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January 9

a map showing the international date line in the middle

I would like to be able to see a world map with the international date-line more centred. (in one piece) - ie: i do not want to see part of the one side of the date-line SQUEEZED in on the right- and the other part SQUEEZED in on the left of the whole image/picture/diagram.

Looking at an existing time-zone map of the world, a more convenient split would be somewhere between 30 to 60 (degrees) West longitudes - as this looks like a longitudinal zone with the least breaks or "zig-zags".

Would you be able to help me, please? 196.210.195.46 (talk) 05:19, 9 January 2013 (UTC)

Does File:Standard time zones of the world (2012) - Pacific Centered.svg work for you? If not, you can type "Pacific-centered map" into Google Images and get hundreds of options. --Jayron32 05:48, 9 January 2013 (UTC)

Hand grenade

How many times can a hand grenade realistically bounce off a wall before either coming to a stop or exploding, whichever comes first? Assume that: the grenade in question is a German stick grenade with a standard 5-second fuse, thrown at the wall at a 45 to 60 degree angle as hard as possible; the thrower is tall and has long arms but only average strength; and the walls are concrete and about 3 feet apart, forming a narrow passageway. 24.23.196.85 (talk) 06:46, 9 January 2013 (UTC)

It could only bounce of a wall once. If you mean bounce between two walls, that would depend on how high along the walls it hit initially, it's angle relative to the ground, and it's initial speed. They don't bounce very much, so it would have to be going quite fast to bounce more than once or twice. StuRat (talk) 06:53, 9 January 2013 (UTC)

That's what I meant, bouncing between the walls of a concrete-walled passageway. 24.23.196.85 (talk) 07:06, 9 January 2013 (UTC)

It still depends on the width of the passageway (imagine a passageway 100 feet wide - there could only possibly be one bounce...now imagine a passageway only a foot wide - and there would obviously be many bounces)...also the height at which the grenade initially hits the first wall...if it hit the first wall very low to the ground then fewer bounces than high up. Then we need to know the speed of impact, the angle of the impact...there are just far too many variables.

Worse still - they have a very irregular shape - how it hit (stick first, head first, sideways) would make a massive difference. The rate and direction of rotation would add a complicating factor. Also the head of the grenade was very thin metal - it would likely dent easily - absorbing energy from that first bounce and drastically reducing it's speed. But if the stick hit first - it's wood, flexible like a very stiff spring - so it would probably retain most of the energy providing more rebound.

If you want to get even more technical - our article says that the 1942 and later versions had a serrated steel sleeve that could be optionally be slid over the head to get a greater fragmentation effect in anti-personnel applications - which would really complicate matters in a head-first impact because the serrations would result in a much more random bounce/spin.

Gut feel says "once"...or maybe "not at all" - but there are too many variables to come up with any kind of informed answer.

If I were you - I'd take a foot of broom-handle and firmly duct-tape a 500g can of soup to the top - then get out there and try it! Nothing short of tossing one around yourself will give you the authentic "feel" you need for how they would bounce.

(We need pictures! :-)

SteveBaker (talk) 14:04, 9 January 2013 (UTC)

Not soup. Anything liquid will slosh and act as a damper. Something solid enough to not slosh when you shake it is better. A can of chili or dog food should do the trick.

I am guessing that straight on to the wall will give you maybe a one foot bounceback, but a glancing hit will retain most of the velocity -- but make the next wall effectively farther away, so maybe two bounces. I really want to see pics of this. Do it! Do it for SCIENCE!! <smile> --Guy Macon (talk) 15:56, 9 January 2013 (UTC)

Good point about the liquid thing...but most regular cans are only about 250 to 350 grams - I was thinking specifically of the larger diameter cans that might weigh more like the 560 grams that the real grenade weighed...minus the weight of the stick...so a 500g soup can would have about the right weight. I've seen dogfood in those larger cans though - that would work. SteveBaker (talk) 17:31, 9 January 2013 (UTC)

@24.23.196.85, are you asking this because you want to incorporate it into a graphic novel, film script, story, or other work of fiction? If so, one, maybe two bounces would be the limit of "realistic". But if you're going for exaggerated violence a la Tarantino, have it bounce as many times as you want! - LuckyLouie (talk) 16:29, 9 January 2013 (UTC)

(In a followup to a previous question (Wikipedia:Reference_desk/Science#Lever_frame), our OP indicated that, he/she is indeed writing a novel set in WWII).

I suspect that one bounce (or possibly no significant rebound at all) is the most likely "realistic" outcome - but two bounces and some rolling would seem "credible" to me - especially in a book where your imagination gets to roam free. It might be harder to make it believable in a movie though. Our article on the later Model 43 grenade suggests a detonation delay of 5.5 to 7 seconds...which might help to extend any exciting rolling and/or bouncing and/or being-"fetched"-by-a-stray-dog deemed necessary for the plot. SteveBaker (talk) 17:28, 9 January 2013 (UTC)

As long as we're working in fiction, maybe have the grenade thrower execute a complicated bank shot off the wall in order to take out the bad guy. - LuckyLouie (talk) 18:36, 9 January 2013 (UTC)

That was my plan all along -- a bank shot to send the potato-masher behind a partition in order to take out a German machine-gunner. Based on the layout of that particular pillbox, I can do it with two bounces, but I'll have to shorten the partition somewhat to make it happen.  :-) BTW, I like the experiment you suggested, but the one thing to which I don't have access is concrete walls 3 feet apart -- all the walls around me are made of wood. Will that make a significant difference? 24.23.196.85 (talk) 00:19, 10 January 2013 (UTC)

I find it really hard to believe that you'd have the time or information to plan that kind of a trick. Pillboxes had all sorts of internal layouts - and it's hard enough to toss the grenade into the firing slit as it is without having to consider bounce angles and all of that stuff. The stick grenade is particularly ill-suited to that kind of trickery anyway because it's such a weird shape and really off-balance! It's not like you can stand a couple of feet outside the firing slit, examine where the internal walls are, consider the angles, wind up for a really accurate toss with just the right spin, speed and direction! There are a bunch of guys inside who are working very hard to be sure that you don't toss ANYTHING in there! You'd be standing with your back to the concrete wall, with grenade in hand - and consider yourself lucky if you could get the thing inside in any way at all without having your hand blown off! It's also very dark inside those pillboxes - it would be tough to discern anything much about the interior structure from outside. So for me, your story's "credibility" is blown long before we have to consider whether the grenade could physically bounce as intended! SteveBaker (talk) 15:08, 10 January 2013 (UTC)

I love it. Even assuming a Jason Bourne-like hero, it seems there's a lot more practical issues to consider in this scenario than just 'could a stick grenade bounce twice'. I think the OP might be envisioning a door at the back of the pillbox with a partition separating the entryway from the front gun port area. Even so I'm sure it has a metal door the German crew keeps closed. But let's say the door is open or blown off. Much easier to shoot the guard (if there is one) and then run inside blasting your Sten gun or whatever, using the partition for cover. Any way you slice it, this is all fantasy, so why restrict fiction to 'what can be tested'? - LuckyLouie (talk) 17:40, 10 January 2013 (UTC)

Sure, there are times when the needs of good fiction override practical reality. However, when something really ridiculous happens, it can also detract from the story. (I could cite countless movies and TV shows that were ruined for me by some ridiculous - and unnecessary - impossible thing.) So if there is no loss of narrative quality, one should err on the side of real-world possibility. Clearly our OP's careful questioning of such minutia as the color of the handles in the signal box that our hero uses to redirect the train - suggest that this will be a very grounded-in-reality kind of a novel. In that case, surely there is another clever & creative way to take out this pillbox without our hero doing such a truly super-human trick. Perhaps start with a document like this one: http://www.lonesentry.com/articles/pillboxwarfare/index.html - which describes how US soldiers would approach a pillbox. It provides the valuable advice that a white-phosphorus grenade is more effective against a pillbox than a fragmentation grenade. But it also adds crucial advice about NOT attacking the rear door and that intersecting fields of fire from adjacent pillboxes is a major threat. There is a lot of scope for our hero to be heroic beyond having the ability to bounce a weird shaped grenade off of half-seen walls through a small slit. SteveBaker (talk) 18:12, 10 January 2013 (UTC)

Not a small slit -- a bent entrance-type passageway that serves as the entry point for the pillbox, which is covered by an MG-42 emplaced in a gunport in the partition around which the passage doubles-back (which machine-gun has to be taken out because it also covers main route of advance). In effect, the passageway leads up a short staircase toward the wall with the machine-gun, then makes a 90-degree left turn for a slightly shorter distance, and doubles back into the pillbox itself. And they don't have to worry about interlocking fire because it's a stand-alone pillbox covering the entrance to a railroad cutting. (If you like to play the Medal of Honor: Allied Assault computer game, at one point you encounter a similar situation in the Normandy level.) 24.23.196.85 (talk) 02:29, 11 January 2013 (UTC)

Just read the document -- what it says is, rather than not attacking the rear door at all, that the attacker must not stand directly in front of it, because there's always a machine gun covering that sector. But that's not my plan in the first place -- I'm not so stupid as to have my hero stand right in front of the doorway in full view of the machine-gunner. That's why I asked about bouncing the grenade off the walls, because the assault team will have to throw it in while standing to one side of the doorway (which means they're throwing essentially "blind") and try to have it it bounce around the corner to land behind the partition. 24.23.196.85 (talk) 02:44, 11 January 2013 (UTC)

Does it really matter that it's a stick grenade? The German army also issued "egg" grenades (Model 39 grenade) - and it seems much more credible that one of those would bounce and roll around much more than the ungainly stick models. The article on the Model 24 grenade actually says that one of the benefits of the stick design was to prevent it from rolling on hilly terrain - so if the plot requires that the grenade take some complicated path to it's target - then an egg grenade would be a better choice. SteveBaker (talk) 17:44, 9 January 2013 (UTC)

As a matter of fact, it does matter -- I've never heard of a Maquisard using an egg grenade (unless you meant a pineapple grenade or a Mills bomb). 24.23.196.85 (talk) 06:59, 10 January 2013 (UTC)

I presume they'd be "liberating" those weapons from the Germans along the way...how else would they have gotten hold of the stick-grenade variety? If they stole the weapons somehow - then they'd be likely to find an occasional "egg" grenade along with the "stick" variety. But if they did that, they'd have to be careful - one sneaky trick the Germans employed when retreating from a position was to swap out the 7 second fuses for 1 second fuses and leave the grenades lying around for the enemy to pick up and attempt to re-use! Yikes! (Of course the hero in a novel would likely know all about this trick and be prepared to re-fuze the grenades before attempting to use them!) SteveBaker (talk) 15:08, 10 January 2013 (UTC)

Hey, that's an interesting idea -- maybe Blanche's jealous ex-boyfriend will acquire some instant-acting Model 39s from a crooked arms dealer and give them to Mike, hoping he'd blow himself up?  ;-) 24.23.196.85 (talk) 02:49, 11 January 2013 (UTC)

Hmmm - our article Maquis des Glières and Maquis du Haut-du-Bois both say that the British air-dropped large numbers of "mills-bomb" grenades for the use of the Maquis. (One drop is mentioned as containing 150 grenades). So they most certainly did have 'egg'- and 'pineapple'-style grenades. It's entirely possible that they used the stick variety if they could steal them from the Germans...but the British hadn't made stick grenades since 1908 so whatever the Maquis got in air-drops in 1944 would have been "pineapple" fragmentation grenades for sure. It seems unlikely that the Brits would have air-dropped grenades if the Maquis had a good supply of German grenades - so it seems highly likely that pineapple grenades would have been in the majority. Whether they'd prefer stick grenades over pineapples is debatable - stick grenades can be thrown further - but they are a pain to transport and difficult to use in confined spaces. For taking out a pillbox with a fancy rebounding throw, a pineapple grenade would be greatly preferred. SteveBaker (talk) 15:36, 11 January 2013 (UTC)

North Pole & South Pole questions

Is it true that sunrise and sunset only happened once a year in the poles? Why these 2 places got so cold? roscoe_x (talk) 08:10, 9 January 2013 (UTC)

1) Kind of. If the horizon is absolutely flat, then yes. However, hills or mountains or even snow drifts mean that as the Sun corkscrews up and down it will pass behind them and then come back out, so you will get multiple "sunsets" and "sunrises".

2) It's so cold in summer because the Sun is at such a shallow angle. In winter, it's far colder because there's no sunlight at all, for months at a time. Also, prevailing wind direction is East-West, meaning very little warm air moves in from warmer areas. StuRat (talk) 08:14, 9 January 2013 (UTC)

Where is East (or West) when standing on any of the poles? bamse (talk) 19:28, 9 January 2013 (UTC)

At the south pole east is clockwise when looking down and west is anticlockwise. Opposite at the north pole. So in winter time you will not see stars rise in the east and set in the west, but they will just circle you. The point is that the wind does not go towards you to carry heat from outside. Graeme Bartlett (talk) 20:24, 9 January 2013 (UTC)

That's the point, the winds blow in a circle around the poles (more or less), not over them, where they would deliver warmer air. StuRat (talk) 20:21, 9 January 2013 (UTC)

So in summer, the sun is at what angle? How low is it? So if the sun will not set, we can see the sun 24 hours a day and we will see it circling in the sky? roscoe_x (talk) 00:43, 10 January 2013 (UTC)

Yes, it circles for around 6 months. StuRat (talk) 00:45, 10 January 2013 (UTC)

When the sun is directly above the equator, it appears from the North Pole at the horizon. At the height of summer for the Northern Hemisphere the sun is about 23° north of the equator, so when standing on the North Pole the sun will be seen circling between 0 and 23° above the horizon (i.e. in the summer season). - Lindert (talk) 09:36, 10 January 2013 (UTC)

Just to clarify that last sentence of Lindert, on any one day the sun will circle at a particular number of degrees above the horizon. That number of degrees will be about 23 (closer to 23 1/2 actually) at the summer solstice, and it will be zero degrees at the autumnal equinox and at the spring equinox. As the days go by after the spring equinox and as we get closer to the summer solstice, the number of degrees above the horizon increases from one day to the next.

