Wikipedia:Reference desk/Archives/Science/2009 May 27

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May 27

Amalgam

Hi, I stumbled upon the article, electrolysis, some of questions were answered but one of them were not.

How is it possible for metals to be solved in mercury? Do metals actually become solved in mercury or do they just form an alloy? How does mercury absorb these metals? -Funper (talk) 01:10, 27 May 2009 (UTC)

Technically, they form an amalgam. Mercury is a liquid under standard laboratory conditions ("room temperature, atmospheric pressure"). When other metals, like gold or lead are added to it, the result is often a "soft" metal solid. For example, take a look at sodium amalgam. This compound ranges from a liquid to a "spongy gray mass" depending on the amount of mercury present. Nimur (talk) 01:32, 27 May 2009 (UTC)

MM Experiment

Michelson Morley Experiment- Sorry about this I'm the same guy who asked the earlier question. Anyway, the theory of the aether was that the aether was stationary right? The "wind" was generated by the earth moving through the field of aether, not the aether moving across earth right? Because from what I understand the results they were seeking were made with the assumption the aether speed was 30 km/s (the speed the earth orbits around the sun).

Secondly: (Sorry for this crappy drawing but w/e) Distance from Mirror A to half slivered mirror = Distance from Mirror B to half slivered mirror. BTW these drawing look weird so to better understand what I meant could you go to "Edit Summary" and look at them because I didn't mean for this formatting boxes.

                MIRROR A
                   .
                   .

 Light source----- /---- MIRROR B

                   .
                   .
                   .
                 Detector

This whole problem is assuming there is an aether wind. I'm trying to understand how Michelson constructed his apparatus, given he thought a wind existed. Suppose the aether wind is coming down parallel to mirror A (suppose mirror A is the north, imagine the wind is blowing from North to South). Given that there is a wind, shouldn't the beam of light be deflected downward a little coming from the light source to the half slivered mirror (the / in the center)? As it won't strike the center of the mirror but rather a point a little below the center at a different incident angle then 45 degrees. In this case both beams would also be deflected and the light beam would not be split equally. If this was compensated by angling the light source a little, so that the light went in a straight line from the light source to the half slivered mirror, then the beam of light going from the half slivered mirror to mirror B would be deflected downward a little.

               MIRROR A
                   .
                   .
                   .
 Light source----- /-
                     -                 DEFLECTED LIGHT BEAM 
                      -
                       - MIRROR B
                   .
                   .
                 Detector

Sorry for asking questions that seem kinda dumb but ever place I looked it up only has a diagram similar to the first one I drew but I can't understand how that would compensate for a wind blowing. —Preceding unsigned comment added by 24.171.145.63 (talk) 02:09, 27 May 2009 (UTC)

I don't understand why you would think that there should be a deflection of the beam going to mirror B. This is simply not the case. The first diagram is the correct one. Dauto (talk) 05:11, 27 May 2009 (UTC)

I'm viewing it from the point of view of Michelson, believing that there WOULD be an aether. I understand that there IS NOT an aether and I'm not trying to prove otherwise (obviously...) but I'm trying to understand how Michelson constructed his apparatus. Imagine swimming across a stream. You are swimming straight (suppose North) at a speed of 5 m/s. The current of the river is 3m/s due east. So in reality you are going 4m/s NE. You are not going in a straight line, you are going in a angled line. Michelson believed along these lines I think. He used the same analogy that I used to explain this experiment (or more correctly I'm using the one he did...)(http://galileoandeinstein.physics.virginia.edu/lectures/michelson.html). This site has a pretty good explanation but when you look at its animated experiment (http://galileoandeinstein.physics.virginia.edu/more_stuff/flashlets/mmexpt6.htm), they state themselves "we have cheated by not taking into account the effect of the aether wind on the direction of motion of the light, but only including its effect on the speed of the light.". How did Michelson take into account the "effect on the direction of motion". His apparatus, at least every one I look at, looks like my first apparatus, the same one seen in the flashlet. Yet as they themselves state, this apparatus (or at least the animation) doesn't take into account the effect on the direction. How did Michelson compensate? —Preceding unsigned comment added by 24.171.145.63 (talk) 05:33, 27 May 2009 (UTC)

Oh yeah btw my first question, that the aether is stationary and the Earth moves through it. That's correct is it not? 24.171.145.63 (talk) 05:57, 27 May 2009 (UTC)

-EDIT: Damnit I'm confusing myself now. On the wikipedia article it states " the beam reflecting back and forth perpendicular to the flow of ether would have to travel farther than the beam reflecting parallel to the ether". However I was under the impression the experiment was conducted thinking that the beams would TRAVEL THE SAME DISTANCE (not, as the article says, travel FARTHER) but merely at different speeds. Keeping the same analogy as the river (which is explained on the linked site), the man going perpendicular to the river is going at 4 m/s. The man going parallel to the river (also with a swimming speed of 5m/s) goes at 8m/s on way (with the current of 3m/s) and 2m/s against the current. So if the river is 10 m long and one man swims 10 m perpendicular to the current and one man swims parallel to the current, it would take the first man 5 seconds (20m at 4m/s) and the other man 6.25 seconds (10 m at 8m/s and 10 m at 2m/s). Ignoring that the swimmer swimming parallel must angle himself (the basis of my original question), I thought the different times each light beam took would cause the fringe shift? If, in fact it is correct he thought the beam going perpendicular would go farther that would resolve my first question; the beam going perpendicular goes the same horizontal distance as the parallel beam but is deflected so it forms a small right triangle, whose hypotenuse is greater than the horizontal distance alone. However; it still doesn't resolve how he compensated his apparatus for the deflection of perpendicular beam. Right? I know I have some major logical fallacy somewhere I just can't think of it myself for some reason... 05:56, 27 May 2009 (UTC)

—Preceding unsigned comment added by 24.171.145.63 (talk) 05:49, 27 May 2009 (UTC) 

The aether wasn't assumed to be stationary as such, just to be moving at a roughly constant speed over a region the size of Earth's orbit. Since Earth's orbital velocity changes by about 60 km/sec in six months, you can be sure of having an aether wind of at least 30 km/sec at least once in the course of a year. Note it makes no difference whether you consider the aether or the Earth to be stationary; the (Galilean) principle of relativity applies here. Also, the paths weren't of equal length (they couldn't achieve that kind of precision), rather, they looked for sinusoidal variation in the fringe shift as they rotated the apparatus. Since you're interested in the detailed experimental setup, I should also mention that the light was not simply reflected back once as shown in most diagrams, but was bounced back and forth numerous times so as to increase the effective path length.

