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March 3

do indoor roses need a night phase?

I notice my indoor miniature rose has a tendency to bloom during my sleep (while the lights are dimmer) and sprout new leaves yet remain static while I'm awake. (Maybe this is a watching the kettle boil thing.) It occurred to me that I don't know what type of photosynthesis a rose would carry out. I suspect C3 (why it needs so much water) -- but if not, does it need a minimum amount of dark per day in order to optimise its growth? I'm not sure if it would schedule some growing phases during the dark.

I know indoor roses often suffer from lack of light. But provided adequate water and fresh, cool air, is it possible to give rose too much light (I'm using purely fluorescent light). The new leaves are remaining yellower longer than expected. I'm growing this in a pot in my dorm until it warms up -- I've basically it elevated the plant until the topmost leaves are barely an inch away from the in-built desk fluorescent light, and I've got another study lamp (fluorescent) with a flexible stem shining on it at the side just centimetres away from the leaves. John Riemann Soong (talk) 03:24, 3 March 2009 (UTC)

Sorry, I don't know a lot about plants and next to nothing about roses. Fluorescent lamps come in many different types and generate various spectra. Plants usually need special grow lamp bulbs for optimum growth. Putting your pot near a window might get you better results. 76.97.245.5 (talk) 09:48, 3 March 2009 (UTC)

Three thoughts: [1] could the yellow leaves be a sign of overwatering? [2] indoor roses have a tendency to not do very well after the initial blooms, unless you let them go through a period of dormancy somewhere cool (like a garage). Are you doing this? [3] Roses require 5 hours of direct sunlight per day. I don't know how many hours of grow-light that translates into. - Nunh-huh 10:13, 3 March 2009 (UTC)

How bad are shrooms for you?

Really...how bad are they for you? I have tried doing research, but I've discovered NOTHING. I can't find anything! Everywhere I go they just talk about the immediate, post-consumption effects of shrooms. Nothing on effects on cognitive ability, memory, recognition of simple shapes/colors..etc. I haven't been able to find a source that describes any sort of long term health issues with chronic mushroom use. This has given me the impression that they aren't bad for you. Am I right? --71.117.36.86 (talk) 03:35, 3 March 2009 (UTC)

Thanks for posting your question. Your question seems to be a request for medical advice. It is against our guidelines to provide medical advice. You might like to re-phrase your question. You may also find it helpful to read the article: Psilocybin, and form your own opinion from the information there. Specific advice below pertaining to the consumption of hallucinogens has been removed. Note to editors: Any response containing prescriptive information or medical advice will be removed. Please ensure your responses are constructed so as not to be construed as medical advice! If you remove a response, please paste it and your reason for removal on the Reference Desk Discussion page If you feel a response you have given has been removed in error, please discuss it at the Reference Desk Discussion page before restoring it.

. Mattopaedia ^{Have a yarn} 06:06, 3 March 2009 (UTC)

Psilocybin#Toxicity is one relevant link. Friday (talk) 03:37, 3 March 2009 (UTC)

No, if you find long-term studies concluding it's safe, then it's safe. If you can't find any such studies because none have been done, then the best answer would be 'We don't know'. Given the track record of the vast majority of hallucinogens I sure wouldn't default towards 'safe'. --Pykk (talk) 03:53, 3 March 2009 (UTC)

There's no clear physiological damage of the kind that you might see with alcohol or cocaine, or with any kind of smoking. On the other hand, changes in cognitive abilities might be difficult to recognize and detect - I don't think anyone's done a controlled study. It seems that it would be difficult to organize one. -GTBacchus^(talk) 04:18, 3 March 2009 (UTC)

Response removed. See discussion page

Please note that this is dangerously close to a medical question, if not over the border. arimareiji (talk) 05:03, 3 March 2009 (UTC)

There are case reports in the scientific literature of Hallucinogen persisting perception disorder as a consequence of psilocybin abuse. HPPD is listed in the Diagnostic and Statistical Manual of Mental Disorders. See for example, PMID 15963699. Rockpocket 07:03, 3 March 2009 (UTC)

Erowid is a good souce for this kind of thing. This is their main mushroom page. Pfly (talk) 09:06, 3 March 2009 (UTC)

That is one big template! --Tango (talk) 13:51, 3 March 2009 (UTC)

To our OP: Absence of information most certainly DOES NOT indicate that there are no problems. There is probably no good online information on the consequences of hitting yourself on the head with the pointy and of an icepick either...but it's not generally recommended. SteveBaker (talk) 15:46, 3 March 2009 (UTC)

Thank you guys for your responses so far, I've got some interesting reading to do. Firstly, I was most certainly not requesting medical advice. I have never experimented with shrooms, but rather I inquiring about studies or general information regarding and demonstrating the long term effects of mushroom use. And yes, you guys who said that just because there is no definitive information about the negative effects of something doesn't mean it isn't harmful are absolutely right...I just found it unusual that I could not find much info on how horrible they are for you, considering how (esp. the government) publishes and propagandizes studies showing how terrible illicit drugs are for the body. I just figured if they didn't go on a huge crusade about the evils of mushrooms, then they might not actually be THAT bad for you. Certainly there is the more obvious reason of no credible or viable studies being undertaken..and @Steve--Just because there is an absence of information (and the lack of any information regarding negative long term effects) does not indicate that there are problems. Obviously, one can see how hitting oneself in the head with a heavy, metal object may be detrimental to one's health. Drugs, on the other hand, are not so easily categorized as some are beneficial and have no negative side effects in moderate doses. --71.117.38.74 (talk) 01:27, 4 March 2009 (UTC)

Yeah - well, everyone who I ever knew who messed with drugs in the 1970's and onwards either ended up in a very bad way for one reason or another (mostly because they escalated to worse and worse things) - or they got out of it eventually - but still come over as slow, dull intellects who have lost that sparkle they had when I knew them beforehand in college. When I go to college reunions - you can instantly tell who was in which crowd. The people who didn't touch the stuff are much more interesting to work with and talk to - and 99% of the time, they are earning more money for less work and are VASTLY happier in later life. That's anecdotal evidence - but it's over a fairly wide sample from the tail end of the hippie era when that stuff was pretty rampant. It's pretty clear that the effects these things have on your brain are the biochemical equivalent of that ice-pick. Every time you do it you get more stupid and you notice it less and less - it's amazing to me that every time a pro-drug-legalization person comes on TV or the radio, they come over as amazingly slow and stupid...but they don't seem to realize it. But do it over enough years - you'll wind up dull and stupid too - so perhaps you won't care anymore. My brain matters to me - it's where I spend most of my time! I intend to look after it and not hit it with random concoctions and just hope that because I couldn't find any mention of problems, that there are no problems. Modern medicine can do a lot to fix up abuse of your body - but to date there is hardly anything they can do if you screw with your brain. SteveBaker (talk) 04:22, 4 March 2009 (UTC)

Steve, you misunderstood the point of my question. It was in no way intended to push a pro-drug agenda or try to rationalize the use of mushrooms by myself. I don't plan on getting mixed up with illicit substances or abusing them. I was simply curious, however odd that may be, and was playing devil's advocate earlier (in regards to the fact that there is no evidence that it is very harmful over long term use). I don't doubt for a second though that any form of drug abuse will not have adverse effects if used long enough or in high enough doses. I appreciate the impassioned censure of abusing illegal drugs...largely in part because it's common knowledge that 99% of those substances will mess up your brain and its neurochemistry! Which leads me to why I originally asked the question in the first place...cocaine, marijuana, ecstasy, heroin, meth, etc., all have terrible long term side effects that are quite noticeable and dangerous, while mushrooms, on the other hand, apparently have no known long term use side effects which I thought was unusual. Hence my curiosity. So please do not misinterpret this as I was saying earlier as a rationalization for drug abuse- it's not. All it is, is simple curiosity. --71.117.38.74 (talk) 05:58, 4 March 2009 (UTC)

Steve, although I have much respect for you, I think your anecdotes aren't necessary here. Many people turn "slow and dull" after college. Correlation-causation problems also arise in that people who take recreational drugs may be predisposed to, and may also be predisposed to being slow and dull people (risk-seeking people are quite biochemically different to risk-averse people). Also, in order to get hold of recreational drugs, people will often start to hang around with those they can get them from (dealers). In order to befriend a dealer (usually someone lacking success in life and of a low intellect), they must start to behave differently, to be accepted in that group (peer pressure). Eventually people adapt to that lifestyle, a sort of "being dumb is cool" attitude, and the self-fulfilling prophecy comes true (acting dumb turns into being dumb). As for 5-HT_2A agonists being "biochemical icepicks", well, I don't quite understand what you are trying to say. They cause lesions? Or they just destroy one's intellect? I have found a review study (free, full text) which should be of much interest: "Role of the Serotonin 5-HT_2A Receptor in Learning". [1] To quote the abstract:

Agonists at the 5-HT2A receptor including LSD (d-lysergic acid diethylamide) enhanced associative learning at doses that produce cognitive effects in humans.

I'm not saying that we should take psychedelics whilst reading through a ton of papers, of course they produce many other effects. What I am saying is that there is no solid evidence that consuming a psychedelic drug will cause you to be "dumb". Unless Albert Hofmann, Alexander Shulgin and probably thousands of other scientists are dumb as well. --Mark PEA (talk) 13:34, 4 March 2009 (UTC)

I'm not sure I would characterize Carl Sagan as being stupid or dull-witted. Matt Deres (talk) 14:48, 4 March 2009 (UTC)

Another of the reasons I suspect there aren't very many studies of long-term shroom use is that, in my limited experience, it's not a drug that is regularly used over an extended period. While there are certainly some people that are sufficiently enamoured with it that they do it regularly, everyone I know that has taken shrooms has done it as a very occasional thing: they seem to be used far more for occasional fun trips rather than as a daily/weekly habit. It may well be that for most people the effect, while generally pleasant, is not something you actually want to do that often - I've heard the same about LSD. This is in contrast to drugs like marijuana, where studies of the long-term effects are most important as it is often used regularly (in some cases multiple times daily) over a long time. ~ mazca ^t|c 08:54, 4 March 2009 (UTC)

To OP, the original question is quite ambiguous. Asking if water is safe can be ambiguous (hyponatraemia). Due to ethical and legal reasons, psychedelic drugs are very poorly researched in humans (and you can't get solid evidence without placebo-controlled studies). As far as I'm aware, there are no "psychedelic models" in animals either. We can see if their 5-HT2a receptors are up/downregulated, but that is about it. As already mentioned, HPPD is a reported problem in some users. There is also some anecdotal evidence of "flashbacks", and a "bad trip" may lead to some form of PTSD. As for the government, don't they normally say that psilocybes are dangerous because they can change your behaviour and make you jump out of a window? (as for ketamine, you might walk into a road, not that anyone under the influence of ethanol has ever done that). --Mark PEA (talk) 13:34, 4 March 2009 (UTC)

Yeah, that dihydrogen monoxide is dangerous stuff. Inhaling a small quantity can kill. Axl ¤ [Talk] 18:06, 4 March 2009 (UTC)

LOL. Thank you for your comments everyone, especially Mark. --71.98.15.188 (talk) 00:54, 5 March 2009 (UTC)

I don't think chronic consumption of magic shroom is widespread and that would make another reason (beyond ethical and legal reasons) why you can't find much of a study out there regarding long term health effects. Besides, health issues related to psychedelic drugs being largely psychological in nature, a study about drugs with similar effects such as LSD or mescaline would likely be just as relevant. Equendil Talk 17:25, 5 March 2009 (UTC)

Are chard and beets the same plant? "beta vulgaris"

If so, is there a link to the USDA or a Dept. of Agriculture website that states this so I can be sure?Troyster87 (talk) 05:00, 3 March 2009 (UTC)

I think this site provides what you want - the family tree of chard, showing it's a member of the beet family. Our page on Chard essentially states this, but provides no references (eww!). --Scray (talk) 06:02, 3 March 2009 (UTC)

This link from our beet article provides very thorough scientific/taxonomic names and multi-lingual common names. It is from The University of Melbourne (article), may also be reliable for academic/citation purposes. Note that beets are classified into a large number of subspecies. "Swiss chard" is a type of beet, but it may be a different breed or cultivar, depending on your classification scheme. As this topic comes up often, classifying things as the "same species" is entirely a matter of your taxonomy preference. Nimur (talk) 07:08, 3 March 2009 (UTC)

When it comes to plant relatedness, agriculture has often created widely different cultivars or breeds of plants which are essentially genetically the same "species", but have been bred to force certain traits to express themselves in an "unnatural" way, i.e. in ways that they could never do in the wild. There are wildly different members of the cabbage family, for example Kale. Brussel Sprouts, and Broccoli which are all essentially descend from the same wild "proto-cabbage". See also the relationship between Teosinte and Maize. --Jayron32.talk.contribs 13:07, 3 March 2009 (UTC)

To make a analogy to something people may be a little more familiar with, a chihuahua, a poodle, a St. Bernard, a German Shepherd(Alsatian), and a wolf are all the same animal/species (a "dog"), but are vary different in their characteristics and their use due to selective breeding. -- 128.104.112.117 (talk) 19:06, 3 March 2009 (UTC)

okay so my question is a little more specific than perceived, i would like to know if beats and chard can be harvested from the same plant, i.e. i plant some beta vulgaris seeds, could i eat the root (beet) and the leaves (chard) and if so would they be the same i find in the supermarket or would they be the leaves that grow on beets that are not commonly eaten and the chard root that is not commonly eaten?

In a word, no. The plants grown for chard and the plants grown for beetroots, while the same species, are different varieties (see Beet#Taxonomy). That said, you can probably use the tops of garden beets as a leafy vegetable. Doing an internet search on "beet greens" reveals a lot of hits. (Although I can't be sure if they're all talking about the leaves of garden beets, or might instead be referring to the spinach beet, which is grown especially for its leaves.) -- 128.104.112.117 (talk) 00:37, 5 March 2009 (UTC)

You can eat both the root and leaves of the turnip. It might have a different name in American English - I'm not really sure what a "beet" is, I assume it is not a beetroot. 78.149.172.237 (talk) 12:20, 6 March 2009 (UTC)

sub : Quantum mechanics

The wave funtion corresponding to np hydrogenic orbital are imaginary the howI conceive of np orbitals in reality.Supriyochowdhury (talk) 06:06, 3 March 2009 (UTC)
I have edited this into a format that I believe was intended Mattopaedia ^{Have a yarn} 06:21, 3 March 2009 (UTC)

It's not clear exactly what your asking here, but perhaps you could first look at our article on quantum mechanics then direct any further questions here. Mattopaedia ^{Have a yarn} 06:21, 3 March 2009 (UTC)

If I understand S's question, the square of the wave function gives the probability of an electron "being" at a specified position at a specified time. You should try reading that article; it also has some nifty orbital diagrams. Clarityfiend (talk) 07:48, 3 March 2009 (UTC)

While the wave equations may be imaginary, certain sums and differences of wave equations can also valid solutions (a general property of solutions to differential equations). The imaginary terms can be made to cancel out, allowing three completely "real" p orbitals to exist on any energy level. Someguy1221 (talk) 08:36, 3 March 2009 (UTC)

More specifically, the square of an imaginary number is always real, which is why Ψ² is the relevent function here, not Ψ. --Jayron32.talk.contribs 12:59, 3 March 2009 (UTC)

It's not the square, it's the square of the absolute value. This is always a positive real number, as expected of probabilities. Algebraist 13:04, 3 March 2009 (UTC)

Is Ψ imaginary? I thought it was complex (ie. can contain both real and imaginary parts). While the square of a strictly imaginary number is always real (a negative real number, in fact), the square of a complex number can be absolutely anything. That's why, as Algebraist says, you take the the square of the absolute value, or equivalently the product of Ψ and its complex conjugate. --Tango (talk) 13:49, 3 March 2009 (UTC)

Tango is correct. Ψ is properly treated as a complex value, though for some special circumstances it only has a real or an imaginary component. For probability calculations, we use the square of the absolute value: |ψ|². Conveniently, one can calculate this value by multiplying ψ by its complex conjugate, often denoted ψ^*. So |ψ|² = ψ^*ψ. TenOfAllTrades(talk) 14:30, 3 March 2009 (UTC)

I do not understand Faster-Than-Light( physics, relativity) article

B and E fields travel faster than light but energy travels at the speed of light? How is it possible? How we know that magnetic and electric fields travel faster? By Maxwell's equations? Is the photon speed constant and it is 3*10^8 m/s? —Preceding unsigned comment added by Logicman112 (talk • contribs) 12:26, 3 March 2009 (UTC)

B and E fields propagate at the speed of light. What made you think they go faster? Dragons flight (talk) 12:28, 3 March 2009 (UTC)

Is there some confusion involving group velocity and phase velocity? --Tango (talk) 13:40, 3 March 2009 (UTC)

What article are you reading? I can't find B and E fields mentioned in Faster-than-light, although it does cover phase and group velocities which, as Tango suggests, might be the root of your problem. SpinningSpark 17:57, 3 March 2009 (UTC)

Could it be that OP fell into the "in a vacuum" trap? Light propagates through different media at different speeds. It is possible to exceed the speed of light in a given medium. (See Čerenkov radiation.) It's one of my pet peeves that last bit of the saying usually gets left out. 76.97.245.5 (talk) 21:26, 3 March 2009 (UTC)

This part of physics is really a horrible mess because of the choices people have made for the names of things.

• The speed of light IN A VACUUM ('c') is unchanging...and it's the cosmic speed limit beyond which energy, mass and information cannot travel.
• Photons always move at 'c' - even when they are travelling through (for example) water.
• The speed of light in a material like water (which is about 75% of 'c') is not the speed that the photons travel - for they HAVE to travel at 'c', no matter what. But if you take a flashlight and a large tank of water with a mirror at the other end - turn on the flashlight and start your stopwatch, then when you see the light bouncing back at you through the water - you'll notice that it took longer to do it than if the light was moving at 'c'.
• This ought to be obvious because from the perspective of a photon, most of what's in a glass of water is vacuum...the spaces between the molecules and between electron clouds and nucleus is all big open space as far as the photon is concerned.

The reason that the photons can be moving at 'c' but your light beam is only moving at 75% of 'c' is because the photons aren't able to make a simple straight-line trip through the water. They are being bounced around by the water molecules - absorbed and re-emitted and all sorts of other exciting things - which means it takes them longer to get from A to B - even through they are going at 'c' all the time. Personally - I thing physicist should stick with 'c' as "The Speed of Light" and explain that the water merely makes it travel further some factor due to all of these interactions. Talking about "The Speed of Light in Water" is a stupid and meaningless confusion.

So: that said - if the B and E fields carry energy, mass or information - they can't go faster than 'c' - but they may possibly be able to take a shorter route through water than a photon of visible light can - and thereby get there first. That's not the same thing as "Travelling faster than 'c'" - it's only "taking a short cut" - which is much less exciting.

SteveBaker (talk) 23:40, 3 March 2009 (UTC)

SteveBaker, the reason physicists don't stick with 'c' as "The Speed of Light" and then explain things the way you explained is because your explanation is wrong. If it was true that the bouncing of photons off other particles inside the material were slowing them down, you would get light scattering as well as dispertion (even for photons with identical frequencies). In fact that happens (see Rayleigh scattering), but that is another matter and is not the cause of the photon slowing down. Dauto (talk) 01:40, 4 March 2009 (UTC)

You aren't telling me that the photon slows down are you? Relativity applies equally in water and in vacuum - and the 'c' it uses is the speed of light in a vacuum - not the speed of light in water. Photons can't literally slow down because in order to have non-infinite mass when travelling at lightspeed in a vacuum - they would have to have zero mass when they slowed down in water...and that doesn't make sense. So while the photon is in the water - it has to be travelling (over short distances) at 'c' - and to be interfered with in some manner in order for it to take longer to travel over a given distance.

Our article: Čerenkov radiation says: "It is important to note, however, that the speed at which the photons travel is always the same. That is, the speed of light, commonly designated as c, does not change. The light appears to travel more slowly while traversing a medium due to the frequent interactions of the photons with matter. This is similar to a train that, while moving, travels at a constant velocity. If such a train were to travel on a set of tracks with many stops it would appear to be moving more slowly overall; i.e., have a lower average velocity, despite having a constant higher velocity while moving.".

In Speed of light we have: "In passing through materials, the observed speed of light differs from c. When light enters materials its energy is absorbed. In the case of transparent materials (dielectrics) this energy is quickly re-radiated. However, this absorption and re-radiation introduces a delay. As light propagates through dielectric material it undergoes continuous absorption and re-radiation. Therefore when the speed of light in a medium is said to be less than c, this should be read as the speed of energy propagation at the macroscopic level. At the microscopic level electromagnetic waves always travel at c."

Which is what I endeavored to convey...perhaps badly! SteveBaker (talk) 04:06, 4 March 2009 (UTC)

I find the second quotation to be misleading the point of being partially wrong. The delayed speed of light can be understood entirely classically (one doesn't need to introduce photons at all). The propagation of an electromagnetic wave into a dielectric excites a polarization wave in the medium of opposite sign (i.e. locally charges move to partially cancel the external excitation). In the continuum approximation of matter (useful since EM waves are useful much larger than atoms), the superposition of the excitation wave and polarization wave is a new wavefront of the same frequency but slower velocity. The net result is that the electromagnetic wave, expressed as changes in the E and B field, is honestly propagating at less than the speed of light and one doesn't need to invoke any silliness about macro vs. micro waves to get that. At a quantum level the wave is generated by (usually) a very large number of photons. The excitation of the polarization wave is caused by photons being absorbed by the medium. As the polarization wave collapses, new photons are coherently re-emitted in the same direction of travel, after some effective retardation in time. So, yes, the net flow of photons is delayed by interacting with the medium, but the physics of wave propagation in dielectric medium and the consequent delay is better understood by the reaction that retards the purely classical evolution of the wavefront. Dragons flight (talk) 09:46, 4 March 2009 (UTC)

SteveBaker, both your quotations from the Čerenkov radiation and Speed of light articles are rubbish. If I were in a particularly generous mood, I would say that the first one isn't entirely wrong, but needs clarification. I don't think I'm feeling that generous though. The second one really is wrong. Dragons flight already explained what's really going on. In short: Light in vacuum consists of oscillations on the electromagnetic field. Light in a medium consists of oscillations of the electromagnetic field plus oscillations of the charged constituents of the medium (mainly electrons). A different kind of animal entirely. Dauto (talk) 14:25, 4 March 2009 (UTC)

For what my opinion is worth, I don't think SteveBaker (or his quotations) said anything incorrect. It is worth bearing in mind that although you can consider wave propogation in a dielectric as a classical phenomenon, we understand that the world acutally behaves in a quantum manner. Any such classical model must be acknowledged as simply a model which is ony valid if it correctly describes the limiting quantum behaviour. So it's not silly to look at the interactions on a micro- level just because one can find a model which gives the same answers as the quantum case. I agree that the slowing of electromagnetic waves can be 'explained' by the classical continuum model but really we should try to understand this at a quantum level where all quanta of the electromagnetic field necessarily travel at c.

Dragons flight, It seems to me that (ignoring any classical model) your description actually agrees with the second quotation. You say that there are a large number of photons entering the material, this causes some kind of excitation of the material due to photon absorption which in turn leads to re-emitted photons after some delay. Could you elucidate your disagreement? Vespertine1215 (talk) 10:45, 5 March 2009 (UTC)

Vespertine, The interpretation of the slowing down of electromagnetic radiation as due to light being absorbed and re-radiated or following a zigzag path due to bouncing off other particles is not correct even within quantum mechanics. Dauto (talk) 14:52, 6 March 2009 (UTC)

Dauto, can you expand on that then? What do you claim is happening on the quantum level? As I said above, I don't see the difference between what the speed of light article says and Dragons flight's explanation which you seemed to agree with. Surely the only way an incident field can interact with matter is by absorbing/scattering photons. What process is occuring for it to interact in another way? Vespertine1215 (talk) 16:12, 6 March 2009 (UTC)

The problem with the idea that light slows down inside a medium due to constant bouncing off of electrons and being absorbed and re-emitted is the fact that it gives the wrong idea that light follows a zigzag line (it doesn't) or that the photon disappears part of the time and reappears latter. That would be a more apt description for what happens inside the sun, for instance. Photons produced at sun's core are constantly absorbed and re-emitted. Those photons take tens of thousands of years to find their way out of the sun (That's some serious slowing down). They follow a zigzag path and thermalize on the way out. photons inside a (perfectly) transparent medium don't thermalize. So why are photons inside a medium slower then c? Those photons are more complex then free photons. The charged particles inside the medium also oscillate along with the electromagnetic field forming what sometimes is called a quasi-particle but which in my opinion is better described as a dressed photon. In short, the charged particle oscillation is an integral part of the photon itself. Dauto (talk) 02:07, 7 March 2009 (UTC)

Ok, I think I see your point. We can't really think of our system (which is composed of coupled fields representing the matter excitations (e.g phonons) and the electromagnetic field) as simply some photons moving between interaction events inside the matter. A proper treatment of the excitations of this system leads us to introduce some group excitations (the dressed photons) which don't have the same properties as the free photons, specifically the possibility of non-zero mass. (If this is still faintly on topic for the OP, there is a little more about this in Photons#Photons_in_matter and Polariton). Thanks for your explanation. Vespertine1215 (talk) 15:47, 7 March 2009 (UTC)

Unpleasant screeching noises

Why is it that humans find it difficult to stand certain screeching noises like the one produced on scratching one's nails against a granite board, or steal, or even rubbing two metals against each other. What is the scientific and evolutionary reason for humans (like me) find such noises so unpleasant and anxiety producing? Thanks. --ReluctantPhilosopher (talk) 14:08, 3 March 2009 (UTC)

I'd say it's because the sounds resemble screams people (and before them, other animals) gave out as a warning of danger, causing us to flee immediately. Those who ran immediately when hearing such sounds are more likely to have survived and passed on their genes. StuRat (talk) 14:47, 3 March 2009 (UTC)

Equal loudness curve, with "perceived loudness" plotted vs. frequency. Nimur (talk) 15:33, 3 March 2009 (UTC)

Also, you may find phon interesting. A human's sensitivity to loudness is not "flat" - certain tones which contain the same total sound energy (or same sound pressure level) seem louder or quieter depending on their frequency. (This should be no surprise to any engineer who's worked with complex frequency-responses - we see poles and nulls of frequency response in all kinds of mechanical and electronic systems). Anyway, it's possible that your ear/brain audio perception pathway is "amplifying" the specific frequency of the screeching noise to a much higher level than equivalent non-screech-sounds. Nimur (talk) 15:31, 3 March 2009 (UTC)

The question you are asking has been researched rather extensively. The research culminated in the 2006 IgNobel Prize being awarded to people researching Sound of fingernails scraping chalkboard. The latter article lists a few ideas as to why the said sound is so disagreeable. --Dr Dima (talk) 18:44, 3 March 2009 (UTC)

You could try an experiment - play Chris Crocker vids at extremely high volume and ask people at the limit of hearing range to describe what they think it sounds like. If you get a lot of "Sounds like an animal being eaten alive," or "Sounds like the screech of a predator attacking," etc, you have an answer. Personally, I'd go with StuRat's answer for its simplicity, with Nimur's answer providing an excellent backdrop for a perception mechanism to amplify it. arimareiji (talk) 15:06, 6 March 2009 (UTC)

dual exhaust and fuel efficiency

My buddy and I are debating the merits of having dual exhaust. I have a 2000 F-150 with a single exhaust. Would having a dual exhaust improve the mileage? If so, what are the physics behind this? —Preceding unsigned comment added by 216.154.22.180 (talk) 14:40, 3 March 2009 (UTC)

I'd say probably not on mileage. Dual exhaust is normally used to make a car faster, not to improve mileage. By reducing back pressure, dual exhaust can allow for slightly more horsepower, but the added weight of the dual exhaust system will also reduce the mileage slightly. StuRat (talk) 14:43, 3 March 2009 (UTC)

No, actually, a less-restrictive exhaust system tends to improve engine efficiency by dint of reduced pumping losses. Depending on how restrictive the baseline (single) system was, the gain may be small or large. If the driver operates the vehicle so as to produce the same performance level as before, then fuel economy will improve on account of the increased efficiency. If the driver routinely takes advantage of the increased efficiency to accelerate faster, then fuel economy will not improve. Unless the original system is extremely restrictive — generally not the case — the efficiency gains are rather trivial at low, normal engine speeds. On anything but a vehicle specifically designed for minimal weight, and especially on a very heavy vehicle like the pickup truck under discussion, the weight of a dual vs. single exhaust system is insignificant with respect to the vehicle's overall weight and will therefore not materially affect fuel economy. It can be difficult and costly to retrofit a dual exhaust system while remaining in compliance with applicable emissions regulations, unless the vehicle was originally offered by the manufacturer with dual exhaust, in which case it is merely costly — the expense of doing so must be figured into the reckoning of whether it makes financial sense to proceed. Unfortunately, our exhaust system article is presently of low quality and in need of much work. —Scheinwerfermann ^T·_C15:07, 3 March 2009 (UTC)

Thanks. So, technically: we both win . . . and we both lose! Being a gentleman, I'll buy the beer as a gesture of good sportsmanship! —Preceding unsigned comment added by 216.154.22.180 (talk) 15:32, 3 March 2009 (UTC)

Maybe. The amount of 'back pressure' exerted on the engine is a rather important tuning parameter - and changing it has implications for engine power - which may or may not require it to burn more fuel. On a turbocharged car - where the exhaust is fed through the turbocharger's turbine to spin it up and allow better air compression, adding a more freely flowing exhaust will generally give you a few more horsepower because it allows more pressure to build up between engine and turbo. This improved efficiency might cut gas consumption - but if you actually DEMAND that extra horsepower, you'll burn more fuel doing it. On a normally aspirated engine (no turbo) you might not improve things at all - and you could make matters worse. But going from a single to a dual exhaust on most cars is nothing more than a decorative feature - since most of them feed all of the exhaust gasses through a single catalytic converter and silencer (aka muffler) before splitting the exhaust in two. In such cases, the effect is most likely to be zero - no matter what technology is used in the engine - because the limiting factor on flow rate is the catalytic converter and muffler. Doubling up on the catalytic converter and muffer gets around that - but it does add weight - and that might adversely affect your fuel consumption if the original single pipe was already perfectly adequate. SteveBaker (talk) 15:41, 3 March 2009 (UTC)

Angular momentum

http://img183.imageshack.us/img183/887/habitat.png
Say you constructed a Stanford torus, spun it, and climbed up to the exact center. You're just spinning in place, so if you let go your angular momentum is conserved and you continue spinning about your navel and stay perfectly still relative to the supports you were just holding. The article says you're probably spinning about one revolution per minute. But say you were down on the habitat level, facing forward, and you fell through a trap door out into space. Yes you fly off tangentially but do you additionally spin once per minute head over heels? Or do you spin a fraction of that depending on how far you were from the center? Or do you not spin at all? If the last case, where does angular momentum cease to be conserved? Is it when your axis of rotation is no longer inside your body and becomes kind of an axis of revolution?

http://img410.imageshack.us/img410/113/earth.png
Also, say you had a device, gyroscopically stabilized against any change in rotation from outside wind forces. It's on the north pole and it's lifted up and dropped. During the short free-fall the Earth didn't rotate below it because it spun at the same speed. But what if the device is on the equator, tipped over horizontally? It is spinning one rotation per day relative to the stars, same as on the north pole, as you make it around the globe, but is this really the type of rotation that's conserved or just a side effect of the centripetal force? Will the cylindrical device shown over the equator land on a different number than was pointing down when it was picked up? .froth. (talk) 19:23, 3 March 2009 (UTC)

When talking about angular momentum, you have to specify the point you are taking as the centre. In this case, that's the centre of the torus. When you move off tangentially, your angle to that centre will still be changing, since the point isn't on your line of travel. That means you still have angular momentum and, if there aren't any external influences (like the Earth's gravity) that angular momentum will remain constant. --Tango (talk) 19:52, 3 March 2009 (UTC)

Interesting.. but that angle-changing isn't constant. The rate of change of the angle is ${\frac {30\Pi }{t^{2}+900}}$ radians/second at t seconds, given the figures in the article. It starts out at the point of release to be equal to the rate of angle change of the wheel, but then rapidly decreases. In fact, the angle relative to the point of release will never be greater than 90 degrees. So how can you say that you still have the same angular momentum, when before it was whipping around at a steady π/30 radians per second? .froth. (talk) 20:32, 3 March 2009 (UTC)

With respect to your original question, the angular speed $\omega$ will indeed be the same, no matter where you are inside the space torus. With respect to your follow up question, The angular momentum $L\,$ will be conserved and from the formula $L=I\omega \,$ you can se that if your moment of inertial with respect to the center of coordinates $I=mr^{2}\,$ varies, so will your angular velocity around that center $\omega ={\frac {d\theta }{dt}}$, $r\,$ is the distance to the center of coordinates. As you pointed out, once you "fall" off the torus, $r\,$ will increase over time and $d\theta ={\frac {L}{I}}dt={\frac {L}{mr^{2}}}dt$ will decrease over time (for fixed $dt\,$). Do not confuse the angular velocity around the center (which is in fact decreasing over time) with the angular velocity that the poor fellow will have around himself (rotation). That last one will be constant. Dauto (talk) 21:47, 3 March 2009 (UTC)

But the angular velocity he will have about himself (rotation).. if he falls out of the bottom, will he have the same angular velocity about himself as the fellow standing at the hub of the wheel? I think you're saying No but it's hard to decipher .froth. (talk) 21:54, 3 March 2009 (UTC)

He may be spinning around his own centre of gravity, he may not, it's irrelevant. It will depend on exacting how he leaves the station - if he pushes off with just one arm, that would provide a torque that sets him spinning. That won't affect his angular momentum around the centre of the station, though. --Tango (talk) 22:15, 3 March 2009 (UTC)

Tango is right that any torque at the moment he leaves the station will afect his angular velocity around himself. But assuming that there was no torque, it is safe to say that his angular velocity around himself will be the same as the fellow standing at the hub. Dauto (talk) 22:22, 3 March 2009 (UTC)

I don't think that's true. The angular velocity of someone at the hub around their centre of gravity is the same as that around the centre of the station, since that is where their centre of gravity is. Assuming there is no ground underneath them and they just fall away from the centre unhindered then their angular momentum around that centre will remain constant, their angular momentum around their centre of gravity will not since their centre of gravity is moving (obviously, I'm working in an inertial, non-rotating reference frame, if you do it in terms of the person's inherent reference frame you will get different results - you'll have centrifugal force and things to contend with). I can't see anything that would set the person spinning. --Tango (talk) 22:46, 3 March 2009 (UTC)

His angular momentum relative to the hub will be unchanged from what it was just before he left the station. It will be much larger than that of the dude at the hub, because he was further from the hub to begin with. He may or may not be rotating about his navel depending on how cleanly he left the station, but that's irrelevant when it comes to computing his angular momentum relative to the hub.