Here's how to visualize things like this. Get a globe, which will be tilted at 23 1/2 degrees. Put it on a table top so that the interior center of the globe is a certain height above the floor. Hold a thin flashlight (a penlight)(representing the sun) at that same height but some distance away and shine it at the north pole. Spin the globe around to see what is happening during the course of one day. To show the summer solstice, shine the penlight toward the globe from the horizontal direction that the top of the globe is pointing toward. To show one of the equinoxes, shine the light from the same height but after you and the penlight have moved 90 degrees around the globe. You can also look at in-between dates using in-between locations of the penlight. Duoduoduo (talk) 20:16, 10 January 2013 (UTC)

So the phenomenon is called midnight sun. Okay, so the people in north pole still know the time of day (even at night) by looking at the sun's position relative to objects near the observer? And if I built a house in north pole I wouldn't make a window that will pass sunshine at night time. And another question can you see Aurora from the poles? And if North Pole and North Magnetic Pole is different, also its moving, how far North Magnetic Pole can moved from North Pole? If we make an experiment of flowing water in a tank, will it also moving clockwise in the North Pole? Thanks guys, interesting phenomenon and answers. roscoe_x (talk) 01:41, 11 January 2013 (UTC)

(outdent) You couldn't build a house at the geographic north pole because it's an ever-shifting (and these days quite unstable) ice floe. So telling the time by the position of the sun or stars would actually be quite difficult. I guess you could use the direction of the magnetic north pole (see below) to provide a fixed line of reference, and from that calculate the time of day in any given time zone. In practice, permanent antarctic stations maintain the time zones of their control centres in nearby southern hemisphere countries. As for the windows: obviously during the nearly-six-month polar night, no window is going to admit light anyway. But when the sun is above the horizon anywhere, Rayleigh scattering makes the whole sky pretty bright. So you'd definitely want blackout curtains, or a bedroom with no windows and only artificial light. (I spent two weeks in the Swedish sub-arctic just after midwinter once; the weirdness of the daylight hours got to me pretty quickly.) I believe the aurora can be seen at the pole. The magnetic poles move pretty slowly, but fast enough that (for example) British Ordnance Survey maps include a magnetic north line, with details on when it was computed, and how far it's expected to deviate in subsequent years. However, in the very long term, it's believed by geologists that the north and south magnetic poles change ends, so the current north magnetic pole could end up arbitrarily close to the south geographic pole. And lastly, unless your experiment is very carefully controlled, the shape of the tank will have more effect than the rotation of the earth. (The earth's rotation does not, for example, affect which was water goes down an ordinary domestic plughole.) Our article Coriolis effect has the details - but the south geographic pole would be a slightly easier place to that experiment, and see the real effect of the earth's rotation on the water, than anywhere else on earth. AlexTiefling (talk) 02:07, 11 January 2013 (UTC)

Why do electrons, nucleons, stars, and planets have spherical shape ?

I have no microscope to observe electrons, protons, and neutrons in an atom, but I satisfy myself by only looking their pictures in books, on Wikipedia, etc. I usually see that they are spherical. Are they really spherical ? If yes, then, why not other shape ? Why do stars and planets have spherical shape, not other shape ? On the other hand, meteorites are not spherical but irregular. Why ? Parimal Kumar Singh (talk) 09:08, 9 January 2013 (UTC)

For the astronomical objects, gravity is the culprit. Large enough objects have enough gravity that it crushes anything that sticks up. However, if they rotate quickly, the shape is more of an oblate spheroid. For the subatomic particles, I don't think they really have a shape, just a probability density. It's just simpler to represent them as spheres. See probability amplitude for an alternative representation of an electron in a particular atomic orbital. StuRat (talk) 09:20, 9 January 2013 (UTC)

That isn't the electron. That's the region where the electron might be found. The electron itself, as far as anyone knows, is a point charge/point mass. Maybe something like string theory would make it something other than a point, but no one knows how to test it. --Trovatore (talk) 09:31, 9 January 2013 (UTC)

My point is that it's probability envelope is probably the best way to represent it, as that at least has some geometric definition. See atomic orbitals for some others. StuRat (talk) 09:37, 9 January 2013 (UTC)

I think that's a mistake. Admittedly it's one you see in writing from time to time, but still a mistake. To see the difference, note that, say, protons also have a probability distribution for where they might be found — but if you take that to be the "shape of the proton", then you completely lose the ability to talk about the proton's internal structure, with the three quarks floating around and exchanging gluons. The proton does have a shape, sort of, that being the shape given by the positions of the quarks, and definitely not given by the probability density function for position of the proton as a whole.

So the correct answer to "what is the shape of the electron?" is "no one knows; it might not have one at all", but is definitely not "the shape of its probability density function". --Trovatore (talk) 09:48, 9 January 2013 (UTC)

Regarding the proton shape: You've still got the same problem as with an electron, insofar as quarks are point particles like electrons, which themselves obey quantum rules and thus have the same problems with concepts like localizability and volume. So, since the "shape" of a proton is dependent on the "shape" and "position" of quarks (which is essentially as meaningless a concept as it is with electrons), so I don't think you can meaningfully discuss the shape of a proton any more than of an electron. Even the nucleus of the atom has a structure and a shape that defies easy definition. The smallest objects whereby shape takes on specific, definable, meaning are atoms and molecules, and even there there is some "fuzziness" (i.e. various ways to define atomic radius). --Jayron32 13:39, 9 January 2013 (UTC)

Well now, hold on. The position of a quark is not "meaningless", it's just quantumly weird. The proton is a quantum superposition of infinitely many states in which all three quarks have precise positions, and each of those states has a precise shape (a triangle, though not the same triangle for each of the states), and where each of the quarks is, as far as anyone knows, a point mass. Anyway I agree that it's the same issue; that was kind of my point. I was explaining why the shape of the orbital is not correctly identified with the shape of the electron. --Trovatore (talk) 18:50, 9 January 2013 (UTC)

Wait a moment there! Take any three points in space and just try to position them so they aren't in a triangle! That's not "a precise shape"! Literally any position they might be in would be a triangle. (Albeit a "degenerate" one if they lay on the same straight line or two or more of them were at the same position).

I think that was my point. --Trovatore (talk) 20:32, 9 January 2013 (UTC)

A proton certainly has a size although what it is precisely isn't clear.[1] And there are people looking at the shape of electrons.[2] Sean.hoyland - talk 19:04, 9 January 2013 (UTC)

Just glanced at it — is there anything there that's inconsistent with the hypothesis that the bare electron is a point mass? If so I didn't see it. --Trovatore (talk) 19:07, 9 January 2013 (UTC)

No, not yet but I posted that in response to the comment "The smallest objects whereby shape takes on specific, definable, meaning..." to show that people are looking at the shape of smaller objects. Sean.hoyland - talk 06:27, 10 January 2013 (UTC)

I'm not sure what those people measured but it has nothing to do with the pointlike nature of electrons. Saying that the electron is pointlike means that it's coupled to other fields individually at each point of spacetime (in the Standard Model Lagrangian). In contrast an extended object could interact with other objects at different spatial locations at the same time. Any evidence of that kind of nonlocality would be huge news, much bigger than the Higgs discovery. (It's an expected feature of quantum gravity, though, at least in string theory, since strings aren't points. But no one expects to be able to detect their size.) -- BenRG (talk) 03:32, 12 January 2013 (UTC)

The strong force field of protons and neutrons is well approximated by a sphere with a diameter of about 1 fm within which the three "valence" quarks move freely. Electrons are point particles in a sense, but don't forget that the Standard Model is a quantized classical field theory. The quantization leads to pointlike behavior but there's a sense in which electrons can spread out even at the classical level. But unlike nucleons they have no intrinsic size as far as anyone can tell. -- BenRG (talk) 17:32, 9 January 2013 (UTC)

I'm not sure electrons have a "shape", per se. As far as I know, no one has ever demonstrated that they are anything but pure geometrical points (though of uncertain position). Whether the question even makes sense at all might depend on your interpretation of quantum mechanics.

However, if they do take up space, what shape should they be, except a sphere? Why prefer one direction over another? (They do have spin, so I suppose you could argue for some anisotropy based on the spin vector.) --Trovatore (talk) 09:25, 9 January 2013 (UTC)

The whole discussion revolves around electrons, most of which is beyond my knowledge. The questions about astronomical objects are not completely answered. Please clarify it. Parimal Kumar Singh (talk) 04:58, 10 January 2013 (UTC)

Solids are generally held together by chemical bonds. This is the force that gives structure to a rock or an asteroid for example. For small to medium sized solid bodies, the force of gravity is too small to substantially change this. However, once a solid body gets very large (i.e. > 1000 km or so), the gravitational force starts to overcome the chemical bonds and pull it into an approximate sphere. On planets, mountains are held together with the same basic forces that hold together a rock. In general, the larger the planet gets, the greater the gravity at its surface, and the smaller the size the mountains that can exist without gravity breaking the rock apart and causing the structure to collapse. For stars and gas giants, there isn't a solid surface at all. Gravity simply pulls on the gas and it flows towards the center until the pressure of underlying gas can exert an equal outward force. Because the gravitational force is essentially uniform in all directions, the gas also ends up uniformly distributed (i.e. spherical), with small corrections if the object is rotating. Dragons flight (talk) 11:58, 10 January 2013 (UTC)

Essentially, one can appeal to symmetry. Large objects are only held together by gravity. Gravity is a force that acts equally in all directions - so material will end up uniformly distributed - and the only shape that has this perfect symmetry is a sphere. However, if the sphere is rotating (as is the case for almost all heavenly bodies) - the centrifugal force will be stronger at the points furthest from the axis of rotation - resulting in slight bulge around the equator. So none of these bodies are perfectly spherical.

That said, real planets are incredibly close to being perfect spheres. At smaller scales, such as mountains and such - the atomic forces holding the rock together is stronger than gravity - so more complicated, asymmetrical, shapes become possible. Despite that, the earth is more perfectly smooth and round than a regulation billard ball - and the atmosphere and oceans are thinner than a layer of paint at that same scale. SteveBaker (talk) 14:54, 10 January 2013 (UTC)

Capacitor article, what does Pand Vc stand for?

In the article Capacitor section "Energy of electric field" what does $P$ and $V_{C}$ stand for in the specified formulas? Electron9 (talk) 09:16, 9 January 2013 (UTC)

P stands for (electrical) power, i.e. how much energy is used per unit of time (in Watt or J/s); Vc is simply the voltage over the capacitor. - Lindert (talk) 13:14, 9 January 2013 (UTC)

I updated the article part you had added, Electron9. DMacks (talk) 15:57, 9 January 2013 (UTC)

How do you know that P is for power? Electron9 (talk) 16:48, 9 January 2013 (UTC)

Its use as "P=IV" and related equations seems to meet the definition of Electric power. DMacks (talk) 16:53, 9 January 2013 (UTC)

Where do you see "I" defined as a variable for current in the article? I did think exactly like you until I found it depended on other undefined variables. Electron9 (talk) 19:44, 9 January 2013 (UTC)

Yes, I was assuming standard symbols there. But also "Power = work per unit time", which seems consistent with the integral form. DMacks (talk) 19:52, 9 January 2013 (UTC)

Strength of gravity anomalies on earth

The image File:GRACE globe 1.png shows the differences in gravitational acceleration on different parts of Earth, after normalizing the differences caused by the rotation of earth and the polar radius being smaller than the equational radius. But the image doesn't include a legend for the colors, so I can't tell what the red and blue colors represent. So my question is, how large are these variations in the gravitational acceleration? – b_jonas 11:23, 9 January 2013 (UTC)

PS. the image description links to [3]. I tried to look there, but a quick look didn't give an answer. – b_jonas 11:25, 9 January 2013 (UTC)

There is a version of that same image in our the article: Gravity Recovery and Climate Experiment that includes the legend:

I have no idea why that was cropped out in the version you refer to!