There are several ways to think about the issue of the direction of the light. First, any correction would be very small since the wind speed (~30 km/sec) is around 0.0001c. Second, calibrating the experiment would include fiddling around with the light source and the mirrors until the light goes where you want it to; it's a feedback-driven process that automatically adjusts for any bias in the direction. Keep in mind that any effect would apply equally to every light source in every experiment ever done, whether or not it was intended to detect the aether wind. Third, in fact there is no effect. Consider objects being fired "horizontally" through a tube that's moving vertically downward.

    _______
    _*_*_*_    _______
               ___*_*_*   _______
                          _____*_* * _______
                                     _______* * *

The velocity of each object is diagonal down and to the right, but the line of objects as a whole points horizontally. From the rest frame of the tube, the objects move horizontally despite the "wind". A real object moving in the wind might be blown to one side, especially if it's of low density, but that's just because the analogy is a lousy one. The light is not an object blown by aether wind, it's motion of the aether itself. A better analogy is sound waves in the wind, but most people don't have good intuition for that (I know I don't). The boat analogy can be made to work. Suppose you're trying to row east against some unknown north-south current while staying between parallel barriers (the walls of my tube). After you clear the barriers you continue rowing as you were before; then you will continue moving horizontally. This isn't exactly an airtight argument, and I'm not sure that there wouldn't be, say, some aether-speed-dependent effect on the displacement of the light transmitted by the half-silvered mirror, but I hope this gives you the intuition you were missing.

Whether the difference of travel time is due to distance or speed is a matter of perspective. With respect to the rest frame of the apparatus, the beams travel the same distance at different speeds. With respect to the rest frame of the aether, they travel different distances at the same speed. -- BenRG (talk) 10:19, 27 May 2009 (UTC)

Note the article was wrong when it said the path perpendicular to the aether wind is longer. It's shorter. (Now fixed.) -- BenRG (talk) 15:22, 27 May 2009 (UTC)

Aight thanks a bunch dude! I think I get it better now. —Preceding unsigned comment added by 24.171.145.63 (talk) 23:21, 27 May 2009 (UTC)

Root growth in cut roses

About two weeks ago, I brought home some cut roses, which were placed in a vase containing tap water and the preservative that came with them. The roses withered slightly as one would expect, but they also seemed to develop small roots below the waterline. Does this happen often, and what might have caused it? Can these cut roses be re-rooted? 69.224.113.202 (talk) 02:25, 27 May 2009 (UTC)

Cutting (plant) does not specifically mention roses, but this is a common way to breed plants. I have heard it described as a special form of asexual reproduction as it can generate an entirely new organism without going through the standard pollination process. If conditions are right, the plant can survive and be replanted. Nimur (talk) 03:07, 27 May 2009 (UTC)

Thanks. I wasn't aware this could work with roses, as I'd only ever seen it done with succulent plants. 69.224.113.202 (talk) 03:41, 27 May 2009 (UTC)

Yeah - it's certainly possible to grow plants from cuttings - you can even buy hormonal rooting compound that you dip cut stems into that promotes root growth. I'm a little surprised that roses would do it spontaneously - but it's clearly not beyond the realms of reason! SteveBaker (talk) 03:43, 27 May 2009 (UTC)

My grandmother grew a rosebush from cut flowers, and kept it for several decades. Edison (talk) 03:42, 28 May 2009 (UTC)

Dont get your hopes up. commercial roses are often grafted onto a different root stock. the root stock is wild and very hardy and disease resistant but produces smaller flowers on its own. I'm sure that they have done this deliberately so you cant do exactly what you are wanting to do. they want you to have to buy their product not grow it on your own. my advice is just buy a rose, chop the top off, and, if you can get the root stock to grow, just be satisfied with a nice disease free wild rose that grows like a weed. just-emery (talk) 17:02, 31 May 2009 (UTC)

That wasnt very clear was it? I mean that non-wild roses dont grow well unless they are grafted onto wild root stock. the wild roses grow great but dont produce flowers as well. just-emery (talk) 19:30, 31 May 2009 (UTC)

Who are these things?

What the heck are these things?

Who could these critters be? They're all over the leaves of this manzanita near Kernville, California, a quarter mile or so from the Kern River. Of course they're the larvae of something, but I couldn't find anything like them on caterpillar identification websites. The green verging on pink is quite pretty; it's like a blend of the green of the manzanita leaves and the red of the stems and bark. --jpgordon^∇∆∇∆ 04:33, 27 May 2009 (UTC)

Gastropoda (without shell) might be another possibility if they aren't larvae.71.236.24.129 (talk) 05:47, 27 May 2009 (UTC)

To me it looks more like a form of plant desease, since one can see clearly, that the leaves writher up from the sides and then turn the shade of red you described. That also seems to be the reason for mixing colours. Maybe some kind of Rust?--91.6.48.74 (talk) 06:10, 27 May 2009 (UTC)

I am assuming you did not actually pick off one of theses "critters". I would not disagree with rust but they may be some sort of leaf gall caused by a small mite or fly laying an egg and the larva causes this peculiar damage. If you Google image 'leaf gall' you will see the weird and wonderful shapes and distortions that can occur. Richard Avery (talk) 06:44, 27 May 2009 (UTC)

Ah-ha! I think they are indeed galls caused by the Manzanita Leaf-gall Aphid (Tamalia coweni). Thanks! (and, no, we didn't try to pick 'em off. Dunno why.) --jpgordon^∇∆∇∆ 07:08, 27 May 2009 (UTC)

You seem satisfied with that, but if you want more help from local experts, I would suggest contacting the Kern River Preserve. When I lived in the area, I visited the Preserve a few times, and the folks there didn't bite. -- Coneslayer (talk) 17:50, 27 May 2009 (UTC)

Oh yes. Great place. But I got an answer here faster than I did from Alison (who runs the place.) She sure knows her birds! --jpgordon^∇∆∇∆ 20:06, 27 May 2009 (UTC)

How are the hummingbirds these days? -- Coneslayer (talk) 11:54, 28 May 2009 (UTC)

A Zeppelin filled with helium

If you built an exact replica of a Zeppelin or similar 1930s airship, but filled it with helium rather than hydrogen, would it fly? And would it fly without any significant problems because of the different gas? 78.146.52.248 (talk) 09:44, 27 May 2009 (UTC)

Yes, it probably would. Helium has an atomic weight of 4 (and is monoatomic). Hydrogen is H₂ and has an atomic weight of 2. Both are close enough to ideal gases that this translates to about the same difference in weight per volume. That seems like a lot less lift from Helium, but what provides the lift is the difference to the density of air, which is mostly determined by the molecular weight of of N₂ at 28 and O₂ at 30. I do think Helium is harder to contain, so you may have a bigger loss of gas due to diffusion over time. On the other hand, it is chemically more benign. --Stephan Schulz (talk) 09:56, 27 May 2009 (UTC)

