Wikipedia:Reference desk/Archives/Science/2007 January 17

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January 17

Source of salt in ocean water

What are the sources of saline in ocean water?209.6.248.169 00:37, 17 January 2007 (UTC)Ed

Have you checked our article on sea water? — Kieff 00:50, 17 January 2007 (UTC)

Escalator handrails

Why do the escalator handrails often move slightly slower than the steps, requiring you to change your handhold periodically or risk falling backwards ? StuRat 01:13, 17 January 2007 (UTC)

HAH! Sturat?? I can't believe it! or has someone hijacked your account?? I've wondered this too, have you read the escalator article ;) Nah just kidding, but I found this under the 'safety' section: Handrail speed sensors — located somewhere inside of the escalator unit. These sensors are usually optical, they are positioned to sense how fast the handrail is going. In case of a drive chain/belt breaking, in order to protect the drive and people on the escalator, if the sensor notices a speed difference between the handrail and the steps it will sound an alarm... So, supposedly, a different drive operates the hand rail and the stairs, fancy that, and the difference in speed we've noticed is not enough to trigger the sensor. Vespine 01:27, 17 January 2007 (UTC)

Actually *scratching head*, i've re read the above and I don't beleve my self anymore, that says in case of the drive belt breaking implying it IS the same.. Back to the drawing board. ....Vespine 01:29, 17 January 2007 (UTC)

Yea, I hadn't even considered that they would have separate drives, and assumed they used a gearing mechanism to account for the handrail going slightly farther in one revolution than the steps, if that is, in fact, the case. The question is, how could they be off by so much that it's obvious ? This seems to be a common occurrence, too. StuRat 02:53, 17 January 2007 (UTC)

I've been thinking more and I think it must be something to do with the elbows of the escalator... Consider this, the diameter of the hand rail is a good metre or more wider then the stairs them selves right? Now, rotating two rings of different diameters in unison is no problem but the stairs are not perfect rings, they are VERY exaggerated ovals, with a pretty severe kink on each end. So, visualise (looking from the bottom) what happens when the escalator bends up and bends back down at the top. When you get on at the bottom there is a flat bit where stair and hand rail parallel, then quite quickly it turns into a up sloping section. The radius of that change is much greater for the stairs then it is for the hand rail, then the two are parallel again until the top where it has to turn flat again, this time, the radius for the hand rail is much greater then for the stair. Haven't quite worked out how that directly affects the speed of the hand rail yet, but I bet it has something to do with it.. Vespine 04:30, 17 January 2007 (UTC)

You might be on to something there, on an "up" escalator (and who really needs a "down" escalator, anyway ?) I think that would cause the handrail to pull ahead of the steps at the bottom, then pull backwards relative to the steps at the top. However, since you aren't positioned perpendicular to the centerline of the steps anymore, but at perhaps a 30 degree angle "leaning forward", relative to that centerline, that might work out to be just about right. This is becoming a geometry question, perhaps I should repost on the math board ? Does anyone have the dimensions and radii of a typical escalator that I could use to do the math ? StuRat 20:19, 20 January 2007 (UTC)

, causing anyone who doesn't want to be pulled over to change their grip at both locations.

I have found it possible to ignore the differential in the velocity of the handrail versus the velocity of the stair treads, although at the terminus of the stairs I am sometimes at a 30 degree angle with respect to the accepted vertical when I hold on tenaciously to the handrail and do not change grip. Edison 06:42, 17 January 2007 (UTC)

This must be fun to watch ! StuRat 20:19, 20 January 2007 (UTC)

After years of riding those things, I think it is just a maintenance issue. There is probably no direct mechanical connection between the two, and it looks like (when they are opened up) that different motors are involved. --Zeizmic 13:04, 17 January 2007 (UTC)

Howstuffworks has this diagram which shows the handrail going around a loop that is similar in shape to the loop traveled by the steps but offset vertically. An electric motor drives the steps, and the steps drive is in turn connected to the handrail drive by a drive belt. If this drive belt broke then the handrail would stop while the steps continued to move - hence the need for a handrail speed sensor. I imagine is it difficult to synrchronise the speeds of the two drives precisely. On some escalators the motion of the handrail is noticeably uneven, which could be due to the drive belt slipping. Gandalf61 13:40, 17 January 2007 (UTC)

You mean they actually travel at differant speeds? I never noticed it! I'll see if I can next time I "go up". | AndonicO ^{Talk · Sign Here} 20:16, 17 January 2007 (UTC)

You will never ride an escalator the same way after seeing this: [1] alteripse 00:22, 19 January 2007 (UTC)

Economical Nutrition (+ side question)

I've found I need to save (for my education) a lot more than I had originally anicipated. I currently have 4600 euro and I need 12000 euro by September. I pay rent of 175 (about the cheapest I'm likely to find in this country so pretty irreducable) and 78 euro health insurance per month. If I can save 250 per week for 28 weeks (best case senario of extending my work contract which is actually due to expire in June) then I'll have an additonal 7000 euro. This leaves me a food budget of 23.57 euro per week. Could someone suggest the most economical foods in terms of nutrition (both vitamins and energy), particularly in the Netherlands?

I don't know about the Netherlands, but food in the US is usually much cheaper, and also healthier, if you buy it unprocessed. For example, you can get a big cylinder of oats (for making oatmeal), for about 1/10th the price of the premixed oatmeal in little bags with added sugar, flavorings, and assorted chemicals. I like to buy bananas and slice them up in the oatmeal to make breakfast for about US$0.50. Spaghetti is also quite cheap and the sauce can have lots of vitamins. Salads are healthy and cheap, too, just buy whichever vegetables are on sale that week. You can also make soups from potatoes and vegetables. Cheap protein is a bit harder to find, perhaps peanut butter sandwiches or tunafish sandwiches are your best bet. StuRat 03:21, 17 January 2007 (UTC)

For nutrition at low cost, you'd do well with a primarily vegetarian diet, with vegetable sources of protein (including minerals and fibre) supplemented by dairy, eggs, and perhaps fish. Pay particular attention to legumes and whole grains, focal foods in vegetarian systems such as described in Diet for a Small Planet based on the essential amino acids. Add some locally-grown or plentiful imported fresh fruit for the range of vitamins, and you've got the basics covered. Unprocessed "whole" foods will give you better nutrition at lower cost than processed (e.g. peanuts vs. peanut butter), but you'll have to take into account the need to cook, involving expenses of time, effort, fuel, and some basic equipment. For shopping, check your vicinity for farmers' markets and food co-ops that sell direct from the producer to the consumer, or markets in immigrant neighborhoods for non-native items such as hummus. You can also contact your health services provider for nutritional advice, that may include low-cost or free counseling.-- Deborahjay 15:42, 20 January 2007 (UTC)

