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November 14

Blood Type Compatibility

Just forestalling any possible misunderstandings, this IS NOT a request for medical advice. And now that that's out of the way, the question: Is it possible (I have heard stories places) to determine whether two people are compatible to donate blood to each other by having each prick their finger and mixing their blood on something like a microscope slide, then watching to see if it clots like crazy? Ks0stm ^(T•C•G) 03:53, 14 November 2009 (UTC)

No, it's not that simple. For one thing, clotting, or the production of a blood clot, is distinct from the agglutination reaction that indicates incompatibility. Second, while agglutination is a clear indication of incompatibility (for one or both potential recipients), more sophisticated tests are needed to ensure compatibility. -- Scray (talk) 04:31, 14 November 2009 (UTC)

Schrödinger's cat - can you actually stop observing it?

With respect to the Schrödinger's cat thought experiment, is it possible, even in theory, to set up a situation where a cat is not observable?

As a thought experiment, the Schrödinger's cat scenario is not constrained by practical limitations, but does it even make sense to have a cat so completely cut off from the rest of the universe that it is not observable, even in principle? I am curious specifically about the fact that a live cat, in contrast to a dead cat, has a metabolism generating heat, has a heartbeat, has a nervous system with electrial currents, etc., and must therefore be continuously interacting with the universe at large. I realize that the point of the thought experiment is to demonstrate the paradox, but discussions always gloss over this point. Peter Grey (talk) 06:05, 14 November 2009 (UTC)

Different assumptions would make it a different scenario. -- Scray (talk) 06:12, 14 November 2009 (UTC)

It's not necessary for the cat to be completely isolated from you, only that the effect it has on you is something that could have been a consequence of either state. I think enough insulation, or just being far away from the box would make it work. Even with full knowledge of the initial state of the system, \there will be a wide range of possible observable outcomes for each the live and dead cat. If what you observe is in the intersection of those two sets of possibilities, then the cat is to you still in a superposition of both alive and dead. Once you observe something that couldn't be caused by one of the fates of the cat (or is extremely unlikely to be caused by one of them) then you're entangled with the cat's alive/dead-ness and to you the cat is definitely alive or definitely dead. Rckrone (talk) 09:32, 14 November 2009 (UTC)

It'd pretty difficult with an object the size of a cat, never mind the ethical issues. There are proposals though to do the equivalent with a virus. Not quite so impressive having a 'Schrödinger's virus' but few people will worry about its fate. Dmcq (talk) 12:03, 14 November 2009 (UTC)

Paper here. Apparently they propose to maglev a small object like a virus and cool it down to the ground state of quantum harmonic oscillation, then put it into a superposition of the ground state and the first excited state. They don't create a superposition of internal states of the virus, much less a difference as complicated as "alive" and "dead" (whatever that would mean for a virus). This experiment is only possible because viruses are inert hunks of matter when they're not infecting a cell; you couldn't do it with a living cell because of all the chemical activity going on inside (I think). Also, a superposition of ground and first excited states is only a "superposition" in the sense that it's not an energy eigenstate. But complicated systems are never in energy eigenstates anyway. The cooling to the ground state seems more interesting than the subsequent excitation, which just makes it slightly more normal again. Nevertheless, if this experiment is performed, it will of course be reported by the media as "an experimental realization of Schrödinger's cat". -- BenRG (talk) 13:15, 14 November 2009 (UTC)

In practice it is absolutely impossible to shield something of the size and temperature of a cat from the outside world. All that's necessary for the system to become classical is that the environment contain enough information to distinguish the states in principle—whether or not that information is accessible in practice—and that's inevitable when enough particles are involved. The heat radiating from your computer case contains information about the calculations being performed by the CPU. If nothing else, the cat's gravitational field will give it away through any amount of insulation, I think. Even if the system's state remains unknown to you, you still have to model it as a classical mixed state (1/2 chance of live cat, 1/2 chance of dead cat) and not as a quantum superposition (1/√2 alive + 1/√2 dead) to reflect the fact that it has objectively collapsed by environmental decoherence. -- BenRG (talk) 13:02, 14 November 2009 (UTC)

Maybe you could set up noise around the cat, like randomly moving weights, sounds, etc, determined by a lot of different quantum measurements. Would it be possible to create enough noise so that from your perspective it would be impossible to distinguish the two cat fates even in theory from the observables available to you? Rckrone (talk) 17:23, 14 November 2009 (UTC)

Unless I'm missing something, that's impossible. Because of unitarity, the only way to eliminate the information from the environment is by, in effect, undoing the process that produced it. If that was a thermodynamic process (like blackbody radiation) then you can't undo it because of the second law. -- BenRG (talk) 18:00, 14 November 2009 (UTC)

The wave function is fully determined, but when you take a measurement, you aren't finding the full wave function. Two different wave functions can produce the same measurement. That's the idea behind interference. Rckrone (talk) 18:42, 14 November 2009 (UTC)

Noise doesn't do it. It may make it harder, or perhaps impossible to determine which information comes from the cat, and which information comes from the noise, but the information is still leaving the box. APL (talk) 21:23, 14 November 2009 (UTC)

Right, but it's not enough for information to be leaving the box, it has to be information that is determined by the fate of the cat. If the same measurement could as likely come out of the box with a live cat in it as the box with a dead cat, then making that measurement doesn't lead you be entangled with the cat's alive/dead state. BenRG is right that the measurement you're making includes any way that the box affects you which includes quite a lot of information, but I'm wondering if it wouldn't still be realistically possible to set up the box so that the measurement isn't necessarily indicative of the cat's state, at least for some short amount of time after the event. Rckrone (talk) 22:02, 14 November 2009 (UTC)

In principle it's very simple: you put the cat (in a box) in the middle of interstellar space, with the closest observer a billion miles away. The cat is then unobservable over the time course of the experiment simply because of the finite speed of light. Looie496 (talk) 18:38, 14 November 2009 (UTC)

Ahhh....but who put the cat there? Myles325a (talk) 02:21, 17 November 2009 (UTC)

No. Because ANY interaction with the universe is deemed an 'observation'. So as soon as anything observes it (or interacts with it ), the WF collapses into a definite state.--79.75.63.71 (talk) 00:50, 18 November 2009 (UTC)

origin of a cyclone

formation of cyclones —Preceding unsigned comment added by 124.43.90.158 (talk) 08:32, 14 November 2009 (UTC)

Are you asking, "How does a cyclone form?" If so, see Cyclone#Formation.--CurtisSwain (talk) 08:59, 14 November 2009 (UTC)

Ferrofluid buoyancy?

Supposing a powerful (perhaps superconducting) permanent magnet was placed over a tube of ferrofluid. Would pressure still increase with depth, and what would happen to an object of neutral buoyancy in such a liquid at different depths?Trevor Loughlin (talk) 14:19, 14 November 2009 (UTC)

It would depend on if the magnetic "up" force more than counteracted the gravity "down" force. Pressure in a liquid (condensed fluid) is just controlled by the forces acting on the fluid (gas pressure works differently). Under normal circumstances, gravity is the only force acting on it. If you had a stronger force pulling straight up, such that the net force vector on the fluid was up rather than down, I would expect the pressure gradient to act differently. Of course, since the magnet will lose strength with distance, this effect could result in some unusual pressure gradients. --Jayron32 16:05, 14 November 2009 (UTC)

Having neutral buoyancy by definition means an object neither rises nor falls from its position in a presure gradient. Cuddlyable3 (talk) 16:36, 14 November 2009 (UTC)

Supposing the magnet was strong enough to completely reverse the pressure gradient. Would an object which would normally float upward float downward? And if it was moved sideways out of the gradient (since the float is not magnetic itself this takes little energy) when it reached the bottom, would it float up again? And if it was moved sideways back into the reverse gradient when it reached the top, would it sink again, creating a mechanical over-unity device?Trevor Loughlin (talk) 12:37, 15 November 2009 (UTC)

Moving it sideways into or out of the gradient takes energy -- specifically, exactly as much energy as you get from it moving along the gradient. --Carnildo (talk) 01:34, 18 November 2009 (UTC)

Hanging

The OP is asked not to edit responses to their question. Cuddlyable3 (talk) 23:25, 15 November 2009 (UTC)

how come profesional hangings the victom goes out quick even if the neck is not broke iv watched 30 iran and german hangings they are all instent alothough they are all suspension. but suicide hangings iv seen take at least 10 secs to pass out why?

examples: http://video.google.com/videoplay?docid=7181755851454128977#

http://www.liveleak.com/view?i=317_1218265064

there are many others many in which the are slowly raised by hand as well . the result is the same. why? —Preceding unsigned comment added by 74.65.3.30 (talk) 16:34, 14 November 2009 (UTC)

There are different ways of hanging a man by the neck until he is dead. The long drop, favoured by English hangmen, produced death by breaking the neck. You may also wish to consider whether censorship was applied to the video clips you have been watching: was a long struggle cut from the end result so that it could be distributed? --TammyMoet (talk) 17:33, 14 November 2009 (UTC)

Breaking the neck does not, of course, produce instant death. What it produces is instant paralysis, sparing the feelings of the onlookers; the interested party stops moving, because he can no longer send signals to any muscles below the neck, and usually his face is covered. --Trovatore (talk) 20:53, 14 November 2009 (UTC)

The article Death erection cites from a RS that one in three hanging men have an erection. That statistic means the OP may have watched 10 males with erections but no associated enjoyment. Unless any were female or very very peculiar. Cuddlyable3 (talk) 22:54, 14 November 2009 (UTC)

The OP is asked not to edit responses to their question. Cuddlyable3 (talk) 23:25, 15 November 2009 (UTC)

bipolar disorder

percentage of people affected by bipolar disorder globally and age wise .. —Preceding unsigned comment added by Arun vvv (talk • contribs) 17:29, 14 November 2009 (UTC)

Is the information on epidemiology in our article on bipolar disorder helpful? TenOfAllTrades(talk) 18:53, 14 November 2009 (UTC)

homeostasis during illness

Hello! I've been asked to look at the role of homeostasis in the human body during health and illness. As for health, I thought this seemed quite simple - homeostatic mechanisms such as regulation of blood glucose concentration, blood pressure, serum potassium concentration, osmoregulation etc. help maitain our health and without them we would obviously quickly die. When it comes to the role of homeostasis in illness I got stuck and I need someone to point me in the right direction. What examples of homeostasis occur during illness? Would the mechanism of a fever be an example? Please help! RichYPE (talk) 19:33, 14 November 2009 (UTC)

You might look at CO₂ levels, pulseox and respiratory volume when O₂ is administered. You might look at the blood sugar levels in diabetecs when they have an infection. Edison (talk) 20:18, 14 November 2009 (UTC)

Additional pointers:

• Villous adenoma, anemia, tissue hypoxia, erythropoietin, reticulocytosis, iron deficiency
• Physical exercise, muscle hypertrophy
• Hypertension, ventricular hypertrophy
• Sound, Tensor tympani
• Infection, Inflammation, Chemotaxis, Diapedesis, G-CSF

Hope this helps. -- Scray (talk) 05:46, 15 November 2009 (UTC)

I think perhaps the article on Stress (biology) is the best place to begin. It will point you to other relevant articles, such as HPA axis. Looie496 (talk) 18:15, 15 November 2009 (UTC)

Many thanks for the contributions everyone. Scray provided a good example of what I am looking for by mentioning reticulocytosis. I'm just basically looking for some examples of homeostatic mechanisms that occur during illness. Any more ideas about the kind of thing I need to look for will be great. Thanks all! RichYPE (talk) 23:07, 16 November 2009 (UTC)

LHC beam dump

The LHC has around 8000 miles of rock and metal around and under it. The beam dump of the LHC has to absorb high particle energies, and needs to be several meters long to do so.

Why isn't the earth itself suitable for absorbing the energies of the beam? It's less absorbent than custom materials (graphite, etc) but there's miles of rock compared to meters of custom material, and a less efficient but longer absorber would presumably spread the heat dissipation over a larger volume. Heat dissipation is its main purpose, and presumably nobody really cares how warm a chunk of off-site rock at the end of a separate tunnel 50 - 175 m underground gets.

FT2 ^{(Talk | email)} 21:00, 14 November 2009 (UTC)

They may care how radioactive it gets. It could well become a safety issue. Groundwater can move radioactive isotopes to unwanted places. Graeme Bartlett (talk) 21:28, 14 November 2009 (UTC)

Rising longevity and the remaining number of years of expected survival

Its 2009, I'm X years old and I've got a 50% chance of surviving for another Y years. Going back 100 years say with a much lower longevity for the population, then to have the same chance of surviving another Y years I would have to be very much younger - I would need to be Z years old. Is there anywhere on the internet where I can see my Z-age (to coin a term) during the 20th and earlier centuries? Or get the data to estimate it? 78.147.25.95 (talk) 21:50, 14 November 2009 (UTC)

I don't know where to point you for the specific data — I could Google it but so could you. But when you find it, I think you may find that the differences are not as dramatic as you think. As I understand it the life expectancy of adults has not really risen that awfully much. The huge increases in life expectancy at birth are largely due to the fact that far fewer people die in childhood than they used to (at least in the industrialized world). --Trovatore (talk) 22:01, 14 November 2009 (UTC)

I've read that idea old chestnut several times here, but I think its not particularly true. My grandfathers for example died in their sixties probably due to unwittingly consuming too much saturated fat and alcohol and not taking much exercise. In the early 20th. century at least even people who survived childood still died much younger than currently. 84.13.173.43 (talk) 11:53, 15 November 2009 (UTC)

There certainly has been an increase in how long people that reach adulthood live, but it is small compared to the increases in life expectancy at birth. According to Life expectancy#Lifespan variation over time, the average life expectancy at birth in mediaeval Britain was 20-30 years. It is now about 80. That is an increase of at least 50 years. I can't find figures for adult life expectancy, but I think we can be sure it has increased by significantly less than 50 years. --Tango (talk) 12:13, 15 November 2009 (UTC)

Nevertheless, the lifespan for people who have for example reached the age of twenty has still been rising considerably. The number of people over 100 has risen greatly. 92.27.154.139 (talk) 13:55, 18 November 2009 (UTC)

Is X=Y in the question or is it a two parameter question? i.e. do you just want the age at which you have a 50% chance of living as long again? By the way of course the chance of you surviving for another Y years is technically unknown since we don't know what will happen to the curve of longevity in the future (obviously). Incidentally an appreciable fraction of all the people who have ever lived are still alive (bout 10-15% I think) which does not imply you have a 10-15% chance of not dying but does illustrate the growth in the population. --BozMo talk 22:09, 14 November 2009 (UTC)

X=Y?? You mean if I'm two years old I'm going to only survive another two years? You've misunderstood the question. 84.13.173.43 (talk) 11:56, 15 November 2009 (UTC)

That last statistic depends heavily on what you mean by "people". You have to draw the line somewhere, but where you draw it can make a big difference (population numbers were low in proto-humans, but they were around for so long that the total numbers are high). We have some discussion of this topic at World population#Number of humans who have ever lived. --Tango (talk) 22:27, 14 November 2009 (UTC)

The questions seems to be about the estimated lifetime remaining, conditional upon reaching a given age. Insurance and census data would be a major source, it would also depend upon other factors such as locale, health, employment, family/medical backgrounds, and so on. The question can be paraphrased (as I understand it) this way:

Holding all other matters constant: - "For any given age of a person (A) and calendar year (B), there will be an age (C) such that a person who is A years old in year B, has a 50% chance of living to C years old. Where can I find a table of (A, B) -> C?"

Or more generally: - "For any given age of a person (A) and calendar year (B), there will be a distribution (C) for eventual age at death vs. probability of dying at that age. Where can I find a table of (A, B) -> C?"

FT2 ^{(Talk | email)} 22:33, 14 November 2009 (UTC)

The article Life expectancy will help. Life insurance companies keep data for life expectancy estimates when selling a Life annuity which is a form of Longevity insurance. Cuddlyable3 (talk) 22:39, 14 November 2009 (UTC)

Life tables typically give you A->C for fixed B. What the OP wants is B->A for fixed C. I don't think that exists ready made. --Tango (talk) 23:39, 14 November 2009 (UTC)

What I'm effectively looking for are life tables for various times in the past. 84.13.173.43 (talk) 12:02, 15 November 2009 (UTC)

November 15

Lucid dreaming

How can I develop this skill? —Preceding unsigned comment added by 79.67.82.206 (talk) 01:10, 15 November 2009 (UTC)

Did you try looking it up on Wikipedia, seeing as you are here? If you had, you would have very quickly found this: Lucid dreaming#Induction methods. --Tango (talk) 02:32, 15 November 2009 (UTC)

Yes thanks dont know how I missed that. Must have been asleep when I asked the Q--79.67.82.206 (talk) 12:12, 15 November 2009 (UTC)

Lucid dreams can be very hard work. It is funny when one wakes up from a realistic dream wherein he worked harder than in real life. I woke up from dreaming about having to devise computer systems for tracking billing and document management for a law firm, and designing a complete physical plant for the firm, all of which were far removed from tasks I ever did in a job. On waking, i felt ripped off, as if I had done work without compensation. Why would you assume lucid dreaming is a good thing? Edison (talk) 03:41, 15 November 2009 (UTC)

If it were really a "lucid dream", you would have known it was a dream, so you could have just told your boss to go jump in a lake. APL (talk) 04:35, 15 November 2009 (UTC)

Indeed. I think Edison is getting confused between "lucid" and "vivid". --Tango (talk) 13:25, 15 November 2009 (UTC)

I don't think you can develop it. There is no evidence whatesoever that these dreams are indeed lucid. As we can dream just about everything, we can also dream that we are lucidly (aka consciously) dreaming, just like we can dream we that we are cold, or hungry or whatever. It's an illusion. DVdm (talk) 13:34, 15 November 2009 (UTC)

Huh? I don't quite follow you -- would there be any empirical difference between actually dreaming, versus merely dreaming that you are dreaming? I have lucid dreams occasionally (not deliberately induced), and I find that I can easily make myself wake up from one if I want to. It seems to me that that's inconsistent with what you're saying, but I'm not sure I actually understand you. Looie496 (talk) 18:09, 15 November 2009 (UTC)

"I can easily make myself wake up from one if I want to." ==> You mean that you dream that you easily can make yourself wake up.

We dream that we can can fly. Do we actually fly?

We dream that we can make ourselves wake up. Do we actually make ourselves wake up? You might think so, but I don't - we just dream it.

We can dream anything, remember, so why not this?

Perhaps this clarifies :-) DVdm (talk) 19:15, 15 November 2009 (UTC)

I lucid dream and sometimes it goes a bit all wrong, and I concetrate extremely hard on moving my real life arm instead of my in dream arm and it wakes up. Like, actually wakes me up in real life. I've done it relatively consistently so it's not just a coincidence. Plus if you're aare you're dreaming then you're aware you're dreaming, surely that's that? 82.11.245.145 (talk) 19:48, 15 November 2009 (UTC)

I don't think so. If you think you are aware you're dreaming then surely you agree that you are dreaming. Now, what are you dreaming? You are dreaming that you are aware you're dreaming. DVdm (talk) 19:50, 15 November 2009 (UTC)

But I'd say lucid dreaming is being aware you're dreaming, and if you know you're dreaming in any sense I'd say you are lucid. Generally realising you aren't awake whilst in a dream would be lucid to me in some way, even if you are dreaming you're dreaming. I get what you're saying, but it seems more philosophical/a technicality than anything. Guess it depends on how you think of the term. Jimothyjim (talk) 20:02, 15 November 2009 (UTC)

Well, starting from the premise that one can dream anything, I just apply Occam's razor in this case. I always found this a school book example.

Cheers, and sweet dreams :-) DVdm (talk) 20:36, 15 November 2009 (UTC)

Nonsense. First of all, in it's purest form, a "lucid dream" is just a dream where you're aware that you're dreaming. There's no difference between being aware of something during a dream, and dreaming that you are aware of something. Perhaps you're objecting to the idea that dreams can be controlled. That's entirely testable. (By the dreamer, perhaps not by an outside observer) People who can lucid dream often decide before they go to bed what direction they'll take a dream in. Since this is typically a direction that their dreams to not normally go in (else, why bother?) and since they are typically satisfied with the results, I deduce that lucid dreamers are getting results far better than random chance.

Incidentally, I'm not sure if this is a correct application of Occam's razor. You're positing an unusual sort of meta-dream. Why does this multiply entities less than positing a lucid-dream? APL (talk) 00:52, 16 November 2009 (UTC)

"First of all, in it's purest form, a "lucid dream" is just a dream where you're aware that you're dreaming." ==> Yes, like you say, "a dream where you're aware...". So you dream that you're aware that you're dreaming. That does not mean that you are aware.

"There's no difference between being aware of something during a dream, and dreaming that you are aware of something. " ==> Of course there is a difference, just like there is a difference between feeling cold during a dream, and dreaming that you are feeling cold.

