution, using the most accurate procedure. Should I evaporate all the solvent and water of hydration, measure the mass, and calculate the amount of anhydrous CuSO₄? Or should I add magnesium until no more can react, filter the residue, dry it, measure the mass, and calculate the amount of copper deposit? If I choose to conduct a chemical change, I must consider percentage yield as a source of error. However, I cannot see anything wrong with a physical change. My teacher, who likes my physical change idea, on the other hand, is more comfortable with a chemical change but I do not know why. Thanks in advance. --Mayfare (talk) 00:24, 31 May 2009 (UTC)

The deal with the evaporation method is that evaporation at room temperature will likely only yield the hydrate; and the additional heat needed to produce the anhydrous salt could also cause some decomposition of the sulfate to the oxide + SO3 gas. Plus, the anhydrous salt is likely so hygroscopic that it may start to rehydrate too rapidly to get an accurate mass. How is this for a third option: since Barium sulfate is both insoluble in water, and does not produce hydrate crystals like copper sulfate does, why not add excess BaCl2 or Ba(NO3)2 to the copper sulfate solution, filter the precipitate, and mass that? What do you think of that one? --Jayron32.talk.contribs 00:40, 31 May 2009 (UTC)

Maybe you could use an osmometer. --JWSurf (talk) 01:03, 31 May 2009 (UTC)

An osmometer can tell you the concentration of all solutes, so could be used, but only if it is certain that CuSO4 is the only solute (which is also true of the evaporation method). Gravimetric analysis was how we did this for first year undergraduate experiments - either by adding a solvent that precipitates the salt, or reacting it as in the question or Jayrons reply. Hydration of the solid is removed by drying for a longer period, and weighing the sample periodically (once the weight stabilises, it is assumed to be dry - drying temparatures are usually not high enough to cause reactions in stable salts). The question of the yield of any precipitating reaction is basically ignored by assuming 100% yield if an excess of reactant is used.YobMod 10:24, 31 May 2009 (UTC)

I think if you know that there's pretty much no other solute, you should just evaporate and measure the mass, without heating to dehydrate, then calculate the concentration from there. That way you don't have to worry about decomposing the solute. I think you can safely asume that the solute will be left fully hydrated if you evaporate it at room temperature. 209.148.195.177 (talk) 10:50, 31 May 2009 (UTC)

Particle interactions

While looking at Feynman diagrams, I noticed that all interactions between particles seem to fit into three categories: a vertex with two fermions and a boson, one with three bosons, and one with four bosons. Why are there no other possibilities? I don't think any laws of physics would be violated by a four-edge vertex where, say, a gluon and a quark interact to form a new gluon and quark (though the same thing could be accomplished by two successive interactions). However, there are three-Higgs and four-Higgs vertices. Why are Higgs bosons allowed to compress two steps into one, but quarks and gluons cannot? Why are there no five- or even six-Higgs interactions? Thanks, *Max* (talk) 04:44, 31 May 2009 (UTC).

This is an excellent question and the answer is a bit technical, so please bear with me. The best way to understand that is through dimensional analysis. This analysis is particularly easy to make if you chose units such that both the speed of light and the Planck's constant are adimensional $c=\hbar =1\,$ (no units). That choice leaves only one unit unspecified and that unit is usually chosen to be a unit of energy given in electronvolts (eV). With that choice of units the lagrangian density ${\mathcal {L}}$ has units eV${}^{4}$. Usually this is simply expressed by saying that the lagrangian ha dimension 4. Now if you look at the kinetic terms (the ones with partial derivatives of fields with respect to space-time coordinates) in the lagrangian you will find out that boson fields have dimension 1 while fermion fields have dimension 3/2. It is easy to see now that all the interaction terms present in the lagrangian have product of fields with total dimension 4 or less, while the hypothetical term you described with two quarks and two gluons would have dimension 5. That means that all the terms actually present in the lagrangian have coefficients attached to them with non-negative dimensions while the hypothetical term you described would have dimension -1. The rule of thumb is: no coefficients with negative dimension are allowed. Why? It turns out that these terms are non-renormalizable. A simple (if a bit too naive) way to understand that is to realize that those theories are actually effective (low energy) approximate theories for an (as yet unknown) theory and that the natural energy scale for the real theory is probabily around the grand unification energy scale (GUT) or higher. That effectively supresses those non-renormalizable terms by powers of $\left[{\frac {M_{weak}}{M_{GUT}}}\right]^{n}$, where $M_{weak}\sim 100GeV\,$is the weak scale (the scale of the effective theory), $M_{GUT}\sim 10^{16}GeV\,$ is the GUT scale and $-n\,$ is the dimension of the coefficient of the lagrangian. Those terms of the lagrangian become effectivelly negligible. Dauto (talk) 15:27, 31 May 2009 (UTC)

Thank you; your answer was very clear and helpful. *Max* (talk) 00:08, 1 June 2009 (UTC).

New islands found in aerial/satellite photos?

Have aerial or satellite photos ever revealed any previously undiscovered islands? NeonMerlin 05:47, 31 May 2009 (UTC)

Yes. Landsat Island is the only example of discovery by satellite photo. Plenty of islands were first revealed by aerial photograph, including, for example, numerous of the 30000 islands in Lake Huron. An aerial survey of the Georgian Bay Islands National Park area was carried out in the 1920s which "discovered" many new islands. Rockpocket 06:19, 31 May 2009 (UTC)

Indonesians could only estimate how many islands their country has, of which 8,844 have been named and 922 are permanently inhabited, until a satellite survey in 2002 found they had 18,306 islands. Or are there more when the tide goes down? Cuddlyable3 (talk) 10:35, 31 May 2009 (UTC)

Relationship b/w focal length and magnification of a lens and of a mirror

This Question was given in our summer assignment. (OK, I know I am not supposed to ask homework question. But i have not been able to crack the question for 2 weeks!) What is the relationship b/w focal length and magnification of a lens and of a mirror? The mirror formula is 1/u + 1/v = 1/f and m = -v/u Putting v = -mu in mirror formula gives 1/u - 1/mu = 1/f or 1/u (1 - 1/m) = 1/f Now is m directly proportional to f or inversely proportional? (Same procedure can be done for lens formula) shanu 07:04, 31 May 2009 (UTC) —Preceding unsigned comment added by Rohit..god does not exist (talk • contribs)

As you yourself would have done, m = 1/(1-u*f). Now, looking at this relation, it is clear that m is neither directly proportional nor inversely, but if you plot this function, you can say that m always increases with f, but there is a discontinuity at f = 1/u. It goes to infinity from the left and starts off from minus infinity from the right. Similarly you can do an analysis for the lens formula. Rkr1991 (talk) 08:01, 31 May 2009 (UTC)

Basic advantage of hybrid cars

I don't understand how hybrid vehicles can make sense. Okay, from what I understand, 90% efficiency for the generator is pretty good, and so is 90% efficiency for the motor at converting electricity to mechanical energy. So your generator wastes about 10% of your energy, and your motor wastes another 10% just to get the engines mechanical energy converted/stored and returned into mechanical energy. Also, most early and current production models DO NOT take advantage of solar panels or plug-in as an extra source of electricity. So that leaves what, just regenerative braking to recover more than that 20% of the energy lost? What about highway driving, when regenerative breaking is not going to be used. Didn't some models not even include regenerative breaking? So where does the energy savings come from? It sounds like a bunch of converting the energy into different forms for no reason. Am I missing something here? Is there ANY source of electricity besides the engine/generator itself and regenerative breaking in the basic hybrid vehicle? I don't think popular models like the Prius and Insight come with any solar panels or plug-in options. How do they get better mileage? Just by comprimising power? If so, why not comprimise the power and still use just a gas engine? I have one possible explanation, but I'm not sure--does the electric part have a higher PEAK power, alowing the smaller engine to keep running at a steady power and the electric motor provide peak power? That doesn't work however if you need to sustain maximum power, such as when the car is loaded and climbing a mountain side or long hill at high speed. 209.148.195.177 (talk) 10:45, 31 May 2009 (UTC)

Actually, you hit upon one of the disadvantages of hybrids. Regenerative braking means that hybrids actually get BETTER milleage in stop-and-go driving than in highway driving. If you live in a place where your commute consists mostly of freeway driving, then you will not get much advantage from a hybrid. Basically, a hybrid gives its biggest advantage at the low end of the gas milleage range, bringing up what is the most inefficient part of one's driving. They do nothing to raise the "high end" of the milleage range; except that they are usually small, light cars with small engines, so they tend to use less gas than say, a Ford Expedition might. From an emissions point of view, hybrids are usually better than the average car regardless of what style of driving you do; but from an economic one, if you don't do lots of stop and go driving it will take a long time to recoved the added expense of buying a hybrid in terms of fuel savings. --Jayron32.talk.contribs 12:04, 31 May 2009 (UTC)

This question has come up recently. See Steve Baker's answer here. Dauto (talk) 12:45, 31 May 2009 (UTC)

I'll cut/paste that reply here - because I need to expand upon it:

The reason the Prius hybrid saves energy is a three-way thing:

• Gasoline powered engines work most efficiently at one particular speed - perhaps 3,000 rpm. If you push them harder than that - or less hard - then they need more gasoline per unit of energy they deliver. With a normal car, the number of rpm's you need depends on what gear you are in and on what speed you are going - but it's only rarely turning the engine at the best speed. In the Prius, the engine only ever runs at this perfect speed - and when the battery is fully charged, the engine shuts off and stays shut off until the battery drains down and needs a recharge.
• When you push on the brake in a normal car, you are wasting the kinetic energy in the motion of the car to wear down the brake pads and heat up the disks. With a hybrid, the electric motors that normally power the wheels can be used 'backwards' as generators - so you slow the car down by (effectively) using the battery charger to extract energy from the car's motion. Of course you need conventional brakes too - and this process doesn't work when the battery is already fully charged...but still, it makes some significant savings. This is called 'regenerative braking'.
• Because you don't need that peak power from the gasoline engine when you do a (rare) hard acceleration - you can have a smaller engine. The engine only has to be large enough to provide the AVERAGE amount of power the car needs - not the MAXIMUM amount. Since you (mostly) don't go around accelerating hard all the time - this means that you have a smaller, lighter engine, more fuel-efficient engine - and let the battery provide the power for short bursts of speed.

Having said that, hybrid cars are not the perfect thing some would tell you. Most of the reason the Prius gets such good gas mileage is because it's super-streamlined, it's actually not a very fast car and it has relatively poor air-conditioning and such. If you did all of those things to a conventional car - and DIDN'T have to carry around all of those heavy batteries - you can do just as good as the Prius. The Prius actually gets rather poor miles per gallon on long freeway trips because in that case, the regenerative braking and the average-versus-peak thing doesn't work out too well - and pretty much any decent car, when driven in "overdrive" or topmost gear will have the engine running at it's most efficient rpm's. Hence the Prius has no special advantages in that case. However, for in-town stop/start driving, it works amazingly well.

Yep. Re-reading my earlier response (which was mostly about the Prius) - I should add that there are a lot of cars out there that SAY they are hybrids which really are not. It's pretty safe to say that if the car's gasoline engine is driving the wheels - then it's not really a hybrid. Some claims for being a hybrid include cars that use the electric power only to improve acceleration - and thereby allow a slightly smaller gasoline engine to be used. They offer no benefits whatever to drivers who do not floor the gas pedal at every opportunity!

It's something of a mystery why the Prius doesn't come with a plug-in option. You can certainly buy these as after-market options though - and I'm told that they work amazingly well.

Solar panels mounted on the roof of the car are useless. The amount of energy a solar panel can produce is so tiny that you'd be hardly able to drive a mile after a whole day of charging. The weight and cost of the panels simply don't make it worth-while. Moreover - if you wanted solar panels for charging your car - why not leave them at home next to your garage - use them to charge a battery - then recharge your car from the battery? That way you don't have to carry the weight around with you all the time. No - solar panels are quite utterly useless for car - worse than useless in fact.

The Prius (and presumably Insight too) does indeed suffer badly if you are doing long freeway trips. The battery needs to be continuously recharged - so the gasoline engine runs all the time - and what you have is a decidedly underpowered car that's wasting much of it's limited power in the losses involved with going to the wheels via a generator, battery and electric motor. EPA estimates are wildly wrong for the Prius - and my 140mph 6.5 second 0-60 MINI Cooper'S gets better practical freeway miles than the Prius. On long uphill sections, the car may actually limit your speed - I've heard stories of Prius owners who had been doing long freeway runs and then heading up a mountain finding that the car would slow down to 15mph - which is the fastest it's pathetic little gasoline engine can manage uphill and without a fully charged battery!

So we have to be careful. Hybrids are a useful way of getting better gas-engine mileage for in-city driving...but electric cars are better still at doing that. Electric cars don't have the range you need for road-trips, however - and for that a gasoline engine is currently the only solution. So hybrids are not just hybrid in the technology they use - but also hybrid in the range of applications they can cover. Personally - I'd love to have a MINI-E (all-electric, 100 mile range, 110mph, blistering accelleration) for my daily commute - and an efficient ~40mpg gasoline-only car for road trips. The technology for both is available...but trying to cram those two vehicles into one car seems like a relatively bad idea.

Incidentally - there are technologies out there to do regenerative braking using gasoline engines. The idea is that when you push on the brake pedal, the fuel supply and spark to the engine would be cut off and valve timing changed such that the pistons of the engine would be used to compress air and any remaining exhaust gasses into a high-pressure storage cylinder. This would provide a kind of super-efficient "engine braking". Then, when you need to accelerate again, the compressed gasses would be allowed back into the cylinders under high pressure to get the car moving again with no fuel being injected and no spark provided. Once the tank is depleted, you start injecting fuel and sparking the plugs again - and the engine runs normally. With this kind of technology, an efficient, modern gasoline engine could out-perform the Prius even in in-town driving situations.

SteveBaker (talk) 17:21, 31 May 2009 (UTC)

Well-said. One of the hardest things an automobile manufacturer can do is decide its product-lineup, though. As Steve Baker points out, the optimal solution might well be two separate vehicles: a short range, super-efficient-for-city-driving minicar, and a long-range, high-mileage-on-freeways midsize or compact car. However, designing and engineering these vehicles leaves out one important (and incredibly non-negligible) factor - these cars will compete with each other for sales! Given that a market exists for economic, environmentally-friendly vehicles, an automobile manufacturer must estimate how many people will be able to purchase the cars in question. Releasing two "eco-cars" will saturate the already small market, and neither car will hit sufficient production volumes to make the economies of scale that allow effective manufacturing. No intelligent auto manufacturer will release multiple cars of the same type because it will drive them into bankruptcy. For this reason, the successful hybrid cars are really a sub-optimal car like the Prius - which aims to combine the 80th percentile of the desired features for the 80th percentile of the expected market (or some other marketing-ese voodoo statistics). These design requirements get kicked back to the poor engineers, who have to figure out how to make a 50 mpg engine fit on to a sleek-looking body, run quiet in heavy traffic, and still handle speed on the highways. The result is sort of a slapped-together "hybrid", which makes some pretty severe tradeoffs as Steve mentioned above. So, we have the Prius and the Volt and the Insight. If your only goal is fuel-efficiency, you are probably best buying a diesel compact, which will darn well beat the Prius in true miles-per-gallon across a wider range of driving conditions (and won't be stumbling up those steep hills). And lay off the jackrabbit starts - if you're an average driver, something like 10% of your gasoline is used while your car is going zero miles per hour, and 50 or 60% is used during acceleration - which means a piddling 20% of your fuel consumption is actually useful. Changing your driving habits will save more fuel than changing your car. Nimur (talk) 19:01, 31 May 2009 (UTC)

Well, BMW aren't stupid - and the all-electric MINI-E (if/when it becomes a mainstream product) will certainly be produced alongside the normal 40mpg gas-powered MINI and the diesel MINI/One-D - and all three cars are otherwise pretty much identical (except the electric version is a two-seater - the back seat area being basically full of batteries).

Diesel cars are also a very good thing - and they're very popular in Europe. But the legal issues surrounding the amount of sulphur in diesel fuels prevents the good ones such as the Golf and MINI/One-D from making it into the USA.

That's one of those bloody stupid regulations where the amount of pollutants coming out of the tailpipe is measured as a percentage of the total exhaust gasses. The consequence of which is that a car that burns more gas and produces more pollutants is permitted when one that burns a LOT less gas and produces a little less pollutants is not! These kinds of dumb laws are in severe need of re-thinking. SteveBaker (talk) 20:04, 31 May 2009 (UTC)

That's because politicians are rarely scientists or engineers. If we had informed decision-makers, we wouldn't have that situation. The diesel issue in particular is very frustrating - diesel is easier and cheaper and more environmentally friendly to produce than gasoline. It has better mile-per-gallon and ton-per-gallon characteristics. The latter is not brought up nearly enough - it's easy to get a lot of miles-per-gallon by making a very small vehicle, but most of our transportation fuel is consumed by commercial trucking - where the vehicle weight is almost negligible compared to the cargo weight. Fortunately, most trucks do run on diesel - and if the rest of the automobile drivers realized how much of a cost-savings this is, we would dramatically reduce our emissions and fossil-fuel consumption. Nimur (talk) 21:02, 31 May 2009 (UTC)

I'm not sure that the amount of energy you'd get from solar is as completely insignificant as Steve suggests. Our article on solar car suggests that it's not unreasonable to get 2kw from car-mounted solar panels. According to the electric car article the EV1 consumes 2.7kwh for the equivalent of a liter of gas. Granted, a liter is not a lot of gas. But if I could park my car in the sun while I'm at work and get four free liters of gas, I would not say that this was "unnoticeable".

I also notice that a solar panel is an factory option for the Xebra electric cars mentioned earlier in this thread. APL (talk) 13:56, 1 June 2009 (UTC)

I disagree - 2 kilowatts is abysmally negligible compared to your gasoline engine. For every second that you charged your battery, you would get one second of a 2 horsepower boost if you had a perfectly efficient conversion. In reality, you will get much worse performance. I doubt this tiny boost would even come close to making up for the excess weight of lugging around a solar panel and battery system. If you want to store more energy, you need a heavier battery - it's a no-win situation. Nimur (talk) 14:38, 1 June 2009 (UTC)

We're talking about Hybrid-Electric cars. They already have batteries. APL (talk) 15:56, 1 June 2009 (UTC)

But those batteries are already being used. They'll have optimised the size and number of batteries based on weight and reducing the amount of time the battery is full but there is still excess energy from the engine/breaks which gets wasted. If you added solar panels without adding more batteries you would just end up wasting the energy sources you already have. --Tango (talk) 18:14, 1 June 2009 (UTC)

I agree with Nimur - your numbers are hopelessly optimistic. The Zap Xebra does indeed come with a solar panel roof option - and go take a look at their web site and see what they have to say about it. Firstly, it costs $1,500 (a costly option on an $12,000 car!) so it's not at all cheap. Secondly - if you read the specs on the panel on the Zapworld web page - it doesn't produce 2kilowatts - it produces 150 watts. Parking the car in the sun all day for 4 liters of gas sounds reasonable - but you're not getting 4 liters - you're getting a little under a third of a liter. A third of a liter is 0.07 US gallons - so with gas at around $3 a gallon, a full day of recharging saved you about 25 cents. So the payoff time for that solar panel on a hybrid car is something like 6,000 sunny days...maybe 30 years in sunny parts of the world! Certainly longer than the life of either car or solar panel. But worse - the solar panel weighs 85lbs. The odds are pretty good that it's actually going to cost you more in additional electricity consumption than it actually provides! Possibly the only reason people buy them is (as the Zap page coyly suggests) is to "appear even more Green to your neighbors!". Solar panels are not as good as you think. Partly that's because they need to be tilted at right angles to the sun's rays to produce optimum amounts of power...and a car's roof is rarely (if ever) at the optimum angle. Secondly, they are adversely affected by dirt (another problem on a car roof). Thirdly, they gradually lose effectiveness as they age...so you do have to replace them if you plan on keeping your car for a long time. Fourthly - when solar panels are used effectively, they are on the roofs of buildings where they are unlikely to be shaded - and tilted towards the prevailing sun direction for the location they are in. You can't always park in the sun. There are many cities where above-ground parking is rare - or where you are blocked from the sun by tall buildings - or where there are trees overshadowing you. On the little 3-wheeled Xebra, adding all that weight to the top of the roof....I'd worry about how much they add to the roll-over risk. SteveBaker (talk) 18:24, 1 June 2009 (UTC)

I got the 2kw number from the solar car article. I wonder if that doesn't refer to special super-expensive panels used on solar race cars. Oh well. APL (talk) 19:24, 1 June 2009 (UTC)

I will add that there is really only a single main reason: Conventional internal combustion engines are generally fuel efficient only at one particular speed. My vechicle is most effiecient at 90km/hour in its 4th gear. This is when it can achieve 7 litres of fuel per 100km. In every other situation it is far less efficient. When accelerating for example, even at low speeds (from 10km/hour to 50km/hour) the fuel consumption can be 40L per 100km or worse. At high speeds (~110km/hour) the fuel consumption goes upto 14L per 100km. At low speeds (50km/hour) its 11L/100km. The cars are engineered normally around typical highway driving speeds. The reason for this is that you need 4 times as much energy to move a car at twice a higher speed. For example a car that does a trip at 50km/hour could use 1/4 as much energy as a car that does the same trip at 100km/hour speed, because airdrag increased 8x and the speed of the trip only decreased by 1/2. So when the go to design a car, even one for the city, they know that it still needs to be able to travel at 100km/hour some times, so this is where they should make it most energy efficient. This is why for 99.9% of convential cars are fuel efficient at speeds of around 80 to 90 km/hour. You can have you manufacturer modify your car so that it is most fuel efficient around 50km/hour (and get say 7L per 100km out of even 4L V6 engines), but the fuel consumption at high speeds like 100KM/hour would go upto 28L per 100km or worse. Electric cars don't have this problem that internal combustion engines have. The electric motor and work at variable speeds easily. For an internal combustion engine to work efficiently at all different speeds it would have to be capable of dynamically changing many fixed variables such as piston stroke length, value timing, huge changes (order of significance) changes in the amount of fuel injected based on speed, instead of only minor changes. Most engines run fixed stroke, fixed value timing and very little change to fuel injection amounts, then they just vary their speed - even though they can only run optimally at one speed. --Dacium (talk) 06:24, 2 June 2009 (UTC)

How many human beings can Australia support?

