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March 22

Automatic crossbow

Has there ever been such a device as a fully automatic crossbow? If not, is there any technical reason why not? --Kurt Shaped Box (talk) 01:14, 22 March 2008 (UTC)

Well we have an article repeating crossbow. Also take a look at Zhuge Liang#Legacy the ancient chinese supposed inventor of these.

Also this thread [1] describes unmanned automatic crossbows mounted on chariots driven by the turning chariot wheels and flung at the enemy by setting fire to the horses tails. No idea how reliable this source is, but it conjures up a wonderful picture. SpinningSpark 01:36, 22 March 2008 (UTC)

I'll test this next time I go by a stable, assuming I can find a used chariot. But what happens when the horses turn around and come running back? Maybe that's why this method of warfare didn't catch on? :) Franamax (talk) 12:27, 22 March 2008 (UTC)

Just be thankful that you weren't fighting alongside war pigs (if they ever existed). --Kurt Shaped Box (talk) 13:17, 22 March 2008 (UTC)

Why would they come running back? If someone set your arse on fire would you go back there? SpinningSpark 13:29, 22 March 2008 (UTC)

If I was on fire, I probably wouldn't be paying that much attention to where I was running. --Kurt Shaped Box (talk) 13:37, 22 March 2008 (UTC)

(e/c) Ahh, war pigs, I always wondered what Black Sabbath was going on about! SS, why would the horses keep running in a straight line? If your butt's on fire, do you keep track of directions? (Don't try this at home kids) What I was thinking of though is that they might run back towards some of the unburnt horses they were just hanging around with, horses tend to do that. And they would have kept at least one horse for the general to ride afterwards, right? Who wants to ride a smelly burnt horse? :) Franamax (talk) 13:45, 22 March 2008 (UTC)

water heater is making a whining sound

I live in a two story house. Our water heater is making a whining sound that can be heard all through the house. I'm afraid that a pipe or the water heater is going to blow and cause a terrible problem. Do you know what could be making the whining sound that has never been heard in our house before? What can we do about it?

Gas? Fueloil? Electric? Immersion? A little more detail would help. --BozMo talk 06:55, 22 March 2008 (UTC)

It sounds like you need a plumber to not only examine the water heater, butt crack this problem wide open before a serious leak occurs. StuRat (talk) 11:41, 22 March 2008 (UTC)

Googling on "water heater" whining provides many useful links. I have heard that they can make noises when there is a layer of deposits in the bottom in which water can become superheated and be forced through the deposits. It is possible that the pressure relief valve is starting to leak. I would warn you that the water heater is nothing to mess around with; when things go wrong they can go wrong big. Here is a video from Mythbusters that proves that. --Milkbreath (talk) 13:35, 22 March 2008 (UTC)

I'd amend that to "the water heater is nothing to mess around with if you don't know what you're doing". In my opinion that Mythbusters video is (like much popular entertainment) somewhat alarmist. The fact that you never hear about water heaters exploding like that in real life is good proof that, virtually all of the time, the designed-in safety mechanisms work as they're supposed to. I'm not saying it never happens, but anyone who tampers with or disables a safety device such as a T&P valve displays criminal negligence and stupidity. —Steve Summit (talk) 14:05, 22 March 2008 (UTC)

Addendum: Never? Well, hardly ever. Yikes. —scs 14:10, 22 March 2008 (UTC)

Yes, the Mythbusters are not a reliable primary source as a rule, but I watched that one, and we're seeing the true consequences of defeating the safety devices, turning the thermostat up, and then simply turning the thing on and waiting. No extra explosives or other heroic measures were used for dramatic effect. Both they and I were astonished at the violence of the event. Apparently, such explosions were commonplace before the introduction of the safety valve. --Milkbreath (talk) 14:41, 22 March 2008 (UTC)

Right. But the nice thing is, today, simultaneous failures of both the thermostat and the safety valve are exceedingly rare. I'd wager that all such failures are due to capping off of the safety valve (as in the referenced Seattle P-I article, presumably because the valve was leaking). —Steve Summit (talk) 15:16, 22 March 2008 (UTC)

Best Food

If a human had to survive on just water and one other substance, what would that substance be ? —Preceding unsigned comment added by 80.5.206.57 (talk • contribs) 15:19, 22 March 2008

In order to survive as long as possible, I think it would be sodium chloride. Without it he would die pretty soon from water poisoning. Icek (talk) 15:31, 22 March 2008 (UTC)

Does cornish pasty count as a substance? Or how about earth (soil) - with earth and water you could grow your own food..87.102.16.238 (talk) 16:22, 22 March 2008 (UTC)

Guinness? Heh, I know it's probably an urban legend - but has anyone else heard it said that you can supposedly get all/most of your nutritional needs from five pints of Guinness per day? --Kurt Shaped Box (talk) 19:24, 22 March 2008 (UTC)

Much as I am always in favour of beer theories, I would go with milk, being as it is designed to do just that - provide you with all the nutrients you need to survive. SpinningSpark 21:29, 22 March 2008 (UTC)

I think a "substance" is something with a definite chemical composition, which is not true for milk, beer and the like. Icek (talk) 11:18, 23 March 2008 (UTC)

I'd go with oxygen. — DanielLC 16:30, 23 March 2008 (UTC)

Garlic for treatment of wounds

Hello, there is hearsay about usage of garlic for the treatment of wounds up to the time of WWI. For the respective WP articles, I'd need at least one account that it was official treatment. Google was no use, neither the Project Gutenberg full text search.

Do you know of a passage in a book (even fiction) where garlic was used on a wound, or its usage was recommended by an official about 100 years ago? --85.179.13.254 (talk) 17:10, 22 March 2008 (UTC)

would this help http://news.bbc.co.uk/2/hi/health/3344325.stm

Also try searching for 'allicin' if you haven't already87.102.16.238 (talk) 17:47, 22 March 2008 (UTC)

http://www.bulkherbstore.com/GM

In his book, Advanced Treatise in Herbology, Dr. Edward Shook had this to say about the valuable antibiotic properties of garlic: "The use of garlic in the 1st World War (WW1) as an antiseptic was most sensational. In 1916, the British government asked for tons of the bulbs, offering one shilling a pound for as much as could be produced. A great quantity of it was used for the control of suppuration in wounds. The raw juice was expressed, diluted with water, and put on swabs of sterilized sphagnum moss which was applied to the wounds. Where this treatment was given, it has been proved that there has never been one single case of sepsis or septic results. Consequently, the lives of tens of thousands have been saved by this one miraculous herb."

does that help87.102.16.238 (talk) 17:51, 22 March 2008 (UTC)

Can you give me the page number of that passage, please? I would like to read it myself, and see if Dr. Shook has references for that opinion. Many thanks!

To the other poster: the antimicrobial activity of garlic compounds is well established, thanks. The question is specifically about official former usage. --85.179.15.63 (talk) 07:37, 23 March 2008 (UTC)

Sorry I haven't got the page number87.102.16.238 (talk) 10:43, 23 March 2008 (UTC)

How were you able to produce that passage, then? --85.179.24.245 (talk) 15:29, 24 March 2008 (UTC)

It comes from the link he provided right before it. -Elmer Clark (talk) 00:45, 26 March 2008 (UTC)

Genetic mutation resulting in deformities of the offspring

1. In sexual reproduction, i.e., fertilization of egg by sperm, does mutation of the egg or sperm producing organs, say by means of radiation, always result in the failure of the organs to produce viable egg or sperm, i.e., egg or sperm that can result in a fertilized egg? In other words, are deformities in an offspring due to mutated egg or sperm producing organs?
2. If mutated egg or sperm producing organs are not responsible for deformities in an offspring then is mutation of the egg or sperm, say by irradiation, after they are produced and prior to fertilization responsible for deformities in the offspring?
3. If deformities do not result from mutated egg or sperm occurring after they are produced, say by irradiation, then are deformities in the offspring the result of a faulty union of egg and sperm?
4. If faulty union of egg and sperm are not responsible for deformities in the offspring then is the genetic mechanism by which deformities occur in the offspring the result of mutation of the fertilized egg after it is fertilized, by say irradiation of the fertilized egg? 71.100.1.14 (talk) 17:18, 22 March 2008 (UTC)

1. Mutation is a process involving alteration of the genetic code. Now, mutation affecting the reproductive organs can lead to effects in the sperm/egg's DNA or their body, both of which can lead to offspring deformities. Now, your other question is backwards, and it's a fact that there are also deformities caused by other processes than mutation, e.g., folate deficiency of the mother, to name one.

2. Radiation can affect sperm as in my answer 1, or it can damage sperm's DNA directly. All radiation damages are highly dependent on the radiation dosage and the time when the mutation happens (like in the midst of cell dupication or such), and even then, the body has means to neutralize a good deal of such damage, provided it's healthy (no alcohol, no smoking).

4. Yes, also eggs' DNA can be damaged after eggs were produced (all human eggs are produced beforehand, anyway. That's why mothers are advised not to have children after 40 for mutation and other damage risk reasons, like Down's syndrome). -- 85.179.13.254 (talk) 17:37, 22 March 2008 (UTC)

So are you saying that a mutation in the parent before egg or sperm production or mutation in the egg or sperm after production but before fertilization or mutation after fertilization can result in a deformity or difference in an offspring? 71.100.1.14 (talk) 18:18, 22 March 2008 (UTC)

Yes, definitely. It wouldn't happen often, normally, as said, because of the body's defenses. The risk, however, is not exactly zero.

BTW, coincidentally, folate deficiency affects even males and their sperm, according to this fresh news article. --85.179.15.63 (talk) 07:32, 23 March 2008 (UTC)

Children's medicine 100 years ago.

In books such as The house at Pooh Corner or Peter Pan, children (specifically Roo and Peter respectively) are described as drinking medicine or tonic each day "to make them grow up strong". What was in these concoctions, would they have been prescribed by a doctor, an apothecary or made up at home? Zeimusu | Talk page 17:22, 22 March 2008 (UTC)

Mostly patent medicines, which really thrived in the early 20th century when both of those books were written, before any meaningful drug and advertising regulation was done. (Even today, under the guise of "natural" cures all sorts of hogwash is sold with fantastical claims, e.g. Airborne (dietary supplement). Let we think they were so stupid then, let us look at ourselves and our own propensity for such things!) --Captain Ref Desk (talk) 19:03, 22 March 2008 (UTC)

On the other hand, some of those concoctions might have helped, by providing vitamins and minerals which might otherwise be deficient in the child's diet. Cod liver oil is one such example. StuRat (talk) 21:13, 22 March 2008 (UTC)

The Smallest?

Is there a limit to how small a particle can be? Is there a point where a particle no longer MOVES to a point, but GOES to a point because it is so small that you can't be half way there?--Xtothe3rd (talk) 18:05, 22 March 2008 (UTC)

String theory is based on the idea that there is a minimum (1-dimensional) particle size, rather than zero-dimensional point particles. It isn't clear whether string theory is really going to work out physically and mathematically but yeah, that's the basic question it asks. More generally, though, there is Planck length, the smallest distance at which our physical theories make any sense. At a point much larger than that, though, the uncertainty principle keeps us from knowing whether a given particle is in a specific space or not. --Captain Ref Desk (talk) 18:53, 22 March 2008 (UTC)

However, the gravitational singularity of a black hole is a mathematical point. That is, it's infinitely small with no volume (but a definite mass). StuRat (talk) 21:07, 22 March 2008 (UTC)

Resolution of the naked eye

With my naked eye on an overcast day I can tell whether someone on a covered porch 500 feet away is wearing a black hat with a 3/4 inch white pendant or patch. How can I translate this to the resolution capability of my naked eye and compare it with a standard resolution capability for the human eye? 71.100.1.14 (talk) 18:53, 22 March 2008 (UTC)

The standard resolution capability is about one minute of arc (1/60 of a degree) which equals 0.0003 radians. For small angles, the angle in radians can be calculated by dividing the length of the object or separation of objects (perpendicular to the line of sight) by the distance. Now, if you see just one white patch on a black background that does not mean that your resolution is actually (width of the patch)/distance. What you would need is 2 white patches on a black background, and then determine the largest distance at which you can still see that it's 2 patches and not 1.

You can only conclude anything about the resolution capability of your eye from your experiment if the background around the hat was bright, and you could clearly see a pattern (e. g. along a horizontal line) of bright background - black hat - white patch - black hat - bright background. Then your resolution capability is at least ((width of the hat)/2)/distance.

If you are interested in the general calculation of the resolution of optical instruments (including eyes), you could start at Airy disc. Icek (talk) 19:22, 22 March 2008 (UTC)

To verify then at standard resolution capability for reflected ambient light then should I be able to see with a bright background a white patch on a 3.6 inch black object 500 feet away?

The Airy disc article seems to suggest that the reason I can see stars at night in the sky is due to the intensity of the light being emitted by the star attenuated by background and the distance, i.e., I can not see them when the background light is bright and I would not be able to see them at night at that distance if they were only reflecting ambient light like the moon.

Regarding the verification of standard resolution capability: Yes, but two white patches on a larger black background and a friend placing randomly one or two of the patches onto the background without you knowing whether it's one or two patches would be better.

Sorry, I'm still not clear on the size of the patches and their distances apart. Would I say start with a single patch that was so small it could not be seen and increase the size until it could be seen, then use of these patches at some relevant distance apart to determine my resolution. Is there a formula for patch size and their distance apart, the size of the black easel and the intensity of the background light?

The white patches should be just as small as possible, so your method should work. If the background is dark enough, you should see a white patch even when it is fairly smaller than the resolution limit. Take the distance between the white patches center-to-center. In principle you could compute the theoretical diffraction pattern for extended patches instead of points, but I don't think that's necessary. Icek (talk) 06:55, 25 March 2008 (UTC)

Regarding the Airy disc, yes, the intensity of the light lets you see objects that are far smaller than your resolution limit.

Interestingly, one could even go beyond the Airy limit if one used a monochromatic filter and light detecting elements far smaller than the Airy resolution limit. Then you could calculate the distribution of brightness from the diffraction pattern. But of course that is assuming that your optical instrument is nearly perfect with no stray light etc. Icek (talk) 11:59, 23 March 2008 (UTC)

hummm... is it possible that this is how in part the Hubble telescope is constructed? 71.100.1.14 (talk) 18:33, 23 March 2008 (UTC)

No. Remember that the Airy disc is an idealized model. For telescopes below the atmosphere, atmospheric turbulence causes distortions of the image (see Astronomical seeing), preventing us from reaching the Airy limit (the images can nowadays improved by adaptive optics, but currently only for long-wavelength light). The resolution of the Hubble Space Telescope is about 1/20 of a second of arc - about what you get with the Airy formula for a 2.4 m mirror at visible wavelengths. Icek (talk) 19:25, 23 March 2008 (UTC)

speed of an ant

I've clocked a frightened ant at 1 foot in 3.1 seconds and faster. This give me .32 feet per second or 116 feet per hour or .02 miles per hour. Where can I find a list of speeds for other insects? 71.100.1.14 (talk) 19:09, 22 March 2008 (UTC)

Since ants vary dramatically in size, I'd expect them to also vary dramatically in speed. This will also be true for many other insects. So, a chart listing the speed of "ants", "centipedes", "beetles", "flies", etc., would be meaningless. You'd need to list the individual species of each. StuRat (talk) 21:04, 22 March 2008 (UTC)

Okay, I have no problem with that. Even though there are vast differences in speed for even the same species (humans) there is statistics which can provide a maximum, a mean and a standard deviation. 71.100.1.14 (talk) 08:26, 23 March 2008 (UTC)

There are several sources on the internet that list the speed of various animals. A published list is in Natural History Magazine, March 1974, The American Museum of Natural History; and James G. Doherty, general curator, The Wildlife Conservation Society. That list is reproduced here. A compendium that compares the collates reported in various sources for the speeds of a range of animals is points 730-745 here. IBangMyHead (talk) 12:18, 23 March 2008 (UTC)

71.100.1.14, your last two speed figures are a factor of 10 too low. We wouldn't want the ref desk to be sued by someone who was outrun by an ant. --Heron (talk) 13:16, 23 March 2008 (UTC)

These figures are based on 1 foot in 3 seconds. I originally named then "Darters" but they are an invasive species which I have forgotten the name of now. They may be moving along at 1 inch per second or less foraging and then when frightened dart off at 3 to 4 inches per second - too fast to follow with them a finger to give them a good smash. 71.100.1.14 (talk) 08:37, 24 March 2008 (UTC)

As Stu said, it really depends on the species. Of the large Old World ants, Cataglyphis ants run pretty damn fast, easily over 10 cm/s, maybe as much as 20 cm/s. Messor and Camponotus are slower, several cm/s is probably the limit. Smaller ants are around 1 cm/s or less. However, these are just my non-scientific observations, so you should definitely NOT use them as a reference. As for other insects - please be more specific, then we (the Ref Desk) will probably be able to help. Cheers, --Dr Dima (talk) 15:26, 23 March 2008 (UTC)

I'm not real sure but these look allot like Argentine ants. 71.100.1.14 (talk) 20:53, 24 March 2008 (UTC)

Fixed previous link. Pallida  Mors 04:43, 25 March 2008 (UTC)

Why are you frightening ants to measure their speed?

The fabric of space

Did Einstine say that his math would not work unless space was actualy something. In other words, space could not simply be an empty void that matter exists in but an actual physical thing. e.g. "fabrick of space and time" I read somewhere that he called it ether.

You may be interested in general relativity and spacetime. — Matt Eason ^{(Talk • Contribs)} 20:40, 22 March 2008 (UTC)

For Einstein, space and time are bound together inextricably—you cannot reasonably talk about one without talking about the other (you cannot measure space without time, you cannot measure time without space, and you cannot talk about what you cannot measure—a few of Einstein's fundamental axiomatic realizations), and the composition of space affects the way in which time is perceived (and thus, because of relativity, the way time operates itself, as there is no time outside of space). So instead of space and time we have "spacetime".

It is not the same thing as the luminiferous aether, which was an earlier theory that Einstein rejected.

To elaborate a bit: it is not so much that empty space is not "empty" (that is, devoid of matter), it is that the idea of "space" itself is a geometrical construct, and it is more flexible than one might normally assume. The presence of any mass at all, for example, deforms spacetime, and the result is the effect that we call "gravity". We slide along this deformation in spacetime without even realizing it, towards the center of large masses, in this case, the planet Earth, along the path of least resistance.

Hopefully that will clarify things a little bit—I've oversimplified things a bit but I don't think I've committed any major errors. --Captain Ref Desk (talk) 20:40, 22 March 2008 (UTC)

Where is the centre of the universe?

