Wikipedia:Reference desk/Archives/Science/2013 May 2

= May 2 =

How do scientist/astronomer figure out the star loss mass at giant/supergiant tip
I have heard when higher mass main sequence runs out of hydrogen and fuse helium by the time they get to giant or supergiant tip they lose roughly 7/8 of their mass. I don't know how do scientist figure out the variables, if the variable are guaranteed to be right, or they can as well guess out. I hear when sun gets to giant tip it will lose roughly 1/3 of the original mass, previous calculations shows 1/4. Do scientist even know how much mass sun will have lost when it gets to RGB and AGB tip, or they just group all the stars together and find a pattern. Or the variables they present is at least 70% cavity guess. Is there ways to say how much accuracies and errors academic research documents contains. Or the best answer is some academic paper contains more error, some academic paper may contain more accuracies. Is Academic research paper (=) dumping information they have available (+) fill in the gap (any missing and uncertain cavities they make wild guess). The thing is most people cannot see the guesses research documents have.--69.233.254.115 (talk) 01:30, 2 May 2013 (UTC)


 * Oops, everything is found over . I forgot the query type so long ago.--69.233.254.115 (talk) 01:43, 3 May 2013 (UTC)


 * OK, glad you found it. I'll mark this Q resolved. StuRat (talk) 07:00, 3 May 2013 (UTC)

Temple of the rats
See Karni_Mata. Apparently rats are protected and fed there. So, what controls their population ? StuRat (talk) 03:53, 2 May 2013 (UTC)


 * From what I understand, they're only protected as long as they remain in the temple. When they venture outside, they are are at the mercy of their natural predators. Plasmic Physics (talk) 03:56, 2 May 2013 (UTC)


 * If I brought a few pet cats in, would that be trouble? ←Baseball Bugs What's up, Doc? carrots→ 04:05, 2 May 2013 (UTC)


 * I imagine 20,000 rats would make short work of "a few pet cats".--Shantavira|feed me 15:26, 2 May 2013 (UTC)
 * That might depend on the sizes of the cats and the rats. ←Baseball Bugs What's up, Doc? carrots→ 16:38, 2 May 2013 (UTC)
 * A rat terrier would be a lot more trouble. Looie496 (talk) 16:58, 2 May 2013 (UTC)
 * Whatever it takes. ←Baseball Bugs What's up, Doc? carrots→ 22:13, 2 May 2013 (UTC)

Hemorrhoid infections
Why don't hemorrhoids instantly become infected or cause serious infection that would surely result if an open wound on some other body part were so directly exposed to feces?68.36.148.100 (talk) 04:09, 2 May 2013 (UTC)


 * They are covered with "anoderm" (kinda like skin) - that presumably prevents fecal material from entering and infecting. SteveBaker (talk) 04:13, 2 May 2013 (UTC)

Butt, some break don't they? The blood in stool article says they are the #1 reason for it.68.36.148.100 (talk) 04:18, 2 May 2013 (UTC)


 * Only in New Jersey. Otherwise, see the section about fissures. ←Baseball Bugs What's up, Doc? carrots→ 04:39, 2 May 2013 (UTC)


 * Wow, I wanted to ask this exact same question a few days ago. Yes, it certainly seems that if blood gets into stool then stool might get into the blood.  I wonder if there is some special amped up immune response in that area, and, if so, if we could learn to extend that the the rest of the body, when needed. StuRat (talk) 04:49, 2 May 2013 (UTC)
 * Best typo ever. Evanh2008 (talk&#124;contribs) 01:54, 3 May 2013 (UTC)


 * Found, but neither is quite what I'd call an answer. Wnt (talk) 01:37, 3 May 2013 (UTC)

Deballocker
Is it true that in World War 2, the Germans used a type of landmine that was specially designed to castrate its victims rather than kill them? 24.23.196.85 (talk) 05:36, 2 May 2013 (UTC)


 * Our article Anti-personnel mine explains that such mines are usually intended to injure, not kill, their victims. I guess that the German S-mine could earn a reputation as designed for castration since it was launched about a metre into the air before detonating. However, there is no way that the S-mine or other mines of the same type could be accurate enough to castrate someone, except by chance. Sjö (talk) 05:45, 2 May 2013 (UTC)


 * I agree - damage to the enemies' legs was the real goal of these things - take people out of action as effective combatants - but without killing them, so they clog up the medical facilities, consume resources behind the lines, slow any advance, cause uninjured fellow soldiers to take extra risks to save them...that kind of thing. Castrating someone won't necessarily stop them from fighting again in the future - but ripping their legs to shreds most certainly will. SteveBaker (talk) 13:15, 2 May 2013 (UTC)


 * On a pedantic note shouldn't it be "debollocker". Richard Avery (talk) 13:23, 2 May 2013 (UTC)


 * 'Ballocks' is a known alternative spelling. Chaucer uses it in (I think) the Pardoner's Prologue, and there's a type of Renaissance fighting-knife known as a ballock-dagger (apparently due to the handle-shape, rather than any potential target). AlexTiefling (talk) 15:36, 2 May 2013 (UTC)


 * The late Kingsley Amis steadfastly used the spelling 'ballocks', and I think his son inherited the affectation. AndrewWTaylor (talk) 21:08, 2 May 2013 (UTC)
 * There is a famous letter to Abraham Lincoln which (among other things) urges him to "call my Bolics[sic] your Uncle Dick." Interesting that the word now seems to have died out altogether in the States... Tevildo (talk) 23:18, 3 May 2013 (UTC)
 * Richard, best to be frank about this. It's clear that pedantry is not your true calling (which may make you very happy).  Your pseudopedanticism is betrayed by the absence of a comma after 'note' and a question mark at the end of your question. There are still openings at my Winter Pedantry School; special rates for Wikipedia editors. :) --   Jack of Oz  [Talk]  20:53, 2 May 2013 (UTC)


 * We should also consider the effect such a weapon would have on enemy morale. While a dead soldier returned home and buried with honor can actual inspire patriotism, a live soldier returned home, but missing a few key bits and pieces, can rather have the opposite effect.  Not many men will rush to the recruiting office after seeing that. StuRat (talk) 07:05, 3 May 2013 (UTC)