This begins to make me look pretty pathetic but does anyone know of extra things I might be able to do (again, in the Netherlands) during spare time to earn more money? Even more tragically, my only example is the film Dancer In The Dark, where the lady get's these sewing needles that she has to put into the cardboard holders that are then hung on those racks in shops - I can do that! My current job is in these crazy rotating shifts which means I can't commit to a normal second job (it's almost like they designed it to be like that). --83.84.74.28 01:39, 17 January 2007 (UTC)

Can you sell blood or plasma there ? StuRat 03:23, 17 January 2007 (UTC)

I don't think you can. Do they pay enough in America to cover the nutritional cost of replacing it? In England you get a couple of biscuits and a cup of tea... --83.84.74.28 20:10, 22 January 2007 (UTC)

I've never been to Europe, so I can only add information I know from the U.S. Pinto beans and corn are not expensive either, and those together will give you enough protein to stay healthy. Over here, pinto beans are extremely cheap. Rice is fairly cheap too, since a large bag will go a long way. Lemons are a great source of vitamin C and not a bad flavoring for many foods, though I'm not sure how available lemons are in the Netherlands. Good luck! --Wirbelwindヴィルヴェルヴィント (talk) 03:58, 17 January 2007 (UTC)

In 1972 I was able to eat for $1 US per day, and today I believe it would be possible to eat for $3 per day. Buy groceries in bulk and cook. Dried beans, dried pasta, flour, rice, cornmeal, canola oil, fruit, much peanut butter, some canned vegetables, meat and fruit occasionally, . Edison 06:49, 17 January 2007 (UTC)

I echo Edison above; rice, beans, and whatever is on sale or 2-for-1. I don't think peanut butter is all the rage in the Netherlands though. :-) | AndonicO ^{Talk · Sign Here} 20:20, 17 January 2007 (UTC)

Three of us ate literally 40 pounds (18 kilograms) of peanut butter in one 9 month school year. Avoid buying restaurant or vending machine food or beverages if money is an issue, since groceries cost maybe 1/3 as much. Edison 16:00, 18 January 2007 (UTC)

Rather than seek yet another conventional job, you might consider cutting housing costs and living expenses by finding a situation that provides room and board in exchange for services: house- and pet-sitting, child care (perhaps with a premium for bilingual homework help), aid to an elderly or disabled shut-in. Investigate options for cooperative and shared housing. Your school may have advice for students on grants and loans, but also check your municipality's or county services to low-income residents. Good luck! -- Deborahjay 15:50, 20 January 2007 (UTC)

And you guys thought it wasn't a great idea... ;) — Kieff 15:58, 20 January 2007 (UTC)

Thanks for the advice everyone. Some suggestions will need some looking into. It's nice to know you all care :) --83.84.74.28 20:10, 22 January 2007 (UTC)

Unnatural Star Creation

Hello. This is probably a weak question, but I wanted to know if stars could possibly be formed by human means, and, if they could, if perhaps humans could use them for energy? (Read "The Last Question" a while ago and I just started thinking about it) Thanks for any comments! Robinson0120 01:40, 17 January 2007 (UTC)

Not with current technology, but there's nothing indicating that it's completely impossible. Possibly infeasible considering the required resources, but who knows? To harness the energy said future humans might use a Dyson sphere, an Alderson disk, or something similar. -- Consumed Crustacean (talk) 02:10, 17 January 2007 (UTC)

Many things we take for granted today were similarly infeasible in 1807. Edison 06:50, 17 January 2007 (UTC)

I seem to remember that Jupiter’s mass is relatively close to the point at which it could have formed a star. If you could some how increase Jupiter’s size by a little (say push Mars into it) it might very well form a star. Of course doing this would kill us all. Also, we already do use a star for energy. See Solar power. Creating a new star would serve no purpose then. I should also mention that the mass cutoff point for a star precludes one from creating a “mini-star.” S.dedalus 07:10, 17 January 2007 (UTC)

Jupiter is almost 3000 times as massive as Mars, and according to its article, it would need to be 75 times as massive as it is to become a star. So, we'd need to find something a little more massive to push Jupiter over the threshold. But if we can develop the technology to put enough mass in one place, there's no reason we can't make an artificial star. Dave6 09:16, 17 January 2007 (UTC)

In response to Dave6’s coment above. Actually according to this [2] you would only need to increase Jupiter’s mass by about 16%. Perhaps the Jupiter article should be corrected? You’re right of course that Mars still wouldn’t do it however. Hmm. . . Pushing Saturn into Jupiter might create a star however if New Scientist is to believed. S.dedalus 20:17, 17 January 2007 (UTC)

Ups, my mistake OGLE-TR-122b is only 16% larger. However it’s mass is still above the 75 Jupiter-masses. How about pushing all the gas giants in our solar system together? That might work. ;-) S.dedalus 22:45, 17 January 2007 (UTC)

The idea of turning Jupiter into a star has been explored in fiction - see 2010: Odyssey Two - although it was achieved by non-human technology. Gandalf61 10:48, 17 January 2007 (UTC)

In a manner of speaking, man creates a star every time he detonates a nuclear bomb... it's just that they're very short-lived. Vranak

The only nuclear weapons which utilize nuclear fusion, as stars do, are fusion bombs (i.e. H-Bombs). The process is similar, though I'm not sure that H-Bombs use the the proton-proton chain and the CNO cycle which occur in stars. Not to mention the size/gravity differences. -- Consumed Crustacean (talk) 17:20, 17 January 2007 (UTC)

So if Jupiter gets hit by more comets, we would live (or die) in a binary star system? Or would the sun eventually suck the "Jupiter star" into itself? | AndonicO ^{Talk · Sign Here} 21:02, 17 January 2007 (UTC)

It would take a lot more than just comets. If the lowest estimate for the minimum size of a brown dwarf is correct, you could turn Jupiter into a short-lived star by dropping Saturn into it, or maybe by adding the entire Oort cloud. --Carnildo 21:43, 17 January 2007 (UTC)

