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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)

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:[1]. 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. [2]. 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 [3]. 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)

• I think you're missing my point. I'm saying that what you see as a big difference (between "Walkies" and "Tomato sandwiches") may be a small difference in the dog's perceptual system, just as the difference between "fat" and "vat" is small in yours. And when you say that language consists of sounds and does not include body language, that's like an English-speaker saying that tone is not phonemic, even though Chinese it is; in dog "language", your body language seems like just another part of your utterance and is to be taken into accuont. --Anonymous, 00:09 UTC, November 28.

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)

Actually, there is a significant difference between moths and butterflies beyond superficial taxonomy, which is why there is an article for differences between butterflies and moths. It's a common myth that the differences are just taxonomic, at least among taxonomists ironically. It would help to know if you found it eating anything; that narrows down things. I would agree with Richard that it's some sort of hawk-moth because of what looks like a horn on its posterior with a false-head and false-eyes. --76.214.203.95 (talk) 06:07, 30 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)

Bicarbonate is only a partial buffer. The carbonic anhydrase reaction (H₂O + CO₂ <=> H₂CO₃ <=> H⁺ + HCO₃^-) explains where your acid comes from - more CO₂ drives H⁺ + HCO₃^- production. The rest of the compensation comes from other buffers including phosphate, and renal excretion of H⁺. Mattopaedia (talk) 05:08, 28 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)

Murder

In response to the answers above, my friend says, "OK, so we are going to get someone to OD on it and then shoot them with a flaming arrow." But I don't think that would work. Would the [alcohol, glycerol, ghee, oil] remain flammable after being introduced into the stomach? HYENASTE 23:19, 27 November 2007 (UTC)

In sufficient quantities to perpetrate arson? I doubt that, but also doubt that the substance would catch on fire, would there be enough oxygen present to allow it? Also, the substance in question, when being reacted on by the stomach acid may not be flammable either. 68.39.174.238 (talk) 03:45, 28 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 [4]. 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)

The whole point of urination is to remove toxic substances from the blood e.g. excess salt, urea, uric acid, creatinine etc., so drinking it cannot be healthy in any large quantity (although it is sterile). And I once heard that cat's urine has ammonia Tomi P (talk) 22:51, 27 November 2007 (UTC)

Other than possibly consuming too much salt, there is nothing dangerous about urine. See Urophagia. Btw, we are talking about human urine, not cat urine. 64.236.121.129 (talk) 16:42, 28 November 2007 (UTC)

Actually as the article mentions (admitedly with a citation needed tag), you probably should take care if the person is taking medications Nil Einne 08:32, 1 December 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)

Yup, stress hormones from chronic stress can suppress the immune system. See Ask A Scientist - Stress and immune system. As for your "patient 0", that person might have existed centuries ago, and the virus just keeps circulating through the population. Or, as is the case with new flu viruses, existing viruses co-mingle and/or mutate in a host (pig, chicken, duck, human, etc.) and produce a new virus. There are lots of ways viruses are created and spread, so there isn't just one answer to that question. -- HiEv 19:47, 27 November 2007 (UTC)

Well, the being cold - catching cold connection may have some fact behind it. The thing is, when you're cold, your body tries to conserve heat, and keep the heat in, leaving less heat at the extremities. This can include your head, if it is not well covered. If you are wet, there is a good probability your hair will be too. When your head becomes cold, it starts to restrict blood flow, but of course not hinder it altogether. When this happens, your immune system in the cold area can decline, since the blood carries white blood cells. The area, in this case your head, becomes cold, but still warm enough for the viruses to develop. There are viruses all around us, but usually they are kept at bay by your white blood cells. The viruses and bacteria can now reproduce, because there aren't as many white blood cells to attack them. When you come back inside, the viruses are still there, but now more heat is induced, so the body no longer has to conserve, and the viruses multiply even faster, giving it time to spread, but now since the blood flow is increased, the white blood cells come back to attack the viruses. Now, your immune system will take care of the rest, so you usually don't get an automatic cold that way, but you may see the early symtoms of one: high head temperature, when the blood flow increases to get rid of the germs; runny nose, when the mucus attempts to wash away the viruses in your nose; sneezing, to get rid of viruses in your nasal system; coughing, to get rid of viruses in the throat; stuffy nose, caused by excess mucous and nasal activity, etc. So, the correlation may be there, but usually isn't as direct as you may think. Now, if you wear too much clothing outside on a cold day, it will increase your body heat substantially, but since your head is usually exposed, the temperature at the surface of your face may go down. This prevents large amounts of white blood cells from entering the area, but produces enough heat so that the viruses can multiply profusely. Plus, the excess clothing causes you to sweat, and wind can allow the cold to enter your body, potentially degrading your immune system. The numbing cold near the surface of your face, supplied with feeling by your warm interior, can cause pain in your face and sinuses, and possibly cause a headache. A risk of not wearing enough clothing in the cold is more of hypothermia than getting a cold. Plus, if you're not wearing excess clothing because you're going to be excersizing strenously, it could cause further complications. Excersize causes sweat to be produced, and the sweat, along with the wind and cold, can allow coldness to enter your body. I don't think this has been proven, but not tucking your shirt in can expose your stomach areas to the cold, and supplied with enough body heat, can allow invasive viruses to develop in the stomach and intestines, potentially causing diarrhea. Also, the sudden warming of extremities after coming inside might explain why my hands, for example, often feel warm instead of uncomfortably cold to the rest of my body. Remember that this is mostly theoretical, and science seems to want to reject any "myths" based on experience rather than scientific fact. Hope this helps. Thanks. ~AH1^(TCU) 21:59, 27 November 2007 (UTC)

Ok so now some statements are contradicting each other. Astro said viruses are around us all the time, so that means we can get infected even without being close to someone who is already infected. Which means the so called, patient 0 can be anyone who happens to catch a cold from the enviroment. But HiEv said patient 0 existed since the cold virus was first contracted, and has simply spread from person to person since then. This implies that one does not catch the cold from the enviroment, but rather from people. Who is correct? 64.236.121.129 (talk) 16:40, 28 November 2007 (UTC)

Well, the thing is, if someone sneezed in a building, the viruses do not go away immediately, correct? So, if someone walked through the sneezed area, there will be a higher concentration of viruses in that particular area, which means there can be viruses in the air, especially in an enclosed public building. Also, viruses can live on uncleaned surfaces for days, so if you touched the surface and rubbed your nose, some viruses might enter your nose. What I also meant was, there can be viruses inside you, although they are usually controlled so you don't get sick. Sorry if you misunderstood, and I'm not really an expert, so make sure you understand that when you're deciding the general answer to your question. Hope this helps. Thanks. ~AH1^(TCU) 18:45, 28 November 2007 (UTC)

Let's clear up a few things. Some viruses, like HIV need bodily fluids to survive and are destroyed on contact with air, while other viruses can live briefly outside of the body, like cold and flu viruses, some of which can survive up to about 48 hours depending on conditions.[5] Also, "patient zero" generally refers to the first/main person who caused the disease to spread within a population, which is not necessarily the person who spread it to you. Finally, viruses cannot reproduce without a host. What this means is that any viruses in the environment come from another host, though that host may not be a human. This is not a contradiction, it's just neglecting to mention that the "viruses around us" come from other living things. -- HiEv 03:39, 2 December 2007 (UTC)

I didn't read the whole thread but a few points to mention. It has been suggested although as far as I'm aware is completely unproven that people may have slightly weaker immune systems in cold weather and also that viruses may last longer in the environment which are some of the reasons why cold and flus are more common in winter. In any case, it's generally accepted that the closer contact between people etc in the winter season are the primary reasons. Bear in mind it AFAIK isn't just winter, cold and flus tend to be more common in the rainy season in tropical countries when it's colder (although to a far less degree) and people also spend more time in close quarters. Nil Einne 08:40, 1 December 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)

Howdy mean, Milky, they aren't much help? I find them quite enlightening. Do you have any suggestions on how they might be improved? —Preceding unsigned comment added by TreeSmiler (talk • contribs) 01:42, 28 November 2007 (UTC)

I was hoping for a down-and-dirty walkthrough of power reflection, which was the original question. The impedance matching article blows right by that as if it's self-evident. Power is reflected?!!! What the hell does that mean, we ask ourselves, and we're left to imagine it. I used to be a First Phone, but even back when I had a clue, transmission lines and antennas seemed like magic to me. "Thou shalt build the antenna 2.7 cubits by 3.31 cubits by the square root of five cubits...." It's pure math, pure applied theory. So I can tell when I'm not being told something, but that's about it. --Milkbreath (talk) 03:00, 28 November 2007 (UTC)

Seen reflection coefficient yet? —Preceding unsigned comment added by TreeSmiler (talk • contribs) 03:03, 28 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[6][7], 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)

Sorry, water is created during the chemical reaction. The balanced equation would then be Ca(OH)₂ + CO₂ --> CaCO₃ + H₂O. --Bowlhover (talk) 23:17, 27 November 2007 (UTC)

Otherwise it would act similar to spectator ions. 81.158.37.78 (talk) 23:14, 29 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 [8]. 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)

Hi. That answer makes sense, but there is one small problem. When I shifted my eyes, similar objects (yes the probably were floaters) to the ones I saw in the lens floated on my eyes. However, heres the problem: the ones in my eyes were floaters, but the ones I saw in the lens were similar, but were more magnified, more easy to see, and didn't drift with my eye motion. Also, the ones int he lens didn't seem to differ whether I ued either eye. Are the objects dust-sized, or are they bacteria-sized? If the object I saw moving was a floater, how come it appeared deep in the lens rather than on my eye, and didn't move back into view when my eye shifted back? Are the objects more likely to have come from the eyepiece, the mirror, or the objective? Thanks. ~AH1^(TCU) 18:41, 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)

Okay thanks that's what I thought! 75.42.209.73 (talk) 17:50, 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)

That's why I prefer gulls to cats - gulls have honesty. Compare your average Herring Gull to your average HouseCat. The gull is every bit as loud, aggressive, raucous and cold-hearted as the cat (and - to bring up an old running joke, could probably equal it in a vs. battle) - but it never pretends to be anything different. --Kurt Shaped Box (talk) 17:54, 27 November 2007 (UTC)

You've never fed a gull? They can be very good at begging and acting nice if they learn it gets them fed. I remember one year my mother leaving out fish (leftovers from our cats — how's that for a tie-in?) for a young herring gull that had fallen out of its nest. For the rest of the year, until the weather got cold and the gulls flew south, we basically had a semi-tame pet gull. He (or she) learned to recognize my mom by sight, and would wait on the rooftops among the other gulls for her to come out. Then, if no other people or gulls were in sight, he'd glide down and land some distance away, all very quiet, and then walk up to my mom and stand there looking at her and giving her the "puppy eyes". Probably would've let us pet him if we'd wanted to. He may not have been physically as cute and cuddly as a cat, but he was most definitely on his best behavior towards my mother, even despite our efforts to convince him that there were other, more appropriate food sources for a gull. —Ilmari Karonen (talk) 19:13, 27 November 2007 (UTC)

I'd heard that cats watch you and decide that somehow you never seem to catch any mice. This elicits a behavior similar to how they train their kittens to hunt. They catch a mouse - deliberately not killing it and bring it to you so you can practice on it. If you don't succeed with live mice, they'll bring you ones they've wounded to slow them down so you'll have a chance to get some practice in. If all else fails, it's on to dead mice. If you pick up the dead mouse and chuck it out somewhere, the cat figures you've finally gotten the idea - so it's back to live and wounded ones. Yeah - dogs rule. They may be stupid - but at least they know it. They don't pretend to be smart like cats do. SteveBaker (talk) 18:46, 27 November 2007 (UTC)

So what does it say when my neighbor's cat decided to show up at my doorstep with half a mouse? (It was the back half, for what its worth.) Dragons flight (talk) 18:56, 27 November 2007 (UTC)

I'd guess it's either "here, I've saved the best part for you" or "here, I ate the best part, you can have the rest if you like", but, without firsthand knowledge of that particular cat's idiosyncratic dietary preferences, I can't really tell which. Or perhaps she was just halfway through her meal and taking a short break when you interrupted her. —Ilmari Karonen (talk) 19:19, 27 November 2007 (UTC)

I don't think it was accidental. A) My doorstep is not really a normal place for her to visit and B) She seemed very enthusiastic about delivering the half a mouse to me. Dragons flight (talk) 19:23, 27 November 2007 (UTC)

I think this cat has gotten to the point where it suspects you are an especially slow learner and you aren't really ready for an ENTIRE dead mouse - so perhaps you'd better start with a half of one and work your way up. SteveBaker (talk) 22:11, 27 November 2007 (UTC)

There seem to be different schools of thought on this behaviour, essentially coming down to a) the mouse is for the human and b) the mouse is for the cat, she just wants to get away from other cats while she toys with it. In this case, she isn't bringing me the mice - I've had to fight her for them. Peter Grey (talk) 07:40, 28 November 2007 (UTC)

There probably isn't a lot of research in this area. I'd guess that, as long as your cat is well fed, having a habitat for mice that the cat can watch is probably no more cruel than giving the cat toys that it can't eat. In other words, it's probably not a problem. I often see people trying to anthropomorphize animals by attributing human-like thinking to them, but they don't try to see if their hypothesis is correct or think about simpler explanations that would produce the same behavior. Don't overthink things. If your cat looks entertained, then it's probably entertained. If it looks stressed, then it's probably stressed. However, as long as your cat isn't starving, threatened, sick, injured, lacking sleep, or too hot/cold/wet/dirty, then it probably isn't under much stress. -- HiEv 20:33, 27 November 2007 (UTC)

The mice, on the other hand...may be nervous. SteveBaker (talk) 22:11, 27 November 2007 (UTC)

Who can say? Mice always look a little twitchy to me. And, for the dog lovers/cat haters who seem to have used this question as a dumping ground for their vile hatred towards nature's most perfect animal, I can only say this: Yes, a cat might shit inside your house, but even it, in contrast to a dog, is smart not to EAT cat shit. For all the tricks they can learn, even the smartest dog has struck me as being no smarter than a bug. Matt Deres (talk) 02:34, 28 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)

You are on an, "Every question someone asks that a doctor could answer is a request for medical advice." kick. If you are going to work the science desk I suggest you get off this kick. 71.100.0.196 (talk) 23:43, 27 November 2007 (UTC)

This topic was in the Canadian news yesterday [9], 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)

Normally the police try to match, if not exceed, any potential level of violence with which they feel they may be faced. In the US it is common for the police to aim their weapons for their own protection on mere suspicion or "just in case" their subject has a gun.

If the police tailor their actions to match the situation exactly and the situation is as described above then the police will escalate their reaction to be greater than the subject can overcome - including choke holds, placing too much weight on the subject's chest, tazerring the subject for too long or at too high a current setting, or not calling for medical help if the subject stops breathing or begins turning purple - all on their own assessment of being necessary to do their job and to protect their own lives while the subject may have been resisting at a level he felt necessary due to his own internal conditions to protect his life.

