Wikipedia:Reference desk/Archives/Science/2013 May 7

= May 7 =

Practically insoluble
Is there a defining characteristic according to any particular school of thought, that distinguishes between 'partically insoluble' and 'insoluble'. My question is inspired by the difining characteristic of an 'existant isotope', that it must have a half-life greater than the time it takes for the nucleus to internally differenciate (~10-14 s). Plasmic Physics (talk) 01:23, 7 May 2013 (UTC)
 * Please clarify. By "partically insoluble", did you mean "partially insoluble", or "practically insoluble"?  And what does the half-life of an isotope have to do with this? 24.23.196.85 (talk) 04:12, 7 May 2013 (UTC)


 * I mean 'practically insoluble'. The isotope statement demonstrates a pragmatic approach to semantics in an area of science. Plasmic Physics (talk) 04:22, 7 May 2013 (UTC)


 * Terms like "practically insoluble" and merely "insoluble" are imprecise terms. If you want precision, you would use defined numerical measures of solubility such as solubility product and molar solubility and mass percent solubility as shown at solubility table.  There aren't "hard and fast" cut-offs between terms like "slightly soluble" "practically insoluble" and "totally insoluble".  It's a bit fuzzy around the edges.  Generally, something is "soluble" if the solubility product indicates that it will dissolve extensively, that is the solubility product is significantly higher than 1.  Things which are considered insoluble have solubility products which are very tiny, while something "slightly soluble" would have a solubility product near 1.  But yet again, there are no hard cut-off lines here.  It's somewhat subjective.  -- Jayron  32  05:09, 7 May 2013 (UTC)


 * Personally, I'd say a substance is "practically insoluble" if no decrease in weight of the solid phase can be detected after placing it in the solvent, and "completely insoluble" if the dissolved phase doesn't even show up in spectroscopic analysis. But that's just me. 24.23.196.85 (talk) 05:43, 7 May 2013 (UTC)

Explosive experiments
Why is there no speciality laboratory glassware for experiments that involve explosively unstable compounds, like nitroglycerine? Such experiments seem to involve ordinairy glassware, that readily turns to shrapnel in these explosions. Is it not possible to create thickly walled composite glassware that is heavy and shock resistant? Take a test tube as an example, to enable efficient heating and cooling, a thermally conductive metal bottom can be fused into the underside of the test tube. Of course, this will result in a make-shift cannon, but it should be possible to attach a force dissipator. I'd like to think that chemists would try and keep their lab in one peace. Plasmic Physics (talk) 01:50, 7 May 2013 (UTC)
 * Is this actually a wide spread problem? How many scientists do you know who have been injured or killed by explosions? Or how many labs have been blown up? I suspect anyone working with explosive compounds has strict operating and safety procedures in place already. If they are working with quantities large enough to blow up the lab, I hazard a guess they have bunkers or similar special areas where the compounds are restricted to. Vespine (talk) 02:12, 7 May 2013 (UTC)


 * It's not a problem very often encountered. For scenarios, see as linked in a previous discussion on this reference desk. Plasmic Physics (talk) 02:38, 7 May 2013 (UTC)


 * There are bombs and hoods and vessels and even ranges to handle explosives. Why would someone with more than one year's chemistry think a test tube would be an ideal or idealizable place to conduct such experiments? μηδείς (talk) 02:48, 7 May 2013 (UTC)


 * Concerning chemical experimentation of such explosives. Plasmic Physics (talk) 02:52, 7 May 2013 (UTC)


 * I see that I probably should never have given you advice on how to make that nitric acid after all... 24.23.196.85 (talk) 04:00, 7 May 2013 (UTC)


 * No, that was fun, but I did not make nitroglycerine, if that's what you're infering. Plasmic Physics (talk) 04:17, 7 May 2013 (UTC)


 * Have you had two years of chemistry, Plasmic Physics? Knowing that (and the meaning of your last sentence fragment) will help us guide our suggestions. μηδείς (talk) 04:21, 7 May 2013 (UTC)


 * Yes, I've had two years. My last sentence fragment reasserts the cntext of my query, since you seem to have missed that from the link I gave. You speak of bombs and such, which is hardly applicable. Plasmic Physics (talk) 04:26, 7 May 2013 (UTC)
 * Actually, do you know what a bomb is? μηδείς (talk) 05:00, 7 May 2013 (UTC)
 * Hint: This word has a different meaning in chemistry than in everyday usage. 24.23.196.85 (talk) 06:00, 7 May 2013 (UTC)


 * I see: you're talking of a bomb calorimetre. It is still not applicable. I'm talking about experiments, where detonation (or deflagration) is an undesireable reaction. Plasmic Physics (talk) 06:53, 7 May 2013 (UTC)


 * No, a bomb calorimeter is a specific type of bomb, there are others about which we don't seem to have articles, although the sense is mentioned at wiktionary. μηδείς (talk) 16:24, 7 May 2013 (UTC)

Thomas Klapötke is a professor in Munich, the link above also mentions him. He has a large interest in high energetic materials and green bombs. One of his favorites is hydrazine azide (N5H5). I saw the material which is highly explosive and the people used normal glass ware to handle it. They were behind a several layer glass window reaching around with their arms. The used a set of leather and chainmail gloves for their hands. The use of more than a few hundred milligramms was not considered a problem but nobody I knew did it. Uranium hexaazide and the selenium and tellurium azides were handled in a very similar way. Klapötke also told the story of having a bromoazide in a flask and somebody opened a door and the induced pressure difference was enough to induce the explosion. The high speed of the explosion leaves only fine dust of the glass mostly incapable to penetrate the normal labcoat. He said only a few glass particles reached him making it very painful to close the safety belt when he went home that evening.--Stone (talk) 07:48, 7 May 2013 (UTC)


 * For a lack of better words: Bingo! Plasmic Physics (talk) 07:53, 7 May 2013 (UTC)

I think Plasmic might like this series, not to seem like I'm spamming it, but I did find it good reading, and I don't know a thing about chemistry. Shadowjams (talk) 07:54, 7 May 2013 (UTC)


