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.
I just finished Ender's Game and have a question about the use of ultrahigh speed trips to extend someone's life. Obviously this is a work of science fiction, but assuming the premise of Ender's Game is true, would such a thing work? I tried to read the special relativity article but I didn't get enough information before it went into formulae and the like. If they needed Mazer Rackham (a general who was probably 40-60 years old) to be able to train new generals and they knew they wouldn't need him for 50 years but he would be dead when they did need him, can they send him on a starcruise that will take up 50 years of everyone's time except his own and then when he returns, he's just 2 years older? How does one's speed affect the physiology of one's biology (cells, tissues, organs, etc.) so that they don't shut down when they would ordinarily have (after 80 years, let's say)? Perhaps I'm just asking a basic question on special relativity -- I don't know -- but this book got me thinking about this. DRosenbach(Talk | Contribs)02:11, 4 August 2010 (UTC)[reply]
The physics of the time dilation is spot on - we would certainly argue that getting a ship up to those speeds would be a spectacularly difficult challenge - but if you could, then this would work as advertised. The deal here is that time for the general seems to happen perfectly normally - it's just like someone pressed the 'fast-forward' button on the rest of the universe. His body chemistry/cells/tissues/organs and every other aspect of his life are perfectly normal. This isn't even a theoretical matter - astronauts have taken sensitive clocks on long space missions and measured this time distortion effect. Of course they aren't moving at anything like the speeds suggested in the book - and the time distortion is on the millisecond scale - not years. But the principle is well understood and quite in line with mainstream physics. SteveBaker (talk) 02:48, 4 August 2010 (UTC)[reply]
I'll add a 'me too' to SteveBaker's (as-usual-spot-on) response. Physicists are wont to say that "there are no privileged frames of reference" — in other words, the little bit of space inside a relativistic starship behaves no differently from a little bit of space at rest relative to the Solar System. There isn't any experiment that I could conduct inside the starship (at least, no experiment that didn't involve looking out the windows) that would tell me how fast I was going, nor how fast or slow my clock inside the ship would appear to an observer outside. On-board starship physics (and chemistry, and biology) are exactly the same as physics everywhere else. The cells in my body age normally, as far as the clocks on board ship are concerned. It's only when an observer looks in the window of my speeding starship and observes my apparently slowed clocks (and all the other sequalae of relativistic travel) that the magic happens.
As a matter of kinematics, I'll add as an aside that one year of acceleration at one gee (9.8 meters per second, per second) would take you just a hair (3%) over the speed of light in one year — if we lived in a universe without relativity. Since there are relativistic considerations, our starship never quite manages to exceed the speed of light, but about a year at one gee acceleration gets us just about close enough for government work. After that year of acceleration Rackham's aging would be slowed to a crawl. (Incidentally, was that a year of acceleration measured from the outside, or a year as seen on shipboard? Those two are actually going to be quite different durations....) TenOfAllTrades(talk) 05:46, 4 August 2010 (UTC)[reply]
... and, agreeing with everything said above, I'll just add that there are serious considerations of energy requirements to maintain one "g" acceleration, especially when one gets within a few percent of the speed of light, but presumably a future technology has almost unlimited energy at its disposal, even on a spaceship. Dbfirs06:23, 4 August 2010 (UTC)[reply]
For the specific scientific discussion of this, see twin paradox. It has been a classic thought experiment of special relativity since the 1910s, and has since been experimentally verified in a number of different ways. --Mr.98 (talk) 12:08, 4 August 2010 (UTC)[reply]
I haven't read the novel, but I have some fair knowledge in Special Relativity. If we neglect gravitational fields, and if we need the general to age only 2 years while on the earth, 50 years have elapsed, then using the equation for time in SR, we find that his space ship must be travelling for 2 years continuously at the speed of 299552504.116 metres per second. thats just 239954 metres per second lesser than the speed of light. I have given u the idea. Now all you have to do is, to just find a space ship that can go at such a speed for 2 years!!! harish (talk) 15:59, 4 August 2010 (UTC)[reply]
The acceleration would be pretty killer, but iirc, the book does make vague mentions of technology for manipulating gravity and momentum being stolen from the Buggers in the First War, so that could probably hand-waved well enough for the book's purposes. APL (talk) 16:51, 4 August 2010 (UTC)[reply]
I haven't read Ender's game, but it seems a similar "delaying your aging with relativity" plot device is used in Joe Haldeman's Forever War. The hero's lover spends some time travelling at relativistic speeds so that she doesn't age and die while waiting for him to return from the distant war. Astronaut (talk) 11:46, 6 August 2010 (UTC)[reply]
High levels of elements in the blood related to skin and eye color
Just out of curiosity, i recently learned that high levels of copper in the blood causes a copper colored ring around the eyes, and even more dramatic, silver causes not only your eyes, but your skin too to change grey-bue. Are there any other elements, and maybe to a lesser extant compounds, that cause changing in coloration? 99.114.94.169 (talk) 03:05, 4 August 2010 (UTC)[reply]
Thanks, I should probably just google ever color and see :P, well sense we don't have a wikipedia article on , Lycopenodermia, maybe you can elaborate the condition? 99.114.94.169 (talk) 04:02, 4 August 2010 (UTC)[reply]
While on holiday in France recently, I happened to look into a wine glass which had been emptied some fifteen minutes earlier and not touched since. In doing so, I noticed that the sediment in the small amount of liquid that had gathered in the bottom was moving quite rapidly, in a roughly toroidal pattern (this was probably due to the raised dimple in the centre providing an obstruction). The glass was not in the sun, the table was hefty and not easily moved and there were no obvious sources of vibration anywhere around. My question then is, where was the energy for this movement coming from? At the time I didn't pay more than a few moment's attention, but now I find my curiosity is still piqued. I have tried to research this myself, but where to start?
Does anyone have any ideas, based on the scant information above, what was going on in that glass? The wine was an excellent Bordeaux red by the way!
I was close to the bushfires in Victoria, Australia 18 months ago, that took 173 lives and burned for many weeks afterwards. There have naturally been in depth investigations and many words written about them since, and I drove through the smoke to work for a month. I heard nothing at all about possible engine damage. My car is fine. HiLo48 (talk) 12:31, 4 August 2010 (UTC)[reply]
Volcanic ash bears no resemblance to smoke. Your (implied) comparison is like looking at the result of sandblasting your car and extrapolating to figure out what water from a garden hose will do. --Carnildo (talk) 00:36, 5 August 2010 (UTC)[reply]
Yeah - absolutely.
Volcanic ash is made of incombustible silicates and is incredible abrasive - when it's sucked into the cylinder and gets heated in a combustion cycle, it melts - when the cylinder pressure drops, it condenses back onto the colder cylinder walls - and you have a nice solid rock coating the inside of your cylinder. It's like you coated your cylinder with sandpaper! That wrecks the piston rings in no time flat! The advice from the USGS to change oil frequently is an effort to flush out any of this sand-like stuff and to give your piston rings the best possible chance. But the only defense is really to have a really good air filter. (Something after-market - not the crappy paper ones that came with your car. Because of the propensity for the air filter to clog - you need to either change it or clean it very frequently.
Smoke is mostly water vapor and unburned carbon - which your engine will happily burn up if it gets into the engine. It's also soft, so the engine can clear it out easily. Modern gasoline often contains detergents that are there specifically to help the engine get rid of the carbon it might generate as it burns gasoline less than 100% efficiently - and this helps a lot to clear the particulates from the smoke.
Smog is smoke and fog - and we all know that our cars run just fine on a foggy day. (Actually, fog can improve your engine's running because the water mist slows down the combustion and make it more even and complete...but the effect is admittedly minimal).
I suppose that if the nearby fires were able to suck a large enough fraction of the oxygen in the air, then your car's performance might be kinda poor - but it still wouldn't wreck the engine. SteveBaker (talk) 02:25, 5 August 2010 (UTC)[reply]
During World War II the Japanese scientist Hidetsugu Yagi apparently was working on some kind of "beam ray" (e.g. radio transmitter) that could stop automobile engines by disrupting the firing of their spark plugs. He apparently (according to some Congressional testimony from the 1940s) could get it to work if the hood of the engine was up on some Fords, but when the hood was down it didn't work, presumably because of reflections and so forth. He stopped working on it at that point.
My questions:
1. What's the likely explanation for his "success"? How would this really operate? Would the principle only apply to 1940s cars, or would it work on modern cars?
2. More speculatively, is there any technology or advancements since the 1940s that would lead one to expect us to be able to improve upon this sort of thing today? That is, Yagi found only very limited success at the time. Is there reason to think someone could do better now, in terms of whatever problems Yagi was presumably coming up against?
Any thoughts you had would be appreciated. I am not in the slightest an electrical engineer so any explanations that can be done without reams of equations would be appreciated. --Mr.98 (talk) 13:31, 4 August 2010 (UTC)[reply]
Well, it was reported to Congress by Karl T. Compton in October 1945, who was part of the investigation into the Japanese scientific work during WWII, so it probably isn't wholly false. It certainly wasn't effective, as is clear from the description above, and was abandoned. It seems unlikely to me that the whole story is fabricated—Compton was no scientific rube, and Yagi was a pretty serious guy himself. (I am getting this information from the transcript itself, not secondhand through some kind of Tesla-nut website.) --Mr.98 (talk) 15:03, 4 August 2010 (UTC)[reply]
Electromagnetic pulse guns like this one get reported in the press from time to time. Disrupting the ignition system on a pre-electronic car would take a lot more energy than crashing the electronics in a modern car. --Heron (talk) 18:29, 4 August 2010 (UTC)[reply]
Cars from that era are incredibly chunky things - I know a guy with a fully restored c.1945 jeep - and the electrical system is so insanely simple - it's hard to believe you could do much to hurt them. I suppose you could induce a large voltage in the ignition coil - but the problem is that the wiring around them is designed to cope with huge voltages - so at best you might just cause a back-fire or some other kind of 'hiccup'. Even a car from the 1960's would be immune to most of those kinds of tricks. It's not until the era of electronic ignition that your could do something nasty to the low-voltage systems and stop the car.SteveBaker (talk) 22:03, 4 August 2010 (UTC)[reply]
Here's the exact quote from Compton:
Well, we talked to Professor Yagi, and this is what we found: Some years ago, in talking to Dr. Coolidge at our General Electric Co., Dr. Yagi had suggested that it might be possible to stop the action of an internal-combustion engine by focusing an intense beam of an electro-magnetic wave, which would cause sparking and interrupt the operation of the spark plugs. When he got back to Japan and he tried it, he said he could make it work on a Ford car if the hood was up, but if the hood was down, unfortunately the metal shielding prevented its work. [At what range did he say he could make it work?] Oh, 30 or 40 yards.
He then goes on to say that Yagi went from there to work on directed energy weapons (e.g. death rays), and could make them work to some degree for killing rabbits, but power consumption was enormous and even though it could kill rabbits, it couldn't kill muskrats. (I am not making this up!) Compton says the idea was dumb because you could use a rifle more effectively than whatever ray they came up with. Compton then says that they doubt they could get the power consumption they claimed they could anyway (they were claiming they could produce an oscillator to produce 80 cm radio waves with 200 kilowatts of continuous power output, but the oscillator manufacture said they could get 40 kw at best).
This story reminds me of the "engine-stopping ray" that Germany was thought to be developing in the late 1930s. Here's the story as told by Reginald Victor Jones in his book Most Secret War:
There was also, incidentally, the story that whatever was in the tower at the summit [of the Brocken, i.e. the Sender Brocken — Gdr] was able to paralyse internal combustion engines. As usually reported, the phenomenon consisted of a tourist driving his car on one of the roads in the vicinity, and the engine suddenly ceasing to operate. A German Air Force sentry would then appear from the side of the road and tell him that it was no use his trying to get the car going again for the time being. The sentry would, however, return and tell him when he would be able to do so. [...]
It was from my contact with one refugee that I found at last the explanation for the stories about the engine-stopping rays. This particular refugee had been an announcer at the Frankfurt radio station, and I therefore wondered whether he might know anything about the work on the nearby Feldberg television tower that was said to be one of the engine-stopping transmitters. When I told him the story he said that he had not heard it, but he could see how it might have happened. When the site for the transmitter was being surveyed, trials were done by placing a transmitter at a promising spot, and then measuring the field strength that it would provide for radio sigals in the areas around it. Since the signals concerned were of very high frequency, the receivers could easily be jammed by the unscreened ignition system of the average motor car. Any car travelling through the area at the time of the trial would cause so much interference as to ruin the test. In Germany, with its authoritarian regime, it was a simple matter to decide that no cars should run in the area at the relevant time, and so sentries were posted on all the roads to stop the cars. After the twenty minutes or so of a test the sentries would then tell the cars that they could proceed. In retailing the incident it only required the driver to transpose the first appearance of the sentry and the stopping of the engine for the story to give rise to the engine-stopping ray.
Apparently he extracted his eyes as well, and put them in a safe deposit box.[1] One wonders how they were preserved. Googling around, there are some people who claim to have locks of Einstein's hair, which is not an ideal place to get DNA from, though. --Mr.98 (talk) 15:09, 4 August 2010 (UTC)[reply]
Remember, an adult is determined by far more than just their DNA. A clone of Einstein wouldn't necessarily be a genius and he wouldn't necessarily have any interest in physics. --Tango (talk) 16:27, 4 August 2010 (UTC)[reply]
Not really. His hair looked like that because he wasn't interested in making it look like anything else. If the clone chose to cut it short or tie it back or straighten it, it would look completely different. --Tango (talk) 17:27, 4 August 2010 (UTC)[reply]
Using modern Polymerase chain reaction methods, you really don't need more than one intact DNA molecule - so this isn't about whether there is "enough" DNA - it's whether there is "any" DNA left. I think it would be surprising if we couldn't track down even the tiniest amount of the stuff. However, I agree with Tango - your Einstein clone might be completely useless at physics. Einstein certainly had a flair for physics - but in almost every other respect of his life, he was a total jerk/loser. It's not that he had general intelligence - it's that he had it all focussed in one incredibly narrow field. If you read his biographies - it's hard not to be horrified at his dealings with wife, kids, relatives, etc. It's incredibly unlikely that there is a "Physics expertise" gene - but it might well be that there is a "single-minded narrow-skill-set obsession gene". Clones of Einstein might just become fanatical stamp collectors for all we know. SteveBaker (talk) 21:56, 4 August 2010 (UTC)[reply]
You need one intact DNA molecule per chromosome. Having some, but not enough, DNA would mean you either have non-intact molecules or some missing chromosomes. --Tango (talk) 00:43, 5 August 2010 (UTC)[reply]
Oh! Yes, of course, silly me! But still - it's not much. I presume it wouldn't have to be intact either - the first thing the gene sequencers do is to chop the stuff up into smaller bits. It only matters that somewhere in your sample of fragmented section you have enough pieces to make up the entire genome - and in long enough sections that you have overlaps that tell you how to stitch them back together again. Even if a few bits were totally missing, the odds are good that those sections wouldn't code for anything interesting about Einstein - so you could probably fill in the bits that were missing with sections of someone else's genes without much risk of significant non-Einstein bits cropping up in the finished clone. SteveBaker (talk) 02:10, 5 August 2010 (UTC)[reply]
Diamonds are forever (?)
This problem needs someone who has in-depth knowledge about diamonds.
To make my point clear I have to summarize a story I read lately. Two Englishmen find a diamond, a rather big diamond (so big that they even compare it to Kohinoor). The first one who discovers it knows his stones, i.e. can tell beyond doubt if a diamond is real. He inspects it, firstly with naked eye, then with a lens and confirms it's genuine. The second also falls in line. Then both go to a jeweler who also tells them there is no doubt about it. It is real, it is big. He is willing to buy it for £ 10,000. But one of the sellers becomes stubborn and express his disbelief over the valubillity of the stone. The jeweler says that he is in this business for years and there is no room for doubt. But the idiot insists upon a test. So just to satisfy his whim the jeweler switches on a grinding wheel and rubs the stone on it. Immediately the stone shows "faults". Next moment it is lying there, valueless as dust !
Then the author explains us : though the diamond was real it was lying under fire and pressure for so long that it became "splintered". That is on inspection by an expert it will look real (and strictly speaking is real) but on slightest touch it will come into it's true state, that's nothingness.