Alright, thanks. I figured there would probably be some way to do so; I might have heard about the Jupiter thing a little while ago (even though we probably wouldn't use it for the reasons stated above). Thanks for the information, all! Robinson0120 22:14, 17 January 2007 (UTC)

Believe it or not Jupiter actually makes up more then 50% of the mass in our solar system. Even if you collided the whole solar system into Jupiter (Except for the sun it self of course) you wouldn't have more then twice the mass of jupiter to begin with. Vespine 05:53, 18 January 2007 (UTC)

Sounds like an engineering nightmare. I guess we won’t be creating new stares any time soon! S.dedalus 07:50, 18 January 2007 (UTC)

Humans create stars every year when they put little no-talents into movies and promote the shows. Edison 16:01, 18 January 2007 (UTC)

It depends on exactly what your definition of a star is:) Would it help if the material was at a higher density instead of a higher mass:)Hidden secret 7 18:38, 22 January 2007 (UTC)

Physics question

Our teacher has set us a hard question this week. I know you dont do homework, but maybe you could give me some pointers. Our teachers is a bit strange in the questions he gives us ,but could you please help thanks

OK the question is: A man is standing on the top of everest and we assume the outside temperature is -30C, and there is a sheer drop down to earth from where hes standin, then if he was to urinate over the side, upto what distance would the stream remain liquid. Bertie

There is no answer to that. Too many other variables. X [Mac Davis] (DESK|How's my driving?) 02:05, 17 January 2007 (UTC)

And also he didn't specify what distance he want, the distance the urine stream travel or the height drop until it freezes, neither does he specify the pressure, the amount, the composition, the temperature and the angle of the urine stream, nor wind speed, humidity of the environment etc. etc. etc. So ask him about those variables and see what happens... :-p --antilived^{T | C | G} 03:14, 17 January 2007 (UTC)

The question is just another way of asking [1] how long does it take urine to go from body temperature to freezing in a temperature of -30C, and [2] how far would gravity take it in that time. It's the first part that's hard. If it helps, normal urine osmolality is 50 to 1400 mOsm/kg. - Nunh-huh 05:37, 17 January 2007 (UTC)

You would have to know how long it would take to freeze, assume no air/wind resitstance, and then take the time it took to freeze and the acceleration due to gravity (10m/s^2) and then its easy. Rya Min 02:28, 17 January 2007 (UTC)

I seem to recall reading that you can tell if it's -50F or below because your spit will freeze and shatter when it lands at those temps. StuRat 03:28, 17 January 2007 (UTC)

To the original poster: Is this question for marks at all? I remember my Physics teacher giving several weird questions "to chew on" overnight.--JDitto 03:44, 17 January 2007 (UTC)

Trick question. Everest is already part of the earth. And if you do the calculation of time to go from body temperature to freezing, keep in mind the freeze point is dependant on altitidue. Also keep in mind the dry adiabatic lapse rate. From the altitude of Mt. Everest and the given temperature, you can find the difference between standard temp and pressure. Calculus is your friend. --Tbeatty 06:25, 17 January 2007 (UTC)

Qualitatively, the stream would break up into droplets which would reach their Terminal velocity quickly, then it would freeze into droplets like lead in a Shot tower. There would be some Sublimation (chemistry) as they dropped from the mountain to the land below. The high speed would facilitate heat loss, but I cannot think of a straightforward calculation. Edison 06:57, 17 January 2007 (UTC)

Among all the unknowns, the most important one is the speed with which the stream or droplets loose heat to the environment. While tiny droplets will freeze almost instantly, large drops or a wide stream require more time. The stream will start to cool immediately, but will the stream start to freeze already before it would break up into droplets? How do we find out how wide the stream is? Measure it with a caliper? :) Our article Urination offers no clue. And what is the freezing point of urine? There is a formula for the freezing-point depression, but I don't immediately see how to apply it. Is this for a graduate course on Applications of Cryophysics in Mountaineering?  --Lambiam^Talk 10:25, 17 January 2007 (UTC)

Ah! I would expect this is a "chewing on" question. Maybe he (or she, I suppose) wants you to think about how to go about solving it! What variables should you need? You don't necessarily have to solve it to get a constant. Don't forget air pressure! How do we find out how wide a stream is? I know Mythbusters measured that one. Does air humidity belong in the equation? X [Mac Davis] (DESK|How's my driving?) 12:33, 17 January 2007 (UTC)

One author of a book said that, on an expedition to Greenland, he and his comrades threw up a bucket of hot water. Result: it came down as ice. I don't know how much of a differance there is between urine and water. | AndonicO ^{Talk · Sign Here} 21:07, 17 January 2007 (UTC)

I'd just work out how long it would take for 37C -> 0C in this situation, then use this number to calculate how far anything would travel in this time in freefall, and hope it doesn't get to terminal velocity. Aaadddaaammm 03:06, 19 January 2007 (UTC)

zetasizer in small sizes

Are zetasizers available in miniature size (as in microcameras so as to fix in human body for detection)? Or can they be made for research? If yes company to be approached? 02:43, 17 January 2007 (UTC)

The internet doesn't seem to know what a zetasissor is, even if you spell it zetascissor, maybe you can clarify a little? Vespine 04:17, 17 January 2007 (UTC)

" Zeta Scissor: Mas poderosa que la shotgun, ademas que es facil y rapido de usar se obtiene muchos puntos con ella mas que la Laser, si escuchastes bien mas puntos que la laser esta belleza avienta una navaja en forma de media luna y no tiene contratiempos al igual que el laser y la heavy machine gun." Did you know that ? -- DLL ^{.. T} 19:11, 17 January 2007 (UTC)

The above somewhat rendered into English by Babel fish: "Zeta Scissor: But powerful that shotgun, ademas that is facil and fast to use obtains many points with her but who the Laser, if escuchastes well but points that the laser this beauty throws a knife in form of average moon and does not have misfortunes like the laser and heavy machine gun." Clear? Edison 16:05, 18 January 2007 (UTC)

Are you thinking of particle sizing by using the zeta potential? i.e. a "zeta sizer"? There are companies that make equipment for this: here's one company based about 10 miles from where I live [3] Don't know if they make micro scaleimplantable versions... Malcolm Farmer 00:46, 19 January 2007 (UTC)

