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July 7

Wood catching fire from propane or natural gas

How hard is to catch a wooden structure on fire from a propane or natural gas flash (say, one from a barbecue)? I would imagine pretty hard since it is gone very fast, the heat rises and as a gas it doesn't carry nearly as much heat for the same area as a liquid or solid would, but I don't know. Any insights? --T H F S W (T · C · E) 00:10, 7 July 2011 (UTC)[reply]

It depends on the surface area and moisture of the wood, along with the length of exposure. Most pieces of wood that can fit on barbecues can be ignited by them, but healthy twigs six feet above a barbecue are unlikely to catch fire unless a lot of exploding grease or the like is involved. 99.24.223.58 (talk) 00:19, 7 July 2011 (UTC)[reply]

I don't mean if you've got a piece of wood sitting above a barbecue, I mean from the sudden flash if the gas is left running with the lid closed too long. --T H F S W (T · C · E) 01:01, 7 July 2011 (UTC)[reply]

If you filled a cubic meter of space with propane until something ignited it, whether it could ignite adjacent wood would depend more on what actually ends up igniting it. If there is a source of ignition, that is something to mitigate. If your barbecue is leaking, then you need to mitigate that or you will always be out of gas or pay too much for your gas bill. You need to describe the situational geometry and surroundings of the grill to get a better answer. 99.24.223.58 (talk) 01:53, 7 July 2011 (UTC)[reply]

The structure would be unlikely to ignite directly, but there could be something else that does catch fire, like clothes on an attached clothes line, that then provides the sustained flame needed to light the structure on fire. StuRat (talk) 07:21, 7 July 2011 (UTC)[reply]

Pollination prospects

"One-third of the honeybee population has died off every year since 2006, and evidence points to pesticides used on corn, soy, and wheat crops as the culprits."[1] True? What is the anticipated effect on fruit and vegetable production? 99.24.223.58 (talk) 01:49, 7 July 2011 (UTC)[reply]

You may find the article Colony collapse disorder interesting. --Jayron32 01:54, 7 July 2011 (UTC)[reply]

If bees all went extinct (which is quite unlikely), then we would need to rely on other pollinators, like hummingbirds and humans, or move to crops which don't require pollination. StuRat (talk) 07:17, 7 July 2011 (UTC)[reply]

The pesticides used on corn (i.e. maize), at least, are intended to kill the larvae of corn borers and rootworms; and more and more often those pesticides are being generated from within the plants, as a result of genetic modification. Maize relies on wind pollination, so bees wouldn't be a factor. Wheat and soybeans can self-pollinate. The primary impact from loss of bees would be on fruits and vegetables. ←Baseball Bugs ^{What's up, Doc?} carrots→ 11:20, 7 July 2011 (UTC)[reply]

It's rather telling that the original link is by a guy who apparently signed a petition without bothering to see if the claims were true or not. Pesticides have been used for generations. What's special about 2006? ←Baseball Bugs ^{What's up, Doc?} carrots→ 11:22, 7 July 2011 (UTC)[reply]

I am ambivalent about this. On one hand I wonder if it is an opportunity to control pollination, which is otherwise a random process, and at the same time reduce the probability of accidental bee stings, which I'd love to see happen. On the other hand, I'm not sure what I would do with control of pollination. Probably more brazil nuts. I'm not sure what most people would do with control of pollination, but I'm not sure it would be better than what bees have been doing. When I was in elementary school the "africanized killer bee sweeping north from Mexico" was the number one impending environmental threat. (Ha! Take that! In your face, africanized killer bees! You all better start making better brazil nuts or I'm cutting my honey budget even further.) 99.24.223.58 (talk) 17:56, 8 July 2011 (UTC)[reply]

Without bees, it may not be economically viable to hand-pollinate many crops. StuRat (talk) 04:57, 9 July 2011 (UTC)[reply]

That is certainly true. I expect that if bees die out enough that lack of pollination affects crop yields, farmers will introduce more (healthier?) bees, or other insects or birds which can take up the slack. Honestly, I think it's a very serious situation which needs a lot more thought and action by people independent of the manufacturers of the implicated insecticides. I wonder how many more years of decline to 2/3rds of the previous years' population it will take before bees get on the endangered species list. I wonder if fruit and vegetable supplies and prices have already been impacted. 99.24.223.58 (talk) 09:38, 9 July 2011 (UTC)[reply]

Most commons monkeys

What are the most common monkeys known to humans? --111Engo (talk) 02:55, 7 July 2011 (UTC)[reply]

I would guess the Rhesus Macaque but I am not seeing a good reference yet. Rmhermen (talk) 03:22, 7 July 2011 (UTC)[reply]

If you use the term 'monkey' loosely, I'd suggest that you look in a mirror. AndyTheGrump (talk) 03:33, 7 July 2011 (UTC)[reply]

Um, you are not monkey, you are an ape. No joke, please be scientific. :) --111Engo (talk) 03:41, 7 July 2011 (UTC)[reply]

Not necessarily. ←Baseball Bugs ^{What's up, Doc?} carrots→ 11:26, 7 July 2011 (UTC)[reply]

Also, humans are not apes, either. We are primates. ←Baseball Bugs ^{What's up, Doc?} carrots→ 11:27, 7 July 2011 (UTC)[reply]

Well, it depends upon how you define "ape", but if you take it to be equivalent to a monophyletic taxonomic grouping, then yes, humans are apes (and apes are a subset of primates). The only way humans aren't considered apes is if you define the term "ape" to be a paraphyletic group explicitly excluding humans (which is not common in scientific circles), or completely reject scientific consensus of human evolution. -- 174.31.204.164 (talk) 15:26, 7 July 2011 (UTC)[reply]

Well he did say loosely. More importantly, if you want to be scientific, monkeys are a paraphyletic group. So from a scientific view, it's questionable if it makes sense to ask a question where the answer can be either in parvorder Platyrrhini or superfamily Cercopithecidae or but not superfamily Hominoidea.... Nil Einne (talk) 04:30, 7 July 2011 (UTC)[reply]

Yup. 'monkey' is a vague term, so I gave a vague answer. (And 'ape' isn't exactly clear either, though I'll suggest that whatever they are, we are too...). AndyTheGrump (talk) 14:09, 7 July 2011 (UTC)[reply]

Ok, will anyone go to the original question? --111Engo (talk) 12:19, 7 July 2011 (UTC)[reply]

For the most "commons monkeys", check out wikimedia commons.[2] For the most "common monkeys"... first, define what you mean by "common". Most populous? Most often used in circus acts? ←Baseball Bugs ^{What's up, Doc?} carrots→ 12:27, 7 July 2011 (UTC)[reply]

I'd assume 'most populous', i.e. which species of Platyrrhini or Cercopithecidae (and not Hominoidea) has the largest total living population. Even this may be difficult to answer, given that large populations tend to be genetically diverse, and it may not always be clear whether they are all the same species. And then there is observer bias - generally speaking, primatologists tend to be more interested in counting rare species than common ones. AndyTheGrump (talk) 14:09, 7 July 2011 (UTC)[reply]

On that basis the Vervet monkey of East and Southern Africa is possibly also a contender. Roger (talk) 14:14, 7 July 2011 (UTC)[reply]

I should think this question would be a no-brainer.[3] Bus stop (talk) 14:23, 7 July 2011 (UTC)[reply]

Clarification: By "most common", I mean monkeys which are known to most people i.e. monkeys about which most people have heard of and monkeys humans interact with most. --111Engo (talk) 14:27, 7 July 2011 (UTC)[reply]

I think you are asking what is the quintessential monkey—is that correct? As in—what is the iconic monkey, or what monkey comes to most people's minds when they hear the word monkey. If that is what you are asking, I think that different sorts of monkeys would come to mind, depending on which human group were queried. In a society bombarded by media images, I think the most common one is the chimpanzee. Bus stop (talk) 14:44, 7 July 2011 (UTC)[reply]

... which is actually an ape, not a monkey. Gandalf61 (talk) 15:00, 7 July 2011 (UTC)[reply]

In that case the clear winner is the Rhesus Macaque as hundreds of millions of Asian people are familiar with them. Many people interact with them on a practically a daily basis - particularly in India. Roger (talk) 14:53, 7 July 2011 (UTC)[reply]

Year the Duwamish Railroad Bridge in Seattle was built?

I a attempting to finish off a list and create an article on a bridge in Seattle. I have found some in-depth info from engineering journals through Google Books searches, but I am struggling to find a year it was built and think some more info could be useful to create an article. Some keywords and other information that might assist in any searches:

One of the earliest "heel trunnion" bridges
Operated by Northern Pacific Railway (I think it is now operated by Burlington Northern)
Built around 1912
Seattle landmark (I cannot find an ordinance #) but not NHRP

Any assistance would be appreciated.Cptnono (talk) 03:55, 7 July 2011 (UTC)[reply]

BirAli Crater

I've visited this area and uploaded the photo here. How can I know if this were an impact crater, (see also the other one beside on Google maps)?--Almuhammedi (talk) 04:45, 7 July 2011 (UTC)[reply]

You can search on the web -- every mention says that it is volcanic. The fact that it is not perfectly round (as you see on the map) also means it is pretty surely not an impact crater. Looking around on the map, there are a number of clear volcanic cones in the area -- you can see one in the background of your photo. The second crater is much more difficult to recognize based on shape, but since there are so many volcanic craters and cones around, it must surely be volcanic as well. Looie496 (talk) 05:20, 7 July 2011 (UTC)[reply]

Then can I consider it as a volcanic crater lake? Can I also add it to the list of volcanic crater lakes? --Almuhammedi (talk) 13:24, 7 July 2011 (UTC)[reply]

Well, I saw at least a dozen sites that identify it as volcanic, but none of them was a reliable source. It would be good to find a book or other published source for the information before adding it to an article. Looie496 (talk) 16:30, 7 July 2011 (UTC)[reply]

The lake is Shouran lake according to Wikimapia here [4]. It looks like a maar, formed by an explosive phreatomagmatic eruption, but that's pure OR. Mikenorton (talk) 22:10, 7 July 2011 (UTC)[reply]

Try one of the following links on Google Scholar: Metasomatism of the shallow mantle beneath Yemen by the Afar plume—Implications for mantle plumes, flood volcanism, and intraplate volcanism (ABSTRACT) or Clinopyroxene-rich lherzolite xenoliths from Bir Ali, Yemen—possible product of peridotite/melt reactions (PDF, 6 pg.). ~AH1 ^(discuss!) 16:46, 8 July 2011 (UTC)[reply]

Why not adopt measurement scales better suited for very large quantities?

I find that I can imagine the scale of some colossal entities if they are given in large but familiar units, even where those units are Olympic pools of water, or elephants. What is the use of telling me that a large ocean has so many litres in it? They might as well use thimble-fulls. And you get figures like 10 ^ 17, which mean nothing to anyone.

My prime target for amendment would be using miles or kilometres for astronomical distances. I remember a mile as being from my back fence to Mrs Carruther's chook pen. It's a short walk. We use light years for very large distances - why not use them for distances in our local solar system. For example, it is about 8 light minutes to the sun, and about 1.5 light seconds to the moon. This gives one a pretty good idea of the relative distance of the sun and moon from Earth. The distances to Jupiter and the other gas giants are about 4 to 8 hours.

Voyager 1, launched over 30 years ago is the furthest man-made object from Earth. The NASA site http://voyager.jpl.nasa.gov/ gives it as being 17,481,723,800 kilometers away, a figure which is billons of times further than Mrs Carruthers chook pen - and means nothing to most people. It also gives the distance as 117 AU (Astronomical Units - a single one being the distance between the Earth and the Sun.) Now, if we accept that 1 AU is about 8 light minutes, then Voyager 1 is about 15.5 light hours away, or nearly double the distance to Jupiter. The Sun is 8 minutes away, and Voyager is 15.6 hours away. Hey, suddenly everyone can see these distances in perspective! This is just common sense. Why doesn't NASA use this instead of AU's and kilometers? And the speed of light is totally constant too, an additional plus.

Same goes for Olympic swimming pools. Everyone has been in one and has a good idea of how much water they hold. If you had a unit "Kilopool", i.e. a thousand swimming pools, you could express the scale of very large quantities of liquid in a way that a person could easily visualise. For example, a Kilopool would be a cube, with each side having 10 Olympic pools. In my view, the whole system of measuring large quantities in thimblefuls and feathers and then announcing that something is 10^17 is absurd, and we should adopt scales like the ones I've suggeted here. It's a no-brainer really, or I should say, a one-pea brainer.

I blame the frogs (the French) for starting this. The centimetre was apparenty picked as a basic lengh unit because it did not naturally measure anything, unlike the inch, which is about the length of man's thumb. The metre is too long to be a step, too short to be a room length, and so on.

Now, watch, the Kilopool idea will suddenly and quite by "coincidence" be put forward as an official unit. And will I get a jot of recognition? No sir! I'm going to put on my alfoil thought blocking cap right now. Myles325a (talk) 04:49, 7 July 2011 (UTC)[reply]

If you don't mind removing your tin foil hat for a minute...

You seem to be ranting about the lack of using measurements which result in small numbers. I am with you on this matter; for some godforsaken reason the astronomical community continues to use CGS units. I always found it ironic that the people who study the largest and heaviest objects in the universe use smaller units than the kilograms and meters that most scientists use. I believe in using units that result in small numbers for the scales you are using, although not to the point of making unit conversions awkward.

However, you have to see the conundrum that we scientists have when communicating to the general public: if we use crazy units like megaparsecs, light minutes, and AUs, Joe Shmoe has no idea what those are. Kilometers, as you say, are about 60% of the walk from your back fence to Mrs Carruther's chook pen, which was a short, easy walk, and an easy distance for you to comprehend. Could you tell me how long it would take to walk a parsec? To me, the best solution is to give both a normal unit (miles) and a small-number unit (parsecs or what have you), which would satisfy both crowds. ~~And contrary to your assertion that NASA does not do this, on this page they list Voyager 1 as being "16.9 billion kilometers (~ 113 AU)" from Earth.~~

Additionally, if you look at meter, you can see that it was originally defined as one ten-millionth of the distance from pole-to-pole, to avoid using arbitrary objects to define the measurement like "foot". Having a standard unit of measurement was useful for science. Now if only we could convince those damn Americans to use it. You can put your foil hat back on now :) -RunningOnBrains^(talk) 05:08, 7 July 2011 (UTC)[reply]

The metre is actually one ten-millionth of (North) pole to equator. AndrewWTaylor (talk) 08:03, 7 July 2011 (UTC) [reply]

I have struck one of my previous comments, since apparently I need to learn how to read, but this leads me to a further point: why do you think light years or light minutes are easier for the public to understand than an Astronomical Unit (AU)? To me, AUs make more sense in the solar system, especially because we're often talking about distance from the sun, so when I see that Voyager is 117 AUs from the sun, I think "hm, so it's more than 100 times further away from the sun than we are!". To me that's much more understandable than "light minutes", but it's all personal preference.

I don't know about you, but I'm sure that not every one has been in (or even seen) an Olympic size swimming pool. I certainly haven't, at least not recently. And no scientist that I know of actually uses this measure. Your idea for using pool-length for volume makes no sense, since these pools have different length, width, and depth, so it wouldn't really be even on each side (they aren't a standardized depth anyway: if you read the link, they only have to be a minimum depth). Vulcanologists and oceanographers deal with extremely large volumes all the time, and so they use units like cubic miles and cubic kilometers (and my favorite-sounding one: Sverdrups). Why aren't these acceptable? As I said above, you can't really satisfy everybody at once.

I'm personally a fan of Rhode Islands as a unit of measure for area. Which do you prefer?-RunningOnBrains^(talk) 06:05, 7 July 2011 (UTC)[reply]

OPmyles325a back live. Hi RunningOnBrains, I was writing a hefty reply to your note when a glitch occurred and I lost the lot. When I got back, you had made another entry. Thanks for the effort. As I wrote initially, I can understand kilometers and miles very well, because I experience such directly every day from childhood, as I had earlier supposed everyone else did. My objection to miles / kays being used for astronomical distances is that the familiarity we have with these distances is drowned out by the sheer number of the miles/kays involved. I don’t know where the cutoff point is, but I strongly suspect that billion is about the farthest an ordinary human mind can take in. The problems with AU’s are twofold. First, most laypeople have little notion of how far the Earth is from the Sun (or the Moon for that matter). The value of AU is depleted if many think Earth /Sun distance is a matter of thousands or trillions of miles / kays. The second problem is that AU is only good for the Solar System and really only the inner Solar System at that. Once you get into interstellar space and then intergalactic space, AU’s become very much like miles / kays – there are just too many of them to get a grip.

The great thing about light speed is that it is based on time, which humans experience directly and fundamentally. EVERYONE knows what 10 minutes is, and also 10 years. If a driver asks for directions and you tell him that a warehouse is “10 minutes yonder”, then you will never get a request for clarification. It’s as clear as can be. That’s because he knows the normal speed of a car, and he knows what 10 minutes is. You can tell someone that light could travel around the equator 7 times in a second. Anyone who has an atlas will take that on board. Now if you tell them that the Moon is about 1.5 seconds away, he can see that means that it is about 11 Earth circumferences away. And if you tell him that the Sun is 8 minutes away, he can compare that with the distance from the Moon, and start to get a very good idea of the general nature of where we are. This is not the case when you start rabbiting on about “billions of miles” and so on. And as I said initially, you can then proceed to tell him that the gas giant planets are about 4 to 8 hours away, and Voyager is about 15 hours away. What could be simpler? It is a matter of taking what the reader is well familiar with, and then building on that, but not in a way where suddenly you expect him to visualize figures with 15 zeros in them.

Once we get beyond the planets, the system still works well. Anyone who has done some history will have a good idea of what “a thousand years” means. After all, people can live to be a hundred, and a thousand is no more than 10 of them, with one born as the other reaches 100. Galactic distances are amenable to figures no larger than thousands of light years, so we are in a position to comprehend them with relative ease. Try telling someone how far we are from the galactic centre in AU’s - it might as well be centimeters. So I cannot fathom why the NASA site - and thousands like it - don’t permanently ditch this ridiculous, and artificial, feathers and thimbles approach, and use the superb scale that has been provided for us in the constant ruler of light. I was surprised to hear you say that you had never been in, peed in, or been seen in, an Olympic swimming pool. What, have you never even watched a swimming event at the Olympics? Not to worry, we could have a base unit of a Wading Pool. I guess being an Aussie, I just assumed that everyone spent summer diving and cavorting in large pools. Yes, a flaw with the Kilopool idea is that an Olympic Pool is rectangular, not square, and it is deep at one end and shallow at the other. But these flaws are not serious. The important thing is that from early childhood, an Aussie kid is up and down the lanes in the pool, dives down to the bottom, and thus gets a very good idea of how much water there is, not only with his or her mind, but with every inch of their bodies.

In the case of employing units which, as you put well, give small and comprehensible numbers to describe large quantities, it is necessary to use entities which are well-known to those likely to come across them and be interested in them. So it appears that I have been guilty of cultural imperialism when I suggested the Kilopool. In much the same way as using "Rhode islands" as a base is culturally insensitive, because outside of the U.S. few people would know how big that means. (On an aside, it is interesting to see how often Belgium is used to denote large areas, because Belgium is quite small, probably smaller than most people realize.)

The reason that elephants are often used for large weight concerns is that writers are assuming that people have seen them in zoos, and have a rough idea of how heavy they would be. Blue whales are much heavier, but then they float and that massive weight is not so evident. Myles325a (talk) 07:00, 7 July 2011 (UTC)[reply]

Ask yourself how accurately in percent you could establish, maintain and transfer to others your proposed pool-length unit. Then see the article Metre and compare. Then please look into the usefulness of the Logarithmic scale which is a good way of managing very small and very large quantities that are inevitably beyond tangible comprehension. In some cases such as sound amplitude and sound frequencies in music the log scale actually agrees better with human experience than a simple linear scale. Please don't call the citizens of France "frogs". They are a proud nation with nuclear capability and veto right at the UN so it is unwise to get them hopping mad. See Australia–France relations. Cuddlyable3 (talk) 08:23, 7 July 2011 (UTC)[reply]

I have a better idea. Why don't educate the public better so they can understand what a power like 10 ^ 17 mean? Dauto (talk) 17:49, 7 July 2011 (UTC)[reply]

What does 10^17 mean to you Dauto? It is a difficult number to conceptualize. Think of it this way, if 10^17 grains of rice were given to each person on earth, that would be around 1000 lbs per person. That much rice would fill enough grain cars to make a train long enough to circle the earth 13 times. Education can only go so far when it comes to conceptualizing incredibly large numbers. Googlemeister (talk) 18:50, 7 July 2011 (UTC)[reply]

I think you did a pretty good job at conceptualizing it proving my point, thank you. Dauto (talk) 19:21, 7 July 2011 (UTC)[reply]

Granted, but it took me 8 minutes, a graphing calculator and looking up the size of a railroad hopper car to do it. Googlemeister (talk) 14:09, 8 July 2011 (UTC)[reply]

A 60-bit binary computer can keep track of every grain of rice through a calculation without losing or gaining a single grain. Conceptualise that. Cuddlyable3 (talk) 20:03, 7 July 2011 (UTC)[reply]

The ocean volume is often measured in cubic kilometres, rather than in mass units of "1.024 ± ~0.005 x 10⁹ metric tonnes _s.v.". ~AH1 ^(discuss!) 16:37, 8 July 2011 (UTC)[reply]

To the original question, how does making the base units larger help? A light year is so utterly unimaginably large and literally inconceivable (I mean 'literally' literally here.) I can't imagine 1 minute compared to one year on any practical level, so using numbers this big actually help illustrate just how crazy huge (and terribly small) nature is. I mean, at a certain point, the difference between a billion miles and a billion kilometers loses much meaning to the average Joe, even if the difference is so big. Mingmingla (talk) 01:04, 12 July 2011 (UTC)[reply]

Species identification request

Hello, I was wondering if anybody could help me identify a few species of insects and plants before I upload the pictures to Commons. There are three different species of plants, one with pink flowers, one with white and pink flowers, and one with white flowers. There are also two species of dragonfly, one which is bright green and black (see pictures here, here, and here) and a yellow and black one. All pictures except the first were taken at Tirta Gangga lake in East Lampung Regency, Lampung, Sumatra while the first picture was taken near the regent's office in Sukadana, Lampung. Any help would be greatly appreciated. Crisco 1492 (talk) 05:03, 7 July 2011 (UTC)[reply]

"one with white and pink flowers" = Plumeria
"one with white flowers" = Bougainvillea

Sean.hoyland - talk 11:31, 7 July 2011 (UTC)[reply]

Would Plumeria rubra be the best guess for the one with white and pink flowers? Crisco 1492 (talk) 15:20, 7 July 2011 (UTC)[reply]

Yes, I guess from the leaf shape but there are many named cultivars. Sean.hoyland - talk 15:45, 7 July 2011 (UTC)[reply]

The joys of being a botanist. I have uploaded the Plumeria at File:Plumeria at Tirta Gangga, Sumatra.jpg, but we have many, many, many ad infinitum better pictures of Bougainvillea. So one plant and two dragonflies to go. Crisco 1492 (talk) 16:01, 7 July 2011 (UTC)[reply]

what will happen If any massive star comes to be black hole and it has planets?