I know nothing about whether faults could show up only after grinding, but as for the hardness of diamonds, I can tell you that tools used for grinding and cutting diamonds are often made from diamond themselves in order to be hard enough to affect the diamond. --Tango (talk) 16:30, 4 August 2010 (UTC)[reply]
Diamond has the highest hardness Moh = 10 of any bulk material. The Wikipedia article Diamond notes that the most time-consuming part of cutting a gemstone is the preliminary analysis of the rough stone. It needs to address a large number of issues (see article) and can last years in case of unique diamonds. It is possible that a major flaw would not be discovered in the initial rough state of a diamond, though the sudden reduction of the value of a Koh-i-Noor-like diamond from £ 10,000 to valueless sounds incredible.
I have found no references to splintered diamonds apart from a diamond trader who uses that name.
Sounds like nonsense to me (not pseduscience - nonsense) for a number of reasons:
Diamonds are not tested by grinding - that's crazy. They are tested by temperature conduction.
Faults in the diamond would show up if you looked at it with a magnifying glass. For the scenario given, the diamond would have to be powder on the inside, with a thin sheet of diamond holding it together - that's just nuts. And would be very visible anyway. It's not like a Prince Rupert's Drop (very cool, watch the video) where there are tremendous internal stresses, covered with glass. Diamonds just aren't like that, glass is amorphous, but diamonds are crystal. An amorphous diamond would be graphite, i.e. black.
Was the diamond they found rough or cut? Probably cut since a jeweler was going to buy it. If it was cut that means it already was near a grinding wheel, so why would doing it a second time cause such a catastrophe?
Really? Won't it just make a lot of CO2? (For the metastability of the perchlorate -- maybe it was trapped inside a mineral impurity that gave the diamond a valuable coloured hue.) John Riemann Soong (talk) 20:37, 4 August 2010 (UTC)[reply]
(original question) It's possible that the stone was a 'mash-up' eg made of smaller diamonds glued together with optical paste - that would fall apart .. however I don't think there is an optical paste with the same refractive index of diamond (?) 77.86.119.98 (talk) 19:51, 4 August 2010 (UTC)[reply]
You might consider a 'scratch test' - try to scratch it with something a little less hard than diamond...if you were in a jeweller's shop - you could grab a handy Topaz or Corundum and just try to scratch the diamond with it...or try to scratch a topaz with the supposed diamond. Topaz and Corundum are pretty hard stones in their own right. It's even possible that the grinding wheel in the story would be a corundum wheel (they are pretty common - and a lot cheaper than diamond wheels)- but why turn the thing on? You could just drag the diamond across the wheel and see if it was scratched. I guess the theory in the story was that this diamond had many flaws - which would obviously be weaker and maybe cause it to break...but crumbling to dust just doesn't seem likely. A large diamond that was that massively flawed wouldn't be worth that much anyway. SteveBaker (talk) 21:46, 4 August 2010 (UTC)[reply]
With a disclaimer that I'm far from an expert on diamonds, the story seems ridiculous to me. Any fracture plane inside a diamond will produce internal reflections, so a diamond fractured so extensively would look like crap quartz -- translucent rather than transparent. Looie496 (talk) 01:11, 5 August 2010 (UTC)[reply]
I know how to tell a nearsighted prescription from a non-nearsighted prescription by looking through the lenses. Is it possible to estimate the prescription (of any kind) of a pair of eyeglasses by looking through the lenses? If so how? —Preceding unsigned comment added by 68.76.147.53 (talk) 15:10, 4 August 2010 (UTC)[reply]
Yeah. The more bigger the number be the more concave the lens will be. The more positive they will be the more convex they will be. I think the near-sighted are always concave (negative) while the farsighted are always convex (positive) -- Jon Ascton (talk)15:34, 4 August 2010 (UTC)[reply]
Eyeglass prescription#Lens power describes how the prescription strength (in diopters) relates to the focal length of the lenses. Briefly, the strength in diopters is just one over the lens' focal length in meters. If you are able to estimate the focal length of the lens, then invert to get the prescription's approximate strength. (This assumes spherical lenses with no correction for astigmatism; it gets more complicated if you want to be able to extract a significant cylindrical contribution as well.) TenOfAllTrades(talk) 15:36, 4 August 2010 (UTC)[reply]
I don't need to estimate the astigmatism correction but it'd be nice if I could tell if there is some correction for it. how could I do that? Thankx 68.76.147.53 (talk) 15:55, 4 August 2010 (UTC)[reply]
(This only works for farsighted prescriptions.) Using a distant lamp as the source (you can use the sun, but don't burn anything), find the distance from the lens to the wall where the projected image is clear and sharp, in meters. 1 over this number is the power in diopters. Ariel. (talk) 17:31, 4 August 2010 (UTC)[reply]
(original question) Simply put - lens for nearsighted people (Myopia) make things look smaller. For the opposite type "longsightedness" (Hyperopia) the lens is like a magnifying glass - close up to things it will magnify, or further away it will invert (upsidedown) things you look at through it. A lens for a nearsighted person won't do this. For people with weak nearsightedness it may be difficult to tell by looking a the lens.77.86.119.98 (talk) 19:48, 4 August 2010 (UTC)[reply]
For a quick evaluation of eyeglasses: Hold them between you and a wall or desktop and move them back and forth. If the lenses have no correction, the background will not move. If they correct for nearsightedness, the image will move in the same direction you move the lens. If they correct for farsightedness, the image will move in the direction opposite from your movement of the lens. Now to check for astigmatism correction: Look through one lens and rotate it. If the image changes in its vertical and horizontal size with rotation, there is astigmatism correction. In each case, a stronger correction produces a larger effect. Bifocals/trifocals will show a gradation from top to bottom in the lens strength. In side to side movement, if the effect varies from top to bottom in a lens but no abrupt change is seen, then they are "progressive bifocals." For a simple lens correcting for farsightedness, you can form an image on paper of a distant light and measure the distance from the lens to the paper to determine the focal length, then the diopter rating is 1/f where f is the focal length in meters. With such a known positive lens, you can stack a weaker negative (nearsighted correction) lens next to it and from the combined focal length calculate the diopters of the negative lens. Despite what was said above, the curvature of the outside of the lens is largely unrelated to its power, since eyeglasses use meniscus lenses, with the inner and outer surfaces both curved to differing degrees. Edison (talk) 03:05, 5 August 2010 (UTC)[reply]
Positive and Negative Overlap
Positive overlap means overlap between two orbital lobes where the wave function is positive right?? Since on one lobe of the px orbital, the wave function is positive and on the other, the wave function is negative, there is equal chance that in two atoms about to bond with each other, the positive lobe of one atomic orbital may overlap with either the positive or negative lobe of the other atom to form positive or negative overlap, right? So is there equal chance for a formation of positive or negative overlap for a given pair of atoms? I am now just in Class eleven and I just know only basic quantum mechanics, so please explain clearly... Thank You. —Preceding unsigned comment added by 117.193.236.184 (talk) 15:39, 4 August 2010 (UTC)[reply]
The actual sign is not a real physical property, it's just an mathematical artifact of the way the orbitals are described. However, the sign does allow one to explain certain bonding types. First, remember that the sign itself isn't a real thing, so the actual "+" or "–" is arbitrary, but the relative sign ("same" vs "opposite") is a viable comparison. You have to be consistent, but you can pick an arbitrary starting point:) So positive overlap (a bonding molecular orbital) means the "same sign" (both positive lobes, or both negative lobes) on the two atoms, whereas an antibonding molecular orbital (a high-energy thing that tends to make the atoms move apart rather than stay bonded) is "opposite signs". So if you're describing bonding, you pick the same signs of the lobes that overlap, and there's your stable electronic state. And once you have that, the "other way" is the unstable state. Sometimes a graphical representation (using arbitrary colors) helps avoid getting misled by the actual signs of the lobes--just pick two colors. See Molecular orbital diagram for some more information, and ask more if you get stuck. DMacks (talk) 19:30, 4 August 2010 (UTC)[reply]
Positive overlap usually means that the lobes have the same sign, so that the combined wavefunction is greater than either, rather than less as when happens when they have different signs.77.86.119.98 (talk) 19:35, 4 August 2010 (UTC)[reply]
In terms of chances - take two H atoms - containing each one atom - the probability of either atom having a given sign of the 1s orbital is normal 50% .. so yes.. However in a magnetic field the different orbitals "+" or "-" sign are split in energy - so that the probability is not 50%.
When the "+" and "-" forms of the same orbitals have the same energy it can interconvert to the opposite sign with no barrier - so effectively creating a 50:50 chance as you describe.
Since the oribitals can change their sign value under normal conditions this means that the 50:50 probability of bonding or anitbonding orbital formation is obscured - since the formation of a bonding orbital is favoured energetically - thus when 2 H atoms meet the probability of forming a bonding orbital is more than 50% (in zero magnetic field the "+" and "-" orbitals are practically equivalent).77.86.119.98 (talk) 19:43, 4 August 2010 (UTC)[reply]
So, finally, it means that the chance of two opposite signed lobes approaching each other is 50-50, but since they are degenerate, they exchange their positions... so the probability that a positive overlap will be formed in H-H atoms close to each other is near 100%, is it?? and is this what we call bonding molecular orbital and anti-bonding molecular orbital? harish (talk) 01:17, 5 August 2010 (UTC)[reply]
Yes - positive overlap results in a bonding orbital .. negative=antibonding. Probability is better than 50% I can't be more specific than that - the product H2 has isomers see Spin_isomers_of_hydrogen - which very slightly complicates things. If two hydrogens with arbitary opposite orbital sign approached each other - they'd bounce off each other and not bond - this is a possibility - someone else may know how to better calculated the chances - but I guarantee it is better than 50% for the reasons given above.77.86.119.98 (talk) 02:17, 5 August 2010 (UTC)[reply]
Expense of oscilloscopes
I was wondering why oscilloscopes, even USB oscilloscopes, are so expensive? Is it a case of charging what the market will bear or is the consumer base so small that it is necessary to charge this much in order to make business viable? How complex are they, in comparison to a television? I don't study electronics but just wanted to make my own dynamo-powered bike lights and learn something as I go. ----SeansPotato Business16:03, 4 August 2010 (UTC)[reply]
See the Wikipedia article Oscilloscope. It is a complex measuring instrument that needs accurate calibration. It is intended to be rugged, portable and to have a longer life than a domestic TV. It has many more user controls. Very few of its components are those that are mass produced for TV production. It contains beam deflection circuits that are capable of operating at a wide range of different scan frequencies compared to a TV that has only 2 scan frequencies. All these factors contribute to its relatively high price, as well as the small production volume that the OP has noted. Cuddlyable3 (talk) 16:38, 4 August 2010 (UTC)[reply]
It's also a much more specialized piece of equipment. Something designed to sell ten million units will be cheaper than something to sell ten thousand units, all else being equal.
However, if your needs are simple, There are pretty cheap scopes. Here is one with the form-factor of an iPod for $99. And here is a kit for $60. You might be able to find these slightly cheaper elsewhere. However notice that they are single-signal and lack advanced features like FFT. APL (talk) 16:45, 4 August 2010 (UTC)[reply]
You can also use the audio input of your computer for nothing, though the top frequency is usuauly about 200kHz (sampling rate), and you have to calibrate it yourself. Inputs shouldn't be over 1V or 0.5 but resistors are cheap - if you know what to do. There are free programs that convert the computer into a simple oscilloscope. eg http://www.zeitnitz.de/Christian/scope_en
On the other hand .. all scientific instruments are expensive - a laboratory sonic bath supplied by a laboratory supply firm will cost typically 10x what an equivalent mass produced sonicator will cost.. the reasons for this are purely economic.Sf5xeplus (talk) 17:39, 4 August 2010 (UTC)[reply]
(ec) A few reasons why scopes (and other test equipment) are expensive. First, compared to consumer devices, test equipment like oscilloscopes are sold at very low-volume. Economically speaking, this means that every unit must be sold at higher margin per each unit, in order to amortize the costs of engineering, manufacturing, and distribution (which are the same or greater than an "equivalently-complex" high-volume consumer device like an HD TV). Furthermore, the costs of designing and manufacturing each unit are much higher than for an "equivalently complex" consumer device. The thing to keep in mind is that for most purposes, an oscilloscope must be extremely high quality. For example, on a consumer device like a music player, if the audio amplifier is out of spec by 0.2 dB, nobody cares, and you adjust the volume knob slightly and move on with life. If a company sells oscilloscopes that are out of spec by 0.2 dB, because it is test equipment, this is totally unacceptable. Every single voltage, every single frequency, every indicator knob, must be exactly to spec out to several decimal places, because the oscilloscope (or the multimeter, or the network analyzer, ...) is the device that is used to calibrate all the other devices. So it has to be the best piece of equipment on the bench. It can't be flakey, it can't have strange voltage spikes or frequency spurs or unwanted parasitics; and particularly for a `scope, it's impossible to "hide" these sorts of parasitics "out of band" because a scope will operate over a very wide range of operating conditions (e.g., voltage, frequency, and even lab conditions like temperature and humidity). The design is therefore much more complicated. You can buy a cheap scope, or build a scope as a hobbyist project - but it will be nigh impossible to match the quality across all ranges of operation of a $1000 or $10,000 Agilent bench scope $50,000 wide-band scope or $350,000 mobile-telephoney network analyzer with protocol-stack decoding. The way I have heard these outrageous product costs explained is something to the effect of "without this equipment, an entire team of 20 RF engineers are useless, and their cumulative salaries are much more expensive than the gear that they require to do their jobs." Nimur (talk) 17:44, 4 August 2010 (UTC)[reply]
A little simplistic perhaps but the general sentiment surely holds. If there is no advantage to the $350k scope then sure, they should go with the cheaper one. But if the more expensive scope reduce the number of person hours or does things that they need that the other one can't or whatever then the price may be worth it.
Your keyboard example is interesting. For a typist or someone who uses the keyboard a lot, they may find the $10 keyboard doesn't suit them well and slows down their typing (there may also be OSH concerns something which doesn't fit the scope example so well) then getting the $100 (or whatever) keyboard may be worth the extra cost given the increased productivity.
I've seen similar arguments made e.g. for large monitors in the past when they were still relatively expensive (they increase productivity so even if it costs $2000 it may make up for it fairly quick) or software and while I'd agree that the analysis is sometimes a little simplistic I would say there is some validity in the reasoning. Even if you can 'make do' with cheaper equipement the more expensive equipement could make up for it in the long run.
Note that for the keyboard example there may be some cases, e.g. when you need wireless or perhaps in a hospital where you need to worry about contamination or in an extreme environment where the $10 is really not up to the job. I suspect there are some similar cases where the $1000 scope, or even $50k scope simply won't do.
Of course the price of even fancier keyboards is so small relatively speaking that if you're just talking a small number it's not really going to be significant. And the room to innovate on a keyboard is also a lot smaller so the keyboard comparison somewhat falls through. There is I presume a very big difference between the $1000 and $350k scope and the cost difference even for a largish business is not so small. But it seems some business are either very stupid, or do feel the gain of the extra features and associated productivity or capability of their business makes up for the cost.
It really depends on what you need. There are programs for the PC ($0) that use the sound card to capture voltages and display them in an oscilloscope-like form. Sadly, they only work for voltages and frequencies that the sound card can handle - and you still need a 'probe' with the right impedance, etc to do a good job of picking up the signal without disrupting it. Second to that are some hardware gizmos that you can plug into a PC or into an Arduino board with an LCD display that do a somewhat better job. But those things are still going to be limited to maybe 8 to 10 bits of precision and maybe 100kHz of frequency. To see faster signals, there is really no substitute for a proper (and expensive) scope. They are the price they are because they don't sell many of them - and that's the price the market can stand. SteveBaker (talk) 21:27, 4 August 2010 (UTC)[reply]
I don't know if I would go for a sound card, but a pretty cheap solution is to get a basic A/D card and set up a software oscilloscope. Also I expect that there is a strong market in oscopes on Ebay (not that I've actually looked or anything). They've been around for decades and must pop up whenever an electronics repair shop goes out of business. Looie496 (talk) 01:05, 5 August 2010 (UTC)[reply]
"Eco" water bottles have more BPA?
