Wikipedia:Reference desk/Archives/Science/2007 October 16

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October 16

Why lengthwise instead of widthwise

But even before the A380 takes to the skies on a commercial basis, Airbus chief operating officer John Leahy is talking of stretching the giant lengthways.

My question is why do they want to stretch it lengthwise instead of widthwise. There is a limit of how long you can stretch it lengthwise but no limit on widthwise. 202.168.50.40 00:26, 16 October 2007 (UTC)

There will be many issues, sich as facilities designed for the planes, such as how wide is the runway, the gate space for the plane. A fatter shape will have more air resistance, more so than a longer one, after all an arrow is long and thin. Graeme Bartlett 00:45, 16 October 2007 (UTC)

In terms of redesign, longer is less effort too - just stick in another section identical to the ones you used before. If you make it wider, the wings have to be further apart - the entire cockpit shape changes - the center fuel tank design would change, tha flare down to the tail would block more airflow over the tailplane. There would be issues with how food service could reach through to the new rows of seats...it would be a 'start from scratch' kind of a thing from an engineering perspective. Making it longer is very little engineering effort by comparison. SteveBaker 01:29, 16 October 2007 (UTC)

Indeed. Lengthwise stretching (for ships as well as aircraft) is simple from an engineering perspective - just keep building the hull a little while longer than normal - but widthwise stretching requires new design, new stesting, new machinery... Shimgray | talk | 17:31, 17 October 2007 (UTC)

...and now I've got the picture of a Limousine stuck in my head... by this one is stretched the other way. It seems like a good example, though. Lengthened vehicles work, but I couldn't fit a double-wide vehicle down my driveway, let alone in my garage. --Mdwyer 02:18, 18 October 2007 (UTC)

You may be interested in Image:Giant planes comparison.svg. Note that the A380 is in fact shorter then the 747-8 will be. This means a lengthed A380 may not be much longer then a 747-8 Nil Einne 09:56, 22 October 2007 (UTC)

Body mass index

Where can I find a correlation between BMI, age and death? In other words do people who have a lower BMI live longer and if so how much longer per lower BMI? Clem 02:18, 16 October 2007 (UTC)

The Framingham Heart Study data are fairly famous. Another recent study: Overweight, obesity, and mortality in a large prospective cohort of persons 50 to 71 years old. --JWSchmidt 04:34, 16 October 2007 (UTC)

Is it the case that, sadly, fat people die young? Edison —Preceding comment was added at 04:55, 16 October 2007 (UTC)

Indeed, haven't you heard the famous saying: "Live Fat, Die Young"...(and leave a good-looking, albeit rather heavy, corpse?) Facts and figures from other studies can be found here, damningly, one study quoted found "the risk of mortality increased with increasing BMI at all ages and for all categories of death." Rockpocket 06:55, 16 October 2007 (UTC)

Is homosexuality a STD

Is homosexuality a sexually transmitted disease? Let me explain what I meant. Assume that there is a unknown STD. Let's called it H. Let assume that people with H shows no symptoms.

Now suppose, a woman contracted H from another person. Then the woman became pregnant. Because of the disease H, the fetus is "deprived" of certain chemicals. When the baby is born, the baby becomes a homosexual person.

So scientifically, how should a scientist prove or disproves this assertion?202.168.50.40 05:29, 16 October 2007 (UTC)

I'm no scientist, but I'd say homosexuality - and heterosexuality, for that matter - are STDs only in the same way that life itself is an STD. Homosexuality isn't a disease at all, ergo it isn't an STD. -- JackofOz 05:40, 16 October 2007 (UTC)

Well hypothetically, a scientist with such an hypothesis could test several things:

1. Are mothers that had many sexual partners more likely to have homosexual children?
2. Are mothers that had one homosexual child more likely to have additional homosexual children?
3. Since the prevelance of H would presumably vary across different populations, one could look for large variations in homosexuality across populations, especially for isolated populations. (Though this could be hard to distinguish from cultural variations.)
4. Look for physiological indicators in mother or child that are associated with homosexuality.

For the record, I think it is quite unlikely that homosexuality is a disease. Dragons flight 05:53, 16 October 2007 (UTC)

I am a scientist and your hypothesis doesn't make a much sense. If that were the case, then twins would always be gay or straight, but never one of each. Moreover, parents who had just one sexual partner would never (or rarely) have gay children. It is possible, I suppose, that some form of STD could result in a uterine environment that, in turn, increased the probability one's child is homosexual, but even that would be tractable by statistical analysis. Sexuality, like most aspects of human behaviour, will not be wholely explained by such simple hypotheses. Its clear that a complex interaction of genes and environment (probably both uterine and post partum) are responsible for defining our sexuality. Rockpocket 06:13, 16 October 2007 (UTC)

(edit conflict) Isn't this a matter of definition, and attitude, rather than scientific discovery or statistical analysis? Homosexuality used to be technically classified as a disease in DSM4; nowadays it's not. The only thing that changed was the attitude of the scientific/psychiatric/medical community to homosexuality and to gay people. Which is why psychiatrists etc who claim to be able to "cure the disease" are in some jurisdictions at risk of being disbarred on the grounds of professional malpractice. -- JackofOz 06:22, 16 October 2007 (UTC)

Incidentally, by the same rationale, its equally likely (i.e. not very) that heterosexual children could be the result of an STD. Homosexual children may be the minority among us, born unaffected by the disease... Rockpocket 06:47, 16 October 2007 (UTC)

Life is a sexually transmitted disease. Cyta 06:57, 16 October 2007 (UTC)

With a 100% mortality rate. Cyta 06:58, 16 October 2007 (UTC)

Hmm .. I think I already made that point.  :) -- JackofOz 07:24, 16 October 2007 (UTC)

Shamelessly cut and paste from the web:

First: If one twin is gay, what's the likelihood of the other being gay?

