Wikipedia:Reference desk/Archives/Science/2007 January 7

From Wikipedia, the free encyclopedia

< Wikipedia:Reference desk | Archives | Science

Science desk
< January 6	<< Dec \| January \| Feb >>	January 8 >

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

[edit] January 7

[edit] haploid/diploid

If chromosomal duplication happens twice before tetrad formation in spermatogenesis, while the other steps proceed normally, would the resulting 4 sperm cells be considered diploid because they each have 2 copies of a gene or haploid because the 2 copies are of the same homologue? In other words, does the term "diploid" in humans refer only to the total number of chromosomes (twice the number of the haploid state) or the state of having a pair of homologous chromosomes each with differing alleles for the same genes? thanks, N.S.

Diploid sperm are not very unusual. --JWSchmidt 03:28, 7 January 2007 (UTC)

[edit] Binding energy

I'd like to make my own version of this graph. Where can I get a raw set of values for it? I tried googling a bit but all I found were fairly tedious formulae for computing the average binding energy per nucleon and all of that -- surely it is available somewhere more easily? I'm no physicist and would prefer not to have to try and fumble through the calcuations. Anybody have them at hand (or willing to do the calculations for me?)? I'll donate an SVG version of the resulting graph to Wikipedia if that's worth anything to you. --24.147.86.187 04:24, 7 January 2007 (UTC)

I'm afraid I don't have a terribly easy way to get these, but I can tell you the equations in a simple and friendly manner (I hope). Look at List of isotopes (actually a link to a page per element). For any isotope you consider interesting (probably the ones with natural abundance scores in the next-to-last column), take its isotopic mass (fourth column) and subtract 1.00779487489Z (second column) and 1.00866491979N (third column) to account for protons and electrons (first number) and neutrons (second number). You should get a small negative number (the mass defect); drop its sign. Multiply by 931.493581874 (this converts amus to MeV, which are the units in that plot) and divide by the mass number (the first column, or

A = Z + N

; this is also the abscissa in that plot). As an example, for oxygen-16 I get a mass defect of -0.136763737825 u, which corresponds to an ABEPN of 7.96215900105 MeV (remember to divide by 16) — good agreement with the existing plot.

Well. After writing all that, I've just noticed how to get the raw data from that list's reference; what you want is the left-hand column under Binding Energy/A. Note that it's in keV, unlike the plot we have. Hope this helps, even if the majority of it is just background. --Tardis 06:21, 7 January 2007 (UTC)

That's all very helpful, thank you. --24.147.86.187 15:55, 7 January 2007 (UTC)

OK. I tried to use a combination of that data set and your instructions. Here was my Excel equation:

=(([isotopic mass]-((1.00779487489*Z)+(1.00866491979*N)))*931.493581874)/(Z+N)

I have substituted column references with their meaningful variables, there, and I apologize for all of the nesting (I wanted to make sure it would do the order of operations correctly). Now this all looks pretty good except that I end up with what looks like exactly negative values of what I should be getting (oxygen-16 gives me -7.962159004). Now I know I can just multiple by -1 to reverse the sign, but why is it doing this? Have I made an error? --24.147.86.187 16:32, 7 January 2007 (UTC)

I mentioned that you would get negative numbers and should drop the sign on the mass defect. The reason is just semantics: is the energy (or mass) difference between free nucleons (heavy) and ones in a nucleus (slightly less heavy) positive because energy is released when you combine them or negative because the result (not counting emitted energy) has less mass than the raw materials?

As far as the order of operations goes, you can write that most succinctly as

(m - 1.0078 * Z - 1.0087 * N) * 931.5 / (Z + N)

(decimals abbrevd.) in any program.

