The best answers address the question directly, and back up facts with wikilinks and links to sources. Do not edit others' comments and do not give any medical or legal advice.
Are there any automated services that will convert doi's to ACS-style citations?
I really really hate tedious, mindless work such as this. John Riemann Soong (talk) 00:09, 14 November 2010 (UTC)[reply]
Here on Wikipedia, we have Template:doi and Template:cite doi. I believe "cite doi" will expand to a full citation - though I'm not sure how, I imagine it uses one or more web service APIs either provided by Wikipedia's tool server, or by http://dx.doi.org (the DOI resolving service). You could use the Wikipedia cite-doi tool to generate the citations, and then copy/paste (or screen-scrape, if you need the process to be automated). Note that there seems to be a few minutes of delay when using the cite-doi template while the plain-text is generated and later subst'ed by a bot. Nimur (talk) 04:12, 14 November 2010 (UTC)[reply]
Tensor of Inertia
My book says, without proof, that the tensor of inertia remains unchanged to first order for small angular displacements about the principal axes, but I don't think this is true. Don't the products of inertia gain a first-order factor? 76.68.247.201 (talk) 02:11, 14 November 2010 (UTC)[reply]
which obviously has first-order terms. What is true, though, is that the tensor of inertia viewed as a geometrical object (the ellipsoid of inertia) is symmetric around the principal axes. So, for example, the moment of inertia around an axis inclined from a principal axis doesn't vary to first order in the angle, since it's an even function of the angle. Probably that's what the book was trying to say (or did say?). -- BenRG (talk) 04:31, 14 November 2010 (UTC)[reply]
I'm sorry, but I don't follow :(. I've decided to take a few photos from my book, because I don't think it says what you're trying to say.
Here, the question asks to prove that the products of inertia are unchanged to first order...but they clearly aren't! This is important, because the authors use this result to derive Euler's equations.
Shouldn't there be another term involving the product of inertia? 76.68.247.201 (talk) 18:47, 14 November 2010 (UTC)[reply]
As far as I can tell you're right. Either your textbook is clueless or I am. It may be me. Can anybody else take a look at this? -- BenRG (talk) 10:22, 15 November 2010 (UTC)[reply]
I concur, the book looks wrong to me. Just looking at the first page, anyway, I get that, e.g., to first order in α, Ixy=-4mα, so unless I'm missing something, problem 7.11 b appears to be asking you to show something that isn't actually true. Red Act (talk) 11:16, 15 November 2010 (UTC)[reply]
So what does that imply about Euler's equations? Is there another reason why we'd ignore the products of inertia when finding how the angular momentum changes when an object deviates from its principal axes? 76.68.247.201 (talk) 14:35, 15 November 2010 (UTC)[reply]
You might want to try also asking this question on the Math Reference desk. Ginger Conspiracy (talk) 06:03, 17 November 2010 (UTC)[reply]
Looking for a talk that may have been featured on TED
I'm pretty sure that I saw this on TED talks, but either it's not there anymore, or I am remembering it wrong, but either way, I'm looking for a guy who made a speech about a program (an NGO?) that he was running on (west?) Africa helping to alleviate local desertification by introducing herds of large herbivores into fields periodically to allow their hooves to churn up the soil and their manure to fertilize. He talked about how modern agriculture usually pins overgrazing as a cause for desertification, when in fact historically large herds of herbivores would have periodically grazed small areas completely, allowing the plants to recycle and maintaining the ecosystem. Does this ring bells with anyone? I can't find the specific TED talk but I don't really need it if I could just find out the name of the guy. Thanks! 173.183.68.27 (talk) 03:25, 14 November 2010 (UTC)[reply]
Found it, not on TED though. The guy was Allan Savory if anyone is interested. 173.183.68.27 (talk) 04:23, 14 November 2010 (UTC)[reply]
Why large herbivores? Wouldn't goats do for this sort of thing? Ginger Conspiracy (talk) 08:07, 17 November 2010 (UTC)[reply]
It says that sound can exist as electromagnetic vibrations...but that isn't sound, that's light, no? Am I missing something? 76.68.247.201 (talk) 03:28, 14 November 2010 (UTC)[reply]
Sound can be defined two ways:
Pressure waves of a certain range of frequencies within a fluid medium
The perception caused by vibrations within the ear or other analogous sense organ.
The second definition is key, if you could generate signals to the ear by means other than pressure waves, perhaps one could define that as sound. However, I suspect that under normal circumstances that's unlikely. Sound information can be transmitted via electromagnetic vibrations (that's what radio is), but the information needs to be decoded and broadcast via a speaker of some sort. --Jayron32 03:33, 14 November 2010 (UTC)[reply]
Bear in mind that in the very high atmosphere or in outer space, atoms are typically charged. The solar wind is, for some reason I don't understand, a combination of electrons and protons rather than neutral hydrogen atoms. Thus any pressure wave in the medium is going to be involve variations in charge as well.
I am curious whether the various short sounds in the video represent actual changes over time in the medium, or whether they are spatially localized features that the satellite passes through on its orbit. Wnt (talk) 03:48, 14 November 2010 (UTC)[reply]
These "sounds of Jupiter" are electromagnetic signals. They are detected by an instrument (in this case, a VHF/UHF radio that flew on the Voyager probe. Those radio signals are measured at several megahertz - and they are mixed down to audible bands by a very common process known as heterodyning. Then, they are played through a speaker. So, if you could fly past Jupiter like Voyager did, and if you could survive "sticking your head out the window", you would not hear these sounds: first, they are not acoustic waves; and second, they are not in the audible frequency range. Interestingly, here on Earth, the equivalent radio-processes occur, but the relevant parameters of our planet's magnetic field are a bit different than Jupiter - so the very low frequency radio chirps here on Earth are at audible frequencies. (They are still not acoustic waves, though - so you still need a radio to hear them). Nimur (talk) 04:23, 14 November 2010 (UTC)[reply]
Also, for the advanced readers: there is such a thing as a magneto-acoustic wave - which is a unique coupling of electromagnetic (radio) wave into a pressure disturbance in a sparse plasma). However, the sounds we are hearing in this Jupiter demo-tape are not due to magneto-acoustic waves - they are actually due mostly to electron gyro frequency noise. Anyway, magneto-acoustic waves only occur in sparse plasmas, and the magnitude of the pressure-waves would be too small to be detected with an acoustic microphone - not to mention what would happen if you tried to put a human ear in that environment!) Nimur (talk) 04:26, 14 November 2010 (UTC) [reply]
This isn't my field, but the heterodyning you describe sounds like a cheap cheat, and contrary to what the video says are actual vibrations in the auditory range. I see that Voyager could detect ion acoustic waves with its instruments in the 50 Hz to 12000 Hz range.[1] I didn't look for the provenance of this YouTube recording to figure out exactly what is being measured, but I see no reason to think the video isn't right about them being, essentially, a sort of sound. Wnt (talk) 05:03, 14 November 2010 (UTC)[reply]
For further information, Magnetosphere of Jupiter is a very complete article. Yes, there is radio-emission in the VLF (audible base-band) range at Jupiter. I am pretty sure the sounds in the Youtube link are down-mixed UHF - but I may be incorrect. To find out for certain, you can compare to NASA's Jupiter Sounds archive - these recordings are each accompanied by a bit of scientific explanation. And if you're very interested, Imke de Pater (arguably the world expert on Jupiter's radio emissions, and planetary science in general) has a paper on Jupiter’s radio spectrum from 74 MHz up to 8 GHz and a website of her own on Jupiter sounds. Like a false color image, these sounds are "false-frequency" audio - the actual source data is pre-processed and output at a range that humans can hear. I would say that this process has limited scientific utility, but sure does sound cool. Nimur (talk) 05:32, 14 November 2010 (UTC)[reply]
I saw the date 1979 mentioned, which is when Voyager 2 passed Jupiter, and that article mentions a NASA "Symphonies of the Planets" 5-disk set, from which this audio should have come. It is possible to find out more about the datasets at [2] which has many records for Voyager 2 fluxgate magnetometer readings. Unfortunately, their information for the magnetometer (also linked from the Voyager 2 article) is now giving an error message. [3] describes "dual low field (LFM) and high field magnetometer (HFM) systems. The dual systems provide greater reliability and, in the case of the LFMs, permit the separation of spacecraft magnetic fields from the ambient fields. Additional reliability is achieved through electronic redundancy. The wide dynamic ranges of +/- 0.5 G for the LFMs and +/- 20 G for the HFMs, low quantization uncertainty of +/- 0.002 nT in the most sensitive +/- 8 nT LFM range, low sensor RMS noise level of 0.006 nT, and use of data compaction schemes to optimize the experiment information rate all combine to permit the study of a broad spectrum of phenomena during the mission. Objectives include the study of planetary fields at Jupiter, Saturn, Uranus and Neptune; satellites of these planets; solar wind and satellite interactions with planetary fields; and the large-scale structure and microscale characteristics of the interplanetary magnetic field. The interstellar field may also be measured." Now from the previous reference I take it that stellar winds do involve vibrations in the range of hearing, and the magnetometer is directly measuring some kind of buffeting at the spaceship itself, rather than at a distance by radio. The exact kind of wave, whether it's compression or transverse, I couldn't say from what I've read so far. Wnt (talk) 06:35, 14 November 2010 (UTC)[reply]
Just to clarify one thing: the key difference between acoustic- and magneto-acoustic wave is the mechanism of energy transfer. In the case of acoustic waves, the energy is conveyed by inter-atomic collisions. In space plasmas, the densities are far too low to sustain such aerodynamic/acoustic effects. So, energy is mediated between distant ions via ion/electromagnetic-wave interaction. Most of the time, these result in plasma oscillation. In some situations, this interaction can result in a propagating "pressure-front" in the plasma, but the pressures are still near-vacuum, so it's not quite like an ordinary sound wave in air. The question of measuring "at the spaceship" vs. "at a distance by radio" is moot - you are always measuring at the spacecraft. The question is whether the magnetometer is sensitive to ion pressure or magnetic fields - but from its name, it should be obvious that magnetometers measure magnetic field intensity (and typically, because of geometries, magnetometers are sensitive at ultra low frequency). Comparatively, an ion energy spectrometer would actually measure ion impingement; and a dipole electric field antenna would measure electric fields (because of geometries, a whip antenna will be sensitive at much higher frequencies than a similarly-sized loop magnetometer). The crucial piece of physics is that plasma-interactions describe the relationship between all three types of measurements - ion bulk motion, electric field, and magnetic field. Nimur (talk) 18:50, 15 November 2010 (UTC)[reply]
Very informative, thanks everyone. 76.68.247.201 (talk) 20:43, 15 November 2010 (UTC)[reply]
Middle-grounders on ID--What, If Any, Spokespeople Exist?
It's understood that the subject of what is called Intelligent Design Theory is dominated by those who assert their having already identified good evidence for external involvement in the origin, development, and/or internal workings of Earth and the life on it. What is the status of their claims in terms of whether they have produced even a single piece of purported evidence that has given the actual scientific community at large pause, and what is the nature of any more abstract debate that may be going on about the future prospects for finding such involvement? As the question of the heading asks, are there any substantially middle-of-the-road players who approach the topic holistically without submitting themselves to being committed to employing Occam's Razor?Julzes (talk) 03:37, 14 November 2010 (UTC)[reply]
There really aren't many. Intelligent Design isn't a particularly scientific approach towards working out the manner in which the world came to be. It starts with the premise that the Christian God created the world, assumes that to be true, then seeks to find evidence to support that. That particular approach is not very scientific, and most scientists who work in the fields ID also works in dismiss it offhand because of this. You would find many cosmologists, or evolutionary biologists, or geologists who seriously give it credence. Of course, you likely could find somebody, but the preponderance of respected scientists don't take it seriously in any way. However, please note that this doesn't mean that their aren't religious scientists, or that one must support the idea of Intelligent Design (as a specific theory) in order to be religious. I consider myself a rather devout Christian, but I have no pretense towards needing Intelligent Design in order to reconcile the current scientific understanding of the world, including evolution, the big bang, and anything else the ID people don't want to accept, with my religious view. --Jayron32 03:49, 14 November 2010 (UTC)[reply]
Few middle of the road people would want to associate themselves with the strong statements of intelligent design or creationism. There are other discussions which are relevant, but not easily related to the traditional debate. For example, the weakless universe thought-experiment sought to disprove the anthropic principle by showing that a less elaborate physics could produce a world like ours. But which side is which — does the anthropic principle show that humans, by possessing an "awareness" relatable in concept to the soul or to God, have participated in the process of creation? Or does the idea that the universe contains extra complexity and wonder unneeded for us to merely exist prove the fecundity of the divine imagination?
A concept which interests me is whether the slow, cold end of the expanding universe is truly a barren dustbin of history, or whether there could be interesting "chemistry" among the remaining small particles — or new ones — when the tick of the clock is a googol of years. For example, picture two neutrinos of opposing weak isospin slowly orbiting one another in empty space. Could the weak force hold them together, despite the short range[4] of its carrier particle, if you have 10100 years to wait for the particle to slip out and cross a vast range of empty space "unnoticed". I always see the Heisenberg principle stated as an approximation, after all. Whether the weak force can apply to them or not, or if simply gravity between these tiny particles keeps them clustered, is the angular momentum of the orbit that they make quantized in terms of ? Are there discrete photons or gravitomagnetic particles that might cross between them over vast lengths of time, allowing them to interact? There is something aesthetically appealing to me that our world as we know it is still only one of the first few "moments" of the Big Bang, and that a long succession of interesting worlds of physics and chemistry of ever colder temperatures and smaller particles and larger distances still await their time. If successor regimes of physics exist that are also capable of supporting interesting life and thought, then that would pretty much blow the anthropic principle out of the water, and hint rather strongly at some clever design behind the cosmos. I wouldn't say the absence of it is a disproof, however. Wnt (talk) 04:30, 14 November 2010 (UTC)[reply]
(ec):::The term "intelligent design" has come to exclusively mean a pretty narrow subset of religious beliefs that directly contradict scientific fact; these views tend to be pretty radical, so I agree with Jayron that there isn't really a "middle ground" for intelligent design. However, the phrase "intelligent design" can also be interpreted in other, more benign ways. Isaac Newton's description of a "clockwork universe theory" could be branded "intelligent design" - but it does not stipulate certain insane ideas like young earth creationism. There is scholarly debate - mostly in the humanities and philosophy, and not in the scientific community per se, about whether the universe is deterministic or random; and whether there is a role for a deity in our scientific understanding of the world. These could be classified as a "middle ground." But I would be very reluctant to label any theory "intelligent design" because that term has come to mean a very specific set of far-flung, radical Christian-inspired ideas. Nimur (talk) 04:36, 14 November 2010 (UTC)[reply]
Not quite the subject matter I was trying to address because of how contaminating the influence of ID on 'intelligent design', I suppose. Since I can expect to run up against an edit conflict if I try to fully present what I'm after, and since new Earth creationism has been singled out already, where is old Earth creationism in the debate (particularly with latitude given to the sense of 'create')? What of so-far unknown but plausible influences? Is there any attempt to comprehensively and coherently address plausible specific holes in scientific ontology, or is it entirely each discipline to its specific purview and each scientist to his or her own expertise (which it seems might leave a gap or gaps in reasoning or evidentiary search)?Julzes (talk) 05:51, 14 November 2010 (UTC)[reply]
I cannot see how there can be a "middle ground". Either there is or there isn't an intelligent designer. Pretty binary state of affairs there. And there is no point halfway between zero and one in a binary system. HiLo48 (talk) 05:57, 14 November 2010 (UTC)[reply]
I think you misunderstand the question. The poster is asking if there is anyone doing or proposing research into detection of intelligent design who is actually acting in good faith. The answer is none that I know of. No one has yet come up with a proposal for how to detect evidence of intelligent interference in the evolution of life. thx1138 (talk) 06:02, 14 November 2010 (UTC)[reply]
To do such research would require the hypothesis that there was an intelligent designer. See my comment above. HiLo48 (talk) 06:07, 14 November 2010 (UTC)[reply]
One can present a hypothesis and test it without having an opinion on its veracity. thx1138 (talk) 06:25, 14 November 2010 (UTC)[reply]
Unless the hypothesis is inherently untestable. Like say the existence of an omnipotent being who can break the laws of science at will. Googlemeister (talk) 16:08, 15 November 2010 (UTC)[reply]
There's an article specifically about old Earth creationism. Oddly, it doesn't address what to me seems like the most obvious way to reconcile religious and scientific ideas, which is to recognize that the time scale used in an author's prologue about the writing of a work is not the same as the time scale of the book itself. Just because Tolkien's works cover thousands of years in Middle-Earth doesn't mean it took thousands of years for him to write them, nor does it mean that the writing was in the same order as the plot. It is entirely reasonable in scientific terms to believe that our universe is a lovely four-dimensional sculpture with a splendid internal consistency of design, but that the author isn't finished with it yet. I would suggest that if you look very closely, some of the chisel-marks are still apparent; and it is not hard for anyone to see that there is still some sculpting to be done before perfection can be attained. But these things are primarily if not entirely visible in social terms, in the minds of men, rather than as aberrations in the fundamental rules of science; the purpose of the plan being, I would speculate, that when those who have suffered and striven have developed deep virtues and appreciation, and the cause of their suffering is scoured away as if it never were, one is left not with a meaningless paradise of opium dreams but a real paradise in which all of the joys are rooted in the free will and essence of the people. Wnt (talk) 06:12, 14 November 2010 (UTC)[reply]
The only part of your comment that relates to this discussion is your assertion that the chisel marks are still apparent. The original question was, has anyone proposed a scientific approach to looking for such chisel marks? The answer, so far, is no. thx1138 (talk) 06:25, 14 November 2010 (UTC)[reply]
It is hard to say what is relevant in such matters, and harder to decide on proof. I would say, for example, that if you look at the film of the funeral following the 16th Street Baptist Church bombing, you see people grieving, from such injustice, and yet so unified, so free from hatred, so unaccountably dignified, and with our retrospective knowledge that their firm faith was such a fundamental turning point toward the end of racial injustice, there is just some overwhelming sense that more than random chance is at work; that they were allied with the Holy Spirit. You can't test something like that with a multimeter. The real miracles aren't the achievement of a mundane end by impossible means, but the achievement of an impossible end by mundane means. Wnt (talk) 07:00, 14 November 2010 (UTC)[reply]
In my opinion, what makes the scientific description of the world so fascinating is the idea that surprisingly complex and beautiful results readily spring from such a deceivingly simple looking set of rules. As a student of math I've gotten a front row seat to examples of beauty popping out seemingly from nothing, so I know that it's possible. And yet some people try to convince me that this sort of miracle is a fantasy. They claim that such complexity could only possibly arise from a set of laws that is equally complex (i.e. some active and unpredictable God). This strikes me as a colossal failure of the imagination. I don't ever want to believe that reality is that dull. It's depressing. Rckrone (talk) 17:35, 14 November 2010 (UTC)[reply]
Alright, my opinion: There is nothing wrong with intelligent design as a belief: it's entirely unprovable, and entirely unfalsifiable. basically the question is this: do we assume that the universe (as it is) was designed to be as it is, or do we assume that the universe (as it is) is a product of deterministic/random forces. Either is a belief, and neither belief has any real basis in evidence. The problem with (the dumber) elements of ID is that they start making claims that are contrary to our understanding of the universe in order to support their particular understanding of religious texts. That's just narrow-minded. There is no contradiction between religion and science (in fact someone - I forget who - said that faith transcends and incorporates both evidence and belief), except to the extent that people believe they have to oppose one to advance the other. If you think about it, gravity is such a profound statement of belief that it is surprising that physics doesn't have priests.
end opinion. --Ludwigs2 07:31, 14 November 2010 (UTC)[reply]
So, people with faith are really nice people, eh? So are most of my friends, and a bunch of more profound non-believers you'd be hard pressed to find anywhere. And didn't Isaac Newton prove gravity with an apple? That sure didn't need any god. HiLo48 (talk) 10:06, 14 November 2010 (UTC)[reply]
There is a set of natural laws that describe the falling of an apple, by which you can link the moment when the apple to falling to a future in which it has fallen further by a specified amount. One can postulate that the same moment could be linked to a different moment in which the apple has stopped, or moved sideways, using a different set of physical laws. This is a different dimension of time, moving forward in a different direction from the same moment in spacetime. The known set of laws makes the most sense, because it is what you remember, what you observe, what the textbooks say that you read, what others you speak to have always known. But what if some other set of laws started to acquire some of the same characteristics? What if you have a choice of whether to move your subjective experience entirely in one dimension of time, or in a combination of the two? What if your action in one timeline influences your ability to take part in another? The reason why I emphasize the need of science and faith to respect one another is that while science is the tool to explore a known universe, there may still be some advantage in looking toward others. Wnt (talk) 15:06, 14 November 2010 (UTC)[reply]
LOL'ing at the idea that Newton's argument for gravity did not require belief in a God. Take a look at Isaac Newton's religious views sometime, and the role they played in the formation and expression of his theories. As far as Newton was concerned, gravity was an argument for God, the prime mover who set everything in order, and kept it that way... Newton was a very odd duck and neither atheists nor modern Christians will on the whole find much comfort in his views. --Mr.98 (talk) 19:31, 14 November 2010 (UTC)[reply]
Rupert Sheldrake's ideas fall somewhere between a religious ID position and the mainstream understanding of evolution by natural selection. To his supporters he's a respectable, educated scientist who is making some imaginative but scientific leaps; his opponents decry his work as "magic". -- Finlay McWalter ☻ Talk 17:46, 15 November 2010 (UTC)[reply]
A lot of the UFO believers think aliens have been artificially selecting human evolution for at least millennia, but there's not even any evidence of breeding husbandry in our genetic drift. It sure seems like we've evolved at about the same rate as all the other mammals. But maybe that's not saying much because of the diversity of such rates. We've evolved much faster than horses and much slower than sheep and cattle. Ginger Conspiracy (talk) 06:01, 17 November 2010 (UTC)[reply]
Fuzzball vs. Big Rip
The Big Rip hypothesis supposes all space could be torn apart after cosmic expansion gets off the leash. I would assume that a black hole with a mathematical point singularity at the center should be unaffected by this, since there's no one point to be ripped from another (though I suppose a few things falling in the event horizon at the last minute might discover their status is moot). But a fuzzball (string theory) describes an alternate object, the size and mass of a black hole but filled with strings, that already somehow maintains its structure within highly curved spacetime. What happens if one of these goes up against the Big Rip? Wnt (talk) 05:16, 14 November 2010 (UTC)[reply]
Considering we know nothing about about: Black holes, Cosmic Rips, fuzzballs or Dark Energy it's gonna be tough to answer your question! :) I mean all those things have theories and math, but no direct observations. (The observations of black holes could also be super massive objects, there is no direct evidence that they are singularities.) Ariel. (talk) 07:11, 14 November 2010 (UTC)[reply]
True, there is a certain Godzilla vs. Megalon quality to the question. ;) But it's funny that modern physics has postulated both the irresistible force and the immovable object... Wnt (talk) 15:09, 14 November 2010 (UTC)[reply]
Interesting. To summarize here, they say that phantom energy (with a speed of sound squared greater than 0 and less than 1, whatever that means) will accrete into a black hole, dominating over Hawking radiation "until it reaches the Planck mass" at a time "near" the Big Rip. As what I get the impression is typical when you start combining event horizons and negamatter (well, negative energy) you end up with "traversable wormholes", or at least a possibility thereof. (but would infinite phantom energy follow you?) All hands, abandon universe! Wnt (talk) 18:54, 14 November 2010 (UTC)[reply]
I have a feeling we were just as close to the truth with the Godzilla vs. Megalon analogy. Ginger Conspiracy (talk) 08:04, 17 November 2010 (UTC)[reply]
urine
historically, which has been more effective to make the teeth white; brushing with urine or gargling/rinsing with urine —Preceding unsigned comment added by Kj650 (talk • contribs) 11:32, 14 November 2010 (UTC)[reply]
This site under a disclaimer that anything it publishes need be true claims that in ancient times, human urine was used as a tooth whitening product. By modern standards of whitening efficacy the answer to the OP is "Neither." but that need not diminish any excuse for trying. Cuddlyable3 (talk) 14:50, 14 November 2010 (UTC) WARNING of explicit picture![reply]
With as much money as people spend on teeth whitening products these days, swishing with pharmacy grade hydrogen peroxide is very economical. It's usually something like $1/liter and actually makes a very good mouthwash in every other respect, as well. Just don't let your lips touch the mouth of the bottle, because any spittle or foreign matter which gets into a bottle of peroxide can catalyze it into ordinary water in a matter of hours. Ginger Conspiracy (talk) 08:02, 17 November 2010 (UTC)[reply]
Burping on command
Is there a scientific explanation of how Drumski89 and I can "burp on command"? 173.49.140.141 (talk) 13:04, 14 November 2010 (UTC)[reply]
As burping involves the expelling of air from the oesophagus it is necessary to have air in the stomach in the first place. Repeated burping will exhaust this supply. You have consciously or unknowingly developed the skill of swallowing air to be able to burp at will. This is a very useful skill if you, for some unthinkable reason, lose your larynx as aerophagia facilitates esophageal speech. Some year ago this was bravely used by the actor Jack Hawkins following a condition that required the removal of his larynx. Oddly it does not mention it in his article but I have very clear memories of hearing him being interviewed and collecting an award using this throat voice as it was called. Caesar's Daddy (talk) 16:29, 14 November 2010 (UTC)[reply]
I have this particular ...skill... as well. I don't think the air goes down to the stomach with me. I just swallow some air, restrict the lower part of my larynx for a fraction of a second, and let the air out in a constricted burst that makes a sound in my throat. It's a bit different from proper burping, as swallowed air is momentarily stored in a place that feels higher up, rather than being generated in the stomach. The belching article doesn't really properly describe it... 88.112.56.9 (talk) 18:17, 14 November 2010 (UTC)[reply]
I agree. For me, I just force air out of my mouth while it's closed (I just try) and then I feel this little bump in the higher part of my larynx, then I burp. Περσεύς|Talk to me 18:20, 14 November 2010 (UTC)[reply]
Oh, and you can add my userbox {{User:Perseus, Son of Zeus/UBX/Burp on command}} to your userpage too. I am the same person as 173.49.140.141. Just logged in. Περσεύς|Talk to me 18:21, 14 November 2010 (UTC)[reply]
Those who have a desire to learn how to perform esophageal speech, either for impressing (or disgusting) others or as a real way of communicating (in cases such as larynx removal due to cancer, or similar situations), can attempt the following actions which may or may not induce a belch. A)"Wiggling" the throat. Pressing the tip of the tongue forcefully against the lower front teeth should cause the larynx area to move out, causing air to displace into the esophagus. The throat muscles can then be relaxed, and the belch forced out by contracting the diaphragm muscles, or contracting and relaxing the same throat muscles again.
