Wikipedia:Reference desk/Archives/Science/2008 March 11

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1 March 11

[edit] March 11

[edit] type 2 diabetes and hair loss

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

--Milkbreath (talk) 01:54, 11 March 2008 (UTC)

Seriously, you need to consult a doctor about this - we can't offer medical advice of any kind... Wisdom89 _{(_T / ^C)} 01:47, 11 March 2008 (UTC)

[edit] Electron configuration in Lawrencium

Lawrencium states [Rn] 5f14 6d1 7s2, while Atomic orbitals#Orbitals table says that "This table shows all orbital configurations up to 7s, therefore it covers the simple electronic configuration for all elements from the periodic table up to Ununbium (element 112) with the exception of Lawrencium (element 103), which would require a 7p orbital."

One of these pages is wrong, is it the atomic orbitals page? Also the next electrons in [Rn] 5f14 6d1 7s2 go into the 6d orbital not 7p... How did the atomic orbital page come up with this statement?

PS: "Simplest electronic state" = ground state? --Shniken1 (talk) 03:17, 11 March 2008 (UTC)

re: " "Simplest electronic state" = ground state? " - you might think so - but it doesn't have to be the case - because 'simplest' doesn't have much meaning in this context.87.102.14.194 (talk) 08:54, 11 March 2008 (UTC)

It shouldn't be different here, electron configurations of elements are always given in their ground state, simplest configuration may refer to filling the d orbitals before the next s orbital but that would still leave lawrencium without an 7p electons.--Shniken1 (talk) 10:08, 11 March 2008 (UTC)

[edit] elements

I came across this in a magazine 1. element present in all organic compounds 2.alkane hydrocarbon with straight chain 3.heaviest alkaline earth metal 4.produced by combustion

it seems that 1 and 2 are not elements. but what are the answers? juz curious. not homework.

Uh huh. Anyway, this is an encyclopedia, and you can find answers to simple questions just by typing the relevant word into the search bar. But I'll give you the links right here: Organic compound makes the answer pretty obvious; there are many alkane hydrocarbons that have straight chains; alkaline earth metal, also makes it pretty obvious; combustion, the very first chemical equation in the article gives it away, and I'm guessing you're ~~homework~~ magazine is only concerned with the combustion of hydrocarbons, so that one is all you need. Someguy1221 (talk) 08:39, 11 March 2008 (UTC)

1. try organic compound

2. read alkane see subsection linear alkanes

3. read alkaline earth metal

4. read combustion 87.102.14.194 (talk) 08:52, 11 March 2008 (UTC)

Has the Physics magazine guy gone to chemistry class now? bibliomaniac 1 5 00:22, 12 March 2008 (UTC)

[edit] The Speed Of Dark......?

I was asked a question recently that sounds nonsense but may have some validity in it. "If light travels at the speed of light, what does dark travel at?" We're told light travels and dark is the expulsion of light, but does it travel? and, if so, at what speed? ajcree —Preceding unsigned comment added by 89.241.133.221 (talk) 08:29, 11 March 2008 (UTC)

Dark is the absence of light, and nothing more. If it takes t seconds for light from a bulb to reach the wall of your room after lighting up, then it takes those same t seconds for the wall to darken after the bulb dims. Someguy1221 (talk) 08:33, 11 March 2008 (UTC)

Exactly, so if a star suddenly shut off that it 50 light-years away from us, it would take us 50 years to see that the star had stopped shining. Hope this helps. Thanks. ~A H 1^(TCU) 16:03, 11 March 2008 (UTC)

One complication is that objects rarely stop giving off light instantly. The filament from an incandescent light bulb takes a portion of a second to cool to a temp that no longer produces visible light, for example. A star which has ceased to undergo nuclear fusion may take millions of years to cool to the point where it no longer gives off light. StuRat (talk) 17:40, 11 March 2008 (UTC)

Dark "travels" at the same speed as light because light is just photons, which are perceived using receptors in our eyes. When there are no more photons, we see darkness. Since photons travel at the speed of light by definition, the absence of photons behind them (i.e. dark) expands at the same speed. It's like dropping a stone in a pond: your question is equivalent to asking, "What speed does the trough between the ripples travel at?" Obviously, it travels at the same speed as the ripples themselves! « Aaron Rotenberg « Talk « 09:01, 13 March 2008 (UTC)

[edit] Why do Rabbits hop?

