Wikipedia:Reference desk/Archives/Science/2007 March 8

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March 8

Magnetic field formula derivation

I am curious as to how the equation shown here is derived, specifically, the inverse cube relationship, and with a minimum of calculus, if that's possible. If anyone could point me to a proof/explanation on the Internet or give me some tips as to how to go about deriving it, it would be much appreciated. -Elmer Clark 03:07, 8 March 2007 (UTC)

If you're just interested in where the inverse cube part comes from, it's pretty straightforward. First of all, for a the electric field of a charged particle, or a light source, or a gravitational field, the intensity of the field falls off as the inverse of the square of distance. Conceptually, you might think of a hollow sphere as a model—the field originates with the object at the centre, and the intensity of the field gets 'spread out' over the surface area of the sphere at any given radius. Since surface area increases with the square of radius, the field strength falls of by an inverse square relationship.

Now think about a magnetic field. Magnetic dipoles are just that – dipoles – there's so far never been discovered a magnetic monopole (though there are physicists who hunt for them). Think of each pole of a magnet as having its own field, where each field is equal in strength but the two are opposite in magnitude. Any point around the magnet influenced by one field will see that influence weakened by the effect of the other field.

Treat the net magnetic field, then, as the sum of two fields following an inverse square relation. The first field will be at a distance x, the second at a distance of x + a, where a is some small number relative to x. The total field will then be proportional to 1/x² - 1/(x+a)². Add those up (expand the brackets and bring everything over a common denominator) and...and you'll have a mess of terms. What you do then is make the 'far field' approximation; that is, assume that the distance x is much larger than a, so you need only keep the terms of the highest order in x as terms with fewer xs and more as will tend to be negligibly small. Presto! The inverse cube relationship comes out.

The rest of the terms in the dipole formula come from various physical constants, or from dealing with the effect of 'viewing' the magnet from an orientation other than directly end-on. TenOfAllTrades(talk) 03:41, 8 March 2007 (UTC)

If you look at the electric dipole, the gradient of the potential also kicks out an r^3 term, along with the 4 pi. you might pick up a book on electromagnetics for engineers, cause they are easier to read.172.161.102.213 12:30, 8 March 2007 (UTC)

I took emag centuries ago, and I wish I had bought Div, Grad, Curl, and All That or some other book to supplement that main text. I never understood it very well, but I know EE/physics gets a ton easier if you force yourself to learn the mathematics part.172.161.102.213 12:39, 8 March 2007 (UTC)

Thanks fellas. -Elmer Clark 23:27, 8 March 2007 (UTC)

Ptolematic system

Did retrograde motion inspire the idea of epicycles in the Ptolematic system? Thanks very much for responding. 208.72.125.187 03:32, 8 March 2007 (UTC)

I don't believe that apparent retrograde motion was observed until Tycho Brahe, or at least we have no record of it being observed prior to him. However, I believe the ancient Greeks did notice that the paths the planets traced in the sky were not followed at a constant speed. That is, if an object takes X days to complete an apparent orbit around earth, it's not necessarily 1/4th of the way around the Earth in X/4 days. This discrepancy needed some explanation. The real explanations are that those planets don't orbit the Earth (so the Earth isn't in the center of their orbits), and they follow elliptical orbits, not circular, with the object they orbit at one of the two focus points, not the center. StuRat 08:05, 8 March 2007 (UTC)

Really? That seems to contradict Deferent and epicycle. And if retrograde motion hadn't been observed before, then what was the point of epicycles? --Allen 08:09, 8 March 2007 (UTC) [I left this comment after StuRat had written only the first sentence of his response above. --Allen 08:23, 8 March 2007 (UTC)]

Okay; that explains why we would have had epicycles before. But what you're saying still contradicts our two articles you and I linked to. Why do you say we have no evidence that retrograde motion had been observed before? If you're right, and a source can be found, we ought to change the articles. --Allen 08:23, 8 March 2007 (UTC)

That article states that retrograde motion was used to develop the epicycles system. In that case, Tycho Brahe must have rediscovered retrograde motion and/or documented it to a new level of accuracy. StuRat 08:19, 8 March 2007 (UTC)

Thanks. I don't know why I didn't get an edit conflict warning when I posted my last question. --Allen 08:25, 8 March 2007 (UTC)

More precisely, it is quite easy to observe retrograde motion because the two inner planets, Mercury and Venus, never have a greater distance from the sun than 60 degrees. So, they move one direction, and after that (some months later), back. --Rwst 15:21, 8 March 2007 (UTC)

I wasn't really counting that as retrograde motion, although I suppose technically it is. I was thinking of the more subtle retrograde motion of Mars, etc. StuRat 17:03, 8 March 2007 (UTC)

Retrograde motion was long understood (it is easily observable in Mars) and was exactly the stimulus for epicycles, yes. Epicycles existed before the Ptolemaic system, though. And they were not discovered by Brahe, who came long after Ptolemy. --140.247.252.156 17:41, 8 March 2007 (UTC)

I believe that retrograde motion of planets has been known for a very long time - in fact, the word "planet" means "wanderer" because the ancients noticed that some of those little bright dots wandered about (forward AND backwards) where the majority of the stars only travel in one direction. SteveBaker 22:54, 8 March 2007 (UTC)

Surely "wandered" is because they wandered with respect to the stars, not specifically because they changed direction. --Anon, March 9, 00:44 (UTC).

Energy Supplements

Ive been doing a lot of weight training lately and running and I was wondering if there was anything good out there to give me energy. I'm taking my vitamins and everything, but I'm still always tired. I sleep for about 8 hours. Has anyone used hydroxycut or something else that worked well for them? —The preceding unsigned comment was added by 76.167.159.75 (talk) 04:04, 8 March 2007 (UTC).