"... the idea that dreams can be controlled. That's entirely testable. (By the dreamer, perhaps not by an outside observer)" ==> So it is entirely un-testable and, what's more important, un-falsifiable, which makes it useless idea.

"You're positing an unusual sort of meta-dream." ==> On the contrary. We can dream anything... hunger, awareness, joy, illusion of control, fear, lucidy, extasy... There is no meta-level anywhere near. That is Occam in action.

But hey, don't let me spoil your dreams. By all means enjoy the illusion that you really honestly have control. I just don't buy it :-)

DVdm (talk) 08:37, 16 November 2009 (UTC)

No, seriously. You've got logical errors here. For starters, your abuse of the word "anything" can cut both ways. I could say "If I can dream anything then I can dream precisely what I want to in a wholly interactive way." and it would be just as valid as what you said.

Secondly, not strictly a logic problem, but I still don't see how Occam's famous problem-solving technique applies here. Lucid Dreaming is entirely testable by the dreamer, (As I explained above) and many lucid dreamers claim to have done so. You're positing that they're lairs.

Thirdly, While it annoys those of us who prefer the hard sciences, you can't dismiss, out of hand, phenomena that rely on self-reporting. Otherwise you've just dismissed the largest fraction of psychology, and a significant fraction of medicine. (How do we know that painkillers work?)

Fourthly, but not finally, "Feeling cold" is a perception. Feeling cold during a dream and dreaming that you are feeling cold are the same perception, even if the causes are different, so your example in that case is flawed as well.

Finally, and most importantly, you're ignoring the fact that communication from a dream to reality is entirely possible. So lucid dreaming is entirely testable by third parties. Studies have been done where lucid dreamers have been instructed to perform certain actions, (clench their fists, move their eyes in a particular unusual pattern, etc.) and they were able to successfully do this even when polygraph machines proved that they were asleep. Two such studies, in reputable journals are used as references in the introduction to the article Lucid Dreaming.

(For the record, I cannot lucid dream, I am simply objecting to your misapplication of logic to 'disprove' a common phenomena.)APL (talk) 15:33, 16 November 2009 (UTC)

Very well put, APL. In the same vein, how could you say that the "illusion" of being aware is any different than "actually" being aware? Either way, you are perceiving the same thing. —Akrabbim^talk 15:42, 16 November 2009 (UTC)

I will only comment on your first sentence: "I could say "If I can dream anything then I can dream precisely what I want to...".

==> You still don't get my point. You can dream that you-can-dream-precisely-what-you-want, because dreaming-precisely-what-you-want belongs to "anything".

I think I have repeated myself sufficiently now. For those who still don't understand, don't worry - and don't lose any sleep over it :-) DVdm (talk) 15:47, 16 November 2009 (UTC)

"I think I've repeated myself sufficiently now. No matter how many times I keep repeating exactly the same thing people just keep pointing out the flaws in my logic, my poor understanding of the topic under discussion, and referencing legitimate scientific evidence that I am exactly wrong, It's sad really. Still, a man can only mindlessly repeat the same thing so many times before he's forced to give up on the sad souls who won't listen to his brilliance." APL (talk) 15:58, 16 November 2009 (UTC)

I had a dream once where I was going to do something illegal, but then I realized I was dreaming, so it was ok for me to do the illegal thing since it wasn't real. Ariel. (talk) 08:23, 16 November 2009 (UTC)

Yes, you had a dream once. I had one too :-) DVdm (talk) 08:37, 16 November 2009 (UTC)

I had a dream once where I was Lucid, I can't remember what I was doing, but at the same time I was listening to the TV in the real world. And I wasn't just dreaming I was listening to a real world TV, because when I woke up again I checked the NFL game and everything I had heard whilst dreaming had happened in the game. That's not technically lucid dreaming as something else, but my point is that dreaming isn't a clear cut thing, just cause you can't do it doesn't mean it's not possible. Some people can remember insane amounts of numbers and stuff, and I can't do that but I don't deny others can. The mind is pretty much impossible ot understand at the minute, but it seems odd to disregard things like Lucid dreams. Jimothyjim (talk) 11:59, 16 November 2009 (UTC)

Sure. I had the same experience many times and we probably all have. But note that I don't disregard lucid dreaming - I just find it a hell of a misnomer. DVdm (talk) 12:21, 16 November 2009 (UTC)

I think DVdm is like an ancient Greek philosopher here. He's tumbled onto an explanation of a natural phenomena that is elegant in it's simplicity and has all the grace and symmetry of the finest zen koans, and he refuses to let go of this explanation even when the real world turns out to be more complicated than his initial assumptions. APL (talk) 16:50, 16 November 2009 (UTC)

It's not any sort of explanation in the first place. There is no such thing as "an illusion of being aware". That was Descartes' irrefutable point with his famous line cogito ergo sum, "I think, therefore I am", which many people these days misunderstand.

By the way, DVdm also goes off the track a bit by equating "lucidly dreaming" with "consciously dreaming". When you are dreaming, quite obviously, you are conscious, whether it's a lucid dream or not. You are not conscious (or at least not very) of external stimuli, but that's another matter: You are able to perceive and think, even if your perceptions are internally generated. --Trovatore (talk) 20:23, 16 November 2009 (UTC)

Hunger

Why do I feel hungry about every 5-6 hours while awake, but not when asleep. When I wake up at night I may feel hungry but if I go back to sleep without eating, then, when I wake up in the morning, Im no hungrier than normally at breakfast. Whats going on here? —Preceding unsigned comment added by 79.67.82.206 (talk) 01:14, 15 November 2009 (UTC)

Circadian rhythm, or something similar - hunger isn't only caused by a need for nutrients, your body is conditioned to expect foods at certain times and not to expect them at other times. Vimescarrot (talk) 01:22, 15 November 2009 (UTC)

Sleep is a pleasure too. You have two competing pleasures — sleeping and eating. Why waste good sleep on mundane eating? Bus stop (talk) 03:47, 15 November 2009 (UTC)

You also have a much larger demand for nutrients while awake since you are actually up and about and doing things. Sleeping doesn't require much energy at all (no walking, no intense thinking), so you can make it pretty far on not very much. ~ Amory (u • t • c) 19:47, 15 November 2009 (UTC)

Phone and Paper Shredder

Many times when I receive a cell phone call in my bedroom where my paper shredder also happens to be, the paper shredder will start running (as if I inserted paper) just before the phone rings and will continue to run until I pick up the call. Why does this happen? 69.115.152.137 (talk) 01:32, 15 November 2009 (UTC)

Do the clocks start running backwards when someone rings the doorbell as well? :) Perhaps it's interference. DRosenbach ^{(Talk | Contribs)} 03:10, 15 November 2009 (UTC)

...don't you love flippant responses? Actually it is possible that pre-ringing interaction between your cell phone and the cell towers are responsible for your cell transmitting at a frequency and intensity that triggers the circuitry f the switch that belongs to the paper shredder activation circuit. For instance if the switch is based on a light sensor then the radio frequency may cause the light sensor circuitry in the shredder to activate as if the light beam were interrupted. In some cases all it take is for the signal traveling to the sensor sent by the light beam to deviate from phase or frequency to activate the circuit. 71.100.7.164 (talk) 03:29, 15 November 2009 (UTC)

It could be electromagnetic inductance from the cell phone triggering the circuit on the shredder which detects the introduction of paper to be shredded. Or perhaps the house is built over an old Indian (Native American) burial ground, and poltergeists are at work. Edison (talk) 03:35, 15 November 2009 (UTC)

Right before a cel-phone rings there is a lot of communication going back and forth between the tower and the phone. This interferes with a lot of things. Most commonly people notice this as interference in speakers. Just like speaker wires can pick up the signal, probably there's a wire between the "paper sensor" and the chip the controls the shredder that's picking up this interference. If I had to guess, I'd say that the sensor is probably analog (Optical, perhaps?) with a very tiny voltage difference between "paper" and "no paper". APL (talk) 04:33, 15 November 2009 (UTC)

The shredders I've used have had a mechanical switch that the paper operates. Any design that is capable of being turned on by simple interference sounds dangerous (even if nothing is near the paper slot, the motor could overheat). I would suggest getting rid of the shredder or at least keeping it unplugged when not actually in use. And if it operates even when unplugged, call an exorcist. :-) --Anonymous, 05:50 UTC, November 16, 2009.

Nah, most shredders today use a light sensor and a diode. Mechanical switches tend to clog. But you are right about the overheating part - I hope the motor has protection circuitry in it. There are many kinds of proximity sensors, maybe one of them is affected by strong radio waves. Ariel. (talk) 08:20, 16 November 2009 (UTC)

cancer

Cancer is a mutation of normal cells characterized by uncontrolled growth. If a GM corn or flax cell that produces insecticide gets cancer is it also characterized by uncontrolled growth? 71.100.7.164 (talk) 02:21, 15 November 2009 (UTC)

So you sort of answered your question by defining cancer as mutations that promote uninhibited growth. DRosenbach ^{(Talk | Contribs)} 03:11, 15 November 2009 (UTC)

Only if my understanding of what cancer is or does is correct. 71.100.7.164 (talk) 03:22, 15 November 2009 (UTC)

Plants don't exactly get cancer. Plants can get tumors, but it's not really cancer because it can't spread like it can in animals. Cecil Adams touches on this briefly here. APL (talk) 04:23, 15 November 2009 (UTC)

Your question would make a lot more sense if you began with "Cancer is a mutation of normal animal cells characterized by uncontrolled growth." By redefining a common term, you can make up any ridiculous question you like. For example, I could ask: "If radiation contamination is caused by any exposure to sunlight, are all GM crops grown outside full of radiation contamination?" -- kainaw™ 04:39, 15 November 2009 (UTC)

I don't disagree with you and you are making a reasonable point but where I live there are a lot of phosphate mines and a lot of unmined phosphate. It is ver common to see trees with so called tumors but due to their encompassing size in some cases the tumors are larger than the tree. Although they are usually adjacent to each other and a dividing line is hard to establish between adjacent tumors and they appear not to have been transported to other parts of the tree through the veins of the tree they are obviously uncontrolled growths everyone assumes to be from radon gas or a radiation based interference with genomes, even though hey might be the result of a tumor causing virus. 71.100.7.164 (talk) 08:14, 15 November 2009 (UTC)

Might they be galls? -Craig Pemberton 09:00, 15 November 2009 (UTC)

These nodules, growths, tumors are very large, the largest mass of tumors surround a thirty foot oak tree at the trunk from a foot above the ground to six feet above the ground, if memory serves me correctly. Unless galls are consistently this massive then I can't explain the number of trees effected. 71.100.2.243 (talk) 11:38, 15 November 2009 (UTC)

Could be nematodes or fungi. Fences&Windows 15:29, 15 November 2009 (UTC)

Plants can't get cancer as such because their cells cannot undergo metastasis. But they do get tumour-like growths such as crown galls caused by Agrobacterium tumefaciens. Fences&Windows 15:22, 15 November 2009 (UTC)

Metastasisless malignancies are still malignancies -- basal cell carcinoma is cancer even though it rarely metasticizes. If it would never metasticize, it would still be categorized as cancer because metastasis is just one of the many surrogate biomarkers signs, so to speak, of cancer. (pre)Cancer is diagnosed prior to metastisis based on histologic findings such as mitotic figures, metaplasia/dysplasia, epithelial invasion of the lamina propria, etc. DRosenbach ^{(Talk | Contribs)} 15:41, 15 November 2009 (UTC)

Why do plants get tumors from infection by other organisms only? 68.193.225.106 (talk) 16:06, 15 November 2009 (UTC)

I'm not sure if that is true. On a slightly different note, cancer is commonly linked to infection. -Craig Pemberton 08:33, 16 November 2009 (UTC)

Evolutionary advanage of nervousness?

It seems that nervousness would be a severe detriment to survival, due to making tasks which are important to survival more difficult to perform successfully. Yet somehow nervousness hasn't been eliminated by natural selection. What survival benefit does nervousness provide that has caused this? --75.39.194.221 (talk) 02:23, 15 November 2009 (UTC)

This emotion is supposed to stop the animal from doing something risky, such as showing itself in front of a predator, eating a strange new substance, driving too fast, straying too close to a cliff edge, or jumping from it. Graeme Bartlett (talk) 02:35, 15 November 2009 (UTC)

Nervousness is supposed to stop you doing whatever it is, that is the point. What important things were there for proto-humans (or earlier animals) to do that would make them nervous? I can't think of any. Anything that would make them nervous would be something that they shouldn't do. Eg. you see a big lion sleeping next to the tree you want to pick fruit from you don't overcome your nerves and creep up to the tree, you go and get your dinner somewhere else. --Tango (talk) 02:56, 15 November 2009 (UTC)

I suppose the opposite of "nervousness" would be fearlessness. "The lion is sleeping next to the tree with the fruit I want to eat. I will climb up on the sleeping lion to reach the fruit. If the lion wakes up, I will simply spit in his eye." Very brave, but the individual might not survive to pass on his genes to the next generation. Edison (talk) 03:32, 15 November 2009 (UTC)

Emotions are complex. Nervous is a general term covering many emotional states. As you point out, nervousness can be detrimental. I don't think evolution is the best place to look for evaluating nervousness. Emotions may not leave traces as easily understood over the periods of time involved in human evolution. We may not really be able to know what advantage or disadvantage various emotional states, among them the many types of nervousness, have played at the various stages in the role of human survival over the periods of time in question. Bus stop (talk) 03:35, 15 November 2009 (UTC)

Like most behaviours, nervousness can be dysfunctional in some cases, but in others there would be a survival benefit to having second thoughts, being overly cautious, or even being visibly nervous which could alert other group members or even lead to a better-qualified member taking action. Also you're only likely to overcome nervousness if you judge that the action truly is important, so it screens out casual risk-taking. Peter Grey (talk) 03:53, 15 November 2009 (UTC)

I find that nervousness is usually quite justified. What's the point of embroidering your quilt if you have the notion that a sabretooth tiger is nearby? Vranak (talk) 04:19, 15 November 2009 (UTC)

That's right, put down the quilt, grab your spear, and get yourself a nice sabertoothed fur, instead. Much warmer than a quilt. StuRat (talk) 05:12, 15 November 2009 (UTC)

I've noticed a huge difference in the skittishness of flying insects. If they are sitting on a wall when I enter a room, some will start flying and taking evasive action immediately, while others will let you walk right up and grab them. I have more trouble understanding the latter behavior. I'd expect them to give their camouflage a chance to work, but, at some point, I'd also expect them to realize I've spotted them and flee (or flea, as the case may be). StuRat (talk) 05:17, 15 November 2009 (UTC)

Maybe they were asleep. --Tango (talk) 06:15, 15 November 2009 (UTC)

And they might not be intelligent enough to cope with the unusual environment (big homogeneous wall painted with only one color) --131.188.3.21 (talk) 10:36, 15 November 2009 (UTC)

Pure conjecture here, but the presence of individuals with crippling nervousness or brash bravery in a population might be understandable in terms of heterozygote advantage and balanced polymorphism. -Craig Pemberton 08:57, 15 November 2009 (UTC)

It could be, but I think it is more likely explained by nurture rather than nature. Crippling nervousness usually has an identifiable cause (yelling at your children over minor things a lot tends to make them generally nervous, for example). I think brashness is usually caused by over-estimating ones own abilities rather than bravery - that, and being drunk. --Tango (talk) 09:06, 15 November 2009 (UTC)

Fear and Risk aversion might help, and see The psychology of risk taking behavior. Nervousness isn't per se a pathology, the balance of whether to take risks or not - which is really what underlies nervousness - is something that affects most animals. Work in animal behaviour and ecology often talks about 'neophobia', which is a version of nervousness. "What important things were there for proto-humans (or earlier animals) to do that would make them nervous? I can't think of any." New sources or types of food, crossing rivers, climbing trees, extra-partner mating, predators or other groups of hominids nearby, etc. Fences&Windows 15:13, 15 November 2009 (UTC)

How long will lunar water last?

Scientists have recently confirmed the presence of large amounts of water on the moon. Has anyone done any work estimating how long that water is likely to last if we start using it? Are we likely to hit peak water on the moon at some point? I know we don't have any idea precisely how much water there is on the moon and we don't know how much water we are likely to want to use in the future, but does anyone have a rough order of magnitude? Is there enough for a few decades? A few millennia? Millions of years? --Tango (talk) 04:46, 15 November 2009 (UTC)

I believe you are viewing lunar water as a pure consumable, not a recyclable resource. There is no reason to assume that the water harvested from the Moon won't be recycled over and over as long as it is needed. The issue, from my point of view, is not if we will use it all up. The issue is how many people can the water on the Moon support? -- kainaw™ 04:51, 15 November 2009 (UTC)

If just small amounts are used to replace losses in life support systems, that might be the case (but it probably wouldn't - the lunar bases will almost certainly be in illuminated parts of the moon, at least partially, and water that escapes there would be heated up to sufficient degree to escape the moon's gravity). If large amounts are used to make rocket fuel (which is one of the common proposals) it certainly isn't. --Tango (talk) 06:14, 15 November 2009 (UTC)

Water on Earth is not likely to leave the hydrosphere, but water on the Moon could escape if exposed to the vacuum, so it would be in part non-renewable, with a little replacement by comet impacts. Of course, right now none of it is being used. Peter Grey (talk) 05:29, 15 November 2009 (UTC)

They blasted a 60-100 ft crater with their impactor, equivalent to a volume of 100 thousand to 1 millions gallons of disturbed regolith. As a result approximately 25 gallons of water was kicked up into space in a way the satellite could detect. So we can set a lower limit on the concentration of ice in this permanently dark crater at 25 parts per million by volume (but possibly quite a bit higher). That's not a high concentration, but on the other hand, it would suggest one could get ~100-300 tonnes of water per km² in craters such as this. The space shuttle external launch tank carries about 700 tonnes of fuel for comparison. So, the dream of using water for fuel would seem possible, but not very easy since very large areas may need to be mined. Dragons flight (talk) 10:51, 15 November 2009 (UTC)

Water on the moon is really important to the future of humans in space. How long it lasts depends on what we use it for. If people merely live on the moon - then it can be recycled. We'll need oxygen to breathe and water to drink - and both to raise food - but that could all be recycled (at least in principle - there would of course be losses). With care, it could support a lot of people for a long time - but no recycling will ever be perfect - so it can't last forever. But there is another important use for lunar water. If we use cheap solar power to split lunar water into hydrogen and oxygen - we can use that as rocket fuel - very handy for trips to other planets and such like because we don't have to haul it up from the earth's gravity well. In that case, the water is certainly not recyclable and we would undoubtedly slowly consume what's there. We can't tell how long it'll last unless we know:

• How many people are using it.
• How efficiently are they recycling it (if at all).
• How much is taken off the moon in the form of rocket fuel or whatever.
• How efficiently it can be mined.

In the long run, I'd hope we'd use the moon intelligently - as a stepping stone. There is plenty of even more useful water "out there" in the form of comets, small moons, Saturn's rings and asteroids - we just need a way to get to it - and the moon is a good place to start. For example - if we mined Halley's Comet (picking a comet at random!) - it appears to be approximately 80% water and it's about 1000 cubic kilometers in size. That's a truly insane amount of water! (In reality - we'd want to pick a comet in a more nearly circular orbit.)

We need to use the water on the moon wisely to allow us take that next step.

SteveBaker (talk) 01:19, 16 November 2009 (UTC)

There has been a lot of work done in how to use lunar resources, I was wondering if anyone knew of any work done on estimating how much we would need and how long it would last. I know we can't get accurate answers, but some rough Fermi calculations should be possible to get a range of orders of magnitude. --Tango (talk) 01:28, 16 November 2009 (UTC)

At current moon water usage rates, it should pretty much last forever. Googlemeister (talk) 17:31, 16 November 2009 (UTC)

Copepod parasite?

Anterior bit of the copepod.

Higher magnification.

I found this copepod with an egg sac today. There is some sort of tubular structure in the egg sac. My first guess was that this was how they attached their eggs, but I don't see a similar structure in photos of other egg sacs. Could it be a parasite? Or maybe someone got stuck in egg adhesive and is unwittingly along for the ride? -Craig Pemberton 08:46, 15 November 2009 (UTC)

How do paramedics repair severed arteries?

