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October 16

Manhole question

why is that a person going in a manhole had met with accident and blood came out of his body —Preceding unsigned comment added by 117.197.116.74 (talk) 05:04, 16 October 2008 (UTC)

Why did they go into the manhole? To chase an alligator, perhaps? If so, that would be a clue. --Scray (talk) 05:35, 16 October 2008 (UTC)

Are you sure it's not a hole in a man, that would leak blood. Graeme Bartlett (talk) 05:39, 16 October 2008 (UTC)

Didn't you two read the question? It's not how the person met with a bloody accident, it's why. If you are a religious fundmentalist, the answer is probably because he/she pissed off God. If you are an atheist, it's because he/she was not fit for going into manholes due to genetics. :-P

Right. For the latter, the genetic non-fitness was that he was too stupid to stop traffic before working in a manhole in the middle of the highway:) DMacks (talk) 18:25, 16 October 2008 (UTC)

Who knows? Maybe the person took a printed copy of the wikipedia reference desk and was squinting to look at one of the answers and collided with a wall... Clearly a strong Darwin award candidite, if the person then falls into the sewer water, gets a deadly infection and dies.Nil Einne (talk) 09:35, 17 October 2008 (UTC)

If he was working in an electrical vault, it could have been due to the arcing of 480 volt conductors. That has been known to cause bleeding, third degree burns, and death. Edison (talk) 02:42, 18 October 2008 (UTC)

Thank you to the contributors

Hi everyone. I used to contribute to this reference desk occasionally, but that has fallen off. Nonetheless, I wanted to start a section to thank the contributors of the Science Reference Desk. Not only do you help people everyday in their pursuit of knowledge, you make for some darn good reading. I could put this on the talk page, but you all deserve a slightly more public recognition. Cheers! Eric (EWS23) 09:59, 16 October 2008 (UTC)

I too would like to thank everyone for their contributions. Some of the discussions going on here are quite interesting and often shed a lot of light on subjects that the Wikipedia articles themselves fail to do. 12.10.248.51 (talk) 13:13, 16 October 2008 (UTC)

I agree. One of the often unrecognized goods i asociate with the rd is that a lot of article improvement and expansion is generated here. --Shaggorama (talk) 10:06, 17 October 2008 (UTC)

Heat effects

You know sometimes you get sun shining through a window onto a wall, and if it is a hot day you get sort of wavy shadows in the sunlight hitting the wall? What is this called, and is it linked to the effect you get when heated air distorts what is behind it. What is this effect called as well? I'm sure I have the word somewhere in my head but I can't recall it right now. 88.211.96.3 (talk) 10:45, 16 October 2008 (UTC)

Heat wave? The shadow is simply the same thing as the shadow is just cause by light. 194.221.133.226 (talk) 11:00, 16 October 2008 (UTC)

No that doesn't look right, that seems to be an article about exceptional large area high temperatures. 88.211.96.3 (talk) 11:44, 16 October 2008 (UTC)

It's hard to guess the word you are thinking of - so let's toss in some gratuitous explanation and maybe we'll hit the right word by luck!

So the effect you are thinking of is caused by the air temperature variations causing subtle shifts in refractive index. Glass is a better conductor of heat than air - so the air nearest to the window is likely to be at a different temperature than the air in the remainder of the room. As convection causes warmer air to rise and cooler air to sink, there is likely to be a certain amount of turbulence - although laminar flow is also possible, this would not cause the effect you are seeing. A bubble of turbulent air that is at a different temperature to its surroundings (and hence has a different refractive index) acts like a lens - focussing or dispersing the sunlight that is cast onto the wall - increasing the light intensity in some areas at the cost of decreasing it in others. The areas of decreased light intensity look like shadows and the turbulence makes tham wave around. Hence "wavy shadows".

Words to describe this phenomena would be "heat haze" (a term I've never been very happy with), or perhaps "shimmer". It's possible that you are also thinking of a mirage. But that's a different effect - although it's also caused by temperature variations in the air and consequent changes in refractive index. A shimmer due to turbulance will be more obvious in the case of a mirage. You might also be thinking of the scintillation of stars (more commonly called "twinkling") - or perhaps the word you are after is "dispersion". The pattern of light on the wall might also be called a "caustic" - although that term is more commonly used for things like the pattern of light on the bottom of a swimming pool. The root cause of caustics in a swimming pool is the same as with the shimmering air though - regions of different refractive index (hot and cold air - or air and water) are moving relative to each other and focussing the light in peculiar ways. A plot of the light concentrations in an idealised caustic takes the form of a nephroid.

SteveBaker (talk) 12:31, 16 October 2008 (UTC)

Thanks! I still wonder if wikipedia has an article on the effect. I just thought of another example of what I am (well was, it is raining now, bloody weather) seeing. You know when you have a large fire, and you get distortion. I am sure this is the same effect as what causes the shadows on the wall, and what you describe, but surely it has an actual name? I'd call it heat distortion or something. 88.211.96.3 (talk) 12:46, 16 October 2008 (UTC)

It's the same thing - the heat from the fire is now the source of the temperature variation - and the convection and refractive index changes that result from that are exactly the same as in the case of the window. SteveBaker (talk) 12:49, 16 October 2008 (UTC)

Yes but does it have a name? If it does someone should maybe write a wikipedia article on it, and I may even have a pop at it. 88.211.96.3 (talk) 12:52, 16 October 2008 (UTC)

Schlieren effect. DMacks (talk) 15:01, 16 October 2008 (UTC)

Recommended book reading if you're interested in the many effects that air and moisture can have on light: "The Nature of Light and Color in the Open Air", also known by other title variations such as "Light and Color in the Outdoors", by Marcel Minnaert. --Anonymous, 21:36 UTC, October 17, 2008.

Stability of carbon

I came across the following passage: "The rarest carbon isotope is carbon-14, with eight neutrons. Unlike the other two isotopes, carbon-14 is unsta- ble". Is ¹³C stable? Why is C-14 unstable?Mr.K. (talk) 12:17, 16 October 2008 (UTC)

For smaller elements, the general trend is that elements that deviate greatly from a 1:1 proton-to-neutron ratio are generally less stable. The "stability line" generally trends more towards the neutron side as elements get larger; the actual stability line has a somewhat parabolic character. There are also some trends over the stability of "even-even" proton-neutron nuclei as well. See Isotope#Nuclear properties and stability and Stable isotope for more information on this. The general understanding is that the balance between the three forces which work to hold the nucleus together, which are the nuclear force, strong interactions, and weak interactions, require a certain balance of neutrons to protons (this relationship is not necessarily linear, however). Carbon-14 is "out of balance" with regard to this relationship, and so is unstable. The other two carbon isotopes, C-13 and C-12 are stable. --Jayron32.talk.contribs 12:29, 16 October 2008 (UTC)

The nuclear force is the same thing as the strong interaction. The relevant forces are electromagnetism and the strong nuclear force (the weak force may be involved as well, but as the name suggests, it quite weak!). --Tango (talk) 18:33, 16 October 2008 (UTC)

Actually, the nuclear force is not the same as the strong interaction. Read the articles for more on this. What we call the nuclear force used to be called the strong force, however under Quantum Chromodynamics, the strong interaction (as carried by "gluons") is restricted to cover internal forces inside the neutron and proton holding the quarks together. The nuclear force (as carried by pions) is what holds the nucleons to each other. It is generally assumed that the pions contributed by the neutrons are necessary to overcome the force of electrostatic repulsion to be felt by neighboring protons. Pions themselves are made of quarks, so the strong force holds their internal structure together as well. --Jayron32.talk.contribs 21:00, 16 October 2008 (UTC)

It looks like I'm just not familiar with the terminology (it's not a subject I've studied in depth). They are manifestations of the same fundamental force, aren't they? --Tango (talk) 22:28, 16 October 2008 (UTC)

Yes; the simple answer is that the force between nucleons is a residue of the force between the quarks that, unlike the "real thing", can act on things (nucleons) that have no color charge, much as the van der Waals force is a residue of the electromagnetic force in atoms/molecules and can act on things (atoms/molecules) that have no electric charge. --Tardis (talk) 01:06, 17 October 2008 (UTC)

HIV and hemodialysis

Could a HIV virus load be removed through some sort of hemodialysis ? Mr.K. (talk) 12:23, 16 October 2008 (UTC)

No - dialysis is able to remove certain undesirable substances from the blood by physical and chemical means - but these are typically simple chemical byproducts. The complex biochemistry of a virus makes it hard or perhaps impossible to distinguish and remove by such a simple process. Being a virus also means that HIV has insinuated itself inside the cells of the host's body. Some of those (white blood cells, for example) could perhaps be removed by some hypothetical dialysis process - but there is a limit to the number of white blood cells you can remove and still remain protected against all of the other infectious agents in the environment. But HIV invades all sorts of other cells that are not a part of your blood - so even in theory, with some amazingly high-tech science-fiction blood cleaning machine, you couldn't remove more than some percentage of the HIV load. Viruses (not just HIV - but viruses in general) invade the inside of functioning cells and actually insert their DNA into your DNA. This makes them very hard to eradicate. Viruses replicate by having your own body make new copies - and even if you remove every single independent "virus" from your body - their DNA will still be tucked away inside your DNA waiting for your own cells to produce new viruses the next time the cell replicates. SteveBaker (talk) 12:48, 16 October 2008 (UTC)

Steve is (as always) right on the money - just thought I'd add a fascinating reference to a study of plasmapheresis for HIV and Hepatitis C virus: [[1]]. As Steve said, even removing a large percentage of a virus from the blood still leaves more than enough inside and outside the cells to maintain the infection. --Scray (talk) 12:58, 16 October 2008 (UTC)

Steve's answer is a good one, but a minor clarification would be good here. While many types of virus will make use of some of their host's DNA/RNA processing equipment, most viruses don't insert their DNA into the genomic DNA of the host. Group VI reverse transcribing viruses – including HIV – are the key ones that do; in addition to AIDS, these viruses can also be responsible for an assortment of other unpleasant diseases, including some cancers.

Interestingly, some of these viruses have become permanently incorporated into our genome, and may serve a host of useful purposes. See endogenous retrovirus for more details. TenOfAllTrades(talk) 14:29, 16 October 2008 (UTC)

Note however that even if a virus doesn't incorporate into the human genome, it may still remain latent in the body via episomal latency. See virus latency for some information. For example the Varicella zoster virus, as with other herpes viruses, establishes episomal latency in neurons. After chickenpox resulting from the primary infection it can re-active sometime later in life and result in shingles (something I've personally experienced). Nil Einne (talk) 09:30, 17 October 2008 (UTC)

Fair enough, though I'm not aware of a true RNA virus that has been shown to have a latent form (not talking about clinical latency). --Scray (talk) 01:51, 18 October 2008 (UTC)

Effects of masturbation

I am too embarrassed to ask anyone this question face to face, so I thought this might be a good place find an answer. I just wanted to know what the effects of masturbation are in teenage boys. --203.81.223.178 (talk) 15:41, 16 October 2008 (UTC)

Ejaculation, usually. A feeling of guilt maybe, if you grew up in a culture that still treats masturbation as some vile evil practice that makes your hair fall out. Certainly there are no serious negative health effetcs -- Ferkelparade π 15:47, 16 October 2008 (UTC)

...unless you do it often enough to get raw ;-). Seriously, it's good exercise, may decrease the risk of getting prostate cancer, will have no obvious side-effects, and everybody does it. --Stephan Schulz (talk) 15:55, 16 October 2008 (UTC)

Indeed - the general advice "if it hurts, stop" applies to masturbation just as to anything else. If you're doing it right, it won't hurt! --Tango (talk) 16:00, 16 October 2008 (UTC)

In fact there are possibly some benefits. It won't give you hairy palms, you can rest assured there. If you want more detailed advice, however, you really do need to speak to a doctor (don't be embarrassed, it's a perfectly normal thing to be curious about and doctors will keep your question entirely confidential, you can generally ask specifically to see a male doctor if that would make you more comfortable), we can't give medical advice. I'll give you some general advice, though: People in the playground generally don't have the faintest idea what they're talking about! Ignore any advice you get from a unreliable source, it's probably worse than useless. --Tango (talk) 16:00, 16 October 2008 (UTC)

There is an addiction side-effect. Addiction is often overlooked as a health problem, but it is a problem. Just noticed that orgasm makes no reference of any kind to endorphin. I was going to point out that becoming addicted to an opioid compound is not difficult. -- kainaw™ 16:01, 16 October 2008 (UTC)

Now, be careful. See Chuck Negron. While our article (perhaps rightfully) doesn't cover it, Mr. Negron's penis exploded due to massive overuse of said organ. [2] He reports the incident in gory detail in his own autobiography Three Dog Nightmare (the phrase "split open like a hot dog" appears in the book). He had been warned by his doctor that his level of sexual activity was damaging his L'il Chuck, but he unwisely ignored the advise of medical professionals, and continued to have sex like if he stopped for 10 minutes he might die. He reports an incident that led him to an Emergency Room in Oklahoma; the incident involved an audible tearing sound, lots of blood, and a groupie who will likely be in serious, intensive therapy for the rest of her life. Gives new meaning to the song Mama Told Me Not to Come, now don't it? Moderate levels of any sexual activity is perfectly safe (and some medical studies indicate that a regularly emptied scrotum is vital to helping prevent prostate cancer: [3]), but as with anything, you CAN overdo it. The above does not constitute medical advice in any way. --Jayron32.talk.contribs 16:03, 16 October 2008 (UTC)

Maybe Mr. Negron unwillingly pressed some Tsubo spot, like in the Hokuto Shinken martial art. Seriously, nobody hurted himself using hands. Some people are injured because they tried drugs or dangerous tools. But if you are worried, talk to a doctor. PMajer (talk) 10:12, 17 October 2008 (UTC)

ON the contrary, as mentioned by other above, the general friction, even lubricated, of overubbing can cause inflamation and discomfort or injury... Rub the same spot on your arm for hours on end, day after day, and you are likely to wear a sore into your arm. Now, apply that same test to your penis... SOund like fun? The general cautionary tale is that regular masturbation isn't harmful, but obsessive masturbation can be. --Jayron32.talk.contribs 12:13, 17 October 2008 (UTC)

Sorry but this analogy with rubbing one's hand is not convincing... The mechanics is totally different, in particular there is no friction at all on the skin in masturbation. Among all activities of a teenager, I would say this is the less dangerous (and let's add that normally it is the penis itself who decides when it is enough, and just goes to sleep). Of course too much is bad, but mainly because one misses other important things (reading, studying, socializing, making sport etc). An excessive masturbation activity is often due to a situation of stress, this is the point. Should one understand that his son is doing it too much, I would suggest to check if he is under stress, and why. Just repression would only add other stress. PMajer (talk) 16:45, 17 October 2008 (UTC)

there is no friction at all on the skin in masturbation - you are clearly basing that view on your own experience, PMajer. I can personally attest to the contrary. If the skin of the palm and penis is totally dry, there's no problem. And if it's well lubricated, there's no problem. But if there's only a small amount of moisture present, that does present a friction problem, and can lead to inflammation. -- JackofOz (talk) 22:38, 17 October 2008 (UTC)

Then I agree. In particular, it should be recommended not to handle chili peppers before. This is also based on one ancient personal experience :( --PMajer (talk) 19:25, 18 October 2008 (UTC)

Is it just me or "masturbation in teenage boys" is ambiguous? Indeed, it can be quite destructive to the personality of teenage boys. Mr.K. (talk) 16:11, 16 October 2008 (UTC)

I don't see an ambiguity and it's only likely to destroy someone's personality if they become addicted, which is unlikely. --Tango (talk) 16:38, 16 October 2008 (UTC)

I think Mr K. is playing on the word in there. As in, "The sixty year old felon who performs masturbation in teenage boys...". Personally, I think the terms masturbation and teenage boys are pretty much redundant. Matt Deres (talk) 17:33, 16 October 2008 (UTC)

Are you suggesting that adults and girls don't masturbate? I think the statistics would disagree with you there... --Tango (talk) 17:38, 16 October 2008 (UTC)

It's a superset/subset, not equivalency. He didn't say which term is redundant (and could be omitted without changing meaning) vs which term is the more limited in scope. Given "a hot fire", consider "a fire" vs "something hot" (assuming you have more experience with flames than with chicken-chokin' and...whatever the comparable female slang would be:). DMacks (talk) 18:16, 16 October 2008 (UTC)

Ok, I suppose that makes sense - since said both were redundant I assumed he meant they were mutually redundant (ie. equivalent), it makes more sense if he only meant one of them was redundant given the other. --Tango (talk) 18:27, 16 October 2008 (UTC)

Saying that teenage boys masturbate and other people masturbate too is like saying bullets are dangerous when fired from a machine gun and also when thrown freehand. Matt Deres (talk) 13:28, 17 October 2008 (UTC)

You should maybe redirect your question to the Reference desk/Masturbation in order to get an expert opinion. PMajer (talk) 13:12, 17 October 2008 (UTC)

The expert? DMacks (talk) 20:30, 17 October 2008 (UTC)

Why does pressure increase with depth

If pressure is caused by experiencing the sum total of elastic collisions of fluid molecules against an arbitrary plane (my words as I'm writing them)...

but given my current definition for studying fluid mechanics, this doesn't explain why the collisions are "stronger" at deeper depths because the density is the same and the temperature is the same.

If water molecules are crashing into the vertical wall of a dam then why should forces coming from above affect the frequency or impulse of collisions? If the impulse was greater, that would imply greater kinetic energy in the fluid molecules, which means they have more energy.

Take a 100 meter high dam, the horizontal collisions near the bottom should not depend on molecules above them, which act in a perpendicular direction, right? Water has the same density, and lets stipulate that the fluid is iso-thermic

How does defining pressure this way not explain why at greater depths, pressure is higher? I think it is because pressure exists in all directions right? So the upward force = the horizontal force. Right? So does that mean that the collision frequency is higher? or that the impulse per collision, greater? Or am I just completely wrong. Sentriclecub (talk) 17:49, 16 October 2008 (UTC)

I'll take a stab at it (though admitedly by stat-mech/thermo is a bit rusty… Pressure really does exert "in all directions" as you suggest. Molecules don't just bounce "up and down or side to side", but at all other angles as well. So vertical pressure (weight of what's above, or the effect of vertical collisions each pushing down upon the next) can exert a non-vertical force if any molecule has a non-zero horizontal component to its motion. DMacks (talk) 18:08, 16 October 2008 (UTC)

Additionally, I've spent 5 days studying the topic, and know it can be explained by Pascal's law, but I want to know why it can't be explained or deduced from the method of looking at pressure as ultimately a result of elastic collisions on an arbitrary surface. There's only two ways to increase the average force of a series of impulses... either increase the frequency, or increase the impulse per collision. How does the random translational motion increase with depth, if density and thermal energy and temperature stay the same? I've already asked on yahoo answers, and got a starred question award, and 2 wrongs answers ("because density increases") and the other answers are not helpful, and they use weasel words "well could be..." Sentriclecub (talk) 18:13, 16 October 2008 (UTC)

DMACKs, Yes I understand they exert a force downward onto other molecules, but the bottom line is that somehow there is a resultant increase in collision frequency or an increase in impulse magnitude. I fully understand Pascal's law, but my book doesn't answer my specific question, nor the related wikipedia articles. Sentriclecub (talk) 18:18, 16 October 2008 (UTC)

So far the best answer from the other website is...You asked a very good question. You can't quite compare gas and fluid but for simplicity, I will. Water is NOT incompressible. As you go deeper, its density increases with pressure. Before you go down, there is very little room between the molecules. But you go down 30 m, there is now even less room. This means that the number of collisions will go up dramatically. So the pressure increases. The water, however, keeps the same kinetic energy and temperature. BTW: The reality is a little different. The water molecules vibibrate against each other, but they also impinge on each other's electron clouds. Kinda of a spring effect, so it is not quite so straight-forward.

My next guess is through statistics and a normal distribution. Maybe if the layer of water molecules on the bottom of the fluid can only bounce between 0 and 180 degrees, then the second layer has an extremely small chance of colliding straight down because of the concentrated upward range of the the molecules directly below it. In other words, near the bottom, the statistical distribution of all possible collisions that can occur in 3d space isn't equally probable. Molecules on the bottom have zero probability of being able to return from a collision against the ground with a downward momentum. That is a majority of molecules near the very bottom can only have an upward momentum at any given time. This "fact" must be balanced by the second layer of water molecules who must pass the "fact" along, and give this problem to the layer higher up, who must eventually "resolve" the fact, by being basically free to have zero net momentum as observed in the top layer. This is just a educated guess, based on creativity, not science. Sentriclecub (talk) 18:46, 16 October 2008 (UTC)

To put in better terms, 100% of molecules on the bottom layer must have a upward momentum immediately after a collision. 50% of molecules on the bottom layer have an upward momentum before a collision. Thus the net momentum of the bottom layer is 75% upward, if a reasonable assumption is that all the bottom layer fluid molecules are returning from a collision, and fixing to collide again. A net downward force would need to act on the bottom layer to counteract the upward momentum as suggested by the 50%/100% theory. Still this is all a guess, but I have been unable to finish writing my notes because I hate the feeling of a lingering doubt on pressure. Sentriclecub (talk) 18:52, 16 October 2008 (UTC)

Just a teaser, and I plan to write a long response this afternoon when I get a chance. However, some of the confusion stems from drawing a false analogy between pressure in gases (mediated primarily by kinetic energy) and pressure in liquids/solids (mediated primarily by bond energy). Dragons flight (talk) 18:58, 16 October 2008 (UTC)

I think I'll take a wild guess. How about gravity? Looking at a free water particle outside of a gravitational field, any of the 360 degrees are equally possible. Within Earth's gravity, however, it becomes more probable that the particle has some "downward" component to its velocity vector. These add up the deeper you go, resulting in higher pressure. The interesting question would be: If you had a jug of water (maybe a large pool-sized jug) in space, would the pressure change the "deeper" (more towards the center) you go? I don't really have an answer to that. --Bennybp (talk) 19:50, 16 October 2008 (UTC)

Actually I didn't really answer the question (why it would be omni-directional, and not just downwards). It's probably a pretty flimsy theory, but - Due to the pressure from the molecules coming from the top, the molecules at the bottom would be given more side-to-side velocity, since 1.) They have the same average speed (same temperature), and 2.) There's a limit on their direction of motion ("up" is no longer available, so all others become more probable). Man, I think I'm just digging myself a nice hole. I eagerly await Dragons' answer :) --Bennybp (talk) 20:03, 16 October 2008 (UTC)

The false analogy here is that the treatment of "pressure" for the gas phase is the same as for "condensed" phases. It isn't. For gases, there is roughly a linear relationship between pressure and density; double the pressure, double the density (I say roughly; its exact under the Ideal gas law; the Van der Waals corrections alter this slightly). That is because, for gases, the intermolecular distance is roughly 1000x greater than the molecular radii, meaning that gases are compressable (you can simply "push" the gases molecules together). The entire question by the OP assumes this compressable model of pressure; it works fairly well for gases. However, liquids and solids are condensed phases; for all intents and purposes the intermolecular distance between them is essentially nil. (they can be compressed slightly; water at 100 m below the surface is slightly more dense than the water at the surface). In the case of condensed phases, pressure is determined by weight of the bulk material above you. That's it. Pressure is only force per unit area, and weight is only a force. With a gas, the force is primarily determined by collisions, since the gas molecules don't remain in contact with the surface for any meaningful length of time. With condensed phases, the surface is essentially in constant contact with the molecules (and for a liquid, the exact molecules shift places because it is a fluid, but in bulk, essentially the entire surface where the pressure is measured is totally covered with the molecules). Consider two thought experiments:

1. Imagine burying someone under a 100 m tall pile of sand. What happens? We say they are crushed to death because of the weight of the sand on top of them But this is merely convention. The weight is a force, and it crushes them by pressing in on the surface of their body? What is a force distributed over a surface? Pressure... Now, replace "pile of sand" with "depth of water". Its the exact same problem.
2. Imagine the same person, with appropriate breathing apparatus, encased in a cube of water 100 m on a side, but the person and the water are in a zero-g situation, like floating in space. What happens? Nothing. They survive fine, because the water doesn't press them because there is no gravity to force the water in any one direction. Even if they swim to one side or the other of the cube, there is no net pressure effect, because there is no gravitational force. No force equals no pressure.

Does that make sense to everyone, the OP's question is in error because it makes assumptions about pressure which are incorrect to the situation; liquids are fundementally different than gases WRT molecular organization, and that fundemental difference affects the way that the molecules exert a "force" on their surroundings. --Jayron32.talk.contribs 20:26, 16 October 2008 (UTC)

Hooray for that answer (well, for the first part - the second part is muddled ;-). People are (mostly) water, so with "appropriate breathing apparatus", we survive fine under a hundred meters of water, even under gravity. See SCUBA. We are crushed only if the pressure does not come from all sides equally, or of there are unequalized air spaces in the body. --Stephan Schulz (talk) 20:43, 16 October 2008 (UTC)

I think you are mostly correct. There's still a little bit of explaining to do as far as it acting on all sides at once, with equal pressure. Consider a perfect structurally-sound sphere. In my mind, under 100m of sand (with plenty on the sides, too), it would be crushed flat. The pressure is not equal all around. In water, in my mind, it would implode - the pressure being equal on all sides. This would be due to the fact that water cannot be treated completely as a bulk material - there still is plenty of molecular motion to account for - sand is held in place with friction. If the sand were frictionless, it would be just like macroscopic water (ignoring hydrogen-bonding, van der Waals forces, etc.)

I believe modeling water as a pseudo-gas is correct. The amount of material above you does cause the increase in pressure - for condensed phases and the gas phase as well. On Earth, our air pressure is omnidirectional - we are under a bunch of atmosphere. Same with water at the bottom of the ocean. Where does the "sideways" pressure come from? I guessed at that above. (I say authoritatively, but I might run to my p-chem book to find some equations) --Bennybp (talk) 20:57, 16 October 2008 (UTC)

In answer to Bennybp's question about water in zero-g, the water will attempt to form a sphere since that's the least energy configuration (because of surface tension, I believe - a sphere has the least surface area for a given volume). The pressure will increase as you move towards the centre because of the gravity of the water itself, however for a swimming pool sized amount of water that gravity (and therefore the pressure) would be minimal (in fact, it may not even be enough to keep the water together depending on initial conditions and outside influences - the water may break up into lots of smaller spheres). For a planet sized amount of water, the pressure at the centre will be very great. --Tango (talk) 20:40, 16 October 2008 (UTC)

Thanks Tango. I feel I knew that at one time. The more I read the answers above and below the more I realize I think I have the right answer but to the wrong question. Ah well, better luck next time :) --Bennybp (talk) 15:38, 17 October 2008 (UTC)

DF answer

Sentriclecub, your problem is mostly one of a false analogy. In gases, particles act more or less independently. In that case, pressure is primarily the result of elastic collisions and is proportional to density times temperature/kinetic energy. Hence increasing pressure implies increasing either the density or the energy per particle.

