Wikipedia:Reference desk/Archives/Science/2007 November 21

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November 21

Sociology

Is there report on Bangladeshi-Canadian community in Canada? —Preceding unsigned comment added by 76.64.133.44 (talk) 03:08, 21 November 2007 (UTC)

What sort of report are you looking for? Perhaps you should ask your question on the Humanities reference desk. (EhJJ) 14:27, 21 November 2007 (UTC)

Take a look at Demography of Canada, Ethnic groups in Canada and Canadians of Asian ancestry. Gandalf61 (talk) 14:44, 21 November 2007 (UTC)

Psychology

What would be a good hypothesis when it comes to Antisocial personality disorder? —Preceding unsigned comment added by 76.64.133.44 (talk) 03:16, 21 November 2007 (UTC)

Have you looked at Antisocial personality disorder, by any chance? Someguy1221 (talk) 03:21, 21 November 2007 (UTC)

information technology in 21st century

REMOVED.

Do your own homework. The reference desk will not give you answers for your homework, although we will try to help you out if there is a specific part of your homework you do not understand. Make an effort to show that you have tried solving it first.

Do not crosspost. Post your question at one section of the reference desk only. Lanfear's Bane | t 10:56, 21 November 2007 (UTC)

Arsenic Level in Diet

What types of food, particulary fish, can cause an abnormally high arsenic level? 71.218.1.121 (talk) 05:00, 21 November 2007 (UTC)

Any food that's been grown in the presence of Arsenic contaminated groundwater. Toward the bottom of the article, the only food mentioned is rice. Presumably any other plant watered with arsenic contaminated groundwater would cause the same poisoning, as well as any animals that eat those plants. Indeed, fish living in contaminated water also have high arsenic levels [1]. So it's not so much related to particular types of food, but any food grown with contaminated water. Someguy1221 (talk) 05:21, 21 November 2007 (UTC)

Mushroms are particularly good at concentrating toxins. Otherwise perfectly edible mushrooms can turn poisonous in the presence of contaminated water. --Milkbreath (talk) 13:43, 21 November 2007 (UTC)

Prawns contain arsenic. My nutrition book says that arsenic is an essential element in human nutrition. Graeme Bartlett (talk) 20:25, 22 November 2007 (UTC)

Fertilization

About how soon after ejaculation does the physical penetration of the spem into the egg happen? I've noticed runoff within minutes so I figure the timeframe is rather short, but we're arguing about the exact time frame. Kuronue | Talk 05:50, 21 November 2007 (UTC)

Runoff? :)!?! It's not minutes, it's from several hours up to three days. - Nunh-huh 07:06, 21 November 2007 (UTC)

On that note, I see that Human fertilization is sorely lacking. Oh well. Someguy1221 (talk) 07:08, 21 November 2007 (UTC)

There is some debate about whether it's as long as "three days" - and some debate about whether it's as short as "several hours" - but it's certainly more than a few minutes! The various prescription 'morning after pills' (eg RU486) that are available in some countries to prevent pregnancy AFTER unprotected sex can be taken a day or two after intercourse and still have a good 80% to 90% chance to prevent fertilisation. They aren't approved for use after 72 hours though - so three days is the probably the outside limit. (They also have all sorts of nasty side-effects - so don't even think about relying on them routinely!) SteveBaker (talk) 15:50, 21 November 2007 (UTC)

RU486 (like most other emergency contraceptives) apparently prevents implantation, not fertilization. -Arch dude (talk) 17:37, 21 November 2007 (UTC)

I thought it was implantation that takes hours to days? It takes hours for them to physically swim up to the egg itself? Kuronue | Talk 18:24, 21 November 2007 (UTC)

Yeah, it's a long path to a small cell. The sperm starts at the bottom of the uterus and typically meet the ovum in the Fallopian tube. It's a large trip in microspic scale. 200.255.9.38 (talk) 14:41, 22 November 2007 (UTC)

Please don't confuse RU-486, an abortion medication, with emergency contraception, which is contraception. Plan B and similar emergency contraception pills are NOT abortion pills, at least by the conventional definition of pregnancy and therefore abortion. Plan B works mostly by preventing ovulation. It used to be believed that it also significantly decreased the chances of implantation, but recent research has called that into question. RU-486, on the other hand, will destroy a pregnancy that has already started, meaning ovulation, fertilization, and implantation have already happened. moink (talk) 00:42, 22 November 2007 (UTC)