When a paramedic, combat medic, or some other first response health provider encounters a person with a severed artery (or vein I suppose) that needs treatment right away (i.e cannot wait for transportation to a hospital), what do they typically do to treat the person? Do paramedics carry an "artery repair kit"? Also, how is an artery repaired and is there any difference between how a first response surgeon with limited equipment and a someone in a hospital with the full breadth of equipment would go about reconnecting an artery? I tried looking for information and some websites mentioned stitches and grafts, but I don't think I got an accurate picture of how the severed ends are actually stuck back together. 96.253.247.216 (talk) 10:04, 15 November 2009 (UTC)

They won't repair the artery. They will stop the bleeding through a combination of direct pressure, elevation, pressure points and, as a last resort, a tourniquet. The artery will be repaired by a surgeon once they get to hospital. --Tango (talk) 10:12, 15 November 2009 (UTC)

Regarding the second half of your question, the most commonly-used technique for repairing an artery was described by Alexis Carrel in 1902 (Lyon Med 1902; 98:859–863, too early to appear in Pubmed) and illustrated here. The arterial wall is fragile and all three layers (intima, media, adventitia from inner to outer) must be rejoined in the repair, because separation and retraction of one or more of these layers, i.e. delamination, is common with severed arteries. This is made even more difficult because direct clamping or grasping with forceps can damage the arterial wall and 'kill' it (it is living tissue, after all). Thus, arterial repair is a fairly demanding task - not saying it couldn't be done in the field, but it would be a serious challenge. -- Scray (talk) 15:52, 15 November 2009 (UTC)

Thanks very much for the answers! 96.253.247.216 (talk) 22:25, 15 November 2009 (UTC)

How to apply a pressure dressing 75.41.110.200 (talk) 23:14, 15 November 2009 (UTC)

Paramedics provide first aid. Vascular surgeons reconnect arteries in operating rooms. There is a century of medical technology and about 10 years of training difference between the two. alteripse (talk) 13:49, 17 November 2009 (UTC)

Psychology

Hi, I know a person who is always very calm and it seems like nothing can surprise her.She never shows any emotions. If something strange or incredible happens, she just says "Oh." or smth like this. (Like Robin from Robin (TV series) if you know it...) Once I've heard of alexithymia but I'm not sure she has it because she can recognize other people's feelings very well. She is quite lonely and doesn't talk much to other people because she talks very silently and no one hears her. She really can't express herself and I feel sorry for her. Any ideas which illness could this be? —Preceding unsigned comment added by Atacamadesert12 (talk • contribs) 10:53, 15 November 2009 (UTC)

I afraid we can't make diagnoses here. You will need to consult a professional. --Tango (talk) 11:02, 15 November 2009 (UTC)

This question appears to be a request for medical advice. It is against our guidelines to provide medical advice. You might like to clarify your question. Thank you. Responses containing prescriptive information or medical advice should be removed and an explanatory note posted on the discussion page. If you feel a response has been removed in error, please discuss it before restoring it.

This removal is discussed here -- Scray (talk) 16:02, 15 November 2009 (UTC)

The common element whenever you observe these strange behaviors is that you are observing her. If you cease observing, perhaps the symptoms will also disappear! Vranak (talk) 15:50, 16 November 2009 (UTC)

Too many possibilities. According to FlashForward she has addisons (joke), she could also have aspergers or (light) autisim. Or she's just not an emotional person, or just shy. There is no way someone on wikipedia could help you diagnose. But if you want to help, how about just sitting silently (with her) and letting her be herself before trying to change her. See what she does by herself, and then you do the same, but with/near her. Maybe you'll learn more about her. Ariel. (talk) 08:15, 16 November 2009 (UTC)

Queen Ant

I have a queen ant and she has laid some eggs. When the eggs hatch what will the little worker ants need to be fed? I know in nature they'd eat dead files or stuff, but in captivity what can I give them? —Preceding unsigned comment added by 82.43.89.85 (talk) 23:39, 13 November 2009 (UTC)

Do you know the species ? I suppose, if you don't, you can leave them a bit of everything, from leaves to fruit to meat, and they can take what they want. Leave small enough quantities so you can tell what they take. Also leave water. StuRat (talk) 13:33, 15 November 2009 (UTC)

Different ants eat different things - from leaves (actually fungus growing on the leaf) to aphid "honey", to sugar, to meat. There is a tremendous variation. I would start by trying sugar and meat. If they like the sugar don't keep feeding them that, use something else that is sweet (like an apple). If they eat fungus from leaves you probably will not be able to feed them. If you are lucky they are omnivores, and will eat anything. Ariel. (talk) 08:11, 16 November 2009 (UTC)

bipolar disorder

i am repeating this question as i didn't get relevant answer. i would like to know percentage of global people affected by bipolar disorder and age wise distribution of this disorder globally ... pl help some one .. —Preceding unsigned comment added by Arun vvv (talk • contribs) 12:33, 15 November 2009 (UTC)

You might find some figures in some countries for the number (and ages) of diagnosed cases, but I don't think anyone has attempted the difficult task of guessing the rate of occurrence or age distribution world-wide. The condition is not easy to diagnose in an individual, so it is even more difficult to estimate global figures. Is it even recognised as a disorder in some countries? I assume that you have read our article linked in answer to your previous question. It suggests that about 1% of children and 2% of the population from teenage upwards suffer from the clinical condition, with perhaps a further 2% or more having a minor form. The condition is never considered to be "cured", so an age distribution is not appropriate. Dbfirs 13:16, 15 November 2009 (UTC)

PMID 17162652 is probably the best source of up-to-date information, if you have access to it. Looie496 (talk) 17:30, 15 November 2009 (UTC)

Thanks. Is there anywhere that someone without access can read a reasonably detailed summary? Dbfirs 23:36, 16 November 2009 (UTC)

Feeling in eyes.

Do your eyes feel heat? I assume they do but I don't think I've ever though 'man my eyes feel cold' so I'm unsure. —Preceding unsigned comment added by Jimothyjim (talk • contribs) 13:22, 15 November 2009 (UTC)

It's not your eyes, but sensory neuron on your cornea -it respond to heat and so it should also respond to loss of heat. Meaning that I guess that a hit of liquid oxygen would heart (P.S. it's not the best example as such hit would also cause to extensive damage-but there is such thing as cold pain) .--Gilisa (talk) 13:41, 15 November 2009 (UTC)

Thermoception isn't a very well developed article, but it notes correctly that hot and cold thermoreceptors in mammals are in the skin. However, some animals do have thermoreceptors in their eyes, e.g. cats have cold receptors.[1] There's evidence that humans can detect cold on the cornea and conjunctiva.[2][3] Fences&Windows 14:38, 15 November 2009 (UTC)

You've never felt cold in your eyes? I have....is that unusual? Vimescarrot (talk) 15:13, 15 November 2009 (UTC)

I'd say that most people would reflexively shut their eyelids, thus reducing the stimulus that would kick ofs a response -- sort of like people who experience less tooth pain to cold air when they shut their mouth. DRosenbach ^{(Talk | Contribs)} 15:35, 15 November 2009 (UTC)

Try the opposite - if you sit close to a fire in a fireplace, you'll get a hot headache, and can often feel the heat "behind" your eyeballs (as implied above). ~ Amory (u • t • c) 19:41, 15 November 2009 (UTC)

Certainly cold water feels cold, I think. 68.193.225.106 (talk) 15:59, 15 November 2009 (UTC)

Hmm, maybe my eyes do feel cold but I just don't notice.

Looking for the name of a knot similar to the clove hitch

I'm looking for the name of a hitch knot, which is similar to the clove hitch. In the clove hitch, a part of the rope runs diagonally, compressing other parts of the rope forming the knot. In the knot I'm talking about, there's a twist in the part of the knot under the "diagonal" section. Supposedly the knot is more secure that the clove hitch. Does anyone know the name of the knot? (Sorry if my description is not very clear.) —Preceding unsigned comment added by 173.49.12.245 (talk) 15:43, 15 November 2009 (UTC)

The constrictor knot, ground-line hitch and snuggle hitch are all similar to the clove hitch, but more secure. Are you thinking of one of those? Red Act (talk) 16:33, 15 November 2009 (UTC)

The constrictor knot was what I had in mind. Thanks. --173.49.12.245 (talk) 16:49, 15 November 2009 (UTC)

activity vs sleep on mountains

i'm not asking for medical advice here, i have no intention of climbing a mountain but i'm wondering if it's true that you need to stay awake on mountains to keep your body temperature up? i'm pretty sure that sleeping well in a safe place is just as important to get your energy back up? —Preceding unsigned comment added by 87.114.162.77 (talk) 16:22, 15 November 2009 (UTC)

If you're severely hypothermic (so cold that you've stopped shivering), then falling asleep would be bad, but at that point you'd be on the verge of dying anyway. Body temperature drops a little bit during sleep automatically, but if it drops enough to be harmful, you will start shivering and that's sure to wake you up. In my experience (never been actually hypothermic), it's impossible to fall asleep if you're shivering. I have spent a few very unpleasant nights on mountains that way. Looie496 (talk) 18:29, 15 November 2009 (UTC)

If you're in a place dangerous enough that you shouldn't sleep to avoid dying, you are already very hypothermic and in danger and should calmly and carefully get off the mountain. The first step is to always avoid a dangerous situation like that by planning ahead and being safe. You will not think clearly when severely hypothermic. You should only ever go up a mountain if you have adequate shelter and warm clothing, in which case it will often be okay to sleep. ~ Amory (u • t • c) 19:38, 15 November 2009 (UTC)

I agree with what has already been said. On a related note, however, at very high altitude (eg. Everest Camp IV) sleep apparently becomes very difficult. It's not that it is dangerous to sleep, it's just difficult to get to sleep. --Tango (talk) 21:56, 15 November 2009 (UTC)

Ah ok, maybe i misunderstood what i was told then. Stay awake if you're about to die, nice lol! Tx for hypothermia link, that explains a lot. —Preceding unsigned comment added by 87.114.162.77 (talk) 23:50, 15 November 2009 (UTC) --87.114.162.77 (talk) 23:52, 15 November 2009 (UTC)

self-serve check-outs and phone answering systems

Most of these registers are manned by one cashier to four registers. In many cases this cashier is busy with another customer when a problem happens. For this reason many people are exposed to a talking register that treats them as if they were a computer. An even worse situation of computers treating people like they were computers are telephone, bank and other business and institutional phone answering systems (USPS is one of the worst). Are such systems a threat to the civility of mankind and perhaps in part responsible for indiscriminate psycho crimes like terrorism? 71.100.2.243 (talk) 16:37, 15 November 2009 (UTC)

I don't think this is a very scientific question, and I don't have a very scientific answer. These computers you speak of do not pass the Turing test, so people can consistently tell the difference between talking to a human and dealing with one of these computers; thus, I don't think any confusion between the two contributes to violent behavior. My sense is that if people relax and focus on the task at hand, the task gets done. -- Scray (talk) 16:47, 15 November 2009 (UTC)

"Are such systems a threat to the civility of mankind and perhaps in part responsible for indiscriminate psycho crimes like terrorism?" I don't think there's any evidence that such things contribute to threats against the "civility of mankind" (whatever that means), and have seen zero evidence that such systems have any responsibility for "indiscriminate psycho crimes like terrorism". I think it would be fairly idiotic to assume without any evidence that frustration with phone answering systems has any connection to terrorism. The systems probably do contribute to a decreasing satisfaction amongst consumers with customer service (I cannot stand the phone systems and find them unhelpful; if you keep pressing the zero key, you often end up with a live person, though), but and they do have economic effects (they are used to avoid hiring live human beings), but other than that, I don't see any reason whatsoever to ascribe them much influence. --Mr.98 (talk) 17:04, 15 November 2009 (UTC)

I actually prefer the self-checkout, for these reasons:

1) I can check each price and make sure it's correct. You can try this in a traditional check-out, but the display is often aimed at the cashier, not you, and the cashier may check things so quickly that you can't keep up. In almost every load of groceries, I'm overcharged on at least one item, so missing this is expensive.

2) I can bag things properly. I put the frozen items together, the refrigerated items together, etc., while many baggers don't bother.

3) I can avoid have my food damaged by the cashier and bagger. I've had bananas slammed down, only to get bruises almost immediately, and have had a greeting card placed in the leaking milk sludge on the conveyor belt, even after I handed it directly to the cashier.

That said, they really need to work on a few problems:

A) They don't assign enough people to oversee them. Perhaps one cashier for every 2 or 3 would work. However, they need to actually keep the cashiers present. They frequently seem to walk away to do God-knows what, leaving the customers totally unattended. Maybe they can put a location sensor on the cashiers and dock them pay for every minute they are out of the area ? (Or fire them if they take it off.) There has to be some way to get them to do their jobs.

B) Many tasks require a cashier that shouldn't. If I have a coupon, I have to hand it to a cashier. If I want to cancel an item I scanned, I need a cashier. If I have an item with a hand-marked price, I need a cashier (in this case they need to stop hand-marking prices).

C) Many of the automatic check-out lanes need repair. There's some where the scale doesn't work, some where the voice part is broken, etc. They continue to use these defective lanes, which cause even more time demands on the cashiers. StuRat (talk) 18:45, 15 November 2009 (UTC)

With all of your points I agree. I usually buy canned goods in bulk and people behind me in line get perturbed whenever I start scanning individual cans. One cashier refused to override and enter the number of cans saying it was against chain policy. In another instance when my card was not approved due to faulty communication link the cashier refused to return my card until I threatened to call the police and have him charged with theft. My bank backed up my contention and he would have gone to jail. The problem I experience most is that recently there is some kind of holdup every time I use the self-checkout register. Repeatedly pressing zero usually results in the phone system hanging up.

I can't seem to find an alternate system or solution. Perhaps I can find a store that will allow me to fax, email or call ahead to place an order and have it ready for me to pick up in a couple of hours. 71.100.2.243 (talk) 20:30, 15 November 2009 (UTC)

As for the dehumanizing effects, the monotone voice is high among them, especially when it says something like "Have a good day". It just doesn't work when it comes from a machine. With a cashier you may suspect that they don't mean it, but at least it's possible that they do. And a monotone voice repeating the same thing ad infinitum actually seems even worse for the people who work there; I've seen them go to extremes to shut it up. StuRat (talk) 21:02, 15 November 2009 (UTC)

Do other people get "Unexpected item in the bagging area" every time they place an item in their bag, or is it just me? Certainly contributes to the stress level. Itsmejudith (talk) 21:19, 15 November 2009 (UTC)

I have had that problem at one particular chain of home improvement stores, but it's now been resolved. I think this reflects an important aspect of these systems - they will improve when people complain and companies listen, and the improvements scale well (compared to human training, for example). While I like to see people employed, there are some tasks that are so mindless and repetitive that machines can do the job better. Scanning groceries seems like one of those. -- Scray (talk) 21:26, 15 November 2009 (UTC)

In the case of self-check outs, a human still does the scanning, it's just now the customer. StuRat (talk) 21:53, 15 November 2009 (UTC)

Point taken - thanks for setting me straight there. I do anticipate greater automation being the next step, probably eliminating checkout aisles as we currently recognize them, but I don't want to treat the RD as a forum. -- Scray (talk) 22:30, 15 November 2009 (UTC)

Do you mean like the Quick Check system used in Waitrose? That is awesome, and does pretty much eliminate the normal checkout for everything except random rescans. And it alerts you to special offers when you scan things in, which is surprisingly useful. Doesn't quite cancel the greater expense of shopping at Waitrose, though. I can see it catching on in a lot of other shops if the initial cost comes down: remember how quickly the self-service checkouts caught on? 86.142.231.220 (talk) 23:43, 15 November 2009 (UTC)

The customer still scans there, just when they put the items in the cart instead of at checkout time. I can imagine a system that's fully automated, but not with bar codes, as those need to be pointed at a scanner to be read. The type of inventory tags they use on clothes have the ability to do a remote scan, so it's possible you could put your cart on a conveyor belt and it could go through a shielded scanner (so you don't get charged for the next customer's cart contents), and scan everything at once. I'm not sure that this would be a good thing, though, as pricing errors and unscanned items are likely to go unnoticed under such a system. StuRat (talk) 12:23, 18 November 2009 (UTC)

I think he means more like the self scan checkouts at ASDA and Tesco.  Ronhjones  ^(Talk) 00:23, 16 November 2009 (UTC)

Oh, I thought that was already covered in the previous comments. How do they include greater automation that other self checkouts? 86.142.231.220 (talk) 00:57, 16 November 2009 (UTC)

In the case of telephone companies who have perfected the technology to the greatest extent the monotone is almost gone but the resistance to turning the call over to a human operator even greater. (same for USPS who use this technology). To speak with an operator versus the system hanging up you first must provide your telephone number or account number, if its about data versus voice and if its data what your operating system is, what type of modem you have and on and on and on. An even more expensive lunch for the added speaking capability with even greater resistance to putting you in contact with a real live human including substantial wait time and failure to allow contact if your particular issue is not in its list. Try to get in touch with the right party to report a tree that is now so large it hs grown three inches around the cable or to report a thousand other problems. The menus are never well developed or based on proper classification principals. (see http://academia.wikia.com/wiki/Optimal_Classification) 71.100.7.189 (talk) 23:40, 15 November 2009 (UTC)

Automated systems have the potential to answer a few basic questions well, like their hours, location, driving directions, etc. It's when they try to use them for everything that the problems begin. Don't you just love the automated phone systems that repeatedly ask you for your all your info, including a 40 digit account number, timing out because you can't enter it quickly enough, until you eventually get it right, then they transfer you to a human who asks for all the same info again ? One trick to get hold of a human is to call the sales department, since they actually want to give the impression of having proper customer service until they get your money (then they never want to talk to you again). Of course, getting a salesman to transfer you to an actual person in the service department, instead of the infernal automated system, is another challenge: "Your call is important to us, although obviously not important enough to actually answer". StuRat (talk) 12:33, 18 November 2009 (UTC)

On the subject of self-checkouts, my local library has a system where no scanning is involved. Every book is fitted with a sticky label containing a radio tag (RFID I guess?) and the customer just plonks their stack of books onto a pad containing a sensor and it automatically checks out the lot. When this technology becomes cheap enough to put on disposable items like groceries rather than just assets with a longer life, such as library books, the "checkout rage" caused by scanning groceries will become a thing of the past, I can see having some kind of a scanner that you wheel your trolley through (like an airport security scanner) or a floor-mounted device that automatically scans your shopping and so all you have to do is pay.

Also, 'contactless' payment cards (like in that Barclaycard advert with the waterslide) may even automate that - you walk through the scanner and it deducts the value of your shopping from your contactless card. The security issues with that could be resolved by iris-recognition technology.GaryReggae (talk) 13:27, 19 November 2009 (UTC)

Rechargeable battery

How does the total life of a rechargeable battery compare with a non-rechargeable ? By "total life", I mean all the milliAmp hours you can get out of either battery until it's voltage drops permanently below the rating. In particular, I'm interested in AAA batteries, so I can decide whether rechargeables make sense in my walky talky. The rechargeables in question are Ni-MH and the non-rechargeables are "super heavy duty", which I think means "not alkaline". StuRat (talk) 18:06, 15 November 2009 (UTC)

I don't know about AAA batteries, but I did find this piece on how rechargeable vs. non-rechargeable AA batteries work for long term use in electronics. It recommends that for devices that are used often or "draw bursts of power" (such as a digital camera for taking a picture with flash), use rechargeables, and for seldom used or low power devices, such as flashlights or remote controls, use single-use batteries. Ks0stm ^(T•C•G) 18:49, 15 November 2009 (UTC)

The issue is that my price structure may well be different than theirs, since I can get permanent AAA cells in an 8-pack for a dollar, while I have to pay 20 times as much for rechargeables. So then, the question is if the rechargeables last 20 times longer. StuRat (talk) 18:57, 15 November 2009 (UTC)

Permanent AAAs aren't - that would be great ;-). The answer to your question depends not only on the battery type, but also on the application. Most rechargeables provide a fairly constant voltage (and current) until they are fairly drained, and then drop quickly towards (nearly) zero. Conventional batteries drop more evenly. If your walky talky is digital, it will need a certain minimum voltage, and you may not be able to use plain batteries to their full capacity. Also, most rechargeables can be used a lot more often than 20 times. As far as I can tell, for all items that use significant current and are in frequent use, rechargeables are the more economic choice. On the down side, they have a much quicker self-discharge rate, so they are unsuitable for storage or items like an alarm clock, that runs for years on a plain battery. ---Stephan Schulz (talk) 20:48, 15 November 2009 (UTC)

You seem to have assumed that both types of battery last just as long on the initial charge. I don't agree. I think rechargeables discharge faster, especially when old, but I don't know by how much. StuRat (talk) 21:06, 15 November 2009 (UTC)

No, I did not assume such. Yes, older rechargeables eventually loose capacity. As for initial capacity, look at List of battery sizes, which indicates non-rechargeables have between 50% and 20% higher initial rated capacity. But, since rechargeables hold voltage longer, they will discharge faster over the same resistance than non-rechargeables. Of course, they will typically also give higher performance. Anyways, due to the fact that they have much more than 20 recharge cycles, my point stands. --Stephan Schulz (talk) 22:05, 15 November 2009 (UTC)

The reason rechargeables are not good for slow draws, or infrequent uses is that they self discharge, and most will not last more than a month or two. Regular batteries don't self discharge (as much), because they have a higher internal resistance - but that internal resistance means that can not support a high draw without wasting energy. So it's a balancing act: do you want high power, low shelf life, or low power, long shelf life. PS. I don't think anyone makes low power long shelf life rechargables because it doesn't make sense from an economic point of view - why pay so much for a battery to sit and do nothing? Ariel. (talk) 08:06, 16 November 2009 (UTC)

The "super heavy duty" cells are zinc chloride battery and they are near useless at high current drains, which would include walkie-talkies in transmit mode. Rechargeables are much better for that. One problem with rechargeables was an "arms race" between NiMH battery manufacturers in the 1990's to make cells of higher and higher capacity, by making the insulating layer inside the cell thinner and thinner until the cells became unreliable (they lose the ability to hold a charge soon after you buy them). The cure is to buy pre-charged cells (low self-discharge NiMH battery). They have slightly lower capacity but the advertised advantage for them is they mostly eliminate the self-discharge effect (which they do), making it possible to ship them pre-charged and have them retain their charge on the retail shelf. I don't have an RS for it but I've seen stated in several places that what they basically did was go back to a thicker insulating layer, which not only gets rid of self-discharge but also makes the cells more reliable. I've been using these cells for a few years and have had very good results from them, unlike the max-capacity ones I used earlier which crapped out all the time. 69.228.171.150 (talk) 21:47, 16 November 2009 (UTC)

Thanks for the replies so far. I leave my walkie-talkies in the charger most of the time, but occasionally leave one out all night, and it then dies if I try to use it. I assume this is the ugly self-discharge problem. I will investigate the "pre-charged rechargeable" batteries as an alternative. StuRat (talk) 01:26, 18 November 2009 (UTC)

Human Scent

I had asked a previous question about human scent, but didn't find the answer to one part: Why can people not smell their own scent? Is there any way to make this possible? Thanks in advance... Ks0stm ^(T•C•G) 18:39, 15 November 2009 (UTC)

I suppose if anybody was in any way 'cut off' from their own scent, either by intensively using deodorant or perfume or by some mechanical means (i. e. carrying a clothes pin on your nose for a year, or any other nasty way), then I suppose after the foreign means had been removed one could become conscious of their own smell. IMHO. --Ouro (blah blah) 18:48, 15 November 2009 (UTC)

I think people can. You may get accustomed to any smell you are exposed to continuously, though, so may need a higher concentration to detect it. So, if you run a marathon and sniff your pits, I bet you will smell something. StuRat (talk) 18:51, 15 November 2009 (UTC)

It's called habituation, but when one raise his hand to enjoy the wonderful aroma of his armpit, just after intensive training in a gym, then he can smell himself very well. But if you leave him in a room filled with this odor for one-two hours, it would be more than enough to make it imperceivable. The first to describe the molecular mechanism for it (in Aplysia) was Eric Kandel and along with other studies he performed, his studies on the Aplysia's habituation mechanism actually founded the modern study of memory processes. Much more interesting thing happen when people try to tickle themselves, here-in different from habituation, the brain 'predicts' the action and it knows what areas exactly are going to be tickled, so it won't have any effect.--Gilisa (talk) 19:51, 15 November 2009 (UTC)

Everything Gilisa posted applies to females too. "Horses sweat, men perspire, women glow". Cuddlyable3 (talk) 21:46, 16 November 2009 (UTC)

a purely conceptual thought experiment

In a purely conceptual thought experiment I have discovered the CONTIUM.

