Wikipedia:Reference desk/Archives/Science/2011 February 16

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February 16

Scsbot & SineBot

Can I use these bots in the Arabic Wikipedia questions? If Yes, then what shall I do or can it work by itself there? Because we receive rare questions, we do archiving once a month and this can be done manually but other tasks would be really hectic.--Email4mobile (talk) 01:12, 16 February 2011 (UTC)

If you leave a message on the talkpages of the bot operators directly, they could probably do a better job of helping you out. --Jayron32 01:49, 16 February 2011 (UTC)

Storing DNA for decades

An odd question that ran through my mind this evening:

Let's imagine that somebody wanted to store the DNA of a loved one, child, favorite pet, etc., with the idea that in the future that DNA could be used to create a biological clone of the original organism. (Of course, the clone would not be a duplicate, and would not be identical, except in terms of its nuclear DNA.) What would be the most ideal way to do this from a biological perspective, making conservative guesses about cloning technology advances in the next 20-50 years? E.g. would blood be an ideal fluid, and would it need to be cooled but not frozen, or what? What would prevent or stall the decay of the DNA to the degree that the overall genome would still be constructable? Would the nuclear DNA in the stored cells be actually usable for cloning, or would it require "resequencing" it in some way? I'm not asking for far-out assumptions about cloning, just reasonable scaling up of existing state of the art to the point in which it would be fairly cheap. --Mr.98 (talk) 03:16, 16 February 2011 (UTC)

Viable cells can be frozen for years, probably decades, in a DMSO/DMEM solution, in liquid nitrogen (<200^oC). So sure, you could use those. Even if you were looking tens of thousands of years in the future, beyond the stability of frozen cells or even frozen DNA, you can always reconstruct the genome. A large enough sample can survive arbitrary lengths of time. You can then use deep sequencing to reconstruct the genome. This has been done to reconstruct something like 70% of the Neanderthal genome, even though the only samples were very poorly preserved and tens of thousands of years old. Now, you want 100%, not 70%, but you'll have the benefit of better preservation techniques. Once you have the sequence reconstructed, you'll have to physically reconstruct the chromosomes. That's actually not possible right now in the case of human chromosomes. The record for synthesizing a piece of DNA is a roughly one million base-pair-long chromosome, compared to human chromsomes that can be over 200 million base pairs long. Someguy1221 (talk) 04:11, 16 February 2011 (UTC)

Unfortunately, no special effort may even be required. Due to policies for prolonged archiving of blood spots on filter paper for dried blood spot testing, obtained from newborns under mandatory laws, de facto DNA database samples exist going back as far as the 1960s These data have apparently been widely available in some cases, even for potential dissemination to insurance companies^[1] I am surprised to read that even RNA can be detected on such cards stored at room temperature for 21 years.^[2] The uncertain part is what degree of genome assembly can be done in 20-50 years - typical shotgun sequencing allows for construction of whole genome sequences from small fragments, so that part is less of a problem, but currently the reassembly of large numbers of little fragments of sequence into a genome is still a major practical problem. Wnt (talk) 04:15, 16 February 2011 (UTC)

The last point is a very good one. Nanopore sequencing and similar methods will allow for (theroetically) flawless sequencing of whole chromosomes provided you have at least one intact chromosome in the sample. If the DNA has degraded to a point that no consecutive sequences span a gap...you're screwed unless you can guess what it is. Someguy1221 (talk) 04:21, 16 February 2011 (UTC)

Blood is not so good because red blood cells don't have nuclei. It would be more reasonable to store hair. But really the most certain way to do it is probably to sequence the DNA and store the data on a CD or DVD. As already noted, we couldn't currently reconstruct the full DNA from that data, but it's pretty conservative to assume that it will be possible in 20-50 years. Looie496 (talk) 04:56, 16 February 2011 (UTC)

However, blood also contains leukocytes, which do have nuclei. This is the standard source of DNA for most genetic tests. If one is concerned about long term storage of high-quality DNA, the best thing would be to purify it from the blood sample and store it at -80C in a buffer (such as one containing EDTA) that would neutralize any enzymes that might degrade the DNA. On the other hand, if what the OP is after is a source of cells that could be used for somatic cell nuclear transfer or some other type of cloning procedure, then one could generate a cell line from a tissue such as skin, freeze aliquots of those cells and store them in liquid nitrogen. Then, they can be thawed and passaged for whatever future procedure the OP envisions. All of this (except the cloning part, of course) is standard laboratory practice. --- Medical geneticist (talk) 13:48, 16 February 2011 (UTC)

All very interesting discussion, thank you. --Mr.98 (talk) 13:35, 17 February 2011 (UTC)

A science news article today said that a high proportion. nearly 20%, of DNA sequences of animals and vegetables had been found to be contaminated with the DNA of the (human) researchers who handled them. This might interfere with any effort to "reconstruct" some organism from a saved DNA sequence or some blood sample. Your child, brought back via the preserved DNA, might look like the doctor or technician who took or processed the sample. Edison (talk) 03:09, 18 February 2011 (UTC)