  : Thanks Malcolm,..i was actually looking for the same thing, a nano sized zetasizer, to fit it  
    inside a host...the way doctors put minicameras during surgeries.
    Please do suggest about the companies which can device it... User: Manju.setti 

hydroelectricity and fishees

I just read in this website that fish can easily swim through hydroelectric dam turbines turning at 81.8 rpms. Is this true? Those giant turbines are spinning more than once every second! --JDitto 03:38, 17 January 2007 (UTC)

Remember a fish in water is VERY different from your hand in the air. When the turbine is spinning it is displacing the water with the fish IN the water. As the water gets pushed through/by the turbine, the fish is IN that water and would get pushed out with it, I'm sure a dolphin or shark might get messed up, but a regular fish would be small enough just to get pushed out with the water. I don't think it's unreasonable. Vespine 04:13, 17 January 2007 (UTC)

Hydroturbines do kill fish, even small ones[4]. There is active development of new turbine designs to reduce fish mortality[5]. --Duk 06:38, 17 January 2007 (UTC)

I have seen large fish chopped in pieces by such a turbine. I expect small (or lucky) fish come out slightly perturbed (and a bit let down) after their adventure through the turbine. Edison 07:00, 17 January 2007 (UTC)

What I hear from friends who do salmon passage (through large dams) studies on the Columbia River is the principle danger is the dramatic changes in pressure rather than the turbines. It may be different for smaller hydroplants. --TeaDrinker 08:24, 17 January 2007 (UTC)

Change in pressure? So the pressure inside gets so strong that it crushes the fish inside? --JDitto 05:15, 18 January 2007 (UTC)

Remember, the liquid passing through a hydro dam's generator can't change in volume (much), so if we're to extract any energy from the liquid, it must be through a reduction in pressure. The liquid's pressure is very high going into the turbine and much lower exiting the turbine; the fish have a tough time accommodating to this very sudden change.

Atlant 14:58, 18 January 2007 (UTC)

pixel counter

Is there any software (hopefully free) that can calculate the number of pixels in an image of a certain color? --hello, i'm a member | talk to me! 04:37, 17 January 2007 (UTC)

In some image formats, that will be difficult because the exact color of each pixel is not stored in the file. So, it may change from one renderer to another. Also, what do you mean by "a certain color"? If two pixels are off by 1/256th of a shade of red, are they the same color? Our human eyes would probably say so, but a computer would say they are different. --Kainaw ^(talk) 07:59, 17 January 2007 (UTC)

You asked this question somewhere else, yes? And you were given a number of answers... --24.147.86.187 15:21, 17 January 2007 (UTC)

sea snake reproduction?

how do sea snakes reproduce? Do they have to return to dry land to lay eggs, or are they live bearing? --Krsont 05:15, 17 January 2007 (UTC)

• It depends, apparently. Some give birth to live young (ovoviviparous), while others are egg-laying (oviparous), and thus must return to land. See Elapidae for details. -- MarcoTolo 05:20, 17 January 2007 (UTC)

Heartbeat sounds

Is it common for any person to feel or hear their pulse from the scalp or the head when healthy.--Biggie 08:18, 17 January 2007 (UTC)

Well, it's not possible to hear your pulse from any external part of the body. It is also not common to be able to "feel" your pulse anywhere normally, except perhaps in your neck during high-intensity physical activity, or in your eardrums. BenC7 11:48, 17 January 2007 (UTC)

Just yesterday I could feel it and hear it... and see it! However I personally attribute this to me having erratic blood pressure. My intraocular pressure is quite feelable, phosphenes are generated on the heartbeat, and I can feel the heartbeat in my eyes. I could also hear it pulsing in my ear. I'm perfectly healthy, as far as my doctor and I know. Except for maybe that. Hope I don't die. X [Mac Davis] (DESK|How's my driving?) 12:29, 17 January 2007 (UTC)

All right Thank you very much for the info--Biggie 20:05, 17 January 2007 (UTC)

This question asks for medical advice. The Reference Desk cannot offer competent professional advice on questions of this kind. If you have concerns about a potentially serious medical problem, please immediately contact a qualified medical professional.

No, this question does not ask for medical advice. It asks for medical information. They are not the same. - Nunh-huh 03:26, 18 January 2007 (UTC)

I can also hear my heart beating sometimes, and see it &c:) I think I am healthy, but my blood pressure is a bit odd and I can usually only hear it when I have just walked up lots of stairs  :( And I can feel it in the sides of my head:( I think this is normal, but I have never been anyone else, so I wouldn't know:]Hidden secret 7 19:19, 18 January 2007 (UTC)

I can hear my heartbeat often at night when lying in bed with my ear against my pillow. I'd say it's pretty normal ("normal" being a very broad range) --Psud 12:06, 25 January 2007 (UTC)

50/60 Hz Microwave oven

Can a microwave oven designed for 60HZ WORK PERFECTLY IN 50HZ SUPPLY ,IF VOLTAGE IS TAKEN CARE OF ? Will its performance & life be affected ?

Pranav samel

From my experience, electric appliances built for 60Hz work fine with 50Hz electricity, except they run a little slower. The exception is electric clocks built for use in the U.S. because they base their time on the 60Hz rate and thus only go 5/6 as fast when plugged into a 50Hz socket. howcheng {chat} 17:12, 17 January 2007 (UTC)

Doubtful. Unless the transformer in the microwave is designed to handle the lower frequency, the slower cycle will cause the core to saturate, turning it from an inductive load to a short circuit. In layman's terms, your microwave will blow a fuse or catch fire. --Carnildo 21:49, 17 January 2007 (UTC)

Also (depending on how the AC is converted to DC in the machine), the DC voltage produced may be lower than what is required, due to the lower frequency and hence the oven may not work properly -- WikiCheng | Talk 07:47, 18 January 2007 (UTC)

Some digital clocks get their timing pulse from the source power, so it might run slow. Maybe that would compensate for the lower oven voltage. Edison 17:52, 18 January 2007 (UTC)

