Wikipedia:Reference desk/Archives/Science/2012 January 6

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January 6

Natural occurrence of the elements

In the article astatine, reference 26 (the 2011 new edition of Emsley's Nature's Building Blocks) is used as a source that berkelium is natural. Which other transplutonium elements does that source list as natural? Does any other source agree with these statements that some elements past Pu (like Bk) are natural? Double sharp (talk) 05:16, 6 January 2012 (UTC)

The largest Primordial nuclide in plutonium-244, however some other transuranium elements may exist in trace amounts in nature due to appearing as short-lived metastable intermediates in decay chains of more stable elements. For example, the Wikipedia article Californium notes that it could hypothetically exist in extremely small amounts in Uranium ore. --Jayron32 05:38, 6 January 2012 (UTC)

So would it be correct to state in the article periodic table that "Some transplutonium elements, such as berkelium,(reference) can be produced in very small quantities (a few atoms) by neutron capture reactions and beta decay in very highly concentrated uranium-bearing deposits, but no significant quantities of these elements are produced in these nuclear reactions and thus are usually classed as synthetic elements."? Double sharp (talk) 12:54, 6 January 2012 (UTC)

And what does Emsley's Nature's Building Blocks have to say about the natural occurrence of other transplutonium elements? Double sharp (talk) 12:55, 6 January 2012 (UTC)

Sex and reproduction

Does any human society not understand the relationship between sex and reproduction? Of course, for societies that have domesticated animals for thousands of years, the relationship can't be more obvious. But what about hunter-gatherer societies? --24.83.53.134 (talk) 07:31, 6 January 2012 (UTC)

Don't think so. --Sp33dyphil ©^hat_ontributions 08:51, 6 January 2012 (UTC)

Obviously the details wouldn't have been understood, but I'm sure people would have noticed very early on that if they stuck this thing in that hole, a baby often came out the same hole later on. HiLo48 (talk) 09:00, 6 January 2012 (UTC)

I was thinking that sticking this thing in that hole very rarely yields a baby. Sometimes the man or woman is infertile, or too old, or too young. Sometimes the woman is having her period, or is already pregnant, or just gave birth. Sometimes, no sperm manages to reach the egg. Even if the woman does get pregnant, the first obvious signs come months later, so she might just attribute it to the thunderbolt from Zeus the day before. --24.83.53.134 (talk) 18:44, 6 January 2012 (UTC)

But they wouldn't have stuck it in there in order to make a baby. They were just horny, and whatever happened, happened. The concept that sexual activity must, on pain of sin, be done only with the view to reproduction is a much later, and a most unnatural, restriction on the capacity of humans to enjoy their own bodies and those of their willing companions. -- Jack of Oz ^{[your turn]} 09:24, 6 January 2012 (UTC)

HiLo, not really. If you're always having sex, and the females are always having babies, the connection wouldn't be clear at all. They would just be two unrelated things that happen on a regular basis. Like eating.

It's animal husbandry that makes it obvious. Partially because animals are often kept apart where they can't interact, and partially because many animals do these things on a definite schedule that makes the connection more clear. APL (talk) 00:30, 7 January 2012 (UTC)

But that's why I mentioned "that hole". It's not used for all that many things. So the events, sex and babies, would not appear unrelated. HiLo48 (talk) 00:48, 7 January 2012 (UTC)

Stop using euphemisms. What hole do you mean, and how does it contradict APL's point that if you're always having sex and females are always having babies, the relationship wouldn't be obvious? --99.237.252.228 (talk) 07:17, 7 January 2012 (UTC)

I'm sure the reason for the euphemism is obvious to most readers here. I don't know the actual word used by the first people who tried to figure this stuff out. The answer to your second question is in my previous post. HiLo48 (talk) 08:06, 7 January 2012 (UTC)

Haha! Really? That didn't stop you from using the word "baby", "Sex" and a number of other words probably not used by the first humans to discover the connection between sex and reproduction.

