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September 19

Surface charge on a conductor

So if there is a net charge in a solid spherical conductor let's say, we know that the charge will flow to the surface and arrange themselves to minimize its electrostatic energy (as far apart from each other as possible). But what happens to its one and two dimensional analogs? For a very super thin circular conducting disk, would the charge all go to the perimeter (the circumference)? And for a very thin needle, does the charge go to the ends? If not then what happens? 67.40.134.8 (talk) 02:23, 19 September 2011 (UTC)

I'd say no, because those things cannot be true 2- or 1-D analogs. In the real world the disk, for example, actually still has two large faces, and even if it were one atom thick it would still effectively have one large face, over which the electrons or holes would distribute. (If it were so thin that its thickness could not accommodate even one layer of electrons, the same would be true of its edge). However, due to the geometry of the edge or ends there would, I suggest, be higher concentrations of charge there, which is what we observe in, for example, St Elmo's fire or on lightning conductors. 90.193.78.7 (talk) 11:35, 19 September 2011 (UTC)

{edit conflict) In the case of the 3d charge at the surface the field inside the sphere is zero (see shell theorem) - because the field is zero everywhere inside the sphere this means that there is no net force on charges inside a spherical surface of charge.. This actually means that you could have a charge distribtion in the solid spherical case of charge on the surface and a percentage of the charge in a spherical shell inside the sphere. A third band of charge is not possible since one of the bands would lie outside the inner band and experience a net force - causing the charge to move to merge with the surface charge..

(This means that your initial assumption of edge charge on a spherical body may not be absolutely true) Sorry about that - just spotted my error - ignore

Did that make sense so far (you probably need to be familiar with "shell theorem" or maybe Gauss' law for gravity as applied to electric charge..?)

As I remember it's a specific property of the spherical case that the field inside is zero. This is definately not true within the 1D (needle) case, and as I recall not true inside the 2D (disc) case either.

Therefor it seems quite possible that you can get equilibriums where the charge is not all at the edge (I ignore the cases where some charge is at the absolute centre).

To be certain in the 2D you would need the field potential inside a symmetrical "flat ring" of charge .. only with this information can you be certain - if it is zero everywhere inside then the case is the same as the 3D case, if not then other equilibrium arrangements will apply.

Can you/ have you got that potential due to a ring of charge?

For the 1D case I can propose at least one case - charge at the edge, charge in the centre, and a pair of charges neither at the edge or in the middle held in equilibrium by the centre and edge charges.. - this is a possibility different from the 3d sphere case. I can't say if there are other cases too.Imgaril (talk) 11:50, 19 September 2011 (UTC)

Just for the record it looks like calculating the field potential inside the 2D ring is fairly tricky (for a non-maths degree holder) and I couldn't find the answer easily searching - if you need to pursue this for the 2D case you might be better off asking at the maths desk..Imgaril (talk) 12:19, 19 September 2011 (UTC)

apologies if all that just muddied the water by the way - the answer in at least the 1d case is that its not the same as for the 3d case - I'll leave a note on the maths desk about this too

You may find this of interest: Lightning rod#Should a lightning rod have a point?. --Tango (talk) 12:02, 19 September 2011 (UTC)

That charges end up at the surface of a conductor doesn't follow from "minimization of electrostatic energy". It follows from that and Coulomb's law, but that means that the intuitive idea that "the chages are repelling each other so they will move as far apart as possible and therefore they end up on the surface" is incorrect. Replace the 1/r^2 law by an 1/r^3 law and you'll find that the charges will reside in the bulk, not on the surface.

What does always happen in electrostatics (Coulomb's law or no Coulomb's law), is that in equilibrium, the electric field has to be zero inside the conductor. If not, then forces would act on charges and they would therefore move around. Applying Gauss' law (which is equivalent to Coulomb's law) then yields the result that charges reside on the surface of a conductor.

In case of a needle, the charges don't go to the point of the needle. What does happen is that a electric field near the needle point is large. You can see this intuitively as follows. The electric field inside the needle is zero, this means that the electric potential in the needle is constant. Now, the electric field jumps if you move from inside the needle to outside the needle because of the surface charges, but the potential changes in a continuous way.

What then matters is how much charge must flow to the point of the needle to make its ptential the same as on the rest of the needle. Of course, the smaller an object, the less charge you need to raise its potential. That the electric field does get large near the point, can be seen as follows. Instrad of the needle, consider a big charged sphere connected to a thin wire. The total charge on that wire will then be very small. Now, you can write the potential V(r) at position r as the summation of Qi/(r-ri) over all charges Qi located at positions ri (this summation can be replaced by an integral over the surfaces involving surface charge densities). Then because there are hardly any charges on the wire, the potential V(r) is practically the same as what it would be if there were no wir cnnected o the sphere, except very close to the wire (small q means that q/(r-ri) will become large only if r becomes close to r1).

A bit away from the wire, the potential is practically the same as what it would be if the wire weren't there. Suppose the wire extends very far for the sphere. If you approach the wire, the potential will at first hardly increase and only at the last moment will the potential increase to the value it has inside the wire (which is the same as the potential of the sphere). So, compared to approaching the sphere, you get the same increase in potential if you approach it from infinity, but in case of the wire it now all happens at the last moment. The rate of potential increase is the maginitude of the electric field, and that is thus much larger near the wire. Count Iblis (talk) 16:11, 19 September 2011 (UTC)

I don't see what's wrong with saying that the charges move to minimize electrostatic energy, and that ends with them all on the surface. It may be false in a fictitious world with a 1/r³ force law, but it's true in the real world. And with a 1/r force law you will end up with a nonzero field in the bulk at equilibrium, unless I'm missing something.

It's qualitatively true that the charges move to be "as far apart as possible"; it's just not clear what that entails. When the charges are all on the surface they'll be much closer to their nearest neighbors than if they were distributed through the bulk, so it's not obviously better. It comes down to the nature of the force. If it falls off quickly then nearer neighbors are more important and the charges might prefer to be in the bulk. If it falls off slowly then the distance to faraway charges matters and it might be better to be on the edge.

As far as I know, the explicit answer to the original question is that in d dimensions with a 1/r^k force law, the particles will end up on the surface if and only if k ≤ d−1. So they don't go to the edge of the disc or the ends of the needle (in 3 dimensions) -- BenRG (talk) 23:29, 21 September 2011 (UTC)

Arctic Survival, Part Deux

Not sure if this is really a science question per se, it's mostly a follow-up from above. I know that Alaska requires pilots to carry survival gear, and I'm guessing that they're far from alone on that, but what is included in that survival gear, and what of that would be present on a commercial airliner? I'm guessing that you could have a pretty good weekend in Dallas Vegas with all of it, but what's typically in it? SDY (talk) 07:07, 19 September 2011 (UTC)

See survival kit, which will give you some idea.--Shantavira|^{feed me} 07:19, 19 September 2011 (UTC)

I don't know if jetliners have a survival kit, but if yes, what for? People rarely survive a jetliner accident. Quest09 (talk) 09:21, 19 September 2011 (UTC)

I believe they usually do. It doesn't cost much to do so, so the gain doesn't need to be much to make it worthwhile - that gain may be mostly PR. Of course, people used to say similar things about life jackets. People said they were just their for show because nobody ever survived a water landing in a commercial passenger jet. People don't say that anymore, since there was an extremely successful water landing on the Hudson recently (extremely successful as in everyone escaped with only a few minor injuries - the plane was obviously a write-off). It is extremely unlikely that a survival kit on a plane will ever get used, since accidents usually happen at take-off or landing (when rescuers are very nearby) and those than happen in mid-flight are usually due to some kind of catastrophic failure that results in everyone being killed on impact. It is possible that circumstances could occur in which it would be useful, though. --Tango (talk) 11:56, 19 September 2011 (UTC)

I don't remember if any one has to use a life jacket to be rescued. I think they were rescued by boats. Quest09 (talk) 13:10, 19 September 2011 (UTC)

In that case yes, but one can't always have their water landing be in the center of a large city with dozens of boats around. Googlemeister (talk) 13:35, 19 September 2011 (UTC)

No, you can't have your water landing the way you like it most. On the Hudson River, without victims, and with TV cameras filming you is fine. However, the most common outcome is that if something happens at take-off or landing, rescue would be easy, as above; and on mid-flight, rescue would b difficult, but you have even less reason to expect survivors. Are life jackets just a question or PR? Quest09 (talk) 18:27, 19 September 2011 (UTC)

Probably not. Ditching an aircraft (a water "landing", really more of a controlled crash) is often easier than trying to set it down on land, especially if there are control failures or the landing gear doesn't work. If you ran into a Gimli Glider or similar situation at sea where you're forced to land well short of your destination, you don't automatically lose all the passengers. Single engine naval aircraft (e.g. the F-35C) are pretty rare for exactly that reason - if you lose your one engine, you're screwed. The Canadian air force specifically went to the two engine CF-18 instead of the single engine F-16 the US uses, precisely because losing an engine in the Great White North is a big deal. SDY (talk) 22:20, 19 September 2011 (UTC)

FYI, according to the article "Ditching", the average survival rate for an emergency water landing is about 75%. This is of course highly dependent on the location and manner of the crash. 67.169.177.176 (talk) 00:44, 20 September 2011 (UTC)

Just because they were rescued by boats doesn't mean they didn't need life jackets. Our own article says "Evacuees, some wearing life-vests, waited for rescue on the partly submerged slides, knee-deep in icy river water. Others stood on the wings or, fearing an explosion, swam away from the plane." but it's not clear if there would have been enough space on the wings and slides for all passengers who wouldn't have wanted to enter the water without lifejackets. Remember plenty of people can't swim or even keep themselves afloat in water for long (and it was very cold and I guess it was fresh water too) so even if it only took 2 minutes for the boats to come there's no guarantee they would have survived, particularly in the panicked situation of that sort. Definitely from a rescuer POV even if they could have saved everyone without life jackets I'm sure they were happier they didn't have to worry (much) about trying to rescue people drowning because they couldn't stay afloat. In any case, this isn't the only water landing. There is incidentally a risk of people opening their life jackets prematurely, if you listen to the instructions they give before takeoff they always say to inflate one side just before or as you jump out and the other side after. I watched a MayDay episode once which mentioned some people died because they trapped when they opened their lifejackets before they reached the doors and then as the plane was already partly full of water they were taken to the surface and couldn't get out. (I believe it is Ethiopian Airlines Flight 961 which is mentioned in the water ditching subsection.) Nil Einne (talk) 01:17, 20 September 2011 (UTC)

Life jackets also make extra floating wreckage to find if everything goes terribly wrong, even if they were not of much help to the passengers on that plane. Googlemeister (talk) 13:09, 20 September 2011 (UTC)

You might like to look at Alaskan Survival Equipment Requirements, and Lets Fly Alaska Aviation Survival Kit, also Alaskan & Canadian Survival Kit Regulations. Alansplodge (talk) 12:38, 19 September 2011 (UTC)

That doesn't apply to jet-pilots. Quest09 (talk) 13:10, 19 September 2011 (UTC)

I was answering the question: "I know that Alaska requires pilots to carry survival gear... but what is included in that survival gear?" Airliners is a seperate issue - I couldn't find much on that I'm afraid. Alansplodge (talk) 18:41, 19 September 2011 (UTC)

Fuel/Air ratio

I have split this question into its own section. Nimur (talk) 21:20, 19 September 2011 (UTC)

Why multi cylinder engines need high fuel air ratios than single cylinder for same throttle opening — Preceding unsigned comment added by 173.254.204.203 (talk) 20:37, 19 September 2011 (UTC)

I know of a couple of considerations regarding multi-cylinder engines and fuel/air ratio. First, balancing the fuel/air ratio between cylinders in a multi-cylinder engine is an issue, there are various tricks to acomplish this, but I imagine in some applications they just up the the mixture to avoid problems. Second, multi-cylinder engines have slightly poorer combustion chamber cooling and at high loads require a richer mixture to avoid knocking. Neither of these issues leads add up to a huge difference and only make a difference under high load, under low load the mixture will be very near 14.7:1 for all gasoline engines. There may be other issues that I don't know about though. --Daniel 00:50, 20 September 2011 (UTC)

Thanks for above answer but as per some books.since fuel is having higher inertia.so the fuel air ratio while distribution into many cylinders gets disturbed.thats why we give a richer mixture for same throttle opening in comparision of single cylinder engines.i am talking according to H.B. gupta .automobile engineering book present in google book.please comment on this argument presented by book author. 203.197.246.3 (talk) —Preceding undated comment added 09:57, 20 September 2011 (UTC).