B), Breathing air into the stomach. This can be done by inhaling while keeping the throat muscles tight and glottis closed, so that no air can get into the lungs. If the throat is kept closed while still attempting to breathe in, the air should divert into the stomach, then the normal maneuver can be used to belch out the air.
Περσεύς|Talk to me 19:26, 14 November 2010 (UTC)[reply]
Burping on command (2)
However, I can burp on command without any preparation. Why? Περσεύς|Talk to me 22:21, 14 November 2010 (UTC)[reply]
I found a wiki-quote by Einstein: "It has become appallingly obvious that our technology has exceeded our humanity", but sadly it's unsourced, and googling doesn't help. It's
a fascinating quote, and I'd love to read it in context. Does anyone know where I can find it? Thanks, Idunius (talk) 15:16, 14 November 2010 (UTC)[reply]
Just search with quotes: "It has become appallingly obvious that our technology has exceeded our humanity" then 350,000 hits. —Preceding unsigned comment added by Perseus, Son of Zeus (talk • contribs) 18:24, 14 November 2010 (UTC)[reply]
And which of those 350,000 also-unsourced results contains the quote in context? Which of them lists where the quote is originally from? This is what the poster is obviously asking for, not more unsourced quotations. Einstein is one of these figures that people for whatever reason love to attribute quotes to, often without any evidence that he actually said what was being attributed to him. --Mr.98 (talk) 19:19, 14 November 2010 (UTC)[reply]
Er no, that's the whole quote that people keep repeating and saying that he said. I assume it was part of a longer statement about some topic or event, or from a book, or in response to a question from someone else. He probably didn't just walk up to a reporter, say it, and then walk away. I remember the lore surrounding some of his other quotes were about nuclear weapons, my WP:OR is that this sounds like it could be a similar theme. DMacks (talk) 19:43, 14 November 2010 (UTC)[reply]
As Mr. 98 says, I was hoping to learn the exact source. (Was the context political? Scientific? Is he referring to any specific event?) Is it certain that it's Einstein? I have, as I said, googled already, and I found a plethora of sites with the quote, but not a single reference except just simple statements that it's Einstein. /--Idunius (talk) 19:50, 14 November 2010 (UTC)[reply]
The OP knows that and has said so. He's asking if we can dig up the original source. (There are some days when I find the Ref Desk to be essentially useless! We've just spent six lines telling the OP what he obviously already knows if anyone had bothered to read his or her question for what it straightforwardly said. Blah.) --Mr.98 (talk) 21:24, 14 November 2010 (UTC)[reply]
I poked around quite a bit in Google Books — it's a quote that is thrown around dubiously and unsourced again and again. I doubt he actually said it, to be honest. It is probably one of these half-remembered things that has just been passed around for a decade or two. --Mr.98 (talk) 21:27, 14 November 2010 (UTC)[reply]
Same here. I also found a German translation, and searched pretty carefully for the entire quote as well as individual words (using Internet search engines as well as searching a digital library of his works). Over and over again, it's attributed to Einstein, but not to a specific writing or lecture. Would be a nice (possibly fruitless, I'll admit) research project, to thread back in the earliest uses of the quote to try and find its source. Would require a very good library. -- Scray (talk) 00:18, 15 November 2010 (UTC)[reply]
Ok. I'd still like to thank you for trying! --Idunius (talk) 07:49, 15 November 2010 (UTC)[reply]
Some of the best science questions are those we can't answer. -- Scray (talk) 21:52, 15 November 2010 (UTC)[reply]
...though this probably doesn't fall into that category, truth be told. It'd be nice to know where the alleged quote came from, but it's not a real secret of the universe. --Mr.98 (talk) 00:17, 16 November 2010 (UTC)[reply]
Proton Gun
In an ancient ZX Spectrum game, The Korth Trilogy, the antagonist aliens used "proton guns" that fired a stream of protons at a target that "simply smash atoms to pieces" on their spaceships and used "proton force fields" force defence that operated on the same principle (they would shred any projectile fired through them). They used ships armed with this technology to blockade Earth, but were unable to invade as the guns couldn't be used in an atmosphere as there would be an explosion as soon as the protons hit the atmospheric molecules and the forcefields would overload when flying through the atmosphere due to the constant impact of the same molecules.
Is this at all realistic, or was this simply dramtic license on the part of the author/programmer? Exxolon (talk) 17:44, 14 November 2010 (UTC)[reply]
Protons are just hydrogen nuclei and they don't really have any exceptional ability to smash stuff. They do have a positive charge which lets you accelerate them with magnets, so maybe the proton gun makes some sense, but I'd better leave it to one of the engineers to explain why it's more effective to just shoot bullets. The proton force field is pretty much nonsense though. Rckrone (talk) 18:10, 14 November 2010 (UTC)[reply]
You can use a particle accelerator in space, sure; see Particle beam weapon. These were investigated quite heavily as part of the Strategic Defense Initiative. I believe that in general using protons would be problematic since they have a positive charge, and generating a negative charge is pretty easy to do. In particle beams that use hydrogen ions (protons), they usually add an electron to them before sending them out, so they are electrically neutral. Anyway, long story short, you can use these, they have some desirable properties and some less desirable ones, but they aren't too essentially different than using a laser or something like that. They have no magical atom smashing properties. In space such weapons are more desirable than on Earth, as I understand it, because the atmosphere would absorb a lot of the energy and make them far less efficient than, say, a stream of bullets. I doubt they'd "blow up" as described; it's more like your particle beam would just be very weak or require exponentially more energy for the same effect. On the other hand, for very long distances in very short timescales (essentially "instantaneous" by human standards), they could be useful, hence their research for missile defense (which would require shooting things hundreds if not thousands of miles away very quickly, for which projectiles — bullets or rockets or kinetic weapons — are ill-suited). --Mr.98 (talk) 20:04, 14 November 2010 (UTC)[reply]
Would not a stream of high energy protons be an kinetic weapon just as a stream of bullets? --Gr8xoz (talk) 21:31, 14 November 2010 (UTC)[reply]
Maybe in a very literal sense, but I think one can recognize that there are different properties to a stream of blocks of lead and a stream of protons. That's the distinction I'm indicating. --Mr.98 (talk) 23:04, 14 November 2010 (UTC)[reply]
Which is completely irrelevant to this question. But thanks for contributing it anyway! --Mr.98 (talk) 00:15, 16 November 2010 (UTC)[reply]
No, a stream of charged particles would be quickly diffused by air. Even if accelerated to several times the speed of bullets, they would diffuse within a few millimeters of air. And you would need a huge tank of hydrogen to match the mass of a single bullet. The amount of energy it would take to ionize that much hydrogen, let alone accelerate it, would be several thousand times the energy of a bullet's gunpowder. Even in space, the like baryonic charges would quickly diffuse the beam and it would spread out into a harmless cloud no more dangerous than solar wind. Heavier nuclei would be better as a weapon, but a free electron laser is probably more suitable for a beam weapon. Ginger Conspiracy (talk) 05:39, 17 November 2010 (UTC)[reply]
Different solvents - which are functionally the same?
Knowledge of solvents would be useful to me, as I often find myself having to do difficult cleaning jobs, where it would be disastrous if the underlying thing was damaged or discoloured. For example, I have a lot of hardened drips of emulsion paint (called latex paint in the US) on the surface of gloss paint (called I think oil-based enamel paint in the US). 1) What commonly available solvents would dissolve or soften the emulsion/latex paint, but not affect the gloss/oil-based-enamel paint underneath?
Some personal research shows that nail polish remover does this. The nail polish remover I used appears to be mostly acetone and water. I've also seen a product on the internet that consists mostly of acetone, toluene, a little methanol, (according to its MSDS sheet) and probably water which claims to do this, but which is not easily available in the UK. A comment in an internet forum suggests that methylated spirits/Denatured alcohol may do the same, in other words ethanol.
There are many different solvents. 2) Is it possible to classify them into groups of similar solvents? 3) Will the ethanol in methylated spirits be functionally equivalent to the acetone and toluene, as solvents?
I have dried paint on some polyester clothing. 4) Would the above solvents dissolve the polyester if I tried to clean it with them, or soaked it in them?
There is another solvent in an expensive specialised cleaner spray that I sometimes use: ethylene glycol. 5) Is there another readily available solvent that is functionally the same as ethylene glycol, in other words dissolves the same things and even more importantly does not dissolve the same things? Thanks 92.15.7.155 (talk) 19:18, 14 November 2010 (UTC)[reply]
I don't know nearly enough to speak about what will work on paint, but to get you started, the solvents article has groups of common solvents, and rates them based on how polar they are. (A main property distinguishing toluene from water is how much the positive and negative charge on the molecule is split up; molecules with all C and H tend to be pretty non-polar, whereas water has two protons sticking out to one side) Problem: if you know acetone works, what is easier than that? If you check the charts, ethanol is not that different from acetone in some ways, but it has a terminal -OH that makes it a polar protic solvent and greatly increases its hydrogen bonding potential. Again, I don't know what this means for latex and oil paints. Wnt (talk) 19:36, 14 November 2010 (UTC)[reply]
I'm a little surprised that you can't buy acetone in the UK - look in a paint store. They may have toluene as well. Ariel. (talk) 01:37, 15 November 2010 (UTC)[reply]
How did you manage to infer that? Not the question asked anyway. 92.29.117.14 (talk) 10:54, 15 November 2010 (UTC)[reply]
(1) it depends on the chemical details; try acetone and alcohol together; (2) yes, in many different ways, but none of them will help you as much as trial and error, sadly; (3) no, combinations of solvents are often quite different than combinations of their solvency because of molecular-level interactions; (4) there is only one way to find out. What kind of paint? (5) I doubt it, ethylene glycol is very unique in a few important ways. Basically, if you aren't in a position to be able to try a lot of combinations of solvents on small areas where it won't matter if both of the substances get dissolved, you're probably screwed. If you are, do it under a fume hood or in plenty of ventilation. Ginger Conspiracy (talk) 05:53, 17 November 2010 (UTC)[reply]
Thanks, is there anything that a non-chemist could read about this? 92.15.28.182 (talk) 18:19, 17 November 2010 (UTC)[reply]
Wave pulse from heavy string to light string
When a wave pulse travels from a heavy string to a light string, what happens? Is its behaviour similar to when a pulse travels from a light string to a heavy string (i.e. it is partially transmitted and partially reflected), or is its behaviour different?--220.253.217.130 (talk) 20:15, 14 November 2010 (UTC)[reply]
Yes. If we view the string as a transmission line, a part of the pulse energy gets reflected back to the source at any discontinuity such as a change (up or down) in the string weight. This is a simple animation.Cuddlyable3 (talk) 23:27, 14 November 2010 (UTC)[reply]
I still don't understand why we can't fix the coastline length precisely via some software, which thoroughly outlines the upscaled coastline and then calculates it length (like tracking down via some flexible stuff and then straightening it to evaluate)? —Preceding unsigned comment added by 89.77.156.31 (talk) 21:53, 14 November 2010 (UTC)[reply]
What we would need to fix precisely would be, not the software, but rather, an agreed-upon smallest scale of wiggle we care about. —Steve Summit (talk) 22:45, 14 November 2010 (UTC)[reply]
The obvious answer is that the coastline is as long as a ship would take to sail around it. The ship is not going to make minute acrobatic curves just to stay a fixed distance from the caost... This is a better solution than a "length of the ruler" version. Just work with a real ship under real conditions. 91.183.62.45 (talk) 23:52, 14 November 2010 (UTC)[reply]
People make useful and functional measurements of coastlines all the time. The paradox does not preclude this, but instead refers to the notion of well-defined exact measurement in a model system. The apparent paradox is that the observed length depends on the scale of measurement. The method you mention could be used to take such a measurement, but this does not matter at all in terms of `solving' the paradox. SemanticMantis (talk) 00:56, 15 November 2010 (UTC)[reply]
There is no paradox here at all. There are two empirical observations, made originally by Lewis Fry Richardson and subsequently put into a wider mathematical context by Mandelbrot:
The measured length of a coastline (or any other natural border) depends on the measurement scale (informally, the "ruler length"). This appears strange at first glance, but is actually not that surprising - even the mesaured distance around a perfectly circular island would depend on whether you were sailing round it in a supertanker or a rowing boat.
The measured length of a coastline (or any other natural border) does not seem to tend to a finite limit as the measurement scale is made smaller and smaller. This is counterintuitive, and is how coastlines differ from smooth curves such as circles. We can assign a definite length to a smooth curve by finding the limit of the measured length for smaller and smaller measurement scales - in effect, the curve is "straightened" by examining it at smaller and smaller scales. Mandelbrot showed that this limiting process does not work for (most) fractals, and so he interpreted Richardson's research as evidence that coastlines and other natural objects are more closely modelled by fractals than by smooth curves. Gandalf61 (talk) 11:37, 15 November 2010 (UTC)[reply]
I still don't fully understand how this applies to real coastlines as opposed to theoretical ones you might find in a math text. Below a certain scale (A few meters) there IS no coastline, fractal or otherwise, there's just a beach. The coastline is a theoretical average of the waterlevels at various times of the day, year, and even minute. That must surely follow a curved line and not a jagged one (Whoever heard of a jagged average?).
It's often implied in these sorts of discussions that the ocean is this frozen, unmoving zone and that individual grains of sand could be definitively assigned to either the ocean or the shore. APL (talk) 22:18, 15 November 2010 (UTC)[reply]
Well, not all coastlines are gently curved sandy beaches, of course.
Suppose you've got a coastline that's jagged rock. Which jags are you going to measure, and which not?
And then there are river mouths. Where a river reaches the sea, and gets wider and wider until it forms a bay, how do you measure that? If you "walked along the shore", you could end up walking dozens (perhaps hundreds) of miles inland.
I'm not saying choices couldn't be made about how to answer each of these questions. But the whole point is that that there's clearly no one, single, obvious answer. And every different answer yields a different coastline length. —Steve Summit (talk) 00:43, 16 November 2010 (UTC)[reply]
As a practical matter, the length of a coastline is the distance a typical commercial boat needs to navigate safely and conveniently at low tide while staying in sight of the shore. This means there are some granularities of coastal features which measure longer than others with the same geodetic distance from start to finish, as you would expect, but shoals will cause more variation than fjords. Ginger Conspiracy (talk) 07:45, 17 November 2010 (UTC)[reply]
FTL communication?
Alice and Bob are 1 ly apart. This should mean that it would take at least 1 yr for Alice to send a message to Bob. However, what if Alice has a pole that's 1 ly long, and she taps on it repeatedly to send Bob a message in binary? Why wouldn't this work? --75.33.217.61 (talk) 22:07, 14 November 2010 (UTC)[reply]
Someone asked this a few weeks ago, but I can't find it in the archives. SmartSE (talk) 22:29, 14 November 2010 (UTC)[reply]
I think we get this question once a month on here? It doesn't work because the pole is not truly rigid — it's a bunch of discrete atoms connected by electron orbits and somesuch, and conveying the "tapping" (or rotating, or whatever) means each atom has to move, turning the atom next to it, at a speed around speed of sound in the material in question. It's not instantaneous. Being perfectly rigid would mean transferring the atoms at infinite speed, which obviously doesn't happen. --Mr.98 (talk) 22:31, 14 November 2010 (UTC)[reply]
November 15
prehistory of the sahara region
I've read somewhere that the Sahara around 800,000 years ago was a hot humid swamp-like area (no information on what it was like 1-2mil years ago), and I'm wonder if there are any biologists/anthropologists linking the emergence of human culture in N.Africa and the migration out of Africa by homo erectus to the later desertification of the region? I'm not necessarily suggesting it's true, but it seems obvious enough a connection that quite a few people would have proposed it. 173.183.68.27 (talk) 00:12, 15 November 2010 (UTC)[reply]
What is the proposed mechanism for anthropogenic desertification of an area the size of Europe? I just don't see it as likely in the slightest. I could see prolonged greenhouse effect and etc. contributing to or accelerating desertification in a desert that size, but causing it outright? I think it's well beyond the capability of human beings until very recently to do such a thing. --Mr.98 (talk) 00:21, 15 November 2010 (UTC)[reply]
Fire, really. It's a long shot I know, but an increased population of hominids with a lot of use for fire could have created large areas of grassland, holding much less moisture and disturbing the monsoon patterns coming in from the atlantic, leading to desertification. obviously positive feedback would be the active mechanism here, I don't think it would have been possible to burn that much forest. 173.183.68.27 (talk) 00:31, 15 November 2010 (UTC) -- I guess the main weakness if that forest fires don't create grassland, so there may be something else. 173.183.68.27 (talk) 00:34, 15 November 2010 (UTC) -- i guess Deforestation in New Zealand supports this somewhat. 173.183.68.27 (talk) 00:45, 15 November 2010 (UTC)[reply]
I don't place much credence in H erectus causing this change - Sahara#Climate_history talks about climate changes impacting the Sahara. FWIW you may be interested in reading about a technique used by Australian Aboriginals called Fire-stick farming which most likely did result in large scale changes to the landscape, flora & fauna (though not necessarily desertification). --jjron (talk) 14:43, 15 November 2010 (UTC)[reply]
Have you never wondered why there can be two completely different ecosystems present at the equator; the Sahara and the Amazon? It is obvious that climate change is what keeps the Sahara in its current state, and that not enough moisture is coming in to replenish the soils, but it is equally as true to say that if there were no trees in the Amazon, there would likely be a lot of desert there too; it is the existence of the rainforest that keeps the rainforest alive because it holds on to the moisture and influences the weather (lowering temperature and increasing precipitation) in the area. I will read up on the Aboriginal situation though, that might make for interesting evidence! Thanks. 173.183.68.27 (talk) 05:34, 16 November 2010 (UTC)[reply]
The Sahara isn't at the equator; the Congo is, and is rainforest like the Amazon. But, in any case, there are lots of instances of places at the same latitude with significantly different climates, so the supposed fact wouldn't be surprising if it was true. --Anonymous, 06:24 UTC, November 16, 2010.
The prevailing winds over the Sahara have a LONG fetch over land, with almost no source of water feeding them. That's why it is so dry. In the past, when landmasses were at slightly different locations, and winds blew from different directions, there may have been more sources of water upwind from the Sahara. As it stands now, the winds over the Sahara, which blow almost straight out of the east, have about a fifth of the earth's surface to blow over before getting to the Atlantic. Generally, you find deserts on the downwind side of continents, and forest upwind. There are also rain shadow effects. Its a complex thing, however, and this is a bit of a simplification. --Jayron32 06:32, 16 November 2010 (UTC)[reply]
The position of the Sahara within the horse latitudes is significant; I've often seen a popular though rather simplistic cartoon of the winds circulating in bands through the upper atmosphere and coming down over drier areas - it must be on Wikipedia somewhere... Wnt (talk) 12:21, 16 November 2010 (UTC)[reply]
The influx of cold fresh water from Lake Aggasiz is the most likely cause according to some of the cooling in subtropical sea temperatures and failing of the North African Monsoon. ~AH1(TCU) 03:49, 18 November 2010 (UTC)[reply]
Guy who blinked a lot after beheaded
I heard a story a long time ago in school that a guy proved that the head is alive briefly after being beheaded, and he did this by stating that after he is beheaded he will blink a lot. I think he was beheaded by guillotine (not sure why), and sure enough he blinked a lot after his head came off. Is this story true? Does anyone know what I'm talking about or who this guy is supposed to be? ScienceApe (talk) 00:50, 15 November 2010 (UTC)[reply]
(edit conflict) The story is told of Antoine Lavoisier, who was indeed beheaded by guillotine. It's a widely told story, but appears to be apocryphal; see The Straight Dope column on the matter. I have yet to see any serious academic supporting the story. That's not to say that a person couldn't blink after his head's chopped off, just that there's no contemporary suggestion that Lavoisier did. even citing the same source, that's pretty impressive, 173 Buddy431 (talk) 01:01, 15 November 2010 (UTC)[reply]
Hm, I can't imagine that the loss of all blood pressure wouldn't lead to unconsciousness from shock at least as quickly as pilots black out from high G-forces. A few seconds, tops. Ginger Conspiracy (talk) 01:07, 17 November 2010 (UTC)[reply]
Well, that's like drying out a sponge in a centrifuge. Just severing the head and leaving it there without messing with it any may give the person a few extra seconds. WikiDao ☯ (talk) 02:11, 17 November 2010 (UTC)[reply]
Our Decapitation article says: "Decapitation is quickly fatal to humans and most animals as brain death occurs within minutes without circulating oxygenated blood." Some eye-blinking behavior in that time seems quite possible, especially if one has made up one's mind to focus on doing that before the event. WikiDao ☯ (talk) 02:16, 17 November 2010 (UTC)[reply]
Little bags of chips vs big bags
I'm talking about the Lay's potato chips. They come in small bags and big bags, and I've noticed that the small bags seem to taste better than the big bags, which before I attributed to scarcity (there's less, so each chip tastes better). Obviously the solution was to perform a double-blind study ;) I set up the project as follows: my assistant put four plates on a table: 2 labelled "small" and "big" respectively, then places the same number of chips (from the correct bag) in the same arrangement on each, then shuffling the plates randomly. She then leaves with the bags. I come in, unaware of which are which, and shuffle them again. The subject then comes in and tastes chips from two of the plates, which s/he selects and guesses on a folded sheet of paper with four circles: s/he writes either s (small), b (big) or Ø (not tasted) for each circle which s/he places in a box, knowing that it is possible that both are from the same bag. My assistant then came in and recorded each selection from the slip, and I looked on the underside of the plate and recorded the correct answers. I did not see the subject's answers, nor my partner the correct answers. I repeated this about 200 times, discarding the "used" plates and chips each time. When I brought all the data together at the end I found the accuracy rate was about 79%, which to me was shocking. Now I know what happens (and got full points on my project :), my question is: what accounts for the difference? 24.92.78.167 (talk) 01:48, 15 November 2010 (UTC) PS: The plates were paper, the writing was in pencil so as not to show through, and the chips were all sour cream and onion flavor. The subject was not allowed to touch the plates except to sample the chips.[reply]
Did you check the date codes on the bags? Ariel. (talk) 02:12, 15 November 2010 (UTC)[reply]
how many subjects were there? How did you explain them to rate the chips? Were they guessing which tasted better? Which they thought was crispier? or were they asked specifically to guess which bag they thought it came from? The chips are purged with nitrogen or something aren't they? Which is inert but maybe a small amount of air still remains in the bag so when the bag is bigger the amount of air is more. My dad does plant maintenance at a smallgoods factory and he says their vac equipment can be running at 85% and it's still "good enough" even tho it normally runs at 97% or something, but even at 100% it's not a perfect vacuum. I realize the nitrogen purging thing is a completely different process, but maybe similar tolerances apply. Vespine (talk) 02:57, 15 November 2010 (UTC)[reply]
(edit conflict)Cool study! Just a few ideas:
- the amount of air in the package
- there may be a significant difference in the way/time/place of packaging that accounts for the taste, though you'd have to ask Lays
- large bags = more chips = more interactions between chips, perhaps oil/salt is being exchanged 173.183.68.27 (talk) 03:02, 15 November 2010 (UTC)[reply]
Date codes as mentioned by Ariel seem the best explanation. But the explanation can simply be unattainable. Without, that is, a lot more information and a lot larger study. Maybe the potatoes vary by packing plant, and maybe one packing plant, carrying potatoes from one source, specializes in packaging large bags, or small bags. And on and on—oil—air pollution—plastic blades in one type of machine—steel blades in another type of machine. The product is uniform, but not perfectly so, and there is probably more than one factor of variability between the large bags and the small bags. Bus stop (talk) 03:14, 15 November 2010 (UTC)[reply]
I agree. There are a whole lot of volatile flavorings and oils which can spontaneously decompose or otherwise change taste even when packed in pure nitrogen, and it's not at all unreasonable to suspect the single serving bags not only sell at higher volumes, but they're more likely to get restocked at the front instead of first-in-first-out as grocers would prefer because there are going to be more of them per unit of volume to have to fiddle around with when restocking shelves. So it's likely a freshness issue. Ginger Conspiracy (talk) 07:04, 17 November 2010 (UTC)[reply]
I try to limit my chip consumption these days, but if I recall correctly, there are a fair amount of loose salts and spices on the chips. In the course of travel and with the help of gravity, I've found that some of this salt makes its way to the bottom of the bag, resulting in the chips at the bottom being saltier and, if it is your preference, "tastier." It stands to reason that this effect is amplified in bigger bags, since, in a smaller bag, you could easily grab a chip from the middle or bottom without much digging. (Or, as in your experiment, you may dump some chips onto a plate; the small bag sample, on the whole, would have the "average" chip flavor, whereas the big bag would biased toward which part of the bag the chips came from.) This is just a theory of mine, but do you (or other readers) think this could be a contributing factor? Eric (EWS23) 13:05, 17 November 2010 (UTC)[reply]
Say you left a pound of deli turkey slices in a bag at room temp for 8 hours.
