Wikipedia:Reference desk/Archives/Science/2007 February 15

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[edit] February 15

[edit] Etymology of the word 'Gooch'?

Insertformulahere Where does the slang term for the perineum, 'Gooch' originate? Thanks in advance. --90.242.5.51 00:42, 15 February 2007 (UTC)

This one sounds like a Language question. GB 05:45, 15 February 2007 (UTC)
According to Urban Dictionary, gooch is a contraction of the phrase "guy cooch". As for the etymology of the word "cooch", here is an interesting article (warning, strong language may be offensive to some). -- C. S. Joiner (talk) 23:49, 15 February 2007 (UTC)

[edit] Genetic mutations

Can a mutation in a gene prevent its transcription? --M1ss1ontomars2k4 (T | C | @) 00:46, 15 February 2007 (UTC)

I can think of two ways a mutation can stop transcription. If the mutation (probably a point mutation) is in the open reading frame of the gene it may create a stop codon, see Genetic code. If it is in promoter in the 5' UTR it may prevent a transcription factor or a component of RNA polymerase II binding, see Transcription (genetics). --Peta 01:11, 15 February 2007 (UTC)
There are stop codons for transcription? I thought that was only translation. I'm assuming then that promoters are considered part of a gene. --M1ss1ontomars2k4 (T | C | @) 04:06, 15 February 2007 (UTC)
Yes. See Termination factor. There are sequences that, by various methods, signal to a polymerase to pop off the DNA, effectively acting as "stop codons." -- Scientizzle 22:22, 15 February 2007 (UTC)
Or an insertion or deletion can shift the reading frame so that a normal coding region gets misread as a STOP. DMacks 01:14, 15 February 2007 (UTC)
A mutation within the protein coding sequence isn't generally expected to affect the synthesis of said gene's mRNA, but can certainly affect gene translation. If on considers the term "gene" to encompass all of the important non-coding sequences associated with each proteins's DNA coding sequence (promoter regions, splice sites, polyadenylation sites), then the answer is most certainly yes. -- Scientizzle 01:18, 15 February 2007 (UTC)

[edit] rhinoplasty

who is the best rhinoplasty revision surgeo n in the world? Is it possible to recover your natural nose or can a revisi n by a good dr. result in a natural outcome that can not be noticed? or is it impossible.

This sounds like a medical question that the science reference desk wont touch! See your doctor for an opionion. GB 05:44, 15 February 2007 (UTC)

[edit] Prefering Own Flatulence Smell

Why do people generally not mind, or even enjoy the smell of their own flatulence, but dislike anyone else's? Imaninjapiratetalk to me 03:15, 15 February 2007 (UTC)

Everybody likes their own brand, don't they? -- mattb @ 2007-02-15T03:59Z
If I've just eaten a big bowl of chili, I find my own flatulence to be the most repulsive smell. − Twas Now ( talk • contribs • e-mail ) 05:14, 15 February 2007 (UTC)
Er, I don't like it. [Mαc Δαvιs] X (How's my driving?) ❖ 15:18, 15 February 2007 (UTC)
I read somewhere that a particulary "flatulent" partner can make you ill from all of the toxins he/she emits all night. Not sure how true this is. You would not enjoy something that makes you ill. Sandman30s 11:15, 16 February 2007 (UTC)

[edit] NPR origin of gold story

This NPR story [1] about the origin of gold and other heavy elements (supernova nucleosynthesis and R-process), states that "common atoms have even numbers of protons....because nature prefers even numbers for stability". I have never heard of such a thing. I have heard of magic numbers but never this 'all even atoms are more stable' thing. Is this true?--Deglr6328 06:44, 15 February 2007 (UTC)

