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December 20

Eye Layers

The eye has 3 liquid to semiliquid layers over the sclera and cornea: tear, mucus, and what is the 3rd one?96.53.149.117 (talk) 01:48, 20 December 2008 (UTC)

You linked to all those articles and yet didn't bother to read them? Nil Einne (talk) 05:05, 20 December 2008 (UTC)

tldr. Why do 99% of people ask questions here?96.53.149.117 (talk) 05:15, 20 December 2008 (UTC)

Too long didn't read? I found the answer to your question within 1 minute. No one said you had to read them all from top to bottom, a bit of common sense and use of the find function that nearly any browser has goes a long way. As to what other people do, quite commonly a lot of questions are not answered so simply and clearly in one of our articles. While there's no doubt some people do ask a question without reading or searching, those questions are often ignored or given less then straight answers, as in this case. As the header says, many people can't be bothered helping those who show no sign of helping themselves and you will often get an answer faster if you make the minimum of effort to look it up. (As it stands, it's taken 3+ hours to get an answer you could have had in a minute). If you want, I could explain how I found the answer within a minute although I would recommend you seek further help since basic search skills are vital in this modern day and age Nil Einne (talk) 05:31, 20 December 2008 (UTC)

yes, that is what tldr means. What amazes me is that you even take the time to make an inflammatory comment at the start. And considering your net savy, you had to ask for clarification of the initialism?96.53.149.117 (talk) —Preceding undated comment was added at 05:58, 20 December 2008 (UTC).

This is all too OT for me. Replied to your talk page Nil Einne (talk) 08:05, 20 December 2008 (UTC)

For the benefit of future readers, the answer is in tears Nil Einne (talk) 08:38, 20 December 2008 (UTC)

Milk

Why drink milk after ingesting SOME (certian) toxins?96.53.149.117 (talk) 02:07, 20 December 2008 (UTC)

Such as Draino; what I mean is that on some of the safety labels, they will say, "If ingested give a glass of milk and call a physician.".96.53.149.117 (talk) 03:56, 20 December 2008 (UTC)

Milk has a mild buffer effect, meaning that it will not only dilute the acid/and/or/base but it will also tend to neutralize it. Pure water will only dilute it, and for particularly strong acids or bases, dilution is not usually enough. The same volume of milk compared to water will have a slightly greater nutralizing effect. Mind you that a) its not likely to be much of a difference and b) if you just drank drano, you just turned your insides into soap. A glass of milk is unlikely to make a huge difference at this point... --Jayron32.talk.contribs 04:03, 20 December 2008 (UTC)

Also, milk contains fat (except skim milk), so helps to dilute fat-soluble poisons, while drinks without fat will not. StuRat (talk) 04:31, 20 December 2008 (UTC)

Actually, that may be a bad idea, since the fat in milk may actually help increase absorbtion of fat-soluble compounds into the bloodstream... --Jayron32.talk.contribs 06:18, 20 December 2008 (UTC)

(wild speculation warning) That was my train of thought, too. But maybe the idea is to absorb fat-soluble compounds and hold them in the milk suspension until the stomach could be pumped. But sodium hydroxide is water soluble (although it would be soluble in milk also). Some other possibilites - Milk might coat the stomach better. Also, with Drano (assuming the amount was fairly small), maybe the milk would provide a substance other than you to undergo saponification (just don't use skim milk). But I've seen "drink milk" on other types of chemicals as well. (Side question: is water is absorbed more quickly than milk? That could be a reason) --Bennybp (talk) 07:10, 20 December 2008 (UTC)

Water must definatly be absorbed faster than milk. Milk is a suspended solution.96.53.149.117 (talk) 01:47, 21 December 2008 (UTC)

Also, that IS my other question. What about other chemicals? I really didn't mean, and didn't want, this question just for draino.96.53.149.117 (talk) 01:47, 21 December 2008 (UTC)

Water passes through the stomach about five times faster than milk. Someguy1221 (talk) 10:40, 20 December 2008 (UTC)

I think the greater thing is the same reasoning behind having kids hide under their desks during a nuclear attack. If they just printed "If you drink this, there's not much you can do for yourself. Go ahead and call an ambulance, but you're likely a goner" on the label, it wouldn't look too good. The idea is that people feel psychologically better doing something, even if that something is entirely ineffectual at solving the problem, like taking off your shoes at the airport or hiding under your desk to somehow save you from a 10 megaton blast from a nuclear bomb... --Jayron32.talk.contribs 03:04, 21 December 2008 (UTC)

Taking off shoes at an airport? What does that do? But I disagree with you about putting something on a label for the sake of reassurance. They didn't choose milk for any reason.96.53.149.117 (talk) 04:51, 21 December 2008 (UTC)

Taking off shoes at an airport? What does that do? Make Dr. Scholl happy because of many added athlete's foot cases. The label designers would also have to consider the added complication of finding something that is considered readily available, even if less effective than some not so common aid. Everyone knows pretty fast where to find their milk. Baking soda or vinegar or whatever could lead to a time consuming search. So a little now is better that a lot, too late. 76.97.245.5 (talk) 12:29, 21 December 2008 (UTC)

But why at an airport?96.53.149.117 (talk) 03:25, 26 December 2008 (UTC)

Drinking milk is Security theater? -- JSBillings 15:12, 21 December 2008 (UTC)

When I was younger a chlorine tank (which my neighbor who ran a pool cleaning business was storing illegally) burst in my neighborhood. I started coughing uncontrollably, the poison control center told me to drink some milk and the coughing subsided. I never really gave any thought to why that worked before, but now I'm confused. -- Mad031683 (talk) 23:37, 22 December 2008 (UTC)

Why do young women giggle all the time?

And I am not just talking about when I am around. Though they seem to do it even more when I am. —Preceding unsigned comment added by Trevor Loughlin (talk • contribs) 06:15, 20 December 2008 (UTC)

If you are talking about teenagers, I would suggest that the onset of puberty leaves them with with more highly charged emotions in general at times, and that therefore they experience joy, giddiness, whatever you want to call it, a lot more. It also *seems* that they also face more "crises" than boys, from what I've seen, so they cry more and such, too, at that age. However, it may only seem that way because females, at least in Western culture, are often more open about showing their emotions.Somebody or his brother (talk) 14:25, 20 December 2008 (UTC)

Indeed, for good or bad western society tends to demand stereotypically masculine behavior from young men. This generally does not include giggling, therefore boys tend to restrain their emotions more. Young woman may also be influenced by equally stereotypical depictions of females in the media, which often tend to fall along the lines of valley girls. --S.dedalus (talk) 04:51, 21 December 2008 (UTC)

I strongly disagree with that explanation. So far as I know, almost every culture's girls express emotions more strongly than do its boys. You can't explain that away using only stereotypes, which have no reason to remain constant across societies that developed nearly independently of each other. --99.237.96.81 (talk) 07:37, 21 December 2008 (UTC)

Perhaps it's related to the fact that the start of puberty often starts earlier in female humans than in male humans? Also, the changes in women occur much faster than in men, and the hormonal changes often lead to an imbalance of neurotransmitters (according to the puberty article) which would make one more emotional. -- JSBillings 15:10, 21 December 2008 (UTC)

While stereotypes may be the wrong word, I don't think you can really rule out cultural factors. For starters, I don't think its true that cultures developed largely independently. A lot of cultures have been quite interconnected for a while. Some like the indigenous Australians for example were isolated for a long while but I doubt we know very well whether they have traditionally shown the trends of females displaying emotions more strongly then males. They didn't have written records and I don't know whether their oral records will really tell us such minutae accurately. There may be records of how they behaved from earlier European encounters but those would have been through the eyes of thoese people and I'm doubtful comparing female and male displays of emotion would have been something they observed in depth unless for whatever reason it seemed highly unusual to them which I doubt it would have been even if their displays were similar. Written records do exist for less isolated cultures, e.g. East Asian ones but given they were less isolated it's hard to rule out cross-cultural influences. Besides has anyone ever looked into the records in detail to find out if displays of emotion by females was stronger then by males? Most significantly perhaps the cultural factors like men as hunters and providers and females as care givers developed a long time ago and are common in the vast majority of cultures. There are obvious genetic and biological reasons why these developed but the important point is that it's easy to see differences in displays of emotions arising out of this, without any real biological or genetic reason (presuming as I've stated these differences are really unanimous throughout tradiotional cultures which I'm not sure we we know). Nil Einne (talk) 11:54, 22 December 2008 (UTC)

Artificially recreating the earth's magnetic field

At some point in the distant future, the earth will lose its magnetic field because its core cools to a point that the current of molten iron will stop flowing. Without its magnetic field, the earth's atmosphere will be stripped away by solar wind. It is impossible to tell if humans will still be around at that time, and if they are, what kinds of technology will be available. However, based on what we know about physics today, are there insurmountable obstacles to replacing the earth's natural magnetic field artificially? —Preceding unsigned comment added by 98.114.98.236 (talk) 08:32, 20 December 2008 (UTC)

Atmosphere will not be stripped away. The field has reversed many times, and during each reversal there was a time when the field was zero, but nothing like that happened. There will be many more cosmic rays reaching the Earth, increasing the frequency of spontaneous mutations in DNA, but not as much as to endanger the survival of the human species. -- Army1987 – Deeds, not words. 14:29, 20 December 2008 (UTC)

I read about the atmospheric loss as a consequence of magnetic field loss in a science article. The theory sounds plausible to me, but I'm not a geophysics expert. Maybe the loss occurs slowly enough that the temporary loss of magnetic field during a geomagnetic reversal only cause a little atmospheric loss. However, if the earth's core cools down, the loss will be permanent; even slow loss will accumulate. In another article that I've read (one about an upcoming global helium shortage), it is stated that when helium floats to the outer edge of the atmosphere, it escapes into space. That tends to lend credence to what solar wind can do to the atmosphere when there's no magnetic field to mitigate the effects. --98.114.98.236 (talk) 14:58, 20 December 2008 (UTC)

What is the basis of your claim that the atmosphere will not be stripped away? The questioner is not asking about a very short period of null magnetism. This question is about a permanent state of no magnetic field - for centuries and centuries - until the Sun expands and swallows the Earth. Looking around, planets without magnetic fields have all the upper atmosphere stripped away. Are you claiming Earth is special and the Sun will be extra gentle to make sure none of the upper atmosphere is harmed? -- kainaw™ 15:03, 20 December 2008 (UTC)

The upper atmosphere? Maybe. But all the atmosphere sounds implausible to me. Also, the other planets you refer to have weaker gravities (the Earth has the greatest acceleration due to gravity of all terrestrial planets in the solar system). -- Army1987 – Deeds, not words. 15:17, 20 December 2008 (UTC)

According to Solar wind, it only stripped away one third of Mars's atmosphere. In four billion years. And Mars is farther from the Sun than the Earth is. And its atmosphere was much less dense than that of Earth. -- Army1987 – Deeds, not words. 15:24, 20 December 2008 (UTC)

Exactly - the upper atmosphere is easy for solar winds to strip. That is what the questioner was asking about. Refusing to answer the question because some heavy gasses might survive is being a bit of an ass. The question is: Is it possible - with any technology that could ever be developed - to create an artificial magnetic field around the Earth. I personally do not believe it is. We create fields like that with electricity. The amount of current we'd need to pump through the Earth to get that big of a field would do more harm than good. If a new way to create magnetic fields was invented, it could be possible. -- kainaw™ 18:40, 20 December 2008 (UTC)

← You're right that I didn't answer the OP's question (I apologize), but I was pointing out that the scenario he described is implausible. (And it is the "some heavy gasses" that we most care about, as we breathe them, not the hydrogen and helium which tend to go up.) Also, I don't think that the Earth's core is going to freeze over within a reasonable amount of time (where by "reasonable" I mean "before mankind will be very likely to be extinct for some other reason"). I suspect he's watched The Core recently and took it too seriously. -- Army1987 – Deeds, not words. 20:38, 20 December 2008 (UTC)

Indeed. When we see these events in isolation, like "Someday, the moon will escape the earth's gravity and drift off into space" or "The earth is slowing down and some day it will stop turning on its axis" or "Someday the core will cool to the point when it is solid" ignores the fact that none of these events happens in isolation. Remember the most important event, that the sun will essentially swallow the earth in 5 billion years or so (see Stellar evolution); all of these scenarios require timespans SIGNIFICANTLY longer than that. So, no, the earth's magnetic field is not going away at any time, unless being vaporized by the expanding sun counts as destroying the magnetic field... --Jayron32.talk.contribs 02:55, 21 December 2008 (UTC)

By the way, the Moon won't drift off into space, it will gain angular momentum until Earth's rotational period equals the period of the Moon's revolution, and at this point it will be still within the Hill sphere (less than 600000 km from Earth). Icek (talk) 08:28, 21 December 2008 (UTC)

What about Venus? It has no internally-generated magnetic field but a dense atmosphere and lower surface gravity than Earth. Icek (talk) 08:28, 21 December 2008 (UTC)

The atmosphere of Venus is primarily CO2. There is a touch of nitrogen and not much of anything else. On Earth, the atmosphere is a good mix of nitrogen and oxygen. They are not comparable. Gravity alone can hold heavy CO2 to the planet. The question is: Did Venus used to have lighter elements in the atmosphere? If so, where did they go? If they went into space, was it lack of gravity, solar ray stripping, or a combination of both? -- kainaw™ 20:54, 21 December 2008 (UTC)

Flash point of fission in atmosphere

What is the flash point of fission in the atmosphere or the hottest temperature in the atmosphere before there are adverse reactions? Tiailds (talk) 08:35, 20 December 2008 (UTC)

For the first, impossibly high (if such a concept even works). Spontaneous uranium fission almost never happens, and that only in ideal underground conditions. Sustained fissioning of atmospheric elements, which we don't produce even in labs, can be safely ignored as a threat to humanity. Certainly your latter question doesn't require such extreme conditions. Air temperatures over 100°C would be catastrophic. Temperatures just 10° greater than those at present (perhaps even less) would be sufficient to melt the bulk of the ice caps. But the whole planet turning into a giant nuclear bomb? That doesn't even meet the threshold for bad science fiction. — Lomn 14:41, 20 December 2008 (UTC)

(Spontaneous fission in general is not that uncommon. Self-sustaining chain reactions almost never happen. There's a big difference there. An atom or two fissioning—who cares. It's only a chain reaction where that becomes an issue.) --98.217.8.46 (talk) 15:56, 20 December 2008 (UTC)

(And before someone else mentions it, there were, of course, some concerns that nuclear reactions set off by the first atomic bomb would accidentally induce a fusion chain-reaction in the atmosphere, turning the planet into a giant hydrogen bomb. But the problem was studied carefully and it was determined that it was not at all likely to occur. It turns out self-propagating fusion reactions are pretty hard to induce even in ideal situations.) --98.217.8.46 (talk) 16:01, 20 December 2008 (UTC)

I think the last thing is what the original poster was asking about, rather than a "before someone else mentions it". Anyway, you've provided a link. --Anonymous, 18:50 UTC, December 20/08.

Why do some children have the concept of growing down after one grows up?

I have heard a number of times that little children have the idea that one grows down after one grows up. Why do some get that idea? I don't think all do, my younger cousins never did, from what I noticed. It usually is with children around 2-3, I think; maybe 4, too.

I'm thinking it has to do with the idea that their minds pick up on patterns like the bedtime routine, days of the week, etc., but it could just be the attempt to make sense of the world. (i.e.: "Mommy has to be a baby sometime, I never saw her as a baby, therefore she must be a baby sometime in the future.") It is definitely from the preoperational stage, as I' think 4 is the oldest I ever heard of tha child thinking this.Somebody or his brother (talk) 14:06, 20 December 2008 (UTC)

"What grows up must grow down" ? StuRat (talk) 17:23, 20 December 2008 (UTC)

"... Last scene of all,

That ends this strange eventful history,

Is second childishness and mere oblivion;

Sans teeth, sans eyes, sans taste, sans everything."

Well, humans do shrink slightly if they make it beyond middle age - the skeleton starts to degenerate, the posture becomes more stooped etc. Exxolon (talk) 02:29, 21 December 2008 (UTC)

Additionally, due mostly to better nutrition, each of the past few generations has been slightly taller, on average, than its predecessor. Your parents are probably taller than your grandparents. A young child may assume that all adults top out at the same height, so the older generation must be now be shrinking. B00P (talk) 08:10, 21 December 2008 (UTC)

I've read, incidentally, that that trend mysteriously stopped in the US at about the end of the Baby Boom (i.e., with me). —Tamfang (talk) 08:23, 28 December 2008 (UTC)

It resumed about thirty years later; I started noticing very tall young people in 2010. —Tamfang (talk) 04:05, 3 September 2023 (UTC)

Why does chronic stress sometimes lead to stroke

I can understand why stress can lead to a heart attack - that's pretty logical, with the strain on the heart. I'm a little confused, though, on why stroke can be a result. Is stroke only a result because of the impact on the heart itself, which thus leds to blockages? Or, does persistent, extreme stress actually do something to the brain itself, which causes clots to form there, just as it can lead to a headache, etc.?

Or, perhaps it can be either, depending ont he type of stroke, which is quite plausible.209.244.30.221 (talk) 16:04, 20 December 2008 (UTC)

Strokes that are caused by chronic stress are due to a disturbance of a blood vessel in the brain. Chronic stress increases your blood pressure, which increases the risk of rupture of a blood vessel. If this blood vessel is in your brain, and it ruptures, it can cause a stroke. —Cyclonenim (talk · contribs · email) 16:21, 20 December 2008 (UTC)

Stress may also drive a general inflammatory state, leading to hypercoagulability (this study is an example: [1]), endothelial dysfunction (e.g. in the carotid artery or other location), and then embolization resulting in ischemic stroke that can sometimes become a hemorrhagic stroke. Stress has many negative effects, and exercise is a positive balancer for almost all of them (whereas watching TV is not). --Scray (talk) 19:12, 20 December 2008 (UTC)

Rare, but in people with Sticky platelet syndrome [2] stress can also set off a stroke. http://www.cli-online.com/products/haemostasis-coagulation/haemostasiscoagulation/clinical-laboratory/testing-the-sticky-platelet-syndrome/index.html?tx_ttproducts_pi1[backPID]=1031&cHash=24a96e1d04 (Don't know the latin name, so we may have a page)76.97.245.5 (talk) 12:07, 21 December 2008 (UTC) Sorry the long link won't work otherwise because it contains angled brackets. If s.o. knows how to fix it, plse. do.

Chronic stress can lead to hypertension. From "Stroke", "Hypertension accounts for 35-50% of stroke risk.... Lowering blood pressure has been conclusively shown to prevent both ischemic and hemorrhagic strokes." Axl ¤ [Talk] 23:32, 25 December 2008 (UTC)

is it possible to produce a novel algorithm USING THE POWER OF THE MIND ALONE? (no other tools of any kind)

Is it possible to produce a novel algorithm USING THE POWER OF THE MIND ALONE? (no other tools of any kind) —Preceding unsigned comment added by 79.122.90.7 (talk) 18:31, 20 December 2008 (UTC)

Since I know of no physical effects associated with a mind as opposed to workings of the brain I would say no. If by mind you mean just thinking about things, power of the mind as th ability to think and find patterns, and algorithm as a way of doing something then I would say yes, where else would the novel bit come from, even noticing something novel is something that has to be thought. Dmcq (talk) 18:52, 20 December 2008 (UTC)

It's hard to imagine any algorithms that were not produced using the power of the mind alone! So, for example, Quicksort is a well-known sorting algorithm developed by C. A. R. Hoare - I imagine he used his mind alone to develop it. My son and I are writing a computer game (to give to my wife for Xmas!) - it has a couple of new algorithms in it (well, they are new to us) - and I just sat down and thought them up. I didn't need a pencil and paper or a computer to do that.