Most people will tell you to toss them. But I'm guessing you want other options. Were they unopened? Because they will cut down on bacteria drastically. Are they very salty? That helps too. You can freeze them, to kill many, but not all bacteria (but freezing does nothing to existing toxins - if there are any). You can also fry or bake them. I would use your built in chemical detector - sniff them. If there is any hint of bad smell toss them, but otherwise you are probably OK. Of course most people work on the better safe than sorry system, but if they smell OK, and you are not an infant or elderly, have a normal immune system, and are not taking antacid drugs (of any type, prescription or over the counter), your risk is low. As soon as you smell them, put them in the freezer (to cool them quickly) or eat them immediately. Ariel. (talk) 05:31, 15 November 2010 (UTC)[reply]
The practices of the deli where you bought the slices will also be significant. Were the slices freshly cut on a clean machine, or had they been in a display for many hours? I agree with Ariel that I personally would take the risk unless the turkey smells bad. A hundred years ago most people would have been happy to eat such meat without question. The human stomach is good at killing bacteria, but it cannot eliminate toxins, and, just occasionally, it fails to eliminate a large intake of acid-resistant bacteria, so there will always be a small risk, even with fresh meat. Dbfirs 10:11, 15 November 2010 (UTC)[reply]
The machine is probably clean, as I've eaten their meat for a couple of months without a problem. The bags were unopened. I put them in the freezer and haven't taken a look since. Imagine Reason (talk) 14:50, 15 November 2010 (UTC)[reply]
Technically this is a medical question, so we aren't supposed to answer it, but if you're really worried, just pop them in the microwave for five minutes. Only if they were infected with botulism will there be any remaining risk. People make turkey sandwiches 8 hours prior to consumption all the time. Ginger Conspiracy (talk) 07:00, 17 November 2010 (UTC)[reply]
Partial reflection when light travels from a fast medium to a slow medium
When light travels from a fast medium to a slow medium, you get refraction, do you also get partial reflection (as you do when the light travels from a slow medium to a fast medium)? 220.253.217.130 (talk) 06:30, 15 November 2010 (UTC)[reply]
Sure you do, else you wouldn't get an effect like this:
Notice how you can see the mountain in the lake? That's because the surface reflects light. The light moves faster in the air than it does in the water, so this is exactly the effect the OP is asking about.
The article Total internal reflection may be of interest; you will see that it mentions the more usual phenomenon of partial internal reflection, although we don't seem to have a separate article on it. 87.81.230.195 (talk) 10:02, 15 November 2010 (UTC)[reply]
Limits of dark enery
Hello. Gravitational energy is not infinite. An object may fall for a long time, but eventually its gravitational potential will reach zero and then no more force will be exerted on it. If this was not the case, falling objects would be accelerated forever and gravity would be a perpetual motion machine.
Dark matter exerts a repulsive force on other matter which is accelerating the expansion of the universe. However, at some point this repulsive force must become zero to prevent it from becoming a perpetual motion machine. Where is that point? Leptictidium (mt) 07:46, 15 November 2010 (UTC)[reply]
You are thinking of Dark energy, not Dark matter. And the simplest answer to your question is "no one has any idea". Dark energy is just an idea, or more accurately it's a way trying to "patch" holes in observations vs. theory. No one has observed it (they have only calculated it), and there could be a wide variation in it's effect, and still match current observations. For example an idea called Big rip does actually suggest the force will become infinite. Ariel. (talk) 08:27, 15 November 2010 (UTC)[reply]
So sorry, "dark energy" then. But if it does become infinite, isn't that a violation of the second law of thermodynamics, since it generates a force perpetually? Leptictidium (mt) 08:49, 15 November 2010 (UTC)[reply]
The "limit" is probably the edge of the observable universe (from the reference frame of the hypothetical dark energy), but since this is all hypothetical, it would be very difficult to try to prove this. Perhaps, one day, we will realise that there is a much simpler explanation. Dbfirs 09:28, 15 November 2010 (UTC)[reply]
You say "An object may fall for a long time, but eventually its gravitational potential will reach zero and then no more force will be exerted on it". This is incorrect. Gravitational potential energy is calculated by integrating the gravitational force with respect to radial displacement. This integration introduces an arbitrary constant of integration, which can be chosen to make the potential energy 0 at whatever point you like. Sometimes it is convenient to take gravitational p.e. as being 0 for some initial configuration; sometimes we take gravitational p.e. to be 0 for a hypothetical infinite separation. The configuration that we choose as a zero point for gravitational p.e. 0 is an arbitrary benchmark - it has no physical significance. Gandalf61 (talk) 10:24, 15 November 2010 (UTC)[reply]
Surely if I am falling towards the Earth, the point at which gravitational potential energy would become zero is the centre of the Earth, no? Leptictidium (mt) 10:30, 15 November 2010 (UTC)[reply]
You can choose to make the gravitational p.e. zero at the centre of the Earth if you want to. Or you can choose it to be zero at the surface of the Earth, or wherever you like. It is arbitrary. The physically meaningful quantity is the gravitational force, which is the gradient of the potential, and so is unchanged by adding or subtracting a constant from the potential. Gandalf61 (talk) 11:13, 15 November 2010 (UTC)[reply]
As (not) explained in gravitational potential energy, but implicit in the formulae given and the statement about separating all bodies to infinity, there actually is a logical zero point for gravitational energy, which is when an object is separated from all other masses by infinite distance. It is (theoretically) possible then to calculate the potential energy as a negative number that is the sum of all the negative gravitational potential energies from all masses. Though in practice distant, little-known astronomical masses tend to be neglected, and often an arbitrary zero is chosen. But I don't think anyone chooses a zero at the center of the Earth, since nothing can fall to there. Wnt (talk) 11:25, 15 November 2010 (UTC)[reply]
There is no logical reason why Leptictidium cannot choose zero of potential energy to be at the centre of the earth. It is a perfectly reasonable treatment for the gravitational potential of a single body and avoids negatives, though I agree that physicists normally take zero at infinity. Dbfirs 14:00, 15 November 2010 (UTC)[reply]
Yes but it has no special meaning on a cosmological scale. Even if a object is at the centre of earth it can fall to lower gravitational potential by falling in to the centre of the sun or the galaxy. The only choice of zero point that has no negative potential energy is when all mass in the universe is collapsed in to a singularity in a black hole. I do not know if such a reference point is meaningful given all the complexities with infinity and time dilations. --Gr8xoz (talk) 15:00, 15 November 2010 (UTC)[reply]
I did say "of a single body", and I know the standard treatment is to take zero at an imaginary point somewhere on the other side of the universe, but the OP was just making a simple analogy and it made perfect sense to me. Dbfirs 23:03, 15 November 2010 (UTC)[reply]
Assume for simplicity that there is a point mass M all alone in the Universe, alone, that is, except for a small test particle of mass m at infinite distance from M. m has kinetic energy K = 0 at this point, and we choose the zero of potential T = 0 at this point, too. Next, m falls towards M, hence its kinetic energy K increases. At the same time, because it falls into the potential well, its potential energy T decreases. Conservation of energy requires that the motion is such that the total energy K+T remains constant (energy restricts motion), namely K+T=0. In fact, since M is assumed to be a point mass, the kinetic energy of m increases without bound - I guess that's what you mean by "gravity would be a perpetual motion machine". But that's not true, because as K increases, T continues to decrease, also with out bound, to minus infinity. Although both K and T become infinite, their sum always remains zero. Your mistake is in looking at kinetic energy alone, whereas you have to think of total energy, then there's no problem. Of course, in reality there are no point masses (except maybe black hole singularities but those cause extra problems), and therefore you cannot get anywhere infinite kinetic energy. Dark energy is a different story again which cannot be satisfactorily treated with classical mechanics. --Wrongfilter (talk) 17:31, 15 November 2010 (UTC)[reply]
Well if the potential energy converted into kinetic energy reaches the rest mass of the falling item, I believe you will reach an event horizon. Past this barrier it will not be possible to extract any more energy. Graeme Bartlett (talk) 19:30, 15 November 2010 (UTC)[reply]
No, this is not correct, it's very easy to exceed the rest mass, particle accelerators do it all the time. Ariel. (talk) 19:49, 15 November 2010 (UTC)[reply]
Note that my argument was purely Newtonian. People should understand one thing before tackling the other. --Wrongfilter (talk) 09:25, 16 November 2010 (UTC)[reply]
I'm not sure I know the answer to this question, but I'll try my best. First of all, at issue is not whether the dark energy is "there" in some abstract sense, but whether you can build an engine that exploits the force to produce an unbounded amount of work. I think I can rule out that possibility. In the distant future, the expansion is well approximated by de Sitter space. Any particular person can be causally influenced by only a part of the de Sitter space, and that part can be covered with static coordinates that resemble a "black hole turned inside out"—in other words, a spherical region with an event horizon at the edge. The event horizon attracts objects in the interior like a black hole would; that's how the dark energy force shows up in this model. At this point it's clear that you can attach a potential energy to every point in the spherical region to make the dark force conservative. To put it another way, there's a limit to how far you can allow two masses to be pushed apart while still extracting energy from the pushing. Beyond that point, the repulsive force itself prevents you from ever receiving any energy from the motion of the masses, because the energy is also pushed away too fast for it to get to you. That shows up in this model as one or both masses crossing the event horizon.
A slightly different question is whether the dark energy itself could somehow be harvested. The nature of the dark energy is totally unknown (it may not even be there) and there's no reason to think that it can be gathered, but even if it can, the amount you can gather would be limited by the radius of the spherical region, I think.
The nature of energy conservation in general relativity is complicated and unclear. I think your question in its most general form may actually be unsolved. -- BenRG (talk) 19:41, 15 November 2010 (UTC)[reply]
There are at least a handful of viable explanations for the accelerating expansion of the universe and would thus characterize dark energy. Some of them are more parsimonious than others, but all of them are presently out of reach of observational evidence and experiment. I like to think that the universe is merely hyperbolic instead of flat, or that there are sources of mass from regions other than the big bang's, perhaps other big bangs, exerting a normal gravitational pull. Ginger Conspiracy (talk) 01:01, 17 November 2010 (UTC)[reply]
Animals suffocated in bed
I'm sure my animals aren't unique in that they like to burrow under the sheets of my bed for the warmth. (It's mostly the cats but also one of the dogs) I've often wondered though, can the animal suffocate and if it can, how will it go? Will it simply fall asleep and never wake up? Or will the, completely healthy, animal's brain realize that it's not getting enough oxygen and make the animal want to escape, meow, whimper, etc? I realize that there are unknown quantities here and those are namely the amount of fabric on top of the animal and whether there is a tunnel to fresh air left from where they burrowed. I suppose that the answer to "can it" will be yes given enough sheets and blankets, so for now let's just assume that there is a sheet, a quilt, and another blanket.
Note: I'm not seeking medical/veterinary advice. I'm just inquiring as to the physiological response of a cat or dog and the possibility of an unfortunate event. I do not plan on testing this out on any animals, unless by "test" you think I mean continuing to let my animals sleep under the covers whenever they like. All my animals are of reasonably good health considering their ages and are seen by a vet on a regular basis. Dismas|(talk) 09:21, 15 November 2010 (UTC)[reply]
Humans - who are a not dissimilar animal - don't commonly suffocate if, as frequently occurs, they are covered by the bedclothes as described. Why then would cats or dogs? FWIW I have on occasion shared a bed with a cat, who indeed liked to get under the bedclothes, and no deleterious outcomes ensued. Without being able to think of any appropriate references, I would have expected that, like you or I, a cat or dog would sense whether it was in an over-stuffy situation even in sleep, and wake up and/or move to improve matters. 87.81.230.195 (talk) 09:54, 15 November 2010 (UTC)[reply]
If I cover face with all that, it becomes incredibly hot and stuffy in a short time. I've seen cats and dogs spend much more time that way. Additionally, while we're all animals of one sort or another, dogs and cats handle heat differently than we do. Dismas|(talk) 10:48, 15 November 2010 (UTC)[reply]
Depends on the temperature of where you're sleeping surely Nil Einne (talk) 12:10, 15 November 2010 (UTC)[reply]
I have never heard of an animal suffocating like that. Aso, when I was a kid, back in the days when winters were cold in the UK and when the house had a single coal fire in the living room, I remember frequently sleeping completely under the covers. The room temperature was probably a little above freezing, there would oftem be ice inside the windows in the morning. -- Q Chris (talk) 12:35, 15 November 2010 (UTC)[reply]
[5] and [6] mention suffocation risk for infants although more from pillows rather then sheets or blankets Nil Einne (talk) 14:26, 15 November 2010 (UTC)[reply]
[7] specifically mentions blankets and duvets as a risk for infants. It also confirms what I had suspected, the risk is more their limited mobility and ability to move these objects or otherwise clear obstructions. Notably I can't find any mention of cats suffocating in sheets or whatever but do find plenty of mention of the behaviour, I myself let the cat sleep under the duvet on occasion. Nil Einne (talk) 14:43, 15 November 2010 (UTC)[reply]
All mammals will wake and become agitated from carbon dioxide buildup in the lungs when they are suffocating, which starts as a feeling of stuffyness and becomes searing pain if ventilation isn't available. Ginger Conspiracy (talk) 00:54, 17 November 2010 (UTC)[reply]
(ec)87, are you using "bedclothes" to refer to sheets and blankets? I've never heard it used that way (though it sounds quaintly appropriate to me); everything else being equal, I would assume you're talking about pyjamas/nightgowns - and having animals stuck in there would probably lead to very little sleep at all... 64.235.97.146 (talk) 14:27, 15 November 2010 (UTC)[reply]
"Bedclothes" does indeed mean "sheets and blankets" (or, more likely, "duvet") in UK usage. I've never noticed the ambiguity until now.. AndrewWTaylor (talk) 14:31, 15 November 2010 (UTC)[reply]
I concur. I suppose they can be thought of as clothing the bed rather than the person. The OED gives a definition from c1440 ". . . Bedclothe, or a rayment for a bed." 87.81.230.195 (talk) 21:19, 15 November 2010 (UTC)[reply]
(Partly OR) There are many references[8][9] about cat problems with breathing, such as after a frantic mouse chase, and it is distressing when this happens to one's own pet. OTOH a cat seems to deliberately to obscure airflow to its nose when sleeping e.g. by curling its tail over the nose as well as burrowing under bedclothes as the OP describes. A cat with a fur coat in a warm place can reduce its metabolic rate e.g. to take a cat nap, where it needs little oxygen. Our article Cat#Physiology notes the range of breathing rate 16-40 breaths per minute of a cat, which is wider than that of a human, typically 12-20 breaths per minute. The OP's question would be answered by an experiment on a sleeping and trusting pet that I am not prepared to do either. Cuddlyable3 (talk) 16:30, 15 November 2010 (UTC)[reply]
Hydrogen sulfide
Under what conditions does hydrogen sulfide exist in the liquid phase, simultaneously as sulfur is in the gas phase? Are there more than one molecular structure for sulfur in this phase combination, maybe diatomic surfur? What does liquified hydrogen sulfide look like? How good a solvent does it make? Compare the solubility of sodium sulfanide in liquid hydrogen sulfide, to that of sodium hydroxide in water. Does it autodissociate like water? Plasmic Physics (talk) 14:14, 15 November 2010 (UTC)[reply]
That's worded very much like a homework question. Please have a look at our hydrogen sulfide article. Especially the properties listed in the right-hand table. The article Ammonium hydrosulfide may also be of interest. EverGreg (talk) 15:21, 15 November 2010 (UTC)[reply]
While the hydrogen sulfide article is very interesting, it does not contain any answers to my questions. Plasmic Physics (talk) 21:50, 15 November 2010 (UTC)[reply]
This querry is still open to discussion. Plasmic Physics (talk) 21:03, 16 November 2010 (UTC)[reply]
As it is similar to water the structure in liquid phase is similar. The exact rection mechanism leading to polysulfide is no longer in my active memory, I thought you need basic conditions.(look at doi:10.1021/je60044a022 As it is similar to water the structure in liquid phase is similar and should look like cold water. the solubility depends on the polarsability of the solvent molecule and the hydrogen bond strength, have some time to calculate this. The auto dissociation should be to be calculated by the pKas of water and hydrogen sulfide.--Stone (talk) 21:46, 16 November 2010 (UTC)[reply]
Is liquid sulfane compatible with gaseous phosphorus as water is with nitrogen? Plasmic Physics (talk) 22:12, 16 November 2010 (UTC)[reply]
The first row elements (N and O) can build up double and triple bonds which is highly unlikely for later rows, this makes them very incomparable.--Stone (talk) 22:21, 16 November 2010 (UTC)[reply]
Do you mean incompatible with everything or just first row non-metals? Oh, by the way, I didn't mean an exact molecular analogue to nitrogen. Tricyclo[1.1.0.02,4]tetraphosphane is an acceptable structure, I did not explicitly mean DiphosphorusPlasmic Physics (talk) 01:02, 17 November 2010 (UTC)[reply]
Cell phones and radiation
I was just reading yet another story about potential correlations between cell phone frequency EM radiation and brain tumors. I don't really want to debate the pros and cons of the argument here — I'm just referencing it for the context, and want to, for the sake of argument here, assume that the correlations are valid.
Most of these articles seem to imply that holding the phone an inch away or so negates the problem, or at least lessens it.
My science question: why would this be the case? Can an inch (or less) of air actually deflect enough of the EM radiation in question to make a difference? If so, shouldn't there be some relatively easy way to build shielding into the casing that would scatter the EM radiation away from the earpiece? --Mr.98 (talk) 17:48, 15 November 2010 (UTC)[reply]
If you want an example of this, test an induction-based recharger. I have one for my watch. If it sits on the recharger, it blinks, so I know it is recharging. If it is about 1/4" off the charger, it blinks. If it is 1" off the recharger, it doesn't blink anymore. At about 1/2", it is flaky. Sometimes it blinks, sometimes it doesn't. All that is between the electromagnetic source (the charger) and the watch (which is designed to absorb and make use of the energy) is air. -- kainaw™ 18:00, 15 November 2010 (UTC)[reply]
Forgot to answer the other questions... Can cell phones be shielded so they don't emit electromagnetic waves? Yes - easily. But, they won't work anymore. The main function of a cell phone is to send/receive EM energy. Can a simple device be made to keep the phone an inch away from your head? Yes. About 10 years ago, I saw a guy on TV telling you that you need to cut 1" off a toilet paper tube and tape it to your phone to keep it 1" away from your head. -- kainaw™ 18:03, 15 November 2010 (UTC)[reply]
Let me clarify, because I think it's not clear what I'm suggesting, or something. (Obviously I know that the phone needs to be emitting to be functional. Obviously I know you can build in some kind of physical means of keeping the phone an appropriate distance.)
Below is a crude but hopefully amusing ASCII diagram of someone holding a banana-shaped phone which is sending out microwave radiation in an approximately spherical pattern, zapping our poor fellow's brains with said EM radiation. (I have placed the phone some distance from the head, but that is just to illustrate the radiation direction. Imagine it is right next to the head.)
ooo . . .
o o . . .
0 x x 0 . . .
| u |...\\....
| P |...||....
\___/ .// .
/ \ . pO .
| | || .
Here is another similarly crude diagram where some sort of barrier has been put on the face-side of the phone which reflects the EM radiation off of it. The result is that only a small part of the overall EM sphere is reflected or scattered away from the head:
ooo . .
o o . .
0 . . 0 . .
| u | \\\....
| U | |||....
\___/ /// .
/ \ pO .
| | || .
It seems to me that this would be relatively trivial and only have a marginal effect on phone quality? (It would be, I presume, a directional effect, so the direction you were facing might change your reception.) Is this a ridiculous notion?
And while I am not a scientist, it strikes me that the induction charger might not be exactly analogous, since it involves a different part of the spectrum and different intensity? --Mr.98 (talk) 21:17, 15 November 2010 (UTC)[reply]
I know some things about science, I can confidently tell you that energy of the EMR used by cellphones do not meet the required threshold to cause you to develop cancer. It is simply a urban myth reslting from a poorly conducted experiment. Plasmic Physics (talk) 22:00, 15 November 2010 (UTC)[reply]
I'm not asking you for an assessment of the threat, as I made clear in the first paragraph of my question. I really do wish people would actually read the question before trying to answer it. This seems to be a real epidemic on here lately. --Mr.98 (talk) 23:54, 15 November 2010 (UTC)[reply]
There is no need for such a contraption as what you're proposing, is what I was trying to say. The air does not absorb the EMR, if it did, then the signal can not travel long distances. The cellphone emits a spherical wavefront, the energy of a wavefront is almost constant at any radius however, the energy is spread over a larger surface when the radius is large. This is propotional to luminous flux. Moving the cell phone away from the ear, increases the radius and consequently decreases the luminous flux. Luminous flux affects rate of possible DNA mutations per unit time. The frequency of EMR affects how DNA reacts. Plasmic Physics (talk) 00:23, 16 November 2010 (UTC)[reply]
Again, I don't really care about your off-the-cuff, undergraduate-physics assessment of the hazard. That's an issue I don't actually think you know enough to answer about. --Mr.98 (talk) 14:09, 16 November 2010 (UTC)[reply]
Why would it only have a marginal effect on quality?!? Going by your illustration, You've just completely cut out reception of all cell-towers to your left! Worse is if you make a call facing one way, and then turn to face the other way you'd lose your connection and the phone would probably not have time to make a new connection so the call would just drop.