That applies only to engines with an intake manifold and not to engines with one carburetor venturi or fuel injector per cylinder. Cuddlyable3 (talk) 16:38, 20 September 2011 (UTC)

Airplanes

Hi. Who was responsible for the invention of airplanes?70.82.113.90 (talk) 21:54, 19 September 2011 (UTC)

Well, many people contributed, but the Wright Brothers are usually given the credit for developing the first one actually capable of flying. StuRat (talk) 21:57, 19 September 2011 (UTC)

The Wright Flyer III was the first practical airplane, but it's far from the first flying machine. Flyer I is recognized as the first powered, controlled, heavier than air human flight, but there are quite a few qualifiers in that "first," and there's a question of whether "invent" implies the idea, which the Wright Brothers didn't come up with, they just made it work. Santos-Dumont would contest their claim anyway, but the original question isn't specific enough to give a rock-solid answer. First flying machine gives a whole bunch of claims to consider. I'm guessing that John Stringfellow (first powered) or George Cayley (first controlled) are good candidates to the original question, though the Wrights get credit for getting "controlled" and "powered" on the same device, which makes the thing actually worth considering instead of just a curiosity. SDY (talk) 22:10, 19 September 2011 (UTC)

Flyer I was not, technically speaking, an airplane (unable to leave ground effect...) Whoop whoop pull up ^{Bitching Betty | Averted crashes} 22:22, 20 September 2011 (UTC)

But the Flyers 2 and 3 certainly were. (Which means that the Wrights still beat Santos-Dumont by at least two years.)67.169.177.176 (talk) 03:54, 21 September 2011 (UTC)

George Cayleyj's gliders were not fully controlled -- it was Otto Lilienthal who first figured out how to control a flying machine during turns, and it was not until the Wright Brothers came up with wing warping that an adequate control system came into existence. Likewise, Stringfellow's machine might have been powered but could not actually fly (insufficient power-to-weight ratio), which makes either the Wright Brothers, Karl Jatho or Gustave Whitehead the first to make a powered flight. (Note that Whitehead's machine, although adequately powered, was not fully controlled, and Jatho's had no controls at all). 67.169.177.176 (talk) 00:39, 20 September 2011 (UTC)

This is similar to the question recently about whether Edison invented the light bulb. He didn't literally invent the light bulb. But he did invent the first practical light bulb. And the Wrights developed the first practical airplane. ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:21, 19 September 2011 (UTC)

Only if you learn about it from American sources. British schoolchildren learn that Joseph Swan invented the first practical lightbulb before Edison, although Edison got the American patents first and loadly claimed in marketing that he invented it first, and they agreed to share the credit and sell Ediswan lightbulbs. No doubt French children learn something else again. 86.164.76.231 (talk) 10:43, 20 September 2011 (UTC)

I know Russian children learn that the lightbulb was invented by Lodygin (whoever he was...) But then again, in Russia they even used to claim until quite recently that Mozhaisky was the one who invented the airplane, even though his steam-powered contraption could do no better than to hop off the ground after running down a ramp and immediately stall out upon leaving the ground. 67.169.177.176 (talk) 03:52, 21 September 2011 (UTC)

See, this is all why I prefer the James Burke perspective on technological and scientific change. We tend to think of history in terms of the Great Man theory, and scientific progress is no different: We assume that scientific and technological progress happens when a lone genius invents some novel idea out of whole cloth and changes the world. We are stuck on looking at "the man" as a scientific hero, and so we have those heroes: Newton, Einstein, Edison, Jobs & Wozniak, etc. ignoring the fact that scientific progress happens not in giant leaps, but in tiny incremental changes. People like Einstein and Edison and the Wright Brothers get the "credit" because they have good marketing more than anything else. What the so-called Great Inventors and Great Minds have in common is more publicity than anything. There are inventions and ideas which do cause major paradigm shifts; but these things are always the product of many years of incremental change, and the final "credit" goes to the guy who was there when it happened; it is quite likely that if the Wright Brothers didn't get there first, someone else would have within a few months or so, given the sheer number of people working in the field. --Jayron32 02:52, 21 September 2011 (UTC)

Make that three years or so. 67.169.177.176 (talk) 03:58, 21 September 2011 (UTC)

Meh. There were many people in the months both before after the very first Wright Flyer in 1903 who had similar success in "flying" a plane (Richard Pearse, Karl Jatho, Horatio Frederick Phillips, etc.) and none of them is any less impressive than the December, 1903 flights by the Wright Brothers. The Wrights simply had better publicity. What Alberto Santos-Dumont did had some good publicity as well, but his was yet another incremental design change over other designs. Had he not done what he did, any of a number of other engineers, through similar trial-and-error, would have arrived at a similar design as well. If the Wrights had never made their flight, we'd still have the same state of modern aviation we have today; the credit would have changed but the ultimate historical events would have occured anyways. Heck, pick anyone of the random other people I cited above; the Wright's credit would have gone to them instead, and we'd be exactly where we are today. --Jayron32 04:13, 21 September 2011 (UTC)

Pearse did not actually fly, but only made a couple of short, practically uncontrolled hops a few yards long, each of those hops ending with a crash into shrubbery. (Is that what you call "impressive"?) Jatho actually made a short flight before the Wrights did, but it was much shorter (200 ft. distance) than the Wrights' flight (852 ft. distance) and was likewise uncontrolled; he then gave up all attempts to further develop his contraption. And Phillips did not make his first flight until 1907, a half year after Santos-Dumont and almost three and a half years after the Wrights! 67.169.177.176 (talk) 04:26, 21 September 2011 (UTC)

Sometimes there are setbacks. Check out this early version of a Batman-like cape/parachute:[1] ←Baseball Bugs ^{What's up, Doc?} carrots→ 06:26, 21 September 2011 (UTC)

Wow, this gives a whole new meaning to the term "crash dummy"... (Not to disrespect his tragic death, but I mean, couldn't he stick to dropping dummies from the tower until he had at least a reasonable chance of survival?) 67.169.177.176 (talk) 06:35, 21 September 2011 (UTC)

Sir George Cayley invented the concept. --Swedmann (talk) 01:23, 23 September 2011 (UTC)

Right, the concept of fixed-wing (as opposed to flapping-wing or lighter-than-air) aircraft using airfoils to create lift. I never said otherwise. However, he did not realize the need for roll control (Lilienthal was the first to do so, and the Wrights were the first to actually achieve it), and of course he didn't put any powerplant on his gliders (for the simple reason that none was available). Which means that his machines were neither powered nor fully controlled, and therefore do not count as airplanes. 67.169.177.176 (talk) 05:59, 23 September 2011 (UTC)

Feces

What is the average buoyancy and density of a regular feces? 75.6.243.251 (talk) 23:51, 19 September 2011 (UTC)

What type of shit are we talking about here? Sir William Matthew Flinders Petrie | ^{Say Shalom!} 23:57, 19 September 2011 (UTC)

Type 3 on the link you gave me. 75.6.243.251 (talk) 00:18, 20 September 2011 (UTC)

The density is about that of water (which makes sense, as it is about 75% water). The average is somewhat greater than water (sorry, I don't have a number): most poop sinks. There has been great debate among the, uh, well, among certain segments of the population, about whether sinking or floating poop is indicative of good or bad health. Hardcore vegetarians and especially vegans have been known to claim that poop in a healthy person should float. Despite these claims, it is generally difficult to get floating poop through diet alone (and, needless to say, I don't think there are any real convincing studies that show that floating poop is indicative of health). The factors that can cause poop to be less dense are

1. Higher Fat Content, and
2. More integrated gas

While some variation in feces is normal, it is true that certain diseases can cause Malabsorption, which can lead to greasy, floating stool. Other chronic, abnormal bowel movements can be indicative of other problems - see the last link I have provided. If you are concerned about your poop, you should seek advice from a medical professional. [2], [3], [4] [5] Buddy431 (talk) 06:31, 20 September 2011 (UTC)

I thought you might be interested in this: Bristol_Stool_Scale --TammyMoet (talk) 08:13, 20 September 2011 (UTC)

That link was the first supplied. Dismas|^(talk) 08:27, 20 September 2011 (UTC)

Yeah, I already saw that, and don't need two links. 75.6.243.251 (talk) 23:52, 21 September 2011 (UTC)

Could you possibly find me the exact number for density and buoyancy? I'm not seeking medical advice; I read the series of notices at the top already. 75.6.243.251 (talk) 23:52, 21 September 2011 (UTC)

September 20

Dynamics of hypercanes

There is a theory (hypothesis) that exists which states that water temperatures around or above 120°F would result in hypercanes, which would taller, faster, and more compact than normal hurricanes. Obviously at this point the dynamics of the hypercane would be different than that of a hurricane, but how would they be different (the plume of water vapor penetrates the stratosphere, different patterns of air currents form, etc.)? --Melab±1 ☎ 02:22, 20 September 2011 (UTC)

The dynamics of ordinary hurricanes aren't understood well enough to simulate their interiors and eyewalls yet, so probably nobody can say. 208.54.38.175 (talk) 04:53, 20 September 2011 (UTC)

I don't think they would penetrate the stratosphere -- the tropopause is essentially a very strong inversion layer, and any weatherman knows how tough it is for air currents to penetrate those. FWiW 67.169.177.176 (talk) 04:59, 20 September 2011 (UTC)

Our article says "A hypercane's clouds would reach 30 km (19 mi) into the stratosphere". StuRat (talk) 05:09, 20 September 2011 (UTC)

Gallium arsenide

If taking the MO diagram into consideration, is it correct to say that for the monomer of gallium arsenide has a bond order of four, and that the resulting molecule is a zwitterion?

There is one sigma bonding orbital, and three degenerate pi bonding bonds, gallium only contributes by one third to the pi orbitals, not by half. As is my understanding, electrons are indistinguishable and there is no way to tell which electrons in the pi orbital associates with which atom. However, since a bond order of four means that gallium has an excess of electron density around it, and arsenic has a defficiancy around it. Meaning that, there is a unit charge of 1- on gallium and 1+ on arsenic. Note that the bond order is an integer, meaning that the charge difference must also be an integer. Plasmic Physics (talk) 02:36, 20 September 2011 (UTC)

Not sure where you get GaAs has a bond order of 4 via the MO diagram. It isn't an "expanded octet" molecule, so you should be able to work out an MO using just the valence level s and p orbitals, I get the resulting monomer to have the following MO configuration:

• σ(4s) = 2
• σ*(4s) = 2
• σ(4p) = 2
• π(4p) = 2
• π*(4p) = 0
• σ*(4p) = 0

That's 6 bonding electron, 2 antibonding electrons, and that give me a net of 4 electrons, or a bond order of 2. So Gallium Arsenide is predicted by M.O. theory to have a double bond, not a quadruple bond. When I work out the formal charge on said molecule, I do get formal charge of -1 on the gallium and +1 on the arsenic, however. The whole "quadruple bond" thing does exist, but not in compounds like this. In this case, the only way a quadruple bond gets predicted is by "lewis theory" or valence bond theory; since you only have 8 valence electrons to play with, the only way to "complete the octet" is to have 4 shared pairs of electrons; but what you see here is an example of where lewis theory falls short compared to MO theory. Actual quadruple bonds require participation of d-orbitals, and I don't see anywhere that this molecule would have d electrons which participate in the bonding. Even if you involve the d-electrons from the nearest d-orbitals in an expanded MO diagram, all of the bonding and antibonding electrons from that contribution should cancel. --Jayron32 17:06, 20 September 2011 (UTC)

Well, I'm looking at the valence MO diagram as given in a lecture slide. It gives the following configuration:

• s² (sigma)
• p_x² (sigma)
• p_y² (pi)
• p_z² (pi)
• s*⁰ (sigma*)

In this diagram, there are no antibonding orbitals. Plasmic Physics (talk) 00:16, 21 September 2011 (UTC)

It shows that the sigma* is higher in energy than the p orbitals. Plasmic Physics (talk) 00:24, 21 September 2011 (UTC)

