Wikipedia:Reference desk/Archives/Science/2007 March 9

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March 9

info photocopiers

Where can I find out how to construct a primitive photocopier? Nate Bernhardt 00:32, 9 March 2007 (UTC)

Here is one built out of Lego...it's pretty darned primitive! http://mindstorms.lego.com/eng/inventions/image.asp?img=14155image1.jpg

But it doesn't work anything like a real photocopier does. These days you might as well use a computer scanner and a printer. SteveBaker 01:26, 9 March 2007 (UTC)

If your interest is in finding a primitive way of copying, rather than a primitive version of a real photocopier, and you're not planning on using the copies for anything important, you could try using jelly. I've never actually done it myself, but I think you set jelly in a tray (it may have to be more or less wobbly than normal), you write/draw what you want copied (perhaps with a particular kind of ink), you carefully place the original on the set jelly and run a roller over it, to transfer the ink to the jelly. Remove the original, then place a clean piece of paper on the surface of the jelly and roller it. Skittle 17:17, 9 March 2007 (UTC)

It might be easier to set up your own printing press and just engrave what you want in metal and cover it with ink, so you can make as many copies as you want without spoiling any jelly :] HS7 20:02, 9 March 2007 (UTC)

You can easily build a pantograph, it's more primitive than you might have expected! Nimur 06:39, 12 March 2007 (UTC)

Plane refuelling

When you have two planes of different size that have just refuelled, with a photo taken from above, and the planes no longer overlap, how can you tell which was the source of fuel? Is it always the larger plane providing fuel for the smaller one? Or is the one in front always providing the fuel? (that would mean there is a rule that you cannot directly "overtake" your refueller, only veer away from it sideways) Thanks for answers. Samsara (talk • contribs) 00:47, 9 March 2007 (UTC)

USAF C-5 approaches a KC-135R

You mean with in-flight refuelling? Generally the larger one is the tanker - and the small one is a fighter or a smaller bomber or even a helicopter - but (as you can see from the photo) they refuel C-5 Galaxies (the largest American military transport and one of the largest military aircraft in the world) from a KC-135. The Galaxy has a wingspan of 222 feet and a length of 247 feet - the KC-135 is just 136 feet long with a wingspan of 131 feet. So you certainly can't go by size if both aircraft are bigger than maybe 100 feet across. When they are transferring fuel, the plane in front is always the one supplying the fuel - but you said that you needed to know this after they have separated. Generally the aircraft that just refuelled falls behind and does a diving turn away from the tanker - but if the aircraft that just got a fill up is a fighter - it might well dive below and then out-accellerate the tanker - so once they are safely separated, it could easily wind up in front. Is there a particular reason for your question? Maybe I can offer more help. I design flight simulators for a living - we do a lot of training of US and other airforce pilots - and that includes in-flight refuelling exercises. I've actually done the manouver several times in our simulators - it's pretty scarey. SteveBaker 01:06, 9 March 2007 (UTC)

I'm not much of a virtual pilot but I've tried to do the manouver in Falcon 4.0 a couple of times, haven't managed to nail it yet. Even a simulator gives you a good appreciation of the surgical like precision with which fighter pilots must control their multi ton multi million dollar super sonic vehicles... As to the question, the one with the dangly thing is usually the source of the fuel. ;)Vespine 01:17, 9 March 2007 (UTC)

Yes, I can get a screenshot. Hang in there. Samsara (talk • contribs) 01:17, 9 March 2007 (UTC)

See above. Samsara (talk • contribs) 01:23, 9 March 2007 (UTC)

If you think it's tough in a fighter - you should try it in a helicopter! (Hint - you really don't want to hit the boom with your rotors - and the tanker is flying so slowly it's about to stall out and your poor helicopter is going absolutely flat out...which isn't good when you are low on fuel!) The manouver is actually quite a bit harder in a simulator than in reality because you don't have the depth-perception cues to get you accurately aligned with the refuelling probe - and on a PC-based simulator, your lack of peripheral vision is kinda annoying. The main hint I would give you is to pay attention to the 'director lights' underneath the tanker - they guide you into the right flight path and speed - then you just have to use a light touch on the stick to get the probe into the drogue. SteveBaker 01:32, 9 March 2007 (UTC)

Actually, that's just reminded me of this great video I saw ages ago, didn't take a lot of looking to find it. Pretty amazing and I bet a little scary! Vespine 03:29, 9 March 2007 (UTC)

