Wikipedia:Reference desk/Archives/Science/2010 September 1

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September 1

Temperature and Chemical Equilibrium

What effect does temperature have on chemical equilibrium? ? ---115.178.29.142 (talk) 00:05, 1 September 2010 (UTC)

I'm sorry, we can't answer homework questions: we can, however, point you in the direc tion of our article on Le Chatelier's principle, which might help you with your problem. Physchim62 (talk) 00:15, 1 September 2010 (UTC)

The textbook, with a couple seconds of studying, should magically release the answer. --Chemicalinterest (talk) 00:18, 1 September 2010 (UTC)

As it happens, when we did Le Chatelier's principle at school, we didn't have textbooks. Vimescarrot (talk) 06:41, 1 September 2010 (UTC)

That would just make it more fun because you have to experiment! --Chemicalinterest (talk) 11:02, 1 September 2010 (UTC)

Map of the Celestial Sphere

I'm looking for a decent star map, not to go stargazing with, but more to understand the "geography" of the sky better. I'm not interested in deep space objects, just visible stars. I would like all the constellations labeled (that is, the entire region on space assigned to each constellation demarkated as well). I want the Declinations and Right ascensions labeled at reasonable intervals (every 30 degrees or so, like you see latitude and longitude labeled on a map of Earth). I'd also like the Milky Way shown, and a lines showing the ecliptic and celestial equator. Basically, I want a map of the sky like you'd see a map of the whole Earth (something like the Mollweide projection, I guess). Here's sort of what I want: [1], but I don't really care about the Caldwell objects, and I want a lot more of the stars labeled, and the declinations and right ascensions labeled. I would have thought such a thing would exist on the internet, but I'm having trouble finding something like I want. Does anyone know of anywhere I could find such a thing? Buddy431 (talk) 01:04, 1 September 2010 (UTC)

Celestia is not a "map" as much as a "simulated planetarium." But it has a very nice user-interface; you can stay at Earth and view the sky from Earth, with or without constellations, text labels, and so on (many options are configurable). Celestia also has a very effective 3D mode that allows you to zoom around in space. The novelty of their approach is the "exponential" zooming - so when you get out far from earth, your speed changes to dynamically match the difference in scale-lengths at large astronomical distances, always tuned to be relevant to whichever scale you're viewing at. It's a great way to see the "geography" of space in 3D. Nimur (talk) 01:57, 1 September 2010 (UTC)

Have you looked at Google Sky ? Not sure it has everything you want, but seems to be heading in the same direction. Wikiscient (talk) 04:33, 1 September 2010 (UTC)

It's not online, but the "SC001 Constellation Chart" (supplemented by SC002 and SC003 for the polar regions) seems to be pretty close to what you want and is used in a number of introductory astronomy courses at colleges. The publisher's Web site—the maps in question are the bottom three items on the page—indicates that the maps are certainly cheap, each costing about the same as a plain cup of coffee at Starbucks. Deor (talk) 11:00, 1 September 2010 (UTC)

Addendum: For the constellation boundaries (and for other purposes), Norton's Star Atlas is very useful. Deor (talk) 11:27, 1 September 2010 (UTC)

Thanks. The SCoo1 looks pretty good, I might go ahead and order it. I have Celestia, but I haven't done much with it. It runs pretty sluggishly on my computer. Buddy431 (talk) 23:22, 1 September 2010 (UTC)

Eyesight and social development

Is it possible that poor eyesight can affect a child's social development in areas such as making friends and daily social interactions? If so, is this also true for adults? Is their any documented evidence for this? Thanks. Clover345 (talk) 01:10, 1 September 2010 (UTC)

Children are cruel when it comes to finding weaknesses in others and exploiting them ruthlessly. It would be quite surprising if they did not do so for people with poor eyesight. Did you never hear one child calling another "Four Eyes"? Heck, adults can be pretty cruel too - Dorothy Parker is famous for saying "Men seldom make passes at girls who wear glasses."...how do you think that would affect a typical 13 year old girl? There is plenty of anecdotal evidence (hubpages.com/hub/Eyeglasses-and-Your-Child-How-I-Overcame-the-Four-Eyes-Jokes - for example) - but surely we don't need much to be convinced of the fact. The real question is what the long term impact might be - and that's nowhere near so clear. SteveBaker (talk) 04:13, 1 September 2010 (UTC)

It's possible, sure, but I think it may not be significant - children make fun of -everything- (names, freckles, ginger hair, socio-economic class, gender, those funny pants someone wore one day...), so I imagine it would be difficult to tell the signal for the noise regarding a specific effect that glasses would have. Anecdotally, I started wearing glasses when I was 10-ish, and never really noticed that they impacted my social development (being quiet and reading a lot seemed to have more of an effect). I'd be curious if there are any actual studies on this...Quietmarc (talk) 12:54, 1 September 2010 (UTC)

Speaking as a spectacles wearer since the age of seven, my OR observation is that because spectacles can easily be broken by accidents in physical play and sports (such as a ball striking the head) or by the deliberate violence of bullies, and because this can entail prolonged inconvenience to the victim and expense to their (consequently displeased) parents, children who wear spectacles may tend to shy away from vigorous sports and social interactions, and be more fearful of bullying behavior, leading to a less assured and more introverted personality. It's difficult to tell from the inside if my solitary and bookish nature (snap, Quietmarc!) was a consequence or merely a corollary: I too would be interested in any research in this area. (87.81 posting from . . .) 87.82.229.195 (talk) 13:53, 1 September 2010 (UTC)

That strikes a chord with me too (wearing specs since 5 yrs old). Alansplodge (talk) 17:07, 1 September 2010 (UTC)

I don't think so. In fact I feel more secure since I begun to wear glasses (at about 14), I think girls find me more interesting with glasses on. Many have in fact protested at my idea of contact-lenses.  Jon Ascton  (talk) 17:51, 1 September 2010 (UTC)

How many more anecdotes before we have data? Quietmarc (talk) 15:32, 3 September 2010 (UTC)

This is the first relevant item I was able to find via G**gle. Most scientific studies seem instead to focus not on the personality of spectacles wearers themselves, but on other people's perceptions of them. 87.81.230.195 (talk) 15:12, 5 September 2010 (UTC)

Massive Stars

there are many stars in the galaxy likewise sun is a star a few days before a star named "aura" was discovered which is many times bigger than the sun and also has more mass comparable to sun. how is it possible? because scientists have estimated that any star with greater mass than the sun may not exist. and there are many galaxies in the universe. so is there possibility to have many other stars which are brighter than sun? —Preceding unsigned comment added by Gwen dollen (talk • contribs) 04:35, 1 September 2010 (UTC)

As you can see, the sun is about in the middle of this diagram

See List of most massive stars. You don't mean R136a1?? Wnt (talk) 04:39, 1 September 2010 (UTC)

I have added a new heading for this section. It appeared to be just piggy backed onto the above question. Vespine (talk) 04:57, 1 September 2010 (UTC)

The statement "scientists have estimated that any star with greater mass than the sun may not exist" is wrong. Models place the upper limit for stable stars at well over 100 times the mass of the Sun. --Wrongfilter (talk) 08:53, 1 September 2010 (UTC)

The sun is nowhere near the largest kind of star - in fact (as you can see from the diagram over on the right here), it's somewhere roughly in the middle of the range. Our sun is a very average kind of a star - nothing special at all. About half of the stars out there in our galaxy and in other galaxies that are near enough for us to study are larger than the sun. About half are brighter than the sun. I don't know where you got the idea that scientists don't believe that - but you are most certainly incorrect. SteveBaker (talk) 12:20, 1 September 2010 (UTC)

Aren't most stars red dwarfs? (Otherwise agreeing) Wnt (talk) 21:45, 1 September 2010 (UTC)

Yeah, I have to disagree with Mr. Baker as well. Most stars are actually rather smaller than the sun (see Sun: it's estimated that the sun is larger than 85% of the stars in the Milky Way). It's also the case that most of the stars that we study are at least comparable to the sun, simply for the reason that those are the ones that we can see and study the easiest. However, being in the 85th percentile still leaves a lot of room at the top for some truly massive stars. Our article List of most massive stars lists R136a1 as the largest, at about 250 times the mass of the sun. Interestingly, most of the prominent stars in the sky are decidedly atypical. The 1st and 4th brightest stars, Sirius and Alpha Centauri are comparable in magnitude to the sun, and are bright due to their proximity to Earth. On the other hand, stars like Canopus, Rigel, Betelgeuse, Beta Centauri are a fairly good distance away (over 100 ly), and are just huge, massive stars that put out a lot of light. These types of stars are definately not common, but because they are so visible, they are much better studied and more well known than even a very close, but dim star, like LHS 292. Buddy431 (talk) 23:20, 1 September 2010 (UTC)

