Wikipedia:Reference desk/Archives/Science/2012 February 29

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February 29

Compressed water

Why aren't people in the army or who might be traveling for a long time in the desert for some other reason issued tablets of compressed water - just take one and it contains as much water as a full water bottle? Wouldn't that allow your average soldier to carry lots more water than he could otherwise? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 00:29, 29 February 2012 (UTC)

Water tablet, just add water. 203.112.82.128 (talk) 19:56, 2 March 2012 (UTC)

Water is an incompressible fluid. XPPaul (talk) 00:38, 29 February 2012 (UTC)

I see whoop whoop is getting bored again and is asking questions he already knows the answer of, thereby probably driving away people with genuine questions. Stop it! 58.169.242.219 (talk) 00:41, 29 February 2012 (UTC)Wickwack

Not everyone knows that, the answer is not evident for all. XPPaul (talk) 00:42, 29 February 2012 (UTC)

Paul is actually incorrect. Water is only approximately incompressible. However, that approximation is extremely good. If you were to compress water at 10,000 atmospheres, you would get room temperature ice that is only 70% denser than liquid water at room temperature. Regardless, the limitation in carrying rations is the weight, not the volume. Someguy1221 (talk) 00:45, 29 February 2012 (UTC)

Looking into this more, just getting water to be 1% denser would require 200 atmospheres [1]. Someguy1221 (talk) 00:48, 29 February 2012 (UTC)

OK, I was not completely right, but I'd say I was approximately correct, water is not an incompressible fluid, it's only approximately incompressible. Anyway, it's incompressible for all practical purposes. XPPaul (talk) 00:50, 29 February 2012 (UTC)

One of the tricks to answering questions well on the ref desk is working out what level of detail the OP actually needs and not unnecessarily confusing them with extraneous information. Your answer, while less accurate than one that talks about what happens under 10,000 atm pressure, was a better answer. --Tango (talk) 00:54, 29 February 2012 (UTC)

Precisely! Now, whoop whoop is a frequent poster of questions and responses, sometimes intelligent, sometimes stupid, sometimes Dorothy Dixers, that it seems obvious the he himself would already know the answer to this one (another Dorothy Dixer), and so he requires no answer at all. Wickwack01:43, 29 February 2012 (UTC)

Are you suggesting the OP is insane? ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:09, 29 February 2012 (UTC)

No. Just a nuisance. I'm concerned that there may be people who know stuff and could spare the time to post good answers will not bother if they sense that the OP does not have a genuine need. Similarly, there may be people who would like some help with a realy good question, who won't bother if they think this is just a DD place. Wickwack58.169.241.13 (talk) 02:28, 29 February 2012 (UTC)

Link for non-Aussies: Dorothy Dixer. XPPaul (talk) 02:16, 29 February 2012 (UTC)

For non-Aussies again: The Wiki articale on Dorathy Dixers gives the original meaning of the term, and the one used in Australian Press (and in the UK) when discussing Govt ministers, but common street meaning include questions that the questioner already know the answer to, or questions asked at a meeting designed to stir people up rather than to get an answer. Wickwack58.169.241.13 (talk) 02:35, 29 February 2012 (UTC)

This sounds like a variation on the old elementary-school-level joke. A kid takes an empty can to show-and-tell. He says it's condensed H2O. Just add water! ←Baseball Bugs ^{What's up, Doc?} carrots→ 00:51, 29 February 2012 (UTC)

Even if you could compress the water by any appreciable amount under a billion atmospheres of pressure and place it in a strong enough tablet sized container made from a digestible and non-toxic material, and even if you were having your soldiers march on the moon so weight is less of an issue and volume is important to minimize, then what happens when you take the pill? The container is breached and explosive decompression happens...in your gut. 203.27.72.5 (talk) 05:01, 29 February 2012 (UTC)

I imagine you could just decompress it into any old container first. Vespine (talk) 06:03, 29 February 2012 (UTC)

Why? So you could use it as a fragmentation grenade? The pressures involved are enormous. 203.27.72.5 (talk) 06:57, 29 February 2012 (UTC)

The pressures involved are enormous only because you made them so - you defined it as a billion atmospheres... Now getting back to the qustion:

No, it was inherent in the OP's question. Compressing a normal bottle of water into a tablet size will require enormous pressure. A billion atmospheres was just a number I plucked out of the air since I couldn't be bothered to calculate exactly how enormous said pressure would be. 203.27.72.5 (talk) 00:06, 1 March 2012 (UTC)

followup

Actually, guys, isn't half of the water all you would need to compress, since water is H2O and oxygen is already in the air? So couldn't you just compress hydrogen gas and "burn off" water to drink it? You would automatically reduce the weight of the "water" carried by 50% anytime you were in a location with oxygen, which is 100% of the time a soldier is breathing the local atmosphere? --80.99.254.208 (talk) 09:23, 29 February 2012 (UTC)

as a cute ancillary benefit, couldn't you even use the heat from burning the water off to do something useful, like heat their meals? Thus you would in one swell foop produce a warm meal and water to go with it... Why wouldn't this work? --80.99.254.208 (talk) 09:24, 29 February 2012 (UTC)

