Wikipedia:Reference desk/Archives/Science/2008 August 26

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August 26

Gas snorting

My freind said that if you keep snorting a mixture of 80% nitrogen and 20% oxygen you will eventually die. Is that true? —Preceding unsigned comment added by ThornCider (talk • contribs) 00:06, 26 August 2008 (UTC)

Yes. Algebraist 00:10, 26 August 2008 (UTC)

How does that link explain anything about the original question? ScienceApe (talk) 00:56, 26 August 2008 (UTC)

It was supposed to indicate that yes, you will eventually die. Breathing something almost identical to the earth's natural (dry) atmosphere isn't going to be very relevant though. Algebraist 01:00, 26 August 2008 (UTC)

I think your friend is having a bit of fun with you. Regular old air (like the one you are currently breathing) is about 80% nitrogen and 20 oxygen (with some argon, water and CO₂ thrown in for good measure). However, eventually, we will all die (it's like that line from Fight Club, "on a long enough timescale, the mortality rate of everyone drops to 0"). If the question is "Will breathing 80% nitrogen and 20% oxygen kill you?", then no. But if the question is "If you only breathe 80% nitrogen and 20% oxygen, will you eventually die?", then of course, yes you will. But the cause of your death wont be the air you breathe. 90.235.4.253 (talk) 01:56, 26 August 2008 (UTC)

Actually, the air could be what kills you - oxidation is one of the major contributors to ageing (just take a look at how many adverts stress the anti-oxidants in their products). --Tango (talk) 02:19, 26 August 2008 (UTC)

Heh, wasn't there a strange craze for huffing pure oxygen a few years back as a supposed cure-all for various ailments and medical conditions? --Kurt Shaped Box (talk) 02:25, 26 August 2008 (UTC)

Of course, we have an article. Algebraist 02:28, 26 August 2008 (UTC)

I wonder if those customers would like to buy a bridge? ;) --Kurt Shaped Box (talk) 02:41, 26 August 2008 (UTC)

Someone already did. Algebraist 02:45, 26 August 2008 (UTC)

Yes, it's true. A surprisingly large percentage of the population did this in the seventeenth century, and they all eventually died. (Note: they snorted the mixture because they called it "breathing", and they must have eventually died since they are not still alive.) -Arch dude (talk) 11:01, 26 August 2008 (UTC)

QUOTING FROM previous post: "on a long enough timescale, the mortality rate of everyone drops to 0" Or is it that the rate rises to 100%? Wanderer57 (talk) 16:20, 26 August 2008 (UTC)

Yeah, you're right, I got that wrong :) The real quote is "On a long enough timeline, the survival rate for everyone drops to zero." 90.235.4.253 (talk) 18:04, 26 August 2008 (UTC)

We can provide no medical advice on Ref Desk, but I am concerned about the absence of carbon dioxide in the posited breathing mixture. Wouldn't the absence of CO₂ suppress respiration? Edison2 (talk) 04:23, 27 August 2008 (UTC)

No - you breathe in a couple of lungfuls of N2 + O2, some of the O2 is absorbed and some CO2 is excreted. It's THAT CO2 that triggers the next breath - not the trace amounts of CO2 brought into the lungs from outside. SteveBaker (talk) 04:39, 27 August 2008 (UTC)

And what about Helium? I know it makes you talk funny, but does it make you light headed? —Preceding unsigned comment added by 79.76.200.98 (talk) 14:37, 28 August 2008 (UTC)

Breathing in anything that does not contain a significant quantity of oxygen will cause light-headedness and death. -- MacAddct  1984 ^{(talk • contribs)} 14:46, 28 August 2008 (UTC)

Any way to discourage my parrot from washing her head in her water pot?

It's just a minor annoyance but it's worth asking. She gets a shower with me every morning if she wants one, but she still feels the need to stick her head in her drinking water, splah around and make a mess. I've tried replacing her water pot with a tube feeder but she didn't like that at all.

Is it even worth trying to discourage her? You know what parrots can be like when they've been doing the same thing every day for years. This is a hyacinth macaw by the way, I've posted here before about her. Thank you. —Preceding unsigned comment added by 84.70.186.194 (talk) 00:43, 26 August 2008 (UTC)

Could it be boredom? Maybe she's trying to cool off - how hot is it? SteveBaker (talk) 01:51, 26 August 2008 (UTC)

A suggestion, not to stop the head dunking but to try to reduce the mess. Get a large open-top plastic container, such as is sold for storing clothes etc. Perhaps 30" long, 18" wide, 12" deep, just as an example. Put the water pot in the container. (Never having lived with a parrot, this suggestion may be completely useless.) Wanderer57 (talk) 05:37, 26 August 2008 (UTC)

Beautiful animals the hyacinths. I would never discourage my parrot doing things. Maybe she wants to tell you that she wants another shower? Try immediately spraying her after she splashes around. If she complains splashing was for another reason. Maybe then she has an itch? They get ticks so that could be the problem. --Ayacop (talk) 08:48, 26 August 2008 (UTC)

Cheap, small, low-power technology for detecting a short-range distance?

I was thinking today about how one could make a cheap, small, low-power technology for detecting whether the detector in question is within, say, an inch of a wall or other object, without touching it.

One obvious idea I had was to use laser diode and a detector like an optical mouse. I thought about just using a light detector but that wouldn't work at night (or under various lighting conditions). I thought about a laser inferometer but those seem fairly large and probably take a lot of power.