I often hear the argument that, while Australia is a vast continent, it is also arid and dry and cannot support much more than its current population of 20 million. (For the record, this argument is usually brought up by people terrified of non-white immigrants.) Is there any truth to this statement? While this is a pretty harsh country, there's plenty of spaces that are green and verdant - Tasmania, for example, is roughly half the size of Great Britain, which has a population of nearly 60 million. 58.161.196.113 (talk) 11:26, 31 May 2009 (UTC)

In the global economy, the number of people that the food supplies of a nation can support are largely moot. Much of the food in the U.S. for example is imported from overseas. There are studies, I suppose, which have been done which indicate how many calories a particular acre of land can produce, and how many calories a person needs to survive; but with the ease at which foodstuffs are moved around the world, assuming that a nation needs only support its own population with its own food growing is kinda silly. --Jayron32.talk.contribs 11:59, 31 May 2009 (UTC)

The united Stated is a massive net exporter of food. Most notably, the US is the largest exporter of rice, but also exports huge amounts of wheat and corn. -Arch dude (talk) 20:17, 31 May 2009 (UTC)

Australia also exports large amounts of wueat. See Export Wheat Commission. -Arch dude (talk) 20:20, 31 May 2009 (UTC)

Australia's population per square mile is tiny. It could very easily support millions more people. Yes there'd need to be major developments to boost infrastructure, but there's no reason (certainly not food) why a developed nation such as Australia couldn't have a major increase in its population. Whether or not it is desirable is another question though, and more of a political question. 194.221.133.226 (talk) 12:54, 31 May 2009 (UTC)

I understood that insufficient water resources may be the limiting factor in the southern part of Australia at least. Mikenorton (talk) 13:22, 31 May 2009 (UTC)

An Australian ecologist (whose name I've forgotten) has argued in a book (whose title I've also forgotten), that Australia is already overpopulated when measured against the maximum number its ecology can support sustainably, which I seem to recall he calculated as 17 million. This low limit, he believed, was due to the unusually impoverished soil of the continent, this resulting from the extermination some tens of thousands of years ago of most Australian megafauna by the Aborigines, thus removing their dung from the ecological cycles. If I manage to remember more (or find the book) in the near future I'll post more references - I'm sure I've seen mention of him on Wikepedia. 87.81.230.195 (talk) 18:23, 31 May 2009 (UTC)

Are yo thinking of Collapse: How Societies Choose to Fail or Succeed, by Jared Diamond? -Arch dude (talk) 20:17, 31 May 2009 (UTC)

No, definitely wasn't it or him. (I've got some of his other books though). 87.81.230.195 (talk) 02:30, 2 June 2009 (UTC)

Cracked it! Tim Flannery, The Future Eaters. 87.81.230.195 (talk) 19:41, 2 June 2009 (UTC)

Incidentally, I believe Jayron32's argument does not stand - imported food (and other goods) must be paid for with exports of some kind, whose production ultimately depends on their extraction from the ecosystem, and "everything is linked to everything else". The ability of the USA and Australia to consume two or three times a sustainable share of the planetary ecosystem's production is balanced by the populations of other countries having to subsist on much less. If everybody on Earth had a USA/Australian/UK standard of living, we'd need several Earths to sustain it; an equitable sustainable standard for everyone would be markedly lower, unless the world population was only about 2 billions. The medium-term future is likely to see one or more of: drastic reduction of First World consumption through drastically more efficient technology, or First World economic collapse; mass migrations from the Third World leading to worldwide social collapse; drastic population reduction through famine and pandemics. It's being so cheerful as keeps me going. 87.81.230.195 (talk) 18:42, 31 May 2009 (UTC)

A higher standard of living doesn't generally take up more space. You still need to eat the same amount of food. --Tango (talk) 20:22, 31 May 2009 (UTC)

It need not (though many rich bastards better-off people do have larger houses than the local norm and eat more expensively produced foods), but currently it usually averages much higher consumption of energy and material resources, and production of pollution and waste. We urgently need to develop technologies giving us the same benefits for less of the aforementioned, and to help the developing nations (e.g. China and India) to skip straight to these rather than replicating the wasteful and polluting methods the "West" went through. 87.81.230.195 (talk) 02:44, 2 June 2009 (UTC)

The question requires rephrasing: "How many human beings can Australia support *now*?" Every over population doomsday projection (they go back hundreds of years) has been wrong because the projections assume that population increases but that technology does not. While an ecosystem is finite, the sustainable use to which the ecosystem can be put is variable and a function of technology. Wikiant (talk) 18:47, 31 May 2009 (UTC)

There is some balance that has to be met at some point between how much energy it cost you to put into each bit of food you produce. You can desalinate saltwater and grow algae and fungi in vats eventually, but that is going to cost energy. Someone is going to have to mine and dispose of your fossil/nuclear energy materials or solar panel raw materials and waste. You can unload some of that cost on to other economies for a while. (We've been doing that as 87. hinted.) But at some point the buck stops. 71.236.26.74 (talk) 06:53, 1 June 2009 (UTC)

Well I guess the simple way to answer this question would be to compare arable land. This list gives arable land in Australia as being the 6th largest in the world. The world as a whole has 325 people per square km of arable land, while Australia has 43. This implies that Australia's population could grow to 7.5 times what is today (151 million) before reaching the average density of the rest of the world. Note that many countries are far above this average and still largely self sufficient agriculturally, India and China have 753 and 943 people per square km of arable land respectively. Were Australia to grow to the same density as China, it would have 438 million people. Of course this comparison is not perfect: there is large variation in the "quality" of arable land in terms of supporting humans. There is also the issue of water, as raised above. It adds another complication and uncertainty, especially for a country such as Australia where there is quite a lot of water but it is nowhere near evenly distributed. TastyCakes (talk) 18:04, 4 June 2009 (UTC)

General Motors EV1

The General Motors EV1 electric cars were leased to customers and later recalled by GM. Why did they lease these unsuccessful test cars to people in California and Arizona where the weather is always very hot? Was it a bad decision? Or did their batteries perform even worse in cold weather?

Only a number of these cars were not destroyed. In a few decades, can we install more advanced batteries to these museum cars and make them usable? -- Toytoy (talk) 13:23, 31 May 2009 (UTC)

For one, California (where most of the EV1s were issued) is not "always hot". Additionally, Arizona participants were not issued the EV1s with the most heat-vulnerable battery systems. At a guess, California was selected largely for the PR opportunities of a zero-emissions car in the most emissions-restrictive state.

As for the remaining cars, its highly unlikely that any will be retrofitted and restored to the road. GM has no incentive to do so, as the retrofit and associated certifications will be far more expensive than making current-model EVs. Museums and other display locations have no incentive to do so, as they don't require roadworthy models for display. Perhaps a private collector, should he be able to acquire an EV1, might have an interest. — Lomn 14:01, 31 May 2009 (UTC)

The cars were not leased to make money for GM - they were leased as an experiment to see how the EV1 would perform out there in the real world with real customers. This is not an unusual thing to do. In fact, BMW's MINI division is doing that exact thing right now with the Electric MINI Cooper. They built something like 500 of these cars and have leased about half of them to customers in the US - in California and New York only. The lease terms are very like the EV1's and stipulate in no uncertain terms that the cars MUST be returned at the end of the lease - no extensions or right to purchase will be made. Why? Well because they want to look at how these cars have survived the ravages of practical driving by real people - and (as with the EV1's) they have no intention of supporting them with spares and maintenance off into the future. If you want to know how well your design works - there is no point in putting them into 'easy' situations - if you suspect that they'll have trouble in extreme heat - then you should absolutely do your trials in Arizona.

No doubt the few remaining EV1's could have new batteries and be made to work - but they are now museum pieces and will probably remain that way.

If you want an electric car - you can buy one very easily. At one end of the scale, the ZAP Xebra has been in production since 2006 and is quite affordable ($11,700) - but with only a 25 mile range...you'd better have a pretty short commute! At the other end of the scale - if you have deep pockets and fancy something a bit more sporty - the Tesla Roadster is a pretty cool car (based on a Lotus body) - it'll go 240 miles on a charge and has a 0-60 time under 4 seconds! Our Category:Production electric vehicles lists many electric cars that are in mainstream production around the world. SteveBaker (talk) 16:55, 31 May 2009 (UTC)

I fixed your category ref, Steve.--Polysylabic Pseudonym (talk) 03:20, 1 June 2009 (UTC)

You can install whatever you want into a car body, but the ultimate questions are: will it be prohibitively expensive, and will you be in violation of state and federal regulations for road-worthy automobiles? The answer to these questions turned out to be "yes" for General Motors, which is why the EV-1 program was ended so abruptly. Though numerous conspiracy theories suggest collusion from the petroleum industry, this is sort of a flimsy argument - cost-effective electric vehicles have been around for a very long time, but are mostly unsatisfactory for the sort of driving we have become accustomed to. Nimur (talk) 19:20, 31 May 2009 (UTC)

Do owls ever get aggressive with people?

I was just out working in my shade garden, and noticed after a few moments that a Great Horned Owl was sitting on the wood pile about 8 feet away, staring at me. I of course went and got my camera and got some pix from about 12 feet away, which he didn't seem to have any problem with (even with the flash!).

I'm just wondering whether I should worry about working so close to him... it's hot and sunny and I was really looking forward to shady work. My wife and daughter will also be getting home any minute now, and I want to show them. So are owls safe to be near? --SB_Johnny | ^talk 15:07, 31 May 2009 (UTC)

If you disturb their nest or corner them, they might turn violent, but I can't see why they wouldn't just fly away in other situations if they felt threatened. If they don't feel threatened, there is no point them attacking you, you clearly aren't good prey. Oh, unless they are wounded - wounded animals can be very dangerous. --Tango (talk) 15:12, 31 May 2009 (UTC)

Owl talons, especially those of large ones defending their nest can be vicious. Check out Eric Hosking and be careful if there is a nest nearby. Shyamal (talk) 15:23, 31 May 2009 (UTC)

No, doesn't seem to be wounded... a couple minutes ago he swooped down onto something, ate it, then lofted himself back onto the pile. I've seen (and shot) baby rabbits near there, so maybe the rabbit nest is under the pile? I'm a bit surprised to see him (or her) hunting at mid-day. We all just went down to see it, and it just stared at us and winked :-). I can't imagine the nest is there... I'm pretty sure he lives in the barn. --SB_Johnny | ^talk 15:39, 31 May 2009 (UTC)

Well I'm jealous, you're one lucky dude. Richard Avery (talk) 21:45, 31 May 2009 (UTC)

Congrats on your winged hunting buddy. It probably got interested by you rustling some leaves. Since you were successful in helping it to a morsel its strategy paid off. Be careful with pest control. You don't want it exposed to any poison. Great Horned Owls prefer hunting at night (?our article says, shouldn't that be dusk and dawn?) because that's when their prey comes out to play. That doesn't mean they won't hunt at other times if opportunity presents itself. They rely on their hearing as much if not more than their vision to hunt. Some falconry shows have horned owls as show birds. Enjoy the show. (...and maybe post us some of your pix in the article :-) 71.236.26.74 (talk) 06:42, 1 June 2009 (UTC)

Muscle Contraction question

By the grace of G.od

Rechovot (Israel, 31/5/09

Peace and benediction!

In your article about muscle contraction, you write about "cross-bridge" in the myalin/actin action. It will be helpfull to add a few lines about the "cross-bridge" process.

Thank you very much for your wonderfull web.

Yehudah F. Rechovot, Israel EMT-P learning —Preceding unsigned comment added by Yehudah770 - Mashiach Now (talk • contribs) 19:19, 31 May 2009 (UTC)

I have moved your question to a new section. Nimur (talk) 19:22, 31 May 2009 (UTC)

The most appropriate place to make a suggestion for a page would be its specific Talk page, which is likely to be watched by people who are both interested and knowledgeable about the topic. In this case, that would seem to be Talk:Muscle_contraction. Of course, if you have a clear sense of what should be said, you are also welcome to be bold and edit the page. --Scray (talk) 19:48, 31 May 2009 (UTC)

Downtown Tokyo

I read the cryptographically written articles Tokyo, Greater Tokyo Area, City of Tokyo, and Special Wards of Tokyo, and I couldn't for the life of me find a clear explanation where "Downtown Tokyo" is, i.e. in wich ward(s) or other subdivisions or administrative regions within Tokyo. When I say Downtown, I mean the cluster of skyscrapers you see when you Google Image Search "Tokyo Skyline". Where exactly are these buildings? 209.148.195.177 (talk) 23:32, 31 May 2009 (UTC)

• This is probably going to be completely wrong, but I was in Tokyo earlier this year and got the impression that there were actually several different clusters of skyscrapers, or "downtown" areas, dotted all over the city. 58.161.196.113 (talk) 16:13, 1 June 2009 (UTC)

La Défense

It's not really downtown.

Is La Défense basically Downtown Paris? Why is it outside the city limits? 209.148.195.177 (talk) 23:33, 31 May 2009 (UTC)

La Défense is sort of in the boonies, actually; it is a business district to the northwest that's the newest of the arrondissements — although I notice it's not even listed in our article Arrondissements of Paris. As a visitor, I claim there's nothing going on in La Défense to speak of culturally, and it's a long, long walk to anything I'd consider "downtown Paris". Tempshill (talk) 23:52, 31 May 2009 (UTC)

I don't think it's correct to refer to La Défense as an arrondissement; that word refers to the 20 districts that Paris itself is divided into, and unless something has changed recently, La Défense is outside the city limits.

Why does this concentration of office towers exist in one suburb? Presumably because urban planners decided that preserving the character of central Paris was desirable but also felt that it was desirable to allow this kind of development, so they passed zoning laws to allow for this. I imagine the construction of the Montparnasse Tower, which many people disliked, must have been a catalyst for this planning decision -- and yes, look at the Criticism section of that article. --Anonymous, 00:42 UTC, June 1, 2009.

As a visitor I claim La Défense itself is culture going on. It is an expression of Gallic gigantilism, full of bold surprises in 3-D. It is the futuristic movie set that could only be imagined for Alphaville (film) and a landscape for artworks that are superhuman but not inhuman. Why is it where it is? Because the Parisians want to reach for the future without mutilating their heritage, and their solution is that long, long axis joining their arch monuments to triumph of courage and triumph of the brain. Vive la différence! they say having digested the painful lesson of immiscible architectural dichotomies. The tourist sees the Grande Arche from afar and may enter its arena that boasts cafés, restaurants, cinemas, occasional grand shows of sound and light, a shopping mall that never ends and a potent motor museum. Cuddlyable3 (talk) 10:00, 1 June 2009 (UTC)

For a parallel in the U.S., see the relationship between Washington, D.C. and Arlington, Virginia. Washington has strict building codes designed to preserve the architectural character of the city, but it is also a major urban center which demands a large, vertically aligned commercial district, like any other major city. Arlington has become the skyscraper farm for Washington DC much the way that La Défense has become so for Paris, for almost exactly the same reasons. --Jayron32.talk.contribs 18:41, 1 June 2009 (UTC)

Incidentally for both this and the previous question, you'd likely receive a better response if you post the question in humanities or perhaps misc, since they don't really seem to concern science much Nil Einne (talk) 22:46, 1 June 2009 (UTC)

June 1

Cholesterol Level/Temporal Arteritis

I am a 79 year of age male married and have five children. On September 9, 1995, a biopsy was taken from the artery on the left side of my temple and was diagnosed as Temporal Arteritis. I am presently on 5 mg of prednisone taken daily and a quarterly (ERS) lab work is done by my family doctor. The present rate is 25.

I continue to have high level cholesterol even after a week of fasting on a low cholesterol diet prior to blood work and taken every precaution to get it down. My cholesterol for the last three years are - 11/14/07 = 221, 01/24/08 = 198, 04/13/09 = 197.

Can the inflammation of the main arteries caused by arteritis create an incorrect reading on the lab test for cholesterol? Thank you. —Preceding unsigned comment added by 76.7.97.223 (talk) 00:11, 1 June 2009 (UTC)

We apologize, but we have a policy that prohibits us from answering medical questions such as this on Wikipedia. -- Tcncv (talk) 00:47, 1 June 2009 (UTC)

As Tcncv says, we cannot give medical advise. You need to go and talk to a doctor. If you suspect your doctor may have made a mistake, you can get a second opinion from another doctor. --Tango (talk) 15:15, 1 June 2009 (UTC)

Seeing a blue tint for a minute - overexcited photosensitive ganglion cell activity?

It was a lovely, lazy Sunday afternoon, and I at out on my deck for a few minutes. With the sun beating down, I looked up into the brilliant blue sky and closed my eyes and relaxed for a few minutes. (Maybe have had a 1-2 minute nap.) When I went back inside, things were in a slight blue tint for a minute, maybe less.

What caused this? In checking the articles on vision, I happened upon the photosensitive ganglion cell article, as one of the cells that picks up informationa nd sends it brainward. Was this from overstimulation of these cells? It's a logical hypothesis, from my estimation, becasue not only was I staring totally at the blue sky, but with my eyes closed, would each pupil also be bigger? After all, with them closed I can still see slight differences in light and dark, such as my room light here versus under my desk.

Thanks And, don't worry, I'd never stare directly at the sun - even with my eyes closed. :-).Somebody or his brother (talk) 00:41, 1 June 2009 (UTC)

I am not familiar with the specific seeing-blue-tint phenomenon you describe, but my guess is that it is caused by adaptation and/or bleaching of L and M cones compared to S cones while you were outside, resulting in higher response from S cones compared to L and M. The thing is, human eyelids are not completely opaque, so some light gets through; and the light that gets through is mostly at the long-wavelength end of the visible spectrum. Thus, L and M cones are exposed to light in their respective opsin absorption bands, and adapt to that light; but S cones are not (as they mostly absorb short-wavelength light), so they adapt to the relative "darkness". If you look at a bright red or orange light for a while, objects projected on that area of the retina will look green or blue for some time after that. I guess that what you have experienced is largely the same effect. Now your second question is on photosensitive ganglion cells. Our article on the photosensitive ganglion cells is extremely detailed, considering how little do we actually know about them. They certainly project to suprachiasmatic nucleus, helping to regulate the circadian rhythm; they also likely have an effect on pupillary contraction via the olives. However, I seriously doubt they have such a strong and direct effect on color perception as the phenomenon you describe. I'm not ruling them out 100% as a "suspect" in your phenomenon, but I think there may be far simpler - and more conventional - explanation for your experience, like the one I gave above. All the best, --Dr Dima (talk) 02:14, 1 June 2009 (UTC)

Yes it'd give the same explanation but a bit simpler than Doc. Your eyes get used to the red colour you see with your eyes closed, so then everything else looks really "not red" afterwards. Aaadddaaammm (talk) 10:11, 1 June 2009 (UTC)

Cool, thanks, y'all.Somebody or his brother (talk) 10:40, 1 June 2009 (UTC)

Young's double slit experiment

Dear Wikipedians:

What does "first order image" mean for Young's double slit experiment? I'm having trouble with this terminology, it seems to be made up by my physics teacher, I can't find it anywhere in double-slit experiment.

Thanks,

70.31.158.159 (talk) 02:10, 1 June 2009 (UTC)

Maybe they mean the first diffraction fringe (strongest, central bright area)? Nimur (talk) 07:31, 1 June 2009 (UTC)

No that's the zeroth order fringe. The first order images are the ones sitting next to it on either side...the peaks of intensity...that's how my teacher taught me :-) Rkr1991 (talk) 08:34, 1 June 2009 (UTC)

Thanks!!! I was able to get the right answer with the definition. 70.31.158.159 (talk) 14:46, 1 June 2009 (UTC)

Technicians on planes

I noticed on the AF447 article, that there were 3 technicians onboard. It made me wonder whether there are always technicians onboard, what they actually do, and where they sit. Can anybody help? Thanks United Bob (talk) 13:32, 1 June 2009 (UTC)

That statement has now been removed from the article, so it may not have been accurate. I don't believe it is routine to have technicians on board, but some planes do carry a Flight engineer, who sits on the flight deck with the pilot and co-pilot. Modern planes don't generally have engineers. I doubt an Airbus A330, like the one involved in this incident, had one. --Tango (talk) 14:10, 1 June 2009 (UTC)

Indeed - flight engineers are pretty rare these days - what they used to do was to monitor the engines for vibration and/or temperature problems - and also track fuel consumption, shift fuel from one tank to another if one engine was consuming more than the others - that kind of thing. Other airline staff such as technicians frequently fly with an aircraft as passengers in order that they can do some maintenance during the next stop-over or something...I suspect that's what happened in this case. It's hard to read anything meaningful into it though. SteveBaker (talk) 17:47, 1 June 2009 (UTC)

Yes, they could have been Deadheading (an unfortunate term, in context). --Tango (talk) 18:11, 1 June 2009 (UTC)

Output Formula question

output for per man per shift formulaSathyavolu sar (talk) 13:35, 1 June 2009 (UTC)

i want to know about the formula for "output per man per shift" in a mass production manufacturing industry

can any body help

Sathyavolu sar (talk) 05:30, 1 June 2009 (UTC)

I have moved your question to a new section so it can be answered. Since you are probably new to Wikipedia, I have also taken the liberty of copying your talk-page message to this location where it will probably be better answered.

Have you looked at the man-hour article? Nimur (talk) 14:46, 1 June 2009 (UTC)

Take the total amount produced and divide it by the total number of shifts (that is the average shifts per person, times the number of people). --Tango (talk) 15:13, 1 June 2009 (UTC)

Adderall vs. recreational speed

Does Adderall differ from the amphetamine pills that are standard among recreational users? If so, how? NeonMerlin 14:07, 1 June 2009 (UTC)

A major issue with all illegal pharmaceuticals is the lack of quality control. For refined drugs (heroin, cocaine) the chief issue is concentration (alloyed with dangers from harmful adulterants and from poor hygiene). Synthesised drugs (ecstasy, lsd, pcp, amphetamine) have additional issues with purity. It's really quite difficult to make exactly the drug desired, without inadvertently making lots of similar compounds as well. Getting that justright is a core business of major pharma companies; bunging stuff out the door is a core business of some gangsters in an industrial park in The Hague. Adderal is a specifically chosen cocktail of related amphetamines, picked to support a desired psychopharmaceutical outcome. By contrast, if someone is buying "amphetamine" from some bloke in a club somewhere, he'll likely be getting pills with a diverse range of related substances, in unknown concentrations and proportions. Moreover, as the Adderall article notes, it's dispensed in a pill which has been engineered to control its release, whereas the illegal pill hasn't been. That all said, related compounds often have very similar effects, so most of the bad things that illegal "amphetamine" pills can do to you are also dangers of their prescribed brethren. Hopper Mine (talk) 17:20, 1 June 2009 (UTC)

Inorganic chemistry

How metal exess defect responsable for violet colour of KCl due to exess k and pink colour due to exess Li ?Rikichowdhury (talk) 15:58, 1 June 2009 (UTC)

Wow. I am not sure I understand your question at all. KCl and LiCl are white solids and/or clear solutions. The colors only become apparent during flame ionization or gas-phase eletrical ionization, as in a Geissler tube. Could you elaborate on your question so that we can answer it better? --Jayron32.talk.contribs 18:34, 1 June 2009 (UTC)

Are you talking about something like KCl_0.99? How do you make this? You could make K deficient KCl due to radioactive decay, if you could find some billion year old KCl. Graeme Bartlett (talk) 01:40, 2 June 2009 (UTC)

I definitely remember studying about it during my school days. It has something to do with that one unpaired excess electron which the excess K provides. It absorbs energy (from incident light rays) and goes up to higher levels, and we see the complimentary color of the wavelength absorbed. I am actually quite amazed that we don't have a page on this (or maybe i looked in all the wrong places), but the fact remains that if you heat (white) KCl with excess potassium vapour, your compound turns purple. The same thing also holds for LiCl. Rkr1991 (talk) 04:38, 2 June 2009 (UTC)

Inorganic chemistry

Two compound NaCl and AlCl3 . Here NaCl is ionic crystal and AlCl3 is covalent in natuer .But when we use highly polar solvent AlCl3 treatet as ionic why ?Supriyochowdhury (talk) 16:04, 1 June 2009 (UTC)

Your understanding of "ionic" and "covalent" is somewhat flawed. Don't think of the two as two sides of a coin, but rather as two ends of a continuum. All bonds basically consist of positive charged nuclei attracted to a negative charged electron cloud consisting of the "bonding electrons". The difference between an ionic or covalent bond is the location of the bonding electron cloud. Consider these extremes:

covalent bond

ionic bond

The deal is, that almost all compounds exist somewhere between these two extremes. Most of the time, the bonding cloud is not localized exactly in the middle, but it is also rare to find it centered on one of the two nuclei. The center of electron density in all compounds will lie somewhere between the midpoint of the bond length and the center of the more electronegative atom. Aluminum Chloride lies almost exactly 50% between the right and left picture; the bonding in aluminum chloride is covalent enough that it has a relatively low melting point, but it is ionic enough for water to seperate the aluminum from the chloride during the solvation process. It would not be unique in this regard; the strong acids like hydrochloric acid and nitric acid behave much the same way; HCl is a gas at room temperature but it ionizes 100% in water. --Jayron32.talk.contribs 18:29, 1 June 2009 (UTC)

In short, no compound is purely ionic, or purely covalent. There is always a balance. In the case of AlCl₃, it is covalent because of the large positive charge of the metalk cation and relatively bis anion (Fajans' rules). However, in polar solvents, this bond is easily broken, and you get the charged ions, because of the large difference in electronegativity between the atoms. The positively charged Al ion is surrounded by the negative part of the solvent (OH^- if the solvent is water) and the negatively charged Cl ion is surrounded by the positive part of the solvent(H⁺ if the solvent is water). This leads to a stabilization called the solvation enthalpy. If this enthalpy is able to compensate the enthalpy required to break the Al-Cl covalent bond, then the compound is solvated, which is what happens here Rkr1991 (talk) 04:32, 2 June 2009 (UTC)

human body

what is the function of the gall bladder —Preceding unsigned comment added by Javedesmail (talk • contribs) 17:56, 1 June 2009 (UTC)

All you have to do is type "gall bladder" into the search box on the left side of the screen, and it will take you to the gall bladder article. Friday (talk) 18:01, 1 June 2009 (UTC)

Does crumpling a piece of paper increase its density?