The scale is in milligals - and the numbers range from -50 to +50, which is 50 thousandths of a 1 cm sec^-2 acceleration...normal gravity is around 9.8 m sec^-2 and these variations are at most -/+ 0.0005m sec^-2 - which is really very tiny! Note that gravity varies by a half percent between equator and pole - so what your latitude is matters vastly more than whether you're standing on a red spot or a blue spot on that map! SteveBaker (talk) 13:45, 9 January 2013 (UTC)

Thank you for the answer. – b_jonas 20:01, 9 January 2013 (UTC)

AL Amyloidosis Prognosis

This site states that there is a 40 month prognosis with AL Amyliodosis, siting a British Medical Journal, without speaking to advanced symptomatic organ failure which accompanies most diagnosis. The actual prognosis of AL Amyliodosis with Cogestive Heart Failure (CHF) is 4-6 months. As it can take 4-6 months for a CHF patient to recieve the Amyliod diagnosis, siting a 40 month prognosis without additional information may lead patients and their families to adopt a wait and see posture early in the discovery process, thus leading to patient mortality. Perhaps someone would like to address this. — Preceding unsigned comment added by 71.232.106.77 (talk) 13:01, 9 January 2013 (UTC)

You really need to point this out and discuss it on the Talk:AL amyloidosis page where people discuss the content of that article. This is the reference desk - we answer questions and do information searches and such but we don't generally edit articles for people. Right now, I can tell you that the editors of that article are going to want to know where you got your information from. They need a reliable source that they can mention in the article...right now, they're going to say that the British Medical Journal is a highly respected source of medical information - and if it says 40 months - then that's the number they're going to put into the article unless there is another, more recent, reliable source that says otherwise. If you can point to a research paper or some kind of study document - then that will help them to get the article sorted out. But please discuss this on the talk page of AL amyloidosis - the reference desk is not the right place. SteveBaker (talk) 13:24, 9 January 2013 (UTC)

Electronic configuration of copper and chromium

Electronic configuration of copper, chromium, and some other elements are different from what it should be. Why is it so ? Show your knowledge (talk) 13:49, 9 January 2013 (UTC)

Because the rubric we learn for predicting the electron configurations is an approximation of reality, and reality is much more complex. --Jayron32 14:08, 9 January 2013 (UTC)

A bit more: The Aufbau principle (aka Madelung's Rule) is a very rough approximation indeed, as it isn't really based on a rigorous mathematical understanding of the quantum mechanics of how electrons interact with the nucleus and with each other to produce a specific configuration. Instead, it is designed as a very rough "rule of thumb" that will get most people the right answer most of the time. There are other, more accurate, approximations , such as the Hartree–Fock method. So the answer is that the reason why copper, chromium, palladium (and indeed many other elements) don't directly obey the Aufbau principle is that the Aufbau principle is wrong, but it's right enough for first year chemistry students to get most elements correct. Indeed, for anyone that never gets to rigorous computational quantum mechanics, the Aufbua principle + memorize the exceptions is usually as far as they will ever get. --Jayron32 14:22, 9 January 2013 (UTC)

You used the word aka, what does it mean ? I still don't understand the reason behind my question. Show your knowledge (talk) 15:16, 9 January 2013 (UTC)

Sorry. Aka is an abbreviation for "also known as". The answer to your question is that the method you were taught for determining electron configurations is wrong. Better methods exist, but they involve the sorts of mathematics that 99% of people (indeed, that the majority of chemists themselves) never learn. All methods are wrong (as the quote goes "All models are wrong, but some are useful"), but the one taught you in your chemistry class is more wrong than others. It's right enough, however, for the purposes of your chemistry class, and teaching you less wrong models would require taking several years to teach the mathematics first. --Jayron32 15:24, 9 January 2013 (UTC)

Thank you Jayron, your second explanation was excellent. According to what have been taught in my chemistry class: In chromium second last shell and last shell contain 5 and 1 electrons respectively. On the other hand, second last shell and last shell of copper contain 10 and 1 electrons respectively. Is this true in reality ? Show your knowledge (talk) 15:49, 9 January 2013 (UTC)

Yes, that is really true. The electron configuration of every element can be determined spectroscopically, such that you can experimentally determine the actual configuration of electrons in an element. The "rules" you are taught in chemistry class (the Aufbau principle) whereby you add electrons to each element based on a simple formula, is mostly right, but it gets certain elements (like Chromium and Copper) wrong, insofar as the Aufbau principle predicts a configuration of 4s²3d⁴ for chromium, but actual experiments have determined that the ground state configuration is actually 4s¹3d⁵. There are models better than the Aufbau principle that closer match reality (i.e. models that actually predict the correct configuration of chromium and copper rather than explain them away as "exceptions" to the rule) but those models require a level of mathematics which is well beyond the average first year chemistry student. --Jayron32 16:03, 9 January 2013 (UTC)

I read this in a book: "The deviation (from Aufbau principle) in electron configuration of some elements is because completely filled (d¹⁰, f¹⁴) or completely half-filled (d⁵, f⁷) configurations are more stable. The stability is due to two factors. One, these configurations are more symmetrical which increases their stability. In symmetrical arrangements, the electrons are farthest away from each other, and their mutual shielding is the minimum. The coulombic repulsive forces between them are also weakest. Due to both these reasons, the electrons are attracted more strongly towards nucleus. Two,the electrons in degenerate orbitals can exchange their position. These exchanges also increase the stability. In completely filled and completely half filled orbitals, the number of such possible exchanges are maximum which make such electron configurations more stable." Is this explanation correct ? Show your knowledge (talk) 05:32, 10 January 2013 (UTC)

Sure. That's pretty much it. There's also probably some small effects from spin-spin coupling of like-spin electrons as well, and larger atoms start to have relativistic effects which affect their configurations. Calculating the exact energy contributions of all of these various effects is quite messy, which is why they don't teach it to you right away, for the most part the Aufbau principle works, except for the "half-filled d" and "all-filled d" exceptions of the copper and chromium groups. There's also other exceptions besides those (there's actually upwards of two dozen of them, at least), and not all of them so easily follow the "half-filled/all-filled" rule-of-thumb, i.e. Ruthenium, Palladium, Cerium, and several more. --Jayron32 06:11, 10 January 2013

(UTC)

You used this sentence There are other, more accurate, approximations , such as the Hartree–Fock method. This means that there are also some other methods to get electron configuration of an element. Can you name some of them ? Show your knowledge (talk) 11:33, 12 January 2013 (UTC)

The exceptions do not matter in real chemistry. These elements have many low-lying excited states that may easily become the ground states in chemical environments (the excitation energies to the Aufbau-predicted "correct" configurations are well within the range of possible chemical bond energies). You will not go terribly wrong even if you mentally have the wrong ground-state configuration in mind for Cr and Cu etc., especially since those ground-state configurations are for gaseous atoms sitting alone by themselves, so don't have much to do with real chemistry. Double sharp (talk) 04:41, 3 June 2020 (UTC)

Why are all milk frothing mugs made out of stainless steel?

Does milk froth better in a stainless steel container than in a container made of another material (like ceramic)? If so, WHY does milk froth best in stainless steel? — Preceding unsigned comment added by Rmravicz (talk • contribs) 14:16, 9 January 2013 (UTC)

I assume that you are referring to coffee machines. My home one came with a plastic frothing jug, but I broke it, so now I use a Pyrex one. Both frothed equally as well as the stainless steel ones used in coffee shops. I suspect stainless steel is used, as it is easier to clean than glass or plastic and it won't break when dropped. I also think the professional jugs are doubled walled, so the Barista can froth enough milk for several cups and keep it hot. --TrogWoolley (talk) 15:24, 9 January 2013 (UTC)

Three questions

1) Why is oxygen necessary for survival? Why not other gaseous element?
2) What make our body to trap only oxygen when we breath in?
3? How long does it take to digest hen meat in our stomach?
Sunny Singh 14:21, 9 January 2013 (UTC) — Preceding unsigned comment added by Sunnysinghthebaba (talk • contribs)

1) The reaction of oxygen with carbon based molecules creates a lot of energy, which we need for our organs and muscles to operate. There is no commonly available gas on this planet apart from oxygen that will perform this function.

2) Our blood vessels contain proteins (hemoglobin) designed to bond with oxygen, thus 'trapping' it, while leaving the nitrogen etc alone. However, they also bond with carbon dioxide and carbon monoxide, so that's why these gases are dangerous in significant concentrations because they take the place of oxygen and so deprive our organs of oxygen. - Lindert (talk) 14:37, 9 January 2013 (UTC)

The reaction of oxygen with carbon also creates carbon monoxide. Sunny Singh 06:01, 10 January 2013 (UTC)

(ec) 1) Because our bodies produce energy by combustion/respiration, which is an oxidation reaction, and thus requires oxygen. More generally, our biology is based on carbohydrates and proteins, both of which contain significant amounts of oxygen. Nitrogen is also needed, but N₂ molecules are very hard to break - no regularly occurring substance burns in nitrogen - so we allow nitrogen-fixing plants (and the animals that eat them, unless we are vegans) to get hold of the nitrogen for us. The other atmospheric gases that come to mind are carbon dioxide, which is a product of respiration, and thus cannot be effectively used in such a reaction, and argon, which as a noble gas is almost (but not quite) impossible to react with anything.

2) The structure of haemoglobin in the blood allows for oxygen atoms to be attached; this takes place in the lungs (roughly speaking). It's not true that we trap only oxygen: for example, carbon monoxide poisoning takes place because the CO molecules bond more readily to the haemoglobin than the oxygen does, and won't come off.

3) As I recall, food (of whatever sort) doesn't stay in the stomach itself more than a couple of hours or so, but takes 24-36 hours to traverse the entire gastrointestinal tract. Digestion takes place throughout most of this period, by several methods. PS: in English, the meat of the hen is referred to as 'chicken'. AlexTiefling (talk) 14:43, 9 January 2013 (UTC)

(edit conflict) 1) Oxygen is involved in numerous biological processes, Dioxygen in biological reactions covers some of them. But basically, oxygen works by reacting with other molecules to release energy. You can see this dramatically in most combustion reactions, where the oxygen combines with things violently and rapidly to release huge amounts of heat very quickly. In biology, similar reactions are mediated by many enzymes which allow for a slow controlled release of energy that allows every other biological process to occur. 2) Oxygen is trapped from the air by hemoglobin, the specifics of which are covered in the Dioxygen in biological reactions article, in the "Oxygen uptake and transport" section. 3) Digestion#Human digestion process covers the specific timing of various parts of the human digestive process, including the amount of time food spends in the stomach. --Jayron32 14:46, 9 January 2013 (UTC)

I got the answers of Q. 1 and 2. In Q.3 I was asking for time in hours. Sunny Singh 11:52, 12 January 2013 (UTC)

nanotube compressed air storage

So, nanotubes supposedly have such high tensile strength just a few molecules wide it can support a space elevator.

Anyhoo forget nanotubes. I'm not sure why I mentioned it. Imagine a sheet of zero weight and infinite tensile strength, and you make a container out of this. You are allowed to pump in air at a small differential to the atmosphere and some kind of mechanism gets it inside, and similarly you are allowed to get air out at the rate you want, magically. However, the container does not have further magical properties, and it is subject to normal laws of thermodynamics. We are just not concentrating on the tensile properties and the mechanism of letting you pump into it and out of it.

So, in this case, what is the limiting factor of how much air you could store in this for use as a mobile power source? Is it the weight of the air? Is it how hot the air inside would get? What happens if, for example, you put a million or a billion cubic feet of air inside?

Basically, I am trying to imagine what happens at the limit of a "perfect container" for storing compressed air.

Now let's turn to practicalities. Practically, what happens to the pressure as you put more and more air in? Where do current known materials have a theoretical limit on how much pressure they can hold? How does the weight of material needed increase in response to the amount of pressure you want? Does something special happen when so much air is put in that the pressure melts it? Freezes it? (What I mean, is would the pressure suddenly spike immensely when you put more air in once the air inside is already liquid, or already solid?)

Forgive me, I assume higher pressure compresses by first liquidizing then freezing the air. Please correct me if I'm wrong.

Now let's turn to the pump. What are the practical limitations on trying to create a pump that you can "easily" pump into and "practically" get power out of in non-explosive bursts, but rather a rate that is more appropriate for driving a car?

Basically, I am trying to imagine what would happen if a nuclear powerplant tried to load a container with several inches of nanotube sheeting with enough air to power a car for ten years. What /would/ happen?

I know I've asked a lot of questions - thanks for any responses!!! --91.120.48.242 (talk) 14:47, 9 January 2013 (UTC)

In the real world, the energy that can be stored in a compressed gas is limited by the material strength of the container. If you assume infinite container strength and a really, really good pump, eventually the container will contain enough mass to hold together without a container. This might be a neutron star or a black hole or it could be a gas giant -- it depends on the size of the container. Also see Bottled gas and Pressure vessel. --Guy Macon (talk) 16:13, 9 January 2013 (UTC)

Well before that, the material would be too heavy to transport. Are you saying that with the above assumptions ("infinite container strength and a really, really good pump") the package is already a lot better than gasoline? (Since we can simply stop once we've pumped enough energy into it for it to surpass the energy densitity of gasoline?) 178.48.114.143 (talk) 16:36, 9 January 2013 (UTC)

You might be interested in the articles Compressed-air vehicle and Compressed air energy storage. In practice, without cooling the container during compression, more and more of the pump energy will go to heat the compressed air (and hence the container, until it melts, or until all the energy of the pump is going into heating the atmosphere round the container). Using cooling, the compressed air can be converted into a pale blue liquid, and that's about as far as it is practical to go since most liquids are very difficult to compress further. Dbfirs 17:33, 9 January 2013 (UTC)

Existing compressed-air cars use air stored at about 50Mpa of pressure and achieve about 1/20th of the energy density of gasoline (so 1/20th of the range for similarly sized "fuel" tanks). You might want to check out Orders of magnitude (pressure) to see what the effect of 1000Mpa pressure would be to get the same range as a gas-powered car. It's considerably higher than (for example) the pressures used to cut steel using high pressure water jets! Actually using that much pressure would be difficult because releasing a 1GPa air flow would destroy anything it hit! To get the pressure up enough to where it could store enough energy to run a car for a year, you're up at pressures where your carbon nanotubes would spontaneously form diamonds and your oxygen would turn into a metal!

