Welcome to the science section
of the Wikipedia reference desk.

Select a section:

WP:RD/S

Want a faster answer?

Main page: Help searching Wikipedia

How can I get my question answered?

Select the section of the desk that best fits the general topic of your question (see the navigation column to the right).
Post your question to only one section, providing a short header that gives the topic of your question.
Type '~~~~' (that is, four tilde characters) at the end – this signs and dates your contribution so we know who wrote what and when.
Don't post personal contact information – it will be removed. Any answers will be provided here.
Please be as specific as possible, and include all relevant context – the usefulness of answers may depend on the context.
Note:
- We don't answer (and may remove) questions that require medical diagnosis or legal advice.
- We don't answer requests for opinions, predictions or debate.
- We don't do your homework for you, though we'll help you past the stuck point.
- We don't conduct original research or provide a free source of ideas, but we'll help you find information you need.

Ready? Ask a new question!

How do I answer a question?

Main page: Wikipedia:Reference desk/Guidelines

The best answers address the question directly, and back up facts with wikilinks and links to sources. Do not edit others' comments and do not give any medical or legal advice.

January 23

air compressor

I want to know that what is two-stage air copressor? and how i done it's intercooling and thermal analysis? —Preceding unsigned comment added by Munish malik (talk • contribs) 00:24, 23 January 2009 (UTC)[reply]

See our article titled Gas compressor, expecially the section with the name Staged compression. Cheers! --Jayron32.talk.contribs 02:42, 23 January 2009 (UTC)[reply]

how do explosions destroy things

will ... i looked about the meaning of explosions , and it was a rapid chang in volume , but i need to understand whats the mechanisem of destruction effect ... how did it destroy objects within the range . —Preceding unsigned comment added by Mjaafreh2008 (talk • contribs) 01:28, 23 January 2009 (UTC)[reply]

Shock wave? Also, even a simple "rapid change in volume" means there's a lot of force pushing out in all directions...push against "something" hard enough and it will break. DMacks (talk) 01:48, 23 January 2009 (UTC)[reply]

Overpressure says that (for example) C4 explosive produces 10 psi (pounds per square inch) of "overpressure" (although it doesn't say how much C4 or in how much volume?!?) - but let's run with that number. Suppose you have a brick wall that's 20' long by 10' high. That's around 30,000 square inches - and at 10psi of pressure, the explosion would exert a third of a million pounds of pressure onto the wall! It's really not hard to imagine why that would destroy the wall! SteveBaker (talk) 03:03, 23 January 2009 (UTC)[reply]

Another way to look at it: The forces exerted by the explosion are not applied equally for all parts of the exposed object – typically having the greatest effect on the near exposed surface of the object. That causes internal stresses (compression, tensile, sheer, or torque) within the object which may exceed its strength. The result is that the object distorts or breaks up. Those same forces may then accelerate different parts to different velocities resulting in a scattering of the remains.

In contrast, if the forces were applied equally to the entire object, down to the atomic level inside and out, the object would remain intact because there would be no internal stresses. Theoretically, the object could survive near-infinite acceleration in such cases. Examples would include gravitational and possibly electrical and magnetically induced acceleration. For example, the earth's gravity exerts an enormous amount of force on the ISS, but the station remains intact because the force is applied uniformly. If an equal force were applied using a thruster pack connected to one module of the station, the resulting stresses would likely cause structural failure. -- Tcncv (talk) 05:15, 23 January 2009 (UTC)[reply]

And note that if it is easier for the object in question to maintain its structure and to just move, it'll do that rather than be destroyed, even if the explosive force is huge. (See, for example, Project Orion (nuclear propulsion)) --98.217.14.211 (talk) 11:18, 23 January 2009 (UTC)[reply]

Viewing memories from a cat's brain?

Did I dream this? I remember reading, a few years ago, an article about a scientific study that was able to somehow find images from the memory of the cat, somehow encoded into its brain cells. It was accompanied by a few blurry pictures of a man that were said to be from the cat's brain. Knowing what I know now about how memory works, this seems somewhat unlikely, but I'd like to find the article again. Does anyone know about it? Was it a hoax? 99.245.92.47 (talk) 01:52, 23 January 2009 (UTC)[reply]

This is the closest I could find on a quick search. I'm pretty sure it's not the article you were after, but will (purr-haps) jog your memory? Cycle~ (talk) 02:36, 23 January 2009 (UTC)[reply]

That's by measuring the neural activity in realtime - that can only work at the instant the cat sees the image. There is no way we know enough to extract a memory of an image - that would require decoding the entire storage mechanism - and we are a tremendous way away from being able to do that. It was either a hoax or you are remembering the research on seeing the images in realtime. SteveBaker (talk) 02:55, 23 January 2009 (UTC)[reply]

I would not be surprised if something like this were possible far in the future, but it seems beyond the capabilities of today's technology. I note that there was a recent report of a brain scan technique which could brain imaging to accurately detect which letter of the alphabet a person was looking at, and iirc they hypothesized that the technique might also allow determining which letter the subject was thinking of. Edison (talk) 05:25, 23 January 2009 (UTC)[reply]

Yes - but that's still "What you are thinking about right now" - and that's a VERY different matter than "Extracting images from memories". It's pretty clear that our memories of scenes from the past do not consist of a bunch of pixels stored away like a photo in your computer. Instead we have a bunch of associations. We have a picture on the wall at home that I "remember" - there is a river with some canal boats and a pub in the background. I can "picture" that painting clearly in my mind - but I can't tell you the colors of the boats or the number of windows on the front of the pub. That's because I'm only remembering the concept of "classic village pub", "river" and "canal boats" - I don't have anywhere in my brain the actual image stored. Hence, in order to reconstruct that image, the computer would have to be able to extract from my memory not just the memory of the painting - but also my general concept of what a village pub typically looks like. That would require decoding more or less the whole of the brain function - and THEN being able to reconstruct the pathways by which we remember things. Worse still - if the person remembering that photo was an expert on 18th century architecture - he wouldn't be remembering a "village pub" - he'd be remembering a particular style of architecture and construction. An expert on canal boats would be remember a particular boat manufacturer and a specific model number they produced. A horticulturalist might remember the species of tree off to the left of the pub. Someone who's been there will also remember the flavor of the beer they serve there and details of the pub interior that aren't even IN the painting. No two people will remember that picture in the same way. We know that memories are stored in a diffuse 'holistic' manner so nothing short of scanning the connections between every neuron in the brain would enable us to do this. So this is AMAZINGLY beyond our current understanding - let alone the technology to measure what we'd need. Worse still - the number of neural connections in even a cat's brain are vastly too great to store in the available RAM + disk space of even a pretty large super-computer. So even if we knew what to do - we don't have the storage space to process it. It's going to be 30 to 40 years of "Moores law" improvements before we have a computer that has the power to do this - I'm betting a hundred years before we know enough about brain organisation to do it. This is science-fiction technology. So our OP is DEFINITELY mistaken. The only question is how/why. SteveBaker (talk) 14:21, 23 January 2009 (UTC)[reply]

Here's the story Edison's referring to — Matt Eason ^{(Talk  Contribs)} 01:35, 25 January 2009 (UTC)[reply]

It was more recent than 1999, and definitely talked about memories, but thanks. 99.245.92.47 (talk) 05:51, 23 January 2009 (UTC)[reply]

Your are either mistaken - or you've been hoaxed. It's not remotely possible with todays technology. SteveBaker (talk) 14:21, 23 January 2009 (UTC)[reply]

They did a study on cats dreaming where they removed the block that keeps cats (and us) from moving their muscles in response to the dreamed reality. They found cats dream about hunting and stalking. But that's not memories either, they might have mentioned those in the report, though. 76.97.245.5 (talk) 09:18, 23 January 2009 (UTC)[reply]

Hmmm - if they'd used dogs they could have saved themselves a lot of trouble! I've owned many dogs over the years and you can EASILY tell that this is what they are dreaming about because that suppression of muscle action during REM sleep isn't as complete as it is with humans (and perhaps cats). Dogs sleep a lot - so you have plenty of chance to watch! When you see their eyes start to move under their eyelids - you know they are entering REM sleep. Then within seconds you can see the tips of their paws twitching as they walk in their dreams - you see the feet first twitch in a 1-2-3-4 pattern like they are walking - then you see them start to twitch in pairs like they are running - you can see their bodies heaving like they are breathing fast (but they really aren't) - then you will see the jaws moving and the cheeks puffing slightly in and out and you may even hear very soft barking (more like little 'yip' sounds). On some occasions, I've seen the dog's running pattern stop and chewing actions happen in the jaw. It's totally compelling - my dog dreams of running and chasing things - sometimes of catching and eating them. No question about it. Cats on the other hand...who knows? SteveBaker (talk) 14:18, 23 January 2009 (UTC)[reply]

Yeah, cats do that too. I don't know why they felt the need to operate on some cats' brains to see this when I've had countless cats go through the same thing curled up on my lap. They run, they creep, they pounce, they bat prey, they eat it. All in twitching paws and jaw, sometimes with little smackings of the mouth. 79.66.105.133 (talk) 12:53, 25 January 2009 (UTC)[reply]

Do female athletes and sportswomen, especially in 'masculine' sports, have more testosterone than average women?

I would expect so but is there any good scientific work on the subject? Just seeing today's featured article made me think about it.--Ib.nib op.cit. (talk) 06:31, 23 January 2009 (UTC)[reply]

Because they say (citation needed) that oestrogen is produced by fat, and that testosterno is produced by muscle. Is this true?--Ib.nib op.cit. (talk) 06:34, 23 January 2009 (UTC)[reply]

Here is a nice review of the scientific literature: Athletes’ Testosterone Levels by Sports Team: An Exploratory Analysis. Note also that during the Cold War, East Germany decided to administer about 60 times the natural level of testosterone per day to their female athletes (under the direction of Manfred Ewald). The result was striking. Although a relatively small country, the GDR excelled in the Olympic medal tables during the late 70s and 80s. Their female athletes and swimmers did particularly well. Rockpocket 07:09, 23 January 2009 (UTC)[reply]

It's important to distinguish between the questions, "do women who have more testosterone tend to end up in 'masculine' sports?", and "do women in masculine sports tend to end up with more testosterone?". --Sean 12:46, 23 January 2009 (UTC)[reply]

One of the problems that the sports officials have had is determining whether some of their "female" competitors are truly female (See: Santhi Soundarajan)- to that end they have defined limits to the amount of testosterone that they consider normally "female" and a few women have been outraged to discover that they are excluded from female sports because the officials consider them to be "men" by virtue of their body chemistry [1]. So I think the answer is likely to be a cautious "yes". Cautious because of the definition of a "masculine" sport...weight lifting? shot putt?...yeah - sure. Is rifle shooting "masculine"?...if so then I need to change my answer and say "no". SteveBaker (talk) 13:48, 23 January 2009 (UTC)[reply]

In the Physical exercise article you see that one of the consequences of exercise is increased testosterone production. So yes, female athletes will have more testosterone than other females, but male athletes also have more testosterone than other males due to the amount of exercise they do. Anythingapplied (talk) 15:00, 23 January 2009 (UTC)[reply]

Neanderthal cranial size

What is the current consensus concerning the cranial capacity of H. neanderthalensis? Was it smaller, about the same, or larger than H. s. sapiens? Viriditas (talk) 09:27, 23 January 2009 (UTC)[reply]

We have an article: Cranial capacity which contains a table of cranial capacities:

Orangutans: 275–500 cc
Chimpanzees: 275–500 cc
Gorillas: 340–752 cc
Humans: 1100–1700 cc
Neanderthals: 1200–1700 cc

So more or less the same. Of course we have FAR more human skulls to measure - so we know where the outliers are in the data set (ie we've seen incredibly small and incredibly large skulls) - but the relatively limited number of Neanderthal skulls that we've found could easily mean that we simply have not yet found any of the larger or smaller-brained individuals yet. That suggests to me that the 1200 to 1700 range is probably narrower than it really was. That's why I'd tend to say "larger".

We should be careful about what we take away from those numbers though. Larger skull capacity doesn't necessarily equate to greater intelligence. Neanderthals also had much larger nasal cavities than modern humans - so they may have had a very acute sense of smell - that being the case, they may have devoted more of their brain to processing, analysing and remembering olfactory sensations. So even with a larger brain than us - they may not have been as smart. Also, while Neanderthals were typically shorter than modern humans - they would have been taller than the humans that were when Neanderthals were common - and their body's were generally chunkier. (Our Neanderthal article somewhat scathingly compares them to modern Americans & Canadians!) But our Brain to body mass ratio and Encephalization articles point out that a rough measure of intelligence can be obtained by comparing the ratio of body mass to brain size between species. So even with slightly bigger brains, if their bodies were significantly larger than the humans of their era then perhaps we have to assume that they were not quite so smart. (Did I just imply that Americans and Canadians are stupid?)

But whatever the difference - it would probably be fairly small and there would certainly have been some Neanderthals who were smarter than some Humans - and vice-versa.

SteveBaker (talk) 13:39, 23 January 2009 (UTC)[reply]

That last bit is an easy claim to make. Clarityfiend (talk) 00:13, 24 January 2009 (UTC)[reply]

Neanderthals (who should probably be considered to be human, but a different subspecies from modern humans) survived under harsh conditions for hundreds of thousands of years. Their tenure might even surpass that of mmodern humans, when all results are in. Not really so stupid as some modern humans like to think. Much of the criticism of Neanderthals sounds like early 20th century "racial superiority" screed of eugenicists about the supposed superiority of some groups of humans over others. Edison (talk) 00:00, 24 January 2009 (UTC)[reply]

The problem is - if they were smarter and stronger - how come they were out-performed by the cromagnons? It's not a matter of 'racism' - it's a matter of scientific enquiry. In the changing environment of that era - they must have had some flaw (compared to modern humans) - it's just a question of what that flaw was. SteveBaker (talk) 00:17, 24 January 2009 (UTC)[reply]

It's possible that their flaw was just a lack of luck, of course. Algebraist 00:20, 24 January 2009 (UTC)[reply]

One theory suggests that the cro-magnons (modern humans) may have out competed the Neanderthals because the environment changed in Paleolithic Europe from dense forests to wide grasslands due to the change in climate.[2] The modern humans were pre adapted to a grassland environment because they migrated to Europe from Africa. The Neanderthals hunting strategies, tools and physical characteristics were better suited to a dense forest habitat. The Neanderthals were ambush hunters while as modern humans were better suited for perusing game across long distances which may have given modern humans a tremendous advantage over the Neanderthals (moderen human's physical build made them better runners[3] and their weapons and hunting stratiges were better adapted to a grassland enviorment). Neanderthals presumably used heavy spears to stab prey while as modern humans used lighter spears to throw at animals from a distance which also was more useful in a grass land environment. Also because of their large stocky builds Neanderthals may have required more calories than modern humans (Neanderthals may have required as much as 5,000 calories a day while as modern humans only require 2,000 or 3,000 calories a day)[4] and because their hunting methods became inefficient with the changed landscape they probably did not get the energy they needed and starved to death.--Apollonius 1236 (talk) 13:39, 24 January 2009 (UTC)[reply]

Thanks. Can anyone recommend the most recent articles or research on the subject? I added this statement to the Neanderthal article: "Neanderthal cranial capacity is thought to have been as large or larger than modern humans, indicating that their brain size may have been the same or greater." Is this accurate? Based on what I've read, I think it is. Recently, User:Tibbets74 added this statement: "however, a 1993 analysis of 118 hominid crania concluded that the cranial capacity of H.s. neandertal averaged 1412cc while that of fossil modern H.s. sapiens averaged 1487cc."[5] I temporarily moved it to a footnote because referring to a study from 1993 raised a red flag for me. Obviously, there's been new research since then and I found it strange to refer to a single paper (from 16 years ago) in the lead section. Any ideas? Or is this discussion best suited for the article talk page? Viriditas (talk) 04:02, 24 January 2009 (UTC)[reply]

OK - we've switched from a RefDesk question to a question about what Wikipedia should or should not state...those are not the same thing! No - a 1993 peer-reviewed paper trumps what we said here. The article should contain Tibbet74's comment and not yours because you have no references. Measurement of skull volumes is not likely to have changed over 16 years so his/her reference is an excellent one despite it's age. (The RefDesk uses references - it doesn't create them!). But (a) a sample of only 118 skulls is not many and (b) it's NOT true to say that brain size matches cranial capacity and (c) a difference of 75cc in a skull of around 1400cc is likely to be close to the limits of experimental error and (d) the range of sizes in one species is something like 1200 to 1700 - so while a 75cc increase might indicate an average brain size - it tells you nothing about one individual Neanderthal versus one individual human. However, a fact is a fact - and Tibbet74's fact is a good one. If you need to dispute it then you need references of your own...and this debate belongs on the Talk: page of the article...not here. SteveBaker (talk) 14:52, 24 January 2009 (UTC)[reply]

Thanks, but I think you misunderstood (and assumed too much from) what I wrote. I know how the RefDesk works, and my edit to the Wikipedia article was made 23 minutes before I asked my question, not after. I never said I didn't have references (I do and I still need to add them) and Tibbet's material is still in the article as a note. What I did request was a) a summary of the current consensus on the matter, and b) any recent, important articles on the subject. As for facts, depending on the field or subject, they tend to change over time, as I'm sure you are aware, so citing a paper from 1993 when there are more recent papers on the subject is a red flag. Also, the lead section isn't the best place to introduce new information, which is why I moved it to a note and made a minor change to what was previously in the lead. Viriditas (talk) 08:33, 25 January 2009 (UTC)[reply]

Brain size does not nessecarily correspond to intelligence. ~A H 1^(TCU) 18:08, 25 January 2009 (UTC)[reply]

spiral bevel gears

Can the teeth of spiral bevl gears can be forged directly without any machining? —Preceding unsigned comment added by 203.90.64.100 (talk) 10:57, 23 January 2009 (UTC)[reply]

First, what size? Microscopic gears can be produced by building them up layer by layer or laser cutting. Small ceramic gears can be baked from powdered metal. As for larger metal gears the question would come to: Would that be feasible and what properties would you gain in the process? AFAIK machining is a cost efficient way to produce the desired precision of pitch and regularity. 76.97.245.5 (talk) 16:06, 23 January 2009 (UTC)[reply]

Electronics

I'm having trouble trying to understand something to do with electricity/electronics. In a circuit current is said to take the path of least resistance. So what I don't understand is why parallel circuits work: wouldn't the current just flow through the path which has the least resistance? --212.120.247.244 (talk) 14:07, 23 January 2009 (UTC)[reply]

Everything that moves is said to take that path. The "resistance" in "path of least resistance" is the general word meaning opposition to movement. The "resistance" in electronics is a special case of the word, borrowed rather than make up a new one, a well-defined term meaning something like "opposition to the gross movement of electrons in non-reactive media". There is another, more specific term, "impedance", that actually applies more accurately to electronics and is the word best thought of when thinking about these things. Bottom line, electrons do not take the path of least resistance, they take all paths available in inverse proportion to the impedance of those paths. --Milkbreath (talk) 14:42, 23 January 2009 (UTC)[reply]

How about if you connect a superconductor and a non-superconducting wire in parallel? Will the non-superconductor get truly no current whatsoever? Not even due to some quantum mechanical random process thingamagic? 88.114.222.252 (talk) 14:50, 23 January 2009 (UTC)[reply]

Let's do the math. Ohm's law says I=E/R. We can't use that, because division by 0 is undefined (boy, am I glad this isn't the math desk—they'd eat me alive). So let's look for the voltage drop across the superconducting leg: E=IR, the voltage drop equals the current through the leg times zero, zero. With zero voltage drop across the parallel array, there can be no current through any resistive leg, because current through that leg would cause voltage drop, and there has to be a potential difference for there to be current. So, right, no current. I'll hand this off now to anybody who feels qualified to do that voodoo that the quantum guys do so well. --Milkbreath (talk) 15:23, 23 January 2009 (UTC)[reply]

It's like a traffic jam. There are two routes from A to B. Route #1 is slightly shorter (less 'resistance') than route #2. So all of the cars start heading down route #1...but this causes a traffic jam - so now, smart motorists will take route #2 because even though it's a bit longer, it'll get them from A to B faster because there is no traffic jam...this relieves the traffic on route #1 - so now people go that way because it's faster. In a perfect world where everyone behaved rationally and everyone had 'perfect information' - the two routes would carry traffic in inverse proportion to their 'resistances' so that everyone gets there in the best possible time. That's what happens with electrical resistance - which is why the current splits in inverse proportion to the resistances of the two paths. The "path of least resistance" thing is a kind of rule of thumb - it's not physically what happens. MOST of the electrons take the easy route - and if there is a significant disparity then it'll SEEM like they all took the path of least resistance. So if you wire up a short length of copper wire (with a resistance of say 0.001 ohms) in parallel with a ten megaohm resistor - then almost all of the current flows down the wire (1/0.001 versus 1/10000000 - so a billionth of the electricity struggles through the resistor and all of the rest takes the copper and your science teacher can boldly tell you that the electricity took the path of least resistance). If you take a 100" length of copper wire and a 101" length of copper wire and put those in parallel - then their resistance is so similar that the voltage will travel down both at almost exactly the same rates. SteveBaker (talk) 14:56, 23 January 2009 (UTC)[reply]

I like to think of it as pipes (conductors) and water (electrons), where a small diameter pipe is like a wire with more resistance. So, if you have two ways for water to drain out of a lake, one being a large pipe and one being a small pipe, water will drain down both pipes, but more will go down the large pipe (which is like the wire with least resistance). StuRat (talk) 15:39, 23 January 2009 (UTC)[reply]

The "path of least resistance" thing is a rule of thumb; but in order to be true it would imply that, ahead of time, each electron knows before it enters a wire which wire it should go down to travel down the "path of least resistance". In reality, the first electrons through will go down both wires at exactly the same probability, until the electrons start to "back up" to the junction, at which point further electrons will still choose their path randomly, but will now not choose 50/50 but will choose by the ratio of the resistance between the wires. --Jayron32.talk.contribs 17:30, 23 January 2009 (UTC)[reply]

I think a philosophical approach must be taken here. In the superconductive branch R is not zero. It simply does not exist. It cannot exist in a superconductor. Since R does not exist, the formula I=E/R cannot be applied - one of the terms is missing. – GlowWorm —Preceding unsigned comment added by 98.17.34.148 (talk) 22:14, 23 January 2009 (UTC)[reply]

IR=E looks less mathematically impossible: Ix0=0 is true for any I. And that's correct...you can load an essentially arbitrary amount of current into a superconductor. An algebraist would say "dividing both sides of IR=E by R is not appropriate if R could be zero" precisely because it would lead to a limitation not present in the original equation...if you're gonna do that, you have to keep separate track of that side-effect of the manipulation. DMacks (talk) 23:19, 23 January 2009 (UTC)[reply]

If someone tells you that - you simply have to point out that the "original" form of the equation could have been IR=E and transforming it into I=E/R could have been the mathematically invalid step. So which form of the equation is the 'real' one? I'm going with the convenient one! SteveBaker (talk) 01:50, 24 January 2009 (UTC)[reply]

Superconductors have no resistance, but there appears to be a limit to how much current they can carry. If one exceeds its critical current, at a given temperature and magnetic field "quench." This quenching property can be used as a fault current limiter [6]. Are there superconductors immune to this limit, or are there ways of operating them (extremely low temperature?) that avoid quenching? Seems doubtful. Maybe someone has studied the phenomenon. It is a real problem in superconduction magnet windings, where quenching results in the stored energy becoming heat and often destroying the winding. Edison (talk) 23:55, 23 January 2009 (UTC)[reply]

Another thing to keep in mind (though I now see it's already been mentioned) is that superconductors have zero resistance, not necessarily zero impedance. That is, current flowing through a superconductor does not lose any energy to dissipation. It can still lose energy to, for example, radiation, and it should be possible for there to be a transient potential difference across it. So to answer 88.114.222.252 is that sure, the non-superconductor can get some (transient) current. --Trovatore (talk) 03:31, 24 January 2009 (UTC)[reply]

What Trovatore says makes sense; the impossibility of perpetual motion and the inviobility of the second law of thermodynamics pretty much guarantees that all systems will "bleed" energy in some form. While a superconductor may lack resistance in the traditional sense, what it does not lack is the fact that there is some friction-analog in the system. If nothing else, electrons in motion generate a magnetic field, and this magnetic field will interact with other availible magnetic fields (even, like, the earth's own magnetic field) such that over time, the magnetic fields in the super conductor will interact these other magnetic fields, gradually slowing down the flow of electricity. It may well be a VERY gradual slow down, but its still real, and it still allows the system to obey the laws of physics. --Jayron32.talk.contribs 04:47, 24 January 2009 (UTC)[reply]

Well, it's not going to slow down because of a static magnetic field. You have to have a changing field to change the current in a superconducting loop. I don't offhand see any reason it wouldn't be as likely to increase the current as to decrease it.

Perpetual motion machines ~~"of the first kind"~~ "of the third kind", the ones that just keep moving but you can't extract any useful work from them, are not a priori impossible -- consider an electron orbiting an atom (assuming there's no such thing as proton decay). --Trovatore (talk) 04:52, 24 January 2009 (UTC)[reply]

Think about it this way. In a circuit, the conducting wires' resistance is so low that there's barely any difference in the different paths of a parallel circuit. Assume that the resistance is zero (which of course isn't the case), and you'll see why 2 x 0 and 4 x 0 both = 0. That little bit of extra distance really doesn't make much of a difference. Unless, of course, there's a resistor lined onto the conducting wire for every centimetre of wire, then there'd be a difference. ~A H 1^(TCU) 16:03, 24 January 2009 (UTC)[reply]

I'm not sure what you're responding to here. In a superconductor, according to currently accepted theory, the resistance really is exactly zero.

But, if I've analyzed this correctly, that doesn't mean that if you put a superconductor parallel to a normal conductor and then apply voltage, you'll get zero current in the normal conductor. The reason is that the DC laws do not apply perfectly except to entirely unchanging systems (of which there aren't any).

When you turn on the voltage, a current starts to flow in the superconductor, which generates a magnetic field, which stores energy. That means you have to supply the energy to create the magnetic field. Therefore it doesn't happen instantly. In the mean time there is a potential difference across the normal conductor, and therefore also some current. --Trovatore (talk) 22:55, 24 January 2009 (UTC)[reply]

Just in case no one has mentioned it above (I cant be bothered to read it all) I should mention the Current splitting rule--GreenSpigot (talk) 04:14, 25 January 2009 (UTC)[reply]

OOoh look we have an article on this. Its called Current divider--GreenSpigot (talk) 04:17, 25 January 2009 (UTC)[reply]

microbiology

what i meant by streptolysin test,where is it applied and which is the procedure of carrying it out? —Preceding unsigned comment added by 196.202.206.37 (talk) 14:48, 23 January 2009 (UTC)[reply]

Do you mean Antistreptolysin O titre? If so, follow the references at the bottom of that article. SteveBaker (talk) 14:59, 23 January 2009 (UTC)[reply]

Question about the hologram universe article in New Scientist issue 2691

I love this article - fantastic stuff [[7]]

But it made me wonder: if 'the amount of information papering the outside must match the number of bits contained inside the volume of the universe', do the theorists believe that includes all the information implicit in everything we do? - do the bits include changes across time in our physical universe? if so, are the bits also changing across time, or are the changes themselves also encoded in the bits?

Thanks Adambrowne666 (talk) 21:21, 23 January 2009 (UTC)[reply]

I'm not sure I understand your question. I've read the article, and it's rather vague, and seems to try to explain everything in layman terms, which probably add more confusion than it resolves. I'm sure the original authors have a solid mathematical description of their theory. Our article about the Holographic principle has some more information about this topic. baszoetekouw (talk) 21:53, 23 January 2009 (UTC)[reply]

In "holographic" theories, there is generally a one-to-one correspondence between states on the boundary and states on the inside. In other words, things on the inside change if and only if things on the boundary also change. Dragons flight (talk) 22:10, 23 January 2009 (UTC)[reply]

Thanks, Dragons - sorry for not explaining myself, Baszoetekouw; will check out the article. Adambrowne666 (talk) 03:55, 25 January 2009 (UTC)[reply]

What does "space is a vacuum" mean?

Does space have atoms? Or just nothingness? It sure would be fun to capture a jar of that! When space bends from nearby mass, what exactly is it that's bending!? This has always confused me. Why does your blood boil in space? --THE WORLD'S MOST CURIOUS MAN (talk) 23:16, 23 January 2009 (UTC)[reply]

We have a detailed Outer space article, which includes a whole section about the environment (i.e., "what is in there?"). Outer space is a definite and fairly simple thing--be careful not to confuse it with the more advanced idea of spacetime. DMacks (talk) 23:26, 23 January 2009 (UTC)[reply]

Every atom has a gravitational field that extends to infinity. Therefore a light beam cannot be outside gravitational fields. In the case posited, the atoms of the glass jar will affect the light except where two atoms cancel each other's gravitational field because they are equidistant on each side of a point position in the light. More distant atoms will augment the gravitional field of the jar atoms. – GlowWom. —Preceding unsigned comment added by 98.17.34.148 (talk) 23:44, 23 January 2009 (UTC)[reply]

So many questions! Fortunately - for today only - the RefDesk has a five-for-the-price-of-one deal!

Does space have atoms? Or just nothingness? - yes, there are atoms - but a LOT less than here on the surface of the earth. As you move out deeper and deeper into space - the number of atoms in every cubic meter gets less and less. In orbit, near the earth, there are still quite a lot of atoms - enought to gradually slow satellites down so that they have to be boosted into higher orbits once in a while. Out near Pluto - there is a lot less. Halfway between our star and the next one - there is almost nothing - but still there will be the odd atom here and there. In the deep voids between galaxies - less even than that.
It sure would be fun to capture a jar of that! - not really. You can get the same effect (a totally empty jar) with a decent vacuum pump down here on earth. But it would have to be quite a sturdy jar not to collapse from the pressure of the earth's atmosphere pushing in on it without any air inside pushing back the other way.
When space bends from nearby mass, what exactly is it that's bending!? - space ITSELF is bending...the actual nothingness bends...
This has always confused me. - you and just about everyone else! The things that go on in the universe frequently only make sense when you look at the mathematics. Most of the time, you have to simply turn off your common sense and trust to the numbers.
Why does your blood boil in space? - it's not exactly true that it does. Liquids behave strangely - they both freeze AND boil at the same time. Water left alone in the vacuum freezes AND evaporates from the surface. It freezes because it's cold - it boils because there is no air pressure to oppose the molecules flying off the surface. When a human is exposed to space, the fluids take a while to cool down to freeze - and your skin applies some tension to prevent it from immediately boiling. It's generally believed that humans could survive a brief exposure to the vacuum. We have an article about that Vacuum#Effects_on_humans_and_animals and Human adaptation to space.

SteveBaker (talk) 00:04, 24 January 2009 (UTC)[reply]

It doesn't freeze because it's 'cold' exactly; it freezes because it is evaporating. Space isn't exactly cold in any meaningful sense. 79.66.105.133 (talk) 12:48, 25 January 2009 (UTC)[reply]

Good answers, but your answer to #2 is not quite right...interstellar space is much emptier than any vacuum achievable at the earth's surface(according to this Tufts page). It would certainly be interesting to some scientists to study the "nothingness" out there in more detail.-Running On Brains 01:54, 24 January 2009 (UTC)[reply]

That's an interesting page and it accords well with our Vacuum#Quality article. However, us humans can employ more ingenious tricks than nature itself, things like getters, and can make an ultra high vacuum that's pretty competitive with most regions of space. Maybe you're thinking of intergalactic space being much emptier, as Steve noted. Franamax (talk) 02:37, 24 January 2009 (UTC)[reply]

Well, yes - indeed. Worse still - even if you got a super-hard vacuum, a few microseconds later, some silicon and oxygen atoms shed from the glass jar itself would contaminate your pure vacuum. Yeah - indeed - you don't get a pure vacuum here on earth.

The actual numbers are rather revealing:

Best artificial vacuum: 10⁹-10⁴ molecules per cm³
On the Moon: 4x10⁵ molecules per cm³
Interplanetary space 10 molecules per cm³
Interstellar space 1 molecule per cm³
Intergalactic space 10^-6 molecules per cm³ (1 molecule per cubic meter!)

So we can maybe get down to ten thousand molecules per cm³ - which is a better vacuum than the surface of the moon...but nowhere near as good as in the space between planets, between stars or between galaxies. SteveBaker (talk) 03:30, 24 January 2009 (UTC)[reply]

What about vacuum energy? ~A H 1^(TCU) 03:22, 24 January 2009 (UTC)[reply]

The source to a lot of these facts are from the book Modern Vacuum Physics by Austin Chambers which is can be read online at google books here —Preceding unsigned comment added by Anythingapplied (talk • contribs) 07:08, 24 January 2009 (UTC)[reply]

Your blood doesn't boil in outer space. At least, not unless you get a cut. It won't freeze unless it boils, as the boiling is what causes it to cool enough to do so. See freeze drying for why this would happen. It would make you saliva and the water on your eyes boil. — DanielLC 22:49, 25 January 2009 (UTC)[reply]

You don't need a particularly sturdy container to contain ultra high vacuum. Most any walled glass vessel will do. The pressure difference across the wall is almost the same whether the vessel contains rough- or ultrahigh- vacuum. ike9898 (talk) 20:33, 26 January 2009 (UTC)[reply]

Energy stored in air, compressed by supersonic object

There is an object, say a flat square, that is accelerated to supersonic speeds. This will create a shock wave behind the object. But also, many waves will all crunch together directly in front of the object and build up an area with high pressure. What is the energy of these waves in front of the object?

This might be hard to figure out without any specific numbers, but you can just assume whatever is reasonable, because I was just wondering whether the energy is enough to knock over a person. --Yanwen (talk) 23:55, 23 January 2009 (UTC)[reply]

That energy is what creates a sonic boom. Where is this person standing? If they are directly in front of the object, then the object itself will knock them over... --Tango (talk) 00:03, 24 January 2009 (UTC)[reply]

Right, the plane or whatever will probably run into the person and kill him because he is in the direct path of the shockwave (and supersonic airplane). But I just need a rough approximation of the energy of the shockwave in Joules or something.--Yanwen (talk) 22:08, 25 January 2009 (UTC)[reply]

Also, as an analogue, I've heard that an unsuitable plane flying into a sonic boom (passing the sound barrier) would be like passing into a brick wall. ~A H 1^(TCU) 03:19, 24 January 2009 (UTC)[reply]

There must be some factors which limit the energy in a sonic boom, or else a plane traveling at the speed of sound would have a wave in front that would build up without end. StuRat (talk) 06:41, 24 January 2009 (UTC)[reply]

Well, the wave spreads out, that's why you can hear it. --Tango (talk) 22:10, 24 January 2009 (UTC)[reply]

Most of the sound waves aren't aimed straight forward, so those you can hear. But, the portion of the waves headed straight forward should theoretically "collect" at the leading tip of an aircraft going exactly mach 1. StuRat (talk) 15:11, 25 January 2009 (UTC)[reply]

Conveniently that portion is 0, since "straight forward" is zero solid angle. Moreover, any air that is being carried with the plane (as would have to happen if there was any collection going on) can now carry energy away and dissipate it, because its bulk speed is that of the plane and it can propagate sound relative to the plane at its sound speed. As you get farther in front of the plane, the bulk speed drops (toward the ambient air's speed) — and the sound speed changes in some more complicated way — until a point is reached where the sum falls to the plane's speed and the disturbance can just keep its lead. The energy added to that disturbance by the oncoming air is dissipated around the aircraft by the intermediate zone which is capable of doing so. --Tardis (talk) 16:58, 26 January 2009 (UTC)[reply]

So you're saying there's a dead spot, straight in front of a plane, where it's absolutely silent ? I find that difficult to believe. StuRat (talk) 21:20, 27 January 2009 (UTC)[reply]

Well, at any non-trivial distance in front it will be silent, because the plane is supersonic. Otherwise, I'm not sure what you mean — are you talking about the leading edge of the disturbance? There's a shock wave there which is (effectively) discontinuous, and there is presumably noise behind it (because information can propagate up to it from behind) and no noise in front of it (where nothing has happened yet). In the shock itself (which is actually at least a few atoms wide) concepts like "sound" don't really apply because the gas does not act like a fluid on that length scale. There will probably be vibrations of some sort in it that decay as you move forward through the shock. --Tardis (talk) 04:54, 28 January 2009 (UTC)[reply]

Chaos Theory. Is this a croc, or what?

