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June 30

Complexity and Self-organization in Thermodynamics

Consider computer simulations of dissipative (open) thermodynamical systems. Some examples include Cellular Automata grids, fluid motion, and autocatalytic sets. Have replicating "units" ever been observed emerging within such simulations, even in very simple ones? What about the so-called, effective dissipaters of gradients? paros (talk) 04:24, 30 June 2008 (UTC)[reply]

Take a look at Conway's Game of Life if you haven't already done so. --Dr Dima (talk) 08:17, 30 June 2008 (UTC)[reply]

If you only need a system of cellular automata with self-replicating entities, John von Neumann discovered one more than 50 years ago. Icek (talk) 09:46, 30 June 2008 (UTC)[reply]

artifact

While looking in a plowed field I found a round 1 inch ball made of stone. Could this be a native american artifact and if so what was its purposeCuriouspatty (talk) 01:02, 30 June 2008 (UTC)[reply]

Could you post a picture? --Shaggorama (talk) 01:04, 30 June 2008 (UTC)[reply]

Sounds like a Tom bowler. Graeme Bartlett (talk) 05:11, 30 June 2008 (UTC)[reply]

I am still very curious but I have to admit to being a computer novice and I don't know how to post a picture. I do know how to take the picture and put it on my computer. What would be the next step without giving my e-mail address? The ball is on tour through the family right now so it may take a couple of days.Curiouspatty (talk) 00:53, 1 July 2008 (UTC)[reply]

Do you have a digital camera? Fribbler (talk) 01:07, 1 July 2008 (UTC)[reply]

Once you have the file on your computer you can upload it with the "upload file" link on the left hand side of the screen. Graeme Bartlett (talk) 01:52, 1 July 2008 (UTC)[reply]

Why are the planets in that order?

Why Mars after Earth (and the moon!)? Venus after Mercury?, Andremeda galaxy after our own solar system?, etc. You get the picture. Is there a particular reason, such as this group of rocks formed over there, that group of rocks gathered yonder why things in space are laid out the way they are? 5 dollars rides on this bet.THE WORLD'S MOST CURIOUS MAN (talk) 01:28, 30 June 2008 (UTC)[reply]

Hi. Have you read Formation and evolution of the solar system? Also, the Andromeda Galaxy after ours is because we live in our own galaxy. Also, is there any reason why they seemingly shouldn't be in that order? Earth, for example, wouldn't support much life were it as close to the sun as Venus or as far as Mars. One theory states that the planets are in that order partly because the rocks were heavier and settled closer to the sun, but this isn't usually true in other solar systems. Venus is hotter than Mercury because it has a heavy Carbon dioxide atmosphere. Hope this helps. Thanks. ~A H 1^(TCU) 01:37, 30 June 2008 (UTC)[reply]

Because we live in the best of all possible worlds. --Shaggorama (talk) 02:12, 30 June 2008 (UTC)[reply]

Or because this is the world we live in. — Lomn 13:03, 30 June 2008 (UTC)[reply]

When the solar system was forming two big rock smashed together. Their combined gravity pulled in more rock. Eventually the was a planet. So in answer to your question: Completely random (Unless you believe in God) 4.159.183.112 (talk) 02:37, 30 June 2008 (UTC)[reply]

Venus can be so bright because it's close enough to the Sun, but not so close as the Mercury so it's still often visible on the sky. It's quite obvious that the planet at that position has to be named after the godess of beuty. —Preceding unsigned comment added by B jonas (talk • contribs) 13:37, June 30, 2008 (UTC)

I don't quite follow your logic, why should the 2nd planet obviously be named Venus simply because of its position (as opposed to it's magnitude and majestic qualities)? Unless you mean that the position of the planet gives it those qualities, although I would say it is more to do with the thick cover of cloud. Additionally, Mercury is certainly visible from Earth, see Observation, although its proximity to the sun does limit how often the planet is visible from earth. Jdrewitt (talk) 14:49, 30 June 2008 (UTC)[reply]

Because calling them by other names makes you look silly--unless you live in another country. Then perhaps you won't. Imagine Reason (talk) 01:19, 1 July 2008 (UTC)[reply]

An "immortal" plant

I am looking for a plant that has a Wikipedia entry:

I don't remember any of its names.
It was probably originated from Africa or Asia.
It also lives in Europe. (?)
It can withstand prolonged dryness.
In dry season, it becomes a brown ball.
If you water it, it comes to life in about 3 hours.
It can withstand multiple dry/wet cycles.
Some people sell them by mail under a product name similar to "immortal plant".
It is possibly a species of fern. (?)
It may live up to 50 years.
The Wikipedia entry has a lousy picture (dried).

What is the plant? -- Toytoy (talk) 02:11, 30 June 2008 (UTC)[reply]

Sounds like Selaginella lepidophylla, except that it's a North American plant. --Allen (talk) 04:01, 30 June 2008 (UTC)[reply]

I was talking about Rose of Jericho. Thank you! -- Toytoy (talk) 04:07, 30 June 2008 (UTC)[reply]

So you were right Allen. The Wikipicture looks fine,that's exactly how it looks when it is dry. another picture in its hydrated form might help. Richard Avery (talk) 07:52, 30 June 2008 (UTC)[reply]

It's also sold as a "dinosaur plant." Mac Davis (talk) 14:16, 30 June 2008 (UTC)[reply]

If you want to look at some truly immortal plants, check out Sequoia, Methuselah (tree), and this swedish Norway Spruce. --Shaggorama (talk) 16:18, 30 June 2008 (UTC)[reply]

But is that Spruce an individual stem that's that old, or is that the age of the genet? --Allen (talk) 17:56, 30 June 2008 (UTC)[reply]

Take a look at List of oldest trees. Apparently the 9550yr figure for this Spruce is just the age of the clone. And since there are much older clones in the world (quaking aspen), I'd say there's a bit of unwarranted hype surrounding this Norway Spruce. --Allen (talk) 18:00, 30 June 2008 (UTC)[reply]

Identify this kelp?

I took a picture of this while visiting tidepools at the Oregon coast, but for the life of me I cannot figure out what it is. I can't find any species of kelp that have so many small, ruffly leaves, which seem to grow out of long, thin strap. Nor can I find anything with air bladders that shape and size. It's not very long, just a few feet. Any ideas? --Masamage ♫ 05:03, 30 June 2008 (UTC)[reply]

After some more hunting, I think it's Egregia menziesii. Here are some other pictures for comparison. Seems like a good match to me? --Masamage ♫ 06:09, 30 June 2008 (UTC)[reply]

Volume percent

What's the usual abbreviation for volume percent in English? %vol or vol% or something else? Our article doesn't say. (I'm more interested in the use in general chemistry, not necessarily in alcohol content of drinks.) 62.145.19.66 (talk) 08:03, 30 June 2008 (UTC)[reply]

For chemistry, I use more explicit "% v/v" or "% w/v" (g/100 mL) to clarify if the solute was measured in volume or mass. A bare "volume percent" value is only unambiguous in meaning--regardless of how it's written--if it's unambiguous what kind of measurements one is using:) DMacks (talk) 08:10, 30 June 2008 (UTC)[reply]

I'm translating a document out of German. I think the context will be clear enough to the reader; the original uses "Vol%", but German allows both "Vol%" and "%Vol" as abbreviations. I'm pretty sure only one of the two is usual in English, I just can't remember which. 62.145.19.66 (talk) 08:17, 30 June 2008 (UTC)[reply]

The ACS Style Guide remains fairly silent on this subject. DMacks is correct as far as the ambiguity, but if you are just translating, there may not be a preferred way for the ambiguous case. I would typically prefer something such as "25% by volume," but that might be just a personal preference. (Note: The style guide does list "vol %" in its list of abbreviations, but I don't know if that can be used as a unit or not). --Bennybp (talk) 18:14, 30 June 2008 (UTC)[reply]

I've usually seen and used vol% in the UK, in the context of chemistry and engineering. 86.141.89.124 (talk) 19:29, 30 June 2008 (UTC)[reply]

I went ahead and used vol%. Thanks for your help! 62.145.19.66 (talk) 06:05, 1 July 2008 (UTC)[reply]

Primates on the Moon

Excuse me, but I watched all the Neil Armstrong stuff on teevee when I was a child. Can someone please explain to me why primates aren't living and working on the Moon right now to help out all the primates and other species on Earth? I was brought up to believe that this would have happened by now, and I'm rather puzzled that it hasn't. Someone please explain this to me. --arkuat (talk) 08:48, 30 June 2008 (UTC)[reply]

Establishing a colony for people or animals on the Moon would be incredibly expensive and I don't see how it would help us on Earth. Itsmejudith (talk) 09:50, 30 June 2008 (UTC)[reply]

Oh, it would. We just have to send the right ones, e.g. this primate there.John Z (talk) 10:09, 30 June 2008 (UTC)[reply]

We have an article on colonization of the Moon but it's probably still far away. Some people have been too optimistic about costs, benefits and willingness. PrimeHunter (talk) 10:18, 30 June 2008 (UTC)[reply]

Okay, that makes sense, but why do some people think it is more important to have primates on Mars before we establish primates on the Moon? I guess that's the part that I really don't understand yet. --arkuat (talk) 11:04, 30 June 2008 (UTC)[reply]

In case the Earth gets shattered by an asteroid, which might take the moon with it. -- adaptron (talk) 20:07, 3 July 2008 (UTC)[reply]

Humans haven't been on Mars yet and many people want to go to new places. Mars is considered scientifically more interesting than the Moon, especially when looking for extraterrestrial life. In the really long run (and very hypothetical), Mars seems better suited for terraforming. PrimeHunter (talk) 11:59, 30 June 2008 (UTC)[reply]

Orbital dynamics can have odd effects: it takes less fuel (but more time) to reach Mars than it takes to reach the Moon. --Carnildo (talk) 21:55, 30 June 2008 (UTC)[reply]

I think that once America won the Space Race, the political point had been proven and there was insufficient imagination among our political leaders to understand why a sustained human presence on the moon would be useful for the long-term progress of our species. (Of course, this was before many folks realized how close we were to actually destroying the conditions on our planet that sustain life, leading to projects such as the Svalbard Global Seed Vault; nowadays, having a back-up planet or even moon might be viewed as handy.)

Atlant (talk) 13:55, 30 June 2008 (UTC)[reply]

Although Earth may be in worsening shape, it is still a much better environment for human life than any other planet or satellite in the solar system. Itsmejudith (talk) 14:56, 30 June 2008 (UTC)[reply]

Thanks to all of you for your many interesting responses, especially to PrimeHunter for posting the relevant link and to Carmildo for the interesting point, new to me, about fuel consumption. I will confess that I am interested in solar power satellites, which will probably require raw materials support from workers established on the Moon if they are to become economically feasible. --arkuat (talk) 05:01, 1 July 2008 (UTC)[reply]

I don't know whether it really requires less fuel to reach Mars than the Moon if the optimal path is used in both cases, but here are some links: Orbital mechanics, Interplanetary Transport Network, Low energy transfers. PrimeHunter (talk) 13:17, 1 July 2008 (UTC)[reply]

CERN

How long (current estimate) before the LHC starts doing crazy stuff? Black Carrot (talk) 11:28, 30 June 2008 (UTC)[reply]

Large Hadron Collider says "The first beams are due for injection in August 2008, with the first collisions planned to take place about two months later.". The source [1] is The New York Times 9 days ago. PrimeHunter (talk) 11:53, 30 June 2008 (UTC)[reply]

Well, I think we're all hoping that the LHC doesn't start doing crazy stuff. But yes, it begins operation soon. Exciting times, no?

Atlant (talk) 13:48, 30 June 2008 (UTC)[reply]

protein energy malnutrition

current stastics of kwashiorkar and marasmas occurence in india????? —Preceding unsigned comment added by 59.92.9.106 (talk) 11:29, 30 June 2008 (UTC)[reply]

This (from 1997) suggests both would be below 1 per cent, based on trends. --WikiJedits (talk) 18:18, 30 June 2008 (UTC)[reply]

Leap second

1. When will the next leap second be? 2. Why was 1972 given two leap seconds just because it was the year the leap second was invented? 208.76.245.162 (talk) 12:42, 30 June 2008 (UTC)[reply]

From the article :
Historically, leap seconds have been inserted about every 18 months. However, because the Earth's rotation rate is unpredictable in the long term, it is not possible to predict the need for them more than six months in advance.

And from INTERNATIONAL EARTH ROTATION AND REFERENCE SYSTEMS SERVICE (IERS)
NO positive leap second will be introduced at the end of June 2008.

Essentially, there isn't one currently scheduled. However, if the 18 months figure it true, we're overdue since the last one was December 2005, 18 months later would have been June 2007. APL (talk) 13:01, 30 June 2008 (UTC)[reply]

The 18 months figure is approximate, and based on past trends which have apparently changed. We really don't know when the next leap second will be needed; we just have to keep monitoring the rotation of the Earth and noticing each time it slows down a little or speeds up a little.

As for your question 2, I'm not sure, but it may have just been a side-effect of a decision to set UTC, at that time, to a particular offset from Ephemeris Time or TAI during the years shortly before the introduction of leap seconds. The Ephemeris Time article may have more info. --arkuat (talk) 04:41, 1 July 2008 (UTC)[reply]

Endorphin half-life

How long does it take until we eliminate endorphin from our body? Mr.K. (talk) 12:51, 30 June 2008 (UTC)[reply]

Have a look-see here. Fribbler (talk) 13:05, 30 June 2008 (UTC)[reply]

Relevance of "Space, Time, and Gravity" by Robert Wald

I'm about to read Robert Wald's "Space, Time, and Gravity: The Theory of the Big Bang and Black Holes," second edition (1992). Should I? I'm wondering if there is anything significant in there refuted by recent discoveries. I might also ask the same question about the Feynman lectures. Cannongrandee (talk) 13:52, 30 June 2008 (UTC)[reply]

A lot has happened since 1992, but the basics are still (mostly) the same. Incidentally, I found Stephen Hawking's A Brief History of Time to be a great read.Plasticup ^T/C 14:03, 30 June 2008 (UTC)[reply]

I can tell you that the Feynman lectures are very unlikely to be refuted anytime soon. See our article, but basically it was intended for first year undergraduates. Consequently, much of the material in there was very well studied by that point. On a side note, they're an excellent text to learn from, good choice. EagleFalconn (talk) 18:41, 30 June 2008 (UTC)[reply]

(Relative) Quantification of Human Genetic Diversity

Someone on the innertubulars asked something along the lines of "Is it true [what I heard from someone in a philosophy discussion channel] that human genetic diversity is tiny, among the least diverse of all animals?". I was, of course, struck by an instant bout of premium-strength dubiosity regarding the source and reliability of the information. However, a brief attempt to remedy with a timely injection of actual scientific results was sadly unforthcoming. To which end, I wonder if anyone knows of any studies that have been conducted into the absolute or relative degree of genetic diversity in humans, or how best to go about finding such a study should one exist. It's possible, I'm aware, that the technology has only recently descended to the level of affordability to undertake such investigations, and as such relevant information may not yet be available, though I'd like to think that such a matter would have aroused scientific interest already. Appreciative regards 153.1.253.80 (talk) 15:26, 30 June 2008 (UTC)[reply]

I recall reading that humans came very close to going extinct relatively recently and that we are all descended from a very small group of survivors, so there is less genetic diversity than other, related species, such as chimps (see Population bottleneck). This article states that the "genetic diversity [of chimpanzees and bonobos] is much larger than that of our species", despite their much smaller numbers. This article concurs. Clarityfiend (talk) 16:47, 30 June 2008 (UTC)[reply]

I've read that as early as Darwin it was realized that diversity in Africa is greater than in any other place in the world, and that was the reason for Darwin's widely ridiculed out-of-Africa theory. Imagine Reason (talk) 11:34, 1 July 2008 (UTC)[reply]

Nemesis

I was just reading Nemesis (star) and the article says that "due to orbiting the Sun it would have a very low proper motion and would escape detection by proper motion surveys". Surely at 1–1½ light years away it would have a large proper motion compared with other stars. Am I missing something?--Shantavira|^{feed me} 17:48, 30 June 2008 (UTC)[reply]

In a bound orbit, the relative velocity of the two objects goes down as the orbit size increases. Hence, if Nemesis orbits the sun at such a great distance then relative to the sun it must be moving quite slowly. Much slower, in fact, than most of the stars we observe in the sky. Dragons flight (talk) 17:54, 30 June 2008 (UTC)[reply]

(ec) The trick is that both the Sun and Nemesis would be moving about a common center of gravity (the barycenter of the system), so the only contribution to proper motion would be from their very low orbital velocity about the barycenter of the system. If we assume that Nemesis has the mass of the Sun and orbits 1 light year out, we're looking at an orbital period of roughly two billion years (if I've plugged in numbers correctly...) which cooks down to a proper motion of something like 0.6 milli-arcseconds per year: very, very small. Of course, that doesn't say anything about improper motions. The parallax shift of such a near companion would be quite large, and would indeed stick out like a sore thumb if noticed. TenOfAllTrades(talk) 18:04, 30 June 2008 (UTC)[reply]

I think you're out by 5 orders of magnitude on the orbital period! At least, one of us is, and my 20 million figure matches the 26 million figure mentioned in the article as the average time between extinction events. --Tango (talk) 18:07, 30 June 2008 (UTC)[reply]

(ec) Nemesis is predicted to have an orbital period somewhere in the 20 million years range. 360 degrees, divided by 20 million years gives a proper motion of about 0.06 arcseconds per year. The star with the largest proper motion, Barnard's Star, has a proper motion of 10.3 arcseconds per year, so you can see that Nemesis wouldn't have a very large proper motion. --Tango (talk) 18:07, 30 June 2008 (UTC)[reply]

It would be exceedingly easy to spot it using a paralax technique. Plasticup ^T/C 18:37, 30 June 2008 (UTC)[reply]