The CONTIUM is simply a neutron, which instead of becoming a proton and electron or Hydrogen-1 becomes a CONTRON and a positron (a positively charged electron ).

The significance of this discovery is that external energy is no longer required to overcome the Coulomb barrier. In fact there is no Coulomb barrier.

The only way to keep Protium and Contium apart is with a polar magnetic field strong enough to do the job. When the field collapses the Protium and Contium are attracted.

My question is do they annihilate each other or do they undergo fusion and if fusion what are the most likely byproducts? 71.100.2.243 (talk) 19:22, 15 November 2009 (UTC)

Anything could happen since it's particles that dosn't exist in reality, but you may want to define their anti-particles and invoke CPT symmetry to run the reactions in reverse. It's a common line of reasoning in particle physics. EverGreg (talk) 19:29, 15 November 2009 (UTC)

We do not speculate about hypothetical things on the reference desk; and we do not encourage publication of original research - Wikipedia is an encyclopedia, not a forum for new ideas. A quick search shows that "contium" or "contron" do not appear in any prior scientific literature. Nimur (talk) 03:03, 16 November 2009 (UTC)

I understand the overpowering fear of academics being wrong and forever having that label on their coattail so let me put the question so you can provide a known answer. What force other than temperature and pressure can overcome the Coulomb barrier? 71.100.7.189 (talk) 05:25, 16 November 2009 (UTC)

Neither temperature nor pressure are a force. The coulomb barrier is a potential energy "barrier". Your use of terminology in this question is not valid, so there's no way to answer it as you have asked it. Nimur (talk) 06:38, 16 November 2009 (UTC)

All forces can "overcome the Coulomb barrier". As for Contium - if you started with a neutron (no charge), and split into a positron (positive charge), and "something" (contium), that something *MUST* has a negative charge, otherwise you violate Conservation of charge. Your "Contium" sounds very much like an anti-proton. If a proton (AKA protium) and an anti-proton annihilate each other a gamma ray will issue. Ariel. (talk) 07:59, 16 November 2009 (UTC)

Keeping the discussion factual, if the contium is basically a neutron, it will have baryon number 1. This means it must decay into a total baryon number of 1, so the contron must have a baryon number of 1. Intrincially, it has lepton number 0, so unless something very strange is happening, lepton conservation is broken. This can be solved with a(n) (electron) neutrino, but you then get n → c- + e+ + νe. Which is very like p+ → n0 + e+ + νe (merged with n0 → p+ + e− + _νe) , except not so explainable. Basically, your particle breaks known rules, or this universe. If you wish to imagine a completely different universe, fine, but you can't carry it accross to here, at least by my reckoning. - Jarry1250 ^{[Humorous? Discuss.]} 18:09, 16 November 2009 (UTC)

Type 1 Diabeetes - Sugar allowed in a can of drink

Really obscure question here, but does anyone know how muc h sugar people with Type 1 diabetees are 'allowed' to have in a can of drink? It's kind of a weird question but I'm asking for a friend :S —Preceding unsigned comment added by 82.11.245.145 (talk) 19:35, 15 November 2009 (UTC)

There is no such allowance. The source of the sugar is largely irrelevant. The amount of sugar they can have will depend on the nature of their condition (everyone is slightly different) and how much insulin they have had/will have. --Tango (talk) 19:45, 15 November 2009 (UTC)

Okay well, let me rephrase, roughly how many grams of sugar do you reckon an average type 1 diabeetes person could have in a drink without it affecting their sugar level? 82.11.245.145 (talk) 19:54, 15 November 2009 (UTC)

This is massively getting into the realm of medical advice, which we aren't allowed to give here. Suffice it to say that even for an "average" type-1 diabetic, if there was such a thing, the amount of sugar they could safely drink in a can would depend on a huge number of factors and there's no number we could give you that would be particularly meaningful without detailed knowledge of the specific situation. ~ mazca ^talk 20:13, 15 November 2009 (UTC)

This is purely hypothetical, nobodys drinking any cans of coke based on the advice here :P Also I don't mean safely, I mean literally no change in their levels, not even a safe change, just no change. Jimothyjim (talk) 20:22, 15 November 2009 (UTC)

None at all, then. Any consumption of sugar will raise blood sugar levels temporarily, in a diabetic or otherwise. --Tango (talk) 21:02, 15 November 2009 (UTC)

Okay, thanks all, I think everythings all sorted out now. More confusion over the question than anything. Jimothyjim (talk) 21:08, 15 November 2009 (UTC)

Here's a link from the American Diabetes Association that might be helpful.Sjö (talk) 12:54, 17 November 2009 (UTC)

Your assumptions are too vague to give you a precise answer, but many of the responses are misinformed as well. What does "allowed" mean? The major difference between the harm of a can of soda to a person with type 1 DM and the harm to you is simply that the person with T1DM needs to take insulin to metabolize the glucose while you make your own insulin. A typical ratio of insulin to carbohydrate needed by a young adult with T1DM is about 1 unit per 10 g of carb (there is wide variation among individuals). If the person takes the correct amount of insulin there is likely no apparent difference between the harm the soda does to him and the harm it does to you. If the person with diabetes does not take the extra insulin then his sugar goes high for a few hours, usually with no discernible immediate consequences, but perhaps contributing in a small way to long-term blood vessel damage. If you drink a soda there are likely no discernible immediate negative consequences but there may still be subtle long-term harm to you in many ways (obesity, bone damage, replacing needed nutrients, perverting your taste and altering your satiety settings, raising your uric acid, etc). alteripse (talk) 13:44, 17 November 2009 (UTC)

This is a medical question.174.3.102.6 (talk) 01:36, 20 November 2009 (UTC)

Good pickup. That's why a doctor is providing the best answer. alteripse (talk) 02:38, 20 November 2009 (UTC)

Toxicity of hydrogen peroxide

In Charlie Chaplin's film Monsieur Verdoux, Chaplin's character thinks he's pouring poison disguised as hydrogen peroxide into a bottle of red wine, but instead, he's pouring real hydrogen peroxide into the wine. He and his lady friend later drink the wine, and suffer no ill effects, save for inebriation. Is hydrogen peroxide actually toxic? Does it have any harmful effects when ingested in such small quantities (only a few centilitres)? JIP | Talk 20:27, 15 November 2009 (UTC)

One of the uses of the common 3% hydrogen peroxide solution is as a gargle, so presumably it's not very toxic. 100% hydrogen peroxide would burn you severly, on the other hand. StuRat (talk) 20:45, 15 November 2009 (UTC)

A 100% solution is hard to get and even harder to store for a long time. The most important thing is the concentration 3% or 30%. Wine has some imputities which will slowly oxidize and the hydrogen peroxide vanishes away. The small particles will also catalyze the decomposition of hydrogen peroxide. --Stone (talk) 20:51, 15 November 2009 (UTC)

Hydrogen Peroxide is most definatly not good to drink in large quantities or concentrations; which is why you gargle it. 3% solutions are generally recognized as safe, but I would still read and heed Hydrogen_peroxide#Safety. Wine may contain some measurable amount of Catalase, which would basically turn the red wine/hydrogen peroxide into Cold Duck... --Jayron32 05:45, 16 November 2009 (UTC)

Heteroaromatic Chemistry Problem

I can see from experimental results that the chlorine in 2-chloropyridine is easily displaced by nucleophiles such as amines. However, this isn't the case with 3-chloropyridine....why?! 188.221.55.165 (talk) 22:44, 15 November 2009 (UTC)

this article outside of Wikipedia explains in some detail the mechanisms of such reactions on pyridine, with electron pushing diagrams. See also Chichibabin reaction. --Jayron32 05:38, 16 November 2009 (UTC)

discoloration in schitzu's hair

This question has been removed. Per the reference desk guidelines, the reference desk is not an appropriate place to request medical, legal or other professional advice, including any kind of medical diagnosis, prognosis, or treatment recommendations. For such advice, please see a qualified professional. If you don't believe this is such a request, please explain what you meant to ask, either here or on the Reference Desk's talk page.

This question has been removed. Per the reference desk guidelines, the reference desk is not an appropriate place to request medical, legal or other professional advice, including any kind of medical diagnosis or prognosis, or treatment recommendations. For such advice, please see a qualified professional. If you don't believe this is such a request, please explain what you meant to ask, either here or on the Reference Desk's talk page. --~~~~

) 188.221.55.165 (talk) 23:49, 15 November 2009 (UTC)

Discoloration of a dog's fur is "medical advice" ? That's quite a stretch. StuRat (talk) 23:37, 17 November 2009 (UTC)

Dicussion is here: [4]. StuRat (talk) 23:43, 17 November 2009 (UTC)

November 16

Centrifugal force

I'm doing a lab report on ficticious forces, and something doesn't seem to make sense. The design of the experiment is as follows: a stationary channel has a ball roll slowly through it, while the channel is overtop some paper on a rotating platform. Again, the ball is NOT rotating (just going in a straight line), but it's making contact with the paper that it rotating, and every 30 ms or so the ball makes a mark on the paper, so that's its trajectory is traced out. Now according to the lab manual (and in agreement with the results we obtained), the ball will slow down as it approaches the centre, and speed up while it's leaving, and apparently this is due to centrifugal forces.

Now to me, this doesn't make much sense. The ball itself shouldn't be experiencing any forces (ignoring friction), and even in the reference frame of the rotating paper, the ficticious force acting on it should be directed towards the centre, allowing it to continue in a circular path. After all, if the ball wasn't moving at all, it wouldn't start moving away from the centre, so I have trouble believing that there would be a ficticious force acting on it. But I wasn't actually there for the lab; is it possible that it was the ball that was rotating while the paper was stationary, and that my lab partner is just an idiot? —Preceding unsigned comment added by 24.200.1.37 (talk) 00:31, 16 November 2009

In the nonrotating lab frame, the velocity of the ball relative to the paper is the velocity of the ball relative to the lab (a constant) minus the velocity of the paper relative to the lab at the point where the ball is at that moment. The paper is moving more slowly near the center of the rotation, so it's reasonable to suppose that the difference of the velocities will be smaller nearer the center. That's why the marks on the paper were more closely spaced there.

In the real world (as real as academic physics gets, anyway), that would be enough. You don't have to analyze the problem in every frame, you can just pick one and do the analysis there. But since this is a lab, I suppose they want you to repeat the analysis in a rotating frame where the paper is at rest. That seems to be a lot more complicated in this case, so if the intent of the lab is to show you the usefulness of fictitious forces then it isn't doing a very good job. In the rotating frame, the ball experiences the centrifugal force (which acts outward from the center) and the Coriolis force (which acts at right angles to the ball's velocity). You're probably supposed to ignore the fact that the ball is constrained by the channel and supported by it against gravity; the important thing is that the ball moves as it would in empty space with no external forces (other than the fictitious forces). You can write down the equations of motion and try to solve them, but it's going to be ugly. I don't see any easy way to do it aside from solving the problem in the nonrotating frame and then changing the coordinates.

In the case of an object at rest in the nonrotating frame, the centrifugal force in the rotating frame points outward, but the Coriolis force points inward and is twice as large. So the net force is inward; that's the centripetal force that keeps the object moving in a circle. In this case, too, it's easier to see what's going on in the nonrotating frame. -- BenRG (talk) 01:11, 16 November 2009 (UTC)

If the ball is stationary, then it's radial velocity is zero. Since the coriolis force is proportional to the radial velocity, how can it cause a centripetal force? —Preceding unsigned comment added by 24.200.1.37 (talk) 08:21, 16 November 2009 (UTC)

An object following a circular path with constant angular velocity $\omega$ relative to a rotating reference frame which is itself rotating with constant angular velocity $\Omega$ (where axis of path coincides with axis of rotation of frame) requires a centripetal force of magnitude

$mr(\omega +\Omega )^{2}=mr\omega ^{2}+mr\Omega ^{2}+2mr\omega \Omega$

The first term is the centripetal force that is "expected" relative to the rotating reference frame; the second term is a "correction" due to centrifugal force; and the third term is a further "correction" due to Coriolis force. In BenRG's example the object is stationary relative to the non-rotating reference frame, so $\omega =-\Omega$, the Coriolis force term is negative, and the net required centripetal force (after the "corrections") is 0. Gandalf61 (talk) 11:59, 16 November 2009 (UTC)

Stone artifact need help with what it is...

I need help with a stone that my daughter found on Myrtle Beach S.C. It is very old and it is either indian or maybe even from the stone age. We have pictures and would appreciate any help with whom we could email for assistance. Thank you for your time —Preceding unsigned comment added by Donald Cohee (talk • contribs) 00:54, 16 November 2009 (UTC)

If you post the pictures, someone here might be able to help identify the stone. Otherwise, we don't have a directory of Wikipedians with expertise in identifying Native American artifacts. —Akrabbim^talk 01:23, 16 November 2009 (UTC)

Since you actually are in possession of this artifact, you might consider talking to a history or archaeology professor at the nearest university, who may be willing to spend some time looking at it. Nimur (talk) 03:07, 16 November 2009 (UTC)

It's worth noting that removal of antiquities can be regulated in some places. -- Scray (talk) 04:59, 16 November 2009 (UTC)

Also, Native American artifacts are "stone age", excepting those acquired through trade or from far into the "historic" period. Pfly (talk) 06:27, 17 November 2009 (UTC)

tuned circuit

I'm trying to create a tuned circuit for a science project to show how 60 Hz power line frequency intensity can be monitored and displayed on a computer based osciliscope. When I calculate the wavelength for 60Hz however I get an antenna length that is way beyond a length of wire that I can mount in the yard and tune. I know there must be harmonic that I can use with a reasonably shorter antenna and with a coil and capacitor circuit to cilate and perfectly match 60 Hz but I can not find any references or information as to how to calculate the length of the size of the coil and capacitor for a specific 60 HZ harmonic antenna length that will work. Does the Wikipedia have any references for the complete calculations? 71.100.7.189 (talk) 01:52, 16 November 2009 (UTC)

You will pick up 60 Hz whether you want to or not... I have a lot of experience setting out antennas of varying sizes and we always get 60Hz interference. Our AWESOME antennas pick up 60Hz and dozens of its harmonics; you can see its antenna size and download schematics for the antennas, as well as the preamplifier and data acquisition system. I think you can even purchase the hardware and equipment at-cost from Stanford for around $500. In any case, if your preamplifier and amplifier have a good low-frequency response (e.g. similar to a high-quality audio amplifier), you'll have no trouble tuning to the 60Hz at baseband ("zeroth harmonic") even with a small ~ 1 meter antenna. Nimur (talk) 03:15, 16 November 2009 (UTC)

I assume the horizontal lines are the 60HZ harmonics but what I need is a circuit specifically tuned to 60Hz or at least the equations necessary to create the antenna, coil and capacitor to resonate at 60Hz. 71.100.7.189 (talk) 03:47, 16 November 2009 (UTC)

The links I've provided show circuit schematics for a broad-band amplifier; if you want to tune to 60 Hz, take a look at tuned circuit and Q factor. The equations are trivially easy; the difficulty is finding components and getting a good amplifier at such low frequencies. That is why I suggest using a broad-band system (like the one I linked above) and digitally processing the result to analyze the 60Hz band. Nimur (talk) 05:03, 16 November 2009 (UTC)

So are Maxwell equations but their usefulness and comprehension exceeds the elegance of their simplicity. 71.100.7.189 (talk) 05:17, 16 November 2009 (UTC)

After reviewing the few questions you have asked, I think the best advice for you is to review some basic physics; we have some good articles on electronics, electromagnetism, and atomic theory that are all very well-sourced. If you still have specific questions after you are up to speed on the fundamentals, or if you're having conceptual problems understanding parts of the articles, feel free to ask here. Nimur (talk) 06:52, 16 November 2009 (UTC)

You should not be trying to establish a pattern of thinking based on any of my questions since only two questions I have asked originated from the same member of our group. Also if you don't know the answer just say so. 71.100.7.189 (talk) 07:42, 16 November 2009 (UTC)

I would avoid constructing a passive resonator circuit for so low a frequency as 60Hz because of the inconveniently large LC product needed. It is easier to make it either as a bandpass Active filter or as a digital Goertzel algorithm. THe latter is used in DTMF detectors in telephony and might be readily implemented in your computer based oscilloscope. Nimur has given good advice above. BTW I have found that in many urban areas one need only bury a couple of earth rods a few meters apart to be able to pick up a few tens of millivolts of power line frequency between them. Cuddlyable3 (talk) 10:45, 16 November 2009 (UTC)

The phrasing of your initial question implies that you think it is necessary to have an LC circuit tuned to 60 Hz in order to "monitor and display" 60 Hz EMF. You also seem to believe that the antenna has to be resonant at 60 Hz to detect that low frequency. Responders have pointed out the error in these assumptions. You need not imply that the responders "Don't know the answer." You may just be asking the wrong question so far as your research goal is concerned. EMF is commonly measured by small instruments which allow display on PC's without some impossible 2500 km antenna. I have used them myself, and they are fairly small. I expect that some of the electronics hobbyist magazines have published "build-it-yourself" instructions for such a meter with 3 small coil antennas. A pickup coil producing 1 mV per 20 mG is available for under $5 online [5]. Edison (talk) 20:16, 16 November 2009 (UTC)

Here is a warning if the OP is considering measuring the electric field near high voltage power or overhead tram cables using some kind of homemade probing antenna. Don't. Cuddlyable3 (talk) 21:29, 16 November 2009 (UTC)

You will easily pick up lots of mains frequency (60Hz) signal just by connecting a short piece of wire to your oscilloscope input. To make the waveform look more sinusoidal, just use a passive RC low pass filter directly at the scope input and connect your wire to that. —Preceding unsigned comment added by 79.75.63.71 (talk) 00:30, 18 November 2009 (UTC)

Tsar Cannon with two ton cannonballs?