There is essentially no randomness. Everything unfolds in a certain order, or else it wouldn't have happened that way. Every single thing is the absolute result of an absolute action. Correct?--Sunburned Baby (talk) 23:46, 23 January 2009 (UTC)[reply]

Moved this question here from the Misc. desk. -- Captain Disdain (talk) 00:21, 24 January 2009 (UTC)[reply]

Sorry, there is randomness. See determinism and quantum indeterminacy. Chaos theory is a little different: it's the idea that even if there *wasn't* any randomness, a complex system is so sensitive to its starting conditions that you can't predict the outcome anyway. --Sean 00:38, 24 January 2009 (UTC)[reply]

No - Sunburned Baby is not correct. If anything, the complete opposite is the case! True, fundamental randomness is everywhere.

Heisenberg's uncertainty principle guarantees that you can't know exactly where a particle is and what speed it's going at - hence randomness at the lowest levels of existence.
Schrodinger's equation is the fundamental description of a particle - it says that (for example) an electron is essentially a "probability cloud" a fuzzy blob of uncertainty.
Quantum theory - particles and antiparticle popping into existence from literally nowhere - more randomness.
At the level of atoms - an atom of uranium 232 has a half-life of around 70 years. This means that if you have a big pile of the stuff - half of it will have decayed down to something else after 70 years. But if you have just one atom - there is a 50/50 chance of it breaking down before 70 years are up. But you don't know when it'll do that. The event of the atom emitting a neutron is completely and utterly random.
Even at the 'macro' level Chaos theory says that no matter how precisely you measure some kinds of events - you can't do so precisely enough to predict what comes next. Take my favorite example. Place a large sheet of paper on a table. Put two magnets a few inches apart onto the paper - mark their positions - call one of them "RED" and the other "BLUE". On some kind of very rigid stand, tie a pendulum with a magnetic 'bob' on the end so it hangs somewhere between the two magnets. You'll need two pencils - one red, the other blue. Now - hold the pendulum over the paper and note the point beneath it. Let the pendulum swing around - it's swing will be disturbed by the two magnets - but eventually - the bob will come to rest hovering over one or other of them. Mark the point where you released the pendulum from with either a red or a blue dot depending on where it ended up. Do this a LOT of times. What you find is that there are some 'release points' where the pendulum always ends up over the red magnet - and others where it ends up over the blue. If you do the experiment enough times - you'll see there are large, solid areas of red marks and large solid areas of blue marks. But there are some areas that are striped or checkered alternately red/blue/red/blue. There are areas where those regions get very small and it becomes impossible to start the pendulum from the EXACT position where you released it before so the red and blue gets all mixed up. But the equation for the motion of the pendulum is well known - it's very simple physics - so we can program a computer to simulate the pendulum's motion. But even when you calculate where the regions of red and blue are in the simplest system with no air resistance and no friction and a perfectly flexible bit of string and idealised perfect magnets - the 'map' of red and blue starting points is a fractal...like the mandelbrot set. So the closer you look at the picture, the more detail it reveals. In some areas of your table - moving the starting point of the pendulum by even a millionth of the width of an atom is enough to change the outcome. Since quantum theory and the uncertainty principle apply to the pendulum bob - this experiment "amplifies" quantum uncertainty to the point where it matters.
It goes on...Hawking radiation from black holes is random. Catastrophy theory induces fundamental randomness. Godel's theorem says there are fundamental pieces of mathematics that can neither be proven true or false.
There are 'for real' infinities and zeroes in the universe - and when you plug those into sane, normal equations - the answer often comes out "undefined" - so some things are fundamentally unpredictable.

The universe is a total mess! Your idea of the clockwork universe is about as far from the truth as it's possible to be. This upsets a lot of people - Einstein spent almost all of his productive life trying to 'fix' this. But sadly - the computer you're sitting in front of right now wouldn't work if the universe worked 'mechanically' without randomness.

SteveBaker (talk) 01:36, 24 January 2009 (UTC)[reply]

Your examples are somewhat incomplete. Schrodinger and Heisenberg don't, by themselves, introduce randomness. They replace our concepts of deterministic point masses, with wave functions that still obey deterministic rules. Rather it is the process of measurement that introduces randomness by forcing the wave function to choose amongst multiple states in a probabilistic manner. It is only that process of wavefunction collapse that is random. The rest of the time, wave functions evolve according to rules that are just as deterministic as the rest of physics (even though the objects they describe act in ways that are hard to understand). In fact, wavefunction collapse might also be just an illusion, in which case, all of quantum mechanics is deterministic, albeit in a way that does not correspond to the classical notions of how matter should behave. Dragons flight (talk) 02:19, 24 January 2009 (UTC)[reply]

On another note, this is one of the areas where I have problems. You say that the randomness becomes apparent when a measurement is made, and looking at that article (through the forest of tags), it mentions "observers" and "measuring apparatus". This implies that physicists have wisely confined themselves to describing only their particular experiment and acknowledged that if they hadn't written down the results, the results might not have actually happened. But that plus a dollar buys me a cup of coffee. If a bird flies through the photon stream, is it an observer? Is its feather a measuring apparatus? What about a rock? What if the cat was late-period pregnant when it went into the box? Does it have a born/unborn kitten? We have pretty solid evidence that kittens are not quantum states, so when that kitten gets born, does it become a measuring apparatus? I can follow the line of reasoning, but it does seem to me that it leads pretty quickly to "stop asking" as the next response. Either that or "many worlds" which to me is mis-stated, it should be "incredibly huge number of worlds within the first two nanoseconds". This stuff has bothered me for a long time. :) Franamax (talk) 03:01, 24 January 2009 (UTC)[reply]

It's worth reading Neal Stephenson's latest book (it's fiction - and oddly compelling) - his idea of 'state space' is another interesting take on many worlds - it takes things yet one step further than classic many-worlds. SteveBaker (talk) 03:36, 24 January 2009 (UTC)[reply]

(ec) I see nothing "sad" about this. I'm kind of mystified why people would want the world to be deterministic. What would be the point of anything, then?

On the other hand, QM's challenge to realism (see for example Aspect experiment) is rather more disturbing. I just recently saw in the article on hidden variable theories that Edward Nelson has a hidden variable interpretation that is still indeterministic, but saves realism (though not, I guess, locality).

On a side note, chaos theory is definitely not a croc. Whether (at least as espoused by some of its exponents) it is a crock is a subtler question. --Trovatore (talk) 02:24, 24 January 2009 (UTC)[reply]

I think OP just had it the wrong way around Crock is chaos. Everything unfolds in a certain order and you still end up with a perfectly chaotic mess in the kitchen. :-) 76.97.245.5 (talk) 03:11, 24 January 2009 (UTC)[reply]

Observer bias? ~A H 1^(TCU) 03:16, 24 January 2009 (UTC)[reply]

(after ec)The OP might like to consider Richard Feynman's theory of sum over histories as an explanation of what is perceived to be "the way things happen". —Preceding unsigned comment added by TammyMoet (talk • contribs) 15:25, 24 January 2009 (UTC)[reply]

will mabye the world is big and complex for us ... will not evry thing could be rulled by mathmatical formula , but i belive that even a particle of sand flaying in the desert is going to some where for a reason ...no thing is happining as a coincidence ... if you read the quraan (islam book) you will find articles about earth ... sky ... oceans ... moon ... sun ... it talked about moon been split in half ... about univers explosion in the future ... about stage of human growing in the mother billy ... about sun and moon is moving ... about that the earth is loosing an amount from its mass with time ... it talked about evry thing ... evry thing will happen for areason ... evry single tiny small thing . —Preceding unsigned comment added by Mjaafreh2008 (talk • contribs) 21:43, 24 January 2009 (UTC)[reply]

Well - sadly, it doesn't matter that you feel like that - or that some book of religious mythology says otherwise - but the science and the mathematics is VERY clear. Quantum theory is all about fundamental randomness - and quantum theory is ESSENTIAL for things like flash memory chips. Chaos theory is right there in the Mandelbrot set.

To deny fundamental randomness is to deny that the very computer that you are reading this post on can work. So - if the Qur'an says that there is no randomness in the universe then you have to face up to this question: EITHER:

The Qur'an is correct and the computer you are using can't possibly work. ...OR...
The Qur'an is in error and the computer you are using works just fine.

Since you are still reading this post - you should probably assume (2). Failing that - you need to take the question off to some bunch of religious nutjobs because science is VERY clear on this point.

There is no fundamental "reason" why a particular atom of uranium should choose some exact moment to spit out a neutron and decay. That's a fundamental scientific truth that you can't dodge. Nuclear power stations and atom bombs wouldn't work the way they evidently do if there was a 'reason' why the neutron picks a particular moment to do it's thing.

It's arguable that the entire universe couldn't exist if there wasn't some kind of fundamental randomness. When the big bang happened, the universe was PERFECTLY symmetrical because it was a zero sized dot. As it expanded, all forces would be pulling precisely equally in all directions - all energy and mass would have to be completely uniformly distributed. You need the tiniest wiggle in there somewhere - the tiniest disparity from mathematically perfect symmetry - or else there is no way for large scale features to ever appear. So if there was no randomness - there would be no way for anything other than a perfectly smooth uniform universe to come from that. Randomness makes atoms and everything else up to and including galaxies.

I know that giving up on the idea of a clockwork universe is tough - great scientists have fought to find other explanations for almost 100 years now...and as yet, there is no alternative theory that really explains what Quantum theory explains.

Now - having said that - the randomness averages out once there are more than a few bazillion atoms so at the 'macro' scale where humans experience life, things do seem to be completely regular and predictable - but we can provoke that fundamental randomness and with the right situation (the two-magnets-and-a-pendulum experiment - or the "butterfly effect" in weather prediction - or with a geiger counter) you can make those microscopic randomnesses become very evident. That's how we know it's true.

SteveBaker (talk) 01:43, 25 January 2009 (UTC)[reply]

Schroedinger's cat and Quantum theory--GreenSpigot (talk) 04:21, 25 January 2009 (UTC)[reply]

Many things we see in the quantum world seems random. Electrons not being where they're supposed to be (Heisenberg's uncertainty principle), nuclei decaying for no apparent reason, and chaos theory etc. But what if it's just our observations that are uncertain, but the universe itself is completely deterministic. This "perceived" randomness is not actually there. Just because we can never determine both the exact position of an electron and it's momentum at the same time doesn't mean that it doesn't have an exact position or momentum. Even when the decay of a nucleus is apparently random, there has to be a reason that it decayed at that specific point in time, we just don't know the reason. As for the magnetic pendulum, the only thing preventing us from determining the outcome is the precision and accuracy (or lack thereof) of our measurements. The angle of release is an exact number; but our perception of the angle of release, however, is not exact and cannot be exact. If you release the pendulum from exactly the same spot every time, you will get the same result every time. If you don't, then that means your measurements are not accurate, not because the universe is random. (I think I might be talking about Hidden variable theory, which has been disproved by Bell's theorem, but I think there is a difference.)--Yanwen (talk) 21:30, 26 January 2009 (UTC)[reply]

January 24

Non-teratogenic mutagens

Are there any human mutagens which are not human teratogens? Neon Merlin 02:38, 24 January 2009 (UTC)[reply]

Look at Mutagen and Teratology. Human cells contain DNA. A substance or process that will alter the DNA is called mutagen. It can, e.g. lead to cancer. If the DNA that gets damaged is in an cell that will develop into a baby's cell then a birth defect may result. 76.97.245.5 (talk) 02:56, 24 January 2009 (UTC)[reply]

How about UV light? lots of skin cancer but no birth defects.--Digrpat (talk) 14:39, 24 January 2009 (UTC)[reply]

Thats only because embryos tend to be protected from UV exposure during development. If you expose embryos to UV light, you see teratogenic effects [8]. Rockpocket 19:05, 24 January 2009 (UTC)[reply]

Space tube: Sucking or Blowing?

If I created a hollow tube to space, like a giant earth straw, would it have any movement of air at the bottom? If I covered the bottom with my hand, would I feel a slight sucking or blowing? Would there be any forces at play that might suck air constantly through it like a siphon? (such as air pressure differences, time dilation, movement of the end of the straw through space). Or might it blow out air? ever so slowly? Would the answer changed if the tube was slowly getting narrower as it went up or wider? I know it wouldn't act as a straw in the same sense because the vacuum of space should be almost exactly countered by the weight of the air, but is this changed at all by putting a tube around it? Thanks. Anythingapplied (talk) 07:12, 24 January 2009 (UTC)[reply]

No, I really don't think so. Assuming that such a tube could really exist, the reason the atmosphere (mostly) stays where it is is that gravity keeps it where it is, just like it keeps us from flying off. Some of that gas would be inside the tube, but I don't see what difference that would make: gravity would still hold it down. I guess if the tube conducted heat really ridiculously well, it might cool way down in the vacuum when it was in the dark and heat up when it was in direct sunlight, and that might have some small effect on some of the gas inside... but, really, no. (And if for some reason I'm wrong, that's great, because in that case the real answer can only be interesting as hell... but I'd be very surprised to hear that.) -- Captain Disdain (talk) 09:00, 24 January 2009 (UTC)[reply]

If the air was moving one would able to extract energy from it; which would break conservation of energy. So one can assume that there would be no air flow in the tube. —Preceding unsigned comment added by 129.67.37.225 (talk) 13:44, 24 January 2009 (UTC)[reply]

I agree - nothing special happens unkess the tube itself is doing something (which, in this kind of thought experiment, it doesn't!) SteveBaker (talk) 14:30, 24 January 2009 (UTC)[reply]

I have a way to convince the OP. Consider a straw in a glass of water. The pressure at the bottom of the glass is higher than the pressure at the surface - just as the pressure at the top of your giant atmosphere straw is greater at the bottom of the atmosphere than at the top. The liquid level in the straw stays level with the top of the liquid in the glass...same deal with the atmosphere. QED. (Oh - if you try to do the experiment with a real straw in a real glass of water - the level in the straw will actually be a millimeter or two higher than in the glass - but that's because of surface tension...if you used a glass of mercury (please don't!) then the level in the straw would be lower than in the glass.) SteveBaker (talk) 15:00, 24 January 2009 (UTC)[reply]

You wouldn't get any net movement of air, but you would get temporary winds blowing in or out when the barometric pressure of the atmosphere changed. Specifically, when the barometric pressure goes up, wind would blow into the straw, and when it went down (which usually means bad weather is on the way), wind would blow out of the straw. This assumes that the straw is perfectly rigid, so it's sides can't expand or contract to compensate for the pressure. Note that this air-blowing-in-or-out-to-equalize-pressure effect doesn't have to do with the straw being vertical, or extending into space, but applies to any large volume of air with a narrow opening to the atmosphere, such as certain caves. StuRat (talk) 15:23, 24 January 2009 (UTC)[reply]

Space/matter

In what sense does matter "create" space? Does it mean that without matter there is no space? Is the quality of space somehow dependent on the amount and distribution of matter? 196.2.124.248 (talk) 08:02, 24 January 2009 (UTC)[reply]

As far as I'm aware, there is no sense in which matter creates space. Where have you encountered the idea? Algebraist 13:36, 24 January 2009 (UTC)[reply]

This might be a reference to the metric expansion of space which is affected by the amount of mass in the universe. Spacetime could exist wothout matter and in that case would be perfectly euclidean. SpinningSpark 13:55, 24 January 2009 (UTC)[reply]

There is unfortunately some religious arguments from some fairly ignorant people on how the universe was clearly created by a deistic entity. They refer to space as 'the distance between obejcts' as one of their steps in the argument. But on the flip side space is to an extent defined by objects; as with a zero or one object universe, space does not exist. —Preceding unsigned comment added by 129.67.37.225 (talk) 13:50, 24 January 2009 (UTC)[reply]

Now now, let's not go ripping on religious people here. You can't disprove God scientifically.-Running On Brains 20:28, 24 January 2009 (UTC)[reply]

That's one of those "If a tree falls in a forest and there is no-one there to hear it - does it make a sound?" questions - to which the answer is an unambiguous "Well, DUH!". If there are no particles around for the space to be measured against then does it exist? This is the kind of thing that gets philosophers very excited. But in truth it's a rather bogus argument because we have virtual particles causing quantum foam - so if there is space-time then there is matter (at least briefly) - and it is sometimes argued that the existence of that foam is what causes space-time to exist. Which means that even in a universe that's completely devoid of galaxies, gas clouds, stars, planets, grand pianos and pink aardvarqs - there would still be virtual particles and hence matter. I don't think we know the answer to our OP's question at the quantum level. At the macro level, it's hard to argue that without at least one object there could be no space - we don't know that and because a universe with no matter in it could not be measured or probed in any way - we can't tell for sure. If you can't put a tape-recorder into the forest then it's hard to demonstrate that the falling tree makes a sound...although all that we know says that theoretically, it must. SteveBaker (talk) 14:26, 24 January 2009 (UTC)[reply]

If matter then has very little to do with space, what is meant by a "finite" universe - is it the matter which is finite (which one can understand even if it is unlikely) or is it the space which is finite (difficult to understand and even more unlikely) or is it both (extremely unlikely and impossible to understand)? 196.2.124.248 (talk) 22:24, 24 January 2009 (UTC)[reply]

I think it usually refers to space, ie. the volume of the universe is finite. I don't see anything particularly difficult to understand about that - it's just like saying the surface area of Earth is finite. --Tango (talk) 22:46, 24 January 2009 (UTC)[reply]

Well now, I think one immediately gets into deep water there. If the volume is finite then what would the bounding surface consist of? Obviously not a rigid structure and also not open space, since that would just be more space - space would have to extend infinitely in all directions holding an infinite amount of matter - see Cosmological principle. 196.2.124.248 (talk) 07:47, 25 January 2009 (UTC)[reply]

You don't need a boundary. Go down a dimension and think of the surface of the Earth. The Earth's surface area is definitely finite, but there is no edge. --Tango (talk) 03:40, 26 January 2009 (UTC)[reply]

No - that argument is totally specious. You wrote "the volume of the universe is finite" which directly implies that it is bounded. There is no need to "go down a dimension". Speak to a mathematician. 196.2.124.248 (talk) 18:59, 26 January 2009 (UTC)[reply]

Compressible liquids

its afact that liquid get heavier as its gets colder , which means that liquid mass increase as the temperature decrease . and recalling that mass dont change , so to have the same mass the volume must get smaller . which lead to the idea that liquid could be compressed . and as you know liquid couldnt be compressed. —Preceding unsigned comment added by 86.108.61.209 (talk) 15:21, 24 January 2009 (UTC)[reply]

It's almost a fact that liquids get 'denser' (not 'heavier') as they get colder. It's not true of water close to freezing point. So a plastic bucket of water won't get any heavier as it cools (it's mass won't change either) - the level of the liquid in the bucket will get lower as the water shrinks (until close to freezing - when it'll get a little bigger). It's almost a fact that liquids are incompressible. But they aren't UTTERLY incompressible. Our article on water explains that water at the bottom of the deep oceans is compressed by about 1.8% compared to water on the surface at the same temperature...not much - but it IS compressible. So, sorry but you're, wrong! SteveBaker (talk)

Many of the "rules of thumb", like that liquids are incompressible, are only convenient approximations. The reality is that they are, but for most casual computations, the amount of compression is low enough so that it may be ignored. StuRat (talk) 20:18, 24 January 2009 (UTC)[reply]

Second moment of area

what is the second moment of area ... i need a text meaning , please no math expressions. thank you ...? —Preceding unsigned comment added by 86.108.61.209 (talk) 15:30, 24 January 2009 (UTC)[reply]

Sadly - there are some things for which you really NEED math - and this is one of them. This is a means to calculate the likely stiffness of a beam by reference to the cross-sectional shape. It's sometimes called "The area moment of inertia". But the property depends on where the beam is being bent so it's not as simple as a number that tells you how stiff something is. You need the math...sorry! SteveBaker (talk) 16:52, 24 January 2009 (UTC)[reply]

Second moment of area will tell you a lot, but again it is a bit math-heavy (calculus included). The lead paragraph of that article gives a pretty good description of "what it is", but there is no way to find its numerical value aside from the math on the page.-Running On Brains 17:53, 24 January 2009 (UTC)[reply]

treeful of goats??

despite the protestions of this article, it's a hoax, right? —Preceding unsigned comment added by 82.120.227.136 (talk) 15:42, 24 January 2009 (UTC)[reply]

We have a picture of goats in an Argan tree at our article. DuncanHill (talk) 15:53, 24 January 2009 (UTC)[reply]

I thought encyclopedia dramatica links were forbidden on Wikipedia?? —Preceding unsigned comment added by 82.120.227.136 (talk) 16:09, 24 January 2009 (UTC)[reply]

The photo in our article really doesn't look like a photoshop job (although it has been processed by the Mac version of photoshop in some way - that's probably just a color tweak and crop). The lighting is perfect and the interaction of the fluffy fur and the complicated leaves doesn't have the signs of the more common tweaks people do when faking photos. The picture in the OP's article is pretty low-rez so it's hard to tell. So no - I think it's real. Mountain goats are insanely nimble - and those trees are pretty gnarled and have plenty of footholds. Our article makes it clear that there is fruit on the trees - and in that barren landscape, the goats would have plenty of incentive to try. SteveBaker (talk) 16:43, 24 January 2009 (UTC)[reply]

There is (or was recently) an advert on British TV which included a treeful of goats - I forget what the advert was for (trees, possibly) but you saw the goats in the tree and their owners saying something about what trees meant to them. DuncanHill (talk) 16:50, 24 January 2009 (UTC)[reply]

Wasn't it one of the HSBC's "we're the world's local bank" adverts? --Tango (talk) 20:33, 24 January 2009 (UTC)[reply]

Could have been - I must admit that trees (and goats) are rarely advertised on British television. DuncanHill (talk) 20:40, 24 January 2009 (UTC)[reply]

See lots more goats in trees, and a video, at [9]. DuncanHill (talk) 16:53, 24 January 2009 (UTC)[reply]

Some of my extended family have goats, and I've seen them climb trees, on top of sheds, even on top of other animals (the stupid sheep, usually). They're pretty nimble, and these are just the domesticated goats. -- JSBillings 17:41, 24 January 2009 (UTC)[reply]

All sorts of kids apparently like to climb trees.Edison (talk) 20:40, 24 January 2009 (UTC)[reply]

There's a picture very similar to this one (7 goats in an argan tree) in the Photo Journal section of the Feb 2009 issue of National Geographic. Seems legit there. --Scray (talk) 22:34, 24 January 2009 (UTC)[reply]

Both the Argan and Argan oil mention goats climb the trees. While the supporting refs I've seen aren't great (one is dead, the other one is not necessarily a reliable source) the argan tree and oil definitely exists as supported by multiple refs and I suspect a number of the refs in the argan article probably mention the goats Nil Einne (talk) 06:34, 25 January 2009 (UTC)[reply]

'Tis moi belief that they're nestin'. : ) 87.81.230.195 (talk) 06:44, 15 February 2009 (UTC)[reply]

What kind of bacterium does this?

Okay, so this might sound like a medical question, which of course is not allowed, but before you delete it, please read the following. The object of my question happened over a decade ago, I am completely healthy and I am not asking for medical advice. It's only for curiosity.

When I was two years old, I was operated of a hernia in the groin. It seems the doctors forgot a couple of sutures inside, which became infected. For eight years, this infection gave no symptoms, until one day I felt a hard thing in my groin, went to the doctor and was operated straight away. It seems a bag of pus had been growing in my groin for eight years, and it was about to burst (and maybe cause sepsis). The operation and subsequent course of antibiotics eliminated all bacteria, so I recovered pretty quickly.

So, I have two questions which, as I said above, are just for curiosity and are in no way a request for medical advice:

How come it took eight full years for the bag of pus to develop? Don't most infections spread quickly?
What kinds of bacterium create bags of pus within the body? I read Staphylococcus aureus does, but surely there must be others?

Thanks for your help! —Preceding unsigned comment added by 83.34.49.91 (talk) 16:23, 24 January 2009 (UTC)[reply]

I'd say there are at least a couple of scenarios to explain the late appearance of the abscess. First it is possible that the infecting organism had been there all along but something changed after 8 years, like an alteration in you immune system, that caused it to suddenly reproduce itself in greater quantity and cause the sign you mention. The other possibility is that the suture caused some minor damage to your internal tissues at some point which was then infected by a passing organism. I guess it is possible that the abscess slowly developed over 8 years but I think you might have discovered it before. Not all infections spread quickly. The tubercle bacillus is an increasingly common example of an organism that can live within the body for months or years not showing signs and undetected. There are a number of bacteria that might cause this type of abscess and with out culturing a swab from the site we can only guess. Richard Avery (talk) 16:55, 24 January 2009 (UTC)[reply]

It most likely didn't take eight years to develop, rather, the suture that was left in place became a focus of infection years later. It was "seeded" by a transient bacteremia, say from a dental procedure or other instrumentation, or from local infection.
Staph is the most likely candidate. Though other organisms cause abscesses, Staph is the most common cause, and is ubiquitous. Tubercular groin abscess would be distinctly unusual - the microbiology of abscesses vary with setting and location. In one study of cutaneous abscesses, 66% of all positive cultures were staph. Streptococcus comes in second; this is what you'd expect, as they're skin organisms. Some abscesses are polymicrobial; others are sterile; almost every organism has been reported to cause abscesses somewhere. You don't mention the size of the abscess, but obviously to acquire an impressive size, the abscess must occur in a place where a small abscess will not cause pain, and where there is sufficient leeway to grow - thus some places are more common than others. - Nunh-huh 03:00, 25 January 2009 (UTC)[reply]

This certainly may have taken years to develop. Small colony variant staphylococci are one example of organisms that can cause occult infections that, even without treatment, can lay dormant for decades.[10] If this was a staph infection, and I agree that's likely, then hematogenous seeding from a dental procedure is exceedingly unlikely since staph are a tiny proportion of dental bacteria. Another explanation that has not been discussed is that the suture may have been infected but walled off in fibrous tissue that was not conducive for bacterial growth; then, some sort of local trauma (stretching/tearing of the tissue surrounding the suture) resulted in disruption of that microenvironment, perhaps a little serum or blood got to the suture, and this provided the right environment for the bacteria to resume growth. Just conjecture. --Scray (talk) 03:33, 25 January 2009 (UTC)[reply]

This paper[11] reports multiple small-colony variant (SCV) staphylococcal infections, some indolent for decades. This paper[12] reviews much of the literature on SCV organisms, noting that SCV strains have been described for a wide variety of Gram-positive and Gram-negative species. Some, including SCV staph, can live dormant for long periods of time intracellularly. --Scray (talk) 04:26, 25 January 2009 (UTC)[reply]

Equations of motion

I've seen the equations of motion for constant acceleration derived using both definite and indefinite integration. Which one is the better approach? —Preceding unsigned comment added by 65.92.228.224 (talk) 19:25, 24 January 2009 (UTC)[reply]

I think it's just personal preference. It just depends on whether you like to work with constants of integration or limits of integration, they end up being equivalent. --Tango (talk) 20:31, 24 January 2009 (UTC)[reply]

Kids holding books upside down

My mother just told me that when I was one or two years old, I held picture books upside down. She was naturally concerned about that, but the pediatrician told her that that was normal and I'd turn out all right, which I think I can confirm. At least I'm not holding the monitor upside down as I'm reading Wikipedia. ;-) But the explanation the doctor gave, or at least what my mother remembers, doesn't make sense to me: It had something to do with the image is projected upside down in the retina. This is true, of course, but it is equally true for the book as for anything else I see. Unless I had been first walking on my hands (which my mother said I didn't), I must have seen the world in the same way I saw any book. So I'm wondering if there is any explantion for this? Do other kids turn their books, too? (My mother didn't remember what my younger siblings did.) — Sebastian 22:43, 24 January 2009 (UTC)[reply]

It seems very possible that it's normal to hold a book upside down as a kid. Think about it: You're new to the world, and don't know what everything is supposed to look like. So you look at it one way and say to yourself, "Hey, that's a picture of something, but I don't know which way it goes, so I'll guess this way." Analogy to an older person: If you find a book of alien texts (which you have never seen before), and you try to read it, there's a good chance that you'd read it upside down, because you had no idea which way it should go. flaming lawyer 22:58, 24 January 2009 (UTC)[reply]

Yes, but that would result in you holding books upside down at most 50% of the time (probably less since you'll usually recognise something in the picture). Is there any explanation for holding them upside down almost all the time (which is what the OP seems to mean)? --Tango (talk) 23:05, 24 January 2009 (UTC)[reply]

Yes, that's what I meant. Of course, I can't be sure about the percentage; it is well possible that my mother selectively noticed the unusual cases. — Sebastian 00:21, 25 January 2009 (UTC)[reply]

The argument the doctor gave is hogwash though. Sure, the lens in your eye does result in the image on the retina coming out upside down and flipped left-to-right. When the doctor was pinned to the wall by an anxious parent and needing to produce a passable answer RIGHT NOW, that's what he pulled out of his memory from Med School. But as an explanation, it simply doesn't hold water. You see all of the world that way up all the time - that's "normal". That IS the right way up. Holding the picture of the moo-cow in the book the opposite way around from moo-cows in the real world isn't explicable in that way. I don't know what the explanation is...but that's CERTAINLY not it. SteveBaker (talk) 01:14, 25 January 2009 (UTC)[reply]

You are right, the image is indeed projected on the retina upside-down; and you are right again, this has nothing to do with how we perceive the "up" and "down" directions in the world. In human infants the connections in the visual cortex, as well as between the visual cortex and other areas of the brain, form largely under the influence of sensory stimuli. AFAIK, we are not born with visual concept of "up" and "down", even though our heads are quite different from our bottoms. The visual sense of "up" and "down", as well as "left" and "right", forms through visual stimulation, and it would have formed largely the same way if the image on the retina was not flipped. Humans learn very fast to use mirrors, so flipping the world around any axis is not a huge problem for our brain; not even for an adult brain. In fact, there are experiments in which adult humans are fitted with prism glasses that flip the visual world by 180 degrees; humans adapt to the flip and function more-or-less normally after a few hours or days. So no, you don't tend to hold the book upside-down because the image on the retina is flipped. Neither do you flip the trees and houses upside-down when you go for a walk (or at least so I hope). Two-year-olds do turn the books upside-down, but I always thought it is just out of curiosity; or more often they would just pretend to be reading, without actually realizing the book is upside-down. That is probably the explanation you are looking for. Now, if you have older siblings, it's a different story entirely. When an older kid learns to read, younger siblings tend to watch. The book can not be easily seen or read from behind the older kid's back; so the younger kids approach from the other side, and end up facing the book from the wrong direction. I heard stories about younger kids in large families who actually started reading upside-down, and had to relearn in school to read the "proper" way. That may also be the case. Hope this helps. --Dr Dima (talk) 02:14, 25 January 2009 (UTC)[reply]

I think you got it. Since I don't have older siblings, I go with the curiosity explanation. If I were a cat, I'd be dead now, despite the bonus lives. — Sebastian 02:46, 25 January 2009 (UTC)[reply]

I can still read anything upside down. It's a handy kind of obscure skill that I'm guessing many people have. Julia Rossi (talk) 05:58, 25 January 2009 (UTC)[reply]

Are you Gemma Williams? [13] Rockpocket 07:00, 25 January 2009 (UTC)[reply]

No, the usual way is fine as well, no colour filters required. :) Julia Rossi (talk) 07:17, 25 January 2009 (UTC)[reply]

ʇǝʞɔodʞɔoȢ ¿os ʇɐɥʇ sI

ףסש ¡әәӋ 07:49, 25 January 2009 (UTC)

Reading upside down is a useful skill when reading a book to children. You can hold the book facing them so they can see the pictures and then lean over the top to read it. --Tango (talk) 17:13, 25 January 2009 (UTC)[reply]

January 25

Burying charcoal to mitigate global warming

James Lovelock recommends burying charcoal in a non-biodegradable fashion. What are the advantages and disadvantages of this form of mitigation?