However, it occurs to me that I omitted one effect -- the ionization energy of the atom shows up as a further mass defect. Ionization energies are much smaller than the nuclear binding energy, but it will cause an error which in extreme cases (heavy elements have much greater total ionization energy) may be as big as 2% or so. Ideally you need to add up all the ionization energies for an element (regardless of your isotope; this is still an approximation, but a very good one) in eV and so divide by a million to combine with your MeV number: $\frac{931.5(1.0078Z+1.0087N-m)+\frac{\sum_{n=1}^{Z}I_n}{10^6}}{Z+N}$ where I have done the sign flip on the mass defect explicitly. I realize, though, that this is rapidly getting complicated; it's probably best just to use the published data. --Tardis 21:02, 7 January 2007 (UTC)

[edit] Waterjets for teeth dangerous?

My dad said that Waterpik waterjets (used instead of flossing) are actually dangerous, because the force of the water pushes bateria and such deeper into the gums and even the bloodstream. Is this true, or even possible if used properly? --RockMaster 05:33, 7 January 2007 (UTC)

Follow the directions that come with the device. I looked around and found mostly good results. Excessive use can cause some gum damage, but nothing with the enamel. --Zeizmic 13:22, 7 January 2007 (UTC)

I do not think I have ever heard of a waterpick being dangerous. This is slightly off topic, but I thought I should mention that water picks are not be considered to have replace dental floss. Maybe someone that knows physics better than I would could explain the problem based on forces placed on fluids, but flossing and brushing are considered the most effective preventative measures. Around your teeth, the gums dip down slightly, forming a little trench that circle the teeth. This trench (called a sulcus) is filled with gingival fluid. Throwing water onto the sulcus is not going to be sufficient to wipe away food or bacteria/plaque present. Only physically disturbing the area, such as when using dental floss, can reduce or remove the stuck material. Waterpicks have their uses, which may be why your dentist suggested you to use it because of your particular situation. Your dentist would be able to recommend which locations a waterpick would benefit you, but dental floss will not be replaced by waterpicks anytime soon. - Dozenist talk 15:07, 7 January 2007 (UTC)

Err...it's Waterpik, as in the company. He mentioned a specific case about their pumps being too powerful. And, according to their site at least, their jets are intended to replace flossing. And shouldn't a concentrated jet of water be just as effective, if no more because it's a liquid? Industrial waterjets are very efficient and often just as effective as their solid conterparts. But, this is really neither here nor there. I was just wondering if there has been any actions against the company's jets. --RockMaster 22:44, 7 January 2007 (UTC)

I don't see how water could forcibly push bacteria that are supposadly inside the muscosa of the gums further in—there's a medium between the outside surface and the inside. Waterpiks are supposed to be the best possible form of dental care when used properly aren't they? Of course "talk to a dentist for dental advice." ;) X [Mac Davis] (DESK|How's my driving?) 05:02, 8 January 2007 (UTC)

Well, thank you all for your help; I think I've got just about everything I need. This should be enough to convince him. A good night to all, and to al a good night. --RockMaster 00:38, 9 January 2007 (UTC)

[edit] Tilt-shift Photography

So I've been wondering this since every time I've seen a photo taken with tilt-shift lenses, but I haven't ever found an explanation. What exactly makes a photo taken with a tilt-shift lens look like it was taken in miniature? What is responsible for the "miniaturization?" Maybe another way of putting it is what is the visual difference between a normal scene and a miniature version of that scene?

I think any discussion would be a great way to expand the stub on tilt-shift photography. For an example picture, see this picture. -Michael 05:42, 7 January 2007 (UTC)

A miniature version will all be effectively at one focus (that is, even a small depth of field can focus all of it) and will show very little perspective. Both of these effects arise because it is typically viewed from a distance much larger than the distance from "front" to "back" within the scene. The article on tilt-shift mentions a removal of perspective, so that makes sense; the linked article on faking mentions focus, so that makes sense too. Does that help? --Tardis 06:31, 7 January 2007 (UTC)

