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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)

November 22

Cooling down -- drink or pour?

I do not seek medical advice, and neither is this a homework question. I have seen people pouring liquid over their heads (presumably in order to cool down). The question is: if it was a very warm day at 30 C, and I had 1 liter of water at, say, 2 deg C; would it be more cooling for me to drink it, or (bearing in mind most heat is generated/lost in the head/brain) for me to pour it over my head( slowly) —Preceding unsigned comment added by 79.76.162.232 (talk) 02:09, 22 November 2007 (UTC)

By drinking it the heat of your body goes into heating up the water, thus cooling you somewhat. By pouring over your head the heat of your body (and the air) go into heating the water. By pouring it over your head you also get the benefit of evaporative cooling which will be much more significant than the cooling you get from just heating the water up. So pour over your head..... unless you are dehydrated, then you should drink.Shniken1 (talk) 02:19, 22 November 2007 (UTC)

But it will also constrict you blood vessels so less heat can be transferred away from your skin, therefore leaving you hotter in the long run. --antilived^{T | C | G} 04:20, 22 November 2007 (UTC)

Also, not much of the water you pour over your head gets evaporated: most of it lands on the ground, whereas all that you drink gets warmed to body temperature. Dribbling water slowly over your head or body might be more helpful than pouring it all at once, but of course that keeps your hands busy while you're presuambly trying to do something else.

Another point is that if you get dehydrated enough, you'll stop sweating, leading to more overheating and possible heat stroke, which can kill you. Drinking the water will prevent that -- unless you drink so much that you suffer water intoxication (hyperhydration), which can also kill you. Giving specific guidelines, of course, would be medical advice. --Anonymous, 05:25 UTC, November 22.

We've had similar questions in the past, such as why it is that dousing yourself in cold water after an intense workout only cools you down for a short period. As explained above, the chief culprit is vasoconstriction. What you need to decide with your bottle in hand is first, do you really need to cool down or do you need to hydrate, and second, how cold is that bottle of water? If the water is as cold as you mention, I would rinse the stuff in my mouth and spit it out. Some of the (now warmed) water would get swallowed to help hydration and the mouth can deal with temperature changes better than, say, your scalp, when it comes to simply cooling. Matt Deres (talk) 17:46, 23 November 2007 (UTC)

• A subjective, originally-researched answer: I'm a marathon runner in the southern USA, where it gets quite warm, and I have found that pouring some ambient-temperature water on my head (which is covered by a hat made of technical fabric) has a *much* greater subjective cooling effect than just drinking it. --Sean 22:01, 23 November 2007 (UTC)

physics

ships r made of iron and other heavy metals so why is it that when a ship is anchored it doesnt sink? —Preceding unsigned comment added by 59.95.15.157 (talk) 03:53, 22 November 2007 (UTC)

Yes, ships are often made of materials that are heavier than water. However, much of their volume is lighter than water, since they contain air. The weight of the ship is less than the weight of water contained in volume equal to the volume displaced by the ship, allowing for buoyancy. If you fill a boat/ship with water, it will sink. moink (talk) 04:04, 22 November 2007 (UTC)

(ec)

First off, it's not the case that lightweight things automatically float and heavy things automatically sink.

If you had a ten pound piece of wood, it would float, and if you had a metal coin that weighed two ounces, it would sink.

Try this: find a metal can, such as soup or canned vegetables come in. Remove the top completely. Fill it with water, and put it in a sink or bathtub full of water. It will sink, as you expect: the steel that the can is made of is "heavier" (or as we'll see, denser) than water, so it sinks.

But then: pick the can back up and empty half the water out, so that it's now half full of water. Put it back in the sink or bathtub, right-side up. It will float! Even though it's still "heavier" than water, and even though it's half full of water! How does this work?

The answer is, you've just made a crude steel-hulled boat. The only reason I had you leave it half-full of water was so that it would stay upright, instead of tipping over, filling all the way up with water, and sinking. But it's still pretty tippy -- water is a lousy ballast; the boat has a terrible righting moment. (There's a reason you don't want your real boat half-full of water!)

So now, try one more experiment. Empty all the water out of the can, and put some coins in the bottom. For a 15 oz. can, I find that using fifty U.S. pennies works well. (Your mileage may vary, depending on the size of can you use and the coins you have available where you live.) With the coins in the bottom, the can floats even better! But this seems really strange, because the coins are heavier than the water was. Or are they? The same volume of coin metal is heavier than the same volume of water, but the volume of the coins is a lot less. So actually the fifty coins in the bottom of the can weigh less than the half-can's worth of water.

So what we're finding out here is that it's not so much how heavy something is, but rather how dense it is, that matters when we're deciding whether it will float in water. It turns out, the rule is simple: if it's denser than water, it sinks, and if it's less dense than water it floats. That's why, everything else being equal, metal sinks and wood floats.

But, when you make a boat out of metal, the boat is obviously not solid metal. (Otherwise it would sink like, well, a stone.) The inside of the boat is full of air, and it's the overall density of the boat+air system that matters. If the boat plus the air inside weighs less than the same volume of water would, its overall density ends up being less than water, and it floats. And if the boat is heavier at the bottom, it will float well, and stay upright, and not tend to tip over. (It turns out that real boats usually have something heavy -- extra metal, or rocks -- down in their keel, as ballast, so that they work this way, just like our can with coins in the bottom. You can read more about this at center of buoyancy.) —Steve Summit (talk) 04:40, 22 November 2007 (UTC)

Take a hypothetical. What if you have bucket of water in a vacuum/airless room. Then you put the empty metal can on the water. Will the can sink? Since there's no air, we don't count the air mass and volume into the density calculation, right? And since the can itself, without air, is greater than that of water, the can should sink, right?199.76.152.229 (talk) 03:23, 24 November 2007 (UTC)

No, It would float even more. It would not have the mass of the air, but it would now it would contain a certain volume of empty space. Empty space is even lighter than air. 72.10.110.107 (talk) 17:05, 26 November 2007 (UTC)

Steve - that was a really good answer! DuncanHill (talk) 06:13, 22 November 2007 (UTC)

(Thanks! —scs 00:20, 24 November 2007 (UTC))

Because math is good, I'd like to add that Archimedes's Principle is that the weight of water displaced is equal to the weight of the object displacing it. So if I have a 2000-ton ship, it will displace 2000 tons of water, which is about 2000m^3 in volume. But suppose the ship has a total volume of 5000m^3 -- then it will float, and the water line will only come as far as about 2/5 of the side if it's a barge-like ship. SamuelRiv (talk) 11:56, 22 November 2007 (UTC)

Zoom lenses

Why do some zoom lenses have a constant f-number? As focal length increases, the entrance pupil must also increase to maintain the same f-number. Since this is the case, do such lenses actually have an enterance pupil that physically expands when the lens is zoomed? If the entrance pupil can expand, why not keep it at its largest, so that, a lens that is a, say, 70-210mm f/4 (at 210mm, the pupil is 52.5mm) is a 70-210mm f/1.3-f/4 (52.5mm constant pupil diameter), so that the lens is faster at its wider end? 70.156.49.65 (talk) 04:03, 22 November 2007 (UTC)

I don't think the pupil changes size, I have a 70-210mm f/4-5.6 (NOT constant aperture) and if I set it on say f/11 at 70mm (supposed pupil size = 6.4mm), the aperture size doesn't change as I zoom, finally becoming f/16 at 210mm (supposed pupil size = 13mm), but it still doesn't solve why the effective aperture changes when the pupil size doesn't. --antilived^{T | C | G} 07:04, 22 November 2007 (UTC)

over working the kidneys

In the past I used to eat a lot of salads but when my schedule kept me from sitting down to eat I followed the great idea of adding water and pureeing my salads to consume as a drink. Now I do the same with yogurt, fruits and vegetables to the point that I must be drinking at least a gallon ever two hours. Can I hurt my kidneys by drinking so much liquid or does it make them work even better? 71.100.5.134 (talk) 08:19, 22 November 2007 (UTC)

• You should probably ask your doctor, but since that would equate to nearly 12 litres in a working day alone, I'd expect it to be unhealthy. You only need around 2-3 litres to stay hydrated and drinking too much can indeed have an adverse effect on your health, especially if you do it in such short periods. - 131.211.161.119 (talk) 09:00, 22 November 2007 (UTC)

If you have a schedule that prevents you from sitting down to eat you need, seriously, to address your life style. Fact - People do die from drinking excess liquids, usually water. Richard Avery (talk) 10:54, 22 November 2007 (UTC)

Well usually it is alcohol :D, but yes water intoxication is possible Shniken1 (talk) 12:32, 22 November 2007 (UTC)

A gallon every 2 hours, that's about 4.5Litres right? So in a day? That's 18L in an 8 hour work day, or if you're talking about your waking hours it's more like 36L! Wow, that's dedication! Water intoxication occurs when the amount of fluid you ingest causes electrolyte washout to such an extent that cell membrane physiology becomes irreparably disturbed and cell death follows. To get it just from drinking you need to drink plain water only, and lots of it. You're also consuming a lot of electrolytes in the puree so that would go a long way to helping you maintain electrolytic homeostasis. Normal kidneys should be able to excrete at least half to 2/3 of that water volume, but you'll also have water loss through perspiration, respiration etc. You're probably peeing like a racehorse and/or sweating like a pig to compensate. If you weren't, you'd probably be rather oedematous by now. The figure of 2-3L of water being required per day is a figure arrived at by looking at the metabolic requirements of a sedentary 70kg man. So if you're very physically active your water requirements will be much higher. Plenty of people don't find time to sit and eat regularly - ask any mother! And while it would be nice to say society is to blame for your salad smoothies and resultant concerns, getting the world to slow down really needs to be addressed in other venues. But the important point is:

• • See your doctor if you're worried. A simple blood test will priovide all the answers to your concerns.

Cheers! Mattopaedia (talk) 03:11, 23 November 2007 (UTC)

Anti-aliasing in human vision

Are there aliasing effects in human vision and what plays the role of the anti-aliasing? Keria (talk) 09:56, 22 November 2007 (UTC)

Correct me if I'm wrong but I always thought our retina is like film, with all the receptors are pretty much randomly distributed at a very high resolution, so that it's pretty much unnecessary. I still see aliasing outside my fovea though, so I guess the resolution outside the fovea is low enough to be able to see aliasing. --antilived^{T | C | G} 10:08, 22 November 2007 (UTC)

I associate aliasing with geometric optics, but the fovea operates pretty close to the diffraction limit. I think the blurring you get from diffraction will have about the same effect as oversampling in 3D graphics. -- BenRG (talk) 12:04, 22 November 2007 (UTC)

There are distortions that occur in human vision that are caused by a lack of spatial (an optical illusion book has tons of these, or even looking through a fine-grained mesh can cause a similar effect) and temporal (a propeller blade that appears to spin backwards) resolution. It's not quite as simple as this, because illusions can occur either as a true aliasing effect in the eye, as a pre-processing effect in the thalamus, as a processing and integration effect in the occipital lobe, or even as a post-processing effect in the rest of the brain as images are linked with memories and higher judgement. All of these areas can cause illusions as all of them also serve to resolve possible illusions in vision, which is itself technically an optical illusion. So I'd say one of the clearest examples of "anti-aliasing" would be our pattern-matching, which fails when we see a triangle when shown three circles with wedges cut out of them. SamuelRiv (talk) 12:08, 22 November 2007 (UTC)

I don't think I've ever seen an optical illusion resulting from spatial or temporal aliasing in the visual system, except perhaps outside the fovea. Looking through a fine-grained mesh can make a moiré pattern, but that's a result of "sampling" by the mesh. I see nothing in the wagon-wheel effect article to suggest that it's ever caused by temporal aliasing in the visual system. The "discrete-frame theory" sounds unlikely to me. The circles-with-wedges illusion has nothing to do with aliasing, not that it isn't interesting in its own right. -- BenRG (talk) 12:08, 23 November 2007 (UTC)

Anti-aliasing is something that is only necessary when you scale an image down, and the eye doesn't do anything like that, so there is no anti-aliasing in human vision. Also, human vision is mostly analog, so our eyes don't really use image sampling, which is what causes spatial aliasing, therefore I'm pretty sure human vision can't cause spatial aliasing. Looking through a real fine-grained mesh (not one on TV) will not produce a Moiré pattern unless there are two imperfectly overlapping meshes, though you may see a pattern anyways if the holes in the mesh are not completely flat and regular. In either case that pattern is not an optical illusion or a product of aliasing, it's simply a varying pattern of blocked and unblocked light. Also, we generally only see temporal aliasing aliasing due to a flickering light source, such as from a TV or a fluorescent lamp, which causes a sampling effect. So, aliasing generally isn't a problem caused by human vision. -- HiEv 15:13, 22 November 2007 (UTC)

You can see what is called the wagon-wheel effect without a flickering (stroboscopic) light source, however there are various explanations why this effect can occur (see here). -- HiEv 15:28, 22 November 2007 (UTC)

Anti-aliasing is not only necessary for downscaling images. It's necessary (or at any rate useful) any time you sample a signal, whether or not that signal was reconstituted from higher-frequency samples. I suppose one could argue that the laws of physics are discrete, and every sampling is a downscaling. -- BenRG (talk) 12:08, 23 November 2007 (UTC)

String theory and the shape of the Universe

String theory seems to imply a particular shape of the Universe. Therefore, could it be that local geometry of the Universe is 3-dimensional (in an Euclidean, spherical or hyperbolic form) but the global geometry of the Universe is quadridimensional?

In such a scenario, the Universe would be a kind of anomalous sphere: just like in our Earth, in such an Universe, one could go westward and return to the starting point from the East; one could go northward and return to the starting point from the South; BUT, differently from Earth, one could also go upwards into space and, after eons of travelling, one would return to the starting point from beneath. In other words, the universe would be a simply connected sphere folded on itself in such a way that each point is in contact with its antipodal point. Is this view consistent with string theory? Is this even plausible? -- Danilot (talk) 10:43, 22 November 2007 (UTC)

It sounds like you're describing a 3-sphere, which has been a popular choice of topology for the universe since the earliest days of modern cosmology. I don't understand what you mean by quadridimensional; the space you're describing has a local dimension of 3 and a global dimension of 3. Also, I don't think this has anything to do with string theory, which doesn't to my knowledge predict the shape of the universe. -- BenRG (talk) 11:57, 22 November 2007 (UTC)

You might be interested in shape of the universe. Someguy1221 (talk) 16:34, 22 November 2007 (UTC)

piezoelectricity

I would like to build a rudimental piezoelectricity sensor (generator) for highschool project. I intend to apply pressure on a sample of Rochelle salt (which I have) and show the resulting current generation using a voltmeter. Is this going to work? Can somebody show me a simple diagram of how to apply the wires which would conduct the current? What is the best metal to use for these conductors? Thanks, Curious Student —Preceding unsigned comment added by 67.189.247.193 (talk) 11:15, 22 November 2007 (UTC)

The short answer is, it depends. The current produced will be transient—just a little blip of current when pressure is applied or released, after which the potential across the crystal will be back at equilibrium. The current is likely to be fairly small for reasonable pressures and crystal sizes. I don't know if you'll be able to see a small, short-lived current, and I suspect that it will be difficult for you to measure with any accuracy (unless you've got some specialized instruments).

I wonder if some sort of rudimentary electrometer might not be a better bet for you—squeeze some charges out of the crystal and into gold-leaf electroscope for your demonstration. (Caveat—I haven't tried this stuff, and can't tell you if it will work.) TenOfAllTrades(talk) 14:48, 22 November 2007 (UTC)

Incidentally, you might find something useful in our articles on piezoelectricity and piezoelectric sensors. TenOfAllTrades(talk) 14:51, 22 November 2007 (UTC)

You could use a gas ignition lighter that makes a spark. You would then just have to wire to the outlet. Beware the voltage is high on the order of several thousand volts, so you will need some special kind of voltmeter, such as TenOfAllTrades electrometer. Graeme Bartlett (talk) 20:31, 22 November 2007 (UTC)

It's the mechanics of the ignitor that result in the high voltage. Absent the over-center mechanism that delivers the sudden impact to the piezo portion, they can produce low voltages quite nicely.

Atlant (talk) 16:06, 26 November 2007 (UTC)

In the classroom, measure voltage, not current. Just get a cheap piezo buzzer (about $2.00USD), remove the piezo element, and place it under stress to produce the voltage, which you can measure with a voltmeter. An actual generator must be a dynamic system, so you will need an oscilloscope to show the varying voltage. Alternatively, you could use the piezo as a microphone and rectify the AC voltage via a full-wave bridge to charge a capacitor, and measure the (relatively small) current as you discharge the capacitor through a resistor. -Arch dude (talk) 05:20, 23 November 2007 (UTC)

Burglar alarm glass breakage detectors are usually piezoelectric as well; you might want to investigate one of those as a "prototype" for your project. If you mention what you're doing, an alarm installer might give you one for free. Old, inexpensive phonographs also used piezo pickups. Interestingly enough, certain ceramic capacitors are also piezoelectric, leading to undesireable microphonic effects when they are used in certain electronic circuits.

Atlant (talk) 16:01, 26 November 2007 (UTC)

Glassware for baking

There is a kind of bowl made of glass that you can put into the oven or into a microwave, primarily for baking vegetable-based food. These are made of a special kind of glass as far as I know. What's the name of them? Is there an article about them? If no, what property of the glass makes them usable in an oven? I'm not interested in how they are created, but the resulting physical properties. Thanks, – b_jonas 19:01, 22 November 2007 (UTC)

I believe you are talking about Pyrex, which is made of soda-lime glass, but originally was constructed of borosilicate glass. --80.229.152.246 (talk) 19:37, 22 November 2007 (UTC)

Glass recyclers consider it to be ceramic material. They hate to find pieces of it in recycled glass containers because it screws up their process: when "regular" glass is melted this ceramic material is still solid. When pouring the glass melt in whatever shape this endproduct has to be rejected because of the ceramic shards enclosed in it. VanBurenen (talk) 22:12, 22 November 2007 (UTC)

Why should Pyrex be primarily for vegetables? --Seans Potato Business 00:13, 23 November 2007 (UTC)

Because in the regular oven, I can use metallic containers, and I rarely use the microwave for baking meat or cookies. Rice or green peas, however, can be cooked just fine in the microwave. – b_jonas 10:07, 23 November 2007 (UTC)

It could also be because acidic vegetables (? Well, acidic fruits, maybe) may pick up flavors from some reactive metals. --Mdwyer (talk) 17:22, 23 November 2007 (UTC)

Besides Pyrex, you can use ceramic, glass-ceramic, and silicone cookware in microwave ovens. See Cookware#Non-metallic cookware. -- HiEv 19:34, 23 November 2007 (UTC)

November 23

Apoptosis

If a man goes fishing, we can say "the man has started to fish", if a cell begins the process of apoptosis, what single word (of the same root) is used in the sentence "the cell is has started to ..."? --Seans Potato Business 00:10, 23 November 2007 (UTC)

In your fish sentence you are using the word as a verb. Apoptosis is a noun, so wouldn't be conjugated. The only sentence I can think of is the same as yours: "As the cell dies, it begins has begun the process of apoptosis." Jeffpw (talk) 00:17, 23 November 2007 (UTC)

Apoptosize is a verb form, so you could say "The cell has started to apoptosize." bibliomaniac15 01:04, 23 November 2007 (UTC)

Or Apoptosise... —Preceding unsigned comment added by Shniken1 (talk • contribs) 01:15, 23 November 2007 (UTC)

In the texts I've read, apoptosis is used as a verb, so we say "the cell has started to undergo apoptosis". Looking at root words, though, we also use the word ptosis, specifically in relation to things like eyelids, the liver, etcetera, and we commonly will make a comment during examination of a patient such as "he had a ptosed liver", to say the lower border of the liver is lower than expected in the abdomen (for a number of possible reasons) --- so, then the answer could also be "apoptose". To me, to "apoptosize", as suggested by Bibliomaniac15, or "apoptosise", for those of us who prefer the Queen's English, would be to cause another cell to undergo apoptosis, rather then a cell undergoing apoptosis itself. Mattopaedia (talk) 02:41, 23 November 2007 (UTC)

That sentence uses it as a noun. Using it as a verb would be "the cell has started to apoptosis". — Daniel 02:57, 23 November 2007 (UTC)

Fair enough. I'm a doctor, not a linguist. I was thinking it might have been a noun and a verb at the same time, but thought that was a bit odd, so left it like that. Mattopaedia (talk) 03:53, 23 November 2007 (UTC)

Linguistically, what you're looking for is the infinitive form of the verb: to run, to swim, to play, et cetera. "to undergo apoptosis" is not using apoptisis as a verb; "to undergo" is the verb and apoptosis is the direct object, which is (in this case) a noun. "Apoptosize" would be a verb (assuming it's a word). Kuronue | Talk 21:14, 23 November 2007 (UTC)

But that's the question, isn't it? "Apoptosize" is, at best, a nonce word: it is certainly not in common use, and would not be used in any even minimally formal document. "Apoptosis" is the noun; "apoptotic" is the adjective, and there is no accepted verb form. - Nunh-huh 21:32, 23 November 2007 (UTC)

Funny, I've always use "Apoptose" as the verb. I have no idea if this is at all correct though. Someguy1221 (talk) 21:54, 23 November 2007 (UTC)

To determine whether it is correct or not, consult a dictionary. I already have. - Nunh-huh 22:12, 23 November 2007 (UTC)

I do hear apoptose, although it's probably a word made by extension (e.g. endocytosis-endocytose). However, I'd probably go with constructing the sentence to use either the noun or adjective form. -- Flyguy649 ^talk 22:15, 23 November 2007 (UTC)

The OED doesn't acknowledge apoptosize or apoptose as words. Speaking from experience, I occasionally see apoptose in scientific presentations. It's a nonce word or neologism, and I'd tend to shy away from it in formal writing. (Apoptosize is definitely not used. Anywhere.) A PubMed search finds about a hundred uses of apoptose in paper titles or abstracts, so at least some authors have been able to sneak it past the blue pencils. TenOfAllTrades(talk) 23:42, 23 November 2007 (UTC)

The part of the OED that covers the letter A was last updated around 1970, except for selected important words in the online edition, so that's not a good reference for new words. But none of the online dictionaries indexed by www.onelook.com has "apoptose" or "apoptosise"/"apoptosize" either. I think "apoptose" is definitely the natural form, though. Several other medical nouns in -osis often form verbs in -ose, like "diagnose", "sclerose", and "thrombose". --Anonymous, 01:32 UTC, November 24, 2007.

