Wikipedia:Reference desk/Archives/Science/2006 October 21

From Wikipedia, the free encyclopedia

Science desk
< October 20 << Sep | October | Nov >> October 22 >
Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.


Contents


[edit] October 21

[edit] James McCollum

Still looking for some biographical info on Canadian engineer, James K McCollum. He was the co-inventor of the Sleeve-Valve mechanism for internal combustion engines along with Scotsman, Peter Burt.

Jerry Wells, Australia.

Weve already tried to answer this question. If these links are red, its pretty pointless asking further. Why dont you Google it?--Light current 00:45, 21 October 2006 (UTC)

[edit] Page updating problems.....

I`m having a terrible time updating this page. I`m usually on AOL,,,get blocked often on account of that. I`m currantly on Mozilla but, even worse...re-fresh/update brings me to about this time, YESTERDAY! Can anyone offer some assistance? TY Dave 172.128.242.194 02:33, 21 October 2006 (UTC)

Simply creating an account would help. This would also make it easier for us to diagnose your problems by referring to your edit history.--Shantavira 08:53, 21 October 2006 (UTC)
Reading Wikipedia:Advice to AOL users would be a good idea =) --`/aksha 12:27, 21 October 2006 (UTC)

[edit] Phase-determination pressure

Is the pressure on a phase diagram the vapor pressure of the substance in question, or is it the total pressure of the substance's environment? It seems to be vapor pressure when discussing the equilibrium between liquid and gas, but it seems to be total pressure when discussing the pure phases (e.g., the diamond/graphite transition). Which is it, or is it some third possibility? --Tardis 02:43, 21 October 2006 (UTC)

It's the external pressure applied, i.e., if you put the substance in a rigid container with a movable piston and apply some pressure to the piston, the phase diagram tells you the phase the subtance will take. It's only equal to the vapor pressure when the gas in equilibrium with another phase. For example, say the temperature is between that of the triple point and the critical point. If the applied pressure is less than the vapor pressure at that temperature, the substance will be completely gaseous. As the pressure is increased, the volume decreases slowly, until the pressure reaches the vapor pressure and the gas begins condensing into a liquid. At this point the piston suddenly slides in without resistance, because the gas condenses into a liquid and the volume changes while the pressure remains at the vapor pressure (moving the piston does no work because dp = 0). Then when the substance is completely liquified, the pressure begins to increase again, now greater than the vapor pressure. —Keenan Pepper 18:25, 21 October 2006 (UTC)
This is all from Atkins' Physical Chemistry, ISBN 0-7167-8759-8. —Keenan Pepper 18:28, 21 October 2006 (UTC)

[edit] Cheese longevity

I buy packages of shredded cheddar cheese in a sealed zippable bag (as in, initially properly sealed and re-sealable). The bag claims that it should be refrigerated, of course, and finished within "3-5 days" of opening. However, I use only a little at a time and so have seen it last much longer than that in an arid environment without any apparent ill effects. Just how long should I expect it to be safely edible, and what would be the first sign that it's not? --Tardis 03:12, 21 October 2006 (UTC)

The first sign will be visible specs of mold. How long they take to develop depends mainly on how sterile you keep it when it is opened. If you reach a grubby hand down in the bag, you will likely heavily contaminate it. If you open it upside down, so nothing can fall in, then let some cheese out and quickly reseal it, then drive the air out, you might get lucky and not have any bacteria in there that like cheese. Another suggestion, buy smaller bags or divide your bag up into single use bags, then freeze each until ready to use. StuRat 03:28, 21 October 2006 (UTC)
no way dude, what's-his-face (keenan pepper???)'s friend worked in the cheese industry!! Wait for his repesonse.
No whey ! :-) StuRat 11:57, 21 October 2006 (UTC)
Ive heard cheesy jokes before 8-(, but that on just about takes the biscuit. 8-)--Light current 17:12, 21 October 2006 (UTC)
I have no idea who you're talking about. —Keenan Pepper 17:53, 21 October 2006 (UTC)
Sorry I cant see the joke here 8-(--Light current 19:27, 21 October 2006 (UTC)
The cleanliness of the processing and packaging have a large effect on the longevity of shredded cheese, which is inherently shorter than that of a wheel or wedge of cheese. If the cheese gets moldy quickly, and you are sure you did not contaminate it, you might just wonder "Who cut the cheese?"Edison 21:52, 21 October 2006 (UTC)
Yes, the much greater surface area of shredded cheese allows it all to get moldy, as opposed to just the surface of a large chunk of cheese. StuRat 00:20, 23 October 2006 (UTC)