Go see a doctor. Ocarina Cave Girl 04:58, 8 March 2007 (UTC)

I don't think many people are going to spend money on an appointment to ask about wanting to feel like you have more energy. I am rather skeptical of any energy-producing or fat-burning pills on television commercials, personally. Vitamins are good for you, don't let anybody tell you they aren't, but you can drop the fish oil and chondroitin sulfate if you have it. I'm sure somebody else can help you more than me. [Mαc Δαvιs] X (How's my driving?) ❖ 07:49, 8 March 2007 (UTC)

It might be a glycemic index problem. Sugars are turned quickly into energy, protein and starches are turned into energy over a moderate period, and fats are turned into energy over a long period. So, ideally each meal should be a combo of those sources of energy. Eating primarily sugar would guarantee a sugar crash when that energy quickly runs out, while eating only fats would leave you low on energy for hours until that energy started to kick in. Also, while not exactly healthy for you, caffeine can help to keep you awake. Just avoid consuming it in the afternoon or evening, or it may interfere with your sleep. StuRat 08:02, 8 March 2007 (UTC)

Sometimes the simple answer is the one we miss quickly. Eat more. This might sound like too quick an answer but you will find it works out very well. Try to eat alot of complex carbohydrates like those found in whole wheat bread and breakfast cereal. It's often a smart idea to have a small meal before a workout. A piece of fruit,some slices of bread and about a glas worth of skimmed/low fat milk can work wonders. Don't overdo it though, a heavy workout on a full stomach is asking for a sore stomach.

I would like to stress that a lot of people tend to forget to increase their nutrient intake when they start an exercise routine. Depending on how often you go to the gym or jog this could mean that you might have to almost double your caloric intake in the span of about a month. Though most of us won't need to increase our daily intake by that amount it might be a good idea to compare what you are taking in to what you are burning off. There are quite a few tables online which list the caloric value of many food stuffs. (which I can't be bothered to look up for you right now because I'm lazy)

Don't forget that it's not all about calories. It all depends where you get it from, most of it will come from complex carbs. You'll need plenty of protein to keep those muscles in tip top shape and a bit of (mainly unsaturated) fat because well we just need fat for alot of body processes. Besides, a diet completely devoid of fat is most likely hell on the tastebuds. You might also want to check out this website http://www.exrx.net .Good luck PvT 09:32, 8 March 2007 (UTC)

I find that occasional small snacks between meals help, especially if they have a lot of sugar :) Or you could just do slightly less each day :] HS7 19:16, 8 March 2007 (UTC)

Eating foods with a lot of sugar is not a great idea if you want to keep your energy levels up. You will end up burning out rather quickly. As Hidden Secret 7 suggested, complex carbs are a good source of energy. − Twas Now ( talk • contribs • e-mail ) 20:23, 9 March 2007 (UTC)

Actually I'm sure I meant simple carbs :) HS7 10:31, 11 March 2007 (UTC)

Inductive Heating

We know that resistive components dissipate heat. Any idea why do we say that domestic electrical water heaters and iron boxes are inductive? Is it because of their design?Can it be eliminated?210.212.194.209

I would assume that it's because to save space, the resistance is looped back and forth so you don't get a super long piece of metal, but a coil like an electric stove etc. However, when you do that, it has induction. --Wirbelwindヴィルヴェルヴィント (talk) 05:41, 8 March 2007 (UTC)

See also the Inductive heating article. DMacks 16:31, 8 March 2007 (UTC)

Well its got nothing to do with RF heating,just plain old heating coils running from the power supply. —The preceding unsigned comment was added by 59.92.240.161 (talk) 12:02, 10 March 2007 (UTC).

Plasma TVs always have to be right side up or broken.

At Best Buy, they told me that Plasma TVs had to always be up and if it tilts too far to the right, lays down, etc. (you know when moving it and it's off) that it is broken for good because the plasma gets out of alignment and your entire TV gets permanent burn marks the next time you turn it on. I was told that for some models where if you wait 48 hours, the plasma will straighten out by then. Well I found nothing on google or Wikipedia about Plasma TVs always having to be upright or it breaks them. Anyone know anything about this or even heard of it? SakotGrimshine 06:01, 8 March 2007 (UTC)

Best Buy employees really seem to enjoy BSing, or generally making stuff up when they don't know something. According to the vast interwebs, the reason for transporting plasma TVs vertically is that the fragile screen is easy to break when they're horizontal (due to the weight of the glass pressing against it). [1] [2], etc. It's definitely something to keep in mind, but not for the reasons you were told. The plasma in a plasma TV consists of ionized (when the TV is on) xenon/neon gas. Turning the TV isn't going to have an effect on it. -- Consumed Crustacean (talk) 06:24, 8 March 2007 (UTC)

When we were setting up our 46-inch plasma part of the set up involved laying it face down on the glass. [Mαc Δαvιs] X (How's my driving?) ❖ 07:44, 8 March 2007 (UTC)

And I just read a shirt that said you know you're an engineer when... people at Best Buy can't answer any of your questions. --Wirbelwindヴィルヴェルヴィント (talk) 16:29, 8 March 2007 (UTC)

Missed periods

How many missed periods are usually taken as "nothing to be worried about" in an adult female? What are the causes and effects? I don't see a part in any of our articles on this! Am I missing it? [Mαc Δαvιs] X (How's my driving?) ❖ 07:41, 8 March 2007 (UTC)

