Wikipedia:Reference desk/Archives/Science/2006 December 3

From Wikipedia, the free encyclopedia

< Wikipedia:Reference desk | Archives | Science

Science desk
< December 2	<< Nov \| December \| Jan >>	December 4 >

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

[edit] December 3

[edit] Cultivation Theory

"television reality, heave/light viewers, mean world syndrome, mainstreaming, and double dose effect" I know what they mean, but just need to find out George Gerbner himself's definitions for them. Thank you a lot!

(edited to fix screen stretch by ⁪froth^{T C})

[edit] chemical bonding

Dear Sir/Madame,

Could you please clarify the following - Why is the H-N-H bond-angle in ammonia molecule (NH3) greater than the H-As-H bond-angle in arsine (AsH3)?

-Sruthi.

This sounds like a homework question, so instead of answering it directly I'll describe the (perfectly analogous) situation of water versus hydrogen sulfide and hydrogen selenide. Water's H-O-H bond angle is closer to the 109° angle of a regular tetrahedron than the 90° angle of two pure p orbitals. This is usually described in terms of sp³ hybrid orbitals and VSEPR theory. The corresponding angles in H₂S and H₂Se, however, are much closer to 90°, because they are larger molecules and electron pair repulsion is less important, so the natural orientation of the unhybridized p orbitals dominates. —Keenan Pepper 04:39, 3 December 2006 (UTC)

[edit] Electrical interference

I hope I'm asking this in the right place. My friend and I are working on a home recording project, and we've encountered an electrical mystery. We've got (a) a mixing board, which is plugged in, (b) powered speakers that are connected to the mixer and plugged in on their own and (c) a laptop, connected to inputs and outputs on the mixer via a RCA-USB hub device, and often also plugged in to the house's AC power supply. Here's the mystery: when the laptop is plugged in, the speakers hum. It's a pretty irritating and inconstant crackly hum. If we unplug the computer, or disconnect it from the mixer, the hum stops. If we move the computer across the room and plug it in far away from the speakers, the hum gets quieter, but we can't get it to go away without disconnecting something.

What in the devil is that hum, and is there some easy trick involving grounding something or breaking a loop somewhere that would make it go away? -GTBacchus^(talk) 03:43, 3 December 2006 (UTC)

This sounds like some sort of loop current problem. Have you made sure you have a star connection to the ground? --HappyCamper 03:53, 3 December 2006 (UTC)

A "star connection"? Do you mean, are all the electrical connections grounded? Everything has three prongs where it plugs in, two for current and one for a ground... -GTBacchus^(talk) 03:58, 3 December 2006 (UTC)

HMMM! Sounds like a hum loop. Youre going to need to break the loop sumhow by removing one on the signal return wires (NOT the safety grounds- leave all those connected). We dont appear to have an article on that. Could try Google.--Light current 03:54, 3 December 2006 (UTC)

So... maybe if we disconnect the mixer --> computer connection while listening to playback? Is that what you mean? I'll try googling, too. -GTBacchus^(talk) 03:58, 3 December 2006 (UTC)

Ground loop (electricity) might have some other reading materials which would be of use. Well, the idea is sort of like this: Say you have 3 things which attach to the ground. Check to make sure the things connected to the ground looks like:

   \  |  /                   |     |     |
    \ | /       or           |     |     |
     \|/                     |     |     |
     GND                     -------------
                                  GND

That is to say, the ground should be a point or a line...there should be no loops there. --HappyCamper 04:06, 3 December 2006 (UTC)

You mention laptop 'plugged-in'. By that I`m guessing you mean via an adapter. Have you tried the same connections with the laptop using only its on-board batteries? Just a first guess. Also, does it sound like a 50/60 hertz hum? Dave172.148.105.56 04:20, 3 December 2006 (UTC)

When the laptop runs on just its battery, there's no hum. I'll have to get back to you on the frequency... What would it mean if it is 50 or 60hz? -GTBacchus^(talk) 09:29, 3 December 2006 (UTC)

THe freq is not important. You have just confirmed it as mains hum. (60Hz in US, 50 Hz in Europe). So it appears you have an unwanted (earth) connection between the computer and the mixer.--Light current 13:45, 3 December 2006 (UTC)

The significance is that AC electricity is sent as 60Hz in the US and 50Hz in the UK, meaning if that's the hum you hear, it's a problem related to that. --Wirbelwindヴィルヴェルヴィント (talk) 19:40, 3 December 2006 (UTC)

Does the problem go away if all electrical components are plugged into the same outlet or outlet strip? That may be more important from a hum point of view than the overall ground impedance to an earth ground. If components are plugged in to outlets in different places, the impedance between the ground connections can set up a ground loop such that a small amount of current carried over the ground sheath of the audio cables induces hum. I once corrected a hum problem in a commercial editing studio by getting them to connect all power cables to the same source. Edison 20:50, 3 December 2006 (UTC)

To further help isoloate the source of your 'hum', try disconnecting one 'peripheral' at a time. Basically trial and error I guess, is what I`m trying to say. Connecting all your equipment to a single power supply, powerbar, sounds like good advice too. Observing, and complying with, all polarities, (i.e. safety precautions) cannot be ignored either. Hope this helps. Please let us know if our advice has solved your problem. Dave172.148.105.56 22:52, 3 December 2006 (UTC)

[edit] Looking for an article

There's an article which addresses the mathematics and probability of humanity going extinct. More specifically, it looks at what percentage of humans who will ever exist have existed. I've seen it before, but I can't find a link to it either at End of civilization or Human extinction. Thanks. --The Radio Star 04:01, 3 December 2006 (UTC)

Never mind, Doomsday argument was what I was looking for. --The Radio Star 04:10, 3 December 2006 (UTC)

Somebody (else) has too much time on their hands. Without wading too far into the math, it looks like a remarkably silly argument. Clarityfiend 09:14, 3 December 2006 (UTC)

[edit] Tuning fork

Why does it need two prongs not one? 8-)--Light current 05:00, 3 December 2006 (UTC)

Because then it would be a tuning knife. - Nunh-huh 05:23, 3 December 2006 (UTC)

That's a bit blunt. :) DirkvdM 07:42, 3 December 2006 (UTC)

For a slightly different explanation, see here. - Nunh-huh 05:25, 3 December 2006 (UTC)

THe link certainly does say why 2 prongs would vibrate in sympathy. But what I asked was why you need two--Light current 00:02, 4 December 2006 (UTC)