This seems (to me at least) like such a ridiculously simple answer - that I have to imagine that the OP is actually asking something more complicated. Perhaps a clarification is needed? SteveBaker (talk) 20:27, 20 December 2008 (UTC)

One way to look at it... You can imagine an algorithm and suspect that it will work as well as you think it will. Until you physically test the algorithm, you will not know if you made a mistake in your thinking. So, the mind will create the algorithm, but you need to test it afterwards. I know, there are thousands of mathematics students who will swear that you can prove an algorithm without testing - but that assumes you didn't make a mistake in your proof. You still need to test it to make sure there were no mistakes in the creation of the algorithm. Want a silly little anecdote? Many years ago (when I got my brand new TI-99 4/A), I thought of a cool algorithm for using an evolutionary approach to solving simple problems. I thought it through, then wrote it down, and finally programmed it in. My test problem was very simple. The bot (I called it) got two single digit numbers, 1 to 9. It was supposed to produce the sum of the numbers. The further away it was from the sum, the worse it was punished. After a few hundred generations, the bot kept answering 10. Why 10? My algorithm was bad. The bot didn't learn to add two numbers. It learned that if it answers 10, it will limit the punishment it receives over the long term. -- kainaw™ 00:58, 21 December 2008 (UTC)

Well - that's not a really fair example - you didn't come up with an algorithm to solve your problem - you essentially said - I don't want to be bothered with figuring out the algorithm, so I'll come up with an algorithm that'll allow the computer to learn - and I'll hope that IT can figure it out. Your algorithm (the learning thing) worked just fine - it learned...but because it's fairly stupid, it learned the wrong thing.

Obviously when we create algorithms using our minds alone, we sometimes make mistakes. Testing to see if a mistake has been made can certainly be done by implementing the algorithm in a computer and testing it - but our OP asks whether we can create algorithms without a computer - and we CERTAINLY can. There are plenty of simple algorithms we can test in our heads. It's the essence of a good computer programmer to be pretty certain that somethings' going to work BEFORE sitting down to write the code. You can't always be 100% certain - but sometimes you are - and the skill of computer programming is in spotting problems as early as possible. At any rate - we CAN and DO produce algorithms 100% in our heads. SteveBaker (talk) 01:30, 21 December 2008 (UTC)

I'm sorry, but you appear to have misread my comment. I came up with an algorithm to have a computer figure out an algorithm. My algorithm was how it would learn. I didn't have the computer figure that out. However, I explained that my algorithm (which seemed fine to me when I thought it through) didn't work. -- kainaw™ 04:16, 21 December 2008 (UTC)

I think the following question is more interesting than the original, "Is there any algorithm that has not originated in a human mind ?"
I realize that the phrasing is fuzzy and the answer will depend upon how we define the terms "algorithm", "originated", "mind" etc - so in order to avoid a semantic or philosophical discussion, let me specify that I am interested in a computer generated algorithm that is analogous to (say) the computer generated proof of the four color theorem. Any examples ? Abecedare (talk) 03:17, 21 December 2008 (UTC)

You have to define "algorithm". It is normally considered something like "a sequence of steps to solve a problem." There are many algorithms that were not created in the human mind. For example, a hedgehog knows that if it feels threatened, the sequence of steps is: 1) Try to run away. 2) If that fails, roll into a ball. It isn't a great algorithm, but it is a series of steps to solve the problem. DNA replication is another (more complicated) algorithm that was not created in the human mind. But, if you want to claim that all biological, social, and natural processes are omitted from the things you want to call "algorithms", then you have decided to limit algorithms to humans and humans alone (assuming humans are not biological, social, or natural). -- kainaw™ 04:21, 21 December 2008 (UTC)

I think the example Kainaw gave of a learning machine is the kind of thing where computers do (in a sense) come up with an algorithm. There is an old story (and it may be apocryphal) of a Japanese subway operator who had problems with the platforms of his stations filling up with so many people that it became dangerous. Doors were added at the entrance to the platform that could be closed when the platform became too crowded. They decided to use a camera and a neural network software package to look at the images of the platform and close the doors when it started to become too crowded. They showed the software lots of pictures of crowded platforms and uncrowded ones - and trained it (as one does with neural nets) to recognise one set of images from the other. When they put the resulting (trained) network into service, it worked just great - reliably shutting the gates when the platform started to fill up - and opening them again as it emptied. The system was in service for almost a year. However, on Xmas day, it failed. Shutting the gates when the platform was completely empty. The story goes that the engineers work hard to find out why the neural network failed and they discover that only the neurons that are looking at the very top of the image from the camera are actually doing anything. The others have shut themselves off. It turns out that the camera was looking at the clock on the wall of the station and shutting the doors at the exact times of day that the station tended to get overly full.

I don't know whether that story is true or not - but (as Kainaw and numerous others have discovered) computer learning software doesn't always learn the things you want or expect it to. The story persists precisely because it is an excellent description of exactly the kinds of things that happen with learning software.

If the Japanese subway story is true - then the neural network "discovered" an algorithm for shutting the gates that worked pretty well. It had not been taught about clocks or anything like that - it had (in essence) 'deduced' an entirely different way of achieving the stated goals. Just as C. A. R. Hoare discovered a better way to sort things when he figured out 'QuickSort'.

SteveBaker (talk) 06:52, 21 December 2008 (UTC)

Are Japanese subways busy on Christmas day? There was a similar story about neural networks being trained to identify tanks in recon photos. Long story short the neural network was just checking for cloudy days. Again, I have no idea of the origins of this story, but I have a nagging suspicion I heard it on "The Machine That Changed the World" or a similar documentary. APL (talk) 17:26, 21 December 2008 (UTC)

I don't know about how busy Japanese subways ACTUALLY are on Xmas day - but the implication from the story is that the station was deserted because of the holiday - and the computer went ahead and shut the gates, not because the platforms were full but because the clock was showing the time of day at which the platform is USUALLY full. I'd heard the ones about tank recognition too. Somewhere in the boxes of books in my garage I have a book on Neural Networks that tells both stories (and several others also). The field of computer learning (be it neural networks or evolutionary algorithms or whatever) is simply littered with these kinds of stories. Some are certainly true.

One that I like (and I know is true) is the guy who was trying to evolve 'virtual creatures' using computer graphics and such. He was interested in having them evolve to be able to move around in their virtual world. He had simulated muscles and bones and such - with neural network intelligence to drive them. He set the simulation up and ran races between creatures with different 'genes' to see which would be the first to cross a line some distance away. The evolutionary part favored the genes that generated creatures who crossed the line the fastest - or in the even that none of them got there within a reasonable amount of time - rewarded the creature that got closest. The simulation ran overnight and the researcher was bitterly disappointed to discover that all of the creatures that survived the process were simply tall vertical columns - no intelligence, no muscles, nothing. The trick was that the creatures simply fell over. They'd grown taller so that when they landed, they'd be closer to the finish line - and the tallest creature 'won' the race every time. In essence, the creatures had found an 'algorithm' (falling over) that solved the given problem (crossing the finish line as quickly as possible) in a manner that was vastly simpler and more efficient than the human designer imagined. SteveBaker (talk) 21:29, 21 December 2008 (UTC)

What does the "LIO" prefix mean in the scientific name of "Pocket Mice"?

Many scientific names of species have prefixes that define a group of animals within a larger group. Thus, among the various mice ("MYS" in classical Greek) the earth-based mice called in English "pocket gophers" are named in the scientific taxonomy Geomys (literally "earth-mice"). In Greek the prefix "Lio" denotes smooth, but in Latin the same prefix means lion-like or leontine. Since Greek and Latin are used indiscriminately in nomenclature, it is impossible to guess what an animal's name with that prefix means. My question is therefore twofold: 1) In the particular case of "LIOMYS", the Mexican Pocket Mouse, does the "Lio" prefix mean smooth or leontine? 2) In general terms, is there a way to tell which is correct, or does one need specific knoledge for each and every case this prefix is used? Thank you! --Bergeronz (talk) 20:11, 20 December 2008 (UTC)

You also asked this on the Language reference desk and it has been answered there. Please do not multi-post. If you really aren't sure which is more appropriate, you could post a query on one desk and a link to it on another. --Anonymous, 03:20 UTC, December 21, 2008.

December 21

Hey, have they ever expanded on that life creating experiment thing?

I mean well beyond the Miller Urey experiment. —Preceding unsigned comment added by THE WORLD'S MOST CURIOUS MAN (talk • contribs) 00:40, 21 December 2008 (UTC)

There's some additional studies mentioned at the end of the Miller-Urey article. Also, check out the references in Abiogenesis article. -- JSBillings 01:03, 21 December 2008 (UTC)

Yes - there have been many recreations of the original experiment - and others with conditions closer to those that we now believe to have been present in the early earth. However, these aren't really serious attempts to create life - only to show that the basic building blocks (Amino acids, carbohydrates, etc) could have formed spontaneously in the early planet. Life itself is likely to have been an extreme statistical flook. When the oceans were full of amino acids and other nutrients, it would only take ONE molecule of a self-replicating DNA/RNA type of substance to appear in order for life to get started and for evolution to rapidly do it's thing. Since the process of creating that one molecule could easily have happened just once - in a half billion years and in trillions of cubic meters of water - the probability of being able to reproduce that in a laboratory using the original conditions during the lifetime of the researcher is essentially zero. So the experiment would certainly appear to fail - in that it would not produce life - but that would only prove how statistically infrequent such events must be. SteveBaker (talk) 01:19, 21 December 2008 (UTC)

For quite different kinds of life creating experiments, see Mycoplasma laboratorium. Icek (talk) 08:17, 21 December 2008 (UTC)

Yes - indeed. It seems very likely that we'll be able to produce a completely synthetic life form in perhaps the next decade - but that's a very different thing from reproducing the means by which the first living thing came about on Earth. SteveBaker (talk) 21:03, 21 December 2008 (UTC)

I thought they had given up on the "live from the big ocean" concept and gone to hydrothermal vents and hot springs because the "chemical soup" there would be more reactive? 76.97.245.5 (talk) 12:51, 21 December 2008 (UTC)

Probably - but in terms of answering this question it's still the same deal. We look at ALL of life on earth and every single living thing is clearly descended from a common ancestor because so much of the DNA is shared. This suggests that the 'abiogenesis' event (the first self-replicating molecule coming out of non-living material) may well have been a one-off event - something so amazingly statistically unlikely that it took billions of years and vast number of "attempts" for it to happen. Even if it had to happen at a hydrothermal vent - there are huge numbers of those - and we still have a billion years or so for just one such event to happen....so it's still spectacularly unlikely that we'd be able to reproduce it experimentally. SteveBaker (talk) 21:03, 21 December 2008 (UTC)

Lipid Layer

Which part of the eye produces the lipid layer?96.53.149.117 (talk) 01:51, 21 December 2008 (UTC)

Aren't you the expert on this by now? [3] [4] ? Perhaps you should consult a physiology textbook if you're having a hard time finding the information you need for these articles on the internet at large - I recommend Tortora and Grabowski as an introductory anatomy and physiology textbook. Nimur (talk) 02:04, 21 December 2008 (UTC)

For readers not aware of prior discussion, the answer is quite prominently displayed in a table near the beginning of our Tears article. If the OP is asking something less blindingly obvious and repetitive of his/her recent questions, please clarify. --Scray (talk) 03:09, 21 December 2008 (UTC)

Oh fuck, you are right! I knew I shouldn't have asked this question. Lol, I knew I'd find it there, my bad!96.53.149.117 (talk) 04:46, 21 December 2008 (UTC)

You did know that you would find this fact in that article, because you put it there, as I pointed out earlier. Nimur (talk) 23:14, 21 December 2008 (UTC)

If you had entered your exact question "Which part of the eye produces the lipid layer?" google would have answered your question fully with its first reply. Not a wiki answer but if you put in this query instead "Which part of the eye produces the lipid layer wiki" the first reply is to the wikipedia entry on tears. Please learn to do these very basic types of search first before wasting peoples time, see the bit at the top of this page about trying to answer your question yourself first. Dmcq (talk) 11:35, 21 December 2008 (UTC)

Identifying an unknown mammal

Can someone please help identify this mammal, found in the forests of Peru?

[5], [6] and [7].

I think it is a shrew opossum (Caenolestes caniventer or Lestoros inca), but then I might not be right. Let's see if we can find out! --Leptictidium (mt) 10:08, 21 December 2008 (UTC)

Guessing more like a Thylamys "mouse opossum"? (shorter snout, bigger eyes, monochrome tail) Julia Rossi (talk) 10:54, 21 December 2008 (UTC)

This [8] site has pictures plus a map of S-American mouse opossumice. --Cookatoo.ergo.ZooM (talk) 11:37, 21 December 2008 (UTC)

Skua vs. Great Black-backed Gull - who would win?

No, this isn't going to be another one of *those* threads - rather it's a question based on something I just read in WPs Skua article, namely this:

“ larger species also regularly kill and eat adult birds, up to the size of Great Black-backed Gulls ”

This is absolute bollocks, right? I could envision a Skua taking GBB chicks or eggs, or battling with an adult over food - but really, a fully-grown GBB is *bigger* than the largest Skua and every bit as mean-tempered and predatory. As far as I am aware, nothing short of one of the great eagles would even attempt to make a meal out of a healthy adult bird. --Kurt Shaped Box (talk) 10:58, 21 December 2008 (UTC)

Do you know whether either or both of those species might hunt in groups? OR We have a flock (?) of about 6 crows flying around that harass everything in the neighborhood, including a bird of prey. (Sorry haven't had time yet to look him up.) I've also seen a crowd of swallows take on a magpie. Size isn't everything. 76.97.245.5 (talk) 11:48, 21 December 2008 (UTC)

Not as far as I know. Gulls and Skuas will defend the nesting areas from potential threats en masse but when it comes to hunting and scavenging, it's strictly a competitive activity, with much (often counter-productive) squabbling and bickering. Sometimes I get the impression that preventing a rival from feeding is almost as important to them as getting a meal for themselves (two birds fight, third bird comes in and steals food). --Kurt Shaped Box (talk) 13:11, 21 December 2008 (UTC)

Whats so special about Half-Integer spin? 59.93.92.192 (talk) 13:23, 21 December 2008 (UTC)

Why is it that only particles with half-integer spin, ie fermions, obey the pauli exclusion principle which disallows more than one of the same particle to exist in the same quantum state? —Preceding unsigned comment added by 59.93.92.192 (talk) 13:21, 21 December 2008 (UTC)

The Pauli exclusion principle applies to states with anti-symmetric wavefunctions (Fermions). The Spin-statistics theorem shows that Fermions have half-integer spins. 86.134.187.65 (talk) 16:06, 21 December 2008 (UTC)

Mystery flower

If there's any botanists here, can anybody identify this flower? Unfortunately, I neglected to look at the stem or take a photograph further out, so this is about all I have to identify it with (other than it's in North Carolina, USA). Tastyduck (talk) 15:18, 21 December 2008 (UTC)

Did you find it in a garden or out in the wild somewhere? Since it's dried up for the winter things like color of the flowers etc. can no longer be used to identify it. That makes it a bit tricky. 76.97.245.5 (talk) 23:59, 21 December 2008 (UTC)

This site [9] might help. 76.97.245.5 (talk) 03:06, 22 December 2008 (UTC)

Overcooked vs. burnt food

Chemically speaking, what's the difference between food that is overcooked and food that is burnt? Can food be burnt and *not* be overcooked? --70.167.58.6 (talk) 16:40, 21 December 2008 (UTC)

Well, sort of. You could char a steak on the outside, yet the steak inside is perfectly done. I'd say that "overdone" typically means that something has been cooked so that the chemical properties break down. Cakes become dry, eggs become rubbery, steak becomes a brick. On the other hand, 'burnt' means that you have actually started combusting thing. --Mdwyer (talk) 17:21, 21 December 2008 (UTC)

(ec) 'Burnt' usually implies that there are products of combustion (or pyrolysis, if in a low-oxygen environment) present. The food has been heated past the point of dehydration, allowing elevated temperatures and charring. Note that 'burnt' can be somewhat subjective. The process of caramelization tends to happen just before you get to burning, lending additional flavours. The savoury 'crunchy bits' of grilled and fried foods may be technically 'burnt', but still important to the overall taste of the dish. (Think grilled chicken, calamari, or steak — they wouldn't taste the same without streaks seared into them from the grill surface.)

Overcooked food, meanwhile, need not be burnt. Think of soggy vegetables that have been steamed or simmered into mush, losing all flavour, texture, and nutrients.

'Burnt but not overcooked' is a bit of a semantic issue. While a particular part of a dish might have trouble meeting both criteria, the entire dish overall can have no difficultly being both 'burnt' and 'undercooked' simultaneously. Think of a cake baked at too high a temperature for too short a time — the outside will be blackened, but the inside can still be raw. (Of course, you can do this deliberately; see Baked Alaska.) TenOfAllTrades(talk) 17:24, 21 December 2008 (UTC)

Just for the record, the outside of a Baked Alaska is supposed to be a "delicate brown", not blackened. At least in this neck of the woods. CBHA (talk) 17:39, 21 December 2008 (UTC)

Yeah, I should have been a bit more specific. I was referring to the general principle of the insulating properties of cake, rather than the specific details of the recipe. :D TenOfAllTrades(talk) 17:52, 21 December 2008 (UTC)

I figured that was probably the case. I just did not want anyone burning their Alaska based on what they read in Wikipedia. After all, one can see Russia from there. Or so I hear. Wanderer57 (talk) 18:42, 21 December 2008 (UTC)

One might want to read about the Maillard reactions, a class of chemical reactions which include both "browning" and "carmelization" and a number of other chemical reactions that make cooked food "tasty". --Jayron32.talk.contribs 02:03, 22 December 2008 (UTC)

Crème brûlée? --Maltelauridsbrigge (talk) 11:02, 22 December 2008 (UTC)

In Fact, you can have food that is burnt, but undercooked. If you put food in the oven at too high a temperature, for example, the exterior may become burnt before the interior has been fully cooked. 142.177.59.188 (talk) 12:35, 31 December 2008 (UTC)

Wood-burning stoves, creosote and soup cans

The local farmer who blows out our driveway and shovels the deck around the house likes to give advice to us former "city slickers". Sometimes, I think he is pulling our collective legs; however, as today's tip was about fire safety, I thougt I'd check it out here. (I have googled various combinations of the title of the section to no avail.) Creosote build-up in a chimney is the biggest danger for house fires. We do all the sensible things: burn only well-seasoned hardwood, clean the chimney at least twice a season, and burn the wood at a sufficiently high temperature to discourage the creosote from sticking to the chimney liner. The farmer says that another trick is to throw in a couple of empty soup cans and burn them daily. He claims there is a chemical given off in the burning that also inhibits the formation of creosote on the liner. He didn't know what chemical it was, or if it was in canned goods other than soup, or if it could be purchased in some other form. I doubt we open two tins in a month, but are willing to make some sacrifices (or borrow tins from the neighbours' recycling bins) if it will help prevent a house fire. Any thoughts, pro or con? Thanks for any help you can provide. ៛ Bielle (talk) 18:03, 21 December 2008 (UTC)

I doubt he's pulling your leg intentionally, but he might be a victim of some old wives' tale. There do exist chemicals that can be burned to clean out your chimney. In theory, they catalyze the creasote into a form that falls down the chimney instead of sticking. However, there seems to be quite a lot of doubt as to if they actually work or not. [10] In any case, a chimney fire can be devastating, so have your chimney inspected at least every couple of years. --Mdwyer (talk) 18:16, 21 December 2008 (UTC)

If you only look down your chimney every couple of years, on the off years you won't be able to enjoy your fire because you'll be sitting there wondering how much creosote is in there. Make a chimney inspection part of your winterization routine, and run a brush down it anyway. There's another old husband's tale about flashlight batteries, but I never tried it, for two reasons: I didn't want whatever was released by burning a battery to be near me (zinc, at least, I guess), and I didn't want stuff in my ashes because I used them for traction on ice in my truck. --Milkbreath (talk) 12:47, 22 December 2008 (UTC)

Have a look at our Bisphenol A page. If your cans are coated inside with synthetic resin, which I assume is precisely what is supposed to create the presumed effect, you would end up with this and similar/worse chemicals in the air around your fire. Ideally it would all go up the chimney and "harmlessly" pollute the air outside, but do you really wish to bet your health on that. If the stuff is caustic enough to scrub creosote off the large surface area of you chimney, I don't want to know what it will do to mucous membranes and lung tissue of your respiratory tract.76.97.245.5 (talk) 07:37, 22 December 2008 (UTC)

Yeah, at best it sounds like an old-wives-tale, at worst actively harmful. I'd say what you're doing now (regular inspection/cleaning of the chimney, not burning dodgy wood) is all you need to be doing. ~ mazca ^t|c 09:22, 22 December 2008 (UTC)

Most hardware stores and supermarkets have commercial "chimney cleaning logs." Most of these are environmentally friendly. So, buring one or two of these a season along with having your chimney inspected and cleaned (if these logs work like they are supposed to, then actual cleaning will be a minimum) would likely be the best bet. Better safe than sorry!