I don't think the weight of air makes a difference in this comparison - twice the weight means half the lift. I doubt Zeppelins carried their weight again in ballast, so it's not going to work. You would need to double the volume of your balloon (which requires increasing the linear dimensions by about 26%). --Tango (talk) 11:42, 27 May 2009 (UTC)

The people at Cargolifter AG seem to be able to make it work. (As long as they don't run into a storm.) 71.236.24.129 (talk) 11:58, 27 May 2009 (UTC)

• Tango is wrong. See Lifting gas#Hydrogen and helium. PrimeHunter (talk) 12:00, 27 May 2009 (UTC)
• (ec)Yes, Tango is wrong. The uplift for any body in the atmosphere is equal to the weight of the atmosphere it replaces. The net uplift is that minus the weight of the body. For air at sea level, the density is about 1.2 kg/m³. For Helium, its 0.1786 kg/m³ and for H₂ its 0.08988 kg/m³. In other words, a cubic meter of Helium (close to standard conditions) provides a net lift of 10 N, and one of Hydrogen one of 10.9 N. For any real vehicle, you also have to take into account the significant weight of the actual structure, so even that difference of 9% overstates the case. --Stephan Schulz (talk) 12:13, 27 May 2009 (UTC)

  Oh, yeah... oops! --Tango (talk) 17:13, 27 May 2009 (UTC)

As stated above, helium has about 90% of the lifting power of hydrogen, so if lift using hydrogen exceeds the weight of the vehicle by more then 10%, it should work, although your controls might be sluggish. 65.121.141.34 (talk) 13:02, 27 May 2009 (UTC)

The dirigible USS Los Angeles was built in Germany and used hydrogen as the lifting gas. It was acquired by America as part of the reparations payments made after World War I. The Americans used helium as the lifting gas in this same dirigible. At the time, helium was a rare gas and the USS Los Angeles and the USS Shenandoa (the firsr American-built dirigible) alternately used the same helium gas. It was pumped from one dirigible to the other. At that time, America was the only country that had an appreciable amount of helium, and it refused to sell Germany any of it's increasing supply for Germany's post-war Zeppelin program. – GlowWorm. —Preceding unsigned comment added by 98.16.66.187 (talk) 13:58, 27 May 2009 (UTC)

Actually, helium is still pretty expensive - prices have gone up by at least a factor of four in just the last decade. This can only get worse. The US still produces 90% of the helium in the world - and that only as a byproduct of natural gas extraction. When global warming remediation seriously kicks in - natural gas will have to be phased out as a fuel - and that will severely impact helium production. Airships are an exceedingly useful technology (albeit very under-utilised right now) - but sooner or later, we're going to have to 'get over' the Hindenburg catastrophy and switch back to hydrogen-filled airships. These can be exceedingly cheap to fill - and with modern safety precautions, we really shouldn't have to worry about catastrophic explosions anymore. SteveBaker (talk) 14:36, 27 May 2009 (UTC)

This sounds exactly like the owners of the Titanic, who felt that with modern safety precautions they didn't have to worry about liners sinking any more. But the reference desk is not the place for debate, so let's stop that now.

As a point of fact, the Hindenburg did not explode; it burned. For it to have exploded, there would have had to be a significant mixing of air and hydrogen before ignition. The result would then probably have devastated the whole airfield, whereas the actual disaster merely destroyed the airship and killed about 1/3 of the people on board.

As another point of fact, the Hindenburg was originally designed to be lifted using about 65% helium and 35% hydrogen, with the helium cells surrounding the hydrogen ones to minimize the number of places where hydrogen came close to the air. Once the Zeppelin company realized that helium was not going to be available as they had optimistically hoped, they canceled the construction of the inner cells, which saved some weight and cost. Using hydrogen instead of helium for the whole volume also gave about 25,000 pounds more lift -- which was needed, because the airship exceeded its design weight, although my source* does not say by how much. (To put this in proportion, the total dead weight of the Hindenburg as built was 118,000 kg or 260,000 lb; on one transatlantic flight in 1936 that the book describes in detail, it carried an estimated 96,000 kg or 211,500 lb of passengers, crew, supplies, etc.)

*The Golden Age of the Great Passenger Airships: Graf Zeppelin & Hindenburg by Harold G. Dick with Douglas H. Robinson, Smithsonian, 1985, ISBN 0-87474-364-8.

I think the answer to the original poster's question is that it might fly, but its operations would be severely crippled. Most of the gas volume is required just to lift the dead weight and necessary supplies such as fuel; with the loss of about 8-10% of the lifting capacity, the usable payload and/or range would be too limited. Airships work on a pretty small margin of lift.

Also, as a side point, because helium is monatomic (and highly inert), it leaks through membranes and joints more easily than most other gases. Gasbags meant for hydrogen might not be quite good enough for use with helium.

--Anonymous, edited 16:52 UTC, May 27, 2009.

I don't think the Titanic comparison is legit. Titanic could be compared to that original Hindeburg design that you mention (hydrogen surrounded by helium). An all-helium airship sounds more like Titanic with an adamantium hull - sure, you can still have problems, but you're never going to get your ship (going up in flames/sinking with a hole in the side). Vimescarrot (talk) 17:43, 27 May 2009 (UTC)

What about deuterium? Is it combustible? How much lift would deuterium compared to hydrogen? ScienceApe (talk) 18:29, 27 May 2009 (UTC)

Chemically, it is pretty much identical to regular hydrogen. Some of the energy levels are a little different, but I doubt they are different enough to stop it burning. --Tango (talk) 19:05, 27 May 2009 (UTC)

[edit conflict] Deuterium, being merely an isotope of hydrogen, is chemically identical (although see also Graham's law; the rates of some processes depend on the molecular speeds). It is twice as heavy as hydrogen, so no help there (but see above how this does not mean "half as useful"). --Tardis (talk) 19:14, 27 May 2009 (UTC)

I see that isotope has the better link kinetic isotope effect. However, it also has a very strange image; what's with the gap near the top, at $Z=83$ or so? Are radon and such really that reliably less stable than the actinides? --Tardis (talk) 19:23, 27 May 2009 (UTC)

Actually, that gap appears to correspond to the Astatine-Thorium (Z=85-89) area. You're right though, the image does look like a chunk is taken out, and it does not seem to correspond to the Isotopes of francium article. -RunningOnBrains^{(talk page)} 20:12, 27 May 2009 (UTC)

I stand corrected: This image represents it a lot better, but apparently that gap is very real (and is analogous to another gap around Z=105). I'm not sure if it has a name or not.

