Wikipedia:Reference desk/Archives/Science/2008 April 30

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April 30

Eyelids

The purpose of eyelids is to clean the surface of the eye. But I know some animals don't have eyelids so I was wondering how do they keep their eyes clean? Astronaut (talk) 04:09, 30 April 2008 (UTC)

Nictitating membrane (caution-graphic chicken eye imagery) is one other option; this is usually in addition to "normal" eyelids. Nimur (talk) 04:55, 30 April 2008 (UTC)

Geckos use their tounges.--Lisa4edit (talk) 05:45, 30 April 2008 (UTC)

So do I. Ditto my eyebrows. The chicks go mad when they see it. Myles325a (talk) 08:01, 6 May 2008 (UTC)

I'd say eyelids have several purposes. Besides cleaning the eye, they also:

1) Keep the eye moist, especially when sleeping.

2) Protect the eye from debris, especially when sleeping.

3) Reduce bright light, by squinting. StuRat (talk) 16:22, 30 April 2008 (UTC)

The eyelids do not keep eyes moist or clean it. it helps in spreadig over the tears through the surface of eye, which is the clealing solution or which keeps the eye moist. In animals without eyelids, the role is played generally by some other membranes and nictitating membrane. - Dr.Rajarshi, India

Backpack helicopter

What are the problems for making a backpack helicopter? 217.168.4.83 (talk) 04:28, 30 April 2008 (UTC)

Efficiently storing enough energy in a light, portable environment would be one problem. You'd need a lot of fuel or electricity or some other energy source to provide enough power to lift a (presumably) full-sized human. Batteries that are powerful enough to power a large motor would be huge and heavy. Gasoline is a possible option, but it could be very dangerous to strap to your back. Control and stability would be difficult hurdles, but the problem is not insurmountable (especially given the effectiveness of modern computerized control and a huge body of research in unconventional flight stability). Safety is a significant concern in any aircraft, and if you intend to put the engine, fuel, or rotors near a human with minimal protection, you would have to devise a pretty good and reliable safety mechanism. Surely if you just brainstorm a bit, or sketch out a few diagrams, you'll see a lot of hurdles. You might be interested in ultralight aircraft; this could give you some idea of more realistic vehicles. Nimur (talk) 04:59, 30 April 2008 (UTC)

Amazingly, we have an article on backpack helicopters. Nimur (talk) 05:05, 30 April 2008 (UTC)

MythBusters did an episode on this, IIRC. Ziggy Sawdust 17:12, 30 April 2008 (UTC)

Fixed your link. Presumably the specific episode you mean is this one, but the designs tried were not helicopter-style. --Anon, 22:07 UTC, April 30, 2008.

More than energy concerns is just design. Helicopters always require at least two rotors (except in the NOTAR system, which I don't think would be practical for a backpack): one oriented parallel to the ground to provide thrust, and one oriented perpedicular to the first rotor counter-act the torque effect that would otherwise cause the body of the craft to spin. TO understand better, sit in a weelie chair and twirl a belt over your head as though it were a helicopters blades: the whole chair should spin. You better have a pretty big backpack if 2 sets of rotors are gonna pop out of it. --Shaggorama (talk) 05:48, 1 May 2008 (UTC)

It should be noted that using two rotors is not a "strict requirement;" it's a very common solution to the torque problem. This is often the simplest and most effective way to cancel out the torque; alternatively, fully articulated single rotors can be controlled to counter this torque). Here is a small aircraft with cyclic control ("flapping rotor"). Nimur (talk) 16:56, 1 May 2008 (UTC)

Would a autogyro backpack be easier to accomplish? It could work like paragliding. The rotor would only generate lift. 217.168.3.246 (talk) 18:13, 1 May 2008 (UTC)

Thermodynamic feasibility of converting creatine to phosphocreatine

I got this doubt reading the 25th edition Harper's Biochemistry (the latest is the 26th edition), which I couldn't get resolved even after searching on the internet including Wikipedia. There is a mitochondrial creatine kinase (miCK) present between the inner & outer mitochondrial membranes, which phosphorylates creatine to phosphocreatine at the cost of an ATP molecule (ATP-->ADP), which is exported out the mitochondrion through the pore protein 'P' (pages 147-148). What is the need for such an enzyme if any way cytosolic creatine kinase can carry out the same reaction? My guess, is that it must be faster to transport phosphocreatine out of the mitochondrion than ATP, but I do not know for sure (as such a thing is not WRITTEN in the text); then, once in the cytosol, the phosphocreatine must be getting converted back to creatine, phosphorylating ADP to ATP in the process. But, an even bigger doubt is how is the reaction creatine-->phosphocreatine (requiring 43.1 kJ/mol)--carried out between the two mitochondrial membranes thermodynamically feasible if ATP-->ADP releases only 30.5 kJ/mol (page 126; table 12-1)? Looking forward to replies--answers/guesses/just about anything.

Regards.