A.mohammadzade--78.38.28.3 (talk) 06:22, 7 July 2011 (UTC)[reply]

While I don't see any reason planets couldn't have stable orbits around a black hole, they couldn't remain after a star has a supernova explosion leaving a black hole, because the portion of the supernova which blasts outward would destroy any planets there. However, there might be some complex multiple-body gravitational interaction which brings new planets into stable orbits about the black hole, later on. StuRat (talk) 06:34, 7 July 2011 (UTC)[reply]

A supernova explosion would not necessarily disperse a planetary system completely; see PSR B1257+12 for an example of a planetary system around a neutron star, which is the end result of some supernovae.-RunningOnBrains^(talk) 07:05, 7 July 2011 (UTC)[reply]

Yes, but the concern here is the larger supernovae which produce black holes. Would any planets survive those ? StuRat (talk) 08:16, 7 July 2011 (UTC)[reply]

The back of my envelope suggests that a supernova is probably survivable for large and distant planets, provided one is only asking whether the planet receives less energy than its gravitational binding energy when exposed to a core collapse supernova. A large fraction of the planet would still be completely ablated, but the event might be survivable (provided survivable merely asks whether any gravitationally bound nugget still exists). Dragons flight (talk) 09:11, 7 July 2011 (UTC)[reply]

Hmmm, I though that the planets of PSR B1257+12 were formed after the neutron star formed... Count Iblis (talk) 14:32, 7 July 2011 (UTC)[reply]

I abslotly think that the black hole (not super nova) cannot change condition and rotational orbit of planets round early star except one of them come to roche limitMohammadzade--it means that if any star had planets and end its energy to be black hole those planets still rotate round main star 78.38.28.3 (talk) 06:41, 7 July 2011 (UTC)[reply]

Consider that all exchangings are happening inside the event horison.and consider the binary star systems which first detected black holes --

78.38.28.3 (talk) 06:58, 7 July 2011 (UTC)A.mohammadzade[reply]

Let's imagine that somehow a planet is shielded from the supernova of its host star and survives that star becoming a black hole. As the star has lost mass in the explosion, its overall gravitational field is diluted, and the planet would move away from the Black Hole, and its orbit would be longer. I would imagine, the orbit would be further altered as the Hole's gravitational attraction comes from a point, not a finite area. The forces involved in the preservation of angular momentum would thus become intensified, and if the planet did not face the Sun all the time before, it might do so now. Also, it would now be very dark on the planet, and life would be much harder. If there was an intelligent and technological species there, they might be able to survive, using the energy released by the tidal forces of the Black Hole on their home planet, and living near hot vents and volcanos and the like. Or alternatively, they might exploit the Black Hole by sending material streaming into it, and collecting the energy dissipated when the Hole rips it apart and spaghettifies it. If they have sophisticated control over genetic processes, they might biologically engineer their species to be only an inch or so high, with work to be done by robots. That way, they would need very little food or fuel, and could live happily on the smell of an oily rag. Myles325a (talk) 07:16, 7 July 2011 (UTC)[reply]

please dont mix supernova with black hole. --78.38.28.3 (talk) 09:30, 7 July 2011 (UTC)[reply]

Do you have another mechanism for forming a black hole that does not involve a supernova? --Jayron32 19:52, 7 July 2011 (UTC)[reply]

The big bang likely made primordial black holes, such as the supermassive one at the center of our galaxy. That could explain dark matter with intermediate mass black holes and according to Lacki and Beacom (2010) that would explain why people haven't found any weakly interacting massive particles. 99.24.223.58 (talk) 20:39, 8 July 2011 (UTC)[reply]

There may be some minor relativistic effects, but the shell theorem tells us that (with Newtonian gravity, which is a good approximation at the distances we're talking about) there is no difference between the gravitational field of a point-mass and the gravitational field of a spherically symmetric object (which a star is, give or take an equatorial bulge). I don't understand your comment about tidal locking. If gravity is reduced, then so are tidal forces. They are also reduced by the increased distance you mention. The chance of becoming tidally locked would reduce (or, perhaps more accurately, the time it would take to become tidally locked would increase). In order for the civilization you describe to exploit the block hole, they would need to get closer to it than the original radius of the star, since outside that radius nothing has really changed. That won't be easy. Geothermal energy would work for a time, although the planet will cool down quicker without a star keeping it warm (although that could still be millions of years, I'd need to look up some numbers). --Tango (talk) 12:03, 8 July 2011 (UTC)[reply]

You are almost certainly right, Tango, as I gain my inspiration telepathically from my overlords from Fubia, and they often pull my leg. But still, granted the tidal forces would decrease as the planet moved away from its sun, but isn't it still true that the concentration of the Sun's mass affects the rate of tidal locking? For example, the Moon is tidally locked to the Earth. Suppose the Earth was made of some very heavy stuff and was only 10 miles in diameter. This would concentrate the Earth's gravitational attraction in a more focussed way, whereas now it must be diluted as a larger part of the Earth is involved in the attraction. To take a reductio ad absurdum approach, imagine the the Earth is a billion miles in diameter. To all intents and purposes, a small satellite of such a large object would feel the attraction of its host almost equally at every point facing the host.

And I am wondering at your point re: geothermal energy running out. I am thinking of Jupiter's moon Io, which is extremely active as it is kneaded by its giant host and other moons. When I first read about this, it came to mind that it is no longer necessary for a planet to be within a Goldilocks band around the Sun in order to obtain enough heat for life to form and endure. A very remote body could be in Io’s situation and have heat created within itself as a result of gravitational flexing. Now, if instead of Jupiter, a Black Hole was the main host body, then a planet could be flexed in this way for as long as the Hole endures, which is close enough to forever. This is more true the more powerful the gravity of the Hole, and the smaller the planet, so that the orbit of the planet is basically stable. Life could evolve near deep underwater fissures (and some experts think this is where life may have first appeared on Earth.) In Io, the kneading is so intense, that the entire surface is in constant flux and turns over regularly. Life probably could not evolve there, even if there was water. But I had never thought that Io’s geothermal energy would run out, I had assumed that it would go on for as long as it was a satellite of Jupiter. Am I wrong in this? Myles325a (talk) 04:36, 9 July 2011 (UTC)[reply]

about the matter said abow:
Jupiter's moon Io, which is extremely active as it is kneaded by its giant host and other moons.let me to say:I am sure existing theories about the formation of planets in solar system might be developed to contain the reason of Io activity and saturns moon volcanic activity , so for titan surface . consider that [[late heavy bombardmant ]] is very poor display for planets and moons molten core . and [[Impact theory for the formation of moon ]] might be developed , excuse me I am studying about them . and I hope to find new results .And I will say them in suitable place.

akbarmohammadzade--78.38.28.3 (talk) 09:30, 10 July 2011 (UTC)[reply]

The supernove makes neutron star and remnant nebula ,any star which changes to black hole , condences to Schwartz shield radius and matter disapiers in any point , that dosenot through the matter to interstellar space , this is diffrence between neutrone star and black hole , neutron star or pulsar is not same to black hole and it send pulses .Ilast said this sentences about them:

I love supernovae for their first brightness as some people suppose them new star , their palpitation such as our heart , and their expanding such as universe , and their rule in our life with sending material of our body" A. mohammadzade somebody used to say something about black holes , I prefer to say about supernovae , the first one is death and being secretary , the second one shows celebrating and brightness , and life .A. mohammadzade — Preceding unsigned comment added by 81.12.40.120 (talk) 20:29, 8 July 2011 (UTC)[reply]

Well, as mohammadzade has put it so poetically "the first one is death and being secretary", You read it here first. I would really like a supernova to take dictation from me. My first note would be "Don't you dare blow up until I am a thousand light years away." Myles325a (talk) 04:39, 9 July 2011 (UTC)[reply]

Estrous vs Menstruation

I've read the Estrous cycle article, and the Menstruation article. The latter is primarily focused on humans, to my disappointment. I have a few questions:

Which appeared first, estrous or menstruation? Do more mammals go through estrous or go through menstruation? Is estrous equally powerful across all species that have it? (example: my female cats became mindless horny robots for ~10 day periods every month or so before they were spayed) Apart from humans, does menstruation not have as strong a mental effect? Why?

Thanks for your help! The Masked Booby (talk) 06:10, 7 July 2011 (UTC)[reply]

Just a spelling note: I think it's going through estrus, not "estrous". Estrous is presumably an adjective. Another one to add to my list of these commonly confused pairs: Mucus/mucous, callus/callous, phosphorus/phosphorous. In every case the second word is an adjective, but commonly misused as a noun. --Trovatore (talk) 23:32, 9 July 2011 (UTC)[reply]

I fixed your Estrous cycle link which was not working. Cuddlyable3 (talk) 07:42, 7 July 2011 (UTC)[reply]

Well, I think it should be oestrous, but I can cope with non-classical spelling. HiLo48 (talk) 00:23, 10 July 2011 (UTC) [reply]

Even in Commonwealth spelling, that's still one too many o's for the noun — should be oestrus (but of course oestrous cycle). --Trovatore (talk) 07:48, 10 July 2011 (UTC)[reply]

After spending the better part of a half hour chasing this, I came up with the following which I added to menstruation: "Though there is some disagreement in definitions between sources, menstruation is generally limited to primates. It is common in simians including Old World monkeys and apes and New World monkey, but variably expressed in prosimians, being completely lacking in strepsirrhine primates and possibly weakly present in tarsiers. Outside the primates it is known only in bats and the elephant shrew, an insectivore.^[1]^[2]^[3]^[4]" I didn't comment on a controversy, running back to 1898, about whether the elephant shrew isn't really menstruating because ovulation occurs at that time (or in a low-grade online source I found, shortly afterward)^[5] Note that aside from the elephant shrew - doubly ambiguous because its taxonomy has also been disputed - all of the menstruators appear to be in Archonta. Wnt (talk) 18:56, 7 July 2011 (UTC)[reply]

checking xray escape from baggage machine

A friend works at an airport, and the other day a passenger had a geiger counter with them them to observe the increased radiation at altitude. He let the staff put it through the xray security machine and it showed a higher reading, no surprise. but then when it was held at the conveyer belt it showed a fluctuating reading when the curtains were moved by baggage coming through.

What device can he use to detect if xrays are getting out? would a digital camera (which detects infrared) also be useful? It would seem that any xrays getting at people would be bad. Polypipe Wrangler (talk) 06:11, 7 July 2011 (UTC)[reply]

He seems to have the right device. If you wanted a movie showing it, you would need a fluoroscope screen. Note that the main danger is to the security guards who stand there all day long, and might want to wear protective clothing. You didn't ask, but the two cures I can think of are either to stop the belt, close the curtains, use the X-ray, then turn the X-rays off and restart the belt, or to make the belt longer with multiple sets of lead curtains. StuRat (talk) 06:37, 7 July 2011 (UTC)[reply]

A Geiger counter responds to any kind of ionising radiation so what came through the curtains may not have been xrays. One can speculate what kind of radioactive trace someone's baggage may have left on the conveyer. I would expect a rubber curtain to be transparent to xrays but it might also act as a diffraction grid. Cuddlyable3 (talk) 07:39, 7 July 2011 (UTC)[reply]

Are they rubber curtains ? What would be the point in those ? I assumed they contained lead or some other heavy element, to act as an X-ray shield. StuRat (talk) 08:12, 7 July 2011 (UTC)[reply]

Yes I was going to say a similar thing, [6] suggests they contain lead. Nil Einne (talk) 08:15, 7 July 2011 (UTC)[reply]

Curtains like these? Cuddlyable3 (talk) 08:35, 7 July 2011 (UTC)[reply]

That photo is of a baggage claim conveyor, not the X-ray machine. The baggage claim conveyor typically connects to some outside area. The rubber curtains are just to keep the cold/hot air out of the building. Rckrone (talk) 15:13, 7 July 2011 (UTC)[reply]

Yes I'm thinking something like [7] or [8]. Unless you work in airport security you only tend to see the smaller ones for hand luggage nowadays from my experience because check in baggage is handled behind the scenes. Nil Einne (talk) 16:13, 9 July 2011 (UTC)[reply]

The proper test for this would be to require TSA employees to wear dosimeters. 99.24.223.58 (talk) 18:42, 8 July 2011 (UTC)[reply]

A dosimeter would be useful, but wouldn't tell you precisely where the radiation leak was. StuRat (talk) 08:39, 10 July 2011 (UTC)[reply]

Electrical Stunning vs Tasers

Can I ask: Is there any fundamental difference in operation and effect between the electrical stunning techniques used on animals pre-slaughter, and the Taser stun-guns used by various police forces?

If the taser is apparently very painful, is the pre-slaughter technique any less painful for the animals? (I've never been tasered, thankfully). Eliyohub (talk) 12:18, 7 July 2011 (UTC)[reply]

The taser is painful because it doesn't kill. However, it is not nearly as painful as it appears to be. We associate tensed muscles with pain. The electrical current causes the muscles to tense up. So, bystanders assume that there is extreme pain. It is actually far less painful than accidentally touching and discharging a CRT (from experience - the CRT knocked me out cold, but the taser was just a sting). In a slaughterhouse that I visited, cow prods give the cows enough of a sting to make them move. It isn't enough to cause them to completely tense up and hit the floor. Before slaughter, the cows had one metal clip attached to an ear and another to a nostril. Then, an extreme amount of current was sent through the cow's brain. The cows didn't tense up or cry out or anything. They went from looking around to being dead on the floor in an instant. So, it is obvious that both the operation and effect are very different. -- kainaw ™ 12:41, 7 July 2011 (UTC)[reply]

Hardest Known Material

So, lonsdaleite is harder than diamond. But... what is the hardest material known to man? 68.48.123.29 (talk) 13:42, 7 July 2011 (UTC)luos[reply]

Diamond is the hardest confirmed naturally occurring substance, but several attempts (i.e. Aggregated diamond nanorods, Rhenium diboride, etc.) have been made to synthetically form a material that is harder. It is hard to say, however, as many of these reports remain unconfirmed. This article may interest you, as it pertains to some very rare substances (including lonsdaleite) w/ similar structures as diamond, but may be much harder due to various reasons. Tyrol5 [Talk] 14:53, 7 July 2011 (UTC)[reply]

Quarkium. Degenerate matter is the densest material in the Universe, so quarkium (which would be to quark stars what neutronium is to neutron stars) would be the most dense. YMMV as to whether this qualifies as "known to man"? -- SmashTheState (talk) 20:09, 7 July 2011 (UTC)[reply]

Dense yes, but hard? You're sure it's not a superfluid? Wnt (talk) 20:20, 7 July 2011 (UTC)[reply]

If we were to use the Mohs hardness scale, then quarkium would easily outmatch any other substance, since attempting to scratch something that dense would be utterly futile. I don't think its state really matters at that density. Although you may be right, the physical properties of something like quarkium are probably wildly bizarre, and I don't have the scientific knowledge to even guess at it. -- SmashTheState (talk) 21:46, 7 July 2011 (UTC)[reply]

The problem is, the conditions under which quarkium exists are conditions under which any matter will be converted to quarkium. (At least, that's my understanding.) If you got a diamond in contact with the quarkium in order to try and scratch it, you wouldn't have a diamond any more. --Tango (talk) 12:06, 8 July 2011 (UTC)[reply]

Depending on how much quarkium you have on Earth, the energies involved in any material attempting to contact it (or even attempting to hold it?) would likely annihalate the entire planet. ~AH1 ^(discuss!) 16:06, 8 July 2011 (UTC)[reply]

At low temperatures diamond is harder than boron nitride, assuming an oxygen atmosphere. 99.24.223.58 (talk) 20:52, 8 July 2011 (UTC)[reply]

Third most important blood property

What is the 3rd most important blood property after blood group and Rh?--188.146.90.106 (talk) 16:21, 7 July 2011 (UTC)[reply]

WHAG here but I'd say it was clotting factor. --TammyMoet (talk) 17:16, 7 July 2011 (UTC)[reply]

I don't think the question is valid. Blood group is practically irrelevant except for the practice of blood transfusion from human donors, which was invented only recently and will probably become obsolete just as quickly. Rh creates a notable fertility problem, yes, but it's only our current level of understanding which makes it important to test in advance. Presently perhaps CCR5-Δ32 is the most important trait, at least in Africa. It shifts over time, and in the long run, perhaps everything is of equal importance in evolution, as otherwise the more important part would receive special attention. Wnt (talk) 19:01, 7 July 2011 (UTC)[reply]

THE most important blood property is its role in transporting nutrients and wastes, right? ←Baseball Bugs ^{What's up, Doc?} carrots→ 20:18, 7 July 2011 (UTC)[reply]

Oxygen/CO2 transportation is much more important.

Hmmm, are we talking simply about characteristics, or about genetically variable traits? My answer concerned the latter. I suppose blood does have specific "purposes" which are indeed more important than others, but these are things which are genetically non-negotiable. Wnt (talk) 22:38, 7 July 2011 (UTC)[reply]

Since blood group and Rh were mentioned, I presume the question refers to properties that determine compatibility. This may be a homework question, but what the hell, I'll answer it anyway: as our Blood transfusion#Compatibility testing article says, once blood type and Rh have been verified, it is important to screen for antibodies that may react with the donor blood. Looie496 (talk) 22:50, 7 July 2011 (UTC)[reply]

"Screening for antibodies" describes all the tests. ABO blood group and Rh blood group are all about antibodies. A, B and Rh are antigens that the person receiving the transfusion may have antibodies to. If they have those antibodies, then the antibodies will attack the blood. The question, therefore, is which antibodies is it the next most important to screen for. --Tango (talk) 12:09, 8 July 2011 (UTC)[reply]

Neither Cross-matching or Blood transfusion seems to mention which antibodies they are testing for. Rmhermen (talk) 13:36, 8 July 2011 (UTC)[reply]

You don't need to test for specific antibodies. You just mix the donor blood with the receiver's blood and watch for a reaction. It doesn't really make any different which antigen in the donor blood is being reacted to. If there is a reaction, then the blood isn't compatible. --Tango (talk) 22:33, 8 July 2011 (UTC)[reply]

Physiology is an interconnected system. This question is like asking which mole in a Whac-A-Mole game is most likely to pop up next. 99.24.223.58 (talk) 20:53, 8 July 2011 (UTC)[reply]

Astronomical observation time

Are there any time corrections being made during Moon/Sun and star observations because of incoming light delay, such as that of 8 minutes in case of the Sun?--188.146.90.106 (talk) 16:26, 7 July 2011 (UTC)[reply]

The timings for regular events (i.e. sunset) are based on actual physical sunset, while sunlight (perceived by humans as the sun itself) is still visible for several minutes due to atmospheric refraction (see image to right). For star observations, however, the timings are determined based on predicted position in the sky (sometimes it can take several millions of years for light to reach Earth, enabling us to "see back in time"). For nearby astronomical objects (i.e. the Moon), the time delay (something like two seconds) is negligible and is not taken into account specifically in determining observational timings. Tyrol5 [Talk] 16:44, 7 July 2011 (UTC)[reply]

I was just reading something neat about that topic - the speed of light was first correctly measured by observations of the moons of Jupiter! It never ceases to amaze me how the invention of lenses opened up so many fields of biology and physics to explosive growth all at once. Wnt (talk) 19:12, 7 July 2011 (UTC)[reply]

The thing is, it doesn't take 8 minutes for "just" the light from the sun to reach us, it takes 8 minutes for ANY information from the sun to reach us. So there's nothing to correct for. From earth, the sun IS on the horizon when we "see" it there, not 8 minutes previous, absolutely no part of the sun is there 8 minutes prior, not the gravity, not the light, not the information, not even any mystical magical "sun" force we haven't discovered yet (well i'm not 100% certain about that one, but call it 99.99% certain) For all we know, the sun might have completely vanished a few minutes ago and it would be completely impossible for us to know until that information reached us, at the speed of light. Vespine (talk) 05:00, 8 July 2011 (UTC)[reply]

Let's say the Sun vanishes exactly at sunset from a given position on Earth with an unobscured western horizon and no refraction. Would we fail to notice the Sun disappearing until it is already no longer visible on the horizon? ~AH1 ^(discuss!) 16:03, 8 July 2011 (UTC)[reply]

i'm no astro physisyst and this really bends my brain.. with the sun 8 minutes away, say it vanishes when it is right on the horizon on earth. Well, the earth will keep rotating for 8 more minutes before the last light reaches it, (light and gravity and everything, that makes me thing of another question, but I'll ask it below).. Now with the sun and the earth that's pretty straight forward, but what about a galaxy 10 billion light years away, but the universe is only 13.75 billion years old, we see that object where it was 3.75 billion years after the big bang, but now we're 10 Billion light years away from it... so we have moved apart 10 Billion light years in 3.75 Billion years? But we're not ACTUALLY 10 billion light years apart, are we? Presumably the ACTUAL distance between us and a galaxy that we see 10 billion light years away is far greater since it has had 10 billion years to move some further distance away? Since the light that we're seeing now originally left.. This is the point where my brain melts down.. Vespine (talk) 02:50, 12 July 2011 (UTC)[reply]

Regarding special relativity and time dilation

Let's say Planet A and Planet B are 100 lightdays apart. A spaceship leaves Planet A and heads to Planet B, travelling at about .99 c (from the relative position of Planet A). While travelling, the spaceship broadcasts a song by radio towards each of the planets.
Now, as I understand it, the following will occur:

The ship will reach Planet B in about 102 days from the viewpoint of Planet A.
The song will be redshifted on Planet A (and thus slowed down), and blueshifted on Planet B (and thus sped up)
Time will pass more slowly on the spaceship, relative to the two planets (although, to the spaceship, time seems to pass normally, and everything else is sped up).

So, the questions I have are:

How long will the journey take relative to the spaceship? (exact figures aren't necessary, just ballpark)
How long will the journey take relative to Planet B? This is what's confusing me the most. So the ship would leave Planet A, and that light would reach Planet B 100 days later, but the ship obviously couldn't then arrive one day later. So time dilation would have the ship move more slowly through time to "correct" this. Err... wait a second, am I answering my own question?

Heh, typing it all out actually made it make more sense. So would it then appear to take about 102 days for the journey from each vantage point (with time dilation affecting the ship)? Also, would the song sent from the ship appear to be the exact same speed to each planet, despite being redshifted for A, and blueshifted for B? I guess my main question is: am I getting this?!
Cheers. --Goodbye Galaxy (talk) 16:30, 7 July 2011 (UTC)[reply]

Not sure about the spaceship's apparent trip duration offhand, but I can answer the others.

If Planets A and B are at rest with respect to each other (you don't specifically say this, but I think it's your intent), then each observes the trip to take the same amount of time. 102 days sounds about right, but I haven't done the math.
Planet B will in fact only see light from the ship's departure a couple days before the ship actually arrives. This is fairly straightforward, since B observes the ship approaching at .99c, moving just behind the light from its departure.
The song will be redshifted towards A and blueshifted towards B. The shifts will be of similar magnitude but opposing direction. Assuming the song is played for the length of the ship's voyage, each planet receives the song over a period of (departure day + transmission lag) to (arrival day + transmission lag). For Planet A, that's Day 0 to Day 202; for Planet B, that's Day 100 to Day 102.

Does that help? — Lomn 18:35, 7 July 2011 (UTC)[reply]

The ship takes 101 days (not 102) to reach planet B from the point of view of either planet.
Calculating the $\gamma \,$ -factor: $\gamma ={\frac {1}{\sqrt {1-{\frac {v^{2}}{c^{2}}}}}}=7.1$
The trip takes ${\frac {100days}{\gamma }}=14days$ from the point of view of the ship. Dauto (talk) 18:39, 7 July 2011 (UTC)[reply]

Hmm... both these response have just made me more confused. Lomn's response doesn't seem right, because if B tracked the ship from its departure, it would see the ship travelling 100 lightdays' distance in two days, which is faster than c, and thus impossible.

Dauto's response confuses me, because it seems the ship would observe itself as approaching B faster than c as well. --Goodbye Galaxy (talk) 19:01, 7 July 2011 (UTC)[reply]

The ship sees itself approaching B at 0.99c. That only takes about 14 days because from the point of view of the ship the distance between the planets is Lorentz contracted to about 14 light-days. Lomn is also right because even though the trip takes 100 days from B's point of view, he sees it happening over only 1 day because of Doppler effect. Dauto (talk) 19:06, 7 July 2011 (UTC)[reply]

To be clear, how long the trip takes from B's point of view, and how long it takes him to observe the trip are different because of time delays due to the finite speed of light (B uses light to observe the trip). Dauto (talk) 19:10, 7 July 2011 (UTC)[reply]

Ah, of course. I forgot that distances are relative as well. I'm still slightly confused about Planet B's point of view. I guess I've been operating under the assumption that no object can even appear to move faster than c, but... I was wrong? (p.s. science is awesome, and thanks for your answers, guys) --Goodbye Galaxy (talk) 19:20, 7 July 2011 (UTC)[reply]

See also superluminal jet, a real-world example. Wnt (talk) 19:31, 7 July 2011 (UTC)[reply]

From the perspective of the "moving" observer, there's a cute unit, the "roddenberry", describing how fast it looks like you're going - alas, we don't have an article on it! Wnt (talk) 19:34, 7 July 2011 (UTC)[reply]

The observers on Planet B know the speed of light and will allow for it. Therefore, then they see the ship leave Planet A, they'll know that it actually left 100 days ago. Therefore, when the ship arrives a day later, they know the trip took 101 days (the people on the ship will disagree, of course). --Tango (talk) 12:13, 8 July 2011 (UTC)[reply]

Weak Interaction - article

Hi, reading the weak interaction article, I have remained with some question ? In quantum physics we have learned that always we have two or more particles with electric charge, they interact exchanging photons and so we have electromagnetic force among them. Also, always we have particles very close, in distances lower to proton diameter, we have strong force interacting based in echanging of gluons among quarks. But I have learned in the article that all fundamental particles have weak isospin that acts as electric charge. So I have two questions: 1. - Do quarks exchange bosons (W+, W-, Z) all the time ? and , or 2. - What conditions cause a down quark decay to up quark since we can´t predict this phenomenon ?