Esclorophile Bush?

The "word" esclorophile appears in the article Tlalpan. Not knowing what it is, I searched for it using Google and found it in only three places on the internet. I'm wondering based on this if it is a real word or an error or vandalism.

Can anyone help with this? Thanks. Wanderer57 (talk) 18:28, 21 December 2008 (UTC)

The three Google hits were all from the Wikipedia page. If you look at the next paragraph in the Wikipedia article, the word appears spelled "esclerophile". This word is not in any online dictionary I could find, including the Oxford English Dictionary, but the "-scler-" part gives us a toehold. In words like "sclera" and "sclerosis" it means "hard" after the Greek. It's my guess that it's really "esclerophile" and means "hard-loving" in reference to the rocky terrain. "Esclerophile" yields a few non-Wikipedia hits on Google. --Milkbreath (talk) 18:54, 21 December 2008 (UTC)

I've just cleaned up that article, and I chose to retranslate that word as "sclerophyllous". How did I know? Because the Spanish WP article es:Esclerófilo is cross-linked to the English WP's Sclerophyll. --Heron (talk) 19:54, 21 December 2008 (UTC)

I have redirected Esclerophile to Sclerophyll in case it pops up in the future. Nimur (talk) 23:34, 21 December 2008 (UTC)

Paranoid park (spoiler warning)

In Paranoid park a guard gets cut into two, if I remember correctly somewhere below the waist, and after this for some seconds his upper part crawls away (supported by the arms) from the lower part. Is this really possible??? Lova Falk (talk) 19:58, 21 December 2008 (UTC)

I would expect the blood loss, organ damage, and likely spinal damage to make such a thing very unlikely... --98.217.8.46 (talk) 20:48, 21 December 2008 (UTC)

It would depend upon where the guard got cut into two pieces. If it was the lower spinal region, it would avoid any paralysis in the upper body so the arms could still be used. This would also avoid damage to organs except, perhaps, the intestines. The blood loss is an issue but if the person was particularly strong willed to pain it might be possible for a few seconds. —Cyclonenim (talk · contribs · email) 21:20, 21 December 2008 (UTC)

Isn’t the guy cut in half by a freight train? It’s not a super clean cut like from a nihontō or something. A train is likely to cause much more physical trauma. I think that degree of movement would be unlikely. --S.dedalus (talk) 21:59, 21 December 2008 (UTC)

I wouldn't know, I've never seen the film. You're right, if it's a train then I doubt very highly it could occur. But if the person were cut in half in a clean cut, it might. —Cyclonenim (talk · contribs · email) 23:21, 21 December 2008 (UTC)

This seems to me just an exaggeration of Mike the Headless Chicken. — Sebastian 05:45, 22 December 2008 (UTC)

Ah, what a sissy! Klaus Störtebeker walked along twelve of his companions after he was beheaded! 95.112.137.182 (talk) 18:14, 22 December 2008 (UTC)

As also St. Denis, who walked about two miles after being beheaded, carrying his head and delivering a sermon. - Nunh-huh 20:52, 22 December 2008 (UTC)

Though some say St.Denis was a ventriloquist [11], and only moved his lips pretending he was speaking --PMajer (talk) 10:24, 23 December 2008 (UTC) 21:08, 22 December 2008 (UTC)

If the injury is sharp (a cut rather than a crush) then what you describe wouldn't happen. Such an injury would sever the inferior vena cava and the descending aorta. Blood would squirt from the openings of both vessels, the arterial blood with some force. This would leave the blood pressure in both vessels very low, and in turn the blood from the superior vena cava and the carotid arteries would drain under pressure into their lower counterparts. The cerebral blood pressure would immediately collapse, causing the prompt cessation of cognitive and motor functions. The uncinematic reality of most mortal injuries is that people just crumple up like a puppet with its strings cut, rather than staggering around delivering lapidary epitaphs before lying down. 87.114.130.249 (talk) 21:36, 22 December 2008 (UTC)

Going back to the OP we should recall that the scene of the guard's death was an oneiric sequence or in any case, a scene in the imagination of the boy, who got shocked hearing about an accident in the news; so the episode is expressly unreal (is it so, or is it mine a dream of a dream?) --PMajer (talk) 10:47, 23 December 2008 (UTC)

Possibly - but it's irrelevent - we know that the scene is in a work of fiction, that it's a fiction inside a fiction doesn't help! The question is about reality...and it's pretty clear that the fiction (or meta-fiction...or fiction²) is incorrect. Certainly, blood pressure would drop to zero pretty much instantly (the veins and arteries are not going to pose much of a resistance to the blood flowing out) - which means that the motive power to the brain gets switched off like a light switch and loss of consciousness is almost instantaneous. Cases of bodies twitching and eyes rolling and other 'spooky' things happening shortly after death are due to now uncontrolled muscles using up the last of their energy...but the idea that there is still intent and consciousness driving them is not reasonable. Mike the chicken is weird...but he wasn't COMPLETELY headless - he still had one ear and enough brain-stem for the kinds of things chickens need to do to behave. That he survived the trauma and blood loss is the amazing thing. SteveBaker (talk) 14:36, 23 December 2008 (UTC)

Well, I assumed the question was mainly about the movie rather than about the human anatomy. The scene appears indeed unreal even without a PhD in medicine, so one can ask, what is the meaning of it. Anyway, I feel better since you confirm that it is scientifically impossible :) --PMajer (talk) 20:16, 23 December 2008 (UTC)

No, the question was about human anatomy. I did not interpret the scene as something happening in the imagination of the boy. Lova Falk (talk) 20:30, 23 December 2008 (UTC)

It is true that blood pressure would collapse immediately, but that is not to say that someone cannot remain conscious even momentarily for a few seconds! We know that cells can survive by anaerobic respiration, which is why the brain can survive for a few minutes without O₂ so with significant pain tollerance it could be possible to remain conscious for a few more seconds. This is why you can survive a heart attack temporarily before CPR is initiated, since cells can survive adequetely for a while on no oxygen. —Cyclonenim (talk · contribs · email) 19:41, 23 December 2008 (UTC)

No blood FLOW is not the same thing as no blood PRESSURE. When your heart stops, the blood still in the vessels inside your brain still contains oxygen that can presumably be extracted to keep you alive for quite a while...after all, blood flows around in a big loop giving up a little oxygen to each part of the body as it goes around. So if it merely stops flowing for a while, you'd presumably still be extracting some oxygen from it for quite a while. But when the pressure drops to zero and it flows out - that's simply not possible - so I'd expect you to black out so much sooner. SteveBaker (talk) 21:23, 23 December 2008 (UTC)

Metal detectors for non-magnetic metals

If I remember right, metal detectors (I'm talking about the security ones, not the ones people use to go and find things underground) can detect non-magnetic metals. For example, if you've had a titanium rod or plate put into your body in an operation, you have to tell the metal detector operator because you'll set it off simply with the metal in your body. The metal detector article seems to say that metal detectors depend on electromagnetic processes (forgive my lack of electromagnetic knowledge) to find metal, but I couldn't find anything in the article regarding non-magnetic metals. How is it that these detectors pick out titanium, aluminium, etc.? Nyttend (talk) 22:15, 21 December 2008 (UTC)

Titanium and aluminium / aluminum are paramagnetic. An external magnetic field will, therefore, still detect the metal as it becomes weakly magnetic, albeit temporarily. --Cookatoo.ergo.ZooM (talk) 22:49, 21 December 2008 (UTC)

How is it, then, that people with titanium in their bodies can, in certain circumstances, undergo MRIs safely? Is it just really weakly magnetic, too little to be pulled out of place by the MRI magnets? I'm not challenging you, just confused. Nyttend (talk) 22:58, 21 December 2008 (UTC)

Titanium is not magnetic enough to be pulled around in an MRI. Also, it produces very little "artifact" (a term used by MRI operators for the weird glows caused by metals in general). Therefore, titanium tools for use around MRI machines is becoming popular, as well as titanium screws, staples, and such. Now, you should note that there is not claim that titanium is not pulled around at all or that it produces no artifact at all. It just isn't enough to be of any concern. -- kainaw™ 00:03, 22 December 2008 (UTC)

Thanks for the helpful explanations — I think I understand this a lot better than when I posted the question in the first place. Nyttend (talk) 00:37, 22 December 2008 (UTC)

As the article says, many (most) metal detectors create an oscillating magnetic field. Therefore the magnetic field strength is changing all the time and a changing magnetic field causes induction of electric currents in a conductor - in this case eddy currents, which in turn create their own magnetic field which is opposed to the original magnetic field (see Lenz's law). Thus, the total magnetic field strength (which is measured by the device) will be smaller in the presence of a conductor. While human tissue is a conductor too, most metals are better conductors, and cell membranes surpress eddy currents (as a side note, when constructing a transformer, you want to minimize eddy currents, and this is usually done by using thin plates electrically insulated from each other as magnetic conductors; vibration of these plates causes the humming sound of transformers). Icek (talk) 09:13, 22 December 2008 (UTC)

And since you brought up the issue of metals and MRI, you might also be interested in the MRImetalDetector.com blog which has information on ferromagnetic (only) metal detection systems for use in MRI patient pre-screening. Tgilk (talk) 14:05, 12 September 2009 (UTC)

December 22

Generator

Why is copper used in generators instead of other metals? —Preceding unsigned comment added by 65.5.174.233 (talk) 01:29, 22 December 2008 (UTC)

Because copper has a high electrical conductivity. Among (relatviely) common metals, copper is one of the most conductive around. Silver is somewhat more conductive, but also prohibitively more expensive. Copper is also one of the most ductile metals, making it well suited for making wire. --Jayron32.talk.contribs 01:58, 22 December 2008 (UTC)

During the second world war the Manhatten Project needed to make large electrical machines for extracting uranium isotopes to make the atom bomb. Copper was in extremely short supply because the sources were cut off and the demand for military applications was high. So the US Mint had to turn over all of its silver bullion stocks to make the cabling the project needed. So I guess the second most suitable "commonly found" metal is indeed silver. SteveBaker (talk) 14:09, 22 December 2008 (UTC)

Alumin(i)um is a third choice, and it probably has a larger installed base than pure silver wiring. While not used extensively in generator windings (as far as I know) aluminum wire is widely employed in utility transmission lines; it was also popular in residential construction during a spike in copper prices in the 1960s and 70s. TenOfAllTrades(talk) 14:41, 22 December 2008 (UTC)

I expect that a generator could be made with the stator and rotor conductors made of various metals other than copper and it could work ok. Probably even mercury could be used, if confined in strong enough tubing. Cost/weight/size/strength are the design factors which suggest copper. Consider superconductive windings, which would not be copper. Edison (talk) 20:18, 22 December 2008 (UTC)

I seem to remember hearing that silver is the best conductor among wires of the same thickness, copper is best with respect to weight, and aluminum is next best either way. —Tamfang (talk) 20:09, 28 December 2008 (UTC)

With the price of copper these days aluminium has the highest conductivity for the cost, I am fairly sure it also has higher conductance than copper for a given mass too. Noodle snacks (talk) 11:05, 30 December 2008 (UTC)

Planet destroying energy

How big would a nuclear blast need to be to destroy Earth? To actually obliterate it into chunks? I stumbled upon this page [12] which shows the size of the Death Star in relation to the moon. I can't imagine something so small blowing up an Earth-like planet that's 60x bigger than the moon. Granted, it's science fiction. But what quantity of energy would the Death Star need to generate to blow up a planet? Is that even in the realm of fusion or matter/anti-matter reactions? --70.167.58.6 (talk) 05:37, 22 December 2008 (UTC)

You can't quite compare an explosion with an Impact force. The two behave differently as you can see from those pages. 76.97.245.5 (talk) 07:10, 22 December 2008 (UTC)

You need to overcome gravitational binding energy. The value for Earth is a bit larger than the number given in the article because Earth is not of uniform density; it's about 2.4*10³² J. That's the energy equivalent of 2.7*10¹⁵ kg. If the chunks are as small as they appear in Star Wars, the gravitational binding energy of these chunks is negligible compared to the 2.4*10³² J, so you'll need approximately that amount of energy. Icek (talk) 08:50, 22 December 2008 (UTC)

For comparison, the theoretical maximum yield of the Tsar Bomba, the largest fusion weapon ever tested, was 100 Mt or 4.2x10¹⁷ J (the actual test bomb was limited to a yield of 50 Mt). So, even if all of this energy could be utilised, you would need 5x10¹⁴ (i.e. 500 trillion) such bombs to reduce the Earth to small chunks. Gandalf61 (talk) 09:17, 22 December 2008 (UTC)

You'd also have to give those chunks enough speed to exceed their mutual escape velocity - or else they'd all come back together in a gigantic collision and form a new planet ("NEW!! Earth 2.0^TM - now with fewer annoyingly destructive lifeforms!"). SteveBaker (talk) 14:04, 22 December 2008 (UTC)

Hmmm.... what do you mean? You can do this if you have 2.4*10³² J at your disposal - at least in principle. Icek (talk) 14:19, 22 December 2008 (UTC)

A pretty good website about it can be found at [13], and some technical data here: [14] --86.125.162.148 (talk) 18:47, 22 December 2008 (UTC)

The energy "to exceed their mutual escape velocity" is what gravitational binding energy means. —Tamfang (talk) 20:14, 28 December 2008 (UTC)

Gravity hole

Could there theoretically be an equivalent for black holes when we are talking about gravity and gravitons ? 69.157.229.14 (talk) 05:40, 22 December 2008 (UTC)

What type of "equivalent" for a black hole are you trying to define? AFA our article states a black hole is a phenomenon related to gravity. Are you trying to have a location not influenced by gravity? (I think that would be impossible, the best you can hope for is offsetting forces e.g. with a magnetic field.[15]) Gravitons are (hypothetical) particles that "carry" gravitational forces, sort of like electrons carry electrical charge. or Are you thinking of supersymmetry, creating an "anti-black hole" with Gravitinos?? P.S. I put hypothetical in brackets so that we don't end up with another one of those "it's only a theory discussions". No one's found one yet, but there are a lot of clues saying there should be one, unless s.o. is going to come up with a better explanation. 76.97.245.5 (talk) 06:56, 22 December 2008 (UTC)

I guess you're asking about a region of space from which gravitons can't escape. That would be a black hole. Nothing can escape across the event horizon of a black hole, including gravity. The field of a black hole is a so-called "fossil field" left over from the collapse. It doesn't come from inside the hole. -- BenRG (talk) 08:08, 22 December 2008 (UTC)

I don't think that's right. A black hole's gravitational attraction to other objects does increase with every object it swallows, doesn't it ? Therefore, those theoretical gravitons must escape. Perhaps this is a flaw in graviton theory itself, and visualizing gravity as a deformation in space-time is more accurate. StuRat (talk) 18:43, 22 December 2008 (UTC)

Yes - it's much easier to think of gravity as space-time deformation. But (to pre-empt Jayron32 who is just ITCHING to say this) "Gravity is gravity, however, and that it sometimes behaves like a space-time deformation and sometimes like a particle is not gravities problem. Its ours."

But it seems entirely unreasonable to me that a graviton is affected by gravity. That doesn't sound right. The (hypothetical) graviton is the force-carrier particle for a gravitational field - just like the photon is for an electromagnetic field. It's what communicates the 'message': "There is a damned great black hole over there - and therefore you should be accelerating towards it!".

Photons don't get bent around by electric fields - so why would we expect gravitons to be affected by a gravitational field? If something in a large chunk of matter is emitting gravitons - and if those gravitons are affected by that gravity - then you'd need a second graviton to carry the message to the first one...then what communicates the message to the second graviton?!? That's just got to be wrong.

So I think BenRG is incorrect - if gravitons exist - they can escape a black hole because they aren't affected by gravity.

The business of the 'fossil field' is to do with the relativistic issues of matter entering the black hole being 'frozen' at it's surface by time dilation.

SteveBaker (talk) 21:19, 22 December 2008 (UTC)

I have lots of other problems with gravitons, or any gauge bosons, really. They all have in common that a seemingly infinite number of undetectable particles be constantly bouncing between every pair of elemental particles in the universe. StuRat (talk) 21:51, 22 December 2008 (UTC)

StuRat: Massive particles that fall into a black hole have gravitational fields of their own. When they get close to the event horizon, you feel the combination of the two fields, which is similar to the field of a uniform (no hair) black hole of the combined mass. Over time the inhomogeneities in the field radiate away and you end up with a larger uniform field.

SteveBaker: Everything gravitates, including the gravitational field. That's one way of understanding why GR is nonlinear: the field interacts with itself. It's classical electromagnetism that's the oddball here—all of the forces in the Standard Model are nonlinear, including electromagnetism, though the nonlinearity there is small. The strong force is extremely nonlinear: the gluons have color charge and the coupling constant is very large.

StuRat, and everyone really: Feynman diagrams are ridiculously oversold in popular books, to the point that a lot of people seem to think that quantum field theory is about virtual particle exchange and you can't have a quantum field theory without virtual particles. That's not how it works at all. Quantum field theory is about fields. Virtual particles and Feynman diagrams are a kind of series expansion for the underlying field theory, similar to a Taylor series. Taylor series are great when they converge quickly, not so great when they converge slowly, and useless outside the radius of convergence where they don't converge at all. The perturbation theory in Feynman diagrams is the same way. You can't "see" the whole field theory through Feynman diagrams, and what you do see is arguably not conducive to a good understanding of the full theory. If you do gravity with Feynman diagrams you have to choose a fixed background and perturb around that, which means you lose the background-free character of GR, which is really the most interesting thing about it. The Standard Model forces also have some of that background-free character—that's what the "gauge" in "gauge boson" means—and that's lost when you think of them in terms of Feynman diagrams. So forget about virtual bosons. "Virtual graviton exchange" is at best just another term for "gravitational attraction", and at worst it's a strictly less general notion. When I see questions about virtual gravitons I usually try to answer as though they were about fields, as I did above. -- BenRG (talk) 08:18, 23 December 2008 (UTC)

Thats an interesting point. So is there still a black hole inside?Trevor Loughlin (talk) 14:33, 22 December 2008 (UTC)

Speed of light in another universe

Could the laws of physics be different in another universe, and if so, could the speed of light be different as well? I heard somewhere that the laws of physics are mostly dictated by the nature of the particle that make up our universe. While this sound plausible, I'm sure it's far from fact. If it were true, could an alternate universe composed by alternative particles making what we would call exotic matter (but to them would be ordinary) then have different rules on how that matter acts? Tiailds (talk) 07:44, 22 December 2008 (UTC). I have shown that the speed of light in another universe is related to the mass of that universe. J Forrest see http://mayennegite.chez-alice.fr/Universes/.

Can't quite see why you shouldn't be able to have a different universe with a different speed of light (in a vacuum!). The crux of the matter is that if you change one thing you have to see what else is affected. You can't just say "in this universe apples fall up". You would then also have to describe all the related issues e.g. how apple trees grow, what makes apple, falling up different from pears, falling down. Since it has taken many generations of physicists to sort out how things are connected in this universe, and we still haven't figured it all out to the last detail, I'd assume you'd have to live with some approximation of how a universe functions where light traverses a vacuum at a different speed, because it would take too long to define everything. 76.97.245.5 (talk) 08:28, 22 December 2008 (UTC)

Simply that the speed of light is determined by the space it is moving through, determined by the total effect object masses and gravitational effects in our universe. These determine the spatial geometry through which light moves so another (parallel) universe for example may have a larger total mass than ours which should change the spatial geometry, hence the speed of light. J Forrest Dec 2010

By definition, we cannot know the laws of physics in another universe. Icek (talk) 08:38, 22 December 2008 (UTC)

It's certainly true that we can't know. Indeed we can't even known that there ARE other universes (although it would certainly explain a whole lot if there were). There are some things like the speed of light or the charge on the electron that I think most physicists would be happy to accept could be different because we have no reason to know why they have the exact values they have in our universe (although the strong anthropic principle is some sort of a reason). But there are other things - more in the realms of mathematics - that I think we'd be unwilling to agree could possibly be different - the value of PI for example. It's fairly easy to imagine a universe where light travelled 0.000001% faster than it does in ours - but it's impossible to imagine a universe in which PI differs AT ALL from the value in ours!