Water is actually only 11% hydrogen by mass. But it's not dense at all, actually. The typical liquid hydrogen used in industrial/scientific applications actually takes up more volume than water containing the same amount of hydrogen. And as a compressed gas, it's even worse. So once gain, you're going to be dealing with absolutely ridiculous pressures, except now you're storing a dangerous explosive :) Someguy1221 (talk) 10:58, 29 February 2012 (UTC)

So if you don't care about volume, only mass, then you can save 88% of the weight of water if you just keep hydrogen with you? Incidentally, if you keep it as a gas wouldn't it just float and follow you around, so a huge hydrogen-fillled balloon would, though quite explosive, actually be a weightless source of water whenever you need it? (with heat a biproduct)? Is this true or am I missing something... Also if hydrogen is lighter than air, couldn't you store it in a parachute with a long string, keeping the flammable explosive thing far from where you're using it? (I use the example of a parachute not because most soldiers carry it around, but because it's only half of a vessel, like a Diving_bell - except instead of water around it, it's air around it, and instead of oxygen in it, it's hydrogen in it. Due to low pressure difference the "bell" could be a very large incredibly thin film like seran wrap, couldn't it? --188.6.93.81 (talk) 11:59, 29 February 2012 (UTC)

The original question is silly, but it led me to a different question that is possibly not. If we can't compress water physically, can we do it chemically? There are compounds called hydrates which consist of a salt and a number of molecules of water. If we can find a sufficiently dense hydrate with a sufficiently large water to salt mass ratio, it would contain more water in a unit of volume than does (liquid) water.--Itinerant1 (talk) 09:34, 29 February 2012 (UTC)

There are some hygroscopic substances which are good dessicants that may meet that requirement. Perhaps something like silica gel or calcium chloride? --Jayron32 12:56, 29 February 2012 (UTC)

They can certainly absorb lots of water, but the hydrate-complex is going to be "less water-dense" (have a larger mass and volume) than the same amount of contained water if it were pure. Dessicants have pores and/or chemical binding sites where water molecules can fit, but that means the water molecules are still present and still taking up space but now dispersed among the matrix atoms. They sometimes don't become noticeably larger when they become wet, but that's because they were originally an open(er) framework. There's just not much space between water molecules themselves to be able to push them closer together physically (hence non-compressible to a good approximation) or be able to wedge something in between that could pull them closer (they are already bonded to each other, not like a parent can insulate two unruly children from each other in a tight back carseat). DMacks (talk) 13:59, 29 February 2012 (UTC)

Now this thread exemplifies why I don't like to shoo people away for asking silly questions. You've made soup from a stone, a pearl from a grain of sand. Good work! Wnt (talk) 17:49, 29 February 2012 (UTC)

There should be no objection to "silly" questions, and I've never objected to them. That's because what can seem silly to one person might not be so for a different person due different education, background, etc. For most people, if they didn't need an answer, they would not have asked. And yes, there are pearls in the posts responding to this one. But what I still object to is one person (whoop whoop) clogging up Science Desk with questions he clearly just thinks up for entertainment and not because he needs an answer. Wickwack124.182.150.144 (talk) 00:20, 1 March 2012 (UTC)

Elemental Composition of Clay

Hello. I was looking for detailed information on the elemental composition of clay (or various types of clay). All the sites I've found give qualitative information, whereas I am looking for quantitative information. Many thanks. 114.77.39.141 (talk) 00:53, 29 February 2012 (UTC)

Clay is mostly made of silicates (phyllosilicates to be precise). You can read more at clay minerals. --Tango (talk) 00:57, 29 February 2012 (UTC)

That will vary enormously from sample to sample, and there's no generallyy useful answer. What do you need this information for? It's a lot easier to help you find an answer when we know exactly what you need. Dominus Vobisdu (talk) 01:02, 29 February 2012 (UTC)

A few types of clay include Kaolinite (Al₂Si₂O₅(OH)₄), Chlorite ((Mg,Fe,Al)₆(Si,Al)₄O₁₀(OH)₈) and Illite (K,H₃O)(Al,Mg,Fe)₂(Si,Al)₄O₁₀[(OH)₂,(H₂O) which as you can see may contain a wide variety of elements.Tobyc75 (talk) 01:08, 29 February 2012 (UTC)

The reason I need the information is because someone ism making a (in my opinion quite ignorant) claim that the composition of the human body and clay are somewhat identical. I looked at http://en.wikipedia.org/wiki/Composition_of_the_human_body, and was looking for something with %mass of the various elements of clay. I understand that the composition will vary from place to place often significantly; either general or specific examples are good for my needs. Whatever you guys find!114.77.39.141 (talk) 13:29, 29 February 2012 (UTC)