[edit] Whistling sine waves

A whistling sound is pretty close to a sine wave. Why? What are the processes behind the sound in whistles that make it like that? I understand the mouth and lips work as a resonant chamber, but why, exactly, no timbres are produced? Our article on whistling mentions this fact, but doesn't give any explanation. ☢ Ҡi∊ff⌇↯ 05:59, 21 October 2006 (UTC)

The mouth and the lips form a high Q resonant chamber. Look at resonance and Q factor. The Q is so high that it filters out frequencies higher and lower than the one you are whistling leaving essentailly only one frequency. This one frequency must be a sine wave. 8-0--Light current 07:31, 21 October 2006 (UTC)
Ah, I've never thought about it like that. Makes sense. Thanks for the explanation. :) ☢ Ҡi∊ff⌇↯ 07:54, 21 October 2006 (UTC)
Light Current, are you sure about your explanation? The Q factor of, say, a woodwind instrument is probably higher than that of the mouth cavity, and they do have a tone that is clearly not sinoidal. After all, also a high-Q resonator gets higher harmonics excited alongside of the fundamental, and the amplitude of the harmonics (in units of the fundamental's amplitude) is what defines the tone or timbre. What a high Q factor rids you of is line broadening, but it does not enforce a pure sine. By the way, Kieff initially asks about whistles and Light Current talk about whistling without a whistle. So, of which one do you two now claim that they had an extraordinary pure sine? I doubt both, actually, but as we all three probably have a microphone input bin our computers, we can easily check. Simon A. 22:43, 21 October 2006 (UTC)
Well the very fact that woodwind instruments have a certain timbre proves that the instrument Q is much less than your mouth/lip system. --Light current 23:11, 21 October 2006 (UTC)
No, Simon, I was actually talking about whistling with the mouth (that's why I wikilinked to whistling instead of whistle.) The reason I asked is that I've already recorded myself whistling and looked at the wave, and it's very close to a sine wave. ☢ Ҡi∊ff⌇↯ 10:36, 23 October 2006 (UTC)

IIRC, the difference between whistling and the sound of a woodwind instrument is that the woodwind instrument has a vibrating reed that produces a range of harmonics, whereas whistling is highly filtered noise (caused by air turbulence). Whistling is unvoiced whereas the woodwind is "voiced" in the way that it is analogous to a vibrating vocal fold.

So whilsting is just noise filtered drastically to single out an individual harmonic. There is of course a bit of noise in the "signal" too, since our mouths aren't perfect. Magic Window 17:31, 24 October 2006 (UTC)

[edit] COSTAS loop

In costas loop, the phase of generated carrier must be such that it matches with that of Incomimg carrier so that angle phi is zero.But why is the error signal given to the Voltage Controlled Oscillator instead of a phase shifter???

What do you mean by phase controller? THe freq and phase of the VCO is controlled by the vco i/p voltage

--Light current 09:02, 21 October 2006 (UTC)

[edit] Transmission line theory

We all learn that circuits have a fixed value of resistance,capacitance and inductance.But why sudden change in theory when it comes to transmission lines with topis such as reflectivity?Any lucid and simple explaination?