Somewhere between those limits we have physics/math things like dimensional analysis that say things like that 'velocity = frequency * wavelength' has to be true because velocity is measured in meters-per-second, frequency in 1/seconds and wavelength in meters - so for the dimensions of the equation to balance, it pretty much has to be that. A universe in which (say) velocity equals frequency SQUARED times wavelength would be seriously screwy! So I think we could be reasonably comfortable saying that some of the equations we're happy with in examining our universe would be fundamental enough to hold in other universes...but others, less so.

If we're happy to entertain things like different values for the speed of light - then we would CERTAINLY expect matter to behave radically differently - it doesn't take much of a change in the charge on the electron to make all atomic matter impossible and reduce the universe into a bunch of black holes with nothing else present but vacuum. Matter with bizarre behavior (and therefore 'exotic' by our standards) would certainly be expected if any of the fundamental constants were off by a relatively small amount. So unless there is some deep underlying reason why the speed of light, the charge on the electron, the universal gravitational constant and the plank length are what they are - then they could be different - and all sorts of wierdness would result.

But other universes might be different in other ways too - more or fewer spatial dimensions certainly seems like a reasonable possibility - and that would result in things being so seriously out-of-whack that it would be almost impossible to imagine the consequences. If string theory is right and our universe has 26 dimensions (or however many it is that string theorists are predicting this week!) - of which 23 are 'tightly coiled up' or 'small' and therefore impossible for us to detect - then who is to say that with different fundamental constants (like the speed of light) that they wouldn't have 17 'small' dimensions and 9 normal dimensions. Right there - we'd have a universe that would be hard to imagine and impossible to visualise.

SteveBaker (talk) 13:57, 22 December 2008 (UTC)

Indeed, if a universe would have 2 or 4 (ordinary) spatial dimensions and by analogy with the universe would have an attractive gravitational force proportional to 1/r or 1/r³, respectively, then planetary orbits wouldn't be stable - the only closed orbits would be circular (and I think this is true for any dimension other than 3; but if we look closely orbits aren't closed in the real universe either, even in the 2-body case - in General Relativity there is perihelion precession, and, even worse, gravitational radiation). Icek (talk) 14:29, 22 December 2008 (UTC)

This is kind of off-topic, but in 2+1 dimensional general relativity there are no closed orbits, even unstable, even approximately. In fact, test particles do not accelerate toward massive objects in 2+1 dimensional general relativity. It's very different from 2-dimensional Newtonian gravity. -- BenRG (talk) 22:17, 22 December 2008 (UTC)

It's hard to say what it means to "change the speed of light". Units like meters and seconds are based on human beings—a meter is about the size of a person and a second is about how long it takes to have a thought. If the speed of light were twice as fast, then we'd think twice as fast, so our second would be half as long, so the speed of light in human-based units would be the same. In some sense 299,792,458 m/s is not a physical constant at all, it's a biological constant, a measure of how much low-level signaling in the brain is needed for conscious thought. What about the speed of light in "natural units"? Well, in the usual "natural units", Planck units, the speed of light is 1 and can't be changed because it's how those units are defined in the first place. So our attempt to change the speed of light failed to change its value in natural units or in human units—in what sense did it change at all? People sometimes say that you can avoid those problems by only talking about unitless constants, but that's not really true either. For example, the proton/electron mass ratio (about 1836.15267) is a unitless constant, but it's not clear what it means to change it in isolation. The problem is the arbitrariness of coordinates. The Standard Model of particle physics has about 26 continuous parameters, but not any particular 26, in the same way that space has three dimensions, but not any particular three. You can't change your x coordinate unless you know how the x coordinate is defined, and you can't change your x coordinate "without changing anything else" unless you know what the other coordinates are too. Nonetheless, you can choose a different point in the 26-dimensional parameter space and get a description of a different universe. It's just hard to say exactly what you've changed.

Most if not all of the continuous parameters in the Standard Model can be interpreted as properties of particles, so in that sense "the laws of physics are mostly dictated by the nature of the particles". In fact (as John Baez mentions in the above-linked web page) most of the constants can be interpreted as properties of the Higgs boson, which is what makes it so interesting. -- BenRG (talk) 22:17, 22 December 2008 (UTC)

I disagree. I understand what you're saying: I suppose you can say that if all of the fundamental constants that relate to time and distance were scaled by the exact same amount - and all of the ones that relate to mass by another...and so on...then the 'absolute' values for these constants could change and you wouldn't notice a difference...and unless you could somehow transport a stopwatch, a tape measure and some kilogram test masses from our universe to the other - there would be no way to know that there even was a difference. So in that sense, two universes could have different speeds of light - and so long as all of the other time and distance values were scaled proportionately - you'd never know.

But if the speed of light was different - yet none of the other constants containing time and distance were ALSO different - then things would behave differently in fundamental and noticable ways. Restating things in Plank units doesn't change that fact. In the article you linked, the masses of the quarks (in Plank units) are now fundamental constants. In that scheme, if the RATIO of the masses of the charm and strange quarks were different than in our universe but the ratio of the up and strange quarks were exactly the same - then we'd have a different universe no matter what units or scaling you apply to it. Unless we can find a fundamental reason WHY the quarks have those particular masses - so we can eliminate all of the quark-masses from the list of constants and relate them all to something more fundamental - then they can (in principle) be different in other universes. But worse still - many of the constants are dimensionless. Change one of those and the universe is different no matter what because you can't compensate for that change.

But in the end we don't (and can't) know...it's perfectly possible for another universe to have no analogs of matter or energy or time or space or anything else - and for our universe to lack their ubiquitous snark, blarth, pling (and anti-pling) upon which all of everything is based on their side of reality. SteveBaker (talk) 14:21, 23 December 2008 (UTC)

I quite agree that other universes could probably have an infinite number of other dimensions, hence different constants. However, my theory is only concerned about a parallel universe which influences ours which has mass and similar dimensions to ours which explains a variety of observations such as dark matter and energy, etc. The double-slit photon experiment also supports this idea that two (or more) universes can exist side-by-side and influence each other at a material and energy level and that the presence of a parallel universe is also likely to be influencing our universe at the atomic level. I have used this experiment to show that our immediate merged bu tsimilar parallel universe is only 16ms out of phase with ours which explains why we can detect its mass (dark matter) but cannot 'see' it because the light from it is out of phase with our detection methods. For this to work the Universes will need to be merged and nearly in-phase, hence sharing dimensions, mass and energy at spatial and atomic levels. Probability dictates that other parallel universes may influence ours but will be too out of phase to influence us significantly. J Forrest Dec 2010

Particle-wave separation/fusion

In light, can the particle ever disappear and leave only the wave, only to return a few instants later? 69.157.229.14 (talk) 08:16, 22 December 2008 (UTC)

No, because that's complete nonsense. Light doesn't have separate wave and particle parts. Algebraist 08:35, 22 December 2008 (UTC)

Have a look at Wave–particle duality.76.97.245.5 (talk) 08:39, 22 December 2008 (UTC)

Light is neither a wave NOR a particle - but it behaves a bit like both of them - sometimes (eg in diffraction) it seems more like a wave and in other times (eg in the photoelectric effect) it seems more like a particle. But these are just ways to describe it's behavior in more or less familiar terms. Light (or more properly 'electromagnetic radiation') is quite different from other kinds of 'stuff' in the universe. So you can't separate out the wave and the particle behaviors because they aren't separate - they are just ways of thinking about something that lies beyond our normal day-to-day human experience. As Jayron32 is fond of telling us "Light is light, however, and that it sometimes behaves like a wave and sometimes like a particle is not lights problem. Its ours." - which sums it up rather eloquently. SteveBaker (talk) 13:09, 22 December 2008 (UTC)

Another way to say it is that people have made up the concepts of waves and particles. They both happen to have some properties of light. — DanielLC 17:59, 22 December 2008 (UTC)

Did I just get quoted there (ego swells)... Thanks Steve! I have nothing further to add, since SteveBaker already said what I was going to say!. --Jayron32.talk.contribs 20:19, 22 December 2008 (UTC)

Don't get too excited - we're all bored with that one. Now you've got to find something cogent and witty to say about the lipid layer in the eye.  :-) SteveBaker (talk) 20:45, 22 December 2008 (UTC)

See the lipid layer is the lipid layer, however, and that it sometimes behaves... oh fuggit. It doesn't work as well there... --Jayron32.talk.contribs 14:20, 23 December 2008 (UTC)

I like to use the term "wavicle" to describe light: poke it one way and it looks like a wave, poke it another way and it looks like a particle. --Carnildo (talk) 02:23, 24 December 2008 (UTC)

Storing solar lights

I got some solar x-mas lights this year. What is the best way to store them, so that they will work again next x-mas? Should I take out the rechargeable batteries? If yes, what's the best way to store them? Should I recharge them at regular intervals during the year? Should I let them drain completely before I put them away? Would it be better to run the lights in the back yard all year round than storing them till next x-mas? Other ideas?76.97.245.5 (talk) 08:48, 22 December 2008 (UTC)

It depends on the kind of battery, but it's usually better to drain them "completely" (see memory effect, but also see "deep discharge" there) and then recharge them before you store them in order to prevent deep discharge. As for the lamps, if they are incandescent lamps they wear out quickly if you turn them on and off often. Just store them. Icek (talk) 12:17, 22 December 2008 (UTC)

Thanks a lot for the info and the link. The lights are led, but I guess their lifespan doesn't improve with use either. I'll just run the batteries though my charger (that takes care if draining them, too) and then put everything away. 76.97.245.5 (talk) 12:50, 22 December 2008 (UTC)

LED's last an awful long time and can take a lot of abuse - there probably isn't much you can do to hurt them. I would keep them someplace dark and dry (more for the sake of the wiring and connections than for the LED's themselves) - but otherwise no special care is needed. The batteries (as Icek said) should probably be allowed to completely discharge - ie turn the lights on - put the solar panel someplace dark until the lights go completely off then store them in the dark so it doesn't recharge! The only kinds of rechargeable battery that don't like to be stored in a discharged state are lead/acid batteries (like car batteries) that should be kept fully charged at all times - but they don't use lead/acid for things like solar-powered lights so that's not a problem here. When you take them out next year - wipe the cover that's over the solar panel to make sure it's clean and you're good to go. SteveBaker (talk) 12:59, 22 December 2008 (UTC)

Well, Li-ion batteries don't like to be stored discharged, either. I think 40% is the optimal charge for long-term storage, at least for Li-ion polymer batteries. -- Aeluwas (talk) 13:55, 22 December 2008 (UTC)

More like 75% for all lithium batteries131.172.99.15 (talk) 14:01, 23 December 2008 (UTC)snaxalotl

Earth's rotation

Looking at the image, Earth apparently spins up every year approximately at the time of Northern Summer. Is this because of snowfall in Antarctic winter which lowers the sea level a bit? (Earth's moment of inertia is about 8*10³⁷ kg m²) it would mean that sea levels change seasonally by maybe 0.2 m (I haven't done a proper calculation) which sounds like too much. Is there another important cause of the seasonal variation? And why was Earth rotating so slow in recent years (no leap second in the years 2000 - 2005)? Icek (talk) 10:30, 22 December 2008 (UTC)

This term is dubbed secular acceleration, which is the phenomenon of earth slowing down every year. ♫Deathgleaner 00:48, 27 December 2008 (UTC)

Someone on sci.physics said that the leaves on trees contribute to the effect (most trees are in the Northern Hemisphere), but the effect of that would be the opposite of what you noticed... -- Army1987 – Deeds, not words. 10:52, 22 December 2008 (UTC)

Indeed, the faster the Earth spins the steepest the descent of the curve is, so, to me, it seems that it's faster in winter, as the above would predict. -- Army1987 – Deeds, not words. 10:58, 22 December 2008 (UTC)

No, the slower the Earth spins the steeper the descent of the curve is: Then leap seconds have to be more frequently, as can be easily seen from the diagram. A leap second means that the Earth hasn't yet spun as far as the 86400 second day would predict and we have to wait an extra second for Earth.

As for the leaves on trees: If the average height of the leaf above ground is h = 20 m, and there is A = 40 million km² more deciduous forest on the Northern Hemisphere than on the Southern Hemisphere (an gross overestimation I think), and the effective (not quite the average) lattitude is θ = 35°, and there is one tree per A_t = 10 m², and there is m_l = 200 kg leaves per tree, then the change in moment of inertia is:

ΔI = 2 * r(θ) * h*cos(θ) * A/A_t * m_l = 1.37*10²³ kg m²

where r(θ) = R_Earth*cos(θ) is the distance from Earth's axis at the effective lattitude. This is a relative change of moment of inertia - and thus of angular velocity - of 1.7*10^-15. I think I certainly didn't underestimate with my choice of the parameters. That relative change would mean a change in slope of the curve equivalent to an extra leap second (or a missing leap second) once every 18.5 million years - and that is clearly way less than what we see in the diagram! Icek (talk) 11:53, 22 December 2008 (UTC)

By the way, the relative change is also at the current limits of accuracy in measuring time. Icek (talk) 11:55, 22 December 2008 (UTC)

No expertise in this but I would expect the earth to be slower in recent years with global warming because the water would be spread out rather than at the poles. The spin up during summer may be because the water goes into the ocean instead of staying on the land. Dmcq (talk) 13:12, 22 December 2008 (UTC)

That's what puzzles me - it's that Earth rotated faster in recent years. How do you think water going into the ocean instead of staying on the land causes Earth to spin up? If some amount of mass is located at a certain lattitude θ and then gets spread out over the whole surface of Earth (yes, I'm ignoring the distribution of water and land by lattitude, I could be substantially more accurate by a detailed calculation), it will decrease Earth's moment of inertia only if it was at a lattitude smaller than arccos(sqrt(2/3)) = 35.26°, and else it will increase Earth's moment of inertia (and thus slow down Earth's rotation). Icek (talk) 14:39, 22 December 2008 (UTC)

The answer (for the seasonal variation) seems to be the exchange of angular momentum between the atmosphere and the the lower part of Earth [16]. Icek (talk) 15:16, 22 December 2008 (UTC)

The atmosphere's mass is about 5*10¹⁸ kg, so its angular momentum is about M*R²*2/3 = 1.35*10³² kg m². The effect is a relative change of maybe 10^-8; that means an average angular velocity of the atmosphere of 0.006 times Earth's angular velocity - which is just 2.7 m/s at the equator. Of course not the whole atmosphere is moving, but the speed will not be that much lower closer to the poles as my calculation assumes (i. e. not like a rigid body), and it seems realistic. Icek (talk) 15:28, 22 December 2008 (UTC)

I think we are grasping at straws here. During northern hemisphere summer, the earth is at its aphelion, its farthest point from the sun. Being farther from the sun, the earth will experience less tidal drag from the sun, thus speeding up its rotation slightly. All the bullshit about this being due to changes in weight distribution due to increased snowfall at the south pole, or leaves falling off of trees, or anything like that seems like some pretty wild stuff. None of those is going to make an effect like this, I am pretty sure its just that, since we are farther away from the sun, we spin a little faster... --Jayron32.talk.contribs 20:16, 22 December 2008 (UTC)

Yep - I agree. These other things seem vastly too small to have a significant effect - tidal forces from the sun account for annual variations - the moon's gradual slowing down in orbit and the drag due to turbulence in the core can account for longer term effects. SteveBaker (talk) 20:41, 22 December 2008 (UTC)

Here's an article that doesn't need subscribing A New Spin on Earth's Rotation. I must admit to being surprised the atmosphere has such a large effect. Dmcq (talk) 22:24, 22 December 2008 (UTC)

I have to disagree with Jayron32 - tidal forces are proportional to m/r³ (with m being the mass of the body causing the tidal forces and r being the distance from this body), so the relative strength of Moon's and Sun's tidal forces can be easily calculated. The Sun's tidal forces on Earth are a bit less than 1/2 that of the Moon, and the difference between the Sun's tidal forces at aphelion (152.1 Gm) and perihelion (147.1 Gm) is a bit less than 1/20 that of the Moon's total tidal forces. That means that the seasonal change due to this effect should be less than the long term slowing due to tidal forces. But from the diagram alone one can see that the total seasonal variation is far larger. Icek (talk) 05:13, 23 December 2008 (UTC)

I disagree. You're comparing long term slowing due to the gradual slowing down of the moon in it's orbit to seasonal slowing - you should be comparing monthly effects of the moon to the annual effect of the sun. The moon raises tides comprising around 100,000 cubic kilometers of water - that dwarfs all of the other effects described (leaves, etc) - and even 1/20th of that (seasonally) is an immense variation. We'd probably see even greater lunar-monthly day-duration changes were it not for the dampening effect of the liquid core and the large inertia of the earth...but an effect that happens on an annual basis is long-lived enough to produce a measurable effect. SteveBaker (talk) 13:54, 23 December 2008 (UTC)

I don't think you are correct here: The tides do not directly change the effective moment of inertia by creating bulges of water, because these bulges don't rotate with Earth. So the change in rotation rate is by friction only, and there shouldn't be an increase in rotation rate when the tidal forces become weaker, but the diagram clearly shows an increase.