From what I can tell, the opposite appears to be the case; the focus is exaggerated, so that only a very small area of the image is in focus. This is a particularly good example that I found on Flickr. Because the trees in the foreground and background are both unfocused, the town in the middle looks very small. I think this effect occurs because focus is proportional to ¹/_{distance to lens}. Because the graph for ¹/_x is steepest for very small values of x, the difference between focus on very small objects is far more exaggerated than very large objects, where since x is often taken to be infinity in photography for objects the size of buildings, the focus is the same for the whole object. The brain notices this gradient of focus, and works out a scale for the object based on this. Laïka 13:39, 7 January 2007 (UTC)

The math in the second post makes sense for sure, but I think that parts of the first ring true as well. I'll digest this a little and see if i can't add anything to the tilf-shift page. Thanks for the answers. -Michael 06:14, 8 January 2007 (UTC)

Or it can simply because we know (through our eyes and macro photography) that at same focal length and same aperture, close focus will have smaller DOF than focused at infinity. Since landscape pictures like that can't possibly be taken with such a low DOF (which would require extremely big aperture), our brain thinks it's a miniature version shot as a close up instead. It has nothing to do with tilt-shift lens, although before the advent of digital image editing, the only way is to tilt your film in the opposite direction to your scene to reduce the DOF, and reverse to keep everything in focus without using very small apertures for specific scenes. --antilived^{T | C | G} 07:03, 9 January 2007 (UTC)

Also this is a lot more comprehensive than tilt-shift photography --antilived^{T | C | G} 07:27, 9 January 2007 (UTC)

[edit] What is type of this huge spider? Please let me know if you can figure out.

Here is my space, You can see the picture I took http://lionongshop.spaces.live.com —The preceding unsigned comment was added by 211.30.34.134 (talk • contribs) 10:03 7 January 2007 (UTC)

I would guess that it is a member of the Argiope genus. BenC7 01:51, 8 January 2007 (UTC)

[edit] confidentiallity

'All that may come to my knowledge in the exercise of my profession or in daily commerce with men, which ought not to be spread abroad, I will keep secret and will never reveal.' This is a part of the Hippocratic oath, but can I still trust a doctor not to tell anyone anything, since apparently the hippocratic oath isn't used much any more?Hidden secret 7 11:56, 7 January 2007 (UTC)

Depends partly on where you live, but see physician-patient privilege.--Shantavira 14:02, 7 January 2007 (UTC)

This is taken as absolute in the US, especially if you make a point of reminding the doctor confidentiality is important to you. Breach is grounds for a malpractice suit. There are lots of flaws in the US system but we sacrifice much (including convenience and even quality of care sometimes) to maintain confidentiality. See HIPAA. alteripse 14:31, 7 January 2007 (UTC)

Although it is not legally binding, many MD graduates do take the hippocratic oath upon graduation. Indeed, to many (the current interpretations of) this oath are more important than the law. If you have embarrassment about something you are considering talking to a doctor about, consider that physicians see a lot people with a lot of different problems, and are likely to have seen whatever your problem is many times before. If you are considering disclosing illegal or illicit behavior, consider that a physician is bound by the privilege discussed above. Though a hospital may be able to hold an individual for a short amount of time (usually no more than 3 days) if that person is a threat to himself or others, the treatment and reason for treatment cannot, under most circumstances, be disclosed to police or prosecutors. Tuckerekcut 20:28, 7 January 2007 (UTC)

[edit] The end of time ?

I have been re-reading The End of Time by Julian Barbour. As far as I understand it, his thesis in summary is:

the most objective descriptions of the physical world are timeless descriptions in terms of geodesics in phase space;
the curve in phase space that represents our own universe happens to have one end in a rare, extremely low entropy state (the Big Bang);
this asymmetry in our cosmological curve gives rise to the second law of thermodynamics;
this asymmetry also gives rise to the psychological arrow of time, because a given state can only contain a record or memory of states which have a lower entropy (Barbour's "time capsules");
and so time is an illusion (although a pervasive and useful one).

