Wikipedia:Reference desk/Science

WP:RD/S C #eee #f5f5f5 #eee #aaa #aaa #aaa #00f #00f #000 #00f science Wikipedia:Reference desk/Science Science WP:RD/S

Welcome to the science reference desk. Want a faster answer? Main page: Help searching Wikipedia     How can I get my question answered? Select the section of the desk that best fits the general topic of your question (see the navigation column to the right). Post your question to only one section, providing a short header that gives the topic of your question. Type '~~~~' (that is, four tilde characters) at the end – this signs and dates your contribution so we know who wrote what and when. Don't post personal contact information – it will be removed. Any answers will be provided here. Please be as specific as possible, and include all relevant context – the usefulness of answers may depend on the context. Note: We don't answer (and may remove) questions that require medical diagnosis or legal advice. We don't answer requests for opinions, predictions or debate. We don't do your homework for you, though we'll help you past the stuck point. We don't conduct original research or provide a free source of ideas, but we'll help you find information you need. Ready? Ask a new question! After reading the above, you may ask a new question by clicking here. How do I answer a question? Main page: Wikipedia:Reference desk/Guidelines The best answers address the question directly, and back up facts with wikilinks and links to sources. Do not edit others' comments and do not give any medical or legal advice.

Choose a topic: Computing desk Science desk Mathematics desk Humanities desk Language desk Entertainment desk Miscellaneous desk Archives   See also: Help desk Village pump Help Manual   skip to bottom

December 7

Need to burp!

I wonder if this counts as a medical question. Whenever I have a stomach full of gas, I have a hard time burping it out, so it ends up being very uncomfortable and painful until it finally happens.

What are best ways to stimulate burping? — Kieff | Talk 00:57, 7 December 2007 (UTC)

With babies you pat them on the back for a while, maybe it can have the same effect on you? —Preceding unsigned comment added by 128.101.53.177 (talk) 01:08, 7 December 2007 (UTC)

Eno's Fruit Salts. DuncanHill (talk) 01:25, 7 December 2007 (UTC)

Yes it does. This could actually be a medical condition (a feind of mine had similar condition). Please see a doctor.--TreeSmiler (talk) 03:17, 7 December 2007 (UTC)

As far as my understanding of our policies is concerned: a) we can tell you how to induce burping, but b) we can't tell you if it's healthy to do so in your case. If this (epigastric discomfort) is a problem for you, you should see a physician or other health care worker, as it may be a sign of a serious condition (or it could just be gas, but since it's causing you grief, why not look into a solution with a doctor that will stop the gas from forming, rather than finding ways of relieving it?) (EhJJ) 04:15, 7 December 2007 (UTC)

Just as with the question "How do you get to Carnegie Hall?", the answer is "Practice!". Drink something highly carbonated such as seltzer. Learn to relax the muscles in your throat and contract the muscles in your abdomen. Seriously. You can train yourself. People who have had their larynx surgically removed learn to swallow air and burp it out to simulate the buzzing of their now-missing vocal cords; you can probably Google up more info regarding how they train themselves. And then there's the contest in Revenge of the Nerds...

Atlant (talk) 14:08, 7 December 2007 (UTC)

Dear Reference Desk: Does telling someone how to make it worse count as medical advice? I'm uncertain. SteveBaker (talk) 16:16, 7 December 2007 (UTC)

Questioner: Remove the opening sentences and just leave your question. "What are best ways to stimulate burping?" is in no way a request for medical advice. Adding personal history confuses some people and makes it difficult for them to see the question. As with any abnormality, you should seek professional medical advice to ensure that you are healthy. Answering the question - as with babies, patting someone on the back and rubbing the center of the back in circles helps with burping. -- kainaw™ 17:28, 7 December 2007 (UTC)

Wikipedia talk:Reference desk

Hydrogen Peroxide

Does anyone know what the heck is that white gunk you get from hydrogen peroxide you put on any unsterile surface (i.e. sink, tub, bathroom floor), or on raw meat? --Agester (talk) 01:19, 7 December 2007 (UTC)

Beyond "white", tell us something about this "gunk". Is it a solid, liquid? Does it dissolve if you pour some water on it? Does it disappear after sitting for a while? Is it foamy (H₂O₂ decomposes to H₂O and O₂ and this reaction is strongly catalyzed by several common biological materials). DMacks (talk) 02:41, 7 December 2007 (UTC)

It sounds like bleached scum. Graeme Bartlett (talk) 21:22, 7 December 2007 (UTC)

Not quite too sure what it is. But it seems very similar to the foamy stuff if you put hydrogen peroxide in a open cut / wound. I figured it might be the dead bacteria, because when i put it in a clean bowl that i just washed it doesn't build up that foamy stuff, but if i accidentally drip some in my sink it'll foam up similar to it being applied to a cut. And if it isn't assumed I'm talking about the hydrogen peroxide you can get in your local pharmacy for antiseptic uses. --Agester (talk) 01:09, 8 December 2007 (UTC)

The hydrogen peroxide article mentions that the human body, most animals and nearly all aerobic bacteria use catalase, which is an enzyme that speeds the reaction 2H₂0₂-->2H₂0+0₂. I assume you use your sink (bathroom one) to brush your teeth and your tub to wash, right? And there's always bacteria there just growing on the water left over and any biological material. So all this bio-matter in those places has catalase, which decomposes the hydrogen peroxide, which gets caught up in any sort of proteinaceous stuff on the surfaces, creating a foam. Same on the meat---it's like the frothing when it is poured on an open wound.Aquaman590 (talk) 00:38, 9 December 2007 (UTC)

Malt liquor

Is malt liquor sweet? Heegoop, 7 December 2007 (UTC)

Our article on malt liquor doesn't really answer the question, aside from mentioning that sugar is sometimes added. I would guess that it would depend on the particular brew, as it is essentially beer with a little more alcohol (like they sell in Canada and Europe). As a scientist, I'd like to suggest a simple experiment :P (EhJJ) 04:20, 7 December 2007 (UTC)

The article says sugar is sometimes added before fermentation, "to boost the beverage's alcoholic strength". Adding sugar before fermentation has somewhat the opposite effect to adding it afterward, because the yeast use up all the sugar present and turn it into alcohol. —Keenan Pepper 06:17, 7 December 2007 (UTC)

Malt liquor is really little other than distilled beer, and as a brewer I can tell you that beer can be made sweet or not so. Depending on mash temperatures (the temperatures at which the malt is steeped), sugars in the grain are broken down to various degrees. At some temperatures you end up with much of the sugar of the kind yeast likes, and little of the stuff yeast can't easily digest; and at other temperatures, the opposite. Any sugars the yeast doesn't digest to ethanol+CO₂ increase the sweetness of the finished product. Psud (talk) 10:09, 7 December 2007 (UTC)

What?!? Maybe this is a difference in terminology between different places, but around here, what we call "malt liquor" is beer that's a bit stronger than typical beers. It is most emphatically not distilled! It's still just beer. The article Malt liquor also does not mention distillation. If it's distilled, it's not beer. Friday (talk) 16:38, 7 December 2007 (UTC)

Ooops. Brain not switched on (never is at 10:00Z). The stuff I was talking about is properly called "Whiskey". Oh well. We call malt liquor "barley wine" here. Being beer, nothing more, nothing less, it can be naturally somewhat sweet, or its sweetness can be increased by adding lactose (which sacromyces cerviseaSaccharomyces cerevisiae can't digest) or an artificial sweetner. It's all up to the brewer. ----Psud (talk) 13:09, 8 December 2007 (UTC)

As with anything that's brewed, the amount of sugar left at the end of fermentation depends on how much you put in at the outset and how long the fermentation went on. Fermentation stops when either the yeast runs out of sugar to convert - or it poisons itself with it's own alcohol production (or maybe if someone stops it prematurely by messing up the temperature or something). So there are a range of possible outcomes here. Obviously, the manufacturers can also alter the final sweetness by adding more sugar after fermentation is complete. So it's not true to say that because something sweet went in at the outset, that the result will be sweet...but "it depends". SteveBaker (talk) 16:11, 7 December 2007 (UTC)

How much sugar went in; how long it fermented for; and how fermentable the sugars are:

• Starting with unfermentable sugars makes the result sweeter
• Adding unfermentable sugars after fermentation makes the result sweeter
• Killing or filtering the yeast then adding fermentable sugars after fermentation makes the result sweeter
• Adding artificial sweeteners makes the result sweeter
• Stopping fermentation early is wrong and bad and only suitable for childrens' drinks, but does make for a sweeter, lower alcohol drink

--Psud (talk) 13:23, 8 December 2007 (UTC)

• You might be thinking of Malt beverage, which is a little different from malt liquor. In the United States, makers of Alcopops such as Mike's Hard, Zima, etc. refer to the drinks as "flavored malt beverage" or "premium malt beverage". These drinks are very different from malt liquors, which more often taste like smooth beers, as Steel Reserve and Hurricane High Gravity Lager do. Also, don't forget Low-end fortified wine like Mad Dog and Thunderbird -- these are often sold in the same section as the malt liquor, and most of them are very sweet to cut the harsh taste. --M@rēino 19:01, 7 December 2007 (UTC)
  • Never heard of those. Surely Colt 45 is the typical malt liquor? Rmhermen (talk) 19:32, 10 December 2007 (UTC)

Gene transfer a mutation?

Would horizontal gene transfer be considered a mutation for the organism that receives the transferred gene? I'm confused. I stumbled across a PNAS article which seemed to refer to it as a "mutational process," [1] but sometimes the two terms may be observed contrasting with eachother (e.g., [2] , scroll down to the section that says "evolutionary genetics in bacteria"). Thanks! Schmitty120 (talk) 01:33, 7 December 2007 (UTC)

One could argue the semantics of describing the effect of horizontal gene transfer as a mutation. From a strictly technical point of view, it could be considered mutational. For instance, if the gene integrated into the recipient genome it would result in a "mutation" of the genetic insertion site. Likewise, of you wish to use the term to describe the phenotype affected then the recepient could be described as having a "mutant phenotype" and it follows that must have occured by a mutational process. In the link where you suggest it is used in a contrasting manner, I think the use of the term "mutational process" is really a shorthand for "classical mutational processes in vertical gene transfer" (meaning indels and point mutations) in contrast to horizontal gene transfer and recombination. I don't think in calling them "mutations" (or not) the author is attempting to make a point about whether they are involved in the evolutionary process (or not). It is fairly well established that both types of genetic changes have driven evolution (at least in bacteria, see Horizontal gene transfer#Evolutionary theory). Rockpocket 08:15, 7 December 2007 (UTC)

Neurobiology: Effects of decreased membrane capacitance

My script says that Myelination reduces the leakage current and decreases the axon's membrane capacitance. By this the speed of signal propagation is increased. However, I do not see which effect decreasing the membrane capacitance has on the speed of signal propagation in addition to reducing the leakage current. Can somebody please explain this to me? Falk (talk) 08:27, 7 December 2007 (UTC)

We are propagating a potential difference up the axon. By $Q=CV$, we see that for this potential to stay constant, there must be a buildup of charge difference on each side of the membrane, and to get this charge difference there must be an ion flow toward the membrane, which takes time. By reducing capacitance, the necessary charge difference becomes lower. Otherwise, we could say $I=CdV/dt$, in which case reducing the capacitance for a given ion current (the rate of flow of ions we'll assume is constant) increases our voltage propagation speed $dV/dt$. SamuelRiv (talk) 13:27, 7 December 2007 (UTC)

Cold Car Experiment

Two identical cars are started, and their heaters turned on, on a cold wintry morning. One car is encased in half an inch of ice; the other car was covered and is clean. In which car will the internal air temperature rise faster? We've come up with several hypotheses:

a) The icy car will warm faster, because it is insulated with an extra layer of ice.

b) The clean car will warm faster, because the ice on the icy car conducts heat away from the windows faster than air could, due to ice's higher thermal conductivity.

c) It depends on how close the ice is to the freezing/melting point, since

d) It depends on the air temperature or velocity outside -- if the air is significantly colder than the freezing point of water, it will cool the windows faster than melting water.

e) More than one of the above are true, and the problem is too complex to definitively answer.

Your thoughts? jeffjon (talk) 14:07, 7 December 2007 (UTC)

Assuming the outside air temperature is the same as the temperature of the ice (which is reasonable) and that it's a lot colder than zero centigrade (ie well below freezing): I think the one covered in ice will win - ice is a reasonably good insulator - but not as good as air. However, with air, as soon as you heat it up just a bit, it drifts upwards to be replaced with new, cold air. Hence any heat that leaks out of the second car is lost immediately. With first car, with an icy jacket, the heat you radiate goes into warming up the ice - at least until it reaches it's melting point - and that warmth is retained close to the surface of the car. Since the rate of heat loss is proportional to the square of the temperature difference (Newtons law of cooling), the ice-encased car will do better.

If the air around the second car was retained close to the car though (eg if it had a loose car-cover thrown over it) then the superior insulation value of air would win out.

SteveBaker (talk) 15:55, 7 December 2007 (UTC)

I agree with Steve. There would be several minutes of ambient temperature air coming out of the vents until the engine warmed up, then the ice-encased car would have less heat loss due to convection, leading to a faster rise from the assumed below zero C interior temp and temp of the ice. Of course if it were warm outside, then the ice-free car would warm up faster. Edison (talk) 23:55, 7 December 2007 (UTC)

Not so fast. If one car is literally encased in half an inch of ice, then you can't get in to start it at all. It will just sit there cold while the other warms up! :-P More seriously... should any thought be given to the blanket of ice essentially acting as a heat sink - for the engine if nothing else? I agree with the theory that the ice will act as an insulator, but the interior of most cars is composed of cloth, plastics, and foams - surely that degree of internal insulation would minimize any difference to heat loss caused by the ice? Matt Deres (talk) 15:52, 8 December 2007 (UTC)

You can't refer to the car's own insulation, as it's the same between the two cars, and insulationA + insulationB is better than insulationA + nothing. --Psud (talk) 16:54, 8 December 2007 (UTC)

I understand that (I think). I'm just saying that the effect of insulation B isn't going to be much compared to the effect of insulation A and in fact might be completely overshadowed by the heat sink effect. Just a guess on my part, though; I assume Steve is probably correct. Matt Deres (talk) 22:02, 8 December 2007 (UTC)

Let us not forget that if the car were encased in ice, the HVAC air intake would be blocked. The heater core itself would warm up faster because there'd be no airflow through it, but the cabin temperature would not, for the same reason.--Scheinwerfermann (talk) 16:30, 8 December 2007 (UTC)

This sounds like a question for Mythbusters.  :-D -- HiEv 06:11, 9 December 2007 (UTC)

Hovercar?

Think these would ever be viable? How would one break or slow down in one? 64.236.121.129 (talk) 14:19, 7 December 2007 (UTC)

Presumably by reversing the means of propulsion (a fan or whatever). If you can figure out how to make it go forward, you can figure out how to make it slow down. And I would think they would break the same way regular cars do—when it's least convenient, and at great expense. -- Coneslayer (talk) 14:23, 7 December 2007 (UTC)

I reckon they'd be too expensive in fuel. Hovering is very energy intensive, especially when compared to rolling. As to braking, consider an already existing vehicle that can hover - the helicopter. Helicopters brake by vectoring their thrust forward, a hover car would presumably do the same. --Psud (talk) 14:39, 7 December 2007 (UTC)

I think by the time the technology is good enough and reliable enough and they are cheap enough to be somewhat popular, there will be other, far better forms of transportation people will use instead. Recury (talk) 14:41, 7 December 2007 (UTC)

Actually, I like the idea of travel by rocket - a short high acceleration burn; a ballistic arc; a short high acceleration burn to stop. Fun and quick whether across town or across continents! --Psud (talk) 14:45, 7 December 2007 (UTC)

Hovering as in hovercraft? The trouble with hovercraft is that they are very unmanouverable - you don't have friction with the ground - hence you have no brakes. Redirecting thrust to slow you down means that you can't slow down any faster than you can accellerate and if there is even the slightest deviation from aiming the thrust dead straight, there is a tendency for the craft to spin or slip sideways. Stopping at traffic signals would be tough. Energy-efficiency-wise, they aren't so good either. The lack of friction with the ground is a net win - but it's very expensive to maintain the hover thrust - so you end up needing more power than with a car. It's nice to be able to travel over water and to not need paved roads (it would be nice if all of our roads could be turned into lawns - or farmed for grain!). Hovercraft are impractical for other reasons: If your lift motor fails, you can't push the vehicle off the road - if your thrust motor (which is also doing the braking remember!) fails then you have a dangerously uncontrolled vehicle on the streets. At stop lights, or in heavy traffic, everyone has to land and lift off again because, again, there is no way to keep a hovercraft stationary. Even the slightest breeze would be enough to blow you onto the sidewalk if you continued to hover.

Using propellors to direct thrust has another set of problems in that the 'blow back' from the rear of the craft will tend to knock pedestrians off their feet and blow out windows! Also, if two or more hovercraft are manouvering close together (again, think busy city streets with people turning, parking, stopping and starting) - then there are lots of dangerous cross-winds induced by one craft turning that would tend to blow other craft sideways.

All in all, hovercraft just aren't really practical in tight areas. Great for lakes and open grassland and such though. SteveBaker (talk) 15:43, 7 December 2007 (UTC)

• my hovercraft is full of eels --M@rēino 19:07, 7 December 2007 (UTC)

You can buy a hovercar today: the M200G Volantor or the Moller Skycar M400. Rockpocket 19:19, 7 December 2007 (UTC)

That's not really true. They are offered to sell one of their prototypes - on the condition that you basically use it as a museum piece and promise not to fly it - but the price was so high, I don't think they actually managed to find a buyer. You can't actually buy a working, flyable, usable flying/hovering car from them - it's always "a few years away"...which is why Moller are being dragged through the courts over it by their investors. SteveBaker (talk) 19:48, 7 December 2007 (UTC)

Also those are flying cars. That's a bit different. A hovercar doesn't lift off the ground by too much, while a flying car can fly very high. 64.236.121.129 (talk) 19:57, 7 December 2007 (UTC)

"The computer system also prevents the machine from flying higher than 10 feet (3 m) above the ground." - sounds like a hover car to me. I didn't say you should buy one, just that could could buy either of those functional prototypes if you had enough money. It would then be up to you to find somewhere to use it legally. ;) Rockpocket 01:14, 8 December 2007 (UTC)

No, no, no! You can't buy a flying/hovering car that you can actually use - at least not from Moller. The company only ever had ONE flying/hovering car for sale - it was their first prototype - and nobody bought it. BUT you had to sign some kind of legal document promising that you would only use it for display purposes and NEVER attempt to fly it. So if you had a HECK of alot of money (it was in the millions of dollars), you could own a car that was theoretically capable of flying/hovering - but you couldn't actually use it. Check the Moller FAQ if you don't believe me. SteveBaker (talk) 03:33, 8 December 2007 (UTC)

Yes, yes, yes! I can't find anything in the FAQ that says you would be legally restricted from attempting to use it, could you elaborate? This suggests the auction was for a car that is "suitable for test and evaluation only." That sounds like you could happily attempt to "hover" your $3.5M "car" under the guise of an evaluation/test, as long as the local air authorities could be convinced to permit it. Rockpocket 21:39, 8 December 2007 (UTC)

Chemical(s) responsible for Pine/Christmas Tree Scent

Can anybody inform me of the name(s) of the chemical(s) responsible for the fragrance associated with Christmas/Pine trees? --Mark PEA (talk) 16:00, 7 December 2007 (UTC)

I presume pine oil. Someguy1221 (talk) 17:54, 7 December 2007 (UTC)

Most fragrances are very complex mixtures of chemicals - I doubt there is one particular one that produces the "Pine tree" smell. SteveBaker (talk) 19:44, 7 December 2007 (UTC)

Okay, thanks for the answers. I thought maybe there would be some research into the constiuents of pine oil but I can't seem to find any without digging deep. --Mark PEA (talk) 23:51, 7 December 2007 (UTC)

There is certainly scientific literature on this because I have seen it. I think that many of the priciple aroma compounds are monoterpenes such as pinene. ike9898 (talk) 13:12, 8 December 2007 (UTC)

Indeed, the igredients have been identified. [3]. 57% alpha-pinene, 8% beta-pinene, 26% carene, 6% limonene and 3% other hydrocarbons. I don't know if the article identifies the other hydrocarbons, as the only online version I could find was here, and I don't have a subscription to that service. Someguy1221 (talk) 22:38, 8 December 2007 (UTC)

I would have thought of esters. 86.150.30.106 (talk) 19:51, 10 December 2007 (UTC)

Testosterone Question

I read something about testosterone and how bodybuilders have to keep using more and more each time they use it to get the same effect. Does that mean, that when your off of synthetic testosterone, the testosterone that is body makes is less effective then it used to be before you started using synthetic testosterone? (assuming your body is making the same amount of testosterone as it did before you started using synthetic testosterone) —Preceding unsigned comment added by 71.106.34.15 (talk) 17:18, 7 December 2007 (UTC)

This is a phenomenon known as downregulation, which occurs when any receptor is overstimulated by a ligand. I've never answered a question here before, so maybe someone else can put more effort into it and explain it better. See also: Desensitization (medicine), Drug tolerance, Physical dependence. --Mark PEA (talk) 23:49, 7 December 2007 (UTC)

With testosterone it's more complex than mere downregulation. In fact, when you massively flood your system with artificial testosterone, your endogenous production is completely knocked out. This is what causes rather extreme withdrawl symtoms for several weeks after going cold turkey from steroids, as your body takes that long to regain normal production levels. Additionally, your body will initiate processes to convert excess testosterone into other hormones, including estrogen (if I recall correctly). I'm not sure if these two processes in combination are the complete reason for any apparent drug resistance seen in steroid abusers. Someguy1221 (talk) 23:57, 7 December 2007 (UTC)

Just a little correction, most people dont know this, especially the media and the people that give steroids a bad rep. Educated steroid users (not the little 17 year old kids, im talking about the people that do research and are parts of different steroid or bodybuilding forums), take drugs such as clomid,nolvadex, etc.. or shoot some HGC to restore natural testosterone production, they dont go cold turkey. If they were dumb enough to not use these drugs to restore natural testosterone fuction, they would lose most the muscle they gained and be depressed, and thats not the case with educated users. —Preceding unsigned comment added by 76.167.132.90 (talk) 03:13, 9 December 2007 (UTC)

Autothermal Reforming and Modelling Software

Okay, this is possibly a little specialised but I'm losing track of what reasonable values are for things and nobody else around me seems to be doing better with the software. I'm modelling autothermal reforming of methane with oxygen and steam using PRO/II (pro2), which has to be the most irritating piece of software ever coded. Putting 16152.7060 kmol/hr of my reactants into a Gibbs reactor, at some temperatures the reactor is giving out 3,000 million kJ/hr in heat. At some lower temperatures it requires nearly 300 million kJ/hr heat to be put in. Now, pro2 being as erratic as it is (and given the weird way the duty is varying with the pressure), I'm suspicious of these values. Are they, in fact, reasonable?

Thanks for any help. I've just reached the stage where I'm so frustrated with the software I can't think clearly about the actual process. Skittle (talk) 17:31, 7 December 2007 (UTC)

I really have no knowledge whatsoever of your problem domain. So I'll respond anyway (that's what teh Intarweb is for!). 3,000 million kJ/hr is 833 megawatts, which is pretty close to the electrical output of Three Mile Island's remaining nuclear reactor. Do you anticipate that what you're trying to do should have energetics on the same scale as a power plant? -- Coneslayer (talk) 17:44, 7 December 2007 (UTC)

Hmm, thanks. I wasn't really expecting to get nuclear power plant levels of heat :) Although, it would provide excellent heat integration opportunities. That was the sort of reality check I needed; I was starting to doubt the size of a kilojoule. So, pro2 screws up again. Hooray! Skittle (talk) 18:05, 7 December 2007 (UTC)

BTW, Google is good for quick unit conversions... 3000 million kJ/hour in watts is what I used. -- Coneslayer (talk) 18:29, 7 December 2007 (UTC)

Yes, but without someone who isn't me to tell me 'that's like a power plant', I couldn't be sure I wasn't just being stupid :) Skittle (talk) 18:31, 7 December 2007 (UTC)

We all came from the sun?