 * I do appreciate a good read, however, I've already linked to that site near the start of this discussion. Plasmic Physics (talk) 09:54, 7 May 2013 (UTC)

The high energy working group was never a place for me to join. The place was dangerous. One PhD student had a hole in his palm and nearly died. The small round flask simply explodes in his hand. Although the fun to do the fall hammer test or the other tests to get physical data of the explosives would have been a nice work. --Stone (talk) 13:38, 7 May 2013 (UTC)


 * My late father in law was an industrial glassblower, and worked for a polytechnic which be came a university. His job was to make such specialist glassware if it was possible. So you may not be able to buy such stuff off the shelf, but it would be bespoke. --TammyMoet (talk) 17:49, 7 May 2013 (UTC)


 * Can such extraordinairy requirements be met by a glassblower's skill? Considering that the walls of such a vessel would be on the order of several centimetres thick (2-3 ?) and would be laminated with two different types of glass? Plasmic Physics (talk) 23:56, 7 May 2013 (UTC)
 * Using an air compressor to inflate the glass "gather" instead of a blowpipe is still a glass blowing skill and the man doing it is still known as a glassblower. And with aircompressors and support tools there's no real limit.  Wickwack 58.169.245.20 (talk) 11:06, 8 May 2013 (UTC)


 * Good, so my question is: why is that not the usual case, why do these experimenters make do with standard glassware, albeit with massive protection measures? Plasmic Physics (talk) 13:20, 8 May 2013 (UTC)
 * Do they? Where's your evidence that they do?  In any field there will always be some idiot who does something stupid, because he doesn't know any better, or doesn't have a real feel for the subject, or is just plain nuts, but that does not mean they are all stupid.  Wickwack 124.182.51.119 (talk) 12:19, 9 May 2013 (UTC)


 * Don't miss the "albeit..."-part, which implies the use of chain-mail gloves, blast proof windows, etc. Ergo, I'm not calling them stupid, or making any sort of judgement on their operandi modi for that matter. Plasmic Physics (talk) 12:28, 9 May 2013 (UTC)
 * It is stupid if somebody uses a complex or expensive solution to a problem where a simpler or cheaper solution will do the job. Again, why do you think they don't use appropriate vessels?  Your evidence?  Can you cite an example?  Wickwack 124.178.140.2 (talk) 23:40, 9 May 2013 (UTC)


 * Rather, I can't find evidence that they do. Plasmic Physics (talk) 00:46, 10 May 2013 (UTC)
 * So, cite some evidence or examples that they don't, then. You've been asked 5 times by 3 different people, over 3 days, so it looks like you can't.  Shall I ask the Ref Desk why don't aliens have the good manners to write us a thankyou note for our hospitality each time they depart Earth?  Heck, there's no evidence that they've ever bothered to write each time.  Wickwack 121.215.3.250 (talk) 15:46, 10 May 2013 (UTC)


 * I keep repeating that I'm not assertions, I making an enquiry. Enquiries don't need evidence, but you seem to miss that it is not an assertion. Plasmic Physics (talk) 03:12, 11 May 2013 (UTC)

Aeronautical Engineering
Why do the technicians, space scientists and engineers wear white coveralls, masks, boots and gloves while working on an spacecraft? — Preceding unsigned comment added by 117.200.240.10 (talk) 05:44, 7 May 2013 (UTC)
 * Same reason that nurses or lab techs wear white coats -- so that any dirt or contamination on their clothes would be immediately visible. Why do British soldiers wear red coats, and French ones wear brown pants?  ;-) 24.23.196.85 (talk) 05:56, 7 May 2013 (UTC)
 * The colour is not that important. In front of my office there is an image of the integration of the Dawn spacecraft and two of the engineers wear black suits. The colour could be used as a colour code like the white ones do the checking while the green ones do the documentation and the black ones do the actual work. The clean room levels like class 10000 force you to wear the protective garment. Most of the dirt in the clean room is introduced by the persons working there and the clean room garment is there to seal it and make it stay with the person. We had the choice for our clean room to get green, light and dark blue, pink, black and white.--Stone (talk) 07:29, 7 May 2013 (UTC)
 * There can be psychological reasons. Not all spacecraft work will require clean room conditions.  The company I worked for in the 1990's had several large data centres at different locations.  The supervisor of one centre set about using every opportunity to tell his team how good they were, and had them all issued with white coats.  It worked - the fault rate in his data centre went down, significantly lower than the other centres, and equally lower than before he took over.  The colour did not matter, and maybe he could just as well issued them with uniform shirts or something.  What did matter, is that wearing a white coat reinsforced in their minds the concept that they were good at their job and took care in it - and people rise or fall to their own perceptions.
 * Some factories I've worked in go to a lot of trouble to keep the place neat and clean, with everything in excellent condition, and issue different sorts of coats to different sorts of workers. It's the same thing - a proud worker is a good worker.  A sloppy workplace tends to get sloppy workers.
 * In many places, wearing a white coat or whatever is what you do - just as managers wear a tie, and senior managers wear a dark suit.
 * Not to be forgoten is that workers like wearing lab coats as they reduce wear and tear on your own clothes, and the cost of cleaning the coats is a tax deduction. — Preceding unsigned comment added by 60.230.238.42 (talk) 12:16, 7 May 2013 (UTC)
 * Wickwack 60.230.238.42 (talk) 09:57, 7 May 2013 (UTC)
 * I am skeptical. How do you know it wasn't some other practice by the same manager?  The mere fact that he was apparently eager to come up with new ideas/directives might have convinced other people there that somebody was paying attention.  I do believe the first response that it is meant to make dirt show up - no matter how clean an area is supposed to be, the way it gets dirty may well be something very obvious. Wnt (talk) 16:43, 7 May 2013 (UTC)
 * There's simply NO issue with dirt in a data centre. There's no issue with dirt in most places lab coats and the like are worn.  In most cases its about convention and image.  If you are a customer (whether you are a representative of a government buying a satellite, or an individual getting a vetinary to look at your sick dog.  All other things being equal, who are you going to deal with - the outfit whose staff are dressed in jeans, t-shirts, and thongs (= flip-flops in USA-speak) or the outfit whose staff are dressed in neat coats, proper leather shoes, and maybe wearing ties?  I knew the data centre guy very well, and I knew everyone in his team.  How he got his team, comprised as it was of techs just the same as the techs in the other centres, to do a lot better did not go unnoticed by management. As I said, the white coats were not the only thing he did - praise was the key to the performance improvement, by making them feel they were the best.  The white coats were a part of his strategy to get them to percieve themselves as top class, and through that, improve.  It's Leadership 101 actually.  Wickwack 120.145.46.40 (talk) 00:35, 8 May 2013 (UTC)
 * I'm sure I've read about other companies with a deliberately casual culture, and of course the same goes for academia. Being forced into uniform, stereotypical clothing seems to speak less of an employee being elite than of being of a low status. Wnt (talk) 04:23, 8 May 2013 (UTC)
 * I bet you have too. So have I.  It all depends.  What works for one workplace will not work somewhere else.  Look up Hawthorne Effect.  Essentially it is this:  In the Hawthorne factory of Western Electric in the 1920's, their best efforts resulted in only barely adequate quality and productivity, due to the limitations of the technology of the day.  Management decided to do a study on what would motivate the factory workers.  The lighting was improved.  Work output improved.  They increased lighting again.  Work output again improved.  Lighting was then degraded somewhat.  Aagin work output improved.  The Hawthorne experience has been studied ever since, and just about anyone who does management courses in the Western World gets to look at it.  The overall conclusion from Hawthorne and studies at other factories is that workers do better if they think management cares about them, not so much on what management actually does.  Workers work better if they see Management spending money on them.  Generally, it is good practice to give workers uniforms or "white coats".  But equally valid is showing you care about workers by allowing them some freedoms - it may be flexibility in dress, flexibility in work hours, or whatever.  That does not invalidate what my data centre coleague did, and does not invalidate that giving workers uniforms or white coats elsewhere can improve morale and pride.
 * Horses for courses. I worked quite a while for a very large company (the same one with multiple data centres) that was a bit like IBM - wearing a tie and a conservative suit was the thing in Head Office, and a sort of natural selection meant we liked wearing suits.  However, the company had a sort of skunk works/think tank in a separate location deliberately staffed by radical bright young university graduates who were expected to think up new ideas and challenge accepted technology solutions.  They got to dress in flip-flops, jeans, and teeshirts.  Right for them but not for me.  More Leadership 101 for you.
 * Wickwack 124.182.9.143 (talk) 05:28, 8 May 2013 (UTC)