 * D&D vets know the S-Mine as "the ultimate balls check" - when it pops up, it'll determine with scientific rigor whether its or your balls are harder. With extreme prejudice.
 * Oz: Do I get discount if I take ten? - ¡Ouch! (hurt me / more pain) 08:21, 3 May 2013 (UTC)
 * By all means. You understand, of course, that you will be required to exhibit decilocation, and empower each of your decuplicate presences to have a separate one of your ten personalities. The auditors get a bit funny about me teaching an apparently almost empty classroom.  --   Jack of Oz  [Talk]  09:23, 3 May 2013 (UTC)

Of the S-Mine:- "...there were extraordinary escapes. The chaplain of the 5th Seaforth Highlanders trod on one which bounced up and knocked his glasses off; perhaps divine intervention prevented the main charge from exploding. Pfc Larry Treff of the US 26th Division was lucky enough to have one bounce up and hit him in the groin without exploding; he was thrown several feet but survived with minor injuries, though his groin area was 'so purple and swollen' that he was temporarily immobile." Alansplodge (talk) 16:13, 3 May 2013 (UTC)


 * (un-indent) Thanks, folks! So I gather that German landmines in WW2 were designed to maim, but not specifically to castrate. 24.23.196.85 (talk) 19:39, 4 May 2013 (UTC)
 * Yes. Sadly, as usual, it takes us an entire page full of babble and small asides to come to that clear statement! SteveBaker (talk) 15:46, 5 May 2013 (UTC)

Deriving the momentum operator.
In quantum mechanics, given the canonical commutation relation $$[\hat x, \hat p_x] = \hat x \hat p_x - \hat p_x \hat x = i \hbar$$ and $$\hat x = x$$, how can one derive the result $$\hat p_x = \frac{\hbar}{i} \frac{\partial}{\partial x}$$? I was told that this can be done, though I am unsure how to go about doing this. -- — Trevor K. —  05:40, 2 May 2013 (UTC)  — Preceding unsigned comment added by Yakeyglee (talk • contribs)


 * Well, you can show calculate the commutator $$[\hat x, \hat p_x]$$ as follows. If F is any function of x, then
 * $$[\hat x, \hat p_x](F) = (\hat x \hat p_x - \hat p_x \hat x)(F) = x\frac{\hbar}{i} \frac{\partial}{\partial x}(F) -\frac{\hbar}{i} \frac{\partial}{\partial x}(xF) = x\frac{\hbar}{i} \frac{\partial}{\partial x}(F) -\left( x\frac{\hbar}{i} \frac{\partial}{\partial x}(F) + F \frac{\hbar}{i} \frac{\partial}{\partial x}(x) \right) = - \frac{\hbar}{i} F = i\hbar F$$
 * Strictly speaking, this is a confirmation rather than a derivation. It shows that $$\hat p_x = \frac{\hbar}{i} \frac{\partial}{\partial x}$$ satisfies the canonical commutation relation, but does not show that it is the only solution. Gandalf61 (talk) 08:02, 2 May 2013 (UTC)


 * It is a consequence of the De Broglie relations as can be seen in the article titled - of all things - Momentum operator. Dauto (talk) 19:20, 2 May 2013 (UTC)


 * this page has a derivation of the reverse relation where x = i hbar d/dp in the momentum representation (start at equation 198). The proof you're looking for is completely analogous. Dauto (talk) 19:36, 2 May 2013 (UTC)

There is a subtle issue involving the theory of distributions involved here. I tried to look this up, but I can't find it in my old university lecture notes. Basically, the argument should go as follows. We want express  in terms of  by invoking only the commutation relation and nothing else. Let's write:

 = Integral dx' 

Then we can evaluate the matrix element  as follows:

x  =  =  = i hbar delta(x-x') + x' 

Therefore, we have:

(x-x')  = i hbar delta(x-x')

The problem is then that can't just divide both sides by x-x', as that doesn't yield a bona fide distribution. If have the equation x T = delta, where we use the official math notation T(f) for a a distribution T acting on a test function f, the solution is not T = 1/x delta, as that doesn't define a distribution, rather it is T = -delta' + A delta. We have

x T(f) = T (x f) = -delta'(x f) + A delta (x f) = delta[(xf)'] = f(0) = delta(f)

We thus have:

 = -i hbar delta'(x-x') + A delta(x-x')

This then gives:

 = Integral dx' psi(x') = -i hbar d psi(x)/dx + A psi(x)

The constant A must be put to zero by hand. You can always add a contant times the identity to an operator without that affecting the commutation relations. Count Iblis (talk) 15:45, 3 May 2013 (UTC)

Inert gas
I was reading Nitrogen asphyxiation and it says suicide using inert gas doesn't cause pain. Is that really true? Btw I'm NOT thinking about suicide just wondering cuz it's pretty crazy that you can die without feeling pain. Money is tight (talk) 08:04, 2 May 2013 (UTC)


 * Yes, it is logical that it is painless. Otherwise, how else could there be accidental death by this manner? Plasmic Physics (talk) 08:09, 2 May 2013 (UTC)


 * Since four fifths of the air we breathe all the time is nitrogen, our bodies are quite tolerant of it. What you're really talking about here is removing the oxygen from the air so that you're breathing 5/5ths nitrogen.  If you tried to breath only carbon-dioxide (for example) you'd start hyperventilating and all sorts of nasty things would result because your body is aware that CO2 needs to be dealt with - but we breathe mostly nitrogen all the time - so our bodies don't notice anything except the lack of oxygen.
 * So we might as well forget about the nitrogen here. What we're talking about is lack of oxygen - Hypoxic hypoxia - and anoxia...some of the symptoms of this are:
 * Cyanosis -- you "turn blue" as your blood loses oxygen.
 * Headache -- not completely painless.
 * Visual impairment, decreased reaction time and impaired judgment time -- hardly painful.
 * Numbness, drowsiness and euphoria -- At least that's going to make the headache seem less bad.
 * Lightheaded or dizzy sensation, tingling in fingers and toes -- not exactly painful but unpleasant.
 * Nausea -- also not great.
 * But it depends on how fast it happens. The above symptoms are likely if the reduction in oxygen is relatively slow...but if it's fast then seizures (painful - and might cause you physical injury through falling or something) and if you're a man, priapism (which can be very painful) are also possible.
 * The amount of time it takes (and therefore how long you suffer these symptoms) is also tricky to get a grip on. If you still have oxygen rich air in your lungs, you can hold your breath for maybe 30 seconds - but if you fill them with pure nitrogen by hyperventilating, you could lose "useful" consciousness in under 10 seconds.
 * I think the devil is in the details here.
 * SteveBaker (talk) 13:07, 2 May 2013 (UTC)


