Wikipedia:Reference desk/Archives/Science/2006 December 10

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December 10

Temperature Rising

Ok, so lets go to the next level... anyways, I was reading Verne's "Journey to the Center of the Earth," and I had a couple questions about the feasibility of a couple of the theories/facts presented in the novel. A) In Axel's arguments of why it is impossible to reach the center the earth, he mentions that the temperature rises 1 degree (I'm assuming Fahrenheit) for every 75 feet or so dug into the earth. Is this true?

*I'm going to interrupt the original long paragraph to answer these questions one by one. I'll mark my insertions with "*".

*First, I checked this passage in the English and original French versions available at Project Gutenberg (PG). Both versions say 1 degree in 70 feet. Therefore it must mean Celsius degrees and Paris feet (about 12.79 inches). The original French goes on to point out that the Earth has a radius of 1,500 leagues (these would be French metric leagues of 4 km, as in Twenty Thousand Leagues Under the Sea) and therefore at this rate of increase a temperature of 2,000,000° could be expected, enough to vaporize anything. The characters go on to discuss whether this is plausible. This calculation and discussion are omitted from the English version at PG, which may be just as well, since the arithmetic is wrong by almost an order of magnitude. However, I see that the original poster read a different translation, since the one at PG has Axel's name changed to Henry, so some of the detail may be in there.

*Does the temperature increase like that? Yes, pretty much. This page says the real increase is typically 30°C/km, although it naturally varies according to the geology of the area. In Verne's units that's 1°C per 100 Paris feet, near enough the number he gave.

*But of course this increase doesn't continue to anywhere near the center of the Earth. Seismology tells us how deep the solid and liquid layers are. The core of the Earth is in the thousands of degrees Celsius, not the hundreds of thousands.

B) On the journey to Sneffel's, the Professor is dismayed to discover that an Icelandic mile is roughly 4 of the standard miles. In the 1800's, was that true?

*Yes, very likely. While the English-speaking and Romance-language countries used "miles" similar to the ancient Roman mile, the German-speaking and Scandinavian countries used units several times larger with similar names. Look up "meile" and "mil [4]" at this excellent web site about units. Iceland isn't mentioned but it would very likely use the same units as mainland Scandinavia. Today people speaking English in Scandinavia may use the word "mile" to mean the metric mil or 10 km, which is about 6 miles (as I found out once when told to drive "3 miles" to a hotel).

C) As for the great sea in the interior of the earth (assuming the Hollow earth theory is true), would said sea curve in the interior of the earth or be roughly straight?

*If the Earth had a hollow center partly filled with air and partly with water, the water would form into a sphere under its own gravity. If the solid part of the Earth was spherically symmetrical, this sphere would float around freely in the hollow space as discussed below.

D) Axel mentions at one point that things become lighter as they become closer to the center of the earth, and mentions that its believed there is no gravity in the center of the earth (once again supposing that the hollow earth theory is correct). I also read a similar thing in an essay, and I was wondering what would happen if a human being managed to dig a hole through the earth (to be clichéd, America to China), would they instantly be caught in a limbo upon reaching the center of the earth, or would they slingshot up to near the surface, then fall back down before exiting, to be repeated ad infinitum until the point in time when the body stops falling? Crisco 1492 01:36, 10 December 2006 (UTC)

http://www.damninteresting.com/?p=696

There is an interesting article about gravity. As for gravity inside a UNIFORM solid sphere if you travel inwards towards the core gravity decreases linearly until it is exactly zero in the center (you are being pulled equally from all directions). Real earth is more dense at the center than in the mantle so it doesn't obey that exactly. If you were to hollow out the the core of the earth, there would be no gravity at all in the center, you would float. Gravity and EM follow the same 1/r^2 rule so you get a gravity version of the Faraday cage. If you made a complete tunnel through the core of the earth to the other side and jumped in, without friction you would oscillate back and forth indefinitely. 152.3.73.203 02:55, 10 December 2006 (UTC)

*To clarify: the part about "not exactly" refers to the decrease in gravity being linear. In any spherically symmetrical body gravity goes to zero at the center and if there is a hollow space at the center then gravity is zero within the entire hollow space.

