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July 23[edit]

Theory of subspace model[edit]

Search for help on theory of subspace model!

'System identification: theory for the user'(2nd edition, 1999) had introduced such theory about subspace model in section 10.4. However, I cannot get that book. If possiable, please help me in finding some materials about that. Your kind help will be appreciated sincerely. —Preceding unsigned comment added by Cjt1982818 (talk • contribs) 01:44, 23 July 2008 (UTC)[reply]

In the case of system identification, I'm guessing that a "subspace model" would refer to Dimensionality reduction. One example is Principal components analysis which projects experimental data onto a subspace of the "parameter space", making for simpler analysis. EverGreg (talk) 09:43, 23 July 2008 (UTC)[reply]

hamburger[edit]

Ground beef is called hamburger. What do you call ground horse meat, ground ham and all of the other ground meats? -- adaptron (talk) 04:19, 23 July 2008 (UTC)[reply]

Just ground meat or mince (outside North America). 81.174.226.229 (talk) 09:03, 23 July 2008 (UTC)[reply]

Isn't 'hamburger something to do with the German city/town of Hamburg? If I wasn't at work i'd research and get a definitive answer - as it stands I hope one of the two articles references it... 194.221.133.226 (talk) 09:28, 23 July 2008 (UTC)[reply]

Just checked the Hamburg article - it is to do with the place - see the 'cuisine' section (http://en.wikipedia.org/wiki/Hamburg#Cuisine) 194.221.133.226 (talk) 09:29, 23 July 2008 (UTC)[reply]

This is also mentioned in the article Hamburger, which you have already linked to, under Definition. Jdrewitt (talk) 11:59, 23 July 2008 (UTC)[reply]

Not everyone calls ground beef hamburger, though, as it can be used for other purposes, especially meatloaf and meatballs. --Russoc4 (talk) 13:09, 23 July 2008 (UTC)[reply]

I'd go further and ask: does anyone call ground/minced beef "Hamburger"? Fribbler (talk) 13:12, 23 July 2008 (UTC)[reply]

My mom calls it "hamburg" (Western Pennsylvania, USA). -- Coneslayer (talk) 13:13, 23 July 2008 (UTC)[reply]

I've never even known it could be a synonym. A hamburger for me is most likely the premade burger or perhaps the pattie but defintely not ground/mince meat. BTW, is ground ham actually common? Ground pork is but I've never heard of ground ham. Nil Einne (talk) 13:38, 23 July 2008 (UTC)[reply]

Presumably the people who named Hamburger Helper? AlmostReadytoFly (talk) 13:50, 23 July 2008 (UTC)[reply]

I believe they call it either hamburg or hamburger in Maine. Not in NY/NJ/CT though.--Russoc4 (talk) 13:56, 23 July 2008 (UTC)[reply]

"Hamburger" has no etymological connection to "ham". It was originally a "hamburger steak", i.e. a steak made the way people in Hamburg make them. Similarly a "frankfurter" is a sausage of the kind they make in Frankfurt. I suppose "hamburger" can then by extension mean meat sold as suitable for making a hamburger. Minced (ground) pork is called "sausagemeat" in the UK; if you wanted to make sausages at home it would be the thing to choose. Itsmejudith (talk) 14:00, 23 July 2008 (UTC)[reply]

Pork mince is available labelled as such in every supermarket I've seen. Sausagemeat contains other ingredients such as rusk. It's not easy to link products, but you can browse here to see. AlmostReadytoFly (talk) 14:08, 23 July 2008 (UTC)[reply]

"Two great nations separated by a common language?" It's hard to imagine sausage made of rusk. On the U.S. side of the pond it is "ground beef" in the store, and might become a hamburger, meatloaf, meatballs, sloppy joe, tacos, or lasagna. One would not list "hamburger" as an ingredient in any of these foods. The repeated findings of E coli or other pathogens in groundbeef made in giant meat processing plants, where intestine contents from one processing mishap may be mixed in with hundreds of other cows in a given serving of ground beef, makes me avoid steak tartare, which was quite tasty back in the day of beef being locally ground. Ive never heard "minced" applied to meat. "Mincemeat" in the U.S usually contains no meat, except perhaps for fat. Edison (talk) 16:20, 23 July 2008 (UTC)[reply]

