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January 8

unknown disorder

Hi there, can a psychologist or a scientist figure out what type of problem I have? (remainder of question removed)

This question has been removed. Per the reference desk guidelines, the reference desk is not an appropriate place to request medical, legal or other professional advice, including any kind of medical diagnosis, prognosis, or treatment recommendations.

I'm afraid that we can't diagnose you here. You should speak to a parent, guardian, doctor, or other person whom you trust about any concerns that you have over your mental or physical health. TenOfAllTrades(talk) 18:18, 8 January 2008 (UTC)[reply]

Cells

Plant cells have cell walls but animals cells do not. Why do animal cells not have cell walls?--Stylin99 (talk) 02:10, 8 January 2008 (UTC)[reply]

See Cell Wall. From this article and some intuition, it seems that differing evolutionary niches that plants and animals inhabit make their differing cell membrane structure advantageous to each group. Plants are generally stationary, whereas animals generally move around. Therefore a cell wall that provides rigidity and stiff structure to an organism is advantageous for plants which must stay in one place and endure stresses. A rigid cell wall structure is not advantageous for animals however, since they generally must move around rapidly to avoid stresses. -Bmk (talk) 02:21, 8 January 2008 (UTC)[reply]

Cells (2)

What is the function of cell membrane?--Stylin99 (talk) 02:27, 8 January 2008 (UTC)[reply]

See cell membrane and in the future, typing your terms in the search box at the top left will save you time. ----Seans Potato Business 03:01, 8 January 2008 (UTC)[reply]

Annihilation - energy of photons from electron-positron interaction

Some lady says that a positron and an electron annihilating each other yields two 511 keV photons, but surely the energy that the electron and positron had at the time of interaction also comes into play? (even if it's negligible, that should be stated rather than pretending it doesn't exist) ----Seans Potato Business 03:00, 8 January 2008 (UTC)[reply]

We have an article called Electron-positron annihilation. See the "high energy state" section. Depending on the context, it may have been proper for her to leave out. What happened? Black Carrot (talk) 03:09, 8 January 2008 (UTC)[reply]

Rail Guns

From what I can understand the main problem with rail guns is the damage done to the rails upon firing. What I want to know is there any reason stopping a system or device that could in essence "reload" the rails every couple of shots? Thanks DTWATKINS (talk) 04:22, 8 January 2008 (UTC)[reply]

Nothing but time and space. Rails are big, so if you need to swap them after every two or three shots, you can't fire for very long. Frequent swapping also means you can't keep up a constant rate of fire: if you need to fire four shots to take down four incoming missiles, but the rails wear out after three, you might not get the new set of rails ready in time to hit the fourth. For long-range artillery, where you can have a machine shop next to the gun to re-surface the rails, it might not be a problem, but for anything else, it is. --67.185.172.158 (talk) 10:07, 8 January 2008 (UTC)[reply]

I assume the questioner is referring to railguns, rather than railway guns ?Gandalf61 (talk) 10:57, 8 January 2008 (UTC)[reply]

If you're willing to give up more space, time won't be a problem. If you need more than three shots to take down incoming missiles, shoot them from more than one gun. That's what they did with the M72 LAW (though I don't think that's why). — Daniel 23:25, 8 January 2008 (UTC)[reply]

Carbon black

I've noticed that soot is a super excellent water repellent. In a survival situation and except for mistaking it for mold would there be any problem with using carbon black to waterproof clothing? 71.100.12.59 (talk) 06:10, 8 January 2008 (UTC)[reply]

The way it blackens anything it touches would seem to be a problem. You could coat it with something, like plastic, to prevent this, but then you would be using the water resistance of the plastic, not the carbon, so why include the carbon at all ? StuRat (talk) 22:51, 8 January 2008 (UTC)[reply]

In a survival situation you might be able to produce soot whereas not plastic. However, the though occurred to me as to whether their is already carbon fiber clothing? 71.100.12.59 (talk) 17:53, 10 January 2008 (UTC)[reply]