Yes, but we still don't have an all-sky survey of paralax extending down to red dwarfs. Nemesis (star)#Looking for Nemesis lists a couple planned projects that would either find or exclude Nemesis (as a red dwarf) by comprehensively measuring paralax through out the local region of space. Dragons flight (talk) 21:36, 30 June 2008 (UTC)[reply]

Yes, the theory says it could be a Red Dwarf, but in its hypothesized orbit it would have an apparent magnitude between 9 and 12. We are talking about an object brighter than Pluto. Amateur astronomers would be able to see it with their own telescopes. A 12 inch aperture would be more than sufficient. An object that big with such a massive parallax shift would have been spotted decades ago. Plasticup ^T/C 12:14, 1 July 2008 (UTC)[reply]

Many thanks everyone. I was confusing proper motion with parallax shift.--Shantavira|^{feed me} 07:51, 1 July 2008 (UTC)[reply]

Another quick question about my parrot

It's nothing of any consequence but I've always wondered about this. Whenever I stroke/scratch my Hyacinth Macaw's head in a certain place, it makes her open her beak wide and stretch her neck, like she's yawning. It's always the same spot that triggers it off, just behind her beak on both sides. Any idea what causes this? It doesn't seem to actually bother her in any way. --84.66.131.165 (talk) 19:44, 30 June 2008 (UTC)[reply]

It's a feeding reflex. Momma touches, beak opens, momma injects food. --jpgordon^∇∆∇∆ 19:52, 30 June 2008 (UTC)[reply]
- Does that really still work for a bird that's 20-something years old? --84.66.131.165 (talk) 20:38, 30 June 2008 (UTC)[reply]
  - If you put your fingers to the back of your throat, you'll soon learn that reflexes can last a lifetime! (I don't actually recommend doing that, throwing up isn't nice, but the point stands) — CycloneNimrod ^talk?_contribs? 20:43, 30 June 2008 (UTC)[reply]

- Thinking about it, my budgies do that sometimes after scratching their cheek areas with their claws or rubbing their faces against the aviary mesh. I always figured that it was just some sort of expression of relief from an itch. Same thing, you think? --Kurt Shaped Box (talk) 02:10, 1 July 2008 (UTC)[reply]

Frozen heart

In the film Rat Race a heart is shown is a cooler box on transit to a patient waiting for it to be installed. The driver says "it's been locked in that cooler box for seven hours". Can this really be true? The heart was not beating and was just shown in a plastic bag on top of ice. Would it really work if it was put into someone? Plemis monter (talk) 20:19, 30 June 2008 (UTC)[reply]

The article Heart transplantation suggests a max of 4-6 hours on ice. Friday (talk) 20:22, 30 June 2008 (UTC)[reply]

Of course, this isn't referenced. Wisdom89 _{(_T / ^C)} 20:26, 30 June 2008 (UTC)[reply]

I don't know if "seven hours" is accurate or not, but even though there's always a great deal of hurry to get the patient into surgery after an organ becomes available, it's certainly true that they can be kept on ice for several hours before they're actually put into the recipient's body. This article, for example, tells us that a kidney was "put aboard an AirNet jet less than an hour after it was picked up from a Miami hospital. After a 2,700-mile flight, it arrived in San Diego the next morning for transplant into the patient." That's going to spend several hours in transport, no matter how you slice it. Of course, maybe kidneys travel better than hearts, I don't know, but seven hours doesn't sound that crazy to me. -- Captain Disdain (talk) 21:19, 30 June 2008 (UTC)[reply]

My understanding is that while 4-6 hours is the gold standard, hearts can and do remain viable for longer periods. This abstract describes a successful transplant with an ischemic time (the heart was without circulating, oxygenated blood) of 13 hours, including 12 hours on ice. There are various experimental procedures for extending the cold shelf life of donor hearts out to 24 hours or more (see [2] for example). Regarding Captain Disdain's comment above, it is indeed correct that different organs tolerate cold ischemia to different degrees. TenOfAllTrades(talk) 21:24, 30 June 2008 (UTC)[reply]

What is the limiting factor? It would be nice if organs could be stored much longer (i.e. years). That way we wouldn't have to waste organs if a donor becomes available but there is no immediately matching recipient. I assume it has been tried with animals, but what goes wrong? Obviously sperm and other more limited cell cultures can be preserved in liquid nitrogen for long times. Dragons flight (talk) 21:43, 30 June 2008 (UTC)[reply]

I have to catch a train, so I'll just cover freezing for now. Have you seen what happens to the texture of a chicken breast when you freeze and then thaw it? Just like chicken breast, the heart is muscle tissue, and freezing it without causing harm is very challenging. Leaving out the biology for a moment, there are two purely mechanical difficulties in freezing living cells and tissues. First, when water freezes, it expands slightly, while it contracts as it thaws. If you've ever had a can of soda explode in your freezer, or watched an ice cube crack when you drop it into warmer liquid, you can see why plain old expansion and contraction over a full-sized organ has the potential for harm. The second mechanical issue arises on a smaller scale—water, when it freezes, has a nasty habit of forming crystals. These crystals are very pretty when they make snowflakes, but their pointy little ends are deadly to delicate cell membranes.

In cell cultures, we can often get around these problems fairly easily. By adding a glassifying agent like DMSO or glycerol to our freezing medium, we can prevent or restrict the formation of ice crystals. (As the cells are chilled, the formation of large, ordered crystals is discouraged; the frozen state is more like a glass.) Expansion is a bit less of a problem for single cells; you don't have the accumulation of stress over large distances, and individual cells can stretch a bit. As well, some water actually comes out of cells during freezing. (Solidification of water happens outside the cell first, drawing liquid out.) Timing is important during the freezing process—freeze too quickly and the cells end up with too much water (ice) inside and are stressed; freeze too slowly and the cells start to find the glassifying agents toxic. Different cell types prefer different freezing regimens: different glassifying agents and different cooling rates.

Now, try and freeze a whole organ. You've got a combination of different cell types that each prefer different freezing conditions. You have a thick lump of material, so you can't chill it uniformly throughout. As the blood vessels freeze, it's difficult to get water in and out of the entire organ. You can see why freezing a heart is a nontrivial challenge. TenOfAllTrades(talk) 22:02, 30 June 2008 (UTC)[reply]

An important point that no one seems ot have made explicitly although everyone's hinting at it is that there is a big difference between "on ice" and "frozen." Laying an organ on top of ice but not in direct contact with the ice will keep it cold but it won't freeze. --Shaggorama (talk) 16:53, 1 July 2008 (UTC)[reply]

July 1

Adultration

how to cure adultration in products purchased from the market? —Preceding unsigned comment added by Jasleen302 (talk • contribs) 12:00, 28 June 2008 (UTC)[reply]

Best to avoid buying them in the first place. Check your product carefully before you buy, and insist on a pure product. Buying this sort of stuff will just encourage more adulteration. What products are you having trouble with. Graeme Bartlett (talk) 01:57, 1 July 2008 (UTC)[reply]

By having an effective network of inspectors, checking for adulteration, and with the power to take action when it is found? (if I have understood the question correctly?)87.102.86.73 (talk) 09:58, 1 July 2008 (UTC)[reply]

This has been a problem for a long time, and it ebbs and flows with waves of government regulation and deregulation. The classical (fictionalized) work on this is Upton Sinclair's muckraking novel The Jungle.

Atlant (talk) 16:57, 1 July 2008 (UTC)[reply]

Unmanned Aircraft

I was watching a documentary, Regulus - The First Nuclear Missile Submarines, after WW2, in that it states how they managed to make the missile from remote go up and down, right and left, and eventually land. More information: [3]. Anyways if can control a missile from remote, why has there been no unmanned aircraft yet? Like a remote control one? I mean with the GPS and satellite technology it is possible. Is the United States Forces holding back on something they have in secret? --69.156.94.136 (talk) 01:17, 1 July 2008 (UTC)[reply]

There are unmanned aircraft. They don't even need to be remote controlled, they can be controlled by computer AI. Unmanned combat aircraft are probably the future of air warfare. Bombers and attack aircraft will be first. Followed by fighter aircraft.ScienceApe (talk) 01:29, 1 July 2008 (UTC)[reply]

It's not a secret, and it's not being held back. The MQ-1 Predator is a remotely-controlled unmanned aerial vehicle that fills a variety of roles, including precision bombing. It has been flying armed missions since at least 2001. TenOfAllTrades(talk) 02:24, 1 July 2008 (UTC)[reply]

Coming soon to an administration near you: Ender's Game.

Atlant (talk) 16:55, 1 July 2008 (UTC)[reply]

Modern commercial airliners with an autopilot are virtually unmanned aircraft, see this section Autopilot#Modern autopilots, and potentially only need a pilot for taxiing. Human pilots are almost a back up system to the aircraft autopilot and to provide a sense of security to the passengers. Tobyc75 (talk) 17:59, 2 July 2008 (UTC)[reply]

Freezing Cheese: Good or Bad

I wanted some input on freezing cheese. I'm taking a five hour flight and want to take a two pound block of cheese with me. I know that many people say, cheese shouldn't be refrigerated because it inhibits the life, and flavor inside the cheese, But hey I'm an American. And I know that freezing turns the moisture inside items into sharp shards, basically perforating what ever your freezing from the inside. But is freezing cheese GOOD or BAD? —Preceding unsigned comment added by Semi-smart (talk • contribs) 03:34, 1 July 2008 (UTC)[reply]

Freezing cheese is mostly successful, hard or soft, but not ricotta, so anything close and without moisture traps inside. Julia Rossi (talk) 07:07, 1 July 2008 (UTC)[reply]

Freezing cheddar is no good, it destroys the texture and it all goes crumbly. Parmesan powder freezes OK though. For a short flight like this, just pre cool it in the fridge, and then wrap it in something insulated like bubble wrap to keep it cool. Graeme Bartlett (talk) 07:13, 1 July 2008 (UTC)[reply]

But freezing cheddar is fine if you're going to use it in cooking, since the texture won't matter [4]. My Googling suggests that this is true of a lot of cheeses... in applications where texture doesn't matter, freezing is usually fine. --Allen (talk) 07:18, 1 July 2008 (UTC)[reply]

I have successfully frozen Stilton style blue cheese, flavour and texture were unaffected after 3 months. Richard Avery (talk) 07:25, 1 July 2008 (UTC)[reply]

I agree with Graeme Bartlett that the best way to deal with this would be to just cool it and keep it cool by insulating it. A simple way to do this would be to buy a small cooler -- I've seen ones that are about the size of a small handbag -- and sticking a couple of ice packs in with the cheese. (The "ice pack" article appears to deal only with the medical ice packs, but what I mean is the thing that is also called a "freezer block" or "ice brick", a rigid plastic brick filled with water that you can freeze and then use to keep things cool, the mainstay of coolers all over the world. (Can it be that we really don't have an article for them, or am I just completely blanking on the terminology here?)) Depending on where you are and how paranoid they are about you using your cheese to destroy the plane in midair, taking that with you as carry-on might be problematic, but you could just stick it in your bag and check it.

That said, a cheaper and more low-tech approach would be simply wrapping the refrigerated cheese tightly in newspaper. It makes a pretty good insulator, and you could always stick in an ice pack with the cheese to make sure it stays cool, if you're worried about that, but the newspaper by itself will probably do the trick, if the cheese is cool to begin with. You can probably get some extra mileage out of the newspaper by sticking it in the fridge with the cheese so it's also cool. As long as the newspaper is dry (water conducts heat very well), it'll work just fine. -- Captain Disdain (talk) 11:02, 1 July 2008 (UTC)[reply]

Why don't you test it out? Try freezing a bit and seeing whether it survives. I would be interested in hearing your results. Plasticup ^T/C 13:01, 1 July 2008 (UTC)~[reply]

I say screw it. The flight is only 5 hours pal, leaving cheese out of the fridge for that long probably won't be that bad for it. Moreover, if it's 2 pounds of cheese it should hold a temperature for a while. I'm all for captain disdain's strategy of insulating the cheese. But for the record, remember that if you're flight is international they're probably going to take the cheese at customs. --Shaggorama (talk) 16:46, 1 July 2008 (UTC)[reply]

When we returned from France, we brought back a variety of cheeses, probably mostly of the semi-dry styles. They were wrapped well in butcher paper at the cheese shop and we then closed the cheese shop's plastic bag as well as we could and chucked them in the middle of the clothes in our luggage. Between the insulation of the clothing and the likely cold baggage hold of the plane, they survived the ten-ish hour trip just fine. And even though the cheeses were from (gasp!) France, we declared them at American customs and were still allowed back into the country, cheeses and and all. (The preceding does not constitute legal advice; it just recounts Wikipedian's one anecdote.)

Atlant (talk) 16:53, 1 July 2008 (UTC)[reply]

This might help clarify matters. [5] But be sure to print out a copy to hold under their noses in case someone makes a fuss. OR: I've encountered customs officials anywhere from waving people through to trying to declare that permitted goods were not so. (Chocolate could cause all sorts of delays in NY for a couple of years while back, but that seems to have dissipated. I assume some overzealous supervisor got retired.) As for transporting the cheese, if you have the spare luggage capacity you might freeze a couple of those soft Ice packs you can buy at drugstores or pharmacies or the like. If you are squeezing for space and weight a wet T-shirt or towel might do the trick to prevent your cheese from suffering in case your luggage ends up baking in the summer sun for a couple of hours instead of going directly from the cool terminal to the cold cargo hold. NB: make sure to unpack immediately once you're home and air out the luggage to prevent moisture damage. Bubble wrap suggested above would additionally prevent your cheese from turning into cheese crumble, thanks to baggage handling. Remember you won't be able to take it as carry-on [6]. 80.171.254.148 (talk) 01:33, 3 July 2008 (UTC)[reply]

The recommendation for hard cheese is probably good for customs reasons as well; you want to avoid bringing back anything like Abbaye de Citeaux, Chevrotin and Chabichou du Poitou, "the forbidden cheeses", which have a moisture content that makes U.S. Customs uncomfortable. (What is specifically banned is raw milk cheese aged less than 60 days, or aged more than 60 days but having a moisture content of more than 67% water). This is sad for Americans, because, in the words of the Amateur Gourmet, the "high moisture content gives a creamy, luxurious texture and the raw milk lends it complexity and depth." You will have to enjoy these abroad.... - Nunh-huh 02:59, 3 July 2008 (UTC)[reply]

QAM query

Hello to all Please if some one can guide me about data rates of different catagerizes of QAM that is the data rate of 8-QAM, 16-QAM, 32-QAM, 64-QAM, 128-QAM, 256-QAM

thanks —Preceding unsigned comment added by Arsalan 80 (talk • contribs) 04:29, 1 July 2008 (UTC)[reply]

The different rates will depend on what bandwidth in general you want. For particular applications such as digital television or ADSL the appropriate standard will specify the rates to select from. With 8-QAM you will get 3 bits per symbol, 16-QAM will give you 4 bits per symbol, and so on till 256-QAM with 8 bits per symbol. Graeme Bartlett (talk) 06:18, 1 July 2008 (UTC)[reply]

statistics

what the the distinction between simulation,models,and experiments? —Preceding unsigned comment added by 72.75.74.106 (talk) 11:46, 1 July 2008 (UTC)[reply]

Experiments are tests on real-world things that yield real-world data. Simulations are more like thought-experiments. They are involve creating a model to imitate the real thing. Plasticup ^T/C 11:58, 1 July 2008 (UTC)[reply]

In my experience, a model is something that is fed into a simulation to give it the information needed to simulate, so to speak. Said in another way, the model is the abstraction and the simulator takes that abstraction and performs calculations on it to produce an expected result. The Monte Carlo method is a good example of this. The model is the input and the simulation is the action taken on it and the final result. In common parlance, they are often used interchangeably. An experiment is a totally different thing. It is an empirical study of something. Rather than having a known model, a series of observations are taken and analysed. In some cases, a model fit can be used to test a hypothesis. It is important to note that the experiment is totally based on observation. Simulation and modelling can be used to create a hypothesis, but experimentation is usually necessary to reject or not reject a hypothesis. Gjmulhol (talk) 12:06, 1 July 2008 (UTC)[reply]

A model can be more than just an idea. In biology, a model could be a live mouse, used to "simulate" a human for a particular purpose. Someguy1221 (talk) 03:22, 3 July 2008 (UTC)[reply]

Help with electronics

redirected from Wikipedia:Reference desk/Computing#Help with electronics

I have just begun building a guitar pedal, but no have no electronics expereience, but a good deal of knowledge (theoretical knowledge) of the subject.

I have become stuck where the schematic tells me to connect to ground.

I am soldering to a sheet of stripboard, and it has a thin copper track running down both sides of the board, but with no holes in them; Is this where i should connect grounded connections to? And do i connect all grounded connections to the one place, or should i cut the track so as to separate them from one another?

Any help would be much appreciated.

Thank you!! —Preceding unsigned comment added by 212.46.129.226 (talk) 09:33, 1 July 2008 (UTC)[reply]

If this is a standalone pedal (not powered by a wall outlet), it is very possible that you do not have ground inside the footpedal at all. In that case, I would assume that you are using a 1/4" plug from the guitar/amp and assume that the shielding of that connector is ground. So, attach there. If, instead, you are powering this from a wall outlet, ensure you are using a grounded plug (three prongs in the U.S.). Then, you will have ground where the power is soldered onto the board. Because this is an audio device, be wary of ground loops. If you ground your pedal and plug it into one outlet, then plug the guitar/amp into another outlet, it is possible that they do not share the same ground. You can easily get a hum or buzz on the speakers. So, inside the pedal, ensure you connect the ground from your power input to the ground on the shield of the cable from the guitar/amp. Then, you will joining the possible difference in grounds and eliminating the buzz. -- kainaw ™ 12:54, 1 July 2008 (UTC)[reply]

Additional Help with Electronics

Thanks to kainaw for answering my previous question about grounding, but i still have some queries.

When you say to connect to the ground from the guitar jack, do you mean the input or the output jack?