Facultative Aerobes

Is there such thing as facultative aerobes? Could somone say so and, if so, direct me a source of informatio (I've already looked in wikipedia, unsuccessfully). Thnx BeefJeaunt (talk) 06:26, 21 November 2007 (UTC)

Do you mean Facultative anaerobes? Aerobic organism gives nice rundown of the terminology used to describe differing tolerances for oxygen, excluding anaerobes themselves. Someguy1221 (talk) 06:41, 21 November 2007 (UTC)

Organisms can be placed into three categories, depending on their tolerance or need of oxygen.

1. Obligatory aerobes require oxygen and will die without it (includes humans)
2. Obligatory anaerobes require the absence of oxygen as they will die from oxygen's toxic effects.
3. Facultative anaerobes can live with oxygen (not poisonous to them) but also without oxygen (they do not need it to live). They could also be called "facultative aerobes", as this is essentially the same thing (can live in oxygen but will survive without it).

Sometimes, I believe the term "facultative aerobes" refers to organisms, such as humans, that require oxygen but can live without it for a short period of time (in humans, we need oxygen to break down glucose to produce carbon dioxide, but can also break it down to lactate when oxygen is not available). Not sure about this last part. (EhJJ) 14:40, 21 November 2007 (UTC)

Humans are not facultative aerobes. Humans are obligate aerobes, though such a term is rarely applied to large animals. The fact that our cellular metabolism retains anaerobic pathways doesn't negate the fact that without oxygen, we're dead. - Nunh-huh 03:40, 22 November 2007 (UTC)

Airplane movement

Suppose a plane fly from La Paz, Bolivia to New York, USA or maybe between two cities that locate on the same longitude but far away north and south. Does the plane need to slightly move to the east (as to chase the movement of the earth to the east)? Thanks for the answer. roscoe_x (talk) 13:15, 21 November 2007 (UTC)

The plane moves through a medium, air, that in general moves with the rotation of the Earth. It has to account for variations in wind speed, but the effects of rotation are already taken care of in the flight path. Now, the Coriolis effect during takeoff and landing is another story, as an aircraft will have additional eastward velocity when dropping from high altitude to low, as the air's linear velocity is generally larger at higher altitudes ($v=r\omega$). SamuelRiv (talk) 14:58, 21 November 2007 (UTC)

Do this experiment: Put your feet together and jump as high as you can. Let's suppose you were off the ground for 1 second. During that one second, the earths surface rotated maybe 400 meters (depending on your latitude). Did you find yourself landing 400 meters from where you started? Is there a 400 meter per second wind blowing right now? You lived to tell the tale, so I guess not. It's basically the same thing for the plane. When the plane, the earth and the air are all moving at the same 400 m/s speed, there is really no way to tell that you are moving at all. However, the effect you are thinking about is called 'The Coriolis effect' and it is really there as you suspected.

As I indicated the speed at which the ground is moving due to the rotation of the planet varies depending on your latitude. At the equator it's 463 meters per second. At the poles, it's zero. So if you fly due north from the equator, the rate that the surface of the earth is moving beneath you gradually reduces - so you are moving sideways at 463m/s at the equator - and if you flew north all the way to the north pole, the ground would not be moving at all due to rotation. Somehow you had to lose that sideways speed along the way - and that would mean flying at a slight angle to your planned course in order to counteract Coriolis 'forces'.

However, aircraft don't fly in a vacuum - if an air stream is blowing from the equator towards the North pole, then it too affected by the Coriolis 'force' and starts off moving with the planet at 463 m/s - and has to gradually slow down to zero by the time it reaches the pole. This results in Northerly and Southerly winds tending to veer off to the side as they shed this lateral motion. That results in a bunch of complicated swirling wind currents and such - that'll tend to blow your aircraft off course.

But that's no different in principle to winds caused by weather events. The net result of all of this is that while theoretically a pilot would have to take account of Coriolis, in practice, the effect seems to him just like various winds blowing him around - and whilst those are driven (at least in part) by Coriolis - other effects such as heating of air over land and cooling over ocean has a much bigger effect. So you plan your course to take account of the prevailing winds and counteracting Coriolis is just a small part of what you end up doing in fighting the prevailing winds.

