Wikipedia:Reference desk/Archives/Science/2007 April 19

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April 19

Turning gray/green

Why do people sometimes turn gray or greenish when they are feeling nauseous? What's the mechanism behind the color change, why does it often coincide with that symptom? Just curious. --24.147.86.187 00:08, 19 April 2007 (UTC)

Probably decreased blood, the opposite of flushing (physiology). See pallor, which is sort of a stub article. Nimur 00:11, 19 April 2007 (UTC)

Unlike fish, frogs and reptiles, humans don't undergo short-term, physiological colour changes using melanin. They do undergo longer-term, morphological colour change (e.g. tanning) though. So all short-term colour changes in human are a result of haem, the pigment in our blood. Rockpocket 01:09, 19 April 2007 (UTC)

Male Contraceptive pill

So how close is this thing (or one of these things) to production in the USA? 75.161.134.92 02:07, 19 April 2007

Hmmm... given the possibilities for forced sterilization, I'd have to say hopefully a long, long way. Vranak

The issue of forced sterilization is no more relevant to the male pill as it is to the use of the female pill, as it will only be marketed if it is completely reversible. We are not talking about castration here, just hormonal modulation. For the last 5-10 years scientists have been telling us that it should be available in the next 5-10 years (e.g. [1]) However, the results of decade long studies are looking promising [2] and some experts are still talking about "the next few years" [3]. The trials are still preliminary, though, to its probably more accurate to say "it's still a long way from being commercially available" [4] Rockpocket 04:37, 19 April 2007 (UTC)

Even if its not reversible, its only forced sterilization if the recipient is unwilling. We're assuming people will take these pills voluntarly? Think outside the box 11:45, 19 April 2007 (UTC)

Yeah - sure we expect them to take them voluntarily. Plenty of people have voluntary vasectomy operations performed on them...why wouldn't they just take a pill instead? SteveBaker 04:40, 20 April 2007 (UTC)

Indeed some men seem to believe that every accidental pregnancy is some evil plot by the woman. Clearly these men would be rather interested in a contraceptive pill Nil Einne 01:35, 24 April 2007 (UTC)

Me, I'm anxiously awaiting Ethical Birth Control. And the return of Howard Johnson's. And Ethical Suicide Parlors. Until then, I suppose there's always Gossypol.

Atlant 16:20, 19 April 2007 (UTC)

Cell Division at Extreme Temperatures

I have a friend that claims that no known bacteria on Earth can reproduce above 150 degrees Celsius, since DNA is simply too unstable to replicate at temperatures that high. I've looked at the articles for cell division, mitosis, and DNA, but haven't found anything helpful. I'm pretty sure that the organisms that live near the hot vents at the bottom of the ocean reproduce at close to this temperature, but I'm not sure...any help? Thanks! --pie4all88 10:35, 19 April 2007 (UTC)

In the article about Hydrothermal vents it says: Other examples of the unique fauna who inhabits this ecosystem is a snail armoured with scales made up of iron and organic materials, and the Pompeii worm (Alvinella Pompejana), which is capable of withstanding temperatures up to 176 degrees Fahrenheit. Think outside the box 11:42, 19 April 2007 (UTC)

176 degrees Fahrenheit = 80 degrees Celsius, which is much lower than what he asked for. Good find, however.--Kirby♥time 07:01, 20 April 2007 (UTC)

You'll want to check out our articles on thermophiles, hyperthermophiles, and Strain 121. Strain 121 is the most extreme thermophile currently known. It is capable of continued survival and reproduction at temperatures as high as 121 °C. TenOfAllTrades(talk) 13:52, 19 April 2007 (UTC)

Largest Bomb in Existence?

What is the largest existing bomb in terms of radius of explosion? I'd imagine it'd be a Hydrogen Bomb, but the article doesn't seem to say the answer. I have a friend who claims that someone (probably Russia, he said) has a bomb that is 23 times more powerful than what is needed to blow up the entire Earth, but I am skeptical. Thanks for the help! --pie4all88 10:35, 19 April 2007 (UTC)

I don't think the US military would be too keen on having that information public, but you may be interested in historical precedent: Tsar Bomba. Vranak