Looking at your illustration again, perhaps you think that the waves bounce off your skull? They don't. They go straight through. Phones just wouldn't be usable otherwise. APL (talk) 22:11, 15 November 2010 (UTC)[reply]
I don't think the bounce off the skull, no. If you conceptualize the radiating frequencies as a sphere coming out of the phone, I think you'd need a wedge of about 25%-30% removed to avoid going through the human skull, based on some rough approximations on my part. Which probably would have an appreciable effect, if you are in an area with only a few cell towers. But I assume that most urban areas are pretty well saturated by towers at this point (at least where I live, it seems like every large building has one). So the worst effect would be that sometimes you'd have to turn to find a better signal? That doesn't seem like the worst outcome to me, if there is actually a long-term risk otherwise.
But if that's the case, why does adding the inch of air between your head and the phone matter? What's the inch get you? To return to one of my original questions, why would it be any safer to hold the phone an inch from your head? --Mr.98 (talk) 00:10, 16 November 2010 (UTC)[reply]
I think most mobile phones already have a directional antenna that mostly radiates away from the head, this gives best signal quality since almost no radiation passes through the head, some are reflected and the most are absorbed.
File:Cellphone head sar 1.pngCalculated specific absorbed radiation (SAR) distribution in an anatomical model of head next to a 125 mW dipole antenna. Peak SAR is 9.5 W/kg averaged over a 1 mg cube. (USAF/AFRL). Note the concentration to the surface, most of the radiation only penetrate a few cm.
I have not heard the recommendation to hold the cellphone a inch from the head. I think it is reasonable to assume that any health effect decrease faster than linearly so it is better to spread the exposure over larger area if the effect exists at all. I also think the recommendation can have to do with the near field of the phone, this can afect both reception and health effects. --Gr8xoz (talk) 02:04, 16 November 2010 (UTC)[reply]
OK, this I get. It's not the air, it's the distance from the point source, so that the amount of EM radiation is more diffusely distributed. That is useful to know and I see where I was confused about the nature of the alleged threat — thanks! --Mr.98 (talk) 15:21, 16 November 2010 (UTC)[reply]
Gr8xoz actually has a relevant point. If holding the phone 1 inch from the head improves reception then this is a good thing if you are concerned about the level of the radiation for whatever reason since this will generally be reduced (as the phone adjusts the signal strength based on the reception). This BTW is a common concern with things that allege to reduce radiation to the body, by screwing with the signal they may just make the signal stronger. Of course if by holding your phone 1 inch away your call lasts longer because you can't hear each other properly this may also negate any purported beneficial effect. Also while I'm less sure of this, I presume if you're using packet switched calling, more noise may mean more transmission may mean more radiation. Nil Einne (talk) 08:50, 16 November 2010 (UTC)[reply]
The industrial solvents which leach out of typical consumer electronics in response to heat and perspiration are far more carcinogenic than any radio frequency electromagnetic radiation. Ginger Conspiracy (talk) 06:55, 17 November 2010 (UTC)[reply]
On the case of shielding, the wavelength of mobile phone RF is from 10 to 30cm. A shield needs to be considerably larger than the wavelength to block otherwise the theory of diffraction applies and the waves move around your little shield. You can try for a cardioid radiation pattern, with a null towards the head, but as mentioned that will cause dropouts in one direction. A tinfoil hat may be needed. Graeme Bartlett (talk) 09:40, 17 November 2010 (UTC)[reply]
As for phones that have an antenna, see ferrite bead. ~AH1(TCU) 03:43, 18 November 2010 (UTC)[reply]
We are all going to die anyway, so it kind of is irrelevant.AdbMonkey (talk) 06:55, 18 November 2010 (UTC)[reply]
Sorry if that sounded terse. I did not mean to be pedantic about life's ephemerality, but it makes me sad when I think about it. AdbMonkey (talk) 07:05, 18 November 2010 (UTC)[reply]
Cell phones and breast cancer
Another one....
As a high school teacher where students are not supposed have phones visible in class, a common storage location used by female students is in their bra. If they can cause brain tumours, what about breast cancer? HiLo48 (talk) 18:09, 15 November 2010 (UTC)[reply]
There is no evidence that cell phones cause any kind of cancer or tumors in humans...although they certainly do lead to rumors! 129.2.129.161 (talk) 18:28, 15 November 2010 (UTC)Nightvid[reply]
I would not summarize the current state of medical opinion on mobile-phone effects so bluntly. There is an enormous body of research on mobile phone health effects, and it is hard to say there is a strong consensus opinion. Our article, Mobile phone radiation and health, summarizes the state of knowledge pretty thoroughly. A few things we do know for sure: the frequency that cell-phones operate at can cause radiological harm. The intensity at which cell-phones operate at might be safe. Numerous studies exist, varying in their level of certainty and scholarly merit; the results variously confirm or refute the idea that mobile phones have increased cancer (and specifically, tumor and glioma) incidence. Nimur (talk) 18:59, 15 November 2010 (UTC)[reply]
I know that we don't yet have scientific certainty on whether cell phones can cause cancer. My question was a hypothetical. Ifthey can cause brain tumours, what about breast cancer? These girls have them close to their breasts for longer periods than normal users would have them close to their heads. HiLo48 (talk) 21:12, 15 November 2010 (UTC)[reply]
Can you please cite A few things we do know for sure: the frequency that cell-phones operate at can cause radiological harm. Microwaves fall between radio waves and infrared and visible light on the electromagnetic spectrum, neither of which cause "radiological harm". I'm not saying the case is shut, but if there is an effect, it isn't great, that is for sure. Very few technologies are perfectly safe, look at cars, the amount of people that die because of cars is staggering, but it's a risk we accept because the benefit of road travel is so great, even if a few people die by mobile phone, I dare say most people would still accept the risk rather then give up their phone. That's not saying that if we do find "something" we shouldn't make phones safer if we can, but it does mean that if we can't find a link we should make one up to panic people into buying magical microwave blocking holograms for $30 that do nothing. Vespine (talk) 22:10, 15 November 2010 (UTC)[reply]
I would hardly panic: I personally think the risks of cancer due to mobile telephony are small. But here are some citations: first, the thermal effects section of our article - it is beyond dispute that microwave radiation can cause tissue heating. A Google scholar search on biological effects of microwave radiation turns up numerous books and papers. And here's an IEEE paper, Biological effects of radiofrequency/microwave radiation, that essentially summarizes 50 years of research, establishing "safe" power exposure thresholds. I'm of the impression that even at full transmit power, the radio-intensities in mobile telephones are below the threshold of "significant" risk, but I would be reluctant to call it "zero" risk. Nimur (talk) 01:00, 16 November 2010 (UTC)[reply]
See the article above or the article I posted in the topic above this one. There is still a lot of scientific uncertainty on the question. The NY Times article cites a number of cases where EM radiation in the frequencies in question did create detectable abnormalities in rats. It's unclear what the epidemiological connection is or whether we can detect one at this point. It's unclear what the long-term risk is, which makes it impossible to make a good cost-benefit decision. Nobody is suggesting that a cell phone will give you cancer tomorrow — the suggestion is that after a few decades of heavy use like we've been doing since the late 1990s, there could be a huge uptick in things. It seems to me like a reasonable thing to wonder about, and to be cautious about, given the volume of people we're talking about here. Automobiles are not a great comparison — people were willing to adopt reasonable measures (which cost time and convenience) for safety (e.g. seat belts). --Mr.98 (talk) 23:47, 15 November 2010 (UTC)[reply]
It strikes me that it would matter whether or not the phone's EM radiation was constant when the phone was in "standby" (not talking) mode, among other things. I think the short answer is "nobody is really sure." Breasts and brains are different types of tissue, for one thing, and would presumably respond differently. It's not clear that causing one kind of cancer would necessarily imply that the other kind would be caused the same way, is what I'm saying. --Mr.98 (talk) 21:22, 15 November 2010 (UTC)[reply]
In any case, phones transmit almost not at all when they're sitting there unused. However, I suppose in this day of wireless headsets, you might have a phone in your bra that was making a call. APL (talk) 22:22, 15 November 2010 (UTC)[reply]
Don't phones do some sort of connection every so often? I know someone who leaves a (GSM) mobile near their speakers/amp all the time (connected to their computer) so you do hear it connecting every so often when not doing anything (even receiving SMS or whatever). I don't know how this power level compares to when it's making a calls or internet connection but it's obviously higher then the normal baseline. It doesn't last extremely long but then again for typical teens in many countries most of their usage may be sending and receiving SMSes anyway although in some I would guess mobile internet usage is increasing. If I were the parent of a teen, I'd be more worried about them getting some sort of RSI or other problem from SMSing too much or perhaps going deaf from listening to loud music then I would breast cancer from storing their phone in their bra. Somewhat OT but some people store their phones in a pouch around their waist, while not as close this is usually fairly near the testicles for males and I know people who don't like it for that reason. Many store their mobiles in their pocket which although further isn't that far. (From a search, the heat from laptops seems to be a more common concern however.) Nil Einne (talk) 08:32, 16 November 2010 (UTC)[reply]
Yes, they do register with the nearby cell towers periodically so the network knows when to do a hand-off, where to send ring signals, so authorities can track your position if you're accused of a crime, etc. Ginger Conspiracy (talk) 06:54, 17 November 2010 (UTC)[reply]
The industrial solvents which leach out of typical consumer electronics in response to heat and perspiration are far more carcinogenic than any radio frequency electromagnetic radiation. Ginger Conspiracy (talk) 06:54, 17 November 2010 (UTC)[reply]
Any cancer risk from cell phones is elevated in adolescents. Other studies show a direct correlation between exposure to mobile phone radiation and reduction in male spermatozoon function. ~AH1(TCU) 03:41, 18 November 2010 (UTC)[reply]
Bipedalism, pelvis size, and childbirth
I often come across the claim that humans evolved to have smaller pelvises because bipedalism wouldn't be practical otherwise...with the price that childbirth becomes much riskier. But this seems hard to reconcile with the obvious fact that a lot more women appear to have difficulty giving birth than have difficulty simply walking upright...so how to justify the claim that they both exert comparable amounts of evolutionary pressure (or at least did before the advent of modern medicine and medicalized childbirth?) 129.2.129.161 (talk) 18:25, 15 November 2010 (UTC)Nightvid[reply]
Bipedalism#Humans discusses speculation as to why we have evolved to be bipeds; it says there are at least 12 theories about this, so it's going to be a little difficult to pick a single answer to your question about evolutionary pressure. Interestingly we have a whole article on Human skeletal changes due to bipedalism which does not mention the pelvis. (It does mention the hip.) Comet Tuttle (talk) 19:16, 15 November 2010 (UTC)[reply]
You've missed that childbirth would not be such a problem if babies did not have such large heads. The question is, when did we start to get such large heads that this caused a problem? Most speculation I've seen places that after the rise of bipedalism. The evolutionary arms race then comes between the baby, 'wanting' to be born with as large a head as possible, and the mother, who needs to survive the process well enough to raise the child. This is speculated as the reason why human babies are born so helpless, effectively premature even at full term, so that they can continue to grow their enormous heads outside the mother, after having made it through the pelvis. 86.164.144.120 (talk) 20:22, 15 November 2010 (UTC)[reply]
Aspartame vs. Sugar on teeth
It's well accepted that Sugar damages your teeth especially in large quantities, but is Aspartame (specifically from diet sodas) as bad, the same, or worse then sugar on teeth? Are there any studies that address this? Thanks! Chris M. (talk) 19:15, 15 November 2010 (UTC)[reply]
From this link, 'The American Dental Association has noted it "welcomes the development and FDA approval of new artificial sweeteners that are shown to be safe and non-contributory to tooth decay. . . . Aspartame is an FDA-approved, safe sweetening agent and flavor enhancer that can be substituted for sugar in the diet."' That doesn't explicitly say apartame is non-contributory to tooth decay though. Franamax (talk) 20:53, 15 November 2010 (UTC)[reply]
Here is a 2001 American Dental Association review which says "Non-nutritive sweeteners found in diet soft drinks may not be directly cariogenic because tooth decay producing bacteria cannot ferment aspartame...". Here is the ADA mentioning "...non-cavity causing sweeteners such as aspartame...". Still haven't found a specific study though. Franamax (talk) 21:04, 15 November 2010 (UTC)[reply]
Think about how sugar damages teeth. Bacteria ferment it to some sort of acid, generally by oxidising the carbon backbone until a carboxylic acid group appears. How are bacteria going to ferment aspartame? It is a peptide yes but the COOH groups are esterified. John Riemann Soong (talk) 23:47, 15 November 2010 (UTC)[reply]
Not to mention that the amount of aspartame needed to get a level of sweetness is much less than an equivalent amount of sugar. There's so little aspartame in most foods that the effect on teeth is really a moot point anyway. Keep in mind, though, that something like Diet cola generally still has Phosphoric acid, which will still attack teeth. Buddy431 (talk) 03:45, 16 November 2010 (UTC)[reply]
A conspiracy theory that doesn't hold up. If there were any truth to this the powerful sugar industry, which in America has kept trade restrictions alive and well, would be all over it. Imagine Reason (talk) 23:20, 16 November 2010 (UTC)[reply]
Why is the Nissan GTR so fast?
Compared to other cars, the Nissan GTR is heavier and less powerful but still is incredibly fast. I've compared it with more powerful cars that also have AWD. I've also compared it with lighter more powerful cars. All of this combined with the low price does not make sense to me. If anyone can help, I would appreciate it. 158.135.169.37 (talk) 19:44, 15 November 2010 (UTC)[reply]
Well, obviously how a car performs in a race isn't just about power and weight, otherwise, the winner of every race could be predicted by just plugging in figures into a simple formula, which is obviously not the case. If you are interested you should probably start by reading the article Nissan Skyline GT-R, It has a lot of information about the car's performance features.Vespine (talk) 21:47, 15 November 2010 (UTC)[reply]
In particular, "tests showed the car had a factory power output of closer to 330 PS (325 hp) at the flywheel. The lower published figure was Nissan's response to the need to abide by a gentleman's agreement between the Japanese auto manufacturers not to release a car to the public exceeding 280 PS (276 hp) of power output," refers to an engine which can easily be adjusted to put out 450-500 horsepower. That and the fact that the GTR body has since the 1990s been far more about aerodynamics than design styling like most of the cars in its class. Ginger Conspiracy (talk) 06:48, 17 November 2010 (UTC)[reply]
You haven't defined "incredibly fast", so it's hard to pin anything down. For stoplight-to-next-stoplight fast, torque will be most important, and the gear ratio will count too. For a highway car, the ratio of the highest gear will decide how fast it can go, in combination with the horsepower. For getting around a road course or rally stage, handling becomes important (steering, brakes). For oval or sprint track racing, you optimize straight-line acceleration, slowing into a corner, and accelerating out of a corner. To keep a "fast" car cheap, match the gear ratios to the torque curve of the motor so it appears fast, then minimize everything else. Take out the standard ABS, rear wiper, comfortable seats, use a smaller HVAC system, allow only 2GB of storage in the MP3 player (if you've gotten to that stage, you're pretty desperate to cut weight and cost :). Automobiles actually made for sale are a whole package, so you have to evaluate all their costs and benefits. You didn't mention fuel costs or insurance rates at all, and those can have a huge impact on just how "incredible" you think a car is once you are the one actually operating it. Franamax (talk) 07:26, 16 November 2010 (UTC)[reply]
In terms of the 'cost' part of the question, some of that comes down to expectations, 'street cred', showoff factor, market psychology, or whatever you may like to call it. In short Nissan is chiefly recognised as a manufacturer of relatively bland, low cost, mass market cars. So even if they produce a killer car like the GTR, they can't expect to get the sort of coin for it that the exclusive marques like Ferrari, Lamborghini, Porsche etc can ask. Why would anyone pay that money for a shopping trolley brand when they could be driving one of the world's exclusive cars, even if the Nissan is faster, more powerful, better optioned, more reliable, or whatever else it may be? Like it or not, you do pay for the badge. --jjron (talk) 12:30, 16 November 2010 (UTC)[reply]
Roaccutane Treatment
The following discussion is closed. Please do not modify it. Subsequent comments should be made on the appropriate discussion page. No further edits should be made to this discussion.
hi, i am using roaccutane treatment since 4 months. however, after i read in the article in this site that it makes back ache, a question crossed my mind: is it dangerous to continue with this treatment if there is a disc problem even if it is not a serious problem? because i used to have back ache before i started roaccutane. i am looking forward to get your reply even if it is medical question because it will help alot. thanks
The reply is that you have to consult your doctor. Please do not trust random strangers over the Internet with important medical questions; your health may be damaged if you follow bad medical advice, even if it's given with good intentions. Comet Tuttle (talk) 20:58, 15 November 2010 (UTC)[reply]
The discussion above is closed. Please do not modify it. Subsequent comments should be made on the appropriate discussion page. No further edits should be made to this discussion.
Conversion from Seconds to Meters
If a distance unit like a meter is used to measure length in 3-dimensions and a unit like a second is used to measure a length in time, which some indicate is the 4th dimension, is there a conversion equation that states the measurement of time in that of distance? For instance, X seconds = a * Y meters. -- Sjschen (talk) 21:58, 15 November 2010 (UTC)[reply]
The conversion equation is d = c t, where d is distance in meters, t is time in seconds, and c is the speed of light in meters per second, i.e., c = 299,792,458. Red Act (talk) 22:13, 15 November 2010 (UTC)[reply]
I'm not entirely sure what you're asking, but it sounds like it has to do with special relativity. At velocities approaching the speed of light, a coordinate or vector of time has to be descibed in terms of space. As in, for this spatial coordinate or vector, time is such. One should be carefull when discussing dimentions, space and time maybe dimensions, but they are different kinds of dimentions. The are, up to date, twelve spatial dimentions, and two temporal dimenstions. Plasmic Physics (talk) 22:19, 15 November 2010 (UTC)[reply]
Only four are accepted in Special relativity where the "conversions" are really rotations in 4-D space-time. Different proposed theories predict different numbers of possible dimensions, but only the four of special relativity have actually been "discovered". Most of the other "predicted dimensions" are too small to measure. Dbfirs 22:31, 15 November 2010 (UTC)[reply]
I'm just curious because if one can use meter to measure the the "first 3" dimensions I'm wondering if one can use the same unit to measure the "4th" dimension, given some imaginary alien that lives in these 4 dimensions just like we do our 3. It certainly would be fun (albeit nerdy) to say that the laundry will be done in some X meters instead of minutes. -- Sjschen (talk) 23:51, 15 November 2010 (UTC)[reply]
You're confusing spatial dimensions for temporal dimensions, there is a hypothetical fourth spatial dimension which is defined in terms of meters. Time is not the fourth spatial dimension, it is the first temporal dimension, it is the fourth perceptable dimension. Everything lives in these four dimentions. Plasmic Physics (talk) 01:29, 16 November 2010 (UTC)[reply]
Us earthlings do it the other way round! We define our metre to be 1⁄299,792,458 of a light-second! We do it that way simply because we can measure time far more precisely than we can measure length: so it makes sense in practical terms to define the unit of length in terms of the unit of time, rather than the other way round. But, logically speaking, there's nothing to stop me saying that it takes my washing maschine about 8 light-micrometres to do a load of laundry ;) Physchim62(talk) 00:48, 16 November 2010 (UTC)[reply]
You have a very fast washing machine, 8 light-micrometres = 0.000 000 026 667 s --Gr8xoz (talk) 01:59, 16 November 2010 (UTC)[reply]
Ah yes, sorry, I gave the wrong result. 8 light-micrometres is about how long I spend each day wondering how I always seem to have clean laundry. My partner tells me that the washing machine takes about 720 light-gigametres to do a load, and has suggested I measure this value more precisely myself ;) Physchim62(talk) 01:37, 16 November 2010 (UTC)[reply]
You can choose to use a system of natural units in which the speed of light is 1 by definition, in which case time can be measured in meters (not "light-meters"), just like spatial distance. Instead of thinking of "space" and "time" as two "different kinds of dimensions", it works fine (better even, when doing general relativity) to think of spacetime as being a 4-dimensional manifold in which "space" and "time" dimensions are not distinguished, except for there being a metric tensor that introduces a local directionality to spacetime. Red Act (talk) 03:39, 16 November 2010 (UTC)[reply]
Hmmm... very cool thanks! But what's this thing with 2 temporal dimensions? -- Sjschen (talk) 00:12, 17 November 2010 (UTC)[reply]
See multiple time dimensions. Two timelike dimensions would be ultrahyperbolic which might not allow for stable physics, but maybe they could[10], but there might more likely be three[11] or seven[12] timelike dimensions if there isn't just the one which we experience directly. Ginger Conspiracy (talk) 00:44, 17 November 2010 (UTC)[reply]
Would there be any tropospheric ozone if humans did not exist? Blackmetalgrandad (talk) 22:57, 15 November 2010 (UTC)[reply]
Yes, there would be atmospheric ozone. Ozone naturally occurs as a product of lightning and ultraviolet radiation. We exist because of ozone. Plasmic Physics (talk) 23:07, 15 November 2010 (UTC)[reply]
Without an ozone shield our pre-pre-pre-pre-pre...-pre ancestors would have been fried to a crisp...ResMar 03:43, 16 November 2010 (UTC)[reply]
The OP is asking for the distinction between tropospheric ozone and stratospheric ozone. The mechanisms for creating the two are very different, and the two sources of ozone do not mix. Stratospheric ozone is generally created from the action of ultraviolet light on oxygen in the stratosphere. This ozone in the stratosphere then absorbs more UV light, and prevents that UV light from reaching the troposphere. Within the troposphere, most of the ozone is anthropogenic (human made); it is generally created in car exhaust. Tropospheric ozone is a serious polutant, as an eye and lung irritant. There would always be trace amounts of tropospheric ozone, due to lightning, but its concentration would be much less without humans. Paradoxically, human activity also tends to decrease the availibility of stratospheric ozone. So the next effect of human life seems to be to remove ozone from the stratosphere, where it can effectively block UV radiation, to the troposphere, where it aggrivates asthma and allergies. --Jayron32 04:24, 16 November 2010 (UTC)[reply]
"it is generally created in car exhaust" kind of, but actually its formed when NO2 is broken down by sunlight and reacts with oxygen. We do have a specific article on tropospheric ozone by the way. I might be wrong here, but I can't think of any natural processes that produce NO2. Whilst there would be a very very tiny amount of tropospheric ozone naturally, our actions definitely significantly increase it. Ah yes, a source, this bascially backs up what I said, but unsurprisingly confirms I was wrong, tiny amounts will be formed due to plant VOC emissions. A google scholar search for "tropospheric ozone natural" brings up papers which you might find interesting. One thing they discuss which our article neglects (been meaning to sort it out) is that tropospheric ozone damages plants as well (thankfully all that CO2 we're producing goes some way to negate the effect. SmartSE (talk) 15:20, 16 November 2010 (UTC)[reply]
Lightning also produces ozone (and this occurs in the troposphere), but the quantities are small compared to the other sources discussed above. In any case, lightning is rarely anthropogenic. Nimur (talk) 17:13, 16 November 2010 (UTC)[reply]
I'm not sure whether any significant concentrations of tropospheric ozone exist naturally, but without anthropogenic emissions there would be no atmospheric halocarbons. ~AH1(TCU) 03:35, 18 November 2010 (UTC)[reply]
A Paradox?