Biplane vs. fighter jet
Suppose there's a dogfight between a World War 1 fighter biplane (for example, the Fokker Dr. 1 -- which was actually a triplane, but you get the idea) and a modern fighter jet (like the Mig-29). What would be the outcome of such a battle? Would it be an easy kill for the Mig, as I believe it would be? Or would both planes be unable to harm each other, as I've been told by a fellow aviation fan? (For the sake of argument, let's suppose both planes are piloted by top aces -- for example, Red Baron in the Fokker, and Ivan Kozhedub in the Mig -- so pilot skill is not a factor.) 24.23.196.85 (talk) 05:53, 7 May 2013 (UTC)
 * I'm not sure the Fokker Dr. 1 has the maneuverability necessary for evasion of an R-73 fired from ten kilometers away. The Fokker also couldn't return fire at that range, as the MG 08 that was its sole armament has a range of 2-3.5 kilometers.  -- Jayron  32  06:02, 7 May 2013 (UTC)
 * That's what I'm thinking too -- provided that the missile can track the Fokker (which is the argument the other guy used -- he claimed that neither heat-seeking nor radar-guided missiles would have enough of a signal to track, and that the Mig wouldn't be able to get a shot with its Gatling gun because its higher stall speed and wider turning radius will make it overshoot. Personally, I don't buy it, but I'm looking for confirmation from someone more knowledgeable.) 24.23.196.85 (talk) 06:15, 7 May 2013 (UTC)
 * Why wouldn't radar-guided missiles have something to track? The Fokker should be large enough to show up, shouldn't it?  It is much smaller than a Jet (5m long x 7 m wingspan for Fokker vs.  17m long x 11m wingspan for the MiG) but the resolution of the radar should be good enough not to confuse the Fokker with a duck... -- Jayron  32  06:31, 7 May 2013 (UTC)


 * ...the Mig wouldn't be able to get a shot with its Gatling gun because its higher stall speed and wider turning radius will make it overshoot... That sounds like wishful thinking. Aircraft routinely destroy slow-moving and stationary surface targets.  While it's plausible that our hypothetical MiG can't sit on the Fokker's six and follow it oh-so-slowly around, I don't see any practical problem with the MiG strafing the Fokker at its leisure.  And it really shouldn't take that many 30mm cannon rounds to finish off the Red Baron. TenOfAllTrades(talk) 06:46, 7 May 2013 (UTC)


 * The OP's friend exhibits (as Spock says of Khan) two-dimensional thinking. The MiG can strafe the Fokker while diving on it or climbing up at it; he does not need to patiently sit right behind it as it chugs along. The MiG's astonishing power means it can trivially climb to a point a mile above the Fokker and then can dive down at its leisure. -- Finlay McWalterჷTalk 09:50, 7 May 2013 (UTC)


 * The Fokker would be helpless, Red Baron or not. The differences in technology, capabilities, and armament are so vast that I don't think there is any scenario where the older plane would pose any sort of threat. This is, after all, a plane that first flew a mere 14 years after the Wright Flyer. To even things up slightly, you'd have to take away the MiG's radar and missiles (or add them to the Fokker, although that might make it too heavy to fly), but I still don't think there's much the Fokker could do. You may as well ask a Model T to outrun a Corvette. --Bongwarrior (talk) 07:05, 7 May 2013 (UTC)


 * I'm going to go out on a limb here, and suggest that none of us are fighter pilots (the 8 year old me would be disappointed)... however that said, I bet if a Mig29 flew over the top of a biplane it might make it crash just because of its wake. Who needs a 30 mm when you have 1000 knots. Shadowjams (talk) 07:52, 7 May 2013 (UTC)