You can look through the different types of clay at Category:Clay minerals group. Unless this someone thinks that the human body is 20% aluminum by mass, he has no idea what's in most clay minerals. Even the few that don't have aluminum have far too much silicon, and are carbon-poor. That list isn't all inclusive, though, so I can't rule out that there is some obscure type of clay somewhere that is reminiscent of the elemental composition of a human body. Someguy1221 (talk) 22:15, 29 February 2012 (UTC)

copper sulphate

In an oxidizing chalcopyrite (CuFeS2)system producing CuSO4 is there a point when an ion exchange could occure producing CuO and CaSO4? — Preceding unsigned comment added by 187.146.184.128 (talk) 02:22, 29 February 2012 (UTC)

Do your own homework. Whoop whoop pull up ^{Bitching Betty | Averted crashes} 02:24, 29 February 2012 (UTC)

Clue - where does the Ca ion come from? Graeme Bartlett (talk) 09:06, 29 February 2012 (UTC)

Other than water, expand as they freeze?

Does anything, other than water, expand as it freezes? Eomund (talk) 04:22, 29 February 2012 (UTC)

Yes. Silica glasses do. 203.27.72.5 (talk) 05:06, 29 February 2012 (UTC)

bismuth Graeme Bartlett (talk) 09:03, 29 February 2012 (UTC)

... and elemental silicon. Gandalf61 (talk) 09:37, 29 February 2012 (UTC)

... and beer. I'll never leave a case of bottles of beer in the garage over winter again. Zzubnik (talk) 10:12, 29 February 2012 (UTC)

You can keep beer from freezing, if you store it in a cooler at above freezing temperature. The cooler not only stops heat from getting in, it also stops heat rom going out. Plasmic Physics (talk) 10:54, 29 February 2012 (UTC)

Beer is certainly due to its water content, it is just dirty water as far as this is concerned. You would be ok with vodka though. This book (1867) claims iron and zinc have this property. I have never heard of this for iron, can someone confirm they are incorrect - casting would be a bit of problem for mould destruction I would think. Whoops, here's another 19th century source that claims it for cast-iron, antimony, and bismuth and now I've started looking there are numerous 19th/early 20th century sources which say cast-iron expands. SpinningSpark 10:57, 29 February 2012 (UTC)

Gallium. According to that article, only gallium, silicon, antimony, and bismuth among the elements have this property. Wnt (talk) 17:42, 29 February 2012 (UTC)

Gray cast iron. Also plutonium. Whoop whoop pull up ^{Bitching Betty | Averted crashes} 19:40, 29 February 2012 (UTC)

See negative thermal expansion. StuRat (talk) 21:03, 29 February 2012 (UTC)

Active galactic nuclei obvious?

Hi I'm a scientific layman who's been wondering about something for at least 10 years now. Reading Active galactic nuclei prompted me to remember this. The article states that the theory of active galactic nuclei has not been widely accepted until recently, as well as supermassive black holes at the centre of galaxies. Even a quasar has only been recently regarded as a 'type of active galaxy where the enormous energy output results from matter falling into a massive black hole in the center of the galaxy'. Now my question is - hasn't all of this been obvious ever since the structure of galaxies has been discovered, as well as the widely accepted Big Bang? If, after all those billions of years ago after the big bang, matter swirled and whirled while expanding outwards, forming planets, stars and galaxies, why is it not obvious that the huge gravitational force at the centre of a galaxy should not arise in a massive black hole? After all the galaxy has enormous mass, and their elliptical structures have shown scientists for decades now that there is still rotation around a centre... and black holes have been talked about for decades... so surely it's obvious that there cannot be anything else but a supermassive black hole at the centre? Did they just not think about the centre of the galaxy before? Sandman30s (talk) 10:44, 29 February 2012 (UTC)

It wasn't obvious that such a thing could actually happen, though. For black holes the mass of our Sun, the average density preceding black hole formation would have to be greater than that of an atomic nucleus. It wasn't until the late '60s that such matter was demonstrated to exist, in the form of neutron stars. And for larger black holes that require less density beforehand, an incredible number of stars would be required. Our article on Schwarzschild radius points out that for an object with an average density of 1000 kilograms per cubic meter (the density of water), a mass of 150 million suns would be required. Again, it may not have been obvious that such a quantity of matter would actually exist all in the same place. We know now that such black holes do indeed exist, along with far larger ones. But none of this was obvious fifty years ago. Someguy1221 (talk) 11:10, 29 February 2012 (UTC)

Consider the powerful forces around an oceanic whirlpool and the incredible suction. Now multiply this by zillions and consider the intense gravimetric forces around the centre of an entire galaxy... isn't (wasn't) it obvious that the maths should still apply? Even if there wasn't empirical evidence before, I'm just saying that it's no great surprise to me that a supermassive black hole exists. Sandman30s (talk) 12:14, 29 February 2012 (UTC)

