Wikipedia:Reference desk/Archives/Science/2011 May 20

= May 20 =

the red end
can somebody please settle a stupid argument for us. What is the temperature in the centre of the burning end of a cigarette.190.56.108.127 (talk) 02:49, 20 May 2011 (UTC)
 * "800−900° C during a puff, 700−800° C during the natural smoulder between puffs, and 800−850° C under steady state continuous draw conditions" from --Tagishsimon (talk) 03:03, 20 May 2011 (UTC)

This is 108.127 Thank you my friend!190.148.135.85 (talk) 04:33, 20 May 2011 (UTC)

device name
What is the proper name for the analog meter in upper left corner of this image? I'm trying to find more example images but not knowing what it's called by those who use them is hampering that. The Masked Booby (talk) 09:56, 20 May 2011 (UTC)
 * VU meters look like this, but I suppose that's not quite the term that you're looking for. --Wrongfilter (talk) 10:10, 20 May 2011 (UTC).


 * S meter has the information you need. Roger (talk) 10:56, 20 May 2011 (UTC)

Please help me to figure it out
1. If there any process to calculate the number of photon emitting from a source of radiation?

2.If we enclose a light emitting source of very high frequency in a vacuum tube which is placed in a varying magnetic field,can we produce mass? —Preceding unsigned comment added by 59.93.210.78 (talk) 10:50, 20 May 2011 (UTC)


 * 1. Yes. The energy of a single photon is given by E = h*c / wavelength, where c is the speed of light and h is plancks constant. So if you know the wavelenght of the light and the total energy emitted, you can easily find the number of photons.


 * 2. I don't see the idea behind what you propose, but it is possible to create equal amounts of matter and anti-matter from photons. It is called pair production. EverGreg (talk) 12:09, 20 May 2011 (UTC)


 * For Q1, yes, the energy carried by a photon is given by the Planck relation, E=hf, where E is energy in Joules (Watts seconds), h is the Planck constant, and f is the frequency of the photon. Thus if you know the frequency and power of the E/M source, then you can calculate the number of photons per second it emits. I'm not sure what you mean by Q2; all photons have a mass given by mc2=E=hf. CS Miller (talk) 12:14, 20 May 2011 (UTC)
 * If the source is non-spectral, you'll need to use some calculus and statistics to estimate the maximally-probable number of photons. In the same way that you need to calculate the expected-value of a gas particle's speed, you will similarly need to calculate the expected value of, say, a blackbody-emission photon's frequency; and then estimate the expected number of photons with any particular frequency; integrate over all frequencies; and estimate the variance/error, based on the governing statistics.  Nimur (talk) 15:12, 20 May 2011 (UTC)

you shouldn't have the right to say it as it is not possible. It is possible to construct a device producing mass from a frequency of a specified for a certain frequency.I've experimented this personally. Hope you would consider it for again.

Drug-producing plants
What is the evolutionary advantage for a plant to produce medicines or drugs? It would seem that producing substances that encourage people to harvest the plant, killing the plant and thus preventing it from reproducing, would provide a strong disincentive, but I'm obviously overlooking something. --75.40.204.106 (talk) 20:31, 20 May 2011 (UTC)


 * It isn't always necessary to destroy a plant to use it medicinally. In some cases, picking a single leaf may do the job.  Some other thoughts:


 * 1) The plant may have evolved meds as an accident, when trying to deal with another problem. For example, a plant that deadens the nerves may work against insects by numbing their nerves, but people may then use it in a lower concentration to reduce pain.  Another example can be poisons, which, in reduced dosage, might actually be a med.  For example, a poison that kills by thinning the blood so much the animal hemorrhages to death might be a useful blood thinner in reduced amounts.


 * 2) People harvesting plants would be careful to replant them (or their seeds) where they would thrive, at least since the agricultural revolution.


 * 3) Animals (including people) might brush against a plant and spread pollen from one to another when picking medicinal leaves, and thus act like bees or hummingbirds, to pollinate them.