You Tube has a video example of this happening to an individual in an airport resulting in the individuals death by tazer. 71.100.0.196 (talk) 23:43, 27 November 2007 (UTC)

The most common cause for people to act out of character is mental illness, particularly bipolar affective disorder and other schizoaffective disorders. There are other causes as well, such as electrolyte disturbances, some cancers (this is rare though), and drugs. The other thing that often happens in these circumstances is the person loses insight, and so may not necessarily be aware of a need t o act in a certain way, or feel there is anything wrong with their behaviour. They may believe there is some threat to their life, but this may not be factual. As for the police, although IANAcop, I would expect them to only use reasonable force to preserve their own safety and the safety of any bystanders. It is a sad thing, but some people who are mentally ill do end up severely injured or dead as a result of an altercation during an acute phase of their illness, but suicide in the mentally ill is certainly a far bigger problem. It must be devastating for police officers to find they'd injured of killed a person whose actions were driven by mental illness. But that risk ultimately is a part of their job, which is a good reason to treat them with the utmost of respect, rather than criticising them for doing their job. Mattopaedia (talk) 05:38, 28 November 2007 (UTC)

I'm suggesting more in terms of life threatening illness generated paranoia (only it's not paranoia, but real) to the extent of causing total lack of cooperation and in fact opposition to anyone or anything versus the suicide-by-police due to mental illness syndrome. 71.100.0.196 (talk) 11:40, 28 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)

This is a quite wide-ranging question that does sound like a homework essay so I am not going to give you anything more than a few bullet points to get you started:

Energy use (therefore carbon emissions) is the primary environmental cause for concern from building services

Heating, ventilation and air conditioning (HVAC) services are the primary use of energy in buildings. Natural ventilation is far better from an environmental perspective than mechanical ventilation. The fuel used for heating is also a consideration, generally coal is worse than oil which is worse than gas. Consider forms of renewable energy such as using photovoltaic panels to heat water, wind turbines or geothermal ground pumps. Combined Heat & Power also helps as it is more efficient than using fuel solely to produce heat.

Lighting is also a big user of energy. Natural lighting should be maximised in buildings where possible and energy efficient light fittings are preferred.

Refrigeration systems, for example cooling in air conditioning often contain gases that can contribute significantly to climate change. While CFCs (a major contributor to the depletion of the [[[ozone layer]]) have been all but phased out, their replacements are not perfect. Refrigerant gases should be treated with care and not allowed to escape to the air. Care must be taken when disposing of redundant refrigeration equipment, particularly older stuff.

Old electrical transformers contain Poly Chlorinated Biphenyls which are a major carcinogen.

Many older buildings (generally prior to the 1980s) may contain asbestos, particularly in heating plant and insulation to pipes.

Older heating systems often utilised underground oil storage tanks and these have a significant chance of leaking into the ground. Newer storage tanks for oil must be bunded, that is located in an enclosure that can trap the contents if the tank leaks.

Water usage is also key. Some cooling systems such as cooling towers can use a large amount of water.

Also consider wastewater disposal. It is better to have separate drains for foul and surface water as surface water can generally be returnerd straight to rivers while foul water has to be trated, which used energy. Where surface water is drained from car parks or roads, oil interceptors should be used to ensure water is not contaminated.

This is only scratching the surface but hopefully it will inspire you to come up with some more ideas. Let me know if you have any specific questions. GaryReggae (talk) 22:53, 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)

Good point. Because they were using a fancy sound desk, I assumed that the connection would be something more sophisticated than a 3.5mm jack plug - but if was just an analogue link, the whole test makes a lot more sense. Gandalf61 (talk) 13:38, 28 November 2007 (UTC)

The available output of the phone would be the limiting factor; they could have had the super-whiz-bangiest desk in the universe, but I'd be surprised to find a mobile phone with a digital output. --LarryMac | Talk 20:12, 28 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)

Regarding the analogy you and others have used: I know you admitted the analogy is not perfect, but I should point out that small streams of very high pressure water can cut through titanium. See the water jet cutter article. Can very high voltage with low amperage do damage in the same way? -- HiEv 20:56, 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)

Yes. Of course, if it's the kind that sticks barbs into your flesh, it won't matter how wet or dry you are. But the cattle-prod kind will be more effective on a salt-water soaked suspect because that will negate the insulating effect of any clothing in the way. Bear in mind that these weapons are pulsed, that is, they provide current in many very, very quick bursts, which is a different ball game from a constant current. We can take a lot more current in little doses. Also, the current mostly runs between the contacts, and so doesn't get to the heart or brain so much, meaning that such weapons can run a higher voltage than a person could take right across the chest. --Milkbreath (talk) 17:56, 27 November 2007 (UTC)

What if it's an electrolaser? 64.236.121.129 (talk) 18:58, 27 November 2007 (UTC)

Then it's insult to injury. Once the holes are burned clean through you, you'll welcome the anaesthetizing effects of the electricity. --Milkbreath (talk) 19:29, 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)

Let's be careful not to confuse the OP with teeny-tiny details here. Mass IS conserved to a truly spectacular degree of precision through almost all 'everyday' events. Utterly, vanishingly tiny amounts of mass are interchanged with energy in rather obscure ways relating to relativity and other stuff - but if we are talking about normal, mundane, day-to-day stuff like antacid pills in your stomach - then it's accurate to say that mass is conserved. This is a valuable principle that one should not toss out in ones zeal to be modern and utterly correct. In a chemical reaction - whatever atoms you started with are the atoms you have left at the end. None appear from nowhere or vanish abruptly...unless you are looking inside a particle accellerator or a nuclear weapon or something much more bizarre. As far as 'classical' physics and chemistry is concerned, mass is conserved. SteveBaker (talk) 18:26, 27 November 2007 (UTC)

When antacid is mixed with acid, you get a chemical reaction that produces some salt, some water and maybe some carbon dioxide or something - but no mass is lost. The mass of the antacid plus the mass of the acid is PRECISELY equal to the total mass of the byproducts you are left with at the end. The atoms that were present in the antacid and the acid merely rearranged themselves. Sodium bicarbonate (a common antacid) is NaHCO3 which means that each molecule contains one sodium atom (Na), one hydrogen (H), one carbon (C) and three oxygen (O). The acid in your stomach is hydrochloric acid (HCl) with one hydrogen (H) and one chlorine (Cl) atom. When an HCl molecule meets an NaHCO3, you get CO2 + H2O + NaCl - which is Carbon dioxide, water and common table salt. No more acid, no more antacid - just salty water and a small (but hopefully polite) <burp>! But at the end, you still have one sodium, two hydrogens, one carbon, three oxygen and one chlorine atom...they just rearranged themselves. Nothing was lost or gained in the process. SteveBaker (talk) 18:17, 27 November 2007 (UTC)

If you take a sealed, air tight, container and put acid and antacid (a base) in it but not mixed, and weigh it, then mix them and allow them to react and then weight them again, the weights will be the same. That is concervation of mass. It's all still there just rearranged. (Note: this assumes the containter doesn't explode or something because of gas pressure, that could be dangerous). RJFJR (talk) 19:08, 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)

That seems like a rather unlikely condition - can this person talk? Talk loudly? Shout? Shout loudly and incoherently? Shout "Aaaaaaarrrrggghhhhhhh" with steadily increasing pitch? 'Cos if so, they are screaming. It's hard to imagine any kind of condition that would strike selectively at one part of that process. SteveBaker (talk) 18:08, 27 November 2007 (UTC)

Spasmodic dysphonia can inhibit certain vocalizations while not affecting others. As I recall, Scott Adams was able to give prepared speeches, yet unable to speak conversationally. I don't know about an inability to scream, specifically. -- Coneslayer (talk) 18:20, 27 November 2007 (UTC)

Actually, it is me. I have no problem speaking in normal tones. I am in a girl in my late 20's but I have an unusually high pitch, soft voice. My mother had the same thing, too. The problem is that no matter what I try to do, I cannot sound my age. When I speak, people assume that I am much younger or dim witted and it's hard for me to get respect. My dentist had mentioned that the roof of my mouth was unusual but I don't know if that affects it. All my life, I cannot scream at all. It's wierd. I remember my teachers in elementary school trying to get me to scream for a school play and I couldn't. I tried to scream lot's of times, even tried to scream into a pillow and I cannot scream at all. It almost sounds like I am exhaling really loud. --WonderFran (talk) 18:24, 27 November 2007 (UTC)

This seems as though it would be general dysphonia, not spasmodic. There is no ICD9 or ICD10 code for an inability to scream. It is classified as dysphonia-unspecified. As a rule, we do not diagnose your specific problem or offer treatment. Dysphonia is merely the medical term for a voice disorder - not a diagnoses of the reason for the disorder. If you are concerned about this, seek advice from a medical professional. -- kainaw™ 18:32, 27 November 2007 (UTC)

Correction - I have just been told by an ENT surgeon that it is adductor spasmodic dysphonia and that it is not very rare. -- kainaw™ 18:36, 27 November 2007 (UTC)

Argh! You blew it. Now we know it's you - this is a medical diagnosis question and we aren't allowed to answer it. If it bothers you - see a doctor. But - did you ever wonder: perhaps your 'exhaling really loud' is sound so high in pitch that you can't hear it? SteveBaker (talk) 18:37, 27 November 2007 (UTC)

How long do you think it will take for someone to delete this whole thread even though no diagnoses were given? -- kainaw™ 18:42, 27 November 2007 (UTC)

You guys are funny! I was looking for a medical term, not a medical help. The only reason why I gave more info was because I wanted to give Steve Baker a better unerstanding of what I was referring to. --WonderFran (talk) 18:49, 27 November 2007 (UTC)

Well, I'm still curious. So indulge me - let me ask some questions - without diagnosing anything. You can shout - right? Can you shout the word "Aaaaaaarrrrrggggggggghhhhhhh!"? If not, what words can you shout? But if so, can you just gradually increase the pitch and volume of your voice? If so, then at this point, I think we have what I would call a scream - but if you can't do that then at some curious point in this process, there was something you were unable to do - some kind of threshold. I can't get my head around where that point is exactly. SteveBaker (talk) 22:03, 27 November 2007 (UTC)

This is a touchy subject because some editors are far too sensitive to the whole "medical advice" issue and some are happy to hand out medical advice without any expertise in the area at all. Everyone else is stuck in the middle between some editors blanking threads and others diagnosing and prescribing treatment. -- kainawBPG7WY 18:52, 27 November 2007 (UTC)

Seriously, she's just asking for a term. Don't be a rules nazi. 64.236.121.129 (talk) 21:17, 27 November 2007 (UTC)

Stop gratuitously insulting people (or is "Nazi" a term of endearment to you?). Kainaw was speculating that other people would think she had violated the rules, and would therefore delete this thread. Seeing as how Kainaw provided a very useful response, it is clear that he or she does not personally believe that a rules violation occurred. -- Coneslayer (talk) 21:57, 27 November 2007 (UTC)

Voice Immodulation Syndrome? :) shoy (^words _words) 23:41, 27 November 2007 (UTC)

Make sure you dont have The Tingler inside you! [10] ARRRRGGHHH! —Preceding unsigned comment added by TreeSmiler (talk • contribs) 02:48, 28 November 2007 (UTC)

By asking for a diagnosis, how can this question be anything but asking for medical advice? 199.76.152.229 (talk) 04:41, 28 November 2007 (UTC)

It is far too common for editors here to have a complete misunderstanding of what a "diagnosis" is. This person asked for the medical term for a physical property. This is no different than asking for the medical term for an ear ache or the medical term for a broken toe. It is not a diagnosis. If, however, she said she couldn't scream and asked what was causing it, it would be a request for a diagnosis. Of course, a person can present a diagnosis without asking for one. She could have said that she was in a car accident and asked if that could lead to an inability to scream. Again, it is not a request for a diagnosis, it is a question about the possibility of one event causing another - similar to asking if I can get liver damage from drinking too much alcohol. I hope that it will be possible for editors to eventually understand what is and what is not a diagnosis. -- kainaw™ 13:08, 28 November 2007 (UTC)

This is just to answer Steve Baker's question. I can shout but not that loud and sometimes it feels very straining to do so. Butwhat came to mind that men in general do not have the ability to do a high pitch scream like some women can, especially in horror films. I don't know if this helps, but I also have a horrible singing voice. Its sounds like cats drowning or mating or something.... :) --WonderFran (talk) 17:45, 28 November 2007 (UTC)

That didn't stop Yoko Ono from singing (sorry - couldn't help it). If you believe that this is purely physical and you have no health problems, you could work with a voice coach. They specifically handle this sort of problem. -- kainaw™ 18:56, 28 November 2007 (UTC)

Can both of you have your discussion about the Desk's policies on the talk page, and leave the Desk for answering questions? TenOfAllTrades(talk) 19:45, 28 November 2007 (UTC)

I wouldn't be sure that most woman can scream in a high pitch just because they seem to do in horror movies. It might be just a pre-recorded effect by some other actrees, like the Wilhelm scream. – b_jonas 16:23, 29 November 2007 (UTC)

What happened to the Michael Pursinger page?

Awhile ago Wikipedia had an excellent page on Dr. Michael Pursinger, a scientist who researches how electromagnetic fields affect the human brain. I'd like to know why this page was taken off Wikipedia; Dr. Pursinger's work is at the cutting edge of psychological research and so it definitely merits to be put back online. ````M.P.

Michael Pursinger does not seem to have been deleted. Is it spelled correctly? RJFJR (talk) 19:01, 27 November 2007 (UTC)

Michael Persinger? Dragons flight (talk) 19:03, 27 November 2007 (UTC)

Thanks a million! I've seen his name spelled differently on other websites (namely the CBC's) that's what was throwing me off... best 216.123.137.85 (talk) 20:00, 27 November 2007 (UTC)M.P.

What was the other spelling? Perhaps we need a redirect. Graeme Bartlett (talk) 02:38, 28 November 2007 (UTC)

We did need one, and we got one, which is why the two links are now both blue. -- 02:41, 28 November 2007 (UTC)

Accessory cell (immunology)

What is an accessory cell (in immunology)? --Seans Potato Business 19:18, 27 November 2007 (UTC)

My medical dictionary says: SYN antigen-presenting cell. (EhJJ) 20:16, 27 November 2007 (UTC)

That's what I had gleaned from other sources too. If anyone knows otherwise, they should go to the antigen presenting cell page and remove the addition I made (and also delete or rewrite the redirect). --Seans Potato Business 20:54, 27 November 2007 (UTC)

Liquidfy Diamonds? Solidify oxygen?