However, liquids and solids are not gases. Pressure is mediated not by kinetic energy but rather primarily by changes in the intermolecular potential energy. To see how this works, let's consider the other extreme: solids. A typical solid at fixed tempertaure can resist very large pressures with very little appreciable deformation (i.e. very little change in density. It does this because the bonds between atoms resist being compressed, and hence provide a spring-like quality to the matrix of the solid. It is that springness, essentially a result of potential energy stored in compressed bonds, that provides the force to resist compression.

Now consider what happens at the interface. For a gas, the force it applies to a wall is caused by particle bouncing off. For a solid, the force is more direct than that. It is caused by the electrostatic repulsion of the electrons in the solid interacting with atoms in the wall at the point of contact. That is a direct steady-state impact, that occurs independently of how rapidly the molecules might be moving.

Like solids, the pressure in liquids is also dominated by the effects of intermolecular "bonding", though it is harder to understand because such bonding in liquids is transitory and mutable. Molecules in a liquid can slide past each other and be rearranged, but nonetheless they try to maintain a roughly constant distance from each other due to the electrostatic interactions between molecules. It is that constant interaction with their nearest neighbors that allows liquids to resist compression and have a preferred density.

So that answers part of your question. Rather than being related to molecules bouncing off of the wall (as in a gas), the pressure the water exerts is caused by the compressed intermolecular interactions within the water and in continuous contact with the wall.

You also ask why is the pressure the same in all directions. Again I am going to start with solids and work my way over to liquids.

In a solid there is a stiff arrangement of atoms that can thought of like masses seperated by little springs. For the sake of discussion let's start with a 1-D set of mass and springs:

 O -vv- O -vv- O

If you apply a force along it's length, you compress it:

 O -w- O -w- O

As long as that is held perfectly linear, the forces balance and cancel. But the real world is not linear. We have vibrations and other imperfections, and given the opportunity, the middle mass would like to relieve the tension in the springs by skewing out of the line.

    |- O -|
 O -|     |- O

For a solid, linear compression creates a relatively small sideways force because other atoms in all the other directions are approximately fixed and restrain this sideways skew. If you kept applying force though, the solid would bulge out sideways and eventually break.

So how does that apply to a liquid. Well like a solid, if you apply a linear force, that tends to squeeze things in the middle. However, unlike with a solid, the individual atoms are free to move. So if you try to squeeze water it will squirt out sideways immediately. The only way to stop it from doing so is also apply an additional sideways force to restrain it. It may not be obvious, but the amount of lateral restraining force ends up being exactly the same as the amount of compression force being applied. Or, more simply, the amount of force in all directions must be the same in order to keep the liquid stationary. And, as if by magic, we arrive at the concept of pressure, i.e. a force acting equally in all directions. Dragons flight (talk) 22:10, 16 October 2008 (UTC)

Perfect explanation. This whole time I was thinking that pressure is just a corollary from the concept of force. This is exactly like the time I sought a relationship between impulse and work, because I just knew there was some deep intuitive relationship, and after several days and dead-ends I finally saw that they are related by average velocity. This explanation through the analysis of force, is exactly the way my brain needed to understand it. It makes sense that if the additional sideways force wasn't as large as the linear force, then a very slight disturbance to the unstable equilibrium would further propel that unequilibrium in that continuing direction.

In my own notes on Pascal's principle, I wrote: An enclosed liquid is extremely inefficient at resisting pressure. If force is applied at one point, the fluid responds everywhere as an equal & opposite reaction, as if the pressure was thought to be coming from everywhere. because this is intuitive and explains how a tall narrow straw filled with water could add several billion newtons of pressure to an enclosed liquid in a multi million gallon rigid tank, according to an ideal fluid. Your answer meshes perfectly with my notes from yesterday, and now I can expand on my notes using the same analysis method proving everything through force. What a swell day! In order to maintain the 3-d matrix, the force must exist everywhere continuously, and varies with respect to height, in order to "balance all the equations" and not violate any force laws which stipulate that an imbalance would cause an acceleration to some part of the system.

The combined answers today are definitely the best help I've had from the ref desk. I don't have a professor or t.a., just a physics book, and youtube[4], and the ref desk. My passion for learning is fueled by making connections between concepts allowing such insights into nature that I feel fortunate for being invited to see. Just as chess grandmasters have their priceless insights into chess, I cherish mine into nature(though I'm still a noob), as nature reveals herself through physics and everything else. Sentriclecub (talk) 22:38, 16 October 2008 (UTC)

Hi. Going back to the OP and the issue of a molecular explanation for pressure in liquids, the stiffened equation of state section of equation of state might be useful for understanding the compressibility of water. Water is "like air that is already under 20000 atmospheres of pressure" which explains why it is essentially incompressible under daily life (taking water from 1 to 2 atmospheres is like taking air from 20001 to 20002 atmospheres). HTH, Robinh 07:12, 17 October 2008 (UTC)

bladder TCC insitu with bone mets

a patient has been diagnosed bladder TCC insitu for many years, is recently found metastasis to bone. is it possible that a bladder TCC insitu patient has a bone mets?

Thanks,

George —Preceding unsigned comment added by Gxu (talk • contribs) 21:22, 16 October 2008 (UTC)

Sorry, no medical advice allowed here (see top of page). --Scray (talk) 22:53, 16 October 2008 (UTC)

Sounds like home work. We do not do homework either. Look up your text book.--GreenSpigot (talk) 00:29, 17 October 2008 (UTC)

Both the above comments are unnecessary. No medical advice was asked for: medical information was ("Can in situ carcinoma (as opposed to invasive carcinoma) metastasize to bone?"). And it's clearly not homework, nor would it need comment, especially one like "look up your text book", if it were. - Nunh-huh 00:53, 17 October 2008 (UTC)

Actually it could be homework. Cancers preferentially metastasize to certain other tissues - that would be a valid "homework" question, although someone at that stage of education would hopefully not be checking Wikipedia (though I know a doctor who regularly checks eMedicine for more reliable, but still background, info). And it could also be a request for "advice", as it's a pretty specific question. If we answer anything other than "maybe, ask your doctor", we are providing specific information - but we don't get to see the biopsy results, X-rays, MRI's, diagnostics from the bloodstream, nothing. So - maybe, see your doctor. Franamax (talk) 06:09, 17 October 2008 (UTC)

I've been through every course it could conceivably be "homework" for, and such classes don't assign that kind of "homework". Clearly not a homework question, and - even if it were - the original questioner will not be in any way enlightened by learning that it "sounds like homework" to a Wikipedia user. And no, a request for information, no matter how specific, is not a request for advice. - Nunh-huh 17:11, 17 October 2008 (UTC)

This statement: I've been through every course it could conceivably be "homework" for, and such classes don't assign that kind of "homework" is remarkable, considering the number of professions (medical, nursing, graduate programs...), cultures, etc that are "conceivable". Wow. --Scray (talk) 01:21, 18 October 2008 (UTC)

No matter the profession, the class would be "clinical pathology (human)", "oncology", or some variant thereof. Wow indeed. - Nunh-huh 01:42, 18 October 2008 (UTC)

Try Metastasis for the mechanics of it. Julia Rossi (talk) 07:21, 17 October 2008 (UTC)

Yes. See this article. Axl ¤ [Talk] 08:26, 17 October 2008 (UTC)

Thanks, I didn't want to post the answer without a reference. Great work! - Nunh-huh 17:11, 17 October 2008 (UTC)

The article this readers wants to read is Transitional cell carcinoma, which is a minimal stub. The question is encyclopedic in nature (just ignore the stated reason for asking; for our purposes it is irrelevant). --Una Smith (talk) 04:46, 21 October 2008 (UTC)

October 17

Uvula

Hi - I think somethings wrong with my uvula. Do you have any recommended sites to help me self- diagnose what could be wrong with my uvula.

Thanks, April 67.182.219.78 (talk) 02:52, 17 October 2008 (UTC) —Preceding unsigned comment added by 67.182.219.78 (talk) 02:51, 17 October 2008 (UTC)

Once again, we cannot legally offer medical advice. See a doctor if you feel that you have a problem.CalamusFortis 03:01, 17 October 2008 (UTC)

There is a site called WebMD. I've never used it, but I'm certain it's not as good as seeing a real doctor. AlmostReadytoFly (talk) 07:57, 17 October 2008 (UTC)

There;s also the article Palatine uvula with pix and pathology. Julia Rossi (talk) 08:35, 17 October 2008 (UTC)

I've tried the symptom checker, and for any given set of symptoms, it'll typically give you two dozen causes, with treatments ranging from "ignore it" to "get to an emergency room yesterday". --Carnildo (talk) 20:32, 17 October 2008 (UTC)

You know, I've heard of these people called "doctors" that have experience with this sort of thing. Maybe you could try one of those?CalamusFortis 03:42, 18 October 2008 (UTC)

Need Genetic Analysis of Japanese people

Historically, various non-Chinese groups like the Central Asian Turks, Iranians and Uyghurs have moved to Central China and were sinified in successive waves and together affecting the ancestry of the Chinese, thereby the Han Chinese are not very pure mongoloids. Similarly, the southeast asians may look mongoloid but they have mixed with arabs and east indians in ancient times. However, the Japanese had not mixed with many various non-mongoloids like what the Chinese and southeast asians had done and therefore they kept their race pure by living in remote, islolated islands for thousands of years.

I need a genetic analysis comparision between the Japanese people and other asians (Chinese and southeast asians) and the analysis explains that the Japanese are more pure mongoloid. Can anyone please provide me with a website that has a genetic analysis comparision between the Japanese and other asians? 72.136.111.205 (talk) 03:11, 17 October 2008 (UTC)

I think you'll have a hard time finding what you're looking for, because most geneticists reject these old conceptions of race. For example, see Mongoloid race and Historical definitions of race. --Allen (talk) 03:55, 17 October 2008 (UTC)

I's also suggest Japanese people. Though if you are trying to prove the superiority of a culturally and genetically isolated people, you'll probably be disappointed. Minorites like the historically repressed Ainu are probably a better approximation of the genetic heritage of the original occupants of Japan than is the current dominant ethnic group, which is itself probably a mixture of the original Japanese with Korean and Han lineages. Dragons flight (talk) 04:31, 17 October 2008 (UTC)

Your question isn't very scientific. You start off with a premise, that may or may not be correct which is fine. But then despite the fact your premise is unproven, you asked for evidence to support your premise rather then simply asking for what evidence there is out there and whether it supports your premise Nil Einne (talk) 09:12, 17 October 2008 (UTC)

If you don't readily see nil einne's point, we have a decent article on the phenomenon. SeeConfirmation bias. --Shaggorama (talk) 09:54, 17 October 2008 (UTC)

Sites of interest: the International HapMap Project [5] (genetic mapping of SNP's); the Yanhuang project (mapping genomes of 100 Chinese individuals); the 1000 genomes project (mapping genomes of 1000 individuals worldwide, including HapMap participants); overview of these projects in Nature [6].

And to the comments above imputing racist motivations for the question: it is actually quite likely that Japan, as a more closed society over the last thousand years or so, will have a more "pure" genetic background similar to that of Iceland, which deCODE genetics, Inc. sought to exploit. The exact meaning of "pure" is of course wide open to interpretation - but the projects I've cited are a scientific attempt to quantify those differences and similarities. Franamax (talk) 22:58, 17 October 2008 (UTC)

Franamax, I don't have access to those sites. I don't care about Ainu and the HapMap. Let's get to the real point. A certain group that live isolated for a long time, is generally more "pure". I simply want a genetic analysis that compares the Japanese people and other asians and to explain that the Japanese people are more pure oriental. 72.136.111.205 (talk) 23:42, 17 October 2008 (UTC)

It's too bad that you don't have such access or you would see that the premise "a certain group that live isolated for a long time" is fatally flawed. Japan and surrounding areas is part of at least three major migration routes: Southern Asian coastal and overland; and mid-Asian overland. mDNA evidence makes this clear. It's important to start with evidence then draw conclusions instead of vice-versa. Saintrain (talk) 00:23, 18 October 2008 (UTC)

And thanks for revealing your true colours in the face of my good faith efforts. The first three of my links are open to all. Those links are where you can watch the efforts and begin to construct your theory of racial purity. The world being what it is, I doubt such evidence will turn up, but watch the science and maybe you can twist it somehow. As to your "simple analysis" to explain Japanese people being "more pure oriental" - I don't know of one existing and I don't know of any scientific group particularly interested in pursuing such a ridiculous notion (since e.g. they would first have to genetically define "oriental", which is an exercise in futility). The concepts are much more complex than you seem to think. Franamax (talk) 00:45, 18 October 2008 (UTC)

Further proof you just don't get it: haplotype maps are the way to identify genetic "purity", through persistent SNP linkage patterns among homogeneous populations. Franamax (talk) 00:51, 18 October 2008 (UTC)

The other question is, what do you mean by 'oriental'? As others have point out, the idea of a Mongoloid race is now not particularly well supported. Furthermore the idea of an 'ideal' specimen of any race is even less supported. You can perhaps say members of race 'X' tend to have features A, B and C but to say an ideal specimen of race 'X' should have features A, B and C is quite a different thing and doesn't make much sense based on out modern understanding of genetics and evolution. So back to the question, what do you mean by 'oriental'? If you define 'oriental' to mean 'like-modern Japanese' then yes you can say modern Japanese are the 'race' most 'pure oriental'. But that's not surprising since basically what you've said is modern Japanese are the 'race' most 'like modern Japanese'. You don't really need any link to tell you that the modern Japanese are more like modern Japanese then modern Han Chinese are like modern Japanese. Of course you may find that modern Japanese are often more different from one another then some modern Koreans or modern Han Chinese are from some modern Japanese. Nil Einne (talk) 05:16, 18 October 2008 (UTC)

As an interesting footnote to this point, I strongly suspect that if one were to define "oriental" as something like a collection of those alleles having the highest frequency in the peoples of East and Southeast Asia, then Japan would probably be less "oriental" than China. By virtue of being somewhat more isolated and less numerous than mainland populations, I'm sure they do a poorer job of reflecting the median phenotype. For example, O is the common blood type among Chinese (~40% of the population), but only 25% of Japanese have that type, with A being most common (~35%). Similarly, there is a "Japan type" Y-linked DNA marker that is more prevalent on the islands than anywhere else and probably originated there. The flip-side of isolation is that a population also has the opportunity to evolve independently of the larger parent group. Dragons flight (talk) 15:25, 18 October 2008 (UTC)

Oriental means mongoloid. You can't find what I want which is okay. 72.136.111.205 (talk) 22:13, 18 October 2008 (UTC)

"Mongoloid" is a historical term pre-dating genetics by nearly a century and doesn't have any widely accepted genetic meaning, hence asking for a genetic analysis of "oriental" or "mongoloid" traits isn't a meaningful question unless you also provide a means of specifying precisely which genetic traits you really mean. Dragons flight (talk) 22:56, 18 October 2008 (UTC)

Mongoloid and oriental in common use simply means something like "people who look like the average individual that one will find in the 'orient' ", and it's a pretty crappy meaning if you look at it from a scientific standpoint. Looks are deceiving and the "looks Oriental/mongoloid = genetically 'Asian' " correlates very poorly with any genetic traits other then the ones that express the phenotype of the "looks". And sometimes not even. If you are simply interested to know the genealogy of the Asian cultures maybe Genealogical DNA test can be a good place to start the learning process. Sjschen (talk) 03:26, 19 October 2008 (UTC)

Movie sound

There's a stereotypical background animal sound that always turns up in jungle movies. It goes something like ooh, ooh, ooh, ooh, aah, aah, aah, aah (you know the one). Is there really some critter that makes this sound, and if so, what is it? Clarityfiend (talk) 05:27, 17 October 2008 (UTC)

I think it's a chimpanzee call you're thinking of. [7]. --Allen (talk) 06:44, 17 October 2008 (UTC)

Or kookaburra?[8] --Rallette (talk) 07:31, 17 October 2008 (UTC)

This could be several types of apes. You may want to listen in at [9] for some samplings of very jungle-like sounds of gibbons —Preceding unsigned comment added by EverGreg (talk • contribs) 12:56, 17 October 2008 (UTC)

I'd say it's certainly the kookaburra. Probably soon to be followed by the Wilhelm scream. --Sean 13:38, 17 October 2008 (UTC)

I was going to say that "there's only one problem with the kookaburra: it's found only in Australia and New Guinea. We do have lots of tropical jungles and rainforests, but not many movies have been made in those locations to my knowledge". But then I was shocked to read that "Although the kookaburras are restricted to a relatively small part of the world, the distinctive sound they make has found its way onto many "jungle sound" soundtracks, used in movies and television as well as certain Disney park attractions no matter where in the world the action is set". This cultural phenomenon must also explain why I blithely assumed for many years that tigers were native to Africa - I saw them in lots of African-set movies as a child. -- JackofOz (talk) 22:19, 17 October 2008 (UTC)

In Ramar of the Jungle this sound was constantly heard, and it sounded like a bird. "Hoo! hoo! hoo! haa! haa! haa!" Either that or a very crazy ape or human.Edison (talk) 02:39, 18 October 2008 (UTC)

The belief that there are penguins in the Arctic seems to be a fairly widespread one. That probably originates from Saturday morning cartoons. Heh, I used to think that dinosaurs lived alongside humans because of cartoons I watched when I was a kid. --Kurt Shaped Box (talk) 23:08, 17 October 2008 (UTC)

Tooky-tooky bird (Tookarus birdoozi). Characteristic call is "Ah ah ee ee tooky tooky". Hope that helps. Saintrain (talk) 00:29, 18 October 2008 (UTC)

Thank you ou ou ou, aah aah aah aah. Clarityfiend (talk) 03:53, 18 October 2008 (UTC)

Distance from nucleus: d or s orbitals

(moved from RefMisc by Franamax (talk) 05:56, 17 October 2008 (UTC))

Yo, just some basic high school chemistry here: Say we take a transition metal in Period 4; the 4s suborbitals fill up before the 3d orbitals right? Yet, the 4d orbital electrons are lost first before the 3d ones in a reaction? So which one is the valence electrons? The ones in the 3d or 4s orbitals? Also, which of these suborbitals is farthest away from the nucleus. ie the greatest radius away? I'm guessing 4s because transition metals are dense because the 3d orbitals increase the atomic mass, without increasing radius. If this is the case, why is the 3d orbital considered a "higher energy" orbital than the 4s?

Peace guys, Hustle (talk) 01:20, 17 October 2008 (UTC)

See Electron configuration#Ionization of the transition metals. That subsection of the article on configurations explains the transition metal paradox, that the filling order does not match the removal order. The assumption that all iso-electronic ions have the same configuration is faulty; the different Z_eff between, say, Fe⁺² and Cr shows that the two systems are not in the same general electric field, so the two systems do not behave identically WRT electron organization. Also, it is helpful to remember that the idea of electron configuration is more descriptive that predictive. We have a limited number of samples, 100 and change, with which to make understandings of the system. Describing the trends in the system is easier than explaining why those trends occur. The common explanation for any deviation from expected norms in chemistry is "Well, that is a more stable state" or "Well, that is a lower-energy state", both of which mean, essentially, "Well, that's just what it does". Its also helpful to remember that all atomic models, even rather complex and detailed models such as quantum mechanics, are models, and by necessity, are incomplete in explaining all aspects of the real system. Nature does what it does, and our models can be adapted if they don't completely fit; however it may be impossible, from a philosophical point of view, to ever create a model which fits nature 100%. --Jayron32.talk.contribs 11:57, 17 October 2008 (UTC)

Alpha Centauri system seen from Saturn

In this image: [10], Cassini took a picture of the Alpha Centauri system just over the limb of Saturns rings. You can clearly see that it is a binary star in the image, but why is this? α Centauri Appears as a single star from Earth and Satrun isn't that much closer (relatively!) to α Centauri, so why is it so much larger? How much magnification is necessary to see that α Centauri is a binary? Did Cassini magnify the image? 63.245.144.77 (talk) 08:44, 17 October 2008 (UTC)

Gravitational lens? PMajer (talk) 09:43, 17 October 2008 (UTC)

It's the nearest star to us, what could get inbetween to create a lens? --Tango (talk) 13:35, 17 October 2008 (UTC)

Our article on Alpha Centauri says that the angular separation of the two brightest stars in the Alpha Centauri system varies between 2 and 22 arc seconds. Let's take a value of, say, 10 arc seconds. Our visual acuity article says that a person with standard visual acuity can distinguish a pair of objects with a separation of 1 arc minute. So a magnification of about 6 is required to visually separate the Alpha Centauri binary pair. Couldn't find any detailed information about Cassini's visual imaging systems, but the flatness of Saturn's rings in that image suggests a considerable amount of magnification, either in the original image or in subsequent processing. Gandalf61 (talk) 10:19, 17 October 2008 (UTC)

And indeed, you can separate Alpha Centauri with a small backyard telescope, or even a pair of decent binoculars. The Cassini Narrow Angle Camera is a 2 m f/10.5 reflector[11]. I know little about optics, but this provides more magnification than a pair of binoculars ;-) . --Stephan Schulz (talk) 11:31, 17 October 2008 (UTC)

The image's filename is Alpha_Centauri_AB_over_limb_of_Saturn_PIA10406.jpg. It appears to me that we're looking at the limb of Saturn itself, with atmosphere – not the rings. In the foreground we see the rings' shadow (fuzzier than we usually see the rings, because the shadow falls on clouds). What does this say about the flatness? —Tamfang (talk) 03:01, 18 October 2008 (UTC)

I really can't see how bright band across the image can be the limb of the planet itself - more likely, as the OP says, the star is appearing over the limb or edge of Saturn's rings. Maybe the filename of the uploaded file is inaccurate or incomplete. But this is all speculation. If we knew the original source of the image, it might have more details of context, exposure time, magnification etc. Gandalf61 (talk) 11:10, 18 October 2008 (UTC)

But the outer edge of the rings doesn't look like that! —Tamfang (talk) 16:40, 18 October 2008 (UTC)

Makes me wish I lived in the Southern Hemisphere so I could look at Alpha Centauri with binoculars. :( Are there binary stars in the Northern Hemisphere that you can tell are binary systems using only binoculars? 63.245.144.77 (talk) 17:58, 18 October 2008 (UTC)

Alpha Centauri is interesting to watch because the two components have very obviously different colours. This search returns info on some Northern hemisphere double stars that can be observed with binoculars. Albireo (β Cygni) is described as quite beautiful. --Stephan Schulz (talk) 19:38, 18 October 2008 (UTC)

Thanks a lot! I'll have to look at some of these objects. Ob the search, one of the first things that shows up is the Moon, and I look at the Moon with binoculars nearly every night it's out, but these other objects look like a lot of fun too. Thank you. 63.245.144.77 (talk) 06:55, 19 October 2008 (UTC)

Frequency of different forms of cancer

Why are some forms of cancer much common than others? For example, why is heart cancer so uncommon?Mr.K. (talk) 09:32, 17 October 2008 (UTC)

See "Carcinogenesis". In cancer, there is a mutation in a cell line that leads to uncontrolled cell division. Certain cell populations already have high rates of natural cell division, notably epithelium and bone marrow. Other tissues, especially connective tissue and muscle, have low natural rates of cell turnover. High turnover tissues require less exposure to carcinogens in order to transform. Also, epithelial surfaces have more contact with the outside world, so have greater exposure. Axl ¤ [Talk] 10:52, 17 October 2008 (UTC)

Length of electric power transmission lines

From out article on Electricity_transmission#Losses: "As of 1980, the longest cost-effective distance for electricity was 4,000 miles (7,000 km), although all present transmission lines are considerably shorter."

