Wikipedia:Reference desk/Archives/Science/2007 March 24

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March 24

why is an ionic compount neutraly charged?

why is an ionic compount neutraly charged? Frankum 00:17, 24 March 2007 (UTC)frankum

Because ionic compounds have equal numbers of negative ions and positive ions, so they balance each other out. MrRedact 00:27, 24 March 2007 (UTC)

This is not true. Ionic compounds have equal total values of positive and negative charges. The ratio between the numbers of each ion is inverseley proportional to the actual charges on them, which is often not the same.G N Frykman 08:28, 24 March 2007 (UTC)

Frykman is right; I stand corrected. MrRedact 11:36, 24 March 2007 (UTC)

Thanks for the help. 69.245.174.196 14:50, 24 March 2007 (UTC)Frankum

identify birds?

Can anybody identify the species of these birds my girfriend saw in Toronto this week? I'm wondering if some might be juvenile.--Sonjaaa 00:27, 24 March 2007 (UTC)

http://www.kisa.ca/lj/bird1.jpg http://www.kisa.ca/lj/bird2.jpg

OOps! Old squaws! Not harlequins as I staed earlier this morn. (Thanks to whomever deleted my boo boo). They are two of my fav ducks & I often get thier names mixed up. 209.226.189.59 14:28, 24 March 2007 (UTC)Canis sylvaticus

Why is there no wikipedia article on this species?--Sonjaaa 21:55, 24 March 2007 (UTC)

OK i added a redirect.--Sonjaaa 22:14, 24 March 2007 (UTC)

Why do different sugar ferment at different rates?

I've searched on line for hours, and everything I come across is too complex for me. I'm in a intro Bio class and we just did a lab with 5 different types of sugar fermenting with yeast. I need to know why they ferment at different rates. I used two monosaccharides, glucose and fructose and three disaccharides, lactose, sucrose, and maltose. Can anyone tell me a simplified answer on why these ferment at different rates?

Homework question? Nebraska bob 02:44, 24 March 2007 (UTC)

It's part of the paper I have to write. If you could send me to a site that is easy to understand, or make it more simple for me, that'd be great. I'd really appreciate it. Tinav215 02:54, 24 March 2007 (UTC)

If I had to guess, I'd say that it might be because some sugars have to be made into a particular (other) type of sugar before they're metabolized. So the rate at which it could be fermented by the yeast would be limited by the rate at which the yeast could make the non-fermentable sugar into a fermentable variety. I could be completely wrong; this is just a wild guess. grendel|khan 04:15, 24 March 2007 (UTC)

Guess is partly right for the disaccharide but there are other factors as well. The major reason is the transport and enzyme affinities and rates of reaction of the molecules vary. See our excellent article on enzyme kinetics to get an idea. alteripse 11:24, 24 March 2007 (UTC)

Biology: looking for a word that describes the synchronzed movements of a swarm (fish, birds, insects, etc.)

I have looked through Wikipedia, Roget's Thesaurus and various dictionaries without success. Yet, I am sure such a word exists.

The grouping of animals (sometimes in the thousands) can be called a swarm, flock, school etc. Many animal swarms move in sycronized fashion that make the swarm seem that it has a life and intelligence of its own. The movement produces patterns that are often fascinating and quite beautiful.

I beleive there is a word either in biology or common language that defines/describs that swarming motion. What is it?

Bill Case 02:23, 24 March 2007 (UTC)

Flocking. grendel|khan 04:01, 24 March 2007 (UTC)

It's a form of emergent behavior. MrRedact 11:47, 24 March 2007 (UTC)

Swarm intelligence Ozone 17:45, 24 March 2007 (UTC)

Swarm has some pretty pictures too. —Pengo 01:35, 25 March 2007 (UTC)

Maybe you just want synchronised :] HS7 15:17, 25 March 2007 (UTC)

Fuel cell size and weight versus capacity

What is the ratio of fuel cell (hydrogen/oxygen or air) size and weight to wattage capacity? 71.100.3.92 02:42, 24 March 2007 (UTC)