Square-cube laws

The size of ground vehicles such as tanks is limited by a square-cube law: the mass of the vehicle increases as the cube of the size, while the available ground area for supporting the vehicle only increases as the square of the size. Is there a similar square-cube limit on the size of ships? --67.185.172.158 (talk) 10:01, 8 January 2008 (UTC)[reply]

Well, bouyancy obeys a cube law, so I imagine the expected answer is "no". However, I would query the premise of the question - I don't think the size of ground vehicles is limited by a square-cube law. If you spread your load out and stick to prepared tracks/highways, you can get very massive land vehicles indeed. The crawler-transporter carries the 2,000 tonne Space Shuttle, and the longest freight trains can be tens of thousands of tonnes. I think the limiting factors on tank size are manoeuverability and speed. Gandalf61 (talk) 10:49, 8 January 2008 (UTC)[reply]

The square-cube limit is quite evident in ground vehicles if you're comparing like to like. For example, look at the tread areas of German tanks of World War II: the Panzer I has skinny tracks, while the Maus has treads 55% of the width of the tank. The crawler-transporter might be able to carry the Space Shuttle without problem, but if you scale it up to carry an 8,000,000-ton "Super Orion" spaceship, it'll sink into that prepared surface. --67.185.172.158 (talk) 11:23, 8 January 2008 (UTC)[reply]

But to design larger vehicles you don't just blindly scale up - you add extra tracks, extra axles etc. Germany had plans for tanks at least five times bigger than the Maus, such as the Landkreuzer P. 1000 Ratte. You can design and build very massive land vehicles - the Bagger 288 tips the scales at 13,500 tonnes, but it can travel across country (very slowly). It's the low speed and manoeuverability that makes massive land vehicles unsuitable for most applications, not a square-cube law limitation. And something as massive as Super Orion would obviously be built in orbit. Gandalf61 (talk) 11:57, 8 January 2008 (UTC)[reply]

Ships can basically be built as large as skyscrapers, although for balance purposes it is best to build them horizontally rather than vertically. In fact, ships today are built as long as skyscrapers. As long as it floats (which is determined by displacement - see the link provided by Gandalf61), then all you have to worry about is structural integrity. Besides, it is not a given that the mass of a ship will cube as the square of the increase in dimensions. Think of it this way - the Square-cube law tells us that the volume cubes as the dimensions square. Note that it says "volume" and not "mass". The mass will increase as the cube of the size increase IF the density of the object remains the same. In other words, if you cram in the same mass per cubic meter as in the smaller version, then the density remains the same and the mass will obey the square-cube law. If you have less mass per cubic meter in the larger object (more height between decks, larger open spaces, etc.) then the density will decrease and the mass will not cube as you would expect. The square-cube law is a handy device for calculating things under certain circumstances. For the example of ships, it would depend. If you use the added space to fit in additional decks and keep room sizes the same (keeping density the same), then the mass of the ship will obey the square-cube law for the most part. However, for a cargo ship, you might want to keep the same number of decks but make each one taller and roomier. If you want to get picky, you could account for the stronger supports needed to support the extra floors (or extra cargo, in the case of a cargo ship). Those stronger supports would add more mass than we would have expected from a straightforward application of the formula. In general, though, if the density of decks remains the same then the square-cube law applies. If the larger version has the same number of decks, but greater room size / ceiling height (i.e. it is roomier), then the density decreased from the small version to the larger, and the square-cube law won't give the right numbers. SWAdair | Talk 11:14, 8 January 2008 (UTC)[reply]

SEARCHING FOR FREE E-BOOKS BASED ON SUBJECT CALLED SYSTEM DYNAMICS

SIR/MADAM, I WAS LIOOKING FOR GUDANCE TO FIND RELATED MATERIALBASED ON SYSTEM DYNAMICS I WAS SPECIFICALLY SEARCHING FOR FREE E-BOOKS BASED ON SUBJECT CALLED SYSTEM DYNAMICS —Preceding unsigned comment added by 202.70.201.120 (talk) 14:52, 8 January 2008 (UTC)[reply]