Note: I originally asked this question at Talk:Mitigation_of_global_warming#Burying_charcoal before it occurred to me that this reference desk might be a better place to ask. Would you please answer at that talk page instead of here? 69.228.235.107 (talk) 02:55, 25 January 2009 (UTC)[reply]

The talk page of articles isn't really the place to ask such questions as they are solely for discussions about improving the article. Technically your question could be removed although I'm not suggesting anyone does so. Since no one has answered there I would suggest you simply direct people here. Nil Einne (talk) 06:17, 25 January 2009 (UTC)[reply]

The reason I asked was because I had hoped to improve the article. 69.228.235.107 (talk) 07:42, 25 January 2009 (UTC)[reply]

I understand that, but most of what's being discussed here has nothing to do with improving the article, as with most RD questions particularly those of this sort which are likely to result in a far amount of discussion which isn't directly sourced. It possible you may eventually get something here which could be added to the article but that's not really the purpose of article talk pages. In talk pages like that, no one tends to mind but in extremely active ones any sort of OT talk such as a question like this will often be deleted or archived or at least you may get people telling you to ask it somewhere else. So it's a good idea to get into the habit of asking questions like that here, your far more likely (in general) to get an answer and it's also easier for someone to find the discussion in future Nil Einne (talk) 08:18, 25 January 2009 (UTC)[reply]

He talks about plowing it into farmer's fields, but then plant roots would get at the carbon, pull it into the plant, and make it part of the carbon cycle again. Carbon sequestering requires putting the carbon somewhere that life can't get to it. StuRat (talk) 06:16, 25 January 2009 (UTC)[reply]

Note that the OP (and the linked article) said non-biodegradable charcoal. I'm not aware there is any form of charcoal that isn't relatively biodegradable although I guess you could make some sort of plastic with it. There's also the question of whether having all this non-degradable material is going to eventually prevent plants from growing when you end up with too much of it. Nil Einne (talk) 06:21, 25 January 2009 (UTC)[reply]

Why charcoal? To make charcoal, you take a lump of wood - and heat it to drive out the water...why bother? The production of that heat uses energy - and that almost certainly produces CO2 which diminishes or even eliminates the benefits of burying the charcoal. Why not just bury the wood? The actual business of burying in farmland seems difficult too - dumping it in old coalmines or worked out open-cast mine pits (and then covering with dirt) would be better. SteveBaker (talk) 06:25, 25 January 2009 (UTC)[reply]

Why charcoal? Because you just want to make sure that the carbon stored in the plant growth doesn't get released as carbon dioxide. If you bury wood, it quickly gets broken down and the carbon is released as carbon dioxide. If you can convert it to nonbiodegradable charcoal (and I don't know how feasible the methods given really are; I agree with the potential effect on farmland) the carbon won't get released as carbon dioxide unless someone burns it. Sure, a little carbon dioxide is produced in making the charcoal, but not nearly as much as would have been produced if the whole thing was broken down as happens when you bury wood or plough your stubble back into a field. 79.66.105.133 (talk) 12:34, 25 January 2009 (UTC)[reply]

Here is an idea. Why don't we just grow trees, cut them down and turn them into furniture. Won't this be just another form of carbon capturing technology? We will make a law that says it is illegal to burn furnitures. 122.107.203.230 (talk) 06:55, 25 January 2009 (UTC)[reply]

@StuRat plant roots don't usually process/transport carbon in plants AFAIK. They draw CO2 from the air for photosynthesis and minerals and water from the ground. But there are a lot of chemical processes going on in soil. As soon as the carbon has reacted and been bound into something that a fungus can use it's back in circulation. These guys also seem to find it palatable [14]. Plowing under the charcoal doesn't sound like a good idea [15]. The article doesn't concern wood specifically grown for carbon sequestering, but farm waste like straw. If you'd compare firing your hearth with straw to using charcoal you might come out ahead, but most of the biofuel from farm waste processes have so far proved to be uneconomical or coming with a negative energy balance. That's one reason why we now make ethanol from sugar rather than straw. (Also see wood gas.) Transporting the charcoal made from straw to a coalmine and sinking it into the pit would also consume energy. Digging up coal and then sinking charcoal in it's place sounds a bit odd anyway. The BTUs you get out of charcoal don't differ that much from what you get from coal (Can't link it, but it's ard. 9,000 BTU for charcoal and 6,000 - 14,000 for coal. The numbers for charcoal from straw would come out somewhat different, though.) That method would also be chucking a lot of nutrients plants need into the hole. You'd either have to separate those out or wait till they concentrated at the bottom and dig them up again after a considerable period. I guess they stumbled over that argument and then refined their original idea to "plowing it under". You'd have to move it to the processing plant and then move it back and spread it onto the field, that would consume energy. If you converted it into charcoal on the field you'd lose the "biofuel" advantage they touted and I guess then their calculations would not come out ahead. Reminds me of the saying, "It's the technology of the future - and always will be." 76.97.245.5 (talk) 10:40, 25 January 2009 (UTC)[reply]

Surely this entire discussion is based on a misunderstanding. It isn't Carbon we want to sequester, but CO2. Surely charcoal is essentially carbon. Planting trees is good because it takes CO2 and breathes out O2 whilst making the C into "tree". -- SGBailey (talk) 11:34, 25 January 2009 (UTC)[reply]

I believe that the idea is that excess carbon in the biosphere will readily be combined with oxygen from the air to form carbon dioxide. StuRat (talk) 14:55, 25 January 2009 (UTC)[reply]

Thus far it (mostly) works. The problem arises when you then burn or decompose the tree. That creates greenhouse gases (CO2). Which is why the guy in the linked article came up with his idea. Charcoal can be created in an anaerobic process (see Pyrolysis). That way less CO2 would be released into the atmosphere. The question is whether the big picture will come out as producing CO2 as a consequence of any component necessary to get from tree (or straw) to charcoal in the ground and whether the charcoal stays in the ground or is used up to make CO2 down the line. There are many examples of seemingly good ideas that turned out to be huge mistakes once all the consequences became obvious. 76.97.245.5 (talk) 13:11, 25 January 2009 (UTC)[reply]

Also, won't burning massive amounts of organic material in a low oxygen environment to produce charcoal also produce carbon monoxide ? StuRat (talk) 15:02, 25 January 2009 (UTC)[reply]

It looks like Biochar is a fairly well-developed article on the topic. 69.228.235.107 (talk) 16:42, 25 January 2009 (UTC)[reply]

Rope bridges over big gaps

[Posting here because it's the closest to engineering] Before modern technology (i.e. helicopters), how were big rope bridges built over gorges? I'm guessing that a small bridge, maybe even something like the Carrick-a-Rede of 20 metres, could be begun by someone strong throwing a rope all the way across the gap, but Inca rope bridge discusses one of 67 metres. I could understand if these were low bridges over rivers, but seeing that these connect cliffs dozens of metres high, I'm assuming that it's not possible simply to carry the rope over. Nyttend (talk) 04:28, 25 January 2009 (UTC)[reply]

You do need someone at each end of where your bridge will be, and you do need to get the rope across - the trick is, you don't try to throw a big heavy rope. You throw a thin, light rope, and use that to haul thicker ones across. Tying a monkey's fist, or a stone, in the end of the light rope makes it easier to throw accurately, and by swinging it around before releasing it will go further. If the chasm is too wide to throw even a light rope across, then you throw it across at the bottom and then climb the sides, paying out as you go. DuncanHill (talk) 04:57, 25 January 2009 (UTC)[reply]

If you can't climb the sides of the gorge at the point you want the bridge, then climb down where you can, and walk along to a point below the bridge site. Your colleagues at the top of the gorge lower a line to you (the same being done on the other side), and you attach this line to your heaving line. The heaving line is then pulled up to the top of the gorge. DuncanHill (talk) 05:01, 25 January 2009 (UTC)[reply]

It would be a lot easier to explain with a) some rope, b) a suitable gorge, and c) a plentiful supply of Scouts to run around carrying things. DuncanHill (talk) 05:16, 25 January 2009 (UTC)[reply]

"Plentiful" gave me another clue: If you have at least three people, you can have one on each side throw down a line to a third one at the bottom. The third person just ties the two lines together, and voilà! — Sebastian 05:23, 25 January 2009 (UTC)[reply]

Now that's good! I must remember that :) DuncanHill (talk) 05:28, 25 January 2009 (UTC)[reply]

The idea of pulling a very fine thread across - and then using that to pull a thicker rope - and that up to the full-sized rope makes sense. But if a fine thread is all you have to get across there then a bow and arrow would get it over there. Perhaps even a trained bird of prey could carry enough fine thread across the gap. Modern archers using 'traditional' bows shoot at targets at 50 yards (and 90 yards is common with modern bows) - it's clear that the best archer the bridge constructors could find could make an arrow go 67 meters...given that accuracy and penetration of the target are irrelevent. However, the Inca's didn't use bows - they used slings...but (amazingly) our sling (weapon) article says that a slinger could fling a rock 600 meters(!) - ten times more than is needed here! So IMHO, it's overwhelmingly likely that this is what they would do. SteveBaker (talk) 06:35, 25 January 2009 (UTC)[reply]

The slings and arrows of outrageous bridge-building... DuncanHill (talk) 16:55, 25 January 2009 (UTC)[reply]

A kite with a following wind could carry a cord for miles...... 196.2.124.248 (talk) 07:40, 25 January 2009 (UTC)[reply]

In fact, a kite is exactly what they used in 1848 to begin the construction of the first bridge over the gorge at Niagara Falls. A prize was offered to the first boy to perform the task. --Anonymous, 04:53 UTC, January 26, 2009.

That reminds me when I was wondering how spiders do it. I know they can drift in the air, but I've seen a web anchored at two branches from different trees, with the upper anchoring points about 8 m apart and about at the same height. Since the spider's body was about 1 cm long, and it was in a dense forest where you wouldn't expect strong winds, I can hardly imagine that the spider drifted horizontally for 8 m. — Sebastian 05:19, 25 January 2009 (UTC)[reply]

@Sebastian There are several ways that spiders get that gap bridged. As described in Spider web some dangle a sticky thread to float in the winds till it gets caught somewhere. Sometimes they also use rappelling, swinging themselves to and fro till they get to a good spot. They lengthen or shorten the thread they are hanging on as needed. Then there's Ballooning (spider) although that's more commonly used to get away from close relatives. [16] (Know thy enemy. Arachnophobia is less productive than informed avoidance.:-) Did Incas use Blowguns? Our article doesn't say, but it isn't a new weapon and is widely used throughout the Americas. I'm not sure you could tie a thread to a dart, though. The slingshot method looks like the most likely scenario. 76.97.245.5 (talk) 08:51, 25 January 2009 (UTC)[reply]

You're right, they just use the threads alone, so the weight of the spider does not play a role. Still, it is amazing that they manage to bridge 8 m that way, even in a calm forest! — Sebastian 23:12, 25 January 2009 (UTC)[reply]

It seems amazing to us chunky humans - but remember that air resistance is proportional to cross-section which is proportional to the square of the size of the animal - but weight is proportional to the cube of the size of the animal - so at the scale of a spider, wind is a force that's VASTLY more powerful than at our scale of experience. A 1cm spider experiences 200 times the amount of wind force (pound-for-pound) than a 2m human does. So we might consider 40cm to be bridgeable with a human-scale parachute in a modest breeze...8m is a snap for a spider. SteveBaker (talk) 02:03, 26 January 2009 (UTC)[reply]

Circuit schematics: are these good?

I've designed the circuits [17] and [18], based on [19] and [20], respectively, and I was wondering if someone could audit the designs for me. I'm planning to build them both and I want to make everything is correct before I order my parts and/or start soldering. I don't things to blow up or to have to spend a lot of money on more parts and/or shipping.

So would these circuits work, theoretically? If there's anything even remotely wrong, please let me know so I can fix it before buying parts. --Link ^(t•c•m) 10:22, 25 January 2009 (UTC)[reply]

I haven't looked at them but the usual thing to do is run them through a simulator, for instance a version of SPICE for analogue circuits, and see what happens. Dmcq (talk) 11:32, 25 January 2009 (UTC)[reply]

There are a number of diy electronic forums on the net which are probably a lot more suitable for this. On a quick look though you're not going to lose a lot of money so why not just go for it? You can always socket something expensive and it's unusual to destroy things if you get the power the right way round and ground yourself. Dmcq (talk) 11:57, 25 January 2009 (UTC)[reply]

Your first two links are PostScript files, which I can print, but can't view (there are PS viewers, but I don't have one). You might want to provide them in another format. StuRat (talk) 14:38, 25 January 2009 (UTC)[reply]

Death by toaster?

I have a habit of fishing bagels, muffins etc out of my toaster with a knife, without switching off the power. People are always telling me that this is dangerous because I risk getting a shock. I have always assumed that touching the elements would be no more dangerous that touching the elements on an electric grill or hob. Am I dicing with death everytime I have a crumpet? ToastShock (talk) 10:38, 25 January 2009 (UTC)[reply]

It depends upon what country you are in. In the UK, the two ends of the toaster element are neutral and live. Iff your socket and toaster are wired correctly then when it has "popped up", one end of the element will be disconnected from the live supply. If the wiring is wrong, it could be the neutral that is disconnected, in which case you stand a chance of connecting to live. I suggest you use a wooden kebab skewer in future or better yet unplug the toaster. -- SGBailey (talk) 11:13, 25 January 2009 (UTC)[reply]

On my toaster (made in China for Philips, sold in Canada), when it has popped up, the element is disconnected from both sides of the plug: in other words, the switch is a double-pole one. I noticed this feature when looking at the wiring of a previous toaster and have just verified it for my present one by using an ohmmeter while it was unplugged. But, of course, even if your toaster has this safety feature, you should not count on it! --Anonymous, 05:16 UTC, January 26, 2009.

Yes, and it isn't even spectacular enough for the Darwin Awards Dmcq (talk) 11:45, 25 January 2009 (UTC)[reply]

Following EC: I'd definitely say you are tempting fate. There are safeguards like fuses, circuit breakers and improved Toaster designs [21] that should take effect in case of an accident. But you are basically relying on those working properly and you not accidentally switching the toaster on or creating a contact. I don't know your grill, but the heating element wires in a toaster are live when the toaster is on [22]. If you damage the insulation you may also create a short to the case and then get shocked when you touch it the next time you make toast. There are a couple of people each year who win the "shouldn't have done that" lottery. The saying goes: "Engineers try to make things fool-proof but fools always prove to be ingenious." Unplug the toaster and use a basting brush or rubber dough scraper if something got stuck. 76.97.245.5 (talk) 11:50, 25 January 2009 (UTC)[reply]

I'd change that last sentence to "or", as you don't need to take any other precautions besides unplugging the toaster, since they don't contain capacitors or batteries (which store electricity). So, once it's unplugged, it's perfectly safe. Also note that if we are including everything that can possibly go wrong, then those toasters with metal housings can also be charged electrically, if a live wire is in contact with the exterior. This could be true when the toaster is on, or off, or both. This, in conjunction with you having wet hands and standing barefoot in a puddle of water connected to ground, and touching the outside of the toaster could cause you to become, well, toast. StuRat (talk) 14:32, 25 January 2009 (UTC)[reply]

I mentioned the soft implements because people have managed to create a short by poking a fork or knife into their toaster and then got zapped when they touched it later, or it started a fire. (Came up during a seminar on warning labels in user manuals, too lazy to look for a web reference.)76.97.245.5 (talk) 15:30, 25 January 2009 (UTC)[reply]

<makes mental note to always remember to turn the toaster off at the mains when not in use> --Kurt Shaped Box (talk) 14:38, 25 January 2009 (UTC)[reply]

You could always get a pair of toaster tongs. I haven't had a pair since I was a kid but basically it's a pair of tongs that are made of plastic and you stick them in to get your bread, bagel, etc out. Since they aren't made of metal, they won't give you a shock. Dismas|^(talk) 16:50, 25 January 2009 (UTC)[reply]

Um...and who in the right mind would manufacture a knife without a non-metal handle?! ~A H 1^(TCU) 17:51, 25 January 2009 (UTC)[reply]

All of our cutlery has metal handles. [23] for example makes steel-handled kitchen knives. They're pretty common. SteveBaker (talk) 20:31, 25 January 2009 (UTC)[reply]

Your have any dinner-knives in your flatware set? Also, it's not necessarily the knife itself that conducts via its handle to the person, it could just be the blade that shorts to other metal parts (as others mentioned) such as an outer metal surface, which is why chassis grounding (the "third prong" on US plugs) is an important safety feature. I've always heard it as "build something idiot-proof, and the world will build a better idiot". DMacks (talk) 17:55, 25 January 2009 (UTC)[reply]

The stovetop or "hob" heating element does not generally have the energized wiring exposed. Calrod heating elements have resistance wire (nichrome) insulated by ceramics from the outer metal shell. Only if the insulation broke down and the outer shell were not grounded would it be energized. In a toaster, by contrast, the nichrome resistance wire is directly exposed to the toast, for faster and more efficient heating. If your fork or knife touches the heating element in a toaster, and you are touching the knife metal and something grounded, you are likely to be electrocuted. Unplugging before toast extraction seems like a fine idea. Edison (talk) 23:23, 25 January 2009 (UTC)[reply]

I was wondering when someone was going to point out the difference in the heating elements. (Fixed your confusing typo in the first sentence.) --Anonymous, 04:57 UTC, January 26, 2009.

Re knives with plastic handles or other, I'd like to restate that it is inadvisable to use any implement with an increased danger of dislodging wires or damaging insulation inside a toaster, whether it is unplugged at the time or not. I lived in quite a few places where relying on the grounding of your home wiring system being up to code as DMacks suggested would have been folly. Even in "3-prong" outlets I've seen way too many that weren't connected, weren't connected properly or had a grounding wire from the patch panel ending somewhere in a wall after s.o. had done some remodeling. (Arguably the most egregious one.) In the US plugging in an adapter so you can plug in a 3 prong plug into an 2 wire outlet - without actually connecting the ground terminal - is an all too common practice. There are those little circuit tester plugs with LEDs that will help you verify your wiring. Using soft implements and thus reducing the risk of causing damage to the innards of your toaster seems like a hardship one can suffer. 76.97.245.5 (talk) 05:28, 26 January 2009 (UTC)[reply]

Choice of anticoagulant

Why is warfarin the anticoagulant of choice in the US and UK? What is its advantage comparing to heparin? What is its advantage comparing to acenocoumarol? --Mr.K. (talk) 12:27, 25 January 2009 (UTC)[reply]

I can't answer your question specifically, but a Google search reveals the advantages/disadvantages of both in different diseases such as venous thrombosis. Another two searches can show you the comparison between low-weight molecular heparin and warfarin against acenocoumarol. —Cyclonenim (talk · contribs · email) 12:41, 25 January 2009 (UTC)[reply]

Compared to heparin, the warfarin article states: "Warfarin is slower-acting than the common anticoagulant heparin, though it has a number of advantages. Heparin must be given by injection, whereas warfarin is available orally." -- Aeluwas (talk) 13:01, 25 January 2009 (UTC)[reply]

Is that a huge advantage? It looks like warfarin is just more convenient...Besides that is there any medical advantage?--Mr.K. (talk) 13:04, 25 January 2009 (UTC)[reply]

Of course it's a huge advantage! It's the difference between being able to walk around and carry out the daily activities of one's life, vs. lying in a hospital bed receiving intravenous fluids 24 hours a day! - Nunh-huh 13:46, 25 January 2009 (UTC)[reply]

It doesn´t say that it has to be intravenous. Heparin can be administered as subcutaneous injection. --Mr.K. (talk) 20:07, 25 January 2009 (UTC)[reply]

Subcutaneous heparin is sometimes used in bedridden or hospitalized patients as a means of preventing deep venous thrombosis or pulmonary embolism, but is not an effective means of fully anticoagulating someone - say in the setting of an artificial heart valve. In those settings - true anticoagulation, in which an actual change in blood parameters of coagulation can be measured - intravenous heparin is used because it has an immediate effect and is titratable to maintain an appropriate level of anticoagulation. After a few days, coumadin is started, because it - unlike heparin - has an oral dosage form which enables the patient to go home. Though they are both used for anti-coagulation, it's not like there's an actual "choice" between them: you use the one that the clinical situation dictates you use. - Nunh-huh 20:19, 25 January 2009 (UTC)[reply]

'More convenient' often equates to significant medical advantage. Patient compliance with a treatment regimen is often better when the treatment is less painful. Oral drug administration doesn't carry the same risk of infection associated with repeated (intravenuous or deep subcutaneous) injections. There are social benefits associated with lower cost-of-treatment, reduced packaging, and the elimination of biohazardous sharps waste. The patient can much more easily self-administer warfarin while working or travelling. Huge advantages. TenOfAllTrades(talk) 17:21, 25 January 2009 (UTC)[reply]

Drug interaction [24] and manufacturing defects [25] might sway the decision one way or another [26]. BTW. cinnamon contains varying amounts of coumarin. OR 2 years ago I asked the FDA whether they monitored levels and they answered "cinnamon is considered safe and is not tested" but coumarin as a food additive is prohibited! 76.97.245.5 (talk) 13:57, 25 January 2009 (UTC)[reply]

There are lots of natural food materials that are (un)regulated as food but that contain chemicals that are not allowable as additives. See Cyanide#Occurrence for example. DMacks (talk) 17:50, 25 January 2009 (UTC)[reply]

Regarding heparins vs. coumadin: Unfractionated iv heparin may be preferable in certain settings (ability to rapidly reverse anticoagulation being the primary one, some advantage in DVT's that extend on coumadin, etc.), but these are situations where patients should be in the hospital. In patients with cancer at high risk for deep venous thrombosis, low molecular weight heparin has been shown to be superior to coumadin in at least two prospective randomized control trials. Aside from these reasons, the convenience and other factors cited by others are the major ones. I'm not sure why other coumarins never made it to the forefront (cost? half life? developed later than coumadin?) -- Samir 08:21, 26 January 2009 (UTC)[reply]

help

While trying to get the tennis, my mother has managed to turn the normally colour digital TV through the set top box into black and white. Obviously she hasn't a clue how to undo this, and I have no idea how she did it, so how can this be undone? —Preceding unsigned comment added by 81.132.159.158 (talk) 15:00, 25 January 2009 (UTC)[reply]

Do you have a make and model ? There is likely a color setting which has been turned down to a very low level. StuRat (talk) 15:06, 25 January 2009 (UTC)[reply]

Turning the saturation setting down will turn a color image into a grey scale one. Check under the menu for image settings or the like. This seems more likely since it affects all the channels. I've also managed to lose color for certain stations when the receiving antenna was moved. (this was about 6 years ago on a homemade setup though.) I suppose you could try moving the set top box and making sure there is nothing sitting on it and checking to make sure the connectors are securely in place. I would check the color settings first. 152.16.15.23 (talk) 23:19, 25 January 2009 (UTC)[reply]

Check the cables between your set top box and the TV. Component cables carry brightness information on a separate cable from the color information. Also, S-video cables carry brightness information on a separate pin from the color information. If these kinds of cables are loose or damaged, this might cause the picture to become black and white. --Bavi H (talk) 04:44, 27 January 2009 (UTC)[reply]

communicating space tube

Following the "space tube" question above (Jan 24): Would the picture change if the tube ended in a U bend. (Provided such a tube could be constructed and wouldn't collapse due to the forces it was exposed to.) I was reminded of something , but had forgotten what it was called. I searched through 3 languages and I don't think we have a page. (Spanish and German do) We do have an image

could s.o. please link this properly

that says it's communicating vessels. (Should s.o. maybe do a page?) So would this be an effect to watch out for with that hypothetical space tube? 71.236.22.103 (talk) 16:35, 25 January 2009 (UTC)[reply]

Can you describe this tube a little more precisely? Where is the U bend and how big is it? Are you talking about a tube that has both ends in space, and just the bottom of the U in the atmosphere? Or something else? --Tango (talk) 17:10, 25 January 2009 (UTC)[reply]

The German article that image comes from is de:Kommunizierende Röhren which seems to be describing a tube linking two vessels which results in the liquid finding a common level in both vessels. It makes no difference, U-bend at the top, U-bend at the bottom, no atmosphere would leak out into space (other than what we are already losing by "evaporation"). The bottom line is that it requires energy to remove anything from earth and that energy has to come from somewhere. A passive tube, no matter how cleverly you bend it, can never provide any energy. This kind of thing is like perpetual motion machines, it can't be done because of a fundamental law of nature, but for each one you disprove, someone comes along with a more complex one that apparently allows it to work, but always there is a subtle, or sometimes not so subtle, flaw in the argument. And always it will come down to that same law of nature, conservation of energy. SpinningSpark 00:33, 26 January 2009 (UTC)[reply]

Yep - after enough years looking at silly ideas like this - you eventually learn that it's a waste of time to track down the root failure of the idea. The laws of thermodynamics say "No!" and that's all you need to know. We can say with utter, 100% confidence that there is no point in tracking down the specific flaw in the idea. It's there somewhere and we don't need to look further. SteveBaker (talk) 01:56, 26 January 2009 (UTC)[reply]

By the way, if you could actually manage to construct such a tube, you could use it as a space elevator. Most of the strength required of a space elevator cable is to support its own weight. That's the major stumbling block at the moment preventing anyone from actually doing it. SpinningSpark 00:38, 26 January 2009 (UTC)[reply]

(Actually - the current 'fatal flaw' is the modes of oscillation of the cable. A month or two ago it was proved that the cable would have fundamental instability issues that seem right now to be insurmountable without actively positioning rocket motors at many places on the cable - which would make it less effective than conventional rocketry. It's a serious blow to the future of mankind in space.SteveBaker (talk) 01:56, 26 January 2009 (UTC))[reply]

This was proposed as a thought experiment, and real world application was never the intention. I was just curious what the effect of the communicating vessels (es:Vasos comunicantes, de:Kommunizierende Röhren) would be. (The Spanish page actually has a nicer picture). I would not expect the specific properties caused by a U bend to have any effect if both ends end in space. If you had one end being shorter than the other though you should get different forces working on both sides and the liquid attempting to reach an equilibrium. Since Spinning Spark pointed out that atmosphere leaking out would not happen. Like in a Barometer you would get liquid pouring out till the pressure of the air on the short end would be the same as the sum of gravity "pulling down" on the liquid and the vacuum pulling it up in the other leg. But what would the influence of the vacuum be? Would you get a vacuum /near vacuum somewhere in the middle of the tube or would the liquid "stretch out" to fewer and fewer atoms per volume all the way up to space? Could we move the space elevator question to a separate item, please? Otherwise this item will get lost in Carbon nanotube feasibility and other unrelated stuff. (What happened folks? This is the first I've seen here that everyone seems to agree that pondering the specifics isn't worth the bother of explanation. :-( Everyone too tired?) 76.97.245.5 (talk) 04:53, 26 January 2009 (UTC)[reply]

power available from daylight

what is the power available from simple daylight say per square metre - i am aware that this will be a variable amount due to all the variabilities of geography-inclination-time of day-etc. as an instance i have a calculator that provides sufficient electrical power from light to run the electronic circuits and display module.Superbigleo (talk) 16:48, 25 January 2009 (UTC)[reply]

See insolation. --Tango (talk) 17:08, 25 January 2009 (UTC)[reply]

Gluten question

Does textured soy flour contain Gluten?Vanatthelake (talk) 17:36, 25 January 2009 (UTC)[reply]

No — the Soyfoods Association of North America says that soy flour and textured soy flour are gluten-free: [27]. TenOfAllTrades(talk) 22:16, 25 January 2009 (UTC)[reply]

Cosmic gods

Einstein spent a good deal of his life working on a Unified Field Theory in which he tried to reconcile the four fields we know of. If there were such a thing as a cosmic god who could turn out a "viable" part of the universe by selecting basic features for his creation from which all physical laws would follow as a consequence, what would such basic options be? 196.2.124.248 (talk) 18:04, 25 January 2009 (UTC)[reply]

Once you accept that God is messing with the laws of physics, then anything you can imagine is possible. This is the problem, actually, as it stops any need to figure out why things are they way they are (that would be science), if you can just say "that's the way God wanted it to be". StuRat (talk) 18:31, 25 January 2009 (UTC)[reply]

Only if one assumes an arbitrary and personified God, which is not what Einstein envisioned with his "Cosmic Religion", and not what most physicists postulate when they assume there is a divine order to the universe (which many believe in). --98.217.14.211 (talk) 23:11, 25 January 2009 (UTC)[reply]

Are you asking what is the simplest set of physical principles from which all known physical laws follow as a consequence? The answer is we don't know. Current physics is as simple as we know how to make it (pretty much by definition). -- BenRG (talk) 18:52, 25 January 2009 (UTC)[reply]

Even the gods must work within their limitations, so that the menu of permissible options is probably quite small (look what can happen with 100 odd elements, themselves logical consequences of simple arrangements, or just 5 nucleotides or 26 letters and a bit of punctuation). I think that a spartan elegance must be high on their list of priorities. 196.2.124.248 (talk) 21:07, 25 January 2009 (UTC)[reply]

Your cosmic gods aren't looking closely enough!

up,down,top,bottom,strange,charm
electron,tau,muon,
electron-neutrino,tau-neutrino,muon-neutrino,
a couple of weak-force bosons,
the gluon and the photon
and maybe we'll toss in a higgs boson or two.

The menu contains just 18 things - six quarks, six leptons and probably six bosons...and that's all ya need!

But then perhaps even that is too complicated and maybe we'll go with nothing more than a simple pan-dimensional vibration.

SteveBaker (talk) 23:07, 25 January 2009 (UTC)[reply]

You're basically asking the question that physicists have been asking since the 1980s—why are there X numbers of things and no more? Why are the values just such? Is there a reason? Can you reduce all of the possible variations of physics down to a few options, and can you find a theory which explains why those options had to be what they were and nothing else? The answer might be "yes", it might be "no", and it might be "we'll never know". --98.217.14.211 (talk) 23:11, 25 January 2009 (UTC)[reply]

There are 'levels' of power your cosmic gods might have - and the answer depends on where that 'level' is. If I had to invent my own degrees of omnipotence scale:

Level 4 gods: Who can do things with technology that almost nobody can understand...yet falls within the bounds of 'known science'.
Level 3 gods: There is the "any advanced technology is indistinguishable from magic" kind - where all you get to play with is the laws of physics and nature of matter that pertain to our universe - but with a complete knowledge of all of those laws.
Level 2 gods: There is the ability to change the fundamental constants for which we have no real explanation (things like the charge on the electron and the speed of light).
Level 1 gods: There would be the ability to change the equations that define the 'rules' of the game - so maybe changing gravity to work on the square of the mass instead of the mass.
Level 0 gods: Then there is the kind of power that's hinted at in Carl Sagan's "Contact" (the book - it's not mentioned in the movie) where analysing the expansion of 'pi' as binary digits reveals a message embedded in the bits of the number...which decode to an image of a circle...implying that some "alien" or "god" put it there deliberately for us to find.

Each level produces a new degree of incomprehensibility on our behalf.

We've "proved" that pi is what it is from raw thought alone - we don't have to measure anything - just have the concept of a circle clearly in mind...and pi just pops out. It just "couldn't" be different. I maintain that this provides fundamental limits on the power of any god - which is why the idea of a christian 'level zero' god is tough to swallow! Level 4 gods are mere present day human scientists and technologists - for most humans, understanding how even the simplest childrens' toys really "work" is beyond them. Level 3 are credible aliens.

So if the OP's question has to be answered - we first need to know what degree of power is being envisaged.

If our OP's cosmic gods are at level 4 - we know exactly what they can do - because they are out there doing it. It's what most people feel when the new iPhone comes out!
At level 3 - we can list many of the laws of physics and particles that these 'gods' have to work with and we can certainly impose restrictions - they can't travel faster than light - they can't travel in time - they can't make perpetual motion machines.
If the OP's gods are at level 2 - we've thought about what the universe would be like with different fundamental constants - and mostly we deduce that life could not exist if many things were much different - so our gods don't have a whole lot of wiggle room to change things without totally screwing everything up - butthe consequences of even the tiniest of change would probably produce profound effects that it's hard for us to predict. However, I think we could figure out (at least in principle) what that would do to the universe.
At level 1, we're in deep trouble. Understanding what it would mean - even conceptually - to have fundamentally different laws of physics would be tough. So we can't answer the OP's question.
And at level zero...there is no way to even form the thought of what the universe would be like if pi was 10% smaller. Truly omnipotent gods are meaninglessly unfalsifiable.

SteveBaker (talk) 01:48, 26 January 2009 (UTC)[reply]

I'm sure for some decoding mechanism there's an image of a circle embedded in the digits of pi. Level 0 gods would have some pretty staggering powers that approach paradoxical.. for one, the pi thing reminded me of this: take a deep breath and dive into it. How can that pi-encoded message even exist without some kind of decoding context? Could a level 0 god create such a message? I'd say no, but it has to be able to by definition, so that seems to imply the non-existence of a level 0 god. Could a level 0 god create a formal system not subject to the constraints of Godel's theorem? It's been proven impossible; what does that mean for a god that has to be able to do it? Of course this could all be subject to the constraints of our reason (including the maths we have proving it's not, heh)... this is all rather stale argument .froth. (talk) 23:10, 26 January 2009 (UTC)[reply]

It is conjectured that pi is normal, which would mean any possible message will be included somewhere in the digits. I think the idea behind Steve's "Level 0 god" is that they aren't even constrained by our concepts of logic, which makes it impossible for us to even contemplate them - they are impossible as far as we can tell, but they exist on some level beyond the ability of our logic to make sense of. Don't think about it too much - it will make your head explode. --Tango (talk) 01:03, 27 January 2009 (UTC)[reply]

Yes - actually, I had already realised that many years ago. There is indeed a perfect image of a circle embedded SOMEWHERE in the infinite digits of pi - because there are only so many patterns of digits possible and all of them must come up sooner or later. After I read the book ("Contact" by Carl Sagan) - I downloaded the longest available expansion of pi (which was then about a billion digits as I recall) and set about converting it to binary (non-trivial on a computer with less than a gig of RAM!) and looking for the largest square of zeroes with an acceptable approximation of a circle of 1's within it. My program crunched for about a month - and then another month looking for a circle of 0's in a sea of 1's. Within the first billion or so digits, the biggest such circle is only about 5 pixels across - and it's a huge stretch to call it a "circle". <sigh> It would have really screwed with people's heads if I had found one. But realistically, the probability of even an 8x8 pixel 'perfect' circle is the probability of a specific sequence of 64 consecutive bits having a specific pattern - and the odds of that happening at random is one in 16,000,000,000,000,000,000 - so we need at least 10¹⁸ digits of PI before we'll see even a circle the size of this letter 'o' popping out. Since that's vastly more memory than all of the computers on earth put together - the odds of ever seeing that circle is tiny.

So that (in some way) validates Carl Sagan's idea. Now, the message of the book is that science and faith both matter...or something like that. But, to quote from our article: "Ellie...computes the digits of π to record lengths and in different bases. Very, very far from the decimal point (10²⁰) and in base 11, it finds that a special pattern does exist when the numbers stop varying randomly and start producing 1's and 0's in a very long string. The string's length is the product of 11 prime numbers. The 1's and 0's when organized as a square of specific dimensions form a perfect circle.".

Well, the probability of what Ellie finds is actually suspiciously close to my estimate of it being pure chance - so perhaps Sagan has a hidden message BEHIND the message that most people read into the book - which is his old (and much quoted) claim that "Extraordinary claims require extraordinary evidence" may apply here. So perhaps he's hidden a message within his book - "Don't accept some wild-assed claim of there being a circle embedded in PI as evidence of there being a level 0 god out there - this could easily happen by chance alone". Sadly, the movie flushed away the hook in the tail of the story - it doesn't mention anything about PI or circles and punts for an easier ending.

But the probability of a sizeable circle image showing up inside PI as a matter of chance within the digits we're ever likely to be able to calculate is effectively zero (calculating 10²⁰ base-11 digits is far beyond what Ellie could do with the technology available to her) - so if it DID happen within the pathetically few digits we actually have to hand - we'd have to suspect some bizarre supernatural connection. However, these supposed "level 0 gods" don't ever seem keen on providing irrefutable proof of their existence...which is a shame because life on earth would be a lot simpler if they did! SteveBaker (talk) 16:06, 27 January 2009 (UTC)[reply]

The normality of pi is still just conjecture, so we can't be certain such a sequence will exist somewhere. Pi could be the sequence we've calculated so far repeated indefinitely with an ever increasing number of zeros between each repetition. If it is, that would be far more interesting than it being normal! --Tango (talk) 16:27, 27 January 2009 (UTC)[reply]

On the other hand, pi encodes the idea of a circle in all of its digits; why look for visual patterns in our arbitrary decimal-expansion of it when we already know circumference = (pi)(diameter)? And decimal expansion really is arbitrary; how do we know the gods don't use roman numerals or one scratch in the dirt for every item counted? .froth. (talk) 18:39, 29 January 2009 (UTC)[reply]

Truly omnipotent gods are incomprehensible and postulating their existence raises the age-old logical paradox of how they came about. So quite possibly one of the options that may be tickable, may be the causality/arrow of time feature. 196.2.124.248 (talk) 06:21, 26 January 2009 (UTC)[reply]

The trouble is that even 'level 3' gods (on my scale, above) are capable of manipulating your thoughts (heck, even us level 4 types get a shot at doing that). So you believe in L3/2/1/0 gods then you don't know what you do or don't know because the god(s) may be tampering with your thoughts. That's one of the things that makes them unfalsifiable. I say "God doesn't exist because I've managed to prove 'X'."...and you say "Aha! That's just because he wants you to think 'X' in order to test your faith."...so it's worse than "incomprehensible" - it's "meaningless - even in principle - to discuss it". At which point we wield our mighty 'razor of Occam' and end the speculation right there. SteveBaker (talk) 19:17, 26 January 2009 (UTC)[reply]

That's why religions often (always?) introduce the concept of "free will" even though their god(s) certainly have the power to influence our thoughts. Without free will, it just becomes impossible to have any meaningful theology. (Also, people like to feel in control - although, interestingly, they rarely like to actually be in control.) --Tango (talk) 19:45, 26 January 2009 (UTC)[reply]

While riding rollercoasters people like to be safe but dont like to feel safe. Sort of the same thing with control sometimes .froth. (talk) 00:34, 27 January 2009 (UTC)[reply]

To answer that - you have to realise that what god(s) say is mostly known because that's what the priests say. If people don't believe that have free will then if they screw up, it's God's fault. That's not good. Now people can (in practice) do what they heck they like and blame their local gods...and the priests can't do a damned thing about it. The priesthood lose power over the populace and it's all over for religion within one generation. On the other hand, if you are responsible for your own actions - then if you screw up, the priests can point out how the god(s) aren't going to be happy with you and you'd better sort out your behavior or you'll be banished to hell for eternity. This is an effective way to get your populace to knuckle under and do what the priests claim is god's will (and which, incidentally, allows them to carry on not having to do their share of the cleaning the cow shit out of the barn). SteveBaker (talk) 00:38, 27 January 2009 (UTC)[reply]

Watch out when people are under threat of social censure or eternal banishment and a convenient scapegoat is around.. Puritans believed that every little thing happened as a result of blesssing and punshment for the righteous and sinful.. if a cows milk is discolored, either the farmer sinned or SHES A WITCH! .froth. (talk) 00:50, 27 January 2009 (UTC)[reply]

With our current understanding of quantum mechanics, I don't think we can talk about "supernatural" as breaking the law of physics. It would be more correct to say, breaking the "law" of probabilities. And that "God is messing with the laws of physics" might as well be better described as god leaving the laws of physics alone, and messing with probability alone. At quantum level everything is possible (teleportation, quantum entanglement, etc.), on higher level it's still possible, but so unlikely we're almost sure it'll never happen. --131.188.3.20 (talk) 12:16, 28 January 2009 (UTC)[reply]

I <3 the refdesk. ReluctantPhilosopher (talk) 11:57, 30 January 2009 (UTC)[reply]

I'd like to add a level -1 to Steve's list:

Level -1 gods: the Superlogical god, or "God beyond logic": able to make contradictions true, like to change the value of pi, and not to change it in the same time. Or: create a stone so big that he is not able to raise, and at the same time, to be so strong to raise it. Such a god can easily bypass every contradiction that we invent to prove that he does not exist. He is also able to exist and not to exist in the same moment. Note: although this level is very difficult to achieve for a standard god, apparently, it is exaclty what all of them would like to be -- and humans also, when they happen to gather too much power :( --pma (talk) 14:42, 21 February 2009 (UTC)[reply]

mt st helens

Hi, I am investigating the eruption of Mt StHelens as part of my geography project.Is there a web address of the local newspaper from that area where i could learn first hand the timeline of the eruption? Thanks Quinnp (talk) 18:19, 25 January 2009 (UTC)[reply]

This was a national event, so you don't have to limit yourself to local sources for info about the timeline of Mount Saint Helens. See 1980 eruption of Mount St. Helens, which has many references at the bottom, and also contains a rough timeline. StuRat (talk) 18:28, 25 January 2009 (UTC)[reply]

http://www.oregonlive.com/oregonian —B00P (talk) 21:05, 25 January 2009 (UTC)[reply]

National Geographic. Twice, once soon after eruption and once a year or so later. Polypipe Wrangler (talk) 03:11, 27 January 2009 (UTC)[reply]

Which lightbulb?