And does it matter whether i connect all the grounded connections directly to the ground terminal of the jack, or if i connect them all (Including the ground from the jack) to the copper track at the side of the stripboard?

Thanks again for your help —Preceding unsigned comment added by 212.46.129.226 (talk) 13:41, 1 July 2008 (UTC)[reply]

"Ground" is often used in an imprecise way. The two most common usages are as "Ground"/"Earth" (yes I know this has reused "Ground") for the purpose of one or more of safety and screening/shielding and as 0V. Eventually Ground/Earthwants to get connected to a physical Ground - eg a copper rod stuck into the planet's soil. For this to work well as a safety connection, it wants to be well connected "in all directions". For it to work well as screening, you don't want current to flow through it, so only one connection to each bit of ground should be made, ideally in a star configuration but at worst as a tree configuration branching out from the trunk where the copper rod is. The other common usage informally means 0V. This has come about since often the 0V terminal of a PSU gets connected to ground to "stop it floating". This often creates loops and current flows in screening circuitry. With your pedals etc, you want all the 0V connected to each other once (no loops). A starter would be to see if, without your circuit in place the screen of the Inlet jack was connected somehow to the screen of the Outlet jack. If not, connect your ground signal to BOTH outers, otherwise choose one - the most convenient. There is an element of art rather than science about getting ground/0V/earth/screening right. -- SGBailey (talk) 13:52, 1 July 2008 (UTC)[reply]

To expand on SGBailey's point, "ground" in the context in which you're asking means "the reference voltage" (which we conventionally then call "0 volts"). All other signals in the circuit are measured "in reference" to this point, "the ground". For your guitar effects pedal, both the input and output jacks each have an outer terminal which should be connected to "the ground" (reference voltage) in your circuit.

Odds are that your guitar effects pedal should be designed to operate solely from battery power. Otherwise, any connection to mains/line power, even through a power supply/wall wart, is likely to cause a ground loop and that can induce your guitar amplifier to produce noise, hum, and other nasty stuff.

Atlant (talk) 16:42, 1 July 2008 (UTC)[reply]

A good book you might want to look into is "Do-It-Yourself Projects fo Guitarists" by Craig Anderton. I used to know a great website too, but I can't find it right now. --Shaggorama (talk) 16:09, 4 July 2008 (UTC)[reply]

Figure of the Earth image

I can't find this anywhere. I would like to know if there is an image which shows the figure of the earth without the water on it. I.e. only the rock part of the earth. Does such an image exist? — Adriaan (T★C) 13:44, 1 July 2008 (UTC)[reply]

Bathymetry, [7]? -- Coneslayer (talk) 13:46, 1 July 2008 (UTC)[reply]

No, not what I'm looking for. I was wondering if there was a pic in true colour of the earth, just with the water edited out. Something like an artist's impression of what the earth would look like if all the water suddenly disappeared. Like a 3D pic of an object supposed to be the earth - but without water. — Adriaan (T★C) 15:52, 1 July 2008 (UTC)[reply]

How about Mars? --Shaggorama (talk) 16:40, 1 July 2008 (UTC)[reply]

There's a 2D texture here. You could create a 3D image out of it quite easily with Xplanet. — Matt Eason ^{(Talk  Contribs)} 20:03, 1 July 2008 (UTC)[reply]

Space program benefits

In reading about the ancillary benefits of NASA's space program in articles like this and this, it strikes me that most the advances that are mentioned aren't dependent on the space travel part of the equation. Rather, they were inspired or triggered by space travel, but could just as easily have been developed for the same cost for a land-based application. For example, water filtration was (according to the NASA site above) developed in part for the Apollo program, but it's not as though it couldn't have been developed for non-space applications. Are there practical benefits to the space program, readily apparent to regular folks, that could only come with space travel? jeffjon (talk) 14:28, 1 July 2008 (UTC)[reply]

Define 'regularly apparent to regular folk'. There are thousands of experiments in space, many of which will have furthered our understanding of the world and how things react in given situations. Do you just want a list of products that use techniques based on the space program? Or do wooly benefits such as "improving the knowledge of mankind" and "continuing the exploration of the universe"? Personally I find that when people start to try to qualify the value of Nasa based on products/technological developments overlook the strongest argument for the space-program - that there's a universe out there that holds limitless possibilities and the more we go out there and the further we venture the more interesting things we will find. Of course this is from an exploratory enthusiast who supports the cause, certainly there are plenty of worthy groups vying for already scarce government funding. 194.221.133.226 (talk) 15:02, 1 July 2008 (UTC)[reply]

I'm with you; I think exploration for sake of pure discovery is motivation enough. My wife isn't convinced, so I was trying to come up with a more tangible benefit that she receives for that almost 1% of every dollar she pays in taxes, whether it's a product, a health benefit, a scientific advance with other implications, etc. jeffjon (talk) 15:10, 1 July 2008 (UTC)[reply]

IMHO the scientific benefits are good enough. But to counter the "they totally could've been developed anyway" argument, I guess the question is why. Why would any of that be built? Why would the US build a water filter when we've got good tapwater? Necessity is the mother of invention. We need a way to recycle water in space. It also happens to work really well on Earth? We should sell that to the third world and people who are superstitious about tap water! As the first source you cite mentions, if you look at a lot of the products, most of them are saying "NASA was doing this obscure scientific thing and it totally improved this product by leaps and bounds!" Thats pretty damn impressive, and I consider it a good testament to the power of a good R&D budget. EagleFalconn (talk) 15:24, 1 July 2008 (UTC)[reply]

I wouldn't expect R&D for space to be any more likely than anything else to have things that help in unexpected ways. If NASA didn't invent water filtration, maybe it wouldn't have occurred to anyone, but, by the same token, maybe there's something that hasn't occurred to us because we weren't spending that money on R&D for something of more obvious practical significance. Doing R&D for something practical has the added advantage of helping in expected ways. For those of you who think NASA does pull its weight, how much of your money do you donate to it? You don't think it's only worth it if it's money the government takes from you forcefully, do you? I'm currently saving up for college, but when I'm done with that, I plan on donating to a microcredit group, like Unitus. I think they have more practical significance than NASA. — DanielLC 15:49, 1 July 2008 (UTC)[reply]

Satellites enable my contributions to Wikipedia. There's your human benefit right there. ;-) Plasticup ^T/C 17:11, 1 July 2008 (UTC)[reply]

That's a bit of a red herring, isn't it? I don't make voluntary cash donations to my local water treatment plant or the city subway system, but I still think it's worthwhile for those projects to receive funding. If you want to talk about research, in the United States good solid research is carried out or funded by government agencies from the Department of Energy to the Department of Veterans Affairs; I don't make donations to those organizations either. TenOfAllTrades(talk) 17:26, 1 July 2008 (UTC)[reply]

Global Positioning System saves a lot of time and needless erring around. LINEAR is another point. And then, for people like me, it's simply interesting and sometimes even exciting to look at real pictures from space. And when I saw Neil Armstrong live on TV stepping on the moon that is something to remember. 77.3.134.249 (talk) 20:27, 1 July 2008 (UTC)[reply]

Though I am certainly no expert, I have read in the past that zero gravity experiments have been done on cultures of bacteria. These have shown unique characteristics. I also remember evidence of a super-bug, but I don't remember where that is from. Gravity is vital to life, it is important that we know how plants and animals react in such an environment. From a materials perspective (I am a materials scientist), some crystals and structures can only be formed in a zero-g environment. If extra-planetary colonization ever takes place, it would be good to know how to take advantage of these new, potentially revolutionary structures. Gjmulhol (talk) 11:55, 2 July 2008 (UTC)[reply]

Note that just because spinoff products are formed does not necessarily mean that NASA is a good way to get them. If you give me a billion dollars I'm sure I could get you some tangible benefit for it—but would that be a better approach to said products than, say, letting them develop on the free market? That is—the return on R&D in terms of secondary benefits is going to be pretty small, most likely, and not very efficient.

In my opinion a better argument focuses on the BIG, non-spinoff benefits. GPS. Satellite communications. Military advances in rocketry. Advances in computing, robotics, materials science, etc. Water filtration? Not impressive. You could easily have gotten something like that without NASA. But GPS? Probably not. (And while "knowledge for its own sake" works great for people who would post on a board like this, it's not that convincing for the common man. Very little of that knowledge for its own sake has any payoff, and there's a lot of different types of "knowledge for its own sake" that one could be funding, much of it for a lot cheaper than space budgets.) --98.217.8.46 (talk) 18:37, 3 July 2008 (UTC)[reply]

physics

Question: When we throw a ball on the wall in a particular direction, then why does the ball comes back to us in some other direction ?'' —Preceding unsigned comment added by 61.2.190.79 (talk) 16:33, 1 July 2008 (UTC)[reply]

Start with Reflection (physics), but the most basic principle is that "the angle of incidence equals the angle of reflection". And remember, gravity is constantly working on the path of the ball.

Atlant (talk) 16:37, 1 July 2008 (UTC)[reply]

More specifically, for a ball: Deflection (physics). This article could do with expansion though ....Jdrewitt (talk) 16:53, 1 July 2008 (UTC)[reply]

More simply: It would take more energy to send the ball back in the direction it came from. Mac Davis (talk) 16:57, 1 July 2008 (UTC)[reply]

Well, yes and no; it would just take a corner cube, but gravity is still affecting the track of the ball (which is probably what you were referring to in the need for "more energy").

Atlant (talk) 19:48, 1 July 2008 (UTC)[reply]

Also, it is very difficult to throw a ball with zero spin. If you are familiar at all with the sport of tennis you will know that depending on the surface the ball is striking, the spin can change the direction dramatically. This is particularly evident if you use a hard rubber ball on a rough surface (e.g., a lacrosse ball on asphalt). The spin will alternate and dampen until the ball rolls flat. Thus, you see a low, long bounce followed by a short, high bounce, and on and on until the ball flies with negligible spin or it simply starts rolling. Gjmulhol (talk) 11:52, 2 July 2008 (UTC)[reply]

Endorphin as drug

Why not simply inject endorphin instead of some artificial substance if the purpose is to feel right? —Preceding unsigned comment added by Mr.K. (talk • contribs) 18:42, 1 July 2008 (UTC)[reply]

And where would you obtain the natural endorphins? You can't just buy it. And if you synthesized it, it would then be an artificial rather than "natural" substance. The closest analogue is morphine, which is routinely injected during childbirth and other painful periods. ~Amatulić (talk) 18:53, 1 July 2008 (UTC)[reply]

I'm under the impression that one would have to inject the endorphin(s) directly into the brain, which sounds rather messy. --Several Times (talk) 20:13, 1 July 2008 (UTC)[reply]

This is a common question with relation to most centrally acting drugs (serotonin vs SSRIs, norepinephrine vs salbutamol, etc). The most common problem with endogenous substances is that they won't cross the blood-brain barrier, other problems are listed in the pharmacokinetics article (absorption, distribution, metabolism and excretion). --82.21.25.219 (talk) 08:21, 2 July 2008 (UTC)[reply]

Also note that administering natural endorphins long-term would likely cause the same problems as other such drugs. A tolerance would develop, requiring more and more to get the same effect. And addiction would occur, so people would feel sick if the endorphin supplement was ever stopped. StuRat (talk) 15:42, 2 July 2008 (UTC)[reply]

Insulators for copper wiring

I'm wondering if there is any way to accuratly measure the resistivity of a substance...is there a way to get a quantitative value for resistivity in substances that could potentially be used to insulate basic copper wiring? 24.34.168.154 (talk) 18:43, 1 July 2008 (UTC)Fiziks[reply]

Using a Megger? Fribbler (talk) 18:46, 1 July 2008 (UTC)[reply]

A megger is a good answer if you're interested in the performance of the insulator at relatively high voltages (~1KV), but at lower voltages, one would use a nanoammeter, a voltage source, and some careful experiment design including guarding. Keithley Instruments is a typical vendor of nanoammeters. And here's a good article from EDN about proper techniques: [8].

Atlant (talk) 19:43, 1 July 2008 (UTC)[reply]

A Megger will measure the insulation resistance not the material resistivity. There are standard ways to measure resistivity: [9]

July 2

Infantry vs. tank

[This is really eight related questions, some of which may share answers.] Consider either (a) one or (b) eight soldiers armed with normal-caliber machine guns and an arbitrary amount of any kind(s) (armor piercing rounds?) of ammunition for them. They are free to walk the top of a tall concrete wall that is, say, 75m on a side. Trapped inside the wall on open ground is either (a) one unarmed enemy tank or (b) one enemy and one friendly tank, armed only with their main cannons. All tanks are modern main battle tanks; the unarmed tank may be considered to be repairing supposedly-minor damage to its anti-personnel weapons in (vain) hopes that it may return fire, and the armed tanks fire only at each other. How may the infantry in each of the four situations disable or destroy the enemy tank (a) in the least time or (b) using the least ammunition?

The purpose of the first bifurcation is to increase the infantry's effectiveness in the situation where there is a friendly tank, as well as to allow them to surround the enemy. The purpose of the second is to distinguish between an enemy that is fighting (albeit not against the infantry) and one that is doing nothing but trying to evade/weather fire. The purpose of the third is obvious, but in the case where there is a friendly tank present the "least ammunition" option should be taken to require some material contribution to the battle. I would also be interested in hearing about the mechanism by which (a large amount of) machine gun fire damages the high-grade armor against which it is not frequently used. Thanks for the myriad answers. --Tardis (talk) 01:11, 2 July 2008 (UTC)[reply]

Good luck. Modern tank armor (e.g. Chobham armor) is really, really tough. I'm no expert, but I doubt that anything fired from a machine gun would have a chance of doing any real damage. You're probably better off having these guys break out their shovels and cover the trapped tank with dirt. Clarityfiend (talk) 06:49, 2 July 2008 (UTC)[reply]

They could try and open the hatch and shoot the people inside. Trying to damage the armour would be in vain, I imagine. --Tango (talk) 14:04, 2 July 2008 (UTC)[reply]

Yeah- small arms fire against modern armor would be useless, no matter what ammo you're using. You'd need to get the hatch open somehow. Trap the tanks somehow, and wait for the people inside to get hungry? I don't know. Friday (talk) 14:39, 2 July 2008 (UTC)[reply]

75m square? What sort of ground? Discharge five 40 tonne road tankers of diesel into the area (so 3cm deep without bothering to do the maths) and ignite it? The thermal conduction of armour is pretty high and baking the people in it cannot be too hard. --BozMo talk 14:55, 2 July 2008 (UTC)[reply]

Best you could with small arms would be to try to blind and deafen them by destroying the optics and antennas. --—— Gadget850 (Ed) ^talk - 14:58, 2 July 2008 (UTC)[reply]

Even with an arbitrary amount (and duration; give the tanks infinite fuel if needed) of sustained fire? Surely something would happen to the armor, even if it shattered or reflected the bullets, and it wouldn't get stronger… --Tardis (talk) 15:02, 2 July 2008 (UTC)[reply]

I suppose if you had a billion rounds of machine-gun bullets, you could eventually wear a hole in the armor, but that's just getting a bit silly, the occupants of the tank would starve to death first. There may be a few weak spots, though, like the exhaust port, which might be more vulnerable to small arms fire. StuRat (talk) 15:38, 2 July 2008 (UTC)[reply]

I suppose water dripping on the tank would eventually wear through the armor, too. Friday (talk) 17:28, 2 July 2008 (UTC)[reply]

Removable armor plates are common. If the tank is disabled and just sitting there, you could rush up and start removing armor. Eventually, the guys inside will try to come out to stop you and it will be man vs. man instead of man vs. tank. -- kainaw ™ 17:33, 2 July 2008 (UTC)[reply]

(EC)

What about MacGyver solutions? Take the gunpowder out, make a kind of bomb, could at least blow the tracks off.

Could destroy the main gun in a similar way. With no movement or firepower you could burn the people out...--Shniken1 (talk) 17:37, 2 July 2008 (UTC)[reply]

I don't know if the Barrett M82 would be useless against the tracks of a tank. It have caliber .50 and the latter are the Achilles' heel of the tank. Just give it a try on a tank that you don't need anymore. Mr.K. (talk) 09:54, 3 July 2008 (UTC)[reply]

The infantry could lay siege to the tank until the crew starve or surrender. D aniel (‽) 19:39, 3 July 2008 (UTC)[reply]

Evolution - Woman as Well?