Regarding the atmospheric effect, note that this is not a redistribution of mass as in the cases of falling leaves and melting polar glaciers; it is that 2 parts (there are actually more than 2, but you get the idea) of Earth have different rotation rates, and we're measuring only one part. The atmosphere spins up in Northern winter and takes angular momentum from the rest of Earth beneath it. Icek (talk) 14:59, 23 December 2008 (UTC)

But there's just not enough atmosphere to have that effect! The mass of the atmosphere relative to the solid part of the earth is just not enough to cause such rather large changes in momentum. One second per year seems rather high for such effects, even if the entire atmosphere shifted to between the poles over the course of a year, we probably wouldn't see such effects. Yes, there are effects slowing the earth down and speeding it up due to redistribution of mass due to "tidal bulges" and the like, but even if the earth was a perfectly rigid ball, there would be a drag effect caused by the force of gravity, which is pulling against the spin of the earth, and I would think THAT effect is greater than any caused by such esoteric and tiny factors as Northern Hemisphere weather... --Jayron32.talk.contribs 18:21, 23 December 2008 (UTC)

Atmosphere moment of inertia (~2/3 M R^2): ~1.3 ×10³² m² kg. Moment of inertia of solid Earth (~2/5 M R^2): 8 ×10³⁷ m² kg. So the ratio of the atmosphere to the solid earth moment of inertia is 1.6 parts per million. A variation of one second per year is 1 part in 32 million. In other words, you only need a 5% change in the angular momentum of the atmosphere to add 1 second to the angular momentum of the solid Earth (or vice versa). Dragons flight (talk) 18:52, 23 December 2008 (UTC)

Jayron32, how do you think that "a drag effect caused by the force of gravity..." will change the angular momentum of a rigid ball? How do you get a torque? Icek (talk) 21:08, 23 December 2008 (UTC)

New image and new headline

Because the annual variations are hard to see in the original image, I plotted the same data over the course of a year. The thin green lines connect consecutive days; the almost horizontal lines are distracting, they are the connections between Dec 31 and Jan 1 of the next year. The big spike occurs on 5/19/1976, it is obviously an error because the next day ∆t is given as 0. — Sebastian 22:02, 23 December 2008 (UTC)

The next highest two peaks occur on Jan 5 1833 and at the beginning of Feb 1983. — Sebastian 22:15, 23 December 2008 (UTC)

Thanks for the image (for anyone else interested in the data: link, format). What you plotted is the derivative of the data in the original image (or isn't it?) - so here a positive slope means that Earth's rotational period is increasing and a negative slope means that Earth is spinning up, while in the original image, a constant slope meant that Earth's rotational period stays constant. One can see that there are monthly variations: When looking closer at the data it seems like there are local minima of the length of day both at Moon's apogee and perigee (the last perigee was on or around December 13, according to Heavens-Above), and the length of day is larger at the perigee (i. e. shortly before the Moon reaches perigee Earth spins up, after perigee it slows down again and reaches a minimum of angular velocity before apogee; then it spins up again in order to reach its largest angular velocity at apogee, and then again slows down to another minimum before perigee and so on). I don't know exactly why this is so, but it's a more subtle effect than what SteveBaker and Jayron32 seem to be thinking. Icek (talk) 09:04, 24 December 2008 (UTC)

Yes, it's the derivative. To be exact, it's the negative of the derivative of UT1-UTC, (or, if you like, the derivative of UTC-UT1) because I wanted the value to be predominantly positive. I'm now aware that that may not have been a good idea, and apologize for any confusion this may have caused. I should also mention that the "months" are actually exactly 1/12 years; I compensated for different month lengths. — Sebastian 04:14, 26 December 2008 (UTC)

I think plotting Earth's rotational period (or rather the difference between Earth's rotational period and 24 hours) is actually better than the original image for the purpose of this discussion. Even the second derivative of the original image wouldn't be all that bad - then one could conclude that some feature is not caused by friction if the curve is below zero. Icek (talk) 16:16, 26 December 2008 (UTC)

I'm now inclined to think that it's really mostly the eccentricity of Earth's orbit: Looking at the data, there are local minima of length of day at both aphelion and perihelion fairly regularly (well, often the perihelion minimum is not quite visible). But why? It seems like changes in effective angular momentum are dominated by the absolute value of the rate of deformation in some way - I don't understand how this works. Icek (talk) 09:30, 24 December 2008 (UTC)

the nearest galaxy

hello, i was wondering, what is the nearest galaxy to ours? —Preceding unsigned comment added by 92.13.130.144 (talk) 18:35, 22 December 2008 (UTC)

The Milky Way (the galaxy which we are in) is part of the Local Group, a cluster of about 35 galaxies (that article, and ones it links, has a lot of good information about nearby galaxies). The nearest spiral galaxy is the Andromeda galaxy (also in the local group). The nearest galaxy of any shape is a little harder to describe. The nearest one of any significant size is the Large Magellanic Cloud. There are dwarf galaxies which are closer, such as the Canis Major Dwarf Galaxy, which is only 42,000 light year from the galactic center, or 25,000 light years from earth. According to the article it "is now thought to be the closest neighbouring galaxy to our location in the Milky Way". However, it was only discovered in 2003 (the Sagittarius Dwarf Elliptical Galaxy held the previous record), so there may be a possibility that an as-yet-undiscovered galaxy is closer still. -- 128.104.112.113 (talk) 18:48, 22 December 2008 (UTC)

Acceleration of particles in a secluded system

I read that space-time travel could be reached by means of acceleration of particles in a secluded system. What would this mean concretely ? 69.157.229.14 (talk) 20:54, 22 December 2008 (UTC)

Er..."space-time travel"? I think we first need to ask what you mean by that. Travelling in space over the course of time is what we normal people call "moving". And it's impossible to achieve movement without some acceleration of particles...but if particles are accelerating then you have movement in space (and time is doing it's usual thing). It doesn't matter whether they are 'secluded' or not.

If you actually mean just "time travel" - then no.

I think you need to clarify what exactly it is you are talking about here. SteveBaker (talk) 21:28, 22 December 2008 (UTC)

I'm not sure, but it has something to do with this. [17][18] 69.157.229.14 (talk) 21:51, 22 December 2008 (UTC)

The first link is a joke, the second is a video of a sculpture of a machine that doesn't work.... —Preceding unsigned comment added by Philc 0780 (talk • contribs) 22:20, 22 December 2008

The second video claims to be of a time machine that travels into the future at a rate of 1 SPS (which one assumes means 'second per second') - which is an old and rather lame joke. However, taken at face value, it DOES work - it just doesn't do anything useful. SteveBaker (talk) 13:41, 23 December 2008 (UTC)

Tech Bump

Look at the palm of your right hand (if you are right handed). As you face it, I believe you may find a noticable bump in the bottom left corner. I'm convinced it's a souveneir from all the time that palm lies on a table as the hand grasps a mouse. For the palm of graphics developers, this bump is absolutely inflamed and even painful. Is there a name for this scar? Sappysap (talk) 23:36, 22 December 2008 (UTC)

Please excuse my "original research" but, no bump here! -hydnjo talk 23:47, 22 December 2008 (UTC)

The hamate bone is often palpable near the hypothenar eminence. This response is simply descriptive regarding the location you describe - the RefDesk is NOT a place to ask for medical advice. --Scray (talk) 00:10, 23 December 2008 (UTC)

Sorry, where was the request for medical advice? WP:OR none found here. Edison (talk) 00:25, 23 December 2008 (UTC)

Thank you, Edison. Sappysap (talk) 00:27, 23 December 2008 (UTC)

I just felt the need to be explicit about what I was saying - that I was describing a structure at that location, as requested, but not explaining the "inflamed and even painful" bump described by the OP. I guess this came off wrong, since Sappysap thanked you. Sorry about any inferred negativism. --Scray (talk) 00:39, 23 December 2008 (UTC)

Thank you, too, Scray. Sappysap (talk) 00:47, 23 December 2008 (UTC)

Have you looked at Callus? Irritation and chronic Inflammation might also hold interesting info for you. 76.97.245.5 (talk) 00:15, 23 December 2008 (UTC)

I am right handed but I hold the mouse with my left, so the mouse bump should be left. Thinking about how the hand would be resting on the table it would be sustained by the flesh at the lower, inner side of the outer edge of the hand. This flesh would be slightly shifted upwards and there would be a bump. Now I'm anxious not to really look at my hands to avoid original research. 95.112.186.8 (talk) 07:53, 23 December 2008 (UTC)

First I went to Repetitive strain injury which seemed to fulfil the condition in concept only, the best is Splints even though it's for a horse, it seems closer to what you mean. Take from it what you can, Julia Rossi (talk) 10:00, 23 December 2008 (UTC)

That bump is the pisiform bone, not the hamate. It is a sesamoid bone, a bone that develops within a ligament/tendon. (Party trick: If you use your other hand to push the pisiform distally [i.e. from your wrist toward your pinky)], it will press on the branch of the ulnar nerve that supplies the palmaris brevis muscle and slightly wrinkle the skin on the side of the palm beyond the wrist.) To avoid resting the weight of your hand on it, I'd suggest using an armrest on your chair so that your forearm is bearing the weight. -- Flyguy649 ^talk 17:17, 27 December 2008 (UTC)

Secondary minerals?

I was trying to improve a "random" page (on Wulfenite) and came across the term "secondary mineral". Searching WP, I found many pages that use the term, but no wiki links for it. Even though I am no geologist, I can guess what this term means, but it seems as though there should be a WP page to cite, or maybe there is a more precise term. Note that I am NOT asking for a definition - I'm looking for an appropriate wiki-link. Thanks. --Scray (talk) 23:58, 22 December 2008 (UTC)

Minerals mentions secondary oxidation under "Sulfate class". Maybe you, or s.o. else could add a paragraph, then everyone could link there and we wouldn't need a new page. 76.97.245.5 (talk) 00:25, 23 December 2008 (UTC)

Thanks. That content (in Mineral) is fairly narrowly-focused, and I don't have the knowledge to make a broader statement defining secondary minerals. Anyone else? --Scray (talk) 00:41, 23 December 2008 (UTC)

I referred this question to the Talk:Mineral page. --Scray (talk) 01:00, 23 December 2008 (UTC)

Secondary minerals are those formed under a weathering or oxidizing environment at or near Earth's surface, most often used in discussing surface expressions of ore deposits (least that's where I've seen the term most). That said, perhaps the best place for clarification would be the weathering article ... still thinking. Vsmith (talk) 14:45, 23 December 2008 (UTC)

For those interested, this was resolved very nicely by Vsmith! --Scray (talk) 03:38, 24 December 2008 (UTC)

December 23

Material with highest melting point?

Hello -- what material has the highest melting point? I've found listings for the melting points of various pure elements by melting points, but nothing which describes what happens to the melting point when you create alloys, etc. Is there anything that has a higher melting point than carbon in amorphous or graphite forms? --98.217.8.46 (talk) 00:51, 23 December 2008 (UTC)

The melting point article you cited lists Tantalum hafnium carbide as having an extremely high melting point. The article for Tantalum hafnium carbide says that it is the compound with the highest known melting point. --Scray (talk) 00:54, 23 December 2008 (UTC)

Wow! That's impressive - it's about 80% of the temperature of the surface of the sun! SteveBaker (talk) 21:17, 23 December 2008 (UTC)

So, what's a refractory compound? — Sebastian 22:33, 23 December 2008 (UTC)

Never mind, found it: Refraction (metallurgy). — Sebastian 22:35, 23 December 2008 (UTC)

TASTE BUDS

WHY WE DON'T GET SWEET TASTE WHEN WE HAD ALREADY A SWEET DISH BEFORE IT?AS IT IS NOT IN THE CASE SOUR TASTEM.meghajain (talk) 02:14, 23 December 2008 (UTC)

See "Neural adaptation" and "Habituation", and don't type in all caps. Our senses grow dull to a constant input. We stop feeling our clothes soon after we put them on, and we don't smell the pig farm next door after a week or two. --Milkbreath (talk) 02:25, 23 December 2008 (UTC)

I'm not an expert, but if I remember correctly sour taste is caused by a low (=acidic) pH inside certain receptor cells, I guess that internal pH is regulated by the cell with only short delays, while sweet substances stick to receptors on the outside for a longer time. Regarding sweetness, an interesting substance to look up is miraculin. Icek (talk) 06:21, 23 December 2008 (UTC)

Science/Humanities question on Egypt's buried tombs

"70 percent of Egypt's ancient monuments remain buried under sand," a news article on two 4300-year-old tombs quotes an official as saying. Was it desertification? Thanks in advance. Imagine Reason (talk) 03:13, 23 December 2008 (UTC)

In any case it is a policy of modern archaeology not to exploit completely an archaeological site. The idea is that in the future more advanced tools and techniques will be available, and doing all the job today would destroy important elements that tomorrow we could be able to detect. This is indeed what has happened in the past: many Egyptian lefts passed 4000 years in perfect state to their end by the enthusiastic hands of archaeologists.--PMajer (talk) 12:34, 23 December 2008 (UTC)

The ancient Egyptians placed tombs and burial pyramids in areas that were desert at the time, since that allows both buildings and bodies to last longer. They lived in moister areas, however. StuRat (talk) 14:44, 23 December 2008 (UTC)

Why is the static between channels loud?

Tuning an analog radio with the knob, one hears static between stations. The static typically has a loudness about equal to the stations themselves. But how is this possible, when the real stations have the same noise layered onto the transmission, and yet manage to produce silences in the programming that are much quieter than the sound heard when there's no transmission at all?--84.70.209.18 (talk) 03:49, 23 December 2008 (UTC)

See Automatic gain control for a start--GreenSpigot (talk) 04:41, 23 December 2008 (UTC)

In short, when you hear static the radio is trying to pick up a weak signal and not really finding one. When you hear silence in a program, it has found the carrier signal and "knows" how loud a broadcast it could carry and therefore that the silence is desired. --Anonymous, 06:09 UTC, December 23, 2008.

AGC reduces the sensitivity of an AM radio receiver when a broadcast signal is being received. The AM RF signal is constantly varying in strength (amplitude) due to the sound modulation imposed on the RF. The AGC circuit smooths the amplitude variations to provide a DC voltage whose amplitude is determined by the average strength of the received signal.(The smoothing capacitors in a simple power supply similarly smooth the AC ripples superimposed on the rectified DC.) The smoothed AGC voltage is used to decrease receiver sensitivity. The stronger the received signal, the higher the AGC voltage and the more the sensitivity is reduced. Silent moments in a signal stay silent because receiver sensitivity remains reduced; that is because the carrier wave (unmodulated signal) is still being received and the carrier wave produces AGC voltage. AGC not only prevents atmospheric noise (white-noise static) from marring a received signal, it also prevents overloading of audio stages when a strong signal is received. Overloading would cause audio distortion. — GlowWorm

Yes - exactly. The radio needs 'AGC' (Automatic Gain Control) because the amount of radio energy received by the radio depends dramatically on how far you are from the transmitter (amongst a bunch of other factors). If you are 1 mile from the transmitter, you get about four times as much energy than if you are 2 miles away and a hundred times more than if you are 10 miles away. This HUGE variation in the amount of signal the radio receives would result in the volume produced by the radio varying by perhaps a factor of ten thousand depending on how close to the transmitter you are, etc. So the radio has to automatically alter the 'gain' (volume) of the signal to try to keep the same audio levels no matter where you are. As GlowWorm says - that circuit has to monitor the level of the 'carrier' wave and use that to adjust the sound volume. When there is no carrier (ie, between stations), the AGC circuit has nothing meaningful to latch onto - and the result is a lot of random noise with the AGC turning up the volume as far as possible in the hope of picking up some very faint signal. With many modern radios, there is additional circuitry to turn the volume down to zero when there is no carrier detected - and in that case you don't get any noise between channels. But that kind of sophistication has not always been present - and cheaper/older radios don't have it. SteveBaker (talk) 13:37, 23 December 2008 (UTC)

Ah yes: squelch (ouch!)--GreenSpigot (talk) 06:58, 24 December 2008 (UTC)

Note that this effect is not present in digital audio or digital television broadcasts. Nimur (talk) 19:16, 24 December 2008 (UTC)

Ion slowing down in plasma

What electrical effect, if any, would cause an ion to slow down in a sparse cloud of ions i.e. outer space? I want to figure out how well the Earth would hold a charge. In case anyone's wondering, I am not a geocidal maniac planing on causing the Earth to spiral into the sun by putting electron guns on the top of a launch loop to build up a charge of over 8*10¹⁷ Coulombs and letting the Abraham-Lorentz force take care of the rest. That would just be silly. Why would you even bring it up? — DanielLC 06:47, 23 December 2008 (UTC)

Short and not-in-depth answer: You have to take into account the magnetic fields in space - homogeneous magnetic change only the direction of the velocity vector (except for the Abraham-Lorentz force of course), but inhomogeneous fields also cause a change in kinetic energy. Icek (talk) 15:09, 23 December 2008 (UTC)

Hmm - the magnetic field never changes the total kinetic energy of a charged particle, regardless of any inhomogeneity. I think what the OP is looking for is Coulomb scattering. An ion traveling through a "cloud of ions" (see plasma) interacts with the background ions via the coulomb interaction, thus transferring some of its kinetic energy to the background ions. This leads to an exponential decay of momentum and energy of the incident ion. I won't comment on the rest of the plans you don't have. --Bmk (talk) 05:35, 24 December 2008 (UTC)

You're right about Coulomb scattering, but the kinetic energy of charged particles is changed by inhomogeneous magnetic fields because in the particle's tangential inertial frame of reference, the magnetic field is varying with time. Time-varying magnetic fields create electric fields (Faraday's law of induction). Icek (talk) 06:50, 25 December 2008 (UTC)

You're right that the particle's tangential and perpendicular (to the B-field) kinetic energies can be changed, but the particle's total kinetic energy is not altered by the field. In a way, your answer was really accurate, since a particle entering a region of higher magnetic field will be slowed in its forward motion, but its total kinetic energy will remain constant (since its gyro kinetic energy, or perpendicular kinetic energy will increase). Here's the proof:

$m{\dot {\vec {v}}}=q({\vec {E}}+{\vec {v}}\times {\vec {B}})~$ (electric field in this frame is zero)

$m{\dot {\vec {v}}}\cdot {\vec {v}}=q({\vec {v}}\times {\vec {B}})\cdot {\vec {v}}~$ (dotting both sides with v)

${\frac {1}{2}}{\frac {d}{dt}}(m{\vec {v}}\cdot {\vec {v}})=0~$ (reverse chain rule, and noting that the v dotted with the cross product of v and something else is zero)

${\frac {d}{dt}}(E_{kinetic})=0~$ (thus the rate of change of the total kinetic energy is zero if there are only magnetic fields) --Bmk (talk) 16:55, 26 December 2008 (UTC)

What happens to sexual desire after penectomy?

Are there any reliable studies about sexual desire in men after a penectomy, particularly if so much has been removed that orgasm is impossible (or at least nearly impossible)? Without being able to orgasm do they go crazy from not being able to orgasm or lose their sexual desire completely? If not reliable studies have been conducted, anecdotal evidence is fine. 67.184.14.87 (talk) 06:54, 23 December 2008 (UTC)

I don't know but I strongly discourage original research. 95.112.186.8 (talk) 07:56, 23 December 2008 (UTC)

Many things[19]... Julia Rossi (talk) 09:54, 23 December 2008 (UTC)

nutrition facts

If a jar of pickles contains 10 pickles and each pickle contains 500 mg of sodium, if one eats all the pickles and drinks the juice does one consume 5000mg sodium. In other words is the juice factored in when computing sodium in such things as pickles,olives, or canned tuna for that matter.206.251.18.119 (talk) 11:50, 23 December 2008 (UTC)

Probably not in the case of pickles or olives. The nutrition 'panel' on the side of the jar tells you only the content of one "serving" - which is likely to be 1 pickle - not 1 pickle and 3 tablespoons of liquid (which is probably more 'brine' - used as a preservative - than 'juice' from the pickles)...so I suspect they leave out the information about the content of the liquid. That's probably NOT the case for canned tuna because it's much harder to separate liquid from solid)...but it's hard to know for sure. One has to be VERY careful reading those nutrition panels because very often their estimate of 'serving size' is very small indeed! SteveBaker (talk) 13:26, 23 December 2008 (UTC)

Genetic Misogyny and sex war?

Could the counter-instinctual mistreatment (to Western eyes) of women and girls in the tribal areas of Pakistan, Afghanistan and the Middle east have some genetic component, and would it ever be acceptable to test this theory on a large scale with DNA analysis? Also could a sex war ever break out, given that women even in secular insurgency groups such as the Tamil Tigers can be a ruthless fighting force? —Preceding unsigned comment added by 80.2.194.166 (talk) 13:24, 23 December 2008 (UTC) 80.2.194.166 (talk) 13:29, 23 December 2008 (UTC) Trevor Loughlin

Not a genetic component, no. However, despite the claims of those who throw acid on women that "the Koran tells us to do it", it says no such thing. It says that both men and women should "dress modestly", but it's a long way from that to "you should throw acid on any woman who shows her face in public". It's strictly a cultural belief, which they use their religion to justify. As for a gender war with actual shooting, I'd say women would lose that war unless they outnumbered the men considerably, as they would have to tend the children, as well, and wouldn't have weapons or military training. Striking women who deny men sex and food is one possibility, but only after the possibility of violence against the strikers has been removed from the table. StuRat (talk) 14:37, 23 December 2008 (UTC)

Was "striking" an adjective, and if so which sense of "striking," or a verb in that last sentence? Edison (talk) 17:32, 23 December 2008 (UTC)

I meant it as "going on strike". However, such striking would be more effective if the women were strikingly beautiful, and less effective if the men were striking them down. StuRat (talk) 19:34, 23 December 2008 (UTC)

A "sex war", or even widespread dissatisfaction, can only break out if (1) the women believe they are being mistreated and (2) the women are not willing to tolerate the mistreatment. I don't think either criterion is fulfilled as of now; a person's beliefs are heavily influenced by her upbringing, and the Muslims are no exception. --Bowlhover (talk) 18:06, 23 December 2008 (UTC)

Have a search for the pink vigilantes in India to see how women can overcome such obstacles. There's many other less extreme examples in India also where women are getting more control of their fate. Dmcq (talk) 22:05, 23 December 2008 (UTC)

The article here is Sampat Pal Devi for the Pink Saree Gang, and there's the late Phoolan Devi, dacoit leader. The less extreme measures include microfinance for women. Julia Rossi (talk) 22:57, 23 December 2008 (UTC)

Modern India is very different from Afghanistan, Iran, and most other Muslim countries in that its laws attempt to guarantee equality for women. Its government is actively trying to educate girls, one example of the way it's breaking down traditional stereotypes. Many females in India grow up being aware that gender equality is being promoted by the government and that it is at least reasonable, not just a crazy idea. The bias against women is not promoted by the courts like it is in many Muslim countries. India obviously offers an environment very conducive to feminism, which is exactly why Indian feminist activists were mentioned here instead of Saudi Arabian or Iranian ones.