Help me settle an argument. Please source this well. Lesath (talk) 19:50, 1 June 2009 (UTC)

No. Depending on how you define it, the density either stays the same or decreases. If you are referring to the density of the paper itself, crumpling it has no significant impact at all. If you are referring to bulk density (the mass divided by the volume it actually takes up), then it decreases - you can fit more uncrumpled pieces of paper in a given box than crumpled ones. --Tango (talk) 20:17, 1 June 2009 (UTC)

We don't have pages. What you may be hunting for is the compressive strength that crumpled paper displays. There are formulas that you can use in package design to calculate the amount of crumpling and the increase in compressive strength. (Corrugated fiberboard needs a section there, pages for BCT and ECT are missing.) For packaging there is another important factor and that is that cumpled paper does not only have compressive strength, but elasticity too. Mechanically crumpled paper has more predictable results than manually crumpled paper. It is used by industry in packaging [12] [13] [14] [15]71.236.26.74 (talk) 01:49, 2 June 2009 (UTC)

Paper is made up of microscopic fibres with spaces between them (see photos), and compressing it would certainly reduce the spaces and increase the density (by close inspection you can see that papers often have a slight hairiness). Whether crumpling up a sheet in your hand would compress the fibres enough to significantly reduce the volume, I'm not so sure. The question of how to measure the volume of a hairy thing is not simple either. --Maltelauridsbrigge (talk) 13:54, 2 June 2009 (UTC)

I don't think crumpling a piece of paper has any bearing on its density. Its configuration changes, but I don't think that its density changes at all. Density is a factor of the material. Changing the configuration of a material such as a sheet of paper has little bearing on the material's density, in my opinion. Bus stop (talk) 14:07, 2 June 2009 (UTC)

Damaged parrot mandible

The upper mandible of this parrot was damaged in an accident, causing it to be much shorter than the lower one - a condition which makes it impossible to feed itself. It has been suggested that the lower mandible be cut back in the hope that the upper would then regrow. Can anyone advise? Rotational (talk) 20:06, 1 June 2009 (UTC)

You really need to talk to your avian veterinarian about that. The reference desk does not provide medical advice. I will say that I have seen and read about birds with prosthetic beaks in the past, though... --Kurt Shaped Box (talk) 20:15, 1 June 2009 (UTC)

Sun limb - how to make sense of the direction

I understand that the edge of the sum is called a limb, but I don't understand why the upper left is called the Northeastern Limb.

Note the new solar prominence and sunspot identified as being on the northeastern limb.

Space Weather 1 June 2009

I get the north - why the east?Sphilbrick (talk) 21:14, 1 June 2009 (UTC)

Imagine facing the south; east would then be to your left. Look up to the sky and east would still be to your left, but north would be "up"--so east is to the left of north. In the heavens, the directions are mirror-reversed simply because one looks up towards the sky and down towards the ground. --Bowlhover (talk) 22:15, 1 June 2009 (UTC)

They can't call it "upper left" because that would depend on where on the Earth you were. What's the top for a viewer at the North Pole would be the bottom for a view at the South Pole (they are, in effect, standing upside-down relative to the person at the North Pole), for people at intermediate latitudes there is a gradual change in orientation. With the Sun, you don't notice this much, but with the Moon it is far more obvious - when I look out the window here with a latitude of about 55 deg N, a crescent moon looks like it is roughly upright. Near the equator it would look like it was lying down. That same happens with the Sun, there is just no way of telling unless you can see sunspots or similar. For that reason, they need a more universal way of naming the directions, so they use compass points in the manner described by Bowlhover. --Tango (talk) 22:34, 1 June 2009 (UTC)

It isn't making sense yet. Obviously, I know they couldn't call it "upper left" I was just clarifying which item on the image I meant. It's also obvious why they can't call it top or bottom, but prefer North and South. Is it simply a convention that East and West directions are reversed in space? The claim that East is to your right when facing north and looking down, so we want that same direction to be East on the sky behind you sounds clever, but I would think it would be cited somewhere - I've looked and I can't find one, which may just mean my search skills aren't up to par. I think the choice is arbitrary, and I'd like to know why they chose the opposite of the intuitive choice. Sphilbrick (talk) 23:07, 1 June 2009 (UTC)

It's not arbitrary, and it was intuitive when it was chosen. Remember that Astronomy is thousands of years old, dating back to long before it was accepted that the Sun and other celestial objects were independent spherical bodies in space, with easts, and wests, and axial rotations of their own. Originally they were though to be minor features on the Earth's sky (itself possibly a revolving solid sphere, hence "firmament"). The convention arose of the eastern side (limb) of the Moon, say, being the one nearest the eastern horizon of the Earth, because an Earth-centred point of view was the only one that seemed important.

We still usually use this convention when describing things as seen from the surface of the Earth, but now we know that the Sun, Moon and planets are worlds in their own right, we also know that if we're describing, say, Mars from a Mars-centered viewpoint, East and West will be reversed (such that on Mars the Sun will still rise in the East). This can occasionally cause confusion, and now that we've actually visited the Moon, modern Moon maps often show East and West opposite to the way they're marked on older, pre-spaceflight maps. 87.81.230.195 (talk) 02:07, 2 June 2009 (UTC)

Imagine looking in the usual way at a globe that represents planet Earth. Obviously, it North is at the top, then East is to the right. Now put yourself inside the globe and look outwards. While North is still upwards, East is now to the left. But that is exactly the situation when we look up at the sky, the "celestial sphere". --Wrongfilter (talk) 10:14, 2 June 2009 (UTC)

I’m not yet persuaded that the decision wasn’t arbitrary. For example, even the choice of north could be chosen in more than one way. Once one has (arbitrarily) assigned north on the Earth, the question arises how to assign north on other planets. We start by saying it is on the axis on rotation, but that still leaves two possibilities. We could choose the end that lies in the same side of the ecliptic as the north of the earth, or w could invoke a right-hand rule to determine north. Note that these two rules do not give the same answer for all bodies in the solar system – the decision to use the right hand rule was an arbitrary choice, albeit a choice that can be defended.

Once north is selected, south is forced, but east is not. So we have to make a choice. Again, we could pick from more than one rule. One possible rule is – orient so north is on top, and choose east so that it is on the right, just as one would do looking at earth. Apparently that rule wasn’t chosen. As wrongfilter suggests, imagine yourself inside the earth, and choose the direction that is closest to the direction you would look is you looked to the east on earth. A rule, to be sure, but a different rule (and one I suspect gives the wrong answer for Uranus).

However, as 87…points out, we don’t use that rule for all celestial bodies, we use it only for those we haven’t visited. I checked some moon maps, and with north on top, east is to the right. Ditto for Mars. Well, have we visited Mars? Humans haven’t been there, but we’ve sent equipment. But if the rule for determining east is use the rule based upon the view from inside the earth, except for bodies we have visited, then why does it apply to the sun? After all we have sent a probe to the sun.

I’m looking for a coherent rule – I’ll even accept that we arbitrarily made a decision and stuck with it, but I’d like to see a source – I don’t see that this is addressed in Wikipedia, and I haven’t found it elsewhere yet. Sphilbrick (talk) 12:24, 2 June 2009 (UTC)

Outdent – incidentally, I accept that it make sense to label sky in the way wrongfilter suggests – so sky maps, with north on top have east of the left. This makes perfect sense, because we can think of ourselves being inside a sphere looking at the inside of a larger sphere. Mirror real makes sense it that case - if someone says Castor and Pollux are in the east, it seems natural to look toward the east to find them. The convention for the celestial sphere makes perfect sense to me. What I am questioning is why the same rule is applied to the sun. From our point of view, we are outside the sun, looking at it from the outside, not the inside. Same for the moon and Mars. In the case of the moon and Mars, we locate east at pi/2 clockwise from north. In the case of the sun, we locate east at pi/2 counterclockwise from north. clearly arbitrary – my question is what was the thinking behind the convention? Sphilbrick (talk) 12:48, 2 June 2009 (UTC)

A consistent system would be for planets and stars to have their own compass directions, with east to the right when north is up, the same as earth, and for it also to be possible to talk about their "limbs" which are oriented to the celestial sphere and therefore have east and west reversed (and might not have north the same way up). I'm only guessing, but I think this might be the way it works. See this page I just dug up: http://www.sidleach.com/mars_081703_21.htm "South is up in this image, and the eastern limb of Mars is to the right." Presumably the eastern limb of mars is different from mars's east, and the same could apply to the sun if we ever talk about the sun's east (I don't know if anyone does). 81.131.66.245 (talk) 19:45, 2 June 2009 (UTC)

Much observation of any celestial body still takes place on Earth, using telescopes. In that case, it would make sense to use the same system of east/west as the rest of the sky to avoid confusion. If you look at amateur astronomy maps of the Moon or Mars, you'll see that they also have east 90 degrees counterclosewise from north. --Bowlhover (talk) 11:33, 3 June 2009 (UTC)

A complication is that astronomical telescopes usually show an inverted image, because this requires the least amount of lens glass (or number of mirror surfaces) in the optical train, thus maximising the brightness of the image and minimising its degredation, given that no lens or mirror is perfect. When such images are photographed and printed, there is endless scope (sorry!) for - deliberately or accidentally - further changing the orientation of the picture. Everyone in the astronomical community (amateur and professional) is well aware of this and double-checks alleged orientations against reality when it matters, but mistakes or ambiguities in published pictures may well mislead the layperson.

Further to Sphilbrick and Bowlhover's remarks above, I've just checked the 2 editions of Norton's Star Atlas I have to hand. In the 1946 edition, the "Sketch Map of the Moon (As seen in an inverting telescope)" marks South at the top and East on the right, with Mare Crisium near the North West (lower left) limb; in the 1973 edition, the (much superior) "Map of the Moon (. . . based on a drawing published in 1926 . . .)" marks South at the top and East on the left, with Crisium near the North East (lower left) limb. In Patrick Moore & Garry Hunt's Atlas of the Solar System (1990 edition), the multi-page lunar maps designate North at the top and East on the right. with Crisium near the North East (upper right) limb. 87.81.230.195 (talk) 20:33, 3 June 2009 (UTC)

Turing test

Is it possible for a human to fail the Turing test? —Preceding unsigned comment added by 81.76.42.229 (talk) 21:29, 1 June 2009 (UTC)

Certainly, but false negatives aren't a result of interest. Anyone could respond to a tester in such a way as to be indistinguishable from a computer program. — Lomn 21:46, 1 June 2009 (UTC)

An autistic person (or Rush Limbaugh) could easily give nonsensical responses. Clarityfiend (talk) 21:50, 1 June 2009 (UTC)

More than that, I could (as a Turing testee) bring the source code to a chat bot and manually interpret it to determine my test responses. It is comparatively trivial for a human to not only fail the Turing test but to be completely indistinguishable from a known computer. — Lomn 02:19, 2 June 2009 (UTC)

You would have to interpret it in real time, though, and that's not so easy. -- BenRG (talk) 14:31, 2 June 2009 (UTC)

Purple, 7, the east. -Arch dude (talk) 22:30, 1 June 2009 (UTC)

Yes it happens sometimes e.g. [16]. Dmcq (talk) 22:32, 1 June 2009 (UTC)

What makes you believe is it possible for a human to fail the Turing test? --Sean 13:16, 2 June 2009 (UTC)

How do you feel about Purple, 7, the east? Nimur (talk) 15:02, 2 June 2009 (UTC)

Oh... believe is it possible for a human to fail the Turing test? SteveBaker (talk) 02:53, 3 June 2009 (UTC)

Quote from Lessons from a Restricted Turing Test: "Ms. Cynthia Clay, the Shakespeare aficionado, was thrice misclassified as a computer. At least one of the judges made her classification on the premise that '[no] human would have that amount of knowledge about Shakespeare.'" -- BenRG (talk) 14:31, 2 June 2009 (UTC)

Easiest cell to extract DNA from

For humans, which cell would be the easiest to extract DNA from? I don't just mean getting the DNA, the cell has to be accessible as well. Any help would be appreciated. --The Dark Side (talk) 22:22, 1 June 2009 (UTC)

You can get DNA from saliva, or from hair, and I believe from skin, blood, and basically anything that makes up a human. Take your pick. --KageTora - (영호 (影虎)) (talk) 22:50, 1 June 2009 (UTC)

But is any one easier to use than the others? --The Dark Side (talk) 22:56, 1 June 2009 (UTC)

Ok, imagine the story of Goldilocks, and imagine an alternative ending where she left before the bears came home. They could find out who it was who ate the porridge, broke the chair, and slept in the beds just by the forensic evidence (assuming she wasn't a first-time offender). From the spoon she used to eat the porridge, there maybe some residual saliva, which could be used to extract DNA. It would also help if she licked the spoon clean, and even more so if she licked the bowl clean. When she sat on the chair that broke, she would have fallen, and possibly cut herself on the broken chair (not mentioned in the original story, but this is an alternative). This would be a perfect source of DNA. Failing that, when she slept in Baby Bear's bed, it's pretty well a sure thing that some of her hair would be on the pillow, and considering baby bears don't usually have long blonde hair, they would be easy to spot. Another source of DNA in the bag. The FBI would be round her house in a shot! --KageTora - (영호 (影虎)) (talk) 23:15, 1 June 2009 (UTC)

Okay, I understand that it's easy to collect cells. What I'm really after is the ease with which the DNA can be extracted. This would probably have to take into account the cell membrane and the features that differentiate the various human cells. --The Dark Side (talk) 23:55, 1 June 2009 (UTC)

Extracting DNA from any recently living nucleated cell is so trivial that its essentially moot to decide which cells one is extracting from. Forensic scientists don't even differentiate it that way. A single microscopic sample may contain DNA from dozens of different kinds of cells from the same individual. For example, take a blood stain. The sample obviously contains DNA from white blood cells, but it also likely contains skin cells (of which there are many different types, vertically striated, from the same cut even!), subcutaneous fat cells, muscle cells, and from any number of other sources. With tools like polymerase chain reaction any DNA sample can be amplified to a useful amount, so it really doesn;t matter where it comes from. --Jayron32.talk.contribs 04:29, 2 June 2009 (UTC)

And that is exactly what I was implying, but said in a more scientific way. --KageTora - (영호 (影虎)) (talk) 10:08, 2 June 2009 (UTC)

A buccal swab (swabbing the inside of the cheek) is the most prevalent way of DNA sampling, assuming you haven't already drawn blood for some other purpose. -- 128.104.112.106 (talk) 20:23, 2 June 2009 (UTC)

Indeed, a buccal swab (can't believe we don't have an article yet) is probably the least invasive method that is most widely used. It isn't as "good" as blood, but its a hell of a lot easier to sample. In a job I used to do, I would extract DNA from both blood (a few ml) and buccal swabs on a daily basis. I must have done many hundreds, if not thousands, of both. The number of nucleated cells in a 1ml of blood outnumbers the best buccal swabs, so you would get much more DNA from blood. The quality of the DNA would also be better as the blood environment is more consistent than the mouth. We found that the quality of DNA from buccal swabs varied greatly depending on what was eaten immediately prior to the swab. Particularly problematic was when a kid ate an apple just prior to swabbing. Then DNA would always be crap. We never formally tested by this, but our assumption was that the acidity of the apple was to blame. Rockpocket 01:28, 3 June 2009 (UTC)

I remember reading that it is easy to extract human DNA in a home experiment suitible for schoolchildren, but do not remember how its done, except that it requires a beaker and a glass rod. 78.144.244.22 (talk) 22:31, 2 June 2009 (UTC)

Untreated Cancer

Horrible subject, this, but I've been thinking. What happens if cancer goes completely untreated? Of course, death is the usual consequence, but I am asking about what happens in the body leading up to that. Also, I know there are many different places in the body that can become cancerous, and so they will all exhibit differing symptoms from onset until the end, so this may be a difficult question to answer. I am interested in this because in the "modern developed world" we have cancer treatments, while in older eras there were none (or at least, none as we have now). To complicate matters more, there seem to have been many studies that suggest that untreated cancer victims tend to live longer than those who are treated (sorry, no reliable links). Another question is, do animals get cancer? I'm sure they do, but how is this treated, if at all? Thanks. And please do not post links with pictures of what it looks like, as I am a tad squeamish. :) --KageTora - (영호 (影虎)) (talk) 22:48, 1 June 2009 (UTC)

"there seem to have been many studies that suggest that untreated cancer victims tend to live longer than those who are treated" — if there aren't any reliable links, I would be inclined to suggest it is because such studies don't exist.

This is not to say that there are no trials which show some individual treatments are ineffective — some drugs and therapies don't work as well as animal models or biological theory might suggest, and the only way to know for sure is to do clinical trials. Further, there are some cases where watchful waiting (monitoring, without immediate treatment) is considered an appropriate response to a cancer diagnosis. Finally, opting for treatment does (potentially) expose a patient to immediate risks in return for the potential later reward. Let's say a surgical intervention cures 90% of patients, but 10% die on the table. One could say that the latter 10% did significantly worse than they would have had they not been treated — but it probably wouldn't be justifiable not to offer treatment. TenOfAllTrades(talk) 00:01, 2 June 2009 (UTC)

Animals do get cancer. In the wild that quickly puts them in the "gets eaten" category, so it's not a top animal channel item. Rats and mice serve as models for cancer studies. There are viruses that cause cancer [e.g. Feline leukemia virus or HPV}. Dogs are listed as having quite a variety of cancers, including one that is transmitted through sexual contact. A new form of cancer in cats is injection site carcinoma (no page??). It is ironically caused at sites of inoculations that are supposed to protect our feline friends from diseases. Vaccinations are now moved to legs, so that amputation becomes an option. Radiation treatment and chemotherapy are costly, so some owners opt to have their animal put down. Some of the criticism of cancer treatments is that tumors get identified and removed/treated aggressively that would have gone into remission or never developed if left to themselves. [17] [18] [19]Clinical study results are hard to come by because of the dire results if the tumor remains untreated and mestastasizes instead of going into remission. We have no way of predicting outcomes. AFAIK it is not disputed that there are cases when the immune system manages to cope with cancerous tumors.(e.g.Phoebe Snetsinger) Another complaint is that biopsies used in diagnosis cause some tumors to mestastasize which would not have done so otherwise. Some cases have been described, but clinical studies hinge on the same problem as above. [20]71.236.26.74 (talk) 01:05, 2 June 2009 (UTC)

Cosmological units

Why does cosmology use such odd units (parsecs, lightyears, solar masses, etc) instead of the SI units like almost all the rest of science? And why are there so many different distance units in use? It seems to be not uncommon to be discussing kilometers, parsecs, lightyears and astronomical units at once. For example, conventionally, Hubble's constant is given in (km/s)/Mpc, which seems insane to me -- would s^-1 have not sufficed? —Preceding unsigned comment added by 79.72.180.91 (talk) 23:02, 1 June 2009 (UTC)

Probably because the numbers would be astronomically large in SI units. It is easier to grasp the mass of a star in terms of solar mass than kilograms or a long distance in light years rather than meters. Bubba73 (talk), 23:19, 1 June 2009 (UTC)

Are there lots of people writing and reading about cosmology who do not understand numbers like 10³¹? Why should one area of science stick with non-SI units? Edison (talk) 23:44, 1 June 2009 (UTC)

The parsec stems directly from one method used to measure the relative distances of stars from the Solar System. It's easier to determine that one star is, say, 2 parsecs away while another is 4 than it is to calculate exactly how far a parsec is, so - especially when you're comparing lots of similar measurements - it saves some trivial and unnecessary maths to leave parsecs unconverted. Parsec is short for 'parallax second', and 1 parsec is the distance (about 3.26 light years) an object would be if the revolution of the Earth about the Sun over 6 months caused it to exhibit an apparent (parallax) shift in position angle of 2 arc seconds; or conversely, it's the distance at which a length of 1 Astronomical Unit (see below) would subtend an angle of 1 second.

Astronomical Units similarly derive directly from comparative methods used to measure the sizes of orbits in the Solar System relative to Earth's (whose orbit is 1 AU in radius, 2 AU in diameter). Again, historically we could measure these sizes relative to each other more accurately than we could measure the actual distances involved.

A light year, as you know Bob, is the distance light travels in one year. Apart from giving usefully low numbers (nearest star 4.2 ly, diameter of Milky Way about 100,000 ly, nearest major external galaxy about 2,000,000 ly), it's a useful reminder that we're seeing something x ly away as it was x years ago.

Hubble's constant is, again, left in the form in which it gets measured, in part because it isn't a pure distance, but rather a consequence of the way the Universe is expanding whose fine details are still subject to some uncertainty.

Of course, it's not a distance at all, but a rate. I knew that really. Doh!. 87.81.230.195 (talk) 20:15, 2 June 2009 (UTC)

These (and other) methods of distance determination do not (yet) give precisely interconvertable results, just as different methods of age determination in archaeology (say C14 and thermoluminescence) give answers that have to be carefully calibrated rather than ones that can be taken at face value. Converting them all to SI would mask these uncertainties.

Solar masses are used because it's more useful and informative to compare the relative masses of other stars to each other and to our Sun's than it is to know their absolute tonnages, which again are far harder to determine (and give insanely large numbers in SI units). The luminosities of stars are also often measured in units of Solar luminosity.

Exactly, and the absolute mass of an astronomical body is hard to pin down because the gravitational constant is not known to great precision. --Bowlhover (talk) 00:26, 3 June 2009 (UTC)

In addition to avoiding often unnecessary conversions, using each of these units in their traditional contexts where likely magnitudes are familiar avoids continually dealing with SI unit quantities containing large exponents, in which it's easy to make unobvious mistakes. Astronomers will cheerfully convert them as necessary to communicate with the lay public (who seem perfectly happy with light years and, often, AUs anyway): if any non-astronomer scientists want measurements in SI units, the conversion factors are readily available and they're quite capable of performing the calculations themselves, and welcome to, ta very much. 87.81.230.195 (talk) 01:27, 2 June 2009 (UTC)

It's not like cosmologists and astronomers are alone in this though. Particle physicists use all sorts of specialised units - Electron volts instead of Joules, an entire system of Plank units that bear no resemblance to SI units. Electrical systems engineers use Kilowatt hours instead of Joules, Aerospace engineers still use 'knots' for airspeed and feet for altitude - despite using metric for almost everything else. Biologists and Atmospheric engineers measure pressures in millimeters of mercury instead of Pascals. Computer scientists abuse the 'k' and 'M' prefixes to mean 1024x and 1048576x respectively. All sorts of people abuse and adapt the system for convenience. If it makes communications clearer - then that's a good thing. It would be a real pain in the ass to have to talk about having 110 m²kg⁻³A⁻¹s electricity coming out of the wall socket. SteveBaker (talk) 02:28, 2 June 2009 (UTC)

And atom masses are measured in atomic units instead of grams, High explosive energy output is measured in tons of TNT instead of joules, food energy is measured with Calories (capital c) which is equivalent to 1kcal istead of joules, there are several different conventions for electromagnetic units, and the cgs system of units is as popular as the SI system of units. The list is quit impressive. There is no rule (neither implicit nor explicit) saying that scientists should use SI units. We are only expected to state the unit system being used clearly. Dauto (talk) 03:24, 2 June 2009 (UTC)

Related question: Why is it that astronomers, who deal with the largest and heaviest things in the universe, generally use CGS units instead of MKS units? I understand it's probably convention, but how did such a bizarre convention come about (as it makes the numbers even more cumbersomely large than they already are)? -RunningOnBrains^{(talk page)} 04:52, 2 June 2009 (UTC)

Historical accident, and in that case it really does not matter much - just add another two to the exponent. Note that most of the non-SI-units in use are units of convenience - lightyears, AU, Parsecs, Electron Volts, u, all have a direct and intuitive connection with the domain of discourse. The SI-units, and many traditional units have lost most of that connection, and are now very abstract and generic. How often do you consider the fact that the meter is approximately a millionth of one quarter of the length of the equator? Or that a mile is 1000 double steps of a Roman legionnaire (well, for frictionless legionnaires of standard weight on the Via Appia, I suppose ;-). --Stephan Schulz (talk) 09:29, 2 June 2009 (UTC)

Assume a spherical legionnaire... —Tamfang (talk) 03:44, 4 June 2009 (UTC)

Well, also remember that the metric system is supposed to be devoid of context. It's not like they created the metric system to measure the equator—they knew the length of the equator and worked backwards, the idea being that anyone could then reconstruct the length if need be. They are meant to be context-free units. Which have their ups and downs, as noted. --98.217.14.211 (talk) 12:38, 2 June 2009 (UTC)

There's a legend that the metre was conceived as the length of a pendulum whose half-period is 1 sec, until someone with colonial experience chimed in with the French equivalent of Afraid that won't do, old chap (gravity, and thus the appropriate pendulum length, varies with latitude). Sadly, one hears that there's no truth in it. —Tamfang (talk) 03:44, 4 June 2009 (UTC)

The use of parsecs, kilocalories, and other special units used above are objectionably non-SI, but still far better than the use by science popularizers such as Science Daily, adapting material from the American Chemical Society, originally published in ACSNano, which says that silver nanoparticles useful in medical treatment are "1/50,000th the diameter of a human hair" without specifying red, blonde or brunette, and from what part of the body. This type of nonsense is like comparing some object in space to so many "city blocks," another widely varying metric. Edison (talk) 15:58, 2 June 2009 (UTC)

See our list of unusual units of measurement and the associated list of humorous units of measurement. My personal favourite is the beard-second. Gandalf61 (talk) 16:32, 2 June 2009 (UTC)

June 2

What are the "tubes" on USB and similar cables?