On an unrelated note, when discussing nuclear energy to you speak in silly euphemisms because you don't know the french words that the Pierre and Marie Curie would have used? APL (talk) 00:22, 8 January 2012 (UTC)

Fertility rite is one of probably countless article on the subject. The relationship between sex and reproduction (and also the role of menstruation) has been well-known for thousands of years. You don't have to know the biological details to understand the cause-and-effect. With the biological specifics unknown until fairly recently, the best analogy they could come up with was planting viable seed in fertile soil, hence the Greek "sperm" and the Latin "semen", both of which mean "seed". ←Baseball Bugs ^{What's up, Doc?} carrots→ 10:42, 6 January 2012 (UTC)

Well... there's the (honestly delightful) concept of spirit children among Native Australians. Think tiny dreamtime babies with very ancient souls choosing their parents. Though that doesn't quite equate with not acknowledging the connection between sex and conception, i.e. the body may have come from sex with the father, but the soul of the child came from an entirely different place.

And was this question in any way influenced by Jean Auel's depiction of stone age cultures? :P Her books are superbly researched, but the prospect of "primitive" cultures not getting the connection between sex and reproduction when they are exposed intimately to the natural world every day of their lives is honestly a bit absurd. And yes, like Bugs pointed out, in virtually every culture, the word for "semen" always seem to be etymologically related to "seed" which indicates they do know what it was for. The issue seem to merely be on the details (which wasn't even that clear until the advent of modern science anyway).

Paternity, for example, is a sticky issue. Some academics argue that monogamy was not the default in human sexual relationships (I would tend to agree, a child with many parents has more chances of surviving). Whether it was polygynous (patriarchal) or polyandrous (matriarchal) is the big question. Polygynous marriages made paternity clear, while it is fuzzier in polyandry. Sex at Dawn (haven't read it myself, but it looks interesting) discusses that concept of partible paternity and argues for the latter being the default in ancient societies (including Celts). In such cases, it would be very difficult trying to determine who the father was anyway so they just either say the child was conceived from the sperm of all the fathers or just attribute the child to the first/senior husband even if they look nothing alike. Not to mention cultures like some tribes in Melanesia and Papua New Guinea which view sex as a recreational pleasurable activity. Figuring out who begat who would be almost impossible in those cases.

The mechanics of heredity is also another concept that wasn't understood at all until relatively recently. Plenty of quite hilarious attempts to explain it in the past. Jacob's spotted sheep in the Bible is one, as well as relatively modern theories like Lamarckism. -- Obsidi♠n Soul 10:59, 6 January 2012 (UTC)

Lamarck's ideas on heritability of derived traits are not so hilarious anymore, in light of horizontal gene transfer, no? SemanticMantis (talk) 13:53, 6 January 2012 (UTC)

No. Not that mythical Lamarckism of science textbooks. The real Lamarckism, a teleological and extremely vague theory about swellings of organs and bodily fluids being passed on to offspring in a race towards perfection.-- Obsidi♠n Soul 18:36, 6 January 2012 (UTC)

This article is a good read The Straight Dope:When did mankind figure out that SEX = BABIES?.

Apparently some remote Australian aboriginal tribes (who don't herd animals) were unclear on the concept as late as the 1900s! APL (talk) 00:33, 7 January 2012 (UTC)

I'd like to see the source for that "apparently". So much completely contradictory (and often deliberately demeaning) crap has been written about Australian aboriginal people over the years that one must be very careful about such claims. HiLo48 (talk) 00:48, 7 January 2012 (UTC)

I also doubt that claim. Their idea of how women get pregnant involves the father. How can you have a concept of a father if you don't understand the connection between sex and reproduction? You could notice that children tend to look a bit like the man their mother spends a lot of time with and assume there is some connection and therefore call that man the father, but if you've noticed that connection you can probably notice to link to sex too. --Tango (talk) 01:39, 7 January 2012 (UTC)

Not at all! Your father is the man who is married to your mother. If you assume that your marriage ceremony has mystical power then that appears to be an explanation for the likeness, that is at least as straightforward as the purely biological one. Perhaps more-so.