Hi. Can anybody help me identify this lightbulb, please? As you can see from the picture it is just over 30mm long and is used in a 6 bulb "chandelier" light fitting, which is the main source of illumination in a room measuring 6m by 6m. Thanks CCorncob (talk) 18:51, 25 January 2009 (UTC)[reply]

Looks like some sort of halogen bulb. DuncanHill (talk) 20:21, 25 January 2009 (UTC)[reply]

I have managed to find some more info on one of the bulbs, that can be seen here. Not sure if it is helpful. Thanks CCorncob (talk) 21:30, 25 January 2009 (UTC)[reply]

I can make out "12V20W" on the bottom line of writing, this means that it is a 12 volt, 20 watt bulb. If I recall correctly these are quite common - your local hardware shop should have them if you need a replacement. DuncanHill (talk) 21:35, 25 January 2009 (UTC)[reply]

The letters "FSL" appear to be a trademark of Foshan Electrical and Lighting Co., Ltd. I think it is a G4 fitting (is it 4mm between the contacts? If so, it is a G4). DuncanHill (talk) 21:59, 25 January 2009 (UTC)[reply]

Yes the spacing is 4mm, so thanks for identifying them. I have seen these bulbs, but the contacts seem a bit thicker. Do you think they would still be appropriate? Thanks again. CCorncob (talk) 00:08, 26 January 2009 (UTC)[reply]

Probably, these things tend to be pretty standard. DuncanHill (talk) 00:10, 26 January 2009 (UTC)[reply]

OK great, thanks again for your help. CCorncob (talk) 00:18, 26 January 2009 (UTC)[reply]

If it's a 12v halogen - it's probably some variety of car headlamp bulb that they've adapted for this use. SteveBaker (talk) 00:53, 26 January 2009 (UTC)[reply]

They are used a lot in desk lamps and the like - I've just realized that the lamp on my computer desk uses one. DuncanHill (talk) 00:55, 26 January 2009 (UTC)[reply]

I have a set of these in some low-profile "hockey-puck" style lights I use around my house in a few applications. The local supermegahardwarestores (here Home Depot and Lowes) both carry LOTS of these kinds of bulbs in various sizes. Just take the bulb to the store and match the shape/size/markings. That's what I usually do. --Jayron32.talk.contribs 04:56, 26 January 2009 (UTC)[reply]

Identifying a street light bulb

So, the question above reminded me about this. The street light outside our kitchen window went out a month or two ago, and the bulb was replaced by some different kind. The light is quite blue-violet, making the white walls and the snow outside look bluish. When starting up, it starts out reddish, and then gradually moves over to the bluish color, in... say, 20-60 seconds. It seems to be pretty high-intensity, lighting a pretty large area. Any ideas what kind of lamp this is? The more important question is, though: do they flicker (like some fluorescent light bulbs)? -- Aeluwas (talk) 19:12, 25 January 2009 (UTC)[reply]

Possibly a mercury vapor bulb =- Nunh-huh 19:55, 25 January 2009 (UTC)[reply]

Or maybe a LED street light. Clarityfiend (talk) 20:03, 25 January 2009 (UTC)[reply]

No - it can't be LED - they don't shift color. SteveBaker (talk) 20:19, 25 January 2009 (UTC)[reply]

Egad, I've been LED astray. Clarityfiend (talk) 20:49, 25 January 2009 (UTC)[reply]

Water Clock Thingie Question

I am trying to build a water clock. My plan was to use a graduated tube and a valve and then have the valve drip at a constant rate. Then, i would measure how much water had drained and (using a graph) would be able to tell about how much time had passed. Unfortunately, after 30 mL have drained, the rate slows significantly. The articles i have read about water clocks say they use sloping sides. Does this help keep the flow constant? and if so, how could i change my plans to make it work accurately? Should i change from a straight tube to a funnellike tube? Any help at all would be appreciated. Buffered Input Output 20:28, 25 January 2009 (UTC)[reply]

Using odd-shaped tubes doesn't change the rate at which water flows out - but it does change the rate at which the level in the container falls when a given volume of water has flowed out. So if you pick a container whose cross section at every height is proportional to the rate of flow when the water is exactly that deep - then the rate that the water level falls is more or less uniform even though the rate of water flow changes. Getting exactly the right container might be tough though - so for a practical project, you might want to look at other ways.

One other way I could think of to do it would be to graduate the time scale non-uniformly so that the distance between the marks indicating that the first minute has elapsed are further apart than the ones indicating the last minute...that makes it harder to read off the time - but at least then you can use a cylinder.

Another idea that comes to mind is to have three containers at different heights. The one at the top supplies water by pouring it into the second. The rate of flow into the second container is designed to be higher than the rate water drips out of it - so it always overflows into a suitable outlet. This wastes water but ensures that the second container is always 100% full - so the pressure inside doesn't change and the flow out of it is precisely constant. Sadly, because the water level in the second container never goes down - you can't use that level to tell the time...but you CAN catch the water that comes out of a spout to fill up a third cylindrical container and use the level in THAT one to tell the time.

There are lots of other ways. SteveBaker (talk) 20:52, 25 January 2009 (UTC)[reply]

While the above approaches work for a few hours (or days using large enough tanks), you might need an automatic method of refilling the tank to make this a permanent clock. The method used in a toilet tank, with a float valve which connects to a tube of pressurized water, is probably the simplest. This still allows the tank volume to vary somewhat, so the drips won't be exactly constant, but you can just average the length of time between drips and use that. Another approach is just to use a dripping faucet, which, being connected to a constant water supply, should only vary if the pressure changes. StuRat (talk) 01:58, 26 January 2009 (UTC)[reply]

Of course - all clocks need a source of power - and that might well be a natural stream or river. But the idea of a constant-pressure tank that's allowed to overflow (with the overflow flowing away someplace) is a really simple way to get constant pressure with the primitive means available to water clock designers. The only real problem is the waste of water - but if you're feeding fountains and such it's a very small deal. The flow rate into the constant-pressure container only has to be a tiny percentage more than the clock's 'useful' outflow rate - just enough to cover the variability in pressure of your ultimate waters source. Kinda like we use zener diodes to limit voltages for our electronics. We are always using the hydraulic analogy to describe electronics - well, you can reverse the analogy to make a water clock using the ideas from electronic clocks! SteveBaker (talk) 02:19, 26 January 2009 (UTC)[reply]

Our article on water clocks has some OK descriptions of some ancient designs and it is also QUITE well referenced with some external links and books. You may find some good information starting there and taking it where it leads you. --Jayron32.talk.contribs 04:53, 26 January 2009 (UTC)[reply]

I'm sorry i wasn't really clear on my question. My question was if i NEED a sloped-side container to make this work with some degree of accuracy. Buffered Input Output 13:48, 26 January 2009 (UTC)[reply]

Then no, you don't . StuRat (talk) 17:04, 26 January 2009 (UTC)[reply]

Definition of Work

Why is work defined as Fd and kinetic energy as 1/2 mv^2? Why not use work=2Fd and KE=mv^2? Is it simply because Fd is more concise than 2Fd, or is there a better reason? --99.237.96.81 (talk) 23:00, 25 January 2009 (UTC)[reply]

It seems to be a matter of how the units of work and energy are defined. If force is mass times acceleration, then in the metric system it can be given as kilogram meters per second squared. Then force times distance is kilogram meters squared per second squared, which is the definition for Newtons. You could have measured force in a new unit called "figs" where two "figs" equals 1 Newton, and then force would be 2Fd. Edison (talk) 23:10, 25 January 2009 (UTC)[reply]

(edit conflict) You are right that it is a matter of definition. However, it is not the units, but rather the quantities. In most areas of physics, formulas don't change with the change of units. Velocity, for instance, is always simply distance/time, no matter if you use meters, kilometers, or miles for the distance and hours or seconds for the time. (To avoid using higher math, I used the formula for no acceleration.) The situation is rather like that of a circle. We know that the circumference is equal to 2πr, where r is the radius. If you don't like the factor 2 there, just use the formula πd, where d=2r is the diameter. — Sebastian 23:38, 25 January 2009 (UTC)[reply]

Suppose that I don't change the units of measurement. I'm under the impression that although Fd=(1/2) mv^2 can be derived from Newton's second law, work and kinetic energy are equal to Fd and (1/2) mv^2 only by definition. If that's the case, why can't I multiply both sides of Fd=(1/2) mv^2 by 2, call the left side "work", and call the right side "kinetic energy"? The units are still consistent; just as multiplying the diameter of a circle by pi doesn't mean a new unit has to be invented for the circumference, 2Fd can still be measured in kilogram meters squared per second squared. --99.237.96.81 (talk) 23:32, 25 January 2009 (UTC)[reply]

Yes, you could build a system based on what you suggest, but it is not very useful. Putting aside the issue that

{1 \over 2}mV^{2}

is only an approximation in the first place, and there are higher order terms if relativistic effects are considered, you will still cause problems. You will be building a factor of two into all sorts of equation, many not obviously related. For instance, it will affect the definition of electrical potential difference which now becomes

-2\int E\cdot dl

instead of

-\int E\cdot dl

, unless of course, you change the definition of the volt, but then you will have to mess with equations like

P=IV\,

. This factor of two is a dimensional constant. The SI system has gone to great lengths to eliminate as many dimensional constants as possible from the system of units. Before then engineers and scientists were required to remember a great number of them. It is a step backwards to start putting them back in. SpinningSpark 00:11, 26 January 2009 (UTC)[reply]

This is kinda silly - you can do this with almost anything. If I decide to measure distances as the "extent as measured from the midpoint" instead of from one end to the other (analogous to measuring the radius of a circle rather than its diameter) - then you end up with velocity being twice the "distance" divided by the time (v=2d/t). To get rid of the 2 you can choose to redefine the meaning of velocity - but you then need to go off and fix a bunch of other things...2's and 0.5's pop up in some places - and disappear in others. Some equations will get more complicated - others will get simpler. I suspect (because we've been doing this for a LONG time) that overall things would get more complicated. But we don't fundamentally gain or lose anything - no additional insight results. We happen to have picked one 'meaning' for work, force, energy, etc - you COULD pick a different one - but that just causes everyone to have to reprint an awful lot of textbooks. You can see this happening in all sorts of areas of engineering where a factor of 'g' (9.8 meters per second per second) creeps in to simplify equations that involve 'weight' rather than 'mass'. The result is generally a lot of confusion...so we work hard not to do that. SteveBaker (talk) 00:51, 26 January 2009 (UTC)[reply]

OK, so a joule is defined as "work done by 1 N over one meter". If energy is discussed in the context of thermodynamics, relativity, quantum mechanics, or anything else, one joule has to be the equivalent of 1 N over one meter. Is that correct? --99.237.96.81 (talk) 01:49, 26 January 2009 (UTC)[reply]

The definition of the unit doesn't change - but you have to be careful because in the context of things like relativity, measuring things like mass, length and time gets tricky - and lots of our basic equations of dynamics and energy are simplified Newtonian equations that are only approximations when you start to consider relativistic objects. At the quantum level, everything gets kinda fuzzy - so again, the definition of what a Joule is doesn't change - but the ability of objects to not be in one place makes measuring properties and plugging them into fundamental equations really tricky. This is dangerous territory for 'armchair physicists'! SteveBaker (talk) 02:10, 26 January 2009 (UTC)[reply]

January 26

Air pressure or surface tension

Have any of you ever noticed this? Let's say you have a plastic cup and a large basin of water. You put the cup in the water sideways so that some water goes into it. Then you turn the cup upside-down and submerge it. When you try and pull it out again (keeping the cup upside-down), it sticks a little at the surface and you have to apply a little extra force in order to pull it out completely. Is that due to surface tension, or have I somehow decreased the amount of air inside the cup (perhaps having displaced some of the air with water), creating a slight vacuum effect? howcheng {chat} 02:51, 26 January 2009 (UTC)[reply]

Surface tension is probably a factor. Another factor could be that the water falling out of the cup creates a vacuum behind it, that vacuum is going to try and hold the water in. It could be the combination of the two, actually - surface tension tries to hold the water together, the air pressure tries to keep the water in the cup, so you have to add extra force to overcome that. --Tango (talk) 03:36, 26 January 2009 (UTC)[reply]

The water you let into the cup is staying in there while the upside-down cup is part way out of the water, because of the pressure of the surrounding air. The force you're feeling is simply the weight of that water. The reason you didn't notice it before you lifted the cup out of the water was that it was buoyant while it was submerged. If you try filling the entire cup with water and lifting it out udside-down, the force at the moment you lift it out of the water will be exactly the same as if you lifted it out right-way-up, also full of water. Surface tension is not involved in any significant way. --Anonymous, 05:24 UTC, January 26, 2009.

Interesting. Will have to try that when bathing the kids tonight. Thanks. howcheng {chat} 19:25, 26 January 2009 (UTC)[reply]

Catching the milk

When heating milk for cocoa, I have noticed that skimmed or semi-skimmed milk is more likely to catch (burn on the bottom of the pan) than full-cream. Why would this be? DuncanHill (talk) 04:13, 26 January 2009 (UTC)[reply]

Because the fat in the cream provides some burning protection to the milk solids (mostly sugars and proteins). Without the fat coating these particles, they are much more susceptible to being affected by the heat. The burning of the milk is a varient of the Maillard reaction, though in this case, its a rather unwanted one. --Jayron32.talk.contribs 04:49, 26 January 2009 (UTC)[reply]

Fat/oil has a much higher boiling point, so I figure this is part of the reason. BTW, try microwaving the milk to avoid burning it. StuRat (talk) 17:00, 26 January 2009 (UTC)[reply]

Just last night, I was reading some related advice in Cook's Illustrated. They suggested putting a small amount of water to cover the bottom of the cold pan, heating that water (to boiling, if I recall correctly), and then adding the milk. This method is supposed to prevent the problem you describe. -- Coneslayer (talk) 14:04, 27 January 2009 (UTC)[reply]

There's even a device to do just that, called a double boiler, where water boils in the bottom part, and the steam then heats the milk in the top part, but not hot enough to burn it. Before microwave ovens, this was the best way to heat milk. StuRat (talk) 16:46, 27 January 2009 (UTC)[reply]

We call them bain maries in English :) DuncanHill (talk) 16:57, 27 January 2009 (UTC)[reply]

Actually - we call them bain marie's in French - even though we're English! SteveBaker (talk) 18:05, 27 January 2009 (UTC)[reply]

A double boiler is a similar idea, but not quite the same thing, since the top pot sits in boiling water in a bain marie, while the top pot is held out of the water in a double boiler. StuRat (talk) 21:14, 27 January 2009 (UTC) [reply]

Or just stir constantly - always works for me. --Tango (talk) 14:12, 27 January 2009 (UTC)[reply]

Thanks for all the answers - very interesting. I prefer full cream milk because it tastes nicer, but circumstances sometimes dictate the use of the watery stuff. I've tried using a microwave, but it is hard to get the milk boiling without it overboiling. DuncanHill (talk) 16:57, 27 January 2009 (UTC)[reply]

I don't think you need to boil it, just get it hot enough for hot cocoa. Does your microwave have variable power levels ? If so, use the lowest setting. StuRat (talk) 15:37, 28 January 2009 (UTC)[reply]

The car of the future!

I remember reading back in high school about guys that had developed engines with unheard of efficiency and gas mileage and such. This was usually in magazines such as Popular Science and Popular Mechanics. I haven't picked up either magazine in quite a few years but I would guess that they still publish these stories from time to time. What happened to these engines? I was told by various cynical and pessimistic people over the years "The oil companies bought the patents to keep people buying more gas!" although, I've never been one to believe in too many cabals. So what's the story with these things, these wonder engines? Where are they? Were they always just figments? Or were they not commercially viable for one reason or another? Dismas|^(talk) 06:24, 26 January 2009 (UTC)[reply]

What you're remembering is known as the "Pogue carburetor." This is what Snopes has to say about it. Also read about the Pogue patents. Interestingly, the only article we have for a Charles Pogue is not this Charles Nelson Pogue. 152.16.59.190 (talk) 09:41, 26 January 2009 (UTC)[reply]

Well now we have Charles Pogue (disambiguation), so if someone writes an article about the Pogue Carburator or that Pogue, it can hang off there. DMacks (talk) 04:30, 27 January 2009 (UTC)[reply]

Free energy suppression and fuel saving devices are an interesting read. DMacks (talk) 14:33, 26 January 2009 (UTC)[reply]

A lot of the inefficiency in car engines comes from running them at variable speeds and temperatures. If an engine could be run continuously, at a constant speed, and was tweaked to perform optimally at that speed and temperature, it would get much better efficiency numbers. Electric/gasoline hybrids, which run the engine at a constant speed to charge the batteries, do get better mileage, but still suffer from temperature changes from starting and stopping the engines periodically. StuRat (talk) 16:54, 26 January 2009 (UTC)[reply]

One point of clarification, as StuRat's commas make this unclear: Hybrids which run the (gasoline) engine at a constant speed, which are presently a very small subset of all hybrid cars, are applicable to this statement. These "series hybrids" include models like the not-yet-released Chevrolet Volt. They do not include the Prius or any other mass-distributed hybrid, in which the gasoline engine still connects directly to the drivetrain. — Lomn 18:27, 26 January 2009 (UTC)[reply]

Thanks for the clarification. Your right, my wording didn't make that clear. StuRat (talk) 21:38, 26 January 2009 (UTC)[reply]

Some of those things have definitely made it - the Wankel engine, for example, had horrible lubrication problems when it was first described (probably in Popular Mechanics!) - but that was solved after maybe 30 to 40 years of engineering effort - and now you can buy several Mazda's that have Wankels in them. But many of these ideas (the Scuderi Engine for example) fall by the wayside for reasons of practicality that the original inventor didn't consider: Cost of manufacture, reliability, wear, pollution, noise, smoothness, overheating on hot days, failure to start on cold days...many of those ideas simply didn't prove practical. Also: If you see some engine that seems impressive because it did 55mpg back in the early 1960's - remember that lots of engines could do that when pulling cars of that era. My 1963 Mini does 55mpg with it's little 37hp engine. My 2007 MINI does barely 40mpg...which is considered pretty good by modern standards. That's not because some mysterious magic thing happens in the 1963 engine - to the contrary, it's crude and horrible in many ways. It's because the '07 car is exactly twice as heavy and can do 140mph and 0-60 in 6.5 seconds with it's 170hp engine, while running the airconditioner, the radio, the computer and so on. The '63 can just barely break 70mph and has a 0-60 time around 12 seconds - no radio, not much of a heater, no A/C, etc. The '07 car needs its first service at 20,000 miles - the '63 requires the owner to do work every 1,000 miles with an oil change and full service every 3,000. So you have to be careful. MPG numbers from old magazines probably have to be halved before you can compare them with modern engines - and MPG is not the only consideration. SteveBaker (talk) 19:08, 26 January 2009 (UTC)[reply]

What's this about cars being heavier today? It was my impression that they were considerably lighter, unless you count things like SUVs and Hummers as cars. You know, to economize on fuel and all that. I remember hearing 2 tons as the typical weight of an ordinary car circa 1970 and 1 ton today. Am I that far off base? --Anonymous, 09:40 UTC, January 27, 2009.

This depends on the location and date, of course, in that those things effect the price of fuel. Europe was known for small cars, and the US for large cars, traditionally, but they are becoming more similar now, due to globalization. As would be expected, large cars were common where and when fuel prices were lowest (as adjusted for inflation): [28]. The biggest cars in the US were perhaps from the early 1970's, right before the 1973 oil crisis, which stopped all our fun. Also, you can't exclude SUVs, minivans, trucks, etc., as more people drive those now than did back then. StuRat (talk) 15:30, 27 January 2009 (UTC)[reply]

The first generation VW Polo was below 700kg and the newest version is 1100kg.--Stone (talk) 10:24, 27 January 2009 (UTC)[reply]

My '63 Mini comes in at 1300lbs - my '07 MINI Cooper weighs 2600lbs - exactly twice as much - and until the SmartCar came on the scene, the modern MINI was the smallest car on sale in the USA. Ironically - there is more luggage space AND more rear legroom in the '63 car...and it handles better. Most cars that were around 20+ years have gained about 50% in weight. Most of that is because of the legal requirements for crash survivability, plus air conditioning, plus higher performance expectations (it really is a pain driving a car with a 72mph top speed on a Texas freeway!), plus luxury, plus emissions control. I'm not saying that the weight gain is necessarily a bad thing - but it does explain why the performance numbers for these bizarro-engines tend to look so good from a modern perspective. Some of them genuinely DO have better power-to-weight or fuel efficiency than conventional otto-cycle engines - but many are not that great. Those that are better on a purely fuel/power basis tend to have other (fatal) practical problems. The [Scuderi Engine]] for example has twice the usual number of cylinders - set up in pairs so that one is hot and the other cold. The latter collects water and corrodes - and the temperature difference between them causes stresses in the engine block which cracks very easily - also, the conduit between the two cylinders gets fouled easily and is almost impossible to clean. So while the Scuderi gets almost twice the power than a conventional engine - it would cost close to twice as much to make and it would fail very easily. SteveBaker (talk) 15:22, 27 January 2009 (UTC)[reply]

With twice the power, it seems like you could use some of that extra power to heat the cold cylinders, using the exhaust, and cool the hot cylinders, using air and unburned fuel, to equalize the temps. Has this been tried ? StuRat (talk) 20:57, 27 January 2009 (UTC)[reply]

As I understand it, the reason the Scuderi cycle is more efficient (on paper) than the Otto cycle is precisely because the exhaust condenses in the cold cylinder so you aren't robbing the engine of power when you push the exhaust gasses out - but rather get benefit from the exhaust gas condensation dropping the pressure in the exhaust cylinder and extracting power on the up-stroke. If you let it get hot, you lose all of that benefit. But the details are sketchy because companies who have been working on these split-cycle engines are pretty secretive.

Interestingly though (looking at the references in our article) it looks like the technology (which has pretty much languished since the 1890's(!)) is undergoing something of a revival - with serious efforts to make a workable/manufacturable engine as recently as the middle of last year. One thing that is really interesting about the Scuderi is the ability to shut down the combustion cylinder and use the exhaust cylinder as an air pump. So you can make an 'air-hybrid' engine where you run the engine at it's most fuel-efficient RPM all the time - using excess power to compress either inlet air or exhaust gas into a pressurized cylinder. Later, when you need more power you use the pressurized gasses to produce extra power by injecting it into the combustion cylinder. If you compress air (from 'active braking') and exhaust gasses (when storing unused engine power) into separate tanks then you can use the pressurized exhaust to produce pneumatic power from the same pair of cylinders and any pressurized air you may have accumulated to supercharge the engine when more power is needed. But for all of those cool things to work out, there are a lot of the more annoying fundamental things to iron out first...like not having the engine block crack! IIRC, there are also issues about what happens to oil that may get into the exhaust cylinder when the engine gets old and the piston rings start to wear. In a normal engine, the excess oil gets burned off (which is not great - but at least the engine still runs) - but in the Scuderi, there is no place to go. If it starts to fill up the cylinder - you'll eventually get a 'hydrolock' and the engine will self-destruct. That kind of annoying practical problem is what always makes these fancy engines take decades to perfect (cf. Wankel engines). SteveBaker (talk) 14:35, 28 January 2009 (UTC)[reply]

To keep the engine block from cracking, how about using a material with little or no coefficient of thermal expansion ? (Is there something cheaper than a platinum-iridium blend, perhaps some type of ceramic ?) You could also occasionally heat up the cold cylinder to drive out accumulated water and oil, say when the car engine is turned off. StuRat (talk) 15:28, 28 January 2009 (UTC)[reply]

Einstein Field Equation

Is the Einstein field equation G_ab=8πKT_ab or G_ab=8πT_ab or G_ab=T_ab(G is the Einstein Tensor, K the Gravitational constant and T the Strees-Energy Tensor)?~~The Successor of Physics~~ 06:43, 26 January 2009 (UTC)[reply]

Doesn't really matter, does it? You can get rid of K through a redefinition of your units, see Natural units and Geometrized unit system. In SI units, the factor is actually 8πK/c⁴ and you seem to have set c=1 already. You could get rid of 8π by a redefinition of either G_ab or T_ab or both, if you wanted to, but that's rather uncommon, I think. There's no "wrong" or "right" here, it's just a matter of convention. Check in your text book what convention they use. --Wrongfilter (talk) 17:52, 26 January 2009 (UTC)[reply]

Remember, if you remove a pi from the field equation, it will be at the expense of adding pi's to other equations. --Tango (talk) 23:28, 26 January 2009 (UTC)[reply]

Thanks!!!~~The Successor of Physics~~ 04:50, 27 January 2009 (UTC)[reply]

Drake equation with infinite L

I think I've found a flaw in the Drake equation.

Suppose that it is possible with non-zero probability for a civilization to break the law of entropy and continue to exist and release radio signals forever. Then the term L in the Drake equation, as an average, is infinite. Since the existence of Earth rules out a zero value for any other term in the equation, this in turn implies that N must be infinite as well. But in reality, this will be true only once the universe is infinitely old.

Would it be possible to adjust the Drake equation to account for the finite age of the universe? Neon Merlin 09:34, 26 January 2009 (UTC)[reply]

I don't think you need to adjust anything. The maximum L cannot be infinity; max L is equal to the age of the universe, although in my unprofessional opinion it is unlikely anything got started for at least the first billion when everything was getting settled out into galaxies and such. If 1% of alien civilizations builds a broadcaster that lasts for 10 billion years and the rest will communicate for 1000 years on average then we get an L of 10,000,990. 152.16.15.23 (talk) 10:14, 26 January 2009 (UTC)[reply]

Reading your question over again I realize that I may have not given you the answer that you wanted. Are you looking for a way to express the Drake equation as a function of time passed since the first possible civilization could have formed with the assumption that a fixed fraction of the civilizations that form continue broadcasting for the rest of eternity and thus accumulate? 152.16.15.23 (talk) 10:29, 26 January 2009 (UTC)[reply]

That's not even the big effect. If civilizations are arising at a uniform rate (in fact, you'd want to tie it to the star formation history of the universe in some entirely unknown way - life as we know it won't arise until you produce some metals), you'd just use half the hubble time as an average age. WilyD 15:03, 26 January 2009 (UTC)[reply]

This is a problem with most predictive mathematical models — they can lead you astray if you don't pay attention to their limitations. In the original Drake formulation, there are just two terms that aren't unitless constants: L, which is the average lifetime of a broadcasting civilization; and R^*, the average rate of star formation in our galaxy. (Note that Drake only contemplates civilizations within our own galaxy, not across the entire Universe.)

Implicit within those terms is the assumption that L will be less than the age of our current galaxy (civilizations require some time to evolve), or at the very least, less than the age of the Universe. Pushing the formula back further in time (with a larger L) would imply that civilizations had been developing around stars that had not yet formed. The alternative form of the Drake equation (Drake equation#Alternative expression) described in our article incorporates this restriction a bit more explicitly. There, the final term L/T_g – the average lifetime of a communicating civilization divided by the age of the galaxy – should end up as not more than 1. (Give or take some fudging I don't want to get into, if that ratio is 1 then every civilization that starts broadcasting continues to do so forever.)

Of course, that formulation falls down on very long time scales, too — as L approaches the lifetime of the average star, species with interstellar capability begint to settle 'new' stars (increasing the odds that a given star system will harbor life). Species without interstellar capability, meanwhile, will tend to get wiped out as their stars go out. TenOfAllTrades(talk) 14:46, 26 January 2009 (UTC)[reply]

The trouble with this hypothesis is the setting of the other attributes to 1.0 because Earth represents one example. Doing that tells you that either:

Earth is eventually able to learn to broadcast radio forever...hence WE are the cause of L=infinity...but N_e (the average number of civilisations per suitable planet) could still be one-over-infinity (there are an infinite number of planets and we are the only one with life). Then the equation boils down to infinity over infinity - which tells you nothing...we may still be alone in the universe.

The various 'N' terms in the equation strictly refer to the number of suns/planets/civilisations THAT ARE CAPABLE OF ACHIEVING LIFESPANS OF DURATION 'L'. Now, you can't count the Earth as 1.0 for any of those N terms because we may never defeat entropy - so any one of the N's could go to zero - and we're back with no aliens out there.

But the Drake equation really needs be used to count the number of civilisations that are NOT us - otherwise it's not very interesting. If you exclude Earth from the math - then the answer can still be zero - even with L=infinity.

But in any case, the idea of a civilisation being able to 'defeat entropy' is kinda silly...as far as we know, entropy can no more be defeated than time travel or superluminal travel be achieved. If you assume that science-fiction physics is allowed - then you need to rewrite the equation to include time travel and instantenous travel. If we aren't talking about "known physics" - but instead "unknown physics" (in which entropy can be defeated for example) then the Drake equation itself is incorrect and would have to be severely amended. The whole POINT of the equation was to estimate the number of civilisations we might hear from given our present knowledge of the universe. Once you start throwing in alternative physics models - all bets are off.

SteveBaker (talk) 15:54, 26 January 2009 (UTC)[reply]

There seem to be several flaws, all dealing with levels of technology reached by other civilizations:

1) I agree with your concept, that, if a civilization survives beyond some length of time, they may have overcome all the problems which tend to cause extinction, like warfare and living on a single planet.

2) They may also develop ways to communicate instantly with other civilizations, over vast distances, and in different times, say by using wormholes.

3) There seems to be an implicit argument in the Drake Equation that only our galaxy matters, while I can imagine a civilization in another galaxy that could spread to ours, either physically, or virtually.

4) There may also be life forms in other dimensions/parallel universes, which manage to develop a technology which allows them to communicate with us. StuRat (talk) 16:46, 26 January 2009 (UTC)[reply]

I would argue that if communication between "parallel universes" is possible, then they aren't really separate universes. I can't think of a reasonable definition of "universe" which would consider them separate. --Tango (talk) 00:53, 27 January 2009 (UTC)[reply]

We may indeed want to redefine the word "universe" at some point if that happens, but my point is that the Drake Equation doesn't consider this possibility. StuRat (talk) 15:18, 27 January 2009 (UTC)[reply]

For a civilization to survive the possibility of extinction, it must be far more advanced than us, and it must also have learned how to keep its civilization alive if its own actions start destroying its environment. Our own species might not even survive 3 million years, and most scientists agree. The Fermi paradox really isn't such a paradox. ~A H 1^(TCU) 18:17, 27 January 2009 (UTC)[reply]

Whether civilizations self-destruct has a lot to do with what nasty weapons science brings us in the future. Nuclear weapons may be capable of destroying all human life on a planet. And perhaps more powerful anti-matter weapons (which may be available in a century or so) might be capable of destroying the planet itself. However, once people have spread to many planets, moons, asteroids, and space-stations, in many solar systems, and floating between them, even this won't be enough to wipe us out. So, we might be safe, unless there's some new super-weapon that will allow anyone to wipe out the galaxy or universe, then self-extinction will become virtually inevitable. StuRat (talk) 20:52, 27 January 2009 (UTC)[reply]

In dogs, say a Great Dane and a Chihuahua were to breed through artificial insemination...

What would the offspring look like? Would this even be possible? This article shows how big the size difference can be. So what might be the effect if the mother was a Great Dane and the father was Chihuahua, and vice versa?--'Cause It's No Good (talk) 11:25, 26 January 2009 (UTC)[reply]

I don't think it is possible to say what they look like, we simply don't know enough about the genetics. Besides it will almost definitely vary a fair amount from cross to cross. I don't however see any reason why it would be impossible if the mother was a great dane. I'm somewhat doubtful the mother and/or puppies will survive if if the chihuahua is the mother however. Nil Einne (talk) 11:51, 26 January 2009 (UTC)[reply]

Couldn't they be prone to sympatric speciation, where the two dogs, currently physically incapable of mating, eventually become speciated where they cannot reproduce genetically? Or does them being in the environment of dog breeders prevent this from happening? -- MacAddct1984 ^{(talk  contribs)} 14:43, 26 January 2009 (UTC)[reply]

I think this is just another example of why the standard definition of "species" doesn't really work. Breeding between Great Danes and medium sized dogs and Chihuahuas and medium sized dogs (which will presumably occur naturally) means there will be an exchange of DNA between the two breeds even though they can't breed together easilly. --Tango (talk) 19:38, 26 January 2009 (UTC)[reply]

I think it is fair to say that the size would be somewhere in between the two, though I doubt it be right in the middle, I'd assume the hight would take after one more than the other. That being said, the father would have to be the Chihuahua since if the Chihuahua was the mother it would not be big enough to carry a baby that potentially would be so much larger than itself. It does matter which one is the mother as you keenly asked. We know some human traits we have are more from our mothers, like baldness in males (That is why they tell men to look at their mother's father to see if they'll be bald). I assume there are similar gender specific attributes in dogs, though there probably hasn't been as much research on it. Anythingapplied (talk) 20:40, 26 January 2009 (UTC)[reply]

I wouldn't be quite so fast to say it's all in the genes. It has been found that many features in fetal development are heavily influenced by conditions in the womb (do you also call it that in dogs?) like e.g. available nutrition, what chemicals are released to trigger certain cellular activities. It may still be that a Great Dane mix cub might grow too big for a Chihuahua mother, but I'd consider it more likely that it would fail to develop because something in the fetus growth pattern would not be compatible it might even be that the cub would drain resources the mother could not afford to lose. Another possibility might be that instead of carrying a litter of several pups most of the fetuses would fail to develop and only one would be carried to term. If the mother then can't birth it and no vet is available to do a C section they'd both die. Her birthing one rather big, but still manageable pup that then grows to something odd looking and significantly larger than a Chihuahua. A lot of a puppy's growth, size wise happens after it's born. So, a Chihuahua as mother has fewer chances, but it's not all because of genes. 76.97.245.5 (talk) 21:51, 26 January 2009 (UTC)[reply]

I think it's unlikely the bitch would die, I would expect the fetus to be aborted if it got bigger than was safe. I guess it's possible the bitch's body wouldn't notice the fetus was too big to be delivered until too late (since it can probably fit in the womb without being able to fit through the cervix), but it seems unlikely to me. --Tango (talk) 23:24, 26 January 2009 (UTC)[reply]

OOhhh. If I ask a question about donkeys, can I use the word "ass" in a totally non-ironical way too? --Jayron32.talk.contribs 15:04, 27 January 2009 (UTC)[reply]

If you want, although donkey is the more common term. --Tango (talk) 15:48, 27 January 2009 (UTC)[reply]

Throw the British term for a Rooster into the question for maximum linguistic titillation on this side of the pond. Edison (talk) 17:45, 27 January 2009 (UTC)[reply]

As for the OP, see a report of such a mix at [29]. This is certainly not a confirmed report, and I could find no such reports at Google News archive or Google books. Might be some discussion in the veterinary literature. Edison (talk) 17:53, 27 January 2009 (UTC)[reply]

Progesterone receptor A - isoform

I would like to know what is the molecular weight of (human) progesterone receptor A (PR-A)? There are a lot of reports that looked at PR expression using western blotting but it is for me still unclear what the 'real' molecular weight is. Some studies report 94 kDa, others 81-82kDa (in both cases there is a single PR-A band visible). Many thanks in advance. Ana. —Preceding unsigned comment added by 131.211.166.194 (talk) 14:37, 26 January 2009 (UTC)[reply]

Estimating the molecular weight of a protein on a western blot is a bit dicey. First, the molecular weight markers that are run alongside the sample are just meant to give an approximate reference point to estimate the sizes of the bands of interest. Second, a gel can run unevenly, throwing off the size estimates. Third, the size markers would typically be invisible on a western blot (since you're using an antibody that should only react with your protein of interest) so in practice one marks the position of the MW standards on the transfer membrane after visualizing the transferred proteins using a stain like Ponceau S. Fourth, the lanes containing the size standards are usually cropped out of the published photos and replaced manually with the approximate molecular weights. Fifth, sometimes only the band of interest is shown and reported to be at some particular MW for which you just have to take the author's word on it.