My wife asked me about this last night. My guess is that it's some sort of inductance coil to reduce RF interference, but I realized that I don't know for sure. Now I'd like to know. Donald Hosek (talk) 01:20, 2 June 2009 (UTC)

A ferrite ring. It stops common mode signals traveling on the cable, and your guess is correct. They may be required to meet an EMI standard, or electromagnetic compatibility to stop the device beding disrupted by a strong nearby signal, such as a mobile phone. Graeme Bartlett (talk) 01:33, 2 June 2009 (UTC)

I fixed your redlink to common mode - hope you don't mind SpinningSpark 18:14, 2 June 2009 (UTC)

Thanks, the red link was a prompt for someone to write an article. I have now made a disamig page as there are two quite distinct meanings and four articles. Graeme Bartlett (talk) 06:20, 3 June 2009 (UTC)

Coughing and sneezing while unconscious

Can humans cough or sneeze while they are unconscious? -- Beland (talk) 05:05, 2 June 2009 (UTC)

It depends on the level of unconsciousness. Look at the Glasgow Coma Scale and you will see that in lighter states of unconsciousness the patient may be able to obey verbal commands. It seems possible that in this condition they would cough and sneeze. Richard Avery (talk) 07:18, 2 June 2009 (UTC)

Cough is a reflex, not requiring any cognitive input. Even in deep coma people will cough with irritation of the trachea (I've seen this many times). I don't know whether the same is true of sneezing, but I would guess that the right irritant could induce a sneeze in an unconscious person. --Scray (talk) 09:48, 2 June 2009 (UTC)

So what would be the purpose of endotracheal suction of saliva and secretions if the unconscious patient is able to cough? 86.4.190.83 (talk) 13:08, 2 June 2009 (UTC)

They may reflexively cough, but still not with enough vigor to clear their own air passages. Like blinking, there are likely both reflexive and voluntary components to coughing, and unconsciousness may hinder the clearing process without completely eliminate the cough reflex. Additionally, as Richard Avery has noted, there are different severities of unconsciousenss, and every patient is in a way unique; one patient may be able to clear his own air passages unconsciously, and another may not. --Jayron32.talk.contribs 13:31, 2 June 2009 (UTC)

Interesting. Has anyone ever seen anyone sneeze while they are unconscious? -- Beland (talk) 15:17, 2 June 2009 (UTC)

GPS in plane

Is current plane doesn't equip with GPS? Or within the black box that can survive crash? With current technology, is it possible to equip life vest with GPS? Thanks for the answer. roscoe_x (talk) 05:14, 2 June 2009 (UTC)

Many commercial aircraft are equiped with GPS: GPS_navigation_device#Commercial_Aviation. Smaller and older aircraft often do not have GPS. The GPS is not part of the black box (flight data recorder), but the data from the GPS is required to be stored on the flight data recorder (see [21] item 39). Yes, it is possible to equip lift vests with GPS. Sancho

Also it would be possible to equip each life vest with a satellite distress beacon. Of course it's not going to happen on a commercial airliner because it is not required by law and it would increase ticket prices by tens of cents. --203.22.236.14 (talk) 07:43, 2 June 2009 (UTC)

I think the op is slightly confused with how GPS works. GPS is passive. A GPS reciver doesn't transmit anything, just recives information from satalites to work out its location, meaning a life vest equipped with GPS wouldn't be much use other than to tell the wearer where they are. As far as I know you cannot be tracked via GPS. Gunrun (talk) 10:47, 2 June 2009 (UTC)

Quite so, GPS is passive (but a nearby GPS receiver could be detected due to it's internal amplification of the GPS signal). But I believe the OP's real question is "That AirFrance plane seems hard to find, couldn't it have some device to make it easy to find?" That device would be something like GPS+distress beacon and yes, it's very possible. Actually, I'm surprised that aeroplanes don't constantly upload all data that would be stored in the blackbox via the satellite phone network. --Polysylabic Pseudonym (talk) 11:03, 2 June 2009 (UTC)

From what i've found there are regulatory rules around carrying distress signals. Virtually all commercial planes must carry some - automated and manual. There are even life-rafts for planes that have them built into them. Not sure about life-jackets commercial wise but they exist. My understanding of the Air France disappearance was that the plane was flying over a part of the world that gets very limited coverage in terms of Radar / satellite and that was what has caused the difficulty of finding. 194.221.133.226 (talk) 11:12, 2 June 2009 (UTC)

Yes - as others have pointed out - you have to combine a GPS unit with some kind of a transmitter in order for someone else to find out where that unit is. However, in the case of the Air France disaster, the plane probably crashed somewhere in the mid-Atlantic - perhaps 800 miles from the nearest land. Being that far from civilisation means that there is certainly no cellphone coverage and you'd need a pretty powerful transmitter to reach anywhere useful. Just about the only practical technology would be a satellite phone. But you can't put all of that technology into something like a life vest because it's simply too expensive. There are something like 50,000 large passenger aircraft in the world - that's probably five million life vests - of which perhaps a few dozen ever get used for their intended purpose! Adding a satellite phone to each one...with a battery that's kept constantly charged - and replaced when it breaks...a phone that'll survive the worst a plane crash can do...that's an expensive thing - many hundreds of dollars each, certainly. You'd perhaps need to spend several billion dollars to add such a feature to the world's airliners...and quite frankly - it's a total waste of money because airline life vests are so very rarely used.

In the case of the Air France disaster - it appears that the aircraft was in mid-Atlantic, so it would have been flying at perhaps 30,000 feet. Whatever happened was so fast that a mayday signal couldn't be gotten out - and involved a sudden loss of cabin pressure and electricity. Basically - that means an explosion or catastrophic structural failure of some kind - and crash from 30,000 feet. Nobody is going to survive that. Having a way to find a few lifejackets floating out from the wreckage afterwards cannot possibly justify the cost.

The aircraft's own flight recorder does have various transmitters to aid in finding it later - but that assumes that the thing survived the initial disaster - and a fall from 30,000' and a good soaking in salt water afterwards. Those things are tough - but they aren't invincible. Finding the one from flight 447 in a search area of perhaps half a million square miles is going to be very hard indeed...it's probably impossible.

SteveBaker (talk) 12:27, 2 June 2009 (UTC)

Steve, an EPIRB radio beacon transmits via Satellite. Also the phones I was talking about were satellite phones which likewise have global coverage. I'm pretty sure there's global coverage. It should be fairly trivial to install at least one EPIRB in a location on an aeroplane where it will in any disaster end up separated from the wreckage and floating (radio isn't much good under hundreds of metres of water). Come to think of it, all of the black box data -- were it not automatically transmitted during flight over the satellite phone network -- could be easily stored on a small solid state memory device attached to such a beacon to make that also easy to find. --Polysylabic Pseudonym (talk) 12:47, 2 June 2009 (UTC)

"...is it possible to equip life vest with GPS?" Sure, here's one such set up. Many are carried on military and general aviation aircraft. Polysylabic Pseudonym above has linked to the two relevant articles.—eric 13:24, 2 June 2009 (UTC)

And the ugly truth of telecommunications finally comes out! Instantaneous, point-to-point radio contact is much less seamless than it appears to the untrained eye. Just because you can whip out your mobile phone and dial a long-distance number without interference from every other mobile phone on the street doesn't mean an airplane can do the same! Our radio systems, in general, are horribly short-range. While it is true that we do have some technologies for long-range transmissions, the amazing web of instantaneous digital connectivity to every other part of the world is only made possible because in most of our daily life, we are never more than one mile from the nearest cell tower, not more than 100 feet from the nearest 802.11 access point. This allows us to use high-frequency, wide-band shared channels. But these channels are not very good for long-range transmissions. Although it appears to be "point-to-point", it's a really complex set of relaying to get your off of the shared radio channel as proximally as possible. So, when you make a "wire-free" long distance call from your mobile phone to your friend in Angola, the wireless hop is not actually all that far. A series of base-stations route you to a cable (optical fiber) network, and the signal travels by wire for a very very large portion of its journey. It crosses the ocean by submarine communications cable, hits a couple more optical cable routers, and finally gets sent out to a field transmitter which is not more than a few thousand meters from the intended recipient.

An aircraft which is 3000 kilometers from the nearest base station has surprisingly few options for telecommunication, and they are not all that high-tech. On board, there is a suite of radios, ranging from VHF and UHF digital radios to very "1950s" style HF (shortwave) radios with ranges of around a few hundred kilometers. While in flight, the aircraft will often fly "convoy-style", maintaining communication to the ground by proxy over an HF channel to another aircraft a few hundred kilometers away. This radio signal is very low-bandwidth and not exactly reliable. (This has caused problems before). Unfortunately, the sort of nifty broad-band technologies we've grown very accustomed to are based on much higher frequency signals which have much shorter range. Trying to transmit a VHF radio or a 2.4 GHz microwave "mobile-phone" over a thousand kilometers is just not practical.

Maintaining a bidirectional satellite-based communication link during the entire flight would be really quite challenging, although not impossible. Therein lies the "ten extra cents per seat" which was casually described above. Now, here comes another ugly truth about satellites - they're not really global in coverage! To receive effective satellite service, a location must have one or more satellites above the horizon and in view of the transceiver. To save power and decrease launch costs, these communication satellites are NOT in a geostationary orbit - rather, they fly in constellations in predetermined orbits. These orbits do not necessarily provide full coverage for the entire planet (at least not out to "five nines" or 24-hours, 7-days-a-week). (Which telecommunication company wants to pay huge sums of money to provide fantastic satellite reception to the middle of the ocean? The number of subscribers out there is a little low). So, even satellite-based schemes might not provide a 100% uptime on the communication link.

In summary, the transoceanic airplane provides an interesting insight into our communication infrastructure. When isolated from the enormous network of ground relays, optical cables, and effective satellite coverage, the only viable solutions are pretty old-fashioned shortwave radios. Because of fundamental bandwidth limitations, these links are not suitable for an "always-on", constant monitor of the aircraft's position - imagine what would happen if every aircraft on the planet started broadcasting wideband digital updates over globally-ranged transmissions at 9 MHz - there's a shared channel, and it'd get used up pretty darn quick. (If you can't imagine, let me present an analogy - the idea is that you want every individual on a football field to yell all their conversations loud enough so that every other person can hear them, even on the other side of the field. But everyone will be yelling at the same time, and constantly hearing all the chatter from every other person - it destroys any hope for effective communication). Nimur (talk) 15:30, 2 June 2009 (UTC)

Awesome explanations! So there is no satellite that covers the crash area of AF447? If there was one, could it have located the wreck by simply looking? Without a 2-way radio communication. Satellite imagery says there are satellites that can distinguish objects on the ground at least 50 cm apart. Jay (talk) 10:03, 3 June 2009 (UTC)

No - you really don't understand the immensity of the task. They have actually found some wreckage now - just a few small parts. But the search area was immense - thousands to hundreds of thousands of square miles...they got lucky because another aircraft spotted burning wreckage on the ocean while it was still dark and that stood out fairly clearly. You don't take satellite photos at night. Suppose you take a photo (even from some super-high rez military spy satellite) with enough resolution that you can spot wreckage. 50cm resolution isn't enough - let's suppose it needs 20cm resolution to see a floating life vest that's maybe 40cm across for what it is. OK so on your (roughly) 1000x1000 resolution computer screen, you can start looking at the photos this satellite produced - right? You're looking for that life vest. But at 20cm resolution, each 1000x1000 pixel photo covers just 200x200 meters of the ocean. To look for wreckage over just one square kilometer, you'd have to carefully inspect 25 photographs looking for a TINY orange spec just a couple of pixels across that's just barely a smudge on your screen. To search 100,000 square kilometers, you have to look CAREFULLY through 2.5 million photographs of dull, boring ocean! Do have any conception about how impossible that is?!! SteveBaker (talk) 13:34, 3 June 2009 (UTC)

I didn't think of the human angle to it after the satellite had done its job. Also, I missed out that night could be a hindrance, though I did consider cloud cover. But shouldn't the task be fairly straightforward for a digital image processing software - to detect an orange, or yellow or red dot within a limited-coloured canvas of ocean? Jay (talk) 14:30, 3 June 2009 (UTC)

That's assuming you actually got a photo that shows the orange life vest. Any number of things could obscure it, or they might not be wearing a vest at all (holding onto debris, for instance). — The Hand That Feeds You:^Bite 20:14, 3 June 2009 (UTC)

"[Sarkozy] said France has asked for help from U.S. satellite equipment to locate the plane." (http://www.wral.com/news/national_world/world/story/5254928/). Would be interesting to see what the US provided. Jay (talk) 03:47, 4 June 2009 (UTC)

Commercial aircraft are equipped with ACARS, which can send low-volume data. The system uses VHF radio when in line of sight of a fixed tower (essentially when over land) SATCOM (Inmarsat) when over ocean except at high latitude, and HF when over the poles. The ACARS unit aboard the aircraft is used, among other things, to send critical maintenance information (engine performing out of specification) and takeoff and landing information. This info is gathered automatically using the datalink that connects the various computers aboard the aircraft. The datalink always has location and time infor from the aircraft navigation system, which generally uses GPS plus an inertial navigator, at least. There is nothing to prevent the ACARS from sending the aircraft's location if something bad happens, but this is has not been done because this was not one of the goals of the ACARS system. Flight 447 sent out several maintenance alerts, presumably via Inmarsat, and could easily have sent a location message if anyone had thought to add this function. This is trivially easy to see -- in retrospect. -Arch dude (talk) 18:45, 2 June 2009 (UTC)

Update: The ACARS messages do in fact contain the location information. The last flight 447 message had location information to 3 decimal places (about 100 meters.) The problem, apparently, is that this classified as "maintenance data" not "critical flight data," so it (apparently) was not conveyed to the SAR crews. I suspect that this will change in th future. -Arch dude (talk) 22:01, 2 June 2009 (UTC)

I am puzzled that it is not required for all planes to continuously send out its location, say once a minute. If something suddenly happens to a plane and communication is cut off then there is not time to only then send a message. A simple flight number and GPS location (which includes altitude) once a minute is not a lot to ask for. That's maybe 30 bytes of data per plane per minute. I'm sure the cost is negligible for hooking into something like Irridium or Globalstar - and besides you probably get great reception from 10km up. Is there any downside to this? 196.210.200.167 (talk) 19:29, 4 June 2009 (UTC) Eon

Evolution denial & genetic engineering

Do evolution denialists usually take a stand on genetic engineering? If yes, for or against? --KnightMove (talk) 09:58, 2 June 2009 (UTC)

Since almost all of them are religious fundamentalists - it's probably safe to say that most of them are against genetic engineering...although logically, they should probably conclude that it simply doesn't work and is therefore harmless...but logic isn't generally their strong point. SteveBaker (talk) 12:03, 2 June 2009 (UTC)

Actually, Steve, you'd be surprised at how some of the even Young Earthers manage to weave modern genetics into their story. The Answers in Genesis people are the best in this respect, going to great lengths to appear biologically sophisticated.) I think they would probably argue that no new species would be created by such genetic engineering, though of course you can make changes to a species (in the same way you can breed dogs to superficially look different, but they are still dogs. (I don't agree with this, but that's likely their argument.) Answers in Genesis has a LOT to say about genetics in general, about stem cells, and about cloning, but I don't see anything about genetic engineering. I'm not sure they would disagree with it if it were just being used for medical activities, but I'm just speculating. --98.217.14.211 (talk) 12:33, 2 June 2009 (UTC)

Re it's probably safe to say that most of them are against genetic engineering: I find that hard to believe considering that half of Iowa is under GM corn with no signs of the Creationists making any fuss. --Sean 13:22, 2 June 2009 (UTC)

Surely evolution and genetics are logically and conceptually independent of one another ? You could (hypothetically) have evolution without genetics or genetic inheritance without evolution. Darwin, Wallace and Huxley formulated evolution without knowing anything about genetics - indeed, Darwin proposed the entirely incorrect idea of gemmules. When Mendel discovered the laws of genetics he knew nothing of evolution. It is only the joining of the two strands of thought in the modern evolutionary synthesis that makes us think they are inextricably intertwined. Gandalf61 (talk) 15:22, 2 June 2009 (UTC)

You're perfectly right, but evolution deniers usually believe in God as the only ruler of life, which plausibly might make them disregard genetic engineering. Whether this really is the case, was my concern. --KnightMove (talk) 19:35, 2 June 2009 (UTC)

Could you have genetic inheritance without evolution? The only way I can see this working is with no copying errors and asexual reproduction. I'm no biologist though; any thoughts? (Oops, this may be derailing. Should I start a new question?) 80.41.123.51 (talk) 20:02, 2 June 2009 (UTC)

They don't deny the possibility of birth defects; some even say that (some) existing species are corrupted varieties of those that existed in Eden. —Tamfang (talk) 16:58, 4 June 2009 (UTC)

It doesn't automatically follow that individuals who dispute evolution on a religious basis are against genetic engineering. Its a little more complex than that. There are practical examples of genetic mutation and by implication, microevolution, that makes it very difficult for scientifically educated anti-evolutionists to dispute the genetic basis of phenotypic inheritance (though millions of uneducated ones do so quite vehemently). Since genetic engineering (at our current level of sophistication) really impacts at this level, is entirely possible to come up with a rationale whereby one can resolve an anti-evolution, pro-GM stance.

For example, a report issued by the National Council of Churches of Christ takes such a positive stance toward GM. The report sees us continuing God's work in genetic engineering: "Dominion carries with it a concept of custody, of stewardship, of being responsible for, of caring for all creation." They believe the Scripture "exalts the idea that men and women are coming into the full exercise of their given powers of co-creation." In other words, they see GM as a fulfillment of our "dominion over the fishes of the sea, and the fowls of the air, and the beasts." (Genesis 1:26).

However, while accepting microevolution one may still reject macroevolution and the common descent, instead believing the range of species today derive from baraminologic "kinds". They key distinction, in their minds, is the genetic "missing link" between micro- and macroevolution, which allows them to accept the former while disputing the latter. Rockpocket 01:09, 3 June 2009 (UTC)

Except that there's really no difference between micro and macro evolution. — The Hand That Feeds You:^Bite 20:19, 3 June 2009 (UTC)

Other then you can observe micro in real time. Macro has to have ancient remains to back it up. 65.121.141.34 (talk) 20:28, 3 June 2009 (UTC)

Output per man per shift

"output per man per shift" in any massproduction manufacturing industry?

Sathyavolu sar (talk) 14:36, 2 June 2009 (UTC)

This question is a double-post. A few answers were provided here. We can't answer your question any better unless you elaborate on what you mean by "output." Output can be measured a lot of ways. If you have a specific industry in mind, then it should be easy - count the number of widgets built, on average, during one shift. Different companies might have dramatically different productivity, but in a commodity industry those sorts of variations either equalize or one company goes bankrupt. The most uniform system for comparing different industries is to measure the value of the items produced, in dollars (or other currency). I would imagine that the output per man per shift is on the same order of magnitude as the wage paid to that man per shift (unless there is a severe case of worker exploitation, with the profits of the output being disproportionately allocated elsewhere). Nimur (talk) 15:38, 2 June 2009 (UTC)

Depending on the what you seek to do with the answer, output-per-worker may not be the correct measure. For example, if you want to know by how much output increases when a plant employs an additional worker, you want the marginal-worker-output, not the average-worker-output. Wikiant (talk) 15:46, 2 June 2009 (UTC)

In fact, we have an article on that, Marginal product of labor. Nimur (talk) 15:58, 2 June 2009 (UTC)

what is the name of the little crab animals that live in the sand that you see when a wave uncovers them

what is the name of the little crab animals that live in the sand that you see when a wave uncovers them. we saw them when we were at Daytona beach. thay look like tiny shells after a wave washes over them then they burrow themselves back into the sand —Preceding unsigned comment added by 72.65.6.228 (talk) 15:13, 2 June 2009 (UTC)

Emerita (genus)? Talitridae? Bus stop (talk)

Sandhoppers maybe? Check out Amphipoda, the family to which the already mentioned Talitridae belong. If you could specify a size it may be Emerita, again mentioned above, however I get the feeling that you mean something smaller. Hope this helps. 144.32.155.203 (talk) 15:56, 2 June 2009 (UTC)

Besides all of the above, you could also include the Uca genus or Fiddler crab. There are likely dozens of genera and hundreds of species of crabs that exhibit this behavior. --Jayron32.talk.contribs 03:47, 3 June 2009 (UTC)

Or better yet, the Ocypode genus, aka Ghost crab aka Sand crabs. These are often tiny (like, corn-kernel-sized) and make those tiny little holes in the sand at the beach. --Jayron32.talk.contribs 03:49, 3 June 2009 (UTC)

Judging by the location and personal experience, Emerita (genus) is definitely my pick. Sifaka ^talk 05:35, 3 June 2009 (UTC)

Missiles

Missile Technology involves which branches of engineering in actual sense????It may look naive but this doubt has been pounding me from a long time!!!! Does Mechanical Engineering play a significant role in this technology???? —Preceding unsigned comment added by 121.246.174.130 (talk) 16:52, 2 June 2009 (UTC)

Mechanical engineering, aerospace engineering, and electrical engineering are the primary contributing disciplines, with a significant amount of computer science, mathematics, chemical engineering, and other fields. It helps to break down the "missile technology" into some constituent elements, such as propulsion, structure, guidance/control, logistics, and so forth. Take a look at this FAQ from Lockheed Martin - they want "Aerospace Engineering, Business, Computer Engineering, Computer Science, Electrical Engineering, Finance, Human Resources, Math, Mechanical Engineering, Nuclear Engineering, Physics, Supply Chain Management, and Systems Engineering." It's worth noting that "missile" is an extremely broad term - an ICBM is designed and built with a host of different technologies than, say, a TOW missile. Nimur (talk) 17:03, 2 June 2009 (UTC)

A missle, like any other manufactured object, requires many disiplines to come together correctly. Mechanical Engineering plays an important role in keeping the missle in one piece while it reaches the target. On top of that, modern missles are most often computer guided, so programmers and computer engineers will need to have a role in building a missle. There are "rocket scientists" who may work on propulsion as well as the fields listed by the poster above. If you are studying to be part of the mechanical engineering field you should have no trouble finding a job anywhere that you find manufatured goods (and often beyond that). 206.131.39.6 (talk) 17:21, 2 June 2009 (UTC)

What do flu virus names mean?

For instance, H1N1 or H5N1. What is the H and the N? What are the numbers? Do these names apply only to influenza A viruses or are they given to B and C viruses as well?