At work, some health conscious types have warned me about water bottles. They say the new thinner, squishy "eco" water bottles contain higher amounts of Bisphenol A (BPA) than the older, thicker bottles. They say that eco water bottles are formed by injecting molten plastic (like normal bottles) but they are also filled at the same time. So the plastic molding and water filling take place simultaneously. The rapid cooling of the hot plastic supposedly releases more BPA into the water? Or something like that. They also mention eco water bottles that have been sitting in sunlight also have raised BPA levels due to some reaction with UV light. It sure sounds plausible to a non-science type. Is there any truth to any of this? --70.167.58.6 (talk) 18:45, 4 August 2010 (UTC)[reply]
The presence of BPA does not have anything to do with the "squishiness" of the plastic, what does matter is type of plastic it is. For instance Polyethylene (HDPE, LDPE, PE,etc.) and Polypropylene (PP) are both squishy but should not contain the compound since it's not manufactured with it or combined with it industrially. BPA however is present in Polycarbonate ("PC", the clear nalgene water bottles) since it is a monomer of certain types of this kind of plastic that was unreacted in the production process. It is also added to PVC (faux leather, notebook binder plastics, pipes) as a plasticizer (to soften plastic). Check what type of "eco" water bottle you have to see if it's likely you have something containing larger amount of BPA. -- Sjschen (talk) 20:56, 4 August 2010 (UTC)[reply]
The "squishiness" does matter because BPA is a plasticizer - meaning it's there to make the plastic more squishy. Some plastics need it, others don't. The resin code doesn't automatically mean it does/doesn't have it because it's possible to make the plastic either way, it's just a resonable shorthand for the more common uses. So for example polycarbonate most definitely can be made without BPA, even though it's on the "bad list". As for create and fill, that sounds very unlikely to me. The machines that make bottles are very different from the ones that fill them. Bottles are blown - with air (inflated like a balloon). They need to stay hot, there is no way you could do it with water unless you used hot water, which is very wastful (i.e. expensive) to heat all that water. So there is no way they do create and fill, so that part of what you heard is wrong. Heat will release more BPA. UV probably won't. Baseline: You can't tell by looking. You'll have to trust the manufacturer to give you accurate info (or a lab). For bottles that are made in massive quantities you can use the resin code since that's the more common use. However bottles that are spec made for a particular company you can NOT use the resin code. Ariel. (talk) 23:44, 4 August 2010 (UTC)[reply]
No. BPA is not/should not be used as a plasticiser - it's a monomer in the production of Polycarbonate plastics, and should not be present in anything other than microscopic amounts in polycarbonate plastics (or any other plastics) for the obvious reason of it's toxicity.
It is possible that the bottle are more squisy due to a plasticiser, or they may be using lower molecular weight plastics.
Even this 'pro BPA' site [3] states "Bisphenol A (BPA) is not used as a plasticiser in plastics" - it is a very toxic compound - it is not and could not be used in the quantities required for plasticising plastics.77.86.119.98 (talk) 01:24, 5 August 2010 (UTC)[reply]
My bad, BPA counld be used in plasticizers (as antioxidants), but not as a plasticizer. While in the end it does depend on what the manufacturer decides to add, plasticizer containing plastics are usually not used for water bottles. As well, plasticizers are usually not added for PE plastics, the typically squishy plastics. As such, the "squishiness" of a plastic does not necessarily mean that contains BPA or plasticizers. You should find the resin code on the bottle and decide if you want to trust it. -- Sjschen (talk) 14:40, 5 August 2010 (UTC)[reply]
Hope this doesn't change the discussion too much, but when I said 'water bottle', I meant single-use throw-away bottles of water (like Aquafina, Dasani, Dannon Purelife, Evian, etc), not reusable water containers. I hope my description of simultaneous plastic molding and water filling made this apparent. --69.148.250.94 (talk) 05:07, 6 August 2010 (UTC)[reply]
Anywho. The takeaway conclusion is: one can't tell from the recycle code. But the whole thing is bunk anyway. And even if it wasn't, the 'squishiness' of the bottle has no relation to BPA levels? And 'squishy' is not a new manufacturing process, but just a new plastic formula. Is that the gist?--69.148.250.94 (talk) 05:12, 6 August 2010 (UTC)[reply]
Yes/No. You can tell from the recycle code (ok if it's 7 there are options) - if it's not 7 there should/will be absolutely no BPA in it. In my experience the bottles (disposable) are usually 1 PET , not 7 , but maybe it's different where you are. As to part of the earlier question - filling the bottle as it is blow molded sounds like hydroforming. This seems very unlikely. As far as I know the plastic has to be hot to be molded - any water would instantly cool it - result cracking - cold plastic Polycarbonate is not ductile like , say Aluminium. (If it was done by hydroforming of hot polycarb the likelyhood of leaching is increased. I don't see an immediate reason why a thinner wall would result in increased leaching, unless it's incredibly thin. (Usually code 7 plastics have a letter code molded onto them as well - eg PC is polycarbonate , ABS is acrylonitrilebutadienesytrene - look for the letter code as well.)
As for uv light increasing levels of BPA in polycarbonate plastics - I can't find anything on this - but it is a possibility that can't be rejected.87.102.72.153 (talk) 16:40, 6 August 2010 (UTC)[reply]
You can usually trust the recycle code, but there may be some fears on whether the manufacture of the bottle "follows regulations". PET, the "single-use throw-away bottles" likely has no BPA, but may have other interesting stuff in it used as a catalyst for the resin's production or possibly harmful unreacted monomers. Use resins 1,3, and 6 at your discretion since different manufacturing processing can make the product less benign (though they seem for the most part quite okay). Resin 3 for example, can contain phthalate plasticizers, which some have argued are unsafe. Resins 2,4,and 5 are quite safe, but it depends if you trust the manufacturer or country of manufacture and whether they are selling you what you say they are. 7 is a mix bag, and you pretty much have to read up on them to make a semi-educated decision. -- Sjschen (talk) 04:05, 7 August 2010 (UTC)[reply]
Retrieving sound of the past
Does any one have some articles/webs related to studying the possibility of sound signals recovery from the past? I mean to hear some old information like our voices in the past. Sorry for not logging in, (Email4mobile)--89.189.76.246 (talk) 20:07, 4 August 2010 (UTC)[reply]
There have been claims that horizontal grooves inscribed on ancient pots while they span on the potter's wheel had inadvertantly recorded (with very low fidelity) words or word fragments being spoken at the time, and that the words had been or might be recovered. This site suggests that some claims were hoaxes, and discusses the provenance of others, as well as giving further links of relevance. 87.81.230.195 (talk) 20:37, 4 August 2010 (UTC)[reply]
(ec)I'd heard that claim too - but it's pure fiction. Fingers don't vibrate much in response to sound they are too heavy and muscular. The gizmo that (for example) Edison used to make the his phonograph was a delicate little contraption being driven by a large diaphragm - so as to capture the maximum possible amount of sound energy and to focus it to displace the minimum amount of wax by the smallest distance. Plus, a pottery wheel rotates about once a second - so at most you'd only grab one second of audio before the fingers came around again and erased it. Nah - it's a great idea - but it's not gonna work.
Having said that, we do have some recordings from 20 years before Edison invented the phonograph. Edison was the first person to invent a machine that could both record AND play back sound - but Édouard-Léon Scott de Martinville invented a machine that could record sound (but not play it back). Those recordings were first replayed just a couple of years ago - and the audio files that they recovered can be replayed right from within our article! That dates back to 9 April 1860. But that's really as far back as you can go. Aside from that, your only chance is listening to early Edison phonographs - and the oldest known one of those dates to 1888. SteveBaker (talk) 21:22, 4 August 2010 (UTC)[reply]
I was wondering if there were some claims about the possibility of restoring sounds of our owns in our medium (air for example) by analysing the spectrum of vibration frequency and tracing for possible eventhough very weak signals since a fraction of energy will always reflect back and forth in the form of echos.--195.94.11.17 (talk) 22:16, 4 August 2010 (UTC)[reply]
Interesting concept - reverberation is real, and conceivably, even if the level of reverb is inaudible, it may still carry information. But, that information would be dispersed to very low energies, and the signal to noise ratio would make it impractical to reconstruct anything. The straw-man version is to be in a large, empty, echo-y room; obviously, if you shout, you will have an echo that could be recorded and used to estimate the "original" version of the shout. But after even a few seconds, the echo level has died away to such a low volume that the ambient noise would totally override any effort to reconstruct the source. In a non-ideal environment, like outdoors or in a non-echoing room, you'd have essentially no chance. Source estimation is an open research problem in signal processing - trying to figure out exactly what pulse was sent out, when all you have is a recording of the result. You would be setting up a very poorly-constrained source-estimation problem; it's safe to say we have no existing problem that could work reliably. Nimur (talk) 22:53, 4 August 2010 (UTC)[reply]
Also, sound propagates by causing vibrations in the air particles. Moving those particles up and down is an expenditure of energy, and, by the laws of thermodynamics, some of that energy will be lost in the form of heat. That lost energy will be taken from the intensity of the wave. So, the wave will die out in the way from one echoing surface to other.
Also, the echoing surface will absorb a small part of the energy of the sound, unless it's a perfect echoing surface. For example, we have perfect mirrors that are used to create laser rays, but they still don't reflect 100% of the energy. If you leave a laser ray bouncing indefinitely between two perfect mirrors, the ray will eventually get absorbed by the mirrors. A sound echoing between two "perfect" echoing surfaces will also die eventually.
Also, unless the echoing surfaces are perfectly aligned, the sound will echo in a slightly different direction, and it will start reflecting out of other surfaces (other walls in the room, for example). You will eventually have thousands of reflections in many directions, canceling and augmenting each other at places. Since they echo at different places that are at different distances, they won't go back to the origin at the same time. This will cause a shift in the sound, increasing the cancellations and augmentations. In other words, the sound will garble itself.
Also, even if the echoing surfaces are perfectly aligned, the sound doesn't echo back in a straight line, like a laser against a mirror, it echoes in an angle, dispersing the energy of the sound over an area even if the echoing surfaces are perfectly aligned, the echo will appear to come from a different place[4] and the sound will disperse over a wider area. This hastens the weakening of the sound since it vibrates over a bigger area, it has to move more air particles, and each echo will carry less energy in a certain direction. Instead of preserving all the energy in one clear echo, the energy will get spread and any listener will be getting a weaker echo that will last less time before disappearing. And if hastens the chance that the sound garbles itself.
Eventually, the sound will be so weak that it will be the same volume as ambient noise, and it will eventually go under the detection threshold of any instrument. Eventually, the sound won't be strong enough to move any air particle, and it will stop.
Air particles bounce continuously against each other due to Molecular diffusion, so any trace left by the sound will disappear immediately. Once the sound loses all its original energy, you will be unable to recover it from the air (and the sound will lose all of its energy, because you can't fight the laws of thermodynamics). --Enric Naval (talk) 23:56, 4 August 2010 (UTC)[reply]
See Archaeoacoustics, "the discipline that explores acoustic phenomena encoded in ancient artifacts". As the article notes, Mythbusters tried to recover sound recordings from pottery, with poor results. Clarityfiend (talk) 22:54, 4 August 2010 (UTC)[reply]
The TV series "Science Fiction Theatre" from the 1950's told of a ceramic object from Pompeii from which could be played back the sounds of panic in the streets when the volcano irrupted in 79 AD. Edison (talk) 02:57, 5 August 2010 (UTC)[reply]
A while ago I asked a question about a strange insect I saw and someone incorrectly said I had seen the caterpillar of a tussok moth. I finally managed to take a picture of the mystery insect and have uploaded it to flickr. Can anyone help me identify it?
Geographic latitude doesn't matter for seeing auroras. What matters is your geomagnetic latitude, which measures where you are relative to the magnetic poles. That said, the recent CME wasn't very strong (only a class C3), so it wouldn't have been visible from anywhere with a latitude of only 44 degrees. --Carnildo (talk) 00:56, 5 August 2010 (UTC)[reply]
It was visible from plenty of locations at 45 latitude north, but I wasn't able to see the aurorae from my light-polluted location last night. ~AH1(TCU)16:32, 5 August 2010 (UTC)[reply]
Number/measurement system
With the increasing prominence of computers, why hasn't human society adopted a number and measurement system based on powers of 16 (hexadecimal)? --138.110.206.101 (talk) 23:06, 4 August 2010 (UTC)[reply]
Computers use Binary numeral system, because it's easy to distinguish between "1" (I'm receiving energy in this cable) and "0" (I'm not receiving energy in this cable). Byte has 8 bits because the most successful computers happened to use 8 (see Byte#Size]), and hexadecimal became popular because it can represent two 8-sized bytes in only two human-readable characters. In other words, hexadecimal exists for arbitrary reasons and not because it's better, and computers don't even use it.
Also, when you interact with a computer, there is layers of abstraction that separates you from how computers really represent their numbers internally (they use weird systems like Two's complement and Floating point, which are very difficult to read for humans). The computer doesn't care what system you use, because the layers of abstraction will always translate it to the internal system before touching it for anything. We should use the system more convenient for humans, since all systems will need a layer of abstraction anyways. --Enric Naval (talk) 00:30, 5 August 2010 (UTC)[reply]
Small quibble: Hex cannot represent two 8-sized bytes in only two human-readable characters, it can represent one 8-sized byte in only two human-readable characters (or 2 in 4, 3 in 6, 4 in 8 - you get my drift ;-). --Stephan Schulz (talk) 09:20, 5 August 2010 (UTC)[reply]
I think your origins for the 8 bit byte are a bit off. 8 bit bytes come about because to represent English-language text conveniently you need 26 uppercase letters plus 26 lowercase plus 10 digits plus at least half a dozen punctuation characters - preferably more. That's annoyingly just a bit more than 64 symbols. So 6 bit 'symbols' aren't really convenient (although there are 6 and even 5 bit character codes that use special 'shift' characters to indicate lowercase, etc). The next handy power of two is 128 - so basic ASCII uses seven bits. The reason we don't have 7 bit bytes is that back when this stuff was being thought out, characters were stored on media like paper tape and magnetic tape - and transmitted over unreliable serial data lines. You needed a way to check that your symbols had been transmitted successfully - so they added an 8th bit (called "parity") which was set in such a way to make sure that the number of '1' bits in the byte would always be an even number. If any single-bit error occurred in the byte, there would be an odd number of '1' bits - and you'd know that something screwed up. Hence 8 bit bytes. A few computers used more or fewer than that - but 8 bit bytes were just so very convenient that they became a de-facto standard. These days, things are much more reliable - and we have more sophisticated ways to do error checking...and 128 (or even 256) characters aren't enough for international character sets. But the 8 bit byte is here to stay.
Please add content (or link to content somewhere else) about that ASCII-origin to Byte#Size. Man, that article's sections are repetitive/overlapping! :( DMacks (talk) 14:24, 5 August 2010 (UTC)[reply]
I'd rather computers adapt to us instead of us adapting to computers. Also the base you use doesn't matter much. (There are couple things that are easier in one base or another, but not many. Base 60 is good because it has lots of integer divisors, balanced ternary is pretty cool. But mostly it doesn't much matter. Ariel. (talk) 23:50, 4 August 2010 (UTC)[reply]
Er... yes it does... The rightmost hex digit is the 1's, the next one is the 16's, the next one is the 162's, etc.. Those are powers of 16. --Tango (talk) 00:46, 5 August 2010 (UTC)[reply]
Computers can easily adapt to any system that humans find convenient - base 16 is mildly useful for programmers - but the rest of the planet shouldn't have to be afflicted with them. Base 16 is also a pain to deal with, mathematically. If we were thinking of changing the base we work in, then base 12 would be much more convenient than either 10 or 16 because it has so many factors: 1,2,3,4 and 6. Much better than 1,2,5 or 1,2,4,8. Being able to divide by three in your head and getting an exact answer without all of those recurring digits would be a blessing!
Also, there is a system called BCD (binary-coded-decimal) that allows computers to do base-10 math with relative ease.
If we're revising the human number system (an inconcievable prospect!) then I'd like to switch to one in which we write only the digits 0,1,2,3,4 and 5 - and write 6,7,8,9 as 14,13,12 and 11. The underscore means 'minus' - but just for this digit. 5 can be written 15 - the two representations are interchangeable, just as 0 and -0 mean the same thing in normal arithmetic. Think of it a bit like roman numerals where IIX means 'ten minus two' - which is what 12 means. Doing this has dramatic effects on doing arithmetic. If you have a long column of numbers to add up - you can cancel matching pairs of 3 and 3 (for example) and you have much less problems with carrying digits. In roman numerals, you can add IIX and XII by cancelling the 'II's that occur either side of the X so IIX+XII=XX. So in this system, 12+12 = 20. Negative numbers are also more naturally represented - and the complications of adding and subtracting positive and negative numbers just goes away, quite naturally. Negative numbers are written like positive numbers - but with underscores flipped over so 0 - 1234 = 1234.