Except for the very centre, the supermassive black hole is not important for the dynamics (rotation etc.) of a galaxy. Overall, the combined mass of the stars (and dark matter) is still much larger than the mass of the black hole. Essentially, galaxies are self-gravitating systems, i.e.~the main components (stars, dark matter) create the gravitational field in which they move. To model the observed motions accurately, one needs the dominant mass distribution to be diffuse, spread out across the entire galaxy. A single compact mass component at the centre (like a black hole) does not do the trick. Dynamical effects of a central black hole only become apparent when one looks closely at the central parts of galaxies, something that has only become possible quite recently. --Wrongfilter (talk) 12:43, 29 February 2012 (UTC)

Would a better analogy than a whirlpool be a hurricane? The eye of the hurricane is not responsible for the rotation effects. --Mr.98 (talk) 15:05, 29 February 2012 (UTC)

The active galaxy nature of quasars was not obvious for quite a long time. Take a look at quasar#History of observation and note that for a long while there were apparently no optical counterparts, just compact radio sources. When an optical component was discovered some 15 years later, it was quickly found to be rushing away from us at the kind of speed usually associated with galaxies. It wasn't until the 1980s, that quasars were classified as a particular kind of active galaxy. Astronaut (talk) 17:32, 29 February 2012 (UTC)

Matryoshka doll pressure chambers

say I have a metal that can hold 30 pounds per square inch. The metal that forms a can of coke will do: http://hypertextbook.com/facts/2000/SeemaMeraj.shtml Now, let's please switch from 3 to two dimensions. Thus, our can of coke at pressure looks like this: a M c M a with M the metal and c the coke, a the air. The M sustains a pressure difference of 30 pounds per inch. (the height of my line of text is one inch).

Now what if I put an M around this whole thing, and increase the volume of coke inside c (now c1) and add some coke at the old pressure of c called c2: a M c M c1 M c M a

Now a is the air, there is a 30 pounds per inch difference between air and c. But inside you have the old can of coke: you add enough coke such that the pressure difference is still 30 pounds per inch between c and c1 (the old c).

In other words, when we went from a M c M a to a M c M c1 M c M a

what we did is "take a can of coke (in 2 dimensions), and add a larger can of coke around it. Fill the larger can of coke such that the pressure difference between it and the outside air is 30 pounds per inch, and add enough extra coke to the original can (now filled with c1) such that it creates a pressure difference of 30 pounds per inch between c1 and c.

My question is: doesn't this allow you to store so much coke in the same size container, that, were it in the outside air, it would be at 60 pounds per inch?

Now let's generalize. Instead of M on one side and M on the other side, let's put M on one side of the coke and E on the other. E is like M - just a metal surface of one inch height. But E contains a small smart-valve (the -) that pumps to the left until there is a pressure difference of 30 pounds per square inch, then stops. If you want you can imagine the top and bottom _ as being leads outward of negative and positive charge, to supply the power to do this work.

Now we start with M c E , an empty can of coke. We submerge it in a large vat of coke and connect the leads (the top and bottom of E (ascii just lets me show _ as the bottom lead). The E pumps the can full of coke, to 30 pounds per inch pressure. Now we reach into the vat and add another layer of M and E and connect the leads of the first E to the leads of the second E.

We now have: M c M c E c E the outside E starts pumping, and as it does the inside E starts pumping.

We repeat until we have M c M c M c E c E c E with the e's all connected. Again the outside E starts pumping, then the second from outside E starts pumping, and so on, until the innermose E starts pumpting.

Now here is the crux of my question. At what point does something strange happen or we can't continue doing this?

What keeps me from making a mile of such layers, and get the innermost can of coke filled with houses or warehouses or planets full of coke? As far as each M is concerned, it still just has to handle 30 pounds per inch of pressure difference....

This question directly addresses itself to the hydrogen question above... Wouldn't this setup allow you to pressurize hydrogen to any pressure you wanted, keeping any amount in as small an volume as you wanted? (referring to the innermost can of coke).

what is wrong with this "invention"? --188.6.93.81 (talk) 12:23, 29 February 2012 (UTC)

First, the extra coke isn't helping — just do MMMc'MMM. Second, for liquids, the density does not go up linearly with pressure. Instead, expect that at (say) 300 psi, your coke will be 110% density or something like that. For a gas (until you liquefy it via pressure!), yes you get lots of extra density (and so we have pressure vessels), but in practical applications the limit is often on the size or mass of the whole vessel, and all those Ms add up. (Also, at high enough pressures you may get problems arising from the severe compressive load on the innermost metal.) --Tardis (talk) 14:37, 29 February 2012 (UTC)

Your final sentence is EXACTLY what my whole thought-experiment is designed to elicit. You say "you get problems arising from the "severe compressive load on the innermose metal.". But my question is: WHAT compressive load. There is 30 pounds of compressing load on that innermost M and E. In fact, the innermost E assures that.