It sounds like a bastardization of the atomic orbital theory. − Twas Now ( talk • contribs • e-mail ) 07:20, 15 February 2007 (UTC)
I had a list with the numbers of protons and neutrons in all stable isotops, and it looked like the even numbered had the majority, there is a strange theory of the shape of atmic nuclei which supports this.--Stone 13:01, 15 February 2007 (UTC)
It's not atomic orbital theory; that's about electrons. But I think there is supposed to be some vaguely similar rule relating to particles within the nucleus as well. The statement that "nature prefers even numbers" is pretty meaningless, but it is true as far as the makeup of atomic nuclei is concerned: isotopes with even numbers of protons are more stable than those with odd numbers, and the same with neutrons. Hence the statistics that Stone mentions. Yes, this is all awfully vague; sorry. --Anon, Feb. 16, 00:16 (UTC).
No, not orbitals, but Nuclear models of which there are several. Moon's version appears to be heavy on the even numbers.--Wjbeaty 13:31, 18 February 2007 (UTC)


Here is a table with the top 10 elements by abundance (of baryonic matter) in the universe.
Element     Z   parts-per-million

Hydrogen    1   739,000
Helium      2   240,000
Oxygen      8    10,700
Carbon      6     4,600
Neon       10     1,340
Iron       26     1,090
Nitrogen    7       950
Silicon    14       650
Magnesium  12       580
Sulfur     16       440


So if you exclude hydrogen since we're talking about stellar nucleosynthesis, there does seem to be something to the rule of thumb. Only nitrogen sticks out. --TotoBaggins 00:46, 16 February 2007 (UTC)

There is a little bit of info at Magic number (physics). There are certain configurations of the nucleus that are more stable than others, although them being just "even" numbers would be an oversimplification. --Bennybp 06:21, 16 February 2007 (UTC)

[edit] Ability to map an object onto the sensory and motor cortexes and so use it as a tool: term?

What is the term for ability to map an object onto the sensory and motor cortexes and so use the object as a tool? SmithBlue 13:44, 15 February 2007 (UTC)

Proprioception describes some of the terminology. -- Beland 03:30, 18 February 2007 (UTC)

[edit] quantum description of flow of electricity through a conductor

I am a school student std.10. I am interested in getting a physical understanding of the nature of electricity described in graphic manner perhaps best at a quantum level.What actually happens?

Also keen to see a 3-dimensional photo of an atom and the electrons in their orbits. thank you. sudharsan chennai india.

It really depends on the material, but the main conduction methods are drift and diffusion. Drift is, on the surface, very easy to understand since it is merely the net response of free charge carriers (like an electron gas) to an electric field (see Coulomb's law and Lorentz force). Diffusion is the response of a perturbed system to a carrier concentration gradient, and is an important conduction mechanism in semiconductor devices. There are also some slightly more exotic mechanisms like tunneling and those involving Bose-Einstein condensates (superconductivity) that come up in particular cases. I'd say drift and diffusion cover the major conduction methods, though. You don't really need to invoke quantum mechanics to understand the principles of these two conduction methods, though the quantitative details of current flow at a micro scale require some understanding of solid state physics. (things like Brillouin zones, periodic potential, Bloch's theorem, the Kronig-Penny model, k-space equipotential surfaces, effective mass, etc) I wouldn't worry about those too much until you know some basic QM. mattb @ 2007-02-15T15:21Z
An important concept in how electricity works, at the smallest level, is that electrons drift through a conductor at an extremely slow speed. You could easily outrace the electron drift through a condctor. But the electricity, when you turn on a light, goes through a wire at the speed of light in the substance. The simplistic explanation in introductory science books, that electrons from a battery enter a wire, race through it and through the device powered, and come into the battery at the other terminal, all at the speed of light, is wrong. Edison 16:15, 15 February 2007 (UTC)
Also remember that an electric current is not always a slow flow of electrons. In plasmas and electrolytes the electric current also involves slowly moving charged atoms (ions.) For example, if you were to receive an electric shock, no electrons would flow within your flesh. Electric currents inside people are entirely composed of moving sodium, potassium, chloride, and other ions. Another topic: AC. If you could see the charged particles in an alternating current, you'd find that they wouldn't move perceptibly. Instead they'd vibrate; they'd behave a bit like air molecules do when sound waves pass by. Electric circuits involve a slow-moving medium: the electrons and ions, plus a fast-moving wave: the electromagnetic energy which propagates at nearly the speed of light. --Wjbeaty 13:24, 18 February 2007 (UTC)

