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April 21

Venus

If people don't start protecting the environment from greenhouse gases, will Earth become like Venus (9 MPa CO2 atmosphere, 850 F surface temperature, sulfuric acid rainstorms, etc.)? --75.40.204.106 (talk) 02:07, 21 April 2011 (UTC)

Unlikely. For one thing, Earth's living systems are surprisingly resiliant, and are quite able to alter the atmospheric composition in dramatic ways. Don't get me wrong, humans impact on the environment, to change it from the world we know, into something far less friendly for us to live in, is a serious deal. We stand in real danger of making the world a less hospitible place for humans, and doing real harm on a timescale which is quite long on human measurements, but short on the Geologic timescale. Lets say we screw up the environment for the next 10,000 years. That's like 500 generations on a human timescale, and longer than there has been evidence of human civilization. It seems like a serious issue, and it is for us. However, 10,000 years is a minor blip on a geologic timescale. Consider that life on earth has existed for something like 2,000,000,000 years, and that 10,000 years seems insignificant to the Earth. And it is. The "earth" will recover, ultimately, from whatever we do to it. The question becomes, for me, if we will be around to enjoy it at that time... --Jayron32 02:15, 21 April 2011 (UTC)

Was Venus like Earth a long time ago until its life destroyed the environment? --75.40.204.106 (talk) 02:17, 21 April 2011 (UTC)

No, quite the contrary, there has never been life on Venus. Indeed, pre-life Earth used to look a lot more like Venus; the introduction of life drastically changed Earth's atmosphere in some very big ways. See Great Oxygenation Event where the atmosphere of the Earth changed drasticly. --Jayron32 02:56, 21 April 2011 (UTC)

According to Oxford Professor Fred Taylor, "In the light of the new data [from Venus Express] it is possible to construct a scenario in which the climates on Venus and Earth were very similar when they started out, and then evolved to the state we see now, like twins separated at birth. Billions of years ago there is even the possibility that Venus would have been habitable." Clarityfiend (talk) 03:01, 21 April 2011 (UTC)

Venus is significantly closer to the sun than is the Earth. (The average distance from the Earth to the sun is about 40% greater than the average distance from Venus to the sun.) The greater intensity of solar radiation on Venus has always represented a significant difference between the two planets and shows they could never have provided similar environments for living things, nor will they ever be similar. Dolphin (t) 03:02, 21 April 2011 (UTC)

(edit conflict) I can accept a similarity between Earth and Venus a long time in the past, but "habitable" does not equal "had life". I'm not saying you or your source said that. But it must be made clear that there's nothing there to indicate that there ever has been life on Venus. I could have married Jennifer Lopez. Doesn't mean it happened... --Jayron32 03:04, 21 April 2011 (UTC)

Hummmn. Got thing for J Lo huh?190.56.105.52 (talk) 04:50, 21 April 2011 (UTC)

People seem to disregard the fact that evolutionary processes are influenced by feedback-loops. So is climate evolution - an increase of atmospheric carbon dioxide will, through a chain of cause and effect, alter our rate of CO2 output.

For instance, assume that the only source of CO2 is industry. A drastic change in atmospheric CO2%, will eventually alter and reallocate sociological and economical priorities, including industrial sectors. As global industry shuts down a number of sectors, atmospheric CO2% decreases. Given a chance, the climate will heal itself and reajust to a new equilibrium. In short, alteration of the climate will automatically affect our ability to alter it.

I'm not argueing against global wariming, infact, I believe that at present the collective effort to change climate altering habits is insuffient to prevent the progress of global warming. Assuming that the effort remains unchanged into the future, then civilaisation will collapse, we will be forced to change our habits as it would no longer be energetically favourable to continue carbon dioxide producing technologies. Over time, global warming will naturally reverse, albeit slowly, as it is reabsorbed by ecogenesis and other minor processes.

Venus atained its current climate without the benefit of a negative feed-back loop, it actually suffered from a positive feedback loop. Plasmic Physics (talk) 11:47, 21 April 2011 (UTC)

Jayron, I don't think we can really make a statement like "there has never been life on Venus". In fact, I don't think that we can state with authority that it isn't there now. APL (talk) 14:00, 21 April 2011 (UTC)

I can't state with authority that I even exist. There's no definitive proof that Wikipedia itself is not a halucination that you are having as a result of being administered powerful mind altering chemicals placed in your tapwater supply by the CIA, and that this entire conversation isn't happening inside of your own deluded mind as you are actually, right now, lying on the floor in your living room drooling on yourself. Can you prove THAT to not be true?

Back to the life on Venus issue: Its the positive assertion that requires evidence to prove it, not the negative one. We don't assume every utterance a human could make to be true by default, and then require others to disprove it. I could make any number of rediculous assertations (Clouds used to be made of cotton candy, but they arent anymore!, Elvis Presley didn't die, he had plastic surgery and became George H. W. Bush! Grilled Cheese sandwiches cause pregnancy!), and there's no requirement that we give them any possibility of being true. You seem to be taking the stance that "any nondisproven idea must be at least considered to be possibly true". That's not necessarily the case, since I can present any number of statements that have not been disproven (to any arbitrary standard of proof I wish to demand) and then demand that you accept them as possibly true, no matter how rediculous they may be. A scientist has presented data that there may have been conditions on Venus, in the past, which may have been similar to conditions under which life on Earth is known to have existed. We can entertain that idea (we are not required to accept it as absolutely true, but we can entertain it) because the assertion is at least backed up with data. However, there is no need to entertain wild speculations that have zero data to back them up, for example, that there was actually life on Venus. Yes, you can say "you don't KNOW there was no life on Venus." But there's no need to prove the negative; the lack of any evidence is enough so far. Since you are making the positive assertion (there may have been life on Venus), you need to supply the evidence to make it. See Argument from ignorance, which is exactly the fallacy you are committing here. --Jayron32 15:34, 21 April 2011 (UTC)

You made a very definite assertion. I'm saying that it was almost completely unevidenced. It's not like you're saying "Many people have observed the Loch Ness, but no one has every produced evidence of a monster. It's safe to say that there is no monster." You're saying "No one has ever even been to Scotland, but we've got a dozen very low-res photographs, so There is no monster.". The first is a scientific statement, the second is not. You can't bluntly say that something doesn't exist because no one has produced evidence, if we haven't looked for that evidence! At that point you have to say that it's unknown.

Confusing the line between "Science is never 100% certain of anything." and "This particular thing is completely unknown" just gives fuel to the creationists and other anti-science types. APL (talk) 16:43, 21 April 2011 (UTC)

Agreed. As for the possibility of life on Venus now, if life can exist near hydrothermal vents at the bottom of our oceans, at extreme temperatures and pressures, then maybe it can on Venus too. Yes, the acidic environment of Venus is also harmful to life, but then so is free oxygen, yet life on Earth evolved to not only survive that, be to take advantage of it. And Venus does have a very reactive environment, with lots of energy available, which would promote both the creation of life and it's evolution. I have no problem imagining something similar to bacteria living on Venus. It may or may not exist, and I will make no definitive statement either way until I see some proof. StuRat (talk) 17:46, 21 April 2011 (UTC)

Here is what I remember having heard about venus. It is nearer to the sun and thus receives more solar energy than earth does. At times of the faint young sun this would have helped venus not to turn into a snowball. Venus is less massive than earth and I read somewhere (not on wikipedia, can't find it again now) that any planets less massive than earth cannot hold hydrogen by gravity. If so, venus, like mars, was bound to dry completely sooner or later. Venus does not have plate tectonics the way earth does. This way the exchange between the atmosphere and ground is limited. CO₂ would not be as dynamically released or bound geochemically like on earth. I think it was somewhere on wikipedia where I have read that the whole of the venus' surface was submerged in one single event. If so, there is no hope of ever finding any traces of life that may or may not have existed. 93.132.132.156 (talk) 22:11, 21 April 2011 (UTC)

I found part of the information here Geology of Venus#Global resurfacing event 93.132.132.156 (talk) 22:26, 21 April 2011 (UTC)

Bosch reaction

Is it endothermic or exothermic? --75.40.204.106 (talk) 02:16, 21 April 2011 (UTC)

According to the Wikipedia article Bosch reaction it is exothermic. You could check yourself with the data at Standard enthalpy change of formation (data table). --Jayron32 02:52, 21 April 2011 (UTC)

What would Earth be like if it was 82% more wonderful?

It's great that you're being creative and imaginative, but this isn't the correct place for it.
The following discussion has been closed. Please do not modify it.
I have collapsed this discussion. This is the science reference desk. On this page, we seek to improve the quality of our encyclopedia by helping people find scientific references. If you want help finding internet discussion forums or other outlets for your creative energies, you might find better answers on the Humanities or Miscellaneous desks. Nimur (talk) 04:21, 21 April 2011 (UTC) When people think of environments much better than those found on Earth, they invariably talk of Heaven and its variants, which are INCOMPARABLY better. Earth is amazing, wonderful, astonishing, charming, exciting and deep, but the world to which I refer is 82% more enhanced in all of these properties. What would such an Earth, one that is better but not incomparably better to the one we know be like? The immediate objection to this question will be that it is not “scientific” because the properties of “amazing, astonishing…etc” are subjective descriptions. This is so, but subjective evaluations can be quantified and measured by psychometric means. We don’t need to do that here; for the time being a respondent can estimate what features such a planet might have that would render it 82% more wonderful in every way to the one we live in. Not 100%, or 200%, but 82% - it is important that the last figure be the one under consideration, although respondents to this query might wish to compare their 82% ideal with what would be the case if the figure were much higher. For myself, I believe the following would be a reality in such an Earth: 1. There would be four sexes, male, female, devotrain and andila. Everyone would be male or female but also be either devotrain or andilian. A devotrainian male could make love to an andilian male without being homosexual. There would be an another entirely different kind of eroticism which would run parallel with the one we know. Human navels would become powerfully erotic organs which, when joined with another’s, would emanate fibres that would extend through the other’s body. When the moment of devotrainian or andilian orgams occurred, it would be felt from head to toe. 2. Humans would have eyes which, when properly trained upon the night sky for half an hour or so, can see the cosmos as clearly as the Hubble Telescope does now. Indeed, humans will be able to see in the infra red and unlta violet, and the brain will be hard wired to see two extra colours. 3. People will be able to glide for considerable distances, and death by falling will no longer occur. To fly like a bird, however, would require an Earth 128% better than the one we have. 4. There will be creatures like vast air ships, 10 times larger than the biggest whale, which will be tame and carry thousands of passengers across the seas in great comfort, requiring only some food and love. 5. The Earth will be 34% larger, but correspondingly less dense so that gravity is largely unaffected. There will be two extra continents. 6. We will share the planet with another species equal to our own in intelligence, and with whom we can communicate. 7. During the night when we sleep, we will be able to join in a universal dream in which all sleeping people of good will can partake, involving vast on-going dramas ranging from passionate love to intense adventure. Can you provide some more background for this world? Myles325a (talk) 02:54, 21 April 2011 (UTC) Wait, you've invented a fantasy world and now you want us to provide you with more information about it? The world is in your head. You can give it all the background information you want. The reference desks aren't really an appropriate place to try to write a crowdsourced science fiction novel. Do you have a specific factual question we can help you find answers to in Wikipedia articles? --Jayron32 02:59, 21 April 2011 (UTC) Op myles325a back live. Sigh...sigh...I DID say, above "The immediate objection to this question will be that it is not “scientific” because the properties of “amazing, astonishing…etc” are subjective descriptions. This is so, but subjective evaluations can be quantified and measured by psychometric means. We don’t need to do that here...". And so you go ahead and make exactly the same objection I had already tried to pre-empt. You very well might not agree with this pre-emption, but you could have at least acknowledged that I made it. A couple of other points. One: These questions are not just for people who can't use the Search function in WP. And two: It's not just IN my head. You are assuming that. The reality is more complicated. Myles325a (talk) 03:13, 21 April 2011 (UTC) You may be interested in Leibniz's 'Theodicy', which argues that we live in the best possible world (and hence it cannot be made 82% more wonderful). Or you may be interested in Voltaire's Candide, which was influenced by Leibniz's work, and largely ridicules this notion. SemanticMantis (talk) 03:15, 21 April 2011 (UTC) And no doubt this world has 82 percent more giant purple mushrooms.190.56.105.52 (talk) 04:01, 21 April 2011 (UTC) You realize you've basically described the movie Avatar right? Ariel. (talk) 04:09, 21 April 2011 (UTC) No ariel .I don't think Pandora had any giant air ship creatures that carried people across the seas in great comfort.190.56.105.52 (talk) 04:19, 21 April 2011 (UTC) OP myles325a back live. Thanks. You have ensured that everyone will want to see what has been censored by you, Nimur, just as surely as they will touch the wood where a sign says "wet paint". But I ask of these potential respondents. Please don't. Don't look at this question. It's just..not something you should see. I have conformed to the wishes of my betters. The question is now posed in the Humanities Board. Myles325a (talk) 05:14, 21 April 2011 (UTC)

Kindle 1 reflective scrolling — how does it work?

The first-generation Amazon Kindle has a visually fascinating way to select on-screen options. Above a scroll wheel is a long vertical grayish-white line which looks plastic or rubber. But as you turn the wheel, portions of this line suddenly become reflective, like a mirror — you can actually see (part of) yourself in it. The location of the reflective part tells you which line on the screen you'll select if you push the wheel down.

It looks like magic; even having owned this thing for a couple hours, I still can't wrap my mind around it. What exactly is it made of? How can something instantly go from "mirror" to solid gray/white? (To clarify, the line seems to respond to the computer input of the Kindle — it doesn't do anything if the Kindle is off, and larger or smaller portions of it become reflective based on the size of what is being selected.) ± Lenoxus (" *** ") 03:10, 21 April 2011 (UTC)

How is that any more "magical" than the rest of the screen where white turns into black (and shades of gray)?

I think the question is how the "mirror" works. (Normal pixels can't "mirror" -- presumably the e-ink allows for the use of reflective coloration, but I don't really know.) --Mr.98 (talk) 16:20, 21 April 2011 (UTC)

No, it's not e-ink. The "Cursor Bar" is not part of the main screen. It's a separate display next to the main screen that updates quickly like a normal LCD.

Except instead black/clear like a normal cheap LCD, the cells turn mirrored when they're on and clear when they're not on.

I have also wondered what kind of technology this is, and why they don't make digital watches with it. APL (talk) 16:51, 21 April 2011 (UTC)

[1] suggests it's as simple as an LCD with a mirror backing instead of a backlight. Nil Einne (talk) 17:06, 21 April 2011 (UTC)

That sounds plausible to me. It would make sense for a device that has no backlight — you'll need to have it in light of some sort anyway, so a mirror backing is a clever way to deal with the LCD lighting issue (like an old microscope). --Mr.98 (talk) 18:54, 21 April 2011 (UTC)

Thanks for the responses! I guess I'd never put much thought to exactly how a normal Liquid crystal display works either; it's pretty fascinating too. In reply to APL above, I would guess that a watch (or similar device, such as a calculator) which used "mirror" instead of black would be rather difficult to read. On the Kindle, you can simply tell that "stuff's there" on the LCD line; more detailed information would likely become difficult to parse, if it were mirror on gray. Although perhaps not mirror on black, come to think of it. I wonder why Amazon didn't go with that instead… ± Lenoxus (" *** ") 23:53, 21 April 2011 (UTC)

unknown herb

Hi, does anyone know the name of this herb: http://img816.imageshack.us/i/photo1jd.jpg/ 84.228.108.151 (talk) 11:24, 21 April 2011 (UTC)

Perhaps some variety of thyme? Note the the variety of thyme foliage, e.g. [2]. Aside from visual ID, you can taste / smell a few crushed leaves, and compare to any known herbs you may have in your kitchen. SemanticMantis (talk) 14:02, 21 April 2011 (UTC)

Looks more like a variety of mint to me. --ColinFine (talk) 16:13, 21 April 2011 (UTC)

Hard to tell from the picture, but mint (or something in the same family like basil or catnip) will have stems with square cross sections. That said, it looks very much like the pot of marjoram I have. (Marjoram smells something like a cross between thyme and oregano.) - Actually, following links tell me that thyme, marjoram, and oregano are also included in Lamiaceae, the mint family. Checking the pot, marjoram does indeed have a square stem cross section (only noticeable on the larger stems). -- 174.31.219.218 (talk) 16:27, 21 April 2011 (UTC)

Glow discharge creation

Whats the best way of creating a glow discharge betweem 2 parallel wires, and would it be better if one or both of the wires had a circular cross section?--92.29.203.164 (talk) 11:37, 21 April 2011 (UTC)

Besides the article you cited, see also Geissler tube and Neon sign. A glass vessel filled with low pressure gas of the appropriate sort and sufficient voltage (AC or DC) to produce ionization, with a resistor to prevent excess current when the gas starts to conduct, with airtight seal for the leads. The voltage to produce a discharge between electrodes decreases as the gas pressure is reduced down to some low pressure, below which the required voltage increases. A neon lamp presents a very high resistance until the voltage is high enough to ionize the gas. One demo was to have a high voltage battery in an RC circuit, which would gradually charge the cap until the conduction voltage was reached, at which point the neon light would flash. Do you have a vacuum pump and glassblowing equipment? I have pondered using a kitchen vacuum food preservation pump, with the plastic jars they supply, and sealing the electrodes through the lid with aquarium seal. This would not work for a long term use such as a a commercial neon sign, but might be ok for a demo or experiment. I would avoid using glass jars due to the danger of implosion and shards flying, and any high voltage has the potential to produce a dangerous shock. Old books on the subject suggest using mercury to pull a vacuum in the tube, which would be considered too dangerous for amateur experimentation now. A discharge tube under some circumstances might put out dangerous xrays, so home experimentation is not a good idea. An old reference on the subject is Townsend, "Electricity in Gases," (1915). The classic Geissler tubes used electrodes at either end of a cylinder or other shape of evacuated tube with a residue of gas. Your question was about parallel wires. We see that configuration in the common NE-2 neon lamp It ionized at about 90 volts. They can be used for lots of interesting projects. See [3] in particular.Edison (talk) 19:19, 21 April 2011 (UTC)

Oh, you're so punny... --Jayron32 19:51, 21 April 2011 (UTC)

I typed "potential" in all innocence and only on rereading noted the pun, so went ahead and bolded it. Edison (talk) 20:08, 21 April 2011 (UTC)

As for circular cross section: at least for high voltage conductors in air, a conductor with a large cross section and no sharp edges is less prone to cause ionization of the gas molecules in the air, and less corona discharge. For a gas discharge tube, the same is likely to be true. I would expect parallel small diameter wires to cause ionization of the trace gas at a lower voltage than larger radius conductors the same distance apart. A sharp edge might concentrate the current and cause more local heating if the current is larger. This is just my expectation, and I have not found a reference on it. Edison (talk) 00:20, 22 April 2011 (UTC)

Where have the "edit" buttons per section gone?