In transmission lines, resistance, capacitance and inductance are still there, but the elements are not lumped. THey are distributed over the length of the line. Any discrete lumped RLC cct (like ther ones youre used to) will also have parameters like input match, reflection coefficient etc. but at low frequencies, these parameters do not matter so much as they do at high freuencies where transmission lines are commonly used.--Light current 09:08, 21 October 2006 (UTC)
I'm not sure who taught you that circuits have a "fixed value" of resistance, capacitance, and inductance, but its usually not true. For example, the resistance of a typical physical resistor changes noticeably depending on the temperature. Variable capacitors can be constructed by using moving plates. Also active circuit elements like transistors and diodes are typically nonlinear -- that means the resistance and capacitance vary depending on the applied voltages or currents. In fact a reverse-biased diode is often a more economic way to form a variable capacitor than a physically moving device. We normally just approximate these circuits as linear circuits, with localized values of the elements, determined at some moment of time, because then we can calclulate the behavior. Our article Electrical network touches on this in the section on Piecewise-linear approximation, but I can't say the discussion is complete enough to give a good understanding. -- The Photon 22:38, 21 October 2006 (UTC)
I dont think the questioner was really asking about nonlinear circuits but just the diff between the circuit theory and em field theory approaches.--Light current 23:01, 21 October 2006 (UTC)

has to do with frequency and size of the components. Lumped is easier to analyze. But consider this: You have a generator with an impedance and a fixed resistive load. If the resistive load is far from the generator and the impedance is changed far from the generator, how does it know? there is a lag in that information. The answer is that the generator sends out a fixed power value and what cannot be aborbed is returned as a reflection. As the frequency increases, that distance is made smaller and smaller until it makes it difficult to speak in terms of voltage and current and the preferrred parameter is power (S parameters). The bottom line is that the source has no idea what the load is until the power is reflected back. Lumped analysis is adequate when the dimension of the circuit far exceed the wavelength. --Tbeatty 07:33, 22 October 2006 (UTC)

[edit] Reality

I present two situations.During the genesis of time, the universal laws of reality came into being:-

1)The Domain of these laws started spreading at the speed of light(max speed limit) across this current diemension after the beginning of the big bang and that the universe is not defined in the domain beyond this hypothetical diemension.

2)The domain of these laws were applicable instantaneously across the whole diemension once the universe was created.

Which of the above is correct??

Given that information cannot travel faster than the speed of light, the only way for us to arbitrate between them (ie going past the universe "horizon" and doing some experiments) is impossible. Hence the question is, in a very fundamental sense, totally unanswerable. Batmanand | Talk 16:40, 21 October 2006 (UTC)
Can you equate information with laws? If laws are instead properties of space, then (2) seems to me to be right. Clarityfiend 21:55, 21 October 2006 (UTC)
The big bang theory gets around this whole question by saying that at the beginning of time, the spacelike diameter of spacetime was infinitesimally small. This means: before time, there also was no space. At te big bang, time and space spread out together. The spreading of time and space was, by the way, not limited by the speed of light, as this limitation applies to motion within spacetime, not to the expansion of spacetime itself. Maybe we have articles on the flatness problem and on cosmic inflation which explain more. This stuff is, however, quite difficult to grasp. Simon A. 22:47, 21 October 2006 (UTC)
But the expansion of spacetime isn't the issue here, he's asking about the expansion of constants within the domain of spacetime. Whether spacetime was inconceivably small or 50% as big as it is now, if the laws were to substantiate after spacetime itself came into existance, size and distance doesn't seem to logically be a factor. On a hunch I'd reject both options, going instead for a neater "the laws came into existance the same instant that space time did" style argument.  freshofftheufoΓΛĿЌ  04:46, 22 October 2006 (UTC)
I think what he's trying to say is that when the universe was scrunched up infintesimally small, any fluctuations in what we now think of as constants had the opportunity to settle down to some kind of average value, and then when the universe expanded it carried those average values out. Or something like that. Confusing Manifestation 09:50, 22 October 2006 (UTC)
Can you have fluctuations in an infinitely small space?  freshofftheufoΓΛĿЌ  12:42, 27 October 2006 (UTC)

[edit] Ic 8038 and Ic 555

Both Ic555 and Ic8038 can be used as free running oscillators.Then why have both of them???