Sorry about the random inquiry, was just interested with reading a random article I found. Apparently the Tsar Cannon has cannonballs placed in front of it, weighing two tons each according to my interpretation. The cannon was also fired at least once, with gunpowder, according to analysis. Although the diameter of the cannonballs is larger than the barrel diameter of 35 inches, and they were made only for the purposes of decoration, if the cannonballs could fit, would a reasonable amount of gunpowder be sufficient enough to propel a two ton cannonball? And if so, to what distance? Thanks, ♠The Ace of Spades^♣♥_♦ 02:00, 16 November 2009 (UTC)

Not a cannonball, but two tons. Nimur (talk) 03:55, 16 November 2009 (UTC)

Well, this Tsar Cannon gun maybe isn't a suitable design; but a modern battleship from the 1980s was armed with a 66-foot long main battery capable of firing a 1200 kg projectile up to twenty miles. The explosive powder propellant is much more advanced than "gunpowder" (as it would have existed in the 16th century). Our article describes the propellant as "smokeless Powder Diphenylamine (SPD)" with a "titanium dioxide and wax compound known as 'Swedish Additive'"; and polyurethane jackets placed over the powder bags. When the USS New Jersey bombarded the coast of Lebanon, the Navy referred to the projectiles as "flying Volkswagens"[6] in an effort to demoralize the enemy[7]. Targeting for these 2-ton projectiles was grossly inaccurate (blamed on calibration errors in the explosive powder mixture). Shells from this barrage missed their intended targets by many miles, resulting in massive civilian casualties; this was cited as a motivation for the subsequent attack on the United States Marine barracks in October 1983. Nimur (talk) 03:43, 16 November 2009 (UTC)

Perhaps, seeing that the grapeshot that the Tsar Cannon fired weighed about a ton and three-quarters, according to the article. bibliomaniac15 04:15, 16 November 2009 (UTC)

20 miles? ha ha ha ha ha ha ha. Lucky if it went 20 yards. Here are my calculations, first the initial assumptions;

• explosive pressure of black powder = 67 ton/m² (might need adjusting - I got that from a fireworks article)
• energy content of black powder = 3 MJ/kg
• mass of projectile = 800 kg (from article - don't know where Bibliomaniac got ton and three quarters, I don't see it)
• calibre: 890 mm
• barrel = 5.34 metres

From the calibre I get a csa of 0.622 m² and from the pressure a force of 44.3 tons. Newtons second law arrives at an acceleration of 543 m/s². From $\scriptstyle v={\sqrt {2ax}}$ we get a muzzle velocity of a measly 76 m/s - you would probably do more damage head butting the enemy. Maximum elevation and ignore aerodynamics etc gets you a flight time of 7.77s and a distance just over 300 metres. The kinetic energy on leaving the barrel is 118 MJ which, if energy is transferred 100% efficiently, requires about 40kg of black powder.

For a 2 ton projectile it comes out at 118 metres and 16 kg of charge. Of course, many subtleties are neglected here, not least of which is the assumption that the charge continues to burn all the way up the barrel and is completely used by the time the projectile exits. That can be wrong both ways, the charge could burn up before we are done accelerating the projectile, or the charge might not burn fast enough leaving part of it uselessly burning after the projectile has exited. An ideal weapon has the barrel length "tuned" to the missile you are trying to launch and the propellant you are using to launch it, but this one most probably isn't. SpinningSpark 22:23, 16 November 2009 (UTC)

Actually, I've made an error in the amount of powder calculation, it comes out the same for both cases and is less than 1kg, but I don't believe for a minute that is the correct load for this gun in reality. SpinningSpark 22:48, 16 November 2009 (UTC)

The 20 mile range I quoted was never for the Tsar Cannon. It was for the main battery of an Iowa-class battleship; I only mentioned it to illustrate that large artillery does exist, but it is a very different and much more modern design than Tsar Cannon. As for "head-butting", an 800 kg object moving at 70 meters per second would have an impact equal to a large car going faster than highway speeds (150+ mph); I don't know why you would consider that weaker than headbutting. It's still no battleship, though. Nimur (talk) 01:01, 18 November 2009 (UTC)

Thanks, all. ♠The Ace of Spades^♣♥_♦ 03:34, 17 November 2009 (UTC)

String theory and GUTs

Could there be string vacua that approximate the standard model without allowing proton decay? 76.67.73.245 (talk) 04:09, 16 November 2009 (UTC)

Nobody knows whether there are string vacua that look enough like the standard model to be consistent with experiment. Of course, the proton lifetime doesn't have to be infinite to be consistent with experiment, it just has to be larger than 10³⁴ years or whatever the latest lower bound is. If you're wondering whether string vacua with an infinite proton lifetime have been ruled out, then I don't know, but I imagine not. -- BenRG (talk) 23:08, 17 November 2009 (UTC)

Recreating extinct species

Okay, this is mostly just a small idea that I've been toying with. With current genetics research, I am fairly sure that at some point we will have the capability to clone and reintroduce extinct animals to the wild, but only some have enough intact DNA to do this. I was just trying to think of a list of the more important extinct species that could be brought back. For example, the passenger pigeon and the Carolina parakeet have enough DNA remaining via feathers to clone them and have genetic variation, but the dodo bird likely does not. I was wondering if anybody could add to the list of animals where enough material remains to clone them and retain genetic variability in the cloned population?

1. Passenger Pigeon
2. Carolina parakeet
3. Elephant bird - long shot unless the eggs retain enough DNA.
4. Great auk
5. Thylacine
6. Quagga

Thanks, Falconus^{p t c} 05:11, 16 November 2009 (UTC)

[8] looks like an interesting read. It's currently cited in the Passenger Pigeon article. --Jayron32 05:19, 16 November 2009 (UTC)

Thanks, that was interesting. Also, apparently feathers don't actually contain DNA. Falconus^{p t c} 05:31, 16 November 2009 (UTC)

Bad idea. Eventually they'd figure out how to mate and then we'd have to listen to some flirty nonsense about chaos theory. In all seriousness though, the issue is going to be the "intact" part. DNA samples won't hold very well and the amount of reconstruction one would have to do would be enormous, to a point where you would likely have a very different animal (assuming viability). It's doable for things like the recreation of the 1918 flu since there are only 8 genes. ~ Amory (u • t • c) 13:58, 16 November 2009 (UTC)

The mammoth is often put forward as a likely candidate for the "Jurassic park" treatment. Large amounts of mammoth meat can be found deep-frozen in the north of Siberia - and it's thought that a modern elephant could provide the necessary egg & womb for turning DNA into living animal. Pidgeons & parakeets could be similarly dealt with if the DNA is in good enough shape - but finding a parent animal for an elephant bird, auk thylacine or quagga might be tough. SteveBaker (talk) 14:03, 16 November 2009 (UTC)

Steve, have a look at Quagga Project. ZUNAID●FOREVER 14:57, 16 November 2009 (UTC)

And Neanderthal genome project for a jockey?.Cuddlyable3 (talk) 21:21, 16 November 2009 (UTC)

Re-expanding a shrunk cotton shirt

Some questions regarding the hydrophilic properties of cellulose fibers such as cotton and wool:

• Why is it that materials made from cotton or wool shrink when immersed in hot water and allowed to dry? I mean, what's happening to the polymer? Does the water become permanently bound into it, resulting in permanent swelling of the fiber, thereby decreasing its length, or does the water evaporate and somehow leave behind a shrunk fiber?
• Why does this not happen with cold water?
• Is it possible to re-expand the fibers to the original length after shrinking in this fashion?

My inquiring mind was unable to find answers in the articles about cellulose, cellulose fiber, or hydrophilic. ~Amatulić (talk) 06:54, 16 November 2009 (UTC)

This is not a perfect fix but it helps if you hang a shrunk tee up wet. It would be nice to understand what is happening. My uninformed guess is that being wet allows the shirt fibers to become more disordered, increasing the entropic force of the fabric against stretching. -Craig Pemberton 08:42, 16 November 2009 (UTC)

The process of turning cotton fibers into threads and then weaving them into clothes involves pulling and twisting the fibers. As a result many of the fibers (and their constituent molecules) are distorted into an elongated state. They are weakly bound into that state by binding against other fibers and threads. Heat, water, and/or agitation (e.g. a hot wash) cause some the fibers to free themselves and relax into their natural, unstressed state. It's that act of relaxing that causes the clothing to shrink. Cotton and other organic fibers that have complex textures are more prone to stretching and shrinking than simple synthetic fibers. To a degree one can reduce / counteract shrinkage by manually stretching out the article with applied force but this will never be more than a partial solution since no about of pulling will really replicate the effects of making thread. Dragons flight (talk) 11:21, 16 November 2009 (UTC)

I guess, then, making a garment from pre-shrunk cotton thread won't prevent the garment itself from shrinking later, because the act of weaving would stress the threads. ~Amatulić (talk) 18:28, 16 November 2009 (UTC)

Flying Machine

Could this machine fly?

Are there theoretical limits on size? (I mean way beyond Spruce Moose size) TheFutureAwaits (talk) 07:26, 16 November 2009 (UTC)

The machine depicted appears to have no wing structures - even in a cutaway diagram one might expect to see spaces for their supports: is it actually meant to be an aircraft, or merely an airscrew-driven hydroplane?

If flight is postulated, I suspect it would be too heavy, especially given the old fashioned and bulky natures of many of its components. I don't think there are any theoretical limits on an aircraft's absolute size, but there must be practical limits determined by the aerodynamics of a given atmosphere and the strengths and weights of available materials. A major consideration would be the square-cube law, which dictates that as the linear size of an object increases, its surface area increases proportionallty to the square of the linear increase, but its volume (and hence weight) increases proportionally to the cube - this rapidly increases the wing loading of a conventional aircraft design beyond what will allow flight. 87.81.230.195 (talk) 08:49, 16 November 2009 (UTC)

You could try to demonstrate infeasibility by using a rough and ready calculation for the torque which would be applied to the propeller shaft, and see if any known material has the required strength. -Craig Pemberton 09:08, 16 November 2009 (UTC)

I don't see anything that indicates that this isn't just a multihull boat.-Craig Pemberton 09:11, 16 November 2009 (UTC)

The pontoons are labeled as being "retractable," which I would think would be more likely in the design for a plane than for a boat. My presumption is that it's intended to be a plane, with the wings just not visible in the cutaway. Red Act (talk) 09:22, 16 November 2009 (UTC)

Silly; any vehicle this extravagant is bound to be pimped out. -Craig Pemberton 22:47, 16 November 2009 (UTC)

Also, the rudder sticks up above the craft, not down below it like would make sense for a boat. Red Act (talk) 09:27, 16 November 2009 (UTC)

From the style of the sketch (that's all it is) especially looking at the cars, this was drawn around 1920-30. Anything can "fly" if it gets enough lift. So start by estimating what this monster weighs. Cuddlyable3 (talk) 10:21, 16 November 2009 (UTC)

From the drawing I would have thought that this is meant to be a blended wing body / flying wing aircraft. See alsoJunkers G.38. Boeing clearly thinks this to be an option for future aircraft and is designing one for 800 passengers which can use existing runways. --Cookatoo.ergo.ZooM (talk) 11:06, 16 November 2009 (UTC)

You only showed us one picture...there are more! [9] and [10]. Clearly it's not intended to be a boat. It's very clear that it wouldn't have stood a chance of flying...at least not with the internal design as shown. The artist clearly didn't understand anything about airplane design.

As a flying machine - it's pretty impractical. Using a steerable rear propeller and more props out on the "wings" for turning the thing is a really clunky idea (especially as there is no indication of how those things are powered) - and the de-icing trick results in the need for a double skin which would be heavy. There is a pathetically small fuel supply - yet the fact that there are "quarters" even for the crew and vast amounts of water storage suggests anticipated flight durations of more than just a few hours. There is essentially zero internal structure that would give the thing strength - all we see are partition walls separating rooms...no structural girders except in areas where the artists couldn't think of any useful purpose for the interior space. The weight of things like fuel and engines - plus water tanks and heavy cargo are not well-distributed through the structure - it looks like it would tear right down the middle where the super-weak elevator shaft splits the two heavy sections! The center-of-gravity of an airfoil needs to be at the same place as the center-of-pressure - and that's at the thickest part of the cross-section - this doesn't look like it would have enough weight up-front...but then with those gigantic diesel engines...who know?

There are certainly a lot of oddities to the design...the elevator motors are gigantic! Any idiot could see that if they had moved some of the cargo storage forwards into the bottom of the craft and put the reception areas and offices on upper floors - they'd have needed far fewer stairwells and elevator shafts and perhaps stood a chance of getting the center of gravity in the right place.

This is a classic example of something an engineer would never come up with. Some artist sketched a design for an interesting-looking exterior in 2 minutes flat and then spent the next couple of days carefully filling every cubic inch with something that a cruise liner might need - without giving any consideration whatever for structural strength, power-to-weight ratio, center of gravity, etc.

Bottom line: No - it wouldn't fly.

SteveBaker (talk) 11:18, 16 November 2009 (UTC)

It would make a great submarine. Cuddlyable3 (talk) 11:57, 16 November 2009 (UTC)

Especially if there was a large body of water right at the end of the runway! :-) SteveBaker (talk) 13:58, 16 November 2009 (UTC)

Look how much it's banking in that cover shot! I hope nobody is in those bathtubs! APL (talk) 16:21, 16 November 2009 (UTC)

It's an ocean liner with wings. It is designed just like an ocean liner and would probably weight as much (thousands of tonnes). There is no way to get something that heavy to fly by conventional means. It's not that it was designed by a non-engineer, it was designed before the realities of flight were well understood. It looks like it was designed by a nautical engineer (or someone with experience of ship design) thinking flight would be the same kind of thing. --Tango (talk) 20:05, 16 November 2009 (UTC)

Now I've seen the full magazine item at the page linked to below I see it doesn't have wings, per se. It is supposed to be one big wing. This seems like an obvious idea until you realise that greater weight requires greater wingspan, which means that you need to be able to increase the wingspan without increase the weight much, which means having light wings. That necessitates a design like a regular aircraft with a central thick body and thin wings (although the wings don't have to stick out the sides, they could go forward and back - there have been some interesting ideas along those lines). --Tango (talk) 21:10, 16 November 2009 (UTC)

The design is from 1932 or 1934 (the page says both), and is estimated by its designer to be 10,000 tons. Dragons flight (talk) 20:31, 16 November 2009 (UTC)

It's from '34. The article refers to an earlier design from '32. --Tango (talk) 20:59, 16 November 2009 (UTC)

BTW, we have an article on the guy that designed this thing: Hugo Gernsback. --Tango (talk) 21:17, 16 November 2009 (UTC)

Another couple of problems with the design:

1) Transonic propellers: At 80 feet in diameter, and at the speeds those propellers would need to rotate to keep this monstrosity aloft, the tips would go supersonic, while near the shaft they would remain subsonic. The forces on such propellers would rip them apart.

2) Unstable flying wing design: A flying wing is inherently unstable, requiring continuous control surface adjustments to keep it flying straight. This made flying wings a bad idea in the 1930's. They are more feasible today, since we can use a computerized fly-by-wire system to make those adjustments many times a second. However, if the computer fails, you're in trouble. StuRat (talk) 23:20, 17 November 2009 (UTC)

not exactly dreaming?

I think dreaming refers to REM sleep, a stage that occurs after you've been asleep for a while. There's another dreamlike experience when initially falling asleep. It's possible to forget where you are and what you're doing, and confuse imagined activities with reality, while drifting off. Is there a name for that, if it's not technically the same thing as a dream? 69.228.171.150 (talk) 07:29, 16 November 2009 (UTC)

The article Hypnagogia may give you some leads, both in itself and through the links in its "See Also" section, such as Hypnopompic. 87.81.230.195 (talk) 08:34, 16 November 2009 (UTC)

Thanks, that article is great. 69.228.171.150 (talk) 21:20, 16 November 2009 (UTC)

mathematcal model of PMSM/AC servo motor

hi everybody my project is to control the position of AC servo motor by FPGA by sliding mode control so i need the mathematical model i am try to derive the model but i m facing a lot of problem i m very new to the electric machines i know the basics of the servo motor but it is three phase motor not like Dc motor which is qite simple and its modeling also so any body on wiki kindly help me i want state space modellike[A][B][C][D] matrix so that i can simulate it in MATLAB/SIMULINK and then implementation of sliding mode control technique on AC servo motor i want help about the sliding mode algoritham thanks in advance kindly reply

regard abhay

anembryonic gestation

does anembryonic gestation negatively affect further pregnancy?202.83.57.17 (talk) 09:33, 16 November 2009 (UTC)remy

Not an answer, I'm just adding a link to the Anembryonic gestation article, for others who might be interested. --NorwegianBlue ^talk 15:20, 16 November 2009 (UTC)

Perhaps you meant subsequent -- apparently, spontaneous abortion is thought to include the subset of anembryonic gestation. DRosenbach ^{(Talk | Contribs)} 17:18, 16 November 2009 (UTC)

Special Relativity

In special relativity, if you measure a particle of having an average lifetime of say n seconds as measured in the rest reference frame, and you know its speed, do you just use distance = speed x time to find the average distance it travels in the rest reference frame? —Preceding unsigned comment added by 94.193.67.204 (talk) 10:24, 16 November 2009 (UTC)

If by "rest reference frame" you mean the reference frame of the laboratory, then the average distance a particle travels as measured in that frame, is calculated as Average_speed x Average_rest_life_time x Gamma, where Gamma is 1/sqrt( 1-v^2/c^2 ). The average "time" that was measured of the "still" particles gets dilated by a factor gamma when the particles are moving. DVdm (talk) 10:48, 16 November 2009 (UTC)

The average lifetime is measured as the particle is moving, in the laboratory reference frame, so to find the average rest life time would you divide the average lifetime by gamma? —Preceding unsigned comment added by 94.193.67.204 (talk) 11:26, 16 November 2009 (UTC)

Yes, if the average lifetime is measured on moving particles. Average_rest_life_time x Gamma = Average_moving_life_time. See Time dilation#Time dilation due to relative velocity.

By the way, please sign your messages with 4 tildes (~~~~)? Thanks. DVdm (talk) 11:38, 16 November 2009 (UTC)

Hang on. I think there is some confusion here. You only need to use gamma if you are converting from one frame to another. So, if you are measuring the average life time and the distance travelled in the same frame then you can just do distance=speed*time. If the average life time is measured with the particle at rest (which is the normal value quoted) and the distance is measured in the laboratory frame, then you need to convert the life time at rest to a life time in the lab frame by multiplying it by gamma. You can multiply that by the speed to get distance. --Tango (talk) 19:40, 16 November 2009 (UTC)

Yes. To avoid that confusion I introduced the names Average_rest_life_time and Average_moving_life_time. DVdm (talk) 20:55, 16 November 2009 (UTC)

Recycling

In the United States, is it generally a problem or not to include paper envelopes with plasticine address "windows" with mixed paper recycling? Thank you --71.111.194.50 (talk) 13:10, 16 November 2009 (UTC)

No it isn't. Recycling plants have techniques for removing small amounts of contaminants like this. I can't believe I just answered a refdesk question with a link to Yahoo Answers... —Akrabbim^talk 15:46, 16 November 2009 (UTC)

Bahahahah... you're a regular though, so we have to let that slide. :-) ♠The Ace of Spades^♣♥_♦ 03:32, 17 November 2009 (UTC)

Many such envelopes have a plastic lining that makes them fairly unrecycleable. If you wet your fingers and rub the envelope, the paper will rub off and you'll see a very thin plastic sheet. Ones like that should just be thrown away. --Sean 17:17, 16 November 2009 (UTC)

I don't think you meant plasticine... --TammyMoet (talk) 19:46, 16 November 2009 (UTC)

I have seen many that simply have a hole cut in the paper, and replaced with a clear plastic piece. —Akrabbim^talk 19:59, 16 November 2009 (UTC)

Yes indeed - but that's simply clear plastic, not plasticine, which if you read the linked article, you will see is based on modelling clay! --TammyMoet (talk) 10:23, 17 November 2009 (UTC)

The OP's "plasticine" was clearly a slip for "glassine". I don't think glassine is used much in window envelopes these days, having been superseded by clear plastics as noted above, but it used to be. Deor (talk) 13:02, 17 November 2009 (UTC)

Do arrows have "lift"?

My question concerns the following claim made in this version of the "Quarrel" article:

"Bolts and arrows have different flight characteristics. Bolts fall at the same rate, independent of the speed of flight. Arrows, in contrast, depend on gaining lift in flight, and hence have their centre of balance at a point about 9% of their length forward of their center. This is called 'point planing'."

No reference is (at present) cited in-line for this information. What I'm wondering is: does that make any sense?
On the "Quarrel" talk page I made the comment:

"To have lift, you need an airfoil, but the fletching article makes it clear that the fletchings are there only to "stabilize the arrow in flight" (ie., they are not wings). There is no mention of "lift" in the arrow article."