A curious thing about angular momentum is that you can take an object undergoing linear motion, select a point, and compute the angular momentum of the object relative to the point. And as the object moves along, the angular momentum will remain constant. --Carnildo (talk) 01:52, 4 March 2009 (UTC)

For the first part of your question: If the floor of the space station beneath your feet simply vanishes - you'll proceed in a straight line at a tangent to your former circular motion - which will seem to you like you fell through the floor. You'll continue to rotate at 1 rpm about your center of mass. If you were to rotate about any other point, that would be a net acceleration - and there is no longer a force present to provide that. Rotational and translational inertia are both preserved and all is well with the universe...until your air supply runs out.

If that's hard to imagine - separate out the rotational motion from the translational. Firstly, while you're inside the space station, you are translating around in a circle, secondly you are spinning about your center of gravity at exactly the right rate to keep your feet on the floor and your head up by the ceiling - which is 1rpm. When you take away the floor - you take away the force that's making you translate in a circle - but your 1rpm rotation remains.

For the second part: This is really the same thing - the object is rotating about it's center of gravity at one rotation per day - and travelling around in a circle at one rotation per day. When your "device" (it's really a kind of dice) is tossed upwards (let's do the experiment someplace where there is no atmosphere), it'll continue to rotate at one revolution per day - so when it comes back down again, it'll land on the exact same number. The result is the same no matter where you are on the earth because you are rotating about an axis that's parallel to the axis of the earth,

SteveBaker (talk) 23:23, 3 March 2009 (UTC)

Tango, nothing sets the person spinning. He is already spinning to begin with, along with everything else inside the station. Dauto (talk) 01:14, 4 March 2009 (UTC)

Yes, I missed the fact that his feet always point away from the centre, which requires a rotation around his centre of mass in addition to the rotation around the hub. --Tango (talk) 12:31, 4 March 2009 (UTC)

March 4

Creation (and use) of mass alternative fuel based cars would solve the petroleum Environmental effects?

So much has been talked nowadays about electric cars, hydrogen cars.... Because of petroleum problems and other things... My question is, would the used of alternative fuel only (or almost only) cars would solve the Environmental effects of petroleum?? I mean, petroleum is used to another things also. 201.79.81.7 (talk) 01:41, 4 March 2009 (UTC)

Hidrogen and electricity are means of distribution of energy. They are not sources of energy and cannot in themselves be a solution to the energy problem. But they can be important links in the distribution of other sources of energy. Dauto (talk) 02:23, 4 March 2009 (UTC)

No - without doubt. Solving the car problem completely with some kind of magical 100% renewable-energy, non-CO2-producing fuel would not be enough to fix the global warming or energy shortage crises. But on the other hand - neither would solving any one of the other problems either. In order for us and our planet to get through the mess we've created, we have to agressively attack all sources of greenhouse gas emission and all source of energy consumption. In truth, the "energy crisis" isn't a problem at all because if we burned all of the oil, coal and gas we know that we have - we'd have made the planet unlivable long before we ran out. Whatever solution we come up with for fixing global warming will (by necessity) result in us not having a shortage of coal, oil or gas.

As you can see from the diagram, transportations (which includes trucks, trains, planes and shipping) is only 28% of our energy consumption. To limit global warming to 2 degrees C worldwide (which is a HELL of a lot of temperature increase), we need to get back to 1990 consumption levels by 2020 and to between 40% and 95% BELOW 1990 levels by 2050...clearly cutting 28% off our consumption won't do that.

I think we could fairly easily halve our domestic energy consumption - using better insulation and energy-efficient appliances, I've managed to get my house down to about one third of my neighbours...and I paid for it using the electricity savings I made amortized over about 5 years. With fairly modest government help - all new homes could EASILY do that with the government paying the difference in price for us and collecting that back from fuel taxation equal to the savings you'd make over those 5 years. The result would be that for new home owners, there would be no cost to building an energy efficient home - and after 5 years, they'd make a huge profit on the savings when the fuel tax would go away. For the government/tax payer, it would be a zero-sum game. For energy producers, they'd win because they'd need fewer new power plants. I would assume that commercial users (office buildings, stores, etc) could make similar savings. The two tough ones are industry and transport. Personally, I drive a 40mpg car (a MINI Cooper'S) - the average fuel consumption of a car in the USA is 19mpg - so without electric/hydrogen/hybrid technology - we could probably halve our consumption in the USA...in Europe it's going to be tougher because everyone is already driving tiny cars...but there are other ways to squeeze more out of less.

I'd like to telecommute - that would cut the energy consumed by my 'commercial' contribution to zero at work. I think we could do more shopping online and such like to cut the need for so many 'big box' stores...but for that we need a more efficient delivery system...electric postal delivery vehicles would make a TON of sense for that.

So it's basically do-able (at some cost) for everything EXCEPT industry...hence the pressure for 'cap and trade' systems to put pressure on the big energy consumers in factories. If more people recycled - and if the recycling system were more streamlined, we could make some significant savings there...but it's tough.

Some of the savings can be had without cutting consumption by using windmills (which seem very popular right now) and solar power (less so)...and I'd really hope to see more nuclear power - but there is no way to get the nuclear industry back up and running in as little as 10 years. It takes longer than that to get through the regulatory hurdles - let alone building the darned things.

However, to hit that 2020 target (WORLDWIDE!!) we have to start now. Houses last a lot longer than 10 years - we're still building energy inefficient homes! Even if a super-efficient-home law were to pass today, we wouldn't have more than maybe a quarter of our houses replaced by the deadline. Cars also last 5 to 10 years - getting the old gas-guzzlers off the streets would be very hard - even if we sold no cars that did less than 40mpg starting today! The longer we leave it - the tougher it becomes. We wasted 8 years with that idiot Bush...let's hope we can kick things into high gear now.

There are also huge problems in the developing world. It's going to be very hard indeed to get China and India to follow the 40% to 95% cut by 2050...especially if the cost of oil and gas drop precipitously as the western world starts to use less of it.

SteveBaker (talk) 03:30, 4 March 2009 (UTC)

The major reason why transport is considered a particular problem is because most moving vehicles are inherently "off the grid". Solar, wind, water, tides, nuclear (fission or fusion) can be used to generate electricity, and electricity is extremely versatile, i.e. it can easily be used for most stationary energy needs. So solving this is a problem of scale, economics, and policy. But Hydrocarbons are extremely attractive as energy sources for mobile needs - they have comparatively high energy density, and they have reasonably benevolent handling properties. And we have the infrastructure for their use in place. So changing transportation to other energy sources is much harder - its an unsolved research problem. Cars can go electric, but with reduced range and/or performance. I don't know of any serious attempts for ship or aircraft that do not involve hydrocarbons in some form (although possibly as biofuels). Well, ships can sail - not quite a stupid idea for bulk goods with modern weather satellites and predictions supporting route planning. --Stephan Schulz (talk) 10:12, 4 March 2009 (UTC)

SteveBaker and Stephan Schulz already covered that one pretty well. I would like to point out that Global Warming may make lieving on earth more unpleasant, but it will not be "unlievable". Even with full blown Global Warming humans will survive to see another day (and do some more enviromental damage). Dauto (talk) 14:04, 4 March 2009 (UTC)

One question for Steve Baker here. Does the average of 19 MPG only cover passenger cars, or does it also include tractor trailers? Because it would appear to me that a significant percentage of the transportation energy would originate from them, and there is absolutely no way that you can get one of those as a hybrid without major sacrifices to pulling power using current technology. 65.167.146.130 (talk) 15:08, 4 March 2009 (UTC)

Yeah - that figure is for passenger vehicles - I'm not sure where the cutoff is for trucks and pickups and such. Also, that's the figure for what vehicles are actually achieving in practice - not the EPA numbers (which tend to be pessimistic for new gasoline vehicles but wildly optimistic for hybrids and old, poorly-maintained vehicles) which I vaguely recall says that the average mpg for passenger vehicles is something like 25 mpg. I agree that work is also needed on tractor-trailers...but there is no reason in principle why a similar application of high-technology shouldn't help them too. You can absolutely build a hybrid-technology truck and it would make perfect sense because truck engines are even more sensitive to the RPM you drive them at than car engines (that's why trucks have so many gears!). The single biggest reason that true hybrids like the Prius produce the benefits they do is that they run the engine ONLY at it's most fuel-efficient RPM level.

But in case you doubt the degree to which these things are being agressively pursued - check out Big-Rig trucks, this...um...hybrid truck, er, pusher, Hybrid-engine tug-boats, of course most submarines and diesel/electric railroad locomotives have been using 'hybrid' technologies since before the name was invented. SteveBaker (talk) 04:17, 5 March 2009 (UTC)

You might want to visit here (http://withouthotair.com/) - it's a very interesting book and is available to be read online for free. The section on cars is here (http://www.inference.phy.cam.ac.uk/withouthotair/c3/page_29.shtml) - the book explores simplified calculations to consider whether or not we can maintain our current way of life and reduce our energy consumption as required based on using different technology etc. It's really rather an interesting read, made me much more appreciative of the scale of the issue at hand. ny156uk (talk) 21:01, 4 March 2009 (UTC)

Density

What are the primary factors that make substances as dense as they are? Say, at STP, why is hydrogen less dense than Iron? Does this correlate at all with Atomic size? Is there any pattern in the density of the elements in the table? 99.226.138.202 (talk) 01:49, 4 March 2009 (UTC)

It really is "how much mass is crammed in a certain volume", just like the definition says:) What are the things that compose a substance? "How much they weigh" and "how close they are together" is what gives density. What gives an atom its weight? What controls how closely you can pack atoms together? What pattern(s) do these properties follow? DMacks (talk) 02:15, 4 March 2009 (UTC)

So I understand that Atomic weight is determined by the number of protons and neutrons in an atom, but what determines how closely they can be packed together? Does this have to do how easily atoms are excited? If so, what determines how easily atoms are excited? If the answer to the previous question was atomic mass, why do noble gases stay gases? —Preceding unsigned comment added by 99.226.138.202 (talk) 02:24, 4 March 2009 (UTC) Well, I was going to sign that, but signbot got there ahead of me. XD 99.226.138.202 (talk) 02:26, 4 March 2009 (UTC)

Well, for gases, the controling factor is simply pressure and temperature, as explained by the Ideal Gas Law. Density of different gases at the same set of pressure and temperature conditions is controled entirely by the atomic mass of the gases. (Well, a real gas differs slightly from an ideal gas due mostly to Van der Waals forces, but these effects are negligible at room conditions). In condensed phases (solids and liquids), the volume is controlled by such things as atomic radius and ionic radius and Intermolecular forces which are all a function of the electrostatics going on at the atomic level. --Jayron32.talk.contribs 02:39, 4 March 2009 (UTC)

edit conflict

Mass is pretty well understood at the atomic level - roughly speaking, "count the number of protons and neutrons and ignore everything else." Volume is a lot more complicated, and it depends entirely on packing density. Atomic packing density is an extremely complicated field and an active area of research. While some simple atomic and molecule packing arrangements (particularly, gases and solid-state crystal structures) can be derived from fundamental atomic physics, most of the more complex substances are too complicated to describe their molecular packing analytically (with equations) at present. (Note that "density" is less useful than "pressure" for a gas, although they will be related by the ideal gas law and its experimental variants. Those variants are exactly meant to account for the "unexpected" volume errors due to atomic spacing, atomic bonding, etc.). For most substances, the density is measured macroscopically as the mass per volume at a large scale. Scientists are developing new techniques, and already have a repertoire of long-existing techniques like x-ray diffraction to probe atomic arrangements at the molecular scale. Nimur (talk) 02:40, 4 March 2009 (UTC)

It's a tricky subject - as others have pointed out, the packing of complex compounds is too complex to easily explain. But broadly speaking - the atomic radius of atoms increases fairly slowly as they go up the periodic table. That's because all of the mass is in protons and neutrons the very center of the atom - packed into 1/100,000th of its total size. Adding more neutrons to an atom doesn't change it's size - adding more protons only increases the size because more electrons are required to neutralize the atom - and the number of electrons alters the size of the entire atom. But if you look at Atomic radius#Empirically measured atomic radius - you'll see a table of atomic radii plotted onto the periodic table. Compare some of the lighter elements: eg Lithium with a radius of 145pm - that's picometers - and an atomic mass of around 7...to and the some of the heavier: eg Lead at 180pm and an atomic mass of 207) only differ by a small factor in radius - but the atomic masses are different by a factor of around 30! Now, admittedly, the 'atomic radius' is a slippery term - and it doesn't directly predict density - but you can see that the size of the atom doesn't get much bigger when you add protons and neutrons to it's nucleus. So the higher numbers in the periodic table tend to be the most dense. SteveBaker (talk) 03:00, 4 March 2009 (UTC)

That's just wrong. The size and weight of the nucleus is wholly irrelevant to the atomic radius, which is entirely dependent on the nuclear charge. Comparing Lithium to Lead is ridiculous. Lithium has a relatively large radius due to its 1s¹ configuration and Lead has a relatively small radius due to the lanthanide contraction and relativistic effects which are entirely insignificant in Lithium's case. It's actually fairly predictable that the densest elements will be the heaviest non-lanthanide/actinide ones. --Pykk (talk) 05:35, 4 March 2009 (UTC)

No, Pykk, you just missed entirely what Steve was saying. First: Steve gives effective atomic radii, not nuclear radii; so he is right. And he clearly says that nucleus size is much smaller, hence irrelevant. Second: Lithium atom has ground state configuration 1s² 2s and not 1s¹. That, however, is again entirely beyond the point, as solid Li is a metal and 2s electron is free (what used to be the 2s orbital becomes a part of the conductivity band). Third, it is quite fair to compare Lithium to Lead; differences in electronic structure don't make them any less comparable. Now, to the original question. H, F, Cl, N, O, and noble gases are in gaseous state at STP. All the other elements are solid or liquid. Now, if you are asking "why H₂ is a gas and Fe is a metal", the answer is "because H₂ molecules don't attract each other strongly enough to keep them together at STP; but Fe atoms do". If you are asking "why all noble gases (Group 18) are gases, but all alkali metals (Group 1) are metals", the answer is "because noble gases have an electronic structure such that makes the attraction between their atoms very weak, and the atoms do not stay together; but alkali metals have electronic structure such that atoms attract more strongly, and furthermore one electron per atom is collectivized, which makes them metals". You surely know that the periodic table arrangement into groups mirrors the regularities of the electronic structure of the atoms of chemical elements. Finally, if you are asking "what determines how closely the atoms are packed in a solid" - that was answered already. --Dr Dima (talk) 06:45, 4 March 2009 (UTC)

A chart of density versus atomic number. Actually I'm a little disappointed that Wikipedia does not appear to already have such a graph. Dragons flight (talk) 03:06, 4 March 2009 (UTC)

Aha! Thanks to all the people who helped. 99.226.138.202 (talk) 23:23, 4 March 2009 (UTC)

Length of one second in meters

As is well know, time is the fourth dimension of the space-time continuum. This means that, fundamentally, duration and physical length are simply two forms of the same thing. What then is the equivalent of one second in meters? If this is not a valid question, why not? —WikiMarshall (talk) 01:50, 4 March 2009 (UTC)

299,792,458 meters? :) Arakunem^Talk 01:54, 4 March 2009 (UTC)

Arakunem's got it right. for some reason he worded it as a question? Dauto (talk) 02:15, 4 March 2009 (UTC)

It is not useful in all physical contexts to treat time duration and spatial extent as equivalent or interchangeable quantities. "One second" and "2.99e8 meters" are not as interchangeable as, for example, one gram and 1000 milligrams. Nimur (talk) 02:22, 4 March 2009 (UTC)

I don't think this is a valid question - we casually talk about time as "the fourth dimension" - and lots of really annoying high school text books say it - but time is so different from spatial distances that this really doesn't make much sense. To the extent you can express something I suppose it's most natural to use the speed of light as the 'conversion factor'...so one nanosecond is a foot...but I really don't think that works. Time is SO different from the three spatial dimensions that it hardly bears comparison - why would we arbitrarily lump them all together? So I'd prefer to answer: "Time is NOT the fourth dimension" and "The space-time continuum comprises three spatial and one temporal dimension". It really goes deeper than that - there are "three spatial dimensions"...OK - so point to one of them! The fact is that you can pick any three 'axes' in space to use as your three dimensions - or you can pick an angle and two distances or two angles and one distance. Certainly it's OK to say that "space is three dimensional"...but there aren't three specific dimensions out there. On the other hand, time just "is" - we can't really swap it with the other axes...and it behaves differently from them too. There are lots of equations where you can't use spatial dimensions instead of temporal ones and vice-versa. SteveBaker (talk) 02:43, 4 March 2009 (UTC)

Time isn't just time, you can change your coordinates to combine space dimensions and time dimensions. When you do so you will always end up with one timelike dimension and three spacelike dimensions, but they can be completely different from the one timelike and three spacelike dimensions you started with. Time dilation and related concepts can be viewed as a change in coordinates. For example, if your coordinates start off as (t,x,y,z) you could change that to (t-x,t+x,y,z) and still have a perfectly valid description of spacetime, just with two of your axes "rotated" 45 degrees. In general relativity, spacetime is modelled as a four-dimensional pseudo-Riemannian manifold, it really is four-dimensional and "time" can be considered as one of those dimensions (for varying definitions of "time").--Tango (talk) 13:24, 4 March 2009 (UTC)

Yes - but that's just a mathematical convenience. I often (in computer graphics) treat (X,Y,Z)-space and (R,G,B)-color as a uniform six-dimensional (X,Y,Z,R,G,B)-space. It doesn't mean that space-color is a meaningful concept - it's just easier to do some math operations that way. Some of the things I do have extended up to 14-dimensional "spaces" - but I certainly don't "see the world" as a 14-dimensional place. Doubtless some calculations could usefully be done with three spatial coordinates and one 'mass' coordinate - that would make things like 'density' fall out with greater elegance - just as 'c' falls out when you consider space and time together. We shouldn't confuse a mathematical convenience for "how things are". SteveBaker (talk) 15:08, 4 March 2009 (UTC)

SteveBaker, what universal constant do you suggest we should use to convert color to distance? Or to convert mass to distance. (Hint:there there is an right answer to the second question). Dauto (talk) 16:10, 4 March 2009 (UTC)

You couldn't meaningfully change your (X,Y,Z,R,G,B) coordinates to anything else (at least, not anything that would mix locations and colours in one coordinate), though. (You could do it, mathematically, but it wouldn't have a real world interpretation. Coordinate transforms of space-time do have real world interpretations.) --Tango (talk) 19:39, 4 March 2009 (UTC)

Why the need for a 'universal' constant? As it happens, we typically scale colors either 0..1 and distances at some points in the 3D calculations are scaled 0..1 in screen X/Y and in depth into the screen (Z) - but in other places we have X,Y,Z in meters or something and R,G,B on a 0..255 scale...and in high dynamic range rendering situations, we may toss in another constant ('S') to allow brighter colors than the 0..255 or 0..1 scale would allow. But we're not arrogant enough to claim that there is "one true way" - it's all just a matter of convenience. It's the same in physics - for some fields, using so-called natural units in which 'c' is 1.0 - and in other fields that's a crazy choice and meters per second makes more sense. It's ridiculous arrogance to claim that there is "one true way". If I have to use a conversion constant of e or pi or c or 7 - then that's what I'll use. So long as you make it clear - everything works out just fine. For example, I've used 14-dimensional math to determine whether a particular pair of triangles with a shared edge form a quadrilateral that is "convex" and "planar" in 14-space...if it is then I can dissect the quadrilateral along the opposite diagonal to form two different triangles without messing up the appearance when I draw them. The fourteen (or so) "dimensions" are things like color, translucency, gloss, lighting and shading 'pseudo-curvatures' (normal, tangent and binormal), texture 'grain'...as well as the traditional (x,y,z). Now - in practical work, the precision of the computer isn't infinite - so hardly any quadrilaterals actually turn out to be perfectly planar - so I need to assess the amount of non-planarity and decide whether it's small enough that we don't care. Now I'm measuring this non-planarity in 14-space and coming out with a 'distance' that's in 14 dimensions. Now - the relative scaling of all of these bizarro 'dimensions' suddenly matters. So the 'natural' units for things like color and texture grain are chosen such that a minimally acceptable visual error is the same amount in all 14 dimensions. Are these now in "natural" units? Well, yes...no...who knows?! The fact is that this is what makes things work. In this application, scaling gloss from 0..0.1 while color goes from 0..1 turns out to make pragmatic sense. Would I claim some 'fundamental' connection between color and gloss and distance? Certainly not! It's merely a notational and computational convenience. What physicists do when they drop out 'c' is exactly the same deal. SteveBaker (talk) 03:53, 5 March 2009 (UTC)

Spacetime is not about saying time = length. It's about saying that time and length are deeply connected. So there isn't "one second in meters"—you don't convert time into length. Spacetime, as Einstein formulated it, is about saying that you can't make a length measurement without a time measurement, and you can't make a time measurement without a length measurement. So instead of saying, "this bus is one meter long," you recognize that what you are really saying is, "I measured the position of the front of the bus at time t, and I measured the position of the back of the bus at time t', and now I can express the length of the bus as the difference between these two points." Which in most cases is pretty trivial and it hardly matters, but when the bus as the person measuring it are moving at different speeds, it becomes more problematic, ergo special relativity. --98.217.14.211 (talk) 02:58, 4 March 2009 (UTC)

WikiMarshall, don't pay attention to the nay sayers. Time is indeed the fourth dimension of spacetime and c=299,792,458 m/s is indeed the conversion factor. This is as much true as, for instance, the conversion factor between calories and joules is 1 cal = 4.18 J (approximately). Dauto (talk) 03:35, 4 March 2009 (UTC)

Okay, so if a car is driving at 60 miles per hour, it is moving at 8.97x10^-8? Your assertion of absolute interchangeability of time and space holds no water in virtually all standard physics contexts. Nimur (talk) 08:45, 4 March 2009 (UTC)

Actually, special relativity tells us that all world lines have a four-velocity whose magnitude is fixed at the speed of light. If you are locally at rest, one could say you are moving through time at the speed of light. As your velocity in purely spatial coordinates increases, then your velocity in time coordinate must decrease by a compensating amount. This is another way of looking at the result that highly relativistic objects experience an apparent decrease in the flow of time (i.e. their velocity in the time dimension is decreased). Also, contrary to what Steve says above, there is not one fixed time dimension, but rather the "direction of time" is also a property of the local reference frame. Lorentz transformations are formally coordinate rotations that partially interchange spatial and time dimensions. In order to fully interchange space and time dimensions (so that the time dimensions behaved in a space-like manner, and vice versa) would require traveling faster than the speed of light and so as a practical matter this is forbidden under our existing understanding. Nonetheless, the perception of the spatial distance and time difference between events will vary significantly depending on the local reference frame of the observer, and one can add apparent distance by subtracting apparent time, and vice versa. Dragons flight (talk) 09:19, 4 March 2009 (UTC)

To Nimur, Yes! a speed of 60 miles per hour is (approximately) equivalent to a speed of 8.947x10^-8 (no units). No problem there. Dauto (talk) 13:42, 4 March 2009 (UTC)

While we're throwing caution to the wind, and canceling units for no good reason, I also found the speed of the 60 mph car to be equal to 3.99x10^-4 ... (no units).

(60 miles per hour)/ sqrt(Boltzmann constant * room temperature/electron mass).

But, in real physics..., there has to be a better reason to multiply a quantity by a physical constant. "Just because" doesn't cut it, even if the units work. Nimur (talk) 14:46, 4 March 2009 (UTC)

Nimur, "room temperature" ain't a physical constant. Dauto (talk) 15:05, 4 March 2009 (UTC)

Yes - exactly. As I said above - don't confuse a mathematical convenience with "how things are". SteveBaker (talk) 15:08, 4 March 2009 (UTC)

Lets make things a little more clear. 'c' is indeed a universal physical constant that can be used to convert distance units into time units. The Boltzmann constant is indeed a universal physical constant that can be used convert temperature units into Energy units. Electron mass is a physical constant but it is not a universal physical constant (You had to specify a particle, making it non-universal) so it cannot be used to convert units. Room temperature isn't a physical constant at all. SteveBaker, that is "how things are". Dauto (talk) 15:59, 4 March 2009 (UTC)

My point was that canceling units is not acceptable justification for a physical operation. Pick the mass of the car and the temperature of the car, and you will get a different value, and the units will still cancel, but it has no physical meaning. Why would you be willing to multiply by the speed of an electromagnetic wave, but unwilling to multiply by the temperature of an electron? Why would either of those operations ever make physical sense when calculating a car's speed? Nimur (talk) 16:04, 4 March 2009 (UTC)

And if I wanted to play with fundamental constants long enough, I can create a "universal mass", let's say (ħ/c^2)/t_planck; and a temperature constant... Still, random changing of variables and units does not make physical sense. Nimur (talk) 16:09, 4 March 2009 (UTC)

The car temperature and mass are not universal physical constants. Yes!! use Plank's mass and Plank's temperature in your expression (those are universal constants). See what you get. It won't be random, I promiss. Dauto (talk) 16:23, 4 March 2009 (UTC)

Clearly you are missing my point; maybe my example is distracting from the main issue here. Take a look at The Application of Dimensional Analysis to Cosmology, by Prof. P.S. Wesson of Harvard. He's got a whole book on the subject! Regarding dimensional transformations resulting in unit cancellation: "Physically, it represents a loss of information and can lead to confusion, as a little thought will reveal." Nimur (talk) 16:31, 4 March 2009 (UTC)

The 3+1 dimensions of space and time are not euclidean. If they were, distance would be ${\sqrt {x^{2}+y^{2}+z^{2}+t^{2}}}$. In special relativity, it's ${\sqrt {x^{2}+y^{2}+z^{2}-t^{2}}}$. This makes rotation work different. For the specifics, see Lorentz transformation. Rotations involving time are really just changing to a moving point of reference. Where in euclidean geometry, you could just rotate <0,0,0,1> (one second) by 90 degrees to get <1,0,0,0> (one light-second), in special relativity, rotating it would increase the time component. You could say that one second is two seconds and, I'm not sure, ${\sqrt {2}}$ light-seconds? Anyway, there's no way to rotate it to get zero seconds, or for that matter, anything less than one second, for the time component. — DanielLC 16:32, 4 March 2009 (UTC) [edit] Come to think of it, you could say that one second is i light-seconds, because if you put them both in that equation for distance I mentioned, they would get the same value. — DanielLC 22:03, 4 March 2009 (UTC)

Nimur, I've seen Paul Wesson's quotation before. He is simply wrong. There's no loss of information. We would still be able to apply dimensional analysis even if we use plank's units.