Bok choy

Wgat is the Latin name of bok choy? What may choy sum in a receipt referr to? (500 g choy sum, chopped) --Ksanyi (talk) 06:59, 1 September 2010 (UTC)

Bok choy, at least here in NZ, often refers to Chinensis or "Chinese mustard". However, the term in Chinese can also be used for its relative the Napa cabbage. Choy sum literally means "vegetable heart", the tender insides of such veggies. sonia♫ 07:13, 1 September 2010 (UTC)

Just in case Ksanyi fails to follow all the links, we have an article Choy sum. Deor (talk) 10:18, 1 September 2010 (UTC)

Understanding the evolutionary process

I was reading today's article on the Balaur. The dromaeosaurs were around for over 100 million years. It seems to me that there was not much significant change (evolution) in this group considering the very long time they were around. In fact the Age of the Dinosaurs was an extremely long period and while there clearly were many different varieties of dinos, there really does not seem to be any real significant difference in the grand scheme of things. This is in comparrison to the genus homo which has only been around for 2.5 to 3 million years (or, a small per centage of time compared the dinosaurs). So, my question is: why did the dinosaurs not develop (evolve) into a "higher" form (intelligence, technology, etc.) as we humans have in such a fraction of the time we have been around? —Preceding unsigned comment added by 142.46.225.77 (talk) 13:44, 1 September 2010 (UTC)

Well, I think you have to throw out the window the idea that there wasn't much variation in dinosaurs. There was. Plenty. We don't have evidence of all of it, because fossilization is a tricky thing, but we have tons of reason to believe that there was a lot of variation. They evolved to fit into basically every niche, including air and sea. I'm impressed by Archaeopteryx — it seems to me at least as impressive, evolutionarily speaking, as developing a big brain. Perhaps even more so; high intelligence is just scaling up an existing property (plus a little bit more). Feathers? Light bones? Flight? That's some impressive stuff.

As for why didn't dinosaurs evolve higher intelligence and technology — you might as well also ask why no other forms of life except for basically a small subset of primates and maybe Cetaceans evolved very impressive brains, much less technology. Insects have been evolving longer than dinos or mammals, yet they are probably not much more intelligent now than they were 300 million years ago. The reason is quite simple: it's not at all clear that high intelligence is worth the tradeoff. It requires a big brain, which is extremely physiologically taxing. (Human brains account for 2% of our body rate, yet require 15% of our cardiac output, 20% of our total body oxygen consumption, and use 25% of our glucose consumption.[2]) Even for Homo, our big brains didn't lead to total domination for quite awhile. (Note that chimpanzees and bonobos and gorillas, though they have massive brains compared to most of the animal kingdom, are not exactly living high on the hog in the way that even Homo erectus was. They can't just pick up and move to the other side of the Earth if they run out of food in their niche, for example.) High intelligence is one possible way to lead to massive gene flow, but it's not at all the easiest way. Insects do just fine, evolutionarily, without them, on their breed-and-feed model. To use a very bad mode of reasoning, one might suggest that if high intelligence and technology was so obviously beneficial from a gene's eye view, we'd see more than basically one species that had it.

Lastly, you shouldn't see evolution as teleological. It doesn't lead in one direction. It's not like "high intelligence/technology" is the "goal". Evolution has no goal other than gene flow. That's it. High intelligence is a means to that end, as are big horns, the ability to hunt at night, the ability to fly, the ability to blend in with your surroundings. It's certainly the case that with enough high intelligence and technology, one species can basically rule over most others. But even that took hundreds of thousands of years, and by some arguments, we aren't quite as mighty as we think we are. (Insects still probably have us beat, and have laid us low more than a few times in our history.) Humans are the odd, weird case, not the normal case. There's still a lot we don't know about why we evolved the brainpower we did — it is awfully excessive, and goes well beyond what we would need to for basic hunter/gatherer lifestyle. --Mr.98 (talk) 14:38, 1 September 2010 (UTC)

"High intelligence is a means to that end, as are big horns, the ability to hunt at night, the ability to fly, the ability to blend in with your surroundings." Ahh, but high intelligence lets humans have all those abilities through tool use such as, spears, night vision goggles, airplanes, and camouflage. If it gives all of those benefits at once, is it safe to say that we are the first species on this planet to "win" the game? Googlemeister (talk) 15:06, 1 September 2010 (UTC)

We clearly win in an engineering contest, which I think is your point. As far as winning an overall game, well, we're just going to have to wait and see, aren't we? I'm putting my money on the Empire of Bacteria to outlast us and therefore "win" on another set of criteria. Comet Tuttle (talk) 15:51, 1 September 2010 (UTC)

Humans are a species, bacteria are a whole phylum. Googlemeister (talk) 16:19, 1 September 2010 (UTC)

If we're going by species, we're sunk. There are species several orders of magnitude older than us that are still around. We'd have to wait for them to become extinct and -then- start counting down the millions of years before Homo sapiens (or even Homo in general, I guess) is even in the running. Quietmarc (talk) 16:28, 1 September 2010 (UTC)

We only 'win' if we spread farther than the other life. It's entirely possible that we've already accidentally contaminated Mars or Venus, so bacteria may be beating us in that respect as well. APL (talk) 16:44, 1 September 2010 (UTC)

But bacteria wouldn't have been able to get there unless an intelligent technological species evolved to get them there. And chances are, bacteria could survive better on Venus than mammals could, given the surface conditions. So if you choose to consider bacteria and space-faring apes as a sort of single "symbiotic organism" for interplanetary travel, where the bacteria are the "reproductive organ"; and the technological apes' only meaningful function is to propel the reproductive organ forth (by inventing metallurgy and learning fluid-dynamics to build the necessary rockets)... then we can say that Earth Creatures have cooperatively worked together as a single organism to colonize other planets. Once the bacteria establish a foothold, they can proceed, over billions of years, to evolve back in to "higher forms" of life that can re-invent interplanetary travel. I see no reason why this contravenes the established norms for biological classification - it's just a different methodology for defining "species" and "reproduction" that scales to cosmological timescales; individual organisms and in fact entire species become mere sub-components of the larger life-cycle. Various SETI researchers have proposed such schemes, sort of "Gaia hypothesis"-esque. Nimur (talk) 18:32, 1 September 2010 (UTC)

We should remember that the creatures which survived the great Cretaceous extinction are those that were capable of making it through a major disaster, by hibernation or maybe by flying to the other end of the Earth. So the extinction of the dinosaurs made way for a world of species more able to survive change ... I wonder if they are also more able to cause it.

When we look to the evolution of humans, we see 1) two million years of Ice Ages, and 2) the extreme variations of wet and dry near the Okavango Delta, which is (give or take a country or two) the location where modern humans arose. I think it is striking that humans seem particularly capable of moving through muddy terrain, sort of like the lechwe or the famous bipedal Chacma Baboons, and I am inclined to think that many of our species' predecessors originate from the area.

