Wikipedia:Reference desk/Archives/Science/2013 January 3

= January 3 =

Hobbitses
This was hatted by Whoop Whoop. I have unhatted it, as while hobbits are indeed fictional characters, such questions are common on Science Desk, and seem a useful way to improve the science knowlege of the OP and others. The discussion on why falling is less haardous for small creatures than it is for large creatures is entirely appropriate on Science Desk Floda 60.228.254.31 (talk) 02:00, 3 January 2013 (UTC)

A hobbit and a lot of dwarves fall a great distance in 3D but don't go splat. Given that Lemmings require parachutes to avoid splatting, but cats always land on their feet, how what properties do hobbitses and dwarves have to be to avoid going splat? — Preceding unsigned comment added by 31.54.80.187 (talk) 22:34, 2 January 2013 (UTC)


 * Being fictional. StuRat (talk) 22:41, 2 January 2013 (UTC)


 * As for what enables some animals to survive falls that kill others, mass is the biggest factor. Insects are light enough that they can gently fall, or might even be blown away in the wind.  Small rodents can fall quite a distance.  Cats and such a bit less.  People, less still.  An elephant might well die just from falling over.


 * Secondary to mass is density. Something light and fluffy won't have as high of a terminal velocity as the same mass jammed into a dense sphere (like a falling balled-up armadillo).


 * Of course having flight surfaces like wings is better yet, but you asked about "falling", and gliding/flying don't really qualify. StuRat (talk) 22:43, 2 January 2013 (UTC)


 * Talking about elephants falling over, in certain parts of Africa the marula tree grows. The fruit ripens, drops on the ground, and ferments.  It appears elephants then find it delicious, eat it and get falling down drunk (as do some other animals).  See http://www.youtube.com/watch?v=EyWd7ozjwbA.  No, they don't die - thats' just some typical off the cuff nonsense from StuRat.  Elephants can fall over for the usual reasons, though being 4-legged, its a lot less likely than it is for a human.  The most common is slipping on mud.  See http://www.youtube.com/watch?v=4ENVL37RjC0.  Wickwack 120.145.8.219 (talk) 00:41, 3 January 2013 (UTC)


 * This site discusses the negatives of using anesthesia in elephants, due to the risk of injury when they fall over: . This site discusses a case where an elephant died as a result of falling into a concrete moat: .  While they attribute the severe injuries to it's attempts to climb out, note their statement that: "Elephants cannot convalesce while sitting or lying down because their weight exerts life-threatening pressure on their lungs".  Thus, even seemingly minor injuries from a fall can become fatal. StuRat (talk) 01:02, 3 January 2013 (UTC)


 * And a typical StuRat comeback seeking to defend an initial error as correct. Your initial post claimed that "an elephant might well die just from falling over", and the context of that post clearly established that you must have meant "from the impact or consequences directly caused by the impact". The references you cited show that elephants are at risk from secondary consequences of unnatural things like falling down man made structures (as it man and just about everything else, and from being unconscious from aneasthesia, as is man and just about everything else.  Humans unconscious are at risk of having breathing blocked off - that's why we are taught in first aid training to put them in the coma position.  The videos I linked clearly show elephants that have fallen over that, once up again, are no worse off for it.  Wickwack 121.221.86.215 (talk) 03:31, 3 January 2013 (UTC)


 * I said "might" die, you apparently think "might" means "must". Read a dictionary, please.  And the difference, as noted in the link I posted, is that elephants can not heal while lying down or sitting, while people can.  You also get something similar with horses, where a broken leg is often fatal, because they can't just lie down until it heals. StuRat (talk) 03:34, 3 January 2013 (UTC)
 * So elephants might die from relatively long term laying down - that's not from the impact of falling over. There is indeed a difference between "might" and "must", but either way you are clearly wrong. There's nothing in what I said that implies "must" anyway.  If you are shot in the chest, you might die directly from that.  But you might not too.  One might say a human might die from sneezing.  A sneeze can initiate a bloody nose, if there is pre-existing or coincident medical condition, it could result in hemorage or infection and death.  But we don't normally go around telling each other sneezing is dangerous.  Wickwack 121.221.86.215 (talk) 03:52, 3 January 2013 (UTC)


 * What do you mean by "Lemmings require parachutes to avoid splatting"? Nyttend (talk) 00:28, 3 January 2013 (UTC)
 * He's referring to an infamous 1950's Walt Disney movie that portrayed lemmings committing suicide en mass by running over a cliff. Lemmings don't do that, but the director thought that the movie was boring and decided to spice it up by having something hidden from camera view throw a large quantity of captured lemmings over the edge.  Wickwack 120.145.8.219 (talk) 00:41, 3 January 2013 (UTC)


 * Lemmings (video game); . -- Finlay McWalterჷTalk 00:44, 3 January 2013 (UTC)


 * Hobbitses have enormous feet that distribute the impact over a greater surface area (and also provide extra drag on the way down). Dwarves are just really tough, the Chuck Norrises of Middle Earth. Clarityfiend (talk) 01:06, 3 January 2013 (UTC)


 * As far as I can recall, the movie showed the falling characters either landing on something somewhat soft, or hitting multiple surfaces on the way down, so no one fall was all that long. Videos of skiers doing that sort of thing while falling down frightfully steep slopes and living to tell about it suggests the movie isn't as much of an exaggeration as it might at first appear. Jc3s5h (talk) 01:13, 3 January 2013 (UTC)