Normally there should be an "[edit]" button with each section. I don't see any any more. I have reloaded about 10 times now. What's wrong? 93.132.132.156 (talk) 21:37, 21 April 2011 (UTC)

They're right where they've always been for me. But I don't see how this is a science question... Dismas|^(talk) 21:39, 21 April 2011 (UTC)

Because I missed them here on this desk, I posed the question here. Why should this not be a science question? is computer science less a science? 93.132.132.156 (talk) 21:43, 21 April 2011 (UTC)

Normally computing questions go on the computing desk. But then again, normally questions about how Wikipedia works should go at the Help Desk. Anyway, it's possible that your CSS or something got messed up, or what Wikipedia just had a hiccup for you. If it's better now, I wouldn't worry about it. --Mr.98 (talk) 22:32, 21 April 2011 (UTC)

(ec) And now I have edit buttons. Do I have to ask a question first in order to see them? Doesn't make much sense. And I haven't altered anything with my browser or computer lately. 93.132.132.156 (talk) 21:43, 21 April 2011 (UTC)

Usually when that happens to me, I'm actually looking at a version from the page history. Those have a notice at the top that you're editing an old version, but on a long page like this you never notice. Wnt (talk) 22:34, 21 April 2011 (UTC)

At the top of the page, did you see the 'edit' tab or a 'view source' tab? If it's the later, it's been discussed before on the talk page and I've encountered it myself that for some strange reason the page appears as protected for anonymous users even though it was never (semi-)protected. Note that when reloading a page you should always try WP:BYC and probably even WP:PURGE since reloading 10 times is no use if your browser or the wikipedia servers just keep sending you the same cached content Nil Einne (talk) 23:54, 21 April 2011 (UTC)

It looks like a case for WP:PURGE. I saw 'view source' instead of 'edit' at the top. After I asked this question (instead of a null edit) it went away. Perhaps you know a workaround for yet another plague: lately some of the formulas display with an incomplete (west north) border that gives the impression of a square root. 95.112.196.91 (talk) 14:31, 22 April 2011 (UTC)

Cookie Monster ate them. Count Iblis (talk) 22:52, 21 April 2011 (UTC)

Same thing happened to me man. All the edit links are gone! When I logged in, they appeared, so this must be part of the movement to disenfranchise anonymous editors. Mac Davis (talk) 01:32, 22 April 2011 (UTC)

"Semi-protection" might do that for other pages, but the Science Refdesk isn't semi-protected, and according to the logs it hasn't been semi-protected, at least not any time this year. Wnt (talk) 06:47, 22 April 2011 (UTC)

See my comment above or check out the latest RD archive. Nil Einne (talk) 14:15, 22 April 2011 (UTC)

Digital signals in space

Analogue signals are broadcast out into space, and any aliens out there within 60 light years will be receiving them and can see/hear what we are like!:

1. would an alien civilisation be able to see/hear them in the same way as they could with the analogue signals, or would they not be able to decipher them?

I looked around for an answer but couldn't find any, so I hope someone can answer this for me!

Regards, -- PhantomSteve.alt/talk\^{[alternative account of Phantomsteve]} 23:18, 21 April 2011 (UTC)

The answer to #1 is unambiguously yes. We can't stop electomagnetic signals generated on Earth from leaving the Earth. However, this signal tends to degrade over time, due to two things: attenuation and the inverse square law which basically states that as a signal travels over space, it "spreads out" and becomes gradually weaker to the point where it becomes so weak it disappears. The answer to #2 is that we're not even sure that an alien civilisation would be able to decode our analogue signals. In the novel and film Contact, an alien civilization beams some our own TV signals back at us. There is, however, no need for them to have decoded them; they could just have reflected the signals back at us. However, given point #1 I made above, its not readily clear that any signals that have been generated at earth would even make it to the nearest star, let alone be able to be decoded... --Jayron32 23:27, 21 April 2011 (UTC)

While it's impossible to know how aliens will think, I'd bet they can make sense out of an analog TV signal. The signal, after all, consists of raster lines which are similar from one to the next, yet differ... before long, they're putting them side by side and realizing it makes an image. They might not know which color is which - yet I'd give them even credit for that, because the observant alien will see occasional rainbow icons and substances such as magma that can only come in certain colors on any planet. I would likewise give them good odds of making sense out of a digital signal because it can be worked over to produce recognizable patterns. I don't know if they'll work out the AACS key, but I wouldn't put it past them. ;) Wnt (talk) 23:52, 21 April 2011 (UTC)

Is that for when they land and take away some Blurays? AACS isn't used in broadcast television or anything but Blurays and the now defunct HD-DVDs AFAIK. Of course smarters aliens would just find it online. Nil Einne (talk) 00:01, 22 April 2011 (UTC)

They probably have a radio telescope made from a network of single-atom filaments, the size of the solar system. It zeroes in and logs every time Earthlings make a cell phone call, play a video, type anything that appears on a computer screen that isn't secured against Van Eck phreaking, or talk somewhere in the open within a hundred yards of a power line. They're supposed to be advanced - they're aliens. And how do you think they made this simulation you're enjoying now if they couldn't properly spy on EM signals? Wnt (talk) 06:53, 22 April 2011 (UTC)

That aliens would be able to figure out that analog TV signals, when arranged a certain way make images than can be "seen" assumes that aliens have vision and are able to see images like we do. Vision is not uncommon for Earthly species, but even here there are alternate ways of "seeing"--like echolocation. For all we know the first aliens to intercept Earthly TV signals live gas giants and "see" via magnetic fields or something similarly unlike human vision. Or perhaps they "see" some aspect of reality we don't even know exists and can't perceive light at all. The idea of aliens with eyes similar to ours strikes me as very unlikely. Seems they'd be as likely to know about Jesus Christ and hot dogs. Perhaps intelligent aliens capable of abstract thought might recognize TV signals as a curious pattern, and perhaps could figure out how to decode the signal into what we would call images. But it seems to me a huge assumption to think they would "see" the images in a way that made any sense, if they could "see" at all. The common stereotypical "alien" we picture is ridiculous anthropomorphic. I wouldn't be surprised if there are sentient aliens out there, but I would be very surprised if they were remotely similar to us--that we would even be able to recognize them as sentient beings at all (and vice versa). Even on our planet we have trouble recognizing sentience or lack thereof among birds, cetaceans, etc etc etc. Pfly (talk) 09:52, 22 April 2011 (UTC)

The eye has evolved almost from scratch many times on Earth. The mammalian eye, the cephalopod eye, the insect compound eye and numerous others each evolved separately (our common ancestor may have had some kind of light sensitive cells, but not a specific eye). That suggests an extremely strong and near-universal selection pressure toward vision. If so many different animals have evolved eyes on Earth, it is highly likely that any life-as-we-know-it on other planets will have eyes too. (Life-as-we-don't-know-it is a very different kettle of fish, and not one we can have any useful discussions about. We just don't have a starting point to understand how such life would work.) --Tango (talk) 13:48, 22 April 2011 (UTC)

As others have mentioned, typical early TV signals will be quite weak by now, but we have occasionally sent radio messages into space at much higher power, with the explicit intent of catching someone's attention. See e.g. the Arecibo_message. Note that in this message, as in the Voyager_Golden_Record, scientists have taken great care to encode the message in terms that are thought to be fairly universal. SemanticMantis (talk) 01:23, 22 April 2011 (UTC)

I would be very surprised if a human seeing the Arecibo message in isolation would be able to interpret it. It's just looks cool. That was the whole purpose of it. If it was actually intended to catch someone's attention, they would have made it much simpler and send it towards a nearby yellow dwarf star. Instead, they made it very complicated and sent it towards a very distant cluster. As our article says, it was just a demonstration of their cool new toy, not a real attempt at making contact with aliens. --Tango (talk) 13:48, 22 April 2011 (UTC)

But by sending it to M13, the signal arrives at all the few hundred thousand stars it is composed of. Count Iblis (talk) 14:54, 22 April 2011 (UTC)

That would be true if they had sent it to M13. They actually sent to where M13 was 25,000 years ago. They should have sent it to where M13 will be in 25,000 years time. Our articles explains this (with references to official press releases - they were perfectly open about the whole thing). --Tango (talk) 15:30, 22 April 2011 (UTC)

I see! This looks rather stupid :) . In Ref 1. where that fact is mentioned it is also clamied that the signal could still be received with similar equipment in M31. If that were to happen, ET would also get the message of just how stupid we are :) . Count Iblis (talk) 16:10, 22 April 2011 (UTC)

Yes, I agree it would be difficult for any single human to decode, and that it was a somewhat symbolic gesture (voyager record even more so). However, if the Arecibo message were given to a room of scientists that were well-educated (but ignorant of this message), I think they could decode it, given a little time and motivation. I believe decoding the Arecibo message or Voyager record would be easier than decoding a TV signal (assuming you could find the properly educated group of scientists with no prior knowledge), but this is potentially debatable. SemanticMantis (talk) 15:17, 22 April 2011 (UTC)

The issue is whether there is a single interpretation that makes more sense that any other. Figuring out the binary should be easy enough, but then why would you interpret the numbers as atomic numbers of elements rather than any number of other things? With a TV signal, there's really only one interpretation that makes sense. It may take a while to stumble across it, but once you have you'll know you've got it right. --Tango (talk) 15:30, 22 April 2011 (UTC)

Advanced civilizations will likely be machine civilizations. Now, intelligent machines can travel at the speed of light, simply by uploading themselves via electromagnetic signals to another machine. That's easy to do within one civilization, but then they can only travel to locations where they have build their machines. However, by contacting distant civilizations, they can travel to those civilizations, if these civilizations are able to download and run the code of the machines.

So, you can imagine that a civilization sends a simple message to catch the attention of other civilizations and then that message is followed by a message containing a schematic outline of a machine so that it is clear how a machine code is to be interpreted. Then the entire code of a machine is sent. This whole sequence of sending the simple message, the message containing information on how to interpret the code and then the code itself is then repeated over and over again.

Civilizations that receive this message do not send a reply, as no reply is expected. All they have to do is build a suitable machine, download the code and run it on the machine. Count Iblis (talk) 16:59, 22 April 2011 (UTC)

What do you mean by "machine"? Any lifeform is a machine, in a sense, but I don't see any reason why organic life forms can't form an advanced civilisation. The idea of mind uploading for interstellar travel isn't a new one, but trying to give instructions on how to build the receiving device to a completely alien civilisation by remote (especially without two-way communication) seems ridiculously difficult to me. --Tango (talk) 19:22, 22 April 2011 (UTC)

Consider our own future. The free market economy has a natural end point. When all human involvement in all production processes from raw materials to finished end product is fully automized, everything will be free of charge (while labor cost only form part of the costs of a product, the costs of raw materials, energy etc. are ultimately also due to labor costs.). In that end state you'll have humans living in a planned economy. Free enterprise will be outlawed, because you don't want out of control growth of machines, like in the grey goo-scenario. Humans are then more or less barred from doing anything productive. Only an elite will be in control of things. But that elite will find it more and more difficult to control things as the civilization becomes more complex.

As the machines get more complicated, the elite need ever more intelligent machines to control things, but then these intelligent machines will, at some point, be so much more intelligent than humans, that the elite won't really control anything at all. Humans will then be prisoners of the machines, much like most animals on Earth are now. Freedom is only tolerated up to a point: as soon as a wild animal interferes with our civilization (e.g. when a lion shows up in a city, claiming the teritory there, we remove the lion). Count Iblis (talk) 20:41, 22 April 2011 (UTC)

Man, CI, sad much? Maybe you need to take a day off and go walk in the sunshine? The doomsters have been around forever, but the world remains a good place. --Trovatore (talk) 06:49, 24 April 2011 (UTC)

You seem to have forgotten about the service economy. In the developed world, agriculture and industry are becoming smaller and smaller portions of the economy and more and more people work in providing services to others, not producing physical things. As some services become automated or obsolete, others become common. That's the trend that's been going on for the last 100 years and I see now reason why it won't continue. --Tango (talk) 21:09, 22 April 2011 (UTC)

You're all making great points, but isn't this straying into forum/soapbox/opinion? Are you editors any longer contributing to a cogent answer to the OP, or just musing now? Franamax (talk) 22:06, 22 April 2011 (UTC)

April 22

What's the species?

Hi. Could someone help me in finding the species of this lizard? I took this photograph last week at the Horton Plains National Park, somewhere near the summit of the Kirigalpoththa mountain, in Sri Lanka. Rehman 01:39, 22 April 2011 (UTC)

Claiming no expertise in this at all, I looked at "Reptiles of Sri Lanka" and decided it looked like one of the Agamidae and not the other groups they list (I was assuming since this is a tourist snap that it's not a very rare species). Among the Agamidae are horned lizards Ceratophora. Searching for these, I found a "Ceratophora stoddartii" (last photo at [4]) which looks a lot like yours to my eye. Caveat: most of the images on a Google image search for this species don't look much like it and are all different colors. I've made no attempt to determine if that is chameleonlike change of color, genetic variation, iridescence, etc. Wnt (talk) 06:43, 22 April 2011 (UTC)

Thanks! After referring to srilankanreptiles.com you mentioned above, I am pretty sure it is the Rhino-horned lizard. Thanks again. Regards. Rehman 07:45, 22 April 2011 (UTC)

potentiometer question

Can a potentiometer that is designed for a tone control (i.e. bass or treble) work properly when used for a regular volume control? Bubba73 ^{You talkin' to me?} 05:25, 22 April 2011 (UTC)

Perhaps. The replacement potentiometer must of course have the same max resistance as the original pot. The wattage rating also has to be high enough, but that’s probably not going to be a problem.

Looking around at a few tone control circuits, I see that the first couple I looked at at least called for linear taper pots. In contrast, pots used for volume control, at least in more expensive devices, are sometimes logarithmic taper. But the difference isn't all that big of a deal; using a linear taper pot where a log taper pot is called for just means that there'll be a bigger perceived change in volume for the same angle change at one end of the dial than the other. But cheap devices generally go ahead and use the cheaper linear taper pots for volume control anyway, so the difference between a linear taper pot and a log taper pot really isn't anywhere near as important as just making sure the replacement pot has the same max resistance as the original pot.

There are a couple contributors here who can run circles around me at EE, so if anybody pipes in to disagree with what I've said above, listen to them instead of me. Red Act (talk) 07:29, 22 April 2011 (UTC)

ELECTRONICS

How an FM transmitter & receiver is designed27.97.64.66 (talk) 08:32, 22 April 2011 (UTC)

They are rather complicated. Have you read transmitter and receiver? Those articles will get you started.--Shantavira|^{feed me} 11:24, 22 April 2011 (UTC)

I feel the OP is more interested in some kind of circuit diagram, something like that. As wikipedia is not a HOWTO, such things are only found externally. 95.112.196.91 (talk) 13:17, 22 April 2011 (UTC)

marsh plant that needs pressure from flowing water to hold structure?

Has anyone heard about such a plant? A friend told me about it years ago - maybe from the northern parts of Australia? - she described it as having a porous or open lower end - the water flows up into it and gives it structure through hydrostatic pressure... Can someone name the plant for me? Thanks Adambrowne666 (talk) 10:00, 22 April 2011 (UTC)

Indian Thundershowers

Does anyone know why Southern India gets thunderstorms during April, but normal showers during Monsoon (July-October)? Yes Michael? •^Talk 11:41, 22 April 2011 (UTC)

What does the word "Pinkie" mean?

The word "Pinkie" is used in terms like "Pinkie finger" and "Pinkie blue"? What is the meaning of the word "Pinkie"? aniketnik 12:06, 22 April 2011 (UTC) — Preceding unsigned comment added by Aniketnik (talk • contribs)

The "pinky" or "pinkie" is the little finger. Gandalf61 (talk) 12:11, 22 April 2011 (UTC)

If you follow the little finger link, you'll find that the "pinky" in "pinky finger" is listed as being from the Dutch word pink, ultimately from a Proto-Indo-European word for "five", "finger". Note that this seems to be unrelated to "pink", the word for the color, as that is listed as being derived from "pinks", a name for Dianthus (carnations), a name referring to the frilled edge of the flower and probably deriving from the German "pinken", to peck. This latter meaning is also seen in the name "pinking shears". -- 174.31.219.218 (talk) 15:41, 22 April 2011 (UTC)

From Wiktionary it's apparent this root also leads to finger, cinco, quintet etc. Wnt (talk) 21:02, 22 April 2011 (UTC)

What connections should scientists explore?

How do scientists decide which variable could correlate? If some crackpot theorist claims that certain stones cure cancer, should scientists go on and test it empirically? Should scientists dismiss intuitively some claims? Quest09 (talk) 13:29, 22 April 2011 (UTC)

In an ideal world, scientists would test everything (with a few exceptions due to ethical concerns, perhaps). In the real world, there are limited resources so scientists test those things that they think are most likely to give an interesting result (of course, what's interesting to a scientist isn't necessary what would be interesting to everybody else!). For medicine in particular, the normal route is to test things in Petri dishes first, which is fairly easy so they can test all kinds of things, and then only test on real people those things that showed promise in the Petri dish. So, they may well test stones on cancer cells in a Petri dish, but unless they actually seemed to work, they wouldn't test them on people. --Tango (talk) 13:57, 22 April 2011 (UTC)

I could play devil's advocate for a moment and note that some therapies – particularly non-drug interventions – are not always amenable to in vitro testing. While I would be unsurprised to discover that therapeutic touch and magic rocks have no ability to slow the growth of malignant cells in culture, I have to admit that it's also difficult to maintain a regimen of healthy diet and aerobic exercise in a petri dish.

Testing a novel protocol in humans depends primarily on three things. First, you need to find a researcher who wants to do the trial; often that means that they believe the trial will work, but someone who's genuinely curious or who is interested in debunking a bad idea will do. Second, you need to be able to get ethics approval to carry out the trial. An ethical clinician can't and won't participate in a trial if they have a reasonable expectation that the experimental therapy will have a worse outcome than the current therapy (see also clinical equipoise). Third, you need to have the resources – trained medical personnel, equipment, magic rocks, and most importantly, willing and informed patient participants – to carry out the trial. In general, this means it is impossible to do a trial of magic rocks versus chemotherapy, because the experimental therapy isn't supported by any evidence and is likely to kill patients. On the other hand, one might be able to do a trial of magic rocks plus chemo versus chemo alone (or, better, chemo plus blinded 'placebo' rocks); the worst-case scenario is anticipated to be that the rocks are ineffective, so the patients do no worse than with chemo alone. The hard part is finding resources to do the trial, since there are many more plausible treatments ahead of the magic rocks in the queue for funding. TenOfAllTrades(talk) 15:29, 22 April 2011 (UTC)

A problem with doing not well motivated tests is that this tends to lead to a bias where only positive results are reported. Suppose you have good theoretical reasons to believe that X may cause Y (but it is not clear that this must be the case). Then you investigate this and you find that in fact X doies not cause Y. This result is then still interesting enough for peer reviewed journals to publish.

But without any good reason to believe that X may cause Y, a negative result wont merit publication in a peer reviewed journal. Now, suppose that in such a case, you find a positive result at 95% significance level and that in reality this is due to chance alone (so no relation exists and you just happen to be in the 1/20 of cases where you find a significant result). Then that is likely to yield a publication in a peer reviewed journal. Certainly, it is now interesting for other researchers to see if X really does cause Y. But this may take time, and all that the public hears is that: "researchers have found that X causes Y". Also, onses the results come in that debunk the relation, these don't make headline news.