What humans have done with this lineage is to take on an invasive character, equipped with such things as fire and clothing to change the landscape and move beyond traditional boundaries. Perhaps intelligence is the highest elaboration of this invasive program, allowing humans to change the Earth beyond all bounds of ecology. Wnt (talk) 17:59, 1 September 2010 (UTC)

Nobody is arguing that high intelligence doesn't open up a lot of doors, or that humans haven't compensated for our pathetic qualities with technology. But that's probably not why we evolved the intelligence in the first place, in any case. Nor does it necessarily lead to long-lasting gene flow. Since humans invented civilization, they've come close to wiping themselves out a number of times, in a relative blink of an eye compared to the dinosaurs, insects, and so on. There's a very real argument to be made that too much intelligence is a bad thing — if you can make weapons of mass destruction (nuclear weapons, new forms of virulent pathogens, evil nanobots — heck, just excessive carbon output) you run the risk of self-extinction. Cockroaches on the other hand will probably always be here. Anyway, it's food for thought, lest we congratulate ourselves too quickly, ten thousand years of civilization onward. In any case, there is no "winning" in evolution in any strict sense. The last species alive doesn't get a prize. I don't mean to be nihilistic, but there is no reason to evolution from a scientific point of view, it is just something that happens when conditions are right, the same as when a star undergoes fusion when you put enough mass together. --Mr.98 (talk) 22:33, 1 September 2010 (UTC)

I consider our front limbs very, very important in our evolution. 67.243.7.245 (talk) 18:55, 5 September 2010 (UTC)

99942 Apophis side effects

Assuming 99942 Apophis has entered the Earth's vicinity in 2029 or 2036, with a minimum distance separating between the two surfaces of about 1000 km (i.e. height). What could be the expected consequences affecting Earth's parameters like gravity, angular momentum and linear momentum. Do you think there will be some significant changes the we feel them directly (the day length for instance)? I will come back after fasting is over lol.--Email4mobile (talk) 14:34, 1 September 2010 (UTC)

Significant, no. Apophis is far too small to impact the length of the earth's day in any amount that would be noticeable to someone without an atomic clock with micro-second accuracy. Now, if apophis were to impact earth, I suppose that it might alter the length of the day a smidge if it impacted at a shallow angle adding angular momentum to the earth, but in that scenario, a barely shorter or longer day would be of minor consequence what with all the death and destruction. Googlemeister (talk) 15:00, 1 September 2010 (UTC)

Assuming no collision or atmospheric entry, no, there will be no changes in any of the above observable by the unassisted human. However, it is reasonable to suggest that Earth's momentum might be measurably affected -- such things aren't really uncommon (certainly not on astronomic time scales). Earth's gravity won't be affected, as its mass won't change. Even while Apophis passes 1000 km overhead, the effect of the moon's gravity on Earth's surface will remain about 15 million times more powerful than Apophis'. Long story short, unless there's an impact event, there will be no impact (as it were). — Lomn 15:00, 1 September 2010 (UTC)

Apophis is 14 orders of magnitude less massive than the Earth: it will have about the same effect as a single bacterium passing within a foot or so of an average adult human, i.e. none at all. Physchim62 (talk) 15:08, 1 September 2010 (UTC)

I think the poster wants to see the nasty, so here goes:

• Apophis mass = 2.7 x 10^10 kg
• Velocity of impact = 12.59 km/s
• Grazing hit (maximum torque) would be 6371 km
• Angular momentum (scalar magnitude, assuming a strike directly perpendicular to the Earth's axis which probably is a lie) is the product of these 2.7 x 12.59 x 6371 x 10^10 kg = 2.17 x 10^15 kg km^2 /s
• Angular momentum of the earth (calculating a different way, L = I ω, using a moment of inertia formula I found on Yahoo answers which I hope is the right one = 2/5 m r^2 * (2 pi/T)
  • Where m (Earth) = 5.978 ^ 10^24 kg, radius = 6371 km, T = 86400 s (1 day)
  • L = 2/5 * 5.978 ^10^24 kg * 6371 km * 6371 km * 2 * 3.14159 / 86400 = 7.058 * 10^27 kg km^2 /s

• Ratio of the asteroid's angular momentum vs. Earth's = 2.17 x 10^15 / 7.058 * 10^27 = 3.074 * 10^-13

• Thus the loss of time for 1 year = above ratio * 86400*365.25 = ( 31557600 s * 3.074 * 10^-13) = 9.701x10^-6 s

Which is 9.7 microseconds per year. If the asteroid actually strikes the Earth, in the year 100,000 or so they'd have to have to have a leap-second. Wnt (talk) 17:09, 1 September 2010 (UTC)

stellar collision

What would happen if two stars were to "crash" into each other? Would they form a single, larger star, or would it upset the fusion reactions and cause a supernova, or would the stars just pass straight through one another with no major changes or what? Googlemeister (talk) 15:10, 1 September 2010 (UTC)

Apparently one theory is they produce a Blue straggler, ("Astronomers: Star collisions are rampant, catastrophic"). Also see Partial impact theory, which seems poorly referenced (a book from 1901) - 220.101 talk^\Contribs 15:37, 1 September 2010 (UTC)

(ec) We have no Stellar collision article, surprisingly. Our Type Ia supernova article, in the Formation section, says, "Collisions of solitary stars within our galaxy are thought to occur only once every 10⁷–10¹³ years; far less frequently than the appearance of novae", and goes on to say that one "likely" scenario out of the possible scenarios, involving a binary system as one of the colliders, is that you end up with two white dwarfs; it supplies 3 references about stellar collisions. Comet Tuttle (talk) 15:39, 1 September 2010 (UTC)

US penny coin composition

Are US pennies really composed of bronze? My science textbook says that. I always thought that they were zinc with a copper plating (after 197x, of course). --Chemicalinterest (talk) 15:33, 1 September 2010 (UTC)

See Cent (United States coin)#Composition --Tagishsimon (talk) 15:38, 1 September 2010 (UTC)

In short, they were bronze from 1864 or 1865 until 1982. Googlemeister (talk) 15:44, 1 September 2010 (UTC)

QR Codes

Hi, I've been looking into QR codes for a few days (yup, that includes reading the article on Wikipedia). You can use a QR generator to generate a qr code from a url, or text. It reads the url and generates a code designed to direct the follow-up user to that url.

However my question is this (thus?): Could I design the QR code first (perhaps including simple text, only a handful of characters in the design), and then use that QR code to throw up a random url that I could then set up a redirect on?

I hope that made sense... All replies appreciated, cheers Darigan (talk) 15:38, 1 September 2010 (UTC)

Excuse me for repeating your question back at you in my own words, but I think what you're asking is: can the black and white squares which form QR codes be rearranged to appear meaningful or decorative to humans, without the code ceasing to produce some data when given to a computer, and ideally without it ceasing to be valid as a URL (however garbled)? That's an interesting question. I see that under QR_code#Variants there is a mention of a variant called Design QR, which sounds like the sort of thing. 213.122.46.180 (talk) 16:42, 1 September 2010 (UTC)

Unfortunately, it appears like those "open standards documents" at ISO are locked behind a serious paywall. But a site for losers like us without money to waste on every passing thought ([3]) says that the http:/ and www and com and / and such all have to be in the barcode. And remember part of the barcode is an error correction code, which will be whatever it comes out as. Maybe someone with full access to the standard and crunching through a lot of possibilities could come up with something stunning... maybe not. Wnt (talk) 17:31, 1 September 2010 (UTC)

You could try asking Roger who left his email address on Talk:QR Code Nil Einne (talk) 17:49, 1 September 2010 (UTC)

To paraphrase the article and earlier responses: there are some parts of the code that are required - like the version information and the data-timing and data-alignment marks. But the rest is "user-space." If you wanted to draw out a pattern, and then decode it to determine the URL, you could do it. But you can't be completely free-form: your pattern must include the spacers, alignment marks, and timing marks. And if you want to use a URL, you need to prepend your server-address. This would still leave you with a lot of blank space - you could draw your pattern of choice within the blank area; decode the whole thing, and then use that as your URL suffix. Nimur (talk) 19:51, 1 September 2010 (UTC)

Excellent, thanks for all the replies - I had to skip out shortly after posting the query yesterday,apologies for not returning sooner. I'll look in to what you have suggested Nimur - I have come across a BBC QR code that has the logo in a pixelated form at the centre of the code, and a Japanese website that creates QR codes with proper images in the centre on some examples, and other examples that use reversed out colours to suggest images or text. Cheers all, if I come across something interesting on the topic I'll put it on my talk page or in the QR Code article talk. Darigan (talk) 08:49, 2 September 2010 (UTC)

AIDS and stem cells

suppose some researches discover how to grow any body parts they wish from stem cells. Would it be possible to completely fry the immune system of an AIDS sufferer and start again from scratch, or would that be too dangerous?--178.167.247.73 (talk) 16:21, 1 September 2010 (UTC)

Possibly, but we're not a magic ball. We can't really guess what will happen in the future. There are unbelievably plentiful viruses and bacteria in the air to take advantage of a host with no immune system, so such a procedure would have to be conducted in a completely clean room -- something that's pretty difficult to achieve. If you try and remove cells and add new ones simultaneously, there's a chance that the virus would just transfer itself to the newer stem cells once they mature into T helper cells. Regards, --—Cyclonenim | Chat  17:01, 1 September 2010 (UTC)