 * Sounds fair. I saw the movie once when it was on TV but it was quite a while ago. According to the Wiki article, the voice over said that the leemings were jumping into the sea and were expecting to swim across, and would socumb to exhaustion and drown.  However, the movie scene was faked, and it became infamous because it was faked, and the incorrect concept of lemmings committing suicide has entered our culture.  Wickwack 60.230.235.129 (talk) 01:26, 3 January 2013 (UTC)


 * Are you sure that myth didn't predate the movie ? StuRat (talk) 02:08, 3 January 2013 (UTC)
 * It could have. One of the references linked in the Wiki articles on lemmings sort of vaguely implies that the Disney people confused suicidal behavior with mass movement from one teritory to another, crossing streams where necessary, which is what some sorts of lemmings actually do.  I recall seeing a TV documentary on animal movie fakery tracing the myth origin to the Disney film, but I cannot recall who made the documentary, and such documentaries are hardly 100% trustworthy anyway.  A number of written sources which I don't have to hand right now said that Disney's delibrately spiced up the movie in this way - it is unfortunatly consistent with what Disney did in the 1950's - such as contriving fights between animals that don't even live in the same regions.  Wickwack 121.221.86.215 (talk) 02:56, 3 January 2013 (UTC)

Whoop was right to hat this. μηδείς (talk) 03:25, 3 January 2013 (UTC)

Name that fish part 2: Green-eyed monster
Still sorting my vacation photos. Seen on a reef, close offshore in Cuba. This time around, I have no idea what this fish is. As before, once identified feel free to add to any articles that might need it. Thanks, KevinHadley (talk) 02:31, 3 January 2013 (UTC)


 * Grouper ? StuRat (talk) 02:33, 3 January 2013 (UTC)


 * Shape looks like a Tetraodontidae or Pufferfish. No idea which species.  -- Jayron  32  02:34, 3 January 2013 (UTC)


 * Although very difficult to see, this fish does appear to have spines and its markings are very similar to this fish which is a Diodon and of the five species listed, the Long-spine porcupinefish is the closest match. Modocc (talk) 05:27, 3 January 2013 (UTC)


 * Thanks to Jayron32 and Modocc. That image does indeed look like...well, a spitting image of my fish.  Looks like the Wikipedia article already has a better image, but I'm still quite pleased to have seen one in the wild.  Cheers! KevinHadley (talk) 00:10, 4 January 2013 (UTC)


 * May we mark this resolved ? StuRat (talk) 00:39, 4 January 2013 (UTC)

Name that flower
Okay, this is the last one for today, I promise.

This photo was taken in mid-October, in Ontario, Canada, about 100 km north of Toronto. Genus? Species? KevinHadley (talk) 02:42, 3 January 2013 (UTC)


 * Chicory? -- Jayron  32  02:45, 3 January 2013 (UTC)


 * Agreed, although this pic is somewhat unusual in that the outer edge of each petal seems to have curled back on itself. StuRat (talk) 03:11, 3 January 2013 (UTC)


 * There are several different varieties of chicory/endive with slightly different shapes and colors to the petals, but they all look broadly like this. this search should be convincing enough that the flower is chicory.  Several have petals that look like the above. -- Jayron  32  04:07, 3 January 2013 (UTC)


 * My immediate thought there is that the particular flower is on the last legs of it's flower-ness, probably a couple hours (iirc as to how long chicory flowers last) before it starts to look like it's dying. Lsfreak (talk) 03:24, 3 January 2013 (UTC)


 * Ah, thanks, Lsfreak (and again to Jayron32). If the curly petals are a sign of a dying flower, then I shan't go shopping for an article for these.  They have artistic value, but probably aren't all that educational. KevinHadley (talk) 00:12, 4 January 2013 (UTC)


 * It might still be useful. The way in which flowers wilt is also helpful for identification, after all. In any event, can we mark this resolved ?  StuRat (talk) 00:34, 4 January 2013 (UTC)

Galvanic action between stainless steel pot and aluminum lid
Is there much worry about corrosion there, if they are only in contact while I'm cooking ? StuRat (talk) 02:56, 3 January 2013 (UTC)


 * No. 24.23.196.85 (talk) 02:59, 3 January 2013 (UTC)


 * I try to avoid mixing aluminum and stainless steel when I can; I've ruined quite a number of aluminum utensils and pots when I carelessly rested them against something stainless steel in the dishwasher, for example. You may be OK, but anything either particularly acidic or basic could create an environment that cause galvanic corrosion of the aluminum lid, which can lead to a nasty grey film which never seems to go away.  -- Jayron  32  04:03, 3 January 2013 (UTC)


 * I'm not as concerned about the aluminum lid as the stainless steel pot. Will it be OK ? StuRat (talk) 06:24, 3 January 2013 (UTC)


 * Yup. Aluminum is a more active metal than iron (see Standard electrode potential (data page), and note that the Al3+ + 3 e− -> Al is much more negative than the Fe2+ + 2 e−  -> Fe) so when in contact aluminum acts as a Sacrificial metal when conditions exist that would normally cause steel to rust.  Your steel pot should do nothing at all.  Your aluminum lid, is iffy.  -- Jayron  32  07:12, 3 January 2013 (UTC)


 * OK, excellent. The lid is old and already looks ugly, while the pot is shiny and new, and I want to keep it looking good.  I will mark this Q resolved. StuRat (talk) 18:36, 3 January 2013 (UTC)

Why do you get x2 times the kinetic energy from x times the joules?
That doesn't seem right to me.