For what it's worth, the online version of the OED includes references as recent as 2004 for apoptosis and 2002 for apoptotic; it's safe to say that they're making an honest effort to stay on top of these new words—but I would agree that they're not the be-all and end-all for new terms. TenOfAllTrades(talk) 18:26, 24 November 2007 (UTC)

As it happens, I was using "apoptose" when my spellchecker rejected it, the first event in a short series that lead to my original post. Since it clearly should be a verb, I move that we resolve to use it as we see fit, since after all, what makes a word (a word) is how many people use it and understand the meaning behind it. I have a dream, that some day, every process will have a verb form... --Seans Potato Business 19:07, 24 November 2007 (UTC)

Michael Faraday established that magnetism could affect rays of light?

Hi, Michael_Faraday established that magnetism could affect rays of light? What? I thought light is not affected by magnetism. Please explain.

Thanks --InverseSubstance (talk) 02:42, 23 November 2007 (UTC)

Good question! This is what our article on Faraday says - "In 1845, he discovered the phenomenon that he named diamagnetism, and what is now called the Faraday effect: The plane of polarization of linearly polarized light propagated through a material medium can be rotated by the application of an external magnetic field aligned in the propagation direction. He wrote in his notebook, "I have at last succeeded in illuminating a magnetic curve or line of force and in magnetising a ray of light". This established that magnetic force and light were related"

Read the linked articles (showing up in blue), hopefully they will explain better than I can. DuncanHill (talk) 02:49, 23 November 2007 (UTC)

Thanks! Thats amazing. This might be a good time to ask another question I've been curious about. Light waves are usually depicted as a series of - well - light waves. If a light wave is the product of a quantum jump from a higher electron orbital to a lower electron orbital, then how many cycles are there in a light wave train? User:InverseSubstance —Preceding comment was added at 03:24, 23 November 2007 (UTC)

Well, the difference in energy of states in the quantum leap determines the energy of the photon, or $E=h\nu$, where $\nu$ is the frequency of the photon in cycles/sec and h is Planck's constant. Just multiply the cycle frequency by the number of seconds you're generating the wave packet for and boom, you have the number of cycles. The result doesn't have much meaning, however, as quantum mechanics describes a wave packet that has an infinite number of cycles that decay to zero exponentially as it propagates away, so you can think of our calculation as more of the average total number of cycles in a series of wave packets generated with certain frequency over a length of time. SamuelRiv (talk) 03:40, 23 November 2007 (UTC)

Ok - that's interesting. So when an atom absorbs a Photon, the entire wave packet is absorbed, including the entire exponentially decaying amplitudes, right?

I'm also curious about how a light wave can interfere with itself in the Double_slit experiment. The probabilistic Wave_packet can describe it, but not explain it. And I imagine that string theory also does not explain self-interference; it only describes its probability, right? --InverseSubstance (talk) 04:12, 23 November 2007 (UTC)

Classical wave theories of light are sufficient to explain the interference pattern (but not the lack thereof) in the double slit experiment. Basically, two waves diffracting at two narrow slits will interfere in an alternating constructive and destructive way (there are many diagrams of this in double slit experiment.) Light interferes with itself as a wave, but there is also light-to-light scattering (Delbruck scattering) which occurs when a virtual particle is exchanged between photons, similar to how electrons scatter off each other by exchanging a virtual photon. This is a nonclassical effect, but it has nothing to do with the double-slit experiment. SamuelRiv (talk) 05:21, 23 November 2007 (UTC) Addendum: none of this has anything to do with string theory, and string theory explains nothing about light. The best theory we have for light is Quantum electrodynamics (QED). SamuelRiv (talk) 05:30, 23 November 2007 (UTC)

String theory does actually have an explanation for diffraction (not that I can remember it). String theory generally has an explanation for everything, and generally these explanations produce no predictions divergent from quantum, and thus they are indistinguishable from quantum. String theory is in general not worth thinking about, except as an exercise of silliness and ammusing thoughts. Someguy1221 (talk) 05:59, 23 November 2007 (UTC)

An electron in a higher orbital has got a certain lifetime, the average time it needs to fall back to a lower orbital. This lifetime also determines the "number of significant cycles" and hence the coherence length - and, as can be calculated with the Fourier transform, the width of the spectral line (the spectral line is narrower if the lifetime is longer). If the atom is not undisturbed during this lifetime of the electron in the higher orbital, e.g. if it collides with other atoms, then the lifetime gets shorter and the spectral line gets broader - see also spectral line. Icek (talk) 10:48, 23 November 2007 (UTC)

I have long been in awe of Faraday, a man who probably could not have passed freshman high school algebra, showing the relationship betwen electricity and magnetism by discovering induction and transformer action, then discovering the relationship between magnetism and light (magnetism can rotate the plane of polarization of light), and in the end attempting (unsuccessfully) to find a relationship between electricity or magnetism and gravity. He was as tireless an experimentor as Einstein was a theorist. Edison (talk) 05:27, 25 November 2007 (UTC)

Spacetime and FTL

Given that:

• space and time are only two different aspects of spacetime;
• FTL travel is not a possibility which can be ruled out;
• and all matter is essentially composed of photons and leptons;

Is it plausible that photons (which are light themselves) or leptons, do accelerate above the speed of light, but that we cannot detect this phenomenon because the surpassing of this "threshold" transforms them into time? This might be a fallacy, but it seems quite logical to think that there exists a "phase change" which works like this: time <=== photons/leptons ===> matter. Remember there are special quantum effects which allow for a violation of the law of conservation of energy, maybe accelerating above the speed of light would be such a singularity. Is this idea really a fallacy or is it plausible? —Preceding unsigned comment added by Danilot (talk • contribs) 12:04, 23 November 2007 (UTC)

Okay, let's start with your givens, all of which are wrong:

• space and time are fundamentally different in our theory of general relativity, which uses Minkowski space in which a "length" is defined as $s^{2}=c^{2}t^{2}-x^{2}-y^{2}-z^{2}$, which shows that our time t is a separate type of coordinate than our space x,y,z. We find velocity (the time derivative) is then $v\cdot r/t=c^{2}$ which sets a fundamental limit on velocity through space (remember $v=\Delta r/\Delta t$) of c, the speed of light.
• Therefore FTL travel is ruled out in space, but we can still acheive it with a warp drive which bends space itself, or a wormhole which topologically tunnels through space.
• Your link to all matter being composed of leptons and photons is only valid for the very early universe, does not describe matter (only leptons exist in matter, photons "do not", and leptons are not as significant in matter as baryons).

And then your conclusions are also mistaken. Massless particles by definition must travel at the speed of light, and massive particles (like leptons and baryons (matter)) must appear to us to travel slower than the speed of light in vacuum in accordance with quantum mechanics, namely the uncertainty principle. What you are describing is called a tachyon, which travels faster than light by definition (but appear to us to be travelling slower than light, since they are travelling backwards in time. There is a model of antimatter that describes them as tachyons, but I believe there is solid evidence against this description. Anyway, it is a fundamental principle that particles travelling faster than light can never reach light speed, so they can never slow down to become slower than light, and vice-versa, so it does not represent a possibility for FTL travel. Finally, the Law of Conservation of Energy may be locally violated, but not globally violated, so it is always true. SamuelRiv (talk) 13:53, 23 November 2007 (UTC)

I'd like to correct one of those statements:

• Therefore FTL travel is ruled out in space, but we can still acheive it with a warp drive which bends space itself, or a wormhole which topologically tunnels through space.

We can't achieve FTL travel with warp drives or wormholes - current science doesn't say that they are practically possible - we have no idea how we could even theoretically make space warp or tunnel without playing around with black holes and other things that we really have no way to do. At best we can say that perhaps they aren't ruled out as utterly impossible. But with everything we actually know FTL travel is ruled out. Tachyons are not science - we havn't observed them and none of our laws either require or predict their existance - they are purely hypothetical. Annoying though the universal speed limit is, it looks certain that we're stuck with it. SteveBaker (talk) 17:13, 23 November 2007 (UTC)

Here's where I add the usual things I like to say about this: First, if a particle could "move" faster than c it wouldn't really be like motion at all, because in one inertial reference frame it would exist at infinitely many points in space but only one point in time (the opposite of the case of motion). For other reference frames, it would be moving the opposite direction! Second, the limitation of relative speed doesn't actually limit your ability to reach faraway destinations. For example, if you had a rocket that could sustain a 1 g acceleration indefinitely, you could reach any point in the galaxy in a matter of years[5] (of your own proper time, of course), even though the points are hundreds of thousands of light-years apart. You can think of this as being due to length contraction, which causes your destination to appear closer to you as you move toward it, hence easier to reach. —Keenan Pepper 06:05, 24 November 2007 (UTC)

And better yet, by the time you get back all of your favorite shows will be out on DVD! ;-) Someguy1221 (talk) 06:34, 24 November 2007 (UTC)

No, by that time most of the videos that you remember will have been destroyed during the second coming of Jesus.

To respond to Steve, I am well aware that there is no currently existing way to build a "warp drive", but I'm sure you are aware of the hypothetical solutions to the hypothetical problems with these topological types of propulsion. There is no hard evidence for any of it, so it's pretty much assumed that it's all science fiction, at least for now. And as for the tachyon nature of antimatter, I'm not in particle research, so I can't comment on the current state of it, but in general quantum field theory certainly holds this tachyon formulation in high regard (see Feynman diagram). SamuelRiv (talk) 06:50, 24 November 2007 (UTC)

Shared blood system

Ok it is stretching it but for the sake of fiction: how realistic would it be (if possible at all) to artificially link two normally constituted persons so that they share the same cardiovascular (bi-cardiovascular?) or blood circulatory system (the blood would go through both persons to do a full circulation)? In the some order of ideas let's imagine a situation where someone is really messed up under the neck and the only way to save him/her would be to tap the head's blood system into the jugular veins of the healthy person. How would the heart cope with the extra strain and how much is the blood compatibility an issue? Is it completely irrealistic or merely highly implausible? Keria (talk) 15:48, 23 November 2007 (UTC) p.s. this question is dedicated to Zaphod Beeblebrox :p

Check out Conjoined_twins#Types_of_conjoined_twins, as thoracopagus twins have a high mortality rate. However, if one twin is parasitic, as an attached head would be, it shouldn't be too much extra strain. SamuelRiv (talk) 16:50, 23 November 2007 (UTC)

A fat person's heart and lungs can keep a large amount of extra tissue supplied with blood and oxygen for years, so supplying an attached head wouldn't be an issue that way. However, establishing the connection would obviously involve major surgery, and there'd be major stress on the artery and vein that were "tapped", as the load on it above and below the junction would be different. Still, in principle the surgical hazards and techniques shouldn't be much different than with an artery bypass.

A severed head might have blood-supply problems in the area of the cut, because some small areas were previously supplied by vessels branching from below the cut, so there could be a risk of gangrene. However, similar issues must arise with amputations generally, so I guess that also ought to be manageable.

The whole-body thing that's also asked about seems much more problematic. --Anonymous, 22:54 UTC, November 24, 2007.

Blood type would, of course, have to match. And even so, there would be problems with each (partial?) person's immune system attacking the other person. But given that organ transplantation exists with usually-adequate rejection control, I suppose it's a reasonable-enough idea for a work of fiction.

Atlant (talk) 15:55, 26 November 2007 (UTC)

definition of latitude

On the surface of an elliptical body, the line through the center of mass and the line of local gravity coincide only at the equator and the poles. So, which one defines latitude? —Tamfang (talk) 19:58, 23 November 2007 (UTC)

You may want to check out types of latitude. In short, you don't have just one measure of latitude. And, since real celestial objects don't have a perfectly elliptical shape, you may also consider gravitatorial deviations of the plumb line (the so called astronomical latitude). Pallida  Mors 20:09, 23 November 2007 (UTC)

To be a bit more specific, you have (at least):

• The geodetic or geographic latitude, (which you may consider the "main" latitude), given by the angle formed between the vertical line normal to the ellipse, and the equatorial plane. As far as I know, this accounts for the "local gravity" reference you gave.
• The geocentric latitude, which is given by the angle between the equatorial plane and a (straight) line joining the local point and the center of the ellipse (the line through the center of mass you metioned in your question.

You have other latitudes explained in the article. Most of them refer to projection topics. Pallida  Mors 20:48, 23 November 2007 (UTC)

November 24

Supercavitation

Hey I was reading a question on the science desk about the fastest way to move through water, and someone mentioned Supercavitation. I was wondering could Supercavitation be used on a plane or rocket to create a vacum throgh the air allowing it to move much faster?67.127.235.74 (talk) 00:03, 24 November 2007 (UTC)

No. The phenomenon of supercavitation depends on the fact that there is a phase boundary between liquid and gas. There can be no such phase boundary between gas and vacuum. Icek (talk) 01:48, 24 November 2007 (UTC)

IUDs and large penises

Are IUDs safe and reliable if the male has a large penis? —Preceding unsigned comment added by 189.15.179.115 (talk) 00:38, 24 November 2007 (UTC)

I would think (but IANAD) that they're just as safe and reliable as with small penises. IUDs, as their name implies, are placed inside the uterus, which is separated from the vagina by the narrow cervix. In normal women who aren't pregnant, the opening of the cervix (the external os) is tiny, maybe a few millimeters wide at most. Obviously the penis is much wider than that, so it never penetrates the cervix during intercourse. —Keenan Pepper 01:35, 24 November 2007 (UTC)

Well, not always entirely inside the uterus. The IUD article has a comment in the "Side effects and complications" section that appears to be the same information as in this ref of the article. Therein is a FAQ item:

10 Q: Should an IUD be removed if a woman's sexual partner complains about the IUD string?

A: Not necessarily. The couple may need reassurance and an explanation of what the string is. If this is not satisfactory, the end of the string can be tucked behind the cervix. If this too is not satisfactory, the string can be cut flush with the cervix. (This should be noted in the woman's record.) Such short strings will mean that the woman will not be able to check the strings and a provider will need narrow forceps to grasp the strings when removing the IUD. The woman should be given the choice of what she wants done, including whether the IUD should be removed.

Anyone know of a free diagram of a uterus with an IUD in it? Would be a good addition to our article. DMacks (talk) 19:35, 24 November 2007 (UTC)

Is suicide unique to our species?

Is there evidence that giving up on life and exiting it purposefully exists beyond our species? Sappysap (talk) 01:09, 24 November 2007 (UTC)

That depends on your definition of "purpose". Icek (talk) 01:49, 24 November 2007 (UTC)

This [6] is a nice short summary of the conventional scientific answer: No. Though you will find tons of anecdotal accounts of animals "pining away", refusing sustenance, or giving up "the will to live" after the death of their master, mate, or companion. Possibly of interest, it often seems in my experience that many of these accounts center around animals in captivity. Take that as you will. Azi Like a Fox (talk) 03:03, 24 November 2007 (UTC)

When a honeybee stings a mammal, the barbed stinger tears loose from the bee’s abdomen, leading to the bee’s death within minutes. Thus, a purposeful act of violence by the bee results in its own death as a side effect. This is comparable to a suicide bomber, whose purposeful act of violence results in the death of the bomber as a side effect. It could be argued that there’s a difference between stinging bees and suicide bombers in that there is no evidence that bees are aware that they will die if they sting. However, many if not most suicide bombers are also unaware that they will indeed completely die if they set off the bomb, instead believing that they will merely go to an afterworld. MrRedact (talk) 04:32, 24 November 2007 (UTC)

That is a very elegant answer, MrRedact. A necessary task is a necessary task. No debate over inference need apply. Death, over an impending and certain jeopardy of livelihood, is the only answer for any organism in extreme peril. Sappysap (talk) 09:36, 24 November 2007 (UTC)

That doesn't really count. Bees aren't aware they are going to die when they sting because they aren't aware they are even alive to begin with. 64.236.121.129 (talk) 16:03, 26 November 2007 (UTC)

Would you count programmed cell death as suicide? Elle _{vécut heureuse} ^{à jamais} (Be eudaimonic!) 04:58, 24 November 2007 (UTC)

Animal suicide is not such an outlandish idea. If resources were scarce, the suicide of a parent could make sense in a selfish gene strategy (consider the classic "you'd be better off without me" suicide note).As MrRedact says, some hive animals, certain ants and bees, will have members that will go out on what are essentially "suicide missions". Although the goal isn't to die per se, death is an inevitable consequence of its actions. In the case of hive animals, its unlikely the thing even has a "choice" - they are genetically hardwired to go on a suicide mission in response to the appropriate cue. The complex genetic relationships between the Queen and her hive means that this actually makes a lot of sense in terms of selfish gene theory, even though it appears very unselfish on the face of it. The excellent book, The Selfish Gene explains in more detail. See also here for previous discussion on the same question. Rockpocket 09:56, 24 November 2007 (UTC)

Surely the concept of suicide requires some ability to understand the act of self-killing. The idea that a bee, for example, gives up its life in some 'heroic' way is rather anthropomorphising the bee somewhat. Does the bee take a concious decision to attack? I think it is governed by genetically installed reaction behaviour that gives it no choice in its response. This is far from anticipating the results of its actions - which is perhaps an essential part of the concept of suicide. Richard Avery (talk) 16:24, 24 November 2007 (UTC)

But do brainwashed suicide bombers have a choice too? Elle _{vécut heureuse} ^{à jamais} (Be eudaimonic!) 18:47, 24 November 2007 (UTC)

They're irrelevant except as an analogy; the question is about suicide in other species. Richard has the right idea. For it to be possible in the terms we were asked about, the species involved would have to be one with the capacity to understand the concept of one's own death and to plan future actions. The more intelligent non-human species, like chimps and dolphins, might well be able of doing this; insects and lower animals generally are irrelevant. --Anonymous, 23:00 UTC, November 24, 2007.