As I'm sure you know (but probably forgot) the HIV virus also exists in body fluids. So the immune system would have to be knocked out for at least the time it takes for all the viral copies to disintegrate extracellularly. Then there'd have to be a way to, as you say, "completely fry" the immune system. I don't think there's a current method of killing all immune system cells without killing the individual, so it's not just an issue of using stem cells to replace the immune system -- we'd have to find a way to kill off all the white blood cells without utterly destroying the body. DRosenbach ^{(Talk | Contribs)} 17:06, 1 September 2010 (UTC)

You're speaking of a bone marrow transplant for HIV. See e.g. [4]. Wnt (talk) 17:33, 1 September 2010 (UTC)

Unfortunately, this isn't possible with today's technology... using chemical agents or radiation to "fry" the immune system are actually frying quickly dividing cells in general because of the type of DNA damage they cause (which is why they're used to treat cancer). More slowly dividing cells are less affected, though, and tend to survive. Therein lies the problem: even if we eradicate the bone marrow in an HIV+ individual, the virus can persist in long-lived macrophages that have taken up long-term residence in various tissues. Those are an awful lot more difficult to fry... – ClockworkSoul 03:33, 2 September 2010 (UTC)

Well, it may be nice to have a highly compatible and very good friend lacking CCR5 and CXCR4, I would think, or a cell culture seeking to replicate this effect... even so, yes, there are non-lymphocyte targets. Wnt (talk) 02:16, 3 September 2010 (UTC)

"Expiry" Date

What it exactly means ? If expiry date of a pill is Nov 2009 what happens if I eat it ? Will I die or the pill just won't have desired effect ?  Jon Ascton  (talk) 16:24, 1 September 2010 (UTC)

It depends. The active ingredient might have gone so it might not do what it's supposed to. Or it could have become dangerous, making you sick, giving you an alergic reaction or even killing you.--178.167.247.73 (talk) 16:44, 1 September 2010 (UTC)

What will exactly happen in case of Alprex (I hope we are not crossing the dangerline into prohibited field of medical consultation)

I think we are.--178.167.247.73 (talk) 16:55, 1 September 2010 (UTC)

We shouldn't give medical advice, especially when we know full well that no doctor is going to advise patients to take expired pills, even if it's probably just CYA. The problem is, nobody has tested such pills on patients, so what happens is a matter of surmise. Wnt (talk) 17:36, 1 September 2010 (UTC)

As a quibble, I call on your assertion that "no doctor" is going to do this. Consider a situation where over the counter drug X has always had an expiration date of 4 years from manufacture, and then one drug manufacturer contracts the expiration date to 3 years without changing the formulation, and without explanation. Is this for a medical reason, or in order to get consumers to purchase the big bottle of their pills more frequently? I'm not suggesting this is common, but it's easy to envision doctors seeing through such a scheme and advising their patients accordingly. Comet Tuttle (talk) 17:57, 1 September 2010 (UTC)

"No doctor" is doubtless a slight exaggeration, since there's always some exception - but not even Palestinians receiving aid on the Gaza Strip want expired drugs![5]

Actually, Wnt, the US Military tested drug expiration, and found that with optimal storage many drugs last MUCH longer, even a decade longer. Most drugs are given an automatic 1 year expiration, and no one checks them for longer times. Ariel. (talk) 18:36, 1 September 2010 (UTC)

That's the Shelf Life Extension Program (SLEP). We had a question about that back in February: Wikipedia:Reference desk/Archives/Science/2010 February 1#Drug expiration dates. Our article could use some beefing up, however. TenOfAllTrades(talk) 19:00, 1 September 2010 (UTC)

Here is a thread from two months ago answering this question. Comet Tuttle (talk) 17:14, 1 September 2010 (UTC)

In the United States at least, pharmaceutical companies have almost no say in what expiration dates go on pill bottles. Expiration dates are highly regulated by the FDA. The FDA requires analytical studies to evaluate the stability of the active ingredient under a variety of conditions. The time at which the amount of active ingredient falls below a specified percentage determines the expiration date. The statement above "Most drugs are given an automatic 1 year expiration, and no one checks them for longer times" is completely inaccurate. —Preceding unsigned comment added by 148.177.1.210 (talk) 20:21, 1 September 2010 (UTC)

Reference please? Comet Tuttle (talk) 20:56, 1 September 2010 (UTC)

Here is an Inspection Technical Guide: Expiration Dating and Stability Testing for Human Drug Products. The FDA is legally obligated to test drugs intended for human consumption. If a drug has a mislabeled or incorrect expiration date, or otherwise deviates from these guidelines, this consititues "cause to initiate regulatory action against the product and/or the responsible firm." The FDA is not a mindless bureaucracy - they actually do regulate the food and drug industry. Their mandate "...requires that test methods be reliable, meaningful, and specific, section 211.165 (e) gives more guidance by stating that the accuracy, sensitivity, specificity, and reproducibility of test methods employed by the firm shall be established and documented. Section 211.194 (a) (2) further requires that all testing methods used shall be verified under actual conditions of use. Testing procedures must include a stability indicating test which will distinguish the active ingredient from any degradation products and be able to make a reliable estimate of the quantity of any degradate." Nimur (talk) 22:51, 1 September 2010 (UTC)

Well, I'm ignorant of this field, but right after the section you quoted, that page goes on to say "The stability indicating test does not have to be the assay method used to determine product strength", and I don't see anything there stating that the expiration date is determined by the time at which the active ingredient amount falls below some percentage. Your assertion I sort of want to challenge here is that the pharma companies have "almost no say" in expiration dates. Comet Tuttle (talk) 06:33, 2 September 2010 (UTC)

148's explanation is true and applies not just to drugs but to food. That's one of the reasons behind the old stand-up comedian's staple "Why does bottled water have an expiration date"... Arakunem^Talk 14:30, 3 September 2010 (UTC)

Negative Terminal and Earthing

If I take a 3 volt battery and appropriate bulb, dutifully attach the battery positive end to one of bulb's but instead attaching the negative to bulb earth it (bulb's other end). Should not theoretically it light up ? Why not ?  Jon Ascton  (talk)

You connected one terminal of the bulb to battery positive. How did you connect the battery negative terminal to "earth?" Various earth or ground connections can have varying resistances. There might be anywhere from 2 ohms to hundreds of ohms resistance between two wires which are "connected to earth," depending on whether the earth connection is a short wire stuck in the ground a few inches, a 20 foot ground rod driven into moist earth, or a cold water pipe connected to a municipal water system. What is the other terminal of the bulb connected to? Is there a complete circuit? Did you connect the other bulb terminal to "earth," and how? Edison (talk) 17:38, 1 September 2010 (UTC)

I didn't do anything with battery's Negative. Just battery's + is connected to bulb. Bulb's other end is earthed.

Changing the absolute electrical potential of an object doesn't really change it much. In thunderstorms the potential of the ground can shift by tens of thousands of volts (I think), but all you feel are tiny, barely annoying sparks from springs in a bed. Also see earth potential rise. A tiny tiny current flows from battery to ground, then the + side of the battery is a volt and a half less +, and the - side is a volt and a half more -, and then the current stops because the potential is equalized. In theory I suppose you could have a commutator that very rapidly switches from the + side to the minus side of the battery, and harvest these tiny currents as the battery goes up and down a full 3 volts each time, but I have no idea if this is doable in reality.

Bottom line: it takes very little current to make a very large change in voltage, if you don't have a completed circuit. Wnt (talk) 17:46, 1 September 2010 (UTC)

There is no such thing as an absolute electrical potential. Voltage can only be defined with respect to a reference point -- it is always relative. Looie496 (talk) 17:58, 1 September 2010 (UTC)

Well, surely there could be, in theory. There must be some way to measure the average potential of the Earth based on its effect on the charged particles of the solar wind, for example. Wnt (talk) 18:02, 1 September 2010 (UTC)

No, there can't be even in theory. As our electric potential article explains: The potential energy and hence also the electric potential is only defined up to an additive constant: one must arbitrarily choose a position where the potential energy and the electric potential are zero. Looie496 (talk) 19:17, 1 September 2010 (UTC)

I have to concede I was mistaken above - establishing the potential at which the charge on the Earth would be zero does not mean establishing that this is a true absolute zero voltage. For example, even if you pegged Earth to stay uncharged somehow, if you ran a long, conductive, uncharged, insulated cable out into deep space, any charge on the solar wind surrounding the Earth would still create a potential difference.