Google video says that the video is "Not currently available" - but if you search for 'Refuelling accident' you can find it on YouTube.com ...but WOW! That was unexpected. The guy clearly over-compensated for a small initial error...but the consequences were not at all what I guessed they would be! He was lucky not to lose a rotor blade - but he may yet have dinged it so badly that the vibration would trash the rotor head bearings. Wow! SteveBaker 16:17, 9 March 2007 (UTC)

I believe the plane with the refueling tube is always the tanker, which is always in front, which is always the one providing fuel. StuRat 01:07, 11 March 2007 (UTC)

Artificial life

I was watching a lecture by Peter Ward (The Undesigned Universe: Part 3: The Construction of the Cosmos) here [1] and at 33:34 into it, Ward mentions something about a scientist who is trying to build artificial life and got a grant from Princeton University to do it. I can't make out his name when it's mentioned from the video. Does anyone know who he mentioned? Imaninjapirate^{talk to me} 03:11, 9 March 2007 (UTC)

This [2] artificial virus (a bacteriophage) was made in 2003. There is some debate about whether viruses should be considered 'alive' - but this one does reproduce. The same guy is trying to do the same thing with a bacterium [3] SteveBaker 03:25, 9 March 2007 (UTC)

Question regarding bacteria.

I have heard somewhere that simple celled animals (like, say, amoeba) can't grow larger than a quarter than starving themselves. Does this apply to bacteria? Raptor Jesus 04:08, 9 March 2007 (UTC)

Yes, because bacteria only have one cell. Unicellular organisms can, however, grow much larger than you might expect by becoming extremely skinny. --Bowlhover 05:22, 9 March 2007 (UTC)

Hmm... then how could bacteria evolve into an organism, if the theory is correct? Raptor Jesus 06:03, 9 March 2007 (UTC)

Bacterial colonies, very likely.--Pharos 06:23, 9 March 2007 (UTC)

Bacteria ARE organisms. --Ķĩřβȳ♥ŤįɱéØ 01:00, 10 March 2007 (UTC)

Bindeez

How do Bindeez work (the colourful beads that join together with a spray of water, sold as a kids art toy)? The websites I go to don't give me any explanation for their joining-together-with-water abilities other than "magic". --Candy-Panda 05:59, 9 March 2007 (UTC)

Well, that's because it is magic; what more did you expect? [Mαc Δαvιs] X (How's my driving?) ❖ 07:04, 9 March 2007 (UTC)

no idea! i never knew something like that existed! Think outside the box 12:14, 9 March 2007 (UTC)

But seriously, it would help if we could have a little bit more information on what happens (i.e. you have to wait for it to dry, it takes about five seconds, it is instant) then we could probably figure it out. Are they made of plastic? [Mαc Δαvιs] X (How's my driving?) ❖ 16:23, 9 March 2007 (UTC)

I've seen them sold alongside Hama beads (the ones you iron to melt together). The packaging suggests that simply spraying them with water does it instantly, although I've never used them myself. I would suspect that it's a bit like those cornstarch bead things, that the outside of beads dissolves slightly, making them sticky to each other. But I don't know. Skittle 17:08, 9 March 2007 (UTC)

well from my experience I would say that it may be some kind of unsaturated fat/oil because oils tend to congregate as beads and come together to form a larger mass. But as for the spraying the water part? to me that doesn't make too much sense, maybe the oils have been altered in some way and need to be hydrated? >.<

-maxx- Maxx4444177 18:37, 9 March 2007 (UTC)

They could be patented, so that you aren't allowed to find out :( Would looking at them under a microscope help :) HS7 19:57, 9 March 2007 (UTC)

Actually, patenting works exactly the opposite from that: you look up the patent application, and it tells you how it works. You just aren't allowed to use that information to make it yourself until the patent expires. --Carnildo 20:56, 9 March 2007 (UTC)

http://patents.google.com ! [Mαc Δαvιs] (How's my driving?) ❖ 23:32, 9 March 2007 (UTC)

HA! Could it be perhaps that the toy contains a chemical that converts to gamma-Hydroxybutyric acid when ingested? [4] Whoops! --Howrealisreal 19:42, 6 November 2007 (UTC)

Rise in temperature

Why is there a rise in body temperature after keeping small onions under the armpit for sometime??? —The preceding unsigned comment was added by 59.92.19.220 (talk) 09:25, 9 March 2007 (UTC).

• I think the real question is, why are you keeping small onions under your armpits for sometime? --Candy-Panda 10:41, 9 March 2007 (UTC)
  • embarrisment? Think outside the box 12:10, 9 March 2007 (UTC)
    • Damn, do you really smell that bad that you have to try and roast onions to cover up the smell? [Mαc Δαvιs] X (How's my driving?) ❖ 16:24, 9 March 2007 (UTC)

Jerking off without using your hands, keeping small vegetables under your armpits!!! I guess we're all freaks & wierdos eh?