The question is pretty self-explanatory, but please don't answer "because that's how their legs work"! I know that, my question is why do rabbits hop instead of walk like most other mammals. 71.57.90.83 (talk) 08:47, 11 March 2008 (UTC)

I'd say it's about propulsion and desired speed, and like it or not the structure of both sets of legs being very unlike "most other mammals". Only Bugs Bunny seems to saunter, stroll, tap dance and so on as an upright. Similar to kangaroos (well, not quite), rabbits don't hop – as in having all four peds off the ground – if they are mooching about eating. And as prey animals of that kind, when they need to speed at a moment's notice, the bounce comes into it due to the configuration of the hind legs. Does that help?Julia Rossi (talk) 10:32, 11 March 2008 (UTC)

Consider a similar animal without the long hoppy back legs - ie a guinea pig if you've ever seen one run you might wonder why they weren't long ago predated out of existence... 87.102.14.194 (talk) 10:42, 11 March 2008 (UTC)

Interesting point – it probably doesn't exist in the wild any longer. Julia Rossi (talk) 11:11, 11 March 2008 (UTC)

The article sort of confirms that - seems they use safety in numbers - including random scattering when a predator approaches.. In general though - in a pack of 100 even a 100% efficient predator will only make one kill before stopping I would guess - all that remains is for the creatures to breed sufficiently fast to cover the predation... Poor little things.87.102.14.194 (talk) 12:16, 11 March 2008 (UTC)

Like when you're being shot at: think zigzag. It's a good way to confuse and loose a predator. 200.127.59.151 (talk) 14:20, 11 March 2008 (UTC)

...which is useful if the predator is tight on your tail. StuRat (talk) 17:45, 11 March 2008 (UTC)

I would think that the rabbit's hop is a result of what sort of animals prey upon it. The fox and the hawk come to mind. These are both very quick animals, so the rabbit must also be quick. Its large back legs enable the rabbit to spring forth in an instant, while a more controlled gait would see it end up as lunch more often than not. Vranak (talk) 15:29, 11 March 2008 (UTC)

Well, if we're just throwing out conjecture, it seems to me that hopping would have evolved in an open environment, grassland maybe, where you won't get snagged in the brush mid-hop or bean yourself on a branch. It is a quickness thing, isn't it? It would have the additional advantage that it would carry you above the grass with each hop, so you could get your bearings. Lots of evolutionary adaptations seem odd, and perhaps this one initially evolved especially to meet the requirements of some small niche, and when the animal spread out it took the form of locomotion with it, retaining it with refinements. It certainly is one good way to make tracks, strange as it seems. --Milkbreath (talk) 19:51, 11 March 2008 (UTC)

Animals also make do with what they've already got. The ancestor of rabbits may have had legs adapted for something else entirely that turned out to be easy to adapt to hopping and zigzagging, which proved to be a very effective escape. Some gazelle have also evolved a leaping zigzagging flight, but since they started out with a different form of locomotion, they ended up with a somewhat different result. — kwami (talk) 01:05, 12 March 2008 (UTC)

Why not some OR? Wandering in a wild field in the evening, spotting young bunnies way off, in grasses up to my hips, when a big (medium dog size) rabbit ran past me parallel to the ground (no arching bounces for reconnaissance) very fast and low. And straight. So those back legs have a strong thrust forward when needed, not just the up and down thing. I'm sure it would have zigzagged if it was being chased. Julia Rossi (talk) 03:46, 12 March 2008 (UTC)

Yes, two different strategies can be employed depending on if the predator is "out of range". If so, running straight and fast to safety makes sense. If the predator would catch the prey before they can reach safety, however, then taking evasive action is the best plan. Zigzagging side to side, hopping up and down, and suddenly reversing direction are all methods that offer some hope that the prey can outmaneuver the predator. Similar methods can be employed by ships, submarines, or planes which are being hunted. StuRat (talk) 14:51, 13 March 2008 (UTC)

Perhaps rabbits hop for the same reason as the kangaroo - their legs etc act like springs so that they use less energy to travel. Some antelope-like animals - the springbok? - hop when a pedator is near to demonstrate that they are fit and that the predator would be wasting its time and energy to chase them. 80.0.108.245 (talk) 19:38, 16 March 2008 (UTC)

Interestingly, the rabbit / hare family (Leporidae) has its closest living relative in the pika family (Ochotonidae), which are terrestrial mammals (to my knowledge) not particularly prone to hopping. Together Leporidae and Ochotonidae make up the order Lagomorpha, and it's quite uncertain to whom this order is most closely related. Some data suggest relation to rodents, but other morphological evidence points to a more recent divergence from Marsupials -- male testes being located anterior of the penis, for example. If that were true -- and it's a big if -- then one can imagine hopping being inherited by both Peter and Roo from a common progenitor. As with all things in evolution, it is desirable that a new trait confers an advantage, but it really only needs to not confer a disadvantage to be passed on. See U Michigan's excellent taxonomy and diversity site, animaldiversity.ummz.umich.edu/site/accounts/classification/Lagomorpha.html for more information. Vance.mcpherson (talk) 16:55, 17 March 2008 (UTC)

[edit] What is this equation?