See the last section of dimensional analysis article. Dauto (talk) 17:39, 4 March 2009 (UTC)

There is a loss of information - you don't know how many factors of pi are floating around. You can deal with all the dimensionfull (is that a word?) constants, but once you introduce dimensionless constants it starts to get confusing. That section talks about using h-bar as a conversion factor, it could just as well talk about using h as the conversion factor, it's an arbitrary choice. --Tango (talk) 19:46, 4 March 2009 (UTC)

Tango, some people use degrees to measure angles, some people use radians. It's an arbitrary choice. Both units are adimensional. Yet there is no loss of information (as long as you tell people what units you are using). What was your point again? Dauto (talk) 20:52, 4 March 2009 (UTC)

Mathematicians always use radians, anything else is just radians multiplied by an arbitrary number. An angle is defined as the ratio of the radius and the arc length, there is no reason to multiply that by anything. But that's beside the point - as you say, you need to tell people what units you are using. If you were working dimensionlessly, then there aren't any units, so it doesn't work. --Tango (talk) 21:16, 4 March 2009 (UTC)

Tango, you are right. angles are defined as the ratio between an arc and an radius which comes out naturally in radians but some people chose to arbitrarily multiply that by a constant for tradition's sake and use degrees instead. hence it is necessary to specify which units you are using (radians or degrees) in order to avoid confusion. Notice that angles are dimensionless but it is still possible to use different units, contrary to your point that when working dimensiolessly there aren't any units, so it doesn't work. You just didn't think it through. The same thing is true about the definition of the speed of an object. it is defined as the ratio between two components of the quadrivector $ds^{\mu }\,$ along the direction of the particle's trajectory (world line) through spacetime. These components must have the same units, since they are components of a single object. Therefore velocity is an adimensional quantity. c=1 comes out of this definition naturally but some people chose to arbitrarily mutiply that by a constant for tradition's sake and use m/s instead. hence it is necessary to specify which units you are using (m/s or natural units) in order to avoid confusion. No loss of information as long as you tell people which units you are using. Dauto (talk) 22:26, 4 March 2009 (UTC)

Mathematicians never use degrees (in any real work, anyway - they might come up in casual conversation) and very rarely use the word "radian". Angles are dimensionless, there are no units, we don't use units. A right angle is "pi-by-2" not "pi-by-2 radians". Using degrees is simply wrong from a mathematical perspective. Any comparison between radians vs degrees and ft/ns vs m/s is misconceived. The four vector you mention is defined in terms of c, you need the c in there otherwise it is wrong (you can, of course, define c=1 and then not worry about it until you get to the end of your calculation and plug in the appropriate constants to get the units to balance). When you work out the velocity as you were doing, you do get a dimensionless quantity, but that quantity isn't velocity, it's velocity/c. c has dimensions, so so does velocity. --Tango (talk) 22:41, 4 March 2009 (UTC)

Mathematicians can get away with skipping mentioning the fact that they are using radians because they know that their audience knows that they are using radians. It goes without saying because, as you said, radians come naturally and any other units would in a sense be wrong. Guess what, quantum field theorist and relativists also get away with skipping mentioning the fact that they are using natural units because they know that their audience knows that they are using natural units. It goes without saying because natural units come naturally (hence the name) and any other units would in a sense be wrong (to use your words). c=1(no units) is more than a mathematical convenience. It is the right way to think about it. In fact, Those physicists I talked about never (to use another of your words) use 'c' in their equations. Think about it. Why should two different components of a single physical object (a quadrivector) be measured using different units? You said I have to stick a 'c' in there in order to make it right. I say you are the one sticking 'c' in there when you arbitrarily chose to use different units to measure time and space. Dauto (talk) 23:50, 4 March 2009 (UTC)

It's not even true that radians are somehow 'natural' units for angles. There are engineering applications where 'grads' are used (100 grads = 90 degrees). There are plenty of situations where a full 360 degrees is more usefully and 'naturally' scaled to a 0..1 or -1..1 scale. There are times in computer-based applications when it's more natural to use 1/256th of a circle. If you ever played a computer game that used the "Unreal Engine", all of your angles are in 1/65536ths of a circle. Math isn't just for mathematicians - we normal people get to use and adapt it too! SteveBaker (talk) 03:27, 5 March 2009 (UTC)

SteveBaker, radians are the natural units for angles. But you are free to introduce arbitrary constants in your choice of units if that is somehow convenient. As you said yourself, "don't confuse a mathematical convenience with 'how things are'". Dauto (talk) 03:54, 5 March 2009 (UTC)

No! That's bullshit. Having 2.pi units in a full circle is undoubtedly convenient in situations where pi is involved for some other reasons (eg when working with sines and cosines) but in other situations where pi is NOT involved, a 0..1 scale is vastly more 'natural'. You have a prediliction for having 2.pi units because that's the kind of field you happen to be working in - but in areas I happen to work in (some of the time), having an irrational number of angle units in a full rotation is not merely inconvenient - it's utterly untenable! There are things you literally cannot do with radians. For example - I have two objects that are spinning - adding some amount of rotation per time-step...and I want to know on any given time-step whether they are pointing in the same direction. Using radians I have to divide their total accumulated rotation by 2.pi and take the remainder and compare the two results. However because pi is irrational - I can't make such a comparison in finite precision. In that case using radians is not only unnatural - its downright useless! So - I store rotations such that a full rotation is 1 unit. This is beautifully natural - I simply compare the fractional parts of the numbers and I'm done...what could be more natural? Radians are also useless for people who have to do actual numerical calculations rapidly in their heads - using degrees is incredibly useful in that situation because you can do exact division by 2,3,4,5,6,8,9,10,12...and so on...jut try calculating the numerical value of a third of two-pi in your head so you can mark it using your (non-existant) radians-scale-protractor!!! One man's "natural" is another man's "completely and utterly impractical". So your 'natural' units are only natural for your applications - and this pigheaded insistence that your way is right and everything else is somehow wrong is just phreaking crazy! We can do calculations using angles using any damned units we like. Get out here in the real world where math is actually used for practical purposes and you'll soon find that what is 'natural' or 'convenient' changes from one day to the next. The sooner you get your head out of the clouds (or wherever it's currently stuck) and into the real world the sooner your contribution to the world will be of practical relevance. SteveBaker (talk) 05:22, 5 March 2009 (UTC)

"Natural" has a very precise meaning in this context, it doesn't just mean "the most obvious/useful". There are plenty of situation where it is best to use unnatural units and conventions, but that doesn't make them natural. --Tango (talk) 15:41, 5 March 2009 (UTC)

SteveBaker, I don't dispute that other angle units can be more useful or practical then radians. I myself find it more practical to use degrees in many situations, and I understand why a computer programmer would prefer to use some power of 2 such as 256 for 360 degrees. That does not change the fact that an angle is defined as the ratio between two lengths (a radius and an arch) and the natural thing to do is to use the same units to measure both lengths. Guess what angle units turn up when you do that? Dauto (talk) 19:27, 5 March 2009 (UTC)

No! You choose to define an angle as the ratio between the length of a radius and an arc...which results in you deciding that radians are "natural". But in many applications, defining an angle as a fraction of a complete planar rotation makes much more sense - especially if you don't give a damn about the lengths of arcs or the areas of pie-wedges. When you work in applications where you're more interested in objects rotating - there is no "ratio of distances - one being an arc", the incredibly ugly use of an irrational number for useful concepts like 'right angle', 'identity rotation', 'reversing direction' simply goes away and the result is a much more natural 'fraction of a full rotation' definition for an angle...in some applications. I'm not claiming that radians are bad - they have their place - I'm just saying that which units seem most 'natural' is in the eye of the beholder and it's extreme arrogance to claim that your application - your definition of 'angle' - is somehow more fundamental than the others. There is no one definition of 'angle' that we somehow all have to assert to be "The One True Definition" - and hence there is no one representation for angular units that is somehow more natural than the others. I use radians sometimes, degrees at other times, 0..1 other times, -1..1 in others and even 0..65536 (urgh!) when I work with the god-awful UnrealEngine. All are perfectly 'natural' in the environment in which they are used. SteveBaker (talk) 20:33, 5 March 2009 (UTC)

It may not be the only definition, but it is the standard definition. I suppose you could define angles as "points in the natural parametrisation of orientation preserving linear isometries of the Euclidean plane by the unit interval" (rather a mouthful!), which would give you angles ranging from 0 to 1. I can't think of any natural definition that yields anything other than radians or 0 to 1, though. Any other units would require a definition that introduces arbitrary elements with no justification in elementary geometry. --Tango (talk) 21:02, 5 March 2009 (UTC)

SteveBaker, I agree with Tango that there is also some naturalness for the definition where 1 = 360 degrees. Instead of defining an angle as a ratio of two lengths it seems equally reasonable to define it as a fraction of a full turn. The other definitions are somewhat more arbitrary. But I don't care about that since naturalness is not definable anyways. I'm actually glad you said that because you are kind of making my original point for me. My point was that despite angles being adimentional quantities, there is still the possibility of choosing different units without any loss of information (what do you know, we're actually agreeing here despite the appearances). Interestingly enough, the factor of 2pi between the radian definition and the 0 to 1 definition is the same factor o 2pi that relates frequency $\nu \,$ and angular frequency $\omega \,$ which is the same factor of 2pi which relates $h\,$ and $\hbar \,$ which started this whole discussion to begin with. Thanks for helping me make my point, Dauto (talk) 21:48, 5 March 2009 (UTC)

So what we've concluded is that there are multiple natural unit systems and you can use whichever you like, you just have to make sure you keep track of the pi's. Did anyone think otherwise to start with? Have we just had a big long debate only to conclude that we didn't really disagree on anything substantial to start with? --Tango (talk) 21:59, 5 March 2009 (UTC)

I don't know, Tango. Do we all agree that 1 second = 299,792,458 meters? if we do, then you may be right that there is no substantial disagreement. Dauto (talk) 23:17, 5 March 2009 (UTC)

Physicists never use c in their equations? I can't tell if you're just making stuff up here or are somehow totally confused. Show me some of this physics that somehow never uses natural units and implies multiplying things by c but doesn't say it. I call foul—you're spouting nonsense. --98.217.14.211 (talk) 01:00, 5 March 2009 (UTC)

May be I didn't make my self clear enough. What I meant to say was that whenever using natural units $(c=\hbar =1\,)$ 'c' or '$\hbar \,$' don't appear in the equations. What would be the point of multiplying by powers of c=1(no units)? That's why c never apears in the equations when natural units are being used. Dauto (talk) 03:29, 5 March 2009 (UTC)

Look at the rightmost column of the table atPlanck units#Planck units simplify key equations. See any physical constants there? That's what I'm talking about. Dauto (talk) 03:47, 5 March 2009 (UTC)

Maybe, but those haven't any special sense, at least, until we find a real correlation between them all (as temperature is medium kinetic energy). Would be i*t, a spacial magnitud, or i*x a time magnitude? I'm intersted in that problem.

Plumbide

I just created an article called Plumbide and was told to come here for help expanding it. Chlorine Trifluoride (talk) 02:07, 4 March 2009 (UTC)

It would help if your footnotes actually explained the reference - WP:CITATIONS will help you with the formatting. From what I see at present, it is not possible for a reader to track your sources down. I've done one as an example for you... (it's not a perfect cite template, but it's at least possible to track down the article without a lot of effort). Nimur (talk) 02:25, 4 March 2009 (UTC)

Well, there are quite a few things here:

• Your 'references' aren't references, they're footnotes. References are links to documents outside of Wikipedia that specifically back up what you are saying - scientific journals, chemistry books for example. You could start by doing a Google search on your subject and see what decent articles have been written about it.
• Your link to rare earth links to a 'disambiguation' page - that's bad because the poor person who follows your link doesn't know which meaning of the term you are referring to. Link instead to rare earth element.
• The article is very short - it'll definitely need some expansion. I recommend you look at other articles on similar topics - phosphite for example. It has diagrams of the structures it's talking about, a 'See Also' section - which you should use to link to other Wikipedia articles that talk about related topics.
• You should do a 'search' on the word 'plumbide' using the regular Wiki search box and see what other articles mention the word - this may give you more ideas for things to write about - and you can edit those articles to link to yours on the first occasion they mention the word.
• If you have a copywrite-free photo of some samples of these materials - add it into your article.
• There are lots of other categories you could add your article to - there are categories "Inorganic compound stubs" and "Lead compounds" that seem reasonable.
• You could try joining the Wikipedia:WikiProject Chemistry - they have MANY resources for people writing on chemistry-related subjects. There are entire specialised manuals-of-style for writing these kinds of article.

I hope that helps! SteveBaker (talk) 02:29, 4 March 2009 (UTC)

Damn, I saw the link to Rare Earth and thought I was gonna get a 22 minute version of Get Ready... --Jayron32.talk.contribs 02:42, 4 March 2009 (UTC)

Well you've definately got a good name for this type of work CF₃.

For some reason you put the page in the category 'plumbates', I changed that to 'lead compounds' - as phosphide is not a phospate etc.

Beyond that I can't see so much wrong with it. Why not go and make another article. It's perfectly acceptable to me after I made tiny changes to it. Keep up the good work, wikipedia needs more articles like this.FengRail (talk) 04:23, 4 March 2009 (UTC)

Right now this article is an ophan, meaning that no other articles link to it. If you can think of some articles that should link to it, you should correct this. ike9898 (talk) 19:59, 6 March 2009 (UTC)

medium oil

what is the composition of medium oil? —Preceding unsigned comment added by 119.154.9.144 (talk) 03:42, 4 March 2009 (UTC)

It depends on the brand and where you bought it. Megilp is a painting medium consisting of a mixture of mastic varnish and linseed oil. Most will be similar, combining a thickener with linseed or synthetic oil. Nimur (talk) 08:48, 4 March 2009 (UTC)

Legal "uppers"

Caffeine and sugar are legal "uppers": something you can take that gives you some more energy for some hours. Are there more "things" a normal healthy person can take to get some more energy? I'm not interested to read about illegal drugs or about stuff that is detrimental for your body, just something comparable to coffee (but that I don't know of). Lova Falk (talk) 07:27, 4 March 2009 (UTC)

Some people find coffee or tea stimulating even if it is decaffeinated. This may be a psychological response, but it's possible there are other compounds in the drink that are also categorically stimulants. Nimur (talk) 08:50, 4 March 2009 (UTC)

Indeed, I am one of those people. —Cyclonenim (talk · contribs · email) 23:22, 4 March 2009 (UTC)

See energy drink and energy bar. Those articles contain a number of links to other compounds people ingest to get some "energy", ranging from outright stimulants like ephedra to Calorie rich food products like starches. Dragons flight (talk) 08:56, 4 March 2009 (UTC)

Starches are converted to sugar by the saliva in your mouth...(try chewing a piece of bread and notice how it gets sweeter as you chew)...so for our purposes, starches ARE sugars. SteveBaker (talk) 14:59, 4 March 2009 (UTC)

If you chew long enough, yes. Saliva isn't the only source of amylase, some starch is broken down later, so it does take longer to get energy from starch than sugar. See glycemic index. --Tango (talk) 19:36, 4 March 2009 (UTC)

Laws vary from country to country. Kava seems to be legal in most places, although perhaps hard to come by other than in the South Pacific. It's also not very pleasant to drink - like mud, but perhaps it's an aquired taste.-gadfium 09:17, 4 March 2009 (UTC)

Hmm, Kava as an "upper"?

Kava is a tranquilizer primarily consumed to relax without disrupting mental clarity. Its active ingredients are called kavalactones. In some parts of the Western World, kava extract is marketed as herbal medicine against stress, insomnia, and anxiety.

— Kava

I have never tried Kava, but its mechanism of action appears similar to benzodiazepines, and they sure don't make me feel "up" (since I take them for sleep!). -- Aeluwas (talk) 11:27, 4 March 2009 (UTC)

Beware of Kava, I don't have a reference right now, but remember reading that one particular part of the plant contains some hepatotoxic compounds. --Mark PEA (talk) 12:41, 4 March 2009 (UTC)

If this piece is to be believed, consuming bicarbonate of soda before exertion leads to amazing increases in performance.[ http://ironpower.biz/sup/sup_energy2.htm] --TammyMoet (talk) 11:57, 4 March 2009 (UTC)

I was expecting that to be a typical pseudoscience piece by some uninformed layperson, but was pleasantly surprised. However, it still isn't peer reviewed (I can't access full studies of 30+ years ago) and if the OP is asking for an alternative to caffeine for mental stimulation, sodium bicarbonate is not going to help. --Mark PEA (talk) 12:41, 4 March 2009 (UTC)

Contrary to popular belief, increased concentration of lactate does not directly cause acidosis, nor is it responsible for delayed onset muscle soreness. Noodle snacks (talk) 06:09, 5 March 2009 (UTC)

Native peoples in Bolivia and similar places chew coca leaves for energy, and it's legal for them to do so. I personally take pseudoephedrine for chronic sinus headaches, and I've noticed that it gives me a big energy and concentration boost. Other stimulants, such as Ritalin, have a similar effect. --Sean 14:00, 4 March 2009 (UTC)

In Brazil it is common to use guarana as an energy boost. It contais more caffaine then coffe as well as Theophylline plus other components. Dauto (talk) 14:49, 4 March 2009 (UTC)

I've seen guarana listed in some energy 'uppers' commonly sold in gas stations in the USA. SteveBaker (talk) 15:00, 4 March 2009 (UTC)

I used to have a friend who ate supari, but the taste is pretty awful (at least to my taste buds). You can check out our articles under the Herbal and fungal stimulants category [2]. If you consult a doctor, there's Adderall. A Quest For Knowledge (talk) 16:03, 4 March 2009 (UTC)

Khat may or may not be legal depending on where you are (legal in UK, not in USA); it contains the stimulant cathinone. --Maltelauridsbrigge (talk) 18:37, 4 March 2009 (UTC)

Something else that hasn't been mentioned: modafinil, piracetam and the various other racetams. Please also see this template: Template:Psychostimulants, agents used for ADHD and nootropics. --Mark PEA (talk) 21:07, 4 March 2009 (UTC)

Abstinence from sexual activity will allow you more energy than its opposite. Cuddlyable3 (talk) 14:17, 5 March 2009 (UTC)

Thank you all for answering! I'll check everyone of them, to see if I'll use it, but the side effects scare me.Lova Falk (talk) 17:18, 5 March 2009 (UTC)

Fluid therapy

Explain the difference between "maintenance" volume, "replacement" volume and "ongoing losses" in fluid therapy? —Preceding unsigned comment added by 124.178.147.147 (talk) 09:10, 4 March 2009 (UTC)

Or article on fluid balance may provide some useful background information for you. As for your questions:
Maintenance = the volume of intravenous fluid required to maintain a neutral (no net loss or gain) fluid balance (so input matches output).
Replacement = the amount of fluid required to correct a negative fluid balance to neutral (so input = fluid volume deficit + ongoing losses).
Ongoing losses = fluid losses through all means, both sensible ( or quantifiable, including urinary output, faecal/diarrhoeal, wound drainage, bleeding) and insensible (or non-quantifiable, including evaporative losses to respiration, perspiration and open wounds, especially burns and other large surface area wounds). Hope that helps. Mattopaedia ^{Have a yarn} 13:17, 4 March 2009 (UTC)

The Rust Process

I need a few minutes of the right person's time and his/her expert opinion on how fast rust can appear on newly exposed steel following removal of paint on a car part - the frame of a door open to the weather. (I'm in dispute with a body shop as to how some damage was caused.) The car was parked outside for ten days in cold, wet conditions. How quickly would a visible layer of rust appear? A few days? A week? Would much more than ten days be needed?

Many thanks

FrancisMacFrancisMac (talk) 09:23, 4 March 2009 (UTC)

This is original research so not actually permissible in the World of Wikipedia, but steel body work can rust in a couple of days in wet conditions, a couple of years ago I was making a steel framed table and this rusted within 36 hours after a shower of rain. Richard Avery (talk) 10:12, 4 March 2009 (UTC)

Original research is not allowed in articles. I don't see how knowledge of rust constitutes original research

However we are not here to give legal advice, and any information given here can't be relied on in a legal dispute at all.

It also depends on the depth of rust. Exposed steel can get a thin layer of rust in seconds213.249.232.187 (talk) 12:13, 4 March 2009 (UTC)

Sorry 187 I missed out a ;-) Richard Avery (talk) 15:03, 4 March 2009 (UTC)

Indeed. High quality knives, such as Honyaki and other Japanese cutlery require constant vigilant maintenance. They must be wiped dry immediately after use, lest moisture rust the blade and ruin the edge. Visible rust and pitting can occur within minutes if the blade is left damp. --Jayron32.talk.contribs 14:43, 4 March 2009 (UTC)

I also agree that exposed steel will start to rust immediately. In my case, I polished steel samples for microscopic viewing, and it was necessary to repolish them the next day because of surface rust. However, the serious type of rust that causes pieces of the metal to flake off will take longer. Also note that the car steel may have had some protective coating underneath the paint. Whether this coating was also stripped off with the paint, I do not know. Salt will greatly speed up the rusting process, so, if they splashed saltwater on it while moving it through an icy lot, that would also have an effect. StuRat (talk) 14:50, 4 March 2009 (UTC)

It's vastly variable.

When I lived on the south coast of the UK, my wife reversed one of our cars into the other (doh!) scraping a 6" swath of metal on one car down to the bare metal. Two days later, it had a patina of rust on it - the metal was no longer shiney and it had little orange splotches. By the time we got it to the body shop, maybe a week later, it was orange-colored all over, rough to the touch and there was no shiney metal visible anywhere.

Here in central Texas, I was rear-ended in my old pickup truck and lost about the same amount of paint in roughly the same area. Since the truck was old and crappy - I pocketed the insurance money and didn't bother to get it repaired and I never did get around to painting the 'ding'. Four years later, when I sold the truck, that patch of metal was still as shiney as the day the accident happened.

The difference was:

• The car in the UK was a Morris Marina - notorious for being built from low-grade steel. The truck in Texas was a Ford Explorer. Made from pretty decent steel.
• The weather in the UK is damp and rainy - the humidity is often high. The weather in Texas is hot and dry - and in central Texas, the humidity is typically close to zero.
• In the UK, it snows and gets icy in the winter and they used to spread a lot of salt onto the roads to melt it. Here in Texas, it only rarely gets icy - and when it does they use grit from inland quarries - not salty beach sand. When the ice melts and the road dries out - the salt stays there. UK roads are salty even in the summertime - and it's well known that salt+water+steel=rust.
• In the UK, we lived in Brighton - close to the sea - lots of salt is in the air. Here in Texas, we're 300 miles inland...so not.
• Although the annual rainfall in this part of Texas is comparable to the southern counties of the UK, the rain happens in a few torrential downpours a few times a year. Cars get wet - but they dry out pretty quickly. In the UK, it drizzles just enough rain to get things wet - then stops for a while - then does it again - and it does that through most of the year. It often doesn't get dry enough or warm enough for things to properly dry out for weeks or even months at a time.
• Even in the winter, in Texas there are cold days (below freezing sometimes) - but they are mixed in with hot days - so again, things don't stay wet for long. (There is a saying here that in the winter: "If you don't like the weather today - wait until tomorrow - it'll be different.")...sometimes we have snow on Xmas day - but other times we can eat our Xmas dinner out in the open air...it's random.

I also have a 1973 VW Bug that spent most of it's life in Arizona (hot, dry, no humidity) and the rest in Texas - despite its age and a total lack of rustproofing, it has zero rust.

Somewhere between two days and 35 years is where your answer lies!

SteveBaker (talk) 14:56, 4 March 2009 (UTC)

(Are very expensive cars ever made of stainless steel?)FengRail (talk) 17:42, 4 March 2009 (UTC)

The added cost and difficulty of working with stainless steel mean that it is seldom used unless absolutely necessary. (Stainless steel is harder than most other steels, and it's a bloody nuisance to work with.) The DeLorean DMC-12 – the car featured in the Back to the Future films – is a famous exception, being equipped with stainless steel body panels. DeLoreans were left unpainted, as their fiberglass and stainless-steel bodies were not vulnerable to rust. A few other vehicles have also been built with stainless steel finish, usually for promotional or demonstration purposes: [3]. TenOfAllTrades(talk) 22:39, 4 March 2009 (UTC)

Thanks.FengRail (talk) 22:52, 4 March 2009 (UTC)

I believe that the DeLorean was the only mass-production car ever to use stainless steel. They don't make regular cars out of the stuff because it doesn't take paint very well - you can have it any color you want so long as it's dull-silver. (Hence the "natural metal" finish on the Deloreans). Sure, DeLorean's don't rust (and because the stainless steel body panels are essentially just decorative - it would still work just fine if it did). But it was far from an easy car to maintain - there were problems with hard-to-remove marks from fingerprints and bird poop and such. You had to clean it with some fairly exotic cleaning agents that you had to get from the DeLorean factory. Without a protective paint finish, fine scratches were more noticable because you couldn't just wax the car to get rid of them - and because you can't use paint and bondo and the body has a 'brushed' finish - you can't either hammer out or fill and paint a ding. SO any kind of minor body damage pretty much requires replacing the entire body panel. SteveBaker (talk) 03:01, 5 March 2009 (UTC)

It would be a lot easier? to make them out of normal steel, polished and then clear lacquered. (by the sounds of it) Such as is found on many shiny steel tools.FengRail (talk) 13:52, 5 March 2009 (UTC)

Birds and sex

Sorry if this is a bit of a vulgar question, but I saw two pigeons having sex outside my window this morning and it got me thinking. How exactly does the male bird manage to get his cum into the female and avoid getting it plastered all over her rump feathers, or his own feathers when he ejacultates, seeing as though he doesn't actually have anything he can 'stick inside'? There seems to be an awful lot of feathers to get in the way of a successfull mating. --81.77.40.134 (talk) 14:19, 4 March 2009 (UTC)

Well, they must work it out somehow, since there do seem to be an awful lot of little pigeons running around. Seriously though, you should read Cloaca, and especially the paragraph on the "Cloacal kiss". It's enlightening. --Jayron32.talk.contribs 14:40, 4 March 2009 (UTC)

I would guess that a lot does miss the target, but enough hits to cause pregnancy, and that's what's important. StuRat (talk) 14:44, 4 March 2009 (UTC)

The cloaca is colloquially known as a "vent", presumably because "cloaca" sounds vulgar. Nimur (talk) 14:56, 4 March 2009 (UTC)

I seem to remember someone mentioning something on here once about how the mating method used by birds is not particularly efficient, compared to the way that most mammals go about it. As someone who's bred birds, I suppose the fact that sometimes you'll get a hen laying an entire clutch of unfertilized eggs, despite being 'serviced' repeatedly by her mate (or only ending up with one or two eggs that develop - out of six) is testament to its (literally!) hit-and-miss nature. As Jayron32 said, I suppose that it works as well as the species needs it to work in order to keep the numbers up. --Kurt Shaped Box (talk) 19:29, 4 March 2009 (UTC)

Ask the quelea how it works, they seem to have got the hang of it! Richard Avery (talk) 07:23, 5 March 2009 (UTC)

There must be more chickens than quelea? Kittybrewster ☎ 07:39, 5 March 2009 (UTC)

Expected decline of the Earth biosphere

Hello. I'm looking for an article about this subject. But I cant find one. Is there one? (Specifically, an article which describes the predicted decay of the biosphere due to the growth of the sun. How and when different aspects of the biosphere would be expected to decline and dissappear. When would the oceans become shallow seas? When would the disappear altogether? When would life begin to decline? When would it dissappear? And so on). Thanks in advance for pointing me in the right direction! —Preceding unsigned comment added by 81.233.212.12 (talk) 15:19, 4 March 2009 (UTC)

According to our article on the Sun, we have about a billion years. A Quest For Knowledge (talk) 16:34, 4 March 2009 (UTC)

I see it. I've no plans to still be here by then, so I should be OK. But is there a full article on the subject? If not, can I request the creation of one? 81.233.212.12 (talk) 16:38, 4 March 2009 (UTC)

Be bold and make it yourself. Just make sure you follow all notability and referral guidelines or you risk having your article deleted. Livewireo (talk) 16:55, 4 March 2009 (UTC)

We have an article, Risks to civilization, humans and planet Earth, if that helps. --Tango (talk) 00:01, 5 March 2009 (UTC)

There is no way to realistically predict that. We have no clue how life would evolve in the presence of gradually increasing heat - and we really don't know precisely what will happen to the sun and when. This would be approximation layered on guesswork layered on wild supposition. SteveBaker (talk) 02:33, 5 March 2009 (UTC)

We can put upper bounds on it, though. Once the average temperature gets above the boiling point of water, life as we know it is going to struggle. That's where the 1 billion years prediction comes from. --Tango (talk) 13:47, 5 March 2009 (UTC)

That's a bold supposition. Evolution has produced some rather impressive extremophiles. It's not beyond the realms of possibility for a creature to be able to operate at those temperatures. Hyperthermophiles are around today that can survive well above boiling point (see Methanopyrus Strain 116...happily living their boring, hot little lives at 122 degrees centigrade...well beyond boiling point. As temperatures rise - those critters will become more prevalent as their competitors are wiped out - evolution will allow some of them to survive at higher and higher temperatures and in increasing salinity...perhaps multicelled hyperthermophiles will evolve? As the oceans boil, the cloud cover over the planet will increase - pushing up our Albedo and reflecting more sunlight away - that'll slow things down somewhat...but precisely how much is a relative unknown because we don't know the geography of that future era. Will the oceans be deep or shallow when they start to boil? Will ocean current mix up the cold, deep layers and the hot top layers or not? We can't predict ocean currents a billion years from now! Heck we can't even predict the effects of global warming to that kind of degree over even 50 to 100 years! But until the oceans are literally boiled dry - I think we'll see life clinging on in some niche environments - because that's what evolution does. However, once all the water has gone - it's certainly gonna be tough. But predicting that with the kind of specificity and precision that our OP demands does not seem likely. Will we have extremophiles above the size of a bacterium? Will there be extremophile Lions and Giraffes? Will they learn to live in the air like birds and insects in clouds of live steam? Due to the random nature of evolution - we can't know - we can't even sensibly speculate. SteveBaker (talk) 14:09, 5 March 2009 (UTC)

Those examples you mention live at above 100C, they don't live at above the boiling point of water, since they are deep underwater where the high pressure increases the boiling point. The Earth may have to heat to somewhere above 100C in order for all the water to boil (especially since the atmospheric pressure would presumably increase will all the extra water vapour), but sooner or later the temperature will reach the boiling point of water even at the bottom of the oceans. Some life may be able to survive after that, but it wouldn't be life as we know it. --Tango (talk) 15:36, 5 March 2009 (UTC)

Does anyone happen to know how warm Mars will be and how habitable it will be by then? A Quest For Knowledge (talk) 17:08, 5 March 2009 (UTC)

While it is possible Mars would warm up to a habitable temperature for a time (probably a fairly short time, geologically speaking), it still wouldn't have much of an atmosphere. The ice caps would sublime, providing some more atmosphere, but probably not enough to support humans without protect (and there certainly wouldn't be any free oxygen without active terraforming). It might make terraforming an easier job, but it would still take a lot of work. --Tango (talk) 18:02, 5 March 2009 (UTC)

looking for a photo

I am looking for a photo of the earth from space at night, however there is a catch. I want one during a large widespread power outage, so I can see how much light there is on emergency power only. Anyone able to help? 65.167.146.130 (talk) 16:31, 4 March 2009 (UTC)

List of power outages is a first place to look. You should be very careful that you are comparing "apples-to-apples" images - with modern processing techniques like image compositing, multispectral cameras, gain adjustment and auto-leveling of brightness and intensity in both acquisition and post-production, it may be hard to tell exactly how much light you are actually receiving (typically, I think Earth at night as viewed from orbit looks pretty dark when viewed with the naked eye). Next, take a look at NASA's Science on a Sphere Night Lights data sets. They specifically mention techniques to display power outages by comparing average data to single-night data. Again, note that these are false-color (enhanced) images. Alternatively, you can look at this Columbia University Earth Institute press release, which has a few low-resolution images, and references further research. Here's a blog which makes a vague citation to "NASA" but no real information on the image processing techniques. Nimur (talk) 16:38, 4 March 2009 (UTC)

After a major outage in the northeast USA a few years back, such a picture made the rounds, but was said to be phony. —Tamfang (talk) 18:37, 4 March 2009 (UTC)

Here are the real images of the 2003 blackout. They're not as impressive as the fake ones, but still pretty neat. APL (talk) 18:55, 4 March 2009 (UTC)

Surely there has never been a world-wide outage? Kittybrewster ☎ 07:36, 5 March 2009 (UTC)

no. an outage can only go as far as the power systems are linked. --98.217.14.211 (talk) 12:55, 5 March 2009 (UTC)