*In fact the Earth is not spherically symmetrical, but is slightly oblate, since it rotates and the centrifugal force makes gravity slightly less near the equator than elsewhere. The resulting "equatorial bulge" is about 14 miles high. If there was a spherical hole at the center of the Earth, this would create a slight gravitational force which I believe would attract anything inside the hole toward the part of the hole's surface directly below the equator. --Anonymous, December 10, 2006, edited 07:04 (UTC).

Thanks anon, seems pretty interesting how much things change over a period of 100 years. Almost as funny as using a giant cannon to get to the moon... hmm... :P However, Verne did have a very good imagination, to be sure. Crisco 1492 11:09, 10 December 2006 (UTC)

That cannon idea isn't quite as absurd as it might sound, especially on a planet or moon with little atmosphere. A ship could be accelerated along a long shaft then launched into space. On Earth, the same technique could be used, but you couldn't accelerate it to escape velocity, as that would be too fast in the thick atmosphere at ground level and the ship would burn up. However, a nice "boost" could be given in this manner, with conventional rockets kicking in to provide the rest of the lift. The advantage of such a system is that the energy source for the initial launch is external to the ship, so the ship doesn't need to have more fuel to lift the fuel, then more fuel to lift that fuel, etc. StuRat 14:37, 10 December 2006 (UTC)

I was referring to Verne's From the Earth to the Moon where I believe it was a straightforward cannon launch. However, the booster style seems to work rather well, but how would the launch forces be dealt with a ground level? I'm thinking that it would require an extra stage, which prevents the entry of any of the explosive forces from the cannon into the bay where the fuel is stored (liquid or solid, probably doesn't matter). Therefore, said rocket might not gain too much of a weight advantage. Crisco 1492 23:21, 10 December 2006 (UTC)

six pack

relating to the top section is there anyway to fix it? —The preceding unsigned comment was added by 222.153.161.173 (talk) 02:25, 10 December 2006 (UTC).

You should click the [edit] button on the section that already exists instead of creating a new one. —Keenan Pepper 03:18, 10 December 2006 (UTC)

i did but no one is responding, so i thought i might create new one. So is there a way to fix this problem? my abs are not aligned

You could always cut open your chest and play around in there. In all seriousness, though, your abs will probably develop the way they do, and there's not much you can do to change that. --Wooty Woot? contribs 06:25, 10 December 2006 (UTC)

Are you sure i can't do anything about it? can tell me why are mine like that and other people's are not?

I think the only person who could tell you that would be a doctor, who will be able inspect it properly. If you are worried about it, get it checked out. We are not in a position to offer medical advice, but it doesn't sound serious to me.--Shantavira 09:32, 10 December 2006 (UTC)

I second Shantavira. A physiotherapist or sport medicine practitioner may help you. We can't. -- Seejyb 11:00, 10 December 2006 (UTC)

ATP

Why is ATP used as an universal energy currency?Why not GTP..which also plays a role in some reactions?What brings the difference..is that the properties of both the purine s(ADENINE AND GUANINE).........Why isnt GTP able to participate in reactions..freely like ATP? (even though only GTP is discussed in the question..a relavant answer may be given..even considering the other nucleotides)--hima 07:24, 10 December 2006 (UTC)

This sounds like homework, but this explains it. --Wooty Woot? contribs 10:03, 10 December 2006 (UTC)

thx for ur..answer..this is not a home work question...its my doubt..anyway ur link has clarified my doubt..upto a large extent..thk u--hima 14:01, 10 December 2006 (UTC)

Some day in the future it might be possible to compare the molecular components of life forms that have evolved on other planets. It would be interesting to see if there are certain molecules that tend to get used for certain functions. Some people such as Stuart Kauffman have discussed the idea that there are non-random effects that channel molecular and biological evolution along certain paths. --JWSchmidt 03:25, 11 December 2006 (UTC)

Thermostat ?

I've added the above template primarily to show it to users, who are then free to add it themselves, if they wish, as:

{{strict}}

I've noticed I have to turn the temp up when it's cold out, and down when it's not so cold. It seems that every room in the house gets colder when it's cold out. Why isn't my thermostat handling things on it's own ? It seems to be substantially colder right in front of the thermostat on cold days, but it still reads the same. The only reason I could think of is that, being mounted on the wall, the temperature of the space between the walls also has an influence, and perhaps the temp there tends to lag the temperature of the air in the room. Can anyone else think of what might be going on here ? StuRat 14:45, 10 December 2006 (UTC)

The principal problem with ordinary thermostats is that they are only capable of regulating the temperature at the exact point where they are mounted. This leads to two problem aspects:

• If the thermostat is mounted on an interior wall, it fails to take into account the temperature gradient that will be experienced as you move towards the outer walls of the building. (For ease of setting our example, let's assume it's winter/the heating season.) So while it may be a nice, toasty temperature right at the thermostat, as you move towards the outer walls (where more heat is being lost), the room air will be found to be colder and colder. Conversely, if it's mounted on an exterior wall, it will tend to overheat the interior spaces.