Would it be a fair statement to say that we all came from the sun? The matter in our bodies came from the sun, and the energy that sustains us also came from the sun in one form or another. 64.236.121.129 (talk) 19:37, 7 December 2007 (UTC)

That assumes (incorrectly in my opinion) that absolutely no matter from outside the solar system or matter that existed in the ooze that became the solar system made it to Earth. -- kainaw™ 19:44, 7 December 2007 (UTC)

That's true, but how much matter from outside the solar system contributed to the ooze? 64.236.121.129 (talk) 19:47, 7 December 2007 (UTC)

The matter in our bodies did not come from the sun. It came from the Earth (and the stuff on the Earth's surface) and thus (ignoring meteorites and so on as negligable), it came from the cloud of gas and dust that collapsed into the solar system. Some or all (not sure which) of this cloud came from a previous supernova, so we come from a star, but not from the sun in any literal sense. See formation and evolution of the solar system. Algebraist 20:16, 7 December 2007 (UTC)

No, little of you came from the Sun. Much of your body consists of hydrogen (either in the water that comprises much of your body, or in the many compounds that comprise the solid bits), which was formed in the aftermath of the big bang. Almost all of the remaining atoms were made in a sun, but not our Sun. Right now the Sun is turning hydrogen into helium; much later in its life it'll make a few heavier elements. The atoms that comprise your body (bar the aforementioned hydrogen) were made by old suns that have since exploded, the wreckage of which condensed to form the planetary nebula from which the Sun, the Earth, and the rest of our solar system formed. Our Nucleosynthesis article is a good place to start. -- Finlay McWalter | Talk 20:12, 7 December 2007 (UTC)

"Us from the sun"? No way…planets and sun all came from a common origin, not one from the other. See Solar System#Formation. DMacks (talk) 20:14, 7 December 2007 (UTC)

As for the energy that sustains us, virtually all of this comes from the sun. The energy contribution of extra-solar sources is truly negligable in comparison. Some primitive organisms, however, obtain their energy from geothermal sources, which certainly didn't originate from the sun. Someguy1221 (talk) 20:17, 7 December 2007 (UTC)

It would perhaps be better to say that we came from A sun - but not from THE sun. Everything we are made from came from the remnents of one or more dying stars someplace. SteveBaker (talk) 03:35, 8 December 2007 (UTC)

As Carl Sagan puts it "We are made of star stuff". I'd say "some suns" rather than "A sun". And of course, those suns were made of the generation of stars before them, with each generation of stars made of heavier elements than the one before. --Psud (talk) 13:30, 8 December 2007 (UTC)

It should be the big bang and suns, right? The stars aren't producing hydrogen. As Finlay pointed out - that was there before the stars were born. -- kainaw™ 19:40, 10 December 2007 (UTC)

Gravity fields, mass, volume, density

Lets say we have two objects. Jupiter, and Mini Jupiter. Jupiter, is the planet Jupiter. Both have exactly the same mass. However, Mini Jupiter has a radius of only 500 miles. As such, Mini Jupiter has less volume, but is much more dense. How do their gravity fields compare? Which is stronger? Which is larger? 64.236.121.129 (talk) 19:45, 7 December 2007 (UTC)

You can use simple Newtonian gravity and the shell theorem to figure this out. Outside the radius of Jupiter, the gravitational fields are identical. Inside the radius of Jupiter, Jupiter's own field weakens, its strength now directly proportional to the radius (if you assume Jupiter's density is irrespective of radius, so this is a very very bad assumption. It's assumed for simple physics problems, and I don't know the actual density vs. radius of Jupiter). MiniJupiter's gravity, on the other hand, keeps getting stronger right up until you reach it's edge. Inside of here, it also decreases as you approach the center, under the same bad assumption for density. So MiniJupiter will have stronger gravity inside Jupiter's outer radius, and outside of that radius, they will have equal gravity. Someguy1221 (talk) 19:59, 7 December 2007 (UTC)

Are living beings mostly comprised of water and carbon?

^Topic 64.236.121.129 (talk) 19:49, 7 December 2007 (UTC)

The average organism is said to be about 70% water. In a sense, living organisms are just aqueous chemical reactors. There are some insects that are considerably less that 70% water (as low as 15% if I recall correctly) as an adaptations for dry environments. There are also plants that contain significantly higher than 70% water. As for carbon, well, carbon is a main constituent of every major chemical group in a living organism. Reading from my years old biochemistry notes, living organisms are 1-3% carbohydrates (made mostly of carbon, oxygen, and hydrogen), 2-3% lipids (mostly carbon and hydrogen), 15% protein (mostly carbon, nitrogen, hydrogen, and oxygen), and 7% nucleic acids (mostly carbon, oxygen, nitrogen, hydrogen, and phosphorus). Carbon, oxygen, hydrogen, and nitrogen constitute 96% of living matter (I believe this number is by mass). Someguy1221 (talk) 20:08, 7 December 2007 (UTC)

The Carbon page tells us that that element "is ubiquitous in all known lifeforms, and in the human body it is the second most abundant element by mass (about 18.5%) after oxygen." DMacks (talk) 20:11, 7 December 2007 (UTC)

See also an elemental breakdown at: [4]. Maybe someone who remembers their chemistry class a little better could figure out how much water might be present based on the H & O content. jeffjon (talk) 21:19, 7 December 2007 (UTC)

Large trees have more carbon than water. Inside the tree is dead wood which contains a massive amount fo carbon but no water. David D. (Talk) 23:41, 7 December 2007 (UTC)

I call that cheating. Someguy1221 (talk) 23:54, 7 December 2007 (UTC)

Maybe but lets not let people think that a whole tree is 70% water. David D. (Talk) 03:05, 9 December 2007 (UTC)

Jellyfish are on the other end of the spectrum with up to 98% water. —Preceding unsigned comment added by 84.187.84.147 (talk) 03:52, 8 December 2007 (UTC)

Grammar note: "comprise" doesn't make sense here. You mean "Are living beings mostly composed of water and carbon?" (If you *really* wanted to use "comprise" you *could* instead ask something like "Does the group of water and carbon-based life forms comprise [exhaustive list of living beings]?", but obviously that would be hugely awkward.)--TyrS (talk) 08:05, 15 November 2010 (UTC)

UK telephone extension wiring

I bought a standard UK telephone extension kit (Homebase), wired it up according to the simple instructions, and plugged it into the master socket. (There are no other extensions.) I have two handsets, an old one (maybe ten years old or more) and a new one. Plugging either handset into either socket on its own works just fine: both handsets will ring and give me a dialtone. Plugging the new handset into the master socket and the old one into the extension works just fine too. However, when I set up the configuration I want, with the old one in the master socket and the new one on the extension, the old handset works but the new one is dead. The old handset seems to be somehow blocking the extension. Any ideas how to solve this? Will I have to get another new handset or can the old one be fixed?--Shantavira|^{feed me} 20:10, 7 December 2007 (UTC)

The description you have given of the problem seems to mean that there is a difference between the two sockets. They should be the same. Me, I would double-check my wiring job, with reference to this site and this one. --Milkbreath (talk) 00:12, 8 December 2007 (UTC)

See Ringer equivalence number. This may ring some bells (or not)--TreeSmiler (talk) 01:11, 8 December 2007 (UTC)

REN matters when you have a lot of phones - but it shouldn't be a problem with just two - and it certainly shouldn't matter if you just swap them over. It kinda sounds like a dodgy connection of some kind or another. SteveBaker (talk) 03:39, 8 December 2007 (UTC)

Do you have any6 extra phone wire? Coil it up and connect the old phone to the master through the extension wire. I suspect the ring circuit inside the old phone clamps the ring voltage so that it doesn't get to the extension. Putting more wire between the master socket and the old phone may fix it. --DHeyward (talk) 05:19, 8 December 2007 (UTC)

How many wires did you connect when installing the extension lead: 2,3 or 4?--TreeSmiler (talk) 07:11, 8 December 2007 (UTC)

Four.--Shantavira|^{feed me} 09:59, 8 December 2007 (UTC)

Maternal depressions effects on the Family

What are the effects of maternal depression on the spouse and children, especially teenagers? —Preceding unsigned comment added by 75.131.194.201 (talk) 21:24, 7 December 2007 (UTC)

Wikipedia has postnatal depression. A starting point in the research literature: Do Parenting and the Home Environment, Maternal Depression, Neighborhood, and Chronic Poverty Affect Child Behavioral Problems Differently in Different Racial-Ethnic Groups?
--JWSchmidt (talk) 00:49, 8 December 2007 (UTC)

Photographs

If I point a camera at a brick wall, I see straight lines of bricks running left and right. I really don't understand how this is possible. Since the far corners of the wall are farther away from the camera than the brick directly in front of the camera, they should logically be both out of focus and smaller than the center. I believe our eye corrects for this because it projects the image on a curved surface, but the film in a camera is flat, so this shouldn't affect it. How does this work? 72.155.209.101 (talk) 21:44, 7 December 2007 (UTC)

The focus is due to the depth of focus (dependant on the aperture). In short there can potentially be a wide range of distance that remains in focus. David D. (Talk) 23:38, 7 December 2007 (UTC)

It does get out of focus, if you're shooting with 85mm f/1.2 at 1m away from the wall, or try some macro photography. Point and shoot cameras usually has enough DOF (which is also dependant on the focal length is well) to get pretty much everything in focus. --antilived^{T | C | G} 01:41, 8 December 2007 (UTC)

That's not what I am saying. There is a focal plane, here represented by the wall - DOF does not factor in if the object is flat. Try shooting a grid; if I'm right, the corners squares will be smaller than the center squares and not on the focal "plane" (since they are farther away from the lens). Even if I have your 85mm f/1.2 pointed at this hypothetical wall, the wall would all be in focus, since it is flat. However, the far corners of the wall are farther away from the lens than the part directly in front of the camera. Thus, rather than a focal plane, should we not be seeing a focal sphere, where the points in focus lie at equal distance from the camera? And since the points farther away from the camera are, well, farther away, should they not be rendered smaller? 72.155.209.101 (talk) 02:32, 8 December 2007 (UTC)

(edit conflict) It all depends on the projection. Normal camera lenses are designed to give a rectilinear projection, which has the desirable property that the resulting image looks "right" (as in undistorted) when displayed on a flat surface (such as a piece of paper or a computer screen) — assuming the viewing distance and angle are correct. (Fortunately, our brains also tend to mostly ignore the small distortions that result from viewing such images from a wrong distance or angle, as long as the mismatch isn't too severe.) Essentially, this is because the rectilinear projection is exactly what you'd get if you, say, held up a flat transparent sheet in front of your face and traced the scene onto it as you saw it.

However, the rectilinear projection does have some disadvantages, particularly in wide-angle photography. One is that it can't possibly produce a field of view wider than 180°, and even at much lower fields of view (say, anything over 60°) it tends to look distorted unless projected on a very large canvas and/or viewed from a very close distance. Another problem is that, contrary to what you might expect, if you rotate the camera the image will not simply scroll left or right — rather, horizontal lines will appear to rotate. This is the price one has to pay for keeping straight lines straight, and is related to the effect known as the corner illusion (or I thought it was, but I can't find an article on it — perhaps I'm misremembering the name). There are alternative projections, commonly used in panoramic photography, which avoid this at the cost of making some straight lines appear curved. —Ilmari Karonen (talk) 02:38, 8 December 2007 (UTC)

Molecular solution

From [5], a distinction is made between a solution and a molecular solution. I have never heard of this before, but I am not a chemist. Can anyone clarify this? If this is important, maybe we should have an article on molecular solution ?--Filll (talk) 23:12, 7 December 2007 (UTC)

They seem to be referring to ionic organometallic compounds. Unlike an inorganic salt, these compounds don't fully dissociate in solution, and instead form complexes of several carbanions and metallic ions. However, I've never heard this term used to describe it. Someguy1221 (talk) 23:27, 7 December 2007 (UTC)

December 8

Final cause of death in cancer

I never understood why cancer was so deadly. Yes, you do have an abnormal growth/tumor growing somewhere in your body, but I don't see why that would eventually cause death. If there was a tumor within a blood vessel that directly caused a stroke or heart attack, then the cause of death in that case is quite obvious. But in "normal cancer" (if such a thing exists), what is usually the final cause of death?

I asked myself that same question a year or two ago, and the answer I came up with after a bit of research is nobody really knows. They don't do autopsies on cancer deaths, and the oncology community seems to be concentrating on getting rid of the cancer to the exclusion of finding out exactly how it kills. Some ideas are that the tumor sometimes, of course, impinges on something vital like the pancreas and you die from the trauma to the vital part. Brain tumors are obviously going to kill you by compressing the brain. But the main deadly effect of a tumor seems to be that it disrupts your chemistry. Tumors produce all sorts of nasty chemicals as though they were a gland, which accounts for the weight loss that accompanies them. But nobody as far as I could find out has determined exactly which chemicals do what when. I remember thinking at the time that there might be a way to live with cancer if we could counteract that process, but what do I know? --Milkbreath (talk) 01:54, 8 December 2007 (UTC)

Take a look at metastasis. In many cases, a primary tumor can be surgically removed, but once cancer cells start to spread away from the primary tumor there is a greater chance that the cancer cells will not be stopped by treatment before they disrupt the function of a vital organ. For example, see melanoma and Surgical Excision of Metastatic Malignant Melanoma Involving the Tricuspid Valve.
--JWSchmidt (talk) 02:54, 8 December 2007 (UTC)

A study of 506 terminal cancer patients (J Med. 1975;6(1):61-4) found the cause of death was:

• Infection (36%, and was a contributing factor an an additional 68%)
• hemorrhagic and thromboembolic phenomena (18%, and were contributory factors in an additional 43%)
• Respiratory failure (19%, and a contributory factor in an additional 3%)
• Organ failure after invasion by neoplastic cells (10%, and was a contributing factor an an additional 5%)
• Cardiovascular insufficiency (7%, and a contributory factor in an additional 3%)
• Cachexia (1% and as contributory factor in another 0.4%)

That was done over 35 years ago, so the distribution may have since changed, but it is nevertheless indicative of how tumors disrupt the normal function of our organs by diverting resources away to feed their growth. This results in organ malfunction as the tumor invades, vascular malfunction as blood vessels are grown to feed the tumor and starve the tissues. As the patient loses weight because the tumor takes all their nourishment, they begin to get weaker which leaves the more prone to infection, and the immune system cannot fight infection as well. Rockpocket 03:03, 8 December 2007 (UTC)

Indeed, a more recent study suggests infection is better controlled these days and has been overtaken by the other causes, in J Thromb Haemost. 2007 Mar;5(3):632-4 the authors report: "Of 4,466 patients enrolled on study, 141 (3.2%) patients died during the period of observation ... A majority of patients died of progression of underlying cancer (n=100, 70.9%). Among non-cancer causes of death, thrombosis and infection were the leading contributors (n=13, 9.2% for each). Thromboembolic events contributing to death included myocardial infarction (n=3), stroke (n=2), cardiac arrest (n=2), ischemic bowel (n=1) and VTE (n=5). Infectious events contributing to death included sepsis (n=10), pneumonia (n=2), and bacterial meningitis (n=1). Other causes of death included respiratory failure (n=5), aspiration pneumonitis (n=2) and bleeding complications (n=2). Cause of death was reported as unknown in 5 patients." Rockpocket 03:16, 8 December 2007 (UTC)

Ummm - A study of 506 terminal cancer patients (J Med. 1975;6(1):61-4) found the cause of death was: Infection (36%, and was a contributing factor an an additional 68%). Now, 36% + 68% = 104%. Shome mishtake shurely? DuncanHill (talk) 07:45, 8 December 2007 (UTC)

Maybe they meant 68% of the remaining deaths? I can't find this paper. J Med. Which journal of medicine? Someguy1221 (talk) 08:06, 8 December 2007 (UTC)

Mmmmm. Good point. Perhaps I paraphrased incorrectly and they meant, as Someguy suggests, 68% of the other deaths. The article is PMID 1056415 Rockpocket 21:03, 8 December 2007 (UTC)

How to solve Physics Problem by Using Kinetic Energy Principle?

So, a ball weighing 2.6 kg falls from a state of rest 55 cm. It then lands on a spring that decompresses 15 cm. Assuming the acceleration of gravity is (-)9.8 m/s and that there is no air resistance, what is the k value of the spring?

OK, so according to KE Principle:

Wnet=deltaKE or Wnet=KE'-KE

Since the ball is at rest in the beginning and end, the right side of the equation equals zero:

Wnet=0

We also know that W=Fd

Fnetd=0

So the net forces is that of the spring, which is described as Fs=-kx, and the force of gravity, which is desribed as Fg=mg,

(-kx+mg)d=0

At this point I am kind of unsure what d is supposed to represent, but I guess d=.7 m. m=2.6 kg, x= (-).15 m, g=(-)9.8:

.7(.15k+2.6*-9.8)=0

k=(25.48/.15)~170

By using the Law of Energy Conservation (E=E'), I got a value that was about 10 times this, and I am certain I did that work right.

I also tried:

d1(-kx)+d2(mg)=0, where d1 is the distance over the force of the spring was applied and d2 is the distance over the force of gravity was applied.

(.15*.15k)+(.7*2.6*-9.8)=0

.0225k=17.836

k~790

Closer, but the answer is still twice that.

Any advice would be greatly appreciated. —Preceding unsigned comment added by 24.125.31.205 (talk) 05:31, 8 December 2007 (UTC)

Your first method is not what you're trying to solve: You're working out the force, not the energy. I would just work out the V of the ball when it was at rest, using $V=mgh=2.6\cdot 9.8\cdot 0.7=17.836$. Hooke's law say $U={\frac {1}{2}}kx^{2}$, substituting in the variables you get $17.836={\frac {1}{2}}k\cdot 0.15^{2}$, simple algebra re-arranging gives $k={\frac {17.836\cdot 2}{0.15^{2}}}=1585.42$. You just forgot to multiply the energy stored in the spring by 2 when you're finding k. --antilived^{T | C | G} 09:14, 8 December 2007 (UTC)

Electric Shavers

In TV commercials, those guys just keep shaving every which way but I wanna know if that is really possible. I mean with a regular razor you cant shave against the grain right? So with an electric razor is it possible? If yes, why? And if not, then what are the consequences of shaving against the grain? —Preceding unsigned comment added by 202.83.169.98 (talk) 07:33, 8 December 2007 (UTC)

I shave against the grain. My face is fine...Someguy1221 (talk) 08:07, 8 December 2007 (UTC)

Shaving#Electric shaving. Moving against the grain can help force the hairs into the small holes that give access to the moving blades. --JWSchmidt (talk) 15:01, 8 December 2007 (UTC)

Some say that (blade) shaving against the grain forces the hair beneath the skin and leads to ingrown hairs, but it doesn't bother me (and leads to a much closer shave). —Steve Summit (talk) 17:07, 8 December 2007 (UTC)

I have very heavy, thick whiskers. Although I have a full beard, I shave my neck and upper cheeks every day, and I use a regular two-bladed disposable razor most of the time. If I did NOT shave against the grain, I'd not be able to have a clean shave, but would have uncomfortable stubble left behind. If I use an electric razor I never get as close a shave as a simple cheap Bic disposable razor. I've never discovered the advantage of using an electric razor. Why would I want to buy an expensive razor that requires electricity to run and doesn't shave as close? Saukkomies 19:18, 8 December 2007 (UTC)

Less time/mess? If I had to bother lathering up every morning, I'd probably have a long, droopy moustache in addition to a long, scruffy beard... ;) --Kurt Shaped Box (talk) 19:22, 8 December 2007 (UTC)

Who lathers up? Heh. I never have used any kind of shaving cream or anything like that. I just find that shaving as soon as possible after I shower in the morning that my skin is moist and warm enough from the shower that I do not need to put anything on my skin to prepare to shave. I do make sure to wash the skin that is going to be shaved while in the shower - freshly washed skin helps the razor to work better. But lathering is such a drag! I agree with you Kurt, if I had to lather to shave, I'd give it up altogether. As it is, I spend perhaps 30 seconds on the entire shaving process each morning - and there is no mess to clean up since the whiskers get washed immediately down the drain when I rinse the razor off in the flowing water. Keep in mind that my whiskers are exceptionally thick and dense, and I am also quite prone to razor burn. But I have very positive results from simply shaving right after I shower, not using shaving cream, going against the grain, and using a regular double bladed non-electric razor. Saukkomies 19:34, 8 December 2007 (UTC)

The rotary electric shavers cut in different directions around the circumpherence of each 'pad' anyway - I don't think it matters that much which direction you move the body of the shaver. (But then, I havn't shaved in 10 years...so what do I know?) SteveBaker (talk) 00:02, 9 December 2007 (UTC)

I went electric(al) because I like it. I find it easy, no lathering and no need to buy a cartridge (razor) every fortnight. Non-electric razors are quite expensive here in Argentina. Well, that's my call.

As Steve points out, electric shavers cut in different directions. I'd usually make a series of movements: against the grain, then circular (clock/counterclockwise) moves, etc. Pallida  Mors 23:54, 9 December 2007 (UTC)

• I use an electric razor almost daily and shave against the grain. My skin tends to be drier than it was when I used a cartridge razor, but I have never suffered a single drop of blood, and to me that's worth it. --M@rēino 20:19, 10 December 2007 (UTC)

Hermaphrodites

What are hermaphrodites? How are they born?--61.2.17.179 (talk) 08:59, 8 December 2007 (UTC)--61.2.17.179 (talk) 08:59, 8 December 2007 (UTC)

Hermaphrodite. If you have a more specific question, feel free to ask it. Someguy1221 (talk) 09:07, 8 December 2007 (UTC)

There happens to be a wonderful article here on human hermaphroditism. (But stay away from the bottom quarter if you don't like yucky things!) Someguy1221 (talk) 09:21, 8 December 2007 (UTC)

I didn't see anything "yucky" there. It was just a description of a different culture's relationship to gender and sex. Not that I'd want to live there, but Western cultures sure don't have it all figured out either! Saudade7 14:51, 8 December 2007 (UTC)

Unknown type of digital or optical distortion

The camera was handheld but in the past whenever I have seen a blur it has included the whole picture. I though digital cameras exposed the whole scene at once rather than scanning the picture maybe like an old TV camera would do. What method of taking the picture and/or what action could cause this type of digital or optical distortion?

Multimillionaire (talk) 11:52, 8 December 2007 (UTC)

Light coming from the bicycle into your camera being refracted due to the difference in density of air in that area. Just a wild guess though, might be wrong :P. Oidia (talk) 11:58, 8 December 2007 (UTC)

Is this the entire photo, or is it the corner of a larger photo? --Psud (talk) 13:45, 8 December 2007 (UTC)

Its the whole photo. Multimillionaire (talk) 22:39, 8 December 2007 (UTC)

The date in the corner suggests it is an entire photo. I'd say you weren't holding the camera/cellular phone still when taking it. The distortion is circular in nature with intensity increasing towards the bottom left hand corner. I'd say you pivoted the camera when shooting. --Ouro (blah blah) 14:08, 8 December 2007 (UTC)

If it's a digital camera which uses a focus feature, it may have decided to focus on the top right of the frame, which would explain why the focus goes from very sharp (top-right) to completely blurry (bottom-left). Some digital cameras zoom in an out to try and focus on certain things usually when you half-depress the button, so it may have been in the middle of doing this when you took the photo and it even seems likely that you did this and moved the camera. There are of course other possibilities. Rfwoolf (talk) 20:05, 11 December 2007 (UTC)

It's a common problem with certain cell-phone cameras. They use a pure electric shutter (no mechanical shutter at all), and it takes a while to read the entire image, during which the camera was moved.

They take a picture by exposing and reading each line of the sensor in turn. The exposure of each individual line is fairly quick, so the image doesn't look blurred, but because the lines aren't all exposed at the same time, the image can look warped. If you want some more examples, there were some spectacular photos of airplane propellors posted here a few months ago. --Carnildo (talk) 23:03, 11 December 2007 (UTC)

Identify squirrel species

Squirrels of this kind are very common where I live. What species is this? [6] [7] - Sikon (talk) 13:19, 8 December 2007 (UTC)

Where do you live? (That's important). It is some type of tassel-eared squirrel. Not a Kaibab Squirrel squirrel though. Saudade7 14:54, 8 December 2007 (UTC)

Novosibirsk, Russia. - Sikon (talk) 16:32, 8 December 2007 (UTC)

Could be a Eurasian red squirrel. --Milkbreath (talk) 17:35, 8 December 2007 (UTC)

I agree - in winter they have grey fur over their bodies with the red fur remaining over head and paws - that's something you don't see in other squirrels (as far as I know). (The [[Red Squirrel article was the first thing I ever edited on Wikipedia!) SteveBaker (talk) 23:57, 8 December 2007 (UTC)

Blacksmithing messes with my hair

Good morning Wikipedians!

I spent the afternoon yesterday (Saturday) working over a coke fuelled forge. The coke proved excessively hard to light, and so we employed barbecue briquettes to get the fire going. I ended up with a fair bit of ash in my hair, and my hair felt tangled and matted. When I got home, I rinsed (but didn't wash) my hair. But my hair remains tangled feeling, and I'm thinking I probably need to wash it to get it back to something like normal.

Other probably relevant things I noted were:

• There was a bit of sulpher in the fire, evidenced by yellow deposits which formed on the coke and sulpherous smell when I rinsed my hair. I'm pretty sure the sulpher came from the briquettes, as there was no evidence of it once the fire was burning only coke.
• There was a fair bit of sweat in my hair
• A diffuse white flame burned over the fuel in the forge while it was burning briquettes and coke at the same time
• My hair is about 15cm long measured from scalp to tip of a handful of hair
• The forge has no hood over it, so my hair was exposed to radiant heat, but there is no evidence that it was scorched at all.