Just in case you were curious about non-nuke bombs, I went to Daisy cutter, officially called the BLU-82. That page states the following: It was the largest conventional bomb for several decades. That title is now held by the GBU-43 Massive Ordnance Air Blast bomb, which contains 18,700 pounds of explosive, although both these weapons were outstripped in weight and size by the T12 Cloud Maker penetration or earthquake bomb developed from the British Grand Slam bomb of World War II. The T12 weighed 43,600 lb, almost twenty metric tons. Dismas|^(talk) 10:57, 19 April 2007 (UTC)

Incidently, the "GBU-43 Massive Ordnance Air Blast" bomb, or the MOAB, is monikered "the Mother Of All Bombs".--JLdesAlpins 11:21, 19 April 2007 (UTC)

There is certainly no bomb large enough to blow up the entire Earth, much less "23 times more powerful" than that. That's a tremendous amount of energy, and the Earth is thought to have absorbed stellar impacts with energies far, far higher than any bomb that has been developed (e.g. Giant impact hypothesis, Cretaceous-Tertiary extinction event). If you want numerical estimates as to how much energy that would be, this page is pretty entertaining. --24.147.86.187 12:09, 19 April 2007 (UTC)

The above answers the question well -- there's absolutely no way for a human-scale bomb to actually "destroy the Earth". To back up to some earlier points, it's worth noting that "largest bomb" (such as the Tsar Bomba or Castle Bravo, the largest US bomb) is an entirely separate military concept from "most useful bomb". For example, the Trident missile carries eight half-megaton warheads. 4 MT is far less explosive force than a single large bomb could produce, but eight warheads are far more flexible than one. The conventional bombs cited by Dismas above are arguably even more effective than modern nukes, despite having drastically less yield, as political realities allow their use while prohibiting the use of nuclear devices. — Lomn 13:56, 19 April 2007 (UTC)

An issue to consider is that a nuclear bomb blast has multiple zones of effect. There is not a discreet radius where you can say the explosion stops. Rather you have radii with descending magnitudes of destruction. Take a look [HERE if you would like to see some interactive examples.-Czmtzc 14:49, 19 April 2007 (UTC)

It should also be noted here that the limiting factor here is not the strength of the bomb, but the curvature of the earth, which means that there is a simple maximum radius. I remember reading somewhere that this was 37 kilometers, but I suppose the exact number depends on the definition of the destructive range. risk 14:59, 19 April 2007 (UTC)

In the Texas City Disaster there was a huge unintentional bomb which exploded due to mismanagement and improper handling.. A ship loaded with 17,000,000 pounds (8,500 tons) of ammonium nitrate exploded in a harbor in 1947 and killed 581 people. The explosion followed a gradually increasing firewhich might have been due to careless smoking or spontaneous combustion. The explosion was comparable to that of 2 to 4 kilotons of TNT. A nearby ship with 2,000,000 pounds (900 tonnes) of ammonium nitrate exploded afterward as an aftereffect of the first explosion. Edison 15:19, 19 April 2007 (UTC)

Ah, but the largest artificial non-nuclear explosion in history seems to be the Halifax Explosion. A munitions ship packed with 2,653,115 kilograms (5,849,117 lbs) of explosives (benzol, nitrocellulose, picric acid, and TNT) collided with another ship, and the explosion killed over 2000 and devastated all buildings within a 2 km (1.24 mi) radius of the blast. − Twas Now ( talk • contribs • e-mail ) 19:30, 19 April 2007 (UTC)

First, any source that gives the amount of explosive material to 7 significant digits is obviously not trustworthy. It wouldn't be known that accurately. According to the Maritime Museum of the Atlantic on this web page, the Halifax Explosion involved 2,300 tons of wet and dry picric acid, 200 tons of TNT, 10 tons of gun cotton, and 35 tons of benzol. The Texas City blast involved 8,500 tons of 32.5% pure ammonium nitrate, or over 2,700 tons of explosive. The comparison between the two events would depend on the relative power of the different explosives. I came across this information somewhere and it turned out that Texas City was the larger explosion, i.e. Halifax was the largest but only until that time. Anyway, there have been still larger non-nuclear explosions since then. In 1995, Chinese engineers used a blast with 12,000 tons of TNT to prepare a site for the expansion of an airport at Zhuhai (according to the Guinness Book, 1995 edition).

Anyway, the original question was about largest bombs, not largest non-nuclear explosions. --Anonymous, April 19, 2007, 23:26 (UTC).