You ned two because one thing can't resonate with itself. You need the resonation to increase the volume. - Nunh-huh 02:35, 4 December 2006 (UTC)

Here's a thought. For a metal bar to resonate freely, the ends need to be free. One way to do that would be to hold it exactly in the middle. A tuning fork is a handier way of doing that, with a handle in the middle, making sure you hold it exactly in the middle and don't even muffle the vibration by holding the bar itself there with your fingers. I don't know if the fact that the bar is bent has a function. It might work just as well if it were straight. DirkvdM 08:45, 4 December 2006 (UTC)

[edit] 3D Molecules

Are there any good free programs (Windows or Linux) for drawing molecules in 3D? ChemSketch is the de facto 2D program here, but it doesn't do 3D. At least not that I'm aware of. Please don't direct me to the computing desk. They already sent me here. --Russoc4 05:38, 3 December 2006 (UTC)

This may not help, but RasMol can be used to render in 3D and there is a large library of PDB sources to use. Not great if you need to render something novel, though. For this Corina may provide what you need. Rockpocket 06:59, 3 December 2006 (UTC)

Well, what is used to make images like this? --Russoc4 19:17, 3 December 2006 (UTC)

Chime? However, ChemSketch (most recent is v10, Sept 2006) does do 3D, and should save you part of a learning curve: tutorial and download -- Seejyb 21:24, 3 December 2006 (UTC)

[edit] Durability of bleach

Chemical bleaches work in one of two ways:

(a) An oxidizing bleach works by breaking the chemical bonds that make up the chromophore.

(b) A reducing bleach works by converting double bonds in the chromophore into single bonds.

Which of the above gives more durable bleaching effects?

Thanks very much indeed for advice.

Since the world around us is oxidising (contains oxygen) a reducing bleach's effects could be reversed by atmospheric oxygen. So I would guess the reducing bleach might be the less durable (there are no many enviromental reductants - becuase of all the O₂). I'm not 100% certain though.?83.100.253.140 14:28, 3 December 2006 (UTC)

[edit] nitric oxide

Moved here from WP:RD/M - Mgm|^(talk) 11:56, 3 December 2006 (UTC)

Dear Wikipedia

please can you forward this enquiry to the correct department / person who can answer my important enquiry regarding NO supplements. its regarding Nitric Oxide supplements with regards to penile erections. viagra works by increasing the amounts of NO so will NO supplements work the same way in dilating your vessels? what is the difference? I read several articles on it in your enclopedia but still confused.

looking forward to your prompt reply

kind regards

Nixon Chan.

I doubt it. According to our Viagra article, the nitric oxide must be released in the corpus cavernosum to have any effect. I doubt if a general supplement would be able to target it directly, like that. Therefore, it would be largely ineffective. StuRat 13:26, 3 December 2006 (UTC)

So the answer is a firm NO --Light current 13:41, 3 December 2006 (UTC)

I believe so, yes, but I'd need to bone up on the issue to be more definitive. StuRat 09:19, 4 December 2006 (UTC)

I am curious, since nitric oxide is a gas, what the enquirer was referring to as "supplements"? alteripse 14:28, 3 December 2006 (UTC)

Viagra is considered to work by slowing down the break down of the cGMP produced by the action of NO, i.e. it does not cause or increase NO as such, but increases the number of molecules "one step down the line", so to speak. The so-called NO-supplements are supposed to help by providing more of the precursor from which NO is made. The supplement would contain something like L-arginine (amino-acid from which NO can be made). The unproven theory is that increasing precursor substance would generally increase NO, and thereby confer some benefit on blood vessel function; claims such as improved "energy, vascular and circulatory health" are made. We do not know whether in normal persons, more precurser would necessarily cause more NO to be made, or whether there would be a sustained increase in cGMP. There is no evidence at present that this makes any difference to body-building, nor to sexual potency. The involvement of a Nobel laureate academic pharmacist in the marketing of a commercial brand of the product is unusual, and the situation is complicated by his failure in the past to declare this "conflict of interest" in a major publication. Any benefit one day proven would likely be due to circulatory effects. -- Seejyb 00:08, 4 December 2006 (UTC)

[edit] -deltaG and positive reduction potential

How does -deltaG correlate with electron movement toward more positive reduction potential? (as in Electron Transport Chain)

I'm not sure of the answer, but I wonder if this relationship helps you:

$\Delta G = -nF \Delta E \,$

Cheers, David Iberri (talk) 19:18, 3 December 2006 (UTC)

See also Complex I, Complex III, and Complex IV all of which produce electrochemical gradients high enough to produce certain quantities of ATP--172.132.202.103 16:19, 4 December 2006 (UTC)

[edit] chrome exploration?

How does one discover chrome? Is it a mineable iron substance? How is chrome discovered? How does one expore for chrome and where is it found? Is it a bi-product of what???someother mineral? Does it have to be drilled or is it a surface observation? Where are chrome desposit found? Is it like ore? Does it have magnetic qualities? Can it be detected from aerial surveilance? Where are the world's deposits of chrome. Is it a covering for knives and forks only? Where it used in the world? What are its main contributions to the world economy? Is it of any value in a global sense? How can it best be used? —The preceding unsigned comment was added by 61.68.8.152 (talk • contribs).

Why don't you start with chromium and then come back here after basic research has been done? We'll be glad to help with questions then. Please sign your posts with four tildes (~~~~). -THB 14:49, 3 December 2006 (UTC)

Some folks think it can best be used on dubs and other forms of bling. 192.168.1.1, 1:05pm, 3 December 2006

The word chrome usually means chromium plating, which was once common for car grills, among other things. StuRat 09:16, 4 December 2006 (UTC)

[edit] Conductivity Data

What are the conductivities of pure silicon and phosphorous doped silicon, can some please provide some sources for this information. Philc _T^E_C^I 14:36, 3 December 2006 (UTC)

Try starting from Semiconductor#Doping? Do you need the actual eV etc? --Wirbelwindヴィルヴェルヴィント (talk) 19:36, 3 December 2006 (UTC)

Guy was asking for the conductivities - (siemens) - answers not there?87.102.9.4 20:23, 3 December 2006 (UTC)

The IP's right, I was just lloking for some seimens m^-1/ohm m data on the resistivity/conductivity of silicon before and after doping. Philc _T^E_C^I 00:13, 4 December 2006 (UTC)

[edit] building a spaceship from scratch

Using the concepts of cost and price analysis to build a spaceship from scratch. What to look for from the viewpoint of a government agency and as a contracting officer for the government.