My first thought was that it was the sweat that turned my hair into a tangled mess, but I expected that to be fixed by a rinse. Any ideas, or suggestions for how to prevent the same in future? --Psud (talk) 15:02, 8 December 2007 (UTC)

We may need a bit more information. Since it sounds like washing (as opposed to rinsing) your hair is a big deal for you, I'm guessing you don't do it every day -- and perhaps you go for long periods without washing your hair. If so, your hair will have a lot more of its natural oils in it than many/most of us are used to. Also, it's possible that you have some unusual (to me) hairdo, such as dreadlocks or a mohawk, perhaps requiring added substances to keep it in place. All of these possibilities increase the number of unusual reactions that could have taken place between your hair and the heat/fumes/ash given off by the forge. —Steve Summit (talk) 16:58, 8 December 2007 (UTC)

Hair washing isn't a big deal, I just didn't have any shampoo handy. Hairstyle is fairly conventional. No "product" to hold it in place. Hair was washed 3 days ago (usually wash it weekly(, but have gone for up to 3 months without washing hair - but that's another story)). --Psud (talk) 17:42, 8 December 2007 (UTC)

Ash is very alkaline and can react with oil in the hair to make soap. Also if you overheated your hair it could be frizzed and weakened, so that it will easily tangle and break. Give the hair a good brushing to remove the broken bits, and dust, and to help untangle it! Graeme Bartlett (talk) 21:41, 8 December 2007 (UTC)

Have you tried a liberal dose of conditioner? Vranak (talk) 22:41, 8 December 2007 (UTC)

I fixed my hair with a washing and far more conditioning than I would normally use. I take it from lack of comments suggesting the possibility that the copious quantities of sweat wasn't the cause. Speaking of sweat, for anyone who hasn't tried it, blacksmithing is an odd thermal experience - ambient air temperature away from the forge was 33°C (~92F), the radiant heat of the forge heated all of me above the top of my leather apron causing me to sweat profusely, all of me below the top of the apron was cooled by the sweat but not particularly heated by the forge, so I felt incredibly hot from the shoulders up, and was shivering below that. --Psud (talk) 11:59, 9 December 2007 (UTC)

I think that Graeme Bartlett got it right. Ash+hair oils+water(sweat) = soap. Soap makes hair clump, lack of oils make hair "bad". Also meshes with what happens when I wash it - shampoo lathers as if my hair was already clean, and I needed two doses of conditioner to get it near normal again. By the way, I notice no one complained that I was asking for medical advice. --Psud (talk) 22:11, 11 December 2007 (UTC)

Hair is already dead. There is probably no rule against giving post mortal advice :) --Cookatoo.ergo.ZooM (talk) 23:49, 11 December 2007 (UTC)

Laptops

Which laptop is the best for home usage:

  1) Acer
  2) HP
  3) Compaq
  4) Dell
  5) Sony Vaio 

In terms of specifications{Speed and hard disk capacity} and the regularity of usage..... —Preceding unsigned comment added by Garb wire (talk • contribs) 15:07, 8 December 2007 (UTC)

You could get all different specifications of laptop from those companies. Some Acer laptops are better than some HP laptops and some HP laptops are better than Acer laptops. What exactly is "home usage"? You sound like you'd be fine with one of the cheapest (internet browsing, typing letters). I'm guessing that someone who needed a more powerful computer (image/video editing, first-person shooter players) would not have asked the question you just did. If you confirm what it is you want to do with the machine, someone else will confirm that you only need something cheap. --Seans Potato Business 15:16, 8 December 2007 (UTC)

Apple. But Really, you should ask this on the Wikipedia:Reference desk/Computing page, this one is just for Science. The People on the Computer page are incredibly smart and helpful. Good Luck. Saudade7 15:31, 8 December 2007 (UTC)

And so he did :) --Ouro (blah blah) 20:24, 8 December 2007 (UTC)

Did Saudade7 just call us all stupid and unhelpful? I feel...somehow abused.  :-) SteveBaker (talk) 23:51, 8 December 2007 (UTC)

Tough one. But seeing as some of us also do participate at the Computing RefDesk, I'd say you shouldn't feel too bad ;) --Ouro (blah blah) 06:43, 9 December 2007 (UTC)

Flame from engine exhaust

In the film Grease, you see flames coming from one of the cars two exhausts. What's that all about? --Seans Potato Business 15:12, 8 December 2007 (UTC)

I've heard of hot rodders making modifications specifically for this purpose. I don't remember details, but the gist is that they inject something flammable into the exhaust system near the end, at the flip of a switch. I don't remember if they also need a spark there or if the exhaust ignites it. Alright, here is a link to a commercial vendor of modern kits for this. They explain how their kit works.. Oh, they're fiddling with the engine to pass unburned fuel through rather than injecting new fuel at that point, then they ignite it with a spark. Hmm, not sure how I feel about that. But, it's all only for looks anyway. You will also see naturally produced exhaust flames from cars like dragsters whose only "exhaust system" are a couple feet of headers, which just open right to the air. In that case, they're not doing anything on purpose to produce the flames, but they get them anyway. Friday (talk) 16:59, 8 December 2007 (UTC)

I don't think such a device would be legal in the UK. There are strict regulations regarding emissions. Does that not apply in the US? —Preceding unsigned comment added by Seans Potato Business (talk • contribs) 17:53, 8 December 2007 (UTC)

I imagine it's not legal in many parts. But, not every place in the US does emissions testing. And, if you don't hit the button during the test I imagine you'd have normal emissions. Friday (talk) 17:57, 8 December 2007 (UTC)

As I understand it, testing is done everywhere but the strictness of the test depends on the level of urbanization. The only exemptions I know of are for the poor. It is illegal to modify any emissions control devices. --DHeyward (talk) 19:53, 8 December 2007 (UTC)

No, testing is not done everywhere in the U.S. In fact, it is not common at all. Only major urban areas which badly fail on pollution tests are subject to EPA testing. A few states may also have testing but I couldn't even tell you which ones, if any. Rmhermen (talk) 19:04, 10 December 2007 (UTC)

These guys: http://www.eatmyflames.com will sell you a kit to do that for around $50. They are of course illegal in most places around the world. They generally require that you remove the catalytic convertor from your exhaust - so it's 100% certain that you aren't going to pass emissions testing even if you don't turn it on during the test. SteveBaker (talk) 23:48, 8 December 2007 (UTC)

Formula One Car Speed

I'm researching the properties of carbon fiber. Could anybody tell me how much force the carbon fiber shell on a Formula One car must withstand? SevenFiveOne (talk) 15:20, 8 December 2007 (UTC)

Here is a document from the FIA that seems to have some info. Sections 3.17 and 16.1 look promising. From what I saw, the shell isn't considered so much part of the impact protection, so the specs for that deal only with deflection caused by the airstream. --Milkbreath (talk) 16:33, 8 December 2007 (UTC)

I the car has good aerodynamics (as it really ought to if it's a Formula 1 car) then there should be very little aero forces on the shell. The strength of the car comes from it's internal metal frame. So I don't think there is much stress on the carbon fibre parts anyway. SteveBaker (talk) 20:22, 8 December 2007 (UTC)

Hydrogen Cars - Potential Future Issue?

understand the only 'output' out of the exhaust for hydrogen cars is water. I was interested whether this might cause a potential problem in the future for high-usage roads like motorways. If there are, say, 10,000 cars an hour going through 1 mile of road all expelling a small amount of water - well would that mean the roads might always be wet/damp thus making braking distances longer? I guess the ouput of one hydrogen car wouldn't be much but with 1000s would it become more of a problem? ny156uk (talk) 16:35, 8 December 2007 (UTC)

Such problems might indeed be a problem, for instance with cold weather, but they will also easily be solved. Think for instance about tyres/asphalt with better water disposal qualities, or simply putting the exhaust on the side or in the middle and building draining facilities at those spots in the roads. - Dammit (talk) 16:43, 8 December 2007 (UTC)

If there is also waste heat, maybe they could use it to evaporate the waste water? No idea if they really do this, just speculating.. Friday (talk) 17:21, 8 December 2007 (UTC)

Of course, the water does come out as vapor. (Indeed, the fact that the water resulting from virtually any combustion reaction comes out as vapor rather than liquid water represents a significant form of waste heat in itself, and accounts for the distinction between HHV and LHV.)

So the first result of large-scale use of hydrogen-fueled cars would be an increase in the humidity immediately surrounding busy motorways. In cold weather, or on a morning following a chilly night when the pavement is still cold, I can easily imagine this resulting in significant condensation on the roadway surface. It would be an interesting back-of-the-envelope calculation (which I am nevertheless not going to undertake just now) to try to quantify this effect. —Steve Summit (talk) 17:48, 8 December 2007 (UTC)

As an aside, water vapor is a greenhouse gas as well. How come this isn't a concern? --DHeyward (talk) 19:55, 8 December 2007 (UTC)

Because the amount of water the atmosphere can hold is a factor of temperature. Once the humidity gets high enough for that temperature, the water just rains back down. It doesn't have the long-term cumulative effects that other greenhouse gasses have. -- HiEv 06:42, 9 December 2007 (UTC)

We should point out that regular gasoline cars generate a lot of water in their exhausts too - perhaps not as much as a hydrogen car - but even so - it's quite a bit. Just watch your car exhaust with the engine running on a cool day and you'll see water dripping out of the end. I really don't think you'd even notice the change over in terms of water production. Water vapour is only a problem as a greenhouse gas if it makes it up into the upper atmosphere. The water vapor from car exhausts is mostly going to wind up like the water that evaporates from rivers, lakes and oceans - forming clouds. Louds do trap sunlight - but they also reflect it away out into space. SteveBaker (talk) 20:19, 8 December 2007 (UTC)

Temperature and Breathing rate

If someone fell into a pool of freezing water and remained there for an hour, would they still survive? And if they did, would temperature somehow be connected to it? Thanks, Valens Impérial Császár 93 17:00, 8 December 2007 (UTC)

They would almost certainly not survive, and of course temperature would have everything to do with it. See hypothermia. —Steve Summit (talk) 17:14, 8 December 2007 (UTC)

There are people who have swum in freezing water - but even with a lot of preparation and vigerously exercising - they can't survive for long. You hear stories of people falling overboard from arctic fishing boats who died from hypothermia in less than two minutes. So evidently a lot depends of preparation - but I don't think it's possible to survive an hour. Your body simply can't generate enough heat to maintain a minimal body temperature with that much loss of heat. SteveBaker (talk) 20:08, 8 December 2007 (UTC)

According to our hypothermia article, there are reports of children being resuscitated after two hours (!!), but those cases are certainly exceptional. (But they're why I said "almost certainly" instead of "certainly".)

Also according to our article, you're "not dead from hypothermia until you're warm and dead". The interesting thing about hypothermia is that it involves (or, depending on how you define things, it is) a natural, biological, hibernative or suspended animation state. But it's very tricky for humans to revive from. There's a story of 16 hale Danish sailors who sometime in the 1980s were rescued alive after bobbing in the North Atlantic for ninety minutes or so after their ship sank out from underneath them. While being fed and warmed in the galley or sick bay of the rescuing vessel, all 16 of them dropped dead. :-( —Steve Summit (talk) 20:57, 8 December 2007 (UTC)

Also take a look at Mammalian diving reflex, which suggests that a dip in cold water changes breathing significantly. --Mdwyer (talk) 20:10, 10 December 2007 (UTC)

December 9

inverse sqaure law for vortices

for a traveling vortex of air, does the amount of pressure it produces decay occording to inverse square law [half the distance, four times the force] or along another line, if so what amount does the amount of pressure transported by the vortex decay by over distance?

Robin —Preceding unsigned comment added by 80.6.37.199 (talk) 00:03, 9 December 2007 (UTC)

I think this is a rather complicated effect. It's unlikely to be inverse-square because you get those amazing Vortex ring guns - or the more reasonable Air bazooka or Vortex ring toys that propel a stable vortex over large distances with seemingly little energy loss. SteveBaker (talk) 00:22, 9 December 2007 (UTC)

It is a complicated effect, however they do loose momentum over distance, and thus exert less pressure, doews anyone have any idea on the equasion or know the way it works?

Robin —Preceding unsigned comment added by 80.6.37.199 (talk) 00:42, 9 December 2007 (UTC)

Aspherical Lenses

Why are aspherical lenses so much harder to make? than spherical ones What's the optimum lens shape? --antilived^{T | C | G} 09:04, 9 December 2007 (UTC)

lenses with circular symmetry can be roughly made by spinning the glass against a grinder as in a lathe, but aspherical lenses are a more complicated shape! Graeme Bartlett (talk) 11:44, 9 December 2007 (UTC)

There isn't a single 'optimum lens shape' - it depends on the task you wish the lens to perform. For example, if you have one of those 'Laser line level' gadgets (especially one of the cheaper ones) that produces a fan-shaped beam of laser light - inside you'll find a cylindrical lens. On the other hand, most contact lenses are spherical - unless used for treating Astigmatism - in which case a non-spherical lens of some kind will be needed. SteveBaker (talk) 13:16, 9 December 2007 (UTC)

By optimum I mean one that has the least aberration. Spherical lenses has spherical aberration, so how about a parabolic lens, or some other shapes? Also, can't you just make the grinder aspherical is well and you can start grinding aspherical lenses in the exact same fashion? --antilived^{T | C | G} 04:55, 10 December 2007 (UTC)

The point is that there is no shape of lens that is optimal (aberration-free) for all conditions and applications. So, for instance, if you work out the best possible shape of a lens for imaging a person standing 20 metres away onto a camera film, then that lens will not be the best possible shape for imaging someone standing 25 metres away. The amount of spherical aberration isn't a fixed quantity for a given (spherical) lens, it also varies depending on exactly what you are using the lens for.

Lens grinding is a complex topic, but in the traditional method for grinding a spherical lens surface, the glass blank is ground against a tool with a hollow spherical interior surface. It doesn't just rotate around one point (like on a lathe), but moves sideways and rotates at the same time. A pair of exterior and interior spherical surfaces are the only surfaces which fit together like this, where they can touch each other at all points in any orientation and position.

The reason you can't just spin it like a lathe is that you end up scoring circular striations in the glass if it can't move and rotate at the same time. Though some modern aspheric grinding systems can place the cutting tool so accurately that they do work like a lathe, grinding away a tiny bit of the glass at a time. --Bob Mellish (talk) 05:42, 10 December 2007 (UTC)

Also, because lens materials have different refractive indices for different colours, you can't focus all colours at the same place - so some amount of fringing is inevitable ("chromatic aberration"). Various coatings and compound lenses (where two lenses with different refractive properties are bonded together) are employed on high quality lenses - but the cost of fixing it 100% correctly are huge. With aspheric lenses, fixing chromatic aberration is even more complicated - so very often people don't bother doing it. SteveBaker (talk) 13:52, 10 December 2007 (UTC)

I also wanted to mention the development of holographic lenses - which is exciting since it enables the production of more or less arbitary lens shapes using computer software with none of that tedious grinding of glass. SteveBaker (talk) 13:52, 10 December 2007 (UTC)

My Mobile Phone Underwent Strange Situation!

My nokia model 3310 (oldest known version) has now got a strange problem! It's accepting any other sim except my sim! If I'm putting my sim it was saying "simcard rejected"! At the same time it was accepting every other sim i tried in it! Same is the case with my sim card! It was working in all other models like sony errickson, motorola, LG, etc, but it was not accepted in any of the nokia model.."simcard rejected"! What might be the reason? & solution? Temuzion (talk) 09:57, 9 December 2007 (UTC)

Must say I'm stumped! I've been using this model of mobile phone since 2001 and nothing like this has happened to me (although I've got one N3310 acting very weird too). Did you do anything just before you experienced these problems (drop the phone, change the battery, tamper with it in any way, receive any strange/unusual SMS/picture message) or did it just happen suddenly? I like the way you spelled sony errickson ;) Cheers, Ouro (blah blah) 10:36, 9 December 2007 (UTC)

I'd expect it to be a problem with your sim card. I expect it's possible to have a sim card fault that your phone cares about but others don't. I don't know where you are, but in Australia the phone company owns the sim card, so I suggest you go to your mobile service provider and tell them that their sim card is faulty. They should replace it. --Psud (talk) 12:07, 9 December 2007 (UTC)

This happened to me once, and was because I had been swapping simcards with people a lot, as well as removing and reinserting the sim a lot because the phone was glitchy. Basically, the sim got scratched in a way that was specific to my phone, because it was the connectors on my phone that did the scratching. I was never able to get that sim and that phone to work together again, so I think you may have to choose between them and replace the other. Needless to say, I now remove the sim very carefully if it's necessary. Skittle (talk) 13:02, 9 December 2007 (UTC)

If I'm reading you correctly, it sounds like you could have abbreviated your situation as, "No phone accepts my SIM card," in which case the answer seems obvious: there's a problem with your SIM card. Your phone is probably fine, you just need to get your SIM card fixed. -- HiEv 00:01, 10 December 2007 (UTC)

But my sim is active in all other models except nokia range! May be nokia software is rejecting the sim! & one more thing! I just dropped my phone twice in the last month & another thing is thatI took the message offer by which I got 500 free messages to be sent to any mobile & by that offer I m using the sms service extensively! & previously once the problem rose when dealing with sms only! But none of the components can be avoided b'coz both are working but in but in diffrent models..so ultimately what should I do? Temuzion (talk) 03:05, 10 December 2007 (UTC)

If it were me nowadays, I would take my sim to get a backup made at one of the places that does that (Carphone Warehouse? I imagine most phone places do it), then see if the backup works in the phone. This is because I suspect something has physically happened to your sim that is specific to the way it connects with the nokia. Getting a physically different sim would solve this problem. If it still doesn't work, something much odder must have happened. In that case I'd get a new phone, unless you don't mind swapping your number and re-inputting your phonebook and losing the pictures saved to your sim in which case you could get a new sim. Skittle (talk) 04:36, 10 December 2007 (UTC)

Journal Article Database

Can anyone suggest a good free-to-use journal database (is there such a thing? I'm sort of spoiled by my memories of computer labs at school...they always seem to have access to those kind of things)? I'm writing a short research paper, and I'd like to flesh out my works cited with a few off-line resources. Love,70.181.41.1 (talk) 16:33, 9 December 2007 (UTC)

Pubmed is free and pretty good. Does not cover some plant journals. An excellent non-free, but often available at libraries, database is Web of Science. David D. (Talk) 16:40, 9 December 2007 (UTC)

Thanks. I'll make a note of that (the PubMed is going to be fun to dig around in, I appreciate it). I should be more specific. I'm writing a quick five page overview of lunar formation, focusing on the strengths and weaknesses of the giant impact hypothesis. The reference links from the article were helpful, but I feel like some off-line citations will give it an air of respectability. 70.181.41.1 (talk) 16:59, 9 December 2007 (UTC)

You may also want to take a look at scholar.google.com. I've had luck with articles linked from their database, when going to the journal's website doesn't work. I'm not sure if perhaps Google is a subscriber (much like your library was at school) or what, exactly, but it seems to work often. (EhJJ) 18:43, 9 December 2007 (UTC)

What's your field? Physics preprints are almost always nowadays posted at the ArXiv. SamuelRiv (talk) 19:01, 9 December 2007 (UTC)

See also the NASA ADS for anything sky-related. --Tardis (talk) 16:26, 10 December 2007 (UTC)

Thanks to everyone who responded. The reports been turned in (with a little rounding out care of ADS and ArXiv). We'll see how it's received. 70.181.41.1 (talk) 23:47, 11 December 2007 (UTC)

THE ABC's OF ONLINE INDEXES

For those who are reading this who might not be completely familiar with what is being discussed, I thought I'd offer a brief explanation, and then proceed to provide a couple of suggestions. I offer my opinions from having had direct experience as a professional Reference Librarian who worked for years at a busy Serials Desk. First off, when a person wants to dig in to deep research about something, he or she will very quickly (depending on the topic) discover that not everything may be found on the open Internet. Instead, the more complex research being done in the world is done through perusing indexes (note: I use the word "indexes", not "indices" for better comprehension here) that are compiled by for-profit companies, and then sold to libraries and research facilities on a subscription basis. Each company organizes its indexes differently than the others, but there are a few similiarities from one index to the next. Most of these indexes have been around for many years, and only recently (in the 1990s and this decade) have most of them acquired an online version of their indexes, which at one time were only available in print format.

Just for clarification, I want to add that indexes do not necessarily provide links to the articles for you to read online. This feature is called "Full Text", and some databases offer it extensively, others a little bit, and still others not at all. So if you're using an online index thinking you will find full text journal articles on your subject, look twice because it may be that the index you're using doesn't do this. However, if you have the time, you can usually order copies of articles to be faxed or emailed to you through your local library - providing you supply them with the full citation (which of course you'd get from the online index).

In recent years the information profession has been attempting to find a way to create software that could search all of these online journal index databases at one time. This kind of global search is known by several terms: federated search, broadcast search, or metasearch. The industry isn't quite at the place where a person may search for a subject that would dig through all the databases available, but that's more or less the direction that things are heading. Until then, one must go through these online indexes one at a time (or more than one, if there is a family of databases connected together, such as FirstSearch).

However, not everything is online yet. Due to the costs of digitizing data and then storing it, most online databases provide access to older archival material only back a couple of decades or less. Depending on what your subject might be that you're researching, this might be a problem. But it is easily solved by going in person to a library that has the print back copies of the index on its shelves, and then doing research the old fashioned way by actually opening books.

Knowing which database to use for what subject material you'll be looking for is part science and part art. Each index lists which journals it covers, and also includes an explanation for what subjects it focuses on. That's the science part. The art part comes in by knowing which databases to search. Here's an example: say that you are searching for information about how agricultural runoff effects fishes in California rivers. There would be some indexes that would cover biological science, some that would cover medical science, some environmental science, and others agricultural science. In each of these databases there may be information indexed that would provide information about this subject. However, some of these databases would do a better job of it than others. Knowing which database would be the BEST choice to look in (and thus saving time and effort on the part of the user) is what provides job security to people like me - Serials Librarians.

Even IF there comes a day when a universal search engine is available that can search all knowledge everywhere, the overwhelming task of finding something specific still is very daunting, because until artificial intelligence is invented, these search engines must use computer algorithms which use the search terms entered to try to find relevant material. However, computers are very stupid and do not really know what is relevant or not much of the time. Nothing can replace the human mind (yet) when it comes to being able to know where to go for the most relevant material for a given search. So it is that if someone makes his or her living doing searches for people on all kinds of subjects all day long, then this person would soon develop a knack for knowing where the best places are for different subjects. Okay, I'll lay off of the plug for Librarians, except to say: it costs nothing but time to go into a library and ask a reference librarian for help in finding something - what a deal!

Now, addressing your question about which databases may be accessed for free online - this is tricky. Of course most of these journal indexes are "for-profit" companies, and they make their money by selling subscriptions to libraries and research facilities, and they do not take kindly to people using their services who are not connected to an institution that has paid for their service. However, the good news is that you don't have to be a scientist or a college student to have access to these subscription databases! Most public libraries have subscribed to multiple journal databases, and most of these libraries have now been able to implement systems in which their patrons may connect to these databases remotely from their own home. If not, then at the very least they will provide access to the databases from the computers in their library building. I'd say the first step for you would be to start by calling your local library and asking whether they offer remote access to their online journal databases.

If such is the case that you do not live in an area that is covered by such a library, then the next step would be to try to do what you're doing now: finding out which online databases are accessible for free. There actually are (as has been mentioned already here) a couple of databases that are fairly decent for finding information. Here is an annotated list of some (the annotations are my own):

• GoogleScholar. GoogleScholar is fantastic, and I use it all the time. However, it has some very serious limitations. The good points are that it covers a LOT of material, most of which is in professional peer-reviewed academic journals. Its limitations are that searching in it can be very difficult sometimes if you're doing anything complicated. It also (contrary to what it claims) does NOT provide full text access to everything it claims to. In addition, one is forced to use the Google search algorithm, which although is a fairly good one, does not allow a lot of flexibility when it comes to fine tuning a search, as many of the other online databasees do. However, GoogleScholar is still a very useful tool. It is not, though, a solution for everyone.
• Most countries in the world have a National Library whose mission is to take a leadership role of the libraries in that country, offering many services and providing for an oversight on quality control, so to speak. The U.S., however, has no National Library. Although many believe the Library of Congress is the National Library, it is not - it is specifically the Library of the United States Congress. However, there are three major libraries in the U.S., that taken together, might represent certain aspects of what a typical National Library does in other countries. These three libraries are the Library of Congress in Washington, D.C., the United States National Library of Medicine in Bethesda, Maryland (which is the largest medical library in the world), and the United States National Agricultural Library (which is the largest library of agriculture in the world), also located in Washington, D.C. Each of these libraries has its own vast collection of journals, as one might imagine. Both the National Library of Medicine and the National Agricultural Library offer a freely-accessible index to their journals. In other words, both of these libraries have a staff of people who index the journals they receive, creating a database that they then share freely to the public. The Library of Congress, however, does not do this. They do maintain a very popular database called thomas.loc.gov whose focus is on legislation and some U.S. history, but instead of providing a free index service to the journals they subscribe to, as does the other two libraries, they sell the rights to do this to an independent company called OCLC. I'll discuss all of these databases below:
• The online journal index database for the National Library of Medicine is called MedLine, whose database is called PubMed. It may be found here: http://www.ncbi.nlm.nih.gov/sites/entrez If you go there, you may set up a free account and perform searches for journal articles that are in their huge collection. However, their search engine software is quite klunky to use. Two indexing companies also offer MedLine through their own services, OCLC's FirstSearch, and Cambridge Scientific Abstracts. I would recommend either of these other two indexes over that of PubMed, due to their more superior searching capabilities. However, in order to access them, you need to go through a library that has a subscription to either of these companies. Fortunately, most libraries (at least in the U.S.) have subscriptions to OCLC.
• The online journal index database for the National Agricultural Library is called Agricola. It too maintains its own search engine, but which is better than that of PubMed. Again, OCLC has also provided a mirror database for Agricola, using its search engine, which is probably easier to use than that of the original. Here is the location of Agricola: http://agricola.nal.usda.gov/
• Thomas is the name given by the Library of Congress to its database for legislation and history. It may be found here: http://thomas.loc.gov/
• OCLC is NOT a free service. However, it has by far the most extensive subscription journal indexing around. Most libraries subscribe to OCLC, which is not a single database, but a family or collection of over 50 different databases, including some that are absolutely superb for what they do. One of these databases, called WorldCat, is fantastic, as it combines of thousands of libraries' online catalogs in one place - it is literally like going to an online catalog that includes almost every library in the U.S., many in Europe, and Asia. WorldCat does not index journal articles, but books (or monographs, if you will). OCLC also has many other journal databases, making it perhaps the single most powerful journal search index in the world.