Edit (hit enter before asking question!) What is this eqation meant to represent? [1] "Pe + (Pe)r" not NaCl....:D --Shniken1 (talk) 10:19, 11 March 2008 (UTC)

It says 'Pepper' - otherwise it seems meaningless87.102.14.194 (talk) 10:30, 11 March 2008 (UTC)

"Pepper, not Salt." Someone likes puns. JohnAspinall (talk) 18:27, 11 March 2008 (UTC)

[edit] Why not swing?

Reflecting on the question about rabbits in motion, it set me wondering how come, as descendants of great apes now walking upright, humans don't swing from things as a means of locomotion? Julia Rossi (talk) 10:42, 11 March 2008 (UTC)

Lack of trees.. imagine if we did though .. we'd have to build adventure playgrounds instead of footpaths.. Seriously though we never would have left the forest.87.102.14.194 (talk) 11:05, 11 March 2008 (UTC)

First, humans are not descendants of great apes - we are great apes, because we are members of the biological family Hominidae (along with chimapnzees, gorillas and orangutans). And not all of the other great apes swing from trees - gorillas are ground dwelling. As the contributor above says, it is a matter of different species adapting to different environments. The same thing happens in the squirrel family, where we see both tree squirrels and ground squirrels. What exactly caused humans to acquire bipedalism is still a matter of research and debate - our bipedalism article says "There are at least twelve distinct hypotheses as to how and why bipedalism evolved in humans". Gandalf61 (talk) 12:37, 11 March 2008 (UTC)

I'd go with the idea that as prehumans moved out onto prairie, which lacked trees, they needed to develop an efficient method of locomotion for that environment. Since many primates can stand on hind legs for short periods, it wasn't too much of a leap to develop full-time bipedal motion. While less efficient than quadruped motion, bipeds had the huge advantage of having their hands free to use tools and weapons, which the opposable thumb our primate ancestors developed for grasping tree limbs first made possible. The relatively high intelligence of primates also made it possible to put tools to good use. StuRat (talk) 17:57, 11 March 2008 (UTC)

But lots of primates have moved out onto the savanna, and they didn't go bipedal. Also, Lucy apparently wasn't much of a tool user, but she was bipedal. All these arguments about what makes us different from other apes - we lost our hair cuz it was hot, we stood on our hind legs to see further or to free our hands - remind me of speculations about the extinction of the dinosaurs back before the extra iridium was discovered in the K-T boundary layer: They all failed, because they didn't address why, for example, plankton should go extinct just because dinosaurs got constipated from flowers (yes, I think that was actual proposal!). — kwami (talk) 00:59, 12 March 2008 (UTC)

There were multiple niches for primates on the savannah, some of which were for bipedal primates. Being a quadruped would have other advantages, like being able to hide from predators and prey in tall grass and running more quickly. As for being a tool user, I expect that the earliest tools were just found objects, like sticks and rocks, so I wouldn't expect to find a collection of chipped flint tools nearby. StuRat (talk) 15:16, 12 March 2008 (UTC)

Back to the original question, humans have retained some ability to climb trees, which is why we have arches in our feet (to fit the tree trunk). StuRat (talk) 17:57, 11 March 2008 (UTC)

I have to say, I'm extremely dubious of the "arches are for climbing trees" idea. Arches of the foot are very important to humans being able to support their weight and to being able to be bipedal. --98.217.18.109 (talk) 23:48, 11 March 2008 (UTC)

In that case, the arches would go all the way across the foot, symetrically, not only on the inside edges of the feet. This form is perfect for grasping tree trunks. StuRat (talk) 03:42, 12 March 2008 (UTC)

Why don't we swing from things? Why should we? Only some of the great apes spend any time swinging from things, and even those spend a lot of time not swinging from things. When not around things to swing from, they don't swing, and get around just fine. Swinging is both difficult and dangerous; it's not an ideal form of locomotion. --98.217.18.109 (talk) 23:48, 11 March 2008 (UTC)