• If the thermostat is subject to localized heating (from, say, a kitchen, a table lamp, or the sun falling on the thermostat), the rest of the space will not be adequately heated. Conversely, if the thermostat is somewhere where a cold draft can blow on it (perhaps as you open an exterior door), the rest of the space may be overheated.

Both of these problems will become more severe (pronounced) as the temperature difference between the interior and exterior spaces increases.

Another aspect, of course, is that the thermostat can only control the temperature of the air. As the exterior temperature drops (and the exterior walls become colder), you lose more and more heat to radiational cooling (to which the thermostat is essentially insensitive). So you need warmer and warmer air to still feel warm as the walls become colder.

An ideal system would be broken up into many more heating zones than are typically used. A somewhat less-ideal system would at least have more temperature sensors and would run the heat based upon some aggregate temperature reading. And both systems would use infrared devices to sense radiational cooling.

Thermostats are, of course, problematic in other ways as well. Because they are usually binary devices, there must be some deadband between the temperature at which they turn on the heat and the (higher) temperature at which they turn it back off again, so your room temperature must at least vary by the width of the deadband. (Depending on your heating system,) Heat also tends to continue being delivered after the thermostat stops calling for heat so they must correctly "anticipate" this effect and switch off a little bit earlier than their setpoint would otherwise indicate.

Old mechanical thermostats had a small adjustable electrical resistor (called, logically enough, the anticipator) that directly heated the thermostat to accomplish this effect. Modern computer-controlled thermostats tend to have a programming parameter that performs the same function. And to avoid too much anticipation, thermostats should not be located directly near the heat source for that room, so don't put it right in the path of the exhaust from an air duct or directly above a hot-water radiator.

Atlant 16:45, 10 December 2006 (UTC)

Okay, these are all fine points but none of them seems relevant to my case. My house has forced-air heating with central air conditioning. There is one conventional thermostat, which is on an outside wall of the ground floor, near the return-air vent. And I find that for each rise of about 12° in the outdoor temperature, I must lower the thermostat by 1° in order to maintain the same temperature as indicated on the thermometer on the thermostat. This applies both in A/C season and in heating season. When the outside temp rises to the point where I switch from heating to A/C, I must raise the thermostat by about 2.5°C to maintain the same indicated temperature. This means there are two temperatures outside where the setting I use matches the indicated temperature: they happen to be about -2°C in winter and about 28°C in the summer.

Right now it's set for about 20° and the thermometer is reading a fraction over 21°, and it's about 6° outside. --Anonymous, December 11, 01:53 (UTC).

Hysteresis is your answer. When you are colling your house, the house starts warm and is cooled to the set point. It then has a lag and differential mostly to protect cycling the compressor but that lag means the house is warming above the setpoint. The opposite happens when the house is heating. This will make a heating cycle seem colder than the cooling cycle even if the set point is the same. It's a prodcut of the control algorythm. --Tbeatty 02:28, 11 December 2006 (UTC)

• No, this does not suffice to explain the effects I described. Thanks anyway. --Anon, Dec. 12, 03:50 (UTC).

The effects you described are indeed strange! Is yours a "conventional"/analog thermostat, or a "modern"/digital one? [Er, oops, blush, you already said that.]

If it's conventional, my first guess is that its thermometer and the temperature sensor in its thermostat proper (which in a conventional thermostat are typically utterly separate) are simply differently calibrated. Ar first blush a 1:12 ratio seems large, but I don't actually know how badly calibrated the bimetallic temperature-sensing strip in a conventional thermostat typically is. The extra 2½° offset between the heating and cooling modes is easily explained by the fact that those typically involve separate contacts (or separate electrodes in an SPDT mercury switch) which I can easily imagine could be that far off from each other.