In closing, I'd like to reiterate that you will not find one single place where everything is located - not even Wikipedia does that (yet). Knowing where to look is very important if you're trying to find out about something. And again, the best person to ask where to look is your friendly local Reference Librarian. Or us here... Saukkomies 04:29, 11 December 2007 (UTC)

Wow, I'm quite impressed. Thank you for the helpful lesson. Ƶ§œš¹ _{[aɪm ˈfɻɛ̃ⁿdˡi]} 06:16, 13 December 2007 (UTC)

How much does solar energy cost to produce ?

How much does solar energy cost to produce? —Preceding unsigned comment added by 68.218.19.20 (talk) 17:20, 9 December 2007 (UTC)

(Added title to question) SteveBaker (talk) 17:34, 9 December 2007 (UTC)

For the time being solar energy is free. --Ouro (blah blah) 18:31, 9 December 2007 (UTC)

I assume they mean the capital costs, etc., of a power system which converted solar energy to electricity. --24.147.86.187 (talk) 21:47, 9 December 2007 (UTC)

It's not just capital costs either - eventually they fail and have to be replaced. In a large scale installation, the panels need to be cleaned to remove dust and dirt that would otherwise reduce their efficiency. However, it's not going to be anything like as expensive as maintaining any other kind of power station. The biggest problem is the capital cost. SteveBaker (talk) 23:21, 9 December 2007 (UTC)

Indeed. Not only is solar energy not free in practice, it's so not free that in general, it can't really compete with fossil fuels yet. That is, the equipment required to capture and use that "free" energy is so expensive per unit of energy captured that it's usually cheaper to use "conventional" sources instead. (The situation is changing, but slowly.) —Steve Summit (talk) 23:38, 9 December 2007 (UTC)

Well, it all depends on how much solar energy you're producing. Small solar panels, like ones for solar powered calculators, sell for under $10. But solar power plants, like these, can cost quite a bit more. This solar power tower, for example, cost about $40 million (USD) to build. So, your question is like, "How much does a motor powered vehicle cost?" It depends on whether you're talking about a scooter or a helicopter and if you're including other things, like long term maintenance. -- HiEv 00:42, 10 December 2007 (UTC)

But even there, in a calculator, is an example of the problem in microcosm. You can buy a AA battery for about 50c - so for a $10 solar cell, you can get 20 batteries. The little 4-function calculators that come with solar cells use so little current that they'll easily run for a year of normal use on one battery - so if you'd spent your $10 on batteries instead, it would take maybe 20 years for you to finally discover that you'd have been better off using a solar cell. The trouble is that nobody keeps a calculator for 20 years because they break, get lost or are outmoded. What's worse is that if you'd invested your $10 in the stock market (with an average return of about 5% per annum), then your interest would be 50c per year - which means that you could keep yourself in batteries for the rest of your life for the price of those solar cells. Sure, you can quibble with the numbers (I don't think calculator solar cells cost anything like $10) - but you get the point. It's not always obvious that "free" electricity is something you can afford to buy. SteveBaker (talk) 03:50, 10 December 2007 (UTC)

But (I have to have this but) there's the additional costs that come into play. Say you went with the batteries, and not the solar cell, it would be good to count in the costs of disposal of the batteries and/or their recycling. I know it's usually something negligible or something that the usual calculator user never ever ponders on or cares about, but still, somebody has got to take care of the refuse. There's also the costs (to the environment) of the production of those umpteen batteries vs the costs (to the environment) of solar cell manufacture. If we're discussing everything, then it should be everything. --Ouro (blah blah) 06:59, 10 December 2007 (UTC)

I think the $10 figure for a calculator solar cell is too pricey, by an order of magnitude or so. Cheap solar-powered calculators are a giveaway item at conferences and such. Here's a calculator for $2.75, retail, in single quantity. Here are calculators for as little as $1.09 in quantity. The solar cell itself must be under a dollar. -- Coneslayer (talk) 12:43, 10 December 2007 (UTC)

Like I said - you can certainly quibble about the numbers...I merely present that little exercise as a way to show the problems with solar power in general. For calculators, solar actually is cost-effective or we wouldn't see them on store shelves. I suspect that in reality, the solar cell is actually cheaper than the empty battery compartment - and it has the advantage that it's thin so you get a smaller calculator as a result. As Ouro points out, these assessments (both on the level of calculators and on the level of bazillion watt power stations) really ought to factor in the cost of other power sources on the environment. Solar can't compete with coal on price - but if you were to factor in the likely costs in terms of global warming of the CO2 and other junk put out by coal, then solar power would probably turn out to be more cost-effective despite the cost of capital. SteveBaker (talk) 13:40, 10 December 2007 (UTC)

A 3000 mAh alkaline battery at 1.5 V that costs 50 cents would be delivering power at a rate of $100 / kWh. A nice solar system has a life cycle cost closer to $1 / kWh, while traditional energy sources are more like $0.1-0.25 / kWh. Batteries are by far the most expensive energy source in common use. In virtually every circumstance where it is practical to replace batteries with an alternative energy source (be it electricity from the grid, or distributed power like solar) it is more cost effective to do so. Or put another way, the ~0.1 W required to run a calculator can be provided by a ~15 cent solar panel, not a $10 one. Dragons flight (talk) 15:12, 10 December 2007 (UTC)

Recent large orders for Stirling engines (40,000 or so ordered for Southern California) and solar trough plants (see List of solar thermal power stations) show that the expense is not that far off coventional sources. Rmhermen (talk) 18:53, 10 December 2007 (UTC)

For the record, I never said solar cells for calculators cost $10. I said they cost under $10, and gave an example of a 6 volt one for $9. The same site had a 3.5v one for $2.49, and if you buy 'em in bulk you can often get 'em even cheaper (as Coneslayer pointed out earlier). So, if a 1.5v AA battery costs $0.50, as argued earlier, then that 3.5v solar panel takes the place of $1.50 worth of batteries, and doesn't need replacing. In other words, it's paid for itself by the time you'd have put in that second set of batteries, and it doesn't create the additional pollution that batteries do either. -- HiEv 22:51, 11 December 2007 (UTC)

<nitpick>Technically, Ouro got it right the first time. Solar energy is produced completely for free: the panels just capture and convert the energy. --Storkk (talk) 15:18, 12 December 2007 (UTC)

Does Cefdinir dehydrate you, or am I getting seriously windburnt?

This question has been removed. Per the reference desk guidelines, the reference desk is not an appropriate place to request medical, legal or other professional advice, including any kind of medical diagnosis, prognosis, or treatment recommendations.

Since you've found our article on cefdinir already, there's not much more we can add. The volunteers at the Reference Desk aren't qualified to diagnose your condition—and even if they were, it's difficult to do a proper examination over the internet. You should speak to a trained and licensed professional – your physician or pharmacist – about your concerns. TenOfAllTrades(talk) 19:43, 9 December 2007 (UTC)

Oh, sorry. I'll ask the doctor at my followup. MalwareSmarts (talk) 19:55, 9 December 2007 (UTC)

NASA's COBE (Cosmic Background Explorer) Satellite

COBE produced an Infra-Red picture, that was unveiled by Eli Dwek at a meeting.

Where and when was this meeting?

Was it, for example, at the Conference held in College Park, MD - in April 1995? Anyone know? - I'm Peter Lamont. —Preceding unsigned comment added by Astrocat0-1 (talk • contribs) 18:52, 9 December 2007 (UTC)

December 10

Fan curve calculation

I'm looking for a fan curve (pressure-volume) for a particular fan - I've been told it's an "RB21 AVON" - and failing that, I've been told to find a "fan formula" so that it be calculated. Is there such a formula (with diameter, air density, and some other coefficients), or are these determined empirically? 150.101.23.102 (talk) 00:26, 10 December 2007 (UTC)

I've only ever seen this done empirically, with a device that measures volume/area/time of air coming out of the fan. Certainly far easier than solving some convoluted aerodynamics equation. Someguy1221 (talk) 00:39, 10 December 2007 (UTC)

Well, I've possibly found a more complicated formula - see here (measuring method, no anchor, about 1/3 down) - but that still looks like more of a "how to use a test rig to plot the curve" than a full CFD with fan parameters. 150.101.23.102 (talk) 01:02, 10 December 2007 (UTC)

Actually, assuming that I did have to perform a CFD analysis on it, what software would I be looking for? 150.101.23.102 (talk) 01:33, 10 December 2007 (UTC)

LED blinking with 555

How many LED's can I control with a 555 timer? It has a nominal output current of 200 mA, if a LED needs 20 mA — I believe this is a realistic value, correct me if it is not — I'll be able to supply 10 LED's. Am I right? Thanks in advance for your help. 217.129.241.169 (talk) 01:47, 10 December 2007 (UTC)

In theory, yes, but look at your datasheet for more accurate information. But I don't think it has any current limiting mechanism built-in so you will still need to have a resistor in series. --antilived^{T | C | G} 04:51, 10 December 2007 (UTC)

Yes, I'll obviously need to insert resistor in series with the LED's, my doubt was just related with the driving capacity of the 555. Meanwhile I saw a project similar to mine and it used a 555 to drive 20 LED's. Thanks! 217.129.241.169 (talk) 13:31, 10 December 2007 (UTC)

LEDs can be operated in series. I don't recall what the breakdown voltage is for the output transistor of the '555, but I'll assume that for the average '55, it's at least 12 volts (and probably 15). In that situation, you could easily operate 7 or 8 red LEDs in each series string connected to the '555's output and you've demonstrated that about ten series strings can be operated. If you need to go beyond that, use the output from the '555 to drive some garden-variety power transistor.

Atlant (talk) 18:06, 10 December 2007 (UTC)

Why do you need a resistor? Wont all the LEDs in series constitute enough resistance? I figure putting a resistor in there just reduces the number of LEDs you can light by wasting energy. --Seans Potato Business 21:36, 10 December 2007 (UTC)

The simple answer is, because LED's aren't resistors, so they don't have a "resistance"!

Think about an ideal diode: it passes current freely in one direction, and not at all in the other direction. So in one direction it acts (almost) like a 0Ω resistor, and in the other, ∞Ω.

Of course, you run a light-emitting diode in a forward-biased condition. But without a current-limiting resistor, it would draw (theoretically) your supply voltage ÷ 0Ω = an infinite amount of current. Not good.

(In fact, a forward-biased diode doesn't act exactly like a 0Ω resistor; there's a relatively constant voltage drop across it -- 0.6V for silicon-based diodes -- regardless of the current passing through it. Take that, Georg!) —Steve Summit (talk) 02:17, 11 December 2007 (UTC)

Erm, actually for a silicon diode under forward bias, its resistance is fairly accurately given in ohms by the expression 25/Ie where Ie is in milliamps. In a similar way, LEDs can also be said to have a non zero resistance altho Im not sure if the above formula applies to LEDs (but I think it may)--TreeSmiler (talk) 03:15, 11 December 2007 (UTC)

If there's a voltage drop with a resistor present, then there must be resistance from the LED - the energy it takes is what it uses to light up and that wouldn't happen unless it was forcing the electrons to do some work. Thus, you should be able to put no resistor and say, I don't know, 1000 LEDs and they will provide sufficient resistance to prevent too much current from flowing. If you insist on putting a resistor in the circuit, then surely you're just going to waste energy and voltage. The voltage drop over something is proportional to the resistance it provides so I don't see how you get a 0.6V drop over an LED without significant resistance. --Seans Potato Business 12:40, 11 December 2007 (UTC)

LEDs are commonly operated without any series resistance. Open up any of those cheap "LED flashlights" and you'll find that the circuit is nothing more than one or more LEDs paralleled across one or more batteries. By carefully choosing the battery size and the LED, you end up with enough series resistance to not blow up the LED. This isn't the way it's done in more "professional" circuits, of course. There, in low-drain appliactions, you'll find a resistor or an "RLED" (with a built-in resistor chip). In high-drain applications (like car tail lights), you'll find a specific IC dedicated to driving the LEDs.

Atlant (talk) 13:24, 11 December 2007 (UTC)

That's not true. Every LED needs a current to limit its current. A LED is, like a diode, formed by a PN junction. The current that flows through a PN junction is exponentially related with the voltage at its terminals, that means that applying a 9V voltage to a LED will make a huge current flow through it, burning it after some seconds. 193.136.173.43 (talk) 16:42, 11 December 2007 (UTC)

I assure you it is true and you can convince yourself of its truth by taking apart just about any cheap "LED flashlight". Your theory ignores the fact that there are lots of parasitic resistances strewn around the circuit: the LED has real resistance, the battery has a non-zero internal resistance, the wiring has resistance,and the switch has resistance. All of those resistances appear in series with the rather-small voltage that is left when you subtract the LED's "ideal diode" voltage drop from the battery's "open circuit" voltage. I also wondered about when I first saw it, but I've seen enough examples now to know that it's dead-standard practice in cheap LED devices.

Atlant (talk) 17:51, 11 December 2007 (UTC)

It doesn't make much sense to say everything "needs a current to limit its current." 193.136.173.43 may have meant every LED needs a resistor to limit its current. It is true that with the proper combination of forward biased voltage drop in the LED and proper battery voltage, the circuit can be operated without a dropping resistor (and with higher efficiency due to that absence of power wasted heating up the resistor rather than producing light). If you had two LEDs with a 0.75 volt forward voltage drop across a 1.5 volt battery, there would be no point in adding a sereies resistor. If you used a 9 volt battery, you would need to drop the voltage to 1.5 volts by means of a resistor which dropped the voltage by 7.5 volts at the current consumed by the LEDs, selected by application of Ohm's Law. Or you could use 12 of the same LEDs in series across the 9 volt battery with no resistor and get more light with the same battery life. A refinement in the cuircuit design would be to make sure the circuit operates not only ith a new battery, but down to some specified "dead battery" voltage. Edison (talk) 17:11, 11 December 2007 (UTC)

(Just FYI: No visible-light LED drops 0.75 volts; they all drop about the same voltage as the energy (in electron volts) of the photons that they emit, so a red LED drops about 1.6 volts, green 2.3V, blue 3.0+V, and so on. See Light-emitting diode#Considerations in use.)

Atlant (talk) 17:51, 11 December 2007 (UTC)

Then make it "2 volts" for the LED forward voltage drop at normal operating current place 6 of them across a 12 volt battery, or 1.5 volts and place one across a 1.5 volt battery. Still no resistor required. Edison (talk) 18:49, 12 December 2007 (UTC)

Also keep in mind that if you light the LEDs briefly in sequence, so they're flashing so rapidly you can't see it, you can probably light quite a few more LEDs with your limited power before the flicker becomes noticeable. Have fun! -- HiEv 23:01, 11 December 2007 (UTC)

So ,Wikibrains, if there were 5 red leds connected in series each dropping a voltage of 1.9V @ 10 mA, and you connected this string across a 12V battery with zero internal resistance, would the leds (or one of them) be destroyed? —Preceding unsigned comment added by TreeSmiler (talk • contribs) 01:50, 12 December 2007 (UTC)

What sort of a battery has zero internal resistance? What sort of an LED has zero internal resistance? What sort of wire? Ultimately, Ohm's law still rules, although it is certainly possible to drive LEDs beyond their I_f maximum rating.

Atlant (talk) 13:35, 12 December 2007 (UTC)

A regulated power supply with the terminals delivering 12 volts would be the equivalent of a 12 volt battery with zero internal resistance, up the the point where its current limit was reached. Edison (talk) 18:29, 12 December 2007 (UTC)

And that, of course, isn't a battery but is closer to an ideal voltage source.

Atlant (talk) 01:12, 13 December 2007 (UTC)

If you have a 12V battery that is only allowed to provide 10 mA of current, then you need 1k2 ohms of resistance or 6 190 ohm LEDs. If LEDs have a lower resistance than this, then I don't see how you could achieve 1.9 V with 10 mA. --Seans Potato Business 14:51, 12 December 2007 (UTC)

A forward biased diode is not well described as having a certain ohmic resistance, but rather by having a certain voltage drop. Even that will increase slightly as the current increases. It is an active device, not a resistor. Edison (talk) 18:46, 12 December 2007 (UTC)

No no. A semiconductor diode is a semiconductor diode. It obeys the diode equation. The incremental resistance at any point is defined as the ratio of the voltage across it to the current through it (Ohm's law)--TreeSmiler (talk) 02:04, 13 December 2007 (UTC)

The real reason for driving an LED from a voltage source through a resistor, rather than directly from a hypothetical voltage source of the exact same voltage as the LED's forward voltage drop, is that the resistor-plus-voltage-source approximates a constant current source. LEDs like to be driven with a constant current. If you tried to drive a LED from a low-impedance voltage source, the output of the LED would be insanely sensitive to the source voltage. Every tiny fluctuation in the source voltage, and every tiny change in the LED's temperature, would cause dramatic changes in the LED's brightness. A small rise in voltage would be enough to destroy the LED. With a series resistor acting as a current source, small changes in the LED's temperature and the source voltage do not noticeably affect the LED's output because they do not affect the current much. Yes, this wastes a bit of power, but not as much as you waste when your LED melts. --Heron (talk) 21:27, 12 December 2007 (UTC)

Surely you waste zero power when your led melts. If it fails o/c there is no current; if it fails s/c there is no voltage. In either case, no power is wasted.

However I think you have hit the nail on the head with the above explanation of why you need resistors in series with leds: to stabilize the current through them. But its ok for a string of leds to be drive by a current source, I think everyone would agree. In this case, power is necessarily dissipated in the current source.--TreeSmiler (talk) 01:58, 13 December 2007 (UTC)

Err if you fail s/c in the real world you draw maximum current and maximum power (not no power). --Dacium (talk) 02:55, 13 December 2007 (UTC)

Sorry but power is volts times current. So a s/c device can dissipate no power however much current flows.--TreeSmiler (talk) 02:59, 13 December 2007 (UTC)

Euler's astronomy

Hello, I was wondering if anyone would be able to point me toward some information on Euler's contributions to Astronomy? The section of the article concerning it doesn't say much, and Google results have been unfortunately sparse. I'm particularly interested in his work on comets, and the moon - anything I've been able to find hasn't offered more than a few sentences. Thank you, 81.102.34.92 (talk) 13:54, 10 December 2007 (UTC)

Corn, an artifact?

I read somewhere that "an ear of corn is an artifact: corn can survive only if man removes the kernels from the cob and plants them." If it is an artifact, how has it come into being in the first place? Thanks. --217.11.17.252 (talk) 14:19, 10 December 2007 (UTC)

I think you find that animals can remove the kernels too.They cache them, forget a few caches & voila, the corn sprouts. BUt domestic corn, I think is a tetraploid of the native maize so the germination rates tend to be lower. —Preceding unsigned comment added by 24.226.90.6 (talk) 15:09, 10 December 2007 (UTC)

I assume you read it here? I honestly wouldn't take that as a source of real philosophical insight (there is nothing so dull and misleading as a dedicated Marxists' view of the world), but the guy's point is that domesticated corn has trouble growing without human intervention. Whatever wild species corn came from (there are many theories, see maize) obviously had no trouble reproducing itself but was quite different from what we eat today. The point of the article there is that corn has been domesticated for over 500 years, and that the domesticators were native American peoples. --24.147.86.187 (talk) 15:18, 10 December 2007 (UTC)

• Basically all domesticated crops and animals are "artifacts" in the sense that they have been altered far beyond their pre-human form, and would either go extinct or be greatly endangered without human intervention. But there's nothing wrong with that (well, at least if you ignore developments in the last few years like genetic modification, which is still controversial). Similar interactions between plants and insects led to the rise of flowers and edible fruits. It's just that we humans have taken the process to an extreme by allowing crops and animals to focus very little energy on defending themselves and more of their energy on being tasty. --M@rēino 20:34, 10 December 2007 (UTC)

You might want to consider though that classical plant breeding is a lot more complicated then people think. Over the last decades in particular, it doesn't just involve people selecting the best traits that arise naturally. Mutants are induced by radiation [8] and chemical means for example. Unlike with genetic modification, no testing is required of the resulting product. Also I disagree with your view that there's nothing wrong with that in the sense that there's no reason to presume that even tradiational crop breeding methods are somehow 'super safe'. There is easily the chance that we will select traits which are harmful to humans or to other organisms (beyond as desired for pest control). If you compare any one of our crops with its ancenstor you can see we have made very major changes. Consider for example the extremely bizzare forms of Brassica oleracea we have like cauliflower, broccoli, cabbage, brussel sprouts and how 'fucked up' these plants are. Bringing it back to the original question take a look at [9] (see section "Corn or Maize") to get an idea how much we have changed our current crop plants. My point is not that I think any of this is wrong but simply that we have and continue to very severely change the crop plants we eat. Genetic modification is significantly faster (so there is a somewhat higher chance we may do something bad which we will notice but it may come a bit late) and does carry some additional risk but a lot of the risks are overplayed (for example when people talk about minor chances of increasing cancer when there is no reason to presume that we haven't already or won't do that via other means but just don't know because the only way you detect such things is by carefully controlled scientific tests). The ironic thing is that given the opposition to genetic modification, many breeders are using GM as a 'proof of concept' and then using tradiational means (i.e. radiation, chemical mutagens etc) to get what they want even though it means that a lot more has changed in the process (most of which the breeder won't know the effect of). This also means the cost is in fact a lot higher and more out of reach of poor farmers. Note that the issue of the introduction roundup resistantance or protection of crop varieties (which existed long before GM) or things such as terminator genes are seperate issues from whether GM itself is somehow a potentially harmful or dangerous technique. Nil Einne (talk) 12:03, 11 December 2007 (UTC)

Thanks for all comments. Omidinist (talk) 08:05, 11 December 2007 (UTC)

medical abbreviation

VDRL (veneral deseas research laboratory) in context with RCPF . What means the abbreviation RCPF? —Preceding unsigned comment added by 217.186.79.16 (talk) 14:31, 10 December 2007 (UTC)

In the context of laboratory testing it may be Rate-Controlled Programmed Freezing. This is to do with the procedure of freezing specimens in a non-damaging way. Richard Avery (talk) 16:01, 10 December 2007 (UTC)

The VDRL and Reiter protein complement-fixation are both tests for syphilis. 152.16.16.75 (talk) 10:34, 11 December 2007 (UTC)

Problems with Blazars

On the article, blazar, it says the accretion disk is quite small. Only 10^-3 parsecs in size. While the article on Q0906+6930 states that the event horizon is on the order of 1000 times that of our solar system, making the accretion disk many times larger than that. Possible error here? 64.236.121.129 (talk) 14:44, 10 December 2007 (UTC)

I agree that the Blazar article is confusing in this respect. I think the answer is that in a blazar, the observed emission does not come from the accretion disc (which would give a broad emission line spectrum, as in a quasar), but instead comes from the relativistic jet. The "tip" of the jet, as you can see in the illustrations, is much smaller than the accretion disc, and could be smaller than the SMBH event horizon. -- Coneslayer (talk) 15:13, 10 December 2007 (UTC)

Q0906+6930 says event horizon volume not size, so presumably they mean a radius 10 times that of the solar system. If one canonically defines the solar system as 40 AU (orbit of Pluto), then that would be 400 AU or 2*10^-3 parsec. That number isn't so different from what blazar says. I think the problem is the fuzzy way in which the terms are being defined, and not that they are actually radically different sizes. Dragons flight (talk) 15:21, 10 December 2007 (UTC)

The problem is, we are talking about the accretion disk, which should be much much larger than the event horizon. Sure enough, most scientists agree, if you look at a black hole, you probably won't even see the event horizon because it will be dwarfed by the much larger accretion disk. So while the event horizon should be 2*10^-3 parsec (if your calcuations are correct), then the accretion disk should be much larger than that. 64.236.121.129 (talk) 15:50, 10 December 2007 (UTC)

Well supermassive black hole suggest 10^5 to 10^10 solar masses. 400 AU is equivalent to 2*10^10 solar masses, i.e. at the extreme upper limit. However, if supermassive black holes really vary over 5 orders of magnitude, then presumably there must be a large range of variation in accretion disks too. Dragons flight (talk) 15:58, 10 December 2007 (UTC)

There is a large variance in sizes. Maybe the article should be changed to relect that? It's a little misleading as it is. I should point out that Q0906+6930 is larger than your upper limit, at 16 billion solar masses. 64.236.121.129 (talk) 16:33, 10 December 2007 (UTC)

Solar Cell Production Cost

Related to a previous question... I'm trying to collect as many peer-reviewed studies on the cost, resource impact, and environmental impact of producing solar cells. This is not the consumer cost as the previous question apparently asked. This is the production cost. Obviously, solar cells don't fall out of gumdrop trees in the butterfly forest. That is why I want to get a well-rounded view of the production cost. -- kainaw™ 19:07, 10 December 2007 (UTC)

I've seen $8 per watt quoted for home/roof installations...with 30 cents per kilowatt hour as the 'lifetime' cost (which is two or three times more than electricity bought from the grid). For large scale power-station stuff $3.10 per watt for currently-available cells - perhaps half that when some of the newer technologies come on-line. "First Solar" claim[10] to have gotten the price down to $1.19 per watt. But even at $1 per watt, it's still borderline whether it's worthwhile - depending on the number of cloudless days you get per year, how close to the equator you are and how long your panels last (which is always an unknown with the latest and greatest solar panels until they've been in service for a few years).