Do your own homework. If you need help with a specific part or concept of your homework, feel free to ask, but please do not post entire homework questions and expect us to give you the answers. -- Ec5618 14:50, 3 December 2006 (UTC)

The first thing is you need to know what the payload will be. That is, what are you transporting and to where ? The next thing to decide is the type of spaceship. A traditional liquid fuel rocket is probably the cheapest. Then decide who will launch it for you. Then pick subcontractors to build the components. StuRat 15:02, 3 December 2006 (UTC)

I'm not sure this is a homework question, so I'll assume good faith and have a stab at answering, although if the asker is a 'government contracting officer' then I have to admit I'm a bit surprised that the Wikipedia Science Reference Desk is now an approved source of advice - maybe we should be flattered ;-). Anyway, StuRat is correct that the first thing you'll need to know, at least vaguely, are the approximate mass of the payload to be launched and where in space you want to get it to. If by 'spaceship' you mean a human-qualified vehicle then the cost is likely to be orders of magnitude greater than for an 'expendable' science payload, and recommended reading for starters would be Pranke & Larson's Human Spaceflight: Mission Analysis and Design. That book includes some basic information on parametric cost estimation, which is the first stage in approximating the cost of your mission. Some useful parametric estimators can be found at Johnson Space Centre's Cost Models. The cheapest launch route, at least for scientific payloads, is likely to be an existing launcher such as ESA's Ariane V. If you want to go somewhere other than a 'conventional' low-earth, geostationary, geosynchronous or Molniya orbit (or even for one of these depending on the launcher used and the size of the payload), you may need to use upper stages which will need their costs estimated separately. When estimating the cost of a spacecraft, you'll need to know not just the 'cost per unit' but also the development cost, which is likely to be very high for 'scratch' projects, and which will need to be amortised over the production run. Then there are the costs of things like software (either COTS or bespoke) and mission operations. I would advise some in-depth background reading if you're new to the subject, before you even embark on basic estimates, as you'll need to know whether your project lies within the limits of applicability of whatever parametric model you're using. Another good book for starting out is SMAD3. If you're working for a government agency then the best option would probably be to seek advice from your country's national space agency if it has one, or from spacecraft mission design experts at academic institutions. Good luck =) --YFB ¿ 04:03, 4 December 2006 (UTC)

That would be cool - if people working for government agencies would come here for advise. We could change world politrics with our answers. Some responsibility! :) DirkvdM 08:52, 4 December 2006 (UTC)

[edit] Mineral Water / Cola Sales

I was wondering recently - which has sold more: any form of mineral water or any form of cola? I imagine that mineral water hasn't been widely available as long as cola has been, since the benifits of mineral water as opposed to tap water were discovered fairly recently (as far as I know). RevenDS 15:38, 3 December 2006 (UTC)

I don't even know if 'health benefits' are the minds of people who drink mineral water. It shouldn't say that it tastes better, but it does taste different, and certainly more pure, than what comes out of most taps. I drank a lot of Gerolsteiner [1] last year, which is very high in calcium and magnesium, and after a couple of glasses it actually made me feel like I had eaten something! Theavatar3 16:46, 3 December 2006 (UTC)

Evian (part of Danone the biggest mineral water selling company in the world) claim to sell 1.5bn bottles a year. Coca-cola distributed 45bn bottles and cans in 2005. The bottled-water industry is a lot more fragmented I would say. There are 2 major brands of cola (Pepsi/Coca-cola) and then lots of 'own brand' and 'local brand' versions, whereas everywhere I go they sell a different 'brand' of bottled water, with Evian being one of the major world-wide recognised brands of water. I think bottled water sales will increase and close the gap but cola is used to flavour drinks in bars/hotels/restaurants and is used in cooking etc. I also think that because it is a 'treat' it will have high sales at holiday resorts/cinemas etc, bottled water is more a 'everyday' bottled drink than a treat (for me at least). ny156uk 18:12, 3 December 2006 (UTC)

Considering that soda is not a particularly healthy drink option, and the world seems to be undergoing a health revolution right now, I'd imagine that its days are numbered. Theavatar3 00:49, 4 December 2006 (UTC)

That's only in the developed world, however. The developing world is actually going for a less healthy diet. KFC is quite popular in China, for example. I suppose that's one way to reduce the "surplus population". StuRat 08:58, 4 December 2006 (UTC)

They will catch up within twenty years though. And I do not feel sorry for them -- the cheerfulness and robustness of their culture more than makes up for any economic deficits. Theavatar3 16:39, 5 December 2006 (UTC)

RevenDS, are you asking only about cola drinks, or about all soft drinks in general? User:Zoe|(talk) 19:32, 4 December 2006 (UTC)

Cola as in the dark brown soft drink, such as Coca-Cola or Pepsi. I asked because I thought it was probably likely that cola sold more than water, which would, on the surface, sound pretty horrific. Of course, the vast majority of people drink the water out of their tap and not from bottles you pay extra for, so after a bit of thought the fact is actually quite reasonable. Still, it kind of highlights one of the obvious reasons for the health issues in the developed world. Thanks, guys. RevenDS 22:24, 4 December 2006 (UTC)

Actually there is no clear evidence that mineral water/bottled water is in any way healthier then tap water. Indeed, there isn't even any clear evidence it taste's better. Many blind/double blind taste tests have failed to show it does. In terms of future trends, note that there is quite a strong lobby against bottled water since it's consired by some to be very environmentally damaging & wasteful Nil Einne 17:08, 5 December 2006 (UTC)

[edit] Carbonated water freezes

My fridge is broken. It's at -0 something Celsius. Just now, I took out a bottle of carbonated (fizzly) water, and as soon as I opened it, it began to froze, seemingly from the top to the bottom. Is there any explanation to this..? 81.93.102.185 16:43, 3 December 2006 (UTC)

Presumably, carbonation inhibits freezing. As the carbon dioxide escapes, the freezing point of the remaining water returns to zero, and the contents begin to freeze. Theavatar3 16:48, 3 December 2006 (UTC)

I just want to say wow, I'd love to see a video of that happening, any chance? (agree with previous - dissolved CO2 will lower the freezing point)83.100.253.140 17:06, 3 December 2006 (UTC)