Yes, the gap is real. There is also a small gap at Z=43 not clearly visible on that picture. But look for it on that table. The shell model is the model used to explain why some number of protons (or neutrons) lead to more stable nuclei then others. The numbers that lead to more stable nuclei are called "magic numbers". So, I guess we are talking about anti-magic numbers here :). Dauto (talk) 03:01, 29 May 2009 (UTC)

I think the idea was that it is lighter than helium but might not be as flammable as hydrogen. Regrettably, this is not the case, but it was a nice idea. --Tango (talk) 22:23, 27 May 2009 (UTC)

So I guess that just leaves the mythical vacuum airship left. But that has even more problems. :P ScienceApe (talk) 19:01, 28 May 2009 (UTC)

How about using a well-mixed blend of hydrogen and helium as a lifting gas, with sufficient helium to prevent explosion deflagration? What would be the proportion of each gas for the minimum use of the more expensive and heavier helium? Would the gases separate due to their difference in weight specific gravity, or would Brownian movement keep them mixed? If they would separate, would a turbulence-creating fan be feasible to keep them mixed? – GlowWorm. —Preceding unsigned comment added by 98.17.40.143 (talk) 23:24, 28 May 2009 (UTC)

Concave tympanic membrane

When a tympanic membrane is concave does it remain so or does it self-correct over time or require medical intervention? What caused it to become concave? —Preceding unsigned comment added by Nicola Chessher (talk • contribs) 10:48, 27 May 2009 (UTC)

In general, the TM returns to its "normal" shape after a distorting force is removed. When allowed to move freely, the TM is shaped like a cone pointed inward due to its circumferential attachments to the external auditory canal and central attachment to the malleus, which maintains the TM under tension. When the Eustacian tube is blocked the TM cannot move freely, and fluid may accumulate in the middle ear. When the TM cannot move freely, the TM may be stretched outward or inward as you suggest. Once allowed to move freely, then like an elastic sheet under tension the normal TM will assume the lowest-energy shape given its attachments. --Scray (talk) 21:42, 27 May 2009 (UTC)

Are gulls lactose intolerant?

Inspired by the question above. From my personal observations when feeding the gulls or watching the local urban gulls scavenging, it would seem that gulls love to eat cheese and butter (in preference to bread, at least - though they go for meat first, if available). In fact, the very first abandoned gull chick I raised when I was a kid was fed on a mixture of gold top milk and mashed tuna - my reasoning at the time being something along the lines of 'the baby needs milk to drink'. She seemed to come out of it absolutely fine. Better than, in fact. I know now that it's very unlikely that a truly wild gull would ever encounter milk in its diet - but considering that gulls will consume just about anything organic if they're hungry enough, are their digestive systems completely incapable of handling lactose? --Kurt Shaped Box (talk) 12:21, 27 May 2009 (UTC)

Only mammals have lactase, the enzyme necessary to break down lactose, in their digestive systems. All birds, gulls included, will lack the enzyme. Butter has low levels of lactose and cheese (depending on type) has much less than milk (our article on lactose intolerance say cheddar has only 10% of the amount in milk), so neither of them may be a problem for a gull in small amounts. As to the gold top milk, if you used the 'top of the milk', there would be less lactose than normal milk due to the increased amount of butterfat - lactose being water soluble. Maybe your chick happened to have enough of the right bacteria to help it process the amount of lactose it got. The general advice, according to all the petcare websites I just looked at, is 'don't give your birds milk'. Mikenorton (talk) 13:09, 27 May 2009 (UTC)

As the article lactose intolerance notes, the symptoms of lactose intolerance aren't really due to the lactose itself, but result from the fermentation of the disaccharide by bacteria in the intestine. Birds, especially wild birds, are likely to have a different set of intestinal flora, as well as different speeds of digestive processes, which might change how lactose will ferment in the intestine. This might make the symptoms from eating lactose worse, better, or even non-existent when compared to a lactose-intolerant human. To be on the safe side, though, I'd agree with the recommendation not to try it. -- 128.104.112.106 (talk) 15:33, 27 May 2009 (UTC)

Could a human break their own neck simply by unassisted extreme rotation?

No using of the hands, no using contact against another object...

Just, by pure rotation via the existing neck muscles, could you turn so far as to... *crunch* -- paralyze yourself? 61.189.63.185 (talk) 12:23, 27 May 2009 (UTC)
Its weird thinking about it... You've just given me some pain in the neck !!. Anyway, i think it should be within the limits of the neck muscle power, but it would definitely require a lot of effort, i don't think anybody has committed suicide this particular way..My guess is that there is there is nothing which says you can't do it..Rkr1991 (talk) 12:54, 27 May 2009 (UTC)

Nope - I just tried - and I'm still here. SteveBaker (talk) 14:24, 27 May 2009 (UTC)

That's funny, I just tried and it actually killed me. Huh. ;-) --98.217.14.211 (talk) 14:33, 27 May 2009 (UTC)

I could not do it either. Maybe the neck and its muscles and pain receptors were intelligently designed, or there is survival value in not being able to inadvertently or intentionally kill yourself that way. Edison (talk) 03:40, 28 May 2009 (UTC)

Hmm, I wonder if you and Steve really tried hard enough. No one said it would be easy. Could be your commitment is lacking. --Trovatore (talk) 01:01, 29 May 2009 (UTC)

Well, Epileptics certainly manage to severely damage themselves by cramping muscles. --Stephan Schulz (talk) 14:45, 27 May 2009 (UTC)

I doubt it could be done voluntarily. Pain is a pretty good way of stopping you doing stupid things. I guess it could happen with muscle spasms or something, but I've never heard of anything like that. --Tango (talk) 19:03, 27 May 2009 (UTC)

I wonder if anyone has ever committed suicide by snapping their own neck, commando-style? A quick Google search turned up nothing useful. Edit: like so... --Kurt Shaped Box (talk) 21:53, 27 May 2009 (UTC)

Different question, but on the same spirit: Could a human stop their own breathing (permanently) simply by unassisted ... well ... will power? No using of the hands, no smothering against another object...no getting into a oxygen-lacking environment. Jay (talk) 12:23, 29 May 2009 (UTC)

No. Even if you had the willpower to override the intense desire to breathe, you will simply pass out and begin breathing while unconscious. 65.121.141.34 (talk) 13:22, 29 May 2009 (UTC)

Since I doubt anybody will try this, I believe it's possible to swallow one's own tongue for the purpose.Julzes (talk) 18:52, 29 May 2009 (UTC)

It's not easy, however.

casimir effect pressure anomalies 2

Hi

The question i asked before seemed to not really get answers just more questions so I will ask it in a simpler way here. If the casimir effect works by vacuum energy pushing the two plates together( since there is more waves outside the plates than inbetween them) , that would mean that given the right conditions the vacuum can produce pressure, so surely if you could manipulate the vacuum in such a way that it could produce more pressure on one side of an object than another, it would move that object. IS this correct or not?