Seriously...this isn't going to happen! SteveBaker (talk) 18:09, 9 January 2013 (UTC)

It's funny you say that, because I decided to look you up. In the Orders of Magnitude (Pressure) article you linked, 50 Mpa is listed next to 10^7 (the exact exponent would be 7.6), and 1000 Mpa is thus 10^9 (the exact exponent). Well guess what is listed under 10^9: "tensile strength of Inconel 625 according to Aircraft metal strength tables and the Mil-Hdbk-5". So, your very own link shows that storing air at 1000 Mpa is just fine, as long as it's stored in Inconel. So tell me: why not load an Inconel container with 1000 Mpa of air? As for the pump, you can simply make it pneumatic, and out of Inconel, like this: a long tube that tapers. You can then wrap it around the pump or whatever. I've uploaded a diagram. http://i.imgur.com/ksZVB.jpg . I'm not sure if it will work, but I'm sure you'll tell me. I don't see why not... — Preceding unsigned comment added by 91.120.48.242 (talk) 09:28, 10 January 2013 (UTC)

Inconel 718 is tough stuff - and it is actually used for cryogenic storage tanks - so it's properties in the realms you're interested in are well explored. The stuff is incredibly hard to work with in manufacturing - so the cost of such things would be incredibly high...but our article notes that it can be cut with a Water jet cutter - which you'll note cannot yet reach 1000 Mpa - topping out at maybe 600 to 700 Mpa. So Inconel isn't a magic pressure-resisting-material that you can just assume can be used to make the various parts of your contraption - it's just not that simple!

Moreover, the best pumps available for water jet cutters can only reach 700 Mpa - and that limit is going to apply to your car tank filler. Even if a 1000 Mpa pump, storage tank and turbine were available - the cost of building something like that out of Inconel would be extreme! That's a really expensive, exotic material...and it's very hard to machine - so even if it were possible, the cost of producing a pneumatic car with similar range to a $10,000 Kia would be spectacular - and because this is a fundamental limitation of the material - it's not likely to reduce with large-scale production or technological advances. So your idea - even if possible - is never going to be practically useful.

But the other problem (which earlier respondants have mentioned - but you've failed to consider) is that air liquifies at around 200 atmospheres - which is 20Mpa - so once you get beyond 20 Mpa, you're trying to compress an incompressible liquid - getting even 10% more liquid into that tank would require pressures vastly larger than 1000 Mpa. Hence you can't be using air if you want a car with a longer range than a couple of miles...which is about what real pneumatically powered cars get.

Then you go on to suggest that you can store enough air to run the car for a year - and that's vastly beyond even this possibility.

SteveBaker (talk) 14:25, 10 January 2013 (UTC)

Steve, thank you for this thoughtful response. In fact the "limitation" (once air is liquid, pumping more in becomes exponentially more difficult I gather - could you show me this on a chart?) was what I first asked about. So, really, your statement was misleading where you suggested "You might want to check out Orders of magnitude (pressure) to see what the effect of 1000Mpa pressure would be to get the same range as a gas-powered car." Because you're saying that, in fact, 1000Mpa are not enough to get the same range as a gas-powered car, because shortly after the 50 Mpa we currently use, the contents are all liquid and increasing the pressure from 50 Mpa to 1000 Mpa hardly gets you a greater volume of gas stored. (If I understand what you are now saying correctly). One thing you did not address however is my pneumatic pump idea: you say "Moreover, the best pumps available for water jet cutters can only reach 700 Mpa - and that limit is going to apply to your car tank filler." But I showed you a diagram that is suppossed to act as a funnel. Does it not work this way? If not, why not? The key insight here is that you don't care about the internal pressure of the 1000 Mpa or 800 Mpa or whatever, you just need it output over a large surface. So although you can store it at such an internal pressure, you can get it out over a large surface, gradually. What would happen if, for example, my diagram had a sturdy pump balloon over it (like a pump) with a one-way valve letting it draw air in from the the outside, you squeezed it over a large area, then you let it draw air again. It would look like this: http://i.imgur.com/StAED.png - single arrows are pressure, double arrows are movement. At the left of the three, the pump is neutral. To get to the middle, squeeze the pump: it now expels over a LARGE surface area into the snail. Once you've finished squeezing it, you release. The one-way valve gets snapped shut and you get to the third of the three pictures in which air streams back into it as it expands due to its rubbery shape. (Or it can be pulled open again mechanically.) What do you think?

For hydrogen this works and is near production. See [4]. However, it depends on specific properties of the nanotube interacting with hydrogen to stabilize it - it's not just a tiny pressure tank, it actually sucks up the hydrogen, more or less. Wnt (talk) 19:46, 9 January 2013 (UTC)

Oh, yeah - FYI: [5] says that the diameter of the carbon nanotube cable needed to support a space elevator would need to vary between one and 16 centimeters...not "a few molecules wide" as you assert. Indeed one of the most cited scholarly papers on the subject ([6]) concludes with "It is the author’s opinion that the cable, if realized as designed today, will break.". It's strongly likely that carbon nanotubes are incapable of supporting such a structure at any diameter. SteveBaker (talk) 14:44, 10 January 2013 (UTC)

Right, which is why in part this wasn't really a question about carbon nanotubes as a magic weight-free substance that obeys physics but can store any pressure. I was interested in aspects such as the heat, and the fact that the result would still have to weigh something, and also we have just found out that pumping into it at arbitrary pressure might not be that easy or fun. 91.120.48.242 (talk) 16:05, 10 January 2013 (UTC)

I still like the thought experiment where you assume perfectly strong materials and an infinitely powerful pump. After all, the original question did specify a container of "infinite tensile strength." Let's assume that you compress your [whatever - it doesn't matter what you start with] down to a tiny, tiny sphere of pure neutronium. Then you let it expand a bit at a time to power your vehicle. And you use that handy infinite-strength material to stop it from falling through the bottom of your car and heading for the earth's core.

Neutronium has some advantages as a fuel. Because it contains no protons, it is not radioactive. Because it has no electrons, it is totally chemically inert. I am not even going to guess at the hardness or tensile strength. And when it expands you can, in theory, have it expand into any element. I want my car to create gold bars as the exhaust.

The main disadvantage is that Neutronium is that it is incredibly dense: 4*10^17 kg/m^3 (four times ten to seventeenth power kilograms per cubic meter) -- about a million million times heavier than lead. So you need your chunk of neutronium to be very tiny, otherwise your vehicle will weigh many tons. And I am not sure whether I want to be on the same planet if it ever expands all at once. --Guy Macon (talk) 21:31, 10 January 2013 (UTC)

I guess people are either taking my "hypothetical" version too far or not far enough. Not far enough when they get bent out of shape about how many PSI we can pump or the PSI that our current materials support: I asked you to assume we could pump, and assume that a weightless material supports any psi. However, they take it too far when they then think that we can get to a neutron star, since I expressly said that my experiment should have NO other special properties: it doesn't insulate, it doesn't make your material weightless, it doesn't prevent the exhaust, etc etc. So, I would think that at the point where I place my mental experiment, where hte ONLY three things we elide are: 1) the pump mechanics; assume we can pump at any PSI into the container; 2) the container itself's weight, 3) the container itself's ability to ohold pressure, which are assumed to be infinite, 0, and infinite respectively. This assumption still leaves you having to deal with the weight of the gas, as well as with any phase transitions as pressure comes out of the pump, and with the temperature problems. Under these circumstances, how much "weight" could we ACTUALLY (asssuming 3 magic assumptions) pump into a car? Surely no more than a few tons. So, how much energy does a few tons (say, ten tons) of air represent when compressed into a gas tank mobile size. What PSI does that get us. How much do we have to deal with the thermal problem? 91.120.48.242 (talk) 07:42, 11 January 2013 (UTC)

Your assumptions allow us to pump gas in until the tank is full of neutronium. Sorry if you don't like where your assumptions lead. Now you are asking us to pretend that your assumptions don't allow us to pump gas in until the tank is full of neutronium, and to pick some other limit. Sorry, but the answer is still that your assumptions allow us to pump gas in until the tank is full of neutronium. (Actually, they allow the formation of a black hole, but you said earlier that you wanted to extract energy by allowing the material in the tank to expand, so i am ruling out a black hole.) --Guy Macon (talk) 19:17, 12 January 2013 (UTC)

Okay, this is fine. Could you show me how it becomes more difficult to continue pumping inside as we go from gas inside to liquid and solid or metal or whatever? Is it just the case that with each milliwatt-hour (or whatever unit) of compressive energy that you pump into, the pressure spikes by a lot more than it did before the phase change? I would like to see this diagram for, for example, air. THanks. 178.48.114.143 (talk) 23:25, 12 January 2013 (UTC)

What is the difference between anode rays and canal rays ?

Last paragraph of article Anode ray says As these perforations were named as canal so these rays are called canal rays. These are not the anode rays as these were not originated from the anode. The article doesn't clearly describes how these two rays are different. Please help ! Want to be Einstein (talk) 15:03, 9 January 2013 (UTC)

This terminology (and this technology) is not in common use in this century. So, it's really a matter of historical interest to quibble over the finer points of this terminology. Our article already links to a reprint of a 1913 article, Rays of positive electricity, published by J. J. Thomson; you can rest assured that he used his terminology consistently. As with all scientific jargon, different scientists have used different variations; but as of today (2013), not many people at all are actively publishing descriptions of these types of devices using that terminology. Most books and papers today will talk about charged ion beams or electron beams, and will talk about the positive and negative particles, or device terminals, (rather than the more confusing "anode" and "cathode" terminology). You'll still hear the term "Cathode Ray Tube" in common use, because those devices had such an important historical impact; but you won't be hearing about CRTs for very much longer, as almost every single use for vacuum-tubes - from display monitors to klystron microwave amplifiers to Bremsstrahlung x-ray sources - have all been replaced by better semiconductor or solid-state alternatives. Nimur (talk) 19:34, 9 January 2013 (UTC)

Every single use, Nimur? Not for a good while yet. To generate microwaves for cooking, at continuous power levels of several hundred watts, nothing beats a cavity magnetron, a type of cathode ray tube that is nothing more than a heated cathode surrounded by a shaped anode. Want to know what is the cheapest, most stable, easiest way to accurately (say 3- to 4-digit accuracy) measure voltages 30 kV and up? A triode valve (preferably a tungsten filament valve) - a type of cathode ray tube! You use the anode as the input, earth the grid, and vary the cathode voltage (typically 10 to 20 V or so) to get a specific cathode current (microamps or less), virtually none of which flows in the grid. The relationship of anode voltage to cathode voltage at a specific current is precisely linear within a good working range, dependent only on the tube physical geometry. The relationship to current is well understood (the "three halves power rule"). At lower voltages, or high voltages at lower accuracy, voltmeters normally use multiplier resistors. However, getting accurate stable resistors for 20 kV and up is not trivial - usually 2 digit accuracy is as good as you can get. There's also the old gold leaf electroscope, but they have woefull accuracy and are not linear. There's other niche applications for vacuum tubes/cathode ray tubes too. Keit 121.215.151.39 (talk) 23:44, 9 January 2013 (UTC)

Valid points. High-power solid-state devices are encroaching, but have not totally replaced tubes in some applications. By 2025, I suspect you'll even see microwave ovens using switch-mode IGBTs instead of cavity resonators. And I am not alone in this speculation: Power Electronics magazine published a technical article on 100 kW solid-state (IGBT) converters - so there's hardly any power- or frequency- regime that is "off-limits" for semiconductors. Pick up your favorite microwave or RF newsletter, and you'll see higher- and higher-power RF implemented in silicon. You are correct; the highest power systems haven't made the switch, yet. But it's a matter of time. Solid-state power is cheaper, safer, easier, better, more efficient, ... all the reasons that all other industry applications have switched to semiconductors. Nimur (talk) 00:09, 10 January 2013 (UTC)

You are certainly correct in saying vacuum tube technology is obsolete for most applications - that is very obvious. However niche applications for tubes continue. IGBT's are inherently low frequency devices and will not replace magnetrons. If you read the article about switch mode power conversion you linked to, you'll see they think 50 kHz is a good achievement. The triode valve method of measuring extra high voltages works well for short (microsecond) pulses too - nothing else does. Keit 124.178.60.57 (talk) 00:21, 10 January 2013 (UTC)

(Edit Conflict)

(Note: every technical explanation on the Internet must by law contain at least one glaring error that makes the writer look like an idiot...)

Start with a bunch of atoms in the form of a gas.

Cosmic rays and natural radioactivity knock electrons off, making (a few) ions - atoms that are missing an electron.

Apply a high voltage across the anode and cathode (typically made of metal)

High voltage accelerates ions toward the negative cathode.

Ions hit atoms in gas.

This knocks electrons off of atoms, making many more ions - a chain reaction

High voltage accelerates ions toward the negative cathode.

So we have ions traveling from the anode to the cathode - Anode rays.

Meanwhile the electrons travel from the cathode to the anode - Cathode rays.

(You can also get electrons from a heated cathode, but that's another story.)

In 1886 when Eugen Goldstein was first figuring this out, it was hard to look at the anode rays and cathode rays going past each other both ways and figure out which was which.

Goldstein put small perforations (canals) in the cathode.

Some of the ions in the anode rays passed though the canals.

Now he had a ray that was just the ions from the anode ray, with no electrons from the cathode ray to confuse the issue.