One more possibility is that the pressure due to CO2 has decreased the freezing point of water. When you released the gas, the pressure is gone and the freezing point has returned to normal -- WikiCheng | Talk 18:09, 3 December 2006 (UTC)

Another cool (but possibly annoying) side effect of this: When the carbonated water freezes in the bottle, it expands. It doesn't take very long for it to expand right out the top of the bottle. --Kainaw ^(talk) 19:12, 3 December 2006 (UTC)

If you buy one of those electrical timers that goes between the appliance and the wall socket, you an make the fridge switch on and off several times throughout the day to try to maintain a suitable temperature. If you have the money though, it mgiht be cheaper in the long run (electric bills) to buy a new, more efficient fridge. --Username132 (talk) 19:20, 3 December 2006 (UTC)

Because water expands when it freezes into ice, you can force it to stay liquid below its normal freezing point by keeping it under pressure. (Wikicheng has it right.) Your bottle of carbonated water was probably at a temperature just below zero Celsius. When you opened the cap, you relieved the pressure on the liquid, allowing it to expand and freeze. I've seen this happen occasionally when I've left a bottle of beer in the freezer to rapidly chill it. The entire contents are liquid while the bottle is sealed, but as soon as the bottle cap comes off the neck of the bottle fills with beer slush. (Note that ice will accumulated at the top of the container because it is less dense than liquid water—any ice the forms automatically floats to the top.) TenOfAllTrades(talk) 19:47, 3 December 2006 (UTC)

The article on supercooling is not very informative for someone who does not understand it already, but the link at the bottom looks interesting. Seejyb 22:43, 3 December 2006 (UTC)

Any release of CO2 really cools things down. Think of a standard CO2 fire extinguisher. Opening the bottle is enough to drive down the temperature below that of freezing sugar water (or beer). --Zeizmic 23:23, 3 December 2006 (UTC)

The water in the bottle can be colder than freezing point if no points for crystalisation are present. The opening formes tiny bubbles wich can be the starting point for crystalisation. The same is possible for boiling. Water in microwave ovens can be heated in a new glas pot to over 100°C, if tea or coffee is added the boiling occures in a kind of explosive way. This would be the explenation from my side!--Stone 08:27, 4 December 2006 (UTC)

An even cooler effect is when glass pop bottles were placed at temps far below freezing. The pop would stay liquid as long as the bottles held. When the bottles finally shattered, the sudden reduction in pressure would cause the pop and glass shards to freeze, mid-explosion, much like popcorn does. Of course, due to the flying shards of glass, this is not something you should try at home. StuRat 08:54, 4 December 2006 (UTC)

On a related note, I left a glass bottle of Pierre in the freezer once. Ooops Nil Einne 17:10, 5 December 2006 (UTC)

[edit] Thomas Kuhn

I am looking for material concerning how Thomas Kuhn's ideas in The Structure of Scientific Revolutions can be applied to the development of an aspect of science. In other words, I need to use Kuhn's ideas to show how an area of science developed. Thanks!

Have you read the book, the Wikipedia article about him and the one about the book, and looked at some of the online links which talk about it? Please do so, and then we will be happy to help. Were you looking for areas of science where his ideas can be supplied? Consider the germ theory of disease. Old school physicians in some cases went to their graves convinced that germs were not the cause of disease. They did not all become converts after Pasteur and the other doctors who said germs caused disease, pointing to diseases where no bacteria could be isolated (such as those caused by viruses.) The field passed them by and the newer doctors all subscribed to the new theory or new paradigm. Edison 20:58, 3 December 2006 (UTC)

[edit] Changing an orbit

Recently I was watching a show that was saying how, in the future, the moon will gradually become more distant from Earth. And then I started thinking, how would you go about modifying the orbit of a world, like the moon, or Mars? (I mean, maybe you could move a planet into the habitable zone of a star in order to facilitate terraforming.) I know it's a really fanciful idea, but if we were an extremely advanced civilization, what are some ways that you could move a world? --Lazar Taxon 17:40, 3 December 2006 (UTC)

if u placed a large object in an orbit near it then the original object will "move" towards it, but it would have to be big ie planet size --Colsmeghead 23:48, 3 December 2006 (UTC)

But then, how do you move the "large object" toward the original object? Maybe you can explode nuclear bombs near it? That's going to take a lot of bombs, though. --Bowlhover 00:27, 4 December 2006 (UTC)

The moon is far beyond the scale of mankind's activities. Now, and in the conceivable future. Theavatar3 00:53, 4 December 2006 (UTC)

The problem is that exploding nuclear bombs near it will probably do more then just move the planet... In regards to the moon, I guess we are lucky that there is one face always towards us and there is a dark side that is always facing away, so theoretically, if we could set up some sort of propulsion on the dark side to push it towards the earth we could maybe push it ever so slightly towards us coutering the 'floating away' effect. There is no atmosphere and friction is very very small so even a relatively small amount of thrust would over time 'add up' so to speak. The problem is to set up a sustainable method of thrust, I guess somehow it would have to be solar powered, even if that meant it only worked the half (probably closer to 1/3) of the time the dark side of the moon was facing the sun. Apart from that, I don't actually have any idea how much thrust over what time frame it would require, but it's an idea at least. Vespine 03:51, 4 December 2006 (UTC)

If I recall correctly, Larry Niven described a way to move a gas giant planet in A World Out of Time. He placed a huge engine in the dense atmosphere. Gasses/fuel entered one end, was ignited, and exited out the other. Clarityfiend 05:50, 4 December 2006 (UTC)

Yep. The trick, as I remember, was that this was a nuclear engine -- so the whole bulk of the planet (being hydrogen) was suitable both as fuel and also as working fluid to be expelled from the engine. Of course we don't have any way to build a hydrogen-1 fusion reactor today, but it's theoretically possible. As I recall, the planet they moved was Uranus, being smaller than Jupiter or Saturn but closer to the inner solar system than Neptune. And the reason they moved Uranus was to use its gravity to tug the Earth into a different orbit: they didn't have a way to move Earth directly. Neat idea. --Anonymous, 09:35 UTC, December 4.

I would imagine you would go about it the same as any orbit transfer, only with a MUCH bigger engine. --anonymous6494 06:45, 4 December 2006 (UTC)

Here's my plan for moving a planet or moon, which is near the sun, with no appreciable atmosphere:

Cover the entire planet, except the poles, with solar cells for power (or just one side, if only one side faces the Sun).