Ketan Panchal, MBBS (talk) 06:58, 30 April 2008 (UTC)

Ring finger

Why is the ring finger hard to move by itself? Interactive Fiction Expert/Talk to me 10:16, 30 April 2008 (UTC)

"It is the weakest of the fingers on the hand, as it shares a flexor muscle with the middle and little fingers. It is the only finger that cannot be fully extended by the majority of people, in itself separately." On the bottom of the wikipedia article. Kingpomba (talk) 11:02, 30 April 2008 (UTC)

I thought it was because of the extensor, actually - extensor digitorum - but I could be wrong, it's been a while since first-year anatomy --131.111.135.84 (talk) 12:07, 30 April 2008 (UTC)

Hi. A similar phenomenon happens when you put the palms of your hands together, then clasp all your fingers except the middle ones towards your hands, so that only your middle fingers are pointing away from your hands. Next, (this is demonstratable by placing a penny between your middle fingers) try to seperate the tips of your middle fingers without moving the other ones: it's hard. However, one way to drop the coin may be to carefully press your palms against each other, then seperate the tips of your middle fingers very slightly, or you could slowly slide the middle fingers past one another by moving them slightly, up and down and side to side, and move the fingers toward the clasp position. Thanks. ~AH1^(TCU) 20:21, 1 May 2008 (UTC)

Cheese

What happens if you sneeze while eating cheese? I am asking this because it says something about this in a book I have. Interactive Fiction Expert/Talk to me 10:16, 30 April 2008 (UTC)

Is this a riddle or a limerick? Perhaps you will get cheese spray. Or shall we say a breeze of cheese? Graeme Bartlett (talk) 11:33, 30 April 2008 (UTC)

Is that what spray cheese really is? DMacks (talk) 16:18, 30 April 2008 (UTC)

Is there water in a virus

Most life needs water, but do viruses? Are they wet? Obviously they need the host body and that has water in it, but does the virus itself have any water because it is so simple? xxx User:Hyper Girl 10:16, 30 April 2008 (UTC)

I am going to guess that there is water in little pockets between the protein and DNA molecules. Graeme Bartlett (talk) 11:26, 30 April 2008 (UTC)

Viruses do not contain water in the way that living cells do. They are simply genetic material DNA or RNA packaged in a protective protein coat. You could say viruses "need" water, though, because they are inert until their genetic material inserts itself into an ordinary, water-filled, living cell.

Atlant (talk) 13:11, 30 April 2008 (UTC)

It depends on how you define 'wet'. Virtually all protein molecules will have water molecules associated with them—proteins pretty much can't fold without the presence of water. Hydrogen bonding between the protein and surrounding water molecules is often a significant contributor to protein stability and structure, as is the preference for hydrophobic amino acid residues to be buried away from the bulk water solvent. (There are many, many, many papers and books written on these topics; I'm dramatically simplifying.) When proteins are crystallized for x-ray crystallography, the protein crystals contain large amounts of bound water.

The amount of water in different viruses varies, but all will contain some water. Exactly how much can be estimated by various means; the most straightforward essentially rely on centrifugation to 'wring out' virus particles. By these sorts of measurements, the influenza virus is about two thirds water (link to PDF), while the vaccinia virus is nearly ninety percent water (abstract).

The necessity of this intrinsic water explains why many viruses don't remain viable for long periods when left out on otherwise clean, dry surfaces. Viruses like HIV are rather flimsy, and are inactivated by drying. Other viruses will survive dehydration and rehydration much more effectively—though even after air drying many will still contain at least some amount of bound water. TenOfAllTrades(talk) 13:44, 30 April 2008 (UTC)

Electrolysis of solution

I cant exactly remember because it was a week or two ago but it interests me. In chemistry class we were testing if solutions were ionic bonded or covalent bonded by passing a mild electrical current supplied from a battery cell through them. Im not sure if it was saline or not but once the current was applied it turned yellow(i think my teacher might of said something about the sodium). Does this sound like saline? if it does why did it do this? Kingpomba (talk) 10:22, 30 April 2008 (UTC)

Sodium ions do not usually cause visible coloring in solutions (a glass of common table-salt dissolved in water is just a bunch of sodium and chloride ions, and you can see it's colorless). Usually when one thinks "ions that make colors in water", one is talking about the transition metals. Putting two electrodes in solution can electrolyze the solution, but it can also electrolyze the electrodes themselves. This process results in one electrode actually dissolving into the electrolyte a little. DMacks (talk) 16:17, 30 April 2008 (UTC)

Indeed Sodium ions do not usually cause visible coloring in solutions-in water that is. Ionic Sodium is of course bright blue to metallic in liquid ammonia. But in this case are you sure you meant water? Or when you said solutions did you mean liquids? Also isn't the big difference that ionic solutions conduct a lot but covalent ones don't? There wasn't a light bulb in a circuit lighting stuff up yellow you forgot to mention is there? --BozMo talk 18:28, 30 April 2008 (UTC)

Just an idea. This might have been an effect of impurities / additives in either the salt or the water. We once had a series of experiments go seriously wrong until we had a look at all the stuff that was in our "table salt". Turned out it didn't have enough sodium chloride in it. Red coloring would indicate iron. Green's copper most likely. Iodine might cause the yellow coloring, although usually it'd be more brown from what I remember. --Lisa4edit (talk) 23:33, 30 April 2008 (UTC)

Is it statistical "insignificance" or "nonsignificance"?