Even so I am still suspicious that some way to define zero voltage should exist, at least at the cosmological scale, that somehow averages all the positive and negative charges in existence. After all, gravity potentials have an established zero point in uncurved spacetime. In an earlier discussion it was suggested that electromagnetic forces can be modelled as a curvature of space, just like gravity. If so, there should be some point at which space is defined to have zero curvature, just as with gravity - this being the zero voltage. Wnt (talk) 21:32, 1 September 2010 (UTC)

My understanding of absolute potential is the energy required to move a unit charge from infinity to the point in question. Infinity is an unhandy place to connect a test lead however, so potential difference to a more convenient reference is used instead. SpinningSpark 12:08, 2 September 2010 (UTC)

What's going on here is that the concept of voltage being purely relative is very difficult for people to grasp, so teachers have a tendency to try to come up with ways to practically treat it as an absolute. The problem with defining it in terms of "infinity" is that it doesn't approach a fixed limit as you get farther away, it keeps fluctuating every time you hit a galaxy. Mathematically voltage is the antiderivative of the electric field, and as such contains an arbitrary constant of integration. There is no universal rule for setting that constant. Looie496 (talk) 21:15, 2 September 2010 (UTC)

There has to be a complete loop - starting at battery +, through the bulb and back to battery -. A part of that loop can run through the earth - but it still has to be a complete loop. So you have to connect battery - to earth, one side of the bulb to earth and the other side of the bulb to battery +. That's theoretically enough - but in practice, you have to have really good earth connections - especially since your battery is just a few volts. SteveBaker (talk) 18:12, 1 September 2010 (UTC)

I can't find mention of it online, but I've held in hand an outlet tester with a single prong and a small light, which lit up when touched to the live AC wire using only the capacitance/inductance elements contained within a very small plastic shell. Wnt (talk) 18:36, 1 September 2010 (UTC)

Like this? It's a type of Electrical tester pen (see article for several different types and their operating principles. The one I have is all-plastic (no exposed conductor), so perhaps it detects stray voltage? I can actually trigger it even on non-powered circuits by moving it rapidly along certain conductors (stops reporting when I hold it still). DMacks (talk) 18:42, 1 September 2010 (UTC)

Perhaps it is reacting to static electricity? "moving it rapidly along certain conductors" generates the charge which dissipates when you stop? 220.101 talk^\Contribs 22:09, 1 September 2010 (UTC)

That's not the "pen-tester" that Wnt is describing. Wnt's tester consists of a neon lamp is series with a high value resistor. One end is connected to the user via a metal plate in the end of the handle. The lamp is lit when (a small) current flows through the user's body to ground. These devices are dangerous, there is necessarily no isolation from the mains voltage. They are mass produced very cheaply to a low standard. Throw it away. SpinningSpark 12:02, 2 September 2010 (UTC)

DMacks described an all plastic one, and I certainly don't remember a metal plate. If I'd had any notion I was grounding the circuit, it wouldn't have seemed nearly so mysterious to me. I don't remember for sure if I managed to test it while not holding any portion of the plastic at all, however. Wnt (talk) 01:30, 3 September 2010 (UTC)

Keep in mind that alternating current (e.g. from a wall outlet) and direct current (e.g. from a battery) are different. The tester is probably looking at the swing of the voltage, rather than the voltage itself. (For example, inducing a phase shift and comparing the shifted potential to the present potential.) A single probe tester won't work with a constant voltage source. -- 140.142.20.229 (talk) 17:27, 2 September 2010 (UTC)

The preceding comment is basically devoid of meaning or contentconfusing and unclear. Edison (talk) 05:35, 3 September 2010 (UTC)

The first and last sentences of 140.142.20.229's comment are ok but the middle is confusing. Cuddlyable3 (talk) 13:58, 3 September 2010 (UTC)

Also remember that a battery uses a chemical reaction to create an electrical potential energy difference (aka voltage) between the 2 poles of the battery, and not between the + pole and earth (ground) unless the - pole is properly grounded. Arakunem^Talk 14:21, 3 September 2010 (UTC)

Low frequency variation in professional music production?

Why is it that with professionally produced music, the final product seems to have less apparent frequency variation over different mediums (different speakers, headphones,, etc.), whereas in amateur music production there is apparently a much wider variation?

In case that isn't clear, to re-phrase it: Some speakers may have more or less bass or treble. Now, if you listen to a professional production, whether on speakers or headphones, it sounds about the same. If you listen to an amateur production, however, there seem to be a big difference. Aspects of it may sound more or less muffled, tinny, or hissy, depending on the type of speaker. ☯  Zenwhat (talk) 16:51, 1 September 2010 (UTC)

This is probably observer bias. Have you actually quantifiably measured this? No matter what the source - whether it is professionally produced or amateur-recorded music, or even white noise, the speakers will imprint their frequency-response on the signal. Perhaps you can't tell the difference as easily when the music is professionally produced, but it is most certainly still there. If you want to test this, you can mic your speakers (play the same song through two or three different speakers), and run the signal through a software-spectrum-analyzer (like the one in Audacity). It is also plausible that the produced music was tested and specifically tuned up (e.g. by equalizing) so that its perceived sound quality was less susceptible to poor speakers. But the actual frequency response played out definitely depends on physical characteristics of the speaker: the amplifier electronics, the loudspeaker magnet and physical parameters, the cabinet, and so on. Nimur (talk) 19:54, 1 September 2010 (UTC)

I am definitely not an audiophile, so treat this suggestion with due caution. What makes amateur music sound that way (to me) is often the amount of "air" on the recording. We don't seem to have an article under that name, but I'm referring to the echo-y noise that comes from having the mic too far away from the sound source (mouth, guitar, etc.). Higher end systems may be cleaning the sound to reduce that noise, while cheaper systems would not. Since professional music doesn't feature much "air", you'd only notice the difference when listening to amateur recordings. Matt Deres (talk) 20:44, 1 September 2010 (UTC)

Professional recordings can use Dynamic range compression and Equalization to fill the whole available spectrum. This can maximise the impact on the listener, while not over-driving the reproducer, in ways that amateurs recordings cannot. Cuddlyable3 (talk) 13:39, 3 September 2010 (UTC)

I agree that compression together with close miking techniques produce that recorded sound. But its not realistic. Amateurs can achieve compression and equalisation of a music wavform with say Adobe Audition.--88.104.91.35 (talk) 21:57, 4 September 2010 (UTC)

Help identifying a fish

Can anyone help me identifying the fish to the right? I took the photo about a year ago in the local aquarium, when I went there again today, the fish wasn't there anymore so I couldn't find out what species it is. It actually walked around on its leg-like front flippers, I'd love to learn more about this species. -- Ferkelparade π 18:06, 1 September 2010 (UTC)

By sheer coincidence I saw this fish in newspaper the day before yesterday  ! Wait till I find the newspaper  Jon Ascton  (talk) 18:33, 1 September 2010 (UTC)

If you are thinking of this, it doesn't look the same to me. Both have hand-like fins, but that is the limit of the similarity. -- kainaw™ 18:40, 1 September 2010 (UTC)

Looks like a Frogfish, but I am not sure. --Dr Dima (talk) 18:37, 1 September 2010 (UTC)

Or a stonefish. DRosenbach ^{(Talk | Contribs)} 20:07, 1 September 2010 (UTC)

It certainly has the frogfish gist, but there are a lot of species of frogfish, so I'm not sure which it is. --Ludwigs2 01:59, 2 September 2010 (UTC)

Compliments on a good photo. Bus stop (talk) 02:07, 2 September 2010 (UTC)

Thank you - we could use it in an article if we knew for sure what species it is. And thanks to everyone for helping to identify it, from comparing photos it looks like it is some species of frogfish. Fascinating stuff, I had no idea there were so many walking fish species -- Ferkelparade π 12:58, 2 September 2010 (UTC)

Why don't you send an email with the picture to your local aquarium? I'm sure someone there knows what it is/was right down to the species. --Sean 18:15, 2 September 2010 (UTC)

Need medical term

Can't find medical term for a "scratch" caused by a sharp object to, i.e., chin BUT DOES NOT BREAK SKIN but leaves a red mark for a couple or three days. Need a medical term for paper. —Preceding unsigned comment added by 99.38.131.71 (talk) 18:25, 1 September 2010 (UTC)

