Wikipedia:Reference desk/Archives/Science/2013 January 14

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.

January 14

The oxide layer of magnesium ribbon

if magnesium oxide is white, why is the oxide layer of magnesium black?--124.172.170.234 (talk) 03:58, 14 January 2013 (UTC)

The oxide layer is silvery white AFAIK [1]. Do you have a reliable source stating that it's black?Dncsky (talk) 04:16, 14 January 2013 (UTC)

Perhaps the MgO crystals are very finely divided -- if this is the case, they can look "black" even though the substance's "natural" color is silvery-white. 24.23.196.85 (talk) 01:25, 15 January 2013 (UTC)

I once thought it might be other magnesium compounds, but both magnesium sulfide and magnesium nitride are not black.--124.172.170.234 (talk) 00:52, 18 January 2013 (UTC)

Dietary supplement question

Since FDA does not evaluate dietary supplements [2], is it safe to believe the claim made in nutrition labels in dietary supplement products? Say, for example, if a multivitamin supplement claim it has 5000 IU vit A., is that claim really true? Is there any way to verify that? How could an ordinary customer know which company is using right label information and which company is using wrong label information? --PlanetEditor (talk) 05:00, 14 January 2013 (UTC)

Well, if they claim it has an ingredient in a certain amount, and doesn't, that's fraud, so they could be prosecuted, if you can show the actual amount is less. It's claims that can't be verified, like "may help reduce the appearance of wrinkles and fine lines", which can't be proven or disproven, that are unenforceable. StuRat (talk) 05:07, 14 January 2013 (UTC)

The FDA monitors dietary supplements for:

• wrong ingredients

• too much or too little of a dietary ingredient

• improper packaging

• improper labeling

• contamination problems due to natural toxins, bacteria, pesticides, glass, lead, or other substances

[3]Dncsky (talk) 06:37, 14 January 2013 (UTC)

But according to Dietary Supplements Labels Database, FDA does not analyze dietary supplements before they are sold to consumers. The manufacturer is responsible for ensuring that the "Supplement Facts" label and ingredient list are accurate". If so, how can FDA monitor dietary supplements for improper labeling? Is not the information in "FDA Consumer Health Information" cited above by Dncsky contradicts what is mentioned in Dietary Supplements Labels Database of the National Library of Medicine? --PlanetEditor (talk) 07:02, 14 January 2013 (UTC)

Sometimes the supplement-maker's direct competitor will analyze the product and report their findings to the FDA if it has too much, too little, etc. --Guy Macon (talk) 07:20, 14 January 2013 (UTC)

The PDF I linked covered this in detail:

"Under DSHEA, dietary supplements are regulated like foods. Unlike new drugs, dietary supplements don’t have to go through review by FDA for safety and effectiveness or be“approved” before they can be marketed. But manufacturers must provide premarket notice and evidence of safety for any supplements they plan to sell that contain dietary ingredients that were not marketed as dietary supplements before DSHEA was passed—except that the premarket notice is not needed if the new dietary ingredient had previously been used as in ingredient in food."

Dncsky (talk) 07:55, 14 January 2013 (UTC)

force versus pressure diagram

We will keep pumping a gas into an idealized container that does not expand. Clearly, the pressure keeps increasing while the force needed to keep pumping also increases.

I would like to see this diagram for a given gas at a given temperature. I am especially interested in what happens when the gas turns liquid or the liquid solid, and we keep pumping.

Are any such diagrams available? For example, consider hydrogen gas being pumped in at room temperature. 12:44, 14 January 2013 (UTC) — Preceding unsigned comment added by 91.120.48.242 (talk)

For a gas, pressure is a force. I'm not completely sure what you are comparing, the force on the pump is trivially equal to the pressure of the gas times the surface area of the pump exposed to the gas (i.e. the area of the opening of the container). This doesn't require a special diagram; it's just the definition of pressure. --Jayron32 13:42, 14 January 2013 (UTC)

The way you have posed the question is a little confusing. You are evidently asking for an isothermal pressure-versus-volume graph, e.g. Boyle's law but for a non-ideal gas. The "force needed to keep pumping" can only be interpreted as the pressure of the gas, but you seem to think that they are distinct. Phase diagram may be of interest, though it does not give quite what you want. — Quondum 13:54, 14 January 2013 (UTC)