Sounds silly now, but if a girl marries a dude, has a magic ceremony, and then nine months later she has a kid that looks like the husband, it's not at all clear what caused the baby. Since they got married their lives probably changed in a number of ways. Why would they single out one thing they now do differently and say that is the baby-making cause and not this ceremony that your priest tells you is the only way to form a baby? (that also happened nine months ago)

I know it's easy to assume that primitive people were also stupid people, and it's important to fight that. But it's also true that we take a lot of knowledge for granted. We shouldn't fall into that trap either. Plato and Aristotle believed things that a modern fourth-grader would laugh at, but not because they were stupid people. APL (talk) 07:43, 7 January 2012 (UTC)

While I agree that the association isn't necessarily obvious, I doubt aboriginal Australians would have attributed children to the marriage ceremony. Surely most people had more than one child, and some people had sex out of wedlock due to adultery or rape. --99.237.252.228 (talk) 09:45, 7 January 2012 (UTC)

Adultery and rape wouldn't clue you in either if all fertile girls have already been married off. Which is very likely in a primitive society.

You're still imagining our society on a camping trip. Babies "out of wedlock" isn't a big deal in societies where girls are married during puberty.

I don't know about the Australian natives to say if that's the case here, but it's not uncommon in simple tribal societies. APL (talk) 00:22, 8 January 2012 (UTC)

There's an assumption here that other animals don't know the link between sex and reproduction. But it doesn't seem like a difficult thing for even a rodent to observe. Is there any data to show they don't know this? (admittedly I'm having a hard time thinking how to run an experiment) Wnt (talk) 19:28, 7 January 2012 (UTC)

That's an interesting question. At a wild guess, I suspect that any species that fails the mirror test for self awareness wouldn't be able to figure it out. But what about the species that pass, like elephants or bottlenoses? Without the ability to communicate that information to others It probably wouldn't do them much good, even if a few of them figured it out. APL (talk) 00:22, 8 January 2012 (UTC)

What is this behaviour?

What is the bird doing from 0:51 to 0:54 in this video? Why do they do so? --Foyrutu (talk) 09:26, 6 January 2012 (UTC)

It is merely mimicking sounds. It does not understand the noises it is making 217.158.236.14 (talk) 10:25, 6 January 2012 (UTC)

Do you mean the scratching? Because it feels good. It may be an indication of skin problems. Von Restorff (talk) 10:26, 6 January 2012 (UTC)

Yeah I am talking about the scratching. Also sometimes the parrot is sitting on one leg only with the other leg folded, example 0:32. Why? --Foyrutu (talk) 11:07, 6 January 2012 (UTC)

That is the normal behavior, it retains body heat and healthy adult parrots don't need to use two legs. Von Restorff (talk) 11:18, 6 January 2012 (UTC) p.s. Sorry for using an URL redirection service, the domain is blacklisted so it is impossible to directly link to it.

Voltage question

Why do electrical components work only with certain voltages? With a lamp I can see why you wouldn't want too much current running through it: the filament would overheat. But I don't know what it is about voltage that affects components other than that voltage is proportional to current but if its just that why rate components for both current and voltage. --212.120.237.70 (talk) 11:06, 6 January 2012 (UTC)

The voltage is the "electrical pressure" that is safe to apply to a component. If this is too low, it may not operate properly, or at all, and if it is too high, then damage is likely. Voltage and current are proportional only for a component of constant resistance (and this is rare except for simple resistors). If you apply mains voltage to a 6v lamp then it will blow (possibly violently -- don't try it!) because too much current will flow, but it is possible to run a 6v lamp from mains electricity just by limiting the current with a rheostat (though you will also be reducing the voltage across the lamp to 6v). Voltage ratings are given for safety reasons. One should always use the correct voltage for optimum operation. Current ratings are usually given just for information. It is useful to know what current will be drawn so that circuits and wiring will not be overloaded. In the case of LEDs, the situation is sometimes reversed. Dbfirs 11:30, 6 January 2012 (UTC)