Scrape, AKA Abrasion. Ariel. (talk) 18:32, 1 September 2010 (UTC)

Abrasion is the common medical term for a scratch on the skin. Most ICD9s related to this use abrasion. Friction burn is often used when a lot of friction is used, but that is not the case here. -- kainaw™ 18:34, 1 September 2010 (UTC)

Triple response of Lewis is an interesting discussion of the progression. DMacks (talk) 18:35, 1 September 2010 (UTC)

That article is a 1-sentence stub, unfortunately, and though the progression is interesting, the discussion of it at that article is not. Comet Tuttle (talk) 20:58, 1 September 2010 (UTC)

I wonder if dermographia is what you are thinking about. Richard Avery (talk) 07:03, 2 September 2010 (UTC)

Gunshots vs. Fireworks

When one hears bangs at night, how do you know for sure that they are gunshots and not firecrackers or the otherwise ?  Jon Ascton  (talk) 18:39, 1 September 2010 (UTC)

You go to the source of the sound and investigate. If you have been around firing ranges, the sound of a firearm is distinctly different than a firecracker. Describing the difference is like trying to describe how a coronet sounds different than a trumpet. Words do not help much. Listening makes it instantly clear. The "kapow" of a firearm is two sounds in one. The "bang" of a firecracker is only one. If it is being fired at you, the sound is even more distinctive. It has a ring to it. -- kainaw™ 18:52, 1 September 2010 (UTC)

Yikes! I'd think being shot vs watching a fireworks display would have a more noticeable difference than "the sound is kind-hard-to-describedly different. DMacks (talk) 18:59, 1 September 2010 (UTC)

What he said. For example the sound of an M-16 is like a kep-owowowow.--178.167.247.73 (talk) 19:17, 1 September 2010 (UTC)

One can find video and audio of various firearms on the internet to get a sense of how gunfire actually sounds. Audio clips would be a good addition to the various firearm articles here on Wikipedia, if somebody could safely set up a sound recording system at a firing range. Nimur (talk) 20:02, 1 September 2010 (UTC)

Though they sound different on an (enclosed) range than they do in the open air. When I worked at Diemaco, for example, I was treated to an extreme version of this when they tested the C3 sniper rifles, which are fired in an extremely narrow range. The sound from each shot bounced back and forth down the tube creating a sound not unlike that made by shaking a musical saw - quite different from what they sound like in the open. Normal small arms aren't affected as much, but echo will still play a big part in the sound. Matt Deres (talk) 20:14, 1 September 2010 (UTC)

Interestingly, it is not possible to faithfully record a gunshot. All you get is klink sound. That's why in movies the sound of firing is added when the film is edited.  Jon Ascton  (talk) 20:11, 1 September 2010 (UTC)

That is sometimes true. Please cite a source when you make claims on the Reference Desk. This article discusses the "microphone shutdown" phenomenon when using a microphone that wasn't designed for the purpose of recording gunshots, but notes the shutdowns were hard for them to duplicate. Comet Tuttle (talk) 21:05, 1 September 2010 (UTC)

That article is also from 1993. Digital audio recording technology has made significant advances since then. Nimur (talk) 23:19, 1 September 2010 (UTC)

Barcodes

What's the purpose of having ridiculous coding methods like Interleaved 2 of 5? What's wrong with binary? --99.237.234.104 (talk) 18:46, 1 September 2010 (UTC)

Error detection in binary isn't as easy as mod 11. Many barcodes use 0-9 and X to create 11 digits. -- kainaw™ 18:57, 1 September 2010 (UTC)

(ec)Apples and pairs. Binary is a counting system. I2/5 is a barcode. I'll hazard a guess, fwiw, that the advantage of I2/5 is efficient use of space. It encodes numbers using the black lines and the spaces between them. If it used only the black lines, then the spaces would be redundant so far as passing number information is concerned, and would serve only as boundaries for the black lines. That being the case, the length of the barcode would have to be longer than would be the case if the white space function as boundaries and pass number information. More generally, there'll tend to be applications for which each "ridiculous coding method" is most appropriate. --Tagishsimon (talk) 19:01, 1 September 2010 (UTC)

I assumed "binary" meant white/black spots as a string of 1/0 bits. Isn't that how QR Code does it? DMacks (talk) 19:08, 1 September 2010 (UTC)

Talking of Barcodes, I too have a question. Generally, or perhaps as a matter of rule, barcodes are black lines, thick and thin, against a while background. Will the barcode work if you change (color-reverse) it i.e. you place white lines on a black background ?  Jon Ascton  (talk) 19:08, 1 September 2010 (UTC)

Doubtful. The standards all require a "quiet area" (blank margin) that would be a "completely not-blank" margin in the negative-image ("all dark" isn't "all light"). Would be easy enough to digitally process such an image, but would have to do so before any attempt at decoding. DMacks (talk) 19:14, 1 September 2010 (UTC)

No. I've tried it myself (I use a barcode printer all the time at work and have played extensively!). I'm sure there's a more technical answer, but it really comes down to this - you wouldn't want your reader to be able do that because it would make it too easy to misread the barcode. When it comes to coded information, failing is much better than misreading. Matt Deres (talk) 20:21, 1 September 2010 (UTC)I've moved my comment to make it clear who I was replying to. Matt Deres (talk) 23:43, 1 September 2010 (UTC)

To Tagishsimon & DMacks: I was thinking that since interleaved 2 of 5 can only represent numbers anyhow, it would be much easier to represent those numbers using binary. DMacks' theme works, but I was thinking of using alternating lines and spaces, with wide lines or wide spaces representing 1 and narrow lines or spaces representing 0. This seems much more intuitive and readable than interleaved 2 of 5. --99.237.234.104 (talk) 19:52, 1 September 2010 (UTC)

That would make a non-uniform width--might be difficult to design forms or other fields to hold that sort of image (11111 would be 2x as wide as 00000) and/or to have users who need to scan them recognize something that isn't a uniform-sized object. You could do it with constant-width "black+white" ("wide-black narrow-white" vs "narrow-black wide-white") but then you're costing 50% of your data density. So heck, why not just use that whitespace for some data instead of just a fixed-width buffer. And then suddenly you're dealing with interleaved patterns:) DMacks (talk) 20:11, 1 September 2010 (UTC)

(ec) Binary might be intuitive, but not easy to design simple and cheap scanner-electronics for (especially because it is not at all resilient to error). These barcodes provide built-in redundancy, error-detection, and easy "start of signal" indications. To give one simplified example: in binary, how do you know when you're reading all zeros, and not just "no signal" ? There is insufficient information density, and so you need metadata or out-of-band signaling to start and stop the message. Barcodes must (by definition) contain this metadata in-line - so they need a more sophisticated coding. 2/5 also guarantees fixed linear length for the code, so it is sort of a monospaced font for numeric coding. Nimur (talk) 20:23, 1 September 2010 (UTC)

Simply put the problem is run length. If you have too many bars in a row the scanner can't read it. The purpose of the codes are to limit the number of identical bars in a row. See Run-length limited for some examples and discussion. Ariel. (talk) 22:24, 1 September 2010 (UTC)

Plane Crash

When an airplane (say Boeing 747) crashes how exactly do people inside it die ? Due to intense heat or the jerk ? Is the death swift or slow and painful ? Are they aware of what is happening to them ?  Jon Ascton  (talk) 18:59, 1 September 2010 (UTC)

^{Note: I placed the same question on this RD a few minutes ago but it mysteriously vanished ! I'd like to know who did that and why ?}

It depends on how it crashes. If it's going fast and crashes on land nearly everyone will die simply from impact. If it's a slow crash landing people who are standing up will die, but people sitting down in the brace position should be fine. If it's somewhere in between different numbers of people will die. Pretty much the same thing goes for water, except more people are likely to die. The materials planes are made from must actually extingiush fires, so they can't catch fire. Aviation fuel, however, can, and as there's so much of it, it can turn a crash site into an inferno and kill people who survive the crash.