The figure you're looking for is generally called energy density, though I don't have a numerical answer for you off the cuff. -- mattb @ 2007-03-24T03:24Z

You'd be looking for the energy density of the fuel--asking for the energy density of a fuel cell is like asking for the energy density of your car's engine: you'd be more interested in the energy density of gasoline. In any case, energy density has what you're looking for, both by volume and by mass. (Note that 'wattage capacity' is the rate at which the energy is used; gasoline has a constant energy density per unit mass, but if you burn it in tiny spurts, it'll have a much lower wattage than it would if you made it into an aerosol and blew up a whole gas tank's worth of it.) grendel|khan 04:06, 24 March 2007 (UTC)

I think the OP is looking for the size of the actual cell, not the tanks and other peripherals. If so, all I can say unhelpfully is quite small, compared with an IC engine of the same power. However, they need much larger radiators, and the tanks are big as well.Greglocock 23:31, 24 March 2007 (UTC)

What I'm looking for is a scale of size and weight to wattage similar to a scale of cubic inch displacement (actually external dimensions) to horsepower. 71.100.3.92 15:48, 25 March 2007 (UTC)

Ah, well then, just find some data on current fuel cells or predictions about future cells and divide their maximum power output by their volume. -- mattb @ 2007-03-25T23:33Z

Distance to sun

Is there a way that I can work out the distance to the sun from my backyard (without knowing its size)? I figure that in order to find out the distance to the moon (without knowing its size), the only way would be to get people on almost opposite sides of the earth to look at it at the same time and take note of the angle at which they were looking at it. The distance could then be worked out trigonometically; you could then use the measurement of distance to get the size. But because the sun is so large and far away, this technique would not work. Any ideas? (P.S. Obviously, I am not interested in just looking up the distance; I am interested in the technique, not the answer.) BenC7 05:08, 24 March 2007 (UTC)

Well, the backyard probably wouldn't work, but if you had a much longer distance, you can use trigonometry to approximate the distance to the sun, which was done by someone who measured the shadow one city, the the shadow in another city, and came within a reasonable accuracy. I don't remember who it was, might have been Eratosthenes. --Wirbelwindヴィルヴェルヴィント (talk) 05:21, 24 March 2007 (UTC)

What an interesting question! I can't think of any great methods. Perhaps, if you observe the moon during a precise half-moon, you could measure the angular separation between the moon and the sun, and given the distance to the moon (from your earlier method), you could get the distance to the sun. I don't know how accurately you could measure it, though. — Knowledge Seeker দ 05:59, 24 March 2007 (UTC)

Er, Wirbelwind, I believe you're describing the method for determining the radius of the Earth; that method assumes an essentially infinitely distant sun with parallel rays. Here's another method. — Knowledge Seeker দ 06:02, 24 March 2007 (UTC)

Ah yes, I was. Thanks for for the correction. --Wirbelwindヴィルヴェルヴィント (talk) 06:09, 24 March 2007 (UTC)

See Astronomical unit#History. Aristarchus of Samos got at least a ballpark figure from his backyard. — Sebastian 07:12, 24 March 2007 (UTC)

Aristarchus estimated the ratio of the distances to the Moon and the Sun - he did not estimate the absolute value of either distance. Eratosthenes is sometimes credited with accurately estimating the distance to the Sun in the 3rd century BC, but the only evidence for this is a few sentences in a book written hundreds of years later by Eusebius of Caesarea, so this is considerable doubt around this claim. He did, however, make a reasonably accurate estimate of the radius of the Earth. The first clearly documented and accurate measurement of the distance to the Sun was made by Cassini in 1672, using a parallax method. As this method requires simultaneous and very precise astronomical measurements made at widely separated locations, I am not sure that it qualifies as a "backyard" method. Gandalf61 14:03, 24 March 2007 (UTC)