 * In almost any situation where someone takes a sedative toxic substance like drugs or alcohol in sufficient amounts to kill them their death will be preceded by drowsiness leading to sleep and then coma, during which it is extremely unlikely that they will be conscious of pain. Indeed, enormous numbers of people die every day under the influence of pain relieving medication in hospitals and hospices all over the world. Richard Avery (talk) 13:19, 2 May 2013 (UTC)


 * Any exertion speeds up the effect. If firemen come running into a computer room where some inert gas has been released to suppress flames they may immediately fall down, if this happens just hold your breath, go in and drag them out straight away into the fresh air. Dmcq (talk) 13:45, 2 May 2013 (UTC)


 * I presume that there are two reasons for that though: Firstly (as I said above), when you're breathing hard (as you would be if you were running with all of that fireman's gear on) then whatever oxygen would otherwise remain in your lungs gets flushed out and replaced with the inert gas more rapidly than if you were breathing at a steady pace. Secondly, the exertion increases your oxygen needs so whatever oxygen is left in there gets used up more quickly.  However, if holding your breath and then exerting yourself to get a victim out of there actually works - then the former is clearly of much more importance than the latter. SteveBaker (talk) 14:21, 2 May 2013 (UTC)
 * Certainly does as four firemen neatly laid out on the grass can testify ;-) I must admit the gas seemed a bit excessive as it caused damage to the ceiling with the extra pressure when it was released. Dmcq (talk) 14:49, 2 May 2013 (UTC)


 * Sorry guys, your answers here are a little messed up. Some bullshit has been posted above. Several things to note:-
 * Presumably SteveBaker meant increased reaction time.
 * Fireman are NOT in the least bit likely to immediately fall down, or even fall down after a while, if they enter a computer room where gas suppression was used, for several reasons, the most important of which are:-
 * The most common system used is Inergen and similar - in these systems the amount of inert gas is selected such that the oxygen content is brought down (by displacement) to about half normal, i.e, roughly 10% by vol. Almost all computer room fires go out at this level, and the ones that don't (such as burning paper) slow down dramatically.  The gas mix also contains carbon dioxide, so that the room carbon dioxide is raised from the natural level of 0.03% to about 0.1%.  This raises the blood CO2 level similarly, which stimulates humans to breath harder, so that the blood oxygen remains close to saturation.  Less commonly, CO2 suppression has been used, as it has been in aircraft flightdecks.  If you enter a room where it has been used, you will know it from the sensation (assuming you didn't notice the mandatory flashing lights and bell), and you will get out.
 * Take a typical fit male human: say 80 kg weight.  By standard medical calculations, such a male will have 7% of body mass as blood, i.e., 5.6 kg of blood.  Each kg of blood has very nearly 210 mL of oxygen bound to haemogobin per kg of blood, i.e., our 80 kg fireman has 1.2 litres of oxygen stored in his haemoglobin, not counting oxygen dissolved in plasma.  Male lung total capacity is aprox 0.53 litres per 10 kg of body mass, so our 80 kg fireman will have about 0.2 x 0.53 x 8 = 0.85 litres of oxygen in his lungs on entry to the room.  Total oxygen he has is then 0.85 + 1.2 = 2.05 litres.  No problem will occur until blood oxygen drops below 90% saturation.  A fit male exercising (assume fireman has run up the stairs) will consume oxygen (the VO2 rate) at approx 50 ml/kg/min.  So he will consume 4 litres per min and it will take him about 30 seconds before any distress or problems occur at all.  It will take a full minute in a zero oxygen atmosphere before he has much distress - plenty of time to either get out or put on oxygen mask, even if there is NO oxygen in the room.  However, as there will be about half the normal level, he would have TWO full minutes to take action.  Even if he has all oxygen flushed out of his lungs upon entry, he can still fully function on blood oxygen for one minute.
 * Firemen are trained - they won't be that silly.
 * Those of us who have flown in an airliner will recall the safety instructions - where they tell you that should a sudden decompression occur (which roughly halves the oxygen partial pressure), put on your oxygen mask, but it isn't urgent - you have plenty of time to ensure your childen have their masks on and working before you put yours on.
 * I have witnessed a test dump of Inergen gas in a large computer room - I was in the room at the time. I noticed no ill effects.
 * I once took a tour of a hospital on an open day. We were taken into an out of service operating theater.  An aneasthetist explained all his equipment, one item of which was a blood oxygen saturation monitor, which works by shining light of two wavelengths thru your finger.  While he was talking, I put it on - it said my O2 sat was 100%, as it should be for a conscious healthy human not doing anything but stand.  I then pinched my nose closed and kept my mouth shut, to see what my blood O2 level would be when I could not hold my breath any longer.  The aneasthetist seeing me do this said "There's one in every group!".  I kept holding my breath while listening to his talk and glancing often at my watch.  After 6 minutes, I could not hold my breath any longer, it was most uncomfortable.  My blood O2 saturation was still showing 99%!  And, no, the machine was not faulty.  When I took a breath, the aneasthetist said "About average, mate."
 * Ratbone 60.230.212.134 (talk) 15:36, 2 May 2013 (UTC)
 * I assure you that what I said was true. There was a fifth fireman who called for help from a bunch of students to get his colleagues out and they revived quite quickly when brought out but whatever you say they did collapse going into the room. And yes they did look a bit sheepish about having ignored the warning light outside the room. We gave them some tea and a biscuit and they went away again. The point about some gases is you don't notice the effect until you conk out and if you have not been running you probably are okay for much longer. Dmcq (talk) 16:04, 2 May 2013 (UTC)
 * Well, my calculations are verifiable from relevant wikipedia articles and elsewhere. What you describe is simply not possible with Inergen systems and it's competitors.  It could happen with a CO2 system, but only if a) the gas dump was excessive, meaning it had not been tested per code requirements, and b) they were really stupid firemen.  While you can conck out without distress with inert gasses, entering a room with CO2 produces immediate distress, even with plenty of oxygen.  Remember that: normal oxygen content of air is 20%; you need much less than that to function; air CO2 is less than 0.03% and any increase triggers heavier breathing.  CO2 has been a standard system to put out aircraft cockpit fires.  Not much point if it puts the pilots out as well.  What country was this in?
 * The only other possiblity I can think of - if lead acid batteries had been used in a UPS system, people can be overcome by stybine gas - stybine is a product of antimony in the pressence of water and other substances. However, a) the fire woukd have to have reached the batteries, b) the batteries would have to be the type using lead antimony plates, not normal in UPS service, and c) you cannot recover spontaneously from stybine inhalation.  Ratbone 60.230.212.134 (talk) 16:12, 2 May 2013 (UTC)
 * Believe what you wish but I have not said a single untruth in all the time I have been on Wikipedia. Dmcq (talk) 16:25, 2 May 2013 (UTC)
 * I'm going to call bullshit on Ratbone item #6 recollection of the Emergency oxygen system instructions. FAA advisory AC 121-24C (7/23/03) appendix 1, item #10 states "passengers should be advised to don their own oxygen masks before assisting children with their masks." and I can't recall ever hearing anything else. Time of useful consciousness suggests you really don't have much time to figure out what to do and then do it. DMacks (talk) 17:14, 2 May 2013 (UTC)
 * We have an article on Gaseous fire suppression which mentions several different kinds with different methods of action. Rmhermen (talk) 17:16, 2 May 2013 (UTC)
 * Yes, I got #6 round the wrong way. I note that the article cited by Rmermen gives times, designed so that an elderly passenger of unknown fitness or baby with mimimal oxygen capacity will be catered for, gives cruise altidue (and therfore roughly the same oxygen partial pressure) times of the same order I calculated for a fireman, who can be expected to be in excellent fitness and do much better.  And, as I said, firemen should not need to spend much time figuring out what to do, because they are trained - which is why I find it hard to believe that 4 firemen would enter a CO2 supprosssed room ignoring the signs, lights, and sound, and if they did, they should recognise the meaning of their immdeiate distress (from their training) and leave.  Ratbone 121.215.74.116 (talk) 01:06, 3 May 2013 (UTC)