If you're sucked out of the plane at altitude you will die of freezing and hypoxia over about 30 seconds. If you are sucked out at a survivable altitude you will probably survive until you hit the ground. If you die on impact it would just be a quick jerk. If you die from smoke inhalation you wouldn't notice you'd just feel sick. Burning would be agony.--178.167.247.73 (talk) 19:14, 1 September 2010 (UTC)

Space exposure suggests 90 seconds for outer space (and mostly due to low pressure, not cooling to due low temperature or due to low-pressure-evaporative effects). Seems like "about 30 seconds" is too short an estimate. DMacks (talk) 19:21, 1 September 2010 (UTC)

178.167, I have some serious doubts about "The materials planes are made from must actually extinguish fires, so they can't catch fire." (my italics) and "If you die from smoke inhalation you wouldn't notice you'd just feel sick" ^{[citation needed]} Planes (an airliner or 747 in the OPs example) tend to burn pretty well actually. It has no doubt improved greatly, in new designs, but there is still material that can burn on possibly the majority of flying planes. Passengers baggage(in-hold and carry-on), clothing and duty free alcohol for example, (perhaps less so now under current 'limited liquid carrying' regulations) polyurethane seat cushions and similar used to be used. Not all planes meet the latest regulations that are required of new aircraft, an old 747 for example could be what 20+ years old? (educated guess! It's 5.30 AM here, have nodded off over keyboard and need to get more sleep so I have limited time to get refs myself), but there was a 'celebrated' case, Saudia Flight 163 of a Lockheed L-1011-200 TriStar, landing in Saudi Arabia in 1980 with a fire on board, "At the time the incident was the second deadliest single aircraft disaster in history". I think the plane was virtually burnt out, article doesn't seem to say. Obviously on that one there was plenty to burn. My readings of descriptions of on board fires refer to extremely thick, choking, and blinding smoke/fumes not something you would not notice! Burning would be agony, but apparently passengers are most often unconcious from inhalation of fumes beforehand (and one would wish so! Sorry for opinionating!) See also: Category: In-flight airliner fires 220.101 talk^\Contribs 20:06, 1 September 2010 (UTC)

You've asked a complicated question that depends on several factors. Do you crash into water? Into concrete? Onto a field? All of those determine the force of the impact and the disintegration of the aircraft. It also depends on the angle of impact (clearly a head-on impact with the ground is more instantly devastating than a slanted one after engines fail!). As for whether death is slow and painful or quick and painless, wouldn't that also depend on the position you're in on the aircraft? I'm afraid this is a question one cannot answer without specifics. Regards, --—Cyclonenim | Chat  19:12, 1 September 2010 (UTC)

You erased your own question here. So, it is up to you to answer "why". -- kainaw™ 19:13, 1 September 2010 (UTC)

No, no, no. That's not it ! That was the "gunshot" question, I deleted it on purpose because it somehow appeared twice. That's not it. What I am talking about is "Airplane crash" question  Jon Ascton  (talk) 19:24, 1 September 2010 (UTC)

The complete history of this page (as with every page) is available for you to browse to see exactly who removed it when--no mystery about it. There are technical glitches we occasionally see where two people posting at nearly identical times results in the second one replacing the first rather than simply compounding the changes, and other things like that. Remember to WP:AGF and see what you can figure out from the history. DMacks (talk) 19:30, 1 September 2010 (UTC)

I like to WP:AAGF better. --Chemicalinterest (talk) 20:07, 1 September 2010 (UTC)

For the main question, our article on aviation accidents and incidents is a good starting point. Fatalities will vary by style of accident -- burning seems reasonable for a ground collision or controlled crash on ground whereas it's less relevant to a midair collision or ocean landing. I expect the primary causes of death are fire, then impact shock while in the aircraft, then free-fall from height. — Lomn 19:16, 1 September 2010 (UTC)

Regarding the missing question, I suggest that in the future you use the "new section" link at the top to add a new question rather than manually editing it into a previous question; that will help prevent such edit conflicts. Of course, it won't prevent you from deleting your own question. — Lomn 19:16, 1 September 2010 (UTC)

How helpful seatbelts really are, about which they are so serious. And why don't they give people parachutes ?  Jon Ascton  (talk) 19:28, 1 September 2010 (UTC)

If you're sitting with your seatbelt on you're almost guarunteed to survive a controlled crash landing. You're also likely to survive other low-angle crashes. If the plane starts tumbling after impact youneed to be strapped in or you will die. Crashes where the plane crashes almost vertically will kill everyone on board though.

And parachutes would be a disaster. Planes fly so high that you would die in that atmosphere. In an accident you couldn't jump to early or you would freeze and suffocate. You couldn't jump too late or you would hit the ground and die. There is only a tiny window, and if the plane is plummting towards the ground nobody is going to be able to jump. In the event of an impact people are far mroe likely to survive strapped in to their seats than standing up waiting to jump.--178.167.247.73 (talk) 19:32, 1 September 2010 (UTC)

We really need a source for this "people would die" thing. HALO jumps are performed from altitudes in line with airliner operating environments. While those personnel use oxygen bottles, it would not be unreasonable for airliners to add those along with parachutes were it otherwise useful. — Lomn 19:39, 1 September 2010 (UTC)

OK so you're sitting in your seat and suddenly the engines fail. How can 300-500 people all get into parachutes, oxygen tanks and thick thermal overalls before the plane impacts? Even if they manage that they won't all be able to get out the doors in time. And if they're caught standing up when the plane hits death is certain. Better to be sitting down strapped in and have some chance.--178.167.247.73 (talk) 19:43, 1 September 2010 (UTC)

That's moving the goalposts. You're claiming that people will die because of the altitude, and DMacks and I have called you on it.

To address the point, though, it appears that rate of decent of an unpowered 747 isn't much different from that of a powered 747. I calculate that you get about 15 minutes of glide time from 35000 feet down to 10000 (that's conservative, as is 10000 for "lowest parachute threshold"). 15 minutes is a plausible amount of time to evac an airplane -- though as noted elsewhere, parachutes are a silly idea for an airliner. — Lomn 20:06, 1 September 2010 (UTC)

It's not moving the goal posts, he's just making an unstated assumption. The point is at those altitudes specialized equipment will be needed. (To say nothing of the specialized training!) His argument is that there would not be sufficient time for hundreds of untrained individuals to put on that equipment, therefore he's assuming that they would have to make the jump with simpler, lower-altitude equipment. If they used that equipment "too early", they'd die. APL (talk) 22:13, 1 September 2010 (UTC)

They're very useful. Perhaps not in a full-on collision with the ground, but it keeps you in your seat during intense turbulence and it keeps you safe during emergency landings. As for parachutes, far too impractical to put on in an emergency situation and if you are unlucky enough to be in a plane that blows up mid-air, then you'll probably die from the fireball or, as mentioned above, from hypoxia/hypothermia. Parachutes won't help there. Regards, --—Cyclonenim | Chat  19:34, 1 September 2010 (UTC)

Seat belts are collectively very effective, particularly for their price and weight. Naturally, they're not Magical Safety Beans that protect from all forms of danger. Mythbusters also tested the brace crash position a few years back and found that it substantially reduced the shock of a crash landing, if I recall correctly. As for parachutes, there are several problems. First, most accidents are at takeoff or landing, where parachutes are useless. Second, airliners aren't built to allow passengers to safely bail out (the D. B. Cooper thing put a stop to that). — Lomn 19:35, 1 September 2010 (UTC)

Parachutes seem like a good idea, but I think weight alone would make them impractical. Likely to render a lot of flying unprofitable without also noticeably raising fares. A person once advocated having the entire passenger cabin seperate from the rest of the aircraft and parachute 'safely' to the ground. This idea has obviously not caught on. 220.101 talk^\Contribs 20:19, 1 September 2010 (UTC)

Reference for "Aircraft Passenger Safety Capsule" [6] - 220.101 talk^\Contribs 20:26, 1 September 2010 (UTC)

Would putting a parachute on the entire fuselage actually be safer than making a controlled emergency-landing? A "parachute" is just a method for controlled descent. So are wings. Airplanes already have those. The problem is what to do when the aircraft's pre-designed, engineered safety systems fail. Nimur (talk) 20:54, 1 September 2010 (UTC)

Nimur, I may be 'misreading' your comments here, but I wasn't advocating the "Aircraft Passenger Safety Capsule" concept. The idea was the parachute/s only attached to the 'capsule' that seperated from the wings, tail, engines etc in an 'emergency', say uncontrolled engine fire. The idea seems unworkable in practice. (& The more I think about it the less practical it gets!) ;-) - 220.101 talk^\Contribs 21:12, 1 September 2010 (UTC)