I imagine there must also be a way to use just high frequency radio waves but I imagine the power requirements would be rather high.

Anyway... just thinking about this. Any ideas? I'm no engineer. This is not homework, just something I was trying to think over. --98.217.8.46 (talk) 01:25, 26 August 2008 (UTC)

In playing with LEGO robotics, I've used both sonar (with a regular speaker and microphone!) and an LED/light detector approach. The former works pretty good - sound is slow enough that you can reasonably measure the time-of-flight so long as you use a really high frequency sound 'blip' and have a small, responsive, speaker & microphone. The latter is highly dependent on the color and shininess of the surface. Since the speed of light is so high - you can't use the time-of-flight of the light at such short ranges (an inch out and an inch back is about 1/6th of a nanosecond - and it's incredibly hard to measure that short an interval effectively. So you're down to measuring the reflected intensity - for that, a laser is a sucky solution because the orientation of the surface to the light makes a DRASTIC difference to the intensity...compared to a more omni-directional LED. I got better results with an IR LED than a red one - I didn't try other colors. But such a solution really gives very variable results depending on the orientation, shininess and color of the surface. Sonar seems to work best. Best of all is a fine whisker - but that requires touching the surface (albeit a VERY gentle touch). I can't imagine radio working better than light - you still can't use time-of-flight - and the reflectivity issues are much more problematic because radio waves go right through most surfaces without much reflection. You could maybe get away with millimeter-band stuff - but that sounds difficult. None of these approaches are going to be very accurate though.

I wonder if you could do something like using the guts of a "stud finder" - those use a change in dialectric constant - they are certainly cheap and at the one I have produces a handy digital output that ought to be easy enough to read with a microcontroller. I don't know how good they are on all kinds of surfaces though...they clearly can detect wood through sheetrock - but that probably means they don't detect sheetrock so well.

I think an awful lot depends on what you know about the kinds of surfaces you are trying to detect.

SteveBaker (talk) 01:50, 26 August 2008 (UTC)

Sonar-based distance finders (as Steve mentioned) are very cheap. The parts are very simple to remove and use for whatever purpose you like. -- kainaw™ 02:21, 26 August 2008 (UTC)

Would it work to project a diffraction pattern and "read" the resulting projection to determine distance? One might use a square aperture to detect a tilted surface, and vary the size of the aperture to improve accuracy for a variety of distances. I've not seen anything like this, so maybe it's just a bad idea. Scray (talk) 02:40, 26 August 2008 (UTC)

Assuming we're thinking of the same method, it's only possible to calculate the angle between a certain interference band and the central antinode in an interference pattern. Without measuring the distance along the wall from the antinode and the band, it's not possible to find the wall-to-sensor distance. --Bowlhover (talk) 08:13, 26 August 2008 (UTC)

Plus it would fail on a sloping surface. SteveBaker (talk) 15:35, 26 August 2008 (UTC)

If you know the orientation of the wall (say, you have a compass and know the general layout), you could bounce a laser off the wall at an angle and see which of a row of detectors it struck; a lit source farther from the laser means the whole array is farther from the wall. If you don't know the orientation, but do know that the wall is flat (on the scale of your detector), you could use two lasers at different angles and see how far apart their reflections onto your detector array are. You could minimize the power consumption by only pulsing the device for a few microseconds several times per second. --Tardis (talk) 15:23, 26 August 2008 (UTC)

You could use a laser to project a spot onto the surface - then use a pair of cameras to image that spot - the resulting stereographic information would yield a distance pretty readily. You could use very crude cameras - such as the one the Wii Remote uses. If lasers are cheaper than cameras - then you could use two lasers firing off parallel rays to project two laser dots onto the surface - then one camera could look at the distance between the two dots in "image space" and let perspective give you the range. With two InfraRed lasers, you might even be able to use an unomodified Wii Remote (it uses bluetooth to talk to the Wii and the protocol it uses is well-documented). In a robotic application, you'll find the accelerometers in the Wii Remote handy too!

More lateral thinking: What about using the mechanism in an optical mouse? Those are amazingly cheap. They contain a cheap, very low-res camera that measures the shift in 'texture' of your desktop over time to determine the speed and direction that your mouse is moving - but if you lift the mouse off the desk, the image becomes very blurry - no "texture" is detected and the mouse ceases to detect motion. That seems to happen at about one inch from the desktop. You could stick a mouse-mechanism onto the front of your machine and make it slowly vibrate somehow. So long as it reports no motion, there is nothing nearby - as soon as it "sees" motion, you're too close. It might fail if the surfaces you are measuring distance too are super-smooth and plain...but maybe you don't care about that?

SteveBaker (talk) 15:35, 26 August 2008 (UTC)

You have a better optical mouse than I do, Steve! It's hard to hold it steady enough to tell definitively, but mine seems to stop working at about 5mm off the (plastic) desk. (But that's still better than the ball mouse I also have, which doesn't seem to work at all when I pick it up…) --Tardis (talk) 15:48, 26 August 2008 (UTC)

I actually studied optical mice when I was looking for cheap navigation systems for LEGO robots. The chip that they all seem to use comes with a plastic lens that focusses the light at the plane of the desktop. Theoretically, every optical mouse on the planet ought to have the focal plane of the camera at the exact same height above the desk. However, I've found (as you just have) that there is some variability going on between one mouse and another. Perhaps they don't all use the plastic lens that comes with the chip - maybe to save money or allow some different internal arrangement for the mouse guts or...something...who knows?! Anyway - by replacing the super-short focal length lens that comes with the mouse for a longer len would allow the OP to choose the range at which it would accurately focus. You'd probably need a brighter light source too.