If the universe is continually expanding outward in every direction, then where is the point from which it is expanding? That must be where the big bang occurred? But where is it, say, in relation to our earth? Are we nearer to the centre of the universe or the "edge" of it? As you will have guessed, I am not a science person. Kaiwhakahaere (talk) 20:34, 22 March 2008 (UTC)

Without knowing the shape of the universe, it is not possible to define a center. And further, there are possible shapes to the universe for which there is no geometric center. Also, there is no position in space "where the big bang occurred." The big bang occurred everywhere. To explain how that might be possible, think of the expansion of the universe. When we look at distant galaxies, we notice that the speed at which the galaxy is receding is directly proportional to its distance from us (Hubble's law), and this seems consistent in every direction. That is, almost everything is moving away from us, and we seem to be at the center of it all. However, this observation would be true no matter which galaxy we were in. It would subsequently be true that if we were to run time backwards, we would see everything rushing towards us and the density of matter/energy would increase towards infinity as we approached the big bang, and this observation would be the case no matter which galaxy we were in! Thus, each galaxy can equally claim that is the central point of expansion, and thus it is probably untrue that an actual "center of the universe" exists anywhere, and it is certainly untrue that the big bang occurred at one point. Someguy1221 (talk) 21:08, 22 March 2008 (UTC)

You must be the universe's fastest typist! Or our locations are actually coming together rather than moving apart! Only 34 seconds after I hit my save page button you posted a reply. And a great reply it was too. Tks. Kaiwhakahaere (talk) 21:15, 22 March 2008 (UTC)

I suspect this was a prepared answer, which took me longer than 34 seconds to read. 71.100.1.14 (talk) 08:32, 23 March 2008 (UTC)

It was 34 minutes, not seconds. -- BenRG (talk) 19:42, 23 March 2008 (UTC)

The big bang is more like a balloon being blown up than an explosion. The big bang happened everywhere - it was an expansion of the distances between things. So if everything in the universe were on the surface of a balloon while it was expanding very quickly, that would sort of be like the big bang. Quantumelfmage (talk) 05:49, 24 March 2008 (UTC)

Leap from a burning building

A question I posted above (Wikipedia:Reference desk/Science#Free falling human body) prompted this follow-up thought. If your house / apartment building is on fire, and you have to jump out the window ... what are some rules of thumb you should observe? In other words, what's the "best" way to jump out? And is there any relevance to what story up you are in the house / apartment building? Or is that essentially irrelevant? In other words, if I was very high up (on the 10th or 20th or 100th floor), would / should my jumping strategy be different than if I was not so high up (on the second or third floor)? Also, what are some considerations a person should factor into making a good decision to "should I jump or should I not?" Ultimately, if you were the Chief of the Fire Department and had to write a "how to manual" for people who find their homes on fire, what would be the best advice in these scenarios described? Thanks. (Joseph A. Spadaro (talk) 21:28, 22 March 2008 (UTC))

From a second floor window, you can break your fall with a "parachute roll" without any serious injury if you are properly trained. A paratrooper friend I used to know used to do this regularly as a party trick after we had been drinking (warning: don't try this at home). I have also read (sorry, forgot where) of a base jumper whose chute failed after jumping off a building at a great height. He managed to keep his fall under terminal velocity by grabbing the ledge on every floor as he went down. The fall is too fast to be able to actually hold on but it slowed him down enough to survive. Multiple fractures in both arms from hitting the ledges and broken legs on landing but he did survive (don't try this at home either). And now you mention it, I do have a "how to" book on surviving worst case scenarios - I'll see if I can find it. SpinningSpark 21:47, 22 March 2008 (UTC)

Thanks for the reply. It would be helpful to know what the term "parachute roll" means ...? Thanks. (Joseph A. Spadaro (talk) 22:15, 22 March 2008 (UTC))

Well, if the building really had been on fire the book would have been completely useless as it took too long to find - note to publisher: you need to embed an emergency siren in the spine so it can be located quickly. So anyway, it lists several falling scenarios, the closest to your question is "How To Jump From A Building Into A Dumpster" (dumpster = skip in UK). They recommend tucking in your head and bringing your legs around so that you are laying on your back. They say the reason for this is that the body tends to be thrown into a V on landing. If you land on your stomach this will break your back. Also, try not to leap outwards as this will carry you away from your aiming point. I would also repeat - don't try this at home - there's a lot that can go wrong with this one. If you miss the dumpster, you hit concrete. If you nearly miss the dumpster you might hit your head or your back on the edge - worse than hitting the concrete. If the dumpster is full of building rubble (what else would be in it? they are only full of empty cardboard boxes in the movies) then you may as well have aimed for the concrete. SpinningSpark 22:25, 22 March 2008 (UTC)

Parachute Roll. I don't think this is used very much anymore, but in the days when parachutes were a lot less controllable it was necessary to break you fall to avoid broken ankles. Basically, it is bending at the knees to absorb some of the shock as your feet touch down and at the same time falling to one side and turning that motion into a roll as your body hits the ground to dissipate even more of your kinetic energy. Practice from standing on the ground at first and then steadily increasing heights. SpinningSpark 22:35, 22 March 2008 (UTC)

Parachute Landing Fall. 152.16.59.190 (talk) 06:11, 26 March 2008 (UTC)

One important thing to do from the 2nd or 3rd story is to hang from the ledge first, to lower your distance to the ground as much as possible, before you jump. Also aim for something relatively soft, like dirt or a bush or an awning. StuRat (talk) 06:32, 23 March 2008 (UTC)

Wow, I would have never thought of that ... but, yes, it makes perfect sense. Thanks. (Joseph A. Spadaro (talk) 18:51, 24 March 2008 (UTC))

How To Survive a 47-Story Fall Make sure you land on your feet. Gzuckier (talk) 19:00, 25 March 2008 (UTC)

Non-pop popcorn

After a nice meal i decided to have some popcorn with my beer and meaningless wikipedia-surfing. I poured the corn into the kettle and went back to my computer, waiting for the first pop. however, no pop occurred, and instead i smelt fire and when I turned around I saw thick smoke from the kettle. The corn had simply started burning instead of popping like usual - ruining the kettle in the process... I was thinking afterwards that I had put to small an amount of oil in the kettle, but after reading the popcorn article it seems that they should pop at a certain temperature, oiled or not. the next batch of popcorn (from the same bag) went fine. this is a slightly odd question, but has anyone got an idea why this might have occurred?

Did you adjust the temperature? Maybe the first lot was too high. Julia Rossi (talk) 03:10, 23 March 2008 (UTC)

Also, wikipedia surfing is never meaningless. Your knowledge increases, your eyesight deteriorates. Live long and prosper. --Dr Dima (talk) 15:54, 23 March 2008 (UTC)

off the top of my head; popping requires moisture trapped within the kernel; burning instead of popping suggests the kernels were dehydrated; if the next batch from the same bag was Ok, then my guess would be that the heating process was a little slow and the kernels dried out before getting to 212 degrees F. Gzuckier (talk) 18:55, 25 March 2008 (UTC)

How the brain processes visuals

I believe that this is a Science question ... or, rather, questions. (Question 1) When we look at a drawing of, say, Charlie Brown (or any cartoon) ... that picture in no way looks like a real human being 8-year-old boy. So, what "tricks" our brain when we see these animations to "accept" that they are people? That question was hard to word, but I hope someone catches my drift. (Question 2) We look at drawings, pictures, paintings, and visuals all the time. What exactly "distinguishes" these normal visuals from what we call "optical illusions"? In other words, in a given optical illusion, it might say: "Do you see a man or a mouse?". Some people can see the man, some the mouse, and some both. Why is that? And what exactly makes that visual different for our brain to process than when we look at a "normal" (unambiguous) visual (like my high school yearbook photo or the Iwo Jima photo)? Thanks. (Joseph A. Spadaro (talk) 22:24, 22 March 2008 (UTC))

While a cartoon face doesn't look anything like a particular human face, it is very close to looking like the Prototype Theory or average face. At a low level, we might analyze Charlie Brown's nose as a half-circle, but there is a top-down mechanism in the brain that makes us recognize it as a nose because it is in the context of a face. Each of Charlie's features do not have enough detail on their own to assert themselves as facial features, but in the context of a prototypical face and prototypical features, we can place them. So at a fine-grain, low level, high detail level, Charlie Brown's face does not look like a face, but at a high level, wholistic, gestaltic level, it does look like a face, and top-down mechanisms make us accept it as a face.

In an optical illusion like the one you described, there are neural mechanisms that force us to settle on one interpretation of an ambiguous image (usually because it is the best interpretation). But the illusionary image is constructed so that neither interpretation is clearly better, so our perception switches back and forth. So the parts of your brain are getting confused and reporting inconsistent output to the part of your brain which isn't sure whether to call it a mouse or a man. So we call it an illusion. Quantumelfmage (talk) 05:43, 24 March 2008 (UTC)

Makes sense. Then, as a corollary question ... how come sometimes I cannot "see" the alternative image until someone directly points it out exactly to me? And how come sometimes I can never "see" the alternative picture, even when someone directly points it out exatly to me? Thanks. (Joseph A. Spadaro (talk) 05:53, 24 March 2008 (UTC))

I believe that we see things as other things due to our ability to handle symbolic logic. That is, to define one thing as representing another. This is important in human communication. The cartoon may only be recognized because, in our past, we have used pictures drawn in dirt with a stick to represent people, and those who could understand had a survival advantage. I doubt if a dog could recognize a cartoon as representing a person or dog, as they lack the ability to use symbolic logic. StuRat (talk) 06:07, 23 March 2008 (UTC)

Unfortunately, we do not have much of an article for associative memory, and it's a shame. I will write one if I have time this week. For the time being, a really lousy short explanation. Objects (visual objects in particular, but any sensory or conceptual objects in general) that we encounter in real life are often incomplete, poorly resolved, or somewhat different from their "standard" form. Yet, we recognize them very reliably. The underlying neural circuitry is usually called an "associative memory" network. The network has many "familiar" or "memorized" states corresponding to familiar objects or notions; these are called attractors. Any incomplete or inaccurate input to such a network (an observed object) brings the network into an attractor state which is usually rather similar to the observed object; this is recognition. Human face, or human shape, are some of the most important visual objects in the evolutionary sense, so we tend to see human shapes even in some definitely inanimate or non-human objects (see Pareidolia). So recognizing a manga or comics character, even super deformed, is really not surprising at all. And, besides, there is also a "symbolic logic" aspect which Stu mentioned: basically, we all drew pretty schematic pictures in kindergarden, at least at first; yet they were quite easy to decipher, in most cases :) . Hope this helps. --Dr Dima (talk) 15:12, 23 March 2008 (UTC)

Thanks for Question 1 (Charlie Brown). And (Question 2): We look at drawings, pictures, paintings, and visuals all the time. What exactly "distinguishes" these normal visuals from what we call "optical illusions"? In other words, in a given optical illusion, it might say: "Do you see a man or a mouse?". Some people can see the man, some the mouse, and some both. Why is that? And what exactly makes that visual different for our brain to process than when we look at a "normal" (unambiguous) visual (like my high school yearbook photo or the Iwo Jima photo)? Thanks. (Joseph A. Spadaro (talk) 20:10, 23 March 2008 (UTC))

Could physicians work as epidemiologists?

Dear Wikipedians:

My dad graduated from a non-American medical school with a MD in public health. Instead of treating patients, he works in a non-American CDC like organization doing body check-ups for primary/secondary school students and does preventive medicine propaganda in the community and also writes out a few research papers per year on the statistics of the prevalence of various diseases in the community, results of the student body checkups, etc.

I am wondering if this qualifies my dad as an epidemiologist? And is it reasonable for physicians to work as epidemiologists?

Thanks.

76.68.9.59 (talk) 22:26, 22 March 2008 (UTC)

I could be wrong, but I don't think you need to be licsenced to work as an epidemiologist. I think that it is like many occupations, if you DO it then you ARE it. (By the way, this belief has gotten me into some arguments. I believe, for example, if you studied chemistry, but don't do chemistry, you are not a chemist). ike9898 (talk) 01:48, 23 March 2008 (UTC)

There's nothing that necessarily disqualifies a physician as working as an epidemiologist, but usually epidemiologists have very rigorous training in statistics and experiment methodology, which may or may not be part of the general med school/public health education. --Captain Ref Desk (talk) 22:49, 23 March 2008 (UTC)

There are masters and Ph.D programs for epidemiology. An allopatric medical degree is not required. Wisdom89 _{(T / ^C)} 06:24, 24 March 2008 (UTC)

if he has a degree in public health and writes a few statistical-type papers a year, he's an epidemiologist. Gzuckier (talk) 18:53, 25 March 2008 (UTC)

March 23

Trying to recall something I read years ago

Dear Wikipedians:

I need your help in discerning a passage that I read years ago but one which I couldn't find anymore. It is related to the role technology plays in medicine.

What I can remember of the passage are as follows (italics means specific details that I can no longer remember, bold means key texts that I knew definitely appeared in the passage that I read):

“ Take the disease disease name (tuberculosis?) for example, in the 1950s there were great debates about the construction of hospitals that are specifically geared to the treatment of patients with the disease, there are back-and-forth arguments in leading medical journals about the quarantine measures, treatment processes, people couldn't even seem to agree on the a treatment process, and the case study of a girl's name, girl is an African-American.

But then the wonder-tech-gizmo-drug (an antibiotic?) was discovered. And it proved to be so effective in treating disease name, that talks of building hospitals also soon died down.

”

Thanks.

76.68.9.59 (talk) 00:16, 23 March 2008 (UTC)

Well, just judging from the dates (1950s), the fears of the epidemics and the importance of the drug, my guess would be that the disease is polio, and that the wonder drug was the Salk vaccine. But this is a wild-guess—lots of antibiotics and vaccines were developed in the 1950s to treat all sorts of things, though the Salk/polio case is one of the most famous. No clue about the case study. --Captain Ref Desk (talk) 04:54, 23 March 2008 (UTC)

But the circumstances seem to fit TB much better. Sanitoriums were actually constructed when the only treatment for the disease was isolation and bedrest; the first antitubercular drug, streptomycin, was discovered in 1943, with the discovery first published in 1947. The discovery was followed by that of para-aminosalicylic acid, and by isoniazid (the wonder drug) in 1952. It became evident that bedrest wasn't important, and sanitarium construction stopped, and existing sanitaria were "repurposed". But I don't know what case study you might be talking about. You may be interest in this article on the history of tuberculosis. - Nunh-huh 11:36, 23 March 2008 (UTC)

The only other institutions I can think of that were "shut-down" as a result of improved medical treatment were "insane asylums", but this was in the 1970s and later. - Nunh-huh 11:47, 23 March 2008 (UTC)

"Insane asylums" became "psychiatric institutions" in the 1940s. Deinstitutionalization was already in play long before the first anti-psychotics were developed, though (which was in the 1950s as well—see thorazine). It's not so much that state care of the mentally ill went away so much as it decentralized. (The dismantling of the American mental health system by Reagan actually had its roots much earlier, as people for decades felt that centralized state institutions were prone to abuse and waste that local, county or community based care was not.) --Captain Ref Desk (talk) 19:56, 23 March 2008 (UTC)

As highlighted by the above discussion, given the importance of the date range in trying to answer this, how sure are you of it? For example, if it could have been like the 1930s that would be different from if it could have been in the 1970s. The example that I can think of that best fits your text to me is leprosy. Leper colonies were of cause not uncommon in the past and I would presume there they are something often debated by the medical community once it was established. As discussed in both the linked articles, it appears to me they are generally no longer considered medically necessary by most of the medical establishment because of both the widespread availability of effective treatments and the fact that leprosy is not nearly as contagious as people believe/d. The dates on this don't really agree with your 1950s, treatments were available in the early 1940s but they weren't that effective and it was only in 1982 that an effective (multidrug) treatment was developed which combined with the acceptance that leprous was not that communicable lead to the decline of leper colonies. Leper colonies weren't of course specific hospitals but segregated communities which is another area where this doesn't fit your memory. Also the case study seems a bit iffy since it doesn't seem that the US led the way in leprosy research. Actually um ignore my example, the more I think of it, the more it doesn't fit, since you're fairly sure of the last sentence but leper colonies aren't hospitals and already existed and had for a long time, it doesn't really fit... I believe HIV was a major scare as well with suggestions for quarantine (Cuba at least put this into practice IIRC but are now consider a shining star in the fight against HIV) but that was even latter and it hasn't been beaten, it's just well understood enough that people know quarantine serves little purpose Nil Einne (talk) 17:23, 23 March 2008 (UTC)

Thank you all for your response. I can now remember it as being TB + Streptomycin. Thank you sooooooooooo much! 76.65.14.58 (talk) 23:06, 23 March 2008 (UTC)

Long-term effects of 0 g

The ISS, that beautiful star in the sky, is coming down in a few short years. Hardly completed as of yet, it will be scrubbed before 2020. I would ask for some imagination from all you readers. Some horrible tragedy inflicts the Earth below. Just for a moment, let us pretend the ISS will maintain its position as a star in our sky for many decades to come, constantly replenished, that our species will continue to inhabit the night's sky. Here's what I would like to know: If I were a crew member on the station (I am a 31 y.o. healthy male), what would happen to me if I were forced to spend a continued twenty or thirty years aboard? Could I survive? Sappysap (talk) 01:02, 23 March 2008 (UTC)

Quick answer, no one really knows the long term effects of extreme long term weightlessness since it has never been done before. However given the importance of understanding this, a lot of studies and theorising has gone on which I'm sure you could find. Human adaptation to space and weightlessness are good starting points. BTW, if something happened to earth, the people on the ISS would I'm pretty sure be screwed. It is not designed and probably isn't capable of independently supporting a human population in the long term amongst other things, they need food from earth. Also, if it's design lifespan is 10+ years, it could probably be extended by say 300-500% but I suspect no longer and even then, probably only with the support of earth. And given the tiny number of people on the ITN, presuming there are even 2 fertile people of the opposite sex on the ISS at the time something happens to earth, the human species will likely be screwed due to the inbreeding depression from the extreme inbreeding that would occur. (Not to mention the ISS would have a very limited population maximum even if it were completely self sufficient so the human species couldn't exactly 'thrive' there) Nil Einne (talk) 02:39, 23 March 2008 (UTC)

Additionally, the ISS would deorbit by itself within maybe 5 years due to air resistance. Icek (talk) 14:20, 23 March 2008 (UTC)

I should mentioned though that some of the studies/theorising may not quite cover what you are suggesting. Most commonly people analyse this from a 'trip to Mars' kind of POV or perhaps colonies on other planets like Mars or the moon (or others). These are not microgravity environments and even if the hope is for the colonies to be capable of being independent (which often doesn't mean an expectation of reproduction in the colonies in the short term), in general no one expects the colonies to be cut off from earth. And people tend to look at fairly long term, but not permanent existance in microgravity (since for all the reasons already explained and more even if we do want a colony capable of surviving without earth, we wouldn't build it in space). What all this means is that most studies consider it important that the people are capable of re-adjusting to life on earth which is one of the biggest problems with people adapted to microgravity environments (or even a lesser gravity environment) but if I understood your question correctly, this doesn't matter for your case. Nil Einne (talk) 16:49, 23 March 2008 (UTC)

WHAT??? The ISS is about to deorbit? Wouldn't that mean that it will impact the Earth like an asteroid? Isn't there anything to prevent this? Or will a shuttle retrieve the astronauts and allow the ISS to deploy safely? Or is there something I misunderstood? Thanks. ~AH1^(TCU) 18:13, 23 March 2008 (UTC)

At the height of the ISS - currently approximately 340 km - typical objects deorbit within a few years (that also depends on the ratio of mass/(area perpendicular to velocity vector) of the object), at 600 km (about the height of the Hubble Space Telescope) it's maybe a few decades. Go to Heavens-Above and click on "Height of the ISS" - there you can see that the height constantly decreases, only to be increased by a boost (which consumes fuel of which there is not much on the ISS) every month or so. The ISS will impact the Earth, but slower than an asteroid would, with only about 8 km/s. They will steer it to an uninhabited region like the southern Pacific, as they did with Mir. Icek (talk) 19:18, 23 March 2008 (UTC)

Hi. Wow. The ISS is the most expensive object ever built by mankind. Well at least it's likely to break up in midair. Thanks. ~AH1^(TCU) 00:15, 24 March 2008 (UTC)

Can we get a citation for the "scrubbed before 2020" part? Our ISS article doesn't mention anything about abandonment. —Steve Summit (talk) 00:22, 24 March 2008 (UTC)

well, basically, longterm exposure to zero g makes you gradually deteriorate, even if you exercise. the occasional collapses of shuttle pilots after landing, for instance. you also get sort of ballooned out in your upper body and head, as the fluid doesn't pool in your legs; folks in zero g always look kind of moonfaced. Gzuckier (talk) 18:51, 25 March 2008 (UTC)

"Jumping" of blood vessels around the eye

Hi. What's the medical term for the pulsating of the blood vessel right below the eye (in the eyebag for those with one)? Thanks. Imagine Reason (talk) 01:09, 23 March 2008 (UTC)

Blepharospasm -- —Preceding unsigned comment added by 79.76.201.53 (talk • contribs)

I don't mean the eyelid. It's more of the nerve or blood vessel under the eye (like at the bottom of the eye socket). Imagine Reason (talk) 02:03, 23 March 2008 (UTC)

Read the article fully. -- —Preceding unsigned comment added by 79.76.201.53 (talk • contribs)

Why should he read it thoroughly? Blepharospasm is unrelated to pulsating blood vessels, and accordingly, the article contains no mention of blood vessels, arteries, veins, or capillaries. Mark this one "unanswered". - Nunh-huh 11:28, 23 March 2008 (UTC)

Blood vessels dont pulsate like that and if they did you would not be able to feel it unless there were nerves in the vicinity. Its obvious you havent read the article Blepharospasm either!