I believe it varies by woman; some have very regular periods, while others have highly irregular periods. Also, athletic women can have their periods stop due to insufficient body fat, and some birth control pills are designed to interfere with the normal cycle. StuRat 07:52, 8 March 2007 (UTC)

do keep in mind that some women go into denial when they miss periods so that is why they start saying "its nothing to worry about" if anything i suggest a test =) also like sturat says maybe shes just to skinny. however most birth controls are ment to stableize the menstral cycle. the pills at the start stop her period while the pills at the bottom allow her to ovulate. but then again it depends on what kind you get (or since i assume your a guy what kind your girl gets)Maverick423 14:37, 8 March 2007 (UTC)

• The pills at the bottom are actually placebos, meaning they don't do anything. If you skip those pills, and just start the next pack, voila! No period! --Candy-Panda 10:55, 9 March 2007 (UTC)

In this era of accurate home testing for pregnancy women don't just wait for their "friend" to arrive to confirm non-pregnancy after they have cause to think they might have become pregnant. Edison 15:47, 8 March 2007 (UTC)

yes true the test are very fast and can give peace of mind however they arnt always accurate. in a well personal issue we went through 4 test just to confirm that she wasnt pregnant. the first one didnt show any lines but see through imprints of them so we didnt know the result of that one. the second showed that she was. the third and forth showed she wasnt. over all outcome of all this. no kid =)Maverick423 15:56, 8 March 2007 (UTC)

I'm so..congr.... I give up. I never know which one people would rather have =P Is she just rather slender or taking birth control then? Don't worry if it's too personal or whatnot, but I'm curious about it for my future. --Wirbelwindヴィルヴェルヴィント (talk) 16:27, 8 March 2007 (UTC)

At the other end of the age range, it's apparently pretty difficult for a perimenopausal woman (or her doctor) to assess her fertility and her periods can become sporadic. Because ordinary birth control pills simulate normal hormonal cycles, they can mask some aspects of menopause and make it difficult to assess the true state of affairs.

Atlant 16:56, 8 March 2007 (UTC)

Weight Training and Fat Loss

I'm trying to lose weight and my trainer has me do a lot of cardio and weight training. Does the weight training reduce the amount of muscle loss while I am losing weight? —The preceding unsigned comment was added by 76.167.136.84 (talk) 08:02, 8 March 2007 (UTC).

Weight training increases your muscle mass. Muscle weights more then fat (it also burns fat for energy, basically). So if you're adding muscle and decreasing your body fat you may gain weight. You will want to keep a log of your body fat percentage if you're trying to lose weight (and by weight I assume you mean fat and not raw weight).--droptone 08:38, 8 March 2007 (UTC)

I can give you a quick answer on that question. Yes he's trying to reduce muscle loss due to all the cardio you are doing. The body becomes catabolic when it's glycogen stores are depleted and will start to break down and burn off the protein in your muscles. This is a bad thing, since you need those muscles to burn of fat. Largers muscles require more energy when active but also when in rest (see basal metabolic rate). Depending on how fast you wish to lose body fat you might be able to actually gain muscle mass, but this requires you to lose body fat very slowly. PvT 09:10, 8 March 2007 (UTC)

I like Richard Muller's articles on the subject.[3][4]. [Mαc Δαvιs] X (How's my driving?) ❖ 17:56, 8 March 2007 (UTC)

Spiriling Mathematical Vortex Phenomenom - name??

Hello, and thank you for your time.

I am trying to find information about including the name of a naturally occurring phenomenon which I saw once and I know it is somewhat well known. This is a mathematically related phenomenom, nothing to do with drugs, spiritulality etc.

It is a kind of spiriling vortex, cone shaped, made up of geometrical shapes.

It's size is not fixed, but imagine an ice-cream cone with the bottom chopped off, except the 'cone', the solid part was made up of non-connected geometrical/mathematical shapes, with spaces in between. It was spinning slowly, and was transparent in that the geometrical shapes seemed to be made of yellow light.

There is a name for this thing, other people have seen it, (I even saw it in a VISA card TV commercial but didn't manage to record it in time) but if you go looking for "spiriling mathematical vortex" on the net you get a million hits about scientists discussing the movement of particles in vortexes, I can't find it in the mess, hence asking you guys who might know about it.

What I mean by geometrical/Mathematical shapes was something like the 3d blocks in the game 'block-out', like 3d tetris blocks, all different, but they all had some relationship with each other, so the whole thing gave the impression of forming a completed mathematical formula, sort of like if you represented the equasions of relativity geometrically.

If anyone knows the name of this thing or anything about it could you please email me at (email removed)

Thank you. (Email removed) (David J Ritter)(blucat) P.S. I don't care if my email address is public, I'm open, please publish it. —The preceding unsigned comment was added by 198.142.40.245 (talk) 08:54, 8 March 2007 (UTC).

is it based on the golden mean or similar?172.161.102.213 10:47, 8 March 2007 (UTC)

I'm going to go ahead and remove your email anyway, I'm pretty sure the rule here is not just if you 'care or not', we care:). Feel free to have your email on your user page, but not here please:). As for your answer, it's not some sort mandlebrot set ? Vespine 21:54, 8 March 2007 (UTC)

I think it's way more complicated than the golden mean. It seems to be on one scale only, so probably isn't a fractal thing. It may be some sort of mandlebrot set, but this is a specific shape, and has a seperate name. No one can get the Lance Henriksen VISA card TV commercial? Gives a computer sim and the name. Thanks, blucat. 198.142.44.82 17:38, 19 March 2007 (UTC)

Animal species: how do they self identify for mating?