Note that driving your car north/south also causes a Coriolis force to be applied to it - but again, it's too small to be noticable.

SteveBaker (talk) 15:35, 21 November 2007 (UTC)

Just a clarification, the Coriolis force acts on air moving in any direction. In the Northern hemisphere, this results in the air taking a right hand turn from the direction it would have followed if the Coriolis force was not acting (ie. air following an eastward pressure gradient will get forced south, air following a northward pressure gradient will get forced east, air following a southward pressure gradient will get forced west, and air following a westward pressure gradient will get forced north). Sancho 16:03, 21 November 2007 (UTC)

Steve, that's the best and clearest way of explaining the Coriolis effect that I've ever read. Much more intuitive (to me, at least) than the ways it's explained in our article on the topic, not to mention countless Physics textbooks. jeffjon (talk) 16:21, 21 November 2007 (UTC)

You absolutely do have to account for the Coriolis effect when you are making large changes in altitude, however, which was my original point. It is the same effect that makes Foucault's pendulum precess, and the British were certainly hit by surprise during the Great War in the Battle of the Falkland Islands when their naval shells weren't hitting on target due to the effect. SamuelRiv (talk) 17:09, 21 November 2007 (UTC)

Good explanation about the nature and magnitude of Coriolis effects, Steve. I once calculated that the Coriolis effect on a French high-speed train at full speed is equivalent to the force of a crosswind of 10 km/h or 6 mph. Enough to detect if you wanted, but not enough to be important. --Anonymous, 18:34 UTC, November 21, 2007.

Wow! That's a lot! Hmmm - I think it's too much. Excuse me while I crunch some numbers: So it's 10,000 km from equator to pole (easy to remember - ten million meters - that was the original definition of a meter) - and over that distance you have to shed 460m/s - so on average (because it's not a linear rate of loss with latitude) for every kilometer you drive north you need to shed 0.046 m/s of lateral speed. So if you drive a car at 100kph (about 60mph) you need to shed 4.6 m/s of lateral speed every hour - that's 0.0013 m/s² or about one ten thousandth of a g! A TGV goes something like 200mph? That's still nothing like the force exerted by a 10kph wind...not even close. Did I make a horrible boo-boo? SteveBaker (talk) 20:48, 21 November 2007 (UTC)

Might the discrepancy be that you're going for a full-trip average, while Anon was calculating the peak momentary Coriolis acceleration? Or maybe acceleration at a France-specific latitude? jeffjon (talk) 20:55, 21 November 2007 (UTC)

Yes, I mentioned France because that established the latitude. Steve's rough method gives an estimate of 1/2,500 gee, while the actual Coriolis acceleration at the relevant latitude is about 1/1,000 gee.

Modeling one car of the train as a flat plate positioned vertically and lengthwise along the track, I calculated the drag force of a 10 km/h crosswind as around 300 N, giving the correct acceleration since the car weighs around 30,000 kg.

--Anon, 00:21 UTC, Nov. 22.

Oh - of course! I was forgetting that to accellerate something as heavy as a train with even a fairly tiny accelleration requires an immense amount of force - hence the higher-than-gut-feel wind speed required. Thanks - there had to be something I was overlooking! SteveBaker (talk) 06:46, 22 November 2007 (UTC)

So you mean actually in real-life plane this Coriolis effect was negligible? Based on your experiment, what about if I'm in equator and I'm not jumping but I'm using certain device that let me go straight 1-km up 90 degrees and go back down 90 degrees. And let see I'm in the air for 1 minute. Am I going to land in the same place or 27600m (460m/sx60s) to the west of my position before? roscoe_x (talk) 13:48, 22 November 2007 (UTC)

If your 460m/s speed around the equator is stopped, yes. The same would go if it just made you hover, and it has nothing to do with the Coriolis effect. If not, the Coriolis effect will make you seem to move less than one six thousanth that speed (the radius of the earth is over 6000km). It would move you around half a meter. Compare that to how much wind would move you. — Daniel 02:33, 23 November 2007 (UTC)

Hypochondria

What would you call a person who is excessively worried about somebody else's (e.g. their child's) health? Exohypochondriac? Any ideas? — Kpalion^(talk) 16:29, 21 November 2007 (UTC)