Mincemeat in the UK no longer contains meat either (though it used to), but minced meat does since mincing = grinding AlmostReadytoFly (talk) 07:54, 24 July 2008 (UTC)[reply]

N.B. In case it wasn't obvious, I was refering to adaptron who asked about ground ham whice I've never heard of before Nil Einne (talk) 17:11, 23 July 2008 (UTC)[reply]

Unindent. Google finds thousands of entries for "ground ham". The few I checked were recipes using both ground ham and ground pork. Perhaps people grind their own ham at home - I can't remember ever seeing ground ham in the meat section. Although there is deviled ham. Rmhermen (talk) 18:05, 23 July 2008 (UTC)[reply]

Apparently it's used industrially [1] Nil Einne (talk) 18:46, 23 July 2008 (UTC)[reply]

And in ham salad (ground at home, in my experience). -- Coneslayer (talk) 19:02, 23 July 2008 (UTC)[reply]

Actually, AlmostReadyToFly, to me mincing certainly does not = grinding. In my idiolect, 'grinding' is pulverisation by crushing or friction, and not by cutting or tearing; something squashy like meat cannot be ground. I am of course aware that Americans talk of 'ground beef' but to me it can only be 'minced'. --ColinFine (talk) 18:52, 26 July 2008 (UTC)[reply]

Ground meat is "pulverized by crushing" through the use of a meat grinder. Mincing meat using some cutting instrument such as a food processor has a different result. Grinding is superior to mincing for most culinary applications such as making hamburger, meatballs, or meatloaf. —D. Monack ^talk 07:42, 28 July 2008 (UTC)[reply]

science[edit]

What is the graph called that has all the scientific symbols on it?— —Preceding unsigned comment added by 203.202.70.133 (talk) 05:12, 23 July 2008 (UTC)[reply]

You'll have to be much more specific than that. What do the scientific symbols look like? Can you post a sample of the graph? What's the title? Where did you see it? --Bowlhover (talk) 05:43, 23 July 2008 (UTC)[reply]

(Winging it here) Periodic table? --Kurt Shaped Box (talk) 06:55, 23 July 2008 (UTC)[reply]

That was gonna be my guess also. I don't know why, but many of my students call any sort of organized display of information a "graph". DMacks (talk) 07:04, 23 July 2008 (UTC)[reply]

They're certainly graphics. I imagine many people either confuse the two words or treat them as synonyms. -- BenRG (talk) 10:51, 23 July 2008 (UTC)[reply]

Technically they're right to call it a graph (ie not incorrect).. if the answer was the periodic table..?87.102.86.73 (talk) 12:18, 23 July 2008 (UTC)[reply]

I suppose it's a bit like how if all you knew were horses, you'd refer to a Frisian cow as 'a fat, funny-shaped, black and white horse'. Or something. :) --Kurt Shaped Box (talk) 18:08, 23 July 2008 (UTC)[reply]

repetitive behavior[edit]

Is there any disorder besides autism or other disorders in the autism spectrum (like Asperger syndrome where the affected person exhibits a pattern of repetitive behavior, specially repetitive verbal behavior? —Preceding unsigned comment added by Mr.K. (talk • contribs) 09:30, 23 July 2008 (UTC)[reply]

OCD? Usually not verbal, though. -- Aeluwas (talk) 09:34, 23 July 2008 (UTC)[reply]

(ec) Schizophrenia can involve stereotyped speech patterns, as can Tourette Syndrome. Also see Echolalia for one specific type of verbal repetition. 12:53, 23 July 2008 (UTC)

Tourette syndrome? -- Coneslayer (talk) 12:51, 23 July 2008 (UTC)[reply]

Then there are those who repeatedly ask the same questions here, I wonder what medical disorder they have ? StuRat (talk) 15:06, 23 July 2008 (UTC)[reply]

(from Forgetfulness#Organic_causes - Alzheimer's, Amnesia, Dementia ?)87.102.86.73 (talk) 15:57, 23 July 2008 (UTC)[reply]