8038 can generate triangle, sine and square [1]. 555 can only generate pulse waveforms [2]--Light current 09:11, 21 October 2006 (UTC)
And the 555 is cheaper (and older). And it even has a Wikipedia article: 555 timer IC Simon A. 22:53, 21 October 2006 (UTC)

[edit] SATA computer

I purchased a laptop computer with an SATA hard disk + XP Home Edition. I want to install my previous copy of XP Pro on it but failed (my last computer was dead so it's legal to transfer the XP to my new laptop). The XP installer could not see my Compaq Presario's SATA hard disk. How do I solve this problem? -- Toytoy 14:15, 21 October 2006 (UTC)

Legal may be, but difficult, as you will have already 'activated' the operating system om your old computer and it may not activate on the new one.
You dont say the make of the 2 computers. Is it possible that you had a special version of XP Pro that was designed for (and only recognises) your old computers hardware?--Light current 14:21, 21 October 2006 (UTC)
Have you downloaded the latest XP SP and SATA drivers? When you say it doesnt see it you mean it doesnt detect it at all ? Sounds duff. Try another SATA port, different drive, different lead, etc. By the way, youre in the wrong section mmatt 15:03, 21 October 2006 (UTC)
My XP is a site licensed copy. At lest in theory, I can install it on a new computer even multiple computers. -- Toytoy 15:10, 21 October 2006 (UTC)
It sounds like you have a crippled version of XP Pro that will only install on the computer it was sold with. You need a generic version of XP Pro that will install on any computer - then hope your product key works with it. --Kainaw (talk) 16:42, 21 October 2006 (UTC)
Put the drivers for the SATA disk on a floppy disk and press F6 during install when it says to do so at the bottom. This way you can install SATA/RAID drivers for the disk that Windows will be installed on. - Dammit 16:45, 21 October 2006 (UTC)

[edit] Youngs experiment

In Youngs experiment, why doesnt the wavefunction collapse when it happens on one of the two slits? Whats the difference between the slit and the detector from the photons point of view ? How do you detect a single photon anyway ? Also, if you slightly offset the light source from the centre point between the two slits, would you able to detect which slit it went through depending on the time it took to reach the detector. The problem with this experiment is that its so simple you feel you should be able to outsmart it ! mmatt 14:41, 21 October 2006 (UTC)

Have you read double-slit experiment? What do you mean by "outsmart it"? There's nothing to outsmart. As for detecting a photon - your eyes do it all the time. So do cameras. There are many forms of photon detectors. From the photon's point of view, the slit is an opening to pass through. The detector is a dead-end that it slams into at the speed of light. --Kainaw (talk) 16:41, 21 October 2006 (UTC)
Wait a minute, a lot of the photons do slam into the walls around the slits, don't they? Still, some slip through and give the double-slit effect. —Bromskloss 17:09, 21 October 2006 (UTC)
By outsmart it I mean that that you feel as if you should be able to somehow infer which slit it went through, but of course you cant. Its a trick of the mind, I know.
How do you detect a single photon? I know it can be done, but how? The eye detects lots of photons, not just one. I dont want to get hung up on this, its not really relevant to the main question.
Are the photons that get cleanly through the slit the only ones that contribute to the effect? I always thought they scattered off the edges, thats how they change direction backwards to contribute to the effect, otherwise you would just get a very narrow band directly in the line-of-site from the light source ? mmatt 19:04, 21 October 2006 (UTC)
The eye can detect a single photon! From Rod cell:
A rod cell is sensitive enough to respond to a single photon of light, and is about 100 times more sensitive to a single photon than cones.
As for the scattering you mention, I don't want to say too much because I'm not absolutely sure, but you seem to view the photon as a particle, rather than a wave. A wave spreads out after a small passage. Think of waves on the surface of water. —Bromskloss 20:53, 21 October 2006 (UTC)
Isnt it a particle and a wave ? matt
It's not that we can't detect a single photon, it's that we can't EMIT a single photon. However, we CAN emit a single electron, and detect this. Watch, as the electron experiences the exact same wave-particle duality, pushing the relevance of this experiment into the macroscopic world. :) 81.93.102.3 19:36, 21 October 2006 (UTC)
but the question still applies to electrons, right ? You have to get some scatter off the grating/slit or the electrons/photons shoot off in the wrong direction to interfere ? So if they interact with the slit in this way, why doesnt the slit ( or the sides of the slit ) collapse the wavefunction ? mmatt
Even before reaching the slits, they pass air molecules without collapsing. (Well, I guess some may collapse, but not all.) —Bromskloss 20:58, 21 October 2006 (UTC)