I don't know about e-books in particular but you could start at System dynamics.Bellum et Pax (talk) 19:28, 8 January 2008 (UTC)okay but please suggest some useful link on related material for freshers[reply]

FUEL CHARACTERISTIC STUDY RELATED E-BOOKS ALTERNATE RESOURCES

SIR/MADAM, I WAS LIOOKING FOR GUDANCE TO FIND RELATED MATERIALBASED ON FUEL CHARACTERISTIC STUDY I WAS SPECIFICALLY SEARCHING FOR FREE E-BOOKS BASED ON SUBJECT OF FUEL CHARACTERISTIC STUDY —Preceding unsigned comment added by 202.70.201.120 (talk) 14:56, 8 January 2008 (UTC)[reply]

water vapor and global warming

A biochemist friend of mine who does not "believe" in global warming told me that carbon dioxide in the atmosphere is measured in parts per million, while water vapor is a few percent, and that water vapor is a far more potent greenhouse gas. Is this true?

Also, what research, if any, is being conducted on water vapor as a factor in global warming? Are any technological interventions proposed or even imagined? --Halcatalyst (talk) 19:12, 8 January 2008 (UTC)[reply]

Some of the stuff in Greenhouse gas may help. Yes, everyone knows that water vapor is the biggest one. Friday (talk) 19:19, 8 January 2008 (UTC)[reply]

The use of the phrase "everyone knows" is just begging for a ^[who?] tag, per WP:WEASEL. Although it is factually correct, you might want to rephrase it. Nimur (talk) 23:18, 9 January 2008 (UTC)[reply]

Also see Talk:Global_warming/FAQ#Water_vapour_is_the_most_important_greenhouse_gas.21. Water vapor is a significant greenhouse gas, but it is not a climate driver, but rather a feedback. Water vapor is in dynamic equilibrium - the average relative humidity is essentially constant and the absolute humidity thus depends on the temperature. As it gets colder, more water is removed via precipation, and as it gets warmer, more water is added via evaporation from the many terrestrial sources (from oceans to soil moisture). --Stephan Schulz (talk) 19:31, 8 January 2008 (UTC)[reply]

Isn't that positive feed back? Hotter -> More water vapour -> More green house effect -> hotter climate -> ... Water vapour do form clouds though, which are very good reflectors, reflecting the son's energy away. --antilived^{T | C | G} 04:51, 9 January 2008 (UTC)[reply]

It is indeed a positive feedback. It's balanced by other feedbacks (e.g. the t^4 blackbody law) and the fact that the reaction to greenhouse gases is, in general, logarithmic, not linear (i.e. the second-order increase is smaller than the first-order increase, and so on) so it does not lead to a runaway effect. Water vapor does not form clouds - clouds consist of water droplets and/or ice crystals, not water in gaseous form. Clouds are a very complex feedback - they can both warm and cool (clouds at night stop energy loss via radiation, most clouds at day increase albedo). --Stephan Schulz (talk) 23:25, 9 January 2008 (UTC)[reply]

CO₂ may be measured in the parts per million, but this NASA web page suggests it's at least a few hundred to a thousand PPM. But we should note it also confirms his observation of a few percentage points for H₂0. Root⁴(one) 04:36, 10 January 2008 (UTC)[reply]

Size of Earth

Earth is within the life zone of the solar system but has anyone determined the range of Earth's diameter before life on Earth would no longer be possible or would drastically change? 71.100.12.59 (talk) 21:20, 8 January 2008 (UTC)[reply]