If it's digital, I can only imagine that its programming is trying to second-guess some of the effects described elsewhere on this page, but guessing wrong. For example, as Atlant correctly notes below, the only real way to correct for differing temperature gradients is with an outside temperature sensor, which is obviously out of the question for a simple, self-contained, consumer device. But it wouldn't surprise me if a programmable thermostat tried to get clever and correct for this effect using some kind of heuristic -- although offhand I'd expect the slope of its self-imposed correction to be different in the heating versus cooling modes, not in the same direction as you've described.

Also, digital thermostats I'm familiar with (including the one I have) often have a switch on the back or a mode flag deeply hidden in one of their menus which lets you specify whether you're using oil or gas heat, or forced air vs. hot water vs. steam, or things like that. I've presumed that these settings adjusted the thermostat's heuristics which attempt to correct for the differing inertia and overshoot effects of these various heating technologies. So if your thermostat has such a switch or mode, it would definitely be worth playing with it to see it it makes any difference.

Is the desired temperature you've collected this data on always 21°, or has it varied? (Stated another way, do the relationships you've observed apply across one fixed, flat, desired temperature, or anywhere?)

Hmm, rereading what you wrote, I see you said "set for about 20°" and "reading a fraction over 21°", which sounds more like a conventional analog thermostat. Oh! And you even said it's conventional! Duh. So my speculation about differential calibration of separate components stands. —Steve Summit (talk) 18:54, 12 December 2006 (UTC)

Thanks for the excellent answers. Incidentally, "Anonymous" isn't me, but apparently somebody else with a similar problem. I wonder, is there a system which uses an outside thermometer to adjust the inside thermostat ? It's quite annoying at present to have to get the weather forecast and set the thermostat accordingly, or risk waking up either shivering or sweating. StuRat 08:38, 11 December 2006 (UTC)

Yes, several vendors sell high-end thermostats that have outside air sensors as well as indoor air sensors. Once you have those, the control system can do all sorts of things better such as:

• Determine the expected heat loss from the house and so calculate approximately how long the heat must run to compensate for that loss (in other words, be pro-active and not just reactive). And it can do this based on history that it has accumulated about your particular house.
• Determine trends in outside air temperature so if the temperature starts dropping rapidly, it can queue up some heat ahead of the outside walls becoming cold.
• With the aid of an indoor humidity sensor, determine just how much moisture a humidifier can put into your house's air without undue condensation on the windows or in the walls.

Honeywell certainly sells such devices.

Atlant 12:33, 11 December 2006 (UTC)

You want a PID controller. And the ability to tune the coefficients. --Tbeatty 03:17, 12 December 2006 (UTC)

Thanks again ! StuRat 05:02, 13 December 2006 (UTC)

Salt and Pepper

how can salt and pepper be separated? —Preceding unsigned comment added by Angelp9 (talk • contribs)

Well, if you have a really strong "pepper magnet", you could pass it over the mixture and separate them. Or maybe another tack: is there a substance which reacts with one and not the other? --- Deville (Talk) 16:06, 10 December 2006 (UTC)

Static electricity. For example, charge a hair comb and pass it over the mixture; it will attract the pepper. P.S.: After you win the bar bet, you owe me 10% of your winnings.

Atlant 16:49, 10 December 2006 (UTC)

If it's fine white pepper I guess you could just winnow it (i.e. blow on it), or shake the mixture through a fine mesh.--Shantavira 16:57, 10 December 2006 (UTC)

I wonder what happens if you try to dissolve it. My hunch is that the pepper will float on top or at the very least will form a suspension whilst the salt will dissolve. Run the stuff through a paper filter to aquire the pepper and let the water evaporate to get the salt. Can anyone confirm my hunch? PvT 17:08, 10 December 2006 (UTC)

The best method depends on your goal: do you want to recover the salt and discard the pepper, discard the salt and recover the pepper, or recover both with minimal losses to either? —The preceding unsigned comment was added by Keenan Pepper (talk • contribs) 19:31, 10 December 2006 (UTC).