But then I started wondering about eg. paper airplanes, hang gliders, etc. – the "wings" of which do not (necessarily) seem to have an airfoil shape, either. Some of the "lift" in those cases apparently derives from "angle of attack" issues, but could that really be what's going on (in a consistent, reliable way) with arrows, too? Wikiscient 17:20, 16 November 2009 (UTC)

Air foil shape is useful for getting lift while minimizing drag. Ever see pieces of plywood flying around during a hurricane? Those are not airfoil shape and certainly have lift. Googlemeister (talk) 17:29, 16 November 2009 (UTC)

Well, that refutes my "to have lift, you need an airfoil" remark, but I had already done that myself by bringing paper airplanes etc. into it.

I'm still trying to understand better how "lift" works with arrows, if, in fact, there is any (which, presumably, would be attributable somehow to the fletchings, which neither bolts nor bullets have). Wikiscient 17:40, 16 November 2009 (UTC)

Some (but not all) crossbow bolts do have fletchings. See Crossbow#Projectiles, and this picture. Red Act (talk) 18:15, 16 November 2009 (UTC)

Ok, thanks for the clarification. I guess that just makes the statement in the crossbow bolt article which prompted my question all the more interesting or "incorrect," I'm still not sure which! :S Wikiscient 18:31, 16 November 2009 (UTC)

Wouldn't a crossbow bolt also have that same sort of lift if it was fired at the appropriate angle of attack? APL (talk) 17:32, 16 November 2009 (UTC)

I'm not completely certain of this, but I think the answer to that would be: yes, but not much! Wikiscient 17:43, 16 November 2009 (UTC)

That doesn't make sense to me - shouldn't the centre of balance be further back than the centre of the arrow in order for it to have positive angle of attack and thus have lift? That said, I think the key difference between arrows and bolts is that bolts go faster. That means they don't really need any lift in order to maintain level flight, there just isn't time for them to fall far before hitting their target. --Tango (talk) 18:31, 16 November 2009 (UTC)

Well, again, my question is about this quote (from the crossbow bolt article):

"Bolts fall at the same rate, independent of the speed of flight. Arrows, in contrast, depend on gaining lift in flight..."

There is no reason an arrow couldn't be launched with a higher velocity than a bolt, so I don't think that is the "key difference" in this case.

The "key difference" does seem to have something to do with the location along the length of the projectile of the center-of-gravity. And I am wondering the same thing: placing that forward of the center-of-length would, intuitively, seem likely to create a downwards angle-of-attack force! On the other hand, if the fletchings were providing lift the way an airfoil does (ie. even in level flight), you'd want to have your center-of-gravity forward of center-of-length to compensate for that "upwards-from-the-rear" force.

So, anyway, I'm still trying to understand what the quote in question is trying to say... Wikiscient 19:00, 16 November 2009 (UTC)

See, I'm just confusing myself with this, *sigh*...Wikiscient 19:04, 16 November 2009 (UTC)

Arrows are fired by a bow, bolts are fired by a crossbow. The ways those two devices work mean that bolts are fired faster. That is (part of) why different projectiles are used. As I understand it, the fletches make the arrow spin, providing stability by the gyroscopic effect. Since the arrow is spinning, there is no way the fletches could provide lift (any such force would rotate with the arrow and could average itself to zero). --Tango (talk) 19:31, 16 November 2009 (UTC)

I should clarify - the fletches probably are aerofoil shaped in order to get optimal torque. Each fletch will provide a force in a different direction and, since they are equally spaced, they will all cancel out so there is no resultant force, just a torque (rotational force). --Tango (talk) 19:33, 16 November 2009 (UTC)

No, both of these claims are wrong. Fletches are, modulo production errors, straight and symmetrical. They do not stabilize the arrow by rotation, but simply act as aerodynamic fins. If the arrows velocity is not parallel with its heading, the increased drag of the fletches acting on a long lever will right it again. --Stephan Schulz (talk) 22:39, 16 November 2009 (UTC)

Agreed. So, hmmm... Wikiscient 22:50, 16 November 2009 (UTC)

Assuming that an arrow/bolt behaves in a similar manner to a javelin, the center of gravity is placed relative to the center of pressure to achieve optimal lift. By sport rule, javelins have the center of gravity pushed forward to make them plummet and stick into the ground as opposed to gliding along and skipping along the ground when they land. -- kainaw™ 18:53, 16 November 2009 (UTC)

Optimal lift for an arrow or bolt would, presumably, be the amount of life required to keep the flight level (so you don't have to compensate for trajectory when aiming). That, I would think, would require the centre of gravity to be just behind the geometric centre. (Of course, arrows are sometimes fired up so they travel a greater distance and hit the enemy from above - that would have a different optimal lift, although to get maximum range I would thing it would still want the centre of gravity behind the geometric centre.) --Tango (talk) 19:31, 16 November 2009 (UTC)

Google finds many sources for the "point planing" claim and 9% figure but I leave it to others to decide if any meet WP:RS. Cuddlyable3 (talk) 20:57, 16 November 2009 (UTC)

Almost all those hits look like Wikipedia mirrors to me. --Tango (talk) 21:41, 16 November 2009 (UTC)

Has anyone found a good way to exclude those pesky mirrors from search results? A lot of them don't even say where they got it from so a simple -wikipedia doesn't work. —Akrabbim^talk 22:32, 16 November 2009 (UTC)

If you only want to exclude mirrors of a particular article, just choose a sentence from the article that doesn't sound likely to appear in other articles by change and do -"that sentence". --Tango (talk) 22:35, 16 November 2009 (UTC)

However, "-" terms don't always work in Google if the page uses frames. I think it applies the search criteria separately to each frame but returns the whole page. Unless it's changed since I asked about it and they answered. --Anonymous, 23:52 UTC, November 16, 2009.

Yes, there is a lift force that acts on arrows. There is also lift on crossbow bolts (especially those bolts that have fletching), but the lift is not as significant there.

The primary purpose of the fletching on an arrow is to provide stability. The stability is the strongest in the case of a helical fletch, which imparts a strong rotation around the roll axis. However, a helical fletch results in a slower arrow, and can cause problems with the fletching clearance on the arrow rest. For that reason, a straight fletch is often used, or an offset fletch, which is intermediate between a helical and a straight fletch.

In addition to stability, the fletching also provides lift. Fletching is not shaped like an airfoil, as a glance at the pictures in the fletching article will show, but that's not necessary for lift to occur.

To visualize the forces involved, it's convenient to first think about a horizontal arrow that you just drop, and then consider how that picture changes due to forward motion of the arrow. That won't work well quantitatively, because Bernoulli's principle makes life complicated, but it will at least help to picture some of the physics involved qualitatively.

When you just drop a horizontal arrow, the air resistance on the arrow causes an upward force, especially on the fletching, that wouldn't exist if the only force involved were gravity. That upward force is considered to be drag, which is defined as the component of the aerodynamic force acting opposite to the direction of the arrow's motion, which in this case is downward. Now suppose the arrow also has a horizontal component to its velocity. The upward aerodynamic force still exists, but now that upward force is mainly considered to be lift, since that's defined as being the component of the aerodynamic force that's perpendicular to the arrow's direction, which is now mainly in the horizontal direction. The fletching doesn't have an airfoil shape, so with a straight fletch and an arrow moving purely horizontally (implying a zero angle of attack), there would be no lift. But during the second half of the arrow's trajectory, at least, the arrow is also falling, and the air's resistance to that vertical motion counts as lift.

The quarrel article gives a poor explanation of why an arrow's center of gravity is placed where it is. The reason is that it's a tradeoff between lift and stability.

First, consider how the arrow's center of gravity affects lift. Suppose most of the arrow's mass was right near the tip. Now if you hold the arrow horizontally and let go, the tip of the arrow will drop faster than the nock end, because the upward force on the fletching is in this case much more effective at holding up the nock end of the arrow than the tip. Now consider the same arrow, with the tip still sagging below the nock end, but now with also a horizontal motion to the arrow. Due to the attack angle of the fletching, there isn't going to be as much lift on the arrow, or the lift might even be negative. So the arrow's going to take a nosedive. In contrast, if the arrow's center of mass was back far enough that it stayed horizontal when it was dropped, the loss of lift would be avoided. So for the sake of lift, it's good to keep the center of mass back away from the tip.

Now, consider how the arrow's center of gravity affects stability. Suppose most of the arrow's mass was in the nock, behind the fletching. In this extreme situation, the inertia of the nock tends to keep the nock going at a constant speed, while the drag on the fletching works to make the fletching part of the arrow lag behind. So the forces on the arrow favor the arrow turning around, in obviously a completely unstable situation. As the center of mass is moved forward, the arrow's stability improves, with the maximum stability occurring when the center of mass is at the tip.

Trading off keeping the center of mass away from the front for the sake of lift, and keeping the center of mass away from the back for the sake of stability, leads to a (somewhat empirically determined) optimal compromise between the two.

For a good discussion of the technical details of arrows, go to here, and click the "Archery Technical" link. The "Fletching Arrows" and "Arrow Rotation" articles are particularly helpful toward this question. Red Act (talk) 01:59, 17 November 2009 (UTC)

Thank you for a very clear explication of the issue! Wikiscient (talk) 21:10, 17 November 2009 (UTC)

Dreaming

Why does it seam so realistic, as to be virtual reality?Accdude92 (talk to me!) (sign) 20:28, 16 November 2009 (UTC)

No one can tell you that it's all nonsense without waking you up, so what else can you believe? Cuddlyable3 (talk) 21:01, 16 November 2009 (UTC)

If it seemed unreal then you could pass off whatever messages your subconscious is giving you as being unimportant. Vranak (talk) 22:48, 16 November 2009 (UTC)

This is a Reference Desk, so let's at least attempt to supply some references, people. My only reference is the obvious Dream article which seems to have a lot of problems and does not address your excellent question. It has many, many links to other interesting articles. Comet Tuttle (talk) 23:07, 16 November 2009 (UTC)

Freud, subconscious, ego. I thought this stuff was common knowledge! Vranak (talk) 01:58, 17 November 2009 (UTC)

I have to point out that Virtual reality is not nearly as realistic as dreams. Not yet, anyway. APL (talk) 23:41, 16 November 2009 (UTC)

Don't forget that it's not your eyes that see during the day, it's your brain. If a dream is just a series of images created by your brain, well then that's no different that what happens when you look at something normally. While awake, you know and can tell the difference between what you are seeing and your imagination (the latter is probably hampered by the former) but you don't have that luxury while asleep. ~ Amory (u • t • c) 23:53, 16 November 2009 (UTC)

That's a good point. It ties into the ideas of some contemporary neurologists (Damasio, Ramachandran), who say that memories of sensory experience seem to activate the same brain centers as actual physical sensations. But memories usually seem less real because we have a constant stream of more vivid sensory information coming in to contradict them. If new sensations stop coming in (sensory deprivation, phantom limbs, possibly other neurological conditions like schizophrenia) we can't make that distinction anymore, and we experience convincing hallucinations. Neat stuff. Indeterminate (talk) 07:33, 17 November 2009 (UTC)

microwave cooker question

What would happen to a person who is standing in front of your standard home microwave for 2 minutes if it was running with the door open? I presume most of the microwaves are focused towards the center of the device and you would only encounter a few stray bits that were reflected? Googlemeister (talk) 21:16, 16 November 2009 (UTC)

The Wikipedia article on Microwaves leads me to believe you might get burns and the radiation could possible cause cataracts, though it seems no long term effects (other than tissue damage) would be suffered. Obviously nothing good can come of this, and since it is non-ionizing radiation, there's no way to get super powers 206.131.39.6 (talk) 21:27, 16 November 2009 (UTC)

Someone with metal or electrical implants might fare worse. Before microwaves were properly shielded they posed a threat to people with pacemakers. APL (talk) 21:30, 16 November 2009 (UTC)

Two summers ago I was living in a place with a shared kitchen and I used the microwave a number of times before I realized that there was a hole two-inches in diameter in the front door. I never used it again, and did not develop anything afaict. ~ Amory (u • t • c) 23:49, 16 November 2009 (UTC)

How could an infinite universe expand?

As far as I understand it the possibility of an infinite universe has not yet been removed from the drawing board but how would this play into the big bang and inflation, can infinity originate from a point and can infinity expand?Bastard Soap (talk) 22:22, 16 November 2009 (UTC)

If the universe is infinite then it as always been infinite. At the big bang it wouldn't have been a point of infinite density, it would have been an infinite volume of infinite density. However, the observable universe (all the space light has had time to reach us from) is definitely finite, so that would have been a point. People often refer to the observable universe as simply "the universe" (since it contains everything that can have any effect on us, meaning we can just ignore anything outside it), which is the cause of this confusion. --Tango (talk) 22:26, 16 November 2009 (UTC)

Think about all the real numbers in [0,1]. They are uncountably infinite. If you take a new set, 2[0,1], it is "larger", yet it is still infinite. You can do the same thing with an unbounded set such as [0,$\infty$). Cardinality theory might help you. -Craig Pemberton 22:54, 16 November 2009 (UTC)

The OP wasn't asking about different sized infinities, but rather how something of zero size can being infinite, which is a good question. Also, what makes you think the OP understands interval notation and terminology like "unbounded set"? While they might well do, it is best not to assume certain prior knowledge without good reason. --Tango (talk) 23:30, 16 November 2009 (UTC)

As BenRG puts it, universal expansion is just "stuff moving away from other stuff". Think about it that way and it shouldn't be so confusing. --Trovatore (talk) 23:03, 16 November 2009 (UTC)

An infinite volume of infinite density? That stuff is still on the drawing board? Doesn't that involve infinite energy?92.251.33.207 (talk) 19:30, 17 November 2009 (UTC)

Does it bother you that an infinite universe might have an infinite energy? Why? Dauto (talk) 19:52, 17 November 2009 (UTC)

Wouldn't infinite energy rule out a final heat death? Googlemeister (talk) 21:36, 17 November 2009 (UTC)

We need Stephen Hawking for this question. Is Stephen Hawking in the house? Bus stop (talk) 21:45, 17 November 2009 (UTC)

Dauto is it being picky now to expect the universe to have finite energy? Universes these days, going to hell in a handbasket I tell ya!! Must be that rock music and violent video games! Can you have the positive and negative forces equalling themselves if mass is infinite? Googlemeister seems to me that if the universe can expand from a state in which every god damn piece of it is undergoing fusion to the current state, it must also be able to expand to ultimate heat death state, at least my common sense suggests so, don't know if the universe is laughing maniacally at my puny notions though.193.188.46.64 (talk) 11:31, 18 November 2009 (UTC)

Why isn't more money spent on SETI?

Why isn't more money spent on SETI, or a similar search for extraterrestrial signals? Although there is no guarantee that there are other intelligent civilisations, or that they would broadcast information that we could use in a short timeframe (rather than us having to make contact and then wait decades, or hundreds of years) - it would seem that the potentially massive technological benefit if we happened upon a broadcast of an advanced civilisation would warrant a bit more of a gamble. Billions, likely trillions, are spent every year on various kinds of scientific research, whereas it seems that SETI has a budget of around $500,000, and finding this stream of information could bypass all of that other spending. On a similar subject, is there an organised effort to transmit our knowledge out into space? I guess that it is likely that any civilisation receiving it would likely not be much less advanced than us, so it may be that our knowledge would not be useful in a pure technological sense, but would be in an athropological sense. I guess the above reasoning for spending money on SETI could also be applied to the development of AI, but it seems that workable that advances our knowledge AI is many, many years away, whereas that signal from the clever aliens could be available right now. QuickSnow (talk) 23:14, 16 November 2009 (UTC)

On the former point, it all comes down to the likelihood of success (small), the enthusiasm for donating money to it (modest), and the political difficulties of dumping public money into a program that has absolutely no realistic prospects for public rewards (difficult), and the fact that trying to communicate with extraterrestrials is rightly considered political poison (crank stuff). All of this, of course, avoids the fact that most people think there are more pressing uses for money (and there are a lot of scientific competitors out there in the "long-shots that could actually pay off" category). Add to it a squeamishness about the fact that meeting extraterrestrials does not, on the face of it, sound like the kind of thing humans would be very good at (how often has the encountering of one advanced civilization with a less advanced one gone well for the former?). On the latter point, see Arecibo message. --Mr.98 (talk) 23:29, 16 November 2009 (UTC)

Transmitting our knowledge into space might not be a good idea. If we ever contact and successfully communicate with aliens we're going to want something to trade with. APL (talk) 23:39, 16 November 2009 (UTC)

What if we're the advanced civilization and find a less-advanced one? The cost of sharing all of our technology could destroy our economy... Seriously though, SETI and similar programs don't get a lot of play because it's hard for people to see the benefit. In the long run, yeah there might be something but compared to that, living on Mars is right around the corner. People would rather see money go towards other things, and it is usually hard to justify spending billions on SETI instead of AIDS or other medical research that will have a much larger benefit much sooner, or any of a thousand other projects. ~ Amory (u • t • c) 23:46, 16 November 2009 (UTC)

I would expect any civilisation we made contact with to be more advanced than we are - we have had the ability to send and receive messages between stars for only a few decades (and even now we can only barely do it). Chances are slim that we would make contact with another civilisation during those few decades where they are less advanced than we are now.

However, regardless of who is we make contact with, we won't get any meaningful communications for a long time. The nearest civilisation might, at best, be 20 light years away, that means a 40 year round trip for any message. The first few messages will probably just be establishing a language to communicate in (it is possible the first message sent will be able to teach a usable language to the other civilisation, but I would expect a bit of trial and error to be required - as we discussed on the Language desk a few days ago, it is very difficult to learn a language (even one designed for the purpose) without 2-way communication. So it would likely be centuries before we could exchange technology. Getting funding for such long term projects is very difficult. Public funding is difficult to get for anything that won't happen before the next election. You'll only get commercial funding if you can turn a profit within a few years, certainly within the lifetime of the investor. That leaves charitable donations and you'll get limited amounts that way.

All that said, there is actually quite a lot being spent on SETI. Consider the recently launched Kepler Mission. That wasn't cheap. While it isn't solely devoted to SETI, discovering terrestrial planets would make it much easier to know where to look for ETIs (or where to send messages to them on spec).

--Tango (talk) 23:55, 16 November 2009 (UTC)

I was imagining a one way communication in the sense that a civilisation mght decide to transmit some, or all (perhaps with the exception of information it thought could be dangerous to itself or the receiver), of its technological informaton along wth the means to decode/translate it, as a constant transmission on a loop. There's no proof that such a signal exists, but it would seem very likely that advanced civilisations do exist out there and perhaps it is likely that they would choose to send such a signal (purely for altruistic purposes, no different to one country sharing its technology with another, simply for the benefit of the receiving country). I can understand that spending billions on this might not be politically sound, but $500,000 a year seems very low (I take on board your point about the Kepler mission though), as there are a lot of people who would spend close to that on a new car. When you take into account that tapping into such a signal would possbly replace decades (or perhaps even hundreads or thousands of years of research)it would seem that somebody somewhere would take a slightly bigger gamble (maybe not with public funds, but with private ones perhaps). QuickSnow (talk) 00:21, 17 November 2009 (UTC)

Finding a way to transmit a message containing instructions to build advanced technology without any pre-existing common language would be very difficult. Anyway, the receiving civilisation would need to technology to receive the message. Assuming a similar technological progression to ours, that puts them at no more than a few decades behind us, we wouldn't have much to teach them, probably nothing. Another issue is that people don't like to devote time and money to something that they won't know worked - we would need a reply to know we had achieved anything, so that's still going to take more than a lifetime for anything but the nearest stars. Also, working out what technology wouldn't be dangerous would be hard - even the simplest technologies can be harmful in the wrong hands. --Tango (talk) 00:59, 17 November 2009 (UTC)

I'm not sure why you think it is "likely". As the Drake equation does a good job of showing, there are a lot of probabilistic factors involved in whether there are even civilizations out there that could communicate with us during the tiny (tiny!) period of geologic history that we have had the ability to listen for them. Taking those and then saying, "so what are the odds that said advanced civilization has decided to broadcast their information to us with a strong-enough signal to be detected and on a continuous loop over the course of at least hundreds of years?"... to me, it doesn't look very likely. The biggest problem here is time itself—look at the history of just our own planet, and how long our civilization has been able to do this kind of thing. Now extrapolate a little bit and say that any civilization that can really grok radio-wave transmission is going to also, within a century or so, grok nuclear weapons and genetic engineering. Now extrapolate the likelihood of any given civilization to survive in a world where there are creatures that grok nuclear weapons and genetic engineering—how many centuries of a "window" does that give you before your civilization can no longer send or receive signals? Much less if we postulate them having anything like politics. Obviously all of this is intangible—we don't know how likely our situation is, much less theirs—but it does seem to imply that there is a much better chance that there is no one out there sending/listening at the same time we can send/listen. --Mr.98 (talk) 00:59, 17 November 2009 (UTC)

I hear this "alien civilisations will probably destroy themselves" argument a lot. The evidence doesn't support that. 100% of species known to have achieved civilisation are still going strong. --Tango (talk) 01:49, 17 November 2009 (UTC)

Human societies have regularly collapsed, e.g. Amazonian civilisations, Ur, Easter Island. So the premise is that if human societies can collapse so easily, so could alien civilisations. See our articles on Societal collapse, Risks to civilization, humans and planet Earth, Existential risk and Extinction event. Fences&Windows 03:35, 17 November 2009 (UTC)

I was careful to speak in terms of species. Human societies and civilisations have certainly collapsed, but they have always been replaced by others. --Tango (talk) 04:03, 17 November 2009 (UTC)

Assuming an alien civilization's lust for bandwidth is similar to ours, they compress their data, which is virtually indistinguishable from background noise. A Quest For Knowledge (talk) 03:50, 17 November 2009 (UTC)

Except it is concentrated in a specific band. However, that only refers to us overhearing their internal communications. It is more likely that we could detect signals intentionally sent into space (we are moving towards wired communication for long range communications so it is likely that other civilisations will do the same, so they would only send out significant amounts of radio pollution for a few decades, we're unlikely to be looking for them during that slot). They would hopefully start with sequences of primes or something else that would stand out from noise very clearly. --Tango (talk) 04:03, 17 November 2009 (UTC)

"It is more likely that we could detect signals intentionally sent into space". Really? Given that a) Homo Sapiens is the only known species who have intentionally attempted such a communication, and b) they've only attempted it once, what is the likelihood that another species would so such a thing? A Quest For Knowledge (talk) 04:28, 17 November 2009 (UTC)

Perhaps it is unlikely that another civilisation will send such a message, but it is even less likely that we'll detect an unintentional message. With the amount of noise we're sending out at the moment and the strength of our radio telescopes we could only detect ourselves if we were at best one light year away, so we could only detect the noise from other civilisations if there is much more of it than we emit and it looks like we aren't going to emit much more than we are now (since we're moving towards wired communications for long range things - ie. the internet vs. regular TV and radio). --Tango (talk) 04:48, 17 November 2009 (UTC)

And that signal power would need to be squared to double the distance right? Googlemeister (talk) 17:18, 17 November 2009 (UTC)

Not quite. Power needs to be multiplied by x² to multiply the distance by x, so you have to quadruple power to double distance. I expect that is what you meant. --Tango (talk) 18:02, 17 November 2009 (UTC)

You all forgot to mention another explanation. It is not scientific (potential benefit and probabilities) or economical (cost effeciency) but political, there is conspiracy in high level government circles to conceal the information that the ETI has been already found and possibly contacted. (Igny (talk) 04:59, 17 November 2009 (UTC))

We didn't all forget - we're all part of the conspiracy. -- Scray (talk) 06:07, 17 November 2009 (UTC)

You were part of it. I'm sure the black helicopters will be arriving soon. --Tango (talk) 08:19, 17 November 2009 (UTC)

Thanks for the warning. I was beamed out by my "friends" just in time. -- Scray (talk) 00:29, 18 November 2009 (UTC)

Somebody forgot a small tag close. Or maybe it was... abducted? Nimur (talk) 01:02, 18 November 2009 (UTC)

November 17

Name of process in which complex material things appear from nowhere?