Seems like the universe just enjoys explosions and doesn't like high-speed rail. Sagittarian Milky Way (talk) 04:28, 3 January 2013 (UTC)
 * What? What makes you think "you get x2 times the kinetic energy" from "x times the Joules"? Work-energy (ΔK=W) says X J of work (if that's what you mean) can be used to impart X J of kinetic energy, not X2. 72.128.82.131 (talk) 05:33, 3 January 2013 (UTC)


 * You use 1 joule of energy to move a stationary kilogram in space, you get 1 m/s, for a kinetic energy of 0.5(12). You use 10 times more joules to move another kg, you get 10 m/s for a kinetic energy of 0.5(102), which does 100 times more damage then the first kilo when it hits something, but is only 10 times harder to stop (by applying 10 joules in the opposite direction). Sagittarian Milky Way (talk) 06:01, 3 January 2013 (UTC)


 * Your premise is false. You use 100 times more joules (energy) to accelerate 1 kg from 0 to 10 m/s as from 0 to 1 m/s. The energy you put in is equal to the final kinetic energy. — Quondum 06:12, 3 January 2013 (UTC)


 * No SMW, you've confused something horribly. KE = 1/2 m * v2.  If you use 1 joule to move 1 kilogram, it moves at a speed of 1.414 m/s √(1/0.5).  If you use 10 joules to move 1 kg, it moves at a speed of 4.47 m/s √(10/0.5).  I'm not sure what math you're doing, but it is a mess. -- Jayron  32  06:15, 3 January 2013 (UTC)


 * You appear to be confusing "Joules" with velocity, because it is indeed correct that you must do x2 times the work to accelerate an object to x times the velocity, starting from rest. The joule is the unit of kinetic energy, however, so I don't believe your question makes sense.--Jasper Deng (talk) 06:52, 3 January 2013 (UTC)


 * Forget the x squared, horrible brain fart on my part. Why should a falling object gain 0.5 kinetic energy (0 to 0.5) the first unit of time and 1.5 the next (0.5-2) when the force on it is the same (well an infintesimal amount more from getting closer to the center of the Earth)? Okay, that's just the way the universe is. It makes punches and car accidents many more times more serious than if it was KE=mv, but there doesn't seem to be an elegant reason for why it's this way. Sagittarian Milky Way (talk) 07:04, 3 January 2013 (UTC)


 * As far as energy and gravitation, (i.e. falling objects), see Equivalence principle. The acceleration of an object doesn't matter whether it is caused by gravity or by a giant jet engine.  Acceleration is acceleration.  Also, (at non-relativistic speeds), a force continually increases the amount of kinetic energy an object has, this is fundemental, first semester physics stuff.  It doesn't matter whether the force is gravity or the force is a jet engine, applied force increases energy, work = force x distance: the longer distance you apply a force, the more kinetic energy you impart on the object.  -- Jayron  32  06:56, 3 January 2013 (UTC)
 * I think what he means is that K=(1/2)mv^2=(1/2)m(at)^2, and then dK/dt=mta^2. However something must be wrong with that math because a constant conservative force must do work at a constant rate as you say and I know.--Jasper Deng (talk) 07:06, 3 January 2013 (UTC)
 * Yeah, my calculus is 20 years old, so I'm not sure I can check you on that, but logically a joule is a kilogram ⋅ meter2 ⋅ second-2 while a newton is a kilogram ⋅ meter ⋅ second-2. They're both second order in time, so over time added force should create a linear response in energy.  Doubling the applied force should cause a doubling of dK/dt.  That's right, isn't it, logically speaking?  -- Jayron  32  07:18, 3 January 2013 (UTC)
 * OK, I now see what's going on. The derivative (i.e. rate of change) of kinetic energy with respect to displacement is constant for a constant force. However, the derivative with respect to time is directly proportional to time. This is actually because although the power (rate of change of kinetic energy w/ respect to time) increases, that is because the force must do the same amount of work over the same distance but in correspondingly less time. --Jasper Deng (talk) 07:23, 3 January 2013 (UTC)
 * ...which is a direct consequence of the fact that the integral of a linear function is a quadratic function. So, if a force is constant, then the integral of force over distance is linearly increasing; and because force induces acceleration according to a law of constant proportionality (at least, to a very good approximation in many cases), the increasing velocity is the solution to a second-order integral of a constant function.  When formulated this way, it is almost self-evident that the parabola should show up so many places in nature: it's among the most simple consequences of the application of mathematical law to the most extremely simple of all natural phenomena.  This is discussed at great length in Isaac Newton's work on the mathematical principals of nature.  We can thoroughly understand how a double-integral of a constant function yields a parabola.  We can show how a constant function well-approximates the force due to gravitation, at least over a short distance near the Earth's surface.  And therefore, we can show how a simple set of rules leads to a squared term with respect to velocity.  If you wish to know why these things are so, neither I nor Sir Isaac frame any hypotheses.  Nimur (talk) 08:25, 3 January 2013 (UTC)