I remember seeing a doco film about capital punishment where they illustrated the painlessness of nitrogen asphyxiation by placing a pig in a room with a feed trough in a fume cupboard that recirculated 100% nitrogen. The pig would stick its head in to eat, pass out from lack of oxygen and fall outside where it would resume normal breathing of air, then wake up and stick its head back in. As for Dmcq's suggestion that you hold your breath and try to save people that have been overwhelmed by some gas; both my confined space and certified atmosphere tester training are telling "don't do that". Most industrial fatalities involving gasses are from trying to save someone else. Only emergency response personnel should take part in rescues of this type. 202.155.85.18 (talk) 02:48, 3 May 2013 (UTC)t
 * Well the last one did come out for help rather than going in himself and I'd guess it was pretty safe as there were a number of people around, it wasn't as though they had to go far. Whatever about that one should wait for trained people I would have difficulty with sitting around letting people die, and I can swim 50 meters underwater quite easily so I really don't see there would be a problem. It was rather a few years ago so I'd guess their training is better now. Dmcq (talk) 08:02, 3 May 2013 (UTC)
 * The first thing they teach in first aid courses is "DRABC" - Danger, Response, Airway, Breathing, Circulation. Or the equivalent in other languages.  "Danger" in this case means you first check that there is no danger to yourself, BEFORE attempting rescue.  I agree with 202.155.85.18 - If I was aware that more than one person collapsed after entering a room, there's no way I would enter.  You don't know just why they collapsed, and if you enter and collpse, that just might mean n+1 fatalities instead of just n falalities.  You last bit about swimming is self contradictory - if you can function for x minutes without breathing, then so should firemen.  The training of firemen won't have changed in this regard since the advent of computer rooms and the like back in the 1950's.   What country did this supposed event occur in?  Ratbone 121.215.32.211 (talk) 11:34, 3 May 2013 (UTC)