As title - I know it's a stats question, but it's intended for use in a psychology paper so, um, think it's probably better in this section. I was told it was "nonsignificant" but Google Scholar gives far more results for "insignificant" (though that may reflect its use as a normal word) - any advice? Thanks! --131.111.135.84 (talk) 11:58, 30 April 2008 (UTC)

When in doubt, it is always acceptable to say that the differences were not statistically significant. TenOfAllTrades(talk) 12:11, 30 April 2008 (UTC)

Agreed. "Statistically significant" has a precise technical meaning, and "not statistically significant" therefore also has a precise technical meaning. The two terms in the title are imprecise, as we can infer by the fact that the question was asked in the first place. -Arch dude (talk) 02:53, 1 May 2008 (UTC)

None of the terms insignificance and nonsignificance is correct in the context of your question. rather it is better to deal with terms 'insignificant' or 'nonsignificant'. The term 'insignificant' means minute or something without having bearings on others. On the other hand the tern 'nonsignificant' carries some sense of statistics but mostly used to show negeligiable impact. In fact the terms 'statistically significant' is absolutely technical one which measures the acceptability of any series of data. As it measures the acceptance and any data is rejected if it does not match the level of acceptance, hence any data array may only either be 'statistically significant', - that matches the criteria or just the opposit - that fails to match. It is therefore always advisible to write 'not statistically significant'. - Dr.Rajarshi, India

elements

How many elements are there as most site say approximately 115 but I want the exat answer (if thereis one) —Preceding unsigned comment added by 78.149.107.50 (talk) 15:04, 30 April 2008 (UTC)

There isn't really. 94 elements occur naturally on Earth, and a further 23 have been created artificially in laboratories, but there might be others elsewhere in the universe (possibly in some alien's lab), and someone'll synthesize another before too long, so there's no clear answer. Algebraist 16:10, 30 April 2008 (UTC)

Then there are some that are so unstable they decay in a millionth of a second, so do you count that as "an element" ? StuRat (talk) 16:15, 30 April 2008 (UTC)

The word "approximately" is not really appropriate here. There is nothing "approximate" about an element. A particular atom is an atom of exactly one element, and this depends on the number of protons in the nucleus of the atom. This number is a specific integer. Humans on earth have observed atoms with each number of protons from 1 to 116, and they have observed atoms with 118 protons. Therefore, we have observed exactly 117 different elements: no more, no less. The "appoximately" is some author's sloppy way of acknowledging two uncertainties: First, not all observation of short-lived elements are uncontested, and second, scientists may observe additional heavier elements in the future. When my mother studied chemistry in high school in 1929, she learned that there were exactly 92 elements. When I studied chemistry in high school in 1966, I learned that there were exactly 104 elements. If an author of a textbook said "approximately 115 elements," the author really meant this: "at the time I am writing this, there is no important disagreement about he observation of 114 elements, but some scientists have claimed to observe another element and that claim is disputed." (Since I attended High school in Oak Ridge, Tennessee, I was somewhat more sensitive to this than most high-schoolers.) -Arch dude (talk) 02:44, 1 May 2008 (UTC)

Well technically, elements exist whether or not they have ever been observed. We can also say "approximately 115" to mean 115 and perhaps more. Just recently there was a claim to have observed element 122 [1]. Incidentally, there is also an implied upper limit. An element is a bound state of protons and neutrons, which means the collective must have lower potential energy than the constituent parts. At some point (presumably not far from the limits of known elements), that will no longer be possible, and there will no longer be additional bound states. Dragons flight (talk) 05:42, 1 May 2008 (UTC)

Chemical element --Shaggorama (talk) 05:29, 1 May 2008 (UTC)

Supplemental question This has been bugging me for a while, I'll ask it here. According to this article (copies on request), the average radial velocity of an electron in the 1s orbital of an atom is Zc/137, or v/c = Z/137. The example given is mercury, Hg, Z = 80, v/c for the 1s electrons = 0.58, so the radial velocity of the electrons is 58% of the speed of light. Relativistic effects (mass increase and radius contraction) follow on. So my question is, no matter how good we get at making trans-uranic elements, is 137 the highest atomic number that could ever be created, no matter what? Because if we could make an element number 138, no matter how transient, what would happen if we put an electron near it? If the electron entered the 1s ground-state, presumably v/c = 138/137, v>c. This may not be a good place or method to frame the question, but it's tormented me greatly for more than a year now, I need some relief!! Franamax (talk) 06:15, 1 May 2008 (UTC)