• I don't think we know, if that is even true at all. [Mαc Δαvιs] X (How's my driving?) ❖ 16:24, 9 March 2007 (UTC)
• The only reference to it I can find is on Snopes (the urban legend debunking site) - but it's a bit confusing and there is no conclusive end to the debate: http://msgboard.snopes.com/message/ultimatebb.php?/ubb/get_topic/f/42/t/000261/p/1.html - I'd be very surprised if this were true. The body is very carefully set up to control body temperature and I doubt that enough of any sort of chemical from the onions could leach through the skin to change that by any measurable amount. I call "Urban Legend". SteveBaker 17:48, 9 March 2007 (UTC)
• I heard this long ago. The basic answer is that a chemcial reaction takes place/nerves go off and the body increases the surface temperature. It was found internal themometeres registered no change, but certain items such as the onion or soap and the skin under the arm pit, actually went up.

Hole punch things

What are the pieces of paper that are punched out using a hole punch called? Thanks, Bioarchie1234 10:27, 9 March 2007 (UTC)

• If they are colourful, Confetti? --Candy-Panda 10:43, 9 March 2007 (UTC)

Chads. --BenBurch 10:45, 9 March 2007 (UTC)

Chad (paper). --hydnjo talk 15:57, 9 March 2007 (UTC)

well for complete lack of a better word (and so as not to make those around you feel stupid) lets just call them little paper hole punch circley thingeys -maxx- Maxx4444177 18:24, 9 March 2007 (UTC)

clinical medicine

pls i want to know more about clinical medicine,and its development so far. —The preceding unsigned comment was added by 195.166.234.42 (talk) 11:40, 9 March 2007 (UTC).

Oddly, our article on Clinical medicine is pretty much useless - which is surprising because we have an entire WikiProject dedicated to the subject. I suggest you start reading there: Wikipedia:WikiProject Clinical medicine. There is a navigational template at the very bottom of that page that links to bunches of useful material. You might want to discuss your studies on the 'discussion' page there - I'm sure the folks at the project will be able to get you onto the articles you need. SteveBaker 17:37, 9 March 2007 (UTC)

Bacteria pathogens with short incubation period

Hi, Could someone please list all bacteria pathogens that have incubation period shorter then 24 hours (except Pasteurella multocida). I'm not looking for foodborne bacteria, but bacteria that infect soft tissues, like infection that occur after skin cut. (I have searched for such a list but haven't found anything other then Pasteurella multocida). DanB88 12:16, 9 March 2007 (UTC)

Some of those 'flesh eating' bacteria (Necrotizing fasciitis) work pretty fast. The article says that 'progression is within hours' - and these are certainly infections of the soft tissues and can sometimes come from some sort of skin trauma (although the article says that a sore throat is a more common first symptom). RTFA dude! SteveBaker 17:31, 9 March 2007 (UTC)

well as for listing all of them that request will be short lived, as there are many more bacteria tthat havent even been discovered yet, although i do know that stapholococcus (sp?) have a relatively quick incubation rate.Maxx4444177 18:47, 9 March 2007 (UTC)

-maxx-

We have an article on them (: although it doesn't mention anything about their incubation rates, so I imagine that it varies a lot from one staph species to another--VectorPotential^Talk 15:47, 11 March 2007 (UTC)

Why? In the evolutionary sense...

This is really 3 qestions so 1)The Naked Ape, why of all primates, do we have the least amount of body hair? 2)Why do human males have the largest penis's in relation to body size of all primates? Sexual selection (so size does matter!)? 3)Why do some fish, such as muskelunge and pike reach old age, senessence? I've asked this 1 before but never really got an answer. I was even called narrow minded to think that every gene is subject to selection but, to my narrow little mind that seems dismissive. I'm just curious as to your opinions/theories. 216.209.110.32 12:38, 9 March 2007 (UTC)Canis sylvaticus

1- humans have less hair because they wear clothes and so the need for exsessive body hair has gone
2- maybe because there is less hair the penis has become lager to keep warm in winter.
3- all things age because mitosis, the replecation of DNA is not always perfect. When cells are made they are copied from previous one. So if a cell were damaged, they copy the damaged cell aswell. Think outside the box 12:46, 9 March 2007 (UTC)

Here's another hypothesis from somewhere: since having too much hair and wearing heavy clothes makes one itchy, and makes the body more likely to retain sweat and sweat-smells (since such things cling to the hair), and because lots of hair can cause one to retain things like fleas which can often live inside clothes, perhaps cultures which demand more heavy clothes-wearing are ones in which there is less body hair. Think outside the box 12:53, 9 March 2007 (UTC) thank Jfarber for that.