Thanks for all, and my comment is based on fact that it is very difficult to get good explanation about weak interaction for begginers. This article can helps a lot. — Preceding unsigned comment added by Futurengineer (talk • contribs) 17:19, 7 July 2011 (UTC)[reply]

1. Yes, quarks do exchange virtual (W+, W-, Z) all the time.

2. The decay is completely random. no special condition is required.

Dauto (talk) 18:29, 7 July 2011 (UTC)[reply]

You may also be interested in strangeness and charm. ~AH1 ^(discuss!) 15:54, 8 July 2011 (UTC)[reply]

Orbits after central mass changes

Can't quite figure out how to approach this. Some satellites are in circular orbits around the Earth. Suddenly the mass of the Earth doubles. What happens to the orbits of the satellites? Twang (talk) 19:07, 7 July 2011 (UTC)[reply]

It becomes elliptic with the satellite at the apogee. Dauto (talk) 19:15, 7 July 2011 (UTC)[reply]

We could also be more rigorous in defining the behavior if you can elaborate on the meaning of "suddenly." Even if the change is (theoretically) instantaneous, the branch of classical mechanics called continuum mechanics elucidates the mathematical procedures you would need to use to model an instantaneous change of mass, based on where the mass came from and how it distributed itself. I'm thinking about an "accretion process" where the mass accretes on a time-scale much faster than the orbital time-scale. Gauss's law for gravity may also help you identify the conceptual behavior for this thought experiment. Nimur (talk) 20:09, 7 July 2011 (UTC)[reply]

Let's try simpler: Given a planet with mass M, and a satellite in circular orbit with radius r. How to find r for a satellite with the same kinetic energy orbiting a planet with mass 2M. (Actually matter accretion is what got me thinking about it, but not trying to build a computer model, just trying to get a handle on what's involved ... I don't really grok orbital mechanics.)Twang (talk) 22:14, 7 July 2011 (UTC)[reply]

If I recall correctly, a satellite in circular orbit has one-half the kinetic energy it needs to achieve escape velocity, i.e. to reach zero gravitational potential energy. Gravitational potential energy is negative and proportional to m₁m₂/r. Since the kinetic energy remains the same, the gravitational potential energy needs to be the same, which means if you double m2 you need to double r. So if you double the planet's mass, the satellite needs to be twice as far out to orbit at the same leisurely speed as before. To put this another way, the orbital period of a satellite with a given semi-major axis will decrease according to the square root of the central mass. Wnt (talk) 22:49, 7 July 2011 (UTC)[reply]

That's a helpful thought. This page [9] on Earth-orbit velocity shows that the orbital velocity decreases with increasing radius. But then, the centripetal force law [10] is Fc=mv^2/r, so if Fc doubles, either r is halved, or v increases by 1.414 ... probably some combination of the two... which is Dauto's line. Imagine a weight twirled in a circle at the end of a rubber band; if the elasticity of the band suddenly increases, the weight's "orbit" would be elongated, and probably precesses depending (as Nimur suggests) on what "sudden" means. I'll hit the books - thanks folks.Twang (talk) 05:03, 9 July 2011 (UTC)[reply]

Why do so many adult males like my little pony?

Question moved to Wikipedia:Reference desk/Entertainment

Genetics of garden flower colours

Some garden flower species can have a variety of different coloured flowers. I have some Hollyhocks, Alcea rosea, in my garden with each plant having flowers of a particular colour. What are the chances of their seeds producing plants with flowers the same colour? Is anything known about the dominance or recessiveness of the genes for flower colour? 92.28.254.38 (talk) 21:00, 7 July 2011 (UTC)[reply]

I think you'll find as much variety in flower color genetics as in any other area of genetics. So, if you have parents of two different colors, you may have a strict dominant-recessive relationship, where 3/4 of offsprings' flowers are the dominant color and 1/4 are the recessive, or some other ratio, if it's a multi-gene interaction, or perhaps you'll get a blended or variegated variety where there isn't a dominance-recessive relationship. StuRat (talk) 21:22, 7 July 2011 (UTC)[reply]

Question about the sun

It's acknowledged that a human couldn't survive long on the Sun not to mention Earth itself. My question is since Jupiter and Saturn are bigger than any of the other planets in our solar system, if the Sun were to consume Jupiter and Saturn, how long would it take for the sun's heat to vanquish the two planets? My question applies to both if the sun were to swallow them at the same time or subsequently, by the way. SwisterTwister talk 23:08, 7 July 2011 (UTC)[reply]

As our Roche limit article explains (although not very understandably), a planet such as Jupiter or Saturn could not even reach the Sun before being torn apart by tidal forces -- so they would be "vanquished" before they even got to the heat. Looie496 (talk) 23:18, 7 July 2011 (UTC)[reply]

I'll explain if the article is insufficient: basically, we know that the closer an object is to the Sun, the faster it completes one revolution around the Sun. This is due to the stronger pull of gravity the closer you get to the Sun. Therefore, if you think about a planet as a 3-d sphere instead of a point mass, you will realize that the point closest to the Sun on a planet will be pulled slightly harder than a point on the far side, leading to internal stresses within the planet. Now, for a faraway and small planet like Earth, the stress is not nearly enough to overcome the gravitational pull holding the Earth together. However, as you get closer and closer to a heavy body (like the Sun in this example), the gravitational force is increasing more and more rapidly, and the difference in forces between the near and far side of the planet get greater and greater. At some point, the difference in gravitational force will be too much for the planet to bear, and it will break apart into smaller pieces. The point at which this happens is called the Roche limit.

See, astrophysics doesn't have to be scary! -RunningOnBrains^(talk) 23:26, 7 July 2011 (UTC)[reply]

The Roche limit varies as a function of density and as the lighter outer layers of the planets are removed the average density of the planet would increase eventually becoming high enough to stop the disintegration (That would only be true for the rocky core likely present at the center of those planets). Dauto (talk) 02:01, 8 July 2011 (UTC)[reply]

But suppose you used duct tape to secure all the surface of the planet before you sent it towards the Sun? Myles325a (talk) 06:38, 8 July 2011 (UTC)[reply]

Even if Jupiter and Saturn had a surface, duct tape would have a negligible effect compared to the gravitational forces involved. There are some things that even duct tape cannot fix.--Shantavira|^{feed me} 07:28, 8 July 2011 (UTC)[reply]

What if the duct tape is made of Quarkium? (See a section farther up the page). As regards the concept of duct-taping Jupiter and Saturn, that's a funny mental picture. Where's Red Green when you need him? :) ←Baseball Bugs ^{What's up, Doc?} carrots→ 08:29, 8 July 2011 (UTC)[reply]

Well, if you used quarkium duct tape, then the tape might not fail, but the glue still would. Googlemeister (talk) 15:46, 8 July 2011 (UTC)[reply]

Some simulations suggest that the Sun's final transition to planetary nebula will blow off the outer gaseous atmosphere of Jupiter and Saturn, although Saturn's rings may have collapsed by then. ~AH1 ^(discuss!) 15:47, 8 July 2011 (UTC)[reply]

July 8

Climate in Kuwait

I have a friend living in Kuwait City, which is currently experiencing temperatures bordering on 50 degrees celsius. Where does this place rank globally in terms of summertime maximum and average temperatures? I've never heard of a place this hot. Thanks. 49.185.136.107 (talk) 03:04, 8 July 2011 (UTC)[reply]

It ranks pretty high, but there are many spots in that region that frequently reach similar temperatures in midsummer. The average temperatures are actually a lot lower, because the dryness and lack of vegetation produce a lot of cooling during the night. For what it's worth, the hottest place on Earth, in terms of average temperature, is said to be the Afar Depression in Ethiopa -- not all that far away from Kuwait. Looie496 (talk) 03:29, 8 July 2011 (UTC)[reply]

See Climate of Kuwait. The hottest recorded temperature in Kuwait was 52.6°C in Abdaly, on June 15, 2010[11]. ~AH1 ^(discuss!) 15:44, 8 July 2011 (UTC)[reply]

Nuclear reticulum

Is nuclear reticulum same as Nuclear lamina? --111Engo (talk) 04:07, 8 July 2011 (UTC)[reply]

No, the nuclear lamina is the meshwork of proteins adjacent the phospholipd nuclear membrane. The nuclear reticulum is a term used to refer to a network like pattern seen in the nucleus. Depending on the context it may be the

the pattern of chromatin when it is stained
the distribution of ribonucleoproteins seen by immunostaining .
the tubules and vesicles formed by the nuclear membrane protruding into the centre of the nucleus.(think of this as an endoplasmic reticulum) in the nucleus.

(maybe the nuclear architecture article needs updating?)Staticd (talk) 07:57, 8 July 2011 (UTC)[reply]

Hello, a question about the article "Wilson's disease"

it says (in the part; "nutrition"); "In general, a diet low in copper-containing foods is recommended, with the avoidance of mushrooms, nuts, chocolate, dried fruit, liver, and shellfish".[1]

my Q;

Nuts, what kind of nuts?, and also, organic for example also contain copper?.

and mushrooms, what kind?.

BTW, is it true that some plants organically contain copper? — Preceding unsigned comment added by 79.182.28.217 (talk) 07:31, 8 July 2011 (UTC)[reply]

All plants contain copper as it is part of many essential enzymes. However the levels vary depending on the species, the part and how it was grown. Regarding what foods to avoid, that would be medical advice, you would have to ask a doctor. It's taboo to offer it here. :). Staticd (talk) 08:01, 8 July 2011 (UTC)[reply]

It's a little bit late telling the OP we can't help with dietary recommendations, when those he listed above came straight from Wikipedia anyway. Even the title of this section says the question is about the Wilson's disease article just as much as the disease itself. And that list of foods to avoid IS questionable, including, as it does, nuts. That's such a catch-all category of foods in English. It includes things as diverse as peanuts, pistachios, walnuts and macadamias. To assign a common characteristic to them all is not very scientific. Given what the OP has already garnered from Wikipedia, I think anyone who can is almost obliged to help clarify further. HiLo48 (talk) 09:07, 8 July 2011 (UTC)[reply]

The book Wilson's disease: a clinician's guide to recognition, diagnosis, and management, (from 2001 though) suggests that diet isn't important apart from liver and shellfish which can be significantly high in copper. See page 73. Sean.hoyland - talk 10:25, 8 July 2011 (UTC)[reply]

Electric Power

IN DIRECT CURRENT,flow of electron is continues i.e.,from negative terminal to positive terminal.but in ALTERNATING CURRENT, electron moves forward and again backward but does not move from negative terminal to the positive terminal so that only current wave travel like when we throw a stone in a river then wave only travels not the water particle. is it true or not. PLEASE GIVE ME BRIEF DETAIL ABOUT ELECTRON FLOW IN A.Cvsnkumar (talk) 12:20, 8 July 2011 (UTC)[reply]

Have a look at Alternating current and Wave. Dolphin (t) 12:44, 8 July 2011 (UTC)[reply]

You seem to have the right idea. For both AC and DC, it is the movement of the charges ("current") that matters, not where they end up. In AC, electrons move into the terminals and out of them again. The electrons do work on the load both when they move in and when they move out. --Srleffler (talk) 17:31, 8 July 2011 (UTC)[reply]

Electric power2

I put a Electric tester in a socket's neutral,it shows zero voltage.we know that Alternating current is a sinusoidal.i.e.,for positive cycle it travels in one direction and for negative half cycle it travel in opposite direction.according to this,is phase and neutral reverses for every cycle in a socket or not? if not how electrons flow in a conductor for A.C. Also in d.c, please give me brief detail about electron flow in a.c according to my questionvsnkumar (talk) 12:23, 8 July 2011 (UTC)[reply]

Have a look at Alternating current. Dolphin (t) 12:46, 8 July 2011 (UTC)[reply]

The electrons flow into and out of both the live and neutral sockets, however this flow is driven by the live socket. The electric field in the live socket pushes electrons into the wire and pulls them out of it. The flow of electrons into and out of the wire pushes and pulls electrons along the whole length of the wire, through the connected device, and back up the wire to the neutral socket. This pushes electrons into the neutral socket and pulls them out of it, on alternating halves of the cycle.--Srleffler (talk) 17:35, 8 July 2011 (UTC)[reply]

Inertial mass, again

This is based on a question I asked earlier.

E=mc² means that the potential energy between particles will manifest as mass. But if the potential energy function is defined up to a constant, then shouldn't the mass of this potential energy likewise be not uniquely determined? What would the actual mass be? — Preceding unsigned comment added by 74.15.136.219 (talk) 15:25, 8 July 2011 (UTC)[reply]

In relativity, unlike in classical mechanics, energy isn't defined up to a constant. (just like classically, temperature was only defined up to a constant (calcius, farenheit) but now we know better and have an absolute scale (kelvin) ). 213.49.89.68 (talk) 15:32, 8 July 2011 (UTC)[reply]

Could you clarify this a bit? Why won't potential energy in SR be defined up to a constant? Where does the constant go, mathematically? 74.15.136.219 (talk) 05:10, 9 July 2011 (UTC)[reply]

The constant is absorbed into the definition of the rest mass. Dauto (talk) 14:10, 9 July 2011 (UTC)[reply]

Why? 74.15.136.219 (talk) 21:22, 9 July 2011 (UTC)[reply]

Because that constant, unlike in non-relativistic mechanics, has real measurable effects such as inertia and gravity. Dauto (talk) 14:28, 10 July 2011 (UTC)[reply]

Okay, thanks. 74.15.136.219 (talk) 14:56, 10 July 2011 (UTC)[reply]

The flagpole experiment

Hi. Imagine about two dozen people gathered arms stretched out, holding hands in a circle centred on a flagpole. Simultaneously, all the participants run toward the centre of the flagpole, keeping their arms streched out. What would occur in this instance? Would the people start rotating in a circle? If this is the case, in what direction would the rotation most likely be psychologically? Would the same occur of all the people were running outwards or facing inwards and running backwards? What would be the average speed of the revolution? Thanks. ~AH1 ^(discuss!) 15:34, 8 July 2011 (UTC)[reply]

Well if they must keep their arms stretched out and if they are not allowed to change the angle of their arms, then the circle will somehow be broken. I don't see how motion towards the center of a circle will translate into a rotation in this scenario. Googlemeister (talk) 15:44, 8 July 2011 (UTC)[reply]

Same response: arms outstretched equals an impossibility as zeroing in on the flagpole progresses beyond a certain degree. But I don't think rotation of the group around the flagpole has to take place. Bus stop (talk) 15:47, 8 July 2011 (UTC)[reply]

I see people falling over but no general rotation. The circle ceases to be a circle as the stronger push aside the weaker. One person reaches the flagpole, though the center of the flagpole is out of reach. In the case of running away from the flagpole the pair of hands with the weakest hold break first. If every runner follows exactly a radial from the flagpole, all the handholds have to break. In any practical experiment some handholds will last longer than others as runners veer off course. Cuddlyable3 (talk) 17:29, 8 July 2011 (UTC)[reply]

If all 12 are of identical strength, I would think they would end up simply running in place. I don't know why they would run in a circle. Now, if they've just been pinged with pixie dust or something, perhaps they'll shrink as they get closer to the flagpole, proportional to their distance from it. ←Baseball Bugs ^{What's up, Doc?} carrots→ 12:34, 9 July 2011 (UTC)[reply]

In the inscrutable way of Wikipedia, Pixie dust links to an article about Tinker Bell who is featured in the opening of all Disney films flying over the Magic Castle (in a counter-clockwise direction, right to left). Such an overflight could create a vortex that sweeps the runners in a circle. Cuddlyable3 (talk) 16:15, 9 July 2011 (UTC)[reply]

Suppose that all the runners start by running in place, before a few of them gain momentum in a certain direction around the flagpole rather than any straight-line velocity relative to it, thus pulling all the other runners around in that particular direction. Iff this were to be the case, in which direction is the rotational movement more likely (50%+) to occur? I was imagining it as a movement that had forces similar to orbital mechanics, in which the "pull" toward the "centre" (i.e. "gravity") and the resulting inward centripetal acceleration (caused both by the running toward the centre and the linking of arms) exactly balances out the outward tangential acceleration (imparted by the vector momentum, which is the force I am asking for whether it would result from this theoretical set-up).

Another way to imagine the situation would be to suppose the runners are all holding onto a single rope instead of holding hands, arms outstreched. Of course, in this scenario the rope would quickly lose its tension and a messy situation would occur. Instead of a rope, however imagine that the circular shape is maintained by compression, which may or may not require a tremendous amount of effort to keep the arms outstreched. (If it helps, suppose that everyone runs in a 30° angle relative to the centre) Now, say there is enough momentum early on in the running, so that less overall compressional force is required to maintain the circular shape. Could this work? ~AH1 ^(discuss!) 18:03, 9 July 2011 (UTC)[reply]

Somehow I missed the radial comment. Would the circle break only owing to the irregularities between the strengths of the runners? ~AH1 ^(discuss!) 18:07, 9 July 2011 (UTC)[reply]

Plant identification

While out chopping down burdocks from the roadside (they get in the dog's fur when on walks), I saw a bunch of these. Can anyone identify them? The pic was taken in Vermont and just a few minutes ago. Dismas|^(talk) 16:06, 8 July 2011 (UTC)[reply]

I think it's wild grape. We had some in my back yard as a kid in Connecticut. -RunningOnBrains^(talk) 17:16, 8 July 2011 (UTC)[reply]

I don't think it is a grape, wild or tame, because the leaf stalks appear to come from a central point which is not a characteristic of a grape which grows leaves along a rambling stem. It looks like it might be petasites, more commonly known as butterbur, specifically the white butterbur (petasites albus). The temperate geographical zone is right. Certain identification is always difficult until one can see the flower and/or the whole mature plant. Richard Avery (talk) 17:53, 8 July 2011 (UTC)[reply]

Let it be known that I am by no means a plant expert, so I default to Richard Avery's assessment. The leaves just looked very similar to what I remembered (and the website I saw). -RunningOnBrains^(talk) 18:27, 8 July 2011 (UTC)[reply]

I don't remember ever seeing them bloom (they do a decent job of cutting down the weeds on the roadsides around here) but I think Richard has it. These don't have any tendrils like the grapes do. So, White Butterbur it is then! Thanks, Dismas|^(talk) 21:40, 8 July 2011 (UTC)[reply]

It's a vine, though, right? In which case, it would be something else (could be a few things). Juliancolton (talk) 21:05, 12 July 2011 (UTC)[reply]

is using a whiteboard and markers a health hazard?

Is using a whiteboard and whiteboard markers a health hazard? (cancerous, small particles into lungs, etc etc). Not asking for medical advice. 188.29.193.67 (talk) 16:19, 8 July 2011 (UTC)[reply]

I'm not sure about small particles. The pigment solvent you are asking about is mostly harmless. I hope it was tested on laboratory animals. Are white board users acting strange? Remind them not to concentrate or inhale the solvent. If the concentration is such as to cause a headache or euphoria, move to a well-ventilated area. This is not medical advice. 99.24.223.58 (talk) 18:24, 8 July 2011 (UTC)[reply]

I noticed that some brands make me light-headed, while others do not. StuRat (talk) 04:46, 9 July 2011 (UTC)[reply]

The brands that don't make you light-headed are the water-based ones. They're the ones I'd recommend. --TammyMoet (talk) 07:47, 9 July 2011 (UTC)[reply]

So, when, as a teacher, I'm having a bad day with the little darlings, they're the ones to avoid, right? ;-) HiLo48 (talk) 07:53, 9 July 2011 (UTC) [reply]

An Interactive whiteboard is a chemical-free gimmicky alternative. Cuddlyable3 (talk) 08:13, 9 July 2011 (UTC)[reply]

Radio waves

Do radio waves have angular momentum? This is unclear. Cuddlyable3 (talk) 16:57, 8 July 2011 (UTC)[reply]

Yes. Not that I have any idea what that means: Photon_polarization#Angular_momentum_density_of_classical_electromagnetic_waves. -RunningOnBrains^(talk) 17:12, 8 July 2011 (UTC)[reply]

Every photon carries a momentum equal to Planck's constant. So radio waves actually carry much more angular momentum than an equivalent mass-energy of visible light. Wnt (talk) 19:16, 8 July 2011 (UTC)[reply]

Does the angular momentum of light from the Sun cause a Solar sail to rotate?
I assume an electromagnetic wave gets angular momentum from its source. Can a transmitter rotating at a certain speed emit a radio wave with zero angular momentum?
The Sun is a rotating omnidirectional radiator. Does that mean that a solar sailor could navigate by measuring his angular acceleration relative to the fixed stars?

Cuddlyable3 (talk) 07:38, 9 July 2011 (UTC)[reply]

Only circular polarized waves will carry a bulk angular momentum. Light from the sun is not very polarized on average. Graeme Bartlett (talk) 09:15, 9 July 2011 (UTC)[reply]

So far as I know, each photon must carry an identical Planck constant angular momentum - the only question is whether it is one way or the other (and whether quantum weirdness means we don't yet know which). So any overall transfer of momentum is a statistical effect based on the degree of overall circular polarization of the light. I don't know the relationship between rotation of the emitter and rotation of the emitted light - but note that the rotation of any given atom in the Sun at a given moment is really very slow. Wnt (talk) 15:48, 9 July 2011 (UTC)[reply]

In addition to the spin angular momentum that other replies are referring to, a photon obviously carries angular momentum due to its linear momentum, ${\vec {L}}={\vec {r}}\times {\vec {p}}$ , with ${\vec {r}}$ being the position of the photon (relative to the origin of your choice), and ${\vec {p}}$ being the linear momentum.

Regarding spin angular momentum, its directly measurable projection (see spin (physics) for details) is $\pm \hbar =\pm {\frac {h}{2\pi }}$ , where $h$ is Planck's constant (and the $\hbar$ or "h-bar" is called the reduced Planck's constant). The absolute value of the spin angular momentum is $\hbar {\sqrt {2}}$ .