The distance at which it 'gets motion' may also depend on the nature of your desktop. I have an old beat-up leather-topped writing desk - so there is probably more "texture" for the mouse to latch onto than a relatively pristine plastic desktop. What do you get if you hold the mouse over the printed page of a book or something? I can get more "altitude" by aiming a desk lamp under the mouse - so light falloff might also be an issue if your mouse had a dimmer LED than mine.

Anyway - it's clear that it's possible. Whether it's good or easy in practice is a harder call.

SteveBaker (talk) 16:36, 26 August 2008 (UTC)

Cats and rats use their vibrissae (whiskers) as highly reliable short range proximity sensors. Cars of the 1950's had curb feelers which served the same function. Electro-optical curb feelers are discussed in that article. In the movie Dam Busters, bombing planes had to release the bombs at an exact height above lakes. A pair of spotlights and predetermined angles converged on the water surface when the plane was at the exact altitude. It would be a simple electronic process to use a pair of light beams to determine distance, or a light beam and a directional sensor or lens plus optical sensor. Bats and dolphins and some blind people use a form of sonar to echolocate and determine distance from objects. Edison2 (talk) 04:16, 27 August 2008 (UTC)

Whiskers would indeed be the simplest solution (Biology usually gets it right!) - but the OP specifically rules out touching the surface. SteveBaker (talk) 15:06, 27 August 2008 (UTC)

Using printed pages doesn't seem to change anything; one problem is that the mouse's light is directed at a shallow angle and thus misses the area under the sensor entirely with only a little vertical displacement. Running the mouse over the monitor (which is an odd concept) doesn't seem to give it any increased range, so perhaps it's the focusing issue. --Tardis (talk) 16:28, 27 August 2008 (UTC)

Testing your mouse on your monitor doesn't really prove much - the monitor flickers at 60Hz - which is probably similar to the update rate of the camera in the mouse - so the mouse is looking at a blank screen most of the time - it's going to be horribly confused! But the angle that the light source is aimed could easily be the real explanation of the problem. Maybe mine aims more vertically down? Anyway - what we know is that not all optical mice would do as range sensors without modification to (at least) the light source - and possibly also to the camera lens. For a one-off project, that's not going to fit the "cheap" criteria - but if you're planning on making a billion of them and taking over the world in a bloody robot revolution - then the cost of a different lens/LED setup would be almost zero. SteveBaker (talk) 04:31, 28 August 2008 (UTC)

General relativity analogy thoughts.

I have only a rudimentary understanding of general relativity, but I've always had a problem when someone tries to use the bowling ball / trampoline analogy. You need gravity to make the bowling ball / trampoline analogy work. I realise this is used as a simple analogy, but using gravity in an analogy to explain gravity is, well, not much of an analogy if you ask me! It's a bit like saying: The night was so dark, it was as black as night! So I was thinking about this and came up with what I think is a better analogy, which admittedly is not quite as simple, but it goes something like this: imagine space-time has a uniform "pressure" or "density", of course these terms are usually applied to things which have mass already, but imagine space-time has a quality which is analogous to "density". Any mass existing in space-time creates an area of low space time density, less dense the closer you get to the mass. So just like a balloon in air, any mass is drawn towards areas of least density, or pushed away from areas of higher density, which ever way you want to look at it. So that when two objects interact, the are drawn towards their "low density zones", the bigger will obviously have a larger zone. However unlike a balloon, the pressure areas are not defined by a membrane, but actually exist as a gradual pressure gradient, dropping off the further away you get, just like how we currently observe gravity. So inverse of the high pressure atmosphere created by our gravity, the atmosphere it self is stuck to our planet by the low pressure time-space near our planet. If you take the analogy one step further, could matter it self be condensed space-time? The area of low "space-time pressure" is in fact the "gap" left in space time by the mass it self coalesced in the middle? I'd be happy to hear what anyone more familiar with general relativity would have to say. Vespine (talk) 02:32, 26 August 2008 (UTC)

I'd just like to say I like the fact that you pointed out that problem. Clever. I didn't read the rest of it, sorry =P --mboverload@ 03:06, 26 August 2008 (UTC)

I don't think your analogy really works. Things move towards areas of low pressure in order to equalise the pressure and remove the gradient, but when things move towards a massive object they actually make the object more massive and increase the gradient. I'd stick with the trampoline analogy, while the reasons behind why it works don't make much sense, the outcome is a very good approximation of the real thing - you can even get marbles to orbit the bowling ball in realistic orbits (although they decay rapidly due to friction). I'm not sure your analogy would be as good at something like that, and it's also much more difficult to understand - people know exactly what happens with bowling balls on trampolines. To be honest, I think you just have to accept that GR is difficult to understand and there's not a lot you can do to make it easier! --Tango (talk) 03:07, 26 August 2008 (UTC)