Right. I though about that, but I thought that because an air molecule is so small, you wouldnt collapse the wave function - you would have a superposition of two possible paths one of which involved collision with an air molecule. But with the slit ( or the sides of the split ), which is macroscopic, the wavefunction would collapse mmatt 21:09, 21 October 2006 (UTC)

[edit] Hub Gears Wont Change

I had to remove the black thing that controls my gears in order to tighten a loose nut for the wheel. When I removed the black thing (that covers the nut through which some pin things protrude), the pins came out quite far. Now that I put back the covering, having tightened the nut; a) the gears don't change (no matter where I push the gear lever on the handlebars) and it's stuck in some lowish gear and

b) the gear lever on the handlebar wont push into 6th or 7th gear.

Can anyone diagnose the problem and suggest a solution? The manufacture is 'Sachs' but this was insufficient to draw useful information for me to fix my bike. --Username132 (talk) 15:00, 21 October 2006 (UTC)

I take it that you are talking about a bicycle with derailleur gears, right?
I also assume that it is a standard modern gear shift. Mounting these is not that difficult but also far from trivial. First check by comparing with a working bike that you have remounted the derailleur correctly. Make sure that both its springs operates in the correct way: there is one spring inside the parallelogram shaped lever that moves the derailleurs two little cogwheels over the gears. This spring pulls the derailelleur over the highest gear (i.e. smallest gearwheel) and if you pull with the Bowden cable against this spring, you switch down to lower gears. That your stuck in a low gear seems to indicate that ever the Bowden cable is too tight or the sping is blocked or the derailleur is mounted the wrong way. There is also a chapter on derailleur adjustment in the Wikibook on Bicycle repair. Reading it might be a good idea. Simon A. 23:08, 21 October 2006 (UTC)
Ok, stupid me, I overlooked that your heading explicitly sais that you are talking about hub gears. These were always a bit of a mystery to me, so I don't have a better suggestion than checking that the Bowden cable is ok. Simon A. 23:10, 21 October 2006 (UTC)

Now, I got interested in hub gears and had a look at the German Wikipedia, which explains quite a lot in its article de:Nabenschaltung. There, you find the hint that before disassembling a rear wheel you should switch to that gear that relaxes all the springs in the hub, i.e. the one where the Bowden cable is not under tension (and the little chain nearly all the way in I suppose). If you want to adjust the gearshift, you have to set the switch at the handlebar to a gear certain setting and the hub gear itself to the same gear (by pulling at the little chain I suppose). They give a table which gear to use for adjustments for different makes. (How many gears do you have, and how old is the bike? That should be sufficient to identify the model.) Then, there should be a little bolt that allows to finetune the length of the cable in order to match hub gear and handlebar switch markings. Simon A. 23:56, 21 October 2006 (UTC)

I fixed it by pushing the pin in until it stopped. The "Schaltbox" has the manufacturer 'Sachs' and 'super 7' written on it (it's a 7-gear bike). I don't know the age, cause I bought it second hand but I'd guess that it was made in the last five, maybe even three years. Username132 (talk) 14:09, 22 October 2006 (UTC)
Congrats for solving the proble. By the way, Fichtel & Sachs has been bought be SRAM a couple of years ago, and on their website you find a link Techical Documents with a manual for a "SRAM S7 hub gear". Maybe that's yours, or at least its successor model? Check it out here. Simon A. 09:44, 23 October 2006 (UTC)
Thanks, that's perfect! --Username132 (talk) 16:13, 23 October 2006 (UTC)

[edit] Atheroma

We were always told this was fatty deposits. Our article says it is other sorts of debris. Which is it and if its not fatty, why should we stop eating fatty food?--Light current 16:45, 21 October 2006 (UTC)