At what point is change noticeable to the human eye? As if I where to add one granule of sand to a heap, at what point would any person recognize change? 66.229.227.191 (talk) 23:29, 15 November 2010 (UTC)[reply]
Your question is not very clear, are you asking if there is a paradox because some changes are too small to perceive with the naked eye? I don't see any paradox. Vespine (talk) 00:19, 16 November 2010 (UTC)[reply]
I guess in the title I was inplying that it is somewhat a paradox, as I was hoping to find a mathematical solution to the Sorites Paradox. But that wasn't apart of the question, I just want to know at what size does change become perceivable? 66.229.227.191 (talk) 00:25, 16 November 2010 (UTC)[reply]
It's not a mathematical solution, per se, but a question about human psychology/physiology. There probably isn't one answer in most cases, but a spectrum of likelihood where people will say it falls on one side or the other. (This is the "group consensus" mentioned in the article, which is probably the most "scientific" way to study the question, though it will aid the philosophers none.) On some issues, though, there are physiological reasons that we detect certain things as being discrete changes. Color, for example: show people a rainbow spectrum of chips with very slight differences between each color, and ask people to point to "red", and they'll all pick the same chip, more or less. This is because it correlates with the firings of the nerves in our eyes, or something like that ("red" is when one cone triggers at the maximum, and a rod at its minimum, or something like that... it's been awhile since I took psych). --Mr.98 (talk) 00:47, 16 November 2010 (UTC)[reply]
Wow, I'd never heard of the Sorites paradox until I read this question, and yet I have a paper in submission at the moment which discusses a very similar problem in metrology... It's amazing what you can learn at the WP Reference Desk! Anyway, the paper hasn't passed the reviewers yet, so let's hope they don't ask me to discuss Greek philosophy on top of everything else ;)
To translate my proposition into the language of the Sorites paradox, I say that a heap is no longer a heap if you can tell the difference on removing a single grain. A bit like saying you're rich if you don't have to worry about your bank balance! In more formal terms, "tell the difference" is related to the measurement uncertainty of whatever method you are using to measure your heap: nowadays, that doesn't just have to be human vision. So, if we define the quantity n as the "size" of the heap (by whatever method of measurement), and the quantity N as the number of grains, the heap remains a heap if the quantity 1/N can be treated as a differential dn/n under the conditions of measurement, the quantity 1/N being the fractional change in the number of grains when N changes by one grain. You can treat 1/N as a differential if the discontinuity in the measurement result when the number of grains changes by one grain is, or would be, significant compared to the uncertainty of the measurement result, discounting the contribution to the uncertainty from any correction for systematic measurement error.
But the entire point of the paradox is that there is no way to indicate a one grain tipping point. --Mr.98 (talk) 01:56, 16 November 2010 (UTC)[reply]
And the metrological problem is that the answer is: "well, it depends"! Physchim62(talk) 02:31, 16 November 2010 (UTC)[reply]
I guess what I am trying to do is disprove the whole paradox idea. I believe everyhing has an answer. Oh, Maybe you can send me your paper, sounds like an interesting read. Post it on my discussion: User_talk:Bugboy52.40. 66.229.227.191 (talk) 03:06, 16 November 2010 (UTC)[reply]
The problem with the paradox is one of human perception and linguistics, not reality. We make the distinction between grains of sand and a heap, not nature. I don't consider it much of a paradox, myself. A term like "heap" has no real scientific meaning, which is why we use precise terms for masses of thing (e.g. a kilogram) for things that have to have real answers. I have heard philosophers banter on about "baldness" in the same way — when do someone become "bald"? What's the hair that does it? It's just navel gazing in my opinion. --Mr.98 (talk) 14:04, 16 November 2010 (UTC)[reply]
My solution would be to define the heap only in the limit of N to infinity (and making the grain size scale inversely with N so that the total volume remains constant in the N to infinity limit). If N is not strictly infinitely large, you only have an approximate heap that gets worse the smaller N becomes.
In statistical mechanics a similar problems arises in the theory of phase transitions. Given some amount of matter, you want to be able to say that it is in one phase or another phase (like liquid or gas). But it turns out that for finite amount of substance, phases are not defined. Obviously, if you have only a few molecules, you can't tell which phase the substance is in, so the situation is analogous here. Strictly speaking, you need to take the limit of an infinite amount of substance (the so-called thermodynamic limit). What happens mathematically, is that the partition function is an analytic function of the temperature for any finite number of particles, but in the limit of an infinite number of particles, a singularity can develop which then defines the phase transition.
The point is then that a Taylor expansion at a point in one phase won't converge into the regime of the other phase. So, an extrapolation based on accurate measurements of the properties of the system in one phase to predict the behavior in the other phase will fail. As long as accurate extrapolation gives the correct result (in the limit of infinite accuracy), you can say that the system is qualitatively the same and thus in the same phase. Strictly speaking, you need an infinite amount of particles for the distinction between phases to arise. Count Iblis (talk) 04:36, 16 November 2010 (UTC)[reply]
An actual answer to the question
In psychology, this concept is called a just-noticeable difference or JND, and has been studied very intensively as part of psychophysics. The principle result is that a JND is generally a constant proportion of the perceived magnitude of a quantity, however the size of that proportion varies according to the nature of the stimulus. This rule is known as the Weber-Fechner law. Looie496 (talk) 17:52, 16 November 2010 (UTC)[reply]
There's already an equation? So I spent all of last night trying to create an equation myself was useless... this actually happens to me quite often... they should make a rule to do more research before trying to solve something that's already been solved :/ 66.229.227.191 (talk) 20:31, 16 November 2010 (UTC)[reply]
A jaded grad student once told me "spending merely a few weeks in lab can easily avoid the necessity for doing a 5-minute literature search." DMacks (talk) 20:54, 16 November 2010 (UTC)[reply]
It wasn't useless: your brain is now slightly different than it would have been if you hadn't tried to solve the problem yourself, presumably for the better. You have shaped yourself slightly. 86.163.213.68 (talk) 00:09, 17 November 2010 (UTC)[reply]
In scientific experiments there is an essentially arbitrary criterion that if statistical tests find that a difference of the size observed would be found 5% of the time just by random chance, that this is significant. I don't know if people decide by eye that one pile of sand is larger than another pile of sand on the same basis (that there is a small risk that they would imagine a difference of the same degree between two equal piles), but it is possible. Wnt (talk) 02:02, 17 November 2010 (UTC)[reply]
There is a mathematical reason that scientists use 95% as a level of significance. If your chains of inferences take place at the 95% confidence level, the likelihood that you will be mislead by random chance is vanishingly small. But at the 90% confidence level, chains of inference can mislead you by random chance fairly often. I have a more concrete quantification in my library; I'll look for it, but for five inferences with random interdependencies the difference is something like 0.001% vs 3% if I remember correctly. Ginger Conspiracy (talk) 06:33, 17 November 2010 (UTC)[reply]
Sorry to be so blunt, but that's totally bogus. Looie496 (talk) 23:34, 17 November 2010 (UTC)[reply]
1) If work is done on a system, then W = ΔE. But how can we calculate the work done by the system on its surroundings? Intuitively, I would think the answer is -ΔE, but I can't prove it :(. When I try, I run into contradictions (two planets at rest, gravitationally attracted to each other; if one planet is considered as the system, then its energy will increase. Wext = -ΔE, then the other planet shouldn't speed up, but it does).
2) The work article says that the total work done in an isolated system is independent of the frame of reference. What's the significant/implications of this? 76.68.247.201 (talk) 02:07, 16 November 2010 (UTC)[reply]
Yes, work is antisymmetric like that: if I do work on you, you're doing negative work on me. However, your planets are each doing work on the other, but they also are losing potential energy in the process, so their actual . A heavy piston sliding down into a cylinder of gas (perhaps because the gas is cooling, so its pressure is dropping) does work on the gas even if it's moving at constant speed; the negative work done on it by the gas annihilates its potential energy.
It means that changing your frame of reference doesn't change, say, the laws of chemistry. If I fire a gun while on a train, the work done by the expanding gas on me and on the bullet is the same, which means that the energy of the chemical reaction is the same. --Tardis (talk) 15:53, 18 November 2010 (UTC)[reply]
November 17
How close does a white dwarf have to be to another star to "steal" hydrogen? —Preceding unsigned comment added by 76.161.251.228 (talk) 14:26, 18 November 2010 (UTC)[reply]
It depends entirely on what conventions you are using. All that matters is that changing the direction of the work switches the sign of ΔE. Under some systems, we take the perspective of the system (chemical thermodynamics takes this perspective, thus exothermic reactions have a ΔE < 0 ). Under other systems, we take the perspective of the observer (who is part of the surroundings), thus the sign convention would be opposite. However, your intuition is correct. All other things being equal, the only difference between the direction of the work is the sign of ΔE. It becomes obvious if you place two objects on a number line. If object A pushes object B in the positive direction, then object A did +ΔE, if object B pushes object A with the same force over the same distance, then object A did -ΔE. As long as you keep the perspective on "work done on/by object A" you will always get opposite signs for those two situations. The implication of the independence of work from the frame of reference is the Law of conservation of energy. If you could vary the amount of work merely by changing the frame of reference, then total energy would not be conserved. --Jayron32 04:17, 16 November 2010 (UTC)[reply]
What you said for part 1 makes sense. For part two, why does it imply the conservation of energy? 76.68.247.201 (talk) 04:54, 16 November 2010 (UTC)[reply]
If I could change the amount of work done in an isolated system just by altering my frame of reference, that would imply that if I was in motion past an isolated system, and observed the work done in the system, that value would be different than if I was stationary relative to that system. That would imply that there were differing amounts of energy exchanged in the two situations; where would the extra energy come from or go to? --Jayron32 05:00, 16 November 2010 (UTC)[reply]
In the original example, both planets gain positive kinetic energy and the system (the two planets together) loses gravitational potential energy. Dbfirs 08:41, 16 November 2010 (UTC)[reply]
Yes, I had just realized that I forgot about PE after I posted. Thanks for the clarification! 76.68.247.201 (talk) 12:10, 16 November 2010 (UTC)[reply]
Wireless v fibre internet
Is it true that wireless internet will never attain the speeds of (optical) fibre internet due to the laws of physics? We're having a debate about an National Broadband Network in Australia at the moment and I hear this statement a lot. I'm wondering if it is theoretically true. 124.149.24.85 (talk) 10:35, 16 November 2010 (UTC)[reply]
I believe that the theorietical maximum is based on the frequency of the carrier, and light has a much higher frequency than radio. However I don't think that radio or fibre are near this maximum (though I could be wrong), so possibly tomorrow's wireless will exceed the maximum speed of today's fibre -- Q Chris (talk) 11:32, 16 November 2010 (UTC)[reply]
'Speed' can be a bit of nebulous term. It's more an issue of bandwidth. The argument goes that due to the finite range of frequencies available for wireless transmission it can only handle so much bandwidth, whereas for fibre, if you're running out of bandwidth you can just lay another optical fibre cable down and increase it. Wireless is often proposed as a solution in low population density areas for two main reasons - the wide spread of the few people makes laying the cable uneconomical, and secondly with only a small number of people accessing the wireless network each can have a bigger share of the limited bandwidth and thus achieve higher speeds than would be possible in high population density areas (but not as high as they'd get with fibre). As the saying goes, never say never, but with current technology and knowledge these limits apply. --jjron (talk) 12:13, 16 November 2010 (UTC)[reply]
Thanks. Do you know the name of the physical principle that limits the bandwidth in wireless communication?124.149.25.247 (talk) 01:25, 17 November 2010 (UTC)[reply]
It is hard to find true theoretical limits without very well defined conditions but for reasonable conditions in the next 30 years or so fibre seams to have a big advantage if you are concerned with bandwidth while wireless can theoretically have a small advantage in Round-trip delay time due to higher speed of electromagnetic waves in air than glass(300 000 km/s and approx. 200 000 km/s).
I define wireless internet as communication in the radio and microwave frequencies. (Ruling out Free-space optical communication and other high frequency devices that has very different properties than current wireless internet such as WIMAX, WLAN, 3G and 4G) The fastest wireless link I found was on 6 Gbit/s, see [14], it uses a frequency band at 85 GHz, it achieves 2.4bits/s/Hz over a distance of 250 m. Depending on definition the microwave band is up to 300 GHz wide. Depending on the signal to noise ratio the number of bits per second and Hz vary, se Spectral efficiency and Shannon–Hartley theorem. With very low noise the best modulations give about 15 bits/s/Hz, this would give a theoretical maximum capacity of 4.5 Tb/s and antenna. With MIMO several antennas (independent channels) can be combined to higher capacity, the number of antennas is theoretically unlimited but due to limits in device size, signal-processing and the need for path diversification the number of effective independent channels are probably limited to less than 10.
This gives a upper limit on the capacity of microwave communication to less than 50 Tb/s for each cell. (A device anywhere near this capacity will probably not be mobile and very directional so it has probably no place in a cellular network)
The physical bandwidth in a conventional fibre are about 150 THz (1000 nm to 2000 nm).
The fastest fibre optical link that has been demonstrated uses 10.8 THz and was able to achive 69.1 Tb/s over 240 km. So a single optical fibre can already get higher capacity than the "theoretical" upper limit for microwave communication.(http://www.ntt.co.jp/news2010/1003e/100325a.html) If they where able to use all the physical bandwidth they would get a capacity about 1 000 Tb/s. This can then be multiplied by an almost unlimited number of fibres. The fastest commercial links to date can archive 1.6 Tb/s, see Wavelength-division multiplexing.
Thanks for your reply. My understanding is that the Shannon-Hartley theorem defines the maximum error free data transfer under a noisy channel. So, my guess is that the physics that puts an upper limit on wireless communication is the existence of Additive white Gaussian noise, which from my understanding models background radiation and other universal physical phenomena. Given that, I might rephrase my original question: is Shannon-Hartley theorem a fundamental physical law? Is there no way to theoretically circumvent the principle? 124.149.25.223 (talk) 02:52, 17 November 2010 (UTC)[reply]
After searching a bit, I think I have already found an answer to my own question. It's all about entropy. Thanks again to all who answered. 124.149.25.223 (talk) 03:23, 17 November 2010 (UTC)[reply]
In order to expand on the image description, so the image can be moved to Commons,
Is anyone on the Science Reference desk able to provide a more specific species
identification?
Image is used on Fauna of Borneo if you need some indication of geographical location.
Just so you don't waste time looking it up rama rama is apparently just Malay for 'butterfly', Google yields nothing. —Preceding unsigned comment added by 86.4.183.90 (talk) 14:08, 16 November 2010 (UTC)[reply]
I can confirm that. I'll provide some more suggestions on Sfan's talk page (out of respect for the uploaders privacy). Nil Einne (talk) 18:28, 16 November 2010 (UTC)[reply]
Red v. grey squirrels
If grey squirrels had not been introduced into the UK, would red squirrels still be in such decline as they are now? In other words, have the grey squirrels merely taken up the space left by the red squirrels, or have they ousted them by direct competition or disease etc? Thanks 92.28.252.5 (talk) 13:26, 16 November 2010 (UTC)[reply]
There are various theories as to why grey squirrels have generally supplanted red squirrels - here - but the consensus does seem to be that the red squirrel has declined due to competition, rather than any other reason. Ghmyrtle (talk) 13:36, 16 November 2010 (UTC)[reply]
If you read that page carefully, you can see that in pine forests, there are about the same number of both kinds of juvenile squirrels. The reds' shorter lifespan, weaker constitutions, and less aggressive foraging behavior could easily be responsible for their decreased prevalence. Ginger Conspiracy (talk) 00:27, 17 November 2010 (UTC)[reply]
Seeing the space station
If I were to buy a medium range consumer available telescope and look at the international space station with it from earth, would I be able to see the station clearly and in detail? —Preceding unsigned comment added by 93.84.7.186 (talk) 14:11, 16 November 2010 (UTC)[reply]
The International Space Station's orbit never brings it lower than 278 km (173 miles) above ground. I'm not certain what is considered a typical "medium range consumer telescope" today, but I doubt it would have useful magnification much above 300 power. Even at 500 power, at the very best the station would look as though it was about 1/5 km (1/3 mile) away -- and usually farther, depending on where it was in its orbit and where on the ground you were. Not what you would call seeing it "clearly and in detail". --Anonymous, 14:31 UTC, November 16, 2010.
The ISS moves very fast, so any telescope would have difficulty keeping up with it.--Shantavira|feed me 15:04, 16 November 2010 (UTC)[reply]
Starting about halfway down this page, there are several images (including some video) of the ISS transiting (passing in front of) the Sun and the Moon. Note that to observe a solar transit you need to have an appropriate telescope with suitable filters, and to get anything that would look space-station-like you need to have a big aperture telescope (several inches). Here's another solar transit, captured using a 160 mm (roughly 6-inch) telescope. Meanwhile, it is also possible to catch the ISS by itself — this image used a 100 mm – 3 inch – refractor.
However, what you aren't going to see when you look through the scope is the ISS hanging there in space. It's in low Earth orbit, moving at more than seventeen thousand miles an hour, and it's going to be rushing across the sky at about 1.25 degrees per second. It's very bright (when illuminated by the Sun) but very, very quick. Chasing it with your telescope is going to be difficult; you'll be lucky to see it slide briskly across your field of view. (The last link I provided above describes the challenge.) Ralf Vandebergh is an old hand at this stuff, however; he's coupled a video camera to his 10-inch Newtonian, and then stacks video frames together to get sharper, lower-noise images. With lots of time, effort, and practice, he's able to generate processed images that look like this or this. This remarkable frame may have captured an astronaut on a spacewalk. TenOfAllTrades(talk) 15:08, 16 November 2010 (UTC)[reply]
You can see the International Space Station with the naked eye; and you can photograph it directly, if you're careful. But it sounds like you want to produce an image of more than a bright dot. So let's clarify: a "medium range consumer scope" will probably not provide enough angular resolution, even in perfect weather and overflight-trajectory conditions, to image small details of the spacecraft. You will need a pretty good sized scope - we could say, eight-inch aperture as an absolute minimum, and a larger scope for better imaging. There are two optical "hard limits of physics" you need to worry about: angular resolution, and field of view. Our article angular resolution describes the physical limitations of angular resolution - it depends on your telescope aperture, so you can calculate a minimum observable feature size for any give down-range distance. The ISS is going to overflying me at about 750 km downrange for the next three weeks, so my eight-inch will allow me to resolve 2.0 meter features. (That's pretty darned good!) Now here's the really hard part: the other limiting factor, field of view, which depends on your telescope focal length. You can think of this as "magnification power." The more you magnify, the smaller the area of sky you can look at. So you're going to need a really accurate computer prediction of the ISS trajectory (which you can find from NASA's website or the various enthusiast tools linked above - I use kstars on Linux). And you're going to need a really carefully aligned telescope (I'm usually pretty darned sloppy, but you should find true astronomical north with a polar scope, weight down your scope with a really good tripod and mount, and very precisely position your sights on the expected overflight path. You'll have one spot of sky - you can't move your scope fast enough to track ISS. (Military-grade fast-tracking scopes that can pan the sky as fast as an orbit-track as an "exercise to the reader"). Now, you've got to wait - depending on how perfectly aligned your clock is to the ISS (in theory, both you and NASA are synchronizing to the GPS clocks). The ISS should enter your field of view exactly on schedule, and you'll have ... about two seconds, if you're lucky. So you'll want your imaging system to capture as many photos as possible (burst mode, or video mode). And you'll want to make sure your imagers are well coupled, optically, to your tube, so that you aren't losing resolution at the film or digital imager. Finally, be certain to run some numbers for your optical system, camera's shutter speed, ISO settings, and set your exposure settings properly - you won't be very happy if you return a photo of a black sky or a washed-out dot! If you're lucky, you'll have captured ten or so photographs of the ISS overflight. With a good deal of image post-processing (to first order, an image stack to denoise, and maybe a superresolution algorithm), and you should be able to produce fine-quality photographs of ISS. As I mentioned, my 2-meter feature resolving capability means I could (theoretically) produce a decent photo of the solar panels and individual modules; but I recognize the inherent challenges in this endeavor. So far I have not been able to capture ISS - but the orbit's approaching my latitude/longitude in end of November! Nimur (talk) 18:14, 16 November 2010 (UTC)[reply]
I've been able to catch the ISS in my telescope, but low power is preferable for this task and the view only lasts for a fraction of a second! Capturing an image would be much easier by mounting the camera "piggyback" to the telescope and shooting a long exposure photograph that captures the space station's trail. ~AH1(TCU) 03:29, 18 November 2010 (UTC)[reply]
Differences between clone and original
What physical differences could be between human clone and its original "prototype"? —Preceding unsigned comment added by 89.77.156.31 (talk) 18:27, 16 November 2010 (UTC)[reply]
Age? Current cloning techniques can't instantly create an exact copy, just an embryo which, in time, will grow up to be a "copy". --131.188.3.20 (talk) 18:39, 16 November 2010 (UTC)[reply]
Fingerprints and obvious stuff like height, weight and various other things. Identical twins should give you a clue although given that the clone would likely be raised in a rather different environment some differences are likely to be more pronounced. (Clones and identical twins also have a relatively different genetic history.) Nil Einne (talk) 18:47, 16 November 2010 (UTC)[reply]
Further to Nil's post, you might find Twin study interesting. Although as it states in the article, twin studies are mostly about behavioral not physical differences. Vespine (talk) 23:02, 16 November 2010 (UTC)[reply]
Absolutely, any difference you expect between identical twins you would also expect in clones. Freckles, birthmarks, that sort of thing visually. Ginger Conspiracy (talk) 06:21, 17 November 2010 (UTC)[reply]
Monozygotic twins might be even more identical than clones, because the in utero environment for twins would be very similar, whereas the environmental experience of the clone would be quite different from the original. -- Scray (talk) 19:44, 17 November 2010 (UTC)[reply]
It's also not yet possible to clone humans, so one of the differences is that the original can exist. Paul (Stansifer) 03:28, 17 November 2010 (UTC)[reply]
Schrödinger's cat
It seems to me that this is a very bad example. Who could believe the cat could be both dead and alive? AdbMonkey (talk) 22:31, 16 November 2010 (UTC)[reply]
Much of quantum mechanics is classically non-intuitive; that does not make representative examples (such as Schrödinger's cat) "bad". Note that our article describes the cat as a reductio ad absurdum intended to critique an interpretation of quantum mechanics. Note also that by the time you get to interpretations you're really into the philosophy aspects of the science: the math is the same, but the explanation for "how" varies. — Lomn 22:40, 16 November 2010 (UTC)[reply]
I thought that was sort of "the point". Vespine (talk) 23:07, 16 November 2010 (UTC)[reply]
It isn't "both dead and alive" -- the cat's wave function is comprised of two juxtaposed but completely different states, only one of which is, has been, or will ever be real. Just because there are two disjoint juxtaposed states doesn't mean that they are both as real as the other. Ginger Conspiracy (talk) 23:55, 16 November 2010 (UTC)[reply]
What do you mean when you say that only one state is real? Are you suggesting a hidden variable theory? Rckrone (talk) 02:30, 17 November 2010 (UTC)[reply]
No, only that the wave function collapses deterministically, so only the one state which eventually prevails was ever real in the first place. Ginger Conspiracy (talk) 06:09, 17 November 2010 (UTC)[reply]
Doesn't work. Not even consistent with the two-slit experiment. If there's a real answer to which slit each photon went through, you don't get an interference pattern. --Trovatore (talk) 09:43, 17 November 2010 (UTC)[reply]
The case where the wavefunction collapses into a density function representing both of its disjoint states is distinct from the case where it can't. Ginger Conspiracy (talk) 17:33, 17 November 2010 (UTC)[reply]
"Anyone who is not shocked by quantum theory has not understood it." — Niels Bohr. --Mr.98 (talk) 02:08, 17 November 2010 (UTC)[reply]
Wouldn't the cat observe itself, thereby collapsing the juxtapostion of states. Plasmic Physics (talk) 06:25, 17 November 2010 (UTC)[reply]
Certainly, but for the purposes of the thought experiment, traditionally the cat isn't considered to observe itself. When this comes up in class, often the cat is removed from the box which then contains only the radioisotope, Geiger counter, relay, solenoid, and poison capsule, which everyone has an easier time believing can't observe itself. Ginger Conspiracy (talk) 08:20, 17 November 2010 (UTC)[reply]
It's not actually a problem that the cat observes itself. The cat is in a superposition of two states: one where it is dead, and one where it has observed itself, and to itself the wave function appears to have collapsed to the state where it's alive. Rckrone (talk) 08:48, 17 November 2010 (UTC)[reply]
Personally, I agree. The difference between classical and quantum mechanics is quite specific and can be illustrated with a number of simple thought-experiments. Schrödinger's cat is not one of those experiments. There is nothing really quantum about Schrödinger's cat; the quantum prediction for anything you might measure in this situation is the same as the classical prediction (unless you believe that there's no such thing as classical randomness—but quantum mechanics is not just classical mechanics with randomness). I think it became popular because of the vivid imagery of killing an innocent cat with poison gas, not because of any pedagogical merit. -- BenRG (talk) 08:20, 17 November 2010 (UTC)[reply]
What is obervation defined as? Does it have to involve a conscious entity? In my opinion, any interaction at all counts as some degree of observation. I think that whether an observation of this definition causes a wavefunction collapse is determined by how far information of the states propagates before being smeared by quantum mechanics; and by some sort of relationship to entropy and time. Thus, I propose a scenario: two equivalent closed cells containing one rod of atoms each. One rod is a micrometer long, the other is a centimeter long rod, both are initially in a juxtaposition of states. If both cells remain closed, there is a probability that both wavefunctions will have collapsed, there should be a larger probability for the longer rod have collapsed. This is my theory. I have never studied quantum mechanics, I just read the occational popular science journal like New Scientist, so I might be completely wrong, but seriously, what is obervation defined as? Plasmic Physics (talk) 09:20, 17 November 2010 (UTC)[reply]
Observation most definitely does not have to do with consciousness. It has somewhat to do with interaction, but more to do with information. If information is transfered from the system it was "observed". You can interact with it (for example a mirror), without transferring information and then it's not "observed". I don't follow your example with the rods. Ariel. (talk) 10:35, 17 November 2010 (UTC)[reply]
I'll explain: The mere presence of the rods within the box counts as an observation, because the electromagetic fields of the constituent atoms that make up the rods themselves transfers information to the cell walls. There is no way to completely isolate the rods, information is always transfered, so there cannot exist a juxtaposition. This is conclussion is clearly not true. As such, the degree of observation must be proportional to the probability of wavefunction collapse. This is different from the norm, where observation is a true or false property. I suggest that it is impossible to describe with perfect certainty whether a juxtaposition of states has collapsed or not without actively observing as in the Schrödinger's cat thought experiment.