 * Indeed: the MiG's engines generate a massive jetwash and the wings a sizeable vortex - safe operating distances to avoid another aircraft's wake turbulence is measured in nautical miles. The MiG can easily get his to envelop the Fokker, which would probably shatter its airframe. -- Finlay McWalterჷTalk 09:59, 7 May 2013 (UTC)


 * During the Falklands war I believe Harrier jump jets were able to avoid Exocet missiles by staying still, this fooled the Exocet missiles into considering them as decoys and looking for something else. I'd guess a Fokker would be considered as practically stationary by such a missile. Dmcq (talk) 09:34, 7 May 2013 (UTC)


 * Exocet is an anti-ship missile. Argentine air forces in the Falklands War lists the AAF's offensive missile capability in 1982. -- Finlay McWalterჷTalk 09:42, 7 May 2013 (UTC)


 * Sorry one of their anti-aircraft missiles anyway and it's about the only name of a missile I heard of in the war!, I'm no expert on military weaponry, I know the NRA goes on at length about assault rifles and automatic rifles but it all passes over my head. Dmcq (talk) 10:31, 7 May 2013 (UTC)


 * It's good that you mention the MiG 29 specifically, because that leaves open (at least theoretically) the possibility of the most Tom Clancy-ish, fighter-jockily silly strategy the MiG can employ. He can fly ahead and beneath the Fokker, perform a Pugachev's Cobra, and strafe the Fokker as it passes in front of him. There's some chance that might not be safe (particularly that the gun exhaust, expelled into such an unusual air envelope, would stall the port engine), and it'd be idiotic to do in an actual conflict. But I'd put good money that somewhere, when his boss was off golfing, that some VVS Colonel has tried this to see if it works. -- Finlay McWalterჷTalk 10:11, 7 May 2013 (UTC)


 * The Fokker can come down to tree top level and jink about between tall trees and hills. This would make it just about impossible for a jet fighter to strafe, and it may make it difficult to hit with rockets as well. Isreali Mirage fighters found it very hard to hit MiGs as the lower stalling speed of the MiGs allowed them to come down to low altitudes and jink about. The Americans had a similar experience in the Korean War - the slower older generation MiGs could avoid being hit by coming down lower, and if the American overflew, pull back and hit the American.  Not that I expect a Fokker with WW1 guns could hit a departing and rotating MiG29.  It wasn't all that easy to hit other WW1 fighters.  And modern fighters can take a lot more punishment anyway.  The "dirty' stalling speed of a MiG29 is thought to be about 230 km/hr whereas the Fokker DR1 triplane stalled at 72 km/hr.  As far a strafing goes, imagine trying to hit a door size target while passing it at 160 km/hr - pretty damm difficult - for both.  So I tend to think the OP's friend is more right than wrong.  Wickwack 60.230.238.42 (talk) 11:57, 7 May 2013 (UTC)


 * Let's do the math. don't know the stall speed of the MiG 29, but its landing speed is higher than that. Looking at a roughly equivalent US fighter, the F/A18 Super Hornet, it lands at about 240 km/h (arresting gear says US equipment can stop an aircraft at 130kt).  The maximum speed of the Fokker is 185 km/h; let's say he's sustaining 170 km/h. So if the MiG is chasing the Fokker, as slowly as he can, he's gaining at about 1 km/minute.   The MiG's Gryazev-Shipunov GSh-301 cannon has an effective range of between 1.2 and 1.8 km. So the MiG comfortably has a full minute to strafe the Fokker.  The MiG carries 150 rounds, which (at the 301's cyclic rate) he can fire off in as little as 5 secondsl; he only needs a handful to kill the Fokker.  This isn't an unusual mission for an air-superiority fighter - it would be expected to be able to shoot down cruise missiles, light aircraft, helicopters, and reconnaisance drones. -- Finlay McWalterჷTalk 12:13, 7 May 2013 (UTC)
 * You've missed the point. The Fokker can evade by flying as SLOW as possible, and he can turn on a sixpence, due to flying slow and because it's a triplane designed for manoeverability.  That's what the MiG pilots did in the Isreali/Arab war and the Korean War - they slowed down as much as they could and darted about at treetop level, thus turning their slow speed to advantage.  The MiGs would sometimes even lower wheels, as the "dirty" stall speed is lower than the "clean" stalling speed (with more drag you can fly a bit nose up with more throttle - the aircraft is then stable at a lower speed).  What matters then is not just the MiG gun range but the rate of fire and the spread.  The MiG29 in this case won't have a steady target for 1 minute, he has a moving target passing through his sights, if he's lucky, for a second or so.  Even if they are flying straight and level, which would only happen if the Fokker pilot is a complete fool, the closing speed is not 230-170=60 km/r, its 230-72 = 158 km/r so the MiG pilot still has only 23 seconds, not one minute. In practice he has even less, because he'll want to pull up to avoid a collision.  He'll have maybe 8 seconds at best if the Fokker pilot is a complete fool. Wickwack 60.230.238.42 (talk) 12:31, 7 May 2013 (UTC)


 * To all intents and purposes, engaging an elderly triplane would present the same problems as engaging a small observation helicopter, a scenario which I imagine fast jet pilots practice regularly. To Dmcq, although it is possible for the Harrier to rotate its jet nozzles to cause rapid deceleration, a tactic known as Vectoring in Forward Flight or "Viffing", I have read that this tactic was not employed during the Falklands War, although there was much press speculation that it would be. Our Vectoring nozzles article disagrees, so more research needed. Alansplodge (talk) 13:30, 7 May 2013 (UTC)


 * Argh - stupid argument. The Mig wins very, very easily...and in at least three or four different ways.  The Fokker will be destroyed before it even knows that the Mig is nearby.


 * Simplistically - the Mig has the capability of deploying nuclear bombs - so it flies at high altitude above the Fokker - drops a nuke and it's game-over for everything within several miles of the target point - but the shock wave would shred the cloth-covered wings from a distance of ten miles. Accuracy isn't needed.


 * OK - let's assume that the Mig doesn't have that weapon load - or that it simply isn't desperate enough to use such a drastic solution.