I suspect that what the OP really needs (but isn't exactly asking for) is for us to imagine a pump of unlimited strength and power that takes in a fixed volume of ambient pressure gas per second and compresses it to put it into his hypothetical infinitely strong, utterly inflexible, tank. What is needed here is a graph of the amount of ambient-pressure gas in the tank versus pressure - over the gas-to-liquid transition and beyond. This translates into a mass-versus-pressure curve at fixed volume (and, presumably, fixed temperature). Boyle's law does indeed cover the problem for ideal gasses (the pressure would be proportional to the mass of gas in that fixed volume/temperature situation) - but a gas that's in the process of liquifying and beyond isn't covered by that. Real gas seems to cover this in some manner - but, again, once you get into liquids, things get complicated. I'm not convinced that our OP needs much more than to know that most liquids are essentially uncompressible for all practical purposes - but (s)he has a mental idea of storing energy by compressing stuff in impossibly strong containers - and being told that it won't work doesn't seem to help! SteveBaker (talk) 17:04, 14 January 2013 (UTC)

There comes a time when you have to simply give up and conclude that no conceivable answer from the science reference desk will satisfy the questioner. Asking again and again will not change this. --Guy Macon (talk) 17:12, 14 January 2013 (UTC)

Right. The graph would look like a nice straight line - going up at some slope - then, when the pressure inside the container is sufficient to liquify the gas - then the graph goes more or less vertical. This "infinite" slope wouldn't happen in reality because we don't have infinitely strong containers and infinitely strong pumps with the ability to exert infinite forces...asking what happens is approximately the same as asking what happens when you divide infinity by infinity. Mathematicians may wish to agonize about this but scientists and engineers just quietly point out that there aren't any infinitely strong/stiff/powerful anything...so the problem simply doesn't arise.

That said, I guess that liquids are not utterly incompressible - after all, you could compress water by dropping a bucket of it onto a handy neutron star...so perhaps someone knows what the equivalent of Boyles law is for liquified air or liquid hydrogen or something...but for all useful, practical purposes, this is a meaningless question because the terms that it's phrased in pose an impossible situation.

SteveBaker (talk) 17:24, 14 January 2013 (UTC)

For the closest thing to an "equivalent of Boyle's law", see bulk modulus.

Note by the way that there is no guarantee that continuing to increase the pressure will ever result in liquefaction of the gas. You may well heat it above the critical temperature first. Not that it probably matters that much for purposes of compressibility; once you're pushing the atoms close enough that electron orbitals start significantly overlapping, I'm guessing it's not too important whether there's an interface between phases; that is, whether the result is a liquid or a supercritical fluid. --Trovatore (talk) 17:31, 14 January 2013 (UTC) (By the way, air, for example, is already well above the critical temperature at room temperature; most familiar gases will never liquefy under pressure if starting from room temperature. --Trovatore (talk) 17:35, 14 January 2013 (UTC) )

Thank you guys. I would like to see this chart with approximate values (even in scientific notation) and have asked this follow-up question at the bottom of the page. I don't see how you can think I want to build something that depends on an infinitely strong container, but suffice to say that I have no such plans and this is an exercise in simply trying to understand something. If you could produce approximate values I would be interested. 86.101.32.82 (talk) 18:34, 15 January 2013 (UTC)

Bulk Viscosity

Hi all, I'm trying to track down the bulk viscosity (aka. volume viscosity) of carbon monoxide, but I'm having a hell of a time. Anyone lend a hand? Thanks. 80.156.44.33 (talk) 13:01, 14 January 2013 (UTC)

Do you mean viscosity of gaseous CO or viscosity of liquid CO? Ruslik_Zero 18:16, 14 January 2013 (UTC)

Gaseous. 80.156.44.33 (talk) 08:10, 15 January 2013 (UTC)