The solubility thing sounds like the best idea, if you don't mind getting the materials wet. If you can't do that (if redried pepper doesn't suit your purposes) use the Brazil nut effect. When you have a mixture of lots of small solid objects like this, vibrating/shaking the mixture will cause a sorting to occur - smaller objects will sink to the bottom, larger objects will rise to the top. The salt grains will be pretty much the same size as one another, the pepper grains of a variety of sizes (it depends on the milling process that ground them). So doing this will likely produce a layer of pepper (the big grains), a layer of salt, and a layer of pepper (the small grains). Skimming off these layers will (largely) separate the salt from the pepper. The salt will be adulterated with pepper grains of a very similar size. If that's an issue (if you require a better seperation) put the mixture into a tall thin container and repeat the vibrate-and-skim process. This will never be perfect (the range of salt grain sizes will likely overlap the range of pepper grain sizes) but you should be able to get to about a 95% separation. -- Finlay McWalter | Talk 19:45, 10 December 2006 (UTC)

Or perhaps cyclonic separation, which also relies on particle size. There's surely a dry process which can additionally exploit the difference in densities between particles of salt and those of pepper (which have already been sorted to be of roughly the same size). Centrifugal separation works for liquids and gasses; I don't know if it's possible to do it with particulates. -- Finlay McWalter | Talk 19:52, 10 December 2006 (UTC)

To separate anything, you rely on the differences between them. Solubility has already been mentioned. Density is the other difference. A simple air separator as used in thrashing or a combine should also work. --Zeizmic 20:29, 10 December 2006 (UTC)

If you want perfect separation and don't have any kind of time limit, a magnifying glass and a pair of tweezers is your best bet. Confusing Manifestation 10:14, 11 December 2006 (UTC)

But see the Terrible Trivium in Norton Juster's The Phantom Tollbooth.

Atlant 12:37, 11 December 2006 (UTC)

Is the pepper ground or whole peppercorns? 80.169.64.22 16:45, 11 December 2006 (UTC)

Homozygous and Heterozygous mutations

What percentage of individuals will show a heterozygous or homozygous mutation? —The preceding unsigned comment was added by 71.241.210.8 (talk) 17:45, 10 December 2006 (UTC).

100%. A mutation is a genetic difference. We are all different. alteripse 18:52, 10 December 2006 (UTC)

It depends on the specific allele you're talking about. For a start see the Hardy-Weinberg principle. Also, remember that the more related two individuals are the greater odds that their offspring will show homozygosity. Also see heterozygote and coalescent theory. Hope that helps. --Cody.Pope 20:32, 10 December 2006 (UTC)

Chemistry joke.

I'm wondering if anyone could explain a joke made on xkcd to me. A man hands another an apple. He takes a bite, and finds it is solid. The first man informs the second that it is an apple infused with tin, and that "those of you who know your periodic table should be laughing about now." I don't know my periodic table. What's the joke? Pesapluvo 17:51, 10 December 2006 (UTC)

Here is the comic. Tin's chemical symbol is Sn. Geddit? If not, highlight or click this: Sn + apple = snapple. Weregerbil 18:16, 10 December 2006 (UTC)

Yeh, the jokes based around it being a snapple, without mentioning this it wont makes sense. Philc _T^E_C^I 18:27, 10 December 2006 (UTC)

"Why does Snapple call their drinks cran-apple and cran-raspberry ?"

"Because crapple and crassberry didn't sell well." StuRat 08:26, 11 December 2006 (UTC)

Sn apple Sn = tin

dSLR Lenses

Hey,

I'm looking at a few dSLRs. Among them, I'm looking at the Nikon D40 and the Canon Digital Rebel XT ( :O Price difference!) Anyways, I was looking at the lenses that come with these and they're all f/3.5-5.6 iirc. That seems like a terrible aperture range for a lens. Am I misunderstanding something, or should I think about saving up, buying only the body, and getting a better lens? In that case, do you have any recommendations? I'm already really stretching my budget by moving up to low-end dSLR (I was originally looking at a Sony DSC-H5), so an extra lens would require more saving. Thanks — Ilyanep (Talk) 19:36, 10 December 2006 (UTC)

It depends on what you want from your camera. Better lenses always mean better images, but if your just going to be pointing and shooting and using a flash most of the time, there's no need to even get a digital SLR. Also remember, you can get a fixed focal length lens with a big aperture range for cheaper. So you might want to get the all purpose mid-range lens now, and save up for the better lens later. --Cody.Pope 20:40, 10 December 2006 (UTC)

Oh and I'd add that most old Nikon lenses work with the new digital models. So you could get used lens for a the D40. --Cody.Pope 20:52, 10 December 2006 (UTC)

1. You DO want a good sensor. Without it, a camera is nothing but garbage.
2. You may buy a reasonably good zoom lens at first. An average lens and a good camera body. Try to upgrade the lens if you have money. You can hardly upgrade the sensor (i.e., buy a new camera body).
3. You may buy 2nd hand film-camera SLR lens.
4. You can reuse your old lens if you already have one.
5. You can learn to maximize the usability of your only lens.
6. Buy the best camera body you can afford.