Concusion, and if you want to call it a condition, Nagging. --Shaggorama (talk) 06:23, 24 July 2008 (UTC)[reply]

Methotrexate in use for RA[edit]

Can it please be explained to me why Methotrexate is used alongside Folic Acid. My boyfriend has been prescribed 5mg of Methotrexate once per week, with 5mg of Folice Acid every other day of the week. How does the Folic Acid react with Methotrexate. What exactly does it do to help RA? thank you

Dawn Gardiner 88.109.199.248 (talk) 09:46, 23 July 2008 (UTC)[reply]

For those (like me) who couldn't guess what "RA" might be, it's rheumatoid arthritis. --Sean 13:07, 23 July 2008 (UTC)[reply]

Methotrexate is an antifolate drug. (I recommend reading these links) Reducing the amount of available folic acid is beneficial to patients with autoimmune diseases such as RA. However, we don't want to eliminate all folic acid as it is needed for cell division. So a supplement is given. This is a bit of a rushed introduction to a relatively complex topic but I hope it helps! Fribbler (talk) 14:06, 23 July 2008 (UTC)[reply]

Folic acid (or folinic acid) is commonly given with methotrexate to decrease methotrexate's gastrointestinal side effects. As Fribbler described above, one of methotrexate's actions is to impair the synthesis of folic acid, an important vitamin in DNA synthesis and cell division. The gastrointestinal side effects presumably result from methotrexate inhibiting cell division in the GI system, leading to irritation, burning, etc. Adding folic acid back into the system restores the ability of the stomach and intestines to regenerate cells efficiently, thus improving the side effect profile of the drug. --David Iberri (talk) 02:50, 26 July 2008 (UTC)[reply]

mostly water[edit]

Since the human body is made mostly of water, is it possible for one to melt, and how would this be achieved? 'cause I know this one girl and I swear when ever she phones me or touches me I start to melt. —Preceding unsigned comment added by 193.115.175.247 (talk) 12:28, 23 July 2008 (UTC)[reply]

You know that ice (solid water) melts at 0 °C and that your body is much warmer than that. Therefore, any water in your body is already "melted". Physically anyway:) DMacks (talk) 12:48, 23 July 2008 (UTC)[reply]

(Insert voice of favorite American sitcom dad.) Awww, how cute. You're not melting; I think you've got puppy love. Known in American slang as a "crush" nowadays. Probably among your first; or, at least you feel different about this girl than any other you've felt; hence you're unsure what that feeling of "melting" is.

While we can't give medical advice, I will say this - if my theory is correct, then the first thing you should do is ask how she feels when she talks to you. It's okay if one feels something and the other doesn't right away, because those feelings aren't what's going to last; feelings come and go. Keep maintaining the friendship, and remember that that friendship should be the key to your relationship. Find out what she likes, and do fun stuff together. Maybe it'll last,a nd maybe it won't. But, I know one thing. That feeling can be pretty intense. But, it's fun, too. Just don't go too fast with any girl, okay? The key to a girl you like is, would you still like her if you were both really old, bald, and incontinent. but, it's okay to have fun and think about this situation now; because those feelings are real. It's part of gorwing up.

Boy, that *did* sound like a sitcom, huh? :-) Yes, that's the way I talk, too.

Oh, and to the original question, for something to melt it has to be at a very high heating point. So, for skin and bones to literally melt, you'd have to be in a blast furnace or something. Yes, the body is mostly water, but the part that isn't is very solid and rugged.Somebody or his brother (talk) 12:56, 23 July 2008 (UTC)[reply]

P.S.: Feel free to show her this response if you struggle for a topic of conversation, or how to approach your puppy love. It may help you talk about and emphasize the friendship part and also be good for a laugh, perhaps. Good luck.Somebody or his brother (talk) 13:20, 23 July 2008 (UTC)[reply]

Rather, the proteins will denaturate on heating which won't make you very attractive. --Ayacop (talk) 16:09, 23 July 2008 (UTC)[reply]

The fat will melt. Wick effect has some interesting if potentially grusome discussion of the potential effects of such Nil Einne (talk) 16:47, 23 July 2008 (UTC)[reply]