Is it ever possible, in our universe somehwere, to liquidy diamonds? Or to solidfy oxygen? --WonderFran (talk) 21:05, 27 November 2007 (UTC)

Diamond is an allotrope of carbon. Presumably, carbon can be liquid, but if it's liquid, it's not diamond anymore. Oxygen presumably has a freezing point, but I don't see it given in the article. - whoops, it's there, under "melting point". Friday (talk) 21:16, 27 November 2007 (UTC)

To rephrase on the point above (in simpler terminology), the name Diamond specifies a how the carbons are bonded together. So by definition, diamond must be solid. Someguy1221 (talk) 02:59, 28 November 2007 (UTC)

According to our article, carbon has a melting point that's higher than it's boiling point - so the only way to get it to liquify would be under huge pressures (it says 10 megapascals in the infobox). Normally, it'll presumably sublimate - which is to say go straight from a solid to a gas (imagine how 'dry ice' (solid CO2) turns into CO2 gas without ever becoming a liquid...that kind of thing). I don't think it matters whether it's diamond, graphite, amorphous or buckyball carbon. "Somewhere in the universe" could mean deep in the heart of a planet - with ridiculous temperatures and pressures - so probably there is liquid carbon somewhere. SteveBaker (talk) 21:50, 27 November 2007 (UTC)

Certainly going from the sublime to the ridiculous there Steve! —Preceding unsigned comment added by TreeSmiler (talk • contribs) 02:40, 28 November 2007 (UTC)

I remember answering a somewhat similar question on Usenet once... ah, here it is: "Boiling diamonds?" (The first link in the message is broken; the article it's supposed to go to, IIRC, is this one, but unfortunately the full text there is subscription-only. You could just Google for "phase diagram of carbon" instead.) —Ilmari Karonen (talk) 18:45, 28 November 2007 (UTC)

Or just see this article (Ghiringhelli et al., "Modeling the Phase Diagram of Carbon", Physical Review Letters 94, 2005). —Ilmari Karonen (talk) 18:52, 28 November 2007 (UTC)

Why doesn't lightning damage antennas when it hits them?

When lightning hits a tree, it can make it explode sometimes. But when it hits an antenna at the top of a sky scraper, no damage occurs. Why is this? 64.236.121.129 (talk) 21:33, 27 November 2007 (UTC)

Lightning is just electricity. When electricity flows through metals, it passes quite easily due to their low resistance. When electricity flows through a tree - the resistance is considerable - so a lot of electrical energy is lost - and converted to heat. Hence the tree gets very hot. If the tree has lots of sap, it may even boil - and when that happens, a lot of steam has to go somewhere in a hurry and KABLAMMO! (That's a scientific term :-) SteveBaker (talk) 21:43, 27 November 2007 (UTC)

So if lightning hits a person covered in salt water, it'll prolly kill him, but won't make him explode. But if he's wearing some thick coat, he might explode? 64.236.121.129 (talk) 21:46, 27 November 2007 (UTC)

Probably not. Humans are rather good conductors (mostly salt water all through), and they also do not resist expansion well enough for a good explosion anyways. Also, as far as I know (but I may be wrong), much of the current will travel along ionized air on the outside of a human. --Stephan Schulz (talk) 22:04, 27 November 2007 (UTC)

( edit conflict) Lightning is unpredictable. Sometimes it mainly flows over the surface, sometimes it does you like a Presto Hotdogger. Antennas often have a spark gap at the base of the mast consisting of two points (> <), one connected right to the transmission line, and the other to ground. The points are just far enough apart not to arc when transmitting, but close enough to arc when lightning strikes. See lightning, lightning rod, spark gap, and lightning safety.--Milkbreath (talk) 22:12, 27 November 2007 (UTC)

Since Lead is a poor conductor of electricity, what would happen if lightning hit a chunk of lead? 64.236.121.129 (talk) 16:47, 28 November 2007 (UTC)

All metals are "good" conductors. Silver, copper, gold, and aluminum are great conductors. Lead has no problem conducting in your car battery. Too, there's lightning, and then there's lightning. It can range in intensity from a piddling couple of million volts up to a billion volts or more. The snappiest strikes can melt a copper antenna no problem, but they are rare, and they tend to hit the mast instead of the antenna, anyhow, because the mast is grounded. I would expect a piece of lead of reasonable size to disappear in a puff of incandescent lead vapor with any decent strike. Lightning is scary stuff. --Milkbreath (talk) 17:05, 28 November 2007 (UTC)

The article on lead said that lead is a poor conductor of electricity. Did it just mean, compared to other metals? Also since it has low resistance, shouldn't it be unharmed by the lightning? I thought lightning only damages objects that have high resistance. 64.236.121.129 (talk) 17:37, 28 November 2007 (UTC)

Poor compared to other metals. Lead has an electrical resistance of 208 nano-ohms per meter. Iron is at 96 and Silver is 16. So, yeah - lead is a poor conductor compared to iron or silver. But take a typical non-metal like (say) Sulphur and it has a resistance of 2x10¹⁵ ohms per meter (that's 1026 times worse than lead!!) Compared to sulphur, lead is a spectacularly good conductor! SteveBaker (talk) 20:23, 28 November 2007 (UTC)

I just did some math, and if a lightning bolt carrying 300,000 amps of current passes through a lead stick one centimeter in cross-sectional area and one meter long, you get 189 million watts dissipated in it. That should be enough to turn it into plasma, don't you think? --Milkbreath (talk) 20:44, 28 November 2007 (UTC)

Don't you also have to factor in voltage? 64.236.121.129 (talk) 21:08, 28 November 2007 (UTC)

The voltage across the lead stick is determined by the current from the bolt; the current from the bolt is determined by the total voltage of the bolt (which doesn't depend at all on what you fire it through) and the total resistance in the bolt's path; the resistance in the bolt's path is almost entirely within the air, not the stick, so the stick has a somewhat negligable effect on the total current of the bolt. It might affect how much of that current goes in, across, or around the stick, but it won't really have an affect on the current (and thus, on the voltage across the stick). Someguy1221 (talk) 21:19, 28 November 2007 (UTC)

Right. All the current would probably go through the stick because its resistance is very much less than that of the air around it. As for the "voltage", power is calculated by P=IE (current times voltage). Algebra and Ohm's law let us do away with voltage if we know the current and the resistance, giving P=I²R. --Milkbreath (talk) 21:29, 28 November 2007 (UTC)

If lightning hit glass, it should shatter it right? But would it penetrate it, and hit whatever was behind it too, or would the glass stop the lightning from advancing further? 64.236.121.129 (talk) 17:43, 28 November 2007 (UTC)

The lighting will keep going until the current reaches the ground. As far as the lighting is concerned, the glass is just another, bothersomely-high-resistance medium to get through on its way to the ground, just like air and trees. --Chris, 20:48, 28 November 2007 (UTC) —Preceding unsigned comment added by 63.138.152.238 (talk)

Lightning is unpredictable. If it wants to go through glass, it will, blowing it to smithereens in the process, I suppose. Thing is, lightning follows a leader, and the leader wouldn't form through glass in the first place. --Milkbreath (talk) 20:57, 28 November 2007 (UTC)

I think the lightning strikes before the leader makes it all the way to the ground, and just arcs through the air. In any case, the lightning isn't going to just stop and have the ions sit next to the glass. — Daniel 02:23, 29 November 2007 (UTC)

I wouldn't say that lightning is unpredictable - it's HARD to predict - but it's not some magical thing, the laws of physics that it follows are well understood. I imagine that the kind of thing that'll happen with a window in (say) an aluminium frame - is that the lightning will be trying to find the lowest resistance path to the ground. That's not the glass - it's the frame - so the frame gets hit - a bazillion amps of current flows - and the frame duly melts, then boils in a very little amount of time. This heat will shatter the glass because it can't expand evenly enough - just as if you pour boiling water into a cold jamjar. As soon as the glass opens up a small crack - the lightning can head through (presuming there is a lower resistance route to ground inside than outside). Your bathroom window is probably next to some nice copper pipes that lead in exactly the right direction - so if your house got struck by lightning, this is a very possible outcome. SteveBaker (talk) 03:05, 29 November 2007 (UTC)

Lightning hasn't read those physics books you put so much faith in. It can hit a chicken standing on a rubber mat two feet away from a 300-foot-high grounded tower if it wants to. The underlying physics may be known, but real-world chaos makes the event unpredictable. --Milkbreath (talk) 03:38, 29 November 2007 (UTC)

That's nonsense - and you know it. "if it wants to"?!? It doesn't "want" anything - it's an application of field theory - and it most certainly follows the same laws of physics as the rest of the universe. If you set up an FEM model of the tower, the air and the chicken with the appropriate laws of physics built into your mesh and cycled it at a small enough time step, you'd be able to predict pretty accurately where any given lightning bolt would disperse to. It's not a chaotic system at all. Not all systems that are complicated are also chaotic (and not all chaotic systems are complicated) - that's a horrible misconception. People can and do model the behavior of lightning. My first job out of college was doing research into telephony systems - and there were people where I worked who calculated how a lightning strike on the telephone exchange would propagate out into the phone lines - and vice-versa. SteveBaker (talk) 04:21, 29 November 2007 (UTC)

Lightning is unpredictable not because it has volition. I'm not a voodoo witch doctor, in case you thought that. Not chaotic? Are you saying that there is a model for the progress of a leader through the atmosphere that can predict its path? That is absurd, and you know it. "According to my calculations, it will strike right over there", he declared confidently, only a moment before a rogue bolt leapt from a thunderhead 10 miles away and vaporized his pointing finger. --Milkbreath (talk) 11:51, 29 November 2007 (UTC)

I didn't say it would be easy to predict - you'd need some insane amount of data about the air on the way down - but it's not SENSITIVELY DEPENDENT on that data in a way that would make it chaotic. Maybe you need to read some more about chaos theory. Not all complicated, hard-to-predict things are chaotic. SteveBaker (talk) 14:10, 29 November 2007 (UTC)

Who said no damage would occur to an antenna from a direct strike? Induced currents can however be mitigated by connecting the mast to earth. I beleive this is normal practice in the professional and ham radio world. —Preceding unsigned comment added by TreeSmiler (talk • contribs) 03:46, 29 November 2007 (UTC)

Heres a link [11]--TreeSmiler (talk) 04:03, 29 November 2007 (UTC)

Theropod dinosaurs and birds

Only Theropod dinosaurs are considered to have evolved into birds right? Other dinosaurs like Sauropods and Cerapods aren't. Correct? Hmm, if this is true, can we consider Sauropods and Cerapods to be 100% reptiles, while Theropods to be part reptile, part bird?64.236.121.129 (talk) 21:37, 27 November 2007 (UTC)

We have an article on bird evolution about this. (And yeah it looks like theropods are considered their ancestors.) I don't know that the second half of the question is very meaningful- we lump things together as reptiles or birds because it's a useful classification. These classifications may be fuzzy around the edges. Friday (talk) 21:47, 27 November 2007 (UTC)

Of course it's meaningful, otherwise we wouldn't classify animals at all. 64.236.121.129 (talk) 21:54, 27 November 2007 (UTC)

We classify, and often reclassify as our understanding improves. Theropod classification is described in the article. They are considered dinosaurs, which are considered reptiles. Friday (talk) 22:03, 27 November 2007 (UTC)

Perhaps what Friday meant by "meaningful" was monophyletic, while your suggestion of some species being "part reptile, part bird" would be paraphyletic along the lines of saying something is "part fruit, part apple". --Sean 00:15, 28 November 2007 (UTC)

The sauropods almost completely died out before the Cretaceous, and the final species died out in the Cretaceous–Tertiary extinction event. Other interesting suborders are the ornithopods (bird-feet, with bird hips and duck bills) which also died out, and don't seem to have connection to modern birds besides analogous evolution. SamuelRiv (talk) 23:17, 27 November 2007 (UTC)

Sauropods didn't die out before the Cretaceous. Argentinasaurus lived in the middle of the Cretaceous for example. 64.236.121.129 (talk) 16:32, 28 November 2007 (UTC)

Why does Carbon nanotube have stronger properties than buckyballs?

They are made out of the same matter right? So why the differences? Would a buckyball have better compression strength due to its shape? 64.236.121.129 (talk) 22:00, 27 November 2007 (UTC)

Buckeyballs contain both hexagonal rings and pentagonal rings, whereas carbon nanotubes ideally contain only hexagonal rings. Hexagonal rings are significantly more stable, and thus require greater strain to break. Indeed, pentagonal rings of carbon are naturally under stress (see ring strain) already due to their non-ideal bonding configuration. Adding further to that, forcing carbon rings to form spheres or cylinders instead of sheets also strains the bonds, and I suspect this to be greater in a buckeyball than a nanotube. And finally, buckyballs aren't resonance stabilized, whereas nanotubes are. Someguy1221 (talk) 10:51, 28 November 2007 (UTC)

Is there any shape that is potentially stronger than a hollow cylinder, since a hollow cylinder is weak in compressive forces? 64.236.121.129 (talk) 17:39, 28 November 2007 (UTC)

I don't know much about that specific question, but it pays to be cautious when considering questions like this. It sounds like you're assuming that what's true on a large scale would also be true on a molecular scale, which is always a dangerous assumption. Friday (talk) 21:24, 28 November 2007 (UTC)

I'm well aware of that. 64.236.121.129 (talk) 20:38, 29 November 2007 (UTC)

When people talk about carbon nanotubes being strong, they're referring to tensile strength, not compressive strength. — Daniel 02:15, 29 November 2007 (UTC)

Yea, I know. They have terrible compressive strength because they are hollow cyclinders. It's naturally bad at compression. That's why I'm asking if there's a better shape to handle that kind of stress, while maintaining CNT's other strong properties. 64.236.121.129 (talk) 20:38, 29 November 2007 (UTC)

How come the buckyballs aren't resonance stabilized? Don't they also have delocalized electrons like the tube or graphite? – b_jonas 16:03, 29 November 2007 (UTC)

How much would someone weigh on mount everest

I weigh 130 pounds and for science class i need to know the formula to calculate how much i would weigh on the summit of mount everest? Any Help???? —Preceding unsigned comment added by 71.219.144.66 (talk) 22:23, 27 November 2007 (UTC)

See Newton's law of universal gravitation RJFJR (talk) 22:28, 27 November 2007 (UTC)

On Mount Everest, your weight will not change much. You will weigh the same as much you weigh here. Though, if you want to be more precise, the value of 'g' will slighly change, because distance between you and the centre of earth has increased, but this will be very insignifacnt because radius of earth is much more than the additional 8 KM that you would add if you reach Mount Everest, so there is not much difference in your weight here and on mount everest. However, your weight will drastically change, if you reach moon. The reason is because of the difference in radius and mass of the moon, that account for your weight on its gravitational field. For further clarification, read article posted by RJFJR and other related articles. DSachan (talk) 22:37, 27 November 2007 (UTC)

If you really want to be pedantic, you can try adding another quite small term for the gravity caused by Everest itself. Historically, trying to directly measure the gravity of mountains was one of the methods used when attempting to quantify Newton's constant, G. Dragons flight (talk) 23:02, 27 November 2007 (UTC)

A gravity map of earth's surface I found here, suggests that the large mass of earth beneath you largely outweighs the decrease in gravity caused by the altitude gain. So you would weigh more on everest then somewhere else. 71.214.181.11 (talk) 03:52, 28 November 2007 (UTC)

Actually, you are misinterpreting a poorly explained graphic. What that shows, I'm virtually certain, is the gravity anomaly from "normal" gravity that general models would predict for each particular latitude and elevation. Not variations is the acceleration of gravity in an absolute sense; not variations from some constant value. These anomalies are much smaller in magnitude than the variations with latitude and elevation. Gene Nygaard (talk) 15:49, 29 November 2007 (UTC)

See Earth's gravity#Altitude (Why doesn't this link work right?). --Milkbreath (talk) 22:43, 27 November 2007 (UTC)

Corrected your link for you. (EhJJ) 22:56, 27 November 2007 (UTC)

For the purposes of your science class: the fact you need to know is that gravity decreases in strength in proportion to the square of the distance you are from the center of gravity of the source. So - your weight at sea level is proportional to one over the radius of the earth squared. Your weight at some altitude is proportional to one over the radius of the earth at sea level PLUS your altitude - all squared. We can lose the annoying constants of proportionality by dividing one equation by the other. Hence your weight at altitude A as a percentage of your sea level weight is: 100 x R²/(R+A)² - so go to Earth and look up the radius of the earth, go to Everest and figure out it's height - get the percentage increase and add that to your present weight. Problem solved.