The technique you describe doesn't even require two people - as the earth rotates, you are on one side of the planet in the morning and on the opposite side 12 hours later in the evening. For the Moon, this ought to work pretty well - except that the moon is orbiting earth and you'd have to allow for the motion of the moon about its orbit over those 12 hours...but with the right math, you could get a reasonably accurate answer with backyard/home-made equipment. But it's a different matter with the sun - the angles you'd be measuring would be tiny - the diameter of the earth versus the distance to the sun are so hugely different that the angle you'd be measuring would be microscopic. Added to this, the outline of the sun isn't a nice clear, hard line like the moon - it's blurred by the corona, etc. Perhaps you could take a sighting on a sunspot or something...but it's a stretch. So whilst it's possible in theory, I don't think that's a good way to approach the problem in practice (and of course you'd have to do all of the measurements using a pinhole camera or something because you can't stare at the sun without wrecking your eyes...especially through a telescope)! But Astronomical unit#History describes several practical ways to get a reasonable answer - one of those should suffice. SteveBaker 14:12, 24 March 2007 (UTC)

It seems to me the best way would be to measure the period of the Earth's rotation around the sun (1 year), then determine the mean radius using orbital mechanics. The period can be measured by sighting stars. anonymous6494 16:07, 24 March 2007 (UTC)

That requires knowing the mass of the sun, which is even more difficult to determine without first knowing the distance. I believe that the method mentioned by Knowledge Seeker gave the best results prior to the modern era. Namely to determine the Earth-Sun-Moon angle by looking at the position of sunlight on the moon when it is exactly half way between a full and a new moon. If the sun were infinitely far away then exactly half the moon would be illuminated at the halfway point, but it appears to be a little more than half since the sun is closer than that. That angle and the distance to the moon (calculated by methods such as suggested by the original poster) are enough to work out the Earth-Sun distance. Dragons flight 16:21, 24 March 2007 (UTC)

I wonder if you could get an estimate by comparing the effect of the Sun and Moon on tide. – b_jonas 17:51, 24 March 2007 (UTC)

Bottom line is that making an accurate measurment of the distance from the Earth to the Sun is simple in theory but very difficult in practice. The parallax methods that have been mentioned are basically applying the techniques of triangulation and surveying on an astonomical scale, using the fixed stars as reference points. Practical difficulties arise because:

• You cannot establish convenient intermediate trig points in space. You have to use the very few objects that are already there - basically, the Moon and the planets.
• These objects are widely spaced. So starting from a baseline of the order of, say, a thousand miles between two points on the Earth, you first have to scale this up several hundred times to measure the distance to the Moon, then you have to scale this distance several hundred times again to measure the distance to the Sun. These big scale factors mean that you need to make precise measurements of angles and differences in angles that are very small - fractions of a degree.
• All of your trig points are constantly moving. You are observing from a revolving Earth that is also in orbit around the Sun, and the Moon is moving relative to both the Earth and the Sun. So you need very precise timekeeping, either to ensure that you have simultaneous observations from the different points at each end of your thousand-mile baseline, or to make sure that you can calculate very precisely how everything has moved between two observations taken at different times from the same point on the Earth's surface.

This is why we did not have an accurate measurement of the distance to the Sun until the seventeenth century. Gandalf61 10:29, 25 March 2007 (UTC)

Couldn't they have worked it out from Kepler and Newtons work, and the Gravitational constant :) HS7 15:07, 25 March 2007 (UTC)

Ignore that, I just checked, and the Gravitational constant wasn't calculated until the 18th century, sorry :) HS7 15:16, 25 March 2007 (UTC)

Hi BenC7: The method you propose, "to get people on almost opposite sides of the earth ..." requires both observerations be at the same time. It was first performed in 1639 by using the Transit of Venus as the clock that both observers could see at the same time. --Saintrain 16:36, 25 March 2007 (UTC)

Didn't they put a mirror on the moon and shine lights at it to find out exactly how far away it was, and if you can find the ratio of distances to the moon and the sun easily, and find this mirror, could you do it like that :) Also the OP didn't ask for the earliest possible method so my suggestion of using maths instead might work, if you can find out everything you need :) HS7 18:40, 25 March 2007 (UTC)