It might be best to avoid being quite so poetic until after the first date - this isn't the renaissance, you might just scare her off! If the first date goes well, though, then go for it! --Tango (talk) 21:35, 23 July 2008 (UTC)[reply]

The human body is made mostly of water in the same general way as a water balloon is. Ever seen a water balloon melt? — DanielLC 17:10, 23 July 2008 (UTC)[reply]

"When your heart's on fire, you must realize, smoke gets in your eyes." Itsmejudith (talk) 17:11, 23 July 2008 (UTC)[reply]

Yes. Just this morning I took a water balloon out from the freezer and watched it melt. Nil Einne (talk) 18:44, 23 July 2008 (UTC)[reply]

Wht did you put a water balloon into your freezer, may I ask? --Bowlhover (talk) 01:49, 24 July 2008 (UTC)[reply]

Nil, clearly that was an ice balloon that melted into a water balloon. :) — Scientizzle 18:50, 23 July 2008 (UTC)[reply]

By the way, when all the water is removed, the human body turns into a cuboctahedron made of some sort of crumbly foam rubber or something. Then the aliens take over your ship and try to fly it back to their own galaxy. --Trovatore (talk) 02:01, 24 July 2008 (UTC)[reply]

Not so! You turn into a small pile of white powder, but adding water will make you OK again. And I have a reference to prove it! [2] 17:31, 26 July 2008 (UTC) —Preceding unsigned comment added by DewiMorgan (talk • contribs)

When in doubt, always seduce the best-looking alien. And speak ... quickly with ... odd pauses. Franamax (talk) 17:44, 26 July 2008 (UTC)[reply]

biochar[edit]

Is there a Wikipedia article or other online reference that shows the yield of biochar, bio-oil and syngas from various types of municipal organic waste such as sludge and bio-mass? —Preceding unsigned comment added by Adaptron (talk • contribs) 15:59, 23 July 2008 (UTC)[reply]

The relevant articles are gasification and pyrolysis though I can't find any figures there - it probably also depends on the exact process used - which you could be more specific about.

I'd recommend trying searching for 'waste gasification' or 'waste pyrolysis' as a start.87.102.86.73 (talk) 16:44, 23 July 2008 (UTC)[reply]

Temperature scales[edit]

What temperature scales other than Fahrenheit were in common use in what countries before adoption of celsius? --Random832 (contribs) 16:10, 23 July 2008 (UTC)[reply]

The Réaumur scale. Itsmejudith (talk) 16:17, 23 July 2008 (UTC)[reply]

I guess this isn't what you mean but Centigrade. You might also be interested in Temperature conversion Nil Einne (talk) 16:41, 23 July 2008 (UTC)[reply]

No temperature scale was in widespread use before the seventeenth century, but according to the thermometer article:

"In 1665 Christian Huygens suggested using the melting and boiling points of water as standards, and in 1694 Carlo Renaldini proposed using them as fixed points on a universal scale. In 1701 Isaac Newton proposed a scale of 12 degrees between the melting point of ice and body temperature. Finally in 1724 Daniel Gabriel Fahrenheit produced a temperature scale which now (slightly adjusted) bears his name."

A more detailed history can be found here. As for the countries that adopted these scales, the Delisle scale was used in Russia from 1738 on and the Reaumur scale was widely used in Europe, particularly in France, Germany, and Russia. --Bowlhover (talk) 22:12, 23 July 2008 (UTC)[reply]

physiology of respiratory system[edit]

How long humans can stay under water holding their breath? How long perl-collectors in Tahiti can hold their breath under water? What is the world record of holding the breath? Dimitar (medical student) —Preceding unsigned comment added by Velimir14 (talk • contribs) 16:40, 23 July 2008 (UTC)[reply]

According to this article the world record is 10 minutes 12 seconds. -- Mad031683 (talk) 17:10, 23 July 2008 (UTC)[reply]

Hi. Remember however, that techniques such as hyperventilation before diving can cause drowning, see shallow water blackout. Thanks. ~A H 1^(TCU) 22:19, 23 July 2008 (UTC)[reply]

According to this Reuters article, the record for underwater breath holding, set by David Blaine, is 17 minutes and 4 seconds. The average time is 1 minute, according to http://www.news.harvard.edu/gazette/2005/10.13/01-divers.html. --Bowlhover (talk) 01:40, 24 July 2008 (UTC)[reply]

Water turns cloudy after boiling[edit]

Please help solve this mystery: water ~~from a water filter~~ turns slightly cloudy after boiling. The water is somewhat high in dissolved minerals. ~~The filter is supposed to reduce a variety contaminants in the water, including lead.~~ Before boiling, the ~~filtered~~ water is clear.