Well, the most widely used numbers are cited from a 1991 study by Northwestern University psychologist Michael Bailey and psychiatrist Richard Pillard of Boston University School of Medicine in which identical and fraternal twins were studied. At least one twin in each pair was gay. The study found that 52 percent of the identical twins were both gay as opposed to only 22 percent for fraternal twins. In other words, there is a 52 percent chance that if one identical twin is gay, both are; and a 22 percent chance both fraternal twins are gay if one is gay.

so if STD H is the cause of homosexuality then we would expect both twins to be gay all the time 211.28.130.81 08:36, 16 October 2007 (UTC)

How many people were investigated in this study. I'd be happy to say that 52% of the identical twins would have the same sexual preference, but if the test subject population is small, drawing any conclusion as to what that preference is would be dangerous. Also, how was homosexual defined by the researchers? - Mgm|^(talk) 09:22, 16 October 2007 (UTC)

The same findings tend to come out of similar studies. See the discussion at Wikipedia:Reference_desk/Science#Gay twin, up there ↑ Rockpocket 16:59, 16 October 2007 (UTC)

"we would expect both twins to be gay all the time" <-- Why? For many genetically-influenced traits there is low penetrance and for many infectious agents there is low infectivity and variability in the course of the infection. --JWSchmidt 14:05, 16 October 2007 (UTC)

Because the OP made the claim that this hypothetical STD would cause homosexuality due to a change in the womb environment. Your suggestion (which is more likely) would be a situation where a STD would increase the probability of having a homosexual child. The difference is key, I think, in attributing "cause" to the development of such characteristics. Rockpocket 16:55, 16 October 2007 (UTC)

The hypothesis also fails to provide a satisfactory explaination for the generally accepted correlation [1] between the number of older fraternal male siblings and homosexuality in males. Even assuming you claim that the more children a women has, the more likely she is to have had other sexual partners (which seems a real stretch to me, for example someone who gets married at a late age is probably more likely to have been more promiscious then someone who gets married young and has multiple children) there's still the question of why only male? Why wouldn't the number of female fraternal older siblings also increase the chance of homosexuality? A woman is likely to be more promiscious when she has male children? Nil Einne 10:07, 22 October 2007 (UTC)

photon momentum and mirror .

A mirror is a device that change the momentum of incident photons; but it's own momentum remain unchanged , how is this possible ? —Preceding unsigned comment added by Shamiul (talk • contribs) 06:07, 16 October 2007 (UTC)

False assumption. Momentum is conserved, and the mirror's momentum must change (or at least transfer that impulse to another body), but the magnitude of this change is generally imperceptibly small, just as the momentum of photons is nearly imperceptible in most situations. Dragons flight 06:17, 16 October 2007 (UTC)

In fact, the change of momentum of a mirror struck by photons is how Nichols radiometers and solar sails work. --Spoon! 06:56, 16 October 2007 (UTC)

How non-charged particles are accelerated in particle accelerator .

Charged particles like electron,proton may be accelerated using voltage difference . How non-charged particles like neutrinos or neutron are accelerated in particle accelerator ? —Preceding unsigned comment added by Shamiul (talk • contribs) 06:49, 16 October 2007 (UTC)

They are normally not accelerated. They come from something that already has a source of energy, they may be decay products of an accelerated charged particle, or taken from a nuclear reactor where they are already emitted with some energy, and you just select those in a particular direction. This is tricky, hence why particle accelerators use charged particles. Neutron/neutrin experiments are not normally considered particle accelerators. Maybe see Neutron source and Neutrino#Neutrino_sources. Cyta 07:03, 16 October 2007 (UTC)

An analogy for the fuel cell?

Having read and re-read the entry on the Fuel cell and studied the diagram, I'm still searching for a way to explain - using a widely understandable analogy - how a hydrogen fuel cell works (in a hydrogen car, for example). I need to reduce its function to an explanation that doesn't feature a set of terms that would also require explanation, such as anode, cathode etc. Naturally this is for a lay audience. My problem is that I don't have a background in science and really am only learning about much of this myself.

Any suggestions? Wolfgangus 08:04, 16 October 2007 (UTC)

http://simple.wikipedia.org/wiki/Hydrogen says "A fuel cell combines Hydrogen thru a catalyst with an Oxygen molecule releasing an electron as electricity." And http://simple.wikipedia.org/wiki/Catalyst says "A catalyst is something that makes a chemical reaction go faster." But I suppose you want more than that. Alas there is no fuel cell article there - hopefully, answers here will lead to one. DirkvdM 08:17, 16 October 2007 (UTC)

Wow, I didn't know that wiki existed. It's like wikipedia for idiots. 64.236.121.129 13:10, 16 October 2007 (UTC)

Alright, here's an attempt.

Water is a molecule that consists of one oxygen atom and two hydrogen atoms. It takes energy to split the two and when they are recombined energy is released. A fuel cell does the latter. Hydrogen (the energy source) and oxygen (which can come in the form of plain air) are fed into it, separated by a membrane that will only let positively charged hydrogen (H+) through to the oxygen (O). At the hydrogen side, a platinum plate helps the electrons of the hydrogen atoms to split off. The now positively charged hydrogen atoms pass through the membrane, while the electrons enter an electric circuit. This produces the electricity required. At the other end of the electrical circuit, it connects to the oxygen side, where the electrons then combine with the positively charged hydrogen and the oxygen to form water (which then comes out the exhaust pipe). These three (H+, O and electrons) 'want' to combine and thus 'pull' the electrons through the electric circuit, thus creating the desired energy.