Back to the example. The implications of this theory are, there is a non-zero probability that the juxtaposition of states will have collapsed for both of the cells, without having opened them. The propability is, among other things, dependent on the number of quantumn particles in a juxtaposition. The probability of the longer rod having a collapsed wavefunction in a closed cell is larger than that of the shorter rod. Plasmic Physics (talk) 11:22, 17 November 2010 (UTC)[reply]
People keep missing the one of the most important aspects of the Schrodinger's Cat paradox. Science requires an uninvolved observer, in order for results to be reproducable, which is a cornerstone part of science, we need to assume that our observations of phenomena indicate that the phenomena would go on even if we weren't there. When we say that a black hole behaves some way, we assume that the black hole behaves that way even when we aren't looking. When a biologist wants to observe the behavior of a lion in the wild, he has to do so without interacting with the lion, lest his presence alter the lion's behavior. Someone analyzing the effect of some substance on living cells wears gloves to avoid contaminating the sample with oils from their skin. Science works to try to isolate the phenomenon from the observer, so we can make universal statements about the phenomenon, and so we can assume that our results are reproducable independent of the observer. Here's the kicker with quantum mechanics: Independent observation is impossible. This is not a function of technology (lacking the proper instruments), it is a function of the nature of quantum mechanics itself. We cannot observe a quantum mechanical phenomenon without interacting with the phenomenon itself. Passive observation is impossible. Thus, when we want to say "How is this electron behaving when we aren't looking", it is actually impossible to predict with accuracy, since ANY test we would do to look at the electron involves bouncing a photon off of it, which alters the nature of the electron. We actually can't say what the electron was doing before we bounced the photon off of it. It is indeterminate. This is why quantum mechanics, as unsettling as it is to most people, is actually MORE unsettling to people of a scientific worldview, since QM violates one of the fundemental principles of science itself. --Jayron32 16:17, 17 November 2010 (UTC)[reply]
Never mind the cat — has anyone created a box? Some way to hold a bit of information that is removed from the original source, which doesn't allow a collapse of states until it is looked into? For example, a way to look at which slit a photon passes through in a double slit experiment, and store the result in a quantum computer, and then you look at the interference pattern, and only after that you decide whether to look at the quantum computer and see which slits each photon went through (retroactively erasing the interference pattern and your memory of having looked at it and seen it) or alternatively you just erase the bits unread and the interference pattern stands. Does something like that exist? Wnt (talk) 09:19, 18 November 2010 (UTC)[reply]
There's no retroactive memory erasure, or retroactive anything, in quantum mechanics. The delayed choice quantum eraser experiment is relevant here, but there is no retroactive disappearance of interference patterns in that experiment. Don't pay much attention to the name, which was chosen more for audience appeal than accuracy, as names so often are. -- BenRG (talk) 21:04, 18 November 2010 (UTC)[reply]
I'm happy to agree that there's no concept of passive measurement in quantum mechanics, though there can be passive measurements in special cases. The quantum Zeno effect illustrates that well. I don't see how Schrödinger's cat illustrates it. In fact, opening the box is a passive measurement, since the internal state has long since collapsed to a mixed state. Schrödinger can be forgiven for not knowing that, but modern presentations can't. -- BenRG (talk) 21:04, 18 November 2010 (UTC)[reply]
Ok so it has nothing to do with the torture of a cat in a box. It has to do with the fact that physicists think they may be getting accurate results but they are not taking into consideration that their presence has probably altered the result. And this is on a micro level. It actually has nothing to do with killing a cat with radiation. And even if it did, it would be wrong, because a cat cannot both be dead and alive at the same time. The cat is really an atom, or isotope or something physics- like. AdbMonkey (talk) 20:35, 18 November 2010 (UTC)[reply]
In Schrödinger's original paper the fact that the cat was a macroscopic living being was important. One could try to recycle the same thought-experiment for a different purpose, but I see no reason to do that except that one likes fictional cat-killing as a way to engage one's students. And I think that Schrödinger's original purpose has been rendered obsolete by the modern understanding of measurement in quantum mechanics.
(And physicists most certainly do take the quantum measurement process into account. It is metaphysically troublesome that the description of isolated systems looks different from the description of systems under observation, but in practice it's known how to correctly model both cases.) -- BenRG (talk) 21:04, 18 November 2010 (UTC)[reply]
Ok, I'm just a tad confused and I'm sorry to ask this, but what key concepts should you walk away from this thought-experiment knowing? AdbMonkey (talk) 21:17, 18 November 2010 (UTC)[reply]
Anacoustic
There seems to be something like Anacoustic, but neither google nor google books nor google scholar gives me at a first glance a good explanation. (The barium sulfate article contains the word and I have no clue what the application in Anacoustic faom could be.) --Stone (talk) 22:44, 16 November 2010 (UTC)[reply]
The anacoustic zone is the atmosphere above 100 miles or so where there are still enough gas molecules to produce substantial drag, but they aren't close enough to transmit sound because the probability of molecular collisions is so low. Ginger Conspiracy (talk) 00:00, 17 November 2010 (UTC)[reply]
November 17
Please, help me decide whether to drink my tea.
I dispensed hot water into my plastic CamelBak water bottle so that the tea-bag can do a better job than it would in cold water. Now I remembered my mother telling me about pouring hot beverages in a plastic container causing cancer. However, no one else said this.
Does a hot beverage leech plastic chemicals into the drink, thereby causing one to develop cancer? If not, what ill effects could it cause?
Also, would anyone please post sources backing this up? Thanks. --98.190.13.3 (talk) 04:22, 17 November 2010 (UTC)[reply]
Our Reuse of water bottles article has some info. I don't know what kind of plastic a CamelBak is made from, so I don't know any specifics of what may be leached out, etc. DMacks (talk) 04:25, 17 November 2010 (UTC)[reply]
Some (but NOT all) plastics contain Bisphenol A which has been shown to be linked to a number of health issues. Hotter water tends to dissolve more Bisphenol A than cold water (this is a nearly universal property; hot water tends to dissolve more of anything than cold water). There are also a host of other chemicals which may (or may not) be linked to health issues depending on the specific type of plastic. Again, you would have to know the specific type of plastic in your water bottle before you could decide if you just killed yourself. --Jayron32 04:29, 17 November 2010 (UTC)[reply]
Your mother may have heard about microwaving plastic. The Mayo Clinic says microwave-safe containers are okay, but notes that the FDA warns that non-safe plastics that melt when you nuke 'em may potentially leak chemicals. So, as long as you don't want your tea really really hot, you should be fine. Clarityfiend (talk) 04:39, 17 November 2010 (UTC)[reply]
The CamelBak article says that their water bottles don't contain Bisphenol A (BPA). Red Act (talk) 04:44, 17 November 2010 (UTC)[reply]
Almost all of the chemicals which can leach out of plastic food containers are not toxic at all (chemists don't want to get sued!) but some of them can taste pretty bad. Even bisphenol A is only a serious threat to fetuses and possibly infants. Ginger Conspiracy (talk) 06:15, 17 November 2010 (UTC)[reply]
You need a teapot. The spherical ceramic kind are best. 92.28.250.11 (talk) 10:20, 17 November 2010 (UTC)[reply]
@Ginger: They're relatively nontoxic. Companies are willing to put up with a small (non-zero) number of lawsuits over their products, if the difference in cost between a product and its alternative (safer) product is GREATER than the money that could be saved by the lower number of lawsuits, companies would then choose to use the less safe, but cheaper, product since the outgoing cash on the lawsuits on it is still small enough to make it worth it. When actuarial science meets economics, that's what you get. The only reason that companies took Bisphenol A out of baby bottles wasn't because some new science indicated they should, it was that the likely cost of keeping it in the bottles grew exponentially such that the more safe, but more expensive, plastic became cheaper when factoring in the likely lawsuits. --Jayron32 16:08, 17 November 2010 (UTC)[reply]
chemistry
if the hydrogen gas is flammable and it burns with pop up sound
oxygen is also necessary for burning
the combination of these two [water] is used to extinguish fire —Preceding unsigned comment added by Bharat.293 (talk • contribs) 04:30, 17 November 2010 (UTC)[reply]
I am guessing that you are asking for an explanation of the relationship between hydrogen, oxygen, water, and burning. Lets see if I can give you the short-short version.
Elemental hydrogen and elemental oxygen are both relatively unstable. Both hydrogen and oxygen would be more stable if they were part of a chemical compound rather than as pure elements (nearly ALL elements, with the notable exceptions of the noble gases, are like this). The reason for this is that both elements have the wrong number of electrons for their most stable state. Hydrogen has too many electrons (it would rather have a positive charge than neutral) and oxygen has too few electrons (it would rather have a negative charge than neutral). When we chemically react hydrogen and oxygen, what happens is hydrogen and oxygen rearrange their electrons such that oxygen gets extra electrons and hydrogen gets to give up some of its electrons. This makes BOTH of them more stable. In chemistry, stability is related to potential energy; the more potential energy stored up in something, the less stable it is. When it releases that potential energy, usually as heat, the new substance that forms is more stable than the substances that formed it. In this case, the new substance is water, which is composed of atoms of hydrogen and oxygen, but in this case arranged such that BOTH have the number of electrons that makes them most stable. This is why water is not very chemically reactive; it already has its electrons in a relatively stable arrangement, so it will no longer burn. Burning is just the outward sign of the chemcial reaction between the fuel (in this case hydrogen) and oxygen.
To sum up, the process of burning involves a rearrangement of the electrons between hydrogen gas and oxygen gas to form a new substance (H2O) which is more stable than the starting state. Because this new state is more stable, it isn't going to react further, so it will now put out flames rather than burn itself. --Jayron32 04:46, 17 November 2010 (UTC)[reply]
Bharat, are you remarking on the oddity that the combustion of hydrogen and oxygen produces water, yet water is what we commonly put fires out with? —Steve Summit (talk) 06:14, 17 November 2010 (UTC)[reply]
That has to be it. So the answer is "Yes, that's right" I'd say. Ginger Conspiracy (talk) 06:17, 17 November 2010 (UTC)[reply]
Water can be used to put out SOME fires. This is because it typically acts either to reduce the 'heat' of the combustion reaction. Other forms of (non-water) extinguisher target other parts of the fuel triangle, like for example a C02 extinquisher works by denying the fire access to oxygen.. Sfan00 IMG (talk) 20:40, 17 November 2010 (UTC)[reply]
Although the water itself does not put out the flame, the instant reaction of hydrogen and oxygen produces a flame that immediately extinguishes itself. Water does not put out all fires, as a grease fire will continue burning as its heat fuel source is removed only briefly, and water can often start electrical fires though even hot water will cool a red-hot iron nail as liquid water cannot be hotter than 100°C under normal circumstances. ~AH1(TCU) 03:23, 18 November 2010 (UTC)[reply]
It's really quite simple: wood will burn, but the ash that's left over will not burn again. Hydrogen and oxygen burn, and the ash is water. Sand is the ash of silicon and oxygen. Since fire needs oxygen, if you cover a fire, it goes out. Of course, the fire may ignite the thing you cover it with, and then you just have a new uncovered fire. If the cover won't burn, then the fire does go out. You can thus put out many fires by covering them with ashes, sand, or water. --Tardis (talk) 15:42, 18 November 2010 (UTC)[reply]
Catfish
I just watched an episdode of River Monsters, and the host would take very large catfish, such as the Piraíba or Jaú, out of water. They made strange grunting and moaning sounds, which he said were because of air moving over the gills, rather than water. This set me wondering: can they breathe in air? Thanks, --TheHighFinSpermWhale 06:20, 17 November 2010 (UTC)[reply]
Yes, I am familiar with airbreathing catfish. My question was whether or not a large one, such as those I mentioned earlier can. --TheHighFinSpermWhale 18:42, 17 November 2010 (UTC)[reply]
My guess is the person writing the answer key should misread the n=1 level for the n=2. Assuming the collision is involving the ground state hydrogen atom, you should be able to use the energy bled off of the colliding electron in an inelastic collision to do the n=1 -> n=2 transition and the n=1 -> n=3 transition. The n=1 -> n=4 transition won't happen because you would need excess energy in the colliding electron. So the only two answers should be 0.4 eV (1->3) and 2.3 eV (1->2). --Jayron32 15:59, 17 November 2010 (UTC)[reply]
Lambert's cosine law
In Lambert's cosine law it describes how if the sun were a perfect black body radiator it would appear to us as a circle the same brightness all over, yet it darkens towards the rim. The full moon on the other hand should darken towards the rim, but it seems almost as bright at the rim as at the centre. There is an explanation about the sun at Limb darkening, but why does the full moon seem brighter at the edge than one might expect thanks? Dmcq (talk) 10:10, 17 November 2010 (UTC)[reply]
Is the moon really brighter at the edge? I've never noticed that. Perhaps it's obvious, but the moon is not a black body radiator, it's a reflector. But I'm not sure if that makes a difference. It probably depends on how directional the reflection from moon rocks is. In a black body the light is emitted evenly in all directions, but in a reflector it may have a preferred direction. Ariel. (talk) 10:30, 17 November 2010 (UTC)[reply]
It should also bear stating that a blackbody is an unrealistic ideal, something like an ideal gas or perfect vacuum. We can do mathematical calculations which show how a blackbody should behave, and some real objects aproximate these calculations, but no real object acts like a blackbody. --Jayron32 15:30, 17 November 2010 (UTC)[reply]
The Moon's maria on the Earth-facing side make it brighter towards the center in total but also brighter on most of its rim. Ginger Conspiracy (talk) 17:49, 17 November 2010 (UTC)[reply]
I got my wording a bit confused, the lambert law should apply to the moon, just the article mentioned the sun. I don't think the maria quite explain the effect, they don't say why the edge shouldn't be fairly dark. I was wondering perhaps the moon isn't as dark as it should be towards the edge because it has lots of craters and what we see at the edge are the reflections from the sides of the craters, does that sound like it might be possible? Dmcq (talk) 10:48, 18 November 2010 (UTC)[reply]
The article isn't talking about the edge of the moon as viewed from here, but rather as viewed from the sun: the edge of the lit part of the moon. Of course, those are the same when it is full; the article goes on to say that the lack of darkening indicates that the moon isn't Lambertian. If it were, we would expect its limb to be bright (which it is), but more terminator darkening than we see. --Tardis (talk) 17:44, 19 November 2010 (UTC)[reply]
Please help me clear up this hogwash about adjusting braces at the SAME orthodontist.
Hi, when I saw that getting braces in India was only going to be as low as $225 to as high as $1800 USD, I then had a desire to travel to India to get the deeply-discounted orthodontic work.
Then someone told me that I'd have to fly back to the same orthodontist to get them readjusted every so often. I thought that was a bunch of hooey, because get THIS logic:
TRUE OR FALSE:A driver who buys his Ford in Texas and moves to Maine, must drive his car all the way back to that same Ford dealer in Texas to realign his axles (and perform other substantial maintenance.)
See the fallacy here? He only has to drive it to the nearest Ford dealer from his house in Maine. Or if an independent mechanic is closer, he can simply drive it to them and they can do all the maintenance needed just so long as they have the right equipment.
Now the orthodontists' equipment is state-of-the-art back Stateside, so they'll undoubtedly have all they'll need to readjust Indian braces.
So since the logic of having to travel back to the same orthodontist to readjust braces falls under the same level of fallacy as the car maintenance analogy, I didn't buy what they said.
(Also, think of military families whose family must move with the active duty serviceperson, and sometimes on short notice. If their child got braces in Fort Hood, and they move to the base in Landstuhl, their child would hate to fly all the way back to Fort Hood for a mere readjustment. Some kind of accommodation would need to be made. That would be to just get it done at a local orthodontist.)
So can someone clear this up? I still hope to get braces at the cheapest possible place, but get them readjusted wherever I happen to be. Thanks. --70.179.178.5 (talk) 10:33, 17 November 2010 (UTC)[reply]
Cool, N.E., that IP user must've been on a similar mental plane as me. Seems like we have a lot in common; I'll have to study his editing history now. --70.179.178.5 (talk) 11:13, 17 November 2010 (UTC)[reply]
You do indeed have a lot in common as it seems you both use the same ISP and appear to live in the same area in or near Manhattan. Nil Einne (talk) 14:07, 17 November 2010 (UTC)[reply]
One thing they don't share is time. The old IP address made edits through mid-September. Then, they stopped. Once the old IP address stopped making edits, this IP address began making very similar edits (similar topics, similar grammar, similar misspellings...). -- kainaw™ 15:29, 17 November 2010 (UTC)[reply]
(ec)As much as possible you need to stick with one person when adjusting, this is because you make a plan for the adjustments, when to do what, which tooth, etc. If you go to a different person each time you'll get a mix. The solution to this is very good records, and presumably the military does that, but I doubt a regular orthodontist is going to carefully read and follow the documented plan. You'll be lucky to even get a written detailed plan. That said, you can probably get them installed in India or wherever, then stick with the same new local person for all the future adjustments. But you better hope that he has tools or equipment to service the exact type of braces you are getting, I believe there is a wide variety of types, and a variety of ways of attaching them. Ariel. (talk) 10:49, 17 November 2010 (UTC)[reply]
"Someone told you"... Did you ever ask an orthodontist if they would be willing to manage the periodic readjustments of braces installed elsewhere? There could be many reasons why an orthodontist would prefer to have the braces be his or her own handiwork, but people move all the time and they don't generally have this problem. I suspect that you won't get an answer that satisfies you here on the RefDesk and would be better suited simply asking the orthodontist that you hope to be followed by. --- Medical geneticist (talk) 16:45, 17 November 2010 (UTC)[reply]
Periodontal resident here -- orthodontics is a field in which comprehensive care can and often does exceed the length of a treating resident's residency -- for example, if the average ortho case takes 18 months to complete, any case began within 18 months of graduating needs to be completed by another resident. That being said, ortho residencies are highly regulated and organized by their administrators and professors, and the case will likely go though a thorough hand-off review. But outside, in the real world, I can certainly see an orthodontist refusing to pick up a case. Excepting death of the original practitioner (and perhaps even not excluding it) there has to be a really good reason to switch mid-therapy, because, as you can probably figure out, there are multiple ways to accomplish most any goal in dentistry, and mixing a case up between clinicians is like having two contractors building your house -- you might have to have good luck to make sure pipe A is able to meet up with pipe B when they're done. There are many orthodontic systems, many possible treatment planning options, many types of appliances, many different springs, hooks, wires, brackets and they can probably be used in different ways depending on the level of training, experience and personal preference. And this is assuming that the Indian orthodontist practices on a level congruent with American standards. Eastern European/Russian root canal therapy is a really strange thing to look at from a United States-trained dentist's perspective, and so is Central/South American restorative work (crown and bridge). Foreign dentistry may be inexpensive because there's no Manhattan premium, but it may also be inexpensive because it's shoddy. DRosenbach(Talk | Contribs) 19:40, 17 November 2010 (UTC)[reply]
Thank you for responding, Dr. Rosenbach. Not having straight teeth could give me dim job prospects because in this kind of economy, employers are looking for any slightest excuse to throw out an applicant, when they have so many resumes/applications for so few job openings, that they may even throw me out just because my teeth aren't straight enough. I would have to walk on so many eggshells just to have the slightest glimmer of hope for a job offer, that having to pay so much just to make it in the world defeats the whole deal. If there was a charity/schooling orthodontist office anywhere close to 66502, please let me know where the nearest location is and I'll consider that. Otherwise, this daunting catch-22 is one more reason why I must move overseas for good. --70.179.178.5 (talk) 08:40, 18 November 2010 (UTC)[reply]
All cars of the same model (and production run) are (or should be) identical, so any garage with suitably experienced staff is usually happy to carry out your repairs and adjustments. Only identical twins have identical teeth (and even then, not always), so there is an element of creative art in the work of an orthodontist. It's rather like asking an interior designer to make small adjustments to your bodged DIY decorating, or an architect to improve the look of your self-built home. They might do it for you, but they will not necessarily be delighted to be asked. Dbfirs 01:17, 18 November 2010 (UTC)[reply]
Why does the sex drive far exceed what is biologically needed for reproduction?