Late 1800 supernaturalism

"The discovery consists," he says, "in subjecting the vapors of volatile liquids to the action of concentrated sun-light, or to the concentrated beam of the electric light." The vapors of certain nitrites, iodides, and acids are subjected to the action of the light in an experimental tube, lying horizontally, and so arranged that the axis of the tube and that of the parallel beams issuing from the lamp are coincident. The vapors form clouds of gorgeous tints, and arrange themselves into the shapes of vases, of bottles and cones, in nests of six or more; of shells, of tulips, roses, sunflowers, leaves, and of involved scrolls. "In one case," he tells us, "the cloud-bud grew rapidly into a serpent's head; a mouth was formed, and from the cloud, a cord of cloud resembling a tongue was discharged." Finally, to cap the climax of marvels, "once it positively assumed the form of a fish, with eyes, gills, and feelers. The twoness of the animal form was displayed throughout, and no disk, coil, or speck existed on one side that did not exist on the other." Professor Tyndall

Is this possible, and what if any would be the practical application thereof? Thank you81.144.161.223 11:55, 17 January 2007 (UTC)

Does this refer to the Tyndall effect? [[John Tyndall] was a sucessor to Michael Faraday as leading scientist of the Royal Society. He was a careful observer, and a famous debunker (spontaneous generation). Please provide the source for your quote so it can be better evaluated. I find the "spiritualist" H. Blavatsky (p127)attributes that quote to Tyndall, in Blavatsky's book "Isis Unveiled" [6], which contains what appears to be a lot of nonsense. It is hard to believe Tyndall was tripping like that unless he found some "magic mushrooms." Maybe the vapors of the heated metals had affected his brain. Blavatsky does not say where in Tyndall's writings he found the quote. The first edition of Blavatsky was 1877, and he says Tyndall's discovery was "not so long ago," so that is a clue to look in the 1870's.Edison 18:12, 18 January 2007 (UTC)

Non-circular pupil

In an optical system what would be the effects of a non-circular pupil? How will the bokeh be changed? What would it be like to see through a sheep's eye? --antilived^{T | C | G} 11:58, 17 January 2007 (UTC)

The pupil shape affects resolution properties as well as the bokeh (the shape of the blur from an out-of-focus point source). The bokeh will in general look like an image of the pupil. The pupil of a typical camera is in fact subtly non-circular due to the finite number of blades in the aperture iris. If you look carefully at an image with an isolated out-of-focus point source, you may be able to see that it looks slightly polygonal, in the same way that the lens reflections seen when sunlight hit the lens do (these are also images of the pupil). If your pupil is oval or slit-like, let's say tall and narrow, then the resolution (the sharpness of the in-focus image) will be different in the horizontal and vertical directions. If your lens is good (or your aperture small), so that the resolution is limited by diffraction, then vertical resolution will be better than horizontal. If the lens is less good, so that resolution is limited by lens aberrations rather than diffraction, then the opposite situation might occur, with horizontal resolution being better than vertical. If you want to know what the world looks like through a long, narrow pupil, just squint! (Or, better, cut a very narrow slit in a piece of paper and hold it in front of your eye - that way your eyelashes won't complicate matters.) --mglg_(talk) 17:27, 17 January 2007 (UTC)

A look at our article on astigmatism may also be of interest to you. Grutness...wha? 07:17, 18 January 2007 (UTC)

You can actually see the effect if you look at a "'scope" (Cinemascope or Panavision) film. In that case, the "pupil" is still circular, but the optical system compresses things from side-to-side. The result is that out-of focus lights appear as vertical elipses rather than circles.

Atlant 15:02, 18 January 2007 (UTC)

How will the amount of light be changed? eg. If an oval pupil that's f/5.6 vertically and f/2.8 horizontally what will happen on the image plane? Thanks. --antilived^{T | C | G} 23:21, 18 January 2007 (UTC)

The amount of light transmitted is proportional to the pupil's area, which for an elliptical pupil is proportional to the product of its long and short diameters. An (f/5.6)x(f/2.8) elliptical pupil will transmit twice as much light as a circular f/5.6 pupil, but half as much as a circular f/2.8 pupil. In other words, the same amount as a circular f/4 pupil. -- 169.230.94.21 23:12, 22 January 2007 (UTC)

Autoclaves

Hi

I have been trying to find out some basic information about non-medical autoclaves, for example those used in laminate glass screen technology, areospace industries, formula 1 racing, etc. I want to know the following:

What is an autoclave? How do they work? What are their main uses outside of sterilisation? How is high pressure air or gas used within the process?

I have searched all the usual places on the web and done general searches through Google, but can't find anything general enough. Wikipedia (which, by the way, I think is great!) only really talks about medical autoclaves.

Any information you could provide would be gratefully received!

Thanks KiwiTS 12:46, 17 January 2007 (UTC) KiwiTS

See the article autoclave for more information. An autoclave is basically just an oven. The autoclave heats up, usually to about 121°C, which kills all the bacteria in the chamber (and in any objects which might be in that chamber) with heat sterilization. However, heat alone in a dry environment doesn't penetrate living tissue very well (a good example of this is the sauna, which can reach temperatures above the boiling point of water, and yet are considered a fine place to have a quick rest), and so steam is added to the equation to better conduct that heat into anything put in the chamber (a steam room as hot as a sauna would rapidly kill a human). However, there is another glitch, what if you want to sterilize water or an aqueous solution? This is where pressure comes in. The chamber is also pressurized so that even at 121 degrees, it won't boil and evaporate/boil over and make a mess. As for "What are their main uses outside of sterilisation?", I suppose they could be used for heat-assisted lamination of water-containing things...? To be honest, I can't think of anything other than sterilization that would be easier and cheaper to do in an autoclave than by some other method. Tuckerekcut 16:24, 17 January 2007 (UTC)

Here we go: Aerated autoclaved concrete. Tuckerekcut 16:25, 17 January 2007 (UTC)

I should point out in case it wasn't obvious from what tuckerercut said that autoclaves are used for sterilisation in many circumstances not just medical. Biologists doing research use autoclaves all the time for example Nil Einne 16:41, 18 January 2007 (UTC)