I'm wondering how animals know what species to mate with? They don't know what species they are, so how do they recognise their own species to mate with? Thanks.Mjm1964 09:31, 8 March 2007 (UTC)

Phermones is related. How do they know what species to mate with? Well, how do you know what species to mate with? Would you mistake an orangutan for a sexy woman? Perhaps this is also related. [Mαc Δαvιs] X (How's my driving?) ❖ 10:13, 8 March 2007 (UTC)

Davis has a point. Humans are wired for facial recognition. I assume a dog is hard-wired to tell if a mammal is a dog, and which dog it is.

There are examples of subviral agents which transfer via conjugation of host and potential host.[5]172.161.102.213 13:12, 8 March 2007 (UTC)

Most animals use pheromone cues. For example, rodents have proteins in their urine (called Major Urinary Proteins or MUPS), saliva and tears that bind tightly to small volatile chemicals. The proteins are thought to stablise the chemicals so that their "smell" is held in urine (and the other excretions) much longer, allowing them to be sniffed by members of their own (and other) species. These chemicals and the proteins are sexually dimorphic, in that different sexes have different combinations (as do different species, obviously). Therefore by detecting and interpreting the "code" of chemicals and/or proteins from the urine, tears or saliva of other conspecifics, males can distinguish between other males (which they are genetically hardwired to fight) and females (which they are genetically hardwired to mate). Interestingly, the organ that detects pheromones, called the vomeronasal organ, is essentially missing in most Catarrhini, including humans. Its likely the evolution of trichromatic vision superceded the use of chemical cues to detect mates, and that is why we watch porn these days instead of smelling it. Rockpocket 04:41, 9 March 2007 (UTC)

Ductility of Uranium

See above...--Howzat11 11:18, 8 March 2007 (UTC)

Googling Ductility of uranium seems to suggest it has high hardness and low ductility making it difficult to roll out into foil. If you want more specific metrics, searching through some of those sites may yield an answer. Vespine 21:46, 8 March 2007 (UTC)

See Uranium for general information about the element, including its physical properties and see Ductility and Young's modulus . For another site giving the physical properties of elements see [6]. Uranioum is apparently a hard, heavy, and not very ductile element, but alloys could probably retain some of those properties and enhance the ductility. Compare to tungsten, which they found a way to draw into lightbulb filaments. Edison 13:23, 9 March 2007 (UTC)

Look mum! No hands!

Is it possible to masturbate without laying my hands on my manhood. Please do not answer back with "get someone else to lay their hand on your manhood." Prehaps I should change the question to Is it possible to ejaculate without touching your manhood. 220.239.111.36 11:47, 8 March 2007 (UTC)

• It depends on how sensitive you are and how much time you are willing spend. For example dry humping can be done without using your hands and there are people who can masturbate and ejaculate with thought alone. A Google search turned up this site for more information on different techniques. - Mgm|^(talk) 11:54, 8 March 2007 (UTC)

Some women can orgasm just by thinking about sex. I don't think men are that lucky.172.161.102.213 12:43, 8 March 2007 (UTC)

• This is known as Psycholagny, although WP doesn't have much of a page for it. —The preceding unsigned comment was added by 130.184.111.192 (talk) 13:13, 8 March 2007 (UTC).

• see masturbation "A less common technique is to lie face down on a comfortable surface such as a mattress or pillow and rub the penis against it until orgasm is achieved"

It is possible to have an orgasm without any external movement or friction, by pulling on the muscle that controls urination and contracts during orgasm. I won't embarrass myself by trying to identify its proper name, but you probably get the idea. For this method, you will need lots of mental stimulation (usually your preferred type of pornography), lots of time (up to an hour) and lots of energy. Age is a factor as well. Mjm1964 13:27, 8 March 2007 (UTC)

Kegel exercises ? StuRat 16:55, 8 March 2007 (UTC)

There was a scene in American Pie I believe where it happened twice. Around that time someone claimed the same thing when meeting Brittney Spears in real life (this was back when she was 17). SakotGrimshine 15:32, 8 March 2007 (UTC)

It is theoretically possible for a man to orgasm strictly from direct prostate stimulation. --DrGaellon (talk | contribs) 17:35, 8 March 2007 (UTC)

See Frottage. Corvus cornix 22:31, 8 March 2007 (UTC)

I am skeptical of being able to orgasm at will without any stimulation. I don't think so. I'd like to see scientific evidence on that first! Ways to masturbate without "laying your hands on your manhood" would include: prostate milking/prostate massage, water pressure (say, from a showerhead, friction against other objects, and... I had a few more but this window was minimized for 5 hours and I forgot. Whoops! :) [Mαc Δαvιs] X (How's my driving?) ❖ 01:16, 9 March 2007 (UTC)

A wet dream would appear to meet the criteria (plus kudos for the question title, best in a while). Rockpocket 04:23, 9 March 2007 (UTC)

Aerosol Deodorant Cans

Are these still harmfull to the ozone? I usually refrain from buying them but a friend recently said that most companies "fixed the problem up".