BUT: We have to whine and complain a bit - because this is the reference desk and we all want to show how complicated things really are! So:

• The earth isn't spherical. It's an oblate sphereoid. You might think this is negligable - but the difference between the polar radius and the equatorial radius is about 20km. Everest is less than 9km tall. So the weird shape of the planet has more to do with where you are in latitude than where you are in altitude!
• The mass of mount everest itself is not negligable. Normally one may assume that the center of gravity of a spherical body is at it's center. But not so when you are standing really close to a GIGANTIC chunk of rock. So while your altitude will reduce your weight a bit...the mass of Everest itself will increase it some. Is this negligable? I don't know and I can't be bothered to work it out.

SteveBaker (talk) 01:04, 28 November 2007 (UTC)

"Increase", I like that.

A really complete, nitpicky solution would also allow for the variation in one's weight with latitude, due to the Earth's rotation.

On the other hand, a counter-nitpick is that if the initial weight is given as "130 pounds", it's a number with only two significant digits and therefore the answer should be rounded o the same precision. In which case it's going to be 130 pounds.

--Anon, 02:54 UTC, November 28, 2007.

I think that the amount of mass underneath a mountain should be about the same as the amount of mass under non-mountain areas, because the crust floats on top of the mantle, so as with all things that float, the crust must displace its equal weight in the underlying mantle. So if the mountain were not there, it would be filled with the same weight of mantle. --Spoon! (talk) 11:59, 28 November 2007 (UTC)

This is true only on the large scale (e.g. ~100 km or so), on the moderate to small scale, the crust is rigid enough to support local anomalies (i.e. mountains) that deviate from bouyancy. That is what the gravity map that an anon linked above is getting at. Dragons flight (talk) 17:50, 28 November 2007 (UTC)

The gravity map was made by a pair of satellites. It doesn't depict the gravity at the elevation of the ground - it measures it at the altitude of the satellite. So it's not taking account of the altitude of the mountains at all. Hence we don't know (without knowing what the colours on that map mean numerically - and doing some more math) whether the effects of the mass of mountains outweighs (hehehe!) the effects of their altitude. SteveBaker (talk) 20:16, 28 November 2007 (UTC)

An even bigger but than Steve Baker's above: But for real-world purposes such as the medical sciences and sports, in contrast to his "for purposes of your science class", your weight on Mount Everest is the same as it is anywhere else: 130 lb, or in the units used for this weight throughout the world including many hospitals in the United States, 59 kilograms. Gene Nygaard (talk) 14:06, 29 November 2007 (UTC)

I also find it rather strange that so many teachers would choose to try to make a point about the strength of the gravitational field, involving that jargon meaning of the word "weight". It is Mount Chimborazo which is the highest mountain on Earth in both ways relevant to this question, something like 2,000 meters farther from the center of mass of the Earth, and hundreds of kilometers farther from the axis of rotation.

Reminds me of an example Aviation Week used to have on their aviationnow.com website (apparently lost in reorganization), concerning the "weight" in the physics jargon sense (even though they used kilograms for the units of this weight, and the kilogram-force is no longer an acceptable unit) of an elephant at the Denver Zoo and at the San Diego Zoo. Problem is, they got it all wrong. An elephant of the same mass will exert more force due to gravity at the Denver Zoo than at the San Diego Zoo, not less. The author of that piece, like the teachers who use Mount Everest as an example, failed to understand the simple fact that latitude is a more inportant factor in this regard than elevation above sea level is. Gene Nygaard (talk) 14:21, 29 November 2007 (UTC)

November 28

Nasal cauterization

When I was quite young I underwent a few treatments of nasal cauterization. I don't remember much about them except that they turned my nose a deep shade of purple that needed to be washed off later (?). What method of cauterization was this? Would it have hurt? (I don't remember—I was quite young, just the purple nose remains in my memory and the notion that it was cauterization of some sort.) --24.147.86.187 (talk) 04:52, 28 November 2007 (UTC)

Its all a bit vague, but here's some possibilities:

1. The purple stuff was an antiseptic, not a cautery agent
2. Whatever the purple stuff was for, the only thing I can think of that might fit the description is potassium permangenate (KMnO₄). Once upon a time it was used as an antiseptic agent, and as I recall it also has some caustic properties, and so may have been used as a chamical cautery agent.
3. Chemical cautery is most often performed with silver nitrate (AgNO₃). Phenol is another popular agent. Not usually very painful.
4. Electrocautery is painful.
5. Cryocautery is only mildly painful
6. If the method they were using was considered painful, its more than likely they used some local anaesthetic prior to the procedure.

Mattopaedia (talk) 05:59, 28 November 2007 (UTC)

So mine is electrocautery eh? Unanaesthetised it felt someone's trying to poke a hole through the middle of my nose. --antilived^{T | C | G} 10:57, 28 November 2007 (UTC)

Also, silver nitrate is a lovely shade of grey, but might conceivably look purplish depending on your skin colour and your memory. Check out this picture; I could see someone calling that "purple". Matt Deres (talk) 11:53, 28 November 2007 (UTC)

I am not a doctor, but I've been used/abused/experimented on by many. Many invasive procedure (meaning that you've been opened some place you shouldn't be open, or that they are going to open you, etc) start with "Scrub area thoroughly with Iodine solution". Betadine is a common brand for such. The solution is a reddish-brown, and under some light, it might look purple. -SandyJax (talk) 15:52, 29 November 2007 (UTC)

Electrochemistry

what is the difference between Formal and standard reduction potential? —Preceding unsigned comment added by 59.163.146.11 (talk) 11:22, 28 November 2007 (UTC)

Standard reduction potential is the reduction potential at 25^oC, 1M concentration of both anion and cation. Formal reduction potential is the actual reduction potential at whatever specific conditions you're concerned with. Someguy1221 (talk) 15:23, 28 November 2007 (UTC)

Brain activity: reading vs TV

What are the differences in active areas of the brain or general brain activity between watching TV and reading a book/article? Have McLuhan's hot and cold medium any basis in brain activity as I think he claims? What are the resulting differences between watching TV or reading for 4 hours a day? Keria (talk) 12:29, 28 November 2007 (UTC)

• The brain has different centers for processing images and text. Each activity thus stimulates a different part of the brain, though invariable there will be some overlap. - 131.211.161.119 (talk) 14:47, 28 November 2007 (UTC)

whey protein

I wasn't sure if this should go in science or misc., but here goes: How many servings of whey protein should I have a day? When should I take it (morning and night, before working out, after, etc.). Should I drink it every day, or just the days I work out? All help would be greatly appreciated. --MKnight9989 13:51, 28 November 2007 (UTC)

The answers to your questions could depend on a number of factors, such as your age, gender, current diet, exercise regime, training goals, medical conditions, etc. Your best bet is likely to speak with a physician, dietician or athletic trainer. Our article on whey protein also has several external links which may be able to provide some insight. (EhJJ) 14:36, 28 November 2007 (UTC)

I'll probably ask my doc, but I'm 17 and weigh approx. 140lb. I want to be reasonably strong (I'm enlisting in the USMC after highschool, so I want to be able to survive boot camp), but by no means do I need to have arms a foot in diameter. I usually take in 2000-3000 Calories a day. --MKnight9989 14:45, 28 November 2007 (UTC)

I'm sorry if I gave you the impression that we would be able to answer your question if you gave us more information. Rather, at the Wikipedia Reference Desk, we can not give you medical (including dietary) advice. We are usually more than happy to aid your understanding of a concept or interpret information that you do not understand (in fact, one of the main reasons this reference desk exists is to find which Wikipedia articles need improvement), but we can not give you regulated advice. Essentially, think of us as volunteers at your local library. I would never even think of asking my librarian for medical, legal or (perhaps especially) body-building advice (I've never met a "built" librarian, but they could be out there). Some of us may be doctors or lawyers (I, for example, am a medical student), but law (and Wikipedia policy) prohibits us from giving you medical or legal advice online. Good luck! (EhJJ) 20:17, 28 November 2007 (UTC)

We may decide not to answer the question, but whether we do or not, it won't be because it's medical advice, since it involves neither diagnosing nor treating a medical condition. Perhaps we should simply change our prohibition to "we don't give advice". - Nunh-huh 20:20, 28 November 2007 (UTC)

As far as I'm concerned, you or anyone else is free to tell him whatever you'd like, but I wouldn't listen to it relating to my personal health. Do you know how tall he is? What if I told you he's 4'10" and 140lbs. Is your advice different from 6'2" and 140lbs? What if he has phenylketouria or any number of other health conditions? Now, I have no problem providing information but I don't feel comfortable providing specific instructions to him. That said, I did point him to our whey protein article and it's external links plus said that he's probably best of talking with a trainer. Was there something wrong with that? (EhJJ) 21:31, 28 November 2007 (UTC)

No, the only thing you've done wrong is suggest that advice on nutritional supplements is medical advice. If it were, thousands of health food store clerks would be in shackles. Not all advice with medical implications is "medical advice". - Nunh-huh 22:37, 28 November 2007 (UTC)

Well, I hope it's OK to direct you to the National Institutes of Health's recommendation, contained somewhere in here. I don't think it specifically mentions whey protein, but it's the amino acids that are important. Someguy1221 (talk) 20:51, 28 November 2007 (UTC)

Chemicals Released while burning...

Hi,

I have read through your articles about Chrome and Nickel Plating, they helped answer my question on how plating is done and the chemicals involved therein but the one thing I have not yet found out is if there are any chemicals (especially piosonous ones) released when an item plated in either Chrome or Nickel is burnt in an open flame. For instance a grill on a fireplace/Barbecue. The companies that I have spoken to that do the plating say that although they have never done any tests themselves they do plate for a certain brand of Barbecue and have never heard of any issues.

Your assistance is much appreciated, Tyron —Preceding unsigned comment added by 41.243.189.182 (talk) 14:01, 28 November 2007 (UTC)

Chrome or nickel plating is safe enough for cooking on even in an oven or barbeque. The chemicals used in plating are toxic, but of your new product is well made and washed it should be safe for cooking. There would be limits to a safe temperature to heat it to, and once the grill is left outside and it rusts, the plating could come off in sharp fragments that will be nasty to eat. Graeme Bartlett (talk) 20:10, 28 November 2007 (UTC)

In terms of toxicity, I would care far more about soot from the fire. Icek (talk) 20:46, 28 November 2007 (UTC)

Do you know what the temperature limit that it could be burn to would be? As an open flame can reach at least 400°C. Jet (talk) —Preceding unsigned comment added by 41.243.189.182 (talk) 05:59, 29 November 2007 (UTC)

The articles Chrome plating and Electroless nickel plating might be of help. shoy (^words _words) 17:13, 29 November 2007 (UTC)

N-glycosylation

Can someone point me to one or more methods I can use to identify the sugar residues on the N-glycosylation sites of a viral protein? I considered using specific enzymes (endo-proteases?) to cut the outer residues in order to find out the attached sugars, but that would be quite a laborious process. Has anyone got a better idea? - 131.211.161.119 (talk) 14:45, 28 November 2007 (UTC)

Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-TOF) is one such technique. 142.20.217.152 (talk) 22:01, 28 November 2007 (UTC)

How would I know which masses are from the protein and which ones come from the glycans? Would this mean a lot of preparation to obtain a suitable sample to put in the mass spec? - Mgm|^(talk) 23:11, 28 November 2007 (UTC)

There are many published articles that describe methods for analysis of oligosaccharides such as this one. One approach is to use a glycosidase to cut off the oligosaccharides and then use some form of chromatography to isolate the oligosaccharides prior to mass spectrometry. --JWSchmidt (talk) 00:37, 29 November 2007 (UTC)

• I'm not sure why this article didn't show up on my pubmed search, but at first glance it appears to be just the sort of thing I'm looking for... Thanks to both of you for your input. I'm still open to more ideas, though. —Preceding unsigned comment added by 131.211.161.119 (talk) 08:30, 29 November 2007 (UTC)

Thermodynamics of heating your house

What's more energy efficient?

• turning the heat down to 58ºF every evening and turning it back up to 68ºF in the morning
• not turning it down too much so that it doesn't have to re-heat the whole house from scratch every morning

This is a practical question of mine. Basically we have the heating set to go down to 58ºF every evening starting at 10PM, and then at 6AM it is set to rise back up to 68ºF. Is this an optimal way to do things (assuming that we want it at 68ºF during the day and not freezing at night)? It seems like it has to do a lot of work in the morning to raise the temperature again—is it better to keep the temperature a bit higher so that it doesn't have as much work to do? Is there a more optimal heating solution? Surely one of you science geeks will have a good answer for this. ;-) And though I know it sounds like a textbook homework question, it isn't—I don't do homework anymore, thank goodness. --24.147.86.187 (talk) 15:27, 28 November 2007 (UTC)

If you have a very simple furnace, it will necessarily require more energy to keep the house warm at night than to cool it up in the morning. Over the course of the night, the house will release, say, X units of heat into the environment when the furnace is off. So the furnace has to generate X units of heat during in the morning. If you leave it on at night, the house will initially be losing energy at the same rate. But hot things lose heat energy faster than cold things (my simplest way of putting Newton's law of cooling), so the house will lose more than X units of heat over the course of the night, so the furnace will have to generate more energy overall to keep the house warm. This could be complicated by a furance that can run at multiple "speeds" as with many new gas furnaces. Such a furnace would have a different energy efficiency for the two situations (ie, it would waste a different percentage of energy heating a warm house or a cold house). Someguy1221 (talk) 15:39, 28 November 2007 (UTC)

Interesting. Well, it's not a new furnace at all (it is quite an old boiler) so it is probably the case that turning it down and up again in the morning is the better approach. Sigh. --24.147.86.187 (talk) 03:33, 30 November 2007 (UTC)

Trust the mass on a bottle label?