That's a neat question! My guess is that the equation breaks down as the size of the nucleus gets larger, but I can't be sure. Remember, this formula gives you an average velocity, so the its is already sort of rough. --Shaggorama (talk) 07:06, 1 May 2008 (UTC)

It's not neat, it's horrible! The "average" velocity I'm pretty sure is because of those Heisenberg and Schrodinger dudes who wrecked it for the rest of us. Nature doesn't usually let sloppy stuff get through and the text in that link is specifically "137 atomic units (a.u.) = c", apparently because of something Dirac figured out in 1929. I'll take anyone's suggestion as to how to rationalize away that z=137, it's really been bugging me. In fact, it's one of the reasons why I've been hanging around this desk for a few months now! Franamax (talk) 09:05, 1 May 2008 (UTC)

It comes from a simple, but crude, analogy. The binding energy of the 1s orbital of an atom with Z protons is approximately 13.6 * Z electron volts. Equate that to an orbital kinetic energy and you get:

${1 \over 2}m_{electron}v^{2}=13.6ZeV$

$\implies {v \over c}={Z \over 137.065}$

The constant of ~1/137 is also known as the fine structure constant.

However, this analogy has a couple flaws. First you are assigning a kinetic energy to a particle that isn't actually moving as such. Secondly, for the analogy to make sense at large values of the energy you really have to use the relativistic kinetic energy = $mc^{2}({1 \over {\sqrt {1-(v/c)^{2}}}}-1)$, which reduces to the conventional expression ${1 \over 2}mv^{2}$ in the limit of small v.

Using that form you'd get $1-({13.6Z \over 5.1*10^{5}}+1)^{-2}=({v \over c})^{2}$

$\implies {\sqrt {1-{1 \over {(2.66*10^{-5}Z)^{2}+5.32*10^{-5}Z+1}}}}={v \over c}$

$\implies {\sqrt {{(2.66*10^{-5}Z)^{2}+5.32*10^{-5}Z} \over {(2.66*10^{-5}Z)^{2}+5.32*10^{-5}Z+1}}}={v \over c}$

$\implies {\sqrt {{4Z^{2}+Z} \over {4Z^{2}+Z+137^{2}}}}={v \over c}$

You can verify that in the limit of small Z, the radical reduces to Z/137 and in the limit of very large Z the radical goes to 1, consistent with never allowing v > c.

Dragons flight (talk) 11:48, 1 May 2008 (UTC)

Woah woah everyone! Before we dive into mathematical equations, are you sure this is not a model of the "average speed"? If the average velocity is non-zero (quantum or otherwise!) the electron will leave the nucleus (ionization!) Something seems extremely suspicious of this "model" which is not explained in the article at all... Why should we accept that "V_r = Z" ? Where does this come from? Do they really mean sqrt(<v²>) = Z, which seems to be derived from the coulomb potential? The real question here is where does this model for radial velocity come from and when may we assume that it is valid? Nimur (talk) 16:58, 1 May 2008 (UTC)

Addendum! See Atomic units - which are not the same as atomic mass units! When they say the speed of light is "137 atomic units," this is in units of "hydrogen bohr radii × Hartree energy / planck constants" and should not in any way be confused with mass of proton or its closely-related atomic mass unit. If you simply convert 137 hydrogen radii×Hartree energy / planck constant, you get ~2.99e8 meters per second. Supposedly nuclear physicists use these horrible units to make ... their... lives... easier. Nimur (talk) 17:16, 1 May 2008 (UTC)

I already told you. It's an analogy introduced by equating the binding energy of the electron to orbital kinetic energy, as if the electron were orbiting the nucleus. The actual average velocity of the electron in a 1s shell is zero. Dragons flight (talk) 01:07, 2 May 2008 (UTC)

However, the article discusses a relativistic contraction of the electron orbital radius in the 6s shell. Presumably this is a consequence of the "analogous" electron velocity? Am I mistaken that a bound electron has a positive kinetic energy, equal to the binding energy? Franamax (talk) 05:16, 3 May 2008 (UTC)

Petrol consumption

How is a car's fuel consumption (per metre) related to speed? If I travel a certain distance at 100km/h I'd spend more time travelling than if I were going at 120km/h and thus the car would be using petrol for longer but at a lower revolution rate (if that's the right term). So what's the trade-off? I'm sure there's a non-linear relationship somewhere that I'm missing. Thanks, Zain Ebrahim (talk) 16:53, 30 April 2008 (UTC)

Air resistance increases non-linearly with speed. That's probably what you're missing. See Drag (physics). The drag force on an object increases with the square of the velocity, but the power required to overcome the drag increases with the cube of the velocity. ~Amatulić (talk) 17:00, 30 April 2008 (UTC)

That makes fuel consumption inefficient at high speeds, but it is also inefficient at low speeds, as internal combustion engines need a certain amount of fuel just to idle. The ideal "cruise speed" varies by car, due to factors such as gearing and the coefficient of drag (which measures how stream-lined it is), but something like 90 km/h is typical (until you strap a mattress on top, that is). StuRat (talk) 17:08, 30 April 2008 (UTC)