I'm not 100% sure if this is still true - but at one stage, there was a premium on square solar cells because where cost is no object (eg in a spacecraft) one can pack them tightly in a grid. Since silicon wafers are circular, this meant that there were a bunch of curved sections of the panel that were cropped off the edges. These were vastly cheaper than the square variety - but you couldn't get so much energy efficiency because they couldn't be packed together very closely. If this is still the case, then you may need to be more specific about the application. SteveBaker (talk) 20:24, 10 December 2007 (UTC)

• The US Dept of Energy has some publications that may be of interest to you. --M@rēino 20:38, 10 December 2007 (UTC)

Why not use hexagonal solar cells? They'd pack just as well, but wouldn't require cutting as much off. By the way, I remember hearing that solar cells only give off a little more energy over their life than is required to produce them, is that correct? — Daniel 01:00, 11 December 2007 (UTC)

Well, taking the numbers I got for domestic rooftop panels (cost $8 per watt to buy, produce electricity averaging 30c per kwatt.hour) - means that they have to be good for 24,000 hours - It's hard to imagine it would take 24 kwatt.hours to make a single 1 watt solar panel...that's a lot of energy. I don't know why they don't make hexagonal panels - but there is no wastage with the round ones - they just have to sell the offcuts for less than the square bits in the middle. SteveBaker (talk) 01:42, 11 December 2007 (UTC)

I'm sorry that I wasn't clear enough that I'm looking for production cost, not installation or operation. I have found that current production creates 1.5 tons of carbon dioxide per ton of silicon processed into half a ton of functional solar cells (assuming the silicon is nearly 100% pure - purification of silicon has cost/waste also). The monetary cost is similar to computer chips since the "wafer" process is very similar. I've found valid research into reducing the cost and environmental impact of solar cell production - which is what I was looking for. -- kainaw™ 14:13, 11 December 2007 (UTC)

It's utterly ridiculous to claim that the CO2 produced in the manufacture of a solar panel is anything other than utterly negligable compared to the amount it saves us over it's lifetime. Let's crunch the numbers to show you how utterly insane that idea is! One ton of lignite coal (which is about 75% carbon) will burn to produce about a ton of CO2. In the process it produces 28 MJ/kg of energy - so if coal-fired power stations were 100% efficient (which they most certainly aren't) then in round figures, it would produce about 7 MWhrs per ton of CO2 emitted. So the question is will 0.33 of a ton of solar panels (which produced 1 ton of CO2 during manufacture) be able to produce 7MWhrs of electricity during their lifetime? Well, the calculation I did above suggests that a domestic solar panel (which is a lot less efficient than a commercial setup) can produce power for an average of 24,000 hours before it craps out on you. So one ton of solar panels only has to be able to produce 300 Watts per hour to save more CO2 than it produced during manufacture. Since one $600 rooftop panel (with probably less than a kilo of cell inside) produces about 150W - then so long as it didn't require more than half a ton of silicon wafers - it's a net CO2 win. I strongly suspect that a 150W panel contains about a kilo of silicon wafers - so solar panels produce about 1/500th the amount of CO2 compared to a coal fired power station...and that's assuming that you didn't produce any CO2 to build the power station (which you did) and that it's 100% efficient (which it isn't) and that digging a ton of coal out of the ground and getting it to the power station didn't create any CO2 (which it did). I also picked a rooftop domestic solar panel for my calculations - and for sure commercial setups are more efficient. No - the claim that solar panels produce more CO2 during manufacture than they save is a statement that is utterly without merit. SteveBaker (talk) 14:54, 11 December 2007 (UTC)

Photovoltaic#Greenhouse_gases says: Life cycle greenhouse gas emissions [...for photovoltaics...] are now in the range of 25-32 g/kWh and this could decrease to 15 g/kWh in the future.[65] For comparison, a combined cycle gas-fired power plant emits some 400 g/kWh and a coal-fired power plant 915 g/kWh and with carbon capture and storage some 200 g/kWh. Nuclear power emits 25 g/kWh on average; only wind power is better with a mere 11 g/kWh....QED. SteveBaker (talk) 15:00, 11 December 2007 (UTC)

Put a different way, it takes 1-4 years for a solar panel to recoup the energy used in its manufacture. Whatever it can produce during the years of operation beyond that might then be considered carbon free. Dragons flight (talk) 15:06, 11 December 2007 (UTC)

Where did you get the statement: "solar panels produce more CO2 during manufacture than they save"? I didn't write that. I didn't imply that. I didn't reference anyone else who stated that. Where did this rant come from? -- kainaw™ 15:14, 11 December 2007 (UTC)

That was in User:User:DanielLC's comment above in response to your question. Rmhermen (talk) 16:04, 11 December 2007 (UTC)

Thanks - I didn't relate the response to the intended statement. -- kainaw™ 17:04, 11 December 2007 (UTC)

Sorry - yes, Wikipedia indentation style makes it tough to target specific responses yet stay in the right order of the flow of the conversation. I was using the "1.5 tons of CO2 per ton of solar panels" number that you provided to respond to Daniel's claim - so I couldn't put my reply immediately after his without making it confusing as to where that number had come from. Sorry if it sounded like I was accusing you of saying something daft. SteveBaker (talk) 19:02, 11 December 2007 (UTC)

Measuring Snowfall vs Rainfall

I've been trying to find a precise answer to this question, but I can't seem to dig it out, so I thought I'd post my first question to the Wiki Ref Desk. When meteorologists predict that there will be 1 to 2 inches of snowfall, what are they exactly saying? Will there be 1 to 2 inches of loose, unpacked, powdery snow, or will there be 1 to 2 inches of water left after the snow has melted? If it is the former, what is the ratio of water within the snowfall? I'm mostly interested in the use of this in the U.S., but if someone in another country has any information about it, I'd be interested in that, too. Thanks. --Saukkomies 19:24, 10 December 2007 (UTC)

This link should help. -- kainaw™ 19:30, 10 December 2007 (UTC)

Yeah, thanks for the link, Kainaw. It did answer part of my question. But there still remains unanswered the question of what exactly do the forecasters mean when they say that we should expect 2 to 4 inches of snowfall? Our Canadian colleague below indicates that when they state "snow accumulation", it means the depth of the freshly fallen snow. But often all they say is "2 to 4 inches" and leave it at that. Does this mean 2 to 4 inches of the snow depth of fresh snowfall, or 2 to 4 inches of precipitated moisture - which would be much deeper than the freshly fallen snowfall depth. I'm still confused... --Saukkomies 20:36, 10 December 2007 (UTC)

What I get from that link is that 2 to 4 inches is an average accumulation over an area. The example from the article is that an area with 6 inches in one spot and no significant cover in another should be marked as 3 inches of accumulation. It also points out that water content is very much a matter of how the person processes it. It explains that snow floating in the wind will have difficulty making it into the precipitation container, reducing the amount of water detected. Another option is to take a plug of snow and melt it, but that depends on how well packed the snow is and where you took it from. Now, another way to ensure that you know 2 to 4 inches is accumulation is to consider what the accumulation would be if it was a measurement of water. Consider the high density level in our article of 15%. In other words, in an inch of snow, 15% of it is water. Using simple algebra, if 2 to 4 inches of water fell as snow, it would be 13 to 27 inches of snow accumulation. Obviously, they are not calling for 1 to 2 feet of accumulation, so they mean 2 to 4 inches of accumulation. -- kainaw™ 13:14, 11 December 2007 (UTC)

They're forecasting the depth of snow, not the equivalent depth of rain. My understanding is that it's approximately a foot of snow to an inch of rain, though this varies wildly based on the sort of snow. Our article notes that newly fallen snow has a density of 5%-15% (which is in the ballpark of the foot-to-inch conversion) but that density increases as packing and settling occur. — Lomn 19:30, 10 December 2007 (UTC)

I was under the impression that it might be even more subtle than that. Here in Texas, it snows about once every couple of years - and initially, the ground surface is generally above freezing. Hence, most of the initial snowfall just goes into chilling the ground so that subsequent snow can settle. So when they make an estimate here, there ought to be much more to it than simply one-foot-per-inch-of-water. SteveBaker (talk) 20:00, 10 December 2007 (UTC)

I would expect that it is more subtle than that. However, it seems that forecasts tend to be things like "6 to 10 inches" or "up to 2 inches", which have quite a lot of room to cover subtleties. — Lomn 21:36, 10 December 2007 (UTC)

Canadian forecasts sometimes refer to "snow accumulation", which makes it clear that they are indeed talking about the depth: the initial snow that (as we say here) "doesn't stick" doesn't count. In after-the-fact reports where they show "precipitation", that's the melted amount, as explained here. --Anonymous, 22:01 UTC, December 10.

Henry Margusity at AccuWeather just put up a blog post on snow ratios. -- Coneslayer (talk) 17:57, 12 December 2007 (UTC)

Why no lightning during a snow storm?

I thought lightning was caused by static electricity from clouds rubbing against each other. Doesn't this happen during snow storms as well? So why no lightning during them? 64.236.121.129 (talk) 20:06, 10 December 2007 (UTC)

See thundersnow.148.177.1.211 (talk) 20:07, 10 December 2007 (UTC)

So the next question is, what's different about cold-weather storms that makes lightning less likely to form? The article describes it as rare, which fits my experience in Toronto -- summer thunderstorms, maybe twice a month if you count small ones; winter thunderstorms, maybe once every 10-15 years. But it doesn't say why. So why? --Anonymous, 22:11 UTC, December 10.

At the bottom of the thundersnow article is a link to a straightdope article explaining the likely reasons why thunder-snowstorms do not often develop. In short, the conditions conducive to lightning-generating storms are not produced frequently in winter weather conditions. Link reproduced here: Straight Dope staff report: Why don't snowstorms produce lightning? User:Sifaka 01:37, 11 December 2007 (UTC) (currently IE-xiled) —Preceding unsigned comment added by 128.196.149.20 (talk)

I saw lightning during a snow storm only once, and it was quite pretty. Edison (talk) 02:58, 11 December 2007 (UTC)

Yes, I too have seen lightning during snowstorms - but on several occasions. One was during the night of my 40th birthday party in Chicago! --Saukkomies 23:35, 10 December 2007 (UTC)

Tongue twister

What makes it hard to say toung twisters?--Sivad4991 (talk) 20:14, 10 December 2007 (UTC)

Most of them require you to align mouth, tongue, vocal cords, lips into some configuration - then require you to switch to a radically different configuration more quickly than is easily possible. Try saying "She sells sea shells on the sea shore" very slowly and pay attention to how your tongue and lips have to move around before each of the S's and you'll feel exactly what I'm saying - each S requires a totally different configuration of mouth parts. Now try the non-tongue-twister "She shears sheep in the shade" (Which I just invented!)- and because all of the S's are "Shhh" sounds, you can feel that it's a lot easier to say. Hmmm - we need a word for these kinds of sentence. "Tongue-straighteners" perhaps! SteveBaker (talk) 20:30, 10 December 2007 (UTC)

She sold sea-shells on the sea shore. DuncanHill (talk) 22:48, 10 December 2007 (UTC)

According to tongue twister, "The sixth sick sheikh's sixth sheep's sick." is the hardest tongue twister. Ow! I think I just pulled a muscle! SteveBaker (talk) 04:39, 11 December 2007 (UTC)

Also, see the bottom of this thread from the ref desk archive which has really good answers to the same question [11]. Azi Like a Fox (talk) 06:29, 11 December 2007 (UTC)

Yes - I was thinking about that myself. The odd thing is that "The sixth sick sheikh's sixth sheep's sick." is hard to read even without speaking or subvocalising it - just looking at the words is tough. But "She sells sea shells on the sea shore" is easy to read in my head but harder to say. So perhaps there is something for the theory that it's a cognitive thing as well as a mechanical musculature issue. SteveBaker (talk) 14:29, 11 December 2007 (UTC)

I would hazard to guess that the similarity between each of the words in "the sixth sick sheikh's sheep's sick" makes saying the rhyme a cognitively-demanding task, as well as physically challenging. This would similar to the phenomenon of semantic overload, when saying the same word over and over reduces the meaning of that word to nil (try it). See also mantra. Vranak (talk) 20:49, 11 December 2007 (UTC)

These are just things you dont say in everyday life (probably)-- thats why they are hard. A few hours practice and you can say any tongue twister-- Its just like learning to play a difficult tune. Practice on this easy one first:

Moses supposes his toses are roses,

Moses supposes his toses to be.

Moses supposes his toses are roses.

Moses supposes erroneously!

--TreeSmiler (talk) 02:14, 12 December 2007 (UTC)

Lightning striking a lake

One time while I was camping there was a giant thunder storm. Before the storm I was walking next to a lake near by and saw some ducks on the lake. During the storm I saw a lightning bolt hit the lake which was amazing I mite add. When the lightning bolt hit it made me think about the ducks, what hapens to ducks if a lightning bolt hits the lake while there are on the lake do they just turn into rost duck (mmm sounds good)? Amd same with the other little lake cretures do they just get fried to?--Sivad4991 (talk) 20:31, 10 December 2007 (UTC)

Lightning can certainly kill people on the water's surface, so the same is true of ducks, but lightning also dissipates fairly quickly when striking water. Additionally, in most lake settings, terrain dictates that actual water strikes will be comparatively rare. — Lomn 21:33, 10 December 2007 (UTC)

The electrons that make up the bolt come from the whole earth, basically, but the intensity of the current in the volume near the place the bolt "hits" will diminish with distance from the strike. It's sort of like the reverse of the way sound gets weaker as the spherical wave that makes it up increases in area. Ducks too near the strike will be zapped, as will the aquatic creatures. Those farther away (how far depends on the strength of that particular bolt) will survive. This does not take into account the direct effect of the field around the bolt, which could be expected to act on nearby fauna as well. --Milkbreath (talk) 22:19, 10 December 2007 (UTC)

Being smaller makes you less vulnerable to lightning striking close by. The voltage difference per meter gets less and less as you get further from the point of impact - and the closer together your points of contact to the ground/water, the less potential difference there is across your body. (One piece of advice they give you when out in the open during a storm is to keep your feet close together). A duck has a considerably smaller voltage across it than a human for that reason. Water conducts electricity better than the ground does - so one would expect the lightning to dissipate outwards faster than on land - and also the resistance of the water and the bodies of the animals bobbing around in it isn't so different - so less of the current will flow through the animal than on land. You're still going to get animals killed - but there are good reasons to assume that it would be less severe than on land. —Preceding unsigned comment added by SteveBaker (talk • contribs) 21:59, 10 December 2007 (UTC)

Unknown arachnid species

I came across this arachnid, which lived at the entrance of these caves in southern Brazil. I assume they're some species of the amblypygi order. Does anyone know exactly what species it might be. I would love to put it in a wikipedia article. -- MacAddct  1984 ^{(talk &#149; contribs)} 20:34, 10 December 2007 (UTC)

I count 7... There is one out of focus on the right of the photo (I think that is a leg anyway) Shniken1 (talk) 04:20, 11 December 2007 (UTC)

There's another out-of-focus one coming straight towards the lens, just by its left mandible. I think this one actually had part of that limb injured, so it's shorter than it should be. -- MacAddct  1984 ^{(talk &#149; contribs)} 04:34, 11 December 2007 (UTC)

Oh that was probably in re: to me when I said I only saw 6 legs, but then I saw the others so I removed my post. I also took the <smalls> off the below comment because it is funny. Like The Ring. Saudade7 23:30, 11 December 2007 (UTC)

That's a Macis deadus. Once you've touched it you die in a year :-P Nil Einne (talk) 11:40, 11 December 2007 (UTC)

I think it is some kind of this (?) Opiliones based on pictures on the web. But maybe you will have to send the picture to an entomologist at a university. Maybe it doesn't even have a name yet. So many living things in South America are disappearing before we even know they exist. Thanks Weyerhaeuser! Saudade7 23:45, 11 December 2007 (UTC)

splenocyte irradiation

Why might someone irradiate splenocytes that they're using to stimulate CD4+ T cells for an in vitro proliferation assay? Is it to stop them from proliferating or alternatively kill any among them that are proliferating, leaving those that aren't? --Seans Potato Business 21:24, 10 December 2007 (UTC)

To prevent the splenocytes, most of which will be lymphocytes, from proliferating as a response to the major histocompatibility antigens of the CD4+ T cells. By irradiating the splenocytes, you measure only the proliferation of the CD4+ T cells, and not the proliferation of the splenocytes. --NorwegianBlue ^talk 15:51, 11 December 2007 (UTC)

Aspirin and Coughing

Not a medical question

Coughing says coughing is a side affect of aspirin?

Is this true it's not mentioned in Aspirin? A quick google finds the opposite might be true.

If aspirin does causing coughing, through what action? Caffm8 (talk) 22:32, 10 December 2007 (UTC)

The British National Formulary No. 29 (March 1995) lists bronchospasm as a possible side-effect in hypersensitive patients. DuncanHill (talk) 22:37, 10 December 2007 (UTC)

As does the current edition (No. 54). DuncanHill (talk) 22:41, 10 December 2007 (UTC)

"Side-effects generally mild and infrequent but high incidence of gastro-intestinal irritation with slight asymptomatic blood loss, increased bleeding time, bronchospasm and skin reactions in hypersensitive patients.". DuncanHill (talk) 22:42, 10 December 2007 (UTC)

A rare side effect then? Most googling shows that aspirin is used to suppress coughs. But I suppose that's not odd, aspirin lists head-ache as a side effect.

Maybe it shouldn't be listed as a cause in Coughing. Perhaps because a lot of articles mention ACE Inhibitors (which do cause cough) given with aspirin (which suppress it) and the article mentions both. Caffm8 (talk) 22:54, 10 December 2007 (UTC)

I am not aware of aspirin being used to suppress coughing - BNF suggests its use as an analgesic, an anti-inflammatory, and an antipyretic, in mild to moderate pain and pyrexia, and in inflammatory joint disease, as well as its use as an anti-platelet. Interestingly, our aspirin article does not seem (at a cursory reading) to mention the special hazard of its interaction with warfarin. I am reluctant to edit the article extensively, but do find this odd. DuncanHill (talk) 23:08, 10 December 2007 (UTC)

Well this is the first google hit.

Yes, the aspirin article is misleading, it states "Taking aspirin with alcohol or warfarin increases the chance of gastrointestinal hemorrhage." and since most people have probably take aspirin with alcohol and suffered no adverse affects they might think the same of warfarin

It's why you shouldn't take medical advice from wikipedia  :). While (i believe) most things are probably correct through the power of many eyes, you never know what's missing and that's often more important Caffm8 (talk) 23:41, 10 December 2007 (UTC)

I always look up any medicines I am given on the BNF (its website allows access to anybody for free, so long as you register). This follows an embarressing incident at the chemists when a doctor had issued an illegal prescription for a controlled drug for a child I was looking after. DuncanHill (talk) 23:45, 10 December 2007 (UTC)

Sweet biscuits (= cookies) and savoury crackers

I've been told by a professional chef that if you put unwrapped sweet biscuits into the same airtight container as unwrapped savoury crackers, they'll all go soggy fairly quickly; whereas if you put them in different containers, each will retain their freshness for a lot longer. Is this true, and if so, what makes it so? -- JackofOz (talk) 22:57, 10 December 2007 (UTC)

Well, crackers tend to be very dry while cookies are moist. So putting them together, the crackers would absorb some of the water given off by the cookies, making the crackers get soggy. I don't see how it would affect cookies much, though. -- MacAddct  1984 ^{(talk &#149; contribs)} 23:21, 10 December 2007 (UTC)

If anything I would presume they would dry out Nil Einne (talk) 11:38, 11 December 2007 (UTC)

OK, so the crackers may go soggy and the biscuits may dry out. In time, they'd approach a sort of equilibrium, I guess. That makes more sense than what I was told (or thought I was told, to be charitable). Thanks for the enlightenment. -- JackofOz (talk) 13:59, 11 December 2007 (UTC)

Being salty - it makes sense that the crackers would absorb water if there is some floating around in the container because they'd be rather strongly hygroscopic. But I wonder if the somewhat oily nature of the crackers is what is messing up the biscuits? We should perhaps be a little more precise with our language here: In the USA, the things that are called 'cookies' are often made deliberately soft - the things that the Brits and Australians call 'biscuits' are only the harder, crunchier types (think 'Oreos') - so they are also pretty dry. The things Americans call 'biscuits' are a totally different thing altogether (more like bread). I find it hard to believe that there is enough water in a sweet biscuit to make anything soggy. An American-style soft choc-chip cookie though - that could easily be moist enough to do it...but then it's SUPPOSED to be soft - so this complaint wouldn't apply. I could believe that mixing soft cookies with crackers would make the crackers soggy and the cookies go excessively hard though. Humectant is an interesting article in this context. SteveBaker (talk) 14:22, 11 December 2007 (UTC)

related (sort of) Cake/biscuit tax conundrum. DuncanHill (talk) 14:25, 11 December 2007 (UTC)

CIDP -- referrence to the Minnesota Quality Pork Processors

I looked at the three references regarding this interesting subject, one as recent as 12-8-2007. I do not see any reference that any of the employees were recovering. The articles only referred to those who were suffering from CIDP.

As I am a physician and have treated people with CIDP (etiology not yet known but I don't they involved brain matter because that's a pet hobby with me), I wanted to see any documentation of these employees' recovery. I did not find one.

Whoever added that little "now you know the rest", please tell me your source. This is a very important subject for me. —Preceding unsigned comment added by Borderbumble (talk • contribs) 23:10, 10 December 2007 (UTC)

The chances that you would reach the editor who made that change via the Reference Desk are rather slim. In searching the CIDP article's history page, it appears that User:Saudade7 first added the information on 4 December. You can ask him about it using his talk page. --LarryMac | Talk 23:30, 10 December 2007 (UTC)

By magical chance I am here! Yes, I listed those articles. At the time of my listing them one of them said that all but two of the people had recovered. I got one or two of the articles from Yahoo News which I have found in the past to edit reports without acknowledging the change. In general this has been due to grievous grammatical issues with the article. By all means, if you find another article that claims that no one is recovering, and if the articles I provide no longer claim that people have recovered, change / edit the story! As a matter of fact, I think stories are more interesting the more apocalyptic they sound! (although I am not religious, waiting for an actual apocalypse, or wanting people to be sick). But that's what the stories said at the time I accessed them and I tried to be NPOV. Best, Saudade7 03:56, 11 December 2007 (UTC)

Update: I left a message for Borderbumble on his/her talk page. Saudade7 04:09, 11 December 2007 (UTC)

Licky fingers & placky bags

Why or how (or why and how) does licking the tips of one's fingers make it easier to seperate and open plastic bags? DuncanHill (talk) 23:31, 10 December 2007 (UTC)

It works for book pages too. Maybe because by licking your fingers you are making them slightly sticky with your saliva, which gives you friction and allows you to grip the edges of the bag or book page. 70.171.229.76 (talk) 23:57, 10 December 2007 (UTC)

I have never needed to do it for books (I must say, if I found anyone using spittle-covered fingers to turn the pages of my books, I'd tear their arms off!). I've also only needed to do it with plastic bags comparitively recently - say in the last year or so. DuncanHill (talk) 01:44, 11 December 2007 (UTC)

If your finger tips are very dry they don't have good grip. Some people will have drier finger tips than others and won't need to lick them.Shniken1 (talk) 01:48, 11 December 2007 (UTC)

At post offices in Australia, the workers are supplied with a damp sponge to use, presumably as it's more hygienic. Confusing Manifestation(Say hi!) 02:57, 11 December 2007 (UTC)

OT but saliva does contain antibacterial agents, so might perhaps be more hygenic than a damp sponge that's had various people's fingers in it??-Shantavira|^{feed me} 10:01, 11 December 2007 (UTC)

Well that depends. Presuming you have good hygenie and don't go putting your unwashed fingers into your mouth or onto your face then probably not. Besides that, if you do it right you barely touch the sponge. The point is to wet the stamp or the envelope flap directly not to use your fingers. In NZ, very often they have wet rollers as opposed to sponges so it's easier to wet envelope flaps. Edit: um sorry didn't read this properly. I thought we were talking about wetting stamps or envelopes flaps hence the post office comment. However I still think a sponge will usually be more hygenic for the first reason Nil Einne (talk) 11:34, 11 December 2007 (UTC)

But consider the murder method in The Name of the Rose / The Name of the Rose (film)...