Have I correctly understood Barbour's position ? Is it a respectable (although possibly minority) position in mainstream physics, or is it closer to pseudoscience ? Have any other physicists written about similar ideas in accessible publications ? Gandalf61 11:57, 7 January 2007 (UTC)

Hello, 61. What is not an illusion ? Our concepts are based upon representations derived from sensations, feelings ... and time, space, univs are useful concepts. Does it make more sense to tell that a given representation eliminates time ? Let's respect the idea and, if it becomes mainstream, why not ? But it may take time. --DLL ^{.. T} 18:33, 7 January 2007 (UTC)

Albert Einstein said: "Reality is merely an illusion, albeit a very persistent one". JackofOz 04:52, 9 January 2007 (UTC)

[edit] Lactose and yeast fermentation

Hi i recently did a biological experiment investigation, involving different respiratory substrates for yeast cells Saccharomyces cerevisiae. I found that lactose hardly respired at all. Why would this be? I thought it could be due to the disaccharide formation of lactose, with galactose, having a sterio isomer which is not fermentable by yeast, but then surely i should get at least some respiration. Or perhaps another angle would be the fact thatthe yeast did not have the appropritate enzyme to break the bond between the saccharides? Any comments or opinions on this matter would be greatley appreciated. —The preceding unsigned comment was added by 81.156.37.191 (talk) 08:47, January 7, 2007

[edit] Saccharomyces cerevisiae

Can Saccharomyces cerevisiae break down lactose? or does it not have the enzyme lactase?thanks —The preceding unsigned comment was added by 81.156.37.191 (talk) 09:03, January 7, 2007

Saccharomyces cerevisiae has nearly no natural lactase activitiy. Genes which provide this activity, such as Aspergillus niger secretory beta-galactosidase, have been inserted into Saccharomyces cerevisiae via recombinent techniques, so there are experimental strains of Saccharomyces cerevisiae which can break down lactose, but no natural strains. ("Saccharomyces cerevisiae Fungemia: An Adverse Effect of Saccharomyces boulardii Probiotic Administration", Raoul Herbrecht and Yasmine Nivoix, Clinical Infectious Diseases, volume 40 (2005), pages 1635–1637: "Saccharomyces cerevisiae expresses significant sucrase and some isomaltase activity but no lactase activity") - Nunh-huh 17:19, 7 January 2007 (UTC)

[edit] liquid nitrogen in the tube

The tube deep lines have a problem with overheating. If they converted an old carriage to become a big tank of liquid nitrogen that went round squirting liquid nitrogen everywhere would it have any effect? Typo squotter 16:16, 7 January 2007 (UTC)

Okay, first let me explain the question. This person is talking about the London Underground (familiarly "the Tube") and specifically its deep-level tube lines (the only ones that are "tube lines" in strict usage). London Underground trains are not air-conditioned, and one reason often cited for this is that the deep tube tunnels are so small that there is no room to add air conditioners to the trains. (The fact that the subsurface lines are also not air-conditioned strongly suggests that this is not the only reason, but we're getting outside of science matters if we discuss that.) So this person is proposing a scheme to cool the tunnels instead.

My response to "would it have any effect" is: Yes, it would create a risk of suffocating the passengers by displacing too much air from the tunnels. This might prevent them from complaining about the heat, but is probably not the most desirable way to do so. :–) (Even if the amounts were properly controlled to avoid this, what if the tank developed a leak?) Using liquid air instead of nitrogen would avoid the suffocation hazard, but I believe it would substitute a fire hazard. In addition, squirting cryogenic liquid about the system could be damaging to any equipment (track, signals, wiring, etc.) that it landed on, due to thermal stress.

It's an interesting idea, though. It might be interesting to try to calculate the cooling available that way, ignoring the safety issues, but I'm not prepared to do it now. I do note that cooling the tunnels rather than the trains would only be helpful on the part of the journey when the trains actually are in tunnel; 5 of the 7 deep-level tube lines have long stretches of surface track as well, where the trains will heat up on a hot day.