Vaporize and ionize matter from the planet or moon.

Use a particle accelerator to accelerate both the positive and negative ions to near the speed of light and point them into space.

Be careful not to point the matter streams at Earth, as that could ruin somebody's whole day.

StuRat 08:48, 4 December 2006 (UTC)

The question of how much nuclear power was needed to move the Moon was asked before, and I don't remember the answer, but it was ridiculously much. You could also have a glance at Space: 1999#Scientific inaccuracy. A central issue here is mass. The Moon weighs 73 500 000 000 000 000 000 000 kg. You'd need the same amount of StuRat's ions or Clarityfriend's gas (no pun) to cause it to start moving at the same speed at which the gas (or whatever) is expulsed. One trillionth of that mass (which would still be a huge amount) would only make it move at one trillionth of that speed. Ions have the advantage of moving very fast, but still. (Can someone do the actual calculations?)

A better method might be to use the butterfly effect. A slight change in one place can have enormous effects elsewhere. If we were to have a better understanding of this, we could nudge one meteorite and then wait until (decades later?) the desired effect takes place. It might drag some other meteorites along towards Mars, causing that to move to align with other planets to make the Moon's orbit unstable through tidal forces. Something like that. There are two problems here. One is that we'd have to make considerable changes to the solar system and that would undoubtedly have loads of other effects. A more fundamental problem is that for any such great effect on something so near we'd have to make sure the calculations are impeccable, so the effects won't throw the Earth (too far) off balance. But because we're talking about small cuases with great effects, the slightest error or lack of precision could have results that are totally different from what we envisioned. So no help here either, sorry. :)

DirkvdM 09:21, 4 December 2006 (UTC)

If I use simple Newtonian calcs, assuming all one-trillionth of the matter is expelled at the speed of light all at the same time, I get that the Moon would move 1 km every 38.6 days or about 10 km per year. The actual numbers would be just a bit lower taking relativity and such into account. This is a bit slow, so perhaps a billionth of the Moon would need to be expelled at c, instead. StuRat 12:58, 4 December 2006 (UTC)

[edit] Born with No Brain

A family member of one of my co-workers just recently had a child with a (genetic?) deformity that I'd never heard of and didn't think was possible... The baby was actually born without a brain. The baby was fully formed but has only fluid where the gray matter should be. Does anybody have an idea of the medical term for this condition, because I'd like to read more about it. TIA

Anencephaly is one condition. Might be different ones. --Tbeatty 17:53, 3 December 2006 (UTC)

Hydrocephalus sounds likely, especially considering the excess fluid you mentioned. --David Iberri (talk) 19:16, 3 December 2006 (UTC)

Anencephaly is correct. A synonym is hydranencephaly. Milder forms are part of the holoprosencephaly spectrum. Hydrocephalus is something different and much less severe and quite treatable if diagnosed early. alteripse 01:07, 4 December 2006 (UTC)

Of course I could be wrong, but it seems to me that both anencephaly and hydrocephalus are compatible with the inquirer's description as being born without a brain. Hydrocephalus seems more likely as the inquirer noted that the baby was fully formed, which is distinct from the clinical picture of an individual born with anencephaly (eg, partial/complete absence of the calvaria). Also, a layperson's description of a child "born without a brain" is often misleading. Several (many?) articles written by laypeople refer to patients with hydrocephalus as "living without a brain", for example. I'm probably missing something, so I'm curious as to how you arrived at the conclusion of anencephaly with such apparent certainty. Cheers, David Iberri (talk) 02:21, 4 December 2006 (UTC)

Go back to those "lay articles" using that phrase and I'll bet that they actually describe anencephaly or severe holoprosencephaly. The conditions are very different from hydrocephaly and I do not think I have ever heard of hydrocephaly described as "having no brain". You can't have hydrocephaly without a brain. Although many years of unshunted hydrocephaly will thin the cortex to very little, that condition is not congenital. alteripse 03:32, 5 December 2006 (UTC)

I did go back to those articles and you're right, they weren't describing congenital conditions; they were describing cases of prolonged, poorly treated or untreated hydrocephalus that resulted in thinning of the cortex to the point that very little brain tissue remained. Good call; I knew I was probably missing something. :-) --David Iberri (talk) 22:37, 5 December 2006 (UTC)

I've never heard of hydrocephalus as a condition described as not having a brain. Shunts are pretty standard these days and it simply drains cerbral spinal fluid into the stomach. The brain produces a large amount of this fluid (like a pint a day) and it needs to drain out of the brain or swelling will occur. I guess this could impair brain development in a fetus. Ananencephaly is fatal so the obvious next question is whether the baby is alive. I had not heard of holoprosencephaly but this is probably the correct answer as it is not as serious or common as anencephaly and fits the "missing brain" description. --Tbeatty 03:27, 4 December 2006 (UTC)

No brain would mean no life, right? So either there is some brain to keep the body alive or the unborn child will die at some point. If this is true (I'm not sure) that raises a very interresting philosophical question. Does this mean that the moment the unborn child dies is the moment it would have become alive? An obvious pracitcal consequence of this would be that abortion before that moment would not constitute murder, as some claim it does. DirkvdM 09:33, 4 December 2006 (UTC)

Brainless birth? I doubt that would be possibe per Dirk. However, if it had a very small or underdeveloped brain, it would be alive, just probably physically impaired. I personally think I could name a few brainless people I know, though. :-) | AndonicO ^{Talk | Sign Here} 16:41, 5 December 2006 (UTC)

[edit] Volcanoes

Why are volcanoes shapes and sizes different?

Different kinds of lava (magma) produce different kinds of mountains. Also sometimes the amount of gas released can catastrophically redesign a volcano. Rmhermen 19:34, 3 December 2006 (UTC)

A "perfect" volcano is conical. However, a portion of the cone can be blown out during an eruption, or smaller cones can form that distort the shape of the main cone. StuRat 08:37, 4 December 2006 (UTC)

And different volcanoes are formed differently. Volcanoes on a fault line can form by two plates in a collission that push up the ground, but volcanoes can also form when magma bursts through the earth's crust in a weak spot. Both form different volcanoes. -Mgm|^(talk) 09:12, 4 December 2006 (UTC)

Is that first case actually called a volcano ? StuRat 12:47, 4 December 2006 (UTC)

Volcano#Shape might help answer your question. Otherwise, as the others have said, different types of lava (runny vs thick) along with various other variables. Skittle 15:18, 4 December 2006 (UTC)

[edit] Router vs. Switch in home networking

Can someone explain the difference between a router and a switch in a home networking environment? (Switch is the new, smarter/faster version of the old Ethernet hub, right?) AFAIK, a router is for sharing the internet connection that comes into your house to mutiple outlets (the equivalent of a cable tv splitter). Is a switch is for sharing the network inside your house? (Like you only had one Ethernet jack in your basement, but you wanted to connect more than one device) Lastly, a router can also be a swtich, but a switch can't be used as a router? And where does a gateway fit into all this?