I've just forgotten this term, but I think it had "brain" in there somewhere. The idea is that in an infinite space, or infinite time, or both, you could have anything happen, including our world simply appearing out of nowhere 5 minutes ago. Myles325a (talk) 01:40, 17 November 2009 (UTC)

Infinite monkey theorem? Mitch Ames (talk) 02:06, 17 November 2009 (UTC)
(That's complex structured data of course, not real physical material) Mitch Ames (talk) 02:19, 17 November 2009 (UTC)

Maybe something to do with brane? DMacks (talk) 02:17, 17 November 2009 (UTC)

Boltzmann brain -- Coneslayer (talk) 02:26, 17 November 2009 (UTC)

OP myles back. Yep, it's Boltzmann's brain (or brane) alright. Thanks. Myles325a (talk) 03:06, 17 November 2009 (UTC)

'For God, all things are possible'. Vranak (talk) 17:06, 17 November 2009 (UTC)

Why is urea planar?

I've drawn the Lewis dot structure of urea, and I just don't understand how it can be a planar molecule with a double bond between the carbon and the oxygen. Why don't the two nitrogen atoms have tetrahedral structures? Is there a double bond that resonates among the O-C and C-N bonds? What's going on here? —Preceding unsigned comment added by 134.10.29.252 (talk) 05:08, 17 November 2009 (UTC)

If we're talking about the configuration of urea around the central carbon atom, it would be expected to be trigonal planar since there are no unpaired valence electrons (using one of the simplest approaches to molecular geometry). Of course, if you mean the amine groups, they will have tetrahedal configuration. So, the entire molecule is not planar, but the carbon is.Thanks Jayron32 for setting me straight below, sloppy work on my part. -- Scray (talk) 06:00, 17 November 2009 (UTC)

The lone pair on the amine nitrogens can enter into conjugation with the pi-bond in the C=O. Lone pairs are not confined to any one geometry, so the amines can take whatever geometry will produce the lowest energy configuration. In this case, the ability for the unbonded pair on the amines to enter into conjugation means that the amins will take on sp² hybridization, and the lone pair will occupy an unhybridized "p" orbital. As a result, the entire molecule will be planar. --Jayron32 06:13, 17 November 2009 (UTC)

To Scray: Its an easy mistake to make. If there is not a neighboring sp² carbon to conjugate with, then amines will take the standard tetrahedral sp³ shape, since that is the lowest energy configuration normally. However, the ability of unbonded pairs in the valence level to move freely, and thus change the geometry of the rest of the molecule, is what makes molecules like Imidazole planar (and thus aromatic) as well; the carbon-only analog, Cyclopentadiene, is clearly NOT planar or aromatic. --Jayron32 06:47, 17 November 2009 (UTC)

I was surprised you used Cyclopentadiene as an example - it seems less than "clearly" non-planar. Our article say's it's planar, as reflected in the Talk page discussion. -- Scray (talk) 12:00, 17 November 2009 (UTC)

The carbons are in a plane, but the hydrogens attached to the non-double-bonded carbon (the sp³ carbon) are not in that plane. Thus, while the ring part of the molecule is in the same plane, the whole molecule is not. This is different from Imidazole, where every single atom is in the same plane. --Jayron32 15:00, 17 November 2009 (UTC)

Resonance in amide functional groups is a pretty important thing...it's one of the reasons proteins are fairly stable (one of the most stable types of acyl group). The result—the C–N bond looks a bit like a double-bond—affects the geometry of protein backbones (like an alkene C=C, a C=N cannot rotate freely the way a single bond can). DMacks (talk) 07:00, 17 November 2009 (UTC)

What is a scientific body of national or international standing?

On Scientific opinion on climate change, we're trying to create a FAQ so the watchers and frequent editors don't have to answer the same questions over and over. One such question is What exactly is a "scientific body of national or international standing"? I've posted the answer I came up with here on the article's talk page. However, I am not a scientist of any kind, so I'm not sure if it's accurate. Any comments, suggestions, or feedback I can get from any scientists out there would be greatly appreciated.

An Academy of Sciences or a scientific society that maintains a national or international membership, and that is well-regarded within the scientific community could be said to be of "national or international standing." Discerning how well-regarded a particular scientific body is requires some familiarity with the scientific community. However, in general, this can be determined by the impact factor ratings of the body's journal as provided by Journal Citation Reports. The journals Science, from the American Association for the Advancement of Science, and PNAS, from the US National Academy of Sciences, are considered amoung the world's most influential and prestigious.[11][12][13]

Thank you.--CurtisSwain (talk) 10:14, 17 November 2009 (UTC)

Well, you may need to be clear whether you mean prestigious in terms of membership, or prestigious in terms of publications. The two are somewhat correlated but not synonymous. For example, NAS membership is highly selective, while membership (as opposed to "Fellow"-ship) in AAAS and most such scientific societies is essentially open to any graduate in the field. On the other hand NAS's sister societies National Academy of Engineering and Institute of Medicine, while being selective, do not publish any journal; while prestigious and high impact journals such as Cell (journal) and Nature (journal) are published by private companies. Finally, the prestige of a society depends on its relevance to a particular field; so IEEE may not be as well known as NAS and the Royal Societies, but when it comes to wireless communication standards, its opinion and publications are more relevant than theirs. Abecedare (talk) 10:37, 17 November 2009 (UTC)

For the UK, probably the best suggestion would the the Royal Society. --Phil Holmes (talk) 10:39, 17 November 2009 (UTC)

Yes, figuring out the best examples is easy - most national academies of science qualify. The question is where to set the lower level. Looking at a fairly harmless field, I'd say AAAI qualifies - what about AAR or FLAIRS? On the one hand, FLAIRS is a Florida group, but both AAR and FLAIRS organize internationally attended conferences. --Stephan Schulz (talk) 17:11, 17 November 2009 (UTC)

Your efforts are noble, but they may be in vain; essentially, you're trying to draw the bottom demarcation line of the "gray zone," which is inherently subject to debate. Take a look at Wikipedia:Reliable sources for previous consensus opinions about how to do this. Nimur (talk) 01:08, 18 November 2009 (UTC)

Further digital television enquiry

This is a UK-related TV problem. I posted a few weeks ago about a solution for digital television in my home and had a useful answer, though not the one I was hoping for. I'm still finding it really hard to get objective information about the best solution for my needs. All I really want is to be able to get TV into several rooms in the house (3 rooms at least) in a way that different channels can be watched simultaneously. Only looking for the main free-to-air channels: BBC1 to 4, Channel 4, ITV. We already have digital co-ax running from a central point to those rooms, so distribution should in theory be possible. At the moment we are with Virgin Media and I have a quote for adding two extra digiboxes (installation plus extra subscription), but I want to work out if Freesat is a better option. Not considering Freeview due to poor reception in the area. At the same time, we want to replace two old analogue TVs with new ones. If we get a Freesat dish, then presumably we can distribute the signal around the house easily enough, either with the current (powered) connections, or with a distribution box that I have seen on the Maplins website? Then should the new TVs be Freesat TVs rather than normal digital TVs? They are much more expensive. I assume that normal digital TVs can actually be used in a Freesat system, since analogue ones can. But what about HD? Most sets sold at the moment are HD-ready, but will a typical HD-ready digital TV receive Freesat HD, either now or in the near future? Many thanks if you have borne with this long explanation and can understand where I have got to. The idea of queuing in Maplins for twenty minutes and then having to go through all this to one of their vendors is a bit daunting. Itsmejudith (talk) 11:44, 17 November 2009 (UTC)

I can't answer your query directly, but you may wish to have a look at Digital Spy forums: here's a link to the Virgin Cable one [14] --TammyMoet (talk) 12:23, 17 November 2009 (UTC)

And I Am Not An Expert, but my understanding is that with Freesat you need a tuner for every TV you want to use to view content. So if you have 3 rooms, then you will need a Freesat dish and LNB with at least 3 (I think 4 is common) outputs. These are distributed (I think with co-ax) to where the TV is. You can then either have a Freesat TV (they are more expensive because the satellite tuner is more expensive) or a "normal" HD one with HDMI in. If you get a Freesat HD tuner, I would expect it to have HDMI out, and so you connect them using that. You then have HD sent from the tuner to the TV where you can view it. If you don't have HD/HDMI on the TV, you could use SD with a SCART cable. Think this is accurate and Hope It Helps. --Phil Holmes (talk) 12:32, 17 November 2009 (UTC)

Does help, thanks both. I also spoke to the local Maplins store on the phone, and they are recommending buying a lot of equipment, so it may work out better to stick to Virgin in the short term at least. The devil you know... Itsmejudith (talk) 13:45, 17 November 2009 (UTC)

Bear in mind that TVs (e.g. Panasonic) are starting to appear which have both Freeview and Freesat receivers built-in. Bazza (talk) 14:13, 17 November 2009 (UTC)

Can confirm some correct data above - 3 TVs on Freesat need a dish with a Quad (4) or Octo (8) LNB (and a cable from the dish to each TV - you cannot split them!) A Freesat recorder also needs it's own cable (and if it's a dual tuner, then it needs 2 cables!) Most Freesat TVs have Freeview as well - hence the high price. Remember that when analogue goes off the digital signal will be much stronger - I'm on Lancaster at 200W, last year we lost a whole day's TV while they modified it to be able to go to 2kW on Dec 4th. Also note that a lot of TVs are marked as HD ready - but they only show 720p, only the more expensive ones will do 1080p. Also BBC & ITV intend to transmit a few HD channels on Freeview, but existing boxes/TVs might not be able to decode the signal without a software update. As you say, it may well pay to sit tight until the dust settles.  Ronhjones  ^(Talk) 19:53, 17 November 2009 (UTC)

To clarify, a 720p TV will still display a 1080 channel, just at the lower resolution. StuRat (talk) 22:55, 17 November 2009 (UTC)

The Mystery of Almond Milk

Hello! Almonds are pretty high in calories (nearly 200 per 1. 0z serving), like all nuts. So why is almond milk so low in calories? (30-50 cals per 8 0z. serving, depending upon brand). Since it's made from almonds, you'd think a cupful of almond milk would be about as many calories as a cupful of almonds, but it's not. O_o Anyone know why? 128.239.150.20 (talk) 12:43, 17 November 2009 (UTC)mimosa

It's not as much of a mystery as you might expect. The process produces an almond "pulp" that needs to be watered down to get the consistency of milk. This dilution reduces the fat by volume content. Fribbler (talk) 12:53, 17 November 2009 (UTC)

species diversity

How species diversity affect ecosystem —Preceding unsigned comment added by 61.2.193.124 (talk) 16:59, 17 November 2009 (UTC)

The more species you have the more complex food chain you get. The rest is very much depend on the kind of species, the enviroment they live in and etc. Humans proved time after time that they not fully understand how different ecosystems work (but they do know how to destroy them).--Gilisa (talk) 18:17, 17 November 2009 (UTC)

See Biodiversity. We have a brief article about the measure Species diversity too. Fences&Windows 00:41, 18 November 2009 (UTC)

Scar removal?

I was wondering if it was possible to remove a scar completely.

I know there are treatments to reduce the appearance of them but I was wondering if it is or if there might be potential with new medical technologies to remove scars completely.

Just emphasizing once again, if there is a way through plastic surgery or dermabrasion or something to remove a scar completely. If they are not too deep like the singer, Seal's and just look normal. —Preceding unsigned comment added by 139.62.167.186 (talk) 18:00, 17 November 2009 (UTC)

This sounds like a request for medical advice. The best person to seek to answer your question would be a dermatologist; without an actual live person to actually examine you, it would be impossible for anyone to make a determination on a correct course of action in your unique case. --Jayron32 19:07, 17 November 2009 (UTC)

That doesn't sound like a request for medical advice at all. He is asking if it is possible to do it, not wheather he should do it. I don't think it is possible. Dauto (talk) 19:33, 17 November 2009 (UTC)

Cosmetic surgery can do all kinds of things to reduce the visual impact of scarring, but I've never heard of anything that can remove them perfectly. --Tango (talk) 19:42, 17 November 2009 (UTC)

Given requisite time and resources, your body takes care of business. That includes scar tissue. It re-absorbs the collagen or something of that nature. Vranak (talk) 21:21, 17 November 2009 (UTC)

Really, because I have several scars, some of which I have had for 20 years or more. Googlemeister (talk) 21:35, 17 November 2009 (UTC)

This is why I also said 'resources'. Rejuvenative juices, if you will. Vranak (talk) 22:06, 17 November 2009 (UTC)

That's interesting Vranak. So what 'rejuvenative juices' are you talking about here. I also have a scar that is about 55 years old. Am I lacking some vital process in my body that should have corrected and repaired this or am I the same as the enormous majority of the human race who have life-long scars? Richard Avery (talk) 08:18, 18 November 2009 (UTC)

Flying birds that are very weak in the air

Which bird species, whilst being capable of flight is considered to be the worst, or weakest flier? I know that domestic chickens are technically able to fly but even without their wings clipped, they can just sort of flutter about four feet off the ground for a few seconds but I'm not counting these as they are not wild birds. --90.241.8.92 (talk) 18:12, 17 November 2009 (UTC)

Well, there are a large variety of birds that will not fly except when absolutely necessary. I don't know which is the weakest, but birds like peacocks and wild turkeys don't seem to be likely candidates for flying long distance. Falconus^{p t c} 19:20, 17 November 2009 (UTC)

I think you are looking for the albatross. It can glide extremely well, but it has a hard time with takeoffs. Googlemeister (talk) 19:30, 17 November 2009 (UTC)

I will second wild turkeys. Vranak (talk) 21:20, 17 November 2009 (UTC)

According to our article on wild turkeys, they are actually agile flyers, but don't fly far off the ground, and rarely for more than 400m.Falconus^{p t c} 21:28, 17 November 2009 (UTC)

Clapper Rail, Hoatzin. Fences&Windows 00:37, 18 November 2009 (UTC)

The Flying Steamer Duck is the only one of the four Steamer Duck species that can actually fly at all (hence its name): however (although our article doesn't mention this) while smaller specimens of the species can get themselves airborne, the largest and heaviest (usually adult males) cannot. More details can be found in this [15] post on Palaeontologist Dr. Darren Naish's excellent Tetrapod Zoology blog. 87.81.230.195 (talk) 11:29, 18 November 2009 (UTC)

Elevator stuck

A couple days ago, one of my friends was stuck on an elevator for 45 minutes. Apparently he and a large group got on on the first floor, and more joined on the second floor. It just stopped soon after. Unsurprisingly, 18 geniuses on board and 700lbs over the weight limit seemed to be a contributing factor. Anyway, my friend commented to me that it's good they didn't try to force the door open, because it may have caused the elevator to fall. The elevators break frequently here, so my guess is that they only told them that so that in the future they wouldn't try and damage the door mechanism. Surely the engineers would not have designed the safety catches to be dependent on closed doors? How does that work? Thanks, Falconus^{p t c} 18:17, 17 November 2009 (UTC)

Oh, I should mention that I am in the US. I know foreign elevators tend to be different. Falconus^{p t c} 18:20, 17 November 2009 (UTC)

Elevator#Cable-borne elevators is your friend: your suspicions are confirmed - the door thing is a canard. --Tagishsimon (talk) 18:21, 17 November 2009 (UTC)

Alright, thank you. That's what I thought. Now that statistic of 10000 out of 120 billion elevators having even minor anomalies is interesting. In this building, it seems someone gets stuck on an elevator weekly (usually it has little to do with overloading). Falconus^{p t c} 18:29, 17 November 2009 (UTC)

That's 120 billion elevator rides, not elevators. That many elevators would mean we would each have over 20, and I barely even own a dozen. :-) StuRat (talk) 22:43, 17 November 2009 (UTC)

Did your friend notice what was the weight rating and the person limit on the elevator? Edison (talk) 18:49, 17 November 2009 (UTC)

There is no posted person limit, but the weight rating is 2500lbs. I'm not sure if he noticed that or cared until they got stuck, at which point they decided to kill time by adding up everybody's weight. Apparently they totalled 3198lbs. Falconus^{p t c} 19:10, 17 November 2009 (UTC)

Might want to add up to a 5% error margin since a lot of people habitually under report. Googlemeister (talk) 19:28, 17 November 2009 (UTC)

If an elevator is overweight, it's supposed to stand and refuse to even close the doors. So how did they get stuck? It stopped midway? It closed the doors and wouldn't open them? The reason I ask is that it doesn't sound like being overweight was the reason they got stuck. If I were making an elevator I would add at least a 50% margin to the weight limit. Ariel. (talk) 21:47, 17 November 2009 (UTC)

I believe that it started to move and then stopped, leaving them stuck. It wouldn't surprise me though if it was just acting up anyway, because it does that stunt regularly (once a week or so) with only a couple people on it. It's somewhat ironic that these elevators are in the dorm of a very well respected engineering school, but yet they can't even figure out how to maintain them. Falconus^{p t c} 23:11, 17 November 2009 (UTC)

What's the strongest acid and the strongest base?