Atlant (talk) 13:28, 11 December 2007 (UTC)

With new plastic bags in which merchandise is placed at a store, the manufacturing process leaves the bags with the opening tightly sealed . Apparently the cutting apart of the bags at the factory seals the plastic together, so that if you try to separate the edges with dry fingers, the adhesion of plastic to plastic is far greater than that of the fingers to the plastic. When the fingertips are moistened, the friction seems to increase allowing the bag to be opened. The sticking together of the plastic may be in part because the manufacturing process actually seals the plastic together (unintentionally) due to the compression, or perhaps to heat from friction. Another factor may be atmospheric pressure, with an absence of air between the tightly adjacent plastic. Bags which have been between rollers to give them a textured surface adhere together less. A third factor may be static electric attraction between the plastic surfaces, for whatever reason. Physics handbooks like the CRC handbook give coefficients of friction for many combinations of materials (diamond on ice has very low friction). Is there a reference anywhere for the friction of human finger on plastic bag material, dry and moist? Licking the fingers is highly inadvisable. A sponge is effective and sanitary. Edison (talk) 17:02, 11 December 2007 (UTC)

A sponge used by hundreds of other shoppers? Some of whom will have personal hygiene problems? Really? DuncanHill (talk) 17:06, 11 December 2007 (UTC)

I did not make clear whose use of the sponge I was advocating. A "personal sponge" is advisable for any store personnel who must open bags, like clerks/baggers/cashiers. I would not recommend sharing. If a stickypad (equivalent to a loop of masking tape) were provided for shoppers the bags would be easy to open. Edison (talk) 18:25, 12 December 2007 (UTC)

This was discussed on the ABC Online Forum. It seems to be due to a "liquid bridge", which is due to the adhesion and cohesion of water, which are due to the polar nature of the water molecule. Presumably this force, though useful for opening plastic bags, is not as strong as the friction between rubber and pavement, which is why water makes roads more slippery. --Heron (talk) 20:56, 12 December 2007 (UTC)

December 11

How can I dilute perfume?

I have a small quantity of perfume, which I want to dilute. (I got a nifty bottle to put it in, but it doesn't fill it up.) Presumably just using water is a poor idea. I don't really have access to lab ethanol, which would be my first choice; the isopropanol they sell in the store is thirty percent water by volume. Do I need to go to a lab? Should I get a bottle of Everclear? grendel|khan 04:23, 11 December 2007 (UTC)

Perfume#Concentration_levels says ethanol or ethanol and water or jojoba, fractionated coconut oil or wax. The precise percentages for various kinds of perfume are listed there too. SteveBaker (talk) 04:34, 11 December 2007 (UTC)

I'm not sure I'd want to use isopropanol, but if one did want to use it, one can get pretty-much anhydrous isopropanol in the form of gas dryer, sold at your local auto parts store. Be sure to get the iso kind and not the methanol kind. Our article claims Dry gas brand actually is ethanol, but I've never confirmed that, and who knows what denaturing agents have been added?

Atlant (talk) 13:35, 11 December 2007 (UTC)

How about Vodka? That ought to be pretty close to ethanol+water - and the cheap stuff doesn't smell of much. SteveBaker (talk) 14:10, 11 December 2007 (UTC)

I would caution against using isopropanol. For me, at least, isopropanol (even lab-grade pure stuff) has a very distinctive, pungent smell - it may make the perfume smell "off". (Although how long it would take for the isopropanol smell to dissipate after application, I don't know.) Whatever you do, don't use n-propanol or butanol - a colleague of mine got sick everytime she smelled n-propanol. -- 18:44, 11 December 2007 (UTC) —Preceding unsigned comment added by 128.104.112.64 (talk)

Assuming you are going to use the perfume why dilute it? You'll only empty the bottle using it leaving you in the same situation. Also it may be stating the obious but the best thing to use is more of the same perfume. However you if it is expensive I can see why this is not an option. Thomashauk (talk) 22:04, 11 December 2007 (UTC)

Magical keycard

The door to my old lab was unlocked by waving a keycard in front of what I could only describe as an anonymous blue box with an LED to let you know your card worked. The keycard itself was a flimsy little piece of plastic with a barcode printed on it. There didn't seem to be anything on the card scanner other than the LED, and certainly nothing that resembled a typical barcode scanner. So how does it work? Someguy1221 (talk) 11:58, 11 December 2007 (UTC)

The card probably contained an RFID chip. -- Coneslayer (talk) 12:09, 11 December 2007 (UTC)

Yes. For simple systems the chip just reports a number (the number printed on the barcode); for more advanced (and secure) systems the chip has some brains and does a proper cryptographic challenge-response exchange with the reader (this is more secure because it prevents card cloning and replay attacks). The reader is mostly a dumb radio-relay box which relays between the RFID and a PC somewhere in the building (over a wiring system like ethernet or LonWorks). -- Finlay McWalter | Talk 12:17, 11 December 2007 (UTC)

Yes, the badge you're describing is almost-certainly an RFID-based badge. But for completeness, I'll note that an earlier system (e.g., the "NCS" card) used a badge that you slid through a reader; I'm pretty certain this used Wiegand wires. You may also want to see our Access badge, Common Access Card, ID Card, Keycard, Proximity card, Swipe card, and Wiegand interface articles. (Maybe we need to do some merging?)

Atlant (talk) 13:42, 11 December 2007 (UTC)

I used a friend's RFID reader to try to see whether the keycards we use at work use RFID - and it didn't produce a response - so I doubt they are standard RFID chips. SteveBaker (talk) 14:07, 11 December 2007 (UTC)

What's a "standard RFID" chip? This stuff isn't all that well standardised yet; you might do better with a signal generator and a spectrum analyzer.

Atlant (talk) 17:42, 11 December 2007 (UTC)

Biology Mark Scheme

Can anyone tell me where the mark scheme for the 2006 January, Biology 2801 AS mark Scheme (OCR) is? and why it can't be found?

Thanks —Preceding unsigned comment added by 213.106.248.77 (talk) 12:34, 11 December 2007 (UTC)

I can add only that this user is talking about AS levels in the United Kingdom (I think). Don't know where you find the "mark scheme" (do you mean the full course specification or the coursework mark scheme?). We had it provided by our teachers. --Seans Potato Business 12:44, 11 December 2007 (UTC)

My guess would be that they're doing a past paper from last January to help revise, and they'd like the mark scheme to check their answers (and possibly improve their knowledge of how the questions are marked). Skittle (talk) 17:13, 11 December 2007 (UTC)

I guess you're right (my eyes skipped over January). We got those from our teachers, too... --Seans Potato Business 17:37, 11 December 2007 (UTC)

Hollow Earth theory and why we can't drill deeper than 15 miles into earth

Sorry if this has been asked before, but even if it has it's good to review...
I've read the article Hollow Earth and it mentions that the deepest that man has dug into the earth is 15 miles. Why haven't we or why can't we drill deeper? And I take it this is 15 miles below sea level.
Secondly the article fails to explain exactly why we can dispel the idea that the earth might be hollow or have deep cavernous enclaves where it may be possible to survive. As an encyclopedia I think it should, encyclopedically expound on why modern science can so easily rule out any such possibility.
What's also interesting is that surely satelites and other technology could relatively easily check for openings at the poles.
And finally, why does the wikiword digging resolve to Death of a Naturalist? Surely we have an article on digging? Found it: excavation. But still.
Thanks Rfwoolf (talk) 13:33, 11 December 2007 (UTC)

OT, but... I changed the redirect to Excavation. What links here doesn't support the redirect to Death of a Naturalist. --Elliskev 13:52, 11 December 2007 (UTC)

The article Mohole may be of interest. DuncanHill (talk) 13:36, 11 December 2007 (UTC)

I would guess that the propagation characteristics of seismic waves (from earthquakes and/or nuclear bomb tests) and the precise mapping of the earth's gravitational field would help to rule out hollow earth theories. -- Coneslayer (talk) 13:38, 11 December 2007 (UTC)

(ec)We can be confident that the Earth does not contain significant voids by observing the propagation of seismic waves - places of different density cause the wave to refract and diffract. By observing this we've obtained a reasonable (to a first order) approximation of the structure of the Earth. That's a crude tool, so we can't entirely rule out their being small voids, but there's no evidence of them. You'll see stuff like this, which talk about an "ocean" under China - but they're being somewhat poetic in calling it that - it's "big area of wet rock" really: the researcher is quoted in that article saysing "It would still look like solid rock ... You would have to put it in the lab to find the water in it." -- Finlay McWalter | Talk 13:45, 11 December 2007 (UTC)

But if the Earth isn't hollow, then where do those weird glowing guys from the Adventures of Superman come from?

Atlant (talk) 13:52, 11 December 2007 (UTC)

Lots of reasons:

1. Certainly we can time the arrival of seismic waves from a distant event as they arrive at different seismographs around the world. We can tell from when they arrive and how attenuated they are the speed and distance travelled. This means we can know for sure that the waves didn't travel around the surface of the earth in a thin shell but instead took a short cut through the center of the earth. From the way they are attenuated and diffracted, we can tell the density of the material through which they travelled - and therefore that they didn't travel through a few thousand miles of air (or whatever the hollow earth is supposed to be filled with). It's completely conclusive proof that the earth is solid with a molten iron core.
2. Think about what it would take to prevent rocks on the inside of the sphere from falling off and accumulating at the center of the earth...gradually filling in the middle and eventually resulting in total collapse to a much smaller planet.
3. We've figured out that the earth/moon system was formed from collision of two smaller planets early in earth's history. There is no reasonable model for how anything hollow could arise from such a thing.
4. In order for the earth to have as much gravity as the earth actually does have, it either has to be solid - or somewhere below the surface there would have to be a layer of extremely dense material - much denser than any material we know of - except perhaps neutron-star material - and that wouldn't be able to hold together under as little gravity as the earth actually has.
5. If there were no large mass of spinning iron at the center of the earth, how would we explain the earth's magnetic field?
6. Where does all the lava come from when a volcano erupts?

So this lame-assed theory is busted, busted, busted and busted! It's hard to imagine how anyone could ever have thought it was true.

Drilling that deep is tough because the amount of friction on the walls of the drill tube gets larger and larger the deeper you go and eventually, the top end of the tube can't transmit that much power without crumpling. Conventional drilling gear can't go that deep - so you need entirely custom built gear - it's not cheap and research dollars are limited! Of course we don't have to drill down there to understand what's going on that deep. We have these (slightly inconvenient) things called volcanoes that provide us with plenty of material from deeper than 15 miles that we can study.

SteveBaker (talk) 14:02, 11 December 2007 (UTC)

Interesting. Obviously there's magma if you go deep enough.. 64.236.121.129 (talk) 14:07, 11 December 2007 (UTC)

No, magma (i.e. liquid rock) forms at high temperatures and low pressures. At high temperatures and high pressures, rock is a plastic solid (think modeling clay or cheese). It will deform over time as a result of stress, but nearly all of the Earth's crust and mantle is a solid. Dragons flight (talk) 14:24, 11 December 2007 (UTC)

The article on Magma says that it can be found beneath the earth's crust. If you drill deep enough, logically, you'll come across it. Especially if you hit a Magma chamber. 64.236.121.129 (talk) 14:48, 11 December 2007 (UTC)

No, nearly all magma forms at local hot spots within a few km of the surface, i.e. hot and relatively low pressure. The bulk is solid and at many locations drilling straight down need never encounter magma. Dragons flight (talk) 14:51, 11 December 2007 (UTC)

No offense, but the article says magma can be found beneath the earth's crust, and I trust that over you. 64.236.121.129 (talk) 16:10, 11 December 2007 (UTC)

They're both right. The earth's crust is very thin in places. Friday (talk) 16:15, 11 December 2007 (UTC)

The article does not imply that magma is present everywhere beneath the earth's crust, and it certainly is not. Dragons flight is correct. Cheers Geologyguy (talk) 16:19, 11 December 2007 (UTC)

The mantle is a rheid, a form of viscous solid. I've clarified this in magma. Magma is molten rock found beneath the Earth surface, but it is certainly not the case that molten rock occurs everywhere under the crust or even in most places. Dragons flight (talk) 16:28, 11 December 2007 (UTC)

Thanks for the answers SteveBaker and all, but I'd still like them to dig mega-deep. What for? For the hell of it, I don't know. I did come across Chikyu Hakken which seems to be the latest attempt to drill deep - but doesn't even intend to beat the record. I mean, 12 miles, that's not even that deep! Furthermore, some of the theories (crackpost or otherwise) don't propose an entirely hollow earth, just "hollow parts". I suppose cosmologically they know how the earth was formed and they ruled out any hollowness up to a certain point. But maybe not Rfwoolf (talk) 14:29, 11 December 2007 (UTC)

"For the hell of it" is not usually persuasive to people for sponsoring extremely expensive scientific endeavors. Anyway, you're arguing a sort of "hollow earth of the gaps" now, retreating to anything that you don't think for sure has been discounted. In the end you're going to be arguing that caves are really all the hollow earth people really mean! --24.147.86.187 (talk) 15:46, 11 December 2007 (UTC)

"you're arguing a sort of 'hollow earth of the graps' now" - I am not arguing anything. Please read the question, and I originally asked "deep cavernous enclaves". If you have no interest in hypothetical, philosophical or scientific questions then you won't appreciate most of the questions on the reference desk. You'll also notice that "for the hell of it" has a pun. Tee hee Rfwoolf (talk) 20:54, 11 December 2007 (UTC)

A solid earth with "hollow parts" would mean...caves? Well, yes - there are caves - I've even been inside some of them. Does that count as a "hollow earth"? If so, it's a rather less exciting thing than I'd imagined! Of course beyond a certain depth, you can't even have caves because the air inside would start to act like a bubble that would float upwards...and beyond an even deeper depth, the air inside would liquify under the pressure - so no more caves beyond that. (I love "hollow earth of the gaps" btw, very poetic!) SteveBaker (talk) 18:21, 11 December 2007 (UTC)

I think the closest we'll get to a hollow earth is a hypothetical dyson sphere.

Actually, the hole by Chikyu Hakken aims to be 7 km (4.3 mi) deep (although they're already starting below sea level). The Kola Superdeep Borehole in Russia was and is the biggest at 12.2 km (7.6 mi) -- MacAddct  1984 ^{(talk &#149; contribs)} 16:32, 11 December 2007 (UTC)

But Dyson spheres can't work - for precisely the same reason that hollow planets can't. Even if you spin them really fast - there is no way to stop them collapsing in on themselves as a result of their own gravitation. SteveBaker (talk) 18:21, 11 December 2007 (UTC)

While there are lots of problems with constructing a Dyson sphere or hollow planet, I don't think rigidity against self-gravity is one of them. An Earth-sized metal shell 3m thick would have only a few millionths the mass of the actual planet. Given that, I think traditional construction materials/methods have enough structural rigidity to resist the much reduced gravity. Dragons flight (talk) 18:40, 11 December 2007 (UTC)

A Dyson sphere is meant to enclose a star (like the sun), so it should be (about) the size of the earth's orbit, not just the size of the earth. -- Coneslayer (talk) 19:00, 11 December 2007 (UTC)

I know, hence the "or" above. Since the questions is about hollow planets, I focused there. Dragons flight (talk) 19:05, 11 December 2007 (UTC)

So if we had a 3cm thick shell the size of the earth - and we spin it so that the equator was supported by centrifugal force against the rather feeble gravity. You could imagine the problem as having two self-supporting hemispheres - each 6300 km in diameter - each supported against their weight in this new, low gravity. The volume of this new earth (assuming the interior is filled with a vacuum) is only about 1.5x10¹³ cubic meters - and if it were made of steel (with a density of 8000kg/m³), it would weigh about 1.2x10¹⁷ kg. The real earth weighs 6x10²⁴kg - so gravity is about five-millionths of a g. So the question is - can an uninterrupted 12 thousand kilometer span of 3cm thick steel support a weight of about 3 million kilograms? Around the equator, you'd have a cross-sectional area of about a million square meters - so I guess there is only about 3kg per square meter of pressure on our shell...so yeah - I guess it might hold up. The trouble is that we know our shell is at least 15km thick because we've drilled down that far. That makes the gravitational forces 500,000 times greater - so we have a more respectible 1/10th g of gravity and each square meter of crust at the equator has to withstand 1.5 million kilograms per square meter of pressure - and the whole thing collapses like a popped balloon. SteveBaker (talk) 06:24, 12 December 2007 (UTC)

I had the pleasure of speaking with a somewhat crazy planetary scientist a few weeks ago (David J. Stevenson), who explained to me that once you have a really deep well to near the mantle, drilling further is very easy. All you have to do is pour several million tons of molten lead into the well, and it will just push its way down through the mantle and into the core, making a nice lead filled well the whole way down (allegedly this wouldn't cost more than the GDP of the United States for one year, so let's do it!). Of course, then you need equipment or probes that can operate in and transmit back from a liquid lead environment, but that's an "engineering problem" so who cares (or use acoustic waves, as in his original proposal which I just found). Someguy1221 (talk) 21:59, 11 December 2007 (UTC)

Just for fun I submit for your horror and

analysis, part of a film that scared the

"holly bejesus" out of me as a kid thinking

about deep holes and what's in 'em:

Rod Serling's "Encounter with the Unknown Part I

Rod Serling's "Encounter with the Unknown Part II

Rod Serling's "Encounter with the Unknown Part III

Saudade7 23:10, 11 December 2007 (UTC)

What species of Lotus Flower is this?

What kind of Lotus is this that Salome is holding in her hand? Thanks in Advance. Saudade7 14:21, 11 December 2007 (UTC)

It doesn't look like a lotus at all. It looks like some kind of lily and may simply be from the imagination of the artist. In any case there is not enough detail in the image you have linked. "Lotus" in English refers to Nelumbo nucifera, which is usually pink, although there are white varieties. The only other species of lotus is the American yellow lotus, Nelumbo lutea. Why do you think it is a lotus?--Eriastrum (talk) 18:59, 11 December 2007 (UTC)

Hey, sorry that image was so bad, it is the only one online. It is claimed to be a lotus but all the critics who have written on the painting by Moreau who mention the flower (1880s to present). Many claim it to be an Egyptian or Indian lotus. I looked at all the lotus pictures I could, and when I could find none that matched I came here. It doesn't matter now. It was for an article that I just submitted sans-flower reference, alas. Thanks though Eriastrum! Saudade7 22:52, 11 December 2007 (UTC)

Enzyme Turnover

This is from a biochem test I am studying for. The original question was longer and I am paraphrasing so you arent doing my homework, just helping me double check my answer and logic. In an enzyme with 4 subunits with its unit of activity(amount enzyme hydrolyzes) being 4 micromoles of ester/minute and Vmax is 1400 units per mg of enzyme. What are the moles of substrate hydrolyzed per second per mg of enzyme at saturating substrate levels. Then determine the turnover rate for this enzyme. Saturing substrate levels implies we are using the Vmax which is a rate of turnover. Product/second. The 4 subunit also implies we are dividing the units of activity by 4. Could someone please connect the dots for me?68.41.111.119 (talk) 16:00, 11 December 2007 (UTC)

Just a hint - look at the units of what you have and what you want, and then puzzle it out with something like the factor-label method (or dimensional analysis). (Be careful to make the distinction between things like "micromoles of product" and "micromoles of protein".) -- 18:53, 11 December 2007 (UTC) —Preceding unsigned comment added by 128.104.112.64 (talk)

Can blackholes produce antimatter?

^Topic 64.236.121.129 (talk) 16:07, 11 December 2007 (UTC)

If Hawking radiation occurs, then either of a particle-antiparticle pair can escape a black hole. I'm not sure if this is what you've got in mind when you say "produce", though. — Lomn 16:29, 11 December 2007 (UTC)

Yes, that counts. 64.236.121.129 (talk) 17:09, 11 December 2007 (UTC)

Christmas trees

How many needles are on the average 8 foot tall blue spruce Christmas tree208.54.7.184 (talk) 16:45, 11 December 2007 (UTC)

Assuming the needles on a Christmas tree are close to the surface the number of needles will be approximately proportional to the area of a cone of the same size (dicounting the bottom). Just count the number of needles in a unit square and multiply by the are and that will be close enough.

More accurate would be to consider the volume in which there are needles which will be the volume of a cone the same size of the tree - the volume of the cone in which there are not needles multiplied by the number of needles per unit volume.

Finding all this is an exercise for the reader. Thomashauk (talk) 21:51, 11 December 2007 (UTC)

I don't know about your Christmas tree, but the ones I've seen are not anything close to "a cone surface of needles". Instead there are lots of concave regions that seem to have at least as much surface as the full-tree cone. That is, it looks like it has deep pockets, where the sides of the pockets (the "depth" dimension) is larger than the bottom (the cross-section parallel to the tree cone). Fractal surfaces are fun. DMacks (talk) 03:01, 12 December 2007 (UTC)

It's much more likely to be proportional to the volume of a cone. But unless someone is going to actually go and count the number of needles on (say) a 10cm section of branch - then figure out the average total branch length within a particular volume - then go on to figure the volume of an 8 foot tree - we aren't likely to be able to figure this out. Knowing what the answer is proportional to is really not too relevent at this stage! Since our tree at home is plastic...that's not really good research material!

Well, let's shoot for some sort of a number at least. On the basis of the detailed photo at right, there appears to be about 200 needles on one 15cm length of branch. So lets go with 13 needles per centimeter of branch. Estimating the branch length per unit volume is tougher without an actual tree to measure - but on the very rough basis of the second photo at right, I'd say that there is probably about 5 branches going through every 10cm x 10cm x 10cm cube of tree volume - which is half a meter of branch length per liter of tree. Which gives us about 0.6 million needles per cubic meter. The cone of this tree appears to have a diameter roughly equal to it's height - but I doubt that's true for an 8' tree - so I'm going to arbitarily guess that our 8' tree is really 2 meters tall (the bottom part doesn't have any branches) with a base radius of maybe 0.75 meters. The volume of a cone is pi.h.r²/3 which means that we have about 1.2 cubic meters of branches...about three quarters of million needles altogether. There are some horrible guesstimates along the way to this number - so I'm going to stick a healthy error bar on that and say "Anywhere between 200,000 and 2 million needles depending on the species and how many there are on your living room carpet.". Feel free to shoot down that number - but until someone actually goes and measures a real tree for us, that's the best answer you're going to get. SteveBaker (talk) 05:50, 12 December 2007 (UTC)

Eat it! Fruit rinds

I would like to know if there's a pleasant, healthy way to acquire the nutrition present in orange rinds that would otherwise go to waste. Candying them seems neither healthy nor efficient (wasted sugar, unless you can keep it somewhere for later reuse) while making tea from them includes all the fun of the pesticides. Is the best option to boil (to cleanse) them and then eat them after that? --Seans Potato Business 17:33, 11 December 2007 (UTC)

How about use them as compost to grow something else that you can then eat? Personally that seems a lot easier than trying to find ways to eat something which is not terribly good tasting. --24.147.86.187 (talk) 19:07, 11 December 2007 (UTC)

I just did a cursory search of our medical journals to see if there is anything on using orange peels in human diets. All that came up was a few studies on using orange peels to remove cadmium ions from aqueous solutions. I have to assume that by "orange peels" it is referring to the rind of the fruit we call an orange and not some weird medical term for some sort of lab device. So, if you have a lot of aqueous solutions polluted with cadmium ions, you can use your orange peels to remove them. -- kainaw™ 19:14, 11 December 2007 (UTC)

Well orange peel is used to make orange zest, marmalade, orange oil and pectin. You can eat these if sufficiently diluted. Would you rather extract the protein and vitamins? Graeme Bartlett (talk) 20:11, 11 December 2007 (UTC)

And underneath the thin zest is the white "pith", which is bitter and unpleasant to eat. -- Coneslayer (talk) 20:26, 11 December 2007 (UTC)

But full of nutrients, I hear. --Seans Potato Business 20:30, 11 December 2007 (UTC)

From which sources? I hear such claims all too often... Icek (talk) 22:38, 11 December 2007 (UTC)

Sources? Well, let's start with Wikipedia to begin with. The white pith that lies between the outer rind and inner fruit of oranges contains massive amounts of the bioflavonoids hesperidin, quercetin, rutin (a glycoside of quercetin), and tangeritin. Bioflavonoids have been clinically proven to be very important for many reasons, including the treatment of allergens, viruses, and carcinogens, and in the prevention of heart disease and cancer. They also greatly help the human body assimilate vitamin C, so that if you eat an orange and strip off all the pith, you will be impeding your body's ability to utilize all of the vitamin C that is in the rest of the fruit. This is why it is better to drink orange juice that contains pulp - without the pulp the orange juice is more or less just flavored, sweetened water, as far as the dietary benefits it can give you. The pulp (or pith) is what allows your body to absorb the vitamin C in the juice. -- Saukkomies 14:09, 12 December 2007 (UTC)

Yes, I ask for sources, not additional claims. And by the way, ascorbic acid is absorbed equally well whether it is in oranges, in orange juice or in pure form. Icek (talk) 22:49, 12 December 2007 (UTC)

(resetting margin)Well, Icek, it appears we're in the game of trumping each other's ace. I looked at the full text of the citation you gave for The Journal of Nutrition article published in 1993, which being 14 years old is sort of pushing the envelope in a field such as nutritional science, but hey, I'm impressed frankly that someone came up with even that! So my hat's off to you, friend! So yes, I realized I was guilty of posting a claim without supportive evidence, and it comes to mind that I should know better than that, but hey, sometimes I walk into walls and put my shirt on inside out, and well, sorry about that. So to rectify my lack of sense, I dug around a bit and came up with an article from The Journal of Biological Chemistry, dated 2002 that directly addresses the issue.