Given the ground dwelling great apes, how come we lost all that upper body strength belonging to the longer arm ratio that they retain? I'm wondering if maybe it had something to do with the homosapiens taking over from the neanderthals and using the hands for specialisation that swinging might otherwise have interfered with. (oops the third part was answered in the thread where it goes back on itself above - I missed that) Julia Rossi (talk) 03:34, 12 March 2008 (UTC)

I expect that it has to do with our weak backs. The spine was really not designed to be used as we use it, so can't support nearly as much weight in bipeds as in quadrupeds. This means our upper bodies had to be minimized, such as having shorter, less muscular arms. We also have thinner skulls than many of our quadruped primate friends. If I had to redesign the spine for bipeds, I'd take the nerves outside the spine into something like a notochord, and replace them with cartilage to try to hold the spine together. StuRat (talk) 15:24, 12 March 2008 (UTC)

Why would we invest in longer, stronger arms when that would interfere with walking and running? Shorter, less strong arms are more convenient for not swinging from tree to tree, so if it's more of an advantage to be walking and running on the savannah than swinging from tree to tree there is a disadvantage in investing energy in those tree-swinging arms. I don't really see what's to explain here :/ Skittle (talk) 18:29, 12 March 2008 (UTC)

Humans stick to the ground because we've grown too tall and heavy to swing from trees. Gorillas suffer the same problem. As you know from Newton's law of universal gravitation, there's an inverse-square relationship at play: $F = G \frac{m_1 m_2}{r^2},$ . What that means is that the proverb "the bigger they come, the harder they fall" is literally true: a taller, heavier creature hits the earth with much, much more force if it falls. At a certain point, evolutionarily speaking, the behavior is too risky to be worth pursuing. --M @r ē ino 20:27, 12 March 2008 (UTC)

I'd just like to point out that some of us do swing. In fact, otherwise, it don't mean a thing. --Trovatore (talk) 20:50, 12 March 2008 (UTC)

[edit] astronomy

the stars in the sky seen from the UK are the same as from Australia?cypru÷90.193.58.40 (talk) 13:51, 11 March 2008 (UTC)alex

Nope. While there is some axial tilt to the Earth's rotation, the UK sees a great many stars well north of the ecliptic plane and Australia sees a great many well south of the same. Stars near the ecliptic will be visible to both places (though constellations will be inverted) but many regularly visible to one are never visible to the other. — Lomn 14:12, 11 March 2008 (UTC)

Two good examples would be the North Star and the Southern Cross. AlmostReadytoFly (talk) 14:34, 11 March 2008 (UTC)

Hi. A good indicator of which stars you can see is to take your latitude, positive if north and negative if south, then add 80 for northern limit and subtract 80 for southern limit. Well, that should be a good indicator of which stars you can see without too much interference from the atmosphere, light pollution, terrestial objects, haze, and all that. So, if for example the southern limit for a location in the UK is -25, then you can see Sirius easily because it is at -17 or so, oh and if you get a number like +120, subtract 120 - 90 to mean that you can see 30 degrees in declination beyond the north pole reigon near the pole star to the north, and similar methods for southern hemisphere. Hope this helps. Thanks. ~A H 1^(TCU) 16:10, 11 March 2008 (UTC)

[edit] Alcohol injection

Is it possible to survive when a small amount of alcohol is injected intravenously (for instance, a 40% vodka within an average syringe capacity, or less, if lethal)? IMO, one should break through because it's similar to drinking alcohol on an empty stomach. No one is experimenting here:) --85.132.14.38 (talk) 18:54, 11 March 2008 (UTC)

Injecting a small amount of ethanol and injecting a small amount of 40% vodka are two different things. If I had to choose, I'd choose the ethanol since I don't know what else might be in the vodka. ----Seans Potato Business 21:08, 11 March 2008 (UTC)

Steve-O did a whole IV bag of vodka intravenously (well, duh!) in one of his videos. It didn't kill him. That's not to say that you should try it at home (or at work, or in someone else's home, or anywhere else for that matter). --Kurt Shaped Box (talk) 00:21, 12 March 2008 (UTC)

Let's consider the math in the reverse direction. A blood alcohol level of >0.40% is usually fatal, so let's consider a BAC of 0.30% (the point where you'll generally lose consciousness). A typical adult male has about 5 litres of blood. So 0.30% of 5L is 15mL of alcohol. So, if you're using a typical 1mL, 3mL or 10mL syringe, then it looks like ~~you'll be fine~~ you may survive, even if it's full of pure ethanol. However, an IV bag with 40% alcohol all at once would almost certainly kill you. There was a problem a few years ago where people were experimenting with inhaling alcohol (you get drunk way faster, but it's also much easier to take a lethal dose vs. ingested alcohol). My advice: stick to the recommended one-drink-per-day (or less). (EhJJ)^TALK 01:01, 12 March 2008 (UTC)