Facial recognition after many years
When I watched the CSI episode "Living Legend," something in that episode puzzled me: Catherine Willows had a chance encounter with Mickey Dunn when she was 16, but the two would not see each other again for another 30 years, when Dunn is arrested after returning to Las Vegas. In the interrogation room, as Willows started to head out after making a brief reference to her earlier encounter with Dunn, Dunn immediately identified her as "Sam Braun's daughter," and stated "You think that I would ever forget a face? That face?" Does this make scientific sense? Is it really possible for someone to recognize a person by their face at age 46 based on a chance encounter with that person at age 16 (and no previous or further encounters), or is this a bit too exaggerated? 24.47.141.254 (talk) 06:04, 3 January 2013 (UTC)


 * I think the specific "chance encounter" would have to be clarified, as some chance encounters would leave lasting memories while other chance encounters would not leave lasting memories. Bus stop (talk) 06:07, 3 January 2013 (UTC)


 * I suspect that people's ability to recognize faces varies dramatically. So, while most people probably couldn't do that, maybe some can. StuRat (talk) 06:22, 3 January 2013 (UTC)


 * This is my reaction as well. Facial change from 16 to 46 is not always dramatic, meaning that many people should be able to recognise someone they knew from the earlier age, especially if they've aged less than most. I have known some people to recognise people under far worse conditions. There are many cues aside from simple facial recognition that people use, including facial expressions, mannerisms, speech characteristics, body movement, etc. It takes one atypical gesture to bring back a memory of someone who previously used that gesture. Add to that a person with an exceptional memory and ability to pattern match from the cues, who might have been struck by the person at the time and thus observed and memorised them more acutely than they were admitting to, and this is not implausible in a plot. I routinely see strategems used by TV serial scriptwriters that I find far less plausible than the one you describe. — Quondum 08:38, 3 January 2013 (UTC)
 * It's possible if you combine little change in one person with good memory in the other. Some years ago, I was at a store with my mother when someone began calling her by her maiden name — it was a high school classmate, and they'd not seen each other since they were slightly older than 16; at this time they were about 46 or slightly older.  Nyttend (talk) 15:03, 3 January 2013 (UTC)


 * Purely anecdotal evidence, but I attended a junior school reunion a couple of years ago. Many of us had not seen each other since the age of 11 and were instantly recognisable. Others had changed beyond recognition and had to to tell us their names. Alansplodge (talk) 18:10, 3 January 2013 (UTC)


 * Also, since girls mature faster, the chances of recognizing a woman at 46 you hadn't seen in 30 years are probably better than for a man, since males still tend to change appearance quite a bit after age 16, before stabilizing into their adult look. However, more women change their looks intentionally, by changing hair color and style and having nose jobs, etc. StuRat (talk) 18:32, 3 January 2013 (UTC)

Taj Mahal question
two ways of protecting the tajmahal from air pollution. — Preceding unsigned comment added by 78.101.62.16 (talk) 06:33, 3 January 2013 (UTC)


 * Maybe you could do what looks like your own homework by looking up what forms of pollution cause damage to marble and how their impacts can be minimised. HiLo48 (talk) 07:28, 3 January 2013 (UTC)


 * 1) Seal it in a large hermetically sealed crypt.
 * 2) Transport it to the moon, where there is no pollution.
 * Hope this gives you some ideas. — Preceding unsigned comment added by 217.158.236.14 (talk) 08:58, 3 January 2013 (UTC)


 * I'm not sure that the second solution would work - if the Taj Mahal were on the moon, wouldn't it end up pock-marked with moon craters of various sizes faster than it would on the Earth, due to lack of atmosphere there? --Demiurge1000 (talk) 19:16, 3 January 2013 (UTC)
 * Yes, but it's not as fast as you might think. Many of the tiny craters on the Moon are millions of years old.  With no erosion, they stick around for a long time. StuRat (talk) 00:45, 4 January 2013 (UTC)
 * (ec) Sure, it would end up eroded by meteor impacts faster than it would on Earth&mdash;but 'faster' isn't he same as 'fast'. I do wonder what the time scale of that erosion actually is, and how it compares to the effects of air pollution (or, for that matter, plain old erosion by wind and rain) on Earth. This paper estimates that there would be a bit less than one new one-millimeter crater formed per square meter of exposed surface, per decade.  Sure, one could get really unlucky and catch a larger rock that destroyed the whole building, but the odds are very much against it. TenOfAllTrades(talk) 01:00, 4 January 2013 (UTC)