Regarding the solar sail, the reflected light wouldn't transfer its spin angular momentum onto the sail, only the absorbed light. If you would have a highly polarized light source (unlike the Sun), you might be able to see a rotation from the absorption of a large amount of the light. I don't quite understand how you want to navigate around the Sun by measuring the angular acceleration - the Sun is not a source of polarized light, but you might have heard of the Sun's magnetic field and the Zeeman effect, which produces a bit of polarized light, but only at certain frequencies at certain spots on the surface of the Sun (sunspots occur due to strong magnetic fields). Icek (talk) 18:15, 9 July 2011 (UTC)[reply]

Current plan for NASA

What is the current (perhaps read yet-to-be-cancelled) plan for NASA that isn't cancelled? I know there used to be Constellation, but that is no longer. 20.137.18.50 (talk) 17:57, 8 July 2011 (UTC)[reply]

For human space flight, robots to clear the dangerous Low earth orbit#Space debris. Those can probably be similar to the robots which weld asteroids together for shielding from cosmic radiation on extended trips outside the LEO's Van Allen belts. The most cost effective James Webb Space Telescope replacement is a far side lunar cryostat cooled infrared VLBI array capable of detecting exoplanet ozone and the first two infrared spectral lines of hydrogen. 99.24.223.58 (talk) 18:11, 8 July 2011 (UTC)[reply]

The Space Launch System is the current project filling the role of the now-cancelled Ares rocket. Note that, like Ares, it is a Shuttle-Derived Launch Vehicle. Similarly, Constellation's Orion capsule has morphed into the Multi-Purpose Crew Vehicle program. — Lomn 18:20, 8 July 2011 (UTC)[reply]

Last I heard, the MPCV reentry testing was scheduled for 2013. Is that still on? 99.24.223.58 (talk) 18:26, 8 July 2011 (UTC)[reply]

Also, is NASA going to do a synthetic fuel demonstration? I'd love to see that. 99.24.223.58 (talk) 20:14, 8 July 2011 (UTC)[reply]

There's sometimes a very easy way to answer questions like the OP's. Just yesterday I went to nasa.gov, and on the very first screen was a button labelled What's next? Suggest you look there. HiLo48 (talk) 23:14, 8 July 2011 (UTC)[reply]

Another good question is what is NASA's track record for programs accomplishing the goals they set out to accomplish before the projects get canceled. 76.27.175.80 (talk) 00:50, 9 July 2011 (UTC)[reply]

That depends on what you think the goals are, and I suspect the goals might be far more advanced than what most people think they are. 99.24.223.58 (talk) 01:49, 9 July 2011 (UTC)[reply]

You mean programs don't by habit have specific, measurable, objective goals stated outright with time tables such as "we will put a man on the moon by the end of this decade" (though of course not always as big)? How many times has NASA themselves said "we will do X within Y years" and made it? That's what I'd like to know.76.27.175.80 (talk) 02:08, 9 July 2011 (UTC)[reply]

They do that all the time, but nobody notices when they achieve something early or cancel it because it's no longer necessary. 99.24.223.58 (talk) 10:06, 9 July 2011 (UTC)[reply]

"They do that all the time" great! Then I'd just be pleased to see the cold hard numbers out of curiosity. What baseball fan would be satisfied with "Babe Ruth hits home runs all the time!"?76.27.175.80 (talk) 12:06, 9 July 2011 (UTC)[reply]

Budget cuts, budget cuts, budget cuts. ~AH1 ^(discuss!) 02:21, 9 July 2011 (UTC)[reply]

Meanwhile, other nations move on and leave us behind, with our visionless bean counters. The only thing bean counters ever invented was double-entry bookkeeping. ←Baseball Bugs ^{What's up, Doc?} carrots→ 12:30, 9 July 2011 (UTC)[reply]

Haven't the actual decisions to cut budgets and cancel major projects been ultimately made largely by politicians, rather than the bean counters? HiLo48 (talk) 18:23, 9 July 2011 (UTC)[reply]

Seeing how often they get the rug pulled out from them or how often they can chew what they bite off--it's all valuable information in seeing how functional or dysfunctional the complete system is at being able to do what it says it wants to do. 76.27.175.80 (talk) 18:29, 9 July 2011 (UTC)[reply]

There's a factor that may make your assessment somewhat difficult. Much of what they have wanted to do at any given time has never been done before, by anybody, anywhere. It's a lot harder to predict than if one is building say roads or houses. From experience, not with NASA but in a couple of other bleeding edge endeavours, that factor really confounds the bean counters. HiLo48 (talk) 02:29, 10 July 2011 (UTC)[reply]

Does special relativistic length contraction "hide" matter?

I get that if something is travelling at the speed of light (relative to you), it has zero length in the direction of travel. But does that mean that there could be complex, large objects that are "collapsed" out of sight because they are travelling too quickly for you to see? I guess I don't understand whether photons are the only things that travel at the speed of light, and how it is that we can "see" photons if they have zero length. johnpseudo 18:47, 8 July 2011 (UTC)[reply]

We don't see photons! We see other things, by way of the photons they emit or reflect. Photons themselves are invisible, because (barring extremely minor quibbles) they neither scatter nor emit photons. --Trovatore (talk) 22:57, 8 July 2011 (UTC)[reply]

Nonsense. Photons are all that we do see. Everything else is inferred. Photons that don't hit your retina are invisible, of course, but you wouldn't say "we don't taste salt" just because most salt never enters your mouth. -- BenRG (talk) 00:44, 9 July 2011 (UTC)[reply]

The claim that "photons are all we do see" is incorrect. Right now I see, for example, my keyboard. My keyboard is not made of photons.

CCDs are one technology that captures and records data collections of photons. ~AH1 ^(discuss!) 02:25, 9 July 2011 (UTC)[reply]

So what? I wasn't talking about recording the incidence of photons. I was talking about seeing. Seeing is something that people and animals do, and what they do it to is not so much photons, as the cause of the disturbance of the photons. The seen thing might even be indicated by an absence of photons, rather than their presence (you see a shadow, for example).

As I say, it's a linguistic point. This is what the word see standardly means in English, and what it has meant for various centuries, long before anyone knew anything about photons. I won't disagree that people also generally understand what you mean if you say you see a photon, but this is a secondary and subordinate usage; the principal usage is the one I'm explaining. --Trovatore (talk) 02:47, 9 July 2011 (UTC)[reply]

This is a linguistic point, of course, not a physical one. Nevertheless I think I have a very good argument here. When a photon hits your retina, you do not see the photon (if you did, what shape was it?) You see what caused the photon to enter your eye. --Trovatore (talk) 00:51, 9 July 2011 (UTC)[reply]

The thing is, when talking about relativity and cosmology it's really important to understand that we don't have a sense that directly perceives a 3D external world, that what the eye actually detects is light that is local to us. Everybody knows that in a Socratic sense, but they often don't think about it unless you point it out, and this is a cause of a lot of misunderstanding and confusion about relativity. Even the fact that for fifty-five years no physicist realized that length contraction can't be seen is probably attributable to this unconscious prejudice.

I said below that a moving observer will see the face of the cube as a trapezoidal shape with curved edges. The cube itself isn't physically distorted in that way; the only thing distorted in that way is the observer's field of view, which is an abstraction of the image formed on the retina. (Or CCD.) I think that's a reasonable and natural use of the word "see". -- BenRG (talk) 20:07, 9 July 2011 (UTC)[reply]

Quite so. You see the distorted cube that isn't really there in any sense of the word. What you do not see, however, is the photons. You se the abstract, not-quite-existent object that you infer from the photons. --Trovatore (talk) 21:20, 9 July 2011 (UTC)[reply]

Well, the classical approximation is either that a photon is a point particle with zero length, width, and breadth; or else that it is a wave that diffuses out for some distance in all directions. Quantum mechanics combines this in particle-wave duality. But the point is, the probability distribution or waveform of the photon isn't compressed down to nothing, because there's an uncertainty in the time when it was emitted, not just a physical length. Though the difference between these might be interesting to consider... for example, I suppose a particle of slow light, crawling through a medium at some few km/h, must be much more compressed from front to back than it is in free space. Odd... Wnt (talk) 19:15, 8 July 2011 (UTC)[reply]

Also, to answer your other question, nothing with mass can ever reach the speed of light, where it would theoretically have zero length in a "stationary" rest frame, since it would take an infinite amount of energy to do so. If you managed to somehow accelerate a macroscopic object to near the speed of light (impossible with today's technology), it would appear massively distorted (shrunk) in the direction of travel, but all scales would be affected; even down to the atoms themselves. No matter is "hidden". You might be interested in the ladder paradox.-RunningOnBrains^(talk) 19:37, 8 July 2011 (UTC)[reply]

Don't confuse the Lorentz contraction with the actual visual appearance of the object. That (to the extent that you'd have time to see it) is different, because light reaching you from different parts of the object was reflected at different times (in your inertial coordinate system).

An approximation is to say that the object appears rotated, rather than shrunk. I am not sure how well "rotated" really captures the exact distortions involved. We should probably have an article on this, if we don't. Here is the classic paper on the subject. --Trovatore (talk) 22:02, 8 July 2011 (UTC)[reply]

Although that is the classic paper, in the sense that it's the one that everyone cites, I think it does a poor job of explaining the situation. It uses two objects at the same location but moving at different speeds, and a single stationary observer. It's much easier if you use a single stationary object and two observers. Then it's easy to see that the two observers will see the same view of the object, because their eyes receive the same light. If the object is a cube, then there is a region of space which is only reached by light from one face, and if they are in that region of space then they will both see only that face. They won't both see it as square, because of the aberration of light. But relativistic aberration is conformal (preserves angles), so they will both see 90° angles at the four corners of the shape they do see. Conformal transformations also preserve circles, so if you draw a circle on the face that touches the four edges, both observers will see it as a circle touching all four edges. This gives you an idea of the limits of the distortion introduced by aberration. There's no way it can "length contract" the square, for example, because you can't draw a circle inside a narrow rectangle that touches all four edges. In fact what you get is a trapezoid-like shape, with curved edges that meet at 90° angles. All of this is true even if the object is close by, contrary to Weisskopf's analysis which only works when it's far away.

So why does Weisskopf say that the object is rotated? Because he's treating the two objects as coincident when the emit the light, while I'm treating the observers as coincident when they receive the light, and these aren't the same thing. If you split Weisskopf's observer into two separate observers in two separate experiments, each with one object, and boost so that both objects are at rest in the same place, the observers aren't in the same place when they receive the light, so they really are seeing the object from different angles (in addition to the distortion introduced by aberration).

The behavior in the speed-of-light limit depends on how you take the limit. If you do it Weisskopf-style, with the object suddenly accelerating to high speed, you see a highly redshifted and slightly distorted square of pretty much the same size as before. It may be redshifted out of detectability, though. It doesn't shrink away, but does fade away. If you take the limit my style, with the observer accelerating to high speed, the object shrinks to a point (the headlight effect), blueshifts, and actually gets brighter overall. It shrinks away, but doesn't fade away. So this question has no easy answer; it depends on how you set it up. -- BenRG (talk) 00:44, 9 July 2011 (UTC)[reply]

Picture quality in digital cameras

Which factors are the most important to choose? I know that the MBs are only secondary, and that the lens is probably the most important, but what else should I choose? Wikiweek (talk) 21:53, 8 July 2011 (UTC)[reply]

That depends almost entirely on what you intend to use it for. --Tango (talk) 22:43, 8 July 2011 (UTC)[reply]

Are you asking, perchance, that you should obtain a camera which is not also a cell phone? I can not say. 99.24.223.58 (talk) 23:46, 8 July 2011 (UTC)[reply]

I know that cell-phone cameras are horrible. I intend to use the camera for making pictures, I don't know what are other options. Wikiweek (talk) 00:24, 9 July 2011 (UTC)[reply]

For sensors of a given generation, the single biggest impact on image quality is pixel density: a big sensor with a small megapixel count will produce a better image than a small sensor with a high count. Larger sensors in general do better than smaller ones because of this. --Carnildo (talk) 00:32, 9 July 2011 (UTC)[reply]

See Image sensor format. As mentioned, bigger is generally better (though also gives a bigger camera, and costs more). Buddy431 (talk) 04:59, 9 July 2011 (UTC)[reply]

Wikiweek, Tango was asking you what type of pictures you intend to take and what type of quality you require. Landscape, portrait, action, low light snap shot, macro? Do you plan on using a tripod? This makes a fairly big difference in what factors to consider. I'm sure many people here could recommend a particular camera or camera type if you were specific about your plans for use or tell you which stats are more important. When people who don't know much about photography ask me what camera to buy, I tend to just recommend the Canon S95, it is a decent all around camera although it isn't all that cheap. --Daniel 05:10, 9 July 2011 (UTC)[reply]

Do you intend to go out for the specific purpose of making photographs? In that case consider an SLR; with a few objectives this can get pretty expensive though. If you don't know if photography will be an active hobby for you, a point-and-shoot camera that you always have with you gets better photographs than a bulky SLR you left at home. For a first camera I'd suggest a point-and-shoot; even if you get an SLR later you can have a camera in your pocket whenever you go out the door. I bought my point-and-shoot by looking at photography magazines' "editor's choice" lists - google will be your friend there. 88.112.59.31 (talk) 10:37, 9 July 2011 (UTC)[reply]

To clarify (the last poster geolocates to Finnland): The Finnish term "objektiiv" translates as "lens".

OR only: A year ago, when I considered the option of taking up photography after a break of 25 years (in the last millennium we had analogue cameras:) I invested into a bridge camera, a pre-loved Lumix costing EUR 250. My prime purpose was to find out if a) I could still "see" a scene and b) to "learn" the required new tricks which are available with digital cameras. This is a step up from the above mentioned P&S boxes, but it was important to me to be able to control aperture / shutter speed and ISO manually. I still use this camera (having purchased in the mean time a DX camera and a few lenses at an initial outlay of approximately EUR 2 000) as a "note pad".

As has been stated above, photography is a vast field and it depends on what are your interests. Architecture / landscape / animals / insects / humans / stage work / sports / photography as a basis for graphic work / etc ad infinitum. The required equipment will vary accordingly.

Amongst many other sites, you may be interested in this website, which has numerous reviews on cameras and lenses.

As you state correctly, an excellent lens (which costs a whack, if you want a measly three) is desirable for IQ / image quality. However, kit lenses may be adequate for learning and - if you want to work with manual control - "old" lenses of high optical performance can be obtained at surprisingly good prices.

If you want to go the whole hog and invest in full-frame digital SLR cameras, you will require a better nourished piggy bank. Good luck! --Cookatoo.ergo.ZooM (talk) 18:30, 9 July 2011 (UTC)[reply]

It should be mentioned that some modern point-and-shoot cameras (generally at the middle or high end of the market) offer many of the same manual controls (aperture, shutter speed, ISO speed, and even focus) that once were exclusively found on (d)SLRs. A friend of mine owns a Canon PowerShot SX210 IS (review), for instance, which includes all of those features coupled with an extremely wide zoom range (14x, corresponding to 28mm-392mm focal lengths on a regular 35mm full-frame camera), which takes a lot of the sting out of not being able to swap lenses. Plus, it's all in a compact P&S form factor, which means that it comfortably fits in any reasonably-sized pocket. The SX210 running about $300 on Amazon right now, which puts it at less than half the price of pretty much any new dSLR.

That said, going P&S does entail some tradeoffs. Smaller pixels have inherently worse low-light performance, a problem exacerbated by the smaller sensors of P&S cameras and the drive to cram more megapixels onto each sensor; this can make taking high-quality indoor and night shots a challenge. The built-in flash will be located physically close to the lens, which maximizes the opportunity for glare and redeye; the built-in flash will generally be smaller and less powerful than even the built-in on a dSLR (and the dSLR will have a hot shoe where you can attach all manner of additional lighting accessories). Where manual control modes and settings are available on a P&S, they may be more difficult to access and adjust—you may have to 'drill down' through menus and whatnot, because there just isn't room on the camera body (or in the design and construction budget) for the dedicated buttons, toggles, and wheels one can fit on the exterior of a full-sized dSLR. Unlike an SLR, the viewfinder of a P&S does not display exactly the same frame as the lens and sensor see; many P&S cameras these days are also dispensing with the viewfinder altogether. The LCD-only preview has pros and cons, but be aware that it can be difficult or uncomfortable to view the display when outdoors in bright sunlight. Generally P&S cameras don't give access to RAW image files, though there exist firmware hacks for some P&S cameras now. Residents of larger cities with well-stocked camera stores may enjoy being able to rent premium and specialty lenses for their dSLRs. TenOfAllTrades(talk) 15:57, 10 July 2011 (UTC)[reply]

What looks like peas? We may soon know

I asked the question here and here and was referred here in the second section. The conclusion was that it was Crape myrtle, and what I believe to be Crape myrtles are now blooming. The trees near my house are not blooming yet and I won't be going to Myrtle Beach, South Carolina until the blooms are gone and what looks like peas are back. I'll update this as the trees bloom.Vchimpanzee · talk · contributions · 21:54, 8 July 2011 (UTC)[reply]

Peas are pulses which would be fruits if they had not been defined to be vegetables. Long story. 99.24.223.58 (talk) 22:45, 8 July 2011 (UTC)[reply]

What's your point, exactly? --Mr.98 (talk) 23:28, 8 July 2011 (UTC)[reply]

Well, that is a difficult question having to do with the fact that vegetables and fruits were named before biology was understood. 99.24.223.58 (talk) 00:04, 9 July 2011 (UTC)[reply]

What in the world does that have to do with it? The culinary uses of fruit and vegetable don't have much to do with botany, and there's no real reason they should. Culinarily, "fruits" have a lot of sugar, and usually some dibasic acids like citric acid and malic acid. Vegetables don't have that much of either one. Who cares what they do for the plant? When I'm eating it, that's the last thing on my mind. --Trovatore (talk) 08:27, 9 July 2011 (UTC)[reply]

Oops — I guess citric acid is actually tribasic. Polybasic acids, I guess.

Anyway, there apear to be small white blooms on some of the trees, with tiny yellow blooms in the middle. They sort of look like daisies. Thie other Crape myrtles, if that's what they are, have poink or purple blooms.Vchimpanzee · talk · contributions · 15:23, 9 July 2011 (UTC)[reply]

After scrolling down in the Lagerstroemia article, I see blooms (on the actual trees) that look very much like the ones I saw in the second photo from the left, and the "peas" in the third photo from the right, after they are no longer green.Vchimpanzee · talk · contributions · 15:26, 9 July 2011 (UTC)[reply]

Thank you for the update Vchimpanzee, I'm looking forward to getting this finally and definately resolved. 2.101.8.57 (talk) 19:46, 9 July 2011 (UTC)[reply]

Based on what I've seen now, I think we know for sure.Vchimpanzee · talk · contributions · 17:08, 11 July 2011 (UTC)[reply]

July 9

Solid Oxygen Combustion

Hi, I resintly han a discussion with my mom about the dangers of consentrated oxygen, specificly using solid oxygen to disperse smoke in a controlled amount while it dissolves.

I have witnessed alen nursall freely handling solid oxygen with no apperent ill affects. Dose this mean that it's safe to handle?

More basiclly, is oxygen combustable or dose it require a fuel to oxidize with? — Preceding unsigned comment added by 174.2.44.103 (talk) 04:56, 9 July 2011 (UTC)[reply]

Ordinary combustion is basically a fuel reacting with oxygen (or something that supplies oxygen). Some substances will spontaneously react with oxygen at room temperature, others not. Combustion can be very rapid (explosion!) or not, so there's definitely a safety question depending on the reactivity of the fuel, the temperature, and the concentration. Twang (talk) 05:13, 9 July 2011 (UTC)[reply]

Solid oxygen ? You have to seriously lower the temperature and/or raise the pressure just to get oxygen to liquify. To get it to freeze at normal pressure you need to lower the temp to -361.82 °F. That seems rather dangerous to handle because of the low temp. StuRat (talk) 05:17, 9 July 2011 (UTC)[reply]

Oh yes, oxygen will definitely freeze if you get it cold enough. The only thing that won't freeze at 1 atmosphere pressure, at any temperature no matter how cold, is helium (that's for some rather strange quantum reasons).

However I do seriously doubt that the OP saw someone "handling" solid oxygen. More likely it was something like sodium oxide, which is a solid that can be used to generate oxygen. --Trovatore (talk) 05:21, 9 July 2011 (UTC)[reply]

Hmm, don't know what I was thinking there. You can get oxygen from sodium oxide, but it's not easy. Maybe I was thinking of sodium peroxide. Our oxygen generator article has more possibilities. --Trovatore (talk) 07:28, 9 July 2011 (UTC)[reply]

I don't know - the OP mentions Alan Nursall, who I gather is a television personality with his own popular science television show: the Alan Nursall Experience on the Discovery Channel. It's quite possible that he did get to play with some frozen oxygen as part of a demo. That said, except under carefully controlled conditions any condensed-phase (solid or liquid) oxygen is potentially very dangerous, as it will sustain vigorous combustion. (The last half of this video shows a test tube containing a small volume of liquid oxygen 'eating' several lit wooden splints: [12].) TenOfAllTrades(talk) 13:15, 9 July 2011 (UTC)[reply]

We have an article on solid oxygen, with some interesting forms, such as red oxygen and metallic oxygen. StuRat (talk) 05:25, 9 July 2011 (UTC)[reply]

I think that "solid oxygen" is being used colloquially here, to mean e.g. lithium perchlorate, potassium perchlorate, sodium or potassium chlorate, iodine pentoxide etc. I don't think there's any fixed definition for this usage, so we can't make any statement about the safety of doing something with "solid oxygen" in general. We'd need to know the specifics. Note however that all strong oxidizers have certain basic hazards. I'm not quite sure what "disperse smoke" means - is it to clear a room, or to make a firework? Obviously the only general statement we can make about pyrotechnics and bomb-making is you'd better know what you're doing, and knowing the name of the chemical is only the first baby step in that direction. (Al Qaida is free to ignore that last, since they have Allah on their side they shouldn't have to worry about safety!) Wnt (talk) 15:36, 9 July 2011 (UTC)[reply]

Well, of course the thing that is commonly used to generate fake smoke is dry ice, i.e., solid CO², not solid oxygen. Looie496 (talk) 17:02, 9 July 2011 (UTC)[reply]

Hi, It's me again. I just want to clarify that I am NOT making a bomb, and for my (hypothetical, just speculation) porposes , I think that dry ice wont last long enough, as I wold only have maybe 1 liter of space to make steam-locomotive smoke for 2-3 hours. On the "frozen" note, I think it was compressed and it may have been regular air (it was white), but he Definitly handled it, and it did dissolve back into the atmosphere. And what about Sublimination and Deposition (solid directly to gas and vice-versa)? 174.2.44.103 (talk) 06:14, 10 July 2011 (UTC)[reply]

Sounds like it was dry ice to me, since it could be easily handled (but you'd probably want to wear gloves). A liter might be enough to last 2-3 hours, depending on the flow rate you need. And yes, it sublimes directly into the air. The next step would be liquid nitrogen, but now you're getting into the danger category, so have to buy it at a chemical supply company and keep it in an approved thermos, versus dry ice which you can buy at many grocery stores. StuRat (talk) 08:27, 10 July 2011 (UTC)[reply]

Jehovah's Witnesses and oxygen

The Jehovah's Witnesses doctrine expounded to me by a national overseer is that oxygen is pneu the breath of God which was imparted to living things at their creation. He insisted than man can never duplicate pneu. I countered by telling that one can demonstrate keeping a mouse alive breathing oxygen generated by a chemical reaction, and that I therefore could also breathe synthetic oxygen, He became angry and stalked away. Will a Witness or someone who understands their teaching comment about any misunderstanding here? Cuddlyable3 (talk) 08:01, 9 July 2011 (UTC)[reply]

What you generate in your chemical reaction is not a "duplicate" of oxygen, nor synthetic oxygen. It is simply oxygen. It's really no different from noting that the oxygen we normally breathe is generated chemically too, by photosynthesis. While seeming to be an odd thing for a religion to be concerned about, on this one the perspective seems realistic, whether God made it or not. (Hope you don't mind me having a crack at this, even though I'm not a Witness, nor do I claim to understand their teachings) HiLo48 (talk) 08:09, 9 July 2011 (UTC)[reply]

Humans can make oxygen through Nuclear transmutation which seems to counter what the Witness was claiming, but HiLo is right that chemical reactions don't create oxygen molecules, they just release them from other bonded elements. --Daniel 08:16, 9 July 2011 (UTC)[reply]

From a JW publication: The account of the creation of man states that God formed man from the dust of the ground and proceeded to "blow (na-phahh') into his nostrils the breath (nesha-mah') of life, and the man came to be a lving soul (ne-phesh)." (Gen. 2:7) I think the overseer referred to the ancient greek word πνεῦμα (pneuma, "wind, air, breath, spirit") today a root of the word pneumatic. I don't see any understanding of elemental oxygen here which in pure form is toxic. Cuddlyable3 (talk) 10:52, 9 July 2011 (UTC)[reply]

Jehovah's Witnesses are not known for their scientific knowledge, and don't tend to hang out at the science desk.--Shantavira|^{feed me} 11:59, 9 July 2011 (UTC)[reply]

It would appear that that particular JW didn't even understand what the Bible was saying, never mind how it works scientifically. The "breath of life" is not "oxygen", but rather it's a metaphor for the spirit, the spark of life, whatever you want to call it. No amount of oxygen will revive a dead person, i.e. one whose spark of life has been fully extinguished. Realizing that he must have had it wrong might be what impelled him to leave in a huff (or if that's too soon, a minute 'n a huff). Ironically, though, he was almost right; unless humans have figured out a way to resurrect the dead (in real life, not in Plan 9 from OUter Space) and I didn't hear about it, only God (or Mother Nature, or whatever metaphor) can provide the spark of life. ←Baseball Bugs ^{What's up, Doc?} carrots→ 12:23, 9 July 2011 (UTC)[reply]

Maybe he did understand and thought the OP was making fun of it by taking a different meaning. Grandiose (me, talk, contribs) 14:14, 9 July 2011 (UTC)[reply]

Maybe just a failure to communicate? ←Baseball Bugs ^{What's up, Doc?} carrots→ 14:25, 9 July 2011 (UTC)[reply]

I don't think there's any reason to call "the breath of life" in Gen. 2:7 a metaphor, it's just an honest attempt by the author to describe something that he was not in a position to understand due to the insufficient development of biology and physics at the time. The sentence is very down-to-earth and materialistic, with quite specific natural substances and organs being mentioned by name. "Gen. 2:7: Then the LORD God formed a man from the dust of the ground and breathed into his nostrils the breath of life, and the man became a living being." If it were about "the spark of life", abstractly, there would have been no reason to specify the organ through which the breath was introduced into the body - namely, the nostrils. It's just that the author and his culture knew from experience that what distinguishes living bodies from dead ones is that the former breathe, while the latter don't. Furthermore, this seemed to imply that the soul and the breath, whose presence apparently made a body living, were somehow connected or indeed identical. Thus, in a dying person, the life=soul=breath was thought to exit the body through one last exhalation (this is still visible in various expressions, now really as a mere metaphor). This notion is even expressed in word derivations: in Hebrew, from the verb nāšam "to breathe", one has derived nəšāmā and nešem, both of which can mean "spirit", "soul" (and "breath", although the former may have retained only the abstract meaning in modern Hebrew, I'm not sure about that). Similar connections are found in Latin and Slavic (spiro - spiritus, duh - duša). So it seemed logical that, conversely, in order to make the body living at the final stage of creation, the Creator had to transfer the breath=soul=life into the body.