I'm tempted to say that the original questioner, being American, thinks that America makes up 99% of the world. A very common idea, apparantly. 78.146.195.92 (talk) 00:47, 7 March 2009 (UTC)

Hypothetically speaking, an external event (like an extraordinarily strong geomagnetic storm) could affect multiple power grids simultaneously. It would take a heck of a solar storm to bring down all the electric grids in the world (or even in just one hemisphere), though. TenOfAllTrades(talk) 18:09, 5 March 2009 (UTC)

Being American, I'm blind to the bias mentioned, so: What? —Tamfang (talk) 04:41, 8 March 2009 (UTC)

Comparing the nightime views from space of the North and South Koreas supports the contention that the South may suffer an occasional power outage but the North never enjoys a power inage. Cuddlyable3 (talk) 14:25, 5 March 2009 (UTC)

March 5

Osseous structures and soft tissue uptake in L3 vertebra

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

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

--Milkbreath (talk) 17:46, 5 March 2009 (UTC)

The discussion about whether this is a request for medical advice is here. StuRat (talk) 05:18, 5 March 2009 (UTC)

This question may be a request for medical advice. It is against our guidelines to provide medical advice. You may find it helpful to read the article: Positron emission tomography, osteoblasts, and osseous tissue, and form your own opinion from the information there. Thank you. StuRat (talk) 19:25, 5 March 2009 (UTC) (edited to remove "contentious" statement – 74  20:40, 5 March 2009 (UTC))

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magnatizing a charged body

some one has told me that we can magnatized a uncharged body but charged body can not be magnatized.I could not understand this.Is it true ,plz explain —Preceding unsigned comment added by 119.154.28.19 (talk) 01:06, 5 March 2009 (UTC)

Not true, a magnet can be charged. Graeme Bartlett (talk) 05:14, 5 March 2009 (UTC)

There might be a misunderstanding here - in general permanent magnets cannot be made from good conductors. But being a poor conductor does not mean the material will make a good magnet. (Before anyone says - Iron which can be magnetised contains a lot of ceramic paricles in the matrix - which are respondsible for it's ability to be magnetised as well as its brittleness - any conduction of electricity is around the particles held in the matrix - pure iron which does not contain any ceramic particles does not make a permanent magnet)FengRail (talk) 13:49, 5 March 2009 (UTC)

The OP may also be confused because electric charge does exist, while magnetic charge does not. Magnetism in materials is not caused by a (magnetic) charge, but it can co-exist with an electric charge and will certainly interact with moving electric charge. It sounds like you misinterpreted someone explaining: there is no way to put a magnetic charge on an object; but it is definitely possible to put an electric charge on a magnet.. Nimur (talk) 15:34, 5 March 2009 (UTC)

It is also possible to magnetize a piece of iron after an electric charge is placed on it. Edison (talk) 19:36, 5 March 2009 (UTC)

Is it possible to magnatise the charge ? ~)

Not in the conventional sense, which is ferromagnetism. In solid matter, charge is carried by free electrons (either present in excess, as negative charge), or missing (because they moved somewhere else, leaving positive charge behind). Since the charge is carried at an atomic-sized level, and ferromagnetism is the macroscopic alignment of magnetic moments, it would not be possible to "magnetize" the free electrons. However - two more exotic forms of magnetism exist: diamagnetism and paramagnetism, which are both directly related to interaction between electron magnetic moments and an applied external field. I don't think either of these are usually observed in relation to free electrons, though; usually they interact with electrons that are bound in atomic-orbitals. Nimur (talk) 05:45, 6 March 2009 (UTC)

Either way it's definately possible to magnetise a thing that has an electric charge. As long as it's the sort of thing that can be magnetised. I've no idea if potentially magnetic things are hard to put a charge on - could this be true?FengRail (talk) 00:39, 6 March 2009 (UTC)

Many ferromagnetic materials are also conductors, which do not hold charge very well because they are hard to electrically isolate (one could be wrapped in rubber or plastic, though). Some of the more exotic ferromagnetic materials are more akin to a ceramic or glass (or a semiconductor) and are likely electrical insulators. Those should hold a static charge without too much difficulty. Yttrium iron garnet shows up in a lot of materials research because it interacts in interesting ways with light, (as polarizing filters and rotators), which of course can be explained at the atomic level as having to do with the electromagnetic interactions with the material's intrinsic atomic-scale magnetic moments and dipole moments. Nimur (talk) 05:41, 6 March 2009 (UTC)

If a metal magnet is placed on a piece of PVC pipe or glass, or hung from a silk it is easy to charge it with electricity, positively or negatively. The charge is able to move around in a conductive magnet . If it is resting on a wooden table or held by someone not insulated from the earth, the charge will naturally leak off. A nonmagnetized piece of ferromagnetic conductor or nonferromagneetivc conductor, such as copper, can also be charged the same way. An uncharged magnet or nonmagetic metal will also be attracted to a charged object. I am not sure what the uncertainty or confusion is here. Edison (talk) 18:52, 6 March 2009 (UTC)

How do we know how high the sea level was 500 million years ago?

I heard that the last time we had the same level of greenhouse gases was some 500 million years ago, and the sea level was then several hundred feet above what it is now. I checked the sea level article, which led me to sequence stratigraphy, but I must admit, I don’t understand that article well enough to get that information. The whole earth crust is continuously in motion, and some of the highest mountains contain sediments from the bottom of the sea. What does it tell us about the sea level 500 million years ago if we find sediments from what was 10,000 feet below sea level then 10,000 feet above sea level now? Mary Moor (talk) 02:03, 5 March 2009 (UTC)

That article makes precious little sense to me as well, but it appears to be mostly about methods for oil prospecting. I'm also not an expert (sad but true, I'm related to a sad number of them and they would all laugh at my pathetic attempt at a response), but rocks that are under water for extended periods are different than those that are above water. Fossils are the obvious difference (very few cnidarians on land, for example), but there are chemical and physical features as well. If you have a network of points, you can create a map from dot to dot and from known rates of continental drift, and you can give an estimate of where the land was and where the sea was. Just a guess. SDY (talk) 03:25, 5 March 2009 (UTC)

True - but the OP's question is an entirely valid one - we know that over geological timescales, mountain ranges may be formed by upward buckling of the crust as two plates are forced together (kinda like you can create an upwards ruck in a rug by sliding one end of it towards the other). So just because you find fossils 10,000 feet up a mountain - even if they were fossils of horseshoe crabs or something that could only have formed at close to sea level - that doesn't prove that the ocean was once 10,000 feet deeper than it is now. The problem here is that you should be asking: "Sea level was then several hundred feet above what it is now...relative to what??" You can't just put a mark on the side of a mountain where the sea level was then - and take a tape measure and measure down to where sea level is now - because the mountain itself has moved up or down in the meantime. The only MEANINGFUL measure would be if you could say that "The radius of the earth measured to the surface of the ocean was several hundred feet greater than it is now"...but I very much doubt that's what's being measured here. So I don't know that this measurement is terribly meaningful when you are comparing ocean levels over geological timescales. BUT when we say that global warming might raise ocean levels by 7 meters (or whatever the current estimate is) - we're talking about this happening on timescales of perhaps just 50 years - and the continents, mountains and everything else won't have moved noticiably over that amount of time. So this measure of sea level rise is entirely meaningful...it tells us how many major cities - and even entire nations will vanish beneath the waves. SteveBaker (talk) 04:52, 5 March 2009 (UTC)

I wasn't clear. Something can be 10,000 feet up or down because the plates and rocks that make up the plates are moving. If you're talking 500mya, the world looks rather different (the map is a little ways down the page). If we assume that the mountains aren't drastically steeper (et cetera), if there is FOO% less dry land then there must be BAR% more ocean therefore there must be BAZ% more water and BAZ% more water equals QUX% feet deeper. SDY (talk) 05:54, 5 March 2009 (UTC)

No - you were perfectly clear - but I don't see how you can make that equation without also knowing things like how the continents are depressed by the weight of the oceans on top of them (a not inconsiderable matter) - and also the extent of water locked up in the ice caps. I think these claims from so far in the past would be tough to substantiate. SteveBaker (talk) 13:52, 5 March 2009 (UTC)

I would say that the answer is that while some of the Earth's surface is uplifted or subsides, this is not true of all of the surface, at least over a time scale of 500 million years. So, the goal would then be to find a geologically stable area and measure historic sea levels there. StuRat (talk) 05:13, 5 March 2009 (UTC)

There is so much assumptions one is making when looking at sea level 500,000,000 years ago relative to today. Lets look at how these interfere with making a meaningful comparison.

1. There was the same amount of water (including ice and atmospheric water) on earth 500m years ago... Possibly not true. Water comes and goes as it evaporates into space (slowly) and also as more water lands on earth on meteorites, and is released from volcanic activity. On human timescales (measured in the thousands or tens of thousands of years) such effects may not be noticable, but on the multi-million-year timescale, there is likely to be marked differences in the total amount of availible water on Earth.
2. There was the same amount of availible space for that water to take up... Also possibly not true. The level of the oceans is due not only to the amount of water in them, but also their shape. Plate tectonics is a complex process, and depending on what the surface of the earth looked like; even assuming we had the same amount of total water to deal with (see above, we may not) then differences in sea level could be due almost entirely to differences in the shape of the surface of the earth; i.e. where the continents were, how low the ocean floors were in comparison to this, yada yada yada.
3. That the level of greenhouse gases is the ONLY controling factor in the Earth's temperature... Also not true. The earth's temperature can also be affected by solar output, by surface albedo, by surface area of the oceans vs. land, by overall volcanic activity, etc. etc. These factors remain relatively constant on the short term, which is why measureing greenhouse gases and their effect on climate, say over the past 10,000 years, may be useful, it isn't going to be terribly useful over 500,000,000 years, since so many other parts of the system are changing that we can't necessarily say "The temperature the earth was 500,000,000 years ago should be the same as it is today solely because the greenhouse gases are at comparible levels"...

Throw all of this stuff in, and even if we COULD actually tell what the greenhouse gas levels and the climate of earth was really like to any detail (and I am not sure we can); it still doesn't mean we can make meaningful statements about sea level based on those statements. --Jayron32.talk.contribs 06:14, 5 March 2009 (UTC)

The existence of one REALLY deep/wide ocean trench at one period in time - and it closing up or filling in some other period in time would erase any hope of appealing to any idea of the total volume of water remaining constant - and therefore the ratio of dry land to ocean surface giving you this answer. If you don't know how deep the ocean went below (or above) present day levels - you can't use the constant volume argument to say very much about overall levels. But unless you're talking about knowing the average radius of the earth measured at "sea level" half a billion years ago - to a rather impressive precision of a couple of hundred feet...you can't make this kind of statement in any meaningful way - no matter what fossil or geological evidence you have. SteveBaker (talk) 13:52, 5 March 2009 (UTC)

Global sea levels changing by hundreds of feet is not very precise at all, we're talking a couple percent change or so in average ocean depth (current average is about 10k ft/3km). Not a huge change, but not impossible precision either. SDY (talk) 16:14, 5 March 2009 (UTC)

It's much easier to find out if the sea-level was LOWER than present levels, because the evidence will exist in sedimentary rocks. But, it's complicated - the current height of the shoreline in the rock layer is not necessarily the original height of the water, because on geological timescales, rocks don't stay in the same place. The crust sort of flows and moves, and float up or down, convecting like a very very slow fluid, and occasionally collide catastrophically. Geologists can estimate how fast a vertical upwelling occurs by a number of techniques, ranging from physics-based modeling of material densities, to observations of broken layers and index fossils.

Old shore-lines and rivers still exist in geological strata and are often CLEARLY visible. In some cases, they can be exposed by erosion, like the amazing canyons carved through the American west. We can also find old geological strata by digging (impractical but possible), or by subsurface imaging. This excerpt, from Geophysical Estimation by Example, shows a marine sounding sonar used to survey the Sea of Galilee, and a bit of signal processing theory to help view what's happening: "The output of the roughening operator is an image, a filtered version of the depth, a filtered version of something real. Such filtering can enhance the appearance of interesting features. For example, scanning the shoreline of the roughened image (after missing data was filled), we see several ancient shorelines, now submerged." Nimur (talk) 15:46, 5 March 2009 (UTC)

At any rate, I'm not an expert, I'm just speculating on how it might have been done and I'm probably wrong. Note that the CO2 level was not claimed to be the cause of high sea levels, simply that it was associated with high sea levels. Chicken and egg possibilities abound, as does pure coincidence. I am, however, almost certain that it has nothing to do with sea level compared with radius of the earth, since that's such a tiny percentage (The stupendously deep Mariana trench is ~10k, radius of the earth is ~6,370 km) that I don't see how it could have been meaningfully measured, and the variability in shape of the earth's crust is such that not only is Kansas flatter than a pancake, but so is Mount Everest. Improbable research is your friend. SDY (talk) 15:55, 5 March 2009 (UTC)

In a recent paper (October 2008) Haq & Schutter [4] describe evidence for a major but gradual sea level rise throughout the Cambrian, culminating in the late Ordovician about 450 million years ago, also shown in this diagram [5]. This rise is recorded by marine transgressions across previously non-marine strata in stable cratonic areas (much as suggested by StuRat above). How accurate such estimates are compared to present day values, that's another issue. Note that 500 million years ago is not associated with an unusually high sea level on these estimates, it happens to be about half way through a 100 Ma period of gradual rise. Mikenorton (talk) 16:04, 5 March 2009 (UTC)

To go back to the original question: As far as I know nobody seriously claims that "the last time we had the same level of greenhouse gases was some 500 million years ago". This seems to be a case of Chinese whispers. We have good evidence that CO2 is higher than during the last 800000 years, and we believe it to be higher than during the last 20 million years. Not a short while, but very different from 500 million years. James Hansen's somewhat famous quote is "The last time the world was three degrees warmer than today - which is what we expect later this century - sea levels were 25m higher." Hansen was talking about a period about 3 million years ago. --Stephan Schulz (talk) 16:34, 5 March 2009 (UTC)

Thank you; it was indeed Chinese whispers. I think it originally comes from Field Notes from a Catastrophe, and I would have to get the book to see the actual numbers. But that was only the background for my question. I wanted to know how we even know how high the sea level was many years ago. The beautiful diagram Mikenorton showed us has three very different curves for the sea level, which could indicate that there is so little consensus among scientists as to render it practically useless. But then again, the diagram was funded by the oil industry, which has used precisely this argument of "there's no consensus among scientists" to persuade the last administration to do nothing about climate change. Mary Moor (talk) 17:55, 5 March 2009(UTC)

Mary, the curves in that diagram are actually very similar. The two to the left that cover the whole time interval both come from the Haq & Schutter paper and appear to be slightly different ways of presenting the same base data (with different smoothing etc.). The third curve, from a source that I haven't managed to find yet, shows a similar overall shape (at least to my eye) but rather greater short term variation. There are plenty of critics of these curves but I'd be surprised if anyone suggested that they were anything other than a genuine attempt to estimate past sea level changes. They were created to better understand observed sedimentary sequences in the geological record. Mikenorton (talk) 22:21, 6 March 2009 (UTC)

Thank you, this is very helpful! I also better understand your earlier comment now: There are areas that are so stable that we can consider them as static, correct? I now see the similarity between the two first curves. (The sudden drops of sea levels of 50m or more in the left curve were a bit scary, anyway.) As for the third curve, however, it still seems very different to me: During Sheinwoodian, the left curves experience one of their highest periods, above 200m, but the third curve varies between 50m and 0m. Mary Moor (talk) 22:11, 7 March 2009 (UTC)

The trouble is that modern estimates for sea level increase for (say) 3 degrees of global warming are not calculated by looking back in time to when we last had those temperatures. They are estimated based on several things:

• When the temperatures rise 3 degrees - any ice that's currently within 3 degrees of melting - will melt. We can pretty much know the volume of that ice. Of course floating sea ice (such as at the North Pole) doesn't count because it's already displacing its own weight of seawater. The main concern is glaciers, snow-pack and antarctica.
• Water that's more than a few degrees above freezing expands as it gets hotter. So knowing the present volume of all of the oceans - it's easy to calculate how much all of that water will expand by.

So those two things give us an idea of just how much more water (by volume) there will be in a 3 degree warmer world...and it's a heck of a lot. Divide that by the surface area of the oceans and what you have left is a rough idea of how much the ocean will rise. There are a couple of secondary effects - one is that as land is inundated by water, it's under more pressure - and that extra weight sitting on top of our continents could push them downwards - allowing yet more flooding. Secondly - (and annoyingly) the exact opposite of that effect happens in the antarctic - where the loss of ice above the land of that continent will allow antarctica to rise up somewhat because of the loss of weight pushing down on it...this displaces more water - which then floods the other continents still more.

25 meters is definitely on the upper end of scientific consensus - but even the lower estimate of 7 meters is pretty frightening if you live in a low-lying city such as New York, London, Paris...you name it. Claiming that "scientists don't agree" is a reasonable claim providing that you are quite clear on what it is that they don't agree on. It's not a matter of "Is this going to be a total disaster or not?" - it's a matter of "25 meters or only 7 meters." - or to put it more pointedly: "Do we lose 100 major cities world-wide or only 30? Are three billion people going to be made homeless or only two? Will loss of low lying fertile farmland result in 50% of humanity starving to death or only 30%." To claim that scientists can't agree on whether this is or is not the single most important thing for the world to focus on fixing - is quite incorrect. The agreement on that point is as close to unanimous as matters. SteveBaker (talk) 20:04, 5 March 2009 (UTC)

The point was that, based on what we know about the ancient situation, we can make assumptions about our time, not the other way round. I assumed that this was a finding of geology. Mary Moor (talk) 03:26, 6 March 2009 (UTC)

As an approximate estimate, melting all the ice on Earth into the ocean would raise sea levels by about 75 metres (250 ft). However, there are factors that can raise this level further, such as isostatic rebound in coastal or undersea areas (land displaces the water, forcing the global sea level to rise), thermal expansion, or a decreased atmospheric water vapor content (more of it being in the ocean). ~AH1^(TCU) 00:52, 8 March 2009 (UTC)

Also, finding the volume of all the ice at a certain melting threshold really isn't a good indicator of how much sea levels will rise. For one thing, a global temperature rise of 3C means that the poles will usually warm faster than at the equator, and land warms faster than ocean. Also, some ice shelves, especially West Antarctica, are vulnerable to being flooded from underneath, lubricating the ice and sending it into the ocean faster, and one example of where this could occur is at Pine Island Bay. ~AH1^(TCU) 01:49, 8 March 2009 (UTC)

Chlorine in tap water

How poisonous is Chlorine in tap water?--Mr.K. (talk) 13:06, 5 March 2009 (UTC)

To you or the bacteria? 76.97.245.5 (talk) 13:58, 5 March 2009 (UTC)

Sufficiently poisonous to kill the things it's supposed to kill, particularly E. coli, which, believe me, is good news for all of us. There isn't enough of it to be harmful to humans, though. -- Captain Disdain (talk) 14:05, 5 March 2009 (UTC)

Some reading material [6] - 76.97.245.5 (talk) 14:34, 5 March 2009 (UTC)

This one's better [7] and also see Risk assessment. To reduce health risks you would do better giving up commuting than water chlorination. Living is detrimental to one's health, but beats the alternative :-)76.97.245.5 (talk) 16:56, 5 March 2009 (UTC)

To answer as simply as possible, not nearly as poisonous as Cholera. --Jayron32.talk.contribs 01:43, 6 March 2009 (UTC)

Ordinary E coli are not dangerous. The reason why E coli content is used as a measure of contamination is usually because it's an indicator of the presence of other bacteria, which are not as benign. If you get sick from bacteria in your drinking water, it's statistically unlikely to be due to E Coli. --Pykk (talk) 09:27, 6 March 2009 (UTC)

Chlorine is an essential nutrient provided by tap water, as is fluoride. See Nutrients in Drinking Water, Page 3.71.30.254.216 (talk) 04:03, 6 March 2009 (UTC)

The link is actually talking about chloride, Cl^-. Chlorine in drinking water is hypochlorous acid, HOCl / OCl^-. Even if you accept them as the same, describing it as an essential nutrient is an extreme stretch in Western society. Our diet is far too rich in sodium chloride (table salt); any contribution from drinking water is vanishingly small by comparison. arimareiji (talk) 15:22, 6 March 2009 (UTC)

Chlorine in tap water is dangerous to fish. Also, see opposition to water fluoridation. ~AH1^(TCU) 00:44, 8 March 2009 (UTC)

Interchangeable left and right hand driving

Is there a car where you can interchange the wheel from left to right and back? At least, was any car designed so that this is easier to accomplish?--Mr.K. (talk) 13:12, 5 March 2009 (UTC)

There are a few cars out there that have a center steering wheel - exotic three seaters sports cars and concept cars, typically[8]. The Toyota Alessandro Volta has three seats in the front - and because it's completely drive by wire, any one of the three people can drive! But sadly, it's just another concept car. Of course there are also driving instruction cars fitted with steering wheels and pedals in both front seats...although these days those are very rare and most instructors have just a set of pedals on the passenger side. Many years ago, BMW ran a newspaper ad showing how their cars could be easily switched from left to right hand drive...and later advertised a car with no steering wheel and center console...but alas, both were just an April Fools pranks. [9]

My classic 1963 Mini has a steering wheel and pedals that can be switched sides in perhaps 4 hours with the right tools...but I suspect you're looking for something a lot more convenient than that. SteveBaker (talk) 13:42, 5 March 2009 (UTC)

Yes, 4 hours would be too much. I was thinking about something more convenient for casual drivers in Europe. The strange thing is that the auto industry doesn't offer this extra. Thousands of vehicles cross the Channel everyday and some drivers would be clearly happy of being able to drive on the proper side of the road. --Mr.K. (talk) 16:48, 5 March 2009 (UTC)

I would hope that most UK drivers, having crossed the Channel, DO drive on the "proper side of the road". Evolutionary processes will reduce the numbers of those who do not. --Cookatoo.ergo.ZooM (talk) 19:51, 5 March 2009 (UTC)

Some ways it could be done and the advantages and disadvantages of each:

1) Center driver position. This has the advantage of being safer, for the driver, as they are not close to either side of the car, making them less likely to be killed if the car is "T-boned". It has the disadvantage of making the driver slide to the center when they get in, could make using drive-through windows difficult, and could make it difficult to fit another passenger in front. A triangular-shaped car addresses some of these issues, but also brings in some stability concerns.

2) Duplicate driver positions. This is best for driver flexibility, but does increase the complexity and thus cost of the vehicle. It might be either more or less reliable, depending on whether the systems are truly independent of each other. A front seat passenger may also find the unused steering wheel and controls are "in the way".

3) Movable driver position. This would make it necessary to make the car "drive by wire", as mentioned above. This has it's own risks, as losing control of the vehicle at high speed is a distinct possibility, since electrical systems are prone to sudden, catastrophic failure, while mechanical systems more often suffer from gradual reduction in function. StuRat (talk) 20:01, 5 March 2009 (UTC)

The Unimog can be changed from LHD to RHD "in the field".195.128.251.103 (talk) 23:11, 5 March 2009 (UTC)

FWIW, British Army soldiers get posted to Germany a lot, and usually take their RHD cars with them - in fact, they often buy a new car just before going as the purchase of a new car for "export" is subject to a little less tax. Though the added difficulty (slightly reduced visibility on right-hand bends) of the driver being on the "wrong" side while driving on the Continent is not zero, in practice it doesn't seem to be sufficient to warrant temporarily switching to a LHD car, the expense of which would probably be roughly comparable to the higher cost of a car designed to be L-R convertible.

Moreover, any visibility advantage of switching from one's accustomed driving side might be more than negated by the potential danger of the gearstick and other controls being in an unaccustomed position. Otherwise, as international lorry drivers constantly move between the two driving regimes, it might be thought that their vehicles would more economically benefit from convertability, although the much improved visibility from their high cabs probably reduces what visibility problem there is.

I dimly recall that a couple or so decades ago, some model of family car built for both UK and Continental sales with the corresponding variations in driver position actually had pedal mechanisms on both sides, those on the passenger side obviously lacking the actual pedal extensions through the floor. Unfortunately the floor was over-flexible and it was found that a passenger could, when bracing a foot on the floor, operate the accelerator, with predictably interesting consequences. Probably that particular design also retained some portions of the steering-column mounting on the passenger side, and would have been more readily convertible than most cars. 87.81.230.195 (talk) 04:39, 6 March 2009 (UTC)

I've driven all four ways (RHD car on UK roads, RHD car on French and US roads, LHD car in the US and a French LHD car in the UK)...switching from one to another is EASY - and the flipping of the shifter to the opposite side takes no adaptation at all. Being on the correct side of the road is a little confusing in big areas like parking lots - but once you're out on the open road, it's not at all difficult - and after 10 minutes of driving around town - you've go it nailed. The difficulty of adapting is very overrated. The only weird thing is that even after 15 years of driving (mostly) LHD, I still occasionally walk up to the wrong side of the car when I approach it from the front in a parking lot! The hard (and dangerous) thing is that for RHD in France/USA and LHD in UK, you can't overtake safely - you have to pull so far out past the vehicle in front before you can see around it...if there is something coming the other way - you're doomed. For my restored 1963 RHD Mini here in Texas, I've turned the passenger-side door mirror around 180 degrees so I can nudge the car out just a little and then see around using the mirror. It works pretty well and I'm surprised that things like that aren't sold as accessories for Brits taking their cars across the channel to France & Belgium. SteveBaker (talk) 05:30, 6 March 2009 (UTC)

Systemic Beta Hemolysis Infection

Is it possible that one can get systemic Beta hemolysis (Beta Strep) infection? I know that some women can get a Beta Strep infection vaginally but it possible that it could spread throughout the body? Also, does anyone know why more research hasn't been done on this? --Emyn ned (talk) 14:19, 5 March 2009 (UTC)

Well, yes, it's possible. Streptococcus agalactiae is an important cause of neonatal sepsis, especially effecting premature babies. Less commonly, it can effect pregnant women or non-pregnant adults. [10] - Nunh-huh 14:24, 5 March 2009 (UTC)

We have a page for almost everything, including the beta-hemolytic streptococci, which notably include Streptococcus pyogenes. --Scray (talk) 00:16, 6 March 2009 (UTC)

Woman with 3 breasts

Warning: The video linked hereunder is sexually explicit.

The specific link is www.redtube.com/21290 Does the this unusual thoracic development shown in the linked video seem credible or faked?

I remember seeing cases of people having an extra nipple or two that are located under the standard two, and underdeveloped. I presume these are so easily removed surgically that their actual rate of occurrence is unrecorded - or does anyone know about these? Can anyone add any knowledge about the fully formed triplet exhibited by the actress in the video? Is it practical to "build" such a chest by cosmetic surgery? If her triple breasts are a genuine mutation are other internal abnormalities likely, and should all 3 breasts lactate? What can one say about human breast number and evolution? Is there evidence that human mutation is increasing? Cuddlyable3 (talk) 14:38, 5 March 2009 (UTC)

We have an article, Accessory breast, that would be a good place to start. --Tango (talk) 15:13, 5 March 2009 (UTC)

Milk lines extend from the axilla to the groin, both on the left and the right frontal side of the body (see the teats of cats or pigs). It would seem to be anatomically impossible for a mammary gland to develop in the centre. --Cookatoo.ergo.ZooM (talk) 16:53, 5 March 2009 (UTC)

The article I linked to describes cases of extra breasts growing on the feet, so I guess it is possible for them to grow pretty much anywhere. I do think the case shown in the video is rather unlikely, though - the three breasts are very symmetrical and equal in size, which I think would be extremely rare. --Tango (talk) 17:01, 5 March 2009 (UTC)

The only way I can imagine a third breast between the other two is in the case of conjoined twins, in particular, the parapagus type. However, they would likely have other duplicated body parts, as well, such as heads. StuRat (talk) 19:35, 5 March 2009 (UTC)

I was sure to have noticed a third head somewhere in this shortish documentary. --Cookatoo.ergo.ZooM (talk) 19:56, 5 March 2009 (UTC)

In another video the girl says that her two side boobs (hehe) were originally small, but she got implants to make all three about the same size. —Preceding unsigned comment added by 99.255.228.5 (talk) 00:44, 6 March 2009 (UTC)

That is so fake - the middle boob has zero jiggle factor - it's glued on there. Clever makeup work - nothing more. SteveBaker (talk) 05:16, 6 March 2009 (UTC)

I agree with Steve. Frankly, most anatomical oddities seen in porn should probably be assumed to be fake, unless they're incredibly convincing and constantly interacted with... which this one hardly is. The simple fact that she's extremely unwilling to let the middle breast just hang loose and is almost constantly holding on to it should be a an obvious hint: if she didn't do that, it'd fall off. It is a pretty good makeup job, though. -- Captain Disdain (talk) 08:48, 6 March 2009 (UTC)

"Jiggle factor" - never thought I'd hear that term outside of anime reviews. ^_~ And although I haven't seen said video, CD's argument sounds intuitively correct. arimareiji (talk) 14:32, 6 March 2009 (UTC)

I'm a computer graphics engineer and I work in the field of computer games. In my chosen profession, "jiggle factor" (as applied specifically to ridiculously oversized boobs in female game characters) is an entirely accepted term which appears in any number of serious papers published at conferences on graphics technology. It is typically scaled from 0 to 1. The person in the video has an 0.0 boob in the center - and I'd judge about an 0.6 or so on either side. "Trust me - I'm an expert!"  :-) SteveBaker (talk) 20:57, 6 March 2009 (UTC)

And what would the "jiggle factor" be in Dead or Alive Xtreme 2? 2? 3? --Carnildo (talk) 00:59, 7 March 2009 (UTC)

On a scale of 0 to 1? 11. --Tango (talk) 16:24, 7 March 2009 (UTC)

Oh so now you're a "computer graphics engineer" eh? Last time you were some mini driving texan. Just sayin'. 85.181.144.5 (talk) 19:21, 7 March 2009 (UTC)

Yeah, because no one in Texas drives a Mini and works as a computer graphics engineer. Sir, you appear to have forgotten your stupid on. -- Captain Disdain (talk) 09:50, 8 March 2009 (UTC)

LC/NE system and the ascending activating systems

Resolved

Sometimes it is hard to connect information from different sources. In the article on stress, the "LC/NE system" is mentioned. In my textbook on neuropsychology, the authors mention "the four ascending activating systems, classified by the dominant transmitter and their neurons: the cholinergic, noradrenergic, dopaminergic and serotonergic systems". My question: is the LC/NE system the same as the noradrenergic system? And if not, what is the difference? Lova Falk (talk) 17:27, 5 March 2009 (UTC)

This [11] source has: "The principal components of the stress response consist of the hypothalamic-pituitary-adrenal (HPA) system (most commonly known as the HPA axis), the locus coeruleus-norepinephrine (LC-NE) system, and the extrahypothalamic corticotropin releasing hormone (CRH) system." --Cookatoo.ergo.ZooM (talk) 18:04, 5 March 2009 (UTC)

Thank you, but that is not an answer to my question... Lova Falk (talk) 20:33, 5 March 2009 (UTC)

LC refers to the locus coeruleus, which is the primary brain stem nucleus where norepinephrine (NE) is produced. The neurons of the LC project widely throughout the brain (see the norepinephrine article for a list) and have an "activating" effect under conditions of stress. So, yes, the LC/NE is most likely the ascending activating system described by your textbook. --- Medical geneticist (talk) 23:11, 5 March 2009 (UTC)

Thank you! Personally I think that neuroscience textbooks should mention all alternative names for the structures or systems they describe. All those different names for the same thing just creates so much unnecessary confusion... Lova Falk (talk) 11:09, 6 March 2009 (UTC)

Question on mag fields and EMF

A magnetic field is perpendicular to the plane of a single-turn circular coil. The magnitude of the field is changing, so that an emf of 0.70 V and a current of 3.5 A are induced in the coil. The wire is the re-formed into a single-turn square coil, which is used in the same magnetic field (again perpendicular to the plane of the coil and with a magnitude changing at the same rate). What emf and current are induced in the square coil?