 * Since this does sound a lot like a homework question - I'm not going to give you the answer directly - but instead offer some help in finding the answer yourself. This is an interesting question, not because the answer is interesting - but because of what you have to learn in order to find possible answers.
 * For that reason, you need to read the following articles: Taj Mahal (specifically, the section: Taj_mahal) and also White marble (which is what the Taj is mostly made from). Then look at Acid rain - and follow links from the White marble article to calcium carbonate and calcium magnesium carbonate (constituents of white marble).  Pay special attention to calcium carbonate where it discusses what happens when acid meets up with it.  Taj_mahal also mentions the Mathura Refinery - and reading that will tell you much more about where the acid rain is coming from and why it's about to get a whole lot worse if someone doesn't intervene to prevent that.
 * Then, the other problem described in Taj_mahal relates to the water levels in the Yamuna river - so read that article to figure out why the level of water in that river is dropping so rapidly. Ask yourself where the water is going.  Is it being consumed, dammed or diverted somewhere up-stream from the Taj - or is the flow rate of the river being reduced because of less rainfall - could it be that climate change is involved here?  Maybe there is more than one reason.
 * Once you understand the reasons why the Taj Mahal is in so much trouble - you should think carefully about whether it would be possible to add protection to it (Could you coat the marble with something to keep out the acid rain and do something shore up the disintegrating foundations?) or whether you could reduce the problems that beset it (Cut out some of the pollution and solve the problems of the Yamuna river?)...which will lead you to more interesting articles in the largest repository of all human knowledge...Wikipedia. That should give you at least two possible ways to save the building.
 * Having read all of those things in order to provide you with the articles that will answer your question, I don't think things will end up well for the Taj Mahal. However, India should realize that it's like the canary in a coal mine - the Taj is only the most publicly and internationally noticeable symptom of the general state of environmental problems there.  If you can't save something as important artistically, culturally (and tourism dollar raising!) as the Taj Mahal - how can you possibly hope to keep a reasonable standard of air and water quality elsewhere in the country?
 * SteveBaker (talk) 14:04, 3 January 2013 (UTC)


 * Shrink wrap. ←Baseball Bugs What's up, Doc? carrots→ 00:41, 4 January 2013 (UTC)


 * Give Christo a call. --   Jack of Oz   [Talk]  00:47, 4 January 2013 (UTC)


 * Human extinction. - ¡Ouch! (hurt me / more pain) 18:14, 5 January 2013 (UTC)

Clean big city water supplies
I live on the outskirts of Melbourne, Australia, a city with over 4 million residents. Yesterday I went up into the nearby mountains where a lot of the city's water catchments are, and saw some of the signs I've been seeing all my life telling me that (as our supplier's website tells me)...


 * Melbourne has some of the cleanest drinking water in the world. What falls in the water catchments is pretty close to what comes out of our taps.


 * Any activities which could contaminate or pollute the water are not allowed in our catchments and reservoirs....

This is all very nice, and it's true that the catchments are pretty well locked up, but it got me wondering. Is the claim of "some of the cleanest drinking water in the world" a valid one? Has anyone really done the comparison? Who else has got clean water? HiLo48 (talk) 07:24, 3 January 2013 (UTC)


 * New York City. --NorwegianBluetalk 14:53, 3 January 2013 (UTC)


 * But its all based on weasel words, "some of the cleanest...", "world class", what do they mean, on which scale (not the lime scale!), compared to what. If any editor included those phrases without a ref in WP they would get a warning template muy pronto. Advertising bull***t. Richard Avery (talk) 15:35, 3 January 2013 (UTC)


 * Not necessarily cleanest but they have contests for best-tasting tap water: Rmhermen (talk) 16:01, 3 January 2013 (UTC)


 * Australia, being rather isolated geographically, is far from most of the world's sources of particulate air pollution (especially in the prevailing wind direction). So, in that sense, the rainwater there is likely relatively clean.  Places with cleaner precipitation, like the South Pole, don't collect it on a large scale like that. StuRat (talk) 18:26, 3 January 2013 (UTC)


 * Australian cities do not in general have particularly good water supplies, by Western standards. One never hears much about water quality in Melbourne, but Sydney has over recent years often been in the news media due to unacceptable water quality.  StuRat is correct in his point about pollution, but he has overlooked that Australia is a dry country forcing us to use water sources that other countries would avoid.  (Most locations have water rationing - by law I can only water my garden in twilight hours on Wednesdays and Saturdays.) Perth gets up to 30% or so of it's water from underground resevours - this water requires considerable treatment to get it drinkable, and as delivered at your tap, is not particularly good.  Some Australian cities are in the next few years are going to begin recycling sewage water into drinking water supplies as that is the only water they can meet the needs of a growing population at low cost - the risks are hard to quantify and probably significant, but they are going to do it anyway.  Sea water desalination has been implemented, but it just too darn expensive in energy requirements and the saline discharge adversely affects marine life, forcing shutdowns.  The West Aust State Health department some years ago put out a pamphlet encouraging rainwater tanks for better health, but as the Water Authority is another State Govt body, a bun fight ensued and the Health Dept got told to pull their head in.
 * We look with envy at water qunatity and quality in the USA. The USA uses ultraviolet treatment to kill microbes. As far as I know, this is not done in Australia for municipal water for houses etc, its only used in the better private hospitals.
 * The New York pamphlet provided by NorwegionBlue is actually very good. The claim about weasel words is not relavent because in the last page it has a detailed technical analysis.  What we need is someone to post similar analysises for Australia and other countries.
 * Wickwack 60.230.194.70 (talk) 00:05, 4 January 2013 (UTC)


 * With regards to the USA and ultraviolet, the USA has thousands of water districts and millions of private wells, so any treatment you can think of is probably used somewhere. Chlorination is the most popular antimicrobial treatment, simply because it has the longest history and is best-understood, but you can also find public water supplies that use ultraviolet, ozone, micropore filters, or even no treatment at all (deep aquifers often have no dangerous microbes in them). --Carnildo (talk) 02:09, 4 January 2013 (UTC)