Electricity

Electrical_conduction might be a good place to start, a bit more detail into a scientific theory of conduction can be found at Electronic band structure - effectively atomic orbitals are assumed to combine to make one large 'molecular orbital' - in the case of metals this 'molecular orbital' is often called a 'band' see Electronic band structure - there are other (many) theories/models of conduction behaviour including Free electron model - read what you can understand and good luck.213.249.237.49 17:05, 15 February 2007 (UTC)

Second question

atomic orbitals would be a place to start - note these are not photographs as such - more like an artists impression - to confuse things further the atomic orbitals shown are a 'dissection of the atom' the real thing would be a result of adding all the atomic orbitals. (Also some of the orbitals shown are of debateable accuracy)213.249.237.49 17:07, 15 February 2007 (UTC)
Currently though there aren't any definative photographs (or other images) of atoms.213.249.237.49 17:10, 15 February 2007 (UTC)

[edit] Milky Way Galaxy

If the center of our galaxy is so huge and bright, why can we not see it with the human eye? Also if Andromenda is so huge and bright, why can we not see it with the human eye?

For our galaxy the direct line is a bit foggy and most of the light is absorbed by the dust. And Andromeda is bright! But like a flash light in several km distance it looks relaivly weak.--Stone 17:32, 15 February 2007 (UTC)

According to Galactic center: Because of cool interstellar dust along the line of sight, the Galactic Center cannot be studied at visible, ultraviolet or soft X-ray wavelengths. The available information about the Galactic Center comes from observations at gamma ray, hard X-ray, infrared, sub-millimetre and radio wavelengths. According to Andromeda galaxy: The Andromeda Galaxy is easily visible to the naked eye in a moderately dark sky, though such a sky is available only in smaller towns and isolated areas reasonably far from population centers and sources of light pollution. --169.230.94.28 17:39, 15 February 2007 (UTC)

I do have an idea of what you guys mean however, why is it that we can view Andromeda but not our galactic center which should be much closer?!

Please correct me if I'm wrong, but isn't the galactic center very near the horizon at all times? So, it rarely peeks up high enough in the night sky so we could see it if we wanted to. --Kainaw (talk) 19:00, 15 February 2007 (UTC)
Not really - the galactic north pole is is atRA 12h51m26.282s, Dec 27°07′42.01″, so the plane runs at about 60 degrees to the horizon, however, IIRC the galactic centre is located in the southern celestial hemisphere, and in most northern latitudes would be invisible. --Neo 19:42, 15 February 2007 (UTC)
You can see the Moon a quarter of a million miles away, but you can't see a building one block over because the view is obstructed. Clarityfiend 19:26, 15 February 2007 (UTC)
That's a good analogy. A further point is that Andromeda is tilted towards us, so we view it partially face-on. By contrast, trying to see the Milky Way's centre is like trying to see the centre of a frisbee by looking at it edge-on. The rest of it's in the way. Spiral Wave 20:09, 15 February 2007 (UTC)

Pardon me if I sound ignorant but i understand the building example however, is cosmic dust so "dense" that it completeley obstructs our view of our enornmous galactic center?

Clouds aren't very dense, and the full Moon is pretty big, but one can easily get in the way of the other if it's thick enough. It just depends how bright the source is and how much of the other stuff it has to pass through. It's a long way to the galactic centre, and there's a lot of dust in that gap. Spiral Wave 20:22, 15 February 2007 (UTC)
The galactic center is some 240,000,000,000,000,000 km away. It doesn't take a very high density of dust to be opaque at that thickness. And it is just barely opaque: we can see through it at longer wavelengths, see above. Take a look at the first image at Milky way; it shows the how the bright bulge near the galactic center is clearly visible, and how dust clouds obscure the galactic center itself from our vantage point. --mglg(talk) 20:33, 15 February 2007 (UTC)

So, in conclusion to all of the above statements, would our galactic center be as small (or smaller) as our moon to our vantage point here on earth?