Hypochondria is actually quite a broad term, and could well include morbid feelings about one's family. I'm mot aware of a more specific term, but you might well do better to ask on the Language desk.--Shantavira|^{feed me} 18:30, 21 November 2007 (UTC)

You might want to have a look at Munchausen syndrome, Fabricated or Induced Illness, Factitious disorder, Anxiety and Psychosomatic illness. Keria (talk) 18:54, 21 November 2007 (UTC)

You might also look at codependency. 70.171.229.76 (talk) 23:31, 21 November 2007 (UTC)

Overconcern? bibliomaniac15 05:48, 22 November 2007 (UTC)

Parenthood. -- Kesh (talk) 14:35, 22 November 2007 (UTC)

collagen/gelatin

I'm trying to understand what exactly makes gelatin so much better at forming gels and adhesives that hydrolysates of other proteins. I know that it has an unusual amino acid composition (high in Gly, Pro, Hyp, ...) but it is not clear to me that this explains its properties. ike9898 (talk) 17:34, 21 November 2007 (UTC)

I'm new to this as an area of research, so no fun equations for you, but generally such action occurs due to cross-links that links each protein chain to each other, forming a very tough but flexible substance in the end. I suspect water catalyzes this by some hydrolysis reaction, but I don't know. This is the same process that occurs in most polymers that gives them a stiff flexibility. I'm no chemist, so I don't know if this is the specific case for gelatin. SamuelRiv (talk) 18:15, 21 November 2007 (UTC)

I don't think any covalent crosslinks are formed. ike9898 (talk) 19:54, 21 November 2007 (UTC)

Crosslinks don't have to be covalent - sometimes they can just be polarized and that will work too for a polymer. You can also have weird cases like polyethylene where the polymer chain makes nonpolar branches that get physically entangled with those of other chains, making a less elastic and more breakable polymer. SamuelRiv (talk) 23:03, 21 November 2007 (UTC)

What is coulombic interaction energy?

What is coulombic interaction energy? Is coulombic interaction energy the same as lattice energy/enthalpy? Thanks in advance. AshLin (talk) 17:45, 21 November 2007 (UTC)

Yes indeed - it is effectively the same as lattice energy. Enthalpy is a bit different as it depends on the excitation of states (that is, the internal energy of each "atom" (a general term) independent of Coulomb energy). See the article on lattice energy for a formal definition: basically, you calculate the coulomb interaction energy between each atom, and sum it all up to get the lattice energy. Note that since atomic orbitals are not fixed, there is some polarization between atoms that changes the interaction energy a little bit (see Van der Waals force, but for an ionic compound this is not very significant. SamuelRiv (talk) 17:59, 21 November 2007 (UTC)

Does lava/magma conduct electricity?

Would molten rock conduct electricity in the same way water does? --86.142.170.168 (talk) 21:19, 21 November 2007 (UTC)

Water is actually an excellent insulator. It's impurities in the water that let it conduct. Lava is also a good insulator. This link gives its conductivity as "10x10-9 mho/m (basalt) at 300 K in the dark". Compare that with copper at 59.6 × 10+6 and deionized water at 5.5 × 10-6. --Milkbreath (talk) 22:30, 21 November 2007 (UTC)

If you like equations, and I hope you do, Electrical conduction has some great ones. Conductors work by having room for charge carriers (like electrons or salt ions) to move around relatively freely. Metals are great conductors because they have lots of free energy states, so electrons travel by making jumps to nearby energy states around other atoms. Water doesn't have this property unless, like Milkbreath said, you add some kind of polar or ionic molecule to it that will dissolve (water dissolves a lot of stuff), and so when you run electric current through it those molecules will propagate the current by aligning or moving their positive ends with the current and negative ends against it, making a current appear out the other side! Quiz: which conducts electricity better, salt water or fresh water? SamuelRiv (talk) 22:58, 21 November 2007 (UTC)

Salt water - that's why you should never take an electric fire into the sea. DuncanHill (talk) 05:52, 22 November 2007 (UTC)

Does the "300K" mean 300 Kelvin? That's what I call a warm rock, not lava/magma... --antilived^{T | C | G} 06:47, 22 November 2007 (UTC)

I was just about the raise the same point. Melting the rock would allow for ions (charged particles) to travel (more) freely from place to place; the resistance would be appreciably lower than that of solid rock. One sees this effect in the industrial production of sodium metal by the electrolysis of sodium chloride (table salt) in a Downs' cell. Solid, room-temperature sodium chloride is an extremely poor conductor. In contrast, molten sodium chloride will pass a significant current, as the individual sodium and chloride ions (Na⁺ and Cl^-) are free to move.