Brightness-dependent monitor buzzing

I recently bought an LCD monitor (a Videoseven W17PS) secondhand, and it came with an interesting issue. It would emit a high-pitched whine. Eventually I realized that the whine was sometimes much louder than at other times, and finally realized that it was determined by the brightness/darkness of the screen - if the content of the screen was more white, there would be very little whining, but if it was more black, it'd be loud (and something in between for other colors). Tabbing between Google and Blackle, for example, would make the whine much more and then less strong. So I tried increasing the brightness, and once it hit 100%, the whining became imperceptible no matter what was on the screen. I've since lowered it back to where it was, and oddly, the whine is still gone, unless I put my ear right up to the back of the monitor. I've found quite a few similar accounts online (like here) with a wide variety of LCD monitors, but I've yet to find any explanation for why this might happen other than just general technical defects, which (at least as far as my understanding goes) doesn't explain why it would be brightness-dependent. Does anyone have any ideas? (As I said I seem to have solved the problem, so I'm looking more for technical explanations than practical solutions.) Thanks. -Elmer Clark (talk) 15:14, 14 January 2013 (UTC)

To put it in non-technical terms, in general, buzzing is caused by a transformer that didn't get fully soaked in goop. (We soak transformers in goop and then let it harden.) Maybe they didn't use enough goop, or maybe there was a bubble inside. This allows the wires inside the transformer to move and rattle against each other as electricity goes through them and makes them act like like magnets. I am guessing in this case that the transformers power the backlighting, and that the monitor turns the backlighting up and down as the displayed image changes in an attempt to give you brighter whites and darker blacks. Sometimes the wires will get stuck and not buzz for a while. Sometimes turning the power up or down or cycling the power or even hitting or shaking the monitor causes them to get stuck or unstuck. --Guy Macon (talk) 17:34, 14 January 2013 (UTC)

For more info on why this happens, see http://en.wiki.x.io/wiki/Magnetostriction. It's interesting that your monitor changes it's buzz based on the content displayed on screen, as one would assume the backlight intensity remains constant for any given scenario. Perhaps your monitor is like some more modern "dynamic" TV's in the sense that it alters the backlight intensity to produce a dynamic contrast enhancement? Otherwise, your monitor just has a layer in the screen that switches polarity of pixels so as not to let the light through, thus appearing black, which doesn't explain the difference in sound heard. --Happymulletuk —Preceding undated comment added 23:25, 14 January 2013 (UTC)

Rainbow and stars

Why does rainbow appear arc shaped? Why do stars twinkle but planets don't? Yellow Hole (talk) 15:21, 14 January 2013 (UTC)

For the first question, refer to this. For the second, see Scintillation (astronomy). --PlanetEditor (talk) 15:31, 14 January 2013 (UTC)

If your air is crappy enough (looking over the chimneys of millions of people on a cold winter day, planets can twinkle. Less than the stars, though. Sagittarian Milky Way (talk) 20:16, 14 January 2013 (UTC)

Computer analysis of writing style

Can computers be used to analyze writing style of an anonymous work? I think the Bible has a collection of anonymous authors; can computers be used on the Bible to narrow down the number of possible authors for a particular passage? 140.254.227.61 (talk) 17:19, 14 January 2013 (UTC)

Stylometry -- Finlay McWalterჷTalk 17:23, 14 January 2013 (UTC)

In general, Authorship of the Bible discusses academic thought about the subject, which attempts to use various methods, including style analysis. -- Finlay McWalterჷTalk 17:29, 14 January 2013 (UTC)

"...Can computers be used..." is trivially answered: "yes." But, a distinct issue arises: how sound is the methodology when computers are used? Take, for example, the very straightforward case, the direct computation of a readability "score". In this case, a simple equation defines a single parameter for a text corpus. If we ignore the numerous quibbles about trivial details (like, what constitutes a syllable?)... there is still debate about the utility and universality of this numeric score. By extension, any more-sophisticated processing algorithm that uses a greater number of tunable parameters will have even more quibbles. Even if experts agree on an algorithm, they must select an optimal parameter set. And there are infinitely many algorithms that can be used to analyze text. Even if we restrict discussion only to Markov chain analysis, there are still an infinite number of possible ways to construct a Markov system. We have articles on natural language processing and semantic natural language processing that can present an introduction to the subject. But the ultimate moral of the story: despite portrayal in fiction, we can't just feed text into a computer and ask the computer to "analyze" it for us. We must first express the method of text-analysis that we want to perform, in the form of a computer program, which is really the hard part. Nimur (talk) 03:43, 15 January 2013 (UTC)

