Wikipedia:Reference desk/Archives/Science/2009 April 28

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April 28

Microgravity and Moon missions

Astronauts in orbit around the Earth experience microgravity because they are in free fall--there are lots of explanations of this phenomena out there. But what gravitational effects did the Apollo astronauts experience while they were in transit to the Moon, since they weren't in orbit anymore? 128.103.197.57 (talk) 00:11, 28 April 2009 (UTC)

In earth orbit, in moon orbit, or in a trajectory between the earth and moon or between the earth and another planet, for all the recent talk of "microgravity" the astronauts and everything in and near their craft are essentially weightless, in free fall. They are literally falling. Only when the craft is spinning or is accelerated by rockets are they other than weightless. Food or liquid released in midair stays there, affected only perhaps by air currents of static charges. Anyone can put on his/her pants two legs at a time with ease (as one astronaut demonstrated). There is no "up" or "down." Edison (talk) 00:17, 28 April 2009 (UTC)

Some astronauts vomit because of the weightlessness. How many of them undergo that? Wouldn't it be a good idea to use sailors as astronauts?—Preceding unsigned comment added by 98.21.107.234 (talk) 00:37, 28 April 2009 (UTC)

I suppose that's why astronauts undergo training, and those who manage not to vomit in training, or learn to control their reactions, are those that actually get a ticket to orbit. --Ouro (blah blah) 06:20, 28 April 2009 (UTC)

Apparently, about half of astronauts suffer from Space adaptation syndrome (space sickness), but it doesn't last too long so it is usually just accepted as part of life in space. I'm not sure if being used to dealing with motion sickness would actually help, our article doesn't say if any particular people are more susceptible than others. --Tango (talk) 12:13, 28 April 2009 (UTC)

Astronauts returning to earth experience deceleration as soon as their craft enters the atmosphere. Cuddlyable3 (talk) 13:01, 28 April 2009 (UTC)

Spaceships don't normally rock back and forth like boats (with one exception). Throw in the fact that the sailors would have to have a lot of advanced education and training, and it would seem to be an impractical idea. Clarityfiend (talk) 18:40, 28 April 2009 (UTC)

The Apollo astronauts did not follow a straight-line course to the moon. So I am pretty sure that you'll find that the answer is that the astronauts were in freefall any time they weren't accelerating.

Consider this thought experiment : If the Apollo capsule was stationary with its engines off halfway between the Earth and the Moon, would the astronauts feel Earth's gravity? No. Because the capsule would fall. With nothing holding it up the capsule would fall like a broken elevator. When you're falling you don't feel gravity. APL (talk) 14:07, 28 April 2009 (UTC)

It goes without saying that if their engines were not turned on and there is no air or ground or other form of drag or thrust forces on their spacecraft then there could only be free-fall. Since that was the case for most of the trip - they were in zero g most of the time. However, whenever they turned the engines on - there would be acceleration - and therefore some kind of pull that they would feel just like gravity. The term "free fall" is really better than "zero-g" - any time you're falling freely you're not going to feel the force of whatever gravity there is. It is a common misconception that the people on the International Space Station are "in zero g" just because they are out in space. But that's not the reason - it's because they are falling freely. If they tried to hover over one spot on the earth at their present altitude (which would require some seriously impressive engines) - they'd feel gravity almost as strongly as we do. SteveBaker (talk) 23:00, 28 April 2009 (UTC)

The principle of equivalence seems like a relevant link here. --98.217.14.211 (talk) 00:58, 29 April 2009 (UTC)

Dogs with "hair" instead of "fur"

Often I'll talk with a dog owner who claims their particular breed of dog has "hair" instead of "fur". Is this a bunch of nonsense? Our fur article says that "fur" means "the hair of a nonhuman mammal". I think the distinction these dog owners are trying to make is that their dog's breed doesn't shed, or doesn't shed as much, as dog breeds that have "fur". Nonsense or truth? Tempshill (talk) 02:26, 28 April 2009 (UTC)

Well, the distinction between "hair" and "fur" is pretty arbitrary (making humans the special case has nothing to do with biology). What they probably mean is that the fur in question more resembles human hair than it does other dog furs. --98.217.14.211 (talk) 02:37, 28 April 2009 (UTC)