(Edited to add:) A simple experiment reveals that water from the source turns cloudy after boiling, filtered or not. —Preceding unsigned comment added by 96.245.76.192 (talk) 17:44, 23 July 2008 (UTC)[reply]

Could this not merely be lots and lots of tiny air bubbles? I know that the water from my hot tap sometimes comes out milky-white due to this. If I put some in a glass and leave it to settle, I can see the bubbles (quite slowly) rising to the top, with the water below clearing. --Kurt Shaped Box (talk) 18:44, 23 July 2008 (UTC)[reply]

I'm aware of that possibility, but this is not a case of it. Water from the tap is initially clear. It only turns slightly cloudy after boiling. Giving things time to settle doesn't change the cloudiness. --96.245.76.192 (talk) 23:31, 23 July 2008 (UTC)[reply]

Could it be water hardness coming out as a fine suspension after boiling - some sorts of hard water do this. Also are you sure it's not your heating device - have you tried boiling in a different thing - eg a very clean pan or dish?87.102.86.73 (talk) 19:05, 23 July 2008 (UTC)[reply]

Not likely to be the "heating device"—the cloudiness is observed after the water has been boiled in a glass kettle, which seems clean. Your hardness explanation seems more plausible. --96.245.76.192 (talk) 23:31, 23 July 2008 (UTC)[reply]

Sounds like carbonate hardness. If you have high levels of carbonate minerals in your water, boiling the water causes a portion of them to precipitate. My guess is that your water comes from a limestone aquifer. -- 128.104.112.147 (talk) 21:14, 23 July 2008 (UTC)[reply]

That seems plausible. So the cloudiness is dissolved calcium bicarbonate turning into calcium carbonate? --96.245.76.192 (talk) 23:31, 23 July 2008 (UTC)[reply]

Yes exactly, and if you live in a hard water area it's probably the answer. Wait a minute - your filter should remove this I think?87.102.86.73 (talk) 00:07, 24 July 2008 (UTC)[reply]

Salmons - polyphyletic or paraphyletic?[edit]

Given that the common name "salmon" does not correspond exactly with any taxonomical group, and that some "salmon" species are closer to trouts than to other "salmons", should the term "salmon" be considered as:

a) a paraphyletic grouping
b) a polyphiletic grouping
c) a vernacular name with no corresponding taxonomical group (or groups)

Which of these would fit best? Thanks. Leptictidium (mt) 19:32, 23 July 2008 (UTC)[reply]

I believe that C is correct. "A" might be correct if it was determined that the common ancestor to the group was a salmon and that trout form a monophyetic group that could be pruned from the tree (see paraphyly). "B" would only be correct if the term salmon included multiple monophyletic groups separated by other groups and I don't think that's the case (hence my qualifier at the beginning). Matt Deres (talk) 20:01, 23 July 2008 (UTC)[reply]

[edit conflict] I'd say C. To determine whether the group was paraphyletic or polyphyletic, you'd have to know whether the most recent common ancestor of all salmon was called a salmon. My guess would be that we don't know exactly what fish that was, and that we certainly haven't thought to decide whether it was a "salmon" or a "trout". --Allen (talk) 20:08, 23 July 2008 (UTC)[reply]

I don't think that really makes sense <quote> It was shown, however, that the inclusion of ancestors in the classification leads to unavoidable logical inconsistencies</quote>

You should ignore that inconsistency.87.102.86.73 (talk) 20:22, 23 July 2008 (UTC)[reply]

(edit conflict) A:

I'd assume 'A' in the absense of contrary data.