 * I have to agree with Dmcq on all points here as most of you  appear to be confusing theory with real life situations. Now lets get back to the firemen. Yes they are trained and are not stupid. Yet training costs money. It is more than likely in  Dmcq case that these firemen had never before rushed into a building full of  Inergen. These call-outs  are rare compared to putting out cars, set afire  by vandals etc. All the adrenaline is pumping with a focus to  get into the computer room  as fast as possible  and save human life. Yes, the theory that has no doubt been taught to them in the class room  leads them to understand you can breath in this atmosphere.  Yet. isn't this a little bit like going on holiday and on arrival playing ball with your kids only to find you have collapsed  in a gaping heap - because of the altitude. The holiday brochure pointed out the altitude but still you played foot-ball! Yes, the higher CO2 invokes faster lung action but if the available oxygen is  only half that as sea level when one's action causes a high biological oxygen demand then whoops.  This can happen without warning because of oxygen debt. Put simply, once you have stop running do you immediately stop panting? Of course not. One has to keep a high rate of respiration to stop from passing out.  So for a fireman in such a situation. Just suddenly realizing that respiration is distressed, one  has left it too late -but hey, in the class room weren't we were told we can still breath in this atmosphere? I would be interested to know from a current fire-fighter if his/her  training included the cost of going into an Intergen atmosphere. In the days of Halon, such exercises where prohibitively expensive because fire-services are paid for by local taxation and nobody like paying tax – so they didn't do it. It may be the same to day. Are there any fire-fighters  here that have had gas suppression training for real?Aspro (talk) 18:32, 3 May 2013 (UTC)
 * I doubt that many firmen would have actually had experience of Inergen during training, because it is expensive. The test dump that I witnessed cost ~$80,000.  However, firemen do get to experience oxygen starved and smoke filled chambers during their training - at least they do here in Australia.  But they'll get to hear about Inergen in classroom talk.
 * At least here in Australia, when called out to commercial buildings large enough to have a computer room with fire suppression, their normal practice is to send at least one guy in with breathing apparatus anyway, as burning plastics and electronics in commercial buildings can emit a range hazardous fumes, and rooms can be filled with smoke.
 * In fire suppression systems, the oxygen content is only brought down to no less than half the normal value. This is well and truely enough to function normally on, providing breathing is stimulated, as the CO2 content of Inergen does.  Yes, if you are exercising heavily it won't be enough - after all if we run at maximum speed, we get puffed out in a normal atmosphere.  But if the firemen actually collapsed, their body oxygen demand would have drops to the rest value, so they should spontaneously recover - within less than a minute.  That's not what Dcmq said.  It is possible that if the computer room was in a third world country that Western standards of workmanship, commissioning tests, and firemen training were not up to the situation, which is why I asked twice "what country was it in?"  However, as a) Dcmg's intial post reads a hypothethical, but later posts after a challenge changed that, b) it is quite unlikely for technical reasons as explained, and c) Dcmq has not come back and answered the question, I rather think his story is just a story.  Maybe he heard about an incident he wasn't personally involved in, and the facts got muddled up in the gossip - chinese wisper effect.
 * Ratbone 121.215.32.202 (talk) 01:15, 4 May 2013 (UTC)
 * As I said above 'they revived quite quickly when brought out'. I am glad standards for construction and firemens' training are so good nowadays that none of the incidents in can happen. Yes I do refuse to say where or when. Dmcq (talk) 09:09, 4 May 2013 (UTC)
 * Several things to note about the EPA report you linked to:-
 * You said the incident occured in a computer room. None of the incidents listed occurred in a computer room.
 * You said firemen were affected - but the reported incidents involved all sorts of other workers.
 * The most common gas system in computer rooms is Inergen, which will not aspixiate as expalined. All the reported incidents involved CO2 suppression.
 * Many of the incidents reported occurrerd in US Navy vessels. I don't know much about the USN, but I do know about the Australian Navy, which largely tries to emulate the USN and mostly buys the same ships and equipment.  The Aust Navy is notorious for ignoring civilian safety standards, not training crews properly, and consequently have an accident rate to match.
 * Many of the incidents occurred in facilities totally unlike computer rooms and may well require a greater degree of oxygen dispalcement than do computer rooms.
 * Ratbone 124.178.43.47 (talk) 09:26, 4 May 2013 (UTC)
 * Inergen was only patented in 1989 and introduced in 1992. I don't know what gas was used. I think I have had enough of this so bye. Dmcq (talk) 09:50, 4 May 2013 (UTC)


 * Some are forgetting about partial pressure. In a normal atmosphere a fire fighter might recover in about a minute but CO2 is heavy  and forms a low blanket. The lungs can't vent the blood CO2 so quickly  in that environment. I was trained to get people out in 20 sec. If anyone collapsed – then were trained to  endeavor  to drag them out PDQ. One point I remember, is that on recover they may be disorientated – so get them out to a point of safety first. Don't leave them to find their own way out. This is  sensible, when you consider how quickly fires can get out of control. For a fire-fighter in unfamiliar surroundings,  this disorientation problem is even more critical. The company I worked for had its own fire brigade as first responders and to be in attendance  when the professionals arrived, to advise them on where welding bottles and other hazards where situated. Fires can get out of control much faster than one can anticipate.  This is why I support Dmcq, because I don't think any of Dmcq critics have actually under gone industrial firefighting instruction. Nor, have they seen the instruction films of actual conflagrations and the aftermath. To rub it in, they often contained  graphic  images of the remains of people that got it wrong. If fire fighting was a simple as some of  Dmcq critics suggest, then we would not have all these deaths. Anyway, you have transgressed well off the OP question in pursuit of your faux augments.Aspro (talk) 18:32, 4 May 2013 (UTC)
 * Well, I have been personally involved in the construction of computer rooms as the project Engineer, and been involved in the specification and sign-off acceptance of Inergen fire suppression systems. So I do know something about it.  Like 202.155.85.18 I hold Confined Space certification in accordance with Australian Govt legal requirments, as well as a Senior First Aid certificate.  It certainly would violate the training for both to enter a room as Dcmq described.  Regarding "all these deaths" as you wrote, well, the cited EPA report appears to cover a period of 30 years.  There was not one single listing for an Inergen system - they are all CO2 or unstated.  In 30 years in the USA (with a population of 270 million and thousands of computer rooms) there was just ONE death!  Internationally there was a couple more.  Almost all the incidents were not computer rooms.  Incidentally, at least in my country, it is a legal requirment that any building that contains storage of hazardous chemicals or gasses must prominently display on the street frontage a standardised warning sign listing the classification of what's there - just so that firemen on arrival will know.  When brigades get called out to commercial buildings, they consult their file on that building.  Most building probably have no information, but if there is anything that materially alters risks to firemen or how any fire should be fought, the file will tell them.  They do inspections now and then. Maybe things are not as good in other countries, though I would be suprised if we do it better than the USA or any European country - that's where we get out good ideas from. Ratbone 120.145.65.37 (talk) 03:28, 5 May 2013 (UTC)


 * When I said all these deaths it should have been clear form my context that I was talking about industrial fires in general. As you said: “Almost all the incidents were not computer rooms” Dmcq  is obviously talking about an event with a legacy system.  These days, buildings may have haz-chem signage but in a large complex there can  still be doubt about exactly where the hazard is within, because  welding bottles and other stuff are mobile. If first responders are not available to assist, then the whole site  gets evacuated, ensuring that the fire can spread. The low death rate with CO2 suppression may be because people got dragged out in time. Your appearing to use modern practices that you have learnt to pass judgement on how thing were back then and their effectiveness, considering the technology  available and systems in use back  then. Next:  “It certainly would violate the training for both to enter a room as Dcmq described.” Lets take a side swipe first. Before going down a coal mine, I was instructed that if I was told to use  my respirator (of this type  I was to put it on and just calmly walk out – AND NOT TRY AND HELP ANYBODY THAT HAD COLLAPED. Asking 'why' we could not stop to help others, we  told that we hadn’t been trained in such a way that  we could help  without putting ourselves in danger. If we delayed our exist we could  collapsed ourselves  and so  would   just present more problems for the rescuers (this respirators only had a 10 minute duration -just time to get into the next  clear ventilated passage). Right, back to a conflagration in a commercial complex. Fires can spread so quick some-times that  the company I worked for and many other companies, trained some of their staff, so that if an incident occurred  we could either quickly deal with it ourselves (and not do something stupid like spaying water on burning aluminium swarf)  so by  the time it took the fire brigade to arrive, other employees did not end up as the blackened chard corpses that we saw in the training films.  In short, your comments seem too insular to add value any to value to  Dcmq's  comments.--Aspro (talk) 21:55, 5 May 2013 (UTC)