Are author and scribe the same, for your purpose? I would think that the two could be quite separable, in which case handwriting analysis might be useless for author identification. -- Scray (talk) 05:21, 15 January 2013 (UTC)

Fossil Diatoms in a New Carbonaceous Meteorite

• direct link
• Google cached link

As Carl Sagan said, extraordinary claims require extraordinary evidence. Does anyone know if Journal of Cosmology is considered a reliable source? What are the next steps the scientific community will take to verify these claims? Braincricket (talk) 17:47, 14 January 2013 (UTC)

Note that Wikipedia has an article about the lead author, Chandra Wickramasinghe. -- Finlay McWalterჷTalk 17:57, 14 January 2013 (UTC)

Thanks. I just read our article about the Journal of Cosmology, and it seems the quality of its review process has been questioned before. Apparently this is not the first time they've published an article about the discovery of fossilized extraterrestrial bacteria. I guess I'll just keep my eyes peeled for new journal and news articles about the discovery. Braincricket (talk) 18:09, 14 January 2013 (UTC)

We have a couple of noticeboards that address these sort of issues:

Wikipedia:Fringe theories/Noticeboard for discussing the reliability of the Journal of Cosmology.

Wikipedia:Reliable sources/Noticeboard for general discussion of Wikipedia's coverage of the topics of Panspermia or Chandra Wickramasinghe.

Talk:Panspermia (where there is currently a discussion about the same[4] article we are talking about here)

Talk:Chandra Wickramasinghe --Guy Macon (talk) 21:22, 14 January 2013 (UTC)

(ec) Here is an article about a previous fossil claim, also by the Journal of Cosmology. Admittedly I know little about biology, but what Wickramasinghe seems to have done is looked at the meteorite and found something that resembles Sellaphora blackfordensis, which is particularly structurally simple, even for a diatom. Actually, the images in their own article show that their so-called fossil is much simpler than Sellaphora, and the only structure is the uniformly-spaced straight lines. --140.180.240.178 (talk) 21:36, 14 January 2013 (UTC)

Heh. This is summa cum weird, and grist for science fiction. Are aliens trying to terraform our planet with red rain in Kerala, mixed in with occasional chunks of rock with fossilized organisms from the same source? Well, maybe... maybe not. What strikes me about the paper is that there is only a brief mention of microscopic analysis to diagnose the meteorite fragment sent to them as a carbonaceous chondrite. As the red rain phenomenon is tied in with other documented absurdities of nature, such as raining animals, I have to wonder ... is there a chance that this rock suffered whatever peculiar meteorological abduction that befell the animals, and been taken up from some terrestrial source? But I'm just speculating! There is a mystery surrounding the red rain phenomenon that remains untamed. Wnt (talk) 23:34, 14 January 2013 (UTC)

The time between fall of the meteorite and publication is less than one month! This looks strange.--Stone (talk) 10:47, 15 January 2013 (UTC)

Interesting article from Slate Magazine's Bad Astronomy blog: No, Diatoms Have Not Been Found in a Meteorite. --Guy Macon (talk) 09:50, 16 January 2013 (UTC)

This is very, very "busted". There is now doubt being thrown on whether the rock in question is a meteorite at all! SteveBaker (talk) 13:53, 16 January 2013 (UTC)

Why can I sometimes understand meow intonation (I think)?

It's a different order of life. Well we're mammals, but so what, bear speak always sounds angry or annoyed.

I once read though that Scandinavians can sound angry when they're not. (the same language subfamily of the same l. family of the same subspecies of the same species of the same genus of the same family of the same biological order) Sagittarian Milky Way (talk) 20:03, 14 January 2013 (UTC)

Well, consider that cats are domestic animals. As such, one quality that has been selected for is communication with humans. We have a domestication of the dog, but no domestication of the cat. See the list at Domestication#Animals. Both dogs and cats already had some social structure and vocal communication before we mucked around with them, and both only got better at communicating with humans in the last ~10k years. Note that bears do not have much social structure or vocal communication, and are not domesticated. So we would expect them to be harder to understand than an average cat. See also meow (which is a great redirect). SemanticMantis (talk) 20:09, 14 January 2013 (UTC)