This effect is partially to blame for the paranoia about mobile phones causing cancer, mobile phone relay transmitters near building being involved in all sorts of illnesses, GM foods possibly not being safe etc. etc. etc. Count Iblis (talk) 14:47, 22 April 2011 (UTC)

As usual, there is an all-too-close-to-reality xkcd on this topic. Don't forget to read the mouseover text. TenOfAllTrades(talk) 14:54, 22 April 2011 (UTC)

And for a more serious treatment, see also publication bias, including the bit about the 'file drawer effect'. TenOfAllTrades(talk) 14:56, 22 April 2011 (UTC)

There is no one prescription that describes how scientists do or should approach the question of what areas would be fruitful or interesting. In practice it is almost certainly about who is willing to fund what — all of these things cost money, and finding creative ways to justify a project to a sponsor is a full-time occupation of many PIs. Even the philosophers of science who believe in strict demarcation, like Karl Popper, do not believe that you can apply that kind of criteria to the sources of inspiration or interest, which are often haphazard (e.g., at the extreme end, dreams, hallucinations, falling fruit). The question is perhaps more systematically stated as to what studies should be funded — which is a trickier question that balances likelihood of success, benefits from success, reputation of researcher, things like that. --Mr.98 (talk) 15:40, 22 April 2011 (UTC)

What do you mean by "success"? A study that shows a null result conclusively is just as successful as one that shows a positive result conclusively, in my opinion. --Tango (talk) 16:31, 22 April 2011 (UTC)

Scientifically, yes, but economically, no. That is, most studies are funded in the hope of eventually making money off them. Finding that a (patentable) drug works well may lead to economic success, while finding that one doesn't work isn't as likely to do so. The economics behind science can lead to both a poor choice of studies and, even worse, biased results. Finding a neutral source of funding is difficult, though. Government funding (from taxpayer dollars) of university research may be less profit-motivated, and thus allow studies of things like herbal remedies and traditional Chinese medicine, where profit potential is limited. Political considerations may come into play there, though, such as prohibiting any research on the benefits of stem cells. Use of charitable donations is another option, but major contributors may also have agendas they wish to purse. StuRat (talk) 19:22, 22 April 2011 (UTC)

Proving, based on currently accepted principles, that something (say, a perpetuum mobile) is impossible saves a real lot of money and effort. The major back-draw is that the poor guy who publishes such a result gets nothing in return but the hatred of those who hoped for funds for investigation and building one. 95.112.196.91 (talk) 20:45, 22 April 2011 (UTC)

"Success" would be defined differently in different contexts. I'm not trying to claim one standard for it. Proving a null result conclusively is only "successful" in some contexts, not all. Proving that unicorns don't exist on the moon conclusively would do little to benefit scientific knowledge. Proving that there is no luminiferous aether in the early 20th century did. --Mr.98 (talk) 20:48, 22 April 2011 (UTC)

Thomas Kuhn's work deals extensively with this question. See Paradigm shift for information on his work. In essence his idea is that, contrary to the traditional idea that "ideally" scientists should treat all hypotheses equally, in fact scientists work within a model he called a paradigm, which guides their evaluation of which hypotheses are worth exploring. Hypotheses that make sense within the currently accepted paradigm are investigated, and various forms of peer pressure strongly discourage investigation of hypotheses that fall outside the current paradigm. The paradigm changes infrequently; perhaps every several generations. Paradigm shifts are usually a dramatic change rather than a gradual evolution.

This selection of hypothesis is, Kuhn argues, essential for science to work. The transition from prescientific research (e.g. alchemy) to true science (e.g. chemistry) is marked by the creation of the first paradigm for that field.--Srleffler (talk) 17:02, 25 April 2011 (UTC)

See also The Structure of Scientific Revolutions.--Srleffler (talk) 17:03, 25 April 2011 (UTC)

Reaction Gone Wrong

Hello. When I mix KI, HCl, and starch, my solution turns blue without adding any KIO₃. Why? Thanks in advance. --Mayfare (talk) 15:33, 22 April 2011 (UTC)

Are you sure your original KI was pure enough not to contain any I₂ impurities? 95.112.196.91 (talk) 15:49, 22 April 2011 (UTC)

The KI is pure enough not to contain any I₂. --Mayfare (talk) 20:40, 22 April 2011 (UTC)

Potassium iodide in the first paragraph states that "Aged and impure samples are yellow because of aerial oxidation of the iodide to iodine". Did you try your KI to the starch without HCl? I have no idea how sensitive the starch test is but I remember my wild days when I did some testing for iron and always got false positive until I found out that the test is so sensitive that it gives positive results on the little iron that is contained in the tap water used. 95.112.196.91 (talk) 20:53, 22 April 2011 (UTC)

can a relativistic proton change into a neutron? or break up into various particles?

Are these processes possible? They seem possible to me, if the proton has enough energy ... but can kinetic energy transfer into the weak or the strong interactions?

1. highly energised proton ---> neutron + positron + e-antineutrino
2. neutrino + highly energised proton ---> neutron + positron
3. proton ----> pion+ + positron + electron

John Riemann Soong (talk) 17:41, 22 April 2011 (UTC)

The principle of relativity implies that the internal structure of the proton does not change when the proton is moving. Just imagine the situation from the point of view of the proton: the proton thinks that it is at rest and that you are moving. Since there is no absolute motion there is no absolute "energisation" through kinetic energy and the proton doesn't care whether its moving in your frame of reference or not; if it doesn't decay in its own reference frame, it will not decay in yours either. --Wrongfilter (talk) 17:56, 22 April 2011 (UTC)

Why is this different for electron states then? The kinetic energy of a reactant is important in whether it overcomes a barrioer or not, e.g. there's a transition temperature in which singlet oxygen will be the dominant species over triplet oxygen. -- John Riemann Soong (talk) 21:25, 22 April 2011 (UTC)

I've taken the liberty of formatting your question so it renders properly. (Line-breaks are ignored in wiki-syntax). #1 is Positron emission; #2 is beta decay, with the anti-neutrino written "backwards," and I don't recognize #3. Nimur (talk) 18:26, 22 April 2011 (UTC)

Positron emission and beta (plus) decay are the same thing. 1 and 2 are the same formula, except that 2 assumes the existence of a neutrino that annihilates the antineutrino. 3 looks like nonsense to me. The positron and electron can just annihilate each other, so you have a proton changing into a pion+, which is equivalent to an up quark and a down quark changing into a single anti-down quark. I can't see any reason to believe that could ever happen. --Tango (talk) 18:49, 22 April 2011 (UTC)

Your first two reactions don't conserve lepton number. You can fix that by swapping the antineutrino with the neutrino.

The first reaction (decay) can't happen because the principle of relativity says it's physically the same as the decay of a proton at rest. In the second case the frame-independent properties of the input include a single relative velocity, and the reaction can happen if that is large enough.

Your third reaction (decay) isn't prevented by conservation of energy, because the total rest mass of a pion and two electrons is smaller than the proton rest mass. But it doesn't conserve baryon number, and more strongly, it doesn't conserve B − L. Decays that change the baryon number but not B−L, such as
p⁺
→
π⁺
+
ν
_e, are allowed by grand unified theories but have never been observed. In any case, the proton's speed makes no difference, because these theories still obey the principle of relativity. -- BenRG (talk) 21:28, 22 April 2011 (UTC)

What about the case of electronic transitions? Can't a highly kinetically energised hydrogen atom excite its shell electron? (Isn't that what happens in a plasma?) How is this different from an energetic proton exciting one of its quarks? Also, isn't it possible under a strong electric or gravitational field, to breakup a moving nucleus or a moving nucleon by tidal forces? John Riemann Soong (talk) 22:15, 22 April 2011 (UTC)

You're right, a proton excited state can decay to neutron + positron + neutrino. We all assumed you were talking about overall kinetic energy of the proton. This decay is probably also possible in a background electromagnetic field, although additional particles are involved then, so it's not exactly a decay. I see no reason why gravitational tidal forces couldn't break a proton apart, but that's not an experiment we can do, and nobody really understands quantum gravity. -- BenRG (talk) 23:12, 22 April 2011 (UTC)

But in electronic transitions, mere temperature alone provides the kinetic energy that supplies the activation energy to excite an excited electronic state. John Riemann Soong (talk) 06:35, 23 April 2011 (UTC)

Yes, but that happens because the oxygen molecules are colliding with each other allowing the kinetic energy to be released in the transition you describe. If a oxygen molecule is flying at high speed by itself and doesn't collide with anything else, the transition won't happen. Dauto (talk) 18:07, 23 April 2011 (UTC)

What kind of flowering tree?

I took this photo on 10 April at 39°48′44″N 86°12′9″W. Can anyone identify the species of the trees in this picture? All I can guess is that they're way too big for apples or cherries, and definitely the wrong shape and size and color for redbuds; I don't know what any other kind of tree flower looks like. Nyttend (talk) 19:57, 22 April 2011 (UTC)

I'm guessing dogwood. Looie496 (talk) 20:11, 22 April 2011 (UTC)

Dogwoods tend to be more rounded or slightly flattened. I think it might be a fastigiate pear like this. Obviously the trees are much older than the example, as one can see from the bark which has the cracked and flaky appearance of an old pear tree. Richard Avery (talk) 21:51, 22 April 2011 (UTC)

The species that you linked as "this" is Callery Pear, which sounds right: it's one of the most common ornamental trees in North America. Thanks for the help. Nyttend (talk) 23:03, 22 April 2011 (UTC)

Ornamental pears are excedingly common in the U.S. because they are super cheap and super fast growing, so builders often put them in all over the place. My neighborhood has one in front of just about every house. It would not be uncommon at all. Callery pears, cited above, are often called "Bradford Pears" or "Cleveland Pears" in the U.S., and have a distinctive odor when in bloom, reminiscient of ammonia or old fish; if you've got hundreds in one area it can be overwhelming. --Jayron32 02:44, 23 April 2011 (UTC)

Fission2

I asked a question about binding energy above and now am more confused than before, and feel like an idiot. Please explain the defect in my understanding:

In the nuclear fission of uranium, about 1/10th of 1% of the mass of the nucleus is converted to energy. (I added this information myself in this edit, quoting a 1950 article from the Bulletin of the Atomic Scientists.) That's super. However, our binding energy article, our nuclear fission article, our E=mc2 article, and the responses of knowledgeable editors to my previous question all agree that the masses of the fission products add up to a higher mass than the mass of the original uranium atom.

Some crucial part of this is clearly sailing about a foot above my head. If a uranium atom is in an imaginary box and the atom fissions, and the resulting gamma rays are allowed to escape the box but the fission products (say, krypton and barium) stay in the box, the contents of that box must be lighter, by the mass of the gamma rays. But, contradicting this understanding, all the information above informs me that the krypton and barium have a greater mass combined than the original uranium atom. The box is now heavier. Huh?

Your idiot,

Comet Tuttle (talk) 21:15, 22 April 2011 (UTC)

To give an example ²³⁵U + n -> ⁹²Kr + ¹⁴¹Ba + 3 n.

I get that the rest masses in amu are 235.044 + 1.009 -> 91.926 + 140.914 + 3*1.009

Which gives 236.053 -> 235.867, a mass loss of 0.186 amu (0.08% of the initial uranium mass).

Does that clarify things? Dragons flight (talk) 21:37, 22 April 2011 (UTC)

Yes; this is great; but see below. Comet Tuttle (talk) 22:08, 22 April 2011 (UTC)

If energy is released by a reaction then the total rest mass of the products is smaller than the total rest mass of the inputs; you're quite right about that. I don't think anybody said otherwise in the previous thread. It's confusing because of inconsistent use of the word "smaller" with negative numbers, as I said there. (But rest masses are never negative, so there's no ambiguity in what I said here.) -- BenRG (talk) 21:44, 22 April 2011 (UTC)

TenOfAllTrades wrote: "the atomic nucleus will always have a slightly lower mass than the sum of the masses of its constituent particles." (I'm not challenging him or her here because the same thing is echoed in the articles I cited above in this thread.) Wouldn't that mean atomic fission is endothermic, contradicting my imaginary box mass statements and reality? Comet Tuttle (talk) 22:08, 22 April 2011 (UTC)

Those "constituent particles" are the nucleons. Splitting a nucleus into individual nucleons does always consume energy (unless it's ¹H); therefore, creating a nucleus from nucleons releases energy. If you build two smaller nuclei using nucleons obtained from a big nucleus, you may release more energy than you spent breaking the larger nucleus apart. -- BenRG (talk) 22:24, 22 April 2011 (UTC)

Ahhhhhh! — so in Binding energy, in the line stating "Classically a bound system is at a lower energy level than its unbound constituents, its mass must be less than the total mass of its unbound constituents", by "constituents" it means to say "individual nucleons"? I had taken "constituents" to mean "any combination of smaller nuclei", so a barium nucleus and a krypton nucleus would count as "constituents" of the uranium nucleus and when added up, their masses had to add up to be greater than the uranium nucleus's mass. Comet Tuttle (talk) 22:46, 22 April 2011 (UTC)

Yep, that's the ticket. The binding energy is calculated relative to the completely disassembled nucleus: individual, separated protons and neutrons. TenOfAllTrades(talk) 23:25, 22 April 2011 (UTC)

"Individual nucleons" would be too narrow a definition of "constituents" to use in the binding energy article. In fact, I disagree with the sentence you quoted. It may be true when you take "constituents" to mean "nucleons", but there's no deep reason why it has to be true even in that case. In quantum mechanics, any system that can decay into components with a lower total rest mass will eventually do so, but the decay half life can be extremely large, like 10²⁰ years or more. Even a free neutron's 15-minute half lifeone second is incredibly long compared to the usual time scale of nuclear physics, which is attoseconds or less. It's reasonable to call these bound systems, and physicists do call them that. -- BenRG (talk) 05:22, 23 April 2011 (UTC)

I don't see that it's unreasonable to consider the individual nucleons as the specific "constituents" of a nucleus. If one were to ask what a uranium nucleus' constituents were, one would not expect 'krypton and barium nuclei, of course' as a response. The heavy nucleus doesn't exist with smaller nuclei as independent bound components within it. (Similarly, one wouldn't say that the "constituents" of trees are framing lumber, tongue depressors, and sawdust, even though those could be one valid set of 'fission products'.) TenOfAllTrades(talk) 17:24, 23 April 2011 (UTC)

I think I phrased it badly. What I meant to say is (1) the binding energy article can't reasonably define "constituents" as "nucleons" (that wouldn't make sense for gravitational binding energy, etc.), (2) I disagree with the idea that it's essential to the nature of a bound system that there's a net energy cost to separating the parts. There has to be an up-front energy cost (i.e., a potential barrier), but it's okay if you subsequently get back more energy than you put in. In a hypothetical world where the nuclear binding energy was positive, all nuclei except ¹H would be technically unstable, but their half-lives could still be long enough to make them stable for practical purposes. I used the free neutron half life only as an example of a long time and forgot that it's a bad example of "splitting into constituents", so I struck that out. -- BenRG (talk) 19:16, 23 April 2011 (UTC)

Nuclear binding energy is positive when you look at when nuclei are built up, say, when energy is released by p-p fusion in the sun. But it is negative in the sense that when you look at the resulting nucleus you get, this energy has gone away, and the net mass of the complete nucleus is lower than the net mass of the protons and neutrons that went into it. You can't split the nucleus back up again - at least, not all the way back to protons and neutrons - without getting energy from somewhere. This is true for any element (except ¹H...) because if the binding energy were positive, the nucleus could emit energy as it blew itself apart, and there would be no barrier to doing so. (Well, the extended periodic table talks about elements over maybe 173 that can't exist, but we haven't seen those. ;) )

Something that may shed some light on this: Nuclei heavier than iron release energy when they undergo nuclear fission. Nuclei lighter than iron do not. Instead, lighter nuclei release energy when undergoing nuclear fusion. Whether a fission reaction is exothermic or endothermic depends on the size of the nucleus and the size of the pieces. --Srleffler (talk) 17:19, 26 April 2011 (UTC)

April 23

Ibuprofen structure

What does the squiggly bond mean?

--75.40.204.106 (talk) 01:42, 23 April 2011 (UTC)

This is depicted in our article but that specific symbol depicts a bond that extends away from the observer. In this case, it is a bond linking a carbon adjacent to a carbonyl group (at right) and a methyl group represented by the end of that "squiggly" line (by convention, hydrogen atoms bound to carbon atoms are not shown). So, that methyl group is farther from the observer than the carbon to which it is attached. -- Scray (talk) 02:30, 23 April 2011 (UTC)

Actually, the squigly bond means that the structure is racemic. If the methyl group were going away from the viewer, it would be a "dashed" bond. A "wedge" bond is going towards the viewer. Racemic means that the actual medicine is a 50/50 mixture of both forms of the molecules. If the line is supposed to mean that it is going away, whoever created the picture used the wrong line. --Jayron32 02:36, 23 April 2011 (UTC)

Thanks for correcting me, Jayron32 - I was careless, thinking of the dashed bond! -- Scray (talk) 03:21, 23 April 2011 (UTC)

The main article about interpretting all the details of this sort of diagam is "Skeletal formula". DMacks (talk) 14:25, 23 April 2011 (UTC)

Perspiration

Why do some men of the same build and age, sweat more than others? —Preceding unsigned comment added by 74.100.193.38 (talk) 01:43, 23 April 2011 (UTC)

For the exact same reason that some men of the same build and age have different sounding voices or different colored eyes. The Wikipedia article titled Perspiration covers the process in more detail, as well as covering various conditions that can lead to increased or decreased perspiration. --Jayron32 02:40, 23 April 2011 (UTC)

how to pass entrance

SIR I AM A STUDENT OF 12 CLASS,HAVING SCIENCE ,OUGHT TO JOIN MEDICAL FIELD, MANY PEOPLE SAYS THAT IT IS DIFFICULT TO CLEAR THE ENTRENCE EXAM THEN WHAT SHOULD I HAVE TO DO. I M BELOGING TO NORMAL FAMILY HENCE CANT BE ABLE TO PAY LOTS OF COLLEGE FEE, i ought to join goverment college then what 2 do? PLEASE GUIDE ME I WILL PAY MY 100% TOWARDS UR ADVICE.... —Preceding unsigned comment added by 223.189.23.145 (talk) 02:47, 23 April 2011 (UTC)

• You need to tell us in what country you are interested in becoming a certified medical professional, and you would also need to say which medical job you want. After all, an American nurse is going to have a very different set of ceretifications and training than a Russian dentist is, and both will be very different from a South African doctor. Its literally impossible to answer your question without knowing where you are from and what your career aspirations are. --Jayron32 02:59, 23 April 2011 (UTC)

The IP geolocates to India.[5] Red Act (talk) 03:50, 23 April 2011 (UTC)

As a rule of thumb, an OP that addresses us as "Sir" is probably Indian. It's nice to be shown a little respect, rather than the insults and demands we get from some of our OPs! --Tango (talk) 13:09, 23 April 2011 (UTC)

To the original querant: It might help you to arrange a meeting with a local medical professional, to discuss options with them. If they take an interest they may be able to help you. You might also see whether they would allow you to work in their clinic. The experience with them may be very educational - in a practical way. -- Scray (talk) 03:25, 23 April 2011 (UTC)

Medical usually means Medicine.Curb Chain (talk) 11:33, 23 April 2011 (UTC)

Of course it does, but that doesn't necessary mean a doctor. The term can be used more generally to include nursing, dentistry, physiotherapy, nutrition, etc., etc., etc.. I expect the OP does want to become a doctor, though. --Tango (talk) 13:09, 23 April 2011 (UTC)

UHT milk in Greece

In Ultra-high-temperature processing, UHT milk's market share in Greece is only 0.9%.