My guess is that by the time 50 years have passed, it will not seem excessive to separate out several individual dried leukocyte nuclei and sequence the entire genome of each one, then compare them. BTW, the most interesting such case may involve a very careful investigation of relics of the True Cross - though, religious matters being such as they are, we would probably get one of the thieves just to serve us right. Wnt (talk) 03:02, 19 February 2011 (UTC)

perm press clothes

im wondering why the usa allows clothing to be treated with formaldehyde resin to perm press them. in some places like germany they dont allow this. what gov organization can i contact to complaint about this? — Preceding unsigned comment added by Tomjohnson357 (talk • contribs) 05:42, 16 February 2011 (UTC)

Depending on the basis for how it might specifically affect you, you might consider a government health agency, an occupational safety agency, or your workers' local union representative. First, you should definitely do some research into the history of that group's position on the matter...nothing worse than saying "hey Senator X, why does the government do Y?" and Sen. X saying "did you read the press release or bill passed a few weeks ago about it?" And also make sure you have some actual science to back up your concern (every public-health issue has tons of false and misleading info out there!). DMacks (talk) 05:55, 16 February 2011 (UTC)

This article shows that the Government Accountability Office has recently investigated and found it not to be a major problem. It says that Senator Bob Casey instigated the investigation. You could contact him to see if he is continuing the campaign. And this indicates the interest of campaigner Samuel S. Epstein and the Cancer Prevention Coalition. Itsmejudith (talk) 11:43, 16 February 2011 (UTC)

Placebo effect question...

How is it that a patient can take a placebo and it works for them, but then finds out its a placebo and it continues to work for them. I saw a few news articles about this within the past month. I thought once the patient knows its a sugar pill, the effect goes away. 76.169.33.234 (talk) 09:11, 16 February 2011 (UTC)Dave

The human mind is capable of much more than any of us give it credit for. If Western medicine can find a way to tap into it, then huge advances will be made. Meanwhile, here's a sugar pill... --TammyMoet (talk) 09:52, 16 February 2011 (UTC)

Why can't Eastern medicine tap into it as well? Perhaps you meant to simply suggest that "Medicine" should tap into it. -- kainaw™ 14:59, 16 February 2011 (UTC)

Well, maybe, but I happen to believe that Eastern medicine does tap into it. But as there is no "scientific proof" for my belief, I decided to stick with "Western" medicine. --TammyMoet (talk) 18:10, 16 February 2011 (UTC)

Whether a scientific fact was discovered in Europe or Africa or Asia may be of great historical interest, (and could potentially be due to strengths or shortcomings of the particular research methodologies used by that culture) - but it has nothing to do with whether the fact is scientifically valid. If there's a particular mechanism of action, and it is describable objectively, then it's moot to label it Eastern or Western medicine, except for purposes of advertising. We have articles on placebo effect and psychosomatic medicine. We also have articles on these exact same topics in Japanese: ja:偽薬, ja:心身医学; and Chinese: zh:安慰劑效應, and in numerous other languages. It should be fair to call those topics "Eastern medicine," if anything deserves that title. However, in common usage in the United States, "Eastern medicine" is often a euphemism for pseudoscience. I think a reputable medical expert should believe in the germ theory of disease and have a solid understanding of modern anatomy (zh:解剖学) and physiology (zh:生理学), as well as the scientific method, irrespective of their country or culture of origin. The placebo effect can be equally well reproduced in the United States and in China. Here's an interesting journal article, Cultural Variations in the Placebo Effect (2000). Nimur (talk) 00:00, 17 February 2011 (UTC)

The popular understanding of the placebo effect (the power of the mind to heal the body) is remarkably limited. There is more information at placebo, but the effect can--depending on the patient and treatment--include components of expectation effects, confirmation bias and regression to the mean. The placebo effect is also largely limited to subjective symptoms (e.g., pain and well-being) and is generally not found in objective measures. Conditions for which placebos have the "strongest" effect are typically self-limiting illnesses, which get better over time on their own (the old joke: an untreated cold will go away in a week, but homeopathy will clear it up in only a week!). The other major source of placebo success chronic illnesses that have up-and-down cycles of symptoms (such that a drug taken at the apex of a flareup will appear to have worked if only because the condition would have normalized on its own. — Scientizzle 15:55, 16 February 2011 (UTC)

Actually, I think that the old joke is that, left untreated, a cold may last up to fourteen days, while advanced medical care can cut that down to just two weeks. Homeopathy really doesn't figure into it. Matt Deres (talk) 16:08, 16 February 2011 (UTC)

Homeopathy is a prime example of the placebo effect. It figures nicely. — Scientizzle 16:10, 16 February 2011 (UTC)

I should think it would also be hard to control for other factors when testing for a placebo effect. A person in a hopeful state of mind might alter their behavior from what it would be otherwise, thus introducing additional factors that might favor recovery. Therefore a placebo effect might not strictly speaking be a "power of the mind to heal the body" but rather the effect of introducing factors that favor healing—facilitated by optimism. This is just wp:original research. Bus stop (talk) 16:14, 16 February 2011 (UTC)