 * 4) Animals that eat the medicinal plants might spread and fertilize seeds in their manure. StuRat (talk) 20:50, 20 May 2011 (UTC)


 * But what about, say, the opium poppy? Harvesting opium destroys the plant and its seeds, so it can't reproduce. --75.40.204.106 (talk) 21:06, 20 May 2011 (UTC)


 * You don't have to destroy every seed. And any smart grower would replant some of the seeds and cultivate them. StuRat (talk) 05:18, 22 May 2011 (UTC)


 * How about a specific example, instead of general speculation? (Sorry, StuRat.)  Our article on the mold Penicillium chrysogenum has a single line discussing this:  It's believed that it produces penicillin to kill bacteria that are competing with the mold for food.  This topic is surely interesting enough to merit a whole section in our antibiotics article, or an article on its own, but I searched for such a thing in vain.  Comet Tuttle (talk) 21:07, 20 May 2011 (UTC)


 * The evolutionary advantage for a plant is that it makes them taste disgusting and makes the grazer feel that its faculties have been altered. Try eating a raw poppy, wormwood, monkshead, skullcap, etc. You wont want do it a second time. Especially  with Datura --Aspro (talk) 21:17, 20 May 2011 (UTC)
 * Given the prohibition against medical advice, perhaps this could be phrased better; not as a dare or challenge. I'm not saying it's likely, but some people will see it that way. Dualus (talk) 22:32, 20 May 2011 (UTC)


 * [Multiple ECs] Off the cuff - First, there's the time scales involved. Plants evolve the production of such substances for their own purposes (often as pest repellents) over tens to hundreds of thousands of years and maintain them for perhaps millions of years. People have only been harvesting most of them for at best a few thousand years and more often for only a few decades, so there will usually not yet have been enough time for evolution to have responded much to such harvesting.
 * Second, evolution through natural selection could only operate if the plants were being significantly harvested, over and above the 'natural harvesting' that non-human consumers of them (insects, grazing mammals etc) already perform, over a good deal of their individual ranges, and perhaps also according to the degree of production of the substances involved: it's likely, however, that human harvesting would usually have only a minor impact on population, so enough unharvested plants will have been left to continue the species unmodified.
 * Third, the original reasons the plants have for evolving the producing of those substances are still operating, providing a 'counter-pressure' to any evolutionary harvesting effects.
 * Fourth, many of those plants that we harvest for such purposes we will actively cultivate and encourage, negating selection against the wild population.
 * Fifth, although the substances are often initially discovered and harvested from wild plants, we usually look for and devise ways of making them more efficiently and in greater quantities artificially, so selection pressures on the wild population are subsequently reduced.
 * Obviously the balance of these and other factors will differ depending on the particular plant in question. I haven't linked any of the concepts I've mentioned, but I'm sure you can pursue them further. {The poster formerly known as 87.81.230.195} 90.201.110.8 (talk) 21:19, 20 May 2011 (UTC)


 * [Yeah. Lot's of Edit conflicts!] Plants evolved to do what they do long before humans existed, let alone thinking of harvesting them for anything, including drugs. The two facts are not related in any way at all. HiLo48 (talk) 21:24, 20 May 2011 (UTC)


 * Likewise. I would disagree on the time scale too. Non-human primates have been observed self-medicating. Thus, one can extrapolate that homo, has done so, from the year dot. Plants that have survived into the modern era have done so, only because the have discourages their major foes.--Aspro (talk) 21:34, 20 May 2011 (UTC)
 * Well now, it's not absurd that some plant somewhere may have evolved the production of mood-altering substances to encourage consumption. That's what fruit is for, by and large, after all.  Making all that sugar is a very significant burden on the plant's metabolic resources; it wouldn't do it, except that it functions as a bribe to animals who eat the fruit, and then disperse the plant's seeds.  Sometimes the plant tries to pick and choose who eats it &mdash; capsaicin apparently functions to discourage mammals from eating the (botanical) fruit, leaving more for the birds, because the seeds of capsicum peppers are destroyed in the mammalian gut, but pass through the birds' alimentary tract undamaged. --Trovatore (talk) 21:40, 20 May 2011 (UTC)


 * The OP is asking about DRUGS not rich energy sources like fruit. In short. Natural selection is sufficient to explain why plants have evolved to the mimic neuro-transmitters of mammals. --Aspro (talk) 21:46, 20 May 2011 (UTC)
 * Who said it wasn't? My point was that it is possible in principle that a plant could use mood-altering substances (what you're calling "drugs"; I'm trying to avoid that word because it has too much baggage and can mean too many other things) to encourage rather than discourage consumption, and that this adaptation could be favored by natural selection. --Trovatore (talk) 21:50, 20 May 2011 (UTC)