I'm not sure if that is all strictly correct - I just now learned the workings of a fuel cell through the diagram. But I think it's roughly correct. Is this more like what you were looking for? DirkvdM 08:35, 16 October 2007 (UTC)

Oh, sorry, you were asking for an analogy. I should read questions a bit more carefully in the future. DirkvdM 08:41, 16 October 2007 (UTC)

Actually, DirkvdM, while yes, I was seeking an analogy, I might be able to make one from your explanation - specifically from your word choice, "want". That word might give the process just enough character for me to build on. So I do appreciate your help. Wolfgangus 15:12, 16 October 2007 (UTC)

I don't think there is a suitable analogy - however the hydrogen/oxygen fuel cell is electrolysis of water in reverse - (which is a school topic) - you should be able to find lots of resources on electrolysis of water.. explain that.. then say "the fuel cell instead of using H20 and energy to make O and H uses O and H to make H2O and energy !" ...87.102.12.235 15:43, 16 October 2007 (UTC)

Beta decay .

Beta decay is a phenomenon where a neutron in an unstable atomic nucleus is converted to proton releasing energy(gamma ray) . After beta-decay process is completed the atomic neuclious contain one more proton which should make the atomic nucleus more unstable because protons in an atom repeal each-other , but neutrons in a nucleus do not repeal each-other . So is'nt a neuclious much stable before beta-decay rather than after beta-decay . Please supply me detailed explanation of this confusing topic ; you are wellcome to write down interactive and interesting web address containing this topic . Thank you all . —Preceding unsigned comment added by Shamiul (talk • contribs) 08:55, 16 October 2007 (UTC)

You could start with the semi-empirical mass formula. Icek 10:18, 16 October 2007 (UTC)

I'm not an expert, but I'll try to give you some info. Have a look at the nuclear force which is a force acting at the subatomic level which binds neutrons and protons. From that article "At short distances, the nuclear force is stronger than the Coulomb force; it can overcome the Coulomb repulsion of protons inside the nucleus." Nucleons have energy levels within the nucleus which can be approximately predicted using the Shell model. Just as atoms favor certain electron orbital configurations, nuclei favor certain "nuclear" orbital configurations. Adding a proton might stabilize a nucleus by filling up a "nuclear orbital." You might also be interested in magic numbers, certain numbers of protons an neutrons that tend to stabilize a nucleus greatly. Sifaka ^talk 04:20, 17 October 2007 (UTC)

TV animals

Have there been studies on the influence on animal behaviour of watching TV (apes, cats dogs,.)? When offered the opportunity, are apes interested in TV at all? Keria 09:12, 16 October 2007 (UTC)

I've seen many reports of non-human apes watching TV, for example Hiasl. Some dogs and cats can notice things on TV, but not all. A published study with chimps. --JWSchmidt 14:29, 16 October 2007 (UTC)

I did an externship at a pharmaceutical lab when I was in school, and part of the required "enrichment time" for the macaques was TV time. The monkeys seemed to have a preference for cartoons, and they would all sit at the front of their cages watching. The only thing that fascinated them more was the occasional escape. --Joelmills 14:55, 16 October 2007 (UTC)

You didn't let them watch MacGuyver, did you?! --Mdwyer 20:30, 16 October 2007 (UTC)

My dogs certainly notice things on TV. But it's never the pictures - firstly, their eyesight isn't that good - and secondly there is a strong possibility that the colours of TV don't look right to dogs (who can see some colour - contrary to urban legend). They definitely hear the sounds of other dogs though - and they'll sometimes prick up their ears and turn to look in that direction when they hear dog barks or (especially) the whining of a dog or puppy in distress. If I play a home movie, they'll prick up their ears and get VERY excited if they hear voices they recognise or each other's barks coming from the TV.

However, the lack of appropriate smell cues coming from the TV seems to tell them that this is just some weird irrelevence because they rapidly lose interest and ignore subsequent dog noises coming from the TV. Even the sound the TV produces doesn't have the high 'ultrasound' frequencies that dogs can hear (Dogs can hear up to 45kHz - a typical TV set only manages around 15kHz) - so it must sound severely muffled to them.

There is a pattern here. Dogs live in a world primarily perceived through smell, secondarily through sound and only lastly through sight. For them, TV's are pretty hopeless contraptions! No smell, really low quality audio and (possibly) very unrealistic colours. It's not surprising they aren't interested in watching. SteveBaker 22:14, 16 October 2007 (UTC)

Another problem may very well be the lack of 3D information. Remember that dogs, cats and other hunters have stereoscopic vision. There is AFAIK some evidence that even humans can't always initially recognise what's being represented on a TV (I believe some African tribes don't recognise 2D representations of 3D objects although I think this was more related to drawings then pictures but I would suspect the same thing applies). The fact that most animals often show at least initial interest in themselves in the mirror but nothing on the TV even a camera-mirror like setup I think suggests to me this may at least partially be the reason. It would be interesting to know if anyone has ever tested animals with 3D monitors that don't require any sort of glasses. Nil Einne 16:28, 18 October 2007 (UTC)

Declining caffein

Someone told me that the content of caffein decreased if you left tea to brew for too long. Is there any truth in this? Keria 09:14, 16 October 2007 (UTC)

• I think leaving tea to brew for too long would release more tannin which means a lower percentage would be caffein. I'm not sure if caffein degrades if left for too long. The molecule seems pretty sturdy. - Mgm|^(talk) 09:19, 16 October 2007 (UTC)

• If you leave it brewing too long, the tea tastes terrible. Which means you get less caffiene, as you won't drink it! -- Kesh 23:43, 16 October 2007 (UTC)

Hydrogen sulfide oxidizing enzyme

Which human enzyme catalyzes the oxidation of hydrogen sulfide (the Wikipedia article says that there are enzymes doing that)? I cannot find it at OMIM. Icek 09:54, 16 October 2007 (UTC)

A starting point in the research literature. --JWSchmidt 14:48, 16 October 2007 (UTC)

kinetic energy of ideal monatomic gas

I get PV=4/3 E_kinetic (or 3PV/4=E_kinetic) , but the ideal gas page gives the internal energy as 3PV/2.