I'm not sure that make sense, unless there is significant overlap between the bonding energies of the s and p orbitals. In nearly all MO diagrams I know of, the order for the valence level MO has the sσ followed by the sσ* before any of the p-orbital contributions. Some molecules have some difference between how the p-orbital MOs order (some go σ - π - π* - σ* and others go π - σ - π* - σ* (see Molecular orbital diagram). I am not ruling out the unusual MO diagram you show above, I suppose it is possible, just not an organization I have ever seen. I would check with your professor after class, and ask them personally to explain the slide. --Jayron32 00:29, 21 September 2011 (UTC)

The gallium arsenide MO diagram is used to describe the formation of exitons in semiconductors. It calls the two degenerate pi-type HOMOs, the valence band; and the antisigma-type LUMO, the conduction band. Plasmic Physics (talk) 00:57, 21 September 2011 (UTC)

Ah. If you are dealing with conduction/valence bands, you have steped outside of molecular bonding into the world of metallic bonding and Network covalent bonding. See Electronic band structure for an overview. Band theory has its own quirks and rules which may not directly corrolate to expectations of discrete molecules as described by standard MO theory, since they have different applications: MO theory is designed for discrete molecules, while band theory is designed for network and metallic solids. There's probably ways to make the theories work together somewhat, but basically it's "Different game, different rules". So go with what your professor says. My band theory is a little rusty. --Jayron32 02:41, 21 September 2011 (UTC)

So, the MO diagram is not correct in this demostration? I'm confused. Plasmic Physics (talk) 03:57, 21 September 2011 (UTC)

No, let me reiterate what I said a few posts ago: it may very well be, but what you need to do is ask him personally to explain it to you to your satisfaction. The MO diagram you described is not one of the "standard" MO diagram orders I am used to (not that it is wrong, just not a standard order) and that may (or may not) be because we're dealing with a different type of bonding, since gallium arsenide is a network solid (and does not exist as discrete molecules, normally) then the band model may be more useful in understanding its electronic structure than the MO model (since MO deals with molecules). I assume that your professor was attempting to demonstrate some connection between the MO model (homo-lumo) and the band model (valence band-conductance band) as there is a connection between them; so you'll have to ask him about the particulars of why he uses that specific MO diagram (or an MO diagram at all, since gallium arsenide is not normally a molecular substance). --Jayron32 04:02, 21 September 2011 (UTC)

Oh. However, the diagram has the title of MO diagram of GaAs monomer. Plasmic Physics (talk) 04:59, 21 September 2011 (UTC)

That's why I said talk to the guy who made the diagram. He would know. --Jayron32 15:18, 21 September 2011 (UTC)

OK, I'll do that. Thanks. Plasmic Physics (talk) 23:18, 21 September 2011 (UTC)

sweet potato flavor

The flavor of sweet potatoes seems to be effected by boiling too long but not by removing sprouts or rotten spots and then boiling for no more than 5 hours. The inside of a sweet potato that has grown sprouts, however, seems to have cavities surrounded by root like projections from the stem inside the potato. Are these cavities just the result of the spouts taking energy and nutrients from the sweet potato itself? --DeeperQA (talk) 03:33, 20 September 2011 (UTC)

I would think so, but mostly the result of taking water out, which is most of the mass. StuRat (talk) 05:04, 20 September 2011 (UTC)

No more than 5 hours? Don't you mean minutes? --TammyMoet (talk) 08:10, 20 September 2011 (UTC)

Boiling for five hours? You have to be British. I've cooked thousands upon thousands of sweet potatoes in my life, and I've never boiled one. Baking is best. As for the cavities, enzymes break down the starch in the sweet potatoes into sugar, which is then absorbed and transported by the root-like projections to the growing sprouts. The loss of mass represents the mass of the sugar transported along with the water it is disolved in. Dominus Vobisdu (talk) 10:21, 20 September 2011 (UTC)

Not neccesarily british. I boil sweet potatoes. I peel and cut them into thin slices, add salt and boil for 20 min (or until soft,) mash the sweet potatoe, add milk or cream, cinnamon, and sugar. Then heat the mixture until it is no longer flows as a liquid, avoid burning by stirring.

I admit, sweet potatoes are take longer to boil, but it can be sped up by using smaller chunks. Plasmic Physics (talk) 12:14, 20 September 2011 (UTC)

We both boil and bake sweet potatoes. And fry em, caramelize them, and mash em, and eat young leaves in salads besides. And @Tammy, they take ages to cook, not like actual potatoes, sweet potatoes are generally massive tubers with thick skin.-- Obsidi♠n Soul 15:31, 20 September 2011 (UTC)

Are you sure you don't mean yams ? They are massive, while a sweet potato is close in size to an russet potato. StuRat (talk) 17:56, 20 September 2011 (UTC)

Sweet potatoes do tend to be slightly larger than regular potatoes and certainly have tougher skin. --Tango (talk) 19:10, 20 September 2011 (UTC)

You can get both very large and fairly small sweet potatoes. E.g. I currently have one that is over 850g and it's far from the largest one I've ever had. It also depends somewhat on the variety. They do tend to be a different shape from potatoes. Nil Einne (talk) 23:31, 20 September 2011 (UTC)

It's also probably a difference in harvesting time. Sweet potatoes are not cultivated extensively here as they can survive pretty easily without human intervention when planted along otherwise unarable land. They are harvested from feral plants, so they've usually been growing for quite a while. More like New Zealand kumara sweet potatoes (which is confusingly called 'yam' in the US), but not quite as large (by far) as true yams of course. I also suspect that smaller sizes are a result of market homogenization, as they are easier to handle and cook at those sizes. Potatoes here on the other hand, are tiny, averaging at only 3 in in diameter. ;) - Obsidi♠n Soul 02:19, 21 September 2011 (UTC)

I'm British. I usually bake or roast sweet potato, although I do sometimes boil and mash them (usually mixed with something else). Baking and roasting are a much better use of them, though. They certainly don't need to be boiled for 5 hours, though (and 5 minutes wouldn't be long enough, so I'm sure what the OP means...). --Tango (talk) 19:10, 20 September 2011 (UTC)

I boil them, along with many other items, as part of a perpetual stew, in winter. Thus, they may be boiled many times over many hours before finally eaten, but they seem to hold up fairly well (although the skin falls off). StuRat (talk) 19:15, 20 September 2011 (UTC)

I prefer nuking the small-to-medium sized ones whole in the microwave for about five to seven minutes, flipping them over about midway though the cycle to redistribute the heat. --Modocc (talk) 21:43, 20 September 2011 (UTC)

You use a nuclear weapon to cook potatoes?! 67.169.177.176 (talk) 05:03, 21 September 2011 (UTC)

In the USA, at least, to "nuke" is slang for using the microwave. ←Baseball Bugs ^{What's up, Doc?} carrots→ 06:17, 21 September 2011 (UTC)

Now added at List of words having different meanings in British and American English: M–Z :-) Ghmyrtle (talk) 08:25, 21 September 2011 (UTC)

"Nuke" is also used in American English the way it's used in British English. The microwave stuff is an additional slang usage in American English. It's also worth pointing out that "nuke" has also been used (at least in America) as a slang term for a nuclear power plant. (See No Nukes) ←Baseball Bugs ^{What's up, Doc?} carrots→ 14:08, 21 September 2011 (UTC)

Nah, it's current slang in the UK too. We all have slang terms we don't recognise: doesn't make it an international difference. And you should have a reliable source to reference the difference before you add it to an article. 86.164.60.149 (talk) 17:54, 21 September 2011 (UTC)

If you look, there doesn't seem to be a reliable reference in the entire list. Googlemeister (talk) 21:02, 21 September 2011 (UTC)

Yes, it does look like junk. Anyone up for finding references, and cleaning out the nonsense? It shouldn't be too hard, given how popular the topic is. I guess I could go through it at the weekend, but that shouldn't stop someone else who's looking for something to do (I do hate formatting proper inline references). 86.164.60.149 (talk) 22:10, 21 September 2011 (UTC)

To me, to "nuke" a foodstuff, is too charr it beyond recognition, unintentionally of course. Plasmic Physics (talk) 10:36, 21 September 2011 (UTC)

Yes, that would be another meaning "to get rid of or destroy". StuRat (talk) 23:09, 21 September 2011 (UTC)

Eyelids twitch when scratching toes

When I scratch my toes (and sometimes other body parts) the scratching sensation somehow transmits and reaches my eyelids, and they begin to twitch. I think this is common to all people. What is this phenomenon? Gil_mo (talk) 06:26, 20 September 2011 (UTC)

It's not universal. I would guess the nerves have some "cross-talk" in your brain, a form of synesthesia, similar to grapheme-color synesthesia, where numbers and colors are linked. StuRat (talk) 06:32, 20 September 2011 (UTC)

It's not common to me either. I can sometimes smell my own nose, strange... Plasmic Physics (talk) 07:00, 20 September 2011 (UTC)

hmmm, puzzling Sean.hoyland - talk 07:35, 20 September 2011 (UTC)

I was referring to scratching a very itchy toe (or between toes), not just anytime. Gil_mo (talk) 07:51, 20 September 2011 (UTC)

What happens when you have very itchy eyelid and scratch it ? Also, since you say it's sometimes other body parts too that trigger the eyelid, perhaps it's the finger that you use for scratching that's wired to your eyelids... Sean.hoyland - talk 08:35, 20 September 2011 (UTC)

hall effect

can a simple hall effect circuit test magnetic fields of the order of picotesla .even a true/false judgement i.e. if the field is present or not judgement would help??can any one help. if the input is provided to a pc could we get some better analysis ..if yes please guide.? 203.197.246.3 (talk) —Preceding undated comment added 09:52, 20 September 2011 (UTC).

I really don't think so.. The potential generated by even the best designed hall probe is going to be very small in a picotesla field - this will have to be amplified - but there is a limited to how much amplification is possible -eg limited by thermal noise etc. Here http://cat.inist.fr/?aModele=afficheN&cpsidt=15394074 they get the sensitivity down to microtesla.. ie ~0.2V per T - that would have you measuring ~~ 0.2 picovolts very small)

I would guess that there might be a way to get it to work - but - it would require a specially designed sensor - or some elaborate microscopic construct using the hall effect in a more complex system (integrated circuit integrated with hall effect sensor?? + low temperatures?) Imgaril (talk) 10:12, 20 September 2011 (UTC)

I note that http://www.tristantech.com/prod_lab_meas.html (which uses a SQUID to detect magnetic fields) mentions a Picovolt Measuring System which is cryogenic - this suggests that a the measurement of the ~pV level signals from a hall effect sensor are within the bounds of possibility - but it would need to be very cold.Imgaril (talk) 11:58, 20 September 2011 (UTC)

What is a chest node?