Today I was speaking to a Jehovah's Witness that came by my door. We got into talking about everyone's favorite topic, evolution. He brought up an objection to the theory that I had not heard before. I don't remember exactly what it was, but it was along the lines of "even if a man evolved into a human, what are the chances that a woman evolved too, at the same place, and the same time?". I'm sure there is an easy rebuttal to this, but I was wondering if this objection has a name and how I can rebut it in layman's terms. (In a somewhat related query, does anyone know where one can find very old (circa 1894) copies of the Watchtower magazine?) Thanks! Ab e g92contribs 03:56, 2 July 2008 (UTC)[reply]

Let me see if I understand the argument first. The idea is that if a male evolves from Species A to Species B, then there has to be a female that goes from Species A to Species B as well, otherwise there would be no-one to breed with? I can see what's wrong with the argument, but I'm finding it hard to put into words, except to point out that (a) evolution isn't sudden jumps, it's a gradual process (at least gradual in the sense that new species don't suddenly crop up in a single generation), (b) speciation occurs when an entire hereditary line becomes so genetically different to another that they cannot reliably interbreed, so it's actually the combination of a man and a woman who are, by necessity, genetically different, passing a particular combination of those different genes onto their offspring that leads to the creation of a new species. I'd try to explain it in terms of the historical development of language, but presumably the Witnesses believe that all happened when God struck down the Tower of Babel. I will leave the understandable explanation to someone with more experience in the subject matter. Confusing Manifestation(Say hi!) 04:56, 2 July 2008 (UTC)[reply]

Put another way, your Jehovah's Witness friend is mistaken in thinking that the process of speciation is something that occurs in an individual. Populations become species, individuals do not. - Nunh-huh 05:06, 2 July 2008 (UTC)[reply]

In addition to speciation, the population genetics article may also be helpful. --arkuat (talk) 05:35, 2 July 2008 (UTC)[reply]

The entire mechanism of reproduction involves males and females sharing their genomes again and again. The amount of genome that differentiates males and females is tiny. Your friend seems to think that males and females are terribly genetically different. They aren't. And again, all members of the species are products of their mating. So the genome isn't going to get out of sync between the two of them. --98.217.8.46 (talk) 13:53, 2 July 2008 (UTC)[reply]

If you want a more technical answer, consider how traits are distributed upon reproduction. Say I have a hypothetical gene for red hair. (Hair is a bit more complicated than one Mendelian trait but for our example it is concrete.) It sits somewhere on one of my chromosomes. I mate with a woman who had a gene for brown hair. It sits on one of her chromosomes. Inside the sperm, egg, etc., half of my genes are randomly thrown together with half of her genes. It's entirely possible that all of our male or female children could have my gene expressed, or half with her gene expressed. The resulting children are a mix-and-match of our two gene pools. It isn't that the "female gene pool" is separate from the "male gene pool" and has to "evolve" at the same time. They'll evolve together, as long as none of the evolutionary changes are great enough to make evolving with another human impossible. The gene pool of course allows for a certain amount of flexibility (if it didn't, even simple reproduction with genetically different members of the same species would be impossible). Beneficial mutations have a certain chance of being passed down to children of either sex. Males and females are, again, genetically (and developmentally, up to a certain point) almost identical—they are both humans, and it is the firing off of different hormones at different times that differentiate the two physically, mentally, etc. --98.217.8.46 (talk) 14:09, 2 July 2008 (UTC)[reply]

The number of chromosome is different in man and chimp, lets asume that the last comon ancestor had the same number than one of the two species. So sometime ago a chromosome split or paired with another to get to the different number. This happened in one single individuum not to the whole group.What I know from genetics this makes interbreeding very complicated what it is seen in donkey and horse. Has this problem of genetics been solved yet?---Stone (talk) 14:25, 2 July 2008 (UTC)[reply]

There are lots of theories as to how this can work. Needless to say, yes, it seems pretty clear that it can work. Even in individual humans you can do weird things like have too many chromosomes (e.g. XYY syndrome, trisomy 21). It is not usually positive in such cases though, but the point is, it can happen—it doesn't mean automatic death of the organism or inability to reproduce. --98.217.8.46 (talk) 15:24, 2 July 2008 (UTC)[reply]

I haven't seen a definite resolution of this "problem", but from genetic sequencing of the human and chimp genomes, it's pretty certain that the Human chromosome 2 is equivalent to a fusion of two chimp chromosomes, including residual portions of the centromere and telomeres that are no longer functional. My best guess is that at some point in the past, a fusion event happened in a human ancestor, creating chromosome 2. At this point, all breeding partners to this individual still had the two separate chromosomes, but as the fused chromosome still had all the regulatory apparatus of both chromosomes, the cells were still able to line up and divide normally (although perhaps at reduced efficiency). Eventually for some reason (potentially unrelated to the chromosomal fusion) the fused chromosome came to be dominant (This can happen very rapidly - see founder effect). At that point the secondary centromere/etc. was superfluous, and could be lost through mutations, leaving us with a single chromosome. (See [10] for a related discussion - no endorcement implied, just the first decent result I got in searching) -- 128.104.112.147 (talk) 19:54, 2 July 2008 (UTC)[reply]

There seems to be a false assumption that males and females evolve completely independently of one another. This is untrue. For the most part, only the X and Y chromosomes evolve independently, in humans. I can try to make this into a reasonable objection to evolution:

"Since, in humans, the X chromosome determines (or at least triggers) female characteristics and the Y chromosome male characteristics, the two must evolve in parallel so that any change in females matches a corresponding change in males. For example, the tendency in females towards nurturing, homemaking, and gathering required a corresponding change in males toward hunting, to ensure that all the child-rearing and food provision needs of the group were met, utilizing a division of labor."

I suppose this is true, but, in cases where both sexes developed noncomplimentary traits, like everyone going hunting and leaving the children unattended, those traits would not be likely to be passed down. StuRat (talk) 15:30, 2 July 2008 (UTC)[reply]

Basically, he doesn't understand how evolution works, because he is making assumptions that aren't true. ScienceApe (talk) 04:55, 6 July 2008 (UTC)[reply]

He thinks there is a point where something is human, and the previous generation is not, but an individual does not change, it's an entire population. Eriorguez (talk) 22:30, 8 July 2008 (UTC)[reply]

What is the process of decompossition of the human body?

Do you need further information for that question? —Preceding unsigned comment added by Ros1701 (talk • contribs) 04:43, 2 July 2008 (UTC)[reply]

Have you read Decomposition#Human decomposition? Gwinva (talk) 05:04, 2 July 2008 (UTC)[reply]

Cavity in a Unifomly charged solid sphere..

consider a uniformly charged sphere with a cavity inside. the electric field inside the cavity is non zero and uniform... but if we draw a gaussian surface inside the cavity, the charge enclosed will be zero. so field zero on the surface... why the contradiction???? —Preceding unsigned comment added by 117.201.49.226 (talk) 07:46, 2 July 2008 (UTC)[reply]

The electric field is zero inside. I think you are confusing electric field and electrostatic potential. The latter is uniform inside and may or may not be zero, as you're free to define a point where it's zero. Icek (talk) 08:50, 2 July 2008 (UTC)[reply]

Maybe they were thinking of Shell_theory#Thick_shells - inside the 'solid' of this shell..

Shell_theory esp. Shell_theory#Inside_a_Shell may help here with the maths..

Shell theory explains the field (works for any inverse square relation ship) both inside and outside hollow spheres..

Note at the centre of the cavity the field is zero. I've no idea what you mean by "but if we draw a gaussian surface inside the cavity..." if you wan't the field then shell theory has a mathematical method of how to get it.

CLARIFY:Did you actually mean a solid sphere, or thick walled sphere with a hollow cavity inside or something else?87.102.86.73 (talk) 12:03, 2 July 2008 (UTC)[reply]

One answer "... inside the cavity, the charge enclosed will be zero. so field zero on the surface.." - the surface is not inside the cavity - it's on the boundary - which is different..87.102.86.73 (talk) 15:10, 2 July 2008 (UTC)[reply]

I hate to quibble, but nothing in the initial question stated that either: A) the cavity is spherical or B) the cavity is centered. Hence it could be inappropriate to jump straight to shell theory. Dragons flight (talk) 23:44, 2 July 2008 (UTC)[reply]

quote "consider a uniformly charged sphere..." - it's easily to miss..87.102.86.73 (talk) 12:05, 3 July 2008 (UTC)[reply]

That says nothing about the shape of the cavity within the sphere. Dragons flight (talk) 16:04, 3 July 2008 (UTC)[reply]

Actually, even if the field is neither centered nor spherical, it will still have zero electric field within, although yes, shell theory wouldn't apply. Someguy1221 (talk) 23:57, 2 July 2008 (UTC)[reply]

That's not true of a uniformly charged (in a volume sense) insolator. You are correct if you assume the sphere is a conductor, which also is not stated. Dragons flight (talk) 00:04, 3 July 2008 (UTC)[reply]

Can I get fully solved IIT-JEE question papers in Physics (mechanics only) of past 10-20 years?

I want to know whether I can get fully solved Physics question papers of past 10-20 years of the IIT-JEE examination from you. If you do this small favor for me,I'll be very very thankful to you.Please send them (if possible) as an attachment to your response mai

--Prateekgreat (talk) 10:22, 2 July 2008 (UTC)prateekgreat[reply]

I guess "Do your own homework" needs to be expanded to "Study for tests on your own." (I presume this person wants this as part of a review for his or her exam - not sure what that ITT-JEE exam is they're asking for.)

And...an attachment? I *really* hope the person means a link to a site with such, because I don't know how a person could even send it to the questioner personally.209.244.30.221 (talk) 21:54, 5 July 2008 (UTC)[reply]

What defines a yeast?

I posted this at Talk:Yeast but thought I should place it here too.

What defines a yeast? Do yeasts have some intrinsic trait that qualifies a particular species as being a "yeast" rather than just generically being a "fungus"? What is special about all (or most) of the species of yeast that qualifies them as yeasts? --Alecmconroy (talk) 15:07, 2 July 2008 (UTC)[reply]

According to yeast, yeast is unicellular. Otherwise, fungi are usually multicellular. I think that's probably the main distinction. — CycloneNimrod ^talk?_contribs? 16:08, 2 July 2008 (UTC)[reply]

How fast does the "wind" go when we blow on something?

Just blew on a crwling bug (likely an ant) to get it off my book outside, and it made me wonder - how fast does that "gust" blow that we creat when we blow?

I'm thikning, just from experimenting, maybe 50 MPH or so at first, but then of course air resistance will slow it down a lot. Plus, the amoung of saliva probably affects things. Holding my hand about a foot away from me (like when blowing out candles on a birthday cake) it still feels gusty, but not too much; maybe 20 MPH or so?209.244.30.221 (talk) 17:35, 2 July 2008 (UTC)[reply]

Sneeze gives some speed estimates. I would expect a sneeze is about the upper limit for how fast we can blow. So, somewhere less than the speed of a sneeze, which is itself the subject of widely varying estimates. Friday (talk) 17:43, 2 July 2008 (UTC)[reply]

Tree identification

My parents had a tree in their back yard, which was about, if I recall, about 3-5 metres tall, and had purple waxy leaves. It shed them in the winter, and was able to survive winter temperatures of -50 degrees celsius. I think it may have lived for about 15 years, and produced wrinkled, cherry like fruit. —Preceding unsigned comment added by Sliver Slave (talk • contribs) 20:25, 2 July 2008 (UTC)[reply]

First guess, purple leaf plum? Seems to survive in the cold, not sure about -50C though. --Wirbelwindヴィルヴェルヴィント (talk) 21:45, 2 July 2008 (UTC)[reply]

Crude oil estimates

Where/how do they come up with estimates for how long our fuel is going to last us? I mean how can they know how much there is when its all underground? --212.120.246.239 (talk) 22:06, 2 July 2008 (UTC)[reply]

Directly, geologists can use techniques like seismic mapping to figure out how large an oil pocket is. Indirectly, they can measure how fast oil is being pumped from the ground -- once the rate slows down, about half the available oil has been pumped out. Interesting articles to read are Hydrocarbon exploration, Exploration geophysics, and Hubbert curve --Carnildo (talk) 22:40, 2 July 2008 (UTC)[reply]

And, of course, how long oil lasts also depends on our rate of consumption. If we conserve energy and switch to alternative energy sources, oil should last longer. StuRat (talk) 03:54, 3 July 2008 (UTC)[reply]

They also have to account for the oil we haven't discovered yet, which can be estimated based on how commonly we find it, and they have to pick an arbitrary point where oil becomes too expensive to extract, and thus not counting things like tar sands. They also have to pick a point for not having enough fuel, as their will always be some left, but the speed at which we extract it will approach zero. — DanielLC 15:51, 3 July 2008 (UTC)[reply]

The traditional point of "too expensive to extract" is when the energy return on energy investment drops below 1: it takes more energy to extract the oil than can be gained by burning the oil. --Carnildo (talk) 21:46, 3 July 2008 (UTC)[reply]

Tar sands are counted as crude oil reserves, that's how Canada leapt at a stroke to become the nation with second-highest crude reserves. And in the case of the tar sands, the resource is at the surface, so it's relatively easy to estimate just how much is there. Franamax (talk) 01:04, 4 July 2008 (UTC)[reply]

Drafting

When driving on the interstate highways, if one wants to "draft" behind a fast moving eighteen wheeler, how close does he have to follow? WSC —Preceding unsigned comment added by 75.85.203.191 (talk) 22:29, 2 July 2008 (UTC)[reply]

Mythbusters did an episode on this. The benefit depends on how close you are: at a safe following distance, you get about a 5%-10% increase in fuel economy; if you're following at ten feet, your fuel economy doubles. --Carnildo (talk) 22:43, 2 July 2008 (UTC)[reply]

A word of caution: A truck driver once told me he really worries when someone drafts behind him. For one thing, you're driving in his blind spot when you're close enough to draft, and furthermore, truck tires sometimes throw their treads (you can see truck tire treads occasionally lying on the shoulders of freeways). These tire treads are heavy steel-belted rubber things that can fly right through your windshield. =Axlq 23:07, 2 July 2008 (UTC)[reply]

I keep hearing "If you can't see my mirrors, I can't see you", warnings about following too closely. I would expect that the truck driver would be more concerned about what's in front of him and to either side, since that is what controls his ability to maneuver. The obvious danger of drafting or tailgating is that the trucker slams his breaks on (presumably for good reason) and you don't, but that danger exists whether the trucker can see you or not.

A related question I've always wondered about: Has anyone ever studied the effect of drafting of the truck? I would think that the car would either (1) cause an increased low pressure behind the truck, thus causing additional drag and effectively stealing the trucks energy, or (2) the car would act as a tapered tail to the truck, thus decreasing the drag in the truck. -- Tcncv (talk) 23:33, 2 July 2008 (UTC)[reply]

A word of caution: with the Mythbusters episode in question, even the farthest distance tested was too close to constitute a safe highway-speed following distance.

As for the question of what drafting does to the truck's fuel economy -- interesting. You can't get something for nothing, but I don't know if car+truck would closely approximate a closed system for those purposes or not. — Lomn 00:11, 3 July 2008 (UTC)[reply]

The truck is already losing energy through air resistance - the car may well just be using that energy, so the truck doesn't lose any more. --Tango (talk) 00:15, 3 July 2008 (UTC)[reply]

At 55 mph, they got an 11% reduction in fuel usage at 100 ft and 39% reduction at 10 ft (Mythbusters' wiki). Whether or not you personally consider 100 ft to be safe may be something of a matter of opinion. It's not that uncommon on highways where I live to see cars following big rigs within that distance (which is about 6 car lengths). A big rig isn't capable of stopping on a dime, so even if he did slam on the brakes (which let's be honest isn't that common on freeways), you'd have the benefit of his slower stopping time to react and stop or dodge. Back when I was growing up 100 ft was actually the recommended distance at 60 mph, but I understand that people now recommend 150 ft. So you be the judge of whether the small reduction at 100 ft is worth the (in my opinion) small risk. Dragons flight (talk) 00:26, 3 July 2008 (UTC)[reply]

Given the huge mass the 18-wheeler carries, is it possible that even if you include reaction time that you would be able to brake safely in a normal vehicle?--droptone (talk) 12:14, 3 July 2008 (UTC)[reply]

By this reasoning a bicycle would out-brake a car, which is clearly not the case. Heavier vehicles have more powerful brakes, plus more wheels = more brakes to dissipate energy. Gandalf61 (talk) 16:17, 3 July 2008 (UTC)[reply]

Empirical evidence says otherwise. I haven't compared my 15-0 stopping distance to that of a bicycle, but I have compared 60-0 stopping distances with a semi (I was passing it when a car ahead of both of us lost control), and my car stopped well before the semi did. --Carnildo (talk) 21:54, 3 July 2008 (UTC)[reply]

The limiting factor in braking a bicycle is not the brakes. It's the tires, geometry, and weight distribution. The question is not whether you can slow down the wheels, but whether you can keep control of the bike when you do. Optimal braking is supposed to be around 70-30 or 75-25, weighting the front brake more, because the front tire presses into the pavement during braking and is therefore less prone to skidding. But hit the front brake too hard and you go over the handlebars. --Trovatore (talk) 22:15, 3 July 2008 (UTC)[reply]

Oh, that said--I think the drafting thing is seriously a bad idea. At highway speeds you should not cruise closer than 3 seconds behind the vehicle ahead of you. At 60 mph that's 264 feet. Of course you will have to get closer than that at times; you just shouldn't stay there. And if you don't stay there, you're not going to get much benefit in fuel economy. --Trovatore (talk) 22:47, 3 July 2008 (UTC)[reply]

Biting fly

Hi. What species of biting fly lives in southern Ontario, has a mildly painful bite, thrives near midday in June-July, and leaves a barely noticeable reddish bump about 1mm wide? I'm not asking for a diagnosis, just a vague species identification. The article doesn't seem to help, as it wasn't a mosquito, Tetse flies live in Africa, horse and deer flies are yellowish in colour, and black flies should be far more painful? I think it was grey-black in colour, had rufous-brown eyes, and was less than 1cm long. Its bite was that of a mild sting. It might sound like a blackfly, but aren't their bites more severe and larger? Thanks. ~A H 1^(TCU) 22:35, 2 July 2008 (UTC)[reply]

Around the Great Lakes, I've been bitten by many basic black biting flies. It is a mild sting - no worse than a mosquito bite. I've been bitten by deer flies also - it is severe. One caused my whole ear to swell up. So, I see no reason for it to be anything more than a basic biting fly. -- kainaw ™ 01:03, 3 July 2008 (UTC)[reply]

Why are Galaxies disc shaped?

Just curious why some galaxies are disc shaped and not 3D collections of stars (like how I imagine Nebulae are). --70.167.58.6 (talk) 23:30, 2 July 2008 (UTC)[reply]

Rotation - and nebulae are gas, not stars. Rmhermen (talk) 00:03, 3 July 2008 (UTC)[reply]

He wasn't saying nebulae were composed of stars actually. He was just referring to the shape. ScienceApe (talk) 18:50, 3 July 2008 (UTC)[reply]

Nebulae often contain stars as the condensing of the gas is what causes the formation of stars. Its why we can usually see them, the gas is illuminated by the stars in there. EagleFalconn (talk) 00:14, 3 July 2008 (UTC)[reply]

Galaxy formation and evolution and spiral galaxy are probably good places to start. As Rmhermen says, it's all to do with the rotation - when you rotate something, it generally flattens out. Just watch someone showing off while making pizza - rather than roll out the dough, they spin it round and it flattens out nicely. The reason for the difference in shape between spiral galaxies and nebulae, I would guess, is the speed of rotation (possibly, relative to their overall mass - it might be angular momentum that's actually important) and the length of time they've existed. It's going to vary from galaxy to galaxy and from nebula to nebula, though. Plenty of galaxies aren't disc shaped (see elliptical galaxy and irregular galaxy), and there may well be some disc shaped nebulae (I honestly don't know!). I hope that helps a little. --Tango (talk) 00:13, 3 July 2008 (UTC)[reply]

July 3

House water pressure from flow rate?