I quote from the symptoms para;

Uncontrollable tics or twitches of the eye muscles and surrounding facial area. Some sufferers have twitching symptoms that radiate into the nose, face and sometimes, the neck area. Mark this one as answered by me!

OK, we'll count you as one satisfied answerer. Of some question.- Nunh-huh 14:46, 24 March 2008 (UTC)

can someone identify this flower for me?

It's a picture of a white flower with a grassy three-sided stem that grows from some tiny bulbs from underneath the grass every spring. The flowers are wrapped in a onion peal like matter before the petals spout out. the flowers smell like onions. Several flowers spout from one little area. This is in Richmond, California in Contra Costa County, California in the United States.Carritotito (talk) 02:22, 23 March 2008 (UTC)

Breaks easily when pulled? Probably onion weed[2]? Aka Asphodelus fistulosus. Our article doesn't have the same variety in the pic. Julia Rossi (talk) 03:05, 23 March 2008 (UTC)

I know Asphodelus fistulosus fairly well, and this is definitely not what you have. Asphodel has its flowers in an open panicle (spike-like), whereas all the true onions (genus Allium) have their flowers in an umbel (all flowers arise from the same point at the top of the stem). Your photo shows an umbel. If it smells like onion, it probably is an onion; there are many species of Allium native to California, plus a few noxious introduced species. The Jepson Manual (1993) lists 47 species native to California and four introduced.--Eriastrum (talk) 15:47, 23 March 2008 (UTC)

I think that I have figured out what species this is: Allium triquetrum, or Three-cornered garlic. It is native to the Mediterranean, but has naturalized in parts of California.--Eriastrum (talk) 17:35, 27 March 2008 (UTC)

Science+nutrition

What vitamin and/or nutrient does alcohol deplete from the human body?

Calcium uptake is most severely diminished with alcohol abuse, for example. In general, as you destroy your bowel's ability to take up nutrients, all those taken up after the stomach are affected more or less. Of course, the lungs an the brain, too. --85.179.15.63 (talk) 07:29, 23 March 2008 (UTC)

B Vitamin deficiency – but I can't figure where to show you except in the article Korsakoff's syndrome – an extreme example that doesn't seem to explain how this happens Julia Rossi (talk) 08:17, 23 March 2008 (UTC)

There are two proposed mechanisms of thiamine deficiency in alcoholics: [1] diminished intestinal absorption of thiamine caused by alcohol, and/or [2] destruction of thiamine by acetaldehyde. There are many other nutritional implications of alcoholism as well. Alcohol inhibits fat absorption, and thus interferes with absorption of vitamins A, D, & E. VItamin C & K are often deficient, which together with impaired hepatic function and impaired hepatic synthesis of clotting factors helps to explain the tendency towards severe bleeding in alcoholics. The B vitamin deficiency, particularly thiamine, leads to not only Wernicke-Korsakoff syndrome, but to other less severe neurological disorders. And there are implications on minerals, as well... though alcohol doesn't affect absorption directly, alcoholism decreases calcium absorption due to fat malabsorption, decreased magnesium levels due to decreased intake, increased urinary excretion, vomiting and diarrhea, iron deficiency related to gastrointestinal bleeding, and zinc deficiencies due to malabsorption or losses related to deficiencies of other minerals. The magnesium deficiency, which is very common in alcoholics, can in itself cause calcium deficiency. - Nunh-huh 11:23, 23 March 2008 (UTC)

Calcium Chloride re Dehumidifier

Is it possible to reuse the calcium chloride that has absorbed moisture from the air by heating the calcium chloride to release the water. Or is this possibly a dangerous experiment.

Yes - put in oven at more than 100C. This is safe, do not eat, do not inhale and dust from dried CaCl2.87.102.16.238 (talk) 14:00, 23 March 2008 (UTC)

There is one product I have seen in stores which apparently contains this chemical, and which has an indicator which changes color when the chemical has absorbed all the water it is designed to. Then you plug it into an electric outlet and a built in heating element dries it out for re-use. Edison (talk) 17:59, 23 March 2008 (UTC)

Black Hole Question

If a black holes "gravity feild" has settled into static equillibrium how do black holes merge and thier gravity merge along with it? Do the fields remain static and just reinforce eachother? I'm confused.11341134a (talk) 16:50, 23 March 2008 (UTC)

I don't think a black hole can be in perfectly static equilibrium because of Hawking radiation. But even disregarding that, saying that a thing is in "static equilibrium" usually means assuming no outside influences (like being hit by a black hole). --Allen (talk) 20:54, 23 March 2008 (UTC)

A system of objects interacting only through gravitational forces can never exist in a stable static equilibrium (except in the trivial cases of there being only one object, or every object occupies the same position and has equal velocity). Someguy1221 (talk) 03:39, 24 March 2008 (UTC)

The Cat's Brain Compared to a Human's Brain

Do you know of some such website that will let me compare a cat's brain to a human's brain? --209.226.138.43 (talk) 17:56, 23 March 2008 (UTC)

Not really, but our articles on cat intelligence and human brain might help. --Allen (talk) 18:18, 23 March 2008 (UTC)

Check out [[3]], produced by U Wisconsin, U Michigan, and the National Museum of Health and Medicine (USA). Vance.mcpherson (talk) 18:55, 27 March 2008 (UTC)

Why The Sky Is Blue?

I heard from a friend that the sky is blue because of the colour being reflected off all the water in the world.Can somebody verify that? (and no I am not doing a science project,I just really want to know) -- 209.226.138.43 (talk) 18:12, 23 March 2008 (UTC)SilverLeaf

No. See Diffuse sky radiation. --Allen (talk) 18:15, 23 March 2008 (UTC)

Hi. By the way, I'm not sure, but I think part of the reason why water (usually) appears blue is because it reflects the blue sky (either that or there is oxygen in water which scatters light). Thanks. ~AH1^(TCU) 18:18, 23 March 2008 (UTC)

Here's something from the Library of Congress about why the ocean is blue. --Allen (talk) 18:25, 23 March 2008 (UTC)

We actually have an article on the Color of water. Someguy1221 (talk) 04:52, 24 March 2008 (UTC)

It doesn't talk about ice, though. If you see a big chunk of ice, like an iceberg or the face of a glacier, it may be brown/gray/black from dirt or it may be white from air bubbles or from snow cover, but in areas where none of these cases is true, you see its true blue color,which can be startlingly strong. --Anonymous, 22:57 UTC, March 24, 2008.

Ah, but in another thread below, someone mentions Blue ice (glacial), which does cover this. I've proposed a merge. --Anon, edited 23:28 UTC, March 25.

Actually, pure water absorption spectrum shows an increased absorption at 600 nm and longer wavelengths (just google "liquid water visible absorption spectrum" - there are plenty of references, but some require subscription for the respective scientific journals). Simply speaking, pure water absorbs red light stronger than yellow, green, blue, and violet light. Thus, white light passing through water loses its red component, and looks "anti-red", that is, blue to the human eye. Actually, violet light is also absorbed a bit stronger, so greenish-blue may be a more accurate description. This is for pure water; any dissolved or suspended impurities may change the perceived water color further. --Dr Dima (talk) 18:38, 23 March 2008 (UTC)

Think about this: if you shine a white light (like a flashlight) on a body of water at night, it still looks blue, right? But there isn't enough intervening air to filter out the red wavelengths in the light, so it must appear blue because the water is absorbing those wavelengths. « Aaron Rotenberg « Talk « 04:49, 24 March 2008 (UTC)

I can't imagine a flashlight producing enough light to be able to see this color. Have you actually done this? --Anonymous, 23:03 UTC, March 24, 2008.

think of it this way; the blue you see in the sky is the blue which is missing from the red and yellow and orange sunset or sunrise for people elsewhere at the same time. Gzuckier (talk) 18:48, 25 March 2008 (UTC)

In short, the sky is blue because air is blue. If you look at the earth from space you can see how very blue it is. --superioridad ^(discusión) 05:39, 27 March 2008 (UTC)

Rayleigh theorized that the degree of scattering of light is inversely proportional to wavelength of light. (raised to its fourth power) Hence blue, which is the shortest wavelength, is scattered the most and the sky appears blue. (Violet has the shortest wavelength in the spectrum but our eyes are more sensitive to the color blue)

FingerPrints

Why are there no 2 fingerprints alike? SilverLeaf209.226.138.43 (talk) 18:29, 23 March 2008 (UTC)

See Fingerprint#Friction Ridges. --Dr Dima (talk) 18:42, 23 March 2008 (UTC)

Also, try this Google search for more information about stochastic pattern formation and fingerprints. By the way, when editing Wikipedia, try not to start a line with spaces; it has odd formatting effects. Also, you can search for articles by typing words into the "search" box to the upper left of any page. --Allen (talk) 18:48, 23 March 2008 (UTC)

The thing I also wonder about is how permanent are fingerprints really? Some years ago I had a skin ailment that affected my fingertips (among other areas). For a time, several of my fingertips had a very smooth, taut appearance with no discernable ridges. Later, when things healed, the ridges returned, but I've always wondered with the ridges that returned actually had the same pattern as before or whether the ridges were regenerated in a different pattern than previously. Since I don't have any record of my previous fingerprints, I have no way of knowing. So how persistent are fingerprint patterns relative to diseases and physical disturbances that might temporary remove the outward manifestation of ridges? Dragons flight (talk) 19:10, 23 March 2008 (UTC)

This Google search turns up some sources like this one suggesting that they do grow back the same after physical disturbances, unless there is too much scar tissue. But I haven't looked closely enough to see if there's info on diseases, or on what mechanism preserves the original pattern. --Allen (talk) 19:31, 23 March 2008 (UTC)

Does water "go off"?

When I buy water in a bottle from the mall it has an expiration date, but I can't see why if its kept in sealed bottle you can't drink it in 100 years time. Does it go gor something?

Here is a response to a person asking the same question: http://www.madsci.org/posts/archives/aug2000/966882443.Ch.r.html

Basically, the substances that makes up the container will also leach into the water, creating unpleasant tastes. --Bowlhover (talk) 19:35, 23 March 2008 (UTC)

See Bill Nye the Science Guy Nothing444 20:00, 23 March 2008 (UTC)

Why? SpinningSpark 20:16, 23 March 2008 (UTC)

Because it's too expensive to use substances for the bottle that don't solve into the water. --85.179.24.245 (talk) 15:35, 24 March 2008 (UTC)

What about simple glass? Vranak (talk) 17:10, 24 March 2008 (UTC)

My "why?" was addressed to N444, ie what was the point of the link provided which as far as I can see is totally irrelevant. I was not referring to the question of the container material. SpinningSpark 18:56, 24 March 2008 (UTC)

Ahh. Vranak (talk) 19:46, 24 March 2008 (UTC)

I guess unless it's sterile water in a sterile container, in time bugs will grow. Julia Rossi (talk) 00:31, 24 March 2008 (UTC)

I don't agree. They would need something to eat in order to grow. StuRat (talk) 02:50, 24 March 2008 (UTC)

I can't pin down the study right now but slime mould is commonly found in bottled water beyond a certain age. I suppose trace nutrients are all they need. Franamax (talk) 02:57, 24 March 2008 (UTC)

This[4] and the article anaerobic bacteria is starting to make tap water look very good. Julia Rossi (talk) 03:19, 24 March 2008 (UTC)

Stagnant does not mean 'closed in a bottle', stagnant means just 'standing'. --85.179.24.245 (talk) 15:37, 24 March 2008 (UTC)

To grow stuff in water, you need – at a minimum – a source of energy and a source of carbon. (Strictly speaking a number of trace minerals are also necessary, but to a limited extent those can be scavenged from the original source of contamination, and many are present at some concentration in the water anyway.) A sealed bottle of water contains no carbon source; there's no raw material for new bugs, so no growth occurs. (If the cap is loose, atmospheric carbon dioxide will provide carbon.) Energy can be drawn from chemical sources (sugars, proteins, or other water contaminants) but these are rare in bottled water. The usual energy source is light, which will drive photosynthesis. Since abiogenesis is unlikely in a water bottle, we also need some initial source of contamination: fungal or algal spores or the like. Most bottled water bottles (when new) are pretty sterile, they shouldn't contain any stuff that will grow.

The picture changes when you look at people who reuse and refill their bottles. biofilms tend to build up in these containers, and they are supplied with ample fresh air and light over time. (That may be what Franamax was thinking of in his comments above).

I would guess that the concern with long-stored bottled water is due to taste or leached chemical contaminants as noted above; unopened factory-packaged bottles should contain no biological contaminants, and – unless the water were badly tainted – those organisms would be too starved to grow even if they were present. TenOfAllTrades(talk) 15:58, 24 March 2008 (UTC)

Water bottles are made of plastic. Isn't that a source of carbon? — DanielLC 16:30, 24 March 2008 (UTC)

I was thinking along the lines of this and the discussion just above the figure. Note they're referring to mineral water which is a little different than regular bottled water. I'm not sure if I was referring only to the NRDC study, I recalled something more specifically along the lines of 30% of bottles with slime mold (which is a particularly resilient animal) after 6 months, but I can't find the specific ref. Cool and dark storage would be important in avoiding contamination of any kind, whether it's chemical leaching or biologic growth. Franamax (talk) 16:37, 24 March 2008 (UTC)

Snake venom - quick question

In general, is a poisonous snake's venom effective against another snake of the same species? --Kurt Shaped Box (talk) 21:07, 23 March 2008 (UTC)

Snake_venom#Among_snakes might be of some use. bibliomaniac15 Midway upon life's journey... 21:53, 23 March 2008 (UTC)

My understand is "usually, yes." Even snakes that eat other snakes are not often immune to snake venom, it's just the difference between digesting venom and having it injected intravenously. But I'm no herpetologist. That particular article section sure has a lot of "citation needed" marks. --Captain Ref Desk (talk) 22:47, 23 March 2008 (UTC)

Eggs?

What are the brown things?

Can anyone identify the brown things in the picture? They were found recently on the lights left outside for a few months near Houston, TX. anonymous6494 22:49, 23 March 2008 (UTC)

They look like aphid eggs to me. —Steve Summit (talk) 00:17, 24 March 2008 (UTC)

Aphids are viviparous, they look a bit like eggs of a lepidoptera of some description. Compare with these. [5] Richard Avery (talk) 08:42, 24 March 2008 (UTC)

Bronner's liquid soap turns white when cold

Why? —Tamfang (talk) 23:59, 23 March 2008 (UTC)

It's just a guess, but oils often do that when they solidify. StuRat (talk) 02:47, 24 March 2008 (UTC)

I was about to guess the same thing. And our article on E. H. Bronner mentions that Dr. Bronner's is castile soap, containing made from vegetable oils. And many vegetable oils turn white when they're cold, due to partial solidification, as StuRat said. I don't know if the saponified oils in liquid soap "freeze" to milkiness in the same way, but it seems vaguely plausible. —Steve Summit (talk) 05:16, 24 March 2008 (UTC) [edited 01:45, 25 March 2008 (UTC)]

The critical micelle concentration is often temperature dependent. You may be observing a phase change where the soap molecules go from a clear, "dissolved" form to a cloudy, structured form. It's hard to say for certain, as the CMC depend heavily on the identity of the amphiphile, and when you have a mix of amphiphile types (like in standard grade soap), it get complicated fast.-- 128.104.112.85 (talk) 21:10, 25 March 2008 (UTC)

March 24

Mean tropical year

Is the "mean tropical year" the average of the four tropical years measured respectively starting at the vernal equinox, summer solstice, autumnal equinox and winter solstice, or is it based on a mathematical "continuous" averaging taken over all possible tropical years through the four seasons? I have seen it described in both ways -- does anyone have a definitive answer? 86.134.46.159 (talk) 01:02, 24 March 2008 (UTC) (BTW... I should mention that the Wikipedia article Tropical year contradicts itself in this respect. In one place it says one thing and in another place it says another.)

how do i become taller?

ow i'm over 20 and my height is 5'4" so i want to more tall than before so how can i do? besides go living in asia 141.149.55.113 (talk)

(moved from WT:RD) :D\=< (talk) 04:45, 24 March 2008 (UTC)

There's nothing you can do.. try wearing shoe inserts or buy shoes with thick soles. There is distraction osteogenesis, but it's stupid and, well, absolutely insane. :D\=< (talk) 04:49, 24 March 2008 (UTC)

Aren't you the same person who asked the same question back in January? Do reread the answers at that link. Also read the "Cosmetic lengthening of limbs" section in the distraction osteogenesis article Froth referenced. —Steve Summit (talk) 05:07, 24 March 2008 (UTC)

I'm over 20 and my height is 5'4" so what's the problem? Why would you want to be taller? I think that I'm the perfect height, don't you? Are you saying that I should want to be shorter or taller? Why the hell would I want to be what I'm not? I also don't write poetry - should I worry about that and want to be a poet? Look 141..., you're asking a question like "I am white and I want to be black" or some other such other bullshit. You can and should develop the things that you are good at and not concern yourself with those things over which you have no control. And, asking the likes of us to address the things over which you have no control is really stupid. --hydnjo talk 05:56, 24 March 2008 (UTC)

No use berating the guy for asking a question. Perhaps he thought there might be an easy way to increase his height. (Certainly several completely bogus 'herbal' products are advertised.) Perhaps he has some legitimate and practical reason for wanting to be taller. (Just because we can't think of one off the top of our heads, doesn't mean it can't be true.) Most of all perhaps the guy was just curious. There's nothing at all wrong with that. The point is that it's crazy to rant at someone based not on what they said, but based on your opinions of what you suppose their motives for saying it might be. 72.10.110.107 (talk) 13:50, 24 March 2008 (UTC)

You know, this question was once asked the Cecil Adams on The Straight Dope. He gave some good answers; I'd recommend reading it. Neal (talk) 16:26, 24 March 2008 (UTC).

There is no available drug therapy which can help you grow taller except for in paediatrics where growth hormone therapy can be used, but in adults this is useless. Other than using the |rack, I think you're stuck at 5'4". CycloneNimrod (talk) 17:55, 27 March 2008 (UTC)

Bamboo

I would like to know the kinds of bamboos. Please!

Is there somthing within the Bamboo article that you don't understand? --hydnjo talk 05:59, 24 March 2008 (UTC)

I mean kinds of bamboos! Names of them!I searched in Bamboo but I didn't see that! so....!

The bamboo article says bamboo's in the subfamily Bambusoideae, which has a list of a bunch of kinds of bamboos. It looks like it lists them all, but may be not(?) -Haikon 06:23, 24 March 2008 (UTC)

) thanks u so much! To u all!

How come so many invasive species come from Japan?

...to the United States and Europe? May be "so many" is an exaggeration. I can only think of two, those ladybugs and kudzu, but if you think of Japan as a group of Pacific islands, two is a lot. I mean you probably couldn't import an invasive species from New Zealand or Hawaii if you tried. And given some of the peculiar animals native to Japan, it would seem like that ecosystem would be more on the receiving end of pest invasion.