I'm unclear what exactly you're asking.. You mean, if the earth were to grow somehow, how big would it need to be to mess up life as we know it? How would you envision the earth growing? Or did you mean to say the sun? Stars expand physically - see Stellar evolution for the lifecycle of stars. We also have Formation and evolution of the Solar System. I'm not aware of any normal process by which a planet would grow after it was formed. The extra matter would have to come from somewhere- it might possibly kill us all by falling on us, long before the size of the planet became a concern. Friday (talk) 21:29, 8 January 2008 (UTC)[reply]

For that matter, diameter isn't even the primary size consideration -- altering the surface gravity would have significantly more effect. See the discussion about square-cube law above. — Lomn 21:54, 8 January 2008 (UTC)[reply]

I'd say a huge range of gravitational forces could support life of some type, from zero gravity to maybe 100g (which is far more than any planet has in our solar system). On the high end of gravitational forces life might be limited to something like moss on land, although oceans could support the weight of more complex creatures. However, secondary effects of low gravity (like no water or atmosphere) or high gravity (high temperatures and violent storms) might make life impossible at those extremes. StuRat (talk) 22:16, 8 January 2008 (UTC)[reply]

So then you are saying gravity and not size is the significant key like watts per square meter versus distance from a sun would be the significant consideration for solar body orbital life zone. So that understood is there a chart that relates amount of gravity to life? 71.100.12.59 (talk) 22:37, 8 January 2008 (UTC)[reply]

Not really, because such a chart would have exactly one data point on it. (Well, maybe more of a "smear" to cover the range of gravity from the extent of the atmosphere to the bottom of the ocean). Life on Earth has evolved to live on Earth, with Earth's gravity. The best we can do is, like StuRat, make educated guesses about what levels of gravity might support life, based on our knowledge of terrestrial life-forms, but that is a heavily biased sample. Still, to paraphrase The Science of Discworld, "life lives everywhere it can, and it lives everywhere it can't", so I agree with StuRat's hypothesis that it would be possible for life to evolve in extremely high and low gravitational fields, but the types of life the two would support would be immensely different. Confusing Manifestation(Say hi!) 23:16, 8 January 2008 (UTC)[reply]

Did you meant the range of Earth's orbit instead of range of Earth's diameter? It's not really the distance that matters but how much heat we get from the Sun. Life as we know it requires water so the distance of the planet to the star must be such that there will be water in liquid form. NYCDA (talk) 23:28, 8 January 2008 (UTC)[reply]

...read above.

Here is a new result from the AAS meeting concerning the size of rocky planets, their plate tectonics, and implications for life. -- Coneslayer (talk) 16:34, 9 January 2008 (UTC)[reply]

Without going into the size/gravity relationship again, a planet with roughly less than 0.5 g would tend to lose its atmosphere, making Life As We Know It impossible. --M@rēino 17:07, 10 January 2008 (UTC)[reply]
- Okay, that's more or less the kind of thing I'm getting at... 0.5 g - no atmosphere to support human life and with an inability to retain water vapor and thus any phase of water would probably not be able to support any other life form as well.

Is ash carbon?

I want to have a little science 'expirement' on the 4th of July, a.k.a. I'm going to make a little gunpowder. So my question is: Is the ash in your fireplace carbon? If it isn't: Is there any other carbon you can find in your house? (Besides charcoal) Parapsycologist (talk) 22:35, 8 January 2008 (UTC)[reply]

Ash is ~~mostly~~ only slightly carbon, with many ~~few~~ other minerals mixed in. The composition will depend on what you burned and how hot it burned. Graphite in pencil "leads" is also carbon. You can buy them for mechanical pencils cheaply at many stores. StuRat (talk) 23:00, 8 January 2008 (UTC)[reply]

Hmm. wouldnt the carbon burn?--TreeSmiler (talk) 01:20, 9 January 2008 (UTC)[reply]

I stand corrected, I didn't think all the carbon would burn in a normal fireplace, but apparently it burns more completely than I expected. StuRat (talk) 16:48, 9 January 2008 (UTC)[reply]