I'd be very surprised if more than a small minority of women in countries like Iran believe their husbands have no right to control them. I'm not claiming, mind you, that such independent thought is absolutely impossible. It's just very unlikely and thus cannot be prevalent. --Bowlhover (talk) 05:53, 24 December 2008 (UTC)

You mean like Shahla Sherkat, Parvin Ardalan, Shirin Ebadi, Mehrangiz Kar and Shadi Sadr? Nil Einne (talk) 11:26, 26 December 2008 (UTC)

Not so bright question...

How do I compare the brightness of a TV projector, given as lumens, with an LCD TV, given as cd/m² ? Obviously, the first step is to figure out the area of the projected image and do some math and conversions. But the second step is to figure out what portion of the lumens produced by the bulb actually makes it to the screen. How do I do that ? StuRat (talk) 14:29, 23 December 2008 (UTC)

Assuming the thing is focussed and aimed correctly, you can assume that all of the lumens produced by the projector make it to the screen (after all - where else would they go?) - but the complication is in how efficient the screen is. There is a trade-off between viewing angle and brightness to be made in the actual material of the screen. Some screens are covered with tiny retro-reflectors that push most of the light back out towards the projector - giving the screen a very narrow visibility angle - but a heck of a lot of brightness within that angle. Others are closer to perfect lambertian reflectors and they spread the light out equally in all directions - so you can see the image equally well from any place in the room - but it's going to be rather dim. Similar considerations apply with your LCD TV - many LCD's have very tight viewing constraints - others don't - so the number of candelas being emitted by each square meter of the screen can be identical between two devices - and yet one appear much brighter than the other. Remember - a one milliwatt laser can take out your eye - a 10 watt light bulb is scarcely bright enough to read by! The light bulb is visible through 360 degrees - the laser through some tiny fraction of a degree. SteveBaker (talk) 14:48, 23 December 2008 (UTC)

Surely there isn't a 100% efficiency at the projector, and much of the light generated becomes heat. Some might also be absorbed or scattered by dust particle in the air between the projector and screen. StuRat (talk) 14:58, 23 December 2008 (UTC)

The scattering due to dust is negligable and the light that is absorbed inside the projector ought not to have been counted in the lumens value you got from the manufacturer (they ought to be stating the brightness on the output side of the final lens - not the brightness of the light source) - so it's only light absorbed by the air (which is pretty transparent over the distance a projector is likely to be used!) or in the screen itself (which ought to be designed to reflect a large percentage of the incoming light - not absorb it as heat). I think you can ignore those concerns. The screen, however, is a critical part of the equation here. SteveBaker (talk) 17:07, 23 December 2008 (UTC)

Sure they should give the actual output lumens of the device, but it's in each manufacturer's interest to be deceptive and instead list the output of the bulb, as that will make it appear that they have a brighter image. So, unless you have a source that confirms that they do the right thing, I'd tend to doubt that they would. StuRat (talk) 17:32, 23 December 2008 (UTC)

Also, what's the range of brightnesses for TVs by type (LCD, plasma, DLP, projector), etc. ? StuRat (talk) 14:58, 23 December 2008 (UTC)

Also, what is the range of brightness between between the white and black areas of various types of screen? For LCD and CRT screens, it varies with the width of the black area. Text, which has narrow lines, is dark grey rather than black. Wider black areas are a darker grey, approaching full black. It would much improve readability if text could be made jet black. I once had a black-and-white CRT computer monitor - the contrast for lettering was much better than on a color LCD or CRT monitor. – GlowWorm —Preceding unsigned comment added by 98.17.46.132 (talk) 15:55, 23 December 2008 (UTC)

The range of brightness (usually called "The Contrast Ratio") is indeed an important concern for overall image quality. If the image is nice and bright - but the contrast ratio is crap - the colors will be very 'pastel' and the black areas will be grey...not a very appealing image. For bright, vibrant colors and deep blacks you need a high constrast ratio AND a bright image. This is where you see a big difference between LCD projectors (where a bright light is shone through an LCD panel to form the image) versus the DLP projectors where the light shines onto about a million tiny mirrors that can be moved such as to either reflect light out through the lens to the screen - or off to the side somewhere. For a long time, DLP's had vastly better contrast ratios than LCD projectors - but I've been out of that business for a couple of years now and things may have changed since then.

The issue of displaying thin vertical lines is to do with the rate at which the display can go from dark to light along the scanline - and that's 'bandwidth' - and 'modulation depth' - which are generally rolled into one "resolution" figure in the spec sheets for the display - but the measurement of it is something of a black art and comparing two monitors on the basis of this number is a bit more subjective. If you can get a set of test patterns displayed on the thing (like a TV 'test card') you should be able to directly compare resolutions. Horizontal lines are a different problem and relate more directly to the monitor's raw screen resolution and have nothing to do with bandwidth. However, StuRat isn't asking about any of those things.

SteveBaker (talk) 17:07, 23 December 2008 (UTC)

I've got a phillips widescreen CRT and I still think they can't be beat on contrast and colour reproduction, even if it's not HD and takes up a lot of room. I've heard a system called SED might achieve the same (but in HD this time) but until then I am sticking with this "obsolete" technology.80.2.195.198 (talk) 10:06, 25 December 2008 (UTC)

A tool for measuring cubic volume

Hi. I would like to measure the cubic volume of some irregular shaped products, specifically folded clothing (think of a folded up pair of jeans with a belt, or a folded t-shirt with a hanger). Does anyone know of a commercially available device that is suitable for this task? Thanks for your help. sparkl_!sm ^hey! 16:27, 23 December 2008 (UTC)

I don't know of any machine for doing this - but you hardly need one. Archemedes principle applies here.

For most irregular shapes - take a large, utterly full, container of water - push the item completely below the surface (water will of course overflow the sides of the container) - then remove the object and measure the amount of water that it takes to completely refill the container (using a kitchen measuring jug for example). The volume of water you have to add to restore the level is the volume of the item. Sadly, for folded up clothing, this is a little tricky since the object is absorbant - and the 'volume' of something like cloth is a little hard to define because it's full of microscopic holes. Probably - you're interested in the volume of the irregular shape surrounding the cloth - ignoring the spaces between the folds and between the fibres of the cloth - in which case you're going to have to seal the item in a waterproof plastic bag having compressed the clothing to the desired degree. The difficulty isn't so much in the measuring as knowing exactly WHAT you're trying to measure! For items that you really can't immerse in water like that (eg because they float or compress too much under the water pressure - or if you really DID want to take account of the space between the folds of cloth, etc) then you could replace the water in the experiment above with some other fluid - perhaps a heavier-than-air gas like SF₆...you can put that stuff into something like a large aquarium tank and use an air-filled balloon as a float to tell you the level of the gas. Put a mark on the balloon and a scale up the side of the tank. Partly fill the tank with SF₆ - note where the balloon floats. Drop in the item of clothing and see how much the balloon rises. Multiply the area of the bottom of the tank by the amount the balloon rises to get the volume of the item. SteveBaker (talk) 16:50, 23 December 2008 (UTC)

Funny, we did think of rigging up a displacement theory solution, but it isn't really practical.

You are correct, the actual volume I am interested in is the volume taken up by the garments when they are stacked - so the space in the folds of the cloth etc is also included in the calculation. You are also correct in suggesting that there will be a degree of compression of the garments, but I can perhaps factor this into the measurement. What I am looking for is something like this, a tool that can be used accurately on an industrial level. That one isn't suitable though, the garments exceed 18 inches in some cases. sparkl_!sm ^hey! 17:19, 23 December 2008 (UTC)

I'm guessing you want to know how much storage space is required per item. In this case, as mentioned above, the clothing can be compressed to varying degrees, but you most likely want to know how much space it takes up without being compressed at all, if you want to avoid wrinkles. I suggest taking a storage unit of known volume, like a box, and pack in as many identical items as fit comfortably. Then divide the container's volume by the number of items to determine the volume per item. StuRat (talk) 17:22, 23 December 2008 (UTC)

(ec)There might be some standard test for the volume of clothing. We could devise several different methods, which would yield different volumes. Water displacement in a plastic bag would yield a different volume from SF₆ displacement because the gas could fill much more of the space between the fibers of the garment, yielding a smaller volume. Another way would be to place the garment in a container and fill it to the top with beans, marbles, rice, styrofoam peanuts, or any other small defined particles which would not soak into the fabric as a liquid or gas would, noting the volume of the filler when the garment is removed. The smaller the filler particles, the smaller the measured volume. Another approach would be to take a box of a certain size, like 1 cubic foot, and see how many of the garments fit in the one box. The variation here would be how much force you apply if any to pack them in. This is the "volume" that would be of interest to a shipper or manufacturer. Edison (talk) 17:26, 23 December 2008 (UTC)

The idea of filling a standard size box is a really good one, particularly as the garments are in a warehouse, and will be order picked into a standard plastic tray. However, the measurement method needs to be fairly accurate as well as simple, and there is a problem when the cubic volume of the garment is not a factor of the cubic volume of the tray. For example, the tray is 1.5 cubic feet, and I can fit 1 folded coat into the tray. The coat fills just over half of the tray, meaning that I cannot fit 2 coats into the tray. What is the cubic volume of the coat? Well, it is less than 1.5 cubic feet, but more than 0.75 cubic feet - this is not an accurate enough method for what is required. sparkl_!sm ^hey! 17:43, 23 December 2008 (UTC)

If your use case is stacking the coats in that 1.5 cubic foot box, then it would be accurate enough for your purposes. If you're looking to fit the coats in a 10 cubic foot box, however, then it wouldn't be. For what it's worth, the volume-in-a-box-divided-by-number-in-a-box technique can be made more accurate by increasing the size of a box. A 0.8 ft³ coat measured with a 1.5 ft³ box gives you a size in the 0.75-1.5 ft³ range, but measured with a 15 ft³ box yields ~0.79-0.83 ft³ (between 18 and 19 coats per box). -- 128.104.112.113 (talk) 17:58, 23 December 2008 (UTC)

Exactly. If 10 garments fit in the box, the accuracy is within 10%. If 100 fit, the accuracy is within 1%. Here we're getting below the variation you would get from trial to trial. Also note that larger sizes of the same garment will, of course, take up more room. If you want the average for all sizes, ensure that you have a representative sample (with more of the most common sizes) in the trial box. StuRat (talk) 19:26, 23 December 2008 (UTC)

The tool in the link you gave us looks like it's measuring the height and width of the object as it passes under that archway. If I were building something like that I'd have a camera looking down on the object while the object moves through a scanning laser in some well-defined manner. Thats something a person with the right knowledge could rig up spectacularly easily with a PC (or even something like an Arduin microprocessor board), a laser pointer, a barcode-scanner lens and a web-cam. The precision of the device would depend on the speed of the measurements you require and resolution of the camera - both of which should be easy to control. If your garments are already passing along a conveyor of some kind - it would be really simple to make a machine to do it.

You may wonder how I know this: Well, a couple of years ago, I actually built something to scan 3D objects (You can read about it on my personal Wiki: Here). It used a Lego(!) turntable, a $25 web cam, a $10 laser pointer and a lens bought on eBay in a pack of miscellaneous lenses for $5. My objective was to make 3D models by sampling the position of the reflected laser light on the surface of the object and slowly rotating the object to get a "radial point cloud" (to use a technical term) which could then be turned into polygons and rendered as a 3D image. But using the 'point cloud' to calculate the volume from the 3D model is pretty simple - and for folded clothing - a linear conveyor belt with TWO cameras and TWO lasers (one red, one green) would do a better job. There are restrictions about things like measuring deep concavities - and the machine works best in the dark - but you could probably handle that in most industrial situations either by enclosing that section of the conveyor belt or by using much brighter lasers. The cost of the parts to make the thing would be under $100 - plus the cost of a computer to drive do the actual work - but if you only need one of these machines then the software and development costs would be your issue here. The image processing software needed to extract the coordinate information from the image on the camera is a little tricky - especially for something like clothing which might have a lot of different surface colors - if you want to discuss it in more detail - my email address can be found via my User: page. SteveBaker (talk) 20:48, 23 December 2008 (UTC)

That's pretty impressive, I must admit!

To put things into context here: this is a BIG warehouse where I need to measure (clothing) products accurately. When I say big, I mean there are 15000 different products stored there, and each week there are 1000+ new products added. Each new product must be measured. Storage in the warehouse is not a problem (the stock is palletised in large storage boxes). However, when the stock is picked for despatch to store, it is picked as individual garments into plastic trays of 1 ft³. Any combination of garment mix could be picked into the plastic tray i.e. there might be 1 t-shirt, 1 coat and 6 pairs of jeans per tray. In order to maximise the shipping operation, there must be minimal gaps left in the tray once the product is picked into it. This is achieved by accurately measuring the products when they first arrive at the warehouse (goods in). Presently, the method is to measure each product with a ruler, and treat each pack as a cuboid. This is wildly inaccurate for many different reasons - the net result is that my lorries are stacked with half-full trays and I am "shipping air". This costs a LOT of money in an operation of this scale. What I am looking for is a tool that will easily, accurately and consistently measure the cubic volume of this product mix - I am surprised there isn't a commercially available tool to do this with - SteveBaker, there is a gap in the market here, you could make millions!!
Thanks for your responses guys! sparkl_!sm ^hey! 21:32, 23 December 2008 (UTC)

You said "the stock is palletised in large storage boxes". Don't you know the number of items in each box ? Is the stock in each item identical ? Do you know the volume of each box (or can you get it from H×W×L) ? If so, it seems like all that is needed is some very simple math to determine the volume per item. If you need a program to determine which items can be packed together, based on the volumes of each, to fit into a given volume, that could be done, too. Beware that you don't want to get too terribly efficient at packing, though, or you'll pack the clothes so closely they will get wrinkled. Also, are there combos that shouldn't be packed together, like fragile clothes and clothes with hooks ? StuRat (talk) 01:01, 24 December 2008 (UTC)

Interesting. The problem that you have is – at least tangentially – related to a classic optimization problem in mathematics: the aptly-named bin packing problem. That problem deals with objects of known size which must be packed into a minimum number of standard bins. TenOfAllTrades(talk) 01:13, 24 December 2008 (UTC)

I wonder - isn't cloth of sufficiently reliable density to at least ESTIMATE the volume by weighing it? If your boxes are literally half full - wouldn't you get at least somewhere close by weighing it? SteveBaker (talk) 02:06, 24 December 2008 (UTC)

Since your target volume is the 1 ft³ tray you can define your clothes as occupying a portion thereof rather simply. Tape a tapemeasure each, to one side and crosswise to the bottom of your tray. Then you get a couple of plexi glass strips. Fold a sample garment. Put one strip on top of the garment, note the measurement, put one on the side of your garment (if it doesn't fill the bottom entirely. Note measurement. Repeat with the 3rd dimension if it isn't the tray's length. Since the way you fold the garment will influence the volume occupied by the garment (OR: crupmpled up laundry takes up more space than folded.) you should try various ways of folding it, unless it's pre-folded and your staff doesn't do any folding. There are a limited number of ways to fold your garments, so you'll end up with a limited number of volumes measured for each garment. (Make sure your staff knows what folding method to use when.) You could probably rig some thingamyjig to do the measuring for you, but I assume, since you only have to do it once when the garment is entered into the inventory, you wouldn't save that much manpower vs. doing it manually. The measurements are also more useful to you than the volume, because, even if 2 leather coats would fit your tray by volume, you might not be able to fold them in a way to occupy the space the way you'd need to. Thus volume is only one parameter you'd have to consider. (Your socks might have enough volume to fit in the L shaped space left between the coats and the Jeans, but I doubt your clients would appreciate if you'd deliver them crunched in there.)76.97.245.5 (talk) 02:57, 24 December 2008 (UTC)

Firstly, I am overwhelmed by the response to the OP, thanks again! There are so many questions you guys have asked above, I'll try to answer some of them now, sorry if this seems a bit disjointed. Weighing is a good idea, but the densities are a bit too varied (we have cotton, wool, leather, denim, silk etc). I do know the volume of each storage box (well, I can easily measure HxWxL), but the suppliers do not necessarily fill the box with the product, so the method of using storage box volumes is not suitable. The product mix in each tray is already calculated by a terrifically clever program, so no need to worry about that. Any products which are not suitable for mixing are also already easily dealt with. Calibrating the tray is a good solution, but will only work effectively for cuboids, and it is the irregularity of the products that is the fundamental problem here (I also manage large non-clothing warehouses, where the products are regular cuboids, and this problem does not exist in those environments).
Let's get back to a very simple level: I work in a warehouse, it is my job to measure the volume of irregular products - what is the simplest and most accurate way to do this, and is there a tool that I can use? Thanks sparkl_!sm ^hey! 08:44, 24 December 2008 (UTC)

Another option is to just give the packers more discretion to pack things best. That is, instead of telling them how much of what to put in each tray, let them figure it out themselves. Perhaps you could implement a bonus system for the most they pack in without wrinkles (you could just weigh the trays when packed to determine the bonus). I suspect they could pack things better, but have no incentive to do so, at present. StuRat (talk) 18:47, 24 December 2008 (UTC)

Non-lethal weapon against gangs

What non-lethal weapons are there against a street gang attack? Mr.K. (talk) 17:47, 23 December 2008 (UTC)

See Less-lethal weapons for more information, there's a whole list of links you can follow from there. --Jayron32.talk.contribs 18:06, 23 December 2008 (UTC)

There is nothing there that I could order through the internet. :( --Mr.K. (talk) 18:20, 23 December 2008 (UTC)

Well, you didn't ask about that, did you? There is an interesting article about something the Israelis have been working on: Skunk. Perhaps you could get ahold of some scent at a hunting supply store, or google on "skunk scent" and pick a purveyor. "Deer scent" isn't much nicer-smelling. --Milkbreath (talk) 18:50, 23 December 2008 (UTC)

If it's an entire gang - you'd be very unlikely to take them all out non-lethally without also doing yourself some kind of injury. Those whom you don't incapacitate are going to be VERY upset with you and the consequences may well end up being a whole lot worse than if you'd done nothing. So this may not turn out to be such a great idea. A cellphone with a GPS and a one-button 911 dialler has to be your best defense. For just one attacker - a Tazer is probably the answer - and even against a gang, waving a Tazer around threateningly with your back to a wall may be enough to hold them off until the cops show up. A multi-shot tazer might even keep back a handful of them. Sadly, they too may have thought of this so there are never any guarantees. SteveBaker (talk) 21:15, 23 December 2008 (UTC)

I personally doubt street gangs would be intimidated by a tazer. It's not quite the same level of threat as an actual gun—it's not quite as much as an investment to take one for the team in such a situation. Frankly, you're better of not trying to violently confront street gangs, if you care about your own health. --98.217.8.46 (talk) 02:57, 24 December 2008 (UTC)

A few stink bombs may be effective if they aren't very determined. It is a non-aggressive way of getting them to go away. Dmcq (talk) 21:55, 23 December 2008 (UTC)

Are tear gas grenades obtainable? Though of course you would need a protective mask. Exxolon (talk) 22:43, 23 December 2008 (UTC)

Air bazooka would have the advantage of not being immediately recognizable as a "weapon". A Water cannon would probably also be available online somewhere. When dealing with a gang, though I'd also like to strongly advise against any vigilante action. They are very likely to sneak up on you next time and not to repay you "in kind" either. Call the cops, that's what they are there for. 76.97.245.5 (talk) 03:09, 24 December 2008 (UTC)

This isn't really a science question, is it? It's a mix between a policy debate and a request for web-search help. Nimur (talk) 19:20, 24 December 2008 (UTC)

Yeah, especially since the first thing I thought of was very loud classical music.209.244.30.221 (talk) 20:45, 24 December 2008 (UTC)

Perhaps a bulletproof inflatable suit that turned the potential victim into a mitchelin man would mean you didn't get hurt as they gave you a kicking, and they would be laughing too much to try. I have been thinking along these lines, and I think on Star Wars I saw a sort of segmented metal hood that instantly sprung up and over (from the back of the neck) protecting the head and face of someone about to be attacked. This might be practical in real life, because whilst body armour can be worn discretly, an armoured helmet kept on all the time would be unsocial. —Preceding unsigned comment added by 80.2.195.198 (talk) 10:20, 25 December 2008 (UTC) -Trevor Loughlin

How about calling the cops? --Shaggorama (talk) 07:46, 26 December 2008 (UTC)

No guarantee they are a non lethal weapon (incidentally I agree this isn't a science question0 Nil Einne (talk) 11:15, 26 December 2008 (UTC)

A gun can be a non-lethal weapon if you're lucky and a good shot. Just like any other weapon can be a lethal weapon if you're unlucky. An unloaded gun is another fairly nonlethal weapon with good scare effect. Unfortunately, numerous studies have shown that people who wave guns around are far more likely to get shot than unarmed people. So...in general you're probably going to get less injured if you are unarmed than if you start threatening people with weapons. --Bmk (talk) 17:03, 26 December 2008 (UTC)

AeroGarden gizmo.