And at his point, I can't help but pointing out our nice Duodecimal article, which discusses a base twelve system. It also has a bunch of fun links to other articles related to alternative counting systems. Buddy431 (talk) 02:00, 5 August 2010 (UTC)[reply]
We already do, when it's convenient for us. For example, debuggers show us memory addresses in base 16 because memory is organized in chunks whose size is multiples of large powers of 2. But for day-to-day use, there's no advantage to it. Paul (Stansifer)02:05, 5 August 2010 (UTC)[reply]
For a substantial fraction of the history of computers, we've used octal (base 8) rather than hex. Radix 50 notation also had a brief following. SteveBaker (talk) 03:27, 5 August 2010 (UTC)[reply]
My personal rule is that computer programmers are officially entitled to state their ages in hex. I feel much more like a 37 year-old than my decimal age. OTOH, tax returns tend to feel like they are being written in base 1. SteveBaker (talk) 13:50, 6 August 2010 (UTC)[reply]
The cancer article has a pretty good overview of the history of awareness of the disease, but focuses mainly on breast cancer. The skin cancer article has no history section whatsoever. I'm very curious about the history of awareness of skin cancer. My guess is that before long distance transportation became feasible, skin cancer acted on geographically fixed (more or less) populations such that after X (or XX) generations the survivors didn't contract skin cancer in noticeable numbers. Following that, it was only once people began to really move around (primarily latitudinally, I suppose) that you end up with humans living in latitudes with amounts of sunlight exceeding that which their bodies' can naturally protect against? I can't recall ever reading about a historical figure dying of skin cancer... though I suppose contemporary historians simply may not have known what it was that killed the person... 218.25.32.210 (talk) 01:23, 5 August 2010 (UTC)[reply]
Famous historical figures didn't spend much time outside. Poor (not-famous) people did that. So it seems unlikely that anyone from more than 100 years ago who was notable for anything would have had enough sun exposure to have skin cancer. Its likely lots of people had it, and some may have died from it, but those people didn't make the history books as individuals. --Jayron3205:43, 5 August 2010 (UTC)[reply]
Oh, I'm sure if you dig far enough, you'll find someone. It's entirely possible to get skin cancer even if you don't spend any time in the sun. It's just that in general, sun exposure is a major risk factor for skin cancer, and most people who did something to get famous weren't out picking turnips in the field 12 hours a day... --Jayron3206:09, 5 August 2010 (UTC)[reply]
I think you're probably over-exaggerating the lack of being in the sun. Whether or not it was fashionable (across very different periods and cultures) to be in the sun, plenty of important people have had to spent their time in the sun. And whether people are famous or not has nothing to do with whether doctors would have discussed the ailment, or would have discussed notable cases. --Mr.98 (talk) 14:51, 5 August 2010 (UTC)[reply]
This page does not exactly beam "reliability", but contains a plausible history of Western medical discussions of skin cancer. Apparently René Laennec first discussed it explicitly in a lecture in 1804, and gave it the name Melanoma. John Hunter operated on a melanoma in 1787 but apparently wasn't aware of what it was. He called it a "cancerous fungus". A certain Samuel Cooper (who does not seem to be any of the Wikipedia "Samuel Cooper"s) reported in 1840 that melanoma was basically untreatable in its advanced stages. It's not much but it's a start. In any case, it seems that awareness of it as a distinct health entity, much less a form of cancer, is pretty recent (i.e. 19th century). The understanding of the link been skin cancer and UV exposure is probably even more recent. If you don't know what causes something, it's hard to have much of a public health campaign about it. --Mr.98 (talk) 14:57, 5 August 2010 (UTC)[reply]
Filopodia can fuse their membranes to make large pseudopodal or epithelial bridges between cells, right? But not traditional cytonemes? I just read this Nature paper that declared in their abstract: Hereafter, we refer to these filopodial bridges as viral cytonemes (neme meaning thread), because they share features with long-lived filopodia previously observed in the imaginal disc of Drosophil. Cytonemes constitute stable cell–cell bridges thought to mediate the long-range transport of signalling molecules between cells.
This confuses the hell out of me! Much thanks and gratitude to anyone who can explain this to me, because my current internship (which ends in 2 days) depends on this question. John Riemann Soong (talk) 02:09, 5 August 2010 (UTC)[reply]
My "simple" definition: Filopodia are thin, finger-like, dynamic actin-filled extensions of the plasma membrane that play roles in sensing the extracellular environment, cell-cell adhesion, and cell-substrate adhesion.
There are a whole lot of words that describe long thin protrusions of the plasma membrane, many of which probably have different functions than traditional filopodia (such as long-range cell-cell contact, intracellular communication, etc.) and I'm sure you will find experts who disagree on how to use the terms -- you're not the only one who is confused! One distinction might be whether the structure is short-lived and dynamic (filopodia) versus long-lived and stable (cytoneme). However, your best bet is to describe the structures you are observing as clearly as possible, without worrying excessively about what to call them. If you have time-lapse imaging that shows the protrusions extending, retracting, making cell-cell contacts, etc. it's probably safe to call them filopodia. If you can demonstrate that your filopodia fuse together or somehow allow intracellular movement of cytoplasm, it's probably safe to call them filopodial bridges. I can't say why the authors of the Nature paper decided to use the term "viral cytoneme," but from quickly skimming it, they seem to be suggesting that the viral envelope proteins are somehow facilitating the generation of filopodial bridges that allow the viruses to pass from one cell to the next. If you have a similar context where a treatment seems to facilitate the generation of long-term filopodial bridges allowing cell-cell transport, perhaps you could use a similar term. Keep in mind, however, that cell culture is a pretty abnormal situation for cells and some of the things we observe in a dish work a little differently in a three-dimensional organism. I'm not sure that was helpful, but the take home message should be to clearly define the structures you are talking about, and then use that term consistently. Good luck! --- Medical geneticist (talk) 13:42, 5 August 2010 (UTC)[reply]
Does anybody have any clue about the different behaviours of filopodia and lamellipodia? I wonder if lamellipodia are in fact responsible for "trapping" my gold particle (in that animated gif) and bringing it in, since lamellipodia are found between filopodia? (According to the literature on growth cones in neurons...) I am also wondering if lamellipodia are responsible for the "bridge widening" I have seen. John Riemann Soong (talk) 00:47, 6 August 2010 (UTC)[reply]
Chimney
Here's the question I was given: Suppose a chimney of length L started to tip and fall. Where would it break?
Here's my attempt at a solution: The angular acceleration of the chimney should be (3/2)(g/L)cosθ (θ being the angle between the chimney and the ground). Consider a small portion of the chimney a distance x from the base. If just gravity were acting on this small portion, it would have an angular acceleration of (g/x)cosθ, so parts of the chimney near the top are rotating "faster than they should" were only gravity acting on it. Thus there must be internal torques, and thus internal forces, acting on within the chimney. Wherever the internal forces are greatest, that's where the chimney will break. For a small portion of the chimney, τint + τext = τint + mgxcosθ =(mx2)(3/2)(g/L)cosθ. Using this, the force becomes greatest at the very top of the chimney, which doesn't seem to make much sense. Can someone point out where I've gone wrong? Thanks. 76.69.241.253 (talk) 02:11, 5 August 2010 (UTC)[reply]
Well - do you trust your math or your instincts? Watch this (the interesting bit starts about a minute into the movie) - I'm pretty sure those two chimneys are both of length 'L' :-) SteveBaker (talk) 02:37, 5 August 2010 (UTC)[reply]
Also don't forget that the inertia of the chimney is not the same along it's length. Your math does not seem to take this into account, lower down when it accelerates the top there is a ton of inertia against do so, in the middle it not only has to accelerate the top, in needs to decelerate the bottom, so you have double force. At the top there is little inertia to fight. Ariel. (talk) 18:44, 5 August 2010 (UTC)[reply]
Does your chimney have an strength at all, or is it just stacked bricks? If it has any strength at all your math will not be right, since it will break wherever the force is greater than the strength (so at multiple locations). If it has no strength then it will break everywhere at once, and it will impart no force to the top, since it broke and it can't. Ariel. (talk) 18:38, 5 August 2010 (UTC)[reply]
Also, the size and number of bricks, as well as the width, hardness and cohesive strength (?) of the coglomerate holding them together may affect your solution by small degrees. ~AH1(TCU)00:49, 7 August 2010 (UTC)[reply]
In words, a description of the gas central heating system in my house: There is a large square vent in the ceiling, air goes in there, through a wide hose to a box in the ceiling space. A gas pipe also feeds that box. The box burns gas to heat air. It vents its exhaust through a chimney to outiside. A fan in the box pushes the heated air out of another wide hose which splits into about eight narrower hoses which connect to vents in the ceiling around the house. So air is sucked into the heater from inside the house; it's heated by burning gas; the hot air is pumped into the house through one hose which splits into several. --203.202.43.53 (talk) 08:15, 5 August 2010 (UTC)[reply]
This schematic show the kind of set up in many UK homes. The boiler is a closed system heating water and pumping it round the radiators and through the heat exchanger coils in the hot water tank. Cold water is supplied to the cold taps around the house and the storage tank(s) in the loft space. Cold water is then gravity fed from the loft tank to the hot water tank (where it is heated by the heat exchanger coils) and then supplied to hot water taps around the house. There are a few variations using on-demand heating or pressurised systems. Astronaut (talk) 14:52, 5 August 2010 (UTC)[reply]
Fuss about Blackberrys and National Security
Im not a blackberry fan, find it to be quite an eyesore in the aesthetics department and I havent used it ever,so technically I wouldnt know whats this security risk stuff everyone is talking about. Saudi and UAE Govt. have banned blackberry services from yesterday. Whats with the Blackberrys that make them a security threat? Im not asking a political question here but whats the scientific reason that makes these handheld devices a risk? Is it restricted only to a blackberry or is an IPhone too capable of such a risque behaviour? And have these risks been a fall out of a new (recently introduced) feature or has the risk been there since blackberry launched? Why this sudden brouhaha?Im sorry for asking too many questions but I feel they are all inter related. Thanks for the answers in advance--Fragrantforever 06:57, 5 August 2010 (UTC) —Preceding unsigned comment added by Fragrantforever (talk • contribs)
I can't see any risk that blackberry devices present that other smartphones don't (although I do know someone who suffered a repetitive strain injury due to heavy use of his blackberry's scrollwheel). One risk of such devices in a secure environment is that they can connect to computers, take photographs, record voice, store huge amounts of data and smuggle that data out of the secure environment. Another is a risk shared by laptop computers -- they're easy to steal. A stolen blackberry could be full of confidential e-mails. --203.202.43.53 (talk) 08:22, 5 August 2010 (UTC)[reply]
But it's not that at all. I just looked up news reports and found this. At a quick reading suggests to me that they are banning the messenger function on blackberrys because it provides secure communications and so it's hard for the government to monitor what people are saying when using it. And worse, Research in Motion (the company that makes Blackberrys) refuse to decrypt messages, even when governments ask nicely... unless the government in question has a US court order unless the government in question has gone through proper processes. Both UAE and Saudi Arabia say they don't want evil terrorists having easy access to secure communications. My take on it is that those countries are unhappy about having to go after specific messages one at a time and through their courts, they'd much rather be able to simply monitor all communications to track down "naughty" people before they know they're naughty. --203.202.43.53 (talk) 08:30, 5 August 2010 (UTC) (edited a couple of times before 08:41, 5 August 2010 (UTC))[reply]
Of course, what the ruling regimes of the UAE and Saudi Arabia consider 'naughty' might not be restricted to terrorism and might not be entirely congruent with definitions prevalent in more, shall we say, liberal societies. 87.81.230.195 (talk) 16:51, 5 August 2010 (UTC)[reply]
From the reference you provide along with [5], it's entirely unclear under what circumstances ('proper processes' as you called them) RIM would decrypt messages and whether RIM would do it in the same circumstances in the UAE and Saudi Arabia that they would in China, Russia or even the US or Canada. I don't even see any evidence they would let them 'go after specific messages one at a time and through their courts'. In any case, I have strong doubts they've been willing to compromise with the UAE or Saudi Arabian governments as much as they have been with the Russian or Chinese ones and from the sources I'm not alone in this view.
If I was a cynic, I would say RIM is playing this for all it's worth since they don't consider UAE or Saudi Arabia that important so are willing to give up those markets if necessery in exchange for the good publicity about protecting their customers. They're perhaps hoping that they can come to some kind of deal with the UAE or Saudi Arabian governments which said governments would let them spin as a backdown on their part (even if it was something said governments would have agreed to all along). On the flipside, the UAE and SA are I think resonably friendly so may have been in contact and decided to apply mutual pressure.
I've heard of India having similar concerns recently also mentioned in your ref, I'm hardly surprised the suggestions are [6] that a deal is close. Who knows, perhaps news of a Indian deal reached the UAE and SA governments and having perhaps negotiated as long as the Indian government they got rather pissed that RIM was happily playing ball with the Indian government, as they may have already done with the Russian and Chinese governments so decided there was no point negotiating any further. Or perhaps RIM decided to play hardball with UAE and SA knowing they'll be cut off so they could use it as part of their negotiations with India (if you want to cut us off, then so be it).
The simple truth as in all of these sort of secretive corporate-goverment negotiations, it's hard on the outside to really know what's going on, or why, behind the scenes. It's almost definitely incredibly complex, and the power of each side generally plays a big part. Trying to paint either side as 'bad guys' or the one causing problems is usually way too simplistic. And as much as anything the lack of knowledge or imperfect knowledge about what's going on most likely doesn't help matters. It may be the Russian, Chinese and US deals are not that great, but as long as the UAE and SA governments think it's better then what they're getting they're likely to be reluctant to agree to something less.
BTW it seems Indonesia has similar issues [7] it would be interesting to see what happens there. Of note, a common thread is many countries don't like the servers being in Canada I wouldn't say this is that surprising or unusual, I think it's a common concern for some countries. While it's true that e-mail servers are commonly in another country one of the things is that for the Blackberry the e-mail is AFAIK strongly integrated with the phone and also it seems usually encrypted. Compare that to MMS or SMS or phone calls where they are not encrypted and go thorough the local service provider.
While I mentioned RIM's possible publicity advantage for their consumers, as somewhat shown by the Indonesian case, these sort of things do have a risk of cascading since when other governments see what's going they start to take notice too. This is of course likely to be a concern to RIM, and I saw a news report saying a similar thing.
It's also worth remembering that some of the people involved, particularly the people in high levels of government may have limited understanding of the technical details yet they will often be the people with the real say and may not always listen to what their more technically inclined advisors or civil service are telling them (if they even dare).
Right. The security threat is that the Blackberry is too secure, as far as these governments are concerned. RIM is reluctant to "fix" the problem for obvious reasons. Looie496 (talk) 01:51, 6 August 2010 (UTC)[reply]
Of course any programmable phone could be provided with an 'app' that would encrypt your data with some ungodly good encryption and send it to someone with a similarly equipped device - any halfway decent programmer could toss that together in a day or two. Even if such applications were banned from phones (and I have no idea how you'd make that kind of a ban enforceable), it would still be possible to encrypt a message on a regular computer (or even on paper with a pencil) and key the resulting gobbledygook message into a completely dumb phone. Heck, you can use a one-time pad or a 'code book' and send a heavily encrypted message in what seems like plain text or speech: "Shall we meet tomorrow at around 2:15?"...look up number 215 in your code book...it says "Blow up the parliament building tomorrow at noon". Encryption is childishly easy. When I was a kid, my parents had me learn a bunch of fake names so that (in an era before cellphones) I could make a 'reverse charge call' (aka 'collect call') from a callbox and when the operator asked who I was, I'd give the fake name appropriate to the message I wanted to send. My parents would then refuse to accept the call and look up the name to discover that "Henry Plantagenet" really meant "Please pick me up from soccer practice"...or whatever.