A kind editor has added the information that the famous operatic tenor Jonas Kaufmann has, as the source puts it, "recovered from surgery to remove a chest node". I would like to wikify this, but when I looked at Node I got rather lost. Any guidance please? almost-instinct 12:14, 20 September 2011 (UTC)

Presumably nodule (medicine) is meant. A vocal fold nodule is a common singing injury. It might be something else, though. This news item [6] with the words "vical nodules" in the URL and the comment "A node in the chest has nothing to do with vocal nodules" doesn't make things much clearer. Sounds like it's one of those probably-not-cancerous lumps people sometimes randomly get. (To be less vague, I was thinking of a benign tumor.)  Card Zero  (talk) 12:21, 20 September 2011 (UTC)

Thank you very much. I've found this from an open letter JK wrote to apologise for pulling out of a tour: "The fact is that I need to have an operation to remove a node in my thoracic area". Does that help? almost-instinct 12:42, 20 September 2011 (UTC)

That letter is also on the page I linked to: it looks like it originates from a Japanese tour promoter's site, and is the official piece of information on the matter. Even Jonas Kaufmann himself might not know what he means by "node". Googling "chest node" brings up some breast cancer forums, though. Perhaps it was even malignant: whatever it was, it's gone now. Tumor seems the best article to link "node" to (unless somebody else knows better). Oh wait! I think it means Lymphoma, possibly, where the node in question is a lymph node?  Card Zero  (talk) 12:49, 20 September 2011 (UTC)

Since all JK has said on the subject is "node in the chest" -("I’m pleased to say that the operation to remove a node from my chest that I had to undertake earlier this month went very well and that the recovery is making good progress") - and there's ambiguity I had best not link either to benign tumour or lymphoma. If people want to be vague about their medical state, that's their perogative I suppose. Thank you for your help: hopefully it'll be useful if more detailed information comes out almost-instinct 13:03, 20 September 2011 (UTC)

Yes, just link to "tumor", it covers all the bases. I searched for Jonas Kaufmann "lymph node", and found a half-visible Google cache of a Twitter comment by one naomip86, which says that JK confirms in a comment left somewhere, written in Japanese, that the node is indeed a lymph node; but I have a feeling this might not qualify as a reliable source.  Card Zero  (talk) 13:15, 20 September 2011 (UTC)

Congratulations on getting so close to Absolute Zero on the Reliability Index ;-) Yes, I'll do that, thanks. almost-instinct 13:21, 20 September 2011 (UTC)

Maybe, though, that refers to the original letter, which is written first in Japanese, here [7] and I think it has the Japanese for "lymph node" in it. Somebody here (Kagetora?) can do a reliable translation of that.  Card Zero  (talk) 13:24, 20 September 2011 (UTC)

Oh yes! Google translate gives it "must undergo surgery for resection of lymph nodes in the chest". I shall await (semi)patiently almost-instinct 13:28, 20 September 2011 (UTC)

I'm a native ja speaker. Yes, it's "lymph nodes" in the letter in ja. The ja word is リンパ節. [8] Oda Mari (talk) 15:07, 20 September 2011 (UTC)

For reference, here is what Eijiro says. KägeTorä - (影虎) (TALK) 16:02, 20 September 2011 (UTC)

Thanks, you two. Sorry for suggesting "tumor", which Almost-instinct added to the article and then had immediately reverted by somebody else. I've changed it to "lymph node" now, let's see how that goes down.  Card Zero  (talk) 16:52, 20 September 2011 (UTC)

Thank you everyone, its all settled and accepted now :-) almost-instinct 21:34, 20 September 2011 (UTC)

dry versus disolved borax powder in air

I am careful not to breathe the dust when adding the powder to laundry but can find no caution about spraying a dissolved solution of borax in water. Is spraying this solution dangerous and if so what kind of respirator mask should be used? --DeeperQA (talk) 17:31, 20 September 2011 (UTC)

A respirator seems like overkill, but do leave the laundry area after spraying and ventilate the area (with an open window). StuRat (talk) 17:58, 20 September 2011 (UTC)

Here's a MSDS http://www.anvilfire.com/21centbs/material/33850-usborax-borax.pdf - generally little threat to you. Don't drink it. It's also alkaline so if you get a lot on your skin it may eventually burn/sting/itch. Washing with water will remove contamination.

Here's a MSDS for a 1% solution - http://www.sciencelab.com/msds.php?msdsId=9925661 - I really couldn't decribe it as dangerous - but don't breath in the spray (this applies to just about every spray you can name - starch, furniture polish, etc - most of which are of greater hazard)

If you are concerned about this sort of thing wearing a cheap dust mask will stop you breathing in any mist. If you are using a lot or use it everyday in a job (like these guys who use to treat timber [9]) then I'd recommend wearing a dust mask, and the gloves. Imgaril (talk) 20:33, 20 September 2011 (UTC)

Yes, thanks. This is just the information I need since the sprayer being used was a paint sprayer and one person had already noticed a reaction like a cold with mucus production but an ironically with an increased ability to breath like he had used an antihistamine. The key was that when he tried to treat a slight sour throat with vinegar it stung well beyond anything he had ever experienced. --DeeperQA (talk) 21:44, 20 September 2011 (UTC)

Just FYI: Breath is a noun, breathe is a verb. --Trovatore (talk) 21:48, 20 September 2011 (UTC)

Anyone who doesn't know that must be a blond (or blonde). StuRat (talk) 02:51, 21 September 2011 (UTC)

I will reprogram my grammar/spell checker. --DeeperQA (talk) 22:12, 20 September 2011 (UTC)

BTW, what's a "sour throat"? Methinks treating it with vinegar would only make the problem worse... 67.169.177.176 (talk) 04:02, 21 September 2011 (UTC)

We can't give you medical advice concerning whether your application of borax is safe for you. In general, borax is something that exists in the environment, in evaporite deposits, and has been dug up and traded for 4000 years.^[10] It is true that in high doses it has health effects, including harmful reproductive effects, but I would think that the wind blowing in a place like Boron, California can't be that tremendously terrible. I'd think a person can get over passing, casual exposure to the compound without the need to take extraordinary precautions. Wnt (talk) 01:57, 21 September 2011 (UTC)

I used a saturated solution (versus 1% as above) for about three of four hours of paint sprayer (blowout orifice) distribution in a light wind outdoors. The next morning I noticed I had a very open and unrestricted airway and lungs like with antihistamines. Mucus and sore throat were present like with a cold. Vinegar caused a very painful stinging sensation in back of throat. The Borax solution is alkaline. It took until now for the airway condition to tapper off but not fully go away. There was no sensation while spraying but slight smell like concrete blocks. I'll use the dusk masks when I fully recover. --DeeperQA (talk) 07:05, 23 September 2011 (UTC) Many days now after the incident, I am quickly out of breath when riding my bike. I am fatigued very easily and sluggish and my muscles ache. A dust mask if not a respirator may have prevented these problems. --DeeperQA (talk) 16:12, 24 September 2011 (UTC)

WTC escape solution

Several people scaled the WTC towers using a camming device and the window washer apparatus channels or rails. Is there any type of descent system using the channels or rails (versus a parachute stored in your cubicle) to get you from high up in a building to the ground without killing you? --DeeperQA (talk) 22:10, 20 September 2011 (UTC)

I wouldn't try to slide down the face of a high-rise building if I was you -- the risk of slipping and falling to your death is just too great. (You have to remember that the people scaling the towers were trained professionals, as are the window washers.) That said, it's often possible to climb to the roof of a burning building, from where you could be rescued by a helicopter. I wonder why they didn't try this on 9/11... 67.169.177.176 (talk) 04:10, 21 September 2011 (UTC)

There probably wasn't time to get such a rescue operation going. While only the first one was burning, they could have tried the Phillipe Petit approach. ←Baseball Bugs ^{What's up, Doc?} carrots→ 06:16, 21 September 2011 (UTC)

Also, a fire of that type would be extremely problematic for a helicopter. The large amount of smoke would have visibility be almost 0, there were those tall spires on top were a hazard, and a fire like that also creates nasty wind conditions above it. I would expect that only military chopper pilots have been trained for that kind of a rescue, unless the NYFD has helicopters of their own for that sort of thing. Googlemeister (talk) 13:49, 21 September 2011 (UTC)

In the 1993 WTC bombing,elevators were stopped and stairways were filled with smoke. Police helicopter did rescue a number of people from the roofs of the two buildings,despite heavy smoke, although that was never part of the official emergency plan. Several groups of people were lifted from the roof of the South Tower. Emergency Services personnel were lowered and sawed off any projections which were in the way of the chopper. One person was similarly rescued by rope from the roof of the North tower. This annoyed the Fire Department, who insists on the right to "rescue" people, so very strong doors with a remote operated lock were installed to prevent a repeat rescue by the police chopper. Unfortunately, the office which could have remotely unlocked the door was destroyed by the plane impacts on 9/11, so there was no roof access for the people trapped in the restaurant. Edison (talk) 18:39, 21 September 2011 (UTC)

And that was the NYFD's doing, you say? If that's true, then whoever ordered this is a mass murderer and deserves to be burned at the stake! 67.169.177.176 (talk) 22:46, 21 September 2011 (UTC)

What??? First murder is an intentional act, unintentional acts are manslaughter at worst, which is not a capital offense. Second, burning at the stake is not a legal method of execution in any of the 50 US states, most likely disqualified by the 8th amendment to the US Constitution. Googlemeister (talk) 13:32, 22 September 2011 (UTC)

The hell you say -- if what Edison said is true, this amounts to INTENTIONALLY impeding a rescue operation resulting in a massive loss of life, and therefore is MASS MURDER! This falls under the same laws/precedents by which causing a fatal plane crash by stealing equipment or siphoning fuel from the plane in question constitutes murder regardless of the culprit's actual intentions! Your so-called "logic" is the same that allowed the owners of the Triangle Shirtwaist Factory to get away with incinerating almost their entire work force! And if burning at the stake is unconstitutional, then the electric chair is the only other fitting punishment for that NYFD official who doomed hundreds of people to a fiery death! 67.169.177.176 (talk) 00:44, 23 September 2011 (UTC)

A long enough rappelling rope could be tied inside the building, but nobody expected to need such a rope, and breaking the window from the inside might have been difficult. Dualus (talk) 06:41, 21 September 2011 (UTC)

And I don't think rappelling past a part of the building that is burning is going to work either from smoke inhalation or the heat. Googlemeister (talk)

There were some sides of the building that weren't spewing flames, and unless the heat melts the rope, it's probably easy enough to slide past 10 floors fast enough to survive. As for breaking the windows, plenty of victims contacted by cellphone before the collapse said that they had been able to break open windows. 70.91.171.54 (talk) 18:59, 21 September 2011 (UTC)

It is very rare for a highrise fire to start out with flames coming out all sides of the building., There is typically a long time during which there is intense fire on one side, with some sides cool enough for a person to be lowered. This is why fire escapes outside buildings were traditionally there: builders and fire safety officials did not dismiss the ability to walk down the north side when there was a fire on the south side. I worked in a high rise building which had an employee who could not walk working in an office several floors up. The boss bought a rescue harness and a l-o-o-ng rope to lower the employee to the ground from a window in the event of elevators being unusable in a fire. The employee and coworkers agreed that the employee would instead be carried down the stairs, either seated in an office chair or over a shoulder in a fireman's carry, rather than having a team of people lower the employee via a rope. But it was feasible, and was tested by lowering an equivalent weight. I've always thought a personal lowering device for a highrise would be easy to build. A long wire cable on a reel, a centrifugal brake to control the unreeling speed to a safe one, and a bosun's chair. Trapped people could be lowered one at a time, and the seat could be cranked back up after each use. Nothing innovative or high tech required. A metal eyebolt could be installed above a window on each side of the building to allow using the noninvolved side. It might even be possible to insert rescuers into a burning highrise at a floor above the fire, to install such several such devices and supervise the lowering of trapped people. One could go fancy and wear fireresistant garb, helmet, gas mask, etc, or just rely on the rapid descent speed to get past any hot or smoky area and get people out faster. Edison (talk) 19:08, 21 September 2011 (UTC)

Are you seriously thinking that hundreds of people rappelling 1000 feet to the ground from a burning building is remotely feasible? Googlemeister (talk) 20:55, 21 September 2011 (UTC)

Yeah, much more sensible to ensure the doom of each and every one of them by a lack of planning, and by ignoring simple means of leaving a high place without going thud. Rarely are the trapped people 1000 feet above the ground, and it rarely is the case that hundreds of people are trapped. The people who survived because of a communal or personal descent rig would be quite happy not to have been incinerated or asphyxiated. Edison (talk) 23:44, 21 September 2011 (UTC)

True, but a system that relies on rappelling 1000 feet down the face of a building would not have been practical, since it can only be used by highly skilled mountaineers. On the other hand, some kind of "communal descent rig" (I'm thinking of something along the lines of an external, rope-suspended elevator) might well have been a practical idea for an emergency escape system. 67.169.177.176 (talk) 01:13, 22 September 2011 (UTC)

Edison, that's easy for you to say. You know that the buildings were going to burn and collapse. But an equally likely outcome was that these risky rescue ideas would be installed, and a lot of people would have died using them in a fire that would otherwise be survivable. It's far more likely that your rescue equipment will be used when it's not needed, then it is that a jet-liner will crash into your building. APL (talk) 08:16, 22 September 2011 (UTC)

Exactly. This is similar logic as to why passenger airliners do not have parachutes on hand. Googlemeister (talk) 13:33, 22 September 2011 (UTC)

Besides, the building DID have a fire escape stairwell in its central core. The building designers could not have anticipated that part of the stairwell would collapse as it did on 9/11, or that the escape doors to the roof would be locked with no way to open them except remotely (according to Edison, but AFAIR corroborated by at least one other source). To them this kind of scenario was simply inconceivable. 67.169.177.176 (talk) 00:49, 23 September 2011 (UTC)