It doesn't matter whether I'm familiar with GR or not because GR is not about analogies or allegorical heuristics - these are just little things to understand some general concepts that don't even matter that much. Gravity is, as far as we know, a field of interaction just like electromagnetism (using gravitons instead of photons). The "rubber sheet" analogy is useful because gravity, unlike EM, is a one-way force in most applications - it can only attract. But the mathematics is general enough that similar tensor equations can be used to solve both GR and EM problems. Mass occurs by the Higgs mechanism, as far as we know, which is really not anything like you described. Mass is also concentrated space-time pretty much by definition of gravity until we get quantum gravity worked out. The pressure analogy sort of works, because that's sort of how an interaction field works, but not really. SamuelRiv (talk) 13:05, 26 August 2008 (UTC)

The bowling ball / trampoline analogy is actually a good model of Newtonian gravity, even though, as you say, it looks like it's begging the question. The gravity well article explains the math behind it. It's not a model of general relativity. A lot of people confuse the curved trampoline with curved spacetime, but they're very different. So don't try to understand general relativity that way, you never will.

It might be possible to model general relativity as a local variation in the "density" of spacetime, but the simplest version of that idea won't work. Newtonian gravity is a scalar field theory, meaning that the field can be described by a single real number at each point in space(time). In the trampoline analogy, that number is the height of the trampoline at each point. Density is also a scalar. But general relativity is a tensor field theory: the field at each point is described by a symmetric 4×4 matrix. So you need more than just a density. You could do it if you allowed the "density" to be different in different directions (making it more like strain), and included time as one of those directions. But I think that model would be harder to visualize than the usual one (curved spacetime).

Could matter be condensed spacetime? Sure. A black hole of mass m and charge q interacts gravitationally and electromagnetically just like any other object with the same mass and charge, even though there's no "real" mass or charge anywhere to be seen. People often say that the mass and charge exist inside the event horizon (where they can't be seen), but we don't know that. Nothing behind the event horizon has any effect on the outside; spacetime could just end unceremoniously right inside the event horizon, and the part outside would still behave like it has mass m and charge q. So the universe doesn't need real charge; you can fake it with black holes. Applying Occam's razor, it's tempting to suppose that it doesn't have real charge. I'm a big fan of this everything's-a-black-hole viewpoint, but whether it has any merit remains to be seen. Nobody's yet concocted a working quantum theory along those lines, and not for lack of trying. -- BenRG (talk) 14:56, 26 August 2008 (UTC)

Given the same amount of sleep

Would you choose more or less REM sleep? I'm asking because a news article says people sleeping east-west may have fewer dreams than those north-south. Thanks. 67.243.6.204 (talk) 02:28, 26 August 2008 (UTC)

Wait, humans have their own compass? --mboverload@ 02:35, 26 August 2008 (UTC)

Maybe, according to magnetoception. I'd like to see this article, though – it sounds fairly likely to be nonsense. Algebraist 02:36, 26 August 2008 (UTC)

Quite a few people seem to believe in the 'sleep alignment' thing. I have no idea what it's actually called - but I think it's one of those new age-type beliefs... --Kurt Shaped Box (talk) 02:40, 26 August 2008 (UTC)

They believe it because <personal opinion> When you change position on your bed there are different pressure points/air flows/light intensities. I constantly switch my sleeping alignment and sleep better in different directions depending on the season/weather/my crazyness.</personal opinion>--mboverload@ 02:45, 26 August 2008 (UTC)

I think just about everyone does *that*. I think what the OP was getting at is the practice of intentionally aligning your bed (i.e. physically moving it) in the direction of the compass/chi flow/ley lines/earth's magnetic field/whatever. --Kurt Shaped Box (talk) 02:52, 26 August 2008 (UTC)

Yes, and it "works" for them due to the placebo effect in addition to the points I laid out above =). --mboverload@ 03:05, 26 August 2008 (UTC)

I'm not sure the placebo effect can do much when you're asleep - it requires concious thought. It's more likely to be confirmation bias. --Tango (talk) 03:08, 26 August 2008 (UTC)

I'm not convinced of that. Based on purely anecdotal evidence, it seems to work in sleep (I'd look for studies, but I'm behind a corporate content filter). ie. after reading about lucid dreams and out-of-body experiences and all that nonsense, I had a couple "lucid" dreams. Of course again, that's anecdotal, but I'm sure there's at least one study that has employed placebo controls and sleep. -- Consumed Crustacean (talk) 03:14, 26 August 2008 (UTC)

As far as I know, lucid dreams are a purely psychological thing anyway, so I'm not sure there's a meaningful distinction between a "real" effect and a placebo, any effect is going to psychological in nature. --Tango (talk) 03:43, 26 August 2008 (UTC)

[1] says "some studies suggest humans who sleep in an East-West position have far shorter" REM sleep. No sources cited. The article is about another study involving deer and cattle. This is an August 25 article, probably where the OP got the idea from. -- Consumed Crustacean (talk)

"Some studies suggest" Ah, the greatest cop out phrase in the history of fake and misleading news. Thanks for the detective work Consumed! --mboverload@ 03:18, 26 August 2008 (UTC)

TO ORIGINAL POSTER: According to Rapid eye movement (sleep) lack of REM sleep is bad. I would go for more, but not too much. You should qualify your question with a base amount of REM sleep you are considering.--mboverload@ 02:47, 26 August 2008 (UTC)