1.Is PV=4/3 E_kinetic correct

2.If so what's the the extra 3PV/4 in the internal energy of a monatomic gas ( 3PV/2_Internal-3PV/4_kinetic = 3PV/4_extra )

3.If (1.) is wrong - Help!87.102.12.235 13:23, 16 October 2007 (UTC)

Let's just say I spotted my mistake - to those that would have helped - a speculative thanks

And a rhetorical 'You are welcome' to you too. (Actually I couldn't have helped, but lets ignore that fact :P ) Lanfear's Bane 13:47, 16 October 2007 (UTC)

Effect of human population growth on global warming

Hi all,

I have been to the climate change and global warming section of wiki. I didn't see anything about the effect of human population growth on global warming. E.g. more humans = more humans breathing out CO2 = increase in one of the greenhouse gases. Is this contribution by humans so insignificant that it does not warrant a mention?

Also, what about the effect of billions of 36.6 oC people on this planet? Surely all those lovely warm bodies exuding heat should heat up the air around us over time?

Can anyone justify why this is so... or add something regarding this on one of these pages? I have looked on the internet and the only reference I found was way too full of jargon for me to make head or tail of it.

ChantalME 13:32, 16 October 2007 (UTC)

Maybe the amount of carbon dioxide a person breathes out is negligable compared to the amount of carbon dioxide pumped out by transport and powerstations and animal farms to supply the "needs" of that same person. I personally agree that increasing human population increases global warming, but this comes mostly from the actions/consumption of that person, more than their breathing/body heat. --Seans Potato Business 14:20, 16 October 2007 (UTC)

Exactly. Expired CO₂ through respiration or body heat is nothing compared to the amount of greenhouse gases or heat produced for energy and food purposes. --24.147.86.187 16:31, 16 October 2007 (UTC)

As Sean says, it is the knock-on effects of a growing population that significantly influences global warming, rather than the people themselves. For example, more people need more space to live, leading to deforestation. Also, more people need more food. More food mean more crops and livestock. Have a read of Livestock's Long Shadow to understand the effect of that on global warming. Rockpocket 16:47, 16 October 2007 (UTC)

Living creatures have no net effect on the amount of CO2 in the atmosphere. For every molecule of CO2 breathed out by a human or other animal, there is a food plant somewhere that will take that molecule and turn it into sugar and oxygen. --Carnildo 21:41, 16 October 2007 (UTC)

Sorry - but all of the previous respondants (except Carnildo who beat me to it with an edit conflict) have utterly missed the point. (They aren't wrong - they just missed the crucial thing!)

The CO2 you breathe out comes from the breakdown of carbon compounds in your body. The carbon in your body came from the food you've been eating. The carbon in the food either came from a plant - or from the meat or milk or eggs of something that ate a plant (or something that ate something that ate....a plant). So all of that carbon basically came from plants. How did the plant get the carbon? Well, it absorbed it as CO2 through its leaves and used photosynthesis to turn it into sugars and starches. So - in the grand scheme of things, humans (and all other animals) are 'carbon-neutral'. By eating big plants and replacing them with little ones - we're effectively removing CO2 from the air - then cycling it through this big chemistry set and pushing the exact same amount of CO2 out again. Every single microgram of CO2 that every single human produces was fairly recently sucked out of the air by a plant somewhere. The more of us there are, the more plants we eat - the more small plants are growing into big plants and consuming CO2. Everything balances (well...almost...see the bit at the end).

The difference with cars and coal fired power stations and other problematic things is that we fuel them by digging up coal and oil that's been locked away for millions of years. Since the coal and oil isn't being replaced at anything like the rate we're digging it up, we're putting CO2 into the atmosphere WITHOUT locking a corresponding amount away again. A wood-burning power plant - based on renewable/sustainable forestry techniques - or a car that ran on ethanol made from saw-grass that could be grown sustainably - would be no problem at all for global warming.

There is a teeny-tiny caveat that messes up an otherwise beautiful picture. There is no nice way to say this...the problem is: farting. The deal is that some of the carbon we ingest turns into methane - which we fart out. Methane is a much nastier greenhouse gas than CO2. So a very, very tiny percentage of the CO2 that we (indirectly) consume gets turned into a nastier form than CO2 by the time we're done with it. Having said that, there is little or no evidence that the tiny amounts involved are in any way a problem for the planet. However, one big concern for global warming is our farming of cows. Cows fart a LOT more than we do - and we humans have dramatically increased the number of cows in the world. Cow farts are a serious part of global warming - and there are (believe it or not) bunches of scientists out there wondering whether we can genetically engineer cows that don't fart as much - and a bunch of technologists wondering whether we can capture the methane that cows produce and use it to generate electricity - and in the process, turn it back into CO2 so that the grand cycle of CO2-plant-cow-fart-methane-CO2 can be completed.

SteveBaker 21:43, 16 October 2007 (UTC)

Indeed, Steve. You will notice I previously mentioned the effect of livestock on global warming and, hence, did not "utterly miss the point". Rockpocket 01:16, 17 October 2007 (UTC)

The critical point you missed (and to directly answer the OP's question) was to explaining that the human metabolism is carbon-neutral. SteveBaker 14:33, 17 October 2007 (UTC)

As I mentioned in an earlier questions, cow methane farts aren't actually the big problem. They primarily burp it. See Burping, Methanogenesis and Cattle Nil Einne 16:18, 18 October 2007 (UTC)

Don't forget to plug our article on the carbon cycle. TenOfAllTrades(talk) 01:57, 17 October 2007 (UTC)

The question reminds me of the one that goes something like, "How much lighter would the Earth be if humans hadn`t evolved?" lol Dave 64.230.233.222 02:04, 17 October 2007 (UTC)