You bring up a good point about the precision with which our very own Wikipedia article, Halifax Explosion, states the amount of munitions stored on board—without inline references even! However, I wouldn't immediately say that this precision is not trustworthy, because I would guess that the British/Canadian military would keep strict tabs on the amount of munitions they were transporting. I know that my response didn't address the initial question (largest bombs), but I was following the developing tangent (large artificial explosions). I brought up the Halifax Explosion because Edison mentioned the Texas City Disaster—and both were accidental. The Zhunai explosion was, I hope, planned, unless the Chinese engineers were just lucky. The Texas City event may be considered two separate explosions, since there was a second ship with 2 million pounds that exploded after the initial explosion. Anyway, I don't think any of these events qualify as "bombs". − Twas Now ( talk • contribs • e-mail ) 02:11, 20 April 2007 (UTC)

You might also check: RAF Fauld Explosion and List of the largest artificial non-nuclear explosions. SteveBaker 15:08, 20 April 2007 (UTC)

photon

Is there a proof that photons exist? I think I have a proof they do NOT exist. By philosophy everything has a use or a goal. Something without use does not exist,said ancient philosophers. Photons have no use. Everything about atoms,e.g. atomic spectra,can be explained by normal, classical (Newton,Maxwell)laws. Rutherford and Bohr could not. But I can.

Verify? Do you want the simple spectrum of Hydrogen, in Dutch or French? I can e-mail it to the adres you give me.

Morp Contributions/Morp

The Photoeffect might be the proof?--Stone 11:17, 19 April 2007 (UTC)

Is light not made of photons? Think outside the box 11:39, 19 April 2007 (UTC)

Counterproof: another branch of philosophy says that everything need not have a use or a goal, ergo "useless" photons can easily exist. What makes photons useless, anyway? What makes atoms "useful" in this sense? In any case, photons are very useful in the fact that they are the force carrier for the electromagnetic force. Try imagining life without them. As for proof of their existence, try researching the early advances in quantum theory - unless energy is quantised in discrete packets (called photons), the Photoelectric effect cannot be explained, and Blackbody radiation produces an infinite amount of energy - obviously ridiculous. Icthyos 12:03, 19 April 2007 (UTC)

Einstein's explanation of the photoelectric effect is the classic, original proof. It cannot be explained using classical Maxwellian laws. If it could be, a generation of very unhappy and reluctant physicists would never have switched over to it. There are other effects that can only be explained by postulating a quanta of light. And the notion that "something without use does not exist" is just a silly axiom, one with no strong philosophical backing. In any case I don't see your assertion that photons "have no use" as being particularly well supported — you might a well say electrons "have no use", or atoms "have no use", or muons "have no use". --24.147.86.187 12:14, 19 April 2007 (UTC)

Stimulated emission and Raman scattering would be rather interesting to try and explain without an understanding of the optical quanta we call the photon... Also, it would be rather difficult to explain the workings and methods of the very real optoelectronic devices I've personally worked on (like the avalanche photodiode). -- mattb 14:28, 19 April 2007 (UTC)

Photons have no use? Now see here... Clarityfiend 18:29, 19 April 2007 (UTC)

Here is proof that photons exists. "The ultimate existence of photons cannot be proven, Mr Bond. It has to be experienced." http://image.guardian.co.uk/sys-images/Film/Pix/gallery/2006/11/03/goldfinger1.jpg 202.168.50.40 23:32, 19 April 2007 (UTC)

If you really can explain every known effect, there is no point in believing that photons exist. You are perfectly correct in that. Most people stopped trying to do this when it was discovered that the current in the photoeffect starts practically instantaniously. You should look closer at this particular point of the experiment, maybe that will convince you that photons do exist.

• There's several scientific experiments that can't be explained without photons. Even if they don't not all things need to physically exist to work. There's plenty of theoretical particles around that haven't been proven to exist, but are supposed to by extrapolation and are nevertheless quite helpful in explaining existing phenomena. Trying to disprove something scientific with the use of philosophy is never going to work anyway. - Mgm|^(talk) 08:18, 20 April 2007 (UTC)

Wow! Where do you start with such a question? Let's take it apart piece by bloody piece:

• Is there a proof that photons exist?