There are many industrial uses of autoclaves. For sterilising medical goods/ supplies an autoclave using ethylene oxide can be used. Years ago I worked in the rubber goods industry, where rubber products were cured in a steam autoclave. I suspect this also used the steam pressure to reduce the volume of any air pockets and improve adhesion of the component materials of the rubber items. A modern use of an autoclave is to produce composite material assemblies such as aircraft tailplanes and other structures. Many modern aircraft use composite assemblies to reduce weight/ improve performance. Think of an autoclave as a very large pressure cooker like you would see in a kitchen. The heat and pressure act to speed chemical linking of molecules into a final, more useful form. A mild form of this is used to cure acrylic resin used in creating dental bridges and dentures :) (207.188.64.234 16:22, 31 January 2007 (UTC))

the free website for science

hi guys i wonder is there any free website for learning science like chemistry, physics, and biology for those who didnt heard of it.thanks 14chung 12:48, 17 January 2007 (UTC)

my grade is 7th grade in singapore and i need basics... wikipedia is hard to understand thanks14chung 15:48, 17 January 2007 (UTC)

Err...wikipedia? If it's a structured course you need, try the courses at wikiversity, they're grrrrrrrreat. yandman 13:02, 17 January 2007 (UTC)

'they're grrrrrrrreat' - I love it; maybe they should adopt a new slogan Wikiversity: As supported by Tony the Tiger! --Neo 13:31, 17 January 2007 (UTC)

Depending on your level you could use anything from enchantedlearning.com to MIT OCW. Could you give us information to help us, such as grade in school? X [Mac Davis] (DESK|How's my driving?) 14:03, 17 January 2007 (UTC)

You can try this and this for a start. -- WikiCheng | Talk 14:09, 17 January 2007 (UTC)

Those are both excellent sites. X [Mac Davis] (DESK|How's my driving?) 14:24, 17 January 2007 (UTC)

Old Age in fish

Why,in the evolutionary sense, do certain fish reach senescense? What possible genetic advantage is there to surviving beyond breeding age? The only possibilty I can come up with is that these pensioners become selectively cannibalistic. That is, they then eat or kill offspring of thier genetic rivals. I know in some amphibian species, cannabalistic individuals DO, somehow distinguish between thier siblings and others. Is that what we believe these olds timers are upto?216.209.138.128 13:01, 17 January 2007 (UTC)

You know, not every phenomenon in the natural world needs to be closely explained by genetic theory. It's a rather narrow view to look at the whole wide world as being nothing more than a medium for gene propagation. Vranak

Well, you know, calling that view narrow is a bit narrow it self in my opinion, gene propagation is after all why the living world exists the way it does. Thinking somehow that this view de values or cheapens life is what I would call narrow. Everything has a reason, even if it is not obvious or intuitive, nothing happens without a reason. That doesn't mean that life isn't ammazing and wonderful! The way I would approach the above question is to turn it around and instead say "What possible genetic advantage is there to dying once beyond breeding age"?? Many fish survive in shoals, they get hunted by relentless predators their whole life and the only way the species survives is by sheer number of individuals. Having a life span past just the breeding age means that if there are any individuals that are lucky enough to survive past breeding age they pad out the numbers. Further, if an old non breeding fish gets eaten, then a young a breeding fish has been spared and the shoal has a greater survivability. Vespine 21:41, 17 January 2007 (UTC)

My narrow view has evolved out of years of trying to pigeon-hole every behaviour as either gene or meme propogation. At a certain point you begin to realize that such a simplified view of life is more a product of human vanity, thinking we can know everything, than actual correspondence to the real world.

Anyway, you left out one thing: an animal can help propogate its genes by dying, in order free up limited resources for its offspring and relatives. Vranak

back on topic: *do* fish actually survive past breeding age, as assumed by the question asker? I would have thought they continue breeding every year until they die. Even in humans, getting so old that you can't have children anymore is probably a very recent phenomenon; "wild" huntergathers rarely live(d) past 40. --Krsont 16:05, 19 January 2007 (UTC)

ecosystems

the way the human population is made up of different races.....

is a walrus in the same category(UTC)(how do i say it...isit population or community or what??)as the seals??? --203.124.2.17 13:19, 17 January 2007 (UTC) is this info i found on the net correct?? [[7]]

How to read a taxoboxEarless Seals
Grey seal
Scientific classification
Kingdom: Animalia Phylum: Chordata Class: Mammalia Order: Carnivora Suborder: Pinnipedia Family: Phocidae

Walrus
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Carnivora
Suborder:	Caniformia
Superfamily:	Pinnipedia
Family:	Odobenidae Allen, 1880
Genus:	Odobenus

Wikipedia is a helpful guide to many things, this included. If you'll look to your right you'll see two information boxes found at the earless seal (true seal) and walrus articles respectively. Under the part that says "scientific classification" is what we want to look at. Biologists try and fit every plant and animal and even bacteria, and sometimes virus into these categories. You can see that both of these animals fall under the Kingdom: Animalia, which means they are animals. Phylum: Chordata means that both of these animals have a backbone. Class: Mammalia means both of these animals are mammals. Order: Carnivora means that both of these animals eat meat and not plants. The next word says "Pinnipedia" and that is where they stop being the same. Being in the same family or order means that the animals are fairly closely related. X [Mac Davis] (DESK|How's my driving?) 14:13, 17 January 2007 (UTC)

... but they are not the same species, so they are not as closely related as the different races of humans. The biological relationship between walruses and seals is more like that between humans and chipanzees. Gandalf61 14:25, 17 January 2007 (UTC)

Actually, they belong to different families, not just different species, whereas chimpanzees and humans belong to the same family Hominidae. The relationship between true seals and walruses is more like that between humans and monkeys. -- mglg_(talk) 17:45, 17 January 2007 (UTC)

In an ecological context, populations consist of members of the same species in the same general area, while communities consist of interacting or potentially interacting populations of different species. Walruses in some area will make up a population. The walruses and seals in an area will be members of a community. Guettarda 22:10, 17 January 2007 (UTC)

If you're looking for an analog with human races, perhaps a color phase might be the closest. A subspecies is a bit more of a difference than human races, I think. StuRat 06:40, 18 January 2007 (UTC)

Humans we tend to think that everything in nature has to have a reason, but maybe not. Species aren’t finished products. To use an analogy if a Martian came from space and saw a car he or she would ask what are the exhaust are gases for. Or why does a computer give of heat.