The iniquitous thing about all of this is that the 'bad guys' can always do good encryption if they need to. But people who merely wish to prevent rivals from stealing industrial secrets, or to avoid telling the papparazzi where they're going to dinner, find it much harder to do so without the convenience of a securely encrypted data service like the Blackberry. SteveBaker (talk) 13:44, 6 August 2010 (UTC)[reply]
Hi,
The use of synthetic colors in food and other edible substances is an area for concern. I understand that the addition of colors to foods such as candies, chocolates, shakes etc, is to increase the product appeal.
But then what is the main reason for adding colors to medicines such as cough syrups, capsule shells etc. After all, medicines are not generally marketed based on their visual appeal. —Preceding unsigned comment added by Kanwar rajan (talk • contribs) 09:58, 5 August 2010 (UTC)[reply]
Having a distinct shape, size and colour would most likely help people recognise a pill so they are less likely to take the wrong thing. It may also be a help to pharmacists. Also most people already don't like taking medicines, so the manufacturers doesn't want them to look too revolting. Particularly true I suspect for anything children are likely to take. (Although I've heard that nowadays many children medicines have been sweetened and flavoured enough that children actually want to take them.) Marketing may sometimes come in to it, for example most everyone knows what the little blue pill is (well apparently not wikipedia until I made the redirect). It may also be a useful way to distinguish your product from other generics and similar products.
Note that if you are taking medicines, even something like an OTC cough syrup I would say any alleged or real potential effects of the tiny amount of colours you consume in what one would hope is the tiny amount of medicine you consume pales in comparison to the side effects and other concerns of taking the medicine and the circumstances that require taking the medicine. Even if you actively avoid colours as much as possible, it's unlikely the amount you consume from medicines while sick is going to be a big proportion of the colours you do consume.
I still have a real urge to go buy some Calpol (a child's, liquid paracetamol... tastes very good). I'm now 19, haven't had it in about 16 years, but still remember it being very, very nice. Just a random comment. Regards, --—Cyclonenim | Chat 11:25, 5 August 2010 (UTC)[reply]
I actually had the same urge a few months ago and bought some - it's just as nice as I remember it. Someone at that medicine company really knows what they're doing. ~ mazcatalk13:18, 5 August 2010 (UTC)[reply]
Interesting. I don't really have any fond memories of taking medicines when I was young. Cough syrup were one of the most horrible. I'm 28 so not much older then Mazca, I don't think my younger brother has any different experience. However I grew up in Malaysia and most of my medicines came from my family doctor (there is no dispensing separation in Malaysia [8]). I would guess calpol is available now, I don't know if doctors commonly offer it or it's only from pharmacies or supermarkets or when it became available but it's not something I ever had AFAIK. Nil Einne (talk) 14:12, 7 August 2010 (UTC)[reply]
I strongly suspect that is part of the reason my mother never gave us Calpol, to the extent that I only learnt it existed when I was about 17. Having babysat several children whose parents assure me they shouldn't be any trouble since "they've had their Calpol", I find myself siding with my mother. 82.24.248.137 (talk) 21:41, 8 August 2010 (UTC)[reply]
Studies show that the placebo effect is affected by the shape and colour of the pills. [9]. It is also useful in telling pills apart, there are drug identification programs that work with the color, shape and text on the pills for instance.[10]EverGreg (talk) 11:28, 5 August 2010 (UTC)[reply]
For a while, I was taking two different medicines regularly; the bottles always described the capsules' appearances, so even if I'd somehow forgotten which pill was which, I could have re-learned quite easily. Nyttend (talk) 13:45, 5 August 2010 (UTC)[reply]
In the case of cough syrups, adding food coloring to them makes the artificial flavoring (a little) more convincing. Imagine taking a colorless, orange-flavored cough syrup. It still tastes like (artificial) orange flavor, but it feels weird because you've been conditioned to expect orange-flavored food to have an orange color. --173.49.16.4 (talk) 12:46, 5 August 2010 (UTC)[reply]
Yup, I'd have to tag the original basis of the question as false assumption: "After all, medicines are not generally marketed based on their visual appeal."[citation needed] Companies spend huge amounts of money on marketing and consumer analysis. If a company thought it could do better with a different approach, for example, lower production cost (leading to lower consumer cost (== higher sales)) or higher profit margin) or improved consumer appeal (leading to increased sales or ability to raise price (==increased profit margin), they would do so. Heck, even increased acceptability by consumers of "now with no artificial colors" is a potential corporate boost that is not done too often in this industry...it's just not what consumers seem to want (enough to justify cost of changing their product-image and its manufacturing, and other potential offsetting loss of sales for reasons others have mentioned). DMacks (talk) 14:14, 5 August 2010 (UTC)[reply]
For what it's worth, I have seen some infant's medication marketed as "Dye-free!" Here's an example from a googled website. Interestingly, before Kanwar rajan's question, I never thought this was a scheme to market to parents who are concerned about the health effects of synthetic dye; I had always thought it was meant to tell the parents: "When you spill this damn stuff onto your clothes because your kid shakes his or her head around while taking this damn stuff, the clothes won't get permanently stained with hot pink and orange dye." Comet Tuttle (talk) 16:28, 5 August 2010 (UTC)[reply]
What is a side of leather? A source that I've used at Charles Wintzer Building says that this building, a former tannery, processed 2,500 sides of leather in a year, but it doesn't explain what it is. Perhaps a complete animal hide? Nyttend (talk) 13:55, 5 August 2010 (UTC)[reply]
Half an animal hide. Oxford English Dictionary sense 9.b. gives this quote: 1885Harper's Mag. Jan. 274/2 After soaking, the hides are..cut through the middle of the back to separate them into ‘sides’." Gdr14:50, 5 August 2010 (UTC)[reply]
Mathematical Tools for General Relativity
I am currently in eleventh grade, and I wish to learn general relativity right from the basics to the derivation of equations, tensors, so on.. What mathematical knowledge is needed for this? Can you please recommend books for learning the mathematics needed for General Relativity? Currently, I am well versed with Differential Calculus and Basic integration, complex numbers, trigonometry, and some other basic mathematics. What further topics do i need to know in mathematics for General Relativity?
harish (talk) 15:06, 5 August 2010 (UTC)[reply]
You can try to study General Relativity any time you like. You'll probably find that it uses techniques you aren't familiar with until you've mostly completed a core curriculum of advanced math and physics. It would be possible to try to learn each concept, piecemeal, but normally in an undergraduate physics or math program, you wait until your junior or senior year of university before even bothering with a GR course, so that you've had the time to build up the necessary classes. Many programs have a sort of "teaser" course in "modern physics" taught at the freshman or sophomore level, covering the basic conceptual ideas of relativity, but it's impossible to expect enough freshmans and sophomores to have finished the requisite math for full-blown GR at such an early stage.
In the United States, a typical undergraduate course for you will follow something along the lines of:
after completing your basic physics run, you will need an advanced mechanics course to learn about coordinate-independent representations of physical laws; and an advanced electromagnetics course
finally, you will have the tools necessary for a course in general relativity, suitable to describe spatial coordinates as they relate to mass, energy, and momentum; and the ability to describe how those things affect particles' and electromagnetic waves' energies and trajectories.
You might consider looking at your preferred university's physics curriculum to see what courses they offer. Many universities offer a specific course in General Relativity, but others lump this in to an advanced math course or cover it during a classical mechanics or electrodynamics course. Ultimately, consider what your objective in learning GR is, and use that objective to guide your coursework. Nimur (talk) 16:04, 5 August 2010 (UTC)[reply]
While I'd agree that all of the above could be useful, I don't think all of it is strictly necessary before tackling a mathematically rigorous treatment of GR as some of it will be included in introductory GR texts. I'd say the fundamental prerequisites are multivariable calculus, partial differential equations, basic linear algebra, and an understanding of how classical mechanics and electromagnetism are handled through partial differential equations. That said, in many places a true course in GR isn't even offered before graduate school. And it certainly true that building up a deeper understanding of math and physics will be genuinely helpful to understanding GR. Since the poster asked about texts, I'd suggest starting with the chapters on multivariable calculus in an introductory text, such as Ellis and Gulick's Calculus with Analytic Geometry. That could be followed by looking at the vector analysis, linear algebra, and differential equations chapters of an intermediate text like Arfken and Weber's Mathematical Methods for Physicists (if your goal is only GR, you can probably skip the half of the book on special functions, as that is more a quantum mechanics thing). That might be followed with an advanced undergrad book on electromagnetism, such as Griffith's Introduction to Electrodynamics. This would probably get you to a point where you could look at a rigorous GR text without your head exploding, though you'd undoubtedly need to consult works on mechanics, linear algebra, and differential equations to fill in gaps as you go. Dragons flight (talk) 18:02, 5 August 2010 (UTC)[reply]
You can get books on GR that teach you a lot of the maths as you go along (you don't need to know anything about tensors, for instance). You might need a bit more calculus (particularly vector calculus/multivariate calculus (they're the same thing)) and you'll need at least some basic linear algebra. You'll need to have taken a basic course in mechanics as well. There is harm in starting on GR now and if you find something you don't understand going back and learning it before carrying on. --Tango (talk) 17:25, 5 August 2010 (UTC)[reply]
The first proper book on it I read was Einstein's own book 'Relativity: The Special and General Theory' which I read when I was sixteen I think. It may be a bit out of date in places but I thought it was very good. It can be better to see things from near the beginning by the original person. Dmcq (talk) 17:53, 5 August 2010 (UTC)[reply]
If you restrict yourself to special relativity (no gravity) it's easy to find books that will teach it. The math isn't that hard at that level.
If you want to press on to general relativity, I would strongly recommend the book "Introducing Einstein's Relativity" by Ray d'Inverno which cover both special and general relativity. It introduces the tensor math as you go along and is an easy read. As in any curriculum involving some math, it's essential that you do the exercises in the book. EverGreg (talk) 07:54, 6 August 2010 (UTC)[reply]
I understood Special Relativity when I was 14, from Einstein's own Book. But the book has very little on the mathematics of general relativity. Thats why I need good books for learning GR from the roots. harish (talk) 11:08, 6 August 2010 (UTC)[reply]
the question is that our chemistry teacher normally say when a tree has been more than 35 years it will form the sumation of coal that is it will change to charcoal
is it true? —Preceding unsigned comment added by Abhay4life (talk • contribs) 17:03, 5 August 2010 (UTC)[reply]
I'm sorry, I don't understand the question. What has the tree been for 35 years? What does "sumation of coal" mean? --Tango (talk) 17:28, 5 August 2010 (UTC)[reply]
Any translation of this question that I can make still produces nonsense. A tree that is living is not coal and never will be. Once a tree dies, it will take far longer than 35 years to become coal - and then only if it is in just the right conditions. -- kainaw™17:33, 5 August 2010 (UTC)[reply]
(ec)You can change wood from a tree to Charcoal whenever you want; just heat it out of contact with the air for a few hours. Coal is a sedimentary rock that began as layers of plant matter that have been covered by other strata for millenia, typically since the Carboniferous period about 330 million years ago. A visitor to a geologic museum asked an attendant how old was the specimen of coal on display, The attendant answered "It's 330 000 004 years old." The visitor said "Are you sure one can know the age so accurately?" The attendant said "Yes, I know because I was here when they brought in that specimen 4 years ago." Cuddlyable3 (talk) 22:45, 5 August 2010 (UTC)[reply]
I'm guessing there was supposed to be a 'dead' in the OP's question (when a tree has been dead more than 35 years) even if it's still rather confused. Nil Einne (talk) 01:52, 6 August 2010 (UTC)[reply]
On the other hand, peat, (which is basically "fresh coal") doesn't necessarily have to be millions of years old. It makes a pretty decent fuel. --Jayron3203:54, 6 August 2010 (UTC)[reply]
Not when I tried it! Even when properly dried, as my grandfather used to do, it is still very much inferior as a fuel. I suppose if you have nothing else .... Dbfirs09:21, 7 August 2010 (UTC)[reply]
Why can't Quantum Teleportation transmit information faster than light?