You are referring to the lunar laser ranging experiment. This involves bouncing laser beams off a retroreflector on the Moon. First, you have to find the retroreflector, which is less than 50 square cm in area. This article says this is like "using a rifle to hit a moving dime two miles away". Then you have to detect the reflected signal; the same article says "Even under good atmospheric viewing conditions, only one photon is received every few seconds". Laser range finding using single photons is not backyard science. Neither is the determination of the gravitational constant, which requires the measurment of forces 100 million times weaker than the Earth's gravitational field. Neither are parallax methods which require angular measurements to a precision of a small fraction of a degree. The simple answer to the OP's question is that there is no "backyard" method of accurately measuring the distance to the Sun. Gandalf61 23:18, 25 March 2007 (UTC)

Thanks guys. A good discussion. BenC7 10:56, 27 March 2007 (UTC)

tuberculosis

Disease tuberculosis can cure completely or not? Whai is the symptom ?

See Tuberculosis treatment. --Wirbelwindヴィルヴェルヴィント (talk) 05:34, 24 March 2007 (UTC)

For more on symptoms (briefly: weight loss, fever, chills, fatigue, night sweats, cough productive of greenish or blood-tinged sputum) see tuberculosis. - Nunh-huh 03:15, 25 March 2007 (UTC)

Today people suffer more from overconsumption than consumption. StuRat 06:42, 25 March 2007 (UTC)

Yes, very good :@ HS7 13:22, 25 March 2007 (UTC)

smell of photocopying rooms?

What's that smell that photocopyng rooms and laser printers sometimes emit? Is it static or something like that? There is a certain smell.--Sonjaaa 06:24, 24 March 2007 (UTC)

I've been told that it's ozone, but I don't know if that's correct. Anchoress 06:25, 24 March 2007 (UTC)

Yes, it's ozone.

I love that smell. For some reason, I love the smell of petrol too. Some people think that's weird. --Kurt Shaped Box 12:37, 24 March 2007 (UTC)

It's quite common to like ionized air, which is associated with ozone. Large quantities of ozone give the air a "burnt" smell, however, and can damage the lungs. I like the smell of gasoline, too, so does that mean I'm destined to have an unnatural attachment to seagulls ? :-) StuRat 15:52, 24 March 2007 (UTC)

Give it another six months. :) Tell you what I also like - the smell of a certain type of rubber that I haven't encountered for years. I can tell you no more than that because it's been so long since I last experienced it. --Kurt Shaped Box 13:40, 25 March 2007 (UTC)

That is fine Kurt. There are many who like the smell of petrol. I like it too. In fact, there are some who get a high by smelling things like petrol, show polish etc. Some are even addicts to this (I looked for an article about this in Wikipedia. Surprised to find none) -- WikiCheng | Talk 05:17, 25 March 2007 (UTC)

Glue sniffing ? Huffing ? StuRat 06:39, 25 March 2007 (UTC)

Inhalant (huffing redirects to this article anyway). There's a difference between "enjoying" the scent at a gas station, and intentionally inhaling it to obtain a high, but I suppose only a difference of degree. Nimur 07:06, 25 March 2007 (UTC)

I don't care for that redirect, myself, as inhalants include legit meds, such as those used to treat asthma. StuRat 19:44, 25 March 2007 (UTC)

Just FYI, I have never huffed gasoline to get high. I did used to huff a bit of glue/lighter fluid/paint when I was a kid but that was a *long* time ago now (don't do it kids - it's not even that good). --Kurt Shaped Box 13:38, 25 March 2007 (UTC)

Ah, so now we know why you have that unnatural attachment to seagulls. :-) StuRat 19:41, 25 March 2007 (UTC)

Seagulls don't smell like solvents, silly. :) Actually, they give of a slight scent of freshly made toast... --Kurt Shaped Box 22:02, 25 March 2007 (UTC)

The ones you've just fed freshly made toast (as in the pic on your user page) have that smell, no doubt. StuRat 02:22, 26 March 2007 (UTC)

Heh. You should try it sometime, if you ever find yourself raising an orphaned baby gull - sniff it. When they're little, they love to be held close or wrapped in a shirt, so it shouldn't be a big problem for you... ;) —The preceding unsigned comment was added by Kurt Shaped Box (talk • contribs) 17:23, 26 March 2007 (UTC).