I should also point out that Steve-O was not 'well' as such after his experiment - it just didn't kill him. His body is probably far more accustomed to abuse than yours or mine too. --Kurt Shaped Box (talk) 01:15, 12 March 2008 (UTC)

I would not count on being "fine" after injecting 10 ml of absolute ethanol. Total quantity of alcohol in the bloodstream is not the only issue here. You're going to get all sorts of local damage at the injection site, probably lysis of blood cells, God knows what else. (Not to mention that it's going to hurt like anything.) Could it result in a clot that would wind up in your coronary artery? Don't know; don't see any reason to do the experiment. --Trovatore (talk) 01:17, 12 March 2008 (UTC)

Trovatore's quite right about the concentration effects—pure ethanol does really nasty things to living cells, and I agree with him about the likelihood of damage at the injection site. (Not that I would guarantee 40% ethanol won't do damage, mind you—and case reports indicate that it burns like the devil going in: [2].)

As to EhJJ's calcuation about lethal BAC's, it's worth noting that ethanol is a small molecule, and the concentration of ethanol in surrounding tissue will rapidly come to equilibrium with the ethanol concentration in the blood. This equilibration is a fairly rapid process, so you really need to be looking at a dilution of the injected alcohol into nearly all of the body's water rather than just the circulating blood volume. Even bearing that in mind, of course, a full IV bag is rather a lot of vodka to consume at one sitting, by any route of administration. TenOfAllTrades(talk) 02:22, 12 March 2008 (UTC)

Indeed, one would need to know the volume of distribution of ethanol. The volume of distribution page actually lists ethanol as an example @ 30L (no citation). Therefore EhJJ's back-of-the-envelope calculations may be off by a factor of six. But I imagine anything 40% or greater bust sting like hell as an injection... — Scientizzle 20:06, 12 March 2008 (UTC)

That article mentions snorting vodka. I've done that (a dessertspoonful). Not very much fun and not something I'm planning on doing again - it stung and made my eyes water like crazy. I was already drunk at the time, so I can't tell you if it had any significant intoxicating effect. --Kurt Shaped Box (talk) 02:42, 12 March 2008 (UTC)

Intravenous alcohol is used as a treatment for ethylene glycol poisoning -- common engine antifreeze. Ethyl alcohol (the fun kind) outcompetes antifreeze for an enzyme called ADH, which breaks booze down into vinegar but antifreeze into nasty toxins. So IV alcohol, with a little dextrose and diluted in water, is administered, in conjunction with dialysis to make sure the kidneys maintain the will to live. Obviously, this procedure can only be conducted in a hospital with adequate facilities and professionals with adequate training. See Diseases of the Kidney and Urinary Tract, pp 1201-1202, by Robert W. Schrier. Vance.mcpherson (talk) 17:10, 17 March 2008 (UTC)

[edit] Electron and Hole Concentration in Carbon

I've been trying to find electron and hole concentration data for carbon to calculate the Hall coefficient to predict the Hall p.d. across a thin carbon sheet. I can't seem to find any although I managed to find the data for silicon (http://mems.caltech.edu/courses/EE40%20Web%20Files/Supplements/02_Hall_Effect_Derivation.pdf)

Do these values depend on the sample of carbon or is there any other way of predicting the Hall p.d.? Welsh-pingpong (talk) 21:35, 11 March 2008 (UTC)

What kind of carbon are we talking about here? Graphite, diamond, or some nanomaterial like graphene (which is an atomically "thin carbon sheet")? They all have different energy band structures. Assuming we're talking about a graphite sheet of macroscopic thickness, this paper says the electron and hole concentrations are each about $3 \times 10^{18}$ cm⁻³ at low temperatures. Which brings up another important question: what temperature is the carbon? —Keenan Pepper 23:00, 11 March 2008 (UTC)

It's a graphite sheet of thickness 0.18mm. The temperature was at room temperature with 0.1A passing through it - I didn't notice any significant temperature increase. How does temperature affect electron and hole concentrations? Also where can I find data about electron and hole mobility - I'm trying to make a prediction of the Hall voltage and need these values for the Hall coefficient. —Preceding unsigned comment added by Welsh-pingpong (talk • contribs) 08:51, 12 March 2008 (UTC)