He called these rays that left the cathode in the opposite direction as the cathode rays (but only if the cathode had "canals") "Canal Rays" and the name stuck.

And yes, our article explains this poorly. Canal rays only appear to originate in the "canals". Then again, few engineers talk about "rays" or "cathodes" anymore. We talks about Electrons, Ions, negative terminals and positive terminals. Still, you see the old terms in a lot of the early papers from the scientists who discovered this stuff. --Guy Macon (talk) 19:53, 9 January 2013 (UTC)

"(Note: every technical explanation on the Internet must by law contain at least one glaring error that makes the writer look like an idiot...)" - the entire Reference desk system depends on this fact to keep us all interested! SteveBaker (talk) 20:16, 9 January 2013 (UTC)

Buoyant force

Suppose an object with flat base placed in a container containing water and container also has flat base. The object has rectangular shape and its density is lower than water. The object is submerged (by hand) into water in such a way that its base touches the base of the container. In that situation, there is almost no water below the object and also there is whole water of the container above object and the weight of this water column lies on the object. When the hand submerging the object is removed from water, the object comes on the surface of water as it has lower density than water. The question is:Why does object come on the surface even when there is no water below object to push it up and also the object is forced down by the weight of water column above it ? Does buoyant force depend on the amount of water present below an object ? I tried my best to explain where I got stuck, thank you for answering my question. Sunny Singh (DAV) (talk) 16:48, 9 January 2013 (UTC)

The pressure of the water is proportional to depth, and any air trapped below the object will exert the appropriate pressure under the object for that depth (being greater than the pressure on the top of the object at a lower depth). If you succeed in producing a seal round the edges of the base, and allow a tiny amount of flexibility so that the trapped air can expand, then the pressure under the object may well become lower than that on the top, so the object will not rise but "stick" to the bottom of the container. I think the same could happen to a very small quantity of water if inrush of water below the object is prevented. Dbfirs 17:09, 9 January 2013 (UTC)

There is always going to be some water under the flat-bottomed object - you can't get a perfect contact between those two objects. But just do the thought-experiment of removing the water and just pushing the two objects together in air. If there was a perfect seal between the two objects, they'd be held together by the air pressure just like a suction cup on a sheet of glass! The deal in water is just the same. But if there is *any* gap, then water will intrude and because pressure in a liquid or gas exerts a force equally in all directions - there is nothing to prevent the object from floating away. SteveBaker (talk) 17:54, 9 January 2013 (UTC)

Aquaplaning or hydroplaning might be relevant. A very very tiny amount of water - just a few drops! - can be put into circumstances such that it has a very high dynamic pressure. In those cases, those few drops of water are sustaining the weight of an entire object above them - sometimes resulting in pressures equivalent to many thousands of PSI! That's enough to lift the entire weight of a heavy object - like a truck or a car or a four-hundred-ton cargo aircraft. This is a problem worthy of an entire NASA facility, the Aircraft Landing Dynamics Facility at NASA Langley. Here are some fun videos of this research: NASA Research on Hydroplaning. All this trouble comes from the fact that water is almost totally incompressible. Just a few drops of water will still occupy the same volume even if they are put under the crushing weight of thousands of atmospheres of pressure. Almost no water, if suitably constrained by a container, is therefore able to buoyantly lift a very very heavy object. Nimur (talk) 19:08, 9 January 2013 (UTC)

The same is, of course, true of the bottom of the very very heavy object. Ultimately there is only one layer of atoms at the bottom of anything, yet they hold it up. I think that SteveBaker's thought experiment works very well. Consider an object "stuck" to the bottom of a pool because there is a suction cup or other "vacuum" under it. What makes that a vacuum is that it is lower pressure relative to the water at the very bottom of the pool; in other words, we normally expect that pressure to propagate through perfectly. I suppose what amazes most is that physics is so good at "doing the math" - in other words, that if you have a narrow tube filled with atoms of water constantly moving about, that somehow the water at the near end and at the far end manage to come into such perfect agreement about what the pressure really is. The same amazement strikes people with other events, such as the ability to do DNA hybridization of a primer with a specific sequence out of an entire genome - as we see in that case, the computational power, though extraordinary, does have limits. Still, it is pretty amazing when you consider that the molecules doing the "math" by smashing together are moving only somewhere on the order of the speed of sound (I'm not entirely sure about the relation of this to the thermal speed according to the Boltzmann constant). Wnt (talk) 19:43, 9 January 2013 (UTC)

The point is that although they are only moving at the speed of sound, they are moving an incredibly short distance until they hit something and transfer the information. So the number of collisions per second is an ungodly high number - and that's how come this "calculation" happens so fast. SteveBaker (talk) 20:13, 9 January 2013 (UTC)

A related concept is Choked flow in a hydraulic or pneumatic system, where opening up a valve further downsteam has no effect on flow upsteam because there is a section of pipe with supersonic flow between them. It's the pneumatic/hydraulic equivelant of the speed of light; no information can travel faster than the speed of sound in the gas/liquid, so the upstream system doesn't "know" you opened the valve downstream. --Guy Macon (talk) 20:16, 9 January 2013 (UTC)

Depth won't matter, in fact the deeper it is, the less stable it is.. If the object maintains it's volume and the density is less than water, it will float. Extreme depth submarines used gasoline (incompressible fluid that is less dense than water). There is no "floating force", rather gravity pulls on the denser water harder than on the object. The system is in unstable equilibrium with the less dense object on the bottom and will revert to a lower energy state of stable equilibrium. Think of a rod pinned in the middle with a heavy ball at one end and a lighter ball at the the other. Trying to make the lighter ball stay at the bottom is difficult because the slightest perturbation will cause it to swing to a lower energy state. The same is true for your block in a water column. It is statically in equilibrium, but any perturbation will cause the system to revert to the lowest energy state which is the denser water beneath the floating block. It is directly analogous to mechanical equilibrium. There is a static solution where the block can remain at the bottom, it's just not a stable solution and the system will revert to the lowest energy state --DHeyward (talk) 09:29, 10 January 2013 (UTC)

I thought that Sunny Singh was asking about forces. The "static equilibrium" of your claim will occur only when water is prevented from flowing underneath. This is different from your example of unstable equilibrium. I see why you made the comparison, but I don't think it helps to answer the question (unless I misunderstood the question, of course). Dbfirs 21:02, 10 January 2013 (UTC)

Butterfly flight

this is totally from left field, based on a single observation: a cabbagemoth butterfly was flying right to left - a stiff breeze arose, blowing in the opposite direction - but the butterfly continued unperturbed, whereas one would expect it to be blown away.

Possibly the air current wasn't wide enough to reach both me and the butterfly - but possibly it was. I thought back, and couldn't think of a time when I'd seen a butterfly blown off course. Has anyone here? Have they some as-yet-un-understood mechanism for beating the wind?

Ta

Adambrowne666 (talk) 23:03, 9 January 2013 (UTC)

I think they just stay grounded during heavy winds. As you said, the wind current you observed must not have reached the butterfly. StuRat (talk) 23:09, 9 January 2013 (UTC)

Thanks, StuRat, you're most likely right - but let's wait and see if others have made the same observation and we can end up naming a whole new principle after me. Adambrowne666 (talk) 02:37, 10 January 2013 (UTC)

I live in a suburb in the hills near the edge of a state forest and we get lots of butterflies, I saw easily more then a dozen just the other day while working outside. Nothing about their flight made me think they were not being affected by the breeze, but I always thought butterflies weren't very gracefull fliers even when it's calm. I must admit i wasn't specifically looking for that. I'll make note and watch some butterfiles more closely next time. Vespine (talk) 02:54, 10 January 2013 (UTC)

Thanks, Vespine; maybe they appear to be poor fliers, but are in fact very good. And surely they can't always know when there's about to be a stiff breeze and ground themselves. Let us know if you notice the same thing I did. Adambrowne666 (talk) 12:03, 10 January 2013 (UTC)

January 10

Hand grenade, part 2

What are the lethal radius, stun radius and injury radius for a German stick grenade? I want to know if that pesky German machine-gunner will end up killed outright or not. Thanks! (Oh, BTW, while we're at it, are these radiuses significantly affected if the explosion takes place inside a concrete pillbox?) 24.23.196.85 (talk) 00:25, 10 January 2013 (UTC)

Think of each radius as having a probability of stunning, injuring, or killing, not an absolute. StuRat (talk) 03:42, 10 January 2013 (UTC)

As for the pillbox, it will make damage must worse inside, both from overpressure and fragmentation (with pieces ricocheting off the walls), while those outside should be relatively safe, unless standing right by an opening. StuRat (talk) 00:40, 10 January 2013 (UTC)

So, how much damage can the enemy gunner expect to take (A) 8 feet from the blast (if he stays at his post), or (B) 15-20 feet from the blast (if he leaves his machine gun and retreats deeper into the pillbox)? Assume that in both cases, the blast happens inside the pillbox. 24.23.196.85 (talk) 07:06, 10 January 2013 (UTC)

A "pillbox"

(I am rapidly becoming an expert on stick grenades thanks to User:24.23.196.85's questions!)...The answer will depend to a huge degree on whether the year is before 1942 - when the grenade had a thin metal shell around the explosive - or after 1942 when the person who threw it could choose to place a "Splitterring" over the head of the grenade (or not). The Splitterring was a special cylindrical steel shell that wrapped around the grenade to increase the amount of fragmentation - at the cost of decreased blast radius. If the year is after 1942 and the person who threw the grenade had a splittering about his person and had appropriate training in when to use it - then they would certainly have used it against the pillbox.

There would be two main causes of injury - overpressure from the explosion and injury from the flying fragments. There might also be burn injuries. Inside a very tightly enclosed pillbox, the overpressure would be much higher than out in the open - and the fragments produced by the grenade would ricochet off of the hard concrete walls to produce a much deadlier effect...much more so if the splitterring was used.

The "effective blast radius" of the later model grenades (7oz of TNT) was 16 yards. The earlier models only had 4oz of explosive. Even if reduced by a splitterring - that would be ample to produce lethal overpressure in the confines of a pillbox. The victim might avoid the fragmentation effects if he could hide around a corner or in another chamber - but pillbox bunkers such as the one in the photo are typically nothing more than a hexagonal concrete box with some holes to shoot out of and a door at the back to get into and out of - so that's unlikely.

Best guess is that he's dead if he's 8 feet from the blast...and not many pillboxes are large enough to get 15 to 20 feet away...they really aren't that big. His only real chance is if this is a really large pillbox with an internal concrete wall and the thrower used a splitterring on a early Mk 24 grenade (with only 4oz of TNT) - which together reduced the blast radius by enough to keep the over-pressure survivable - whilst producing fragmentation that the occupant could avoid by getting into the adjacent room. But moving 15 to 20 feet away - and into another room - in the very few seconds available seems extremely unlikely! Hence, IMHO, he's dead no matter what.

SteveBaker (talk) 13:57, 10 January 2013 (UTC)

Part of the Atlantikwall in Ostend

The pillbox in your picture seems to be Czech but bears a striking similarity to the rather amateurish British Type 24 built in a panic the summer of 1940. The Germans. who liked to think of themselves as the masters of mobile warfare, were actually rather fond of hiding in the biggest and most elaborate concrete structures that the Organisation Todt could devise. Alansplodge (talk) 20:58, 10 January 2013 (UTC)

Thanks for the info, everyone! Just FYI, the pillbox I have in mind is of the half-moon type with access by bent entrance, and the gunner in question is manning the gun that is guarding the entrance to the pillbox; as for the grenade, it's a 1944 model (the scene takes place during the Battle of St.-Lo) without a Splitterring (the good guys here are Maquis, who generally didn't have access to such things). So the bottom line is, they'll find the gunner sprawling on the floor and as dead as a depth charge -- just like I thought. 24.23.196.85 (talk) 23:47, 10 January 2013 (UTC)

Oxygen, fire, and inorganic

1. Why do CO and CO₂ is classified as inorganic even when they have carbon atom in their molecule ?
   
2. What make oxygen a supporter of fire and carbon dioxide a detractor (non-supporter) of fire ?
   
3. What is difference between fire and flame ?
   

The articles are not much helpful. Want to be Einstein (talk) 06:16, 10 January 2013 (UTC)

1. CO and CO₂ are not of biological origin, though I'm not particularly good with the definition either.
2. Oxygen is a reactant in the combustion reaction we call fire. In most rate equations I've seen, fire's rate is greatly increased by the concentration of oxygen. This makes sense because the probability that oxygen molecules collide with fuel at sufficient speeds to cause a reaction is greatly increased. Likewise, carbon dioxide is an inhibitor which can act by decreasing this probability.
3. The fire article says that the flame is the visible part of the fire. There also exist non-visible parts of a fire, like the embers. Again I'm no expert with this definition.--Jasper Deng (talk) 06:25, 10 January 2013 (UTC)