I often purchase small amounts of relatively pure chemicals, usually 50mg or so. I need to make solutions of these chemicals at a known concentration. The thing I have never been sure about is whether chemical supply companies take care to put as close as possible to 50mg (or whatever is on the label) into the bottle. You see, life is easier if I can assume that the right amount is in there, and I can add water directly to the bottle to disolve it and make my solution. If I have to transfer it, inevitably I won't be able to recover some from the bottle or the weigh paper, and additionally my balance isn't the best. What do you think, is the stated mass very close to the actual mass in the bottle? ike9898 (talk) 15:31, 28 November 2007 (UTC)

It's going to depend, a great deal, on the particular product and the particular supplier. Usually you won't be getting shortchanged, but the margin over and above the label amount can vary. How precisely do you need to know the quantity and concentration? Is there some sort of assay you could perform (spectrophotometric, etc.) on the stock solution to determine its concentration to an acceptable precision? TenOfAllTrades(talk) 17:12, 28 November 2007 (UTC)

Concurred with TenOfAllTrades: customers would make a hell of a noise if they often found themselves paying for something that wasn't all there. When you say you "need to make solutions of these chemicals at a known concentration", does that mean you have to hit a pre-set (specific) concentration, or you need to be near some value and also know exactly what it is? The latter is much easier, since you can make and then assay. Or else you could weigh the full bottle, then dissolve in the bottle (so you don't lose material) and transfer into another container. Wash the bottle, reweigh it, and now you know the tare and hence the exact (to your instrumental ability) amount of stuff in the solution (you lose a diluted drop or two rather than a few grains of pure material). DMacks (talk) 17:32, 28 November 2007 (UTC)

I wouldn't be able to assay afterwards because this solution is supposed to be the analytical standard. I like the idea of weighing the bottle before and after. ike9898 (talk) 18:53, 28 November 2007 (UTC)

I suppose this goes without saying, but if you're getting your chemicals from a single supplier, you probably only have to weigh one bottle once and then use that as your tare in the future. Obviously, that would depend on how accurate you need everything to be, but if it was essential, I'd presume you'd have a more precise scale for weight and not need to ask! Matt Deres (talk) 02:40, 29 November 2007 (UTC)

The mass of small reagent vials from the same lot usually vary on the order of a few milligrams unless they are specifically matched. ike9898 (talk) 15:04, 29 November 2007 (UTC)

Power lines, and electric shock

If you put one hand on a power line, you won't get shocked right? If you put two hands on the power line you still won't get shocked right? But if you put your two feet on the power line, then put your hands on another power line parallel to it, you will get shocked then right? 64.236.121.129 (talk) 16:37, 28 November 2007 (UTC)

You can get a shock from touching one power line, if you're in good electrical contact with the earth ("grounded"). -- Coneslayer (talk) 16:44, 28 November 2007 (UTC)

What if you are standing on a brick? 64.236.121.129 (talk) 16:49, 28 November 2007 (UTC)

It depends on the electrical conductivity of the brick. I would guess that that might depend on whether the brick is damp. -- Coneslayer (talk)

Don't most shoes have rubber soles? Wouldn't that prevent grounding? Also if you are hanging from the powerline what would happen if you were hanging from one hand, and two hands. 64.236.121.129 (talk) 17:01, 28 November 2007 (UTC)

Also aren't powerlines covered in some kind of rubber usually? Wouldn't this prevent shock? 64.236.121.129 (talk) 16:50, 28 November 2007 (UTC)

According to Overhead powerline#Conductors, most overhead power lines are uninsulated. -- Coneslayer (talk) 16:56, 28 November 2007 (UTC)

You should certainly consider them to be uninsulated, even if they might be insulated. The power company guys certainly think this way: the only time they think it's safe to touch a power line is after they've clamped big grounding cables onto it and proven that the line is then grounded. Before that, they strictly do all their work with their hot stick.

Atlant (talk) 17:56, 28 November 2007 (UTC)

Oh, look: we didn't have an article on hot stick yet. I've stubbed one out; help me fill it in! (And somebody tell Rockpocket.) —Steve Summit (talk) 01:33, 29 November 2007 (UTC)

You ONLY Get shocked if you bridge the gap between two large differences in voltage. One hands or two hands or one hand and one foot on the same power line will have NO result, as long as no other part of your body is touching something else with different voltage potential like the Earth, another power line, etc. Shoe rubber is a fairly unreliable insulator, unless you are wearing something specifically designed to protect you from shock. Disclaimer: DO NOT TRY THIS AT HOME TO PROVE ME WRONG --Jmeden2000 (talk) 17:55, 28 November 2007 (UTC)

This is where I get confused though. The current is still passing through you if you are touching the power line with limbs touching the same power line right? Or... maybe it isn't. So how come a bird doesn't get shocked by this, but a bird can get shocked by a lightning bolt hitting it, when it is flying, and isn't grounded. 64.236.121.129 (talk) 21:16, 28 November 2007 (UTC)

If you were made of aluminum, you'd have a problem. As it is, though, your resistance hand-to-hand is about 50,000 ohms. So, worst case, if you stretch out your arms and grab the line, your 50,000 ohms will be in parallel with about a meter of aluminum as thick as a pool noodle at roughly zero ohms. I wouldn't advise doing that, though, because I'm not sure what role skin effect plays at very high voltages in a case like this. I'd keep my hands close together. I think you'd feel the induced current from the 60-cycle (or 50) field as an unpleasant whole-body sensation if the voltage was high enough.

When a bird is hit by lightning, it's because it was unlucky enough to have been in the path of the leader when it flashed over. The bird becomes part of the conductor, which is a line of ionized air between the cloud and the ground or between two clouds. --Milkbreath (talk) 00:53, 29 November 2007 (UTC)

Power lines (the high voltage ones at least) do not have electrical insulation because electrical insulators also tend to be good heat insulators and it's essential that these lines remain cool. They also have to remain flexible and there are a bunch of other constraints on them that make insulation impractical. SteveBaker (talk) 19:53, 28 November 2007 (UTC)

(edit conflict) Read Ohm's law and alternating current. They are pretty straightforward, but alien to everyday affairs. Once you get them under your belt, you can answer these questions yourself.

Whether you get shocked or not touching a bare conductor will depend on many things, principally the voltage. High-tension lines can have more than million volts on them. The rule of thumb for arc distance in dry air is 10,000 volts per inch, so a million volts will jump 100 inches, or about eight feet. If something more conductive than air enters that zone between a high-tension line and ground, like YOU, for instance, the arc will see you as a shortcut to ground and use you as part of the path. Think how cool you'll look with a blue arc as big around as your arm entering the top of your head and incinerating your Air Jordans on the way out. Your wafer-thin shoes would present no obstacle to that kind of power. Even the best insulator has a breakdown point, and the current would be able to pass through the air around the soles, too.

Another thing is that even if you could approach a million-volt line without being near ground, like in a balloon, the line is going to want very much for you to be at the same potential as it is, and it won't wait for you to touch it to accomplish that. The power line repair guys use great big gloves and a long wand to draw the arc that causes, mostly because they want to live through the experience.

A lot of things are dangerous, but you can get away with messing with them sometimes. Bears, for instance, or ex-girlfriends, or cliffs. Electricity has its own agenda and its own rules, and you get one chance not to screw up. --Milkbreath (talk) 20:02, 28 November 2007 (UTC)

A bird can perch on an uninsulated electric wire and not get shocked, because no current flows through it, because there is no place for the current to flow to.

An ungrounded human can do the same, for the same reason.

There are several ways a human can be ungrounded:

• being in a balloon or helicopter
• jumping in midair
• wearing rubber-soled shoes (though as noted above, their insulating properties vary)
• standing on something insulated, like a wooden bench (though again, the insulating properties vary)
• standing in the basket of an insulated-boom cherry picker

And, there are also several ways for a human to be grounded, and these are why electric shocks are possible (and rather common, among the careless):

• being barefoot, especially while standing on concrete or in water (or on a brick)
• accidentally touching something else grounded, like a water pipe
• being in a bathtub
• accidentally touching someone else who is grounded

And, not only do the insulating properties of various materials differ, but the amount of insulation you need obviously depends on the voltage you're worried about. For "ordinary" household voltages, you can engage in risky behavior and not get electrocuted too much of the time, because (for example) a good pair of tennis shoes will usually withstand 120V. (Although I'm not sure about the 220V that's common in Europe. Can you tell there's some OR here?) But when you get up into the high hundreds of volts or more, the rules are rather different, and unless you know exactly what you're doing and are very careful and use all the right equipment, you can easily get not only a lethal shock, but also electrocute innocent bystanders who try to rescue you by grabbing your energized carcass, or incinerate them in the fire your charred carcass starts.

Finally, there's the matter of inrush current. Even if you're perfectly ungrounded, when you touch an energized wire, there's a relatively small, instantaneous flow of current which brings you up to the potential of the wire. The bigger you are, and the higher the voltage is, the larger this current is. So I think there's a voltage at which the birds are fine, but a human would get a painful (if not fatal) shock from the inrush current. —Steve Summit (talk) 00:13, 29 November 2007 (UTC)

Future of Everyday Travel

Is there a reasonable possiblity that there will be Sky Highways in next 30 years? Meaning flying cars or hover crafts. Is it possible to use solely solar power to fuel these crafts or that would be impossible? --WonderFran (talk) 16:47, 28 November 2007 (UTC)

It's another one of those things where when engineers say "It'll be here in 5 years", it'll probably be here in less. When they say "It'll be here in 20 years" they mean "I have no idea at all when it'll be here - if at all". So, yes, we'll have sky highways within 20 years!

But seriously - the fuel requirements for a flying vehicle are unlikely to ever be as good as they are for a ground vehicle - because you have to generate lift as well as overcome friction and drag. With the pressure to make more fuel-efficient transport, using flying vehicles seems wasteful. Having said that, the ability to travel in a straight line to your destination, the fact that there is more space up there (so no traffic jams) could override that - and I suppose we could get our lift from balloons instead of using motors.

There is also the safety issue. If you have a fender-bender - or any kind of an accident at 30mph on less - or if your car craps out on you on the freeway - you aren't going to die. You'll probably walk away without a scratch. At 10,000 feet, any problem at all will probably be fatal. The people who are building these things say that they'll have multiple redundant engines and that kind of thing - but I've seen cars on the road with TWO of those 'skinny spares' on them driving at 70mph! I've met people who actually wore out a skinny spare bald because they drove on it for 10,000 miles! What happens when your flying car is that poorly maintained?

As for solar power - there simply isn't enough area on the roof/hood/trunk of a car to capture enough energy to propel it through the air at the kinds of speeds that we are used to. The best solar cars go slowly and have interiors that are stripped down to basically being bicycles with supports for the solar panels. No amount of clever engineering can cover for the fact that there simply isn't enough area. Then what about driving in overcast conditions - or at night? At best, you might have a 'Solar Hybrid' that runs on batteries that can be recharged from the sun with a gasoline or hydrogen engine as a backup.

But I doubt we'll see flying cars in our lifetimes. SteveBaker (talk) 19:50, 28 November 2007 (UTC)

The NASA Pathfinder could fly on solar power, and the Zephyr could even store enough energy to fly through the night (but they had to strip out the pilots to make them light enough, though). Maybe Solar Impulse will change that, but I'm not sure if this will ever be, well, safe (or economical, or not a pain in the ass). And in addition to all of the speculations on what fantastical yet-to-be-invented-inventions we'll all be using in the future, remember that it was once speculated that there'd be an autogyro in every American garage by now. Someguy1221 (talk) 20:31, 28 November 2007 (UTC)

Well, yes - but you wouldn't describe an amazingly flimsy plane with a wingspan bigger than a Boeing 747 and a top speed similar to a bicycle that can only fly in calm air with no rain as "practical"! There is a really fundamental problem here - in order to have enough solar cells, you need HUGE wings. In order to get off the ground with so little power, the plane has to be super-lightweight. Super-lightweight with HUGE wings means two things: Obviously, it's going to be very, very fragile because you can't afford the weight to make it strong. Secondly, it's going to have a very low "wing loading" and planes with low wing loading are extremely vulnerable to turbulance. These are not characteristics you want for a mass-produced civilian plane - but what's the alternative? Even 100% efficient solar cells wouldn't gather enough power to do this properly - so there is a really fundamental limit. Increasing the area increases the weight - but increasing the weight increases the power requirement which forces you to increase the area. There is no way out of that! SteveBaker (talk) 21:43, 28 November 2007 (UTC)

I'll just maintain that "pain in the ass" = um, all of what you just said ;-) Someguy1221 (talk) 21:56, 28 November 2007 (UTC)

I agree - but some things are just not meant to be. There is this blind faith that science can always improve things and make magic happen - but sometimes there just isn't. We MIGHT someday make solar cells that are 99% efficient and we MIGHT make stronger, lightweight materials - but the wing-loading issue is still there as is the fact that it's never going to fit into an urban environment with 200' wings. These are all pretty fundamental problems that put practical solar powered cars and aircraft permanently out of reach. Sadly, these incredibly flimsy machines give the public an altogether different idea - which is a shame. 100% computer controlled (but gas-guzzling) helicopters are probably the closest we'll get to flying cars - and those are going to ALWAYS be a lot more expensive than a mere ground-car - and given that we need to be driving fuel consumption DOWN, not UP, that's not a smart way to go. Perhaps hydrogen-filled, hydrogen-fuelled, mini-zepplins might work. SteveBaker (talk) 22:16, 28 November 2007 (UTC)

A minor nitpick: According to the second law of thermodynamics, solar cells are not going to be more efficient than 96% (the temperature of the solar radiation is about 5780 K, the ambient temperature for an aircraft at least about 220 K). Icek (talk) 22:38, 28 November 2007 (UTC)

Solar cells are not heat engines. The Carnot efficiency limit does not apply. There are technical and physical challenges to achieving high efficieny, but that is not one of them. Dragons flight (talk) 01:36, 29 November 2007 (UTC)

Eh - I think you are both wrong. Or maybe you are both right...I'm not sure which! The second law doesn't only talk about heat - it actually says that you can't convert 100% of heat into work - which includes electricity - so the second law definitely says you can't be 100% efficient...or at least it would apply if solar cells converted heat into electricity - but they don't. What solar cells are doing isn't converting HEAT into electricity - they are converting LIGHT (electromagnetic waves) into electricity. Photons knock electrons out of the silicon. However, they certainly can't be 100% efficient. Some photons pass right through the silicon, some reflect off the surface, others don't have enough energy to produce an electron so they turn into heat. SteveBaker (talk) 04:04, 29 November 2007 (UTC)

The Carnot efficiency limit does apply. Else I could simply surround the heat source usually used in my Carnot engine with a vacuum and solar cells. Light does have a temperature. If it's monochromatic, the temperature is zero, being analogous to mechanical energy. If it has a Planckian spectrum, it has the according temperature. Icek (talk) 11:45, 29 November 2007 (UTC)

Temperature (yes, sort of), but it's not a closed system. The Carnot limit is a statement about entropy conservation in closed systems. Not to mention that at no point is the solar cell in thermal equilibrium with sunlight anyway (compare to the cycle of a heat engine where the operating fluid itself varies in temperature from the high to low temperature). Yes, there are physical limits to the efficiency of solar cells. Some even relate to temperature (e.g. the spontaneous recombination of electron-hole pairs), but a solar cell is simply not a heat engine. Dragons flight (talk) 16:37, 29 November 2007 (UTC)

The Carnot limit only needs a warm reservoir - the incident radiation (or the surface of the sun if you like to view it like that) - and a cold reservoir - the surrounding air or whatever; no closed system is needed. It's a very general statement about entropy, and does not depend on the details of the energy conversion, as far as we know. A relevant Wikipedia article: Exergy. Icek (talk) 17:56, 29 November 2007 (UTC)