Anyway, I'm trying to find general rules or theories regarding invasive and non-native species to answer this question, and I'm not coming up with much. (Except a "Baker's rule", and I haven't even found that really, not stated by Baker him/herself anyway.) A lot of isolated ecosystems have been screwed up because of non-native species, and in each case it's understood pretty clearly how and why, but I can't find an explanation of how any why this would happen in general, not just in a given case. Anything at all like an answer or points in the right direction would be greatly appreciated. -Haikon 06:44, 24 March 2008 (UTC)

Your first statement appears to be slightly flawed. New Zealand plants are a problem in other countries, e.g. [6], [7]. It is of course true that exotic plants are more of a problem in NZ then NZ plants in other ecosystems, but then nothing you've said suggests that this is any different from Japan except that the Japanese invasive species are more widespread, but then again, the Japanese ecosystem was always a lot less isolated then NZ or Haiwaii (meaning it was a lot less different). BTW, from what I can tell it is inaccurate to call the Harmonia axyridis a Japanese invasive species. It may be native to Japan but from what I can tell it is also native to other countries. It appears even more clear cut with the kudzu. All these two examples really tell you is that the Japanese ecosystem was not that isolated. You could just as well say any species which is native to Bali or some other small island and invasive comes from a tiny island even if in reality it is native to a lot of places. To answer your second question, in general a species will become invasive if it is able to better fill a niche then any of the existing native species. Countries with highly isolated ecosystems such as New Zealand tend to have a lot of niches which can be more effectively filled by something from somewhere in the very wide world out there. Consider New Zealand for example where the lack of large ground based predators meant that most native animals particularly birds obviously were adapted to such a situation leaving it ripe for invasion by ground based predators. Obviously for very diverse, non-isolated ecosystems like Europe, Asia or whatever, it is unlikely that there will be many niches left unfulfilled or that there will be a whole lot of invasive species coming from the small number of isolated ecosystem which are able to better fill a niche. Nil Einne (talk) 09:16, 24 March 2008 (UTC)

Good answer, Nil. And of course we have an article on Invasive species, which is immensely improved from when I last saw it a couple of years ago. --Allen (talk) 17:04, 24 March 2008 (UTC)

Big bang expansion thing

Okay, space is expanding so from my head it appears my head is the center of expansion. Got it. But am I to understand that at the atomic level space is not expanding? Electrons are not getting further away from the nucleus and the space between atoms and molecules is the same density and the distance between them is the same but what about the distance between planetary orbits? Is that expanding as well? If so by how much in a billion years? 71.100.1.65 (talk) 10:11, 24 March 2008 (UTC)

Short answer is no, space is not expanding at the atomic level because the dominant force that determines the interactions betweens atoms is the electromagnetic force, not gravity. Space is not expanding at the scale of planetary orbits either because the simplifying assumptions on which the Friedmann equations are based are only physically correct on scales of millions of light years or more. For the long answer see this question and its answers on March 21 above, and our metric expansion of space article. Gandalf61 (talk) 13:07, 24 March 2008 (UTC)

Okay, so only gravitational space is expanding? 71.100.1.65 (talk) 20:26, 24 March 2008 (UTC)

Wow, we've got a lot of questions on this lately! --Captain Ref Desk (talk) 14:30, 24 March 2008 (UTC)

Going back to the dots on the balloon analogy in our previous attempt at this question. Draw dots on the balloon, lets call those dots galaxies. Now inflate the balloon - dots get further apart. Now draw some more dots, lets call these dots atoms. take some short pieces of wire and glue the ends to adjacent atoms. Lets call the pieces of wire atomic bonds or crystal lattice. Inflate the balloon again. Do the atoms get further apart? Now give the 5 year old their balloon back. SpinningSpark 23:12, 24 March 2008 (UTC)

Right. Space is expanding on subatomic levels, but nothing is getting farther apart as such things are, in one way or another, stuck together. But if space were expanding fast enough, you might get a big rip. Someguy1221 (talk) 23:33, 24 March 2008 (UTC)

Not sure that we do know that space (or, more precisely, the space-time metric) is expanding on subatomic levels. I see three problems with this:

1. The Friedmann equations, which are used to model the large scale expansion of space, are derived by assuming a homogeneous and isotropic distribution of matter and energy. This is only physically realistic (even as an approximation) on supra-galactic scales of millions of light years or more. The Friedmann equations certainly do not apply to anything smaller than a galactic cluster.
2. The large-scale expansion of space does not have to imply a homogeneous expansion at all places and scales. How do we know that the expansion is not confined to intra-galactic space, for example ? AFAIK, there is no evidence or conclusive argument that says the expansion of space has to be homogeneous.
3. To even begin to model the behaviour of the space-time metric at sub-atomic levels would require a theory of quantum gravity, which does not yet exist. Gandalf61 (talk) 09:51, 25 March 2008 (UTC)

Forgive me for asking a homework question, but how many different hormones are there in the human body?

Discovered at least -- I've searched this all over, and it seems a particularly pointless question to ask (given that we also have to detail every petty step in various signal transduction pathways), but alas, I can't seem to find a source that lists *every* single human hormone, or at least one that tells me that this is every single human hormone discovered so far (and numbers them). John Riemann Soong (talk) 14:33, 24 March 2008 (UTC)

There are hundreds, are you sure this isn't specific to a certain syllabus? --Mark PEA (talk) 16:13, 24 March 2008 (UTC)

Way too numerous to list - there are literally dozens and dozens of small hormones secreted along with the major ones where the physiological function is poorly under stood. However, the predominate hormones are the following (off the top of my head):

• Epinephrine
• Norepinephrine
• Dopamine
• TSH, T4, and T3, Calcitonin
• Parathyroid Hormone
• FSH, LH for reproduction
• The androgens for sexuality and reproduction
• Growth Hormone
• Prolactin
• Oxytocin
• Antidiruetic Hormone
• The hypothalamic tropic hormones (also known as releasing factors)
• Glucagon
• Insulin
• Somatostatin
• Secretin
• Gastrin
• Aldosterone
• Cortisol
• Corticosterone
• Vitamin D3

There are more, but I can't rack my brain any longer Wisdom89 _{(T / ^C)} 18:01, 24 March 2008 (UTC)

Well this is precisely my problem -- I don't want to list them all, I just want a nice (2-digit? 3-digit?) number. John Riemann Soong (talk) 18:16, 24 March 2008 (UTC)

Yeah, extremely difficult per my first comment. Physiologists and endocrinologists incessantly disagree about what substances (mostly small peptides) even constitute a hormone. If I had to give an educated guess (and it is educated) for the major hormones, it would be around 120. Wisdom89 _{(T / ^C)} 18:24, 24 March 2008 (UTC)

here is another list of the major ones, but as others note, some hormones, like the various melanocortins are cleavage products of a pro-hormone (in their case, Proopiomelanocortin). How many different hormones there are from each pro-hormone differs by which criteria you wish to use. Do you wish to count the pro-hormone as 1 or do you wish to count all the possible cleavage products? If you wish to use conservative criteria, there may be around 50, if you wish to include anything anyone has ever called a hormone, perhaps 100-150. Rockpocket 18:45, 24 March 2008 (UTC)

Movie science: what can or can't you tell about a torpedo from its sound?

In the movie The Hunt for Red October, there's a scene in which a sonar operator reports that an incoming torpedo "went active the moment it was launched" and that the torpedo has acquired its target. Is it real science, or is it just artistic license taken by the moviemakers, that a sonar operator is able to tell if a torpedo is armed and has a lock on its target just by listening to its sound? --71.162.242.38 (talk) 16:25, 24 March 2008 (UTC)

I asked myself the same question. A torpedo can be sent out running slow and quiet so that its target might not know it's there until it's too late. Subs maneuver slowly when they aren't going anywhere in a hurry, so the torpedo doesn't need to go very fast to get over near its target. A wire-guided torpedo will be steered by the attacking sub to get it near its target, at which point it will told to turn on its own sonar and home on that, what the movie called going "active", I guess. Faster torpedo propellor speed means higher pitch and louder. (If the torpedo hasn't hit anything after a certain amount of time has passed, and the wire isn't connected any more, it will conduct a search pattern automatically, at which time the attacking sub had better have gotten its butt out of the area.) I would guess that the search sonar and the final homing sonar would differ in some audible way, so that you'd be able to tell when it had "acquired" its target by merely listening. As for whether the torpedo is "armed", I think we're supposed to imagine that Jonsey knows a hell of a lot more about this whole business than we ever will and that some combination of indicators and knowledge of the workings of Russian torpedos clues him in, so just sit back and enjoy the show. --Milkbreath (talk) 16:48, 24 March 2008 (UTC)

As for "has a lock" -- yes, that's easily determined. If you have a bearing to a sound source (e.g. a torpedo) and that bearing doesn't change, the torpedo is on a collision course with you. If the bearing changes, it's heading somewhere else. As far as arming, I'll just go with Milkbreath's encouragement to enjoy the show -- active sonar corresponding with armed torpedo is a reasonable assumption, and I don't recall the dialog precisely enough to nitpick anyway. — Lomn 17:00, 24 March 2008 (UTC)

As said by MilkB, most torpedoes, eg Mark 37 torpedo don't turn on the active sonar until they are close, so when you hear that happen you want to try not to be where the torpedo is going. A sonar operator can tell the difference between a "search" and "tracking" pattern in the same way that an aircraft can tell the difference with radar. A search pattern sweeps the transmission through 360^o, or at least a wide angle. Tracking sweeps over a narrow angle, trying to keep the target illuminated constantly. The military consider tracking an aggressive act and cause for shooting back by the way. So basically, if the sonar operator can hear all the enemy pings or chirps hitting his vessel with no gaps (there would be gaps while the search sonar is pointing somewhere else if it was not tracking) then he can conclude his ship is being tracked. SpinningSpark 19:34, 24 March 2008 (UTC)

arsenic weight per gallon

I am desining an arsenic treatment plant for a small town in CO and I was crious to know how much a gallon of arsenic would weigh?

Thank You,

Michael miklroy04@yahoo.com

The article on Arsenic_contamination_of_groundwater might provide a good place to start. It looks as if most arsenic is in the form of dissolved arsenic salts, and therefore the weight of material to be removed may be dominated by the substance used to remove the arsenic, not by the arsenic itself. JohnAspinall (talk) 16:53, 24 March 2008 (UTC)

1 gallon (US) = 3.785411784 litres, Density of arsenic 5.727  g·cm−3, 1litre = 1000 cm3

So 1 gallon weighs 3.785411784 x 5.727 x  1000 =21679g = approx 21.7kg (that's about (under) 48 pounds)87.102.16.238 (talk) 16:56, 24 March 2008 (UTC)

collapsible longboard???

I heard that some yuppies use a longboard for transportation, which I might be interested in doing also, since I walk for 7 minutes to the metro dozens of times a day. Is this is a nutso idea? Why?

are there any collapsible longboards? THank you!

The positive is it might be slightly quicker, if the pavement is smooth and level. The negatives are that you are more likely to fall or trip other people, you have more weight to carry when not skateboarding, it may be illegal in certain areas, people may view you as childish or a menace, and you won't get as much exercise. I'd say the negatives win. StuRat (talk) 20:03, 24 March 2008 (UTC)

Are people still using folding aluminium micro-scooters in the city? Julia Rossi (talk) 02:15, 25 March 2008 (UTC)

A much easier idea is a moped. ~user:orngjce223 how am I typing? 16:38, 26 March 2008 (UTC)

Static zappage

I work in a library with very fuzzy carpeted floors and metal on the door handles. I am getting shocked almost every time I get up and touch things. It seems that most of the other employees don't get shocked. Are there people who have a higher potential for being shocked? Is there anything I can do to cut down on the number of times I get shocked? I'm starting to get nervous before I open the doors...

It also depends on the clothing you wear - that could be a disparity between you and the other employees. Wisdom89 _{(T / ^C)} 17:54, 24 March 2008 (UTC)

Try comparing the types of shoes you and the others wear, especially the soles. I'm betting that's the answer, as different types of soles pick up a charge more as you trot about. --Captain Ref Desk (talk) 18:09, 24 March 2008 (UTC)

I agree with the previous answers. Also, perhaps your job tends to keep you in one room and/or you walk around on the carpet more, so that a higher charge builds up before you touch the door handles. You might want to intentionally touch the door every few minutes to prevent static buildup. Then again, maybe you are the subject of a secret psychological experiment the other librarians are performing and that would invalidate the results. :-) StuRat (talk) 19:55, 24 March 2008 (UTC)

Leave your hand in contact with something grounded, like a metal lamp, when you get up out of your chair. Carry something metal with you to draw the arc with before you touch the doorknob, maybe a coin or paper clip. Much of the pain of such zaps is actually from the momentary heating of the skin where the arc occurs, and if the arc hits the paper clip first you won't feel that part of it. --Milkbreath (talk) 03:27, 25 March 2008 (UTC)

Why is violet reddish?

Why does violet look more red than green, even though green is closer in wavelength? My first thought was that the higher frequencies of violet are an octave of the lower frequencies of red. However, the shortest wavelength of violet is 380 nm and 740 nm as the longest for red, so the octave of violet is not visible. --196.209.178.23 (talk) 20:13, 24 March 2008 (UTC)

It is because the red receptor in the human eye has a slight response to second harmonic wavelength also. This happens to peak towards the high end of the blue spectrum which causes us to interpret light of this wavelength as violet. SpinningSpark 20:26, 24 March 2008 (UTC)

Oh sorry, I did not bother to read all your question. I have some plots of human eye response somewhere from BBC colour vision research which definitely show a second smaller peak in the red response. Of course, you can never find this stuff when you need to answer a question. I assume you got your figures from the color vision article which seems to fail to show this second peak. Possibly the other figures there are non too accurate. SpinningSpark 20:38, 24 March 2008 (UTC)

Human cone responses

Human cone responses

Take a look at this, you can just see the second peak, it is very small, the plot is relative level instead of dB as any sensible engineer would have done. But you are right that it is well off the second harmonic. SpinningSpark 21:16, 24 March 2008 (UTC)

Cladistic definition of crown groups

Let's imagine metatherians and prototherians become completely extinct in a few years, and eutherians are the only surviving mammals. Cladistics define the class Mammalia as:

"the last common ancestor of all living mammals and all of its descendants"

In this imaginary situation, this would mean "the last common ancestor of all eutherians and all of its descendants", thereby declaring marsupials and monotremes as non-mammals! Isn't this a little absurd? How do you solve this paradox? -- Leptictidium (mammal talk!) 20:14, 24 March 2008 (UTC)

After reading Tudge The Variety of Life I came to the conclusion that all of cladistics is absurd. Non-avian dinosaurs, "no such thing clade as fish" - really whatever next. SpinningSpark 21:21, 24 March 2008 (UTC)

I think the cladistic definition would simply be changed to "the last common ancestor of metatherians, prototherians, and eutherians". It might be stated that way in some technical definitions even now. Note that the ICZN does not currently regulate taxa above family level, so classes, etc. are in flux anyway.

Cladistics only makes sense if you accept that the goal of taxonomy is to reflect evolutionary relationships. As Spinningspark points out, fish are actually 3 or 4 separate clades [depending whether you put hagfish and lampreys together; I'm used to 3 clades, jawless fish, cartilaginous fish, bony fish]. Vultur (talk) 22:16, 25 March 2008 (UTC)

Balloons and teleportation

I'm writing a story in which one of the characters can teleport instantaneously from place to place. At first, I intended this to be silent, but my brother has pointed out to me that her sudden appearance would result in some pretty intense displacement of air, so the sound of her teleporting should be a lot like that of a very large balloon exploding.

I think this is kind of awesome, but I want to make sure it's right before I use it. What do you all think? --Masamage ♫ 21:07, 24 March 2008 (UTC)

I assume that when you say teleport instantaneously you mean not only that the travel time is zero but the rematerialization period is also zero. If the rematerialisation period was longer (i.e. star trek) there would be no massive displacement of air, ir would be gradual. Anyway, I doubt there would be a sound akin to an exploding balloon. The balloon sounds like that because it is a large amount of air being released from a small area having previously been under very high pressure. To suddenly materialise in air (assuming that all the air is deflected away from you from your centre, rather than being trapped between your particles as you materialise?) would produce something akin to a sudden rush of wind, as the amount of air in the space now occupied by your character has been pushed outwards. The speed of which would, in theory, only be enough to get it out of the way (maximum distance is the same as the dimensions of your character) and the air would probably not go very far before hitting other air molecules. Less of an exploding balloon, I'd say, and more of a sudden, thick but short gust of wind? That is again, of course, depending on the speed of your materialisation. SGGH ^speak! 21:26, 24 March 2008 (UTC)

Yes, you have it about right for how fast I was thinking she would materialize (although the idea of slow, Star Trek-style beaming is interesting, too). So then, if I understand you right: the displaced air isn't under enough pressure to make that loud and sharp of a noise, so in actuality all that would happen is a sort of fwoosh sound, and maybe nearby people's clothes wafting a little in the wind. And a similar thing would happen to fill the space where she left, right? --Masamage ♫ 21:36, 24 March 2008 (UTC)

(ec) It depends on the mechanism you've chosen for your particular fiction. If air is forced out of the volume to be occupied by the incoming traveller extremely rapidly (as with a near-instantaneous teleportation) then it will generate a shockwave as it moves—a small sonic boom. It will, indeed, be loud.

Now, your teleporting individual would be in a world of hurt if they don't materialize from their center out—that would trap air molecules within the body. Very messy. Slow materialization could be problematic, too—what happens if the character moves during teleportation? A bit of liver here, a bit of lung over there, blood flows down the left leg and back up the right, no problem....

Of course, you could always choose a mechanism where a 'swap' takes place. Simultaneously beam in your character, and beam out the air. If done correctly, it's quiet at both ends. TenOfAllTrades(talk) 21:43, 24 March 2008 (UTC)

Since the method of travel has some air of unfeasability or even ridicule to it, I'd personaly go for a more humoristic sound like a pop or plop or even a whizz or shebang. Anyways. Think too that you could make the business of teletransportation easier if instead of moving just the physical person, you define a volume (a la Terminator) of air emveloping that person. Since it teletransports indiscriminatly a volume of space it can even be used as a plot twist in a story. See you later. Shwabwabwabwabwaaawawawa ... piuut, pop. 200.127.59.151 (talk) 21:44, 24 March 2008 (UTC)

One more thought, depending on whether you're doing science fiction or fantasy. You could generate a 'force field' or something of that sort at the reception point to move the air out of the way slowly; by 'slowly' I mean the field boundary doesn't expand faster than the speed of sound. Your character (with air from his departure point around him) can just pop into the premade vacuum as quick as he likes. Again, nice and quiet. TenOfAllTrades(talk) 21:47, 24 March 2008 (UTC)

Rematerialization time cannot be zero, because the air molecules can't move faster than light to get out of the way. If you got them moving close to the speed of light, I think you'd have a pretty violent event, especially if the teleportee resembled John Goodman. Either the machine would have to force the air molecules aside before materializing the person where they had been, or the person would have to materialize from the center out, in which case they would be subjected to whatever force was needed to move the air. On the sending end, no such problem, and I'd expect a rather soft unidentifiable slap or pop sound. How about you take the air from where you're going and put it back where you came from; swap the person and the air? --Milkbreath (talk) 21:50, 24 March 2008 (UTC)

Hmm, okay. So one vote for a windy sound, one for a sonic boom, one for a patooie, and one for it not even being possible. Also, two votes for swapping the person with the air; my brother had suggested that, too. The weird thing about that, though, is that anything in the air gets popped over, too; dust, smells, poison gas, etc. Also, if the places had different barometric pressures, there still might be some wind. (And if she teleported into a wall, she'd leave a statue behind.) --Masamage ♫ 21:56, 24 March 2008 (UTC)

Note that apparently this was followed in the recent film Jumper, though I haven't seen it. I read an interview with the director in Entertainment Weekly where he talked about the whoosh you'd hear by suddenly creating a little vacuum where you once were. He was quite proud of himself for figuring that one out. --Captain Ref Desk (talk) 22:00, 24 March 2008 (UTC)

too bad he couldn't figure out how to make a good movie --LarryMac | Talk 15:39, 25 March 2008 (UTC)

Of course, you could always decide that the teleportation mechanism is a swap rather than a one-way jump. If the teleporter jumps from A to B, the volume of air that she displaces jumps simultaneously from B to A. Then it could be totally silent -- although of location A is far enough away that the barometric pressure is different there, then there might be a small sound at location A.

And, doing it this way, what if there is water or a solid object at location B? Then perhaps a person-sized hole would appear in that water or object, and a corresponding chunk of water or other material would be transported to B, where it would fall to the ground with an almighty crash or splash. And if that material was part of a living thing, it could get rather hideous.

Just a thought -- you are welcome to use it if you like it. --Anonymous, 23:11 UTC, March 24, 2008.