So I have no idea how to get the EMF without the area of the circle which the coil creates. I'm assuming the EMF changes due to the area of the coil. I'm also assuming that if you shape a circular coil into a square the area should be the same anyway... I know that the EMF and the current can give me the resistance of the wire. I got .2 ohms of resistance. With this, if I get the EMF of the square coil, I can get the current (I think). But I don't know how to get the EMF of the square coil. I'm really confused as to how to go about this... 98.221.85.188 (talk) 19:34, 5 March 2009 (UTC)

If you are forming it out of the same wire then the perimeter will be the same, not the area. If you know how to calculate EMF given area (unfortunately, I don't!), then do it in reverse to get the area and perimeter. You should then be able to use that, together with the formulae for area and perimeters of circles and squares to get the answer. --Tango (talk) 19:39, 5 March 2009 (UTC)

The magnetic field is changing... EMF= -(number of turns in coil)*[(change in Mag Flux)/(change in time)]. I know Magnetic flux = (Mag field) * (Area of the coil). The magnetic field is changing though, so I'm not sure how to get the Magnetic flux... 98.221.85.188 (talk) 19:45, 5 March 2009 (UTC)

You are given one more piece of information - the current. What formulae do you know with current in? --Tango (talk) 20:28, 5 March 2009 (UTC)

You don't need to compute the magnetic flux. All you need is the fact that the emf is proportional to the area. So the ratio between the two emf's (before and after) = the ratio between the two areas (before and after) which, as Tango pointed out, comes out of the formulae for the perimeters. Dauto (talk) 22:05, 5 March 2009 (UTC)

The OP describes a shorted wire loop that is extracting energy from a varying magnetic field. Energy, not emf, is proportional to the loop area. We must assume the external magnetic field is uniform except where it is perturbed close to the loop, and that the resistance is constant. The emf (to 4 sig. figs.) in the square loop is 0.5190 V and not 0.5498 V.Cuddlyable3 (talk) 23:18, 5 March 2009 (UTC)

Force meter question

Dear Wikipedians:

In the above scenario, if m is also 1 kg, then I know the force meter will register 9.8 N as the tension. However, what will the force meter register if m is 2 kg?

Thanks.

L33th4x0r (talk) 20:12, 5 March 2009 (UTC)

What will it register if M is infinite (i.e. fixed to the floor)? --Stephan Schulz (talk) 21:29, 5 March 2009 (UTC)

With the weight imbalance, the system will begin to accelerate and the tension will be just enough to keep the acceleration of the two masses equal. So the solution can be obtained by calculating the acceleration of each mass in terms of the tension T, setting the two accelerations equal, and solving for T. I don't know if this is homework or not, so I am not giving an explicit answer, but the calculations are pretty straight forward. -- Tcncv (talk) 21:42, 5 March 2009 (UTC)

But the force meter is accelerating too, so the tensions in the two cables are only equal if we assume the force meter has negligible mass. If the force meter has a non-negligible mass than the tensions are not equal - but then we need to know the mass of the force meter to solve the problem. Gandalf61 (talk) 22:19, 5 March 2009 (UTC)

This is a physics problem; real objects need not apply. Force meters are always massless — in exactly the same way that we assume that the pulleys are frictionless and have no moment of rotational inertia, and that the rope in the system is massless, and that the meter doesn't drag on the ideal frictionless physics table.... TenOfAllTrades(talk) 23:10, 5 March 2009 (UTC)

Lets start again, if m=1kg also then the force meter measures (2kg) = 19.6N

If fixed to the floor then the force meter measures (1kg) 9.8N

If the masses are 1kg and 2kg then the thing will move, the net force being (2-1)kg = 1kg = 9.8N on a total mass of 3kg... this gives you the acceleration of the masses as 9.8N/3kg = 1/3 of gravity.. can you work out the final answer from there?FengRail (talk) 00:31, 6 March 2009 (UTC)

The original stated tension of 9.8N is correct. Whether or not one end is fixed in the balanced configuration has no effect. Your third statement is correct (after minor editing for units) and is another way to get to the solution. -- Tcncv (talk) 01:51, 6 March 2009 (UTC)

Why is the tension 9.8N and not 19.6N like FengRail said?

If m is 2kg, then the apparatus is not balanced. m will descend, the 1kg mass will ascend, and the force meter will move to the left; until one of them encounters a pulley or the floor. Astronaut (talk) 02:53, 6 March 2009 (UTC)

If the tension were 19.6N, the upward force of the cable on the masses would be twice the downward force due to gravity. The result would be both masses accelerating upward (at least enough to reduce the cable tension). Another way to look at it: Consider the balanced system of two weights. Now drive a sturdy bolt through the heart of the force meter and into that frictionless table (don't let the lab manager catch you). The cable tension has not changed, but now we effectively have separate cable, pulley and weight systems both anchored at the bolt. -- Tcncv (talk) 03:53, 6 March 2009 (UTC)

I have no idea what you are on about - the tension (forces) due to a mass of 1 kg under gravity is 9.8N, there are 2 of these forces working in opposite directions, therefor the total tension is 2x9.8n

In the orginal question, it is incorrectly stated:

"In the above scenario, if m is also 1 kg, then I know the force meter will register 9.8 N as the tension"

I attempted to correct this statement.FengRail (talk) 10:58, 6 March 2009 (UTC)

No, it will register 9.8N, because there must be an equal and opposite force for the weights to be in equilibrium. Think of it this way: If m was instead a hook on the floor, what would the scale register? 124.169.174.199 (talk) 11:54, 6 March 2009 (UTC)

A force meter does not measure the sum of the forces on either side of it. The way that the hook and scale are attached to the solid body of the force meter introduces an asymmetry - it always registers the force on the hook side only. For an ideal massless force meter or for a force meter in equilibrium, the two forces will be equal in magnitude, so we often loosely say that the force meter registers "the" force, as if there were just one. For an accelerating force meter with non-negligible mass, the two forces will be unequal - but it is still just the force on the hook side that is registered on the force meter. Gandalf61 (talk) 13:49, 6 March 2009 (UTC)

Look at the diagram above, the two equal and opposite forces are on either side of the force-ometer, forces are vectors right, (so if one of the forces was zero, what would the other force have to be to give the same tension?)

Why not try an experiment - find a weight that doesn't quite cause breaking in a length of string or wire, then try to replicate the diagram with two of those weights on either side - see if the sting brakes... signed FengRail —Preceding unsigned comment added by 213.249.232.187 (talk) 14:31, 6 March 2009 (UTC)

Gandalf is right (if the hook can be considered massless, even though the forcemeter isn't). Dauto (talk) 14:12, 6 March 2009 (UTC)

Not really. Consider two people playing tug-of-war, with a force meter connecting the two ropes. Does it measure only the force of one person pulling, or two? arimareiji (talk) 14:28, 6 March 2009 (UTC)

Simpler example: Hold the top of the force meter in your hand and hang a 1kg mass from the hook. For meter will say 9.8N, obviously. Now consider the forces on the meter - there is a force of 9.8N from the mass pulling it down, and there is a force of 9.8N from your hand pulling it up. That's exactly the same forces are are on the meter in the diagram above (just rotated 90 degrees), so the meter will show the exact same value. --Tango (talk) 14:42, 6 March 2009 (UTC)

Tug-of-war - force meter registers force of only one person pulling. Exactly the same as if just one person pulling and other side of force meter attached to solid wall. Gandalf61 (talk) 16:08, 6 March 2009 (UTC)

(undent) Vaguely-related question that this reminds me of, which came up a little while ago among coworkers: Say that a person weighs too much for a scale to register. Can you accurately measure their weight by getting them to step onto two scales, one foot on each scale, and adding the registered weights? arimareiji (talk) 14:52, 6 March 2009 (UTC)

Yes, that should work. The scales measure the force required to stop them falling through the floor (which is equal to their weight), that force is the same regardless of what is applying it and forces in the same direction just add when combined. So, yes, I can't see why that wouldn't work. --Tango (talk) 15:41, 6 March 2009 (UTC)

Oh, I get it now (I think?). The purpose of the experiment is to demonstrate to students that there are two equal and opposite forces at work. The teacher first demonstrates that a 1kg weight suspended from a fixed point registers 9.8N on the force meter. The teacher explains that there are two forces - gravity pulling the weight down with a force of 9.8N, and the fixed point pulling up with an opposite 9.8N force. Some students might doubt the existence of this upwards force, so the teacher sets up the above experiment with m = 1kg. If the force meter reads the same 9.8N then it shows the upwards force must exist and be equal and opposite. Astronaut (talk) 16:22, 6 March 2009 (UTC)

Great little circle jerk, wikipedia reference desk at its best.FengRail (talk) 18:32, 6 March 2009 (UTC)

Let's write down Newton's second law of motion(EOM), for our two masses and the rope, then we can get into the answer: the resultant force acting on a mass is equal mass times of its acceleration. the magnitudes of each acceleration of the masses are equal, which relates our equations. further assumption is the negligible mass of the rope (which according to the EOM of the rope, yields: the magnitudes of two tension forces, acting on each end of it, are equal). the magnitude of acceleration becomes (abs(m2-m1)*g)/(m1+m2) , and tension becomes(in this situation) (4/3)*g . Re444 (talk) 18:55, 6 March 2009 (UTC)

Correct. In terms of force, (4/3) × 9.8N or about 13.1N. That leave a net upward force of 3.3N on the 1kg mass and a net downward force of 6.5N on the 2kg mass. Ignoring round-off errors, that gives the masses the same acceleration. -- Tcncv (talk) 01:19, 7 March 2009 (UTC)

Wow, this is soooo good! Thanks for all the response! L33th4x0r (talk) 03:25, 7 March 2009 (UTC)

Why blood groups and Rh?

I couldn't find in our article or figure out in google why blood groups are needed. What is their actual purpose, why don't we have some universal blood group? And what is the purpose of Rh? 85.132.54.6 (talk) 20:32, 5 March 2009 (UTC)

Why should they be "needed"? As with most evolutionary matters, they simply are. Also, for quick reference: blood type/ABO blood group system and Rhesus blood group system. — Lomn 21:04, 5 March 2009 (UTC)

Blood groups exist because they turned up one day and they don't do any harm, so they stuck around. Blood groups only became significant in any way when we started doing blood transfusions, which was extremely recently in evolutionary terms. (I guess there is a slight disadvantage to them since there are sometimes problems with Rh- mothers having Rh+ babies [I think it's that way around], but it's very rarely a problem because, if memory serves, it's only the second such baby that dies, and even then only if there were complications with the first one.) --Tango (talk) 21:11, 5 March 2009 (UTC)

There was (until recently) no evolutionary pressure in favour of compatibility or homogeneity (and so things just drifted apart, as they are wont to do). Right now there is a modest pressure - if someone has a group that requires transfusion with a rarer type, they run the disk of the hospital not having the right kind, and thus their dying without issue. If medicine were to remain exactly as it is for a few thousand years then you would expect to see a modest increase in the proportion of individuals who have transfusion-friendly blood when compared with those who don't. 87.115.143.223 (talk) 21:13, 5 March 2009 (UTC)

There is one modest piece of evolutionary pressure, Hemolytic disease of the newborn (HDN), which is part of why the Rh system was discovered in the first place. ABO rarely has a role in HDN. The ABO and Rh red cell antigen groups are not known to be functional, but there are some red cell antigens, such as the Duffy antigen system (usually "Fy" in shorthand) which are known to be meaningful outside of blood typing for medical or investigative purposes. In most of these cases, it's likely that no one has found out exactly what these bits of stuff on the extracellular matrix of the cell are for. SDY (talk) 21:15, 5 March 2009 (UTC)

Hmm, that's interesting. So that would imply either that human blood groups are slowly converging (from a more disparate ancestry - RH+ == grandma was a Neanderthal) or there is weak opposing pressure from some unknown utility in heterogeneity (e.g. resistance to some blood-borne disease). 87.115.143.223 (talk) 21:25, 5 March 2009 (UTC)

I'm not sure when the mutation happened which causes some people not to have the RhD antigen (I think everyone had it originally, but I may be wrong), but it wasn't necessarily that long ago. It only takes one mutation followed by the person with that mutation having lots of children for it to spread fairly widely within just a few thousand years. There may be some evolutionary pressure towards heterogeneity, but don't forget the importance of random chance. If the evolutionary pressure, in whatever direction, is very weak then random chance can end up being far more significant, even over the long term. --Tango (talk) 21:34, 5 March 2009 (UTC)

(outdent)

In general, when a genetic polymorphism is maintained in a population, some kind of balancing selection is at work. Polymorphisms that are neutral tend to disappear rather quickly. In this paper, the authors develop a model which attempts to explain the ABO gene frequencies by frequency-dependent selection (a type of balancing selection). They hypothesize that the reason is that bacteria may adapt differentially to the different carbohydrate structures of ABO antigens, and that, in addition, the natural antibodies that we have against the A and B antigens we lack, may offer protection from viruses that carry A and B antigens in their envelope derived from their previous host.

Rh proteins are believed to be ion transporters, involved in ammonia transport. I have not come accross any articles that attempt to explain the maintenance of Rh polymorphisms, although Hemolytic disease of the newborn may play a part, as suggested by SDY. --NorwegianBlue ^talk 21:40, 5 March 2009 (UTC)

[12] discusses the matter, I'm still reading it so I'm not sure what it concludes (it seems to be suggesting there must be a balancing selection of some kind). --Tango (talk) 21:50, 5 March 2009 (UTC)

Not necessarily relevant, but my favorite bit about blood is that the gene for type "O" is the gene for type "A" with single base pair different, a nonsense mutation. Tiny change in genetics, potentially lethal difference in transfusions. SDY (talk) 22:11, 5 March 2009 (UTC)

One of the mysteries in transfusion medicine is why people who have never been exposed to other ABO types have antibodies to those types. For example, a person who is type B (not to be confused with the immune system's B cells) has antibodies to type A immediately after the immune system develops (by about 3-6 months of age). Speculating: this would give a strong evolutionary advantage if both A and B "look like" viral antigens, since even if only half of the population is immune, the disease may have trouble persisting. Type "O" in this case would be the best of both worlds, since it would grant immunity to both "A-like" and "B-like" viral antigens. SDY (talk) 22:55, 5 March 2009 (UTC)

Re the paper that Tango linked to: Note that it was written at a time when the D, c/C and e/E antigens were thought to be encoded by three separate, linked genes. It has since been discovered that the c/C and e/E antigens are two epitopes on the same molecule. --NorwegianBlue ^talk 22:23, 5 March 2009 (UTC)

Didn't I read something somewhere about some mild correlation where people with blood group X were a bit more likely to get disease Y but a bit less likely to get disease Z, for suitable values of X, Y, and Z; and that the geographical distribution of the genes for different groups (if you corrected for recent migrations) could be related to the geographical distribution of the relevant diseases? This would make sense as a factor to preserve a diversity of blood types (in the ABO system) in the global population. (The practice of transfusing blood is too recent to have had any effect on this, of course.) Anyone remember reading something like this? --Anonymous, 05:48 UTC, March 6, 2009.

I don't remember a specific news item like that. In the disease associations that come to mind, negativity for an antigen is associated with resistance to a disease. This is the case for Duffy antigens (malaria), and A and B antigens (malaria and thrombosis). However, fetal A and B antigens may be protective hemolytic disease of the newborn, because anti-A or anti-B antibodies in an Rh(D) negative mother, who carries a child that is Rh(D) positive and positive for the A or B antigen that the mother lacks, protect against maternal Rh-immunisation. --NorwegianBlue ^talk 12:34, 6 March 2009 (UTC)

Moved comment by SDY that was posted in the middle of my reply. --NorwegianBlue ^talk 09:44, 6 March 2009 (UTC)

Can't give a definitive reason but the presence of Blood type (non-human) amongst numerous animals and its persistence from the apes to us indicates having blood groups must have a strong evolutionary advantage. Dmcq (talk)

Malaria: Worst. Disease. Ever?

Hi. Is there any truth to the claim that Malaria has killed about half the people who have ever lived??? --Kreachure (talk) 22:35, 5 March 2009 (UTC)

I very much doubt it. The estimates for the total number of people who have ever lived is all over the map - but 100 billion isn't a bad guesstimate. There are between 6 and 7 billion people alive today - and about half of the 100 billion are estimated to have lived before 1000 AD. This means that in order for this to be true - a CONSIDERABLE fraction of those deaths must have happened long before consistent records were kept - and VERY long before the diagnosis of diseases was good enough to be reliable. We know that half of the people who ever lived can't have died of malaria SINCE 1000 AD because for that to be true, we'd all have to be dead. List of causes of death by rate lists malaria as causing around 2% of deaths worldwide in 2005. So clearly the death rate from malaria would have had to be not just 50% in more ancient times - but VASTLY more than 50% in order to compensate for the miserable 2% rate we're seeing these days...but again, we can't be sure of numbers that far back in history because statistics were not kept - and the germ theory of disease didn't exist - so a death from malaria might be attributed to any number of bizarre causes. SteveBaker (talk) 23:31, 5 March 2009 (UTC)

I wonder (as I have heard this folk-fact before) as to whether it came from somebody saying "The number of people who have ever died as a result of malaria is equal to half the people living today". That would seem consistent with the maths. 2% of 100 billion being 2billion, but 2% being low due to modern anti-malarial drugs, so likely higher in the past. Fribbler (talk) 23:54, 5 March 2009 (UTC)

Sounds quite plausible. arimareiji (talk) 14:23, 6 March 2009 (UTC)

That's a possible reason

Alright, this is rediculous...I have in ten minutes of searching found countless forum discussions, blog postings, websites, and even a national geographic article asserting something along the lines of "some scientists believe that malaria has killed over half the people who have ever lived.] Not a single source I've found gives a citation for this, or ever elaborates on who these "scientists" or sometimes "medical historians" are. I'm starting to wonder if this is one of those factoids that got made up one day and spread around and around...like "humans only use 10% of their brain" (btw, is there a name for "facts" like that?). Someguy1221 (talk) 23:59, 5 March 2009 (UTC)

Ironically, Wikipedia is blamed for propagating false information due to anonymous contributions. In fact we're all here working our hardest to do due diligence on our facts before stating them; meanwhile, out there is a sea of even more anonymous contributors to tens of millions of random websites - and they typically don't have the same good intentions, focus, and presence of mind to evaluate information and its source. Nimur (talk) 05:56, 6 March 2009 (UTC)

Viral verbal encephalitis? --Scray (talk) 00:32, 6 March 2009 (UTC)

Thanks for the laugh. ^_^ arimareiji (talk) 14:23, 6 March 2009 (UTC)

Check out Common misconceptions. Kreachure (talk) 01:44, 6 March 2009 (UTC)

Urban legends of course! SteveBaker (talk) 02:13, 6 March 2009 (UTC)

Malaria is bad, bad news, and it wasn't until the modern era that people were able to do much about it. People still die from it because they can't get the basic care to prevent or cure it. That said, half of all people who have ever lived is a rather extreme claim. To say that half of all people who have ever lived had malaria (as opposed to directly dying from it) wouldn't be quite as ridiculous, but even that is extreme. SDY (talk) 01:16, 6 March 2009 (UTC)

Sure - it's just barely possible that this might be true (although I rather doubt it) - but what is flat out utterly impossible is to KNOW that it's true. Most of the deaths would have to have been so far in the past - that there is no way we could know the cause. SteveBaker (talk) 02:13, 6 March 2009 (UTC)

We can't even "know" the number of people that currently have it, but there are reasonable ways to estimate it. We can estimate that x percent of people with no effective prevention get malaria in an area and without effective treatment y percent of them die. If we know the percent of those people that lived in areas with similar exposure to malaria, we can apply modern case and fatality rates to create a percent of possible infections. It's an estimate, but so is the number of modern deaths from malaria given that many of the places where it takes place don't have the infrastructure to keep good records. "Cannot know" does not mean "have no clue." SDY (talk) 16:28, 6 March 2009 (UTC)

Malaria is a tropical disease, so the population of temperate regions did not get it. Also, it was not present in South America or Central America, or the Pacific islands, until brought by whites. Thus quite a few humans in those areas were beyond its influence until fairly recently. Population growth in the last couple of centuries has put a great many humans in all tropical regions in danger from it, but that is balanced by population growth in temperate regions. Malaria has, of course, been present in Africa from earliest recorded history. Malaria has also been recorded in Ancient China - but that would have to be only in southern China; the more northerly parts of China would be too cool for it. Being present in southern China, it would also undoubtedly have been present in other parts of SE Asia, and perhaps India. But all-in-all, many humans have not lived in malarial zones, so the 50 percent figure does seem too large. - GlowWorm. —Preceding unsigned comment added by 98.17.34.95 (talk) 04:58, 6 March 2009 (UTC)

And of course, the native African population (where malaria was at it's worst) had evolved a gene for resistance to malaria - but because having two copies of the gene results in sickle-cell disease - it could not have been present in 100% of the population. SteveBaker (talk) 05:08, 6 March 2009 (UTC)

Malaria may be a tropical disease but at times the tropics were obviously in civilized places like Rome, too, as at least one pope died of malaria. At least until the 20th century, Sicily was malaria-infested, and it will be the first to become that again, when the climate hits us. --Ayacop (talk) 10:23, 6 March 2009 (UTC)

Humans are basically a tropical species anyway. There were a lot more people in Egypt than there were in Norway for a large percent of human history.

While we may describe malaria as a 'tropical' disease, it's historical range has extended to some very non-tropical areas. Malaria was widespread in England, possibly since Roman times, and certainly from the fifteeth century. It was "endemic along the coasts and estuaries of south-east England, the Fenlands, and estuarine and marshland coastal areas of northern England": [13]. It took a combination of quinine antimalarials, the elimination of mosquito breeding areas, and systemic insecticide use to end local transmission of malaria in England.

Similarly, oh-so-tropical Canada enjoyed its own malaria problems: [14]. Here's a study which looks at endemic malaria in Russia, Finland, and Sweden: [15]. TenOfAllTrades(talk) 16:40, 6 March 2009 (UTC)

Hypertension

What is the reason of hypertension in the patients of Diabetes? —Preceding unsigned comment added by 201.220.215.12 (talk) 23:36, 5 March 2009 (UTC)

There are a number of reasons why hypertension and diabetes are linked. Anyone suffering from either (or both) condition need to consult health professionals in order to understand and treat their own condition. The two conditions have similar risk factors (relating to age, weight, diet, exercise), but also a number of inter-related conditions. Some common causes include insulin resistance (Metabolic syndrome) in Type II diabetes, and diabetic nephropathy. Various alterations to the vascular cells caused by hyperglycaemia can also contribute. In addition, diabetic sufferers are more prone to developing cardiovascular disease. (Note that high blood pressure is a symptom of, complication of, or contributor to a number of conditions.) Gwinva (talk) 00:38, 6 March 2009 (UTC)

It is possible that the questioner is wondering why "normal" blood pressure in a non-diabetic is commonly anything less than 140/90 while "normal" blood pressure in a diabetic is anything less than 130/80. These come from many studies that were used to create the JNC7 guidelines (available here). Of note, patients with chronic kidney disease are also considered "normal" with a BP less than 130/80. Also note that I put "normal" in quotes as it isn't actually "normal". Between 120/80 and 140/90 is prehypertensive. Most people just consider anything non-hypertensive as normal and ignore the prehypertensive category. -- kainaw™ 03:57, 6 March 2009 (UTC)

I am very thankful to Gwinva and Kainaw for ur interest. I had an idea that in patients of Diabetes, normal values of preessure are high (my friend asked to me) Iam myself a medical student but I could not get the reason(answer), so I asked u. But I failed to get some conclusion here. Basically I wanted to know the mechanisms that are responsible for the Hypertension in the patients of diabetes. —Preceding unsigned comment added by 201.220.215.12 (talk) 04:31, 6 March 2009 (UTC)

As Gwinva mentioned, you want Syndrome X; most likely the underlying mechanism is insulin resistance. - Nunh-huh 04:37, 6 March 2009 (UTC)

March 6

Early Lifeforms

Would early lifeforms have used carbon in any way? Shells like those that form chalk? Part of energy source? 99.226.138.202 (talk) 00:26, 6 March 2009 (UTC)

The earliest life, like all life we know of, would have been built up from amino acids and other molecules involving carbon. Carbon is a key component of all life on Earth and always has been (as far as we're aware). --Tango (talk) 00:31, 6 March 2009 (UTC)

Following EC:Life on earth is based on organic chemistry. That is based on carbon (scroll down on the page I linked to get to the juicy parts). Even Anaerobic organisms fall into that category. So, on a very basic level lifeforms as we know them are based on carbon. 76.97.245.5 (talk) 00:34, 6 March 2009 (UTC)

Right! Sorry for my stupidity. Carbon-based life forms, of course. 99.226.138.202 (talk) 02:25, 6 March 2009 (UTC)

All lifeforms on earth are carbon based.--Apollonius 1236 (talk) 15:57, 7 March 2009 (UTC)

As mentioned above, the earliest life did not have shells - those are actually a fairly late-stage arrival after some billion or so years of proto-life and prokaryotic monerans. Nimur (talk) 06:00, 6 March 2009 (UTC)

Asking stupid questions doesn't make you stupid - quite the opposite, in fact. Had you not asked, you would have continued to be ignorant, now you know. --Tango (talk) 10:31, 6 March 2009 (UTC)

There are no stupid questions. There are questions that beg for stupid answers*, but the above was certainly not one of them. ^_^ Like Tango said... a question that results in a gain of knowledge is always for the good.

* - Example: "Please explain your opponent's ideological viewpoint in a quick sound bite." arimareiji (talk) 14:13, 6 March 2009 (UTC)

Carbon again

Can graphite go through pyrolysis to become coal? 99.226.138.202 (talk) 02:26, 6 March 2009 (UTC)

I don't think so, but it can apparently get you nanotubes and fullerenes under the right conditions. [16] Someguy1221 (talk) 02:53, 6 March 2009 (UTC)

The name would suggest you might get this Pyrolytic carbon instead. It might depend on what process you are using. Things like pressure, time, temperature etc. can determine what carbon compounds you end up with. For practical applications things like having to wait for a couple of million years or requiring solar surface temperatures might limit your answers.76.97.245.5 (talk) 04:10, 6 March 2009 (UTC)

What? Coal is graphite. --Pykk (talk) 09:24, 6 March 2009 (UTC)

More like graphite is coal (technically). See Coal. Someguy1221 (talk) 09:32, 6 March 2009 (UTC)

Or even graphite "Graphite may be considered the highest grade of coal, just above anthracite and alternatively called meta-anthracite, although it is not normally used as fuel because it is hard to ignite"

No, it's the other way round - coal can undergo pyrolsis to become graphite (or more often coke). FengRail (talk) 10:51, 6 March 2009 (UTC)

science joke

I don't get it. Can someone explain? The caption says "Science joke. You should probably just move along." Thanks, flaminglawyer 05:10, 6 March 2009 (UTC)

It is a joke based on Kepler's laws of planetary motion, specifically the second law which states "A line joining a planet and the sun sweeps out equal areas during equal intervals of time." - Eron^Talk 05:18, 6 March 2009 (UTC)

Atomic Absorption Spectroscopy

If you're trying to analyze the quantity of iron in some milk, you'd measure the 'absorbance' of the milk at different known concentrations and then plot a line graph. Why is it that milk with no iron concentration registers a small absorbance? Is it a problem with the light source (ie not pure iron), or is a tiny fraction of light not hitting the solution or not being converted? —Preceding unsigned comment added by 124.191.112.219 (talk) 11:02, 6 March 2009 (UTC)

If the atomic absorption spectroscopy shows a small amount of iron, why do you think there isn't any ? (I ask because, whatever other method you used that shows no iron, that might be the method giving the wrong answer.) StuRat (talk) 14:04, 6 March 2009 (UTC)

I don't understand what you mean. If we prepared a solution of milk and we knew for sure that there was no iron in it, and we shone a cathode light made of iron onto it and it still picked up a small absorbance, why is this? —Preceding unsigned comment added by 124.191.112.219 (talk) 09:04, 7 March 2009 (UTC)

I am questioning your assumption that "we knew for sure that there was no iron in it". Iron is very common, and I would expect some contamination (perhaps down in the parts per trillion range) in pretty much everything. A specific mechanism is blood (which contains iron in hemoglobin) in the milk. If you're talking about cow's milk bought at a grocery store, they mix the milk from thousands of cows together at the dairy. Therefore, getting one drop of cow's blood in all that seems almost inevitable. StuRat (talk) 14:21, 7 March 2009 (UTC)

Even air will "absorb" (diffract) a tiny fraction of any given wavelength, let alone milk. For more on the complications inherent in measurement, see absorption spectroscopy. Particularly, take note of how many precautions are needed to make sure that the materials used in the cuvette and/or sample preparation are transparent to light of the specific wavelength the spectrometer uses, and think about whether the proteins and lipids in the milk will be just as transparent, given that they're not transparent in the visible light spectrum. I can't really go farther than that without doing your lab report for you. ^_^ arimareiji (talk) 15:10, 7 March 2009 (UTC)

Unsure...?

Would these clouds be considered cumulus clouds? I'm not very smart when it comes to identifying clouds. I mean...they seem pretty poofy to me. ;) Papercutbiology♫ (talk) 13:43, 6 March 2009 (UTC)

Poofy...yes?