We have turned these notions into mere metaphors, because we now know how these things really work, but the authors and audience of the Bible back then had no reason to see them as metaphors, because they really didn't have anything better than them in terms of a factual description. So the poor fundamentalists' hopeless attempts to tease out from the Bible a precise scientific description of how things work are, in fact, more adequate and faithful to the original purpose of the text than the attempts to avoid the embarrassment by retroactive "metaphoric" readings. --91.148.159.4 (talk) 20:38, 9 July 2011 (UTC)[reply]

Let me see if I got that right. A Jehovah's Witnesses said some strange thing, You countered with science, They got upset and left. - Sounds about right to me. Dauto (talk) 13:52, 9 July 2011 (UTC)[reply]

This sounds like some variation on Gnostic theology, which defines soul as the combination of soma (body) and pneuma (spirit). It's the job of the Holy Spirit to breathe pneuma into the lifeless clay which is soma. Pneuma literally means "air" in Greek, which is what makes me think this is the origin of the confusion regarding oxygen. (For those who may not be aware, much of the original Bible was written in Koine Greek.) -- SmashTheState (talk) 13:54, 9 July 2011 (UTC)[reply]

The Old Testament was Hebrew and the New Testament largely Greek, right? ←Baseball Bugs ^{What's up, Doc?} carrots→ 14:24, 9 July 2011 (UTC)[reply]

The OT is mostly classical Hebrew and Biblical Aramaic. The NT is probably all Koine Greek, although some claim that Matthew may have had a Hebrew precursor. Jesus probably spoke Armaic (or Texan English, according to some sources ;-). --Stephan Schulz (talk) 14:43, 9 July 2011 (UTC)[reply]

Do the Jehovah's Witnesses really believe, as a group, that pneu = oxygen? And is that atomic oxygen or molecular oxygen? Since oxygen was created in the supernova of some star preceding formation of the Earth, the equation with atomic oxygen implies a peculiar but interesting doctrine, which I've never heard before, that the initial "let there be light" was the explosion of this ancient ancestor, to which Earth and moon and sun owe so much of their creation. Wnt (talk) 15:22, 9 July 2011 (UTC)[reply]

Jehovah's Witnesses are taught to welcome changes to their religion's doctrine, regarding such "adjustments" as "new light" or "new understanding" from God and proving that they are on the "path of the righteous", see Development of Jehovah's Witnesses doctrine. All hail Wnt the bearer of New light! Cuddlyable3 (talk) 15:56, 9 July 2011 (UTC)[reply]

Unfortunately, they have yet to see the light regarding the word "Jehovah" being a mis-translation. ←Baseball Bugs ^{What's up, Doc?} carrots→ 19:09, 9 July 2011 (UTC)[reply]

Theory of mind article

The first section begins with, "Theory of mind is a theory insofar as the mind is not directly observable." This seems to me rather odd of a definition of the term theory. I guess it's not a scientific theory then? 66.108.223.179 (talk) 12:39, 9 July 2011 (UTC)[reply]

The article gives a source^[5]for the statement and goes on to explain "The presumption that others have a mind is termed a theory of mind because each human can only intuit the existence of his or her own mind through introspection, and no one has direct access to the mind of another." This is not to define "theory". Instead it uses the dictionary definition[13] of theory n. A coherent statement or set of statements that attempts to explain observed phenomena, A logical structure that enables one to deduce the possible results of every experiment that falls within its purview. Cuddlyable3 (talk) 13:23, 9 July 2011 (UTC)[reply]

I agree, as I have said on the talk page of the article, that the term "theory" is poorly chosen here: "theory of mind", as used in the literature, is really more of a behavior than a theory -- the behavior of attributing mental states to other individuals. The simple fact is that many scientific concepts are poorly named -- once a name becomes established it is very difficult to change, even if it was not well chosen in the first place. The history here is that Premack and Woodruff originated the term in 1978 in an article called "Does the chimpanzee have a theory of mind?", and the literature that followed has simply adopted their term. By now it has been used so widely that it would be virtually impossible to change. I prefer Daniel Dennett's term intentional stance, although that too is less than perfect. Looie496 (talk) 16:48, 9 July 2011 (UTC)[reply]

The use of theory here (which is still not the common use as one would find when people really mean to say "hypothesis") is the same theory one finds when using the word in concepts like color theory and music theory, which is to say it is a collection of ideas and concepts which make up a cohesive whole. This is actually almost exactly what a scientific theory means as well (excepting that the ideas and concepts are those which have undergone rigorous testing using scientific methods). But basically, "a group of related ideas and concepts" is what a theory is. --Jayron32 18:30, 10 July 2011 (UTC)[reply]

Okay -- but to me, saying that monkeys have a "theory of mind" because they do things to deceive other monkeys (this is generally considered evidence for ToM in the literature) is equivalent to saying that animals have a "theory of food" because they eat some things but not others. It might possibly be valid in some technical philosophical sense, but I don't think it is a useful way to describe the data. Looie496 (talk) 19:57, 10 July 2011 (UTC)[reply]

Theory of mind is a clunky phrase for what is probably better described as metacognition. The "theory" in "theory of mind" is there more because of the idea of organization than anything. Just as a theory is an organized set of ideas, the "theory of mind" requires an inherent level of organization in the mind of the subject itself. Look at it this way: Atoms existed before Dalton described the Atomic theory. Evolution existed even before Darwin (and others) organized the Theory of evolution. An organism can have a mind, but that does not mean it has a "theory of mind". My sense is that the concept of "theory of mind", which sounds starkly like metacognition, excepting that metacognition is applied to the self (the ability to think about one's own thinking) while theory of mind is applied to those outside of the self (the ability to think about other people's thinking). But the two concepts seem very intertwined, and the fact that we have two articles, and two terms, probably is more to do with the fact that different people have arrived at roughly the same concept through different means. --Jayron32 22:18, 10 July 2011 (UTC)[reply]

Tsunamis on Atolls and Small Islands?

There are over 25,000 islands in the Pacific, and Tsunamis are very common there. What happens when a tsunami hits these small islands, even coming from far away with a very much diminished wavelength? They don't have anywhere near the defense that a larger and developed island would have, but all the stacking up problems that seems like they'd just be washed over and turned to mud. Yet there are endemic ground nesting flightless birds and plants on many of the islands, so obviously this doesn't happen; or doesn't happen very often. Why not? Are the vast distances involved the only thing that saves them? --96.40.227.54 (talk) 16:09, 9 July 2011 (UTC)[reply]

The devastating effects of tsunamis are largely a product of gradually shallowing water depths, which cause water to pile up as the wave moves toward shore. That doesn't usually happen to small islands if they are surrounded by deep water. For example, the Indian Ocean tsunami, which had devastating effects on Sri Lanka, went past the island of Diego Garcia (not too much farther from the epicenter) with hardly a ripple -- it had larger effects on the coast of Africa, thousands of miles farther away. This is not to say that tsunamis cannot have devastating effects on small islands: they certainly can in some cases. Looie496 (talk) 16:56, 9 July 2011 (UTC)[reply]

Also, try a Google Scholar search like tsunami seamount atoll. Seamounts and mid-ocean ridges tend to focus tsunamis, so that their heights may be higher near atolls over those bathymetric structures. ~AH1 ^(discuss!) 20:03, 9 July 2011 (UTC)[reply]

As life expectancy increases, do other events in our life happen proportionally later?

A hundred years ago the life expectancy was 59 years. It's now around 80, depending ont he country you come from. So is puberty and menopause correspondingly later, or do we have the same length of youth as they did before, with more old age? If they are later, are they proportionally later or just a bit later? Or perhaps they're earlier?--92.251.212.78 (talk) 16:33, 9 July 2011 (UTC)[reply]

Puberty has, I believe, actually become earlier by a fair amount. I think it's down to diet. Grandiose (me, talk, contribs) 16:58, 9 July 2011 (UTC)[reply]

The strongest association with puberty onset time is childhood obesity, which makes puberty earlier in girls and later in boys.[14] As for the original question, most of the extension of lifespans in humans over the past few centuries can be thought of as simply removing early causes of death, whether through improved nutrition, improved hygiene, vaccines, better treatments for disease, accident prevention, etc. 99.24.223.58 (talk) 18:14, 9 July 2011 (UTC)[reply]

Also see Infant mortality, a prime factor - even today - in average life expectancy. --Cookatoo.ergo.ZooM (talk) 18:53, 9 July 2011 (UTC)[reply]

Yes, by implication, we're talking average life expectancy, which does not necessarily have anything to do with individuals. I've got a distant relative who live to be 101 - from the early 18th century to the early 19th century! Another life expectancy factor was the number of women who died in their 20s or 30s in the old days, due to childbirth complications. In the old days, if something serious happened to you, you typically died. If not, then you might live to 80s, 90s, or over 100. Lots of luck factors there. ←Baseball Bugs ^{What's up, Doc?} carrots→ 19:07, 9 July 2011 (UTC)[reply]

Indeed. Take a look at Life expectancy#Life expectancy variation over time. Even in medieval Britain, if you reached adulthood, you could expect to live what we would expect to be a decent lifespan. That page says an aristocrat 800 years ago aged 21 could expect to live to 64 and by 500 years ago, it was 71. It wouldn't have been unusual to live into your 70's or 80's. It doesn't mention peasants, but it's not obvious to me that they would have had a significantly shorter lifespan. They probably had more accidents, but disease was probably about the same. Peasants probably had better diets (less luxurious, but that's usually a good thing - there's a lot to be said for vegetarianism). I expect the article discusses aristocrats simply because they kept better records, so we know how long they lived.

Fast-forward to 1911, and life expectancy once you reached adulthood was very similar to what it is now. Improvements since then have been largely due to fewer people smoking and improved treatments for a few specific diseases (well, that's a best guess - there is still some dispute among actuaries about the exact causes of recent improvements).

--Tango (talk) 18:12, 10 July 2011 (UTC)[reply]

Regarding a business career, if people hang on to their assets or positions because they are living longer, then the advancement of younger people is going to be slower. People living longer gives them more time to accumulate wealth, so inequality may increase. However that does not matter if people innovate and therefore bypass the career ladder. 2.101.12.198 (talk) 10:47, 10 July 2011 (UTC)[reply]

Are you only interested in biological events? I think it has been a trend that achievement of financial independence from the parents has been occurring later and later in life. ike9898 (talk) 16:11, 11 July 2011 (UTC)[reply]

True, and directly proportional to income inequality. 99.24.223.58 (talk) 20:06, 11 July 2011 (UTC)[reply]

Bond film realism

License to Kill
Is the explosive decompression scene scientifically accurate? In particular; increased pressure followed by severe, but not seemingly "instant", pressure release*, and; the effect on the human head.
_* _{As opposed to negative pressure followed by a release.} --Rixxin (talk) 17:58, 9 July 2011 (UTC)[reply]

Yes I think so. I read on this desk (a while ago, I'm a bit of a lurker) about someone who was caught in an explosive decompression and their head was found metres away up some vent, with nothing left of the body. I believe baseball bugs provided the link.--92.251.212.78 (talk) 19:14, 9 July 2011 (UTC)[reply]

In the article you linked "explosive decompression#Exposure to a vacuum causes the body to explode" is listed as a fallacy. They do, however, compare it merely to being in a low-pressure situation rather than a rapdily changing pressure system. Grandiose (me, talk, contribs) 19:16, 9 July 2011 (UTC)[reply]

Whenever this topic comes up on the RDs, it is obligatory to mention the Byford Dolphin incident. Gandalf61 (talk) 19:31, 9 July 2011 (UTC)[reply]

Evolutionary pressure for theropod arms

Having recently seen an exhibit about the T.rex at the Boston Museum of Science, I was wondering (as my title implies) what the pressure towards having such little arms would be, why would the more short fore-limbed individuals be more successful in reproduction than a more long-limbed individual?199.94.68.201 (talk) 19:30, 9 July 2011 (UTC)[reply]

Any body part composed of living cells consumes resources, both to grow and to continue existing -- so if a body part serves no function, its size should be reduced in order to minimize food requirements. Our article on vestigiality gives more information. Looie496 (talk) 19:41, 9 July 2011 (UTC)[reply]

Maybe the females didn't mate with as many guys whose bigger arms pushed down on their backs. 76.27.175.80 (talk) 19:56, 9 July 2011 (UTC)[reply]

The males with shorter arms couldn't play with themselves, so had no choice but to chase females. :-) StuRat (talk) 06:18, 10 July 2011 (UTC) [reply]

Did dinosaurs have penes? I'd have thought, being the ancestors of modern birds, that they'd have had cloaca. -- SmashTheState (talk) 15:10, 10 July 2011 (UTC) [reply]

Couldn't they play with their cloaca? --Jayron32 18:26, 10 July 2011 (UTC)[reply]

I suspect that longer arms interfered with their ability to balance. That is, since they balanced their tail in back against their head and torso in front, having heavy arms in front too would require either a bigger tail or smaller head and torso. All of these have associated costs. Also, big arms would mean more air drag and potential to get snagged on trees, while chasing prey. StuRat (talk) 06:18, 10 July 2011 (UTC)[reply]

Following on from that view, would the kangaroo be a modern animal with similar characteristics? Although their arms are short, a flexible body allows them to reach most extremities when they feel like a good old scratch. Maybe T-rex was a lot more flexible than the bony skeleton we usually see would suggest. Oh, and a Google search for "kangaroo mating" images should relieve all concerns on that front. HiLo48 (talk) 06:34, 10 July 2011 (UTC)[reply]

Just pointing out that any theory seeking to explain the short arms of most giant theropods (such as T-rex) should also explain the relatively long arms of most small-to-medium theropods (such as velociraptor) - why it doesn't apply to them, that is.--91.148.159.4 (talk) 12:59, 10 July 2011 (UTC)[reply]

Anti-adhesive material

Is there a material so smooth (non-adhesive) that any insect wouldn't be able to attach to or walk on it?--46.204.57.249 (talk) 22:14, 9 July 2011 (UTC)[reply]

Maybe only if it also could not retain moisture. ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:30, 9 July 2011 (UTC)[reply]

No, depending on the insect. Smoothness is conducive to housefly foot adhesion.[15] 216.239.45.98 (talk) 23:44, 9 July 2011 (UTC)[reply]

A lab at the University of Cambridge has invented and patented a material called Insectislide that apparently insects cannot stick to, although smoothness is not the cause. This article gives a bit more information. Looie496 (talk) 00:57, 10 July 2011 (UTC)[reply]

Pure sodium ? It should hopefully react with the moisture on their feet and blow them off. StuRat (talk) 06:02, 10 July 2011 (UTC)[reply]

I've heard and read that fluon (teflon in an aqueous adhesive) or teflon tape can be used for this. Apparently most insects cant stick to it.Staticd (talk) 09:24, 10 July 2011 (UTC)[reply]

Any good against slugs and snails? Itsmejudith (talk) 09:51, 10 July 2011 (UTC)[reply]

Doubt it. for snails you will need some repellantStaticd (talk) 11:44, 10 July 2011 (UTC)[reply]

Or diatomaceous earth. -- SmashTheState (talk) 14:41, 10 July 2011 (UTC)[reply]

I watched a caterpiller try to walk across a Teflon skillet. Every time he tried to rear up, he fell over. His feet could not gain traction of the nonstick surface.He had no problem walking vertically up a painted surface Edison (talk) 17:47, 10 July 2011 (UTC)[reply]

July 10

to balance the current

respected

let us take take two ac current wires.The fist one is being converted from DC to Ac and the second one direct ac. Here what i want to know is "is there any device that can connect the both wires by which the output which we are getting is appropriate and the ac current which we converted should be used and if the power from ac is low then it should be balanced with the direct ac for output".Mightyteja (talk) 06:16, 10 July 2011 (UTC)[reply]

Slightly reformatted the question to make it easier to read. Richard Avery (talk) 06:35, 10 July 2011 (UTC)[reply]

The sources should never be directly connected, of course, because the "mains" source could easily destroy the DC to AC converter (is it a switch-mode power supply or an old-fashioned transformer and rectifier?) Devices are available that will automatically switch off the "mains" AC and will switch on the local source, but they work by monitoring voltage and triggering a conventional switch. There is a short delay between the failure of one supply and the starting of the other. An Uninterruptable power supply works by always feeding power from the converter, and by constantly topping up the backup battery from the "mains" source. I suppose it is possible to design some circuitry that "balances" the loads, but I've never heard of it being marketed, and there would be safety considerations that would need to be built in to the design. Dbfirs 07:17, 10 July 2011 (UTC)[reply]

A skilled electrical engineer or electronics designer could certainly design a circuit which had alternating current with a DC offset present on a wire. I can't think of instances where this has been done with generating stations or substations with respect to the power they send out, or with power supplied to a house. It seems more common in signals than in power. The two types of electricity cold be combined at one end of a circuit and separated at the other end. AC and DC power could be made to flow in the same direction or in opposite directions. I wish there were an easy way to draw circuit diagrams here. Inside many amplifiers, the output of the transistor or tube amplifier is exactly that, a combination of direct current and an audio or video signal, which can be considered (by Fourier analysis) as the combination of several AC sinusoids of various frequencies, amplitudes, and phase angles. This combined signal can certainly be decomposed into AC and DC components. A transformer or capacitor could block the DC and pass the AC, for instance. An inductor could oppose (block) the AC but allow the DC to pass. A tuned circuit could block AC of one narrow band of frequencies, or allow passage of AC of one narrow band of frequencies. An output transformer in an audio amplifier or radio receiver sends only the AC to the loudspeaker, for example. Some types of microphones combine a DC power supply with energy sent up to the microphone from the amp input, on a pair of conductors which also sends the audio signal down to the amplifier from the microphone. Some TV antenna amplifiers similarly carry DC power up to the amplifier mounted on the antenna and carry the TV signal down on the same conductors. Trouble comes quickly to such a scheme when there is more than one neutral or ground connection in the system, or when the DC voltage is applied directly across a transformer winding, which has AC reactance but little DC resistance to limit current flow, or when AC is applied directly across a capacitor which opposes DC flow but little reactance to AC flow. Randomly connecting AC and DC power supplies together when one understands little about electricity is very likely to blow fuses or circuit breakers, start fires, damage equipment, or cause personal injury. Edison (talk) 17:41, 10 July 2011 (UTC)[reply]

I see that Edison interprets the question slightly differently from my reading, but we agree in the advice given. Dbfirs 19:20, 10 July 2011 (UTC)[reply]

"The fist one is being converted from DC to Ac" was the part that confused me the most. How is a fist either DC or AC? "Fist" has traditionally been a term for a style or pattern of telegraphy sending which is recognizable. I recall an instance in a utility substation where a battery ground was detected on the (ungrounded) DC station battery, and it turned out to be an inadvertent connection between an AC circuit (with grounded neutral) and the DC power supply. Even with that goof, everything was working ok. If there had been a second (unintentional) ground, a fuse would have blown or there would at least have been some smoke. I love the smell of burning insulation in the morning. Edison (talk) 00:34, 11 July 2011 (UTC)[reply]

I believe what the OP needs is a grid-tie inverter (GTI). He can throw away his DC to AC converter and feed the DC directly into the GTI. His 'direct AC source', whatever it is (grid or local generator) goes to the grid connection of the GTI. The AC source is then reinforced by power from the DC input. GTIs are designed for feeding power from PV installations into the national grid, but presumably they can be used for local, non-grid installations too. --Heron (talk) 18:31, 11 July 2011 (UTC)[reply]

Yes, that might work. It would need to have the cut-out circuitry disabled, and possibly some extra control circuitry added to keep it off when the "mains" is working normally and then switch it on when the "mains" voltage drops. A mains isolator would also be required to disconnect the mains supply in the event of a significant drop in voltage to comply with local regulations and to prevent the output going to feed power to other users free of charge. The cost would be high. Dbfirs 11:33, 12 July 2011 (UTC)[reply]

Memory

In which form memory store in brain or what is the form of encoding in brain ? — Preceding unsigned comment added by Just institutions (talk • contribs) 07:23, 10 July 2011 (UTC)[reply]

It's in the form of the connections between neurons, and perhaps some logic within each neuron, such as "if you get a signal from any of these 3 neurons, but not any of these 5, then send a signal on to this neuron". StuRat (talk) 08:19, 10 July 2011 (UTC)[reply]

Memory storage and recall are enormously complex processes that are still not fully understood. See our articles on neuroanatomy of memory, encoding, storage and recall for an overview. Gandalf61 (talk) 10:59, 10 July 2011 (UTC)[reply]

Here's a recent article [16] from El Reg about Project SpiNNaker, which will investigate the question using quite a large number of ARM chips. Card Zero (talk) 11:48, 10 July 2011 (UTC)[reply]

Just a note that there are competing theories. For example, Sir Roger Penrose believes that memory may be encoded on a quantum level through the superposition of proteins in the microtubules of the neurons of the brain. And Rupert Sheldrake's morphic field model holds that the brain is more like a radio receiver which picks up consciousness from the collective unconscious. -- SmashTheState (talk) 14:34, 10 July 2011 (UTC)[reply]

The vast majority of neuroscientists believe that the main way that the brain stores memory is by strengthening synaptic connections between brain cells. Our articles on Hebbian theory and Long-term potentiation give more details, although they are written at a technical level that may be difficult for a beginner to understand. Looie496 (talk) 17:32, 10 July 2011 (UTC)[reply]

The logic you're looking for is called summation (neurophysiology). There are different neurotransmitters, and depending on the synapse, a neurotransmitter might cause an inhibitory postsynaptic potential or an excitatory postsynaptic potential; these add up in various ways, can interfere with the propagation of each other down the dendrite to the neuron ... and long term potentiation (e.g. via protein kinase C) then customizes this further on a neuron by neuron basis. Bear in mind that if you see a photomicrograph of a dendrite, it is a tremendously long cellular projection which is covered in synapses. It's all quite complicated, naturally... Wnt (talk) 18:12, 10 July 2011 (UTC)[reply]

Were you responding to me or to the OP? I'm afraid I don't get the relevance of what you wrote in either case. Looie496 (talk) 18:31, 10 July 2011 (UTC)[reply]

Questions about Antimatter?

Hi, I have a few questions about antimatter. I tried reading most of it to try to understand it, but for the life of me I can't. I just have a few questions that if answered might help me understand better.

Does antimatter exist on a different dimensional plane?
Does antimatter only take shape in the form of a particle? Can it take the form of an object?
If #1 and #2 are correct, are there antimatter versions of ourselves?
Is it tangible in any way?