How long is the longest line? How long are common lines? Mr.K. (talk) 12:53, 17 October 2008 (UTC)

From the same article: "Longest power line: Inga-Shaba (length: 1,700 kilometres (1,056 mi))", and it also states that intermediate length lines are about 100km. Capuchin (talk) 14:45, 17 October 2008 (UTC)

Interesting note: long power lines are vulnerable to coupling to the weather in space. Franamax (talk) 22:32, 17 October 2008 (UTC)

Solar phenomena can cause substantial DC voltage gradients on earth. These can be controlled by the proper placement of capacitors in neutral connections. Common lines go from substation to substation which can be tens to hundreds of miles.The referenced article says "Longest power line: Inga-Shaba (length: 1,700 kilometres (1,056 mi))" In more highly developed countries, lines would not be that long because of generating stations or load centers being more closely spaced. ("Hey! Gimme access to that power line!") In more war-torn regions, it would be easy to keep the line shut down by obvious means. Since it is high voltage DC, it would be expensive to tap into it to promote local industry along the route, due to the high cost of valve halls and switching yards. Edison (talk) 02:27, 18 October 2008 (UTC)

helicopter lift control

I have been working on creating a model helicopter with some automatic hover control. But I would like to know that what is it: torque or rpm of the motors that would determine the lift? Any shortcut method of creating the driving circuitry of brushless dc motor would be highly appreciated. 218.248.70.235 (talk) 14:52, 17 October 2008 (UTC)

Lift in a helicopter depends on both rpm and collective pitch. Our radio-controlled helicopter article has a section on typical model controls - sounds quite complex. Gandalf61 (talk) 15:10, 17 October 2008 (UTC)

Does your model helicopter have pitch control? If so, it is likely going to be much easier to adjust pitch than to constantly increase/decrease RPM. I would expect it to increase the lifespan of your main rotor motor as well. -- kainaw™ 15:49, 17 October 2008 (UTC)

Remember - that changing the motor rpm (which requires you to change the torque - they aren't independent variables!) also changes the tail rotor rpm (the two are connected via a driveshaft and gearbox). In theory, you have the two nicely balanced by the pitch of the tail rotor blades - but that's rarely a perfect thing - so expect the helicopter to yaw around as you control the lift. When you change the collective - you increase the drag on the main rotor so it will tend to slow down. When hovering (particularly) you get all manner of interactions from 'ground-effect' at low altitude - and if you are hovering in a confined space (eg close to a building or something) then there are lateral forces due to that same effect. If the helicopter does start to move laterally or forwards/backwards, the amount of airflow over the forward-moving rotor is more than that on the backward-going blade - so the helicopter will want to roll or pitch because of increased lift on the faster-moving blade. Even as you attempt to cancel out the original motion, you need to compensate for the induced roll using the cyclic pitch control...but that too increases drag and that changes the required engine torque which cuts rpms which... Well, let's just say that the take-away lesson with helicopters is that no matter what parameter you change - at least two others will change as a consequence of that. Good luck with your project - it sounds fascinating! SteveBaker (talk) 00:35, 18 October 2008 (UTC)

Eskimos

Why do eskimos live in such inhospitable locations? If they settled there when it was inhospitable, why? If it became inhospitable after they settled, why didn't they migrate somewhere else? I suppose they have enough food and other resources, but why didn't they seek out somewhere easier to live? MikeInABox (talk) 15:21, 17 October 2008 (UTC)

Probably because there were already people living in the more hospitable places. It was easier to live in the inhospitable place than to fight for resources elsewhere. --Tango (talk) 15:43, 17 October 2008 (UTC)

Or maybe they didn't know anywhere else was actually more hospitalable? But Tango's response is more convincing :) —Cyclonenim (talk · contribs · email) 15:46, 17 October 2008 (UTC)

That still leaves the question why they do not migrate now.--Radh (talk) 15:56, 17 October 2008 (UTC)

It's what they've always known, it's their cultural tradition. People often choose to stick with what they're familiar with rather than change to something better. --Tango (talk) 16:42, 17 October 2008 (UTC)

Not really. They are perfectly well adapted, culturally speaking, to their environment. They have no reason to leave, and indeed why would they or anyone else want them to. If we judge them from our perspective in our environment (like "I would never want to live there"), then we do the Eskimo culture a disservice. They probably look at modern city life and make the same statement. --Jayron32.talk.contribs 16:41, 17 October 2008 (UTC)

Indeed. Why don't we all move to Tahiti? --Stephan Schulz (talk) 16:48, 17 October 2008 (UTC)

Because we don't really have a better chance of survival there. I am not at greater risk living in Cardiff than Tahiti. I understand they may have a preference for one area over another, but surely they would move to increase their chances of survival. MikeInABox (talk) 16:51, 17 October 2008 (UTC)

I'm sure your quite mistake. Cardiff is rather cold in the winter. It may not be as cold as a number of other places but it still requires adequate heating or good insulating clothes. I don't know if Tahiti is the best example, a place which is too hot or has too much sunlight is not necessarily great either (although it's worth remembering that while nowadays we may spend a lot of our time outdoors in uncovered areas, historically in the hunter-gather era people would have spent a lot of their time in their shelters or under the cover of trees) but there are definitely places that emperically are more habitable. Definitely humans live in a lot of places that, while not as bad as Alaska have extremely cold winters (sub zero) and with regular snow. Are you really trying to convince me that climatically, such places are not more difficult for humans (being without any great level of fur and without hibernation) then a place with a mild 15-25 degrees year round temperature? Sure the temperature is not a great problem for us now because we have homes with good insulation, electricity etc. The key point is that humans are really adaptable which is why we are able to live fine in Tahiti, Cardiff or Alaska. Nil Einne (talk) 04:45, 18 October 2008 (UTC)

I can understand that they might not want to live in a city or leaves their groups/culture, but it is more a question that people (and animals) generally migrate to more hospitable environments where the effort to get a given amount of resources is easier. Not to be lazy, but just to increase their survival chances. If food does become scarce living in a cold environment must significantly reduce you chance of survival. MikeInABox (talk) 16:49, 17 October 2008 (UTC)

Do modern Eskimos often die for reasons they wouldn't have died of in a city? I see no reason why they would. The chance of getting hit by a car in a city is probably higher than the chance of an Eskimo getting frostbite. --Tango (talk) 17:11, 17 October 2008 (UTC)

But wouldn't they still seek out somewhere better and keep looking until they found a better place where there was less competition? If they found a place that was more hospitable but with competition, they would know that there were at least more hospitable places. Also, why didn't they move when they knew there were better places (following contact with people with knowledge of other areas), but before technology (medicine/machinery etc) made life easier for them? MikeInABox (talk) 16:49, 17 October 2008 (UTC)

Live wasn't particularly hard for the Innuit. Why would it be? They are hunters and gatherers, and these, at least on pre-industrial times, have much better quality of life than peasants. The arctic sea is very productive, with lots of fish, birds, and sea mammals. --Stephan Schulz (talk) 16:53, 17 October 2008 (UTC)

This is purely speculation on my part, but the angle of the Earth's axis does change over time. It's possible that when the Eskimos migrated, it wasn't as cold. 12.10.248.51 (talk) 17:01, 17 October 2008 (UTC)

The Innuit arrived in Greenland at about the same time as the Norse. There is some debate about exactly how much colder or warmer than today it was back then, but in any case it was very cold by our middle latitude standards. They simply were well-adapted and knew how to live a good life there. --Stephan Schulz (talk) 17:05, 17 October 2008 (UTC)

While the climate may well have changed, it wouldn't be due to shifts in the Earth's axis over such a short timescale (by geological standards). Also, it would have likely been colder, not warmer. Theories put migration to North America between around 10,000 and 30,000 years ago, which would be during the last glacial period or the very beginning of the current interglacial period, so presumably much colder than currently. --Tango (talk) 17:11, 17 October 2008 (UTC)

Moving around is far harder than staying still, they would need a good reason to move their whole group somewhere else. They wouldn't necessarily know of anywhere that wasn't already populated (if there even was such a place), so they would be walking around randomly constantly running into people that didn't like them using their resources. --Tango (talk) 17:11, 17 October 2008 (UTC)

And if you're perfectly well adapted to a place, know every inch of its geography, know exactly how to survive, and know there won't be other people showing up regularly to take your stuff - why move? Lots of people live today in cold climates (ahem, Canadian talking here :), yes you could die if you get caught in a storm, but you prepare and you harvest the bounty around you while you can. Franamax (talk) 22:15, 17 October 2008 (UTC)

Cultural note: while I personally associate the term "Eskimo" with a people having incredible survival skills and intimate knowledge of the environment, as well as an admirable society, the term is one given by "Indians" (people living where the trees were) and I believe means "eat raw meat", was derogatory, and was indicative of the Indians willingness to kill any and all Eskimos they encountered. The peoples name for themselves is generally Inuit (although there are sub-names which more closely identify those who lived in certain areas). Because of the derivation of the term Eskimo, Inuit is much preferred. Franamax (talk) 22:09, 17 October 2008 (UTC)

As I understand it, Inuit refers only to a subset of Eskimos. See Eskimo#Nomenclature, it would appear you are under a common misconception. --Tango (talk) 22:26, 17 October 2008 (UTC)

My information comes from a professional with intimate knowledge of Inuit people and culture and adoptive mother of an Inuit child. Perhaps the misconception is also shared by the Inuit people themselves? Following the argument that a term is of uncertain etymology and thus not derogatory means that nigger and kike are also perfectly acceptable. As I noted, sub-populations have individual names, but from the link you give above "defines Inuit...as including the Inupiat, Yupik (Alaska), Inuit, Inuvialuit (Canada), Kalaallit (Greenland) and Yupik (Russia) [people]". It's usually better to consult the actual people, for instance to decide how to pronounce your name, I would ask you for advice (and possibly your mother as the ultimate authority :). Franamax (talk) 00:36, 18 October 2008 (UTC)

Or you could actually read the article Eskimo, which says "There are two main groups referred to as Eskimo: Yupik and Inuit. A third group, the Aleut, is related" and leave out mention of other editors' mothers. Edison (talk) 02:22, 18 October 2008 (UTC)

Let me clarify then: in order to discover Tango's name, I would directly ask Tango rather than consult a third party to see what their opinion was. Failing that, I would ask a related party, in this case Tango's parent, who would surely be authoritative on the matter. Sorry if my colloquialism has caused you confusion. And I evidently have read the article, since I quote from it directly in mentioning the preferred naming. I quite understand that Eskimo is a term for North American native peoples generally living north of the treeline. The older of those people are comfortable with the term, the younger are less so. The members of the Inuit Circumpolar Council seem comfortable with the overall term Inuit, although as I said, they will preferentially use their own regional name for themselves. "Eskimo" is an exonym and there is no particular reason to use it. Was there anything else? Franamax (talk) 09:19, 18 October 2008 (UTC)

As to the OP's question: lots of Eskimos have moved far from home, although such a thing is hardly limited to Eskimos. Perhaps the question would be better worded "why don't the Eskimos move en masse, completely abandoning their homelands?" I think it is reasonable to say that that kind of mass migration is quite uncommon. Why hasn't North Dakota been completely abandoned? It's hardly Tahiti. Pfly (talk) 06:47, 18 October 2008 (UTC)

The question begins from a misapprehension - that the arctic is inhospitable. It sure would seem so to me, just as a Floridian would find my Ontario inhospitable, but it's all a question of what you're used to. To them (personal communication) our (Ontario) climate is ridiculous - rain all spring and fall and stinking humidity in the summer. Matt Deres (talk) 14:10, 19 October 2008 (UTC)

Apollo Landing Hoax

I asked this on the Apollo Landing Hoax discussion page and nobody there could come up with a satisfying answer. Watch the following video all the way through. The video begins with the flag at complete stop. At about 37 seconds into the video, an astronaut walks by. The flag begins to wave as if the astronaut's movement created a breeze. Obviously, NASA didn't fake the Apollo lunar landing, but I haven't been able to come up with a definitive explanation. I have a number of possible explanations:

1) The astronaut's bouncing on the ground caused the flag to move. But earlier in the video, an astronaut walks away from the flag and the flag doesn't move. 2) The astronaut's shoulder brushed against the flag. But he looks like he's too far away to make contact. 3) When the astronaut starts moving, he kicks a rock which hits the flag pole. 4) It's caused by static electricity 5) Gas emission from space suit but I have no idea if space suits actually have gas emissions.

Space suits both the material and the air inside both have small gas emisssions. ( usually from oil contaniments ). Even though the suits are tested, cleaned and packed with the *utmost* care. Still some still get finger-prints on them. A finger print is enough to cause a flag to wave. ( I have seen it in a vacuum chamber ).

Btw, this is a really good question. But you seem to have missed:

6) The astronaught bouncing by the flag, jars the ground. ( the lunar surface, aside from the dust is volcanic flows, i.e. its structure allows for the translation of movement rather easily, and since the air is NOT there to absorb any of the sound, likely it all gets translated into the ground. ( and note that the likely vector for the movment is perpendicular to the camera, so you dont see the flag pole wave, but as a result of the flag pole waving, the flag waves ).

Also, just so you know, The Flag was made of nylon.

[12] Information on the flag. —Preceding unsigned comment added by 99.185.0.29 (talk) 14:14, 18 October 2008 (UTC)

Actually, that was #1. 67.184.14.87 (talk) 08:49, 19 October 2008 (UTC)

http://www.youtube.com/watch?v=DWajUJ_NnHs

Does anyone have a definitive answer?12.10.248.51 (talk) 16:10, 17 October 2008 (UTC)

My answer is #2. Lenses on cameras can certainly give false senses of perspective, I see nothing in the video to show that he didn't physically touch the flag. My best interpretation is that he physically brushed the flag when he went by. For an example of the tricks that cameras can play on perspective, see this one: [13] showing Theodore Roosevelt, Jr. and George Patton. Teddy Jr. wasn't a midget, and Patton wasn't a giant; the illusory perspective what causes us to make it look that way. --Jayron32.talk.contribs 16:39, 17 October 2008 (UTC)

I vote for #2 as well. The flag looks like it's pointing towards the camera, so the tip of the flag would have nearer the astronaut than the pole, probably near enough for him to brush it - remember a spacesuit is quite big and bulky and it would only take the slightest contact to set it moving with no atmosphere to damp it. --Tango (talk) 16:55, 17 October 2008 (UTC)

You know, now that I think about it, I recall someone on the YouTube page saying that the flag first moves towards the astronaut. To me, it the video moves too fast for me to tell, but he/she advocated the static electricity hypothesis. 12.10.248.51 (talk) 17:06, 17 October 2008 (UTC)

It moves far too fast to tell without slowing it down and analysing it properly. I'm not sure you could tell even with that, isn't the astronaut in front of the flag, blocking it from view, when it starts moving? --Tango (talk) 17:13, 17 October 2008 (UTC)

No, according to the static electricity proponent, the flag starts moving before the astronaut gets there. If this is true, it would invalidate hypothesis 2 and 5. Maybe if I get time, I'll see if I can analyze the video. 12.10.248.51 (talk) 17:34, 17 October 2008 (UTC)

I'd go with either #1 or #2. When the astronaut walks away from the flag, he's taking baby hops (or the wires are lifting him less, take yer pick), when he moves in front he looks to be taking bigger jumps, although perspective enters the equation there. And there's no way of knowing the soil structure, which might not be uniform around the flag and he hit the bouncy part moving in front. That would explain any movement before the guy gets to the flag. #2 is much the most probable, those spacesuits were pretty bulky. It is of course possible that NASA hired a really lousy continuity clerk and they totally missed that little detail. Anyway, I thought we could already tell by the shadows of the moon lander that they faked the whole thing by filming it in a location with two suns. Franamax (talk) 21:59, 17 October 2008 (UTC)

Is the video real? Anyway, it's possible he brushed against the flag, but consider what is holding the flag up in the first place? I think it's either held up by a string/tether or there's a machine that blows air onto the flag. ~AH1^(TCU) 22:09, 17 October 2008 (UTC)

R u kidding? It's a metallic flag with pre-formed ripples made to look like a US flag waving on the moon - but it is the flag they used. And they wouldn't need a machine more complex than a valve cracked open on an air tank to make it move back and forth, but they didn't do that. Real video - crackpot interpretations to "expose the hoax". Franamax (talk) 00:06, 18 October 2008 (UTC)

I think the flag is normal cloth, but there is a telescopic rod at the top to hold it out. I've read that the ripples are due to the rod on Apollo 11's flag getting stuck and not opening fully and the astronauts on the later missions thinking that looked good so intentionally not opening it fully. --Tango (talk) 16:35, 18 October 2008 (UTC)

You're right. [14] Shows what I remember from my distant youth :) Franamax (talk) 21:05, 19 October 2008 (UTC)

You really can't tell - I stepped through it one frame at a time and whatever happens - it happens when the astronaut is blocking the view of the camera. I'd say this though...depth perception on the moon is seriously screwed up - and so is lighting - and that's the source of almost all of the conspiracy theorist's misconceptions. That pole is only about a meter tall - roughly half as tall as the astronaut. To me, it seems bigger - and further away - and I think that's the problem here. In truth it's close enough that he either just caught the corner of it on his spacesuit - or perhaps he was so close that vibration did the job. One thing that's seems strange about flags on the Moon is that in a vacuum, flags keep swinging for MUCH longer than they do here on earth - the internal stiffness of the cloth damps down the motion very slowly on the moon - but here on earth the lightweight cloth and the denseness of the air conspire to kill that kind of motion very rapidly. Hence, even a small vibration

would have been enough to start it moving - and once started, it would swing more impressively than we'd expect by our normal experience of cloth flapping here on earth. The pole that the flag was hooked onto was also engineered to be as lightweight as possible (easier in 1/6th gravity) - so it would more easily transmit any vibration to the flag than a pole strong enough to keep the flag flying here on earth would manage. Vibrations through the ground also depend on the force of the impact from the astronaut hitting the ground. While gravity is weaker on the moon, momentum depends on the MASS of the astronaut - not on his WEIGHT - so that "high mass" (but not "heavy") suit would have been able to transmit pretty large impacts onto the lunar surface. Astronaut plus space suit weigh about 480lbs - so the momentum transferred to the moon rock would have been pretty high. SteveBaker (talk) 00:21, 18 October 2008 (UTC)

An astronaut adjusts the camera, then moves between the camera and the flag, and the flag moves. There is not basis for assuming that he did not brush against the flag. Occam's Razor. If it were a 20 billion dollar hoax, they could have paid Disney Studios to do a letter-perfect fake. The hoaxologists seem like a jealous bunch who don't want to believe that capable and hard-working scientists and engineers could achieve something they never could. Edison (talk) 02:14, 18 October 2008 (UTC)

Of course I'm not saying that there was a hoax, but it's better to avoid arguments against it that are flawed. "They could have paid to have it faked perfectly" is not a hypothesis that's obviously correct. Study the IMDB goofs sections for big-budget movies and you'll see that they always have slip-ups... not only in movies that are light entertainment but also in the kind that try to meticulously re-create a historical incident. It almost seems as though the more effort and money they put into getting things right, the more goofs people find. Look at the IMDB goofs lists for the movies Apollo 13 and Titanic, for example. --Anonymous, 23:54 UTC, October 18, 2008.

Obviously this and this are involved ;) -hydnjo talk 23:08, 18 October 2008 (UTC)

Well, I watched it a few more times and at least to me, the flag appears ti move away from the astronaut, not towards him. BTW, when Mythbusters tested waving a flag in a vacuum, it waves more due to the lack of air resistence. 67.184.14.87 (talk) 08:53, 19 October 2008 (UTC)

There's another version of the video at http://www.youtube.com/watch?v=mJGZte-k4G0&feature=related. Unlike the previous video, this one allows comments. I'm going to skim through them to see if anyone has a good explanation. 67.184.14.87 (talk) 09:13, 19 October 2008 (UTC)

Highly Evolved Dinosaurs

What are some of the arguments against the theory that dinosuars evolved to higher thinking, more so than human beings today, and developed superior technology and left Earth? I have a friend that believes that this is very possible and that these very same beings are visiting Earth today. His argument is that dinosaurs have been around a lot longer than any humaniods thus had the time to develop into highly evolved dinosaurs. He states that there is no evidence of this because it could have happened so long ago, that the evidence got destroyed or buried beneath tectonic plates.--Emyn ned (talk) 17:54, 17 October 2008 (UTC)

We have fossils of non-highly evolved dinosaurs (size of the scull, lack of opposable thumbs or other means of fine manipulations, etc. show they probably weren't capable of developing space travel). If there were later dinosaurs that were more advanced, their fossils would be easier to find (unless they cremated all their dead, but there should still be something inbetween what we have and something advanced enough to have burial rites). While it is not entirely impossible, there is no evidence of such a thing. There is certainly no evidence of them visiting us today. --Tango (talk) 18:12, 17 October 2008 (UTC)

Extraordinary claims require extraordinary evidence. Lack of evidence can not be used as proof. As Tango said, the theories that we have are derived from the current and best evidence available. -- MacAddct1984 ^{(talk • contribs)} 18:45, 17 October 2008 (UTC)

"Lack of evidence can not be used as proof." Ah, c'mon! Why not? 206.66.66.1 (talk) 19:46, 17 October 2008 (UTC)

'cos. --Tango (talk) 20:20, 17 October 2008 (UTC)

A slightly more sophisticated response is that absence of evidence is not evidence of absence. -- JackofOz (talk) 02:23, 18 October 2008 (UTC)

Your friend should also perhaps be introduced to Occam's Razor. Given the choice of supposing that the dinosaurs died versus evolved to intelligence, created space flight, left Earth, deliberately wiped out all traces of existence, but stuck around close enough to revisit and play pranks on those silly mammals millions of years down the road... well, one clearly requires fewer ridiculous assumptions. — Lomn 19:18, 17 October 2008 (UTC)

Occam's Razor can be used to disprove the existance of the universe. After all, nothing is simpler than something. 206.66.66.1 (talk) 19:46, 17 October 2008 (UTC)

Occam's Razor says we should choose the simplest theory which satisfies our observations. We observe the universe to exist, so a theory that says it doesn't can be rejected long before we need to invoke Occam. --Tango (talk) 20:20, 17 October 2008 (UTC)

1) Occam's Razor does not prove anything. It is a problem solving technique, anyone who 'proves' something with Occam's Razor does not understand what it is. 2) Occam's Razor is not about "Simple" it's about "needlessly multiplying entities". ie: Making stuff up that there's no evidence for. (example: "I lost my keys." verses "Pixies stole my keys". Both possible. One involves making stuff up.) 3) "The universe doesn't exist" does not satisfy observed evidence (I can see stuff.) therefore it is not suggested by Occam's Razor.

You guys do realize I was joking, right? 67.184.14.87 (talk) 21:51, 17 October 2008 (UTC)

This is the internet. All attempts at humor or sarcasm must be accompanied by at least one emoticon to show you aren't serious.  :-) Dragons flight (talk) 21:57, 17 October 2008 (UTC)

Or, here, in small type. —Tamfang (talk) 05:06, 25 August 2023 (UTC)

Which one was you? —Tamfang (talk) 02:43, 18 October 2008 (UTC)

Sorry, I am 12.10.248.51, 67.184.14.87 and 206.66.66.1. 67.184.14.87 (talk) 08:55, 19 October 2008 (UTC)

The problem with things that fail the Occam's razor test is that there are an essentially infinite number of them - and without evidence, there are just too many to believe or even investigate. Sure, there might have been intelligent dinosaurs who did amazing things - but there might have been intelligent sharks/elephants/sea-sponges/penguins/octupii/dogs/herring who did something similar. It's only taken humans maybe 10,000 years to go from an animal-like existance to civilisation-as-we-know-it-today. There has been plenty of time in past history for any of those other species to go through the same cycle we've been through. You don't need to look all the way back to the dinosaurs to make those hypotheses. But why worry about the possibility of there being something for which absolutely zero evidence exists? There is no need to form any of those theories in order to explain some profound thing that we don't already understand. This is why Occam's razor is appropriate under these circumstances. SteveBaker (talk) 23:55, 17 October 2008 (UTC)

Rather than Occam's razor, I thought first of Russell's teapot. —Tamfang (talk) 02:43, 18 October 2008 (UTC)

HAHAHA!! Too funny! THAT'S what I am going to tell my friend. Thanks, Lomn!

The friend (or anybody) might enjoy reading the novels in the Anonymous Rex series by Eric Garcia. --LarryMac | Talk 20:53, 17 October 2008 (UTC)

Ok, that Sarah Palin bit in the Anonymous Rex article is vandalism, right? 84.239.160.166 (talk) 10:14, 18 October 2008 (UTC)

Or in a more serious vein, try Toolmaker Koan, a 1988 novel by John McLoughlin. (Neither the book nor the author has a Wikipedia article currently, although some other people with the same name as the author do.) --Anonymous (although definitely not Rex), 21:55 UTC, October 17, 2008.

One way to think about it is that any civilization on Earth with sufficient resources to eventually leave Earth would have had to consume a lot of resources in the process. Some of these resources would replenish over very long periods of time (like biomatter and all of its derived products like fossil fuels) but many, like heavy metals, would not. There is no evidence that I know of that there were less iron, copper, or uranium reserves, for example, when humans began to use them in quantity than one would have expected there to be. If humans suddenly disappeared today and no evidence was left of them in a million years, I imagine a civilization of the future would still be able to tell that civilized life was here by the relative lack of heavy metals in the soil compared to a null hypothesis. But maybe I'm wrong on that. --98.217.8.46 (talk) 21:18, 17 October 2008 (UTC)

But all the heavy metals are still here (except the very few we've fired off into non-Earth trajectories). All we've done is move them around. Franamax (talk) 21:44, 17 October 2008 (UTC)

Ore deposits are also replenished over time. Ores are formed by various igneous and geologic processes that happen to concentrate certain elements in one location. The metals we mine are only a tiny fraction of those that exist in the Earth, but in general we focus on the fraction that has been naturally concentrated in easy to get at deposits. Given ridiculously long periods of time, like 100 Myr, we can expect that new ore deposits will also be formed. Not to mention that natural erosion can dig down kilometers in that time and expose deposits to the surface that wouldn't be accessible previously. Dragons flight (talk) 21:55, 17 October 2008 (UTC)

This has been covered in science fiction, where the highly evolved dinosaurs left earth due to some climate crisis and came back after eons to find that squirrel-like creatures they remembered as "tree-jontyles,(sp?) quite delicious" had evolved into humans. The dino descendants looked at our society and decided to leave for additional millenia, since we clearly were about to exterminate ourselves with nuclear or biological weapons, so they did not need to exterminate an arguably intelligent species o reclaim their homeworld. And the name of the story is? Edison (talk) 02:10, 18 October 2008 (UTC)

Could it be one of the Astrosaurs series? SpinningSpark 14:34, 18 October 2008 (UTC). Doh, we have an article of course. SpinningSpark 14:39, 18 October 2008 (UTC)

I liked a story about a research group who create alternate timelines to study the effect of, say, reintroducing horses to Kansas a few hundred years before Columbus. Their grandest experiment was to divert the Chicxulub impactor. Shortly after they came home from doing so, there appeared another tardis from which a reptile emerged, saying, "We saw you divert a rock in our past. So we un-diverted it to see what would happen, and here you are!" —Tamfang (talk) 02:43, 18 October 2008 (UTC)

do cleaners age your skin?

if you use cleaners (stuff to clean) without gloves, then does it age your skin faster? If for ten years you cleaned regularly (several times a day) with strong chemical cleaners, just washing your hands afterwards, would your hands end up aged more? Why? —Preceding unsigned comment added by 94.27.166.235 (talk) 22:12, 17 October 2008 (UTC)

I'm not sure there is really a strict definition of "age" in that context. Using strong chemicals without gloves can harm your skin, certainly, and that harm could well be cumulative over a long time. Whether you consider that harm to be ageing or not is up to you, I guess. For advice on what to do to prevent such harm or heal it, see a dermatologist (or your GP, who can refer you). --Tango (talk) 22:39, 17 October 2008 (UTC)

Ceramic Insulation : Cenospheres

Those old Ceramic Insulators that people collect as antiques, glass as well, seen on ebay--do those actually still work in your home? If lets say you lived close to High-Level Power Lines.

Or Cenospheres, The microscopic ceramic beads (balls) have a technical name: Cenospheres, or sometimes called micro-spheres, or nano-spheres for the smallest size. Could you use like a shaman/indian/hippie medicine bag, and put these cenospheres in them to guard yourself from high voltage? Or am I on the road to myth making and Neo-Wives Tales?

Cheers, --i am the kwisatz haderach (talk) 23:20, 17 October 2008 (UTC)

The insulators I have seen people collect are from telegraph wires on railroads, and are not at all suitable for high voltage. Insulators for increasingly high voltages are thicker and have more convolutions or "petticoats." You are talking hundreds of volts rather than thousands of volts. Interestingly, the earliest telegraph insulators were literally glass knobs intended to go on furniture drawers. Edison (talk) 02:03, 18 October 2008 (UTC)

October 18

How large can a Trojan planet be?