  Yes - see above. But even with a device as simple as a pair night vision goggles, you can actually detect an individual photon. If we were somehow mistaken about the existance of such things, there are an awful lot of common modern appliances that wouldn't work. The laser in a CD player wouldn't work if light were not a property of photons (for example). Photons aren't some esoteric thing that we can't detect - we know an awful lot about them and use those facts all the time in building the most commonplace machines about which modern life revolves.

• By philosophy everything has a use or a goal.

  I don't know where you got that from - it's utter nonsense. Useless to whom? There are lots of things that seem useless to us humans - but which undeniably exist. The common cold virus for example.

• Something without use does not exist, said ancient philosophers.

  I'm not aware of any philosophers who believed that - but assuming it's true: Ancient philosophers also thought the world was flat, that everything was made from earth, air, fire and water, that raw tomatoes are poisonous, that heavier-than-air flight was impossible, that any vehicle travelling over 30mph would have all of the air sucked out of it, that the sun revolves around the earth and that the stars are mounted on crystal spheres. They thought that there was no such thing as a negative number and that the earth was only 2000 years old. They believed that diseases were caused by imbalances in blood and bile and that animals like mice were formed spontaneously out of bits of old cheese. They thought...well, that's enough. It's clear that ancient philosophers - far from having some deep and mysterious insight - actually knew very little about the world. You presumably don't believe any of the preceeding things - why on earth would you believe them on this matter?!

• Photons have no use.

  What utter nonsense! Photons are the basis for the phenomena we call light and radio waves. Light is amazingly useful. So even according to this bizarre philosophy, photons are perfectly useful and may therefore exist.

• Everything about atoms,e.g. atomic spectra,can be explained by normal, classical (Newton,Maxwell)laws.

  That's ridiculous. It's utterly untrue - there are plenty of phenomena (such as the quantum tunnelling effect that makes the flash memory in your computer work) that can only be explained by non-classical quantum theory. So, assuming your computer is working right now, we can blow away that nonsense!

• Rutherford and Bohr could not. But I can.

  Rutherford and Bohr didn't know as much about the inner workings of matter and energy as we know now. But you evidently don't know enough science to even realise the depth of what you don't know - so putting yourself anywhere close to level those two gentlemen is ridiculous in the extreme. Rutherford did lots of careful experiments to demonstrate those properties of the atom that he discovered. Neither Rutherford nor Bohr made some random assertion on the basis of ancient philosophers! I think you should be a little more humble in the face of the great minds that came before!

SteveBaker 14:51, 20 April 2007 (UTC)

Solar "Booms"

Is there any way to estimate the power in decibels of the sound waves in the Sun's corona?--JLdesAlpins 16:28, 19 April 2007 (UTC)

The decibel is a dimensionless measure of ratio. It's only meaningful when referenced to some point (like "-3 dB from peak power"). Maybe you're looking for dB(SPL) or dBA. -- mattb 17:21, 19 April 2007 (UTC)

Judging from the fact that you can see the individual compression zones on the picture and considering the sheer size of the sun the waves will probably have a very low frequency and would be "inaudible". So the answer is: zero.

decibels have nothing to do with whether you can hear it or not though... --antilived^{T | C | G} 06:11, 20 April 2007 (UTC)

Strictly speaking, yes, but if you use the aformentioned a-weighting in your definition of "decibel" then the frequency does indeed matter. -- mattb 14:19, 20 April 2007 (UTC)

So just drop the decibels as it's apparently a distraction. Tt's an interesting question. What is the power in the coronal loop wave? --Tbeatty 18:00, 21 April 2007 (UTC)

What's the best way to stop a parrot from swearing??

I've mentiond my trusty hyacinth macaw on this board before. What I didn't mention is that she is an incredibly foul mouthed bird. I've never sworn directly at her but I have a temper and do tend to curse loudly and heavily into thin air when things go wrong and she's picked up on that. She says the 's-word', the 'f-word' and the 'c-word' a lot, over and over and over. It's quite embarssing when I have polite company, or when I take her out in her harness with me. She seems to swaer at strangers a lot, maybe because it's fun for her to see them react (they usually just think it's quite funny when she turns to them from my shoulder in town and calls them a 'f*cking c*nt', though she's said it to little kids too, which isn't so funny) or something.