Any help would be appreciated! 64.229.153.237 (talk) 18:06, 10 July 2011 (UTC)[reply]

Antimatter acts pretty much just like matter, so far as anyone can show. Of course, a complex and fine-tuned system like a human is an exacting test, but so far as I know no one has disproved that you couldn't zap someone with a magic wand and turn him into a perfectly viable antimatter-person by simply flipping every matter particle for the same thing in antimatter. Till he touched something (like the air) and blew up, that is.

Different dimensional plane? Not sure how to define. I remember reading speculations that some part of the universe, now separated from us by further than light can travel since the beginning of time, might have antimatter galaxies. Would that count? Wnt (talk) 18:16, 10 July 2011 (UTC)[reply]

(edit conflict) "No" and "objects are nothing more than certain combinations of particles" are the first two answers. The difference between a particle and its antiparticle is that the fundamental charges are opposite. Antihydrogen is trapped in our earthly dimensions using our earthly-dimensioned tools and physics. DMacks (talk) 18:20, 10 July 2011 (UTC)[reply]

(edit conflict) Antimatter behaves exactly like matter does, excepting that certain fundemental properties (like electric charge) take the exact opposite value. Otherwise, it is expected to behave exactly the same as matter does. If you are interested, you should read antimatter, where a lot of things are explained. --Jayron32 18:23, 10 July 2011 (UTC)[reply]

Well, take a look at CPT symmetry and it particular the section on violations. So maybe not exactly the same, depending on how that comes out. Not that I expect any such thing would be big enough to notice at the level of what is green or sweet-smelling or crumbly. --Trovatore (talk) 19:02, 10 July 2011 (UTC)[reply]

Right: Antimatter atoms might have substantially different chemistry than we're used to, but until we get much better at preserving un-ionized antimatter for study, we won't be able to tell. 99.24.223.58 (talk) 20:42, 10 July 2011 (UTC)[reply]

In answer to the questions: (1) No. (2) Theoretically every particle has a corresponding antiparticle, though there are a few cases, such as the photon, where a particle is its own antiparticle. (3) No, although theoretically there probably could be. (4) Yes, as tangible as ordinary matter -- however if you bring ordinary matter and antimatter into contact, you get a huge explosion. One more point that is perhaps worth noting is that from a certain point of view, an antimatter particle can be thought of as an ordinary particle going backward through time. (That's how they are represented in Feynman diagrams.) Looie496 (talk) 18:37, 10 July 2011 (UTC)[reply]

Although you can think of antimatter that way, it might not be very helpful for someone who doesn't understand Feynman diagrams well to try to do so. 99.24.223.58 (talk) 20:44, 10 July 2011 (UTC)[reply]

Quoting myself from a previous thread: "The particle-antiparticle duality exists because of CPT symmetry. The CPT symmetry applied twice gives you back what you started with (it's a fancy kind of mirror reflection). Therefore, for any given starting state, there are two possibilities: CPT leaves the state unchanged (it's a CPT-invariant state) or CPT switches back and forth between two states that are duals of each other. In the second case, there's a convention of naming one state by 'anti-' prefixed to the name of the other state—for example, electron and antielectron. This is not a universal convention. 'Positron' is another name for 'antielectron', and the W⁺ and W⁻ are never called anti-W⁻ or anti-W⁺, even though they're CPT duals of each other. Furthermore, it's essentially arbitrary which of the two states gets the 'anti' prefix. There's no physical 'antiness' property possessed by the 'anti' particles.

"CPT symmetry includes time reversal (the T), so one could say that the dual states have opposite time directionality. But this is like saying that they have opposite space directionality (the P). It doesn't really mean anything. Particles have no intrinsic time direction to start with, so there's nothing to reverse. And there's nothing 'anti' about the particles with 'anti' in their name, so you can't single them out as the ones going backward in time." -- BenRG (talk) 21:59, 10 July 2011 (UTC)[reply]

Zero-point energy?

I recently read an interesting article regarding a practical experiment demonstrating the effects of some peculiar quantum physics. Virtual particle pairs are constantly being created and annihilating themselves all around us. Generally they're only "real" in potentia, and expressed as a probability. However, if one takes two mirrors and places them very close together, the Casimir effect will draw the two mirrors together.

Now the interesting part.

At relativistic speeds, one of the photon pairs created by the annihilation of the virtual particle can escape -- becoming essentially what we regard as "real." As I understand it, this is zero-point energy. You're extracting photons from virtual particles, from the potential energy of space/time itself. You are creating energy from nothing. The article states that they've actually managed to create the technology necessary to take this from s imple thought experiment into practice, and have observed photons being created from nothing. Does this violate the First Law? Or does the First Law indicate that we will never be able to increase the efficiency of the machines necessary to create the photons to the point where more energy is being created than consumed? Or does this mean we have now discovered the potential to create infinite amounts of energy, the proverbial free lunch? -- SmashTheState (talk) 18:38, 10 July 2011 (UTC)[reply]

It doesn't seem like a violation to me, since you aren't creating energy, but just changing it from one form ("the potential energy of space/time itself") to a more familiar form. It's also not an infinite supply, just far larger than we could ever use. Now, just because it doesn't violate any fundamental laws of physics doesn't necessarily mean it's practical. For comparison, nuclear fusion is absolutely possible as an energy source, but, despite decades of research, we've yet to make it practical. StuRat (talk) 18:50, 10 July 2011 (UTC)[reply]

No, anyone who claims to extract energy from the vacuum is deluded or conning you. That's not because there's no energy to extract. It's because if you do extract energy from the "vacuum", you end up in a different, lower vacuum state, one in which the laws of physics are different and we can't exist. The fact that we're still here means that didn't happen. -- BenRG (talk) 22:22, 10 July 2011 (UTC)[reply]

You must have misunderstood something.Energy is not being created out of nothing. The 1st law of thermodynamics still applies. Dauto (talk) 20:34, 10 July 2011 (UTC)[reply]

It's a myth that the Casimir effect shows the reality of vacuum fluctuations, albeit a myth that a surprising number of professional physicists seem to believe. See "The Casimir Effect and the Quantum Vacuum" by Robert Jaffe. The article that you linked is nonsense. The "phenomenon" these people are investigating is nothing more mysterious than what happens in a light bulb. -- BenRG (talk) 22:22, 10 July 2011 (UTC)[reply]

I'm a little suspicious of anyone who makes truth claims regarding scientific matters. Science is the philosophy of empiricism. Empiricism, by definition, can't reference truth, since truth is a metaphysical property. Rationalism and revelation can make truth claims; empiricism can't. I'm not saying your skepticism is unwarranted, but given that you admit this "myth" is accepted by professional physicists, I'm not sure why I should accept your view over theirs. Can you explain why you're utterly certain that the experiment being referenced doesn't demonstrate what it's claiming to demonstrate? To argue it can't because your first principles won't allow it is, as I understand the theory of scientific method, bad science. -- SmashTheState (talk) 23:46, 10 July 2011 (UTC)[reply]

I don't know that much about the issue being discussed here. But 'Extraordinary claims require extraordinary evidence' is generally an important part of science. The first law of thermodynamics is very well accepted and supported. This doesn't mean it's impossible to be wrong, clearly that's unscientific. But this does mean you're going to need a lot of evidence before anyone is going to believe you've proven it wrong. If someone claims it's disproven, the most likely possibilities are either they've misunderstood the first law, they've misunderstood their results or their results are just plain wrong. That isn't bad science. (And there are so many of these 'free energy' ideas you really have to be doubly sceptical of anyone claiming to have disproven the first law.)

About the 'professional physicists' thing, I don't know what BenRG is referring to but I would note it's generally a bad idea to think someone knows what they're talking about just because they're in a related field. And related field is an important point. Physics is a wide area of science and the fact someone is physicist doesn't mean they are really that informed on one specific area of physics. This of course applies to most areas of science. A marine biologist (which itself is still a fairly wide field) will probably know more about the biology of fungi then a layperson but I wouldn't call them an expert. If you want to know about fungi affecting apples you'd ask a mycologist of some kind or a plant pathologist.

Most people will be careful when talking about a field they're not that familiar with but that may have been BenRG's point. Some physicists may make comments about the Casimir effect when asked, while emphasising it's not really in their area of expertise, and they'll be wrong. In other words, the more important point is not whether BenRG know what they're talking about but whether the person writing the ref does and whether the physicists who believe other things about the Casimir effect do.

Nil Einne (talk) 00:54, 11 July 2011 (UTC)[reply]

Butterfly effect in astronomy

I've often wondered about long-term astronomy predictions (or the reverse, such as determining when eclipses occurred thousands of years ago). Over such time periods, it seems that a close-passing comet or other object is likely to have perturbed the orbits of the Earth and Moon. So, can we tell that this hasn't happened (say from a lack of "wobble"), tell that it has and figure this in, or are we just assuming that any such perturbations are insignificant to the calculations ? StuRat (talk) 19:49, 10 July 2011 (UTC)[reply]

Possible perturbations are taken into consideration to estimate how long before the butterfly effect takes over but thousands of years is too short a period to worry about that. It would take millions of years before planetary chaos takes over. Read Formation and evolution of the Solar System#Long-term stability. Dauto (talk) 20:41, 10 July 2011 (UTC)[reply]

Thanks, but why couldn't there be a long-period comet that passed near Earth, say 10,000 years ago, shifting the orbit of the Moon significantly ? StuRat (talk) 17:49, 11 July 2011 (UTC)[reply]

Highly unlikely that it's mass would be large enough to have an effect. Dauto (talk) 21:43, 11 July 2011 (UTC)[reply]

I was under the impression that there could be Pluto-sized objects way out there. StuRat (talk) 00:33, 12 July 2011 (UTC)[reply]

Yes, there are likely hundreds of them. What you don't seem to grasp is the vastness of space and how short a time frame a few thousand years actually is. When you put those two things together, the chances that a large enough event happens in such a small time scale is utterly negligible. Dauto (talk) 15:40, 12 July 2011 (UTC)[reply]

Skinning beef

I have searched but cannot find a description of the modern method of skinning beef in a slaughter house. Can anyone direct me to an article on this subject, or tell me how it's done? Thanks, wsc — Preceding unsigned comment added by 66.74.14.40 (talk) 19:53, 10 July 2011 (UTC)[reply]

See the section including diagrams 28-33 of [17]. Not for the faint of stomach. 99.24.223.58 (talk) 20:51, 10 July 2011 (UTC)[reply]

I witnessed this process at a commercial beef processing facility in Eastern Pennsylvania. What I saw was consistent with the description in the above reference, specifically the 'vertical method' with partial automation. ike9898 (talk) 16:06, 11 July 2011 (UTC)[reply]

Waves spreading out

Why does a wave, like a water wave, spread out after passing through a thin slit? I'm somewhat familiar with Huygens' Principle, but I would like a more physical and intuitive picture of why it happens. How does the section of water entering into the slit know to spread, when it wouldn't have spread if the barriers hadn't been there? What do the barriers do to communicate their existence to the entering wave? 74.15.136.219 (talk) 20:00, 10 July 2011 (UTC)[reply]

Not sure I understand, a wave does spread out without a slit, just like with one. As to why, think of the wave as a lump of water. Gravity would naturally cause it to spread out in all directions. StuRat (talk) 20:13, 10 July 2011 (UTC)[reply]

No. Diffraction causes a wave that has passed through a slit to spread out differently than one that has not. --Srleffler (talk) 17:22, 12 July 2011 (UTC)[reply]

It's called diffraction. That article may help. Let us know if you still have questions after reading it and we'll be happy to help. --Tango (talk) 20:15, 10 July 2011 (UTC)[reply]

Waves do spread into all directions even when barriers are absent. That IS the meaning of Huygens' Principle. Dauto (talk) 20:44, 10 July 2011 (UTC)[reply]

See above. Passing through a slit does change how a wave spreads out. --Srleffler (talk) 17:22, 12 July 2011 (UTC)[reply]

Maybe this pic, http://tinypic.com/r/11i0d5h/7, will show what I mean. Before the section of water enters the slit, it moves without spreading. So why would it start spreading after leaving the slit? Am I mistaken in thinking that (before the wave hits the slit) if the section of water that would ordinarily not pass through the slit were to magically disappear, the remaining water would continue unperturbed, without spreading? 74.15.136.219 (talk) 21:31, 10 July 2011 (UTC)[reply]

I believe you are mistaken. There's nothing special happening at the slit, aside from blocking the rest of the wave. Before the slit, the wave *does* spread out. It's just that the bit of wave on the right spreading out to the left interferes with the bit of wave on the left spreading out to the right, resulting in it looking like no spreading has occurred. (You can potentially visualize this by looking at the second image in Huygens–Fresnel principle, and then mentally adjusting the size of the slit from a point out to being infinite.) -- 140.142.20.229 (talk) 21:41, 10 July 2011 (UTC)[reply]

You are the one that is mistaken. Diffraction does cause a change in how a wave spreads. You've got the right mechanism though: the wave before the slit does not spread (assuming it is a plane wave) due to interference between different parts of the wave. When some of those parts are blocked by the slit, the portion that is left begins to spread out.--Srleffler (talk) 17:25, 12 July 2011 (UTC)[reply]

Also good pointing out that the water is not moving forward in the picture you've shown. It is moving back and forth, up and down, or a combination of both. Dauto (talk) 22:32, 10 July 2011 (UTC)[reply]

I'm trying to see this more physically. When a small portion of water in the wave pulls upward on the water in front of it, are you saying that it creates a circular wave? So that Huygens' principle is not just a mathematical trick, but something physical?74.15.136.219 (talk) 02:41, 11 July 2011 (UTC)[reply]

Yes, it's a physical principle. Any disturbance in the water propagates in all directions. Why wouldn't it? I don't know what you mean by a mathematical trick. Dauto (talk) 05:09, 11 July 2011 (UTC)[reply]

Thanks a lot. Final question: why isn't there a backwards wave? — Preceding unsigned comment added by 74.15.136.219 (talk) 05:50, 11 July 2011 (UTC)[reply]

There are, but all the little waves coming from different points interfere negatively. If you put a patch of material with different properties somewhere in there, the interference will be imperfect and some wave will come back as a partially reflected wave. Dauto (talk) 08:42, 11 July 2011 (UTC)[reply]

Some thoughts:

1) Waves that originate as a point source will spread out circularly on a planar medium.

2) Waves that originate as a line source will spread out linearly in a planar medium.

3) Waves passing through a small slit are slowed at the edges, so spread more like from a point source from there. StuRat (talk) 17:44, 11 July 2011 (UTC)[reply]

Re (3): a change in velocity is not required.--Srleffler (talk) 17:27, 12 July 2011 (UTC)[reply]

Meaningful speculation on existence of anything possible?

Can science meaningfully speculate on why anything (i.e., the universe) exists? 76.27.175.80 (talk) 21:29, 10 July 2011 (UTC)[reply]

There probably isn't any way to formulate a testable hypothesis concerning the reason for the existence of the universe, but untestable speculation abounds, e.g., at Big Bang#Speculative physics beyond Big Bang theory regarding why the universe came in to existence. 99.24.223.58 (talk) 21:54, 10 July 2011 (UTC)[reply]

Science is a means to describe the universe based on the idea of the testable hypothesis, which is not to say that the entirety of the human experience consists solely of testable hypotheses. Many experiences have facets which subject parts of themselves to testable hypothesis, for example one can study the details of a religious experience via science; what parts of the brain are active during religious experiences, what sorts of genetic markers make people more likely to have religious experiences, etc. It can look at why some sorts of art is better received by certain people, what sorts of music is (in general) thought to be pleasant to listen to, etc. Science can study all of that. But the knowledge behind all of these things is not a substitute for the experience itself. Large parts of the human existence, while explainable by science, are still real parts of the human existence, and cannot be substituted by science. Understanding how acoustics and music theory and sound waves work doesn't make The Dark Side of the Moon a more or less enjoyable musical work to listen to; people will still be moved by a painting like The Scream even if they do (or even if the do not) understand the chemical composition of paint. And people can still have a meaningful relationship with their God even if they understand what physics says that the Big Bang looks like, or how evolution works. Don't mistake the understanding of the details of creation for a substitute for a relationship with the Creator (if indeed you are inclined to believe that sort of thing. I make no pretense that you are required to, just that you are allowed to). The two concepts can exist perfectly well in a normal, healthy, intelligent person. --Jayron32 22:09, 10 July 2011 (UTC)[reply]

Car steering

Does a car follow exactly the same curved path backwards as it did when going forwards if the steering wheel follow the same positions (in reverse order)? If it doesn't, is it possible to "park a car" in some defined restricted space, so that it can't be unparked? -- SGBailey (talk) 21:32, 10 July 2011 (UTC)[reply]

I'm pretty sure the general answer is "yes it does so no it isn't," unless for example you were trying to park on an inclined oil slick, in which case you might be able to slide in to a position from which you could not drive out. 99.24.223.58 (talk) 21:58, 10 July 2011 (UTC)[reply]

Despite the logic of the correct reply above, I usually find it easier to "unpark" than to park in a tight space, but I think this is because I usually drive out forwards. On the rare occasions when I try to reverse out of a tight space, I find that to be harder than it was to drive in forwards. Dbfirs 22:24, 10 July 2011 (UTC)[reply]

Also a properly parked car has lower entropy than an un-parked car which means it takes more effort to find the proper maneuver to park it than to find some maneuver to un-park it. Dauto (talk) 22:37, 10 July 2011 (UTC)[reply]

Ah, yes, I like the entropy argument! I think that's the main factor, with my forward/reverse being a secondary factor. Dbfirs 06:42, 11 July 2011 (UTC)[reply]

In general – and in the absence of significant losses of traction and sliding – the car's path is fully reversible; usually the problem arises because the driver's intuition isn't quite as well developed for driving backwards, not because the car has become irreversibly trapped. (Sometimes, of course, a car may become genuinely trapped if someone else has moved the surrounding cars while you were in the shop.) That said, if the no-sliding condition is not met, one can get into an inescapable spot. See, for instance, this video of extreme parallel parking.

Incidentally, your question reminds me of the Douglas Adams novel Dirk Gently's Holistic Detective Agency, a subplot of which involved the protagonist's attempts to manoeuvre a large sofa up and around a cramped stairwell. The sofa became stuck, apparently irreversibly, and remained in place for much of the novel. Complex simulations of the stairwell were employed in an attempt to compute a path by which the offending furniture could be liberated. TenOfAllTrades(talk) 14:30, 11 July 2011 (UTC)[reply]

As an aside, note that the Moving_sofa_problem is still unsolved, even in the simpler 2D case. So Adams' take is actually somewhat accurate ;) SemanticMantis (talk) 16:31, 11 July 2011 (UTC)[reply]

DEET insect repellent dissolving things

I'm aware that DEET insect repellent can dissolve various materials. I want to know whether it's possible to rub it on skin, wait for a period of time and then make contact with vulnerable materials? Or is it constantly able to dissolve those things for as long as it's present on the skin? --2.216.135.118 (talk) 21:33, 10 July 2011 (UTC)[reply]

I am guessing it's not the actual DEET that's doing the dissolving, but rather the fact it uses alcohol as a carrier. Once dried onto the skin it should be fine, but I'd test first because I know it can stain things too. HominidMachinae (talk) 21:56, 10 July 2011 (UTC)[reply]

I agree. Any solvent absorbed into skin loses potency because of the porosity and absorption of skin. 99.24.223.58 (talk) 22:01, 10 July 2011 (UTC)[reply]

Oh yes, it's the actual DEET that does the dissolving. Absolutely it is. Regarding skin, my experience is that as long as it looks shiny/wet it is dangerous, but once it has absorbed into the skin it isn't any longer. Looie496 (talk) 22:03, 10 July 2011 (UTC)[reply]

Yes, our article on DEET says: DEET is an effective solvent, and may dissolve some plastics, rayon, spandex, other synthetic fabrics, leather, and painted or varnished surfaces including nailpolish. and I expect that the worst effects will disappear once it dries, but remember that the skin produces natural oils and these will act to transfer tiny amounts of DEET to anything touched under some circumstances. Dbfirs 22:21, 10 July 2011 (UTC)[reply]

DEET is a liquid at room temperature. Until not so many years ago, you could readily purchase bottles of 99% DEET in camping supply stores and the like. Nowadays the available formulations top out around 30% or so; cost and health considerations led to these more dilute products. (Lower concentrations may also be kinder to your plastic and synthetic products, and don't smell quite so...pungent.) In any case, once you get up to 20-30% DEET, higher concentrations aren't any more effective at repelling insects; they just last longer before needing to be reapplied. 30% is good for 3-6 hours, whereas the old 99% stuff could be effective for 12 hours—if you didn't sweat too much. TenOfAllTrades(talk) 04:09, 11 July 2011 (UTC)[reply]

DEET causes issues with some garment materials. Have worked in outdoor apparel and the DEET tests challenged some polymers.TCO (reviews needed) 04:15, 11 July 2011 (UTC)[reply]

Destroys acrylic fingernails! Bielle (talk) 04:25, 11 July 2011 (UTC)[reply]

First, note that military bug repellent contains much more DEET than what you can buy at the store. I used it when I was in the Marines. Once, I had DEET on when I went to the beach. I carried a radio with me. When I got to the beach, I put the radio down and I noticed that my DEET-laden fingers melted the plastic handle. I still have the radio and there are clear indentions in the handle for each of my fingers. After that, my friends and I experimented on other things. That nearly pure DEET melts a lot of stuff - even on your skin. A good trick was touching styrofoam and melting it with very little pressure. -- kainaw ™ 02:14, 12 July 2011 (UTC)[reply]

I miss the days when you could buy 100% DEET in civilian stores. When I was a kid it was all we used, and it was the only absolutely effective bug spray I've ever used HominidMachinae (talk) 07:29, 12 July 2011 (UTC)[reply]

I have a bottle of 80% here purchased from a civilian store. I've permanently etched my fingerprint into my camera's shutter button with DEET accidentally. JJ Harrison (talk) 07:52, 12 July 2011 (UTC)[reply]

Brief flash of light in the night sky

Last night (10/07/2011) around 10.30pm (GMT +8), there was a flash of light in the sky. It was shaped like a ball. It just appeared out of nowhere and vanished a few seconds later after travelling what seemed to be 2 inches from our view. What could this flash/ball of light be?202.152.86.5 (talk) 23:11, 10 July 2011 (UTC) Was it a shooting star? Was it a comet (though I don't recall a tail)?[reply]

I'm not sure what you mean by 'about 2 inches'? A meteor might be a possibility - comets don't suddenly appear and disappear. AndyTheGrump (talk) 23:21, 10 July 2011 (UTC)[reply]

The OP geolocates to Brunei. The description is not very clear -- a meteor seems like the most likely possibility, but apparently there was a major military air show very recently, so some sort of military aircraft might also be possible. Looie496 (talk) 23:27, 10 July 2011 (UTC)[reply]

The stated timezone (GMT+8) looks like Brunei as well. OP, can you be a little more specific about what you say you saw? If the "2 inches" bit of a "flash of light … like a ball … 2 inches from our view" is literal may this have been Ball lightning? Tonywalton ^Talk 23:53, 10 July 2011 (UTC)[reply]

I agree that a meteor (also known as a shooting star) is the most likely explanation. It could have been a satellite flare. It could have been an aircraft, although I think 10:30pm is quite a long time after sunset in Brunei so you wouldn't have any reflected sunlight (shortly after sunset, the sun can still be above the horizon from the point of view of an aircraft, so the aircraft can reflect sunlight to the ground). As others have said "2 inches" is a little unclear in this context. How many times the diameter of the moon was it, would you say? --Tango (talk) 23:57, 10 July 2011 (UTC)[reply]

Maybe ball lightning? --Jayron32 00:28, 11 July 2011 (UTC)[reply]

If the sky was clear I'd say it was almost certainly a meteor. I'm not a fan of "ball lightning" as an explanation for anything as there really isn't any very good evidence for that phenomenon, I think it's a "last resort" type explanation.. It's likely it could have been just a random meteor, but there's a chance it might have been associated with a known meteor shower. For example the July Pegasids are active right now in the northern hemisphere in the region of Pegasus. If you remember where it was in the sky, get a program like "stellarium" and you should be able to work out what constellations are in that part of the sky, you might be able to match it with a known meteor shower. Vespine (talk) 04:13, 11 July 2011 (UTC)[reply]

Could it be a plane from that air show, high enough up so it reflects the sunlight, going supersonic and creating a water vapor halo that catches the sunset ? If the plane was black it might not reflect much sunlight itself. StuRat (talk) 17:33, 11 July 2011 (UTC)[reply]

It's hard to say what it was. At 10:30pm local time, a plane probably wouldn't be able to get high enough to catch any sunlight. Apparently it was not an Iridium flare, though: no Iridium flares above that location in the past 48 hours. WikiDao ☯ 17:56, 11 July 2011 (UTC)[reply]

If not sunlight, perhaps a searchlight was pointed at it. It would seem rather odd to do an air show at night without some form of lighting, after all. StuRat (talk) 18:56, 11 July 2011 (UTC)[reply]

The airshow was apparently held on July 9th, the day before.[18] I've only seen airshows held in the daytime. WikiDao ☯ 19:08, 11 July 2011 (UTC)[reply]

What part of this does NOT fit "meteor"? I think that's by far the simplest explanation and seems to fit the given details perfectly. Barring any reason to discount that hypothesis why are people still trying to shoe horn other explanations? Vespine (talk) 02:38, 12 July 2011 (UTC)[reply]

Because wild speculation is what the Ref Desk is all about! :) -RunningOnBrains^(talk) 09:10, 12 July 2011 (UTC)[reply]

I'd expect that to have made the local news, since they described it as a "ball", not a "point", so it's pretty big. Also, meteors aren't very common outside of meteor showers. StuRat (talk) 03:59, 12 July 2011 (UTC)[reply]

In all seriousness though, there is no reason to believe it was anything but a bolide (bright meteor, or shooting star as the original poster puts it); they present in all sorts of colors, shapes, and durations. We are asked to identify an object which

Was a flash of light in the sky
Appeared suddenly
Moved across the sky
Disappeared

All of which easily fit the MO of a meteor. Just because very bright meteors don't happen every day doesn't mean it isn't the most likely explanation. I've seen two in my lifetime, and I'm not exactly outside staring at the night sky all the time (or very often at all); neither of these was during a meteor shower. -RunningOnBrains^(talk) 09:10, 12 July 2011 (UTC) Meteors outside of meteor showers are very common. Under good conditions, if you are actually looking for them, you could easily see several an hour on a typical night [19]. Since we have ruled out an Iridum flare (there are some other satellites that can cause flares, but not many), I think we can be 99% certain it was a meteor. --Tango (talk) 12:09, 12 July 2011 (UTC)[reply]

July 11

looking for a picture of fluorine reacting

Can anyone help here...or point me to more places to ask for help?