According to our lexicon (and also the Jargon File), the sound of teleportation is "bamf", and this comes from the Marvel Universe. Also, in Sam Hughes', "Fine Structure" stories, teleporting sounds like a thunderclap. – b_jonas 18:04, 25 March 2008 (UTC)

well, if you're going to be serious about it.... you've obviously got to deal with the air or whatever occupying your target zone, and displacing it causes a lot of problems, so swapping it makes the most sense.

but also, conservation of momentum; if you're getting teleported from Australia where you're whipping along with the surface of the earth, to the US where the surface happens to be heading in the opposite direction at equal speed, you're going to appear with a net relative velocity of like 1500 mph. this will cause a certain amount of noise, depending on what you smack into, including just the air. Gzuckier (talk) 18:42, 25 March 2008 (UTC)

The conservation of energy issue has come up in fiction before. I recall a murder-mystery-science-fiction story (probably by Asimov, as he liked that sort of thing) in which a key plot point dealt with teleporter travel between points at different altitudes. In the book's early-model teleporters, excess gravitational energy would show up as added heat in the teleported person or object. (My back-of-the-envelope calculations put the temperature change of a human body at about 2.5 degrees Celsius per kilometer of altitude, or about 1.3 degrees Fahrenheit per 1000 feet.) Round-the-world teleportation (and the associated problems of relative velocity) were not addressed. TenOfAllTrades(talk) 16:38, 26 March 2008 (UTC)

b_jonas, Sam Hughes used the swapping method, but the person was teleported into space (technically, they were teleported into a coal seam, which was then teleported into space), so it sounded like the one-way version. 67.182.186.132 (talk) 23:03, 25 March 2008 (UTC)

It certainly wouldn't be a really loud crack/pop, but it could be a bit of a whoosh. Quite unlike Ms. Rowling's Harry Potter. ~user:orngjce223 how am I typing? 16:42, 26 March 2008 (UTC)

More Teleportation

In Robert Heinlein's Stranger in a Strange Land Michael idly toys with the idea of destroying the solar system by teleporting a piece out of the centre of the sun. Although capable of doing this he does not actually go ahead so we never got to see how it would turn out. Would this work, and how big a piece would be necessary? SpinningSpark 23:47, 24 March 2008 (UTC)

I can't see it destroying the solar system unless enough was transported out to alter the gravitational system into essentially a binary star system. However, if a sizable chunk of the Sun's interior was transported onto Earth, it could probably destroy the planet. StuRat (talk) 03:26, 25 March 2008 (UTC)

Not sure, but I think the idea was that the consequent collapse into the now empty space would cause some kind of nova followed by crispy planets. Would it? SpinningSpark 07:47, 25 March 2008 (UTC)

Wouldn't taking out a significant chuck of the core of the Sun effect its fusion reactions as "the core is the only location in the Sun that produces an appreciable amount of heat via fusion: the rest of the star is heated by energy that is transferred outward from the core"? I guess that would be the destruction of the solar system, but certainly life on earth. -- MacAddct  1984 ^{(talk &#149; contribs)} 14:07, 25 March 2008 (UTC)

If you removed enough fuel from the core it would prematurely become a red giant. That would destroy the earth, not sure about planets at more distant orbits.

What about the effect on orbits? if any?Gzuckier (talk) 18:36, 25 March 2008 (UTC)

As the sun loses mass its gravitational force weakens, causing the planets to move to higher orbits. This paper discussed in the NY Times suggests that even despite the higher orbit, a red giant sun will still swallow the earth.66.152.245.18 (talk) 19:05, 25 March 2008 (UTC)

An abrupt change in the Sun's mass would convert each planet's orbit into one that was higher on average, but still passed through the point where it was at the time of the change. So if the planet happened to be near perihelion, its aphelion would get higher but its perihelion would stay about the same: it would be a more eccentric orbit. If it was near aphelion, the orbit could become less eccentric than before (depending on how eccentric it previously was, and on the amount of mass change). --Anonymous, 23:33 UTC, March 25, 2008.

This just reminded me of the Stargate episode, Exodus where a Stargate connected via a wormhole to another stargate that was orbiting a blackhole was shot into a star. Mass from the star was sucked through the wormhole by the black hole and the star went supernova.--Shniken1 (talk) 23:52, 25 March 2008 (UTC)

March 25

Red wine "breathing"

Does it really make a difference if you uncork a red wine bottle a couple hours before drinking it? There can't be more than a square inch exposed to the air. I can't really see how it could affect the rest of the wine. I know some people let it breath in a wide caraffe, but I know a number of wine people who will insist on just uncorking the bottle for an hour or so before serving.

Have there ever been any blind taste tests to see if people really could tell the difference between wine that has breathed or not?

James. 00:51, 25 March 2008 (UTC)

Hello James. You're right in that the small surface area from just uncorking the bottle does very little. It is somewhat of a silly practice. (Like sniffing the cork :p) However the process of decanting can have a pronounced influence on the tannins (at least the perception of them) and aroma development of the wine. The act of pouring the wine, with the motion and the splashing, will also contributes quite a bit to this aeration. While I'm not familiar with any published blind tasting test, there is an easy experiment that you can do at home. You don't need a decanter, just pour yourself a glass of wine and let it sit for half an hour. Even in that short period of time, the wine in your glass (with the larger surface area) will show some change in the aromas and flavors due to the aeration. Though do note that the extent of change will vary depending on the wine. Some wines (like Burgundies) will have more noticeable changes due to aerating than say a California Zinfandel. Agne^Cheese/^Wine 03:14, 25 March 2008 (UTC)

It's very easy to do double-blind. Take out two wine glasses. Tell your friend to stay in the living-room. Pour one glass. Go talk to him for half an hour. Tell him to come into the kitchen for a minute...meanwhile, pour the second glass. See if he can tell which was aerated.

Sorry, to make it DOUBLE-blind, tell him to come in and see which one is aerated before you yourself know :)

Get two bottles of decent Australian Shiraz (should be around US$10-US$20 at the moment). Open one 4 hours before dinner and decant (or pour), the other directly before dinner. Be sure to keep all the wine at room temperature. Even I can taste the difference, and I'm a barbarian.The undecanted wine typically is harsh and has a slightly bitter note, the decanted one is much more mellow and fruitier. --Stephan Schulz (talk) 09:55, 25 March 2008 (UTC)

Even better, to answer James' original question: If you have a Trader Joe's market near you, buy two bottles of "Two Buck Chuck". Both should be the same grape and vintage year. Open one bottle, but don't pour it! Just let it sit open on your kitchen counter for, say, 4 hours, with the other bottle next to it to ensure both stay the same temperature. Then have a friend or family member go alone into the kitchen, open the second bottle, and pour an equal volume of each into two identical glasses, and note secretly which glass is the aired-out one. Your assistant then leaves the kitchen. You go in and taste, and see if you can detect not just a difference, but whether one tastes better than the other.

The reason I suggest Two Buck Chuck is because I have noticed that among all the wines I have bought, Two Buck Chuck experiences the most profound change, almost becoming un-drinkable a day after you open the bottle. This test will determine whether that 1 square inch of surface area makes any difference after opening a bottle. ~Amatulić (talk) 17:24, 25 March 2008 (UTC)

Even better if you can get three samples going - the unopened, the opened, and a decanted one. And then, of course, you're going to have to do something with all that wine you've just opened - sounds like an interesting dinner party experiment to me (which also means you get results from multiple people). Confusing Manifestation(Say hi!) 23:12, 25 March 2008 (UTC)

There is a small pourer which induces air into the wine as it is poured so you don't have to wait (agonising!) before drinking. Use mine every day, Hic, pardon.--Artjo (talk) 08:41, 26 March 2008 (UTC)

Hormonal Cycles In Men

Hello there! I was wondering whether men have some type of hormonal cycle at all, whether it be during certain times of day, of the week, or of the month, and where a certain hormone is more prevalent or at its peak at one moment than at others. I'm not suggesting men would have a similar cycle as the menstrual cycle in women, but I was just wondering whether there are times when a certain hormone is more active or less active.

Men have diurnal hormone cycles for such things as cortisol, ACTH and growth hormone - among others. Wisdom89 _{(T / ^C)} 00:59, 25 March 2008 (UTC)

Melatonin is a good example. Rockpocket 06:51, 25 March 2008 (UTC)

Please read the article on Circadian rhythm. If you have any questions remaining, feel free to ask. Best wishes, --Dr Dima (talk) 12:28, 25 March 2008 (UTC)

Also, there is the GnRH --> LH --> T negative feedback loop. Basically, the hypothalamus (little gland in the brain) releases an hormone called GnRH that tells the pituitary gland (another little gland in the brain) to release a hormone called LH. The LH then proceeds to the testes and tells them to secrete testosterone (T), a steroid hormone with which we are all familiar. But then the testosterone, circulating through the blood, tells the hypothalamus to stop secreting GnRH, which in turn slows down LH production, which in turn slows T production, which permits GnRH secretion again... This is a classic negative feedback loop with a period of, if memory serves, roughly four hours, and again if memory serves this does result in periodic peaks and troughs of adrenaline, which can have both physiological and psychological effects. See [[8]], for example. It is analogous (or homologous) to the female GnRH --> FSH --> E/P cycle. It also bears mention that men have been reported (though the homology is subject to controversy) to undergo "andropause" after middle age. Vance.mcpherson (talk) 13:37, 25 March 2008 (UTC)

How do I become a stuntman?

I love Jackass and Dirty Sanchez. I like doing extreme, painful stunts to impress my friends (found something that I'm good at). How do I get to be on TV like those guys? I don't wanna be just another one of those guys who posts his stuff on YouTube and gets called a reckless idiot. I want to be a reckless idiot on TV.

You must have an exceptional pain threshold that can be put to good use. There's stuntschool.com in the USA here[9] and googling "stunt man training" gets you lots more stuff you might like – our articles stunt performer, stunt double and stunt coordinator look brief. Otherwise popping this whole thing onto the entertainment desk might get more details. Please sign your posts with four ~ and good luck, Julia Rossi (talk) 02:05, 25 March 2008 (UTC)

Hanging swamps

I'd like to start an article on hanging swamps but can only find a few things on google limited to the Blue Mountains outside of Sydney and on wikipedia, only to one in particular though there are more. Does anyone have references they could suggest? Are they found in other parts of the world as well? Thanks, Julia Rossi (talk) 02:08, 25 March 2008 (UTC)

SOunds like they would have another name - perhaps alpine meadow. In the ACT a sphagnum bog is the source for the Cotter River. Graeme Bartlett (talk) 03:52, 25 March 2008 (UTC)

Superficially they look like a combination of both. The trees only come to the edge of it, and it's on a slope rather than level ground, without many rocks. Julia Rossi (talk) 07:33, 25 March 2008 (UTC)

online versus offline wetlands

What is the definition of an online wetland? I expect it has something to do with being in a drainage line but where is the line drawn in terms of the hydrologic capacity of an online versuus offline wetland?

Yeah, I think has something to do with how it drains (online=draining, offline=not draining, most of the time). I don't know where I picked that up, though. But I believe it has nothing to do with the amount of WiFi access within the area tho :P ~user:orngjce223 how am I typing? 16:48, 26 March 2008 (UTC)

Atomic Force Microscopy

I've got an assignment on AFM and one of the questions relates to metal nanoparticles on a teflon coated magnetic stiring bead and how to image them. I'm a bit ^stuck with how one would go about imaging this as the surface needs to be quite flat. Would it simply be a matter of cutting a piece of the stirrer bead off and flattening it with a press of some kind? Any other ways in which the stirring bead can be flattened so that it can be imaged? How flat would it need to be? Thanks --Shniken1 (talk) 05:22, 25 March 2008 (UTC)

I wouldn't suggest flattening it as that could significantly change the structure. Instead, you need to cut a very narrow slice and put it on a slide. StuRat (talk) 06:31, 26 March 2008 (UTC)

What model Saab is this?

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I can't ID it from the Saab article, but am guessing it's one of the older models. BrokenSphere^{Msg me} 05:37, 25 March 2008 (UTC)

Hi Brokensphere, I found something like it here[10] of a 96V4 also butterscotch coloured, but doesn't give the year. Julia Rossi (talk) 07:08, 25 March 2008 (UTC)

Ps, if you scroll down further to the white one, they put it at 1970. Cheers, Julia Rossi (talk) 07:10, 25 March 2008 (UTC)

It looks like a Saab 96 - see especially the picture of the 1965 model near the bottom of the article. Are you sure this is a science question? 84.239.133.86 (talk) 07:56, 25 March 2008 (UTC)

Or maybe a Saab Sport given the chrome striping at the bottom (although strictly speaking it should be a double stripe, unless one's been lost - see here). I don't think the 96 had any chrome stripes, unless they added them later. --jjron (talk) 10:00, 25 March 2008 (UTC)

Stuck in fetal position?

When I was much younger... something like 12, I woke up one morning and couldn't get out of the fetal position. It hurt one of my hips (maybe a hip flexor muscle) so much when I tried to straighten that leg out that I had to straighten up slowly over the period of about half an hour it seemed. I'm not asking for advice, just a list of possible things that might have caused this, or any other insights... but no advice please. Sancho 06:23, 25 March 2008 (UTC)

Muscle cramp? Dismas|^(talk) 09:02, 25 March 2008 (UTC)

Stupidity? Weasly (talk) 12:21, 26 March 2008 (UTC)

Given the following two premises: (1) a large body of science fiction which creates a connection between pregnancy, fetuses, and alien abduction, and (2) the existence of sleep paralysis and its supposed explanation for alien abduction; is it possible you are or were a character in a science fiction novel? Nimur (talk) 14:42, 26 March 2008 (UTC)

Battery life meter

One of the more annoying "features" of my cell phone is that the battery life meter doesn't tell you how much life is left in the battery. It tells you how much is left if you continue doing whatever it is that you're doing with the phone until the battery is depleted. So if I just open the phone up, I could have 3/4 of a charge. If I start taking photos and sending them to my friends, the battery indicator goes down rather quickly and sometimes even causes the phone to warn me that the battery is running low. Although if I close the phone and re-open it, I again have 3/4 charge. Is there a term for this sort of battery meter other than annoying? Dismas|^(talk) 08:26, 25 March 2008 (UTC)

"Typical" :-). But I'm not sure what you want it to do. A battery life meter can't give you some sort of absolute measure of how much time it's got left, because that's dependant on the usage, especially for something like a mobile phone with a small battery and high fluctuations in demand. If you were doing something like playing a radio on batteries where the current draw was constant, an absolute measure would be more feasible. If anything this is a 'smart meter', because it's detecting your current usage and adjusting the available life shown on the meter accordingly. --jjron (talk) 09:44, 25 March 2008 (UTC)

This reminds me of the Rand McNally GPS unit I had. It would estimate my ETA based on my current speed, not on the average speed of the trip so far. The result was that when I stopped at a traffic light it said the trip would take an infinite amount of time to complete. StuRat (talk) 06:27, 26 March 2008 (UTC)

Did it actually use the infinity sign? If so then I must credit the programmers/engineers for having a sense of humor--droptone (talk) 11:35, 26 March 2008 (UTC)

No, it said something like 9999 minutes, the largest number it could display. StuRat (talk) 13:53, 26 March 2008 (UTC)

Hey, it could be worse. My cell phone won't tell me what time it is if it loses signal. I'm all for it checking it dynamically with the tower and updating as necessary, but totally being unable to tell time without a signal? Terrible design. --Captain Ref Desk (talk) 13:02, 26 March 2008 (UTC)

Axes of rotation, revolution, magnetic field, of the earth

Among the axes of rotation, revolution around the sun, and magnetic field, of the earth, which are parallel to each other, and which are not? Why are they parallel (or not)? --Masatran (talk) 09:44, 25 March 2008 (UTC)

See Earth's rotation for starters. The diagram Image:AxialTiltObliquity.png is quite simple to interpret for the relationship between rotation and revolution. For 'why', particularly see the section Origin of rotation and the pages that links to. See Earth's magnetic field for the magnetic field - it is close to the geographical rotational axis, but not the same. --jjron (talk) 10:18, 25 March 2008 (UTC)

As for why the magnetic poles don't match the North and South Poles, I believe that is because the Earth's composition is neither uniform nor static. Different materials conduct the magnetic field better than others, which deforms the field slightly. Interestingly, the magnetic poles aren't necessarily on the exact opposite sides of the Earth, vary over time, and even invert over long time periods, ty[pically after a long period of instability. StuRat (talk) 06:24, 26 March 2008 (UTC)

Effect of elliptical orbit of earth on climate

The distance of the earth from the sun changes over the year because the orbit is elliptical. What effect does this have on the climate of the earth? --Masatran (talk) 09:53, 25 March 2008 (UTC)

Some of the ice ages are thought to be one consequence. Check out Milankovitch cycles. 88.114.125.67 (talk) 10:24, 25 March 2008 (UTC)

The effect should have a time period of one year, right? It will be hotter when the earth is closer to the sun, and colder when the earth is further away from the sun. Is this effect present? And what is this effect called? --Masatran (talk) 10:31, 25 March 2008 (UTC)

Seasons? Dismas|^(talk) 10:35, 25 March 2008 (UTC)

When I was a kid, I thought likewise. But now I know that seasons are caused by the inclination of the north (or south) pole towards the sun. --Masatran (talk) 10:52, 25 March 2008 (UTC)

Masatran is right. There's a very easy way to see this. The effect of an elliptical orbit would be to make the whole earth warmer or cooler. The effect of an orbital tilt will be to make the northern hemisphere warmer while it makes the southern hemisphere cooler. (And vice versa six months later.) As the Season article points out, it's the latter we observe: "At any given time, regardless of season, the northern and southern hemispheres experience opposite seasons." JohnAspinall (talk) 13:52, 25 March 2008 (UTC)

The Earth is slightly hotter at perihelion than at aphelion, and this is a one-year period (give or take, I think there's some precession thrown in there as well) as you surmised. However, any effects are dwarfed by the changes resulting from the Earth's axial tilt (that is, seasons). If I recall correctly, aphelion corresponds roughly with northern summer and southern winter. — Lomn 13:06, 25 March 2008 (UTC)

That is correct. I've heard that this, along with the presence of the gigantic Antarctic ice cap, makes Southern Hemisphere winters colder than Northern Hemisphere ones at the same latitude.

I don't think it is true that northern winters are warmer than southern ones. A quick comparison of the latitudes of North American cities to southern Australian ones shows the opposite is true, c.f New York City with Melbourne or Hobart. I don't know how representative this is though.--Shniken1 (talk) 23:20, 26 March 2008 (UTC)

Concentrating DNA samples

If I have DNA which I want to concentrate 2.5x, could there be a problem with, say storing the tubes open in a container with some of those sodium silicate dissicating crystals to lower humidity? They can't be run through a column because that's where they've been already and that process involves too much loss. --145.29.23.38 (talk) 11:22, 25 March 2008 (UTC)

Why not do a standard ethanol precipitation of the DNA and resuspend the dried pellet in a smaller volume? it won't take more than half an hour or so. -- Flyguy649 ^talk 15:43, 25 March 2008 (UTC)

Never done it before (I'm just a lousy intern) - I'll ask my supervisor if we can do that. Thanks very much :) --145.29.23.38 (talk) 17:00, 25 March 2008 (UTC)

Fairly simple. Just increase the volume of your DNA sample with Tris buffer (doesn't have to be much). Add 3-5 volumes of either cold isopropanol or ethanol and centrifuge for 30 minutes at 15,000 RPMs (JA-20 rotor) or 12,000 RPMs in a microfuge depending on the size your sample. When the pellet is present, simply redissolve it in 2.5x's less Tris buffer. Wisdom89 _{(T / ^C)} 18:48, 25 March 2008 (UTC)

Or you could check if there is a vacuum centrifuge in the building (no article yet, but is basically spins the DNA while evaporating the liquid. Rockpocket 07:19, 27 March 2008 (UTC)

Dutch tulip forecast

It has been snowing and cold in Holland all through the Easter weekend, and beyond. Can anyone refer me to a website with a forecast for the 'peak' of the 2008 tulip season. It must change...with the weather, I would think. Presumably as the weather stays cold, the peak moves further into April. Thanks if you can show me to a reference where I can get an estimate for the peak days/weeks.

The scientific method

This image summarizes the basic technique for study of the Earth's interior. Nimur (talk) 14:46, 26 March 2008 (UTC)

How do scientists find out about the updates and changes in the earth's crust? What are the technolgies needed to find out about the structure/different layers of the earth?