I don't know about east-west versus north-south, but I sleep much better if I am facing the door. I always assumed that it is a basic instinct that I need to face the entrance so as to be more easily alerted to a predator. My girlfriend teases me but if we are set upon by wolves I'll be the first to know. Plasticup ^T/C 13:23, 26 August 2008 (UTC)

There was a recent study that showed cows and deer on Google Earth tended to sleep facing magnetic north-south, but they didn't go so far as to say why (or whether it would apply to humans too, although they had originally planned to look at campers). Confusing Manifestation(Say hi!) 01:56, 27 August 2008 (UTC)

Yes, I read that news article. No, I don't believe in new-age voodoo. Yes, I understand that "some studies" is a copout. No, I don't have a baseline for my question. I know so little about the subject anyway. Thanks a lot for the interesting discussion though. 67.243.6.204 (talk) 04:26, 28 August 2008 (UTC)

Do you mean this article about cows? —Preceding unsigned comment added by 89.243.71.44 (talk) 18:22, 30 August 2008 (UTC)

Listeriosis

This food recall is a little scary because of the 30% death rate and reconfirms for me how much better it is to avoid processed foods when I can just make it myself. My question here is, the news agencies are saying that the people at risk are the elderly, immune-compromised individuals, and pregnant women. Why pregnant women? Is it the woman who is at risk, or is there a likelikood that the bacteria can migrate to the fetus? Franamax (talk) 03:10, 26 August 2008 (UTC)

Please note that the vast majority of food poisonings occur because of UNprocessed foods, such as fresh fruit. I would much prefer my food made in a controlled factory environment with all ingredients irradiated and put through large amounts of sterilization first =) --mboverload@ 03:13, 26 August 2008 (UTC)

Nothing against you by the way, just an interesting tidbit. --mboverload@ 03:16, 26 August 2008 (UTC)

Yeah, I know where you're coming from there. The point though is that poisoning from unprocessed food generally comes from surface contamination - and I'm willing to take responsibility for washing my food. With processed food though, the bacteria/virus is more often right there in the inside of the food, especially with meat. Franamax (talk) 03:48, 26 August 2008 (UTC)

As for Listeriosis, it's both that the woman is at risk, and that an infection can complicate pregnancy. Specifically, most infections occur in the third trimester of pregnancy, because that's when Th1-mediated immunity is most severely suppressed. Pregnant women are 20 times more likely than non-pregnant persons to catch the infection. Listeriosis can cause miscarriages and premature delivery. About 22% of cases of perinatal listeriosis result in the death of the fetus. Listeriosis can be caused, as noted, by uncooked foods, but also by cooked or pasteurized food that have been contaminated between the pasteurization/cooking and the consumption. Pregnant women are usually counselled to avoid unpasterurized milk, soft cheeses, and cold luncheon or deli meats. - Nunh-huh 03:22, 26 August 2008 (UTC)

Hmmm - thanx. TH1 suppression during pregnancy, I wasn't aware of that. I'd be guessing (off-topic) that it is actually the fetus generating the immune-supression? Franamax (talk) 03:48, 26 August 2008 (UTC)

I think it's actually an estrogen effect - but possibly a literature search would turn up other factors as well. - Nunh-huh 04:27, 26 August 2008 (UTC)

Fetuses have no working immune system, see Immune system#Passive memory, they borrow antibodies from the mother. --Ayacop (talk) 08:36, 26 August 2008 (UTC)

Even in the third trimester? Plasticup ^T/C 16:50, 26 August 2008 (UTC)

Well yes, babies have passive immunity using their mother's antibodies (from the pregnancy and milk) for a while after birth. Third trimester is nowt to that :) 79.66.44.182 (talk) 00:10, 27 August 2008 (UTC)

Could be due to one or both of progesterone[2] and/or estrogen[3], probably both. Scray (talk) 04:55, 27 August 2008 (UTC)

My understanding is that the fetus itself produces hormones which affect the mother. For instance (though I'd he hard pressed to find the reference), the fetus produces substances which modulate maternal weight gain in early pregnancy. It seems not unreasonable to consider that the fetus also modulates maternal immune response. After all, the fetus is 50% foreign material, so to speak. Franamax (talk) 08:44, 27 August 2008 (UTC)

Curling a ribbon by scraping it?

When you run one side of scissors along a ribbon, it tends to curl up. I've seen this technique used when wrapping Xmas presents.

Is there an English word or Wikipedia article that describes this simple physics process, or this physical phenomenon? I've noticed it happen to hairs too when they are brushed with knots in them. And I'm sure it may be used in other aspects of engineering or fabrication. --206.248.172.247 (talk) 03:35, 26 August 2008 (UTC)

There does not appear to be a single word, though this article describes the mechanism behind the process. Dostioffski (talk) 05:30, 26 August 2008 (UTC)

Maglev

(Note: I moved this question down from the original date because I added a third question four days after the original posting that seems to be getting overlooked.) —Lowellian (reply) 11:45, 26 August 2008 (UTC)

Are maglev trains generally built along the lines of the locomotive model or the multiple unit model? —Lowellian (reply) 02:44, 21 August 2008 (UTC)

The lift motor also generates thrust - since every car requires lift, every car produces thrust. So I believe they pretty much have to be multiple unit trains. But in another sense, the "motor" is the track - so in a weird way, none of the train is the power unit. SteveBaker (talk) 02:56, 21 August 2008 (UTC)

The locomotive article has a section on maglev (that heading entitled "Magnetic levitation") that gives some information about maglev but does not in the least relate that information to the locomotive or explain what any of it has to do with a locomotive. Perhaps that section should be removed? —Lowellian (reply) 18:45, 21 August 2008 (UTC)

How easily do maglev trains turn (go in reverse) compared to traditional wheeled trains? —Lowellian (reply) 04:07, 23 August 2008 (UTC)

For a maglev MU, what's the difference? It's just a question of the rotation order with which you actuate the drive electromagnets.