 * Flying low and slow isn't going to help the Fokker. It's speed range is 45 to 115mph - about the speed range of a car.  It can turn pretty tight for a plane - but nowhere near as tightly as a modern car.  It's radar and thermal signature is also comparable to a car.  So can the Mig destroy a car?  Sure - it has a bunch of air-to-surface missile options...taking out a moving car is child's play for those kinds of systems.  Truck convoys are classic modern military targets - and a Fokker is not much different.


 * The point is that "dogfighting" simply doesn't enter into the equation...the Fokker will be destroyed from five miles away by any one of dozens of possible guided or unguided missile options.


 * Even if the Mig is somehow forced to use it's cannon - the range of that weapon is about one and a half kilometers...it's perfectly capable of strafing stationary targets - and it has laser guidance...taking out a car (or the Fokker) would be child's play. That gun can take out most "soft" targets with a three round burst.


 * If your friend is still skeptical - ask this: Is the Mig capable of shooting down helicopters? The speed, altitude and manouverability range of a military helicopter is a close match for the Fokker.  Helicopters can fly at any speed from zero to over 100mph - they can literally turn on a dime...manouverability and slow flying won't help the Fokker one iota.  I absolutely guarantee that there is a whole range of weapons that this aircraft can carry that are ideally suited to taking out helicopters.


 * Even without weapons of any kind - a combination of hot jet exhaust, supersonic shock wave and massive air vortices would disrupt the flight path and the health of the pilot enough to do it great harm...being in the open cockpit of a plane made of cloth in the wake of a Mach 2 flyby would not be a survivable thing! You can try to argue that the Fokker can turn fast enough to avoid being close to the Mig - but the math says otherwise.  Let's suppose the Mig lines up on the Fokker from a mile away.  At 1500mph, the Mig will cover that mile in a little over 2 seconds.  The Fokker (at top speed) can cover about 300 feet in that time - and if it's going slowly enough to turn tighly, then it'll be under 100 feet away...so even with the best possible reaction time, and the most direct flightpath away from the oncoming jet the Fokker will be hit by supersonic shockwaves at something like 200 feet from the Mig.  Recall the Mythbusters episode where a blue angel aircraft trashes stuff on the ground in a 200 foot altitude, Mach I flyby?  Well, double the speed and you get four times the energy...yeah...that's what happens to the Fokker.


 * Silly argument - trivially dismissed on multiple grounds.
 * SteveBaker (talk) 13:49, 7 May 2013 (UTC)


 * A very convincing argument by Steve. I had forgotten about laser guided weapons - something not available in the Isreali-Arab and Korean wars I used as examples of succesful evading by slow craft.  My first thought was that you shouldn't include nuclear weapons, on the basis that nobody is going to approve the deployment of such an expensive weapon just to destroy a triplane.  But on second thoughts, you should include it, as the scenario of a Fokker triplane or any of its contempories being used in a war today is silly anyway. Wickwack 120.145.46.40 (talk) 00:51, 8 May 2013 (UTC)
 * My $0.02: The Mig can kill the Fokker and possibly its pilot with its sonic boom, and its vortex will disrupt, if not damage or destroy its control surfaces. Remember that a "Mach 2" plane can often only fly slightly supersonic at low altitudes. Still the cheapest option, and one of the easiest.
 * Cannon might be less than effective. The Fokker may not be heavy enough to make the cannon rounds explode. Enough rounds will be bad news (eventually, one will hit something hard, like the engine), but three hits to the wings will probably do no more than punch holes. How probably, I can only guess. (How effective are they against dirigibles and balloons?)
 * Radar Missiles will probably be all OK. They have been upgraded to be useful against "stealth" planes, so...
 * IR missiles, I don't know. Not sure if there's enough of a signature to trigger the long-rod warhead at the correct time. The blast will still be Bad News(TM), though.
 * Eh, Freudian slip. Continuous-rod warhead. - ¡Ouch! (hurt me / more pain) 07:52, 8 May 2013 (UTC)
 * Nukes: Just NO. Too expensive.
 * Laser-guided Whatever: still on the expensive side. Not sure if the laser will track it that reliably, either
 * Rockets? Like cannon rounds, and not so good overall. More punch, but heavier, slower, more expensive, fewer of them, etc.
 * Free-fall bombs. I think that's where it's at. If the Red Baron stays low, just dive-bomb him, and he's utterly [fokked]. ;) - ¡Ouch! (hurt me / more pain) 07:50, 8 May 2013 (UTC)
 * While it is true that in general supersonic planes cannot go as fast at near sea-level, and that applies to the MiG-29, it is still rated to fly at Mach 2 (~2400 km/hr) at low level. So SteveBaker is probably right - one close fly past and the Fokker is history.  But you'd need a bloody big free fall bomb to do it.  Cannon should work well if it's laser guided from kilometers away as SteveBaker said.  One hit in either the pilot's head or torso, the fuel tank (no self-sealing tank in a WW1 Fokker) or the engine and it's history.  Why worry about cost when a MiG-29 against a Fokker triplane is a nonsense scenario anyway?  Wickwack 60.230.209.84 (talk) 08:17, 8 May 2013 (UTC)
 * Well, sure, if you start adding in more constraint like price and collateral damage - you can make the answer come out any way you want. If you say that the entire mission has to cost less than $100 then the Mig can't even start its engines without consuming $100 of jet fuel...so the fokker swoops low over the stationary Mig and strafes it until it hits something important.  Conversely, without constraints, the total inability of the fokker to place even a single bullet into the Mig means that the Mig pilot can keep trying over and over again until he does something the fokker can't survive.  If nothing else, he can just wait for the triplane to run out of fuel (the Fokker can only stay aloft for about 90 minutes - the Mig is good for at least a couple of hours)...then, when it's a sitting duck - he can use any kind of ground attack weaponry and will kill the fokker in about as long as it takes to push the right button.
 * But within the given parameters, and with any reasonable assumptions, the answer is very clear.
 * SteveBaker (talk) 17:16, 8 May 2013 (UTC)
 * Exactly! How can you set, sensibly, constraints, cost or otherwise, or apply rules of engagment, when the basic scenario of a MiG-29 against a WW1 triplane has no realistic basis at all - it is just plain silly.  It's a situation that can only arise in a pub conversation, so the only way you can answer this is to allow the Fokker to do anything a Fokker could do (in 1916), and the Mig-29 to do anything a MiG-29 can do (today).  Wickwack 120.145.32.250 (talk) 04:10, 9 May 2013 (UTC)

Zero point energy and the volume of the universe.
Why doesn't the zero-point energy density of the vacuum change with changes in the volume of the universe? And related to that, why doesn't the large constant zero-point energy density of the vacuum cause a large cosmological constant?