By the way, how about buying a cheap bridge camera? You may save some money now and use the money next time when you buy your DSLR. If I only have $1000. I may buy a good bridge camera and a large memory card for $400-$500 and use the saved money on traveling. -- Toytoy 22:35, 10 December 2006 (UTC)

The Sony that I was looking at is basically a bridge camera, but I decided that if I was going to spend $500 on a camera, I might as well save up a few hundred more and get a "real" camera. The reason I want to get the Rebel XT is because it is a very good sensor and body. The only thing is that the lens' aperture range seems small. And any SLR lenses I look at either have a fixed aperture or a really small range as well. Is there no SLR lens that'll give me something like f/2.8 or 3.5 to at least f/6.3 or 7.1? Do lens manufacturers assume that I will have multiple lenses? — Ilyanep (Talk) 23:34, 10 December 2006 (UTC)

(Or is this perhaps a stupid question to ask as far as dSLR lenses go?) — Ilyanep (Talk) 23:37, 10 December 2006 (UTC)

Wait...so if a lens says it has an aperture of f/2.8, does that mean it's fixed at that aperture? Or can it be changed? I get the feeling that I'm confusing something. — Ilyanep (Talk) 23:49, 10 December 2006 (UTC)

And also, does f/3.5-5.6 mean that it's minimim 3.5 at it's minumum focal length and minimum 5.6 at fully extended? Because I read it to mean that's the entire range of the aperture. I guess I was drowning in confusion. — Ilyanep (Talk) 23:51, 10 December 2006 (UTC)

Yes, f/3.5-5.6 means what you just said (i.e. it's minimum 3.5 at it's minimum focal length and minimum 5.6 at fully extended). The upper limit is almost always around f22 or a little higher. It's the lower limit that is important. The f-stop is almost never ever fixed, it's the focal length that is usually fixed to get a larger aperture hole (i.e. smaller f-stop number and more light.) --Cody.Pope 01:31, 11 December 2006 (UTC)

Yes, that is definitely a bad misunderstanding on my part. In that case, I think I may want to find a lens with ~f/3.6 and hopefully a focal length of about 22-100 [the focal length multiplier on the XT is 1.6 and I'd like to be able to get fairly wide angle shots and fairly good zoom shots too], and then buy just the body with the lens. — Ilyanep (Talk) 06:06, 11 December 2006 (UTC)

Get yourself a two-lense kit. Something like body + 18-55 + 55-200 (55-300 maybe). If you don't particularly care about the BEST image quality, a superzoom might be to your liking (something like 3.5-5.6 18-250mm comes to mind.) Horst.Burkhardt (talk) 07:06, 14 January 2009 (UTC)

Whoa. I just realised this had cobwebs. Sorry. Horst.Burkhardt (talk) 07:43, 14 January 2009 (UTC)

Symptoms of insufficient sleep

I'm curious as to why I feel nauseated and get headaches when I have had less sleep than I would "naturally" obtain (e.g. due to being woken prematurely by an alarm clock), and how many other people (as a rough proportion of the population) are affected similarly. Available remedies (other than sleeping more) would also be appreciated. —The preceding unsigned comment was added by 74.134.236.157 (talk) 20:03, 10 December 2006 (UTC).

Sleep and sleep deprivation should tell you why your body is reacting this way. Basically, losing sleep is a bad thing. --Zeizmic 20:31, 10 December 2006 (UTC)

It is a kind of self-defense, like pain. Pain is necessary to warn us if something goes wrong, or if we need something essential for our survival. Sleep is essential for our brain, so our body tries to warn us if we are not getting enough of it, and with the use of nausea it even tries to persuade us to sleep. My guessing above is based on a comparison with artificial neural networks. Try to maintain, for example, a binary search tree, without equalizing it from time to time. Try using a hard disk for years without defragmenting it. As I know, an artificial neural network will collapse if it never "sleeps". (it is not reorganized, rebalanced, etc.) This must be true for biological neural networks too. They get so many sensory information, that they need rest to reorganize themselves. See the article on sleep. --V. Szabolcs 20:47, 10 December 2006 (UTC)