Our concept of "suicide" as a result of a conscious decision is obviously unique to humans. As you say, to contemplate one's own death requires before choosing to kill oneself requires a level of self awareness beyond even non-human primates. You have to understand what "living" is before you can understand what "dying" means. However more abstract interpretations of "exiting life purposefully" is relevant to other species, especially when robust innate behaviour removes the concept of "choice" from the equation. Whether that qualifies as suicide is a matter of interpretation. Rockpocket 09:14, 25 November 2007 (UTC)

• I think the honeybee counts as a solid answer, but please oh please, if someone asks you about animals who commit suicide, don't ever propagate the myth about lemmings dropping to their death off cliffs. That is simply an inaccurate urban legend as confirmed by snopes.com - Mgm|^(talk) 10:37, 25 November 2007 (UTC)

Not really. The honeybee doesn't know it's alive in the first place. An animal has to know it's alive to begin with before it can choose to take its own life. 64.236.121.129 (talk) 16:05, 26 November 2007 (UTC)

*Patents 64.236's bee-mind-reading device* Skittle (talk) 16:50, 26 November 2007 (UTC)

*Patents basic knowledge device and gives it to Skittle* 64.236.121.129 (talk) 14:53, 27 November 2007 (UTC)

There is some argument for saying that honey-bees are like cells in the human body. They are merely parts of a larger organism (the "Hive") - much more complex than a single cell of course - but not that much different in concept. An individual worker bee doesn't have the attributes of a proper animal - she can't reproduce and won't live long by herself for example - she is structurally quite different from her parents due to specialisation of function - but she is an exact genetic clone of all of her sisters. Injecting royal jelly into the bee larva produces a queen - just like tweaking the environment of a human stem cell can produce a skin cell or a blood cell or a brain cell. An individual bee is similar to (say) white blood cells from a human. They can survive OK for a while by themselves and behave a bit like little amoebas...but they can't breed. Human cells commit suicide for the betterment of the body all the time - why would we think bees are different? Viewed in that way, the beehive doesn't commit suicide - it just sheds some "cells" in order to protect itself. SteveBaker (talk) 22:09, 26 November 2007 (UTC)

The question referred to 'giving up on life', not high-risk behaviour or sacrificing life for a cause. To my knowledge, suicide as a dysfunctional behaviour only occurs in humans and special cases like parasite-induced brain damage or contrived situations like an animal held in captivity, though I've heard some other primates can have psychiatric issues like depression. Peter Grey (talk) 07:54, 27 November 2007 (UTC)

I thought Lemmings, but apparently not. Mattopaedia (talk) 12:43, 27 November 2007 (UTC)

Genetic possibilty of genius IQ

I am adopted and just discovered that my real father was a mathematical genius. I am not saying that I am a genius but I was in gifted/advanced classes for most of my life and read through books voraciously. Otherwise, I am a normal girl with normal wants/needs. However, I would sometimes freak out my friends for knowing more about a subject than necessary, etc. Is it possible that somehow that this could be genetic? --WonderFran (talk) 02:02, 24 November 2007 (UTC)

Yes, intellectual potential is partially determined by genetics. See genetics of intelligence and related articles. Dragons flight (talk) 02:18, 24 November 2007 (UTC)

One should be careful to read too much of a direct correlation between any given behavior and one's apparent genetic heirs. Genetics are complicated and the only direct relationships one have between genes and behavior are for extremely rare things (usually disorders)—the relationship between genetics and IQ is at this point known only in a purely statistical terms. To claim that your aptitude in school or love of learning is "only" the result of a genetic quirk both devalues your own effort but also the efforts of those around you—in reality, all things genetic require development to even become recognizable as traits, and we are not simply reflections of our genes. --24.147.86.187 (talk) 07:57, 24 November 2007 (UTC)

You might want to take note of the twin studies, which compared traits of identical and fraternal twins that were separated at birth. Identical twins showed more similarity than fraternal twins in a variety of areas, with IQ being at an intermediate level of genetic influence. So, IQ is a product of both genetics and environment. -- HiEv 16:45, 24 November 2007 (UTC)

I completely understand your point of view however, I grew up on the projects and anyone who has can contest the difficulty of achieving academically....not to dismiss the few who have.....--24.151.103.18 (talk) 08:05, 24 November 2007 (UTC)

Antisocial personality disorder

How many famous people have this disorder? —Preceding unsigned comment added by 76.64.130.224 (talk) 02:45, 24 November 2007 (UTC)

See antisocial personality disorder#prevalence. Fame is relative and somewhat subjective, so I don't see how it can be included in the calculation.--Shantavira|^{feed me} 08:25, 24 November 2007 (UTC)

BOOLEAN OPERATORS

boolean operators —Preceding unsigned comment added by 75.26.161.182 (talk) 03:38, 24 November 2007 (UTC)

Boolean operators. Someguy1221 (talk) 04:08, 24 November 2007 (UTC)

Pluto

Why didn't Voyager 2 pass Pluto? 124.176.190.64 (talk) 04:33, 24 November 2007 (UTC)

Presumably because the planets weren't lined up nicely enough for it. Someguy1221 (talk) 04:54, 24 November 2007 (UTC)

The orbit of Pluto is way out of alignment with the orbits of the planets, so although Voyager passed beyond the orbit of Pluto, it would have been far far away at the time.--Shantavira|^{feed me} 08:33, 24 November 2007 (UTC)

This answer confuses two issues. It's true that all the other planets orbit in something close to the same plane while Pluto's orbit is somewhat inclined, but it's not inclined so much that it would be unreachable. The problem is that, at the time of the Voyager probes, it was in a different part of its orbit.

The whole Voyager 2 mission was only possible because the four gas giant planets were in roughly the same direction from the Sun at that time, a rare occurrence. See Planetary Grand Tour. As it says in that article, it would have been possible to reach Pluto by directing the probe appropriately on leaving Saturn -- but then the probe would not have passed Uranus or Neptune.

The thing is that when you want to use the gravity of planet A to direct the probe onward to planet B, this fixes the course that your probe must take near planet A, and it probably won't be the same course you'd route it on if you were only interested in A. NASA was under such budget constraints at the time that they decided it was more important for the Voyagers to be well placed to visit Jupiter and Saturn than it was to pick up all three of the other planets. Only after Voyager I had succesfully visited Saturn, taking the pressure off Voyager II, was the latter probe placed on a course that would allow it to continue with the Grand Tour after Saturn. (Sorry, no cite, but that's what I remember reading.) Without a third probe, there was no way to reach Pluto as well.

--Anonymous, 12:40 UTC, November 24, 2007.

Pluto orbits the sun once in every 248 years (and at a very odd angle to that of all of the major planets). Voyager is heading away from the sun at about 35,000mph and Pluto is only 1500 miles across. The odds of it happening to be in the right place for the trajectory of the spacecraft to intercept it is quite remote unless the mission planners specifically designed things to come out that way. When they designed the route of the spacecraft they had specific things they wanted to survey - they must have had to make all sorts of compromises in order to manage the various gravity slingshot manouvers they did. Evidently they simply couldn't figure a way to get over to Pluto along the way. SteveBaker (talk) 21:56, 24 November 2007 (UTC)

See my answer above. They did figure out a way, but had other priorities. --Anon, 23:02 UTC, Nov. 24.

Path integrals and lightcones

As far as I know, in the the path integral formulation of quantum mechanics, one has to include faster-than-light paths. How would the predictions of quantum mechanics change if one would exclude faster-than=light paths? —Preceding unsigned comment added by 193.171.121.30 (talk) 09:11, 24 November 2007 (UTC)

I'm not sure if FTL paths are necessarily included when Quantum field theory is formulated in Minkowski space, but either way an exclusion of that sort would simply be a change in the geometry of one's space, which is suggested in the article to not have serious or significant consequences to the accuracy of the theory. SamuelRiv (talk) 17:24, 24 November 2007 (UTC)

Orbitofrontal cortex and ventromedial prefrontal cortex

Is the orbitofrontal cortex the same as the ventromedial prefrontal cortex? Or is it a part of the ventromedial cortex??? Lova Falk (talk) 10:33, 24 November 2007 (UTC)

I'm not sure, but they seem to correspond in location and function (see ventromedial prefrontal cortex): both process risk and judgement. SamuelRiv (talk) 13:13, 24 November 2007 (UTC)

Another question on the prefrontal cortex

In picture A one can see the vl-PFC (yellow) and the dl-PFC (blue). But what would be the name of the grey area between these two? Lova Falk (talk) 11:00, 24 November 2007 (UTC)

The mIPFC, medial inferior prefrontal cortex, i would imagine. It's been a while since neuroanatomy. SamuelRiv (talk) 12:50, 24 November 2007 (UTC)

But the medial prefrontal cortex (for some reason called MFd) is the reddish/brownish part of the picture. Would the medial inferior prefrontal cortex be in a complete different place? Lova Falk (talk) 14:13, 24 November 2007 (UTC)

Sorry, I meant medial lateral prefrontal cortex. I really don't know for sure though. Google suggests that this is a legitimate name for that region, but it doesn't look like it's used much in the literature. SamuelRiv (talk) 17:21, 24 November 2007 (UTC)

Symmetry of animals

Why are most of the biological organisms in animalia kingdom symmetric externally, though they are highly asymmetric internally? I was wondering why nature might have chosen the symmetric structure and what great benefits this symmetry brings to animals? This is not the case with plants, though their leaves and flowers also tend to be highly symmetric about at least one plane. I have never seen any asymmetric animal or plant leaf or flower, so to say. DSachan (talk) 19:28, 24 November 2007 (UTC)

I've always wondered about this, too. Here's an article I just found that might be helpful:[7]. 128.163.224.198 (talk) 20:15, 24 November 2007 (UTC)

Thanks for the link. But the article only discusses about what is responsible for the structuring of organs internally the way they are. It does not say anything about that skin deep super symmetry that exists everywhere and it also does not mention anything about why it might be so or the advantages and disadvantages of it. Though one thing I got to know from the article is that it is a pestering problem for scientists today and they are trying to speculate about the evolutionary benefits of skin deep symmetry and then asymmetry there onwards. Any other thoughts on the issue are welcome. DSachan (talk) 20:30, 24 November 2007 (UTC)

One explanation is that the macroscopic external world tends, on average, to be symmetric in the sense that there is no particular advantage to looking or turning left instead of right or vice versa. In fact, it is advantageous for many species to be able to see and turn equally well in either direction, since if they showed a preference for one direction over the other, other species (such as their predators) could evolve to take advantage of this. The easiest way to achieve this ambidexterity is to make the animal's body plan bilaterally symmetric; this also has the advantage of simplifying the ontogeny of the animal, since the development of both of its sides can be controlled by the same genes.

Another, related reason is that many methods of locomotion employed by animals, such as swimming, walking or flying, work best with pairs of symmetric limbs. A fish with bigger fins on one side than the other would tend to swim in circles, a human or any other land-dwelling animal with longer legs on one side than the other would have difficulty running straight ahead, and a bird with one wing bigger than the other could scarcely even take off.

As for why animals don't tend to be more symmetric, this is also explainable by environmental factors: on Earth, gravity breaks up-down symmetry, leading to most animals having distinctive bottom and top sides, while the need to move rapidly tends to create a need for a specialized front and rear end. It's worth noting that quite a few marine species, such as starfish and jellyfish are, in fact, radially symmetric without a distictive front end — but few if any of these are species whose survival strategies would involve rapid movement. —Ilmari Karonen (talk) 20:26, 24 November 2007 (UTC)

Someday I'd like to run artificial life in a universe of higher dimension, and see what kinds of symmetry are favored in the critters there! —Tamfang (talk) 20:36, 24 November 2007 (UTC)

Ilmari Karonen, your logic of locomotion is working fine with the animals, but what about leaves and flowers? I see only ontogenical argument of yours working there. Will this be the only reason in leaves and flowers? and that means to say, nature is also fed up with having a large number of genes required to express the characteristics of biological organisms and it wants to get rid of as many as it can.

The other point is that there are some features even in us which I see having no advantages of them being symmetrically located. For example, the navel (belly button) is also symmetric about the sagittal plane in the middle of our belly. Does this point in our belly tend to be the point making the umbilical cord shortest in length in the early stages of our life? If this is not so, what else is the reason? DSachan (talk) 20:52, 24 November 2007 (UTC)

For plants, I suspect it may indeed be just a case of symmetric leaves being simpler to produce than asymmetric ones. A leaf essentially starts with a stem and then fans out — it's probably simplest to have it fan out equally in both directions. Also note that asymmetric leaves would tend to droop due to gravity pulling the heavier side down, which might be suboptimal for catching sunlight, at least when the sun is high in the sky. As for the navel, I'd guess its location along the body's certerline may be just an accident of evolution — although it's worth noting that mammalian embryos start out highly symmetrical (spherical, in fact) and then gradually develop various asymmetric features as they mature. Since the umbilical cord forms very early during embryogenesis, at the time when the embryo just begins to acquire a distinct head-tail axis, it makes sense for it to be aligned symmetrically; at that stage, everything in the embryo is still symmetric. —Ilmari Karonen (talk) 22:38, 24 November 2007 (UTC)

I read somewhere (I forget where - sorry) that one possible reason for symmetry is that it requires less DNA to code for it - and less DNA means less to go wrong and less 'stuff' to carry around in your cells. SteveBaker (talk) 21:42, 24 November 2007 (UTC)

Plus, it's 'easier' to evolve. Plant evolves leaf. Plant's descendants have simple mutation to carry out 'reading' of leaf code twice. Plant has two symmetrical leaves. Skittle (talk) 23:36, 25 November 2007 (UTC)

Another possibility is that the symmetry seen around us can be traced back to fundamental mathematical symmetries. The golden ratio and the Fibonacci series are good examples of this. It could also reflect the underlying symmetry of the materials from which we are made, and the biochemistry. Build things up in a symmetric way, and the result will be symmetric. Redundancy, as well (only need instructions for one half of the object). Evolutionary history as well - many of our bodily structures still reflect our evolutionary history. We've inherited the symmetry in those early forms of life. Carcharoth (talk) 22:05, 24 November 2007 (UTC)

Great answers, Ilmari Karonen. – b_jonas 12:11, 26 November 2007 (UTC)

Also, symmetry is a simple and often accurate way of detecting the health of an animal. Because of that, most species with bilateral symmetry see symmetry as a form of beauty. Take a look at the faces of attractive people and you will often find a higher than average amount of symmetry. Thus life has evolved to select for external symmetry. See Symmetry (physical attractiveness) for details. -- HiEv 12:41, 26 November 2007 (UTC)

Here's an asymetrical animal, although a result of development rather than original design. Mattopaedia (talk) 12:49, 27 November 2007 (UTC)

Lunar warfare

I've been thinking about what warfare would be like if it took place on the Moon in the near future. While science fiction is in love with laser weapons, it seems the worlds military are rather more conservative, in that they're very happy to go to war with weapons several decades old, but that they know work. My thoughts are below: my question is to ask y'all if I'm on the right track about the science:

• Conventional guns work pretty well. Bullets fly on shallower trajectories and (lacking air turbulence) don't need to be spin stabilised (so barrels are unrifiled). With a decent scope a sniper could be a threat at 10 miles away. Moondust and propellant residue must be cleaned from a gun's action with a can of compressed gas. For hand-held guns recoil is more of an issue that on Earth (because the firer has less weight with which to counteract it by leaning into the shot) so muzzle breaks are found on most guns. The big problem with guns is dumping excess heat. Single-shot and semi-auto guns have black radiative fins to try to dump heat, while automatic weapons must have cooling systems (which work by using the excess heat to warm dry ice, which sublimates and is then vented)

• Conventional unguided rockets work well. They don't need fins for stabilisation (again due to the lack of atmosphere), an have an effective range several times that of comparably sized terrestrial equivalents. Guided missiles must use high-performance motors (e.g sodium azide cells) to adjust their course midflight.

• a Lunar Positioning System (LPS) can be erected much like GPS. Reasonable advances in portable electronics and antennas mean that a system with fewer satellites (in wider orbits) will be sufficient.

• The weapons of artillery pieces and tanks work well (although the vehicles that propel them are obviously different). As with firearms, cooling is a major issue. When integrated with a LPS and an electronic battlefield system they can attack targets well over the horizon.

• No equivalent to close air support is possible. Tactical support of land forces is supplied by artillery or ground-to-ground rockets. Strategic bombing is achieved either by long range g2g missiles or missiles fired from orbital weapons platforms.

• With no cover, no weather, limited opportunities for camouflage, and the extreme ranges at which simple weapons are effective, everyone on the battlefield is very vulnerable. Humans, who are yet more vulnerable in pressurised suits and vehicles, are largely absent from the battlefield; most combatants are semi-autonomous robot vehicles.

Neglecting obvious speculation about energy weapons (which I appreciate would be more effective in a vacuum) does this seem, erm, airtight? 86.131.206.94 (talk) 20:20, 24 November 2007 (UTC)

Instead of weather you get the long lunar night, which may be lit by earthlight, or only starlight on the backside of the moon. Things could very cold when not lit by the sun for weeks. Another factor is the extreme vulnerability of people to puncture wounds in their air containment. Something more like a shotgun may be able to cripple dozens of unprotected people. Graeme Bartlett (talk) 20:34, 24 November 2007 (UTC)

Don't forget that conventional guns usually need air to fire properly, as they propel by a rapidly-expanding gas. New propellants or rail guns are probably a better option. SamuelRiv (talk) 20:55, 24 November 2007 (UTC)

Any recoil vector not tangential to the surface would make the firer jump or fly up, which could be a big factor for artillery. A tank firing a sabot could put the penetrator into low orbit, so it would need to be careful about trajectory and try to figure out where not to be when it comes back around if it screws that up. The same goes for any weapon firing a projectile that goes faster than about 5,500 ft/s. Runaway missiles and stray shots would be raining down all over the moon for days or weeks after a battle, going as fast as they were when fired. Barrels would still be rifled, as the stabilization helps overcome perturbations caused by asymmetry in the gas blowby at the muzzle, which will envelope the projectile quite a ways downrange. Anything like aircraft would only be needed for emergency reconnaissance, as ballistic weapons could hit anything anywhere. Nukes could be used with impunity over the horizon, as all personnel would already be suited or indoors anyhow, and no blast would be felt. --Milkbreath (talk) 21:19, 24 November 2007 (UTC)

I don't believe that's true. Conventional guns turn solid propellant into gas (during its explosion) and that's what pushes the bullet out. Gas from the atmosphere just gets in the bullet's way. -- Finlay McWalter | Talk 21:02, 24 November 2007 (UTC)

I'm not sure that there would be little opportunity for camouflage. The lunar surface isn't particularly flat in most places, so (depending on time of day) there may be lots of shadows to play with and lots of structures to hide behind (erosion is very slow on the Moon...). As well, the surface colour and texture is fairly uniform compared to Earth (just a couple of different broad classes of rock, dusted over in many places with regolith) makes supplying camo uniforms easy (none of this mucking about with separate desert/jungle/winter/city uniforms). Of course, waste heat from warm bodies and equipment will be a dead giveaway on any sort of infrared imaging during the chilly lunar night.... TenOfAllTrades(talk) 21:21, 24 November 2007 (UTC)

Yeah - you don't need air to fire a gun. The oxidizer is mixed into the propellant.

• Conventional guns work pretty well. True.

For hand-held guns recoil is more of an issue that on Earth (because the firer has less weight with which to counteract it by leaning into the shot) so muzzle breaks are found on most guns. - Not true. Every action has an equal and opposite reaction. F=ma - the mass of the bullet (NOT WEIGHT) times it's accelleration produces a force that is absorbed by your body - so your accelleration (the 'recoil') is the mass of the bullet times the accelleration of the bullet divided by your body mass. Hence the recoil will be identical to what it was on earth. Actually rather less because you're wearing that huge chunky space-suit.

The big problem with guns is dumping excess heat. Single-shot and semi-auto guns have black radiative fins to try to dump heat, while automatic weapons must have cooling systems (which work by using the excess heat to warm dry ice, which sublimates and is then vented) - Maybe that's a problem...it's hard to know. I doubt dry ice solutions would be practical though.

• Conventional unguided rockets work well. They don't need fins for stabilisation (again due to the lack of atmosphere), an have an effective range several times that of comparably sized terrestrial equivalents. Guided missiles must use high-performance motors (e.g sodium azide cells) to adjust their course midflight. - The inability to use fins for stabilisation would be a major problem - but you shouldn't be thinking of long, thin missiles - they can be any old shape. Probably gyroscopic stabilisation will suffice.
• a Lunar Positioning System (LPS) can be erected much like GPS. Reasonable advances in portable electronics and antennas mean that a system with fewer satellites (in wider orbits) will be sufficient. - Probably.
• The weapons of artillery pieces and tanks work well (although the vehicles that propel them are obviously different). As with firearms, cooling is a major issue. When integrated with a LPS and an electronic battlefield system they can attack targets well over the horizon. - There is no problem (in principle) with making over-the-horizon weapons here on earth either. But you have to consider the problems of locating your target and that they can sense your incoming weaponry with sufficient time to get out of the way. Hence you need guided weapons...which in turn brings a whole other slew of problems.
• No equivalent to close air support is possible. Tactical support of land forces is supplied by artillery or ground-to-ground rockets. Strategic bombing is achieved either by long range g2g missiles or missiles fired from orbital weapons platforms. - See below.

I don't think you are thinking far enough 'outside the box'. Because there is no atmosphere, you can in principle orbit at very low altitudes - just above the tallest mountains would be just fine. Orbital speeds can be pretty amazingly high with no air resistance or aerodynamic forces - and a weapon in polar orbit can be arranged to cover the entire moon over enough orbits. Also, you don't need to burn fuel to stay up there. So injecting an enormous cloud of low-yield rocket/bomb/satellite things up there - with primitive guidance, a camera and a small rocket to nudge them out of orbit would produce a lethal combination. They could act as their own surveillance - when they spot a likely target, they call someone who is nice and safe a long way off who decides kill/no-kill - and the next available satellite nudges itself out of orbit and comes screaming in for the kill. The speeds would be amazingly high - you probably wouldn't even need explosives. You'd be able to nominate a target to hit from the ground and just have the next available unit drop out of orbit to take it out. With weapons like that, you'd obsolete almost all of the other things you've come up with. However, with both sides taking the same approach, there simply won't be any targets to hit.

The bigger question is why there are targets out there anyway? You won't have huge civilian cities - and with no 'nuclear winter' concerns, why not just nuke the mines, factories and launch facilities out of existance? (In fact - forget the mines and factories - just take out their launch facilities and their mines and factories are irrelevent. I can't see the need for humans and tanks and stuff to be there at all.