Well, exactly what you call the centre is open to a little debate, of course. But it's much larger than the full moon. This site shows a nice Spitzer image of the centre, and puts it down as an area filling 12 full moons (in a 4x3 grid). A mansion is just as invisible as a cottage if it's foggy! Spiral Wave 21:15, 15 February 2007 (UTC)
It's not dust, it is the extremely low amount of light because they are VERY far away, and things much closer to home wash out the image for anyone anywhere near a big city. Go out into a rural area as far as you can and you might be able to see the Milky Way with the unaided eye. Distinguishing the galactic center would be difficult because the Way is much more diffuse than anything else. The Moon only looks "big" (it's only half a degree wide) because it's the only thing that can be resolved as more than a point in the night sky. There was an interesting NASA APOD superimposing the Moon on Andromeda a few months ago for a sense of scale. The light gathering area of a telescope is just as important as anything else, Orion's Belt is pretty familiar to many in the N. hemisphere, but images like this look almost totally foreign. 75.45.91.230 02:10, 16 February 2007 (UTC)
If you are talking about The Center of the Milky Way (i.e. Sagittarius A*), then no. It is not simply far away, it is legitimately obscured by dust, and having a larger telescope won't make a bit of difference. Dragons flight 02:34, 16 February 2007 (UTC)
Extinction (astronomy) discusses the issue of light being absorbed by the gas and dust between here and there. --TotoBaggins 16:33, 16 February 2007 (UTC)

[edit] Reactions of ammonia

If ammonia is reacted with a metal nitrate salt, what would the products be ? I'm thinking an ammonium salt of the metal, but I can't seem to balance the equation with adding another product. Robmods 17:27, 15 February 2007 (UTC)

At which temperature? Stoichiometricaly? But first water and nitrogen will be the main product.--Stone 17:33, 15 February 2007 (UTC)

It could be an ammine complex, alternatively the ammonia may be oxidised by the nitrate as mentioned above.213.249.237.49 18:46, 15 February 2007 (UTC)
It's only at a basic level of chemistry - nitrogen and water suits my equation. Thanks! Robmods 20:02, 15 February 2007 (UTC)

Since ammonia in water is an alkali, it will tend to precipitate a metal hydroxide, and leave an ammoniim nitract solution. This could happen with aluminium nitrate for example. If water is around ammonia will not form a "salt" with a metal. But without water (or nitrate present) prehaps you could get an amine °NH2, eg KNH2. Ammonia nicely reacts with nitrite to produce nitrogen, but you are asking about nitrate! GB 04:57, 16 February 2007 (UTC)

Don't forget that ammonia solubilises many hydoxides eg Copper (II) nitrate + ammonia solution (excess) gives Copper(II)ammine hydroxide (deep blue solution), after initial precipitation of copper(II) hydroxide.
Also nitrate+ammonia doesn't usually give N2 (when the reaction is in solution at room temp) but can in other situations eg explosion of ammonium nitrate.87.102.20.186 10:57, 16 February 2007 (UTC)

[edit] Tiny Stars and Galaxies

What is the reason there are no stars with the same diameter of earth or even a tennis ball? Why are there no galaxies with the same diameter of earth or even a tennis ball?

In short, gravity and other fundamental forces dictate the parameters of things like stars. Our article on stellar evolution notes that around 0.08 solar masses are required for nuclear fusion to begin, that being the commonly-accepted threshold for stars. However, while they do not begin as such, white dwarf stars are approximately Earth-sized (other dwarf stars may be as well; I've not checked). — Lomn 21:50, 15 February 2007 (UTC)


Why is that that around 0.08 solar masses are required for nuclear fusion to form a star? (It would be so cool to have a tennis ball size star or galaxy in one's possession!)