ITC
I read Isothermal titration calorimetry and couldn't find answer to the following question: In context of protein complexs, in ITC expriment there is a "receptor" in the solution (in the cell), and a "lignad" that is titrated into the cell, is it possible to swap them? would we get the same affinity? (for example suppose we find affinty trypsin-BPTI: will we get the same results when (1) have trypsin in the cell and titrating BPTI, or (2) having BPTI in the cell and titrating trypsin). Thanks, 192.114.91.228 (talk) 10:01, 2 May 2013 (UTC)


 * In concept, I don't see why not, but in practice, I think you'd have an issue that you want to add a small aliquot to a larger amount of solution. Because it's hard to purify macromolecules to a very high concentration, you'd be better off using a concentrated chemical to add. Wnt (talk) 17:02, 3 May 2013 (UTC)

Origin of the belief that parrots eat crackers
Anyone know for sure? I heard that it was something to do with parrots on ships eating hardtack and saltine crackers. Yes, they will certainly eat crackers if available and apparently enjoy them, but it's not their main diet. --31.185.233.239 (talk) 20:52, 2 May 2013 (UTC)


 * Obviously. Cracker trees aren't native to the same range as parrots.  Well, they do overlap a bit with the range of the Norwegian Blue parrot, but alas, I think that species is no more, ceased to be, expired and gone to meet his maker... -- Jayron  32  21:09, 2 May 2013 (UTC)


 * No, he's asleep!!! Richard Avery (talk) 07:18, 3 May 2013 (UTC)


 * And now for something completely different ... The phrase "Polly want a cracker" goes back at least as far as 1848. As Cracker (food) notes, the cracker is said to have been invented in 1792. Clarityfiend (talk) 22:20, 2 May 2013 (UTC)


 * Or maybe parrots are all just mildly racist. -- Jayron  32  23:39, 2 May 2013 (UTC)


 * When people first started keeping parrots as pets, you couldn't just head to the nearest pet store and pick up a bag of Purina Parrot Chow. So, crackers were a food item which people had on hand, which parrots could also eat.  If we think of the stereotypical parrot kept on a ship, then fresh food would have been only available during, and shortly after, stops at ports.  In between, parrots would have to make do with things like crackers, as would the rest of the crew.  If you had a parrot with an exceptional vocabulary, he might say "Polly wants some fresh food, but since that's not available, Polly will settle for a cracker". StuRat (talk) 05:44, 3 May 2013 (UTC)

Isn't this just a meme based on classic children's cartoons, the same as the notion that mice like cheese, which they really don't? μηδείς (talk) 08:18, 3 May 2013 (UTC)
 * Did they have classic children's cartoons back in 1848? Or only classic children? --   Jack of Oz  <sup style="font-family:Papyrus;">[Talk]  09:12, 3 May 2013 (UTC)
 * Jack, if you first heard this from 19h century literature and not a cartoon or similar juvenile entertainment, I'll eat a roo raw. μηδείς (talk) 19:31, 3 May 2013 (UTC)
 * A cartoon or one's mother or whoever may well be where you or I first heard the expression. But the question is about the "origin" (see the header) of the belief behind the expression, hence the origin of the expression itself.  It's an etymological matter as much as a scientific one.  We've traced it to at least as far back as 1848 at this stage. --   Jack of Oz  <sup style="font-family:Papyrus;">[Talk]  19:40, 3 May 2013 (UTC)
 * If you had read the post above then you will see this pre-dates children's cartoons: The Knickerbocker: Or, New-York Monthly Magazine, Volume 34  1849... page 544 . Would you like salt and pepper on you're  raw roo or would you rather eat it purely al fresco?--Aspro (talk) 20:01, 3 May 2013 (UTC)
 * Yes, and there's still not a single person reading this thread who didn't learn that little bit of obscure high culture from Looney Toons or the like. Next you'll say the first place anyone ever hears Wagner's in the opera house. μηδείς (talk) 02:02, 4 May 2013 (UTC)
 * Are you deliberately missing the point? The q is not about when, where and how you or I or Joe Bloggs first heard the expression "Polly want a cracker".  It is about how that expression came into being in the first place, and more to the point, why anyone thought a parrot's favourite food would be man-made crackers.  The belief and the expression weren't independently created millions of times over.  They were created way back when, and ever since then people have been copying other people.  --   Jack of Oz  <sup style="font-family:Papyrus;">[Talk]  04:10, 4 May 2013 (UTC)
 * Maybe some of those kangaroo meringues that Noël Coward was talking about. --   Jack of Oz  <sup style="font-family:Papyrus;">[Talk]  20:09, 3 May 2013 (UTC)
 * Stop it Oz. Your making me feel hungry and my doc has warned me that I'm already 'morbidly' obese. Mind you... a kangaroo meringues does sound like it's light and fluffy and Oh, what the hell, a little mouth-full or two (or three) will not not make any difference. Medeis... add a little garlic to my portion please.Aspro (talk) 20:26, 3 May 2013 (UTC)
 * As I recall the classic parrot, Captain Flint, it said "pieces of eight" and ate bark. I never heard "polly want a cracker" until much later, probably as spoken by Disney's parrot in a bit of role-reversal that was lost on me at the time.  I suppose a person's predisposed notions about parrot behavior are highly conditioned by the order in which one is exposed to classic parrots in literature and film.  Nimur (talk) 15:45, 3 May 2013 (UTC)
 * Here's something from 1948, and you can safely assume that the "Polly want a cracker" thing is much old than that. ←Baseball Bugs What's up, Doc? carrots→ 04:04, 4 May 2013 (UTC)
 * There's no need for any such assumption. All you need to do is cast your eyes upwards and read where the expression is known to have been in existence exactly 100 years earlier, in 1848.   And it almost certainly precedes that.  --   Jack of Oz  <sup style="font-family:Papyrus;">[Talk]  20:25, 4 May 2013 (UTC)
 * Not for me there isn't. But there might be if someone thinks it originated with a Robin Williams movie. ←Baseball Bugs What's up, Doc? carrots→ 20:51, 4 May 2013 (UTC)
 * Sorry, but why did you bother tracking down a 1948 source when we already had an 1848 source? --   Jack of Oz  <sup style="font-family:Papyrus;">[Talk]  01:42, 5 May 2013 (UTC)