We have a pretty detailed article on Coat (dog). --Dr Dima (talk) 03:39, 28 April 2009 (UTC)

They are just words - there is no special scientific definition of fur versus hair. SteveBaker (talk) 04:14, 28 April 2009 (UTC)

Coat (dog) seems to imply that the "hair" people are talking about the dog not having an undercoat. Thanks! Tempshill (talk) 05:11, 28 April 2009 (UTC)

Hair IMHO refers collectively or individually to strands that are relatively long and can be directed (combed) individually. Fur is always a collective word for relatively short strands that trap air that can keep one warm. Cuddlyable3 (talk) 12:51, 28 April 2009 (UTC)

the sun's surface

Given that the sun consists of gas, I'd expect it to look like a density gradient rather than suddenly becoming opaque at a well-defined sphere. What changes at that level? —Tamfang (talk) 06:21, 28 April 2009 (UTC)

There is no level. As I said in a response to an earlier post today, photons of different energies escape, on average, from different depths. For any photon, the deeper within the Sun it was emitted, the lower is its probability of escape. For a photon of a given energy, there is formally a certain depth from which the probability of escape is exp(-1); probability of escape from deeper layers is smaller, and probability of escape from less deep layers is higher. That particular depth is the depth where the Sun becomes "opaque" for that particular energy of a photon. The important thing is that that depth is different for different photon energies. X-ray photons escape from deeper layers than visible-light photons, and photons at the centers of spectral lines usually escape from shallower layers than continuum photons. If you need more detail, please see Opacity (optics). --Dr Dima (talk) 07:53, 28 April 2009 (UTC)

So when astronomers speak of the limb of the sun, e.g. for defining the beginning and end of a transit, they mean a level above which, for visible light (of a specified color?), the opacity factor is e? —Tamfang (talk) 18:30, 10 May 2009 (UTC)

You are correct, there is no well defined surface of the sun. The corona extends a long way out from what we would usually consider the surface, it just gets more and more tenuous. The same is true of the Earth's atmosphere, the exosphere doesn't have a well-defined top. --Tango (talk) 12:08, 28 April 2009 (UTC)

(sigh) I'm not fishing for agreement, I'm asking why there is something that "we would usually consider the surface", and what that something is. —Tamfang (talk) 18:32, 10 May 2009 (UTC)

Homo floresiensis and microcephaly

Skeptics are saying the homo floresiensis are homo sapiens ("us") with the serious disorder microcephaly. Given that microcephaly happens to us tragically often, could it be it is an "obsolete" and ancestral trait we share with homo floriensis, and it is blocked from appearing in humans unless the genes that now prevent it are disabled or missing, or (or perhaps the same thing)the genes that caused it are allowed to be expressed? Let me try to say what I mean again:The hobbits do have microcephaly, but it's not a disorder? For us, it's a disorder?Thanks, Rich (talk) 07:14, 28 April 2009 (UTC)

I think basically the question is unanswerable. How could anybody know if microcephaly would have been seen as an disorder in these hominids, if we don't know what was their "normal" state? It all depends on the basic question: Were these people Homo sapiens or where they something different? As long is this is not answered, you cannot derive anything about deviation from any "norm". TheMaster17 (talk) 08:48, 28 April 2009 (UTC)

I don't understand why whether they were homo sapiens or not is the basic question. It seems to me that whether they were diseased or not is at least as basic. After all, if they weren't homo sapiens, they might be a diseased form of some other hominid. In addition, if we find further remains, perhaps of a fetus, we might figure out if the small brains were normal to them. And in us, maybe geneticists will find a large ensemble of unused and perhaps degraded genes that code for the development of microcephalic but potentially "thrivable" offspring. Thank you for your comments.Rich (talk) 09:15, 28 April 2009 (UTC)