Thanks, guys. From the article I see why power increases with the cube of velocity but how does consumption relate to power (if it is trivially related)? Also, I don't quite understand why the energy required to idle causes inefficiency at low speeds. Does it have something to do with gears? Zain Ebrahim (talk) 17:27, 30 April 2008 (UTC)

As for the inefficiency at low speeds, the issue is that a certain minimum fuel is used all the time, even though you don't theoretically need that much to move at low speeds. So, essentially, you are wasting gas just to keep the car running. This is one advantage to electric vehicles, they don't need to waste fuel to keep running. This makes them better for low speed, city, stop-and-go driving, where gasoline engines are worst. Gasoline-electric hybrids also take advantage of this. StuRat (talk) 17:37, 30 April 2008 (UTC)

Fuel consumption is trivially related to power. Fuel contains potential energy realized by burning it to drive an engine. Power is simply energy expended per unit time. Needing more power means you need to expend more energy in a given time increment, which translates to expending more fuel. The fuel consumption vs power graph should theoretically be linear, but as StuRat pointed out above, there are wastes to contend with at low speeds. ~Amatulić (talk) 17:45, 30 April 2008 (UTC)

Thanks a lot, guys! Zain Ebrahim (talk) 17:52, 30 April 2008 (UTC)

As a rule of thumb (I don't know how accurate) you can remember that going 70 has twice the drag of 50, because the square of 70 (4900) is almost double the square of 50 (2500). Same holds true for 100 over 70. I don't really know how the aerodynamics figure into it, though. --67.170.53.118 (talk) 03:54, 1 May 2008 (UTC)

The faster you go, the more molecules of air you hit (because you move further in unit time), that gives you one factor of velocity in the equation for air resistance. However, you also hit each molecule with a greater relative velocity, which gives you a second factor. Hence, air resistance proportional the the square of velocity. That's extremely imprecise, but I think it is essentially correct. --Tango (talk) 21:14, 1 May 2008 (UTC)

Melting plastics

As a hobby, I sometimes get a bunch of junk plastic (drink bottles, packaging, old baby toys, etc.) and put it in a pot, and then melt it over the stove. I've been attempting to pour it into a Play-Doh mold with little success. I need:

1. A material that is malleable with your hands or tools (like clay), can withstand high temperatures, and is structurally strong enough to have some pressure put on it without deforming (the play-doh is too soft and the plastic deforms the cast, turning into a blob).
2. Information about the safety of melting plastics and the fumes created by doing so. I have a gas mask that I wear whilst melting, but I do this in my kitchen and don't want it to smell like ass-and-a-half for the next 3 days. Also, my dog can't wear a gas mask.
3. To be able to tell the difference between different types of plastics; thermoplastic/thermoset, hardness, melting temperature, etc. And a way to find this out from the source of the plastic and its appearance.

Thank you in advance... Ziggy Sawdust 17:11, 30 April 2008 (UTC)

Of course you should be warned that molten plastic is quite dangerous. Aside from the fumes there's the danger of getting some on your skin, where it will be impossible to remove until you are severely burned. Softer plastics will also tend to have lower melting points. Completely avoid hard plastics, as they are likely to be thermoset plastics that just smoke and burn when heated. Try using metal molds sold for cookies.

I suggest doing this all outside at a fire pit or on a bbq (although the neighbors will likely complain about the fumes either way). If it catches fire you will essentially have an oil fire, so have an extinguisher nearby rated for that, and also have a bucket of water to submerge your hands if they get small bits of molten plastic on them. Better yet, wear thick leather gloves. Also, consider bringing an extension cord outside with a cheap microwave so you can heat the plastics that way. This may enable you to heat them more evenly.

The recycle number on the plastic may also give you a clue as to which will work best. It's written inside a triangle with arrows pointing clockwise.

Another suggestion, instead of plastics use crayons, which melt at a lower temp yet, and are nice and colorful, allowing you to indulge both your creativity and pyromania. StuRat (talk) 17:26, 30 April 2008 (UTC)

Yep be very careful. Polyurethane in particular gives off cyanide gas when heated which your dog is not going to appreciate. Getting a candle making kit or similar seems a safer hobby. --BozMo talk 17:48, 30 April 2008 (UTC)

I partially disagree with some of the above. I've encountered some soft plastics that don't readily melt (teflon for example, a thermoset toy-mold plastic from the 1970s called plastigoop, and I think some silicone polymers) whereas some hard plastics such as polystyrene melt readily.