Thanks...BUT... 1)So which came first? The wearing of clothes or the loss of hair? What few examples we have seem to indicate that clothing is minimal at best, so your argument doesn't really hold water. Similarly, retention of scent need not be detrimental to reproductive success or survivibility though certainly BO is not currently in favour. I could almost buy the parasite argument except that, as you concede, parasites can and do exist in clothing. 2) Plausable but this would require that our own evolution occurred in a clime that was colder than that of our fellow apes. 3)Perhaps I haven't made myself clear in my Q. What possible advantage could there be in surviving beyond reproductive age as is the case with Muskie & pike? There is no parental care in these species nor do they school. The only advantage I can imagine is that they somehow are selectively cannibalistic, eating or, at least making it more difficult for the offspring of thier competitors to survive. 216.209.110.32 13:23, 9 March 2007 (UTC)Canis sylvaticus

1. The Naked Ape, why of all primates, do we have the least amount of body hair?

   Well, clearly we don't need it or evolution would make us have it. We do actually have hair over much of our body - it's just become very short, fine hair that's hard to see. It even stands up when we are cold ('goose bumps') in a vain effort to trap some air within it - just as if we were still much more hairy. That suggests that we lost the denser hair of our nearest relatives relatively recently. Since humanity did most of it's evolving in tropical climates - and we'd learned to make primitive clothing at around the time we migrated north into colder climates - it's no so surprising that we don't have much hair.

2. Why do human males have the largest penis's in relation to body size of all primates? Sexual selection (so size does matter!)?

   I suspect it's more to do with our upright walking stance and (in consequence) the mating postures we take...but I don't know for sure.

3. Why do some fish, such as muskelunge and pike reach old age, senessence? I've asked this 1 before but never really got an answer.

   Probably they look after their young for longer than other fish. I don't know for sure. Humans (for example) are able to live much longer than is necessary for us to pass on our genes to the next generation - and that's a bad thing for survival in general because it means that there are all of these older people eating the food that the kids could need to survive - but because of our big brains, children take a ridiculously large amount of time (compared to ANY other animal) to get to the point where they can survive alone - so there is a huge evolutionary benefit to us living long enough to see our children into at least their teens. The same MIGHT be true of these fish - but I think you'd need to be some kind of a fish biologist to know for sure.

SteveBaker 16:06, 9 March 2007 (UTC)

See [|NYT] for some recent suggestions on human hairlessness, but I don't think this is a solved problem. Hairlessness seems to predate wearing clothes. It may have more to do with freeing the body of parasites (only minimal clothing is needed in our hot evolutionary environs, so there is probably a significant net reduction in parasites), or perhaps heating/cooling issues related to an erect posture in a hot climate.

I think penis size is also poorly understood. There is, however, good data relating the ratio of testicle size to body mass in primates based on sperm competition - how likely a female is to be promiscuous in a given troop structure. --JPFlip 16:17, 9 March 2007 (UTC)

Regarding 1), I've heard that the loss of hair might be an adaptation to moving out of the forest and into the savannah. In the already warm climate of tropical Africa, the loss of hair could have helped aid a more active lifestyle by improving evaporative cooling. A lot of hair would trap heat and sweat near the body's surface. I also understand that we are substanitally more prone to sweating than other primates. Evolutionarily speaking many of the changes in homonids over time seem promote the ability to run for prolonged periods and this kind of sustained activity may have been a necessary part of life on the open savannah. Also our ancestors appear to have made at least some controlled use of fire for longer than there have been homo sapiens [5]. Given the climate and these other factors, it may have been that being able to keep cool was a greater evolutionary advantage than the traditional value of having fur for keeping warm. Dragons flight 16:26, 9 March 2007 (UTC)

Well, I know a lot of people don't like this theory (I don't really understand why), but the best explanation for human hairlessness I've seen (the only one that makes sense to me) was explained in The Descent of Woman, and later in The Aquatic Ape. Basically, humans have little fur, but we do have a layer of blubber under our skin. If we lost the hair to keep cool (an explanation I've seen), or because we wore clothes and so didn't need fur any more (which is seriously twisted logic!), why would we gain the layer of blubber? Note: furry mammals don't have a layer of blubber. A layer of blubber is a typical feature of a mammal that lives in the water, as it keeps you warm better when wet, without weighing you down. Add to this the way the hair lies on your body, the way the hairs run in towards your spine rather than straight down your back, and it really does look like our ancestors took to the water at some time in the past. It also explains a lot of other stuff, but you'd do best to read a book on it for that info. 86.140.175.30 16:29, 9 March 2007 (UTC)