Okay, I like the centrifuge governing descent idea. That could really work especially if the window washer channels were toothed on on side - an idea that might accommodate several other speed governing methods. Outside exposed to the elements is not the best way down but in a dire emergency if a controlled "down" is the only solution I'd choose a Mountain Banshee over free fall. --DeeperQA (talk) 04:33, 23 September 2011 (UTC)

Yes, some kind of platform with safety railings all around and a reel with some kind of (FAIL-SAFE!!!) speed governor may well work for high-rise emergency escape. This should preferably accomodate a group of people, so as to expedite descent for all who might be trapped on the upper floors. 67.169.177.176 (talk) 06:05, 23 September 2011 (UTC)

Realize any such system is for dire emergency only after all other options except jumping have failed. Its got to be limited to multiple sets of one or two persons to accommodate carabine latch and swing out. Time is of essence not user comfort. Jam proof design to allow for slower descent below. Think of a rail of reusable devices to accommodate an unlimited number of people in succession. Think mountain climbing not penthouse elevator. --DeeperQA (talk) 07:27, 23 September 2011 (UTC)

I'd think a zipline would work fairly well, and the tourists would either love it or not return their customer satisfaction form. Wnt (talk) 17:49, 23 September 2011 (UTC)

That's a joke, right? 67.169.177.176 (talk) 19:57, 23 September 2011 (UTC)

Well, admittedly, given the height of the towers it would need to be a pretty long zipline ... you might need carbon nanotubes or other advanced materials to make it work. But it would provide quite a tour of the city. ;) Wnt (talk) 03:39, 24 September 2011 (UTC)

With building code to match - multiple ziplines could be fired from one building to another at angles of no greater than 13.5 degrees during an emergency like hooking up two ships for transport of personnel or supplies. Unfortunately the design of the new towers may not permit this. --DeeperQA (talk) 16:06, 24 September 2011 (UTC)

Plane crash on Mount Everest

What would happen if a plane crashed near the top of Mount Everest? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 22:26, 20 September 2011 (UTC)

The plane remains would be there for ever as a monument to human endeavor/stupidity. Dauto (talk) 23:03, 20 September 2011 (UTC)

Depends on the type of plane, the speed it was traveling at, the weather,etc. At that altitude it is likely everyone on board would die, as they would not be prepared for the extreme cold and thin air, presuming they survived the impact in the first place. Specialized high-altitude helicopters can indeed reach such an altitude to perform rescues, as documented at Mt. Everest#2005: Helicopter landing but as I said the survivability of such a crash would be near zero. Also, I'm fairly certain air traffic is re-routed specifically to avoid such a thing. Alaskans know to stay away from Denali in the air because it is so massive it creates its own weather. Beeblebrox (talk) 23:22, 20 September 2011 (UTC)

Something I read in a book about Everest once. "There is no 'trapped on Everest' - only 'dead on Everest'", or something along those lines. If you're up there somewhere and any potential rescue isn't immediately at hand, then you might as well be on the moon for your chances of survival. --Kurt Shaped Box (talk) 00:58, 21 September 2011 (UTC)

In general, mountain peaks above the 8000-meter line are referred to as "the death zone" -- a person who finds himself unexpectedly trapped in that zone would certainly perish. 67.169.177.176 (talk) 04:47, 21 September 2011 (UTC)

Time for a very ignorant question: Suppose a large jet with a large amount of fuel crashed right at the summit. Might the resultant explosion be strong enough to blow away part of the summit, thus shortening the mountain's height? ←Baseball Bugs ^{What's up, Doc?} carrots→ 06:02, 21 September 2011 (UTC)

ABSOLUTELY NOT! To do this would require a multi-megaton atom bomb at the VERY LEAST! 67.169.177.176 (talk) 06:25, 21 September 2011 (UTC)

Apparently Everest's height is measured to an accuracy of ±0.21 m. It may not be unreasonable that a major crash could make a measurable difference. A plane crashing with a near-full fuel tank has been known to make quite an impact. Mitch Ames (talk) 12:16, 21 September 2011 (UTC)

You could knock off the snow on top which is a few feet if I recall. Not enough to help anyone. Googlemeister (talk) 12:59, 21 September 2011 (UTC)

If you dropped a bomb on it, you could probably take a few metres off the top (basically, the same amount as the depth of the crater you would create if you dropped it on flat ground, give or take). Near-full fuel tanks don't really explode, though, they just burn. Empty fuel-tanks explode because they are full of fuel vapour, which is explosive. Liquid fuel isn't. If the tanks were empty, though, the amount of fuel vapour wouldn't be enough to cause any but a small explosion, not enough to significantly damage the mountain. --Tango (talk) 17:23, 21 September 2011 (UTC)

I didn't necessary expect significant damage, but I expected that something would happen. Obviously, it depends on the amount of force involved, and the precise angle and landing point. Looks like it would take a lot more than a conventional airplane to knock it down below the height of K2, which I think is about 800 feet shorter than Everest. The various answers provide a lot of insights. Thank you! Aside: Everest was photographed from the air long before it was climbed, but they kept a safe distance. It also occurs to me that if a plane is in that much trouble, it probably wouldn't even make it to Everest - it would probably crash on one of the somewhat-lower peaks in the vicinity. ←Baseball Bugs ^{What's up, Doc?} carrots→ 17:38, 21 September 2011 (UTC)

As for survivability, what if the plane fell or was knocked down the side of Everest, so that it ended up lower down on the mountain? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 22:58, 24 September 2011 (UTC)

Highest an aircraft can fly

What is the highest up an aircraft can fly (and I mean something like a jet plane, propliner, or helicopter, not something like Apollo 11 or the Space Shuttle)? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 22:35, 20 September 2011 (UTC)

About 100 km altitude. This is where the speed needed for the aerodynamic forces to overcome gravity becomes similar to the speed needed to stay in orbit. Count Iblis (talk) 22:51, 20 September 2011 (UTC)

The current record is less than half that, about 37.5k, set in 1977. See Fédération_Aéronautique_Internationale#Records. SDY (talk) 22:52, 20 September 2011 (UTC)

An airplane can fly a LOT higher than 37,500 feet. And wouldn't the jet engines be starved of air long before the altitude reaches 100 kilometers? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 23:00, 20 September 2011 (UTC)

That's probably intended to mean 37.5 km, not kilo-feet. Yes, getting air-breathing engines up to 100 km would be quite a challenge. Even the MIG-25 record of 35+ km was done using a zoom climb, not sustained engine performance. But several experimental aircraft have been fitted with rocket boosters in addition to their normal jet engines. --Stephan Schulz (talk) 23:12, 20 September 2011 (UTC)

Yes, although the original statement may not have be entirely clear (although can be inferred in the context of the discussion), the article they linked to as their source unsurprisingly is clear. Nil Einne (talk) 23:25, 20 September 2011 (UTC)

As for the highest sustained flight: Lockheed_SR-71_Blackbird#Records says "On 28 July 1976, SR-71 serial number 61-7962 broke the world record for its class: an 'absolute altitude record' of 85,069 feet (25,929 m)." That's 25.9 km. StuRat (talk) 03:05, 21 September 2011 (UTC)

Does the X-15 count? 67.169.177.176 (talk) 04:03, 21 September 2011 (UTC)

The X-15 was a rocket with wings. The Blackbird was a ramjet. So probably not. I do recall reading in The Right Stuff about Yeager taking I think his conventional plane so high that the sky turned black, which means you're pretty much in space. At that point the engine conked out and the plane went into a dive that destroyed it (it "augered in"), but Yeager bailed out successfully. (It's been a long time, I hope I haven't conflated 2 or more stories into 1.) ←Baseball Bugs ^{What's up, Doc?} carrots→ 06:10, 21 September 2011 (UTC)

If the plane in question was the Bell X-1 or any derivative thereof, then the engine was a liquid rocket -- which means that it conked out because of fuel exhaustion, not because of thin air. As for the dive, in this case it might have been caused not by the engine failure, but by inertial coupling. FWIW 67.169.177.176 (talk) 06:29, 21 September 2011 (UTC)

I didn't dream it after all. It was an F-104. The article discusses the Yeager mishap. ←Baseball Bugs ^{What's up, Doc?} carrots→ 06:47, 21 September 2011 (UTC)

For a standard fixed wing aircraft, a very high altitude requires a very high lift body with an extremely high stall angle, and/or a ridiculous amount of excess thrust (which would basically make it more of a rocket than a traditional airplane). Lynch7 17:37, 21 September 2011 (UTC)

As I recall from the last time I read about this in any detail, the ability of a plane to achieve a high altitude is dependent on its type of engine, as you're indicating. A standard prop plane can only go so high because it can only go so fast. A conventional jet can go higher because it can go faster. And a ramjet can go very high because it can go very fast. In fact, I think the way a ramjet works is that, "The faster and higher it goes, the faster and higher it can go. Up to a point, of course, as it still needs air. Rockets don't need air, as their fuel is self-contained. Obviously. :) ←Baseball Bugs ^{What's up, Doc?} carrots→ 17:43, 21 September 2011 (UTC)

The F-15 Eagle can reach 100,000 feet in a zoom climb. The SR-71 can reach even higher altitudes in sustained flight (or at least so they say). 67.169.177.176 (talk) 22:52, 21 September 2011 (UTC)

And I would still call the SR-71 an airplane, so I think it qualifies, ramjet or not. StuRat (talk) 23:05, 21 September 2011 (UTC)

Yes, absolutely, the Blackbird was/is an airplane. The X-15 was a "rocket plane". ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:46, 21 September 2011 (UTC)

Unless I've missed something, nobody has provided a link to our Flight altitude record article. The answers that gives are: Jet plane: 37.65km (Mig 25), Piston prop plane: 20.43km (Boeing Condor UAV), Helicopter: 12.42km (Aérospatiale Lama), Glider: 15.45km. Alansplodge (talk) 23:34, 24 September 2011 (UTC)

Battery acid?

Ok, I've just returned from my yearly camping trip to Interior Alaska. We use a small battery powered fan most nights to supply a little breeze and some "white noise". One night the batteries began to fail while we slept, waking my wife, who replaced the batteries in the dark while half awake. When we woke in the morning the batteries seemed to be dying again already, and upon further inspection a thin, foamy liquid was seeping out of the battery door. It turned out three of the four D cells were in correctly, but one was backward. After discovering this I knocked the batteries into the trash and we cleaned the fan up. I got some of this liquid on my fingers. They seemed to tingle a bit but did not turn green, burn, or begin dissolving. Maybe I've seen too many cheap movies. So my question is: Was this substance battery acid? How corrosive is it? Why did the batteries still work at all when one was improperly installed? Can I guilt trip my wife for endangering my life or should I feel bad for not waking up and doing it myself? (that last one obviously not a scientific question but more of a domestic matter) Beeblebrox (talk) 23:36, 20 September 2011 (UTC)

See Alkaline battery#Leaks and Carbon zinc battery#Leakage and environmental concerns Nil Einne (talk) 00:15, 21 September 2011 (UTC)

I'm surprised that the fan worked on half its normal voltage (the reversed cell would cancel out one third of the three correct cells), but it would be the reverse current that overcharged the reversed cell and caused the leakage because the hydrogen produced in attempting to charge the cell would force zinc chloride out of the cell (your description doesn't sound like potassium hydroxide from an alkaline cell). Zinc chloride is a skin and respiratory irritant, so I hope you washed your hands well, but I've had it on my hands many times without ill effect, so don't accuse your wife of attempted murder. The three cells that were not reversed probably needed only a good wash to be used again. Dbfirs 00:45, 21 September 2011 (UTC)

Small DC motors can operate at various voltages, such that increasing or decreasing a voltage will increase/decrease a motor's torque and speed. The limiting factor is usually the excess heat that is produced in the motor's winding if one is operated too long above its rated voltage. --Modocc (talk) 01:36, 21 September 2011 (UTC)

Indeed it isn't uncommon (well more common in the past before the widespread availability of fan speed controllers) for someone to operate a 12V DC fan on 7V and occasionally even 5V in a computer. They don't always work, particularly at 5V but a fair few do. Nil Einne (talk) 05:31, 21 September 2011 (UTC)

The tingling you felt from the foamy liquid was potassium hydroxide which is not an acid but a base. It's very corrosive to metal, and if you rinsed your hands well, then no harm done. Just be glad you didn't wipe your eyes after touching it, or you would have been in substantial pain and possibly at risk. Dualus (talk) 06:59, 21 September 2011 (UTC)