The article says many northern European countries dislike UHT milk. I thought that Greece is in the south and it has very hot long summers. -- Toytoy (talk) 03:40, 23 April 2011 (UTC)

Do you have a question? That (poorly written and referenced) section also says "these figures conceal wide variations as in most European countries" whatever that means. If you can improve it please do so.--Shantavira|^{feed me} 11:07, 23 April 2011 (UTC)

According to the article "Pasteurization", there are two main types of modern pasteurization: flash pasteurization and ESL (extended shelf life) treatment. UHT is an alternative method of preparing the milk. Axl ¤ [Talk] 20:28, 23 April 2011 (UTC)

Shantavira's quote misses a key part of the sentence: "these figures conceal wide variations as in most European countries High Temperature/Short Time (HTST) pasteurized milk is more popular." Axl ¤ [Talk] 20:32, 23 April 2011 (UTC)

ELECTRONICS

How can we find out any faults in super hectrodyne radio receiver?please explain with the circuit diagramMathematics2011 (talk) 04:03, 23 April 2011 (UTC)

Radio frequency electronics can be very complicated; so it's impossible for us to diagnose every possible fault or error. Check for the usual sorts of things: are the DC bias voltages where you expect them at each stage? Have you accounted for RF parasitics? Depending on the frequency of your RF and IF, it may be impossible to diagnose you circuit unless you have a vector network analyzer (or at the very least an oscilloscope and spectrum analyzer). If you are in a poorly equipped lab, you can also use time domain reflectometry, which may be built in to your oscilloscope, or can be easily constructed from a waveform generator and a regular scope. We have a block-level diagram at Superheterodyne receiver, and each sub-element has its own article; but the circuit diagrams will vary widely based on the technologies available, the desired performance, specifications, and operating parameters. Nimur (talk) 18:05, 23 April 2011 (UTC)

You should not try to repair an AC powered device unless you are fully qualified by training and experience to follow all appropriate safety procedures. You will have to find your own circuit diagram, and a public library can provide you with books on radio circuit theory and troubleshooting. One popular troubleshooting method is signal injection, whereby a signal appropriate for a given stage is introduced from a signal generator. You could start with an audio signal in the final audio stage and work backward to the preamp stage, then inject a modulated radio frequency signal in the RF stages, working back to the antenna terminals. A complementary approach is signal tracing, where you use an oscilloscope or other probe to measure the amplitude and quality of signal at different stages. One good test is to make sure that each part of the circuit has the appropriate voltage. Your eyes can sometimes diagnose a burned out component, a poor solder joint or a short circuit. Your nose can sometimes aid in finding an overheated or burned out component. Sometimes tapping with an insulated probe can diagnose poor connections or microphonic tubes. In tube equipment, a tube tester or simple substitution of a good tube is useful. With the comparison method, you can compare the failed receiver at various points with a well functioning similar unit. In old radios, the filter capacitors often fail, resulting in hum and distortion. A blast of dry air from a can is useful in getting crud out of the tuning capacitor. Edison (talk) 20:00, 23 April 2011 (UTC)

top-antibottom mesons existance?

Do top-antibottom mesons exist, or does the short half-life of top/bottom quarks, and π⁺/D_s^{*+ mesons prevent them from forming? They are not listed on the list of mesons article. CS Miller (talk) 10:56, 23 April 2011 (UTC)}

Our article, top quark, says: "The Standard Model predicts its lifetime to be roughly 5×10⁻²⁵s. This is about 20 times shorter than the timescale for strong interactions, and therefore it does not form hadrons, giving physicists a unique opportunity to study a "bare" quark." So there aren't any hadrons, including mesons, that include top quarks. --Tango (talk) 13:42, 23 April 2011 (UTC)

Gold Vs. Silver

Gold, according to the article, is the most ductile and malleable metal.

Silver is not far behind though. I have a 99.9% gold necklace. Why is it so hard to find comparable purity in silver in jewelry? Most silver, when searched, is sterling silver (92.5% purity). It is said that silver is too soft so it must be alloyed with other metals, but this contradicts gold because gold is even softer; on top of this, but 24 karat gold is common.Curb Chain (talk) 11:31, 23 April 2011 (UTC)

24 Carat gold jewelry isn't that common either, especially in the West [6]. With both silver and gold, pure metal is typically only used when extreme malleability or softness is needed in crafting the part [7]. Where did you get your 24 carat gold necklace? Is it hand made, such that pure gold is necessary? Buddy431 (talk) 14:45, 23 April 2011 (UTC)

Supplemental question, if I may: is this extreme malleability somehow connected to the rareness of gold and silver on Earth, or to their aesthetic lustre? SamuelRiv (talk) 18:19, 23 April 2011 (UTC)

Most certainly, if you look at where they are located on the periodic table of the elements, gold and silver share a column with copper, the three together are sometimes called the coinage metals; and they all share a lot of chemical and physical properties, which are undoubtedly due to having similar electronic structure. --Jayron32 23:13, 23 April 2011 (UTC)

The malleability especially makes silver and gold desirable for jewelry: it would be hard make something like this out of iron or tin. Additionally, these metals (copper, silver, and gold) occur in large quantities in their native form, while others like iron do only occasionally, and some, like Aluminum, not at all. Historically, this means that these metals were some of the first known to man, being used both aesthetically, and also functionally (i.e. Bronze weaponry). Gold is especially valued, in that it won't rust or tarnish at all under normal conditions. Copper and silver will tarnish, but this oxidized layer then protects the rest of the metal from reaction (compare to iron, where rust will flake off, exposing more metal to the atmosphere). This muted reactivity is part of the reason why these metals are found in their native form, rather than in ores. Buddy431 (talk) 03:59, 24 April 2011 (UTC)

Oh, and for the "rareness" of gold and silver, look at the graph on the right. The abundance of metals is more related to their nuclear structure (how often they're formed in stars), and less to their chemical and physical structure. Silver, and even gold, aren't the rarest metals on Earth: Iridium, Ruthenium, and Rhodium are all much rarer, and, in some cases, more expensive (Rhodium briefly shot up to $10,000 per ounce, before the economic downturn brought it to more reasonable levels, currently about $2300 per ounce, still much higher than gold). Buddy431 (talk) 04:13, 24 April 2011 (UTC)

I thought Silver would tarnish under Sulfur. I got my necklace when my grandma died and her gold bangles where traded into divide into 5 parts for her grandchildren. The necklaces where traded in at Hong Kong. Maybe extreme purity silver is not found because of tarnish?Curb Chain (talk) 05:42, 24 April 2011 (UTC)

Even Sterling silver will tarnish, so I don't think that's the reason. You mention that the necklace was obtained in Hong Kong: in eastern Asia, it's much more common to have pure gold jewelry (I'm not sure why): see my first link [8] . Buddy431 (talk) 16:38, 24 April 2011 (UTC)

Yes, definitely: sterling silver does tarnish: According to silver, silver reacts with sulfur and hydrogen sulfide which results in the tarnish. I have read other online sources that the impurity in the silver cause tarnish: Is this true? Thanks Buddy431, I did look at that link when you first provided it. I can say that my 24k necklace does not seem any more fragile than a less pure necklace, so the question is still open as to why pure silver jewelery is so rare, and where one would be able to find pure silver jewelery, and maybe, why pure gold is popular in eastern Asia, but not elsewhere.Curb Chain (talk) 02:35, 25 April 2011 (UTC)

Our carat (purity) article has an dead ref list of common gold jewelry purities in various countries Nil Einne (talk) 16:47, 25 April 2011 (UTC)

Perhaps it has to do with the colors. That is, not too many things are gold, so adding other metals makes it look "less golden". Thus, even though pure gold is really too soft, some people may prefer it, due to the color. With silver, on the other hand, there are plenty of metals with a similar color, so you can get a "silvery" item without needing pure silver. In this case, there's little reason to pay more for a metal that's too soft. (I would probably take it to extremes and get a 100% stainless steel item, which would be less expensive and not tarnish.) Also, I think solid 24K gold is rare, it's more often a less expensive metal plated with 24K gold. This provides the best of everything; price, hardness, and color. See colored gold for a graphic showing how adding other metals changes the color of gold. StuRat (talk) 17:19, 25 April 2011 (UTC)

The necklace (I can not read chinese, I had my mom tranlate it) was traded at a gold shop: My mom, translating the certificate, said that the necklace was 99.9% gold. I even looked at the certificate and I had the arabic numerals 99.9%. Oh, after some research, I found that the gold shop is Chow_Tai_Fook_Enterprises. My necklace comes in a box with the icon and the certificate has the icon too. I don't know how corrupt this shop is though.Curb Chain (talk) 00:47, 26 April 2011 (UTC)

Also, according to silver, silver has a white shine, or is white in color, I guess more brilliant than other metals? So would stainless steel match silver's reflectivity and color? And also, wouldn't silver alloys be less reflective and brilliant than purity silver?Curb Chain (talk) 00:52, 26 April 2011 (UTC)

Young's double slit experiment

Approximately how much time does it take for a "one photon at a time" YDSE to generate a distinguishable (by a computer) pattern, assuming that all photons pass through the slits and do not hit the barrier. Also, are there screen detectors that can detect a single photon and its approximate (x,y) coordinates? Or do we still use photographic plates or click detectors on tracks for YDSE's?

I've added a section header for you. --Tango (talk) 13:31, 23 April 2011 (UTC)

And I changed it from "split" to "slit". StuRat (talk) 17:09, 25 April 2011 (UTC)

There is no number N such that you can distinguish the pattern using data from N subsequent photons but not from N-1 subsequent photons. The position where any given photon strikes is drawn statistically from a distribution. You may as well ask how often you have to toss a coin before you know P(heads)=1/2. The more data you have, the more certain you are that quantum mechanics predicts the correct position distribution for the photons (and the more coins you toss, the more certain you are that P(heads)=1/2), but in neither case is there a well-defined boundary between knowledge and ignorance of the pattern. 213.49.91.141 (talk) 17:35, 23 April 2011 (UTC)

Sure, but what if we say we want 95% confidence in rejecting the null hypothesis that there is no interference between photons? We should be able to find a good estimate for the N required for that. (Of course, we'll need to know things like the size of the slits and the distance between them, but I'm sure the OP won't mind if whoever is clever enough to work this out (which isn't me) just makes up some numbers for them.) --Tango (talk) 20:01, 23 April 2011 (UTC)

(I'm the OP here--forgot to sign--silly me--that's what comes of being in a hurry) I'd just like a rough estimate for an experiment (with given distances etc.) as a formula. It would also be fine if you could give the approx time for a YDSE conducted today (as in, using the technology today to require minimum time.) ManishEarth^{Talk • Stalk} 07:41, 24 April 2011 (UTC)

The effects of dreams on long term memory

Recently, I was recalling something that happened years ago- a conversation with a friend- but, after further thought, I realize that it was actually a dream. I wonder how much of my memories are actually falsified by these "dream memories"? Obviously we remember nightmares or other implausible events that occur in dreams as dreams. But there is a lot of random normal stuff that happens in dreams that, over time, get mixed in with the memories of actual events. Anyway, is there an article about this? I also wonder if there are extreme conditions where a person's dreams and reality are totally indistinguishable...like a psychological condition? I looked at Dream#Other associated phenomena and Memory#Disorderes (as well as scanning the rest of the articles), and am not finding much along these lines. Quinn ^{✩ STARRY NIGHT} 13:37, 23 April 2011 (UTC)

Well our memories are notoriously poor anyway and our brain outright makes things up to fill in gaps (there a number of books on the issues that the fallibility of human memory creates - e.g. reliabilty in court) so I suspect it wouldn't be difficult for dreams to integrate into memories and become things you think happened. The article Interference theory may be of interest though doesn't specifically related to dreams. ny156uk (talk) 16:18, 23 April 2011 (UTC)

Other people have speculated along the same lines, but the question seems nearly impossible to investigate scientifically. Regarding a state where dreams and reality are indistinguishable, it has been suggested that something like that happens in schizophrenia. Looie496 (talk) 01:39, 24 April 2011 (UTC)

Speaker wire

I've read the wiki article on speaker wire and found the information I was interested in but wonder if something should be included about interference on speaker wire such as the 60Hz line voltage? If the power cord and speaker wire are close together is it possible the 60Hz humm may be audible through the speaker?50.46.189.84 (talk) 15:38, 23 April 2011 (UTC)

You're welcome to edit the article and include the relevant information yourself if you believe it belongs somewhere in there, but try to include a reliable source for it. Note that you can do this even without creating an account, just as you edited this page. Try to make sure it's an encyclopaedic piece of information though, not a 'how to' guide, i.e., a 'how to construct a speaker wire' section would not be appropriate as it's not the aim of an encyclopaedia article. --jjron (talk) 16:57, 23 April 2011 (UTC)

It's not only possible, it's a very common source of interference. 60 Hz line noise is audible; it can couple via electromagnetic wave propagation (even though the wires are poor antennas at this frequency). More commonly, 60 Hz noise can couple through the speaker amplifier (hence, the noise gets amplified, even if it was very weakly coupled, and therefore at a low signal level). A good amplifier has a high power supply rejection ratio, meaning that the audio signal should be well isolated from the AC signal input; but in practice, poor- to moderate-quality electronics often propagate the "hum." High-end electronics eliminate this "hum" or line-noise in a variety of ways. Professional musicians may be familiar with "Humbuckers", as they are known in electric guitars; professional audio techs may know them as common-mode rejectors or differential signal transducers / amplifiers. Nimur (talk) 17:54, 23 April 2011 (UTC)

If the geometries of the power cord and the speaker wires are specified, it is pretty straightforward to calculate the induced voltage. This is done all the time for power lines, and the equations would be the same, though the distances would be vastly smaller. Qualitatively speaking, the closer the speaker leads are to the power cord, the higher the voltage induced in the speaker wires. The more current the power cord is carrying, the higher the induced voltage. The farther apart the 2 conductors for power are from each other, the greater the induced voltage. Likewise, the farther apart the two speaker wire conductors are from each other, the greater the induced voltage. If the speaker wires and power cord are parallel, the voltage would be greater than if they are perpendicular, if memory serves. If either pair is twisted, the induced voltage would be lower. In general, the power cord for an audio system would be unlikely to induce enough voltage in the speaker wires for you to hear hum from the speaker, since the speaker impedance is quite low and the current in the power cord to an audio system is not all that great. The voltage induced in an audio cable going from a turntable or microphone to the amplifier would be much more likely to produce audible hum in the output circuit, unless well shielded audio cable is used and ground loops are avoided, since the signal in those input cables is vastly amplified before it goes to the speakers. I expect that a high enough electromagnetic field could be found around a power station or transformer, or near a cable carrying hundreds of amps, to produce audible hum from speaker wires audible through the speaker, even without amplification. Edison (talk) 19:44, 23 April 2011 (UTC)

You can minimize the 60 Hz hum in speaker cables by making sure that, if they MUST cross a power cable, to do so at 90 degree angles; cables which are orthogonal like this should, in theory, not interfere with one another. --Jayron32 23:15, 23 April 2011 (UTC)

Crosstalk between cables is minimised when the cables are Twisted pairs. Cuddlyable3 (talk) 21:39, 24 April 2011 (UTC)

Big echo here. Edison (talk) 00:43, 25 April 2011 (UTC)

What is a Tripletino?

In the wikipedia article on Proton Decay it talks about a 5 dimension mode of proton decay with two fermions and two Sfermions. It also mentioned that this involves a tripletino of mass M. I am a little familiar with supersymmetry and this name fits the naming conventions of supersymmetry particles. However, I have never heard of such a supersymmetric particle. It maybe a generic name like neutralino that refers to any neutral supersymmetric boson. It is the "triple" that throws me. A triple of what? What are the properties of this hypothesized particle? I have only one reference in the whole world wide web. It comes from your article in wikipedia, but is cut and pasted all over the web with no further information.75.201.50.204 (talk) 16:34, 23 April 2011 (UTC)

Maybe its another word for a Neutralino? Just a guess... --Jayron32 17:08, 23 April 2011 (UTC)

A full text search for "tripletino" on the arXiv yields zero hits, which is sufficient reason to remove the term from Wikipedia. A full text search for "tripletinos" yields exactly one hit. In that paper they appear to define it as a superpartner with color charge (i.e., a strongly interacting superpartner). But I'm wary of editing the article on that basis alone. I barely understand the physics.

The word was introduced in 2005 by User:Phys (edit), who unfortunately hasn't edited since 2005. -- BenRG (talk) 19:01, 23 April 2011 (UTC)

I started a thread at Talk:Proton decay#"Tripletino", but the talk page looks pretty inactive. -- BenRG (talk) 07:09, 24 April 2011 (UTC)

Ocean surface lumps above sea mounts

A Natnl. Geo. documentary entitled "Drain the ocean" states that all ocean sea mounts are mirrored by lumps at the ocean surface level, and that the ratio is 1-1000. That is that a 3000 Ft. ocean sea mount is marked by a 3 Ft. lump of water above it. I've searched a number of Sea level cites and find a lot if info. about sea level variations caused by water temperature, atmospheric pressures, currents etc. but I can't find any explanation about how a sea mount deep below the ocean can cause a lump on the surface. It seems understandable that a deep current welling up the side of a mount might produce a lump but not all sea mounts are subjected to the same degree of current. How is this possible?190.149.154.38 (talk) 16:56, 23 April 2011 (UTC)

It's actually just gravity. The rock that makes up a sea mount actually attracts the water, 'bunching it up' and very slightly increasing the local sea level. (There's a more detailed explanation here.) Because of this distortion, sea mounts have been detected by precise satellite altimetry: [9]. TenOfAllTrades(talk) 17:13, 23 April 2011 (UTC)

The technical term is gravity anomaly, which refers to the "anomaly" in measured gravity between a perfectly spheroid (or perfect, complex-geometric-model-oid) earth, and the true gravity, which is affected by topography and geological composition and density. A fluid, such as the ocean, follows the contour of the gravity potential field; but because of surface winds, turbulence, tides, and other dynamic effects, true sea-level measurements are confounded by lots of practical details. In the open ocean, wind waves regularly have crest-to-trough amplitudes of 20 or 30 feet - so if there's a 3 foot "bulge", it's tough (but not impossible) to measure it!

Usually, if you want millimeter-accurate measurements of anything related to geodesy, you start with a reference geoid, such as WGS-84; apply your needed corrections using Shuttle RADAR Topography Mission data. That brings you to around a 2 meter accuracy. If you need more accuracy, you can correct these measurements using a local reference. If you were out in the open ocean, and you wanted to measure the sea depth with accuracy to ~ 1 or 2 feet, you could use a RADAR or SONAR measurement from a fixed object, such as a buoy or a semi-permanent man-made or natural structure on the seafloor, or an acoustic beacon.

Here's a chapter out of a textbook on geophysical estimation; this runs down the entire process of estimating sea-level bulges, with actual data from a satellite overflight of Madagascar. Altitude of Sea Surface near Madagascar; and further related work, Madagascar numerical estimation. Nimur (talk) 17:31, 23 April 2011 (UTC)

Many thanks guys. Even I can understand it. Why didn't I think of that. (Rhetorical). 190.56.18.215 (talk) 17:47, 23 April 2011 (UTC)

Amazing. But that's why I'm glad I don't do real work. SamuelRiv (talk) 18:14, 23 April 2011 (UTC)

Recombining all the oxygen with H then how much more water?

General belief being that the proto earth was virtually devoid of free oxygen. It being a by-product of photosynthesis involving seperation of oxygen from water molecules, it seems that notwithstanding reactions with other elements that the number of water molecules (ie. the amount of water) must be substantially reduced from the original amount on the earth. Is it possible to calculate how much deeper the oceans would be if all the now free oxygen was recombined with Hydrogen.190.56.112.125 (talk) 19:11, 23 April 2011 (UTC)

I'm not sure how accurate your premise is (there has been a lot of reaction with other elements, so we can't really neglect it, for example), but we can do the calculation ignoring everything that could complicate it. Let's work in terms of mass, since that's nice and easy:

The mass of the atmosphere is 5x10¹⁸ kg (see Atmosphere of Earth). 21% of that is oxygen. Water is H₂O. Hydrogen has an atomic mass of 1, oxygen has an atomic mass of 16. That means a water molecule has a mass of 18/16 times the mass of the oxygen it contains. So, the mass of water that would be produced is 5x10¹⁸x0.21x18/16=1.2x10¹⁸ kg.

The density of water is 1kg per litre, so that's 1.2x10¹⁸ litres or 1.2x10¹⁵ m³.

The surface area of the Earth's water is 361,132,000 km² (see Earth). We divide the volume of water produced by the surface area and we get an increase in depth of 3.3 metres. (If someone could check my arithmetic, I would appreciate it!)