I guess an alternative way to phrase this is:

Is there a difference between a compressive load of 30 pounds between, below, (a) and (b) in the following three instances:

I air = (a) M (b) E air = (a)

II air M c2 = (b) M c1 = (a)E c2 = (b) E air

III air ... MMMMM c2 = (b) Mc1 = (a)E c2 = (b) EEEEEE ... a

The layers of coke in between are still there. They are to show you that you are only dealing with a local pressure difference of 30 pounds per inch... --188.6.93.81 (talk) 15:48, 29 February 2012 (UTC)

What you're speaking to is the pressure difference across a metal shell. That governs the net force on the shell and thus the tensile (and with imperfect symmetry, shear) stresses that the metal must withstand in order to avoid expanding (and having its outer surface area increase). However, the total pressure also plays a role: consider a closed shell of inflated balloons on the ocean floor. Even if we somehow allow the water into the cavity, the balloons will still be squashed to nearly no size. The same conditions (though note that the article is about uniaxial compression, which causes very different kinds of failure than isotropic compression causes) on a metal can cause it to change or lose crystal structure, which could ruin its tensile strength and make the whole setup fall apart. --Tardis (talk) 03:08, 2 March 2012 (UTC)

So, given that the whole thing is designed so any given M or E has exactly 30 pounds per inch of pressure to deal with, if I am willing to put enough M's next to each other buffered by coke, and enough E's next to each other buffered by coke and with connected insulated leads, then as long as an M and an E can support 30 pounds per inch of pressure, can I build up any pressure I want with a sufficiently long chain of McMcMcM's and EcEcEcE's? More to the point, why would there be anything dangerous in this, as on the outside, puncturing the E or M would only cause the next layer to have to handle 60 pounds per inch instead of 30, and puncturing the innermost E or M is the same - it would just slightly increase the pressure difference on the next layer. I'm asking why we can't get to a million pounds per inch of pressure if we stack a million M's, or a billion, or whatever. Isn't there some fundamental limit or change that causes you to say "severe compressive load on the innermost metal" where in fact I see no such severe compressive load? What I'm trying to say is that if you were trying to get a very large volume of coke into a can of coke, couldn't you just do it this way with NO ill effects or large compressive loads, just the necessity of a large group of buffered M's and E's... 188.6.93.81 (talk) 15:55, 29 February 2012 (UTC)

an alternative phrasing

does the innermost M "feel" any different from the outermost M, given that it just has coke on both sides of it with a 30 pounds per inch pressure difference and thus absolutely no way of knowing how many layers are outside of coke of decreasing pressure are outside of it and, thus, no way of knowing what volume of coke is represented by the 30 pounds per inch pressure? Note that I don't really care how much the volume is decreased at increasing pressures. I'm just curious why we can't safely and cheaply get to arbitrarily large pressures with an arbitrary number of layers of M's and E's, with the innermost pressure chamber feeling no more pressurized than if it were at 30 pounds per inch pressure compared to the atmosphere just outside it... (instead of compared to the next layer, which is pressurized compared to the next layer, which is pressurized compared to the next layer, etc....) 188.6.93.81 (talk) 15:59, 29 February 2012 (UTC)

" I'm just curious why we can't safely and cheaply get to arbitrarily large pressures with an arbitrary number of layers of M's and E's" Because E is a magical substance that you just made up for a though experiment? 203.27.72.5 (talk) 21:24, 29 February 2012 (UTC)

As the number of shells increases the curvature of the outer-most shell is reduced. This lowers the structural integrity, so for a large enough radius of the shell, it will no longer withstand the pressure differential. See Pressure_vessel#Scaling. Without this effect, gas cylinders could have a square footprint which would make storage much more efficient and increase their stability when standing upright. 203.27.72.5 (talk) 21:41, 29 February 2012 (UTC)

You will also find from the equations in the article Pressure vessel that doubling the pressure differential doubles the mass of vessel material required if all other parameters are kept constant (volume, density and stress tolerance of the vessel material). So by making concentric coke cans, you're just wasting materials since you have a larger volume with each consecutive can with no advantage in terms of withstanding a greater pressure differential. So if you just used all of the material for the concentric coke cans in one extra thick can you would contain a larger pressure differential (though scaling this up is still limited by the aforementioned equations). Crunching the numbers, if you wanted a standard 12oz coke can that held 1 billion atmospheres (and made it from steel since I couldn't find the stress tolerance for aluminum) then it would need to contain 2 million kilograms of steel and it would be 10 meters high and 5.5 meters in diameter. 203.27.72.5 (talk) 22:04, 29 February 2012 (UTC)