 * Have done some digging. Water suppliers in Australia are supposed to comply with Australian Drinking Water Guidelines (ADWG) 2004 - a national standard.  There is an exemption granting process for where it is considered not realistic or necessary to meet the guidelines.  For example, supply to a number of towns in Western Australia have been granted exemptions, and in these cases the water is considered acceptable for adults but is not safe for infants. I have reviewed the fine print in the service contract for my water supply (from the WA Water Corporation - a Govt owned organisation) and it specifically states that while the Water Corporation treats its water to ensure it meets health and quality guidelines, the householder is responsible for ensuring that water he/they consume is of what is deemed adequate quality.  In other words, worse than weasel words - if you get sick from the water, its' your problem.  There is a large quantity of info at http://watercorporation.com.au/P/publications_water_quality.cfm.  Wickwack 58.170.170.50 (talk) 02:58, 5 January 2013 (UTC)

Why doesn't color-safe bleach (or bleach in general) oxidize the material of cotton clothes ?
Cellulose, a component of cotton, seems vulnerable to oxidation because of the presence of activating hydroxyl groups. Does the polymer nature of cellulose sterically hinder the oxidation of cellulose by hydrogen peroxide or sodium hypochlorite? 72.229.155.79 (talk) 08:46, 3 January 2013 (UTC)
 * The C-OH like you find it in methanol H3C-OH is very stable and neither hydrogen peroxide or sodium hypochlorite can oxidize it at room temperature. The aldehyd group is much more reactive against oxidation and would react quickly, but all relevant CHO groups are bound to the next glucose unit in the cellulose chain. The good thing with dye on cellulose is that the fibre is hard to penetrate and the OH groups make it hard for the more hydrophobe groups to attach. So the dye is easy to reach for the bleach and the bleaching is over before the cellulose is attacked. --Stone (talk) 11:18, 3 January 2013 (UTC)

Solving linear equation
Given a set of linear equation AX=B, say A is an ill posed matrix (has a few singular value equal very close to zero), which numerical algorithm (conjugate gradient, least squared or steepest decent etc )  should be used to obtain the best solution? More specifically, is there a concrete comparison between these methods? — Preceding unsigned comment added by 210.212.187.69 (talk) 09:06, 3 January 2013 (UTC)
 * The Mathematics desk is this way... Roger (talk) 11:15, 3 January 2013 (UTC)

Inhaling baby powder
What happends if you inhale babby powder? — Preceding unsigned comment added by 120.148.21.19 (talk) 13:35, 3 January 2013 (UTC)
 * We can't give medical advice. If you are concerned, contact a physician or a poison control center. In the US the number is 1-800-222-1222. 209.131.76.183 (talk) 13:40, 3 January 2013 (UTC)

what happends if you inhale babby powder? — Preceding unsigned comment added by 120.148.21.19 (talk) 13:43, 3 January 2013 (UTC)
 * I see what you did there. I think the answer depends on how the babby powder formed. AlexTiefling (talk) 14:18, 3 January 2013 (UTC)


 * Are you the one who asked "how a babby is formed?" a few weeks ago? If so, please stop with this tired meme. We aren't interested. If you are serious, ring the number listed above. — Preceding unsigned comment added by 217.158.236.14 (talk) 14:48, 3 January 2013 (UTC)


 * (WP:AGF) Our article Baby powder explains this, right there in the first paragraph: "Talcum powder is harmful if inhaled since it may cause aspiration pneumonia or granuloma." Only some brands are made from talcum powder - others use cornstarch precisely to avoid this inhalation problem.  It also explains that "Drugs such as cocaine are sometimes cut with talcum powder." - which is presumably why inhalation is such a big concern. SteveBaker (talk) 14:52, 3 January 2013 (UTC)


 * Note the chemical similarity between talc and certain types of asbestos. As explained in the article, talc is not widely believed to be a carcinogen when it is free of asbestos-like fibers.  But how sure are you that anyone ever really checked the talc in your bottle is free of those?  Note also that talc can be free of "asbestos" fibers but contain "transitional" asbestos-like fibers that do not violate regulations but whose safety is not so clear.  Wnt (talk) 15:13, 3 January 2013 (UTC)


 * I suspected trolling when I saw the babby spelling, but I figured it was simple enough to brush it off with a mention of no medical advice. 209.131.76.183 (talk) 15:24, 3 January 2013 (UTC)


 * No matter how much you don't like a question, you should NEVER "brush it off with a mention of no medical advice". That's a cop out. That's an arrogant, insulting approach. HiLo48 (talk) 17:22, 3 January 2013 (UTC)


 * What should I have done? If the question is serious, then we can't answer it because it is medical advice. By "brush it off..." I meant that I simply told them we can't answer the question without mentioning my suspicion of trolling - I hoped the quick "we can't do that, contact a doctor" answer would stop the thread without really giving a troll a chance to respond (defending against accusations of trolling/adding pointless but attention-generating follow ups) and draw things out. 209.131.76.183 (talk) 18:39, 3 January 2013 (UTC)


 * Sorry if the "What should I have done?" sounds confrontational - it is an honest question. I'd like to handle things correctly here, and even if you don't like my reasoning for why I answered how I did, I feel that I gave a proper response. 209.131.76.183 (talk) 18:48, 3 January 2013 (UTC)