Could also be Cumulonimbus cloud it looks pretty dark underneath. I wouldn't be able to tell that from a Cumulus congestus cloud though. Do you know what weather pattern this cloud went with? Did you get a Thunderstorm or rain or was it fair weather? 76.97.245.5 (talk) 14:18, 6 March 2009 (UTC)

It was a fair day, lots of sunshine, and breezy. It didn't rain until the next day...which was pretty unfortunate after having such a pretty day. Papercutbiology♫ (talk) 15:05, 6 March 2009 (UTC)

That would point towards cumulus, then. 76.97.245.5 (talk) 16:41, 6 March 2009 (UTC)

The difference between Cumulus and Cumulonimbus clouds (AKA "Thunderheads") is usually the vertical stack and anvil head on the cumulonimbus clouds. Of course, cumulus clouds may devlop into cumulonimbus type clouds given sufficient lift, and there are likely transitional forms between the two. I am sure there is room for interpretation between the two, but generally I think of Cumulonimbus clouds as more vertical, and cumulus clouds as more horizontal or poofy-rounded. Also, as cumulus clouds tend to be fair weather clouds, it is often clear beneath them. With cumulonimbus clouds, there is often visible virga below them (i.e. streaks of rain) which can be observed from a distance. --Jayron32.talk.contribs 19:23, 6 March 2009 (UTC)

Yeah - it's not a Cu.Nim - those have a classic "Anvil" shape - kinda like a mushroom cloud after a big explosion! The big rounded cloud in the photo is a cumulus. There are higher altitude, whispy clouds there that are cirrus or maybe cirrostratus (depending on altitude). Pf course these kinds of descriptions are not hard-and-fast - there are all sorts of in-between possibilities. SteveBaker (talk) 20:47, 6 March 2009 (UTC)

These clouds are far too flat to be cumulonimbus. I think cumulus clouds are present near the centre of the image. On Wikipedia Commons, where I have previously categorised many cloud pictures, I would put that image under the categories Cumulus clouds and Stratocumulus clouds (the flatness of the clouds, fractus-like in some areas, and forming a layer-like structure in the distance hint at this). ~AH1^(TCU) 00:36, 8 March 2009 (UTC)

Writing on batteries

Because I use my digital camera frequently (see Commons:Category:Files by User:Nyttend), I have four pairs of Energizer AA rechargeable batteries: one for the camera, one as spares to carry in the camera bag, and two more to replace those when I'm charging pairs 1 and 2. I'm considering writing numbers on the sides of the batteries, so that I don't put used batteries in the camera and recharge the fully-charged ones by accident just before I go somewhere. Would this be safe? I plan to use a rollerball pen, although since I've not tried writing on them, I don't know if the ink will hold. Nyttend (talk) 16:01, 6 March 2009 (UTC)

I don't think a rollerball pen will get the job done; I would think magic marker is more what you need - the permanent kind, not the water soluble. Neither would be dangerous. - Nunh-huh 16:14, 6 March 2009 (UTC)

I suspect that the ink will hold poorly, but your mileage will vary. (Depending on what else you carry in your camera bag, you may also risk transferring pigment to something valuable.) Whether the ink adheres well or not, the batteries won't be harmed. Per Nunh-huh, a felt-tip permanent marker (Sharpie brand, perhaps) might work better, though even that stuff wears off smooth surfaces if abused.

You might consider the use of a little bit of colored nail polish to identify each battery. (Use different colors or different numbers of dots; I wouldn't try to write out the numerals themselves.) Sally Hansen Hard As Nails polish is reliably durable. (I don't wear it, but I use it in the lab.) TenOfAllTrades(talk) 16:23, 6 March 2009 (UTC)

I'm picturing a dozen rats with exquisite pedicures.... - Nunh-huh 16:26, 6 March 2009 (UTC)

Ha! Sadly, my purpose is much more prosaic. Usually it's to secure and seal glass coverslips on microscope slides. It makes a reasonably hard, waterproof seal. I've always bought the clear stuff though I've considered acquiring different colors to make slides easy to distinguish under conditions of low light and barely-legible handwriting. (Experimental samples will be tagged in Seductive Scarlet, while controls can use Sultry Shamrock.) TenOfAllTrades(talk) 17:21, 6 March 2009 (UTC)

(off topic) As an example of US laboratory health and safety guidelines running amok, when I was in lab they used to make us put "not for human use" on the nail polish we used for sealing slides. I think at one point they even wanted us to get a material safety data sheet for it! --- Medical geneticist (talk) 23:42, 6 March 2009 (UTC)

EC: A Paint marker would work best. In the US they most commonly come in metallic gold. In car part or art supply stores you might find other colors. Also see what you local office supply box has to offer. Shake well before use and make sure to let the paint dry before you use/touch the batteries. 76.97.245.5 (talk) 16:29, 6 March 2009 (UTC)

A Sharpie (marker) should get the job done. They have a fairly fine point, and are permanent, and write on most surfaces. Edison (talk) 18:43, 6 March 2009 (UTC)

I wrap mine with a strip of electrical tape. SteveBaker (talk) 20:16, 6 March 2009 (UTC)

Of all the good suggestions above, I think the nail polish would be best. I'd also be careful to apply it to a surface where it would not be scraped during battery insertion and removal. For rectangular batteries, the side that faces out. For cylindrical batteries, the area surrounding the positive knob. Any debris that flakes or scrapes off and gets inside the camera could ruin it if it works its way into the optics. -- Tcncv (talk) 01:01, 7 March 2009 (UTC)

All these battery marking schemes are not that helpful because you still have to remember which batteries are charged and which are discharged. I use battery cases with 4 little slots that hold the cells (you can get them from places like thomas-distributing dot com). I put charged cells into the cases with the positive end facing upwards, and discharged cells with the positive end facing downward. By the way, that brand of rechargeable cells that you mentioned is terrible. They often crap out after just a few charges. You are better off getting pre-charged cells (available in various brands). Their main feature is near-elimination of self-discharge (that's how they are able to hold a charge while sitting on a store shelf). They sacrifice some capacity to gain that, but it makes them much more reliable. 207.241.239.70 (talk) 06:06, 7 March 2009 (UTC)

How does VIH resist reverse transcriptase inhibitors?

I've read in the VIH article that this this virus is treated with reverse transcriptase inhibitors. But the article does not explain how the virus can continue to reproduce (and therefore, why isn't AIDS treatable). Can someone help? Thanks. —Preceding unsigned comment added by 88.1.136.110 (talk) 16:54, 6 March 2009 (UTC)

Do you mean the HIV article? On English Wikipedia, VIH redirects to an airport. Nimur (talk) 17:43, 6 March 2009 (UTC)

(ec) HIV/AIDS is quite treatable; treatment of HIV is highly effective - for example, there are no special limits on the lifespan of people who have access to care and have not developed resistance to antiretroviral drugs. Resistance is just one of the limitations of antiretroviral therapy. The articles I've linked can answer many questions. If you don't find what you need, please be more specific. --Scray (talk) 17:47, 6 March 2009 (UTC)

Reverse transcriptase is blocked by either competitive or non-competitive inhibitors (see reverse transcriptase inhibitors). It's kind of trivial that a structural alteration could make an RT resistant to the non-competitive inhibitor, but not so much how a mutation could make it resistant to the "primer blocking" effects of the competitive inhibitors (many of which, as the article describes, act like ddNTPs). "K65R: a multi-nucleoside resistance mutation of low but increasing frequency" Antiviral Therapy (2003) is supposed to describe how this works, but either the publisher's webiste (or my library's) is having some funkiness right now and I can't actually access it. Someguy1221 (talk) 23:47, 6 March 2009 (UTC)

"Reverse transcriptase is blocked by either competitive or non-competitive inhibitors."

— Someguy1221

That's not correct. The terms "competitive" and "non-competitive" apply to inhibitors of receptors (i.e. receptor antagonists), not enzyme inhibitors. Axl ¤ [Talk] 08:50, 9 March 2009 (UTC)

If you're right, then you might want to tell the editors of Antiviral Research,[17] The Biochemical Journal,[18],[19] and the Biological & Pharmaceutical Bulletin.[20]. Those are just some of the many I found in a quick look for non-competitive HIV RT inhibitors. Is it possible the usage is a little broader? --Scray (talk) 09:43, 9 March 2009 (UTC)

Thanks for pointing that out. You're quite right, Scray. Axl ¤ [Talk] 12:08, 9 March 2009 (UTC)

Clean coal...for real?

I was reading our coal article - in the vain hope of being able to contribute to our earlier question about the stuff...or at least to learn something for the next time a coal question comes up.

What I read in the article is that the principle ingredients of coal are carbon (well, duh) - and hydrogen. We know that burning the carbon is pretty disasterous for global warming - and even the 'carbon sequestration' tricks the 'clean coal' advocates propose don't look particularly promising. But I wonder if there is any possibility that a true "clean coal" technology could be devised that would extract the hydrogen out of the coal without burning it and making all that nasty CO2 - leaving a pile of purer carbon behind and then using the resulting hydrogen (for example) to power our cars? Obviously the energy you'd get out would be less than if you burned the coal - but it would be a very clean technology - and there is an AWFUL lot of coal down there. I wonder if it would still be economic? I also wondering whether there might be a possible means to extract the hydrogen from a coal seam without digging the stuff up? (Maybe pump something heavier like CO2 down there under pressure?)

Does anyone understand how the hydrogen is bound up in the coal well enough to explain this? (I'm not a chemist - so I need baby-talk for that bit!)

SteveBaker (talk) 22:47, 6 March 2009 (UTC)

The United States Department of Energy has spent millions of dollars on this specific project. See an itemization of over $7million handed out in 2006 here. There are two main issues. First, the hydrogen must be separated. It becomes crude hydrogen because it is mixed with a lot of garbage. Then, it must be refined into quality hydrogen. If you look at the projects involved in the 2006 grants, you will see the same thing over and over - research into refining or purifying crude hydrogen. That appears, from what I see, to be the problem. If you burn crude hydrogen, you will be sending all the pollutants in the crude hydrogen into the atmosphere just like burning coal. -- kainaw™ 22:58, 6 March 2009 (UTC)

Well, that led to this that explains exactly how it is done. -- kainaw™ 23:00, 6 March 2009 (UTC)

No - that's the pathway that Arimareiji discusses below - it's still reacting the carbon (in this case with water) and producing CO2 along with hydrogen from the water. I'm asking about whether the hydrogen that's already in the coal can be extracted LEAVING THE CARBON BEHIND. SteveBaker (talk) 02:34, 7 March 2009 (UTC)

Coal, to my knowledge, is more-or-less pure carbon. No appreciable hydrogen in it. Burning it directly gives carbon dioxide, CO2. Hydrogen can be generated if you react that carbon with steam to form synthesis gas (C + H2O -> CO + H2) to serve as fuel. You can further react the CO (carbon monoxide) to get more hydrogen, producing CO2. (CO + H2O -> CO2 + H2) You could see this as analogous to charging a battery - instead of high-energy coal, you now have high-energy hydrogen.

But there's no free lunch. To put it in overly simplistic terms, carbon is high-energy and carbon dioxide is low-energy. You only get the energy difference out of carbon if you turn it to carbon dioxide, regardless of whether you burn it directly or react it to form hydrogen. arimareiji (talk) 23:56, 6 March 2009 (UTC)

@Arimareiji : Yeah - I thought that too - but just go and read our article: coal - there is in fact quite a bit of hydrogen locked up in coal. Hence the question! SteveBaker (talk) 00:55, 7 March 2009 (UTC)

Being 7 months behind in my reading may have paid off, I just read something about this in Nature. Coal can be gasified underground by drilling a well; setting it on fire and adding oxygen; then removing the resulting gas from an adjacent well. The product is synthesis gas (H₂+CO) and CO₂ which can be used to make all the things syngas is already used for in refineries (diesel oil in this case). This is essentially the same thing as coking, which drives almost everything but the carbon out of coal for use in iron smelting - but in reverse, it leaves much of the carbon in the ground. However, if the output carbon is not sequestered, the process produces twice the amount of greenhouse gas as the straight-out petroleum product. That seems to be the best available technology. Steve, I'll mail you the article and anyone else who wants a copy, drop me a line. Franamax (talk) 02:41, 7 March 2009 (UTC)

Someone could actually get a grant for this now? DMacks (talk) 03:44, 7 March 2009 (UTC)

Again, this is a lot messier than what I was hoping to hear. The hope would be to NOT generate any CO2 and just get at the hydrogen...but it's certainly beginning to sound like it's not possible. Oh well - it was worth a try! SteveBaker (talk) 03:43, 7 March 2009 (UTC)

SteveBaker - from [21], "Carbon, by far the major component of coal, is the principal source of heat, generating about 14,500 British thermal units (Btu) per pound. The typical carbon content for coal (dry basis) ranges from more than 60 percent for lignite to more than 80 percent for anthracite. Although hydrogen generates about 62,000 Btu per pound, it accounts for only 5 percent or less of coal and not all of this is available for heat because part of the hydrogen combines with oxygen to form water vapor."

Franamax - setting coal on fire underground is a very very bad idea; look up the fate of Centralia, PA. Gasification is a sharply different process. arimareiji (talk) 03:51, 7 March 2009 (UTC)

March 7

My penis is multicoloured (this is not a joke or vandalism)

Seriously. My penis is a mixture of Olive skin and my regular skin colour, which fits between type II and type III in this because I have dark brown hair and dark blue eyes. Seriously, my penis is multicoloured in random patches. This is not a joke. Is this normal? Not that any girls have ever complained about it, but I have some cousins on my father's side whom I've noticed actually have more olive coloured skin than myself. Weird that.--Get 'Em Out By Friday (talk) 00:08, 7 March 2009 (UTC)

Could it be the result of circumcision, which can leave darker skin closer to the base? arimareiji (talk) 00:14, 7 March 2009 (UTC)

Not circumcised.--Get 'Em Out By Friday (talk) 00:31, 7 March 2009 (UTC)

If you feel you have some medical condition that needs attention, see a doctor. It you simply want to know if anyone else has a penis that has more than one skin tone - yes. It occurs in other men. -- kainaw™ 01:17, 7 March 2009 (UTC)

From my corrupt youth, I remember that the character nicknamed "Pinto" in the movie Animal House got his nickname from having the same condition. 207.241.239.70 (talk) 06:08, 7 March 2009 (UTC)

However, in the original National Lampoon story, Pinto got the discoloration on his penis because he'd gotten tar on it, possibly while masturbating. --LarryMac | Talk 13:49, 9 March 2009 (UTC)

Is the Yangtze River drying up?

In the Ganges River Article, it states that the Ganges River may dry up in 2030 because of receding Himalayas glaciers. Is the Yangtze River in China going to dry up too? When will the Yangtze River completely dry up? Sonic99 (talk) 04:53, 7 March 2009 (UTC)

A government official claims in China Daily the recent drying is due ot lack of rainfall and climate change is blamed. Elsewhere, human activity such as damming are blamed for the Yangtze's tributaries running dry. Glacier melting has been suggested as future problem for the Yangtze but it is not actually happening yet and it is expected that melting glaciers will first cause flooding before causing drying as they run out of material to melt. SpinningSpark 11:54, 7 March 2009 (UTC)

No, the last part is wrong. Glaciers primarily melt in high summer, when water levels are naturally low. Floods typically occur in spring, when seasonal snow melt occurs. So melting glaciers will increase average flow level (all other things being equal), but not usually cause floods. --Stephan Schulz (talk) 12:11, 7 March 2009 (UTC)

That's not what the source says, to quote;

"The rapid melting of Himalayan glaciers will first increase the volume of water in rivers causing widespread flooding," said Jennifer Morgan, director of the WWF's Global Climate Change Programme. "But in a few decades this situation will change and the water level in rivers will decline, meaning massive economic and environmental problems for people in western China, Nepal and northern India."

You are confusing the normal annual cycle of melting and the permanent destruction of glaciers due to global warning. The first is in equilibrium, the second is not. SpinningSpark 12:17, 7 March 2009 (UTC)

No. The long-term reduction of glaciers is overlaid by the seasonal cycle. Even now, most glaciers gain mass in winter. It's just that they lose more of it in summer. If you look at your source (the WWF report here), you will notice that they talk about all areas that are affected by Himalaya glacial run-off, and that that particular piece (increased flooding) applies to the Indian side. There, floods are not primarily resulting from snow melt, but rather are triggered in high summer, when the Monsoon brings massive amounts of precipitation. In that case, seasonal rains and maximum glacier melting coincides. But that does not apply to the Chinese river systems. --Stephan Schulz (talk) 17:24, 7 March 2009 (UTC)

I'm not sure about the Yangtze, but the Huang River is increasingly experiencing more days without water flow each year, due in part to the desertification around the Gobi Desert and receding Himalaya glaciers, both affected by climate change. The Three Gorges Dam on the Yangtze (Chang Jiang) may be able to control water flow for a period of time, however. I've read that the melting of the Himalayan glaciers will affect the main source of water for over 500 million people. ~AH1^(TCU) 00:24, 8 March 2009 (UTC)

The WWF report doesn't say when the glaciers and river water will completely disappear in China. It discusses about the glaciers on the Indian side will vanish within 40 years and that isn't a long time from now. The Indian government better do something quick like reducing their population or else they'll be in very deep trouble. Sonic99 (talk) 00:42, 8 March 2009 (UTC)

perpetual motion machine

without thermal energy utilisation is it possible to make PMM? —Preceding unsigned comment added by Gbhavsar (talk • contribs) 08:03, 7 March 2009 (UTC)

It is not possible to make a perpetual motion machine. Dragons flight (talk) 11:13, 7 March 2009 (UTC)

I think that the questioner may be asking if a perpetual motion machine would be possible if thermal losses could be completely eliminated. It is not possible to eliminate losses entirely due to the second law of thermodynamics. Speculating on whether perpetual motion machines could exist if the second law did not exist is meaningless and unanswerable. If the impossible were possible it might be possible, but as its impossible, it ain't. SpinningSpark 11:27, 7 March 2009 (UTC)

A perpetual motion machine isn't just something in perpetual motion (a pendulum on the moon would satisfy that, to within a negligible margin of error), it has to actually do something. That means there aren't just accidental losses, there is intentional extraction of energy. That energy has to come from somewhere. --Tango (talk) 13:48, 7 March 2009 (UTC)

I'd say a device that does nothing more than stay in motion forever is also a PPM. The pendulum example would eventually slow and stop (although it might take longer than the life of the universe). Even the orbits of the Moon. Earth, and stars would decay eventually. StuRat (talk) 14:02, 7 March 2009 (UTC)

Our article disagrees with you. --Tango (talk) 14:05, 7 March 2009 (UTC)

Well, it's just a matter of words - linguistics, not science. When the free energy nuts talk about 'perpetual motion machines' - they are referring to the 'over unity' variety - from which energy could hypothetically be extracted. This 'first' kind of device is definitely - without any doubt whatever - quite utterly impossible. The 'second' kind is the idealised machine which has no friction, no air resistance, and never physically changes (eg it doesn't wear out or anything) - this enables it to be in motion perpetually. The spinning of the earth - the orbiting of the moon - these are all oft-cited examples. Sadly, none of them are that because there are other bodies in the universe causing tidal effects and other gravitational effects, there are tiny TINY amounts of gas and dust in even the hardest inter-galactic vacuum that will eventually cause drag and so forth. So machines of this second kind are acceptable to science as purely theoretical possibilities - although they may not be possible in practice. However, we must be ETERNALLY vigilant. The nut-jobs simply LOVE to cite the existance of "perpetual motion" of the second kind as "proof" that perpetual motion is indeed possible - and therefore they claim to be able to design whack-job "perpetual motion machines" OF THE FIRST KIND to make 'free energy'.

So there are two problems:

• People confuse machines of the first and second kinds because (stupidly) we use the same words for each.
• People ignore the PRACTICAL problems with the second kind of machine which mean that they do not in fact work PERPETUALLY anyway.

SteveBaker (talk) 15:26, 7 March 2009 (UTC)

I'm pretty sure the second kind is theoretically impossible too. If nothing else, anything with any moving parts whatsoever (technically, anything with jerking parts) will emit gravitational radiation and slowly lose energy. — DanielLC 17:08, 7 March 2009 (UTC)

Does electric current count as "motion?" A superconducting magnetic energy storage unit is said to have no decrease in current over time, as long as you keep it chilled and do not intentionally remove energy. Edison (talk) 20:50, 7 March 2009 (UTC)

Again with the linguistics! Whether we call electric current "motion" or not is irrelevant - what really matters is whether it can indeed go round and round in a superconductor forever without additional energy input. Again, I suspect that in theory it does - and in practice it won't...exactly why it won't in practice, I'm not sure...but I'd bet actual money! SteveBaker (talk) 01:21, 8 March 2009 (UTC)

you may have to wait a long time to collect though SpinningSpark 03:50, 8 March 2009 (UTC)

I'm fairly certain it will still generate cyclotron radiation. — DanielLC 05:11, 8 March 2009 (UTC)

Yes - and since electrons have mass (albeit exceedingly tiny), they must generate their own teeny-tiny gravitational waves...hence, per DanielLC's previous post, they ought to be (s-l-o-w-l-y) losing energy that way too. SteveBaker (talk) 07:55, 8 March 2009 (UTC)

why is there no article about biological (genetic) basis of breeding?

The breeding article is suspiciously silent on the topic. Since Darwin used breeding as an easy to understand example for evolution, this important topic should be covered in wikipedia Northfox (talk) 10:14, 7 March 2009 (UTC)

Please, be bold and write this article! Lova Falk (talk) 10:24, 7 March 2009 (UTC)

The breeding article is merely a disambiguation page, that is, an index to other pages. You might want to look at breed and selective breeding (which specifically refers to Darwin) and several other of the linked articles. SpinningSpark 11:19, 7 March 2009 (UTC)

thanks for the articles, SpinningSpark. But I find that they are somewhat contradictory.

Selective breeding says:

Charles Darwin discussed how selective breeding had been successful in producing change over time in his book, Origin of Species. The first chapter of the book discusses selective breeding and domestication of such animals as pigeons, dogs and cattle. Selective breeding was used by Darwin as a springboard to introduce the theory of natural selection, and to support it.

breed says:

Thus, all specimens of the same breed carry several genetic characteristics of the original foundation animal(s).

The first is often used as evidence for evolution (the breeder just 'speeds up' nature, eventually leading to new species), while the second one states that the bred animal contains just a subgroup of the wild gene pool. This is just my little WP:OR, so I thought that there would me a more fundamental, well referenced article. Well writing it myself is easier said than done. There are some editors that allow no tainting of their beloved theory and its icons. Been there, done that. Northfox (talk) 12:45, 7 March 2009 (UTC)

That's not contradictory. There are two stages in selective breeding, first you breed for the characteristics you want and then you breed to keep those characteristics. The first stage is, essentially, accelerated evolution, the second stage is more of an attempt to prevent evolution. --Tango (talk) 13:51, 7 March 2009 (UTC)

While artificial selection (which, when done intentionally, is called "breeding") is a good analogy to natural selection, it doesn't do anything to "speed up" mutations, which are another important element in evolution. Thus, you can't rapidly create a new species by breeding alone, since you still would need to wait thousands or millions of years for the mutations to occur which you could then select to breed a new species. I suppose you could speed this up by exposing the organisms to mutagens, but that would also make a large portion of them get sick and die. Genetic engineering offers a more practical way to introduce selected "mutations". StuRat (talk) 13:50, 7 March 2009 (UTC)

Your timescale is way off, StuRat. There are plenty of mutations that occur with every single generation. You certainly wouldn't have to wait thousands or millions of years to get enough of them for speciation if you have the right selection criteria. In the lab, artificial species have been derived with selective pressure across as few as 8 to 40 generations from a last common ancestor. In flies, that is around 3 months to a year. Rockpocket 22:20, 7 March 2009 (UTC)

There is an argument that over time, selective breeding is just a variation on natural selection. Animals and plants are effectively evolving to exploit a niche where they are symbiotic with humans. In primitive societies, dogs which are good with children are more likely to be looked after, fed, exercised and ultimately to have puppies. There is an evolutionary pressure to be good with children. SteveBaker (talk) 15:04, 7 March 2009 (UTC)

Alternately, look at human preferences in breeding amongst themselves to see the same pattern. That which we consider "attractive" (symmetric face, symmetric body, good stature, and wide hips among other factors) tends to coincide with having "good genes" for breeding and/or reproduction. Quick thought experiment: Imagine breeding with one of the people pictured here. Now imagine breeding with someone with obvious deformities, or signs of Down syndrome, by comparison. Whether or not this is fair, it's how we're programmed. arimareiji (talk) 15:33, 7 March 2009 (UTC)

(**Removed links and ambiguous commentary with respect to photographs of real people.) If you wish to illustrate "breeding" examples with real people, you should have their permission for the use in this context. And you should make your point clearly and unamibigously. // BL \\ (talk) 16:17, 7 March 2009 (UTC)) Comment now makes no sense as text and links I removed have been reinserted. See the discussion at Ref desk on my talk page. // BL \\ (talk) 17:25, 7 March 2009 (UTC

One thing has always puzzled me. Why is it that pure-bred animals do not breed entirely true unless the parent animals are specially selected as best-of-the-breed? If two average pure-bred animals reproduce, the offspring have worse breed characteristics than the parents. After two or three generations of this, the offspring become quite nondescript. I think the same is true of genetically-engineered plants. How does this relate to evolution? – GlowWorm.

Our article Purebred says: A puppy from two purebred dogs of the same breed, for example, will exhibit the traits of its parents, and not the traits of all breeds in the subject breed's ancestry. That would seem to contradict your statements that purebreds don't "breed true". // BL \\ (talk) 19:18, 7 March 2009 (UTC)

Purebreds are usually so inbred that I would expect they are homozygous for pretty much all genes relevant to the definition of the breed, so offspring would have those same characteristics. It is, however, possible to have an animal that has all those same characteristics, but is heterozygous in those genes that are relevant and where the desired characteristic is dominant (you have to fudge it slightly for those characteristics not determined by a single gene, which is probably most of them!). If two such animals bred then, assuming (completely unrealistically, for the sake of easy calculations) the breed is defined by a single gene, they would have 75% offspring of the same breed and 25% not (for genuine breeds, it will be far more complicated, but the general idea is the same). --Tango (talk) 19:28, 7 March 2009 (UTC)

Yes that's basically it as I understand it. In certain types of breeding, like chickens for food, the grandparents are actually more valuable than the parents: you set it up so that a grandparent breeds a parent who can breed chickens to be eaten of a consistent type. The chickens to be eaten do not breed true and thus can't be parents themselves. Thus the breeder maintains the intellectual property by keeping the grandparent types under lock and key, selling off parents who can create the chickens that are actually eaten. So the business model works—breeders sell producers to chicken farmers, who take the produced chickens and sell them as food. After awhile, they need new producers, and are forced, by the genetics of it, to get them from the breeder again, as they cannot create producers with the genetic stock on hand. (What blows my mind is that they were able to work this out with just a little knowledge of Mendelian ratios in the 1920s and 1930s and a lot of trial and error.) --98.217.14.211 (talk) 20:46, 7 March 2009 (UTC)

"True breeding" is an entirely artificial, subjective concept. If two stud animals were entirely homozygous for the same alleles at every locus, their offspring will (the vast majority of the time) be exactly the same as them, phenotypically speaking. If you define these two animals as "best of the breed" then most of the offspring would also be also be "best of the breed". In reality, the stud animals will not be homozygous at every locus, and so only a proportion of the "best" alleles will be passed on, and offspring will be genetically "inferior" to the artificial standard. However, its also possible that the offspring could have a "better" assortment, in that it got the "best" alleles from both parents and none of the inferior ones. This explains why (in any species that is artificially bred) the cost of the offspring from two best in breeds are so high. It increases you chances of getting an even better specimen, but more often that not all you do is dilute out the genetic combination that makes the two parents so special and you get a good, but not as good, assortment. Rockpocket 21:53, 7 March 2009 (UTC)

In evolution, perhaps the maintenance of a "good bloodline" works like this. If there is an environmental change, the particular members of a species that, by chance variation, are best suited to survive, will live longer and produce more offspring than those members not as well suited to the change. Assuming the environment then ceases its alteration (for simplicity), in each generation of the species there will be an automatic selection of the best-of-the-breed. Those best able to survive will gradually prevail until all members of the species are "best-of-the-breed" in the characteristic(s) suited to the changed environment.

The environmental change could be a climate change, the entry of a new predator, parasite, or disease, or some other adverse change. Or an indigenous predator, parasite, or disease may adapt to a new prey - the subject species. If the environment changes more rapidly than any members of the species can adapt, the species will become extinct.

In human-produced pedigree animals or plants, the "best-of-the-breed" must be re-selected by humans each generation. There is no automatic selection by the environment.

In natural selection, those members of a species best suited to survive might have only a slightly better longevity, and consequential generational relative increase in numbers, over other members of their species. But in the course of thousands of generations, those best suited will eventually be the only ones in existence. I once saw some figures on that. It was assumed that those best suited to survive had only a very slight advantage, say a 0.1% increase in numbers over the others, in each generation. Over a sufficient number of generations, the ones best suited would be the only ones to finally survive. The rest would die out, getting down to the last one to die. But a thousand generations is not long in evolution - in humans it is only about 25,000 years. So some of the tiny minor variations between members of a species can be extremely important in time.

Of course, many things in the environment are changing all the time, Some members of a species may be better suited to one change, and other members of the same species may be better suited to another change. That greatly complicates the matter. But I think the basic principle, and the difference between human selection and natural selection, is as described above. Human selection will produce permanent change only if it is continued for a great many generations, using selected "best-of-the-breed" specimens to produce each new generation.

I don't know where genetic engineering would fit in this. Perhaps the genetically engineered species should just be considered a separate species. – GlowWorm.

One thing I would add to the above. A slight variation that increases survivability would have to be inheritable. It was not inherited to begin with, so, like the rest of this hypothesis, further thought and practical investigation is needed. – GlowWorm.

Ah - the inevitable post from our closet creationist! Indeed, for the beneficial variation to be passed on, it has to be genetically based and therefore inheritable. But then you make the dangerous leap of saying "If was not inherited to begin with..." - but why would you think that is not the case? Well, there are two possibilities here: Firstly that it IS inherited - but that it requires a combination of genes from mother and father that have simply not come together before. Secondly, the variation might indeed not have been inherited in the sense of coming directly from the genes that made mother and father what they were - but instead be a random mutation caused by a copying error in the DNA replication that made sperm or egg - or a mutation caused by some kind of mutagen such as environmental chemicals, radiation, etc - or perhaps as a result of viral DNA segments being inserted into the DNA just prior to copying. So your last sentence doesn't really hang together. We know the reasons why there is variation over time and how those changes get preserved over the generations. We're not discussing the source of the variation - but rather the reasons for those particular variations to be selected (ie either artificially or naturally or some odd hybrid of the two). SteveBaker (talk) 07:51, 8 March 2009 (UTC)

Assuming a wife is faithful to her husband, and excluding identical twins,why are siblings not exactly alike except for differences due to age and gender? I am sure science has provided no proven reason for this. I don't like to see a dogmatic stand taken on an unproven hypothesis. But regardless of the reason for the variation, some of the differences will have an affect on survivability, however slight. – GlowWorm.

I am sure science has provided no proven reason for this. I am astonished that you could be so ignorant of the work of Watson and Crick, Gregor Mendel and many others. The reason for the differences in siblings has been well established by science to be due to them not having the same DNA. The process of DNA combination between parents is well understood and has been investigated by many working in genetics. It is certainly not an unproven hypothesis. SpinningSpark 10:44, 8 March 2009 (UTC)

If my senses didn't tell me better, GlowWorm was being sarcastic, or just a wind-up merchant. The concepts of chromosomal crossover and independent assortment are widely taught to 14-16 year olds in school (in the UK at least). Here are a couple of nice simple animations that would be typically shown: [22] [23] --Mark PEA (talk) 11:45, 8 March 2009 (UTC)

My education in science ended at age 13, except for some later training in electronics in the Air Force. I may not be up on book larnin', but I can take an outsider's view of science. As an earlier poster remarked, education tends to a give tunnel view of the subject learned. Also, well educated persons often take an arrogant attitude about their knowledge of other men's ideas, but they have no original thoughts of their own, not even farther down the tunnel. They are not creative; they are mere memorizers. In a few minutes, I will post on this thread some original ideas of my own about evolution. – GlowWorm.

13? How come? --Tango (talk) 22:19, 8 March 2009 (UTC)

I often feel the same way about professional athletes. All the training makes them so arrogant about their own abilities that it makes it obvious they don't really have those abilities. What good is training, anyway? arimareiji (talk) 22:28, 8 March 2009 (UTC)

(Experts should look away because I'm about to horribly simplify this for the purposes of explanation)

So let's explain to GlowWorm how come two (non-identical) brothers or sisters end up being different. The DNA in our cells is wound up into 23 separate paired 'chromosomes' comprising tens or even hundreds of thousands of 'genes' - and it's 'genes' that pretty much determine how we're going to turn out. When a cell divides, the DNA is duplicated and hence each cell has an identical copy of all of that stuff. When a mommy and a daddy who love each other very much make a baby - the baby gets 23 chromosome pairs - and a complete set of genes but it's random whether a particular set of genes on those chromosomes comes from the mother or the father.