The problem isn't that the scenarios aren't plausible, the problem is that they are very difficult to quantify. The carbon cycle is dominated by forces much larger than anthropogenic contributions so the effect of man on CO2 is a very small forcing function that acts over decades. Since 1750 the net effect of all the oil we burned and methane we've releases is 1.6 Watts/square metere (IPCC) being retained on the surface. This is slightly more than the 1.3 W/square metre variation in the 11 year sunspot cycle and a small fraction of the 1366 W/sq metre from the sun. Sunspots and global warming are not related, but the order of magnitude is good for comparison of the type of measurement we are trying to make. It is very difficult to extract a forcing effect from such a small effect and predict it's long term behaviour with accuracy especially when our accurate temperature record is so short compared to the multitude of natural cycles of varying duration. We also don't really know how components of the carbon cycle will react to man-made CO2 entering the system with rising temperatures. The ocean and rain forest are complicated and dynamic systems. --DHeyward 07:08, 17 October 2007 (UTC)

Well, one effect is that CO2 is absorbed by the oceans. As a result they become acidic. Notice that this is not future tense - the oceans have already absorbed a large part of the CO2. If they hadn't, the global warming would have been considerably bigger. So so far they've been buying us some time. But they can only absorb a certain amount of CO2, one factor for which is the temperature. So, as the oceans warm up, they can not hold as much CO2 (I think - not entirely sure if I remember this correctly). So somewhere in the future (some of) that CO2 will get released again. So even if we would completely stop pouring still more CO2 into the atmosphere, the concentration is likely to still increase. DirkvdM 06:19, 18 October 2007 (UTC)

What are super metals?

—Preceding unsigned comment added by Safeer 123 (talk • contribs) 14:23, 16 October 2007 (UTC)

Really, really good ones. A metal is a metal is a metal, super is just an adjective. The only references I can find to supermetals (all one word) are proper nouns (company names), in reference to music (super metal), ficticious (Lodestar) or hyperbole (this cheese-fibre biscuit-reinforced steel is supermetal!). Lanfear's Bane 15:00, 16 October 2007 (UTC)

Maybe he is thinking about supersolids? 71.226.56.79 15:51, 16 October 2007 (UTC)

Sometimes titanium is considered to be a super metal...87.102.12.235 15:56, 16 October 2007 (UTC)

Also http://www.future.org.au/news_2006/march/building.html apparently 'bulk glassy alloys' are called supermetals..87.102.12.235 15:58, 16 October 2007 (UTC)

See Amorphous metal this is as near to my guess at your answer87.102.12.235 16:01, 16 October 2007 (UTC)

Supermetals usually refer to metals that excel in one or more particular properties. I've usually heard "superalloys" in the context of the metals from which gas turbine and jet engine turbine blades are fabricated.

Atlant 12:23, 17 October 2007 (UTC)

gas ideal - entropy

Another problem

For a gas (in a piston or something) (ideal monatomic) - at constant temperature - in contact with an infinite resovoir at the same temperature..

If I compress the gas slowly to half it's volume so that it is able to equilibriate with the resevoir then then work done is

(1.) Work(gas) = PVln2 (please comment if wrong)

(P=Pressure, V=Volume, N=number of molecules/atoms , n=number of moles)

And the entropy change (of the gas in the piston) is

(2.) ΔS = -Nk ln2 (since the volume has halved and assuming the number of ways to arrange the gas molecules is proportional to V^N therfor Ways_after / Ways_before = (V/2)^N/V^N = 0.5^N and ΔS =k ln Ways_after/Ways_before = k ln 0.5^N = kN ln 0.5 = -Nk ln2

(please comment if wrong)

(The entropy change of the resevoir will be infinitely increase - since it is of infinte size and gets some energy)

Assuming I got 1. and 2. right

TΔS_piston = NkT ln2

and N=Ln (L=avogadros constant and n=moles) so

TΔS_piston= nLkT ln2

and kT=R (the gas constant)

TΔS_piston= nLkT ln2 = nRT ln2

I also have Work(gas) = PVln2 (from 1.)

Which means that the TΔS of the piston gas is equivalent to the work that was done - my question is is this supposed to be significant? or is it coincicidence - or is it a definition (in part) of boltzmann entropy?87.102.12.235 14:28, 16 October 2007 (UTC)

Generically, for a reversible isothermal processes, heat flow (Q) = work (W) = TΔS. Dragons flight 22:32, 16 October 2007 (UTC)

The problem is that I get ΔS = ΔEk ln N for the entropy change of a ideal gas increasing in energy by ΔE (with N atoms) - using S=k ln W2/W1 - but this doesn't fit as well with the ΔE=-TΔS formulation - how can I go about reconsiling these two?87.102.12.235 14:38, 16 October 2007 (UTC)

I don't understand what you are trying to say here. Dragons flight 22:32, 16 October 2007 (UTC)

Probably not clear - what I'm asking is more obvious in a question below - I'm trying to use theorectical statistical entropies (ie from non experimental mathematical models) in the thermodynamic definition of entropy - one of the pages states that the two have been shown to be equivalent (using boltzmanns relationship S=k ln W) - but when I try this I only get equivalence on certain cases.. The example of changing the volume of a ideal gas (at constant T) works well. But other cases such as the when the temperature change show no match at all... The equation "ΔS = ΔEk ln N" was statistically obtained - I've clarified my question below relating to the integral S_TdT and whether or not it makes sense to use it..87.102.12.215 14:08, 17 October 2007 (UTC)

require information on CoMFA (Comparative Molecular Field Analysis)

please send the information about CoMFA —Preceding unsigned comment added by Satyaprasad2007 (talk • contribs) 15:18, 16 October 2007 (UTC)

What do you need exactly - that a web search doesn't find? eg http://ww.google.co.uk/search?hl=en&q=CoMFA&meta= ?87.102.12.235 15:23, 16 October 2007 (UTC)

two bodies - different temperatures

If I have two bodies A and B at two different temperatures T_a T_b that are isolated or insulated from everything else.. and then I join them so that they eventually attain the same temperature..