Thanks for both your answers; however, I've noticed that the sleep deprivation page does not explicitly list "headache" as a symptom, which leads me to further question how "normal" this is. I'd be really interested to know, though (and I acknowledge this is getting OT) what you mean by "sleeping" for ANN--do you have any references to papers on this? All the ANNs I'm familiar with beyond simple perceptron are "opaque" and thus I'm curious how they could be dynamically "rebalanced" or reorganized (certainly one can change the structure of the network to boost performance, but as far as I know this requires retraining). 74.134.236.157 22:23, 10 December 2006 (UTC)

Symptoms of dehydration include headache and fatigue. (Probably lots of other medical conditions as well, though.) Though I've personally also gotten headaches from what I think was just lack of sleep. -- Beland 23:54, 10 December 2006 (UTC)

I googled 'lack sleep headache' and found this was an extremely common effect of lack of sleep. --Zeizmic 01:58, 11 December 2006 (UTC)

You may be familiar with the expression 'bright-eyed and bushy-tailed'. I think that anything being other than 'bright-eyed and bushy-tailed' will be symptomatic of less-than-ideal sleeping patterns. Mathiemood 16:35, 11 December 2006 (UTC)

Static electricity?

How did people explain static electricity before the emergence of modern science? A small devil in your wool coat? -- Toytoy 22:17, 10 December 2006 (UTC)

Our article History of electricity discusses electricity in ancient times to modern, but does not go into depth as to exactly how the ancients described it (ie demons versus fluid). Thales (ca. 624 BC–ca. 546 BC), is credited with discovering that amber (elektron in Greek) which we now know to be an insulator, when rubbed with fur acquired the ability to attract feathers or bit of fluff. Per[1] none of his writings have survived, so right there we lose the ability to determine whether he thought a "fluid" was involved or some other interpretation. Thales says , however, that before him philosophers explained phenomena as the acts of gods, while Thales sought to explain them as the functioning of natural phenomena, without reference to the supernatural.However, the article Thales attributed to him the notion that the magnet or amber attracts things because of a property of a"universal substance of mind" within the object, not quite like modern physics. Per [2] Aristotle noted the production of electricity by certain marine animals. Electricity is not mentioned in Physics (Aristotle) nor did I find the term in his books on physics as cited in that article. I found no mention of electricity in Roger Bacon (c.1214 – 1294), a noted early scientist. By the 1600's electricity was described as a fluid, or fluids specific to every different way of generating electricity. Benjamin Franklin notably determined electricity to be one fluid present to a lesser or greater degree. Edison 15:49, 11 December 2006 (UTC)

Why are mice eyes like black or red beads?

Humans and many other animals have eyes that have pupils, irises, and whites. But mice and similar animals do not have these structures, Their eyes look like black beads. Why is this please? 81.104.12.16 22:25, 10 December 2006 (UTC)

Well, mice are mostly nocturnal, so having bigger eyes and a larger possible pupil opening is probably adaptive for night living. Also, most animals don't have human-like eyes. If fact a recent study suggests that we humans have the unique eye appearance. --Cody.Pope 22:33, 10 December 2006 (UTC)

Rodents certainly have pupils and irises, and I'd hazard that you might find sclera (whites) as well. It's just that in some case, it's hard to distinguish the structures. Our black gerbils have deep brown irises and, of course, black pupils. But they've got 'em.

Atlant 12:41, 11 December 2006 (UTC)

How was cheese invented when pre-Roman population lactose-intolerant?

Only comparatively recently have human been able to drink milk. In Roman times, for example, milk was used as a laxative. So was cheese invented before people began to regularly drink milk? 81.104.12.16 22:34, 10 December 2006 (UTC)

Fully cultured cheese has very little lactose. --68.163.200.64 23:48, 10 December 2006 (UTC)

Sorry, I wasn't logged in for some reason. --Cody.Pope 01:23, 11 December 2006 (UTC)

Yes, bacteria cleave lactose molecules into more readily-digestible particles. However, cheese is fattier than milk, so you can't just rely on cheese all the time. You might end up looking like Scarlett Johansson, eww. Mathiemood 00:33, 11 December 2006 (UTC)