-- Lesath (talk) 16:59, 2 June 2009 (UTC)

Have you seen H1N1#Nomenclature? "Influenza A virus strains are categorized according to two proteins found on the surface of the virus: hemagglutinin (H) and neuraminidase (N)." The numbers represent variations of these proteins. Nimur (talk) 17:16, 2 June 2009 (UTC)

Organometallic Compound

Why sodium ethoxide is not a oganomeallic compoun?Supriyochowdhury (talk) 18:11, 2 June 2009 (UTC)

For a compound to be considered organometallic, there must be a bond between a metal and a carbon atom that posses mainly covalent character. Sodium ethoxide contains a mostly ionic interaction between a sodium (Na⁺) ion and an ethoxide ion (EtO^-). I hope this helps. —Preceding unsigned comment added by 144.32.155.203 (talk) 18:19, 2 June 2009 (UTC)

Exactly. here there is a bond between sodium and oxygen, not carbon. Rkr1991 (talk) 07:56, 3 June 2009 (UTC)

Bees

Hi, i am doing a project on bees at school and i have a few questions.... I am trying to understand why bees bother collecting pollen and nectar from plants? what's motivates them? also why do they bother making honey? again what's in it for them? it seems to me like they are working all their lives, while other animals are busy just pleasing themselves? 80.47.194.97 (talk) 18:13, 2 June 2009 (UTC)

A good place to start would be on our article on the European honey bee which is quite detailed on many of these matters. It specifically talks about what bees do with pollen and nectar and honey. From that article, you can follow blue links to other articles which contain even more information. Honey is a good read as well. --Jayron32.talk.contribs 18:38, 2 June 2009 (UTC)

Briefly summarized, the bees are motivated by nectar, not pollen. However, the flowering plants benefit when bees spread pollen. You might also want to read about pollination, which also discusses the coevolution of bees and flowering plants. Nimur (talk) 18:54, 2 June 2009 (UTC)

They collect the pollen in their pollen baskets and feed it to the baby bees. Bees are built out of pollen and run on nectar (and in the case of honey bees, on honey when they can't get the nectar). 213.122.59.67 (talk) 20:17, 2 June 2009 (UTC)

I don't think it's scientifically accurate to say bees are built out of pollen. Nimur (talk) 21:37, 2 June 2009 (UTC)

Pollen is important for bees too. Pollen baskets evolved to help the bee, not the flower. As our honey bee article notes, pollen is a good source of protein for developing bees. (Nectar and thus honey are low in protein.) -- 128.104.112.106 (talk) 20:16, 2 June 2009 (UTC)

Resonance and Delocalisation

All the important properties of some covalent speices can not be explained by representing single Lewis dot structure or by showing a single structure bbased on theory of hibridisation .Again unusual stability of some covalent speices can not be explained by considaring bond energies and bond length predicted by V.B.T. after that a new thought resonance arise which can explained above property quit sucssessfully. Tell me that how it fulfill these blanck. What is the requirement of the theory of "resonance and delocalisation"?Rikichowdhury (talk) 18:36, 2 June 2009 (UTC)

Resonance is an artifact of an insufficient model. There is no "fliping" between structures or back-and-forth shuffling of electrons in real molecules. The electrons are stable and no different than in molecules whose Lewis dot diagrams do not show resonance. Resonance is a heuristic invented to fit the real behavior of molecules to the Lewis model, especially where the Lewis model cannot accurately represent the actual bonding in the molecule. Valence Bond Theory and the Lewis model cannot, for example, handle fractional bond order. Other theories, developed simultaneously to VBT, such as Molecular orbital theory do a fantastic job of handling fractional bond orders, and there is no need to introduce resonance into molecular orbital theory. However, MOT has its own shortcomings, such as its inability to deal with molecular geometry in a convenient method. Thus VBT or VSEPR theory handles geometry very well, but does not handle bond order well. MOT is complimentary because it handles bond order very well, but not geometry. Of course, real molecules are not identical to either model, and no single model can fully capture reality, but these two work well together in explaining much of molecular behavior. Delocalization is a slightly different issue; it is a real event which occurs in situations where bonding electrons are not "localized" between two atoms, but instead are shared equally among a group of atoms. Two classic examples are the "Three-center two-electron bonding" in diborane and the cyclic delocalized pi-system in aromatic hydrocarbons. --Jayron32.talk.contribs 18:48, 2 June 2009 (UTC)

Grignard Reagents

Would there be a reaction between a grignard reagent and a carboxylic acid, I have drawn a few (probably flawed) mechanisms which would suggest a ketone and water as the products, in addition to HOMgX. This just seems unlikely, it doesnt sit right as it involves OH^- as a leaving group and I felt that as a small ion it would be a poor leaving group. Am I missing some fairly basic organic chemistry?
This would be so much easier to post if I knew how to insert chemical structures in here. —Preceding unsigned comment added by 144.32.155.203 (talk) 18:43, 2 June 2009 (UTC)

The first reaction between a grignard reagent and a carboxylic acid is an acid-base reaction: the carbanion is a wickedly-strong base, removes H+ from the acid to give the carboxylate anion. Later (i.e., if there is still more grignard present), another carbanion can attack the carbonyl (just like for ketones and aldehydes). This tetrahedral (4 sigma bonds) intermediate can collapse to reform the carbonyl and eject an oxygen, but IIRC often does not for magnesium-based reagents. The reaction probably just stops at this stage. When you add water after the reaction is done, you protonate the oxygen anion, and this structure (looks something like a hemiacetal collapses to form a carbonyl. Nucleophilic reactions at carboxyl are not simple replacement of the singly-bonded piece, but rather are reactions of the carbonyl itself. That is, the loss of hydroxyl you propose is not direct. The reason that its instability isn't a problem (if it were to occur by that type of mechanism) is that you aren't just "creating unstable hydroxyl from nothing": the starting material is also an anion. You have to look at the overall reaction, and see that the result is more stable, even though it may have lots of instability. DMacks (talk) 18:59, 2 June 2009 (UTC)

If a grignard reagent gets anywhere near an active hydrogen containing compound (that is even a weak acid), then the immediate product is the corresponding alkane and water. Rkr1991 (talk) 07:54, 3 June 2009 (UTC)

Water? DMacks (talk) 08:00, 3 June 2009 (UTC)

about water quality.

sanitization process and chemicals using in water treatment plants. The concentration and duration period also want to know. —Preceding unsigned comment added by 94.97.53.246 (talk) 19:28, 2 June 2009 (UTC)

See Water purification. 78.144.244.22 (talk) 22:21, 2 June 2009 (UTC)

Cactus Question

I recently impulse purchased this cactus, which may have been poorly cared for in the past. I was just wondering what species it might be, and also what are the brown fuzzy things on it, circling the top of the plant?

Brown Spots Close: http://commons.wikimedia.org/wiki/File:CactusBrownSpots.jpg Full Cactus: http://commons.wikimedia.org/wiki/File:FullCactusWindow.jpg —Preceding unsigned comment added by Mattman723 (talk • contribs) 19:50, 2 June 2009 (UTC)

It looks like a barrel cactus to me, though I'm quite ignorant on such things. --Sean 21:17, 2 June 2009 (UTC)

Well it doesn't have notches that deep, so I doubt it. M@$+@ Ju ~ ♠ 23:18, 2 June 2009 (UTC)

Here is a cactus ID site [22]. The ring of "brown fuzzy things" may be flower buds, but possibly abhorted. Richard Avery (talk) 06:10, 3 June 2009 (UTC)

Here is a "ID request" forum on that site. It might help if you took a better picture, as the detail is in shadow in the window shot. You could also look through all the globose cacti here. --Sean 12:45, 3 June 2009 (UTC)

Does this article sound feasible at all?

This thing Does it defy the laws of physics? --71.234.104.243 (talk) 20:31, 2 June 2009 (UTC)

This invention is not new. It has been 'discovered' many times, but it violates the laws of physics and no one claiming discovery of such a machine has ever successfully demonstrated it. *Max* (talk) 21:37, 2 June 2009 (UTC).

Per Max, any perpetual motion machine of the first kind must violate the law of conservation of energy. Unique arrangements of magnets have been popular among perpetual motion aficionados for years; unsurprisingly, not one such invention has ever been successful. TenOfAllTrades(talk) 21:40, 2 June 2009 (UTC)

Here is the patent application: [23]. (Hmmm - he lives on "Asylum street" - what are the odds?) This is certainly recommended reading for enthusiastic "nut-job" spotters such as myself. (I'm DEFINITELY going to have to figure out a way for someone to pay me a dollar every time someone confuses "force" with "energy".) The Chicago Tribune article says he spins the wheel and it spins for a while and then stops...this is pretty much exactly what you'd expect any claim of a perpetual motion machine to do - so there is no surprise there. On my home Wiki, I have a "You know you are a crank when..." checklist for exactly this kind of occasions: [24]...let's see how this guy does...hmmm...so far only a rather disappointing 3 out of a possible 8 points - but I've decided to award him a bonus point for using his magnets "in cold fusion mode" - which is certainly a novel and exciting breakthrough in perpetual motion machine design. He has "neutron barrier planes" AND "atomic holes" - and it somehow involves the synergy of the entire universe as a part of it's operating mechanism - which is all really quite remarkable for a machine comprising a dozen magnets nailed onto a wheel. It's comforting to know that this wonder of mechanical genius operates equally well in clockwise AND anticlockwise rotations. But I trust that if he gets his patent, he'll be claiming that it proves that his machine works - and if he doesn't get it, he'll claim it's "big oil" putting him down...so we can look forward to plenty more fun in the future. SteveBaker (talk) 22:56, 2 June 2009 (UTC)

I think I have stumbled across a free energy system. I take TIME, and convert it to electricity. You see, I put in some TIME at another place from my home. They in turn give me a slip of paper periodically. In turn, I give this slip of paper to a a person in another building. Following the paper trail, another company sends me a slip of paper in the mail, to which I attach yet another slip of paper and mail back. As a result, I plug into the wall and get electricity! BRILLIANT! :) Arakunem^Talk 23:08, 2 June 2009 (UTC)

Does he get any extra points for "rolling stator magnetic field in the fourth dimension" (beyond the existing point for a reference to magnetism)? I think he should do. --Tango (talk) 01:01, 3 June 2009 (UTC)

Well, perhaps a half point. He might mean time (4th dimension?) in which case this is just a fancy way of saying "it's moving", for which no bonus is possible. A true crazed nut-job wouldn't be satisfied with a mere 4th dimension - it would have to be the 11th or something. To be honest, I'm bitterly disappointed that he's not yet announced that he intends to fit this to his car. Proper perpetual motion machine designers no sooner have an idea for their machine than they're out there pulling the motor out of their 1986 Acura to make way for it. But he's just getting into the role - and he's already comparing himself favorably to Edison...that's a promising start. SteveBaker (talk) 02:20, 3 June 2009 (UTC)

I just ... don't understand. The man has built a prototype. Doesn't he spin it and ... see that it does not continue spinning? Doesn't he see that his prototype is incapable of powering anything? I can understand if he is put off by complex mathematical theories or well-established scientific explanations, because those require either a certain level of comprehension or a blind trust in "smarter" scientists who DO understand. (I mean, I can write out some Maxwell equations and take a Cauchy integral and prove beyond any reasonable doubt that there is no way to have a "continuous never ending force-field" around a closed contour... but that requires knowledge of some higher math!) So my (dis)proof of the concepts in the machine might be worthless to the man. But ... he has built this machine! Can't he see that it doesn't actually work? When he tries to power it up, and it doesn't power up, you don't need any theoretical knowledge to verify that behavior. Why in the heck doesn't he accept empirical evidence? Nimur (talk) 03:24, 3 June 2009 (UTC)

And then he says it doesn't work because the magnets need to be more precision-machined and precisely aligned! That would mean... he would have to have an analytic, mathematical description of where to place the magnets and how to shape them (so that he could give the schematic to a machinist). So, he will have to measure, "by observations of the universe and reason itself," the force induced by each magnet (sort of like experimentally rederiving the Biot-Savart law?) And then he will need to calculate the fluxes and field lines and all that (sort of like, solving some Maxwell equations?) If he actually put in the proper scientific rigor into these measurements and calculations, he would rederive all of electromagnetism, and see for himself that his plan doesn't work. That's experimental physics, but he's apparently two hundred years behind on his reading, because it has been done and confirmed observationally a hundred thousand times by high school physics students. It's very frustrating to see how far these cranks can get, because most of the people who look at their work don't know enough to debunk it. Nimur (talk) 03:38, 3 June 2009 (UTC)

As my "You know you are a crank when..." page points out - 99% of cranks are not just ill educated in the sciences - but actually proud of the fact because (they generally claim) their thinking isn't restricted by the limited world-view of the people who went before them. Sadly, this neglects the solid fact that real earth-shattering advances are always made by building on the work of those who came before. Because they don't know all of this really well known science, they are doomed to repeat the mistakes of others. This failure to understand the difference between a force and energy has resulted in this guy wasting (probably) years of his life - paying a small fortune to patent lawyers and making himself look like a complete idiot to the majority of the people he's trying to impress.

It's not just knowledge though and education though. Even if he's unaware of the laws of thermodynamics - and cannot calculate all of those complicated interactions between magnetic fields (I'm quite sure I couldn't do that) - even if you know nothing of that...using the very basics of the scientific method would tell him he's going nowhere with this: He spins the wheel - it spins for a while, then gradually comes to a stop. He claims that this is just because he doesn't have the magnets quite perfectly set up and machined. But it would take him only minutes to try a 'control' experiment in the time-honored scientific tradition. First give your wheel a push of a known amount (maybe wrap a known length of string around the axle and hang a weight on the end to make it spin at a known rate) - and just measure the amount of time the machine takes to come to a stop. Then replace the magnets with bits of non-magnetic material weighing the same amount - which ought to nullify whatever effect you think you have invented. Now give the wheel the same initial push and time how long it takes to stop in that case. Do the experiment 100 times and average the results.

We all know that if he did that super-simple experiment, he'd discover that his complicated system of magnets has NO effect whatever. Not just that his magnetic motor isn't quite able to overcome friction - he'd find that the wheel would spin for exactly the same amount of time whether the things around the edge are magnets or not. At this point, a rational person would have to concede that they were wrong and go back to the drawing board. THAT is what makes someone a scientist - not the years of training and brain full of laws and equations. Although those kinds of things definitely help you to say "Hmmm - I think I'll try to invent a perpetual motion machine today...oh...but wait...those darned laws of thermodynamics again. OK then - back to making a better mousetrap." - but they aren't NECESSARY to being a scientist. SteveBaker (talk) 13:20, 3 June 2009 (UTC)

Nimur, Perpetual motion enthusiasts are convinced that if they can only "balance" out the forces that are working to slow down their machine. A non-working prototype that "isn't quite balanced" will still be taken as a proof of concept by these people, because they take it as given that they can "balance" the forces in such a way that they get free energy, in their mind the only part of the design that needs testing is everything else.

Of course, to a rational outside observer that's completely backwards. I don't need proof that you can spin some magnets around in a circle. What I need proof of is that you can "balance out" the laws of thermodynamics. APL (talk) 13:44, 3 June 2009 (UTC)

As long as his hydrocoptic marsel vanes are properly fitted to the ambifacient lunar wane shaft, I can't see why it wouldn't work. --Sean 12:56, 3 June 2009 (UTC)

vapourised alcohol after flaming sambuca?

Hi a friend of mine after having downing a shot of flaming sambuca always inverts the shot glass. He then proceeds to lift up the glass marginally (enough to get a straw under), and then inhales. He says that by doing so he is breathing in vapourised alcohol. He claims these actions help one get drunk faster. I thought wouldn't the gases in the glass just be normal gases found in air with perhaps a bit more carbon dioxide? Would there be any vapourised alcohol? Presumeably a little - but I believe alcohol (in this case just talking about ethanol, obviously) is not very well absorbed when inhaled anyway; so I think that these actions wouldn't help him get drunk more quickly. Am I right? Any thoughts on the matter would be much appreiciated! Thanks RichYPE (talk) 20:58, 2 June 2009 (UTC)

The dude wants to get drunk on Sambuca??? That should be your first clue as to how seriously to take his ideas on the subject. --Trovatore (talk) 21:03, 2 June 2009 (UTC)

Sambuca isn't good for anything else... --Tango (talk) 21:07, 2 June 2009 (UTC)

Sure it is. You put it in coffee. Or you drink it in small quantities to appreciate the taste. But drink enough of it to get drunk? What, you're out of Listerine? --Trovatore (talk) 22:36, 2 June 2009 (UTC)

...and here I should probably point out that neither I nor the Wikimedia Foundation advocates drinking Listerine.... --Trovatore (talk) 22:39, 2 June 2009 (UTC)

Inhaling alcohol vapour would probably get it into your blood pretty quickly, but I can't see why there would be more than trace amounts under the shot glass in those circumstances. --Tango (talk) 21:07, 2 June 2009 (UTC)

Vaporized ethanol can certainly get one drunk...it's used in alcohol research quite often and there are vaporizers on the market (of varying legality). It's a rapid onset of intoxication if the vapor is of sufficient quantity, and it's well absorbed. A just-consumed shot glass always has remnants of the prior contents sticking to the sides, so there would be, presumably, some modest amount of ethanol vapor in the trapped space of an inverted shotglass...but probably not much. I'd guess that the effect of the shot itself would be of a considerably greater get-ya-drunk magnitude than a a little extra vapor...consider this: if your friend had had taken a deep breath over the full (pre-lit) shot, he probably would have gotten a similar amount of ethanol vapor exposure, and trying to become inebriated that way would likely have taken a looong time. — Scientizzle 21:09, 2 June 2009 (UTC)

Back-of-the-envelope calculation: Assume a shot glass volume of 50 mL (about 1.7 ounces). Assume further an in-glass gas temperature of 25 degrees Celsius (77 Fahrenheit). If the glass were entirely filled by ethanol vapor (no air, no water vapor, no other volatiles), there would be just under a tenth of a gram of ethanol present. That works out to a little over 0.1 mL (0.004 fluid ounces) of liquid alcohol, or less than one-hundredth of a shot. Those numbers are pretty generous assumptions, too — if the gas is hotter, it will be less dense and contain less alcohol; there's also little likelihood that other gases (including air and water vapor) will not be present to dilute the alcohol. The stuff he's inhaling might have an interesting taste, but it's not going to do a damn thing for his (in)sobriety. TenOfAllTrades(talk) 21:20, 2 June 2009 (UTC)

Those are good calculations. Furthermore, obviously the absolute maximum amount of ethanol vapor that would be possible to inhale is limited by the amount of liquid left in the glass following shot consumption. Considering the poster's friend is clearly out to get hammered, it's doubtful that there'd be more than a few mL total (of a 42% EtOH fluid) left over for straw-vacuum removal. The contribution of this extra step should have minimal effects on insobriety and will likely leave your counter sticky with Sambuca. — Scientizzle 22:35, 2 June 2009 (UTC)

There's a whole lot of mythology and urban legends surrounding alcohol, like most other mild-altering substances. Since feeling drunk is very subjective, it's easy for people to believe all sorts of unreasonable things about what makes them more or less drunk. Pretty much any high schooler will tell you that, for example, drinking beer through a straw gets you drunk faster. It's complete bullshit, but it's often repeated and widely believed. Friday (talk) 21:13, 2 June 2009 (UTC)

To be honest - if you really wanted to get drunk faster (why is that a good idea?) then not setting light to the sambuca in the first place would really be the best idea! What's burning isn't really the little coffee bean in there - it's the alcohol. By burning it off, you're lowering the amount of alcohol you drink. SteveBaker (talk) 12:58, 3 June 2009 (UTC)

Here is an article about some folks trying to open an alcohol vapor bar, with mixed results. --Sean 13:00, 3 June 2009 (UTC)

wow thanks to everyone who helped! Thanks especially to tenofalltrades for the calculation. I shall inform my friend of the error of his ways! Cheers RichYPE (talk) 19:23, 3 June 2009 (UTC)

Phosphorus in Evolution

In evolution of complex organisms from small and primitive ones, how and why was the Phosphorus taken as a candidate to be a part of almost all life in such a vital form, such as in DNA, ATP, Lipid layer etc, even so when it is not available in atmosphere, only present in soil, and that too almost always in complex phosphate ion forms because of its high reactivity? We (organisms in general) are slowly running out of easily accessible phosphorus. If we really run out, what will be the course of evolution from there on? - DSachan (talk) 21:49, 2 June 2009 (UTC)

Why are we running out of phosphorus? How does it get lost (or made inaccessible)? --Tango (talk) 22:33, 2 June 2009 (UTC)

Phosphorus mentions that "In 2007, at the current rate of consumption, the supply of phosphorus was estimated to run out in 345 years." This is for industrial production of phosphorus compounds, which would presumably include fertilizer. I guess that's the question; what does that mean for everything that needs it to live? Someguy1221 (talk) 23:36, 2 June 2009 (UTC)

Actually, I read something (I think) in a recent issue of Scientific American in an editorial which claimed that the current existing phosphate mines will be tapped out in 40 years or so, and they warned of an impending "phosphorus famine". However, I am not sure if they took into account anticipated untapped phosphorus sources. --Jayron32.talk.contribs 23:59, 2 June 2009 (UTC)

Surely that is phosphorous that we are using for industrial/agricultural purposes, most phosphorous will be in some kind of cycle. Organisms die and decompose, the phosphorous gets back into the soil, gets absorbed by plants, the plant gets eaten, whatever ate the plant gets eaten, so and so on until it ends up in an organism that decomposes and it gets back into the soil. I guess it is possible it is gradually getting leached into the oceans, but that's never going to happen on a scale of 40 years. --Tango (talk) 00:54, 3 June 2009 (UTC)

Oh, the phosphorus isn't going anywhere. However, phosphorus deposits in concentrations we need to use to make all the fertilizer to grow all of the food we do now IS, and that seems to be the big problem. Phosphorus basically allows us to grow much higher calories/acre in terms of food production than would be possible without it. The question comes what will happen when all usable phosphate mines pan out. If we have no sources of phosphate fertilizer, what will happen to our farming practices. Its a genuine problem; I am not sure I trust the 40 year figure, but fertilizer phosphorus is a finite resource, and its a problem that we will likely run into some day in the future. --Jayron32.talk.contribs 03:07, 3 June 2009 (UTC)

It's an interesting question, but it isn't the one the OP asked. --Tango (talk) 13:10, 3 June 2009 (UTC)

If you have access to the journal Science, there's the classic article "Why nature chose phosphates." Westheimer, F.H. (1987) Science. 235(4793):1173-8. [25] If you don't have journal access, you'll probably be able to find a pdf copy or two floating around on the internet if you search on the article title.-- 128.104.112.106 (talk) 14:49, 3 June 2009 (UTC)

It has been suggested that life began either inside the earth or at the ocean floor, so the atmosphere may have been largely irrelevant. Also, see Abiogenesis#Polyphosphates. --JWSurf (talk) 15:02, 3 June 2009 (UTC)

overpressure wave calculation

Hi When you calculate the pressure produced by the blast wave from an explosion, when it is an overpressure shockwave, that means it is over regular atmospherice pressure. Does this mean that objects struck by the wave feel 14.7 psi (atmospheric) plus whatever psi the shockwave is ? for example if the shockwave is 3 psi, does this mean it is subjected to 17.7 psi, or would that object already be experiencing atmospheric pressure, like we do everyday, and only experience 3 psi of pressure? I ask because different sites say different things. Thank you

Robert —Preceding unsigned comment added by 79.67.192.228 (talk) 22:06, 2 June 2009 (UTC)

It's called "over"-pressure for a reason! It's the pressure over and above atmospheric pressure. So, yeah - if the air pressure today is 14.7psi and I set off a stick of dynamite that produces 3psi of overpressure - then (say) a brick wall nearby has 17.7 psi pushing on one side of it - and only 14.7 psi pushing on the other side. It might seem at first sight that a mere 3 psi was nothing much - but if you have a 10' x 6' wall in a room then that's 10x6x12x12=8640 square inches - which is 25920 pounds of force - something like 13 tons. SteveBaker (talk) 23:29, 2 June 2009 (UTC)

If you aren't familiar with pressure measurements here's some context. Weather patterns can regularly cause a 1% variation in atmospheric pressure, and really awful hurricanes can maybe cause a 3% variation (underpressure). The worst storm underpressure ever registered about a 13% under-pressure. A shockwave with 3 psi overpressure is about 20% overpressure (twice as bad as a hurricane!), and though it isn't sustained, it's localized - as Steve Baker pointed out above, it can create some pretty nasty forces on anything it hits. (Straightforward multiplication of the shockwave overpressure peak times the area gives you a good estimate, but not an exact value, of the net force on the wall - there are transient time effects and a host of complex fluid-flow issues as well). Nimur (talk) 03:47, 3 June 2009 (UTC)

global warming potential

how can a GWP value decrease if the gas is in the air for a longer amount of years.? Global warming potential thanks, -Bill —Preceding unsigned comment added by 173.30.14.113 (talk) 23:27, 2 June 2009 (UTC)