In the absence of contrary data I'd assume salmon ie Salmonidae subfamily Salmoninae to be paraphyletic

Assuming all 'salmon' ~~(Salmonidae)~~ Salmoninae have a common ancestor (why not?) (additional - common ancestor should not have any descendants outside salmoninae prefereably) then the salmon are paraphyletic, if you describe a group 'salmon' minus trout etc then that group would be monophyletic - but there is no name for such a grouping currently.

In phylogenetics, a group of organisms is said to be paraphyletic if the group contains its most recent common ancestor but does not contain all the descendants of that ancestor.

B is wrong because all salmon are found in the same subfamily - if there were 'salmon' in a different family as well then B would be right.

C is wrong because all salmon are found in the group Salmoninae therefor there is a corresponding taxo-group (that is fairly narrow in its spread). —Preceding unsigned comment added by 87.102.86.73 (talk) 20:19, 23 July 2008 (UTC)[reply]

CORRECTION B could be right as well if the subfamilies Oncorhynchus and Salmo each have a common ancestor, and there is a common ancestor of the common ancestors which has descendants outside these two subfamilies..

How are we supposed to know? is there any 'educational material' associated with this question which may contain answers to this problem?

The question is unanswerable as is.87.102.86.73 (talk) 20:45, 23 July 2008 (UTC)[reply]

I don't follow you. What doesn't make sense? What are you quoting from? Why would I want to ignore an inconsistency? What do you mean by asking whether two groups have a common ancestor? (Any two cellular life forms on Earth have a common ancestor.) It seems like you might be assuming that "salmon" = Salmonidae, but I think the OP was referring to fish called salmon, not all members of Salmonidae. --Allen (talk) 22:12, 23 July 2008 (UTC)[reply]

Oops sorry - mistake I've corrected that (see above)

As to the other bit - what I'm saying is that the question doesn't give enough information for us to decide? even though it says

Quote: some "salmon" species are closer to trouts than to other "salmons"

I can't read enough into that to make a decision either way. I quoted from the articles Paraphyly and Paraphyly as well for the second quote. You might want to ignore an inconsistency if it's of the kind described by yourself above, since the question is not of an (possibly extinct) ancestors 'name'.

The paraphyly/polyphyly question is answer by finding the ancestors (A and B) of both groups (that's two ancestors) and seeing if those two ancestors are either

One or the other is an ancestor of the other (A of B , or , B of A), or their common ancestor (C) has no descendants (along a branch not going through A or B) that are separate from the two groups

Or that the two ancestors of the two branches of 'salmon' (A and B again) have an ancestor themselves (C) that has descendants that have evolved into a set of species going through a branch not including A or B.

Did I get that right after the correction to the name? Maybe I'm not reading enough into the statement at the beginning - if so what is it?87.102.86.73 (talk) 22:59, 23 July 2008 (UTC)[reply]

(obviously common ancestor means 'most recent common ancestor')87.102.86.73 (talk) 23:41, 23 July 2008 (UTC)[reply]

My interpretation was that the OP, by the word "salmon", meant neither Salmonidae nor Salmoninae. Rather, they just meant all those species that have the English word "salmon" in their common name. E.g. Chinook salmon would be a "salmon", while Biwa trout would be a "trout", even though they're both in the same genus of Salmoninae. That's why I said the answer was C: the common word "salmon" does not correspond to any taxonomic group. --Allen (talk) 23:48, 23 July 2008 (UTC)[reply]

I made that assumption too. I suppose it must be C then since I can't show either A or B from the info given, and it states something very similar in the question - I must have been trying to be 'too clever' - C.87.102.86.73 (talk) 07:17, 24 July 2008 (UTC)[reply]

I still don't see how C follows though: "Salmon" could have (from the information given) corresponded to say, a family of 'salmon' and another sub-family of 'salmon' (not closely related or necessarily in the same order etc),but with a 'sister' group consisting of 'trout' in the same family. This would have made C wrong as it did say 'corresponding group or groups'. Thank god it's not my exam.!87.102.86.73 (talk) 07:22, 24 July 2008 (UTC)[reply]