High-power alkaline batteries contain aqueous potassium hydroxide, but it doesn't normally leak as a liquid in my experience, which is why I thought that acidic zinc chloride from cheaper batteries was more likely, especially because of its deliqiescence. We agree that washing hands is important whichever it was. Dbfirs 08:51, 21 September 2011 (UTC)

I've had one alkaline battery leak in decade.. However if the battery was reversed with a voltage of 4.5V across it the chemistry would change - possibly oxygen would be evolved (and maybe hydrogen at the other electrode - though this is supposed to be absorbed by the manganese dioxide) - if so this would cause an increase in pressure and break the safety seal - evolution of gas might also explain the foamy nature of the leak.

generally if it's an alkaline battery the electrolyte (liquid) feels very soapy - and also tends to sting on even the slightest skin cut (or skin damage - including tiny cuts you wouldn't have otherwise noticed) - if you didn't notice this (you have skin like a rhino or) it was a 'dry cell' - these also can produce gas if connected the wrong way round.Imgaril (talk) 11:11, 21 September 2011 (UTC)

Re: guilt tripping your wife - all modern batteries have a safety release valve - that breaks when pressure builds inside the battery - this makes the batteries safe - if they didn't have these than exploding batteries are a real possibility. However the evolved gas may be a mixture of hydrogen and oxygen - a real explosive mixture - it's unlikely to be enough to kill you (though the explosion might have deafened you and set fire to your tent in an extreme example) .. the rest is up to you.Imgaril (talk) 11:19, 21 September 2011 (UTC)

Regarding that battery type, they were non-rechargeable Duracell alkaline batteries. Anyhoo, my fingers didn't fall off, the fan still works, and my wife had to go back to work after our vacation 2 days before I did so I guess the guilt trip is cancelled as well. Thanks for the replies! Beeblebrox (talk) 23:45, 21 September 2011 (UTC)

In that case, Dualus was correct, it was potassium hydroxide (an alkaline), not the acidic zinc chloride in zinc-case batteries. I haven't seen Duracell batteries leak like that -- I'll have to try an experiment on reverse charging them. Glad to hear that both your fingers and your wife are safe! Dbfirs 12:52, 23 September 2011 (UTC)

September 21

Highest internal temperature of cold blooded animals

What is the highest internal temperature cold blooded animals (Ectotherms) can tolerate from their external environment and can warm blooded animals tolerate a higher internal and external temperature? --DeeperQA (talk) 00:49, 21 September 2011 (UTC)

I would expect that cold-blooded animals can withstand a higher internal temperature. After all, they are designed to handle a wider range of internal temperatures. However, that doesn't necessarily mean they can withstand higher external temps, since warm-blooded animals may have more effective cooling methods, like sweating. StuRat (talk) 02:54, 21 September 2011 (UTC)

Okay, so what would be the dividing line? At what temperature would warm blooded survive and cold blooded would not? --DeeperQA (talk) 04:08, 21 September 2011 (UTC)

There isn't really a strong dividing line; animals like the sloth tend to blur it. --T H F S W (T · C · E) 05:14, 21 September 2011 (UTC)

It sounds like the question is more relevant to Poikilotherm and Homeotherms rather then cold or warm blood. In particular this image. Vespine (talk) 05:45, 21 September 2011 (UTC)

If I'm reading that chart correctly, mammals do better than reptiles with internal temperatures over 35°C, reptiles go dormant at 37°C, and mammals go dormant at 42°C (but, in the case of mammals, the exterior temp could be quite a bit higher before their internal temp would reach that). So, that seems to say that mammals can tolerate both higher internal temps (which surprises me) and external temps (which doesn't). StuRat (talk) 03:31, 22 September 2011 (UTC)

You might like to read Boiling frog, though the article doesn't really answer any questions. Dbfirs 08:40, 21 September 2011 (UTC)

It depends on your definition of animal; extremophile lists some simple invertebrates that can live in extreme situations; the tardigrade can survive temperatures up to 151 C. --Colapeninsula (talk) 14:14, 22 September 2011 (UTC)

Moment magnitude conversion

How can I convert a Molment Magnitude measure into a richter scale measure?

See the article Moment magnitude scale. For any medium sized earthquake (from say 3.0-6.0 or so) the scales are almost identical. The Moment Magnitude scale is more accurate for measuring small and large earthquakes than the Ricter scale, so the two scales diverge at either end. --Jayron32 02:32, 21 September 2011 (UTC)

When the moment magnitude scale was set up it was intended to match the Richter scale exactly at lower magnitudes, but provide more accurate magnitudes above about magnitude 7 as the Richter scale tends to saturate at around this value. This is because of the measuring technique, with the Richter scale and the related surface wave magnitude and body wave magnitude scales, using relatively short period (i.e. high frequency) waves, while modern seismometers use a wide range of frequencies, capturing the full energy output of the earthquake. Mikenorton (talk) 15:35, 21 September 2011 (UTC)

Earthquake question

It is known that Earthquakes occur when several tectonic plates move relative to each other.The boundry between them are large areas.Then why we say about the points like hypocenter or epicenter and not large areas? — Preceding unsigned comment added by 49.244.180.209 (talk) 02:10, 21 September 2011 (UTC)

Because the "slips" happen in relatively isolated locations. Rocks seem very rigid, at least on a human scale, but when measured in continent sized chunks they have some elasticity to them (scientists call this Elastic modulus). You can think of it this way: When you tear a paper, you don't tear it all at once, you tear it one little point at a time. An earthquake is generally one little tear happening in one location. The rocks don't break all along the fault, they tear along it. --Jayron32 02:30, 21 September 2011 (UTC)

If the plates moved smoothly past, there would be no quakes. But they "snag" at certain points. When these break free, you have a quake, centered around the snag. StuRat (talk) 03:08, 21 September 2011 (UTC)

Scientists who deal with earthquakes precisely do not really talk about epicenters. They talk about fault mechanics. For example, this research group, Crustal Deformation and Fault Mechanics, uses geophysical data to model the actual rock behavior more accurately than just a point-source earthquake. You can see some illustrative diagrams of their research; including some nice 3D diagrams of earthquake data. Here is some more work from another researcher, shear dynamics. Today's journalists find a dot on a map easier than a thorough scientific analysis, but if they did a little research, they'd see that earthquakes are actually very complicated, dynamic, volumetric events. Nimur (talk) 23:48, 21 September 2011 (UTC)

why are the pictures of actual size molecules are countable?

how is it that we know so much about the structure of molecules (numbers of atoms (from various kinds in it) or their aesthetic arrangement) but we haven't really see them (i know of only 2 photos of molecules in "reality".

i would like to know about a text-book who contains photos of molecules, i must look in it. i believe that there aren't such photos here in Wikipedia in molecule only because of copyright problems. thanks. 109.66.42.35 (talk) 10:17, 21 September 2011 (UTC)

There aren't any photographs possible. Visible light has too long a wavelength to resolve detail on that scale. All that is possible is either a CGI constructed using data obtained by non-optical nanoscopes, or a translated image using an xray crystallography. Plasmic Physics (talk) 10:33, 21 September 2011 (UTC)

(edit conflict) We can't take photographs of molecules because they are too small compared to the wavelength of visible light, so we have to use indirect methods to infer the details of their composition and structure. Some of these methods are described under Molecular geometry determination in the molecular geometry article. Gandalf61 (talk) 10:37, 21 September 2011 (UTC)

One can create images of atoms using a scanning tunneling microscope. That doesn't use light either, but you can definately image individual atoms using the technique. --Jayron32 15:16, 21 September 2011 (UTC)

indeed!, we can see individual atoms.. as we all can see in the article atom. so why are the photographs of molecules are so countable (1-2), you could use google to see this 2...thanks. 81.218.145.251 (talk) 15:34, 21 September 2011 (UTC)

There are no photographs of individual atoms or molecules. What you see are images created by taking the output from some very fancy electronics and doing a lot of complicated signal processing on it. Gandalf61 (talk) 22:39, 21 September 2011 (UTC)

Which is to say, we get into unusual and counterintuitive definitions of "seeing" when we start talking about things the size of atoms or molecules. It's a fair point to say we can visualize them; it's also a fair point to note that this is an especially mediated/manipulated form of visualization. --Mr.98 (talk) 02:03, 22 September 2011 (UTC)

Infact I used an AFM just the other day. Plasmic Physics (talk) 23:14, 21 September 2011 (UTC)

Thinking: if you're not actually perceiving visually the nanometric objects, then is still right too call it microscopy or nanoscopy? Why not call it micrography or something similiar? Plasmic Physics (talk) 03:10, 22 September 2011 (UTC)

There is this, the picture part way down is the letters "IBM" arranged out of individual atoms, I can't find if there is a wiki article about it. Vespine (talk) 03:26, 22 September 2011 (UTC)

Still not a photograph. Plasmic Physics (talk) 10:26, 22 September 2011 (UTC)

redundant rails

When travelling on mainline railways I often find that there are long sections of rusty rails between the rails in use. What are the purposes of these? Difficultly north (talk) 11:49, 21 September 2011 (UTC)

these are holding the rails in allignment, sometimes the rails are upright too

In the UK it's common to leave old rails (or cut off rails) in the track bed, or next to the track when they have been replaced - this is a management/cost issue where the effort/equipment does not exist to recycle the rails.. (or it is more cost effective to allow this wastage)

In some cases what appears to be two rusty rails will be seen between the running rails - these may be fixed to the sleepers (railroad ties) across a rail expansion joint - they are added to add stability keeping the track in allignment at points were there is a gap in the connectivity of the running rails. (I'm assuming you wouldn't have confused what you saw with Gauntlet track).Imgaril (talk) 12:15, 21 September 2011 (UTC)

No not Gauntlet track. I am often seeing it anywhere on the National Rail network. Simply south...... creating lakes for 5 years 18:42, 21 September 2011 (UTC)

Rails left in the track bed tends to be a temporary thing, either delivered and not yet installed or the old rails awaiting uplift. More often than not, somewhat counter-intuitively, the rusty rails are the new ones. --Tagishsimon (talk) 16:54, 21 September 2011 (UTC)

Okay. I'll take a photo of what I mean tomorrow but I think yours sounds more sort of what I'm referring to. Simply south...... creating lakes for 5 years 18:42, 21 September 2011 (UTC)

Yup, I'm fairly confident we're talking about the same thing. Installing long welded rail takes time, and track possession times are short, so the job gets broken down into delivery, assembly, installation, dismantling, uplift, etc. --Tagishsimon (talk) 22:45, 21 September 2011 (UTC)

I think you're talking about guard rails. They are there to make sure the train doesn't go to the side if it derails. You see them mostly on bridges and other sturctures where a train leaving the track during derailment could cause a lot of damage to nearby structures. Here's a good picture: [[11]]. BTW, I remember going through this tunnel as a kid when my folks would take me to New York. The tunnel is in Nay Aug Park in Scranton, PA. Dominus Vobisdu (talk) 16:14, 21 September 2011 (UTC)

Sorry, I'm not referring to guard rails. Simply south...... creating lakes for 5 years 18:42, 21 September 2011 (UTC)

Did you mean like these [12] ? or these [13] ?? or even these [14] ??? . Imgaril (talk) 18:49, 21 September 2011 (UTC)

I see loose rails here too, but never on the tracks, that would just be dangerous. They usually lie next to the tracks. Plasmic Physics (talk) 23:11, 21 September 2011 (UTC)

I'm not sure anyone has alleged they're on the tracks (meaning on the rails), so much as on the track bed. The first two photos in Imgaril's post are them. --Tagishsimon (talk) 23:15, 21 September 2011 (UTC)

I meant track bed. Those rails in the photo clearly serve a purpose. I may not know what it is, but I do know that steel is expensive, and it wouldn't be used if there was no reason. Plasmic Physics (talk) 01:02, 22 September 2011 (UTC)

The 'purpose' is explained in the text in the links - the rails are awaiting installation, or waiting to be taken away - as Tagishsimon described. (Unless you meant the photo above right)94.72.237.125 (talk) 01:10, 22 September 2011 (UTC)

How sealed plastic soda bottle tops are attached

I guess this is an engineering-related question. When you first get a bottle such as a 2-liter bottle of soda, the screw-off top is one with the ring that stays at the base of the neck after purchaser rips the cap/ring connection by twisting the cap. How is that cap/ring piece initially attached? Is it rammed on with high force, with the threads of the bottle and the threads on the inner side of the cap just temporarily distorting as they rub past each other? I've also seen metal cap/ring pieces on glass bottles, but metal would seem to be less elastic than most plastics. 20.137.18.50 (talk) 17:39, 21 September 2011 (UTC)

The rings have little plastic "wings" on the inside which allow them to be threaded on, but which "catch" when threaded off, thus allowing the ring-and-cap assembly to be put on the bottle, but preventing the ring from coming off when twisted the other way. --Jayron32 17:55, 21 September 2011 (UTC)

A ratchet effect then?