For males, at least, and in species that are not 100% monogamous, it's evolutionarily advantageous to have as many offspring as possible. It's just another example of how rank selfishness, much as we'd like to define it as a social ill, is a biological imperative. —Steve Summit (talk) 12:29, 17 November 2010 (UTC)[reply]
(e/c)This is rather open ended. What species are you talking about, or just in general? Are you referring to humans? If so, whose sex drive...? Let's assume you're referring to an 'average' human, though I guess you could generalise and substitute in other species. In a historical and evolutionary sense, the simple answer to your question is that it doesn't. Let's say in basic terms the sex drive spurs the activity that results in reproduction. For the sex drive to "exceed what is biologically needed for reproduction" that would mean the reproduction rate would result in more children born than needed to replace their parents and an ongoing population boom. Historically this is not the case - populations in general remain fairly stable, unless or until something upsets the equilibrium. Now it is true that nature generally does produce more offspring than needed for replacement, and evolution will favour population growth if it can (greater spread of genes, etc), as well as needing to 'hedge its bets' for the bad times; indeed the excess individuals are the fodder for natural selection, but in normal conditions these excess offspring are removed from the population through conflict, starvation, etc and the overall population numbers remain relatively constant. When something does upset the natural balance we can see population booms like the recent one in human populations. As I said at the start, sex drives vary greatly both between and within species, but a generalisation would be that the average sex drive of a species is that which has been favoured by natural selection to maximise that species' long term survival - different species use different strategies (fewer offspring and greater parental care, more offspring and less parental care...) to try to achieve that best balance between producing enough offspring for the species to survive and prosper, and expending too much energy on reproduction. That's all pretty general; really you could do an entire thesis on this. --jjron (talk) 12:39, 17 November 2010 (UTC)[reply]
A relatively higher sex drive will tend to be selected for as long as it isn't detracting from survival or child rearing. Ginger Conspiracy (talk) 17:53, 17 November 2010 (UTC)[reply]
For humans who engage in media and other forms of entertainment, suggestive shows, films and commercials likely help promote the drive. DRosenbach(Talk | Contribs) 19:30, 17 November 2010 (UTC)[reply]
Unlikely to be the case. People have been randy long before there was television. In fact, my understanding is that various studies have shown that people's sex drives decrease as a function of how much television they watch. I don't have references handy, though. --Mr.98 (talk) 01:21, 18 November 2010 (UTC)[reply]
Keep in mind that before the invention of modern medicine, a significant fraction of human babies died in childbirth. thx1138 (talk) 19:33, 17 November 2010 (UTC)[reply]
None of that answered his question. You are talking about how many babies are born, but he asked why humans want to have sex far more often then is needed to get pregnant. The answer is twofold: Humans are the only species with Hidden estrus, so the male does not know when to have sex, so the males will try as often as possible. The the second reason is that sex reinforces pair bonding, so the male is motivated to stay with the female and help raise the babies. In an animal instinct can do this, but in humans a greater incentive is used. Note that contrary to impressions, and sitcoms, married men have sex far more often than single men. Ariel. (talk) 20:36, 17 November 2010 (UTC)[reply]
Only? Are you sure? The article you linked to doesn't think so. It links to a ref on the occurance in vervet monkeys which mentions the occurance in other primates. It doesn't really mention any others per se from what I saw although it does mention others with prolonged sexual receptivity although that's more complicated then concealed ovulation per se (for example it mentions orangutans where it says it's often due to forced encounters). I believe some dolphins may also show concealed ovulation/hidden estrus although I couldn't find a decent ref. Nil Einne (talk) 18:06, 18 November 2010 (UTC)[reply]
I was walking around Norfolk, Virginia this weekend and I saw this piece of moss walking along a concrete pillar. I got a few photographs and videos of it. I feel like I've seen the bug before (without the moss). Such an interesting defense mechanism, I someone out there can help identify it. The insect does look familiar.
Here is a photo of the moss. On the right side you can see what I think are mandibles.
I went out again, and upon closer inspection, I this is the same bug, without the moss covering. The mandibles look the same, the size is similar, the legs look the same (from the upside-down shot), and the movement was similar.
It may not be moss at all, but may instead be Mimicry. Some bugs like planthoppers and walking sticks have amazingly complex ways to mimic their environment. I do not recognize this exact bug you have found, but I would assume that the stuff you are calling moss is actually an integral part of the bug itself. --Jayron32 15:23, 17 November 2010 (UTC)[reply]
Thanks for the ID. Any idea what the deal with the moss is? Is it defense / camouflage? Keegstr (talk) 19:03, 17 November 2010 (UTC)[reply]
Sometimes known as 'trash bugs' apparently [16] and your assumption seem to be correct [17]. Mikenorton (talk) 10:52, 18 November 2010 (UTC)[reply]
Reaction products of opianic acid with strong acid
Is this image likely to be right? Reaction with strong hydrochloric or hydriodic acid. Possibly isomeric phenols are formed? --Wickey-nl (talk) 17:25, 17 November 2010 (UTC)[reply]
Looks OK to me. You shouldn't get any isomerization whith hydrochloric or hydriodic acid, simply the hydrolysis of the two ester groups. I wouldn't like to guarantee that they get hydrolysed in the order that shown, but that's a fairly minor point. Physchim62(talk) 17:58, 17 November 2010 (UTC)[reply]
nit: s/ester/ether/DMacks (talk) 18:04, 17 November 2010 (UTC)[reply]
(ec)It's a plausible reaction, probably SN2-like. Methyl ethers are stable to just about everything except strong acid. My protecting-groups table for "phenols, methyl ether" says the only suitable deprotection conditions are aqueous pH<1 and AlCl3 (but only slowly unless warmed). I don't see an easy mechanism for isomerization. DMacks (talk) 17:59, 17 November 2010 (UTC)[reply]
FWIW, there is a known aqeous-acid-catalyzed isomerization of a different part of the structure in opianic acid and related compounds: the 1,2 acid-aldehyde portion can form cyclic ester-hemiacetal. (see doi:10.1007/BF00568016 and refs therein). DMacks (talk) 18:14, 17 November 2010 (UTC)[reply]
Cold-weather urination
Why does being in the cold make people urinate more? The core body temperature where the kidneys are must be either the same or nearly the same as in warm surroundings. 92.15.28.182 (talk) 18:09, 17 November 2010 (UTC)[reply]
I'm not sure it does, in general. Maybe because people drink more hot diuretic coffee? Ginger Conspiracy (talk) 18:14, 17 November 2010 (UTC)[reply]
People generally sweat less in cold weather but I don't think that's the whole explanation. A quick search for 'urinate more cold weather' comes up with some results, the most promosing looks to be [18]. That links to [19] for rats. From that same search, it seems in humans there's also greater urgency [20], in other words it may not simply be that you have more urine but that you feel a greater urge to urinate. Nil Einne (talk) 19:07, 17 November 2010 (UTC)[reply]
The phenomenon is called "cold-induced diuresis". Exposure to cold temperatures causes your body to respond with vasoconstriction in the extremities, which helps your body retain heat. The vasoconstriction causes blood pressure to become elevated, to which the kidneys respond by removing fluid from the blood stream in order to lower the blood pressure. The kidneys pass that removed fluid through the ureters into your bladder, which makes you need to urinate.[21]Red Act (talk) 19:37, 17 November 2010 (UTC)[reply]
The phenomenon is apparently sometimes also called "cold diuresis", as that's what the polyuria and hypothermia articles refers to it as. Cold diuresis is unfortunately a rather useless redirect. Cold-induced diuresis is part of the cause of immersion diuresis, as is explained a little bit in that article. Red Act (talk) 20:00, 17 November 2010 (UTC)[reply]
Frog dissection
Is there a common species of frog that would usually be dissected in a lab class to measure the contraction of its gastrocnemius muscle? 149.169.142.37 (talk) 22:05, 17 November 2010 (UTC)[reply]
When I was at Uni, we used the Cane Toad (Bufo marinus) in a lot of pracs. --jjron (talk) 12:31, 18 November 2010 (UTC)[reply]
Direction of apparent weight
Is apparent weight a directionless quantity? Or is it a vector equal to the normal force in both magnitude and direction (for instance, in an accelerating lift, in which case the direction would be up). -- 220.253.217.130 (talk) 22:21, 17 November 2010 (UTC)[reply]
There may be more than one way to define "apparent weight" but I would describe it as a force vector equal to the normal reaction with the lift floor, but in the opposite direction. Dbfirs 22:59, 17 November 2010 (UTC)[reply]
So in general, apparent weight is equal to the vector difference Fnet – Fg, but in the opposite direction (including for arbitrary direction for Fnet)? 220.253.217.130 (talk) 23:20, 17 November 2010 (UTC)[reply]
Or equivalently, apparent weight is equal to Fg – Fnet ? 220.253.217.130 (talk) 23:22, 17 November 2010 (UTC)[reply]
Well I would define real weight as a downwards force of magnitude mg (I assume that this is your Fg). If the lift is accelerating upwards with acceleration a, the normal reaction will be mg + ma upwards (assuming that the person or object is not moving relative to the lift floor), so by my definition, the apparent weight will mg + ma downwards. I'm not sure what your Fnet denotes. I think the safest way to deal with the situation is to consider only real forces and apply Newton's second law (Resultant force = mass times acceleration). Dbfirs 23:40, 17 November 2010 (UTC)[reply]
Fnet is the net force, that is the vector sum of the force due to gravity and the normal force, and is equal to ma, where a is the acceleration of the lift and m is the mass of the person. 220.253.217.130 (talk) 23:53, 17 November 2010 (UTC)[reply]
Sorry, yes, I should have realised that you meant the same as my "resultant force". (It's after midnight here.) Dbfirs 00:12, 18 November 2010 (UTC)[reply]
So does that make Fg – Fnet a correct formula for the apparent weight? 115.178.29.142 (talk) 00:32, 18 November 2010 (UTC)[reply]
Only when the lift is accelerating downwards (and a ≤ g), or if you allow Fnet to be negative when the lift is accelerating upwards. The safest method to avoid confusion is always to draw a diagram showing the directions of real forces, then apply Newton's second law. Dbfirs 01:03, 18 November 2010 (UTC)[reply]
How stable is glycerol stored in a clear glass bottle? I see that it's hygroscopic, but would that just make it gradually dilute itself over time, rather than reacting with the water? Also, not much water is going to get in anyway. Does it decompose into anything given time and a small amount of normal air, in the top of te bottle? Does is decompose into anything in sunlight? I'm just wondering, because it seems such a bland thing, and yet I know it's used in various reactions, including making explosives. Would a bottle of the stuff still be just glycerin after a few years? 86.163.213.68 (talk) 23:45, 17 November 2010 (UTC)[reply]
Glycerol is pretty stable, especially if the bottle is kept closed. It can oxidize to compounds such as glyceraldehyde and glyceric acid, but this is very slow in the absence of a catalyst. Physchim62(talk) 23:53, 17 November 2010 (UTC)[reply]
In my personal experience, glycerol is stable when stored at room temperature and out of direct sunlight for years. Proctor and Gamble have verified that room-temperature storage doesn't appreciably degrade glycerin over a the length of a two-year monitoring and testing program: [22]. I don't have (and was unable to find) specific information about the photostability of glycerol exposed to sunlight over extended periods, though I wouldn't be surprised if the sunlight affected the plastic bottle it's shipped in more than the glycerol itself. TenOfAllTrades(talk) 01:25, 18 November 2010 (UTC)[reply]
Thanks, these are both good answers. 86.163.213.68 (talk) 15:42, 18 November 2010 (UTC)[reply]
November 18
Inconstant red
I've noticed that certain rare reds, such as a certain flower that grows along the banks of the Lehigh, seem to be red beyond comprehension, so as to seem to flicker or shimmer continually. It is not so for plain #FF0000 or any other red shade on a computer. Has this effect been observed and named? Wnt (talk) 09:31, 18 November 2010 (UTC)[reply]
You might also be noticing a red that is outside the gamut of the RGB color space. Selective yellow is another color that is not representable by RGB. —Bkell (talk) 11:36, 18 November 2010 (UTC)[reply]
I thought about iridescence, but the shimmering seems to be a function of the color, not the angle; and I do think it is outside the RGB gamut. Wnt (talk) 01:51, 19 November 2010 (UTC)[reply]
Kicking a ball
There are four fundamental forces in nature. Which of them acts on a ball when I kick it forward? To me, the force exerted by me upon the ball does not seem to match the description of any of these forces. --13XIII (talk) 11:15, 18 November 2010 (UTC)[reply]
If you'd got to the second paragraph of the fundamental interaction article you linked you would have read: "The four known fundamental interactions, all of which are non-contact forces...". Kicking a ball is clearly a contact force. Having said which, to quote again "Strictly speaking, contact forces are only a useful simplification for introductory physics classes and other applications of classical mechanics. Everyday objects on Earth do not actually touch each other; rather contact forces are the result of the interactions of the electrons at or near the surfaces of the objects.". --jjron (talk) 12:26, 18 November 2010 (UTC)[reply]
Well, we can rule out the strong and weak nuclear forces straight away, as there are no nuclear reactions taking place - although the strong force "acts" on the ball in the sense that it explains why there is a ball in the first place, rather than a rapidly expanding cloud of quarks and electrons. The ball experiences a gravitational force, but that is essentially the same before, during and after the kick. So that just leaves the electromagnetic force ... Gandalf61 (talk) 12:37, 18 November 2010 (UTC)[reply]
So basically, the ball is kicked because my atoms electronically repel the ball's atoms?--13XIII (talk) 14:46, 18 November 2010 (UTC)[reply]
That's correct. Red Act (talk) 15:12, 18 November 2010 (UTC)[reply]
You'd generally say the atoms electrically repel the ball, not electronically, even though it's the electrons doing the repelling. Sad, but true. --Sean 15:47, 18 November 2010 (UTC)[reply]
It is chemical energy, as per the sliding filament model that makes your muscles contract. Chemical energy is mediated by the electromagnetic force. The electromagnetic force also holds your ligaments et c together and transfers the force from your foot to the ball, rather than your foot piercing the ball. CS Miller (talk) 19:20, 18 November 2010 (UTC)[reply]
Since there aren't any chemical interactions between your shoe and the ball, the transfer of inertia is mediated by the Pauli exclusion principle between electrons in molecular orbitals causing elastic collisions. That is more of a quantum electrodynamical effect than an electromagnetic effect, but the force from your foot certainly originates in the electromagnetic chemical energy in your muscles. Ginger Conspiracy (talk) 20:20, 18 November 2010 (UTC)[reply]
Chances of getting cancer and age
If you compare the age groups 5-6 years and 59-60 years, which one has a higher incidence of cancer? The former group goes through more cell divisions, could that increase the risk of getting some DNA copied in the wrong way? However, could the later be affected by other factors, like some tendency of old cell to produce faulty DNA copies?Mr.K.(talk) 11:51, 18 November 2010 (UTC)[reply]
Adults have a higher cancer incidence by far. I don't have the data for the specific age ranges you are asking about, but according to the American Cancer Society: in the USA the incidence from birth to age 39 is 1 in 70 for males and 1 in 48 for females; the incidence from 40 - 59 is 1 in 12 for males and 1 in 11 for females; the incidence from 60 - 69 is 1 in 6 for men and 1 in 10 for women. As for why this might be the case, the older you are, the more total cell divisions your body has gone through (and hence the more chances for a somatic mutation), and the longer you have been exposed to carcinogens in the environment. This increased occurrence of cancer in older age groups is consistent with the "two-hit" hypothesis of carcinogenesis. --- Medical geneticist (talk) 12:10, 18 November 2010 (UTC)[reply]
The age groups were just an example. The older you are = the higher your chance of getting cancer is clear to me. What is not clear is the older you are = the higher your chance of cancer onset. Cancer takes several years to manifest itself, so if a 20 year old is having lots of cell division (more than a 30 years old), his chances of cancer onset could be higher, but this cancer would only manifest itself when he turns 30 (increasing the statistics of this age group). Right? Quest09 (talk) 12:57, 18 November 2010 (UTC)[reply]
I think you are over-thinking the situation. There isn't a difference between "your chance of getting cancer" and "your chance of cancer onset". It's the same thing: incidence of cancer. Sure, it's true that some cancers are found serendipitously (the person is asymptomatic and cancer is discovered by accident), other cancers are found at an early stage through screening programs before they manifest significant symptoms, others aren't discovered until widely metastatic. Is this what you mean by "cancer onset?" Certainly the biology of tumors is different, and some childhood cancers are particularly aggressive and progress rapidly while some adult cancers are indolent and progress slowly. But the opposite can also be true. There is no way for us to know when the first cancerous cell arose in any given person's body, so cancer incidence numbers simply measure the age at which a cancer was diagnosed. --- Medical geneticist (talk) 14:00, 18 November 2010 (UTC)[reply]
information technology
How and where can information technology be used?
What are the qualities of a good media programme?
What are the materials used for information technology e.g generator,contr —Preceding unsigned comment added by Perooy (talk • contribs) 12:57, 18 November 2010 (UTC)[reply]
Which parts of the US have a winter climate that is about as cold as that of Scotland? Thanks 92.24.187.23 (talk) 13:32, 18 November 2010 (UTC)[reply]
Scotland's weather is maritime, which means the temperature (and the rainfall) is heavily influenced by the sea, and (as with the rest of Britain and Ireland) by the gulf stream. The nearest comparison to Glasgow would be the Pacific Northwest, maybe Portland or Seattle (in that it rains a lot, but doesn't really get that cold and doesn't snow massive amounts). Parts of Georgia or Virginia might be roughly temperature comparable (in the winter), but it's different weather and overall a different climate. -- Finlay McWalter ☻ Talk 13:42, 18 November 2010 (UTC)[reply]
It seems like Dutch Harbor, Alaska corresponds fairly well to Aberdeen, at least for this time of year. Googlemeister (talk) 15:19, 18 November 2010 (UTC)[reply]
Aberdeen is on the east coast, which is colder and dryer than the west. I've seen large patches of snow in June in the Cairngorm mountains. Alansplodge (talk) 15:25, 18 November 2010 (UTC)[reply]
Aberdeen, Scotland and Portland, OR is a pretty good comparison. Having lived in both cities the winters were quite similar in terms of temp, number of times falling over of the ice, some but not much snow in the city etc. Sean.hoyland - talk 15:49, 18 November 2010 (UTC)[reply]
Thanks. Never mind the precipitation, what states away from the coast would be about as cold as Scotland in the winter? 92.15.5.101 (talk) 17:43, 18 November 2010 (UTC)[reply]
You can't ignore the precipitation; it's the presence of water that moderates the temperature. Away from the coasts a continental climate holds, where it's very hot in summer and very cold in winter. For example, right now Glasgow and Omaha are about the same temperature, but compare the climate of the two (Glasgow, Omaha). The average low for Feb in Glasgow is 0C, for Omaha its -10C; they're about the same in November. The only places in North America that are roughly the same temperature as Scotland over the entirety of the winter are the coastal pacific northwest, from Seattle into Alaska. Any given inland place will be roughly the same as Scotland only for a few weeks or so. -- Finlay McWalter ☻ Talk 18:47, 18 November 2010 (UTC)[reply]
I'm just wondering where a hypothetical curvy line across the US would be where the mid-winter (early January?) temperature is similar to what you get in Scotland. In the early or late winter it would be warmer. 92.15.13.70 (talk) 20:28, 18 November 2010 (UTC)[reply]
Very roughly, you could draw a line connecting Norfolk, Virginia, Memphis Tennessee and Tulsa, Oklahoma and get average daily highs and lows within a couple of degrees C of Aberdeen, but because of the continental vs maritime climate difference between the USA and the UK, the record highs and lows will be a greater span for the US cities. Googlemeister (talk) 21:23, 18 November 2010 (UTC)[reply]
Frozen LCD TV
Can LCD TV's be stored in cold tempatures? Can LCD TV's freeze (at what temp.) and will freezing damage the TV? —Preceding unsigned comment added by DB61955 (talk • contribs) 16:05, 18 November 2010 (UTC)[reply]
I'm not sure there is a one-size-fits-all answer. Googling for LCD storage temperature suggests some LCD panels may survive freezing. However, a TV will contain other components, such as electrolytic capacitors, whose liquids may not take well to being frozen. For a specific make and model of a TV, consult its user manual for storage and operating temperatures. When bringing electronic devices in from the cold, be sure to allow them plenty of time before switching them on, to allow for condensed moisture to evaporate - here, too, the user's manual is your friend. 88.112.56.9 (talk) 18:02, 18 November 2010 (UTC)[reply]
One way that electronic devices fail when stored at very low (or very high) temperatures, or when the ambient temp is cycled up and down a lot, is the breakage of connections, either the microscopic connections inside semiconductor chips, or solder joints where devices are attached to the circuit board.Different materials have different thermal expansion coefficients. Edison (talk) 20:09, 18 November 2010 (UTC)[reply]
To illustrate the difficulty of getting an answer to your question, a poster here has been waiting since October 2009 with a question about the operating AND storage temperature limits of a Samsung LCD TV, with no reply yet. Cuddlyable3 (talk) 01:38, 19 November 2010 (UTC)[reply]
Maybe the problem is people are waiting for answers after posting in random irrelevant (not associated with manufacturer) blogs nearly one year after that blog entry was posted? A simple search for 'samsung lcd temperature' comes up with [23] which says they recommend 10°C as a minimum operating temperature. (Specifically "When it is used at low temperature of 10°C or lower, response time and brightness are affected in such a way that the proper display may not be obtained.")
If you want more detailed specs, from experience the manual of most products commonly have such storage and operating conditions in their manuals. The blog entry was about the Samsung LN52A580 in particular. Since the blog and TV appears to be directed to the US, a look on their US (but not UK or Malaysian) site finds [24] which has the manuals for the LN52A580P6F. Sure enough from the user manual we find:
Environmental Considerations
Operating Temperature 50°F to 104°F (10°C to 40°C)
Storage Temperature -4°F to 113°F (-20°C to 45°C)
Of course simply asking the manufacturer of the TV your interested in is also likely to be a better bet then a random blog post in a random blog.
Each manufacturer may choose to rate their products differently. For example I earlier looked at some random Sony LCD TV (KDL-40HX701). The manual I got appears to be one of those limited/user friendly ones and it only has 24 pages. I couldn't find a more detailed one for that model on Sony's site but didn't look very hard. Anyway as you may expect it did lack detailed storage and operating conditions but it did at least say "Avoid operating the TV at temperatures below 41°F (5°C)".
In other words it isn't hard. You just have to look or ask in the right place. (In other words help yourself and use a little common sense.)
From these statements, I'll take a punt that as the temperature goes down, the performance changes I guess because the liquid in the LCD changes. Above freezing but presuming no condensation or other such problems I would guess your TV isn't going to blow up but it may not perform as you would expect. But for that reason, manufacturers generally recommend 5-10°C. Actual performance at such low temperatures is likely to vary depending on several factors and is not something you'd expect there to be any real guarantee for cheap consumer TVs.
In terms of storage, from what I've seen most electronics can be stored below freezing. I would guess if they can't this would require greater care to be taken during transport and storage so is something usually avoided. So it's not really surprising that LCD TVs can (at least the Samsung one mentioned above).
In terms of at precisely what temperature the LCD will begin to be irreversible damaged, I suspect that will vary. Finding an answer is probably going to be difficult since manufacturers may not bother to test such details instead just setting minimum temperatures they are sure will be tolerated.
I have not been able to find any transpired solar collector for sale.I have sent many emails and have had not one reply.Would you be able to tell me where I could purchase 200 sq ft to see if it will work in my sisuation ?
Thanks you, George Jackson
208.127.199.228 (talk) 17:19, 18 November 2010 (UTC)[reply]
Have you tried just phoning the companies that make transpired solar collectors? They all appear to have phone numbers listed on their web sites, and that way you don't need to worry about things like an overzealous spam filter or something causing e-mail messages to get lost. Red Act (talk) 03:37, 19 November 2010 (UTC)[reply]
Type of ruler used to show size of objects
Hi There, What is the name of the type of ruler/measuring device that you see in science pictures where there are squares of alternating color, 1 inch or centimeter or whatever, to make the scale easy to see? Thanks! —Preceding unsigned comment added by 148.66.156.170 (talk) 18:29, 18 November 2010 (UTC)[reply]
There doesn't appear to be a standard name for a ruler with a feature like that. There is no mention of such a type of ruler at Ruler#Types, and rulers I can find on the web with that feature are variously described as "[featuring] alternately colored bars"[25], "divided into ... segments by color"[26] or "marked in blocks ... in alternating ... segments"[27]. Red Act (talk) 19:24, 18 November 2010 (UTC)[reply]
Despite its name a scale ruler is used in making drawings to scale, not for giving the scale in a photograph. I would call the ruler a scale bar, which is what most people (1.6 million hits on google) use for the thing described in linear scale. Mikenorton (talk) 22:32, 18 November 2010 (UTC)[reply]
How realistic are the species, descriptions, evolutions, geologics, and so on given at www.metazoica.com?