To pour something molten into a mold, it helps to heat up the mold to the melting temperature of what you're pouring into it. You may be experiencing the problem of your mold sucking out all the heat from the plastic before it can flow fully into the mold. ~Amatulić (talk) 17:55, 30 April 2008 (UTC)

If you had a metal mould, could you melt your plastic in the mold itself? Then you wouldn't have to pour it at all and you wouldn't have to be anywhere near it except for a short while you remove it from the BBQ with a pair of tongs. Astronaut (talk) 18:34, 30 April 2008 (UTC)

Note that it isn't just a problem with the smell for 3 days. If there is a smell for 3 days then there is a good chance some of the potentially toxic or carciogenic fumes are around. (While cyanide may be a concern, IMHO it's only a minor one since if I'm not mistaken and supported by the Cyanide poisoning cyanide may kill you or make you weak and sick for a few days but if you're carefully, I think that unlikely and the chronic effects of a minor acute exposure to cyanide which is readily metabolised are probably less concerning then the chronic effects of some of the other stuff you will produce which may hang around in your body or the environment for years.) Unless you are planning to wear a gas mask for the next 3 days or whatever (I presume you live alone) the gas mask may not solve the problem. You could do it outside of course or at least make sure your kitchen is very well ventilated. But other then your poor dog, depending on what kind of quantity we're talking about here, how close your neighbours are, the wind, etc others could be affected. Then there is the issue of whether it may be illegal. Personally I wouldn't recommend it. Some science experiments are fine to do in the home. Some are not. Generally speaking, any science experiment where you produce a significant amount of nasty fumes which may affect you and perhaps more importantly, innocent bystanders, should be avoided. Melting plastics, except by accident, is one of them. If you really want to do this, I suggest you at least go to an isolated area without anything that's likely to catch fire. Nil Einne (talk) 19:38, 30 April 2008 (UTC)

I'd say you should find another hobby before you find out in a couple of years that this was a really bad idea. Plastic recycling will give you the material code. That does not mean that that's all that's in there. There are things like plasticizers that are also really nasty. Plastics are polymers and if you split those chains (or circles) there's no telling what they'll react with and where they break and link up again. It's all a game of ratios and probabilities. The problem is that some of the possible results are toxic, mutagenic or carcinogenic at very low concentrations and effects can be delayed and cumulative. It's like hitting your head, if you do it occasionally that's within the usual "life is detrimental to your health" limits. If you make a regular and repeated habit of it, it will eventually kill you. Since the more heat you put in the more broken links you get and the more fumes develop, using an counter-top oven at lower temperatures and reshaping the plastic rather than melting the stuff in a pot is safer by a sizable margin. You can use oven safe ceramic cake molds. Make sure your vent is on at full tilt and you use the highest grade filter in it you can lay your hands on (I've seen some pretty high grade composite ones in Europe). Exchange filter after you're done and dispose of the old one. (Environmentalists will hate you forever). Open every outside door and window you have after you are done to reduce relative concentration of airborne residuals. This gets you from running into the wall at full tilt to bumping your head from a standing position going with the above analogy.Lisa4edit (talk) 21:12, 30 April 2008 (UTC)

Do not assume that your gas mask protects you. It should have a rating on it and it probably allows cyanide through it.--Shniken1 (talk) 00:14, 1 May 2008 (UTC)

Well, as far as safety goes, I do it outside, wearing a gas mask/goggles/chemical gloves/apron as well as setting up a leaf blower, shop vac (set to blow), and a fan blowing into the wind... Ziggy Sawdust 01:23, 1 May 2008 (UTC)

someone mentioned crayons before, and that follows with my own suggestion - waxes. there are a few different types, but they all mostly have the properties you are looking for, are less toxic, and require less preparation than it seems you are currently using - hell you can melt most in your kitchen with the ventilation fan on.... -ΖαππερΝαππερ ^Babel_Alexandria 20:27, 6 May 2008 (UTC)

Chemical Name

In the 1960's there was an insecticide commonly known as C40. What is the chemical name for this compoundTraudt1 (talk) 18:46, 30 April 2008 (UTC)

This? DMacks (talk) 18:55, 30 April 2008 (UTC)

Which, as it turns out, we have an article on. —Ilmari Karonen (talk) 04:14, 1 May 2008 (UTC)

Colours in Transition Metal Complexes

Hi all. From what I understand of the reason for colour in compounds like hydrated copper (II) sulphate, it's caused by the promotion of d electrons. My question is, why does this promotion then mean that light is absorbed over a range of frequencies? I've been told that this is because of collisions with other atoms or molecules (essentially Brownian motion) meaning that the energy gap varies a bit. I'm puzzled though, as that implies to me that if you cooled copper sulphate to near absolute zero, it would become colourless as the range of -frequencies- (edit - I meant wavelengths)absorbed by the energy gaps would become so small as to be insignificant to the naked eye when you pass white light through it. Does copper sulphate really become colourless near absolute zero, or is there something I have wrong here? Thanks Trebor27trebor (talk) 18:50, 30 April 2008 (UTC)

How did you conclude that "light is absorbed over a range of frequencies"? DMacks (talk) 18:53, 30 April 2008 (UTC)