I'm trying to get a rough, seat-of-the-pants idea of how large a Trojan Planet or Trojan Moon could be relative the closer of the two bodies creating its L4 or L5 Lagrangian points. The Lagrangian point article only says "it needs not be negligible mass." How large of a Trojan Moon could Jupiter-Sun L4/L5 support, for instance? How massive a space station could Earth-Sun L4/L5 support? I anticipate that the main problem has to do with planet formation, and that the fuzzy nature of a Lagrange point causes formation-by-accretion to be unlikely. What I'm wondering is how large a planet could be held-onto in the unlikely event of capture. Thanks in advance for anything anyone has to say. DeepSkyFrontier (talk) 03:49, 18 October 2008 (UTC)

Theia (planet) mentions this issue, although it doesn't give any exact numbers. From that article, it would seem that a planet larger than Mars would not be stable at the Sun-Earth L4 or L5 points, but it doesn't say how much less than that it needs to be to be stable (it was about Mars sized when it is presumed to have hit the Earth, but that could well have been some time after it lost stability so it could have kept growing for a time). --Tango (talk) 12:27, 18 October 2008 (UTC)

Giant impact hypothesis says it was about Mars sized when it lost stability. --Tango (talk) 12:30, 18 October 2008 (UTC)

I remember discussing this on Usenet once... ah, here it is. The conclusion is that the restricted three-body system is stable regardless of the mass ratio of the smaller bodies, as long as the largest body's mass is at least 25.23 times the total mass of the other two bodies. Conversely, if the largest mass is less than 24.96 times the sum of the other two, the L4/L5 points will be unstable — only in that rather narrow range does the mass ratio of the smaller bodies matter. The Sun is about 1000 times as massive as Jupiter, so it seems that Jupiter's L4/L5 points ought to be stable regardless of what you put there (at least ignoring perturbations from other bodies in the solar system), as long as it's smaller than about 40 Jupiter masses. —Ilmari Karonen (talk) 00:36, 21 October 2008 (UTC)

orchic

Is orchic supplement bennificial ? —Preceding unsigned comment added by 68.221.224.43 (talk) 05:05, 18 October 2008 (UTC)

I don't see how. "Orchic supplements" (bovine testicular extracts) are broken down by the digestive tract, meaning they cannot be pharmacologically effective. They may exert a placebo effect, but other than that....they're pure bollocks ;-) Fribbler (talk) 11:58, 18 October 2008 (UTC)

I couldn't find any reliable sources about this. However Fribbler's second comment: "Orchic supplements are broken down by the digestive tract, meaning they cannot be pharmacologically effective" is not necessarily correct. Prescribed oral medications do have pharmacological activity, despite digestion. There are many plant extracts (medicinal herbs) that do have pharmacological effect: opium, belladonna, digitalis, etc.. Axl ¤ [Talk] 13:24, 18 October 2008 (UTC)

Of course oral medications are pharmacologically active. I should have been more clear. Testosterone, the "active ingredient" of Orchic Supplements, is heavily affected by digestion. Here is a link: [15]. This is why testosterone used in the treatment of hypogonadism is given either intramuscularly or transdermally: [16] Fribbler (talk) 16:12, 18 October 2008 (UTC)

Sure, testosterone would not be absorbed when eaten. However this might not be the only "active" component of orchic. I couldn't find any reliable evidence of appropriate testing of orchic. Axl ¤ [Talk] 16:39, 18 October 2008 (UTC)

Me neither. A red flag in my book. The medical community appear to be uninterested in this supplement. Fribbler (talk) 15:35, 19 October 2008 (UTC)

sex without condom

What are the most probable infections for a person who practices sex without condom?Mr.K. (talk) 09:32, 18 October 2008 (UTC)

Try reading the article Sexually transmitted disease. Jdrewitt (talk) 09:40, 18 October 2008 (UTC)

Note that I think you are implicitly meaning "with multiple partners" here. --98.217.8.46 (talk) 09:44, 18 October 2008 (UTC)

There are, in fact, two separate questions. One is how likely it is to become infected from an infected partner, the second is closely related to the statistical distribution of STDs in the population. Actually, a third interpretation would lead to an answer like Herpes simplex (infection rates of close to 90%), athletes foot or common cold ;-). --Stephan Schulz (talk) 11:33, 18 October 2008 (UTC)

Genital Herpies is pretty easily the most common STD, and it can infect you ( its a virus ) with a comdom, so condom or hot, the most probible infection is going to be the most common STD. $--~~~~$ —Preceding unsigned comment added by 99.185.0.29 (talk) 13:56, 18 October 2008 (UTC)

While HSV is exceedingly common, it is cumulative and most people don't have constant heavy shedding. This illustrates why you should not use prevalence to estimate incidence. Chlamydia may have higher incidence in some populations. Stephen Schulz was right in saying that it depends on specific factors (including locale, ages of involved persons, and what sexual practices are involved). --Scray (talk) 14:25, 18 October 2008 (UTC)

I was actually surprised a while back reading our article on HIV that vaginal unprotected sexual intercourse only gets you a 5 to 10 in 10,000 chance of receiving the virus, I had thought it was much much higher. (Not that it's worth even that risk!) -- MacAddct1984 ^{(talk • contribs)} 19:56, 18 October 2008 (UTC)

Those estimates are averages from multi-year follow-up of couples in whom coital frequencies have been recorded. This type of research involves finding discordant couples, i.e. couples with one person who has HIV and another who does not, then following them for years to determine risk. If you ask them on a regular basis how often they are having sex, and what they do when they have sex, then you can get an estimate per act. The problem with this approach is that these couples may not represent the setting in which HIV is usually spread.

It's known that there is an early phase of HIV infection when the individual tends to have very high levels of HIV in blood and body fluids. People are more susceptible to getting infected if they have ulcerating STDs, and they may be promiscuous. Thus, susceptibility to infection might occur in peaks and valleys, and when someone is at their peak of susceptibility they may also then be most infectious - with a high level of virus in body fluids, ulcers, and promiscuity - sort of super-transmitters. This would explain observations of rapid spread within mini-epidemics, and is supported by what's known about transmission mechanisms. It's likely to be very hard to find these people, in part because it's a transient state.

Adding to the confusion is that the same person could be highly infectious for a few weeks or months, then a year or two later might be different in many ways, with lower HIV level (their viral load "set point"), ulcers healed, and in a stable relationship. --Scray (talk) 00:42, 19 October 2008 (UTC)

STDs have different prevalences in different populations, so it depends on where you are, but really it only depends on who you are sleeping with. If your partner is clean, then the only STD you really have to worry about is pregnancy. --71.178.135.144 (talk) 06:41, 20 October 2008 (UTC)

size of a lysosome?

Hi could anyone give me an estimate of the length of a lysosome? The article on lysosomes does not give a value. Presumably we're talking nm here. I realise sizes will vary from cell to cell but a rough estimate would be good. Thanks in advance. —Preceding unsigned comment added by 139.222.240.110 (talk) 15:39, 18 October 2008 (UTC)

On a similar topic, does anyone have some kind of semi-visual (the parts that are possible) to compare sizes between things such as cells, mitochondria, chromosomes, genes, neurons... and then atoms, certain proteins/amino acids, you get the idea. I'm well aware that a cell has an insane amount of atoms, which is why I said semi-visual. :) -- Aeluwas (talk) 15:54, 18 October 2008 (UTC)

From "Cytology & Histology" by Wolfgang Kuehnel, p. 34: "Their sizes are 0.1 – 1.2 μm." Axl ¤ [Talk] 17:31, 18 October 2008 (UTC)

...With the caveat that they can get much larger in the lysosomal storage disorders. TenOfAllTrades(talk) 18:49, 18 October 2008 (UTC)

Thanks —Preceding unsigned comment added by 139.222.241.15 (talk) 11:36, 20 October 2008 (UTC)

where does the air in hypercaviation come from?

the supercavitation article says "drag is normally about 1,000 times greater in water than in air."

However, isn't the gas water vapor (h2o in gas form) NOT air (homogenous mixture, largely nitrogen, o2, etc)...? If it is indeed "air", where would it come from? —Preceding unsigned comment added by 79.122.55.76 (talk) 17:35, 18 October 2008 (UTC)

Yes, it's water vapour. The supercavitation article says "The pressure of the fluid can drop due to its high speed (Bernoulli's principle) and when the pressure drops below the vapor pressure of the water or the temperature increases thus vapor pressure increases reaching water pressure, it vaporizes — typically forming small bubbles of water vapour (water in its gas phase)." -- Finlay McWalter | Talk 17:42, 18 October 2008 (UTC)

Defrosting beef

Is it possible to defrost minced beef by putting it in the oven at a low temperature (about 50 degrees centigrade)? —Preceding unsigned comment added by The Defroster (talk • contribs) 18:21, 18 October 2008 (UTC)

Of course it is possible, but the outer part will tend to cook before the center is melted. Externally-applied heat will maximize the temperature gradient between center and exterior meat. If you were to slice the minced beef thinly, this effect won't be much of a problem. I don't see a WP article right off, but here's a link: [[17]] --Scray (talk) 18:36, 18 October 2008 (UTC)

It's worth noting that prolonged incubation at 50C could encourage bacterial growth in the interior of the meat. This is another reason to thaw at refrigeration temperature, or warm using more rapid or uniform heating methods (see the link previously provided). —Preceding unsigned comment added by Scray (talk • contribs) 18:46, 18 October 2008 (UTC)

In the case of minced beef, I generally find that it works fine to just start cooking it as you normally would - if you're frying it it defrosts pretty quickly as you do it as it has such a high surface area. ~ mazca ^t|c 19:03, 18 October 2008 (UTC)

I agree. If frying it, I usually (more or less) take it out of the freezer. Microwaving it for a while helps, and that's what I would do if I needed it thawed (to make meatballs, for instance). -- Aeluwas (talk) 19:11, 18 October 2008 (UTC)

Are you referring to Ground beef? Edison (talk) 19:19, 18 October 2008 (UTC)

I assumed he was... what else does the phrase "minced beef" refer to that could be confused? ~ mazca ^t|c 23:58, 18 October 2008 (UTC)

Mince means "cut into small pieces," which sort of fits ground beef, but it also means "to pronounce in an affected way," like saying "boeuf" for "beef" in English speaking countries, or it means to "walk with short steps or exaggerated primness," which would be atypical behavior for cattle. Edison (talk) 01:14, 19 October 2008 (UTC)

It depends on the person you ask, but to me ground meat is produced using a meat grinder and usually passed through the machine one ore twice. Mince beef, on the other hand is cut finely by hand and usually has a meatier and less "floury" texture when compare dot ground beef.Sjschen (talk) 02:47, 19 October 2008 (UTC)

If a recipe told me to prepare a quantity of "minced beef" I would slice and dice it as finely as possible with a sharp knife on a cutting board. As Sjschen said, to make "ground beef" I would run it twice through a grinder. "Two great nations divided by a common language." Edison (talk) 04:13, 19 October 2008 (UTC)

...and don't confuse your minced meat with your mincemeat. Gandalf61 (talk) 08:49, 19 October 2008 (UTC)

I have no problem understanding what someone means when they say mince beef or ground beef (even if the second is not something I'd use in conversation/writing) as I expect many kiwis and I expect Brits and Australians. It's only other people who have funny ideas about what mince beef is... Perhaps it's only one great nation that is at fault? :-P P.S. Before you argue it's my fault for not understanding your meaning for mince beef, I should ask, how often do you use or encounter 'mince beef'? Surely the more common use of the term should be given preference of one used rarely... ;-) Nil Einne (talk) 09:41, 19 October 2008 (UTC)

Heh, I was unaware of the extent of the American use of "grind" for where I (as a Brit) would use "mince". An American apparently uses a "meat grinder" to produce "ground beef" while I would use a "mincer" to produce "minced beef", with both the equipment and the final product being exactly the same. While to an American "mince" may instead mean "chop finely", to me "grind" implies reducing the meat to a horrible homogenous paste. ~ mazca ^t|c 11:54, 19 October 2008 (UTC)

Same here in Oz but being so far away from birth of the terms, we can mix them too, getting mince from a grinder. The current answer to an otherwise homogenous paste is to pack it with wavy grooves resembling nothing I can think of. ~:\ Julia Rossi (talk) 13:27, 19 October 2008 (UTC)

Don't forget spraying red dye on the outside of the lump to make it look fresh-killed. At least, that's how they do it here in Canadian supermarkets (another country where we (or at least I) can assimilate the concept of ground and minced being the same). Franamax (talk) 20:45, 19 October 2008 (UTC)

I don't think that's red dye, at least not in the U.S.A. It's a tiny amount of carbon monoxide gas placed in the package just before sealing, considered safe and simply cosmetic by the FDA and meat-packing industry. Seems people won't buy brown meat generally, and I would guess that's true. --Scray (talk) 01:30, 20 October 2008 (UTC)

To defrost something quickly and safely, place it in your sink with a small amount of water. Turn your tap on so that barely a trickle of cold water comes out. You want a stream, not drops. The purpose is to keep the piece immersed in moving cold water; the coldness of the water delays the proliferation of bacteria, the movement facilitates the contact of fresh water with the frozen product. Before long, the piece will assume the temperature of the surrounding water (i.e. defrost). Because of water's thermal properties, the meat will defrost faster than it would on the counter. And much more safely. Matt Deres (talk) 14:24, 19 October 2008 (UTC)

Yes, this is what was recommended in the link at the end of my original answer to the post. --Scray (talk) 15:42, 19 October 2008 (UTC)

Toaster in the ocean.

What would happend if you threw a toaster with a very long extension into the ocean?Bastard Soap (talk) 19:50, 18 October 2008 (UTC)

Lots of sparks around the toaster, then shortly a wire will burn through, breaking the circuit. Charge density will tend to disipate with the square of distance from the charge source, so anyone or anything near the toaster is likely to get a nasty shock; anyone a considerable distance away will notice nothing. --Jayron32.talk.contribs 20:18, 18 October 2008 (UTC)

If you threw a whole toaster in the ocean there is no obvious reason that melting would kill the circuit. A) the water will cool the wires, and B) conductive salt water will continue to carry current around the break even if some wires melt. Obviously a circuit breaker/GFI could stop the thing, and I suppose one might also melt part of the extension cord above the water, but if neither of those things happened I don't see any obvious reason for the circuit to ever shut down on its own. Dragons flight (talk) 00:15, 19 October 2008 (UTC)

It would get wet. Hopefully you unplugged the cord first for safety. If still plugged in the element would heat up the water and put some hazardous currents in the sea water. Hopefully a fuse would blow before the wires melt or ELP would disconnect it. Graeme Bartlett (talk) 20:38, 18 October 2008 (UTC)

Who is ELP? —Preceding unsigned comment added by Seans Potato Business (talk • contribs) 22:22, 18 October 2008

Most likely Earth Leakage Protection. -hydnjo talk 22:50, 18 October 2008 (UTC)

If you were smart/lucky enough to have plugged the extension cord into a GFI protected outlet then the stupid act of tossing a plugged-in toaster into the ocean would cause little harm except to the toaster. I suppose you could pull it back by the extension cord and try and try again but the tripped safety device would remain tripped and you would have no clue as to what was going on. How about making some toast instead? -hydnjo talk 22:34, 18 October 2008 (UTC)

For the sake of clarity: ELP and GFI (or GFCI) are the same thing. This form of protection has a large number of different names and the best-known ones vary from one country to another. Another one I remember seeing is RCCB. --Anonymous, 23:56 UTC, October 18, 2008.

Oh, and besides the usual "don't try this at home" admonishment regarding this dangerous stunt you'll probably not know how to properly secure the toaster cord to the extension cord so forget about pulling it back, it'll be sleeping with the the fishes. -hydnjo talk 00:18, 19 October 2008 (UTC)

I would not expect sparks, despite the drama shown in movies when electrical appliances encounter water. I have seen flooded electrical vaults where the water simply boils without great drama due to submerged 120/208 volt bus bars. Saltwater is not as conductive as some think. Current would flow through the salt water from the phase to the neutral connected wires near the entry point of the power cord, where the switch is, but only a small area of conductor is exposed with full phase to neutral voltage between the conductors. The heating element would continue to carry the current it carried in normal use (neglecting the slightly lower voltage due to the additional drop in the extension cord). More current would likely flow through the heating element than directly through the water. The heating element would not get red hot due to the cooling effect of the water. Current would also flow from the heating element directly to the ground connection afforded by the ocean, so that if it were connected to a Ground fault interrupter it would trip offline in milliseconds. Any bread in the toaster might cook, but it would never toast satisfactorily.There would be bubbles of hydrogen and oxygen liberated due to Electrolysis. Anyone attempting the experiment runs a serious risk of death from electrocution, and anyone in the water near the toaster might be electrocuted. Edison (talk) 00:51, 19 October 2008 (UTC)

Thanks Edison for your serious and comprehensive response to an inquiry that some of took as frivolous. -hydnjo talk 01:37, 19 October 2008 (UTC)

Bah! Cut the praise. I don't like Edison's answer. Specifically, the claims that "The heating element would continue to carry the current it carried in normal use" - and that "Saltwater is not as conductive as some think" are entirely misleading. We need to look at the numbers here...(So many of my answers start that way!)

The current has to follow the lowest resistance path - so we need to look at the resistances involved here. Since this is the science desk rather than the guessing desk - I just performed the simple experiment of measuring the resistance of the heating element in my toaster with a meter. I used the cold resistance on the assumption that the ocean water will prevent it from heating up so much (and because I didn't want to plug my toaster in while it was in pieces on my bench!)...and it measures 6,000 ohms. The hot resistance is going to be different - but (as we'll see) - it's not going to matter a damn. The resistance of sea water is just 0.2 ohms per meter. Is this "not as conductive as some think"? It's hard to tell.

So will the current flow through the sea-water between the two exposed metal contacts inside the switch of the toaster (less than 1cm apart in my toaster) or will it flow through the 6kohm heating element? Well, let's approximate this as a simple parallel circuit comprising one 6kohm resistor (the heating element) and one 0.002 ohm resistor (1cm of salt water). In a parallel circuit, the current splits by the reciprocal of the resistance - so the current that flows through the heating element is 0.002/6000 times less than flows through the water. Yes, TECHNICALLY, some electricity will still flow through the element - but unless the extension cord can carry 6 megawatts (the output of a small powerstation) - the heating element WON'T carry more than an utterly negligable much of the available current and it certainly won't get even slightly warm. In fact, it doesn't matter a damn whether it's a toaster or just the exposed end of an extension cord that we toss into the ocean - the result will be the exactly same.

If we assume that any protection device inside the toaster gets wet also - then it will get shorted out by the water on the 'hot' side of the circuit and since almost zero current will flow through it, it will utterly fail to operate. So a lot of current will flow through the water - at 110volts, ohms law says: I = V/R = 110/0.002 = 55,000amps. At 110 volts - that's 6,000,000 watts. That's a LOT of current. If the other end of the extension cord is plugged into any kind of protection device (a simple fuze, an ELCB, GFI or whatever) - it's obviously going to trip with that much current flowing. But if we hypothesise that there is no protection of any kind - then the next question is whether the copper in the cord will melt before the water boils. Certainly there is no extension cord in existence that can carry six megawatts - so clearly it'll break somewhere if it has to carry anything like that much current.

But it's a bit more subtle than that. If the water does boil - then you're concerned with the electrical resistance of steam - which is in the many-mega-ohms per meter range (a lot depends on temperature and pressure). But once the water boils, the circuit is broken and hardly any current flows until the bubble rises and is replaced by more sea water - so the average current flow will be vastly less than 6 megawatts - and perhaps the cable can survive. If so, then the system can keep that up until the ocean boils dry. Over one second, 6 million watts will produce 6 million Joules of heat energy. The Latent heat of water is 2.5MJ/kg - so one second of 6 million watts is enough to flash-boil more than two liters of water and the little bit of water between the the two wires might only represent a couple of cc's - so it's going to boil in a fraction of a millisecond. Since this is actually AC current - the current flowing as the voltage reaches some small fraction of a volt will be enough to create a bubble of steam and cut the current for a while. Since there is some capacitance in the system, when the connection re-establishes as the bubble moves out of the way, the voltage will build up slowly until enough current flows to boil another bubble. The voltage will never reach 110v and the current will be limited by the amount required to boil water at whatever rate it flows in as bubbles move out of the way. As soon as a continuous wet-path between the contacts forms, it'll immediately boil out of the way and cut the circuit again.

It's harder to figure the melting of the copper because too much depends on how well cooled it is by the sea water and on whether there are weak points in the cable (eg at the connections at either end. However, because the mechanism of bubble formation moderates the current flow to that required to boil fairly small amounts of water - I strongly suspect that the formation of bubbles at the end of the cable in the water will moderate the average current flow to the extent that the copper would not melt.

Conclusion. If there is any kind of protection device present in the circuit - it'll trip and end the experiment. If there is no protection whatever - then almost certainly the water near the end of the cable will boil and not much else will happen.

SteveBaker (talk) 15:30, 19 October 2008 (UTC)

This question should be graced by the answer "A wet salty toaster" ;) Sjschen (talk) 02:44, 19 October 2008 (UTC)

My answer would have been "wet toast", but I think that Steve's (usually great) answers have gone a little off track on this one. First of all, the units of resistivity are ohm-metres, not ohms per metre. The resistance of a 1 cm cube is not the resistance of a 1 metre cube divided by 100. The 1 cm cube is x100x less because of the decrease in length but x100² more because of the decrease in csa, making a net x100 increase in resistance. If a metre cube of material has a resistance of 0.2Ω then a 1 cm cube of the same material will have a resistance of 20Ω. Secondly, you will only get that resistance if the field is linearly distributed throughout the cube. This can be achieved by metallising the ends of the sample cube with a near perfect conductor (copper is good enough for most materials). The field from a point contact, eg your meter probes or the ends of the cable chucked into the sea will give you a completely different (much higher) result which needs some more than simple maths to calculate. So being a simple person, I have just put the probes of my meter in a half-pint glass of warm water saturated with salt. At a distance apart of 1 cm my meter measures around 100kΩ betwen the points of the probes and 55-60kΩ if I immerse them in the liquid. more than most peaple think . . it is cetainly more than I was expecting. I don't think you are going to get 55,000 amps going through that very easily. By the way, I have come across the use of a jar of water as a makeshift fuse while testing high current machinery. Too much current causes the water to boil away and break the circuit. SpinningSpark 18:08, 19 October 2008 (UTC)

How would we get wet toast? I thought we've established the toaster isn't going to toast in sea water? :-P Unless you put toast in to re-heat it you're going to end up with soggy, mushy bread Nil Einne (talk) 04:34, 22 October 2008 (UTC)

Steve's answer , excellent if off by a few orders of magnitude, assumes that the resistance of the heating element is higher than I expect it would be found in practice, and that the area of the exposed-to-seawater conductors is far greater, and possible at a closer spacing that I expect. I have used saltwater as a resistive element and a large area of electrode had to be immersed in the water to get appreciable current. I hate to ses the incorrect notion "electricity follows the lowest resistance path" repeated when, in fact, electricity follows ALL paths, in inverse proportion to the resistance. A resistance heating element immersed in water gets quite hot, if not red hot, changing the resistance from the value measured cold. If Steve's toaster had 6000 ohms resistance with 120 volts applied, it would only have 2.4 watts of energy dissipated. My toaster is rated 120 volts, 780 watts, which would imply a hot resistance of 18.5 ohms, which was about what I found the cold resistance to be, although the measurement was with a battered analog volt-ohm meter of dubious accuracy. The heating element would draw 6.5 amps in normal operation. I do not see evidence that it would draw much less immersed in seawater, or that the area of the exposed wires is sufficient to allow a large current to flow through the water from conductor to conductor. The inevitable buildup of bubbles of hydrogen and oxygen on the wires would further decrease the current flow through the water. I have not found a protective device inside toasters I have disassembled which would cause them to trip when immersed, unless the unit is plugged into a residual current device/ground fault interrupter. Edison (talk) 00:25, 21 October 2008 (UTC)

MRI history

When, where and which manufacturer installed the first commercially-available clinical MRI? —Preceding unsigned comment added by Henpecked (talk • contribs) 20:12, 18 October 2008 (UTC)

Not sure on commercial availibilty, but there is considerable controversy over the first workable NMR machine. There are dueling claims from both Raymond Vahan Damadian, who holds the first patent on what would later be called MRI, while Paul Lauterbur and Peter Mansfield won the Nobel Prize for producing theraputically viable MRI. No one disputes Damadian's contributions as coming first; there is however considerable debate over how much Lauterbur and Mansfield contributed to the field. Some say that Damadian's initial discoveries were the most important discovery; others claim that it was Lauterbur and Mansfield's work that made it a viable technology in the medical field. Click the links to get more info on all of these topics. I hope that helps some! --Jayron32.talk.contribs 20:22, 18 October 2008 (UTC)

As for where the first clinical MRI scanner was installed, I believe it was in my home town of Nottingham in the Queen's Medical Centre. —Cyclonenim (talk · contribs · email) 22:42, 18 October 2008 (UTC)

Quick eye shift breaking white into RGB

I was watching a movie which was being projected via one of those projectors which I suppose was fairly cheap and marketed to domestic users (not sure if the cost is relevant). When I looked at the screen and then shifted my eyes quickly, I noticed that the white areas of the screen appeared to break down into red, green and blue components. What's going on there? I've noticed it before, very occasionally, but it doesn't happen for example, with my PC monitor.

Cool! I wonder if it was a technology with sequential presentation of the three images and a fairly slow scan rate? Edison (talk) 01:00, 19 October 2008 (UTC)

Assuming you have a DLP projection system, see the DLP "rainbow effect" in single-chip systems. -- Tcncv (talk) 01:15, 19 October 2008 (UTC)

Yep. Normal TV's and computer monitors show the red, green and blue images simultaneously. In a single-chip projector, there is a monochrome image and a rapidly spinning three-color wheel in front of it that allows the system to display first all of the red, then all of the green and finally, all of the blue. There are three images displayed over every 1/60th of a second - so each image is there for 1/180'th second - but persistance of vision merges all three together visually into a single image. If you blink, you miss one or two of the colors so you get a brief flash of a magenta, yellow, cyan, red, green or blue image. (I find this effect particularly disturbing) But if some small object moves quickly across the screen there is something more complex going on. Because the three images are displayed separately - they appear at different times. Yet all three images are of the object have it in the same place on the screen - we get a rather peculiar effect. Imagine you plotted a graph of position on the screen versus time. The graph would look like this:

  ^   |                           . . .
  |   |                    . . . 
Posi- |              . . .
tion  |       . . .
      | . . .
      +------------------------------------
            Time ==>

(each dot being a red, green or blue 'rendering' of the object)

...instead of a nice straight line, we have a staircase. What our brains do with this ought to be something like seeing a jerky motion instead of smooth motion - but at these kinds of frame rates, what we actually "see" is three objects moving on a set of parallel paths across the screen. Since each one is a different color, we see a red object, a green object and a blue object moving close to each other - separated by one third of the distance the object moves in a single 1/60th second frame. For slow objects, this isn't noticable - for faster objects, you see a rainbow fringing effect and for very fast objects, you see three separate things tracking across the screen.

When you move your eye rapidly across the screen - it's just like the entire scene is moving rapidly in the opposite direction - and the result is the same as if the entire picture were moving quickly - so the fringing happens all over the screen instead of in just one place. That's why the effect is most noticable when you do that.

More modern projectors (or at least, more expensive ones) have three separate projectors inside - so it can display red, green and blue at the same time - which completely eliminates all three problems (fast eye motion, fast object motion AND blinking). Some intermediate price systems display at even higher than 180 frames per second (eg 360 frames per second) and they show red,green,blue,green,red,blue in every 1/60th second frame. This helps by confusing the eye and making it harder for the eye to misinterpret what you're seeing. That helps the blink problem a lot (because you can't blink and miss (for example) both green presentations and end up seeing a magenta image. The color fringing is also somewhat disguised.

SteveBaker (talk) 13:29, 20 October 2008 (UTC)

Weight of bones

A bird skeleton equals only about 5% of its mass. How does this compare with mammals? —Preceding unsigned comment added by 66.121.22.163 (talk) 22:27, 18 October 2008 (UTC)

According to our article on the Human skeleton, it accounts for about 20% of a human's body mass. I am not sure how representative we are for all mammals, but there you go... --Jayron32.talk.contribs 22:32, 18 October 2008 (UTC)

Heavier animals devote a larger percentage of their body mass to their skeleton than do lighter animals. Small mammals (e.g. mice and things) are generally also in the several percent range. [18] Dragons flight (talk) 23:07, 18 October 2008 (UTC)

• For the reason this is true, see square-cube law and particularly the "Biomechanics" section. --Anonymous, 23:59 UTC, October 18, 2008.