 * We're all overlooking something... when did parrots get to be named Polly? how do we even assume they're female? or that a male would want to be called Polly? Gzuckier (talk) 21:03, 3 May 2013 (UTC)


 * Read the posts above!:“Polly is a diminutive of Poll "as a female name, and name for a parrot," and Poll, altered from Moll, familiar form of Mary, is the traditional name for any parrot. The earliest quotation the OED gives for Polly as a name or designation for a parrot is from Ben Jonson's "Epigrams," 1616. ”  If it is a he, then you can you can call him  Joe. Or,  if he is your-pal you can call him Al.  He, she or it, wont care as long as Polly gets a cracker. They might have bird brains but they know how to train the humans around them to give them what they want. Aspro (talk) 21:41, 3 May 2013 (UTC)
 * Actually, Molly and Polly come from Mary. Moll or Poll would be single-syllable nicknames for Molly and Polly, as Mare is for Mary. How that figures into parrot names is anybody's guess. Maybe it's from "Paul"? As with the male bird in "Little Poll Parrot". ←Baseball Bugs What's up, Doc? carrots→ 03:46, 4 May 2013 (UTC)
 * Paulie wants a cracker? -- Jayron  32  03:50, 4 May 2013 (UTC)
 * Various google items indicate that Poll is indeed a variant of Paul. So why Paul Parrot? Maybe just because it's nice and alliterative. ←Baseball Bugs What's up, Doc? carrots→ 03:59, 4 May 2013 (UTC)
 * I know a lovely lady named Polly. Her legal name is Paulette.  --   Jack of Oz  <sup style="font-family:Papyrus;">[Talk]  04:12, 4 May 2013 (UTC)


 * You can ask the World Parrot Trust.
 * World Parrot Trust - Ask an Expert
 * —Wavelength (talk) 04:28, 4 May 2013 (UTC)

Paulina cupit crustulum? Even the Romans were familiar with parrots, and could have asked polly if she wanted a cracker. Earliest known attestation is not proof of origin. We do, however, have documentary evidence. μηδείς (talk) 21:20, 4 May 2013 (UTC)


 * Maybe not proof of origin, but an earlier attestation still trumps a later one. --   Jack of Oz  <sup style="font-family:Papyrus;">[Talk]  09:14, 6 May 2013 (UTC)