The damage is probably done already but does anyone know a way I might discourage her from doing it so often? Anything that doesn't involve punishing my bird. --84.65.77.1 17:28, 19 April 2007 (UTC)

Electric shock therapy Its more then a solution to weak musles if that doesnt work Nuke it ;-) User:Maverick423 If It Looks Good Nuke It 17:54, 19 April 2007 (UTC)

It is very difficult to train an animal to "do what I say, not what I do." However, the bird may be trying to get attention. So, give it excessive attention when it says something nice and ignore it when it says something bad. If it isn't trying to get attention, find out what the bird is trying to get and give it to the bird when she is nice and don't provide it when she is bad. For example, I had a hedgehog who took to biting my hand to see if I had food. To stop it, I put food in my hand and, if she bit me, I'd make sure she saw me give it to another hedgehog. If she ran up to me without biting, I'd give it to her. She stopped biting in three days. --Kainaw ^(talk) 19:03, 19 April 2007 (UTC)

I also hope you learn not to swear out loud in front of the bird. This could be a good lesson to learn before you have kids that pick up the same language. As embarrassing as this may be in a bird, imagine if your kid's teacher called to complain that your kid is calling the other kids and teachers those names. StuRat 19:09, 19 April 2007 (UTC)

The bird's name isn't Ruby is it? There's a bird on YouTube that calls its owner a f*cking c*nt, quite funny if you ask me.

Honestly, the easiest and perhaps best option is simply to accept the bird's potty mouth.Vranak

The Law of Effect says "responses to stimuli that produce a satisfying or pleasant state of affairs in a particular situation are more likely to occur again in the situation. Conversely, responses that produce a discomforting, annoying or unpleasant effect are less likely to occur again in the situation." Having your attention, such as pleading with him not to swear, might be a "pleasing state of affairs." As a principle of Operant conditioning, this means that if you reward the parrot in some way, as by paying more attention, when he cusses, then he will cuss more. If you reward other vocalizations, and ignore curses, then the vocabulary should shift in the direction you want. It is hard to punish a bird without harming it or causing more undesirable behavior, and it is hard to be sure the punishment will not just lead to more of the undesired behavior, as well as making the animal hate and fear you. See Animal training for more info. From experience, promptness and consistency are important, along with patience and repetition. Like a child, the bird may note that your swear words are important, so controlling your vocalizations may be a necessary step toward controlling the birds vocalizations. Edison 21:47, 19 April 2007 (UTC)

Agreed. Bird hears human vocalizing loudly and harshly whilst behaving in a particularly animated manner - bird is interested by this. Bird doesn't know what sounds mean but knows that they probably have some significance to the creature it lives with. Bird attempts to use these new sounds - bird gets attention from companion creature. Bird likes attention, bird continues to make sounds, other creatures like the one the bird lives with show bird attention when bird uses new sounds. Bird likes attention - etc., etc., etc.. As birds go, hyacinth macaws are pretty high up there in terms of intelligence. --Kurt Shaped Box 21:56, 19 April 2007 (UTC)

You could try jumping around and seeming angry whilst yelling "Polly wants a craker" or whatever you'd like your bird to say! If you teach a wide-enough vocabulary of 'good' things - maybe the bad stuff will get nudged out of it's feathery little brain! SteveBaker 02:57, 20 April 2007 (UTC)

I suspect you'll end up with a bit of each: "Polly wants a cracker, you f***ing c**t". :-) StuRat 04:29, 20 April 2007 (UTC)

I read it in a book once about that grey parrot that allegedly have 100 word vocabulary and things and one thing the owner said is to cover the bird (or the cage, forgot which) up with a piece of cloth for a few second when they do bad things. Eventually they will learn not to do them and your problems would be gone. --antilived^{T | C | G} 06:11, 20 April 2007 (UTC)

Or "Pollywannacunt", as is the habit of parrots to mix/match their words and leave out the pauses... ;) --Kurt Shaped Box 11:29, 20 April 2007 (UTC)

Parrot stew? ;-) ~ hydnjo talk  08:07, 20 April 2007 (UTC)

Hyacinth macaws are worth around $10,000 - I don't thing stewing them is a good plan. SteveBaker 14:21, 20 April 2007 (UTC)

Well, a hyacinth macaw with that big a vocabulary is probably worth a lot more. I'd suggest either a swear jar or eBay. Anchoress 14:26, 20 April 2007 (UTC)