Well you need massive, massive amounts of pressure to start nuclear fusion. Normally you're not going to fit that into a very small space. But you can, in fact, get something very similar to a star in a very small space like that: see inertial confinement fusion. Something that small will burn out quite quickly, of course. --140.247.249.15 22:26, 15 February 2007 (UTC)
Plus it needs a lot of heat. Human-built nuclear fusion reactors require much higher temperatures than you get at the centre of the Sun. In a star, the immense pressure is what drives the reactions. We can't generate those kinds of pressures without the immense gravity of a star, so very high temperatures are needed instead, tens of millions of degrees.
As for your question about galaxies, well, galaxies are made of billions (or even trillions) of stars. Even if they were really small, you'd need a lot of space to keep them all in.
As a side note, you might like to know that if you could compress the Sun down to the size of an orange, it would become a black hole. Another good reason not to have it too small! Spiral Wave 23:49, 15 February 2007 (UTC)

Another reason is that a cloud of gas in space cannot collapse into a star unless it is at least one Jeans mass in size. If you did somehow create a "star" the size of a tennis ball, the gas in it would just disperse instantly, since its gravity wouldn't be anywhere near high enough to hold it together. (The reason asteroids, rocks and, indeed, tennis balls can stay together is that they're solid, not gaseous like stars, and thus bound by forces other than gravity.) —Ilmari Karonen (talk) 23:45, 15 February 2007 (UTC)

Yes, you're quite correct to say something that small couldn't collapse of its own accord. However, asteroids (and planets) do stay together because of gravity - see rubble pile for an extreme example. Just because they're solid doesn't make the various bits any more inclined to stick together for any other reason, at least not once you get big enough that the electrostatic force no longer matters. That's because solid bodies don't collapse; they accrete, piece by piece, and so the Jeans mass no longer applies. Spiral Wave 00:31, 16 February 2007 (UTC)
Even in a rubble pile, the atoms in the individual pebbles and dust grains are still held together by chemical bonds. If you somehow magically replaced all the atoms in an asteroid with noble gas atoms (which don't bond), the whole thing would evaporate instantly, since, freed from their bonds, the thermal velocity of the atoms would greatly exceed escape velocity. Indeed, this is evident from the fact that asteroids don't retain gaseous atmospheres. (Somewhat incidentally, the thermal escape of gas from a planet's gravity well is known as Jeans escape. Both are named after Sir James Jeans.) —Ilmari Karonen (talk) 01:01, 16 February 2007 (UTC)
Atmospheres, yes. Because they're gas, and possess random motions that allow them to escape easily. The random velocities of boulders are remarkably small. Chemical bonds - or electrostatic ones - between distinct piles of rock are virtually non-existant, and once you get above a certain size, they have virtually no effect. Indeed, this is a major sticking point (astronomical pun) in the theory of how planets form. Those small-scale bonds just don't apply for larger objects. Spiral Wave 01:26, 16 February 2007 (UTC)
Addendum: perhaps I have misread you. I'm not claiming for a minute that individual atoms and molecules aren't held together in this way; rocks don't simply evaporate, true! But the same forces can't hold two distinct boulders together, that's what I mean. And a (terrestrial) planet is nought but a collection of rocks (and ices). Spiral Wave 01:29, 16 February 2007 (UTC)
Addendum 2(!): Reading through it all again, I see I have definitely misread you; you were originally talking about the internal bonds that hold together a single 'rock'. (Although asteroid is slightly misleading in that context, as I noted.) My apologies. Spiral Wave 02:25, 16 February 2007 (UTC)

Well as far as small stars are concerned i read on my science book a long time ago (8 years or so) that before the big bang the concentration of all elements and stars were more then likely no bigger then the size of this ----> . period. since i havent heard about this theory anymore (or at least havent looked) i take it it was probably disproved. Maverick423 18:54, 16 February 2007 (UTC)

The Big Bang theory remains well-supported. However, the existence of the primordial gravitational singularity isn't a parallel to the formation of a star. — Lomn 00:36, 17 February 2007 (UTC)