According to the Natural History Museum of Los Angeles Co., the weights of a bird's skeleton and that of a mammal of equal size are comparable, noting Dragons flight's observation that the larger the animal the heavier the bones. - Nunh-huh 23:11, 18 October 2008 (UTC)

October 19

nigilism

a foreign friend referred in passing to 'nigilism' - what could she have meant? —Preceding unsigned comment added by 79.122.55.76 (talk) 00:45, 19 October 2008 (UTC)

or niginism or something similar. I first thought she was trying to say "nihilism" but no... —Preceding unsigned comment added by 79.122.55.76 (talk) 00:47, 19 October 2008 (UTC)

COuld you provide more context to the conversation? If we knew what she or you were discussing at the time, it might help figure out what she was trying to say... --Jayron32.talk.contribs 00:54, 19 October 2008 (UTC)

Google book search for "nigilism" produced 25 hits:[19]. Seems to come from Russian literature, in the character of Bazarof introduced in 1861 by Turgenief. Too turgid for me to follow: [20]. Some of the hits are bad optical character reading of "nihilism" and it seems to be nothing more than a quirky Russian spelling of same, per [21], which says nigilism=nihilism " g in Russian doing service for h." Edison (talk) 01:07, 19 October 2008 (UTC)

I think you're right on. In Russian Cyrillic the concept is spelled "Нигилизм" which can be romanized to "Nigilizm" 02:40, 19 October 2008 (UTC)

Weren't inhabitants of parts of the Soviet Union in WW2 under the impression that they were being persecuted and killed by "Gitler?" See "Re: Gooray for Gollywood"[22]. AGoogle search shows that a number of persons apparently from non-English speaking backgrounds spell the name in English "Adolf Gitler."Edison (talk) 04:08, 19 October 2008 (UTC)

'h' in loanwords often becomes 'g' in Russian; I guess this is because some other Slavic languages regularly have /h/ where Russian has /g/ – see e.g. Ukrainian city-names with –hrad vs Russian –grad. —Tamfang (talk) 20:39, 19 October 2008 (UTC)

My brain is niggling at me, and has asked me to mention that it's surprised the Russians didn't have a word such as ничевизм (nichevizm), from ничего (pron. nichevó, meaning "nothing"). -- JackofOz (talk) 07:03, 20 October 2008 (UTC)

Just as another example, there's Ibraham Petrovich Gannibal, the "black slave" of Peter the Great. Gannibal/Hannibal was an ancestor of Pushkin. - Nunh-huh 07:44, 20 October 2008 (UTC)

I suppose this should more likely be at the Linguistics desk...but anyway, as noted, Russian has no letter directly corresponding to our H. Although it's typically Г (for example, О. Генри, the writer O. Henry), it's occasionally something else: for example, hobbit becomes Хоббит. Nyttend (talk) 17:15, 22 October 2008 (UTC)

Skin condition photos

I added some old photos to Erythema multiforme. However, this photo shows what is meant by Erythema multiforme target lesion, and the target lesion do not appear to be in either photo set in the Erythema multiforme article. If you have a chance, would you take a stab at identifying the skin conditions in the photos in the Erythema multiforme article so that the photos can be placed in the correct skin condition article. Thanks. -- Suntag ☼ 01:37, 19 October 2008 (UTC)

This seems closer for the first set having three photos. -- Suntag ☼ 01:56, 19 October 2008 (UTC)

Dream On! Dream On! Dream until your dreams come ... on a small video monitor?

• http://www.telegraph.co.uk/earth/main.jhtml?view=DETAILS&grid=&xml=/earth/2008/10/17/scidream117.xml

Black and white TV generation have monochrome dreams

By Richard Alleyne, Science Correspondent

Last Updated: 5:01pm BST 17/10/2008

While almost all under 25s dream in colour, thousands of over 55s, all of whom were brought up with black and white sets, often dream in monchrome - even now. ...

This is funny, however, ...

• why wouldn't people have commercials inserted in their dreams?
• why don't people dream in flat-colored pencil outlines thanks to all the animations they have seen during childhood?
• why don't people have silent movie dreams, i.e., scratched frames, exaggerated moves, flash cards ...?
• why don't people have radio drama dreams?
• why don't people have "pulp fiction dreams," i.e., a text-based dream printed on cheap and lousy paper?

Tell you the truth. I have had a dream with a commercial in it. I could not recall the dream itself. While I was dreaming, a man interrupted my dream with a book commercial. I returned to the dream after the sponsor of my dream has done his spamming. I woke up feeling really bad about it. My dream has a commercial in it but I could not get any money. It was the only time some greedy book seller in the Twilight Zone stole air time from me. -- Toytoy (talk) 01:50, 19 October 2008 (UTC)

I know I used to dream about Pokemon, in a visual style resembling the cartoon, back when I watched it. But my dreams are often a jumble of "live action" images, spoken words, and more surreal/artistic imagery, often with some books/TV images/online content integrated into the dream. So all I can really conclude is that, yes, the media we're exposed to gradually creeps into our subconscious minds just as much as any "real world" influence. 69.107.248.192 (talk) 02:58, 22 October 2008 (UTC)

Wouldn't this mean that before TV humans didn't have dreams?203.59.155.251 (talk) 03:16, 19 October 2008 (UTC)

More likely that TV sometimes influences our dreams now, whereas before TV people sometimes dreamed about what they heard on the radio, or the Sheriff of Nottingham, or the sabretooth tiger they killed the day before. Astronaut (talk) 07:16, 19 October 2008 (UTC)

I expect that before the existence of telly, radio, printing or gossip, that we all dreamt in cave paintings. SpinningSpark 14:09, 19 October 2008 (UTC)

I've dreamt a dream was a book I was reading, and that it was a film I was watching. I've dreamt I was in a Philip K. Dick short story. I think all those types of dream are possible. I even had sepia dreams when I was small and reading a lot of old picture books. 79.66.121.198 (talk) 15:25, 19 October 2008 (UTC)

When my bed faced a window, I once woke up from/through a dream in which the window (a pale rectangle) was a website. —Tamfang (talk) 20:31, 19 October 2008 (UTC)

I suspect observer bias. Let's suppose that we have always had some dreams in color and some in monochrome. It's possible that before the era of television and film, nobody thought very much about whether there was color or not. Things naturally tend to look monochromatic in dim light because the 'cone' cells in our eyes that detect color don't work well in low light levels and our 'rod' cells - that work well in low light levels - don't produce color information. This is so ingrained into us that very few people even realise that it's happening. So it's possible that before we saw monochromatic-in-full-daylight scenes in the movies and early model TV's - we'd have simply interpreted monochromatic dreams as happening in low light conditions. When monochrome TV's appeared, we had this other interpretation thrust upon us - resulting in reports of seeing dreams in monochrome - then when that period went away and we all started seeing monochrome only in dim light again - that we'd go back to reporting monochromatic dreams as not being unusual - just like we don't report dim-light vision as being unusual.

SteveBaker (talk) 13:11, 20 October 2008 (UTC)

Is there evidence to suggest that the Black and White ness isn't age correlated? That would seem to be the simplest assumption to make, 137.108.145.10 (talk) 13:43, 20 October 2008 (UTC)

Monochrome images were available before the invention of BW photos and TV. Charcoal sketches are monochrome. However, if you were an ordinary poor farmer 100 years ago, you could have seen no art at all. -- Toytoy (talk) 09:23, 21 October 2008 (UTC)

Genetic mutation- Double tail gourami

I was at the pet store today looking at the fish for sale. I noticed in one of the tanks a dwarf gourami with a true split tail (double tail). It looks like a split tail betta splendens. Ive looked online for some information on genetic mutations of the gourami but havent found anything. I was curious what causes this and if there is any information available to breeding true split tail gourami.

http://en.wikipedia.org/wiki/Gourami —Preceding unsigned comment added by 69.45.184.77 (talk) 06:34, 19 October 2008 (UTC)

This[23] finds double tail betta females and possibly others. If it's what you're looking for, specialised aquariums might be able to help. Julia Rossi (talk) 22:20, 19 October 2008 (UTC)

Ultimate fate of the universe

I tried pointing this out at Talk:Ultimate fate of the universe, but I received no response, so I'll repeat it here.

• 

The graph from the section "Role of the shape of the universe" shows the accelerating universe as a sinusoidal curve, with "Now" on the inflection point. In my opinion, it seems more likely that an accelerating universe would be concave all the way along, with a constantly rising gradient. Axl ¤ [Talk] 09:01, 19 October 2008 (UTC)

I don't think the shape of the curve is quite right, but the inflection is. If you assume a cosmological constant version of dark energy then the curve should decelleration due to gravity initially until dark energy starts to dominate and only then does it start to accelerate. As I recall, that transition was a few billion years ago more or less. Dragons flight (talk) 09:25, 19 October 2008 (UTC)

The correct ΛCDM curve is roughly $a(t)\propto (\sinh(t/{\mbox{11 Gyr}}))^{2/3}$. The curve in that diagram has the right general shape, but it's not drawn very accurately. -- BenRG (talk) 14:14, 19 October 2008 (UTC)

Gibbs free energy

ΔG⁰=RTlog_eK

The K used here is the equilibrium constant. But there is a problem in knowing that is it K_p or K_c

If we use either of the constants the values come out to be different. Please Explain. —Preceding unsigned comment added by 122.173.65.66 (talk) 14:41, 19 October 2008 (UTC)

You will have to refresh my memory as to what the "p" and "c" subscripts mean (constant pressure and ??), but I believe the real equation is ΔG=RTln(Q), which takes into account concentrations of the reactants and products. Under standard conditions (superscript °), then that would mean various things (concentrations of reactants are 1 molar, STP). This calculation of ΔG is for the instant at the beginning of the reaction. Once the reaction starts to proceed, ΔG will change (due to mass action and Le Chatelier's principle) until it reaches zero - equilibrium. --Bennybp (talk) 20:05, 19 October 2008 (UTC)

K_c is the constant for concentration. —Cyclonenim (talk · contribs · email) 22:17, 19 October 2008 (UTC)

ΔG⁰ is the instantaneous free energy change at the start of a reaction, at standard conditions (273K, 1 atm, 1 molar concentrations) and constant pressure, whose equilibrium constant is K. K is generally assumed to be unitless and calculated from the "activity" of the compounds involved. Since actvity is not directly measureable, a "surrogate" which can be measured is often used. K_c is the equilibrium constant as calculated from molar concentrations (aqueous solutions or gasses) and K_p is the same constant as calculated from pressures. For gases, K_c = K_p divided by (RT)^Δn, where Δn is teh number of moles of gas that changes in the balnced reaction. --Jayron32.talk.contribs 22:38, 19 October 2008 (UTC)

The shape of the orbit of the Moon over the Earth

Imagine a line from the centre of the moon to the centre of the earth. At the surface of the earth, this line forms a dot which moves with the rotating orbit of the moon, and the rotation of the earth. If this moving dot was plotted on a stationary globe, what shape would it make? Some sort of spiral? Thanks 78.149.192.49 (talk) 17:40, 19 October 2008 (UTC)

Hm. This may be a start for you: Orbit of the Moon. From that, it appears that there are some rather complex motions to consider. If you picture the moon's orbit as a big coin, the coin is at an angle to the earth's equator (called inclination) and that coin is itself "wobbling" (called precession). The wobbling is in two different planes (parallel to and perpendicular to the ecliptic). The periods of these two precessions is quite short, 8.5 years for one and 18.6 years for the other. Not sure what this means for the overall pattern you are looking for, but if you can wrap your head around all of that (the article is more detailed) then there ya go. --Jayron32.talk.contribs 18:19, 19 October 2008 (UTC)

If you unwrap the earth into a typical rectangular Mercator projection map - the path of the moon would be (more or less) a series of overlapping sine-waves. SteveBaker (talk) 12:56, 20 October 2008 (UTC)

Similar to the map that is always in the background during film scenes set in mission control. That was my first thought, but I'm a little unsure how the fact that the Earth's rotation is orders of magnitude faster than the orbit (with an artificial satellite it's usually the other way around) would affect that. I think that it would still, technically, be overlapping sine-waves, but the wavelength would be extremely long so the wave goes all the way round the Earth 28 days per period (ish, I'm not sure exactly which definition of lunar month we need). Therefore what you would actually see is basically a series of straight lines across the surface of the Earth (well, straight as in constant latitude, whether they are actually straight lines depends on the choice of projection). --Tango (talk) 13:12, 20 October 2008 (UTC)

Actually, it probably wouldn't be all that different. The absolute motion of the moon around the center-of-mass of the earth (the Month) is not what is relevent here, its the relative motion of the moon to the earth's surface, which is still about a 24 hour period. The question is kinda vague, since the picture is different whether one wants to know what the pattern would look like projected on the real map of the earth OR a theoretically static earth. The two wavepatterns would look very different, since one takes into account the earth's day-rotation, while the other only takes into account the moon's month-revolution. --Jayron32.talk.contribs 13:54, 20 October 2008 (UTC)

While the longitude of the point goes in a roughly daily cycle, the latitude will go in a monthly cycle since the Earth's rotation doesn't affect where the moon is in relation to the plane of the Earth's equator. I think the OP's question was quite clear, since it specifically mentioned the rotation of the Earth, so the reference to a static Earth refers to a co-rotating frame of reference rather than actually stopping the Earth moving. --Tango (talk) 14:49, 20 October 2008 (UTC)

Thanks. So how far north or south from the equator would the dot go? I assume that at the poles, the moon is never directly overhead. 78.149.175.26 (talk) 14:11, 20 October 2008 (UTC)

The Moon's orbital inclination relative to the Earth's equator is (according to the infobox on Moon) "between 18.29° and 28.58°". That means the dot will never go north of 28.58°N or south of 28.58°S (and will rarely get even that far from the equator, I'm not sure precisely what determines the inclination at any given time, but the difference is almost exactly twice the inclination from the ecliptic which suggests to me that it's probably an annual cycle). --Tango (talk) 14:49, 20 October 2008 (UTC)

Earth's equator to the ecliptic is constant ~23°; Moon's orbit to the ecliptic is constant ~5°. As the Moon's orbit precesses, the 5° sometimes adds to the 23° and sometimes partially cancels it, resulting in the numbers you see, as you apparently guessed; though there's no annual cycle to it. —Tamfang (talk) 02:40, 21 October 2008 (UTC)

Ah, that makes sense. Thanks! --Tango (talk) 14:32, 21 October 2008 (UTC)

Thanks again. What prompted these questions - and what really interests me - is the track of the moon in the sky over time. Where I habitually sit, I see the moon through the window pass in an arc across the night sky during the evening. I think the centre of the curve of the arc is to the south. As the nights go by, this arc gets lower and lower in the sky. I can only see a small part of the sky through the window. I'm wondering what the track of the position of the moon would look like overall. A few nights ago I went out of the house and was surprised to see the moon in the north-east or east of the sky, I think. I'm also wondering if the moon is capable of being in any part of the sky (from my point of view) or in just some of it. If in just some of it, then how does the moon get into position to draw the arcs I have described? 78.147.35.151 (talk) 21:39, 20 October 2008 (UTC)

The track of the moon in the sky from a fixed point on Earth is quite a different matter to the track on Earth of the point below the moon. The moon will follow a similar path along the sky as the Sun, rising in the east and setting in the west once a day. It will never stray more than about 5 degrees from the ecliptic (the path travelled by the Sun, where that is depends on the time of year and your latitude). I suppose you are in the northern hemisphere, so the moon is getting lower and lower in the sky for the same reason the sun is - it's getting into winter. That's caused by the Earth's axis being tilted with respect to the Sun's/Moon's orbit (the sun's and moon's orbits are at pretty much the same angle (only 5 degs different), so the tilt is pretty similar). --Tango (talk) 22:02, 20 October 2008 (UTC)

Thanks, but I have to disagree with the moon getting lower in the sky with the seasons - it seems to happen about every month, not every year. And in the small part of the sky I see out of the window, the moon is more or less full. I wish there was some nice freeware software somewhere that could show what I have described. 78.151.133.172 (talk) 22:55, 20 October 2008 (UTC)

There is excellent astronomical software available for free that allows you to pick a point on the Earth and a time and see exactly what the night sky should look like, you can then fast forward and see what changes. I have Celestia installed on my computer, although I haven't used it in a while, and found it quite good. There are plenty of alternatives, though. When you see the moon lower in the sky, it could simply be because it's at a different point in it's path across the night sky - it will rise and set at different times each night. --Tango (talk) 14:31, 21 October 2008 (UTC)

Helicopter under a bridge?

This question has one foot in the Entertainment Desk, but it's the science side I'm asking about.

Last night I watched Terminator 2 (a documentary that hasn't been made yet:) and in one scene a helicopter flies under a fair-sized road bridge, six-lane overpass type. Now I know they built a real polyalloy cyborg for the movie, but is the helicopter shot faked? Helicopters generate downwash, so the air has to come from somewhere, seems to me having a bridge deck just over the rotor would seriously disrupt the aerodynamics - lifting the 'copter as it ate away the air above it and causing it to hit the bridge deck above.

Is it actually possible to fly a 'copter under a bridge, let's say an 80-foot span-breadth with 30-foot clearance? Thanks! Franamax (talk) 20:30, 19 October 2008 (UTC)

I know that they regularly fly helicopters under the Golden Gate Bridge, but that is several hundred feet high. I don't know what the lower limit would be. --71.106.183.17 (talk) 20:38, 19 October 2008 (UTC)

Even if the scene in the movie is possible, I cannot imagine it would be legal in the US. So the filmmakers would certainly have used special effects to simulate it. At least it's not as obviously impossible as the helicopter scene in the 1996 "Mission: Impossible" movie. --Anonymous, 22:12 UTC, October 19, 2008.

I don't remember that scene in the movie. Is it particularly spectacular? Is a big deal made of the fact that they flew a 'copter under a bridge? If not, they probably wouldn't have wasted special effects on it. Anyway, I think pretty much anything is legal if you get it approved for movie-making purposes. --Masamage ♫ 03:59, 20 October 2008 (UTC)

Mission Impossible scene - helicopter flies into Channel Tunnel in pursuit of high speed train to which it has rather carelessly become tethered. Gandalf61 (talk) 09:30, 20 October 2008 (UTC)

Sorry, I meant the Terminator scene. --Masamage ♫ 21:23, 20 October 2008 (UTC)

It's not obvious to me that this would be illegal, for the same reason I doubt there is any law that says don't use a bullwhip on high voltage electrical wires. It is so incredibly dumb and unusual that quite possibly no one has wasted the time required to write a law addressing it. Dragons flight (talk) 09:36, 20 October 2008 (UTC)

I'm assuming in any case that the stunt would be legal. They presumably got the highway below blocked off to film, and (almost) anything is possible in movie-shoot areas (punch buggy alert, but watch the chase scene in Bullit). I'm asking physics-wise two cases: could you fly a helicopter at speed under a bridge with the parameters I described (confined space longer than it is high, 100'L x 50'W x 30'H)? And could you even edge a helicopter into that space and traverse it? We're talking a light 'copter like the ones they rent to movie companies or use for traffic reports, and no, it wasn't that spectacular of a scene. Similar to flying into the Chunnel (although that's much less likely, how would they get it back out?) - is it physically possible to perform such a maneuver? Franamax (talk) 10:50, 20 October 2008 (UTC)

There are probably laws about how close you can fly to solid objects, but there's no reason they couldn't have gotten permission from the relevant authorities. --Tango (talk) 10:56, 20 October 2008 (UTC)

The Wikipedia page Stunt seems to suggest this is genuine, but it's very vague. The page says "The killer robot T-1000 flies a helicopter in a freeway chase after a S.W.A.T. van driven by The Terminator and at one point flies under an overpass. As if to prove the stunt was done for real, the pilot attempts a second underpass, but flies away at the last second." There is no cite for this claim. --Maltelauridsbrigge (talk) 11:50, 20 October 2008 (UTC)

I'd also mention "The Italian Job" (the recent remake - not the 1960's original) where there is a helicopter inside a warehouse chopping up a poor-defenseless MINI Cooper.

The problem is that the rotors are sucking air from above the helicopter and pushing it downwards to support it's weight. When you get close up to the underside of a bridge or other enclosed structure, that sucking causes an increase in lift - which forces the helicopter closer to the bridge and that in turn causes an even more powerful upward force. This positive feedback effect makes flying under covered areas quite hazardous. Flying quickly under a narrow structure like a bridge is reasonably OK because you aren't under the bridge for more than a couple of seconds - but hovering under a bridge, or inside a building or (god forbid) inside a railway tunnel - would be very hazardous indeed.

We can get an estimate of "how close is close?" by noting that the ground effect occurs at about one to one-and-a-half times the rotor disk diameter. Below this height, the extra pressure caused by the ground interacting with the downward-moving air column dramatically increases the efficiency of the rotors. So when a helicopter comes in to land, it's like it hits this soft cushion at about one rotor-diameter above the ground. That's really convenient - and the lower you go, the stronger the effect. So I would guess that if you flew under a structure at a low enough height that there was at least (say) two rotor diameters of air between the top of the helicopter and the underside of the structure - then you'd barely notice that there was a problem. But if you got within (say) one rotor diameter of the structure, it would go badly wrong quite quickly. If the pilot was expecting this to happen, he could probably throttle back or reduce the collective pitch to cut the helicopter's lift - but unlike coming in to land where the negative feedback gives you a gentle cushioning effect that makes landing easy - the positive feedback sucking you upwards would be like a magnet pulling you where the closer you get, the more pull there would be. Flying the helicopter accurately under those circumstances would be exceedingly difficult.

So flying 100' below the golden gate bridge with a 30' diameter helicopter is no problem whatever - but the flying-though-the-rail-tunnel thing in Mission Impossible is...Impossible.

SteveBaker (talk) 12:50, 20 October 2008 (UTC)

It says above that helicopters are regularly flown under the Golden Gate Bridge. Is this legal?

(I do not consider that I'm asking for legal advice here. I'm just seeking factual information about the law. Also, for the record, I'm not planning to make any such flight.)

If it is legal, do the applicable laws cover what size of helicopters may be used? After all, there are helicopters and then there are HELICOPTERS.

Similar question for fixed wing aircraft. Piper Cubs good? Concordes not good? Where is the line drawn? Thanks, Wanderer57 (talk) 17:36, 20 October 2008 (UTC)

Yep - it's a similar deal. There isn't a hard line - but the bigger the wing the greater the effect. When I was a flight simulator designer, it was a moderately well-kept secret that we deliberately put invisible walls under all of the bridges in our 3D graphic simulations so that if a pilot tried to fly under a bridge in the simulator, they'd crash 100% of the time. The instructors who taught military fighter jocks using our simulators wanted it this way because they didn't want to encourage fighter pilots to practice flying under bridges in the simulator and then go and do something stupid in the real world once they'd gotten the hang of it. They assumed the pilot would try it a few times in the simulator - conclude that it was just WAY too difficult and give up on the idea! SteveBaker (talk) 14:10, 21 October 2008 (UTC)

As far as the law part of it, I had a look through FAA flight rules. They're pretty dense but I think I found 500-foot minimum altitude in there (except TOL of course). There was an exception for helicopters and they had to be operated in a "safe manner" below the limit altitude. I suppose that would mean that you would need to file your operating plan and if it said "flying under a few bridges today" they might ask you in for a chat. Have a read through those regs and see if you can find anything better. I couldn't find where they defined Class A - D airspaces for example. Now that I think of it, maybe Sikorsky's website would have something for 'copters. Franamax (talk) 17:37, 21 October 2008 (UTC)

Well, at least on a smaller scale, clearly this is not impossible, as this YouTube video shows us. I don't recall the T2 scene exactly, but I believe the bridge was wider in that. -- Captain Disdain (talk) 08:16, 21 October 2008 (UTC)

He's under the bridge for less than a second - and it's not even as wide as the rotor disk - so the upward force effect would be pretty limited given the momentum of the helicopter. He's gotta be much more concerned over the turbulence from the vertical side-walls - which can also create aerodynamic mayhem with helicopters when you get that close to them. You can see he's manouvering very slowly and carefully...and stunt pilots have a lot of experience with flying in odd situations like that. SteveBaker (talk) 14:10, 21 October 2008 (UTC)

The T2 scene had the 'copter filling maybe half the space under the overpass and flying through for several seconds. Against a black background, now that I try to recall. And flying over the second (higher and less broad) bridge makes no sense at all, I mean it's a Terminator fer-gawd's-sake, why would it chicken out? Franamax (talk) 17:46, 21 October 2008 (UTC)

Carbon-neutrality of paper waste

Does paper waste contribute to global warming, or is it an offsetting factor? Most paper waste is put in landfills and does not biodegrade over the short term. This would suggest that paper waste reduces the amount of carbon in the atmosphere, and thus offsets global warming. On the other hand, energy must be consumed in order to convert the wood into paper and to transport the timber, paper products, and waste paper. What is the net effect? John M Baker (talk) 20:55, 19 October 2008 (UTC)

Assuming the paper is produced from wood produced in sustainable forestry, the carbon content in the paper itself will be neutral, since new trees are absorbing carbon where the old trees were cut down. To the extent that the waste paper conributes to production of methane in the landfill (where the methane is not captured from the dump), the paper will contribute in the short term (10-20 years) to global warming since methane is a much more potent heat-trapping gas than CO2. And to the extent that the waste paper could have been diverted to a recycling stream, it will also contribute to global warming, since more energy is required to make paper from virgin wood than from recycled, and the net effect will generally be to cause increased consumption of fossil fuels. Franamax (talk) 21:23, 19 October 2008 (UTC)

Are we sure that most waste paper is sent to landfill? Collection and recycling of waste paper is advanced compared to many other forms of recycling. Note that one of the uses of recycled paper is cellulose fibre insulation for buildings - environmentally benign. Itsmejudith (talk) 21:29, 19 October 2008 (UTC)

Responses to the points made so far:

• As to the sustainable forestry point: Yes, cutting the tree down is itself a carbon-neutral act, since a new tree will be planted in its place. It's after the tree is cut down that carbon is affected.
• Waste paper in landfills generally does not produce methane over short periods of time, perhaps not for millennia. Newspapers from landfills a half century ago remain readable. My source is Rathje & Murphy, Rubbish!: The Archaeology of Garbage (which I recommend as an excellent read, as well as being enormously informative).
• My question really asks about carbon-neutrality in absolute terms, and not in comparison to some other, perhaps superior, method of disposal, such as recycling. That said, I am intrigued by the comparison to a recycling stream. Are the incremental carbon savings from recycling greater than the amount of carbon removed from the atmosphere by burial in a landfill? That seems intuitively unlikely, but I'm prepared to be influenced by actual facts. Of course, there are reasons other than global warming to favor recycling.
• I don't have statistics on disposition of waste paper, but I think most is sent to landfills. Recycling would also have favorable carbon effects, while other methods of disposition, such as incineration, generally would have unfavorable effects. I don't know which of these effects predominates. John M Baker (talk) 22:04, 19 October 2008 (UTC)

Hmm, those are some cogent points. To a certain extent, you are suggesting cutting down whole trees and burying them to sequester their carbon (not that you're saying that, but extend the argument that way...). I have no statistics on buried paper conversion by bacteria, you're right about reading old newspapers, whether that applies to non-chlorine-bleached vegetable-ink modern newsprint, I dunno. Certainly in my area, the majority of paper goes to the blue-boxes, either newsprint or cardboard/fine-paper. Of course by observation, people aren't able to recognize the pictures and words asking them not to throw in their waxed-paper milk cartons (or pizza boxes with the pizza still in them, or their old VCR in the paper bin) - so I can't estimate how much "recycled paper" gets rejected at the plant and sent to landfill. We would need to look at the energy balance - new paper vs recycled. We will always be using more new pieces of paper, how much (presumably carbon-intensive) energy do we expend to produce virgin vs. recycled material? How does that balance with the putative benefit of burying carbon for some millenia? I've got no good numbers on that and it's an interesting question. For comparison though, why don't we just cut down trees and bury them? Franamax (talk) 00:57, 20 October 2008 (UTC)

One minor point. I would wager that household use of paper probably pales to office/commercial use of paper. My experience in that field suggests that office workers do a very poor job of separating their recyclables leading to a great deal of supposedly recyclable goods getting dumpstered. Matt Deres (talk) 13:42, 20 October 2008 (UTC)

And dang, I missed a point - incineration works out, give or take 10-100 years, to be not that bad. In the case of clean incineration and efficient use of the energy, as in combined cycles of incineration to produce steam for power generation combined with district heating schemes (I'm thinking Sweden and Denmark especially), again fossil fuel use is reduced in proportion. Given a sustainable forestry scheme, the carbon is directly recycled - again, need to consider here the energy balance between producing the finished good and incinerating it (and having enough burnable material to sustain an incineration scheme). Franamax (talk) 01:06, 20 October 2008 (UTC)

Burying paper cut from a managed forest should be a net carbon win. Burying trees would also be a win - providing the energy you consume in doing so is small enough. Of course nature has been solving the carbon problem by burying trees for a very long time - and that's been working out pretty well, right up to the point where humans started digging them up again (as coal) and burning them. I very much doubt that deliberately cutting down trees in order to bury them is a good idea - it's probably better to simply leave the forest alone and let it bury its own trees - thereby saving all of the fuel and manpower needed to cut and bury. Using wood to build houses is a net carbon win - but only so long as the total number of houses increases over time. As soon as you reach some kind of market saturation where old houses are demolished in order to make new ones, the question becomes one of what you do with the refuse coming from the demolition of old houses. If you bury it - then you're still winning the carbon battle - but if you burn them it's a break-even thing.