Elaine Morgan Skittle 16:32, 9 March 2007 (UTC)

I'd propose penis size is so out of proportion because we stopped having to worry about part of it being ripped off and completely losing function. We were so far ahead we were more leisurely, and that gave us room for each other's sexual turn-ons to get better and better because the people that weren't as sexy died. [Mαc Δαvιs] X (How's my driving?) ❖ 16:29, 9 March 2007 (UTC)

Hypothesese (sp) I've heard for penis size have tended to focus on 1)sexual position demanded by an upright posture altering the female form and 2)promiscuity, in that more promiscuous species tend to have longer penises (among other things) to try to get their sperm to the egg first. Skittle 16:35, 9 March 2007 (UTC)

I'm not suggesting that we lost hair because we wore clothes - that would be seriously twisted logic! No - I'm saying that in Africa we didn't need hair (or clothes for that matter - people who live in the wilds of Africa, Australia or South America don't wear much clothing) - but as populations migrated North into Europe and Asia, we simply couldn't evolve fast enough to get our fur back - so given that we are smart, dexterous, tool-using hunters, we took to wearing animal skins (ie clothes) instead. At that point, we didn't need to evolve hair - so we didn't do so. Clothing is a much better option for a species with that kind of life-style because you can dump them when you need to run fast - and in summer - and pile it on for slower movement in winter. Discovering fire is all well and good - but when it's ten below freezing and you are sneaking around stalking an animal, it's just not all that practical to carry a bonfire with you! SteveBaker 17:25, 9 March 2007 (UTC)

Concerning hair-loss, to argue that a warmer climate leads to hair loss is un-parsimonious, since almost all mammals living in warm environments have hair (elephants, humans, and naked mole rats being exceptions). I'd take a more complex approach, and argue parasitism, climate, and "cultural habits" all played a role in hairless humans. Remember also, that hair can protect from extreme heat and sun. Check out this article. --Cody.Pope 18:44, 9 March 2007 (UTC)

well to me #2 doesnt make that much sense by saying that human penises are that big, comparatively asians can be much smaller in comparrison to a lowland gorilla —The preceding unsigned comment was added by Maxx4444177 (talk • contribs) 18:41, 9 March 2007 (UTC).

Wrong, the average gorilla penis size when erect is on the order of 1.5in. Only humans with actual genetic disorders have penises that small. --Cody.Pope 18:47, 9 March 2007 (UTC)

The averages between races are only about 2 cm apart, if I remember correctly. The article would be race and penis size I think. [Mαc Δαvιs] (How's my driving?) ❖ 23:30, 9 March 2007 (UTC)

Could the loss of hair be due to sexual selection too, since as far as I can tell most women wouldn't like men who have lots of hair, and if this was true in the past too, people would have evolved to have less hair, and since we didn't need it there wasn't any reason not to lose it :) HS7 19:49, 9 March 2007 (UTC)

The hugely popular and highly regarded book The Naked Ape addresses your first and second questions. Grab it at your local library. -Arch dude 03:52, 10 March 2007 (UTC)

And it may all simply be completely random. There are two problems with these causal interpretations. The first is that hypothesis are untestable. For example, if humans were hairier than other primates, there would be equally plausible theories put forward to explain what we know in hindsight. There is no predictive value because the answer must be known before the theory is advanced. This is the opposite of the scientific method. The second problem is that there are related traits of natural selection that are not distinguishable from the selective ones. For example: there was a population bottleneck that led to a dramatic reduction in gene variation in human beings. What the selection criteria for the surviving humans is unknown. But the survivors had traits. Those traits may have had nothing to do with why they survived but the narrowing eliminated the variation. This could easily explain all your questions, but highlights a fundamental problem in applying natural selection theory to specific traits. It could simply be random chance. --Tbeatty 06:50, 10 March 2007 (UTC)

2) If you walk on all fours, having a long penis can be a real drag. :-) StuRat 00:33, 11 March 2007 (UTC)

Binaural Beat Brainwaves?

I need some information on the long term effects of Binaural Beat Brainwaves.

Can these affect the brain in a negative way ?

