Wikipedia:Reference desk/Archives/Science/2008 June 30

Science desk
< June 29	<< May | June | Jul >>	July 1 >

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

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)

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)

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)

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)

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

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

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)

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

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)

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)

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. ~AH1^(TCU) 01:37, 30 June 2008 (UTC)

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

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

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)

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)

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)

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)

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

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

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)

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

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)

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)

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)

Identify this kelp?

What is it??

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)

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)

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)

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)

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)

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)

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)

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

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)

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)

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)

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)

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)

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

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)

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)

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)

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)

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)

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)

CERN

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

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)

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)

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)

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

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)

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)

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)

Endorphin half-life

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

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

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)

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)

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)

(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)

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)

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)

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)

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)

(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)

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)

(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)

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

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)

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)

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

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)

• It's a feeding reflex. Momma touches, beak opens, momma injects food. --jpgordon^∇∆∇∆ 19:52, 30 June 2008 (UTC)
  • 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)
    • 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)

• • 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)

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)

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

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

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)

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)

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)

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)

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)