Robin —Preceding unsigned comment added by 79.68.147.218 (talk) 14:48, 27 May 2009 (UTC)

People answered you last time. May be you didn't like the answer? The answer is no, you can't do that. It would violate conservation of momentum and energy. Dauto (talk) 15:07, 27 May 2009 (UTC)

The Casimir effect (as beloved by free-energy nuts and science fiction authors) as a means for extracting free energy from vacuum simply doesn't exist. It exists as a force between two VERY close, parallel plates - but force is not energy. We get an AMAZING number of questions here where people confuse force with energy - and I'm starting to believe that this is one of the most misunderstood parts of physics amongst the general public. Vacuum energy is a horribly misleading term. When you have a force between two parallel plates (imagine holding two fridge magnets apart by a tiny distance - you can only 'extract energy' by releasing them and letting them smack together. Once you've done that - there is no more energy to extract. To get them to do it again, you have to pull them apart - and that takes (at best) the same amount of energy as you just gained in letting them smack together. So there is no free lunch - no violation of the laws of Thermodynamics - just an interesting demonstration of quantum effects at the "macro" scale. In the situation that you're thinking of ("if you could manipulate the vacuum...") there is just one plate - that's like just one fridge magnet. There is no force unless there are two parallel plates very close together - and if there are two plates and you let them move then they're going to move about a micrometer then hit each other and stop. You can't make a perpetual motion machine in this (or any other) way. SteveBaker (talk) 16:26, 27 May 2009 (UTC)

Ok there appears to be a misunderstanding here, i was not inquiring about free energy, just the vacuum being able to move stuff and this article i have just found answers my question, harvard scientists have done it ( on a small scale at least)http://www.seas.harvard.edu/capasso/publications/Munday_Nature_457_170_2009.pdf and there may also be other ways. http://www.telegraph.co.uk/news/1559579/Physicists-have-solved-mystery-of-levitation.html Thanks anyway, guess you guys were mistaken or I didnt ask the question very well.

Robin —Preceding unsigned comment added by 79.68.147.218 (talk) 20:42, 27 May 2009 (UTC)

No, it is the articles that are wrong. As I said, the Casimir force is no different from any other force. It is not caused by vacuum fluctuations. It is a relativistic-quantum correction to the electromagnetic force, as these authors point out in their abstract. A repulsive Casimir force is not going to lead to levitation technology, and the authors of course make no such claim. We already have maglev. Universities like Harvard turn these papers into pop-science press releases in the hope of getting free publicity. Newspapers and magazines publish them uncritically because they don't employ anyone who can tell good science from bad and because they think it will entertain their readers. It's a terrible situation that could hurt funding for genuinely important research that doesn't play well as infotainment. Please don't encourage this system. -- BenRG (talk) 22:23, 27 May 2009 (UTC)

Reliability of Air Armament

What are the methods to ensure correct preservation of Air Armament while under storage? What are the common mistakes made while undertaking storage of Air Armament and how to avoid them?Why should a missile when fired in the air at correct range miss its target?Fighterflyboy (talk) 14:54, 27 May 2009 (UTC)

This sounds like a series of AFROTC homework questions. Sorry, we do not do homework for you, but we will help if you are stuck on something specific. Please look at the relevant articles ahbd then come back her if you have specific questions that the articles do not answer. -Arch dude (talk) 15:19, 27 May 2009 (UTC)

Hopefully, the methods to ensure correct preservation of weapons of any type (air armament included) are centered around a competent, highly trained corps of military officers. If Wikipedia is the preferred reference for aforementioned officers, we are all in a lot of trouble. Nimur (talk) 16:05, 27 May 2009 (UTC)

Actually I would think that the preservation of such weps would be the responsibility of enlisted personnel, since they are the ones who load the aircraft. 65.121.141.34 (talk) 16:14, 27 May 2009 (UTC)

Any effective military will certainly have well-defined roles for the enlisted and commissioned ranks; let me clarify my previous statement, and just say that weapons policy is rarely decided by an enlisted personnel; execution of that policy is certainly performed by them. Nimur (talk) 16:39, 27 May 2009 (UTC)

Part of the problem seemed to be just that, emlisted men were deciding procedures of their own devizing, and not following the official script. SpinningSpark 14:08, 29 May 2009 (UTC)

Medical term

What is the medical term for anus pain? --83.38.248.119 (talk) 15:54, 27 May 2009 (UTC)

Pain comes in many varieties. Pruritus ani refers to anal itching which can be quite painful in many cases. Are we refering to that sort of pain, or to pain from trauma or some other sort of pain? --Jayron32.talk.contribs 16:01, 27 May 2009 (UTC)

Proctalgia. [1]. --NorwegianBlue ^talk 18:10, 27 May 2009 (UTC)

There is a spasm pain of the anus that causes considerable discomfort usually for relatively short periods called Proctalgia fugax. Trust Wikipedia to have a good article about it. Richard Avery (talk) 19:52, 27 May 2009 (UTC)

Hemorrhoids are a source of anus pain. Cuddlyable3 (talk) 10:42, 28 May 2009 (UTC)

The non medical term is " a pain in the ass!" But I geuss you knew that. —Preceding unsigned comment added by ThrobbingTrousers (talk • contribs) 00:14, 29 May 2009 (UTC)

helium production

Since alpha particles are the same as a helium nucleus, can one produce helium by alpha decay of Uranium? How do you get electrons into the alpha particles? 65.121.141.34 (talk) 16:01, 27 May 2009 (UTC)

Yes, an alpha particle is a helium nucleus, so technically it is already helium. It is just very hot, as it is carrying much of the kinetic energy of the nuclear decay (you can think of the decay as "the second half" of an elastic collision between a heavy nucleus and a light alpha particle. The alpha particle goes flying off at high speed). This high kinetic energy needs to be transferred somewhere else, because hot atoms tend to thermally ionize their electrons away. But, if you could get electrons from some other source (or the original atom, which should have released some free electrons as well), electrostatic attraction will eventually reattach them and neutral helium will form. Nimur (talk) 16:18, 27 May 2009 (UTC)

(EC) Yes, an alpha particle is an ionized helium and it will readily collect any electrons it may find in the enviroment and spontaneously produce a helium atom. Just remember that the radioactive decay does not produce any net charge, so there should be no problem for the helium ion to eventually find electrons for itself. Dauto (talk) 16:19, 27 May 2009 (UTC)

Well, it won't readily collect electrons, because the nucleus will be at high temperature and will remain as a free ion plasma until its thermal energy decreases to a level that can support stable electron orbitals. Any individual alpha particle might capture an electron, but it would immediately reionize due to the thermal energy. You really do have to find a way to cool the plasma down if you want to form atomic helium. If the experiment is taking place in air (not in vacuum), then thermal collisions with the air might be sufficient to cool the alpha particles within a few centimeters or meters, depending on the decay process. Nimur (talk) 16:24, 27 May 2009 (UTC)