Doubtful, but I do not know. Try the Wikipedia article on binaural beats; a search on Google Scholar will give you more detailed information. Just notice that while they stimulate neurons in an interesting way, any possible long or short-term effects aren't nearly as certain as the people who sell binaural CDs/software make them out to be. -- Consumed Crustacean (talk) 18:52, 9 March 2007 (UTC)

wave equations that represent atomic orbitals

we just had a test on atomic structure and chemical bonding.there was this one question which i dont think anyone was able to answer.there was a weird equation of the form psi=f(r,a0) and we were asked which orbital it represented 2s 2p 1s or 3d. i had no clue though i thought obviously it had something to do with schrodinger's wave equation because of the psi symbolcan anyone explain the question and solution.59.183.34.200 18:34, 9 March 2007 (UTC)

the wave equation may have something to do with the frequency of variation in the path of an electron in the orbital shells. as for the rest of it well, i'm only 15 and i have no idea.

-maxx- Maxx4444177 18:44, 9 March 2007 (UTC)

Was the question about a hydrogen atom, or a hydrogen-like atom? These can both be represented by the Schrödinger equation with a suitable potential, which can be solved analytically to give solutions of the form $\psi _{nlm}=R_{nl}(r)\,Y_{lm}(\theta ,\phi )$. The details of this are on the hydrogen-like atom page. If the equation you were given only depends on r (I assume a0 is the bohr radius, so constant for a given atom) then l and m must both be 0, as only $Y_{00}=constant$ (ie, not a function). So as l is the angular momentum quantum number, l = 0 corresponds to an s shell. To determine the principal quantum number, n, you'll have to look at the exact form of the equation your given and compare it with the solutions given on the hydrogen-like atom page. The main bit to match it to will probably be the generalized Laguerre polynomials. Once you have n, this is the orbital number.Centie 23:39, 9 March 2007 (UTC)

You can tell the principle and azimuthal quantum numbers by looking at the wavefunction. For simplicity, say it is of the form $\psi =f(r)\,g(\theta )\,h(\phi )$, i.e. can be separated into a product of a function of the radial coordinate, and functions of the angular coordinates. The azimuthal quantum number is the number of angular nodes, i.e. how many zeros there are in $g(\theta )$ for $0\leq \theta <2\pi$, plus how many zeros there are in $h(\phi )$ for $0<\phi <\pi$. The number of radial nodes is how many zeros there are in $f(r)$ for $r>0$. The principle quantum number is (the number of angular nodes) + (the number of radial nodes) + 1. --Spoon! 01:35, 10 March 2007 (UTC)

Superconducting Magnetic Levitation Materials

Does anyone know the specifications for the materials in this video, and where I would be able to buy those materials? Thanks. --JianLi 19:41, 9 March 2007 (UTC)

Oh jeez. Do some google searching until you find recipes for them, since you would have to make your own, I'm pretty sure. I don't know how sculpting a normal one would be into a train shape. It involves a ceramic composition of Ytterbium and some other things, which has to be cooled by liquid nitrogen and suspended in the air by the meissner effect. You'll also need resin, a fume hood, and a really hot scientific oven. Or you could buy a 40 dollar kit on WONDERMAGNET (reputable). [Mαc Δαvιs] (How's my driving?) ❖ 23:26, 9 March 2007 (UTC)

Actually, you can buy the whole train set from a Chinese company. --mglg_(talk) 18:28, 10 March 2007 (UTC)

Thanks for the links. This stuff is quite expensive! --JianLi 20:47, 10 March 2007 (UTC)

Yes, but I'm sure it's worth it for the enjoyment you'd get. In fact, you'd be positively floating on air. StuRat 00:18, 11 March 2007 (UTC)

Sycosis

So. Global warming, are we causing it or not? The idea seems to be that there is a lot of evidence that global temperature changes are caused by changes in the amount of cloud and the temperature of the sun, and is on a 1200 year cycle. They say the modern fear of global warming was created by Margaret Thatcher to persuade us more nuclear power plants were a good idea, and that last time the temperature rose as much as it is now nothing to bad happened. And also that scientists get paid more if they predict something dramatic. But a lot of people say we are causing global warming, and if there really was all this evidence surely at least some of them might realise it isn't anything to do with us. But they haven't. So is this really true, or are we destroying the planet? And how much help will slightly cutting CO2 release be? HS7 20:28, 9 March 2007 (UTC)

The reference desk is not for rehashing debates on controversial subjects. You might want to read some encyclopedia articles on global warming if you want to learn more. Friday (talk) 22:39, 9 March 2007 (UTC)