I think you misunderstood what I wanted to express: The presence of a disorder can only be stated if the normal state is known. So only when we know what kind of hominids these people were, can we say anything about disorders. There is no alternative to this approach I could think of, because every other method to infer "disorders" of some kind are just speculation and extrapolation from known hominids. And how would you, to mention your example, infer from a fetus what the "normal" state would be in an adult? Human fetusses are far from finished when you look at body proportions, and as long as you don't know what kind of hominids you are looking at, you cannot safely transfer any proportion of growth (even when you know the species, this may not be possible, as growth patterns have changed during hominid evolution). I think I didn't get your last point: What would an unexpressed gene in humans tell you about the unknown kind of hominid on Flores? (btw: There is no such thing as a degraded gene. Genes change all the time, and these changes are what enables evolution, allowing changes in the function of the geneproduct.) It is not possible to infer a function from a genomic sequence, just to make an educated guess at the parts that the product would have. So finding a gene (or the remnants of a once-active gene) would never tell you that it would cause microcephaly in humans. TheMaster17 (talk) 09:47, 28 April 2009 (UTC)

The Nova documentary I just finished watching on this very topic said (with convincing detail) that the microcephaly theory is busted and it's pretty clear now that they were indeed a separate species. Small bones in the Hobbit's hands are a close match for apes and are quite different from those in later hominids. Also, most of their anatomy is very close indeed to "Lucy" - another early hominid specimin. Conclusion was that the Hobbits were simply a parallel thread of evolution - an almost completely separate species (far more separate than, for example, the Neanderthals). Still around on their idyllic island until maybe 18,000 years ago - probably wiped out by a volcanic eruption. SteveBaker (talk) 02:30, 29 April 2009 (UTC)

blank (colored) skew-T

Hi, does anyone have a high-resolution blank skew T, like the on at [1] but without the artifact in the midddle. It's kind of urgent. John Riemann Soong (talk) 07:20, 28 April 2009 (UTC)

Also, why is it so hard to get a proper high-resolution computer image of a *real* skew-T diagram? Isn't this supposed to be like, public domain information? John Riemann Soong (talk) 07:59, 28 April 2009 (UTC)

Do either of the diagrams at Skew-T log-P diagram help? Cuddlyable3 (talk) 12:28, 28 April 2009 (UTC)

I'm guessing that while the information ON the diagram may be in the public domain, the weird triangular graph paper it's drawn onto belongs to some graph-paper printing company who's copyright you'd be violating if you posted a blank sheet of the stuff online and at useful resolutions. You can get free graph paper in PDF form here (A very useful site that should be in every working scientist's bookmark folder!) - but not with all of the shading and peripheral annotations in the JPEG image you linked to. Still, since it's an emergency - perhaps something there will suffice for your needs. SteveBaker (talk) 12:30, 28 April 2009 (UTC)

Is a simple geometric pattern copyrightable? --Tango (talk) 12:33, 28 April 2009 (UTC)`

No. But if applied to a product as a novel part of its design (artistic or functional) then yes. The graph on a graph paper is not IMO novel. Cuddlyable3 (talk) 12:43, 28 April 2009 (UTC)

viruses again

How many viral diseases can be cured by modern medicine? Is it more then 100? 65.121.141.34 (talk) 12:59, 28 April 2009 (UTC)

Cured??? Most viral illnesses are self-limited and don't need to be "cured". For the common viral illnesses everyone is familiar with (the "common cold", the "flu", "viral gastroenteritis" etc.) we treat the symptoms and let the immune system do the rest. There are very few modern medicines that directly kill a virus or interfere with the mechanisms of viral entry into the host cell, replication, or dissemination. Far fewer than 100. Probably 10-20 at best (at least in widespread use). The antiviral drug article has a useful summary of some of the approaches. --- Medical geneticist (talk) 13:52, 28 April 2009 (UTC)

(EC)Check out Oseltamivir for a topical example, and antiviral drug, which even links to a list of antiviral drugs! You'll notice most of these aren't cures, rather treatments. Aaadddaaammm (talk) 13:58, 28 April 2009 (UTC)

(multiple ec) In the strictest sense: none. Medicine does not cure a disease, it only treats the disease so that the body itself can cope with it better. Another problem is in numbering virusses: They mutate very fast, so would you count every different strain as a new kind of virus? Or only broader groups, like influenza? So it depends on the perspective. Have a look at viral disease, but this list is far from complete, as stated. In what context do you want to know this "number"? Concerning the previous answer to this topic: what is "killing a virus"? It's as meaningful as "killing a shoe", because virusses are not considered to be living by most if not all current definitions. TheMaster17 (talk) 13:59, 28 April 2009 (UTC)