Nutshell version: Alice and Bob separate entangled particles. Bob watches his particle change state and knows that Alice's changed state right then, too! Instant FTL knowledge! However, Bob doesn't know what that means -- did the state change because Alice triggered it (a message) or because of natural processes (quantum mechanical noise)? There's no way to know until Alice sends a separate message, one way or another, by standard speed-of-light-limited means. Thus, no true information can be passed FTL via this method. — Lomn21:22, 5 August 2010 (UTC)[reply]
Actually bob can not watch his particle change state. He can only measure it once, and you can't tell if alice measures it! Probably the easiest way to think of it is to imagine there are hidden variables. Your particle already knows if it's in one state or the other, and the other particle is guaranteed to be in the opposite state. But those states are already there - measuring them tells you nothing that was not already known. You are simply revealing the information to yourself, but transmitting nothing. Big caveat: hidden variables might not be a description of reality, it's much more complicated than that. But for an initial understanding it's a good start. Ariel. (talk) 21:32, 5 August 2010 (UTC)[reply]
Quantum teleportation works like this: Alice and Bob generate two qubits in a Bell state and each take one. Alice does a certain calculation with her half of the Bell pair and the qubit to be transmitted (the "message qubit"), obtaining two classical bits, which she sends to Bob. Bob does a certain calcuation with his half of the Bell pair and the two bits from Alice, and obtains the message qubit. Here's the classical equivalent of that: Alice and Bob generate a pair of equal bits (both zero or both one) and each keep one. Alice does a certain calculation with her half of that pair and the message bit (namely, an exclusive-or of the two), obtaining one bit, which she sends to Bob. Bob does a certain calcuation with his half of the pair and the bit from Alice (namely, another exclusive-or) and recovers the message bit. This protocol is simply encryption with a one-time pad. The bit that Alice sends to Bob contains no information about the message bit (that is, an eavesdropper learns nothing by observing it). Bob's original bit also contains no information about the message bit. Nevertheless, the message bit can be recovered by combining the two. This is also true of quantum teleportation. Bob needs both his half of the Bell pair and the two bits from Alice in order to learn anything about the message qubit. -- BenRG (talk) 03:22, 6 August 2010 (UTC)[reply]
Bob , alice , what ever , thay teleport statistic informaition , if you want it faster then light ,you have to do statistic fast . then you get the information . thanks —Preceding unsigned comment added by 212.199.175.104 (talk) 07:18, 6 August 2010 (UTC)[reply]
If there was some way to predict the true random bit, and Bob and Alice had all the keys in advance, it might be possible to do this. The trouble is predicting the random encrypted bit is a bit-erm...challenging. But I'm still working on it. —Preceding unsigned comment added by 80.1.88.20 (talk) 14:03, 6 August 2010 (UTC)[reply]
No. The colour and brightness can vary quite widely depending on what is going on in the upper atmosphere (where the sunlight has to go through to hit the moon during an eclipse). If there is lots of dust in the atmosphere (eg. following a volcanic eruption), you can get very dramatic lunar eclipses. --Tango (talk) 01:59, 6 August 2010 (UTC)[reply]
What's happening during the eclipse is that the only light that's reaching the moon has to pass through the earth's atmosphere. If you imagine the light from the sun just skimming the edge of the planet - you realize that the sunlight that makes it to the moon is light from a sunset - so it's always orangy-red but whether it's really that bloody red depends on which parts of the earth are in the way - what the atmosphere is doing. If it's passing mostly over the oceans then there probably isn't much dust or pollution filtering out the yellows and oranges...if it's passing over polluted areas or dusty deserts - then only the red light makes it through the air to the moon. SteveBaker (talk) 02:54, 6 August 2010 (UTC)[reply]
August 6
Scent + washing
I kneaded some ground beef into patties this evening barehanded and then rinsed my hands with water. My hands still smelled of the ground beef (be it the actual beef or the spices I used). What generates the smell? Is it antigen? Is it actual beef/spice on my hands? And is washing enough to get rid of the smell a good indicator that any harmful bacteria from the raw beef is also gone? DRosenbach(Talk | Contribs)03:07, 6 August 2010 (UTC)[reply]
Lots of spices and other food smells can dissolve in skin, and then remain behind for a considerable time afterwards. Onion is particularly potent for me, after cutting onions I can smell them for days. What I discovered works for me is to use undiluted automatic dishwasher liquid (like Cascade or the like) directly on my hands. Most handsoaps, in order to avoid drying out your hands, end up being as much moisturizer as soap (moisturizers and soaps work at cross purposes with regards to cleaning. One is trying to get grease off of your hand, the other is trying to put grease into your hands). Since the automatic dishwasher liquid is not normally designed to wash hands, it tends to be harsher as a soap, which is generally what you need to clean these smells off. This is of course all [original research?] and YMMV. --Jayron3203:52, 6 August 2010 (UTC)[reply]
I don't think you could use smell to indicate whether there's harmful bacteria on your hands. If the chemical making the smell has gotten right into your skin cells - in essence "staining" them - your hands might be perfectly clean (i.e. there's nothing "on" them), but still smell off. I mostly use ground chicken rather than ground beef, but I usually make use of disposable plastic gloves. Between the smell and the risk of contamination, to me it's worth the nickel to slip on pair of cheap plastics and toss them afterwards. Matt Deres (talk) 13:23, 6 August 2010 (UTC)[reply]
You might also try some of the hand-cleanser goop that they sell in DIY and Auto-parts stores - those are grey and don't smell of fruit and come in one gallon bright orange containers that don't look nice on your bathroom counter-tops - but they are really powerful degreasers with ground pumice as an abrasive. They do a spectacularly better job at cleaning your hands than the namby-pampy-girly stuff they sell in the soap aisle of a regular store...although you might want to apply some pretty scented moisturizer afterwards! SteveBaker (talk) 13:23, 6 August 2010 (UTC)[reply]
The stuff contained in the bright orange container has lots of pumice in it. Sure, it may scrape your skin cells off, but after a cleaning like that your hands won't smell like ground beef anymore! -- Sjschen (talk) 03:48, 7 August 2010 (UTC)[reply]
I don't know about ground beef, but I find the same can happen after chopping chillies (lick your fingers hours after washing your hands and it still burns your tongue) and that's because the capsaicin in the chilli isn't very soluble in water. If you wash you hands in oil (just normal cooking oil is fine), it gets them clean. It is possible some of the spices you were using are also oil-soluble. --Tango (talk) 16:28, 6 August 2010 (UTC)[reply]
I want to use terms like "north" and "south" instead of "above" or "below" to avoid ambiguity with structures below or above the focal plane. Is this permissible in a formal paper or a poster? John Riemann Soong (talk) 04:06, 6 August 2010 (UTC)[reply]
I would say that if there are no pre-existing conventions for describing such things and providing you define your terms clearly - then it should be acceptable. If you're going to do that, I would suggest that you use North/South/East/West to describe positions within the focal plane and Above/Below to describe positions along an axis perpendicular to the plane. But there are other approaches you might consider: X, Y, Z with (X,Y) being in the focal plane and Z being above/below it. You could also define a couple of acronyms: AFP and BFP for 'Above focal plane' and 'Below focal plane' (eg "In this image, the longitudinal structures are ~10um AFP"). So long as you are very clear about your conventions up-front, you should be OK. If there is an established convention that you're merely unaware of, then I'd expect the peer-reviewer or editor to suggest an alternative - I doubt that an otherwise meritorious paper would be rejected on those grounds so long as you take care to clearly state the conventions you are using. SteveBaker (talk) 13:17, 6 August 2010 (UTC)[reply]
I don't believe I've ever seen that nomenclature used in a formal poster, and certainly not in a paper. You might hear a more casual speaker use that sort of terminology with a friendly audience. While I completely understand why you'd want to use unambiguous terms here, I'd be afraid that such non-standard terminology would be very jarring to a reader or a reviewer. In most cases, you can write your text and figure captions in such a way that the intent of "above" is clear from context. In the remaining situations – as SteveBaker says – your best bet is to go with x, y, and z. The xy plane is almost always taken to be coplanar with a focal plane, while the z direction takes you through different focal planes. If there is any potential for confusion about the orientation of any images or renderings, you can even include a little two-arrow legend adjacent to or overlaid on the image that explicitly identifies the axes shown. TenOfAllTrades(talk) 13:52, 6 August 2010 (UTC)[reply]
This picture (at right) is a typical kind of resin chair - they are cheap because they can be injection molded with a simple two-part mold, they are lightweight and stackable (which makes shipping them cheap) and they are made from an inexpensive resin-based plastic. From an industrial design perspective, they are the perfect solution. From the customer's perspective, they are cheap, moderately comfortable and waterproof - but the plastic gets brittle from prolonged exposure to UV light and tend to break catastrophically - so they actually do a fairly poor job as lawn furniture. SteveBaker (talk) 13:02, 6 August 2010 (UTC)[reply]
This is rather odd, but I've noticed my underarms smell like bacon cheeseburgers sometimes. Even thought I haven't eaten one in months. (And I don't sleep with cheeseburgers nestled in my pits either). And I bathe 1-2x daily with non-cheeseburger scented body wash. Any ideas on how a person's body could make such a scent? (Please don't let this fall under the dreaded 'medical advice') I'm just curious how a cooked meat scent could be manufactured from a body. Or is my nose just picking up similar compounds and it's firing the same triggers in my brain that equal cheeseburgers? --69.148.250.94 (talk) 06:12, 6 August 2010 (UTC)[reply]
Odor in the underarms in not created by the body. It's created by bacteria. However the bacteria eat food that is secreted by the body, so the body can influence them to some degree. It seems to me you were colonized by bacteria that happen to excrete that particular smell (which is not strange, the smell of lots of foods is created by bacteria, for example cheese, wine, etc.) If you can culture them, maybe you can sell it :) If you want to change the smell first you need to serializesterilize your underarms (harder than it sounds), then colonize them with your choice of bacteria - another person is probably your best source. Ariel. (talk) 09:26, 6 August 2010 (UTC)[reply]
I cannot fucking believe you just told this guy to culture his underarm flora and (presumably) proceed to sell it as all-natural natural cheesburger-flavoring. Would your mother be proud of you if she knew you were enabling a guy to feed his underarm flora to millions? 84.153.230.246 (talk) 12:38, 6 August 2010 (UTC)[reply]
Woaah...calm down! I think everyone but you understands that this is a little gentle humor - which is permitted on the reference desk. We might, perhaps, encourage Ariel to toss a couple of <small> tags into an otherwise interesting and relevant answer. SteveBaker (talk) 13:07, 6 August 2010 (UTC)[reply]
I put a smiley on there! It was a joke, and like the best jokes it has an element of truth - he really could do that, and I bet people would buy it (but not to eat, to use in their own underarms). But it would be very difficult, many bacteria are hard to culture out of their home environments. Ariel. (talk) 19:35, 6 August 2010 (UTC)[reply]
Similarly, I have noticed a close similarity between the white matter I scrape from under the nails of my big toes, and certain expensive varieties of cheese. I truly believe that the sweaty fatty exudate from the human body can ferment to duplicate various pungent gourmet dairy flavors/odors. Evolutionarily, in primitive mammals, before there were milk glands, there was fatty sweat, as from monotremes. Edison (talk) 02:50, 7 August 2010 (UTC)[reply]
Reasons include toxicity and odor of the fumes, as well as potential ozone-layer-damaging chemicals. But frankly, this is proving a pain in the ass to find good information on; my google searches are only turning up blogs and forums. Someguy1221 (talk) 08:42, 6 August 2010 (UTC)[reply]
Several states in that area have banned oil paint (the kind used for walls, etc.; not sure if it also applies to artists' materials) in 2005. See for example [11]DMacks (talk) 08:48, 6 August 2010 (UTC)[reply]
Disposal of the stuff is very difficult - it clogs drains alarmingly easily and it's pretty toxic too. There are plenty of modern, water-based, paints that do a comparably good job and are much less harmful both to the environment and the city infrastructure. SteveBaker (talk) 12:54, 6 August 2010 (UTC)[reply]
Type of engineering degree
Help me please :) Chemical engineering or mechanical engineering at university - which one gives better career prospects? I would like a job involving foreign travel. Thanks! 86.144.112.57 (talk) 11:57, 6 August 2010 (UTC)[reply]
Both career tracks have reasonably good prospects over so many broad fields that it's hard to answer your question meaningfully. Though, with the decline of the auto-industry, there's been a bit of a deflationary trend in mechanical engineering, compared to other disciplines. The U.S. Bureau of Labor Statistics introduction to Engineers has some useful links and you can find hard numbers for number-of-hires across disciplines. (But, analyzing those kinds of statistics is not as straightforward as counting the number of new-hires). Also, whether these current trends will be relevant over the timescales of your entire career is all speculation. Chemical engineers can work in all kinds of fields; if you work in upstream petroleum, your prospects of foreign travel are very high; but chemical engineers more often find careers in refining and petrochemical companies. Chemical engineers can also work in materials, biological/medical/pharmaceutical industries, and like all engineers, can cross discipline-boundaries depending on individual specializations. Nimur (talk) 13:51, 6 August 2010 (UTC)[reply]
I was already thinking of oil, actually. Just wasn't sure which subject (or perhaps a totally different one?) would be most useful in that industry. So you think chemical engineering is a better bet? My problem is I really don't know how oil exploration or drilling works in detail, so not sure what the most important skills to pick up would be. There's not much chance of a school trip to an offshore rig in the North Sea (I'm in England btw). 86.144.112.57 (talk) 14:57, 6 August 2010 (UTC)[reply]
You might be surprised the kinds of programs and educational opportunities available in the oil industry. Society of Exploration Geophysicists' Student Education Program is geared toward advanced undergraduate and graduate students (so, wait a year or two), but they can provide funding for travel and training. So can EAGE's Student program - both are international, but EAGE has a definite European concentration. As a chemical engineer working upstream, you can be a valuable asset - geochemistry, mud logging, and assaying all happen in the field. As a chemical engineer working in the refinery, you'd be focused on process control, efficiency, and the world's largest stoichiometry problem: balancing the carbon in and the carbon out, and making sure you have enough hydrogen atoms (and energy) for the reaction. Also consider if your university offers a course in petrochemistry or petroleum engineering. Nimur (talk) 16:05, 6 August 2010 (UTC)[reply]
The major aircraft manufacturer I used to work for hires a lot of mechanical engineers and is often involved in long-term multinational projects. For some engineers, there is a great deal of travel between international partners and/or suppliers, though not all engineers get to travel.
Of course, you shouldn't pick your degree based on which one could result in international travel. If you are good enough in your stay-at-home job, the rewards could lead to you being able to travel for leisure, and I think most people will tell you it is nicer to travel the world as a tourist, than going great places and only ever seeing the inside of an office. On the other hand, whenever I've travelled on business, I've made a point of getting out of the hotel and taking weekends off (working extra hard during the week makes that easier to do :-)). Astronaut (talk) 21:54, 6 August 2010 (UTC)[reply]
Chronobiology of sunsets
If we assume that most people find sunsets pleasing in some way, perhaps even beautiful, we should ask why. Could it be that the pleasure derived from watching a sunset leads to calm and relaxation, and helps us sleep? Do sunsets have light effects on circadian rhythm in mammals? Viriditas (talk) 12:25, 6 August 2010 (UTC)[reply]
I think you've probably nailed it already. To humans living out in the wilds with no electric light, etc - the setting of the sun would indicate the end of the main work for the day - a time to start unwinding and getting ready for sleep. Such cues to behavior are ingrained into our bodies more deeply than many of us realize. But I'm not aware (and was not able to easily find) any research on the subject. SteveBaker (talk) 12:52, 6 August 2010 (UTC)[reply]
But we also find sunrises beautiful. I think it's an unintended consequence. As primates,we have good colour vision and we find bright colours pleasing (usually) as part of our "programming" to find ripe fruit. Sunrises and sunsets are beautiful for the same reason rainbows and bright blue skies and strawberries are beautiful - because they are full of bright colour. Matt Deres (talk) 13:29, 6 August 2010 (UTC)[reply]
Not everything needs an evolutionary explanation. I'd venture the guess that sunsets, like many natural phenomena with a dramatic visual component, are actually aesthetically pleasing. Paul (Stansifer)16:26, 6 August 2010 (UTC)[reply]
Actually, everything has an evolutionary explanation, whether you think it's needed or not. Even if the explanation is "Because it randomly occurred in my ancestor and any survival disadvantage to the trait was not very significant". Comet Tuttle (talk) 17:07, 6 August 2010 (UTC)[reply]
The article Aesthetics considers why we appreciate Beauty. Some sunsets are shown in the article Sunset and in wide varieties here. (OR) No printed photograph captures the brilliance and surprise value of some real sunsets, and they make one aware of the temporary and unique nature of what one is seeing. It's a lovely way to round off the day. Cuddlyable3 (talk) 19:55, 6 August 2010 (UTC)[reply]
I'm a bit confused about surface tension. I know that surface tension should act parallel to the surface, but the diagram of water molecules on the surface tension page seems to suggest that the force is perpendicular to the surface. Can someone help me visualize why, from the molecular picture of a liquid, the force would be parallel? Thanks. Related question: If water is placed in a capillary, why will the surface tension pull it up?76.69.241.253 (talk) 14:01, 6 August 2010 (UTC)[reply]
Surface tension#Cause offers an explanation. When an isolated (from gravity) drop of water attains a spherical shape, no inward movement of the surface molecules is possible and only forces parallel to the surface ( = tangential to the sphere) are demonstrable (think of a balloon). Surface tension#Liquid in a vertical tube explains capillary action. Example: The attraction between water & glass molecules is greater than water & water molecules. That results in a non 90 degree contact angle between the water surface and the inside of a glass tube. In a thin tube or capillary the water column is pulled up. Cuddlyable3 (talk) 19:39, 6 August 2010 (UTC)[reply]
Okay, I get the balloon analogy. But about the capillary action; I would think that the surface tension would pull the liquid inward, and stop the surface from rising... 70.52.44.90 (talk) 21:15, 6 August 2010 (UTC)[reply]
I know, but I'm talking about in all cases (like, say, water and glass). The adhesive forces of the glass are stronger than the cohesive forces of water, so the miniscus is U-shaped. But if the surface tension pulls the water inward, then wouldn't the water be drawn in and not rise? 70.52.44.90 (talk) 22:33, 6 August 2010 (UTC)[reply]
I got a new water heater
This refers back to this question. Since the Sears store where I bought it didn't have one, they ordered online for me, and I believe it's model 32636 on this page.
The plumber who installed it said, after I specifically asked that the water not be too hot, that he turned it up a little because it was set real low. It is the perfect temperature, as it turns out, so it makes me wonder what is "real low" and how did they (whoever set it before the plumber) decide to set it there in the first place?Vchimpanzee· talk·contributions·20:02, 6 August 2010 (UTC)[reply]
Not all dishwashers do that, you have to check your model specifically. But the biggest problem with low water temperature is the growth of legionnaires bacteria. Personally I would not risk it. Ariel. (talk) 23:17, 6 August 2010 (UTC)[reply]
Is this true? It says that zinc ions oxidize copper to copper(II), themselves being reduced to zinc metal. I though it was the other way around (copper sulfate reacts with zinc). If it is wrong, then how does it work? Thanks. --Chemicalinterest (talk) 22:46, 6 August 2010 (UTC)[reply]
Sub-woofer orientation
Should the sub woofer port point up or down? If down, then what clearance does it need from the floor, and is this affected by the type of floor covering: carpet, lino, wood etc? Also, can other structures in the room detract from the sub woofer output level?--88.104.88.126 (talk) 23:25, 6 August 2010 (UTC)[reply]
It is best to point to the listener, but second best would be into the largest volume of air, so down does not sound good if it is on the floor, it is more likely to vibrate the floor and produce other vibrating and shaking noises. Graeme Bartlett (talk) 00:31, 7 August 2010 (UTC)[reply]
August 7
Katha from acacia catechu tree
This material Katha is used in making paan masalas and used for other medicinal purposes.For manufacturing Katha rooms are build where specified temperature are required and there are two rooms which are used to produce the final material.
First Room:Material in liquid form(water content 60percent) is brought in Al/Steel Containers and stored for 10days at 1.5Deg.C and 90percentRH and the liquid get thicker as the water content is removed by providing air circulation with refrigeration.
Second Room:Material from the first room is converted in biscuits form(water content 44percent) and are brought in Al/Steel trays and stacked in racks and stored for 4days at 7Deg.C and 65percentRH and the water content is removed by providing air circulation with refrigeration.
QUESTIONS:
To find the refrigeration load the following is required by me.
What is the specific heat of Katha before freezing and after freezing.