It's probably worth noting that the amount of helium you could produce by this process would be very small, and there's no way to conceive of it as the basis for an efficient industrial process for the production of helium. Dcoetzee 17:48, 27 May 2009 (UTC)

In fact, that's the way all the helium you see on Earth *was* produced. Helium, being very light and unreactive, quickly makes it's way to the upper atmosphere and is stripped away by the solar winds. There is negligibly little in the atmosphere. The helium we do have is obtained from natural gas wells. The helium is in the natural gas because the low levels of radioactive isotopes in the surrounding rocks decay over millions of years, producing helium which cannot escape because of the geology of the rocks (the helium can't escape for the same reasons the natural gas cannot escape). As Dauto indicates above, there is no net change in charge for radioactive decay, so if an atom of uranium spits out a +2 alpha particle, the thorium particle that's left behind carries a -2 charge (2 electrons). The alpha particle will then grab electrons from the material it passes through (that's why it's called ionizing radiation). The atom which it pulls it from will then pull other electrons to make itself neutral from somewhere else, which will pull electrons from somewhere else, etc. etc. On the other side, the excess electrons on the thorium will get dumped onto some other atom, which will dump them onto another atom, etc. etc. until the positive charges and negative charges eventually meet each other, restoring neutrality (this may take a while). -- 128.104.112.106 (talk) 21:48, 27 May 2009 (UTC)

Burning fat

Why is it recommended to do cardio to burn fat? When does the body start to burn fat? If a person just do push-up (aka press-ups) will he loose fat, since he needs energy to it?--Mr.K. (talk) 16:07, 27 May 2009 (UTC)

Yes, but very slowly. Push-ups require strength more than energy. Basically, you need to get your heart rate up, it doesn't really matter what kind of exercise you do in order to do that, but cardio is specifically intended for that purpose (hence the name). --Tango (talk) 17:09, 27 May 2009 (UTC)

You may also want to start with an article like Aerobic exercise, and see where it takes you. --Jayron32.talk.contribs 17:14, 27 May 2009 (UTC)

@Tango: yes, but strength is energy. The question is that if a person has a balanced diet - in the sense that he whether earns nor looses weight - and he starts to do push-ups (=> more consume of energy) will he loose weight without cardio? The energy/strength has to come from somewhere. Cardio may help you deplete the glucose from your blood and start using your fat, but in the scenario above, isn't it logical to expect to burn fat?Mr.K. (talk) 17:50, 28 May 2009 (UTC)

I think what happens is the body will typically use carbohydrates before it uses fat. Therefore you will probably burn primarily carbohydrates rather than fat when you do some pushups. I believe that is why aerobic exercise is usually recommended to lose fat - once your body consumes the "easy to use" carbohydrates, it will start to look to its fat stores (so you might be running off carbohydrates for the first hour and then start "burning fat"). However, if you build muscle from doing things like pushups, your basal metabolic rate will increase and you will find it easier to keep weight (fat) off. TastyCakes (talk) 17:58, 28 May 2009 (UTC)

Sure, but the energy expended to do a few pushups is trivial. To burn a significant amount of calories, you need to be doing pushups for a long time (some estimates: http://wiki.answers.com/Q/How_many_calories_are_burned_by_doing_push_ups ~650 kcal/hr] ~500/hr). Doing pushups for an hour is an aerobic exercise, of a rather rubbish variety (the same person should be able to burn more calories running or swimming with much less effort). The real trouble is that, in most people, the muscles in the arms and chest just aren't very big, so their capacity to expend large amounts of energy is pretty limited. Worse, their endurance is very poor (who on earth can do vigorous pushups for an hour?), so even a fit person will have to quit before they've burned very many calories. If you want to expend large amounts of energy then only the big muscles of the legs and lower torso are up to the job. TastyCakes is absolutely right that building muscle through strength training will raise BMR (and thus, given the same diet as a less muscled person, lead to fat loss), which is why most fitness instructors set training plans that include weights, even for people who say they only want to lose weight. 87.114.167.162 (talk) 21:57, 29 May 2009 (UTC)

chemistry

Why does 2-methyl propanal gives cannizaro reaction instead of having alpha H atom —Preceding unsigned comment added by 59.89.110.103 (talk) 16:13, 27 May 2009 (UTC)

I don't understand the question. 2-methyl propanal does have an "alpha" hydrogen; all aldehydes do. Also, the best place to find answers to the questions at the end of the chapter in your chemistry textbook is in the chapter immediately preceding it. --Jayron32.talk.contribs 17:08, 27 May 2009 (UTC)

I'm sorry but the above statement appears erroneous. Not all aldehydes have an alpha hydrogen. For example Benzaldehyde, or 2,2 di-methylpropanal. But 2-methylpropanal does have an alpha hydrogen. The question the OP asks is that despite having an alpha hydrogen, why does this compound also undergo Cannizaro reaction, instead of Aldol reaction, under basic conditions ? I would say that this compound would indeed undergo Cannizaro, but in only limited amounts. It has only one alpha hydrogen, which is sterically hindered as well. So under strong basic conditions(like 50% NaOH) it might also undergo Cannizaro in competition with Aldol condensation. However, the reaction probably does not take place to a great extent, so it shouldn't be used even for writing conversions on paper, let alone industrially. It yields a mixture of products, but overall the Cannizaro product must be quite a low fraction. Rkr1991 (talk) 02:54, 28 May 2009 (UTC)

Self-published scientific magazine

What can be called "self-published"? If a faculty has a magazine and this magazine publish many works of its own teachers - and some articles of external researchers - , is it self-published?--Mr.K. (talk) 16:14, 27 May 2009 (UTC)

If the university press publishes such a report, it is not self published. Also, there is an important distinction between self-published and "non-peer-reviewed" research. For example, my research group self-publishes our bi-annual journal, since we maintain and contract our own document management and printing services (rather than the Stanford University Press); but our research is peer reviewed by a consortium of academic and industry experts, sponsors, and collaborators. We also publish other work in academic and industry journals. Nimur (talk) 16:30, 27 May 2009 (UTC)

What makes organisms yellow?

Does anyone know of any natural pigments that make things yellow other than the carotenoids? This includes carotenes and xanthophylls. Yellow#Biology needs some work and starting on the pigments would be a good idea. Thanks Smartse (talk) 16:52, 27 May 2009 (UTC)

Curcumin --Dr Dima (talk) 01:30, 28 May 2009 (UTC)

Also quinone-based yellow dyes present in (and extracted from) a number of plants. I don't think we have an article on that :( --Dr Dima (talk) 01:41, 28 May 2009 (UTC)

Well, there is phaeomelanin, and other yellowish pigments in some fish and frogs. I'll browse my literature collection and see what examples I can find. Rockpocket 03:10, 28 May 2009 (UTC)

Turns out many of the other yellowish pigments in fish appear to be breakdown products or modification of xanthophylls or carotenoids, probably not what you are looking for. However, another type of yellowish pigment is ceroid, also known as lipofuscin, and the yellow pigments found in many insects are pteridine derivatives such as Xanthopterin. Rockpocket 17:08, 28 May 2009 (UTC)

calluses on fingers

I'm an electric bass player--I regularly get blisters then calluses from my playing

BUT THEN! the calluses peel off! How do I keep those calluses strong and firm without peeling off after a while.