You may be interested to know that the Channel Tunnel has a pipe carrying cold water through each tunnel, just for cooling. If a decision was made to cool the tunnels, this would probably be a safer approach, although there might not be enough cooling capacity in view of the fact that so much more of the cross-sectional area of the Tube tunnels is filled by the trains than is the case in the Channel Tunnel.

--Anonymous, January 07, '07, 20:52 (UTC).

Such an approach (water in pipes, not liquid nitrogen) is in fact being considered by the Tube ^sauce; since the River Thames soaks into the tunnels, pumps are constantly at work removing thus water from the tunnels. This water could then be used in a heat exchange system to cool the tunnels, but only at the riverside stations. Unfortunately, this means that your idea (basically the same concept) has come too late to win Ken Livingstone's £100,000 prize, though. Laïka 21:34, 7 January 2007 (UTC)

[edit] Price of Copper and Brass

Hi,

Does anyone know whether copper is more expensive than brass (because it's purer?) There's nothing about it on any of the wikipedia articles on either copper or brass or their talk pages. I couldn't find anything about it on the web.

Thanks, Bioarchie1234 17:40, 7 January 2007 (UTC)

ys, copper is more expensive than brass. You can get some values byt googling "copper cost per ton" and "brass cost per ton", but you'll find that the prices fluctuate widely. - Nunh-huh 18:00, 7 January 2007 (UTC)

Thanks very much! I really appreciate the help. Bioarchie1234 18:04, 7 January 2007 (UTC)

[edit] Sculpting a sphere

What are some good techniques for sculpting and measuring a smooth sphere? I'm pretty sure there must be an ingenious way to do it, I just can't think of anything that won't be eye-measured and prone to distortions.

The case in question is that I have a round shape already, and I want to use sandpaper to finish the sphere (by hand, unfortunately that's all I have). I need it as close to a sphere as possible. — Kieff 17:58, 7 January 2007 (UTC)

What is your sphere made of? Bioarchie1234 18:03, 7 January 2007 (UTC)

Wood. — Kieff 18:10, 7 January 2007 (UTC)

This is kind of eye-measured, but it might help:

Get two rectangular pieces of wood that are the same thickness as each other. Clamp them together to make a square(ish) shape. Make sure the sides are longer than the diameter of your sphere. Mark the centre of this square with a pencil, then, with pair of compasses, draw a circle the size of your sphere round this point. Take the two pieces of wood apart and cut out all the wood inside the circle, then file it or use sandpaper on it to get it perfectly circular. Glue the two pieces together and put your sphere in the circular hole. If you hold the square so it is parallel to a flat surface like a table, and so it passes through the diameter of the sphere, and then roll it around the table, you should be able to tell where it is bumpy because it will get slightly stuck. This might only work in principle, but it might work in practice too. I know you were looking for a more scientific method, but this is the best I could do! Hope it helps, if not, leave another message here or on my talk page. Bioarchie1234 19:04, 7 January 2007 (UTC)

I remember a television program (Like Mythbusters -- best guess is the Discovery Channel show "Debunked: Secrets of the Stone Spheres") which discussed the Stone spheres of Costa Rica. They came up with a relatively low tech way of getting the stones to be spherical, although I can't remember what it was. -- 22:32, 7 January 2007 (UTC)

This reminds me of when I learned how to grind a spherical mirror to use in a telescope. The strange thing being that it is a lot easier to grind a perfect sphere then you'd think, all that it involves, surprisingly, is randomness! Take for example a handful of clay, or mince, and roll them randomly between your hands, like you are making a meatball, the same principle applies, if you have a high enough degree of randomness you will end up with a perfect sphere. For a spherical mirror, all you have to do is rotate the mirror and randomly grind the surface, and as if by itself, the mirror will grind to a perfect sphere. Don't really know how to apply that to a wooden sphere but it may get you thinking, I'm thinking of two planks covered in sandpaper and the sphere rolled between them, but not sure how that would work practically, if the sandpaper removes enough material, if you could get it random enough, if it would create flat spots which then might cause bigger deviations… How big is the wooden sphere? Vespine 23:38, 7 January 2007 (UTC)