I bet familiarity has a lot to do with it. Similarly how someone might ignorantly say "chinese people all look the same to me", all bear growls might sound the same to someone unfamiliar with bears. All country and western music sounds exactly the same to me and I bet all the industrial and electronic music I love sounds exactly the same to someone who likes country and western. Vespine (talk) 21:47, 14 January 2013 (UTC)

I seem to recall reading that cats were not, in the first place, domesticated by humans. Instead, when humans first built grain stores, which attracted rodents, the cats moved in to the stores to hunt rodents, and then into human homes to forage for other food, which the humans seem happy to supply. Although the humans clearly started encouraging this behaviour, it's arguable that cats domesticated h. sapiens rather than the other way round. AlexTiefling (talk) 11:14, 15 January 2013 (UTC)

Cats make louder meows and different sounds when communicating with humans rather than with other cats. Perhaps they think 'stupid deaf human, I'll meow louder and more distinctly then perhaps I'll get through' ;-) I see we have an article on Cat communication. Dmcq (talk) 22:30, 14 January 2013 (UTC)

• I remember reading an article a while back that said that there's a high selection pressure in favor of (i.e., people pay well for the offspring of) animals like Tiggy and Oh Long Johnson. μηδείς (talk) 02:00, 15 January 2013 (UTC)

• I can understand it as well (and I have a Siamese, so I've had lots of practice). According to Desmond Morris (in Catwatching, I think, but maybe it was elsewhere), cats in the wild meow only rarely or not at all, with the suggestion being that it's a kind of meta-language developed by cats to talk to their humans. If that's true, it should be no surprise that you can understand the meowing to some extent; when two animals are both trying to communicate through the same channel, you'd expect there to be a good chance of success. Matt Deres (talk) 14:58, 15 January 2013 (UTC)
  • Isn't meowing a type of neoteny? A girlfriend of mine had her adult cats so well trained one would think they were dogs, and she said the trick was to keep them kittenlike from kittenhood. They would vocalize most when she called them to the couch after dinner and they would come alternately press their forepaws on her belly. She said this was what kittens do to get the mother to express milk, and it did look odly like cow-milking. They would purr up a ruckus. μηδείς (talk) 21:32, 15 January 2013 (UTC)
    • I honestly don't know if meowing is neotenic, but domestic cats are an odd mix of behaviours (wild-ness, domestication, neoteny, sociopathic...) so it wouldn't surprise me if the standard "meow" is just a grownup version of the kitten's "mew". The behaviour your girlfriend described can also be tricky; I've raised a cat that was taken away too soon from its mother and while it did remain kitten-like, it never lost some bizarre behaviours that I have to think were related (it never learned to eat on its own unless utterly desperate, we always had to stir the food for it to smell like us). Matt Deres (talk) 22:35, 15 January 2013 (UTC)

That's "kneading", described at Cat behavior#Kneading. It is not exotic, and does not require special training... AnonMoos (talk) 01:49, 17 January 2013 (UTC)

There was this recent study [5] showing domestic cats are evoking baby cries, which we interpret as being urgent. --Modocc (talk) 00:48, 16 January 2013 (UTC)

Will earth change its axial tilt

Now Earth is tilt at 23.5 degree axis, sometimes earth's axis may be 22.5 or 24 degree, Is this possible in one billion years in the future Earth's axis may be 0 degrees or 10 degrees. is Mercury and Venus's axis always close to upright, or it did have the similar tilt as Earth and Mars did once. In 7.5 billion years if Earth still exist, is it possible that Earth's axial tilt will be close to 0 degree? Is this possible someday Uranus and Pluto will no longer be that sideways at 60 and 80 degrees tilt?--69.228.25.10 (talk) 22:05, 14 January 2013 (UTC)