[edit] Month8fetus.jpg image review

I was wondering if science knowledgeable editors wouldn't mind reviewing this image: Image:Month8fetus.jpg. It was uploaded today and placed on prenatal development. The source of the image is standupgirl.com, a pro-life advocacy site/support group for teen mothers. I am suspicious when a partisan, advocacy site starts contributing content to articles of a medical nature. So my questions: Is the image accurate? Second of all, is the image useful and encyclopedic? and third of all, having the webpage watermark in the bottom seems wrong to me, does anyone else agree? If the answers to one and two are "yes", I could create a modified version without any text and upload it to the commons for everyone to use (the image was released under the GFDL). This way, other language wikipedias could use the image because it wouldn't be English language specific anymore (and it would alleviate my concerns about content clearly sponsored by politically motivated, biased 3rd party webpages). However, I am skeptical that this image has encyclopedic value in the first place, so I am requesting the opinion of more medically knowledgeable editors. Thanks for your consideration.-Andrew c 23:30, 15 February 2007 (UTC)

I don't know, but the statement "as a fair use image for the sake of education" is technically an oxymoron. The copyright status needs to be clarified. Fair use is completely different than GFDL. As for the picture itself..I'd be interested in the answer as well. --Wooty Woot? contribs 00:21, 16 February 2007 (UTC)
The uploader has both typed "{{GFDL-self}}" in the upload summary box and selected the same license from the drop-down license menu. Assuming that their claim of being the author of the image is valid, that seems like pretty good evidence that they intended to release the image under the GFDL. Of course, that doesn't mean they can't release it under other terms as well. Still, I do agree that the "fair use" comment is somewhat confusing, and it would be nice if the uploaded clarified the licensing status of the image. —Ilmari Karonen (talk) 00:40, 16 February 2007 (UTC)
Addressing your issues in reverse order, the third one (the website name on the image) is obvious, and WP:IUP agrees with you: "user-created images may not be watermarked, distorted, [or] have any credits in the image itself". I've uploaded a losslessly cropped version of the image over the original. As for the second, I'd say that insofar as it's accurate (or even approximately so), it's useful. We used to have a nice series of images illustrating the stages of pregnancy, but they turned out to be copyvios (from [2]). Anything that can replace then would be useful. As to the accuracy itself, I can see no obvious errors myself, though I might not spot them even if there were some. Remember that a 32-week fetus is very close to being born, and indeed has a good chance of survival if born prematurely. The only issue I noticed is that the baby appears to be in breech, though that's hardly unusual. —Ilmari Karonen (talk) 00:30, 16 February 2007 (UTC)
The website you linked to is a U.S. government site with no copyright claims that I can see. Why do you think that those pictures were copyright violations? Was this discussed somewhere? Rmhermen 05:16, 17 February 2007 (UTC)

--edit conflict--

Certainly this is an idealized picture. The head is a little small, the general body proportions are generous (these two are for the most part relative to each other, though). At 8 months the head wouldn't have much hair, really the only hair would be a fine "fur" all over the body (later, fat will replace the fur as the body fills out a little before birth). Also, this is a little hard to describe, but fetal skin has a sort of translucent quality that is not depicted here. Also, the fetus is upside-down, his head should be pointing down at this point. There are better pictures out there for the sake of information, this is more of a stylized rendition than anything else. That said, it seems like a reasonable surrogate until a better, free-licensed image can be found. tucker/rekcut 00:36, 16 February 2007 (UTC)
Thank everyone for their comments. I have contacted the uploader, asking for more detail about their copyright intent. Also, Tuckerekcut, you sound pretty knowledgeable, would you mind perhaps writing a good caption for the image page? You say that at 8 months the head wouldn't have as much hair, and the skin would be more translucent, etc. Does that mean this image is actually depicting a full term fetus? Could we change the timing description to make the image more accurate? I agree that it was quite a loss when we found out the pregnancy images taken from a US government source were actually copyrighted, so this is better than nothing. Thank you Ilmari Karonen for uploading the cropped version.-Andrew c 01:30, 16 February 2007 (UTC)