I've seen diagrams of light being absorbed across a range of wavelengths (not frequencies, sorry) in transition metal complexes. Sorry, my dopey mistake. They look a bit like [2]. Trebor27trebor (talk) 19:33, 30 April 2008 (UTC)

Er, light is absorbed over a range of frequencies – and wavelengths, since frequency is just c divided by wavelength – when you're in any sort of condensed phase. (At least) two factors contribute to the broadening of the absorbance peaks. First, molecules at room temperature may be a variety of different rotational and vibrational energy levels, and may be excited to different rotational and vibrational levels; this means that the difference between the ground and first excited electronic energy levels is slightly shifted. Second, there are constant interactions with adjacent molecules (water if you're in solution; with other hydrated copper complexes if in the solid phase) that act to slightly shift the effective energy levels of both ground and excited electronic states—again broadening the absorbance range for the compound.

You only get nice sharp absorption lines if you're working with gases at not-too-high pressures. Under those circumstances, individual molecules are effectively not interacting with each other, so they don't mess up each other's energy levels. TenOfAllTrades(talk) 21:37, 30 April 2008 (UTC)

An energy level diagram showing some of the transitions involved in the spectrum of a linear molecule: P branch (where $\Delta J=-1$), Q branch (not always allowed, $\Delta J=0$) and R branch ($\Delta J=1$)

This image shows the energy levels involved in a rovibrational transition. Each line will appear in a gas phase spectra as a sharp peak. In the condensed phase these will all broaden because of intermolecular interactions to give a broad peak. Similar, but more complex, transitions are seen in electronic transitions.

HIV/Antibodies

Upon contact in the bloodstream with the HIV virus, (which are part of the retrovirus family so seem to have virus envelopes, from what I can make out from the article) why can't antibodies attack this virus and render it useless? Thanks, 86.159.224.183 (talk) 20:04, 30 April 2008 (UTC)

I think, but i'm not certain, that the HIV virus attacks T cells which are the cells, amongst others, which attack invaders in the body. This means that the body cannot fight off HIV since it has nothing uncompromised to fight it with. That's almost certainly wrong, just my assumption. Regards, CycloneNimrod^Talk? 21:23, 30 April 2008 (UTC)

The other half of the answer is that the infected T-cells and cetain other cell types will not be eliminated by the rest of the immune system once infected (so far as I'm aware, at least not too many of them, certainly), so some HIV will always survive the onslaught of the immune system while simultaneously wearing it down. As some evidence of just how hard HIV is for the body to fight off, recent studies that attempted to vaccinate individuals against HIV by promoting deveopment of HIV antibodies prior to infection have shown absolutely no effectiveness. Someguy1221 (talk) 22:21, 30 April 2008 (UTC)

Antibodies do attack the virus, and Cyto-toxic T cells do destroy virally infected cells. However, helper T cells are absolutely essential for the proper functioning of the immune system, both humoral and cell-mediated via secretion of cytokines and clonal expansion. This is one of the subtypes of immune cells (in addition to dendritic cells and macrophages) that become infected by HIV via the CD4 receptor protein. At first the virus is kept at bay, but decreased T cell count creates a derangement in cell-mediated immunity and consequently the development of AIDS. Wisdom89 _{(T / ^C)} 00:09, 1 May 2008 (UTC)

Also, I think we're giving an idea of how HIV affects our immune system, but I think the question is asking why can't the body get rid of it straight away before it builds up into a full scale 'invasion'. Normally, as Wisdom said, the body keeps HIV at bay and the person will remain asymptomatic for a period of time. Soon after, when the immune system starts becoming exhausted and depleted of T cells to remove the virus. This is where HIV really starts to kick in and several years later it develops into AIDS. Occasionally, however, the body is effective at removing HIV from the bloodstream upon infection and people do not catch the disease in those cases. It's unknown just how their bodies do that, though. Regards, CycloneNimrod^Talk? 07:30, 1 May 2008 (UTC)

Electron microscopes

Certain particles, such as electrons and protons, exhibit wave-particle duality, correct? If this is the case, and protons too act like waves, why can we not use protons in a microscope like we do with electrons? Surely with their shorter wavelength they could allow us to visualise things like atoms? Regards, CycloneNimrod^Talk? 21:26, 30 April 2008 (UTC)

They are called nuclear microscopes, although our article on them is unfortunately short. Someguy1221 (talk) 22:23, 30 April 2008 (UTC)

They contain much more energy, and cause more damage to it item irradiated by them. Graeme Bartlett (talk) 22:25, 30 April 2008 (UTC)

Neutrons are used in similar ways see Neutron scattering and links therein.--Shniken1 (talk) 23:58, 30 April 2008 (UTC)

Is it common for doctors to be unable to dress/bandage a leg?

So, I took my grandma to the doctors' the other day for a checkup on the healing of her leg ulcer (which is getting better, thankfully). We sat down and reminded the doctor (not my nan's usual GP) that we were there to get the leg looked at, at which point she stopped me and said that she'd better go have a look to see if there were still any nurses in the building (this was late afternoon), as if she were to remove the bandage and dressing to examine the ulcer, she would be unable to put a new one on - because she didn't know how!