I believe they have removed the CFCs, yes. But aerosol cans still aren't that good for the environment because they still release the propellant gas into the environment. Other types of deodorant are better, and pumps can be used for hair spray, etc. StuRat 13:22, 8 March 2007 (UTC) StuRat 13:20, 8 March 2007 (UTC)

Correct, no CFCs in anything now! They even changed my asthma inhaler recently so that it no longer used CFCs as a propellant. It was one of the few uses of CFCs left. --BenBurch 14:41, 8 March 2007 (UTC)

Most of the CFC's have been replace with HFC's which are still "global warming gases" but the mechansism that was proposed to explain ozone depletion only has chlorine as the destructuve chemical. There is still some concern however as the "ozone hole" has not reduced as expected since the reduction of CFC's and the models all had a very fast predicted recovery (it should have been very noticeable by now). --Tbeatty 14:58, 8 March 2007 (UTC)

There has also been studies that show ozone levels have rebounded, there being more than before, although that may have been me just looking at the certificate of stability[7]. Atmospheric ozone is measured in Dobson units, named for Gordan Miller Bourne Dobson, who invented the spectrophotometer, which was used to measure atmospheric ozone from the ground. There was a significant increase in the number of devices in 1956, when the Halley Bay anomaly in Antarctica was discovered. The anomaly however, was a November increase, in ozone levels over antarctica, this was three years before the big scare. To quote G. M. B. Dobson, "Forty years' research on atmospheric ozone at Oxford: a history," Appl. Opt. 7, 387- (1968) "the values in September and October 1956 were about 150 [Dobson] units lower than expected. ... In November the ozone values suddenly jumped up to those expected." Research is disputed over which bands of UV are more or less carcinogenic. De Fabo et al, Eureakalert, conflict for melanoma, and the 320-400 nm band UV is not blocked by the ozone layer, therefore, many would argue if we should even care at all, since it is all seasonal. Every instance of a visible ozone hole in the TOMS monthly average, has been in September. If that's not seasonal what is? [8][9][10][11][12][13][14] We also find exactly as much ozone that was missing in an "anti-hole," in, guess when? March! This reminds me of solstices and equinoxes[15][16][17][18][19][20][21]. The line looks pretty constant[22][23], although sometimes I wonder where the data went, with 2004 to 2005 changes like this[24][25]. So, there's the other side of the whole thing for you.

Spray Deoderant also has the problem of getting everywhere, probably costing more, and taking up more space than a stick. I heard to avoid stick deoderants with aluminum because it causes breast cancer even in men (and it happened to Isaac Hayes) -- this later may be incorrect at least as there's nothing in Isaac's wikipedia article, just something in the deoderant article about aluminum being a neurotoxin. SakotGrimshine 15:29, 8 March 2007 (UTC)

Oh please, when one study comes out that says something is carcinogenic that hasn't even gone through any peer review, that's called scaremongering. People love to share juicy scary stories and urban legends, and that's why this myth was perpetuated on the Internet so much. NCI [Mαc Δαvιs] X (How's my driving?) ❖ 17:40, 8 March 2007 (UTC)

Aluminium is carcinogenic? But most modern things are made from aluminium :) Althought there is a lot more cancer around recently :( HS7 19:15, 8 March 2007 (UTC)

Those ubiquitous "things...made from aluminum" are possibly not of an absorption-risk form such as might be the case with the aluminum zirconium in the product on the bathroom cabinet shelf, nor are they likely to be applied directly to [broken] skin. The warning to avoid the latter is displayed on solid (stick) deodorant/antiperspirant labels, such as on products produced by Procter & Gamble. Reputed carcinogenesis aside, I can recall (though without citation; sorry!) talk going back decades, of the aluminum in these products being implicated in the memory loss and similar brain damage associated with aging. -- Deborahjay 04:41, 10 March 2007 (UTC)

Physiology Videos

Just wondering if anyone could help by suggesting an sites/places(torrents) to get medical physiology videos? If they cover such topics as respiratory/nerve/muscle physiology etc.?

Much appreciated.

If there is a science torrent tracker site... *twitch* I want it! For text and audio, you can just type in "physiology torrent" in Google, Yahoo, The Pirate Bay[26] and Torrent Locomotive. But I actually have been searching for medical science videos recently, and found nothing. Any help would be doubly appreciated.[Mαc Δαvιs] X (How's my driving?) ❖ 17:50, 8 March 2007 (UTC)

I would suggest you do a search for Opencourseware looking for physiology courses. For example, Berkeley University have done an excellent videoed general human anatomy course that includes some physiology, although probably not in enough depth for you. But other universities are also videoing lectures and putting then on the internet. Hexane2000 06:50, 9 March 2007 (UTC)

A moon of a moon

Would it be theoretically possible for a moon to have a moon of its own? Say, something the size of Phobos orbiting something the size of Ganymede orbiting soemthing the size of Jupiter? Battle Ape 14:11, 8 March 2007 (UTC)

• When the Apollo crafts orbited the moon, they were satellites of a satellite. Just imagine a rock the same size as one of those ships. — BRIAN0918 • 2007-03-08 14:13Z

Entirely possible. The question is how stable are those orbits over millions of years? And the answer is "not very". This is why we don't see any moon-on-moon action here in our solar system though I would venture a guess that there HAVE been moons of moons during its history, and will be again. --BenBurch 14:40, 8 March 2007 (UTC)

It's worth noting that this isn't a terribly different scenario than a Sun-planet-moon system. The key consideration (discussed at n-body problem) is that the smallest body must have a mass insignificant with regards to the largest body. It's also worth noting, while we're on the subject, that the Sun-Earth-Moon system doesn't meet this criteria. Isaac Asimov notes (I believe in The Double Planet) that the Moon's orbit, observed from the Sun, is always concave about the Sun, a characteristic not shared by any other moon but shared by every other planet / minor planet. Some basic discussion of this can be found at [27], [28]. It's not directly relevant, but it may be interesting. — Lomn 16:19, 8 March 2007 (UTC)