Baryons, Quarks and the Pauli Exclusion Principle

Almost at the top of http://en.wikipedia.org/wiki/List_of_baryons, it says that: "Baryons composed of one type of quark (uuu, ddd, ...) can exist in J = 3⁄2 configuration, but J = 1⁄2 is forbidden by the Pauli exclusion principle." I must be missing something here, because I thought the concept of colour and its inclusion as another quantum number for a quark was purely to overcome the Pauli exclusion problem. As a follow-up question, am I right to assume that the value of J is merely the arithmetic sum of the individual spins of the 3 quarks? My thinking is that they each have a spin of one-half, so J=3/2 if all are pointing in the same direction and 1/2 if one quark is pointing the opposite way to the other two. — Preceding unsigned comment added by Mrt47 (talk • contribs) 13:54, 29 February 2012 (UTC)

I asked the same question here and got very detailed, though (to me) incomprehensible answers. Ratzd'mishukribo (talk) 14:03, 29 February 2012 (UTC)

Spectral line chart

Is there a chart anywhere that shows the spectral lines for all elements? You'd think this would be easy to find, but Google is failing me. (Really, it should be a wiki article!) - Goodbye Galaxy (talk) 15:26, 29 February 2012 (UTC)

If you look at the emission spectrum article you will see that the spectrum of iron alone covers a lerge band. So putting other elements on top would lead to a very confused and useless jumble. --92.29.203.125 (talk) 15:39, 29 February 2012 (UTC)

Why would you put them on top of each other? o_O A simple list is what I'm looking for. - Goodbye Galaxy (talk) 15:43, 29 February 2012 (UTC)

Here's one. — Lomn 15:47, 29 February 2012 (UTC)

Thanks! (I have to wonder why they would put the elements in alphabetical order though!) Goodbye Galaxy (talk) 15:52, 29 February 2012 (UTC)

They are in symbol order. However, each spectrum is in its own file, so you could write a bit of HTML to show them in any order you want. Personally, I'd have done it in atomic number order. 62.56.52.55 (talk) 22:20, 29 February 2012 (UTC)

The problem is that there are so many lines and so much detail, no one spectrum would suffice. Depending on what you're trying to do, you may care about only visible, or also into the UV (if you're considering a tanning bed or plant lights, for example). Or IR, if you've got a sunlamp to keep yourself warm. And you might want just the lines all clearly visible iff above a certain cutoff intensity, in order to identify an unknown gas tube in lab. Or you might want intensities if you're considering the overall "color" (additive result, weighted average of the lines). Is it enough to see the approximate colors and positions on the axis, or do you need more detail than a low-res image can provide? For example, hydrogen has 568 lines, and a real database (hello NIST!) lets you see the whole set of their numerical data or just pick what range you want. Then it's easy to make a pretty picture for whatever range, level of detail, etc is useful to you.

An interesting project would be to generate SVG for the spectra--color for the vis range, b/w for a wider range at least covering uv/vis, since that would allow one to zoom in on regions of interest to see detail or zoom out to see the main bands. Stash 'em on commons, then make a wikipedia page with them all in a table. Tables can be automatically sortable by column. DMacks (talk) 16:24, 29 February 2012 (UTC)

Lomn's link is basically exactly what I was looking for, but what you're describing sounds like a great idea too. Goodbye Galaxy (talk) 16:52, 29 February 2012 (UTC)

Does the data exist as a simple table of numbers? It would be a lot easier to create svg images from the numbers, and we cannot simply copy someone elses images. Boron seems to be missing by the way. SpinningSpark 22:36, 29 February 2012 (UTC)

Hunger for exercise

I've been thinking about why obesity proves such a difficult problem, and I've been wondering if we are missing a really basic, obvious core concept: the mechanism by which people develop a craving or hunger for exercise.

It's a hard thing to search for thoroughly, but I really can't think of any research I've seen where people try to quantify and study this in the way that has been done for Neuropeptide Y and food hunger, for example. Searching for "hunger for exercise" on Google gets a number of informal results that seem to skirt what I'm thinking of, and searching for "craving for exercise" in Google Scholar/PubMed gets a number of reports about exercise dependence. But I am not sure that this is precisely the same concept - while it is well known that exercise produces endorphins (even a "runner's high"), which are potentially addictive, by analogy, it is arguable that food addiction is distinct from simple hunger. (See also POMC) I also suspect that there is a third, localized, sensation, the "desire to stretch your legs", diaphragm, etc., which is distinct from either. I suspect restless legs syndrome might be linked to this third, while hyperactivity might reflect one of the other two.

Now I'll be very specific here, and say that what I'm starting to suspect is going on is that there is a mix-up between two homologous mechanisms of behavioral control. In other words, that hunger for exercise and hunger for food use some related if not identical proteins to signal to the CNS, and that in the obese, the hunger for exercise is misconstrued as hunger for food due to overlap in the mechanisms and possible defects in one of them. Therefore, the underlying hunger for exercise is poorly addressed if at all, while the apparent hunger for food persists beyond satiation. After all, getting food and getting exercise have been linked - especially for ancestral humans, but even the chronic Wikipedian may get more exercise hauling groceries from the market than at other times. And for whatever reason, exercise seems to be required to keep the body functional at all, so there must be basic mechanisms to cause it just as there are for eating.