Now, if you were talking about a protein gel stained with Coomassie or Silver stain to visualize all the proteins, then you would only have the first 2 problems. However, you would still have the universal problem of post-translational modifications, which can either increase the apparent molecular weight (by adding on a phosphate, acetyl, ubiquitin, or lipid side chain, etc.) or decrease the molecular weight by cleaving the protein.

The "real" molecular weight of the A isoform of the progesterone receptor? You can get a predicted MW based on the weight of each individual amino acid in the chain (see http://ca.expasy.org/ for a good set of proteomics resources). In this case, the predicted MW of PGR-A is ~99 kDa. Of course, then you have the final problem with proteins... sometimes they don't behave themselves and they run out on the gel faster or slower than you expect them to. --- Medical geneticist (talk) 15:26, 26 January 2009 (UTC)[reply]

greatest possible scientific progress 40 years ago from single twitter?

thinking of working scientists with a 50+ year career:

if they could, today, send back 1 twitter's worth* of information (a clue) to themselves of 40 years ago regarding what to explore, what is the greatest progress they possibly could have made (early) as a result?

Actually I am interested by discipline: chemistry; biology; physics; mathematics; economics; medicine

Thank you!

* (140 characters) —Preceding unsigned comment added by 82.120.111.130 (talk) 17:37, 26 January 2009 (UTC)[reply]

Thats an interesting question. My first inclination would actually be for social purposes. Instead of giving them what we value the most, give them what they could use the most at that time in history. To me, the answer to that question would be something to try and prevent the cold war or any of the other wars that have occured in the last 40 years. Science will always move on. The fact that we would be sending them something we now know is proof that we would have will be eventualling have been going to learn it, and thus isn't necessarially of a crucial need to transmit, where as the lives lost in wars or the recources lost in economics collapses maybe of more importance. That said: In the field of math I'd probably transmit hints to the proof for Fermat's Last Theorem. Anythingapplied (talk) 17:56, 26 January 2009 (UTC)[reply]

I doubt you could get a significant amount of useful information about FLT into 140 characters. Wile's proof built upon large amounts of recent work - all Wiles actually proved was "All elliptic curves are modular." (although one shouldn't diminish the significance of that proof), that only proves FLT because of lots of work done before. I guess you could say "The proof of Fermat's Last Theorem involves modular forms." so people have an idea of what stuff to study, but that's about it. --Tango (talk) 18:14, 26 January 2009 (UTC)[reply]

I have a truly marvellous hint to give you which this SMS sized mesasge is too small to contain. --LarryMac | Talk 18:35, 26 January 2009 (UTC)[reply]

I think I'd go with "Fermat's last theorem didn't fit in the margin!"...well, if I were sending back something about Fermat...which I think would be a waste. 40 years ago is 1969 - that's around the time when most of the fundamental physics stuff had already been figured out. Look at the MANY Wikipedia timelines - it's tough to find a suffiently compelling single breakthrough since the mid-1970's. Using our one super-valuable 'twitter' to save them 5 years by mentioning Quarks or Dark Matter seems like a wasted opportunity. I wonder if there is enough space in our 140 characters to tell them how to send twitters back in time - it would be good to tell Newton to give up Alchemy or to tell Einstein about Quantum theory while he was still young enough to work on it...but if we're really stuck with 40 years then neither of those things is any good. I'd be awfully tempted to say "Make REALLY SURE that the 'twitter' standard allows unlimited-length message attachments" - then go on to dump all of Wikipedia and the results of the Human genome project onto the end of the message. But I sense you're not going to let me do that...so we're down to: "Arrest G.H.W.Bush'sOldestSon&BillGates.GlobalWarmingCausedByCO2-SERIOUS!!TellSteveBaker:BuyGoogle,DiseaseOfRobert R. don'tLetItSpread.". But specific scientific advice is tricky in so few characters. SteveBaker (talk) 18:48, 26 January 2009 (UTC)[reply]

The OP let us have one twitter per discipline, so you don't need to be quite so careful about what you choose. I'm struggling to think of good things, though - it seems there have been disappointingly few major discoveries in the last 40 years... There has been lots of incremental development, but few major breakthroughs. The biggest development in the last 40 years has to be computers, but even the major breakthroughs for that were made more than 40 years ago, it's just been incremental development since (pretty rapid incremental development, sure, but not anything a twitter is likely to help with). You could send back warnings about various disasters, of course, but I don't think that's really what the OP had in mind. --Tango (talk) 19:03, 26 January 2009 (UTC)[reply]

How about a message on the importance of the Internet, using words they would understand at the time, like "ARPA-NET, on home personal computers, will revolutionize how people communicate". Be sure to send it to Al Gore, so his claims to have invented the Internet will then become true. :-) StuRat (talk) 20:47, 26 January 2009 (UTC)[reply]

Would knowing how important the internet will become actually help develop it? It moved pretty quickly as it was... --Tango (talk) 21:45, 26 January 2009 (UTC)[reply]

It took from the 1960's to the 1990's for the Internet to become widely available for home users. I suspect that this could have happened a couple decades earlier, although, due to bandwidth limitations on dial-up modems, that text-only pages would be all that could be passed easily between computers at that time. Still, that could have been quite useful, and Wikipedia could have even started in the 1970's. StuRat (talk) 03:41, 27 January 2009 (UTC)[reply]

I think the essentials of the Polymerase chain reaction could be boiled down to 140 characters.-gadfium 23:07, 26 January 2009 (UTC)[reply]

"Useful fluorescent protein for tagging in Aequorea victoria" => Win Nobel Prize. Dragons flight (talk) 23:16, 26 January 2009 (UTC)[reply]

Apparently I need a better time machine. GFP was first isolated in 1962. Dragons flight (talk) 23:19, 26 January 2009 (UTC)[reply]

I'm also partial to sending lottery dates and numbers but that's not very scientific. Dragons flight (talk) 23:16, 26 January 2009 (UTC)[reply]

Computer science: "32 bit network addresses are too small, but go for a flat 32 bit memory model for RAM. Emacs, not vi, and never NotePad!" --Stephan Schulz (talk) 23:26, 26 January 2009 (UTC)[reply]

Er - you mean "vi, not emacs" - right? SteveBaker (talk) 00:18, 27 January 2009 (UTC)[reply]

Will all of the women please leave the audience? Now where did I put that bag of stones... --Stephan Schulz (talk) 10:20, 27 January 2009 (UTC)[reply]

Eighty Megs And Continually Swapping - Ha!! (Oh - it's OK - the chicks have left - we can just pretend like we're doing a bunch of macho/geek posturing).OW! That rock really stung!<wink, wink> SteveBaker (talk) 15:07, 27 January 2009 (UTC)[reply]

Plastics. -- Coneslayer (talk) 12:46, 27 January 2009 (UTC)[reply]

Nylon:1935, Polystyrene:1839, Polypropylene:1951...nope. (Oh, wait - I just followed your link - Hahahaha!). SteveBaker (talk) 15:11, 27 January 2009 (UTC)[reply]

What about 200 years?

Since we seem to be struggling with 40 years, how about 200 years? "The speed of light in a vacuum is constant for all inertial observers." has to be pretty high on the list of options for physics - once you have that, you can work out most of special relativity in an afternoon. Is there a similarly short statement that sums up quantum mechanics? What about for other disciplines? --Tango (talk) 19:15, 26 January 2009 (UTC)[reply]

Forget pure science. Go for technology: "Wires carrying current have a magnetic field. Conductor cutting through magnetic field gets voltage induced. Build motors and generators." Edison (talk) 19:54, 26 January 2009 (UTC)[reply]

I certainly would not send anything back. Humanity has teetered on the edge of self-annihilation too long for me to be comfortable making sweeping changes in the discipline that has defined the last 200 years. 200 years isn't long at all anyway; let them work it out for themselves. Who knows what kind of other advances were made trying to solve problems that we might spoil for them. The key article here is Serendipity. And don't even think of trying to avert wars or disasters; I'd argue confidently that nothing has more impact on the future than war. For one, the modern large-scale conflicts have marked remarkable leaps in manufacturing technology, not to mention paradigm shifts in popular culture- billions of people thinking and behaving differently. Yes the price was unimaginable suffering and the blood of millions, and the world might be better if things had happened differently, but we're not talking about a stable, post-scarcity world culture; we're talking about an era in which the world is stockpiling enough nuclear weaponry to turn the earth into molten slag, we're talking about progressive changes positively straining at the fabric of society to change slavery and torture into equality and humanitarianism and to accept radical changes in our way of life. That may be the best or the worst time to confront Earth with a greeting from the future, but it's certainly not the best time to meddle with things. .froth. (talk) 21:06, 26 January 2009 (UTC)[reply]

And anyway don't assume the message has to tell the truth.. Seldon lies to the Foundationers to great effect, and telling them the truth would have destroyed them, although a little 40- or 200- year hop is hardly comparable. .froth. (talk) 21:06, 26 January 2009 (UTC)[reply]

I'd go with disease prevention: "Boil water before you drink it and surgical instruments before you use them; eat fruits, veggies, grains, milk, and meat to be healthy." Alternatively: "Don't poop into rivers you drink from, bury it instead" (although they might have figured that out by then). StuRat (talk) 20:51, 26 January 2009 (UTC)[reply]

Except those things aren't sufficient. The link between peaches and cholera was real when they were being washed in contaminated water; someone who knows eating fruit has an unhealthy effect will discount the rest of your advice. You'd need to give them some clue as to what your motive was for boiling the water; it's not just something you do before drinking it. And sticking to the old-fashioned American food pyramid groups might make healthy eating easier in modern-day America, but it isn't an absolute healthy diet guide. There's no reason to add milk to an adult's diet if they're already getting what they need elsewhere, particularly if they don't retain the ability to digest lactose into adulthood. There's no need to tell them to eat meat if they're eating enough protein without it, and if they aren't they probably can't afford meat anyway. If they're getting enough carbs elsewhere there's no need for grains. Etc. Find an influential person and seed them with germ theory instead - "Miasma theory is onto the right idea, but it's tiny creatures not bad smells and they can travel through water too. Look into it." 79.66.105.133 (talk) 21:53, 26 January 2009 (UTC)[reply]

I believe germ theory goes back further than 200 years, and the invention of the microscope allowed people to actually see bacteria. Saying "boil water before you drink it, wash food with it, or wash dishes with it" might be a good addition, though. StuRat (talk) 03:36, 27 January 2009 (UTC)[reply]

Yes, but it wasn't taken seriously until the mid 19th century. Seeing micro-organisms doesn't tell you they cause disease. By giving someone the reassurance it would prove to be right 40 years before it was being seriously explored, you could provoke research that would save thousands of lives. 79.66.105.133 (talk) 18:38, 27 January 2009 (UTC)[reply]

"Marie, use a much longer stick when stirring the pitchblende" . DuncanHill (talk) 16:47, 27 January 2009 (UTC)[reply]

obviously this isn't working - so how about without a length limit

obviously I'm not getting answers about physics, chemistry, etc, and 40. So what if you can only relate one discovery, but without length limit. What discovery of the past 40 years would have the biggest impact 40 years ago?

We're talking about biggest impact now? Hm, I'd have to go with "you can't tell now, but the sun has become unstable and will destroy the entire earth in 40 years and there's absolutely nothing you can do about it. make your peace." 72.236.192.238 (talk) 22:09, 26 January 2009 (UTC)[reply]

I think you mean you have no chance to survive make your time. --Trovatore (talk) 23:13, 26 January 2009 (UTC)[reply]

~~"Rub sticks together"? --Tango (talk) 23:16, 26 January 2009 (UTC)~~ Sorry, I wasn't reading properly... --Tango (talk) 00:21, 27 January 2009 (UTC)[reply]

I really don't think 40 years is enough. It's not the length of the message (well, not within reason) - even with a couple of pages, I doubt we could make a big impact. Part of the problem is that most of the work we do these days requires modern technology. It's no use telling them to look for the Higgs boson because the technology to do that simply wasn't there in the 1970's. Even if we tell them that computers are seriously important and the internet matters and to use open systems to allow scientists (and laymen) to collaborate on writing an encyclopedia...they simply couldn't do that back then because first you had to make smaller/cheaper computers - then you could use those to push the technology - which in turn allows still smaller/cheaper computers - which means that more people have them - which turns computer networking from a cliquish "UseNet" into the Internet and thence into the world-wide-web. Back when I was in college in the mid 1970's, we couldn't have built the internet if our lives depended on it. Sure, we can tell them about the rise of text messaging - but without the battery technology and the mass-production of tiny RAM chips - they couldn't make the cell phone to exploit that. Some things just have to evolve slowly.

That's why Tango's idea to stretch the time limit to 200 years has started to provoke some interesting answers while increasing the message length has not. If we had something important to say - I'm sure we could figure out a way to say it in 140 characters and add enough information to speed up the work...but we just don't have anything profound to say. I think a global warming warning would be the best thing we could do. What we're trying to do now would have been so much easier if we'd had another 40 years to do it in.

So (within limits) it's not the length of the message - it's the amount of time we can send it back. If the limit TRULY is 40 years - then the idea of telling some scientists how to make a ridiculous amount of money on the stock market isn't so silly - lack of funding has probably done more to limit our technological progress than anything else...fix that and everything moves faster. SteveBaker (talk) 00:18, 27 January 2009 (UTC)[reply]

Re the Higgs boson: the theory was pretty well understood forty years ago. I don't think there's much we could send. Algebraist 00:22, 27 January 2009 (UTC)[reply]

If there's no size limit to the message, perhaps the people of the late sixties would enjoy a copy of the human genome. APL (talk) 06:14, 27 January 2009 (UTC)[reply]

Physics and chemistry like most technical things advance gradualy and if you lift somebody up 200 years in knowledge in a small area he has no foundation to stand on. The design of a microchip is usles in 1809, same with airplanes. Penicillin extraction from fungus might work even with technics in 1809 and this will make the differnce in the growth of the nations. The ammonia synthesis of Haber Bosch is complicated, but if you get this running in 1809 the food production would increas drastic. To chnge the outcome of the wars in the 19th century would have the largest impact. Machinegun design to one of the fighting groups in a war done in the old fashoned way would make clear winners. The French under Napoleon would be my choice before or after Watergate the map of Europe would be a lot different than. The composition of sulfur mustard or chlorine gas might be a good tip to the armies of the world too. --Stone (talk) 10:15, 27 January 2009 (UTC)[reply]

I believe the main threat to humanity is our technology outpacing the social structures necessary to survive it (nuclear weapons in the last century, probably nanotech and biotech in this one). I would send something like "it is a sin to put the tools of adults into the hands of children", and then maybe some lotto numbers so they'd know I wasn't just some goofball. --Sean 13:51, 27 January 2009 (UTC)[reply]

You're just guessing, though, they can do that just as well. We've had nuclear weapons for over 60 years and haven't destroyed ourselves yet, so the benefit of hindsight should make you less concerned about such things than someone 40 years ago rather than more. --Tango (talk) 14:10, 27 January 2009 (UTC)[reply]

The problems of technology outpacing our ability to deal with it were well known in the late 1960's - there is nothing we can possibly tell them about that except, perhaps, "You were right about that". That's not going to change anything that happened. As for the nuclear weapons thing - it was only the presence of all of those nukes that prevented a third world war. Trust me, I was there. Everyone was so freaking terrified that the end of the world was coming that we were forced to work with the 'enemy' to make sure that it didn't. The result was exactly what the pre-nuclear weapon people said: A policy of mutually-assured destruction works. That surprised me at the time - but hindsight helps a lot! If we told them it would all turn out OK in the end - they might have caused one side or the other to drastically scale back weapons production before the moment of reconciliation - and THAT could easily cause the very thing we'd be trying to avoid. Besides - we're talking 1969 - by which time the worst of the madness was over. We were much more concerned then about the Soviet's conventional army nibbling away at the edges of Europe and our inability to prevent that OTHER than by starting a nuclear exchange that would end the world. Fortunately, the soviets had much the same concern...(see how that works?!). 14:59, 27 January 2009 (UTC)

In what way were they "right about that"? People fear problems with too advanced technology all the time (and have done for centuries), but can you give an example of a time they were actually right? --Tango (talk) 15:13, 27 January 2009 (UTC)[reply]

Internal combustion engines and global warming? SteveBaker (talk) 16:40, 27 January 2009 (UTC)[reply]

That's still a fear about the future - global warming hasn't done any major damage yet (a few extra hurricanes, maybe, but nothing on a global scale) and we may yet get emissions under control and prevent a complete disaster. --Tango (talk) 16:45, 27 January 2009 (UTC)[reply]

Just a guess - you aren't a polar bear are you?

It's completely UTTERLY incorrect to say that global warming hasn't done any major damage yet. There is strong evidence that the number of hurricanes is increasing due to global warming - and that means that the victims of Katrina and the total annihilation of Galveston could easily be suffering those consequences. Low lying island communities all around the world are actually starting to notice the sea level rise and a few are losing crops due to salt water getting into the groundwater beneath their fields. Plants that live on mountain slopes are vanishing from the lower slopes and being found at higher altitudes. Migratory birds are being found further North than they've ever been seen before - and in other areas, whole populations of animals and plants have simply 'vanished' because one species growth spurt or breeding cycle that is triggered by temperature are appearing out of sync with other species who time their young based on day-length - so one species thrives to 'plague' proportions while the other starves. Heck - find a photo of ANY glacier in the world as it was 10 years ago and as it is today! If that's not "major damage" - I don't know what is! SteveBaker (talk) 17:50, 27 January 2009 (UTC)[reply]

Oh - and to your other comment: getting emissions under control ain't enough. A big climatology study that came out a few weeks ago reported that the timescale for the atmospheric CO2 level to return to 'normal' even if we went back to a pre-fossil-fuel economy overnight (yeah...right!) would be on a scale of thousands of years and that indeed CO2 levels will continue to climb slowly for decades - even after we stop making matters worse. That's because of the knock-on effects of the temperature rise slowly feeding back into CO2 release from the oceans. Even if we "get emissions under control" - we are still in for a disaster. At this point it's more about the depth of the disaster we're just starting to head into than whether it gets worse or not...it's definitely going to get worse no matter what we do. SteveBaker (talk) 17:58, 27 January 2009 (UTC)[reply]

Well, if the human race gets wiped out in the next 50 years, I'll buy you a pint! ;) I take all claims of impending doom with a very large pinch of salt - none of them have been correct so far, what makes this one any different? Once it gets bad enough that people can't get away with just doing it lip service, we'll find a workable solution - we always do. --Tango (talk) 18:04, 27 January 2009 (UTC)[reply]

I guess it depends on your definition of "major". None of those things are even remotely comparable to a nuclear winter, which was the main fear regarding technology getting out of hand 40 years ago. Also, such statements are only meaningful if compared to non-global warming figures - there are always lots of hurricanes, there are always lots of species going extinct, glaciers have been melting for the past 10,000 years, etc.. There is undeniably an increase in those things and it is undeniably getting worse, but it isn't easy to actually make a meaningful comparison which you need to do before you can claim that global warming (particularly, man-made global warming) has already caused major damage. --Tango (talk) 18:04, 27 January 2009 (UTC)[reply]

Displacement, s

Why is displacement notated with the letter s? Any particular reason, or just what ended up as convention in the end? --80.229.152.246 (talk) 19:49, 26 January 2009 (UTC)[reply]

Not much more than guessing: Latin la:spatium denotes the length of a path. v is velocitas, t is tempus. --Wrongfilter (talk) 20:02, 26 January 2009 (UTC)[reply]

Thanks, that sounds extremely plausible. --80.229.152.246 (talk) 22:50, 26 January 2009 (UTC)[reply]

I'm also going to pipe in with my opinion. Notation varies from place to place, but in my experience, the most uniform and consistent systems always use "X,Y,Z" as the standard Cartesian grid, because they are the last letters of the English alphabet. When we do a

\mathbb {R} ^{3}

to

\mathbb {R} ^{3}

mapping to some other abstract coordinate system, we generate other coordinates in

\mathbb {R} ^{3}

, so we just count back three more letters and get "U,V,W". These are common notations in computer graphics - "UVW" Mapping. Now, we're running out of letters at the end of the alphabet, (U-Z are taken), and t is usually reserved for "time", so we now have to step back one more letter... "S" - for a mapping of

\mathbb {R} ^{3}

to

\mathbb {R} ^{1}

. I actually came up with this explanation for myself; I had a similar question about this notation during my first vector-calculus classes. This explanation seems to make the most sense to me. Nimur (talk) 18:01, 27 January 2009 (UTC)[reply]

Not really. Computer graphics mostly uses 'homogeneous' coordinates - (X,Y,Z,W) - with 4x4 matrix math that can accomodate translation, scaling, skewing and perspective operations in a single matrix.

We originally used (U,V) for texture coordinates - but when 3D textures came along maybe 10 years ago we needed a third coordinate, we'd already used 'W' - and homogeneous 3D texture coordinates proved useful - so we needed a fourth letter anyway), it was necessary to dump (U,V) - but somehow (S,T,U,V) or (U,V,S,T) didn't work out and most modern API's use (S,T,P,Q).

R is right out because we need (R,G,B) for color and (R,G,B,A) to conveniently roll in 'Alpha' or transparency. But with high-dynamic-range (HDR) rendering, we used 'S' for intensity - so we have (R,G,B,S) - which clashes with (S,T,P,Q)...

But in the end - the whole sorry mess and lack of foresight has evaporated. We have so many different things that are groups of three or four numbers that increasingly we talk about 'Position', 'Color', 'TexCoord', 'Normal', etc - and toss them around as 4-vector objects without looking too carefully at what's inside. Both PC and GPU hardware can do operations on 4-vectors in parallel - and C++ lets you 'overload' operations so you can say "Position += Velocity * Time;" - and all of the (X,Y,Z,W) stuff 'just works'. So that's the simplest answer. In shader languages, a 4-vector is a fundamental unit of calculation - and the underlying shader language lets you access it interchangeably as (X,Y,Z,W), (S,T,P,Q), (R,G,B,A) or [0],[1],[2],[3]. So it's common to see people accessing (say) the Red component of a color using 'Color.x' rather than 'Color.r'. I never use either (U,V) or (S,T,P,Q) for textures anymore - it's just TexCoord.x .y .z and .w as needed. SteveBaker (talk) 02:08, 28 January 2009 (UTC)[reply]

Anyway, in my experience, X, Y, Z are quite uncommon variable names for Cartesian coordinates. Usually it's x, y, z. The uppercase variables are more likely to be sets, or random variables, or something other than Cartesian coordinates. --Trovatore (talk) 02:11, 28 January 2009 (UTC)[reply]

Well, yes - but for programmers (who are NOT mathematicians, in general), capitalisation or not is a separate matter and often depends simply on local programming practices. Hence (to pick some silly examples to illustrate some common conventions):

#define X 1234.0f

const float x = 1234.0f ;

class X () { ... } ;

inline float x ( float *vector ) { return vector [ 0 ] ; }

In every case, we're talking about a single, simple number.

SteveBaker (talk) 19:39, 28 January 2009 (UTC)[reply]

Another guess: since r (for radius) is used as the symbol for the vector position of a point relative to the origin, s might have been chosen as the next letter to represent the subsequent displacement of that point. --Heron (talk) 10:41, 28 January 2009 (UTC)[reply]

Actually, I don't think we have to guess - the first answer from User:WrongFilter was the correct. Newton wrote his laws of motion in Latin - and 's' stands for 'spatium'. SteveBaker (talk) 19:39, 28 January 2009 (UTC)[reply]

viscosity vs. temp

Is it safe to assume that the viscosity of an aqueous solution will drop as its temperature goes up? ike9898 (talk) 20:21, 26 January 2009 (UTC)[reply]

Temperature dependence of liquid viscosity. But I'd keep an eye on Evaporation, Vapor pressure.76.97.245.5 (talk) 21:30, 26 January 2009 (UTC)[reply]

Alternating current outlet

Why do outlets have one hole larger or different than the other so you have to put the plug in a certain way? I thought that alternating current, well you know, alternates; the only difference between putting it in one way or the other is a tiny (1/60 second in america I believe) phase change.. I read Neutral_wire and it confused me. It seems to suggest that AC comes in on a live wire and out on a neutral wire, like direct current. I thought the relative safety and interesting electrical properties of AC were precisely due to it not flowing in any particular direction for more than a tiny fraction of a second.. 72.236.192.238 (talk) 20:30, 26 January 2009 (UTC)[reply]

Here, I think, is an explanation, from our article on AC power plugs and sockets:

Polarised plugs and sockets are those designed to connect only in the correct orientation, so the hot and neutral conductors in the connected equipment are connected to the hot and neutral poles of the outlet. Polarisation is maintained by the shape, size, and/or position of plug pins and socket holes to ensure that a plug fits only one way into a socket. This is so that switches, for example, interrupt the live wire of the circuit. If the neutral wire were interrupted instead, although the device would deactivate due to the opening of the electrical circuit, its internal wiring would still be energised. This can present a shock hazard if the device is opened, because the human body would create a circuit — a path to a voltage different from that of the live wire. In toasters and other appliances with exposed heat elements, reversed polarity can cause the elements to be electrically live even when they are cool to the touch, posing the risk of electrocution even if the device is not deliberately disassembled or otherwise tampered with.

Reverse polarity can also create a hazard with screw-in light bulbs, where the shell of the socket may be energized even though the lamp is switched off.

Interchange of the live and neutral wires in the behind-the-walls household wiring can defeat the safety purpose of polarised sockets and plugs; a circuit tester can detect swapped wires.

ike9898 (talk) 20:49, 26 January 2009 (UTC)[reply]

That can't possibly be right. If you interrupt the circuit then there's no current, correct? It doesn't matter where you interrupt it. And again, how is there a hot lead and a neutral lead if alternating current just goes back and forth through the whole circuit? Every lead is hot, or rather each lead alternates between being the + and the - 72.236.192.238 (talk) 21:14, 26 January 2009 (UTC)[reply]

The hot lead alternates, yes. But both + and - will flow to ground. It doesn't have to be the ground in that particular socket. It could be the ground from some other socket, or can be the ground in the actual ground. APL (talk) 21:27, 26 January 2009 (UTC)[reply]

I understand that both leads (1 and 2) flow to the ground (3) but why are 1 and 2 different sizes as if it matters which is which? ( http://img220.imageshack.us/img220/2696/782455zp3.jpg ) 72.236.192.238 (talk) 21:39, 26 January 2009 (UTC)[reply]

Because only one lead is "hot" (Alternating from + to -). The other is neutral, similar to ground. APL (talk) 22:01, 26 January 2009 (UTC)[reply]

There is one hot lead which alternates between positive and negative. The other lead remains at (or near) 0v, so the effective voltage and current change directions (signs), but the second lead is never hot. You could theoretically implement a system where both leads changed voltages, but it wouldn't provide any real advantages and it wouldn't allow simple safety measures like polarised plugs. -- 74.137.108.115 (talk) 21:53, 26 January 2009 (UTC)[reply]

How can the other lead remain at 0v? Volts are electric potential, it has to be measured between two different points. So the hot lead is +120v relative to neutral, then -120v relative to neutral. Which should be another way of saying hot is +120v relative to neutral, then neutral is +120v to hot. Which should be another way of saying the two leads are identical except for phase, so it shouldn't matter which is which. We can ignore the additional grounding lead since it isn't used unless there's a problem. I really don't know where you're coming from saying "the effective voltage and current change directions (signs), but the second lead is never hot" ... if the current is flowing into the hot lead that means it's coming out of the neutral lead, and uh isn't current coming out of a lead the definition of hot? The electrons have to come from somewhere; you're not pumping charge into and out of a giant tank, you're dealing with a giant electrical circuit starting and ending at the power plant. 72.236.192.238 (talk) 22:05, 26 January 2009 (UTC)[reply]

You just explained it well, actually. Ground really can act as a "giant tank". The neutral wire does not go back to the power plant. It is simply connected to ground. (There is no 'complete circuit' between your lamp and the power station.)

So if you imagine two hoses, one constantly vibrating between pressure and suction, and another connected to the infinite "tank" of ground-water at neutral pressure, you can see how it makes a difference which "hose" you accidentally tap into. APL (talk) 22:30, 26 January 2009 (UTC)[reply]

Hm ok it's not a circuit But if ground can act like a giant tank then -120v on the hot (relative to 0v on the neutral) really is equivalent to 120v on the neutral (relative to 0v on the hot). That's the only thing I was worried about being wrong about, but apparently I'm not. Think about it... if the live wire is alternating between 0 and 120 relative to ground, and the neutral is equivalently alternating between 120 and 0 relative to ground, then they're the same.. :( 72.236.192.238 (talk) 22:49, 26 January 2009 (UTC)[reply]

Oh oh oh I see. As explained above it's useful for breaking the connection before the appliance instead of after. I was assuming that it's a circuit and it wouldn't matter which side, but I see now that I learn that one end is just ground, not a circuit back to the power station: your body could be that one end! Whew that was a doozy. I have no non wikipedian training in electricity and it shows im afraid 72.236.192.238 (talk) 22:55, 26 January 2009 (UTC)[reply]

There is a hot lead, a neutral lead and often a ground. The voltage is from hot to neutral or ground. Where there is a power switch, it must interrupt the hot line; interrupting the neutral would turn the device off, but would leave live power. Devices such as a GFCI work by detecting residual current; reversing the leads render them useless. --—— Gadget850 (Ed) ^talk - 20:48, 26 January 2009 (UTC)[reply]

Of course, I usually just file those polarized plugs down so that they'll fit into older sockets. APL (talk) 22:02, 26 January 2009 (UTC)[reply]

Let me try to clear this up a bit. If you live in the U.S., you have 2 lines coming into your house: One is at +120 V (relative to ground) and one is at -120 V (relative to ground). Now, in your house, there are two types of plugs. You major appliances, which draw lots of current, like the dryer, are likely hooked up to the +120, -120, and ground. This supplies a net voltage of 240 V across the appliance. These are those funny round fat plugs. The normal "frowny-face" outlet is hooked up to one of the two "hot" wires (either +120 or -120, it doesn't matter which) a "neutral" wire (which is hooked up to ground at the breaker box) and a "ground" wire, which is generally grounded firectly at the junction box. So, at this outlet, the net voltage is 120 V, because the appliance you attach is hooked into the hot wire and the neutral wire, and the two are 120 V apart relative to each other. The deal with alternating (rather than direct) current, is that the "direction" or "sign" of the current flow doesn't matter. The sign only effects the wave function of the current (i.e. a +hot wire has a mirror image wavefunction profile to a -hot wire) and as such, all that usually matters is that the hot wire is hooked up to where the appliance expects it to be. It doesn't matter whether its the +hot or -hot. In fact, for some applications (like a regular incandescent bulb, or a toaster) it doesn't even matter which wire gets the hot, and which gets the neutral. --Jayron32.talk.contribs 22:10, 26 January 2009 (UTC)[reply]

There is no + or - in an AC line. If you measured across +120 and -120 DC, you would get 0. Residential U.S. power is two 120 volt hot leads and a neutral. In a standard breaker box, odd numbered breakers tap onto one hot and even the other hot, balancing the load. 220v breakers are double and tap into both hots. --—— Gadget850 (Ed) ^talk - 23:29, 26 January 2009 (UTC)[reply]

I'm sure he meant instantaneously one is + while the other is - (on a sine curve), even though overall both average 0 .froth. (talk) 00:29, 27 January 2009 (UTC)[reply]

As I actually explained in my own words, the +120 and -120 refer to the sign of the wavefunction. The neutral, of course, is a flat line at 0. The two lines have an alternating wave function which are mirror images of each other, so arbitrarily one can be called + and one -. Tapping into these two lines will give a net difference of 240 V relative to each other, which is used for high demand appliances like you drier. --Jayron32.talk.contribs 16:38, 27 January 2009 (UTC)[reply]

Nit: US breakers aren't "odd-breakers one hot, evens the other". It would sure make running the two internal bus-bars easier (one feed to the left column, other to the right), but makes it much harder to configure a "two-hot" (240V) breaker. See Breaker box#Breaker arrangement. DMacks (talk) 17:25, 27 January 2009 (UTC)[reply]

Ah, that helps a lot. But doesn't that prove my point? Like you said it doesn't matter for frowny face sockets which house line you connect the hot lead to. Equivalently it doesn't matter which direction you plug your power cord into, for any application, not just lamps and toasters. By connecting to only one house line (and the neutral goes to 0v, ground) you change nothing except the net voltage. Instead of 240v you have 120v. But it can't matter which side you connect the live wire to, because electrically the live and neutral are only distiguishable by phase, exactly the case with the two lines coming into the house! One end of the cycle the live is +120 (relative to the neutral being 0v) the other end of the cycle neutral is +120 (relative to the live being 0v). 72.236.192.238 (talk) 22:42, 26 January 2009 (UTC)[reply]

The holes are different sizes so that if you plug in a device the off switch, fuse and breakers are interrupting the circuit on the live side. If you have a short in the device and the off switch only disconnected the neutral line you could still get power flowing from your hot lead to whatever ground (e.g. your body) was available. If the disconnecting element is where the hot line connects to the device and will effectively interrupt the circuit. Some devices are designed to disconnect both poles. For those it would not matter which way you plug in the plug. So don't reshape your plugs or widen your outlet holes.76.97.245.5 (talk) 22:16, 26 January 2009 (UTC)[reply]

Let's say you have a toaster. The lever on the toaster turns on the hot lead. When it is off, you can jam a fork in it all you want to get that last bit of bagel off. If hot and neutral are reversed, then the lever only turns off neutral. If you stick that fork in while you are grounded (touching the fridge, oven, sink, etc.) then you are going to get toasted by that hot lead. --—— Gadget850 (Ed) ^talk - 23:29, 26 January 2009 (UTC)[reply]

As an added precaution to the polarized plugs, you should install the sockets with the grounding plug *up*, not down (i.e., not a frowny face). That way when a picture frame or some other metal object slides down the wall it won't have any chance of being energized. --Sean 16:51, 27 January 2009 (UTC)[reply]

Compact fluorescent light bulb hooked up backwards

If a CFL is hooked up with the hot and neutral wires reversed, would it work correctly? I have a lightbulb socket that causes otherwise normal CFLs to light up dimly and flash. I'm wondering if reversed wiring is a possible explanation. ike9898 (talk) 20:45, 26 January 2009 (UTC)[reply]

Do you have it on a dimmer switch? Sometimes if you have an ordinary fluorecent tube fixture in the same circuit this can also happen.76.97.245.5 (talk) 21:06, 26 January 2009 (UTC)[reply]

No but it is on a circuit with a GFCI breaker (a breaker, not an outlet). Does that matter? ike9898 (talk) 17:26, 27 January 2009 (UTC)[reply]

Reversing hot and neutral wires cannot possibly affect operation of any device. It can only increase safety hazard for some (improperly designed) devices. -Yyy (talk) 07:51, 27 January 2009 (UTC)[reply]

Certainly reversing the hot and neutral can affect the operation of a device. My home had some light fixtures with an obsolete scheme of three-way switching which could energize the light socket with the tip of the bulb connected to neutral and the shell of the socket at 120 volts from neutral. The hot part was separated from a grounded metal outer surround of the socket only by paper, as in the normal construction of such a socket. One time when it was switched on, the 120 volt potential difference arced across the old paper insulation and before the breaker operated a glob of molten metal fell on the carpet. Had the phase and neutral been connected to the socket properly, such a large voltage difference from shell to surround would have not occurred. I rewired the circuit for modern 3-way switching, which required an additional conductor, and replaced the light fixture. Edison (talk) 17:32, 27 January 2009 (UTC)[reply]

Why do octane raings vary?