Maybe "inactivate" or "destroy" would be better terms? Although I was under the impression that the jury was still out on considering viruses a life form or not.-RunningOnBrains 14:08, 28 April 2009 (UTC)

Ok, I used "kill" in the colloquial sense -- as in the way you can "kill" the motor on a machine. --- Medical geneticist (talk) 14:38, 28 April 2009 (UTC)

I can just judge from what I know: In my studies of biology, I never met any biologist who considered virusses to be lifeforms. Every definition of life I know excludes virusses, because they always lack central properties of life: homeostasis, response to stimuli, growth and/or undergoing cellular division, a metabolism of their own. For sure it is possible to speculate about some form of "non-cellular life", i.e. some other kind of physical system which shows all characteristics of life. But this only blurs the everyday meaning of the word life: life as we know it on earth. And in this sense, a virus is "just" a very complex transportation device for nucleic acids. Without the machinery of a living cell it is only sitting around, slowly degrading. TheMaster17 (talk) 14:44, 28 April 2009 (UTC)

Medical geneticist, I could guess that you meant it colloquial, but as the initial question had some rather blurry words and concepts, I wanted to make clear that a virus is not living, and that many other misconceptions follow from this original one. A blurry answer to a blurry question usually helps nobody ;-). TheMaster17 (talk) 14:50, 28 April 2009 (UTC)

Viruses are not individually living any more than toenail clippings are, but they are clearly part of life in a holistic sense. They certainly require other living beings to aid them in most of their life processes, but they aren't "non-living" either. So, are my toenail clippings living? Well, no. But are they entirely outside of the concept of "life". No on that either, since they would not exist without life. The convenience of classifying something as living or not is arbitrary; even deciding what constitutes an individual organism can be tricky (see Lichen). So the question is more Is a virus an organism No, it probably isn't. But it still part of "life". --Jayron32.talk.contribs 01:43, 29 April 2009 (UTC)

Jayron, I don't agree with your definition of life, but I can understand that some people like the idea of "the entire earth constituting a living being", then that is what you are running into when you follow this line of thought. I'm perfectly fine with calling my toenail clippings dead and never living: Just because they were built by living cells, they are not anymore living than for example the skeleton that corals built or the slime that snails excrete. Whatever you do with your toenail clippings, they will never have a metabolism or be able to divide and grow on their own. But we are getting rather off-topic. TheMaster17 (talk) 06:54, 29 April 2009 (UTC)

Well, if what you said were my definition of life, i would disagree with it too. What I said was that Viruses were part of life in the sense that they are not part of geology. Granite is certainly not living. I never once said that the whole earth constituted a living being That bullshit never was typed by me, and I would appreciate it that if you were going to refute my arguements, it would be helpful if you actually refuted my arguements, and not arguements you decided I made. Seriously. Now, back to this issue. If we have to draw a bright line somewhere and say "this stuff is part of life and its processes" and "this stuff on the other side has nothing at all to do with life and its processes" then viruses clearly fall on the "life" side of the equation. They certainly are not part of geologic processes; the weather does not create them. They are here on earth, and they exist because of life, and are part of life. Look at it another way: If we take an earthlike planet that never had life on it at all, and never would ever produce life in the future, could you imagine viruses existing? --Jayron32.talk.contribs 01:36, 30 April 2009 (UTC)

Viruses are much closer to living organisms than toenail clippings are. No matter where you put a toenail clipping, it will not cause another toenail clipping to be generated.

The distinction about whether viruses reproduce "on their own" is specious. Do we reproduce on our own? Viruses (some of them at least) have clearly functional machinery adapted to parasitizing cells and thereby reproducing themselves. They do need the cells to do it, but so what? The cells are prey. Lots of organisms can't reproduce without a specific parasitic host.

It's also not true that viruses (some of them at least) don't respond to stimuli — they attach to specific surface features of cells, and respond by inserting their genetic material.