At least if you're flying in the US, planes crash so rarely that clear air turbulence may be a bigger threat to your life (rarely, people are killed by being tossed around in flight) than any failure of the plane itself. So seatbelts are more useful than a zero-zero ejection seat could possibly be, even ignoring the major safety issues having ejection seats would create. Paul (Stansifer) 16:27, 3 September 2010 (UTC)

The FAA and the NTSB make accident and incident reports available to the public. They collect statistics on all incidents that occur in the United States (or involve American aircraft or American airspace or American passengers - actually, the boundaries of how they cover international incidents are kind of fuzzy). But they make all this data public, including final investigation reports that explain cause of aircraft accident and cause of death if there were fatalities. So if you are curious for a specific aircraft, like the 747, you can find full investigative reports. Wikipedia also has a section on accidents and incidents for the Boeing 747 and a full list of Boeing 747 hull losses (with quick summaries of fatalities and cause of accident). You can use this to guide your search through the FAA's list of specific incident-reports. Every incident is unique; but common causes of death are fires and traumatic impacts, depending on circumstances. For example, China Airlines Flight 611 links to a report that indicates many recovered passengers showed signs of traumatic decompression, serious fractures, and massive impact trauma. TWA Flight 800, which exploded in the air, links to this NTSB report, that states: "Injury and burn patterns to the victims as well as some body locations suggest that there was a severe break up of the passenger cabin early in the crash sequence." They clarify,

“ Although some of the accident airplane occupants may not have received injuries that were instantaneously fatal, all occupants received fatal injuries; therefore, the accident was considered nonsurvivable. Sufficient remains were recovered of 202 of the 230 occupants for investigators to make a determination of the level of severity of the injuries received. The following severity criteria was used: severe trauma was defined as "trauma that resulted in instantaneously fatal injuries"; moderate trauma was defined as "trauma that resulted in fatal injuries that could not be determined with certainty to be instantaneously fatal"; and minimal trauma was defined as "trauma in which fatal injuries were present, but not considered instantaneously fatal." On the basis of these criteria, investigators determined that 183 of the 202 occupants received severe trauma injuries, 15 of the 202 occupants received moderate trauma injuries, and 4 of the 202 occupants received minimal trauma injuries. Occupants identified as receiving minimal trauma injuries were all assigned to seats in zone C of the airplane passenger cabin; two of these four occupants were recovered from the surface of the ocean during the first hours after the accident. ” — NTSB Report

You can follow up as much as you like on similar incidents. Nimur (talk) 20:32, 1 September 2010 (UTC)

Parachutes for airplane passengers is one of those perennial suggestions. The usual cited problems are (a) the weight of all that gear; (b) the impracticality of instructing all the passengers, on every flight, about how to put on the gear; (c) the impracticality of instructing all the passengers, on every flight, on how to properly execute a parachute jump; (d) envisioning what would occur with actually exiting the plane; (e) extensive aircraft redesign necessary (try opening a 747's doors at 30,000 feet. Go ahead, push as hard as you want). If the plane is "at altitude" and is able to fly straight and level enough for people to jump out with a parachute, then the passengers are going to be at less risk if they sit down with their seat belts on and the pilot executes an emergency landing. The Gimli Glider incident at 26,000 feet is the nice example. On the other hand, this company is selling whole-aircraft parachutes for small general aviation aircraft. Comet Tuttle (talk) 21:19, 1 September 2010 (UTC)

Jon: The reason why your question 'disappeared' (it's actually still there) is because you asked it at Wikipedia:Reference desk/Archives/Science/2010 July 1#Plane Crash not here (see [7] for proof). I was looking at the archive earlier today (in fact looking in my browser history only a few minutes after you asked) and noticed your question and was surprised I didn't recognise it and particularly that there was no answer at all, did notice it had been asked just recently until you asked again here. I presume you ended up at the archive from the link above on the expiration of medicines (that was how I did anyway). Nil Einne (talk) 02:23, 2 September 2010 (UTC)

Chromium(III) sulfate

Is it really red-brown crystals? The picture looks like a purple-gray compound. Thank you as I am created an article on simple.wikipedia and wondering whether to include it. --Chemicalinterest (talk) 19:45, 1 September 2010 (UTC)

The red-brown compound is the anhydrous form. Most hydrated forms are deep purple, a clearer purple than the sample in the picture. At a guess, the sample in the picture is already partially dehydrated; I'm not suggesting that the picture uploader made a mistake in the compound. Physchim62 (talk) 02:27, 2 September 2010 (UTC)

knock someone out with a blow to the head

Is it as easy to knock someone out by hitting them on the head as it is shown on TV and in movies? Bubba73 ^{(You talkin' to me?)}, 22:45, 1 September 2010 (UTC)

You could ask someone to try it on you :) --Chemicalinterest (talk) 22:48, 1 September 2010 (UTC)

Yes, but it's very dangerous. Knocking somebody out means inducing a concussion, which is likely to produce headaches, dizziness, and difficulty concentrating for weeks. At worst it can cause a skull fracture, hematoma or cerebral hemmorhage that can be fatal. The TV thing of somebody being knocked out, being out for a while, then staggering to his feet and going about his business, would be quite exceptional. Looie496 (talk) 22:53, 1 September 2010 (UTC)

-EDIT: some answers above were deleted now my post doesn't make sense, this wasn't referring to Looie- That last answer is a bit creepy dude! I think both of those answers are not very appropriate.. I think a more appropriate answer is NO the MOVIES DO NOT REALISTICALLY depict how to knock someone out or what happens to an average person when they are punched or knocked out. There have been several widely reported cases in Australia over the last few years of people DYING from being punched in the head once. David Hookes was probably one of the most publicised ones because he was somewhat of a local celebrity. Vespine (talk) 23:24, 1 September 2010 (UTC)

Yes, I used to watch a movie where people would be knocked out. Then they would just sit up, rub their head a little, and be completely back to normal. --Chemicalinterest (talk) 23:50, 1 September 2010 (UTC)

I agree with Vespine. Movies and comic books convey the impression that a person can be readily rendered unconscious by a single blow with the fist to the chin or the head; and shortly afterwards the person regains consciousness with no side-effects! This impression is entirely unrealistic. A blow from the fist is unlikely to render the victim unconscious, but it is highly likely to leave the victim extremely angry! When a person is rendered unconscious by a blow to the head there is usually some side-effects, and it is not uncommon for there to be long-lasting injury. Dolphin (t) 00:08, 2 September 2010 (UTC)

Good thing we still have the old reliable Vulcan nerve pinch :-) --Trovatore (talk) 00:10, 2 September 2010 (UTC)

Actually, as a child I was knocked unconscious twice, under circumstances that closely resembled the movie scenes (i.e. fallen off sliding board, woke up and felt alright while being carried to the nurse). As a child I also saw an apparent "Vulcan nerve pinch" done (though apparently by pinching either side of the spine, rather than the shoulder) under circumstances where it didn't seem likely to be a practical joke. But I know, this isn't evidence. Wnt (talk) 00:32, 2 September 2010 (UTC)

Thank you for the replies. As I understand it, it would be easy to knock someone out by hitting them in the head with a hard object, but they would not recover as easily as shown in movies/TV. It is not likely to knock someone out by hitting them in the face with a fist. Bubba73 ^{(You talkin' to me?)}, 02:03, 2 September 2010 (UTC)

What you're missing in the summary is that it's not easy to "knock someone out" in such a way that you have any degree of confidence that you won't kill the person. If your main concern is, say, to stop an attacker, in a situation where you can justifiably kill him to stop him from doing whatever he's doing, then it's just a matter of making the blow hard enough. If you put further constraints on it, it's not so straightforward anymore. --Trovatore (talk) 02:09, 2 September 2010 (UTC)

I didn't state it, but I did get the point that it would be easy to knock them out - or worse. Bubba73 ^{(You talkin' to me?)}, 02:14, 2 September 2010 (UTC)

Blows to the back of the head (closer to the brainstem) are more likely to cause unconsciousness (and death). 213.122.36.160 (talk) 06:43, 2 September 2010 (UTC)

Dancer in the Dark

I know this is fictionalized and these disease is just a plot element but are there any real diseases that fit Selma's affliction in the abovementioned film? 76.199.146.176 (talk) 23:56, 1 September 2010 (UTC)

Three that come to mind are retinitis pigmentosa, macular degeneration, and Stargardt disease. --Tagishsimon (talk) 00:06, 2 September 2010 (UTC)