Photocopiers and laser printers often smell of (poly)styrene as well; the toner uses polystyrenes as one of its components.

Atlant 19:29, 25 March 2007 (UTC)

Are the spellings of minor planet names official?

I have noticed that some minor planets had different spellings in earlier publications, e.g. Kalliope was often "Calliope" in the nineteenth century [1].

I am interested in finding out if the IAU or MPC has ever ruled on official spellings of early-discovered asteroids. Was there a ruling that recommended only "Kalliope"? Is there a technical sense (other than "no one spells it that way") in which "Calliope" is no longer correct? --Cam 15:56, 24 March 2007 (UTC)

The spelling of Kalliope was changed as it was the same as that of Jupiters moon Calliope, so they decided to have two slightly different versions to reduce confusion :) HS7 13:21, 25 March 2007 (UTC)

Thanks, Jupiter doesn't have a satellite named Calliope though. Some of the modern spellings have a German look, like 184 Dejopeja (instead of Deiopea/Deiopeia which I have seen in older texts). I am wondering if the IAU decided to use the German transliteration of minor planets named after Greek mythological figures. --Cam 18:35, 26 March 2007 (UTC)

Odour question

How is it explained that we dittect different smells from the same chemicals in different concentrations? (Ex Inodole smells of flowers in small doses, but has an aroma of shit in higher ammounts)

I find some horrible smells to be pleasant in small concentrations, specifically skunk smell and tear gas. Edison 18:24, 24 March 2007 (UTC)

I find a little skunk smell refreshing myself. I've never had the pleasure of having tear gas fired at me yet, however, as I don't give out my address to Wikipedians. :-) StuRat 06:36, 25 March 2007 (UTC)

The odorants simply activate different odorant receptors at different concentrations. This is a fairly common phenomenon, see e.g. indole. E.g. "flowery smell receptors" are activated more potently (i.e. at lower concentrations) by this compound, while at higher concentrations the "fecal smell receptors" are also activated, shifting the sensation. Cacycle 20:51, 24 March 2007 (UTC)

Aren't olfactory receptors thought to be receptive to particular molecular structures of the compounds encountered? The molecular structure doesn't change in higher quantities does it?

Ligand (in this case: odorant) binding to receptors is an equilibrium process: Ligands bind to an empty receptor and they dissociate from it (according to the law of mass action). A measure of how good a certain molecule fits into a given receptor is the affinity (measured as the Kd constant; high affinity means good fit). A biological response (e.g. smelling a compound) is achieved only when a significant number of receptors are activated by a bound ligand at a certain time point.

That means: A high-affinity compound activates a receptor at a very low concentration, but a low-affinity compound can also activate the receptor if you add it at a higher concentration.

Or: one compound can have a high affinity for one receptor and a low affinity for another. The first receptor population is activated at a very low concentration (→ flowery smell). By increasing the compound's concentration, the second receptor population becomes also activated (→ fecal smell).

Cacycle 02:04, 25 March 2007 (UTC)

So we smell only molecules that can act as ligands?

Yes, but a ligand is just a name for any molecule that binds to a receptor. Cacycle 17:09, 25 March 2007 (UTC)

Some odour compounds in some flowers will also block receptors, making a smell last a fleeting moment and stop you from smelling it more. —Pengo 12:25, 25 March 2007 (UTC)

This common mechanism is called 'desensitization' and has different mechanisms, all caused by receptor activation, including removing receptors by internalization into the cell, making the receptors less sensitive, making the second messenger cascade less sensitive, or alleviating the biological response. Cacycle 17:10, 25 March 2007 (UTC)

Isn't a ligand anything that contains a lone pair? When receptors are internalised they will be sensible to the internal components of the cell right?