The main distinction, which is true, is that they don't have a metabolism. If you think that makes them "not life", then fine, that's your definition and you're welcome to it. But I think you can see how others might reasonably disagree. --Trovatore (talk) 07:49, 29 April 2009 (UTC)

(unindent) I think we are really getting into a philosophical discussion here: What is "on its own" (so basically, what constitutes "self")? What is "reacting to stimuli" (Is a lock reacting to stimuli when it opens the door after I have turned the key? Basically this is the way that insertion mechanisms in virusses work.)? If you want, we can talk about this on my talk page, but for the starting question, this is off-topic. But you are totally right that I can see how others can reasonably disagree: This is really muddy water and many generations of very bright people have discussed this, and all depends on very personal definitions of cause and effect. TheMaster17 (talk) 08:31, 29 April 2009 (UTC)

anatomy of urinary system

What is the importance of the adipose capsule that surround the kidney? —Preceding unsigned comment added by 151.202.113.5 (talk) 19:00, 28 April 2009 (UTC)

Mostly protection from trauma, see renal capsule. Regards, --—Cyclonenim | Chat  19:04, 28 April 2009 (UTC)

Labratory construction

what are the Requirements for a legal research lab? are there forms that would needed so it would be reconized by the state? —Preceding unsigned comment added by 66.237.50.35 (talk) 19:11, 28 April 2009 (UTC)

Recognized for what purpose, and by what state? You'll need to give us more to go on. APL (talk) 19:15, 28 April 2009 (UTC)

The purpose and use are extremely important. You need to think about biological and chemical hazards, radiation safety, and protocols for any animal work - among a slew of other things. Wisdom89 _{(T / ^C)} 19:32, 28 April 2009 (UTC)

An easy place to check for local regulations is your local City Hall, if such a thing exists where you live. There are permits needed for places that serve food, places that handle food ... there are possibly permits for places that handle such-and-such types of chemicals or animals or nuclear fusion reactors or whatever it is you're planning to conduct research on. Tempshill (talk) 00:50, 29 April 2009 (UTC)

Wearing Black on a hot day

People keep telling me to wear lighter colors when it's hot. None of them seem to know precisely why they think this is a good idea.

Is this sound science, that the lighter the color, the less hot you'll be?192.136.22.6 (talk) 19:15, 28 April 2009 (UTC)

I don't think it is quite that simple. Light colours reflect heat better so they stop you getting warmed up, however they are worse at radiating heat, so they stop you cooling down. There are desert tribes that traditionally wear black, and they probably know what they're doing when it comes to staying cool. Dark colours can also help protect your eyes from the bright sunlight (I've seen it suggested that you wear black paint/soot/whatever under your eyes in bright sunlight if you don't have any sunglasses). I think it is more important to wear lose fitting clothing that covers most of your body (exposed skin is at risk of sunburn, etc.). An unbuttoned shirt worn over a t-shirt is supposed to work well. --Tango (talk) 19:31, 28 April 2009 (UTC)

As a long-time desert dweller, I can tell you from experience that in a hot sun, light is a lot better than dark -- the heat absorption of dark clothes is the dominant factor. If it's hot because you're in the jungle, it might not make much of a difference. Looie496 (talk) 20:09, 28 April 2009 (UTC)

As a camper, one of the luxery items you can buy are shower bags. They are entirely black, you fill them up with water and leave them in the sun and they warm up. Then you hang them from a tree and have a warm shower. If it weren't black it probably would get much hotter than the ground around it, but the can get quite warm. Anythingapplied (talk) 20:33, 28 April 2009 (UTC)

You need to read "Why Do Bedouins Wear Black Robes in Hot Deserts?" by Taylor, Finch, Shkolnik and Borut, Nature 283, 373-375 (24 January 1980). That's a subscription-only link, but there's a summary in the Guardian here. To summarise, white garments let more radiation in while black ones absorb more, so the effects almost balance out. --Heron (talk) 21:08, 28 April 2009 (UTC)

QI says it makes no significant difference what you wear. Vimescarrot (talk) 21:20, 28 April 2009 (UTC)

The simple answer is that the color black absorbs light (that's why its black.), the energy from that absorbed light is transformed into heat. Therefore, on a sunny day, a black object will be noticeably warmer than a similar white object.