SteveBaker (talk) 21:30, 24 November 2007 (UTC)

• Hold on there. It's true that without air resistance an orbit at very low altitude is possible, but it won't necessarily be stable. The Moon's gravitational field has irregularities and the Earth causes sizable perturbations. Your orbiting weapons would need fuel for stationkeeping, although I don't know how soon. Also, from a position close to the ground, they could only strike targets along a narrow path on each orbit... so you'd need an awful lot of them to be able to cover a reasonable amount of the Moon's surface. --Anon, 23:17 UTC, November 24, 2007, Earth.

That's true - but it's likely to be a pretty tiny amount. You only have to account for gravitational variation - a very gentle adjustment is all that's likely to be required. The craft need some kind of motor to nudge themselves out of orbit anyway - so I doubt that's a huge deal - a hydrazine thruster would probably suffice. As for the number you'd need - that would depend on how urgently you need to hit your target. A polar orbit would take half of a lunar month (14 days) to cover the entire surface - but the orbital speed would be something like a kilometer per second - taking about two hours to complete an orbit - with the orbits being about 80km apart at the equator - it doesn't take much of an orbital 'nudge' at 1km/sec to deflect your orbit by 80km. So if you had 14 of these satellites you could hit any target within a day of deciding to do so. If you had 150 of them, then you have to plan your attacks a couple of hours ahead of time. With 3000 of them you can hit any target within 5 minutes - which is pretty good by military planning times. I envisage these things as being cheap - highly networked (so you can't take out a command unit or disrupt their communications because they can pass messages over very short range radio from one satellite to the next) - and with each one carrying a camera (which they'd need for station-keeping and targetting) - you have constant surveillance of the entire moon. You'd launch them from orbit and since they're cheap you'd have a heck of a lot of them. With the kinetic energy from travelling at 1km/sec, something about the size of a football is all you'd need to vaporize your target. I had in mind satellites like the size and complexity of a cellphone - with the same communications ability and a similar kind of camera - plus a few ounces of hydrazine fuel and gyroscopic stabilisation. Cost in bulk could be thousands of dollars each - so a few million dollars (about the cost of one tank and about a lot less than the cost to get one infantryman to the moon) would allow you to bring down huge destruction on anything on the surface of the moon within a few minutes. SteveBaker (talk) 17:33, 25 November 2007 (UTC)

(edit conflict) Okay, my bad, according to MythBusters_(season_4)#Guns_Fired_Underwater, oxygen is not needed with modern guns. The ignition of gunpowder and primer does not require oxygen. I guess enough gas is produced to accelerate the bullets effectively: Smokeless powder converts almost everything to gas, but gunpowder only gets about 40% yield. There also should not be any leakage of gas behind the bullet, though maybe some is there as the cartridge is loaded... if this is the case, you'll want to manufacture some new guns and bullets that are optimized to this change in environment. Heat buildup is a big problem, as that's normally dealt with by air cooling (yes, in the end almost everything here is air-cooled). Any type of radiative cooling would kill any hope of camouflage, but I don't see any other solution besides dumping excess heat into some type of electromagnetic radiation. SamuelRiv (talk) 21:45, 24 November 2007 (UTC)

You could drive a big spike into the lunar soil and use that as a heat sink. If you find somewhere in permenant shadow, it'll be pretty amazingly cold. If you have cheap access to water (unlikely), you could build a cooling jacket that oozed water to the surface. It would boil off in the vacuum taking substantial amounts of heat with it. But I very much doubt that conventional projectile weapons are the way to go. Infantry on the ground would be horribly vulnerable - even a blast of low speed buckshot would penetrate a spacesuit. Firing a bazillion small ballbearings on a ballistic trajectory (with no air resistance to slow them down) would take out large formations of infantrymen very easily indeed. Ergo there won't be large formations of infantrymen. The lack of air resistance (and hence the absence of terminal velocities) means that if you are killable by high speed metal - you're dead. So you have to be moving fast or buried underground or very expendable. With no reason not to use nuclear weapons (no civilians, no wind-born fallout, no nuclear winter issues - and if your technology is good enough to get you to the moon in the first place, then it's good enough to build nukes with), being buried a little way underground won't help you - so you'd have to be in a gigantic bunker - very tough to construct in a lunar environment. Moving fast is possible - but moving fast in a nice, predictable, straight line is death - so you need to be accellerating unpredictably. For that you need something with no humans inside. Since you can use insanely low altitude orbits to stay airborn without using fuel, you probably want very manouverable, very low altitude satellites. Being very numerous is another way to be safe - so (as I said before) a vast number of very low altitude orbiting bombs can take out anything that moves on the surface.

But still - why fight on the moon to start with? If there are any people there at all then clobbering their supply lines from Earth is the simplest solution. Those supply craft will be big, sluggish and predictable. Fire a cloud of ball bearings at a few hundred mph in the direction of a resupply craft and they are without food and water within a month. Do it two or three times in a row and they are dead.

SteveBaker (talk) 22:16, 24 November 2007 (UTC)

a cardiac procedure called mase

What is a cardiac procedure called mase? —Preceding unsigned comment added by 67.177.212.215 (talk) 18:50, 24 November 2007 (UTC)

There's nothing in the book of medical abbreviations on my desk. Could it be something done with a maser? —Tamfang (talk) 20:32, 24 November 2007 (UTC)

MACE appears to stand for "major adverse cardiac events", which includes infarctions and other (dunno what) bad heart happenings. [8]. But that's not a procedure. -- Finlay McWalter | Talk 20:34, 24 November 2007 (UTC)

See Maze procedure. --Arcadian (talk) 23:09, 24 November 2007 (UTC)

Artificial gravity

If a spaceship, which is not near any object large enough to cause significant gravity, would generate its own gravity by rotating around its own axis, what would happen? If someone standing on the edge would climb up all the way to the centre, and then keep on climbing further, would they start falling down, but actually not back where they started, but in the same direction that they had been climbing? And where is "down" exactly when it is towards an entire area, not towards a single point? Is it towards the point on the surface that is nearest to your current location? Does that mean that if someone were to jump up on a rotating spaceship, they would land on a different spot than they originally jumped from? JIP | Talk 20:38, 24 November 2007 (UTC)

If you can, watch the movie 2001: A Space Odyssey (film) - it does a great job of showing what spin-gravity would be like. But let's imagine a vast spacecraft that's a cylinder spinning around it's long axis. You'd build the 'decks' of the craft as concentric cylinders inside the craft. The decks closest to the outside of the craft would have the strongest gravity - those closest to the central axis would have less gravity - and at the very center of the craft, you'd be in zero g. If there were windows on the curved outside surface of the cylinder, they would be in the floor of the strongest-gravity deck. If you imagine a ladder running "up" from one of the outer decks, up through the center of the ship and through to the opposite side, then someone starting out to climb the ladder up from the outermost deck would feel strong gravity at first, then slightly less and less still until reaching the center of the spaceship where there is no gravity. If you continued 'climbing' the ladder through the zero g region, you'd start to feel like you were hanging upside down and the direction that was "up" is now "down"...and as you climbed further "down" the ladder, you'd find the gravity getting stronger and stronger until you reached the outermost deck - 180 degrees around the other side of the ship from where you started.

If the spacecraft was small enough with no internal decks - then yes, as you say - you could jump upwards gently and land back where you started from - but a really big jump would take you sailing up into less and less gravity - floating gently across the middle of the ship - then (alarmingly) plummeting head-down towards the opposite side of the ship with increasing accelleration until you whacked your head on the floor on the opposite side.

However, everything I've said has missed one important thing. Coriolis forces. Since you are moving sideways at a fairly large speed on the outer surface of the ship, as you go upwards, you'd find yourself not going in a straight line because the space craft is spinning beneath you. One of the problems with producing a spin-stabilised craft "for real" is that these coriolis forces might make it's occupants have all sorts of puke-making feelings from being pushed sideways everytime they stood up too quickly - or that different gravity between their heads and their feet would cause severe disorientation. Hence spin-stabilised craft have to be big enough to where coriolis forces are sufficiently negligable to not cause problems.

SteveBaker (talk) 20:58, 24 November 2007 (UTC)

(edit conflict) The acceleration you feel due to gravity on Earth is a pretty constant 9.8m/s/s. In a spinning spaceship, acceleration looks like $a=r\omega ^{2}$, where r is the radius and ω is the angular velocity, which is constant throughout. So as you go farther from the axis, as you noted, gravity feels stronger. So you could conceivably jump and get stuck in the middle of the ship or fall towards the other side, but the effect would be gradual, not sudden. Now if you jump and fall back to the same side, you may see yourself drift a bit due to the z-terms of the Coriolis effect. There shouldn't be any force from the air as it will reach an equilibrium position inside the ship--the acceleration is always outwards and constant at each point. SamuelRiv (talk) 21:09, 24 November 2007 (UTC)

Consider also what an outside observer sees. You jump off the rim – that is, you push yourself inward by a kick against the wall, as in a swimming pool – and proceed in a straight line. Your vector is the lateral velocity of the rim at that moment plus whatever impulse your legs can impart; so to reach the axis you need to jump at an angle to negate the rotation. You "land" when you collide again with the rim; where you land depends in part on how far the rim has turned during your jump, and thus on the speed of your jump. —Tamfang (talk) 22:13, 24 November 2007 (UTC)

It's only the friction between your feet and the deck - plus any air resistance from the air inside the ship that keeps you going around in a circle as you stand "still" on the deck. In true high-school physics style, let's neglect the air resistance. Let's suppose you can jump high enough to sail across the ship and land on the other side. Let's suppose you try to jump straight upwards through the exact center of the ship. The moment you leave the floor, there are no more forces acting on you. (Remember, this isn't "real" gravity - this is just a spinning cylinder in zero g). With no forces acting on it, your body travels in a straight line - at a constant velocity. So your velocity vector is the sum of a vector that is acting tangential to the floor at the moment your feet left the ground (friction) with a inward radial vector due to the force your legs applied in the jump. Let's call the lateral vector 'F' (friction) and the vertical vector 'J' (jump). From your perspective, you would have been trying to jump "stright up" towards the center of the spacecraft - but find that you miss that point by some amount that depends on the size of the spacecraft and the amount of spin it has (this is the Coriolis effect). In ADDITION, the spacecaft is rotating so that the point you were aiming for on the opposite wall has moved by some amount by the time you get there.

Suppose your spacecraft is spinning clockwise from the perspective of our outside observer. If you aim your jump at a point exactly 180 degrees away from your start point then the coriolis effect (the addition of the small 'F' vector to your 'J' vector) forces you to land at a point a little anticlockwise of where you aimed - BUT while you were in the air, the rotation of the craft moved your aim point clockwise as you were in motion so you land even further anticlockwise of your aim point than you expect.

This means that the slower you jump, the bigger 'F' is compared to 'J' - the bigger the coriolis effect - and the further anticlockwise of your aim point you land.

But we just said that from the moment your feet leave the floor, there is no more gravity (there never was any gravity - it just felt like there was) - so how does this feel so natural? When you are standing still, the 'F' vector is pointing slightly outside the craft (it's a tangent to the curved deck), your inertia wants to put you outside the spaceship - but the deck is forcing you inwards all the time. That force feels just like gravity...well, almost.

What's going to be weird for the occupants is small vertical jumps. In a small vertical jump the coriolis effect and the rotation of the craft are more or less equal - so the point where you land is almost exactly where you jumped from - just like if you jump straight up here on earth.

The 'F' vector is tangential to the floor when you jump and the 'J' vector is tiny by comparison - so the combined vector points to a place on the deck only a little clockwise from you. More or less exactly where the deck plate you were standing on rotated to while you were in the air. However, if that distance is a significant fraction of the circumpherence of the craft - you'll be landing with your body at an angle to the deck. If the craft rotateds at 10 degrees per second and you spend a second in the air during your jump - then when you land, your body is leaning 10 degrees to the local "vertical" and you'll probably fall over when you hit the deck. So only small jumps feel natural - just like gravity providing the ship is huge and rotating slowly. If it's smaller and still trying to produce one g of similated gravity - then these peculiar coriolis-related matters will become very disturbing. Walking and bending down, picking things up and tossing them to your fellow astronauts will all feel ever so slightly 'off' from what you are used to on earth. If the space ship is too small, it's likely that nausia and other problems would be common.

SteveBaker (talk) 17:16, 25 November 2007 (UTC)

Short answer: In a spaceship rotating on an axis about its center of mass, the axis of rotation is "up" and the directions away from the axis are "down". The amount of "gravity" (actually centrifugal force) depends on how close you are to the axis of rotation and the revolutions per. minute of the spaceship. The further from the axis and/or the faster the rotation, the more "gravity" you feel. For more see Artificial gravity#Rotation. -- HiEv 13:16, 26 November 2007 (UTC)

That answer may be short - but it's not exactly true...well...no...not exactly.

(This is SUCH a fun thing to think about! I do hope people are still reading!)

Here is a thought experiment for you (again, neglecting air resistance). Suppose you started off with the spacecraft not spinning - so you are in zero g - you lift your feet off the floor - so you are floating six inches away from the curved deck. Now someone starts the spacecraft spinning (maybe using some thrusters mounted on opposite sides of the cylinder)...do you feel gravity and fall down? Nope! No gravity! You carry on floating there with the deck spinning just inches beneath your feet! So what happened to the gravity (which the previous respondant claim acts depending only on your distance from the central axis)??? The thing is that from the point of view of someone who is standing on the deck, whizzing around with it, everything appears to them as if the room is still, there is gravity - except that you are "orbiting" the deck at high speed! Now, if we add some air - which will gradually start to spin with the spacecraft due to friction/viscosity - it will gradually start to (from your perspective) speed you up to start to match the speed of the spacecraft's spin...or (from the perspective of your crewmate, standing on the deck) the air resistance will start to slow you down. This is in every respect like an inside-out planet...so (from his perspective) as you slow down, you fall out of orbit towards the deck. From your perspective, the wind applies a force that moves you off IN A STRAIGHT LINE - which means that you gradually get closer to the spinning deck until you hit it, get accellerated around into a circle and start to feel like there is gravity. Like an inside-out planet, gravity points outwards from the center instead of inwards. Objects can orbit "above" the surface if they have enough speed relative to the deck - so if you run around the deck at a speed equal to it's rotational speed and give yourself a little upwards 'push' you'll find yourself in one of those peculiar 'inside' orbits again! And (to extend the metaphor) if you can launch yourself upwards fast enough, you reach escape velocity (although the deck on the opposite side gets in the way of true escape). Coriolis forces also apply - just like on a normal planet - except they are reversed. Everything that happens on a real planet can happen here - but inside-out! SteveBaker (talk) 21:45, 26 November 2007 (UTC)

I was trying to be brief, and my assumption was that you were rotating with the spaceship. The original question did involve standing or climbing within the ship, not floating freely. Yes, there are some differences between this kind of "gravity" and the kind of gravity you'd feel on a planet, but in general what I said is reasonably accurate as far as how you'd determine "up" and "down". Some more information on the perception of gravity in a rotating space station can be found here. Also, a 900 meter radius station would need to revolve at 1 rpm, or 679 km/hr (398 mph), to maintain 1 G (source), so we probably won't have to worry about people jumping into "synchronous orbit" within the outer rim of such space stations. -- HiEv 22:24, 26

November 2007 (UTC)

The trouble with a 900m radius ship is the mechanical strength required. Building something toroidal or cylindrical that's that big that's got to hold together under 1g is like building a 5.6 kilometer single-span bridge! The longest single-span we've ever built on earth is just under 2km - can you imagine the engineering effort to build one of those in orbit?! It's also an awfully large ship! So, yeah- we're not really going to be jumping around and such...fun though it might seem. We might want to start with something a little more reasonable. A more likely thing is to have a spacecraft where the main power plant (or something like that) is on one end of a long cable and the crew quarters are like an elevator cab hanging on the other. The two masses rotate about a common center. The cable has to be strong enough to support the entire weight of the craft under 1g of accelleration - but we have cables with very large breaking strains - so that's do-able (technically, it only has to be strong enough to bear twice the weight of the crew compartment). Of course you don't necessarily need a full 1g to maintain crew health and comfort. It's argued that if they are going to Mars (the most likely destination for our first spin-gravity ship) then they might as well get acclimated to Mars gravity on the trip - so you can spin three times more slowly or use a shorter cable and get the desired effect. The nice thing about a system like this is that you can keep the coriolis forces under control by the relatively simple process of making the cable longer and spinning the ship more slowly. SteveBaker (talk) 23:57, 26 November 2007 (UTC)

It's better (for humans) than no gravity at all, but to maintain 1g you have to stay at a specific radius and not move with or against the motion of the spinning, though with a very big structure the variations can be reduced. A lot of the issues where thought through reasonably well on Babylon 5, including the idea of falling from the centre to the deck, where you could go from weightless with a descent at arbitrarily low speeds, to going to 1g and landing on a moving surface the equivalent of being ejected from a car moving at high speed. Peter Grey (talk) 08:16, 27 November 2007 (UTC)

Which spacecraft was it where the science part had filing cabinets all around arranged in a cylindrical fashion where the scientists/astronauts noticed they could do their jogging kind of 2001 space odyssey style just by running around the (not very large) cylinder? Keria (talk) 12:18, 27 November 2007 (UTC)

That would be SkyLab - they used a left-over second-stage Saturn V rocket and kitted it out as a temporary space station. The interior was ENORMOUS even by ISS standards. SteveBaker (talk) 17:10, 27 November 2007 (UTC)

It's not a your mum joke, promise.

What is the relationship between gravitational and inertial mass? Why are they the same? Do they have the same cause? Please answer ungriftingly! Samuel P. Lemminghornsworth —Preceding unsigned comment added by 217.43.117.20 (talk) 23:07, 24 November 2007 (UTC)

Until someone who understands this turns up, you could do worse than read Mass#Inertial and gravitational mass. Algebraist 01:53, 25 November 2007 (UTC)

Inertial mass is the mass related to F=ma, one of Newton's laws. Gravitational mass is the mass related to F_g=mg or F_g=Gm₁m₂/r². Their equivalence was well known to Newton, but not understood by him. Einstein solved the problem by showing (in General relativity) that acceleration and gravitation are essentially the same thing. Someguy1221 (talk) 02:48, 25 November 2007 (UTC)

Actually, he didn't "show" they are the same thing, but rather assumed it. General relativity doesn't provide any compelling explanation for why it must be true (other than that GR works). We certainly have examples of forces (e.g. electromagnetism) where the ability to create force is determined by something (charge) that is different from the resistance to acceleration (inertial mass). There is no fundemental reason why one couldn't construct a GR-like theory in which something other than intertial mass appeared in relavant spots of the stress-energy tensor that determined the shape of space time. Dragons flight (talk) 03:14, 25 November 2007 (UTC)

General relativity works from the premise that accelleration and gravitation are indistinguishable (that's the thing that started Einstein off on his quest to establish it) - one consequence of which is that inertial mass and gravitational mass MUST be the same. If they were not, general relativity wouldn't work because you'd be able to tell whether you were out in deep space with a rocket motor pushing you along with a 1g accelleration or sitting still on the launch pad here on earth. The problem here is to ask whether general relativity is true BECAUSE of some amazing coincidence between the two interpretations of mass - or whether the two meanings of mass are the same BECAUSE general relativity is true. Asking WHY a fundamental law is true is an unanswerable question. It's more philosophy than science! SteveBaker (talk) 10:10, 25 November 2007 (UTC)

That's only true to the extent you assume there isn't an answer. Or put another way, it means you assume there isn't anything more fundemental than GR. Equivalence is still basically an assumption of GR, and my physicists' intuition wants there to be some deeper physical principle to explain why there must be a force whose magnitude is proportional to inertial mass. Dragons flight (talk) 12:36, 26 November 2007 (UTC)

Oh - I agree, you might well be correct. But it's also possible that there is a deeper reason why GR is right that's unrelated to the original principle that lead Einstein toward it. If that were the case then the reason that inertial and gravitational mass is the same thing is BECAUSE accelleration and gravity are the same thing and we are making an artificial distinction because as mere humans who can't directly see the curvature of space/time it seems that accelleration and gravity are different things. We don't know which of those viewpoints is "correct" - what is a cause and what is an effect? SteveBaker (talk) 21:23, 26 November 2007 (UTC)

What is the best way to self-study string theory?

Are there free online text books, etc? -- Taku (talk) 23:20, 24 November 2007 (UTC)

It really would depend on your level of knowledge to begin with. Are you a serious student of theoretical physics? Or are you an interested amateur? If the latter, you can't go too wrong by reading the popularized books first. --24.147.86.187 (talk) 23:42, 24 November 2007 (UTC)

My background is mathematics, so I'm basically interested in how math is used in physics. (For example, I vaguely know the use of functional analysis in quantum physics.) Since popular books tend to have almost no math, I was wondering if there is a textbook or something comparable on string theory (because academic papers are way beyond my knowledge.) -- Taku (talk) 08:58, 25 November 2007 (UTC)

A First Course in String Theory might be at the level you're looking for. I've only leafed through it, but it's aimed at undergraduates and fairly heavy on mathematics. -- BenRG (talk) 15:59, 26 November 2007 (UTC)

November 25

Can chiropractors prescribe scheduled medicines?