I think the Carnot efficiency applies, but not quite in the way you suggest. Solar radiation at the Earth's surface is actually more like 100°C: that is, an object at that temperature cannot be heated by sunlight because it emits as much radiation as it could absorb. However, radiation that is streaming in a particular direction (rather than suffusing an enclosed space) cannot be said to be in thermal equilibrium with itself (because it does not have appropriately random velocities), so it does not have a true thermodynamic temperature. This is good: it means that the Carnot restriction only operates on the source temperature, and we get your 96% number instead of something pathetic like 17%. But I'm not entirely sure that Carnot applies at all; a heat source in a vacuum is also not in thermal equilibrium (because it has not equilibrated with the vacuum), so it may have more free energy than the corresponding equilibrium situation with the same "temperature" (of the object). --Tardis (talk) 18:26, 29 November 2007 (UTC)

How did you come up with 100 °C? The greenhouse effect can occur in macroscopic solid objects as well, and I doubt that you couldn't get more than 100 °C. Anyways, that's beside the point, the solar radiation does in no sense have such a low temperature. I don't quite get what you are trying to say: Even if a solar cell was enclosed within a sphere or bubble of gas of a temperature of 5780 K, the solar cell would work as long as its temperature is kept low enough. Icek (talk) 22:24, 29 November 2007 (UTC)

SteveBaker made some excellent points about efficiency, but there's more than just that. Flying cars exist; and if you paid me enough I would design a custom one for you. But most flying cars still need to take off from airports. How are you going to get to the airport? For a flying car to be practical it would have to be VTOL, that is, take off vertically from the top of your house. This adds considerably to the complexity of the aircraft, and therefore its costs. It also takes a lot of energy to take off vertically. And the safety concerns addressed above also are important: if a car's electrical system totally craps out, meaning the spark plugs aren't firing, the driver can pull to the side of the road. General aviation aircraft with internal combustion engines have totally redundant systems: dual magnetos with dual spark plugs in each cylinder, completely independent of one another. This is true of every system in an aircraft; safety through redundancy. It makes them very expensive. You could buy a flying car, and afford to operate it, if you were filthy rich, but in order to have an air highway system lots of people would have to be able to afford it. moink (talk) 02:50, 29 November 2007 (UTC)

Ok it wouldn't be as Zipadidooda but mini Zeppelins are relatively safe and fuel efficient, no zipping around though. Keria (talk) 09:20, 29 November 2007 (UTC) Maybe a blimp is a more appropriate term. Keria (talk) 15:32, 29 November 2007 (UTC)

The difference between a blimp and a zepplin is that the zepplin has a rigid structure where a blimp is held in shape purely by the pressure of the gas. The original name "blimp" comes from a British term for a particular kind of barrage balloon (designed to prevent enemy planes from flying low over cities) called a "B-type Limp Balloon" (limp as opposed to rigid). This got shortened to "B-limp" and the rest is history. I wonder what became of the Alimp?

Anyway - the cool thing about hydrogen as a lifting gas is that it's cheap, renewable and provides more lift per cubic meter than helium. You can also use it to fuel your motors - so you have this ENORMOUS gas tank and as you consume it, you are forced to gradually lose altitude such that you are always on the ground LONG before you run out of fuel...a handy built-in safety thing since a Blimp without engine power can be exceedingly dangerous! But more interestingly, the fact that you'd continually be using and replenishing your lift gas would go a long way to avoiding the key problem with hydrogen balloons - which is that oxygen can slowly diffuse into your tanks and if too much accumulates: KABOOM! With care, that could be completely avoided here since you can consume hydrogen AND the dissolved oxygen in your engines and always refill with pure hydrogen - so the oxygen levels can never build up to a dangerous degree so long as the vehicle is used reasonably regularly. A practical machine would use hydrogen fuel cells to make electricity and use electric motors to drive the thing around. When you "park" it at home, sensors could monitor the oxygen levels and when they approach the danger level, start the hydrogen fuel cells to consume it safely - putting the 'spare' electricity into your home or back into the electrical grid.

The huge problem is the size of the things and the top speed. Unless we're going to have HUGE parking lots - we'd need ways to tether and stack them. Also, 'runaway' blimps would be a serious matter in strong winds. SteveBaker (talk) 20:44, 29 November 2007 (UTC)

What happens during the cooking process (and what are those black bits)

So when you slap a piece of meat on the grill, it usually comes off the grill in some shade of brown, with black lines wherever it touched the grill. My general understanding of what happens when stuff is heated up is as follows:

1)various condensation reactions occur, releasing water 2)H2 gas comes off and burns, leaving unsaturated carbons behind. (this is why aromatic/carbon-rich compounds give a sooty flame - there isn't enough H2 given off to facilitate the burning of the carbon itself)

My theory is that those black strips are essentially carbon/aromatic compounds that form from the protein on the surface of the meat. If so, wouldn't those black bits be carcinogenic? Maybe it's not the consumption of red meat itself that causes cancer, but the consumption of those black bits. If so, would cooking on a surface that doesn't leave black bits be healthier/no cancer? (I also notice a shitload of powdery, black residue on the bottom of oven-cooked pizzas)

thoughts? 18.60.12.185 (talk) 20:14, 28 November 2007 (UTC)

Start with Browning (chemical process) --Mdwyer (talk) 20:20, 28 November 2007 (UTC)

And then hit The Straight Dope. -- Coneslayer (talk) 20:28, 28 November 2007 (UTC)

For some of the black products, see polycyclic aromatic hydrocarbon. Icek (talk) 20:54, 28 November 2007 (UTC)

Eating just before bedtime

Many people believe that eating before bedtime would increase weight gain. My thoughts are that (calories in) = (calories out)and that what matters is how many calories you consume in a day, not when you ingest them. Is there a physiological reason why eating at bedtime would increase fat/weight gain? Are there references available to explain this?

David Winkelaar —Preceding unsigned comment added by Davidwinkelaar (talk • contribs) 22:24, 28 November 2007 (UTC)

As far as I know, the thinking behind not eating big meals before bedtime is that the digestive system slows down significantly while we are asleep..however, it is often easier to sleep after having a big meal as the body diverts energy to digesting the meal (until you actually fall asleep!) GaryReggae (talk) 22:34, 28 November 2007 (UTC)

The process is (assuming you're not on the Atkins diet): Sugar enters your body. Sugar that your body needs is put into the blood and taken up by cells. Sugar your body doesn't need is turned into glycogen. When your sugar starts running low, your body converts that glycogen back into sugar (glucose, specifically) so your cells can use it. Glycogen is simultaneously being converted into fat. When you start running low on both sugar and glycogen, your body could just start burning that fat, but instead it decides to be a whiner and make you hungry so it'll get more sugar. The idea is that by eating at night, you increase the proportion of sugar intake that gets converted into fat, calories that your body would rather leave be and make you eat more than actually eliminate. If you actually make sure to balance your calorie intake with exercise, this won't be a problem, as your body will have no choice but to consume the fat once the glycogen runs down. Someguy1221 (talk) 22:59, 28 November 2007 (UTC)

Machine lubrication oil contaminates kitchen...

Yesterday, my special needs brother cut open a full can of general purpose lubrication oil (for machines and weaponry) in the kitchen, causing it to spray all over the kitchen counters and on a lot of our dishes and cookware. The label on the can says that it's toxic and should not be used on or come in contact with any surface used to prepare food.

My mom seems to think that a simple washing of everything will correct the problem, but I fear otherwise. My question is, what materials must be thrown away and which ones can be cleaned? The oil contaminated things made of glass, metal, wood, plastic, and rubber, as well as metal cooking implements with wood or plastic handles and non-stick pans. It also got on sponges and dish rags.

If any of these things CAN be cleaned, should I use any methods beyond dish soap and water?

Thank you. --69.207.99.230 (talk) 22:41, 28 November 2007 (UTC)

At the risk of offering something that may sound like medical advice, I agree with your mom. Soap and water will clean the stuff off of hard surfaces very well. Depending on the fabric, a good detergent should also be able to get it out of many cloth items. While motor oil must (in today's climate) be labeled as "toxic", it's not like Arsenic or Plutonium or anything.

For peace of mind, though, you'll want to discard any contaminated food. And if the oil soaked into anything porous (such as wooden cooking implements), you may want to discard them as well, because you probably won't be able to get all the oil out, and the odor and discoloration will be unpleasant even if the contamination doesn't kill you. —Steve Summit (talk) 23:28, 28 November 2007 (UTC)

Thanks. My boyfriend told me that the oil would be absorbed by and thus ruin all things that are plastic, but I don't know if he's being paranoid or not (one of the plastic things covered in oil belongs to him). He might just be looking for an excuse for my mom to replace it, though. Unfortunately for me, now I need to do the dishes... —Preceding unsigned comment added by 69.207.99.230 (talk) 23:38, 28 November 2007 (UTC)

Plastic tends to be nonpolar, just like oil, and there are some polar substances which can more-or-less permanently attach themselves to and/or intermingle with plastic molecules. You can notice this with some plastic cookware, especially those ubiquitous semitransparent food containers -- they eventually get discolored by some of the foods they come into contact with. (Oily foods reheated in the microwave are definitely the worst. I've seen this happen both with spaghetti sauces containing tomato products and beef or sausage oil, and Oriental foods containing chili oils.) But while this could be a problem in your situation, I doubt it would happen noticeably unless there were also heat involved. If after a good detergent wash, the plastic thing in question is still slippery or smells like oil, then it may be indelibly contaminated, but if not, it's probably fine. (But far be it from me to intervene in this heaven-sent opportunity for the bf to guilt-trip you, if that's how the stars have aligned here...) —Steve Summit (talk) 00:33, 29 November 2007 (UTC)

If you are looking for something stronger than dish soap, then I would recommend Simple Green. It is essentially an industrial strength degreaser, but also non-toxic, so unlike most comparable products, it would be safe to use on food surfaces. We use it in a variety of applications around our lab. It is sold in some grocery stores and most hardware stores. Dragons flight (talk) 01:09, 29 November 2007 (UTC)

Clearly the stuff can't be that toxic. People handle things lubricated with that oil all the time - it gets onto their hands and - yes - people do eat without washing their hands and they don't get sick as a result. I'd toss out things made of wood or cloth just because you'll never get them clean. Anything that's made of plastic or metal - run through the dishwasher on it's hottest/longest cycle. Anything that's metal or plastic that won't fit into the dishwasher, wipe off the excess oil then scrub down with some detergent - washing up liquid will be fine. SteveBaker (talk) 01:25, 29 November 2007 (UTC)

Just to reiterate a basic point... go ahead and clean the stuff you can (wipe off, then wash, etc.) and then use your brain. Look at the stuff that got splattered and ask yourself whether it looks, smells, and feels like it did before or whether it is different. If it's different: toss it. Blowing twenty bucks on some replacement Tupperware is a pretty small price to pay to avoid even a potential problem. In other words, why risk it? Matt Deres (talk) 02:51, 29 November 2007 (UTC)

November 29

How many SigFigs?

When performing the following simple addition:

    -260
   + 273.15

How many sigfigs should the answer, 13.15, carry? Intuitively, it should be 13. However, when this is inputted into the Science Tools Significant Figures calculator on a TI-84+, the answer says 10 (1 sigfig)

Which is correct? Thanks. Acceptable (talk) 00:09, 29 November 2007 (UTC)

Your calculator. The 260 has the tens place as its lowest significant figure, so the final answer should only be specified to the tens place. Someguy1221 (talk) 00:28, 29 November 2007 (UTC)

That's BOGUS. Sure, if the 'true' value is 261 and it was written as 260 then you have 2 digits of precision - but you don't know that. Perhaps the 'true' value was really 260.00000000 - it's written as 260 which is THREE significant digits. The fact is that with normal arithmetic symbolism, you simply can't tell whether it's 2 digits or 3. So you must calculate out to three digits in order to be sure you aren't losing information. It's not a "real" problem though - in any real situation, you know where the data came from and therefore how precise it is - and you know how much precision you need in the result. SteveBaker (talk) 01:16, 29 November 2007 (UTC)

Um, steve, that's what the period is for, dude. I'll agree with you though that this doesn't generally apply to "real" problems. Someguy1221 (talk) 01:22, 29 November 2007 (UTC)

OK - so you weaseled out of that one (damn!) - but I don't give up debunking bogosity that easily! How about this sum?

 -2600
+ 1234.45

Does 2600 have 2 or 3 significant digits? What about 26,000,000 ? You have no way to know - you are left guessing. If I tell you that the population of France is 26,000,000 people - you might guess that I gave you only two significant digits - but you don't know that there are really 26,012,345 people living there and I gave you 3 sig digits. In truth, if you aren't specifically told - you don't know. Teaching people that there are rules that tell you this stuff is BOGUS. SteveBaker (talk) 03:19, 29 November 2007 (UTC)

If it's possible for it to be ambiguous, you use scientific notation. :-p neener neener neeeeenerrrrrr. Anyway, I'm happy to say that I use plain old means and standard deviations when I do analytical experiments :-) Someguy1221 (talk) 03:23, 29 November 2007 (UTC)

Excuse me!?! I've never seen the population of France represented in scientific notation - NEVER! That's an utterly useless rule. SteveBaker (talk) 03:35, 29 November 2007 (UTC)

Population of France: 2.60×10⁷. Now you have! Dragons flight (talk) 04:51, 29 November 2007 (UTC)

Oh no - now you've gone and done it. Here, let me fix that number for you: 02.60x10.00^07.00 ...there, much better! SteveBaker (talk) 06:22, 29 November 2007 (UTC)

In the scientific-notation version, the "10" and "7" are considered exact numbers, giving them an infinite number of significant digits. --Carnildo (talk) 01:16, 30 November 2007 (UTC)

By the way...how many significant digits does '2' have? You're going to say "just one". So if I want to add 2 to 101. - the rule is that I have to do it to one significant digit so the answer is only 100 - unless I write 2.00 + 101. then I get 103. ?? That's something else I've NEVER seen anyone do? What's relevent in addition is the number of digits before/after the decimal point - not the number of significant digits. This supposed formalism is utterly useless in practice - and it's definitely going to cause horrible mistakes. Why are we even bothering to teach it to people? SteveBaker (talk) 03:44, 29 November 2007 (UTC)

For an amusing real-world conundrum involving trailing-zeros ambiguity, see the "Measurement" section of our article on Mt. Everest. —Steve Summit (talk) 03:53, 29 November 2007 (UTC)

Oh sorry, that'd my mistake, I guess I forgot to mention that. (-260) has 2 sigfigs, while (273.15) has 5. Acceptable (talk) 01:19, 29 November 2007 (UTC)

New question: how do I inform the calculator that this particuloar 260 accurate to three significat figures, if "260" is two significatn figures, and "260.0" is four significant figures? -Arch dude (talk) 01:05, 29 November 2007 (UTC)

And 260. has three sig figs ;-) Someguy1221 (talk) 01:06, 29 November 2007 (UTC)

AFTER EC: Oh, I thought when adding/subtracting sigfigs, the answer should have the decimal places of the value with the least decimal places. Acceptable (talk) 01:07, 29 November 2007 (UTC)

No it doesn't. It's one less. If you are really adding 100.6 to 100.6 but we do the sum accurate to three significant digits, you get 101. + 101. = 202. - but the real answer is 201.2 - so your answer isn't accurate to 3 significant digits anymore - it's now only accurate to 2. When you add two inaccurate things - the result is less accurate than the two numbers you added. Real math isn't done with 'significant digits' - it's done with error bars. So the right way to do this is to say 100.6 can be represented as 101 plus or minus 0.4, so when you add 101 (+/-0.4) to 101 (+/-0.4) you get 202 (+/-0.8) - which means that you know the true answer is between 202.8 and 201.2...which is good. This whole business of "significant digits" is just a VERY rough way to represent error bars and to make sure people don't over-specify the precision of the result. But to pretend that this is some kind of mathematical formalism is nonsense (but totally typical of the nonsense they fill school-kid's heads with when they could be teaching them REAL math). It's main purpose in practical math, science and engineering is to allow you to do 'back of envelope' calculations and not be ridiculously over-precise in your results. When it matters, you use proper error bars with all the formalism that entails. SteveBaker (talk) 03:33, 29 November 2007 (UTC)

If you do as scientists often do and treat your errors are normally distributed, then the standard error propagation tells you that 101 +/- 0.4 + 101 +/- 0.4 = 202 +/- (0.4*sqrt(2)) = 202 +/- 0.6. Though, for that matter, I can't imagine anyone looking at 100.6 and rushing to 101 +/- 0.4. The default position would be to ask the uncertainty, but if that is not available the customary assumption (at least back in my lab classes) is to assume the last digit is meaningful but on the threshold of not being so and go with 100.6 +/- 0.5, which would give the sum as 201.2 +/- 0.7. Dragons flight (talk) 04:48, 29 November 2007 (UTC)

Indeed, for many sorts of error, a normal distribution is an appropriate error model - and I agree that if you use that then no answer is "wrong" because it could simply be off in the long tail of the distribution. Hence if you calculate the answer to my little sum to be 202 +/- 0.6, you aren't saying that the true answer must lie between 201.4 and 202.6 (as indeed, it does not) - you are merely saying that the odds are much better that the true answer lies within that range than outside of it. However, it's not always the case that a normal distribution is appropriate. For example if you are using a computer to crunch your numbers, the error due to finite precision machine arithmetic is sharply delimited and equiprobable - it's certainly not gaussian.