I saw a really interesting article a couple of years ago that not only listed several trials that showed improvements with placebo, but also gave a particular case that seemed to suggest a particular medicine only worked in conjunction with the placebo effect: that is, by itself if did nothing, without it but with expectation, it did nothing, but with both the medicine and a powerful expectation, it worked. Does anyone recall what this was about? 86.164.25.178 (talk) 19:20, 16 February 2011 (UTC)

Not only that, but more expensive placebos are more effective than otherwise-identical less-expensive counterparts. TenOfAllTrades(talk) 20:43, 16 February 2011 (UTC)

I think that the new joke is that echinacea is worthless against the flu because it reduces symptoms and severity by about 10 percent, whereas Tamiflu is a vital new drug because it reduces symptoms and severity by about this amount in the 1% of strains which are not yet resistant... Anyway, as for placebos, I think it's important to look at the details. If you take a placebo with a glass of water, this glass of water, twice daily, is a significant therapy (as someone with the gout can tell you with certainty). Wnt (talk) 08:10, 17 February 2011 (UTC)

Proton mass - How standard model can explain ?

The proton mass is estimated around 1 GeV. But we understand that proton is a group of 02 quarks up (mass = 2 eV) and 01 quark down (mass = 5 Mev). It´s suposed that gluon keeps the quarks retained in proton. As gluon is estimated with mass = 0 eV, the addition should be proton mass = 09 MeV. So, How can the total mass from proton be estimated in 1 GeV. From where it cames that mass ? —Preceding unsigned comment added by 177.17.23.86 (talk) 09:56, 16 February 2011 (UTC)

What you have specified is the bare mass, the effective mass of up quarks in a proton is around 330 MeV/c² (from up quark#Mass) and the effective mass of down quarks in a proton is around 330 MeV (from down quark#Mass) the difference made up by binding energy. However I would have expected binding energy to be negative, as in nuclei. Graeme Bartlett (talk) 10:47, 16 February 2011 (UTC)

Yes, most of the proton mass comes from energy -- the energy of the quarks and gluons that make up the proton -- but this energy is positive, not negative. To pull a proton and an antiproton from the void you invested about 2 GeV, now each one has 1 GeV worth of energy "stored in it", hence its mass. This energy cannot be released, as the quarks cannot simply "fly apart"; that is because the strong interaction force between two quarks does not decay with distance like most other forces do. Hope this helps. --Dr Dima (talk) 19:37, 16 February 2011 (UTC)

It is not binding energy which would indeed be negative. It is the kinetic energy of the motion of the quarks and gluons inside the proton. Dauto (talk) 06:29, 17 February 2011 (UTC)

The Year of the Higgs? A Live Webcast From NSF

Has any of our Science Reference desk volunteers participated [3]?--Email4mobile (talk) 12:19, 16 February 2011 (UTC)

I have one peer who worked with the ATLAS group and one who is likely finishing her PhD at CERN soon. That said, I really think this all gets a bit over-hyped, not just because I do another more-relevant type of physics, but because I don't think the theory has been developed as extensively as it should be to justify building this gigantic thing in the first place. That said, it's way better than dropping bombs, and I don't believe for a second that one can just not spend the money on this and expect the same amount of funding to be distributed to, oh, say oceanography or geophysics or even, if we want to stay in space, EJSM or IXO. /rant. SamuelRiv (talk) 04:44, 18 February 2011 (UTC)

The idea that the LHC was built to look for the Higgs boson is basically fiction. The point of the LHC is to explore a new energy regime where there are strong theoretical arguments that some new physics appears. The Higgs boson is considered by far the most likely bet for something the LHC will find, and that may be why it has been hyped so much to the media—the idea is that when the LHC finds the Higgs, that will be seen as "success" by the general public, who are ultimately the ones who decide whether to fund future research in particle physics. It's a con game, in other words, and a somewhat dangerous one since the Higgs might not be found. But most physicists would probably prefer that the LHC exclude the Higgs, because that would be startling and interesting, and would suggest directions for future research instead of reinforcing what we think we already know. More generally, they are desperate for anything that will narrow down the possible candidates for a successor to the Standard Model. The worst possible outcome of the LHC experiment is the outcome that the general public seems to associate with success—that it finds the Higgs and absolutely nothing else.

As for more-relevant research... what is the point of it? You can build flying cars so that people can commute more quickly to work to do... what? You can cure malaria and AIDS so that people can live longer, healthier lives, giving them time to do... what? Sooner or later people have got to do something other than (do things that make it easier for other people to)ⁿ eat, sleep and reproduce, where n ∊ { 0, 1, 2, … }. In practice, the other something is usually watching TV (the large cheap flat-panel TV that you invented), but it might as well be particle physics, especially since there's only one LHC in the world and it cost a lot less than all those TVs. Honestly, I think applied research is great. I'm glad you want to make me happier, but I'm afraid that particle physics makes me happy. -- BenRG (talk) 07:49, 19 February 2011 (UTC)

Is milk disadvantageous?