A recent trip to Best Buy had me very confused. Almost every product box seemed to be marketed at people who already knew what each device did, not explaining what each product did. --68.103.154.140 19:39, 3 December 2006 (UTC)

Radia Perlman, one of the world's leading experts on networking, says a switch is "a marketing term that means fast :) Technically a hub is an ethernet-level interconnection, a switch is a smart hub with clever dedicated paths, and a router is an IP level interconnection. And the things that are generally sold as "routers" in the home marget are more than that - they have NAT, firewalls, and frequently an ADSL "modem" too. The distinction between switches and routers is still meaningful in a corporate infrastructure environment (where a cisco switch and a cisco router are very different beasts) but for the home market you just look at the ports on the back of the thing and see if it interconnects what you want. -- Finlay McWalter | Talk 19:53, 3 December 2006 (UTC)

And a gateway is just "a box that joins one network to another" (Gateway (telecommunications)). One of those Linksys/Netgear/Belkin boxes that has an ADSL modem and a bunch of ethernet ports is at once a firewall, a modem, a gateway, a router, a switch, a bridge, and a hub. -- Finlay McWalter | Talk 20:03, 3 December 2006 (UTC)

I work for a major bank's IT support, at a branch you have a pile of computers, tellers and ATMs connect to a switch, the switch connects to a router and the router connects to a gateway which in turn is connected to out WAN. At home, the gateway effectively is the socket in the wall, and the rest of the devices, plus more, are contained in one of those devices they call a 'router', like the above says. Vespine 03:37, 4 December 2006 (UTC)

A simple definition: A "switch" can redirect the entire bandwidth of the connection to each port. A hub shares the bandwidth. Therefore, each port on a 1 gigabit switch can utiize the full 1 gigabit bandwidth of each port. Switches replace hubs. A switch is used within a network. A router connects two or more networks together using rules. For typical home networking, the rules are pretty simple. Forward all non-192.168 traffic to the internet and do not forward the local traffic. A router uses name address translation to repackage non-local traffic with routers IP. A router is what connects your cable modem or DSL link (i.e. the ISP network) to your home network. Harware firewalls are implemented in a router. A switch is used to connect all your local computers to form a network. Router, Switch and DHCP are all three separate that are sometimes implemented in single device. I believe terms like "gateway" is more of a description of the routing rules rather than a differnt piece of hardware. Just as "firewall" is a description of the routing rules. Tbeatty 03:50, 4 December 2006 (UTC)

BTW, this question belongs on the Computer Ref Desk. StuRat 08:35, 4 December 2006 (UTC)

[edit] If I took HRT

I am an 18 year old boy and wondered what would happen if I took my menopausal mother's HRT tablets? Like. how many and how often would I have to take them to notice anyt differences and what would they be and how long would they last after me ceasing taking the medication- All of this is just hypothetical of course.

Take a look at this article and Hormone replacement therapy (trans). --JWSchmidt 03:37, 4 December 2006 (UTC)

[edit] gerbil behaviour

over the last few weeks my gerbils have become exceedingly fat and have also started mounting each other even though they are all female. i was wondering if you know why.

thanks —The preceding unsigned comment was added by 81.158.81.209 (talk • contribs).

Have they been watching Oprah? Seriously, though, how much do you feed them? If they're fat, then you're either overfeeding them or they have some sort of metabolic disorder. --Wo o ty Woot? contribs 22:26, 3 December 2006 (UTC)

I suggest looking into what gerbils and their relatives (rats, mice, hamsters, guinea pigs, degus) eat in the wild, and doing your best to mimic that. Also, let them run free around the house as much as is practically possible. At bare minimum, consider shopping around for a high-quality (and of course more expensive) food supply. Situations where you do not get what you pay for are the exception rather than the rule. Theavatar3 00:58, 4 December 2006 (UTC)

Are you sure they're all female?? Maybe you should recheck. ;) Vespine 03:28, 4 December 2006 (UTC)

Letting them run around the house isn't advisable, as the may get lost, or at the very least, pee and poop on your carpet. I suggest an exercise wheel, instead. StuRat 08:31, 4 December 2006 (UTC)

thanks for all that but whenever i buy them an excercise wheel or anything else plastic they chew it to pieces within the first couple of weeks. i agree with you though saying its a bad idea letting them out. also i have been feeding them exactly the same for a year or so and nothing like this has ever happened. and yes im sure they're all female.

Excercise wheels must be made of metal or, yes, they become chew toys. Running on the exercise wheel is also a learned behavior. If this particular set of gerbils has never done that, then they may not ever use the wheel. (We had one generation of gerbils that didn't know how to use their wheel.)

I've also noticed that, pregnancy aside, rapid weight gain in older gerbils may be a sign that the end is near; several of our gerbils "got fatter" near the end of their life, although I'd actually bet it was water retention or some other disorder.

Finally, depending on your household environment, your tolerance for mess, and your willingness to walk carefully, you can actually "free range" your gerbils if you wish. For one of our generations of gerbils, when all but one of them had died off, we let the sole survivor roam freely around the house. We put food and water out consistently much as we would for a cat or dog, she established several places as her toilet, and she lived very happily for a number of months. Her favorite place was somewhere in the mechanical guts of the refrigerator in the kitchen (because of the constant warmth); it's a wonder, though, that she didn't chop her little rodent head off with the condenser's cooling fan, though). What finally did her in was she found a sneaky way into an air conditioning duct and ended up trapped down in the area near the AC's heat exchanger. Her demise was aided by the fact that we got used to not necessarily seeing her for a day or two at a time so it wasn't immediately obvious she had gone missing.