I saw this done for a wood sphere once - they lined a side-loading drier with sandpaper and put the block in it. After running for a day or so, they had a sphere. The same concept as a rock tumbler I believe. --Kainaw ^(talk) 04:40, 8 January 2007 (UTC)

[1] is the ball race method

[edit] channel form efficiency and hydraulic radius

Sorry if this doesn't come under science but I think it does. Anyway: Channel form efficiency and Hydraulic Radius, are they the same thing? I'm pretty sure they are but just need to double check. Thanks. 62.136.81.50 20:49, 7 January 2007 (UTC)

[edit] Light pollution

How do I measure how light pollution relates to the population of a certain area? And I'm doing this for a science project (hopefully you haven't seen me on another RD yet). —The preceding unsigned comment was added by Member (talk • contribs) 21:46, 7 January 2007 (UTC).

The population of humans, or some sort of fauna? The latter would be far more interesting, but you have to remember that correlation does not equal causation. Anyway, if it is humans, as I am suspecting, then the best way to do it would be get a light metre, and test several, random, spots within a certain area, then calculate the population/km² (or similar measurement) of that area. Do this in many places, and see what you come up with. --liquidGhoul 00:00, 8 January 2007 (UTC)

Also be wary of the moon's phase. --liquidGhoul 00:01, 8 January 2007 (UTC)

Light is not the same as light pollution. I you use a light metre directly on the sky in the middle of night when it is new moon, once with a clear sky and once when it is fully overcast, the difference should be an indication of the local light pollution. Make sure no light from street lights and such can directly reach the light metre; put it in an upward pointing cardboard tube. If done correctly, the reading for the clear sky should be the same as in a totally dark room, since the light from the stars is negligeable. Of course, the exercise is somewhat meaningless if this is done for one place only. That would be as if I invented a new temperature scale and told you that where I am it is currently 714 degrees on the scale of Lambiam: that conveys no information. --Lambiam ^Talk 06:33, 8 January 2007 (UTC)

[edit] Biological night vision

Do animals with very good night vision detect colors in "more" brightness? From searching around, what I understand is that animals like owls have more sensitive rods that allow them to see more colors in the dark. But what does that really mean? Do owls see more colors but that the colors are still in low brightness/intensity, or do they somehow see the colors in more brightness (thus they can sense better contrast, etc.)? Thanks in advance 128.163.241.210 21:49, 7 January 2007 (UTC)

There was recently an article in New Scientist where they touched on this. Apparently, people used to think animals that saw in the dark saw only in black and white. However, they now find that nocturnal geckos definitely have colour vision at night, as do certain moths. Work is still needed as to which other animals have colour night vision. The cones in these animals are much longer than in diurnal animals, closer to rods, which is why people initially mistook them for rods. In case this was unclear, Rods are the sensitive, black-and-white cells, cones are usually less sensitive, but used for colour vision. Skittle 22:46, 7 January 2007 (UTC)

Many animals also have a tapetum lucidum at the very back of their eyes, which reflects light back to the retina to give it a second chance of being detected. If the tapetum lucidum can brighten the image enough for cone cells to function, the animal will have colour vision. --Bowlhover 22:54, 7 January 2007 (UTC)

[edit] Percentages regarding gas and water components in inspired and expired air

I have searched etc, and to no avail. I have to do a pie chart with % regarding the gas and water components in inspired air, and then in expired air. Do you have any ideas as to the answer, or where I could source it?