A balanced intake of all the bone minerals, along with adequate vitamin A, C, and D, is what is truly needed. A balanced intake of minerals cannot occur when the diet emphasizes dairy. Dairy's high calcium causes relative deficiencies in magnesium and other bone-building minerals, and its high phosphorus and animal protein reduces calcium availability. http://www.naturalchild.org/guest/linda_folden_palmer.html Is this true? —Preceding unsigned comment added by 1.23.14.249 (talk) 15:41, 16 February 2011 (UTC)

That is from a chiropractic doctor who has made a career out of making claims that cow's milk is harmful. Her claims have been refuted repeatedly, but it isn't newsworthy to claim that over 400 years of drinking cow's milk hasn't produced extremely harmful effects. It is only newsworthy to claim that what everyone has done for the last 400 years will kill your baby. -- kainaw™ 15:48, 16 February 2011 (UTC)

It can be tricky to get a correctly balanced response. On the one hand, saying that milk is "bad" when people have been drinking it for thousands of years seems unwarranted. On the other hand, having it as one of the "four food groups" (though that term is now deprecated and is a redirect) when three quarters or so of the population is lactose intolerant seems more the work of dairy lobbyist groups than actual science. Matt Deres (talk) 16:03, 16 February 2011 (UTC)

For those without an actual intolerance or milk allergy, dairy has a good record of being a nutritious component of a balanced, healthful diet. For those living in wealthy industrialized nations, the rate of actual vitamin & mineral deficiencies is quite low. The author's simultaneous assertions that milk contains too much calcium but low calcium availability is fatuously absurd. It wouldn't surprise me if the book she's peddling in that article isn't also full of other contradictory and biologically ignorant claims...There's quite a lot of nutritional nonsense out there, and, frankly naturalchild.org looks like it suffers from a severe endemic case of the naturalistic fallacy. — Scientizzle 16:08, 16 February 2011 (UTC)

I don't think absurd is the right word. For example, I've read claims (from actual scientist-types, not anti-dairy advocates) that the presence of animal fat in milk inhibits the uptake of the calcium (and/or vitamin D). If true (and I'll try to find a cite), that would be a rather large mark against milk consumption, as it's often marketed for its ability to provide those nutrients. I drink milk all the time, but the fact that three quarters of the world is built in such a way that they couldn't drink it even if they wanted to, frankly leaves me suspicious of how great it is. Matt Deres (talk) 19:32, 16 February 2011 (UTC)

I am not sure of your reasoning Matt. If 75% of the world was allergic to potatoes, would that make potatoes any less of a good food? Googlemeister (talk) 21:59, 16 February 2011 (UTC)

Well, to those who are in the 75% at least :). I guess my beef (ahem) is with health organizations like those in the US and Canada essentially saying that milk is a required part of a healthy diet - as if the 75% or so of the world that's lactose intolerant is consuming an unhealthy diet. To rephrase your question a bit: if 75% of the world was unable to eat potatoes, how would you feel about the validity of a diet scheme that said they were a necessary part of a healthy diet? That's what I mean about the situation being tricky. Consider dog meat. If we're generous, we'll say that about 25% of the world would consider dog meat perfectly acceptable (it's probably a bit less than that, but it's in the ballpark). If China or Korea released a food pyramid that said that eating dog or dog substitute was a necessary part of a balanced diet, you'd probably look at it a little cross-eyed, but you'd at least admit that red meat is pretty much red meat and dog probably has quite a bit of nutrition in it. But what would your opinion be if most people in the non-dog-meat eating world got violently ill when they tried dog? I think an unbiased observer would say that it obviously couldn't be as necessary as the Koreans or Chinese thought. That's the situation cow milk is in: billions of people never touch the stuff (after reaching childhood), yet there are folks who claim that not drinking milk all your life leads to an unhealthy diet. That doesn't add up for me. Matt Deres (talk) 04:35, 17 February 2011 (UTC) (now stepping off of soapbox)

Ah, much clarified. Googlemeister (talk) 15:21, 17 February 2011 (UTC)

Homo Sapiens was doing ok. without dairy products since 200,000 years ago right until about 8,000 years ago... Count Iblis (talk) 17:10, 16 February 2011 (UTC)

By that argument, anything new should be trashed. Homo sapiens didn't need cars or computers or even buildings for hundreds of thousands of years. So, they must be bad. -- kainaw™ 17:12, 16 February 2011 (UTC)

Unfortunately, public debate on milk seems to be tainted by industry groups on the one side and animal rights believers on the other. It is already difficult to evaluate whether a food with longstanding use is healthier or less healthy than others, because people vary according to genetics and in what other foods they eat. It is clear that neither cow's milk nor anything else is a satisfactory substitute for human milk for babies, but we vaguely assume adults with a varied diet will hit on a better balanced mix of nutrition by statistical accident or by instinct. Yet obesity and other metabolic variations show that this mechanism isn't working very well, - maybe due to inactive lifestyles, viral infection, epigenetics ... who knows? If that is the case, then is the problem in the milk or in the mechanism by which human hungers are regulated? Wnt (talk) 18:56, 16 February 2011 (UTC)