1.What 'measure of energy' should I be using for this process - is it G (gibbs energy)

and

2.What ways are known to calculated the entropy change for the temperature equilibriation process? (assume if you want that it's a very simple system if that help)?87.102.12.235 15:53, 16 October 2007 (UTC)

Can't you just measure the temperatures? Isn't temperature a measure of heat energy? You would just need to know their specific heat values? Don't worry, the real scientists will be with you in a short while :) --Seans Potato Business 16:15, 16 October 2007 (UTC)

What do you know about the system? Do you know the masses? What else? Or are you looking for some sort of general equation? (I struggle with thermodynamics, but I'm sure there'll be others...) Skittle 16:32, 16 October 2007 (UTC)

It's sort of irrelevent to the question but you can assume that the heat capacities are the same and there is the same amount of both... Couldn't you both have not answered? (smiles horribly...)87.102.12.235 17:08, 16 October 2007 (UTC)

I was trying to make sure your answer was sufficiently clear that it could be quickly, thoroughly answered by the first person who could, hopefully getting you your answer quicker. After all, you'd be annoyed if someone who could have answered gave you the answer to a different question to what you had intended, then went offline leaving you waiting hours longer than necessary. Skittle 21:03, 16 October 2007 (UTC)

Assuming no mechanical work is going to be done on the system, you would look at the internal energy, U and find the temperature T such that Ua(Ta) + Ub(Tb) = Ua(T) + Ub(T), where Ua and Ub are internal energy functions for A and B respectively. For simple gases, you often have things like U = 3/2*N*k*T where N is the number of particles, and k is Boltzmann's constant, but for arbitrary materials U can be a more complicated function.

(Good so far thanks 87.102.12.235 18:41, 16 October 2007 (UTC))

The change in entropy calculation is discussed in Entropy (classical thermodynamics). In the simplest case, e.g. equal masses of the same material with constant heat capacity, C, then T = (Ta + Tb)/2 and

$\Delta S=\int _{T_{a}}^{(T_{a}+T_{b})/2}{{C \over T}dT}+\int _{T_{b}}^{(T_{a}+T_{b})/2}{{C \over T}dT}$

$=C*(Ln({(T_{a}+T_{b})^{2} \over {T_{a}T_{b}}})-2Ln(2))$

Dragons flight 18:20, 16 October 2007 (UTC)

What about the common formula ΔG=ΔH-TΔS can I use that here in the form ΔG=ΔH-ʃS_TdT ( ΔH=0 ? ) to calculate if ΔG is negative (and hence if the process occurs)

I was really thinking about a theoretical treatment so I'd be using a derived estimate for S (or maybe C) at a given temperature.87.102.12.235 18:29, 16 October 2007 (UTC)

Specifically if I have an equation for S at a given temperature is ΔG=ΔH-ʃS_TdT workable (and if it is wrong please explain why.. thanks) 87.102.12.235 18:41, 16 October 2007 (UTC)

In the above example if T1=T2 then the entropy change is zero - but if the masses are initially separated (thermally) and then allowed to exchange energy (even though T remains the same) by removal of the thermal barrier this causes an increase in entropy (statistically - and possibly depending on your point of view..) (this can be considered like a sort of phase change - depending on your point of view) How does classius's definition of entropy deal with phase changes of the example I gave above in general?87.102.66.248 21:09, 16 October 2007 (UTC)

NOTE: I think I've resolved this - if I make atoms distinguishable but energy indistinguishable as particles then boltzmanns S=k lnW is ok - otherwise not. Anyway if anyone can answer my bolded question above I'd still appreciate it, and if anyoen can tell me more or help out I'd still appreciate that too.87.102.12.215 15:21, 17 October 2007 (UTC)

24 hr urine - checking that we got a full sample

Apparently from creatinine clearance, we can infer whether or not the full 24 hr urine was collected. You can take the concentration of creatine in the blood, the amount in the urine, and divide the amount by the concentration, to determine the GFR necessary to provide this amount in the urine, assuming 100% transfer from glomerulus to urine. Now sure, if you know for a fact that there is nothing wrong with the kidney, an apparently low GFR, could simply be due to a reduced amount of creatinine in urine, directly resulting from the patient not voiding into their container D:< but how is it possible to tell from this test alone, that it is infact, not due to an abnormally low GFR? This whole test seems kinda useless to me, if an actual low GFR could be written off as a failure to collect the full 24 hrs worth of urine. --Seans Potato Business 16:11, 16 October 2007 (UTC)

I haven't thought through this extensively, but it's commonly understood (at least at the hospital I'm training at) that 24-hour urine collections are fraught with errors, including the one you mention. In practice, GFR isn't measured using creatinine clearance; instead, the steady-state plasma concentration of creatinine (along with age, gender, etc.) is plugged into something like the MDRD equation (no page!?). Similar approximations are used in the measurement of urinary protein to avoid having to collect a 24-hour urine sample. In that case, a spot urine test is done and the ratio of urinary protein to urinary creatinine is taken to approximate urinary protein (in grams) per 24 hour period. The point is exactly what you've realized: the utility of the 24-hour urine sample in determining GFR (and other values) is waning. --David Iberri (talk) 21:02, 16 October 2007 (UTC)

Tongue

Is a healthy human tongue supposed to be completely smooth, or would you expect to find bumps towards the back of the tongue? If not, what do the bumps mean? 172.206.176.138 16:21, 16 October 2007 (UTC)

If you're asking for advice about your own health, you should be warned that there's a very good reason why we say "Do not ask for medical advice" (or used to, until we had to make it broader). Anyone with sufficient medical training to give you a good answer to this question will not do so, because they know it would be unethical and dangerous (for example, they can't see or feel what you mean by 'bumps', nor can they see your medical history or examine anything else about you). The only people who will attempt to give you an answer as to what the bumps mean will not be trained or qualified to do so, as well as having all the problems a doctor would have in this situation. So they will offer even worse advice than the doctor would have thought was dangerous and unethical! If this is about yourself, or someone you know, get to a real, physical doctor and show them what you mean :) That's the only way you'll get a reliable answer. Skittle 16:28, 16 October 2007 (UTC)