There are many possible reasons to specify a voltage rating. One is simply to state "if you apply this voltage directly, the operating current will be OK without external limiting". A lot of electronic components more advanced than passive resistors can fail even with external current limiting, though. A capacitor, for example, can be charged through a resistor (ensuring the current is limited); if left to charge this way, the voltage across it will eventually approach the voltage applied in front of the resistor - and if that voltage exceeds the capacitor's dielectric breakdown voltage, the capacitor will be destroyed. Semiconductors break down if you apply too much voltage as well (e.g. avalanche breakdown). There are also numerous cases in which the voltage rating doesn't actually mean much beyond "we've tested it to be safe at this voltage; if you exceed it, you're probably not using our product the way we intended it to be used, and in that case we can't be held accountable if it goes boom or arc welds itself to your face", but if you exceed the recommended voltage rating, you often need additional cooling to keep things safe. --Link ^(t•c•m) 17:24, 6 January 2012 (UTC)

There are some electrical devices which are rated in current, such as Current transformer. They may also have a limit as to high high of a voltage the conductor they are attached to can carry, because they only have so much insulation between the conductor whose current they are monitoring and the winding which goes to instruments or meters. Edison (talk) 18:50, 6 January 2012 (UTC)

natural selection

In a youtube discussion, I found someone who said that natural selection is not the only driving force of evolution and that there are others that seem to be "intelligent".And then referred to symbiogenesis and natural genetic engineering.Now are there "intelligent" forces? I read the symbiogenesis article and I don't see how it is "intelligent".and there was no article on natural genetic engineering.--Irrational number (talk) 13:13, 6 January 2012 (UTC)

Natural selection isn't the only driving force of evolution: there's genetic drift, sexual selection and others. Ultimately, I suggest you read modern evolutionary synthesis for an overview. 'Natural genetic engineering' is a strange idea, is it theistic or spiritualist perhaps? Certainly the comments you paraphrase have no basis in science Jebus989^✰ 13:19, 6 January 2012 (UTC)

I suppose by "natural genetic engineering" they meant horizontal gene transfer? As for "intelligent" selection, Darwin famously hypothesized that the lack of much hair in modern humans was the result of sexual selection, with males preferring less hairier women. See Sexual selection in human evolution. Then there's also the different cultural rites of passage, isolationism, taboos etc. that do steer or focus genetic diversity in a given population somewhat. For example incest taboos prevent inbreeding and intercultural marriage taboos keep populations more or less isolated genetically for longer times than they would without. At the extreme end is early 20th century eugenics, though I wouldn't exactly call that intelligent.-- Obsidi♠n Soul 13:36, 6 January 2012 (UTC)

Hmmm, seems to be "intelligent"? I would ask the person you are debating with to define "intelligence"; he/she is probably referring to a myth that is well and truly busted. Evolution sometimes produces good solutions to difficult problems, but intelligence is not the correct word to describe that. Von Restorff (talk) 13:40, 6 January 2012 (UTC)

I have to disagree on both points. I have never, nor would I ever expect, any scientist to call horizontal gene transfer 'natural genetic engineering'. A quick google search exposes it as a creationist/otherwise unscientific concept of organisms making "deliberate changes to their DNA".^ref Sexual selection is no more 'intelligent' than natural selection Jebus989^✰ 13:45, 6 January 2012 (UTC)

With the possible exception of humans (and even that's arguable), sexual selection is just another type of natural selection. One might even believe it's the most potent variety—no matter how 'fit' an organism is by any other objective or subjective standard, if it can't find a mate, its genes don't get passed on. TenOfAllTrades(talk) 16:15, 6 January 2012 (UTC)

Whoa. I guess I shouldn't have lumped everything together in a single paragraph.

@Von Restorff/TenOfAllTrades: At no point did I imply that sexual selection is not natural selection. The only thing I emphasized is that in human beings (notice I linked sexual selection in human beings not sexual selection alone), sexual selection is the result of conscious deliberate choices that did have significant results in terms of genetics in human populations. Not divine intelligence - human intelligence. We have been driving our own evolution for a long time now, something that spilled over to our domesticated plants and animals.