--Tango (talk) 20:14, 23 April 2011 (UTC)

This is a complex question, which brings interesting attention to the homeostasis of the deep earth and the unknown organisms that dwell within it. There are igneous rocks with differing levels of acidic or basic composition - though I typically think of basic as reducing, I'm not quite sure how well this matches up to their ability to react with oxygen. For example, pyrite decomposes in air, and both the sulfur and the iron take up oxygen. Ultramafic rock also contains a large amount of iron... anyway, there are rocks that have the potential to take up oxygen, and in our air they do; but if all the oxygen were bound into water, they would no longer do so - so there would be more oxygen left over. I have no idea how much oxygen you could draw out of the Earth in this way, given enough free hydrogen. The ability of deep microbes to catalyze specific chemical reactions would doubtless have much control over the rate. So while normally I think of photosynthesis as controlling the amount of oxygen, the process must really be more complicated than that. But we need some real geologists to chime in here.

If you look at our photosynthesis article, you will see that only half of the Earth's oxygen comes from water -- the other half comes from CO2, which is present in vast quantities dissolved in the Earth's mantle. Moreover, when the products of photosynthesis are metabolized, most of the water is returned. The numbers will be substantially reduced if those factors are taken into account. Looie496 (talk) 01:35, 24 April 2011 (UTC)

Gah, I'm an idiot. Actually all of the oxygen comes from CO2. Water plays a role in the reaction, but the amount of oxygen that the water contributes is equal to the amount that gets incorporated in sugar. Some of this oxygen may however eventually be released if the sugar is converted into hydrocarbons or fats. Looie496 (talk) 06:12, 24 April 2011 (UTC)

I don't think it makes sense to talk about whether the oxygen comes from the water or the carbon dioxide. The reaction breaks them up and recombines them. Which specific atoms go where doesn't make much difference. You could look at the reaction in stages and see what happens to each atom, which I tried to do based on our articles and rather struggled, but it actually looked to me like the free oxygen comes from the water. If you look at Photosynthesis#Light reactions it seems the first stage is breaking the water up into free oxygen and hydrogen ions, and then those hydrogen ions react the the carbon dioxide to produce glucose and some more water. --Tango (talk) 14:57, 24 April 2011 (UTC)

That's right. It doesn't really matter where the oxygen comes from. what matters is that for every oxygen molecule produced with a molecular mass of 32 one water molecule is consumed with molecular mass of 18. Looies's calculation is almost correct (within the simplified framework assumed in his answer). The only mistake is that a factor of 18/32 should be used instead of a factor of 18/16 which gives 1.6 meters of water. Dauto (talk) 15:44, 24 April 2011 (UTC)

Well, what does matter is that photosynthesis does not generate any free hydrogen. It generates carbohydrates and oxygen; and the carbohydrates contain H and O in the same proportion as water does. Looie496 (talk) 16:19, 24 April 2011 (UTC)

I think you are referring to my calculation, not Looie's. The 18/16 is correct. The mass of a water molecule is 18/16 times the mass of the oxygen atom it contains. That is where the 18/16 comes from. --Tango (talk) 17:40, 24 April 2011 (UTC)

You're right, I meant your calculation, and you are wrong, 18/16 should be replaced with 18/32 because you're comparing the molecular mass of the water with the molecular mass of the oxygen (not its atomic mass) since for every molecule of water consumed, one molecule of oxygen is produced. Dauto (talk) 11:30, 25 April 2011 (UTC)

THE SUPERNOVA 1987A

THE SUPERNOVA 1987A had charged neighbor cloud after exploding , the best idea for formation of planets in o'ort nebula (''such as now upgrades''I will discuss next time about in other field )shows that this nebula was charged by neighborhood supernova for containing oxygen carbon and heavy elements ,and it might create the pressure and temperature condition for production of water , methane and water contain carbon and oxygen and ammonia contain nitrogen which produce in carbon cycle , and all metals in earth crust have been oxidized , 23 %of earth crust and 21%of air contain oxygen--Akbarmohammadzade (talk) 06:26, 24 April 2011 (UTC)

I assume you mean the Oort cloud. I'm sorry, but it is difficult for us to understand your English. Wnt (talk) 06:54, 24 April 2011 (UTC)

Akbarmohammadzade

the first cloud which produced solar system could not produce water for its complex of hydrogen and helium ,this cloud might be charged with supernova remnant matter to contain elements which be produced at the core of stars and migrate here with supernova exploding event , so although the sun has carbon cycle but existing of heavy elements in terrestrial planets and ice and methane and ammonia in outer planets and comets shows that the inner system of o'ort cloud might be charged secondary , specially for the reason of this :if first prestellar nebula had such elements ,the percent of existing of them in sun and planetary system was equal , then the sun had absorbed 99percent of those elements and that could not be 4percent of total planetary system , but the fact is wise . notice that the condition which cause the production of water is special ,finally can earth's own global condition produce water?--78.38.28.3 (talk) 10:07, 24 April 2011 (UTC)

--78.38.28.3 (talk) 08:04, 24 April 2011 (UTC)

Active electronic metamaterials.

Does anybody have references to Metamaterials that change function by adding or removing electrons?

Just as an LCD display has an individually addressable transistor per pixel, each molecule in the active electronic metamaterial will act as a transistor that can selected and charged or discharged. The patterns formed would then interact with and direct electromagnetic waves and these patterns can be changed at the speed of electricity. Hcobb (talk) 19:47, 23 April 2011 (UTC)

Are you looking for the Sketched oxide single-electron transistor (SketchSET)?Smallman12q (talk) 21:22, 23 April 2011 (UTC)

No, that's an isolated electronic device that doesn't greatly change the properties of the bulk matter around it. Hcobb (talk) 22:48, 23 April 2011 (UTC)

Echos in the Treasury of Atreus

On a recent trip to Mycenae, my peers and I noticed that a person standing on one side of the interior of the Treasury of Atreus speaking softly into the wall could be heard very clearly from a person on the other side -- the speaker's voice is heard as coming out from the diametrically opposite point on the wall. What is the reason for this phenomenon? What is it about the shape of the tomb that causes the sound to be focused at that point, and are there any other points at which this happens? jftsang 23:26, 23 April 2011 (UTC)

Check out Whispering gallery. Clarityfiend (talk) 23:40, 23 April 2011 (UTC)

But the inside of the tomb is circular, so the two foci coincide at the centre. Why does this work if one stands at the edge? jftsang 23:51, 23 April 2011 (UTC)

Besides the center, there will be other nodes where the sound waves collect to have the same effect; its quite possible to create a room where one of those nodes is at the speaker's own head. --Jayron32 23:55, 23 April 2011 (UTC)

Also note that whereas the floor may be more or less circular, the "inside of the tomb" as a whole is rather complicated in shape (similar to a paraboloid or half of a prolate ellipsoid). Sound doesn't travel in only two dimensions. Deor (talk) 10:24, 24 April 2011 (UTC)

Whispering gallery modes primarily happen in circular rooms. Contrary to what the article implies, the phenomenon is distinct from the concentration of sound at the foci of an ellipse or circle. A true whispering gallery mode forms antinodes around the perimeter of the room, not in the center.--Srleffler (talk) 17:34, 26 April 2011 (UTC)

April 24

How should antibacterial news be added to Wikipedia?

Is Antibacterial the right article to add these news items?

• http://www.scientificamerican.com/article.cfm?id=our-big-pig-problem
  • "Since 1995 Denmark has enforced progressively tighter rules on the use of antibiotics in the raising of pigs, poultry and other livestock. In the process, it has shown that it is possible to protect human health without hurting farmers."
• http://www.latimes.com/health/la-he-antibiotics-agriculture-20110425,0,7598829.story
• http://www.businessweek.com/lifestyle/content/healthday/651982.html

If so, what should the article say and in which section? Are there other article(s) where this would be (more) appropriate? Is this sort of thing appropriate for the article introduction?

Sorry for asking a help desk question on the reference desk, but I'm much more confused about the science component here than the how-to-edit component. If you figure out a good way to put this, please do go ahead and add it to the appropriate article(s). 99.39.5.103 (talk) 00:23, 24 April 2011 (UTC)

Looks like a place for it at Antibiotic_resistance#Role_of_other_animals. More so at Factory farming. I'd encourage you to consider adding your own references though - I'm just answering your question, not promising to do your editing for you. ;) Wnt (talk) 00:50, 24 April 2011 (UTC)

Also, please note that WP is not a news outlet - for that, Wikinews may be more appropriate. -- Scray (talk) 04:55, 24 April 2011 (UTC)

Not true. The policy cited above says "Wikipedia should not offer first-hand news reports on breaking stories." ... which should not discourage you from adding these or other recent sources. Wnt (talk) 06:42, 24 April 2011 (UTC)

human as a mammal

how did "Adam" created first time ?why he created as a mammal ?and for DNA , was it first program for DNA, to produce such mammal? I have not religion proposes of this question , there is scientific ideas in my mind for this filed , such as coming to be alive again based on DNA program for human and remaining that in nature for next time for our coming to be alive after death

.akbar mohammadzade--78.38.28.3 (talk) 05:54, 24 April 2011 (UTC)

Um, I'm not sure I can parse that. Humans are mammals because we all share a common ancestor. Broadly speaking, all mammals bear hair and give milk to their young, which humans do as well. Adam was the first man created by God, according to the Bible. I seriously cannot make heads or tails of anything else you say here. --Jayron32 06:01, 24 April 2011 (UTC)

By "Adam" I'll assume you mean "the first human man". The truth is that species rarely if ever start with one single individual. ("Hopeful monsters" were a popular idea in the early 1900s after X-ray mutations caused radical changes in flies, but eventually people realized those were caused by major damage to chromosomes and aren't representative of real evolution ... though nothing is impossible in biology) The way species actually start is that populations slowly change over time. You can point at one individual and say that he was the last common ancestor of all humans, but he lived in a group with many other individuals who were common ancestors of most humans. Wnt (talk) 06:39, 24 April 2011 (UTC)

Adam is just part of a religious story; he's not somebody who actually existed. There was a man who is known scientifically as Y-chromosomal Adam, but he wasn't the first human male. And although I don't really understand your question pertaining to life after death, life after death in any of its various proposed forms is purely a religious notion, that has nothing to do with science. Red Act (talk) 07:17, 24 April 2011 (UTC)

both of the wayes in thinking about "Adam" from accepting to dont accepting come to same result of which we said about the rule of DNA , I said that "DNA" as it contain our celles formula can product us again , and it is genetic discussion ,for that , I said that Ihave not religen propose .

My discuss for coming to be alive after death is so relagion based "life after death " but only give your reply according to our chemical complex . The water and carbon nitrates and other elements in our body is equal for me and you ,and other natural complexes and for air and soil , the combination and way of lying them together changes for the formula of DNA .if we replay to this question :

was it possible for breeds and fishes or crocodils to have our ability and mined ? then we will be able to imagin the creation of "ADAM" akbar mohammadzade--78.38.28.3 (talk) 05:54, 24 April 2011 (UTC)

I don't understand your question clearly, but DNA is only a minor factor of personality. Look at monozygotic twins. They have exactly the same DNA and so are some kind of natural clones, but they are different persons with different personality. 93.132.153.177 (talk) 11:22, 24 April 2011 (UTC)

Perhaps it would be easier for the questioner to write in their original language, so that the question can then be translated. As it is, it cannot be understood. Ghmyrtle (talk) 11:31, 24 April 2011 (UTC)

A good way to check if a word is correct is to look it up in wikipedia, in different languages. For example, I am quite sure that the above word "breeds" should really be "birds". What makes the OPs questions unintelligible is mostly the syntax, especially the order of the words. Then, Farsi and English have a different set of vowels. That the English vowels are not always represented by the same letters makes it even more difficult. 93.132.153.177 (talk) 11:48, 24 April 2011 (UTC)

I think the questioner is asking whether an individual's DNA could be used to restore that person to life after their death, in a process like cloning. This is a common misperception about what DNA actually does -- it is a framework for a living being, nothing more. The "environment" (in this case the sum total of all life experiences) is what shapes the "person" you become, and aside from epigenetic marks that accumulate in different cells of the body, this life experience is not written into the DNA. Thus, while it would be theoretically possible to use an individual's DNA to generate a living being with a nearly identical genetic make-up, this individual would have none of the unique experiences that contributed to the original and would for all practical purposes be his or her own unique person (like the example of identical twins given above). --- Medical geneticist (talk) 12:55, 24 April 2011 (UTC)

I think this question goes beyond what is scientifically known. "The Mind's I" is a good book to define some of the mysteries. Which neurons are part of the "self", and how many can be replaced with new neurons, or mechanical prostheses? Some of these things are unknown, and perhaps some are unknowable. Wnt (talk) 23:12, 24 April 2011 (UTC)

I agree that cloning generally creates a physical copy of an individual, but does not replicate that person's memories or most of their personality. Those are created as synapses in the brain, based on life experiences. DNA, which doesn't change much from birth, doesn't contain that info. StuRat (talk) 16:56, 25 April 2011 (UTC)

What kind of engineering will be required to make sphere wheels possible?

It has already been imagined. Now, what barriers will need to be torn down in order to make them usable on new cars? --70.179.169.115 (talk) 06:16, 24 April 2011 (UTC)

What advantage would spherical wheels give us to make it worth it to put them into production? --Jayron32 06:19, 24 April 2011 (UTC)

If you get to watch I, Robot, then you'll see how the RSQ maneuvers in ways impossible for today's vehicles. --70.179.169.115 (talk) 08:03, 24 April 2011 (UTC)

That thing looks like it has zero clearance. I'm skeptical it would clear paved roads in Pennsylvania... Wnt (talk) 06:33, 24 April 2011 (UTC)

I am confident that by '35, cars will have variable clearance mechanisms that will raise or lower the body based on what the road sensors detect up ahead. --70.179.169.115 (talk) 08:03, 24 April 2011 (UTC)

Dyson vacuum cleaners already have something similar. --TammyMoet (talk) 08:14, 24 April 2011 (UTC)

I wouldn't say a Dyson ball vacuum has a spherical wheel. The wheel is fixed and won't rotate in every possible direction, only backward and forward like a normal wheel. It is simply shaped differently from a normal wheel and looks more like a ball than it actually acts like one. – Kerαunoςcopia^◁_galaxies 16:47, 25 April 2011 (UTC)

To take advantage of a spherical wheel shape you'd have to get rid of the axle/hub design (axle/hub arrangements only allow rotation in one plane, making a sphere meaningless). This would mean that you'd need to develop entirely new types of suspension systems to allow the wheel to rotate freely while supporting the weight of the car, and entirely new power transmission systems since there would be no axle to apply torque to. Simplest, I imagine, would be to have some sort of friction system (e.g. a small, conventional axle/hub system that pressed down on the top of the spherical tire, supporting the weight of the car and applying torque to the wheel in a wide range of directions). for something more science fictionish, I imagine you could invent a mag-lev system (maybe a spherical hub inside the spherical tire that contained a superconducting magnet?). propulsion in this case would be trickier - I can visualize a system for rotating the wheels based on things like maglev trains or rail guns, but it would basically involve turning the entire wheel-well into a complex electromagnetic control system, and I can't imagine it would be practical or efficient.

Of course, in either of these scenarios you risk your wheels falling off if you hit a bad bump. --Ludwigs2 08:35, 24 April 2011 (UTC)

Spherical wheels shouldn't be too hard. Anyone who has ever looked inside a mechanical computer mouse ought to be able to toss off a quick design for drive system and mounting. DuncanHill (talk) 11:55, 24 April 2011 (UTC)

A mouse is used in a relative pristine environment, yet still eventually gets hair and such caught up inside it. If something similar was used on the street, it would suck up bits of sand, mud, etc. into the works. It might work better underwater, though, for use on a vehicle that rolls on the bottom, since the friction between the sphere and housing could be reduced by the water, and the water could also be used to clean out that area and keep it cool. I visualize a 4 wheeled vehicle with 2 conventional wheels used for drive and steering, with the other two being spherical wheels. StuRat (talk) 16:38, 25 April 2011 (UTC)

I don't believe that's a sensible design for a vehicle wheel. A ball mouse has two planetary sensor wheels (and usually one more sprung planetary wheel, to keep the ball in place). Let's just talk about the two sensor ones. They're mounted at 90 degrees to one another: call them "top" and "left". When the mouse is moved left-right, the left wheel rolls smoothly. In the same motion, the top wheel is still forced against the ball (against what is the pole of rotation of the ball). It doesn't roll, it just scrapes over the surface. Because of the forces involved in a mouse (which are pretty trivial) this isn't an issue. But for an automotive wheel you'd incur significant friction, and wear, all the time (as at least one one wheel would be dragging like this). You could probably design a more complex system where the planets are themselves balls, and their motion is restricted by some interlink that adapts to the vehicle's directions, but by this point it's a very complex design. -- Finlay McWalter ☻ Talk 13:31, 24 April 2011 (UTC)

Of relevance: Mecanum wheel, omni wheel. 94.172.116.125 (talk) 13:41, 24 April 2011 (UTC)

Besides, the goal is to create a holonomic vehicle (one that can freely navigate in the X-Y plane). There are easier ways to do this instead of using spheres: the caster wheel, as you see on office chairs, allows the chair to "glide" in X and Y directions, by offsetting the vertical rotating mount from the horizontal axis of the wheel. It's not very good for propulsion, and has some stability concerns, but it does simplify artificial intelligence path planning quite a bit. Here's an IEEE paper on robot automobiles with holonomic locomotion using conventional tires: Holonomic and omnidirectional vehicle with conventional tires. Nimur (talk) 14:40, 24 April 2011 (UTC)

Great links 94, I knew those wheels, but not those terms :) SemanticMantis (talk) 23:18, 24 April 2011 (UTC)

I had the nagging feeling we've discussed this before and seeing those links confirms it since I distinctly remember giving them before so there may be something in the archives. Nil Einne (talk) 05:43, 25 April 2011 (UTC)

window

vinyl window top sash falling? I have a sash that won't quite stay up the whole way when you open it. how do i fix it — Preceding unsigned comment added by Kci357 (talk • contribs) 07:57, 24 April 2011 (UTC)

We can't fix a sash window over the internet. You'll have to find somebody to come and look at it. Perhaps a friend, relative or neighbour that is good with that kind of thing? --Tango (talk) 13:18, 24 April 2011 (UTC)

This is a very common problem on old sash windows. I don't have any experience with "vinyl" ones. (Do you mean uPVC?) Anyway, the most likely cause is that dirt or debris has got into the sash box, so that the counterweight doesn't go all the way to the bottom, which means it won't pull the window all the way to the top. Pry open the sash box and clean it out. The other possibility is that the rope has stretched, so it needs to be untied and shortened. If it runs on a spring or chain rather than a counterweight I'm not sure how to fix it.--Shantavira|^{feed me} 15:57, 24 April 2011 (UTC)

Chemicals in the body to counteract other chemicals in mood change- e.g., caffeine

I've noticed that frequently, if there is a drug for one thing, there is not a drug to cancel it out. Sometimes this is obvious, like in the case of alcohol: alcohol simply contains too many poisons, which have to be removed from the body.

But in other cases, the drug in question is not a poison, and common sense tells me another drug should be able to nullify its effects. Specifically, I can't think of any drug that will necessarily cancel out the effect of caffeine. Caffeine's side-effects:

• Caffeine will make the individual hyper.
• Caffeine may put an individual in a good mood at first, and kind of a lousy one later. At least it does that with me (I've been a chronic drinker at times in my life... no more)
• Caffeine can make it impossible for some individuals to sleep for long periods of time. Again, it does this for me, at least.

Now I can think of several depressants, but they all have problems:

• Alcohol will make the individual mellow, and while the individual might fall asleep immediately, he will experience a rebound a few hours later. For example, after a night of heavy drinking, he may have trouble getting a normal amount of sleep that night. This rebound effect doesn't exist with caffeine.
• Marijuana - I know nothing about how this drug works, only that it makes people goofy and stupider than normal. So maybe it could effectively counter caffeine, although I doubt it from what I've seen.
• Sleeping pills - in general, I think these might be a good candidate for reversing a caffeine effect, or vice versa. However, I've had at least one occasion where I took a sleeping pill together with caffeine, and instead it just left me in a zombified state - unable to sleep deeply, but tired to the point that I still didn't want to move.
• Xanax - an anti-anxielitic, I have used this drug before. At first, it helped me sleep, but after a while, this effect disappeared for me. I never combined it with caffeine like above (I'm not stupid).