What's the strongest acid and the strongest base? Are they known to be the strongest possible, or have there merely been no stronger ones found? --75.6.4.21 (talk) 22:04, 17 November 2009 (UTC)

Fluoroantimonic acid. Vimescarrot (talk) 22:22, 17 November 2009 (UTC)

I'd also like to point out the redirect, strongest acid. Which makes the link for strongest base a little annoying. Vimescarrot (talk) 22:23, 17 November 2009 (UTC)

The answer is somewhat ambiguous, and depends on the definition of 'base' one prefers. Is a base a material which produces hydroxide ions when dissolved in water (the Arrhenius definition), a material which is a proton acceptor (the Brønsted definition), or a material which can act as an electron pair donor in a chemical reaction (the Lewis definition)? You can find some useful discussion in our article on superbase, however. TenOfAllTrades(talk) 22:51, 17 November 2009 (UTC)

Not sure if it is strictly the strongest under all definitions, but tert-Butyllithium is the strongest I have ever worked with. Its particularly unpleasant stuff. --Jayron32 23:08, 17 November 2009 (UTC)

The strongest acid is actually helium hydride Which will add a proton to any other material (apart from a proton). Graeme Bartlett (talk) 01:37, 18 November 2009 (UTC)

That's pretty exotic stuff, though, considering that you can't even keep it in a jar, since it will protonate the material making up the jar. It is literally impossible to handle in any way, and all its properties, save basic spectroscopic properties, are only known theoretically, and not empirically. We can say that it exists, but there is almost nothing else that could be said about it. As far as a substance a person could reasonably consider to handle, the strongest acid would be HSbF₆. --Jayron32 04:38, 18 November 2009 (UTC)

Pretty exotic indeed. I hereby invent hydrogen hydride (H₃), which would even outclass helium hydride :-) DVdm (talk) 08:28, 18 November 2009 (UTC)

Expansion of the universe

If we were to lay a rope from here to some distant galaxy and tie the end there, will it stretch and break because the distance increases but the electromagnetic force overpowers the expansion of the universe within the rope? Or will it just "lengthen" without stretching, expanding along the universe? --78.176.22.9 (talk) 23:12, 17 November 2009 (UTC)

The expansion of the universe is actually overcome quite easily by small forces such as gravity, the effect is not generally visible on anything smaller than the galaxy size; that being said, if you could attach such a rope to said galaxy and hold it to yourself, the two objects would be "bound" and thus would not be suject to the Metric expansion of space. There are some patrollers at these refdesks who hold that the so-called expansion of space isn't real; that its just the objects in the universe moving out into emptiness, but many cosmologists would disagree with that assessment. --Jayron32 00:18, 18 November 2009 (UTC)

So is that to say that the rope is strong enough that it could exert enough force accelerate an entire galaxy enough to overcome the expansion? Rckrone (talk) 00:30, 18 November 2009 (UTC)

In the light of what you have just said, does an object larger than galaxy-size expand within (along?) the space? The article states that the cosmological constant acts as a repulsive force even on individual atoms. So, am I right thinking that the rope that "binds" the galaxies together will be subject to tremendous forces? --78.176.22.9 (talk) 00:47, 18 November 2009 (UTC)

Tremendous forces, yes. But dark energy is largely irrelevant. You'd encounter tremendous force for the same reason that one sees tremendous force if you throw a lasso around a moving car. In other words, simply because it has a lot of momentum from it's existing motion and you are trying to stop it. Dragons flight (talk) 01:17, 18 November 2009 (UTC)

Attach a rope to anything that is currently moving away from you and there are only two outcomes. Either the rope exerts sufficient force to slow and stop the object it is attached to from moving further away (relative to you), or the rope breaks. Same holds at astronomical scales, except it is virtually certain your rope would break for any physically constructed rope. Dragons flight (talk) 01:02, 18 November 2009 (UTC)

Sorry, maybe I should rephrase the question, Forget the galaxies seperating and pulling the rope. Let's just have the rope. Does a rope or rod-like object millions of light years long expand/stretch ordinarily? I mean, does this object experience a force like being pulled from each end? Or does it expand "freely" without "being pulled", similar to relativistic length contraction? Like its "coordinates" moving or something? I'm not a native English speaker, I hope I made myself clear... --78.176.22.9 (talk) 01:33, 18 November 2009 (UTC)

Neither. It doesn't expand. Assuming you laid it out so that the rope was stationary to begin with (and ignoring the self-gravity of the rope) then it would stay that way. Dragons flight (talk) 01:38, 18 November 2009 (UTC)

The electromagnetic forces holding the atoms and molecules together would be more than enough to stop there being an expansion. Even if the rope were long enough for the two ends to be causally disconnected (that is, one end is not within the observable universe of the other end) it still wouldn't be ripped apart since the expansion on an atomic scale is tiny so it is easily overcome by the EM forces and if there is no expansion on small scales there can be no expansion on large scales, since the expansion between A and C is just the sum of the expansions between A and B and between B and C (assuming the points are in alphabetical order). --Tango (talk) 02:50, 18 November 2009 (UTC)

That doesn't seem quite right. The longer the rope is, the more either end is forced to accelerate in order for the rope to remain the same length. There's only so much acceleration the end of the rope can withstand before it simply breaks off. In other words, the very small amount of acceleration needed locally to overcome the tendency to expand is cumulative over the full length of the rope. Rckrone (talk) 03:21, 18 November 2009 (UTC)

Acceleration relative to what? What matters is acceleration relative to the bit of rope it is connected to, which is the bit right next to it. --Tango (talk) 03:28, 18 November 2009 (UTC)

Acceleration relative to a local inertial frame. Assume the first bit of rope is not accelerating in its frame (for example it's the center of the rope). The second bit of rope has to accelerate a little in its frame to stay next to the first bit. The third bit has to accelerate a little to stay next to where the second used to be, but the second bit is also accelerating away from the third bit due to the bond with the first bit, so the third bit has to accelerate twice as much to stay with the second bit. The fourth bit has to accelerate more, etc. Rckrone (talk) 03:46, 18 November 2009 (UTC)

A rope at rest will stay at rest. All local frames are equivalent and it doesn't need to accelerate anywhere. Now creating a rope at rest would be complicated since at least one end of the rope would appear to be moving very rapidly compared to the inertial frame of the local stars, but that's a problem of experimental design, not one of physics. All each bit of the rope knows is that it is at rest with respect to neighboring bits of the rope, and nothing about the expansion of the universe acts in such a way to change that. Dragons flight (talk) 05:22, 18 November 2009 (UTC)

Is it not the case that two very distant inertial objects that start at rest relative to one another will begin to move away from each other? I'm not an expert on cosmology, but that's the impression I got from articles like Metric expansion of space and Cosmological constant. I know there are still a lot of different theories, but I thought there was evidence that the expansion of the universe was accelerating, and not just caused by objects moving away from each other due to inertia. Is this incorrect? Rckrone (talk) 06:44, 18 November 2009 (UTC)

For Hubble expansion they never move. Cosmological constant type dark energy can be modeled as a psuedoforce $F={4\pi \over 3}Gm\rho r$ where ρ = 1×10⁻²⁵ kg/m^3. So at a megaparsec it is the same as applying an acceleration on the rope of order 1 ×10⁻¹² m/s^2, or thirteen orders of magnitude less than Earth's gravity. Any real rope would have sufficient tensile strength to resist such forces. So again, the ends wouldn't move appreciably (just enough to provide the tension to counter dark energy and then stop). Dark energy is only just observable if you consider objects at cosmological scales and assume if has been acting for billions of years. It is not a big force. Dragons flight (talk) 07:15, 18 November 2009 (UTC)

Quite true. My answer below was predicated on a rope (tether) of length comparable to cosmological distances; a thought experiment similar to that in Davis and Lineweaver's paper. Such a rope is not something that could ever be constructed physically. The main thing is... expansion isn't a force that would make things expand or contract. Galaxies continue to expand by inertia. Local concentrations of matter easily hold together by their own gravity regardless of the tiny hypothesized pressure from dark energy to accelerate expansion; our galaxy does not expand, for example. —Duae Quartunciae (talk · cont) 07:38, 18 November 2009 (UTC)

Whether inertial objects that start out at rest relative to each other will accelerate away from each other depends on whether the rate of expansion is accelerating or not. The point is, as many people have been saying, is that the expansion of the universe is not a force that makes things expand. It is a description of the large scale motions. Galaxies expand away from each other not because they are being pushed, but because they they started out expanding away from each other. So what about a really long rope that DOESN'T start out expanding or contracting? Expansion is not a force to push on it and change it. However, there are forces to consider; forces that also work to change the rate at which the universe in general is expanding.

In the models of the universe before dark energy was inferred, it was thought that expansion was slowing due to the effect of gravity to pull everything back together again. In this case, the very very long rope initially at rest with respect to itself (zero rate of change of proper distance all along the rope, to get technical) would start to compress (the second derivative of proper distance along the rope is negative). With dark energy, there is a kind of pressure that accelerates expansion; if dark energy is sufficiently dominant (as it appears to be in the current epoch) then the rope will start to stretch.

This does get pretty technical. The best account is probably Davis, Tamara M; Lineweaver, Charles H.; Webb, John K. (2003), "Solutions to the tethered galaxy problem in an expanding universe and the observation of receding blueshifted objects", American Journal of Physics: 358–364 {{citation}}: Cite has empty unknown parameter: |1= (help); Unknown parameter |volumne= ignored (help). —Duae Quartunciae (talk · cont) 07:06, 18 November 2009 (UTC)

Hmm.. what I understand from this is: The universe started with an initial push causing the expansion and that initial push exists no more. But we also have the dark energy, which pushes today and the expansion accelerates.

So, does the rope stretch? 78.176.22.9 (talk) 09:49, 18 November 2009 (UTC)

Yes; you can call the inflationary epoch the initial push; after which everything was flying away from everything else, and the space everything occupies increases in volume also. Once inflation shut down, the universe "coasts", with gravity working to slow the rate of expansion. But (apparently) there's still a tiny little bit of dark energy around, so that after 5 to 8 billion years or so, density has dropped enough that the effects of dark energy actually overcome the effect of gravitation from mass, and the expansion rate starts to accelerate again. Or at least, that's how it looks at present.

But as for the rope, it depends. As has been pointed out, dark energy is really really weak, up until you get to cosmological scales. pretty much any kind of force within a "rope" binding it together would be enough to hold it together just fine.... unless perhaps you have a rope hundreds of Megaparsecs long. The Davis and Lineweaver thought experiment may be more useful. Just think of the end points of rope. Take two galaxies, give them peculiar (local) motion so that the "proper" distance between them has a rate of change of zero, and then release them and just let them coast along with the rest of the universe. Ensure they are far enough apart that you can neglect gravity between them. You can image a rope between them if you like; but the question is, do they start to recede from each other, or remain at a fixed distance?

1. In the empty universe model, they remain always at the same distance from each other.
2. In a matter or radiation dominated universe, the expansion rate is slowing, and the two galaxies actually start to approach. In the long run, they pass through each other and then asymptotically approach the Hubble flow on the other side of the sky.
3. In a dark energy dominated universe (which is the present leading model), the two galaxies will start to recede from each other, with a very slow acceleration.

Full gory details in Davis and Lineweaver (2003). —Duae Quartunciae (talk · cont) 11:13, 18 November 2009 (UTC)

fermentation - what's the correct term for this?

Which is the correct term for one whose profession is fermenting? Fermenter OR fermentor? (I'm not interested in other synonyms) I already checked multiple dictionaries. ike9898 (talk) 23:25, 17 November 2009 (UTC)

This question stands a better chance of being answered at the Language Desk. You might try moving it over there. --Jayron32 23:46, 17 November 2009 (UTC)

Brewer. 75.41.110.200 (talk) 01:33, 18 November 2009 (UTC)

Narrower term of Brewer or Vintner. Graeme Bartlett (talk) 01:32, 18 November 2009 (UTC)

Dunno if it exists, but zymurgist would suit. From zymurgy. [16] --TammyMoet (talk) 11:05, 18 November 2009 (UTC)

snowboard jump equation/formula

if i were to snowboard straight off an 8 foot tall ledge at about 7mph how far from the ledge would i land given there tas no wind and i rode right off the edge w/o jumping?. what would the formula be for this? ihave been trying to find it but all the equation i have found are extremly complicated. thanks for the help --99.89.176.228 (talk) 23:27, 17 November 2009 (UTC)

The vertical motion and the horizontal motion can be considered separately. In the vertical direction you start with no velocity, but there's acceleration from gravity pulling you down (about 32 ft/s²). Given that figure out how long it would take to fall 8 feet. In the horizontal direction you start with a velocity of 7 mph (you should probably convert that to ft/s), with no acceleration. Figure out how far that would get you in the horizontal direction during the time it takes to fall. Rckrone (talk) 23:41, 17 November 2009 (UTC)

(edit conflict)Everything has the same acceleration downward while falling thanks to gravity, and that is 9.8 m/s². In order to figure out how far you would land you need to first figure out how long you would fall for, which is given by the equation h=.5at² where h is the height, a is the acceleration due to gravity, and t is the time taken to fall. Make sure your units are correct! 9.8 m/s² is roughly 32 feet/s². Next, you just have to multiply your horizontal speed by the time you have to move before hitting the ground (again, making sure your units are the same - convert mph to feet per second) and then you'd have a good estimate! ~ Amory (u • t • c) 23:41, 17 November 2009 (UTC)

It's slightly more complex than that. All decent snowboard and ski jumps are sloping, usually quite steeply, in the landing zone, so as to minimize the impact. Jumping onto a flat is quit difficult, unpleasant, and dangerous, especially if you start with an 8 foot drop. So for a real answer, we would need a better specification of the slope. --Stephan Schulz (talk) 00:07, 18 November 2009 (UTC)

No i wouldnt jump the ledge onto flat ground so me and my friend were going to make a landing ramp. i needed to know the distance so that i dont missjudge the jump and miss the landing.I also needed to know this so that i can angle the jump to minimize the impact of landing. Is there a straight clear forward formula to find all these things out such as a formula i can enter into a graphing calculator?--99.89.176.228 (talk) 01:00, 18 November 2009 (UTC)

All the equations you need are found at Trajectory of a projectile. It is probably worth calculating the sensitivities to various parameters, if you are really building a ramp - i.e. "what would happen if you mis-estimate the slope by 10%?" "What would happen if you miscalculate the initial velocity by 10%? 50%?" This is called sensitivity analysis and can become very complex, but you can do a simplified version by varying your inputs to the formulae. This will help you design a safety factor into your ramp. Also keep in mind that simplified ballistic equations don't account for non-point-like, non-spherical humans - you have significant air resistance, rotational inertia, non-rigid dynamics, etc. All of this should be considered - at least, in the simplest sense, by having a robust safety factor. It would be a big error to assume that you will exactly land at a particular spot unless you are a small marble in a vacuum chamber launched by a precisely calibrated launcher at an exact velocity and angle. Nimur (talk) 01:18, 18 November 2009 (UTC)

November 18

Fluoroantimonic acid

Is fluoroantimonic acid only considered the strongest acid because no one has discovered any stronger acid, or is it physically impossible for a stronger acid to exist? --75.50.50.76 (talk) 02:40, 18 November 2009 (UTC)

I;m not sure what you mean by "physically impossible". Acid strength is determined relatively; it is determined by how the acid reacts with other substances. Consider the model Brønsted–Lowry reaction:

HA + B^- <---> A^- + HB

The strength of two acids HA and HB are determined relative to each other such that if HA is the stronger acid, then the equilibrium above will favor the forward reaction, while if HB were the stronger acid, the equilibrium would favor the reverse reaction. There is a "standard acid equilibrium constant" known as K_a, which is calibrated for B to be water, and HB to be hydronium; however in practice HA and HB could be any two acids. Thus, to compare acid strength, you just compare how the equilibrium lies, and you can literally "rank" every acid against every other acid based on how well it reacts compared to each other. The acid at the top of this list is fluoroantimonic acid; there is nothing about the structure that would make a stronger acid actually impossible, its just that for every known substance so far, fluoroantimonic acid is the one at the top of the list. Hypothetcially, any number of substances could be discovered/isolated/created which may end up being even stronger; there is no theoretical upper limit to acid strength, since its not an absolute value; it is only a relative value. --Jayron32 04:30, 18 November 2009 (UTC)

Need derivations of the solar insolation inside earths atmosphere and latitude at any point

I need derivations of all insolation related parameters like latitude, declination and insolation itself...please help —Preceding unsigned comment added by 220.225.125.246 (talk) 03:53, 18 November 2009 (UTC)

There isn't much to derive; it's just trigonometry. The insolation is the solar constant times the cosine of the angle that the sun makes with the zenith. That angle depends on both the latitude and the day-of-year/time-of-day. We have a nice diagram of this effect in the insolation article. We also have a formulation for the position of the sun as a function of time and date. (If you want to derive this, it will be a matter of geometric projection of the orbital parameters of Earth - the math is not complicated, but there is a lot of it). Earth's orbit explains these parameters; ironically, they are derived by the inverse process - measuring the sun's declination and reprojecting it back to an orbital specification. So, you might as well take the solar declination formula at face-value, since it is basically an empirical (observation-based) formula.

As far as other parameters - are you working with a more sophisticated atmospheric absorption model? Usually, the effect of longer travel through the atmosphere is negligible compared to the geometric projection (that I described above), but you can read about optical depth if you want to try to apply that formula and estimate the total amount of gas between the sun and a particular location on earth. For this approach, you would also need an atmospheric profile model - you can look at Earth atmosphere to get some background. I believe there are several reference atmosphere profiles published by NOAA and the American Geophysical Union; I will try to dig up some links. Nimur (talk) 04:55, 18 November 2009 (UTC)

The "U.S. Standard Atmosphere" and the Jacchia's thermosphere profile are hosted at NASA Goddard's website; I know people who have used COSPAR parameters for pressure as a function of height; you can use these to estimate atmospheric absorption if you dare... this approach may require some integral calculus... but as I mentioned above, if you actually calculate it out, you will find that the optical depth variation with angle is negligible for most purposes. This is because the "longer paths" traced out end up traversing through the (sparse) high atmosphere. If you don't like these atmospheric profiles, our article has a list of other common atmosphere models; or you can create your own simple gas-density model based on the hydrostatic equilibrium approximation (e.g. exponential fall-off with height). Nimur (talk) 05:00, 18 November 2009 (UTC)

Dog Whisperer

On the Dog Whisperer last night (I'm in Edmonton, Canada), a woman is bound via wheelchair because of a 3 last name disease (Cabot is a name?). It affected her brother, mother and I think their dad. They died. Her leg muscles don't work that well, I think. What is this disease?174.3.102.6 (talk) 05:31, 18 November 2009 (UTC)

Charcot-Marie-Tooth disease? --TammyMoet (talk) 11:02, 18 November 2009 (UTC)

what canadian animal stores apples in the fork of branches ?

This fall, I've found apples (presumably fallen for nearby apple trees) stuck in the fork of branches in trees near my south-eastern canadian home and I'm wondering what kind of animal stores fruits that way ? The apples seem damaged on top, but sides and bottom look undamaged to me. They are placed 2 to 4 meters (6 to 12 feet) high in the forks of main branches of young trees, quite near the trunk. The tree trunks are 5 to 8 cm (2 to 3 inches) in diameter at that height and the branches are about 1 to 2 cm (3/8 to 3/4 of an inch) in diameter at the fork. The apples are all quite solidly stuck. 207.96.217.70 (talk) 05:45, 18 November 2009 (UTC)

Occam's Razor gut reaction - someone is placing those there intentionally to feed birds & small mammals. Just a guess, though. 218.25.32.210 (talk) 07:38, 18 November 2009 (UTC)

I would guess a squirrel. Normally they bury things, but an apple is too big, plus maybe it knows it would rot. I would guess it went to eat it, and got distracted, or in a fight and lost it. If it then got stuck it was unable to remove it, so just ate the top. Just a guess. Ariel. (talk) 09:49, 18 November 2009 (UTC)

Knife against bone / nails on a chalkboard

I've read the Wikipedia articles about nails on a chalkboard and psychoacoustics, but have another twist I'd like to share/ask about on the SciRefDesk. When I'm cutting apart raw chicken thighs, occasionally the knife will strike the bone at an angle. I find this kinetic sensation even more immediately revolting than nails on a chalkboard. I'm feeling physically uncomfortable right now just thinking about it. Note that I've never had any bad experiences with knives, been stabbed, lost a loved one to a stabbing, or suffered any other sort of event that might provoke an unusual psychological reaction to this particular situation. I've also noticed that at work when I slice the plastic seals off new watercooler bottles with scissors I feel vibrations/textures/whathaveyou quite similar to the knife into bone, and then of course the corresponding involuntary physical reaction is also quite similar. The nails-chalkboard example is an auditory stimulus, but mine with the knife is a kinetic stimulus - is this a personal quirk, or is there an equally well-recognized phenomenon for particular vibrations and such? Thank you! 218.25.32.210 (talk) 07:07, 18 November 2009 (UTC)

Directed graph condensation terminology

The strongly connected components of a directed graph form a poset. What is the terminology for lesser, greater, minimal, maximal components?

For example, some websites (strongly connected components made of pages (nodes)), can't be reached from the rest of the internet (have no hyperlinks coming back in). So in a sense this site is locally maximal, or "outgoing only". But what is the actual term? -Craig Pemberton 08:41, 18 November 2009 (UTC)

We have a glossary of graph theory which might help you, which suggests k-edge-connected graph may be what you are looking for. This is more a question for the Mathematics desk though. I'm not sure I really understand your question though, a poset does not have to be strongly connected and just because a graph is strongly connected does not make it a poset. They are two different things. SpinningSpark 10:06, 18 November 2009 (UTC)

Accuracy of Sonar?

I was just thinking, sonar works by sending out pings and then timing the time it takes to come back from different directions right? Is there a reason why you couldn't make sonar goggles, for seeing in total black conditions or something, or even being able to see through things sound can go through, or is there an inherant low resolution to it? What about radar? Gunrun (talk) 10:46, 18 November 2009 (UTC)