@Jebus989: Er no. At no point did I imply any conscious decision when I said "natural genetic engineering" either. As for the "no scientist would ever call HGT 'natural genetic engineering'" assertion, actually they do. While it has been hijacked by creationists (as usual) who don't really understand it anyway, that doesn't mean it's their idea. Did you know that the vast majority of genetic engineering is actually artificial horizontal gene transfer? Specifically those which recombine genetic material from two organisms that are not direct ancestors or even closely related to each other. -- Obsidi♠n Soul 16:58, 6 January 2012 (UTC)

Oops; I did not indent correctly, I was replying to Irrational number. Von Restorff (talk) 17:03, 6 January 2012 (UTC)

Oh. :P -- Obsidi♠n Soul 18:04, 6 January 2012 (UTC)

There is a logical fallacy here, you're saying: the majority of genetic engineering is HGT (it's not, by the way) therefore it follows that HGT and "natural genetic engineering" are synonymous? Where is the link between those two ideas? You also seem to have confused creating recombinants using a vector and the natural phenomenon of mobilome interchange in bacteria Jebus989^✰ 19:27, 6 January 2012 (UTC)

Ugh. All this from a single sentence complete with scare quotes of how I suppose the youtube guy meant HGT, and now you're accusing me of equating the two unequivocally. Wasn't your original objection that I seemed to imply that HGT was deliberately directed? (which I assure you, I did not. Let me put this very clearly: I think creationism and ID is bullshit and I'm highly critical of some of the interpretations of adaptive mutation. So there.) Now we're arguing semantics. Take a long hard look at what I said before please, and don't filter it through the misplaced comments of other posters.

HGT by definition is any transfer of genetic material from one organism to another by means other than one being the offspring of the other. Doesn't that define most kinds of genetic engineering? If not, do tell this guy he got it all wrong. You're probably going to argue now that synthetic genes are used more often or something, yada yada... so change it to "a lot", or whatever works for you.

I am not confusing viral vectors as the sole definition of HGT either. I was giving an example of how HGT has some of the same mechanisms as genetic engineering. And no, HGT is not restricted to bacteria either, I think it's you who needs to reexamine what HGT really means.-- Obsidi♠n Soul 22:28, 6 January 2012 (UTC)

I didn't mean necessarily viral vectors, I apologise, I should have pointed you to vector but I try to avoid blue links where they may not be needed. Also, I do disagree with your source, the always reputable third world network has dropped the ball on this massively simplified (to the point of being insulting) FAQ text. If you wish to learn about HGT, istead of searching the deep depths and beyond, try this special nature rev. microbiol. issue (e.g. here is a nice introduction). Finally, I'll be sure to let my dissertation supervisor know that he should remark my year-long project entitled "HGT in Rhizobium" on account that I do not know what HGT 'really' means Jebus989^✰ 11:09, 7 January 2012 (UTC)

Paywall. And of course it's massively simplified, but is what it's saying really that farfetched? HGT clearly does include any introduction of foreign DNA to an organism other than from its parent, regardless if it's done through the intervention of man or the flying spaghetti monster. Is this not true? Are you restricting HGT solely to prokaryotes in some kind of exceptionalism, or is this just one of those old arguments about the differences between "natural" and "artificial" and how the twain shall never meet?-- Obsidi♠n Soul 12:20, 7 January 2012 (UTC)

Forgetting the issue of "intelligence" of processes (because it seems this is based on someone's theistic axe to grind...), other large factors influencing evolution (and not included in Darwin's original notion of natural selection) are kin selection and group selection. SemanticMantis (talk) 13:49, 6 January 2012 (UTC)

I don't mean to seem disagreeable, but it should be noted group selection is not, by any means, widely accepted as a large factor influencing evolution Jebus989^✰ 13:59, 6 January 2012 (UTC)

Good point; I should have phrased more carefully. Still, group selection is a widely known concept, though the strength and common-ness of its effects are indeed debated. SemanticMantis (talk) 15:59, 6 January 2012 (UTC)

Selective breeding can be used to drive the evolution of animal species in very unnatural ways, and is definitely the result of applied intelligence - human intelligence, obviously. And it can be argued that natural selection has not been the main driver of modern human evolution since the invention of agriculture around 10,000 years ago. But there is no scientifically accepted evidence that the evolution of animal species in a natural environment has ever been influenced by any non-human intelligence. We have an article on symbiogenesis but I don't see how it involves or implies intelligence. "Natural genetic enginneering" sounds like an oxymoron - if something is natural then it is by definition not engineered. Gandalf61 (talk) 13:54, 6 January 2012 (UTC)