Per above. Especially, I want to know about the possibility of the listed mammal species/genera/whatever. --Eu-151 (talk) 18:33, 18 November 2010 (UTC)[reply]
As per the introduction at the top of this page, "the reference desk does not answer requests for opinions or predictions about future events". Any discussion of Speculative evolution#Future Evolution would require purely speculative predictions about future events. Red Act (talk) 19:40, 18 November 2010 (UTC)[reply]
Actually this is a question about a present website rather than a future event. I think it's quite clear that the website involves a rather arbitrary imagination rather than any observed trend. Also, even if an evolutionary trend is observed, it can't be relied upon in a post-human world. For example, under ordinary circumstances new species often diversify from a small, generalist ancestor that is good at dispersing itself; but in a post-human society many exotic animals like lions and pythons and housecats and chickens will be dispersed all over the world to start with. The site seems to postulate both wide radiations e.g. from an elephant shrewand diversifications of highly specialized species like the edentates. It is an open question in biology to what degree wide radiations of species depend on catastrophism, especially where the diversification of mammals prior to the K-T event are concerned, but well known stories like the cichlids in more recent times depend on significant geologic change. It would probably take a rather specific scenario to allow both sorts of events to occur at the same time. Wnt (talk) 02:16, 19 November 2010 (UTC)[reply]
thanks, especially pay attention to one Species name in the genus "Procyon" (raccoons)!. But Why or how should carnivorous deer and antelope evolve (see Deinognathids), and is it a external link worthy of inclusion in Speculative Evolution? —Preceding unsigned comment added by Eu-151 (talk • contribs) 11:45, 19 November 2010 (UTC)[reply]
nicotine
Why do nicotine patches induce vivid dreams?. My dad was trying to quit smoking many years ago and we bought him patches, and he forgot to take it off when going to bed one night. He said he had the scariest most vivid dreams of his life. I've searched online and found similar accounts from many people, but no scientific reason for it. 92.158.144.48 (talk) 19:35, 18 November 2010 (UTC)[reply]
Any substantial metabolic perturbation during dreaming--including indigestion--can produce disturbing dreams, in my experience. Ginger Conspiracy (talk) 19:54, 18 November 2010 (UTC)[reply]
You didn't find [28] in your searches? It was the second result for me for 'nicotine dreaming'. Some of the related cites also look relevant. Nil Einne (talk) 19:54, 18 November 2010 (UTC)[reply]
What happens if you touch anti-matter?
Will your hand be hurt? AdbMonkey (talk) 20:22, 18 November 2010 (UTC)[reply]
How much antimatter? A single positronannihilating with an electron in your body would produce about 1 MeV of energy in the form of photons, which is only about 1.6 x 10-13joules, which is negligible. But if you tried to hold an entire gram of antimatter in your hand, you would not survive the experience, to say the least. Red Act (talk) 20:42, 18 November 2010 (UTC)[reply]
If you touched one gram of it, the blast would be about equivalent to a 40 kilotons explosion. (The bomb dropped on Hiroshima was 15 kilotons.)
However, modern science doesn't have the capability to create anywhere NEAR that much antimatter. APL (talk) 20:53, 18 November 2010 (UTC)[reply]
PET scans generate antimatter inside your skull, so it's not magical annihilation dust. It all depends on how much there is, as Red Act mentioned. --Sean 20:50, 18 November 2010 (UTC)[reply]
Pet scans do certainly use positrons, but not anywhere near enough to be called "dust". APL (talk) 20:57, 18 November 2010 (UTC)[reply]
So how did the scientists in Switzerland contain it? And how will they study it without it evaporating? Or exploding. AdbMonkey (talk) 21:20, 18 November 2010 (UTC)[reply]
Difficult to say without knowing what scientists you are referring to. But the article on antimatter Red Act linked to above has general info in the #Preservation section. Nil Einne (talk) 21:41, 18 November 2010 (UTC)[reply]
If you're referring to "the ALPHA collaboration announced that they had so trapped 38 antihydrogen atoms for about a sixth of a second.[24] This was the first time that neutral antimatter had been trapped" it may be helpful if after reading the article Red Act linked to in particular the the parts before my quote, you ask while explaining what still confuses you about how they trapped the antihydrogen. The Nature article the collaboration published that our article uses as a ref may be the best source if you can understand it and have access. But as I expect it's too technical, reading some of the writeups in more general sources may help like [29][30][31]. Nil Einne (talk) 21:47, 18 November 2010 (UTC)[reply]
The short, non-technical explanation is "they used magnets in a vacuum." Magnets are a nice way of containing charged particles without having them touch anything. The same kind of technique is used for trying to contain fusion reactions as well. --Mr.98 (talk) 01:56, 19 November 2010 (UTC)[reply]
Magnets without metal?
Is it possible to generate magnetic fields without metal? Googlemeister (talk) 21:13, 18 November 2010 (UTC)[reply]
The FDA has estimated that the risk of fatal cancer from the maximum allowable dose would be 1 in 80 million per backscatter screening. And doses from a single scan are considerably lower than the maximum, Kassiday said.
General-use systems operating in accordance with this standard produce a maximum reference effective dose of 0.25 μSv (25 μrem) per screening. Therefore, an individual may be screened up to 1,000 times each year without exceeding the annual 0.25 mSv (25 mrem) limit. The associated incremental risk of death is 1 in 80,000,000 per screening.
Is this supposed to be interpreted as for every 80 million screenings, 1 lucky soul will receive a dose of radiation resulting in fatal cancer?Smallman12q (talk) 21:35, 18 November 2010 (UTC)[reply]
No. Rather, as noted both in the summary and in the details, a screening at maximum allowable radiation dosage results in such a risk. The summary notes that the scanners do not operate at that maximum (though offhand I see no details as to what dosage they dole out), and so the risk should be further lessened. I'll note as a matter of personal opinion that I'd be more concerned with the possibility that the dosage could be inadvertently increased to catastrophic levels via software than the risk of long-term low-dose accumulation. — Lomn 21:59, 18 November 2010 (UTC)[reply]
Just as an aside, the amount of radiation you are exposed to from natural sources while on the airplane is significantly higher than the maximum dose per scan. --Mr.98 (talk) 01:40, 19 November 2010 (UTC)[reply]
It would be more correct to say that "1 additional person will develop cancer and die for every 80 million screened", than "1 lucky soul will receive a dose of radiation resulting in fatal cancer". It would be impossible to look at any given cancer case and say that it was the result of getting an x-ray at the airport. However, we can look at a large number of cancer deaths, and see that populations that receive more radiation get cancer at higher incidence than those who receive lower doses. We can even come up with some sort of "marginal deaths per mrem", which appears to be the case here. It's obvious that no one has studied the effects of getting just one extra 25 mrem dose; it would be impossible to draw any Statistically significant conclusions from such a study, even if you could control other exposures to ionizing radiation that accurately over a person's lifetime. It will be interesting to see if (assuming this backscattering thing catches on) research starts coming in 30 years from now looking at cancer rates among frequent fliers who have had lots of these scans, vs. people who hadn't. I suspect that even then, it will be hard to draw significant conclusions; as Mr. 98 pointed out, the act of flying itself contributes a non-zero extra dose of ionizing radiation. Buddy431 (talk) 02:10, 19 November 2010 (UTC)[reply]
The TSA and Backscatter X-ray articles are useful in sketching out some of the controversies, for example in skin vs. whole-body exposure. Regrettably the articles on rem and Sievert are woefully incomplete, and some of the most confusing that I've seen on Wikipedia. I will say though that I am suspicious of the idea that the absorbed energy of radiation in joules is the only factor in determining cancer risk, especially when you contrast cosmic rays striking an airplane with a machine deliberately designed to produce (I assume) a larger number of much lower energy gamma ray particles. But I don't know the specifics about this.
Another specific to nail down is how many people are to be subjected to this treatment. I've seen a number of very unreliable looking estimates of how many passengers fly yearly; one claimed over 1 billion. That figure should be nailed down, since it establishes just how many people we propose to sacrifice to the Minotaur yearly; a rough guess of 120 around the world would apply from this data. It would also be nice to have more data about terror attacks; this seems approximately equal to the number killed by terrorists. This is, to my mind, in keeping with an equipartition theorem-based First Law of Natural Disasters, which is that a catastrophic event and its government response are equally dangerous.
It seems like discussion of terahertz scanners seems to have quietly dropped out of sight, and I suspect there's a reason... Wnt (talk) 02:55, 19 November 2010 (UTC)[reply]
Looking at the number of terrorist related deaths involving airplanes is useful, but what's really more important is how many terrorist related deaths will these things stop? That's even harder to figure out, especially now when this technology is being introduced. Presumably this technology would have caught the underwear bomber, but he didn't cause any deaths anyway, so we couldn't credit these machines with saving lives in that case. If the List of aircraft hijackings is to be believed, since 2000, there have been only three hijacking incidents that resulted in fatalities, the well known September 11 attacks (almost 3000 deaths)(which fine, was four seperate hijackings) and the lesser known incidents in November 2000 and March 2001 in which 1 (the hijacker) and 3 (one of the hijackers, a passenger, and a stewerdess) were killed. The airport bomb in the 2005 Songkhla bombings (2 killed) presumably could have prevented something like this, although it sounds like any sort of baggage screening could have prevented it (the bomb wasn't on a person, I don't think, but rather in a bag). The 2004_Russian_aircraft_bombings could have probably been stopped by screening; they killed 89. That's all of the fatalities that I could find related to people intentionally trying to cause deaths on commercial aircraft since 2000 (looking at things like List of aircraft hijackings, List of terrorist incidents, and List of accidents and incidents involving commercial aircraft). The 9/11 attacks skew things considerably, but if you put your finger over them, these backscattering x-ray scanners seem awfully expensive for the number of fatalities that they're going to reduce (in financial terms, as well as possible health effects, as well as the goodwill of the public in having TSA guys see them naked). Buddy431 (talk) 03:45, 19 November 2010 (UTC)[reply]
Well all the above assumes that these scanners will simply be implemented alongside all existing technologies and procedures, but my guess is that they will replace some current technologies and procedures. The benefit might not be "deaths prevented" but instead it might simply make screening easier, less labor intensive, less technical or prone to error, etc. Vespine (talk) 05:46, 19 November 2010 (UTC)[reply]
Yes, but Buddy431 consider that the scanners make excellent Security theater. Indeed, the very fact that they are controversial makes them very well suited as security theater, since such controversy raises the consciousness of them, and thus improves their profile in our minds. --Jayron32 08:09, 19 November 2010 (UTC)[reply]
Here's an interview with Bruce Schneier in which he says the new TSA measures "won't catch anybody" compared to the old measures. Schneier has stated that the only two important differences between 2001 and now are (a) maybe the reinforced cockpit doors, and (b) definitely that the passengers have now learned to attack anyone who is a threat. The success of the underwear bomber incident was because in order to get through the old security measures he had to resort to an ignition contraption involving a syringe and 90 minutes in the bathroom; and because the passengers attacked as soon as it was apparent something was awry. (b) also stopped the shoe bomber. Comet Tuttle (talk) 17:57, 19 November 2010 (UTC)[reply]
How evolution explains the division into autonomic nervous system and somatic nervous system
I know why we are unable to control such things as heart rate for example, but how evolution explains the division of nervous system into somatic and autonomic one (and thus determining what we can control and what not)? Thanx.
Wikipedia has articles about the Autonomic nervous system and the Somatic nervous system. Primitive living things have only autonomic responses. Evolution of consciousness is accompanied by introduction of conscious control of parts of the body. The tradeoff is that conscious control increases the precision and adaptability of the controlled function, at the cost of making it slower. Modern humans have evolved towards an unprecedented level of conscious control and therefore see most animals as relatively quick and stupid. Cuddlyable3 (talk) 01:11, 19 November 2010 (UTC)[reply]
At the same time conscious thought is energy intensive - the human brain consumes about 20% of the body's energy already (far higher than in less intelligent animals). The body does not want to waste energy 'thinking' about functions that can be performed automatically, thus evolution would favour continuing to perform functions that can be performed automatically to remain that way, and thus the retention of the autonomic nervous system. --jjron (talk) 13:14, 19 November 2010 (UTC)[reply]
In environments that are relatively stable (stable "unchanging" food sources, predation pattern, temperature, rainfall), autonomic responses are all one needs since there are no immediate significant advantages to select for generalists that perform well in quickly changing or unstable environments. A specialist could survive and prosper by being less complicated and having doing the same task better. It's the same idea as with tools, for instance if all you will be doing is either drinking soup or skewering solid foods, you really only need a spoon or a fork (specialists) and something like a spork (generalist) would be less ideal since it does neither task very well. The evolution of more non-autonomic controlled "generalized" creatures such as humans are shown in geological records to have evolved in fluctuating or variable environments where creatures need to quickly adapt and be able to do a bit of everything (although perhaps less well). In the case of heart rate control in the heart's environment (the body), the change of pulse is either (1) detrimental to the survival of the heart and the body or (2) simply does not require complex interpretation of numerous body parameters, which is maybe why it is not selected for somatic response. -- Sjschen (talk) 19:45, 19 November 2010 (UTC)[reply]
animals natural disasters
How come animals seem to sense natural disasters before they even happen and Humans don't sense natural disasters naturally. —Preceding unsigned comment added by 83.71.80.54 (talk) 23:45, 18 November 2010 (UTC)[reply]
Our article on earthquake prediction has a bit about this here. Matt Deres (talk) 00:10, 19 November 2010 (UTC)[reply]
They typically don't, actually. It's mostly human power of suggestion. (After the earthquake people say "Hmm! No wonder kitty was acting funny!" never mind that cats tend to have mood swings every couple of days anyway.)
Here's an article that discusses the question as regards to earth quakes.
On the other hand, storms can often be predicted by sudden changes in air pressure, (up or down), even some humans can do that unaided. (Arthritis patients mostly.) APL (talk) 00:15, 19 November 2010 (UTC)[reply]
Are earthquakes preceded by low frequency sounds that somehow would not show up as a seismograph signal? Because many people act as if oblivious to very loud low frequency sound. Wnt (talk) 03:00, 19 November 2010 (UTC)[reply]
There's probably some of that, but it is far more likely that such an explanation is still more after-the-fact justification for what APL mentions; pets cannot predict earthquakes, but we believe they did, so we come up with justifications to explain how they did it. I am not aware of any actual controlled experiments which show that our pets can predict earthquakes, just a lot of unverified beliefs that they can. I am, of course, willing to be shown wrong, but I haven't seen anything yet. --Jayron32 05:00, 19 November 2010 (UTC)[reply]
I'm pretty sure, based on my own personal observations that gulls know when there's a big storm coming. Probably the same way that I can feel/smell it in the air as the skies begin to darken. They mass on the surface of the sea (or fly out seawards in their tens), emitting short, low-pitched, repetitive barking calls - quite different from the standard gull vocalizations that you normally hear. --Kurt Shaped Box (talk) 05:17, 19 November 2010 (UTC)[reply]
I'm not sure I would necessarily agree with a statement as strong as "They typically don't, actually. It's mostly human power of suggestion". It's reasonable to expect evolution to have found many different ways for animals to avoid death from natural disasters. It's probably unreasonable to assume that we know anything much about them yet especially when it comes to something very complex like earthquake precursors. At least it's clear is that we're still pretty terrible at earthquake prediction. As for other things, one species of ant in my part of the world is exceptionally good at predicting heavy rain hours before it starts. Thousands of workers, multiple queens and males, thousands of eggs and larvae all carefully arranged into staging groups metres off the ground on vertical surfaces. Very impressive. Anyway, perhaps the IP will find this paper interesting "Earthquake prediction by animals: evolution and sensory perception". Sean.hoyland - talk 07:18, 19 November 2010 (UTC)[reply]
I don't think Earthquakes are frequent enough that natural selection would have have worked and shaped behaviour in that manner. Also in the wild, most natural disasters don't kill you except flooding and fire. Earthquakes, for example, only kills you if you have a roof over your head. --85.119.25.27 (talk) 08:48, 19 November 2010 (UTC)[reply]
The paper I linked to tries to address those questions. Also, tens of thousands of land animal species have a roof over their heads. Sean.hoyland - talk 09:04, 19 November 2010 (UTC)[reply]
Hmm, so for example rats and rabbits could have evolved an escape behaviour (so that not to be burried alive), as well as birds nesting on the coast (to avoid a tsunami). Interesting.
But, like humans, dogs and cats wouldn't have evolved it, because of their lifestyle in the open, an earthquake in the wild would not kill them unless they are very very unluky and a tree fals onto their head. --Lgriot (talk) 13:23, 19 November 2010 (UTC)[reply]
Regarding weather, big storms are typically preceded by a drop in atmospheric pressure -- in the days before weather satellites, a barometer was the best tool for predicting storms. Some people with rheumatism can feel a drop in air pressure in their joints. Since birds have hollow bones, there is a decent chance that they can feel a drop in air pressure literally in their bones. Looie496 (talk) 18:12, 19 November 2010 (UTC)[reply]
Would it not be possible from evolution that the animals in there enviroment and habitat somehow learned of warning signs like for instance animals know to move up to higher ground if a tsunami triggered by an earthquake is approaching. --213.94.232.102 (talk) 21:26, 19 November 2010 (UTC)[reply]
November 19
Time Dilation? Time speeding?
I think the following section in Special Relativity has a wrong conclusion, “This phenomenon is called time dilation.”, △t’=γ△t should mean time speeding, isn’t it? Please help. Thanks.
Time dilation and length contraction
Writing the Lorentz transformation and its inverse in terms of coordinate differences, where for instance one event has coordinates (x1,t1) and (x'1,t'1), another event has coordinates (x2,t2) and (x'2,t'2), and the differences are defined as Δx = x2 − x1, Δt = t2 − t1, Δx' = x'2 − x'1, Δt' = t'2 − t'1 , we get
△t’=γ(△t-(v△x/c^2))，
△x’=γ(△x-v△t)，
and
△t=γ(△t’+(v△x’/c^2)),
△x=γ(△x’+v△t’)，
Suppose we have a clock at rest in the unprimed system S. Two consecutive ticks of this clock are then characterized by Δx = 0. If we want to know the relation between the times between these ticks as measured in both systems, we can use the first equation and find:
△t’=γ△t (for events satisfying Δx = 0)
This shows that the time Δt' between the two ticks as seen in the 'moving' frame S' is larger than the time Δt between these ticks as measured in the rest frame of the clock. This phenomenon is called time dilation.
Jh17710 (talk) 05:09, 19 November 2010 (UTC)[reply]
I am having a bit of deja vu. Oh, yeah, that's because this question has been asked, by you, before, and answered already. To save everyone the trouble of answering it again, here are the responses from the first time it was answered. If there is something you need clarified from those responses, please feel free to ask that. --Jayron32 05:19, 19 November 2010 (UTC)[reply]
Jayron, Thanks for you link. There were 3 responses and only the 2nd one responded to my explanation, however, there is no name to that 2nd response.
This time, I did not put my explanation and just ask question. If △t’=γ△t and △t'=△t/γ are both for the same moving frame S' and rest frame S, even thay are for different events, △t’ is for the moving clock and △t is for the rest clock. My question is so simple, if we call △t'=△t/γ "time dilation" or "moving clock runs slow" then, we should not call △t’=γ△t the same names, right?
I will respond to your comment and the comment from RedAct when I have time to study it. What I hope is that someone else could help me to understand my simple question.Jh17710 (talk) 06:22, 19 November 2010 (UTC)[reply]
Actually, since neither clock has a privileged frame of reference, when each observer views the other person's clock, he sees it as running slower than his own. There is no time speeding because no observer will ever view another clock as running faster than his own; every observer takes their own frame of reference to be at rest. This is covered at Time_dilation#Relative_velocity_time_dilation. --Jayron32 06:57, 19 November 2010 (UTC)[reply]
You're still making the same conceptual error I pointed out last time, by considering there to be "the moving clock" and "the rest clock". Each observer uses a system of synchronized clocks that are at rest according to that observer, not just one clock. In the example in the article, the clock being examined is a clock in the unprimed system. That clock is "moving", from the perspective of the primed observer. For the two events in the example, △t' is measured with two different clocks in the primed system, so there isn't a clock in the primed system that appears to be running fast according to the unprimed observer. △t' appears "too large" to the unprimed observer, not because there's a clock in the primed system that appears to be running fast, but because the unprimed observer considers the primed system's clocks to not be synchronized properly. Red Act (talk) 12:28, 19 November 2010 (UTC)[reply]
I'm supposed to find the change in voltage across the central voltmeter as Rx is moved away from equilibrium, assuming the first three resistors have a common resistance R.
However, I am obstructed by several conceptual problems.
Theoretically the voltmeter should have an infinite resistance, right? Yet it permits a finite current. Even for an ideal circuit? I have the relation ΔV / I_v = resistance of the voltmeter = ΔRx + R(I1/I_v - 2). John Riemann Soong (talk) 06:07, 19 November 2010 (UTC)[reply]
The current through an ideal voltmeter is zero. So an ideal voltmeter doesn't affect the circuit it's in at all. You basically analyze the voltages and currents in the circuit as if the voltmeter wasn't there. The voltage measured by the voltmeter is then the difference between the voltages of the two points in the circuit that the voltmeter is connected to. Red Act (talk) 12:51, 19 November 2010 (UTC)[reply]
The galvanometer used in a Wheatstone bridge is not an ideal voltmeter: it has a finite resistance. When the bridge is unbalanced, a current flows through the galvo and deflects it. You then adjust one of the resistors to balance the bridge so that the galvo does not deflect. Once the bridge is balanced, the resistance of the galvo doesn't matter since there is no voltage across it. --Heron (talk) 18:35, 19 November 2010 (UTC)[reply]
I'm presuming the current through the galvanometer is to be neglected in this problem, or else the galvanometer's resistance would have to have been specified as part of the problem. Red Act (talk) 19:33, 19 November 2010 (UTC)[reply]
Yes, I see what you mean. In which case we need to know where John gets his term I_v from, because that implies a non-ideal voltmeter. If I_v is non-zero then of course the equation in our article doesn't apply. --Heron (talk) 19:51, 19 November 2010 (UTC)[reply]
JRS gets a non-zero I_v because he doesn't understand the problem. The problem is completely soluble if I_v is taken to be zero, trivial even, the solution is given in the article. Physchim62(talk) 20:00, 19 November 2010 (UTC)[reply]
From the article: "The direction of the current indicates whether R2 is too high or too low. Detecting zero current can be done to extremely high accuracy (see galvanometer)." 128.143.181.23 (talk) 20:41, 19 November 2010 (UTC)[reply]
I imagine that as an anti-bitterant it would mask the taste of alcohol really well -- or does it not? John Riemann Soong (talk) 10:14, 19 November 2010 (UTC)[reply]
Why would you want to mask the taste of alcohol? Some people actually enjoy the flavor of their drinks, indeed that is generally the idea. If you really wanted to, you could use a much less expensive alternatives, like fruit juices, simple syrup, colas, etc. A properly trained bartender can mix a drink to suit anyones taste without exotic chemicals. --Jayron32 16:16, 19 November 2010 (UTC)[reply]
I tweaked the wikilink to fix typo in anchor. Hope you don't mind the third-party mod, Nil! DMacks (talk) 19:13, 19 November 2010 (UTC)[reply]
I'm not sure I see the logic of using an anti-bitterant to mask the taste of something that most people don't describe as bitter and that is chemically unlike general bitter things or the more specific molecules noted as blocked by AMP. DMacks (talk) 19:08, 19 November 2010 (UTC)[reply]
The thing is, AMP is apparently a bitter reception antagonist. It's not a mere masker. I would describe the fire of vodka for example, as just really intense bitter. 128.143.181.23 (talk) 20:37, 19 November 2010 (UTC)[reply]
In order to expand on the image description, so the image can be moved to Commons,
Is anyone on the Science Reference desk able to provide a more specific species
identification?
It appears when the is uploaded, there was some discussion, it may have been mis-identifed..
Sfan00 IMG (talk) 12:46, 16 November 2010 (UTC)[reply]
definitive deletion of a phobia(classical conditionning)
By considering absence of the Renewal effect and the Spontaneous recovery a proof of a definitive deletion of a phobia, can one expect a definitive deletion of a phobia after sufficiently repeated extinctions?--Kooz (talk) 19:27, 19 November 2010 (UTC)[reply]
Orgasmic sensation during pull-ups
When doing pull-ups or chin-ups, what is causing the tingling, sexual sensation in the groin area? This question is not looking for medical diagnoses or opinions. Thanks Reflectionsinglass (talk) 20:49, 19 November 2010 (UTC)[reply]
Orgasm#Spontaneous_orgasms covers some of this; it is entirely possible to experience orgasm, or orgasm-like sensations, without any direct stimulation of the genitals. --Jayron32 21:08, 19 November 2010 (UTC)[reply]
--Ludwigs2 07:31, 14 November 2010 (UTC)
--Wickey-nl (talk) 17:25, 17 November 2010 (UTC)