209.6.18.79 (talk) 17:16, 27 May 2009 (UTC)

If you're getting blisters, then you're playing too much. And what you're calling calluses is just skin that's grown as part of the healing to the damage you've done, not a callus. So quit playing until your fingers are back to normal, and then return to playing gradually. When your fingertips hurt, stop for the day. Do a little more each day, and real calluses will gradually form (my fretting fingertips look almost identical to the other hand; no cracking or peeling here, but with tougher skin nevertheless). Ignore that Ted Nugent "play til your fingers bleed" nonsense. 87.114.167.162 (talk) 19:49, 27 May 2009 (UTC)

This happened to me for a while (like a year) when I started playing, but eventually my fingers realized that I wasn't going to stop playing the guitar. There are two things that happened to me over time. First, my callouses became more permanent, and the blister-peel cycle stopped. Second, my finger tips just became less sensitive to it; I wouldn't say that my fingers are numb, I just learned to "play through the pain". I don't even notice it anymore. Other than that, I would agree with the above. Don't play until you bleed, but always play a little each day. You're body will eventually change. --Jayron32.talk.contribs 19:52, 27 May 2009 (UTC)

Drumming your fingertips on wood might help a bit. (OR note: Side effect of driving those around you crazy might be undesirable, depending on your age:-) It gets the skin stressed over a wider area than just the string/fret and may help with building Calluses instead of blisters.71.236.24.129 (talk) 07:50, 28 May 2009 (UTC)

Use a little hand cream. You want callous skin that is firm but not dry and brittle. Heel skin sometimes gets that way too. Cuddlyable3 (talk) 10:35, 28 May 2009 (UTC)

i found that the skin under the peeled callouses is a little stronger than before the callous formed. Eventually you will have slightly harder skin on your fingertips but no callouses and no pain. Dont play with sore fingers however! —Preceding unsigned comment added by ThrobbingTrousers (talk • contribs) 00:12, 29 May 2009 (UTC)

Spelling note: The original poster got it right. Callus is a noun; callous is an adjective. Cuddlyable3's reference to callous skin is just barely possible, though it makes one think of skin that doesn't take others' feelings into account. The other uses of callous above are wrong.

Similar pairs are mucus / mucous and phosphorus / phosphorous. Rule of thumb is that mucous is almost always wrong unless followed by membrane or secretion; phosphorous is almost always wrong unless followed by acid. --Trovatore (talk) 01:30, 29 May 2009 (UTC)

Callus can be a noun or a verb. Do you feel more sympathetic to callused skin ? Cuddlyable3 (talk) 18:57, 30 May 2009 (UTC)

Passage of matter through descendents

This is kind of a weird question, but I was looking over my family tree and wondering: are any of the molecules that were present in my great, great great etc. grandmother present in ME? Or are fetuses entirely produced on matter taken in by the mother from outside the body? 58.161.196.113 (talk) 17:41, 27 May 2009 (UTC)

Wierd, yes, but also a very intriguing question. I would seriously doubt that any molecules from your distant ancestors are still present in you, since each embryo starts from a single fertilized egg, meaning that any direct molecular contribution from your parents is limited to the contents of 2 cells, which then becomes diluted over the course of multitudes of cell divisions (the materials for which must come from external sources). There's quite a bit of cellular turnover throughout development and life. So, statistically speaking I'd guess that there's basically no chance that you actually have any of the same molecules that came from your distant ancestors. Unless, of course, you happen to grow and eat food from an area nearby where your ancestors were buried, in which case it's certainly possible that their molecules were recycled into the soil and somehow made their way into your body that way. It sure gets spooky when you start to think about what your molecules were doing before you occupied them! --- Medical geneticist (talk) 18:23, 27 May 2009 (UTC)

Someone should do a C14 labelling experiment on the subject ;) 131.111.8.104 (talk) 18:33, 27 May 2009 (UTC)

C14 dating needs a sample of many C atoms all known to have come from the atmosphere at the same time. Cuddlyable3 (talk) 10:26, 28 May 2009 (UTC)

I agree that the chance of any molecules being directly inherited is pretty much zero, however there are so many molecules in you and were so many in your great-great-great-...-grandmother that there is actually a pretty good chance that just by pure coincidence some of the ones from her are in you. This kind of thing is usually formulated as questions like "Are their any atoms of oxygen in me that there exhaled in Julius Caesar's last breath?". If you go back far enough there is almost complete mixing of the atmosphere over that time so the chances end up being pretty high. It's a similar issue with your question, although slightly complicated by the fact that you haven't specified a time - most molecules don't stay in your body for your entire life (some in your bones might, I think that's about it). --Tango (talk) 18:49, 27 May 2009 (UTC)

I think that particular thought experiment has more to do with the concept of equal ratios, in this case molecules/breath and breaths/atmosphere, and the two equal each other suggesting that supposing all the molecules from his last breath are still around, the average Caesars-last-breath molecule inhalation rate is 1. I would be inclined to agree with the 'plausible' camp in this "hereditary atoms/molecules myth", at least along the maternal line. Since a woman's eggs are all produced very close to the beginning of her life, she is much more likely to make them out of some of the molecules from her predecessor. Conversely, for men, since sperm are produced in an ongoing basis, the later in a man's life he produces offspring the less likely he will be to contribute any of his predecessor's molecules to it.--66.195.232.121 (talk) 20:31, 27 May 2009 (UTC)

Is it close to 1? I know it works out to be at least 1, but I think it is mostly a thought experiment to do with just how many atoms there are in a small amount of air, rather than the ratios. Your argument suggests that it is quite likely for someone to contain molecules from their maternal grandmother, but it doesn't suggest anything about longer lines - the chance of having molecules from your great-grandmother would still be extremely low. --Tango (talk) 22:19, 27 May 2009 (UTC)

If the turnover time for cellular is something like five years, then individual atoms might get passed over a century. There are ~10^14 atoms in a cell (give or take), which would be ~45 half-lifes before the expectation drops to zero for any matter still being there. If cellular matter, on average, persists for years, then things might get passed around 2 centuries or so. Of course one has to worry about dilution and mixing and other effects, but I wouldn't rule out direct passage of a few atoms from your grandparents, etc. Dragons flight (talk) 19:01, 27 May 2009 (UTC)