You'll probably want to start with the Composition and structure section of our article on the Earth and work out from the links there to get all the details. TenOfAllTrades(talk) 16:15, 25 March 2008 (UTC)

You can also look at the geology, Plate tectonics and stratum articles. Sandman30s (talk) 14:24, 26 March 2008 (UTC)

Don't forget to read about seismic waves. Seismometers are essential instruments (technology) and by comparing the readings at different locations, we can infer the structure of the earth. Nimur (talk) 14:45, 26 March 2008 (UTC)

Mobile Phone Noise

First of all, I live in the UK, which I guess may be relevant.

When I leave my mobile phone next to seemingly another peice of electrical equipment, there is a noise which prempts text messages and calls. My tv, computer, hi-fi, anything.

It's that strange "du duh-de-duh duh-de-duh" noise (which I put into Google, but alas...) What causes it and why does it show up on everything, even things that wouldn't be thought to be interferred with my a mobile's signal? A good example of that would be through my Ipod, and out of my earphones.

Thanks a lot. Fenton Bailey (talk) 16:04, 25 March 2008 (UTC)

Every time your telephone communications with a central cellular tower (when you have an incoming call or message, or periodically when the phone handshakes with the tower) it broadcasts a fairly strong radio signal. The wires of your headphones, speakers, stereo, or television act as (not-very-good) antennas which pick up some of that radio signal and overlay it on top of whatever else you're listening to. TenOfAllTrades(talk) 16:13, 25 March 2008 (UTC)

I have found the effect is more severe when the phone is near an amplifying device (powered speakers, for example); this suggests that the cell phone's RF transmissions may couple directly into the amplifier, rather than the feed wires as antennas. Surely it's some combination of the two. Nimur (talk) 14:48, 26 March 2008 (UTC)

That is correct. I use this little fact to tell my friends their phone is about to ring by paying attention to the car radio, they still haven't figured out how I do it. 206.252.74.48 (talk) 16:59, 25 March 2008 (UTC)

Heh, I do that too. They ask how do I do it, and I just say "nerd-sense". — Kieff | Talk 01:31, 26 March 2008 (UTC)

Electromagnetic interference.--Shantavira|^{feed me} 17:40, 26 March 2008 (UTC)

Why do deep footprints in snow look blue?

I was walking in the snow with my daughter today, and we had to cross some deep drifts, where our feet sunk over a foot into the snow. When we looked into the holes there was a distinct blue tinge, though the snow itself was white. My daughter asked me why this is, and I didn't know. Pools of melt-water were crystal clear, with maybe a slight greenish tint but that could have been because of the grass at the bottom, so it is not because of absorption by the water, unless it acts differently as ice. -- Q Chris (talk) 18:21, 25 March 2008 (UTC)

I don't know if this is the explanation, but water is a bit blue. See color of water. Ahh, here we go- one of the references used in that article is this which I think is pretty relevant. Friday (talk) 18:24, 25 March 2008 (UTC)

If the surface of the snow was in direct sunlight, the bottom of your footprint could look blue because it is shadowed by the wall of your footprint. Outdoor shadows look blue because they are illuminated by the blue sky, a phenomenon that photographers will be familiar with. I have found the color difference to be very noticeable on snowfall. -- Coneslayer (talk) 18:45, 25 March 2008 (UTC)

Indeed, red is scattered less than blue by the atmosphere, so a larger fraction of red (than of blue) comes straight along the direction from the sun, and smaller fraction of red (than of blue) comes from the other directions. If the hole walls block the direct sunlight, the bottom of the hole will be illuminated by the light which has a larger fraction of blue (compared to the fraction of blue in the white light, that is, the light you see on the snow that is illuminated from all directions). So the snow is not blue, it is white; rather, the light illuminating it is relatively rich in blue. On the other hand, water and transparent ice are genuinely blue, see blue ice (glacial). --Dr Dima (talk) 20:58, 25 March 2008 (UTC)

Quantum Number Sets

The quantum numbers article (http://en.wikipedia.org/wiki/Quantum_numbers) says that the magnetic quantum number should be between the negative and positive values of the azimuthal quantum number.

If I come across the notation 3d₄,+1/2 or 5f₅,-1/2, would those be considered wrong? Because d=2, so the magnetic quantum number should be between -2 and 2, so 4 doesn't make sense. Same with f being 3 so 5 doesn't fit between -3 and 3. -- Zealz (talk) 23:49, 25 March 2008 (UTC)

That's correct. Those symbols don't refer to any real states. —Keenan Pepper 02:41, 26 March 2008 (UTC)

March 26

Faster than light/Big Bang question

Whatever universe theory currently has scientific consensus (which I assume is based on the Big Bang model) seems to suggest that the universe is 13.73 billion years old and 93 billion light years in diameter. The Big Bang theory also states that the universe started from one point of infinite density. Therefore what seems to add up in my head is that the matter in this point which is now at the far reaches of the observable universe must have moved at least 46.5 billion light years in 13.73 billion years at most, which is faster than light. Is this the case, and if so how is moving FTL possible in this case? 212.49.210.38 (talk) 02:56, 26 March 2008 (UTC)

Take a read of this URL http://www.astro.ucla.edu/~wright/Dltt_is_Dumb.html which is the reference given to expalin the misconceptions in the time. The basic reason is that you cannot measure a distance between two point seperated so far in time. At great distances the relationship becomes non-linear. Graeme Bartlett (talk) 03:13, 26 March 2008 (UTC)

(ec) See Observable universe#Misconceptions. DMacks (talk) 03:14, 26 March 2008 (UTC)

Simplified explanation: the oldest photons that we can detect are the photons in the Cosmic microwave background radiation, which were emitted about 400,000 years after the Big Bang. It has taken those photons about 13.7 bn years to reach us. But in those 13.7 bn years the space between here and the places where those photons were emitted has expanded. It is possible for space itself to expand faster than light - the speed of light is only a limit for objects moving through space. So the places where these photons were emitted 13.7 bn years ago are now about 46 bn light years away from us, not because anything has moved, but because space itself has expanded. (Yes, yes, I know I haven't mentioned the cosmological constant, the changing value of the Hubble parameter, red-shift, the curvature of space, the difference between comoving co-ordinates and proper distance etc. etc. etc. - that's why I called it a simplified epxlanation) Gandalf61 (talk) 12:26, 26 March 2008 (UTC)

The explanation leaves the impression that if objects A and B are at points 1 and 2, 1 billion light years apart, then the "space" between them could "expand" to 4 billion light years in a period 1 billion years, somehow without objects A and B moving faster than the speed of light. Would this same process be applicable to 2 objects 1 light year apart, which could via "space expansion" become 4 light years apart in 1 year? Why couldn't Spaceman Biff use "space contraction" to travel between 2 planets 4 light years apart in 1 yea4 without travelling faster than the speed of light. If the distance between points can increase via expansion, why is the process irreversible? Sorry for the simplistic question, but the usual explanations lead to such conjecture. Edison (talk) 13:44, 26 March 2008 (UTC)

If the planets are 1 light year apart when Biff sets out from planet A and Biff travels at the speed of light and we assume that the planets are stationary with respect to each other but the space between them is rapidly expanding then it will take Biff longer than 1 year to reach planet B. On the other hand, if planet B is 4 light years from planet A when Biff reaches it, then his journey will have taken less than 4 years, because of the expansion of space. To see the hypotehtical effects of a rapidly contracting space-time metric, I guess you could run the movie in reverse. All these times are in the frame of reference of both planets - in Biff's frame of reference, travelling at the speed of light, the journey takes zero time and he covers zero distance. Gandalf61 (talk) 14:53, 26 March 2008 (UTC)

You may want to read the article on the Alcubierre drive. — DanielLC 20:30, 26 March 2008 (UTC)

The quick answer as to why we couldn't use contraction of space to travel FTL is that we haven't found a decent way yet - various models have been proposed to do just that, but almost invariably they require at least one of two things: (a) thousands of times more energy than is available in the known universe, and (b) some unknown type of exotic matter that could somehow generate "negative energy". The Alcubierre drive apparently doesn't require much exotic matter any more, but it still needs some, and as yet there's no proof that such a thing even exists. Confusing Manifestation(Say hi!) 23:18, 26 March 2008 (UTC)

I am no expert by any means but my understanding is that shortly after the big bang the universe was indeed expanding much faster than the speed of light.Em3ryguy (talk) 00:24, 28 March 2008 (UTC)

Red cross society in Taiwan?

Hi, maybe this can be a sensitive issue. Since (the current elections in republic of china), among protests on tibet, etc. But i want to focus on the question putting aside any political blur.

Okay, basically, i have been trying to look here Category:Red Cross national societies, but i didn't get any clue about this

Is there a Red cross society in Taiwan (R.O.C) and in China (P.R.C)?, are those countries represented in one of them? or splitted?.

I really need to get a clue about this. Thanks in advance. --HappyApple (talk) 06:59, 26 March 2008 (UTC)

Taiwan appears to have a Red Cross Society, see [11]. The graphic of the website identifies itself as "The Red Cross Society of the Republic of China".

Blood/urine tests

This is not a request for medical information, as you'll see. I had blood work/urine test last Saturday, and the doctor's office called today to tell me there's a "slight problem." They can't tell me what it is over the phone, and I'm not free for the next two days. I had already made an appointment to review the results this Saturday, so I'm worried that they called me now. Do doctors make these calls if it's just high cholesterol? Thanks. Imagine Reason (talk) 15:36, 26 March 2008 (UTC)

Quite possibly. If you have high cholesterol (the fact that a lot of people have high cholesterol doesn't lessen the problem) your doctor will want to advise you what you can do about it and possibly perform further tests.--Shantavira|^{feed me} 15:50, 26 March 2008 (UTC)

Why would they tell you the results over the phone for free when they can make money if you come in for an appointment? I wouldn't worry yet.

72.211.184.40 (talk) 15:51, 26 March 2008 (UTC)

If the tests indicated anything that might represent an urgent medical problem then your doctor would have advised you to present yourself at the local emergency ward or after-hours clinic. Beyond that, it would be entirely inappropriate – not to mention futile – for us to speculate as to what your test results might mean. TenOfAllTrades(talk) 15:53, 26 March 2008 (UTC)

That's not good. I'd rather it be cancer than AIDS! Imagine Reason (talk) 16:12, 26 March 2008 (UTC)

User:TenOfAllTrades/Why_not? - to further expand on TenOfAllTrades point! Good luck with your results. CycloneNimrod (talk) 17:44, 27 March 2008 (UTC)

I could be wrong, but I don't expect in most cases your doctor would have advised you to present yourself at the emergency ward or after-hours clinic for either AIDS or cancer (in other words, you shouldn't rule any of these out, although I'm not suggesting you expect them either). Urgent medical attention is something like 'you might be going to have a heart attack soon' or 'someone spiked your food with arsenic'. Nil Einne (talk) 18:29, 27 March 2008 (UTC)

" a slight problem" often means that the lab messed up the sample and needs another, so don't panic just yet.

Hail

Why does hail never seem to settle (unlike snow)? If and when it does settle, is there a name for it?--Shantavira|^{feed me} 15:46, 26 March 2008 (UTC)

Possibly because, per the article, hail comes from thunderclouds, which require reasonably warm surface temperatures to form. Algebraist 16:01, 26 March 2008 (UTC)

Hail is little balls of ice, so can't compact much. The best you could get is to force the air between the hail stones out to form a solid sheet of ice. This might happen if it's near freezing and you put a lot of weight on it, like by driving a car over it. StuRat (talk) 16:17, 26 March 2008 (UTC)

I may not understand the question, but what about this hail is not settled? File:DSC010250.jpg

Hail is the closest thing to snow here in the tropics. I don't think it settles into a deposit as it melts away even during the thunderstorm.--Lenticel ^(talk) 23:34, 26 March 2008 (UTC)

I'm assuming that Shantavira is referring to the fact Given a little time, and maybe a little wind, A foot of light-fluffy snow can "settle" into half a foot of heavier snow. Hail, being rigid balls of ice, won't do that. Or maybe he means to say "accumulate" in which case the answer is "Because hail shows up with above-freezing temperatures, so usually it melts instantly. But sometimes it doesn't as in that photo. I don't know what you'd call that except 'hail, on the ground'." APL (talk) 06:49, 27 March 2008 (UTC)

There have been occasions of hail forming "drifts" due to floating along with runoff from the parent thunderstorm, even piling several feet high. -RunningOnBrains 23:34, 27 March 2008 (UTC)

Regenerating Limbs

Has anyone heard any recent updates on the possibility of human limb regeneration just like the starfish?

Also, when our skin heals say from a cut, why does it not "remember" what that particular section of skin was before the cut? I mean is, why does it leave a scar? --Jonasmanohar (talk) 17:50, 26 March 2008 (UTC)

I don't think human ability to regenerate limbs is changing much. You may be interested in the article scar. Friday (talk) 17:55, 26 March 2008 (UTC)

Depending on the severity of the wound, excessive deposition of collagen by fibroblasts at the expense of re-epithelialization (the epidermis) causes the scar. Wisdom89 _{(T / ^C)} 21:05, 26 March 2008 (UTC)

The current edition of Scientific American has an article on the subject. --Gerry Ashton (talk) 21:40, 26 March 2008 (UTC)

See Regeneration (biology) as well. There are some human sections there. --Lenticel ^(talk) 22:26, 26 March 2008 (UTC)

This was actually the featured article in Scientific American this month[12]. Check it out, this might be what you're looking for. Mac Davis (talk) 23:21, 27 March 2008 (UTC)

Here [13] is a news story about a man who managed to chop off a fingertip, and doctors regrew it. All it took was sprinkling on the wound a powder developed by Dr. Steven Badylak of the University of Pittsburgh's McGowan Institute of Regenerative Medicine. The powder was "a substance made from pig bladders called extracellular matrix." Edison (talk) 23:48, 27 March 2008 (UTC)

Intestinal Dysbiosis

Does anyone know where I can read valid information on Intestinal Dysbiosis? Is it anywhere in Wiki?

Our (inadequate) article is at dysbiosis. --Sean 18:41, 26 March 2008 (UTC)

global warming

what evidence that global warming is occuring, and what evidence is there that it isnt occuring?

See global warming and related articles. At this point there's little doubt that it's occurring- scientific disagreements are generally over the details these days. Friday (talk) 21:22, 26 March 2008 (UTC)

See in particular scientific opinion on climate change. It looks like it's now almost impossible to find scientists who deny that anthropogenic global warming is occuring and has been for some time. Algebraist 21:54, 26 March 2008 (UTC)

I'd like to cut in and mention that he wasn't asking for numbers of scientists, he was asking for evidence pro or con. Mac Davis (talk) 23:10, 27 March 2008 (UTC)

At this point most of the serious opposition has taken to arguing that it doesn't matter, or it isn't really caused by humans all that much, or that it can't be stopped, or that measures to stop it would be economically prohibitive, etc., with only the real fringe arguing that no change is happening at all. (At least, that's what I've noticed.) --Captain Ref Desk (talk) 21:58, 26 March 2008 (UTC)

The intersting data are those that indicate, not that global warming is happening (this is indisputable, but it could be a cyclic phenomenon), but that it's happening faster than it ever has before. Core samples of glacial ice at the poles, and analysis of fossilized pollen (thus indicating periodicity of tropical / temperate cycles over millions of years) indicate that the globe is warming more and faster than at any other point in at least a few million years since the Industrial Revolution. At the risk of climbing upon a soap-box, it is frustrating as a scientist and an educator to hear people talking about "opinions" regarding global warming. Everyone's entitled to their own opion. But no one is entitled to their own facts. Facts are facts. One can argue that the data are corrupted or inaccurate, one can dispute the rigor of the methodology in collecting the data, one can even produce a contradictory data set. But one cannot simply say that they don't believe in global warming, for example, without first accounting for the data that support it. This is not an even-handed debate. It really isn't a debate at all. Vance.mcpherson (talk) 16:29, 27 March 2008 (UTC)

No argument at all -- and I share your frustration about the "opinionization" of reasonable facts -- but for clarity, may I ask if you in fact meant "since the Industrial Revolution the globe is warming more and faster than at any other point in at least a few million years"? :-) —Steve Summit (talk) 02:47, 28 March 2008 (UTC)

Time on the moon

This maybe a strange (or even a rather dumb) question but I was wondering whether the moon has been divided in different timezones. For example: if you were to live on the moon on the place where Neil Armstrong made his famous small step, what time would it be when on earth it's 12:00 pm (GMT)?

No, it hasn't; there would be no reason. On the Apollo missions, I believe they simply used Houston local time, so 12:00 pm GMT would have been 7:00 am CDT during Apollo 10, 11, and 15; and 6:00 am CST during Apollo 8, 12, 13, 14, 16, and 17. --Anonymous, 6:22:22 pm EDT = 22:22:22 UTC, March 26, 2008.

Bear in mind that the length of a lunar day is a little bit more than 27 Earth days. (The Moon doesn't turn very quickly on its axis.) Time zones on Earth mean that the sun rises at about the same local time all around the world; people go to work, have lunch, return home, go to sleep, etc. at similar times by their local clocks.

On the moon, one would go through about two weeks of daily activities between local sunrise and sunset, and two more weeks of activity between that sunset and the next sunrise. You're not worrying about local sunlight as a cue to tell you (and your body) when to get up and when to go to sleep. If you called your buddy on the night side of the moon, you wouldn't have to worry about waking him up; he's not going to stay in bed for two solid weeks. It's much more convenient to not have time zones on the Moon—that way, you can do business with someone on the lunar farside and have everyone awake at the same time. Up until now, there's only ever been one small group of Americans on the Moon at any given time, so they've simply stayed on Houston time—the local time zone that they were talking to on Earth.

The question of what local time will be chosen for use by permanent settlers on the Moon is still open. Will Russians insist on Moscow time for their moonbase while Americans use Houston or Washington? TenOfAllTrades(talk) 23:03, 26 March 2008 (UTC)

Armstrong & co probably did use Houston time among themselves because they were in communication with Houston and that made sense in the context of the mission, which was only a few days duration. But they "came in peace for all mankind'', so we now generally use UTC time when referring to it; our article says that they "touched down on the moon at 20:17:39 UTC on 20 July 1969". As for future settlements, regardless of which country's citizens do the settling, why on Earth (no pun intended) would they use a time system that applies only to the Earth for a heavenly body that, well, isn't the Earth? That would seem to come from an attitude that the Moon is somehow part of the Earth, or at least owned by Earth. It would be like American colonists of some newly discovered island in the Mediterranean making it run on Los Angeles time - absurd. They'd have to establish a base meridian, probably the place where Armstrong & co touched down, and divide the Moon up into an appropriate number of zones, which wouldn't be 24, by the way. -- JackofOz (talk) 23:24, 26 March 2008 (UTC)

I object to the bit about "They came in peace for all mankind, so we use UTC." Wikipedia uses UTC because that's appropriately neutral Wikipedia style. But anyone who remembers the event is likely to describe it in terms of their own local time zone. --Anonymous, 04:09 UTC, March 27, 2008.

Objection noted. What you say is true for individual memories; but if asked, free of any other context, the exact date on which the first Moon landing occurred, a more accurate answer would be "It's arbitrary because calendars aren't defined on the Moon. Even if we align it to the Gregorian Calendar used on Earth, it would still depend on which place on Earth you chose as the reference point, because Earth uses many different time zones, and it happened on 19 July 1969 in some time zones and 20 July 1969 in others. As a compromise, scientists usually resort to UTC as a standard - but still arbitrary - way of expressing time, and work out the date accordingly. On this basis, it happened on 20 July 1969". -- JackofOz (talk) 07:08, 27 March 2008 (UTC)

Having a time system based on the Moon's local day/night cycle doesn't strike me as a practical approach. The only reason we need time zones on Earth is so that local clock time follows our diurnal rhythm wich follows local solar time. On the Moon, that just wouldn't happen—no one can stay away for two weeks and then sleep for two weeks. On what basis, and for what purpose, would one create time zones on the Moon?

What new clock system would you propose? You can't alter the length of the second without creating massive headaches for every scientist and engineer on the Moon. If you create a clock system or calendar based on the Earth second, you're stuck with having odd numbers of minutes in an hour or hours in a day to get the hour/day to line up with some natural cycle of the Moon's orbit or rotation. Further, if the Moon isn't tied to a terrestrial clock, then the difference between lunar time and Earth time will be constantly changing—is noon here going to be in the middle of the 'night' on the Moon next week? Three months from now?