Can I determine the pressure of my water lines just from the flow rate and the physical dimensions of the tubing? Thanks.

I measured 2.1 GPM through a 1/2" copper tube.

--jcmaco (talk) 01:35, 3 July 2008 (UTC)[reply]

You may be able to get an approximation (e.g. water will flow through a hole at a rate determined by pressure based on its pressure coefficient) but in the case of water lines, you don't have any way to account for friction or restrictions upstream. When the water isn't flowing, your water pressure is independent of restrictions or friction that would affect the flow.

I recently measured my pressure after installing a reverse osmosis water filter in my kitchen. The manufacturer provided a table showing how much water would be drainable out of the storage tank for various water pressures. I drained 1.8 gallons out of a 4 gallon tank (meaning that my water pressure was sufficient to push 1.8 gallons into the tank), which equated to a fairly low pressure of 40 psi. =Axlq 05:43, 3 July 2008 (UTC)[reply]

Not unless you could work out the resistance of the pipes to water flow. A much easier way to get your pressure would be to use a manometer.if you cant get hold of a mercury manometer, one could be made with a long length of garden hose with a transparent bit at the open end. Having connected the other end to your tap, you climb up a ladder holding the transparent end. When the water stops flowing out the end, the pressures are equal and you measure the height of the tube above the ground. Since pressure is height times density, you know the pressure on your system. —Preceding unsigned comment added by 79.76.137.118 (talk) 02:45, 6 July 2008 (UTC)[reply]

Tell diffrence

If man and woman are berried in same grave how can u tell the diffrence after 1000 years/ —Preceding unsigned comment added by 79.76.174.168 (talk) 01:51, 3 July 2008 (UTC)[reply]

Human skeleton#Sex-based differences. PrimeHunter (talk) 02:02, 3 July 2008 (UTC)[reply]

I'd expect the boys to be blue-berried. :-) StuRat (talk) 03:38, 3 July 2008 (UTC)[reply]

Skin color of ancient Egyptians

So I've come across the debate of whether ancient Egyptians were black, white or something in-between. It seems that neither side has conclusive proof. My question is whether there are any accounts by travelers about the skin color of the country they had visited? If there are, then why is the debate still going on? —Preceding unsigned comment added by 24.7.54.224 (talk) 02:50, 3 July 2008 (UTC)[reply]

Mostly "white", or what essentially is the ethnic group we now call Arabs, I believe. Ancient Egypt consisted of Lower Egypt, in the North, and Upper Egypt, in the South, which were later united. South of that was Nubia and the kingdom of Kush, which, I believe were populated, then, as now, by "blacks". Since there was some interchange of populations, I'd expect some "blacks" to have been in ancient Egypt, especially Upper Egypt, as well. StuRat (talk) 03:27, 3 July 2008 (UTC)[reply]

As for evidence, there were many surviving color paintings in Egyptian tombs, so there's no need to resort to 2nd or third-hand accounts. Here's one that shows a nice racial blend: [11]. Forgive me if I break into a round of Ebony and Ivory while viewing it. :-) StuRat (talk) 03:31, 3 July 2008 (UTC)[reply]

Some people get confused about this because Cleopatra was white, but she had only four great-grandparents and all of them were of European descent. In general, you'd expect the skin shade of ancient Egyptian people to be about the same as that of peoples from around the world at the same latitudes, which would probably count as "somewhere in-between" on OP's proposed scale. --arkuat (talk) 03:44, 3 July 2008 (UTC)[reply]

It boggles my mind how anyone can have only four great-grandparents. Having eight should be more typical, no? Thank you for your replies, StuRat and Arkuat, but if what you said is correct, I don't understand why the debate still goes on. —Preceding unsigned comment added by 24.7.54.224 (talk) 05:02, 3 July 2008 (UTC)[reply]

Why the debate still goes on is perhaps a question better taken to the Humanities desk, but I think it has to do with the intellectual history of the African diaspora. Personally, I feel that it is important to recognize that people from all over Africa contributed to ancient Egyptian civilization, mostly for the simple reason that this is true.

As for having only four great-grandparents, that comes easy if your family culture encourages first-cousin marriage, or aunts marrying nephews, or uncles marrying nieces, or, as was expected of Egyptian royal families off and on since time immemorial, sisters marrying brothers. --arkuat (talk) 05:39, 3 July 2008 (UTC)[reply]

See pedigree collapse. Rmhermen (talk) 13:54, 3 July 2008 (UTC)[reply]

Pedigree of Don Carlos, illustrating pedigree collapse: grandparents (4) in yellow, great-grandparents (4) in blue

You may also be interested in Serious inbreeding among European Royals, which features several with four great-grandparents. - Nunh-huh 03:08, 4 July 2008 (UTC)[reply]

Good thing they didn't have Christmas then, talk about getting ripped off for presents! Franamax (talk) 19:55, 3 July 2008 (UTC)[reply]

We have an article on this debate: Race of ancient Egyptians. Rmhermen (talk) 13:54, 3 July 2008 (UTC)[reply]

"How" is quite simple: her grandparents on her father's side were siblings, and her grandfather on her mother's side was the brother of her paternal grandparents. The family tree at Cleopatra#Ancestry shows a remarkable degree of inbreeding. --Carnildo (talk) 22:02, 3 July 2008 (UTC)[reply]

The current majority in Egypt are arabs I believe, but they weren't the original inhabitants of Egypt when talking about ancient Egypt. I believe the copts are survivors of the original inhabitants of ancient Egypt. ScienceApe (talk) 17:26, 3 July 2008 (UTC)[reply]

hypoglycemia vs hypertriglycerides

what is the relationship of sugar to triglycerides? is it normal to have hypoglycemia with high triglycerides? —Preceding unsigned comment added by Docbenjie (talk • contribs) 05:54, 3 July 2008 (UTC)[reply]

Well, firstly hypoglycaemia is not normal. Secondly, hypoglycaemia (lack of glucose) is not affected by the level of triglycerides (which are fats). It's true that fat can be used as an energy source when glucose has been used up but that does not affect hypoglycaemia itself. That's just my knowledge though, if this affects you medically you should see a doctor. — CycloneNimrod ^talk?_contribs? 11:53, 3 July 2008 (UTC)[reply]

Hyperglycaemia (high sugar), seen in poor diabetic control, is associated with higher triglyceride levels. Not sure direct link, rather via common factor of hyperinsulinaemia (raised insulin levels in those who are insulin resistant due to obesity)... for a quick synopsis, see the PubMed abstract of: Reaven GM, Javorski WC, Reaven E (1975). "Diabetic hypertriglyceridemia". Am. J. Med. Sci. 269 (3): 382–9. PMID 168773.{{cite journal}}: CS1 maint: multiple names: authors list (link)David Ruben ^Talk 13:28, 3 July 2008 (UTC)[reply]

Cyclone: Hypoglycemia is not normal, but it's also not really abnormal, if that makes sense. Your body is constantly operating to maintain homeostasis, but sometimes one parameter or other shifts too much and your blood sugar drops. It's abnormal the same way dehydration is abnormal: it's an abnormal state of the body that can occur transiently to otherwise healthy people. Sometimes folks who exercise to hard without carb loading or people who eat an especailly carb heavy meal end up experiencing attacks of hypoglycemia. See Hypoglycemia#Causes and Reactive hypoglycemia --Shaggorama (talk) 07:13, 4 July 2008 (UTC)[reply]

Why don't spaceships turn into blackholes

According to Einstein, as a spaceship goes faster and faster towards the speed of light, the mass of the spaceship gets larger and larger while the lenght of the spaceship gets shorter and shorter.

So why don't spaceships turn into blackholes? 122.107.135.140 (talk) 12:17, 3 July 2008 (UTC)[reply]

Interesting question... I've never thought about it. I think it's just a matter of perspective, though - the spaceship gets denser from the point of view of a "stationary" observer, but it's density remains constant from its own point of view, and that's the reference frame you need to work in to tell if it's going to collapse into a black hole. --Tango (talk) 12:23, 3 July 2008 (UTC)[reply]

The question assumes you could accelerate the spaceship to a meaningful fraction of the spead of light, but as its mass increases, so does the force needed to accelerate further. Using the Lorentz transformation a ship at 99% the spead of light has a Mass 7 times that before and a length one seventh. Tango is correct that onboard every seems as normal, but to an outside observer indeed the density (M/V) would seem to be 7 / (1/7) = 49 times as great, which for any reasonable size ship is not going to have any real gravitational effect. 99.99% of c gets us to outside observer measured denisty x5000 and 99.9999%c to 500,000 density; so still not even in our thought experiments getting anywhere close to a density that might cause us problems. Schwarzschild radius indicates one would need to compress the Earth's 6,371km radius into just 9mm radius to become a black hole; that's a compression of over 700million !

See also Gravitational singularity#Curvature, about our assumptions about measurments of weight and distance need to be rethought.

Finally see Micro black hole#Creation of micro black holes for the effort to smash just a few atoms together (accelerator of 1000 light years) so I think we're safe from any fast spaceship ! David Ruben ^Talk 13:19, 3 July 2008 (UTC)[reply]

There is no physical limit on how close to the speed of light you can get. It may not be physically possible even under the most extreme assumptions to do it, but we can still discuss what would happen (as you can probably tell, I'm a mathematician, not a physicist!). So, if I got in a spaceship and travelled past the Earth at such an enormous that I observed the Earth's mass and dimensions to be such that it ought to collapse into a black hole, what would I see? The Earth obviously doesn't actually collapse, from the point of view of someone on Earth, but what would I see? I've been thinking about this, and I just don't know. --Tango (talk) 13:40, 4 July 2008 (UTC)[reply]

What, you think you might see the Earth collapse, even though it doesn't? No, that's not going to happen. Relativity isn't that relative. Gravitation is controlled by the stress-energy tensor, which is a frame-invariant quantity.

That's not to say that velocity is never relevant at all. The invariant mass of a complex system involving multiple bodies that are not at rest with respect to one another does depend on their relative velocities. I can imagine something like, say, a system of two sets of rods approaching each other very fast, both in checkerboard patterns so that they slide past each other. The invariant mass of this system would depend on the speed at which that happened, and maybe if you made that speed high enough you could get the system to undergo gravitational collapse in principle. --Trovatore (talk) 17:32, 5 July 2008 (UTC)[reply]

Oh, or here's another way of putting it: Suppose you fly your ship fast enough, and close enough to the Earth, that the Schwarzchild radius for the invariant mass of the combined system (Earth+spaceship) envelops both the Earth and your ship. Then, perhaps, the combined system collapses, both you and the Earth, and both you and observers on Earth agree this happens, though they may not agree on why. There are some possible gotchas here, not sure whether the Schwarzchild solution is still a solution for a system this asymmetrical, but it's at least sort of plausible. But note that the rest mass of your ship is a key ingredient. If your ship is just a massless, energyless, metaphysical point of view flying past, there is no speed at all that would cause the Earth to collapse, either as it observes it or as you do. --Trovatore (talk) 18:05, 5 July 2008 (UTC)[reply]

The rest mass doesn't change. Only the relative mass changes. The matter that makes up the ship doesn't increase, nor does it become more dense. In order for a black hole to form, you need to mash a large mass into a very dense form. Like collapsing Mount Everest into something smaller than a human cell. ScienceApe (talk) 17:20, 3 July 2008 (UTC)[reply]

Also, the situation described sounds an awful lot like a situation where you'd need quantum gravity. -RunningOnBrains 22:59, 3 July 2008 (UTC)[reply]

Our article on mass in general relativity answers this question. It says "Can an object move so fast that it turns into a black hole? No. An object that is not a black hole in its rest frame will not be a black hole in any other frame ...". There is also a link to this page in the Usenet Physics FAQ. Gandalf61 (talk) 14:55, 4 July 2008 (UTC)[reply]

Thanks Gandalf61 for pointing to that answer. I also not the later Q&A re heated atoms possibly having more mass because thay have kinetic energy when heated. David Ruben ^Talk 20:53, 4 July 2008 (UTC)[reply]

Wheat allergies

Hi. I'm curious about wheat allergies as someone I know has one. Could it be that such a person would have a worse reaction from eating a "whole wheat" product (say pasta) than a regular one? --Dweller (talk) 13:42, 3 July 2008 (UTC)[reply]

Wikipedia cannot, does not, and will not provide medical advice. That said, you may want to read our Wheat allergy article, a more medical website, or consult a physician. Plasticup ^T/C 13:57, 3 July 2008 (UTC)[reply]

I'm not looking for medical advice, nor do I need to consult a physician as there's nothing wrong with me. I'm just curious. But thanks for the articles - I'll read them. --Dweller (talk) 14:24, 3 July 2008 (UTC)[reply]

The first of those articles does mention whole wheat, but the reference comes in an incomprehensible paragraph. The second article does not mention whole wheat. --Dweller (talk) 14:29, 3 July 2008 (UTC)[reply]

Everything I look at merely lists foods to be avoided, with refined wheat and whole-wheat considered to be the same. It could be that the difference in allergic reaction, if any, is not significant enough to be mentioned. Fribbler (talk) 14:37, 3 July 2008 (UTC)[reply]

Thanks. --Dweller (talk) 14:47, 3 July 2008 (UTC)[reply]

Based on reading the wheat allergy article, it looks to me like, because there are many allergenic components in wheat, you get all of those components with whole wheat and less of them with processed wheat. The processing may remove some of the minor allergens (but seems to preserve the main one, gluten). A hypersensitive person could conceivably have a worse reaction if more allergens are present. ~Amatulić (talk) 17:43, 3 July 2008 (UTC)[reply]

Also, remember that allergies are funny things. People with a severe allergy can have a bad reaction to tiny amounts of allergen and past reactions are not necessarily indicative of future reactions. So the distinction between whole wheat and refined wheat products may be entirely irrelevant. 86.141.89.124 (talk) 23:39, 4 July 2008 (UTC)[reply]

botanical name

What is the botanical name of the tree that is supposed to go to sleep when the sun sets and rise up again with the sun? Its leaves droop down in the night and freshen up in the morning.

Shyam59.92.72.54 (talk) 14:47, 3 July 2008 (UTC)shyam[reply]

With heliotropism, flowers and leaves track the sun as it moves through the sky. At night they either default back to facing east or just some random orientation. -- MacAddct  1984 ^{(talk  contribs)} 16:31, 3 July 2008 (UTC)[reply]

There are several types of trees that do this. Albizia julibrissin is the one that came to mind first.--Eriastrum (talk) 23:19, 3 July 2008 (UTC)[reply]

I like the ones you touch and they fold, like Mimosa pudica. Then there's one with a folding name: Prayer plant. But they're not trees. Julia Rossi (talk) 09:56, 4 July 2008 (UTC)[reply]

Species with long luteal phase

I am interested in which species have a long luteal phase of the estrus cycle. So far I only know that dogs and elephants fall in that category. Any other species? Thanks in advance. Arisa. —Preceding unsigned comment added by 131.211.166.194 (talk) 15:05, 3 July 2008 (UTC)[reply]

After googling a bit, I gotta admit this information is difficult to find. I did confirm that elephants have the longest cycle. I thought maybe other large mammals like whales may also qualify, but I couldn't confirm that. ~Amatulić (talk) 21:59, 3 July 2008 (UTC)[reply]

Material acting like Maxwell's demon?

Hi all,

Is there anything theoretically impossible about a material, say some kind of not-yet-invented cloth made out of nanotubes, which only lets fast-moving molecules through? How about a material which only lets molecules through in one direction? I can't see anything wrong with the idea except that it may never be invented. But wouldn't such a material essentially act as Maxwell's demon and break the Second Law of Thermodynamics (allowing us to create order out of disorder)?

All the arguments against the demon seem to involve the energy that he must exert separating the molecules, or the energy that he adds observing them, or the lack of infinite memory to know where they all are (I've never really understood that one). This material, however, wouldn't need to "know" which molecules are fast any more than a coffee filter "knows" that water can pass through and larger particles can't. And likewise, like a filter, it wouldn't need to do any work to let the fast molecules through.

So is there anything theoretically wrong with this idea?

Thanks! Sam 16:51, 3 July 2008 (UTC)

I don't really see anything theoretically wrong, per se, with a membrane that would only allow things moving quickly to pass through. As I think about it more, theres plenty of those in existence...pretty much everything fits the criteria. Its just a matter of how you define fast. The penetration of cosmic rays through buildings and such is a good example. Unidirectional motion is also possible, but usually in cases like veins where you've got some kind of pressure being exerted and valves used to control flow.

A common error made when people look at the Second Law of Thermodynamics is they forget the caveat to that rule. You cannot create order out of disorder without adding energy. There is energy in the membrane. If it stops slow moving particles, then it is doing some kind of work from some energy source (mechanical, chemical or otherwise) to stop them. If we were to use a piece of paper as the membrane, its still doing that same work on a fast moving particle, but the fast moving particle has so much energy that it keeps going anyway and breaks the bonds or whatever. This seems a little convoluted, but I hope it helps. Lemme know if I should try again...EagleFalconn (talk) 17:14, 3 July 2008 (UTC)[reply]

This is an interesting question. Although I am certainly not the scientist that Maxwell was, nor do I claim to be anything close, I will give it a try. First, this is a thought experiment for a reason. We have several ideal parts of this system: the box, the particles, the wall, the evil-looking green demon, and an ideal separation from the rest of the universe. It is hard to imagine anything close to this level of ideality in a real world system. With that said, the second law of thermodynamics is built to work for ideal systems, too.