So my question is - is there a drug, illegal or legal, over the counter or prescription, which exists that could exactly reverse the effect of caffeine, and for which caffeine could exactly reverse its effect? If not, is it theoretically possible for such a drug to exist? And could such an anti-drug exist for most non-poisonous drugs (e.g., Xanax, anti-depressants, sleeping pills).

You'll note my question is theoretical only and general. I don't want this discussion to involve specifics like last time I asked about medication, where my thread ended up getting shut down. So if we have to, we can avoid the subject of caffeine and talk about other drugs.

</textwall> Magog the Ogre (talk) 08:28, 24 April 2011 (UTC)

Adenosine is probably the closest candidate. Axl ¤ [Talk] 09:27, 24 April 2011 (UTC)

Adenosine apparently doesn't cross the blood-brain barrier very effectively, so it wouldn't function as an anti-caffeine unless administered directly into the brain. (Caffeine goes right through the barrier as though it didn't exist.) There are a number of known non-selective adenosine agonists, some of which are apparently better at crossing the BBB, but the literature on this topic is too scattered for me to grasp without doing more work than I want to. Let me by the way note a glaring omission: our article on adenosine says absolutely nothing about how it is synthesized within the body. Looie496 (talk) 16:14, 24 April 2011 (UTC)

I think Looie is on the right track; see adenosine receptor for lists of agonists. In general there is no guarantee that a drug has an antidote; however agonists and antagonists often work in opposite ways at one particular receptor. Common small molecules like caffeine probably affect many receptors to some extent, but very likely hitting the adenosine receptors will affect the main effects. In general though, this is a research question: you don't really know what will happen when you mix agonists and antagonists until you try. There could be more than one type of receptor; the drug might have mixed agonist and antagonist activity; the drug might even be causing two subunits from two different related signalling pathways to come together in a way that doesn't happen in normal biology! I wouldn't rule out the possibility that a BBB-crossing drug isn't actually needed - I think that increased heart rate by itself has many subjective effects, and it seems conceivable that if you cancel that out, the other effects aren't so much of a problem. Oh, and I'll look at linking adenosine to purine biosynthesis. P.S. Be careful you don't catch the gout screwing around with experimental purines. Wnt (talk) 18:19, 24 April 2011 (UTC)

control valves in aircrafts.

hi. what are the different types of Flow control valves used in Aircrafts. — Preceding unsigned comment added by Venkata chaitanya (talk • contribs) 10:01, 24 April 2011 (UTC)

Fuel or Air? Dismas|^(talk) 10:40, 24 April 2011 (UTC)

also hydraulic 173.58.233.95 (talk) 11:03, 24 April 2011 (UTC)

The passenger compartment, especially in a pressurized cabin aircraft, will also have a totally independent set of air flow systems and valves. Nimur (talk) 14:44, 24 April 2011 (UTC)

can cerebral palsy lead to...

1) speech impairment? 2) adverse reactions to excessive noise? —Preceding unsigned comment added by 59.189.217.21 (talk) 10:43, 24 April 2011 (UTC)

I don't know about #2, but #1 is truth. Sometimes, palsy can leave the victim's nerves so impaired that they'll need diapers due to not being able to control it. --70.179.169.115 (talk) 10:51, 24 April 2011 (UTC)

You may wish to read the article "Cerebral palsy". The article states "Speech and language disorders are common in people with Cerebral Palsy." Axl ¤ [Talk] 10:52, 24 April 2011 (UTC)

It's quite common for people with cerebral palsy to have an exaggerated startle reflex, meaning that sudden loud noises can be a significant problem. I'm not aware that steady loud noise is usually any more of an issue than it is for others. HiLo48 (talk) 12:00, 24 April 2011 (UTC)

The Primitive reflexes article says that in people with cerebral palsy, reflexes such as the startle reflex aren't as attenuated during childhood development as they are in normal children. The more pronounced startle reflex in children with cerebral palsy is also discussed in this article. Red Act (talk) 20:12, 24 April 2011 (UTC)

If there are call queues, why aren't there fax queues?

When I tried to fax an item, the fax lines were busy so I could not get it through. Why hasn't anybody ever prototyped a fax queuing system? If anyone else has even thought of putting faxes in a queue for a busy line, why hasn't it been done? What's the difficulty? What kind of invisible barrier would we need to blast down in order to make this happen? --70.179.169.115 (talk) 10:49, 24 April 2011 (UTC)

Check out the page on fax servers 173.58.233.95 (talk) 11:06, 24 April 2011 (UTC)

Even for traditional faxes, many professional fax machines have had fax queuing at the sending machine for decades, where they store faxes and repeatedly redial the sender's number until they are able to transmit the fax. The problem with a queue on the receiving end is that it usually relies on a single slow telephone line, so queuing would have to be implemented at the exchange. The actual printing was done as data was received, so there was no advantage in a print queue at the receiving end (though this was also an option on many machines). Telephone companies probably didn't have the technology decades ago to implement a queue at the exchange, and by the time they were installing sophisticated electronics in their exchanges, they would be able to foresee the end of traditional faxes, so why waste money on a technology that was being superseded by the internet? Dbfirs 08:14, 25 April 2011 (UTC)

Is there a service to send a text at a preset time?

If I send a text at 5:45, but only want the recipient to receive it at 7:45, is there an app or anything like it that will opt me to only get it to the recipient at a preset time? I'd hate to wake a recipient up to a text chime, but something spur of the moment wants me to send it before I forget it. --70.179.169.115 (talk) 10:49, 24 April 2011 (UTC)

ohdontforget.com 173.58.233.95 (talk) 10:56, 24 April 2011 (UTC)

Origin of Potential Energy

Given two massive particales seperated by a distance in a vacuum, they will accellerate towards eachother due to gravity (ignoring other forces: magnetic, Casmir, etc.).

The fist law of thermodynamics explains that energy can be transformed but not created or destroyed. Where does the kinetic energy to move the particles come from?

Do the partiles loose a small amount of mass? Or is it truly the loss of some innate "potential energy" that the particles inherited from nucleosynthesis?

~TrickSpoon0 173.58.233.95 (talk) 10:52, 24 April 2011 (UTC)

The kinetic energy does come from the potential energy and, yes, that potential energy contributes to the mass of the particles. The particles get lighter as they move together, although by a pretty insignificant amount. Two particles each of mass m a distance r apart have potential energy (relative to being zero distance apart) of ${\frac {Gm^{2}}{r}}$. If you plug that into E=mc² you find that the extra mass is ${\frac {Gm^{2}}{rc^{2}}}$. Since c is such a large number and G is such a small number, that extra mass is tiny. --Tango (talk) 13:24, 24 April 2011 (UTC)

That's not the right way of looking at it. The potential energy is actually in the gravitational field. For visualisation, picture the magnetic field between two magnets, traced by iron filings. As you move the magnets towards or away from each other, the magnetic field pattern changes. With that, the energy stored in the magnetic field changes. The same thing happens with the gravitational field. As the two masses (which determine the gravitational field) fall towards each other, the field changes and its energy decreases. That gravitational energy is converted to the kinetic energy of the particles. Saying "a particle has potential energy" is actually sloppy (although of course everybody does it). --Wrongfilter (talk) 15:11, 24 April 2011 (UTC)

Ok, technically I should say that is the mass of the field, rather than the extra mass of the particles. It's the extra mass of the system as a whole (neglecting kinetic energy, of course - we know the total is always going to be the same as long as it is a closed system), which is what I was thinking about. It's not what I wrote, though, so I apologise for that! --Tango (talk) 15:25, 24 April 2011 (UTC)

Sorry Tango, but what you said above seems wrong to me. Since energy is conserved, the relativistic mass of the system as a whole is also conserved, and the rest mass of each individual particle is also conserved, so I don't know in which sense do you claim that their masses have changed. Also, the potential energy is measured relative to an infinite distance apart, not a zero distance apart as you claimed. Dauto (talk) 15:13, 24 April 2011 (UTC)

Potential energy can be measured relative to whatever zero point you like. It often most convenient to define zero to be infinite separation and have potential energies that are always negative, but you don't have to define it that way. That said, I still did it wrong. You can't actually use zero separation, since you get problems with infinities. I should have used two finite separations, in which case you get the extra mass to be ${\frac {Gm^{2}}{c^{2}}}\left({\frac {1}{r_{1}}}-{\frac {1}{r_{2}}}\right)$. The principle is sound, though, I just messed up the maths. --Tango (talk) 15:25, 24 April 2011 (UTC)

Ultimately, the potential energy came from the big bang, which scattered matter through the universe, and, thus, we now have particles at a distance from each other. StuRat (talk) 17:38, 25 April 2011 (UTC)

Typical discharge current

Bearing in mind that it is a glow discharge (which normally has an upper limit of about 1A before transitioning to arc), what is the typical current in the discharge between the electrodes of a TEA nitrogen laser? --92.28.77.227 (talk) 11:21, 24 April 2011 (UTC)

Continuously tunable multi- atmosphere small size CO2 TEA laser - "In this work we report the operational characteristics and the spectral properties ... " - as I've said before, your best bet is to refer to experts in this field. Nimur (talk) 14:46, 24 April 2011 (UTC)

Thanks but i cant get acess to that paper. I just like to know some ball park figures for current and voltage reqired to initiate lasing in atmoshpheric nitrogen. I dont have any facilities to make one. Im just interested in the theory.--92.28.77.227 (talk) 20:06, 24 April 2011 (UTC)

Here's a pretty good text book, Fundamentals of Light Sources and Lasers; and the author's accompanying webpage. I'm pretty sure there's coverage of power sources. The magnitude of your discharge or light pump current will depend entirely on your desired output; since you are particularly interested in atmospheric pressure lasers, certain domains will be off limits to you (in terms of peak power, average power, and duty cycle). In general, your average pump power must be greater than the average LASER light output power; and because an atmospheric pressure discharge will only LASE sporadically, you should consider the effect of low efficiency. The exact value of the current you need will depend on your atmosphere, and the Q factor of your optical resonator. If, as you say, you are interested in the theory, you should start with our article on LASERs; you can progress to population inversion, and optical pumping (and other types of Laser pumping), then solve the necessary equations for your specific conditions to estimate a ball-park figure for your pump current. Nimur (talk) 20:15, 24 April 2011 (UTC)

Also, Principles of Lasers, (Svelto), has an entire chapter on electrical pumping. Nimur (talk) 20:25, 24 April 2011 (UTC)

Time travel

Time travel into the past would violate causality, but time travel into the future well possible, we do it at a rate of 60 minutes per hour. In science fiction, you step inside a time machine, pull a lever and after some minutes of your time, centuries have passed on the outside. During that process interaction between the outside and the inside is limited. What real world things come closest to that? Moving near the speed of light would do the trick. Cryostasis works very well, only that nobody has been successfully revived yet. Taking a nap, hoping that at least biologically you don't age quite as fast is quite limited in effect. What other ways are there? 93.132.153.177 (talk) 13:29, 24 April 2011 (UTC)

See here. Count Iblis (talk) 14:43, 24 April 2011 (UTC)

So what they did was breed mice who suffered from the lack of a specific enzyme. They injected the missing enzyme, and, what a big surprise, the condition improved. The most interesting thing about this is that it made its way to a newspaper article. 93.132.153.177 (talk) 14:54, 24 April 2011 (UTC)

Such experiments are common. Often, the only way to work out what an enzyme does (or what the effects are of what it does) is to see what happens when it isn't there any more. It isn't really relevant to this question, though. --Tango (talk) 15:04, 24 April 2011 (UTC)

Well, it looks a bit like this: imagine they had a dog breed that can't produce ascorbic acid. They discover the dogs develop scorbut and lose their teeth. They feed ascorbic acid to other dogs, and these dogs keep their teeth. Now the scientists propose to feed huge amounts of ascorbic acid to old age toothless people in the hope they will grow new teeth. 93.132.153.177 (talk) 15:47, 24 April 2011 (UTC)

. The non-trivial effect that was observed was that the damage done by the increased rate of aging was reversed. It was not just that the mice kept aging at the normal age, their effective biological age became less. So, in the dog analogy, the observation was that the dogs that had already lost their teeth grew new teeth. Count Iblis (talk) 16:26, 24 April 2011 (UTC)

I would appreciate the result very much if it worked on mice without that specific genetic defect that were simply "ill with old age". 93.132.153.177 (talk) 17:06, 24 April 2011 (UTC)

Using mice with that defect just makes the effects more dramatic so they are easier to study. Basically, the study shows that telomerase plays a very important role in ageing. The exact details of that role and how (and if) it can be used to reduce the effects of ageing in humans will be the purpose of other studies, which will now get funding because it's been shown that they are onto something with telomerase. --Tango (talk) 17:45, 24 April 2011 (UTC)

I don't see why they didn't do the tests with a control group of simply old mice already. This could have been done easily, without much need for extra funding. That telomerase plays some role in ageing is neither surprising nor new. The key question is if working telomerase is sufficient or only necessary to slow down (or possibly stop) ageing. To me, this smells like the main purpose is to get perpetual funding. 93.132.153.177 (talk) 18:10, 24 April 2011 (UTC)

I read here that you can actually try this out yourself. Count Iblis (talk) 18:38, 24 April 2011 (UTC)

And you did? I actually would be willing to try telomerase on myself. But as an enzyme it would be very,very difficult to develop a pill that goes through your stomac and delivers the protein intact into your bloodstream, not to mention the problems to get it into your cells. The first article you mentioned could very probably give hints on how to administer telomerase. BTW, you know the joke about the man who was sentenced to prison because of deception for selling pills to prolong life? The judge was especially enraged when he found out that the culprit was a repeated offender who was previously sentenced for the same crime already in 1923, 1878 and 1492. 93.132.153.177 (talk) 19:02, 24 April 2011 (UTC)

One things you didn't mention is spending time near a massive body. Gravity causes time dilation in the same way motion does. If you rode a spacecraft on a trajectory that went near, but not past, the event horizon of a black hole you would, from your perspective, seem to have travelled into the future. --Tango (talk) 15:04, 24 April 2011 (UTC)

Of course, since there aren't any black holes nearby, we'd need another means of "time travel" (such as suspended animation or relativistic travel) to allow our "time traveller" to actually get to a black hole within his or her lifetime. ;) --Link ^(t•c•m) 16:27, 24 April 2011 (UTC)

I think that causality is more of a myth than a scientific phenomenon. If our four-dimensional spacetime includes a trip into the past at some point, then the solution for the events occurring within it simply adjusts itself to that situation. That requires the recognition that in some cases "free will" or "luck" may be distorted - you may not choose to kill your grandfather, or you may not succeed - but the universe moves on, oblivious to your dismay. Wnt (talk) 18:05, 24 April 2011 (UTC)

If you read my question again you will notice that I carefully left out the words "is impossible because it" between the "Time travel into the past" and the "would violate causality" 93.132.153.177 (talk) 18:46, 24 April 2011 (UTC)

chemistry

law of constant proportion 117.206.3.136 (talk) 14:22, 24 April 2011 (UTC)

This is a wiki, and not a search box; you will get better answers if you ask complete questions in English. Are you looking for our article on the law of definite proportions? Nimur (talk) 14:32, 24 April 2011 (UTC)

I created a redirect. Graeme Bartlett (talk) 09:00, 25 April 2011 (UTC)

Potential pollution in sea salt

Since sea salt seems to be growing in prominence as a kind of "exotic" salt, I read the sea salt article looking for an answer to one thing that has been bothering me: the potential for contamination from various sources of pollution. Our article shows that sea salt is produced worldwide, not just the Mediterranean. My worry would stem more with production in Hawaii, or anywhere along the US west coast. The Pacific Ocean has the wonderful Great Pacific Ocean Garbage Patch. Also, I'm curious about run-off from inland that may be polluted. And maybe now (this is an ignorant guess at the moment) there will be an increase, however negligible, in radiation in sea water from Japan. Finally, oceans around certain coastlines are popular for humans to boat around and surf and swim in. I haven't read anywhere that sea salt is free from any potential contaminants from these and other sources. Is it anything to be concerned about? – Kerαunoςcopia^◁_galaxies 16:22, 24 April 2011 (UTC)

Crystallisation, as happens naturally when gaining salt from sea water, is used as a method of purifying chemicals. So I think you shouldn't worry too much. Any garbage like that from Great Pacific Ocean Garbage Patch is highly unlikely to show up in your salt shaker. And if you are not anywhere near Fukushima any radioactive waste will be diluted below the amount of naturally occuring radioactive potassium. 93.132.153.177 (talk) 17:23, 24 April 2011 (UTC)

I'd always assumed that it was the unique combination of dead fish, agricultural run-off and human sewage that gave sea-salt its distinctive flavour. DuncanHill (talk) 17:27, 24 April 2011 (UTC)

I think the contaminants to look for might be other salts rather than plastic, since plastic floats but maybe salt co-crystallizes. It seems more plausible to look for lead, mercury, cadmium and such (especially near rivers that have seen extensive mining in their watersheds). And of course radioactive iodine and cesium near Fukushima... Wnt (talk) 17:44, 24 April 2011 (UTC)

Top hit off the pile:

"Our laboratory also tests for these elements that are sometimes referred to as "heavy metals" and that are present in many things we come into contact with every day in our environment. The Codex Alimentarius Commission -- formed by the FAO (Food and Agriculture Organization) and the WHO (World Health Organization) -- has established the maximum safe levels acceptable in food grade salt for some of these elements. In our most recent analysis all these elements were either non detectable (Arsenic, Cadmium, Mercury) or were well under the published safe limits specified by Codex (Lead - present at levels no higher than .000076% while the Codex limit is .000200%). There are no limits specified for Nickel (present at levels no higher than .000004%)."^[10]

While that manufacturer gives a reassuring message, no doubt there will be some who are not so responsible. Wnt (talk) 17:48, 24 April 2011 (UTC)

Here's the manufacturer of a kit for testing sea salt that claims one of their customers found 5 ppm of mercury in sea salt.^[11] (OTOH I don't know if the customer broke a thermometer the same day, and it makes for good marketing, doesn't it?) Wnt (talk) 17:52, 24 April 2011 (UTC)

Was this the customer who uses exclusively those morally and ecologically favourable Compact fluorescent lamps one of which he accidentally broke just before measuring? 93.132.153.177 (talk) 18:21, 24 April 2011 (UTC)

I didn't have much luck with NCBI just now - here's one paper about copper in sea salt for aquaria, but I don't know if it's relevant: [12] Wnt (talk) 17:58, 24 April 2011 (UTC)

What about Methylmercury, could this be a part of sea salt in some way? – Kerαunoςcopia^◁_galaxies 18:43, 24 April 2011 (UTC)

I doubt that it can be integrated into the crystal lattice of NaCl in any relevant quantity. So it will remain in the not crystallised brine. If the producer of the sea salt washes that away, as he should, instead of waiting until all liquid has evaporated (and thus every solid has crystallised) you won't find any of this in your salt. 93.132.153.177 (talk) 19:24, 24 April 2011 (UTC)

Well, methylmercury is a salt. And remember that sea salt's main claim to fame, as marketed in the U.S. is the wide variety of micronutrients it is supposed to bring - bits of potassium, magnesium, calcium, iron etc. But methylmercury is best known for bioconcentration, leading to high doses in fish eaten, which shouldn't happen in sea salt. Wnt (talk) 19:55, 24 April 2011 (UTC)