Why do unbranched hydrocarbons have lower octane ratings that branced or cyclic ones. Andy (talk) 22:01, 26 January 2009 (UTC)[reply]

They are easier to burn, probably due to more surface area exposed to oxygen. Graeme Bartlett (talk) 23:11, 26 January 2009 (UTC)[reply]

Cheers Graeme. Andy (talk) 07:11, 27 January 2009 (UTC)[reply]

Skin temperature and freezing

Hot water freezes faster than cold water.[30] Does the same hold true for flesh? In other words, if you were to sit in a sauna for a while and then go out naked into crazy cold temperatures, roll in the snow, etc. would you develop frost bite FASTER than you would with a normal skin temperature? --S.dedalus (talk) 22:09, 26 January 2009 (UTC)[reply]

I read that article and it looks like most of the proposed explanations are specific to it being a jar of water. Anyway, I'm certain that the determining factor in this case is how the wind flows past your body, which parts of yourself you rub deepest and more often into the snow, which parts of the snow are colder, which parts of your body were warmer than others to start with... the effect you referenced is only reliably measurable in consistent laboratory conditions; there's no way you could possibly roll around in the snow consistently. .froth. (talk) 22:25, 26 January 2009 (UTC)[reply]

The effect that makes hot water freeze faster almost certainly doesn't apply to flesh. However, other effects could cause you to get frostbite quicker after being very hot - your body will be adjusted to stay cool, so when you suddenly go outside it will take just time for your body to adjust to staying warm and you will lose a lot of body heat very quickly (I'm not sure how much "a lot" is - it depends on how quickly the body can adjust). --Tango (talk) 23:18, 26 January 2009 (UTC)[reply]

Your body works hard to maintain its temperature - going into a sauna makes it work harder to do that - but if you take your body temp with a proper core-temp thermometer - it's not going to vary by so much as one degree between the sauna and the snow...at least not until you're in a lot of distress. Also, the thing about hot water freezing faster than cold isn't REALLY true...at least not in a proper controlled experiment where the ONLY difference between the two pots of water is their initial temperature. If you think about it, it couldn't be any other way. Hot water has to first turn into cold water before it freezes! There are some rather specific circumstances where the nature of the stuff dissolved in water boils off and the nature of the cooling happening from the outside in when something is cooled rapidly rather than slowly CAN make it happen - but none of those special effects are true of your body. So not directly. However, one of the CRUCIAL things they tell you about being out and about in very cold conditions is not to work up a sweat - because as soon as you stop exercising, the sweat freezes and puts you in a lot of danger. So while a hot/dry body should do no worse than a cold/dry body, a hot/sweaty body will indeed be WAY more susceptible to the cold than a cold/dry one. SteveBaker (talk) 00:01, 27 January 2009 (UTC)[reply]

But the initial temperature apparently changes something about the chemical properties of the water to make it freeze faster. Or as the article said, convection currents (as parts of the water cool, the warmer water rises.. aka closer to the surface, so it can be more efficiently cooled) could play part .froth. (talk) 00:18, 27 January 2009 (UTC)[reply]

Yes indeed - all kinds of things that are not true 'in general' (and certainly aren't true for the human body). SteveBaker (talk) 00:48, 27 January 2009 (UTC)[reply]

The Mpemba effect really is true, you don't need really obscure circumstances, just two beakers of water and a freezer. --Tango (talk) 00:08, 27 January 2009 (UTC)[reply]

Actually - if you read the acticle - you'll find that 'special' circumstances are indeed needed. It just happens to be that the 'special' conditions are two cups stuck in a freezer! "The Mpemba effect is the observation that, in certain specific circumstances, warmer water freezes faster than colder water" - it's definitely not true in general. SteveBaker (talk) 00:46, 27 January 2009 (UTC)[reply]

Sure, but they aren't obscure circumstances, which is what I said. In fact, they are exactly the circumstances you would first use if you wanted to test for such an effect existing. --Tango (talk) 00:50, 27 January 2009 (UTC)[reply]

Yeah - I absolutely agree that the conditions aren't "obscure" (in the sense that you don't need a titanium klein-bottle in a helium/neon atmosphere with exactly 3.4 parts per million of iodine dissolved in the water) - but they are SPECIFIC - in that if you vary the conditions of the test to even a fairly small degree - the effect completely goes away. It's one of those odd coincidences that the simplest possible test of the effect works just fine - but any significant variation on the experiment fails to demonstrate it...and that's what matters here. An exposed human body out in the snow is not at all like a cup of tap water placed into a freezer (it's salty - it has an irregular shape - the liquid inside can't use convection to move around - it has an internal homeostatic heat source...you name it). Hence it's exceedingly unlikely to meet the SPECIFIC (but not OBSCURE) conditions of the Mpemba experiment and we can be reasonably confident (certainly to the degree required in a WP:RD response) in saying that the Mpemba effect does not apply in the situation our OP describes. SteveBaker (talk) 14:46, 27 January 2009 (UTC)[reply]

So can we say with confidence that, when thoroughly dried with a towel, a person immerging from a sauna will take slightly longer too developed frostbitten than a person with a normal skin temperature? --S.dedalus (talk) 19:31, 27 January 2009 (UTC)[reply]

Perhaps very, VERY slightly...but my best guess would be "No". There is another thought which does occur to me though. When you're hot, your body expands the blood vessels close to the skin to allow the blood to cool - and contracts them to keep the blood warm at your core when it's cold. Coming out of the sauna MIGHT have the effect of giving you an initial period of time while the body adapts when the blood would cool faster than for the person who is already kinda chilly. This is the reason given for NOT warming people with hypothermia up too quickly - and also for not drinking alcohol to warm yourself up in a cold situation. So the sauna would (I think) tend to cause hypothermia (because the skin is getting all of the blood supply and cooling it down dangerously quickly) and perhaps HELP the frostbite (because the warm blood is still getting to the extremities rather than being pulled back into your core. But I think the body would adapt before either of those things would be too terrible - so the judges are still out on this one. 21:59, 27 January 2009 (UTC)

January 27

Errors in casting plastics

Hi - I need a piece of terminology - what's it called when a mold produces a bad casting and you get something that's not the shape you intended?

Thanks,

Adambrowne666 (talk) 00:55, 27 January 2009 (UTC)[reply]

A dud ? I'm not sure if a malformed plastic casting has a specific name. StuRat (talk) 03:28, 27 January 2009 (UTC)[reply]

One type of imperfection in casting is flash, though this may be removed to obtain the shape you intended. -- KathrynLybarger (talk) 03:39, 27 January 2009 (UTC)[reply]

Thanks, yeah, probably there's no global term - I'm gonna go for a 'miscast', I think. Adambrowne666 (talk) 04:14, 27 January 2009 (UTC)[reply]

Id call it a blob--GreenSpigot (talk) 13:52, 28 January 2009 (UTC)[reply]

I read through two rather large online glossaries to do with metal casting, and although there were lots and lots of words for the particular defects, I couldn't find a general one. There were many places where they might have used such a word if it existed, but they always just called it a defective casting. I expected to find some nice, slangy wordling, something like "glippet" or "pfnisch", but no dice. (I should imagine that the terminology of metal casting would have transferred to plastic casting more or less entire.) --Milkbreath (talk) 14:11, 28 January 2009 (UTC)[reply]

Spontaneous absorption of water waves

What is the formula for the rate at which deep water surface waves (both gravity and capillary) are absorbed by the water and the air above it, if they do not run into anything?

129.2.43.42 (talk) 01:22, 27 January 2009 (UTC)Nightvid (unregistered)[reply]

Well, I was really hoping you'd get a good answer - because it's great question. But I've looked all over for an equation and I don't see one. From reading around the subject, some things become evident:

Water waves at different frequencies and directions can be considered independantly.
Waves move at different speeds and are attenuated at different rates depending on their frequency.
Higher frequency waves are attenuated more rapidly than low frequencies.
Wind has a huge effect on energy transfer into and out of waves.
Tides make a big difference too...even in deep water.
Breaking waves behave very differently from 'smooth' waves.
When the water is more than 1.5 wavelengths deep - it may be considered to be a 'deep water' wave.

But I couldn't find a single, simple equation anywhere...which is surprising.

SteveBaker (talk) 01:30, 28 January 2009 (UTC)[reply]

soap

Good day!

I would like to ask what is a germicidal soap and what are its effects?! or shall we say what are its applications-for what and for whom...

Your answer would be greatly appreciated.

Thank you and God bless! —Preceding unsigned comment added by 125.5.144.109 (talk) 02:50, 27 January 2009 (UTC)[reply]

An antibacterial soap is one that tends to kill bacteria. This is usually unnecessary, as washing bacteria off your hands is sufficient. There are some negatives, as well:

1) It can kill off helpful bacteria that control other health threats, like fungus.

2) It can kill off helpful bacteria in septic tanks, which decompose waste.

3) It can cause bacteria to develop a resistance, which makes it more difficult to kill them when they really do pose a threat. StuRat (talk) 03:23, 27 January 2009 (UTC)[reply]

That's why there's an increasing move to switch to bacteriostatic rather than antibacterial soap. 76.97.245.5 (talk) 03:46, 27 January 2009 (UTC)[reply]

Soap was invented around 3000 BC, During the 1970's someone thought "why don't we make soap that's BAD for bacteria." Apparently up to that time soap was enjoyed by bacteria as a nutritious food stuff. Bacteria fought back, hiring lobbyists who argue that use of antibacterial soaps should be restricted. —Preceding unsigned comment added by 76.125.8.141 (talk) 13:42, 27 January 2009 (UTC)[reply]

antibiotic resistance

Something has long bothered me about the antibiotic resistance discussions as applied to hand soap. The active ingredients usually used in antibacterial soap are triclosan or ethanol. However, it is physically impossible to use either of these compounds as internal antibiotics. The ratio required for ethanol (>60% by volume) would be fatal in the bloodstream, and triclosan is too insoluble in water to reach bactericidal concentrations in blood (normally it is suspended in an nonpolar solvent). Further, my understanding is that their chemistry and method of action is simply not related to any of the widely used internal antibiotics, so the risk of cross-resistance ought to be very low.

Hence my question is: Should people really worry about bacteria developing resistance to triclosan or ethanol? Would it matter? It would appear that even if bacteria developed resistance to hand sanitizer it would have little to no relevance in deciding how to fight an infection of that bacteria. Sure, it might be a little bad if hand soaps and the like lost their edge, but in the grand scheme of things being resistant to hand soap would appear to be independent of and far less troubling than resistance to things like methicillin. Dragons flight (talk) 05:36, 27 January 2009 (UTC)[reply]

No, the issue of resistance doesn't pertain, as the agents in hand soaps are antiseptics rather than antibiotics. - Nunh-huh 06:05, 27 January 2009 (UTC)[reply]

I think it's just a case of mislabeling. What they probably mean is that any surviving pathogens are likely to be very hardy and might be harder to kill with conventional methods. I agree that there is a lot of confusing (confused?) info out there. I read an article (reputable science site) where the interviewed researcher within 4 sentences first complained that increasing use of antibacterial cleaning agents in households would influence bacterial susceptibility to drugs, then he stated that although that had been shown in a petri dish an experiment conducted on an actual kitchen countertop failed to yield the same result. He followed that by saying if it were up to him he would only advocate use in hospitals because in a household you wouldn't need it anyway because the bacterial load was rather low whereas in hospitals it was high. Somewhere lower down was a comment that hospitals are breeding grounds for drug resistant strains. (So he advocates use of chemicals he suspects of increasing drug resistance in a place that already has a lot of that, instead of where it could not be shown to develop?) I read it several times, and then actually went and looked the guy up. He really was a researcher in a university lab. 76.97.245.5 (talk) 10:01, 27 January 2009 (UTC)[reply]

I have to disagree with both of the two previous posters.

@76.97.245.5: Sure - that was a bad report - but it doesn't mean that what the guy is saying isn't true - and it CERTAINLY doesn't mean that the reverse of what he says IS true!

@Nunh-huh: Your distinction between antiseptics and antibiotics is irrelevent.

But in general:

Whenever we provide some kind of stress factor in the life of a creature (be it a bacterium or an aardvarq), we're going to be affecting it's evolutionary development in such a way that it'll tend to be better at surviving in that stressed environment in the future. That's absolutely unavoidable - and it doesn't matter whether it's an "antiseptic" or an "antibiotic" - the result is the same. (From the lead paragraph of our Antiseptic article:

"Antiseptics are antimicrobial substances that are applied to living tissue/skin to reduce the possibility of infection, sepsis, or putrefaction. They should generally be distinguished from antibiotics that destroy bacteria within the body, and from disinfectants, which destroy microorganisms found on non-living objects. Some antiseptics are true germicides, capable of destroying microbes (bacteriocidal), whilst others are bacteriostatic and only prevent or inhibit their growth. Antibacterials are antiseptics that only act against bacteria. Microbicides which kill virus particles are called viricides."

But it really doesn't matter. Antiseptics, antibiotics, disinfectants, germicides, bacteriocides, bacteriostatics, antibacterials, microbicides AND viricides - all apply stress to their intended targets and if they are anything less than 100% effective at preventing their chosen victims from ultimately reproducing - they WILL cause evolutionary pressure. (It's tough to be 100% effective because at the boundaries of the area the substance was applied over, there is guaranteed to be some place where it's present in non-lethal doses - and right there, a creature can survive and evolve tolerance)

Once you have evolutionary pressure - you'll tend to get resistant strains developing.

Hence, the rule is that you shouldn't use ANY of those things unless you actually need to. We got along just fine without antibacterial/whatever soaps, baby-wipes, TOYS(!), etc - and introducing them is a bad idea regardless of whether you happen to be able to induce evolutionary effects in the lab. Evolution is a valid scientific theory and you don't need to keep doing experiments to prove it. Just as we know that brand X bowling balls will fall if you let go of them without having to do the experiment - so we know that creatures will tend to evolve without doing the experiment. If you can't reproduce it in the kitchen but you can make it happen in the petri dish then you certainly need to ask why that is and set up experiments to find out why - but it shouldn't lead you to conclude that evolution doesn't work in the kitchen because extraordinary claims require extraordinary evidence. We should behave as if the hypothesis that evolution doesn't work on kitchen countertops is false until such time as someone proves it and manages to explain why.

So, with what we currently know (which is all we ever have to go on) - we shouldn't use these products in the kitchen because the consequences of failing to do so are not severe. But we may be forced to use them in hospitals where the consequences of infection are vastly more serious because of all of the sick people spreading nasty bacteria everywhere - and all of the open wounds and so forth. Resolving the issue of bacterial and viral resistance to antimicrobials in hospitals is a serious one - but it's not relevent to the question of whether we should make matters worse by using them when we don't need to in our own homes.

SteveBaker (talk) 14:24, 27 January 2009 (UTC)[reply]

Steve, There's some kind of flaw in this argument, in its most general form, isn't there? I see some sort of assumption that organisms have an unlimited capacity to cope with any number of evolutionary pressures. In practice if you put a pressure on a zillion parameter system sure it will adapt to that pressure but the adapted point will not be as optimal at some other things as the unpressured system. So your bacteria may adapt to survive repeated exposure to 55% alcohol when it couldn't before but it will be worse at something else. Which depending on your reliance on the hard soap may or may not be a worse situation than before. Sure if you are talking about an antibiotic you need to cure someone you don't want to stress it that way but if you are talking about something which doesn'r really matter I find it hard to buy the argument.--BozMo talk 15:03, 27 January 2009 (UTC)[reply]

Sure - the bacterium that's resistant to dilute alcohol will be worse at something else - but in evolutionary terms, it only has to be better off than it's competition. So every time you use dilute alcohol, you'll wipe out more of the 'capable' bacteria and give the resistant (but otherwise worse) ones room to grow and thrive. The problem is that the 'worsening' may be (say) the loss of the ability to metabolize pink food coloring or something. That loss isn't measurably to our gain - and we can't control or (easily) predict what that 'worsening' might be. Worse still, when you set loose a new set of genes, you don't know WHAT the effect will be. It could just as easily result in a change of the 'coating' of the bacteria and thereby cause all of us humans to lose our antibody-resistance to the darned thing. SteveBaker (talk) 16:36, 27 January 2009 (UTC)[reply]

Agree but AFAICT in general "big" stresses (e.g. surviving in salt water or Dettol) seem to take a lot out of bacteria: they don't seem to ever manage one of these and still be able to compete with other bacteria well when the stress is absent. --BozMo talk 21:05, 27 January 2009 (UTC)[reply]

Lots and lots of things can place an evolutionary pressure on bacteria though, and almost no one worries about their impact. For example, ordinary (non-bactericidal) bar soap, dish soap, and laundry detergent will all remove bacteria. Presumably this creates an evolutionary pressure for bacteria that cling more firmly to their environment to avoid being washed away. However, you'll never hear people advocate that we stop using soaps entirely. Similarly, the wide spread use of food preservatives presumably encourages "preservative resistant" bacteria, but I've never seen people get crazy about preservative resistance the way some people do about hand soap. It just strikes me that the way some people focus on antibacterial hand soap is way out of proportion to the danger. Dragons flight (talk) 15:41, 27 January 2009 (UTC)[reply]

That's true - but the things you've described are truly necessary to us. Antimicrobial washing up liquid is of negligable benefit - it's purely an advertising bullshit thing - and we don't need to use it. Food preservatives, however are necessary to our way of life. SteveBaker (talk) 16:36, 27 January 2009 (UTC)[reply]

For an example of where antibacterial soaps should be used, hand-washing in areas prone to MRSA comes to mind: MRSA#Hand_washing. StuRat (talk) 15:14, 27 January 2009 (UTC)[reply]

Despite SteveBaker's assertions and theoretical dissertation, the facts are: there are no significant clinical effects that can be attributed to "antiseptic resistance", and there are significant clinical consequences of "antibiotic resistance". - Nunh-huh 07:26, 28 January 2009 (UTC)[reply]

question about HIV/AIDS

how does science, technology and communications address issues of HIV/AIDS and gender mainstreaming —Preceding unsigned comment added by 196.33.11.13 (talk) 12:21, 27 January 2009 (UTC)[reply]

This sounds like a homework question to me. On the off chance it isn't, perhaps you would care to provide a little more information about what, specifically, you're interested in? -- Captain Disdain (talk) 12:47, 27 January 2009 (UTC)[reply]

Writing a college essay involves first determining what the question means. College professors are often not models of clarity. I think they sometimes get fed up and try to trip the class up. Sometimes they actually think what they wrote makes sense, not realizing that they're begging the question. Sometimes they're drunk when they write it, I suppose, which would explain a lot. The second step is to guess what the professor wants to see. This is important only to the extent that your grade is important. You can learn the material thoroughly and become the most proficient person in the world in your pursuit and still get only a "C" if you don't follow this second step. Often, too, your paper will be graded by a graduate student with a checklist looking for key concepts and facts, and you should try to guess what these will be. In this case, we start at a disadvantage because the grammar of the question is bad ("does" should be "do"), so we can look forward to getting marked off for correct English, always frustrating. Another problem is the jargon. What is an "issue"? Professors love that word. I've never been able to tell whether they use it because they think it has a meaning, because they want to leave things open-ended, or because they're just being bloody-minded. And good luck figuring out what "gender mainstreaming" is. That really pisses me off. I'll bet your professor just got done having a big argument with his mistress over the term, and he wants to see what you'll all say about it so he'll have more arrows in his quiver the next time it comes up in a symposium. Anyway, good luck, and don't sweat it. Think it's easy, and it will become easy. --Milkbreath (talk) 12:57, 27 January 2009 (UTC)[reply]

...OR...

You could just say:

Please do your own homework.

Welcome to the Wikipedia Reference Desk. Your question appears to be a homework question. I apologize if this is a misinterpretation, but it is our aim here not to do people's homework for them, but to merely aid them in doing it themselves. Letting someone else do your homework does not help you learn nearly as much as doing it yourself. Please attempt to solve the problem or answer the question yourself first. If you need help with a specific part of your homework, feel free to tell us where you are stuck and ask for help. If you need help grasping the concept of a problem, by all means let us know.

SteveBaker (talk) 14:03, 27 January 2009 (UTC)[reply]

There's nothing wrong with telling people generally how to go about thinking of how to answer questions when it is clear that's probably what is at stake here. Saying "do your own homework" is concise but it isn't always the most useful answer (and I mean "useful" here in the true sense, not in the sense that giving them the answer would be "useful" in the long run). Teach a man to fish, and all that. --140.247.241.150 (talk) 17:51, 27 January 2009 (UTC)[reply]

I too thought "gender mainstreaming" was just meaningless jargon, but truly we have an article on everything. Gandalf61 (talk) 17:01, 27 January 2009 (UTC)[reply]

Silly me. Now that I know it's about differential implications.... --Milkbreath (talk) 17:28, 27 January 2009 (UTC)[reply]

If it was about differential integrations it would be much easier, by the Fundamental Theorem of Calculus. You could probably submit the question, (+C), and not get a C+ ... Nimur (talk) 18:32, 27 January 2009 (UTC)[reply]

Vines climbing around a tree

Why do vines climb upwards around a tree in a clockwise direction(if looked from above)? —Preceding unsigned comment added by 202.70.74.137 (talk) 15:15, 27 January 2009 (UTC)[reply]

You may have selection bias. I spent three years trying to tame the wisteria on my trees. It grows wherever it likes, in whatever direction it likes. -- kainaw ™ 15:17, 27 January 2009 (UTC)[reply]

Apparently this is an active area of research; try googling "vines clockwise". It seems most vines twist counterclockwise, but that we haven't figured out why yet. Perhaps something to do with the chirality of biological molecules. --Allen (talk) 15:37, 27 January 2009 (UTC)[reply]

Why are 90% of people right handed? Why do most sea shells twist in one direction? Why do (nearly) all of us have our hearts, livers and pancreases on one particular side? Why do ALL animals and plants have the same chirality of biological molecules? If there is not advantage to one asymmetry over the other - why isn't there a 50/50 mix? The reason is that we're all descended from a single individual. So in this case, once the gene for a particular direction of twist got to become the ancestor of all modern vines - only an evolutionary change in the twist-direction gene could cause opposite-direction-twist to happen. Since there is likely to be ZERO evolutionary benefit to twisting in the opposite direction to all of the other plants - that gene would not reproduce preferentially to the 'normal' direction and could easily simply fade from the gene pool because it's so rare. Genes only spread when there is some benefit to the creature that possesses that gene. Left-handedness in humans is a bit different - it is thought to hang around because we are tribal creatures and there is a benefit to every community of humans to have a few left-handed people because our brains are wired up differently. Hence communities in which left-handedness dies out are at a disadvantage compared to those where it remains - and hence there are always a few lefties around (including an unreasonably large percentage of US presidents, architects and 3D computer graphics people!). SteveBaker (talk) 16:23, 27 January 2009 (UTC)[reply]

Before we compare to handedness, we could at least provide a non-google reference that it's intrinsic to the plant and not the environment. There seem to be a lot of news stories re-hashing this same research. [31] [32] APL (talk) 17:12, 27 January 2009 (UTC)[reply]

I agree with APL. Steve's explanation sounds plausible, with the quibble that vines are not a monophyletic group, so any shared twist-direction gene would probably be doing more than determining twist-direction. But most researchers seem to agree that vine twining is an unsolved question. Same with handedness... there seem to be multiple active hypotheses for the proportion of left-handedness. And Steve's explanation requires group selection, which is controversial. --Allen (talk) 20:24, 27 January 2009 (UTC)[reply]

I wonder if the OP is from a hemisphere opposite Kainaw's, though; there's part of me that remembers an experiment with toilets flushing a different direction in the northern hemisphere from the southern, and wondering if vine growth has to do with the rotation of the earth. —Preceding unsigned comment added by DTF955 (talk • contribs) 17:59, 27 January 2009 (UTC)[reply]

Er - you do know that the toilet-flushing thing is a myth don't you? The coriolis forces are VASTLY too tiny to produce either that - or the vine rotations...so no. SteveBaker (talk) 18:31, 27 January 2009 (UTC)[reply]

Ohh, now I donno about that…surely if the Coriolis forces are strong enough to create left- rather than right-hand traffic in Australia and New Zealand, they're strong enough to make water spiral the wrong way down the sink. ← The preceeding text is a joke. It is not intended to inform or educate. —Scheinwerfermann ^T·_C21:01, 27 January 2009 (UTC)[reply]

Vine-twisting direction seems to have been noticed only quite recently. I wonder why botanists did not notice it generations ago. What else is being overlooked in botany? And what is being overlooked in other branches of science? Medical school students are told to pay attention to details about a patient and his ailment; but that does not seem to be stressed for college students in other areas of learning. In everyday life we ignore many, many, small details - we would go nuts if we paid great attention to everything. But in science, and in professions, attention to details within the area of interest is needed. (The transistor was discovered by investigating a small detail in the action of diodes.) On the other hand, a scientist should not become so immersed in details that he overlooks the big picture. In this regard, details may be sought in order to support a pre-existing conjecture. For instance, Darwin studied details in biology with a predetermined objective. He wasn't just accumulating facts (though that can be useful to aid further work in science by others). Darwin's predetermined objective was to place evolution on a firm basis. Thus, there are two goals in science. One is to accumulate facts. The other is to put 2 and 2 together to make 5 (idea synthesis). Sometimes the "accumulating" approach in science leads to the other approach – the very act of accumulating related facts can bring to light an overall concept that was not seen at all before. Even in everyday life a serendipitous juxtaposition of seemingly unrelated facts will occasionally reveal an overall concept not seen before. – GlowWorm. —Preceding unsigned comment added by 98.17.34.148 (talk) 18:22, 27 January 2009 (UTC)[reply]

It's not a recent discovery, Charles Darwin wrote about it. I always thought it was because the plant was phototropic following the sun as it went around the sky. Graeme Bartlett (talk) 20:12, 27 January 2009 (UTC)[reply]

Surely that would only work if they were growing an entire loop around the tree each day? I don't think they grow that fast. --Tango (talk) 20:19, 27 January 2009 (UTC)[reply]

No, it could just be that they're influenced at some critical point. But the articles I link indicate that the influence of the sun's motion has been ruled out as the cause. APL (talk) 20:25, 27 January 2009 (UTC)[reply]

Yeah - I mean it would work during the summer at the North or South polar regions where the sun doesn't set for months at a time - and it couldn't possibly work near the equator where the sun doesn't "circle" a tree but ascends pretty much vertically into the sky - across the zenith and vertically back down again on the opposite side. The acid test would be whether the same plant would coil in the opposite direction when planted in the southern hemisphere...that's worth thinking about...just so long as nobody else says the word "coriolis"! SteveBaker (talk) 21:51, 27 January 2009 (UTC)[reply]

Actually -- and it's surprising to me, too -- the [CENSORED] effect was one of the hypotheses of these Australian researchers. --Allen (talk) 22:08, 27 January 2009 (UTC)[reply]

Puh!...botanists...what'ya gonna do? They aren't even proper biologists. May I refer you to this handy chart and invite you to place botanists on that scale! That effect relies on the magnitude of two properties - speed of motion and North/South distance travelled - two properties that a vine has in astoundingly negligable quantities! Bozo's. :-) SteveBaker (talk) 01:03, 28 January 2009 (UTC)[reply]

Botany is scorned because it has not progressed much beyond description and classification. The reason it has not progressed much is because it is very difficult. Physics is child's play compared to botany. – GlowWorm —Preceding unsigned comment added by 98.17.34.148 (talk) 16:42, 28 January 2009 (UTC)[reply]

It's not a matter of difficulty. We were talking a few days ago about economists and I was saying that what they do isn't really science. That doesn't make economics 'easy' - it just means that they aren't doing science while they are doing it. Botany is indeed mostly a matter of 'stamp collecting' with relatively little actual science going on. That doesn't make it less worth-while or less difficult - it just means that it's mostly not 'science'. Hence, it comes as no surprise to me that some botanist would make the incredibly stupid suggestion that coriolis forces caused this when the briefest glance at what that force actually IS would make it blatently obvious that it cannot be the culprit. A proper scientist might do an experiment - but when a back-of-envelope calculation shows the effect has to be utterly negligable, one would not consider doing THAT experiment until all other reasonable lines of inquiry had been excluded. If it we're me, I'd want to try to make one grow the other way by having artificial lighting that moved in the opposite direction to the real sun in the vine's habitat. I'd look to see if there were EVER a vine that grew the opposite way and do a DNA study to try to isolate the 'clockwise' gene. I'd try a whole bunch of much more likely things before I'd EVERY go on record as saying that coriolis was even the remotest possibility. So this particular botanist is not behaving like a proper scientist and is showing a lamentable lack of scientific knowledge. SteveBaker (talk) 19:27, 28 January 2009 (UTC)[reply]

Botanists are just a cross-section of humanity, and as with reference desk authorities you get the whole spectrum from awesomely wise to thick as two bricks. Left- and right-handedness in creepers has been known since our ancestors started oozing around on dry land. Even Flanders and Swann wrote a ditty celebrating the phenomenon
Said the right-handed Honeysuckle to the left handed Bindweed
oh let us get married if our parents don't mind we'd
be loving and inseparable, inextricably entwined we'd
live happily ever after' said the Honeysuckle to the Bindweed..
Rotational (talk) 09:48, 29 January 2009 (UTC)[reply]

Help on Forces

Does Contact force exist even when there is no gravity. Bold text CAN YOU DIFFERENTIATE NORMAL CONTACT FORCE FROM CONTACT FORCE??? And further more...what is the newtons third law pair for contact force acting on the feet of a gecko that clings to a wall which is perpendicular to the ground??? —Preceding unsigned comment added by 123.49.43.236 (talk) 17:52, 27 January 2009 (UTC)[reply]

Certainly. Gravity is just a force - you could substitute a different force. Magnetism, say. Also, that nice Mr Einstein told us that acceleration and gravity are indistinguishable for all laws of physics - so in deep space an object accelerating at 1g would produce exactly the same effect. The teeny-tiny hairs in the gecko's foot are sticking to the glass through Van-de-Waal's forces at the atomic level. SteveBaker (talk) 18:30, 27 January 2009 (UTC)[reply]

See Sticky Secrets of the Gecko and van der Waals force ciao Rotational (talk) 10:04, 29 January 2009 (UTC)[reply]

It seems really unlikely that in any circumstance, the Contact Force would be in any other direction than normal. Does anyone know of any counter-examples? If there are any, they are probably not in macroscopic, "standard" situations. Nimur (talk) 18:39, 27 January 2009 (UTC)[reply]

I think there is some confusion here between contact force and normal force. Our contact force article explains the difference as follows: "A contact force has two components. The part of the force that lies within the plane of contact is friction ... The part of the force that is perpendicular to the plane of contact is called the normal force." For example, an object in equilibrium on a rough sloping surface experiences a contact force that is not normal to the surface (the contact force must be vertical so that it is equal and opposite to the object's weight), but the normal force is always, by definition, normal to the surface. Gandalf61 (talk) 10:36, 28 January 2009 (UTC)[reply]

I'd better review my basic physics terminology... Nimur (talk) 15:15, 28 January 2009 (UTC)[reply]

Most stuff eaten at once and eating things whole

Since I'll be gone on April Fools Day, I ask this question now that was on my mind.

The song about the old lady who swallowed a fly has her eating huge amounts of things at once, apparently whole (though it's not said for sure; she's likely nuts as it is, so she could have odd ideas about what can catch what, but anyway...).

My questions are: 1. How much is the most one person has eaten at one time? I've heard of ten-pound burgers someplace, I think. 2. I doubt one could even get a cat down one's throat, so we'll go with a bird; suppose someone was able to swallow a very small bird whole; how long would it survive in the stomach before being attacked by the stomach fluids and killed? Long enough to find the spider?

Take note - anyone who claims this question is asking for medical advice will be laughed at for days. :-)Somebody or his brother (talk) 18:08, 27 January 2009 (UTC)[reply]

Well, our stomach article states "in humans, the stomach has a relaxed volume of about 45 ml, it generally expands to hold about 1 litre of food, but can hold as much as 4 liters." Certainly the limiting factor is the circumference of one's esophagus. According to this article average diameter is 2-3cm (.78-1.1 in), so 6.3-9.4 cm (2.4-3.5 in) circumference. -- MacAddct1984 ^{(talk  contribs)} 18:30, 27 January 2009 (UTC)[reply]

Surely the esophageal cross-section is not of fixed size? Nimur (talk) 18:37, 27 January 2009 (UTC)[reply]

Yeah, it must expand to a point, I couldn't find much about it though. If a bird did manage to get down someone's throat, I'm sure finding and eating an already decomposing spider is the last thing on its mind. Also, we happen to have an article on There Was an Old Lady Who Swallowed a Fly. -- MacAddct1984 ^{(talk  contribs)} 18:43, 27 January 2009 (UTC)[reply]

Wow, there is an article on everything here. :-)Somebody or his brother (talk) 19:21, 27 January 2009 (UTC)[reply]

Not forgetting 'a waffer thin meent' [33] Laughed at for days, eh? - ooh, blimey!! Richard Avery (talk) 19:41, 27 January 2009 (UTC)[reply]

66 hot dogs in one sitting. You might also want to check competitive eating. Clarityfiend (talk) 20:04, 27 January 2009 (UTC)[reply]

Please see the International Federation of Competitive Eating Records List. These guys are pretty much the authority. The most impressive item on the list in my opinion is the 21 lbs of grits eaten in 10 minutes. Anythingapplied (talk) 20:51, 27 January 2009 (UTC)[reply]

Hmmm...less than 2 pounds of chocolate in 7 min.? On the other hand, 65 hard boiled eggs, and by a woman. In your face, Cool Hand Luke. Clarityfiend (talk) 00:13, 28 January 2009 (UTC)[reply]

In my old school times a guy tried to eat two krapfen at once, but suddenly became red and almost died.--pma (talk) 00:55, 28 January 2009 (UTC)--pma (talk) 00:55, 28 January 2009 (UTC)[reply]

Does this count as "whistling"?

Hi. I know a method of "whistling" different from conventional whistling. Place the tip of your tongue loosely on top of your lower teeth, then place your upper teeth loosely on top of your tongue, and very slightly behind your lower teeth. Pucker your upper lips up towards your nose, close your jaws slightly, then blow a steady stream of air through your upper teeth and the gap in your lips, while slightly puffing your central and upper cheeks. It should make a high-pitched sound. Now, I find that using this method, I cannot control the pitch of the whistled note, and it isn't always continuous. However, would this still count as whistling or not? Thanks. ~A H 1^(TCU) 19:17, 27 January 2009 (UTC)[reply]

See Whistling#Types. Seems to me like it's still whistling, unless by "still count" you mean you're planning to enter a whistling contest and don't want to be disqualified. Coreycubed (talk) 19:50, 27 January 2009 (UTC)[reply]

Whistling can be done lots of ways, even with a whistle, your hands, or a blade of grass. To decide if something is whistling or not all depends on the noise that is made. If it makes that high pitch whining "whistling" noise then it is indeed a whistle regardless of how you do it. Even when a teapot makes that noise it is considered to be whistling. Anythingapplied (talk) 22:43, 27 January 2009 (UTC)[reply]

Autoclaving liquid

When autoclaving liquid, one is always instructed to use an oversized container so that the liquid will not escape if it starts to boil. When you use the 'liquid' cycle on the autoclave, at the end of the cycle the pressure drops slowly to prevent boiling over.