Yes. 70.91.171.54 (talk) 19:02, 21 September 2011 (UTC)

I'm fairly certain that the metal ones are placed on as oversize caps, and then cold formed to a tight fit (I'm sure there will be a video of this on youtube, but can't find one as yet). There's an article on these metal ones Screw_cap_(wine) - the links have more info about how they are attached.Imgaril (talk) 18:14, 21 September 2011 (UTC)

Those kinds with anti-tamper or lock rings are called PP (pilfer-proof) screw caps. Like Jayron said, notice the teeth inside the bottom-most portion of the cap (the bank) which is only loosely attached to the top. They are all pointing in one direction. When you screw them on, they are flattened against the skirt of the cap, thus offer no resistance. But once they reach the end of the threads, they encounter an open space underneath a flange, and they pop out, pointing against the thread. Screwing it off will now make the teeth catch on the lower rim and it will instead break along the pre-cut stress points and be retained. And yes they are screwed on by machines. From labor-intensive ones for small-scale production to fully automatic ones.-- Obsidi♠n Soul 19:11, 21 September 2011 (UTC)

Actually I used to have a job putting the tops on 2litre bottles of milk - a machine filled them, but humans screwed the tops on... The trick is to hold the top steady and rotate the bottle by pulling.. Working inside a fridge in the middle of summer and all the milk you can drink - paradise. (they probably have a machine now - that was 20 years ago when milk in plastic bottles, in metric quanities was still a novelty) These were the "ratchet type", a bit like File:Milk jugs in a row.jpg. The clicking of the rachetting action is quite a pleasurable sound. Imgaril (talk) 00:49, 22 September 2011 (UTC)

Heh, I imagine it would have been very dreary. :P And yeah. There's a dairy (for water buffalo milk) nearby, and they use small machines that still require a person to hold the bottle up to it, but the actual spinning of the cap into it are all done by the machine very quickly.-- Obsidi♠n Soul 06:33, 22 September 2011 (UTC)

Unrelated but quite wonderful. Bus stop (talk) 23:36, 21 September 2011 (UTC)

Where do I go wrong in this statics problem?

Problem: If the load has a mass of 3.0Mg with its center of mass located at G, determine the horizontal and vertical components of reaction at the pin C when x = 3.9m

See a diagram here: http://postimage.org/image/358oy4cxw/. Image text: The jib crane is supported by a pin at C and rod AB.

I understand that there are essentially three unknowns (the magnitude of the force along the rod and the vertical and horizontal components of the force at the pin) and three equations (the sum of vertical and horizontal forces and the sum of moments must be zero):

$\sum F_{x}=\mathrm {pin} _{x}+\mathrm {rod} _{x}=0$

$\sum F_{y}=\mathrm {pin} _{y}+\mathrm {rod} _{y}-3000\mathrm {kg} *9.8\mathrm {m/s^{2}} =0$

$\sum M=4\mathrm {m} *\mathrm {rod} _{y}-0.2\mathrm {m} *\mathrm {rod} _{x}-3.9\mathrm {m} *3000\mathrm {kg} *9.8\mathrm {m/s^{2}} =0$

${\frac {-3.2\mathrm {m} *\mathrm {rod_{x}} }{4\mathrm {m} }}=\mathrm {rod} _{y}$

I solve this with matlab like this:

solve('pinx + rodx = 0',
      'piny + rody - 3000 * 9.8 = 0',
      '4 * rody - .2 * rodx - 3.9 * 3000 * 9.8 = 0',
      '-3.2 / 4 * rodx = rody')

The results are pinx = 33.72kN, piny = 2.421kN (and rodx = -33.72kN, rody = 26.98kN).

However when I enter the answer to the online system I got the problem from it says "Term 2: Not quite. Check through your calculations; you may have made a rounding error or used the wrong number of significant figures." Term 2 refers to pin_y. The system is very lax with rounding and accepts any answer as long as the relative error is below a few percent. The value of g the system uses is exactly 9.8m/s^2.

Since I can enter the answer an unlimited number of times I varied pin_y in steps of .01kN a few steps to both directions until the message went away. That suggests that while pin_y might be close to correct pin_x is not. I've been thinking about this for a few hours and just cannot see my error. It's getting very frustrating. I'd appreciate if you could check that I have solved at least something correctly. If you can think out of the box and tell what is the real problem my online system wants answered it would be great. --19:49, 21 September 2011 (UTC) — Preceding unsigned comment added by 145.94.77.43 (talk)

In your last equation, I think the 3.2m should be 3m. Also, the second argument to solve is missing an "= 0", but not using Matlab I don't know if that's a bug or not. -- BenRG (talk) 22:16, 21 September 2011 (UTC)

Matlab solve() equates to zero by default, I failed to add a ' = 0' when copypasting. That 3.2 - .2 part was it. Thank you! This was a shamefully huge help. --145.94.77.43 (talk) 23:31, 21 September 2011 (UTC)

condensation in lungs

the inside of lungs is a fairly damp environment I presume, so does condensation form on the inside of the lungs when breathing cold air? If it does, where does all the liquid go? Does the person need to cough it out later? Googlemeister (talk) 21:11, 21 September 2011 (UTC)

Cold air contains very little moisture. Drying out would be a bigger problem. The inside of the lungs is warm enough to hold a lot of moisture, which is respirated. Remaining excess moisture would either be expectorated or be absorbed by the lung tissue. Dominus Vobisdu (talk) 21:17, 21 September 2011 (UTC)

Well cold air does not have to be dry. I was thinking where it was near freezing but foggy. Googlemeister (talk) 21:20, 21 September 2011 (UTC)

Even extremely humid cold air contains little moisture. Cold air can hold far less moisure than warm air can. When near freezing cold air with 100% relative humidity is warmed up to body temperature, it becomes very dry warm air. Dominus Vobisdu (talk) 21:31, 21 September 2011 (UTC)

Without directly answering: inhaled air is humidified and warmed by the upper airway, so that the partial pressure of water in alveoli is a fairly uniform 47 mmHg.). See Alveolar gas equation, Pulmonary gas pressures, Nasal concha. - Nunh-huh 21:22, 21 September 2011 (UTC)

Condensation forms when you have warm air and a cold surface. The situation you are describing is the reverse of that, so there shouldn't be any significant condensation. Looie496 (talk) 21:27, 21 September 2011 (UTC)

Well, it is possible, if you have air significantly hotter than body temperature at 100% relative humidity (or even supersaturated). I think I've had that happen in a hot shower, with the door closed, where it seems to become difficult to get enough oxygen. Opening the door solves the problem. A sauna might be another place where this might be an issue. Note that these same conditions would tend to cause hyperthermia, as well, although that seems to take a bit longer. StuRat (talk) 00:29, 22 September 2011 (UTC)

Pulmonary alveoli absorb moisture into the body along with oxygen; they have to do the former to be able to do the latter. When they fail to do so adequately, bronchitis results. 70.91.171.54 (talk) 22:37, 21 September 2011 (UTC)

Can you tell me something about vultures?

Do we know how intelligent vultures are, compared to humans and other birds? --95.150.167.139 (talk) 23:10, 21 September 2011 (UTC)

"humans and other birds"? ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:39, 21 September 2011 (UTC)

It would depend on deciding on a definition of intelligence that could be validly applied to both birds and humans. Even if you restricted it to just birds, there are many different "intelligences" that could be looked at. HiLo48 (talk) 00:20, 22 September 2011 (UTC)

Well, way above chickens, below parrots, and well below humans, for a start. StuRat (talk) 00:34, 22 September 2011 (UTC)

Vultures seem to be good at finding food, which is more than I can say for some humans and other birds. ←Baseball Bugs ^{What's up, Doc?} carrots→ 00:43, 22 September 2011 (UTC)

Here in the US, humans appear to be way too good at finding food. :-) StuRat (talk) 06:44, 22 September 2011 (UTC)

We have bad definitions of "intelligence" even for just human beings. But a rough estimate in comparing species can be found using the brain-to-body mass ratio and/or the encephalization quotient. I haven't been able to easily locate the numbers for a vulture. But that's what I would look for, anyway, to figure out where vultures in particular stand. Humans rank about twice of any animals for EQ. Some birds — especially corvids — have relatively high EQs. Most birds do not. I know very little about vultures in particular. --Mr.98 (talk) 02:00, 22 September 2011 (UTC)

There's plenty of videos of other birds (crows in particular) showing surprisingly high intelligence/problem solving skills - http://www.youtube.com/watch?v=dbwRHIuXqMU and http://www.youtube.com/watch?v=riqtFvZg1mI&feature=related for example. I've no idea about vultures relative to crows though.ny156uk (talk) 06:57, 22 September 2011 (UTC)

One way vultures do have distinctive brains is in respect to the olfactory lobe. Most birds have very poor senses of smell (even by human standards), but vultures are highly developed in this regard. They also have some interesting communication and sharing behaviors. You know how you see 1-3 vultures circling for hours? That is to tell other vulture that food is to be found. It makes evolutionary sense to share when food comes in large amounts, but rarely (other species can also 'listen in' on this signal). Thus, they will circle for much longer over a bison than they would a rabbit. Whether these features count as 'intelligence' is up to you :) SemanticMantis (talk) 15:44, 22 September 2011 (UTC)

September 22

What are/ may be floating conditions to float any thing over water surface

Sir/ Madam I wish to know what are the floating conditions to make any thing float over water surface(Normal potable water not salty).

Wish for an early reply

Thanx a lot — Preceding unsigned comment added by 182.156.153.151 (talk) 04:20, 22 September 2011 (UTC)

Is this a homework question? 67.169.177.176 (talk) 04:45, 22 September 2011 (UTC)

For specifically FLOATING, you're probably after buoyancy. Vespine (talk) 04:47, 22 September 2011 (UTC)

(EC) For a large object in a stable configuration, the object will float if the mass of the object is no more than the mass of a volume of water equivalent to the portion of the volume of the object that’s below the surface of the water, i.e., the mass of the object is no more than the mass of the displaced water. See Displacement (ship) and Displacement (fluid). For very small objects, surface tension can cause an object to float even if it has a greater mass than the displaced water. Red Act (talk) 04:49, 22 September 2011 (UTC)

In other words, for all but the smallest objects, if the object's density is less than that of water, it will float. Very small objects (sewing needles, etc.) can sometimes float despite being more dense than water, because they are supported by surface tension. 67.169.177.176 (talk) 05:11, 22 September 2011 (UTC)

And, of course, an object can still float despite being made of materials far denser than water, like steel, so long as they contain a far lighter material, like air, beneath the waterline, so that the average density of everything is less than water. StuRat (talk) 06:25, 22 September 2011 (UTC)

And, with a more liberal interpretation of the word "float", we could include a hydroplane, hydrofoil, hovercraft, or ground effects airplane (only the first two actually require water). StuRat (talk) 06:36, 22 September 2011 (UTC)

Conditions:

1. Being Jesus.
2. Being an ice skater when it's cold
3. Any theologically admissible combination of the above. Cuddlyable3 (talk) 11:22, 22 September 2011 (UTC)

A solid sphere can float if the radius is less than

$R={\sqrt {\frac {3\gamma }{2\rho g}}}$

where $\gamma$ is the surface tension of water and $\rho$ is the density of the sphere. Count Iblis (talk) 16:02, 22 September 2011 (UTC)

Wouldn't $\rho$ rather be the density of the sphere minus the density of water? Dauto (talk) 21:06, 22 September 2011 (UTC)

If a vessel such as a nuclear submarine violated the "floating criteria" given by Red Act, as by having some compartments flooded, but had 200 megawatt nuclear reactors powering propellers driving it forward, and diving planes set to drive it upwards, couldn't it remain with a portion above the surface (of "potable water" such as Lake Michigan)? Would such a vessel be "floating?" This would be analogous to an airplane (as opposed to a "lighter than air craft" flying. Edison (talk) 04:15, 23 September 2011 (UTC)

To call that situation "floating" would be literary license at best, and abuse of terminology at worst. The submarine you just described is not "floating," it is "propelling itself upwards above the water." It's not buoyant. On the other hand, people do sometimes describe a heavier-than-air airplane as "floating," even in technical contexts like the FAA's Airplane Flying Handbook (Chapter 8, "Floating During Roundout," an undesired condition); but even then, the conditions are not due to buoyancy - it's used as an analogy to describe a dynamic effect. Nimur (talk) 04:55, 23 September 2011 (UTC)

OK, now I'm confused myself. What about a sub that's neutrally buoyant and cruising underwater at constant depth (say 60 feet)? Would that be considered "floating"? 67.169.177.176 (talk) 06:11, 23 September 2011 (UTC)

low boiling dopamine receptor agonists

Can someone help me brainstorm of new agonists I could use for fruit fly experiments? We've been working with cocaine for ... years and months, but I also want to try something else. For one, the success rate of aerosolising cocaine with a consistency amenable to experiment is rather unpredictable.