But, isn't natural selection not an all embracing concept of all mechanisms within evolution? Sexual selection or being too stupid are simply concrete realizations within natural selection. (I'm not entering into the aforementioned selective breeding). 88.14.198.215 (talk) 16:17, 6 January 2012 (UTC)

Irrational Number, the creationsist are everywhere on the web, and you will find them posting many times in your browsing. They are absolutely convinced that their particular god has a hand in what is going on on this planet, performing miracles like creating the Earth adn designing species. Just remember that there is simply no scientific evidence at all for any claim of such miracles. Since you are studying Chemistry, you probably start to have an idea of how experimenting is done by scientists to prove theories, how the peer review system allows other scientists to reproduce the same experiments and validate (or invalidate if a mistake was made) the results of previous scientist. You probably also understand how human selective breeding could create new species, so you know we can now "experiment" with evolution (dogs created from wolves etc.). However, you must also see that there is no way that we can design an experiment that will prove that an animal was designed by a supernatural deity, or supernatural intelligent force, or whatever. Since this theory cannot be rejected or validated by any experiment that we can conceive, it cannot be scientific. --Lgriot (talk) 17:39, 6 January 2012 (UTC)

@88.14 No, "natural selection" is not in modern practice an all-inclusive term for all evolutionary processes. SemanticMantis (talk) 17:49, 6 January 2012 (UTC)

@Lgriot The problem is that at the moment, I'm in the process of learning, and every now and then I see some creationist claim that kind of... well makes me doubt my understanding of scientific concepts.And I know that even if they proved evolution is false, it won't make their claims any more true than they were before, but I think I need to ask the questions here for clarification!--Irrational number (talk) 21:37, 6 January 2012 (UTC)

@SemanticMantis: but the article Natural selection includes sexual selection (mates' preferences) and ecological selection (external pressure). So, what is left, that cannot be included into these two broad subcategories of natural selection? I'm aware that there is also several types of mutation, but that's is not natural selection per se, and it's not an "intelligent force" (in the sense that it would 'choose' better specimens). Genetic drift, for example, would produce genetic changes in the population, but it's not evolution, since it doesn't make fitter specimens. 88.14.198.215 (talk) 22:15, 6 January 2012 (UTC)

Have you read genetic drift? Or evolution for that matter. Making specimens 'fitter' (itself an imprecise term, do you mean inclusive fitness?) is not part of the definition of evolution. An outcome it may be, but as the article neatly states: Evolution is any change across successive generations in the heritable characteristics of biological populations Jebus989^✰ 22:35, 6 January 2012 (UTC)

OK, I was thinking in terms of "evolution = changes which improves something". 88.9.214.197 (talk) 23:47, 6 January 2012 (UTC)

• I've been fond of the notion of inheritance of acquired characteristics even before its recent rehabilitation in epigenetics. The idea is that environmental factors might control the levels of circulating hormones, which directly control the expression of certain genes as a matter of ordinary physiology, but also might control their regulation by the binding of transcription factors and modifications of histones even in the gonads. These modifications might change the susceptibility of the DNA to mutation, especially when they affect the level of methylation of CpG islands and other cytosine containing motifs. Thus, an environmental stimulus that triggers the body to produce more of a growth hormone can, in the short term, lead to an increase in growth; but in the long term it might lead to permanent changes in the target genes which cause more growth. Moreover, it might lead to targeted mutations in those genes which allow natural selection to do more testing of the effects of increasing one aspect or another of growth hormone's effects independently of one another, thereby, potentially, increasing the rate of evolutionary progress in that area. The evidence for this is scanty, and despite its provocativeness, it probably has relatively little real effect compared to plain old Darwinian selection. But it's fun to think about, and fun to consider whether evolution on another planet might have made more extensive use of such mechanisms - and whether, in the long term, allowing physiology to take a more active control over the direction of evolution would turn out to be a good thing or a bad thing in terms of evolution of new characteristics such as intelligence. I don't have many of these answers at all. ;) Wnt (talk) 19:25, 7 January 2012 (UTC)
  • We don't know everything about how genetics work, so the possibility of inheritance of acquired characteristics doesn't seem too far-fetched. And given the practically limitless amount of time available to the evolutionary process, even if you get 1 good trait for every 1,000 disastrous traits, it's still something that could work its way into the Darwinian process. ←Baseball Bugs ^{What's up, Doc?} carrots→ 13:33, 8 January 2012 (UTC)