There's been several research done about milk. I recall one about a decade ago saying that milk actually removes calcium from your bones, and isn't unthinkable, since osteoporosis is apparently more prominent in societies where milk consumption is high. Vitamin D is also added to aid the absorption, which in combination with adult mammals losing the enzyme to process lactose, point toward the idea that unadulterated milk wasn't really meant for adult consumption. And the research pointing to poor absorption of calcium from supplements made from seashells could suggest that a high calcium content in milk doesn't mean most of it is absorbed by the body any ways. I'll try to find the articles after work if I'm able (currently on lunch break). --Wirbelwindヴィルヴェルヴィント (talk) 20:40, 16 February 2011 (UTC)

I'd say human breast milk is healthiest for babies, followed by substitutes, like Enfamil, then cow's milk, then real juice, with fake juice and soda-pop being the worst, nutritionally (and soda-pop with artificial sweeteners being the worst of the worst). And, of course, when they don't need food but are just thirsty, water is best. In an older child or adult, it's probably similar (although finding a woman willing to breast feed you might be difficult :-) ), provided you aren't lactose intolerant. Adults also need to worry more about excess calories and fat intake, so that might move all forms of milk down the list, to be replaced by black coffee or tea, at the top, and, perhaps next, alcoholic drinks, in moderation. StuRat (talk) 18:54, 17 February 2011 (UTC)

I suppose most nutritionists would broadly agree to that ranking, but you really can't make such a thing in a vacuum. For example, even real juice is heavily sweetened with what is euphemistically referred to "grape juice from concentrate" or similar (I can't believe we don't have an article on that; I must not be searching correctly - grape juice is processed to remove the nutrients, the flavour, and much of the water until all that's left is sugary syrup. This can then be labelled as "concentrated grape juice" on the ingredients list so it will look healthier to the public than "sugar" despite being exactly the same thing). Like soft-drinks, the nutritional difference between them and their lower-sugar counterparts depends heavily on circumstances. For most people those empty calories are just an excess, but someone with an otherwise low calorie diet might have need for that sugar water. Matt Deres (talk) 21:29, 17 February 2011 (UTC)

Things like that are what I classified as "fake juice", which I put close to the bottom of the list. Real juice would be 100% apple, orange, grapefruit, etc., without anything else removed or added. StuRat (talk) 00:30, 18 February 2011 (UTC)

The trick there is that it is 100% real juice with no added sugar and can say so on the ingredients list. At least "fake" juice will get its sweetness from something like aspartame, allowing you to consume whatever nutrients might be present without requiring you to down a whole lot of empty calories. Even something like Kool-Aid might be better since it will at least make you aware of the sugar content you're doling out. A lot of the literature I read when reading up about childhood nutrition suggested always giving the child water (we're talking kids, not babies, obviously), but providing plenty of whole fruit. Real fruit will contain lots of nutrients and fibre not found in juice (however legitimately made it is) and also won't be adulterated: win-win. Matt Deres (talk) 02:04, 18 February 2011 (UTC)

I don't think, at least in the US, such a product could be sold as "100% juice", although it could possibly say "contains 100% juice". The grams of sugar are also listed directly on the product bottle, so it's not difficult to determine how much is present. I tend to agree with you about eating whole fruit versus drinking juice, even for adults, but there are times when juice is far more convenient, such as when driving. I don't agree, however, on artificial sweeteners being healthier than sugars. Sugars, in moderation, can be part of a healthy diet, as our body is designed to process them, while artificial sweeteners can break down into toxic components like formaldehyde. StuRat (talk) 19:57, 18 February 2011 (UTC) StuRat (talk) 19:51, 18 February 2011 (UTC)

Shinkansen

If a shinkansen was heading at 500 miles an hour (which it can't) and another shinkansen was heading in the opposite direction at 500 miles an hour, the relative passing speed would be 1000 miles an hour, would there be a sonic boom? --Perseus8235 18:19, 16 February 2011 (UTC)

It depends how closely they pass. Each train will cause a (subsonic) shock wave, though at 500 mph, this is near the transsonic regime. If the air masses "impact" each other at a relative speed of 1000 mph, a sonic shock will occur; but this would be a really difficult fluid dynamics problem. Transsonic shockwaves are complicated - they behave turbulently, and you're asking about a complicated interaction between two of them. Here are some thorough mathematical treatments: Shock-wave laminar boundary-layer interaction in supercritical transonic flow, (found with a Google Scholar search). Nimur (talk) 18:45, 16 February 2011 (UTC)

If you want a sonic boom, they could meet in a common tunnel, but they would also most likely damage each other. Googlemeister (talk) 19:18, 16 February 2011 (UTC)

If the two shinkansen trains approached each other at the speed of sound, I'd expect each to hear a sonic boom from the other, but no sonic boom to be audible to a stationary observer. Since trains aren't all that loud, relative to airplanes, I'd expect the volume of the sonic boom to be less. StuRat (talk) 18:38, 17 February 2011 (UTC)