The underlying problem is that for the earth to reach equilibrium, we have to bury carbon at a rate equal to the rate that we dig it up and burn it. Since coal is essentially dead trees with all of the non-carbon squeezed out of them - it would take many tons of modern tree burial to cover every ton of coal dug. When you look at the numbers - a typical mid-sized power station consumes 10,000 tons of coal per day - and consider the number of acres of trees that would represent...[24] says that around 50% of the mass of a tree is carbon. [25] says that around 500 trees per acre is typical for a managed forest and that turns out to be about 8 tons per acre. So to compensate for the carbon created by just one medium-sized coal fired power station, you need to chop down, bury and replant 1250 acres of managed forest every single day. The fastest growing trees can be cut and replanted every 10 years - the slowest, every 60 years - so to sustainably cover the carbon from one powerstation requires at the very least, 1250x356x10 or about 4 million acres of managed forest - and at the worst 1250x356x60 or about 24 million acres. In the whole of the USA, there are about 600,000,000 acres of managed forest - which (if you buried every single tree they grew) would cancel out the carbon emissions from between 25 and 150 medium sized power plants. Sadly, there are over 600 of those plants in the USA - so even if you eventually buried every single piece of wood and paper we ever used - you'd only be saving between a 4% and 25% of the carbon we're producing from coal power plants alone.

However, there are faster-growing plants than trees. So if we were serious about this, we could grow (for example) saw-grass - and perhaps reach the break-even point that way. But the idea of turning over all of the managed forests in the USA for the entirely non-productive growing and burying of plants seems like an economic non-starter. Replacing the coal fired power stations with nuclear power and using just a few of those 600 million acres for the intensive storage of nuclear waste seems like a much simpler proposition. SteveBaker (talk) 12:32, 20 October 2008 (UTC)

Yes, it's true that cutting and burying trees is a form of carbon sequestration, and one that is being taken seriously; Dyson, for example, has written about genetically engineered carbon-eating trees. My question, however, is about paper waste that would be generated in any case. John M Baker (talk) 14:51, 20 October 2008 (UTC)

Going by this, pulping waste paper saves 5-7GJ/ton compared to virgin pulp. Using 57 lb carbon/MBTU for coal energy [26] and a very ragged envelope back gives me 342 lb. carbon saved by recycling one ton of paper, versus 1000 lb. sequestered by burial (using Steve's 50% ratio). This would look like an argument for throwing the paper away. However I'm not sure on the energy intensity for coal, i.e. the conversion efficiency from primary energy to usable energy. If the efficiency is 30%, it's a wash. If it's 50%, you could feel good about throwing paper into the trash. Additionally, this depends on the assumption that all the carbon in the paper will in fact be sequestered, and this suggests that it actually supports methane production, so you're going to get a lot of it back out again over a period of 30 or so years [27]. Maybe Steve has a better calculator than me. Franamax (talk) 22:39, 20 October 2008 (UTC)

No - I agree. It's a tricky thing. So long as the energy cost of recycling 'old' paper is less than the energy cost of cutting down (and replanting) a tree and making 'new' paper - then recycling makes sense. Remember that ultimately, the paper gets buried in a landfill one way or the other whether you recycle or not because recycled paper often goes into products that can't easily be re-recycled and therefore get buried. If recycling was perfect and no new trees needed to be harvested ever again - then we'd have to balance whatever new use all that land was put to against the 'sequestration' of the carbon in the paper in landfills. But if they are left as natural forests then they'll sequester carbon and eventually make coal all by themselves. (We need to contact some landfill operators and advise them to rename their businesses "Waste sequestration" - it makes them sound like really 'green' businesses!)

And given the longevity of some items in landfills (see the archaeology point above), they could also use "Preserving Our Nation's Heritage". :) Franamax (talk) 17:27, 21 October 2008 (UTC)

"Future historic artifact repository". Yeah - I think we're on to something! SteveBaker (talk) 00:34, 22 October 2008 (UTC)

Extremely interesting discussion. While all participants have my thanks, I note that there in fact was no answer seriously comparing the carbon sequestered by waste paper in landfills with the carbon expelled into the atmosphere in connection with the production, use, and disposal of the paper (although Franamax did point out that landfills may not be all that effective at carbon sequestration). It sounds like it might be an interesting area for research. John M Baker (talk) 00:32, 23 October 2008 (UTC)

October 20

Stuffy noses -- one side is blocked, then the other, then both.

During a cold or the flu, how does one nostril become completely blocked? Sometimes they both are, sometimes none. And it seems to change sides for no apparent reason. What's going on inside my head? --64.123.119.182 (talk) 01:56, 20 October 2008 (UTC)

We cannot offer medical advice. Please see the medical disclaimer. Contact your General Practitioner. Paragon¹²³²¹ 03:07, 20 October 2008 (UTC)

Good thing no one asked for advice then, isn't it? - Nunh-huh 03:08, 20 October 2008 (UTC)

Definitely not a medical advice question; anatomical curiosities are different. Unfortunately, I have no idea what the answer is. Something to do with sinus pressure. --Masamage ♫ 03:57, 20 October 2008 (UTC)

Since it's your face and not mine, I can't speak directly to your experience. Here's mine: I've had ear nose and throat problems all my life, especially terrbile sinus headaches (took me a decade of living with a cat to figure out I was allergic to it). I almost always get them on the same side of my head, which puzzled me until I realized: it was the side I slept on. Mucus is a fluid, albeit an especially goopy one, and if you preferentially sleep on one side more often than on the other, I wouldn't be surprised if that's also the nostril that's getting stuffed first. --Shaggorama (talk) 04:49, 20 October 2008 (UTC)

It's also not simply that "nostril that feels clogged" = "nostril that's obstructed by mucus". Congestion consists of swelling of the nasal mucosa; it's as likely to be this swelling as it is actual mucus obstructing air passage. In a paper discussing a system to measure differential air flow in the left and right nares, , there's a statement of some things that can change the sensation of which nostril is obstructed:"left naris becomes less congested ", " patient changes head position that affects air flow or swelling").[28]. The side you sleep on is also the side that's more "dependent" and could be more congested as well as more blocked by mucus. - Nunh-huh 06:31, 20 October 2008 (UTC)

One would also have to take into account the state of the nose before it became infected. It is possible that your nose has been injured at some time and the airway somewhat reduced during the healing process or you may have a small nasal polyp that is affecting one side of the nose, but only causing a blocked sensation when the mucosa is inflamed and swollen. Richard Avery (talk) 13:44, 20 October 2008 (UTC)

I did read/hear that it's normal to breathe predominantly through one nostril, with the nostril used alternating every couple of hours. Unfortunately I can't remember where or cite a reliable source, as it's just one of those factoids you pick up. AlmostReadytoFly (talk) 15:13, 20 October 2008 (UTC)

Yes I heard that. But here is a source [29]--GreenSpigot (talk) 01:06, 21 October 2008 (UTC)

Hmm, not what one could call a reliable source. A blogger citing other dodgy sites. Mentalphysics?? Richard Avery (talk) 07:52, 21 October 2008 (UTC)

OK heres another nostril--GreenSpigot (talk) 17:04, 21 October 2008 (UTC)

And another: Nasal cycle--GreenSpigot (talk) 17:08, 21 October 2008 (UTC)

Gravity waves

See Gravity wave. Anyone know what shape the wave is? It obviously isn't a sine wave. -- SGBailey (talk) 16:46, 20 October 2008 (UTC)

Do you mean the waves that that article are talking about (waves on the ocean, for example) or the waves in general relativity? The former are probably sine waves (if they're periodic at all, a tsunami is a gravity wave, but is just a single wave). The latter will depend on the source, two objects in a circular orbit around their centre of mass will probably give off sine waves (a GR expert may come along and say I'm wrong in a minute, I'm just guessing based on the animations in our article, gravitional waves, they look to me like they are oscillating as a sine wave). A more complicated system will give off something more complicated. --Tango (talk) 18:33, 20 October 2008 (UTC)

The shape of a gravity wave is too complex to have a simple name, it seems. See Airy wave theory for the simple, sinusoidal approximation. That article links to the more complex, nonlinear models. One of them is the trochoid, a shape that resembles simple nonlinear waves reasonably well. --Heron (talk) 21:14, 20 October 2008 (UTC)

I suppose I meant what shape is the animation of a surface gravity wave shown. What reason did the author have for making it the shape he has? -- SGBailey (talk) 21:39, 20 October 2008 (UTC)

Ah, I get you. Sorry. It's pretty close to a sine wave, but I agree it doesn't look exactly like one. I no idea why the creator chose that particularly wave, but they are still active so you could always ask! --Tango (talk) 22:07, 20 October 2008 (UTC)

The proper word is cnoidal wave, (google it!) but this does not have a wiki entry. And I learned about these 20 years ago, so I'm not an expert! Robinh 07:23, 21 October 2008 (UTC)

Vaccine versus Control group testing

In the information sheet for an oral vaccine against travellers' diarrhea and cholera, there is a table comparing "adverse events reported".

The two most commonly reported "events" are:

• abdominal pain, reported by 16% of those who received the vaccine and 14% of the control group, and

• diarrhea, reported by 12% of those who received the vaccine and 11% of the control group.

My question is about the methodology of such a comparision. I assume that people in the two groups are given the same information. What information are they likely given about what they are receiving?

Speaking personally, I think I would be likely to react differently if I were told:

"Please drink this. It contains one hundred billion inactivated cholera bacteria."

than if I were told:

"Please drink this. It will stop you from getting diarrhea."

- - -

Aside from the specific question of what the people in this test were told, in general what is the proper approach as to what people in such tests SHOULD be told? Wanderer57 (talk) 17:14, 20 October 2008 (UTC)

See double-blind study for more information on the generally accepted means of doing medical research of this nature.--Jayron32.talk.contribs 17:29, 20 October 2008 (UTC)

That article says: "Single blind describes experiments wherein information that could introduce bias or otherwise skew the result is withheld from the participants." I suppose either of my suggested wordings would introduce bias and thus could not be used. But it seems to me the participants have to be told "something". What can they be told? The article doesn't cover this. Wanderer57 (talk) 18:00, 20 October 2008 (UTC)

They'll be told something along the lines of: "Please drink this, it is either a vaccine against diarrhoea or a placebo." Everyone will be told the same thing and the person saying it doesn't know which one each person is getting (that's the "double" bit of "double blind"). --Tango (talk) 18:36, 20 October 2008 (UTC)

Bouncing off the atmosphere

You often hear people using the expression "bouncing off the atmosphere" to describe what happens if a spacecraft re-enters the atmosphere at too shallow an angle. This makes it sound as if the atmosphere is an elastic substance that can absorb the kinetic energy and return it - that can't be right, can it?

I think that the spacecraft would experience a force directly opposite to its direction of travel, and that this would slow it down. If the deceleration was inadequate, the spacecraft would return to space, but with reduced kinetic energy.

I remember when young reading about this affecting the height of the apogee, and I think I now know why. If the craft was in an elliptical orbit, the loss of kinetic energy at the perigee would reduce the potential energy of the apogee, due to the exchange between the two energy types as the craft orbits. This would progressively reduce the apogee until the orbit was near circular, when it would re-enter properly and land, crash or burn up.

If the craft was in a hyperbolic orbit it would still lose energy, possibly enough to be captured by the earth.

Is this what actually happens, or have I got this wrong? If correct, why "bouncing off"?

--J987 (talk) 19:56, 20 October 2008 (UTC)

I don't think the force is directly opposite the direction of travel - there will be lift as well as drag. I'm not quite sure how all that works, though, so I'll leave that to someone else. You are right about air resistance circularising an orbit, although it would probably re-enter some time before the orbit became circular. As the apogee drops, the object spends more and more time in the thicker part of the atmosphere and the apogee drops faster and faster, the final drop from being above significantly atmosphere to being on the ground would probably happen in less than one orbit. A hyperbolic orbit will certainly lose energy if it goes through an atmosphere, whether that could lead to capture or not, I don't know, it's certainly plausible. When probes to Mars, and similar, enter Martian orbit they sometimes (maybe always, I don't know) use their rockets to enter a higher elliptical orbit and then use atmospheric breaking near periapsis to circularise the orbit - they have rockets to prevent it going beyond circular and crashing, of course (I believe they keep the periapsis above the significant atmosphere and use rockets to periodically dip down into it, lose some energy, and then use the rockets to lift them back to safety). --Tango (talk) 20:16, 20 October 2008 (UTC)

Think "rock skipping off a pond". SteveBaker (talk) 02:50, 21 October 2008 (UTC)

The command module is almost exactly cylindrically symmetric. So one would think that the drag would indeed be opposite in direction to its motion through the upper atmosphere. But the mass distribution is non-symmetric; the spacecraft thus travels non-axially. This is (apparently) enough to generate a lateral force that can indeed cause the skipping phenomenon that stevebaker mentions [I find to my horror that rock skipping does not exist! There was a brilliant paper in Nature a few years back. I'll write a stub when I get a minute]. HTH, Robinh 07:17, 21 October 2008 (UTC)

Er, that's my bad. See stone skipping. Robinh 07:51, 21 October 2008 (UTC)

Fixed with a redirect. (It's a weird dialectic thing: British-English reserves the word 'rock' for things bigger than your head (or so) - smaller 'rocks' are called 'stones'...hence: stone skipping. This usage doesn't appear in US English where 'rocks' can be as small as maybe a centimeter or so before they might be called 'stones' - so the article needs to be called rock skipping...which would be an altogether more impressive feat in Britain!) SteveBaker (talk) 13:46, 21 October 2008 (UTC)

Thanks Steve. I'm British but never really thought about this difference between rocks and stones. I think 'rock' is the substance and so stones are made out of rock. Anyway, the Nature article I referred to uses 'stone skipping'. I ought to reference it in the article. Happy Wednesday, Robinh 06:58, 22 October 2008 (UTC)

4D

I've read part of Flatland and a sequel to it, and I've read The Planiverse, and I've run across a few other stories that ponder life in two or fewer dimensions. What about more dimensions? It seems like there would be even more technical problems to overcome in building a sensible lifeform and an environment for it to live in, but it shouldn't be impossible. Obviously the musculature would have to be as different from ours as ours is from that of an Ardean, since it has four dimensions to grow in and probably more complicated shapes to move around, and naturally ratios like height-to-weight would have to be rethought, but there's no reason it shouldn't work. Anyone run into anything like that? Black Carrot (talk) 20:24, 20 October 2008 (UTC)

I'm pretty sure people have considered life in 4D, although I can't find anything explicitly about it. I remember hearing somewhere that the extra dimension means particles are less likely to meet eachother (more ways to miss, I guess) which slows down reactions so life might not be possible (or would at least be less likely) - that was as part of an attempt to explain why our universe has 3 dimensions using the anthropic principle (in 2 dimensions you have problems with things like a body falling apart if you try and have a tube going all the way through to make a digestive system which causes lots of restrictions on how life could work, and in 1 dimension you can't change the order of particles from their initial conditions which restricts pretty much everything, so 3 dimensions turns out to be the optimal number for life to evolve). --Tango (talk) 22:14, 20 October 2008 (UTC)

Hi. Wouldn't the fourth dimension be time (and 5-11 branes)? Thanks. ~AH1^(TCU) 22:49, 20 October 2008 (UTC)

(sigh) Yes, this universe has three space dimensions (plus an unknown number at the very tiny scale, yada yada) and one time dimension, but when such questions are raised I, at least, assume that they're about a universe with N macroscopic space dimensions. —Tamfang (talk) 00:20, 21 October 2008 (UTC)

Another reason for exactly three dimensions is that in higher spaces there are no stable orbits (which I don't entirely understand so don't ask me). Also, in even-numbered spaces every signal rings forever, they say (which I understand even less). —Tamfang (talk) 00:23, 21 October 2008 (UTC)

I'm sure it has appeared several times in science fiction. The best example I can think of off the top of my head is Greg Egan's novel Diaspora, which has parts of it set in a five-dimensional universe (and other parts in weirder settings yet). Digging further, some novels in Iain M. Banks's Culture series (I think Excession in particular, but it's been a while since I read them) depict normal space as a "brane" in a higher-dimensional hyperspace, but I don't recall much being really made of it. Robert Reed's short story "Coelacanths" includes the memorable phrase "The universe is fat with dimensions." And of course there's Robert A. Heinlein's classic short story "And He Built a Crooked House". —Ilmari Karonen (talk) 23:32, 20 October 2008 (UTC)

Yes, I mean life in more-or-less R^4. Yes, I realize that the fancies of theoretical physics would have to be drastically re-fantasized. I'm thinking macroscopic, and assuming that the tiny things will sort themselves out. Macro things include gravity (Should it drop as the cube of the distance?), ratios of forces (No tree can be more than 350 feet tall, no land animal much bigger than an elephant), friction (Can you tie a rope?), and geometry (WTF with the skeleton?). I've read And He Built a Crooked House, which is a good story but more like life in a three-dimensional CW complex than life in R^4. I'll take a look at the five-dimensional one, but I'm guessing it goes more for "dimensions are really nifty" in its exposition than laying out a blueprint. To give some idea what direction I'm going in with this, I was inspired by the comic-off between Munroe and Katz, specifically Munroe's string theory comic. The joke is fun, but flawed. If you put people into four dimensions directly, they'll fall apart. If you expand them into lifeforms with four-dimensional volume, then you could just as easily weave four-dimensional ropes to hold them in. So... what would that look like? I'm surprised nobody's written about this. Black Carrot (talk) 18:19, 21 October 2008 (UTC)

The knots didn't fall apart because the ropes they were tied in were woven in three dimensions. They fell apart because they were essentially one-dimensional. If you used a two-dimensional sheet, it would work. See Knot theory#Higher dimensions. — DanielLC 23:35, 21 October 2008 (UTC)

Egan's Diaspora actually goes into some detail about physics and the geometry of life in 5-space. —Tamfang (talk) 01:12, 22 October 2008 (UTC)

Well, to see how odd would be life in a many dimensional world (as the ones conjectured by modern phisic theories), consider the following situation. You live in a 50 dimensional spheric planet, say of the same diameter of our old 3D Earth. Imagine you are having your whisky, or whatever, a gin tonic if you prefer, at home, so you have taken some small cubes of ice from the fridge, and now you go to the terrace with your glass. Now suppose you forgot one ice cube on the table in the kitchen... Question: how much will be increased the level of seas on the planet, due to your lazy behaviour? :) --PMajer (talk) 20:43, 22 October 2008 (UTC)

Possible non-conventional ways to counter global warming?

Hi. First of all, this is neither homework nor legal/medical advice, and I'm not exactly probing for oponions, I just want to know about the plausibility of these scenarios.

• Jumping simutaneously

This occured to me after remembering a joke on an April Fools' day, but I thought it might have a bit of plausibility. Consider people around the world simutaneously jumping at diffent times of each 24-hour period, say during the local early afternoon. People would jump at timed intervals around the world at a set local time, so that about 3 billion jumps would occur in one 24-hour period, daily, more so in the summertime than in the winter. I don't know if this would violate conservation of momentum or something, but if people simutaneously jump when their heads are facing closer to the sun, their downward forces would be pushed into the ground, and their upward forces into their bodies and thus not into the Earth. Would that be able to, over a long period of time, propel Earth into a very slightly farther (and more eccentric) orbit? Or, would it cause more problems than it would solve (they're saying that river dams and strong cyclones could cause earthquakes on stressed fault line zones)?

• Due to conservation of mementum this does not work. Graeme Bartlett (talk) 22:57, 20 October 2008 (UTC)

  I don't know if this is so much "conservation of momentum" as "...then you land". CoM is what makes the Earth move in response to your jump. Then, however, gravity kicks in and undoes everything you just did. — Lomn 03:22, 21 October 2008 (UTC)

• Painting albedo:

This idea is to paint urban items such as buildings, roofs, roads, etc, white, as long as it doesn't use much more oil, such as painting a roof white instead of a different colour. After all, there is the "urban heat island" effect, so this would cool down the city and also reflect more heat into space.

• could assist Graeme Bartlett (talk) 23:01, 20 October 2008 (UTC)

• Firing gravitons

Yeah, I know, gravitons aren't even proven to exist. However, if they do exist, and we can find out the mechanism for their creation, then maybe we could place graviton-generating stations around the world, and when it's dark at night, the machines could either point toward the Earth and switch on, and pull the Earth toward the machine, or they could point toward space, and the stream of gravitons could pull the Earth away from the sun, and they wouldn't propel the Earth toward the sun because they have no mass. Or, is this technicly not plausible, or would have too little effect even if we did somehow succesfully make one?

• You would be better off typing a rope to Mars. The theoretical graviton still has to obey conservation of momentum, so unless they move something else it will not work. Also it will require colossal energy, perhaps by burning fossil fuels? I don't think so. Graeme Bartlett (talk) 23:01, 20 October 2008 (UTC)

• Complete sequestration

I know, you've all heard of carbon sequestration, but this time without storing the carbon dioxide somewhere. Some sort of catacystic converter would separate the CO2 into oxygen and pure carbon, which would then be made into diamonds.

• would require too much energy to do, and burning coal to carbon dioxide and then forming pure carbon produces no energy, Graeme Bartlett (talk) 22:57, 20 October 2008 (UTC)

I'm not talking about producing energy, I'm talking about removing greenhouse gases from the atmosphere. ~AH1^(TCU) 23:47, 20 October 2008 (UTC)

But the greenhouse gases are in the atmosphere because of the need to produce energy! You might end up producing more gases than you would convert. Also, it would far more useful to produce carbon nanotubes instead of diamonds. =) « Aaron Rotenberg « Talk « 12:15, 21 October 2008 (UTC)

• Methane removal

Instead of burning methane in oxygen, store them with tubes, whether it be animal gas or garbage gas or clathrate gas or permafrost gas, and burn them in an oxygen-free environment, under high pressure. The hydrogen would float off into space, and the carbon would again be made into diamonds.

• Produces no energy. You will have to look at the Standard enthalpy change of formation of methane which is negative. Graeme Bartlett (talk) 22:57, 20 October 2008 (UTC)

I'm not talking about producing energy, I'm talking about removing greenhouse gases, and if it requires energy then what's wrong with using renewable energy. ~AH1^(TCU) 23:47, 20 October 2008 (UTC)

Where is this reneweable energy going to come from? One of our biggest problems is that we are still outputting a lot of CO2 and other greenhouse gases from fossil fuel power stations and this is forecas to rise in a number of countries. If we could magically switch to using 100% renewable energy everywhere, we would probably have done enough that global warming is no longer a significant concern Nil Einne (talk) 04:19, 22 October 2008 (UTC)

• Filling in of sea water

It's impossible to tell by looking at the title, but there are small spaces left in the Earth's layers when oil and gas are drilled, correct? Why not direct some of the sea water into a tunnel system that works like a piston, so that the water can go down, and heat cannot go up. Next, the water would be channeled into those gaps in the Earth's layers. This, if plausible, would allow for less sea level rise.

• the space here is very small compared to the rise in ocean levels. Graeme Bartlett (talk) 22:57, 20 October 2008 (UTC)

• Ocean water supply

If the freshwater resources in the future are too small, and sea level rise has risen a lot, then could it be possible to get water from a bit below the surface of the sea especially near polar countries, to avoid the oil slicks and also avoid the lower salty layer, so you'd have almost fresh but slightly brackish water that would take less energy to convert?

• Under the sea surface the water is usually salty. More salty water sinks below fresh water, so any fresh water would be floating on top (temporarily). It would be easier to melt the ice to get fresh water. Graeme Bartlett (talk) 22:57, 20 October 2008 (UTC)

Is any of this plausible? Again, I'm not asking for opinions, just for if this might be plausible, which is a factual query. Thanks. ~AH1^(TCU) 22:46, 20 October 2008 (UTC)

Seawater is already pumped into the spaces from which oil is extracted, to force the oil out. It's really a very small amount of water. -- Finlay McWalter | Talk 22:58, 20 October 2008 (UTC)

The only one that does not require Science Fiction technology, does not violate major natural laws, and is not based based on misconceptions, is number 2 (painting). It is a minor effect, but will be somewhat amplified since you can also reduce aircon in those building.--Stephan Schulz (talk) 23:00, 20 October 2008 (UTC)

And white roofs are already widely advocated to reduce urban heating and keep buildings cool: [30]. Dragons flight (talk) 23:04, 20 October 2008 (UTC)

Number 2 is not only possible, but it has even already been implemented, although unintended. In Almeria, the widest greenhouse area in the world, they could measure a surface air temperature reduction of 0.3°C in one decade. More about it here Mr.K. (talk) 09:41, 21 October 2008 (UTC)

Physics (Electric fields)

2 charges are separated by a distance of $4.3\times 10^{-9}$ m. The force between them is $2.8\times 10^{-8}$ N

(a) What will be the force between them at separations of $8.6\times 10^{-9}$ m and $1.29\times 10^{-8}$ m? (b) The potential energy stored in the field between the charges is $1.2\times 10^{-16}$ J when they are at a separation of $4.3\times 10^{-9}$. What will be the energies stored in the field when they are at separations of $8.6\times 10^{-9}$ m and $1.29\times 10^{-8}$ m?