Methylmercury a salt? I'm not a chemist, but that doesn't fit the nomenclature I'm aware of. I'd have called it an organometallic. If you'd said mercury chloride, you'd be right, of course. --Trovatore (talk) 05:16, 25 April 2011 (UTC)

CH3Hg+ X-, as per the article. Wnt (talk) 06:25, 25 April 2011 (UTC)

What's the X-? I thought methylmercury was (CH3)2 Hg, with the C-Hg bonds being a covalent-ionic mix, but more to the covalent side. --Trovatore (talk) 20:56, 25 April 2011 (UTC)

My mistake — I guess that's dimethyl mercury. So methylmercury would show up in crystalline form as a salt, although strictly speaking it's not a salt itself, but rather a cation. Methylmercury chloride, for example, would be a salt. --Trovatore (talk) 23:36, 25 April 2011 (UTC)

Potassium? Really? PANIC!!!! You know that it is radioactive!?! And BTW, not every salt has affinity to the same structure of crystal lattice, otherwise recrystallization would not work. 93.132.153.177 (talk) 20:03, 24 April 2011 (UTC)

Oh, I know that - but this isn't a chemistry lab. Who knows how many kinds of crystals they're starting with, or how far the crystallization progresses? Wnt (talk) 20:20, 24 April 2011 (UTC)

I guess the first things to form crystals are those with the highest concentration, that is, NaCl. But analogous with distillation, you should discard the first and the last part. If you don't trust the producers, you might as well assume that they mix in sand or other things. 93.132.153.177 (talk) 20:41, 24 April 2011 (UTC)

It's not that I don't trust them - it's just that they're not being paid to produce pure NaCl, but impure NaCl. If they're making pure NaCl they might as well open a salt mine. As the case I gave demonstrated, the levels of impurities in sea salt are not orders of magnitude below the defined permissible limits. If a sea salt operation is abruptly subjected to pollution (say by illegal dumping at sea, or a shift of the current from a polluted watershed) then someone has to be awake at the switch or they could indeed have impermissible levels. Not saying that's a meaningful danger, just that there is valid reason to watch. Wnt (talk) 23:03, 24 April 2011 (UTC)

There are radioactive isotopes of potassium (just as there are for most, if not all, elements), but the two most abundant abundant isotopes aren't radioactive (see the infobox on the potassium article). You don't really get abundant radioactive isotopes except where they are being produced by human activity, since radioactive means they decay, so they don't last long. There are some abundant long half-life radioactive isotopes (such as those of uranium), but long half-life means they aren't very radioactive. --Tango (talk) 21:52, 24 April 2011 (UTC)

There are naturally occuring radioactive isotopes potassium in quite large quantities. Otherwise the earth's core would not be molten any more. And no one has to feel guilty for that. But OK, for those who like it: The END is coming! Save your souls! Repent of your sins to me, do what I tell you and send me all your money.95.112.225.249 (talk) 09:33, 25 April 2011 (UTC)

The radiation from potassium in the body actually is the largest part of background radiation. See Background_radiation#Radiation_inside_the_human_body. Wnt (talk) 06:28, 25 April 2011 (UTC)

And yet here we are, alive and well. I think that is evidence supporting my point that the abundance of radioactive potassium is not sufficient to cause any problems. --Tango (talk) 10:58, 25 April 2011 (UTC)

I didn't say otherwise. Background is background - people have been surviving it since there were people. Wnt (talk) 19:57, 25 April 2011 (UTC)

Kevlar Production

It's about the production of Kevlar by the reaction between 1,4-phenylene-diamine (para-phenylenediamine) and terephthaloyl chloride. http://en.wikipedia.org/wiki/Kevlar. By analyzing the given chemical equation, I got confused in the product of the equation. Shouldn't it be -Cl on the outside of the bracket and not -OH? Jaypril27 (talk) 16:55, 24 April 2011 (UTC)

At some point the terminal -Cl group will hydrolyze very easily with even the smallest amount of water. See Acyl_chloride#Reactions. So, I'm not sure when the terminal -Cl becomes hydrolyzed, but I am pretty confident that it is correctly converted to an -OH in the final product. --Jayron32 19:57, 24 April 2011 (UTC)

Water splitting on a worldwide scale

I'm to understand that splitting water into hydrogen and oxygen is something considered for powering hydrogen fuel vehicles. My question is...on an industrial scale what impact would this have on the world's water supply? If, say, 1 tonne of water is split into hydrogen and oxygen does that mean that the world now has 1 tonne less water? I ask this purely because I thought the earth is a 'closed' system of water and that the volume of water doesn't change, just the 'state' the water is in (e.g. solid, liquid, gas) but if we split it apart does that mean we 'lose' the water or will it recombine later? Sorry if completely daft question! ny156uk (talk) 20:49, 24 April 2011 (UTC)

Yes, there would be one ton less water; that one ton of water would have been converted into a few hundred pounds of oxygen and a few pounds of hydrogen. Later, the hydrogen would be burned, and would recombine back with oxygen to form the same amount of water. Nimur (talk) 20:53, 24 April 2011 (UTC)

Hydrogen isn't an energy source. It's just a way of storing energy. You split the water into oxygen and hydrogen, using energy that you have got from somewhere else, and then store the hydrogen until you need the energy. You then react it with oxygen (ie. burn it) and the energy is released again. The water isn't used up in this process, just temporarily transformed. --Tango (talk) 21:55, 24 April 2011 (UTC)

I suppose some leaked hydrogen might rise to the top of the atmosphere and get blown away on the solar wind - no idea if that is even a hypothetically detectable amount, though. Wnt (talk) 22:59, 24 April 2011 (UTC)

Let me just note that by a back-of-the-envelope calculation I just did, if we derived all of our energy from splitting water, and lost all of the byproducts, it would take a few hundred million years for us to run out of water. There's a lot of it out there. Looie496 (talk) 05:47, 25 April 2011 (UTC)

We don't have to run out of water to have problem. A reduction in sea level by a few feet could cause a problem, although rising sea levels from melting glaciers may cancel this out. However, if lake water was used, then we could have falling lake levels at the same time as rising oceans. StuRat (talk) 14:15, 25 April 2011 (UTC)

Yes, there's no shortage of water, so there would be negligible impact on the world's water supply, especially since most of it will be recovered (as mentioned above). There might be a slight modification in rainfall patterns as a result of moving water around the planet (either as liquid or as its constituent gases). The real problem is where will you get the energy from to split the water? Dbfirs 07:56, 25 April 2011 (UTC)

Plants do that all the time. Only they are intelligent enough not to produce hard to handle elementary hydrogen gas but to bind it to carbon. H₂O + CO₂ → O₂ + "sugar", where "sugar" is anything built from HCOH fragments. 95.112.225.249 (talk) 09:13, 25 April 2011 (UTC)

... so a genetically modified plant that has its intelligence reduced so that it produces raw hydrogen and oxygen from sunlight would be a cheap alternative to solar panels. The problem would be in safely collecting the hydrogen. Perhaps it could be modified to excrete the gases from separate ducts, or perhaps our current system of biofuels is safer? Dbfirs 11:30, 25 April 2011 (UTC)

I just imagine a hollow dandelion stem swollen to ball size with hydrogen and oxygen, waiting for someone to come along and then to go booooom 95.112.225.249 (talk) 12:01, 25 April 2011 (UTC)

Amazingly, we actually have an article on biological hydrogen production! Looie496 (talk) 04:51, 26 April 2011 (UTC)

April 25

PBS series about a family using 1980's computer

I saw a few minutes yesterday of a US Public Broadcasting System program (likely originally BBC) in which a British family was forced to use old electronics. They had to choose a 1982 computer, and chose a "BBC computer" over a Sinclair or Commodore. Later, they acquired a VHS player and huge camcorder. What was the series? It seemed almost like a Twilight Zone episode, when they went to the "Computer Museum" (rather than my living room or attic) to get electronics of the 1980's. Edison (talk) 00:53, 25 April 2011 (UTC)

It was probably Electric Dreams (TV series). I still have a BBC computer and a VHS recorder from the 1980s, and I remember using a shoulder-size video camera, though they were too expensive for me to own one. Dbfirs 07:47, 25 April 2011 (UTC) (Apologies for edit conflict with Ny156uk whose apparently earlier reply has mysteriously appeared below mine.) Dbfirs 07:59, 25 April 2011 (UTC)

Is it the series 'Electric dreams' by the BBC? (http://www.bbc.co.uk/electricdreams/) The family spend some time in the 70s, the 80s and then the 90s. We've an article on it Electric Dreams (TV series) ny156uk (talk) 07:43, 25 April 2011 (UTC)

Thanks! Edison (talk) 18:55, 25 April 2011 (UTC)

Do avocados contain cholesterol?

Do Avocados contain cholesterol? Also, why does the label on the bottle of vegatable oil at my local supermarket read "No cholesterol" if vegatable oil doesn't normally contain cholesterol anyways? Which foods DO contain cholesterol? Thank you. 161.165.196.84 (talk) 03:39, 25 April 2011 (UTC)

The short answer is "no". Cholesterol is only present in any reasonable amount in animal tissue. Cholesterol is a molecule that forms part of the cellular membrane in animals. Plants have a different architecture in their cell walls that does not require cholesterol to regulate fluidity, therefore only animal derived foods contain it. Vegetables and vegetable-derived products, such as avocados and vegetable oil do not contain cholesterol. The statement on your vegetable oil bottle may be obvious to an informed consumer like yourself, but nevertheless is put on for marketing to make the product more desirable for buyers. —Preceding unsigned comment added by 160.79.139.10 (talk) 05:01, 25 April 2011 (UTC)

It should also be noted that choloesterol intake does not directly corrolate to blood cholesterol levels. Your body manufactures cholesterol and cholesterol derivatives from all sorts of sources, so its quite possible to subsist on a fully vegetarian diet and have a high cholesterol. People still have that silly "you are what you eat" mentality, so when the doctor says "You need to get your cholesterol down" they think they can simply cut cholesterol out of their diet and that will help. Its way more complex than that. --Jayron32 05:11, 25 April 2011 (UTC)

Understood; It has always been my understanding that the purpose of cholesterol is to act as a sort of temperature buffer (regulating fluidity) in the phospholipid bi-layers of animal cell membranes; so it makes sense that plant products would not contain cholesterol. thank you for the responses and helping me put this debate to rest. Sorry Roberto / Charissa —Preceding unsigned comment added by 161.165.196.84 (talk) 05:30, 25 April 2011 (UTC)

I always thought the main purpose of cholesterol was to serve as a reservoir of raw material for the manufacture of steroids. Hadn't heard of the temperature thing; sounds interesting though. --Trovatore (talk) 05:41, 25 April 2011 (UTC)

Plants have no substantial reservoirs of cholesterol, but do produce lots of steroids, see Phytosterol. I'm pretty sure that the steroids, being terpenes, can all be synthesized from first principles without going through cholesterol directly. --Jayron32 05:56, 25 April 2011 (UTC)

See also Lanosterol, which IS the starting material for steroids. I think cholesterol, being a steroid, is actually synthesized from Lanosterol like the rest of them. --Jayron32 05:58, 25 April 2011 (UTC)

As per Cholesterol#Dietary sources, fat intake, particularly of saturated fat and trans fat, actually plays a larger role in blood cholesterol than consumption of cholesterol itself. Saturated fat is mainly found in animal fats, but there are also a few plant foods containing large amounts of saturated fat, in particular palm oil and its relatives. However, palm oil might not be as bad for you as animal sources of saturated fat; see Palm oil#Comparison with animal saturated fat. Animal fats used to be the only source of dietary trans fats, but they are now also in partially hydrogenated vegetable oils. (Regular liquid vegetable oil hasn't been hydrogenated.) Red Act (talk) 06:13, 25 April 2011 (UTC)

You are aware that hydrogenating removes a double bond? That is you saturate the fat. 95.112.225.249 (talk) 09:07, 25 April 2011 (UTC)

Not if it has more than one double bond, hence partially hydrogenated. --Jayron32 12:59, 25 April 2011 (UTC)

blood type

If the mother is type B and the father is Type AB is it possible to have a type A baby? If both parents are type B is it possible to have a type A baby? — Preceding unsigned comment added by Everlalin (talk • contribs) 09:51, 25 April 2011 (UTC)

Yes for the first question, no for the second. See ABO blood group system. As with everything that has to do with biology, there might be very rare exceptions to the rules. Type B has either double genes for B or one for B, one for O. AB always has both A and B genes. Type A has either double A or A and O. So if the mother has genes B and O and the father A and B there is a 1 in 4 chance that the child will have A and O genes and as the O genes don't express anything that is measured by the tests the resulting blood type will be A. If both parents lack the A gene it is impossible for the child to have one. 95.112.225.249 (talk) 10:24, 25 April 2011 (UTC)

Before anyone makes any conclusions such as diagnosing a "nonpaternity event," he should also note that occasionally the blood type for an individual is reported incorrectly. In a case where both parents are reported to be or or thought to be type B, one might be in fact something else. Even if someone with incorrectly reported blood type received a transfusion in an operation, there are variations in which it would not have caused a serious reaction (like 60% of the time, on average), so the incorrect report would not have been caught (for other mismatches there would be fatal results). Edison (talk) 18:53, 25 April 2011 (UTC)

Does Diet Coke cause cancer?

People have told me not to drink Diet Coke or any diet sodas because they contain aspartame which causes cancer, is there any truth to this? --112.213.139.29 (talk) 10:47, 25 April 2011 (UTC)

We have an article about aspartame, where you can read all about this ingredient, and follow further to the Aspartame controversy article about health concerns. Both of these appear to be well-referenced from many reliable sources (rather than just "I heard...") to explain the concerns and currently available research and conclusions. Also, there are diet sodas that use other artificial sweeteners instead, so you can easily avoid this ingredient rather than the broader category of products that might contain it. DMacks (talk) 10:50, 25 April 2011 (UTC)

Pretty much everything you can imagine has been reported to cause cancer in one study or another. There is no way you can avoid them all. See Carcinogen for some details. --Tango (talk) 11:02, 25 April 2011 (UTC)

You may be interested in the Daily Mail Oncological Ontology Project.--Shantavira|^{feed me} 11:31, 25 April 2011 (UTC)

But some chemicals have stronger correlations than others, obviously. (Or put more precisely, all cancer-causing agents are probabilistic — some increase your risk factor more than others.) That's what the OP is most likely concerned about. There are quite a lot of studies on aspartame in particular, which are discussed in the article. --Mr.98 (talk) 11:35, 25 April 2011 (UTC)

I think that when looking into chemical controversies, the first thing to put into context is the patent expiration date. In the case of aspartame that was December 14, 1992, at which time the price fell from $70 per pound to $20-$35 per pound.^[13] When the same or other companies have new patented products to compete on the market, such a cheap competitor is clearly a major problem.

Now by comparison to other chemicals, the situation with aspartame was adjudicated with great integrity. By contrast, the FDA had just made up a new power to ban the herb stevia in 1991, requiring congressional action (DSHEA) four years afterward.

Also consider Accutane, which upon its patent expiration in 2002 was found to be so teratogenic that special restrictions had to be placed on it. Then the FDA, finding that the original manufacturer had abused its first program, decreed that once generics would become available, it was necessary to impose iPLEDGE, a program so draconian and lunatic that, for example, men had to promise not to become pregnant.

For a similar example, consider Oxycontin, which in slow-release form was patented as a "less addictive opiate". This turned out to be bogus advertising, and the manufacturer was hit up with an unprecedented $600 million fine (for its $1.2 billion annual profit on the drug). After that they introduced a new "safer" form and have ten more years on that patent.

I don't think it is unreasonable to conclude that proving a compound unsafe at the end of its patent term is as important to the pharmaceutical company as proving it safe when it is introduced. (And often not so difficult for those who know all the little details glossed over in the original studies) Wnt (talk) 19:52, 25 April 2011 (UTC)

Laser pump design

In electrically pumped TEA lasers, what consideration is given to the efficient matching of the source and load impedances? I mean, do designers of this type of laser ever think about efficiently matching, or is this not possible? What is the effictive load impedance of the discharge etc? Also, why do the designs waste half of the energy by shorting out one of the capacitor plates with a spark gap and therby losing half the stored energy? This seems most inefficient.--79.66.81.54 (talk) 10:56, 25 April 2011 (UTC)

If you're referring to the circuit designs linked from Professor Csele's webpage above, that was a "homemade TEA laser," (albeit, made by a professional laser physicist). An industrially designed LASER from one of the major vendors will probably have a team of power electronics engineers specifically dedicated to optimizing the power supply. A major problem in lasers, particularly of the sort you've been investigating, is thermal loss in the gain medium due to poor quantum efficiency; the power supply should be tuned to deliver a pulse duration and intensity that is suitable for the statistics of the gain medium. The chemical and physical properties of the gain medium will determine its electrical impedance, and cannot be easily summarized, even as a complex impedance. See active laser medium for details. It's not unlike asking for the impedance of a transistor or a vacuum tube; the device is active and has multiple ports, so the system as a whole requires a more elaborate treatment. Other common power supply efficiency can be analyzed as well, such as power factor correction, albeit that the load impedance is very very very nonlinear/non-uniform/non-ideal. In an ordinary experimental setup, it's up to the physicist to determine if that thermal energy loss interferes with his/her measurement, or affects his electric bill in any meaningful way. Nimur (talk) 14:31, 25 April 2011 (UTC)

Can a dish washer dissolve rubber compeletely?

I had a rubber band for home canning the like of which you can see here in my dish washer and can't find the least trace of it now, not even tiny bits spread around in an ugly way and sticking to everything else, as sometimes happens with other things. Is it possible that it has been completely dissolved? 95.112.225.249 (talk) 14:33, 25 April 2011 (UTC)

It's unlikely that the temperatures of the dishwasher could melt the rubber; nor that any chemical in the detergents would dissolve rubber completely. However, the combination of heat and detergent sounds like a great scenario to denature the rubber - it probably loses its elasticity, becomes crumbly, and the pieces easily flow down the drain. We have discussion of the chemistry behind natural rubber elasticity at our article. Nimur (talk) 14:38, 25 April 2011 (UTC)

I am astonished. So you could make a kind of fridge that uses rubber instead of a gas? My late rubber band would be originally designed to withstand boiling temperatures whereas the dish washer nominally gets only up to 70C°. 95.112.225.249 (talk) 14:49, 25 April 2011 (UTC)

It's true that rubber has interesting thermoelastic properties, and the thermodynamics of elasticity has been heavily studied by physicists and material scientists. I don't think you could make a practical refrigerator out of it; we have several articles related to refrigerator thermodynamics, start with heat pump and refrigeration cycle for an overview. Numerous lab demos exist to show the effect of temperature on elasticity; it's harder (but not impossible) to show the effect of elastic expansion on temperature. Nimur (talk) 16:27, 25 April 2011 (UTC)

From the section natural rubber elasticity you gave I can see that you can "wring out" the heat energy from rubber by stretching it like water from a sponge. This is what normally happens in the condenser step of the refrigerator cycle. So I imagine it is easy to put up a cycle where rubber is stretched and, loosing degrees of freedom, gains temperature and looses heat energy by exchange with the environment. When relaxed again, it gains degrees of freedom, the heat capacity goes up and it takes heat energy from the environment. I cannot believe I'm the first one to think of it. Either there is some flaw in my reasoning or there must be some rubber-fridge already. 95.112.225.249 (talk) 22:10, 25 April 2011 (UTC)

You may be interested in thermoplastic. Also, some descriptions of kevlar attribute the armor's "bullet-stopping" capability to the thermal properties of the fibers. While it is possible to transform bulk kinetic energy into thermal energy, and therefore transfer heat, a practical refrigerator needs a medium with a high heat capacity; the quantity of thermal energy you can transfer using only elastic deformation of a polymer is very small, compared to a conventional refrigerant. Nimur (talk) 22:57, 25 April 2011 (UTC)

Do you have any figures at hand? (I admit I'm too tired and lazy right now to search for myself9. The key figures would be the heat capacity of the rubber when stretched compared to when relaxed. I don't see how any melting points or glass temperatures would come in. 95.112.225.249 (talk) 23:11, 25 April 2011 (UTC)

No, I don't have any hard numbers; but if you don't have the physical intuition to see why a rubber band stores very little heat as it expands, compared to a refrigerant, what makes you think you've got the physical intuition to interpret a numeric measure of heat capacity? At the end of the day, the universe does what it should, irrespective of any equation we wrote to model it numerically. Nimur (talk) 03:23, 26 April 2011 (UTC)

Nimur's words with Voltaire's Pangloss express the Leibnizian optimism of Pangloss about the Universe. The OP may inspect the door seal on their dishwasher that I wager is made of Neoprene, a synthetic rubber that hopefully has not perished as unvulcanized caoutchouc is prone to do. Cuddlyable3 (talk) 08:54, 26 April 2011 (UTC)

Pharmacology - Dose Effect Curves

A standard pharmacology experiment is to place a piece of smooth muscle into an organ bath, that contains a concentration of drug and to measure the contraction / relaxation of the drug.