I want a video (or perhaps a photo) of fluorine gas reacting with something. There is nothing PD (or even that I can think of as an easy donation). Looking for something like in the videos below. Will go into a Featured Article Candidate. Either someone to make it for us or who has it.

http://www.youtube.com/watch?v=mG6EG_igTGw

-or-

http://www.youtube.com/watch?v=V1FsO5zaf6M

TCO (reviews needed) 23:50, 10 July 2011 (UTC

aerospace

how to be an aerospace engineer ???? — Preceding unsigned comment added by Sourabh007sak (talk • contribs) 03:13, 11 July 2011 (UTC)[reply]

Go to college/university, and study aerospace engineering, which is a subdiscipline of mechanical engineering. --Jayron32 03:15, 11 July 2011 (UTC)[reply]

Be sure to heavily emphasize the study of computers, electronics, and software, which are now a significant component of modern aerospace design. Also heavily emphasize the pure sciences, such as physics, chemistry, and mathematics. Aerospace engineering is very broad, so investigate some of its subdisciplines: fluid dynamics; material science; propulsion engineering; control theory; and of course the more broad topics that apply to large engineering projects, such as optimization and operations research. Nimur (talk) 18:35, 11 July 2011 (UTC)[reply]

Start by making paper airplanes. StuRat (talk) 17:25, 11 July 2011 (UTC)[reply]

Be financially prepared to be laid off when the aerospace project is finished. I recall reading about a former aerospace engineer laid off when the Apollo program was done. He was one of the world's experts on electrostatic.electromagnetic shielding of spacecraft, and the only job he could find was driving a cab. NASA just cycled down from 5000 to 1000 employees at Cape Canaveral. Edison (talk) 19:33, 11 July 2011 (UTC)[reply]

A lot of people with an aerospace engineering degree work in a job which is more general engineering. I don't think that fellow would have needed to drive a cab if he would have asked Caterpillar or DuPont if they were interested in a engineer (not specifically a spacecraft static specialist position). Googlemeister (talk) 20:50, 11 July 2011 (UTC)[reply]

The Cambrian explosion

Hello.

I've noticed that a lot of scientific papers of the late 1980s and early 1990s spoke of "dozens" of extinct animal phyla that originated during the Cambrian explosion and have since become extinct. On the other hand, recent scientific literature has declared [almost] all of these phyla to be invalid and has reclassified their members into extant phyla.

I would like to know whether this shift in thinking is the consequence of new palaeontological data becoming available, or it is merely an attempt by scientists to make the phylogeny of the Cambrian fauna appear simpler than it really was.

Is the reclassification of members of these "extinct" phyla into extant phyla supported by the data available in the fossil record? If so, what data has become available since the early 1990s? Thank you very much. Leptictidium (mt) 06:03, 11 July 2011 (UTC)[reply]

It sounds like you are doubting the integrity of the scientists that did the more recent classifications. Do you have any reason for that? Dauto (talk) 08:52, 11 July 2011 (UTC)[reply]

I think the major differences are that cladistics has, more-or-less, taken over, and that we can now use anatomical, genetic and protein markers to figure out phylogenetic trees to get a much better understanding of the tree of life as a whole. Also, we have additional fossil finds that connect different animals and groupings - see e.g. the story of Anomalocaris, which turned from 3 animals into one. --Stephan Schulz (talk) 09:59, 11 July 2011 (UTC)[reply]

A large part of what we know about the Cambrian explosion has come from studying the fossils of the Burgess Shale. One of the proponents of the "many phyla" interpretation was Stephen Jay Gould, whose book Wonderful Life summarises the early Burgess Shale research. An alternative and more "conservative" interpretation, based around convergent evolution, has been championed by Simon Conway Morris. The whole area is the subject of ongoing research. Gandalf61 (talk) 10:07, 11 July 2011 (UTC)[reply]

Are there any specific reasons the "many phyla" interpretation has lost favour in the last couple of decades? Leptictidium (mt) 10:56, 11 July 2011 (UTC)[reply]

I'm not very familiar with the Cambrian explosion fauna, but it could simply be that Stephen Jay Gould's death has removed the most vocal proponent of the hypothesis. Gould literally wrote the book popularizing the Burgess Shale fauna and was also a supporter of what he called "bushiness" of taxonomic families (see Full House for more). Matt Deres (talk) 16:06, 11 July 2011 (UTC)[reply]

It is important to realize that all of our commonly used classification levels (kingdom, phylum, class, etc) are basically artificial. Evolution shows us tree structures with hundreds of branch points if not more -- picking out one particular branch point and calling it the "phylum" level is rather arbitrary. There is tremendous dispute nowadays about the best way to do that. Even when the evolutionary history of a species is well understood (which is often not the case), it may be quite difficult to map it onto the very limited set of levels that Linnaeus defined. Looie496 (talk) 22:03, 11 July 2011 (UTC)[reply]

As we get more details from fossils, the most likely classifications by lineage change. 99.24.223.58 (talk) 23:48, 11 July 2011 (UTC)[reply]

Bear in mind that more and more Vendian fossils have come out, giving more reason to suspect a longer timeline. Wnt (talk) 05:31, 12 July 2011 (UTC)[reply]

Swimming in Jello

I remember a that some university in the Midwest (maybe Minnesota) conducted a study where they compared swimming in water versus various viscous liquids. I think they found that the speeds where the same. Does anyone know the study that I am talking about? I have a reference question (talk) 11:10, 11 July 2011 (UTC)[reply]

http://www.nature.com/news/2004/040920/full/news040920-2.html --Sean 13:42, 11 July 2011 (UTC)[reply]

Mythbusters also tackled the question in their Swimming in Syrup episode, and came to the same conclusion as the University of Minnesota team, i.e., that swimming in a liquid that was about the same viscosity as syrup, i.e., a bit more viscous than water, resulted in a speed that was as fast as swimming through water, within their judgement of experimental error. However, swimming in a liquid that was much more viscous than water resulted in a speed that was much (28%) slower than swimming through water. Red Act (talk) 13:56, 11 July 2011 (UTC)[reply]

I read the above with disbelief until I realised that the syrup was the less-viscous form, not the Golden syrup that immediately springs to mind for readers in the UK. Has anyone ever tried swimming in treacle? Dbfirs 11:52, 12 July 2011 (UTC)[reply]

what is the palm theory？

what is the palm theory？how to use it？ — Preceding unsigned comment added by Wenwenlover07 (talk • contribs) 12:09, 11 July 2011 (UTC)[reply]

Do you mean the Palm–Khintchine theorem? Also, why do you type strange question marks? --Jayron32 12:19, 11 July 2011 (UTC)[reply]

There's nothing particularly strange about the question mark. It's just the 'fullwidth' form ([20]) which likely is the default on a Chinese-language keyboard setup, for compatibility with the wider Chinese glyphs: [21]. TenOfAllTrades(talk) 13:13, 11 July 2011 (UTC)[reply]

They certainly look strange to me, since that font apparently isn't supported on my PC. StuRat (talk) 17:22, 11 July 2011 (UTC)[reply]

There is a literature on Palm theory, but it is very esoteric mathematical stuff -- the study of so-called "Palm measures". Looie496 (talk) 21:56, 11 July 2011 (UTC)[reply]

See Point process and Chapter 13 of [22]. 99.24.223.58 (talk) 00:23, 12 July 2011 (UTC)[reply]

Breeder reactor

They apparantly make more nuclear fuel than what you put in them. My question is, where does the extra energy come from? If they truely created more fuel, wouldnt they be able to both run for ever and supply fuel for other reactors, so that no new nuclear fuel was wever needed. 92.24.187.78 (talk) 14:19, 11 July 2011 (UTC)[reply]

It's not so much that they create more energy than is contained in the starting materials; you're quite right that that would be impossible. Rather, the breeder reaction allows the conversion of stable, heavy nuclei (so-called fertile material) into fissile isotopes which can be used in a reactor. Only a small initial investment of fissile material is required as a source of neutrons to start the breeder process, after that it's theoretically possible to fuel the whole thing with the freshly-transmuted isotopes.

Make no mistake, the breeder reactor is 'consuming' those fertile isotopes; in principle their supply is finite, and eventually even a breeder reactor would run out of fuel. In practice, the fertile isotopes are enormously abundant naturally (at least compared to the naturally-occurring fissile isotopes), and readily-available supplies would last for thousands of years. TenOfAllTrades(talk) 14:43, 11 July 2011 (UTC)[reply]

To elaborate a little bit:

The nuclear reactions in a reactor are generated by the fissioning of fissile isotopes. Fissile isotopes are pretty rare in nature. Far more abundant are fertile isotopes, which, after absorbing a neutron, eventually become fissile isotopes.

So let us imagine our reactor fuel that contains 5% fissile isotopes (U-235, in this case), and 95% fertile isotopes (U-238, for example). While the fissile isotopes burn up, a large number of neutrons are generated. Some of these will deposit in the fertile isotopes, and create more fissile isotopes. In this case, U-238 absorbs a neutron and eventually, after a few days of decaying, becomes Pu-239, which is fissile.

Then we use a big chemical processing plant (see nuclear reprocessing) to extract all of the new fissile isotopes from the used ("spent") fuel, and use that to create new fuel.

As for relative abundance, consider the case of uranium, where less than 1% of all uranium in the world is U-235, and the rest is U-238. (There are other fertile isotopes as well beyond uranium-238.) Now if you could turn all of that U-238 into Pu-239, using just some of that initial less than 1% of U-235, that means you'd have nearly 100X as much nuclear fuel as there is without breeding. In reality the percentages are not necessarily that high (you lose some of the material while reprocessing, and the inside of a reactor is a complicated environment), but it's still a pretty impressive amount (the number our reprocessing article gives is +60X). You're not creating "new energy" so much as using a small amount of "start-up" energy to convert the other isotopes into forms that would be useful for producing energy. (U-238, as found in the wild, is not useful for producing energy — it needs to be put into a reactor and slightly changed before that is the case.) --Mr.98 (talk) 15:01, 11 July 2011 (UTC)[reply]

The short answer: basically any large nucleus will release energy if you break it up into smaller pieces. The problem is that most of the readily available large nuclei are types that are nearly impossible to break. A breeder reactor converts some of the hard to break nuclei into something breakable ("fissile") so that their energy can be released. Rckrone (talk) 16:54, 11 July 2011 (UTC)[reply]

I think that's a little too short and simplistic, personally... --Mr.98 (talk) 21:55, 11 July 2011 (UTC)[reply]

The OP explicitly asks where the energy came from. That question has a simple answer: As with all nuclear reactions, the energy released by a reactor comes from the nuclear binding energy of the atoms. Energy was placed in the atomic nucleus during stellar nucleosynthesis, a very long time ago. A breeder reactor is essentially converting a stable nucleus (with lots of energy that's hard to get out) into an unstable nucleus (with the same amount of energy, or even a little bit less energy, but this energy is easy to release). The energy we harness when we fission atoms in nuclear reactors is basically coming from millions of years of stored heat from stellar fusion: the ultimate fossil fuel. Extreme heat and pressure inside a sun caused small atoms to fuse into larger atoms, locking in that energy in a very stable form, embodied by the strong nuclear force. When we split the atom back apart, we're returning the energy into a useful form: thermal energy, which is used to heat water and drive a steam-turbine. Nimur (talk) 23:36, 11 July 2011 (UTC)[reply]

Er, they asked where the extra energy comes from. Which to me implies that the confusion is over fertile vs. fissile, and why you end up with more fissile material when you end than when you started. (And the rest of the question, beyond the second sentence, makes that more clear.) I don't think it's a question about the origins of binding energy in general. --Mr.98 (talk) 01:38, 12 July 2011 (UTC)[reply]

Large edible leaves ?

I'm trying a low-carb diet, part of which involves making lunch-meat sandwiches using leaves in place of bread. I've been using romaine lettuce. I'd prefer spinach, but the leaves aren't big enough. Is there a variety of spinach with bigger leaves ? Are there any other plants with large, edible leaves ? I seem to recall that stuffed grape leaves are used in Greek cuisine, but do they need to be cooked ? Do we have an article on this topic ? StuRat (talk) 17:19, 11 July 2011 (UTC)[reply]

You could try kale, it should be plenty large enough for sandwiches. 108.15.155.91 (talk) 17:36, 11 July 2011 (UTC)[reply]

Banana leaves are large and inexpensive. Incidentally, you'd be better off replacing the meat than the bread. Instead of your "lunch meat" of ground up lips, eyelids, and anuses, try tempeh or seitan, both of which are high-protein, have a pleasantly meaty texture, and can be made to taste like just about anything with any of a million different recipes you can find easily online. -- SmashTheState (talk) 18:02, 11 July 2011 (UTC)[reply]

If you don't already have a wheat gluten sensitivity, it sounds like seitan would give you one. StuRat (talk) 18:20, 11 July 2011 (UTC) [reply]

Banana leaves are large and inexpensive and inedible. --Sean 18:43, 11 July 2011 (UTC)[reply]

Yes there are plenty of different varieties of spinach, not just the unappetising stuff that comes in bags. I get different ones from my local Indian food shop. When I used to grow spinach, I used to grow Perpetual spinach which had larger leaves if you let them grow. You might also want to try and get Swiss chard or spinach beet. --TammyMoet (talk) 18:05, 11 July 2011 (UTC)[reply]

I rather like the flat-leafed spinach that comes in bags, but it's too small for this purpose. StuRat (talk) 18:21, 11 July 2011 (UTC)[reply]

Cabbage has large leaves and is often eaten raw, e.g., in cole slaw. You might also try Napa cabbage - a better shape for rolling or for making "flat" sandwiches. Or other types of Chinese cabbage.

Grape leaves are wrapped around other foods and cooked. I'm told that the big leaves are too tough to use for this purpose and the small ones are probably smaller than you want. Wanderer57 (talk) 18:42, 11 July 2011 (UTC)[reply]

Would using the concave region of one or more celery stalks count? Those are very high in fiber, so they go well with meats, and they technically have negative net calories. It might be possible to use the leafy regions of celery, which are just as edible and healthy as the stalks, for one half of a meat-celery sandwich, but appropriately cutting, forming, or deviling the meat might turn out to be more labor intensive. *goes to perform an experiment with the celery, chicken and talapia in the fridge* 99.24.223.58 (talk) 23:06, 11 July 2011 (UTC)[reply]

I actually do fill celery with peanut butter (see next question), but lunch-meat doesn't seem like a good fit. StuRat (talk) 00:26, 12 July 2011 (UTC)[reply]

Celery filled with cream cheese and paprika on top! YUM! Vespine (talk) 02:35, 12 July 2011 (UTC)[reply]

No, with cream cheese you need raisins ! StuRat (talk) 03:54, 12 July 2011 (UTC)[reply]

Filling celery with creme cheese or PB kind of defeats the point of celery though. Googlemeister (talk) 13:19, 12 July 2011 (UTC)[reply]

My celery was too droopy to work well with meat, so I ended up having chicken without any vegetables. I would have been far better off with brazil nut butter. I wonder how long that keeps. — Preceding unsigned comment added by 99.24.223.58 (talk) 04:06, 12 July 2011 (UTC)[reply]

Vine leaves are often used for wrapping food in middle-eastern cuisine. --Colapeninsula (talk) 10:25, 12 July 2011 (UTC)[reply]

Making my own peanut butter

I'd like to pour peanuts (or real nuts) into a machine and have a single serving of peanut butter or nut butter come out. This is because jars of peanut butter either seem to contain unhealthy hydrogenated vegetable oil or separate into a layer of oil and a layer of concrete. I supposed I could use a blender, but that would result in peanut butter all clumped around the sharp blades. So, the machine would really need to have it's own method of ejecting the peanut butter. Is there such a device ? I'm also worried that cleaning it after each use may be too difficult, is there a way to make that easier ? StuRat (talk) 17:19, 11 July 2011 (UTC)[reply]

"Peanut butter maker". ~ Mesoderm (talk) 17:21, 11 July 2011 (UTC)[reply]

Thanks. How easy are those to clean ? StuRat (talk) 17:58, 11 July 2011 (UTC)[reply]

Also, if you don't want to buy the machine, many grocery stores (especially co-ops and places that sell good-quality bulk foods) have the machine there, and you can just take a re-usable container with you to fill up with fresh ground PB. It would still probably be cheaper to use your own machine in the long run (and you don't have to worry about what they are cleaning the machine out with at the store). ~ Mesoderm (talk) 17:24, 11 July 2011 (UTC)[reply]

That wouldn't really work for a single serving. If I get more than that, it's going to form concrete between uses. StuRat (talk) 17:58, 11 July 2011 (UTC)[reply]

I'm not sure what you mean about forming concrete between uses. I usually get about a pound or so of it at a time, and it keeps fine. ~ Mesoderm (talk) 18:17, 11 July 2011 (UTC)[reply]

Also, isn't there an emulsifier they can use in peanut butter that's healthier than hydrogenated vegetable oil ? (Our peanut butter article say that palm oil can be used, but that's also unhealthy.) StuRat (talk) 17:58, 11 July 2011 (UTC)[reply]

If you went to a health food shop, no doubt you could find organic peanut butter which would meet your criteria. --TammyMoet (talk) 18:01, 11 July 2011 (UTC)[reply]

Are you sure ? They all seem to separate. StuRat (talk) 18:02, 11 July 2011 (UTC)[reply]

I've been eating pure peanut butter for decades, and separation is perfectly normal. All you do is mix it up before you eat it. I've never had it turn into "concrete," no matter how long it's been sitting. When you mix it up, it turns back into peanut butter. The whole point of eating pure peanut butter is to eliminate the additives like emulsifier in the commercial brands (and to get rid of the aflatoxin contamination that results from mass production). -- SmashTheState (talk) 18:18, 11 July 2011 (UTC)[reply]

And get rid of the salt and the sugar. Bielle (talk) 18:36, 11 July 2011 (UTC)[reply]

^{[citation needed]} please. There's nothing about aflatoxin contamination that is intrinsicly associated with mass production when it comes to food like peanut butter which come from a source (peanuts) at strong risk of contamination.

And I would actually expect organic peanut butter is a greater risk then high quality non organic peanut butter given non usage of fungacides and common poor scientific knowledge of many of those involved. (This mentions a study which found something similar although apparently not specifically on organics [23]/[24] and BTW read Andrew Weil before making any accusations of corporate shill.)

At the very least [25] choosing a reputable organic brand who test their peanut butter for aflatoxin contamination as required by the FDA in the US (e.g. [26]) and actually understand what aflatoxin is, how contamination happens and how to reduce* it; rather then some random home made brand who may not be required to test their products and probably don't and may not even be properly aware of the risk or otherwise believe silly things. *reduce is a key word, anyone who claims their peanut butter has no contamination almost definitely doesn't know what they're talking about.

Nil Einne (talk) 15:51, 12 July 2011 (UTC)[reply]

There's nothing wrong with emulsifiers like lecithin, found in egg white. Elle _{vécut heureuse} ^{à jamais} (be free) 21:59, 11 July 2011 (UTC)[reply]

And does anybody add that to peanut butter ? StuRat (talk) 23:00, 11 July 2011 (UTC)[reply]

Yes, emulsifiers are common in peanut butter, and if I remember correctly, lecithin need not be listed on the ingredients. 99.24.223.58 (talk) 00:10, 12 July 2011 (UTC)[reply]

OK then, is there a brand of PB which uses lecithin in place of hydrogenated vegetable oil, and doesn't separate ? StuRat (talk) 00:21, 12 July 2011 (UTC)[reply]

I'm not sure. Lecithin is a vegetable oil which is usually hydrolyzed, which is like being hydrogenated with enzymes instead of hydrogen. 99.24.223.58 (talk) 01:21, 12 July 2011 (UTC)[reply]

Is that as harmful as hydrogenation ? StuRat (talk) 01:49, 12 July 2011 (UTC)[reply]

Hydrolysis is not the same as hydrogenation.

To my knowledge, lecithin is not harmful, though I wouldn't swear to that. But really, you should just get over caring about the peanut butter separating. As STS said, you just mix it up again. Alternatively, keep it in the fridge (when it's not separated), and it won't separate. Once you get used to natural peanut butter, you'll never go back. --Trovatore (talk) 01:54, 12 July 2011 (UTC)[reply]

I'm certain lecithin is less harmful than its calories, but I'm not sure by how much. Hydrolyzed lecithin is not dangerous in the same way as trans fats, at least not more than about 10% enough to matter, if I remember correctly. Check PubMed for details. 99.24.223.58 (talk) 03:59, 12 July 2011 (UTC)[reply]

Why, if there's a perfectly good emulsifier they could use ? Apparently, we need to dig George Washington Carver up, and put him back to work. :-) StuRat (talk) 03:51, 12 July 2011 (UTC)[reply]

Emulsified doesn't taste as good, that's why not. Try it; you'll see. --Trovatore (talk) 06:48, 12 July 2011 (UTC)[reply]

I had always heard that GW Carver did not invent PB. Googlemeister (talk) 13:17, 12 July 2011 (UTC)[reply]

May be you should consider taking your peanut butter to your local construction supply store and ask them if you could use their paint mixer :). Dauto (talk) 23:47, 11 July 2011 (UTC)[reply]

I learned a few years ago that with simple peanut butter (without whatever chemicals are added to Jif that prevents separation), you just have to mix the concrete and oil with a butter knife for a few minutes (an unpleasant experience because the oil always sloshes out) ... but afterward it does keep mixed for months without separating. I don't know how long the peanut butter has to sit in the jar before it becomes separated in the way you describe. Comet Tuttle (talk) 06:31, 12 July 2011 (UTC)[reply]

Surely the oil that comes out of peanuts is groundnut oil? What's the problem with eating that? --TammyMoet (talk) 09:09, 12 July 2011 (UTC)[reply]

When the butter is first made, and I would try an ordinary food processor first to see if it works, it is an emulsion, right? So if you want it thinner for spreading, you add water as you mix. You could add oil as well or instead but then it will be a little more high in calories. Just like making hummus, really. Itsmejudith (talk) 16:50, 12 July 2011 (UTC)[reply]

Is Coeliac_disease an allergy?