Check out Carbon Cycle. Think of all the animal/plant life and take into account the amount being released by all naturally occurring sources on the planet. When carbon is liberated from stored sources, like wood (i.e. a forest fire) about 100-200 years of trapped carbon is released. Decomposition also liberates carbon trapped over about 100 years. Other large releases of carbon occur sometimes on mass by the ocean or by volcanoes (though this happens rarely). Now consider human actions. By burning fossil fuels we're releasing trapped carbon that was slowly "captured" over millions of years in a few decades. While there are some uncertainties concerning global warming, our actions can have unpredictable consequences, since nothing like this has ever occurred on the planet while we were around. Since these consequences could have devastating effects on the world economy and thus western quality of life, doesn't it make sense to err on the side of caution? Small changes that could be some what costly now, may prevent a world-wide depression. The only viable arguments against curbing emissions are generally economic, but when you consider large scale industrial saves by things as simple as changing the start of daylight savings time, these arguments seem tenuous at best. --Cody.Pope 22:45, 9 March 2007 (UTC)

You sound like you are already against the "skeptical view." I probably shouldn't get started on it. You can read some of the past discussions on it (three or four). Off the top of my head September 23, 2006 was the first one. Then the next one was in October. [Mαc Δαvιs] (How's my driving?) ❖ 23:22, 9 March 2007 (UTC)

"The idea", "they say" — you helpfully don't attribute your points of view, likely on purpose. The unstated "they" in these cases are people who are viewed as rather fringe in the scientific community. "A lot of people" are most scientists. But heck, if you've already made up your mind, why even ask? --24.147.86.187 00:16, 10 March 2007 (UTC)

I suspect the questioner saw a documentary on UK Channel 4 television on Thursday which was entitled The Great Global Warming Swindle. It was an interesting programme but would have benefited from interviewing scientists from both sides of the debate. Hexane2000 08:24, 10 March 2007 (UTC)

I'll quickly mention a few things. Margaret Thatcher had her part to do with it[6], there is a lot of evidence that global temperature changes are caused by changes in the amount of cloud and the temperature of the sun, and is on a 1200 year cycle. We know clouds and sun have a lot to do with it. Not the temperature of the Sun, but the intensity of electromagnetic radiation the Earth intercepts. more nuclear power plants were a good idea They are, there is no scientific evidence to prove otherwise. last time the temperature rose as much as it is now nothing to bad happened Right. if there really was all this evidence surely at least some of them might realise it isn't anything to do with us But they haven't. Yes they have. And how much help will slightly cutting CO2 release be? No help. There we are! Quick short answers. [Mαc Δαvιs] (How's my driving?) ❖ 23:14, 10 March 2007 (UTC)

Just a quick note: Mac Davis is often at odds with the scientific concensus when it comes to climate change. This doesn't mean that he's wrong, just that he differs from the concensus. Something to bear in mind. Skittle 20:51, 11 March 2007 (UTC)

Like many things people are constantly behind the times. It is true that as late as 2002 there was no proof that the rising temperature was not cyclic. This is until the new core samples, and abrupt temperature and C02 increases in 2003-2007 have jumped all the values beyond cyclical historic values. I would strongly ignore anything that uses data pre 2003, which is probably 99.99% of the work out there. The lastest data has the temp rise over twice as high as cyclical changes for over half a million years and is correlated to C02 levels (the only question is if or not the C02 is caustation as well, the only way to know is to drop C02 levels and get a drop in temperature).--155.144.251.120 03:04, 12 March 2007 (UTC)

Scientific consensus is overrated, and insists that a level of certainty exists simply because an idea appeals to a lot of people. The idea that global warming exists, and that it is due to human activity, must be evaluated independently of the "democratic vote." A lot of scientists make convincing arguments that human activity causes global climate change. In my opinion, a lot more scientists make unconvincing arguments that human activity causes global climate change. Hopefully within the next few years, a conclusive explanation will be available thanks to better experimentation. In the meantime, the whole field is much more subjective than a lot of scientists would have us believe. Nimur 20:28, 12 March 2007 (UTC)

function generator project

how to design the function generator of about 1MHz frequency and arbitrary waves like triangular,square and sine funtion —The preceding unsigned comment was added by Fayyaz1606 (talk • contribs) 21:40, 9 March 2007 (UTC).

Try this link for a low cost function generator design. --hydnjo talk 21:55, 9 March 2007 (UTC)

Emission Spectra

I have an idea about loop quantum gravity, but I need to know some information to develop it into a theory. What is the emission spectrum of a free electron? Also, it would help if you could tell me the best estimate of how many electron masses equal one Plank mass. Thanks, Max. *Max* 23:28, 9 March 2007 (UTC)

Google says ... Nimur 00:06, 10 March 2007 (UTC)

I tried that, but I wondered if I could get a better estimate. *Max* 03:32, 10 March 2007 (UTC)