Can then plot a dose effect curve for the results at different concentrations and use this to work out the maximum response that a drug can produce and the EC50 value.

My question is... Since the concentration of the drug in the organ bath is completely different from the concentration of drug at the receptors, what is the point of this experiment? Is not the drug concentration at which a 50% maximal response obtained then completely arbitrary? Or can the results of this experiment only be used to compare other drugs in exact some situations?

Hope that makes sense!

Thanks :) — Preceding unsigned comment added by 138.38.187.77 (talk • contribs)

Trees and/or plants affected by white-tailed deer and invasive species in Maryland

I'm looking to research a plant or tree whose future is potentially compromised by both overgrazing of the white-tailed deer population and the presence of invasive species, specifically in the state of Maryland. Any suggestions, links or reading recommendations would be greatly appreciated. — Preceding unsigned comment added by Marie Poling 03 (talk • contribs) 19:05, 25 April 2011 (UTC)

Have you tried using Google Scholar to start your research? --Jayron32 19:08, 25 April 2011 (UTC)

Also try the invasive species listing for Maryland. ~AH1 ^(discuss!) 21:16, 25 April 2011 (UTC)

motional electric field

http://www.rexresearch.com/hooper/horizon.htm#intro 'During World War II the writer, working on an invention for a "drift and ground speed meter for aircraft", arrived at a plan for utilizing the vertical component of the earth's magnetic field. If the voltage induced between the ends of two oriented linear conductors traveling horizontally across the vertical component could be measured within an aircraft, a self-contained meter, independent of ground instrumentalities, would be forthcoming. The plan was reviewed by the U.S. Bureau of Standards, and its workability confirmed under a certain restriction. It was stated that the device would be inoperable within a conducting cavity such as a metal-clad aircraft. Our textbbooks have taught us that when a linear conductor moves with a velocity V across a magnetic flux of intensity B, an electric field of vector intensity VxB is induced within the wire and gives rise to a voltage at its terminals. This electromagnetically induced electric field, often called a motional electric field, we have been taught, would be electrostatic in character, that is, identical and indistinguishable from an electric field arising from charges of electricity. We know that radio tubes, silvered on the inside, shield the interior from stray electrostatic fields. In the same way, it was explained, such a drift and ground speed meter within a metal-clad aircraft would be shielded from the electric field induced in a conductor by motion across the vertical component of the earth's magnetic field. This explanation was a jolt to the writer. How could we know, without experimental evidence, that such would be the case? This presented a great challenge! Some of the foremost thinkers in physics were consulted. It was discovered that there was no experimental evidence to support the popular belief held by physicists that the motionally induced V x B field was electrostatic in its fundamental character and therefore subject to shielding. It will be shown how, step by step, the writer has been guided over a period of 20 years to experimental means which at last reveal experimentally, beyond all doubt, the beautiful unique properties of the motional electric field. It is not electrostatic! Its immunity to shielding, magnetic or electrostatic, is the exciting property which it shares with the gravitational field and thereby indicates their kinship. By a general theorem in electric field theory we know that a non-uniform B x V field must also act attractively on matter! Thus the motional electric field has acquired a status which makes it quite unique.'

What are your thoughts on the article how the electric field should be shielded? and the fact that we do not know that the the motionally induced V X B field was electrostatic in its nature and the fact that the non uniform B x V field must attractively on matter is this true from the article? How has not modern traditional science not seen this? — Preceding unsigned comment added by Lufc88 (talk • contribs) 20:38, 25 April 2011 (UTC)

Bluntly, you've stumbled on the self-published work of a crank who thinks he's discovered some sort of new fundamental theory of electromagnetism, and wants to use it to build gravity-cancelling devices. TenOfAllTrades(talk) 22:02, 25 April 2011 (UTC)

The Earth's magnetic field indeed penetrates an aluminium-clad aircraft but you will find it does not penetrate a thick iron-walled sphere. I don't know why you wish to shield an electric field but a Faraday cage is a means. The linked article notes that Faraday cages cannot block static and slowly varying magnetic fields, such as Earth's magnetic field (a compass will still work inside), and they are only partially effective in blocking electromagnetic radiation. I apologise that the OP's initial link was TLDR for me and I still need convincing that a "non-uniform B x V field must [act?] attractively on matter". Does that cause radio transmitter antennas to collect dust? Cuddlyable3 (talk) 08:37, 26 April 2011 (UTC)

The linked article really isn't worth reading all of. I only read a bit of it myself, but in what I did read, the author was racking up points on crackpot index items 11, 17, and 18, at least, which just isn't a good sign. Red Act (talk) 13:07, 26 April 2011 (UTC)

oh right any one else got any thoughts on this Lufc88 (talk) 16:13, 26 April 2011 (UTC) Lufc 88

NNRTIs and Hep B

Are any NNRTIs used to treat Hepatitis B infection? The drugs used to prevent Hep B replication only appear to be of the NRTI class. I've had a look on each NNRTI page but they all seem to be used to treat HIV. Trying to search for it on Google only seems to bring up a side-effect of NNRTI usage as hepatitis... So even judging from that, it does seem unlikely they would be used but maybe someone knows better than I do. Thanks! 86.185.188.62 (talk) 21:13, 25 April 2011 (UTC)

I never bothered to learn about HBV, so I started with Hepatitis B and Hepatitis B virus. The latter article describes only four genes, of which three don't sound like they have known enzymatic activity. So I focused on Hepatitis B virus DNA polymerase. Specifically, I typed into Google "Hepatitis B virus DNA polymerase inhibitor". Unfortunately, no direct hits. The non-quoted phrase hits cover all sorts of nucleotide inhibitors - I looked at one page of hits. Among these I ran across description of IFN alfa-2b as a treatment, but not curative.^[14] That isn't what I'd call NNRTI though. So I tried the phrase without quotes and added quoted term "non-nucleoside". This gave some 34 hits, including [15]: this includes foscarnet as a "non-nucleotide inhibitor", but it's a product analogue (pyrophosphate). In my mind that doesn't count either. To quote (Google serves up pages from this $439.95 book, written 2007):

"As described above, nucleoside analogues can inhibit cellular as well as viral enzymes, and viruses can mutate to resist to these drugs. As a result, efforts have been made to discover compounds that might inhibit viral polymerases by other mechanisms. The first of these to be approved for clinical use was foscarnet (phosphonoformic acid [PFA]), whose structure is shown in Figure 14.6. Although it is not orally available and intravenous administration is required, it is nephrotoxic; it is approved for treatment of severe HSV, VZV, and HCMV infections that are resistant to front-line drugs.

Foscarnet is an analogue of pyrophosphate, which is a product of polymerization of nucleic acids. Unlike the nucleoside analogues described above, it does not require activation by either cell or viral enzymes but rather inhibits Pol directly. Inhibition is not competitive with deoxynucleoside triphosphates. Rather, it appears that foscarnet acts as a product analogue, evidently by binding to the site normally occupied by pyrophosphate and preventing normal pyrophosphate release so the polymerase cannot complete the catalytic cycle (97,248). Selectivity arises from the viral Pol being more sensitive than cellular enzymes, which is confirmed by the existence of foscarnet-resistant pol mutants (82,96,114). Resistance is caused by an altered polymerase that is less susceptible to foscarnet inhibition.

Because foscarnet is not a nucleoside analogue HSV tk mutants and HCMV UL97 mutants are not resistant to it. Although foscarnet inhibits DNA polymerase by a mechanism that differs substantially from the nucleoside analogs, many pol mutants that are resistant to nucleoside analogs are resistant to foscarnet. Moreover, most foscarnet-resistant mutants are resistant to one or more nucleoside analogs (116). Thus, for some patients with serious herpesvirus infections, no viable treatment options are available. This should be an impetus to further drug development."^[16]

Now searching "foscarnet hepatitis B" on PubMed,^[17] I don't find any recent papers mentioning it, which I would think would happen if someone were testing a new non-nucleoside inhibitor for the viral polymerase. But I haven't searched those other funny proteins with other functions yet. At the most fundamental level, HBV doesn't look like it has a protease, so it doesn't have HIV protease inhibitor like drugs as an option. I hope that by tracing my steps here, I've shown those interested how to continue researching these things over time as drug development progresses. Wnt (talk) 23:35, 25 April 2011 (UTC)

Hmmm, taking another look, it seems like HBx now has a known function as a transcriptional activator (It's not a transcription factor that binds DNA directly^[18] - it just changes the effect of something like E2F).^[19] It sounds like it makes the liver cell more vulnerable to apoptosis from other causes (such as transient ischemia).^[20] But according to PMID 21468663 the bastard little protein actually protects expressing cells from death by etoposide, reducing the effectiveness of this as an anti-cancer treatment. (But not cisplatin) And if that's not enough, it interferes with DNA repair.^{[PMID 21375739]} According to PMID 21490166, it predisposes the liver to hepatocellular carcinoma more when a particular mutation, HBx5, is present. It is actually essential to the HBV life cycle.^{PMID 21376091}

Now transcriptional factor activity is conceptually a sort of vast neural network of cellular decision-making, and there are many ways to try to counteract an effect. One I found in the search was PMID 19172229 (2010), concerning a Phase II clinical trial to test PXD101 (belinostat), a histone deacetylase inhibitor, in inoperable hepatitis B hepatocellular carcinoma. As you can see this has been a really quick and dirty search; hopefully there is more I missed, and more on the way. Wnt (talk) 00:02, 26 April 2011 (UTC)

(response to OP, further indented to avoid confusion with post above) For NRTIs (which are nucleoside/nucleotide RT substrate analogs), there are shared binding determinants because both HIV RT and HBV Pol have reverse transcriptase activity, resulting in substantial active site homology. NNRTIs bind at sites removed from the active site; therefore, there's little reason to expect that NNRTIs developed for HIV would be active against HBV - here is an example: PMID 10377169. With over a billion people infected with HBV, and many of those infected with both HIV and HBV, you can be assured that the pharma companies are looking for such activity for two reasons: (i) market, and (ii) safety issues of inadvertent HBV treatment when treating HIV - due to issues of resistance and HBV flares when HIV treatment is stopped PMID 18447614. -- 00:40, 26 April 2011 (UTC)

the kinetics of 3H + 2H ---> 4He + n

How do I calculate the final kinetic energies of each particle, if Q is 17.7 MeV and final momentum is zero? This apparently should be a really really easy two-body problem, but all the google guides on collisions out there assume your masses don't change mass and release energy. John Riemann Soong (talk) 22:22, 25 April 2011 (UTC)

The equations are simple: E₁+E₂=E₃+E₄ with E_i= (c₀²+1/2 v_i²)m_i and v₁m₁ + v₂m₂=0. When I said the equations are simple I didn't mean to say it is easy to resolve them, not at my given local time of day. But I don't see any higher maths involved either.95.112.225.249 (talk) 22:51, 25 April 2011 (UTC)

The solution given above assumes non-relativistic speeds which may or may not be the case. If that's indeed the case, than the solution is really trivial. use the second equation to express one of the final velocities in terms of the other and substitute it on the first equation, which will then have only one unknown and will be easy to solve. Dauto (talk) 23:20, 25 April 2011 (UTC)

I'm afraid that with neutrons of that energy we are on the brink of leaving the range of Newtonian mechanics. Neutron temperature#Fast neutrons. 93.132.131.100 (talk) 23:41, 25 April 2011 (UTC)

Nah... The neutron mass is about 50 times larger than that energy. Newtonian mechanics should still give a reasonable approximation. Dauto (talk) 04:33, 26 April 2011 (UTC)

Application of brain lateralization to UI design?

The article Lateralization of brain function doesn't discuss the phenomenon's applications. This article claims that gamers should place UI elements that they respond to with the right hand on the right side of the screen, and those that they respond to with the left hand on the left side, to shorten reaction time. Do any ergonomic studies support this claim? Is it possible that a gamer might be able to process some elements of the game state faster in one lobe than the other? NeonMerlin 00:43, 26 April 2011 (UTC)

A lot of "left-brain" and "right-brain" theory was never founded on scientific experiment, and most of it has been pretty thoroughly discredited. What we're left with is a much more vague, but much more believable, theory of functional specialization (brain). It may take decades for "pop psychology" to let the numerous invalid ideas go to rest, though. There is very little actual evidence to suggest, for example, that the "left side" of the brain is more suited to (or more active during) quantitative or numeric cognitive activity. Nimur (talk) 00:50, 26 April 2011 (UTC)

That's all true, but there is some pretty solid evidence that simple visuomotor reactions are faster when they use the hand on the same side as the stimulus (for example PMID 7128169). It is much less clear what happens when the stimuli are more complex or require sophisticated decision-making. From an anatomical point of view, the brain is wired such that the visual input from the right side of the world goes to the hemisphere that controls the right hand, and the left side matches with the left hand, so the basis for such an effect is certainly there. Looie496 (talk) 01:28, 26 April 2011 (UTC)

How to save generic annotated DNA sequences?

There is a sequence here in a generic form with annotations. How do I save it so that I can open it in a capable program which will feature the described annotations? Thanks. --129.215.47.59 (talk) 14:24, 26 April 2011 (UTC)

Can you be more specific about what you want to ultimately be able to do with the sequence? The "capable program" you choose (and there are lots of options) is going to depend on your application, and each program probably has a different input format. If you already have a program you want to use, then there should be some kind of FAQ or user guide that describes the required input. If you haven't already selected a program, then the question you really want to ask is "what program should I use to accomplish X". --- Medical geneticist (talk) 15:01, 26 April 2011 (UTC)

Hi. Thanks for your response. The program is called SeqBuilder; it's a miserable excuse for a cloning tool which we use because our Institute cannot afford Vector NTI. However, the page that I link to presents the genetic and annotation information in a way which I have seen time and time again in my short scientific life and this leads me to believe that it is some sort of generic format, capable of being understood by a number of different programs. If I save it as an .sbd file, SeqBuilder will open the sequence but ignore the annotations. I hope that by appending the correct file extension, I'll achieve an annotated sequence. --129.215.47.59 (talk) 19:33, 26 April 2011 (UTC)

Fermi Paradox and data encryption

Our article on the Fermi paradox says that compressed data streams would be almost indistinguishable from white noise. Would not the same apply if the data was encrypted? A Quest For Knowledge (talk) 17:06, 26 April 2011 (UTC)

If it's good encryption, then absolutely. See page 13 of this book. So you're hypothesizing that the galaxy is teeming with life that communicates by radio, but it's encrypted, so we have no idea? Comet Tuttle (talk) 17:13, 26 April 2011 (UTC)

Both for compressed and encrypted streams, this assumes the data is sent with no kind of framing. You can communicate over an unreliable medium with a self-synchronising code, but why would you bother (unless you were trying to conceal the transmission)? Note that the assertion about compressed streams in that article is unsourced. -- Finlay McWalter ☻ Talk 17:23, 26 April 2011 (UTC)

I'm also not convinced, absent a decent reference, either that a) a compressed stream resembles white noise as opposed to another colour (particularly for schemes which periodically flush their dictionaries) or b) that the cosmic or galactic noise you'd typically see is white either. -- Finlay McWalter ☻ Talk 17:36, 26 April 2011 (UTC)

It also depends on what your definition of a "resemblance" is. A wide band signal will fill the fourier-domain spectrum, but not with random data. So, if you define a signal to "resemble" white noise, solely on the basis of whether it occupies a wide frequency band, then a lot of things "resemble" white noise. Ultimately, if you use a deterministic compression methodology, each compressed input stream will have a unique spectral signature; so the characteristics of the output stream will depend entirely on what data is being transmitted. If you use a lossy compression scheme, any particular source stream will map to one of a finite set of possible compressed stream spectral signatures. I'm not very happy about our "color of noise" article, which seems to blur the terminology. I like our noise shaping article much better; and will toss in that digital signal quantization has unique spectral properties that are easily detectable as "band limiting;" the modulation scheme for any particular signal will dictate whether the band limitation exists as a fourier frequency band, or as some other more abstract vector-space spectrum (such as phase-space, or generalized wavelet spectrum, etc). Nimur (talk) 18:13, 26 April 2011 (UTC)

Toasted bread

why does the toasted bread tastes sweeter than the normal bread? —Preceding unsigned comment added by 122.162.128.226 (talk) 17:29, 26 April 2011 (UTC)

See Maillard reaction. --Jayron32 17:38, 26 April 2011 (UTC)

The sugar components of starch (amylose, glucose, etc) are relatively tastless in starch form. But when subjected to dry heat it produces pyrodextrins through process called pydrodextrinization (strange as it may seem). More like the sugars we use for sweetening. Wiki article (starch)scroll to pyrodextrinization.Phalcor (talk) 18:48, 26 April 2011 (UTC)

Without reading the article, I will tell you that you can link to the 'starch' article on this wiki by typing [[starch]], which gives you a blue link like this: starch. If there is a header 'pyrodextrinization' in the article, you can link to it by typing [[starch#pyrodextrinization]] which produces starch#pyrodextrinization. 82.24.248.137 (talk) 20:43, 26 April 2011 (UTC)

Oh, and I see that you probably meant people to read the bit under starch#dextrinization. 82.24.248.137 (talk) 20:44, 26 April 2011 (UTC)

perennial

Resolved

The Taraxacum officinale article says that they are perennial, but I can't see any mention of exactly how long they usually live. I know perennial means more than 2 years, I would like to know more specifically how long they can live for. 82.43.89.63 (talk) 18:56, 26 April 2011 (UTC)

The thing is, 'death by old age' doesn't really apply here. Dandelions exhibit indeterminate growth. So, death of a mature plant will usually be due to Plant_pathogens, herbivory, roundup, etc. In this light, the average life-span of a dandelion in a given population will depend on how prevalent these sources of mortality are. In principle, I know of no reason why a well-cared for specimen couldn't live 100 years or more. SemanticMantis (talk) 19:23, 26 April 2011 (UTC)

Thanks! 82.43.89.63 (talk) 20:33, 26 April 2011 (UTC)

Higgs boson

How does the Higgs boson explain the difference between the massless photon, which mediates electromagnetism, and the massive W and Z bosons — Preceding unsigned comment added by Lufc88 (talk • contribs) 20:04, 26 April 2011 (UTC)

Assuming you understand the contents of these articles (I certainly don't), you may find your answer at Higgs mechanism or 1964 PRL symmetry breaking papers or Higgs_boson#Theoretical_overview. Presumably, the information therin could be summarized in a way that someone who isn't familiar with the mathematics involved, which I will leave to someone else to do. --Jayron32 20:14, 26 April 2011 (UTC)