As mentioned above, the situation with clothing is complex because so many additional factors go into it, including how the clothes "breath", how much sun penetrates the cloth and hits your skin, etc.

If I had to theorize, I'd bet that a cloth that was black on the inside and white on the outside might keep you coolest, but that's just a wild guess. APL (talk) 21:25, 28 April 2009 (UTC)

The question is largely to do with whether the heat is conducted into your body (because the air temperature is above body heat) or radiated into your body (from the sun). If the heat is in the air itself - then no amount of light-colored clothing will help you to avoid that - and the light colored cloth reflects heat that your body is trying to radiate back in again - so black clothing would be cooler. However, if the heat is coming from the rays of the sun - then reflecting them away is a big win compared to the downside of a reduction in the amount of heat your body can radiate. Hence - (although I'm slightly hesitant of my conclusion) it ought to be better to wear dark clothing in the shade - and when the air temperature is above body heat - and you're better off with light clothing in sunlight and when the air temperature is below body heat.

Furthermore - let's examine the whole premise of this. Do Bedouins really wear black out in the desert? Sure, we're all leaping to that conclusion - but is it actually true? Let's take a look at the WikiCommons photos in Category:Bedouins [2] - and the first few pages of photos from a Google/Images search on "Bedouin" - a rough count says that about two thirds of those photos are of people wearing light colored clothing - with only a third or so in black or other dark colors (there are some judgment calls to be made on blue, green and striped clothing - also white headgear with black robes - so it's not a "Black and white" question!). Perhaps these people are aware of the kinds of distinctions I describe. If you're planning to spend the day in the shade of your tent on a hot day - wear black - if you're out on your camel doing whatever it is you do - wear white. If you're in your honking great SUV - crank up the A/C and wear a hawaiian shirt? SteveBaker (talk) 22:44, 28 April 2009 (UTC)

Well to be fair it was in Nature. Also if you look more carefully at the category, most of the black and white images show dark coloured clothing. These are likely I expect to be the older images (in general) so it's possible Bendouin clothing colour choice has changed over the past 100 years or so particularly since anyone there is obviously interacting enough with the outside community to be photographed. (It's also quite ORry.) None of this of course means the reason they choose black coloured clothing has anything to do with whether it keeps them cooler Nil Einne (talk) 02:20, 29 April 2009 (UTC)

Environmental Science

What two words define the lack of minimal neccesities of life? —Preceding unsigned comment added by 12.175.230.58 (talk) 20:01, 28 April 2009 (UTC)

Death and dying. Looie496 (talk) 20:10, 28 April 2009 (UTC)

Starvation and dehydration? Tempshill (talk) 00:48, 29 April 2009 (UTC)

That doesn't work - oxygen and air pressure are also minimal necessities and without them, starvation and dehydration are not a problem! SteveBaker (talk) 02:26, 29 April 2009 (UTC)

Doyour and ownhomework? --Jayron32.talk.contribs 01:35, 29 April 2009 (UTC)

drinking hot liquid through a straw

why does drinking hot liquid through a straw make it taste hotter than just drinking it out of the cup?

Fuzzi logic (talk) 20:36, 28 April 2009 (UTC)

It may literally be hotter if you're taking fluid from the center of the cup instead of sipping at the surface. Do you still notice the effect if your stir the drink well right before you take your sip? APL (talk) 21:27, 28 April 2009 (UTC)

"Taste hotter"?

Anyway, another reason might be partial cooling of the liquid as it passes your lips on its way to the tongue, rather than being channeled straight to your tongue through a straw. ~Amatulić (talk) 22:04, 28 April 2009 (UTC)

Indeed and I would expect the initial contact (surface) area when your sipping to be larger then when you're drinking from a straw Nil Einne (talk) 02:25, 29 April 2009 (UTC)

You'd expect the straw to allow for extra cooling of the liquid - so my bet is with User:APL - try placing the end of the straw as close to the surface and as near to the edge of the container as possible. That's where you'd be sipping liquid from if you weren't using a straw - not the middle/bottom of the cup where it's undoubtedly hotter. SteveBaker (talk) 22:28, 28 April 2009 (UTC)