Is it allowed to postulate / hypothesize on this topic on the reference desk, or is there a separate science forum / talk page for that? Robert van der Hoff (talk) 06:49, 7 May 2013 (UTC)


 * Robert, the idea is that a header is a **short** (up to about 7 words) pointer to what the question is about, the meat of which then appears below the header. --   Jack of Oz   [Talk]  07:32, 7 May 2013 (UTC)


 * (I made a more concise title and transferred the L-O-N-G title into the message body). SteveBaker (talk) 12:59, 7 May 2013 (UTC)


 * We don't encourage using the reference desk simply to initiate discussion - especially when it's to discuss some idea that you had. However, there is a reasonable question here that we can possibly answer. SteveBaker (talk) 13:01, 7 May 2013 (UTC)


 * You hit the nail right on the head. That is indeed a very deep mystery that is yet to be satisfactorily answer by modern physics. Naive calculations show that the cosmologic is about 120 orders of magnitude off (If memory serves). Supersymmetry improves that to "only" 60 orders of magnitude. Dauto (talk) 22:28, 7 May 2013 (UTC)


 * And did you read the Zero-point energy article? where energy per particle is ½hν, not necessarily a very high density by cosmological standards. And this article also mentions renormalization to deal with the possibility of the lowest energy level of fields also containing energy. Graeme Bartlett (talk) 08:05, 8 May 2013 (UTC)


 * It's not ½hν per particle. It's ½hν per vibration mode of each bosonic field which strictly speaking is infinite hence the need for renormalization. Dauto (talk) 17:18, 8 May 2013 (UTC)

Why do we need omega-3 fatty acids?
What would the evolutionairy basis be for the need for omega-3 fatty acids? As a land based species it doesn't make sense that we require a nutrient which is most prevelant in oceanic fish.11:17, 7 May 2013 (UTC) — Preceding unsigned comment added by 137.224.252.10 (talk)


 * Just a relavent thought; omega-3 supplements are a waste of money, since they have a poor bioavailability. To quote a certain Big Bang character, "All you're buying, is expensive urine". Plasmic Physics (talk) 12:20, 7 May 2013 (UTC)


 * There are many plant sources of omega-3 fatty acids, so since the premise of your question is false, your question is ultimately unanswerable. It is certainly very highly present in fish, but it's also bioavailable in many foods that would have been food sources for people for thousands of years.  -- Jayron  32  12:41, 7 May 2013 (UTC)
 * Also, if you go back far enough, we were oceanic fish! If Omega-3 fatty acids became an essential part of our piscine metabolism back then, they may have persisted as such after we (i.e. the ancestors of all the tetrapods) crawled up on land. {The poster formerly known as 87.81.230.195} 212.95.237.92 (talk) 13:32, 7 May 2013 (UTC)


 * Omega-3 is important for brain development.  et al.  That is why the Aquatic ape hypothesis has developed traction over resent years. Later on, when farming was learnt, other sources of  were found. Plasmic Physics appears to be  confusing water soluble vitamins. The excess of those, get extricated in urine but dietary fatty acids are  broken down and used by the body as fuel. The kidneys don't filter them out. They get metabolized instead into useful fuel in most cases. An excess of Vitamin A (fatty acid based) however can lead to Vitamin poisoning and you can't piss that out either; hence hypervitaminosis. Therefore, I can't see what befit  Plasmic  comment was to this OP's question. Perhaps he knows something I don't?--Aspro (talk) 15:24, 7 May 2013 (UTC)


 * Not at all Aspro, the study I that read, specifically refers to omega-3 acids administered orally. It states that they generally have low bioavailability, or are not in a form which is readily absorbed through the digestion tract. Plasmic Physics (talk) 23:32, 7 May 2013 (UTC)
 * Don't see you point PP. You state: that you  specifically refers to  fatty-acids administered orally”. So, did our  ancestors have access  to hypodermic syringe administration  of   fatty acids not administered orally ? - I don't think so.... orally yes. You are here, and I'm am here- now!,  communicating to you via the internet!!.  Your are an  [[Issue (legal)|

issue]] of your ancestors who 'must have' had an adequate   bio-available source of  omega 3  so that your linage  has  survived into the modern day. So, Engage brain, before engaging fingers to keyboard. Then you stated: nor are they  in a form which is readily absorbed through the digestion tract???? Fatty-acids are fatty-acids. The human body looks at all fatty -acids all as fuel................ – mind you.... PP might just have some superior knowledge (scientifically  proven in the last few months -weeks-days) that we have all missed. Reference desk is about about answering the OP's-questions-the best-we-can …....not about confusing them with scientific piddle.-- Just sick to physics PP. As always, Wikipedia has an article for guidance in this instance. Sutor, ne ultra crepidam.--Aspro (talk) 18:31, 9 May 2013 (UTC)


 * . Here is a nice summary of the investigation. Plasmic Physics (talk) 22:59, 9 May 2013 (UTC)
 * Thanks for posting a report which actual supports my drift. Quote from the article: “Because of the wide variability in the results between individual subjects and other factors, acute studies appear not to be as dependable as chronic studies in making conclusions with respect to bioavailability.” There is a WP article to explain (me thinks) your last inclusion -Obfuscation. From memory (but I am sure others will back me up) the DHA/EPA mentioned the   article you posted can be manufactured in the body from alpha-linolenic acid  (LNA 18:3w3) found in seeds etc. But how many unprocessed seed do you have in your diet?  Going back to your first comment. It is the efficiency which your body converts alpha-linolenic acid that depends on  your survival.  If your ethnic stock is of Irish or Norwegian or some other European decent then your body may well l have trouble doing this  alpha-linolenic acid conversion. Thus you will need  DHA & EPA dietary  sources (whether they be fish, or bought over-the-counter supplements, etc.,) to keep you healthy. Most medical doctors are not interested in this because they sell “health care”.  Can I make my self anymore clear!??? Just stick to  commenting on queries about levers,  force, vectors  and other physical things.Aspro (talk) 14:23, 10 May 2013 (UTC)