My wife has been afflicted by the TV adverts for a gadget called 'AeroGarden' (http://www.aerogrow.com) and wanted one for Xmas. This is a gadget that lets you grow stuff like lettuce and baby tomatoes indoors, hydroponically. Leaving it to the last minute - I wandered into the local store that sells them and was shocked...SHOCKED to see that these things cost $140...plus supplies...plus other crap. Figuring that a lettuce costs about $1 and the machine takes several weeks to grow one - I figure we'd save about $12 a year on food - so this gadget might maybe pay for itself in 10 years...oh - but you need 'supplies' and it eats 60W of electricity...so probably more like 20 years.

But not being one to disappoint - I've been wondering if I can make one...tomorrow (I have the day off and nothing better to do than to sit and chat to you guys!).

It looks like the thing consists of a container for the plant with water and nutrients underneath - and a pair of CFL lamps with a timer to do day/night cycles...plus some stuff to tell you when to add water and nutrient tablets - which can only be some other kind of timer hooked up to an LED. I'm thinking that a couple of nested plastic popcorn serving bowls with some light fittings and such plus a regular 24 hour timer would get me something functionally identical for about $10 plus lightbulbs...which at least stands a chance of reducing the payback period to something close to the 'novelty-wearing-off' period which historically has been under 6 months for this kind of gadget. (cf Breadmaker, Icecream Maker, Pizza cooker).

Does anyone here actually have one of these machines? Or some insight as to how the plant and the water make contact? Our hydroponics article offers loads of suggestions - mostly that there needs to be some kind of substrate to bring the water up to the roots by capillary action...I'm guessing that stuff like that could be found in a gardening store.

Any information that would increase the probability of it actually growing something would help. Failing that I'm just going to have to buy lettuces of steadily increasing size at the store and sneak them into the container at dead of night in order to convey the impression that whatever I make actually works! SteveBaker (talk) 21:05, 23 December 2008 (UTC)

I'm under the impression (I don't have one) that they actually use aeroponics rather than hydroponics. Same general concept, different technical implication. (Might be relevant if trying to build one yourself.) -- 128.104.112.113 (talk) 22:04, 23 December 2008 (UTC)

My first piece of advice is to grown an herb like basil, which picked fresh will add flavor not found in dried seasoning. There are a dozen varieties of basil so you'll feel like a gourmet in selecting the right blend for your pizza or spaghetti. Herbs can be harvested at any point in their life cycle and tend to be low maintenance. My second piece of advice is spend the $140 and spare yourself some grief. --Digrpat (talk) 22:12, 23 December 2008 (UTC)

Although grief may set in later when it's gathering dust. Julia Rossi (talk) 22:50, 23 December 2008 (UTC)

"Hydroponics" and "aeroponics" in ebay list over 2,700 items for growing plants indoors in artificial medium. There is equipment, lights, books, chemicals, and more. "Marijuana" also lists stuff of that kind – for educational purposes only, of course. – GlowWorm

To answer SteveBaker's question of repaying costs, a sizable portion of the hydroponic/aeroponic/indoor gardening market is people who want to grow wacky tobacky in their basement, where it is not easily detectable by authorities. There's probably a small market for people who genuinely want to grow some tomatoes and summer squash in January, but for the most part the entire industry exists to support Mary Jane production. And a crop of said weed will likely pay for the entire operation in the very first growing season. So yeah, go ahead and get the set-up for those greenhouse tomatoes in February, but also understand that you aren't really the target market for this equipment. People buying this stuff are the same people who are buying "tobacco pipes" and "rolling papers"... --Jayron32.talk.contribs 00:35, 24 December 2008 (UTC)

You've listed the financial aspects, so let me say outright that this gizmo isn't about saving money. Why else grow food at home then ? Here's some reasons:

1) If you have small kids it's a good lesson on where food comes from (and far less likely to make your kids run away from home than if you start slaughtering your own livestock). Why not just grow it in a garden then ? Well, you could, but isn't that where the neighbor's cat likes to tinkle ?

2) It enables you to control what goes into the food, so you really know it's "organic", as opposed to trusting some combination agricultural company and chemical company that claims their food is organic (even though you've seen their food glowing in the dark).

3) It's fun. OK, you're not likely to to die from excitement, but it's still a bit of a thrill to grow something yourself.

4) You have to give some piece of crap gift to everyone to honor the Holy Day of Commercialism, so why not give this ? StuRat (talk) 00:51, 24 December 2008 (UTC)

Oh, no, I think its a great idea. I mean, we do LOTS of things just for fun, and this one seems like quite a cool adventure. I wasn't disparaging the idea of gardening, just noting that SteveBaker's frustration over the cost was likely misplaced, as he's not really the target market for this product. But still, I think this is an AWESOME gift, for the record... --Jayron32.talk.contribs 01:00, 24 December 2008 (UTC)

It's not that I don't think you should grow things like herbs indoors - it's handy in the winter - the stuff comes out clean (no soil), etc. It would make my wife happy, etc. But $140 for what appears to be two CFL's and a timer is nuts - it's a complete ripoff. So I plan to make a 'clone' - but (to reiterate my actual question) - I don't know what kind of 'substrate' to put the plants in - or what fertiliser/chemicals are needed.

Right now - I'm thinking of buying three white plastic 'popcorn' bowls (there are heavy plastic - about 18" across by about 6" deep - and nearly hemispherical). These are $1 each in the 'everything's a dollar' store. I plan to drill a dozen 1" holes in the bottom of one of the bowls and stack it inside one of the others with some kind of 'substrate' trapped between them (coconut matting perhaps) which will be kept wet - and onto which seeds will be dropped. The third bowl will be inverted and will have two 30W broad spectrum CFL's mounted inside - plugged into a 24 hour programmable timer. Two pieces of concentric plumbing pipe will run vertically up through the center of all three bowls with a pipe clamp on the inner one so it can slide up and down so that the top bowl plus lights can be moved as the plant grows. The outer pipe will have holes drilled around the base so that you can replenish water and 'chemicals' by pouring them down the center of the pipe from the top.

I figure I can buy the parts for $20 or less and assemble it in an hour...but the problem is that I don't know whether I've got enough of the salient details right to make it actually 'work'. Hence my request for help.

SteveBaker (talk) 16:16, 24 December 2008 (UTC)

From my experience with friends who grow "herbs": rockwool is a very good substrate (but make sure that you only cut it while it's wetted); if you are using pure hydroponic, you need to pay attention to oxygenation of the roots, so you need a bubbler or use the ebb-and-flow method, where the rockwool sits in a pan that is periodically drained. A more advanced design uses a rotating wheel where the rockwool enters the pan of nutrient & water every hour or so. The lights are placed at the centre and this maximizes absorption from the light, while also providing the necessary aeration (and also produces compact plants, but likely wouldn't work for tomatoes). The single biggest factor is light intensity, and a proper nutrient mix and aeration/circulation are also important. Depending on how often you replace the water, you might need a UV sterilizer too.

I've seen those same ads for the AeroGarden and my impression is also that it's a "gizmo" whose best effect is to separate the public from their money. (Hint: do they offer to throw in a set of knives? :) But you certainly can build a very effective hydroponic system for not a lot of money. You need some tubing, some rockwool, some PVC pipe, timer & pump, and your budget will be constrained by the light intensity. Franamax (talk) 02:53, 25 December 2008 (UTC)

Sail all wet?

Why do submarines have sails? It looks to me like it would add drag and weaken the structure. Clarityfiend (talk) 21:22, 23 December 2008 (UTC)

According to Conning tower (which is part of the 'sail'): "A conning tower is a raised platform on a ship or submarine, often armored, from which an officer can con the vessel; i.e., give directions to the helmsman. It is usually located as high on the ship as practical, to give the conning team good visibility.". The 'sail' is there to get the conning tower up as high as possible. SteveBaker (talk) 21:27, 23 December 2008 (UTC)

Wheres on a sailing ship giving directions to the helmsman from the conning tower makes lots of sense, on a sub I suppose it's more to do with keeping your feet dry. (The bridge being downstairs, inside the sub) If you wouldn't have the sail you'd have to raise the entire top of the sub out of the water to go "topside" for a look-see. In calm sea that wouldn't be that big a deal, but give it a bit of a chop and you'd be real happy to be a bit farther up. Apart from making the sub as easy to spot as a boat from afar, if you'd raise the whole thing up above the waves, it would add all sort of engineering challenges as to the shape of the hull where to put the ballast and pump outlets etc. 76.97.245.5 (talk) 22:27, 23 December 2008 (UTC)

Looking up that article led me to the question: Why was a French submarine called "Casabianca (Q183)" in 1935? — Sebastian 22:52, 23 December 2008 (UTC)

Well, just looking at the Casabianca disambiguation page, the obvious thing would be that it was named after the place.

Incidentally, there has been a movie named after this submarine, which means that there have been movies named Casabianca and Casablanca. Hard to tell those words apart in some typefaces! --Anonymous, 07:07 UTC, December 24, 2008.

Not quite. Looking at the lede of the sub's article makes it quite clear that the vessel was named for the person, not the place (and it's not the only French vessel to have been so named). As for why they'd name a sub after him, my best guess would be the rather poignant death of he and his son in battle -- but that's purely guesswork. — Lomn 13:59, 24 December 2008 (UTC)

In addition to giving the commander a dry place to stand, it provides a handy place to put communications antennas, radar equipment, and other stuff that you want to have high up and clear of the water when the boat is surfaced (or nearly surfaced). It also makes it easier for crew to board and exit the craft in less-than-perfectly calm weather. (If you opened a hatch that was flush with the top of the rest of the hull in any sort of wave action then you'd very quickly get a sub full of water.) TenOfAllTrades(talk) 00:27, 24 December 2008 (UTC)

This is sort of a kid's site from the Office of Naval Research, but it also explains that the Sail houses some control surfaces, and has historically been the location for steering and other controls. My guess is that before the digital era, placing controls for periscopes, control-surfaces, etc, far from the locations of the actual instruments was much more difficult. Nimur (talk) 19:39, 24 December 2008 (UTC)

Red Panda, Giant Panda thumb.

The Red Panda articles says "[The Red Panda and the Giant Panda] are only very distantly related by remote common ancestry from the Early Tertiary Period." Is the specialised thumb (extra digit formed formed at the wrist), which they both have, derived from their common ancestry, or is it a case of convergent evolution? Jooler (talk) 22:39, 23 December 2008 (UTC)

Convergent evolution indeed, according to this paper. Nice! --Dr Dima (talk) 00:21, 24 December 2008 (UTC)

My understanding is that the Red Panda is closely related to racoons, while the Giant Panda is closer related to the bears. --Jayron32.talk.contribs 00:29, 24 December 2008 (UTC)

Correct. According to Flynn et. al. (2005) Syst. Biol. 54(2) pp. 317–337 (see figure 3 therein if you have full access), Red Panda's closest living relatives are Mephitidae (skunks) and Procyonidae (raccoons, coatis, kinkajous, and the like) of Musteloidea (weasel) superfamily; while the Giant Panda is closely related to bears and hence is placed in Ursidae (bear) family, superfamily Ursoidea. Happy Holidays! --Dr Dima (talk) 02:02, 24 December 2008 (UTC)

Great answer Dr Dima. Jooler (talk) 14:06, 24 December 2008 (UTC)

December 24

Happy Holidays!

Just saying, as per Dr Dima, happy holidays to all from here in brown Australia. o<]:-) Julia Rossi (talk) 04:12, 24 December 2008 (UTC)

Hey, no ranting!! Happy Christmas to you JR from economically and climatically gloomy UK. Richard Avery (talk) 07:25, 24 December 2008 (UTC)

Happy holidays from the origin of the global economic crisis. Imagine Reason (talk) 13:46, 24 December 2008 (UTC)

Might as well join in....happy holidays to you all from the southern most tip of the darkest continent, and the most beautiful city in the world! And Julia, better luck in the cricket tomorrow! I sure hope McGrath is enjoying some humble pie with his Christmas lunch :P Zunaid 16:03, 25 December 2008 (UTC)

deleet! deleet! :-> Julia Rossi (talk) 00:00, 26 December 2008 (UTC)

Happy holidays from...Canada! So what's your question? ~AH1^(TCU) 16:49, 25 December 2008 (UTC)

Test for fullerenes

How can I test for fullerenes? I remember a chemical experiment I did decades ago when the previously clear liquid very suddenly turned dark black with a shade of violet. I told my chemistry teacher and he repeated the experiment with the same result but could not tell me what it was. Now the vision haunts me that I was creating, well, "some nano stuff" in a cheap and easy way (very probably I wasn't). So how can I have peace by either knowing that it wasn't some precious nano stuff or, preferably, getting famous, rich and wealthy by creating nanos en mass and selling it? 95.112.140.196 (talk) 09:31, 24 December 2008 (UTC)

I don't know the answer to your question, but I'd just like to say that even if you do find a way to bulk-produce nanos, it's highly unlikely you'll be able to sell them, because they'll probably be extremely impure. AFAIK it's relatively to produce fullerenes, but getting the different kinds separated and tossing out the junk ones isn't something you could just do in your basement without putting a f*ckton of money into the necessary equipment. Yeah, I know you were (probably) kidding about the getting famous, rich and wealthy part, but I figured I'd debunk it anyway.

As for becoming famous, well, you might make the news if you poison or blow up half the block trying to find a cheap way to create fullerenes. ;) --Link ^(t•c•m) 11:30, 24 December 2008 (UTC)

Looking through the article you linked, getting rich is only within reach if your method would produce pure fullerenes. Since they do appear in nature (albeit in miniscule quantities) in soot and rocks, just making them isn't enough. Look though the list of properties and test your sample for those. That way you should be able to narrow it down if your test tube doesn't contain something like that. 76.97.245.5 (talk) 11:24, 24 December 2008 (UTC)

Unfortunately the properties stated are not good for testing. If I had the equipment, I could take IR, Raman and UV spectra but still was at loss on what these spectra should look like. What would be the way to distinguish nanos from ordinary soot? And on the pureness I was hoping that by a defined chemical process would lead to a more defined product than the random product generated by the plasma discharge of an electric arc. 95.112.140.196 (talk) 12:07, 24 December 2008 (UTC)

As to the experiment you did decades ago, I remember that one from high school. It's a clock reaction involving iodine compounds. You mix your reagents and there are two chemicals that would react but the presence of a third chemical inhibits this. However, that chemical reacts slowly with one of the others (or a fourth one in the mix) and is consumed over a few seconds (or up to about a minute, depending on the exact mixture). Once it's all gone, the other reaction happens and you get the dramatic color change. Ah, here we are: iodine clock reaction. No nano needed, nanoo nanoo. --Anonymous, 21:38 UTC, December 24, 2008.

material science

give examples of nano piezo electric crystals having electro catalytic properties —Preceding unsigned comment added by 202.88.239.150 (talk) 10:30, 24 December 2008 (UTC)

Sounds like you want us to do your homework for you. StuRat (talk) 15:14, 24 December 2008 (UTC)

OK then, we'll do it for you: give examples of nano piezo electric crystals having electro catalytic properties - the Wikipedia Reference desk answers all.  ;) -hydnjo talk 23:51, 24 December 2008 (UTC)

Hardware design

I've been interested in electronics for a while, and I've recently found myself becoming more and more fascinated by digital hardware design (the kind you hook up to a computer). The problem here: I know very little about it.

Does anyone have any links/book titles regarding layman/DIY hardware design? I'm especially looking for a simple way to pack up numbers and transmit them over USB, since - should I pursue this any further - the first hardware I'll build will probably be sensors and the like. As for the software end, this shouldn't be too great a problem; I'm sure I could write a Linux kernel module that unzips a few numbers and dumps them somewhere in /proc.

I'm aware that most DIY hardware uses RS-232, but that standard is, well, OLD. My computer doesn't even have an RS-232 port. So I thought it'd be better to delve into USB immediately. I've read that USB microcontrollers are pretty cheap anyway.

P.S. I decided to put this here rather than in /Computing, since I'm primarily interested in the non-computer part (except for the SoC part, if you really want to call a microcontroller a computer).

Thanks in advance! --Link ^(t•c•m) 11:18, 24 December 2008 (UTC)

Lego has a robotics line that comes with lots of useful bits and pieces. I think it's called "mindstorm". You can just get a couple of their gizmos and then see what you can add or build yourself based on that. Should have known we have a page Lego Mindstorms.76.97.245.5 (talk) 11:37, 24 December 2008 (UTC)

RS-232 is still very common in the DIY world, as you noticed. Ultimately, once you get downstream of the communications controller, it shouldn't matter if you are RS-232 or USB, but I suspect you will have more options for connecting equipment with 232. Incidentally a USB to 232 converter costs about $10. Moving beyond that, if you like very low level hardware design, you might want to look at the LPT interface. Unlike USB and RS-232, LPT allows one to set and hold individual bits for arbitrary lengths of time, which can be very useful for low level digital experimentation. At a higher level, I heavily recommend the products of Rabbit for high-end hobbyist projects. Starting at around $200, Rabbit provides a 40 MHz single board microcomputer that supports ethernet, rs-232, and multiple A-to-D and D-to-A. The Rabbit design runs a single program at a time, written in a variant of C, and is quite versatile. Starting out you'd want a "starter package" which includes manuals and software for doing the programming. We use Rabbit single board computers fairly often for research applications. Dragons flight (talk) 13:11, 24 December 2008 (UTC)

The PIC microcontroller and the I²C bus are worth a look if you want to get down to basics. Dmcq (talk) 13:41, 24 December 2008 (UTC)

PIC is OK if you want to build your own board - but ready-made development systems are expensive. I²C is cool though. SteveBaker (talk) 02:07, 25 December 2008 (UTC)

I strongly recommend the Arduino range of microprocessor motherboards. You can interface to them with USB - they are dirt cheap (Around $25 for a 'developer' board) - there is a HUGE community of users - and the board design is 'opensourced'. The tools work under Linux, Windows and Mac - and those are also OpenSourced. SteveBaker (talk) 14:53, 24 December 2008 (UTC)

SparkFun.com has a variaety of hobbiest electronics componants, including a few dev-boards with built in USB interfaces. And some USB->serial components. APL (talk) 15:26, 24 December 2008 (UTC)

The sparkfun boards are around $100 and have nothing like the support or functionality that Arduino cards have at a quarter the price. SteveBaker (talk) 02:07, 25 December 2008 (UTC)

Arduino seems very interesting. Thanks! --Link ^(t•c•m) 09:08, 25 December 2008 (UTC)

on chemistry

Which is basic manganic oxide? MnO(OH)2 or Mn2O3? —Preceding unsigned comment added by Sriraga (talk • contribs) 14:48, 24 December 2008 (UTC)

The articles linked from Manganese oxide may be of some help. SteveBaker (talk) 14:50, 24 December 2008 (UTC)

We don't have a page on Mn(OH)₂, but you will find it listed in the Solubility table or as pyrochroite in the minerals. Homework at X-mas?? 76.97.245.5 (talk) 18:09, 24 December 2008 (UTC)

My guess is that the alkali article may help. It's been a long time since I studied chemistry, but I think the OH group basically answers the question for you. Nimur (talk) 19:26, 24 December 2008 (UTC)

A scientist today?