Besides, the Moon is part of the Earth, as far as I'm concerned. It's stuck in our gravity well. Unless we do something really blindingly stupid, the population of the Moon is always going to be a tiny fraction of the Earth's. Why set up a time system that has no readily apparent benefit for the lunar colonists, and makes it more difficult for them to communicate and do business with the billions of people on Earth? TenOfAllTrades(talk) 00:27, 27 March 2008 (UTC)

That strikes me as more of an argument for fixing our own problems on Earth and not worry about ever colonising the Moon. We're obviously talking hypothetical here. But for the sake of argument, if there were a permanent colony on the Moon, and if they used an Earth-based time system, how would that work? It would have as much relevance as using the time system they use on Uranus. The Moon doesn't have the same relationship with the Sun as we do, so diurnal patterns are out the window for starters, and the 24-hour clock which is based on the rotation of the Earth would be utterly confusing, counter-intuitive and hopeless. I appreciate that our body clocks are more-or-less in line with the 24-hour clock, and they'd have to deal with the same problem that people from the tropics or the temperate zones experience when they go to the Arctic and have months of daylight and months of darkness. Yes, they'd have to stay in communication with their Earth-bound colleagues, but that presents no greater an intellectual problem than Russians in Vladivostok communicating with their cousins in Kalinigrad, 14 (?) time zones away. There would have to be a system for converting the "time" at any moment in time at any point on the Moon's surface to the the corresponding moment of time at any point on the Earth's surface, and vice-versa. If they can get to the Moon and back safely, that would be child's play. -- JackofOz (talk) 01:02, 27 March 2008 (UTC)

Up above, someone asked, "why on Earth would they use a time system that applies only to the Earth?" Because we're creatures of habit, that's why, and we really like our units. Units of time, for some reason, most of all: though systems of length and mass measurement have come and gone, the hour, minute, and particularly the second have been just about universal since they were invented (except for one short-lived experiment during the French revolution). My guess is that we'll be using hours, minutes, and seconds for quite a while after we have an Earth day to synchronize them to. (And once we stop caring about days, the leap year and leap second problems will go away!)

In the far-future civilization described by Vernor Vinge in his novel A Deepness in the Sky, the hour and minute have fallen out of use as well, but the second is still going strong, and properly decimalized. A kilosecond is about 15 minutes or a quarter of an hour (a perfectly useful amount of time); a megasecond is about 11 days, and also perfectly useful (not too far from our week); and so forth. It's not clear what they use for an absolute reference, but there's a delightful passage describing the origin they use for computer timekeeping:

Programming went back to the beginning of time. It was a little like the midden out back of his father's castle. Where the creek had worn that away, ten meters down, there were the crumpled hulks of machines -- flying machines, the peasants said -- from the great days of Canberra's original colonial era. But the castle midden was clean and fresh compared to what lay within [his own ship's] local net. There were programs here that had been written five thousand years ago, before Humankind ever left earth. The wonder of it -- the horror of it, Sura said -- was that unlike the useless wrecks of Canberra's past, these programs still worked! And via a million million circuitous threads of inheritance, many of the oldest programs still ran in the bowels of the Qeng Ho system. Take the Traders' method of timekeeping. The frame corrections were incredibly complex -- and down at the very bottom of it was a little program that ran a counter. Second by second, the Qeng Ho counted from the instant that a human had first set foot on Old Earth's moon. But if you looked at it still more closely... the starting instant was actually about fifteen million seconds later, the 0-second of one of Humankind's first computer operating systems.

—Vernor Vinge, A Deepness in the Sky, ch. 17

—Steve Summit (talk) 02:21, 27 March 2008 (UTC)

No, no, and no. They kept time on the Apollo missions using Mission Elapsed Time, which starts at zero at liftoff. 98.201.87.17 (talk) 05:15, 27 March 2008 (UTC)

The question has been asked "for what purpose would we propose a new time system for the Moon ?". Obviously it couldn't guide our sleep/wake cycle, since we can't make that 27.3 Earth days long. However, one purpose would be for adjusting solar panels which are aimed at the Sun. Many such system are likely automated, but for those which must manually be adjusted (say a portable unit used by an exploration team), a daily adjustment, or perhaps twice daily adjustment, might be appropriate. Knowing which lunar time zone you were in would help you determine how to aim it. You would also need to know how far north or south you are. Of course, you could just visually aim it at the Sun and ignore the math. Perhaps the more serious issue is knowing when the Sun will set, depending on your lunar time zone, so you can get back to base for the 14 Earth day lunar night, when solar power will be useless. Hopefully the base either has a sufficient capacity to store solar power over that period or uses nuclear power. StuRat (talk) 19:28, 27 March 2008 (UTC)

Medical equipment grounding

I have noticed that medical equipment seems to have a grounding terminal of some sort (the symbol is something like a circle within a triangle) which is separate from the normal earth ground. The ground (electricity) article doesn't mention anything about it, and I can't find it on commons:Category:Power supply symbols. What is that pin for? --cesarb (talk) 23:18, 26 March 2008 (UTC)

Is it a ground symbol within a circle? If so, this seems to indicate a connection to safety ground via the equipment. Usually, you will find that this terminal is connected to the metal casing of the instrument and therefore to the mains ground lead (and hence real ground). Such a terminal would allow the protective connections of transducers external to the equipment to be connected easily to safety (mains) ground. Say you had some gear that might tend to float to high or dangerous voltages, then connecting it to this terminal would prevent it. Simply, if you want a real ground connection, you have it here! —Preceding unsigned comment added by 79.76.201.53 (talk) 02:17, 27 March 2008 (UTC)

No, it's the opposite: the circle is within the symbol. --cesarb (talk) 03:43, 27 March 2008 (UTC)

Are you in Brazil? What is an example of one machine that has this so we can look for a picture? When you say "grounding terminal", is it a female banana jack or a screw or what? How do you know that it is separate from the normal earth ground, and what does the "normal earth ground" look like? --Milkbreath (talk) 15:28, 27 March 2008 (UTC)

Lots of medical equipment can run from an internal battery, right? I wonder if these terminals are there to "tie together" multiple pieces of equipment that aren't plugged in to the mains, to prevent sparking, ground-loops, etc. -- Coneslayer (talk) 15:35, 27 March 2008 (UTC)

(ec) Its not the symbol for signal ground shown in ground (electricity)#electronics? I don't know about medical equipment, but professional audio broadcast equipment commonly has a separate terminal for technical ground which is isolated from the safety ground connection. This is so the studio or whatever can provide a 'clean' signal ground to the equipment free of the 'dirty' noise going down the safety earth wire due to power supplies and the like. As I say, I don't really know much about medical instruments but I would guess they have a similar problem in that a small amount of noise on the ground connection can cause large errors in the readings. When a technical ground is not available the signal ground would normally be linked to safety ground since this is better than nothing. Most equipment I have come across have a terminal internally connected to safety ground immediately adjacent to the technical ground terminal in order to enable this linking to be conveniently easy and the manufacturer supplies the equipment with the link in place. It is therefore good to go out of the box and only an installer who has a technical ground facility needs to mess with it. You could also try [Symbols.com on-line encyclopedia of symbols] which allows you to search by graphic symbol type as well meaning although I could not find what you describe. SpinningSpark 15:45, 27 March 2008 (UTC)

Spinningspark is on the right track. There is a ground-loop connection on most of my medical equipment. It is used to ensure that the signals from the equipment have the same ground reference. This is important when using multiple machines to get a running history of data on more than one patient (primarily for studies). Some machines are very susceptible to this, such as EKG machines. It is not truly a ground because the wire I use to connect the machines couldn't handle the current if something were to spike. There is still a real ground going to the power outlet. -- kainaw™ 16:03, 27 March 2008 (UTC)

Almost it; it's the one shown for signal ground but with an extra circle within the triangle. --cesarb (talk) 03:38, 28 March 2008 (UTC)

March 27

Turtles

When a turtle pulls its head into its shell, does its spine buckle or contract? 70.162.25.53 (talk) 01:11, 27 March 2008 (UTC)

Have you been reading Cat's Cradle? Anyway, the article you linked has the answer: it depends on the turtle. Pleurodira fold their neck to the side, while Cryptodira pull their neck straight back. Algebraist 01:51, 27 March 2008 (UTC)

I disagree. The article does not seem to answer his question. Now that 70.162.25.53 has mentioned it, I'm sort of curious too. How is the spine in the neck constructed so that it can change length so dramatically? APL (talk) 06:37, 27 March 2008 (UTC)

The "spine" of a tortoise is more like part of its shell. See this cutaway section of a tortoise and the mechanics will be obvious.--Shantavira|^{feed me} 15:07, 27 March 2008 (UTC)

Why a Horseshoe-shaped Gamut of Visible Colors?

The color space article describes visible colors in the RGB color model, the gamut, represented as a 2-D horseshoe shape. Are all 10 million visible colors found in this (idealized) 2-D image? Why a horseshoe shape? Is the shape a horseshoe on account of the underlying physiology of color reception in humans? Mark465 (talk) 14:52, 27 March 2008 (UTC)

The article on gamut wasn't wikilinked, see specifically Gamut#Representation_of_gamuts. It's really shaped more like a triangle with one rounded side and one rounded corner (the three corners being the three primary colors), than like a horseshoe. I too am interested in understanding the reasons why the range of possible chromaticities has a rounded blue-green side and straight blue-red side. ---Sluzzelin talk 15:11, 27 March 2008 (UTC)

See also CIE 1931 color space. ---Sluzzelin talk 15:17, 27 March 2008 (UTC)

There are three fixed points on these kinds of diagrams representing the three primary colours, which in turn are the wavelength of peak responses of the three kinds of cone detector in the human eye. These three points form the apexes of a triange. The straight line from the Red apex to the Green apex represents a fully saturated mix of the Red and Green wavelengths represented at the apexes. The colour along this line varies continuously from the red through orange and yellow to green. Similarly, the straight line between the Green and Blue apexes represents a fully saturated mix of green and blue light. However, not all light in nature is a mix of these particular three wavelengths, in fact most of it is not. Monachromatic yellow light, for instance, may appear as the same yellow as a mix of red and green light but it has a greater saturation. Since a mix of red and green light with no blue is considered to be 100% saturated, monochromatic yellow must be more than 100% saturated and is described as supersaturated. It must, therefore, lie outside the linear triangle thus accounting for the curves on the diagram. The Red-Blue axis is not curved because mixes of red and blue can only be achieved by mixing two wavelengths and so monochromatic supersaturation cannot occur and the line is therefore straight.

Anticipating the next question - why is monochromatic yellow supersaturated? The reason for this is that red/green mixed yellow obviously has wavelength component of green which is a shorter wavelength than the monochromatic yellow. At this wavelength there is some stimulation of the blue receptor also (mono yellow also stimulates the blue cone but to a much lesser degree). This stimulation of blue means that there is some component of red, green and blue in the eyes response. All three are interpreted as white, so the net result is yellow plus white or in other words desaturated yellow. Since this desaturated yellow has been predefined as 100% saturation, a more saturated yellow must consequently be supersaturated. Luckily for the television companies, supersaturated colours do not occur in nature much, so the fact that RGB television cannot reproduce them is of little consequence. SpinningSpark 16:13, 27 March 2008 (UTC)

It isn't that clear that there are three specified primaries which result from the maxima of cone receptors. The CIE color space isn't set up that way. How about magenta, cyan and yellow as alternative primaries? Edison (talk) 03:53, 28 March 2008 (UTC)

The CIE colour space uses three primaries (called the tristimulus in the article) which are arbitrarily chosen but close to the average human peak cone responses. The difficulty with humans is that they are all different so the human tristimulus is fuzzy, varying from person to person. My post above was really trying to describe the concept of supersaturation in general and was not particulary referring to the CIE colour space (although it does apply). Red-green-blue (RGB) colour spaces are used because light is detected in the human eye in terms of RGB. RGB is also most convenient where colours are being reproduced by an additive process of light such as in television or computer monitors. Where colours are reproduced by a subtractive process such as in printing then it becomes more convenient to use a cyan-magenta-yellow (CMY) colour space. In particular, printers favour the CMYK colour space. It is also worth noting that tristimulus based colour spaces only work for humans and other species with equally useless colour vision. Many species of birds, bees and moths have five colour receptors so RGB colour reproduction would not fool them for one minute. As for species like the pistol shrimp or mantis shrimp, their colour vision is so good that it would be necessary to reproduce a mix of wavelengths near identical to the original scene before they would be satisfied with television pictures. SpinningSpark 10:02, 28 March 2008 (UTC)

From what the other poster said I would guess that it has to do with the fact that the 3 primaries that we perceive are not the same as the 3 photoreceptors in our retina. We perceive red yellow and blue but the 3 photoreptors are red green and blue.Em3ryguy (talk) 04:36, 28 March 2008 (UTC)

Alternative medicine

Is there any branch of conventional (western) medicine that would at one time in the past have been considered alternative medicine, or is that by definition impossible?--Shantavira|^{feed me} 14:58, 27 March 2008 (UTC)

I don't know how far back the term "alternative medicine" was used, but there are examples of things that are mainstream thinking now and were not in the past. A great example is the good old germ theory of disease- now accepted by all but the quackiest of quacks, yet it was seen as quite outlandish by the medical establishment when first introduced. "Tiny little bugs made you sick?? Ridiculous. Come on by and I'll fix your humors for you, and you'll be all better." Friday (talk) 15:06, 27 March 2008 (UTC)

Right. Good question. My answer was going to be "Yes, practically all of it", for the reasons Friday mentions. I was thinking of Ambroise Paré and the treatment of battlefield wounds by ligation and clean compress when the rule was cauterize for bleeding and pour hot oil in any holes. (Say what you will about the French, they have produced some bright boys.) --Milkbreath (talk) 15:20, 27 March 2008 (UTC)

Germ Theory is a good answer, but I'm not sure "Practically all of it" works. It seems like there is a lot of modern medicine that never passed through a phase where it was practiced regularly, but not by mainstream doctors. (Though it depends a lot on how narrow you're allowed to define a "branch...of medicine") However, The first paragraph Wikipedia's article on alternative medicine offers a surprisingly broad definition of the term that probably covers even techniques undergoing legitimate clinical trials by mainstream researchers. By that definition "All of it" would be the right answer. APL (talk) 16:14, 27 March 2008 (UTC)

"The Web That Has No Weaver" is a fantastic resource on Chinese Traditional Medicine that may help untangle the philosophical kinks. Western Medicine is evidence-based, and has been for some time, and is largely based upon the principle that different people, with similar medical conditions and similar bodily make-up, should be treated in roughly the same way. TCM is also evidence based, in the sense that it works, but is based upon the principle that every individual must be treated individually based upon their unique energy patterns and fluid movements. That makes it virtually impossible to compare TCM and Western medicine; it is impossible to do a double blind study on a TCM treatment because the practitioner must necessarily know what they are doing. It is also impossible to do a rigorous statistical analysis with statistical significance on TCM treatment for a given condition, because in TCM every patient will be treated differently, and consistency cannot be assured. Western forms of naturopathic medicine follow similar philosophies. So while the treatments themselves may share homology, the philosophies are too divergent for appropriate comparison. Vance.mcpherson (talk) 16:37, 27 March 2008 (UTC)

I'm sorry to derail, but I can't let that pass. Statistical comparisons are ideal for comparing situations with inconsistencies if you use a large enough sample. Are you honestly saying you couldn't do a study that says "Of Ten thousand people with illness X who were treated with western medicine Y% recovered, and of ten thousand other people with illness X who were treated with traditional Chinese medicine Z% recovered." because there's a chance that one of the TCM patients might have gotten lucky and gotten a better treatment? Granted, It may not tell you the scientific validity of TCM,(or western medicine for that matter.) but it would give you an idea which of the two approaches are more likely to work, which is far more useful. APL (talk) 18:00, 27 March 2008 (UTC)

Continuing the derailment... yes. TCM is not disease based, but rather patient based. It is the patient, not the disease, that is treated. Therefore, for example, two people with acute angina, of the same height, weight, race, and sex, may be treated with a completely different set of medications, acupuncture and other regimens, based upon factors like Qi flow, etc. Every patient is different. Further, TCM focusses upon prevention; by the time the disease sets in, it's argued, it's for the most part too late. One could say, for example, that X people with angina were treated with TCM and Z% recovered, as you say, but there would be implied thereby X different treatments. Contrast this to Western Medicine statistics, where one would never say y people were treated for angina in a bunch of different ways, and z% recovered. We'd be insisting on a highly controlled experiment. Sorry to be unclear. Vance.mcpherson (talk) 18:30, 27 March 2008 (UTC)

I'd still say a comparison could be done with a suite a treatments, so "X% recovered using Western treatment A while Y% recovered using TCM treatments B-Z". However, a more useful approach might be to have all patients evaluated for TCM and determine which TCM treatment would be recommended. You could then split each group into two, and conclude "X1% recovered using Western treatment A while Y1% recovered using TCM treatment B", and "X2% recovered using Western treatment A while Y2% recovered using TCM treatment C", etc. You might thus find that some TCM treatments are useless while others are quite effective. As for the preventative aspect of TCM, western medicine also has preventative meds, like those that keep cholesterol or high blood pressure in check. Those could be compared with TCM methods and we could study which prevents a heart attack or other negative health effect the longest. Again, we could break down the study groups based on recommended TCM treatment. Of course, as far as prevention goes, I'd say a healthy diet and lifestyle, exercise, not smoking, avoiding stress, etc., will win every time. Those should ideally be also included in any study, so we don't end up with large numbers of people eating double bacon cheeseburgers every meal and taking drugs to try to prevent the damage, when the far better option is to just eat better. StuRat (talk) 18:59, 27 March 2008 (UTC)

I'm no statistician, but it seems to me that a look at world life expectancies constitutes a very good study of the relative efficacy of the two philosophies, and others, to boot. This is especially true if we're talking about prevention, and the numbers include unweighted infant mortality, which they usually do, I believe. The map I've linked to indicates that Western is better than Chinese, which is better than Indian, and African might just be worse than nothing. --Milkbreath (talk) 19:31, 27 March 2008 (UTC)

I don't think that approach is very useful because there are so many factors which vary from place to place. For example, one of the single most important factors is probably basic sanitation. Do they dump raw sewage into the same rivers from which they drink untreated water ? If so, take 20 years off their life expectancy. So, using such figures to determine which specific medical treatment is best is unlikely to work. StuRat (talk) 20:29, 27 March 2008 (UTC)

The comparison being made is between two schools of thought, two incompatible conceptions of the mechanism of disease. Civilizations that fail to pay due heed to the role of pathogenic organisms in disease will not practice adequate sanitation. That's what I meant by "prevention". --Milkbreath (talk) 21:56, 27 March 2008 (UTC)

The reason they don't have sewage and water treatment plants isn't that they don't believe in germs, it's because they lack the resources to do so. That map seems to correspond very well with per capita income, not philosophy. Haiti, for example, is the one spot of red in the Western Hemisphere. Why ? Not because they have a radical different approach to disease treatment and prevention, but because they are dirt poor. StuRat (talk) 00:05, 28 March 2008 (UTC)

I don't feel qualified to debate world health issues, and this is not the place for that. But I would add that however poor people are, they can choose to reject a religion that makes them ritualistically drink and bathe in some of the most polluted water on earth with dead bodies in it and buffalo dreck, etc. And perhaps per capita income correlates pretty well with the realistic world view and rejection of mysticism that goes along with Western medicine. I'm outta here. --Milkbreath (talk) 00:22, 28 March 2008 (UTC)