My question is, in practice does liquid (an aqueous solution such as microbial media) commonly boil in a autoclave run on the liquid cycle? That is, is the oversized container really just a redundant precaution, and the liquid will not boil as long as the autoclave works correctly? ike9898 (talk) 21:08, 27 January 2009 (UTC)[reply]

There might be some liquid expansion issues but I think you've answered your own questions. In practice many things can go "wrong". Preparation can determine if the "wrong" event is a) of no consequence or b) requires the process to be repeated without getting anything "wrong". If a redundancy doesn't cost anything, for example grabbing a moderately larger dish over a smaller one, than there is no reason not to take the extra precaution.--OMCV (talk) 01:21, 28 January 2009 (UTC)[reply]

Usually the problem with boiling is that the pressure drops much faster than the temperature does. Theoretically if the autoclave is working and designed properly it wouldn't happen, but in practice people get antsy and try to open the door too soon or the control isn't exactly 100%. I know with the media I've autoclaved (been a few years, though!) it wasn't unusual to see it churning a little bit when I took it out, albeit not enough to boil out of anything. I may have been a little trigger-happy with the door, though. SDY (talk) 01:17, 28 January 2009 (UTC)[reply]

I used to make LB all the time and, while I couldn't tell what was going on once the doors shut, I would often see evidence of broth that had crept up the inside of the flash. Also, after taking out the flasks, the slightest movements would cause it to bubble up rather violently. -- MacAddct1984 ^{(talk  contribs)} 18:14, 28 January 2009 (UTC)[reply]

Thanks, all. I'm basically being cheap and trying to avoid bigger flasks, but I think I'm going to just bite the bullet buy them. It's better than making a mess and/or ruining an experiment. ike9898 (talk) 19:36, 28 January 2009 (UTC)[reply]

osmole confusion

I`m just reviewing some renal stuff, and I`ve realized I`m confused on a pretty question:

If I took 500 sodium molecules and put them in 1 L in one container. In another contained, I put 500 glucose molecules.

Which would have the greater osmolality?

--Cacofonie (talk) 21:39, 27 January 2009 (UTC)[reply]

Did you review osmolarity? The first paragraph has a discussion of a similar question. See also molality within the concentration article. On a related note, you probably mean "sodium chloride" or some other sodium salt since pure sodium would be pretty reactive in water (which is what I assume you are dissolving in, since you didn't specify). --- Medical geneticist (talk) 23:27, 27 January 2009 (UTC)[reply]

Besides the fact that sodium doesn't really form molecules. If you're talking about sodium chloride I guess you could consider a pair of Na+ and Cl- as one "molecule", at least for the purpose of molarities. Confusing Manifestation(Say hi!) 04:16, 28 January 2009 (UTC)[reply]

Actually, see Van't Hoff factor. Sodium chloride has a colligative molarity double its measured molarity because it is not a molecule, but rather, an ionic substance. Strong electrolytes like NaCl have Van't Hoff factors equal to the number of discrete particles they form in solution, for sodium chloride each "NaCl" formula unit (which are not molecules) results in TWO discrete particles, an Na+ and Cl-. Non-electrolytes, like glucose, have a Van't Hoff factor of exactly 1, since they don't dissociate at all in solution, so one mole of glucose molecules produces exactly one mole of particles in solution. So a 1 molar solution of NaCl will have double the osmolarity of a 1 molar solution of glucose, because dissolving 1 mole of NaCl in a liter of solution will produce double the number of particles that dissolving 1 mole of glucose will. --Jayron32.talk.contribs 04:41, 28 January 2009 (UTC)[reply]

January 28

Can one guess the mass of a dice?

Suppose we have a cube with labeled faces (e.g., one of those objects called dice), with (possibly) inhomogeneous mass. Given the probabilities of the outcomes 1,..,6, (say that we have thrown it so many times that we agree on them), can we at least locate the baricenter? Or conversely: besides the symmetric case, is there a distribution of mass in a cube for which we can guess the frequencies of the outcomes? (Disclaimer: I am not planning to cheat people) --pma (talk) 00:43, 28 January 2009 (UTC) ~~hopefully fixed~~[reply]

Discussion of whether it matters that the OP called it "a dice" instead of "a die" hidden here

There is no such thing as "a dice". --Trovatore (talk) 00:58, 28 January 2009 (UTC)[reply]

You can make a guess, but only within certain statistical parameters. Note that casino dice have the pips filled so as to maintain symmetry of mass. — Lomn 01:02, 28 January 2009 (UTC)[reply]

He never did say "a dice", he quite correctly and grammatically said "one of those objects called dice" (objects dice plural). Don't be pedantic and wrong. Rotational (talk) 13:40, 29 January 2009 (UTC)[reply]

He did say (correctly) "a dice", but has since edited the original question to avoid confusing Americans. DuncanHill (talk) 14:57, 29 January 2009 (UTC)[reply]

My mistake......sorry Rotational (talk) 17:19, 29 January 2009 (UTC)[reply]

What Trovatore is saying is that "dice" is the plural form of "die". Saying "a dice" is like saying "a cars" or "a books", it doesn't really make sense. -- Mad031683 (talk) 01:21, 28 January 2009 (UTC)[reply]

Surely the OP means a die. Surprised no one linked this--GreenSpigot (talk) 01:51, 28 January 2009 (UTC)[reply]

Well, the relevant article is at dice, which is far and away the most common form of the word. I'm more surprised that three of four responses ignored the question. — Lomn 01:54, 28 January 2009 (UTC)[reply]

OK die redirects to dice. But die is the singular.--GreenSpigot (talk) 01:57, 28 January 2009 (UTC)[reply]

We're not really supposed to correct the OP's grammar/vocabulary. If you can't answer the question...don't. SteveBaker (talk) 02:19, 28 January 2009 (UTC)[reply]

Correction in this case gives the OP more of a chance of finding what (s)he was looking for: therefore it is legitimate.--GreenSpigot (talk) 02:27, 28 January 2009 (UTC)[reply]

Dice is perfectly acceptable as a singular. DuncanHill (talk) 02:32, 28 January 2009 (UTC)[reply]

No, it isn't. It sounds seriously uneducated. --Trovatore (talk) 02:34, 28 January 2009 (UTC)[reply]

Dice is the normal singular, and the old singular die is confined to a few fixed phrases and certain mathematical contexts. DuncanHill (talk) 02:43, 28 January 2009 (UTC)[reply]

No, it isn't. A dice is substandard English, like a bacteria or a criteria. Absolutely unacceptable in formal writing. --Trovatore (talk) 02:45, 28 January 2009 (UTC)[reply]

Will you write and tell the OUP that or shall I? DuncanHill (talk) 02:47, 28 January 2009 (UTC)[reply]

The Brits do seem to see these things differently. They're wrong, of course. But I'd be surprised about Oxford; I'd need to see evidence there. --Trovatore (talk) 02:51, 28 January 2009 (UTC)[reply]

Edmund Weiner, Andrew Delahunty, Oxford Guide to English Usage, 2nd edition 1993, page 130. That do you? DuncanHill (talk) 02:55, 28 January 2009 (UTC)[reply]

What does it say, exactly? --Trovatore (talk) 02:56, 28 January 2009 (UTC)[reply]

"dice is the normal singular as well as the plural (one dice, two dice); the old singular, die, is found only in the die is cast, straight (or true) as a die, and in mathematical discussions, e.g. Rolling a die will generate a string of random numbers." Further down the same page it has "die (noun); see dice." DuncanHill (talk) 03:00, 28 January 2009 (UTC)[reply]

Boy, good thing we Americans are around to save the language. Y'all aren't taking care of it at all.

Anyway, you should be aware that a dice is seriously grating on American ears. In shared situations, if you can't bring yourself to say a die, it would be better to rephrase. --Trovatore (talk) 03:04, 28 January 2009 (UTC)[reply]

(ec)God forbid Americans should have to put up with English as She is Spoke in England :) David Crystal in The Cambridge Encyclopedia of the English Language, CUP, 1995, makes a similar point to the Oxford, at page 201. DuncanHill (talk) 03:08, 28 January 2009 (UTC)[reply]

Both 'die' and 'dice' are unacceptably vague here, and 'cubic die' sounds unnatural to my ears. The object in question is a d6. Algebraist 03:07, 28 January 2009 (UTC)[reply]

I second d6. All Dungeons and Dragons players know that the only acceptable way to reference dice is to day 'd' followed by the number of sides on the dice (die) in question, most commonly d20. -04:00, 28 January 2009 (UTC) —Preceding unsigned comment added by Pete5x5 (talk • contribs)

English is defined solely by how it is used (we don't have an equivalent of the Academie Francaise, for example), dictionaries just report what is used. If enough people make the same mistake, as in this case (or the case of "begging the question", for example), it becomes correct. --Tango (talk) 15:10, 28 January 2009 (UTC)[reply]

An easier way than relying on random movements and outcome while rolling the die/dice would be to build yourself a contraption where you could stand/clamp the thingy in question in by 2 diagonally opposed corners [34] and give it a controlled push with a known and repeatable force and speed. Dice with centered mass should spin at the same rate and slow down to a stop within the same time no matter which corners you used. Dice instead of die is common because most of us encounter them before we get to school. (Even in the US.) I learned about a die for casting before I found out it was also (officially) the singular for dice.76.97.245.5 (talk) 03:54, 28 January 2009 (UTC)[reply]

Yes, well, that's sort of why it sounds uneducated. --Trovatore (talk) 05:27, 28 January 2009 (UTC)[reply]

Thank you everybody! So, I understand that the singular of dice is not so used, like in latin. Maybe I tried the Language desk for the mechanical side of the question...--pma (talk) 09:36, 28 January 2009 (UTC)[reply]

Some interesting discussions on two subjects!! The grammar bits were especially entertaining, but neither the title nor the question referred to "a dice". Bazza (talk) 13:41, 28 January 2009 (UTC)[reply]

Yes it did. It's been changed. Algebraist 13:44, 28 January 2009 (UTC)[reply]

And now I'have re-corrected at least the title so as to keep memory of the lucky occasion that gave origin to this debate. Note that, as a non-native english speaker, I am really glad to be corrected. In fact, I started writing here also to improve my english. And, of course, because I believe in sharing the knowledge with people from different countries. pma (talk) 14:39, 28 January 2009 (UTC)[reply]

Determining the centre of mass for the die by how it rolls is probably impossible in practice. The actual way to do it is to attach a string to the die to a bunch of points, one point at a time. The centre of mass will lie along the line that extends downward from the string (to maintain no torques on the die). Do this twice and the intersection of the two lines reveals the location of the centre of mass, but in practice, you're best to do several measurements to beat down the experimental error. WilyD 14:45, 28 January 2009 (UTC)[reply]

If we could all just use impeccable grammar, it would be a pair o' dice. Edison (talk) 16:20, 28 January 2009 (UTC)[reply]

Thanks Wily. Yes, we can determine geometrically the baricenter, but what I had in mind is another issue: is there a relation between the frequencies and the position of the baricenter? Roughly, the dice will stop more often with their baricenters in the lower position; I just wonder how this can be made quantitative. I had in mind a kind of approach via statistical mechanics and... no matter. I found interesting the linguistic aspect, and even more the anthropological one ;) --pma (talk) 17:42, 28 January 2009 (UTC)[reply]

Err, realistically, you'd never work out the relationship theoretically. Depends on the details on the friction in the die roll, the non-cubicity of the die, many unpleasant bits. You could make a simplified model, but the devilish details would cause me, a theorectical physcists to say "This problem is impossibe" - the easiest way to do it would be a bunch of dies with known baricentres, an undergraduate and some money from NSERC (or the NSF or whatnot). WilyD 18:13, 28 January 2009 (UTC)[reply]

Ok, that's what I also suspect; too many details are to be fixed. Now, trying to answer by myself, a simple model is: an cubic die with sharp edges, rolling under the effect of impulses randomly distributed. The six positions are local minima for the energy, and a 90 degrees rotation from one face (i) to another (j) needs a small amount of energy, δ_ij -it's how much the baricenter has to be raised. This should give a transition probability p_ij for any pairs of adjacent faces; p_ij is related to δ_ij according to the distribution of the random impulses. Now we have a Markov chain and I may think that the corresponding stationary distribution is the probability distribution for the stopping positions. The idea is that at a certain moment the die just decides to stop for reason of his own (otherwise, in alternative one may think of a slowly decaying energy, acting till the die can't move any longer). Anyway, my interest about it is just linked to dinner conversations; I'm not a physicist nor a probabilist and can't say how fool is this picture. pma (talk) 19:59, 28 January 2009 (UTC)[reply]

(Thanks for hiding the off topic!) The problem is there are even more details than just the dice itself. Even consider the initial position as random, the initial hight and spin have an impact. If it drops from a large hight with little spin, it is much more likely to make it into some equilibrium position before hitting the ground. It also depends on how much the die bounces on the surface it is being dropped. A lot of bouncing would again lead to more randomness and less predictability which would mean you'd have to use a die with a weight even more from the center. If you wanted to make a situation where the dice would land more predictably I may suggest dropping into a large tank of undisturbed water with sand at the bottom. The large decent would give it enough time to reach its equilibrium state and its landing would be slow because of the water so it'd probably just stick into the sand the same direction that it was falling. Even for a dice that was just off a little, you may find that you get the same number almost every time in this situation. Anythingapplied (talk) 21:40, 28 January 2009 (UTC)[reply]

Yes, the way it's thrown is clearly relevant. For the slow die in water that you are describing, the probability to land on a face should be proportional to the solid angle subtended by that face at the baricenter, I think. Anyway, I would expect just a rough correspondence between a true die and a mathematical model. Thanks again pma (talk) 22:10, 28 January 2009 (UTC)[reply]

I think you're model is solid. If you use some sort of machine to throw dice consistantly and fit variables to the model, I think it'd work quite well for a controlled situation. If you could use a high speed camera to record the initial side that hit the ground, the number of bounces, and all the intermediary sides to be face up when making contact with the ground you'd be able to fit your variables with much higher relaibilty and far fewer experimental throws. Determining what probability distrabution to use for the amount of initial energy would be the most difficult part in my opinion. Anythingapplied (talk) 22:23, 28 January 2009 (UTC)[reply]

Actually, I think one could get an approximate answer that while far from complete might none the less be interesting. If you watch a die, then at any given instant there is nearly always one side that is more approximately "up" than the others, and the die will either settle on that side or rotate to another. The question of whether it rotates to another side is dependent on whether it has enough angular momentum to carry its center of mass against gravity across a pivot point. A higher center of mass is easier to flip than a lower one. If one chooses to consider only the "last flip", when the angular momentum of the die is sufficient to rotate over once more but no further, one should be able to state roughly how much easier it is to flip the die in one configuration versus another based on the position of that center of mass. If one assumes that the last part of the roll, when the die is about to settle, is the most important, then this would give a rough way of estimating. Obviously there are a lot of other details that could modify that conclusion, but I think there is nonetheless a tractable (though still complicated) starting point for making such estimates. Dragons flight (talk) 22:35, 28 January 2009 (UTC)[reply]

Hey! Someone deleted my answer!! (restoring it) I've been thinking about this for the past day or so while all of the babble about die/dice was going on. I think we don't have enough information. Think about the mechanisms by which a 'weighted' dice ends up being 'unfair':

If it were being tossed in a vacuum, then while it was in the air, it would rotate about it's center of gravity (which would be off-center) but that would only affect it's rate of rotation because of the changed moment of inertia of an off-center center of gravity compared to a dice with the CofG in the middle. So the initial force imparted to roll the dice would have a different resulting spin rate - but once launched, it would still land (essentially) randomly depending on the precise speed and height it was thrown from...and (of course) what orientation it was in at the start of the toss. But a dice with a heavy weight just under the '1' face wouldn't preferentially come up '6' for this reason.
In the presence of air resistance, there would be a tendency for it to slowly stop rotating and to fall 'heavy-side-down'. But the degree to which that happens would have to depend on the lightness of the body of the dice. Imagine something like a shuttle-cock - those lightweight feathers result in it's flight rapidly stabilising to a 'heavy-end-first' approach. But if you imagine a 4 ton solid steel dice with a similarly off-center weight, you'd imagine that air resistance would be negligable. So this tells us that the weight, size, aerodynamics of the dice will affect the degree to which the thing will or will not tend to stabilise.
Then, when the dice hits the ground and starts rolling there will be the question of whether the corner of the dice has enough friction to allow it to flip over onto the next face instead of merely sliding along the table without rolling. Offsetting the weight further from the point where the friction is applied gives it a greater turning moment when the weight is high up - and reduces the turning moment when the weight is at the bottom - so that's going to increase the probability of it ending up heavy-side down rather than managing to rotate another 90 degrees. The degree to which this effect works depends on how steeply the dice is dropped (if it's vertical - then this has little effect - if it's rolled horizontally - such as as a casino 'craps' table - then it's very significant).

So here's the problem. The degree to which weighting the dice affects the outcome depends on (at least) the air resistance, the moment of inertia of the unweighted version of the dice, the frictional forces between dice and table and the angle from which the dice is thrown. All of those things will alter the probability of the dice to be 'unfair'. If the degree of unfairness (statistical irregularity) depends on something OTHER than the placement of the weight in the volume of the dice - then you can't use statistical methods to determine how far the weight is from the center. You almost certainly can determine the direction in which it's displaced because that's just the degree of asymmetry in the statistics. But the AMOUNT of displacement would require knowing an awful lot about the detailed physics.

SteveBaker (talk) 00:38, 29 January 2009 (UTC)[reply]

Very clear. By the way, now I understand why casino dice have sharp edges: one good reason is that rounded corners would make it easier to stop on the lower position of the baricenter, if it's not perfectly centered - as extreme case, a ball would do it certainly. --pma (talk) 07:36, 29 January 2009 (UTC)[reply]

PS: It seems it was me the vandal... sorry Steve.pma (talk) 11:58, 29 January 2009 (UTC)[reply]

Backwards FET operation

Can I use a FET backwards to generate the square root of the drain current by looking at the Vgs?--GreenSpigot (talk) 02:05, 28 January 2009 (UTC)[reply]

It won't work if you just use the FET on its own, which is what I think you mean. The FET won't 'know' that you want the Vgs to vary with the drain current. You can, however, put the FET in the feedback loop of an amplifier and reverse its operation that way. There's an example here. --Heron (talk) 09:55, 28 January 2009 (UTC)[reply]

Yes but the opamp in that cct is only used to generate a drain (actually source current in that config) current proportional to the signal voltage. Id rather not use an op amp as Im considering very high frequencies. So if I was to force a drain current and use the developed Vds to act on the gate as feedback, do you think it may work?--GreenSpigot (talk) 13:33, 28 January 2009 (UTC)[reply]

In essence, you can't "reverse" the FET but you can ask the question "What voltage, when squared, would equal this voltage?" - and that is the answer you want. Hence User:Heron's idea of using a feedback approach. So (effectively) you compare the output of the FET to the voltage you are trying to take the square root of - and adjust the input of the FET up or down until they match. (Or if you don't need to do it too quickly you could use a $5 microprocessor that has A/D and D/A and do it in software!) SteveBaker (talk) 14:01, 28 January 2009 (UTC)[reply]

Its ok I modelled it on spice and it works.--79.75.56.52 (talk) 17:14, 28 January 2009 (UTC)[reply]

BTW thats SPICE--GreenSpigot (talk) 01:13, 29 January 2009 (UTC)[reply]

intensity light

SteveBaker, You said if I'm on Mars I won't notice the vermilion color becasue my eyes is in vermilion color, and the color I'll see is just tranparent light. Then why on Earth, on foggy day the I still notcie white, I see sky everyday, they always look azure (light blue). The yellow (signal light), I think way inside, humans can notice the yellow colour. But on Saturn/Titan, the problem is the light we get is 1/100 that of Earth, that is only light of a thunder hit our house at night. If I orbit around looking down, would Saturn look almost black? When I descend in Titan's atmosphere, you said I won't see the orange color because orange colour is in my eyes. I thought the color won't burn my eyes blind, just turn my color vision off? is strong color not rich just burn off vision?--69.226.46.118 (talk) 02:00, 28 January 2009 (UTC)[reply]

You seem to be referring to this thread. Be aware that if you show up here continuing a discussion from a week ago, and speaking directly to an unspecified person (who are you talking to, anyway?), most people here will wonder what on earth you're talking about. Algebraist 03:12, 28 January 2009 (UTC)[reply]

I think it's a steganographic message of some sort. Taking 1=color and 0=colour, it comes out 111010111. Not very good steganography — low information density; easily broken. Reminds me of this. --Trovatore (talk) 03:21, 28 January 2009 (UTC)[reply]

To avoid confusion the OP modified the post, original was here [35]. To the OP, it is usually considered poor form to modify your post in such a way that you make proceeding discussion meaningless. You should at least mention it was modified or better still, if modifying your post will confuse the situation, just reply to your post with the additional information Nil Einne (talk) 11:16, 28 January 2009 (UTC)[reply]

Trova, What??--69.226.46.118 (talk) 04:26, 28 January 2009 (UTC)[reply]

He's referring to the fact your original message was fairly cryptic. Nil Einne (talk) 11:16, 28 January 2009 (UTC)[reply]

Unfortunately, he feels very bad when he finds mis-spells and typos, and goes crazy. Usually these are results of a severe education... --pma (talk) 11:55, 28 January 2009 (UTC)[reply]

(Background: The OP had been asking a lot of questions - with a lot of follow-ups about the general topic of the color that planets would seem to be if you were really there. (S)he started asking more of these questions over on my UserTalk: page - and I requested that they not be posted there - but here, where they belong. IMHO, between several L-O-N-G answers here - and more on my UserTalk: the question has already been fully answered and there is little (if anything) more to be said on the subject. IMHO, the OP should carefully read the previous replies and desist from further posting on the subject until all of that material has been properly absorbed. At any rate - I've had enough.) SteveBaker (talk) 13:54, 28 January 2009 (UTC)[reply]

What matters isn't what colour the things you're seeing are, but rather what colour the ambient light is. On Earth, the ambient light is almost always white (that's why our eyes see the frequencies they do) - while the sky is blue, the sun is yellow, and they add together to make white (in fact, the light from the sun started out as white and was split into blue and yellow by the atmosphere). On Mars, the ambient light is going to be more red because the dust in the atmosphere absorbs other colours (this is different from the scattering that makes our sky blue - that just makes different colours seem to come from different places, it doesn't absorb anything so the result is still white), and your eyes would very quickly get used to that and you wouldn't notice (if it was too red you would notice because certain colours (eg. blue) would appear extremely dark, even black, but on Mars it wouldn't be that severe). --Tango (talk) 15:05, 28 January 2009 (UTC)[reply]

This reminds me of the Goethe vs. Newton dispute on the theory of colours... even Newton had enough of it, at a certain point ;) pma (talk) 18:18, 28 January 2009 (UTC)[reply]

Newton avoided the worst of that dispute by dying two decades before Goethe was born. Algebraist 15:13, 29 January 2009 (UTC)[reply]

Feed the sailors with carrots so they'll have better eyesight.

The Japanese battleship Yamato was the last serious and also the largest navy battleship ever built. It was sunken by U.S. navy pilots in 1945. In 1941, it had a very traditional battleship vs. battleship configuration. In 1944, they removed two 155 mm turrets and installed 138 25 mm AA guns.

Armament	1941	1944
46 cm (18.1 in)	9	9
155 mm (6.1 in)	12	6
127 mm (5 in)	12	24
25 mm anti-aircraft	24	162
13.2 mm anti-aircraft	4	4

Nevertheless, Yamato was still sunken. They had too few AA guns. The first wave of attack consists of 280 planes and the second one over 100. It had taken 386 airplanes to bring down Yamato which only had 162 25 mm AA guns and a very small fleet of 9 escort ships. The special AA ammunitions for the 18.1" guns were found useless. Yes, they used the 18.1" guns as if they were shotguns.

The 25 mm AA guns, clustered around the bridge, were mostly destroyed by the bombs before Yamato's demise. Then the battleship had taken 10 torpedo hits (1 starboard, 9 port, the U.S. navy was very clever) and went off-balanced.

Since the Japanese Empire did not have the resources to build additional aircraft carriers and more airplanes in 1944, air support was out of the question. From a 20-20 hindsight point of view, how many 25 mm AA guns were required to defend against 386 U.S. airplanes? How many anti-torpedo weapons did it take? How many 18.1" turrets needed to go to make room for all these self-defense weapons? Did Yamato still have a chance if it cleans up the whole deck and give each of its sailor a 25 mm AA gun? -- Toytoy (talk) 09:58, 28 January 2009 (UTC)[reply]

Japan did not have the proximity fuse at that time, using time fuses or barometric fuses as always, and nobody had radar-guided anti-aircraft guns on their ships. It's surprisingly hard to hit a moving airplane from a moving ship with a projectile by eye, and it's almost impossible to set a fuse so it goes off near an approaching plane. If the entire deck of the Yamato had been covered in AA guns, it would still have taken only one well-placed bomb to sink her. The battleship was a doomed dinosaur even before the Yamato was commissioned. (It was a beautiful ship, though, wasn't it?) --Milkbreath (talk) 12:37, 28 January 2009 (UTC)[reply]

Also, if it was sufficiently well defended from air attack, it would have been attacked in other ways, such as a submarine torpedo attack or even a traditional battleship-to-battleship "crossing the T" engagement. High altitude bombers, which are out of range of anti-aircraft guns, would be another option, although their low accuracy means that many more bombs would need to be dropped. They also might not destroy the battleship directly, but could disable most of the anti-aircraft guns, allowing for low-altitude torpedo plane attacks. Mines could also be laid in it's path. If, by some miracle, the Yamato managed to survive all such attacks, the US might have even used an atomic bomb on it, when they became available, but, having only 2, they were in short supply. Still, if an "unsinkable" ship could be sunk instantly, especially if close enough to Japan to provide a sufficient demonstration, it might be a good use, perhaps sparing the 2nd city bombed, Nagasaki, of it's fate. Some of these approaches would have required a "strategic withdrawal" of the US fleet, to give time to prepare an adequate "reception". StuRat (talk) 14:51, 28 January 2009 (UTC)[reply]

I don't know that nuking a battleship would have done much. The US didn't know at the time (and so it can't really be used to justify the theoretical decision), but Crossroads Able wasn't much of a ship-killer, and that sort of airburst is a good approximation of how an attack would have gone. — Lomn 18:25, 28 January 2009 (UTC)[reply]

It sank 5 ships, despite having missed the target, and disabled many more. Also, I'm not sure if an air-burst is the best way to sink a single ship; a surface burst might be more effective, by swamping the ship. StuRat (talk) 15:07, 29 January 2009 (UTC)[reply]

Incidentally, in reference to your topic heading, the idea that carrots significantly boost eyesight is a myth [36]. The myth was created intentionally by the British during WWII as a cover story to explain why the British were able to locate approaching German bombers so easily at night. The real answer is that the British had a top secret new invention: radar! Dragons flight (talk) 16:08, 28 January 2009 (UTC)[reply]

Indeed. As I understand it carrots are only going to improve your night vision (day vision is completely unaffected) if you actually have a vitamin A deficiency (which cases nightblindness). If you have reasonable night vision already, it's not going to get any better. --Tango (talk) 18:11, 28 January 2009 (UTC)[reply]

To take a different tack, I'll address the US Army Air Corps' approach to this problem. Faced with bombers that were outranging their fighter cover (and being mauled by the Luftwaffe for it), the AAC decided that the Flying Fortress, with its 10 or so antiaircraft guns, was insufficient to hold fighters at bay. They rebuilt B-17s into YB-40s, flying gunships that eschewed bomb loads in favor of additional powered turrets, ammunition, and armor. The effort, in short, flopped. YB-40s could not keep fighters at bay, could not keep up with the standard bomber formations, and could not drop bombs to salvage any cause for their inclusion in the flight line. It seems likely that the same sort of result would have come of a full conversion of a battleship to an antiaircraft platform -- as far as I know, no modern air assault has ever been substantially ablated by fixed-position fire (and yes, I'm lumping aerial and naval gunships into "fixed" -- relative to the attacking aircraft, they're effectively immobile), and a potentially effective battleship would have been lost in the process to boot. — Lomn 18:25, 28 January 2009 (UTC)[reply]

The combination of radar gunlaying and radar proximity fuses permitted an 82% kill rate for antiaircraft guns defending against the V-1 cruise missile during World War II. --Carnildo (talk) 02:19, 29 January 2009 (UTC)[reply]

Without a radar-controlled AA system, you can hardly hit any airplane with no matter how many guns. And without a radar system capable of tracking and engaging dozens of targets at once (good computers + phase-array antennas), your defense can be saturated in a matter of seconds. But just how good were these WWII planes and their ammunitions? The steel hull of Yamato was very thick. It was designed to take serious punishments. Its sister ship Shinano was sunken by torpedos because of some poor design mistakes. If the design and manufacturing were perfect, could these outdated heavy weight battleships survive non-nuclear air attacks? Could a thick-shelled turtle return home? -- Toytoy (talk) 18:31, 28 January 2009 (UTC)[reply]

Given that the Yamato and the Musashi were both sunk via aerial attacks, the answer is quite obviously "no". By 1944, US Naval bombers were lugging around one-ton bombs or torpedoes -- about the same throw weight as battleship shells. Since this wasn't an era where armor reigned supreme (contrast with the Battle of Hampton Roads for such a case]]), it's not controversial to say that any conventional ship* of the era could be sunk by any conventional aerial attack.

*See Project Habakkuk for what could have been an interesting exception. — Lomn 21:18, 28 January 2009 (UTC)[reply]

Organ donor records

Who is the youngest organ donor? And who holds the record for being the oldest at the time of organ donation? In multiple organ donors, what is the maximum number of organs that have been donated by a person? Or is there any article similar to World records in medical science? Jay (talk) 10:03, 28 January 2009 (UTC)[reply]

Youngest? Stillborn babies can become organ donors [37]. If you want to get technical, I guess you should count from conception. I'm somewhat doubtful anyone has records of that sort of thing Nil Einne (talk) 11:11, 28 January 2009 (UTC)[reply]

Does destroying a few day old embryo in order to harvest embryonic stem cells count as "organ donation"? Technically, I suppose there weren't any "organs" yet. But in general, I believe finding the youngest organ donor is mostly a question of how one chooses to define "organ" and "donor". Dragons flight (talk) 16:01, 28 January 2009 (UTC)[reply]

If you accept it, younger than this seems difficult! pma (talk) 22:30, 28 January 2009 (UTC)[reply]

Making the queries more specific, I would like age to mean post live childbirth, and organ donation in the context of organ transplantation. Rather than the exact answers, what I'm looking for, in the absence of an available article, is ideas on which articles these details can be inserted into, or suggestions on title of a new article. Jay (talk) 08:36, 29 January 2009 (UTC)[reply]

Osmole Confusion Part II

I asked a previous question (here) here, that was partially answered, but I find myself still confused.

The question was (edited a little): If I took 500 sodium ions and put them in 1 L in one container. In another contained, I put 500 glucose molecules. which has the greater osmolarity?

The answer that I found most helpful was this one, by Jayron32: So a 1 molar solution of NaCl will have double the osmolarity of a 1 molar solution of glucose, because dissolving 1 mole of NaCl in a liter of solution will produce double the number of particles that dissolving 1 mole of glucose will.

What I`m really confused about is the plasma osmolality equation. Posm=2xNA+GLUC/18+BUN/2.8 or something like that. Why does the concentration of sodium atoms contribute 36 times more to the osmolality than glucose?

Thanks! --Cacofonie (talk) 16:16, 28 January 2009 (UTC)[reply]

The sodium does not contribute 36x more than the glucose -- you have to pay attention to the units. The short-hand calculation for plasma osmolality corrects for the different units that are given for the measurement of sodium (mEq/L), glucose (mg/dL), and BUN (mg/dL).

The mass of glucose is ~180g/mol. Let's say you measure a typical plasma glucose of 90 mg/dL. First, let's convert to g/L for a plasma glucose of 0.9 g/L. Divide by 180g/mol and you get 0.005 mol/L or 5 mM. This is the same thing as dividing the plasma glucose by 18. A similar calculation is made for BUN. (corrected numbers... oops... stupid math... --- Medical geneticist (talk) 19:37, 28 January 2009 (UTC))[reply]
Jayron already stated this, but again, in a biological context, sodium is never present on it's own but as a sodium salt, predominantly sodium chloride (but also, importantly, sodium bicarbonate). When in aqueous solution (as in blood), one mole of sodium chloride dissociates into a mole of sodium and a mole of chloride. Thus, in the calculation, you just double the amount of measured plasma sodium milliequivalents to account for the fact that the other (unmeasured) components (chloride and bicarbonate) of the sodium salts are present in solution.
Adding together the molarity of sodium+chloride, glucose, and BUN gives a decent approximation of plasma osmolality.

--- Medical geneticist (talk) 18:31, 28 January 2009 (UTC)[reply]

It should also be noted that bicarbonate, being a weak electrolyte, introduces some serious complications should you want to be scrupulously correct in your calculations. Because bicarbonate, in a water solution, produces small amounts of SEVERAL different kinds of particles, it has a non-integer Van't Hoff factor, and as such, makes the calculations quite messy. However, as a first approximation, assuming sodium bicarbonate has a Van't Hoff factor of "approximately 2" usually gets things close enough for government work... Thus, as noted, you can assume "sodium" in this context to mean "sodium, and whatever negative ions it is draging along". So, we have some assumed NaX compound, which produces 2 moles of ions (Na+ and X-) and we just take it to mean that the identity of X (be it chloride, bicarbonate, or melange of several different kinds of ions) to be moot for colligative purposes. --Jayron32.talk.contribs 04:56, 29 January 2009 (UTC)[reply]

Wearing a coat inside making the cold outside feel colder.

I wear my winter jacket inside a lot of the time. I'm told that doing this will make the outside "colder" (it's winter) when I go outside. People recommend that I take off my coat when inside so that I don't get as cold outside.

Is this true? If so, how/why is this?