No, a ligand can be any molecule, its defined as "anything that binds to a certain receptor" with a reasonable affinity (like a table - which is solely defined by what people use as a table, not by its properties or structure).

Check the topology of a membrane-bound G protein-coupled receptor. It is internalized in a membrane vesicle and the ligand binding site never comes into contact with the cytoplasm, only with the vesicle interior. Internalized receptors can either be degraded or recycled back to the surface later. Cacycle 01:44, 27 March 2007 (UTC)

Butane

If you had a container of pressurized liquid butane and then let out the pressure what would happen? It would start to boil after a while but at the moment you released the pressure would some immediately evaporate, or not? How long would it take to get to boiling point? What would happen? Ozone 17:39, 24 March 2007 (UTC)

The boiling temp of butane is 4.6° C. Assuming you depressurize it from room temp to one atmosphere, butane would start to boil immediately, but this vaporization would lower it's temp below the boiling point, then it would only slowly boil as the temp increased back to boiling. I'm not sure if you would see cycles of boiling rapidly then no boiling or continuous boiling at a lower rate. StuRat 06:31, 25 March 2007 (UTC)

The above comment has inspired me to write out analytic equations to model the re-addition of environmental heat and the constant heat-loss due to vaporization, and see if they can be set to oscillate in some arrangement (I imagine it depends a lot on the rate of heat re-addition, i.e. the geometry of the container, and the amount of insulation). I'll let you know if I finish them, or if I get bored and stop. After all, I'm on vacation after a terribly complicated academic session! (I have not yet decided whether I want to do equations while on vacation or not - I think answering that question will be a major turning point in my self-concept process. Nimur 07:13, 25 March 2007 (UTC)

Sounds like fun ! (But I'd avoid doing equations while on vacation with a significant other, as that may cause them to consider you to be an insignificant other.) My best guess is that it would boil rapidly at first, then slowly boil once the temp dropped to near 4.6° C, and continue to boil at a relatively constant slow rate until completely vaporized.StuRat 19:31, 25 March 2007 (UTC)

It shouldn't, while possible for it to occur for a finite amount of time without breaking the 2lotd, there are (I hope this isn't red) oscillating chemical reactions Belousov-Zhabotinsky reaction but they are very complicated involving self-metabolising chemicals. Some change color back and forth for a finite amount of time. Ozone

Thank you, would a portion of the liquid boil away immediately at the time the pressure was released, like when you open a soda bottle? Ozone 06:59, 25 March 2007 (UTC)

Yes, I believe that it would. StuRat 19:26, 25 March 2007 (UTC)

Heisenberg Uncertainty Principle

Could not the universe be deterministic in quantum mechanics? Not scientifically deterministic though. A particle appears to be in one position due to a faulty measurement caused by the HUP, it is affected by a field, its new location appears to be slightly influenced by randomness because of both the original and second the error in measurement.

Or, does this conflict with the Bell inequality?Ozone 17:42, 24 March 2007 (UTC)

A physical theory that postulates that quantum mechanics is an incomplete description of some more fundamental deterministic reality is called a hidden variable theory. Bell's theorem rules out any local hidden variable theory. It still allows non-local hidden variable theories, which feature instantaneous action at a distance. However, most physicists would prefer to give up the idea of hidden variables if they can only be retained at the price of losing the principle of locality. Gandalf61 19:09, 24 March 2007 (UTC)