 * I didn't purposefully becloud the study. In anycase, none appreciates being denigrated. I'm wrong, sure, by all means, say so, but don't denigrate. Plasmic Physics (talk) 03:06, 11 May 2013 (UTC)


 * OK. Then, from here on in, can you engage brain before engaging fingers on keyboards? So by avoiding adding confusing piffle to any  OP'S question as you did with your first  post? Academics, review WP Ref all the time,  and the accuracy  of our answers (or lack of)  get spread all-round the internet pretty dam quick.  15:37, 11 May 2013 (UTC)


 * Even if there is not such a disclaimer already, it is common knowledge that the reference desk cannot be cited as a trustworthy source. A person who cites the reference desk as their source, can only bring shame upon themselves for their own ignorance'sake.
 * The Desk's responsibility is to redirect the enquirers to actual sources, and to develop their train of thought around their particular query. We don't have to put in effort to be correct 100% of the time, unlike our articles. PS That is still considered as denigration, implying that I don't think before I post. Plasmic Physics (talk) 23:22, 11 May 2013 (UTC)

We produce chemicals we need internally with enzymes (coded for by genes) that create a metabolic pathway for the chemical to be produced. Some such pathways may be unique and metabolically costly. In any case, if a nutrient is highly available in your natural diet (like vitamin C in the vegetables our ancestors ate) then the gene for the enzyme necessary to make that nutrient may be mutated or lost without harm. Once the gene is lost, people whose diet becomes unnaturally restricted can become ill (scurvy, beri beri) due to the lack of the nutrient. μηδείς (talk) 16:21, 7 May 2013 (UTC)


 * I found another source - seal oil - while searching omega-3 and Namibia (I continue to suspect an ancient origin of human feet and hairlessness in the wildly variable conditions of the Okavango, even if very good evidence traces the known origin further north) - anyway, apparently Nambia exports, or recently used to export, substantial qualities of seal oil as an omega-3 supplement. Here's one manufacturer's claim from Canada.   Apparently high omega-3 levels are true of all fish-eating mammals .  (It wouldn't surprise me if fish-eating birds were another source for less finicky palates...) Wnt (talk) 16:31, 7 May 2013 (UTC)

bioremediation
Can Tetrahydrofuran be phytoremediated? According to http://apps.echa.europa.eu/registered/data/dossiers/DISS-9d87f855-86db-4392-e044-00144f67d249/AGGR-9e7de3e4-b992-48c1-b99b-cbbabe912a48_DISS-9d87f855-86db-4392-e044-00144f67d249.html Tetrahydrofuran is not very bioaccumilative, which leads me to think phytoremediation is not effective. — Preceding unsigned comment added by 149.152.23.34 (talk) 15:25, 7 May 2013 (UTC)

Also, can tetrahydrofuran be removed from the Seymour Hazardous Waste Site by Air sparging?--149.152.23.34 (talk) 18:26, 7 May 2013 (UTC)


 * Based on the properties of THF, I think some form of bacterial remediation would be the most promising method. BTW, what exactly is the nature of contamination at the Seymour waste site? 24.23.196.85 (talk) 00:00, 8 May 2013 (UTC)

Remote Sensing
I am trying to learn how remote sensing developed over the course of time beginning in the seventies. It would be helpful to find the Proceedings for the Annual Meetings of The American Society for Photogrammetry during that period of time. Where can I find them? Clues: not WorldCat and not the American Society for Photogrammetry and Remote Sensing. — Preceding unsigned comment added by Bobgustafson1 (talk • contribs) 19:21, 7 May 2013 (UTC)
 * While trying to answer this question I came across the Monroe Institute. Are you familiar with it? --TammyMoet (talk) 20:47, 8 May 2013 (UTC)

Venus fly trap digestion
I understand that the digestion process of the prey of a Venus fly trap may take several days, but how long does it take for the prey to actually die? What is the process that kills it? Against the current (talk) 20:07, 7 May 2013 (UTC)


 * If no one is able to answer here, you could ask at Wikipedia talk:WikiProject Carnivorous plants.
 * —Wavelength (talk) 21:30, 7 May 2013 (UTC)


 * I don't know how long it takes for the bug to die, but the process that kills it is almost certainly chemical poisoning. 24.23.196.85 (talk) 00:18, 8 May 2013 (UTC)


 * Insects breathe through trachea that open via spiracles on the sides of their abdomen. Once digestive juices get in these they will smother, if not already. μηδείς (talk) 00:56, 8 May 2013 (UTC)

Why does stirred water reverse direction slightly just before reaching a stop?
Stirred me tea with a tea bag in it. Round and round the tea bag goes, in the direction stirred. Eventually the tea bag comes to rest... well, almost: before it does it goes back a small amount in the opposite direction. What causes this reverse? It's as if the water is slightly elastic. At first I thought it may be an illusion caused by watching the bag going round. But on careful observation I am sure it does go backwards. --bodnotbod (talk) 22:44, 7 May 2013 (UTC)