This wasn't a case of "a nurse could bandage a leg better than me" or "it's a nurse's job to put the bandages on, not mine", she literally told my nan and I that she'd never put a bandage on a patient before and that she had no idea how to do it. As it turns out, all the nurses had gone home for the day, so she was going to send my nan home and make her come back early the following day (which would be quite a slog for her, in her current state of health). Luckily, *I've* dressed my nan's leg several times and know exactly how it's done (it's not particularly complex), so we managed to get it looked at in the end.

So, when training, are doctors in the UK not taught how to do basic treatments such as this, with the assumption that there will always be a nurse on hand to do it for them, or is this an isolated case? This particular doctor is far, far from being young and inexperienced (I'd be able to understand it more if she had been newly-qualified). Any UK medical-type people here?

My nan is currently in a care home (not permanently, I hope) and we were having a laugh about it tonight with an African nurse that looks after her - she was gobsmacked when she heard the story and told us that where she was from (I forget where exactly), it would be unthinkable for a doctor not to know how to change a simple dressing. --Kurt Shaped Box (talk) 23:58, 30 April 2008 (UTC)

Is it possible that this doctor was in training? Maybe your nan was one of their first patients. Granted, this is pretty ridiculous, but there are alot of new doctors who have never laid hands on a patient until their first rounds. --Shaggorama (talk) 05:04, 1 May 2008 (UTC)

The OP ruled that out - KSB said that the doctor did not appear to be new to the job. Is it possible that it was a union issue? I don't know about nurses in the UK, but in many industries, agreements between employers and unions include strict clauses that require that only a certain type of employee is permitted to perform some tasks; i.e. in this case the nurses union won't allow doctors to do nurses' jobs like changing bandages, or else nurses could be put out of business. Just a possibility --Bmk (talk) 06:42, 1 May 2008 (UTC)

It's not clear to me why though. Age is not necessarily a good indicator of experience. If it was simply a case of 'the doctor looked too old to be in training' well it's impossible to say for sure IMHO. Nil Einne (talk) 10:14, 1 May 2008 (UTC)

This particular doctor has been at my nan's practice for several years (and qualified in 1986, according to her bio in practice booklet - we wondered if she was just new to the profession too, so we looked her up). It's just that she's not my nan's usual doctor. --Kurt Shaped Box (talk) 11:14, 1 May 2008 (UTC)

Alternatively, and ignoring the claim your doctor made about never having done it before, maybe it's the opposite? If the doctor is rather experience and it's been a long time since their training perhaps it was really a case of 'I once knew but I can't remember now'. It's definitely said I believe that with some procedures doctors actually get worse with experience because they so rarely do them themselves. Nil Einne (talk) 10:14, 1 May 2008 (UTC)

That's scarcely credible, my two (Canadian) doctor sisters would be horrified to hear that (they'd certainly agree with finding a nurse who could do it better if one was around). Since it's not really "medical advice", I would suggest calling the hospital or clinic director to ask for an explanation at first hand. Advocacy is the best medicine. Franamax (talk) 09:35, 1 May 2008 (UTC)

Suggested that. My nan wouldn't do it (or let me do it). To her, complaining about a doctor when you're currently ill is about as wise as insulting a chef before he cooks your food... :) --Kurt Shaped Box (talk) 11:14, 1 May 2008 (UTC)

Heh, that's how I get my hot/spicy food hot/spicy enough. After explaining to the server how I'd like it to be actually hot, I suggest a personal insult they could deliver to the cook on my behalf, then followed up with "oh, he wants his dish extra-hot". A little incentive goes a long way :) Franamax (talk) 05:00, 3 May 2008 (UTC)

And I'll hedge that, your nan may have a condition that the doctor recognized as needing a specific dressing with which she was not familiar, realized that a simple dressing would not be adequate, and made a judgement that less harm would be done by having your nan come back in 12 hours rather than the potential damage that could be caused because she was unfamiliar with the specific procedure. Was your nan's life or limb at risk if she made you come back the next day? Would either have been more at risk if she tried something she wasn't completely knowledgeable about? That's the decision doctors have to make, it's not about what's most convenient. Franamax (talk) 09:47, 1 May 2008 (UTC)

It's possible, I suppose. On the other hand, it's a very simply dressing (or it appears to be when I've done it myself). Mesh pad over the ulcer (which is quite small now anyway), wrap the bandage from knee to ankle, tape the end down. --Kurt Shaped Box (talk) 11:14, 1 May 2008 (UTC)

We can speculate all we want on what's going on here, but whatever the case may be I think we can all agree that the poster would be justified complaining to this physician's superiors. This is a basic first aid skill that, regardless of when the doctor last performed it in the field, should have been kept up to date via continuing education. --Shaggorama (talk) 12:41, 1 May 2008 (UTC)