I am going to guess the answer, and that your substance is gum acacia. The specific heat will be largely due to water, so it will be proportional to the fraction of water. If you are spending a lot of money on this, you may not want to rely on Wikipedia volunteers! The solidification point will be closely related to the water content, but it will freeze at close to 0 degrees if a large amount of water is present due to the molecular weight of the gum being high. Graeme Bartlett (talk) 00:39, 7 August 2010 (UTC)[reply]
Uphill running
At the risk of asking a stupid question, do rivers ever run uphill? Maybe there are some quirks of geography such that some rivers have points at a higher elevation further along their course? Stanstaple (talk) 00:34, 7 August 2010 (UTC)[reply]
I think only for a short distance of a few meters, if they have built up a bit of speed, it could push up and over a bar across the river. Normally if there was a higher elevation it could split the river into two streams flowing away from the high point. Graeme Bartlett (talk) 00:43, 7 August 2010 (UTC)[reply]
If they have to, they will make a deep pool (as many feet deep as feet uphill it has to run), until it reaches the level where it can flow over the hill. But it would probably erode away the streambed before that happens. Or it could go around it. --Chemicalinterest (talk) 01:10, 7 August 2010 (UTC)[reply]
It's not a stupid question at all, it's just a bit poorly defined. We all know water runs downhill, but does that mean that no part of the river downstream could possibly be higher than any part of the water upstream? Of course not; waves may lap higher, rocks or other obstructions may cause a bit of the stream to shoot upwards, and so on. What you need to keep in mind is that the water, like everything else, is being acted on by gravity. That's what forces the water to typically run downhill. However, just as we can still lift our leg despite gravity pulling it down, so too can a river roll over rocks and other obstructions. When the current of the stream is no longer strong enough to overcome gravity, then the water will pool, forming a lake. Now, on a slightly different tack, I recall reading an article in Discover magazine some years ago where water was indeed forced to run up an incline (though we're talking about a few drops of water, not a river here) after being placed on a surface that had been sprayed with an extremely hydrophobic substance in a gradient so that the most hydrophobic area was lower than the less hydrophobic area. The water was sufficiently repelled by the material that it would rise against the force of gravity. Obviously that's a special case scenario, but it illustrates that there are more forces at play on a river than simply gravity and they need to be factored in rather than giving the mostly true but incomplete and inaccurate reply of "No, water doesn't run uphill." You may also be interested in the phenomenon of the tidal bore where water is indeed forced uphill - and against the river's current to boot! Matt Deres (talk) 18:39, 7 August 2010 (UTC)[reply]
When a river turns, the water on the outside of the bend will be significantly higher than on the inside of the bend. Edison (talk) 19:30, 7 August 2010 (UTC)[reply]
Have a look at this discussion from January[12] (scroll down to "Engineering Question -Flipper's Ditch"). The gist of it is that there are a number of famous places where water seems to flow uphill, but it's an optical illusion. Alansplodge (talk) 13:04, 8 August 2010 (UTC)[reply]
Drinking diethyl ether
The diethyl ether page mentions that peasants in Silesia used to drink it. It doesn't say very clearly how dangerous that is, and neither does the reference link. Would a shot glass of ether do an adult any lasting damage? 86.140.52.244 (talk) 00:44, 7 August 2010 (UTC)[reply]
I had a good dose of it as an anesthetic as a child and it stank quite a bit, and also led to vomiting. Is there no beer, wine, whiskey, gin, rum, vodka, mead or hard cider available in the region where folks supposedly drink the stinky and nauseating stuff? Drinking diluted ether sounds akin to the dangerous practice of huffing volatile compounds. Edison (talk) 02:40, 7 August 2010 (UTC)[reply]
Hundreds of years ago in Europe, basically everything found in nature that was not described as immediately poisonous was being consumed. I don't see why Polish peasants didn't drink a highly diluted form of it. Remember that pure ethanol is quite dangerous to drink, but billions do drink it diluted anyways. hello, i'm a member | talk to me!02:45, 7 August 2010 (UTC)[reply]
I'd be interested, but I don't actually need to know. Just curious. The reference for our article here says the Polish government tried to ban ether drinking, but doesn't make it clear if that was for medical, fiscal (ie loss of alcohol taxes) or moral reasons. 86.140.52.244 (talk) 17:12, 7 August 2010 (UTC)[reply]
My cousin used to work for the Hudson Bay Company at a trading post in arctic Canada. They weren't allowed to sell hairspray to some of they locals as they were likely to drink it. My father once told me that there was a problem in WWII with RAF groundcrew making merry with the engine coolant. Some will drink anything they can get their hands on. Alansplodge (talk) 12:56, 8 August 2010 (UTC)[reply]
what is this plant?
It lives in my backyard in CA. It's got dandelion-like yellow flowers (but somewhat smaller and more compact, like that of the yellow starthistle, except more sunken in), and when the plant "dries up", the flowers turn into little irritating spikes that stick on one's clothing and skin. It's fairly green and leafy when not "dry". hello, i'm a member | talk to me! 03:44, 6 August 2010 (UTC)
It could be catsear or hawkweed or hawksbeard, any of which is commonly confused with true Dandelion. --Jayron32 03:48, 6 August 2010 (UTC)
It is aster-like, but it has leaves that are elliptic, almost ovate, kinda roundish-long. They are dark green, and they fall off when the plant dries and the little spikes form. It those that those spikes are the fruit (seeds); they don't seem to fly away with the wind...they stick on to whomever touches it. hello, i'm a member | talk to me! 04:21, 6 August 2010 (UTC)
I was recently sick and I had a really weird dream, it was like I was high, but of course I would never do something like that. Anyway, has any research been done on the phenomenon of the vivid, distorted dreams you have when you're sick? Is ther a wikipedia article? —Preceding unsigned comment added by 76.199.154.44 (talk) 02:45, 7 August 2010 (UTC)[reply]
If you were delirious in a lucid dream would you be "just dreaming" or could you be experiencing the feelings you would actually get if you are delirious? -- Sjschen (talk) 04:15, 7 August 2010 (UTC)[reply]
I've had both fever dreams and lucid dreams, and they are not at all similar. Lucid dreams tend to be characterized by being in control of the situation, whereas the fever dreams lean heavily towards nightmares and hallucinations. Viriditas (talk) 10:06, 7 August 2010 (UTC)[reply]
I concur. Fever dreams are quite distinct. When I've had fever dreams, part of the problem was that I seemed to slip in and out of them and into wakefulness (kind of like an inverted night terror, I guess), so that reality and the dream state became even more blurred than normal. There can be times where you're completely unsure whether you're dreaming or awake and hallucinating. Lucid dreams are exactly the opposite of that: you become aware of the dream and take hold of it. You also get a completely different feeling upon waking. Fever dream may be a bit of a misnomer, though; I've experienced them with no fever at all, but where I was sick enough (usually a severe sore throat) that it interrupted my sleeping. That interruption of the sleep cycle is probably part of the cause for the so-called fever dream. Matt Deres (talk) 15:27, 7 August 2010 (UTC)[reply]
The only reason I brought it up, is because in my experience, the nightmarish quality of a diphenhydramine dream was almost identical to the fever dream I had as a child. I doubt anyone has ever made this connection before, so have at it. Viriditas (talk) 01:46, 8 August 2010 (UTC)[reply]
Viriditas raised a good point. Before I had ever heard of "tussing" I once experienced hallucinations from taking too much dextromethorphan cough suppressant, and for several days I assumed that it was due to my high fever at the time. -- 119.31.121.72 (talk) 06:05, 8 August 2010 (UTC)[reply]
Scientific names of hybrid species
We know the scientific names are unique name for a species. eg. Magnifera indica is scientific name for common mango. But what about the scientific names of the hybrid species? How their names are determined? e.g. We see many different kinds of mangoes in the market, are all of them are Magnifera indica or they have some different name? From where can we find exact name of a particular species? Thanks! Shivashree (talk) 04:11, 7 August 2010 (UTC)[reply]
Known hybrids are named with "×" between the genus and the species terms. For instance, loganberry is Rubus × loganobaccus and grapefruit is Citrus × paradisi. Of course if people did not know it was a hybrid they sometimes gave it the normal biological classification name Genusname speciesname instead of Genusname × hybridname. It helps to remember that ideas like genus, hybrid, and species can be a bit blurred depending at what you are looking at. -- Sjschen (talk) 04:27, 7 August 2010 (UTC)[reply]
Thanks, Sjschen, for your quick response. But is there any database from where we can get the scientific names of the species in our neighborhood? Shivashree (talk) 06:01, 7 August 2010 (UTC)[reply]
Well, there are scissors specifically made for us left handed people. And for it not working upside down, your probably holding it incorrectly. Maybe if you try to hold right handed scissors upside down in your left hand or viceversa it might somehow make it easier to cut. wiooiw (talk) 05:19, 7 August 2010 (UTC)[reply]
As for why left/right handed scissors are harder to use for other handed people... Whether you realize it or not, when you use scissors, you are imparting a slight sideways force on the blades which brings them together not only in the up and down direction but the side to side direction as well. When you use a pair of opposite handed scissors, you are making the blades push away from one another. Take a look at our scissors article where it shows left and right handed scissors. You'll notice the blades are opposite of one another. Dismas|(talk)05:31, 7 August 2010 (UTC)[reply]
Turning an object upside down doesn't change its parity. Scissors don't have an "upside down" except for those with shaped handles. You can learn to use right-handed scissors with your left hand, or left-handed scissors with you right hand. You just need to pull with your thumb and push with your fingers. At first, this seems unnatural, but you soon get used to it. Dbfirs09:01, 7 August 2010 (UTC)[reply]
I think by "upside-down" the OP means holding a pair of scissors upside down so that the blades are on the side of your fist where your pinkie is. --173.49.16.4 (talk) 18:25, 8 August 2010 (UTC)[reply]
I saw this 50% chance dwarfism gene on some medical documentary years ago. What's that condition called?
On this documentary years ago, I watched about how if a certain pair of parents conceive, there was a 25% chance that the baby would be a healthy one, with a normal height. Then there was a 50% chance that the baby would become a dwarf; have pretty stunted growth.
Then there was a 25% chance that the baby would have some kind of non-survivable condition. The diagram shown while the narrator was speaking this, was a negative picture of a fetus. That condition was called some ominous Latin-sounding name that I have of course long-forgotten.
You are probably thinking about achondroplasia, which is the most common type of dwarfism. Since it is autosomal dominant, each affected parent has one normal copy of the gene (call it "A") and one that isn't working properly (call it "a"). If you draw out a typical Aa x Aa punnett square you'll see that the different combinations are AA (normal), Aa and aA (both affected), and aa (severely affected, likely lethal). --- Medical geneticist (talk) 11:50, 7 August 2010 (UTC)[reply]
For the "aa" genotype I should have written "likely perinatal lethal" to be more precise, although there are case reports of such individuals living several months. It is certainly safe to say that being homozygous for the common achondroplasia mutation results in early mortality, typically during infancy, due to severely restricted lung capacity and other problems such as hydrocephalus. There is variability in how long different individuals have survived, likely depending on the degree of medical intervention early in life (see example here), but it would be hard to imagine someone surviving into childhood or adulthood with homozygous achondroplasia. Can I say that it has never happened? No, but it is exceedingly unlikely. So, "lethality" really boils down to "when" a particular condition is likely to be lethal. --- Medical geneticist (talk) 11:28, 8 August 2010 (UTC)[reply]
musical memory
Unlike books, it's hard for me to forget the lyrics and the notes of a song...I have about 2500 songs on my iPhone. When will I reach my "capacity"?
Too much remembering is a problem, because for some really good songs I'd really like that experience of listening to an awesome song for the first time. John Riemann Soong (talk) 09:38, 7 August 2010 (UTC)[reply]
Here's an interesting read [13]. It doesn't particularly address your question of where your limit is though. I'm not sure anyone can answer that. Regards, --—Cyclonenim | Chat 11:00, 7 August 2010 (UTC)[reply]
I think the mind can also create new tunes out of bits of other songs in the memory, but not everybody does that. ~AH1(TCU)15:19, 7 August 2010 (UTC)[reply]
Many people find that they can remember the "hook" lyrics of even the most popular songs of their youth, but the rest of the lyrics are just bum-de-dum-dum. If you remember the lyrics of 2500 songs you may have unusually good recall. Edison (talk) 19:27, 7 August 2010 (UTC)[reply]
Why do you think he does? I have about 10,000 songs with lyrics and I'm fairly certain I know the lyrics to most if not all of those songs. It's different to eidetic/photographic memory, where you can remember, say, every word in any book you read. Regards, --—Cyclonenim | Chat 13:58, 8 August 2010 (UTC)[reply]
Do you mean that you remember all the lyrics of every song, for example can you recall all the lyrics of XXX song, or do you mean that when you are listening to a song, you know the lyrics that are coming up? Like Cycloneim I have almost 10,000 songs and whilst I can remember the lyrics of a song as it plays, there's no way that I could recall the lyrics from cold. Similarly I find it strange that I can nearly always remember whether I've heard a song before or not, but cannot remember all the songs I've ever heard, and that must include ~20,000 songs. Smartse (talk) 16:35, 8 August 2010 (UTC)[reply]
Is it possible, maybe through training, for a person to be able to listen to 2 or more simultaneous messages ?
I know I can quickly switch between processing the two messages, but they become jumbled, im wondering if this could change though training.. would be an interesting skill to have :) —Preceding unsigned comment added by Rowen121 (talk • contribs) 19:35, 7 August 2010 (UTC)[reply]
I agree the first is an ash and the second is possibly a gean. I say possibly because the fruit seems a bit big for a wild cherry and it may just be a rogue hybrid plum. The context of the discovery would help and a description of the size of the tree, colour and texture of the bark. Richard Avery (talk) 07:01, 8 August 2010 (UTC)[reply]
I don't think they are deliberately manufactured to be incompatible, and some brands will be interchangeable, but in general, tips fit a particular design, and there are so many different designs that you are unlikely to find a matching one by a different manufacturer. Some designs (such as "Weller" - apologies for the advertising. I'm sure that others make a similar product.) have tips designed to be quickly swapped for different applications, but full irons are so cheap in some outlets that it is hardly worth replacing tips. Dbfirs07:33, 8 August 2010 (UTC)[reply]
Wikipedia has an article Soldering iron (also Soldering gun can be of interest). Reasons for changing soldering iron tips are: they become eroded by solder (bare copper tips erode faster than iron-plated tips), different sizes of tip are suited to particular jobs, and some temperature-controlled soldering irons, e.g. from Weller a brand of Cooper Tools, allow operating temperature to be set by a thermostatic part in the tip. In general the tips are not interchangeable between brands of iron. (OR) The looped tip of a soldering gun is not much more than a bent copper wire, and that can be used as an emergency replacement.Cuddlyable3 (talk) 14:56, 8 August 2010 (UTC)[reply]
Evolution
What proof is there for evolution/Darwinism? Isn't it just an atheist myth created to insert anti-religion propaganda into the public school system? What evidence is there to support Darwinian dogma? --138.110.206.99 (talk) 20:38, 7 August 2010 (UTC)[reply]
It actually doesn't say that (which would make sense, given that Darwinism and naturalistic evolution more generally are concepts that came much later in time). I have a hard time believing you're not just trolling us, though. If you really want to know about evolution, we've already referred you to a place to start. If you're just here to state what opinions you already have, that's going to get your question deleted. Let me phrase it one other way: if you are here to learn something, we're happy to help; if you're here to convince us of something, you'll be politely (or perhaps impolitely) shown the door. --Mr.98 (talk) 21:20, 7 August 2010 (UTC)[reply]
I'll try to restrain my "fire breathing" now. Most people believe in evolution (not Darwinism, he just thought of a hypothesis and someone else promoted it) because they do not like what the Bible says about creation. Evolutionists have many proofs; some in favor of evolution, but most not in favor. This is what I believe. This is what most people believe: The Bible is a story written by man. Evolution is fact. Religion is just an evolutionary mishap. This is a WP:NPOV statement, although it is slightly biased. --Chemicalinterest (talk) 00:36, 8 August 2010 (UTC)[reply]
[citation needed] I don't know if anyone has ever done a survey on why people accept evolution, but it seems more likely people accept it because of the overwhelming weight of evidence in support of it, and its overwhelming support by biological scientists not because of what they may think about what the bible says about the creation. The fact that it makes more sense to them then other suggestions, like creationism probably helps for a few but that isn't quite the same thing. In any case, I have no idea why you believe most people in China or India or many other countries will give a damn about what the bible says about creation, they probably aren't even aware of what it says.