So you die later instead of earlier. - Nunh-huh 17:24, 21 October 2006 (UTC)
New Iraq strategy: open a chain of fast food restaurants selling triple cheeseburgers, all the fries you can eat. Clarityfiend 17:37, 21 October 2006 (UTC)
Thirty years ago, the diet police were hating on animal-fat based butter, and proclaimed transfat-based margarine to be healthy. That's why my grandma only uses margarine, hehe. It has flipped around, with transfat being bad too. Then fat was generally bad. But mostly it was saturated fat... but also unsaturated too, except for olive oil, and rapeseed. There was the anti-sugar craze, and the idea that carbohydrates were what really got us fat, not fat. Maybe we should detox or go raw, or vegetarian at least. Organic? Cereal used to be great for you, but it has too much sugar. We don't get enough vitamins and minerals. Ah, chloresterol is what causes heartattacks now, not fat. Heavy metals concentrate in fish. The Cato Institute published an article: As Taubes pointed out in his article, the simplistic notion that dietary fat is bad was a political and business judgment, not a scientific one. Despite ambiguous science, in 1977 a Senate committee led by Sen. George McGovern issued a report advising Americans to consume less fat to avoid "killer diseases" supposedly sweeping the country. The politically dutiful National Institutes of Health soon joined the anti-fat bandwagon, a move that spawned the low-fat food industry. What exactly is the basis for trusting the food alarmists again? The best way I believe is to read the journals yourself, not watch the news. The news will tell you that french fries and breastmilk cause cancer. Remember those days? Atherosclerosis is caused soley due to LDL and VLDL cholesterol, according to every single source I have heard in the mainstream media—even though macrophages, and calcification have quite major roles. I bet the media pushes the chloresterol part because it is scary, and there is someone to blame. What you eat is partially based on your decision—some foods have more or less cholesterol. You don't decide if macrophages or ossification will obstruct or harden your arteries, but you can be to blame for eating yourslef to death.X [Mac Davis] (SUPERDESK|Help me improve) 00:12, 22 October 2006 (UTC)
Here's another free bit of advice: don't get your dietary recommendations from teenagers, and don't get your understanding of the pathogenesis of atherosclerosis from them, either. - Nunh-huh 05:24, 22 October 2006 (UTC)
How can we tell whos a teenager? Most people here act like one (including me) 8-)--Light current 14:08, 22 October 2006 (UTC)


Excellent work from mac davis! I think a lot of the confusion with health is disinformation in the media. they take a "phase 1" study of about 30 people and tout it immediatly as fact just to fill in column inches (or webspace) the result for us is now complete confusion and having to use the wikipedia reference desk and wikipedia to seperate fact from fiction! chocolate helps your heart This one from the BBC is a good example, so now I think "hey maybe a bit of chocolate is good for you" and its a headline based on 20 people!!!

[edit] Sauropod size

I'm trying to write a book on the largest sauropods. The technical information like the discovery, etc., is easy. However, it's the size that continues to differ. Various references such as different books and websites give different statistics. My main sources are EnchantedLearning.com, DinoRuss' Lair, Wikipedia itself, and the DinoArchive and a few of my own calculations. As you can see below, the estimates vary considerably.

1. Argentinosaurus: 22-45 m, 60-100 tons 2. Paralititan: 20-32 m, 60-80 tons 3. Seismosaurus : 30-54 m, 25-150 tons 4. Supersaurus : 24-45 m, 30-100 tons 5. Bruhathkayosaurus: 28-44 m, 150-220 tons 6. Amphicoelias: 37-62 m, 50-170 tons 7. Brachiosaurus: 21-30 m, 15-80 tons 9. Argyosaurus: 20-40 m, 45-80+ tons 10.Ultrasauros: 25-35 m, 40-180 tons

As you can see, the variation is not negligible. I am also aware that these creatures are known for very little fossil evidence. If you can,please suggest corrections for this table (taking into account that these creatures are known for very little fossil evidence). I appreciate the help.

You're using Wikipedia as a source? It's very unrealiable. I suggest using books as your main source, instead of websites.
As for the question, I think it's better to include the range of size estimates in your book. But if you really need to come up with a single figure, try taking the more reliable size/weight estimates and averaging them, while noting in your book that estimates vary wildly. --Bowlhover 19:47, 21 October 2006 (UTC)

[edit] What does KIBRA stand for?