Having a sweary parrot can be a problem if you ever need to re-home her (due to illness, work, having kids, moving to a smaller place, etc). I can't imagine there'd be many people willing to take on an old, foul-mouthed bird with its own habits when they could just get a cuddly little fledgling. Probably easier to re-home than a feather-plucker/OCD (i.e. pretty much psychotic) bird though. I'd personally be happy to adopt a parrot with a colourful vocabulary if given the opportunity - I have a thick skin. --Kurt Shaped Box 17:34, 20 April 2007 (UTC)

You won't even need eBay. After a trek down the mighty Monongahela River between Fairmont, WV and Pittsburg, PA and in Charleroi, PA as a matter of fact the boys that operate the Campbell Barge Line are as profane a cursers as ever won a championship for blue streak cursin'. As a matter of fact they won't hire anyone who can't be trained to lay down a blue streak of cursin'. Sounds like ol' poly would fit right in. Just contact Mike Sosnak, Safety and Traning Manager for the Line. I'm sure he'd appreciate havin' some company thar in his Deckhands School after the barges done been all manned and loaded. 71.100.8.252 04:06, 21 April 2007 (UTC)

Insulin and Blood Sugar

From what I understand, its bad for your blood sugar to rise rapidly because it releases insulin which stores fat, then why do bodybuilders who use growth hormone also inject insulin?

If you eat too much sugar, you store more fat. If bodybuilders take insulin hey don't need, and then eat enough carbohydrate to keep from being hypoglycemic, they store more fat. alteripse 20:55, 19 April 2007 (UTC)

Growth hormone promotes gluconeogenesis, which can lead to hyperglycemia. Some bodybuilders add insulin, which promotes the cellular uptake of glucose from the blood, to counter this effect. Insulin is also a growth factor, which is another reason bodybuilders may abuse it.^ref However, insulin supplementation can cause hypoglycemia, especially during exercise.^ref --David Iberri (talk) 23:56, 19 April 2007 (UTC)

Principle Rotation Axis in D_2d and D_3d Groups (Inorganic Chemistry & Symmetry)

How are the irreducible representations for point groups generated? My book says that A represents symmetry about the principle rotation axis and B represents antisymmetry. I'm ok so far. However, upon flipping to the character tables for D_2d and D_3d a few pages after that, here's what I see (I removed some impertinent info, such as E rows).

D2d	E	2S4	C2	2C2'	2σd
A1	1	1	1	1	1
A2	1	1	1	-1	-1
B1	1	-1	1	1	-1
B2	1	-1	1	-1	1

D3d	E	2C3	3C2	i	2S6	3σd
A1g	1	1	1	1	1	1
A2g	1	1	-1	1	1	-1
A1u	1	1	1	-1	-1	-1
A2u	1	1	-1	-1	-1	1

In the D_2d table, it shows that A and B are BOTH +1 under what I assumed is the principle rotation axis (the C₂). It almost appears that they are using one of the S₄ as the principle rotation axis, since under that column A's are +1 and B's are -1. Kinda weird, but I suppose it could be seen as the highest order axis.

But then, it looks like they are using the C₃ axis as the principle rotation axis in the D_3d group, despite the presence of two S₆ improper rotation axes (A's are +1 under S₆ and not C₃). Am I going crazy? (probably, but not even my professor could figure it out.) Thanks for at least reading this, even if you don't know the answer :) --129.21.126.178 19:55, 19 April 2007 (UTC)

Correction: In the last paragraph, A's are all +1 under C₃ and not S₆. I had them switched. Sorry --129.21.126.178 19:58, 19 April 2007 (UTC)

This looks like more a math question than a science question; try the math desk. NeonMerlin 16:52, 20 April 2007 (UTC)

It's definitely a chemistry question, but it involves the application of math (geometry) principles. TenOfAllTrades(talk) 17:03, 20 April 2007 (UTC)

(outdent) Note that the C₂ and S₄ axes themselves are the same, however. So that criterion is probably not useful beyond the simplest of groups.