I think you've somewhat misunderstood. The amount of a gas typically decreases over the years - it's broken down in one way or another. So the amount of damage you do by putting (say) a ton of Methane into the upper atmosphere gets less and less as that gas breaks down over the years. SteveBaker (talk) 23:32, 2 June 2009 (UTC)

but why after 500 years does the total potential of methane summed over the 500 yrs equal 7.2 and over all 20 yrs it's so much higher at 72? —Preceding unsigned comment added by 173.30.14.113 (talk) 01:11, 3 June 2009 (UTC)

The GWP is how much worse that gas is than CO2, it depends on the timescale because different gasses break down or are removed from the atmosphere at different rates. The GWP of methane decreases over time, which means it must be breaking down or being removed faster than CO2. --Tango (talk) 01:20, 3 June 2009 (UTC)

Indeed. GWP compares the effect of an instantaneous release of a given GHG to an instantaneous release of the same amount of CO₂ over a given number of years. CO₂ is relatively slowly removed from the atmosphere - it's lifetime is hundreds of years (albeit its not quite so simple). Methane (CH_{4)is, molecule for molecule, a stronger GHG than CO2. But it breaks down over only a few years into CO2 and water (and the water is removed from the atmosphere nearly instantaneously). So over time, the GWP of methane approches that of CO2. One important take-home is that a naked GWP value is useless - you always need to know the time frame over which it is computed. If none is specified, often but not universally 100 years is assumed. See Global warming potential#Importance_of_time_horizon. --Stephan Schulz (talk) 09:51, 3 June 2009 (UTC)}

Ultimate Fate of Mankind

Has anyone ever done a survey of what the general populace believes the ultimate future of humanity is? For example, 40% say we'll colonize the universe, 40% say we'll blow ourselves up, 20% believe some deity will end it all, something along those lines? TheFutureAwaits (talk) 23:28, 2 June 2009 (UTC)

I imagine such a survey would depend very much on when you did it (during the cold war I expect a very large proportion expected use to blow ourselves up, probably fewer do now, although maybe a few more since North Korea started making significant progress with its nuclear program), and the populace you targeted (basically, the more religious people you ask, the more people are going to give a religious response). It would be interesting to find out, though (I don't know if such surveys have been done). It's not really what we're here for, but we could hold a mini-survey of ref deskers (whose opinions are far more interesting that the general populace!). Personally, I think the two most likely ultimate fates are colonising the solar system and then getting wiped out when the sun dies (that gives us few billion years - one billion on Earth, but we could move further out, although our population may need to dramatically reduce), or colonising the galaxy (I very much doubt we'll ever leave the galaxy, the distances involved are just too vast and faster-than-light travel is just too unlikely) and getting wiped out when the galaxy runs out of stuff to make new stars out of and the old ones all die (which gives us about 100 trillion years). I know this is far longer than other animal species have generally lasted, but intelligence means we adapt to new environments without evolving physiologically (so staying the same species), other species have had to become new species in order to deal with new environments. --Tango (talk) 23:42, 2 June 2009 (UTC)

Everything must have an end, so one day humans will no longer exist. 78.151.147.255 (talk) 00:16, 3 June 2009 (UTC)

Why must everything have an end? --Tango (talk) 00:50, 3 June 2009 (UTC)

Humanity will replace itself within the next 20 years. See Technological singularity. -Arch dude (talk) 01:31, 3 June 2009 (UTC)

I'm not at all convinced. I haven't even seen a reliable quantification of human mental capacity, so how could anyone possibly make such a prediction? --Tango (talk) 01:44, 3 June 2009 (UTC)

Twenty Years? Care to ... make a wager on that? APL (talk) 13:51, 3 June 2009 (UTC)

Sheesh, you know, it would be nice if the Refdesk regulars would try to answer the OP's question while citing some sources, so the OP can do some research on his or her own, instead of spouting opinions without any citations. He didn't want our opinions; he wanted to know about everyone's opinions. OP, I found this link on Google Books that says that a 1995 Gallup poll conducted in the US said that 61% of the adults and 71% of the teenagers agreed that "the world will come to an end or be destroyed". In a separate study, a sample of 17,000 high school seniors (meaning 17 or 18 years old), "more than one-third" agreed with the statement, "Nuclear or biological annihilation will probably be the fate of all mankind within my generation." As you can probably guess, the book itself is called "The End of the World As We Know It", so it doesn't dwell on the other options that people chose; but you can presumably track down the footnotes in the book or use search engines to find these polls (and hopefully followup polls to indicate trends). Tempshill (talk) 02:23, 3 June 2009 (UTC)

According to Christianity in the United States, about 76% of the US population is Christian, and 40% of the Christians are evangelical. The bulk of these profess literal belief in the bible, and therefore believe that the rapture will occur "soon." That pretty much does it for mankind. -Arch dude (talk) 03:48, 3 June 2009 (UTC)

As always, it's going to depend on what you define as the "ultimate fate." For example, if humans don't extinguish themselves, but gradually evolve, there will be some point when we are, beyond any reasonable doubt, decisively not human (unless we genetically stagnate indefinitely). So, would that be the end of humanity? You have to precisely define all the other terms as well: "human", "civilization", "ultimate", etc... Nimur (talk) 03:53, 3 June 2009 (UTC)

Our OP isn't interested in what WE thing the end of humanity will be - but what the population in general believes. The trouble is that most of the general public are very susceptible to suggestion. If you ask "What do you think the chances of us blowing ourselves up with nuclear weapons is?" you'll get some highish number. If you ask "Will we get wiped out by a massive meteor strike like the Dinosaurs?" you'll get another high number. You can keep this up indefinitely and the probabilities will soon add up to more than 100%! But if you go and ask "Do you think humanity will get off the earth and live on other planets?" which would preclude any abrupt, disaster-type ending - then they also pick a highish number. People don't think these things through very carefully and they are terrible at understanding probabilities. So this kind of survey depends very sensitively on the questions you ask. SteveBaker (talk) 12:54, 3 June 2009 (UTC)

Steve, again, some source citations would be useful for our OP instead of just ragging on some of his possible assumptions. Tempshill (talk) 20:26, 3 June 2009 (UTC)

June 3

Earth is seriously moving away from sun?

Is earth seriously moving away from sun? I saw it was update like last night earth moving 20 centimeters apart each year they said because sun is losing solar winds and masses. Is it just earth or this is also happening to venus, mars, and others? If sun is losing mass now, then sun will just lose more and more, I don't think sun will gain mass back again.--69.229.240.187 (talk) 00:25, 3 June 2009 (UTC)

Yes. Tidal forces and loss of solar mass both result in the Earth receding slightly from the Sun. Without checking numbers, I'd expect tidal forces to be the dominant mechanism. The same effect occurs at varying rates on all other bodies orbiting the Sun. The Sun can gain mass (any time a long-period comet crashes into it, for instance) but is a net loser of mass. — Lomn 00:46, 3 June 2009 (UTC)

It is true, but it is a negligible amount. Our measurements of the distance from the Earth to the Sun are only accurate to a few metres (according to Astronomical unit), so a change of 20 centimetres isn't even measurable. It is happening to all planets, though. When the sun nears the end of its life it will throw off its outer layers, dramatically reducing its mass, and then the Earth will move significantly further away, but that won't happen for billions of years. --Tango (talk) 00:49, 3 June 2009 (UTC)

• Does all planets including Mercury and Venus? Venus have backwar orbit, so I always thought Venus will just end up like Triton vs.Neptune or Phobos vs. Mars. But how is Mercury moving farther when it is so close to sun?--69.229.240.187 (talk) 00:58, 3 June 2009 (UTC)

• I honestly can't dig anymore. I couldn't find the source said all the planets is now moving out. Formation and evolution of the solar system don't give us enough informations though.--69.229.240.187 (talk) 02:31, 3 June 2009 (UTC)

• • Venus does NOT have a backwards orbit. It has a backwards rotation, which means that it turns through a day in the opposite direction as the other planets do (or if you prefer, it is upside-down. Same difference). It turns so slowly, however, that a venusian "day" is longer than a venusian "year". And it orbits in the same direction as all of the other planets. However, as noted, the sun is losing mass via mass-energy conversion, which means that as the mass decreases, its gravity decreases over time. Since the force of gravity is decreasing, ALL objects gravitationally bound to the sun will drift farther away. It doesn't matter if we are talking about Mercury or the Oort cloud. Less mass = less gravity. Less gravity = larger orbits. Its that simple. --Jayron32.talk.contribs 03:02, 3 June 2009 (UTC)

Even if it was a retrograde orbit (which is not the case), it would still move out to a larger radius if the sun's mass decreased. Nimur (talk) 03:55, 3 June 2009 (UTC)

For perspective, at a rate of 20 cm / yr, the Earth's orbit would take 7.5 billion years to change 1% in radius. In other words, the current rate of expansion is utterly negligible for any practical purpose. Dragons flight (talk) 03:58, 3 June 2009 (UTC)

• If Dragon Flights is talking about in 7.5 billion years. It is still the same game as usual. Nothing have changed. Earth survival or not is still an even money (50/50). Mercury is going to go definitely. Venus' odd to doom is obviously better than a 50/50, Mars could be a doom one but highly unlikely. When sun expands, then it's surface area will increase drastically, then sun's mass and gravity will probably climb. This is possibly another story.--69.229.240.187 (talk) 04:26, 3 June 2009 (UTC)

Surface area expands OK, but why would mass/gravity climb? It will only decrease. - manya (talk) 04:54, 3 June 2009 (UTC)

We don't even know if earth will still exist at that time or not. It got to be some theory to make earth getting engulf, it's still a 50/50 odds.--69.229.240.187 (talk) 05:00, 3 June 2009 (UTC)

69': You have the ending of the sun all wrong. When it runs out of hydrogen and starts running on helium, it suddenly starts generating a LOT more energy (but not for very long) it blows off an immense amount of material - which is certainly enough to kill everything on earth, blow away it's atmosphere and oceans and generally trash the place. Once that's happened, both the mass and gravity of the sun are a lot less and the gravity can no longer stop the sun from expanding due to photon pressure from all the energy it's putting out - THAT'S why it expands. It doesn't gain mass or gravity - quite the opposite in fact!

You have to think of stars as fighting a continual battle between their immense gravity trying to collapse them into something much smaller and more exotic (like a black hole or a neutron star) and the photon pressure from the energy they put out that's trying to inflate them. If the gravity loses the battle, the star grows to a larger, dimmer red giant - if gravity wins, it shrinks to a white dwarf, a neutron star or a black hole depending on how much gravity there is. Ironically - the bigger the star is, the smaller it ends up being! The Sun - being relatively tiny gets bigger - but NOT heavier. SteveBaker (talk) 12:47, 3 June 2009 (UTC)

As the core fills up with heavier and heavier atoms it becomes denser and so so the pressure at the core increases (due to the stronger gravity) and the fusion rate increases. The sun expands because it is producing so much more energy. the expansion reduces the pressure in the core and slows down the rate of fusion. its a feedback process. (disclamer:I am not an expert) just-emery (talk) 20:04, 3 June 2009 (UTC)

I'm not getting the whole thing wrong just mass and gravity. I didn't know that in past, but I got it now. Yes, when sun gets bigger, it's mass and gravity plummets quickly, mass and gravity just dives way down. I got weight-size thing upside down. Yes I know neutron star and black hole comes from high mass star not sun since our sun is average mass star. yes, I know once sun runs out of hydrogen, earth ocean and life will run out first, earth will become a hell instantly until earth atmosphere runs out earth is a char garbage. But have you seen Formation and evolution of the Solar System#Future yet. They siad because of tidal interaction, earth will get destroy at end of sun's peak size, when mass and gravity drops suddenly. Studys 6 month ago hadn't change yet. Yes, if earth survives, then earth is a trash hell black-out scorchland with nothing on it. Maybe earth will be gone, destroy by sun. With tidal interaction between sun and earth I don't know what it is about.--69.229.240.187 (talk) 22:37, 3 June 2009 (UTC)

Actually what is a tidal force thing when sun gets to peak of it's diameter about? how can tidal force happen when gravity and mass drops.--69.229.240.187 (talk) 00:32, 4 June 2009 (UTC)

All the informations is on this site and source on Formation and evolution of the Solar System#Notes and references numbers 86-89, if my questions is clear fully.--69.229.240.187 (talk) 02:24, 4 June 2009 (UTC)

I haven't read all those posts yet, but the Earth really is moving away from the Sun, and it's not due to nuclear fusion: http://www.skyandtelescope.com/news/46618862.html. That article suggests tidal interactions between Earth and the Sun. Sky and Telescope is a reputable amateur astronomy magazine, but I don't know how scientifically reliable that specific article is. --Bowlhover (talk) 10:54, 4 June 2009 (UTC)

MM Experiment

When Michelson and Morley did their experiment they were looking for variations in the brightness of the light right? I was under the impresssions that the split beams were recombined into a eyepiece. As they rotated the apparatus they were looking for variations in the brightness of the light right? Because they knew they couldn't make the arms exactly the same length apart. They weren't looking for actual fringe shift, just the effect. —Preceding unsigned comment added by 24.171.145.63 (talk) 00:53, 3 June 2009 (UTC)

Basically you are correct. They could not measure the exact length of each arm with sufficient accuracy with any instrument at their disposal, but by looking at the interference pattern, you can obseerve changes in the difference between the lengths. Whe I set up an interformeter I used a laser, so I had a nice long coherence length to work with. With a laser, you start with two paths that ate roughly the same length. as you vary one length by one wavelength, you cah observe the pattern shift through an entire cycle. I used a mirror mounted to a piezoleletric actuator to vary the length through several wavelengths and observed the repeating cyclic pattern. When using a white light as Michelson did, you need to get the paths a lot closer to the same length to start with. -Arch dude (talk) 01:28, 3 June 2009 (UTC)

Just one more quick question:

http://spiff.rit.edu/classes/phys314/images/mm/mm3_rot.jpg On pg. 336 it says (little below the middle), that if the whole apparatus is turned through 90 degrees the fringe shift would double. Why? —Preceding unsigned comment added by 24.171.145.63 (talk) 04:34, 3 June 2009 (UTC)

That's what would happen if the speed of light *did* depend on motion through the "luminiferous aether". In actual fact, it doesn't, so there is no change. --Tango (talk) 14:56, 3 June 2009 (UTC)

Smallest number of neutrons

What is the smallest number of neutrons to start the formation of a Black Hole?

---- Taxa (talk) 01:04, 3 June 2009 (UTC)

Neutrons do not form black holes. Generally, they are formed by collapsed stars, as such they are called Stellar black holes (there are other types of black holes, but when most people talk about black holes, they mean stellar black holes). According to our article, which I link, there are several factors besides the mass of a star which will lead to it forming a black hole, but the threshold limit seems to be roughly 20 solar masses. That is, stars which are larger than 20x the size of our sun will generally form black holes upon their death, while stars smaller than that will not. --Jayron32.talk.contribs 02:57, 3 June 2009 (UTC)

Neutrons typically form neutron stars, which can not collapse to small enough size to form a black hole. This is because the Pauli Exclusion Principle forbids two neutrons from occupying the same spatial location with the same quantum state. This quantum-mechanical explanation can be "summarized": even though they have no electric charge, neutrons will repel each other if they get squished close enough together via a repulsive nuclear "force" (in truth, this is not a repulsive force because it can't be written as the gradient of an energy potential, which is why the quantum mechanical explanation is "better", but you can sort of conceptualize the idea). NeutronsPure neutrons can't get close enough together for gravity to dominate (which is required for black hole formation) - they must start off with other particle types present, or accrete extra mass in order to form a black hole. Nimur (talk) 04:02, 3 June 2009 (UTC)

Actually the degeneracy pressure can be expressed as a gradient of a potential in the mesoscopic limit. It's still not a force in the everyday understanding of the word as applied to isolated nucleons, but the potential formulation is plenty useful. For example, the Tolman–Oppenheimer–Volkoff limit describes the point at which degeneracy pressure is no longer able to counter gravity and a neutron star would inevitably become a black hole. According to the article it is between 1.5 and 3 solar masses (with uncertainties due to limited understanding of the behavior of nuclear matter at extreme density). So a neutron star can have at most something less than 3 solar masses, which translates to ~4×10⁵⁷ neutrons. Dragons flight (talk) 04:30, 3 June 2009 (UTC)

Of course all this applies for a neutron star under only gravitational contraction. If some other force compresses it, it should be able to go black earlier. Romulan force fields come to mind, but more realistically: What if two minimum mass neutron star smash into each other? Gamma ray burst? --Stephan Schulz (talk) 13:19, 3 June 2009 (UTC)

If you're asking how big a neutron star has to be before its gravitational force is too large for it to keep form collapsing into a black hole, I have no idea. If you're asking for the smallest number required for a black hole to be physically possible, regardless of what forces them together, the answer is a Planck mass divided by the mass of a proton which is 2.1764411×10^-8 kg / 1.672621637×10⁻²⁷ kg = 3.6403606×10¹⁹ neutrons. I think it's actually somewhat less than that, as the energy required to force the neutrons together would raise the mass. Also, the black hole would evaporate almost instantly. — DanielLC 21:45, 3 June 2009 (UTC)

Why does a black hole need to be at least the Planck mass? I believe a smaller black hole would have a Schwarschild radius of less than the Planck length, which is a somewhat meaningless concept, but does that mean the black hole can't exist, rather than just that our theory of black holes breaks down? --Tango (talk) 22:03, 3 June 2009 (UTC)

The latter. We don't have an accepted theory that can understand gravity at such small scales, so whether a black hole could have less than a Planck mass of material or be less than a Planck length in size is unknown. General relativity would no longer be an adequate theory to describe such objects. Dragons flight (talk) 08:28, 4 June 2009 (UTC)

But could you (hypothetically) take a single neutron and accelerate it until its mass exceeded the Planck mass, thus creating a black hole from one neutron (plus a lot of energy) ? Gandalf61 (talk) 15:59, 4 June 2009 (UTC)

The energy used to accelerate a particle does not help creating a black whole, after all there will always be a coordinate system in which the particle is at rest. Dauto (talk) 18:18, 4 June 2009 (UTC)

I think the problem lies in the definition of what a "black hole" is. A single point-sized particle (a neutron, for example) is a black hole according to some definitions. (Mathematically, there is some distance that lies outside the (zero) size of the particle at which it's gravity becomes so strong that light cannot escape.) Does that make it a black hole? Well, maybe, maybe not. You certainly can't get close enough to a neutron to be 'sucked in' as you would with a black hole created by a collapsing star. I think the problem here is not what nature does or does not do - but merely that we've decided to attach a name to a somewhat flawed definition. SteveBaker (talk) 17:26, 4 June 2009 (UTC)

If a neutron is a black whole, than the no hair theorem is not valid. Dauto (talk) 18:18, 4 June 2009 (UTC)

How to cure fungal plant pathogens

My Mango tree with leaf spots.

My Mango tree has some kind of fungus which is causing it's leafs to produce spots. I think it might be Cercospora capsici but I am not sure since there are many different kinds of plant fungus that might have similar outcomes.

I would like to know what I can do to get rid of the infestation and also how I can prevent it in the future. I have added a photo of the actual plant in question to better illustrate the problem. Joel M. (talk) 02:46, 3 June 2009 (UTC)

Sorry for the lack of responses - have you tried contacting a "master gardener"? Where I live, the local university seems to loan them out to public places like shopping malls and tree nurseries, where they run a (physical) reference desk of their own for a few hours a weekend. (Photo moved) Tempshill (talk) 20:30, 3 June 2009 (UTC)

Fungicide has a couple of natural things you can try that aren't that difficult to find. (If you can't find them at your local grocery store, health food store, drug store or pharmacy, try ordering online) I'm not sure how specific you'll have to target your fungus. Most fungicides seem to be pretty broad spectrum.71.236.26.74 (talk) 15:22, 4 June 2009 (UTC)

Understanding another part of the MM experiment

Scrap my old questions; I get them now. Anyway- I hope this doesn't go against your reference desk policy since this isn't homework that I'm not trying on. here on page 340, first line, it says something along the lines of the width of the fringes varied from 40-60 divisions (im interpreting it to mean there were between 40 and 60 fringes). It than says the average is 50 and says one division means.02 wavelength. Where did this last statement come from?

One divided by 50 is 0.02. They are taking the reciprocal. The "divisions" are not number of fringes - it's the width of each fringe, measured in "Divisions of the screw head" instead of "millimeters" or "centimeters". I don't know why they use such arbitrary units - it's just like the number of marks on a ruler or optical viewer or other measurement device, and needs some conversion to standard units. Nimur (talk) 15:55, 3 June 2009 (UTC)

Lens and mirror placed in water

We have been given following question in summer assignment:-
"A concave mirror and a convex lens are placed in water. What change, if any, do you expect in their focal length"
Since f = 1/R and curvature of lens and mirror won't change if placed in water, am I correct in assuming that focal length won't change? --shanu 05:36, 3 June 2009 (UTC)

For a reflective system, the main concern is the geometry of the surface; but for a refractive system, I think you need to consider the refractive index when calculating the focal length. DMacks (talk) 05:51, 3 June 2009 (UTC)

Take a look art the articles on mirror and refraction. A key point in the mirror article is that "a beam of light reflects off a mirror at an angle of reflection that is equal to its angle of incidence." A key point in the refraction article is "refraction occurs when light waves travel from a medium with a given refractive index to a medium with another." You may need to read more of the refraction article to better understand what this saying. Once you have a better understanding of the two principles, you can revisit the question of what effect water immersion has. A couple of related questions that may test your understanding: (1) When swimming, if you open your eyes underwater, can you see as well as above water? Why? (2) If you wear goggles or a face mask, does this change your vision? Why? (Hint: What shape is the outer surface of the face mask?). Feel free to ask follow-up questions after you've had a look. -- Tcncv (talk) 06:00, 3 June 2009 (UTC)

The question is discussed here. Cuddlyable3 (talk) 09:14, 3 June 2009 (UTC)

The key here is in the precise definition of refractive index. Since this is borderline homework - I'll point you to the "Definition" section of Refractive index - read it carefully. SteveBaker (talk) 12:35, 3 June 2009 (UTC)

Thanks for your help. By the way does it also mean that R = 2f won't work for lens in water? And also since thin lens formula will change, microscopes will be affected when placed in water.--shanu 05:21, 4 June 2009 (UTC) —Preceding unsigned comment added by Rohit..god does not exist (talk • contribs)

That should also help. Dauto (talk) 15:36, 3 June 2009 (UTC)

Thanks for your help. By the way does it also mean that R = 2f won't work for lens in water? And also since thin lens formula will change, microscopes will be affected when placed in water.--shanu 05:23, 4 June 2009 (UTC) —Preceding unsigned comment added by Rohit..god does not exist (talk • contribs)

For an importatn application, see Immersion lithography.-Arch dude (talk) 08:11, 4 June 2009 (UTC)

Sperm Count

Good day,

I was wondering - what is the time frame for the sperm count to reach its maximum ounce the person has ejaculated ? ( how long will it take from a count of 0 to reach 20 000 000)

Thank you

Marcello —Preceding unsigned comment added by Saladza (talk • contribs) 07:21, 3 June 2009 (UTC)

If I understand your question correctly, I do not believe it's normal for the sperm count to reach zero even after multiple ejaculations in a short space of time. If a sperm count is zero, that would likely indicate fertility problems like azoospermia or perhaps that the person has had a vasectomy. In fact according to our article "How long the man has abstained prior to providing the sample for analysis affects the results. Longer periods of abstinence correlate with poorer results - one study found that men with repeated normal results produced abnormal samples if they abstained for more than 10 days. It is recommended not to abstain for more than one or two days before providing the semen sample for analysis" although it's not clear if this includes sperm count or other factors like motility and morphology. Note that sperm counts are only really meaningful in when measuring them from ejaculations. Nil Einne (talk) 07:45, 3 June 2009 (UTC)

Three Step Process Of Lethal Injection

Why is it that we have a three step process for lethal injection, while pets only have one simple injection when they are getting put down? Wouldn't it be better just to use the one? It'd be cheaper and wouldn't last as long, and there have been no known accounts of pets still being alive and conscious yet paralysed when the final injection stops the heart and collapses the lungs (obviously because there is only one injection that kills them outright). Why not just do it like that? --KageTora - (영호 (影虎)) (talk) 10:52, 3 June 2009 (UTC)

You are evidently talking about the US procedure. There has been much debate about this - our article Lethal injection covers this in some detail. The idea is to use the first shot to briefly aneasthetise the victim - the second to relax the muscles so there is no embarrassing thrashing around - and the third to stop the heart. There is much controversy over this because there is a belief that the first injection might not work - or might not work for more than a couple of seconds - resulting in the victim being conscious but unable to move or speak (because of the muscle relaxant) while a painful heart attack ensues from the third injection...also the possibility of surviving the heart attack and then slowly suffocating while the muscle relaxant prevents breathing. For smaller animals (cats, dogs, etc) a single massive shot of barbiturates causes unconsciousness and then both heart stopping and a cessation of breathing in about 30 seconds. The problem is (as our Animal euthanasia article indicates), this doesn't work well on large animals because the barbiturate dose required is too high. I can only presume that humans fall into the "large animals" category...hence the controversial three-step process. SteveBaker (talk) 12:29, 3 June 2009 (UTC)

• Please avoid attempting a debate here by using loaded words like "victim". --Anonymous, 03:45 UTC, June 4, 2009.