Also in many countries most people still have some sort of religious belief. These may not be strong, but are still enough that the person describes themselves as having religious beliefs. Even here in NZ, hardly an extremely religious country most people still described themselves as Christians as of the most recent census, see religion in New Zealand. While some of these people may describe their religious beliefs or the bible as an 'evolutionary mishap' it would seem odd that a large number would. (They may believe the bible has been modified by humans or isn't a reliable source for the word of god or more likely perhaps just not really care about the bible.) Finally a large number of religious people, including those who still believe the bible is the word of god have no problem accepting evolution.
The Bible does not mention evolution; not surprising as the Bible was completed around (IIRC) 200AD. However, evolution, plate tectonics, astronomy, and several other areas of the natural sciences conflict with a literal reading of Genesis, and thus are heretical to those who believe the Bible is the literal inerrant word of God. For a Christian perspective of evolution, see http://community.berea.edu/scienceandfaith/essay05.asp. Some of the major Christian churches, including the Roman Catholic Church, accept evolution, and consider Genesis to be allegorical. CS Miller (talk) 09:55, 8 August 2010 (UTC)[reply]
Thanks I seemed to remember a similar question before but didn't have any luck finding it so decided a brief and to the point link to our articles would be best. In case anyone hasn't noticed, both the OP and J4V4 are interested in Pokémon and Quebec. Nil Einne (talk) 15:33, 8 August 2010 (UTC)[reply]
I want to build an insulated cabinet out of wood with a 40W heater inside. It's for keeping fermenting bins in, which suprisingly enough I don't think we have a wiki article on!
I was under the impression that a Cavity_wall mainly acted by trapping air and creating a Thermal break but after reading the articles I'm guessing that I should really have some sort of insulating material in the cavity? 3 questions:
Does the size of the cavity make much difference to the insulation, eg. 3mm vs 10mm?
Is there a cheap material that I could use to fill the cavity that's readily available?
Would lining the inside of the cabinet with aluminium foil be more important than insulating material?
If you want to go as cheap as possible you can use crumpled newspaper. But polystyrene foam could be good as long as you don't let it get too hot. Al-foil is good on the inside of the newspaper. Graeme Bartlett (talk) 02:32, 8 August 2010 (UTC)[reply]
Air is a perfectly good insulator, but you need something in a large gap to prevent convection currents from carrying heat from inside to outside, hence the crumpled newspaper or polystyrene foam (any old random pieces from packaging material will suffice). Another alternative would be rock wool used for loft insulation. Dbfirs07:22, 8 August 2010 (UTC)[reply]
Aluminium foil will mainly help at higher temperatures, at fermenting temperatures ordinary insulation will work better (that's if you have to choose between them). You can buy foam sheets with foil already on them. They are not expensive, and they hold their own shape so I think that would be the easiest to install. I wouldn't use rock wool or fiberglass insulation unless you had a way to isolate it from the cabinet. It's not good to touch it or let it get into food. To your question about the size of the cavity I'm not sure. Do you mean just an empty space? And are wondering if a bigger space is better? Obviously if the space is filled with insulation then a bigger one is better, but if it's just empty it's not so obvious. Insulation is all about the empty space, but it's not about having a larger empty space - it's about having more of them (i.e. space, wall, space, wall). Ariel. (talk) 19:11, 8 August 2010 (UTC)[reply]
File:LateJurassicGlobal.jpgLate Jurassic map There are lots of places with no volcanoes. There is nothing special about the North Pole in that respect, so I don't see why there needs to be a reason. This map from the late Jurassic period (so about 150 million years ago) shows land very close to, if not actually at, the pole (it's hard to tell from the image). That seems to be the most recent time there was any land near the pole. You can see the recent (last half a billion years or so) changes in the placements of continents in this animation: File:TectonicReconstructionGlobal.gif. --Tango (talk) 00:59, 8 August 2010 (UTC)[reply]
Are you sure? I was going to say the same but then I came across File:Plates tect2 en.svg...a line goes off the top of the map and comes down the other side. Which suggests to me it passes pretty close to the North Pole. I realise flat maps can't properly illustrate a spherical(ish) globe, but... Vimescarrot (talk) 16:18, 8 August 2010 (UTC)[reply]
That map doesn't actually show the north pole. The north pole on that projection is a horizontal line infinitely far above the map, if I'm recognising the projection correctly. There is no way to know what that plate does north of the boundary of the map just by looking at that map. There is a whole chunk of the plate missing. --Tango (talk) 16:55, 8 August 2010 (UTC)[reply]
You misunderstand. The map Vimes links to doesn't show the North Pole. The map I embedded certainly does, otherwise my answer wouldn't have made any sense. --Tango (talk) 17:54, 8 August 2010 (UTC)[reply]
Do we have any images of the major plates superimposed on a more modern projection, or something that preserves the curve a little better? (I'm also surprised by how weird it is to see a map like this centred over the Americas, but I don't think it would be reasonable to ask for one that matches my own expectations) Is Vimes's link a Mercator projection? The British Isles looks huge on it, and Africa very small. 82.24.248.137 (talk) 19:32, 8 August 2010 (UTC)[reply]
The Neurons or the synapses
Does it improve a person's memory or intelligence to have many neurons or is it in the synapses or the way that the neurons send the signals that is responsible for why some people have better memories than others? I believe Kim Peek (Rain man inspiration) was said to not have the corpus callosum, and it is in theory that some believe because of this his brain found a way of connecting around that at a superfast speed and that is what is responsible for his memory. Also, can the neurons or the way signals are sent be changed, I ask because I watched this documentary that had a guy from Enland who after an epilectic seizure when he was three he started to get this incredible memory and brilliance for numbers and on the same documentary there was a kid who got hit in the head with a baseball as a kid and ever since that he too had an afinnity to memorize dates and so on? —Preceding unsigned comment added by 70.136.158.173 (talk) 01:12, 8 August 2010 (UTC)[reply]
Also, could the size or shape of the brain have anything to do with it? (In the MRI taken of a woman who has memorized every day of her life from 1980 on and others like her there bains were slightly different shape and they were all left-handed.)
Most neuroscientists believe that memory is stored by changing the strength of synapses, so the total number of synapses sets a limit on the amount of memory the brain can store. But this is only one factor: an effective memory depends on a whole range of systems for formatting, storing, and recalling memories. It's like in a computer memory is stored in little magnetic things, but if you just throw a pile of magnetic things on the floor, you don't get a usable memory system -- it all has to be organized properly.
It is very common for autistic savants to have extraordinary memory for details. Most don't have a missing corpus callosum, so I doubt that that has anything important to do with it. The stuff about signals connecting around at superfast speed is just nonsense. Basically we don't know where those extraordinary memories come from -- it clearly involves a higher level of brain organization than we yet understand. Changes in brain shape might be relevant, or they might not -- we just don't know yet. Looie496 (talk) 02:26, 8 August 2010 (UTC)[reply]
Are the parts and even the strength of the synapses continually growing? Like for example our bones even though we stop growing and reach our full height our bones are still constantly rebuilding themselves and continue to go through a process? —Preceding unsigned comment added by 71.156.2.13 (talk) 03:52, 8 August 2010 (UTC)[reply]
There is quite a bit of evidence that synapses change continuously. A synapse is only a single signal channel, so they don't get more complicated over time, but they do get stronger or weaker. Among other things, Giulio Tononi's theory of sleep proposes that synapses steadily strengthen over the course of each day, and then weaken when we are asleep -- there is substantial evidence to support this. Looie496 (talk) 04:52, 8 August 2010 (UTC)[reply]
Absolutely. In fact, nearly every psychoactive drug exerts its effects by making some group of synapses either more or less effective. There are a small number, such as caffeine, that act on neurons by non-synaptic mechanisms, but the great majority act on synapses. There are also internal chemicals, such as norepinephrine, that act at least partly by modifying the strength of synapses in specific brain pathways. Looie496 (talk) 17:42, 8 August 2010 (UTC)[reply]
When is a heat sink necessary for a 7805 voltage regulator?
Hello! I'm a (newbie) hobby electrician. I'm planning on using an AC adapter that outputs 9V 210mA connected to a 7805 voltage regulator for my project. How do I know if a significant amount of energy will be wasted as heat? The circuit will be in operation mostly 24/7. When is a heatsink connected to the regulator required? The circuit will be working at room temperature. I think part of the difficulty I'm having understanding how the voltage regulator will work is because I've only worked with DC from batteries, and learned that when 9V is connected with a 1KΩ resistor in series to an ammeter, the reading will be 9mA, but I don't know why the AC adapter's specs show 9V at 210 mA. I would think (probably wrongly) that 9V would output 9A because of the ammeter example I gave. I'd also appreciate any help on understanding this now that I'm moving on from working with AA batteries. Thank you!--el Aprel (facta-facienda) 02:21, 8 August 2010 (UTC)[reply]
The regulator will reduce the voltage by varying its resistance. The current flowing through times the voltage drop will turn into heat. The AC adapter rating is just the maximum, so you have to know how much current your circuit will consume, If it only takes 10mA then no heat sink will be needed, but the full 200mA dropped by several volts, will need one. Graeme Bartlett (talk) 03:15, 8 August 2010 (UTC)[reply]
At risk of straying into wikibooks/wikiversity territory, you need the output voltage of the bridge rectifier. This will be the RMS of the step-down transformer you are using. Then take (Vin - Vout) / Iout. This will give the power drop across the voltage regulator. The voltage regulator's datasheet will give a maximum operating temperature. Say it is 70°C, this is fairly typical. Given a room temperature of around 30°C (a bit on the high side), the voltage regulator can not be more than 40°C above ambient. Say the transformer is at 12V AC. RMS is 17V DC. The drop across a 9V regulator is 8V (check the maximum input voltage, but they are normally around 50V). 8V * 210mA is 1.68W. That is 0.04W/°C or 25°C/W, assuming the heatsink is in free air. In enclosed cases you need a bigger heatsink (higher value for W/°C, smaller for °C/W), if you are using fan-cooling then a smaller heat sink is needed. CS Miller (talk) 11:04, 8 August 2010 (UTC)[reply]
Omniscience is impossible. For instance, the uncertainty principle states that we can not simultaneously know an elementary particle's position and momentum. So what is the maximum level of knowledge that can be attained, and is there any realistic measure of attaining it?--220.253.219.83 (talk) 04:24, 8 August 2010 (UTC)[reply]
The maximum knowledge that can be obtained is the amount of knowledge that our brains are capable of holding. That's an infinitesimal fraction of the information in the universe, so it doesn't really make sense to talk about obtaining it. The information in a teaspoon of water is vastly beyond our ability to comprehend. Looie496 (talk) 05:04, 8 August 2010 (UTC)[reply]
I think you may be misunderstanding the uncertainty principle. We often say things like "we can not simultaneously know", but that is misleading. The correct understanding is that particles do not ever have both a fixed position and momentum. It's not a statement about our lack of knowledge. It is an expression that trying to assign momentum and position to everything is inherently futile because those properties do not exist. A hypothetical omniscient deity could know everything there is to know, and still wouldn't know both position and momentum, because the universe simply doesn't allow particles to ever have well-defined values for both. Personally, I don't see any objections in quantum mechanics to a deity having omniscient knowledge of the present and past. However, the principle of wavefunction collapse (as presently understood within our limited knowledge) would seem to imply that even a deity would never be able to uniquely predict what would happen in the future, since quantum mechanics inherently involves randomness. Dragons flight (talk) 05:26, 8 August 2010 (UTC)[reply]
Unless the deity is the source of the randomness. You are assuming a deity that lives in the universe, but the deity could be the universe. i.e. the deity is to the universe as you are to a thought in your mind. Meaning each and every particle and interaction in the universe is specifically "animated" by the thoughts of the deity. Ariel. (talk) 07:59, 8 August 2010 (UTC)[reply]
No. All of those are the same as saying quantum mechanics is wrong, because the events would no longer be truly random. You can either say the universe isn't random (because the deity guides it, etc), or you can say the universe is random and future outcomes aren't known till they occur, but you can't have it both ways. Of course, a deity could certainly make a predestined universe appear random to beyond our ability to ever tell the difference, but that's not the same as saying the universe actually is random. Dragons flight (talk) 08:19, 8 August 2010 (UTC)[reply]
What's the difference? From a physics point of view I mean, not a philosophical one. If it's random beyond our ability to tell the difference, if there is no physical test or ability to tell otherwise, then it is random. The Equivalence principle works exactly the same way: Since there is no way to tell the two forces apart, they are the same. Ariel. (talk) 08:30, 8 August 2010 (UTC)[reply]
Information (not exactly the same as knowledge, but close enough) is strongly tied to energy. It takes energy to manipulate and store information. See Limits to computation and google for "Ultimate physical limits to computation" for more exact numbers. Another limitation is the speed of light - you can not know about anything not within your light cone. Additionally as you store more information the size of your "brain" gets larger - eventually it gets large enough that it takes a long time (because of the speed of light) to retrieve information from the other "side" of it. This greatly limits the speed at which you can think. (So you can know a lot, but not be able to think fast, or know less and think faster.) There is no direct answer to your question since you did not specify what is doing the "knowing", but maybe what I wrote was interesting anyway. Ariel. (talk) 07:59, 8 August 2010 (UTC)[reply]
Infinite knowledge may or may not be impossible, as infinite knowledge of information would be impossible, but knowledge is distinct from information. There are also ways that ordinary people use to increase knowledge to much higher levels (ie. mysticalself-hypnoticmind-expandingintrospectivespiritual experience), but not in a way that true omniscience could be achieved at any given point in time. The electron conundrum is likely connected to the quantum zeno effect. Knowledge cannot be quantified, and therefore may have little to do with the possible interconnections between neurons and synapses (~∞). As for the deity as universe argument, this is called pantheism. Also, it would be possible for an omnipotent being to create a door he cannot open. All the being has to do is make the door so that it is impossible to open at a specific time, but make it able to be opened when he decides it can. ~AH1(TCU)18:14, 8 August 2010 (UTC)[reply]
Tetra Fish Fins
DO THE FINS OF A TETRA FISH GROW BACK? MY WIFE AND I HAVE A 150 GALLON AQUARIUM FILLED WITH ALL KINDS OF TETRA FISH,AND THE OTHER DAY WE NOTICED THAT ONE OF THE SMALLER FISHES FRONT FINS WERE NIBBLED ON AND THE FISH IS FLAPPING CONSTANTLY.WE SEPERATED THE FISH FROM THE PACK AND WE WERE WONDERING IF THE FISHES FINS WILL EVER GROW BACK? IF SO HOW LONG? —Preceding unsigned comment added by 173.105.146.216 (talk) 10:04, 8 August 2010 (UTC)[reply]
This recent article at Ars Technica mentions [15] (from a report it covered) : ..result of a stronger cooling effect from sulfate aerosols.. (I'm not particularily interested in the article or conclusions/methodology)
I was wondering if any figures were available on the cooling effect of 'sulphate aerosols' - ie what magnitude of effect has/will have Flue-gas desulfurization had/will have on the worlds temperature, particularily the isolated effect of not adding sulphur to the atmosphere - not the overall balance taking into account burning coal. Thanks.87.102.23.179 (talk) 11:46, 8 August 2010 (UTC)[reply]
Our Strained yoghurt says that what's called 'Greek yoghurt' typically just means some form of strained yoghurt. So I would guess taste as Cyclonenim mention and texture would be a big reason why some may want Greek yoghurt. Our article also notes "strained yoghurt is a traditional food in the Middle East and South Asia, where it is often used in cooking, as it is high enough in fat not to curdle at higher temperatures" which may be what you're referring to and it indeed seems likely that advantage would be lost but I guess quite a number of people aren't choosing it so it doesn't curdle at higher temperatures as you have presumed Nil Einne (talk) 19:51, 8 August 2010 (UTC)[reply]
How does a car's wheels get out of alignment?
How does a car's wheels get out of alignment? My understanding is that driving over potholes and hitting the curb hard when parking can both cause alignment problems. What are some other causes? Also, what exactly happens when something causes your car's wheels to be misaligned? Is something in your car deformed? --173.49.16.4 (talk) 18:53, 8 August 2010 (UTC)[reply]
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