Maybe I don't understand how sonic booms work (this is highly probable), but I don't see why the two trains would hear sonic booms from each other, assuming that each train is traveling slightly less than the speed of sound. If a jet flying above the speed of sound flies past a mountain, does the jet hear a sonic boom from the mountain? Maybe the answer is no because the mountain doesn't make noise. In that case my question becomes, if we rig up a big loud speaker system on top of the mountain, does the jet hear a sonic boom then? I would think the answer would be no, since the sound waves from the mountain aren't "piling up" in the atmosphere, so there is no shock wave that the jet passes through. The jet causes a sonic boom to a stationary observer on the mountaintop because it is moving through the atmosphere faster than the speed of sound, not because its relative velocity to the mountain is greater than the speed of sound, right? If my interpretation of the jet/mountain scenario is more or less correct, then I would think that two trains, each moving through the atmosphere slightly less than the speed of sound, would not cause any sonic booms, either to each other or to a stationary observer. —Bkell (talk) 00:12, 18 February 2011 (UTC)

I would think that the jet moving towards a loud mountain (or any loud stationary object) at the speed of sound would, indeed, hear a sonic boom. The reason is that all the sound coming from the mountain would hit the jet at the same time. Of course, it would need to be a heck of a loudspeaker to replicate the volume of a jet, and anyone playing rap music in his car would be proud to blow out his eardrums (and those of all his neighbors) with that. Also note, though, that a jet has quite a bit of sound protection, so the sonic boom may not be audible inside the jet, over the sound of it's own engines, unless the mountain-top loudspeaker was far louder than the jet. StuRat (talk) 00:24, 18 February 2011 (UTC)

"All the sound coming from the mountain would hit the jet at the same time"—no, it wouldn't. The sound would be quite Doppler shifted from the perspective of the jet, so the jet will hear the sound at a higher frequency as the jet approaches the mountain, but the peaks of the sound wave will still be separated in the atmosphere by a distance equal to the wavelength of the sound, so the jet will encounter them one after the other, more rapidly than a stationary observer, but not all at once. Imagine a jet and a mountain initially 1236 km apart (the speed of sound in air is about 1236 km/h). Simultaneously, at noon, the jet begins flying toward the mountain at Mach 1, and a very loud speaker starts blasting a sound wave at the top of the mountain. The jet will meet the first sound waves when it is halfway to the mountain, at half past noon; by the time the jet reaches the mountain an hour after noon, it will have heard all of the sound emitted by the speaker in that hour. So the jet hears the sound at a frequency twice that emitted by the speaker (i.e., the jet hears the sound shifted up an octave). At no point in its flight does the jet suddenly hit a "wall" of all the sound energy emitted by the speaker. (On the other hand, after the jet passes the mountain, it hears no more sound, because the sound waves can't catch up to the jet.) —Bkell (talk) 02:17, 18 February 2011 (UTC)

You're right, but the volume would also increase, in addition to going up in frequency, since it all hits during half the time. If the plane was going mach 10, then 11x as much sound would hit it every second it approached the mountain, at 11x the frequency, and, after it passed, it would hear the sounds backwards, with more recent sounds first, at 9x the normal frequency and volume. StuRat (talk) 19:44, 18 February 2011 (UTC)

Note that the opposite sort of thing happens from the perspective of the mountain. Let's imagine the same scenario, but with an observer on the mountaintop rather than a speaker system. The observer cannot hear the jet approach before it arrives, because the sound waves cannot travel through the atmosphere faster than the jet; when the jet arrives, so does all the sound the jet has been producing for an hour, and the observer hears a sonic boom. In contrast to the jet's approach, as the jet flies away, the observer can hear it; the sound traveling toward the mountain from the jet will be Doppler shifted down an octave, but it will reach the observer's ears. The difference between the jet's perspective and the mountain's perspective is that the jet is traveling at the speed of sound relative to the atmosphere, which is the medium the sound is traveling in, while the mountain is stationary relative to the atmosphere. —Bkell (talk) 02:28, 18 February 2011 (UTC)

Guys, this isn't that strange or unintuitive. A shockwave can interact with a stationary object. At normal speeds, we call that an "echo." At supersonic speeds, things are a little different, because supersonic flow means that air isn't behaving the way it "wants" to (it's outside the regime where simple models of pressure waves and laminar flow can apply). Now, the thing you need to keep in mind is "faster than the speed of sound" is a bit of a laymans-description. A better name would be "faster than the equilibrium speed of sound waves, when behaving as normal, linear, propagating waves." Sound barriers are not hard-limits like the speed of light - air particles can and do move faster than the speed of sound, it's just that when they do, their behaviors and interactions are more complicated. What happens when an object is moving supersonically, or even transsonically, is that the object (let's say, the edge of the metal jet) is slamming in to new air molecules all the time. Normally, when traveling at subsonic speeds, the metal of the jet "nudges" air out of the way, and the air molecules can "nudge" fast enough to push other air molecules away - in other words, "a sound wave." Supersonic velocity means that the air is getting "nudged" faster than it can sustainably communicate the kinetic energy to other air - in other words, the metal of the jet is constantly creating a new disturbance with new air molecules.

Now, when a jet does that at 50,000 feet, far away from anything else, a steady-state equilibrium can be established - a boundary layer of perturbed air, which is called the sonic shock front, takes on a particular shape based on complicated effects of supersonic flow. This represents the capability of the ensemble of air molecules to slam into the jet and (within some characteristic time and length span), convey away the excess energy, eventually decelerating to a sonic speed.