Like pain killers? Biochemza, 00:07, 25 November 2007 (UTC)

Not in the UK, unless they are also one of the following :-

"NHS prescriptions are most commonly written by your GP for you to take to your community pharmacist (chemist) to collect.

From 1 May 2006, qualified Nurse Independent Prescribers (formerly known as Extended Formulary Nurse Prescribers) are able to prescribe any licensed medicine for any medical condition within their competence, including some controlled drugs.

Doctors working in NHS hospitals also write NHS prescriptions. In most cases, you will be asked to take your prescription to the hospital pharmacy to pick up your medicine. Sometimes you will be asked to take your prescription to your local chemist - usually when the hospital pharmacy cannot supply your medicine.

An NHS dentist can also provide you with an NHS prescription if you need treatment for a dental or oral condition.

Supplementary Prescribers are pharmacists, chiropodists, podiatrists, physiotherapists and radiographers who have undergone specialist training. They may prescribe any NHS medicine provided it is in partnership with an independent prescriber who gives the initial diagnosis and starts the treatment. The Supplementary Prescriber then monitors the patient and prescribes further supplies of medication when necessary." - Source is http://www.nhsdirect.nhs.uk/articles/article.aspx?articleId=1629 Exxolon (talk) 00:24, 25 November 2007 (UTC)

In the U.S., all States currently exclude prescribing drugs from chiropractic practice [9]. There have been lawsuits from chiropractors seeking to change this; none have been successful. - Nunh-huh 03:31, 25 November 2007 (UTC)

That's probably because many chiropractors are homeopaths. -- JSBillings 17:23, 25 November 2007 (UTC)

Actually, it's probably the other way around. Because they're not allowed to prescribe real, scientifically tested, working medicines, they resort to prescribing the unregulated, pseudoscientific placebos called "homeopathic remedies", which are usually just sugar/lactose pills or water/alcohol, thus are generally harmless and don't count as drugs. -- HiEv 13:35, 26 November 2007 (UTC)

Illegal Plant - USA

What plants are illegal to own/possess in the US? --WonderFran (talk) 00:22, 25 November 2007 (UTC)

A number are on the Controlled Substances Act schedule list, which depending on their "schedule" gives them various degrees of legality. Marijuana, psilocybin mushrooms, and peyote are always illegal (under US federal law). Without a prescription, opium poppies and coca leaves are illegal. Those are the ones that jump out immediately to me. --24.147.86.187 (talk) 00:43, 25 November 2007 (UTC)

Note that in some local jurisdictions there are plants that are illegal because of the threat they pose to the ecosystem and/or invasive. See, for example, the Illinois Exotic Weed Act, which bans a number of plants from the state of Illinois. To compile all of those would be a very long list and require a lot of digging into state and probably local laws. --24.147.86.187 (talk) 00:51, 25 November 2007 (UTC)

(Edit conflict) Certain plants are also considered noxious weeds and are illegal to possess on the basis that various governments (local, state, or federal) are trying to stamp out those plants. We used to use a particular weed in our fish pond as an oxygenator, but the fish loved to eat it as well; we can't get that weed any more as it is now illegal in New Hampshire.

Atlant (talk) 00:52, 25 November 2007 (UTC)

• Nuclear plants, unless you have the proper permits, which can be quite a headache to acquire. --Sean 01:17, 25 November 2007 (UTC)

Does my sun conure have another name?

My sun conure is named Sally. She responds and comes over to me when I call her by name. It's pretty clear that she knows that this is the 'human speak' call I use to refer to her in particular as an individual. Do sun conures also have names in their own 'parrot speak'? It would seem obvious that she does not sit and think of herself as "Sally the Sun Conure" - how would a bird which can speak only a few words of English be expected to know what name humans have given to her entire species? —Preceding unsigned comment added by 84.66.52.166 (talk) 00:25, 25 November 2007 (UTC)

My brother used to do research trying to decipher parrot-speak. He said that in groups of parrots (in some species) a single member could alter its song to more closely match that of another individual parrot, and in this manner would attract the attention of that parrot. Not a "name" per se, but certainly some species have ways of calling to a specific individual. Someguy1221 (talk) 02:42, 25 November 2007 (UTC)

Avian_intelligence#Language. This article is beautiful. SamuelRiv (talk) 03:18, 25 November 2007 (UTC)

Hmmm. I wonder if that goes some way to explain why many species of parrot mimic human sounds in the first place? I know from my experience with budgerigars that they (the males in particular) will often weave the various human words and phrases that they've learned together into a 'song'. --Kurt Shaped Box (talk) 12:57, 25 November 2007 (UTC)

I don't think names are things that animals naturally deal with. It seems that dogs, cats and parrots (at least) can be trained to recognise some specific sound as being 'theirs' but whether they even think of it as a 'name' is hard to say. Whether your Sun Conure is recognising "Sally" as her name - or whether it is the intonation of your voice for the entire senntence "Sally come here" that works is anyone's guess. Our Cocker Spaniel dog would get very excited when we said the word "Walkies!" because he loved going for walks. He would actually run off and find his leash and bring it to us when we said "Walkies!". My wife contended that he understood the word - but I convinced her not because I could say "Tomato Sandwiches!" in the exact same tone of voice and cause the dog to rush off and fetch the walkies apparatus. Furthermore, if I used the word "Walkies" in a completely neutral tone of voice in the middle of another sentence, the dog didn't recognise it at all. I eventually discovered that if I mimed saying "Walkies!" without making a single sound, the dog would respond. Dogs (and probably parrots too) are sensitive to a wider range of human expression (including body language, voice intonation, maybe even pheremones) than we are conscious of delivering to them. It's easy to assume they detect one kind of communication (words for example) when in fact it's something completely different.

• Inserting a response to this point: what that this means is that the dog isn't correctly discriminating which aspects of your pronunciation are phonemic and which aren't. It's like the way some speakers of other languages can't tell the difference between the English words "ship" and "sheep", or "fat" and "vat"; and speakers of English have to learn that in Chinese the same word pronounced in a different tone becomes an unrelated word, or that in Hindi the aspirated K in English "kin" is a different consonant than the unaspirated K in English "skin". This sort of thing doesn't prove that the dog doesn't have the concepts you're using when you talk to it, only that it has trouble with human-accented pronunciation. (Of course this also doesn't mean that it does have those concepts; I'm only talking about what is evidence for what.) --Anonymous, 22:08 UTC, November 25, 2007.

• But the difference wasn't as small as "fat" and "vat" or "ship" and "sheep". It was "Walkies" and "Tomato Sandwiches" (or any other phrase of many, many syllables. But even miming saying the word without making any sound produced the same response. Dogs are AMAZING at interpreting 'body language' signals that we aren't even aware we're giving off. I'm convinced that the sound helps (eg if the dog can't see you) - but that's not the only component of the dog's perception that's involved. SteveBaker (talk) 21:19, 26 November 2007 (UTC)

The only case I'm aware of where animals have invented names themselves is in whale song - where I believe researchers have noted specific phrases in their song that are used by many members of a pod but only when one specific individual is present or being searched for. That suggests that whales have names...although there are perhaps other interpretations.

I bet that if you start calling your bird by a different name every day - but call her with the same tone of voice and body language - then you'll get exactly the same result you get when you call her "Sally". It's an easy experiment to try. Start off with names that are similar ("Betty" - has a similar number of syllables) and then try wilder combinations.

SteveBaker (talk) 10:01, 25 November 2007 (UTC)

Another thing to consider is whether your bird takes your calling of her name to be a signal that you (the large beastie that provides her with her only regular form of social contact) are ready to 'interact' with her, feed her some tasty fruit (or nuts, or whatever snacks you give her) and perhaps preen her itchy head feathers. --Kurt Shaped Box (talk) 12:57, 25 November 2007 (UTC)

Yep - exactly. The parrot translation of the word "Sally" could easily be "Hi! It's me!" or something like that. Have you ever seen the British TV comedy "Coupling"? There is a great episode ("The Girl with Two Breasts") in which one of the characters, Jeff, is chatting with a woman in a bar who doesn't speak English. The first half of the show has Jeff speaking English and her speaking Hebrew (I think). They both think they are managing to understand what's going on and they are getting on just fine but - in the second half of the show they replay the exact same scene but with him speaking Italian and her speaking English so you can hear the conversation from her point of view. The degree of misunderstanding is of course SPECTACULAR - and somehow he mistakenly assumes that the Hebrew word for "breast" is the girls' name...um...I guess you need to have seen the show! But if that level of miscommunication is even plausible between two humans (and it does seem pretty plausible) - then on an interspecies basis, anything is possible! SteveBaker (talk) 16:31, 25 November 2007 (UTC)

Identify this plant

I bought a plant, but it had no tag saying what the species was, so I was hoping for an answer. I took a photograph of the plant, and uploaded it here.

It was purchased at a home depot store in the Twin Cities, Minnesota for 15USD, and only came with one tag, which says "Tropical in Winter G/S". —Zachary ^talk 03:58, 25 November 2007 (UTC)

It looks likely to be Dracaena Marginata. Take a look at Google images: here and the Wikipedia article here -- dharma —Preceding unsigned comment added by 24.86.250.218 (talk) 04:21, 25 November 2007 (UTC)

Yes, it sure is of Dracaena genus (which is a common houseplant), but it could either be Dracaena Marginata as was pointed earlier or it could also be Dracaena Cincta. These two species are known for their distinct pinkish edge in the leaves which is evident from the picture you have provided. Hope it helped. DSachan (talk) 04:39, 25 November 2007 (UTC)

Good point - the Wikipedia article mentions that D. marginata is often confused with D. cincta or D. concinna. -- dharma —Preceding unsigned comment added by 24.86.250.218 (talk) 05:33, 25 November 2007 (UTC)

Another identification, please

My mom found this weird looking caterpillar at home, so I took a snap, when I blew some air on to it, it curled up a bit and showed me these faux eyes that it has got, and I admit, it scared me a bit. Is this going to be a moth or a butterfly when it undergoes metamorphosis ?

Thanks for the help in advance :) SiegerKranzMeer 08:13, 25 November 2007 (UTC)

It looks a lot like some sort of hawk-moth caterpillar, especially with the faux eyes that you mention. Richard Avery (talk) 08:55, 25 November 2007 (UTC)

Oh dear, this is very difficult one. First of all, are you sure that this is a caterpillar? It could be some weird worm also. But it sure looks like a caterpillar seeing its segmented body and structure. The problem is there are about 180000 species in this lepidoptera order (which is huge) and all of them form caterpillar. So, it is obviously a tough task to pick out one of them. Furthermore, some organisms of order hymenoptera also produce larvae which look very similar to caterpillars produced by lepidopterans and hymenoptera is another big order. But here also, I can be sure that it is of lepidoptera order only because these caterpillar tend to have shorter abdominal length in contrast to the hymenoptera larvae which have longer abdominal length to generally accomodate more prolegs. So their body tends to have more segments. In this picture I can see only about 8 segments, which is quite common in lepidopteran caterpillars. This creature showed you its eyes because it always does so to frighten away or trick its predators but in your case, its predator happened to be a human, so this trick didn't work. :) Now if you have a garden around your home, the possibility could be that it may be a caterpillar of geometer moth, but that also you can tell by the way it was moving. If you noticed how many prolegs it had, things would be a bit easier. If it had only one pair of abdominal proleg, it could be the caterpillar of Geometer moth, which makes a very large family and are fairly abundant in gardens. If it had 5 pairs of prolegs, it could be caterpillar of hawk moth also. Butterfly caterpillars generally tend to be shorter, hairy and more vividly colored. But having said that, I must admit that this could be anything ranging from being a worm, some skipper's larva, some weird moth's caterpillar or even a caterpillar of a beautiful butterfly. I pointed out the difficuly in the beginning. Biological world can always be bizarre and astonishing. It always has surprises for you in its store. So, don't take my suggestions as final. DSachan (talk) 09:26, 25 November 2007 (UTC)

Thank you Richard and, DSachan: for taking the time out to write such a long but detailed explanation. :) 123.176.43.125 (talk) 11:42, 25 November 2007 (UTC)

I'm hopeless at these 'please identify this insect' questions, but there is one part of your question I can help on. Will it become a moth or a butterfly? Our article on Moth says "The division of Lepidopterans into moths and butterflies is a popular taxonomy, not a scientific one" - in other words these words "moth" and "butterfly" are not meaningful in a scientific sense. Basically, we humans have decided that "pretty" lepidoptera are butterflies and "ugly" ones are moths - but since this is in the eye of the beholder - it doesn't really fit the underlying science so until someone can nail it down exactly what species this is, we have no way to guess based on some general characteristic of "moth" catapillars that might differ from "butterfly" catapillars.

Also, in general, please - when you ask us to ID plants or animals tell us where in the world you found it! Knowing which region of which country it comes from narrows down the search to much smaller number and perhaps directs us to online resources specific to that area. Having some idea of the local habitat (woodland, grassy plains, farmland, urban, etc) also provides a little more information.

SteveBaker (talk) 16:13, 25 November 2007 (UTC)

Will keep that in mind (about the 'giving the location' part) This one was taken at hyderabad, India. And I did not know that the distinction between moths and butterflies was a man-made one. Thank you for clearing that up. SiegerKranzMeer 21:33, 25 November 2007 (UTC)

What's That Bug? and BugGuide can also help, if you're not in a hurry. :) --Kjoonlee 20:48, 26 November 2007 (UTC)

Ammonium chloride

In the article entitled Ammonium chloride shouldn't the following sentence, "Ammonium salts are irritantt to the gastric mucosa and may reduce nausea and vomiting." read "Ammonium salts are an irritant to the gastric mucosa and may induce nausea and vomiting." ${\aleph _{0}}^{\aleph _{0}}$ _{(talk) (email)} 08:33, 25 November 2007 (UTC)

Yes it should, according to this classic text. Rockpocket 09:00, 25 November 2007 (UTC)

Thanks. Corrected. ${\aleph _{0}}^{\aleph _{0}}$ _{(talk) (email)} 09:21, 25 November 2007 (UTC)

Lysogeny

At lysogeny, the article includes mention of herpes, on the basis of its genomic integration, yet HIV is not considered lysogenic. Either herpes is not lysogenic because the term 'lysogenic' refers to bacteria-infecting viruses or else HIV is lysogenic... right? --Seans Potato Business 15:48, 25 November 2007 (UTC)

I'm not sure but I think the term lysogeny could mean two things: One is like you said, genomic integration of phage DNA to bacterial DNA (a definition I suspect doesn't apply to HSV or HIV because the viruses attack human cells, not bacteria). Two, it refers to the latent state of the virus, where the virus stays dormant inside the host's cell for some time. (Which would apply to both HSV and HIV) 128.163.224.198 (talk) 19:31, 25 November 2007 (UTC)

In the context of viruses that infect bacteria, see this textbook. I would not use the term "lysogeny" with viruses that infect eukaryotic cells....I'd use the term "latent infection". --JWSchmidt (talk) 03:37, 26 November 2007 (UTC)

I've removed the herpes section from the lysogeny article. --Seans Potato Business 07:36, 26 November 2007 (UTC)

Respiratory Acidosis

In chronic respiratory acidosis, what is the purpose of HCO3- (bicarbonate), if it can't actually buffer the H+ (the elevated pCO2, resulting in the cause of the acidosis, would prevent buffering?). The system wouldn't be able to compensate for a failure of itself would it? (hope it makes sense)

I'm not sure at all, but my initial guess would be that it comes from the reaction CO2 + H2O -> H2CO3, carbonic acid, which HCO3- salts would buffer. Respiratory_acidosis#Mechanism seems to confirm this to some extent. SamuelRiv (talk) 19:43, 25 November 2007 (UTC)

Rodents

What is the differences between a Gerbil, Hamster and a Guinea Pig?

XX##XX —Preceding unsigned comment added by 196.208.75.208 (talk) 17:09, 25 November 2007 (UTC)

I've wikified the different animals in your question. The quick answer is their original native habitat, both the gerbil and hamster are from europe and asia, and the guinea pig is from south america. -- JSBillings 17:20, 25 November 2007 (UTC)

Guinea pigs are huge - 8" long - about the size of a large, domesticated rabbit. Hamsters and Gerbils are both just a couple of inches long - the same size as a mouse. Gerbils are distinctive because of their large hind legs and feet. All three are rodents and they all eat similar things and make good pets. Hamsters are loners - they don't very much like the company of other hamsters - which means you can have just one of them without causing them stress - they live in tunnels and are naturally nocturnal, They adapt well to those crasy cages with the maze of twisty tubes (which are quite amusing but a pain to clean out a couple of times a week). They can be grumpy (and may bite) if you try to interact with them during the day. Guinea pigs (being large) need lots of space to roam around in - so you're going to need a large (possibly outdoor) enclosure for them. You can keep guinea pigs and rabbits together - they get along quite well and eat similar foods. SteveBaker (talk) 18:19, 25 November 2007 (UTC)

I recommend looking at the articles on them in Wikipedia, perhaps by following the links JSBillings gave you. Steve's guide is pretty good, but there are different species of hamster (Syrian hamster, Russian dwarf hamster, Chinese hamster, etc). A russian dwarf is about the same size or smaller than a mouse, but a syrian hamster is rather bigger (unless you've got huge mice!), and dwarf hamsters are frequently kept with each other. A grown gerbil is also rather bigger than a mouse, but these things vary. Anyway, read the articles and look at the pictures. Skittle (talk) 22:59, 25 November 2007 (UTC)

Another key difference between hamsters and gerbils is that hamsters only have very short tails (as do guinea pigs and rabbits) while gerbils have long rat-like tails.GaryReggae (talk) 13:14, 26 November 2007 (UTC)

Gerbils have long furry tails, not like rats :) Anyway, I still feel viewing the articles would be the best course of action, since there are a lot of differences and it's hard to prioritise what is wanted. Skittle (talk) 16:47, 26 November 2007 (UTC)

Also a crucial point: gerbils are about the only rodents that don't smell up the place, because they are desert dwellers and don't drink much so they don't urinate much. Otherwise, i find hamsters nicer, and guinea pigs even nicer than that. Gzuckier (talk) 21:42, 26 November 2007 (UTC)

Tornado's

Most likely locations for tornadoes to occur.

Why is it that there is no tornado's in South Africa?

Antoinette —Preceding unsigned comment added by 196.208.75.208 (talk) 17:14, 25 November 2007 (UTC)

Actually, South Africa is one of the most likely places for a tornado to occur. Sancho 18:12, 25 November 2007 (UTC)

Dust devils are a common sight on the Karoo. Rockpocket 20:06, 25 November 2007 (UTC)

Stars on moon

Can you see stars when your on the surface of the moon? I seem to remember from somewhere that you cannot, but why would that be? Is the Earth so bright that it outbrightens (new word) all of them, just as the Sun does here? Imaninjapirate^{talk to me} 18:25, 25 November 2007 (UTC)

It depends on the direction you look and if you're in lunar day - see this. See also examination of Apollo moon photos#There are no stars in any of the photos. -- Finlay McWalter | Talk 18:33, 25 November 2007 (UTC)

I don't like the first answer in the first source you attached. In lunar day, the sun is indeed very bright and the moon surface reflects a significant amount of that light. However, the light is not diffused into the atmosphere, so conceivably you should be able to look straight up while shielding the light from the surface, the Earth, and the sun, and see plenty of stars, even in the daytime. SamuelRiv (talk) 19:47, 25 November 2007 (UTC)

Yes - you can see LOTS of stars from the moon - more so than here on earth because (a) there is no atmosphere to get in the way and (b) at night there is no light pollution. From the side of the moon nearest the earth, the earth is a very bright object that might make nearby stars a little hard to see - but on the other side of the moon it should be no problem at all. During the two-week-long night, on the far side of the moon from the earth, the view of the stars would be absolutely unparalleled. The reason you think there might not be stars is probably because of the annoying conspiracy theorists who claimed that the lack of stars in photographs taken during the Apollo landings was proof that the missions had never taken place and that the photos were faked. In truth, the reason there were no obvious stars in the photos (actually, you can see some) was because the brighter objects in the foreground (the astronauts, lander and lunar surface) were being lit by EXTREMELY bright sunlight (brighter than on earth because of no atmosphere) - and the camera's lens had to be stopped down to prevent it from over-exposing the film and washing out the whole image to a white blur. When you do that, dimmer objects like stars get dimmed down to almost nothing. SteveBaker (talk) 19:50, 25 November 2007 (UTC)

It's possible to see stars on the Moon even when the Sun and the Earth are above the horizon. The sky will be pitch black because there is no diffraction of light, so as long as empty sky fills your field of view and you cannot see the Sun, Moon, or surface objects, night vision will set in and stars will become visible.