One comparison you draw is the difference between a coffee filter and a fast-molecule filter. This is a broken simile I think. A coffee filter distinguishes water from grounds based on size. Energy is a totally different beast. One of the facets of the uncertainty principle is that momentum and position cannot be measured simultaneously. This is because in the act of measuring, the particle is perturbed, changing the other property. In the same way, if a barrier were created such that only particles of a certain energy could pass through, it would strip the particles of that energy as it passed through the barrier, eliminating any gain in entropy. I say this carefully though, because if the particles being discussed were electrons, by using a tunnel barrier you could take advantage of the quantum tunnelling effect and allow particles of certain energy to pass through without such a loss in energy. The risk here is that tunnelling is itself a probabilistic process. ANY electron could conceivably tunnel without losing energy. Higher energy ones just have a larger probability of making the leap so to speak.

What all of these theories lack, however, is an impetus for separation. In your coffee filter example, water and beans are on the same side of the filter and gravity pushes the water through. Now imagine trying to operate the same system in a zero-g environment. That wouldn't really work. Sure all the grounds would stay on one side, but the water would be everywhere. In the same way, unless some gradient were created to move the particles in the right direction, equilibrium would still exist. If you started with all particles on one side and allowed them to move to the other via any of the previously mentioned methods without field, the particles could just as easily move back again, given a high energy. What you are talking about is some sort of thermodynamic diode or valve that requires no potential.

My last comment is this: great thinking. Diodes exist, spin valves exist, many things for separating particles of different properties exist. All need energy. Minimizing that energy is key. It is possible that Maxwell's demon may never exist, but something close to it (operating on the energy of room temperature, for example) would not violate the second law, and may well be very useful. Gjmulhol (talk) 17:18, 3 July 2008 (UTC)[reply]

Thanks for the two comments. In response to the argument about the "impetus for separation," I'm not sure that this is needed. (1) If we have a zero-g box with coffee and water on one side of a coffee filter, eventually there will be a mix on one side and pure water on the other, so some separation has occurred (even if not all the way), and (2) If it is a one-way filter (like I mentioned above), eventually each water molecule will have randomly gone to the other side and not been able to get back, thus completing the separation.

I think you're both probably right about the fact that it may be impossible to separate fast- and slow-moving molecules without slowing down the fast-moving ones -- making them rip through the filter, for instance. (I don't think, however, that a barrier has to do work on a slow-moving molecule to make it bounce off -- the molecule's energy would be maintained).

Does the energy that it seems that a molecule loses as it goes through the barrier have to be so much that the fast molecules that pass through it a turned into "slow" molecules? By which I mean, would it be theoretically possible for a barrier to stop all molecules with V < x, and when fast molecules (V > x) break through, their speed is still greater than x? If so, we're still creating a potential difference between the two sides of our box that could be used to generate work, right?

Thanks, Sam 17:45, 3 July 2008 (UTC)

Well, I think we need to distinguish between molecules and electrons here. I am not an expert in physical chemistry. I do have some training in solid state physics. When an electron impinges on a surface, it can do one of 3 things:

bounce back
tunnel through
go over

By go over, I mean have enough energy that it is able to go through the barrier. If the barrier is an energetic one, which I think is what we are talking about here, it will sacrifice the energy used to overcome that barrier and fall to the lowest state available. If you were to erect a barrier of a specific height x (to use you example from before), then the only reason that the particle can pass is that it has enough energy to give. It is like buying a ticket, if you don't have the money, you don't get in. If you do have the money, you get it, but you leave the money.

I still stick with my p-n junction argument that I posted a few minutes ago farther down. I think that is the closest thing of a separating barrier. A solar cell is based on the exact principle described here, but you need that pesky addition of sun to provide some nominal amount of energy to cause current flow.

I honestly have no idea whether there is some corollary to molecular movement as I have described electron movement. Gjmulhol (talk) 23:28, 3 July 2008 (UTC)[reply]

Slightly different question, brought to mind from the comments above: Is a one-way filter alone theoretically plausible? If so, would this be a great way to produce usable energy out of un-ordered states? Say I strap a one-way filter to one side of a box, so that air can only go in. The pressure in the box can only increase. If I punch a hole in the other side and add a turbine, my one-way filter will create a stream of air, which could be used to generate electricity, right? Any theoretical objections to that one? Thanks again! — Sam 17:51, 3 July 2008 (UTC)

Well, other than being a perpetual motion machine... (The act of ordering states from unordered states requires energy. Pure and simple. Any instance when you find yourself suddenly getting lots of energy out without putting any energy in is a sure sign that something has gone wrong in your calculations.) --98.217.8.46 (talk) 18:26, 3 July 2008 (UTC)[reply]

The input energy in his example is from the random movement of particles in the air. I don't see any immediate flaws. Oh, and I like to think of your theoretical material as fish trap. Plasticup ^T/C 19:26, 3 July 2008 (UTC)[reply]

Probably the best example of something that seems to violate the second law is an optical isolator. But even a hypothetical perfect optical isolator doesn't do it, not that I really understand the explanation [12] Someguy1221 (talk) 19:37, 3 July 2008 (UTC)[reply]

One example of something similar is a solar cell. Although it does absorb energy, based on the p-n junction's built in potential, electrons flow one way and holes the other. This creates a current. It is a one-way system. Even when no light is on it, there is some small generated 'dark' current from heat effects. Like I said though, it is not a closed system and does require some sort of energy. Gjmulhol (talk) 23:16, 3 July 2008 (UTC)[reply]

(ec)Scale matters for this question. Newer research points out that the Second Law of Thermodynamics does not apply to nanoscale systems.[13] I read a few weeks ago^{[citation needed]} that one of the most promising future ideas in nanotech is harnesing Brownian motion to power molecular machinery.-RunningOnBrains 23:18, 3 July 2008 (UTC)[reply]

I would be very interested to see the full text of that article. Much of the BBC coverage seems simplistic for a such bold claims. Do you have the DOI, author name, or date of the article? I know from personal experience that forces at the nanoscale level are much different than at even the micro level. For example, capillary action and surface tension are the dominant forces in any system with nanoscale features. I would guess (and remember I haven't yet read the article, so I don't know the details) that the Second Law of Thermodynamics is not being violated. There must be energy coming from somewhere (the shaking of the canister? heat from the room? potential energy of the charge on the bead? again, I don't even know what they measured). Do the researchers make such claims of violating the second law explicitly? If so, this paper really should have been in Nature or Science rather than PRL ;).

Much Brownian motion comes from heat. Motion cannot exist without energy. By harvesting the energy from Brownian motion, we will simply be absorbing heat. This could be done from phonons or diffusion current. Gjmulhol (talk) 23:36, 3 July 2008 (UTC)[reply]

The second law of thermodynamics has been put through every thought experiment anyone can think of. Have some faith in these scientists. Don't ask if your idea will work; ask why it won't. As for why it won't:

I don't see how a material that only lets fast-moving particles through can be used to break the second law of thermodynamics. Maxwell's demon requires it to only allow fast particles one way and only allow slow the other. I don't know if it's possible.

The one-way filter is impossible. ~~In addition to breaking the second law, it wouldn't be time reversible.~~ After writing the next part, I noticed it could be time reversible.

I don't know much about the optical isolator, but I'm going to guess that it either can't be made reflective (so entropy is gained from light turning to heat). It's time-reversible because switching the direction time runs would switch the direction of the magnetic field, causing the isolator to face the other direction, and if it can absorb light, it can also spontaneously emit it.

This part's not really related, but it's a pet peve of mine: Gjmulhol, the uncertainty principle is because of inaccuracies in measuring. It's possible to make multiple particles with the same quantum properties, and to measure different properties in different ones, thus bypassing the observer effect.

98.217.8.46 and Plasticup, this isn't about creating energy; it's about destroying entropy.

RunningOnBrains, they don't go into much detail so I'm going to say that it's A: talking about the fact that at a small scale, entropy has some chance of decreasing, but won't consistently, or B: wrong. Also, take a look at the Brownian ratchet, which is based on building up small scale chance decreases in entropy, and still doesn't work. — DanielLC 22:46, 4 July 2008 (UTC)[reply]

Shooting down the barrel of a tank

Kinda inspired by a previous question. Lets say you have a high caliber machine gun, and you shoot down the barrel of the main gun of a tank with full automatic fire. What would happen? Would the cannon be damaged? Could it still fire as if nothing happened? Would the bullets cause a "clog" eventually? ScienceApe (talk) 17:16, 3 July 2008 (UTC)[reply]

That depends on a couple of things: (a) your aim, and (b) the cannon bore size. You could probably fairly easily shoot a 50-caliber machine gun down the barrel of a 155mm howitzer cannon, without the bullets touching the cannon barrel.

Even if the bullets did touch the side of the barrel, they impact at a grazing angle and will likely not cause any more damage than a cannon projectile being shot through it.

If a cannon barrel is clogged, you wouldn't want to fire the cannon, or you risk rupturing the barrel. ~Amatulić (talk) 17:30, 3 July 2008 (UTC)[reply]

Well basically what I'm asking is if you took a 50 cal and fired down the barrel of the cannon of a tank. Would it damage it, and/or would it clog it? ScienceApe (talk) 18:48, 3 July 2008 (UTC)[reply]

If there was a shell loaded, you might be able to detonate the shell (cover your face if you're looking down the barrel). Otherwise, the bullets would strike the breech - likely they wouldn't damage it all that much, unless you hit the firing mechanism, but you could stick enough lead onto the breech to make it unusable to seat the shell. And yes, if you keep firing an infinite number of bullets, eventually you'll clog the barrel with hot lead. Franamax (talk) 19:39, 3 July 2008 (UTC)[reply]

Ah... I assumed your original question was about firing a gun through a tank barrel from the inside of the tank. You're asking about firing a gun into the muzzle? That could damage the breech if the cannon isn't loaded, not only in the way Franamax describes, but also in that some cannons use a laser to detonate the propellant, and you could damage the laser window. If the gun is loaded, you might hit the fuzing mechanism of the round, or even clog the barrel, which would get cleared out when the cannon is fired, possible with damage to the barrel. However, I doubt you would do serious damage to the barrel by firing into it due to the grazing angle the bullets make with the inner wall of the barrel. ~Amatulić (talk) 21:53, 3 July 2008 (UTC)[reply]

If you simply roll a rock down the barrel or pack some mud in it and induce the tank crew to fire through the barrel, that should cause the gun to explode , possibly killing the crew. This recommendation is from a friend who says this was a tactic used against German tanks in WW2 when it was infantry against armor with no antitank weapons. A tank without infantry support is not all that secure against infantry attack. Edison (talk) 14:11, 4 July 2008 (UTC)[reply]

Imagine that - Sarge hands you a rock and says "go fight that tank" :) Franamax (talk) 23:05, 5 July 2008 (UTC)[reply]

Strange skull

Hi guys, I was wondering if somebody could identify the animal this skull belongs (belonged :p) to:
It was found on the beach somewhere in northern Crete. It is around 5-6 cm in length.
http://img20.imageshack.us/img20/2782/scull1ad2.jpg
http://img20.imageshack.us/img20/4995/scull2gc4.jpg
http://img503.imageshack.us/img503/6638/scull3ft8.jpg
Thanx a lot!
PervyPirate (talk) 17:25, 3 July 2008 (UTC)[reply]

At first I thought it might be some sort of bird, but it looks like there are teeth in the front. A big rat, maybe? It doesn't look like what I'd expect for a fish. Great pictures, though. If someone can identify it, and Wikipedia has an article on it, please put that picture in the article. ~Amatulić (talk) 17:35, 3 July 2008 (UTC)[reply]

Was I the only person who saw those and immediately thought 'dragon'? :) At a guess, I'd say some sort of predatory eel... --Kurt Shaped Box (talk) 17:46, 3 July 2008 (UTC)[reply]

That was my first guess as well, since moray eels are quite common in that part of Greece, but a quick google image search proved me wrong... PervyPirate (talk) 17:54, 3 July 2008 (UTC)[reply]

Are you sure it's a skull? It looks to me like a pelvic bone. Compare the third image above with this of a seagulls pelvis: [14]. Fribbler (talk) 17:57, 3 July 2008 (UTC)[reply]

Wow! I would never have guessed! Thank you Fribbler (and everybody else)! However, since it's not a skull after all, I doubt the pics will be of any use in an article. PervyPirate (talk) 18:06, 3 July 2008 (UTC)[reply]

Why not? Bird anatomy in the skeletal section, or pelvis (currently an overly human-centric article) could benefit from one of those nice, clear pics! Fribbler (talk) 18:11, 3 July 2008 (UTC)[reply]

Fair enough. I will ask permission from the friend who made the pictures, upload them properly, and update the talk pages of the articles you mentioned. PervyPirate (talk) 22:12, 3 July 2008 (UTC)[reply]

Pelvis? Whoa. How utterly unexpected. Shades of three blind men and an elephant? ;) --Kurt Shaped Box (talk) 18:37, 3 July 2008 (UTC)[reply]

Or at least a few men who haven't spent much time around comparative anatomy courses... skulls are pretty distinctive, and even though I arrived to this question pretty late in the game it was clear that those pictures weren't of a skull. --98.217.8.46 (talk) 19:18, 5 July 2008 (UTC)[reply]

Great pictures by the way, you've got some skill, like that as a desktop background...(got any more?)87.102.86.73 (talk) 19:49, 3 July 2008 (UTC)[reply]

To be honest, these are not really my pics. But I'll pass the good words to the friend who made them. Cheers! PervyPirate (talk) 22:12, 3 July 2008 (UTC)[reply]

basic difference between stroke and depression?

Okay, first, let me assure you I'm not looking for a diagnosis. Rather, I have a question more about the basic differences in these two.

It seems in depression, some of the basic themes apply as to those in strokes. A person may have difficulty speaking, moving, etc.; becuase strokes apparently don't have to affect only one side of the body. And, that in severe enough depression, close to a nervous breakdown, such things can, in fact, stop, just like in a stroke.

Is it common for people to mistake the two? Or, to miss a stroke in a person who has severe depression? Becasue, if the person can't bring themselves to move, and suddenly can't move, how do you know the difference?

Also, has anyone ever tried stroke recovery methods for combatting depression? My guess is it wouldn't work, but a lot of those symptoms are seeming the same right now.

I'm sure things that confuse the common person (like myself) are very clear to someone who has spent 4 years in medical school, another 4 in residency :-)209.244.187.155 (talk) 18:25, 3 July 2008 (UTC)[reply]

They are totally different. Tennis elbow and amputation might both leave you with a sore arm, but they are not related in any way. A stroke is a physical disease and depression is a psychological one. Plasticup ^T/C 18:47, 3 July 2008 (UTC)[reply]

Depression does not cause paralysis! Jdrewitt (talk) 19:50, 3 July 2008 (UTC)[reply]

Perhaps you're confusing depression with a total nervous breakdown? They can prevent the body from functioning, but only because the central nervous system is so ovreloaded. It's not a clinical term per se, but a pshycological condition, in general, is a function of chemical imbalance, I believe, not like a stroke, where it is somply a blood clot blocking something. Also, during a nervous breakdown, cells don't die. (I'm putting it in very simple terms, but seening as you could be confused between physical and psychological conditions themselves, so I felt that might be helpful.)

I'm not sure that stroke therapy could help with a nervous breakdown, becasue the object of stroke therapy is to teach the brain to function again. (Again, making it very simple.) My guess is that it could help to some small degree, if the person views him or herself incapable of simple tasks (for instance, they had stopped speaking), and they need to be encouraged to do them...but that would only be part of the treatment.

I know this kind of goes off the OT, but...I'm struggling to understand the nature of the question, and I felt I had to try *something*. Somebody or his brother (talk) 01:08, 4 July 2008 (UTC)[reply]

One general way to think of it is that a stroke is neurological -- lack of oxygen to the brain -- whereas depression is psychological (very broad generalization that I realize treats chemical imbalances too lightly). As they are so different in nature, the treatment of one doesn't really apply to the other. One important difference between the two is that a stroke (also reffered to as a brain attack) is an emergency condition. If chronic depression is left untreated, over time the person may lose control of their lives and potentially kill themselves. If a stroke is left untreated for a matter of hours, the individual may suffer permanent nerve damage and die within days. --Shaggorama (talk) 06:59, 4 July 2008 (UTC)[reply]

There are several reasons why these two conditions should not be confused by a competent medical professional. Firstly the onset of the two conditions will be different. In the case of a stroke caused by a thrombus (as opposed to a cerebral bleed) there will be a fairly quick onset, varying from instantaneous to tens of minutes. Immobility caused by depression is likely to take weeks or months to develop, a gradual process that should be apparent to the person's family or friends. The presentation of the two conditions are quite different. Following a stroke the person will have variable paralysis and impairment of conciousness depending on the severity of the thrombus. There will be specific neurological signs present in a person who has suffered a stroke that will be absent in a person who has impaired movements caused by deep depression. In a person with incapacitating depression all their concious mental and physical bodily processes are inhibited but in a person who has suffered a stroke there will be some variability in the movements of the body, and their thought processes (those still working) will react at normal speed. The main difference will however show itself in the onset of the condition. It is very unlikely that 'stroke therapy' will assist someone suffering from a deep depression - or vice versa. Richard Avery (talk) 07:07, 4 July 2008 (UTC)[reply]

While trying to avoid giving actual medical advice, let me also add that a person who has suffered a stroke can lapse into depression - i.e.: person who suffers is too weak to get out of bed easily, or paralyzed for a short time with a transient ischemic attack, winds up becoming depressed about this and may begin to get more depressed, but the depression does not relate directly from the death of brain cells, but rather from the notion that said person is not able to function at their previous level. (So, to the untrained eye, it may *look* like they're related in that instance, when they're not. I shan't delve too much further, though, because it is possible that there is a medical concern on the Op'ers part, and that this is where the confusion lay.Somebody or his brother (talk) 22:02, 5 July 2008 (UTC)[reply]

Gnat ID

I'm trying to identify a Gnat that has a black abdomen which is clearly separated from the thorax (although this could be an illusion produced by a black intrail or its contents and a clear thorax) like that of an ant and extremely large red eyes and relatively short wings which is about a mm long.