 * Oh hell, your right. On the second reading, I see the OP also asks about medicine, and that would included things like mucilage, allicin, etc., (I nearly included calamine – obviously a  sure sign of  presenile dementia setting in).--Aspro (talk) 22:22, 20 May 2011 (UTC)

The big evolutionary advantage is yet to come. While we are destroying the biosphere, these plants will be protected. It's a bit similar to how Western Europe is becoming one big mega city with hardly any wild animals there: There are huge numbers of chicken, pigs and cows there. Count Iblis (talk) 23:21, 20 May 2011 (UTC)


 * Check out The Botany of Desire. It discusses how humans in particular have been wonderful agents in making sure that a few evolutionary freaks (marijuana, for example) become extremely successful from a biological perspective because we cultivate the heck out of them. The whole approach Pollan takes is that we have a terribly symbiotic relationship with these plants: these plants "win" at evolution because they produced something that we end up thinking is valuable to cultivate.
 * As for why plants would produce the sorts of complex molecules that happen to turn on the human brain — they often turn on the brains of other animals, also, and often have some mechanism in them that makes our interest in them result in their genes getting spread. Alternatively, many of these complex chemicals (e.g. the complex alkaloids that are responsible for cocaine, caffeine, and nicotine) probably have some sort of poisonous effect against insects and other animals.
 * As for the idea that evolution hasn't had enough time to operate on these plants — that's false. Evolution operates all the time. (Evolution is just gene flow plus selection. It is not speciation.) Opium poppies are doing great by evolutionary standards — look at how many there are! Look how many competitors they have displaced! Look at how well cared for they are! They're doing great. Marijuana as well — it has evolved to be the more delicately tended plant on Earth, most likely, with humans as its googly-eyed worshipers. We are the "human bumblebees" for these plants. We've done it with lots of other plants, too (Pollan looks at apples, tulips, and potatos in particular, along with marijuana — all plants that are massively successful because of human intervention). --Mr.98 (talk) 01:53, 21 May 2011 (UTC)
 * In general one wonders whether humans evolve to grow crops or crops evolve to grow humans... still, it isn't really an explanation for so many wonderful wild plants that have been used for medicinal purposes. True, of course, weeds along many roadways began as garden medicines, but like the domestic drug crops they didn't first evolve their active ingredients for this purpose.  I'm afraid I don't really have the answer for this one either, but to begin, let's consider how frequently flowering plants turn out to be medicinal, as opposed to seaweeds, algae, bacteria, mushrooms etc. which would also have been available to ancient human trial and error  I have a nagging suspicion that some of the drugs began as part of their friendly and unfriendly relations with insects and other animals, which are not vastly different from humans in fundamental biochemistry. Wnt (talk) 09:03, 22 May 2011 (UTC)

Sunscreen
Can anyone explain this photo? Why does the sunscreen make his skin reflect less UV? That's not going to offer any protection... --Tango (talk) 23:14, 20 May 2011 (UTC)


 * Sunscreen absorbs UV light so it can't reach the underlying skin. Increased absorption leads to darker appearance.  Dragons flight (talk) 23:22, 20 May 2011 (UTC)
 * Right, presumably if he'd been using zinc oxide as sunblock, the protected side would have appeared brighter rather than darker. But it's hard to imagine any clear liquid that soaks into the skin and increases reflectivity, rather than absorptivity, in the UV band.
 * I seem to recall that there is some controversy over this strategy, though. Supposedly some sunblock compounds can become dangerous (maybe generating free radicals?) on activation by UV light.  The recommendation I seem to recall reading was to make sure you always had sunscreen on the surface of the skin, so the UV couldn't penetrate far enough to create dangerous substances from the sunscreen that had already soaked in.  --Trovatore (talk) 00:54, 21 May 2011 (UTC)


 * I Can't see that and not think of Let That Be Your Last Battlefield. APL (talk) 04:16, 21 May 2011 (UTC)
 * Same here... especially if he forgets to even out before he goes out in the sun! Wnt (talk) 09:05, 22 May 2011 (UTC)