An astronaut enjoying the heavens in daytime must of course avoid looking at the lunar surface without going indoors and allowing his eyes to adjust to highler light levels. --Bowlhover (talk) 21:33, 25 November 2007 (UTC)

Stars are rather dim objects, and eyes adjust depending on levels of brightness. So, if there is something bright enough in your visual field, your eyes will adjust so you can see the bright object properly, but that will also make the stars effectively invisible to you. However, if you block out other light, then the stars should become visible again (though your eyes may take a little while to readjust.) Cameras work the same way. Whether you can see the stars from the Moon depends on whether or not there is any other light in your visual field that would hide them (and also the transparency of your helmet, I suppose.) -- HiEv 14:03, 26 November 2007 (UTC)

However, something as simple as an old toilet roll tube would serve to block out the light and enable you to see stars in daylight. To get the best view, you'd want to be dark-adapted - which either means waiting a week or two until nighttime - or spending 20 to 30 minutes with the blast shield of your helmet down first. (You DO have a blast shield - right?! All the trendy space-suits have them these days! :-) —Preceding unsigned comment added by SteveBaker (talk • contribs) 21:14, 26 November 2007 (UTC)

Somehow I don't think holding a toilet paper roll tube up to your space helmet's face shield would work too well.  :-P -- HiEv 22:30, 26 November 2007 (UTC)

Oh - so the excuse that I'd used up all of the toilet paper wiping sticky fingerprints off of the visor isn't going to cut it either? Darn! SteveBaker (talk) 23:23, 26 November 2007 (UTC)

November 26

Fire Accelerants

Are there any fire accelerants that aren't immediately lethal when consumed in considerable quantities? I know drinking a cup of gasoline will be unpleasant, but is there something that doesn't kill you, unless you then swallow a match or something... 74.230.231.13 (talk) 00:04, 26 November 2007 (UTC)

It depends on your definition of fire accelerant. From the article, "an accelerant is any substance or mixture that "accelerates" the development of fire", I think bottles of pure oxygen will accelerate a fire very quickly, but won't immediately kill you. --antilived^{T | C | G} 02:12, 26 November 2007 (UTC)

Define "considerable" - almost anything will kill you if consumed in high enough quantities. Many spirits are flammable, as demonstrated by party tricks such as flaming sambuca; and I expect something like an overproof rum would serve as an accelerant - according to our article, a mix of water & ethanol with over about 50% ethanol is flammable, so a spirit which is in the 60-70% ABV range should go up easily enough (although it's drinkability is another matter...) -- AJR | Talk 02:14, 26 November 2007 (UTC)

Some substance such as vegetable oil, ghee, or glycerol are actually food items and will also accelerate a flame. Others such as wax may not be food, but are fairly harmless to eat. Graeme Bartlett (talk) 07:56, 26 November 2007 (UTC)

Balancing a chemical equation with silver nitrate copper and water

Alright I have this problem. I disolved .0185 moles of silver nitrate into a unkown amount of water to form a solution. I then dissolved 2.81 grams of copper oixide water into the solution until there was 1.25 grams left. I need to write the chemical equation for it if the copper is suppose to be +2 and +1 in charge. Does anyone know how to do that? —Preceding unsigned comment added by 70.249.230.252 (talk) 00:26, 26 November 2007 (UTC)

It sounds like homework or schoolwork help. The question also seems to have a typo ("2.81 grams ... until there was 1.25 grams left"). Just try writing out your reaction equation: the question is asking to use two forms: cupric and cuprous oxide, which are CuO and Cu₂O, respectively. SamuelRiv (talk) 02:03, 26 November 2007 (UTC)

Kinetic energy released by expansion of space

If space is expanding everywhere then the space in which all solid bodies exist must be expanding. As it expands the bodies themselves do not because the atoms that make up the body are attracted to each other and the nuclear forces keep the particles at a constant distance.

But this must mean that the atoms, if effect, move downhill a to keep that constant distance and, as such, there is a conversion of potential energy to kinetic energy.

Has anyone calculated the rate of kinetic energy being imparted to the earth as a result of the expansion of space?

Also, where does this energy come from? Or is this question completely off base?

Doug Moffat

209.5.192.16 (talk) 00:34, 26 November 2007 (UTC)

Energy doesn't come from anything. It cannot be created or destroyed but can only change energy types of change into matter. I'm not sure what you mean when you say there is a conversion of potential energy to kinetic due to space expanding. I'm not sure if that actually occurs, because space expanding has little effect on the bodies occupying that space, it just causes the bodies to move away from each other, yet still retain there current position in space. Space (which is not matter) is expanding and doesn't really effect the matter. —Preceding unsigned comment added by 70.249.230.252 (talk) 00:55, 26 November 2007 (UTC)

No, the point is a fair one. Anon is basically saying that if we take two massive bodies stuck to each other by gravity, inflation will try to pull them apart. If it succeeds, then you suddenly have gravitational potential energy that can be exploited if you stopped inflation for a second. Unfortunately, stopping inflation is the only scenario in which that energy can be exploited, so the end effect is just an effectively lower force between objects, if I'm reading this right. That is part of the reason we need dark matter: we find that certain clusters are not being pulled apart like they should be, so obviously the gravity in the cluster is higher than that due to visible mass. SamuelRiv (talk) 02:37, 26 November 2007 (UTC)

Space is only expanding between galaxies that are far apart and have very little gravitational influence on each other. Where matter exists, space does not expand (I think). Although your point is still valid (I think) because there would still be some gravitation force between them however small. Does the energy come from vacuum energy? Shniken1 (talk) 06:07, 26 November 2007 (UTC)

I don't believe that's correct. From what I understand, space is expanding evenly throughout the universe. In fact, if portions did not expand evenly, then that would either warp space or require that other sections expand faster to make up for the non-expanding portions. Expansion is slow, and gravitation can usually hold objects together despite space expanding. Of course with gravity, the closer together the objects are, the stronger it is. So, far apart objects, like galaxies, are more affected by expansion than the objects in a solar system would be. Essentially, gravity helps prevent the objects from expanding, but not space from expanding. While I don't see that explicitly stated there, you might try looking through metric expansion of space for more information on this topic. -- HiEv 14:39, 26 November 2007 (UTC)

Absent a cosmological constant, the expansion is nothing more or less than objects moving away from each other. There's no outward pull on anything; it's just inertia. Space is only "expanding" in areas where things are still moving apart (i.e. far from galactic superclusters). I suppose you can think of the cosmological constant as adding a ubiquitous outward pull, but all this does, like any other (sufficiently small) source of tension, is perturb the object into a different equilibrium state. So maybe the ground-state energy of hydrogen is slightly (undetectably) different than it would be without a cosmological constant, but that can't be used as a source of energy because there's no lower energy state to push it into. -- BenRG (talk) 15:42, 26 November 2007 (UTC)

I think you're confusing the expansion of the universe with inflation. The universe is still expanding, but inflation, if it happened at all, ended 13.7 billion years ago. -- BenRG (talk) 15:42, 26 November 2007 (UTC)

The kinematics of dark energy can be reasonably well approximated by adding an extra force to the universe such that every object experiences an apparent F_dark = D*M*x, where D is a small constant, M is it's mass, and x is its distance from the observer. In other words, the apparent force is trivial at short range and large at great distances. It also follows that adding a small constant force, doesn't generate additional energy for an object like the Earth which is held together by much larger forces. Dragons flight (talk) 11:30, 26 November 2007 (UTC)

Two Point Function

I was reading this book awhile ago and it talked about something called the two point function. It was caused by two flucuations in a vacumm in space diverging until they became so close that their energy density matrices became infinite. Thus causing for the equation having to be renormalized, and this somehow caused an expansion in space-time. Does anyone know what I'm talking about or does this sound like nonsense? —Preceding unsigned comment added by 70.249.230.252 (talk) 01:01, 26 November 2007 (UTC)

Could it be Zero-point energy, and the related cosmological constant problem it apparently poses? -- Finlay McWalter | Talk 02:16, 26 November 2007 (UTC)

My bet is that it's the vacuum fluctuations of Edward Tyron that describes how the universe may have been created out of nothing. There is an excellent nontechnical overview of this here [10]. It could also be bubble nucleation of a false vacuum, which is another common pre-inflationary scenario. SamuelRiv (talk) 02:26, 26 November 2007 (UTC)

Reading the link you provided SamuelRiv Inflation for beginners paragraph 4 reads:

If the Universe starts out with the parameter less than one, O gets smaller as the Universe ages, while if it starts out bigger than one O gets bigger as the Universe ages. The fact that O is between 0.1 and 1 today means that in the first second of the Big Bang it was precisely 1 to within 1 part in 10⁶⁰). This makes the value of the density parameter in the beginning one of the most precisely determined numbers in all of science, and the natural inference is that the value is, and always has been, exactly 1. One important implication of this is that there must be a large amount of dark matter in the Universe. Another is that the Universe was made flat by inflation.

Now 1^st sentence make sense. Then: how do we observe it to be smaller than 1? If it is anything from 0.1 to 1 (does it mean it's not precisely determined or that it varies localy?) today how do we calculate it would have been precisely close to 1 in the first second of the Big Bang? "the value is, and always has been, exactly 1", hang on didn't they just say it would be anything between 0 and 1? I'll carry on reading. Keria (talk) 10:34, 26 November 2007 (UTC)

Qualitatively, it is like O(t2) is approximately O(t1)^(s(t2)/s(t1)) where O(t) denotes O at time t, and s(t) is the size of the universe at time t. If O is approximately 0.5 now, then when the universe was 1/10 this size, O would have needed to be 0.5^(1/10) = 0.93. To allow for an O roughly near 1 today, it implies that O was very, very near 1 in the distant past when the universe was very small. An appealing solution is to posit that O is exactly 1 at all times. Incidentally, if O is much different than 1, it would imply that the ultimate fate of the universe would already have been realized (either through collapse or run away expansion). Hence O approximately 1 can also be looked at through the anthropic principle since we could not exist in a universe that was otherwise. Dragons flight (talk) 11:06, 26 November 2007 (UTC)

Query related to Urine

Is there any harm (or what are the results), if a girl drinks a man urine mistakenly / willingly. —Preceding unsigned comment added by Ashish.k.garg (talk • contribs) 06:57, 26 November 2007 (UTC)

Amazingly, we have an article on this. Urophagia. Someguy1221 (talk) 07:05, 26 November 2007 (UTC)

If the person in question doesn't have any diseases and is healthy, it should be ok. Urine straight out of the body is sterile. But it can be contaminated, and that's what causes that urine smell. 64.236.121.129 (talk) 15:53, 26 November 2007 (UTC)

I think the urine smell is due to the ammonia in the urine. 128.163.170.161 (talk) 17:39, 26 November 2007 (UTC)

There is no ammonia in urine. If there was, it would be unsafe to drink, which it isn't. Ammonia is converted into urea before it is excreted. 64.236.121.129 (talk) 14:44, 27 November 2007 (UTC)

gide us

Dear sir,

We want to make one controlling project for university and we need some information and help for designig a pc bord or programing a one plc with this specification:

voltsge source:12 V

it sould be have 40-60 Switchs and this equipmet sould be control with progaram and it's capacity is 2Km.

please send us yor guids and name of some company that can help us.  —Preceding unsigned comment added by 91.184.66.107 (talk) 07:53, 26 November 2007 (UTC) 

So to attempt to clarify, you want to remotely control something 2 kilometers away, by operating 40 to 60 switches at the remote position. What do you want to switch at the remote location - do you want relays? Are you willing to run a copper pair or optic fibre between your controlling point and the remote device, or do you need a wireless system? Graeme Bartlett (talk) 08:01, 26 November 2007 (UTC)

GREATMIND Q ABT. DOG

can I detect pregnancy in dogs by a Hcg hormone pregnancy tester used in human females? —Preceding unsigned comment added by 59.95.178.103 (talk) 08:41, 26 November 2007 (UTC)

No, human pregnancy tests are useless in dogs. Dogs are an estrous species, rather than a menstrual one: dogs undergo the same hormonal changes whether pregnant or not. Dog pregnancies are traditionally "diagnosed" by ultrasound or palpation.... there is a blood hormone that is elevated in pregnant dogs, called relaxin, and a blood test is available for this, but it's useful only later in pregnancy than the human tests we're used to are. - Nunh-huh 08:56, 26 November 2007 (UTC)

Does being cold and wet, increase your chances of getting a virus like a cold or flu?

Why or why not? 64.236.121.129 (talk) 15:51, 26 November 2007 (UTC)

There have been studies that have found a correlation between being cold (or cold and wet) and catching a cold. I haven't seen such studies on the flu. They are usually dismissed due to poor management of the control and test groups (or a complete lack of a control group). In the U.S. NIH book, being cold or wet is not listed as a cause for the cold or the flu. However, both are listed as "seasonal" - meaning that they occur predominantly during a certain time of the year. Anyone who has kids knows that a lot of things pass from children to parents. In the winter, we send kids to school where they share all kinds of things and then bring them home. So, it is pretty much a no-brainer as to why there are more cold/flu issues during the children's school-year. -- kainaw™ 16:03, 26 November 2007 (UTC)

Why do these viruses exist during one time of the year, but not the others? 64.236.121.129 (talk) 16:07, 26 November 2007 (UTC)

Keeping everyone in close quarters (in the winter) makes it easier to spread viruses around. Plus, the lower relative humidity probably also makes it easier to become infected from a given number of virions.

Atlant (talk) 16:39, 26 November 2007 (UTC)

I don't know about that. I don't see complete strangers huddling around just because it's colder outside. How does lower humidity make it easier to become infected? 64.236.121.129 (talk) 17:03, 26 November 2007 (UTC)

You don't need to huddle, you just need to spend more time breathing in recirculated air. Haven't you ever seen waydowntown??

Atlant (talk) 17:32, 26 November 2007 (UTC)

No. No I have not. And people spend time in the same building through other seasons too. Whether you go to school or work, you are still spending time in a building with other people, through all the seasons. 64.236.121.129 (talk) 18:50, 26 November 2007 (UTC)

Did you read the first reply above? It is colder in the winter. The school year tends to be in the winter. Children spend more time around each other during the school year. So... children are closer to more children when it is colder outside. It is all about proximity. The viruses don't gather super-virus strength from the cold. They still need people to be close to one another to travel from host to host. -- kainaw™ 17:43, 26 November 2007 (UTC)

The school year is during part of the summer, fall, winter, and spring. It's not mostly in the winter. The only time school is out is during the summer, but the school year does extend to parts of the summer. Also, I question whether your assumption is correct. You are assuming children are the source. You are also assuming children are closer together during the winter. That's just speculation. Also how does one get the virus in the first place? In order to catch it from someone else, someone initially had to catch it. 64.236.121.129 (talk) 18:47, 26 November 2007 (UTC)

I know that the Wikipedia rules insist that we assume good faith, but I'm starting to feel like you've simply come here for an argument.

Atlant (talk) 19:01, 26 November 2007 (UTC)

Nope. Assume good faith. I'm just asking questions. 64.236.121.129 (talk) 19:31, 26 November 2007 (UTC)

So if people catch colds more during the Winter because they spend more time indoors with others, does that mean that in places such as Phoenix, Arizona where people spend more time indoors in the Summer, people get more colds in the Summer? Deli nk (talk) 18:56, 26 November 2007 (UTC)

You have a bit of a point there. Contrary to the OPs assumption that I'm just speculating, it is my job to manage health data for millions of patients. There are exceptions, but the rule is that cold/flu cases spike in September. That is when children go back to school. They slowly go down until January when kids come back from the winter break (smaller spike than sept). Then, they keep dropping and dropping until there are no significant number of cases by summer. However, there are many cases of summer colds and flus (just not enough to be significant). Comparing desert regions to non-desert regions, the percentage of people with summer cold/flu cases is higher in the desert regions. While I don't have enough Phoenix patients in my database to draw a real conclusion for that particular city, I do have over three million patients Arizona and New Mexico - which is to my knowledge mostly desert. So, you have some data to back up your claim that desert-dwelling people have higher rates of summer colds and flus.

To the OP... you appear to believe that cold/flu viruses go away and then come back. They don't go away. In any large population, there is always someone with a cold/flu virus. Most often, it is the children (again, I can look at the data and see that the younger the person the higher rate of having cold/flu diagnoses - so this is not just speculation). To catch the cold/flu, you must be around someone who has it and have the virus physically travel from the other person to you and then successfully make it past your body's defenses and start multiplying. At that point, you will risk infecting everyone around you. The more people you have around you, the higher chance you have of infecting someone else. That is why having people near each other is the key to spreading the cold/flu virus. -- kainaw™ 19:14, 26 November 2007 (UTC)

What about anecdotes like that one President of the United States who gave a really long inaugural address out in the cold and then died a few weeks later? Also, wasn't there an American football coach who was doused by the customary, celebratory cooler of Gatorade only to get sick and die afterward? Besides frostbite and hypothermia, can exposure to the cold give you other problems?--The Fat Man Who Never Came Back (talk) 18:52, 26 November 2007 (UTC)

For the U.S. President, see William Henry Harrison.

Atlant (talk) 19:01, 26 November 2007 (UTC)

This is an interesting discussion (though I'm sure it's been discussed since time immemorial). Can being cold and wet give you, say, pneumonia or other conditions?--The Fat Man Who Never Came Back (talk) 19:38, 26 November 2007 (UTC)

Weakening your immune system when you have a cold/flu can lead to further complications - such as pneumonia. So, the question is, "Does being cold and wet weaken your immune system?" I did a quick AMA search and found nothing on that topic. I'm sure you can find many hits on Google - but not necessarily proper medical studies. -- kainaw™ 19:56, 26 November 2007 (UTC)

A lot of it is to do with heating systems, viruses like warmth as much as humans and any systems that recirculate air (such as that found in large buildings) is going to ensure the microbes get maximum circulation. The more people that get these bugs, the more carriers there are to ensure they keep spreading. The start of the heating season always brings the bugs out. GaryReggae (talk) 21:43, 26 November 2007 (UTC)

You might want to try reading The Straight Dope article "Why is winter the season for colds, flu, etc.?" It explains that being cold or wet does not increase your chances of getting sick, and also notes that some "seasonal" illnesses are actually encountered at various times throughout the year, and that some factors such as cold stress, which can cause cold/flu-like symptoms, and seasonal psychological stress, which can weaken the immune system, may be adding to the winter cold/flu stats. Hope that helps! -- HiEv 22:50, 26 November 2007 (UTC)

Psychological stress can weaken the immune system? Has this been proven? My other question is, if it is true that one usually catches it from another person, how did patient 0 catch the cold in the first place? Just incompetance by touching dirty objects, then putting their hands in their mouth/nose? 64.236.121.129 (talk) 16:46, 27 November 2007 (UTC)

Reflection of voltage/current ???

Hi, I was reading web(including wikipedia) articles on what the characteristic impedance aka 75 ohms mean, and some related stuff about transmission. I've seen and how generic waves reflect a part of their energy (at the interface) when they enter a medium of different 'elasticity' than in which they were traveling.
But I don't understand how electricity(or any wave for that matter) can reflect off an interface of different impedance. Can some one direct me to a wiki/web page which deals with this sort of reflection of current/voltage as i don't know how any technical terminology to search with. I haven't so far dealt with electric fields inside conductors and their role in conduction and I find it confusing to think about infinitely long conductors and effect of transmission being non-instantaneous. 59.93.3.188 (talk) —Preceding comment was added at 15:55, 26 November 2007 (UTC)

See impedance matching, standing wave, and standing wave ratio. These aren't much help, admittedly. Remember that it's the impedance of the load we care about, and that depends on frequency. If it matches, all the energy will be taken up. You can see the load sort of like the physical equivalent spring-and-mass system. If the load fails to use up the power, it has to go somewhere, so it reflects back and forms standing waves in the transmission line. A wave in a jumprope is an honest-to-goodness wave just like an electromagnetic one, at least as far as power transmission goes. This is a dumbed-down version, not because I think you're dumb, but because I have forgotten most of it. --Milkbreath (talk) 16:21, 26 November 2007 (UTC)

Rather than thinking about electrical signals, you might want to think about electromagnetic energy of a shorter wavelength: light. When it is travelling in a material of one impedance (which optics folks tend to call refractive index) and it meets material of a different refractive index, some of the light is transmitted into the new material but the rest of the light (that wasn't transmitted) is reflected back. Electrical impedance works the same way; when the impedance changes, a reflection occurs. For radical changes of impedance (to an open circuit or a short circuit), the entire electrical wave is reflected back to the source. You might also enjoy our articles about time-domain reflectometry and the time-domain reflectometer.

Atlant (talk) 16:33, 26 November 2007 (UTC)

Possible to destroy a virus by smashing it?

If you knew a virus was on a stone, and you took a sledgehammer and you smashed the area it is in, is it possible to destroy it? 64.236.121.129 (talk) 15:58, 26 November 2007 (UTC)

Localized heating of the impact area might denature your virus, destroying it. But I think it would be a very chancy thing, with a good chance of aerosolizing virions as well, so if you thing there is, say, some Captain Trips on the rock, why not just walk away?