The remarkable thing about this Gnat is its ability to hover and to precisely adjust its location to maintain a distance of about 3 to 6 inches from any object which comes close and to relocate itself to its original position when the object moves away in sync with the objects motion.

What species might this Gnat be? -- adaptron (talk) 19:57, 3 July 2008 (UTC)[reply]

Could be a fruitfly. Take a look at this [15].--Eriastrum (talk) 23:14, 3 July 2008 (UTC)[reply]

Yes, very close for the eyes, thorax also is orange but only a transparent tint. The legs are also clear. Wings, however, are much shorter. The hovering behavior is so controlled and precise its scary - as if being operated remotely in real time by a much bigger brain. :-) -- adaptron (talk) 23:31, 3 July 2008 (UTC)[reply]

...as a matter of fact here it is... Drosophila melanogaster. -- adaptron (talk) 23:33, 3 July 2008 (UTC)[reply]

July 4

Trivalve moluscs

Do these actually exist? It's just that I seem to remember reading something about them years and years ago somewhere...^{[dubious – discuss]} --Kurt Shaped Box (talk) 00:30, 4 July 2008 (UTC)[reply]

I see trivalves mentioned fairly often in fantasy fiction and science fiction. There's also this story about Constantine Samuel Rafinesque concerning a discovery of a trivalve mollusk, which was a joke played on him by John James Audubon. There's also a page from Google books about the incident. ~Amatulić (talk) 00:52, 4 July 2008 (UTC)[reply]

Is tungsten ferromagnetic?

I checked the article, and all it said was no data... ScienceApe (talk) 06:12, 4 July 2008 (UTC)[reply]

I am pretty sure the answer is no. Graeme Bartlett (talk) 06:48, 4 July 2008 (UTC)[reply]

No, it isn't. Though some tungsten-containing compounds are. 131.111.228.15 (talk) 07:44, 4 July 2008 (UTC)[reply]

Well I know they use tungsten projectiles in railguns, so if it isn't ferrous, then how do they propel it? ScienceApe (talk) 16:32, 4 July 2008 (UTC)[reply]

The projectile (and rails) of a railgun only need to be good conductors; no ferromagnetism required. Algebraist 16:40, 4 July 2008 (UTC)[reply]

Seems like it. Thanks. ScienceApe (talk) 17:52, 5 July 2008 (UTC)[reply]

where do herring gulls and black back gulls sleep at night?

Does anyone know what sort of places they usually sleep in? They seem to all leave the town and the local landfill area at night and all go off in the same direction. I'd like to be able to drive out and see them sleeping one night. —Preceding unsigned comment added by 84.67.233.220 (talk) 07:29, 4 July 2008 (UTC)[reply]

I believe Gulls are naturally cliff dwellers, I imagine they would roost on cliff faces if they're near the sea. For urban gulls, buildings would present a similiar landscape. —Preceding unsigned comment added by 62.25.96.244 (talk) 09:42, 4 July 2008 (UTC)[reply]

Just to note that I am not a Gull and am not called Cliff. --Dweller (talk) 15:05, 4 July 2008 (UTC)[reply]

Battery-powered microphone amplifier

Can someone suggest a battery-powered circuit for amplifying the output of an electret mike to drive a headphone (the type commonly used for portable media players)? The circuit should draw very little power, require no more than 2 AA batteries, and be buildable using easy-to-find parts. —Preceding unsigned comment added by 71.175.20.73 (talk) 11:45, 4 July 2008 (UTC)[reply]

You might look at [16], they are a huge producer of ICs and sell all kinds of audio amps. You would probably be best to purchase from [17]. Depending on your requirements, this could be a good starting point for selecting them [18]. You should know the impedance of your headphones. The data sheets of all these audio amplifiers should have sample schematics of simple circuits that you can start from. Depending on your input, you might need a preamp. It is also important to note that if it is a condenser mic, you will need to bias the microphone as well. Gjmulhol (talk) 12:13, 4 July 2008 (UTC)[reply]

On a side note, be careful about grounding. Audio signals are very sensitive to bouncing ground planes. Gjmulhol (talk) 12:17, 4 July 2008 (UTC)[reply]

"Grounding" is important, as is shielding of microphone leads, to prevent hum from influence of the powerline frequency electricity, but certainly no earth-ground connection would be needed. Edison (talk) 14:04, 4 July 2008 (UTC)[reply]

Termite control in Scarborough, Ontario, Canada

Dear Wikipedians:

Does anyone know some termite control shops that are located in Scarborough, Ontario, Canada?

Thanks.

74.12.39.232 (talk) 15:31, 4 July 2008 (UTC)[reply]

PCO Pest Control used to sponser my T-Ball team, but a phonebook or a google are better bets. WilyD 15:34, 4 July 2008 (UTC)[reply]

Hi. Have you tried yellowpages.ca? Thanks. ~A H 1^(TCU) 15:41, 4 July 2008 (UTC)[reply]

Overlapping tidal radii

Hi. On an issue of SkyNews magazine, I read that stars can have large zones where an object will orbit it, 1.5 - 15 light-years in radius. It said that the Sun's zone, called the tidal radius, is 3.5 light-years. It also said that they can overlap. This made me wonder.

The nearest star system, Alpha Centauri/Rigil Kentarus/Toliman, is 4.3 light-years away from us. If the sun's tidal radius is 3.5 light-years, I'd expect Alpha Centauri's radius to be a bit larger as it has higher total mass, say 4.0 light-years. This leaves 3.2 light-years of overlapping tidal space at the horizontal plane diametre. Well, is it plausable that AlphaCen has an oort cloud of comets, just like the sun?

I would like to know (and this is not homework, and I don't know if I'm able to calculate this):

The volume of overlapping space, in cubic light-years;
The number of Oort cloud comets estimated to be orbiting the Sun in that space;
The approximate percent of the Sun's tidal sphere surface that is within the overlapping zone;

Or, is the tidal zone not a sphere, but an elliptoid, just like the Heliophere? Oh no!!! Is the spherical model a good approximation? Or is it possible to calculate the same parameters for an elliptoidical model? Would we know in which direction the tidal elliptoid extends farthest and its shape, if it is indeed an elliptoid? Why is the Heliosphere elliptoidical, does its direction change over time, what direction does it point in, does it have any effects on comets just entering the Heliosphere, and could its shape be caused by Nemisis?

Consider the known non-returning comets, with eccentricities of ≥1. Do we know any which have the open end of the parabola(/hyperbola?) pointing towards the AlphaCen direction? Might they be from/going towards the AlphaCen system? Might some be coming back? Are there any other star systems which have tidal radii overlapping ours? Three or more overlapping together? Could this explain some Oort cloud collisions that send the comets plunging towards the sun?

How will AlphaCen's negative radial velocity change this zone over time? What about Gliese...(something, forgot its number, in Ophiuchus) and Barnard's Star as they approach our Sun? Is there an article concerning the subject of orbital tidal radii (and I'm not referring to the Roche limit, which "orbital radius" redirects to)? Might this explain some extinctions?

Using current extimates, about how many comets are sent towards our sun due to the overlapping tidal zone from AlphaCen per each specified specific period of time (eg. per year, per century, per millenium, and how many actually arrive)? Or is it not possible to answer some of these questions due to limited knowledge data? Thanks. ~A H 1^(TCU) 16:17, 4 July 2008 (UTC)[reply]

I've never heard of "tidal radius" before, and our article on it redirects to Roche limit, which has nothing to do with what you're talking about. The closest term to what you describe that I've heard is Hill sphere, but that's for one object orbiting another, rather than two separate stars. So, I'm not really sure what a tidal radius is meant to be (I can't see what your description has to do with tidal forces, for a start!). The maximum distance at which you can have a stable orbit around a star is going to depend on the other stars around it, and there won't be any overlap (they might go right up to eachother, though, I'm not sure if there would be a region of instability inbetween or not). It's certainly not going to be a sphere. An orbit around the sun in a plane perpendicular to the direction of Alpha Centauri could be larger than the distance to Alpha Centauri, I suppose, but one in the same plane as Alpha Centauri would be unstable if it got too close to the star. --Tango (talk) 16:47, 4 July 2008 (UTC)[reply]

Hi. What I (and the magazine) mean by tidal radius might have nothing to do with tidal forces. It states that close orbits around a star can be stable, but the tidal radius, according to the magazine, is, beyond which, an object will no longer be within the gravitational reaches of the star.

Within the "tidal radius", objects like planets, comets, and other bodies are close enough to the star to be able to orbit it. Beyond that distance, the gravitaional forces of the rest of the galaxy cause any object to be lost to the star's grip. It also says that wandering comets might enter the Sun's tidal radius, perhaps from another star's orbital field, and be captured by the sun's gravity and form an orbit.

I see how a star's gravitational field can be affected by other stars, but perhaps it is referring to the zone in which a minor body (and perhaps another star) can be affected by/orbit the star. It also refers it to as the "tidal limit". It also says that some stars' tidal limits can overlap. The tidal limits may, indeed, go right up to another star, but I don't think it does in the case of Sol/AlphaCen.

The magazine goes on to approximate the tidal zone as a sphere, saying Altair's stretches 30 deg across the sky. It says that some comets may have entered the tidal limits of other stars or were flung out to empty space to become "vagabonds", and that those might enter our Sun's tidal radius and possibly may have been seen from Earth, but that is speculation.

Also, some orbits of comets are not a complete ellipse, but have two parallel or angled ends, forming a parabola. My question is, might some of those parabolic comets' orbits have come from or are heading towards the orbital boundaries of other stars? What about AlphaCen in particular?

The estimate of 3.5 light-years for our Sun's tidal boundaries would suggest that an orbit leaving this zone, probably already parabolic as opposed to elliptical, would be lost from the Sun's gravitational force and become an interstellar "vagabond". If it enters AlphaCen's zone of gravitational attraction but have already exited ours, might it form a new orbit, perhaps still parabolic due to its great distance of entry, around AlphaCen?

The distances in space are great, but if say AlphaCen had an Oort cloud similar to ours, and our Oort clouds overlapped, could a select few comets be influenced by other comets' orbits and gravitational attraction, so that their own orbits end up destabilised and plunge towards one of the stars?

If a comet was heading towards or around the AlphaCen system, could Proxima, itself more massive than Jupiter and (currently) closer to us than AlphaCen itself, act like Jupiter does in our solar system, flinging comets' orbits towards AlphaCen or our own Sun? If a comet approaches AlphaCen, could interactions between stars A and B cause a star-grazing comet to act differently than one near the Sun, and have its orbit drasticly changed (if it survives)?

Also, and this is speculation: if comets were theorised to have been one of the harbingers of life on Earth, might some of those same comets, containing similar organic compounds, have survived an interstellar journey and struck a planet in another star system, producing life there? Could the same have happened to Earth, from other star systems? Thanks. ~A H 1^(TCU) 01:16, 5 July 2008 (UTC)[reply]

I can't see anything to stop comets from our Oort cloud being perturbed and ending up orbiting another star, but I expect it would be very unlikely due to the distances involves (the perturbation would have to be very precise, or it would miss the other star). If this kind of thing did happen, it could possibly transfer life between stars, this is called exogenesis. However, I really don't see how the regions in which you can have stable (closed) orbits around two stars could possibly overlap - how would an object in that overlap "know" which star to orbit? If you had an object orbiting one star and an object orbiting the other such that their orbits intersect at one point, their apoapsis (further distance from the star they are orbiting), directly between the two stars. Then, at that intersection point, both objects would be travelling in the same direction (perpendicular to both stars), although possibly at different speeds. One object would then need to fall towards one star and the other towards the other star, but why would they go in different directions if they started out going in the same direction? The objects could "choose" to fall towards either star, so the orbits would be unstable. --Tango (talk) 01:32, 5 July 2008 (UTC)[reply]

convert -

A hole guage of 10-32 -> diameter(inches) —Preceding unsigned comment added by 75.60.90.55 (talk) 19:50, 4 July 2008 (UTC)[reply]

I'm assuming that 10-32 is refering to a screw size. Take a look at [19] for dimensional information. -- Tcncv (talk) 20:02, 4 July 2008 (UTC)[reply]

Or here: Unified Thread Standard. --Heron (talk) 21:02, 4 July 2008 (UTC)[reply]

Simple mechanics.

Let's say there's a stick lying on the ground and I kick it. Well depending on where I hit it and at what angle, the stick will gain some linear momentum and some angular momentum. If I always kick it staight on (i.e. perpendicular to the stick), then only the position matters. So my question is, how can I determine how much angular and linear momentum the stick will possess as a function of the kick's position? Now I gave this question a shot, and my guess is that because the stick has a bit of thickness, the angle between the force and the radius of rotation changes depending on rotation, and that product of the sin of the angle and the force would give the angular acceleration and so on. Is this right? A second and somewhat related question, why does the stick always spin around the center? —Preceding unsigned comment added by 65.92.4.238 (talk) 22:43, 4 July 2008

This is actually a bit difficult to work out (and easily confuses me still)

Basically it depends on amongst other things, the way the weight in distributed in the stick, I'll assume that the stick is straight and has equal thickness - so that the weight is evenly distributed along the length of the stick.

You can work this out using newtonian mechanics, you need to know about conservation of momentum, conservation of angular momentum (see also torque)

Let's say the stick is L long and you kick it at distance d from the middle (ie d<L/2)

(You also need to be able to calculate the Moment of inertia of the stick by integration, this is in fact mL²/12 (from List_of_moments_of_inertia) IF you want to calculate the exact numbers)

Suppose your kick at distance d gives an impulse 'S' to the stick, this impulse can be split into rotational and translational (straight line) momentums..

Assuming that the stick rotates about the centre for simplicity.

The rotational momentum can be viewed as one end of the stick moving forwards at speed V2 and one end moving backwards at speed V2, the translational motion can be viewed as the stick moving at speed V1 from the middle (combining all these gives the overall motion)

The linear motion is therefor mV1 (m is the mass of the stick) (ie the momentum)

The speed of rotation about the centre is given by V2=L/2 x A (A is the angular speed of rotation in radians per second.

The rotational torque is given by speed of angular rotation x angular moment of inertia = A x m x L² /12

since A = 2 x V2/L the torque = V2 x m x L /6

If you supplied an impulse of 'S' to the stick at distance d the torque about the centre was S x d

So S x d = V2 x m x L /6

and S = mV1

So m x V1 = V2 x m x L /6d

ie rearanging gives V1/V2 = L/6d

This means the ratio of the angular speed and linear speed can be calculated and it depends on how far from the centre it was kicked.

Additional work gives a general formula for collisions of two objects using similar methods.

(Apologies for any mistakes I've made whihc I'm sure other will point out..) The method is similar to what I've tried to describe above.87.102.86.73 (talk) 01:46, 5 July 2008 (UTC)[reply]

Your second and related question is one I find difficult to explain.. BUT if you consider the stick mentioned above, and consider it rotating about somewhere other than the centre of mass - you'll find that the stick would be violating the 'laws of conservation of momentum' since it's centre of mass would be moving about.. there for its momentum would be changing over time without an external force (ie newtons law that a body moves in a straight line unless acted upon by another force - in this case the body would be effectively 'spiraling about a point') - in general if you try to make a stick do this it will tend to rotate about it's centre and any extra speed will simply turn into linear momentum. Sorry if I haven't explained that very well.87.102.86.73 (talk) 01:52, 5 July 2008 (UTC)[reply]

Bounce

Why does a ball bounce when it hits the floor? —Preceding unsigned comment added by 65.92.4.238 (talk) 22:44, 4 July 2008 (UTC)[reply]

When it impacts the floor, it deforms by flattening at the bottom, this absorbs the kinetic energy of its motion and converts it into elastic potential energy. That elasticity then causes the deformation to undo, the ball returns the being spherical and is propelled upwards. Does that help? --Tango (talk) 23:27, 4 July 2008 (UTC)[reply]

Why does a steel ball bounce higher than a tennis ball when the tennis ball deforms more then? --antilived^{T | C | G} 01:15, 5 July 2008 (UTC)[reply]

Because more energy is lost to heat and sound when the tennis ball deforms and reforms than when the steel ball does. I'm not really sure why... --Tango (talk) 01:34, 5 July 2008 (UTC)[reply]

I have never seen a steel ball bounce higher than a tennis ball... Plasticup ^T/C 03:47, 5 July 2008 (UTC)[reply]

You haven't bounced it on the right surface. Try bouncing it off of another piece of steel. Someguy1221 (talk) 09:38, 5 July 2008 (UTC)[reply]

There's an excellent demonstration of this at the Exploratorium. There, the steel ball bounces off a very large piece of steel and each bounce of the ball is nearly as high as the previous bounce (so very little energy is being lost on each bounce).