1. The Wikipedia article Organic compound states it rather eloquently "The distinction between "organic" and "inorganic" carbon compounds, while "useful in organizing the vast subject of chemistry... is somewhat arbitrary". the ultimate answer is that there is not a good, sound reason for it besides the fact that its a historical artifact that has been dragged through the classification system. The article has some background of how they came to be excluded, but ultimately CO, CO₂ and the Carbonates are not considered organic just because. That's the best we can say, really. Sorry.
2. Oxygen atoms form strong bonds with other atoms. The stronger the bond formed, the more energy released in the process of forming it. So, just about any reaction that results in atoms that were formerly bonded to other atoms to bond to oxygen results in a large release of energy. The converse is true: to break bonds to oxygen, or to replace bonds to oxygen with bonds to other atoms, would require a huge input of energy. Thus, reacting a hydrocarbon with oxygen gas (forming water and CO₂) releases a bunch of energy, because of the formation of the stronger H-O and C=O bonds (compared to the original C-H and O=O bonds), and would require the same input of energy to reverse. Now, it isn't strictly true that nothing burns in CO₂; you just need to find a way to make a compound that is even more stable than CO₂. See This reaction of magnesium in carbon dioxide, a common demonstration.
3. Flame is the glowing gases in a fire. The fire is the entire reaction itself, including the solids and liquids and smoke and all together. It may be better to think of fire as the process and flame as the glowing gas. --Jayron32 06:45, 10 January 2013 (UTC)

Last time I checked CO₂ is respirated by biological forms; it is of biological origin. Plasmic Physics (talk) 09:53, 10 January 2013 (UTC)

Carbon monoxide is also biologically relevant. DMacks (talk) 14:40, 10 January 2013 (UTC)

The synthesis of urea (and other organic substances) from inorganic compounds refuted the idea that organic matter possessed a vital force

As noted in the article organic compound there isn't universal agreement on which molecules are "organic". Some textbooks, including one I had years ago, consider all carbon based molecules to be "organic", including CO2 and CO. I think it is more common to simply define some small carbon-based molecules as inorganic, but the set of molecules to exclude is largely historical and the result of drawing fairly arbitrary lines. For example, saying that "organic" molecules must have C-H or C-C bonds in them, while excluding molecules with only C-O or C-N bonds, even though the latter are also widely present in biology. Dragons flight (talk) 11:36, 10 January 2013 (UTC)

• The historical origin of the term is a common theme in books on the history of science. While many life forms do produce CO2, oxygen-carbon aerobic respiration is a late development so far as the history of evolution. That CO2 is found in nature without being produced by living organisms, unlike compounds such as urea provides the origin of the term. Originally, organic compounds were those that were only found in or produced by living organisms. Eventually it was discovered that those compounds almost universally contained carbon. The synthesis of urea in the lab was highly significant in the history of science, since it showed that no special vital force unique only to living beings as had been supposed was necessary for the creation of these substances.

The term has generally evolved to refer to hydrocarbons and their more or less complex derivatives in general and of whatever origin, given the hypothesis of a vital force was found false and unuseful. Whether one prefers the carbon-based or hydrocarbon-based definition is simply a matter of convenience. There are a relatively (!) small number of simple carbon compounds not containing any hydrogen, and their behavior is different enough from typical hydrocarbon derivatives that excluding them from consideration may be convenient, say, for biologists rather than chemists. μηδείς (talk) 20:32, 10 January 2013 (UTC)

Well, except that isn't strictly true. Carbon dioxide participates in reactions not unlike analogous "proper" organic molecules, for example it undergoes Grignard reactions, a common synthesis of carboxyls: R-MgBr + CO₂, acid workup --> RCOOH[7]) This is exactly analogous to the Grignard reaction with an aldehyde: R-MgBr + R'CHO, acid workup --> R-CHOH-R'[8]. --Jayron32 20:40, 10 January 2013 (UTC)

Are you talkin' to me? Hehe. I am not sure what you are denying the truth of, Jayron, something I said or someone else said. μηδείς (talk) 20:43, 10 January 2013 (UTC)

You stated "simple carbon compounds not containing any hydrogen, and their behavior is different enough from typical hydrocarbon derivatives...," which isn't really that true. In many ways, CO₂, one of the "simple carbon compounds not containing any hydrogen" does not significantly deviate from organic molecules in terms of its reactivity or behavior. Sure, CO₂ doesn't behave exactly like any other molecule, but only insofar as no two molecules behave exactly the same anyways, and CO₂s chemical properties behave pretty much as would be expected as if it were treated like an organic molecule. The Grignard example I gave above is representative, not exhaustive, of the way in which CO₂ works in organic chemistry. --Jayron32 20:50, 10 January 2013 (UTC)

Oh. Well, I am not myself saying that CO2 should or should not be excluded--it is a matter of convenience. I am quite aware that CO2 is a reagent in a lot of organic chemical syntheses. But the properties of CO2 are very different from hydrocarbons. The basic point is that historically, the term was used in a way that excluded CO2 for biological reasons, which is the strict answer to the OP's question. Nowadays chemists use the term synonymously with carbon chemistry. That doesn't befront me. μηδείς (talk) 21:00, 10 January 2013 (UTC)

First question is very important for me and it seems to be completely answered. Dragons flight said this "organic molecules must have C-H or C-C bonds in them, while excluding molecules with only C-O or C-N bonds". Is there any exception to this statement ? Please give some argument. Thank you! Want to be Einstein (talk) 16:51, 12 January 2013 (UTC)

Why is the ampere and not the coulomb an SI fundamental unit?

As a fourth year high school student, I'm currently studying high school physics. I know that the SI unit of charge is the coulomb while the SI unit of electric current is the ampere. They can be defined by each other (1 C = 1 As while 1 A = 1 C/s). However, it is the charge of an atom's protons and electrons which allow electric currents to occur in the first place. By this logic, shouldn't it be the coulomb and not the ampere that should be an SI fundamental unit, since the coulomb measures charges, and electric currents are just a manifestation of charges? Is this because of historical reasons, convenience or calculation reasons? Narutolovehinata5 ^tccsdnew 11:06, 10 January 2013 (UTC)

Yes, it is mainly for historic reasons. It is also easier in practice to measure a current than to measure a quantity of stationary charges. In calculations however, it doesn't really matter which is the fundamental unit. Oh, and I think you made a small mistake: (1 C = 1 As while 1 A = 1 C/s) - Lindert (talk) 11:24, 10 January 2013 (UTC)

As discussed in new SI definitions, there is a current proposal to define the electric charge as an exact constant with the effect that a Coulomb would represent an exact number of charges. Even so, the Ampere would still be considered the "base" SI unit for historical reasons. Dragons flight (talk) 11:41, 10 January 2013 (UTC)

Narutolovehinata5 has asked an excellent question. It demonstrates clear thinking about physics and units of measurement. Well done! Dolphin (t) 11:47, 10 January 2013 (UTC)

Last time I looked, the elementary charge, symbol e, value 1.602 176 565 x 10^-19 Colomb, IS a fundamental physical constant. What's fundamental and what is derived gets changed in the SI system from time to time as knowlege and measurement capability improves. Perhaps you are using an out of date textbook, or your texbook has regurgitated out of date information from another textbook. That happens very frequently in high school texts (and college texts too for that matter). It's importnat too, to understand the difference between standards and fundamental constants. While the ampere can be calculated from fundamental units of charge and time, the calibration of instruments will proceed from a primary standard apparatus held in Standards labs that provide a standard ampere. A known ampere can then be used to calibrate instruments that measure other things. See http://en.wikipedia.org/wiki/Elementary_charge Ratbone 121.215.62.231 (talk) 12:05, 10 January 2013 (UTC)

See SI base unit. The elementary charge is a basic physical constant (though not a fundamental constant), however it is not a base unit for the SI system. The original poster is correct that the Ampere and not the Coulomb / elementary charge is the basis of the SI system. Dragons flight (talk) 12:16, 10 January 2013 (UTC)

Hmmmm... The Wikipedia article I linked says in its second sentence "This elementary charge is a fundamental physical constant." It appears we have a conflict between two articles. I notice that the SI Base units article is based on the 2005 SI standard (Ref 1 in the article). The change was proposed back then. Was it not changed in 2007? Ratbone 124.178.177.177 (talk) 13:14, 10 January 2013 (UTC)

The 2005 (and later) proposals do not change the list of units defined as "base units" by the SI system, even though it would change how the Ampere is calibrated experimentally. Dragons flight (talk) 13:21, 10 January 2013 (UTC)

There is no conflict. The fundamental constant article clarifies the two distinct meanings for the term. Dauto (talk) 16:14, 10 January 2013 (UTC)

I don't understand why people are discussing the elementary charge, because it's irrelevant to the question. The ampere is a base unit because current is easily measurable and very commonplace in electronics, whereas charge is not. That's as much a historical reason as a current convenience reason.

Literally everything about the SI system--from its design, to its choice of units, to the continually-changing definitions of those units--are for the convenience of us humans. If we can't easily use a unit or reproduce its value based on its definition, it's useless, because the Universe couldn't care less about what humans use to describe it. --140.180.240.178 (talk) 05:00, 11 January 2013 (UTC)

Precor treadmill's interval settings

There are only Precor treadmills in my gym. I started my interval training this week. I plan to do high-intensity interval training maybe twice a week.

I noticed that Precor's presets are 2, 4, or 6 mins of work and 2 mins of rest. Some more advanced models are programmable but the model in my gym seems to be fixed. Very few people bothered to tweak the settings.

• http://www.trainingdimensions.net/tdArticles/Treadmill%20Manual.pdf

However, most articles that I have read about HIIT said that the intervals shall be much shorter in order to be very very intense. Such as Wikipedia's HIIT article:

The original protocol set a 2:1 ratio of work to recovery periods, for example, 30–40 seconds of hard sprinting alternated with 15–20 seconds of jogging or walking.

Many Android interval apps also have similarly burst settings.

Certainly I can do two minutes of sprinting. But I can run much faster if the interval is set to 30 seconds. Are the two minutes intervals compromise the HIIT? -- Toytoy (talk) 12:48, 10 January 2013 (UTC)

It's pretty dangerous to use a treadmill at sprinting pace, and especially to bring it up to sprinting pace very rapidly, or down from sprinting pace. If you want to follow such a protocol, I wouldn't do it with a treadmill. Looie496 (talk) 18:18, 10 January 2013 (UTC)

Agreed, you'd need a special much larger treadmill, to make falling off less likely, and nice soft surfaces on all the sides, in case you still managed to fall off at full speed. StuRat (talk) 04:16, 11 January 2013 (UTC)

If you can't keep up with the pace, running on the treadmill can be very dangerous indeed.

I wonder why the Precor 954i does not have some sort of alarm that flashes red light and makes a little noise to let you know it's going to get faster.

If danger is a reason why treadmills do not provide HIIT options, you can still set the treadmill to switch between 12 mph (the maximum speed) and 0.5 mph every two minutes. This can still be very dangerous. I use inclination change (0 to 5%) to get me notified. The Precor model allows up to 15% inclination. However, I think the gym disabled anything steeper than 5%.

OK, maybe next time I'll do HIIT on a stationary bike or an elliptical machine. They are not supposed to kill you. Otherwise I'll do HIIT when I am jogging (if the weather becomes a little better). I'll wear a heartbeat monitor just in case. -- Toytoy (talk) 16:04, 11 January 2013 (UTC)

How does the Mola Mola defend itself

A 3,500 lb specimen of the Ocean Sunfish, or Mola Mola

This fish is huge (up to 5,000 lbs) and ungainly, and supposedly non-toxic. It seems so much like floating meat it reminds me of this animal. Has anybody got any information on how it defends itself? Thanks. μηδείς (talk) 20:06, 10 January 2013 (UTC)

Did you read the second paragraph under "Life cycle" in our article? Deor (talk) 20:14, 10 January 2013 (UTC)

Yes, the point of it seeming to be they don't have any defenses. Kind of one of the Creator's cruel jokes, like the animal in the video I linked to. I realize the small ones have spikes. What I am curious of is if the large ones taste bad (in Asia they're a delicacy) or something else. Being big enough only to be a slow-moving shark and aquatic-mammal appetizer doesn't exactly strike me as a "defense". μηδείς (talk) 20:50, 10 January 2013 (UTC)

Of course, before there was the Ameglian major cow there was the shmoo (shmoo)... - Nunh-huh 03:45, 12 January 2013 (UTC)

Animals don't need "defenses". To persist as a population, they just need to reproduce more than they die (or about equally on average). Our article says that Mola Mola females "produce more eggs than any other known vertebrate." Sure, a lot get eaten, but some don't (see r/K selection). Also, fecund females can produce eggs over several years. This could potentially form a storage effect that buffers the population against bad bouts of predation, but that's approaching WP:OR.

We don't have an article on it, but the main thing governing species persistence is the long-term, low-density growth rate, which quantifies how strongly a population can "bounce back" after some perturbation to low density. You can search that term on google scholar to find several interesting articles, though they tend to be theoretical. From a more applied perspective, you may be interested in Population_viability_analysis. And really, their adult size does surely reduce their predation, compared to smaller fishes. Finally, you may enjoy these course notes on population growth [9]. SemanticMantis (talk) 21:55, 10 January 2013 (UTC)

You know, you are absolutely right, because although I noted the very high value of r, I was still thinking of them as a K-selected species because of their huge adult size. (It still amazes me that any of them live past the spiky fry stage.) And even though they are obviously r-selected, they may still have undesirable traits such as their skin, which is compared to color-changing mucus covered sandpaper. Their similarity to sea turtles, which also graze jelly-fish, is also interesting. μηδείς (talk) 23:26, 10 January 2013 (UTC)

Right, the article even mentions that sea lions kill them, but don't eat them, so maybe the skin is a taste deterrent... SemanticMantis (talk) 23:30, 10 January 2013 (UTC)

It still amazes me that any of them live past the spiky fry stage ... Does living with the jellyfish help them survive? I mean if you eat jellyfish, you probably spend much of you time living with them. Jellyfish around them may prevent them from being eaten by sharks. -- Toytoy (talk) 15:40, 11 January 2013 (UTC)

Yes, passive protection by their prey would be similar to clownfish hiding among anemones. Back to the r-selection, the growth rate of these animals seems incredibly huge as well, reaching adult size in a few years and not living past ten in captivity. μηδείς (talk) 20:38, 12 January 2013 (UTC)

January 11

Bonus question: the Mola Mola 'Niche'?