The article Axial tilt gives answers to most of your questions. The moon stabilises the tilt to between about 22 degrees and 24.5 degrees (varying with a cycle of just over 41 thousand years) and this will continue for at least another million years (if models are accurate), but anything could happen in another billion years because of the disruptive influence of other planets. The same applies to other planets, especially the inner ones, but their tilts are less stable in some cases, with the tilt of Mars possibly being the least stable, having varied between 10 degrees and 60 degrees in the past, and (according to some) likely to change significantly over the next couple of millions of years under the influence of Jupiter and Saturn. You mention 7.5 billion years in the future. This is longer than the current age of the solar system (4.567 B y) and more than half the age of the universe (13.73 B y), and the sun will have rotated 30 times round the galaxy, become a red giant (possibly swallowing the Earth), then become a white dwarf, so lots of changes could happen by then. Dbfirs 23:09, 14 January 2013 (UTC)

Does it go that way- bigger planets is likely to change axial tilt slower, and the smaller ones change axial tilt faster, or it doesn't necessarily go that way. I don't understand that sentence"and (according to some) likely to change significantly over the next couple of millions of years under the influence of Jupiter and Saturn" very well please rephrase that one.--69.228.25.10 (talk) 01:23, 15 January 2013 (UTC)

Some experts think that the axial tilt of Mars has now stabilised under the influence of Phobos (moon) and Deimos (moon), but Phobos will eventually either break up or crash into Mars (unlike our Moon that is very gradually moving away), and Mars is smaller and slightly closer to the giant planets, so will be more influenced by them. Gravitational interaction between the sun and the planets is surprisingly (to me at least) difficult to predict in the long-term (see n-body problem) and sometimes there can be instabilities in unexpected places, so the general principle of bigger planets being more stable is often valid, but it's not always true. Dbfirs 07:52, 15 January 2013 (UTC)

Estimated solar radii

In astronomy when they estimate the size of future sun will be, is 100 times sun's current size 1.0 AU or is it 0.93 AU. I calculated myself 100 times sun's current size suppose to be 0.93 AU. Some estimated predicted sun in 7.5 billion year future will be about 1.2 AU, some articles said 120 is equivalent to 120 times current solar diameter. Which type of rounding do planetary scientist use commonly? Even rounding (ie 130 rounded to 120), (110 rounded to 100). Or they round solar diameter times current according to planet's AU decimal place. 0.40 xs 100 for example of Mercury 40 and 1.5 xs 100 example of Mars 150? I figured out myself Earth's current orbit 1.0 AU suppose to be 110 times solar current diameter.--69.228.25.10 (talk) 22:12, 14 January 2013 (UTC)

You'll need to give us a link to where you are getting the 100X figure, since it has entirely different meanings if it's refering to diameter, circumference, or volume. μηδείς (talk) 03:54, 15 January 2013 (UTC)

It said it few times on few of my planet book and on the youtube (I can't find it anymore) In 5 bilion years sun will grow to 100 times its current diameter engulfing Mercury and Venus and possibly Earth. The solar radii said 1 AU is 110 times, and 100 times is 0.93 AU. Do people use different methods to compute solar radii, like doubling values or avoiding lousy numbers?--69.228.25.10 (talk) 04:57, 15 January 2013 (UTC)

It depends on what you are measuring to get that diameter. Photosphere? Chromosphere? Solar transition region? Corona? If the earth ends up outside the Chromosphere but inside the Corona it will still be swallowed by the sun. --Guy Macon (talk) 05:38, 15 January 2013 (UTC)

I didn't think Earth can get swallowed up if sun only reached 0.90 AU if I didn't completely understand the tidal drag. But Smith and Schroeder quotes The solar wind, which the pair did not include in their calculations, should also hinder the motion of the Earth in its orbit and encourage it to spiral inwards.[6]. I thought solar wind suppose to allow planet to shift outward, even Smith calculated Earth may get swallowed up when sun only gets to 0.90 AU just 10% deficit of earth's current orbit. I am not clear enough how earth's orbit will get contracted, I thought is the solar wind and loss of sun's mass allow its orbit to shift outward.--69.228.25.10 (talk) 06:33, 15 January 2013 (UTC)

According to Sun#Earth's fate the radius of the sun will increase to 250 times its present radius. Future_of_the_Earth#Solar_evolution says the sun will reach a maximum radius of 1.2 AU, which is the same thing. If you want compare the size of the sun to earths orbital radius it makes more sense to use the radius of the sun than the diameter. Ulflund (talk) 18:03, 15 January 2013 (UTC)