Please avoid being uneducated in the use of the English language...pick up a dictionary sometime. From Wiktionary, meaning (2) for the word "victim" is: "Anyone who is physically harmed by another."...being killed by the state executioner certainly counts as being "physically harmed". I chose that word with great care. I you choose to pick a different, and perhaps more 'loaded' meaning - that's a debate of your own making! SteveBaker (talk) 15:39, 4 June 2009 (UTC)

Also, a different ethical standard is clearly being applied to animal euthanasia than to human euthanasia (which is used more sparingly). It seems to follow that the procedures would reflect that difference in ethical concerns. Nimur (talk) 16:00, 3 June 2009 (UTC)

Having used barbiturates to anesthetize animals for surgery, I can tell you that they are pretty tricky. Even huge doses with small animals don't lead to quick death with 100% reliability -- once in a hundred times the animal continues to breathe at a very slow rate for quite a while. Barbiturates don't actually stop the heart, by the way -- so suppression of breathing is the way they kill. Looie496 (talk) 18:45, 3 June 2009 (UTC)

Animal euthanasia says there is cardiac arrest - is it incorrect? SteveBaker (talk) 20:03, 3 June 2009 (UTC)

Pushing a helicopter

Suppose there's a helicopter (something small like a Bell 206, not a Chinook) hovering a few feet off the ground. Would it be possible for a human standing on the ground to push/pull the helicopter enough to move it, in any direction, without the aid of any other equipment? — Matt Eason ^{(Talk &#149; Contribs)} 11:06, 3 June 2009 (UTC)

Well, there is no friction and very little air resistance involved - so all you've got to do is overcome the inertia - which is considerable. The classic Bell 212 helicopter weighs in at 3000 to 5000kg depending on fuel and passenger load (actually, technically, what we care about here is the mass not the weight - but it's still 3000 to 5000kg) so it would take quite a bit of effort to get it moving at any kind of speed - and quite a bit more to stop it: Force = Mass x Acceleration - so with a normal kind of force and a big mass, you don't get much acceleration. However even the smallest push would impart some acceleration and if you continue to push, the speed will gradually get faster and faster until you couldn't keep up with it anymore - so technically, in the purest theoretical sense - yes, you could push the helicopter around with no particular problem.

However, a helicopter doesn't just hover in one place passively. If the ground beneath has even a slight slope or unevenness - or there is any kind of wind - or a vertical surface is within maybe 50' in any direction - or if the helicopter isn't set up just perfectly - then without the pilot actively working to keep the helicopter still - it would drift off and spin all over the place at accelerations much greater than you could overcome with your puny muscles! So realistically, the pilot (or perhaps some autopilot hovering aid) is actively and continually making tiny adjustments to keep the helicopter still - and those adjustments would easily counter your puny efforts to move it. If he stops making the adjustments - then the helicopter is going to drift and you're not going to be able to stop it or make a significant difference.

So I'm pretty sure that the theoretical answer is "Yes" and the practical answer is at best "No" and at worst "Not a sufficiently precise question to yield a meaningful response"! SteveBaker (talk) 12:19, 3 June 2009 (UTC)

Very interesting - thanks Steve — Matt Eason ^{(Talk &#149; Contribs)} 12:30, 3 June 2009 (UTC)

Here is a guy doing the fairly common stunt of pulling a train with his teeth. They claim 300 tonnes in this case, and the situation seems analogous to Steve's theoretical perfectly tuned helicopter, with far greater mass. --Sean 13:10, 3 June 2009 (UTC)

The practicality of this can be changed to a similar problem: Can the kick of shooting a gun move a helicopter? Humans are capable of countering the kick of large rifles. However, it was noted during Vietnam that firing rifles that were bolted down to the helicopter would cause it to rock enough to notice. So, humans can push with more force than the kick of the rifle and the kick of the rifle is enough force to cause the helicopter to rock. So, it is feasible that a human would have enough pushing force to cause a helicopter to noticeably move. -- kainaw™ 13:54, 3 June 2009 (UTC)

"Humans are capable of countering the kick of large rifles." But a human probably cannot counter the kick of a .50 caliber machine gun fired rapidly - it's sort of a totally different animal. Even small machine gun like a Squad automatic weapon requires a bipod or a tripod to keep it from blowing back out of control. A large gun such as a GAU-19 (standard fare on a Black Hawk) is going to impart tens or hundreds of kilogram-meters per second of momentum (according to our article, 500 pounds force sustained). I doubt any human sustain such a push. Nimur (talk) 16:06, 3 June 2009 (UTC)

There is no doubt about that. As TotoBaggins points out, humans can move trains that are far heavier than a helicopter. The only problem is the one Steve points out about the natural movement of the helicopter due to the difficulties of keeping it steady are going to be greater than the movement a human could produce. --Tango (talk) 15:37, 3 June 2009 (UTC)

You would probably be pushing below the center of mass, causing the helicopter to pitch or roll a little depending on where you push. I'm not sure which net effect this would have without corrections by the helicopter. PrimeHunter (talk) 16:04, 3 June 2009 (UTC)

OK - I'm going to have to explain helicopter aerodynamics...bear with me! A civilian helicopter - or a heavy-lift military one - would have rotors that bend upwards a little (it's called the "coneing angle"). If you think about the helicoptors rotors - instead of being a couple of separate blades that are sweeping around really fast - imagine them as if they made a solid disk...that's kinda what it looks like. So that when the weight of the helicopter's body is supported by the rotors - the rotor disk is pulled down into a cone (with the point of the cone pointing downwards). Now, when the helicopter rolls (or pitches) that tilts that cone - right? So one side of the rotor disk/cone is now more horizontal and the other side is more steeply tilted upwards. As the rotors travel around the surface of the cone - the one that's moving more horizontally to the ground pushes down the air directly towards the ground - getting the maximum possible upward push - but the rotor that's on the opposite side is nowhere near horizontal - its at some angle to the ground - so the air it pushes goes out at an angle. This does two things. Firstly, it means that when you push on the skids at the bottom of the helicopter - the steeper blade (which is on the far side of the helicopter) pushes the air slightly away from you - which makes the helicopter try to push back against you. But because that air isn't being pushed as hard against the ground as on the blade that's nearest to you - the far side of the helicopter loses a bit of lift - and the side that's nearest to you gains a bit...for as long as you push. This tends to make the helicopter level back out again. So the effect of this coning angle thing - is to give the aircraft some inherent stability...if you make it roll - it tries to roll back to the level position again. That's actually the only thing that makes the helicopter flyable...it would be impossible to have good enough reaction time if it didn't do that. So the fact that you are pushing below the center of gravity turns out not to matter very much! The other thing that helps with stability is that the center of gravity is about halfway up the helicopter - where the engine, gearbox and fueltank probably are. However, the lift from the rotors pulls upwards from the top of the 'mast' - so (in physics 101 terms) you have a 'moment' - you have gravity acting on the center of gravity and the lift acting on the top of the mast. So long as those two forces are in a straight line - nothing much happens. But if the helicopter rolls (or pitches) the two forces are no longer in a straight line - which imparts a rotation - which in turn tries to keep the helicopter level. It's as if the body of the chopper was a plumb-bob hanging under the rotor disk. Anyway - I didn't want to complicate the earlier discussion with all of this complicated stuff. Suffice to say - this ISN'T the reason you couldn't (in theory) push a hovering helicopter. SteveBaker (talk) 19:58, 3 June 2009 (UTC)

Is it possible that the "pushing back against you" bit you mention would be strong enough to actually result in the helicopter moving towards you when you pushed it away from you? That would be a rather interesting bit of trivia. --Tango (talk) 22:00, 3 June 2009 (UTC)

I don't see how. But helicopters are complicated machines - all sorts of bizarre gyroscopic effects - and the way the tail-rotor figures into things...it's tough to reason all of the forces out. SteveBaker (talk) 22:50, 3 June 2009 (UTC)

It's irrelevant to the original question, but it might be worth noting that the effect Steve describes in relation to coning has an analog on some airplanes. Rather than both wings being in a single plane, they may be tilted slightly to form a gentle V-shape, called "dihedral", and this contributes to the airplane's stability in the same way that Steve describes. On the other hand, on fighter aircraft where a bit of instability is desired so the plane is more maneuverable, the tilt may be reversed, which is called "anhedral". See dihedral (aircraft).

One other point. Steve mentioned the helicopter pushing the air "against the ground". Either an airplane or a helicopter makes its lift by pushing air toward the ground, i.e. down. Newton's third law and all that. However, if the vehicle is near enough the ground that the air is pushed substantially against the ground, it gets more lift, as the ground bounces it back up: see ground effect in aircraft.

--Anonymous, 04:02 UTC, June 4, 2009.

"… the wing keeps the airplane up by pushing the air down" eh? True but useless. An aerodynamic force on a body moving through a fluid is accompanied by an equal and opposite force on the fluid, but one does not "make" the other. A body which pushes air down generates lift—a body which generates lift pushes air down.—eric 06:43, 4 June 2009 (UTC)

(Actually - I said it pushes the air "towards" the ground - not "against" it - I picked my words carefully.) I assume that if you're pushing against a helicopter - that it's close enough to the ground for "ground effect" to matter. That greatly increases the amount of lift the helicopter has - but it doesn't change the 'coning angle' effect - which is indeed similar to the effect of dihedral on a fixed-wing aircraft - except that in the case of the helicopter it helps pitch stability as well as roll.

Eric's criticism is technically valid but I can't agree that the original statement was useless - it enabled both he and I (and hopefully, the OP) to perfectly well understand what was being described...and I think it's a clearer statement to the layman. We have to tailor our ref desk responses to a typical layperson - because we can't make assumptions about their scientific background. Saying that pushing the air down keeps the plane up is a perfectly valid statement - it merely fails to explain the REASON why pushing air down keeps the plane up. But then we also say that gasoline propels your car along the road without going into the details of the fluid dynamics, chemistry, thermodynamics and mechanics that makes that happen. Nit picking is unnecessary here - so long as the meaning is clear. 15:32, 4 June 2009 (UTC)

The lice were in Anonymous' hair, not yours. You were explaining dihedral, he was directly discussing lift, and based on his response i suspected did not fully understand your shorthand. Apologies if this was an incorrect assumption.—eric 16:23, 4 June 2009 (UTC)

Monitoring blood glucose levels

A friend of mine is diabetic and she usually tests herself once before a meal and two hours afterwards. I was curious why she has to wait two hours. After a meal, does blood sugar slowly climb to its maximum point after two hours? Or does it quickly surge high and then comes back to a "normal" level over a two hour period. Why not test one hour after eating? or three? --68.92.139.62 (talk) 12:38, 3 June 2009 (UTC)

It depends to some extent on what she's eating. If it is high in sugar then it will increase her blood sugar level pretty quickly. If it more complex carbohydrates, or mostly protein, say, then it takes longer to digest. You may find glycemic index interesting. --Tango (talk) 12:51, 3 June 2009 (UTC)

The timing of glucose testing in diabetes management mostly has to do with the medication regimen the patient is taking. In patients who take insulin, there are different formulations that have short-term (i.e. within a couple hours) and long-term (i.e. over the course of 24 hours) effects. See insulin therapy for details. Every patient will have a different regimen, depending on their own situation. One typical regimen is to take long-term insulin to maintain blood sugar throughout the day, coupled with short-term insulin doses corresponding to each meal to cope with the influx of glucose that happens after eating. The "fasting" blood test (before the meal) is meant to verify that the long-term insulin dose is correct. The 2-hour "post-prandial" blood test checks that the insulin that was taken with the meal was appropriate. You can see from the glycemic index article that in normal individuals, the blood glucose should be about back to normal by 120 minutes = 2 hours. This is the result of the pancreas releasing a burst of insulin, which is what is being simulated by the dose of insulin at mealtime. This, along with the usual time of action of the short-term insulin, is why 2 hours is a good time for a post-prandial check. Often, the patient will be given instructions about what to do if the post-prandial glucose level is too high (take some more insulin) or too low (eat something). The doctor managing the diabetes treatment will look at the test records to make sure that the dosage regimen is appropriate. --- Medical geneticist (talk) 13:33, 3 June 2009 (UTC)

Energy of a point charge

I have read that that the self energy of a point charge, that is, the energy required to assemble a point charge, is infinite, and i am still struggling to come to terms with it. Does it mean that there cannot exist any point charges in the universe, or does it mean that it is just an embarrassing result of classical electrodynamics? I mean, you can say even the fundamental units of charge, the electron and the proton, are not point charges, but i am asking in principle. Also, we have found that even these fundamental entities are made of quarks, and quarks are made up of what not i don't know, but is there a limit? Say we somehow find the structure of a quark, and find its made up of little xions, and now we start to analyze these xions-its back to square one... is there a limit to exploring the structure of matter? And going by this notion that there can be no point charges, will we ever be able to find an end to this non stop search inside an atom ? Rkr1991 (talk) 12:52, 3 June 2009 (UTC)

The energy required to reduce the separation between two like charges increases as they get closer together. Roughly speaking, the energy for the last bit involves dividing by zero, which gives you infinity (the more precise answer involves improper integrals). We often think about fundamental particles as being point particles, but that's really just because we don't really know what they are, talking about sizes at that scale is largely meaningless because of quantum mechanical effects. So we have to make exceptions for fundamental particles, but any charge made up of more than one such particle can't have zero size. --Tango (talk) 14:39, 3 June 2009 (UTC)

You can't get around this problem by supposing that point charges exist a priori, because even an always-present point charge has an electric field, and the energy in the field (½ ∫ E²) equals the energy required to assemble the point charge from infinity. The field energy shows up as inertial and gravitational mass of the particle. This is a classical result, but in quantum field theory the problem gets worse, not better. The workaround is renormalization, which amounts to treating the particles as though they had a small but nonzero size, or introducing some other small-scale cutoff with a similar effect. Fortunately the predictions of the Standard Model are independent of the cutoff scale as long as it's small enough (the Standard Model is renormalizable). This is understood to mean that the Standard Model is just a large-scale approximation to the real physics, which presumably avoids the infinity in some unknown way, possibly by being discrete or (as in string theory) by distributing the charge over a 1-D structure instead of concentrating it in a point. This is a lot like the use of calculus to model systems that we know are discrete, like fluids or biological populations. -- BenRG (talk) 16:00, 3 June 2009 (UTC)

A finite amount of charge in a one dimensional string would also have infinite amount of energy in its field unless it was infinitely long. the idea that the mass of an electron comes from its electric field through self induction has long be abandoned. just-emery (talk) 20:12, 3 June 2009 (UTC)

BenRG, sure you must be aware that what you described (the introduction of a small arbitrary size) is not the renormalization itself but an essential housekeeping step - the regularization - that must be taken before the renormalization proper can be performed. There are several different ways to regularize the formally divergent integrals that show up in the solutions. Not all of those regularization schemes are based in the introduction of a cutoff. The renormalization itself is done by carefully subtracting the physically unorbservable (and often formally divergent) part of those integrals and keeping only the physically relevant terms. All point particles self energies gets taken care of that way. Dauto (talk) 21:25, 3 June 2009 (UTC)

Well i am able to understand and few points but unable to certain others (having had no formal education in QM), so i can only ask where this leaves us. Does it mean we shouldn't ask questions like what is the energy of a point charge, or that QM has somehow overcome this problem and say this much Joules is the energy of the point charge, or that we are still in the dark and don't know what to make of things ? Can there exeist any point charges in the universe, or is that forbidden ?Rkr1991 (talk) 05:00, 4 June 2009 (UTC)

A little bit of each. Firt: yes, you probabily shouldn't be asking that question because a point particle is a theoretical construct any ways which may not be a valid description of nature, second: yes, QFT solves the problem but it does so by sweeping it under the rug, and third: yes, we are somewhat still in the dark since we don't have a final theory yet. Dauto (talk) 17:52, 4 June 2009 (UTC)

Is it possible to set your own innards on fire?

Is it really possible to set your own innards on fire if you're chainsmoking while drinking your Neutral grain spirit (Everclear and similar) straight? --90.240.197.75 (talk) 14:46, 3 June 2009 (UTC)

The autoignition temperature of ethanol is 425°C ([26]). I doubt the smoke from a cigarette could get it up to that temperature, although I can't find a source for the temperature of cigarette smoke... --Tango (talk) 15:34, 3 June 2009 (UTC)

I'm trying to imagine where the oxygen to maintain the combustion would come from. I guess you'd have to keep taking deep breaths, but then ... Richard Avery (talk) 15:56, 3 June 2009 (UTC)

Did you swallow the booze and then swallow the cig, otherwise I can't imagine smoking gets temps that high inside a person. I am skeptical. 65.121.141.34 (talk) 16:04, 3 June 2009 (UTC)

It may be feasible to, with a combination of a lit cigarette and alcohol vapors, set your face and/or inside of your mouth on fire. But there is no way I could imagine that any such combination could burn your internal organs like lungs or GI-tract. --Jayron32.talk.contribs 18:13, 3 June 2009 (UTC)

I could sorta kinda imagine your breath catching fire (although it seems unlikely) - but not your throat or stomach - there is just not enough oxygen down there to sustain anything like that. SteveBaker (talk) 19:40, 3 June 2009 (UTC)

Sure, an accelerant and central nervous system depressant (Everclear), ignition source (cigarette), make it an obese person who maybe does not wash their clothes very often, and you've all the makings of a case of spontaneous human combustion.—eric 23:30, 3 June 2009 (UTC)

Was anyone else reminded of Helpless (Buffy the Vampire Slayer)? —Tamfang (talk) 18:49, 4 June 2009 (UTC)

What is VCR doing to my TV signal?

I have a coaxial cable from the aerial going into the VCR input socket, and another short coaxial cable connecting from the VCR output socket to the TV. I've noticed that when the VCR is completely unplugged from the power, rather than being just on standby, then the TV signal almost disapears with a very bad very noisy picture quality. So my question, please, is what is the VCR doing to my TV signal? I thought the input and output sockets on the VCR were just passively connected, but apparantly not. 89.243.113.64 (talk) 20:36, 3 June 2009 (UTC)

Almost exactly the same question was asked further up: Wikipedia:Reference_desk/Science#Poor_TV_picture_improves_a_lot_when_VCR_on. See if that answer is any help. --Tango (talk) 20:51, 3 June 2009 (UTC)

I've already seen that thanks. This is a different question about the same items. 89.243.74.161 (talk) 08:53, 4 June 2009 (UTC)

If the only connection between the VCR and the TV is a coaxial cable, that single cable carries either the off-air signal from the aerial OR the video from the VCR in the form of a modulated r.f. signal. The choice is made by an active switch circuit in the VCR. Without power the switch circuit can't pass either signal. Cuddlyable3 (talk) 10:13, 4 June 2009 (UTC)

The VCRs I've owned have passed the input coaxial signal to the output coax when powered off. -- Coneslayer (talk) 17:16, 4 June 2009 (UTC)

Is there any connection?

Is there any correlation between people who have Irritable Bowel Syndrome and Panic Attacks? —Preceding unsigned comment added by 86.167.247.150 (talk) 21:23, 3 June 2009 (UTC)

I am not a medical practitioner and this is merely an observation from articles I read on Wikipedia. I seems that selective serotonin re-uptake inhibitors are listed as possible treatments for both conditions. I can imagine how frequent panic attacks could result from low serotonin levels and the same could possibly be true for IBS. If you added obsessive compulsive disorder to that list then it would definitely have my vote. But again, I'm not an expert or a professional and you should probably ignore me.

It's unlikely that you'd get an official answer here as that would violate the terms of this page. 196.210.200.167 (talk) 16:32, 4 June 2009 (UTC) Eon

Space inside a Black Hole

It appears then there are other requirements to form a Black Hole besides minimum number of neutrons. Is there a complete and ordered list of requirements, in addition to minimum number of neutrons, necessary to form a Black Hole? Also can a Black Hole be described (or defined) as matter in space which contains no space? ---- Taxa (talk) 21:57, 3 June 2009 (UTC)

There is only one requirement for a black hole - that the matter in question be contained within a ball of radius smaller than the Schwarzschild radius corresponding to the mass of the matter. (Actually, that's for a non-charged, non-rotating black hole. Without those assumptions you need a slightly more complicated formula, but the principle is the same.) --Tango (talk) 23:19, 3 June 2009 (UTC)

Applications of invisible light frequencies

I need a summer project for school. I have understood that variable lighting is a problem in computer vision, my just physics is not quite strong enough to tell if there are light frequecies that are not so dependent on sun's position on the sky or nearby lamps as visible light and cheap to generate/capture in good quality. I have feeling the answer is no, but it would be better to know for sure. Anyone have any idea? --194.197.235.28 (talk) 23:02, 3 June 2009 (UTC)

Actually this is quite commonly used in image processing. For example, a lot of toll-booths have a camera to catch the license plate of anyone who does not pay the toll. To cope with varying light conditions, the cameras are often sensitive only to infrared light, and the area is illuminated by an infrared bulb. This reduces interference from other sources of light and provides a controlled, constant illumination for the Optical Character Recognition program which will identify the vehicle. One reason this method is easy is because a lot of digital CCD cameras are already sensitive to infrared, so visible light can be filtered out (or left in as supplemental illumination). You might find Infrared photography interesting as well. We also have Thermographic camera, which describes passive infrared photography (using infrared cameras without an illuminating infrared lightbulb). These are commonly used as a type of night vision (not to be confused with low-light amplification). Thermographic infrared images make it very easy to spot vehicles, trucks, humans, and other hot objects, and are also often used in automatic image-processing (for example, automatic aim correction on a combat helicopter). Nimur (talk) 02:41, 4 June 2009 (UTC)

It's not the frequency of the light - after all, the computer's camera only really sees red, green and blue - and some computer vision is done in black and white just because it's easier and the color doesn't really help much. No - the problem is uneven lighting - where some things in the scene are lit by brighter light than others - or when the lights flicker or change brightness while the computer is gathering imagery - or when the light is strongly directional producing super-bright highlights and deep shadows. You really start to appreciate how amazingly adaptable human vision is. SteveBaker (talk) 02:43, 4 June 2009 (UTC)

Right - the point of using active infrared illumination is to control the illumination environment. We could probably also control the visible-light environment too - but in the case of covert military or traffic cameras, flashing visible light around the imaging target is not an option. Using "invisible" infrared allows the operator to produce uniform illumination for the computer-vision system, without directly affecting the human-perceptible parts of the environment. Also, sometimes infrared just has better signal-to-noise qualities - I used a (mostly) infrared beacon for my robotic target-tracker project last year. Nimur (talk) 02:49, 4 June 2009 (UTC)

That answered my question perfectly. Thank you. --194.197.235.28 (talk) 15:17, 4 June 2009 (UTC)

June 4

NDE recovery, fiction vs real life

I've seen it a hundred times on the tube: someone is found completely inert, often in water, and there's a moment of suspense – is the character pining for the fiords? – while CPR is attempted; then the rescuee noisily resumes breathing, and immediately is fully awake (though disoriented).