The significant thing about the uncertainty principle is that it's not just that we are unsure of where the particle is - the particle itself simply isn't at a particular location. It's not an error in our measurement - it's an inherent 'fuzziness' of the universe at those tiny scales. This effect is exploited 'for real' in devices called 'Tunnel diodes' (without which your computer memory wouldn't work - so we're pretty sure these things work as advertised!). They exploit a phenomenon known a 'quantum tunneling' that comes about because of uncertainty. The idea being that you create a barrier that a 'classical' electron would not be able to cross - but by constraining it carefully the electron manages the cross the barrier ('tunnel through it') by virtue of it's uncertainty. It's easier to think of a physical barrier and a spatial 'teleport' across to the other side of the barrier because we don't know the position of the electron accurately - but in the case of a tunnel diode it's an energy barrier that is jumped because we don't know the energy of the electron accurately. If the electron refused to teleport across this impassable barrier we would know it's position more accurately than we're allowed to - so it teleports...in effect. SteveBaker 17:54, 25 March 2007 (UTC)

Tunneling is a lot more common in semiconductor devices than you may think! Most practical ohmic contacts to semiconductor devices are usually realized by heavy doping on the semiconductor side, which causes the depletion region formed by the Schottky contact to become very thin, allowing significant field electron emission current (a form of tunneling). I don't know a whole lot about sub-micron scale DRAM, but I don't think tunneling is a part of the primary ideal operation of the device (I could be wrong). It is, of course, a major parasitic current component that nano-scale VLSI people (the Intels and IBMs of the world) have to deal with. Certain types of multi-quantum well lasers also can suffer some unwanted effects due to field-induced tunneling. Flash memory, on the other hand, uses tunneling in its principle operation. A few other common devices that use tunneling as a principle operation effect (that is, in which tunneling isn't merely a parasitic effect) are Zener diodes, Resonant tunnelling diodes, several sorts of heterostructure based designs (especially low-noise HFETs).

I'm somewhat suspicious of your explanation of quantum tunneling in terms of energy uncertainty. I'm not a physicist, but usually when a particle has enough kinetic energy to hop over an energy barrier, the process is called thermionic emission (the primary conduction mechanism in Schottky diodes). I don't think that tunneling is so much a product of energy uncertainty as it is a side effect of a wave function being able to extend into and through an energy barrier. The curious thing about quantum tunneling is exactly that tunneling particles don't have sufficient energy to surmount the barrier, yet end up on the other side anyway (something that is classically impossible). Incidentally, at the scales where quantum tunneling is possible, there isn't much distinction between physical barriers and energy barriers. The "energy barrier" used in flash memory is a thin layer (few nanometers) of insulator.

P.S. - The first few sentences of your (Steve's) response reflect one type of interpretation of quantum mechanics, there are in fact other interpretations which hold that particle quantities do actually have a value before they are measured, and there are some hidden variables not described by current QM theory which dictate what these values are (these are often called "realist" views, though the name doesn't allude to their relative "correctness" in comparison with orthodox interpretations). This was a view supported by Einstein, who helped formulate the eponymous EPR paradox (which has since been debunked). Gandalf commented on the issue of hidden variables in his response. See interpretation of quantum mechanics for a rather interesting read. Anyway, sorry for deviating so much from the original question... -- mattb @ 2007-03-25T23:31Z

My intended description was exactly as you said (maybe I didn't explain it too well - you certainly did a better job than I) - but the width of the 'wave function' is a measure of the uncertainty - the particle extends through (teleports through?) the barrier without (classically) having the energy to go over it or around it or whatever. It's exactly as if you drove your car towards a brick wall and instead of smacking into it - you suddenly ended up, completely unharmed, on the other side of it - that's what electrons can do - and if they didn't, your computer wouldn't work because some classes of memory chip use this exact quatum-mechanical-weirdness to store data. They can do it because we can never be 100% sure which side of the wall the electron is on - even though we know for sure they can't get over, around or through it - and we know which side of the wall they started out on. It's not that we can't measure where the electron is exactly - it's that it fundamentally isn't at some precise place and can therefore randomly be on the other side of a 'classically' impenetrable barrier. But at any rate, the important part of the message is: "Uncertainty is not the same thing as experimental error". SteveBaker 04:12, 26 March 2007 (UTC)