Suppose another object is "in the way" though - in other words, the shock front is perturbed by a mountain, or another jet, or another sonic or supersonic shockwave, then the effect is going to be a nonlinear superposition of the pressure at each point - because supersonic shocks are outside the linear regime where nice, simple models of sound-wave still apply. We'd get something kind of like an "echo", but not quite - because an echo is a linear superposition of an incident wave and its reflection. So, we could solve the resulting airflow numerically, or we could build a test model and experiment in a supersonic wind-tunnel. Or we could go for a literature search, and find a book, like this one: Supersonic flow and shock waves, to learn all about what's going to happen when a flow interacts with an external object. Nimur (talk) 16:24, 18 February 2011 (UTC)

Chemotherapy drug

How many days does the chemotherapeutic drugs stay in your blood? Does the body try to eliminate it right away after being administered? Is there any add-on, so it stays longer (and therefore kills more budding cancer cells)? Quest09 (talk) 19:08, 16 February 2011 (UTC)

-There is no universal answer for this, because not only do people's metabolisms differ, but also each drug used. 65.29.47.55 (talk) 21:12, 16 February 2011 (UTC)

Drugs will usually list a half life for how long they stay in the body. By about 3 to 6 half lives the drug is considered cleared. There are drugs that can interfere with enzymes needed to neutralize certain drugs, but different drugs are neutralized by different enzymes, so there is not one pill that stops all. Some drugs are just excreted unchanged, and don't use enzymes. But taking one of those enzyme blockers can be extremely dangerous! Here's a sampling of some articles that talk about this subject: Grapefruit juice#Drug interactions List of drugs affected by grapefruit Cytochrome P450 (AKA CYP450) CYP3A4 CYP2D6. And here is an example of someone blocking those enzymes to abuse drugs. Ariel. (talk) 23:51, 16 February 2011 (UTC)

Electron Capture

What condition is necessary to have a electron capture by a proton ? In this case could we think that one quark up is changed in a quark down by this electron capture ? — Preceding unsigned comment added by Futurengineer (talk • contribs) 19:09, 16 February 2011 (UTC)

The total energy after has to equal the total energy before, which is usually impossible because the mass of a hydrogen atom (938.8 MeV) is slightly less than the mass of a free neutron (939.6 MeV). You can think of it as an interaction with one of the three quarks, although strictly speaking, in quantum field theory, no interaction is ever that simple. -- BenRG (talk) 23:26, 16 February 2011 (UTC)

To complement what BenRG said above, it is usually impossible but there are situations when it can happen:

1. Inside neutron deficient nuclei.
2. In a collapsing star about to form a neutron star

Dauto (talk)

Don't forget the formation of a neutrino, which affects energy, spin and momentum. Graeme Bartlett (talk) 13:51, 17 February 2011 (UTC)

Hydrocarbon chemistry

What is the opposite of cracking? I am not referring to polymerization where the result is a some huge molecule; I mean something like joining two ethanes to make a butane. Or is this polymerization as well? --T H F S W (T · C · E) 19:20, 16 February 2011 (UTC)

In principle it's just an example of polymerization in which the reaction is controlled to prevent having a third (or subsequent) monomer unit link into the chain. The term "cracking" is commonly a used to identify a processing stage in petroleum refining. See if Oil refinery#Common process units found in a refinery has anything that sounds like what you want with a more specific term? DMacks (talk) 20:47, 16 February 2011 (UTC)

I've seen "condensing" being (ab)used in this sense, but please don't ask me for a cite right now. The term dimerisation is used for the restricted sense of the example - combining two monomers. Roger (talk) 07:50, 17 February 2011 (UTC)

See also Fischer–Tropsch process and Synthetic Liquid Fuels Program. Graeme Bartlett (talk) 08:01, 17 February 2011 (UTC)

Transmission question

how does transmission take place in an axial flow fan having variable blade pitch mechanism? if it is by hydraulic force how the stationary part is connected to rotary part. —Preceding unsigned comment added by 117.201.4.216 (talk) 19:42, 16 February 2011 (UTC)

Your question is unclear. I suggest you look at Axial fans and Gas turbine. Then you should clarify your question. For example, by transmission do you mean transmission of air through a fan; transmission of torque from an electric motor to the blades of a cooling fan; or something else. I doubt there is any axial flow fan that is driven by a hydraulic motor. Dolphin (t) 06:48, 17 February 2011 (UTC)

I found a document Consider Variable Pitch Fans which explains their design. If I understand your question correctly, the stationary part is connected (in the example cited in the paper) to the rotary part via a Rotery Air Joint; see figure 7, and the description on pgaes 2 & 3. Come back for more if you find the paper indigetable; I had to read it a number of times before I grokked it. --Tagishsimon (talk) 13:29, 17 February 2011 (UTC)

Electron Capture and Quark Interaction

Since in normal condition electrons don´t decay in proton direction, what are the special condition to cause a electron in K level be captured by a proton ? In this case can we suppose that a quark up is changed in quark down by this electron capture ? In terms of quark interaction what should ocurr ? — Preceding unsigned comment added by Futurengineer (talk • contribs) 20:17, 16 February 2011 (UTC)