Not Injecting coffee

Why we cannot inject cafeine on the vein? Would it kill us?.Mr.K. 14:30, 17 January 2007 (UTC)

From Caffeine:

An acute overdose of caffeine, usually in excess of 400 milligrams (more than 3-4 cups of brewed coffee), can result in a state of central nervous system overstimulation called caffeine intoxication. Some people seeking caffeine intoxication resort to insuffilation (snorting) of caffeine powder, usually finely crushed caffeine tablets. This induces a faster more intense reaction. The symptoms of caffeine intoxication may include restlessness, nervousness, excitement, insomnia, flushing of the face, increased urination, gastrointestinal disturbance, muscle twitching, a rambling flow of thought and speech, irregular or rapid heart beat, and psychomotor agitation. In cases of much larger overdoses mania, depression, lapses in judgment, disorientation, loss of social inhibition, delusions, hallucinations, psychosis, rhabdomyolysis, and death may occur.

In cases of extreme overdose, death can result. The median lethal dose (LD₅₀) of caffeine is 192 milligrams per kilogram in rats. The LD₅₀ of caffeine in humans is dependent on weight and individual sensitivity and estimated to be about 150 to 200 milligrams per kilogram of body mass, roughly 80 to 100 cups of coffee for an average adult taken within a limited timeframe that is dependent on half-life. Though achieving lethal dose with caffeine would be exceptionally difficult with regular coffee, there have been reported deaths from overdosing on caffeine pills, with serious symptoms of overdose requiring hospitalization occurring from as little as 2 grams of caffeine.

Treatment of severe caffeine intoxication is generally supportive, providing treatment of the immediate symptoms, but if the patient has very high serum levels of caffeine then peritoneal dialysis, hemodialysis, or hemofiltration may be required.

LD₅₀ would be, by the way the concentration at which a toxin kills 50% of a population. I'm not sure he's asking for "medical advice." He's asking a question about something medically-related. X [Mac Davis] (DESK|How's my driving?) 14:54, 17 January 2007 (UTC)

"Can I inject myself..." is a question that the reference desks will not answer. Hipocrite - «Talk» 14:57, 17 January 2007 (UTC)

Well good, because I didn't answer it! X [Mac Davis] (DESK|How's my driving?) 15:01, 17 January 2007 (UTC)

Ok, I have reformulated the question. Again: I am not trying to do it. I just want to know why some drugs can be taken in tea, injected, and so on, and others cannot.Mr.K. 15:46, 17 January 2007 (UTC)

If your question asks us if something will kill you, our answer will be "it might, talk to a doctor." If you would like to know about drug delivery you should read the article on it, the sources it references, and come back with a more specific question. Hipocrite - «Talk» 15:47, 17 January 2007 (UTC)

Caffeine can be and is injected into veins. As a medication, caffeine is used intravenously in newborn infants to stimulate breathing. It is safe and well-tolerated. There are no indications for intravenous caffeine outside of the newborn period that I know of. If there were a reason to do it medically, it could certainly be done. InvictaHOG 17:34, 17 January 2007 (UTC)

ThanksMr.K. 18:20, 17 January 2007 (UTC)

This is not accurate. The injectible medication referred to is Caffeine citrate. Hipocrite - «Talk» 20:19, 17 January 2007 (UTC)

Thanks for that too Hipocrite.

Only in the sense that "crack" is not cocaine. It is caffeine and it is injected, so I think it satisfies the initial question. InvictaHOG 13:48, 18 January 2007 (UTC)

Weather

The weather info on Weather.com and NOAA is very different. Why?129.112.109.252 19:49, 17 January 2007 (UTC)

Weather forecasting isn't an exact science, different groups can come to different conclusions about what they think the weather will be like. That article has a lot of information. Vespine 21:17, 17 January 2007 (UTC)

eel

What types of eel are safe to ingest, as opposed to those that are toxic and therefore not safe to ingest?

From the article: Freshwater eels (unagi) and marine eels (Conger eel, anago) are commonly used in Japanese cuisine. Unadon is a very popular but rather expensive food. Eels are used in Cantonese and Shanghai cuisine too. The European eel and other freshwater eels are eaten in Europe, the United States, and other places around the world. A traditional East London food is jellied eels. The Basque delicacy angulas consists of deep-fried elvers.[8]. Eel blood is toxic. The toxic protein it contains is destroyed by cooking. The toxin derived from eel blood serum was used by Charles Robert Richet in his Nobel winning research which discovered anaphylaxis (by injecting it into dogs and observing the effect). X [Mac Davis] (DESK|How's my driving?) 22:23, 17 January 2007 (UTC)

Here in South Africa we eat Kingklip. Sandman30s 13:53, 18 January 2007 (UTC)

Not really an eel, there's the hagfish. Its skin is used to make "eel skin" wallets, and hagfish are eaten in Korea. --125.189.164.34 15:54, 18 January 2007 (UTC)

Unidentified Sea Creature

Anyone have an idea what this is? They kind of look like very small pippies, they were found on the beach and are 3-4mm long. I have no idea what they are attached to, it kind of looks like plastic, but could be biological (calcium carbonate?). I posted this on WT:TOL, but got no response. Thanks. --liquidGhoul 06:17, 16 January 2007 (UTC)

I can't get the image to load, but my internet has been playing up, is it just me?Vespine 22:59, 17 January 2007 (UTC)

Looks like a group of young bivalves growing on a piece of plastic tubing to me. --Kurt Shaped Box 23:49, 17 January 2007 (UTC)

That's exactly what it looks like to me. X [Mac Davis] (DESK|How's my driving?) 00:15, 18 January 2007 (UTC)

Thanks guys. --liquidGhoul 01:42, 18 January 2007 (UTC)

Sex demarkation in llamas?

What are all the differences between adult male and female llamas (or mammals in general)? What are the most obvious differences besides of course the genitals?--Sonjaaa 23:01, 17 January 2007 (UTC)

This source implies there is little or no sexual dimorphism. X [Mac Davis] (DESK|How's my driving?) 00:17, 18 January 2007 (UTC)

Thanks!!--Sonjaaa 15:00, 19 January 2007 (UTC)

Carnivorous bird species as housepets?