Now it is well known that exercising tends to decrease food intake somehow; I just haven't seen it put in such terms. But what intrigues me is that positive feedback of any sort (addictive or otherwise) should be amplified by a person's understanding of the stimulus. For example, it appears that historically a Native American could smoke a ceremonial peace pipe and not be addicted to tobacco, because he perceived that the positive reinforcement came from his religious action/perception, rather than from the tobacco itself. So I'm thinking that if we understand the exact nature of how exercise relieves the hunger for exercise - how much is needed, how quick the effect sets in, how long it lasts - then even if there is much confusion between this and food hunger, it should be possible to better reinforce the effect of exercise and shift things back toward the healthy situation.

Now admittedly this is starting to look more like a treatise than a question, but I'm curious if people have seen similar ideas expressed, studies of the signalling mechanisms and circumstances, anything which can be used to fine-tune this model and hopefully make it functional. (And to begin with, has anyone even named a craving for exercise in a normal or non-exercising person, as opposed to "exercise dependence"?) Wnt (talk) 17:23, 29 February 2012 (UTC)

One thing I've always wondered about is why humans would evolve a hunger for exercise. After all, people were facing starvation for much of our evolution, so any unnecessary expenditure of calories seems unwise. And exercising outside back then would have been more dangerous than staying inside. I can think of a few reasons why exercise craving might have evolved:

1) To develop survival skills, like running ability. This would be particularly important in childhood, where it's noted that they feel the need to exercise when they consume excess calories, particularly sugars.

2) To aid digestion. With difficult to digest foods, some exercise may help the food move through the digestive tract.

3) To advertise fitness to potential mates.

One reason that doesn't make sense to me, evolutionarily, is craving exercise to develop muscle mass, since we could have just evolved the ability to create muscle mass without exercise, when we have excess calories. It does seem odd to me, that we never did develop this ability. Starvation must have been so widespread that packing excess calories on as fat was the better survival strategy. StuRat (talk) 20:41, 29 February 2012 (UTC)

It is conceivable to me that muscle simply can't direct its own growth without receiving constant input about what the load will be. People are adapted for all kinds of weird circumstances - think about it, an ape that evolved in Africa can survive sub-freezing temperatures without the skin freezing. Surely we've had ancestors who camped out under the fig tree many times in the past. I don't think evolution would have abandoned people to be in poor health and incapable of outrunning predators simply due to lack of exercise, unless there was some compelling constraint on what can be done. Wnt (talk) 22:52, 29 February 2012 (UTC)

Considering hibernating animals, like bears. If we hibernated all winter, we would be incapable of moving in spring, due to muscular atrophy. So clearly the bears have a way to maintain muscle mass without constant exercise, which we lack. I've often thought that if we can isolate whatever hormone the bear has that does this, this would be quite a valuable medication, for comatose or bed-ridden patients, astronauts, and perhaps people who just want to be muscular without constantly exercising. (As I understand steroids, they still require exercise to work.) StuRat (talk) 23:05, 29 February 2012 (UTC)

Isn't this the same thing that makes children want to play with things or each other? A group of small children free to do whatever they like, will end up running around, chasing each other etc. etc. Count Iblis (talk) 02:12, 1 March 2012 (UTC)

Air gills

Since gills can extract an amount of oxygen adequate for the needs of a fish from water, which contains relatively little dissolved oxygen, why don't they work even better in air, which has far more available oxygen than water? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 19:51, 29 February 2012 (UTC)

First, have you read gill? As a matter of definition, a gill is necessarily used to obtain oxygen from water. So if it's found in a terrestrial animal, it is not called a gill. On the other hand, gill-like structures can also work well in the air. See branchiostegal lung and book lung. You may also be interested in perusing this list of respiration organs. Note that air has so much oxygen that most terrestrial animals don't need any dedicated breathing organs at all, because they get their oxygen requirements by simple diffusion. SemanticMantis (talk) 20:01, 29 February 2012 (UTC)

Thanks. Whoop whoop pull up ^{Bitching Betty | Averted crashes} 20:05, 29 February 2012 (UTC)

A more general question is why land animals use a breathing mode where we breath in and out through the same opening, as opposed to in through one opening and out through another. This would be more efficient, since less mixing of "good air" and "bad air" would occur. I can think of two possible reasons:

1) Two openings would increase the chances of infection.

2) In cold weather, the exhaled breath is needed to preheat and pre-humidify the incoming air.