The more I think about it, the greater it seems that as grazers of the ever-abundant jellyfish, sea turtles and the Mola Mola have converged on a r-selected niche with bodies adapted for low-energy stability in the water column. Is there any mention of such a niche, and would there be any mesozoic creatures, perhaps reptiles or cephalopods that fit it? Thanks. μηδείς (talk) 01:38, 11 January 2013 (UTC)

Plesiosauria? --Jayron32 01:44, 11 January 2013 (UTC)

Along those lines, but the elasmosaurs are usually portrayed as darting after fish and the pliosaurs are more like carnivorous whales. I'll have to get a good illustrated book on the marine reptiles from the library, anybody have suggestions? μηδείς (talk) 03:55, 11 January 2013 (UTC)

If I understand your question correctly, the nautilus seems to fit all your criteria: lays lots of eggs, neutrally buoyant, around since before the Mesozoic, and a cephalopod.--Wikimedes (talk) 10:51, 11 January 2013 (UTC)

Yes, it was thinking or the nautilus that made me mention cephalopods, but they eat carrion. Still, similar in several ways. I am not sure if there's an easy way to tell exactly whether mesozoic forms ate jellyfish or not though.

Some species of jellyfish may also fit the bill (see Jellyfish#Predation). The other predators mentioned (except sea turtles) are pretty active.--Wikimedes (talk) 21:06, 11 January 2013 (UTC)

Last grenade question, I promise

If a grenade detonates inside a concrete pillbox, is it plausible for the blast wave to reflect off a wall and travel around a corner to hurt/stun or even kill an occupant despite him not having a direct line of sight to the point of the explosion? (No, I haven't changed my mind about bouncing the thing off the walls and around the corner -- I'm pretty sure that can be done with no more than two bounces -- but if it lands short, would it still be capable of hurting or even killing the gunner?) 24.23.196.85 (talk) 04:35, 11 January 2013 (UTC)

http://www.fema.gov/library/file?type=publishedFile&file=fema426_ch4.pdf&fileid=45ea8a10-65bb-11db-8645-000bdba87d5b

(Search on "Reflect")

Also see: Blast wave --Guy Macon (talk) 06:37, 11 January 2013 (UTC)

(ec)

I'd say it's even more effective than relying on fragments to ricochet at the angle needed to hit the victim. Concrete walls will probably be as close to perfect mirrors WRT sound as they come on a WWII battlefield. With fragments, you need to get lucky. With pressure shock, it's just cold hard mathematics (followed by quite messy forensics). I'd really hate to get caught in the focus of some concave wall... - ¡Ouch! (^{hurt me} / _{more pain}) 07:20, 11 January 2013 (UTC)

The next one to ask a grenade question will have it thrown back at them! Just kidding.

Think of the pressure wave as if it were sound (which, it technically is!) - sound would bounce ("echo") from a concrete wall very well - and so will the blast wave. Sound has very long wavelengths and will also refract through doorways and outwards as it leaves your short corridor. SteveBaker (talk) 07:30, 11 January 2013 (UTC)

Concrete walls are pretty good acoustic mirrors, sure - but explosive shock waves are often supersonic - hence shock wave - so intuition may not lead to the correct conclusion. In shock, pressure waves do not superimpose in a straightforward way. So, while I agree with Steve, the pressure-front will expand, and will reflect; but we need to tread carefully if we use any simplifying assumptions about exactly where the reflections go, or how strong they will be. For example, an explosive front doesn't propagate at the sound speed. And the intensity doesn't fall off with the square of the distance. (Both are pretty good equations for modeling sound waves). There's an incredibly huge volume of published research - entire text-books - on the subject. The interested readers can start browsing articles and links from, e.g., detonation; deflagration to detonation transition.

Now, as far as a reliable source specific to warfare, I recently read through most of 'Sharpening the Combat Edge', "THE USE OF ANALYSIS TO REINFORCE MILITARY JUDGMENT", written by the commander of the 9th Infantry Division in southern Vietnam in 1968 and 1969. This takes a totally different, but equally-analytic approach: instead of trying to derive blast-radius from first principles of physics, the authors statistically studied the actual effects of the explosives they encountered during combat: and then performed fact-based and statistics-based analysis to determine things like blast-radius. There's a chapter on mines and booby-traps: " approximately three-fourths of all devices were trip-wires attached to a grenade..." As the commander of the infantry division notes, it's important to know this simple fact: how far away from a grenade is "safe"? "The advantages of an analytical approach are demonstrated by setting optimum distances between men based on simple field tests with the most frequent types of traps. If this distance was maintained, multiple casualties were infrequent. ...The 25th Division elaborated upon this type of analysis by placing the data on their computer, thus giving them the capability to present and study the problem with minimum clerical effort." As a computer-enthusiast, I am absolutely astonished that a combat infantry division, staffed primarily by conscripted riflemen, was operating a computer in the field ... in Viet Nam ... in 1967. Forward-thinking! Innovation manifests itself in the most unexpected places... Nimur (talk) 15:49, 11 January 2013 (UTC)

Another way to look at the lethality is that 7oz of TNT produces about 0.6 MJoule of explosive energy and about 3MJoules of heat. The resulting shockwave leaves the surface of the explosive at about 15,000 mph. In a very enclosed space (and a pillbox is about the most enclosed space imaginable!) with efficient reflectors (reinforced concrete!) - where will all of that energy end up? An easily deformable/compressible human body will end up collecting a good proportion of it one way or another. SteveBaker (talk) 16:51, 11 January 2013 (UTC)

Thanks, everyone! So I take it as a yes. 24.23.196.85 (talk) 01:40, 12 January 2013 (UTC)

Death

When do children know that humans are mortal? When do they know that they will eventually die, and never live again? I've found two unreliable websites that claim children begin to appreciate the finality of death when they're around 10 years old. I'm young enough to remember some of my childhood, and that seems extremely implausible--I remember thinking about murder and suicide around that age, and definitely didn't believe either was temporary. --140.180.240.178 (talk) 04:36, 11 January 2013 (UTC)

It will depend greatly on culture, the attitude of parents, and the child's environment. I grew up on a farm and definitely understood death and that life doesn't go forever as far back as I can remember particular animals dying, at about 5 years of age. Children who have fragile pets such ginea pigs will certainly understand it. What might be harder to figure out is at what age children assign a level of distress to people, mammals and birds they know dying, as distinct from merely accepting that the dead person/mammal/bird/etc has had life extinguished and won't be back.

In management training, I was taught that there are 5 distinct stages of grief that people go though whn receiving bad news, always in the same order. Depending on which book you read, they are something like denial, anger, bargaining, acceptance, conversion. See http://en.wikipedia.org/wiki/Five_stages_of_grief. Some people pass thru one or more stages almost immediately - some people stay in one stage for a long time - even months or years. It may be of greater value to ascertain how children at various ages go thru the 5 stages, rather than over-simplifying it to understanding/not understanding the finality, as I would think that a child old enough to talk fluently can understand simple concepts like life extinguishing of life - that can be a young as age 3. But I would not expect a 3 year old to easily cope with the death of a parent or sister and readily understand they have gone for good.

I have known an 8 year old, upon the death of a pet rabit, to cry and suffer considerable distress - she certainly understood that rabit was gone. But the following day she was fine.

The concepts of life after death, reincarnation, and going to heaven/paradise in almost all major religions indicates that even mature intelligent adults can have difficulty with accepting death as the end - it isn't meraly a matter of consoling the bereaved.

Wickwack 120.145.137.176 (talk) 05:06, 11 January 2013 (UTC)

• Pure OR, but my nephews started asking about death when they were three, and the elder announced at four he wanted to be a fossil when he died, which let him be okay with the subject. (I had given him a fossil trilobite and explained it was a real animal that had lived very long ago. He concluded that meant it was dead without me having to tell him.) They still ask questions at five and seven but they certainly seem to have realistic views for their ages, despite the scary, pernicious, age-inappropriate, believe-or-you-will-go-to-hell religious comments of one of their grandparents μηδείς (talk) 05:34, 11 January 2013 (UTC).
• Pure OR again: I understood the permanence of the death of an animal (a lamb that I saw die) at the age of 31⁄2. I have only the faintest recollection of the event, but I was subsequently reminded of it several times and thus renewed my memory. I don't think I'd have coped easily with the death of a human at that age -- fortunately no-one close to me died until I was 10, and I can still recall the shock, but I coped because I'd been prepared for the event. I think it also helps if people around you are coping. Dbfirs 13:09, 11 January 2013 (UTC)
• Yet more OR. My daughter is ten and has had her family tree pruned repeatedly since her birth. Before three or four, she had no concept that the other person was gone - not sad at the funeral, doesn't ask where they are, has no current memory of them. By around five, she began to worry about her mortality and that of her parents, but it was somewhat disorganized (What happens to my toys if you and mommy die? What do you see when you're dead? How do you know if someone else is dead?) By seven, she had the full response that you'd expect an adult to have: anger, sadness, disappointment, grief, etc. Having gone through it so often, though, I sometimes wonder how much of her grief was just mimicking those around around her to better fit in. For that matter, how would anyone react to death if their culture hadn't already told them how such things get expressed? Matt Deres (talk) 15:01, 11 January 2013 (UTC)

This preview of The Concept of Death in Early Childhood gives an overview of previous studies on this subject. It appears to support the 10 year-old age quoted by the OP, but it seems to depend on the definition of "the awareness of the universality and irrevocability of death". Alansplodge (talk) 19:01, 11 January 2013 (UTC)

I was aware of the universality and irrevocability of death at 7 or 6, and was terrified of nonexistance. (though also realizing that, after nonexisting, you won't be scared anymore). I also estimated that, since world population rapidly increases, assuming most people don't die young (not true in real life), and barring an unbelievably late year that humans hadn't existed yet (cause people would probably be telling me about it, like "3 lifetimes ago there were no lifetimes before that") at least a half to 2 trillion years of human life have happened (cumulative), including all living persons' future lives. Finally I decided, God would provide a Heaven. That lasted about one year, till I thought that there's no absolute 100.00000000000000000000000...% guarantee that I won't be in Hell starting this very second, and burn in fire for all eternity, so this reality could be like a false-vacuum (though I had never heard of that). And that since the downside is infinite, even with only an infintessimal chance, even less likely than everything false-vacuum transitioning to a non-hell reality this second and staying for all of eternity, this is something to worry about. Sagittarian Milky Way (talk) 06:27, 13 January 2013 (UTC)

hydraulics question

This concerns my previous question about infinite-tensile-strength containers. Can we use this principle:

http://www.dynamicscience.com.au/tester/solutions/hydraulicus/hydraulicsforceandwork2.htm

To keep being able to add pressure at an ever slower rate, but without having to push ever harder? Assume you have access to materials of infinite strength, tensile strength, brittleness, whatever you want. I am just interested in whether in theory you can always convert a reasonable force into increasing pressure. Is the limitation only the materials at hand? --91.120.48.242 (talk) 13:28, 11 January 2013 (UTC)

Let's suppose you can push your finger on the piston with about 1kPa of pressure (that's like lifting a can of soda with your fingertip) and with a fingertip area of 1 square centimeter. Let's suppose you need to get up to 1000MPa - which is what you'd need to fill your hypothetical pneumatic tank the size of a regular car gas tank and with the capacity of some hypothetical non-liquifying gas that would give your pneumatic car roughly the same range as a regular car.

Well, to get from 1kPa to 1000Mpa - you'd need a million-fold increase in pressure. You suggested to me on my talk page (please don't use that for ref desk-related questions!) that you had in mind some number of pistons connected end to end, each with a cross-sectional area 10x larger than the one before it. So let's go with that - and let's be generous and neglect thinks like leaks and friction and temperature changes and such like. Hence, to get from 1kPa to 1000Mpa, there would need to be six pistons, each 10x thinner in cross-section than the previous one...well, if the low pressure cylinder has the same area as your fingertip (let's say 1cm x 1cm) then the second is ~0.3mm, the third 1mm, then 0.3mm, then 0.1mm, and the last high pressure cylinder would be 0.03mm in diameter. So in pushing that cylinder in a distance that your finger can comfortably move (let's say 5cm?) then pushing on the lowest pressure cylinder once - you'd have produced an amount of compressed gas in the highest pressure cylinder that would be around 5cm long by 0.03mm wide by 0.03mm deep...a total volume of 0.05x0.00003x0.00003 cubic meters. That's 0.000000000045 cubic meters. That's a remarkably small amount of gas!

So to fill your gas-tank-sized container (let's say it's 1/10th of a cubic meter), at a rate of 0.000000000045 cubic meters per push - you'll need to push that first cylinder in and out 2.2 billion times. At one push per second, it would take you about 70 years to fill your tank. If you tried to do it with one pump of a very long cylinder, then the cylinder would be about 7,000 miles long.