Ive done (a) (answer = $7.0\times 10^{-9}$ N and $3.1\times 10^{-9}$ N) but I have no idea how to do (b). Can someone help me out a bit --RMFan1 (talk) 23:19, 20 October 2008 (UTC)

The potential energy is larger if the charges are larger, and is larger if they are closer together. In fact, it is equal to a constant times the charge of one object, times the charge of the other object, divided by the distance between them. If the charges are in Coulombs and the distance is in meters, then the constant is 8.99x10⁹ Newton meter²/Coulomb², per [31]. The Wikipedia article Electric potential energy explains this in detail. The Simple English Wikipedia also explains it at [32] , but they round the constant to 9 x 10⁹. Does that help? Edison (talk) 23:50, 20 October 2008 (UTC)

Part (b) is very similar to part (a) and you should be able to do the same thing you did for part (a) (whatever that was) but using the potential energy formula instead of the force formula. -- BenRG (talk) 23:54, 20 October 2008 (UTC)

energy obeys an inverse square law. The energy will vary inversely with the square of the distance. Thus E1 * D1² = E2 * D2². The point of the first energy/distance pairing is to give you the values of E1 and D1. D2 values are given in in the second part of part (b); that makes this a one unknown equation (E2). --Jayron32.talk.contribs 00:34, 21 October 2008 (UTC)

There's a mistake in that solution, but I think the corrected version would be too close to a giveaway given this was a homework question, so I'm going to stick to this warning... -- BenRG (talk) 13:00, 21 October 2008 (UTC)

Scientific Formula

Hello, I am looking for a scientific formula relating to an experiment on this webpage: [33]. Is there an equation that allows one to use the length of the tube and the width of the tube to determine the wavelength? I hope my question is clear, thank you ahead of time. Marcus Lupus (talk) 23:44, 20 October 2008 (UTC)

read the page itself. Its there, about 1/5th to 1/4th of the way through the page. --Jayron32.talk.contribs 00:30, 21 October 2008 (UTC)

October 21

Molecules that pass through membranes

If a membrane allows molecules to pass through, you say it's permeable. What do you say of a molecule that is able to pass through a membrane? 00:48, 21 October 2008 (UTC)

permeative? —Tamfang (talk) 02:40, 21 October 2008 (UTC)

Permeative seems to be along the right lines but I would like a work that fits here "...inhibitors of superior affinity, specificity and membrane XXX" ----Seans Potato Business 08:30, 21 October 2008 (UTC)

small? I think it depends on the membrane. Wanderer57 (talk) 02:49, 21 October 2008 (UTC)

Small would be ambiguous and not really stress the point that I'm trying to make. Thanks anyway. ----Seans Potato Business 08:30, 21 October 2008 (UTC)

The stuff that passes through makes up the 'permeate'...

Dioxin in Plastic Container and Foam Container?

I know that dioxin is highly carcinogenic. I heard that when you freeze a plastic water bottle, the dioxin is released into the water and when you heat a foam container, the dioxin is also released. Is this true or false? Sonic99 (talk) 00:59, 21 October 2008 (UTC)

Urban legend. Plastics for human use are not allowed to contain Polychlorinated dibenzodioxins and the loose term dioxin covers many different chemicals, most of which are not extremely dangerous. Graeme Bartlett (talk) 01:41, 21 October 2008 (UTC)

I read the Polychlorinated dibenzodioxins article and it says that the dioxins are present in minuscule amounts in plastics. Sonic99 (talk) 03:41, 21 October 2008 (UTC)

On snopes see[34]. Graeme Bartlett (talk) 05:22, 21 October 2008 (UTC)

How funny: someone just sent me that email yesterday (taken 6 years to make its way to me it seems). I'd already deleted it on the basis it was nonsense, but I've just dug it out again and can confirm it was that one! Gwinva (talk) 07:30, 21 October 2008 (UTC)

Stay or go?

If you are at Point A and need to get to Point B as soon as possible, and will not learn the location of Point B for another hour - are you better to set off in a random direction or to wait for directions? Does it make any difference if you need to get to Point B for a set time (more than a hour in the future), rather than as soon as possible? —Preceding unsigned comment added by WAYB (talk • contribs) 10:12, 21 October 2008 (UTC)

It depends on the abstractions used and the topology of your space. Assuming that you can start traveling instantly, and that you are moving on a perfect plane where you can choose any route, you are just as likely to move away from your target than towards it. So you have no gain. But if you know that your point B is 90 minutes travel time away, and you will only get the information 60 minutes prior to your deadline, you can at least improve your chances of making it from 0 to something - essentially, if you stay put, you will never make it, but if you guess right, you can reach point B. If you guess wrong, you are no worse of than before, as you would not have made it anyways. In a less abstract setting, if you start moving now, at least you know that you have the luggage and kids bundled into the car, the engine starts, and you did not overlook that wheel clamp ;-) --Stephan Schulz (talk) 11:29, 21 October 2008 (UTC)

(edit conflict) The concept of a point being in a "random" position in a plane does not make sense—you have to give a (joint) probability density function. So, for example, the location of Point B might have a uniform distribution in a circle centered at Point A. To put it another way, if you want to assume that B is equally likely to be in any direction and distance from A, you have to give a maximum distance. As it stands, the problem is meaningless. (Also, you might want to consider moving this to the mathematics desk; in fact, you might find the section titled "Points on a plane" interesting.) « Aaron Rotenberg « Talk « 11:42, 21 October 2008 (UTC)

Let's consider the more tractable 1-dimensional case. Suppose you are at point 0, and you know that in one hour you will be told to go to either point a or point −a, with equal probability. Suppose you set off and travel to a point d where d may be positive or negative, but |d| is less than or equal to a (it is obviously counter-productive to go past a or −a). When your destination is announced, you may have to travel a further distance e = a−d, or, equally likely, you may have to travel a further distance e = a+d. The expected value of e is therefore a; in other words, it makes no difference whether you set off in one direction or the other, or how far you travel before your destination is announced.

However, suppose you are told that your destination will be a point chosen at random (with uniform distribution) between −a and a. Once again, you set off and travel to a point d where |d| <= a. On one side of you is a line segment with length a−|d|; the probability that your destination is in this segment is (a−|d)|/2a, and the average further distance to travel is them e = (a−|d|)/2. On the other side of you is a line segment with length a+|d|; the probability that your destination is in this segment is (a+|d|)/2a, and the average further distance to travel is them e = (a+|d)|/2. So the expected value of e is now:

${\frac {(a-|d|)^{2}}{4a}}+{\frac {(a+|d|)^{2}}{4a}}={\frac {a^{2}+d^{2}}{2a}}$

Now you can minimise the expected value of e by choosing to make d = 0 - in other words, don't move until you know your destination. Gandalf61 (talk) 12:19, 21 October 2008 (UTC)

The above derivation sounds like a version of the Monty Hall paradox where foreknowledge of an outcome changes the odds of that outcome. If I understand the implcations of Gandalf61's solution, then if someone (not you) already knows where your destination ends then it doesn't matter if you leave or stay, the odds are equally as good that you will end up closer or farther. However, if the destination is chosen AFTER you have made the decision to stay or go, then it is better to stay. Is that right? --Jayron32.talk.contribs 13:05, 21 October 2008 (UTC)

That's incorrect, as the "destination chosen after deciding" case still uses no knowledge about what your stay/go decision is. Monty Hall varies from this because that additional knowledge comes into play. — Lomn 13:16, 21 October 2008 (UTC)

Thinking about this problem in 2-dimensional space, I think it would always be better to stay than to leave early. Think about it as the intersection of two circles. Circle "a" has its center at your destination and its radius equal to the distance between your starting point and your destination. Circle "b" has its center at your starting point and the distance you travel before you arrive. Now, look at circle "b". The area of circle "b" that lies outside of the overlap between the two circles is the "bad" area; this area is essentially everywhere you can reach that is farther from your destination. The overlap area is the "good" area, because this area is all closer to your destination. For any distance less than the minimum distance between your starting and end points, the area of the "bad" part of circle b will exceed the area of the "good" part of circle b, thus you have a greater chance of wandering into a point farther from your destination than closer to it... --Jayron32.talk.contribs 13:12, 21 October 2008 (UTC)

If B is in a totally random location relative to A - then if you first walk in some random direction and arrive at C when you finally find out where B is - then the vector C-B is no more or less random than A-B - so there is no point in leaving A - and no benefit either. However (as others have obliquely mentioned) it's unlikely that B is TRULY randomly placed compared to A. This matters. For example...suppose B is one hour away from A and you'll find out where B is in one hour from now. If B turns out to be due north of A then when you walked off to C, if you walked for an hour on a heading anywhere between +60 and -60 degrees of due north then you'll arrive at B sooner than if you'd stayed at A. That's a 120 degree range of directions. But if you walked off in any other direction for an hour - then you'll be further away from B when you finally find out where it is. So in that case (a 1 hour wait for information followed by a 1 hour walk from A to B) - then walking in a random direction while you're waiting has only a 1 in 3 chance (360 degrees divided by 120 degrees) of saving you any time - so you shouldn't do it. Envisage a triangle A-C-B. The length of the A-C edge is the wait time before you get instructions, the A-B line is the time to walk from A to B. In order to 'win' the line C-B has to be shorter than A-B for whatever A-C turns out to be. For all 'winning' triangles C-B has to be shorter than A-B and therefore the angle C-A-B must be less than 90 degrees. So no matter what the 'wait' time and 'walk' times are - there the range of headings you can walk in MUST be less than 90 degrees either side of A-B. That means that the total 'arc' of winning headings is always less than 180 degrees - and therefore you ALWAYS have a worse than 50/50 chance of winning - no matter what the 'wait' and 'walk' times are. So you should NEVER leave A...it can't ever give you an improved probability of doing better.

So if "winning" means that your average arrival time at B is shorter - then your best plan is to remain at A. However, there are other versions of "winning". Suppose there is someone dying at B - the search party is out there - and they are going to call you and tell you where B is so you can go rescue them. If you know that they'll die if you don't get there within an hour - and suppose you also know that B is definitely more than an hour from A because you'd already be able to hear him shouting for help if he was less than an hour away. In that case, your probability of winning if you wait at A is zero. So setting off in a random direction gives you at least some probability of success - so reluctantly, you must set off at random. Doing that makes your average arrival time at B much worse - but the probability of getting there within an hour is better than zero - so setting off in a random direction is better than losing for sure.

SteveBaker (talk) 13:37, 21 October 2008 (UTC)

I'm not sure what "truly random" really means, but if it means "uniformly distributed over the entire plane" then it's not just unlikely, it's impossible. Your density function ends up being identically zero which means the point isn't anywhere. --Tango (talk) 15:06, 21 October 2008 (UTC)

Now I got confused. I thought I had grasped the concept of Almost surely, but your statement that the point isn't anywhere contradicts what I thought I had understood. Isn't it correct to state that for any given location in the plane, the probability is zero that B will be there, i.e. it almost surely isn't there? I don't see a contradiction with the point being somewhere, even if the probability of it being in any finite part of the plane is zero. I'd appreciate if someone would clear this up for me. --NorwegianBlue ^talk 19:27, 21 October 2008 (UTC)

"Almost surely" is used to describe things like the probability of getting get 0.5 when you have a uniform distribution over the range 0 to 1. There are infinitely many possible values between 0 and 1, so the chance of getting a specific one of them is basically zero. However, the chance of getting somewhere between 0.4999 and 0.5001 is non-zero and that's what we're normally interested in. If the uniform distribution were to go over the entire real line then even that chance would be zero, as would the chance of it being in any finite range. If you add up all those 0's you still get 0 ($\Sigma _{n=1}^{\infty }0=0$), which contradicts the requirement that the total probability always be 1, which is why such a distribution can't exist. --Tango (talk) 00:23, 22 October 2008 (UTC)

That's a limitation with the mathematics of probability, and does not preclude the concept of choosing an arbitrary point from the plane (especially for subsets of finite area). Though the probability density function goes to zero, one can still find non-zero expectation values and other probablistic operations by tiling the space in discrete regions of finite area and using those to perform probabilistic operations in the limit as the size of those regions goes to zero. Dragons flight (talk) 17:38, 21 October 2008 (UTC)

Dragons flight and NorwegianBlue, it is possible to choose a random point on the plane, but not in a way that's uniformly random, that is, that doesn't favor any point over any other. -- BenRG (talk) 20:27, 21 October 2008 (UTC)

Can we (once we formulate this problem precisely) profit by considering the limit of more and more diffuse distributions for B, or do the limits (A) always diverge or (B) inextricably depend on our choice of distribution, so that we're not really being impartial? --Tardis (talk) 23:30, 21 October 2008 (UTC)

If you take this as a purely theoretical math problem on an infinite plane - then point B can be anywhere from 0 to infinity hours walk away in any direction. The average distance from A to B and from C to B is therefore infinite and walking to point C can't possibly make any difference to the average time it takes to get to B (which is infinite, no matter what). Here in the real world, the distance to B is typically going to be constrained in some way - which means that for any real application - the infinite case is of no interest or relevence whatever. Back here in the real world, there is meaning to the question - but the answer turns out to be the same - you can't win by walking in a random direction while you wait...unless "winning" means something a little non-obvious as I discussed earlier. SteveBaker (talk) 00:02, 22 October 2008 (UTC)

Of course, if we realise that we're actually on a sphere, not a plane, it becomes a little easier. You can have a uniform distribution over a sphere and none of the distances are infinite. Of course, the conclusion will still be that there is no point moving, since a sphere is homogeneous so there is no difference between the point you started at and the point you moved to - they will both be equally good places to get to point B from. --Tango (talk) 00:13, 22 October 2008 (UTC)

Columbia vs. Challenger disaster

Is it just my impression or the causes of the Space Shuttle Challenger disaster were terribly similar to those of the Space Shuttle Columbia disaster? Did any commission also come to this conclusion? Mr.K. (talk) 11:23, 21 October 2008 (UTC)

• I don't know. Is that your impression? But no, the causes aren't similar, except in the broad general sense that both spacecraft suffered a catastrophic failure. The Challenger was destroyed because an O-ring seal failed in its right solid rocket booster during launch, which led to the liquid hydrogen fuel exploding, whereas the Columbia was destroyed because a piece of foam insulation broke off the main propellant tank and damaged the shuttle's thermal protection system, causing the shuttle to disintegrate during atmospheric re-entry because the heat destroyed the shuttle's right wing (which didn't do any favors to the rest of the shuttle). They aren't similar incidents, and I doubt any commission ever came to a conclusion that they were. -- Captain Disdain (talk) 11:34, 21 October 2008 (UTC)
• (ec) Not to my knowledge, and I would be surprised if. Challenger exploded on the way up because of problems with the booster section connections. Columbia disintegrated during descent due to prior damage caused by insulation foam falling onto the leading edge of the wing. Of course both point to failures in the safety processes within NASA, but that is a trivial commonality that affects all but sheer freak accidents. --Stephan Schulz (talk) 11:38, 21 October 2008 (UTC)

Yes, I meant the safety processes within the NASA: a management team that underestimated the risks and pushed to go on and an engineer team that calculated reliably the risks and wanted to go other way. I don't believe that all accidents are caused through these tensions (technical vs. non-technical staff).Mr.K. (talk) 12:11, 21 October 2008 (UTC)

Well, a lot of comparable disasters can be traced back to a situation where someone had to approve an additional expense and said "no, it's good enough", even though there are engineers who say that it'll be safer if they get to spend the money. That's not necessarily a sign of bad management in itself; there's a difference between ignoring a known fault and ignoring a known risk of a fault, for instance. Still, it's certainly safe to say that NASA's organizational culture contributed to both accidents; the Columbia Accident Investigation Board did state that NASA had failed to learn enough from the Challenger disaster. Perhaps that's what you're looking for? But there's a really major difference between the actual cause of a disaster and the culture that has enabled such a cause to exist. Certainly, it can be said with justification that NASA should have learned more from the Challenger disaster, but even if they had, that wouldn't necessarily have prevented another accident. It's difficult to show cause and effect like that; things like operating budgets and changing administrations and whatnot have a huge impact on how an organization like NASA operates... Which, I should stress, isn't a valid excuse for negligence. -- Captain Disdain (talk) 13:04, 21 October 2008 (UTC)

You can view these disasters on two levels - there was some kind of an engineering/design error - and the necessary oversight/management to prevent such errors was not present. Viewed as an oversight/management failure - then, yes - these were essentially identical. Viewed at an engineering level, no - they were totally different. In one case, the O-rings of the SRB had insufficient flexibility to seal the solid propellant at low air temperatures found at the launch site - in the other case, chunks of foam insulation falling from the external fuel tank on takeoff hit a part of the leading edge of the wing - allowing hot gasses to jet into the wing structure during reentry. From an engineering perspective - those could not be more different. But from a managerial point of view - in both cases, the problem was known about in advance. Engineers had complained about launching in temperatures below which the O-rings would function adequately - and those warnings had been ignored. Chunks of foam and ice had been observed falling off of the external fuel tank many times in the past and nobody had funded a serious study to investigate the damage they might cause to the orbiter. In both cases, NASA failed to address safety concerns in a timely manner - and THAT was an organizational failing that was largely identical in the two cases.

I have seen this kind of thing happen only once in my career - where I'd spotted a serious problem and management ignored my complaints. This was when I worked in flight simulation. We had a requirement from the customer to provide the pilot with a simulator with a 100 degree field of view in the graphics display. This required us to mount a large monitor in front of the pilot such that it subtended an angle of 100 degrees at his head. Sadly, management decided to save money and ship a smaller monitor - but to continue to display 100 degrees worth of graphics on it - creating a slight "fisheye" distortion on the image (very slight as it happens). I did the math and realized that this distortion would cause the pilot to mis-judge his speed by about 5% if he used visual cues alone. If he learns to fly (and in particular, to land on an aircraft carrier flight deck) with a 5% error in his perception of speed from visual cues - then when he comes to land a real aircraft, he'd come in 5% too fast (assuming he's looking out of the window rather than at his instruments). This would be a potentially life-threatening thing - so I urged management to pay the extra for the larger monitor - for the sake of safety. Needless to say, they ignored my increasingly strident warnings because it save a couple of thousand dollars on each of a hundred or so simulators.

In that case, I eventually walked into my immediate bosses office with a formal-looking one-page statement of my position (along with all of the math) and I asked him to read it and sign at the bottom to SAY that he'd read it - so that my ass would at least be covered. Then I refused to leave his office until he did so. This got his attention and the problem was addressed rather quickly after that. But in some corporate and government cultures - what I did would have gotten me fired. In places like NASA - where safety is really a huge issue - people who find problems need to be listened to - and rewarded for their discoveries.

SteveBaker (talk) 12:56, 21 October 2008 (UTC)

There's a third level too: the macro-level design and political level. The shuttle embodies a bunch of design decisions unlike any other spacecraft, and reflects political compromises that conflict with purely technical demands. One could argue (and the return of NASA to very un-shuttle-like designs might indicate they'd agree) that some aspects of the shuttle platform are intrinsically unsafe (or are too expensive to really make safe) and that the real errors were made when the system was specified. These include:

• building a reusable system when no reusable orbital spacecraft had ever been built; this was motivated by the theory the shuttle would be a low-cost "space truck", but in practice it turned out to be as or more expensive than comparable launchers
• combining crew launch with heavy lift; Constellation deliberately separates these out
• reported conflicts with the Air Force over its requirements
• the solid-booster strapped to giant scary liquid bomb configuration; with a "stack" configuration you have some chance that an explosion might not destroy the payload, with the sandwich configuration that's much less likely
• building the SRBs at Thiokol's plant in landlocked Utah meant that the SRBs had to be sectional for shipping, and thus had to have o-rings between the sections. Had they been build somewhere on the coast or a major river they could have been shipped to Florida by sea, and thus the designers would have the option to have the SRBs be all one piece.

-- Finlay McWalter | Talk 13:16, 21 October 2008 (UTC)

Plus the US space program seems to have a great fondness for making new stuff, even though the old stuff worked okay. Bar the very questionable reality of reusability, it's not clear what STS does that they couldn't have reengineered Saturn to do. And I really don't understand what Ares will do that Delta IV Heavy doesn't do or couldn't be improved to do sooner. The Russian programme seems to have been philosophically much more incremental and conservative (which I guess explains both why their rockets look so old-fashioned, and why they're more reliable). -- Finlay McWalter | Talk 13:31, 21 October 2008 (UTC)

I read some time after the Challenger disaster that it was caused by the fuel in the Solid Rocket Booster becoming brittle. This was a result of the cold temperature before launch. The fuel is made to have a rubbery consistency so that vibration during burning will not cause it to crack. However, the cold temperature made it lose its resilience.

The report I read said that cracks probably developed in the fuel mass because the fuel had become brittle. This allowed burning to take place along the cracks toward the outer wall of the RSB. The burning enlarged and extended the cracks. One crack reached an O-ring and burned its way through it. The pressure within RSB forced a jet of hot gas to exude from the side of the RSB, resulting in the disaster.

The brittleness may not have extended all the way through the fuel tube. Possibly only the outer portion became cold enough to be brittle.

I have also read that after earlier launches, 17 of the RSB sections recovered from the ocean showed signs of burning where part of an O-ring had burned through. It was not a problem on those occasions because the fuel had burned evenly. By the time burning reached the O-rings, the fuel was practically all expended and pressure within the RSB had dropped to a low value. AndMeToo —Preceding unsigned comment added by 98.17.45.184 (talk) 18:07, 21 October 2008 (UTC)

The similarity is not that the same component failed in the two aerospace disasters, but that both were "System accidents:" "The unanticipated interaction of multiple failures" in a complex system. Charles Perrow said it was when "Two or more failures, none of them devastating in themselves, come together in unexpected ways and defeat the safety systems." Such failures can be technical or organizational. See also [35] and [36]. Edison (talk) 19:35, 21 October 2008 (UTC)

Silicon Chips

I'm curious to know - What is the property of Silicon chips which makes them so useful as integrated circuits,microchips,etc?

Thanks! —Preceding unsigned comment added by 89.100.217.103 (talk) 15:23, 21 October 2008 (UTC)

I believe it's high conductivity and low cost that are most benefitial. It's also incredibly abundant in the Earth's crust so we're not running out in a hurry. There are probably other reasons. —Cyclonenim (talk · contribs · email) 15:35, 21 October 2008 (UTC)

"Conductivity" is correct, but "high conductivity" is not. Rather, silicon is a widely-available semiconductor. — Lomn 15:44, 21 October 2008 (UTC)

Indeed. The important property is that Silicon is a semi-conductor with a very regular crystal lattice, so it's properties can be changed via doping. This makes it possible to construct transistors directly on/in the chip. Being widely available and fairly benign in general properties also helps. --Stephan Schulz (talk) 15:50, 21 October 2008 (UTC)

Another property of silicon that gave it an advantage in the early days of integrated circuits is that if you put it in an oven with some oxygen, it grows a nice layer of silicon dioxide on the surface that makes a good insulator. Creating an insulator on other semiconductors is more complicated. In recent years the processes have become so complicated that I'm not sure this convenience is a decisive advantage any more. --Gerry Ashton (talk) 03:09, 22 October 2008 (UTC)

Can the process of transesterification be duplicated?

Can the process of transesterification be duplicated? —Preceding unsigned comment added by 207.166.31.13 (talk) 16:53, 21 October 2008 (UTC)

I'm not sure what you mean by "duplicated" but we have an article, Transesterification, if you haven't seen it. --Tango (talk) 17:07, 21 October 2008 (UTC)

Do you mean perhaps reversed? Mr.K. (talk) 12:09, 22 October 2008 (UTC)

About a graph

Hi! There was a question in my textbook that asked about the energy v/s time graph of a ball, that moved on a frictionless floor and kept on colliding inelastically between 2 parallel walls.[coefficient of restitution= 'e'(<1)] My teacher taught that it would be a rectangular hyperbola(I believe that's what its called, and I don't know how to draw a graph in here), because energy decreases exponentially, ie., Initial E= 1/2 m v² After 1st collision, E= 1/2 m e²v² After 2nd collision, E= 1/2 m e⁴v² and so on..... My doubt is, how can the graph be a continuous hyperbola? When it moves between the walls, as it faces no resistance or friction(it's an ideal theoretical situation, in the question), its energy does not decrease with time, and shouldn't it be a straight line there, and since the time taken for a collision is very small compared to the time taken to traverse the distance between the walls, at that point there should be a sharp drop in the energy?? —Preceding unsigned comment added by 116.68.77.73 (talk) 17:23, 21 October 2008 (UTC)

You are correct, it will be a straight line while it is between walls. How sharp the drop is will depend on the details, but it will still be smooth and continuous, you won't have vertical lines in the graph. --Tango (talk) 18:01, 21 October 2008 (UTC)

In the real world - there could never be discontinuous jumps - but that's because in the real world there could never be a perfectly inelastic collision. If you're going to claim some hypothetical (but impossible) perfectly inelastic collision - then impossible perfectly vertical jumps in energy come with the territory. The graph would approximate a rectangular hyperbola if you imagine the gap between the walls to be just a hairs-breadth wider than the size of the ball. The little vertical stairsteps would be very little indeed as the ball travelled in ALMOST a straight line with just a slight rattle from side to side. In the real world - with somewhat elastic collisions and at least SOME friction with the floor - the approximation might be rather good. SteveBaker (talk) 23:51, 21 October 2008 (UTC)

Thank You ! —Preceding unsigned comment added by 116.68.77.73 (talk) 01:54, 22 October 2008 (UTC)

Trees on a slope

I've noticed something interesting about trees on sloping hillsides: some grow roughly perpendicular to the slope(slanted relative to level ground nearby), but some stand more or less upright(relative to level ground, and pointing to the zenith). There doesn't seem to be a consistent difference between tree species as far as I can tell, but what genetic or environmental factors could be involved here? 137.151.174.128 (talk) 19:39, 21 October 2008 (UTC)

The principle is called tropism, which is the growth response of plants to their environment. Roughly speaking, factors in an environment such as light, soil composition, moisture, or gravitational changes (such as an unstable, sliding hillside) can all effect the way in which a plant grows. The Tropism is article expalins the general trends, and will lead you to specific articles about different types of tropism. --Jayron32.talk.contribs 19:52, 21 October 2008 (UTC)

Mylar

"Mylar" can refer to either metallized nylon or to (usually metallized) biaxially-oriented polyethylene terephthalate film. If I've got a sample of material, how can I tell which it is? --67.185.172.158 (talk) 22:19, 21 October 2008 (UTC)

Stick it in your cassette recorder. The metalized nylon wont record--GreenSpigot (talk) 23:02, 21 October 2008 (UTC)

Run current through it and see which one has the highest resistance. Metallized nylon will conduct, the real Mylar won't.[37] Mac Davis (talk) 03:40, 23 October 2008 (UTC)

Double Suspension Gallop

What is the difference between a Single and a Double Suspension Gallop —Preceding unsigned comment added by 98.244.174.49 (talk) 23:59, 21 October 2008 (UTC)

In short, an animal running in a double suspension gallop has two points in each stride where all four legs are off the ground - once during the extended phase and once during the contracted phase. See this site for some illustrations. (It's the first one I came across.) -- Tcncv (talk) 01:06, 22 October 2008 (UTC)

I thought this might have something to do with Conductor gallop and how many maxima and minima appear between suspension points.