I would expect a similar behaviour from molten rock; magmas will be molten solutions of an assortment of ionic chemical species. Compared to any sort of reasonably pure water, it will be a pretty good conductor, though not quite as good as a pure metal. TenOfAllTrades(talk) 07:07, 22 November 2007 (UTC)

The electrical conductivities of magmas have been measured under lab conditions, and it seems that sodium is the main charge carrying phase in silicate liquids [2]. It is also clear that melting increases the conductivity [3] but I'm a bit short on actual numbers. Geophysicists need to know this in order to interpret MT (magnetotellurics) and other electromagnetic data.--Mikenorton (talk) 14:25, 22 November 2007 (UTC)

I found a few references to values of about 1 S.m^-1 (1 Siemen = 1 mho) for a partially molten rock, matching observed values beneath mid-oceanic ridges[4] (Note: the values on the diagram are actually resistivities but as the one is the inverse of the other, for values near 1 it's all much the same) where we know that there should be magma chambers.--Mikenorton (talk) 17:16, 22 November 2007 (UTC)

Outdoor warm-weather ice-skating rinks

How do these work? There are at least two in downtown Los Angeles, is it a big giant freezer unit under there? Any links to info on the tech or the companies who run them would be welcome. Donald Hosek (talk) 22:10, 21 November 2007 (UTC)

There are artificial ice rinks with a surface made of high density plastic. Several companies come up on google if you search.--TrogWoolley (talk) 22:42, 21 November 2007 (UTC)

For how they work, see ice rink: "This consists of a bed of sand, or occasionally a slab of concrete, through (or on top of) which pipes run. The pipes carry a chilled fluid (usually either a salt brine or water with antifreeze) which can lower the temperature of the slab so that water placed atop it will freeze."--Shantavira|^{feed me} 08:36, 22 November 2007 (UTC)

To follow up, does anyone know whether it's plastic or ice at the outdoor skating rinks in Pershing Square (Los Angeles) and Santa Monica? The latter, I can stop by over lunch on Monday and ask, but downtown is a bit more of a trick to get to. Donald Hosek (talk) 18:59, 22 November 2007 (UTC)

Regaining consciousness

What is happening as one regains consciousness? Regaining consciousness after fainting, I start off with blurred vision and confused about my circumstances. It's like not all my mind is functional, and what parts are that are there are trying hard to figure out what's going on. It's like I've no sense of the past, but only the present until the rest of my brain comes back online. (this is not a medical question - I fainted because I had a catheter inserted, which I think is a perfectly satisfactory response to such an ordeal! I do not need to see a doctor. I'm just wondering about the human brain seeming to switch on slowly) --Seans Potato Business 23:46, 21 November 2007 (UTC)

I recall speaking with an anaesthesiologist who told me the following tidbit: as people are anaesthetized, they are usually asked to count to ten. While most people remember counting up to (around) 4, they actually typically count to (around) 7. Sorry this doesn't answer your question, but I couldn't help sharing this second-hand anecdote. (EhJJ) 01:14, 22 November 2007 (UTC)

IANAMD, but I believe fainting (or loss of consciousness) is often due to quick change in blood pressure. So I assume the recovery is due to your body regulating your blood pressure back to normal levels. -- MacAddct  1984 ^{(talk • contribs)} 03:36, 22 November 2007 (UTC)

Technically, it all has to do with the reticular activating system. There are several reasons why you might lose consciousness (i.e. being knocked in the head, stress, drugs, sleep...) The one main common factor is inhibition/reduction in activity of the reticular activating system. When you are gaining consciousness, your are becoming more and more aware of all stimuli inputs into your brain. The reticular activating system has a "late, slow, excitatory" effect on the entire brain which results in increased level of consciousness. When sleeping, fainting, or under general anesthesia it's function is inhibited and the brain moves into a state of synchronization (as determined by an EEG) in which "consciousness" is lost. Now that I have said all that, you should note how you think about consciousness now. You only know it subjectively. There is a scientific reason and explanation for consciousness, and most of the concrete knowledge there came from the study of implications of the EEG signal and the reticular activating system. Mrdeath5493 (talk) 07:07, 22 November 2007 (UTC)