Atlant 14:08, 4 December 2006 (UTC)

Your not exactly selling the free range thing. Let's see, the gerbil will crap and piss all over the floor, then die a horrible death and quite possible smell up the entire house because you don't know where they did themselves in. Sounds like a really bad idea to me. I do agree with the metal wheel idea, though. If they don't figure it out after a few days, you might want to put the gerbil on the wheel and rotate it slowly until they get the idea. StuRat 14:48, 4 December 2006 (UTC)

Actually, the gerbil was quite restrained in the locations she used as a toilet and it was no problem to clean up after her. Gerbils tend not to foul their nests and so she chose a tiled-floor closet as her principal toilet; easy to clean-up after. And as I mentioned, this gerbil was nearing the end of its life anyway. It had always been our "tough gerbil"; somewhere in her early life, long before her "free range" days, she had managed to lose a part of her tail (so her name was "Short Tail). You can actually see two pictures of her during her free-range days here, although the cutest picture (of her standing atop a nice, warm Sony Vaio power adapter) isn't there right now.

Atlant 15:55, 4 December 2006 (UTC)

OK, all I can say is, if that qualifies as cleanliness for you, I will be sure to only crap on tile floors when I come over for a visit. :-) StuRat 19:58, 4 December 2006 (UTC)

As long as your excrement is the size, quantity, and character of gerbil doots...

Atlant 17:18, 5 December 2006 (UTC)

If you're buying a wheel, whatever it's made of, remember that gerbils can break their legs in the ones that are like ladder rungs; you're better off getting a solid one. Also, a nice half-way between free-range and stuck in a cage is an exercise ball. You know, those clear plastic balls you put the gerbil in, then let it run around a room. Of course, unlike free-ranging, you have to watch out for stairs, but on the other hand you don't have to block off all possible gaps a gerbil could creep through. As for them mounting each other, my gerbils used to do that too. I imagine it's a combination of urges with no other output, and dominating behaviour to assert their social position, but I don't really know. Skittle 15:14, 4 December 2006 (UTC)

Well, if I were a gerbil, I would rather be given a quick death than be kept in a little metal cage without reprieve. I feel it to be in error to suppose that because they are small, and don't speak any human languages, that they wouldn't regard life in a cage as being a cruel existential nightmare, as we would.

Also note that I suggested letting them roam free as much as practically possible. If you have no ability or interest in supervising them, of course this amount of time will be zero. Theavatar3 17:24, 4 December 2006 (UTC)

I would like to let them out but since we also have one dog 3 cats and various other animals i think that's hardly possible. it happened by accident when the cage was knocked off and it took us ages to find them. the exercise wheel might be a no because none of them have used one before. thanks to everyone for their answers aswell

I once witnessed an incident where three unloved degus were let out of their cage, in a room containing two cats perfectly capable of killing them. They were not at all interested in such. The elder cat simply batted one contemptuously across the concrete floor. Animals are not nearly as wicked and bloodthirsty as we suppose them to be. That said, if your larger animals are at all jumpy, I guess you're stuck with obese lesbian gerbils.Theavatar3 05:11, 5 December 2006 (UTC)

"Obese lesbian gerbils" ? Sounds like a good name for a band. StuRat 08:49, 5 December 2006 (UTC)

Well, if I were a gerbil, I would rather be given a quick death than be kept in a little metal cage without reprieve.

Once the last of her cagemates had died, we thought that Short Tail would feel the same way. And up to her end, she seemed to thrive and enjoy her time out of the cage.

Atlant 13:58, 5 December 2006 (UTC)

I suppose that if one has a great love for tiny critters, it is very easy to suppose that because they are so small, and have such tiny brains, that they wouldn't notice that they're even in a cage.

When I had a hamster, most of his waking energies were put towards climbing up the walls of his little metal cage, and trying to work his way out the top -- never with any success.

Oh yes -- to the original poster -- are your gerbils kept in a metal or plastic cage? Metal bars will mean the interior will have a massively-better air supply, and they may be more inclined to run on their wheels, and lose weight. Theavatar3 16:45, 5 December 2006 (UTC)

well the bottom half is opaque plastic and the top half is clear plastic with metal covered in plastic bars for the roof.

If it were me, I would think about going near a mall where they might have a pet store where they might sell metal cages for a price that I won't have to sell tooo much blood to obtain, sometime in the next seven cycles. But, what do I know... Theavatar3 23:20, 5 December 2006 (UTC)

well the last time we got a metal cage it fell off and smashed so thats why we bought a plastic one

[edit] the power of water currents depending on depth

I was wondering if anyone knew if the power of a water current changed depending on the depth of the water. also, which depth has the greatest amount of force.

thank you —The preceding unsigned comment was added by 142.68.205.18 (talk • contribs).

When you say power, you mean velocity, right?--Light current 23:08, 3 December 2006 (UTC)

The velocity of water currents do vary by depth, but not in any consistent way. In some locations, the surface currents are the fastest, while in others, the underwater currents are stronger. The directions of the current also may vary by depth. StuRat 08:29, 4 December 2006 (UTC)

I would tend to agree, although I dont have any evidence. Upper atmosphere winds can also have markedly different velocites cf surface winds. See Jet stream Hmm and Rossby waves for the oceans(although these latter appear to be a surface phenomenon)--Light current 14:52, 4 December 2006 (UTC)

Some evidence could be found under the Gulf Stream article, since that is a "river" of high velocity within the Atlantic Ocean, at varying depths, rather similar to the Jet Stream, in the air. One difference, however, is that the Gulf Stream is more stable, while the Jet Stream is constantly changing location, direction, and intensity. StuRat 18:07, 4 December 2006 (UTC)

[edit] The Playstation 3

Im from the UK and was wondering about the Playstation 3. I know it sounds complex but how does the whole system work? What goes on when you turn it on inside the machine and how does it know what to do? I suppose this applies to all computer and technical innovations, but because the PS3 employs new technology I just wondered what happened, so could anybody enlighten me? —The preceding unsigned comment was added by 82.36.182.217 (talk • contribs).

The description of how a computer (for that's what a PS3 is) starts up is described at Booting. The specifics vary for different machines, but the basics are the same. -- Finlay McWalter | Talk 21:20, 3 December 2006 (UTC)

All computers (and game consoles) boil down to logic gates. These simply take two inputs and produce an output. For instance an OR gate looks at two binary input values, where a 'one' means a signal is received, and a zero means no signal is detected, and if either of the inputs is one, the output will also be a one. An AND gate only produces a 'one' output only if both inputs are one. You can build an entire computer using only one type of gate, by combining a few gates to emulate the behaviour of other gates.