Visibility of geostationary satellite

Till what latitude on earth are the geostationary satellites visible? Assuming a mean radius of 6372km and the distance of the satellite from the surface as 35786km, I suppose it is cos^-1($6372/(6372+35786)$) = 81.31^o ? -- WikiCheng | Talk 19:46, 24 March 2007 (UTC)

Looks right. You might take into account that the Earth is closer to an oblate spheroid; I don't know how much that affects it. --Spoon! 21:40, 24 March 2007 (UTC)

Aren't some GPS satellites in near-polar orbits? Gien their primary function I'd be a bit surprised if that were not the case. Anyway you are wrong I think, you can almost see something in the plane of the ecliptic from the pole, it'll be on the horzion, not overhead. Greglocock 00:11, 25 March 2007 (UTC)

GPS satellites are not geostationary. Satellite TV is geostationary. I think they limit how far north offer service. Not sure if that is line of sight or the amount of atmosphere it has to travel through. --Tbeatty 06:49, 25 March 2007 (UTC)

Yes, if you're at the pole, you can see some things in the plane of the equator (not the same thing as the plane of the ecliptic), but you can't see the entire plane, because the curvature of the Earth gets in the way. —Bkell (talk) 00:20, 25 March 2007 (UTC)

Echo satellite had a satellite radius of less than 42 meters. I saw it. Today's satellites are smaller. Edison 04:49, 25 March 2007 (UTC)

I assume they were asking about having a direct line of sight to geosynchronous satellites, as opposed to being able to see them with the naked eye. This must be an important consideration for coverage of polar and subpolar regions. Also note that the satellite may not be useful if very low on the horizon, due to the increased thickness of the atmosphere at that angle and the possibility of local geography (such as mountains) blocking the satellite. StuRat 06:18, 25 March 2007 (UTC)

You need to know the longitituge of the satellite, and latitude, longitude, and altitude of the earth station. Google for "look angle calculator" to find a great many, like this one. You also need to know the minimum usful look angle for you location. If you are transmitting, there is a legal minimum. If you are receive-only, you are constrained by thermal noise from the ground, with a smaller dish seeing more noise. -Arch dude 14:52, 25 March 2007 (UTC)

Epidemiology is to disease as "_______" is to benefit

Hi, I'm looking for the name of the science of finding a correlation between a positive effect, say longer lifespan within a population, and diet, for instance. Another example would be how grades are linked to the intake of (or abstinence from) sugar drinks. And the comparison of populations (of different countries, for instance) to look for possible correlative factors.

It's some form of statistical analysis similar to epidemiology, but I don't know what it is called.

What is the name of the field, method, etc?

Chill Factor Five 20:27, 24 March 2007 (UTC)

Well there's research into Life extension (see also: anti-aging and rejuvenation, and perhaps fitness (in the Darwinian sense)). They might have -ologies associated with them. But beyond looking for the fountain of youth, science and medicine does tend indeed to have a morbid focus on disease far more than on health and wellness. —Pengo 12:32, 25 March 2007 (UTC)

Also check out the hard term PhenomonologyPolypipe Wrangler 02:33, 8 April 2007 (UTC)

Mental Health statistics

What part of the United States has the highest cases of Mental Illness ?

Do you have a specific mental illness in mind? The geographical prevalence of a mental illness would depend a lot on what the specific illness is. For example, Florida has a lot of retirees, so it would have a greater than usual number of people with mental illnesses that affect the elderly more, like dementia and insomnia, and presumably a smaller than usual number people with mental illnesses that mainly affect kids, like ADHD. The male/female ratio is quite high in Alaska, so Alaska presumably has more than its share of people with autism, which is 4 times more common in men than women, and a lower than usual rate of people with androphobia. Nevada presumably has one of the highest fractions of people who suffer from pathalogical gambling (an impulse control disorder). Seasonal affective disorder is going to be diagnosed much more frequently in dark, northern states than in sunny southern states. San Francisco presumably has more than its share of people with gender identity disorder. I could go on and on. You really need to specify a particular mental illness for this question to be meaningful. MrRedact 00:28, 25 March 2007 (UTC)