So to compare what we've come up with so far, you asked to see sources for the claim that Seans made about orange rind pith being full of nutrients. I believe I addressed this by providing several sources in my post above, most notably a wiki article that discusses this. I then made a claim about how the bioflavonoids in orange rind pith aid the absorption of vitamin C in the human body, but did not provide sources. You then apparently neglected to notice that I provided sources, but in your frank manner pointed out that I'd neglected to source my own new claim. I then went out and found a source that discusses this, and to my surprise I discover that the study that this article discusses actually demonstrates that both of our claims are false! Namely, that bioflavonoids do indeed have an effect on the absorption of vitamin c (ascorbic acid) which contradicts the article you cited, but then it goes on to show that this effect is actually contrary to what I was claiming - that bioflavonoids actually inhibit the absorption of ascorbic acid! So we're both busted!

Allow me to present some brief excerpts (which since they are merely short quotes are supported by copyright law to include here) that provide the main thesis of each of our articles regarding this subject. Note that when I insert space in the quote (by using three dots ...), that I'm only cutting out references to other articles or studies, not content. First from the article you cited from The Journal of Nutrition:

"Early reports have suggested little difference in ascorbic acid bioavailability from fruits or vegetables compared with synthetic ascorbic acid...Small numbers of subjects and insensitive techniques may, however, have obscured differences in these studies. Although few studies have assessed the impact of such factors as the fiber or mineral content of a meal or the presence or absence of other substances including bioflavonoids...on vitamin C absorption in vivo, the bioavailability of other substances, such as carotenoids, does seem to be affected by dietary factors."

So what this article is saying is that --- they don't know. If you go back and examine it, you'll pick that up in the article. It does say that ascorbic acid seems to be absorbed equally well whether it's being ingested in oranges, orange juice or in pure form, which is what you said, but they then go on to state that not enough studies have been done - not enough data have been gathered as of the date of that article (1993) to firmly state whether the presence of bioflanonoids has an effect on the absorption of ascorbic acid. To report that this article firmly states that ascorbic acid is NOT effected by the presence of bioflavonoids would, therefore, be inaccurate.

Now for my article, which appeared 9 years after yours in The Journal of Biological Chemistry. Here's the citation. It's entitled "Flavonoid inhibition of sodium-dependent vitamin C transporter 1 (SVCT1) and glucose transporter isoform 2 (GLUT2), intestinal transporters for vitamin C and Glucose." Here's the excerpt:

"We propose that novel functions of flavonoids may be to distribute nutrient absorption throughout the small intestine or to frankly inhibit absorption. Flavonoids in vivo might possibly delay or inhibit ascorbate and glucose absorption by more than one pathway... The data in this paper suggest that flavonoids could inhibit transport of ascorbate and glucose from the intestinal lumen into cells."

Not to put all my eggs in one basket, I went ahead and dug around some more, and came up with the following article in The Journal of Nutrition appearing in May of 2000 that supports the same claim as the one I cited above that bioflavonoids suppress the absorption of ascorbic acid.

In my digging, I came across numerous articles that provided hard substantial evidence showing that bioflavonoids (again, that are found a lot in orange pith) have incredible benefits for all manner of things. Thus, at least we can state with some authority that eating orange rind pith is good for you... Saukkomies 23:34, 12 December 2007 (UTC)

Thank you for the interesting and informative answer. What I dispute is not that the flavonoids are contained in the white pith, but that they are nutrients - they do not seem to be essential for human survival. Seans' claim that the pith is "full of nutrients" is misleading. Sugar is "full of nutrients" (about 100%); in comparison, white orange pith is devoid of nutrients. Of course Seans probably wanted to say something different, but I don't know exactly what.

Showing that some flavonoids from the pith are beneficial in some circumstances (if you were digging for something else, I guess you didn't read these articles very carefully; neither did I, but I'm hesitant to conclude too much only because there is a large amount of studies without knowing about their quality and exact nature) does not show that the pith itself is beneficial; it may contain harmful substances as well. What causes its bitter taste? Natural poisonous substances are (for obvious evolutionary reasons) often bitter, but of course that doesn't prove anything. Icek (talk) 07:45, 13 December 2007 (UTC)

Certified organic oranges shouldn't have any pesticide on them. Also, try throwing some orange zest into a stirfry. Vranak (talk) 20:38, 11 December 2007 (UTC)

Just FYI, citrus fruits are often (in addition to being treated with pesticides while on the tree) treated with a certain wax after harvest to prevent mold from growing. I often see the label saying that the wax contains 2-Phenylphenol, thiabendazole and imazalil. Icek (talk) 22:36, 11 December 2007 (UTC)

Gravitational effect of an ellipsoid

I want to create a simulation of how satellites orbit around earth. I've done this in the past with perfectly uniform spheres or spheres consisting of concentric regions of varying density as both of these can be approximated by a point mass (assume Newtonian mechanics). I do this numerically by taking very small time steps and adding an acceleration on the satellite which resulted from the gravity at its current location.

I know that earth is not a perfect sphere and there are some good Reference ellipsoids. First, do these only offer an approximation for the shape of earth's surface or are they also usable approximations for orbital calculations? Secondly, is there an analytical solution or even a good numerical one for calculating acceleration at a 3D coordinate relative to such an ellipsoid? I'm guessing they can't as easily be reduced as a sphere to something elementary.

Why I'm so interested in the ellipsoid approximation is to see if I can simulate (for fun) the effects of orbital precession. It might be that I need to use an even more complex geoid approximation or relativity but I'm hoping not as I only have a moderately powerful CPU. 41.243.33.25 (talk) 20:04, 11 December 2007 (UTC) Eon Zuurmond

It depends on the orbit, for an orbit around the equator there would be no difference, for other orbits however I am unsure.

But there have been several investigations into this (as you would imagine) and it seems that the local gravity is more important which is caused by differing decities of material in different parts of the earth not just in concentric regions. Thomashauk (talk) 21:57, 11 December 2007 (UTC)

The technical approach is to use a multipole expansion to describe the gravitational potential function to high accuracy from which one can then extract the relevant forces as the gradient of that potential. The low order terms in the multipole can be thought of as ellipsoidal corrections, and subsequent terms build in every more detailed structure. The relevant multipole coefficients have been measured to high accuracy and tables exists somewhere (NASA?). If you are interested in this approach, I'd suggest you google "multipole gravity", etc. Dragons flight (talk) 22:03, 11 December 2007 (UTC)

According to my satellite geodesy text, the derivatives from the multipole expansion are then substituted into the Lagrange perturbation equations, and integration would yield time dependent functions for the Keplerian elements. It's possible to do analytically, but "extremely laborious". The numeric methods are more accurate anyway as the analytic method uses truncated series expansions. Your simulation should result in not only precession, but rotation of the apsides in eccentric orbits.—eric 01:21, 12 December 2007 (UTC)

Cold Chill or Holy Shiver

I have been working on an article for Cold chill and was wondering if anyone could explain the physiology behind music or memories and such causing cold chills. --DatDoo (talk) 22:56, 11 December 2007 (UTC)

Sounds like an example of synesthesia. I would say this is just a miswiring of the brain such that one sense is misinterpreted as another (in this case music is interpreted as cold). StuRat (talk) 04:50, 12 December 2007 (UTC)

Do you know where I might get some sources on that?--DatDoo (talk) 05:11, 12 December 2007 (UTC)

See the further reading, references and external links sections for that article. StuRat (talk) 11:03, 12 December 2007 (UTC)

SNRIs/Anti-depressants

(Removed medical question - it is contrary to our policies to answer medical questions) SteveBaker (talk) 05:21, 12 December 2007 (UTC)

Cold confused with wet

Is there a reason why it's often hard to tell the difference between something being just cold rather than wet? I think I find it happening with clothing the most. I assume it's due to the fact that most wet things that we touch are also cold, so items that are just cold we assume there's wetness as well. --MacAddct  1984 ^{(talk &#149; contribs)} 23:54, 11 December 2007 (UTC)

Short answer, as far as I know, is that there is no such thing as a "wetness" receptor. Our brains figure out whether something is wet or not by combining different signals, one being cold. You could probably learn more by reading this and associated articles: Somatosensory system. (EhJJ) 02:04, 12 December 2007 (UTC)

Ah, I like that answer! That actually makes a lot of sense, I'll definitely have to look around more. -- MacAddct  1984 ^{(talk &#149; contribs)} 03:59, 12 December 2007 (UTC)

The human temperature sense is a bit weird. It's not really measuring the temperature per-se but the rate at which heat is being gained or lost through the skin. A chunk of wood feels warmer to the touch than a chunk of metal even if they are at the exact same temperature because the wood doesn't conduct the heat from your skin away as well as the metal does. Liquids feel especially cold because they contact your skin very closely - every little fold and wrinkle is in contact with the liquid - where when you touch a solid object, only a smaller part of the skin is actually in contact. With a dry powder, there are lots of air gaps between the solid particles - so again there is plenty of insulation preventing the heat from being conducted away. So that's the reason why wet things generally feel colder than dry things - even if they are really at the exact same temperature. SteveBaker (talk) 05:19, 12 December 2007 (UTC)

December 12

Amount of ohms and stereo speakers

Hello, I'm getting a new stereo and the speakers are 6 ohms (it's 400w, 200 per channel, 6 1/2 inch sub, 3-way bass reflex). A pretty smart guy told me that less ohms means less resistance and better response. I have some pretty small speakers here that are 3.2 ohm, how can they have better response than these high quality 6 ohm ones I'm getting? It seems like bigger speakers have more ohms, then how could my crappy little Audiovox speakers out-respond some top of the line ones with 6 ohms? Is more ohms bad? NIRVANA2764 (talk) 00:40, 12 December 2007 (UTC)

Ohms has no effect on sound or response. The only thing the ohms rating is for is to match the impedance. If you connect your 3.2-ohm speakers to an amplifier that wants 6-ohm speakers, you will probably blow out the amplifier. You can connect speakers with an ohms rating higher than 6 to an amplifier that wants 6 ohms, but the higher the ohms rating of the speakers, the less sound you'll get. This is for amps that don't run on vacuum tubes; that's a horse of a different color. By the way, a good rule of thumb is to get speakers with a power rating double that of the amp. Another good rule is to put most of your money into the speakers, and better speaker simply sound better—compare by ear. --Milkbreath (talk) 01:21, 12 December 2007 (UTC)

According to the impedance matching article, stereo amplifiers actually use impedance bridging (which is news to me). Also, I've used speakers with lower than recommended impedance before (on old equipment, so I wasn't that worried about damaging the equipment), and it worked OK. I don't remember if I've ever used speakers with half of the recommended impedance before, but I may have plugged two speakers into one speaker output at one time, and wouldn't this cut the total impedance in half? It seemed to work, but I wouldn't try it if you're not willing to fry your amplifier.

Also, if I recall correctly, most home audio equipment tends to be 8 ohms. I only remember seeing 6 ohms on smaller "shelf systems". Maybe larger speakers have higher impedance, in general. Philbert^2.71828 02:26, 12 December 2007 (UTC)

Speaker impedance used to matter back in the days of vacuum tube amplifiers, but it's practically meaningless nowadays. Nowadays, impedance only matters in the following two ways:

1. A given amp can drive more power into speakers with a lower impedance than speakers with a higher impedance. But a 200W amp can probably go plenty loud with speakers of any reasonable impedance.
2. There's usually some minimum impedance that a given amp will be happy driving, but it's usually quite, quite low. Go below that impedance and the amp will think that the output is shorted and will current-limit (which you'll hear as clipping). This usually matters the most if you try to drive multiple sets of speakers simultaneously; placed in parallel, the multiple speakers may end up presenting too-low an aggregate impedance to the amplifier.

I haven't worried about speaker impedences for decades.

Atlant (talk) 13:24, 12 December 2007 (UTC)

Benzoylecgonine levels

Is a level of 0.06 mg/l pleural fluid of Benzoylecgonine considered high? 99.251.194.41 (talk) 00:58, 12 December 2007 (UTC)

Do you mean high for a cocaine user or high for a non-user? Rockpocket 01:28, 12 December 2007 (UTC)

I mean high for an occasional user.My son was in an accident (fatal) and his remains showed this level. He told me he never did cocaine. Obviously that was false. I am wondering if he did a lot or this level shows "occasional" use only. — Preceding unsigned comment added by 99.251.194.41 (talk) 02:03, December 12, 2007 (UTC)

Based on [12] and related Google results, 0.06 mg/L is a low but significant number. For typical cocaine consumption amounts, it suggests use more than 12 hours prior to death but less than 60 hours. Dragons flight (talk) 02:35, 12 December 2007 (UTC)

Please accept our sympathies for your loss. As Dragons flight notes, assuming typical consumption amounts, the data you provide can some idea as to the last time your son took cocaine prior to the accident. However, with this data alone its not really possible to infer anything meaningful about frequency of use. The best source of this information would probably be your son's friends. Rockpocket 18:02, 12 December 2007 (UTC)

Thank you Rockport, and thank you both for your replies. My sons friends aren't saying anything. They are 5000k from us in north western Canada. (I am on the east coast) Until we get out there and actually talk to them I guess we are in the dark as to what really happened.. —Preceding unsigned comment added by 99.251.194.41 (talk) 01:52, 13 December 2007 (UTC)

Medicine

Do doctors use a lot of physics? Is it necessary to learn physics in order to get in medical school especially in new zealand? —Preceding unsigned comment added by 118.90.0.137 (talk) 02:35, 12 December 2007 (UTC)

No, and probably. I can't speak for NZ, but the equivalent of two semesters of college physics is required in the US. Dragons flight (talk) 02:38, 12 December 2007 (UTC)

I just remembered, medical school in the US is a post-collegiate program. Outside the US, many medical programs are post-secondary programs. In other words in those countries you enter a 6-8 year medical program instead of going to college, while in the US it is 4 year program beginning after college. Given that fundemental difference, the entry requirements are likely to depend on the structure of NZ medical school programs. Dragons flight (talk) 02:45, 12 December 2007 (UTC)

The amount of physics used, if any, depends heavily on the area of treatment that a doctor specializes in and the specific area of physics you are referring to. Both are extremely wide fields of study with a little overlap. -- kainaw™ 03:26, 12 December 2007 (UTC)

In practice, most doctors would not use much that we would recognize as 'pure physics' in their day-to-day work. Exceptions would include physicians in fields like radiation oncology and radiology, as well as certain branches of sports medicine, kinesiology, and the like. (Often doctors in these fields are supported by medical physicists: individuals with PhD rather than MD degrees who have intensive training in physics.) Some knowledge of physics is important (arguably, essential) to all doctors in order for them to be able to properly understand and interpret a wide range of diagnostic tests and physical maladies. I can't comment on the level of formal physics training required for doctors in Oz. TenOfAllTrades(talk) 04:06, 12 December 2007 (UTC)

Chemistry (gases)

I'm supposed to find out the volume of NH3 (g) produced from 200 L of H2 (g), and the gases are measured at 350C and 400 atm.

I tried the PV/T, and a couple of other methods, but none of my answers still don't match up. Someone please help. --Jeevies (talk) 02:44, 12 December 2007 (UTC)

Chemistry always happens in ratios of moles: find out how many moles of H₂ you have, and then how many moles of NH₃ that makes (write a balanced net ionic equation for the reaction). Then figure out the volume of ammonia that that number of moles is. Are you given the amount of N₂ also (and therefore have to figure out the moles of that, and then the limiting reagent)? DMacks (talk) 02:55, 12 December 2007 (UTC)

How do I get the moles? Apart from that all the info I got was N₂ + 3H₂ -> 2NH₃ --Jeevies (talk) 05:56, 12 December 2007 (UTC)

For a rough answer you do not need to know as each mole of gas takes up the same volume at a given pressure and tempreature. You can see that there is 1 and a half times as many moles of hydrogen as ammonia, so the volume also follows the same ratio. However still you are assuming that there is enough of the nitrogen, and that the reaction goes to completion, this will need to be checked out. Graeme Bartlett (talk) 05:57, 12 December 2007 (UTC)

Oh, thanks a lot! I thought I was going insane for a while there. --Jeevies (talk) 06:36, 12 December 2007 (UTC)

Orange Ice Cream

I was discussing orange ice cream with some friends. This delicious treat sounds like a great idea. But, two questions come to mind.

1. Would the orange's citric acid curdle the milk?
2. Follow-up - what techniques do commercial orange-ice-cream makers use to prevent milk from curdling when adding acidic flavorings?

Thanks! Nimur (talk) 05:08, 12 December 2007 (UTC)

It doesn't seem to be an issue. (Perhaps the other ingredients, like sugar, dilute the acidic effect?). There are lots and lots and lots of recipes for orange ice cream on the web, and they all seem to just mix the ingredients together. - Nunh-huh 05:14, 12 December 2007 (UTC)

I had this idea that the citric acid doesn't affect the milk so much. I've seen it added to yoghurt for example Rfwoolf (talk) 10:05, 12 December 2007 (UTC)

What about having an orange sorbet instead? Lanfear's Bane | t 13:03, 12 December 2007 (UTC)

I've eaten lemon ice cream so it's obviously possible to make citrus-flavoured ice creams.

Atlant (talk) 13:31, 12 December 2007 (UTC)

It would be an easy enough experiment to do. Now, I have some citric acid but I have no milk here to try it with... --BenBurch (talk) 16:42, 12 December 2007 (UTC)

Citrus ice creams may be flavored mostly with zest, oils, or extracts, instead of juice. -- Coneslayer (talk) 16:46, 12 December 2007 (UTC)

Frozen Desserts by Liddell & Weir contains a recipe for orange ice cream, using the zest and juice of 3 oranges. While I will not reproduce the recipe here, the liquids are about 250 ml orange juice, 125 ml milk, and 500 ml heavy cream. -- Coneslayer (talk) 03:00, 13 December 2007 (UTC)

Today's xkcd

In today's xkcd, what's the solution to the problem? My intuition says 0, since $R_{t}^{-1}=R_{1}^{-1}+R_{2}^{-1}...+R_{\infty }^{-1}$, which the right side will be infinite. Since ${\frac {1}{\infty }}=0$, $R_{t}$ must also equal to 0 is well. Am I correct, and is there any formal proof on this problem? --antilived^{T | C | G} 06:07, 12 December 2007 (UTC)

At first I thought it might be zero, but now I think otherwise. Every possible path is in parallel. However, most of these paths are "very long" - so they act as a large resistor in parallel. At a certain path-length, these large resistors in parallel are negligible. The total resistance is dominated by the shortest path(s). Nimur (talk) 06:18, 12 December 2007 (UTC)

I'm going to boldly assert that the answer isn't zero or infinity. Here is a thought experiment: You have a close analogy of this problem if you stick two probes into the ocean about 1cm apart and try to measure the resistance of the sea water between those two points. The oceans of the earth are pretty darned close to being infinite compared to 1cm - and you don't expect to get either zero or infinity as the answer in that case. In fact, I think you'd be surprised if you could measure a different resistance in a bucket of sea water compared to the entire oceans of the world. So we know that the answer doesn't depend significantly on those longer paths. So it's easy to get an approximate answer.

So the real question here is: Why are physicists are only worth two points and mathematicians three? It ought to be the other way around because the physicist can say - "oh about three ohms" and carry on walking. Mathematicians are going to end up worrying about the contribution of an infinite number of paths - each with infinite resistance and wind up with infinity-divided-by-infinity - then FOOOOOMMMM! Maybe they mean theoretical physicists? (You see how you'd find it so hard to score points from a Ref Desk person? We're worth a LOT more than three points!) SteveBaker (talk) 06:42, 12 December 2007 (UTC)

It's definitely less than 3 ohms, since disregarding all the resistor outside the little rectangle drawn up by the two dots, there're 3 paths of 3 ohms resistance so it would be somewhere below 1 ohm IHMO. --antilived^{T | C | G} 07:02, 12 December 2007 (UTC)

F-ing xkcd! 4/pi - 1/2 ≈ 0.77 Dragons flight (talk) 08:16, 12 December 2007 (UTC)

How did you get that? --antilived^{T | C | G} 08:53, 12 December 2007 (UTC)

Q10 on the Google Test answers carries the answer; the paper Application of the lattice Green's function for calculating the resistance of an infinite networks of resistors explains in more detail. Laïka 12:32, 12 December 2007 (UTC)

Backing off a bit, let's consider the inner lattice of 7 resistors between the two points. Is the resistance in that 7-resistor lattice going to be ${\frac {1}{{\frac {1}{2}}+{\frac {1}{3}}}}$ ohms? It's been ages since I've studied physics or electronics so other than simple series/parallel stuff, I'm not necessarily up to snuff. Do I need to consider every possible non-repeating path between the two points in the calculation? Donald Hosek (talk) 17:19, 12 December 2007 (UTC)

For any reasonable answer, you need to consider every path that influences the answer. For example, if I had a 1 ohm resister in parallel with a 1 trillion ohm resistor and asked how many ohms the combined two are to the nearest ohm, it would be 1 ohm. The larger of the two is so large that it doesn't come into play enough to affect the answer. So, you have to consider every path between the two points that changes the answer within the precision you are looking for - which is not an infinite number of paths. -- kainaw™ 17:32, 12 December 2007 (UTC)

So for the seven-resistor lattice, I need to do something along the lines of ${\frac {1}{{\frac {1}{3}}+{\frac {1}{5}}+{\frac {1}{3}}+{\frac {1}{3}}}}$ then (assuming I found all the paths)? Donald Hosek (talk) 17:58, 12 December 2007 (UTC)

Just counting the paths isn't going to work, if those paths overlap... consider, two 2Ω resistors in parallel, vs two 1Ω resistors in parallel with another 1Ω resistor in series. Both have two paths, and all the paths are 2Ω... but the total resistances are 1Ω and 1½Ω, respectively... since, in the latter case, the two paths share a resistor. To solve the small 7-resistor case, you can collapse two pairs of series resistors (the corners that aren't the nodes you're trying to measure), and get 5 resistors arranged like a Wheatstone bridge (except with another resistor in the middle instead of a voltmeter... I only link to that article for the picture). You then need to use the Y-Δ transform on one of the two triangles, and you'll get two resistors in parallel with another two resistors, and a fifth resistor in series with the whole thing... which is solvable with just the series/parallel rules, to get exactly 1.4Ω. Phlip (talk) 22:49, 12 December 2007 (UTC)

Geomagnetism

It is taught that the earth has a molten iron core.How does the molten iron core of the earth support permanent magnetism.Molten iron is not usualy permanently magnetic.82.15.53.173 (talk) 10:00, 12 December 2007 (UTC)

It's not a permanent magnet. See geodynamo. It is more analogous to an electromagnet, where the magnetic field is generated by moving charged fluids. Dragons flight (talk) 10:10, 12 December 2007 (UTC)

Also, your initial statement was not completely correct. While the Earth's outer core is molten, the inner core is solid, due to the higher pressure. StuRat (talk) 12:04, 12 December 2007 (UTC)

Dragons flight and StuRat are both correct. The earth's core is theorized to be a solid, mostly iron, crystal that is extremely hot, due in part to the enormous pressure that it is under from the gravitational energy of all the mass of the planet pushing in to the center. However, there are also several other possible reasons that the core of the planet is so hot: 1) leftover heat from the initial accretion phase during which time most of the planet was molten, and 2) heat that is generated from radioactive minerals that are within the earth, 3) the theory that within the earth's inner core there is a fission reactor process known as a Georeactor that produces heat, and 4) heat created through the solidification of the inner core. The reason that the inner core of the earth is not molten, though, is due to the fact that there is just so much pressure that it has been squeezed into a solid mass, instead of a liquid ooze. As one journeys away from the center of the earth, the pressures begin to let up, since there is less mass lying above to push down, and as the pressure is eased, the extremely hot iron no longer is being forced into a solid state, and therefore it becomes liquid, or molten. This is why the outer core and the mantle layers of the earth are molten. Then, of course, the crust of the planet's surface is hard, due to the lack of pressure and also to the cooling effect of being exposed to the thin blanket of ocean and atmosphere before encountering cold space.

Now, as the earth spins on its axis, parts of the interior of the planet spin at slightly different rates from one another. Think of this in terms of when you try to spin a fresh unboiled egg. The egg will very quickly lose its spin. However, if you hard boil the egg, it spins much better because it is solid all the way through. The liquid parts inside a fresh egg want to spin at different velocities from the outer shell, and this is why it doesn't spin so well. With the case of the earth, the inner layers are spinning at different rates from one another - specifically, the inner solid core is spinning at a slightly different rate than the liquid outer core and mantle, which also spin at a slightly different rate from the crust. What this creates is the condition in which iron molecules are passed against one another as these different layers rub against each other due to their different spin rates. Whenever you have such a situation of iron molecules rubbing against other iron molecules, you have created a dynamo (or generator), as Dragons flight described above). What happens as the iron molecules pass one another is that ions are stripped from the molecules and then caught up in the pre-existing magnetic current that makes up the magnetosphere through a process known as Faraday's law of induction. Think of this in terms of a pump pushing water along a closed system. So this is what creates the magnetosphere of the earth, which in turn helps to shield the earth from bombardment of harmful levels of radiation that come from the sun. Most planets that we know of do not have a magnetosphere. We're lucky to have one.