Just been thinking about this now - people have been keeping carnivorous mammals, reptiles and fish as pets for a long time. Why is it that very few people keep pet carnivorous birds? --Kurt Shaped Box 23:46, 17 January 2007 (UTC)

See Falconry. --Zeizmic 23:51, 17 January 2007 (UTC)

I was meaning 'pet' in the more conventional sense - i.e. keeping as a companion animal in one's own home. I know that a few people keep owls and vultures in this way but it's far from common. --Kurt Shaped Box 23:54, 17 January 2007 (UTC)

Owls and penguins are the only carnivorous birds I've seen kept as pets in the sense of purely companion pets and not working pets. Owls are very messy and make a lot of noise at night. Penguins are illegal to be kept as pets in most places - but it happens. I feel that the carnivorous bird's need to hunt makes it hard to keep them satisfied as pets - which is why falcons are trained to return after hunting, not tamed into losing the need to hunt. --Kainaw ^(talk) 00:16, 18 January 2007 (UTC)

Are owls any messier or noisier than your average macaw or cockatoo? I suppose that they're not quite as entertaining or interesting-looking... --Kurt Shaped Box 01:39, 18 January 2007 (UTC)

Some owls do not make any noise, but most do. They are much messier however, their crap is full of skeletons and such, and they will also regurgitate a lot. Birds are very intelligent, and taking an intelligent carnivore from the wild, and having it not hunt, can cause lots of problems. They have extremely stong feet and sharp beaks. Cats and dogs are not nearly as intelligent as large birds. When I was young, we cared for an injured kestral, and it was not fun finding food for it. We eventually fed it lamb chops, but for a long time, we were out catching large grasshoppers for it to eat. If we had it for a long time, there would be a need for a supplement, as their prey is extremely varied in the wild, and feeding it one thing would result in deficiencies. --liquidGhoul 01:48, 18 January 2007 (UTC)

Carnivorous pets like dogs and cats were of course domesticated thousands of years ago, in fact dogs are thought to be the very first domesticated animal. I suppose no one thought it was worth domesticating a carnivorous bird, or maybe they tried and couldn't benefit enough to make it worth their wile? I guess it is interesting why there are no examples at all.. Vespine 02:07, 18 January 2007 (UTC)

Yeah, I'd have thought that it might be useful to keep a raptor around for ratting and mousing (maybe before domestic cats became ubiquitous). --Kurt Shaped Box 08:01, 18 January 2007 (UTC)

I feel that cats do work well. I live near the water. If I walk along the marsh, there are plenty of mice and bunnies (we call them alligator food). I never see a mouse or bunny near my house. I believe it is because there are two cats that my neighbor feeds (I chucked rocks at them until they learned to stay away from me). In fact, I rarely see a squirrel either - but I attribute that to the excessive number of blue jays and cardinals that wage gang warfare in my backyard all summer long. --Kainaw ^(talk) 08:06, 18 January 2007 (UTC)

'Gravity' increase if earth stopped spinning

On the earth we are pulled down by gravity, but since the earth revolves then particularly at the equator we are at the same time pulled up by.....forgotten the name of the force. If the earth stopped spinning, then how much would the net 'gravity' increase by?

Depends of your latitude. People at the equator would feel a greater change than people at the poles (who would feel nothing different). See acceleration due to gravity for more explicit info on this question. — Kieff 00:07, 18 January 2007 (UTC)

Didn't we have this question a week or two ago? Anyway, the centrifugal force produces an acceleration of v²/r, which at the equator works out to about 1/300 of the acceleration due to gravity. In other words, people at the equator would weigh roughly 0.3% more. --Anonymous, January 18, 2007, 00:16 (UTC).

Of course, we shouldn't forget that the Earth – like just about any other rotating astronomical body of appreciable size – has an equatorial bulge. Because the Earth is spinning, it has been stretched about its middle from a perfect sphere into an oblate spheroid. Consequently, the Earth's surface is about 21 km further from the Earth's centre when measured at the equator versus at the poles.

That article contains a useful discussion (see equatorial bulge#Differences in gravitational acceleration) of the relative sizes of those two factors (oblateness and accleration caused by rotation) and their contribution to a lower apparent force of gravity at the equator. The question is, if the earth stopped spinning, would its shape relax back to a (nearly) perfect sphere? If so, then you'd also need to take that contraction into account. TenOfAllTrades(talk) 02:25, 18 January 2007 (UTC)

Probably, but I think that'd take quite a long while. It's a lot of mass to be rearranged. — Kieff 02:32, 18 January 2007 (UTC)

Except in the case of oceans, where the water could be rearranged quite quickly, with a great deal of sloshing in the process. Since the oceans aren't 21 km deep anywhere, I imagine the oceans would completely move from the equator and a good deal of the tropical zone, and slosh towards the poles, where the water might become several kilometers deeper, completely submerging Antarctica. This makes for some interesting speculation. StuRat 05:23, 18 January 2007 (UTC)

That'd make a good storyline (excuse?) for a Hollywood special effects movie. Just add a few intrepid scientists, military men and nerds trying to prevent a disaster as huge tidal waves threaten to swamp all the world's coastal zones as the earth gradually stops spinning (due to an asteroid strike at the beginning?)... --Kurt Shaped Box 06:36, 18 January 2007 (UTC)

More to the point, the atmosphere would do the same. The ex-equatorial landmasses (indeed, the whole of the tropics) would be left poking out into space. –EdC 14:31, 18 January 2007 (UTC)

I think that for any mass such as the earth, if it stopped rotating but remained the same shape (which it would not; it would fly apart if stopped suddenly, and if it had never rotated it would be more of a sphere and have no equatorial bulge) the gravity does not change if it is rotating or stationary. The weight will change, but that is because of the elimination of centrifugal force. The equation for gravitational attraction does not include a rotational term, just the gravitational constant, the distance, and the masses. The weight is a superposition of gravitational attraction less centrifugal force. Edison 16:39, 18 January 2007 (UTC)

The local apparent gravity is in fact dependent on the rotation of the earth; you have the actual gravity which is always radial, and then you have the centrifugal acceleration which is always directed directly away from the earth's axis. (On the equator, this is straight up; at the poles it's due south/north, horizontal, and nearly 0 in magnitude; elsewhere it's toward the equator and pitched up by your colatitude.) This means that "down" is not only weakened but redirected; it doesn't point at the center of the earth. As such, if you stop the Earth rotating (somehow, and gradually) you change which direction is considered down and thus which things are level. In short, the entire temperate zones would take on a slope toward the poles, and it is this effect which would drive the de-oceaning and de-airing of the tropics. Of course, there is still some air at 21km altitude, and I don't know how fast the crust (riding on semi-liquid mantle as it is) would react compared to the air and water, but the effect could be real. --Tardis 04:11, 20 January 2007 (UTC)