 * Maybe the teabag strayed across the centre of the vortex, and the remaining angular momentum created a torque in just the right way to turn the teabag in the other direction. Plasmic Physics (talk) 23:19, 7 May 2013 (UTC)
 * Water is most certainly not elastic, it does not retain a memory of a previous state. Plasmic Physics (talk) 23:23, 7 May 2013 (UTC)
 * It is worth considering that we are dealing with a three-dimensional flow here. It might be worth trying it in a glass rather than a cup, to see if that helps explain it. AndyTheGrump (talk) 23:28, 7 May 2013 (UTC)
 * I think this could be a backflow caused by the vortex collapsing on itself as the flow velocity drops toward zero. FWiW 24.23.196.85 (talk) 00:12, 8 May 2013 (UTC)
 * The teabag could be "elastic".... It would almost certainly have less mass then the water, could it be somehow rebounding off the water? Vespine (talk) 00:14, 8 May 2013 (UTC)
 * Isn't this how they power the TARDIS? μηδείς (talk) 00:52, 8 May 2013 (UTC)
 * You're thinking of the Heart Of Gold, but close. Tevildo (talk) 01:04, 8 May 2013 (UTC)
 * Actually, I was just making sure people were paying attention. :D μηδείς (talk) 01:44, 8 May 2013 (UTC)
 * The teabag may be an impediment to the circular motion of the stirred water. If it is an impediment to the circular motion of the stirred water perhaps we can assume that to a slight degree the water level is higher at the trailing edge of the teabag than at the leading edge. At the point at which circular motion of the water ceases, the higher water level "falls", and in so doing it momentarily falls below the water level of the cup of tea at complete rest. This overshooting of the higher level of water to a lower level of water creates a lower level which the teabag itself falls into. This "falling" of the teabag creates a slight backward motion. This is just an explanation that seems likely to me, but it might be wrong. Bus stop (talk) 02:19, 8 May 2013 (UTC)
 * It occurs to me that the opposite may be occurring at the leading edge of the teabag. A "depression" may exist in the surface of the liquid while the teabag is in forward motion. When motion ceases, water may "fall" into this slightly lower water level at the "leading edge" of the teabag. This filling in may result in an overshooting of the amount of water to result in a completely uniform water level throughout the body of water. That momentary overshooting of water into a depression at the leading edge of the teabag may result in a momentary higher water level at this point, which may serve to push the teabag in a small backward motion. Bus stop (talk) 02:46, 8 May 2013 (UTC)
 * The way to really see this effect is during a large plasmid preparation. For some reason, perhaps the elasticity of the DNA (?), a flask filled with bacterial lysate in 10% SDS will very noticeably rebound and come back the other way. Wnt (talk) 04:20, 8 May 2013 (UTC)
 * Thank you for the many replies thus far. I think I shall have to read some of them a few times more to grasp them. I wondered whether someone might say "ah, this is the '[Scientist's name Effect]'". Thanks again everyone. --bodnotbod (talk) 11:25, 8 May 2013 (UTC)
 * Some variation on this explanation is certainly at work here. As another way of visualizing the fluid dynamics at work here, imagine a wave breaking against a cliffbase; it's foreward momentum drives the water upwards initially until gravity and various complexities tidal forces cause it to fall back.  The water in the cup (which I assume to be roughly circular) also has momentum, but it is not nearly as uniform in direction (and likewise the surface is curved).  Nonetheless, the two do interact with many of the same principles described above and eventually the overall momentum will decrease to a point where where the flow cannot be maintained in a generally uniform ("forward") direction and the water becomes choppy, with portions of it conveying different mechanical waves with overlapping and "competing" momentum operating across a three-dimensional space.  It is even possible under the right conditions, that a brief counter motion (also circular, but moving in the opposite direction) could occur.  Snow (talk) 08:51, 11 May 2013 (UTC)

Another possibility is that this an optical illusion. If you look intently at something thats visibly rotating for about 20 seconds, then transfer your gaze to a textured surface (concrete works well), the textured surface appears to start rotating in the opposite direction. (Well it does for me!)122.108.189.192 (talk) 07:24, 9 May 2013 (UTC)

Sodium carbonate electrolysis?
Carbon dioxide scrubber says that you could electrolyze a sodium carbonate solution to get CO2 out from the carbonate returning it back to sodium hydroxide. But there is very little about that in google (like searching for sodium carbonate electrolysis) so I have a question: What gasses will be generated at the cathode and the anode while electrolyzing sodium carbonate in water?118.136.5.235 (talk) 23:28, 7 May 2013 (UTC)
 * Anode -- CO2 only; cathode -- none (if the product is NaOH). However, it is possible to electrolyze molten sodium carbonate all the way to sodium metal, in which case both CO2 and oxygen will be generated at the anode, and hydrogen at the cathode.  Also, converting sodium carbonate to sodium hydroxide does not require electrolysis -- simply distilling a hot solution of the carbonate with steam under vacuum can produce the hydroxide by stripping out the CO2 (this is actually done on an industrial scale in some coke plants). 24.23.196.85 (talk) 23:55, 7 May 2013 (UTC)
 * This isn't strictly electrolysis, as this is not a redox reaction. The oxidation states of all elements stay the same on both sides of the reaction.  It is merely a non-redox Chemical decomposition of a metal carbonate.  You get sodium hydroxide merely because sodium oxide pretty much instantly forms sodium hydroxide in water.  You need to use electric current to generate enough energy in a water based solution, as you can't get enough energy from heating it, but you can use heat to decompose solid sodium carbonate into sodium oxide and carbon dioxide just fine.  The water present in solution, however, prevents this from happening when heated: you can't get the solution much above the boiling point, which is not a high enough temperature to cause the decomposition.  -- Jayron  32  00:01, 8 May 2013 (UTC)
 * Seems really cool to know that we can strip out CO2 just by distilling it, but after a quick search in google (carbonate distillation) it returns home brewery thingy... so is you can provide the source, it will be good and anyway thanks for the answer118.136.5.235 (talk) 23:23, 8 May 2013 (UTC)
 * Sorry, I was wrong about that -- what I was referring to was stripping out excess CO2 from sodium bicarbonate solution to regenerate sodium carbonate (Seaboard process), NOT converting sodium carbonate to sodium hydroxide. BTW, the source is the book Coke, Tar and Coal Chemicals, which is available at our city library (I don't remember the author's name). 24.23.196.85 (talk) 04:47, 9 May 2013 (UTC)
 * Seems good enough to scrub CO2 from air.. or might not.. thanks (its vacuum carbonate process you describing not seaboard process) 118.136.5.235 (talk) 00:44, 10 May 2013 (UTC)