I'm not sure if this should be in the Humanities section, but I'm looking for a current scientist who captures the characteristics that made Darwin successful, such as compassion, dedication and vision. Who is a current scientist who is expanding the horizons of knowledge today, and how does their work reflect this dedication to science? Thanks. —Preceding unsigned comment added by 98.226.140.27 (talk) 17:36, 24 December 2008 (UTC)

E. O. Wilson stands out.--Eriastrum (talk) 18:04, 24 December 2008 (UTC)

Since you didn't say biologist but scientist my money is on Stephen Hawking. If you are looking for s.o. younger this list may have some candidates [20]76.97.245.5 (talk) 18:20, 24 December 2008 (UTC)

You could go for Rupert Sheldrake, who is famous for unpopular theories which are the subject of much debate: or maybe James Lovelock.

--TammyMoet (talk) 18:26, 24 December 2008 (UTC)

You might also want to read about Great Man Theory, which explores the idea that heroic accomplishments of single individuals may actually be overstated in importance. Some historians consider that the impact of one man (such as Darwin, or the hypothetical contemporary who you seek) is a defining element of the narrative of history; others consider this perspective as flawed because it elevates small accomplishments into the positive-feedback mechanism that perpetuates the impact and importance of said person. Complicated. Nimur (talk) 19:29, 24 December 2008 (UTC)

Thomas Edison, I think, has a "Great Man" reputation but of a different kind from an over-rated minor discoverer. He was certainly a very intelligent person and very important practical things were developed in his lab. but it seems impossible that one man could get as many patents as he did. I think many of his patents were inventions of his assistants, and were assigned to Edison. Before he hired an assistant, he gave them an intelligence test to see if they were suitable. What he needed were craftsmen to make models of his inventions, but I think he was also looking for important suggestions from intelligent craftsmen that he could take over as his own. One of the questions on his intelligence test was, "Where is Timbuctoo?" What has that to do with craftsmanship? Edison also had copious financial aid for his R and D work from banker J.P. Morgan, which helped him get all those patents. – GlowWorm —Preceding unsigned comment added by 98.17.46.132 (talk) 21:08, 24 December 2008 (UTC)

Brings up the principle of what rises to the top... urg. I'm for E.O. Wilson for content over form. Julia Rossi (talk) 22:53, 24 December 2008 (UTC)

Note that Thomas Edison did not start out with "copious finances." He started out as a penniless itenerant telegrapher who worked after hours on improvements to the device. Business men invested in his projects because he had a track record on improving telegraph devices and inventing new and useful electromechanical devices. As for the view that he just hired smart people and then patented their inventions as his own, the writings of Jehl and others of his workers refutes this. He gave them assignments, then constantly went around working with the many "pairs of hands" at work in his lab. Jehl said that if TAE was sick or away, the pace of invention slowed mightily. His lab notebooks also show the sequence from idea to assignment to improvement. Further, few of his assistants invented anything of note after they left his employment, Nikola Tesla being a notable exception. The phonograph was clearly Edison's invention. The practical incandescent light was a team effort, but he was at the center of it. Dickson's work on the motion picture is something of an exception, with more independent invention by Dickson. Edison (talk) 06:23, 25 December 2008 (UTC)

As people are talking about Edison, Craig Venter comes to mind. Icek (talk) 06:44, 25 December 2008 (UTC)

Another thing about Thomas Edison is that he lived at the right time in history for his talent to be of use. Knowledge of electrity and magnetism had advanced to a "tipping point" where many great practical advances suddenly became possible. If he had lived 50 years earlier, his particular talents would have found no outlet and he would have been an unknown. – GlowWorm —Preceding unsigned comment added by 174.130.253.174 (talk) 08:01, 25 December 2008 (UTC)

Edison said, "Invention is 1% inspiration and 99% perspiration". However, Nikola Tesla worked for Edison for a time, and here is what he said about Edison, "His method was inefficient in the extreme, for an immense ground had to be covered to get anything at all unless blind chance intervened and, at first, I was almost a sorry witness of his doings, knowing that just a little theory and calculation would have saved him 90 percent of the labour. But he had a veritable contempt for book learning and mathematical knowledge, trusting himself entirely to his inventor's instinct and practical American sense." Edison had told employee Tesla that if he could make a certain invention by a certain time, he would pay Tesla $50,000. Tesla did the job within the time limit, but Edison would not pay him. So Tesla had a grudge against Edison; but that does not mean he was wrong in what he said of Edison. I suspect there was ill will between them even before the $50,000 incident. Even today there is sometimes ill will between a talented employee and a manager who is not as good as the employee. It is said that two kinds of people get fired – the very best and the very worst. – GlowWorm —Preceding unsigned comment added by 174.130.253.174 (talk) 14:43, 25 December 2008 (UTC)

The claim of a $50,000 promise was first mentioned by Tesla decades later and some present scholars doubt its truth. That would have been more than the initial capitalization of the company! It is hard to find what the claimed improvements were, and in fact Tesla left when he was denied a small raise. Sounds like a fantasy. Edison (talk) 16:45, 26 December 2008 (UTC)

Not that anyone asked, but I would argue that Darwin's compassion had nothing to do with his success. His dedication was far more prominent, with vision as necessary-but-insufficient quality. --98.217.8.46 (talk) 21:12, 25 December 2008 (UTC)

December 25

Swimming in Purified Water

With so much controversy over the science of swimming during these most recent Olympic games (LZR suits, lane standards, turbulence-reducing walls etc.), I am curious: is the density of the water solution the athletes swim in an issue? Would the difference of buoyancy in a 100% pure water pool without chlorine and other additives be noticable? Sappysap (talk) 04:10, 25 December 2008 (UTC)

While I can't definitely answer the question there doesn't seem to be any regulations on this [21] or Olympic-size swimming pool. Obviously pure water is not what you want, that will just make you slower if anything. A salt water pool may make you faster. This ref mentions they used to contain salt water [22] but no mention if why they changed Nil Einne (talk) 11:13, 26 December 2008 (UTC)

Testing for lead

Lead testing kits for sale in stores cost 8 to 10 dollars for enough reagent to do 4 swab tests, such as the First Alert LT1 test kit. It has a tiny bottle of a clear reagent which changes color when swabbed on something containing lead. Where can such a reagent be purchased in bulk? Edison (talk) 06:42, 25 December 2008 (UTC)

In particular, I am interested in testing pieces of fabric. It could be, preferably, dunked in a test tube to leach out any lead, or swabbed with something. I note that Wikipedia has an article on Lead and one on Lead poisoning but none on Lead test. There is great interest in the presence of trace amounts of lead in paint, and with California Proposition 65 (1986) in lead present in, for instance, children's jewelry and even brass keys. There is California's Assembly Bill 2901 of 2008, dealing specifically with lead in children's jewelry. Then there is the Consumer Product Safety Improvement Act which kicks in in the U.S. early next year, and which is expected to have devastating effects on small businesses such as clothing manufacturers due to the apparent requirement for third part lab testing of every minor product variation. Edison (talk) 16:27, 26 December 2008 (UTC)

electric fuse

i read that thick wires shouldn't be used to make elctric fuses because their resistance is low, so the heat produced will be low. but its low resistance means more current will flow & heat is directly proportional to current flowing. so, the heat produced will be more. so, why shouldn't thick wire be used? —Preceding unsigned comment added by 122.50.128.178 (talk) 06:52, 25 December 2008 (UTC)

The fuse should melt and interrupt the current long before the actual wires heat up and start a fire. That is why large low resistance wires generally make poor fuses. The fuse wire is also likely to be a material which melts at a lower temperature than the actual wires carrying the current from the fuse box to the load. Since the fuse wires are themselves extremely short, like a fraction of an inch in some cases, the higher resistance per foot does not cause much of a voltage drop during normal operation. More current flowing through a larger wire would not necessarily produce more heat, since the resistance of the larger wire would be lower, and the heat is inversely proportional to the resistance. Edison (talk) 07:02, 25 December 2008 (UTC)

A fuse of thick wire, as compared to one of thinner wire, will make very little difference in current flow. Current depends on total circuit resistance, of which a fuse (thick or thin) is only a very small part. It must be a small part otherwise electrical power would be wasted in heating the fuse (assuming current is not enough to melt the fuse). – GlowWorm

Lead test kit

How do home lead tests work? (I'm assuming they at least give some idea if lead is present even if they don't tell you how much). What compound do they use? Nadando (talk) 07:23, 25 December 2008 (UTC)

Oh, I see Edison asked pretty much the same question above me. Disregard this. Nadando (talk) 07:49, 25 December 2008 (UTC)

They don't. Even worse, they fail by giving false negatives. There was a recent Reference Desk discussion about them, citing this study from the CPSC. --Sean 23:58, 25 December 2008 (UTC)

determination of muscle mass

Hello. Since blood creatinine depends on GFR and muscle mass, is it possible, if one has the GFR (from cystatine C eg) and the creatinine to compute muscle mass? If not: How can overall muscle mass be determined most accurately? --Ayacop (talk) 08:39, 25 December 2008 (UTC)

This reference looks helpful. Of note "While it is generally accepted, based on a review of the literature, that urinary creatinine output on

a constant diet composition is proportional to muscle mass, it is also well known that even under these conditions the day to day variations in creatinine excretion can be of the order of 4 to 8 per cent which cannot be explained by small variations in diet or physical activity." I think that Magnetic resonance imaging is the most accurate (although expensive and labour-intensive). Quantitative computed tomography and dual energy X-ray absorptiometry are also highly accurate. Axl ¤ [Talk] 00:22, 26 December 2008 (UTC)

Indeed, many thanks. Always a pity that it's not that simple and needs further work. --Ayacop (talk) 08:08, 26 December 2008 (UTC)

Chemical reaction (was "test for fullerenes")

Decades ago I dissolved naphtalene in formaldehyde and added concentrated sulfuric acid. The solution turned black instantly. Now when I remember this I wonder if I was creating nanotubes, fullerenes or something like that. The reaction doesn't work when one of the components is absent. The reaction was reproduced using chemicals from different source, so it's unlikely that they were contaminated by something that went into the reaction. Can anyone give a clue what I produced? 93.132.134.138 (talk) 09:12, 25 December 2008 (UTC)

Toxic waste! The black will be short chain carbon, or soot (carbon plus other chemicals) but probably not fullerenes. Napthalene is 2 conjoined 6-carbon rings, which will break down into something related to coal tar. Thus says my hubby who did his degree in chemistry: I merely relay the information.

--TammyMoet (talk) 09:59, 25 December 2008 (UTC)

I don't understand that properly. Naphtalene has 10 C and if it 'breaks down' there would be even less. Are there C-chains that short with a black color? Neither the article soot nor coal tar gives a concise chemical description. For the toxicity, I guess it's something in between of the original formaldehyde and the soot from christmas candles. (I never planed to eat, inhale, drink or smoke it, not even to use it as an ointment against dandruff). 93.132.134.138 (talk) 10:46, 25 December 2008 (UTC)

Band Planet

Hi. I was leafing through an old high school physics textbook, and stumbled across an interesting problem:

A science fiction tale describes an artificial "planet" in the form of a band completely encircling a sun. The inhabitants live on the inside surface (where it is always noon). Imagine that the sun is exactly like our own, that the distance to the band is the same as the Earth-Sun distance (to make the climate temperate). and that the ring rotates quickly enough to produce an apparent gravity of g as on Earth. What will be the period of revolution, this planet's year, in Earth days?

The back of the book said the answer was 9 days. But I still want to know:

1) Is this a real science fiction tale the book is describing?

2) Could humans survive on the outer surface of the band?

3) Is there anything else about the ring, it's environment, or it's inhabitants that would differ from us and that on Earth? --Ye Olde Luke (talk) 23:15, 25 December 2008 (UTC)

I remember there was an episode of Star Trek that had something similar to this, the enterprise got sucked into it because it had such huge gravity. If I recall there were no people living in it but they didn't give a reason why it was abandoned. SN0WKITT3N 23:24, 25 December 2008 (UTC)

Episode was Relics. The Dyson sphere and Dyson spheres in fiction articles might have more info. SN0WKITT3N 23:27, 25 December 2008 (UTC)

That would be a rather unpleasant place. As it is always noon, at least unless the band is comparatively thin, it will be extremely hot on the inside. You also have the problem that, unlike in Columbus case, there *is* a border at which the sea and the atmosphere simply fall down into space, because as you remember the ring accelerates at 1g. —Preceding unsigned comment added by 84.187.72.95 (talk) 01:34, 26 December 2008 (UTC)

The problem of high temps could easily be addressed by placing the ring slightly farther from the Sun than the Earth's orbit, and the problem of losing the atmosphere into space could be addressed by making the cross section of the ring concave. StuRat (talk) 04:04, 26 December 2008 (UTC)

The book (or books - because there are several sequels is Larry Niven's Ringworld. It's a classic - but some of the details are better than described in your book. Nivan supposes there would be gigantic plates tied together with stong cables in orbit around the sun between the ringworld and the sun. These he calls 'shadow squares' - and they are designed to provide an earth-like 24 hour day/night cycle (although 'sunrise' and 'sunset' don't happen at the horizon - they happen vertically overheads.

Sadly - this idea doesn't work in practice - aside from the practical matter of finding a material strong enough to form the substrate - the resulting ring structure would not be stable. It would rapidly become wobbly - then Very Bad Things would happen.

SteveBaker (talk) 01:36, 26 December 2008 (UTC)

Niven may not have realized that the Ringworld would be unstable when he wrote the original novel, but he made it a major plot element in the sequels, revealing that it was artificially stabilized by a series of motors along the rims. Incidentally, the Ringworld series is just a part of Niven's larger Known Space series, and was written after most of the other stories and novels in the series. Consequently, it uses a number of species and devices with little introduction, as it might be assumed that the reader would have been familiar with them from the earlier books. --Anonymous, 03:06 UTC, December 26, 2008.

Is it just me, or isn't it significant that they don't give the mass of the ring? --Shaggorama (talk) 07:52, 26 December 2008 (UTC)

Well, the Wikipedia article does give a mass. I don't know if it's mentioned in one of the novels or comes from another source. I don't see any great significance to it anyway. --Anonymous, 03:06 UTC, December 26, 2008.

Oh, and to answer question 2: the outer surface of the ring is not habitable. Not only does the centrifugal "gravity" pull upwards, but it's in vacuum. --Anon, 03:08 UTC, December 26, 2008.

Don't forget Gauss' law for gravity There's probably enough material to create a net gravitational force inward. It would depend on the structure of the "band". Nimur (talk) 16:27, 26 December 2008 (UTC)

Parades on a "band" planet would be awesome, but it could get ugly when everyone was selling Band candy at the same time. BTW, the mass is hundreds of times greater than that of the Earth. The notion seems quite silly, unless magic is proposed as the means of building it, or it is so far in the technological future that most things they do would seem like magic to us. Edison (talk) 16:17, 26 December 2008 (UTC)

December 26

Ashes in the garden

What is the PH of ash from burnt wood? And what substance (that is not too toxic to put in a compost pile) has a base that can neutralize the acidity of the ashes?--Apollonius 1236 (talk) 00:54, 26 December 2008 (UTC)

I would (wood?) expect the ashes to be a base, since in frontier America they used water dripped through wood ashes to combine with rendered animal fat to make soap, like lye was later used. The material leached from wood ashes was apparently weaker than lye, since the soap tended to be soft, per The Foxfire Book (1972)edited by Eliot Wigginton [23] , [24] , [25]. Note that any substance strong enough of a base to make soap is hazardous. Here is a Purdue University source on using wood ashes in the garden if the plants need soil with less acidity: http://www.hort.purdue.edu/ext/woodash.html]. In a compost pile the decay of plant material should tend to make the material more acidic. That is one reason why farmers add lime to fields which laid fallow and had organic material decompose for years. A gardening site [26] says sulfur can be used to lower the pH if the soil is too alkaline. Edison (talk) 01:30, 26 December 2008 (UTC)

Any detrimental effect of ashes in your garden depend on the amount of ash and what you grow. Small amounts are quickly diluted by rain and even act as fertilizer (potash). I wouldn't worry too much. If you are on arid land and the salt content of the ground is an issue, that's different. 93.132.154.92 (talk) 11:44, 26 December 2008 (UTC)

Electrical Charges

My question has to do with protons and electrons. I would like to know what classifies a positive charge, as well as a negative charge.I have no idea how electricity can take on two forms. I appologize for such a 'trivial' type of question but I cannot find the answer anywhere I look. Thank you very much for your time and I hope to hear an answer shortly! —Preceding unsigned comment added by 216.54.110.130 (talk) 02:05, 26 December 2008 (UTC)

The same way that numbers can be positive or negative, a charge can take any real value, that is any number that lies on the real axis. Which includes both positive and negative values, just like a bank balance can be positive or negative. Now which is positive and which is negative is just defined by convention, and has no underlying scientific reason. Like charges repel and different one attract. —Preceding unsigned comment added by 92.3.10.246 (talk) 02:22, 26 December 2008 (UTC)

Did you by any chance look up proton or electron yet? When you have come back her if you need further explanation--GreenSpigot (talk) 02:23, 26 December 2008 (UTC)

There is an explanation of why protons are positive and electrons are negative, but this has to do with their constituent quarks, which just leads to questions on why quarks are like that, and so on. Ultimately you hit a point where you just have to accept that things are the way they are, as no further explanation is possible. StuRat (talk) 03:57, 26 December 2008 (UTC)

There is no explanation as to why positive objects are positive and negative objects are negative (not to mention that electrons have no constituent quarks) it is simply convention, and all that is important is that whichever you define as positive is the opposite sign to which ever you define as negative. The charges of quarks were defined by the accepted convention for proton charges (hence the awkward fractional charges) and not the other way round. —Preceding unsigned comment added by 92.1.240.165 (talk) 15:42, 26 December 2008 (UTC)

For hundreds of years prior to the 1700's people studied electricity and wondered if there were two kinds of electricity, one kind created by rubbing a glass rod with a silk cloth, and another created by rubbing amber with fur. Two amber rods rubbed with fur repel each other. Two glass rods rubbed with silk repel each other. But the amber rod and the glass rod when charged this way attract each other. Benjamin Franklin in the 1700's established that lightning is also electricityu, and that the two kinds of electricity are really more or less of one kind of electricity. He called the charge on amber "negative" meaning less of the one "electric fluid" and the charge on glass "positive" for more of the one substance. He knew nothing of electrons or ions. A century and a half later scientists discovered that the charge carriers are subatomic "electrons" with negative charge which can be stripped away from neutral atoms inn a glass rod to leave the rod positively charged and the silk negatively charged. Edison (talk) 16:11, 26 December 2008 (UTC)

Proactive Competitor

In Fort McMurray, there is advertised a competitor to Proactive in a commercial similar to the proactive commercials. In the commercial, it says it is cheaper than proactive and that it has delayed release benzoperoxide. What is it?96.53.149.117 (talk) 02:53, 26 December 2008 (UTC)

I think you mean benzoyl peroxide. But what is your question exactly ? StuRat (talk) 03:53, 26 December 2008 (UTC)

I think he/she wants to know the brand name of the competitive product advertised in Fort McMurrary as a competitor of Proactive that is cheaper and has delayed release. That isn't really a science question though. While perhaps someone in the RD is familiar with the ad in question, my recommendation would be just to pay more attention next time it comes on. It must mention the brand name sometime, otherwise it's a pretty useless ad Nil Einne (talk) 09:56, 26 December 2008 (UTC)

Hey, it's about chemicals which people have trouble spelling, so it sounds more like a science question than miscellaneous or humanities. A competitor for Proactiv which is advertised on TV is AcneFree, per [27] and [28]. Other competitors are mentioned at [29] Please understand that we cannot give any medical advice, including advice on effectiveness or gentleness of acne remedies, and this information is not an endorsement. You might wish to see a dermatologist. Edison (talk) 16:01, 26 December 2008 (UTC)