Jumping fish

What's up with the fish in this video? Does anyone know where this happens in the world? DRosenbach ^{(Talk | Contribs)} 16:05, 6 January 2012 (UTC)

Shalom! Flying fish live in all of the oceans, particularly in tropical and warm subtropical waters. Here you can find a map, the yellow part is where most of them live. The video shows Asian carp in the Spoon River, Illinois, United States of America according to this source. Von Restorff (talk) 16:08, 6 January 2012 (UTC)

Note that the Asian carp is not a flying fish. The carp jump as an evasive maneuver, described in Asian_carp#Jumping_ability. This can become problematic as illustrated in the video, when the invasive species reaches densities much higher than it would it its native range. SemanticMantis (talk) 17:43, 6 January 2012 (UTC)

How LEDs display different colours?

I have read various pages over the internet that say LEDs come in red, blue and green colour. I am curious about how colours other than red, blue and green are displayed on LEDs? MAQ — Preceding unsigned comment added by 188.48.113.230 (talk) 17:15, 6 January 2012 (UTC)

There's nothing particularly unique about LEDs in this regard. Additive color has used red, green, and blue primaries to recreate a large color space for decades now. — Lomn 17:22, 6 January 2012 (UTC)

If you want to make your own colored leds that is very easy. They also emit different colors at different temperatures and currents BTW. Von Restorff (talk) 17:28, 6 January 2012 (UTC)

LEDs emit light when an electron inside it drops from a higher energy level to a lower one. The color of the light given off corresponds to the energy difference between the two levels. The manufacturer can choose the color of light by choosing different atoms to make the LED. LEDs are available in many colors including red, orange, yellow, green, and blue. Colors that can't be produced with a single LED, such as white, can be produced by combining several LEDs of different colors in a single package. Jc3s5h (talk) 17:43, 6 January 2012 (UTC)

Just for fun, grab yourself a magnifying glass and look at a LED display with it. You should be able to actually see the three colour LEDs doing their job to make the colours. The higher magnification the better (in the past I have found microscope lenses work really well). --jjron (talk) 18:32, 6 January 2012 (UTC)

Or just get out a smartphone/tablet in a light rain shower - the lenses formed by the drops of water have just about enough manification to see this effect. Equisetum (talk | contributions) 19:15, 6 January 2012 (UTC)

LEDs can be produced in many colors by selecting different semiconductor compounds (and you can also produce IR or UV). However the colors they produce are generally pretty close to "pure spectral" colors (not as close as lasers but pretty close). To produce colors that are further from pure spectral colors two techniques can be used. One is to use multiple LED elements made from different semiconductors in the same package (this is usually used if there is a desire to change the color dynamically). The other is to use a phosphor coating to downconvert some or all of the light to other wavelengths (this is how most "white LEDs" are produced. Plugwash (talk) 19:32, 6 January 2012 (UTC)

Note that most "LED TVs" are not actually LED displays. They are LCD displays with LED back-lights. They do rather misrepresent them, IMHO. StuRat (talk) 19:44, 6 January 2012 (UTC)

How much Helium-3 in the atmosphere of the gas giants?