Did you mean "the Moon's orbit, observed from the Sun, is always concave about the Sun"? Have I misunderstood what you mean by 'concave'? Surely what is special is that the Moon's orbit never doubles back on itself. It still has to be convex (if I understand how you're using concave) sometimes, as the Earth and the Moon orbit the sun with their paths 'weaving'. Both the Earth and the moon have to have a 'convex' orbit sometimes. Skittle 01:13, 9 March 2007 (UTC)

Certainly the Moon is at times closer to and at times farther away from the Sun. But because it orbits so slowly, the Earth's orbit bends the "sine wave" back on itself such that it's always curving towards the Sun, just about half the time it's turning less tightly than is necessary to maintain its distance. This curving is what's meant by "concave" in this context. (It's concave because the Sun is on the inside of the curve.) --Tardis 14:39, 9 March 2007 (UTC)

Moon on moon action. Nice. —The preceding unsigned comment was added by 199.197.124.144 (talk) 16:57, 8 March 2007 (UTC).

A similar situation may be where the smallest object is in a Lagrange point relative to the two larger objects, specifically Lagrange points 1 and 2. StuRat 16:34, 8 March 2007 (UTC)

This question came up not so long ago... You might want to check the archives for the past couple of weeks. SteveBaker 16:54, 8 March 2007 (UTC)

That was the question I asked :) Don't bother looking in the archives, I got the same answers as those above :( HS7 19:13, 8 March 2007 (UTC)

about the PTSD

what this the risk factor of this post traumatic Stress Disorder?how about the clinical picture of it? —The preceding unsigned comment was added by 196.218.135.2 (talk) 15:59, 8 March 2007 (UTC).

The Wikipedia page conveniently titled Post Traumatic Stress Disorder is a good place to start. I assume you searched the website before asking on the Reference Desk, right? DMacks 16:05, 8 March 2007 (UTC)

Looking for source

I've found there's an entry for Paul L. Kirk in volume 56 of the "National Cyclopedia of American Biography", but unfortunately my local academic library doesn't cary it. Can someone who has access send me a copy of the text and the info I need to properly cite the book? On a side note, I know of the existence of Wikipedia:Newspapers and magazines request service. Is there a similar service for books? - Mgm|^(talk) 16:56, 8 March 2007 (UTC)

Calculating errors

I've got several sets of experimental data, and am trying to find the total error inherent in reading this. I've found the pressure acting on an area using a millimetre-graded ruler and an accurate forcemeter, so the error inherent in the ruler is ±0.0005 m, while the error measuring the force is ±0.005 N. However, when I find the confidence in the pressure readings by the formula p=F/A, I get ±20000 Nm^-2, which is way larger than any readings taken! Surely the experiment cannot be this inaccurate, given that all the results form a good line of best fit. Laïka 17:29, 8 March 2007 (UTC)

[29] might be useful, specifically the final formulas at the bottom of the Multiplication and Division sections. It's the same way I've been taught to do it in my first-year Physics course. -- Consumed Crustacean (talk) 17:40, 8 March 2007 (UTC)

[30] would be my recommendation. Basically if C = A / B and you know the error in A is eA and the error in B is eB then the error in C (eC) is given by: (eC/C)² = (eA/A)² + (eB/B)² - so the magnitude of the error depends on the magnitude of the data. This means that strictly you need to calculate the error bounds for each data value - although in a lot of scientific endeavors, it's enough to plug in 'typical' values for A, B and C to get an idea of the 'typical' amount of error - since your error terms are somewhat estimated anyway. (eg: If your millimeter ruler is not temperature-compensated then the result you got using it depends on the temperature when you used it - that adds more error that you hadn't included in your estimate). SteveBaker 17:53, 8 March 2007 (UTC)

Thanks for those links; they've helped a lot! Laïka 21:01, 8 March 2007 (UTC)

Broken solar water heaters

Does anyone here know of a way to find cheap broken flat plate collectors to use for an experiment/project? I have already tried eBay. -User: Nightvid

Maybe you can build one from scratch. It should just be a hose, some plexiglass, and a bunch of insulation, in a box. Or you can look at Froogle. Nimur 18:54, 8 March 2007 (UTC)

The experiment I am working on is about the potential for modified low-tech (non-evacuated, non-concentrating) solar collectors to reach temperatures in excess of 200 or 220 degrees Celsius (with no water of course). I need something like at least the parts or pieces of parts (fragments) for a commercial collector, but on a two-digit (USD) budget. Plexiglass and most other plastics melt at too low a temperature for my purpose. -User: Nightvid

how about a large dish made from metal that would focus the sunlight onto, say, a cooking pot or something? Think outside the box 12:58, 9 March 2007 (UTC)

Apparently you didn't notice that I said 'non-concentrating'. -User: Nightvid

The 200 C and 220 C temperatures you specify are pretty high for low-tech non concentrating solar panels I have seen over the past several decades. Then you want it to be cheap. You need a material on the sun side which lets the solar energy in (around one kilowatt per square meter) and does not allow the infrared to radiate back out. Cheap lowtech front panels let the IR radiate out, limiting the max temp. Then the energy has to hit something like a flat black painted metal surface to absorb the energy, then it needs a very high R value insulation on the back and sides, which is able to withstand the high temperature specified. The tiniest air leakage or lack of a uniform high R value thermal insulation dramatically lowers the temperature. You did not specify if the goal was to heat air, water, or some other working fluid, or if you proposed to use this device as, say, an oven for cooking or other processes. You want 220 C or higher, which would obviously be able to generate steam to run a steam engine. It generally gets hardeer and harder to achieve higher and higher temperatures. Good luck. If you succeed I want one too. You might contact companies which manufacture solar panels, such as [31] and see if they sell rejects or blemished panels at a discount. Sometimes manufacturers have products which have cosmetic problems and they would sell them rather than invest more time in attempts to correct the blemish, or they might fail quality control but still be somewhat useful to an experimenter. Their concern in selling thim would obviously be that they would not want a purchaser to then demand that the devices perform like ones sold at full price, and they might want to be sure that the purchaser of blems or rejects does not then try to sell them in competition with the manufacturer or its normal sales outlets, or does not reverse engineer the product and start up a competing manufacture. Edison 15:56, 9 March 2007 (UTC)