But whatever - the point is that if you actually care about the precision of your results, you do something about it. The whole "significant digits" thing is vague, poorly determined and patchily implemented. It's simply a rule of thumb to prevent gross over-specification of precision. Once people start getting dogmatic about how it's treated, the system simply falls apart because of those weaknesses.

The computer geek in me is particularly upset because the rate at which precision is preserved, amplified or casually discarded by this so-called system depends entirely on what base of arithmetic you use! If you do your math in binary - then knowing how many significant binary-digits the number has preserves precision better than knowing how many significant decimal digits it has - and MUCH better than doing it in hexadecimal or radix 50 or counting the number of bytes (radix 256). Since the choice of a base-10 number scheme is ENTIRELY arbitrary, anything which bandies about "significant digits" is doomed to failure in the face of proper numerical analysis. SteveBaker (talk) 06:40, 29 November 2007 (UTC)

Significance arithmetic summarises quite a lot of what has been said here. 130.88.79.39 (talk) 14:30, 29 November 2007 (UTC)

One of the references in that article [12] says: The whole notion of significant digits is heavily flawed; see section 9 for more on this. Anything that can be done by means of significant digits can be done much better and more easily by other means. People who care about their data don’t use significant digits. There are plenty of important cases where following the usual "significant figures" rules would introduce large errors into the calculations. ...which is precisely my point (although I'll admit to VERY informally using the significant figures "rule" when I'm doing strictly back-of-envelope math. SteveBaker (talk) 20:31, 29 November 2007 (UTC)

This addition problem doesn't really involve the number of significant digits anyway. That's a multiplication/division factor. What is inolved here is that we don't know that the digits of one of the numbers is significant beyond the tens place (it might be significant in the units place, but not beyond there or it should have included significant digits after the decimal point. Gene Nygaard (talk) 22:02, 29 November 2007 (UTC)

Particle Accelerators use electric fields to accelerate and magnetic fields to bend particles?

Hi, in reading about the Large_Hadron_Collider and the article on Magnetism, I'm wondering some simple questions, like... 1) If a Proton at rest sees an electric field, the proton accelerates towards the negative voltage. As the proton attains the speed of Light (c), the electric field starts looking like a magnetic field, right? 2) The Large_Hadron_Collider has a round track 26.6 km long that bends the moving protons using magnetic fields. As the proton attains the speed of light (c), doesn't the proton see that magnetic field more and more as an electric field?

Just curious. Thanks! --InverseSubstance (talk) 02:43, 29 November 2007 (UTC)

(1) not quite, and (2) no. To be more specific, it isn't that an electric field "looks like" a magnetic field - put simply, when you have some charged particles and you are in a frame of reference where they are at rest, they have an electric field and no magnetic field, that will exert a certain force on another charged particle. When you are in a different (intertial) frame of reference, those particles will be moving, but by the rules of special relativity the force they exert on that other particle should be the same, even though length dilation means that the separation between them appears to have changed, and thus their electric field is different. The magnetic field is essentially the difference between the two possible electric fields. So yes, if you start with a "pure electric field", then as you accelerate you'll see some of the electric field "become" a magnetic field. However, if you start with a magnetic field, then as you accelerate the magnetic field will change, as will the associated electric field, but the one won't completely turn into the other. Confusing Manifestation(Say hi!) 02:53, 29 November 2007 (UTC)

One thing - the proton doesn't attain the speed of light - it can get close but it can never quite get there. SteveBaker (talk) 03:09, 29 November 2007 (UTC)

Extended/Extra Optical Zoom?

I bought Panasonic Lumix DMC-FZ18 recently, I have heard that its got "Extended Optical Zoom" but it works with lower resolution output only. http://panasonic.co.jp/pavc/global/lumix/fz18/18zoom.html . Does anyone know whats the difference between Extended/Extra Optical Zoom and Digital Zoom?

Thanks --Spundun (talk) 03:59, 29 November 2007 (UTC)

It's just precropped digital zoom. Uh, so basically, it's digital zoom :-) Someguy1221 (talk) 04:09, 29 November 2007 (UTC)

EOZ isn't truly digital zoom - it doesn't "stretch" pixels like digital zoom does. It is only used when you have chosen to take smaller pictures than your camera can take - for example, to save space on your memory card. Normally in this case the camera "squashes" pixels. However, if you wish to zoom in, the camera will use only pixels from the middle of your sensor - no "stretching" required. 138.38.151.57 (talk) 12:32, 29 November 2007 (UTC)

So in other words, it takes a full picture and crops it - that's "electronic zoom" - calling it "optical" is a nasty deception! Electronic zoom is by far inferior to optical zoom - but it's cheaper. If this were an optical zoom, the optics would have reconfigured to cover the entire sensor - then if a lower resolution were demanded by the user, "squashing" (as you put it) could be performed. However, by merging together a larger number of sensor pixels to get one stored pixel, you improve the quality of the image. SteveBaker (talk) 13:53, 29 November 2007 (UTC)

While I agree with you that "digital zoom" is vastly inferior (personally, in fact, I'd go farther and say that it's no zoom at all), based on the evidence at hand, I don't think we can quite prove malfeasance in this case.

Consider my camera (a 3.2 megapixel Canon PowerShot A510). I can shoot in four different resolutions:

L	2048x1536	(3.14MP)
M1	1600x1200	(1.92MP)
M2	1024x768	(0.78MP)
S	640x480	(0.30MP)

Normally I shoot in M1 mode, because my pictures aren't that great and mostly I use them on-line where anything bigger is just overkill. (And it doesn't even bother me that I've effectively castrated my already-puny 3.2 MP camera down to 1.9, because it's no contest for me.)

Obviously, the camera's internal CCD is 2048x1536, and when you shoot in one of the lower-resolution modes, the camera downsamples by a factor of 1.28, 2, or 3.2. Thus, the M1 images (for example) require 60% of the storage of an L image.

Now, suppose there was a way to divide the raw CCD image up into thirds, both horizontally and vertically. Suppose the camera downsampled the outer 8 of the resulting 9 subimages as usual, but left the center one at full CCD resolution, and stored this composite somehow. For M1, this would require 8/9 x 1.92MP + 1/9 x 3.14MP = 2.06 MP, or 65% of full-resolution storage. So for a 5% increase in storage (above normal M1, that is), you'd retain the ability to zoom back in to full CCD resolution, as long as you limited yourself to the image's fovea, so to speak.

I doubt you could store this "composite" image using a standard image file format, although I suppose you could arrange to use a higher JPEG quality factor on the center of the image than the periphery, and gain something. (Or perhaps you could store a 2048x1536 image as a 2048x1536 JPEG, with normal JPEG quality in the center and a much lower JPEG quality at the periphery, and then make a note to always display the image shrunk by 78%, so that the coarseness around the edges wouldn't show, but so that -- again -- you could digitally zoom in on the center without loss of sharpness.)

I have no idea if this is actually what the DMC-FZ18 is doing, but it's not completely outside the bounds of possibility. —Steve Summit (talk) 01:30, 30 November 2007 (UTC)

Time to fall

If a point mass of mass m is released at some distance d above the surface of a perfect sphere of uniform density, with mass M and radius r, then, using Newtonian universal gravitation and assuming there are no other forces acting within the system and ignoring the effect of the point mass' gravity on the sphere, how long does it take the point mass to fall to the surface of the sphere? This question occurred to me a while back and I have been trying to figure it out, but I have no idea how it would be calculated, since the distance travelled at any time depends on the velocity/acceleration, but the acceleration is constantly changing and depends on the distance from the centre of the sphere. --superioridad ^(discusión) 04:57, 29 November 2007 (UTC)

The answer is calculus (mostly integral) - consider acceleration, velocity and radius/position all as functions of time, use calculus to find an expression for the position, and solve to find the two time points. As for an actual answer ... give me a second (or perhaps someone else will take care of it). Confusing Manifestation(Say hi!) 05:55, 29 November 2007 (UTC)

We do have an article on this. It's not the most apparent method of approaching this, but it starts with more general conditions. Someguy1221 (talk) 06:07, 29 November 2007 (UTC)

And I suppose you could use that solution, then transfer to a co-ordinate system where the second mass is stationary, if you wanted the "Earth/bigger object doesn't move" solution. Confusing Manifestation(Say hi!) 06:12, 29 November 2007 (UTC)

(e/c)... OK, time for some TeX. Acceleration is given by Newton as

$a=-{\frac {GM}{r^{2}}}$

But $a={\frac {dv}{dt}}$, and using a little fiddling we get

$-{\frac {GM}{r^{2}}}={\frac {dv}{dt}}={\frac {dv}{dr}}{\frac {dr}{dt}}=v{\frac {dv}{dr}}$

And if we integrate with respect to r, we have

${\begin{aligned}\int \limits _{r_{1}}^{r_{2}}-{\frac {GM}{r^{2}}}dr&=\int \limits _{r_{1}}^{r_{2}}v{\frac {dv}{dr}}dr\\\left[{\frac {GM}{r}}\right]_{r_{1}}^{r_{2}}&=\int \limits _{v_{1}}^{v_{2}}v\ dv\\{\frac {GM}{r_{1}}}-{\frac {GM}{r_{2}}}&=\left[{\frac {1}{2}}v^{2}\right]_{v_{1}}^{v_{2}}\\&={\frac {1}{2}}{v_{1}}^{2}-{\frac {1}{2}}{v_{2}}^{2}\end{aligned}}$

... and then you use the fact that $v={\frac {dr}{dt}}$ and do some more calculus, and plug in your known values, and get some kind of answer. I have to go now, but I'm sure you or someone else can happily work away at this step. Confusing Manifestation(Say hi!) 06:12, 29 November 2007 (UTC)

${\sqrt {d^{3} \over {2GM}}}$ - Dragons flight (talk) 06:28, 29 November 2007 (UTC)

Drunken vampire bats

If a vampire bat sucks the blood of a drunk person, does the bat become drunk too? --Candy-Panda (talk) 09:55, 29 November 2007 (UTC)

I don't believe it would because of the way it can quickly excrete it.--58.111.143.164 (talk) 12:50, 29 November 2007 (UTC)

Also consider how the body dilutes alcohol that's ingested. You can drink 95% pure alcohol, which your body will dilute down -- half a percent of alcohol in your blood has a 50% chance of killing you. So if the bat is drinking blood, chances are good that it's drinking at most a 0.5% alcoholic drink, which in the U.S. is the upper limit to be considered a non-alcoholic drink. So, given a lot of other unfounded assumptions about a bat's metabolism and response to alcohol, the answer is: the bat becomes about as drunk as you could get on O'Douls. jeffjon (talk) 14:34, 29 November 2007 (UTC)

Using carbon nanotubes to transport electrons?

I read on the article on CNT's that certain CNT structures are excellent conductors of electricity, while others are semi conductors. Could CNT's be used instead of metal wires to transport electricity? Are there any advantages to this over what we currently use? 64.236.121.129 (talk) 14:43, 29 November 2007 (UTC)

You might enjoy our article about field emission displays for one such use of carbon nanotubes. I think a lot of the possible applications haven't yet been explored because of the relative shortage of long nanotubes.

Atlant (talk) 16:42, 29 November 2007 (UTC)

CNT's could certainly do that (and they are also very strong - which would be handy). However, the longest ones we can make are a few millimeters long - and the longest ones we can make in industrial quantities are utterly microscopic in length. So the technology just isn't there yet. However, there is huge interest in making long buckytubes - they have HUGE implications for materials science and a lot of very smart people are trying very hard to crack the problem of making them. I think our kids are going to have a lot of fun with these things. SteveBaker (talk) 20:16, 29 November 2007 (UTC)

If you fill an airtight car with helium, will it become lighter?

^Topic 64.236.121.129 (talk) 14:52, 29 November 2007 (UTC)

• No, you can only pump Helium in if the air can be displaced. With the car airtight, there is no place for the air to go, so no more room inside for the helium. - 131.211.161.119 (talk) 14:54, 29 November 2007 (UTC)

That's not what I meant. I meant the car is already filled with helium, and is sealed airtight to prevent the gas from escaping. 64.236.121.129 (talk) 15:05, 29 November 2007 (UTC)

• A car filled with helium would weigh less than a car filled with air, all else being equal. From a practical point of view, helium is a very small molecule and can often escape from containers that are "air-tight" (for example, certain types of balloons). ike9898 (talk) 15:00, 29 November 2007 (UTC)

I see. If this is true, why not fill compartments on airplanes (seperate from the cabin which contains people) with helium to make the plane lighter. 64.236.121.129 (talk) 15:05, 29 November 2007 (UTC)

As stated - the helium will escape. Also, to get any substantial effect, you would need to create a helium cavity the size of a zeppelin - which would greatly inhibit the aircraft's ability to fly. All in all - the benefit is not worth the effort. You'd get a much better benefit by banning all luggage from aircraft. -- kainaw™ 15:08, 29 November 2007 (UTC)

Ok lets say the airplane is a military fighter. We have a couple of lightweight tanks filled with helium. Once the helium escapes, it can drop the tanks. Wouldn't this help? 64.236.121.129 (talk) 15:11, 29 November 2007 (UTC)

• To get any significant benefit you would very large helium tanks with very lightweight walls. Maybe some sort of fabric or plastic walls. Then you want to make sure your centre of lift is above your centre of gravity, for stability - so put your crew cabin underneath your big helium tanks. No need for a fuselage or those heavy wings - just stick a rudder and elevators onto your big helium tanks. What you now have is called a dirigible. Gandalf61 (talk) 15:25, 29 November 2007 (UTC)
• No. It's very unlikely that you can build tanks that can withstand military-style maneuvers and still have positive buoyancy even if you assume they contain a vacuum. Also, you would still increase mass and, presumably, air resistance. The lift you can get from the surrounding air is fairly low - about 1.2 kg/m³ at sea level. --Stephan Schulz (talk) 15:34, 29 November 2007 (UTC)

Ahh! Is it time for our next round regarding "vacuum balloons"? If we went with the version inflated by photons, perhaps they could perform double-duty by both providing buoyancy and, later, allowing them to be dropped on the enemy as a sort of photon torpedo? This would be especially effective if they were inflated with some nasty photons such as gamma rays.