Helium is present in the atmosphere of Neptune 19%, Uranus 15%, Saturn 3%, Jupiter 10.2%. But how much of it is Helium-3 ..? And the extractable amount in moon soil is such that one need to process 150 million kg to get on kg Helium-3. How does that compare to the mentioned gas planets? Electron9 (talk) 17:37, 6 January 2012 (UTC)

That is not known. The Helium-3 article accurately reflects the discrepancy in current studies that estimate between 1 ppb and 50 ppb. Even at 1 ppb, Jupiter will have more Helium-3 than the Earth has water. As for extraction, the Moon is close - which is nice. The gas giants are far away and have extremely high gravity - and even nasty lunar issues with the moons. Therefore, hypothetical mining operations tend to look towards Neptune and Uranus instead of Saturn and Jupiter. -- kainaw™ 18:30, 6 January 2012 (UTC)

Supposedly Neptune contains gas layers such that a balloon can be used to extract Helium-3 "in flight". However, I think a suitable reactor process is the largest hurdle. But reading reports on the matter. It seems we will likely know if it works by 2016. Electron9 (talk) 20:10, 6 January 2012 (UTC)

Of course, I guess it goes without saying that there's unlikely to be any extraterrestrial means of getting helium-3 that is more efficient than just making tritium in a reactor and letting it decay, at least with the space technology of the next 50 years or so. --Mr.98 (talk) 01:31, 7 January 2012 (UTC)

Taking off from earth to fetch and then return is likely uneconomic. The point is to have machines in space that does the collection and send to earth without human intervention. Electron9 (talk) 09:48, 7 January 2012 (UTC)

Glacier Image Database?

Hi there, I'm not sure if i should post this here or in the computing section. I'm looking to do a tracking problem for my college project, and was looking to apply some image processing techniques to the glacier tracking problem. However I'm not sure if a database of a series of such images on glaciers over a period of time are publicly available (like you get for face recognition or fingerprint matching purposes). Some of the existing works on this have used SAR images or ASTER images but i can't find any such database on the internet. Can anybody shed some light on this, if such databases are available or not, or how such work is actually done?--tathagata 19:11, 6 January 2012 (UTC) — Preceding unsigned comment added by Nonstop funstop (talk • contribs)

It is pretty easy to find Terra ASTER or Terra MODIS images (choose terra at the righthandside on this page, scroll down and chose ASTER or MODIS) or pictures that are tagged with "glacier", but multiple photographs from the same glacier over a period of time are much harder to find! I would recommend visiting this webpage and/or emailing NASA directly. Von Restorff (talk) 19:28, 6 January 2012 (UTC)

There are lots of databases available for free to the public. (Almost) all NASA and NOAA satellite data is available for no charge; usually through anonymous FTP (though some data products do require more effort to obtain). For example, MODIS data is available for no charge from NASA; it is one of the most common satellite observation platforms for determining ice coverage. LANDSAT data is available from NASA, if you want to work with more conventional photographic imaging. It has considerable amount of documentation for science-data users. ICESat data is also available from NASA at its webpage, also from NASA. NOAA also makes its data available, through NESDIS, at no charge. You are probably familiar with the GOES satellites (if you ever watch the local weather reports); but there are lots of other satellites.

Ultimately, if you've never worked with satellite imagery, you need to do a little prep-work:

• What are you trying to observe? What sort of data do you need? (Spectral data? Visible/infrared/photographic data? RADAR? Primary- or secondary- or tertiary data products (e.g., raw satellite sensor data? JPEG- or TIFF images? Charts, analyses, and statistics).
• How long do you need a backlog of data archives?
• Which satellite or satellites (or other remote sensor platform, such as the NEXRAD radars) can provide that data for you?

As I mentioned, MODIS is very commonly used for ice coverage: it has infrared imagers, and these typically give better data than visible light photography when trying to determine ice coverage. But, you will need to become familiar with infrared spectroscopy as it will be an integral part of your data processing.

If I can find it in my archive, I think I have a good review-article of various research that used MODIS infrared spectrometry for long-term ice coverage analysis. Nimur (talk) 19:29, 6 January 2012 (UTC)

Oh, and of course, National Snow and Ice Data Center - a consortium of university and government researchers based in Colorado. Their web page links to research, data, and information. Nimur (talk) 19:37, 6 January 2012 (UTC)

Thanks a lot for the suggestions. I was looking for jpeg/tif images over a period of a few years at least . I think the landsat images would do fine for me. --tathagata 08:41, 7 January 2012 (UTC) — Preceding unsigned comment added by Nonstop funstop (talk • contribs)