References:

Schneider, David (Oct 1996) A Spinning Crystal Ball, Scientific American

Lehmann, I. (1936) Inner Earth, Bur. Cent. Seismol. Int. 14, 3-31

Herndon, J. Marvin (1996) Substructure of the inner core of the Earth Vol. 93, Issue 2, 646-648, January 23, 1996, PNAS

http://www.nytimes.com/2005/08/25/science/25cnd-core.html

-- Saukkomies 09:27, 12 December, 2007. (UTC)

Sigh. For the second time in two days on this board, the mantle is a solid (specifically a rheid). Dragons flight (talk) 15:16, 12 December 2007 (UTC)

Another small correction to Saukkonies' explanation - pressure by itself does not generate heat, because a stationary force does not transfer energy. Gravitational energy could only be transformed into heat energy if the Earth were contracting, which it is not. Our article on geothermal geology gives a list of the sources of geothermal energy. Gandalf61 (talk) 16:52, 12 December 2007 (UTC)

I stand corrected. Thanks for pointing this out to me, since geology is one of my favorite subjects, and lo! I find I've been under misconceptions in these regards for so many years. ::-- Saukkomies 16:39, 12 December, 2007. (UTC)

sources

wiki pls give two sources of information about water quality in kerala202.88.234.8 (talk) 10:02, 12 December 2007 (UTC)

For these general sorts of questions, google is often a great place to quickly find what you want. See here. Someguy1221 (talk) 10:56, 12 December 2007 (UTC)

Pigeons always pecking the tarmac for invisible food

Does anybody know what the city (and suburban) pigeons are always pecking? They seem to always walk around pecking even when there is clearly no food. I considered that might be pecking small seeds or breadcrumbs but from my observation this doesn't seem to fit - such things aren't scattered so abundantly in the suburbs and city. Maybe they are actually eating small stones, or grains of salt. Rfwoolf (talk) 10:04, 12 December 2007 (UTC)

Some birds' digestive systems rely on having small stones in their digestive tract to help grind food. They're sometimes referred to as "gizzard stones", but are apparently properly known as Gastroliths. EvilCouch (talk) 11:38, 12 December 2007 (UTC)

Thanks! That seems to answer the question. "...Particles as small as sand and stones the size of cobbles or greater have been found" " Domestic fowl, for instance, require access to 'grit', for the purpose of food-grinding." Thanks. Rfwoolf (talk) 11:47, 12 December 2007 (UTC)

why frogs disappear

give me atleast two explanations for why some frogs are disappearing world wide202.88.234.8 (talk) 10:05, 12 December 2007 (UTC)

As in the above, google is a great first place to look. Someguy1221 (talk) 10:57, 12 December 2007 (UTC)

Decline in amphibian populations and Frog#Distribution_and_conservation_status are other good places to look. SteveBaker (talk) 12:48, 12 December 2007 (UTC)

But some are on the increase - see cane toad, particularly about what's happening Down Under. -- JackofOz (talk) 19:44, 12 December 2007 (UTC)

carrying capacity

define human carrying capacity202.88.234.8 (talk) 10:09, 12 December 2007 (UTC)

Carrying capacity is very well defined. Applying the concept to humanity is notoriously debatable, and attempts are discussed in that article. Someguy1221 (talk) 10:54, 12 December 2007 (UTC)

I think we can all agree only on the concept that there is a carrying capacity. Personally, I think we are ultimately limited by arable land unless we can make some real breakthroughs in hydroponics, sea-farming, or completely synthetic foodstuffs. --BenBurch (talk) 16:48, 12 December 2007 (UTC)

Gravity

When I worked in a coal mine, I felt that coal was lighter to shovel, than when on the surface.Are things lighter when below the surface considering the mass of the earth that is now above and acting contrary to the normal pull of gravity?Could this effect be percieved by a young miner?Are things perceptively lighter in a submarine as it goes deep under the sea?82.15.53.173 (talk) 10:18, 12 December 2007 (UTC)

If you assume the Earth is uniformly dense, then by Newton's law of universal gravitation the strength gravity inside the earth is directly proportional to your distance from the center of the earth. So even if you're three kilometers beneath the surface of the earth, you're only 0.5% closer than you were at the surface, and so gravity is only 0.5% weaker. While you could certainly measure the difference with a good balance, this would not be perceptible at all. Someguy1221 (talk) 10:51, 12 December 2007 (UTC)

See shell theorem. StuRat (talk) 11:48, 12 December 2007 (UTC)

This is a wild guess, but if the tunnels are on a slight gradient - and I think that it usually the case - you wouldn't normally notice it as you have no frame of reference underground such as a horizon. However, shovelling coal would be easier if you were moving it downhill, even though your brain assumes you are moving it on the level.--Shantavira|^{feed me} 11:15, 12 December 2007 (UTC)

If gravity is 0.5% weaker, a 30-pound shovelful will be 2.4 ounces lighter. As one who has shoveled all day several times in his life, I think I can say that that weight reduction would become noticeable by about 3 in the afternoon. --Milkbreath (talk) 21:28, 12 December 2007 (UTC)

But Someguy1221's calculation is off by a factor of 10 – i. e. 3 km is only 0.05%. Icek (talk) 22:35, 12 December 2007 (UTC)

Maximum/minumum temperature forecasts.

In South Africa the temperature forecast is first the minimum (morning) and then the max (afternoon)[13]; but I've seen British[14] and American[F] forecasts put the max first. Are these minimums the next morning's, or are they just the wrong way round? -- Jeandré, 2007-12-12t13:47z

In US forecasts, the high usually comes first, followed by the "overnight low" that occurs after it. So they give the "Saturday High" that probably occurs Saturday afternoon, then the "Saturday Low" which occurs "Saturday night", but is probably actually early Sunday morning. (It is common here to say "Saturday night" to describe the time between going-to-bed Saturday and waking up on Sunday. This imprecision results in people saying things like, "So Saturday night, the phone rings at 3 in the morning...") -- Coneslayer (talk) 14:06, 12 December 2007 (UTC)

Respiration protocols

Some mammals were treated to three different respiration schemes: group 1: 6.2±0.4 ml/kg VT (PIP 40/0), 30bpm, 95% O2; group 2: 6.2±0.4 ml/kg VT (PIP 40/0), 30 bpm, 95% N2; group 3: PEEP 5cmH2O, 95% O2. I'm trying to figure out what this means. Where it says VT, by the way, T should be subscript.

30 bpm? Beats per minute? I tried searching with google but can't figure it out. I've found out that PIP = positive inspiratory pressure and PEEP = positive end expiratory pressure - does PEEP make it harder to breathe out and therefore generally harder to breathe than PIP? Also what's the 6.2±0.4 ml/kg VT in groups one and two about and the reference to H2O in group three? Thanks for any insight. --Seans Potato Business 16:04, 12 December 2007 (UTC)

I assume that bpm in this context is breaths per minute. 5 cmH₂O is a pressure of five centimeters of water. (A column of water five centimeters tall will exert this much pressure at its base.) One centimeter of water is equivalent to 0.76 mmHg or 98 Pascals: [15]. I wouldn't want to guess at the rest. TenOfAllTrades(talk) 16:19, 12 December 2007 (UTC)

Gold that's heavier than pure gold?

I've finally decided to finish the damn Baroque Cycle, having read the first two when they came out and then just put it aside. So I read the second one again (having totally forgotten everything that had happened) and have now just begun with the third book, The System of the World. A major plot point in books two and three is concerning something called "Solomonic Gold", that is, Gold that is heavier than ordinary gold. Newton and others use a lot of alchemical mumbo-jumbo to try and explain this ("It is infused with the Philosophick Mercury!", etc.) , however what is clear is that in this book this is a real metal. Is there such a thing? Can you perhaps make "heavy" gold much like heavy water, by only selecting larger isotopes? Or is it an alloy with some other heavier metal (depleted uranium-gold?) Or did Neal Stephenson just make this up? 83.250.203.75 (talk) 18:43, 12 December 2007 (UTC)

Gold only has one stable isotope (197). The only other nearly stable isotope is 195 with a half-life of 186 days. So, you'd find it very difficult to make heavy gold using heavy isotopes. -- kainaw™ 18:52, 12 December 2007 (UTC)

Gold-Osmium alloy? Osmium is the densest known element. Although, platinum is also more dense than gold and is used in jewelery, too. — Scientizzle 18:56, 12 December 2007 (UTC)

I haven't read the book, but I've spoken to people who have, and I'm reasonably sure the damn stuff is infused with the Philosophick Mercury. Thus Stephenson has decided to make some of alchemy true rather than make up an isotope. Algebraist 21:33, 12 December 2007 (UTC)

He really doesn't explain why the gold is heavier than it should be. A modern reader should probably assume he's talking about an isotope - but (as already explained) that doesn't really work. The point is that the book is written from the point of view of a 17th century alchemical society - and the impact of screwy gold on their currency would indeed be problematic. I suspect (from Stephenson's writing style) that we'll find out more in subsequent books. The business of the same family names carrying on between the Barque Cycle and the Cryptonomicon - and one of the characters in it seeming to be immortal means that the science within those stories cannot be taken as literally true. The mythic compactness of the Qwelgmian language - and a whole lot of other things he talks about - are also impossible. However, the Cryptonomicon is certainly in my top 10 list of best ever works of fiction - the Baroque cycle...is too long to re-read - so I'm not sure! SteveBaker (talk) 00:18, 13 December 2007 (UTC)

Aliens

What is the probability for the existence of aliens? 64.236.121.129 (talk) 19:19, 12 December 2007 (UTC)

See Drake equation, and consider refining your question. Do you mean aliens we will make contact with in your lifetime? Aliens in our galaxy? Aliens anywhere in the universe? If it's aliens anywhere in the universe (with no requirement that we ever find out about them), then the only realistic answers are 0 (if you believe that we are the unique creations of God, for example), or 1 (if you don't). It would require incredible fine-tuning for life to exist on one and only one planet in the universe. -- Coneslayer (talk) 19:26, 12 December 2007 (UTC)

The probability for aliens to exist somewhere in the universe at some time is so high as to be almost certain. The probability for aliens to exist within the brief (geologically speaking) lifetime of the human race with the ability of physically visiting us on earth is so low as to be almost impossible. There's a lot of wiggle room in between. Personally I take a very pessimistic view of the Drake equation—it makes the idea of any sort of communication (defined as two-way contact, not simply "an alien picks up one of our radio signals someday, long after we're gone") at all seem practically impossible. --24.147.86.187 (talk) 19:48, 12 December 2007 (UTC)

The Drake equation and all speculation on the matter depend on an unknowable variable, what the probability is that life will spontaneously arise given the right conditions, leaving aside mystical ideas about the genesis, no pun intended, of life. Some think the probability is high, or even one. With a tip of the hat to Descartes, it's obviously not zero. The area in between is the very best sort of ground to grow unending pointless debate in, so I'm not going to tell you what I myself think. --Milkbreath (talk) 21:21, 12 December 2007 (UTC)

The problem with the Drake equation is that we have a good idea of the first factor, are working on the second and third, and know nothing whatsoever about the remaining 4. Incidentally, the fact something has happened does not imply its probability was non-zero, at least in the usual mathematical theory of probability. That reminds me: someone ought to point out that questions of the form 'what is the probability of [event in real world]' are fraught with philosophical difficulties. For an extreme example, one could say that the existence of aliens is nonrandom (they either exist currently or they don't) so the answer is 1 or 0 depending on whether they exist or not. Algebraist 21:30, 12 December 2007 (UTC)

If you're interested, there's a recent Damn Interesting article on the odds of aliens and radio communications with them titled "Space Radio: More Static, Less Talk" that includes an interactive Drake equation calculator. You can plug in your own figures and it will give an estimate for the number of communicating civilizations in the Milky Way galaxy. -- HiEv 23:42, 12 December 2007 (UTC)

Technically - there is nothing wrong with the Drake equation - the problem is only with the numbers you plug into it. However, because we know that humans exist, none of the parameters of the equation can possibly be zero. Hence, if the universe is large enough - there will be other lifeforms out there. However, knowing that there are definitely aliens out there is a very different thing from being able to detect them - let alone communicate, meet, cooperate with. The section of the universe that we can ever reach is finite - and that section could be utterly devoid of alien species if the numbers in the equation are small enough. SteveBaker (talk) 23:53, 12 December 2007 (UTC)

Oh - yeah - the other thing about the Drake equation is that it doesn't predict the number of populated alien worlds (which I guess is what the OP is asking) - but the number that have intelligent aliens, that know how to make big radio transmitters and who decide to transmit and who are in roughly the same phase of technology that we are (so they aren't trying to communicate by wormholes or something) and who havn't died out from global warming or nuclear holocaust or something. If you just want to know whether there are primitive alien bacteria out there - then the odds are not only much better - but the answer has a lot fewer unknowns in it. SteveBaker (talk) 00:02, 13 December 2007 (UTC)

SETI doesnt seem to have found any evidence of extraterrestrial intelligence. So draw your own conclusions--TreeSmiler (talk) 02:16, 13 December 2007 (UTC)

I lost what faith I had in SETI when I read somewhere (source forgotten, I fear) that if our present radio emissions had (by the intervention of mischievous time-travelling aliens perhaps) by humanity 50 years ago, then they would have considered it random noise due to the complexity of modern coding. (Hopefully someone here will know if this is a load of marsh gas) Algebraist 02:49, 13 December 2007 (UTC)

That seems quite unlikely. Digital signals are most certainly not natural analog noise. Would the encoding be decipherable? Perhaps not; MP3 isn't really intended as a first-contact codec. It would absolutely be artificial though. — Lomn 04:13, 13 December 2007 (UTC)

Power and duration are also obvious give-aways. Artificial radio signals will always make the detected signal louder than noise, since they add to the noise, and a sudden burst of radio waves that lasts three minutes before suddenly disappearing is definitely conspicuous. The Wow signal is the strongest candidate for an extraterrestrial transmission because it was the most powerful signal Big Ear ever detected, and because it was only received once. --Bowlhover (talk) 06:05, 13 December 2007 (UTC)

I've always found it interesting that science fiction portrays aliens as being only a little more advanced than us. If there really were intelligent beings who were capable of visiting us, there is a good chance that they would be not just thousands but millions of years ahead of us technologically, and would regard us as we regard animals. Rather than beaming "hi there" messages into space we should be keeping our heads well down.--Shantavira|^{feed me} 09:39, 13 December 2007 (UTC)

Backcrossing

MyD88-/- mice were generated as described and backcrossed for 9 generations on an H-2d (BALB/c) background. - what's the backcrossing necessary for? --Seans Potato Business 20:15, 12 December 2007 (UTC)

When generating knockout mice, it's generally necessary to mix two different strains of mice. Backcrossing is used to reduce the genetic components of one of the founding strains. — Scientizzle 21:16, 12 December 2007 (UTC)

Here is an ugly graphical representation. After several generations of backcrossing, one can assume that the only non-BALB/c DNA in these mice is from the regions flanking the knocked-out gene — Scientizzle 21:21, 12 December 2007 (UTC)

Ice Cream

I've heard that you can die from eating re-frozen ice-cream, because of salmonella. Is this true? —Preceding unsigned comment added by 89.242.7.45 (talk) 21:23, 12 December 2007 (UTC)

I assume it would depend on how long it was defrosted for. If it was long enough for a significant salmonella colony to develop then yes - you could certainly have active salmonella in the icecream when you eat (and thereby warm it up). But if it only defrosted a little bit on the way home from the store, I can't believe there would be a problem. SteveBaker (talk) 23:30, 12 December 2007 (UTC)

Not to mention salmonellosis isn't typically fatal, although it isn't the most fun experience in life. --Bennybp (talk) 04:58, 13 December 2007 (UTC)

Light perception and evolution

Little background: Sun and moon have been present around earth since quite some time before the evolution started taking place. Specifically, humans have always seen during the whole evolutionary process either sun or moon at any point of time in the whole day. During the day, sun emits light in the whole electromagnetic spectrum, but due to the intense temperature in the sun, its peak wavelength of radiation lies around 550 nm (middle of the spectrum that we actually see). In the night also, moon shines earth by the reflected light of sun that falls on the moon, then again the peak is around the 550 nm. Since light around nature is abundant in this wavelength range, we have actually adapted ourselves to sense the light in this range only.

The question: However, I must say that all bodies on earth (e.g. solid bodies or living organisms etc.) have been emitting infrared radiation also at all points of time ever since humans started evolving. Yet, we can't sense infrared radiation. My question is what could be the reason for this selective evolution. Is it because of the fact that intensity of infrared radiation always tends to be much less than that of the normal visible light that is found in the nature. But then, why did some other creatures develop this infrared sensing feature? And ultraviolet light is generally not present at all in the nature in normal circumstances, yet some creatures develop this sensing also. Why did humans lose? Does it have to be something related to the human intelligence also? DSachan (talk) 22:21, 12 December 2007 (UTC)

You've got a lot of "human exclusivity" in that question ("Why did humans lose?") but keep in mind that homo sapiens may not have gained/lost anything that primates, mammals, etc. had before that. To my knowledge no mammals can see very far into the infrared or into the ultraviolet (as we humans define the visible spectrum), it's not a human-specific thing, you're probably talking about mammal eyes in general. (Some reptiles can see in the infrared, and with bugs and shellfish and etc. there is a whole variety in types of eyes and what they can see.) It probably has nothing to do with humans in particular. --24.147.86.187 (talk) 22:38, 12 December 2007 (UTC)

Given that infrared radiation has also been present all the time in addition to the visible radiation, why did we not evolve to the see this kind of radiation? You did not answer my question. DSachan (talk) 22:45, 12 December 2007 (UTC)

I wasn't trying to answer the question, I was just pointing out that you're probably asking the wrong question. The "right" question (in my mind) is not centered on humans but mammals in general; if mice can't see in the infrared (and as mostly noctural animals you'd think they'd have a lot more to gain from it than humans, who sleep all night and wouldn't benefit much), then humans probably aren't going to have evolved it. --24.147.86.187 (talk) 00:47, 13 December 2007 (UTC)

It would be very hard for an animal that can see in the infrared to get around during the day. Everything would be really bright to them. It would give some advantage when it is really dark but most nocturnal mammals get by without it. Shniken1 (talk) 23:13, 12 December 2007 (UTC)

I don't understand this answer. Why would everything necessarily be "really bright"? Why couldn't they just have a less sensitive retina, or smaller pupils, or something? What part of the spectrum are we talking about here, anyway? —Keenan Pepper 23:19, 12 December 2007 (UTC)

First, let me point out that infrared refers to a much wider range of wavelengths than visible light. "Thermal infrared", emitted by objects around room temperature and with a wavelength about 10 microns, is very different from "near infrared", which is only emitted by very hot objects and has a wavelength around 1 micron.

I think the main reason why animals didn't evolve eyes capable of seeing thermal infrared is because it's fundamentally harder to see those frequencies. It's the same reason why thermographic cameras are in general so much more expensive than visible light cameras. One of the problems that comes up in making thermal infrared cameras is that the inside of the camera should be dark to make good low-noise images. For visible light, this is easy, but for thermal infrared it's quite difficult, because most things glow in the thermal infrared spectrum. That's why good thermal infrared cameras are cryogenically cooled. If an animal had some kind of thermal infrared eyes, it would have to have a way of keeping them cold, which would probably take a lot of metabolic energy that could be used for other things.

That's just the first problem with thermal infrared eyes that comes to mind. I don't think it has anything to do with humans in particular. —Keenan Pepper 23:16, 12 December 2007 (UTC)

The question is not what we COULD evolve (there are owls that can see in the infrared and bees can see in ultraviolet) - it's what is efficient for us to evolve. We would need more sensors in the back of our eyes to be able to see in IR. So either:

• We'd have fewer sensors for colour - but we need daylight colour perception for finding juicy ripe red fruit in the green leaves of a tree - and to distinguish a brown rotten apple from a fresh red one. That failure would be selected against - so IR vision would vanish from the gene pool.
• Or - we'd need bigger eyes...think "Owl". But bigger eyes would require either:
  • A smaller brain. (definitely contrary to what humans needed to survive).
  • A bigger head. But we already are right on the edge of what size head will fit down a womans' birth canal - the death rate from giving birth (without medical assistance and before ceasareans) is already alarmingly large - making it worse would be a problem. Women could perhaps also evolve larger birth canals - but I'm sure there are problems consequent on that change.

So it's impossible to get IR vision without losing something else. Since we sleep at night and gather food in the day - there isn't a VAST benefit to IR vision - but there are significant costs in terms of lost colour vision or smaller brains or larger incidence of birthing problems.

But in any case, evolution doesn't always find the optimum path - it selects the best genes from what shows up from breeding and mutation. If an IR vision mutation never shows up - we'll never evolve it. SteveBaker (talk) 23:21, 12 December 2007 (UTC)

Great answer as usual, Steve! —Keenan Pepper 23:43, 12 December 2007 (UTC)

SteveBaker really should have his own phone-in show! He knows about everything from Mathematics to Computer Programming to Evolution to Red Squirrels !!! Unbelievable! It is sad that someone so smart and helpful is here on the Wikipedia (only as in relation to) while a certain other man, not so smart or helpful is the most powerful person on the planet. That said, hopefully the Wiki will be here forever. I think it is one of the most important projects of our time! So please stay SteveBaker! Saudade7 23:49, 12 December 2007 (UTC)

I have a hard time deciding whether or not I'd like to be Oliver ;-) hydnjo talk 00:52, 13 December 2007 (UTC)

There are animals that can see thermal infrared: the pit vipers. However, they also demonstrate the limitations of being able to see thermal infrared. They can only detect objects that are warmer than the environment (imagine not being able to see plants or any cold-blooded animals) and the resolution is far lower than that of the human eye (imagine not being able to tell the head of an elephant from its rear). --Carnildo (talk) 00:43, 13 December 2007 (UTC)

First of all, evolution is not "directed", it's "opportunistic". This means that species usually don't evolve properties that will become useful, but are not currently useful, nor do they have fully-formed complex features spring into place. Instead, minor traits are adapted into complex features if there is an opportunity and a benefit for that to occur, and then evolution continues to refine it if possible. In other words, just because a trait may have advantages, doesn't mean a species will ever get the chance to evolve it.

Second of all, larger animals don't sense infrared with their eyes because IIRC the lens is opaque to infrared. (I couldn't find any good site that says owls see IR, and here is an unscientific test where an owl couldn't see IR.) Precision thermoception is normally done using pits, such as the ones on the heads of snakes or in the noses of some bats, that contain an especially thermo-sensitive membrane. However, as the latter article notes, the accuracy of that sense is rather poor.

Finally, some adaptations have tradeoffs. For example, such a sense organ might be easily damaged by cold or prone to damage and infection. Or, it could be that it also requires "expensive" to produce materials to create such a sensor. Thus, such an adaptation might not be worth the cost. The fact that so few species have thermoception suggests that this might be the case.

So, the answer is that it may not have been worth it for most mammals to evolve thermoception, and even if it is/was, there may have been little or no opportunity to it to evolve. -- HiEv 02:21, 13 December 2007 (UTC)

• "there are owls that can see in the infrared"<-- can you provide some references? --JWSchmidt (talk) 02:52, 13 December 2007 (UTC)

evolution is not "directed", it's "opportunistic". Love this! Excellent quick summary of a lot of ideas. DMacks (talk) 03:03, 13 December 2007 (UTC)

December 13

loss of power in optical frequencies

Is there a way to work out the loss of power in a coherent beam of electromagnetic energy in near optical frequencies? My purpose is to work out an effective range for a scifi laser gun working in either IR or x-ray. --203.171.195.34 (talk) 00:48, 13 December 2007 (UTC)

The angle of divergence is very roughly equal to the wavelength divided by the initial diameter of the beam. For details see Angular resolution, Diffraction limited, Airy disc. Icek (talk) 02:32, 13 December 2007 (UTC)

Child pyromaniac

Is child pyromania an actual diagnosed disorder. I asked a Psychologist who is a friend of mine, and they said it was real, but didn't know if it was a diagnosed disorder. This information is for the AFD. Thanks, Malinaccier (talk) 01:33, 13 December 2007 (UTC)

It's in the DSM-IV (see here), so I'd say yes. For more see the "Encyclopedia of Mental Disorders" pyromania entry here. -- HiEv 02:38, 13 December 2007 (UTC)

Though I should have noted that it's not specific to children. -- HiEv —Preceding comment was added at 02:43, 13 December 2007 (UTC)

If you've been standing all day...

I'm in no way asking for medical advice here. I just have a general knowledge question about something that happens occasionally with me and some people I know: Say you've been on your feet all day, standing more than usual. In the evening you go to bed, feeling perfectly fine. You lie down but then your lower back gets tight and you can't stretch your back out all the way, so you lie on the bed with a slightly arched back (curved forward or a maybe curved backwards a bit). It doesn't hurt but it's not especially comfortable. It goes away immediately if you sit up or stand (and returns upon laying down again), or it goes away of its own accord after a couple minutes, and then you can stretch out and go to sleep. What causes this? Philbert^2.71828 07:31, 13 December 2007 (UTC)

rationale behind intraperitoneal injection of immune cells?

What's the rationale behind intraperitoneal injection of immune cells in lab experiments? Is it easier for them to migrate from there than from under the cutis of the skin? If so, any idea why? Do you know of any other options? The journal club presentation I give tomorrow is on a paper that used this mode of injection and it's not likely to be questioned but I'd like to be prepared just in case as well as understand for my own knowledge. --Seans Potato Business 09:10, 13 December 2007 (UTC)

crystallization

In the early stages of crystallization of a solution the solute molecules begin to come together from the solvent and begin to form clusters.But what is the idea behind the crystallization of water into frost we generally see on a nasty winter morning.