(edit conflict) (info conflict, too)Wood ash contains little carbon, which stands to reason when you think about what's happening when wood burns (see Fire). Here is a document that shows the composition of a typical wood ash on PDF page 9. I don't see what's wrong with charcoal, but the only other relatively pure carbon I'd expect to find in my house would be soot or graphite. --Milkbreath (talk) 23:09, 8 January 2008 (UTC)[reply]

Old-style, non-alkaline, non-lithium batteries contain a carbon rod as the anode. Or they did when I took a D-cell apart about 40 years ago. But buying pencil leads would be an easier source, since you don't have to deal with the chemical paste. Leads actually contain a mixture of carbon (graphite) and some other substance such as clay, with the mix adjusted to give the desired hardness.

Whatever you do, please do it safely, so that your experiment is not really an "expirement"!

--Anonymous, 23:35 UTC, January 8, 2008.

Fireplace ashes are the non-combustible residue of combustion. Better to use charcoal. Also need sulfur and saltpeter. (This may not end well).

How and why do these injuries occur? Experimentation: Homemade fireworks (for example, ones made of the powder from several firecrackers) can lead to dangerous explosions (CDC 2004). Linkage]. I know it's about fireworks but I feel that it's a good comparison. Ask yourself does the reward outweigh the risk? I can't imagine that in this case that it would. Lanfear's Bane | t 14:08, 9 January 2008 (UTC)[reply]

What's the difference between fireplace coals and firplace ashes?Parapsycologist (talk) 23:03, 11 January 2008 (UTC)[reply]

You ask what source for carbon except charcoal. The interior of a battery if you wash the ionic crude out of it is another source I've used. --BozMo talk 14:21, 9 January 2008 (UTC)[reply]

If using graphite I would suggest you choose the darkest pencil you can find. Something like 8B or 9B (see pencil). Coal is of course another source for carbon. Oh and finally to state the obvious, diamonds even if that's rather expensive and not an allotrope that you're likely to find of much use (I don't recommend you steal your mother's ring and try use the diamond from it, it won't work and she won't be happy) Nil Einne (talk) 17:35, 9 January 2008 (UTC)[reply]

This is all a tad bizarre, we are not allowed to give medical, legal or whatever advice and here's a whole lot of folks helping Parapsychologist to potentially injure himself. Can I be the first to nominate him for a Darwin Award. Richard Avery (talk) 20:23, 9 January 2008 (UTC)[reply]

Thanks (sarcastically) Parapsycologist (talk) 23:07, 11 January 2008 (UTC)[reply]

There are laws about unlicensed persons giving medical or legal advice. I'm not aware of any laws about unlicensed persons giving pyrotechnic advice. --Carnildo (talk) 23:06, 9 January 2008 (UTC)[reply]

Perhaps it's covered in the Patriot Act? Nimur (talk) 23:19, 9 January 2008 (UTC)[reply]

There is a difference I think between when someone says I want to do X, where can I get Y (where Y is a completely legal and innocous substance) and we say don't do X, but Y can be found from ... And when someone comes along and says I have problems A what could the cause be and we say well you should see a doctor but your problem may be ... In the first case we are simply providing information which may be of interest even if the OP isn't stupid enough to try something which may kill him/her and which realisticly is easy to find anyway. In the second case, you are basically offering a diagnosis which you are not qualified to do and which might negatively influence the person's decision to see a doctor. Nil Einne (talk) 06:09, 10 January 2008 (UTC)[reply]

I think The Anarchist Cookbook may have some useful advice for the OP - I really must dig my copy out. DuncanHill (talk) 04:15, 10 January 2008 (UTC)[reply]

The Anarchist Cookbook is a good way to blow your own ass off -- and at that, it's safer than most of the knockoffs floating around on the Internet. --Carnildo (talk) 00:05, 12 January 2008 (UTC)[reply]