I'm not a particle physicist, but I don't know if it's appropriate to talk about emission spectra of single free particles. Most of the quantum interactions that produce photons involve multi-particle or multi-state systems. Spectral lines in atomic emission spectra, in particular, are the result of excited electrons falling from a higher energy state to a lower one, producing a photon. The energy (and therefore wavelength) of the released photon is usually equal (or close to) to the amount of energy lost by the electron in its downward transition. So again, I don't think it's correct to think of a single particle as having any characteristic electromagnetic emission spectrum. I could be wrong though, I know little QED and my QM is rough. -- mattb @ 2007-03-10T00:18Z

Note: If the energy levels depend on the electron's velocity relative to the observer, assume that the electron is at rest before it emits the photon. Thanks. *Max* 03:32, 10 March 2007 (UTC)

Orders of magnitude (mass) says that the electron mass is 9.1×10⁻³¹ kg and the Planck mass is 2.2×10⁻⁸ kg. Ther fore, Planck mass is about 4×10²² electron masses. A Plank mass is about the mass of seven grains of sand. -Arch dude 03:34, 10 March 2007 (UTC)

The first one is more precise. *Max* 13:46, 10 March 2007 (UTC)

Free particles can possess any amount of energy and thus have a continuous emission spectrum. 75.138.84.159 05:15, 10 March 2007 (UTC)

Thanks. My formula won't work on a continuous spectrum, so I've decided to try it on the hydrogen atom. What is the frequency (waves/second) of an electron on the lowest energy level in a hydrogen atom? Thanks, *Max* 13:46, 10 March 2007 (UTC)

See if Rydberg formula helps. --HappyCamper 18:55, 10 March 2007 (UTC)

That only says how much energy an electron can gain or lose, not how much it has on each energy level (and frequency because E=h f). *Max* 12:59, 11 March 2007 (UTC)

I think you may be over-reaching, trying to develop a theory of loop quantum gravity. Your first step is to formally develop your understanding of fundamental physics. This will provide you with the mathematical background you need, and teach you about the ongoing work in the field. In response to your last post: "E = hf" is the correct formula for an emitted photon, which is only emitted if the electron changes its energy level. The crucial bit about atomic physics is that an electron does not continuously emit photons - this is quite the opposite of what you may have learned in classical electrodynamics, and probably what you are hoping to solve for as the "emission spectrum of a free electron." Should you choose to proceed classically, I suggest you study Maxwell's equations, which involve some really hard math. Should you choose to proceed in tune with the best physical model available, you will need quantum electrodynamics and will probably encounter some really, really, really hard mathematics. I hope this helps. Nimur 20:45, 11 March 2007 (UTC)

P.S. I went looking for this and ended up having to create it. This horrible set of equations governs the "emission spectrum of a free electron", but you're not gonna like it. Nimur 21:55, 11 March 2007 (UTC)

I'm asking for the electron's energy on different energy levels, not the photons' enrgies; doesn't E=hf also apply for an electron's wavelength and frequency? I got one answer on google[7] that said on the first orbital an electron had -2.18 * 10^-18 joules, but i don't understand how the energy could be negative. All I need now is a more precise value than that. Thanks. *Max* 01:00, 12 March 2007 (UTC)

P.S. Electrons continuously emit virtual photons. *Max* 01:06, 12 March 2007 (UTC)

That value is a bit confusing. The negative sign means that your electron is in a potential well (i.e., bound to the atom). You would need 2.18 * 10^-18 joules to completely ionize the electron (remove it from the atom). This does not mean that the energy is 2.18 * 10^-18 J, it means that the electron is attached to the atom by an electrostatic potential of that amount. You really should read up on some basic atomic physics before you proceed farther. As User:HappyCamper suggested, you would benefit from the Rydberg formula, but I also think some introductory quantum physics will help you build a conceptual understanding of what is happening. As far as virtual photons are concerned, check the article: "a virtual particle is a particle which exists for such a short time and space that its energy and momentum do not have to obey the usual relationship." As far as you are concerned, the emission spectrum strictly depends on the far-field radiation. This is the opposite of a virtual photon, which does not exist long enough to radiate. You should think of "virtual particles" as fluctuations in the fundamental properties of the electron, not as an actual emitted particle. These fluctuations must satisfy the Heisenberg uncertainty principle, which means they must be less than the uncertainty of the electron. Once again, I suggest you build up some basic physics before you tackle such a difficult problem as quantum gravity. You will benefit from work that has already been done (and checked experimentally), and you will avoid going down long paths of incorrect theoretical equation-manipulation. Many physics books for "lay-people" make deceptive, hand-wavy analogies about theoretical physical that can mislead the reader, in an effort to over-simplify a complex problem. Nimur 04:48, 12 March 2007 (UTC)