I don't buy the argument that we never developed this method because the current system is "good enough" (due to the high oxygen content in air). This is because land animals are descendents of marine animals, which already had this ability. Thus, we must have evolved to lose this ability, which means it must be a net negative to land animals. StuRat (talk) 20:21, 29 February 2012 (UTC)

Most fish gills fail to work in air because the fish cannot push water through them and they dry out. The lung was the solution to this problem in the line that we are descended from. However, lungs evolved from a completely different organ - the fish swim bladder - which is essentially the reason they only have one opening. Doubtless, a better engineering solution would be as you suggest, a continuous flow of air, but evolution is not intelligent design. Evolution can only improve a solution in slow incremental steps and moving from a reciprocating pump to a turbine is one giant leap all in one go. SpinningSpark 21:29, 29 February 2012 (UTC)

(e/c and echoing Spinningspark, lol) It's not quite like that. While evolution can usually easily modify or build upon existing structures, creating entirely new structures is a whole different ballgame. One that is far less frequent and requires far more time. And that includes creating new orifices. That is actually evident already in the way different organisms acquired different breathing structures. They can take the form of folded, feathery, maze-like, balloon-like, pump-like structures, which can originate from all manner of body parts, though becoming similar in appearance and function through convergent evolution. They often start out as simple modifications of existing structures as organisms start becoming too big for simple diffusion to work.

Lungs, in particular, did not evolve from gills. Thus the mechanisms for how gills extracted oxygen from water is irrelevant. Lungs actually developed from what was once the swim bladders of fish. Unlike gills which developed from pharyngeal pouches (themselves remnants of body segmentation in more ancient ancestors), lungs are derived from an infolding of the ancestral digestive tube. Oh, and an interesting aside - humans hear through what are basically fish "lungs" (some of parts of their gills are parts of our ears). Fish, in turn, hear through what are basically human "gills" (they detect sounds primarily through their swim bladders). -- OBSIDIAN†SOUL 21:31, 29 February 2012 (UTC)

No, swim bladders evolved from lungs. All early Osteichthyes had lungs (see lungfish and bichirs), but they evolved into swim bladders in the sturgeons, Holostei, and Teleostei. Whoop whoop pull up ^{Bitching Betty | Averted crashes} 01:44, 2 March 2012 (UTC)

My mistake. Already mentioned by Wnt below. Just replace "evolved from" with "homologous with". The point was that lungs did not evolve from gills. The use of "swim bladders" was for simplicity" as it doesn't sound any more enlightening to say "lungs" evolved from "lungs". -- OBSIDIAN†SOUL 16:37, 2 March 2012 (UTC)

Right, but lungs could have evolved from gills, if there was a selective pressure in that direction, and this would seem to be the evolutionarily shortest path. Therefore, there must be a reason why they didn't. The problem with them drying out relates to my point number 2. StuRat (talk) 22:59, 29 February 2012 (UTC)

The evolution of lungs from gills has been well known; for example it is discussed in [2], and our article lung, though it would be useful to run down better image detail. I'm not so sure that Darwin's comment that swim bladders were converted to lungs [3] is entirely accurate, though mostly so; my thought is that from a very early stage, air-swallowing surface fish might have done so to get extra oxygen in oxygen-poor waters, just like carp today, though certainly it would also tend to keep them up. It is clear that evolution went two ways here - one, in deep-dwelling fish, to abandon the gulping of air and use the swim bladder for internally regulated buoyancy; the other, to exaggerate the minor air breathing we see in carp to the point that fish could invade dry land. Wnt (talk) 23:36, 29 February 2012 (UTC)

Another interesting point is that fish become the ancestor of all Tetrapods over the course of about 60 million years by evolving the ability to breathe air (amongst other things). However tetrapods never "re" evolved the ability to breathe underwater, even though mammals have been in the water for 40-50 Million years and sea turtles moved back to the ocean about 110 million years ago. This illustrates how evolution doesn't work for a "purpose" and there's obviously reasons why underwater breathing hasn't reappeared, which could be a whole discussion in it self. Also, in that example I think there's a strong argument against intelligent design, even though ID supporters would not admit it. Vespine (talk) 00:12, 1 March 2012 (UTC)

A breathing organ with air flowing in one and and out the other doesn't need to be a turbine. It could be more like a diaphragm pump which is really just a slight modification on what we have right now. 203.27.72.5 (talk) 00:14, 1 March 2012 (UTC)

Birds actually do things much that way. See Bird_anatomy#Respiratory_system Wnt (talk) 05:14, 1 March 2012 (UTC)

@StuRat, they actually did in some invertebrates. The branchiostegal lungs of terrestrial coconut crabs and hermit crabs for example, are basically air-breathing gills which are constantly kept moist. The book lungs of pulmonate arachnids is another example. It may have been derived (perhaps multiple times) from the book gills of horseshoe crabs or the Blatfüsse ("plate feet") of the extinct sea scorpions, both of the latter were themselves modified from legs.-- OBSIDIAN†SOUL 06:51, 1 March 2012 (UTC)