As far as I can see you'd need a time machine to answer this, or more information.87.102.86.73 (talk) 23:43, 23 July 2008 (UTC)[reply]

Nuclear Physics[edit]

Kindly please answer me why don't Bosons obey the 'Pauli Exclusion Principle'?Asim Chatterjee (talk) 20:04, 23 July 2008 (UTC)[reply]

Did you read the Pauli Exclusion Principle article? DMacks (talk) 20:08, 23 July 2008 (UTC)[reply]

Yes —Preceding unsigned comment added by Asim Chatterjee (talk • contribs) 20:10, 23 July 2008 (UTC)[reply]

Did its many paragraphs explaining the answer to your question in several different ways not suffice? DMacks (talk) 20:14, 23 July 2008 (UTC)[reply]

HEY! It didn't explain why - It just said they don't obey..87.102.86.73 (talk) 20:25, 23 July 2008 (UTC)[reply]

Sorry but it did not.I'll be immensely thankful to anyone who would like explain to me the answer in brief. —Preceding unsigned comment added by Asim Chatterjee (talk • contribs) 20:18, 23 July 2008 (UTC)[reply]

It is not perfectly explained therein. —Preceding unsigned comment added by Asim Chatterjee (talk • contribs) 20:51, 23 July 2008 (UTC)[reply]

In brief, the exclusion principle is a result of particles having anti-symmetric wave-functions. That means only fermions, not bosons, are subject to it.

Let's look at the PEP article: "According to the spin-statistics theorem, particles with integer spin occupy symmetric quantum states, and particles with half-integer spin occupy antisymmetric states". The math in the "Connection to quantum state symmetry" section starts from the antisymmetry property and leads to exclusion. You asked about bosons, which by definition are integer-spin particles, and therefore have symmetric wavefunctions. I'll try the same math, but with a symmetric wave-function: if there is symmetry, A(x,y) = A(y,x), which does not lead to a conclusion of A(x,x)=0. Therefore, there can be a non-zero chance that two such particles could both be in state x. DMacks (talk) 20:56, 23 July 2008 (UTC)[reply]

So why are The wave functions of a system of identical half-integer-spin .. (are)... anti-symmetric under exchange - what does this mean, are the 'particles' (fermions) distinguishable then? Is there a simple way to understand this?87.102.86.73 (talk) 21:05, 23 July 2008 (UTC) fuck it - i remembered I don't care87.102.86.73 (talk) 21:09, 23 July 2008 (UTC)[reply]

I'm not a quantum physicist, but I'll give you a stab at it, given my The Elegant Universe/A Brief History of Time/etc. inspired understanding. (With the hope that more knowledgeable people will correct/expand upon my misstatements.) The key point is that, if they have the same quantum numbers, particles are indistinguishable. An electron is an electron is an electron, and a photon is a photon is a photon (assuming identical energy, momentum, etc.). Given this, when you do all the fancy quantum mechanical calculations you have to take into account the possibility of exchange. That is, if we have electron 'A' over here and electron 'B' over there (metaphorically speaking), we have to write all the equations such that the equations still work if we'd have electron 'B' over here and electron 'A' over there (since the electrons aren't carrying little 'A' and 'B' labels). So why does this matter? Well, since electrons are Fermions, and thus carry spin 1/2, their wavefunctions are anti-symmetrical. This means that you can't write quantum mechanical equations where two electrons have the same quantum state - if you did, you'd find out that once you include the exchange terms, the terms cancel out and your probability density goes to zero, violating a whole slew of conservation laws. Bosons, on the other hand, have symmetric wavefunctions, on account of having integer spins. This means that the probability densities don't cancel when you include all the exchange terms, leaving you with a non-zero (i.e. possible) probability density. This means that almost an infinite number of bosons can have identical quantum numbers. (The articles Bose–Einstein statistics and Fermi–Dirac statistics may help to clarify.) So the surprising result is not that Bosons don't obey the exclusion principle, but that the equations for Fermions work out such that they do. (Again, not an expert - please correct where needed.) -- 128.104.112.147 (talk) 21:09, 23 July 2008 (UTC)[reply]

Yes -you didn't explain anything - ie you didn't answer the question at all- you just restated the result, and quoted some books. That is not an explanation.