Atlant (talk) 20:55, 5 July 2008 (UTC)[reply]

Or off another steel ball, as in the Newton's cradle. There's a good reason why they make those things out of steel balls and not tennis balls - steel is more elastic than a rubber bladder. --Heron (talk) 13:41, 5 July 2008 (UTC)[reply]

Okay cool. So theoretically, an object which is perfectly rigid would not bounce, right? —Preceding unsigned comment added by 65.92.4.238 (talk) 04:09, 5 July 2008 (UTC)[reply]

That's an excellent question. I think it depends on how you take limits. A "perfectly rigid" body should have an infinite elastic modulus, because it never has any strain, regardless of its stress. So one logical way to end up with a "perfectly rigid" body is to take an elastic body and let its elastic modulus go to infinity. When this body is at rest on the ground, the gravitational potential energy it started out with is completely in the form of elastic energy, which I believe is

{\frac {1}{2}}\,{\text{stress}}\times {\text{strain}}

. If the elastic modulus continues to increase, the stress must also increase to keep the elastic energy the same, so our "perfectly rigid" body would end up having infinite stress (in order to have a finite elastic energy with zero strain). If you accept this, then the body should bounce perfectly elastically (i.e. it should return to the same height it was dropped from and never lose any energy), because inelasticities are caused by strain. —Keenan Pepper 05:23, 5 July 2008 (UTC)[reply]

An alternative way of looking at this would be to say that a perfectly rigid body has no way of absorbing/losing the energy on impact (since it cannot deform)- therefor it would bounce perfectly.87.102.86.73 (talk) 12:07, 5 July 2008 (UTC)[reply]

For illustration, see the ball bouncer demonstration in the references of the Liquidmetal article, showing how steel balls bounce against three different materials: steel, titanium, and a metallic-glass compound called LiquidMetal. =Axlq 18:11, 5 July 2008 (UTC)[reply]

From Collision: "Collisions can be elastic, meaning they conserve energy and momentum, inelastic, meaning they conserve momentum but not energy, or totally inelastic (or plastic), meaning they conserve momentum and the two objects stick together." I'm not sure what perfectly rigid would mean, but the type of ball that doesn't bounce at all is called totally inelastic (the energy is absorbed by making the floor move down). --Tango (talk) 12:27, 5 July 2008 (UTC)[reply]

Well not really. The ball could have collided with the earth in a perfectly elastic manner, but the mass of the earth made its movement imperceptible. —Preceding unsigned comment added by 65.92.4.238 (talk) 17:02, 5 July 2008 (UTC)[reply]

It's not actually possible for something perfectly rigid to exist. Because of that, it's impossible to say what would happen if it did. If you were to magically fix the atoms in position with relation to each other, the electron orbitals in the atoms would distort as they get closer, so the atoms themselves wouldn't be perfectly rigid. If you were to throw two such bodies against each other, my best guess is that the enormous pressure would cause the two bodies to pass through each other somewhat, and the parts inside each other would be forced in every direction, canceling it out. The circle where the two surfaces overlap would still exert a huge pressure and force the two apart. More simply, they'd bounce off of each other perfectly elastically and extremely quickly, but still slowly enough that for a short time, they'd be partially inside each other. If only one body was "perfectly rigid" as I defined it, I have no idea what would happen. If you want to make the object more rigid by not having the electron orbits distort, their waveforms would take up the whole universe, and the Pauli exclusion principle would mean that no electron could have the same state as any in the rigid body, and they couldn't be the same as each other. Besides the ridiculously high energy states of the electrons this would require, it would also mean that said principle wouldn't be keeping the atoms from occupying the same space, so the rigid body probably wouldn't have any resistance from falling through the ground. Disclaimer: I'm not only not a physicist, but I only just finished high school, and the physics I learned there really doesn't apply here, so don't be surprised if I'm wrong. — DanielLC 16:29, 5 July 2008 (UTC)[reply]

Just because it can't exist, that doesn't mean we can't address the question. Usually when we deal with things like objects bouncing, we focus on the arangement of atoms indirectly by assigning certain constants, which were determined experentally, and don't take quantum mechanichs into account, just like we may, in classical mechanics, we cometimes treat an object as a single point, even though that would violate Heisenberg's uncertainty principle. So what my question is really asking is, using the laws of physics that we normally use to adress such phenomena as bouncing, how would a perfectly rigid body act? —Preceding unsigned comment added by 65.92.4.238 (talk) 17:13, 5 July 2008 (UTC)[reply]

Relativity and communication speed

If a spaceship traveling at near light speed were equipped with a radio-wave Internet connection, how would special relativity affect measurements of its bandwidth and latency? Neon Merlin 23:05, 4 July 2008 (UTC)[reply]

The latency depends on the distance. As the latency changes quickly, the time-out would need to be rather large or change with the predicted distance of the spaceship.

If the spaceship travels towards Earth, then the bandwidth is larger, if it travels away from Earth, the bandwidth is smaller (see Relativistic Doppler effect). This just means that the spaceship traveling towards Earth will receive the bits at a higher rate, and the one traveling away from Earth will receive the bits at a lower rate. Icek (talk) 07:48, 5 July 2008 (UTC)[reply]

July 5

Houdini exhumation

I followed the story of the proposal to exhume Houdini's remains. Some of his relatives wish to examine his remains to confirm whether or not he was the victim of arsenic poisoning, while others object to the exhumation. The latest information I can find dates from March, 2007. Joseph Tacopina represented the pro-exhumation faction then, but I would like to know who prevailed. Does anyone have current status on this case?Avid Djinn (talk) 00:08, 5 July 2008 (UTC)[reply]

Not exhumed as of 2008-03-04 according to:

Costella, Annmarie (2008-03-04). "Houdini exhumation to test for poison". NYDailyNews.com. Retrieved 2008-07-05. they have yet to file court papers to have Houdini's body exhumed.

-- Jeandré, 2008-07-05t18:26z

Future Indian Ocean Earthquake

Hi. Will there be another possible Indian Ocean Earthquake like the 2004 Indian Ocean Earthquake in the future? When will it happen again? What will be the possible magnitude of another future Indian Ocean earthquake? Sonic99 (talk) 00:52, 5 July 2008 (UTC)[reply]

It's not known. Earthquake prediction is poor. PrimeHunter (talk) 01:10, 5 July 2008 (UTC)[reply]

Hello again there Sonic, take a look here for some insight. ;-) -hydnjo talk 01:12, 5 July 2008 (UTC)[reply]

The answer to the first question is yes. There will be another very large earthquake on that fault eventually. Whether it will be tomorrow, next year, next decade, or 5000 years from now is largely impossible to predict. Dragons flight (talk) 01:45, 5 July 2008 (UTC)[reply]

According to Nature (journal), the recent earthquakes did not sufficiently release the accumulated fault strain and there is still the possibility of a magnitude 9.0 quake. The fault ruptures every 200-230 years and there is a 200-km zone that has not ruptured since 1797, so do the math.

Furthermore, it now appears that the active fault extends northward along the coast of Burma up to the coast of Bangladesh, and large quakes there would produce devastating tsunamis in the Bay of Bengal.

That said, the comments above about trying to predict exactly when an earthquake will strike are quite valid. (Although I did just read something interesting about using increased neutron flux for short-term prediction [20]). Franamax (talk) 22:59, 5 July 2008 (UTC)[reply]

Antarcticine

can anyone tell me more about this glycoprotein in terms of anti-aging? I have googled it but cannot find a suitable answerSwinstarr (talk) 02:46, 5 July 2008 (UTC)[reply]

There's a good bit of information in this article. Someguy1221 (talk) 09:34, 5 July 2008 (UTC)[reply]

Metrication in Greece

According to an 1866 report in the US House of Representatives, "Greece has introduced [the metric system] with some modifications." - I'm wondering what exactly these modifications are. It'd also be interesting in general to have more information about the history of metrication in places other than France and English-speaking countries. --Random832 (contribs) 07:33, 5 July 2008 (UTC)[reply]

For Greece, see Konstantinos Nikolantonakis' "Weights and measures: the Greek efforts to integrate the metric system" from section 5.1. For Italy, Spain, Portugal, and the Netherlands see the abstracts and PDFs at the 2nd International Conference of the European Society for the History of Science, Symposium R-8 pages. -- Jeandré, 2008-07-05t18:11z

Spin

Do electrons actually spin?? where does the intrinsic angular momentum value come from? —Preceding unsigned comment added by 116.68.73.39 (talk) 07:58, 5 July 2008 (UTC)[reply]

No one knows. Their electromagnetic properties (charge, magnetic dipole moment, conservation of angular momentum during particle interactions, etc.) exhibit behaviors similar to what a spinning macroscopic object with a non-zero charge distribution would produce, which is I believe why that characteristic is called "spin". --Prestidigitator (talk) 08:46, 5 July 2008 (UTC)[reply]

Overview of spin might be of interest. Jdrewitt (talk) 11:13, 5 July 2008 (UTC)[reply]

Some hold the view that the 'spin' is not in any way equivalent to a rotation, but is in fact comparable to a chirality of the electron - the two spins being equivalent to 'left' and 'right handed versions' of the particle.87.102.86.73 (talk) 12:35, 5 July 2008 (UTC)[reply]

Electrons have zero size but non-zero angular momentum. This is weird. Make your own mind up about what to call it. "Spin" seemed like a good word at the time. -- Tim Starling (talk) 13:35, 5 July 2008 (UTC)[reply]

Then how/why is the Classical_electron_radius defined? Jdrewitt (talk) 15:43, 5 July 2008 (UTC)[reply]

It answers how and why in that article you just linked to. — DanielLC 15:53, 5 July 2008 (UTC)[reply]

Well I wouldn't say it answers exactly how and why (at least why r_e isn't defined) but then that's quantum mechanics for you! Jdrewitt (talk) 15:58, 5 July 2008 (UTC)[reply]

Classical electron radius is a useful characteristic length for the extent of the electric field around an electron. However, the mass and charge of the electron is concentrated at a point at the centre. Models for the electron involving a distribution of charge have been rigorously disproven. Under classical electrostatic theory, this leads to the rather embarrassing result that an electron has infinite electric potential energy. Solving this problem was one of the early challenges for quantum electrodynamics. -- Tim Starling (talk) 00:17, 6 July 2008 (UTC)[reply]

Quantum numbers

I've learnt about quantum numbers describing electrons, but are there quantum numbers for other particles(fermions, in particular)? If they have spin, there must be other quantum numbers too. If so, how are they different from those of the electrons? —Preceding unsigned comment added by 116.68.73.39 (talk) 08:02, 5 July 2008 (UTC)[reply]

The quantum numbers you refer to come about from the wave equation for an electron "orbiting" the nucleus of an atom. There will be quantum numbers describing any particle in any kind of potential, but there may not be the same number of them and they may not take on the same values. Some quantum numbers (such as spin) do seem to be intrinsic to the particle though. The quantum number and spin (physics) articles may be a good place to start learning. --Prestidigitator (talk) 08:59, 5 July 2008 (UTC)[reply]

Can crouching, breathing deeply, rising quickly lead to fainting?

Is this an old wives' (or young high schoolers' :-) tale or not? Someone at school said if you bend your knees in a crouch, take bout 15-20 deep breaths, then try to stand up quickly, you pass out. Do you?

Either way, exactly what problems can this cause? I was tempted to try taking 20 deep breaths like that, then lay down from that position one night but even that I was too scared to do, just in case. Would that have caused a problem.

And, in case, there is anyone else reading this - please be like me, don't try it at home.209.244.187.155 (talk) 15:11, 5 July 2008 (UTC)[reply]

Finally fixed my edit - sorry for the apparent incompetence :-)

Anyway, I would think it might, by inhaling and exhaling deeply 10-20 times, you relax the muscles enough that they become too weak to supprt you right away, but aside from fainting I'm not sure there would be any other problem, unless you hit your head on something.

Still, I agree - NEVER do that.Somebody or his brother (talk) 15:14, 5 July 2008 (UTC)[reply]

Hi. Have you read our article on brownouts? Thanks. ~A H 1^(TCU) 16:10, 5 July 2008 (UTC)[reply]

I think this is similar to the choking game. --Mark PEA (talk) 17:26, 5 July 2008 (UTC)[reply]

This sounds like nothing to be worried about, but you might find Orthostatic hypotension and Hyperventilation interesting reads. Even if this did cause you to black out, I'd be more concerned about hitting your head when you collapsed than from hypoxic brain damage. --Shaggorama (talk) 00:40, 6 July 2008 (UTC)[reply]

electromagnetic force uses photons as a mediator

is this saying that when I play with magnets there are photons being exchanged?

How about when I play with built-up charges in a Van de Graaff generator? —Preceding unsigned comment added by 71.147.33.238 (talk) 16:15, 5 July 2008 (UTC)[reply]

Why do s-orbitals always take part in hybridistion?

In hybridisation of atomic orbitals, why do s-orbitals always take part?Ashudeep2singh (talk) 16:54, 5 July 2008 (UTC)[reply]

Hybridization leads to stabilization: if s overlaps p, the s electrons go down in energy (see LCAO). But more philosophically, why not? No seriously...the s orbital is spherically symmetric, so no matter what direction you look (i.e., the directional orbitals (p, d, etc) with which you might hybridize), there is electron-density there in the s. An s orbital can constructively overlap with p, d, etc because it is in the same place, and electron delocalization is a good thing. DMacks (talk) 18:52, 5 July 2008 (UTC)[reply]

Platypus evolution

Regarding the platypus, according to this, http://en.wikipedia.org/wiki/Platypus#Evolution it seems the platypus contains some genes that are more similar to birds. This I found unusual because mammals evolved from Synapsids, and not birds, which evolved from true reptiles. So basically I'm asking how do you explain this similarity with birds, when mammals did not evolve from birds?

I would also like to know what kind of sex chromosomes reptiles have. The article said, "the sex chromosomes of the Platypus are more similar to the ZZ/ZW sex chromosomes found in birds.", well if amphibians and reptiles don't have those chromosomes, then that would raise a lot of questions about what platypus evolved from. The article in Nature said that the platypus shares two genes found previously only in birds, amphibians and fish. I'm not sure if they are referring to the sex chromosome though. But even if they are, they are insinuating that reptiles don't have those sex chromosomes. Well that's strange because birds evolved from true reptiles and not synapsids which probably did have those sex chromosomes. If reptiles don't have those chromosomes, well it raises a lot of questions. ScienceApe (talk) 17:51, 5 July 2008 (UTC)[reply]

Well, I think the point is that the platypus diverged from the rest of mammals very early on. My guess is that the genes in question that are no longer found in any other mammals probably have to do with the egg laying aspects, etc. To my mind the issue is not "what the platypus evolved from" but "what did the very early mammal genome look like?" It seems not unreasonable to me that it could contain all sorts of elements in it that were quickly filtered out (through a number of possible issues, like founder's effect) but the monotremes seem to have skipped out on the big filter. But this is just speculation. --98.217.8.46 (talk) 19:15, 5 July 2008 (UTC)[reply]

That doesn't really address the concerns I mentioned. In particular the sex chromosomes reptiles have. ScienceApe (talk) 23:41, 5 July 2008 (UTC)[reply]

The LHC and the end of the world

Recently, someone asked here whether or not the Large Hadron Collider would cause the end of the world. Our answer was, of course, inconclusive but if you're keeping track, you can at least find the minimum value of how much longer we have here. Just FYI...

Atlant (talk) 21:00, 5 July 2008 (UTC)[reply]

Personally, I'm convinced the continued failure of the LHC to go online is a global example of quantum immortality ;-) Someguy1221 (talk) 21:18, 5 July 2008 (UTC)[reply]

What the hell is going on here!?

Quantum gravity, quantum black holes, quantum chemistry (?!!). gravity bends time (and is really just acceleration), multiverses, etc., etc., etc. The world of the big and the small is just so mentally.....megawhelming! Please, -someone help me get a grip!--THE WORLD'S MOST CURIOUS MAN (talk) 21:32, 5 July 2008 (UTC)[reply]

Quantum gravity, quantum black hole, quantum chemistry, general relativity, multiverse...You'll really have to ask a more specific question if you want us to help you find an answer. Someguy1221 (talk) 22:04, 5 July 2008 (UTC)[reply]

Quantum theory in general? Fribbler (talk) 22:59, 5 July 2008 (UTC)[reply]

Instrumentalism might make you feel a little more comfortable as a way of reading scientific theories. Or less. I think it was Steve Martin who said that, "College philosophy teaches you just enough to really fuck you up." --Shaggorama (talk) 00:33, 6 July 2008 (UTC)[reply]

July 6

Colorado 14ers

I am curious about Colorado peaks. How many are there over fourteen thousand feet high? I have seen many different numbers, most of them in the fifties. —Preceding unsigned comment added by 75.169.1.13 (talk) 00:28, 6 July 2008 (UTC)[reply]

Here's the list of them. See also a WP list. Oded (talk) 01:05, 6 July 2008 (UTC)[reply]

Trans Ischemic Attack - same symptoms as stroke in sever cases?

Reading elsewhere, it seems like a transient ischemic attack is only a warning and brain cells don't actually die. Yet, your article speaks of TIAs that can last more than 10 minutes, and seems to say that brain cells do die. So, would the same things as mentioned in stroke apply when it comes to symptoms and treatment, then? In other words, can one experience weakness afterward, maybe periods of aphaxia where one can't talk for a few minutes at a time, etc.? Would rehabilitation be needed even with a TIA or series of them, even if there was no actual stroke that occurred?

Side question - can one be paralyzed on both dies of the body with a TIA/stroke? My hunch is "yes," if in the right place.

I guess it's one of those thigs that will really only be helped once the TIA article grows.209.244.30.221 (talk) 00:35, 6 July 2008 (UTC)[reply]

Yes and yes. TIA is code for "Minor stroke." The key is "transient." A stroke is ischemia caused by a thrombus (blood clot) in the brain that often requires thrombolytic therapy to be corrected and may cause permanent brain damage if not treated in time. The difference between a stroke and a TIA is that in a TIA, the thrombus often dislodges itself before serious damage occurs. Sometimes not. A TIA that causes damage is basically a stroke that treated itself, but a little late. Usually if there's any serious damage, they call it a stroke instead of a TIA. --Shaggorama (talk) 02:22, 6 July 2008 (UTC)[reply]

The difference between a transient ischemic attack and a stroke is the duration. If the symptoms last less than a day, what happened was a TIA; if longer, it was a stroke. They can't be told apart until the 24 hours passes. By definition, though, if the symptoms have disappeared within 24 hours, then there is no residual deficit after that time. A TIA by definition doesn't need rehabilitation, because the neurologic symptoms have disappeared. - Nunh-huh 02:27, 6 July 2008 (UTC)[reply]