Kibra is the name of a gene associated with memory performance in humans. Kibra sounds interesting and exotic. What is the origin of this name? It is an acronym? Tavilis 18:40, 21 October 2006 (UTC)

Sounds like it is is short for kidney and brain MeltBanana 23:07, 21 October 2006 (UTC)

[edit] Surfaces and bonding

Suppose you got a block of some metal, say gold, and cut it with a sharp blade in a good vacuum, so the cut surfaces had no gases adsorbed on then. Then you pressed the two cut surfaces back together. Would they stick together? Would the cut disappear and the metal become one solid block again? If not, why not?

Also, same question for a network covalent solid, like diamond. Would the cut surface be covered with dangling bonds (unpaired electrons)? Would the cut surfaces attract each other and stick?

Any good books about this stuff? —Keenan Pepper 19:14, 21 October 2006 (UTC)

Yes, I think cut metal parts would fuse together. How would you cut diamond neatly? Diamonds dont stick together for some reason unknown to me. Try welding diamonds!--Light current 19:31, 21 October 2006 (UTC)

What you described with metals is called a cold weld, and you can even do it with two different metals. I don't think it would work with diamonds unless you had an extremely high pressure and temperature to reform the bonds, however. StuRat 20:12, 21 October 2006 (UTC)

Yeah thats what I was trying to say. I suppose it must be possible with diamond given enough temp and pressure as Sturat says. After all, we are told that diamond only forms under condtions of extreme temperature and pressure.--Light current 20:21, 21 October 2006 (UTC)
Thanks, cold weld and asperities (once I figured out the latter was misspelled in the article =P) are much better strings to search for. I don't understand why you say a network covalent solid wouldn't do the same thing, though. There are dangling bonds and no adsorbed gases... why wouldn't they stick together? —Keenan Pepper 23:00, 21 October 2006 (UTC)
I would assume the 'dangling bonds' of the network covalent diamond would just form bonds across the surface. So one 'dangling bond' forming a proper bond with another 'dangling bond' that you've just cut. Meaning when you stick the two pieces together, the 'dangling bonds' won't be dangling anymore. So instead of having one piece of diamond with a cut through it, you'll end up with two discrete pieces of diamond that won't bond with each other. --`/aksha 02:34, 22 October 2006 (UTC)
It seems some of the surface atoms do move and form pi bonds (a process called reconstruction), but the most stable environment for an atom is inside the crystal, so there is still an unavoidable surface energy. —Keenan Pepper 20:48, 22 October 2006 (UTC)

[edit] Zero-point energy and substance compatabilty.

I have read on one of the sites on NASA that they want to use Zero-point energy equilibrium state distruptions, It claims that ZPE is almost like atmospheric pressure, and making changes in its density or distribution might move objects. But how can this be if it is EM and some objects are not effected by EM? Are there any kinds of materials ZPE cannot effect? physicsmoron

Could you at least link to the NASA page so we know what you're talking about? —Keenan Pepper 23:17, 21 October 2006 (UTC)
That is rather speculative. I suggest Casimir effect. I do not believe any objects could be unaffected by the Casimir effect. X [Mac Davis] (SUPERDESK|Help me improve) 00:21, 22 October 2006 (UTC)

[edit] General Relativity

While researching General Relativity, a broad range of theories, mathematic equations, and list of related topics come up. I need to create a project on BASIC ideas of general relativity on a ninth grade level and am wondering what should I include. I'm planning on including Einstien, Gravity, Wormhole, Black holes, and the unification of Special Relativity. Are there any aspects of General Relativity that I am missing that can be explained in layman's terms and pictures? Am I including things that I should not be? Thanks in advance for your speedy replies. I am thankful to have this resource. 72.77.122.83 21:51, 21 October 2006 (UTC) BeBe2