I don't see why it would though. The liquid doesn't stay in the straw for long. A straw has a low heat capacity and quickly heats up and is surrounded by an insulator (air). Your lips have a large heat capacity and are better conductors. Of course either way it may or may not be enough to make a significant difference Nil Einne (talk) 02:25, 29 April 2009 (UTC)

This is my theory, and it depends on how you drink from the cup. If you "slurp" from the edge of the cup like I think many people do, you may actually be drinking the hot liquid at a slow rate, and you're sucking quite a bit of air into the mouth in the process. The air flow causes both convective(?) and evaporative cooling of the hot liquid right before it gets into your mouth. Compare this with drinking through a straw, you may be drinking at a faster rate in the latter case. A plastic straw is not a good conductor of heat and there's little convective and no evaporative cooling as the hot liquid is sucked into your mouth. (There's another mechanism I can think of that contributes to the difference, which would be more significant if you're drinking from a relatively empty cup and/or if the cup is a good conductor of heat.) --98.114.146.142 (talk) 04:52, 29 April 2009 (UTC)

According to this patent, the problem arises when the liquid hits the roof of the mouth first, which is more sensitive to heat. I've noticed that to a certain extent, but it still feels hotter when it reaches my tongue. bibliomaniac15 The annual review... 04:59, 29 April 2009 (UTC)

I don't think the patent's explanation accounts for all the factors that contribute to the perception. --98.114.146.142 (talk) 11:58, 29 April 2009 (UTC)

Bleeding from the eyes

Is it possible to sniff blood from the nose into the eyes during a nosebleed?

In my experience, most medical people say it is impossible to bleed from the eyes. Many online posts from the general public on the subject though suggest that if fluid can drain from the eye into the nose, when you cry or with an allergy for example, surely it could also go the other way, resulting in the blood from the nose being secreted from the tear duct.

Can anyone clarify this for me please?

Kazlox (talk) 20:48, 28 April 2009 (UTC)

There is a duct or channel from the eye to the nasal cavity that allows for drainage of tears. After Lasik surgery, a common complication is dry eyes, and a common cure is for an optometrist to put tiny plugs into the channel openings to prevent the tears from draining and keep the eye moist.

Because that duct exists (and I have seen some people hold their nose and manage to force air up into them and out the eyelids), it would be possible to force a blood through those ducts, if you have a noseful of blood to start with. ~Amatulić (talk) 22:02, 28 April 2009 (UTC)

Wikipedia has an article: "Haemolacria" (albeit a stub). Axl ¤ [Talk] 06:47, 29 April 2009 (UTC)

It's possible to suck milk up the nose and squirt it out the eyes[3]; YouTube has videos. So blood would be similar. --Maltelauridsbrigge (talk) 15:00, 29 April 2009 (UTC)

I have personally seen a kid who had excessive (and habitual) nosebleed bleeding from his eyes. He had much more than a noseful of blood in there and it went up the Nasolacrimal canal. So, quite possible. 88.242.252.196 (talk) 15:12, 29 April 2009 (UTC)

Huge lack of Vitamine K can result in bleeding eyes, or, it could also occur if it is an allergic reaction. I've had it happen to me before, but then again, my family has very bad medical history... That's just me though, if people can sniff milk and make it come from their eyes, and cry milk, then it IS possible to do the same with a REALLY bad nose bleed(AKA Not Minor). Look it up on YouTube. It happens. Another way to bleed from the eyes, is if when you cry, your tear ducts produce too much adic, and burn the inside of your eye lids, and you eye ball, resulting in you, quite literally, crying tears of blood. Hope I was of any help for you..! ^^ Gothrokkprincess (talk) 20:03, 4 May 2009 (UTC)

Testing for 2009 swine flu

What lab test is done to see if a flu virus is a case of the 2009 swine flu outbreak? What is the false positive rate and false negative rate, and how long does it take to get a result? Edison (talk) 20:49, 28 April 2009 (UTC)