So if (say) there is gene for eye color and a gene for hair color is on (I have no idea whether that's true or not...but it'll be something like that) - and if mommy is a blue-eyed blond and daddy is a green-eyed redhead - then in a large family, on average, roughly half of the kids will get that hair color gene from their mother and half will get it from their father...so half of them will have blue eyes, the other half will have green eyes - half will have blond hair and half will have red hair. But that means that there are 4 possible types of kid - blue/blond, green/redhead, blue/redhead and green/blond. (In practice, it's nowhere NEAR as simple as that...but this is the basic mechanism). Now, if there is a third characteristic...sex, for example - then because that too can come from either mommy or daddy - you'll have eight possibilities for the kids: blue/blond/boy, green/red/boy, blue/red/boy, green/blond/boy, blue/blond/girl, green/red/girl, blue/red/girl and green/blond/girl (phew!). Add in the gene for colorblindness - now you have 16 possible children, add in the gene for hating the taste of broccoli and you have 32...you double the number of possibilities for each additional gene you consider. Each characteristic from a separate gene doubles the number of 'types' of kid. So the total number of different children that a pair of unrelated parents might have is 2x2x2x2x2x2x2x2x2x2x2x2x....2x2x2x2x2x2x2x2x2x2x2x2...the number of 2's in that huge number is something like the number of genes. There are 10's of thousands of genes...so two people could have more 'kinds' of child than there are grains of sand on all the beaches of all of the oceans of all of the planets of the galaxy. So it's no surprise that our children turn out differently...unless they are 'identical' because they came from the same fertilised egg and therefore have the same mix of mommy-genes and daddy-genes.

In truth, that's a horrible over-simplification because (for example) some genes control the 'expression' of others so you might inherit the gene for blue eyes - but the gene for red hair might turn it off and you might get something totally different like brown eyes as a result...and genes are typically inherited in groups - but that's the simple view of why all of the kids of a particular pair of parents come out slightly different...yet all of the kids look like their parents (somewhat) because they picked up all of their genes from one or them.

I hope this helps. (And now I'm going to get my response shot to hell by the experts!)

SteveBaker (talk) 02:05, 9 March 2009 (UTC)

Prevailing winds in Israel?

Excuse me - does anyone know anything about the prevailing winds in Israel - in other words, what direction that weather fronts tend to move in there? I've been looking around online, and the best source I could find was this map. It looks like Israel should be just on the edge between the trade winds and the westerlies, but I'm unable to figure out which the region tends to belong to. Can anyone help me out with this? Thanks. --Brasswatchman (talk) 19:21, 7 March 2009 (UTC)

Given that Israel is on the Mediterranean, and smack in the middle between major continental land masses, I doubt that the idealized global wind map has any value. Winds will be very much dominated by local effects. --Stephan Schulz (talk) 22:41, 7 March 2009 (UTC)

According to the seasonal weather search for various locations in Israel on Ask.com, average wind direction varies throught the year and for different locations, from west to northwest to east. ~AH1^(TCU) 00:17, 8 March 2009 (UTC)

So I guess there's no real telling, then. Okay. Thank you both very much. --Brasswatchman (talk) 00:53, 8 March 2009 (UTC)

Work done by magnetic fields

It's true that work can never be done on a charged particle that is moving through a magnetic field correct? But a magnetic field can do work on a conductive piece of matter right? ScienceApe (talk) 22:33, 7 March 2009 (UTC)

I don't know what makes you think that no work is being done on a charged particle moving through a magnetic field. There is a force acting on the charge given by;

$F=q\mathbf {v} \times \mathbf {B}$

where,

q is the charge

v x B is the vector cross product of the charge velocity and the magnetic field flux density

so clearly work is being done unless the charge is stationary or moving in the same direction as the field. Similarly work is done by a magnetic field on a conductor only if there is current flowing in it and the conductor "cuts" through the magnetic field, that is, moves in a direction not aligned with the field. In this case the force is given by,

$F=B_{\perp }Il$

where $B_{\perp }$ is the component of field perpendicular to the current.

SpinningSpark 03:44, 8 March 2009 (UTC)

Work is force acting through a distance. As your formula shows above, the force is always perpendicular to the particle's velocity. No work is done on the particle by the magnetic field.—eric 03:56, 8 March 2009 (UTC)

SienceApe, Yes, that's correct (if there is an electry current flowing through the wire), but with a caveat: The work is actually done by the electric field necessary to keep the current flowing. Dauto (talk) 04:11, 8 March 2009 (UTC)

Apart from the work which could be done on a charged particle by a magnetic field, work could be done on the same charged particle by an electric field. Edison (talk) 05:01, 8 March 2009 (UTC)

Species commonly known by binomial name?

File:Aloe vera yoghurt.jpg

Proof!

I noticed in the article for Boa constrictor it notes that the species' common name is the same as its binomial name, which is unusual. Are there any other species for which this is true? (Other than bacteria, of course.) I'd like to see those for which the common name is the full binomial name, not just the specific name, since the latter is far more common. 99.245.92.47 (talk) 23:16, 7 March 2009 (UTC)

This is true of Homo habilis and Homo erectus in my experience. Algebraist 23:19, 7 March 2009 (UTC)

Lots of bacteria are, or at least by abbreviations of the binomial name. E. coli for example, short for Escherichia coli. Lots of species that simply don't have a common name due to not being very common - extinct species, like the ones Algebraist mentions, as a good example of that. --Tango (talk) 23:26, 7 March 2009 (UTC)

Tyrannosaurus rex, orca (although some call it Killer Whale, orca is becoming more popular). ScienceApe (talk) 00:31, 8 March 2009 (UTC)

Have you really seen 'Orcinus orca' used as a common name? Algebraist 00:35, 8 March 2009 (UTC)

I recall seeing the name as Orca orca a long time ago. ScienceApe (talk) 01:57, 8 March 2009 (UTC)

This is a great question, apart from Boa constrictor I can't think of any extant species that commonly goes by a full binomial name. Rockpocket 01:00, 8 March 2009 (UTC)

Its pretty weak, but perhaps Pichia pastoris might be another? Rockpocket 01:08, 8 March 2009 (UTC)

The downside of that one is that it makes the lab smell like feet. Ugh. Saccharomyces cerevisiae smells so much better.... TenOfAllTrades(talk) 01:16, 8 March 2009 (UTC)

I have one! Aloe vera. Rockpocket 01:12, 8 March 2009 (UTC)

Great question, and this (Aloe vera) is the best response I've seen. --Scray (talk) 03:50, 8 March 2009 (UTC)

I think T.Rex, E.Coli, Homo Habilis and such are cheating - they just don't have common names - they were named by scientists and the scientific names have stuck. I think Boa Constrictor is actually pretty unusual. SteveBaker (talk) 01:13, 8 March 2009 (UTC)

Model organisms used in lab work are popular candidates. Since Pichia and E. coli have already been mentioned, let me throw in the nematode C. elegans.

I'd also be tempted to argue that baker's yeast – Saccharomyces cerevisiae – might be a legitimate candidate. When baker's yeast is used out the real world, most people aren't thinking of it as a living organism — it's just an 'ingredient'. I suspect that when people talk about Saccharomyces as a living creature rather than a kitchen aid, it's more often referred to by its binomial name. TenOfAllTrades(talk) 01:16, 8 March 2009 (UTC)

Not sure this is as pure and example as the Boa but how about Glis glis aka the Edible Dormouse. In the UK around Tring in Hertfordshire and Buckinghamshire where it has become naturalised following escape from the Rothschilds Estate it is only known by its binomial name. Use Edible Dormouse and you are likely to get blank looks. See [24] Tmol42 (talk) 01:38, 8 March 2009 (UTC)

Aha ha ha! Classic Daily Mail: "The area contains many highly desirable and expensive properties and some residents even fear their house prices could suffer." :D 79.66.56.21 (talk) 17:15, 8 March 2009 (UTC)

In the spirit of Aloe vera above, perhaps Ginkgo biloba counts? I seem to recall hearing something about how it improves your memory or some such… I'm not quite sure. – 74  07:15, 8 March 2009 (UTC)

Does Echinacea count? It's a genus with several species, but at least the binomial name is commonly used. 76.97.245.5 (talk) 08:38, 8 March 2009 (UTC)

Same for Acacia and Eucalyptus. --Mark PEA (talk) 11:18, 8 March 2009 (UTC)

And gorilla. --NorwegianBlue ^talk 11:45, 8 March 2009 (UTC)

As has been emphasized a few times, the question was about binomial names, therefore these last few don't qualify. Ginkgo biloba does seem like another winner. By my count, that's 3: Boa constrictor, Aloe vera, and Gingko biloba. Did I miss any? --Scray (talk) 16:44, 8 March 2009 (UTC)

Gorilla sort of counts since the binomial name is Gorilla Gorilla. --Tango (talk) 18:44, 8 March 2009 (UTC)

I'd dispute the Ginkgo. The books all say its common name is the 'maidenhair tree', but even if you discount that, I would argue that its common name is 'ginkgo', not 'ginkgo biloba'. --ColinFine (talk) 19:29, 8 March 2009 (UTC)

One organism that goes by its binomial name in Norway, is Gyrodactylus salaris (link to various news items). And since model organisms were mentioned above, let's not forget Drosophila melanogaster. --NorwegianBlue ^talk 19:51, 8 March 2009 (UTC)

D. melanogaster is commonly called a "fruit fly". However, I'd say that Tyrannosaurus rex should qualify. It's a well-known beast and the only way its name is shortened in common use is by reducing the first word to an initial, which is also scentific practice as in E. coli. --Anonymous, 20:27 UTC, March 8, 2009.

I've never heard the term "maidenhair tree" (131,000 hits on Google), but I see "Ginkgo biloba" all the time (2,290,000 hits on Google). I agree that Tyrannosaurus rex is the common name (but less compelling than some of the others since it's extinct and thus has had less chance than some of the others to have a common name, IMHO). --Scray (talk) 00:08, 9 March 2009 (UTC)

Agree with scray about Ginkgo biloba vs maidenhair tree. Also Aloe may sometimes be used in place of Aloe vera the same as Boas for Boa constrictor (although both are these may be confusing because they are also frequently used to refer to other members of the group). It's worth remembering that we're only refering to English here. Ginkgo biloba does have a common name in Mandarin and probably other Chinese dialects/languages Nil Einne (talk) 04:34, 9 March 2009 (UTC)

I did say "other than bacteria", since things like E. coli and Staphylococcus aureus seemed too obvious. But thanks for all the suggestions. The count is now Boa constrictor, Tyrannosaurus rex, Aloe vera, Glis glis and Ginkgo biloba? 99.245.92.47 (talk) 02:45, 9 March 2009 (UTC)

This question has cropped up before here and here. – 74  03:47, 9 March 2009 (UTC)

Nice pickup, but the current discussion appears to be both more legible and more complete. --Scray (talk) 04:24, 9 March 2009 (UTC)

The OP seemed to be looking for a definitive answer; I was just establishing some baselines that show we're doing pretty good. – 74  04:43, 9 March 2009 (UTC)

I thought public logs of #wikipedia were verboten?! *ducks incoming meteor of wrath from Bureaucrats* 99.245.92.47 (talk) 10:17, 9 March 2009 (UTC)

March 8

King Faisal's Dream

Bodies of 2 Sahaba removed from the grave in iraq ,This event held ,when king Faisal see a dream about this .[25] Can any body tell me about facts .How this event was happened .Any thing which we can not explain by every day science about this event. —Preceding unsigned comment added by True path finder (talk • contribs) 01:40, 8 March 2009

Well, if you follow the links back to the source, you arrive at this: http://www.themajlis.net/Sections-article139-p1.html - which is from some journal called "VOICE of ISLAM" published in South Africa. There appears to be a bunch of articles in every edition - each containing a rather sketchy description of some kind of miraculous Islamic happening (of which there appears to be a very great number). In this case, the entire text is:

"SHAHEED SAHAABAH

In 1932, the Sahaabi Hadhrat Huzaifah (radhiyallahu anhu) in a dream instructed king Faisal of Iraq to relocate their graves elsewhere since water from the river was seeping in.

The king issued orders for the bodies of Hadhrat Huzaifah (radhiyallahu anhu) and Hadhrat Jaabir Bin Abdullah (radhiyallahu anhu) to be exhumed. The exhumation was done in great style and pomp. Thousands of people witnessed the event. When the bodies were removed, it seemed as if they were buried o­nly a couple of hours ago inspite of the lapse of almost 14 centuries. The bodies were fresh and glittering with Noor.Thousands witnessed the exhumation and many non-Muslims who were present embraced Islam."

This exact same story (word-for-word) occurs in some other places such as this.

So what we have here is that in 1932 King Faisal of Iraq claims to have had a dream. OK - there were two kings of Iraq named Faisal. Faisal I of Iraq died in 1933 - Faisal II was born in 1935. So it must have been Faisal I. There is no mention of this miraculous event in our article about him - so we first have to wonder where is the evidence that he claims to have had the dream. We'll never know whether he truly DID have it - because even if we have primary evidence, it's just his claim. There is no scientific evidence that he truly did have the dream.

Then we are told that as absolute monarch - he demands that some bodies are dug up, with great ceremony - and we're told that the bodies are in surprisingly good condition considering their claimed age. Well, firstly, how do we know that these really were the right bodies? If they'd been there for 14 centuries - then records of their precise burial location would have to be sketchy at best. So if Faisal wanted to do this to make himself seem more self-important, he could EASILY have framed the whole thing. Had two recently deceased men buried at dead of night - then invited an entire crowd to come see them dug up again just hours later. His motives for doing this would have been strong. He was very interested in uniting the people and forwarding a 'pan-arab' agenda - and being told stuff in a dream and then pulling off a miracle could easily be his idea for making that happen! We're told that a ton of people came to watch - so evidently there was HUGE publicity value here. Given that it happened in the very same year as the independence of Iraq - this would not be at all surprising if he faked the whole thing.

Then there is the issue of whether - even if the event were genuine - did the reporting of the freshness of the bodies get exaggerated in the retellings? Certainly the claims of the intactness of Shaheed martyr's bodies is claimed all over the place (just try Googling the term!) - so this result was certainly expected. Mummification would have been well known in 500 AD when these martyrs are claimed to have been buried - so it's perfectly possible that they were in more reasonable condition than observers might expect - and it's EASY to imagine a simple "Wow! They're amazingly well preserved for a 1400 year old body." to gradually turn into "as if they were buried only a couple of hours ago" after many re-tellings and hype.

"Noor" is an arabic word meaning "light" - so the bodies were "glittering with light". I'm not sure what that proves - maybe they were still wet from the ingress of river water?

So that's the range of possibilities. Anything from a 'miracle' to a corrupt politician working the minds of the public to meet his ends of unification to a simple progressive exaggeration of a somewhat surprising - but not earth-shattering event.

The scientific view is that we don't overturn all of science and suppose a 'miracle' if there is a simpler explanation. I think we have two explanations that are each VASTLY simpler than that some godlike or miraculous event magically preserved bodies and caused a king to have a dream.

Hence, I have to say to our OP - categorically: No. Science cannot not regard this as anything in any way out of the ordinary - because there are MUCH simpler explanations than those claimed in the "Voice of Islam" article. If a proper, controlled scientific examination of the bodies had been possible - then perhaps some other conclusion might be arrived at - but "Extraordinary claims require extraordinary evidence" - this is most certainly an extraordinary claim...and there is essentially zero evidence - so science isn't going to jump to that conclusion.

SteveBaker (talk) 07:28, 8 March 2009 (UTC)

When saints were exhumed hundreds of years ago in europe by monks, it was also sometimes reported that they looked as if recently buried. I recall there might be a scientific reason for this, or it could be that since the abbeys earnt a lot from pilgrims, they may have distorted that facts one way or another. 89.243.46.238 (talk) 14:04, 8 March 2009 (UTC)

It's the same deal though. When the people doing the exhuming have a stake in the results - you can't expect a balanced view of the ensuing event. SteveBaker (talk) 17:02, 8 March 2009 (UTC)

Excellent answer by SteveBaker, who, however, did not emphasize the most obvious explanation. Is "The Majlis (the Voice of Islam)" the most reliable source, or might one consider its articles on the level of the fictional accounts one finds in supermarket tabloids? Is there any independent source for this story which, supposedly, occured 77 years before the posting? Without one, we can doubt this tale from top to bottom. B00P (talk) 05:01, 9 March 2009 (UTC)

Crystal structures in Anza Borrego (California) State Park

End view of lines of crystals

A few days ago I noticed these crystals embedded in a stream bank in Anza-Borrego Desert State Park in California. At first I thought they were shells, as the area is the former delta of the Colorado River. They're 6"-12" in diameter and located in a dirt/sand matrix. The bank is 12'-15' high.

The light-colored crystals faces can be seen arranged in several lines in the accompanying picture, especially in the upper-right. While there was stratification of the dirt/sand, there didn't seem to be any major difference in the composition/texture of the strata near the lines of crystals. Just these things in (very dry) mud.

Section of crystal

There were several pieces that had fallen from the bank. The one in the picture is (ahem) fresher than the others. Each was roughly cylindrical. The exposed parts of the crystals in the bank were nearly horizontal and roughly parallel, although only a few inches of each were exposed. It is a natural area with a high tourist load, so (ahem, much) excavation was out of the question.

There is no obvious ring structure such as found in stalactites, except for the outer 1/4" or so which is darker.

I asked a ranger at the visitor center and he started going off about "concretions". So I stopped asking.

What process would lead to formation of such crystals in a river delta? Is this a form of caliche?

Thanks. Saintrain (talk) 01:53, 8 March 2009 (UTC)

I'm just guessing here - but it looks to me like a chunk of fossilised tree. If the tree were to be surrounded by the sand/sandstone up to some depth - then gradually, a few inches of the wood in the trunk would be dissolved away by water soaking through it - and replaced by whatever material is in these rocks. I think you could probably describe that as a 'concretion' - and it would certainly explain the smooth shape. SteveBaker (talk) 06:47, 8 March 2009 (UTC)

I'm with the ranger on this, look like concretions to me, the area is well known for them apparently [26]. Concretions can be extremely smooth and regular, our article has some nice examples. Mikenorton (talk) 10:47, 8 March 2009 (UTC)

I agree with Mikenorton that they appear to be concretions. The way that the exposed ends appear to be weathered away in the outcrop makes me wonder whether the cementing material mightn't be something more water-soluble than the more usual calcite—gypsum, perhaps? Deor (talk) 20:09, 8 March 2009 (UTC)

The first time I scrolled past the photo today I thought it was a pork pie - I had to stop and look more closely. Just now I scrolled past, and thought of scotch pies. Must be hungry. Gwinva (talk) 06:23, 9 March 2009 (UTC)

destroy the copper

BSM(=bismlah alrahman alrahim). We want to destroy a copper screw in a brass plate, fast with a chemical reagent and without damaging to brass. what is the way?unsigned post by 94.101.128.70 (talk) 05:38, 8 March 2009 (UTC)

• What's "BSM"? One of these? --Anon, 20:31 UTC, March 8, 2009.

Since brass is an alloy of copper and zinc - any reagent that would dissolve the screw would also dissolve the copper in the brass - thereby greatly damaging it. So although I'm not a chemist - I'm going to go out on a limb and predict that it's not going to be possible. SteveBaker (talk) 06:41, 8 March 2009 (UTC)

EC.: Beat me to it. Can't you just take a drill and drill it out? 76.97.245.5 (talk) 06:50, 8 March 2009 (UTC)

There are tools specifically for this, see drill bit#Screw extractor. SpinningSpark 09:34, 8 March 2009 (UTC)

Yeah - and they actually work...about one time in three! But if this genuinely is a copper screw as opposed to a copper-plated steel screw - then it'll be very soft and prone to shearing off. I'd be very surprised if a screw extractor would get it out without snapping it. By all means give it a shot - but I'm pretty sure you'll wind up drilling it out. But this must be a pretty special situation - copper is not a metal usually used for making screws. Screw#Materials_and_strength doesn't mention copper being used for making screws (because, mechanically, it makes no sense!). Would our OP care to divulge what exactly this is all about? SteveBaker (talk) 17:30, 8 March 2009 (UTC)

I'd guess it's a copper-based alloy; some of them, like some bronzes, are the same color as copper but stronger. Since the brass and the bronze are both mostly copper, the problem that the same reagents will attack both still applies. I presume a penetrating oil like WD-40 has already been tried? Then I think you're stuck, no pun intended, with a mechanical approach. --Anon, 20:34 UTC, March 8, 2009.

It will also help if you know the alloy numbers[27] of each material. Machine copper is weird stuff, I think it's only something like 50% or 70% copper. A screw made of "copper" would most likely be made of machine copper. It's designed not to be so soft, so that it can hold things like a screw-thread. Normal copper sort of sluffs off like playdoh if you try to mill it or work it in any way. Nimur (talk) 03:57, 9 March 2009 (UTC)

For example, this company actually classifies CDA936 as a "bronze" (though I'm pretty sure I've seen it marketed as a copper - it's been awhile since I did anything close to the metalshop). They specifically state that it is particularly resistant to acid and chemical corrosion. Nimur (talk) 04:14, 9 March 2009 (UTC)

By the way, BSM is Basmala. Polypipe Wrangler (talk) 11:58, 9 March 2009 (UTC)

Strange Lamarckian studies...

I was recently listening to an episode of BBC's In Our Time on Trofim Lysenko (I have a weird fascination with communist agricultural policies, whether they be Chinese or Soviet). In that very interesting episode, they go on a short tangent about how very recent studies have indicated that some aspects of Lamarckism/Lysenkoism might actually be real (they also made it perfectly clear that Lysenko was a nutcase, it's not like they were defending him). They talked about how people who lived through famines tended to pass some sort of genetic imprint of that famine (as an example they said that the grandchildren of people who had lived through a famine in Holland were shorter than the average person).

Is this true? Can someone link to one of these studies, or direct me to the appropriate Wikipedia article? I mean, this seems shocking to me, and I would like to find out more about it. Belisarius (talk) 13:30, 8 March 2009 (UTC)

Check out Epigenetics. --98.217.14.211 (talk) 14:48, 8 March 2009 (UTC)

(After EC) You're probably hearing about epigenetic changes that can be transmitted transgenerationally (see [28]). These examples are quite different than classical Lamarckism or Lysenkoism, which postulated that adaptive changes acquired by an individual could be passed down (the classic example being the giraffe, who stretches its neck by reaching for higher leaves and then "passes down" a trait for a longer neck to its offspring).

Epigenetic changes, in contrast, do not change the DNA sequence but rather alter the characteristics of gene expression (the best example being methylation of certain DNA nucleotides) that can persist across many cell divisions (and in some cases across generations). In the example I linked to, it is shown that famine conditions in the 1940's led to DNA methylation changes -- within the growing fetuses -- that persisted into adulthood. There's quite a lot of research on the effects of in utero nutritional exposure and later onset of obesity, diabetes, etc. but less is known about the transgenerational persistence of these traits.

The epigenetic changes reported in the "famine offspring" could be adaptive if the next generation became slighly smaller because of the altered gene expression and were therefore able to survive better in the famine conditions. However, this is hardly classical Lamarckism... it isn't as though individuals exposed to famine changed genetically in order to be able to survive the famine and then passed on those genetic changes to their offspring. --- Medical geneticist (talk) 15:17, 8 March 2009 (UTC)

I don't understand how "the grandchildren of people who had lived through a famine in Holland were shorter than the average person" proves anything other than an entirely normal, predictable evolutionary pressure. Prior to the famine, some people were taller than average and others were shorter than average. If we believe that height has a genetic component then the famine strikes - the tall people need more nutrition so die off in larger numbers than small people. The "tall" gene is selected against and the "short" gene survives in larger numbers. Guess what? Two generations later, you have kids of below-average height. Why the heck do we have to invoke Lamarkism to have this work? SteveBaker (talk) 17:42, 8 March 2009 (UTC)

Can you point to any evidence that tall people die disproportionately during famine, or is that just conjecture? On the flip side, recent experience suggests height increases within 1-2 generations of shift to higher-calorie diet, and I don't think that's because increases in calorie intake kill the short people. --Scray (talk) 17:58, 8 March 2009 (UTC)

Well, the taller you are the more calories you need, so it makes sense that taller people would do less well in famines. --Tango (talk) 18:34, 8 March 2009 (UTC)

I understand the basis of the specific assumptions being made. It's also possible that tall people would be able to compete effectively for food that is in short supply, depending on how food is distributed. So, rather than make these assumptions, I was wondering if this is anything more than speculation. --Scray (talk) 00:03, 9 March 2009 (UTC)

Yeah - please don't go away with the idea that I'm saying that it's DEFINITELY evolution. I'm merely pointing out that evolution could quite easily produce this effect. There are any number of other possible causes (maybe people wore shoes with thicker heels before the last remaining "thick shoe heel tree" died during the famine and now everyone just seems shorter!!)...I don't know that...I'm just trying to point out that we DO NOT have to assume the highly discredited theories of Lamarckism/Lysenkoism are true as a result of this finding about Dutch children. There are much easier reasons and extraordinary claims demand extraordinary evidence...which this finding is not. SteveBaker (talk) 00:52, 9 March 2009 (UTC)

I also believe it's well established that areas with little food produce dwarf animals, since the smaller versions require fewer nutrients (and the larger ones die off during periods of starvation). There's no reason to think that humans would be immune to this trend. As for people getting taller when there's more food, this probably isn't much due to short people dying, in the short term, but rather because their growth isn't stunted by periods of malnutrition, as it was for their ancestors. In the long run, being taller may have certain evolutionary advantages, such that people would eventually evolve to be taller in the presence of abundant food, but this effect would likely take thousands of years to become apparent. StuRat (talk) 21:08, 8 March 2009 (UTC)

I think we're saying the same thing - it's not clear to me that changes in height over a short period of time would have a genetic basis, but an epigenetic influence might well play a role. --Scray (talk) 00:03, 9 March 2009 (UTC)

Steve, I'm fairly sure they would only conclude it is an epigentic effect if the genome appeared to be basically unchanged but the expression of the given genes it in was affected. That's what epigenetics is about. It is not Lamarckism and it is not woolly-mindedness. Check out the article. Real chemistry and genes and everything. --98.217.14.211 (talk) 22:16, 8 March 2009 (UTC)

Responding to Scray's last: In the mid-19th century, the average height of Frenchmen was less than it was in 1800 despite improved nutrition. Napoleon barely passed the height requirement in the French Army, and such a large percentage of taller young Frenchmen were killed in the wars from 1879 to 1812, thus siring less children, that there was a noticable shortening in the next two generations. B00P (talk) 05:30, 9 March 2009 (UTC)

Why do cancers seem to have purposeful ways of spreading or resisting death, yet cannot have evolved?

Cancers do not have generations so cannot have evolved, yet they seem to exhibit purposeful 'behaviour' which promotes their spreading in the body (see for example http://news.bbc.co.uk/1/hi/health/7813072.stm ) or resisting anti-cancer treatment. Why is this, what is the reason? Is it perhaps just an illusion, rather like a chess computer that simultaneously plays moves at random with millions of skilled opponents, so that those very few games which it wins seem to be the result of cleverness? Or what? 89.243.46.238 (talk) 15:56, 8 March 2009 (UTC)

The trick is in your very first phrase. Cells within a tumor divide, and so there are 'generations' of malignant cells. Many of the mutations which permit uncontrolled cell division also inhibit or disable the cell's mechanisms for detecting and repairing DNA damage. Consequently, every time a malignant cell divides, there are copy errors: additional mutations.

Many of these mutations will have no effect or will render the daughter cell less fit for its environment, but a few will aid the survival of the cell. External selection pressures – the body's immune system, chemotherapeutic agents, etc. – will encourage the survival and proliferation of cells best able to resist those challenges. The parallels with species evolution are evident.

We have an article at Somatic evolution in cancer which goes into the matter in much greater depth and takes a more technical approach. TenOfAllTrades(talk) 16:15, 8 March 2009 (UTC)

Thank you for the explaination, now I understand. 89.241.34.62 (talk) 17:31, 8 March 2009 (UTC)

Also note that, while we think of cancer as a disease people sometimes get, we probably all have multiple cancers inside us all the time. However, the vast majority of them aren't very efficient at spreading, and are easily dealt with by our immune systems long before they become noticeable. One piece of evidence for this is the case of the bubble boy, who lacked an immune system. When he receive a bone marrow transplant from his sister, this resulted in hundreds of cancerous tumors as a result of her Epstein-Barr virus. However, his sister showed no signs of cancer. It's logical to conclude that this virus also caused as many cancerous tumors in her, but which were wiped out immediately by her fully functional immune system. StuRat (talk) 20:59, 8 March 2009 (UTC)

Excellent answer. It's also worth note that we consider some extremely non-malignant cancers "normal," like warts. The virus that causes them belongs to the same family of viruses that cause a few different types of cancer. arimareiji (talk) 22:10, 8 March 2009 (UTC)

A lot of the reason cancer is so difficult to treat isn't that the cancer cells are particularly adept at evading drugs, but that it's really bloody difficult to "hit" the cancer cells without hitting the normal ones. An explanation of the nature of drugs which kill cells might also help in understanding. If you're designing a drug to kill the disease-causing cells (foreign or malignant) in a patient, you have to make sure it's something that won't kill the good cells too. To use a crude analogy, think of it as if you were a police sniper - you can only shoot at parts of the bad guy that are exposed; you can't hit the hostage.
This is relatively easy for antibiotics, because there are huge differences between bacteria and human cells. There are a lot of cellular mechanisms in bacteria which don't exist in human cells, or are so radically different that a drug which stops XYZ process in bacteria won't have any effect on XYZ process in human cells.
But almost all of the cellular machinery is exactly the same for normal human cells and cancerous human cells. You can target cells which are rapidly dividing, but then you'll hit hair cells just for starters (one common side effect of chemo is for hair to fall out). You can target the out-of-control enzymes, but then you'll wreak havoc on general metabolism. And so on.
Usually, the only hope chemotherapy offers is to kill the vast majority of the cancer cells and hope the body will recognize and kill the rest. In my personal opinion, the only real hope for a long-term treatment for aggressive cancers is to help train the body to more easily recognize the cancer cells so it can kill them. Some therapies based on this are already in the works. (Full disclosure: I own stock in a company which works on one of these treatments. But I bought it after examining it closely and deciding it had high potential, not the other way around. ;-)
Does this help explain, or does it just make it more confusing? arimareiji (talk) 22:10, 8 March 2009 (UTC)

Rather than anthropomorphizing ("particularly adept at evading drugs", and the OP's "purposeful"), which is quite common and understandable, it might be more accurate to describe cancers as genetically unstable, large in population size, and therefore highly diverse. As a result, maneuvers that are reliant on genetically-determined traits (such as drug transport and metabolism) are unlikely to kill all cancer cells. Combine that with continual growth, and relapse becomes likely, without ascribing any organized intelligence or intent to the cancer cells. I don't mean this to be criticism - it's just a good habit to consider the process as it is. --Scray (talk) 22:39, 8 March 2009 (UTC)

Some people, led by Leigh Van Valen, have proposed that some cancers cells have evolved sufficiently to be classed as a new species (though most disagree): Helacyton gartleri. Rockpocket 02:05, 9 March 2009 (UTC)

Also of note here is the propensity of cancer cells to overexpress the genes for the ABC transporter, which seems to be a natural mechanism co-opted to pump anti-cancer drugs right back out of the cell; and the recently developed concept of cancer stem cells. These are cells that have escaped the normal controls on division frequency and genetic integrity, and continue to divide to produce the continuing stem cell and a "daughter" cell. The continuing stem cell line is already genetically compromised (by definition) and is thus prone to further genetic mutations. To that degree, cancer stem cells constitute a rapidly evolving population subject to selection pressure == evolution. See also The Selfish Gene - everything wants to survive.