 * The rule of thumb to decide whether a questioner is asking for medical advice, by more-or-less consensus after countless discussions on Wikipedia_talk:Reference desk, is Kainaw's criterion: Can the question be answered completely without providing a diagnosis, prognosis, or treatment advice?. In this case, there was no question about diagnosis or treatment advice. One could argue that the questioner in this case asked for a prognosis after a hypothetical inhalation of "babby powder". However, my understanding of the prognosis part of Kainaw's criterion, is that it applies to the prognosis for a real person (such as the questioner or someone they know), and not the prognosis for a hypothetical person after a hypothetical exposure to a possibly harmful substance. I would therefore regard this as a question about medical facts (albeit a silly one), and not a request for medical advice. Since a smart questioner who needs medical advice could camouflage the question as a question seeking facts only, a warning about contacting a poison control center or a doctor if the question relates to a real-life situation could be appropriate. But there is IMO no reason to reject the question in this case. --NorwegianBluetalk 19:44, 3 January 2013 (UTC)


 * This debate about how to answer a question belongs on the Talk: page - not here. SteveBaker (talk) 19:51, 3 January 2013 (UTC)
 * Agreed. However, this topic has been discussed there ad nauseam. I'll just collapse the side discussion for now. If anyone wants to move it, feel free! --NorwegianBluetalk 20:36, 3 January 2013 (UTC)

Cleaning a fish tank
This is really nice (I'd jump through it because it's like 40 minutes long), but how would such a fishtank be cleaned? Any gravel siphoning would destroy the aquascaped design?  DRosenbach  ( Talk 18:02, 3 January 2013 (UTC)


 * Ideally an aquarium is naturally in balance such that the organisms in it clean the tank itself. Catfish are good for this, for example.  This isn't always possible, of course.  Filtering the water as it's pumped also can clean it, somewhat.  StuRat (talk) 18:18, 3 January 2013 (UTC)


 * With an aquarium like this, regular water changes would be done to keep the levels of nitrites->nitrates down. This inhibits algae. Species like Amano shrimp can be introduced to help keep plants clean. I've had tanks similar to this. They require good bacterial filtration (external) as well as regular water changes and a lot of maintenance. If you want to see some amazing examples of tanks like this, search for "Amano tank". Zzubnik (talk) 09:44, 4 January 2013 (UTC)

Is this aircraft an A330?
In File:Delta Air Lines Boeing 747-400 KvW.jpg I suspect the Air France jet in the back is an A330 series. Would anyone tell me if this is correct? WhisperToMe (talk) 19:06, 3 January 2013 (UTC)
 * I really don't know my airplanes (pardon me, BDD (talk) 20:23, 3 January 2013 (UTC)
 * (It's called a winglet.)...and they are indeed standard features on the A330 - so I think this must be an older model than that. Winglets were only a retrofit option on the A320 - so maybe that's what this is? SteveBaker (talk) 20:40, 3 January 2013 (UTC)

The aircraft in the background of your linked picture appears to be a Boeing 777-200. The shape of the tail and the triple wheeled bogeys give it away. http://en.wikipedia.org/wiki/777-200#777-200. Happymulletuk (talk) 22:26, 3 January 2013 (UTC)
 * What Happymulletuk says, it's a 777: an A330 has a round tailcone with an APU exhaust and four-wheel bogies .  Acroterion   (talk)   22:31, 3 January 2013 (UTC)

Alcohol and illness
This is just a request for some science, not medical advice. What effect do alcoholic beverages have on everyday sicknesses, such as the common cold or flu? Folk wisdom is always to drink plenty of fluids, so why not some beer and wine? Probably because alcohol dehydrates, and the point of those fluids is to stay hydrated. But alcohol is a proven disinfectant, so it doesn't seem wildly implausible that ingesting it could kill some internal pathogens. So my question is not "Should I drink booze when I'm sick?" It's more like "What effect does booze have on sick people?" --BDD (talk) 20:21, 3 January 2013 (UTC)
 * There is to my knowledge no evidence that ethanol has any therapeutic effect against virus infections such as the common cold or influenza. A pubmed search returned one paper where the authors suggested that wine intake may have a protective effect against common cold (prophylactically, not therapeutically): . Another study concluded that acute intake of moderate amounts of red wine or alcohol had no effect on the immune system of healthy men: . There is evidence that a moderate intake of alcoholic beverages (especially red wine) may have a protective effect against cardiovascular disease and certain types of cancer:, but it is not clear whether the effect is caused by the ethanol or other constituents of the beverage. Finally, ethanol may be used as an antidote against methanol poisoning:.
 * See also:
 * Alcoholic beverage
 * Ethanol
 * Alcohol and cardiovascular disease
 * Alcohol dementia
 * Alcohol and cancer
 * Long-term effects of alcohol
 * --NorwegianBluetalk 21:07, 3 January 2013 (UTC)


 * The thing about colds and flu is that they are viral diseases - not bacterial. Viruses spend a good deal of time inside your cells, making more viruses - but they are just DNA, which makes them extremely hard to eradicate without also killing your own DNA.  Alcohol has no effect whatever on them once they are inside your body.