I'm a biology student and this is part of an assignment of mine. I've tried looking around the web, but as yet I've found nothing written in a level of English that I can understand and so Wikipedia now seems like my best option. 172.206.176.138 16:40, 16 October 2007 (UTC)

Notwithstanding what Skittle said, a human tongue is typically not smooth. There are four types of papillae on the human tongue: foliate, filiform, fungiform and, towards the back, circumvallate papillae. Rockpocket 16:40, 16 October 2007 (UTC)

However, when the tongue is infected, (not a common occurence), the condition is called glossitis and is characterised by a smoother than normal tongue. Richard Avery 17:34, 16 October 2007 (UTC)

As purely anecdotal evidence, I have had bumps on the back of my tongue for as long as I can remember, in exactly the way described in circumvallate papillae. --24.147.86.187 18:02, 16 October 2007 (UTC)

A human tongue should be bumpy but not as rough as a cat's tongue Nil Einne 10:09, 22 October 2007 (UTC)

Lack of oxygen and sleepiness

Today I had a meeting in a room with "bad air" (no circulation) and we all got very tired and sleepy. However, usual recommendations for a good night's sleep is that the sleeping room is well aired. Wouldn't it be easier for sleepless people to fall asleep in a room that is badly aired? Lova Falk 17:24, 16 October 2007 (UTC)

I imagine it would be easier to fall unconscious, but that doesn't necessarily mean restful sleep. You might get some enlightenment from the article on sleep apnea. --Mdwyer 20:28, 16 October 2007 (UTC)

Not to mention Carbon dioxide. It's unlikely to build up too quickly, but poor circulation can't help. -- Kesh 23:44, 16 October 2007 (UTC)

Technically I think it would be easier to fall asleep in a "badly aired" room. However, I think the point of the advice you cited is not to help people fall asleep, but to make sure nothing happens to them while they are sleeping. You can add a good amount of carbon monoxide to a room, go lay down, and you'll fall asleep within no time, but you also won't wake up.
Mrdeath5493 04:41, 17 October 2007 (UTC)

As Kesh said, carbon dioxide is probably the key, but the general heating of the room and boredom probably provides the rest of the explanation. Next time, may I suggest buzzword bingo as a remedy? Or clandestinely edit Wikipedia...

Atlant 12:26, 17 October 2007 (UTC)

:) Thanks! Lova Falk 11:31, 18 October 2007 (UTC)

LASIK

"LASIK" stands for "Laser-assisted in situ keratomileusis". Since they feel it neccessary to mention that the process is in situ, this implies that there is a process where they don't work on your eye in place -- that they pop the eyeball out, reshape the lens, and put it back in. What's this process? --67.185.172.158 18:59, 16 October 2007 (UTC)

Um, just because they point out that they are doing something doesn't mean that the converse exists. Especially when you are talking about a name that happens to make a cool-sounding acronym. In any case, see keratomileusis for discussions of how it was done before lasers. --24.147.86.187 19:44, 16 October 2007 (UTC)

First of all, in situ means (generally) "in the normal location". Therefore the eye is left in it's normal location. Please see the article on LASIK for more on LASIK and Dictionary.com (http://www.dictionary.net/in+situ) for the definition of in situ. I have had LASIK, and you are awake during the entire operation, and believe me, the eyeball is not taken out of it's socket. Josborne2382 07:43, 21 October 2007 (UTC)

medicine online

Is there any serious university in the US or UK offer medicine online? At least the first two years. —Preceding unsigned comment added by 88.0.101.106 (talk) 19:28, 16 October 2007 (UTC)

Not to my knowledge. What would be the purpose of providing two years of medical school online? Generally speaking, the medical profession is not keen on the idea of many people becoming only half-versed in medicine. Entering medical students are generally warned to not provide medical advice until after completing their degree. The patient experience gained in the clinical years (third and fourth years of a four-year M.D. degree) are crucial. Andrewjuren(talk) 22:03, 16 October 2007 (UTC)

• A study in medicine is also pretty useless if you don't have any practical experience in a laboratory or with patients. - Mgm|^(talk) 08:52, 17 October 2007 (UTC)

I just thought that I could do online the two years until the usmed step 1 and then go to the practical experience...Actually there are some 'schools' offering online programs, but they are clearly not serious. —Preceding unsigned comment added by 88.0.101.106 (talk) 12:18, 17 October 2007 (UTC)

How to minimise my exposure to halogens in my food and water?

I no longer wish to be subjected to forced halogenation by government agencies against my individual will. How can I remove all fluourine and chlorine compounds from my water supply and the iodine from my salt, leaving only the untainted product behind? —Preceding unsigned comment added by 62.136.234.82 (talk) 21:44, 16 October 2007 (UTC)

If you can, you could dig a well for your water, it'd probably be easier to just go to the source rather than try to remove fluorine and chlorine. You'll find that Kosher salt is iodine free. -- JSBillings 22:42, 16 October 2007 (UTC)

Buy your water from a difference source, or buy expensive filtering systems that can remove it. The former is probably cheaper than the latter, especially if you are only talking about drinking water. As for salt, simply don't purchase iodized salt—there are lots of non-iodized varieties out there (i.e. sea salt or kosher salt) and purchasing them is surely easier and less expensive than trying to remove the iodine from the salt. Note that I think being paranoid about these sorts of public health measures is a bit silly, but hey, it's your choice, right? --24.147.86.187 22:35, 16 October 2007 (UTC)

Nethertheless you needs chloride and iodine in your diet to survive. Don't try to reduce these to zero. Well water will almost certainly contain chloride, and some fluoride dissolved from the rocks. Graeme Bartlett 23:25, 16 October 2007 (UTC)

Don't worry, if he ever eats out of the house he'd bound to pick up enough. There's a futility to trying to remove things like iodized salt from your diet when almost all salt you consume outside the house is probably going to be iodized anyway. --24.147.86.187 01:02, 17 October 2007 (UTC)