Munchkin MunchkinNZ 22:13, 7 January 2007 (UTC)

% gas and water in inspired air is just a factor of humidity isn't it? If you need percentages of the components of air then that article discusses them. As for Expired or exhalation, that's got to do with cellular respiration, but I'm not sure that article talks about % humidity of exhaled air.. Vespine 23:14, 7 January 2007 (UTC)

For inspiratory air Earth's atmosphere has data which I think comes from NASA. I can't find a Wikipedia reference right now, but you can use the following to get your own figures.You have to assume that the expiratory gas you are describing is end-expiratory gas, i.e. gas from the alveoli. Otherwise the effect of dead space ventilation becomes a problem (fortunately one which one cannot illustrate in a pie chart anyway). One also assumes that you ignore trace gases (e.g. Xenon). I'll give you the normal human end-expiratory PO₂ and PCO₂. End expiratory gas has the following characteristics: The PO₂ is 100 mmHg, the PCO₂ is 40 mmHg, the water vapour pressure would be the saturated water vapour pressure at 37°C, the rest of the expired gas would for practical purposes be N₂. The total pressure of the gas would be 1 atmosphere. The partial pressure of a specifc gas divided by the total pressure of the gas mixture gives you the percentage of gas in the mixture (why is that?) So the figures you require for your graph would be: Atmospheric pressure (mmHg), Water vapour pressure at 37°C (mmHg), PCO₂ 40 mmHg, PO₂ 100 mmHg, PN₂ is (Atmospheric - PO₂ - CO₂ - Water vapour at 37°C). Your whole pie would be 1 atmosphere, and the slices the proportion of each of the four gases. Make sure you understand why percentage of composition can be equated to partial pressure (it has to do with one Avogadro). --Seejyb 04:17, 8 January 2007 (UTC)

[edit] VSEPR Bonding

Doing some work with the VSEPR theory which is really not my field. Under VSEPR, what's the shape and bond angle of SCl₂, and is it polar? I imagine that's a terribly simple question to you chemists out there, but I'd like to know. Thanks. Cool3 22:20, 7 January 2007 (UTC)

Sulfur dichloride should be very similar to water given the valences of the atoms involved. Two free pairs should give a roughly tetrahedral shape (thus bent for just the atoms) with a bond angle somewhat less than 109°. However, its polarity would be reversed and much reduced because the electronegativity difference between sulfur and chlorine is less than half that between oxygen and hydrogen and has the opposite sign. See also the reference on water's molecular structure linked from the article. (I also linked your theory and gave you the subscript you wanted.) Does that help? --Tardis 01:12, 8 January 2007 (UTC)

Thanks for the answer. That's what I wanted. Would the angle be about 105 degrees like water, or closer to 109 because of the different polarity? Thanks for the subscript too, I've been on wikibreak for a while and forgot the tag. Cool3 01:55, 8 January 2007 (UTC)

The article here on it gives it as 103°, even less than water's. Sorry, but I don't have any explanation for that real value, nor do I know whether VSEPR would predict it. --Tardis 04:25, 8 January 2007 (UTC)

[edit] What is oxidation?

I tried looking it up, but I couldn't understand it. Especially, I can't understand how aldehyde: R-CHO is derived from the oxidation of a primary alcohol. In that context, what does oxidation mean? Thank. —The preceding unsigned comment was added by Legolas52 (talk • contribs) 00:44, 8 January 2007 (UTC).

[An] oxidant removes electrons from another substance, and is thus reduced itself. And because it "accepts" electrons it is also called an electron acceptor. Do you understand this? X [Mac Davis] (DESK|How's my driving?) 05:41, 8 January 2007 (UTC)

Oxidation is the loss of electrons. I'm not an organic chemist, but I would say that the primary alcohol loses electrons, thereby allowing it to bind to the R-group. BenC7 11:06, 8 January 2007 (UTC)

This is a fairly high-school level chemistry problem. At that level, there are three mnemonics to keep in mind

OIL RIG 1 (Oxidation Is Loss of electrons, Reduction Is Gain)
OIL RIG 2 (Oxidation Is Loss of hydrogen, Reduction Is Gain)
Oxidation is gain of Oxygen. To reduce, reduce the number of oxygen atoms