 * To be completely clear (and according to common cold):


 * There is no medical treatment whatever that will prevent you from getting a cold.
 * There is no cure whatever for a cold.
 * Once you have the cold, there is no proven way to reduce the duration of it.
 * Very few "treatments" even help to relieve symptoms more than placebo.
 * Frequent hand washing will help you to avoid getting a cold. There is no evidence that particular soap additives improve hand washing effectiveness.
 * People are asymptomatic for a while after getting an infection - but they are still spreading the disease everywhere - so simply staying away from obviously sick people only helps to a small degree.
 * Wearing a face mask may help you to avoid catching a cold.
 * There is no innoculation against the disease because it evolves too quickly and there are far too many strains of it out there (and no, contrary to what some people claim, flu shots only help you to avoid influenza - not the common cold).
 * Ibuprofen, acetaminophen. paracetamol, etc will get your temperature down - which may make you feel a little better - but because your body is pushing up your temperature in order to help it fight off the virus, it's not going to help you rid yourself of the virus any faster - and arguably might slow that process down, thereby prolonging the cold.
 * Anti-histamines and decongestants may help you breathe a little more easily - but most of the truly effective ones are no longer available over-the-counter in many countries - and the replacements fare no better than placebo. However, some will make you sleepy - and you might prefer sleeping to being away while sick with a cold.
 * Same deal with cough medicines - most are no better than placebo...the good ones are prescription only.
 * There is no evidence whatever that increased fluid intake either improves symptoms or shortens the course of the cold.
 * Humidified air, alcohol and honey are all no better than placebo...same deal for herbal, homeopathic medicines and stuff like reflexology and the like.
 * Antibiotics might help if you get secondary infections (like ear-aches) - but they don't affect viruses - so they don't help your cold at all.
 * Zinc, echinacia and vitamin C might be helpful - but evidence from scientific research is patchy. If there is an effect, it's a very small one.  Zinc is bad for you in larger doses - so you should probably avoid that one.  However, taking vitamin C BEFORE you get the cold might help reduce it's severity...but again, the research is patchy and the statistical reduction isn't more than a few hours out of a week-long cold...and by the time you're getting symptoms, it's too late.
 * Just about every cold cure/treatment/preventative out there is junk - don't waste your money on them.


 * Bottom line is that we're totally helpless here. Nothing you do will completely prevent you from getting a cold, nothing will cure it, nothing will shorten the duration. Only the very obvious general pain killers will relieve your symptoms to any significant degree.


 * The common cold is a really, REALLY tough disease to deal with. SteveBaker (talk) 21:16, 3 January 2013 (UTC)


 * Not just zinc, echinacia, and vitamin C—chicken soup also reduces the severity of a cold. Whoop whoop pull up Bitching Betty 02:38, 4 January 2013 (UTC)


 * I think the advice to drink lots of fluids isn't to cure the cold, but rather to prevent dehydration, which could otherwise result from constantly blowing your nose, etc. Other treatments may lessen symptoms, such as inflammation. StuRat (talk) 23:06, 5 January 2013 (UTC)


 * SteveBaker - that's a great post. It combines a lot of stuff I mostly knew, but you said it all so clearly and firmly.

Thank you. HiLo48 (talk) 21:23, 3 January 2013 (UTC)
 * Very interesting! How about bacterial infections, then? --BDD (talk) 21:31, 3 January 2013 (UTC)


 * If you put pure spirits on a bacterial infection on your skin, it can help, but it might sting a lot, and you won't really be enjoying a drink. HiLo48 (talk) 21:39, 3 January 2013 (UTC)


 * It has been suggested that the beneficial effect of (a moderate intake of) alcohol on the risk of getting a myocardial infarction could be a consequence of its bactericidal effect on oral bacteria:, see also . There is evidence that moderate alcohol consumption facilitates the elimination of Helicobacter pylori: . Finally, excessive alcohol intake increases the risk of acquiring gonorrhea and other sexually transmitted diseases. --NorwegianBluetalk 22:01, 3 January 2013 (UTC)


 * I suspect the latter has more to do with behaviors while under the influence of alcohol, but thanks, this is good. --BDD (talk) 22:39, 3 January 2013 (UTC)


 * Yep, see beer goggles. :-) StuRat (talk) 22:51, 3 January 2013 (UTC)


 * If you want the disinfectant effects of ethyl alcohol without the harmful effects, try gargling with it and spitting it out. Then again, why not save some money and use mouthwash ? StuRat (talk) 22:04, 3 January 2013 (UTC)


 * Even better, (except for the savings), is what a colleague of mine did on at trip to India recently. He brought a large bottle of Aquavit and used it for gargling, thus reducing oral bacterial flora. He then swallowed it, as a prophylactic against Helicobacter pylori in his stomach. Finally, the mildly sedative effect gave him a good night's sleep until the next morning. Hey, but that's three good things all in one - a gargle, a Helicobacterfree stomach, and a surprisingly good nights sleep. --NorwegianBluetalk 00:06, 4 January 2013 (UTC)


 * Alcohol is a surface disinfectant. When consumed it is well under 1% by volume of a person's blood. μηδείς (talk) 04:07, 4 January 2013 (UTC)


 * If it's obnoxious enough to kill bacteria, and especially viruses, it's probably going to kill your cells too. That's why antibiotics and antiviral medication are so amazing (maybe pesticides too). They interfere with very specific bacterial processes (see gram negative bacteria, for example), often cell membrane construction that don't apply to our cells. Besides, the immune system is ultimately what defeats almost all of these diseases, and alcohol probably slows it down to some extent (see the links above). Shadowjams (talk) 11:51, 4 January 2013 (UTC)


 * Well, your cells are protected by a layer of mucus, so the concentration at the live cells is hopefully low enough to prevent them from being killed. And those meds cause resistant strains to develop, so should only be used when absolutely necessary. StuRat (talk) 06:03, 5 January 2013 (UTC)