Don't go near the seashore. There are a lot of aerosols that come off the water. There's bound to be iodine in them. And I would guess a few naturally produced chlorinated organics as well. Delmlsfan 02:44, 17 October 2007 (UTC)

Firstly, well water is highly fluorinated. Secondly, avoiding iodine is not a good idea. The reason iodine comes in salt is because long ago iodine deficiency was common; This caused public health issues such as goiters and cretinism. About removing chlorine... That doesn't make sense. Chlorine is one of two atoms that combine to make table salt. So if you buy Kosher salt to avoid iodine (which is stupid in and of itself) then you'll still be ingesting chloride from the salt. My thoughts: Judging by the content and tone of your question, I believe you have a niacin deficiency.
Mrdeath5493 04:37, 17 October 2007 (UTC)

I think the poster was saying that they wanted food products without having any additives - I assume your description of a niacin defficiency was intended as a joke. Mostly though you were a little insulting - what vitamin deficiency to you attribute to that?87.102.12.215 14:24, 17 October 2007 (UTC)

You could always launch an air strike on Russia. Confusing Manifestation 06:43, 17 October 2007 (UTC)

(Assuming you're cocerned about halomethanes and the like,) would an air stripper do the trick? Are they available for home use?

Atlant 12:28, 17 October 2007 (UTC)

In my experience, most table salt in the UK (which is where the OP appears to come from), is not iodized (some shops like Lidl sell iodized salt as default, but this is because it is the same salt they sell in Germany, where it has to be iodized). I would suspect that sea salt would contain significant amounts of iodine, as well as various other impurities (sewage, dead fish, etc) which are not present in the purified rock salt usually sold for table use. However, as the OP wishes to avoid chlorine compounds, then he will not be using any salt at all, and will die a slow and painful death as a result of electrolyte depletion. Water filters aren't that expenxive nowadays (I use one, because the water in Brighton tastes foul, and cannot be used to make a decent cup of tea). OP cold move to an area without fluoridated water if a filter would not be practicable. DuncanHill 12:37, 17 October 2007 (UTC)

In the US, restaurant salt is typically not iodized (because some people have mdeical iodine restrictions), and everywhere sea salt actually contains much less iodine than iodized table salt. Seafood has lots of iodine, but the salt doesn't. --Tardis 19:58, 17 October 2007 (UTC)

Sea salt indeed usually has less iodine then iodised salt and some people buy it for this reason (and the false belief it's better because it's 'natural'). But personally I would much rather eat the iodised salt then have an iodine deficiency. It can be in a problem, particularly in some countries because of issues like a low level of iodine occuring naturally [2]. Nil Einne 10:24, 22 October 2007 (UTC)

If tap water has lots of chlorine, it helps to pour some to a glass or bottle, and wait while it bubbles out. I, however, have only seen water chlorinated in such an amount right after a breakage of water pipes, when they need to fertilize the pipes. – b_jonas 20:33, 18 October 2007 (UTC)

Radio Transmissions and Camera Transmissions

This question relates to the other question previously posted. Is it difficult to get a closed circuit camera signals if it were in a cave or sewer or underground? Would there be a way to boost those signals or does the ground and other interferences cut off the signal? —Preceding unsigned comment added by 67.121.107.157 (talk) 21:49, 16 October 2007 (UTC)

The closed-circuit television system itself is irrelevant to the question. If you have a wire-based transmission (which is the case for most CCTV installations), then the environment is of little consequence. If wireless, then yes, transmission is impeded to various degrees. A more powerful transmitter and a higher-gain antenna are two means of boosting wireless reception. The broadcast frequency is also a significant factor. — Lomn 22:56, 16 October 2007 (UTC)

So, if it is wireless and you boost wireless reception and a more powerful transmitter and a higher gain antenna then it is possible to still get transmissions if it were underground and the receiving end was above ground or down in a sewer, there would still be a way to receive signals? —Preceding unsigned comment added by 67.121.107.157 (talk) 23:23, 16 October 2007 (UTC)

Maybe. There are too many variables to give a definitive answer (e.g. how deep, what material, what transmitter, what antenna...). For instance, FM radio tends to do fine through basic road tunnels and steep valleys and such whereas AM radio doesn't, with the only distinction being frequency. — Lomn 04:14, 17 October 2007 (UTC)

What makes FM car radio work better than AM in tunnels and such is not the frequency but the method of modulation. In AM, the whole carrier is modulated, and in FM, the carrier's frequency is modulated. This means that in AM the strength of the signal available to the audio amplifier in your radio falls off with the strength of the radio wave at the antenna and will get down into the noise pretty quickly. In FM, the audio is more or less encoded in a frequency shift, so that practically any signal at all at the antenna will deliver full audio. This is a simplified version of what really happens, to be sure, but close enough for jazz.

As for underground radio, it seems to me that it can't be done. The ground is, well, ground, and radio waves are produced with respect to ground. There is a ground wave that will run along the surface to an extent, more with lower frequencies, so that if you want to send and receive from inside a cave to a spot at the cave's entrance, you might get something by using a strong low-frequency transmitter at each end.

If you really want to go nuts with it, try ELF. --Milkbreath 13:00, 17 October 2007 (UTC)

Hornworms

Do Hornworms develop under water? —Preceding unsigned comment added by 75.44.152.111 (talk) 22:40, 16 October 2007 (UTC)

It would not appear so. Hornworm. Someguy1221 03:25, 17 October 2007 (UTC)

Which article starts with the following quote: "M. sexta have a short life cycle, lasting about 30 to 50 days. In most areas, M. sexta have about two generations per year, but they can have about three or four generations per year in Florida.[2]" From this, I conclude that a year is about 60-100 days long, except in Florida. I was unable to find any other data on this page to explain why Florida has a different length year than the rest of the world. SandyJax 15:28, 22 October 2007 (UTC)