I should back up a bit. I was very interested in researching the scientific and medical basis of TCM a few years back, and ultimately in investigating a possibility of the synthesis of TCM and Western medicine. I was told vehemently by some in the TCM community that this could never be done. It's counterintuitive because we're used to Western approaches to thinking about scientific method. Take StuRat's excellent example. "Some TCM treatments are useless while others are quite effective"... this would make sense to the Western scientist, but not in TCM. TCM is predicated upon the idea that the treatment will work if administered in the right context... and if it doesn't work, then there were other factors not considered. For example, if I have anxiety prior to a test, I might take a liver tonic because liver heat results in anxiety. But I couldn't only do this; if I have a weak spleen, for example, (which may predispose me for example to autoimmune disease, allergy, etc., but also governs liver, if memory serves), then it may be more advantageous to achieve spleen yin-yang balance. This may be achieved through a combination of herbs and acupuncture, or medicinal soups, or even a simple diet change. For example, my TCM doctor says that my spleen is cold and damp, which means I should avoid grains except rice and drink warm liquids. This is especially necessary to control insomnia. See, it's really a very different, quite incomparable system. I can't just say "take ginseng to increase your energy" in quite the same way as I can say "take this antibiotic to clear this disease". I highly recommend looking at "The Web That Has No Weaver", ([[14]]) by Ted Kaptchuk for an excellent review of this system. The title of the book is a good analogy -- the human body is "the web that has no weaver" -- there's no beginning or end, and there's not exactly a cause-effect relationship between a pathogen and a disease. Anger could be caused by liver heat or disrupted qi... and on and on like that. Vance.mcpherson (talk) 19:41, 27 March 2008 (UTC)

You're spleen is damp ? LOL. I'd be worried if it wasn't. But seriously, beware that those with a questionable treatment method often come up with some reason to claim it can't possibly be tested, so it can never be shown to be ineffective. A trick chiropractors like to use is to push down on your extended arm before and after a treatment and amaze you by how much better you are able to resist their push, which they swear is just as hard as before the treatment. Of course, this could logically be solved simply be substituting a fixed weight to apply the same force both times, but they aren't interested in doing it that way, for obvious reasons. Another favorite of charlatans is to say "your negative energy (skepticism) is what made the treatment ineffective". Back to the TCM discussion, I'd ignore TCM treatments for "damp spleen" and such. Those people who are concerned that their spleens are damp can go right to the nearest TCM practitioner, as western meds has nothing for this "serious problem". However, I believe TCM does indeed tackle a number of issues which western meds also tackle, such as headaches. And, as I've noted previously, there are ways to design a scientific study to compare the two treatment approaches for such conditions. StuRat (talk) 20:41, 27 March 2008 (UTC)

Actually my chiropractor used an electronic force measuring device. Totally objective measurement. My left arm showed a pronounced difference, right arm was unchanged. There is no need for charlatanry in your example. ~Amatulić (talk) 20:49, 27 March 2008 (UTC)

An "electronic force measuring device" sounds like something that could be tampered with, possibly using a remote control, while a fixed weight could not (unless they can pull a switch on you when your back is turned). A needlessly complex device should be another warning sign that something weird is going on. More generally, the scientific method demands that you not use subjective methods of evaluating effectiveness, which is what TCM will suggest, but instead use objective measures. If they feel people's skin and tell them their "qi" is flowing better, this is of no use in evaluating effectiveness. If, on the other hand, the patient's bad cholesterol level is down in multiple blood tests, this indicates the treatment is doing some good. StuRat (talk) 20:54, 27 March 2008 (UTC)

(Sigh). Some folks just can't let go of preconceived notions. You could do it with a spring scale (which another chiropractor did, with similar result). Using an electronic device doesn't make the chiropractor dishonest; in my case it simply allowed him to record the data more easily in his computer. There was no calibration or adjustment between tests, just comparison of forces each time. If your chiropractor doesn't perform the measurement objectively, that doesn't mean that others don't. ~Amatulić (talk) 21:04, 27 March 2008 (UTC)

You mean you failed to observe any calibration or adjustment between tests. This doesn't mean it didn't happen, just that you didn't see it. It could be as simple as a lever that's pressed or dial that's turned when the device is handled to as complex as a remote control or timer. The only way to be certain it was not changed is to use a device which can't be changed, such as a fixed weight. StuRat (talk) 21:49, 27 March 2008 (UTC)

...or a fixed spring scale, as I already mentioned. Pay attention. ~Amatulić (talk) 22:12, 27 March 2008 (UTC)

I did, and you didn't say "fixed". I have a spring scale at home that is adjustable. Did you examine the scale thoroughly to determine that it can't be adjusted ? StuRat (talk) 23:57, 27 March 2008 (UTC)

Ok, but NONE of that would stop you from treating "traditional Chinese techniques as administered by a well trained doctor" as a single unit and comparing that unit against western medicine in general. To say that the medical techniques are not "disease based" is fine, but presumably, if someone has a disease, their doctor will attempt to either cure it or relieve the symptoms, correct? We could find ten thousand people from each of the two categories that all have disease X, wait a few months, and compare the results. This would provide useful information even if each of the TCM patients received different treatments, so long as those treatments were expertly chosen by whatever rules and criteria TCM doctors normally use.

Statistics could be used even within TCM. You could do a study that says something like "Of the 10,000 TCM patients with disease X, 159 of them recieved treatment Q. Of those 159, a large percentage dropped dead instantly. Treatment Q's effectiveness is therefore in question." I'm exaggerating for comedic effect, but you get my drift. APL (talk) 21:12, 27 March 2008 (UTC)

(outdent)

Derailing further: some aspects of TCM do lend themselves to western-style clinical testing. Regular intake of the herb jiaogulan, for example, has been shown consistently to reduce cholesterol. It's one of the few examples I know of that has solid test results behind it. That's one example where one can use TCM to treat a specific condition rather than adapting a different treatmen to a patient.

Getting back on topic: To answer the OP's question, I'd say one example of conventional medicine that may have once been considered "alternative" is physical therapy. And most herbal treatments are considered "alternative" until some drug company comes along and figures out how to synthesize the active ingredient, as was the case with ephedra, from which pseudoephedrine was derived. ~Amatulić (talk) 20:50, 27 March 2008 (UTC)

...not to mention willow bark. -- Coneslayer (talk) 01:42, 28 March 2008 (UTC)

Moon falling into Earth

How close does the moon have to be to fall into Earth's gravity? --Jonasmanohar (talk) 17:38, 27 March 2008 (UTC)

It's already in earth's gravity. We do have an article on the orbit of the Moon. Someguy1221 (talk) 17:46, 27 March 2008 (UTC)

Ok, then I meant crash into earth... --Jonasmanohar (talk) 17:50, 27 March 2008 (UTC)

How close does it have to be to crash? Very close indeed. ;-) As the article linked to above explained, the Moon is (very slowly) getting further from the Earth. Friday (talk) 17:53, 27 March 2008 (UTC)

(Edit conflict) Just to be clear, the moon is already significantly affected by the Earth's gravity. Otherwise it wouldn't orbit the earth. What I presume you really want to know is how close does the moon have to be to the earth such that it will no longer be in a stable orbit around the earth and will eventually crash into the earth. Unfortunately I don't know the answer except that as I expected, the moon isn't actually a truly stable orbit around the earth, see [15]. Not remembering physics well enough, I can't calculate what sort of distance change is necessary. But to bear in mind it's not that the moon is going to suddenly start 'falling' into the earth at high speed. Rather, there will be a distance where the moon is in a truly stable orbit, beyond which the moon will get closer over time. However at first, the distance change will be minimal such that even though the moon will eventually theoretically crash into earth, it will take billions and billions of years for this to actually happen such that the sun will become a red giant before then so presuming the earth and moon even last that long, it will never actually have happened in any case. Of course, the closer the moon gets to the earth, the less time it will take for it to collide with the earth so that at a certain distance, it will possibly have happened were the moon really the close Nil Einne (talk) 17:56, 27 March 2008 (UTC)

You also have to decide at what velocity the moon is traveling in whatever reference frame. You could keep it where it is but just slow it down enough, and it will hit the Earth right quick. But I also forget how to calculate the velocity/distance necessary for crash for an elliptic orbit. Someguy1221 (talk) 18:03, 27 March 2008 (UTC)

(EC again) BTW, do bear in mind this isn't a simple calculation. Both the earth and the moon have a momentum.[16] This momentum was gained during their formation, it's not as if someone simply dumped a planet and a moon in the middle of space and let them start moving. If these momentums had been different, then things would be different. [17] In other words, what I'm trying to say is you can't simply visualise it as a simple system as I have a moon with mass M and a planet with mass E, what will happen when they are distance ME from each other? (Answer I think, many different things could happen including the moon could simply crash into the earth without ever actually orbiting presuming both were simply completely static from the beginning and there was actually no other mass at all [NB this is obviously an impossible system]) Nil Einne (talk) 18:09, 27 March 2008 (UTC)

Final comment: The note on the Orbit of the Moon article about how no one is actually sure what will happen to the earth-moon system after the orbit of the moon reaches 47 days sums up quite well the fact that when you actually start to think about them, these are quite complex systems Nil Einne (talk) 18:16, 27 March 2008 (UTC)

Since we're clearly talking about different things, let's make it clear, there is a distinction between placing the moon in an unstable orbit such that it eventually hits the Earth, and placing the moon in an orbit that actually comes with a moon radius of the Earth's surface (i.e., they will hit during a single orbit). The latter is what could be calculate with relative ease, not that I remember how. Someguy1221 (talk) 18:20, 27 March 2008 (UTC)

I think it's safe to say that if you could place the Moon into any orbit you liked, you would not want to place it close enough that it could hit our atmosphere, because that would cause its orbit to decay and it would almost certainly crash eventually. According to wikipedia The Exosphere ends at about 10,000km from the surface. (for reference, the moon currently does not get close than 363,104km) APL (talk) 18:26, 27 March 2008 (UTC)

OK, placing the moon in an orbit that actually comes with a moon radius of the Earth's surface (i.e., they will hit during a single orbit). --Jonasmanohar (talk) 18:24, 27 March 2008 (UTC)

Actually, the better answer is if the Moon is within the Earth's atmosphere, or closer than 10,000 km, as APL said above. The Moon's radius is only 1,737 km. StuRat (talk) 18:40, 27 March 2008 (UTC)

Correct my if I'm wrong, but in order to maintain a stable orbit, distance is inversely proportional to velocity. That is, a closer orbit will need to be faster in order to be stable. Now, the moon isn't exactly stable, but it's pretty close. If we were to slow it down substantially or pull it closer to earth without speeding it up, the orbit would begin to decay. How long will it take? Not sure. --uǝʌǝsʎʇɹoɟʇs(st47) 19:50, 27 March 2008 (UTC)

Actually I think if you go faster, you fly away. A closer orbit is slower, but gets round the Earth faster. However, once the Moon comes within the Roche limit, wouldn't it break into pieces anyway? Franamax (talk) 20:10, 27 March 2008 (UTC)

If you can just satisfy yourself that orbital energy for a circular orbit is one half the kinetic energy at escape velocity, it's pretty clear that the minimum velocity for orbit increases as the radius of the orbit decreases. It's thetotal travel time around the Earth that decreases. Someguy1221 (talk) 20:17, 27 March 2008 (UTC)

Huh? The converse of your statement is that as the radius of orbit increases, the minimum velocity decreases, right? I don't think that's correct. The faster you move, the more energy you have, the farther away you fly. Isn't that how the shuttle does it? Franamax (talk) 20:31, 27 March 2008 (UTC)

I take that back. Brain is smoking and making funny noises. Franamax (talk) 20:39, 27 March 2008 (UTC)

Roche Limit. Objects only break up inside the Roche limit if there is nothing other than gravity holding them together. This is sometimes stated as the pile-of-sand model. Crystalline rock, on the other hand, is held together by forces a lot stronger than gravity. There are many examples of objects in the solar system quite happily existing inside the parents Roche limit. SpinningSpark 22:58, 27 March 2008 (UTC)

Yes, some moon-sized objects can exist within the Roche limit, but not by much. At some point, the tidal forces will rip it apart, and I am almost completely certain that this would be well before the moon would impact the atmosphere. Of course, all of this is assuming the moon's orbit is coming closer to the earth; it is actually receding at a few millimeters a year. -RunningOnBrains 23:20, 27 March 2008 (UTC)

True, but even if the Moon did break up, that wouldn't mean that the parts would crash into Earth. They might just form a ring. However, the lack of rings around the terrestrial planets seems to imply that those rings don't last for long. StuRat (talk) 23:52, 27 March 2008 (UTC)

(unindent) The Moon's gravitation produces tides which raise the water level over a meter at numerous locations. Would not a closer Moon produce higher tides, ultimately inundating most of the land mass, even before the Earth was rendered uninhabitable by movement of its crust resulting in earthquakes and volcanoes as the Moon drew nearer, long before there was any contact? Edison (talk) 03:49, 28 March 2008 (UTC)

E=MC^2

What is the whole proof to the equation E=MC^2? —Preceding unsigned comment added by 68.252.70.175 (talk) 23:37, 27 March 2008 (UTC)

Mass-energy equivalence might be useful. Algebraist 23:44, 27 March 2008 (UTC)

If you mean the derivation, the original form of it is here. It's a little opaque if you aren't used to the notation and math Einstein is using but if I recall it relates to the energy a photon imparts on the inside of a box in space or something along those lines. --Captain Ref Desk (talk) 23:53, 27 March 2008 (UTC)

One way of checking the equation for reasonableness is by dimensional analysis. The units of energy (on the left side) are kilograms times meters ² per second², by definition. The units of the right side are kilograms times C², which is equivalent to kilograms times meters ² per second², just like the left side. The only thing missing is a constant to allow for the choice of units. The equation would not balance in dimensions if it were E=MC, or E=M²C, or E=MC³, etc. Edison (talk) 03:38, 28 March 2008 (UTC)

March 28

Shape of the Milky Way Galaxy

I remember when I was younger and more interested in astronomy reading that the Milky Way was a spiral galaxy, like the Andromeda galaxy, but while browsing various articles, I came upon the Milky Way article, which said that it was a barred spiral galaxy, which surprised me. When did astronomers figure out that it's a barred spiral galaxy instead of a spiral galaxy? Was there some discovery in the past decade that allowed them to see that it is in fact a barred spiral instead of a spiral galaxy? How do astronomers know what shape the Milky Way is and where the arms are? By judging the distance of tons of stars and laying out a map? How are astronomers able to guess at what lies on the other of the core? Thanks in advance. – Psyche825 _(talk) 04:28, 28 March 2008 (UTC)

Adaptive optics is certainly one breakthrough during the last ten years, that has helped astronomers to dramatically enhance the accuracy and resolution of star charts among other things. I cannot elaborate as I am by no means an expert in astronomical modelling. Sandman30s (talk) 09:36, 28 March 2008 (UTC)

Yes, this conclusion must have been reached by an analysis of the distribution of stars and interstellar gas and dust clouds using observations at various wavelengths. Radio astronomy, for example, allows us to see details of the Galactic Center that are hidden at visible wavelengths. Apparently the crucial evidence that clinched the case for a barred spiral structure were infrared observations made in 2005 using the Spitzer Space Telescope. Gandalf61 (talk) 11:13, 28 March 2008 (UTC)

Quantum: Measurement vs. Schrödinger Equation

1. Article Copenhagen interpretation: Each measurement causes a change in the state of the particle, known as wavefunction collapse.

2. Article Schrödinger equation: The Schrödinger equation is commonly written as an operator equation describing how the state vector evolves over time.

Although I don't fully understand quantum mechanics, the two items above seem to be related to each other.

When an observable of a quantum system is measured, the state $|\psi (t)\rangle$ of the system can be expressed as

$|\psi (t)\rangle =\sum _{i}\psi _{i}|i\rangle$ (1)

where $|i\rangle$ is the $i$th eigenfunction, which is associated to eigenvalue $i$, of the observable and

$\psi _{i}=\langle i|\psi (t)\rangle$ (2)

which will "suddenly" or "discretely" collapse from $|\psi \rangle$ to one of terms, say $\psi _{a}|a\rangle$, of the right-hand side of (1). The rest of the terms not associated to eigenvalue $a$ simply vanish after the measurement.

On the other hand, Schrödinger equation

${\hat {H}}(t)\left|\psi \left(t\right)\right\rangle =\mathrm {i} \hbar {\frac {d}{dt}}\left|\psi \left(t\right)\right\rangle$ (3)

where

${\hat {H}}(t)=-{\frac {\hbar ^{2}}{2m}}\nabla ^{2}+V\left(\mathbf {r} ,t\right)$ (4)

describing how the state vector $|\psi (t)\rangle$ evolves over time. When the state $|\psi (t)\rangle$ of the system is measured, the apparatus measuring the system will interact with the system and makes change to the potential field $V\left(\mathbf {r} ,t\right)$. Therefore, the state $|\psi (t)\rangle$ should evolve "smoothly" or "continuously" according to the varying potential $V\left(\mathbf {r} ,t\right)$ during the measurement. According to Schrödinger Equation (3) and (4) together with $V\left(\mathbf {r} ,t\right)$, we should be able to figure out the final state of the system after the measurement.

It seems that the measuring process can be explained by the two ways, wavefunction collapse & Schrödinger equation, above. Do they contradict? Is "wavefunction collapse" compatible with "Schrödinger Equation"? - Justin545 (talk) 08:12, 26 March 2008 (UTC)

Yes, they do contradict. There is no place for a collapse in Schrödinger's Equation, which is one reason why David Bohm concluded that there can be no collapse of a wave function, that it's a figment of the model. — kwami (talk) 08:34, 28 March 2008 (UTC)

Figment of the model? I'm amazed that they do contradict since the two items are considered to be postulate of quantum mechanics in some textbook of quatum mechanics IIRC. It should imply at least one of the two items is wrong. So has David Bohm or some one else solved the contradiction? And how about the experimental evidence? Experimental evidence supports which one? - Justin545 (talk) 08:55, 28 March 2008 (UTC)

The Copenhagen interpretation is just that, an interpretation. It has no empirical support (or at least it didn't some years ago) and is in no way an axiom of QM. I've heard people who use it make the excuse that none of the other interpretations have any empirical support either, even though some of them are less counter-intuitive than Copenhagen. Bohm attempted to create a deterministic hidden-variable QM, but was unable to solve some fundamental problems before he died. One of his students continued with his work, but I don't know if he ever got anywhere. — kwami (talk) 09:04, 28 March 2008 (UTC)

I think neither Schrödinger equation nor wavefunction collapse could be axiom of QM. Therefore, they are considered to be "postulates" of QM. Schrödinger equation seems to correctly predict the spectral lines of each atomic models. On the other hand, wavefunction collapse seems to correctly predict the phenomenon of quantum entanglement. And both of the predictions has been observed by many experiments. The experimental results seem to support both of the two items. But there may be some subtle differences are missing (enough precision? relativity?). When reading the article Copenhagen interpretation, we should also notice the sentence "The Copenhagen interpretation consists of attempts to explain the experiments and their mathematical formulations in ways that do not go beyond the evidence to suggest more (or less) than is actually there." - Justin545 (talk) 09:41, 28 March 2008 (UTC)

>> "There is no place for a collapse in Schrödinger's Equation"

Theoretically, is it possible to build a thought experiment in which the measuring process is simulated and use the Schrödinger equation to find out the result of the experiment? Had some one done this job before? - Justin545 (talk) 10:02, 28 March 2008 (UTC)

Nuclear fission

What is the formula for the typ eof Nuclear fission used in power plants? The article has no formulae at all. —Preceding unsigned comment added by Anthrcer (talk • contribs) 09:36, 28 March 2008 (UTC)

The reaction in the top picture is ²³⁵U + n → ²³⁶U → ⁹²Kr + ¹⁴¹Ba + n + n + n. I think that would be fairly typical for anything other than a breeder reactor. The daughter nuclei aren't always the same though. There are a range of possibilities, but the first two steps stay the same. AlmostReadytoFly (talk) 09:48, 28 March 2008 (UTC)

In the case of fission, formulae don't tell you much, as there is a fairly even chance as to what the end-products (the fission products) will be. Pick two arbitrary fission products and you can figure out how many neutrons will be released, and by doing the binding energy calculations, how much energy will be released (in one of a few forms). Power plants don't use a different type of nuclear fission than anything else; where they differ is in the arrangements used to facilitate the fission reactions in different concentrations of uranium, etc. --Captain Ref Desk (talk) 11:18, 28 March 2008 (UTC)

STS-123

Why was the hydrazine exhaust more pronounced in this flight than others?