When you put enough gates together, you may get a machine that can perform useful (or entertaining) functions. The more gates you can pack into a given area, the more potential power a computer has. This is the domain of the scientist/engineer. The real art of computing lies in combining gates in sophisticated ways that will provide sophisticated outputs, such as dynamic video and audio displays that make you think you're fighting in World War II. Some of this artfulness is applied at the hardware level, providing general routines that can be used by a wide variety of applications (i.e. software, games), but most is done by software (or game) developers.

Funny also that the leading figure in computing has the surname of Gates.Theavatar3 01:23, 4 December 2006 (UTC)

I think he was looking for more abstraction than that o_o Basically when you turn it on, some boot code is loaded from read-only-memory on the CPU or mainboard. This code initializes all of the components and then devices on a computer (this is called POST). At this point code in the ROM looks for a boot partition (on a hard drive, or a CD, or a thumbdrive, or the network- in the case of the ps3 it may be some different flash ROM), loads the data from that partition into memory, and executes the code there, usually a bootloader (like windows's NT bootloader). At this point the operating system takes over, applies whatever arbitrary levels of abstraction it wants to the BIOS (basic input/output system) and might sync system peripherals. --⁪froth^{T C} 05:44, 4 December 2006 (UTC)

Thank you very much for your help, so what is the Blu-ray thingy it has in it. What's so special about it and why is it causing 'em so much hassle?

CD-ROM, DVD, Blu-Ray. It's the next step up in packing lots of data onto your standard disc. It's one of two technologies though, and I've heard that the alternative is actually better. My feeling is that any enterprise that uses the word 'blu' may not be so clever. Theavatar3 05:26, 5 December 2006 (UTC)

[edit] Mass/Force Distribution

What is the force exterted on the wall and ground by an object leaning statically against a wall? For example, a ladder leaning against the side of a house. And, how are the force/mass on the wall, the force/mass on the ground, and the angle θ that the object makes with the ground related? --AstoVidatu 22:45, 3 December 2006 (UTC)

If the ladder is slippy against the wall, then it can exert no downward force on the wall. It can however extert an horizontal force. THe value of this force can be solved by taking moments about the base of the ladder and using the wieght (W) of the ladder. 8-)--Light current 23:12, 3 December 2006 (UTC)

[edit] telescopes

i was thinking of getting into amateur astronomy but was looking round for a telescope but i was wondering if any1 knew the best places to look and what would be a good size for an complete amateurs first telescope (budget £100 ish) and if any1 knew any "good" shops. i did google and looked at some places but i'm a little wary of places advertising specs that sound good but mean absolutely nothing.--Colsmeghead 23:57, 3 December 2006 (UTC)

Avoid any product that advertises magnification. Aperture is everything and amateur astronomers know it so reputable/good scopes sell by the inch or cm of aperture. Some purists recommend against computerized scopes as it takes away from the art of star hopping and celestial navigation but I think it adds to the enjoyment. You can always turn it off but if you don't have it, you can't turn it on. --Tbeatty 00:02, 4 December 2006 (UTC)

I always remember Patrick Moore advising a reflecting telescope with at least 3" diameter. THese are cheaper than the equivalent size refractrors.--Light current 00:05, 4 December 2006 (UTC)

Yes, per aperture, reflecting telescopes are cheaper espeically in the larger aptertures. Refractors have lower distortion but not enough to be noticed by beginners. Interestingly, some reflectors such as Schmidt-Cassegrain fold the light more than once (as oppose to Newtonian reflectors). This is to reduce the moment arm of force when attaching cameras and other accessories. I wouldn't recommend a refractor unless you know what an apochromatic telelscope is and can appreciate it. I wouldn't buy one because I am not that picky. Consider that a 5" apochromatic refractor can cost as much as a 16" Schmidt Cassegrain ($16,000 last time I checked) and a 125mm (5") f/10 schmidt-cassegrain reflector can be had for a hundred quid in the U.S. (your VAT and shipping cost may vary). --Tbeatty 00:20, 4 December 2006 (UTC)

There are many good 'buying guides' on the internet and lots of message boards, I'm a member of www.iceinspace.com.au, it's an Australian board, but there is a lot of universal information on there. I ended up buying a nice dobsonian which is a kind of newtonian reflector and I am very very happy with it. If anything, i would recommend looking up your local astronomical society and trying to get out to one of their 'open nights' to try out some of their scopes before you commit. A big thing to rememebr is the stars aren't going anywhere, I eneded up waiting and saving up a bit more, now I have a really nice piece of kit and it will still have resale value if I ever decide to off load it. Vespine 03:11, 4 December 2006 (UTC)

And for clarification, a Dobsonian telescope has a cannon-like mount, rather than a more expensive tripod-like one. Dobs are a nice idea as they offer large apertures at a decent price. The larger ones are pretty difficult to move around, though. Schmidt-Cassegrain telescopes are more compact reflectors, but the size comes at a premium, and their added complexity often results in lowered image quality, especially amongst the lower end. -- Consumed Crustacean (talk) 08:04, 4 December 2006 (UTC)

Is that 16 thousand or 16 ten-thousand? --⁪froth^{T C} 05:46, 4 December 2006 (UTC)

Oops 16k. fixed.--Tbeatty 07:52, 4 December 2006 (UTC)

I`d like to add this Cols...This might not be important to you, or what the other fine folks here have mentioned but, to me at least, it depends on what YOU want to observe. If you are mainly interested in observing 'static' things, such as other galaxies and stuff, (i.e. far distant 'objects') then SIZE might be what you want. If you`re more interested in things/objects that MOVE, such as the Planets in our solar system, or the Moon, for instance, then I`d aim more towards the smaller, even though more expensive per inch of aperture, refractors. They offer a more detailed/sharper image, and are far easier to carry around than the 'big' ones. Remember this: You get far more use, and enjoyment, out of the `scope you USE the most. If you purchase a telescope that`s so large that it`ll end-up only gathering dust in your basement, or attic, then all your efforts will be wasted. What you intend on spending could surely affect your decision too. I hope this helps somewhat in your final decision...please consider them. Dave172.135.3.189 02:39, 5 December 2006 (UTC)

Retrieved from "http://en.wikipedia.org../../../r/e/f/Wikipedia%7EReference_desk_Archives_Science_2006_December_3_360a.html"

Category: Reference Desk Archives