The one that applies here is OIL RIG 2, since the alcohol is losing hydrogen. I'm a third-year chemistry undergraduate, so yeah, I'm aware that the above is in absolutely no way rigorous. But it works for the purposes of revising for a high-school-level exam. GeeJo ^(t)⁄_(c) • 12:45, 8 January 2007 (UTC)

[edit] effects of solvents on styrofoam

On Wikipedia's "Polystyrene" article, I noticed that it mentions that there are U.S. regulations prohibiting the use of solvents on styrofoam because it "de-foams" it. What is doesn't mention is what specific kinds of non-aqueas solvents de-foam styrofoam and why. Can anyone tell me (very specifically) why solvents have such an effect on polystyrene? EDIT: Sorry, I found it.—The preceding unsigned comment was added by 68.190.7.99 (talk) 23:29, 7 January 2007 (UTC).

Probably the same reasons acetone defoams it! X [Mac Davis] (DESK|How's my driving?) 04:13, 8 January 2007 (UTC)

...why does Acetone dissolve it?

[edit] Architectural / structural terminology

I once lived in San Francisco's Tenderloin in a 1920s Edwardian apartment building. Looking down on it from above, it was shaped like a capital I (although on preview I see that the font here is giving me a straight, stick-shaped I, as opposed to one with a discernable top and bottom). Two store-fronts and a basement constitued the ground floor. Facing the building from the street, on the left there was a maintenance door. If you went through it, you first went through a short passageway before emerging into an open area (by open I mean exposed to the sky). All the buildings' windows that looked down onto this middle area saw an entrance into the basement, access to the boiler, and the tail end of the trash chute, among other things. I've been to the City's official home page, I've gone through the Architectural glossary and more here on Wikipedia, poured over myriad other sites, and I can not, to save my life, put a construction, building, or architectural term to this open area. Mere curiosity isn't fueling my interest; rather, it's work-related. I realize my description is poor, but I hope it will be enough. Guesses, suggestions, site referrals and more - all welcome. Thanks. Wolfgangus 00:02, 8 January 2007 (UTC)

Are you referring to a "well"? I have looked for something in the line of a "service well", but the overwhelming number of hits are for the adverb and adjective "well", and a very few as part of "stairwell". --Seejyb 16:55, 8 January 2007 (UTC)

Coming from a position of total ignorance, and in light of your efforts, I'm uncomfortable saying this, but according to what I'm reading as definitions for a "well", it doesn't seem to qualify. Service well actually has an attractive ring to me, but in usage it may prove misleading. A while back I'd consulted a construction-management friend who suggested the term draftway but this didn't fit either.

Of course, it's entirely possible that it has no name at all, it's just a structural feature, incidental or otherwise ... but even something so insignificant as a nook is honored with a title, and the space I'm trying to name was probably 10 x 30 ft.

Perhaps I can convince someone in the City offices to glance at the blueprints. Surely they're on file and in some fashion a matter of public record. At any rate, thank you so much for your efforts; I'm grateful. Wolfgangus 19:25, 8 January 2007 (UTC)

Think you're talking about an airshaft as it applies to a building. The quickest I could find an on-line reference was to this article, which, unfortunately, doesn't have a picture. 192.168.1.1 7:13pm, 8 January 2006 (PST)

Oh, wait, found one: Follow this link, and click on the link for the "Dumbell tenement air shaft" picture. 192.168.1.1 7:16pm, 8 January 2006 (PST)

Holy s**t. That's it. That's it! The diagram of the two tenements shows the general capital I shape, the opening, everything. Thank you so much; I can not adequately express my gratitude, but if I could, I could not possibly overstate it.Wolfgangus 03:39, 9 January 2007 (UTC)

Retrieved from "http://en.wikipedia.org../../../r/e/f/Wikipedia%7EReference_desk_Archives_Science_2007_January_7_f9a4.html"