She was kinda hot in the Island.--Cody.Pope 01:22, 11 December 2006 (UTC)

To be totally honest, there have been brief moments in my life when I thought Scarlett was not wholly unattractive. :) Mathiemood 16:37, 11 December 2006 (UTC)

Is it really a fact that lactose intolerance in much less prevalent now, compared to 2000 years ago? How could that be determined? ike9898 18:17, 11 December 2006 (UTC)

There's some info on the lactose intolerance page. See also the recent NYTimes extlink from that page. DMacks 18:40, 11 December 2006 (UTC)

I am with Ike in his or her cynicism. Mathiemood 18:45, 11 December 2006 (UTC)

Pure speculation here...I think that if you don't take precautions against it, milk collected from an animal and stored in an open container at ambient temperatute will begin to ferment pretty quickly. It won't turn into cheese, but you can get a yogurt or kefir type product. It seems reasonable that lactose intolerant people would discover that fresh milk upsets their bowels but day old milk was less of a problem. In fact, I think it is only fairly recently that people have understood how to prevent fermentation of stored milk. So, I think the answer to the original question could be yes. ike9898 21:30, 11 December 2006 (UTC)

Supplementary prescribing.

I am about to start a career as a Clinical Respiratory Physiologist. I wanted to know whether the option to supplementarily prescribve was open to me, and if not, who is it open to? I googled it and all I could see were nurses and pharmacists. I am fro the UK by the way. Chistopher

Peculiar question. I assume if you don't know this, you are starting school, rather than finishing school and beginning your career. Ask one of your instructors. Most, if not all, health care professional training involves exposure to real people performing the job you are training for, so eventually you will see whether clinical respiratory physiologists prescribe in the UK. I assume this is the UK equivalent of what in the US we call a respiratory therapist, and they do not have independent prescribing privileges here. alteripse 02:16, 11 December 2006 (UTC)

I am just about to start a job as a Trainee Clinical Respiratory Physiotherapist so haven't yet met any instructors. I was just wondering, as to the future of my career. —The preceding unsigned comment was added by 130.209.6.40 (talk • contribs).

The whale

Evolutionarily speaking, how and why did the whale become so big?

Good diet, plenty of exercize, and not smoking. B00P 23:23, 10 December 2006 (UTC)

Well -- look how big the oceans are. Also, water-born mammals can get much larger than land-born animals, it's a matter of physics and/or density. Mathiemood 00:31, 11 December 2006 (UTC)

When you're not fighting gravity (by virtue of being supported by water), your size is far less limited than land or air animals.

Atlant 00:37, 11 December 2006 (UTC)

Harder to get eaten when you're so big I guess. Vespine 00:44, 11 December 2006 (UTC)

These explanations don't explain why krill and plankton are so small, or why the vast majority of sea creatures are nowhere near as large as whales. JackofOz 01:16, 11 December 2006 (UTC)

I daresay that the Sea is the cradle of life -- it is natural for there to be both immense and infinitesimally-small creatures living harmoniously within it. Mathiemood 16:40, 11 December 2006 (UTC)

Also check out: Evolution of cetaceans --Cody.Pope 01:20, 11 December 2006 (UTC) And also see Ecological niche. Whales may be so big just because nothing else was that big anymore. --Cody.Pope 03:26, 11 December 2006 (UTC)

There can only be so many top-level predators.

Atlant 12:44, 11 December 2006 (UTC)

Each size represents a different evolutionary niche. All possible niches tend to eventually be filled. Their methods of eating, where they either use baleens to filter out plankton or catch many fish at once, are both quite efficient, allowing them to get very large. Floating on water has many advantages that overcome size limitations on land. The buoyancy of the water means they don't need to have a skeleton system capable of supporting their own weight. Large whales which are beached, in fact, can't support their own weight and are thus crushed under it. Movement through water also can be accomplished with slow, rhythmic motions, while movement on land requires more complex and variable feedback to "balance" on legs. This would be a problem for a very large creature, as the speed of the nervous system wouldn't provide for rapid enough control and feedback for control on land. Thermal control is also easier in the water, as ocean temperature is less variable than air temperature. One of the main advantages of size is that it provides protection from natural predators. StuRat 08:15, 11 December 2006 (UTC)

Try looking at article Jumbo Whales. E Liquere 02:55, 15 December 2006 (UTC) [JOKE]