Does that really happen? —Tamfang (talk) 00:20, 4 June 2009 (UTC)

While it's possible for a victim to regain consciousness, any good CPR will break ribs. Going from unresponsive to verbal (making sounds without any meaning) is probably the best you can hope for. Certainly most CPR will not result in a save, and you can ask anyone in the field. M@$+[[@]] Ju ~ ♠ 00:33, 4 June 2009 (UTC)

In that situation, would the heart necessarily have stopped? If all that is required is mouth-to-mouth then I think full conciousness can return pretty quickly. CPR is normally just to keep the person alive until someone with a defibrillator gets there (and even then, your chances aren't anywhere near as good as TV hospital dramas would have you believe). --Tango (talk) 01:39, 4 June 2009 (UTC)

Isn't it the case that in Real Life, the vast majority of 'flatlines' still result in death, despite the best efforts of everyone? EDIT: Also, that a defibrillator is useless in this situation, despite what TV tells us? --Kurt Shaped Box (talk) 02:45, 4 June 2009 (UTC)

Properly done CPR need not break ribs. Edison (talk) 02:58, 4 June 2009 (UTC)

I have no idea if this is actually true but I remember reading one of those 'true medical confessions!' books ages ago in which an anonymous MD stated that it was not unknown for doctors to deliberately break the patients ribs by performing rough CPR on a patient that they already knew was toast - if the relatives were watching. The thinking being that they'd see that and be assured that absolutely everything that could've be done had been done in an attempt to save the patient... --Kurt Shaped Box (talk) 03:06, 4 June 2009 (UTC)

That is correct; the ever-popular 'flatline' (beeeeeeeeeeeeeeeeeep) in televised medical dramas is not a shockable rhythm. (See asystole). Cardiac arrests can be divided into two broad groups: those which still include some mechanical action by the heart (ventricular tachycardia, atrial fibrillation), and those which don't (asystole, pulseless electrical activity). The former are susceptible to defibrillation and have a much higher survival rate. The latter aren't shockable, and have a very poor prognosis.

Our article on cardiac arrest notes an overall survival rate of about 15% for in-hospital arrests. (Out of hospital rates are lower.) Patients with shockable rhythms fare about ten times better than those with asystole. TenOfAllTrades(talk) 13:48, 4 June 2009 (UTC)

There are many studies of near drowning events, unfortunately i don't have access to any that would answer your question. 100% of victims will survive in the short term (otherwise it's a drowning and not a near drowning). Approximately 80% will survive beyond 24 hours, perhaps with some degree of neurological deficit. Many children with cyanosis or hypoxia following recovery resume breathing after clearing the airway and one or two rescue breaths, and are conscious and alert immediately thereafter.

If the victim is in arrest the prognosis is much poorer, hypoxia has been prolonged and the brain is now ischemic. CPR alone will probably not result in a return of spontaneous circulation, let alone regaining consciousness, defibrillation and/or drugs are required. One thing to note tho is that even professional healthcare providers have a poor success rate at finding a carotid pulse during a suspected arrest event. The following scenario most likely could happen: an apneic victim is removed from the water, rescuers begin CPR but fail to note the presence of a pulse. The victim resumes breathing and shortly regains consciousness. Chest compressions were performed but were not required.—eric 15:37, 4 June 2009 (UTC)

To clarify, my question is not about the odds of survival after (near)drowning or heart attack or whatever, but about the TV cliché of sudden recovery of full consciousness. —Tamfang (talk) 19:02, 4 June 2009 (UTC)

Penile's Erectiom Angel

plz answeer, how can i measure my Penile's Erection angle ? —Preceding unsigned comment added by Greatfencer (talk • contribs) 01:11, 4 June 2009 (UTC)

I suppose a mirror might help. —Tamfang (talk) 02:33, 4 June 2009 (UTC)

Protractor? --Kurt Shaped Box (talk) 02:43, 4 June 2009 (UTC)

Of course, the angle of the dangle is inversely proportional to the heat of the beat... --Jayron32.talk.contribs 02:50, 4 June 2009 (UTC)

(EC)Use your goniometer. If you do not have one handy, the angle of the dangle has been said to be inversely proportionate to the heat of the meat, so a Meat thermometer might allow an accurate indirect measurement. Other anatomical surrogate measurements are mentioned in the work cited. Edison (talk) 02:54, 4 June 2009 (UTC)

(EC)How's about making an appointment for a visit to your local hospital's Penile tumescence lab? For some reason, the hospital seen on House M.D. would appear to have more than one. --Kurt Shaped Box (talk) 03:00, 4 June 2009 (UTC)

Employ the service of a fluffer who charges by the degree and read the invoice. Cuddlyable3 (talk) 09:53, 4 June 2009 (UTC)

<applause> —Tamfang (talk) 19:14, 4 June 2009 (UTC)

Drop a barometer from the top to determine the height, and use trigonometry. I am assuming that you know, or can measure, the length. -- Coneslayer (talk) 13:08, 4 June 2009 (UTC)

<applause> —Tamfang (talk) 19:14, 4 June 2009 (UTC)

global warming and human water retention

06:34, 4 June 2009 (UTC)Paul fitts (talk)What year did the true science of global warming start? what was the Earth's population at that time? What is the percentage of the human body that is made of water? If you had a 3ft cube of ice, and you melted it...how much water would that be in gallons??

the main reason for my questions.....it doesn't really apprear that sea levels are rising, so if ice caps and glaciers are "melting", and the water levels aren't really rising.....wouldn't it stand to reason that, that the "melted" water has to go somewhere, why not human water retention to make up 3+ billion more we've created over ther last 30 years???

Paul Fitts

The Tuvaluans beg to differ. According to this Reuters article, their whole country could disappear under the waves in 30-50 years. Another factor (which I was reminded of by An Inconvenient Truth) is that if the glaciers are in the water, their melting won't raise the water level. It's when the land-based ice melts that we have to worry. Clarityfiend (talk) 07:29, 4 June 2009 (UTC)

We have, of course, and article at Current sea level rise. Sea level is rising several mm per year. I'm too lazy to work in feet and gallons (which gallons, anyways?), but one cubic meter of ice has 1000 l and will melt into very roughly 900 l of water. --Stephan Schulz (talk) 07:36, 4 June 2009 (UTC)

Google can convert between units, put in something like "3 cubic feet in gallons". After that go outside and watch some grass carefully for a few hours. Did you see it grow? Dmcq (talk) 08:00, 4 June 2009 (UTC)

To put this in context - sea levels are rising a few millimeters each year - but each millimeter of rise represents 360,000,000,000 cubic meters of water. There are about 7 billion people - even if each of us was retaining a cubic meter of water (not even close!) we'd represent only about 0.02 millimeters of ocean depth. No - the reason the rate seems low is that 360,000,000,000 cubic meters means that it takes an awful lot of water to raise all of the oceans in the world by one millimeter. But while a few millimeters may not sound much - over 100 years, that's enough to drown quite a few coastal cities. Sadly, the evidence is that the rate of increase is going up year on year - so we could easily have a dozen or more meters of ocean level rise during the lifetimes of our children - of the younger Ref.Desk denizens. SteveBaker (talk) 15:00, 4 June 2009 (UTC)

Why are washers so called?

It was one of those idle, late night conversations in the tour van on the way home from a gig ... which led precisely nowhere. My theory is that the bigger examples are called penny washers because they are the size of pre-decimal pennies, but what about smaller varieties, and where does 'washer' come from? Any ideas please? Turbotechie (talk) 07:58, 4 June 2009 (UTC)

According to [27] (80% down the page) the origin of the term "washer" for that piece of metal is unknown, though it has had that meaning for at least 400 years and perhaps as many as 650 years. Dragons flight (talk) 08:23, 4 June 2009 (UTC)

Outside a hardware store hung the alarming sign "Nut screws washer and bolts". Cuddlyable3 (talk) 09:42, 4 June 2009 (UTC)

Not forgetting there was a launderette next door Mikenorton (talk) 10:01, 4 June 2009 (UTC)

You are right that penny washers are named for the old pennies, and often they are a similar size, but the term can actually be applied to any size washer. It is a washer with a disproportionately small centre-hole. SpinningSpark 16:34, 4 June 2009 (UTC)

Do facial products work?

Is there any scientific evidence that any face creams, anti wrinkle creams, eye treatments etc are any better than just splashing water on your face or is it really just hype? Kirk Uk —Preceding unsigned comment added by 87.82.79.175 (talk) 09:26, 4 June 2009 (UTC)

All 3 are better than water at generating profit for someone. Medical eye treatments have to be certified as safe. Cuddlyable3 (talk) 09:46, 4 June 2009 (UTC)

Many of the anti-wrinkle creams are proven to give a temporary lift and do so by using proven science, similarly darkness-removal creams can be proven to remove the appearance of darkness by masking/covering it. You may notice that in adverts of these types the claims are always quite vague (to paraphrase Charlie Brooker)...terms such as "98% of respondents agree", "help reduce appearance of", "helps fight" are all very 'vague' and undetailed - throw in a few random science-sounding (merged with natural-sounding) words and you've got something that says nothing when reviewed by a legal team but can suggest 'proof' to the average consumer. 194.221.133.226 (talk) 10:22, 4 June 2009 (UTC)

In the UK, they have to say "improves the appearance of wrinkles" rather than "removes wrinkles" on the ads now. There was one company a couple of years back that got absolutely castigated for making completely false claims about the abilities of their product (Google for 'Boxwellox'). Not quite as bad as the toothpaste that claimed to be able to split water molecules, producing free oxygen for a deeper clean - but still... --Kurt Shaped Box (talk) 10:47, 4 June 2009 (UTC)

Sunscreen definitely helps us against wrinkles. It can be scientifically tested that protecting your face against UV rays will make you look younger than you are. For example, faces of truck drivers that have been laterally exposed to sun light have been analyzed, and the half exposed to sun light looked older than the other half.--Mr.K. (talk) 10:57, 4 June 2009 (UTC)

It helps preventively against wrinkles, by the way. --Mr.K. (talk) 12:01, 4 June 2009 (UTC)

The big hype of these things in the UK ended quite a few years ago when the manufacturers were faced with either having to downsize their claims - or be treated as medical/pharmacuticals. The fair trade people argued that if they ACTUALLY reduced wrinkles, then these creams must be penetrating the skin and acting on the tissues beneath - which would require them to be classified as drugs. If all they do is fill in the wrinkles - or change their color/reflectivity to make them temporarily less noticable - then that's OK, it's just a cosmetic effect. I don't understand why that's not also the case in the USA. Certainly the claims they make are ridiculously impossible - and if they were possible, these cosmetics would certainly have to be seriously tested because they could have any number of dangerous side-effects. To the extent that they block sunlight, they might work...but their effects are essentially just changes in appearance. SteveBaker (talk) 14:52, 4 June 2009 (UTC)

Well, they also work as well as any other Moisturizer; that is by providing a barrier against evaporation, they cause the underlying skin to retain more moisture. Higher moisture content equals plumper epithelial cells, and plumper cells equals less wrinkles. Of course, a $5.00 bottle of any decent mositurizing lotion will do that; dropping $40.00 on a small 4 ounce tub of the same stuff mixed with a little make-up to cover over dark patches seems excessive to me... But then again, I'm not an aging woman trying to recapture my lost youth, what do I know. --Jayron32.talk.contribs 17:34, 4 June 2009 (UTC)

Hey, wait, here's [28] a SCIENTIFIC assessment of a particular facial product sold by that 'well known high street chemist'. Whether you are impressed by the fact that 43% of the meagre sample thought their skin had improved is up to you. 23% of the placebo sample thought their skin had improved. Richard Avery (talk) 17:38, 4 June 2009 (UTC)

A study involving 50 people; I assume half received the placebo and half the cream? That means of 25 receiving the placebo, 6 liked it, and of 25 receiving the cream, 12 liked it? I wouldn't call such small sample size "statistically significant". The error bars on a sample size of 25 would probably be bigger than the difference between the samples. Heck, I could flip a coin 25 times and get the same results. Additionally, as the sample did not compare the expensive treatment to a cheap one, only to a placebo, it only addresses the possibility that the expensive cream is better than nothing but not neccessarily better than cheaper alternatives. What you have here is a clear example of How to Lie with Statistics. --Jayron32.talk.contribs 17:45, 4 June 2009 (UTC)

According to the Mayo Clinic, "Research suggests that some wrinkle creams contain ingredients that may improve wrinkles. But many of these ingredients haven't undergone scientific research to prove this benefit. If you're looking for a face-lift in a bottle, you probably won't find it in over-the-counter (nonprescription) wrinkle creams. But they may slightly improve the appearance of your skin, depending on how long you use the product and the amount and type of the active ingredient in the wrinkle cream."[29] A Quest For Knowledge (talk) 17:58, 4 June 2009 (UTC)

What happens to toxic sewage sludge?

About 40 - 60% (depending on whether you are in the EU or USA) of treated sewage sludge (biosolids) is reused as agricultural fertilizer. From what I can see on the article on biosolids, the main reason some biosolids cannot be used as fertilizer is that they have a heavy metal and toxic substance content that is too high. Is this true? If so, what happens to this waste? Is it incinerated, landfilled etc? —Preceding unsigned comment added by 157.203.42.175 (talk) 13:23, 4 June 2009 (UTC)

According to this parliamentary note [30], in the UK 62% is applied to agricultural land, 19% is incinerated, 11% is being used in land reclamation with the remainder going to landfill or composting. It also discusses the use of sludge to generate energy from biogas through anaerobic digestion. The report does not mention toxicity as a problem, apart from the issue of Endocrine-Disrupting Chemicals. Mikenorton (talk) 14:11, 4 June 2009 (UTC)

Frozen peas float when cooked

When you put frozen peas in a saucepan of cold water they sink to the bottom. When the water is heated up the peas float to the surface. But as ice is lighter than water, and frozen peas must contain some ice, I would expect the opposite to happen, i.e. they would start off floating then sink when heated. What is going on here? Lonegroover (talk) 14:45, 4 June 2009 (UTC)

Peas contain lots of stuff besides just water, so maybe enough to overcome the buoyancy from decrease in density of the water being frozen. Do the peas remain the same size, or do they expand when they thaw/heat? Does this happen only if the water gets hot, or can you reproduce it with room-temp water (to exclude nucleated steam giving the lift)? DMacks (talk) 14:53, 4 June 2009 (UTC)

Don't forget that water is densest at about 4C. My guess (and it really is just speculation) would be the following:

Water, in a saucepan at about 10 degrees C, combined with peas at about -18C. Peas initially float in cold water before sinking so clearly the water is denser for a short period. Presumably due to the low temperature of the peas? I would assume that the peas rapidly warm due to their high surface area to volume ratio. As such, the water within the peas would be denser than the water in the pan. Peas have other constituent components, but I would suggest the density of the water in the peas outweighs and (lower) density from the solid matter of the pea. The overall density of the pea should approach the point where they are denser than the surrounding water - this shouldn't be too difficult, the water will be getting colder from the peas but also warmer from the heat input.

I would imagine that the peas remain denser (colder) than the surrounding water for a while - since the source of heat would warm the water first, then the peas When the water boils, the peas could reach a temperature equilibrium with the water (since the water cannot get hotter, regardless of heat input, without turning to steam), or at least become warm enough such that the weighted average of the density of the pea (i.e. the solid matter and water contained within the pea) could overcome the density of the hot/boiling water. —Preceding unsigned comment added by 157.203.42.175 (talk) 15:07, 4 June 2009 (UTC)

What happens if I drink five-year-old soda?

Not fridged, the 12-pack wasn't even opened. Just curious. I think I'll throw it out anyway. 67.243.7.41 (talk) 15:34, 4 June 2009 (UTC)

OR having tried it once. It won't be toxic, but it may be unpalatable as the bubbles will be gone and it may be a bit sludgy on the bottom of the can. 65.121.141.34 (talk) 16:23, 4 June 2009 (UTC)

This is not medical advice BUT: you might gain super powers. It's a possibility. Consider your future life as Soda Man, and whether or not you are willing to take on that responsibility. --98.217.14.211 (talk) 16:55, 4 June 2009 (UTC)

Throwing it away it probably wise. I doubt there will be anything harmful about it, but it probably won't taste very nice (depending on how it was stored). It is possible the seal has been broken somehow which might have allowed something harmful to get in, so probably not worth the risk. --Tango (talk) 18:38, 4 June 2009 (UTC)

Sugar soda may retain its flavor longer than artificially sweetened soda. I once had some old pop sweetened with Nutrasweet and all sweetness was gone. It tasted like unsweetened Coke with pineapple juice added. Heat speeds the breakdown of Nutrasweet. There is always a possibility that over time there could be greater leaching of metal or plastic from the can into the drink. If it is sealed, how would any carbon dioxide escape to make it flat? Edison (talk) 18:42, 4 June 2009 (UTC)

Major OR here, but I had some cans of orange soda that actually started leaking through the bottom of the cans after eight or nine years. They were unopened and keep in a closet. The soda actually caused corrosion and leaked out. cheers, 10draftsdeep (talk) 19:38, 4 June 2009 (UTC)

Capturing a warm bath's heat

It's winter in the southern hemisphere and a nice way to heat up is by taking a warm bath. I couldn't help thinking though of all the energy that gets lost when the warm water flows out the drain after a bath. Given that:

• a kilocalorie is the amount of energy it takes to heat a liter of water by 1 degree Celsius
• lets assume my bathtub holds 150 liters of water
• it's about 17 degrees in my apartment, the water after I'm done bathing is 40 degrees Celsius, a 23 degree difference

I asked Google: "(150 * 23) * kilocalories in kilowatt hours" and got "(150 * 23) * kilocalories = 4.00966667 kilowatt hours"

That's 4 kilowatt hours of energy down the drain! That's like a 1000 watt heater staying on for 4 hours. so this makes me ask, does it make sense to keep the water in the bathtub until it has cooled down so that my place will heat up a bit? One concern is evaporation that might cause the humidity to rise and thus the energy is kept as latent heat rather than actual. In that case, is there something simple one can do to prevent evaporation?

196.210.200.167 (talk) 16:14, 4 June 2009 (UTC) Eon

Any added humidity will make you feel warmer, which is just as good, isn't it? --Sean 18:25, 4 June 2009 (UTC)

I'm not sure. The formulas are given in Fahrenheit, but I suspect at 17 degrees a higher humidity might even make you feel colder. Seems counter intuitive though that just leaving the water in the bathtub can make such a huge difference. 196.210.200.167 (talk) 19:39, 4 June 2009 (UTC) Eon

A lid on the bath would prevent evaporation. --Tango (talk) 18:36, 4 June 2009 (UTC)

gravitational equations

Is/are the equation/equations for gravity at the center of a Black Hole the same as the equation/equations for gravity in unoccupied (empty) space? ---- Taxa (talk) 17:20, 4 June 2009 (UTC)

At the very centre of a black hole, the singularity, the laws of physics break down (ie. we don't really know what happens), so there are no equations. In an appropriate coordinate system (eg. Kruskal–Szekeres coordinates) you can use the same equations to describe everywhere except the singularity, though. --Tango (talk) 18:47, 4 June 2009 (UTC)

The singularity at the very center of a black hole does things to the equations that physics depends on that are essentially the same as dividing by zero on your pocket calculator. There is no meaningful answer. But a billionth of a trillionth of a gnat's eyebrow from the center, the laws of physics should be pretty well-behaved. The equations are exactly the same - but because these are rather extreme circumstances, you have to use the full relativistic forms of these equations, not the 'low speed/low gravity' approximations that we all learned in high school. SteveBaker (talk) 19:41, 4 June 2009 (UTC)

DO GRAVITATIONAL ENERGY OF EARTH REDUCE BY TIME?Surabhi12 (talk) 18:06, 4 June 2009 (UTC)

Earth keeps the moon in it's gravity spending it's energy .From where do earth gain this energy? If earth do not gain energy,then is it's gravitational energy reducing by time?

The earth does not spend energy in order to keep its moon. Dauto (talk) 18:19, 4 June 2009 (UTC)

Well, not in classical physics. But in relativistic physics, the circling moon will cause gravitational waves, which will carry away some of the potential energy of the Earth-Moon system. The effect is very small, and, at the moment, entirely overshadowed by the tidal transfer of rotational momentum from the Earth to the Moon. See Gravitational wave#Power_radiated_by_Orbiting_Bodies. --Stephan Schulz (talk) 18:26, 4 June 2009 (UTC)

The moon is falling towards the Earth, but luckily it keeps missing, just like cannonball "C" shown in the picture. It doesn't take any energy for this to happen. See orbit. --Sean 18:31, 4 June 2009 (UTC)

Somebody owes me a dollar. (I've decided that I'm charging the universe a dollar every time someone confuses a 'force' (gravity in this case) with 'energy' - I plan to earn enough money from this confusion to replenish my poor 401K). The force and energy are very different things. When you stick a fridge magnet onto your fridge, the magnet exerts a force on the metal. But so long as the magnet doesn't move - it doesn't take any energy whatever for it to just hang there...magnets don't "run down". It's the same with the moon. The gravity pull between earth and moon is just a force. So long as the two bodies don't get closer or further apart - there is no energy transaction involved. Forces don't "run down" - they just are. If you hang something from the ceiling with a rope - the rope exerts a force...the rope doesn't "run down". Now, if something were to pull the moon further from the earth - that 'something' would have to expend some energy to do it...if the moon (for some reason) were to fall closer to the earth - then it would actually gain energy (kinetic energy initially - then one hell of a lot of heat energy when it kersplatted into the middle of the pacific ocean!). SteveBaker (talk) 19:35, 4 June 2009 (UTC)

problem of race

Imagine:

A car travels 10km in an hour 
A bus travels 20km in an hour  
both have a race
Car is ahead of bus at point A.
By the time bus moves to the point A,car must have move little ahead say to point b.
By the time bus moves to the point b,car must have move little ahead again say to point c.
By the time bus moves to the point c,car must have move little ahead say to point d.
This continues .........
Thus car has to become the winner.
IS THIS POSSIBLE?  —Preceding unsigned comment added by Surabhi12 (talk • contribs) 18:30, 4 June 2009 (UTC) 

See Zeno's paradoxes. Short answer - it takes an infinite number of steps for the bus to overtake the car but because each of those steps takes sufficiently less time than the one before the total amount of time required to overtake is finite. See convergent series for the maths behind that. --Tango (talk) 18:35, 4 June 2009 (UTC)

Another way to look at this is that suppose the car starts off with a lead of (say) 10km. We know that using 'sensible' math, that the bus will travel at a distance D in time T=D/20 hours and the car at time T=(D-10)/10 hours. When the bus overtakes the car, they are at the same distance at the same time - so we can solve the simultaneous equations and calculate T as 1 hour. The bus catches the car after 1 hour - then zooms right past it. No problem, no controversy, no paradox.

But the crazy Zeno's paradox way says: The time it takes the bus to reach A is 1/2 hour. By that time, the car has travelled 5km to point B. 15 minutes later, the bus reaches B and the car has gone on another 2.5km to C. 7.5 minutes later, the bus reaches C...so Zeno tells us where the bus and the car are after 30+15+7.5+3.75+1.875+... minutes. Mathematically, that infinite series adds up to 59.999... minutes. And the distance that the car and bus have travelled in that time is 19.999...km from the start. Well, that's all very interesting and exciting - but by refusing to every allow the 'victim' of the paradox to just go ahead and ask where the vehicles are after a longer amount of time, he arbitarily forces us to look only at times before the two vehicles actually meet. If you limit your calculations to only times before the vehicles meet - you're obviously never going to find the time when they do actually meet. It's not a paradox - it's a dumb way of stopping the person from answering a ridiculously simple question!

But why doe Xeno insist on calculating all of these intermediate positions and stubbornly refuse to calculate where they are after exactly one hour? Because he's some stupid philosopher trying to make a name for himself by inventing a "paradox". This is why philosophers are a waste of quarks. We have a perfectly simple, completely understood problem with a VERY simple, non-paradoxical conclusion...but NO...the dumb-as-a-bag-of-hammers philosopher has to insist on never calculating the answer but instead answering an infinite series of questions that we don't need to know the answer to.

It's really no different to me saying "What is 2+2?" - but instead of just going ahead and counting it out on your fingers, I arbitarily insist that you first calculate a totally unrelated sum: 1+0.5+0.25+0.125+... which (if you try to do it the hard way) will take you an infinite amount of time - and thereby cunningly prevent you from calculating 2+2. Why the heck would you ever want to do it like that? It's obviously a stupid and unnecessary way to answer my question. So - please treat anything any philosopher says much as you would a comedian. Amusing, possibly mildly entertaining - but in no way relating to reality. SteveBaker (talk) 19:22, 4 June 2009 (UTC)

Labour and multiple births

Given that Twins, and higher number births, are individuals, do mothers ever experience a sort of delayed labor, in which the second child is born at a vastly different time or even date then their sibling? For example, Paul and John are twins, Paul is born first, and John is born 2 days later, after the mother reentered labor.--Honeymane_{Heghlu meH QaQ jajvam} 19:31, 4 June 2009 (UTC)