141.117.29.242 (talk) 16:40, 28 January 2009 (UTC)[reply]

Perhaps it is because sweat glands, our natural cooling system, adjust to current conditions. When a coat is worn indoors, the glands open to produce more cooling. If the coat wearer then goes outdoors, it takes a little time for the sweat glands to adjust to the new condition. – GlowWorm. —Preceding unsigned comment added by 98.17.34.148 (talk) 16:58, 28 January 2009 (UTC)[reply]

I agree with the above, in that if you're so hot you're sweating indoors, you should definitely take the coat off indoors. However, if you are cold enough to feel you need it indoors, then wear it. StuRat (talk) 17:04, 28 January 2009 (UTC)[reply]

See Thermoregulation in humans. 76.97.245.5 (talk) 17:07, 28 January 2009 (UTC)[reply]

That sounds about right, thanks a lot. 141.117.29.242 (talk) 17:17, 28 January 2009 (UTC)[reply]

The article on thermoregulation says, "Horses and humans are two of the few animals capable of sweating." I wonder whether monkeys and apes sweat. It is also surprising that two creatures as unlike as horses and humans both sweat. Where did it start in the evolutionary chain? Did the same thing crop up twice in evolution? Also, sweating is one of those things that are a stumbling block to the theory of evolution - an organ cannot perform its function unless it is already perfected, or nearly perfected. – GlowWorm. —Preceding unsigned comment added by 98.17.34.148 (talk) 18:21, 28 January 2009 (UTC)[reply]

Dogs have things that are essentially sweat glands in the their paws. This appears to be so that they can leave a scent trail for their pack-mates to follow rather than to cool themselves. That suggests an evolutionary means to adapt that kind of capability into something for cooling through relatively simple genetic changes. These "stumbling blocks to the theory of evolution" almost always turn out to be something like that. Some piece of biological machinery that was originally intended for one purpose gets re-purposed in some unexpected manner. The business about it only being in horses and humans sounds unlikely - but bear in mind that it's possible for the common ancestor of humans and horses to have had functioning sweat glands and that all of the other species descended from that point didn't need them anymore and lost the capability. Evolution is just as capable of deleting a feature as adding one. SteveBaker (talk) 18:48, 28 January 2009 (UTC)[reply]

Or, it could be convergent evolution, although that seems even more unlikely. Interesting, sweat gland says that mammary glands are often considered modified sweat glands, which would suggest sweating pre-dates the evolution of mammals. --Tango (talk) 20:26, 28 January 2009 (UTC) --Tango (talk) 20:26, 28 January 2009 (UTC)[reply]

The use of sweating for thermoregulation is rare, but many organisms, including mammals, reptiles and insects, all excrete pheromones for various purposes, and it would not surprise me if scent glands developed for that purpose were modified to produce sweat glands. Dragons flight (talk) 20:42, 28 January 2009 (UTC)[reply]

Sweat glands in dog's feet still had to be nearly perfected if they were to work at all. Sweat glands have to perform the complex function of converting bodily fluids, probably blood, into sweat. A duct to the surface also had to be developed. The same requrements apply to mammary glands. - GlowWorm —Preceding unsigned comment added by 98.17.34.148 (talk) 19:31, 28 January 2009 (UTC)[reply]

Sweat could have started off as just blood plasma or interstitial fluid and still served a purpose, so there it doesn't have to be one big leap. --Tango (talk) 20:26, 28 January 2009 (UTC)[reply]

I still think the organ-specialism problem presents a serious difficulty to the theory of evolution. Those who wish to deny this difficulty say, in any particular case, that there was adaptation of something else. But they cannot show a partially-adapted organ (midway between two functions) in living things or in fossils. Their denial of the difficulty seems to me to be in the same category as the original denial of evolution itself. There was immense opposition to the theory - in England especially - when Darwin's work was first published. However, by now a great mass of supporting evidence for the theory of evolution has been adduced. There is so much supporting evidence that the main thrust of the theory cannot be denied except by religious fundamentalists, who take a nonscientific approach. But I think there is more to be said - in a scientific manner - about evolution. And it is something important. – GlowWorm

One major part of the problem may just be that soft tissue doesn't fossilise particularly well so it is very difficult to tell when organs an extinct creature had. Even if these missing links exist, we would probably struggle to find them. --Tango (talk) 22:47, 28 January 2009 (UTC)[reply]

Organs are never "partially adapted". To suggest such a thing implies a teleology to evolution — as if an organ starts out performing function A, but then somehow decides that it should instead be performing function B and starts moving that way. The only way organs can be repurposed is if, at every single step along the way, the changes provide a larger advantage (in performing function B better) than they do disadvantage (in performing function A worse). Every organism in the evolutionary chain that leads to us was a successful reproducer in its own right, there are no inferior halfway points between well-adapted creatures. Maelin (Talk | Contribs) 00:50, 29 January 2009 (UTC)[reply]

That's not entirely true - as long as there isn't a significant disadvantage to the change it may spread just by random chance, especially in a small population. Advantageous mutations are more likely to spread, but that doesn't mean that all neutral mutations die out. --Tango (talk) 14:00, 29 January 2009 (UTC)[reply]

Another simpler explination is that if you wear your jacket indoors you will sweat in it (not necessarially because you are hot but because you normally sweat a little in most of your normal daily activities). When you go back outside this slight dampness will make you significantly colder. It is the same effect if you've ever worn the same socks two days in a row and notice that on the second day your feet are colder. This is also why they advice changing cloths before bed when doing winter camping, to make sure the cloths are dry and clean to keep you as warm as possible. Anythingapplied (talk) 20:36, 28 January 2009 (UTC)[reply]

Synthesis of Benzene

Hi, I was told you cannot "make" benzene from cyclohexane as Benzene cannot be treated as a molecule with 3 isolated double bonds- as bond lengths indicate equal bond lengths. So is the following not possible then? Because you can Birch reduce Benzene to cyclohexane.
Notify me of a response by copying and pasting the following on my talk page, Thanks --DFS454 (talk) 17:12, 28 January 2009 (UTC)[reply]
{{newmessages|Wikipedia:Reference desk/Science#Synthesis of Benzene}}

Birch reduction of benzene gives cyclohexadiene, not cyclohexane, and dissolving-metal reductions don't usually touch simple alkenes at all. That's two bits of evidence that benzene is something other than "cyclohexatriene". DMacks (talk) 18:36, 28 January 2009 (UTC)[reply]

The alternating-double-bond model that makes benzene appear to be "cyclohexatriene" is largely an artifact of the diagrams used to draw benzene, or reliance upon models of molecular bonding which fall short of fully explaining the situation. There are several good models of bonding which actually reliably predict that benzene will NOT behave as "cyclohexatriene" would be expected to. For example, hybridization theory shows that every carbon atom is "sp2" hybridized, and its just not possible to justify having 6 identical atoms bonded to each other with alternatingly different length and strength bonds. It just doesn't make sense. Likewise, Molecular Orbital Theory, sort of a "hybridization theory on steroids", makes a perfect prediction of the "correct" structure of benzene. The problem is that the standard "stick and ball" model, or the condensed structural formula model shown above, do not allow themselves to easily represent the reality of the delocalized pi-bonding system present in benzene. Its a case of inadequate models more than anything. Once you realize what benzene really is, as explained by hybridization theory and MOT, then its properties and reactions make MUCH more sense. --Jayron32.talk.contribs 04:48, 29 January 2009 (UTC)[reply]

Such excellent answers have rarely benzene at the Ref Desk. StuRat (talk) 14:56, 29 January 2009 (UTC) [reply]

ha! DMacks (talk) 18:22, 29 January 2009 (UTC)[reply]

Yeah, without MO theory, it's hard to explain why benzene is like this, but cyclooctatetraene is really just cyclooctatetraene alternating single and double bonds. DMacks (talk) 18:22, 29 January 2009 (UTC)[reply]

Letter to the BMJ

While reading, with some amusement, about the cello scrotum hoax, I noticed the original letter to the editor finishes, "... — I am, etc. <signed>" It appears, from the other letters on that page and Ghits, [38] that this is a standard sign off for letters published in this journal. What does the etc replace and why is it used by all correspondents? Rockpocket 18:10, 28 January 2009 (UTC)[reply]

I'm guessing - but I get the impression that somewhen in (roughly) Victorian times, there was a large amount of flowery crap you had to put on the end of a letter ("I am yours faithfully") with the complexity of the protocol required to say 'faithfully' on business letters unless it's to a loved one ('eternally') or to a lawyer ('respectfully') or a government official or some minor royalty ('loyally'). Keeping all of that straight - especially when writing (in effect) to a large number of unknown people in a journal - got so bothersome that people would just stick an 'etc' in there an let people figure it out for themselves! It's come a long way from there to ~~~~ or '-- Steve' which is what I use on email! SteveBaker (talk) 18:36, 28 January 2009 (UTC)[reply]

Yes, you are correct. I just looked at some of the letters from the first issues in the 1840s and, back then the standard sign-off was "... — I am, gentlemen, your very obedient servant,<signed>." The "gentlemen" are the editors of the journal to whom the letters are addressed. Rockpocket 19:11, 28 January 2009 (UTC)[reply]

Note, "yours" in "yours faithfully",etc., is short for "your servant" (as in "I'm at your service", not necessary actually employed to scrub floors!). We do, of course, have an article: Valediction. --Tango (talk) 19:35, 28 January 2009 (UTC)[reply]

Which somehow fails to mention the Italian form sono vostro schiavo, "I am your slave"; a flowery formula of the highborn that somehow morphed into today's extremely informal ciao. --Trovatore (talk) 23:26, 28 January 2009 (UTC)[reply]

Wikipedia - the free encyclopedia that anyone can edit. SteveBaker (talk) 00:29, 29 January 2009 (UTC)[reply]

Well, true. I can't be bothered at the moment to look up sources and so on. I wasn't really criticizing the article, just remarking on the fact itself, which seemed germane to the discussion. --Trovatore (talk) 01:44, 29 January 2009 (UTC)[reply]

Isn't the "etc." put in by the editors? the original letter would still have a valediction.124.176.236.32 (talk) 07:41, 29 January 2009 (UTC)[reply]

Such letters to the editor are always published in exactly the same format, so I would expect people to just write them in that format to start with. If they don't, it might well be edited to fit the standard format (there is usually a disclaimer somewhere saying they might edit your letters). --Tango (talk) 13:49, 29 January 2009 (UTC)[reply]

Autodidact: how to prove that you learned something

How can an autodidact prove that he learned something about this or that science? Is there any independent examination out there?--80.58.205.37 (talk) 18:16, 28 January 2009 (UTC)[reply]

Well, you could try answering 10 questions a day on the WP RefDesk and if you get through a month without getting ripped to shreds by the other editors then you've probably made it! But seriously: I don't know at what level you are working - but you could take a look at the resources available to parents of home-schooled children...somehow they must be able to do it. SteveBaker (talk) 18:39, 28 January 2009 (UTC)[reply]

Actually, if you answer enough Q's here you will get ripped to shreds, even if the answers are correct, if they lack references to expert sources (even though they agree with the experts). If, on the other hand, your answers are correct, but disagree with the current experts, then God help you. StuRat (talk) 14:51, 29 January 2009 (UTC)[reply]

In the same line: General Educational Development certifies that the taker has American or Canadian high school-level academic skills. For more advanced skills you could try the GRE. It is done before graduate school, however, I don't think you have to have a Bachelor degree to apply for it. There are also several IT certificates that don't require that you follow an specific path. Mr.K. (talk) 18:58, 28 January 2009 (UTC)[reply]

You could make and publish ground-breaking discoveries. --NorwegianBlue^talk 19:36, 28 January 2009 (UTC)[reply]

For jobs at my organization, experience can be substituted for formal education. The idea being that if you have done a type of work sucessfully for a long time, that is as good as or better that a degree saying that you know how to do the job. ike9898 (talk) 19:48, 28 January 2009 (UTC)[reply]

I think we would be better able to address your question if we know: (1) the (equivalent) education level; (2) area of study; and, (3) country you are interested in, since there is a huge difference between being a "certified" autodidact in, say, web-design vs surgery. Abecedare (talk) 20:08, 28 January 2009 (UTC)[reply]

No, I don't have any interest in becoming a certified surgeon or certifying my knowledge in another highly regulated profession. I only have an interest in certifying my knowledge in some natural sciences above undergraduate level without putting a huge amount of money and time into a degree program. So far I found Graduate_Record_Examination#GRE_Subject_Tests. --88.0.97.125 (talk) 10:43, 29 January 2009 (UTC)[reply]

January 29

Parallel Universes' Laws of Physics

Hello,

According to String Theory ("M" theory in particular), there is the possibility of many other parallel universes just out of our "dimensional reach". Interestingly, The Elegant Universe by Brian Greene, gives rise to the possibility that these universes (if they exist) could reasonably have different laws regarding physics as we know it. My question is how is this possible?

Why would other universes have completely different laws? I can understand that there may be different parameters than ours (temperature, structure, makeup, etc...) but I don't understand that there can be a universe with laws that wouldn't make any sense! For example, if our universe had different laws, such as "F=m/a" or "E=mc", it would fall apart quite quickly, correct? Can universes really exist if they, say, violate the Laws of Thermodynamics? Or am I reading too much into the hypothetical implications to a hypothetical theory?

On a side note, could anyone please provide links or reading from a respectable (read "scientifically accepted") journal, website, book etc... for either the acceptance or denial of the Laws of Physics changing over time? Multiple sources or conflicting viewpoints are fine as well!

Thank you for your time, additional reading or information would be greatly appreciated!

Cheers! ❦ECH3LON ❦ 00:28, 29 January 2009 (UTC)[reply]

Scroll up and read Cosmic gods Rotational (talk) 13:52, 29 January 2009 (UTC)[reply]

I suspect a lot of assumptions are hidden here under the term "laws of physics". Are we talking about "laws" like E=mc^2 or "F=m/a" or are we talking about, say, the number of quarks in existence, the relative strength of gravity, the same bestiary of particle physics? It's easy to imagine a universe where gravity is more powerful than it currently is; it's hard to imagine a universe in which simple relationships were not the same. --98.217.14.211 (talk) 00:43, 29 January 2009 (UTC)[reply]

The problem is that any parallel universe which is 'inaccessible' to us is inaccessible to our theories too. So we have no way (even in principle) to probe the other universe to figure out what its' laws are. Do we have any reason to assume the laws ARE the same? Npt really. Heck, we don't even know for 100% sure whether the laws we've worked out apply everywhere in OUR universe. We don't know - we can't know - so the safe assumption is that they could be different. SteveBaker (talk) 00:48, 29 January 2009 (UTC)[reply]

Well, I don't know if it's a "safe assumption." I hate invoking anything resembling the anthropic principle, because I find it less than explanatory, but from an issue of pure incidences, we certainly know that our particular configuration seems to work and appear fairly steady. We have no evidence that anything else could be. We have no evidence (and no reason to assume) our particular universe is anything special, that our particular place in it is particularly privileged. So it seems to me like we'd have more reason to assume that things elsewhere are similar to the way they are here. That's no rigorous proof, obviously. But I'm not sure there's any reason to assume they are different elsewhere. I don't see why, in the absence of evidence, it makes sense to assume that something is different than the case we know, even though the sample size is blindingly small (n=1). --98.217.14.211 (talk) 01:41, 29 January 2009 (UTC)[reply]

(Edit Conflict) By "laws of physics" (sorry for the vague term), I meant the relationships (mathematically) that we understand. For example, F=ma,

E=mc^2, Laws of thermodynamics, Maxwell's equations, etc... Does this help? Cheers! ❦ECH3LON ❦ 00:51, 29 January 2009 (UTC)[reply]

If I recall that book correctly, he was talking about different values for physical constants such as c, μ₀, and particle masses, though I might be wrong. They say that if the strong nuclear force were only a few percent stronger than it is, then tetraneutrons could exist, which would make for an interesting universe (and would also throw our notions of radioactivity to hell). There are actually theories that some physical constants might change over time. It's a fun thought experiment to imagine a universe where the speed of light is only a few hundred miles an hour. But I digress.

Any notion of different laws of physics would be completely incomprehensible; asking how other physical laws are possible in other universes is like saying "how is it possible that God exists"? We only say it's "possible" because its outside of the realm of physics to say it's impossible. It's all a thought experiment anyway, like working with four-dimensional geometry. It doesn't exist in any way that we could ever observe it, so it isn't worth worrying about.-RunningOnBrains 01:31, 29 January 2009 (UTC)[reply]

Heh, I'm reading that book at the moment too. I wonder if I know you ;) —Cyclonenim (talk · contribs · email) 07:45, 29 January 2009 (UTC)[reply]

Unfortunately, I lost my copy of that book years ago (I should buy another one...), so I'm not sure quite what he was talking about. However, things like the inverse square law are easy to change - in a universe with 4 spacial dimensions, you get an inverse cube law (which messes with things like orbits to the point where everything either flies apart or crashes together). --Tango (talk) 13:55, 29 January 2009 (UTC)[reply]

Centripetal vs. Centrifugal

Could someone please explain to me the difference between centripetal acceleration and centrifugal acceleration? Also, what is the dostinction between centripetal acceleration and centripetal force? Yakeyglee (talk) 01:58, 29 January 2009 (UTC)[reply]

If you swing a mass round in a circle, there must be a force acting on the mass to stop it flying off in a straight line (as per Newton). This force is directed toward the center of rotation and is called the centripetal force. Every action has an equal and opposite reaction (some one called Newton again) so the centripetal force is balanced by the centrifugal force (which is what you feel when in a centrifuge. Force = mass*acceleration (that Newton chap again)--GreenSpigot (talk) 02:17, 29 January 2009 (UTC)[reply]

That last part isn't entirely correct. Every action has an equal and opposite reaction, yes, but you're confusing where the reaction is. The string is pulling the mass inwards, and the equal and opposite reaction is the string pulling your hand outwards. (When you're wondering about equal and opposite reactions, it's always best to consider that the forces are almost always applied to different objects, because if they were applied to the same object the equal forces would mean that nothing would ever move). For a better explanation of centrifugal force, see the article linked. It's a tricky one, because many over-zealous physics teachers will tell you that centrifugal forces "do not exist." This isn't quite true, it's just that they only exist in the frame of reference of the object being spun. — Sam 146.115.120.108 (talk) 03:40, 29 January 2009 (UTC)[reply]

Our article on inertial frames of reference has a nice explanation too. Basically, if you have to invoke forces that have no obvious physical origin and that act on all particles within a body (like centrifugal force and Coriolis force) then this shows that you are working in a non-inertial reference frame. A hypothetical Foucault pendulum at the North pole illustrates the difference nicely - what causes its plane of oscillation to rotate through 360 degrees every 24 hours ? Non-inertial frame answer - Coriolis force. Inertial frame answer - the plane of oscillation doesn't rotate, the Earth rotates around it. Gandalf61 (talk) 12:20, 29 January 2009 (UTC)[reply]

Obligatory xkcd reference. — DanielLC 16:48, 29 January 2009 (UTC)[reply]

Seeing bubbles on a leaf in water

If I put a leaf in water for a while, I see lots of bubbles. "Weeee!!! The plant is photosynthesizing!" I think, "I'll demo this for my students!" But... then I put a pen in water for a while, and I see just as many bubbles. Hmmm....

1) Why do bubbles build on the pen? Yes, I know there are dissolved gasses in the water, but why to they build on the pen?

2) Does anyone know a good lab that makes it clear that the bubbles on the leaf are being produced by photosynthesis?

Thanks! — Sam 146.115.120.108 (talk) 03:17, 29 January 2009 (UTC)[reply]

1) Nucleation

2) Not right off, since leaves are not exempt from nucreation you'd have to separate that out. The article hints that pure water might work, but then how do you prove to your students that they are seeing two different effects. Someone probably has a nicer set up up their sleeve. 76.97.245.5 (talk) 04:01, 29 January 2009 (UTC)[reply]

It might work if you degas the water immediately before. I can't comment on if you'd actually see the bubbles from photosynthesis - I'm not much of a biologist. --Bennybp (talk) 04:07, 29 January 2009 (UTC)[reply]

I think the water can be degasified by boiling it. Then, of course, let it cool before putting the leaf in. — GlowWorm. —Preceding unsigned comment added by 98.17.34.148 (talk) 04:24, 29 January 2009 (UTC)[reply]

The leaf will need CO2 to be in the water, so you can't de-gas it. --Milkbreath (talk) 11:50, 29 January 2009 (UTC)[reply]

You're right, Milk. Boiling the water will remove the CO2. But that could be the basis of another classroom demonstration. Put a leaf in an inverted test tube full of unboiled water in a beaker of unboiled water. Put another leaf in the same situation with boiled water. Put both beakers under a strong light. I think oxygen bubbles will appear only on the leaf in the unboiled-water. This will demonstrate that the leaf takes in CO2, extracts the carbon and keeps it, and exhales the oxygen. Perhaps it could be demonstrated that the gas which collect at the top of the unboiled water test tube is actually oxygen, though I don't know of an easy way to do that. The leaf being under water is not its natural conditiion, but still... - GlowWorm. —Preceding unsigned comment added by 98.17.34.148 (talk) 18:34, 29 January 2009 (UTC)[reply]

(ec)1) Dunno. Maybe the air is coming out of the plastic as the water cools it; maybe the rough surface of the pen is providing nucleation sites for dissolved gases that are coming out of solution as the water comes up to room temperature.

2) Fill a test tube with water and place a sprig of elodea inside. Invert the tube in a pan of water. You might have to set up a clamp or something to keep it from falling over. Do the same with a fake plastic sprig of elodea as a control. Keep the rig well lit and the live elodea should outpace the plastic one in bubble production by quite a lot. --Milkbreath (talk) 04:12, 29 January 2009 (UTC)[reply]

I think that nailed it pretty neatly. Does anyone know if the Lotus effect would also work in reverse, i.e. would gas bubbles in water on a lotus leaf behave like water in air? 76.97.245.5 (talk) 04:25, 29 January 2009 (UTC)[reply]

Thanks! That sounds like a great setup. — Sam 146.115.120.108 (talk) 12:08, 29 January 2009 (UTC)[reply]

Atomic Bombs and Radiation Burns

On the recent episode of Lost, they make reference to the fact that several people suffered radiation burns/radiation poisoning from an unexploded nuclear weapon (a hydrogen bomb). I was under the impression that the uranium/plutonium used in nuclear weapons is comparatively inert and relatively not that radioactive, at least up to the point it goes supercritical. Given the amount and type of radioactive material in an unexploded nuclear bomb, how close would you have to be to the bomb, and how long would you have to stay there to get enough radiation for acute effects to occur? (The bomb was depicted as leaking, so figures for both with and without typical shielding are appreciated.) -- 76.204.94.153 (talk) 04:46, 29 January 2009 (UTC)[reply]

You won't get radiation burns from the core of a nuclear weapon unless it is having some sort of criticality accident (i.e. if a gun-type weapon was submerged in water it could basically become a light-water reactor). But that doesn't sound like the case here—just Hollywood B.S. (no h-bomb would use a gun-type design). (Something similar happens in the film version of Sum of All Fears, if I recall.) To be sure, a hydrogen bomb contains a lot of unpleasant and exotic material, but until it goes critical its hazards are not radioactive (they are toxic, but that's a different issue). If just being near a nuclear weapon would burn you up, you can be sure that a lot of photos would probably indicate that. --98.217.14.211 (talk) 05:02, 29 January 2009 (UTC)[reply]

When the last poster writes "its hazards are not radioactive", I'm sure the intended meaning is that there is not enough radioactivity to be an immediate hazard. I mention this because it might be taken as saying that there is no radioactive material in the bomb; and since it contains a fission bomb, that would of course be wrong. --Anonymous, 07:25 UTC, January 29, 2009.

Well, right. What I meant is, "radioactivity is really not your biggest problem in a situation like that." There are far more dangerous materials in an unexploded bomb (high explosives, beryllium, etc.). The radioactivity of an unexploded bomb will only be a problem if, say, the high explosives go off and litter the surrounding area with a nice mist of plutonium, but even that won't give you radiation burns, per se, which is characteristic of highly radioactive material. (Materials of low radioactivity are still dangerous, mind you, but not because they will burn you or give you radiation sickness—they'll get in your lungs and bones and just radiate for ages, and eventually you'll get cancer and die. hooray.) --98.217.14.211 (talk) 12:37, 29 January 2009 (UTC)[reply]

But given the timetravel and other such events on the show, I think its safe to say the laws of physics as we know them do not apply to the island and therefore anything is possible. I try to turn the scientific portion of my brain off when watching, since its more of a fantasy setting than sci-fi. I'm not quite sure why bad science doesn't bother me on "Lost" but it does on "Fringe". Maybe its because Fringe acts like it is based on real science while Lost is so far out there they don't even try. -- Mad031683 (talk) 18:21, 29 January 2009 (UTC)[reply]

Loss of memory cells

If you lose a lot of blood, will you also lose the immunological memory contained in those memory B cells you lost? Will you be once again susceptible to some diseases you've suffered in the past? Thanks for your answers. --Leptictidium (mt) 10:56, 29 January 2009 (UTC)[reply]

Typically you will retain more than one memory B cell per pathogen, so the odds of all of one of a particular type being flushed out – even with extended bleeding and multiple transfusions – is low. Further, at least some cells will likely remain in areas that won't drain readily, including the spleen and lymphatic system. TenOfAllTrades(talk) 14:20, 29 January 2009 (UTC)[reply]

Another thing to consider is the distribution of B lymphocytes in your body: Only roughly 2% of your total B cells are at any timepoint in your blood, 98% are in your tissues and lymphatic system. So the chance of completely eradicating a specific memory clone is rather low. In addition, even a heavy blood loss normally leaves several liters of blood even in a smaller human body (otherwise you will die rather quickly). So even the 2% that actually swim in your blood will not be drained completely. TheMaster17 (talk) 14:45, 29 January 2009 (UTC)[reply]

Doctors in Médecins Sans Frontières

When Médecins Sans Frontières sends a doctor to say Rwanda, Sierra Leone or whatever, what is the status of this doctor? Does he have a degree to be a doctor in these countries? Is he illegally working as a doctor but since nobody cares, he can get away with it?--Mr.K. (talk) 11:06, 29 January 2009 (UTC)[reply]

From the article Médecins Sans Frontières:

Medical volunteers include physicians, surgeons, nurses, and various other specialists, all of whom usually have training in tropical medicine and epidemiology. In addition to operating the medical and nutrition components of the field mission, these volunteers are sometimes in charge of a group of local medical staff and provide training for them.

So the doctors definitely have degrees at least in the own countries. I would assume that they don't have degrees in the countries they are flying to, but I'm not sure why you would call this "illegal." They are not prescribing drugs, and I don't think there are laws that prevent anyone at all from giving medical care, or even performing surgery. If you wanted to reset my broken arm, and I was ok with you doing it, there is no legal reason that you couldn't. — Sam 146.115.120.108 (talk) 12:18, 29 January 2009 (UTC)[reply]

This string is a bit off topic but I think the word "volunteers" is a bit misleading since although hats off to them for volunteering to go, AFAICT they are still paid a salary comparable to an expat doctor for a multi-national? However since they are paid by MSF in whatever offshore location they may not have to be qualified to practice (meaning doing paid work) locally. I know plenty of people who were medically qualified in the UK who couldn't work for pay as a doctor in whatever non-Commonwealth country Africa but were welcomed to work as unpaid volunteers there. Paid by an offshore NGO is probably similar--BozMo talk 12:31, 29 January 2009 (UTC)[reply]

It should also be noted that MSF tends to operate in areas which are often described as "Failed states" or "failing states". In many of these areas, there are may be so few qualified doctors that there does not exist any real regulatory apparatus; or the government has so little control that any regulation on paper, especially one as esoteric as the regulation of doctors (which the country may not have many of to begin with), is essentially unenforcable. Even if the doctors are not technically "certified" in the states in which they are working, its hard to imagine that, if someone showed up and said "Hey, we want to cure your 3-year old kids of Diphtheria" that anyone would turn them away. It happens (in Rwanda, for example) that sometimes the doctors are unwelcome, and are murdered as such; however in general many places recognize the charity they provide for what it is and raise no objections.--Jayron32.talk.contribs 14:48, 29 January 2009 (UTC)[reply]

@Sam 146.115.120.108: I do believe there are laws in many countries regulating medicine in general and not just people prescribing drugs.

There is still a third possibility: there may be a special UN regulation for the case of catastrophic events, and doctors working for a specific international institution only have to be certified at home. MSF - and other international institutions like Red Cross- often works in failed stated, but also in war-torn regions, earthquakes...80.58.205.37 (talk) 15:20, 29 January 2009 (UTC)[reply]

About Ocean Tides

Moon has less gravitational pull when compared to Earth's gravity.But how it is possible for moon to pull the water body(ocean) of the earth? —Preceding unsigned comment added by 117.200.112.103 (talk) 13:09, 29 January 2009 (UTC)[reply]

It's not the gravitational "pull" itself that causes the tides, it is the difference between the pulling forces at that side of the Earth that faces the moon, the centre of the Earth, and the side that faces away from the moon. Those differences are large enough to cause the tides as we see them (locally the effect can be enhanced by resonant and even interferometric effects due to the shape and size of ocean and sea basins). --Wrongfilter (talk) 13:32, 29 January 2009 (UTC)[reply]

But, if the Moon had comparable oceans, it would indeed have tides. StuRat (talk) 14:39, 29 January 2009 (UTC)[reply]

Even without oceans, the moon can have "solid" tides in the crust or mantle. That's how the moon's rotational energy dissipated to the point that now the moon always shows the same side to earth. Dauto (talk) 15:19, 29 January 2009 (UTC)[reply]

Perhaps the easiest way to think about it is that the ocean water that's closest to (vertically below) the moon feels the earth's gravity MINUS the gravity of the moon. That makes the effective gravity (and therefore the weight of the water) be a bit less there. That reduces the pressure of the water - and the higher pressure water off to the sides and further away that aren't feeling the moon's gravity quite so much are able to push inwards towards the point of least "gravity". That causes a bulge in the ocean vertically beneath the moon. It's actually more complicated than that because there are actually TWO high tides per day - one when the moon is overhead and ANOTHER when it's vertically beneath your feet.

That second tide is harder to explain:

Because the earth and the moon are rotating about a common point that's at the center of gravity of the two bodies, the earth doesn't spin perfectly about it's center - it orbits about a point that's a bit closer to the moon than the true center of the globe. So the part of the ocean that's furthest from the moon experiences centrifugal force that's a little higher than for the rest of the ocean. This results in an outward centrifugal force that ALSO causes the water to bulge outwards - but opposite from where the moon is.

To add to the complication, the sun also causes tides - but much smaller ones than the moon. So depending on the time of year and the time of the month and day - the sun's tidal force may add to or reduce the height of the tides. It ends up being rather complicated!

SteveBaker (talk) 18:32, 29 January 2009 (UTC)[reply]

Crystal violet staining for cell-counting

In a lab where I'm an intern, we perform crystal violet staining of cells for subsequent assessment of cell-growth inhibition of certain compounds. My problem is thus: the current protocol requires the removal of the medium (DMEM, 10% FBS, 1% P/S antibiotics) before addition of the crystal violet/ethanol solution. The methods for currently employed for medium removal are a) shake the (96-well) plate in a large beaker or b) pipette the medium off the bottom. Option a) results in the cell culture leaving the bottom of the plate in a more or less random pattern, leading to large irregular patches of cells disappearing. Option b) results in small marks in almost every well where abrasion by the pipette tip has resulted in removal of cells from the bottom of the plate. My solution is to add 100% formaldehyde directly to the medium without removing first (intended end concentration 10% = 20 ul formaldehyde + 200 ul medium), fixing the cells and preventing them from leaving the plate during the exercise of medium-removal-option a) (shaking the plate). Thus, my question is: will formaldehyde be able to fix cells to the bottom of the plate in the presence of the DMEM? ----Seans Potato Business 14:17, 29 January 2009 (UTC)[reply]

Not an answer to your Q, but have you considered using a needle and syringe instead of a pipette ? An even better option may be to put a sterile paper towel at the lower corner of the plate, to absorb the solution. StuRat (talk) 14:37, 29 January 2009 (UTC)[reply]

Swollen abdomen in Kwashiorkor

From the article "One important factor in the development of kwashiorkor is aflatoxin poisoning. Aflatoxins are produced by molds and ingested with moldy foods. They are toxified by the cytochrome P450 system in the liver, the resulting epoxides damage liver DNA. Since many serum proteins, in particular albumin, are produced in the liver, the symptoms of kwashiorkor are easily explained. "

Does this albumin deficiency causes the abdomen to swell? Why does it happen? 80.58.205.37 (talk) 16:32, 29 January 2009 (UTC)[reply]

According to the german language WP, albumin is mainly responsible for the colloid-osmotic pressure of blood, i.e., its content of solved substances. If that goes down, tissues near the blood will draw water, and this water can't be reuptaken by the veins---which are the most numerous in the belly. --Ayacop (talk) 17:08, 29 January 2009 (UTC)[reply]

Cause of death in the ocean

I’m curious as to what the frailest part of a person is while in the ocean. In particular say a person is in the ocean, perhaps a few miles off the coast of Florida, I’m wondering what factor would kill them if they don’t or can’t get help/swim to shore. Presumably the person would be able to float sufficiently well to not drown. And they probably don’t look enough like food to be eaten by something. So I would guess that either hypothermia, dehydration or salt overdose would be the actual killer. Any ideas as to which would come first, or how I would figure this out? Thanks 130.127.186.172 (talk) 17:41, 29 January 2009 (UTC)[reply]

In cold water, hypothermia is probably your primary concern. In extremely hot conditions, dehydration would be a problem. In more temperate conditions, exhaustion, leading to drowning, would probably be what gets you (while people float pretty well in salt water, it does take a certain amount of effort to keep your head above water, particularly in rough seas). This is just off the top of my head, though, we don't seem to have a relevant article (at least, not one I can find)... --Tango (talk) 18:00, 29 January 2009 (UTC)[reply]

Without flotation aids, I'd expect that both hypothermia and salt ingestion lead to drowning as the immediate cause of death, since those conditions would cause on to lose the ability to keep one's head above water before they actually become fatal. With a life jacket, I'd guess hypothermia is the killer for large portions of the ocean. Dragons flight (talk) 18:16, 29 January 2009 (UTC)[reply]

Guidance required.

Hello all, most initially, sorry for putting such an odd question here. But I want to create a new Project about Development of Science in Ancient India. Can anyone please tell me how should I proceed since I am new to this site? Anirban16chatterjee (talk) 17:50, 29 January 2009 (UTC)[reply]

Try the Wikipedia:Help desk for advice on how to contribute to Wikipedia (the Ref Desk is more about helping people get the most out of what is already written). It sounds like an interesting topic to write about - good luck with it! --Tango (talk) 17:54, 29 January 2009 (UTC)[reply]

Thank you very much, for rendering your kind hand of cooperation. And, thank you for your best wish! Best Regards. Anirban16chatterjee (talk) 18:09, 29 January 2009 (UTC)[reply]

Do you really mean "Project" (as in WikiProject) or do you just want to write an article? Writing an article is very easy and there are lots of tutorials out there. However, if you really do want to start a project (as in a collaboration between a number of editors to write, grade, produce standards and maintain a body of articles relating to a common topic) then I STRONGLY recommend that you write some articles in the areas of your interest, gradually find out who the active editors in those areas are - get to know them and gradually form a consensus to start a 'Project'. If a relative newcomer just dives in and starts trying to do such ambitious things - well, let's just say that it won't end well!

If you do actually just want to write an article then I recommend starting with Wikipedia:Introduction, then Wikipedia:Introduction_2, then go to the full Wikipedia:Tutorial. There are lots of quick guides out there - I'm going to recommend the one on my own off-site Wiki: http://www.sjbaker.org/wiki/index.php?title=The_simplest_possible_guide_to_writing_MediaWiki

There are already a couple of dozen WikiProjects relating to India Wikipedia:WikiProject_Council/Directory/Geographical/Asia#India and also a fairly large and active project that handles issues relating to the history of science in general: Wikipedia:WikiProject_History_of_Science. You might want to talk to the people on those projects about your ideas...I'm sure you'll find them a helpful and useful resource.

SteveBaker (talk) 18:18, 29 January 2009 (UTC)[reply]

Tons to kN conversion

I've found a source relating to the collapse of a bridge saying that the wind "applied an estimated lateral force of 90 tons (40 kN)" I pretty sure "kN" is kilonewtons, but which type of ton (short ton-force, long ton-force ect) is given? I have tried converting them myself, but I couldn't get the numbers to match up. --D.B.^{talk•contribs} 17:58, 29 January 2009 (UTC) [reply]

I can't get the numbers to match either... If I'm doing the conversion right (well, typing the right things into google!), 90 short tons-force is 816 kN, 90 long tons-force is 914 kN and 90 metric tons-force (tonnes) is 900 kN. Perhaps tons-force isn't related to tons-mass in the way I would think (1 tons-force being the weight of 1 ton at the Earth's surface). Our article, Ton#Units of force has the necessary numbers, and they give roughly the same answers as I got (the difference is probably because I used g=10m/s², not 9.81), and certainly not anything close to 40kN. I think your source is wrong. --Tango (talk) 18:08, 29 January 2009 (UTC)[reply]

NPN transistor as a switch

Would this work? If not, why? Normally the transistor is wired up differently (emitter connected to ground).

File:NPN transistor switch inverse.png