Your explanation "..the terms cancel out and your probability density goes to zero..." may well be true when the two particles have spin +1/2 and -1/2 but what about the same situation with particles spin +1 and -1 ... as far as I can see the situation is the same.. maybe there is an explanation for this?87.102.86.73 (talk) —Preceding undated comment was added at 21:18, 23 July 2008 (UTC)[reply]

So what do I read to find out why W(x,y)=-W(y,x) (W represents wavefunction?) for fermions (I see that this can explain the exclusion principle).87.102.86.73 (talk) 21:37, 23 July 2008 (UTC)[reply]

That's the definition of antisymmetry. The spin statistics theorem article is pretty technical, but it links this site that might be more understandable.

It's just a technical way of saying that the wave-function (the mathematical description of a thing) of a half-integer-spin particle is antisymmetric ("half integer spin means that the phase change for a 360 degree rotation is -1") whereas an integer-spin particle's is symmetric ("[i]nteger spin means that the phase change for a 360 degree rotation is 1").

Consider the difference between a half-wave and a full-wave of the sine function: going from the start to the end of each of these shapes begins at zero and ends at zero and both start out by going "up" (increasing y values). However, one comes back to zero by going down whereas the other comes back to zero by going up. You wind up back where you started, but in one case you're now there going the same way you started and the other you're now going in the opposite direction from how you started. Thus, the symmetry of these two cases is different. These two cases are similar to integer vs half-integer spins: the number of half-waves corresponding to the particle.

Now, if two things are symmetric, you can exchange them easily, like the you and your reflection in a mirror (you and your reflection could swap places and nobody could detect that). If two things are anti-symmetric, the mirror image is not the same (it's the opposite, like a trick mirror or a simple microscope). You and the image are now distinguishable because you go in opposite ways (move a microscope slide to the left, and you see the image through the eyepiece move right, etc.).

Two things that are antisymmetric are always distinguishable (they never exist in completely the same state) because something about them is noticeably different. Two things that are completely the not distinguishable are symmetric (could be secretly swapped for one another).

So there we have it: antisymmetry implies distinguishability, which is the Pauli Exclusion Principle. Multiple bosons indeed can exist in identical states (Bose–Einstein condensates). DMacks (talk) 21:40, 23 July 2008 (UTC)[reply]

When you quote "..half integer spin means that the phase change for a 360 degree rotation is -1 .. [i]nteger spin means that the phase change for a 360 degree rotation is 1..." is that any more than restatement of

W(x,y)=-W(y,x) for half integer spin

W(x,y)=W(y,x) for integer spin

?

Also "360 rotation" - what is that - is it another way of saying swapping, or is there more to it? If so where can I read about the properties of things that change on undergoing a "360 rotation" and why they do it. Specifically those whose 'phase' changes sign upon 360 rotation (since the other seems trivial)? 87.102.86.73 (talk) 22:02, 23 July 2008 (UTC)[reply]

I thank you both whole-heartedly for helping me.Dmacks, I'll be ever grateful to you for answering me.Now it does not appear to me tough indeed to find out the reason.Thank you once again.117.201.97.128 (talk) 05:54, 24 July 2008 (UTC)[reply]

Thanks to yuu both.Both of you have done an immense favour to me.117.201.97.128 (talk) 05:56, 24 July 2008 (UTC)[reply]

is cortisone synthetic cortisol?[edit]

Is cortisone a patented form of cortisol? I understand the drug companies pushed cortisone because of that, is that true? Thanks Mathityahu (talk) 20:08, 23 July 2008 (UTC)[reply]

No. see cortisone and cortisol - the chemical structures and formulae are different.87.102.86.73 (talk) 20:28, 23 July 2008 (UTC)[reply]

I assume by 'patented' you mean 'trade name for' - perhaps you didn't - if so please expand.87.102.86.73 (talk) 20:29, 23 July 2008 (UTC)[reply]

You may be confusing cortisone with hydrocortisone; the latter is the name commonly given to synthetic cortisol. --David Iberri (talk) 02:40, 26 July 2008 (UTC)[reply]