Atlant (talk) 14:19, 23 August 2008 (UTC)

So, suppose a maglev train was running along at, say, 300 mph. Could it just almost instantaneously reverse direction and go in the other way, still at 300 mph? —Lowellian (reply) 01:28, 24 August 2008 (UTC)

Could you instantaneously reverse? Of course not! But neither can a traditional wheeled train. What you could do, of course, is reverse the direction of the driving force and begin decelerating at (approximately) the same G-force with which the maglev originally accelerated. In fact, for a maglev (as compared to a wheeled train) that's really your only means of braking unless you dump the maglev system and let the train slide along the guideway in what's probably an amazing shower of sparks. (Wheeled trains have friction brakes on the wheels, axles, or directly engaging the steel track.)

Atlant (talk) 14:27, 24 August 2008 (UTC)

Are maglev trains the trains of the future, or is there some other competing advanced technology with the same potential? Fifty or one hundred years from now, is it likely that most trains will be maglev? (Yes, I know Wikipedia is not a crystal ball, but we're not in the main article space.) —Lowellian (reply) 08:19, 25 August 2008 (UTC)

From reading our Maglev (transport) article and this survey article, it seems that the answer is "probably not". The lower operating costs, greater people-carrying efficiencies and environmental benefits of maglev trains are only realised over long distances. However, the high costs of constructing a new permanent way (from $100 million/km to $500 million/km) mean that a long-distance maglev network will require a huge initial investment, and will take a long time to break even. Short-distance point-to-point systems may be cheaper, but they don't seem to be economical. Just because something is technologically feasible doesn't necessarily mean it will become commercially viable - to coin a phrase, we could call this the Concorde syndrome. Gandalf61 (talk) 12:41, 26 August 2008 (UTC)

This is still the reference desk though and not the place for idle speculation. Gandald has some good points. Also, the high speeds maglev trains are capable of achieving is likely to be pointless for urban trains, the short distance between stations means you don't have enough time to accelerate (presuming you don't want to kill all your passengers). But more generally, we simply don't know. It will depend on what sort of new technologies we achieve and a whole lot of o ther stuff (e.g. how much energy ends up costing). E.g. room temperature superconductors will help a lot but I'm not convinced they are possible. IIRC last time I read the article, there is also some techs using more permanent magnets but they're still in initial development. Nil Einne (talk) 14:27, 26 August 2008 (UTC)

There is a general trade-off between Speed and Cost:

• Maglev's produce an almost frictionless surface - speeds are high - but costs are astronomical.
• Conventional steel wheels on steel rail is still fairly low friction - speeds can still be reasonable (150mph to 200mph is no problem) - and it's cheaper. Monorails are pretty much a similar deal.
• Rubber on concrete is higher friction - speeds over 70mph start to become problematic - but it's very cheap.
• Dirt tracks and draft animals...?!

Getting rid of friction costs money but it gains you speed. But over a short run, you don't need the speed (and you can't get it without high accelerations - which are uncomfortable for the passengers). So you end up with this uncomfortable problem that high speed is only useful over long runs when the track costs kill you. Over short runs, you can maybe afford the high cost of the track - but you don't need (and can't use) the speed - so why pay extra?

So you find that steel rail works best over most of the speed/distance envelope - with rubber-on-concrete being used for really short runs like the trains that run around between airport terminals and such. Monorails tend to be used mostly for reasons of novelty (eg at Disneyland). Under-slung monorails may offer advantages in tight urban areas where they have to be added as an afterthought into existing infrastructure.

Hence, no maglev trains. It's a solution in search of a problem.

SteveBaker (talk) 15:13, 26 August 2008 (UTC)

SteveBaker, are you saying that the lower-friction of steel-on-steel results in higher speed capability? I think this cannot be correct. See traction - if you want high speeds, you want high static friction between the wheel and the "road", and low friction between the wheel and the axle. Some other factor must be the limiter here. Nimur (talk) 21:27, 27 August 2008 (UTC)

"Friction" might not be the correct term, but it's a reasonably accurate description of the effect. The difference between rubber-on-concrete and steel-on-steel is the amount of deformation: a rubber wheel flattens on the bottom as it rotates, converting forward motion into heat in a very friction-like way. A steel wheel doesn't deform anywhere near as much, so there's very little energy loss. --Carnildo (talk) 23:12, 27 August 2008 (UTC)

Okay, thanks for the answers, though let me ask for a little bit more clarification: if maglev trains won't be predominant, what type of trains will be dominant then in the near (50-100 yr) future? Still the same steel-wheels-on-steel-rail trains as today? There's no other competing new technology besides maglev? —Lowellian (reply) 18:38, 27 August 2008 (UTC)

No, there isn't. There is no reason to expect anything but steel-on-steel to become dominant for the foreseeable future. (I would say that the foreseeable future in this context is more like 20-30 years than 50-100.) Trains using conventional steel-on-steel now run at up to almost 200 mph in regular service, with good energy-efficiency, and have been tested at over 350 mph. The same cost and political considerations for obtaining a route suitable to build a high-speed line apply no matter what the technology, but conventional trains can run onto conventional tracks, so the high-speed routes can stop at the city limits and trains can run through onto other parts of the network. It seems to me that the most likely thing to change this picture is a global war or energy shortage, and that would simply lead to the discontinuation of all high-speed trains, not the introduction of new technology. --Anonymous, 19:43 UTC, August 27, 2008.