And of course there is Devil facial tumour disease, which could conceivably be classed as a new species. Franamax (talk) 02:26, 9 March 2009 (UTC)

HDU

What can HDU stand for, please?

Since you asked at the science desk I'd bet you were looking for high density urethane. These [29] are other options. 76.97.245.5 (talk) 16:26, 8 March 2009 (UTC)

Urgh - our HDU page was a complete mess - so I've written a new one especially for you! Check it out! SteveBaker (talk) 18:39, 8 March 2009 (UTC)

Thanks to 76.97.245.5 for the first answer, and to SteveBaker for the vastly-improved HDU page. Much appreciated.

Doe anybody have the Book introduction to Biotechnogy By Thieman

I need chapter 6 and I don't have the book and I was wondering if anybody could copy the pages on the web so I can look over them and do my assignment for them

It would be most appreciated Mike0078 (talk | contribs)

It doesn't seem to be available for any preview. You might find it at a local library e.g. [30] or

Wikipedia:WikiProject Resource Exchange more specifically Wikipedia:WikiProject Resource Exchange/Resource Request might help. 76.97.245.5 (talk) 16:39, 8 March 2009 (UTC)

Copying them would be a fairly horrendous copyright violation. Not good. Check out the library. SteveBaker (talk) 17:52, 8 March 2009 (UTC)

Copying one chapter is often considered fair use, but I think only for personal use (so you can take it home from the library if it's a reference only copy, for example) - distributing it to someone else would probably be a violation. --Tango (talk) 19:57, 8 March 2009 (UTC)

Interpreting food nutritional value data

In tables which give you the nutrient content of 100 grams of each kind of food, are the numbers based on the only edible part of the foods? Particularly, in the case of fruits, is the "100 grams" number based on only the parts of the fruit that you eat (i.e. no peel, pits, etc)? Or is that 100 grams of fruit weighed intact? --173.49.9.169 (talk) 17:50, 8 March 2009 (UTC)

It's a pretty safe bet that it's based on only the edible portion, and it's also a pretty safe bet that with almost anything except melons the difference wouldn't be significant regardless. With most fruits and veggies, by far the more the better. arimareiji (talk) 21:03, 8 March 2009 (UTC)

Serving size has some info. arimareiji's statement is for healthy people. Individuals on certain restricted diets should consult their physician or dietitian. Those should be able to point you towards reliable information, calculation tables and the like. For unprocessed foods all information should be taken as "averages". Actual content does vary significantly. (E.g. onions grown in some parts are high in Selenium whereas those from parts with selenium poor soils have virtually none.) They don't withdraw a lab sample from each apple before they sell it to you :-)76.97.245.5 (talk) 00:15, 9 March 2009 (UTC)

What are the lower limits for RDA for saturated fat

I've been keeping a record of the amount of fat I eat every day, and as I do not like junk food, am vegetarian, and cook my own food, then I eat very little fat every day. I might not be eating enough. What are the LOWER limits for the amount of saturated and other fats that should be eaten each day please? I've spent a while googling for this information without success. Thanks. 89.241.34.62 (talk) 19:57, 8 March 2009 (UTC)

The USRDA for saturated fat seems to be around 20 grams, but I take that to be a maximum. I'm not sure that there is a minimum requirement for saturated fat. Our Dietary Reference Intake article says the RDA for "saturated fatty acids" is "As low as possible". There does seem to be a minimum for fats, in general, though, but no requirement that any portion of them be saturated. StuRat (talk) 20:43, 8 March 2009 (UTC)

It's quite accurate to say that there is a minimum intake of fat, though that's rarely a problem in Western culture. ^_~ I've heard 10% of calories as one estimate, YMMV. Since fat calories are more "dense" than carbohydrates and protein (9, 4, and 4 kcal/g respectively), that would mean 4-5% of intake per gram. There are specific fatty acids that your body can't synthesize, but they're not saturated. This provides a decent synopsis. Sorry I can't be more specific, but this is already treading on thin ice wrt not asking or answering medical questions. arimareiji (talk) 20:56, 8 March 2009 (UTC)

Is This a Valid Concept in Evolution?

When speaking of evolutionary change, often only a single characteristic of a creature is considered. Similarly, only a single external influence affecting a creature is considered. But, of course, there are many characteristics in each member of a species that relate to evolution (fitness to survive), and many external influences have an effect on evolutionary change.

Furthermore, each member of a species is unique. It differs from other members of the same species in many small ways. The totality of the characteristics held in common, the unique characteristics, and external influences, determine a member's survivability and longevity, and hence its direction of evolution. (Long life normally results in more offspring being produced. Members with the most offspring will come to prevail in numbers over other members of the species, and will establish the evolutionary trend. This assumes that at least some unique characteristics are inheritable.)

Each unique characteristic will vary in its potency in relation to longevity. Also, the degree of potency may vary from one generation to the next, or even disappear from a new generation. External influences which affect longevity may also vary in potency from generation to generation. To clarify the principle being described, it will be assumed in this discussion that the potency of a unique characteristic, and the potency of environmental factors, remain unchanged over generations.

For any particular member of a species, the various unique characteristics that aid longevity can be expressed, respectively, by the capital letters A, B, C, …. The unique characteristics that hamper longevity can be expressed by the letters a, b, c, …. The total effect of all unique characteristics (U) on longevity can be expressed as U = A+B+C…. – (a+b+c ….).

Characteristics held in common that affect longevity can be expressed as C.

The external influences that aid longevity can be expressed by the Italic capital letters A, B, C, …. The external influences that hamper longevity can be expressed as a, b, c, …. The total effect of all external influences (I) on longevity can be expressed as I = A+B+C…. – (a+b+c ….).

The combined effect of unique characteristics, common characteristics, and external influences on longevity (L) can be expressed as L = U + C + I.

The above considers only an individual member of a species, and its descendents that breed true. Other members have their own unique characteristics and will have their own survivability and longevity. There will be unwitting competition between members with regard to which member will have the most true-breed descendents. The true-breed descendants of a member that has the highest L will eventually prevail over all other descendants. The descendants of other members will eventually become extinct because they will be in competion for food with increasing numbers of high-L (long-lived, more offspring) members.

Complicating the matter is the fact that unique characteristics, common characteristics, and external influences are not quantifiable in their effect on longevity. Indeed, some of the characteristics and influences would probably be unknown to science. Therefore, while the above formulas express general principles, they cannot give specific results.

A further complication is that nearly all species of living things reproduce sexually. Therefore, species members may interchange any unique characteristics that can be passed on by sexual reproduction. None of the resulting half breeds will have maximum longevity.

Maximum L may be only very slightly longer than other values of L. But over thousands of generations it will make a big difference in the numbers of members that will survive.

A single species member that by chance had an extra long life, and its descendents which inherit that capability, will determine the direction of evolution of the species. Shorter lived members, with their uniqe characteristics, will die out.

With regard to a single member of a species determining the direction of species evolution, I remember reading something about that for humans. The effect is indicated in cells and in the female line of descent. – GlowWorm.

External influences are not inherited, so what you are saying makes no sense. How well a particular organism reproduces depends on how well its inherited characteristics suit the environment it is in and a generous dose of luck. Over a long enough time the influence of luck reduces and those organisms which best suit the environment will prevail over the others. That is evolution. The environment is continually changing (both due to changes over time and due to organisms moving from one place to another), so evolution is a continuous process. One key part of the environment is other living organisms (of the same and different species), which are also subject to evolution, which means you get all kinds of complex interactions making the whole thing rather chaotic and unpredictable. --Tango (talk) 23:42, 8 March 2009 (UTC)

I did not say external influence is inherited. I said it affects evolution. Also, earlier on this thread I mentioned that other living things may be considered part of the environment. – GlowWorm.

You said "A single species member that by chance had an extra long life, and its descendents which inherit that capability", that's just not the case. Its descendants only inherit the genetics, which is only one component in determining longevity. (And longevity isn't the only thing to consider - number of offspring that reach breeding age is related to longevity, but it isn't directly proportional.) --Tango (talk) 00:12, 9 March 2009 (UTC)

So many errors - so little time!

• When speaking of evolutionary change, often only a single characteristic of a creature is considered. - Well, in the simple examples quoted for simplicity in text books and such - but in reality, no.
• Similarly, only a single external influence affecting a creature is considered. - Again, not in practical applications of evolutionary theory.
• Furthermore, each member of a species is unique. - No, in many animals there are identical twins and in the case of creatures that reproduce asexually (an Amoeba, for example) - the offspring are essentially clones of the parent - except for DNA transcription errors and such.
• Long life normally results in more offspring being produced. - Not so - in fact most species are programmed to cease reproductive capability later in life. Female humans (for example) cease to be reproductively capable at about the same age all around the world - despite drastically different life expectancies.
• Members with the most offspring will come to prevail in numbers over other members of the species, - PROVIDING that the reason they were able to produce more offspring is (a) genetically heritable and (b) exposed to a similar set of environmental pressures. If (for example) a species is exposed to extreme drought - but ample food is available - then a drought-resistant strain that can more efficiently extract moisture from the food will survive into the next generation. However, if in ensuing years there is plenty of rain - but horrible food shortages - then the offspring of that successful earlier generation may suffer horribly.
• Each unique characteristic will vary in its potency in relation to longevity. - No. Longevity isn't everything - proclivity and reproductive success is very important. It's not as simple as you try to make it sound.
• To clarify the principle being described, it will be assumed in this discussion that the potency of a unique characteristic, and the potency of environmental factors, remain unchanged over generations. - That might clarify your explanation - but it's far from being true. When you look at very successful species, you come across animals like Wolves and Bears - which will eat almost anything - species which are HIGHLY adapted to (for example) eat just one food or hunt in just one way or which can only produce young if they swim up some highly specific river to spawn...those are very fragile...and a tiny change in the environment can wipe them out. Response to change is a vital part of why evolution works. Consider sexual versus asexual reproduction: Species that reproduce asexually can reproduce much more efficiently - but the problem is that there is very little genetic variation - so they are unable to change rapidly when the need arises. The evolution of sex itself is in response to the somewhat abstract evolutionary pressure - which is the ability to respond rapidly to changes in evolutionary pressure!
• For any particular member of a species, the various unique characteristics that aid longevity can be expressed, respectively, by the capital letters A, B, C, …. The unique characteristics that hamper longevity can be expressed by the letters a, b, c, …. The total effect of all unique characteristics (U) on longevity can be expressed as U = A+B+C…. – (a+b+c ….). - I disagree - it's more likely to be something like U = A x a + B x b + C x c. If you have the gene for 'B' (ability to survive a drought, say) and the environmental pressure 'b' is zero because it rains a lot - then B has no benefit so it's contribution is zero. But in reality it's going to be a VASTLY more complex equation U = ( A + B ) x ( a + b ) + A x C x c ...or something.
• The combined effect of unique characteristics, common characteristics, and external influences on longevity (L) can be expressed as L = U + C + I. - but Longevity isn't it - it's ability to reproduce...which is not at all the same thing.
• The descendants of other members will eventually become extinct because they will be in competition for food with increasing numbers of high-L (long-lived, more offspring) members. - Not always. The Origin Of Species (to coin a phrase) requires that sometimes the members with the new and novel genetic makeup may be geographically separate (eg stuck on an island) or may have evolved to exploit a different ecological niche. Hence there are now two species where there was once one - and hence there may be no extinction involved.
• A further complication is that nearly all species of living things reproduce sexually. - Is that true? I really doubt it. Bacteria, many plants, fungii, worms...lots of species do not.
• Therefore, species members may interchange any unique characteristics that can be passed on by sexual reproduction. None of the resulting half breeds will have maximum longevity. - That's nonsense. If some individuals of the (say) anteater species have a gene for longer noses - and other individuals have a gene for longer tongues - then neither of them may be able to reach into the deepest termite mounds. But a lucky breeding might produce an anteater with both the gene for long noses and the gene for long tongues - and therefore succeed where neither of it's parents could. The resulting "half breed" (poor choice of terminology...but whatever) has only characteristics that were present in the general population - yet is better than any of them.
• A single species member that by chance had an extra long life, and its descendents which inherit that capability... - No - if they lived longer by CHANCE then there is nothing to pass on genetically. Only those that reproduce more efficiently BECAUSE of their genes will pass that on to their offspring. The Zebra that happens not to meet any big lions (because it lives in a zoo) will have offspring that are no more 'lion-resistant' than their parent - and if returned to the wild will do no better than all of the other zebras.
• With regard to a single member of a species determining the direction of species evolution, I remember reading something about that for humans. The effect is indicated in cells and in the female line of descent. - all humans are descendants of a single person - all animals are descendants of a single animal. There are characteristics (in humans at least) that are carried on X chromosome. Women have two X chromosomes - men have an X and a Y instead. If a child is born that gets the X chromosome from the man (and, inevitably, an X from the mother) - then it must have two X's and therefore be female. If it gets the Y chromosome from the father, it will be a boy and his X chromosome will be from the mother. So X information carried on the X chromosome follows the female line because a father cannot pass his X chromosome onto his son(s). But that's a small minority of genes - and it's not true in all species.

PHEW! SteveBaker (talk) 00:30, 9 March 2009 (UTC)

Regarding your last point - the organelles all come from the ovum, so the mother, so things like mitochondrial DNA are inherited solely through the female line. Y-chromosomal DNA is inherited solely through male line. That doesn't mean we all get of mitochondria and Y chromosomes from the same individual, though. There isn't a single "first human" from whom everyone is solely descended. There are common ancestors of all the individuals in a species, but there are lots of them. See most recent common ancestor and identical ancestors point for more discussion of this. --Tango (talk) 00:46, 9 March 2009 (UTC)

• Actually, both chance and how well an individual is adapted to survive in its current environment play their part. Evolution is statistical mechanics in action.
  • Hypothetical: You have 100 zebras. 50 can run faster but need more food as a result (group A), and 50 zebras are "normal" (group B).
  • 7 A's and 4 B's die by random chance.
  • 8 A's and 4 B's starve to death.
  • 5 A's and 22 B's get eaten by lions.
  • All the rest reproduce, giving 2 offspring per individual.
• Next generation has 60 A descendants and 40 B descendants. If this pattern keeps up, soon B's will be a small minority. (But if food and/or lions become scarce, those proportions could easily change.) This also serves to illustrate why single genes are rarely the single determining factor in an individual's likelihood of reproducing. There's almost always a tradeoff for every "advantage," and the balance can easily shift depending on changes in the environment.
• I know the above is oversimplified, i.e. not taking into account that A's and B's can mate, dominant/recessive genes, multiple alleles, polygenic traits, etc. But I thought it might be illustrative.
• Finally, yeah - humans have 23 chromosome pairs. Only one is sex-linked. And don't even get me started about the plethora of ways gender is determined, and determines how genes get passed, in other species. XY isn't the only model, by far. arimareiji (talk) 01:08, 9 March 2009 (UTC)

If your model would hold water we'd have a hard time explaining why we still have genetic disorders that kill their carriers at a young age. Sickle cell anemia is one of the more commonly known, but not the only one. As it happens this trait offers its carriers some protection against Malaria. So, although longevity is very much curtailed, individuals have a higher chance of reaching reproductive age and reproducing. Fits evolution very nicely. One thing that often gets mixed up is that benefiting the individual and benefiting the survival of the species aren't the same. The world is full of examples of odd appendages, bright colors instinctive behaviors that serve no other function than to attract a mate. This can be and often is very detrimental to the individual. But as long as that individual manages to mate with more females than an individual without, the trait will get passed on. Looking around lots of short lived creatures from bacteria that live in your gut to cockroaches (Hopefully not under your floorboards:) to mice contradict your equation. A single mouse can spawn thousands of descendants in several generations in the time it takes a long lived human just to reach sexual maturity. Adding a couple of examples to Steve's list of asexual reproduction: many species of snails choose their sexual orientation when they meet. Female sharks can reproduce with or without males. 76.97.245.5 (talk) 02:25, 9 March 2009 (UTC)

"So many errors" that even the eagle-eyed SteveBaker missed an obvious one. The OP states, "Characteristics held in common that affect longevity can be expressed as C." However, he has previously defined C otherwise. He needs a different symbol. Here, try §.
— B00P (talk) 06:05, 9 March 2009 (UTC)

Exploding Cell Phones During Recharging

A friend who lives in Spain sent me an email warning about not using a cell (mobile) phone while it is recharging. I will spare you all the gory photos, but the text read:

Don't know if any of you have seen this before, but if you're prone to answering the phone whilst its plugged into the charger you might want to rethink that practice !!!

A few days ago, a person was recharging his mobile phone at home. Just at that time a call came in and he answered it with the instrument still connected to the power outlet. After a few seconds electricity flowed into the cell phone unrestrained and the young man was thrown to the ground with a heavy thud. His parents rushed to the room only to find him unconscious, with a weak heartbeat and burnt fingers. He was rushed to the nearby hospital, but was pronounced dead on arrival. Cell phones are a very useful modern invention. However, we must be aware that it can also be dangerous...

Never use the cell phone while it is hooked to the electrical outlet!

I tried a few variations on "exploding cell phones" and "dangers of recharging cell phones" in the Archives' Search box, but didn't find anything useful to me, as I had no plans to use the cell phone while pumping gas. Is this email warning reasonable; that is, is it true or possibly true? Would it make a difference if the phone was recharging in Europe at 220 V as opposed to in North America, at 125 v? Thanks for your help. // BL \\ (talk) 00:29, 9 March 2009 (UTC)

This stinks of "Urban legend" - if this were a common occurrence, you can bet there would be HUGE warning stickers all over your cellphone telling you not to do it - and they'd probably make the phone so it would refuse to take or accept calls while charging in order to discourage this terrible practice. As always, urban legends should be checked out at http://www.snopes.com - and indeed it has a page about it: [31]. The second example they quote - is your email...word for word! It concludes that this is an exceedingly rare thing - but that once in a while, cellphone batteries can explode. (They point out that the ONLY proven cases have been Nokia phones WITH COUNTERFEIT BATTERIES...they also point out that in a couple of cases, the person was merely sleeping a few feet away from the phone when it exploded...so making calls on the phone isn't the problem). But there are maybe half a dozen cases worldwide over a period of several years. It's also dangerous to eat lunch (you could choke and die - the food could have been poisoned or it could harbor deadly diseases) - it's exceedingly dangerous to drive your car - all of these things are VASTLY more likely than that you'll be killed - or even harmed - or even mildy inconvenienced - by an exploding cellphone. So the advice "Never use the cell phone while it is hooked to the electrical outlet!" is about as useful as "NEVER EAT LUNCH!" or "NEVER DRIVE YOUR CAR!!!". It's quite utterly bogus, terrible advice. By all means carry on using your phone - and if you own a Nokia and ever have cause to change the batteries - make sure you buy them from Nokia and not from some guy at your local market! Please - when you hear this crap via email - either check it out on snopes.com - or just ignore it. SteveBaker (talk) 00:38, 9 March 2009 (UTC)

Yeah, because talking on your cell phone 24/7 is a basic human need like food and transportation. A better analogy would be "not driving your car after midnight (when the drunks are driving home)". Each person is capable of weighing the odds and deciding if the risks are acceptable to him or her—if not talking on your cellphone while it's charging makes *you* feel better then by all means go ahead and ignore my hyperbolic collegue. – 74  01:14, 9 March 2009 (UTC)

Actually it has been pretty well established by risk communicators that most people are pretty bad at weighing risks for them sensibly, even if they have really good sources of information. (Ergo, Las Vegas.) The human brain is not a terribly rational organism—it gives certain perceived outcomes vast more weight than others even if the odds are astoundingly against them. (On a side note, is talking on a cell phone a basic human need like food? No, of course not. Like transportation? Yes, almost exactly...) --98.217.14.211 (talk) 01:57, 9 March 2009 (UTC)

(After e/c, and I have read your amendments, Steve - I added your name as 74.137.108.115's comment has intervened, and I was not directing my remarks to him/her.) I shall forgive you for the "Duh" in the original edit summary. (Please understand that I am laughing as I type this.) I think the photos short-circuited my brain and I forgot common sense, and S.O.P, which includes checking Snopes and Mythbusters and a general look around the Net. And, given how thoroughly, albeit relatively gently, you dissected the argument presented by the OP in the immediately preceding query, I am not surprised your patience for those who may not "think before they type" is in current short supply. So, thank you, and I shall slink off to whimper quietly in the further reaches of cyberspace, but not before I email the friend the Snopes's link. // BL \\ (talk) 01:06, 9 March 2009 (UTC)

The interesting question is whether the friend who forwarded this junk to you will, in turn, forward it to all of the other people (s)he sent it to - and also back to the person who sent it to him/her? I strongly suspect not. Dramatic news of exploding cellphones travels fast - news that the world is a calmer, simpler place without all of these dread dangers...that travels much more slowly. SteveBaker (talk) 01:24, 9 March 2009 (UTC)

P.S. I don't even have a cell phone. // BL \\ (talk) 01:36, 9 March 2009 (UTC)

Just a general note on this story: whenever you see something that warns that an everyday activity that seems harmless is actually horribly dangerous and could kill you at the drop of a hat, there are generally some telltale signs of an urban legend:

• Someone dies or is horribly mutilated in a dramatic fashion.
• It's telling you that something you may do all the time is a very bad idea.
• It's too good or too bad to be true, or violates common sense -- that is to say, the results of the action are dramatically disproportionate to the action itself.
• There are no dates, names, or places included in the warning, so there's no way for you to verify the story.
• It's told as a story, with a degree of drama and a punch line or a moral at the end.
• It's reported in an e-mail that's obviously being passed around, rather than a news site, and you are encouraged to pass it on to everyone you know.

This particular story hits just about all of the above points. Not all urban legends do, of course -- and just because something is an urban legend, that doesn't necessarily mean it's not basically true. But if someone tells you something that hits, oh, let's say three of the above points, your bullshit detector should be tingling, and you probably shouldn't accept it at face value. (Which you didn't, of course, so good job there!) -- Captain Disdain (talk) 08:03, 9 March 2009 (UTC)

Hardness of diorite?

Can someone tell me the Mohs scale of mineral hardness value for diorite? (It's not in the list.) RJFJR (talk) 02:47, 9 March 2009 (UTC)

I'll guess at around 6, based on a quick look at the hardness of the components of diorite. I imagine the exact value would depend on the relative concentrations of the constitiuent minerals. Mattopaedia ^{Have a yarn} 03:36, 9 March 2009 (UTC)

Assuming that the main components are feldspar and hornblende, then around 6 would be about right. If there is a lot of biotite (hardness 2.5-3) in a particular variety, that's a different matter. Mikenorton (talk) 09:04, 9 March 2009 (UTC)

Identify an insect

Good day. Can someone identify this insect? I photographed it today, in the Anza-Borrego Desert State Park, California. It was about 1.5 to 2 inches long. Thanks. Rockpocket 03:17, 9 March 2009 (UTC)

• 
• 
• 

Looks like a soldier beetle to me. --Dr Dima (talk) 04:43, 9 March 2009 (UTC)

I think you may be correct, thank you. Next question, can anyone identify a species? Rockpocket 05:56, 9 March 2009 (UTC)

Actually, after a bit more research, I think it is the Desert blister beetle (Lytta magister). [32] Rockpocket 06:21, 9 March 2009 (UTC)

Can well be. Lytta genus is in Meloidae (blister beetles) rather than Cantharidae (soldier beetles), so I was wrong, then. My apologies. For the fans of entomological confusion, here's a semi-famous fact: Meloidae contain and secrete cantharidin, Cantharidae do not. Actually, the historic confusion between the two families is to blame for that. The "Spanish fly", Lytta versicatoria, has been known as Cantharis vesicatoria or (usually dead and dried) as cantharides. Still, my bad. --Dr Dima (talk) 07:18, 9 March 2009 (UTC)

Not at all, your answer got me looking in the right direction. Thanks again. Rockpocket 07:32, 9 March 2009 (UTC)

I made a few tweaks to your new article, Rockpocket. Now we need someone to create an article on the species' describer, George Horn, who seems notable enough. Deor (talk) 15:22, 9 March 2009 (UTC)

Are all treatments that depend on belief placebos?

If a patient has to believe in the viability of a health treatment for it to work, is it necessarily a placebo? NeonMerlin 04:48, 9 March 2009 (UTC)

If a "treatment" requires belief for any recuperative action than it must not be bioactive. Any recuperative action it does have must therefore be by placebo effect, so yes. However, I would hazard that there is a middle ground where bioactive compounds are more effective when the patient believes it is a cure-all. In these cases you would have to define "work", before your question could be answered. Rockpocket 06:14, 9 March 2009 (UTC)

No. There's an interesting article in the New Scientist regarding placebo and the placebo effect, which among other things tells us that belief is not the main factor in the placebo effect: rather there are other factors such as being made to feel comfortable with the consulting environment and physician. [33] This article also gives the information that people who believed the morphine they were being given was going to work, experienced a greater analgesic response than those who didn't. Nobody would suggest that morphine came under the placebo category! --TammyMoet (talk) 10:06, 9 March 2009 (UTC)

There are a couple of "mind over body" techniques that basically work by the person controlling their breathing, heart rate, thought processes etc. I don't think they would be effective if people didn't think it would work. They also work differently from placebos because the individual tries to actively control bodily functions. There is unfortunately a grab bag for this kind of thing that spans from tried and established relaxation techniques to the latest and greatest loony cure-all fads. Someone learning not to turn into a quivering bag of hysterics or fainting whenever there's a thunderstorm without taking any "little pink pills" is likely to depend on that individual starting to believe that the sky isn't going to fall and hit him. That's a far cry from things like "curing infections through willpower". I'd suggest antibiotics for the latter which will work whether you hold the firm conviction that pharmaceutical companies are run by crooks or not. I was trying to find some examples for you, but anything even remotely going in that direction is likely to come under much scrutiny and as a layperson it's hard to distinguish the ones that deserve it from the "friendly fire" casualties. 76.97.245.5 (talk) 10:57, 9 March 2009 (UTC)

does atmospheric pressure include the vapor pressure of the water vapor in it?

I'm trying to do a lab with some psychrometric equations. Atmospheric pressure for the room (I believe) in which our experiments took place was measured, but I am not sure whether this is total pressure or the pressure of dry air. Does atmospheric pressure normally include the water vapor pressure? Thus in a closed system the atmospheric pressure surrounding a reservoir of water should increase with further evaporation? (This is different from saturation water vapor pressure and water vapor pressure being equal, I believe.)

Particularly I am confused by an equation I'm given for specific humidity -- the ratio of the molecular weight of water and dry air (0.622) multiplied by the water vapor pressure , divided by (total pressure - 0.378*water vapor pressure). Maybe the math is not working at 4 am in the morning, but why subtract water vapor pressure from the total pressure of the air, if I'm trying to calculate specific humidity which tries to relate the amount of water vapor to the amount of mixture? John Riemann Soong (talk) 08:16, 9 March 2009 (UTC)

Vapor pressure has a separate section (albeit brief) on use in meteorology at the bottom. 76.97.245.5 (talk) 11:02, 9 March 2009 (UTC)

air sacs

What is the name of air sac which is found in human's lung? —Preceding unsigned comment added by 196.200.102.42 (talk) 09:16, 9 March 2009 (UTC)

The normal structure is an alveolus, whereas disease can result in blebs and cysts. --Scray (talk) 09:28, 9 March 2009 (UTC)

Meson number

We have baryon number, but, apparently, "meson number" is not a noted concept. Can someone shed light? —Anonymous Dissident^Talk 09:52, 9 March 2009 (UTC)

Ah, don't worry. I guess (1-1)/2 doesn't make sense, so I answer my own question. —Anonymous Dissident^Talk 10:02, 9 March 2009 (UTC)

photons

how do photons carry light? —Preceding unsigned comment added by Lightfreak (talk • contribs) 12:28, 9 March 2009 (UTC)

Photons are light. Light isn't some separate thing which they carry. Algebraist 12:31, 9 March 2009 (UTC)

light

is light an electromagnetic radiation or the theory of photons right?```` —Preceding unsigned comment added by Lightfreak (talk • contribs) 12:40, 9 March 2009 (UTC)

Your question doesn't make much sense, but I think you want Wave–particle duality. Algebraist 12:44, 9 March 2009 (UTC)

light

i have some doubts in the article "light".Please help me out with it.--Lightfreak (talk) 13:04, 9 March 2009 (UTC)

You're really going to have to be more specific than that. Could you describe your doubts? -- Captain Disdain (talk) 13:27, 9 March 2009 (UTC)

The meaning of Frequency in physics

Usually c(transmission speed) = f(frequency)• w(wavelength) ;

However, if I, per second, send 3 photons(wave packets) of wavelength 1cm at the speed of light, there would be gaps between the wave packets, so the rule above above fails.

I feel insecure/unsure about this, and I have not succeeded in finding a measure covering the situation above.

Should there not be an explicit statement, that the wave packets should be immediately adjacent, for the rule above to work ?

Should there not be a special measure for the example above to work ?

83.226.97.214 (talk) 13:29, 9 March 2009 (UTC)

You need to either think about light in terms of photons, or waves, not both. Combining the two interpretations is rather tricky. If you want to think it terms of wavelengths, do everything with waves, no photons. If you want to work with photons, think in terms of energy (E=hf). --Tango (talk) 13:36, 9 March 2009 (UTC)

What would be the problem? There would be three separate "pulses" of light; each pulse would have its own frequency and wavelength (these would be dependent on the energy of the single photon, primarily due to the method you used to make those photons). If you wanted to, you could also "time-average" over a long period of time, and you would begin to see the repetitive nature of the pulses showing up as a frequency-component in your received spectrum (note that only special cases of light have a "single" frequency - most light is best described by a combination of frequencies - in your case, this would include both the individual photon frequency AND the 3-pulse-per-second pulse repetition frequency). The problem is that with only 3 photons per second, you would need to average many many time-cycles to show any meaningful "spectrum" wave-like behavior (because there is not a large amount of energy per pulse). All in all, this is a situation which is best treated exclusively with the particle model. Nimur (talk) 15:11, 9 March 2009 (UTC)

Phrased another way, "gaps" in the spatial extent of the wave packet really just means that the individual photons do not interfere with each other. If you space the photons closer together, their wave-nature will cause them to interact. The result will be a different distribution of received photons at the receiver. This distribution is slightly random, but again, on the long-term average, it will be exactly described by the interference pattern of the wave representation of the individual photons. Nimur (talk) 15:13, 9 March 2009 (UTC)

Heparin and Bleeding Tests

Heparin acts by decreasing the activity of thrombin, the common endpoint of coagulation cascades

Why then, does it only affect pTT blood times (intrinsic pathway), and not the PT(extrinsic pathway)?

--Cacofonie (talk) 15:40, 9 March 2009 (UTC)