PCR is performed on a nasal swab to detect Influenza A (Swine flu falls within this category) or Influenza B. The turnaround time in a good clinical lab should be within 8-12 hours, or 24 hours at the longest. If positive, the lab should reflex to type the specimen. That probably takes another few days, but they wouldn't wait to initiate therapy if the PCR was positive. The PCR-based assays are very sensitive (95-99%) and specific (90-99%). With the second typing assay on all PCR positives you'd end up with very few false positives. The rapid antigen screens that are sometimes used would be less reliable and give significantly higher false positives. --- Medical geneticist (talk) 21:09, 28 April 2009 (UTC)

Agree, but would add that Electrospray ionization mass spectrometry is accurate, much faster than conventional analysis of PCR products, can provide results in under 3 hours, and the sample processing rate is about 1 specimen per minute (PMID 17534439). Amazing - though the hardware isn't available in many places at this point. --Scray (talk) 01:26, 29 April 2009 (UTC)

What does "the lab should reflex to type the specimen" mean? --Sean 15:51, 29 April 2009 (UTC)

Sorry for the jargon. What I should have written was: If the PCR is positive for Influenza A, The "reflex response" from the lab should be to perform an additional test to determine the specific subtype. --- Medical geneticist (talk) 16:49, 29 April 2009 (UTC)

OK, thanks. Is there movement towards having a generic system wherein you could stick a swabbed sample into a machine, download H1N1.xml from www.cdc.gov, and have the machine say "match" or "no match"? --Sean 14:37, 30 April 2009 (UTC)

Elastic Potential energy

If you apply stress pass the point where the potential energy growth is linear, will you get less energy back, or does it just mean you're applying less energy to store the energy? 99.227.94.24 (talk) 21:14, 28 April 2009 (UTC)

If you applied less energy than was stored, that would involve energy appearing from nowhere, so that can't be happening. When you go past the elastic limit of an object it permanently deforms, which uses up energy, that is why you get less back. --Tango (talk) 21:56, 28 April 2009 (UTC)

Sorry about that, I was referring to the growth in energy in graphs. Probably should have made that clearer. But that answers the question anyhow. 99.227.94.24 (talk) 23:16, 28 April 2009 (UTC)

Electrodynamic potential energy

How can electrodynamic potential energy be liberated? When a electric motor spins, is it turning electrodynamic potential energy in to mechanical energy? 99.227.94.24 (talk) 23:55, 28 April 2009 (UTC)

Electrodynamic potential energy is a term I am unfamiliar with, but it sounds like the energy stored by electrically charged particles which are in the presence of other electrically charged particles. If I have two electrons which are being held stationary near each other, the repulsive force between them implies that there is a potential energy generated by their proximity. Anything which causes these electrons to go from a stationary state into one of motion away from each other will convert that potential energy into kinetic energy. --Jayron32.talk.contribs 01:31, 29 April 2009 (UTC)

Apparently, electrodynamic potential energy is the same as magnetic potential energy. The power supply to the motor creates a current in the motor windings. The entire circuit consisting of the power supply and the windings induces a magnetic field, which contains magnetic potential energy. The magnetic field exerts a force on the rotor. As the rotor moves, energy is transferred from the magnetic field to the rotor, which gains kinetic energy. So the answer to the question appears to be "yes". --Heron (talk) 09:35, 29 April 2009 (UTC)

But the whole setup is in a steady state: as long as the motor keeps getting power it will keep producing useful work, but the energy stored in the electromagnetic field won't change. The energy source that's ultimately being depleted in exchange for the work is probably chemical or nuclear or hydroelectric or wind or solar. Only if you powered the motor by a capacitor would you really be converting stored-up electromagnetic field energy into work. -- BenRG (talk) 18:55, 29 April 2009 (UTC)

I'm not saying you're wrong, BenRG, but there are two ways of looking at this. It's only a steady state if you think in the frequency domain and ignore the fact that the magnetic field in the motor is alternating or rotating. I was thinking in the time domain, where a non-steady state exists as the magnetic field alternates. As one half-cycle of the field builds up, the power supply feeds energy into the field, which pushes the rotor round a bit. As the field collapses, some of the energy returns to the source minus the energy that it took to push the rotor. Then the cycle begins again with the opposite polarity. In that sense, some of the magnetic energy of each half-cycle is being transformed into mechanical energy, isn't it? --Heron (talk) 18:39, 30 April 2009 (UTC)