Why is 3d10 configuration so stable??

Why is 3d10 configuration so stable?? According to Hund's rule, pairing decrease stability ..So why is 3d1 where every electron is paired so stable?? —Preceding unsigned comment added by Tetsuya26 (talk • contribs) 11:54, 26 August 2008 (UTC)

"Stable" compared to what? DMacks (talk) 14:17, 26 August 2008 (UTC)

Hund's rule is saying that, once you have decided to place electrons in the same set of orbitals (like 3d taken as a whole), placing them in different orbitals gives a lower energy (better) state than placing them in the same orbital. However, you don't even see this in the spectroscopic notation: we just write 3d⁵ without bothering to say that this should be one electron in each orbital rather than, say, 2 full orbitals and a half-full. 3d¹⁰ is just fine because the only alternatives after you get to the obviously desirable 3d⁵ are to go to 4p or higher, which is worse. There are some near-degeneracies, though, where Hund's rule trumps the Aufbau principle; for example, copper is 3d¹⁰4s¹ even though 4s is "lower" than 3d. --Tardis (talk) 15:36, 26 August 2008 (UTC)

Geomagnetic reversal and the End of the World

I was watching a program about the End of the World (predicted to occur in 2012). In it, there was reference to Geomagnetic reversal and catastrophic (environmental, geologic, etc.)results when this occurs. I read the wiki artical but it is unclear if such a reversal would be "catastrophic" or if it would really make much difference in the grand scheme of things (other than wreaking havoc on our electronics!). Can anyone shed any light on this? —Preceding unsigned comment added by 216.154.16.106 (talk) 21:12, 26 August 2008 (UTC)

We talked about this just a few days ago. As I understand it, the problem is not that the field is reversed (ok - so your compass points the wrong way - I think we can deal with that!) It's that the reversal doesn't happen overnight. It might take years to decades for it to happen. During that interval, there might be either no magnetic field at all - or a wildly oscillating field. If the field were to "go away" for any amount of time, there is a risk that the mechanisms like the Van Allen belt might collapse and cease to protect us from hard solar radiation. A rapidly moving or oscillating field would induce electrical currents into large metal objects - and might do very bad things to electronics and such like. Since this kind of field reversal has happened MANY times in the past - certainly within the period since humans have evolved, it's not an "end of the world" event. Our species - and most others on the earth would survive. However, the number of deaths and associated problems with electronics and such might make it seem like a really major catastrophy to individual humans. But it's really hard to tell what all the ramifications of such an event would be on a technologically advanced civilisation. SteveBaker (talk) 21:30, 26 August 2008 (UTC)

The transition period is ~800 years, not decades. A terawatt geomagnetic engine does not stop (or reverse) on a dime. Dragons flight (talk) 02:11, 27 August 2008 (UTC)

Not really, we don't know exactly what would happen. The world has undergone plenty of reversals in the past and it's still here, so won't result in the end of the world, it might possibly result in the end of civilisation, but I doubt it (proto-humans survived the last reversal, so why can't we survive the next? We can protect ourselves with technology if we need to). Also, it's not going to happen in 2012 - it's a pretty quick thing by geological standards, but I don't think it's that quick, we would have detected changes by now if anything major was going to happen in 2012 (the changes we have measured suggest we've got another thousand years or two to go, at least). --Tango (talk) 21:32, 26 August 2008 (UTC)

Linear extrapolation from current trends suggest that a reversal could occur one or two thousand years in the future—there merest eyeblink on geological timescales, but a long, long time after 2012. (See geomagnetic reversal). Any effect on human society is purely speculative; penetration of the solar wind into the upper atmosphere may result in damage to electronic and electrical systems, and there may be an elevation in ambient radiation levels as more cosmic rays reach the Earth's surface. TenOfAllTrades(talk) 22:36, 26 August 2008 (UTC)

The year 2012 has become a popular choice by doomsayers based on interpretations of, among other things, the Mayan calendar. These doomsayers then tend to latch onto any possible explanation they can find for their predicted apocalypse, particularly things like planetary alignments and magnetic pole reversal, even if scientists know that these events are either not going to have the effect the doomsayers think they will (the gravitational effects of a perfect planetary alignment could be counteracted with a jumbo jet) or are almost certainly not going to happen as soon as 2012 (as TOAT points out, we suspect there will be a pole reversal in the next few thousand years, but thats three orders of magnitude bigger than the 4 years until 2012). Confusing Manifestation(Say hi!) 01:35, 27 August 2008 (UTC)

I'll see you in four years and tell off that program. Imagine Reason (talk) 04:13, 1 September 2008 (UTC)

Keep a "hard(permanent) magnet" floating

I have searched the internet and read the article on magnets and magnetic fields, but there are still questions I feel unanswered.