Electromagnetic induction thru an unclosed ring
in a changing magnetic field. It's easy to see how an EMF comes about in the case of a closed conducting ring fixed in place in a magnetic field, since the the change in flux is related to the change in the magnetic field, while the area enclosed by the ring is constant. But how can we explain what happens in an incomplete ring (suppose a piece of the ring is cut away, leaving it unclosed) on the basis of change in flux ? In other words, how can we define an area here, in the first place (an open ring develops an EMF, but no induced current of course) ? BentzyCo (talk) 21:02, 2 May 2013 (UTC)
 * Area enclosed has nothing to do with it. A straight wire moving across a magnetic field will have a voltage induced along it.   The voltage is proportional to the length of the wire, the strength of the magnetic field, and the rate at which the field moves in respect to the wire.  In the case of a uniform magnetic field moving through a conducting ring that is gapped at one point, there will be no voltage across the gap, as the voltage induced in each half-turn will be the same.  In the case of a straight wire subject to a moving/changing magnetic field, which will have a voltage induced along it, current will flow if, and only if, the ends of the wire are connected to a circuit outside the magnetic field (or a part of the field that is of lower intensity). Ratbone 121.215.74.116 (talk) 00:51, 3 May 2013 (UTC)
 * Your 1st sentence is wrong. Completely wrong. Do you how AC voltage is produced ? And the rest of your reply is redundant, since you weren't tuned to what was asked and its context. It's an incomplete ring. Stationary. Nothing's moving. Only the intensity of the magnetic field is changing. BentzyCo (talk) 10:38, 3 May 2013 (UTC)
 * Well, if you know so much about it, why ask the question?
 * AC is commonly produced in an alternator, which, at its most basic, is a loop conductor rotating in a constant and evenly distributed magnetic field, the loop being interrupted at the slip rings and connected to a circuit external to the magnetic field. As rotation means, during each half rotation, half the loop is going one way thru the field and the other half is going in the reverse direction thru the field, the induced voltage in each half turn is such that they add around the loop, instead of opposing in the case of a loop moving bodily thru a field.  At each half turn, the direction each half turn is moving wrt the field in the opposite direction, thus the voltage at the slip rings reverses.  Practical alternators are of course more complex both in conductors and in magnetic arrangements, but all of us who studied electrical engineering have studied simple loop-in-field alternators in 1st year, and, usually, done tests on lab models.
 * Now back to your loop conductor in your question, any magnetic field not penetrating the conductor cannot be inducing any electric tension in it - so area can have nothing to with it. Or, looking at it another way, you could have a great number of parallelled conductors entirely within a magnetic field, so that a considerable amount of the field cuts a conductor.  You still get the same voltage end to end and no current.  A loop is just two parallel conductors.  Ratbone 121.215.32.211 (talk) 11:02, 3 May 2013 (UTC)
 * a. Your reply should be relevant to the question asked, irrespective of backgroung of the person asking the question, either he knows something about physics or even more than that. It isn't. Your 1st row up there is patronizing, just because I'm on the side of the question. Isn't it legimate to ask and consult with colleagues ?
 * b. You repeat your previous mistake regarding the consistuent of the flux, the effective area traversed by the magnetic field lines. Again, the part of describing how AC current comes about is redundant too, and part of it even repeats what I said. In other words, AC current is a phenomenon originating from a periodically changing effective area. I hope you know what magnetic flux is, and what Faraday's law says.
 * c. I think it's evident from my both writings that I'm quite in the field. My question is thus of an irregular kind, very intriguing and interesting, and I wanted to share it with others. It was very cut and clear - what's the origin of EMF across a bent wire making an arc of, say, 2700 ?
 * d. A complete loop is exactly one round conductor. BentzyCo (talk) 12:37, 3 May 2013 (UTC)
 * The emf is equal to minus the integral of E dot ds from one end to the other, but this is path dependent. If you e.g. measure the voltage betwen the two ends using a volt meter, then what the voltmeter will indicate is given by minus the integral the closed path that includes the connecting wires to the voltmenter and the voltmeter itself. Then the Maxwell equation nabla times E = -1/c dB/dt, makes that equal to Faradays law where the area is the area enclosed by the integration path. Note that any fields generated by moving charges don't contribute, because their electric fields are conservative (integral of E dot ds along a closed contour vanishes), therefore you can compute the contour integral for the hypothetical cases where all conductors are relaced by insulators. Count Iblis (talk) 12:34, 3 May 2013 (UTC)
 * For an loop conductor, broken by an infintessimal gap in a uniform magnetic field, the EMF across the loop gap is always zero. It matters not whether the loop is moving through the field (or a moving field is moving across a stationary loop, or the magnetic field is increasing or decreasing in intensity.  So long as the field is uniform, that is everywhere the same strength, the EMF across the small gap gap is zero.  If the incomplete loop is in fact a straight wire at right angles to the field, and the field is changing, then there will be an EMF from end to end.  A partial loop acts between these two extremes - you can consider it as a number of straight wire segments, and add up the EMF's to get the total, which must be between the two limiting cases of EMF.  Note that any voltmeter and its connecting wires used to measure the emf must lie outside the field, or EMF's induced in the meter and wires will oppose the EMF in the loop conductor, resulting in reduced or zero reading.  It is indeed odd to attack a person answering.  Is BentzyCo a troll?  Certainly he writes in an odd way - his 1st sentence in his question is a nonsense, for a start, and he seems to want an argument.  Wickwack 121.215.147.92 (talk) 13:05, 3 May 2013 (UTC)
 * a. 1st: put your reply in its right place.
 * b. 2nd: Your last sentences are just offensive & insultive, and will be treated as such. "attacking an answering person" ?, "troll" ? "my 1st sentence is nonsence" ? "want an argument" ? Your claims are unsubstantiated, to say the least. Will you, please, remain on disciplinary ground ?
 * c. Concluding my claim in the 1st place: the previous replies weren't relevant to what was asked, deviating the discussion from its intended focus. I think you've to apologize, Thank you. BentzyCo (talk) 13:34, 3 May 2013 (UTC)
 * @BendtyCo: Please bear in mind that this is a volunteer service - and that even as a questioner here, you are bound by the Wikipedia guideline to Assume Good Faith. If you don't like the answers, don't use them.  Ratbone is trying hard to be helpful and explain his thoughts on this matter - there is no need to insult him for doing so.
 * @Wickwack: Same deal...not cool: WP:AGF OK?
 * SteveBaker (talk) 14:17, 3 May 2013 (UTC)
 * It seems like the wire is a distraction. We're only interested in how the electrons move when exposed to a changing magnetic field - given that they can't usually leave the wire.  Unless it's a superconductor the field lines enter it, so the electrons inside are exposed to a changing magnetic field and by Faraday%27s_law_of_induction experience electromotive force.  I'm afraid I'm quite rusty with this topic but working through it you should be able to see how the EMF adds up even without a closed loop.  I suppose it doesn't with a superconductor because the electrons at the outer edge can just madly move to compensate for any induced potential without any force ever ... needing to be applied??? Wnt (talk) 15:26, 3 May 2013 (UTC)

Let's take the magnetic field to be non-zero only withing the ring. We take it zero also at the location of all the conductors, e.g. put a long thin coil at the center of the loop, and let the current in that coil increase or decrease, the magnetic field is fully contained in the interior of the coil, which is well away from the boundary of the loop. The potential difference between the (infinitesimal) gap is simply the induced voltage as follows from Faraday's induction law. To see this, write the voltage difference as minus the integral of E dot ds from one end of the gap P to the other Q where E is the total electric field (both induced by the changing magnetic field and the build up of charges at the ends due to them responding to the induced electric field).

Then because the charges in the conductor will make the total electric field zero inside the conductor, we can add to the integral from P to Q across the gap, the integral from Q back to P taken over the conducting loop, as the latter integral is zero. We then have an integral along a closed path to which the Coulomb fields of the charges do not make a net contribution. So we can compute this integral by replacing the total electric field by the induced electric field that follows from nabla times E = -1/c dB/dt. Then Stokes theorem says that the integral along a closed path of E dot ds equals the integral of nabla times E over the area enclosed by the path, substituting -1/c dB/dt for nabla times E then yields the Faraday's law result. Count Iblis (talk) 14:13, 4 May 2013 (UTC)


 * Count Iblis, what's a nabla?  What does all this double dutch mean in words of standard English?  What is your conclusion wrt the OP's question?
 * In your second sentence, you've written "the magnetic field is fully contained in the interior of the coil" - a long thin coil. A magnetic field essentially stretches out to infinity, though it dies away in strength quite quickly cf electromagnetic radiation.  The only case where a magnetic field is completely confined to within a coil, is where the coil is a perfectly even toriod made with thin sheet wire and zero distance between adjacent turns (that are never the less somehow insulated) - a rather theorectical situation.
 * . — Preceding unsigned comment added by 120.145.136.237 (talk) 15:56, 4 May 2013 (UTC)
 * See Nabla symbol - which should be familiar to anyone who knows anything about electromagnetic induction. 80.254.147.84 (talk) 11:47, 5 May 2013 (UTC)
 * Well, one learns something new every day. The lecturer I had in electromagnetics called it "del".  My copy of Morrison says to pronounce it "del". Wickwack 120.145.80.171 (talk) 15:16, 5 May 2013 (UTC)
 * Yes, indeed, the _operators_ are called "del dot" and "del cross", but the _symbol_ is called "nabla". See Haddocks' Eyes. Tevildo (talk) 16:39, 5 May 2013 (UTC)