I have a device that works too well. In fact you will need some arrangement for automatic thermostatically controlled venting. I want to patent the device but have the same problem as to funding. I can only share it with you under a non-disclosure agreement and a venture capital commitment so that I can get the patent. Sorry but I want to get married and raise a family without subjecting them to the poverty I'm likewise in. Max temperature of the device at solar noon clear sky is 350 Fahrenheit. Construction materials are as cheap as they get but without automation somewhat labor intensive. Let me know. 71.100.166.228 18:17, 10 March 2007 (UTC)

Great advice! I have contacted the SolMaxx folks just now. Currently, my project is merely "proof-of-concept", although I would at least try to use it to make/mold plastic items with. The first device I attempted to build, at home in less than one day, did just that (read: self-destructed).

The second thing I built gave me a measured internal air temperature of almost 150 Celsius (on a cold day, too!), and could've been much higher if I could've spent more time on it or had the right parts. (150 C isn't bad for a non-concentrating solar device built in under an hour, is it?) As far as venting is concerned, I am trying to avoid that need due to expense and complicatedness. This is precisely why I am seeking materials that can take the heat.

Good luck on getting your patent some day. -User: Nightvid

Maybe you could put a car in the sun and close all the windows. That'll heat up pretty good. Warning: Do not lock pets or babies inside a hot car (or inside your device) [32] [33] [34] [35]. Nimur 20:32, 11 March 2007 (UTC)

First commercial portable data projector?

Middle school teacher (and his student) getting lost in too many types of data projector for research project, having trouble figuring out when the first portable data projectors hit the market, and related ideas -- cost, etc. Anyone help us find our way to the relevant article? Thanks... Jfarber 18:49, 8 March 2007 (UTC)

Overhead projector? Perhaps you mean projector...? Nimur 19:05, 8 March 2007 (UTC)

We do indeed mean the latter -- the computer projector. Sadly, however, there is no HISTORY section in that disambiguation page, and there's no single page about the type of thing we're looking at, as there would be in articles about other objects / object types which have evolved over time. The closest I can find is this section of the LCD Projector page -- but while the section is labeled "history", there are no real dates here. The article needs to be overhauled, I'd say -- I'd even vote for a page about computer/digital data projectors instead of the disambig page -- but in the short term, the student would like some help finding the relevant historical/timeline-esque information. When did the first data projector that was NOT for use with Overheads hit the market? When did they become portable? Who was first? Heck, even a google search of "first data projector" only finds company-specific examples...is this really so rare a tpic that there's no good history out there? Jfarber 19:10, 8 March 2007 (UTC)

I fear you will need to do original research on this one. Go to a library and look at back issues of PC Week or a similar magazine and check the advertizements. Step back in one-year increments (e.g., look at the first issue each year.) You may get lucky and find a feature article in PC Week also. -Arch dude 21:37, 8 March 2007 (UTC)

It would be easier, in my opinion, to find the patent of a current projector and then step through the patents it references on Google Patents. --140.247.252.156 21:58, 8 March 2007 (UTC)

Last call...Really? No one? Interesting that such an obvious and ubiquitous object in modern culture would have none of the information usually associated with other evolving technologies in its Wiki-presence. The topic isn't that obscure -- every business or educational setting I've encountered in the last decade knows what these things are, and covets more.

I don't think it's 7th grade-level work to ask my student to sift through old magazine archives, nor do I think she'd make much sense of Google Patent, though that was a great idea, and thanks for it. I guess if no one else steps forward, we'll make the teachable moment work for us. In the long run, maybe I'll do the research and write the entry -- I can't be the only one out there who would find this information useful. Jfarber 00:45, 9 March 2007 (UTC)

The first consumer-level designs that I was aware of were not complete, self-contained projectors. Instead, they were liquid crystal display cells that sat over an ordinary overhead projector. They were usually fan-cooled. I'm pretty sure I remember them being popular in the late 80s.

Before that, data projectors were either giant CRT affairs or, rarely during my lifetime, Eidophor systems.

Atlant 11:58, 9 March 2007 (UTC)

That is helpful, Atlant, thanks -- though I was still a student in the late 80s, and not yet a teacher, I remember learning from such displays fondly, and also remember seeing them in use in my early teaching days (early-mid nineties) in those schools not yet lucky enough to have the funds for true stand-alone computer-interfaced projectors.