Yes, the up quark turns into a down quark.Dauto (talk) 06:49, 17 February 2011 (UTC)

Top speed of TRA TEMU1000

What is the top speed of the TRA TEMU1000? --Perseus8235 23:18, 16 February 2011 (UTC)

According to our Hitachi A-train article, these Taiwanese trains are based on the Japanese 885 series, which have a maximum speed of only 130 km/h but are good on curvy track because they are capable of tilting. Looie496 (talk) 23:29, 16 February 2011 (UTC)

A Google 3D Warehouse submission gives 150 kph maximum, limited to 130 kph, fwiw. --Tagishsimon (talk) 23:35, 16 February 2011 (UTC)

Adults catch between two to four colds a year and children up to 10 a year????

This statement was made here and I can't believe this. I have had two colds in the last ten years and even people I know who get this a lot more frequently than I don't get this 4 times per year, year after year. When I was a child I got colds more frequently, but surely not ten times per year. Count Iblis (talk) 23:30, 16 February 2011 (UTC)

Our article on the common cold gives the same numbers, with PMID 4014285 as source for the adult figure. It seems a bit high to me too, though -- even though I know a few people who travel a lot who seem to have a cold every time I run into them. Looie496 (talk) 23:34, 16 February 2011 (UTC)

Note their use of the weasel words "up to". My 9-year-old probably gets a half dozen colds on an average a year - two or three in the fall and early winter, two or three in the late winter and spring, maybe one or two more spread out the remainder. Matt Deres (talk) 04:41, 17 February 2011 (UTC)

In my experience, life style has a lot to do with it. People who live and work in buildings that are draught proofed, often overlook the need for getting enough ventilation. This leaves them walking around in an environment with a high virus count. Also, they are unaware of how low the relative humidity can get in heated buildings. This dries out one's nasal airways and eyes, so removing the natural barrier against viruses. As soon as the heating comes on with the approach of winter they all get colds. Tropical fish tanks and house plants can do a lot to offset this but a proper automatic humidifier is worth every cent IMHO. So too is an solid state humidity meter. Later on in the year, if they are not in the habit of spending some time out in the open each day, their body's store of vitamin D can get depleted, leaving them vulnerable to influenza. Breathing cold air also appears to ward off colds. Just travailing to work by motor bike or bicycle seems to give added protection against colds. So, if the OP checks his life style with the people who get frequent colds he might find some differences.--Aspro (talk) 14:35, 17 February 2011 (UTC)

And note that there's a gray area as to when you have, or do not have, "a cold". Probably everyone has a few cold-causing microbes in them all the time, so the question is how many you need to have to be considered to have a cold or "just the sniffles". Confusion with allergies is also common, and could lead to people reporting more colds than they really had. StuRat (talk) 18:26, 17 February 2011 (UTC)

I second StuRat's observation, but in the opposite direction; people with hay fever may not notice a minor cold because they're accustomed to sniffles. Comet Tuttle (talk) 20:58, 17 February 2011 (UTC)

If you live in a small community then you may be exposed to very few new varieties of cold germs every year, and hence already have natural immunisation to most of them. If you meet lots of people in a large cosmopolitan city then you would be exposed to many new varieties of viral infection and hence get lots of colds. Many are transmitted via the hands, so washing hands frequently helps. 92.24.182.65 (talk) 22:03, 17 February 2011 (UTC)

I get why less exposure would lead to fewer colds, but why would it lead to greater immunity ? StuRat (talk) 00:17, 18 February 2011 (UTC)

Because you've already caught and recovered from the particular strains of cold germs that are circulating in your small community in the past, and hence have a natural immunity to them. 92.15.7.1 (talk) 12:56, 18 February 2011 (UTC)

That seems to assume that many strains never make it into the small community at all. I doubt that this is the case, as the small community would need to be almost totally isolated for this to happen. More likely is that each strain does make it there, carried by mail carriers, delivery men, travelers, visitors, etc., although perhaps not as quickly as to large cities. I'm reminded of the horror film Children of the Corn where all the adults, save one, were killed by the kids in a small town, and nobody seemed to notice for 3 years. The people in that town must have had some rather forgiving creditors, among other things: "I see your mortgage payments are now 3 years overdue, this is your final warning !" :-) StuRat (talk) 19:29, 18 February 2011 (UTC)

New strains of viral infections are being created by nature all the time, and spread around the world. So it is true that the strains in a small community are only a fraction of those available worldwide. Didnt you ever read or see the news about for example swine flue or bird flue? Or in the past Spanish flue? Don't they teach biology in American schools? 92.29.119.194 (talk) 00:15, 19 February 2011 (UTC)

Nobody has yet linked to our article on the common cold. It has citations for school children getting up to a dozen colds a year. Matt Deres (talk) 14:17, 18 February 2011 (UTC)

That just reinforces the OP's statement that this claim has been made. They asked why this seems at odds with their experience. StuRat (talk) 20:04, 18 February 2011 (UTC)