The chances of an atom being transmitted from egg>egg>egg for however many generations without it leaving the body is remote (this is a crude calculation): There are 7x10²⁷ atoms in an average body, and ~5x10¹³ cells. Each egg cell will contain ~1.4x10¹⁴ atoms. The number of atoms from that egg that get into the next egg to be produced would be around 1 (1.4x10¹⁴/5x10¹³) but that one atom is likely to have been lost at some point over 20 or 30 years anyway.But take a look at this - it calculates that everytime we breath in, we breathe five molecules that Leonardo da Vinci breathed out in his dying breath! I'd guess that if this was expanded to all the atoms that have ever passed through your ancestors there's a good chance there will be some in you now. Perhaps someone can do the maths. It is even more likely that one atom that passed through your ancestors at some point has also passed through you. Smartse (talk) 22:13, 27 May 2009 (UTC)

That's a good start as an approximation, but you're neglecting the vast number of cells that are produced and die over the lifespan of an individual. Think first about the embryo itself. At the time that the fertilized egg has undergone enough cell divisions to approximate a small hollow sphere only a fraction of the cells will actually become part of the embryo proper. The rest of the cells go on to form parts of the placenta which will not significantly contribute molecules to the adult organism. A few cells from the inner cell mass are the primordial germ cells which will migrate to the site of the gonads and divide a large number of times during the process of gametogenesis. As noted above, the likelihood of any molecules remaining in the egg or sperm depends on the number of cell divisions required for production (more divisions for sperm than eggs). The rest of the cells of the body are just a vehicle for the germ cells to be able to ultimately reproduce. Keep in mind that while all of this is going on, every cell is constantly breaking down and building up cellular components, which means that even basic molecules are likely to be reduced to waste (carbon dioxide and urea) and excreted. So, it isn't inconceivable that your egg contained some molecules from your mother's parents, or even your mother's maternal grandparents. Just highly unlikely... --- Medical geneticist (talk) 23:47, 27 May 2009 (UTC)

• It's worth noting that a fetus acquires many cells directly from its mother, particularly those used for immune defense, and continues to receive them after birth via breast milk. The question of whether these cells are really "part" of the mother is sometimes fuzzy, but many of them actively served a biological function in the mother before their conveyance. In fact, you continue to receive cells from the bodies of people in your environment on a routine basis, for example by inhaling or eating particles of dead skin and hair. Dcoetzee 22:24, 27 May 2009 (UTC)

Could you point me toward a good source that shows many cells from the mother's immune system are preserved in the newborn, either before or after birth? Certainly, antibodies are passed from mother to child, but I seriously doubt many cells are transferred and survive, particularly from breast milk. --Scray (talk) 01:06, 28 May 2009 (UTC)

I'm afraid this is a meaningless question in most cases because small molecules lose their identity completely in a homogeneous fluid. It's quite meaningless to ask whether a molecule removed at a later time is the same as one you put in earlier. Larger objects like cells do have individual identities, and atoms fixed in some solid part of the cell might retain an identity for some period of time. I don't know if any could be traced from parent to child, but I guess probably not since they all end up floating through cytoplasm at some point. At any rate it's a totally different calculation from the classical one with billiard balls. In the case of Caesar's last breath it's much simpler: quantum mechanics says unequivocally that there's no answer. -- BenRG (talk) 23:38, 27 May 2009 (UTC)

The finite amount of water on Earth is continually being recycled through people, animals, sea and atmosphere. I think the statistics show it to be very unlikely that any two people have not employed the same water molecule. Cuddlyable3 (talk) 10:31, 28 May 2009 (UTC)

Again, there's no such thing as "the same water molecule" in this situation. The ocean only has a total water molecule (or ion) count; it doesn't have individual molecules of water! Having n molecules of water is the same as having k liters of water, except that quantum field theory constrains n to be a nonnegative integer. But it only constrains it to an integer, it doesn't partition the water into n pieces each of which is one molecule. Sometimes n = 1 and in that case you can say that you have a single, isolated molecule of water. But when n = 2 you don't have this one and that one, you just have two. -- BenRG (talk) 20:03, 29 May 2009 (UTC)

What if one of the two water molecules is heavy water? Cuddlyable3 (talk) 18:48, 30 May 2009 (UTC)

There would be no advantage to having specific matter from ones ancestors, rather than duplicates, unless someone can think of a specific scenario where passing material is simpler and more logical. On a reverse sort of notion, women who have been pregnant may have an immune or other advantage compared with men and women who haven't because of what passes back to the mother through the placenta.Julzes (talk) 19:00, 29 May 2009 (UTC)

Genetic crossing notation

I'm trying to understand a paper about genetic manipulations performed with Drosophila; it describes a cross in the form:

AB⁺; CD¹¹¹⁸;[PQR][STU];[VW][XYZ]/blah X AB⁺; +;[CD⁺cheese]

I changed the genes for simplifcation. Can someone explain what is being described in this notation? Sometimes I also see things like blah::blahblah - what does the :: mean? Thanks in advance :) --94.212.39.7 (talk) 23:04, 27 May 2009 (UTC)

I'm afraid that changing the gene names didn't really simplify the question. It might be better to just write out the cross that you're confused about. In any case, with regard to the "blah::blahblah" notation, I've seen that done for fusion proteins, for example when a particular protein is hooked up to green fluorescent protein it might be written "GFP::Mygene". The other parts of your notation seem to relate to particular genetic variants but I can't really be sure. --- Medical geneticist (talk) 01:17, 28 May 2009 (UTC)

This is a side issue, but since green fluoresence in living things is mentioned, here is a link to a new development in that area: http://news.bbc.co.uk/2/low/science/nature/8070252.stm
- GlowWorm.

I'll give this a go. Your changing the notation makes it hard to read at first. Drosophila (usually Drosophila melanogaster) have four chromosomes. Genes are almost always written using their abbreviation, e.g. white is abbreviated w. The convention is to list mutations on each chromosome separated by semicolons (;). If there are two different versions of a chromosome in the same fly, then those two versions are separated by a forward slash (/), otherwise both copies of the chromosome are assumed to be the same. Superscripts are used to denote different alleles, with the superscript plus (+) denoting a wild-type (i.e. non-mutant) version of the gene. The "X" would be the cross sign, as in you mate the fly to the left of the X to the fly on the right. For the first fly in your example, "AB", on chromosome 1 (the X choromosome) is wild-type. Allele 1118 of "CD" is on chromosome 2. Chromosome 3 has unspecified alleles of "PQR" and "STU". Chromosome 4 has is "VW" and "XYZ" on one copy and "blah" on the other (it is spoken as VW XYZ over blah). You can read the gory details of Drosophila gene nomenclature here. As for the blah::blahblah, I agree with Medical geneticist above. -- Flyguy649 ^talk 04:16, 2 June 2009 (UTC)