Atlant (talk) 16:45, 29 November 2007 (UTC)

On the topic of vacuum balloons, I saw one when I was watching an episode of Pushing Daisies last night on television. The protagonist had a flashback to a childhood boarding school's science lab, and he recalled an incident with a friend who had been an expert at constructing paper airplanes. One of the characters filled a balloon from a benchtop gas hose barb; once inflated and tied off, the balloon floated away. (Appropriately enough for this thread, I believe the balloon was actually used to provide lift to a paper airplane.) There was a very quick cut that showed the gas valve as it was being turned on, it bore the legend VAC. I thought that it was a very clever touch. TenOfAllTrades(talk) 17:47, 29 November 2007 (UTC)

Imagine a helium balloon. Think of how little a helium balloon can lift. Those little plastic tags they put on the end of the string are usually sufficient to keep the balloon from flying away. Even if your helium 'tanks' are made of the same lightweight material as the balloon you got at the fair the 'tanks' would only make the plane lighter by the weight of that little plastic tag. Not very useful. The problem is that air is already so incredibly light that replacing it with something even lighter does not achieve much. That is why even small, four passenger blimps have gas-bags the size of an office building. 72.10.110.107 (talk) 15:50, 29 November 2007 (UTC)

Also - aircraft flies at an altitude where there is almost no buoyancy offered by helium. -- kainaw™ 16:07, 29 November 2007 (UTC)

Not to mention that all your passengers would suffocate. shoy (^words _words) 17:24, 29 November 2007 (UTC)

No they wouldn't. In my first question, I didn't specify people were in the car, and in my second question, the helium would be in either compartments seperate from the cabin, or in tanks. But I agree with the other users that they prolly wouldn't contribute much lift to the airplane. 64.236.121.129 (talk) 17:42, 29 November 2007 (UTC)

This is definitely a non-starter. The trouble with the aircraft idea is that very little volume can be enclosed within the plane and the additional weight required to get it airtight (seals and whatnot) would easily outweigh the benefits. One liter of helium can only lift just over a gram. Take an F16 fighter - it's 14m long and the fuselage is about 3x3 m - the wings are 27 sq.m in area and about 20cm thick. So we have a total volume of about 130 cubic meters - which is 130,000 liters. If the ENTIRE plane was filled with nothing but helium (ie we take out the engine, fuel tanks, instruments, landing gear, internal bracing...the lot), it would be lighter by 130,000 grams - 130kg. Fully fuelled, the plane weighs 12,000kg. So at VERY best, you'd get about a 1% weight saving. But in truth there is very little free space inside an F16 - perhaps a hundedth of it might be utilised giving us an 0.01% weight reduction overall. The hassle involved is simply not worth it. Worse still - if that gas is pressurised to sea level then as you take off and the air gets less and less dense, the helium produces less and less lift. In a zepplin or a blimp, the lift bags expand to take account of that - but you can't do that in these confined little spaces. So in the end, this is certainly a lot more trouble than it's worth - and in all likelyhood would actually make the plane heavier - not lighter. A similar argument applies to a car. My MINI Cooper'S has 1.47 cubic meters of interior volume, that's 1470 liters - so 1.47kg of lift from filling it with helium. Sadly, it weighs 1200kg - so now we are looking at 0.1% reduction in weight. But its hard to imagine you could seal up all of the little holes and escape routes with less than 1.47kg of material - so in practice, you wouldn't save anything. SteveBaker (talk) 20:07, 29 November 2007 (UTC)

Indeed hmm. Is it possible to just shove more gas in there by force, and increase the density of helium in the tanks. Just hypothetically, assume the tanks are invincible, and won't explode. 64.236.121.129 (talk) 20:17, 29 November 2007 (UTC)

Helium atoms still have positive mass (just lighter than the molecules that make up air). If you shove more helium into the tank, increasing its density, you make it heavier, not lighter. -- Coneslayer (talk) 20:21, 29 November 2007 (UTC)

Going by what Alant said, if you had tanks that were filled with nothing, there's a vacuum in them, they would provide more lift than helium? 64.236.121.129 (talk) 20:27, 29 November 2007 (UTC)

Yes, vacuum (nothing) is lighter than helium (something). But it requires a much stronger, and hence more massive, container. -- Coneslayer (talk) 20:36, 29 November 2007 (UTC)

Yep - vacuum balloons sound like a great idea - but air pressure is 15psi - that's fifteen pounds pushing in on every square inch of the surface. It takes a pretty heavy construction to resist that much force - and that's going to be heavier than a fairly small amount of helium. SteveBaker (talk) 00:25, 30 November 2007 (UTC)

ionic,covalent,coordinate bonds

Which one of the following compounds contains all the three ionic, covalent and coordinate compounds?? A-hydrogen cyanide B-ammonium nitrate C-potassium permanganate D-sulphuric acid —Preceding unsigned comment added by Knowiteverything (talk • contribs) 15:54, 29 November 2007 (UTC)

This a really easy homework question!--Stone (talk) 16:53, 29 November 2007 (UTC)

One of three relevant wiki articles gives the right answer in a nice picture!!!!--Stone (talk) 16:57, 29 November 2007 (UTC)

ornamental millet

Yesterday I saw a plant at a Nursery named as an ornamental millet. It was a feathery gras like plant with a deep puple head. The staff was unable to give me any information on it and I can't find any reference to ornamental millets in Western Garden Book or on line. Can you help? —Preceding unsigned comment added by 69.3.233.29 (talk) 17:54, 29 November 2007 (UTC)

Tall, dark and handsome describes this purple-leaved millet. Young plants are green-leaved, direct sunlight induces the purple leaf color. Capable of growing 3 to 5 feet tall, the plants are embellished with 8 to 12 inch flower spikes. The immature spikes can be cut and used dramatically in floral arrangements. Left on the plant, the millet seed spike attracts birds that snack on seed. 'Purple Majesty' is very easy to grow and is very tolerant of heat and low moisture. The purple leaf blades and spike are distinctly different from all other ornamentals.

Purple Majesty is best started outdoors when temperatures are consistently above 60 degrees or indoors in warmed seed trays. Chilly weather will stop plant growth or weaken its stems, so don't start your seeds too far in advance. Germination is very quick -- just 3 days! -- and plant growth is rapid and vigorous under good conditions. If you begin seeds indoors, the plants will remain green until set outside, then burnish a lovely violet within several days! You might like to buy some from here, [13]Richard Avery (talk) 18:15, 29 November 2007 (UTC)

Largest marine animal in captivity

Quick question: what is the largest marine animal ever kept in a zoo or aquarium? 68.23.172.215 (talk) 18:36, 29 November 2007 (UTC)

I think Japan has an aquarium with a whale shark in it. Whale sharks are larger than orcas which should come in 2nd. 64.236.121.129 (talk) 19:45, 29 November 2007 (UTC)

The Georgia Aquarium also has whale sharks. --Sean 23:45, 29 November 2007 (UTC)

How big would your arms have to be in order to fly/glide?

Lets assume you weigh 140 pounds, and you want to glide by stretching out your arms like a plane and running forward off of a cliff. If your arm width is normal, how long would they have to be in order for the air moving around it to provide enough lift to glide? 64.236.121.129 (talk) 20:24, 29 November 2007 (UTC)

I doubt you'd ever glide, no matter how long they are. Ignore your body for a moment, and just consider the arms. If you make your arm a foot longer, then that extra foot of arm has to produce at least enough lift to support itself, or you're no better off. But an arm, being roughly cylindrical and fairly dense, is not a very good airfoil. If you think about objects similar to a piece of arm, like a baseball bat or slender log, they don't "glide" if you throw them. That is, they don't produce much lift compared to their own weight. Thus, I don't think that making your arms longer is going to produce enough lift to support your arms, let alone your body. -- Coneslayer (talk) 20:34, 29 November 2007 (UTC)

I guess, we will have to change the shape of the arms also in addition to changing the size only. Airplave wings have very specific shapes, which provide the airplane enough lift to fly. Once the shape based on small prototypes has been determined, we will accordingly fix the size depending upon our weight. But our lower body also has to be in accordance with the aerodynamic structure. So, I guess if you have distended belly for example, you will have more problem than those having 6 pack :). DSachan (talk) 20:37, 29 November 2007 (UTC)

Shape helps a lot, but I think air moving over any object should eventually provide lift, depending on the speed of the airflow, and the weight of the object. Hmm, that's why cars have rear spoilers. When they go fast, the air moving around it can cause lift, which makes the tires lose traction with the ground. The spoiler keeps the car in contact with the ground. 64.236.121.129 (talk) 20:43, 29 November 2007 (UTC)

I guess, this is a wrong statement to make that air moving over any object should eventually provide lift, depending on the speed of the airflow, and the weight of the object. It will be possible only when the body itself is such that it is able to create the pressure difference on its two sides. This will eventually depend on the shape, and texture of the body. Of course, speed of the airflow plays a role in it, but only a part of the whole. DSachan (talk) 20:51, 29 November 2007 (UTC)

I read that the pressure difference thing is a fallacy when it comes to wings and lift. The articles here say that something as simple as a flat board, angled up will cause lift. 64.236.121.129 (talk) 20:56, 29 November 2007 (UTC)

(edit conflict) Why do you say "any object"? You're contradicting yourself. If air moving over "any object" caused lift, then the air moving over the spoiler (or, say, a Formula 1 wing) would cause lift, rather than downforce. If you have a perfect cylinder in air (as a model for your arm), why should airflow cause lift? You could flip the whole scene upside down, and it would look the same. -- Coneslayer (talk) 20:52, 29 November 2007 (UTC)

Right, I should say any object that isn't shaped at an angle so that the airflow pushes the object down. 64.236.121.129 (talk) 20:56, 29 November 2007 (UTC)

To elaborate, another example on wiki also says that if you stick your arm out of a moving car and angle it up, the air flow will push your arm back and up, causing lift. Factors that affect lift are airflow, weight of the wing, shape of the wing, and wing area. 64.236.121.129 (talk) 20:59, 29 November 2007 (UTC)

'Glide' can have many meanings—how much lift will you settle for? Take the Space Shuttle orbiter—it glides in to a landing, but it lands very steeply and very quickly compared to a commercial airliner, owing to its great weight and short, stubby wings. (It's been said that the Shuttle 'glides like a toolbox'.) See also our article on lifting body. TenOfAllTrades(talk) 21:48, 29 November 2007 (UTC)

Take a look at a hang glider - now you have your answer. SteveBaker (talk) 00:04, 30 November 2007 (UTC)

Actually, Wingsuit flying is just about...kinda/sorta gliding. It's all a matter of what glide ratio you anticipate getting! SteveBaker (talk) 01:55, 30 November 2007 (UTC)

Why doesn't boyancy work in solids?

It works in liquids, and gas... Why not solids? 64.236.121.129 (talk) 20:40, 29 November 2007 (UTC)

It does. Dragons flight (talk) 20:43, 29 November 2007 (UTC)

Ok lets say, we cover a person in lead, then let it solidify. Since he weighs less than the lead, his corpse should come to the top? 64.236.121.129 (talk) 20:47, 29 November 2007 (UTC)

Most solids have enough internal rigidity to resist the bouyant force, but on very large scales or long timescales, the same principle applies. For example, salt diapirs. Dragons flight (talk) 20:54, 29 November 2007 (UTC)

Or the ballast in the basement of the Kansai Airport to prevent it from floating, perhaps? Or am I remembering it wrong... --Mdwyer (talk) 22:27, 29 November 2007 (UTC)

• If you vibrate a container full of balls made of wood and others made of lead, all the same size, presumably the wooden ones will float to the top due to buoyancy. --Sean 23:51, 29 November 2007 (UTC)

Natural and Phenomena and Natural Resources

People from Europe came to the New World, noe the United States, for the natural resources.What kinds of resources or products did they ship back to Europe? —Preceding unsigned comment added by Felicia25 (talk • contribs) 22:44, 29 November 2007 (UTC)

Colonization_of_America#Economic_immigrants. Someguy1221 (talk) 23:35, 29 November 2007 (UTC)

November 30

MO theory

Hey, I'm in Chem II and we are doing MO theory. We did easy ones in class like O₂ and N₂ and the n=2 elements. But I have no clue how to do like Al₂³⁺! Does the d orbital even have anything to do with MO theory? Thank you! —Preceding unsigned comment added by HALPpls (talk • contribs) 02:04, 30 November 2007 (UTC)

I assume you're referring to molecular orbitals. However, I still have no idea what exactly you're trying to do. Someone versed in the field might understand your question as asked, but it might be a good idea to explain your goals more precisely. For example, are you looking for a qualitative statement or a quantitative calculation? Algebraist —Preceding comment was added at 03:11, 30 November 2007 (UTC)

d atomic orbitals are quite important for the molecular orbitals for some bonds and molecules. It would be hard to get 10 (!) bonds from the central iron atom in ferrocene with just s and p. At the level I think you're working, I think you do Al₂³⁺ the same way you have done other examples (that's how things are usually taught, no?): list the atomic orbitals of each atom, hybridize and mix'n'match them by symmetry. Perhaps you could tell us how far you've gotten on your own and what specific problem you're having? DMacks (talk) 03:19, 30 November 2007 (UTC)

It's a way of telling what electron configuration of a molecule is most likely, and how stable it is, if it exists at all. It uses quantum mechanics. —Preceding unsigned comment added by HALPpls (talk • contribs) 03:31, 30 November 2007 (UTC)

Light green slime

What metal would react with human sweat/salt to give a light green colored slime. i just scraped some off my glasses frame wher they contact the side of my head.--TreeSmiler (talk) 03:34, 30 November 2007 (UTC)

Anything with copper in it will produce a green "slime" when it is in contact with sweat. You mention glasses though. It is common for glasses to go day after day in contact with the skin (dirt and sweat) without being cleaned. So, just about anything can grow on them. I found that boiling my glasses once a week helped a great deal - more often during football season. -- kainaw™ 03:39, 30 November 2007 (UTC)

Planet Venus

If the poisonous gases and voilent weather did not exist on Venus, what would happen to you if you landed on Venus?--WonderFran (talk) 03:40, 30 November 2007 (UTC)

You would be crushed by the atmosphere that is 300 times as dense as the Earth's. Oh and it is a bit warm there so pack your shortsShniken1 (talk) 03:43, 30 November 2007 (UTC)

What would the pressure be like compared to the deepest part of the ocean? --WonderFran (talk) 03:45, 30 November 2007 (UTC)