I don't know if I'd include wormholes. They're strictly hypothetical and certainly not a central part of relativity. Clarityfiend 22:02, 21 October 2006 (UTC)
I wouldn't give 9th graders any of the math involved. I would include the theory that gravity works like a sheet of rubber, where if you have a small marble and a baseball on it, they would go toward each other, but the small marble will go toward the baseball more. Gravity wells, which do include blackholes/wormholes. How we orbit the sun, and how satelites are launched to stay in orbit. How gyroscopes work and how they're used for navigation (I never understood that back in high school myself). These are really the ones I would include for 9th graders. How long does this have to be? --Wirbelwindヴィルヴェルヴィント (talk) 22:47, 21 October 2006 (UTC)
Well, I have to be able to disply it on a flat poster board with pictures and captions. 72.77.122.83 23:27, 21 October 2006 (UTC) BeBe2
I like the research topic. Organizationally, special relativity was developed first, and does not include gravity. It is mathematically fairly simple (compared to other topics), and may be accessible to someone with knowledge of algebra (books like Wheeler and Taylor's Spacetime physics assume a knowledge of about algebra 2). The idea is if you assume two things, some interesting results can be shown. For more on this, see Introduction to special relativity, Postulates of special relativity, and (if you're daring) special relativity. One of the results of this work was to show that the distance (as we ordinarily measure it) is not fixed between two points in space. You might see two things one meter apart, while I see them occur two meters apart.
Gravity, in the pre-relatavistic (called "Newtonian") system, depends on the distance between two objects. For instance, the sun is gravitationally far more attractive than the earth, but we feel the earth considerably more since we are closer to it. But in the relatavistic framework, distance is not fixed between two objects... So dealing with gravity becomes a challenge. General relativity deals with gravitation, and is mathematically quite complicated (requiring college level mathematics). Gravity, under general relativity, is not a force but bending of space. An analogy is riding in an elevator: you feel heavier as the elevator starts moving up. You might (if you had never been in an elevator before) think that you're sitting still and gravity had changed to make you heavier. Equivelently, as I sit in my chair, I don't see myself speeding up (just as you don't see any difference in the elevator), however I am, for the purposes of relativistic calculations, being moved in bent space. See Introduction to general relativity.
Black holes form when enough mass gets packed together that nothing can escape from it. It is a consequence of general relativity, and observations seem to support their existence. Wormholes are somewhat more theoretical, in the sense that they are not observed to exist. Hope this helps, --TeaDrinker 23:59, 21 October 2006 (UTC)

[edit] Quantum mechanics? wave theory?

I have been reading a book on quantum mechanics - and I found one section confusing. I hope that I can phrase the question clearly.

When a series of electrons are sent through a slit - then the resulting pattern formed is a wave. The probability that a particular electron lands at any position on the wave is given by the square of the amplitude of the wave.

My question- Why square the amplitude? (I think this is what is happening -see the Wikipedia article "Normalisable wavefunction" )- I know that squaring makes the mathematics more convenient (gets rid of negatives and also gives a convenient sum of 1 when squaring components sine and cosine)But I'm still left with the basic question - why the square?

any help will be very interesting to me

We know that the probability is a real number between 0 and 1. We can observe, say by doing a one-slit experiment, that the probability doesn't have any phase information itself. Yet we also observe the diffraction occurring in the two-slit experiment. Therefore we (well, some very smart physicists like Schrödinger) invent a model that can predict the results of the two-slit and other experiments. For convenience, we express this model in terms of complex numbers inside the unit circle, which can carry phase information, but when multiplied by their complex conjugates always give a real number between 0 and 1.
So the answer is not that there is a reason to square the wavefunction value to get the probability, but that the wave function was invented as a complex number with magnitude equal to the sqare root of the probability in order to explain and predict the experimental observations. -- The Photon 22:25, 21 October 2006 (UTC)
Also note that a wave function whose interpretation is the probability of finding a particle at a particular position would not be a correct model of the observed phenomenon — not if we model the combined effect of two waves using superposition, as we normally do. Since probability is a value between 0 and 1, you will never have destructive interference in the model, which is inconsistent with observations. --71.246.5.19 13:38, 22 October 2006 (UTC)

[edit] G Protein Coupled Receptors

Does anybody have any thoughts on how many GPCRs there are in the human genome? I've read papers that give values of 750, 900, >1000. What's the latest, or most accepted value I should use?

Thanks very much for your help.

Aaadddaaammm 23:38, 21 October 2006 (UTC)

According to this recent article, "the family of G protein–coupled receptors (GPCRs), which in man contains about 791 proteins". --JWSchmidt 23:52, 22 October 2006 (UTC)