We are still hoping for some information which would fill the gap between then and now, however -- for example, on when self-contained projectors showed up, and when they became portable. Or even when they started projecting color would be helpful. So much (surprisingly) missing in our entry, and int he cultural knowledge pool... Jfarber 14:03, 9 March 2007 (UTC)

As to how far back to look, Don Lancaster published plans for a TV Typewriter in 1973 with improved kits available in 1975 with a serial input, so the technology was there to convert ASCII to video on any TV screen. By about 1975 people had home built "portable" computers. By 1981 there was the Osborne and by 1982 the Kaypro, commercially made 29 pound or so portable computers (hardly laptops). Then see " Movies in the Sky with V-Star 3 " Rosenberg, Hilary. Financial World. New York: Aug 31, 1983.Vol.152, Iss. 15; pg. 29, 2 pgs obtained (subscription) from Proquest.comSays that airliners had video projectors for inflight movies and the V-Star 4, was a land-based version of the inflight V-Star 3, which could be used with computer systems for teleconferencing. The article said that competitive data projector systems cost $60,000, but the . The V-Star 4 could be had for $13,000. It was manufactured by Barco Electronics of Belgium. You can see the inflight version at E-Bay at [36] and it is clearly portable, being no wider or taller than the lenses, and way smaller than the earlier Advent video projector. I expect that like any invention there would be competing claims to the invention based on some tinkerer interfacing his 1974 Altair home build computer to a portable TV, then putting a projection lens in front of the TV, and projecting data onto a screen for a science fair or computer club meeting in 1975, or perhaps doing the same projection lens in front of the portable 1950 TV or oscilloscope and somehow hooking it up to a primitive analog or digital computer of that era to display some sort of output. You have to decide when something is "invented" on a basis of commercially available, or simply reduced to practice, or impractical but showing the basic principle, and then there are the wild claims of people that they invented the thing decades ago but the invention was stolen or suppressed.You specified "commercial" which helps to eliminate the first efforts. So now the trick is to see if there was anything prior to the Barco Vstar 4. There were certainly earlier commercial video projectors, and I saw them set up and removed for special showings like an away football game broadcast on TV by 1970, but it took a couple of guys to haul it in and out. Someone somewhere could have used one of those for data projection in the early 1970's. "In-Flight Movies Update Content and Equipment" By Aljean Harmetz, New York Times Apr 27, 1982. pg. C11, 1 pgs says that as of that date there were 465 airplanes with video projectors for inflight movies. The first New York Times story about video data projectors was "Who Lives by Technology Dies -- Slowly -- by Technology; Portables are so useful when giving speeches -- but only if they work. by Peter H. Lewis. New York Times Aug 16, 1992. pg. F10, 1 pgs . It said that "the latest" LCD projectors with their own light sources, capable of photo quality video and data projection, for connection to computers, cost $6,000 to $8,000, and mentioned the earlier LCD projectors which went on the screen of an overhead projector. Edison 20:50, 9 March 2007 (UTC) "Edison 16:32, 9 March 2007 (UTC)

Thanks, Edison. This was a great response, clear, dense, and very helpful (though I did need to help the student in question figure out why laptops were so important to the answer -- certainly having a portable projector doesn't necessarily mean having a portable computer!). Jfarber 01:21, 11 March 2007 (UTC)

Does size matter?

My friend says that larger bananas have been forced to grow to that size and therby spread their nutritional value through a larger mass. Thus she says a smaller banana is better value since it contains the same quantity of vitamins but weights less and therefore is cheaper. Is this true? --Seans Potato Business 19:24, 8 March 2007 (UTC)

• It's true smaller bananas are generally cheaper, but to grow larger a banana needs more nutrients, so it wouldn't be spreading the same amount of nutrients through a larger mass. - Mgm|^(talk) 19:51, 8 March 2007 (UTC)

Experiment time: if sugar is considered a nutrient, then the smaller banana should taste sweeter than the larger one. Does it? --Bowlhover 21:33, 8 March 2007 (UTC)

I wouldn't say "larger bananas are forced to grow to that size." That sounds like "baby ducks, bunnies, and pandas are forced to.." jeez! The bananas got to their size and taste through genetic engineering and selective breeding. There are also, different kinds of bananas that taste different. [Mαc Δαvιs] X (How's my driving?) ❖ 22:02, 8 March 2007 (UTC)

Also, a larger banana has a greater ratio of flesh to peel, so I would say that larger bananas are a better value, if they are sold by weight. ^tucker/_rekcut 22:32, 8 March 2007 (UTC)

I've heard the phrase 'force-grown' quite a lot in newspapers, etc. It seems to be used to mean 'grown artificially out of season' - at least, that's what a quick google and our force (disambiguation) page say. I can't find a good source to lend some authority and detail, though. I'd assume that it means that the food is grown with fertilizer for its size and appearance, rather than in good soil for taste and nutrition. I don't think it's a rigorously defined term. --HughCharlesParker (talk - contribs) 22:49, 8 March 2007 (UTC)

Ah, I see. Thanks for that. [Mαc Δαvιs] X (How's my driving?) ❖ 23:55, 8 March 2007 (UTC)

Some fruits have chemicals sprayed on them to make them ripen after they have been picked, maybe this was what they meant :) I don't think it would make them grow much, but since the fruit isn't ripe when it is picked, it might have less nutrients in :( HS7 20:05, 9 March 2007 (UTC)

Bear in mind, too, that there are different varieties of banana grown and marketed, and that the size of the mature fruit is one of the characteristics that may vary from one type to another. (You're probably more familiar with commercially available varieties of apples, for example, that differ in sweetness and flavor as well as color and shape, etc.) Check with your local growers' board, or the Department/Ministry of Agriculture for your country, for information on the relative nutritional qualities of the bananas available to you. -- Deborahjay 04:29, 10 March 2007 (UTC)

separate populations and species

i am look for information that can help me answer a question. Factors can separate population and species —The preceding unsigned comment was added by 208.233.37.66 (talk) 20:41, 8 March 2007 (UTC).

Well, it sounds more like a statement more then a question but the answer is definitely "Yes", factors can indeed separate population and species. Information that can help answer that 'question' can most likely be found in the speciation article. If you mean What factors can separate population and species", then that article will still help.Vespine 21:26, 8 March 2007 (UTC)