It's clear to me that it's not wheat allergy, but as a "is an autoimmune disorder of the small intestine", does it count as allergy ("a hypersensitivity disorder of the immune system")? Quest09 (talk) 20:01, 11 July 2011 (UTC)[reply]

It seems like there is a lot of confusion regarding this question. Doing a quick google I've found lots of pages that say it is an allergy and some pages even say coeliac disease is caused by a wheat allergy, but not many of them count as what I'd call reputable sources and I think that is incorrect. I think this excerpt has a reasonable and concise explanation. (In short, no, there are some similarities but they are different things.) Vespine (talk) 22:38, 11 July 2011 (UTC)[reply]

Question about scintilating scotoma

My younger brother is interested in being a pilot for the US Air Force, but he has rare occassions where he experiences a Scintillating scotoma. He says he gets one about 5-6 times a year and they last from 15 minutes to an hour. Does anyone know if that kind of thing would disqualify him from that kind of a position? Googlemeister (talk) 20:47, 11 July 2011 (UTC)[reply]

I believe those are far more common than the literature indicates -- I've looked into it because I get them too every so often. I believe that many people get them without realizing it. It's potentially a problem because if the scotoma passes through the foveal area, you get a small blind spot right at the center of vision. Recommending what to do, however, would constitute medical advice in my opinion, so I won't. Looie496 (talk) 21:46, 11 July 2011 (UTC)[reply]

I agree that these are probably fairly common, but I am not sure they are always associated with a stationary blind spot. The occular muscles would need to be paralyzed for that to be the case, unless they were very large compared to those depicted in the article. It isn't medical advice to recommend being honest with the recruiter if asked about vision. I would hope military recruiters would have some kind of a guideline on their intake physical questionnaires, but those aren't known for being read very carefully. The frequency does seem to be high, but I recall that my phosphene, which is much more striking and likely to be remembered, was at least twice as frequent when I was decades younger; perhaps because I was getting more exertion. 99.24.223.58 (talk) 22:57, 11 July 2011 (UTC)[reply]

The problem is that when a scotoma occurs in the fovea, you can still see things by looking off to the side, but they won't be sharp -- the sharp part of your visual field is roughly the size of your fist held at arm's length. Reading, for example, becomes very difficult. That's the thing that first clued me in that I was experiencing a scotoma -- otherwise I probably never would have noticed. Looie496 (talk) 23:05, 11 July 2011 (UTC)[reply]

Wow! I've totally had this and never knew what it was: Thanks again ref desk:) It only happens rarely and doesn't last very long and I don't get migraines, but it's actually made me wonder if I'm having a stroke or something, lol. (i'm mid 30s so didn't think it was likely).. Now I know! it won't bother me so much. Vespine (talk) 02:33, 12 July 2011 (UTC)[reply]

I get these painfree migraine symptoms occasionally too. We have an article on their likely cause, Cortical spreading depression, but this Scientific American article is quite good. Sean.hoyland - talk 03:12, 12 July 2011 (UTC)[reply]

The majority of that article seems to require a paid subscription. Googlemeister (talk) 16:44, 12 July 2011 (UTC)[reply]

I can read it all without a subscription. Try this single page version. Sean.hoyland - talk 16:55, 12 July 2011 (UTC)[reply]

software filter on imageJ/photoshop

I need this for my research, and it would help my lab a lot. Is there a way to apply a software filter or script to remove out of focus objects (and the background) and keep in-focus particles? The particles in question are fruit flies, viewed from the bottom of a vial. We want to count the number of flies that are strictly in the focal plane of the bottom of the vial, and not count the flies not on the bottom (the ones at the bottom are suffering from the effects of cocaine).

I've tried some resources online, but they seem optimised for cells. I was thinking of also "scoring" the flies -- to see how far away from the bottom they are, so the ones at the bottom (the most in focus) would have a strong score, and the ones that are near the bottom have a weak score. Any variety of attacks would help. Thanks so much! Elle _{vécut heureuse} ^{à jamais} (be free) 22:12, 11 July 2011 (UTC)[reply]

This question would probably be more appropriate for the Computing desk, but basically I believe what you want is an edge detection filter. Edge detection works by picking out points that have a strong contrast with neighboring points, and that's what you want. Looie496 (talk) 22:33, 11 July 2011 (UTC)[reply]

[27] might be a place to start. Cells are diverse enough that if you want to do better, you might need to look at [28], but that might be a lot more work than simply counting the number of background pixels showing through the region at the bottom from one or more side view(s) of the vial instead of trying to use focus blur from a top or bottom view. 99.24.223.58 (talk) 00:11, 12 July 2011 (UTC)[reply]

Sounds related to focus stacking, except you only want to keep/extract the focal-plane of one image rather than extract and merge from multiple. DMacks (talk) 01:06, 12 July 2011 (UTC)[reply]

The simpler technique is to grab an undergrad, give him some of the cocaine, and order him to count the flies on the bottom of the vial. You'll find the proper amount of cocaine will produce results at 3 Hz. Comet Tuttle (talk) 06:25, 12 July 2011 (UTC)[reply]

Fluorescent lights in a brown-out

We recently had a brown-out (reduced voltage to around 83 V versus normal 110-120V). The incandescent and LED lights got dimmer, but still functioned, and even the compact fluorescents were OK, while the traditional (long tube) fluorescent lights went nuts, flashing frenetically. This was quite annoying, as the basement has all fluorescent lights, and that's where the fuse box is, which is where we wanted to go to investigate the brown out. We ended up using flashlights. So, is there a type of long tube fluorescent light which is more tolerant of voltage swings ? StuRat (talk) 23:11, 11 July 2011 (UTC)[reply]

Nope, that's one of the trade offs for their efficiency relative to incandescent and low cost relative to LEDs. 99.24.223.58 (talk) 23:46, 11 July 2011 (UTC)[reply]

Compact fluorescents with their electronic ballasts are apt to fail and even ignite when the applied voltage drops that low, unless they are the "dimmable" ones which cost several times as much as generic ones. An intentional "brownout" by a US utility usually aims to drop the voltage far less than to some value way higher than the reported 83 volts, which is likely to destroy many motor operated appliances, unless their circuit breakers or fuses open due to the excess current drawn. Computers and TVs are unlikely to operate at that low a voltage. Gas appliances which use an electric igniter typically do not operate correctly either (some gas ovens spew out gas without igniting it, with the possibility of a gas explosion). Personally, I would kill the power to everything but an incandescent bulb, using it or a voltmeter as an indicator of when the power came back on. The utility would typically trip distribution circuits offline if they had central control of the substation. Maybe there was something weird about the local transformer or connections to the residence, like a loose neutral. Edison (talk) 03:26, 12 July 2011 (UTC)[reply]

Do you have any sources supporting the use of "apt" there as meaning more likely than not? 99.24.223.58 (talk) 03:37, 12 July 2011 (UTC)[reply]

Here. He used the word correctly. Comet Tuttle (talk) 06:22, 12 July 2011 (UTC)[reply]

I could be wrong but I think 99 is asking for a source supporting the claim the electronic ballasts in CFLs intended for a 120V/US supply are apt to fail at 83V Nil Einne (talk) 15:58, 12 July 2011 (UTC)[reply]

I considered that providing only 83 volts to a 120 volt bulb was comparable to operating it on a dimmer, although modern dimmers remove portion of the sine wave from each cyclo rather than proving a full sine wave at a reduced voltage. Some lighting installations I maintain actually use a hugh Variac (rotating variable autotransformer) to dim a room full of incandescent bulbs smoothly. Here is a 1995 reference: [29] "First, be sure not to use compact fluorescent bulbs in circuits that have dimmers - they could present a fire hazard in these uses." Here is a 2009 report on a home which, according to fire investigators, caught fire due to compact fluorescent bulbs controlled by a dimmer. An article from 2008 says "Never use a CFL with a dimmer in the circuit, even if it is set (and kept) at the maximum setting. It will keep you at risk of fire, and will significantly shorten the lifetime of the lamp and the dimmer." General Electric advises against using CFLs on a dimmer if they are not labelled as suitable for such, but understandably they do not mention the fire hazard. I've heard numerous recent reports of early failures of CFLs (without fire) when they are improperly used on a dimmer. Compact fluorescents can also start fires if they are used in a fully enclosed fixture, and they sometimes emit smoke and a burning smell, and have discoloration of the base when they fail in normal use at the end of their service life, per [30]. A "normal " end-of-life CFL burnout may result in smoke being emitted for 30 seconds, sometimes sufficient to set off a smoke alarm, per [31], along with popping sounds, flickering of the light, and a charred base. In October, 2010 the US Consumer Product Safety Commission recalled 124,000 compact fluorescent bulbs sold in 2008 because they could "overheat and catch fire" with no statement that dimmers were involved. Edison (talk) 17:49, 12 July 2011 (UTC)[reply]

Metals

I recently found a piece of metal at the beach. My local jewler did a test, his machine said it was 99% SE. What is SE? — Preceding unsigned comment added by 98.77.106.79 (talk) 23:33, 11 July 2011 (UTC)[reply]

Se (formatted with a lower-case "e") is the chemical symbol for Selenium; but that seems very unlikely for a piece of scrap metal. (Pure selenium is rarely used in industrial metallurgy, and almost never occurs in nature). Maybe your report is using some more specialized domain-specific nomenclature. Or, it might mean "something else" - for example, if he performs a standard chemical test for gold, silver, or precious metals, the test may simply indicate any other material as "something else." Nimur (talk) 23:43, 11 July 2011 (UTC)[reply]

I'm guessing it just means it's a "stainless (steel) equivalent." Ask the jeweler. 99.24.223.58 (talk) 00:00, 12 July 2011 (UTC)[reply]

July 12

Astronomical interferometer wavebands

What are the wavelength or frequency endpoints of the "waveband" designations on List of astronomical interferometers at visible and infrared wavelengths? 99.24.223.58 (talk) 01:45, 12 July 2011 (UTC)[reply]

The article Photometric_system has a table. --Wrongfilter (talk) 07:19, 12 July 2011 (UTC)[reply]

Evolution

We know many different species evolved in the history of animal kingdom. But why evolution has stopped after the arrival of Homo sapiens? We are the last product of evolution. Why no new species in being evolved? --111Engo (talk) 11:17, 12 July 2011 (UTC)[reply]

Your premise is incorrect. Humans are not "the last product of evolution." Evolution continues, new species are being evolved. We are just too short-lived to see it happening. --- Medical geneticist (talk) 11:38, 12 July 2011 (UTC)[reply]

(edit conflict):Who says that evolution has stopped and that we are the "last product"? Evolution is a very slow process and is continuing (as far as I know), though only adaptation has been directly observed in real time. We haven't been around for long enough to observe it happening in our species, though tiny changes currently observed might be part of the long-term process. The view of evolution as being a linear process from simplest to highest lifeforms is not generally accepted. The actual path is often very complex, with "dead ends" and convergence. Dbfirs 11:42, 12 July 2011 (UTC)[reply]

Evolution is a continuous and ongoing process and did not mysteriously stop with the arrival of Homo sapiens. One example of a new species that is much younger than Homo sapiens is the polar bear, which diverged from the brown bear about 150,000 years ago. Another even younger species is the London Underground mosquito. Gandalf61 (talk) 11:43, 12 July 2011 (UTC)[reply]

Is any new biological trait observed among Homo sapiens within the last 10,000 years? --111Engo (talk) 12:19, 12 July 2011 (UTC)[reply]

Lactose tolerance in adults, see here. Mikenorton (talk) 12:23, 12 July 2011 (UTC)[reply]

(edit conflict) The ability to digest lactose into adulthood (known as "lactase persistence") is a likely candidate. Lactose intolerance#Evolutionary history says it has only reached significant proportions in human populations within the last 10,000 years, linked to the spread of animal husbandry. Gandalf61 (talk) 12:26, 12 July 2011 (UTC)[reply]

Also the prevalence of the Sickle cell trait in areas of high incidence on malaria (not sure that this one is proven). Mikenorton (talk) 12:45, 12 July 2011 (UTC)[reply]

Your initial premise is clearly wrong, as others have pointed out. However, if you want to say, "why do humans seem to be less selected against genetically than other animals?", and we want to grant that perhaps this is true, the obvious answer is that humans are the first animals to develop big enough brains, and some happened to be under the right conditions to develop what we call civilization, technology, and so on, to the degree that we have. Note that it took humans a loooonnggg time to escape "nature, red in tooth and claw," and arguably we haven't escaped it all that well, even so. It is not like Homo sapiens showed up and suddenly humans were the dominant animal on Earth, or suddenly had control over our natural environment. If you want to know, "what factors led to the emergence of the kind of modern, big-city, big-production, big-technology civilizations?" you might take a look at Jared Diamond's Guns, Germs, and Steel which does a very nice job of articulating all of the many factors that had to fall into place for the big, organized societies to rise up in the last few thousand years, which allowed for the kind of apparent "insulation" from natural selection that you are no doubt referring to. Even then, it isn't really perfect insulation, and to call that non-"natural" is a stretch. --Mr.98 (talk) 14:33, 12 July 2011 (UTC)[reply]

Indeed. Consider that anatomically modern humans are first observed in the fossil record at about 200,000 years ago and that the first human civilizations developed sometime in the Neolithic Revolution about 10,000 years ago. That means that essentially modern humans existed for 190,000 years before deciding that farming and living in cities would be a good idea, or if you prefer that only 0.5% of human history has been civilized. --Jayron32 15:40, 12 July 2011 (UTC)[reply]

Farming in particular is not an obvious thing, as Diamond points out. It's not like early man sat around and said, "you what would be great? To be a farmer, a style of living that has not yet been invented!" It was a slow and difficult process and very early on it did not confer any major benefits over a hunter-gatherer lifestyle. (In fact, Diamond points out, early farmers probably had much poorer diets and caloric sources than did hunter-gatherers.) Furthermore, as Diamond points out, living in farming communities exposes you to all sorts of other risks, like epidemic diseases brought about through close contacts with domesticated animals. Anyway, the whole point is that it's too big (and interesting) a question to sum up as being somehow humans being magically "outside" of evolution. --Mr.98 (talk) 15:47, 12 July 2011 (UTC)[reply]

wireless power transmission

what is the circuit diagram ofireless power transmission??? — Preceding unsigned comment added by Maryam chaudhry (talk • contribs) 12:19, 12 July 2011 (UTC)[reply]

what is the circuit diagram of wireless technology????? — Preceding unsigned comment added by Maryam chaudhry (talk • contribs) 12:21, 12 July 2011 (UTC)[reply]

Wireless energy transfer gives some detail but not a circuit diagram. At its simplest, just two coils would be sufficient. Wireless technology often refers to the transfer of data over a wireless network, but I assume this is not what you were asking about. Dbfirs 15:47, 12 July 2011 (UTC)[reply]

How shall we name the phenomenon?

When material "Escapes" from inside the organ through it's membrane --- out. ?

Thanks. — Preceding unsigned comment added by 79.181.33.137 (talk) 13:17, 12 July 2011 (UTC)[reply]

Do you refer to the serous membrane? EverGreg (talk) 13:27, 12 July 2011 (UTC)[reply]

Osmosis is a method of passage through a membrane. Wanderer57 (talk) 13:33, 12 July 2011 (UTC)[reply]

Neither really describes the phenomenon, if it exists without rupture of the cell walls. Osmosis is only water passing through the semi-permeable membrane, and serous fluid is a secretion rather than an escape, but I'm at a loss to provide a better answer. Dbfirs 15:57, 12 July 2011 (UTC)[reply]

Red-violet

Looking through a box of crayons, I encounter a color dubbed "red-violet". Red and violet are on opposite ends of the visible light spectrum. However, violet is a mix of blue and red. How can there be a cycle in a spectrum? Where on the spectrum does the "red-violet" color exist? 75.73.225.224 (talk) 14:33, 12 July 2011 (UTC)[reply]

I believe you're confusing two things: the spectrum as a physical phenomena, and the colors our brain interpret the physical phenomena as being (as qualia). The human eye does not use a linear spectrum to interpret light; it uses a series of rods and cones which fire signals depending on what hits them. It's the way the eyes and brain are wired which makes the ends of the spectrum appear to loop together. Color vision has a lot more detail on this sort of thing. You might also look at Color_wheel#The_color_circle_and_color_vision, which discusses a bit the difference between actual human color vision and a perfectly looped color wheel. --Mr.98 (talk) 14:43, 12 July 2011 (UTC)[reply]

Other good reads in this regard are Imaginary color and Line of purples. There are many "non spectral colors" in the world, besides the purples are the browns and the pinks, and things like that. They are usually made (spectrally) by combinations of lights of many different wavelengths, though some combinations are actually impossible (called Impossible colors). For example, there is no "reddish-green" color. --Jayron32 15:35, 12 July 2011 (UTC)[reply]

84,000 chemicals

What are the names and uses of the 84,000 chemicals in use today in the USA? — Preceding unsigned comment added by 75.181.43.47 (talk) 15:10, 12 July 2011 (UTC)[reply]

All of them? --Jayron32 15:29, 12 July 2011 (UTC)[reply]

I started writing a list of the usage of dihydrogen monoxide got about 1% of the way and then my browser crashed. Nil Einne (talk) 16:05, 12 July 2011 (UTC)[reply]

Here are few off the top of my head to get you started. Acetone, Benzene, Chloroform, Diethyl ether, ethane, Formaldehyde, gasoline, heptane, Iodine, kerosene, liquid nitrogen, Monosodium glutamate, naptha, oxygen, pentane, Salicylic acid, taurine. Googlemeister (talk) 16:33, 12 July 2011 (UTC)[reply]

If you're looking to round out the alphabet, I suggest jasmone, quinine, rubidium chloride, uranium hexafluoride, vanadium carbide, water, xenon hexafluoroplatinate, yttrium aluminium garnet, and zinc telluride. -RunningOnBrains^(talk) 18:10, 12 July 2011 (UTC)[reply]

This question is perhaps more sensible than it sounds. I believe the question refers to the TSCA Inventory, the list of chemicals registered under the Toxic Substances Control Act of 1976, which includes about 84000 chemicals. The full dataset can be downloaded from the US government here. --Colapeninsula (talk) 16:53, 12 July 2011 (UTC)[reply]

Then we need to correct the OP's view that chemicals are all bad, perhaps by pointing that a lot more than 84,000 chemicals exist, including those that make up the human body and everything else around us. Most of them are quite nice chemicals. HiLo48 (talk) 17:22, 12 July 2011 (UTC)[reply]

I would hazard an educated guess that there are indeed more than 84,000 times 84,000 chemicals known to man, especially if you include theorized compounds not yet isolated. -RunningOnBrains^(talk) 18:10, 12 July 2011 (UTC)[reply]

Sycon

Is Sycon radially symmetric? — Preceding unsigned comment added by 122.179.68.190 (talk) 16:01, 12 July 2011 (UTC)[reply]

Are you referring to a genus of sponge? If so, then it appears from diagrams that at least the arms of some genus members are typically radially symmetric, if not the entire organism. -RunningOnBrains^(talk) 17:56, 12 July 2011 (UTC)[reply]

Natural gas ownership in the US

I'm an American, and as I suspect is the case for most people like me, I have one and only one choice when it comes to who is my natural gas provider. In other words, they have a monopoly on my area. I would suspect this is the case in most localities (I have no reason to believe my locality is exceptional). To my own sense of right and wrong (which I realize has no jurisdiction on reality), this only seems fair if the company owns the land where the natural gas came from and paid to lay ALL the pipe to the houses from which it collects money. Do the natural gas companies in fact usually own the land from which they extract their product? If not, how does one company get into such a favorable position over all other hopefuls? 76.27.175.80 (talk) 18:23, 12 July 2011 (UTC)[reply]

There are several related issues which confounds answering all of your questions.

First, natural gas is extracted from the ground by a company who owns the mineral rights to do so. Mineral rights is a tricky thing, but generally different entities may own the surface of the land and the land underneath. This entity which extracts the oil and/or gas is usually a completely private company, and can be of any size, from a small "mom-and-pop" operation to a large multinational corporation like BP or Exxon/Mobil. These extraction companies sell the natural gas to the company that sells it to you. That is, the "Gas Company" doesn't extract and refine the gas, they are simply the retailer. They buy it on the wholesale gas market, much the same way that Walmart doesn't actually make the blue jeans you buy there.
Secondly, distribution of natural gas to your house is managed by a public utility. In the U.S., public utilities are semi-private companies which are heavily regulated by the government; in exchange for the monopoly they have on distribution, they give up a lot of their own freedom with regards to the rates they charge, how much profit they make, etc, which are regulated by the state governments. The rationale they have over distribution is that, unlike many goods which are efficient to be produced and distributed by a single company, like say a car or bread or landscaping services, utilities like gas require a complex distribution system which would be HIGHLY inefficient if you had, say, several companies distributing gas to your city.
Lets say you decide to buy your gas from Joe's Natural Gas. So Joe's comes and lays pipes to your house. Lets say your neighbor decides to buy from Bill's Natural Gas. Does Bill's now lay another set of pipes to your neighbor's house? Does every company have its own network of pipes? What a mess if every time someone wants to install natural gas, they pick a company and that company has to find a way to dig giant trenches all over the place to lay new pipe! Furthermore, what if you decided to leave Joe's and take your business to Bill's. Does that mean Joe's comes and digs out all of the pipes that used to bring you gas, and Bill's has to lay new pipe? What a complete mess that would be.
Instead, a single company is in charge of distributing natural gas to a jurisdiction. They lay one set of pipes, and everybody buys from them. Yes, it isn't competitive, but in this case competition isn't so great, since the result of having an open market on public utilities is a rediculously inefficient thing. So certain services, such as power, water, electric, solid waste removal, local landline phone services, etc. are managed as public utilities. Since there isn't a "free market" regulating price, these services are heavily regulated by the state instead.
Thirdly, the company that laid the pipe isn't necessarily the company selling you the gas. Instead, the company selling you the gas probably leases the pipe from the pipeline company.

As a final note, you may find Oil and gas law in the United States an interesting read. --Jayron32 18:50, 12 July 2011 (UTC)[reply]

Thanks for that very informative answer, Jayron32. The "Gas Company" retailer from your first bullet, is that the same entity as the semi-private "Public utility" in your second bullet? 76.27.175.80 (talk) 19:05, 12 July 2011 (UTC)[reply]

^ PMID 8210311
^ PMID 18046752
^ Elsimar M. Coutinho and Sheldon J. Segal (1999). Is menstruation obsolete?. Oxford University Press.
^ Paul Bischof and Marie Cohen. "Course 4:Implantation" (PDF). European Society of Human Reproduction and Embryology.
^ Cite error: The named reference Premack, D. G. 1978 was invoked but never defined (see the help page).

[1] PMID 8210311

[2] PMID 18046752

[3] Elsimar M. Coutinho and Sheldon J. Segal (1999). Is menstruation obsolete?. Oxford University Press.

[4] Paul Bischof and Marie Cohen. "Course 4:Implantation" (PDF). European Society of Human Reproduction and Embryology.

[Premack,_D._G._1978-5] Cite error: The named reference Premack, D. G. 1978 was invoked but never defined (see the help page).

[1]

[2]

[3]

[4]

[5]

@@ Line 684: / Line 684: @@
 :*Thirdly, the company that laid the pipe isn't necessarily the company selling you the gas.  Instead, the company selling you the gas probably leases the pipe from the pipeline company.
 :As a final note, you may find [[Oil and gas law in the United States]] an interesting read.  --[[User:Jayron32|<font style="color:#000099">Jayron</font>]]'''''[[User talk:Jayron32|<font style="color:#009900">32</font>]]''''' 18:50, 12 July 2011 (UTC)
+::Thanks for that very informative answer, Jayron32. The "Gas Company" retailer from your first bullet, is that the same entity as the semi-private "Public utility" in your second bullet? [[Special:Contributions/76.27.175.80|76.27.175.80]] ([[User talk:76.27.175.80|talk]]) 19:05, 12 July 2011 (UTC)