Feeding it into a test chamber by say, distillation often means the cocaine crashes out and crystallises on random surfaces, unable to be taken up by flies. For the love of the flying spaghetti monster, are there any agents better than cocaine that might be easier to administer through the air? (We cannot administer through their food, for various complex reasons.) elle _{vécut heureuse} ^{à jamais} (be free) 04:53, 22 September 2011 (UTC)

THC ? Nicotine ? Ethanol (might be a bit of an irritant, though) ? Or how about the chemical in some dry erase markers that just about makes me pass out ? StuRat (talk) 06:27, 22 September 2011 (UTC)

Those aren't dopamine agonists. While Methamphetamine and apomorphine have relatively low molecular weights, that's a lousy huristic for organic compounds, so what you really need is to go through Category:Dopamine agonists in CAS for an hour or two until you find something sufficiently soluble and volatile. 69.171.160.5 (talk) 06:52, 22 September 2011 (UTC)

Looking at the category on wikipedia - nearly all of those are essentially involatile - exceptions are amphetamine, and Propylhexedrine. These would need to be in the free base form - amphetamine is volatile enough to have a strong distinctive amine smell, and cause excitation if you leave the top of the bottle and smell it.. So it might create a great enough concentration in air naturally to affect your flies.

It's possible that there is dopamine agonist so potent that is it more effective than amphetamine despite lower volatility - but I don't know it - not my subject.Imgaril (talk) 13:17, 22 September 2011 (UTC)

Generally the way to introduce a non-volatile compound would be to convert to Aerosol form, generally using a Atomizer nozzle.Imgaril (talk) 13:36, 22 September 2011 (UTC)

The experiments are very sensitive to the size of the aerosol particles -- too big and the flies will simply not be affected by it! elle _{vécut heureuse} ^{à jamais} (be free) 21:41, 22 September 2011 (UTC)

Amphetamine free base looks like your best bet by far, and if you're already licensed for cocaine, it should be easy to come by. Are there any reasons it won't do what you want? 75.71.64.74 (talk) 21:48, 22 September 2011 (UTC)

Why are you trying to get flies high on hard drugs? 208.54.40.213 (talk) 04:56, 23 September 2011 (UTC)

I think she's trying to study the mechanisms of drug addiction. 67.169.177.176 (talk) 06:14, 23 September 2011 (UTC)

Why does collagen cross-link in scar tissue?

After reading the scar tissue article, http://en.wikipedia.org/wiki/Scar, I came across this tidbit: "Sherratt et al, explain that scar tissue is the same protein (collagen) as the tissue that it replaces,[1] but the fiber composition of the protein is different; he explains that instead of a random basketweave formation of the collagen fibers found in normal tissue,[1] in fibrosis the collagen cross-links and forms a pronounced alignment in a single direction.[1] This collagen scar tissue alignment is usually of inferior functional quality to the normal collagen randomised alignment. For example, scars in the skin are less resistant to ultraviolet radiation, and sweat glands and hair follicles do not grow back within scar tissue. A myocardial infarction, commonly known as a heart attack, causes scar formation in the heart muscle, which leads to loss of muscular power and possibly heart failure. However, there are some tissues (e.g. bone) that can heal without any structural or functional deterioration."

I was wondering what exactly cause the collagen fibers to cross link and possible why the scar tissue replicates itself instead of normal skin since its constantly being replaced. Is there a specific gene for this? — Preceding unsigned comment added by 139.62.167.82 (talk) 20:42, 22 September 2011 (UTC)

I'm not sure that scar tissue does replicate itself. I think the same scar tissue may just remain with you for the rest of your life, similar to adult teeth (if they don't fall off). StuRat (talk) 04:31, 23 September 2011 (UTC)

Neutrinos

Sorry to be the first cranky neutrino question after the CERN release of data, and this is probably a very stupid question. Is there a good reason to think that neutrinos must have a positive mass? I'm sure there must be, but I can't see it in our article neutrino. Our article says that neutrinos must have a non-zero mass, and that our main source of information on the masses depends on the squares of the masses (if I'm reading that right)? Please disappoint me with a reasonable explanation, or I'll be too excited to sleep :P 86.164.78.26 (talk) 21:59, 22 September 2011 (UTC)

Okay, we need to distinguish three different things here:

1. Negative mass. This has nothing directly to do with tachyons. Tachyons don't have negative mass.
2. Negative mass-squared (also called imaginary mass) in classical relativistic particle theory. Classical particles with negative m² go faster than light.
3. Negative mass-squared in relativistic field theory. This is mathematically related to the classical particle case, but the practical upshot is very different. In a field theory, the mass-squared behaves like a spring constant—if you think of the field as a rubber sheet then the higher the mass, the more resistant the sheet is to stretching. If the mass-squared is negative, then not only does the sheet not resist stretching but it actually pushes in the same direction you pull it, leading to an exponential feedback loop if the field is even slightly disturbed. The only way for this to make any sense is if there's a counterbalancing effect that comes into play at larger amounts of stretching, so the sheet only stretches to the point that these opposing effects balance each other. This actually happens in the Standard Model with the Higgs field, and is called tachyon condensation. The result is a field that behaves for practical purposes like it has a positive mass-squared.

I know nothing about this new announcement from OPERA except that they claim to have found actual superluminal propagation. This sounds like the second case above, but modern particle physics is built on quantum field theory, where the second case is irrelevant; "tachyons" don't propagate superluminally in quantum field theory. So, if this is real, it would pretty much require rebuilding modern particle physics from the ground up. It could be a quantum gravity effect, and this might give a hint as to the right theory of quantum gravity. But more likely it's experimental error. -- BenRG (talk) 23:05, 22 September 2011 (UTC)

Might you be referring to the Reuters article that they are travelling faster than light? I just got it linked to me. Excitement should be withheld as it's almost certainly an error, but honestly, given the fact that the scientists aren't crackpots, my heart did rush a little when I got to the end of the article without indication that they're crackpots. SamuelRiv (talk) 23:21, 22 September 2011 (UTC)

[15]. Nil Einne (talk) 00:54, 23 September 2011 (UTC)

Here's the preprint. The official announcement doesn't happen until 4PM Friday in Geneva (13 hours from now). As that blog post says, it's way too early to get excited about this. -- BenRG (talk) 01:01, 23 September 2011 (UTC)

Note from some reports [16] [17] it appears that while the team think there is a possibility their results are correct and would be confirmed by independent replication and that would obviously be their preference, they think the more likely explanation is there's an error they didn't notice. Some further comment on the Sn1987A neutrinos [18] Nil Einne (talk) 01:08, 23 September 2011 (UTC)

September 23

Photon Mass?

So, I heard that, even though photons do have zero rest mass, they have relativistic mass due to their motion. Could anyone care to explain this in wide detail? Thanks.186.29.118.196 (talk) 01:45, 23 September 2011 (UTC)

Sure. Energy is mass. As long as a photon has energy, it has mass. QED. See mass-energy equivalence and relativistic mass and rest mass for more details. --Jayron32 02:24, 23 September 2011 (UTC)

Any given photon has EVERY mass value from the tiniest amount above zero to as high as you want to count. The observed mass is purely in the eye of the beholder. (Pun intended.) The electron is different. Each electron can be found at any mass level from the base "rest mass" to as high as you want to count. It all depends on who catches it. Hcobb (talk) 02:34, 23 September 2011 (UTC)

If, indeed there is more than one electron. Maybe, there isn't. --Jayron32 03:15, 23 September 2011 (UTC)

Bode phase plot guidelines

(I'm not sure if this might belong in Maths). I've got a set of Bode plots for a bunch of different circuits. On each one, I am supposed to (by analysing the transfer function) "sketch the Bode amplitude plot asymptotes and phase guidelines". However, I have no idea what "phase guidelines" are, and Google is unhelpful. Does anybody here know? --130.216.55.172 (talk) 03:24, 23 September 2011 (UTC)

Yes! Have a look at how to draw a Bode plot by hand. You need to decompose the transfer function into poles and zeros, usually by factoring the denominator of your transfer function. There are many related techniques to accomplish this - partial fraction analysis is the most common - have you covered any of these methods before?

This section explains the rules of thumb for a phase plot. All these "rules" are derived from more rigorous mathematical analysis (frequency-domain analysis, formally by taking the partial derivative of phase and amplitude of the transfer function with respect to frequency. By writing the function in canonical form, you can just churn out the various asymptotes and estimate the value of the phase for any frequency, without ever having to crunch it computationally. Nimur (talk) 04:32, 23 September 2011 (UTC)

Electra 10-E

Does anyone here happen to know where to find a maintenance manual for the Lockheed L-10 Electra? I'd like to know how to (non-fatally) sabotage and then repair one (for a writing project, of course), and for that I'd like to know how the mixture control linkages are arranged on that aircraft. (Don't worry, I'm not trying to sabotage an actual aircraft, just trying to arrange a malfunction and consequent forced landing as a plot device...) 67.169.177.176 (talk) 06:42, 23 September 2011 (UTC)

Does this relate to your shabbat navigation? What are you trying to do, find some way to kill a kharedi? :p Sir William Matthew Flinders Petrie | ^{Say Shalom!} 24 Elul 5771 06:45, 23 September 2011 (UTC)

No, no, no. The only thing these two questions have in common is that they're for the same writing project. And BTW, didn't I specify that the malfunction and force-landing would be non-fatal? Just for the record, I don't want to kill my characters in this case, but I want to have them force-land in a hostile area after running out of fuel (this condition caused by the mixtures sticking in full-rich position) and barely escape with their lives. Any deaths (if such there be) can wait until later. ;-) 67.169.177.176 (talk) 06:56, 23 September 2011 (UTC)

You could go for the simpler approach: have your saboteur drain some of the fuel pre-flight. According to the forums of people asking the same thing as you, there was one website that had the information, but I can't get it to load. It's [19] in case the problem's on my end. You're probably best off tracking down an enthusiast and asking them. Teshmanesh (talk) 08:10, 23 September 2011 (UTC)

Do you disagree?

The law which prevents doing anything in the past is the law which states a distance above zero can not be traveled in zero or less time rather than the distance light travels in unit time can not be exceeded. In other words light might get somewhere faster than sound and warn of an explosion faster but that does not mean light (compared to sound) can send information into the past and to do that requires time reversal not speed faster than light. --DeeperQA (talk) 07:35, 23 September 2011 (UTC)

If I understand what you're getting at, see tachyonic antitelephone.

Summary: Sending information faster than the speed of light in your frame of reference doesn't send it backwards in time, in your frame of reference. But it does send it backwards in time in some other frame of reference.

If the mechanism by which you can send the information faster than light is frame-invariant and isotropic, that is if it works the same in everyone's frame of reference and in all directions, then you can combine forces with someone moving quickly with respect to you, to send information backwards in time even in your own frame of reference.

It takes two steps: You send the information to the other party. This takes positive time in your frame, but negative time in his. He repeats the trick, sending it backwards in time in your frame. --Trovatore (talk) 07:53, 23 September 2011 (UTC)

exceding speed of light

1. REDIRECT [[20]]

Now i am not a science guy but nothing could exceed the speed of light right?but than whats this?