October 22

Temperature of Distillate during distillation

My chemistry teacher claims that during a salt water distillation, the temperature of the vapour should be equal to water's boiling point and not salt water's boiling point. He did not even give the name of this phenomenon, let alone an explanation. Can someone point me to a relevant article or external link? Thanks in advance. --99.237.96.81 (talk) 00:01, 22 October 2008 (UTC)

Distillation is interesting...you're "boiling" a mixture, but you're only monitoring the vapor coming out (the distillate, not the pot). During distillation of salt water, what is the vapor (mostly)...salt, water, or both? That tells you what (mostly) is "actually" boiling into the vapor. To think another way, what is the boiling point of salt, or water, and of salt-water? During distillation, you started at room temperature and heated until "distillation occurred", so you got to "the temperature of the lower of those answers" first, at which point you're distilling "whatever that is". Okay, I'm glossing over some details for the sake of what is mostly happening for this particular case. See our article about how distillation works for more technical info. DMacks (talk) 01:42, 22 October 2008 (UTC)

Sorry for not being clear. My class was divided into groups and each group conducted a distillation. The temperature was taken many minutes after the salt water started to boil. My group's thermometer indicated 102 degrees Celsius, which is near salt water's boiling point, but the teacher claimed it was broken and that it should read 100 degrees. I have no idea what the reason is.

Suppose the salt water is maintained at a temperature slightly below its boiling point. Since water is not yet escaping quickly, surely it's possible to wait for thermal equilibrium, make the solution a tad hotter, and have water vapour at least as hot as the water was? Or do all water molecules that reach 100 degrees escape? If the latter, why is it necessary to heat the solution a few degrees above 100 just because some ions are in the way? --99.237.96.81 (talk) 02:45, 22 October 2008 (UTC)

The question is good. Consider the salt solution, which has - ideally, assuming the activity is the same as the mole fraction - less water in it than pure water, so at the boiling point of pure water the vapor pressure will be less. You will have to heat it higher for its vapor pressure to reach atmospheric pressure and boil. The vapor is in your case pure water (because salt boils IIRC at 900 °C), but in the general case the composition depends on the requisite vepor pressures. Then consider your distillation apparatus. If done correctly, there ought to be a drop of condensate hanging from it. The temperature measured at the top of the apparatus is the boiling point of the condensate.

As usual, sadly, the teacher is a dunce. When you teach distillation you must introduce p-x diagrams, 'cause without them it won't make sense. 74.67.113.167 (talk) 05:25, 22 October 2008 (UTC)

Unfortunately, there is way to much variability that we don't know about to answer the question reliably. Any of the following could be what is going on. Measureing the temperature of the vapor is going to be tricky at best. There is LOTS going on. Lets look at some of these.

1. You are right in assuming that the temperature of the vapor immediately upon boiling will be the same as the boiling salt-water solution, however, this temperature quickly drops for several reasons, not the least of which is that this vapor is instantly hitting 25 degree air, and is condensing (which is an endothermic process, and thus removing heat energy from your thermometer as it does this) and all sorts of really complicated dynamic effects are going on. If you measure the vapor immediately above the boiling solution it will be warmer than even a few centimeters away.
2. Classroom analog thermometers are notoriously imprecise. Its not that the thermometer is "broken;" a 2 degree differenc on an alcohol thermometer of the type represents less than a 1% error (2 degrees out of 373 kelvin). This is pretty good, actually.
3. Barometric pressure will have an effect as well. Weather can vary the barometric pressure by +/- 30-40 torr or so and this could easily throw off boiling points by 1-2 degrees celsius. Also, a partially closed system, where the release of the steam is constricted in some way, will likely raise the local barometric pressure over the water, further raising the boiling point.

The upshot is that your teacher is probably expecting a level of precision that is unreasonable. The experiment could be done to precision, just not with the equipment you would likely have access to... --Jayron32.talk.contribs 11:41, 22 October 2008 (UTC)

20 minute chimes

I have acquired an antique spring-powered pendulum clock with a strange malady: instead of chiming N times at N:00 and once at N:30, it chimes N times at some time, then once a half hour later, then once again a half hour after that, and then $(N{\bmod {1}}2)+1$ times after a further half hour. (Obviously this quickly bears no relation to N:00 or any other time.) It gives the warning at N:22 and N:52 as one would expect, but somehow its internal notion of time is only advancing "20 minutes" per half hour. What could possibly be causing this, and how might I fix it?

As it is new to me, I unfortunately do not know what put it into this state, except that it may have been working properly before an attempt to set it that included moving its hands (forward) while it was preparing to chime or chiming. I suppose that it is possible that it is meant to chime at every quarter-hour and is missing one instead of every half-hour and gaining one, but the chiming mechanism starts very reliably every half-turn of the minute hand, so that seems unlikely. --Tardis (talk) 01:14, 22 October 2008 (UTC)

Sounds like the hands are no longer on the shaft in the same orientation as whatever tells the chimes what the time is (i.e. forcing the hands twisted them on the shaft; if so this is likely not the correct way of setting the time). If so then they need to be reset on the shaft. It would probably be fairly inexpensive to have someone who knows what they are doing fix this. If you can find a local clock repair facility you could call and ask for an estimate. RJFJR (talk) 21:10, 22 October 2008 (UTC)

How could any constant phase difference between the hands and the arbors (or any other object) explain that it performs the half-hour chime twice before doing the whole hour again? --Tardis (talk) 21:38, 22 October 2008 (UTC)

The Reference Desk volunteers should refrain from giving horological advice, and refer the questioner to a qualified clockmaker. Edison (talk) 21:48, 22 October 2008 (UTC)

Medical, legal, now horological. Where will it end? ;O) Wanderer57 (talk) 01:11, 23 October 2008 (UTC)

Energy output of hydrogen using oxygen, fusion, and antimatter?

Hi all. I was wondering, given a fixed amount of hydrogen (let's say a gram), what it's energy output would be for:

1. chemically bonding it to oxygen.

2. nuclear fusion into helium.

3. energy discharge from antihydrogen.

Much help appreciated ! -=- Xhin -=- (talk) 03:18, 22 October 2008 (UTC)

1. Oxyhydrogen

2. Proton-proton chain reaction

3. e=mc²

All three give the answeres you want.--Stone (talk) 07:33, 22 October 2008 (UTC)

Wow. Answer 3 looks like about $250,000 worth of energy if it were in the form of electricity at 10 cents per kilowatt hour. Edison (talk) 14:22, 22 October 2008 (UTC)

Yeah, as long as you can find a way of making a gram of antihydrogen for less than $250,000. Confusing Manifestation(Say hi!) 22:23, 22 October 2008 (UTC)

According to Antimatter, a gram of antimatter costs $300 trillion. - Akamad (talk) 02:09, 23 October 2008 (UTC)

Keep in mind, there are losses in energy in antimatter-matter annihilation due to neutrinos. 98.221.85.188 (talk) 23:04, 22 October 2008 (UTC)

UK BODY FARM

I would be interested in donating my body to a Body Farm upon my death - does anybody have any idea who to contact in the United Kingdom - to be able to carry out my wish - all help appreciated - thank you ROEBUCK32 (talk) 06:50, 22 October 2008 (UTC)

I'm not sure that there are body farms in the UK. But you can donate your body to medical science (which is what I intend to do). Go to the Human Tissue Authority website http://www.hta.gov.uk/about_hta/faqs/body_donation_faqs.cfm you can donate to a specific medical school but usually they will only accept bodies of people who died locally. Local authorities impose a fee for transporting dead bodies across county borders, shocking but true. Jooler (talk) 08:04, 22 October 2008 (UTC)

According to Body farm, there is currently no body farms in the UK. Only 3 in the US. The complexity of an international donation may discourage any of the body farms from accepting your donation although they may be willing if you are responsible for the costs and arrangements. For example the University of Tennessee Anthropological Research Facility will only pay for transport if you are within a 200 mile range of them so you'd definitely need to make arrangments to fly the body out to them. This will probably be quite complicated since the body obviously can't be embalmed before being sent and there will be a bunch of regulations that would need to be take care. All in all, I personally don't think it'll be worth the effort but it's obviously up to you. There are a bunch of other things you could donate your body for. The most obvious one is for medical schools where it will be used in teaching (either anatomical or for to practice). I'm sure this has been discussed on the reference desk before and while some people seemed to disagree, those who have encountered the process and common sense suggests your body will be treated with a great deal of respect. Bodies can also be donated for various research. I also came across Body Worlds (although I'm not sure if they have any centres in the UK, they have them in Canada, US and of course Germany, however there is Bodies Revealed in the UK which does similar things). Obviously in most cases your body may only be accepted if it is local, or you pay for transport costs although at least if it's not international it's not going to be so complicated. You should also consider organ donation. While this is often mutually incompatible with body donation (although you may be able to donate organs or tissue) there's no guarantee you will be suitable for organ donation (and of course it is possible your body may not be suitable for donation either). Since there is definitely greater need for live organ donations then body donations, I would presume live organ donations always take precedence. These links should hopefully answer the specifics for the UK [38] & [39]. One key point... Whatever you do it is important that not only do you ensure the consent process is complete but you make your wishes clear to your family/next of kin. The death of a loved one can be a traumatic time and by making sure they know what you want, they hopefully won't have to worry whether they are making the right decision. For organ donation, and I suspect body donation, in most countries your next of kin can overide any prior consent you have given. Nil Einne (talk) 08:50, 22 October 2008 (UTC)

Clipperton Island lagoon

Two questions concerning the lagoon on (inside?) Clipperton Island:

• The bottom of the lagoon is known to be highly acidic due to sulfuric acid. In one article I found on the web, it was mentioned that this acid is a product of the decay of vegetable matter in the absence of oxygen. What's the chemical mechanism behind that?
• It is also mentioned that the lagoon's water is "undrinkable". Being stagnant, I doubt it's healthy, but is it really totally undrinkable, i.e. will it not save you from death if you were stranded on the island during a dry spell? 24.160.175.196 (talk) 06:55, 22 October 2008 (UTC)

There is a two stop process, first anaerobic decay produces hydrogen sulfide and iron sulfides. This is then oxidized by oxygen from the air to make sulfuric acid or iron sulfate. The water probably tastes foul. Graeme Bartlett (talk) 02:05, 23 October 2008 (UTC)

Mutation in mitosis

On average how often does a mutation occur during mitosis? Only a rough estimate is required. But a sourced answer is preferred. Jooler (talk) 08:05, 22 October 2008 (UTC)

Our article on Mutation has some references that may lead to the right answer. Mutation is a rather vague term, there errors that can occur at ANY point in the transcription or translation process, and many different mechanisms by which this occur. --Jayron32.talk.contribs 10:39, 22 October 2008 (UTC)

Try this article, which estimates the somatic (i.e. mitotic) mutation rate for one particular gene at 10.6 x 10(-7) mutations per cell division. Assuming that all stretches of DNA have the same mutation rate (a big assumption) one could then estimate the number of mutations per genome per cell division, which is (I think) what you are really asking. However, there are some BIG caveats to this estimate.

• First, they are basing their estimate on the detection of alterations in post-translational modifications of cell-surface molecules caused by mutations that change the functional properties of a particular enzyme that catalyzes those post-translational modifications. It is definitely a clever and elegant assay, but I'm almost certain that this assay would be "blind" to either mutations that do not cause an amino acid substitution or mutations that cause only a slight decrease in enzyme function (hypomorphic alleles). So perhaps what they are really estimating is the rate of pathologic mutations at a given gene per cell division.
• Second, the assay uses an immortalized cell line derived largely from B-lymphocytes, which are already known to have different characteristics in terms of somatic hypermutation duing immunoglobulin formation. Therefore, the mutation rate estimate may be true only for this cell line and not necessarily generalizable to all other tissues of the body.
• Third, there are other types of DNA mutations (amply described in the Mutation article) that involve larger genome-scale changes such as deletions, duplications, inversions, translocations, loss of heterozygosity, aneuploidy, etc. which are not necessarily considered in the typical "mutation rate" question (i.e. changes at the level of the DNA nucleotide) but are just as important (perhaps more-so, depending on your point of view) in terms of human disease.

I hope this helps. It turns out that by asking a simple question you have discovered that it's actually a VERY complicated question (which, in my experience with biology, is almost always the case). Medical geneticist (talk) 14:36, 22 October 2008 (UTC)

Biting your lip

Why, when you bite your lip, does the small cut in your lip expand so much that you can readily feel it with your tongue? And why does feeling it with your tongue sting so much? Attn: Over zealous editors, I'm not asking for medical advice! Dismas|^(talk) 09:40, 22 October 2008 (UTC)

Aphthous ulcer is what this is called, and the article is pretty detailed. Cheers! --Jayron32.talk.contribs 10:35, 22 October 2008 (UTC)

Didn't know they had a name! Thanks! Dismas|^(talk) 12:20, 22 October 2008 (UTC)

Most commonly, they are called "canker sores". I typed "canker sore" into the search box, and it redirected there... --Jayron32.talk.contribs 12:23, 22 October 2008 (UTC)

I didn't know what a canker sore was but I thought it was something different. I've learned a few things today... Dismas|^(talk) 12:26, 22 October 2008 (UTC)

jet flow

what are researching centers aboat "jet flow". —Preceding unsigned comment added by 78.39.192.29 (talk) 09:43, 22 October 2008 (UTC)

Do you mean the Jet stream? Or do you mean Wind tunnels used to test the aerodynamics of Jet aircraft? --Jayron32.talk.contribs 10:34, 22 October 2008 (UTC)

Osmosis Experiment

Hi all I am doing the age old osmosis experiment where u chuck discs of potato into different molarities of sucrose solution and record the change in mass. However one of the questions I have to answer is: 'When you dry the discs with a paper towel before putting them in the solution should you try and get them as dry as possible by squeezing all the water out?' Well I presume the answer is no, but I can't really think of a good explanation why not. Would squeezing the discs be a bad idea as it would damage the cell membranes of the potato cells and therefore when the discs are put into a very dilute solution/water the cells will not be able to take up water because their membranes have been ruptured and the water will just come out of the cell (I'm picturing a burst water balloon here!) even though water should diffuse in. Hope this makes sense and please share your thoughts! Thanks. —Preceding unsigned comment added by 139.222.241.40 (talk) 11:01, 22 October 2008 (UTC)

Your impressions of the situation look accurate to me. Causing excess cellular damage would likely ruin the experiment as described. --Jayron32.talk.contribs 12:22, 22 October 2008 (UTC)

Discoveries made on space

From Feynman, What do you care what other people think?: "In the newspaper I used to read about shuttles going up and down all the time, but it bothered me a little bit that I never saw in any scientific journal any results of anything that had ever come out of the experiments on the shuttle that were supposed to be so important".

Is there any notable discovery made on space? Or any notable discovery based on data gathered on in space? Mr.K. (talk) 12:12, 22 October 2008 (UTC)

Yes, innumerably many so. See our article on NASA spinoffs for a start on the practical applications. Also, "in space" rather than "on space" is the correct usage. — Lomn 12:45, 22 October 2008 (UTC)

This article lists many discoveries made for space. Mr.K. (talk) 13:10, 22 October 2008 (UTC)

See also this RefDesk thread from last summer, where I asked a similar question: Wikipedia:Reference_desk/Archives/Science/2008_July_1#Space_program_benefits. jeffjon (talk) 12:47, 22 October 2008 (UTC)

Yes, that answers my question. Mr.K. (talk) 13:10, 22 October 2008 (UTC)

A lot of these are from the Aeronautics part of National Aeronautics and Space Association. The ones that are related to space exploration seem to be stuff that they developed in order to make space travel easier, rather than principals learned from the experiments themselves. Although they are useful, you will find similar things in extreme sports. Nobody talks about car racing as scientific, even if it did improve tires and engines. — DanielLC 15:13, 22 October 2008 (UTC)

Also, it would be fair to acknowledge the contributions made with scientific instruments installed and serviced by the shuttle, most notably the Hubble Space Telescope. --Sean 15:16, 22 October 2008 (UTC)

There's also the notion that patience needs to be practiced here. Initial forays into space are needed to set up future success. An arguement can be made that the progress has stalled somewhat, but one cannot judge the success or failure of the space program merely on short-term financial returns. If, 200 years from now, we are able to mine mineral wealth on asteroids, we may well see the early space program as entirely vital to that development. We don't have enough history to judge the situation on yet. Indeed, its if we judged all of the Age of Exploration only on Columbus's first voyage. If we said "Look, all this guy brought back was some trinkets and a nasty case of syphilis" then it may not have been judged a success. One could make the case, with the exponentially hard task of exploring extraterrestrial space, we are still at the "proof of concept" phase of space exploration, and may be there for many decades to come. The real returns of space travel may not be realized in our life time, but that does not mean that the entire project has been a failue... --Jayron32.talk.contribs 15:45, 22 October 2008 (UTC)

Of course, Columbus was not really doing his work for its own sake. He was looking for a trade route, which would have been worth a lot. It wasn't exploration for exploration's sake. For the record, most scientists hate the idea of funding science for its own sake as the only justification. Why? Because there's no way to tell what an appropriate budget expenditure is for something like that; there's no way to pressure politicians for more funding than they currently have. --98.217.8.46 (talk) 01:49, 23 October 2008 (UTC)

Does the wavelength of light change in a time varying magnetic field?

I am part of a research project which requires the use of optical fiber to send a constant frequency clock through a 3 Tesla pulsed magnetic field. There has been a debate centered on the idea that the varying magnetic field will shift the frequency of the light in the optical fiber adding jitter to the encoded clock. I have not been able to find any research on anything similar. My simple understanding of the wave properties of light are that it is composed of "B" field and "H" field components. As these propagate down the fiber, the magnetic field component would receive a local temporary "bias", but since there is not a corresponding shift in the electric field, the wavelength of the light should be unchanged. Monkeyfire (talk) 16:20, 22 October 2008 (UTC)

Due to the glass or impurities in the glass you may get some sort of low level effect. Even if the field causes vibration in the fibre, this can affect the light traveling though, with phase or amplitude modulation. With intense enough fields you will get a distortion of space with a general relativistic effect. To a first approximation though the electromagnetic effects will be linear and add without affecting each other. If you use frequencies close to absorption lines due to impurities you will likely get the biggest effects due to changes in magnetic field. Graeme Bartlett (talk) 21:12, 22 October 2008 (UTC)

More specifically look at Magneto-optic effect. Here a magnetic field causes a delay in circular polarized light. This will affect the wavelength. Graeme Bartlett (talk) 01:25, 23 October 2008 (UTC)

Internal organs

While watching replays of an American football game, I saw a bit about a player having a spleen injury; they didn't say what it was exactly, but I'd guess a ruptured spleen. We hear about ruptured spleens occasionally, and very occasionally about gall bladder injuries, but why do some organs (for example, the pancreas) never get injured this way? Or do they get injured, and I simply don't remember hearing about it? Nyttend (talk) 17:10, 22 October 2008 (UTC)

According to Pancreas#Diseases of the pancreas (a section that needs to be rewritten so as to actually summarise the article it's meant to be a summary of...), a punctured pancreas is a serious injury, however I've never heard of one either which probably means they aren't very common. It may be due to the relative positions in the body, perhaps the spleen is less protected. --Tango (talk) 17:17, 22 October 2008 (UTC)

The spleen sits under the lower left rib cage margin, so in principle is well protected unlike the pancreas in upper abdomen. To injur some organ as implied above, it needs to be compressed between things, and the pancrease is burried under loads of squishy guts that would absorb most blows. By contrast one American Footballer landing on another's chest may crack a rib, the sharp end of which may cut the spleen. Also will depend upon how friable the various organs are - maybe the spleen will tend split easily for a blow landing below & under the rib cage. Anyway that's my best guesses David Ruben ^Talk 19:41, 22 October 2008 (UTC)

According to the Grey's anatomy links from our articles on spleen and pancreas, the spleen weighs 2 or 3 times as much as the pancreas. Perhaps the larger size makes the spleen more susceptible to damage? Wanderer57 (talk) 01:31, 23 October 2008 (UTC)

speed of ripple vs speed of sound

The article speed of sound discusses the speed of sound, a longitudinal wave. A ripple on the surface of water is a transverse wave. Does it have a constant velocity? Do we have an article discussing the velocity of transverse waves? RJFJR (talk) 20:11, 22 October 2008 (UTC)

Actually, a ripple on the surface of the water is a surface wave. The characteristics of a surface makes it behave distinctly different from a transverse wave. The velocity of transverse waves is calculated exactly like all other waves. Velocity = Wavelength * Frequency, or v = λ*ν --Jayron32.talk.contribs 20:24, 22 October 2008 (UTC)

I think part of the question was whether the product is constant. If you throw a pebble into a lake, you will create a wave which travels at a certain speed. Same thing if you throw a big rock into the lake. Will the velocities of the two waves be equal? (No lake nearby, can't do the experiment right now). --NorwegianBlue ^talk 20:36, 22 October 2008 (UTC)

It's an excellent question and I'm watching this space... --Tango (talk) 21:52, 22 October 2008 (UTC)

I can't remember well, but I *think* that in the general solution the velocity of propagation is constant, but dependent on wavelength. Of course, they probably derive that from an equation that assumes those two things anyway, so I'm not sure how useful it is. Confusing Manifestation(Say hi!) 22:17, 22 October 2008 (UTC)

For a surface wave the velocity is not constant, and longer wavelengths travel much faster, eg tsunamis are much faster than normal ocean waves or ripples. Read Ocean surface wave#Science_of_wavesGraeme Bartlett (talk) 01:56, 23 October 2008 (UTC)

Spurs

What's going wrong? —Preceding unsigned comment added by Tony May (talk • contribs) 22:14, 22 October 2008 (UTC)

You're going to have to be a *lot* more specific than that. What spurs? Where? What makes you think something's going wrong? What *appears* to be going wrong? Confusing Manifestation(Say hi!) 22:20, 22 October 2008 (UTC)

Why do I get the feeling this question is about the terrible start to the football season for the British club Tottenham Hotspur (a.k.a. the Spurs) However, I don't think it has anything to do with science. —Cyclonenim (talk · contribs · email) 22:27, 22 October 2008 (UTC)

It might, if the Daleks have slipped them a tailored pathogen so as to clean up in wagers. —Tamfang (talk) 02:27, 23 October 2008 (UTC)

I accidentally an entire spur! Mac Davis (talk) 03:33, 23 October 2008 (UTC)

"Natural" and "artificial" selection in humans

In humans, is it possible to cleanly distinguish natural from artificial selection? NeonMerlin 23:08, 22 October 2008 (UTC)

Since humans are, by any definition, "natural", what are you asking? Saintrain (talk) 00:42, 23 October 2008 (UTC)

What he's getting at is that the "artificial/natural" distinction is usually one of human agency or not. I would say, "it really depends on your definitions of artificial and natural selection here." The differences between the two are not really scientific in nature—humans exist as part of the "natural" world, and human agency does not have any particularly non-natural component than, say, termite or chimpanzee agency. Keep in mind that even trying to determine the most extreme form of human agency into human selection, eugenics, is fraught with definitional difficulties. --98.217.8.46 (talk) 00:49, 23 October 2008 (UTC)

Only if you're against it. Mac Davis (talk) 03:32, 23 October 2008 (UTC)

Longevity of satellites

With our current quality of satellites, is it possible to build a satellite capable of surviving at least 1,000 years without contact with Earth, and then broadcasting a signal to a specified location? (Also, if possible could you provide a source for me to cite?) --Ye Olde Luke (talk) 01:59, 23 October 2008 (UTC)

no, things like batteries wear out, solar cells degrade, attitude fuel runs out, metal recrystallizes or migrates in the circuits, electrolytic capacitors dry out, cosmic rays damage the small stuff and insulation. It may be possible to build one though! Graeme Bartlett (talk) 02:12, 23 October 2008 (UTC)

But Vanguard 1 is still floating, and they think it'll continue to float for another thousand years. Would there be a way to keep the satellite in sleep mode or something until it comes time to transmit the broadcast? --Ye Olde Luke (talk) 02:25, 23 October 2008 (UTC)

Longevity in a dormant state does not seem to be a factor that has been studied to any great degree. Engineers design things to be economical and to meet the specifications. I have maintained equipment which has functioned in power systems for as long as 80 years, when longevity was not a major objective. I have seen light bulbs which still work after 100 years (not 100 years of being continuously illuminated). I own telegraph relays which work after 110 years, telephones which work after 100 years, and vacuum tubes which work after 75 years. Certainly lubricants can gum up, and copper conductors exposed to oxygen corrode and fail, batteries fail, and insulation can crack and shorts out. If long dormancy and revival after 1000 years (in space) were the goal, I would look to develop suitable technology. I have seen Egyptian glass and ceramics, and implements made of gold and copper. Ceramics can insulate and survive thousands of years. So clearly copper or gold conductors with ceramic insulation on jeweled bearings could function as electromagnets, motors, or relays after a thousand years in space. Vacuum tubes could likely function after a thousand years in space. Ways could likely be found to extend the service life of semiconductors such as solar cells and transistors. This has not generally been an important design goal. Attitude control fuel? Let it twist slowly in the solar wind without control, until it reaches the target solar system, or until sufficient time has passed in our own solar system.. Stored energy? A superconductor can store energy in the form of current without appreciable loss for a thousand years, out where it is cold and no nitrogen flow is needed to maintain the low temperature. Ordinary lead acid storage batteries have an extremely long shelf life when the electrolyte is stored separately, to be thawed and added when the time is right. Solar cells? Drift of dopant might be a problem, leading to degradation. Perhaps solar energy could be used via a heat engine poweredby the sun or some distant star the probe has reached. Chips and microminiaturization of electronic components would seem to lead to early failure, but redundant circuits could be used with the failed ones detected and turned off by devices such as a "deadman switch" circuit. Nuclear fuel would not be a solution with types of fuel assemblies I have read about. Edison (talk) 03:59, 23 October 2008 (UTC)

Time to replenish an oil well

Sorry to ask two questions, but how long does it take to replenish an oil well? (I know it takes longer than a lifetime, but does it take less than 1,000 years? If so, how long? And again, if possible, could I get a source?) --Ye Olde Luke (talk) 03:35, 23 October 2008 (UTC)

Guinea worm extinction

If the attempts to eradicate dracunculiasis succeed, is there any way to keep the worm itself from going extinct? I understand that ending the disease will improvbe people's lives, and I support it -- but could the species be saved, too? Unlike smallpox, it's not just a germ, but a complex animal - and we saved samples of smallpox anyway. It seems like there's a non-negligible amount of genetic information and, well, biological uniqueness in this creature, more than in germs which evolve new species in mere years. Could they be somehow kept alive in some sort of human-substitute chemical bath for that phase of their life cycle? It seems like that might be the only possibility, as finding human volunteers to host it would be nearly impossible and counterproductive anyway.

Even if not, has someone sequenced the DNA so that information, at least, survives? 128.194.161.154 (talk) 03:54, 23 October 2008 (UTC)