Atlant (talk) 16:28, 26 November 2007 (UTC)

Of course you should just walk away. But that's not what my question is. 64.236.121.129 (talk) 17:00, 26 November 2007 (UTC)

Viruses are very, very small. So small that when you are talking about mechanically smashing them, you have to think about how tight a seal it is going to be. Your hammer, no matter how smooth it might seem, has lots and lots of imperfections and the odds are that you're not going to smash it. Even very small bugs (e.g. fleas) are incredibly hard to smash for this reason (along with the fact that they have slippery shells that are meant to make it hard to smash them). Something as small as a virus, I would say that your odds of actually making contact with it are very minimal. --24.147.86.187 (talk) 16:57, 26 November 2007 (UTC)

I agree. Hmm. But if you had, say a nanomachine on the scale of a virus, and it went up to the virus and ripped it up, it would die then right? 64.236.121.129 (talk) 17:00, 26 November 2007 (UTC)

It's arguable whether the virus was "alive" before you smashed it. But yes, if it can move xenon atoms around to spell IBM[11][12], then something like an atomic force microscope or scanning tunneling microscope could probably "dismantle" a virion.

Atlant (talk) 17:25, 26 November 2007 (UTC)

Your problem will not just be one virus, but there could easily be 1000000 viruses on your stone. Even if you destroy 90% you still have 100000 infectious particles. Graeme Bartlett (talk) 20:09, 26 November 2007 (UTC)

The goal would be making a manmade virus that is attracted to a certain virus and then restructures that virus to clone the manmade anti-virus virus. So, every time the manmade virus meets a virus it is supposed to kill, it actually makes another one of itself to fight off the entire virus population. I wonder if there'll be enough D&D fans on the team that invents this to give a name that references the charm spell used to make enemy monsters fight for you. -- kainaw™ 20:23, 26 November 2007 (UTC)

Sounds like a really big prion. (sorry, not a D&D fan.) Someguy1221 (talk) 20:50, 26 November 2007 (UTC)

Well, viruses can't reproduce by themselves - they need the facilities of a host cell in order to reproduce (think like the aliens in the movie "Alien"!) - that's why they are arguably not 'alive' at all. So if your manmade "virus" is truly a virus and not some other form of science-fiction nanotechnological assembler - then it can't really make copies of itself at will like that. But even a nanotech assembler would need energy and raw materials in order to make a copy of itself. That would likely be a time-consuming thing compared to the time a virus needs to reproduce (if it has a host). So whilst it may one day be possible to build tiny robots that can shred viruses mechanically, I doubt they'd do it by duplicating themselves and then committing suicide in order to take down their opponent. However, since we have no way to build such machines - nor any real certainty that they'll actually be possible at all - it's tough to speculate. SteveBaker (talk) 21:05, 26 November 2007 (UTC)

Smashing? Well, no, but then smashing isn't really good at destroying things anyway. Smashing a piece of wood and you get lots of little pieces of wood. Smash a rock and you get smaller rocks, etc. But smashing does little to change the basic nature of the substance. However if we are going to try sterilize with machine shop tools, I bet an arc welder would be pretty effective. More ambigously, I wonder how well an angle grinder would do at killing virii? If you grind down a surface, I'd lay good odds that most of the virii that were removed (at the least). Dragons flight (talk) 21:25, 26 November 2007 (UTC)

Why do I get cold after I eat?

Sometimes it's said that people get drowsy after lunch (or any big meal), because 'the blood goes to the stomach to aid digestion'. I don't know if that makes sense or not. I do know that I seem to get cold after I eat, which corresponds with my recollection that it always seems colder outside when one goes back on the ski slope after lunch. So, the question is, does it make sense, physiologically, that the body sends extra blood to the stomach to aid digestion, and this takes blood away from the task of keeping me warm? Are there other physiological functions that would be impacted in the same way, after eating? I know of someone who claims that its harder to keep an erection after eating a big meal...would it be the same story? —Preceding unsigned comment added by 213.84.41.211 (talk) 16:30, 26 November 2007 (UTC)

The sensation of warmth and cold is most directly related to how cold your skin is. So if the body does indeed direct an overly large amount of blood to your digestive system to the detriment of blood flow to your skin, then your skin will certainly feel colder, though this says nothing about your internal body temperature. Someguy1221 (talk) 16:41, 26 November 2007 (UTC)

One factor in getting sleepy when you eat is serotonin, which comes from 5hydroxytryptophan which comes from tryptophan which as is widely known comes from food. But, everybody gets it wrong; tryptophan is an amino acid and comes from protein, but it's relatively rare with respect to the other amino acids so that the presence of a lot of protein to be digested causes a lot of competition and saturates the transport sites and it actually gets taken up less. In fact, more carbohydrates in the meal causes serotonin to go up, and drowsiness. So it's not the turkey on thanksgiving. Judith Wurtman at MIT did a bunch of work on this for the defense department, who were interested in questions like how to make sure the folks with their fingers on the triggers in the missile silos wouldn't fall asleep. she found some folks who were so sensitive they couldn't stay awake after the highcarb lunch, period. other folks had a self-medicating thing, i.e. got really antsy midafternoon if they couldn't get a carb break. here's a couple of general public type refs: http://www.fastcompany.com/magazine/06/diet.html http://www.healthsystem.virginia.edu/uvahealth/news_mindbody/0610mb.cfm Gzuckier (talk) 21:50, 26 November 2007 (UTC)

Metal case enclosure heat transfer coefficient

What would be a good way to calculate the capacity of a metal case to dissipate energy by natural convection.

I'm thinking of building a case 20 x 15 x 10 cm in aluminium and would like to know how much heat can be produced inside without overheating. The internal temperature would probably be 40-45 degrees and the maximum external temperature 35 degrees.

Most of the websites I've seen don't offer a simple way to calculate the convective heat transfer coefficient of the walls.

I'm guessing 50W might be the limit at 35 degrees outside and maybe 80W at 20 degrees. --Jcmaco (talk) 16:40, 26 November 2007 (UTC)

It would depend a lot on whether the internal and or external air is stirred by a fan or left to natural convection. For the convective situations, it would also depend on the orientation of the enclosure. Normally, to dissipate 50W, you'd want some method to directly couple the heat source to the aluminum enclosure. You can experiment with all of this rather easily by using resistors as the heat source and your favorite thermometer (thermocouples, thermistors, infrared thermometer, whatever) as the measuring device(s).

Completely off-the-cuff, managing to dissipate 50W and achieving a 10C temperature differential using only natural convection sounds optimistic to me; I'll bet you'll at least need cooling fins on the outside of the case.

Atlant (talk) 16:45, 26 November 2007 (UTC)

The heat transfer coefficient is not easily calculable from what you have, so you may have to run an experiment first using the relevant equations from that article. We can do an estimate, but to start we need two things: Newton's Law of Cooling $T=T_{e}+(T_{0}-T_{e})e^{-kt}$ with k predetermined for aluminum in air (try google or experiment, or just set = 0.5), and the Heat law $Q=\sum mc\Delta T$, with the specific heat c being widely available for both aluminum and air (both are about 1 J/g/K). Now we take the time derivative and get $dQ/dt=P=\sum mc(-k(T_{0}-T_{e})e^{-kt})$ for our power dissipation, then set that equal to $dQ/dt=hA(T_{0}-T_{e})$ and we get our heat transfer coefficient $h=-(k/A)e^{-kt}\sum mc$.

Now let's say we're adding power P0 to the system, from whatever's heating your case. Equilibrium then occurs where $dT/dt=0$, or $P0=dQ/dt=hA(T_{0}-T_{e})$, which you can plug in values for at t=0. SamuelRiv (talk) 21:45, 26 November 2007 (UTC)

What metal is the worst conductor of heat?

^Topic 64.236.121.129 (talk) 17:04, 26 November 2007 (UTC)

There's a chart here: http://www.engineersedge.com/properties_of_metals.htm --JDitto (talk) 19:10, 26 November 2007 (UTC)

According to that chart, it's stainless steel - which suprises me a lot - but in any case, that's kinda cheating because there is a ton of (non-metallic) carbon in steel so it's really not a pure metal. In terms of pure metals, Lead wins the prize - which is about what I'd expect - lead is nowhere near as "cold to the touch" as most other metals (which is a good quick way to guess what the thermal conductivity of a material is). That chart seems to cover only the more common engineering metals - whether you'd find that something weird like metallic liquid hydrogen or one of the transuranics had a lower coefficient is hard to guess. SteveBaker (talk) 20:54, 26 November 2007 (UTC)

Mercury has a lower thermal conductivity, though I don't know whether that would hold true when it was solid. In either state, I'd guess it's not practical for any application you'd be considering. jeffjon (talk) 21:41, 26 November 2007 (UTC)

According to this list of the thermal conductivities of all elements, neptunium is the worst conductor of heat amongst the metal elements, followed by plutonium and manganese. --Bowlhover (talk) 00:27, 27 November 2007 (UTC)

How does stainless steel compare to say... Concrete or stone? 64.236.121.129 (talk) 14:41, 27 November 2007 (UTC)

Concrete conducts heat MUCH less well than stainless steel. The coefficient of conductivity for steel is around 14 to 16, for concrete it's 0.8 to 1.3. For comparison, metals like copper and silver that conduct heat very well have coefficients up around 400. But check our article List of thermal conductivities - it has an extensive list. SteveBaker (talk) 17:01, 27 November 2007 (UTC)

Quartz

Hello

My queastion is as follows. I found a geod near the town I live in, upon opening it the cyrstal inside was a light, medium brown. I looked through the entire area of this site on quartz cyrstal and did not see the same crystal. So i would like to know if there is a possability that someone could tell me what variety it is. Thank you. --63.245.189.4 (talk) 17:18, 26 November 2007 (UTC)

Your talking about a geode right? This site, has several brown crystal geodes, each one described as calcite crystals. Check out the 2nd picture in the calcite article to see if it's similar to yours. --JDitto (talk) 19:08, 26 November 2007 (UTC)

Quartz in geodes is often coated by iron oxide, making it look brown. Cheers Geologyguy (talk) 22:04, 26 November 2007 (UTC)

Smoky quartz is brown. DuncanHill (talk) 09:04, 27 November 2007 (UTC)

Spacetime Dipping

According to general relativity all masses make a dip in the sort of sheet of space time, making a potential well, and thats how masses have gravity. But if two massive particles, say a low energy electron and positron annihilate, what happens to the 'dips' in space time that they both have, seeing as the energy is carried away by two photons which do not have mass anywhere equivalent to the electron positron pair. ΦΙΛ Κ 20:23, 26 November 2007 (UTC)

I'd suspect the mass would be converted into energy. No mass, no gravity well. --Kjoonlee 20:41, 26 November 2007 (UTC)

Actually, the photons will have mass exactly equivalent to the electron/positron pair (if we're talking about relativistic mass, that is). Someguy1221 (talk) 20:48, 26 November 2007 (UTC)

Ok, almost exactly. Maybe some gets radiated as EM waves, maybe a tiny bit as gravity waves. Someguy1221 (talk) 20:49, 26 November 2007 (UTC)

But if there is some loss, does this require some instantaneous movement of space time to account for this, to just sort of instantly pop into a different shape to coincide with the annihilation ΦΙΛ Κ 21:13, 26 November 2007 (UTC)

Not at all. At the the "moment" right after annihilation has two photons with the same mass and approximate position as the two particles that preceded them. As far as spacetime curvature is concerned, nothing has really changed. When I referred to loss, these would be gradual losses as the two particles approach, not at the moment they annihilate. Someguy1221 (talk) 21:18, 26 November 2007 (UTC)

Mass-energy is conserved, and mass-energy is the source of spacetime curvature in GR, so the shape of spacetime immediately before the interaction is the same as its shape immediately after. —Keenan Pepper 21:46, 26 November 2007 (UTC)

Heh, I should have known better. :) --Kjoonlee 22:47, 26 November 2007 (UTC)

Calcium carbonate from breathing into a solution

I recently performed a scientific experiment. We were, in class, given a filtered solution of what I believe to be some kind of "chalk water". This was put in a glass, and once one breathed into it through a straw, calcium carbonate would form and settle at the bottom (with time). My question is then, what was the solution I added CO2 to? And I assume that, in order to balance the equation, H2O must be added (so it is CO2 + ? = CaHO3 + H20)?

This is not a homework question, I've simply forgotten what the equation went like =) Also, my teacher balanced it the wrong way, saying in fact that calcium carbonate is CaHO2. Thank you for your help! 81.93.102.185 (talk) 22:30, 26 November 2007 (UTC)

Your equation can't be right - you have a carbon atom on the left side - but no carbon on the right. Oh - I see. You said that Calcium Carbonate was formed...that's CaCO3. Anyway, the answer is in our Calcium Carbonate article Ca(OH)2 + CO2 → CaCO3 + H2O - so the missing ingredient is Calcium hydroxide. Woohoo! Steve gets to answer a chemistry question! With a more than 1% chance of being correct! SteveBaker (talk) 22:54, 26 November 2007 (UTC)

(after edit conflict) The unbalanced equation would then be CO₂+Ca(OH)₂

--> CaCO₃ (note that calcium carbonate is CaCO₃, not CaHO₂). Since water is neither created nor used up during the reaction, I don't think it is not part of the equation; it simply helps the reaction. --Bowlhover (talk) 23:03, 26 November 2007 (UTC)

What is the biological basis for appreciation of music?

That is, what is it in our genes that makes us react to a pattern of arbitrary sounds? —Preceding unsigned comment added by Xhin (talk • contribs) 22:50, 26 November 2007 (UTC)

Honestly, I'd be surprised if anyone had anything other than speculation and a few unconnected tidbits of information on this topic at this point in time. The brain and genetic expression are probably the two biggest mysteries left in explaining how organisms work. Toss in the rather subjective appreciation of auditory beauty and you're asking for something that is at the far boundaries of human knowledge. Good luck on your quest for an answer. -- HiEv 23:08, 26 November 2007 (UTC)

I agree that we don't know for sure - but one thing that's interesting is the mathematical basis of many musical systems. The fact that we like music where there are simple mathematical relationships between the frequencies and durations of the notes cannot be a mere coincidence. I suspect this has something to do with it - but precisely what is uncertain. SteveBaker (talk) 23:16, 26 November 2007 (UTC)

Unless the mathematical aspect of music is simply Emergent. -=- Xhin -=- (talk) 23:27, 26 November 2007 (UTC)

Try music theory. The mathematics of musical perception are a subject of continuing research, but it is fairly well understood how thirds, fifths, octaves and inversions make up the geometry of music. Physically, our cochlea does something similar to taking a Fourier transform of the sound waveform, giving us a range of frequencies that harmonize according to mathematical rules. Thus chords sound like the fundamental, etc. Chord progressions are not well understood, but there is some very promising research by Dmitri Tymoczko on their geometry based on 2, 3, and 4 dimensional topological mappings of the chord symmetries. See [13]. SamuelRiv (talk) 23:52, 26 November 2007 (UTC)

I worked on a research project a few years ago: "Can a computer tell the difference between pleasing and non-pleasing music?" Yes - it can. This was based on the realization that many "zipfian" distributions exist in "pleasing" music. Since the same balances exist in pleasing poetry, paintings, and throughout nature, it is possible that our brains pick up the natural balance and "appreciates" it. If you are interested in the research, it is here. -- kainaw™ 23:54, 26 November 2007 (UTC)

The only problem with that is the subjectivity of music appreciation -- for example, I've heard songs which somehow got record labels, but sound like cacophany to my ears. Anyway, you guys are helping -- slowly. Keep it up! -=- Xhin -=- (talk) 00:16, 27 November 2007 (UTC)

It probably poses more questions than it answers, but Oliver Sacks' book, Musicophilia: Tales of Music and the Brain offers a fascinating insight into the neural coding for music and its appreciation. Here is a podcast of Sacks talking about it (he addresses the question of subjectivity too). Rockpocket 00:22, 27 November 2007 (UTC)

I've read reviews of that book, and I plan to be delightfully surprised to find it in my Christmas stocking. Another very good one is Music, the Brain and Ecstasy by Robert Jourdain. Re cacophony, I was going to make the point that it's fascinating how a computer can distinguish between pleasing and non-pleasing music but many humans seem incapable of so doing (and here I'm thinking of things from post-Schoenbergian squarks to heavy metal) - but then, it's all subjective, and what I enjoy would be rubbish to someone else, I guess. -- JackofOz (talk) 00:33, 27 November 2007 (UTC)

Appreciation of a particular sequence of pitches? Doubtful. But given that an appreciation of music something found in countless cultures throughout time and location (and I do believe Brown included music in his list of Human Universals). It seems likely that there is a biological basis for this universal appreciation.--droptone (talk) 02:21, 27 November 2007 (UTC)

How do you derive the properties of chemistry (ie, flowing liquids) from physics?

Unloaded question, but much help appreciated ! -=- Xhin -=- (talk) 22:51, 26 November 2007 (UTC)

You solve the quantum mechanical equations for material...Computational Chemistry may help.Shniken1 (talk) 23:24, 26 November 2007 (UTC)

By far the greatest success in understanding physical chemistry has been statistical mechanics for molecular structure combined with quantum mechanics for atomic structure and electrodynamics for interaction. Flowing liquids, for example, are described quite well by Bernoulli's principle, which can be derived statistically. The ideal gas law is very simply derived from first principles in stat mech as well. For a good, thorough book on the subject, see Thermal Physics by Kittel and Kroemer. SamuelRiv (talk) 23:56, 26 November 2007 (UTC)

Failing audio cables

I have a lot of trouble with audio cables 'breaking'. I use various types of these a lot for connecting musical instruments, amps, speakers, mics, computers etc such as mic leads, jack leads, RCA leads anbd various combinations. For example the 3.5mm stereo jack to double mono RCA lead I use to connect my laptop to my main PC's speakers (as the laptop's speakers are vey poor) has just started playing up, I only so much have to breathe on it and one side of the stereo signal cuts out, when I wiggle it near the jack plug, the dodgy side cuts in and out although the other side is OK (I have been testing it by shifting the balance to the affected channel only).

I know the easy answer is simply to buy a new cable which in this case is fairly cheap but when £10 mic leads fail it is no joke and it seems a waste to keep buying new leads. I just wondering what actually causes these leads to fail? I presume they are made of copper wire which somehow breaks but why is it such a problem with audio/video leads? I have never had this problem with mains leads or any other type of lead, ie USB, parallel, firewire etc and as the latter types are digital rather than analogue, I would have thought broken wires would cause more problems than with analogue leads. I don't exactly pull on the leads, I coil them up when not in use but not tightly so I can't think that I am doing anything beyond what they are designed for.

Secondly, is it possible to repair them? Obviously, this depends on what the actual problem is! GaryReggae (talk) 22:53, 26 November 2007 (UTC)

Mine always fail from other bending so I suspect it is something to do with this. Perhaps a little more slack would reduce wear, or perhaps higher-quality cable would be more sturdily built. I was told to loop them together up/down against each other to stop wear. When it's occurred to me it has always been near the headphone socket/headphone so I guess it must be strain/stress and bending that is causing it. Not sure if it is repairable, I would expect for the cost it wouldn't be worthwhile. ny156uk (talk) 23:09, 26 November 2007 (UTC)

Generally, it's just because the wire is bending a lot. If you take a piece of wire like a paperclip and bend it back and forth over and over, eventually, it'll break. Copper is pretty flexible - but eventually, it goes. Probably the wire at your laptop end broke because it's being moved more often (or plugged and unplugged more often) than the ends at the speakers or whatever. You can mend those wires reasonably easily - there are two approaches. Firstly, if you can tell where it's broken (usually within an inch or two of the connector) then cut the wire an inch or so beyond the break - get a wire stripper (or a pair of scissors if desperate) and now you need to re-attach the connector. There are three approaches:

1. Cut the wire on the other side of the break, strip those wires - then twist the ends together and wrap them up with a few inches of electrical tape so they don't short out. This isn't 100% the best thing - and if the break is too close to the connector, you can't do it this way - but it's very easy and gets you going with no tools more sophisticated than scissors and electrical tape!
2. Carefully remove the plastic shroud on the connector and thread it onto the cut/stripped side of the wire. De-solder the short bits of wire from the connector, solder on the new ends and replace the shroud. Of course this assumes you have a soldering iron (and possibly a desoldering gun) along with the necessary skills to do it. I suspect you don't or you wouldn't be asking...but hey - we all had to learn sometime!
3. Go to your local Radio Shack (or whatever national equivelent you have) - locate the rows of little, beautifully labelled drawers - find a connector that looks like the one you cut off BUT WHICH HAS SCREW CONNECTIONS instead of solder joints. Now you can wrap the stripped ends of wire around the screws and tighten them up. This is easy and has one HUGE advantage over the other two ways. When the wire breaks AGAIN (as I'm sure it will), you can just trim off a bit more wire and fix it again with no more tools than a screwdriver and a wire stripper (or scissors if you are careful!).

Good luck! SteveBaker (talk) 23:13, 26 November 2007 (UTC)

Thanks Steve, I will try fixing it later, the break seems to be right by the jack connector and it's a moulded plastic one so I think I'll just go to Maplin's and buy a new plug with screw fittings if they have them as I'm not very good at soldering. As you say, the next time it breaks, probably in the same place near the connector, it will be easy to fix! GaryReggae (talk) 09:07, 27 November 2007 (UTC)

Actually, if it does break often, some kinds of connector come with strain relief widgets. These take the form of a long plastic or rubber sleeve that covers the wire out to a distance of a couple of inches out from the connector. Others are like a stiff spring that you thread over the wire+connector. They take some of the load off the wire and prevent it from bending unnecessarily. If you are buying a new connector - you might look to see if any of them have superior strain relief. SteveBaker (talk) 16:51, 27 November 2007 (UTC)

November 27

Lighting yourself?