Would it be possible for a sphere shaped "hard magnet" to float above another "hard magnet" or flawlessly being repelled whenever the magnet would touch or get close to the other magnets surface? I do know that monopole magnets are just hypothetic, so I wonder rather if there is a possibility to "wrap" a pole inside another or possibly balance the poles, so it's 100% controllable?

To help illustrate my point, you could imagine a series of slides standing in a row on a flat ground. I would like to drop a ball on the first slide, make it "bounce" on to the next, slide down, and bounce up to the next one again - all by just using regular magnets. Is this plausible?

Thanks in advance!

Kim, Norway —Preceding unsigned comment added by 89.10.23.121 (talk) 22:14, 26 August 2008 (UTC)

Not with ferrimagnetic materials alone. But you could some diamagnetic material (like bismuth orpyrolytic carbon) to stabilise the system. See Earnshaw's theorem. —Preceding unsigned comment added by LCMk2 (talk • contribs) 22:19, 26 August 2008 (UTC)

You mentioned a "spherical magnet." It would still have a north and a south pole, and if suspended over a north pole would flip so he south pole was down and crash into the magnet below. We know of no way to have a spherical magnet with the horth pole, say on the outside and the south pole on the inside, and no one has ever found a magnetic monopole, even though I don't think anyone has proved such to be impossible. Edison2 (talk) 04:02, 27 August 2008 (UTC)

He's referring to having north in the middle of the magnet and south on the outside, or vice versa. If this is done, the north and south will cancel each other out, and there will be no magnetism outside of the magnet. Besides using a diamagnet, you can spin the magnet, and use the gyroscopic effect to keep it balanced. These will both allow you to levitate the magnets, but the example you mentioned would be impossible because if the force is strong enough to push the magnet up to the next slide, it will be strong enough to keep the magnet from going down the slide. Get it? In general, if you think you found a perpetual motion machine, and you're not using general relativity, you messed up somewhere. — DanielLC 15:48, 27 August 2008 (UTC)

Lifespan of an American Spadefoot toad

I have had two male and one female American Spadefoot Toads for over seven years now. Seven years ago, my father told me they'd only live about three years. Is this generally true? --Ye Olde Luke (talk) 03:01, 26 August 2008 (UTC)

I don't know about this specific case, but it's not unusual for pets to live longer than the same animal would in the wild due to having a reliable source of food, protection from predators, etc. Perhaps your father was basing it on the life span of these toads in the wild. --Tango (talk) 03:12, 26 August 2008 (UTC)

A Google search suggests different wild populations of American Spadefoot Toads live from between 5 and 12 years. Dostioffski (talk) 05:40, 26 August 2008 (UTC)

An entirely new problem: they've escaped.

Somehow, my asking of this question seems to have correlated with my first real problem with the frogs.

Yesterday, I found that the frog case had been swarmed by ants. I rescued the three frogs, and relocated them temporarily to a large tupperware container filled almost to the top with sand. I placed a lid on the container, but not tight, since I wanted air to get in. Last night, the frogs were able to pop the top and escape into the house. This morning, I found the female and one male in the basement. I'm still searching for the other one. The family has made sure to keep all doors shut, so there's no way the frog can escape the house. My questions:

1) Is the final frog probably in the basement? Should I concentrate my search there?

2) Is the fact that two were in the basement relevant? Do spadefoot toads, who are burrowers, have some sort of inner sense helping them find the lowest place in the house?

3) After seven years of captivity, is the frog still capable of finding itelf food and staying alive until I locate it?

4) Will the frog move around? Or will it probably sit in the same place until nighttime? All they ever seemed to do is sit around while in the case.

5) Is there any way to set a trap for the frog? Maybe some type of cage with a cricket that the frog can enter but not exit (remember they can jump as well as burrow; I've seen it).

6) Anything else I should be aware of or take into consideration?

Thanks for any help you can give me. Depending on the answer for #3, time may be of the essence. --Ye Olde Luke (talk) 00:23, 27 August 2008 (UTC)

It will probably try and find somewhere damp, the basement may well qualify. You could try putting large tubs of damp sand (with food in, if possible) around the house that it can choose to burrow into (include one or two in the basement) and check on them every few hours until you find it. I doubt food will be an issue for a while, water will be more of a problem, but you've probably got some time to find it, especially if is succeeds in finding somewhere damp to stay. --Tango (talk) 01:42, 27 August 2008 (UTC)

I talked it over with my dad, and he's considering the idea, but he hasn't okayed it yet. We've decided towels would work better then tubs, to ensure that the frog can successfully get into the sand. Only problem is the frog eats live crickets. There's no concievable way to keep live crickets to stay on a pile of sand, is there? Oh, one last thing: any idea how frogs find their food/shelter? Visual? Olfactory? I just want to know if the only way the frog's gonna find our sand pile is by running into it. --Ye Olde Luke (talk) 01:59, 27 August 2008 (UTC)

I don't know, sorry! Hopefully someone else has some experience of catching frogs, I'm just guessing based on what little I know about them. --Tango (talk) 02:23, 27 August 2008 (UTC)

I once kept frogs. I put them in a terrarium with gravel on the botton and a terracotta dish filled with water. They burrowed under the dish and could not be seen. So a runaway frog might burrow under something damp and cool. Edison2 (talk) 04:00, 27 August 2008 (UTC)