Hi Sean, IAAMD, and I can tell you that, firstly, fainting is what happens when your brain does not get enough blood to it (for a stack of reasons, including medical procedure anxiety! Believe me, I've seen it plenty) - lack of bloods inhibits the RAS (aforementioned by the deadly pharmacist) and off you go. The reason for the amnesia and the visual disturbance is also because of the lack of blood and oxygen and its effects on the other parts of the brain responsible for these things. The slow return to function occurs becuase the brain needs to have its normal physiological environment restored, and that requires delivering enough O2, electrolytes, sugar and removing metabolic wastes accumulated during the lack of perfusion that caused the faint. It's not like flicking a switch off and on, its more like cleaning up after a party - it takes a little while for things to come good! Cheers! Mattopaedia (talk) 03:33, 23 November 2007 (UTC)

particle - antiparticle pairs

a T.A. of mine told our physics class that particle-antiparticle pairs can be produced spontaneously even in the "vacuum of space", which got me thinking if this is bs or not. he said they usually anhilliate each other shortly thereafter unless one of them is sucked into a black hole or something. anywho, how can these pairs be produced spontaneously unless there's energy to make them? if they don't require energy then that contradicts thermodynamics since they hav a mass (and velocity) and so would add to the total energy of the universe. if they do require energy then how is it spontaneous, as we could expect them to appear where the necessary amount of energy exists? —Preceding unsigned comment added by 67.70.31.61 (talk) 23:57, 21 November 2007 (UTC)

You answered your self, they can occur naturally where the energy require exists and indeed this is how they are made manually as well see Antiparticle--Dacium (talk) 01:26, 22 November 2007 (UTC)

If I recall correctly, they can skirt around thermodynamics because they destroy themselves within a given amount of time, something to do with the uncertainty principle. At least, I'm pretty sure that's what they told me at some point when I was in college. See virtual particle, or the small bit on conservation and uncertainty at virtual pair. --24.147.86.187 (talk) 01:33, 22 November 2007 (UTC)

So far this is mostly accurate. See Pair production for the full story. Note that virtual particles are usually referring to the exchange particles of the fundamental forces, which have slightly different properties than their real counterparts. Pair-produced particles are entirely real, however. SamuelRiv (talk) 02:28, 22 November 2007 (UTC)

Hmm. I didn't think they always self destroyed... don't pairs around the edge of a black hole which don't self destroy have something to do with Hawking Radiation? So that's not quite the correct skirt round... --BozMo talk 14:18, 22 November 2007 (UTC)

Okay, to clarify, pair production occurs by energy in = energy out, so an amount of energy is absorbed to produce a positron-electron pair. They don't have to annhilate in certain reference frames, that is, in the reference frame where you have a high-energy particle that slows down as it creates a pair. They do have to annhilate if you see a pair produced out of nothing, as in a vacuum fluctuation or a higher-order interaction effect (electrons scatter by a virtual photon that can create a particle-antiparticle pair that annhilate and recreate the photon that finally interacts with the other electron, for example. See Feynman diagram for a picture). In the case of Hawking radiation, a particle-antiparticle pair is created in a vacuum, one particle gets sucked into a black hole and the other escapes. Does this violate conservation of energy? No, because the vacuum fluctuation that created the particles was in effect a defect in space that "borrowed" energy from the black hole's mass-energy (or gravitational energy). When a particle escapes, the energy goes with it, so the black hole loses mass. Again, this depends on your reference frame (this part I'm not fully sure on - I don't do GR), so from inside a black hole you wouldn't see any Hawking radiation because the energy from that perspective doesn't exist to create it.

Side note - it's easy to understand how energy is "relative". Think of it as if I'm moving quickly past you - I obviously have energy relative to you, because I'm moving. However, if you are moving at the same speed next to me, then I have no extra energy from your perspective since I'm not moving any faster. It's the same principle here, except using General relativity instead of Galilean relativity. SamuelRiv (talk) 15:00, 22 November 2007 (UTC)