Continuing the thread about fire accelerants above, would it actually be possible to light yourself on fire by drinking gasoline and then swallowing a match or something? I am certainly not contemplating doing this, but I'm just wondering. bibliomaniac15 00:34, 27 November 2007 (UTC)

No, there is no oxygen (or at least not enough) —Preceding unsigned comment added by Shniken1 (talk • contribs) 01:08, 27 November 2007 (UTC)

If it was possible, then either they would've either done it on Jackass (or similar) by now, or someone would've done it whilst trying to get on Jackass (or similar) and we'd have read about it in the papers... :) --Kurt Shaped Box (talk) 01:16, 27 November 2007 (UTC)

Or Darwin Awards. --antilived^{T | C | G} 01:28, 27 November 2007 (UTC)

Since they can make fuel from pigs and chickens I guess they could make it out of us too. Its the third way between burial and classic cremation: get cremated in an internal combustion engine. "Help your children and become a galon of petrol". Keria (talk) 11:55, 27 November 2007 (UTC)

Beta decay and W bosons?

From W and Z bosons, "the W and Z0 particles are almost 100 times as massive as the proton — heavier than entire atoms of iron.", and beta decay is changing a down quark into an up quark, which gives out a W^- boson and decays into e and antineutrino. I don't really understand the whole quantum physics thing and I'm wondering, if W boson is so massive, where does all the mass come from? And where did it all go after decay? Also, why are the arrows for antiparticles backwards on Feynman diagrams? --antilived^{T | C | G} 01:22, 27 November 2007 (UTC)

Mass is generated by the Higgs mechanism, according to the Standard Model. In terms of beta decay, the W generated is a virtual particle and has different mass properties than a free W, which are calculated by simple conservation of mass-energy. I don't do particle stuff, so I'm not sure why this is. As for the arrows being forward or backward, it is for a couple reasons: one is to show the functional (Feynman diagrams are abbreviations for equations) equivalence of particles and their anti-particles, and another poses the suggestion that anti-particles are actually particles travelling backward in time (though this is not actually true). Again, I don't have much depth in this area. SamuelRiv (talk) 02:26, 27 November 2007 (UTC)

But from the article Virtual particle, "Virtual particles exhibit some of the phenomena that real particles do, such as obedience to the conservation laws." , and it seems to violate the conservation of energy here. --antilived^{T | C | G} 05:45, 27 November 2007 (UTC)

In general, virtual particles do not have the mass you expect of real particles. They aren't violating conservation of energy because unlike real particles they don't require energy in order to exist. Dragons flight (talk) 12:12, 27 November 2007 (UTC)

Right. Each vertex of the diagram (three or more lines meeting at a pont) satisfies conservation of energy, and any particle that begins and ends inside the diagram may be considered virtual and has properties such that it conserves mass-energy. SamuelRiv (talk) 12:56, 27 November 2007 (UTC)

Conservation of energy is not really violated because of the Energy-time_uncertainty_principle. Over a short enough time horizon the uncertainty in the energy of the system is large enough to allow a virtual particle such as the W^- boson to be created and then decay (or, at least, the asymptotic information that we can observe about the system is consistent with the creation and decay of a virtual W^- boson, although we cannot observe it directly). Interactions involving virtual particles must still obey other, more fundamental, conservation laws such as conservation of charge. Gandalf61 (talk) 13:00, 27 November 2007 (UTC)

What did I see?

Hi. I got a bright LED light, and shined it at the objective of my 50mm refractor at ~48x. I saw on the top layer objects that looked like tiny specks, kind of like dust. However, on the lower layer, I saw what looked like lint, but moved. It more of slid than wriggled, and it resembled bacteria. I've seen similar objects before, and always assumed it was dust, but I've never seen it move, as I did here. The eyepiece was Hyugens, if that helps. No, it probably wasn't because my eye moved, because it didn't come back once it left the FOV. What could it be? I've seen similar objects before on microscopes, telescopes, and binoculars, but I don't think I've seen it move. If I remeber correctly, the worm-like thing moved independantly of the rest of the screen, although I'm not 100% sure. What could it be? Thanks. ~AH1^(TCU) 02:31, 27 November 2007 (UTC)

I have no way of ascertaining exactly what you saw, but from youthful experience with optical systems, it is possible that the objects you saw were "floaters" inside your eyeball. Edison (talk) 03:39, 27 November 2007 (UTC)

We even have an article on them: floaters. They move independently because they're floating in your eyes (and in all likelihood its less "independently" than you realize, because your eyes make lots of little involuntary movements that you aren't aware of while they are engaged in seeing things). (As an aside, one of the grossest things I ever read on Wikipedia—a long time ago—involved the surgical procedures used to remove excessive floaters; vitrectomy if you've got the stomach for it. Eye surgery in general grosses me out in an unreasonable manner, but that one really takes the cake for me...) --24.147.86.187 (talk) 03:45, 27 November 2007 (UTC)

Floaters sound right to me. Also check out phosphenes and saccades as related interesting information. Mac Davis (talk) 05:08, 27 November 2007 (UTC)

Rechargeable batteries

Why do rechargeable batteries have only 1.2 volts while other batteries have 1.5V? I'm referring to the common types: AA and AAA.

And I've heard that overcharging a rechargeable battery reduces its life. Is this actually true? Why is the life shortened? --Yanwen (talk) 03:21, 27 November 2007 (UTC)

The chemicals which make up the electrodes of a battery determine the open circuit voltage it produces. Alkaline batteries or Carboin Zinc have a higher voltage in each cell than rechargeable Nicad batteries because of the chemicals used for electrodes. Lead-acid batteries are rechargeable but have a higher voltage per cell than alkaline. Overcharging a battery is a bad idea because it can cause it to heat up and can cause the electrolyte to evaporate. Edison (talk) 03:37, 27 November 2007 (UTC)

You may also be interested in our article about nickel-cadmium batteries (i.e. rechargeable batteries). ›mysid (☎∆) 05:50, 27 November 2007 (UTC)

Overcharging can reduce the life of a rechargeable battery by driving water out of the cell, either directly as water vapor or as hydrogen and oxygen gases resulting from the electrolysis of the water within the cell. Most batteries contain a "recombination catalyst" that will burn small amounts of evolved hydrogen and oxygen back into water but serious overcharging will overcome the ability of the catalyst to cope with evolving gases.

Atlant (talk) 13:14, 27 November 2007 (UTC)

Actually, it depends on what kind of battery chemistry is being used - some of the rechargables have 1.3v, 1.4v or 1.5v. I used to mess around in the Lego robotics community - and the Lego computer runs off of 6 AA's to get 9v total - if you used NiCd rechargeables, you only got 7.2v and the computer couldn't run on so little. Since these things chewed through a set of disposable batteries in a couple of hours it was an expensive hobby. However, rechargeable Lithium batteries produced something like 1.4v and that was enough to run the computer. The subtleties of recharging them also depends on the chemistry of the battery. Some can be overcharged and need special rechargers that detect the fact that the battery is full and turn off - some cannot. Some batteries NEED to be fully discharged before you recharge them (NiCd's, certainly), others need to be kept fully charged as much as possible (Lead-Acid batteries like in your car), others don't care. With the wild profusion of battery types out there, you need to be careful that the 'rules' you are following are the right ones! SteveBaker (talk) 16:45, 27 November 2007 (UTC)

Endosteum: soft tissue?

Would the endostuem be considered, technically speaking, a soft tissue? Thanks. 75.42.209.73 (talk) 03:22, 27 November 2007 (UTC)

Yes. Its bascically mesenchymal cells in a collagen matrix that lines the cortical bone at the corticomedullary junction in long bones. Its function is to conduct nutrient blood vessels to the medullary surface of the cortical bone, and also contains undifferentiated osteoprogenitor cells that are recruited in Bone_healing. The article on endosteum is a bit light on detail, but you may find it helpful. Mattopaedia (talk) 13:05, 27 November 2007 (UTC)

Cats, the hunting instinct, and feline psychology

My domestic cat brought a number of live mice into my home and I started putting the ones I rescued into a habitat so the cat would have mice around without letting them loose in the house. Now she spends a lot of time watching the mice, actually strongly resembling a human sitting in front of a television. (Feline reality TV! She's even gained weight with her new couch-potato lifestyle!) My question: Is the presence of mice giving the cat hours of lively entertainment, or is it horribly cruel to expose her to mice that she will never be able to catch? Thanks for any insight. Peter Grey (talk) 08:30, 27 November 2007 (UTC)

Kudos to you for not knocking the mice on the head or necking them when the cat brought them in - but is it really fair on/healthy for them in terms of stress to be placed on constant display in front of a fearsome (to them) predator many times their own size? --Kurt Shaped Box (talk) 08:42, 27 November 2007 (UTC)

I have heard (paraphrasing somewhat) that, while for a human being stalked by a carnivorous predator a hundred times their size would probably lead to post-traumatic stress disorder or worse, for animals like mice it would just be an average day. Plus I'm guessing a habitat with unlimited food, even with a cat nearby, is still preferable to being mauled to death. Peter Grey (talk) 12:17, 27 November 2007 (UTC)

If your cat was bringing in live mice for you and has stopped, she might be waiting for you to eat them or give one to her. If she's not desperately trying to open or get into the habitat, then she's probably not stressed about it. If she's stressed, she'll let you know (with piercing whines, for one). The mice may very well be under stress, but likely then they wouldn't be eating or drinking (I had a cat who had to live with a big dog for a couple months. She lost a lot of weight because she would only eat when the dog wasn't around, i.e. taken on walks). SamuelRiv (talk) 12:52, 27 November 2007 (UTC)

Still, it couldn't hurt to stick the mouse cage up on a shelf, table or something. You don't want a mess on the floor/massacre when the cat finally gets hungry, do you? --Kurt Shaped Box (talk) 17:25, 27 November 2007 (UTC)

Mice are hard-wired to feel fear when they smell cats, so it's possible that the mice in the habitat are suffereing from constant fear, unless they happen to be the genetically altered mice with no fear of cats. -- JSBillings 13:32, 27 November 2007 (UTC)

Don't worry about the cat. Cats are evil. They were created by Satan in mockery of the blessed Dog, who can be trained not to defecate in your house. Proofs of the cat's malignancy abound: cat scratch fever, fur balls, spraying, the infernal yowling when they copulate, that murderer's blank stare. They are often found in the company of witches, where their true nature as a mere receptacle for an otherwise incorporeal demon is revealed. Your "cat" will be content to gloat over your captive rodents and revel in their delicious terror at his presence. --Milkbreath (talk) 14:00, 27 November 2007 (UTC)

And a bunch of Animal lovers is hampering the efforts of Italians to rid the world of evil. Keria (talk) 16:20, 27 November 2007 (UTC)

Hence I don't want to inadvertently annoy my evil housemate. Peter Grey (talk) 17:12, 27 November 2007 (UTC)

acting out of character

Does anyone know in how many cases where someone has started acting selfish, self-centered and strange have refused to cooperate even with the police that something has gone wring with them physically internally. I am not refereeing to the brain purse but rather to things like some form of body cancer that has finally reached the stage that it is noticeably to the individual interfering with body functions or weakening the individual to the point of representing a clear threat of death where the individual does not know the cause but only that their life is threatened and at risk unless they do something even to the point of causing a public disturbance while refusing to cooperate in any way? The second part of my question is if the police were aware of this possibility - a feeling on the part of individual of a life threatening situation, the cause to them unknown, would the police act less violently toward the individual, especially to the extent of causing the individuals death? 71.100.0.58 (talk) 08:37, 27 November 2007 (UTC)

Hypochondria? Munchausen syndrome? ›mysid (☎∆) 12:26, 27 November 2007 (UTC)

We can't give professional advice. Seek medical help. --Sean 14:59, 27 November 2007 (UTC)

This topic was in the Canadian news yesterday [14], although specific to mental disorders. Conditions such as hypoglycemia and electrolyte imbalances (which themselves could be as a result of pancreatic beta-cell cancer or any variation of renal diseases, respectively) could cause changes in mental status. (EhJJ) 16:10, 27 November 2007 (UTC)

The second part of this question assumes that police normally act in a violent deadly manner because it asks if the normal violent deadly action would be changed. What is the basis for assuming that police normally act in a violent deadly manner? -- kainaw™ 16:13, 27 November 2007 (UTC)

Building services

what are the environmental impact of the use and abuse of building services? —Preceding unsigned comment added by 81.199.59.84 (talk) 15:10, 27 November 2007 (UTC)

We don't normally do homework. Is this a homework question?

Atlant (talk) 16:44, 27 November 2007 (UTC)

Gadget Show phone comparison

Last night's Gadget Show featured a comparison of three multimedia phones. To compare the music capabilities of the devices, identical MP3 files were loaded onto the phones, then each phone was connected in turn to a sound desk in a music studio and the track was played through the studio's speakers. Since the link between the phones and the sound desk was presumably digital, I expected there to be no difference at all in the quality of the playback - it seemed it should be just like plugging three different makes of USB flash drive into your laptop. Indeed, I failed to see what the point of the test was. Yet the testers claimed to notice differences in the quality of the sound depending on which phone the track was "played" on. What am I missing here ? Gandalf61 (talk) —Preceding comment was added at 15:12, 27 November 2007 (UTC)

Why do you presume that the connection from the phone to the sound deck was digital? My guess would be that it was analog, but I did not see the show. -- Coneslayer (talk) 15:27, 27 November 2007 (UTC)

Why do amps kill you, but volts don't?

Like when being hit with an electroshock weapon. Why is it that a large number of amps can kill you, but a large amount of volts do not? 64.236.121.129 (talk) 15:56, 27 November 2007 (UTC)

I usually simplify electrical stuff to water and plumbing. I feel this helps people understand it - even though it is not a perfect analogy. Voltage is roughly equivalent to water pressure while amperage is roughly equivalent to the amount of water that is flowing. I can take a squirt gun and hit you with high pressure water, but not hurt you at all because there is very little water flowing. Alternately, I can hit you with 500 gallons of water at very low pressure and you'd definitely feel it. So, you can see that water pressure can be felt, but it is the quantity of water that is required to cause damage. Similarly, high voltage can be felt, but is high current that kills. -- kainaw™ 16:08, 27 November 2007 (UTC)

That's more or less the kind of explanation I was going to attempt. All I can think of to add is that we have articles on electric current and voltage which also explain the difference, altho not necessarily specifically in the context of injuries they cause. Oh, it looks like Electric_shock is the article most relevant. Friday (talk) 16:11, 27 November 2007 (UTC)

Yes - the electric shock article also covers what kind of physical damage high electrical current can cause - which I didn't mention in any way. -- kainaw™ 16:15, 27 November 2007 (UTC)

(Darn - beaten to it by an edit conflict!)

The Hydraulic analogy often helps here: Voltage is like the pressure of the water, Amps (current) is like the amount of water flowing. Ohms (resistance) has to do with the diameter of the hole or pipe through which the water is flowing (small pipe - lots of resistance, big pipe - less resistance). Ohms law says V=IxR (V=Voltage volts, I=Current in amps, R=Resistance in ohms). In water-analogy terms, more pressure (voltage) comes about when there is a lot of resistance to the flow or when a lot of water is flowing.

When a pipe bursts, it's the volume of water that causes the damage to your basement (When you touch the bare wire it's the Amps that kill you). But even if the pressure in the pipe is huge - if it's squirting out through a tiny pinhole - it doesn't bother you much because not much water comes out. (If the voltage is high, then so long as the resistance is high, you don't get many amps). But if the pressure in the pipe is high and there is a HUGE hole (so not much resistance), then lots of water is going to flow and you're in trouble. (If the voltage is high and the resistance is low then the current is high and you're in trouble). So voltage does matter. The other part of the analogy is that if whatever is pumping the water has a limited capacity - so even if there is a big hole in your water pipe, if there isn't much pressure then not much water ends up in your basement (So if the power supply is a little 1.5v AAA battery, then even if the resistance is low, not much current will flow and you'll be OK).

The pressure of water can be high (like inside a coke can that you just shook up), and the resistance can be low (like you suddenly pulled the tab on the can) but because there is only 8 ounces of liquid in there - the resulting high current won't flow for very long. This is like one of those static electricity demonstrations where there is a million volts (lots of pressure!) built up in a nice shiney dome - and as you touch it, a spark ionises the air (making a low resistance path) and you get a very short, sharp 'zap' of current - then it's all discharged (the coke can is now empty).

SteveBaker (talk) 16:19, 27 November 2007 (UTC)

I see, thank you. How do Watts fit in? Is there a water analogy for it too? 64.236.121.129 (talk) 16:38, 27 November 2007 (UTC)

Watts represent power, so there are still water analogies. A huge river (high current) can be flowing by you at quite a low pressure (voltage) yet still represent a large amount of mechanical power. A fire nozzle or water cannon, spraying a relatively small volume of water (low current) but at very high pressure (high voltage) can also represent a large amount of mechanical power. But a very large volume of water that's just sitting there with no pressure (zero volts) isn't doing any work (right now) nor is a tank of water at very high pressure with no outlet (zero current).

Atlant (talk) 16:48, 27 November 2007 (UTC)

(edit conflict) "Voltage" is nothing. It is "potential difference", that's all. Nothing happens. Some electrons over there want to get over here, and how bad they want to is what we call voltage. It's when the electrons actually move that the party begins. That's current. Current generates heat and disrupts the body's electical stuff, the heart's most importantly because that can kill you quick.

It does seem counterintuitive that 5,000 volts can leave you unharmed and 300 volts can kill you, but the truth is that the harmless kind of 5,000 volts is not really 5,000 volts at all. A power supply, be it a circuit or transformer or battery, can only provide so much current all at once, not infinite current. As soon as you exceed its capacity, its voltage goes down. A supply rated at 5,000 volts at one milliamp will only stay at 5,000 volts if you draw one milliamp or less, and will fall in voltage as necessary to maintain that maximum level of current if you try to draw more. Or smoke, pop, and melt. Or blow the fuse. On the other hand, if you get across 5,000 volts from one of those power company transformers that looks like a refrigerator, we're talking closed casket.

Another thing to bear in mind is that the human body has a fixed resistance, and that will dictate the maximum current that can be drawn at a given voltage. This means that no matter how many 12-volt batteries you strap together in parallel, they can't hurt you if you get across them with your hands, even if their current capacity is a zillion amps. At the body's 50,000 ohms, you get 240 microamps, period. With dry hands, one hand on each pole, it takes about 300 volts at 100+ milliamps to have a good chance of stopping your clock. Wet hands or something like taser darts bring the lethal voltage way down, because the resistance is less and the lethal current of about 100 milliamps can be more easily produced. So in this respect you can say that it is the voltage that kills you.

When I said that "nothing happens" with voltage, that was for voltages we're likely to encounter in our everyday lives. Something like lightning is a bit different. Electrical current creates a field in its vicinity (you can feel the effects of a field by holding a hairy arm near the front of a TV screen). If the field is strong enough and sudden enough it will make the electrons in your body move violently all by itself. People get knocked out or even killed by near misses of lightning all the time. --Milkbreath (talk) 17:00, 27 November 2007 (UTC)

So if you dump water or salt water on someone, it will decrease his electrical resistance, and thus increase the amount of amps he recieves? Even if he is shot by the same exact electroshock weapon? 64.236.121.129 (talk) 17:37, 27 November 2007 (UTC)

Big Idea of Particles, Mass Conservation

Hi im afraid that i have three q.that i would like to ask. I would firstly like to know, what is the big idea of particles? I h ave searched in books and on the internet and i have so far found nothing that can help me. I would also like to know as to how mass is conserved in a reaction between an antacid tablet and the hydrochloric acid in ones' stomach. I would finally also like to know about a particle diagram.

Thank you for your help in advance.

P.S. Please try to explain this in simple terms.

I believe mass is conserved as long as it is converted into another form. Either another form of matter, or into energy. 64.236.121.129 (talk) 16:42, 27 November 2007 (UTC)

That's a pretty general question. What do you mean by particle--are you asking about the physics concept of subatomic particles, or about something else? Also, mass is not conserved--conservation of mass is a historical theory which, like Newton's physics, is close enough in most situations. In the same way that Newtonian physics start to fail obviously at high velocities and tiny scales, mass becomes very obviously not conserved in nuclear reactions. What is conserved is energy; a bit of mass is converted into energy, released as heat and light. What you're talking about seems to be stoichiometry--does that article help at all? And can you provide an example of what you mean by a "particle diagram"? grendel|khan 17:18, 27 November 2007 (UTC)

Inability to Scream

Is there a medical term for someone who has the inability to scream? I am not referring to any dreams nor any type of sleep or awakenings. --WonderFran (talk) 17:42, 27 November 2007 (UTC)