A way to see the A/B distinction is to note that A₁ is the representation of spherical symmetry (every operation is the same as the identity), and to see which is the representation of the rotation about the principal axis, like this. Consider a circle around the principal axis but with an arrow in it (like this $\circlearrowleft$). What is the representation of this? Yup, it's A₂, since C₂ and the S₄s do not change the direction of rotation (σ in S₄ is normal to the rotation), but σ_ds and C'₂s do change its direction (to this $\circlearrowright$). But note that that "rotation" is neither a two fold, four fold, or anything like that. It is just general "rotation". Baccyak4H (Yak!) 17:35, 20 April 2007 (UTC)

Update. In hindsight, I am not so sure of my previous answer; let me dig around... Baccyak4H (Yak!) 18:29, 20 April 2007 (UTC)

Yeah I'm not sure I understand you completely. Let me explain how this came about. On a test question, the professor asked "What is the irreducible representation of a p orbital in the D_2d point group?". Using the table (one of the columns I cut out) I answered "B₂" and continued. He marked it wrong and said it should be "A₂" (although he still gave me credit. Nice guy :) ).

He was assuming the C₂ axis was the principle (z) axis, in which it would indeed be A₂. However, using the S₄ axis as the principle it would be B₂. Even though the axes are the same, reflection through the mirror plane would result in changing the phase signs and resulting in a "B". So to me, it looks like they are using the S₄ axis in D_2d and the C₃ axis in the D_3d groups as the principle rotation axis. Is this just that selecting the princple rotation axis arbitrary, or is there a deeper meaning? Thanks for the help - this is really stretching my brain. (BTW, I am the one that asked the question - I completely forgot to log in.) --Bennybp 18:52, 20 April 2007 (UTC)

I am finding that material about A reps having "1"s for the principal axis entries (Drago 1977), and most groups do just that (Cn, Dn, Cnv, Cnh), but not Dnh, Dnd, or Sn. Not sure why...maybe you are right and that the coincident S axis has something to do with it. The deeper meaning that we both miss has to do with A being symmetric w/respect to that axis, but which operation thereof? I would say your assumption appears correct, but I cannot justify why it's done that way (esp within D_nd, different for n=2 and n=3).

Although I agree with your answer for the z-orbital! For a group that's not too big you can figure out what each operation does to each orbital (like I described for a simple rotation), then match to the table (caveat: nonsingly degenerate reps like E, T, etc. are hard to do this way). In D_2d, what does the identity do to the z-orbital? An S4? What about the principal C₂? Either C'₂? a σ_d? Answers: nothing, flip sign, nothing, flip sign, nothing. That makes it B₂. Now for the x-orbital, you could go through this again, but note what S₄ does to it: make it a y-orbital, so these two are coupled somehow (hint!). For D_3d, you can do the same thing, it's just a little more work. Drago explicitly states that the z-orbital has a B₂ representation too—maybe the conventions have changed since 1977.

Hope I've been a help. Baccyak4H (Yak!) 19:44, 20 April 2007 (UTC)

You've been a great help to me. At least I'm not the only one seeing an inconsistency. According to the "What does each operation do to it" approach, it should be B₂. But the other approach keeps nagging me. I've got a book from my school library "Chemical Applications of Group Theory" by F.A. Cotton that I'm going to peruse this weekend. Let's hope I find something :) Thanks again --Bennybp 00:20, 21 April 2007 (UTC)

Great! Cotton's book is indeed the gold standard for this material. Baccyak4H (Yak!) 01:57, 21 April 2007 (UTC)

Diarrea and Weight loss

If I have diarrhea, will I lose weight other than water weight? Will everything I ate just come out without the calories being absorbed by the body?

Yes, you will lose weight, but it will cause malnutrition, so I wouldn't want to use this as a weight loss method.Czmtzc 20:34, 19 April 2007 (UTC)

I have removed a comment from this space which offered medical advice. If you feel that I am in error, please feel free to revert. ^tucker/_rekcut 23:35, 19 April 2007 (UTC)

I feel it was in error but you won't get my sage wisdom back. :) Vranak

For whatever it's worth, here is a link to the aforementioned and deleted Vranak's sage wisdom. ~ hydnjo talk  07:01, 20 April 2007 (UTC)

The short answer to your question is that you will definitely lose water, but the diarrhea may or may not also contain any one of the components of your diet (for instance, excess glucose or excess salt could both cause watery stool). Thus the question cannot be answered in general, as different diarrheas have different causes and waste different things that may be useful to the body. Please consult a physician if you seek medical advice. If you are interested only in information, perhaps diarrhea, malabsorption, osmole, dehydration would be a helpful.^tucker/_rekcut 23:35, 19 April 2007 (UTC)