You don't get something for nothing...that's the First law of thermodynamics...and it's a fundamental unbreakable law of nature. Because of that, we don't even need to look at the design of some hypothetical machine to tell you that it won't work. It quite simply cannot work - no matter how cleverly you design it because it is a fundamental part of the very fabric of the universe that we live in that "There ain't no such thing as a free lunch"! SteveBaker (talk) 15:10, 11 January 2013 (UTC)

Steve, thank you - this is a remarkable analysis! Remarkable particularly because of your first paragraph, which correctly summarizes the constraints we're doing away with! You then make very good conclusions logically. But I wonder if you miss the point of the remarkable contraption we now are hypothetically talking about. We goal isn't really to pressurize the gas - it doesn't matter how small the amount of extra volume we add by pushing with 0.1 newtons (which you called 1 kPa over 1cm * 1 cm = https://www.google.com/search?q=1kPa+in+newtons) over 5 cm we get https://www.google.com/q=0.1+newtons+*+5+cm+in+joules 0.005 joules or 0.00138888889 milliwatt hours. If you push the last piston, you get to add 0.005 joules. If you push the next piston directly (using whatever source of torque you want) you get to add 0.05 joules; if you push the next piston down 5 cm you get to add 0.5 joules, and so forth. So, I would say your "70 years" to fill the tank is misleading: you can fill the tank at whatever rate your power source can output torque at! (To the nearest power of ten).

Secondly, I find it very easy to use a finger to push down on a square area that is a lot larger than a single square centimeter: this is my whole point. By making the final area slightly larger, or by playing with the number of differential pumps and their power factors, under the HYPOTHETICAL situation you have first described, can't we continue to fill a gas tank to any point?

Thirdly, when we want that power back OUT again, again under the hypothetical situation we have described, can't we simply open the appropriate valves and let the frictionless pistons (should have mentioned this as well :) push up with whatever force we need, to the nearest power of ten?

Basically, I am asking whether, indeed, this idealized hypothetical solution would not indeed let you store energy by inputing it at whatever torque you want and getting it back out again at whatever torque you want (to the nearest realized piston)? Without (under your hypothetical limits) any constraints other than the weight of the gas and its growing ever hotter as you pump it in?

Thanks again for your great response! 91.120.48.242 (talk) 15:49, 11 January 2013 (UTC)

If you allow yourself to use unobtainium materials with infinite strength, zero elasticity, ignore friction, allow unobtainium infinitely compressible gasses and so forth - then obviously there are all manner of ways to store energy, to input it slowly and extract it slowly - but this is all quite utterly pointless because none of those conditions is even close to being practically realizable.

If you have magical materials then why not build a clockwork car and power it by winding up a giant spring made of unobtainium - or by twisting other unobtainium materials like a rubber band and powering the car like that - or just imagining an ultracapacitor that can store infinite electrical charge - or if you're going to ignore friction and air resistance then a car can be driven any distance (at a constant speed) with no engine at all!

Well, enough - it's trivial to come up with fifty new car power sources that are theoretically viable if you ignore all of the important details. It's all complete B.S though because you're ignoring 100% of the engineering difficulties that make it all quite utterly impossible in practice. Sure, there are theoretical ways to do all sorts of crazy things - but you can't do them for real - so why put so much effort into designing them?

Frankly, your line of questioning has become tiresome - you can't do this, it won't work. Period.

SteveBaker (talk) 16:11, 11 January 2013 (UTC)

Steve, I apologize. I tried to make it 100% clear from opening with "Imagine a sheet of zero weight and infinite tensile strength" in this question and "Imagine a sheet of zero weight and infinite tensile strength, and you make a container out of this....Basically, I am trying to imagine what happens at the limit of a 'perfect container' for storing compressed air" that I had zero practical interest but was trying to understand something fundamental. The fact that I didn't know a snail is at uniform pressure should also show you that I am not serious but a curious student. I am not very interested in springs, tensile energy storage, vacuum tunnels, supercapacitors or battery technologies at present. This is why I didn't mention them. I wish you would take a slightly better attempt to see the source of my questions, since, in point of fact, compressed air is a currently used form of energy storage. I'm trying to understand it. 178.48.114.143 (talk) 19:00, 11 January 2013 (UTC)

I don't have a problem with thought experiments, and I am assuming that you knew that we aren't talking about things that can actually happen the moment you mentioned an infinite strength container. That being said, there are fundamental limits even with the assumptions. Let me try an analogy:

Assume that you can achieve any speed you want or take as much time as you want. Given those assumptions, can a snail go from Los Angeles to New York? Of course. It can reach NYC at 0.0001 MPH if you give it enough time. It can reach NYC in 0.0001 seconds if you give it enough speed. But is cannot reach NYC in 0.0001 seconds at a speed of 0.0001 MPH no matter what assumptions you make. That is a more fundamental limit than the real-world limits associated with actual snails. This is an important distinction to learn. It's the difference between "can't do it with a real snail" and "can't do it, period". It's the difference between "can't reach that goal with existing technology, but if we work very hard at it we might be able to get closer to the goal" and "don't bother trying. It's impossible." --Guy Macon (talk) 19:53, 11 January 2013 (UTC)

I like your analogy. It is a way to understand the relationship between speed, time, and distance. I similarly want to understand the relationship between pressure, energy stored, and force needed to be able to either store that amount of energy, or how much of it you can recover. The intermediate "snail" itself doesn't interest me nearly as much. So it is QUITE like the the speed/distance relationship which is linear, until it curves up exponentially at relativisit speeds and asymptotically to C which it can only approach. Would you feel that I should not be given this curve if I ask for it?

Likewise, I have heard vague mention made to the "pressure/energy stored" relationship NOT being linear (specifically, you guys are vaguely alluding to a diagram where at each phase stage - gas to liquid, liquid to solid - it suddenly spikes same as extra energy spikes as you want to accelerate at high fractions of c).

But beyond that vague 'reference' I still have not been given specifics as to how. This would be akin to saying "In point of fact the energy needed to keep accelerating starts going up exponentially as you reach relativistic speeds but even though the whole point of the thought experiment was to ask abut this diagram, we won't give it to you - we will just say it goes up, and that you're dumb for asking." 178.48.114.143 (talk) 21:45, 11 January 2013 (UTC)

Leave relativity out of it. Not needed to get an answer abd confuses the issue. As for gas to liquid, liquid to solid and energy, here are the numbers:

http://www.barr-rosin.com/images/applications/fig10_relationship_enthalpy_water.gif

Or, (and I highly advise doing this yourself) get a metal pan and a thermometer that goes below 0 degrees C and above 100 degrees C, fill the pan with water and freeze it with the thermometer in the same freezer. That's your starting temperature. Put it on a stove burner until it starts to melt. Verify that it does what the chart says -- you pour in more heat and the temperature of the water doesn't change. After the last of the ice melts watch as the water gets warmer as you pour in heat. Then watch as it hits 100 degrees C and once again it does what the chart says -- you pour in more heat and the temperature of the water doesn't change.

In theory you could do the same thing with, say, pressure and propane, but heat and water gets the point across. --Guy Macon (talk) 23:59, 11 January 2013 (UTC)

Hi, what I meant is that if you read the first thread on this topic above, people suggest that the reason we can't pump more air into a compressed air tank is because after the blue stuff is liquid it hardly compresses, it becomes a lot harder to compress. So, let's see this on a diagram - amount of compression achieved versus amount of force required to achieve it. Relativism is not needed but is a good proxy for an easy, linear relationship that starts behaving strangely. Well, by the time air is a metal if you pump it full enough (high enough pressure) that would be just as strange and non-linear. SteveBakr didn't address this point at all, for example. I don't know what these pressure curves look like... 178.48.114.143 (talk) 00:37, 12 January 2013 (UTC)

ImageJ macro for batch merge of images

I have image files named in the format:

Exp.SS.4.4.170 - DF1 - MSTN HDR donor candidate 1 - 2 ul Lipofectamine 2000 - 15x - Field 1 - Brightfield - 2012-12-16.tif

Exp.SS.4.4.170 - DF1 - MSTN HDR donor candidate 1 - 2 ul Lipofectamine 2000 - 15x - Field 1 - UV red - 2012-12-16.tif

Exp.SS.4.4.170 - DF1 - MSTN HDR donor candidate 1 - 2 ul Lipofectamine 2000 - 15x - Field 2 - Brightfield - 2012-12-16.tif

Exp.SS.4.4.170 - DF1 - MSTN HDR donor candidate 1 - 2 ul Lipofectamine 2000 - 15x - Field 2 - UV red - 2012-12-16.tif

etc

I would like to merge each "Brightfield" image with its associated "UV red" image using ImageJ. Can anyone help me put together a macro to do this?

I tried using the built-in macro recorder but it doesn't pay attention to how much I increased the contrast of the red images and it also uses specfic file names which is useless when each file is named differently (obviously; you can't have two files with the exact same path!) 129.215.47.59 (talk) 14:23, 11 January 2013 (UTC)

Maybe better to ask this at the Computing Desk. - Lindert (talk) 14:39, 11 January 2013 (UTC)

Computing people probably don't deal with ImageJ. ImageJ is an NIH application. 72.229.155.79 (talk) 19:21, 11 January 2013 (UTC)

One can always try, and most people here on the science desk don't work for the NIH either (if there are any at all). Also ImageJ is open-source and has many useful functions, so maybe some 'computing people' have used it. Anyway, if you still think this is the best place, just forget I said anything. I'm afraid I can't be of much help, but good luck finding an answer. - Lindert (talk) 20:38, 11 January 2013 (UTC)

It would help if you could upload the actual images. What exactly would this merge do ? Are you talking about combining the red from one image with the blue and green from another ? Are the images of the same size and already properly aligned ? StuRat (talk) 23:16, 11 January 2013 (UTC)

is Asian male facial hair easier to wax than Caucasian facial hair?

I wonder if women's facial waxing products would work on Asian male facial hair. Thanks. 72.229.155.79 (talk) 18:07, 11 January 2013 (UTC)

I see no reason why not as they work on Caucasian male facial hair too! --TammyMoet (talk) 12:27, 12 January 2013 (UTC)

I am pretty sure there was an episode of 24 where they did this. I can tell you from personal experience that the black hair care product "snap back" and protein hair gels work admirably on us whitefolk. Back in college we even had get-togethers where the black and white people fondled each other's (unremoved) hair. Shame there weren't any asian students in college. μηδείς (talk) 03:57, 13 January 2013 (UTC)

Laser harp making

I have been interested for a while in acquiring and learning to play one of these new laser harps, but they are rather expensive. However, I recently learnt that one of my housemates plans to build his own musical tesla coil and so, not to be outdone (or at least not by as much) I thought I could at least look into the possibility of making my own laser harp, which might well also work out cheaper, and allow me to modify it to exactly suit my needs. So, is it possible, and where might I go to find instructions on how to do so, and to buy the parts I would need?

86.15.83.223 (talk) 21:25, 11 January 2013 (UTC)

You might get decent results with just Kinect; that article links to various development resources. With a little software you could probably build something that played when a hand was held in front of it, and which changed the frequency as the hand moved around - it might sound a bit like a Theremin. Or you could use rangerfinders - Googling for Arduino rangefinder projects finds several people working on those kind of things. -- Finlay McWalterჷTalk 22:01, 11 January 2013 (UTC)

Although it seems the spacial resolution of the current Kinect, and their relatively high latency, limits the technology's current use for musical input. -- Finlay McWalterჷTalk 22:06, 11 January 2013 (UTC)

and it doesn't have pretty colour lights around it 86.15.83.223 (talk) 22:20, 11 January 2013 (UTC)

so, no actual ideas on where to find this information? 86.15.83.223 (talk) 23:08, 12 January 2013 (UTC)

The clock's onomatopoeia

This is possibly a silly question, but does a clock really do tick tock ? If so, what is the "tick" and what's the "tock"? My ears are used to hear a clear tick-tock, but if I decide so, I can even hear "tick-tick" or even a Waltz-like "tick tock tock, tick tock tock..." Therefore, I think it should just do a series of indistinguishable "tick"; but why do we believe to hear, and say, tick-tock, then. --pma 23:14, 11 January 2013 (UTC)

I would guess this comes from a pendulum clock, which may do different things, and therefore make different sounds, during the right-to-left and left-to-right passes. StuRat (talk) 23:19, 11 January 2013 (UTC)

The tick-tock is the back and forth movement of the escapement. -- Finlay McWalterჷTalk 23:23, 11 January 2013 (UTC)

Actually, this is a great question. I've seen a lot of clock mechanisms - pendulum clocks, sprung wrist-watches with all sorts of movements; weight-driven grandfather clocks; true analog cuckoo clocks... and I can't actually recall ever hearing a "tock" sound. Especially with the weight-drop systems, there's a lot of other assorted noise - sort of gear-like grinding noises - in addition to the ticking of the ratchet. And of course, now that everything's gone quartz, there's usually just one ticking ratchet, with very little else to the mechanism at all. I'm surprised that we don't have history of clockwork; but we do have movement (clockwork). Given that ticking clocks are only a few centuries old, the first recorded usage of the "tick-tock" can't yet have disappeared into obscurity! Maybe posting on the language desk will help you track down how this description became so commonplace. Nimur (talk) 02:17, 12 January 2013 (UTC)

We have an article on exactly that, but it's fairly short. The study of timekeeping devices is called Horology. --Jayron32 02:36, 12 January 2013 (UTC)

French clocks don't go "tick tock", mais ils faisent "tic tac"[10]. Alansplodge (talk) 02:55, 12 January 2013 (UTC)

And do they all have a refreshing cinnamon, orange, or mint flavor ? :-) StuRat (talk) 03:01, 12 January 2013 (UTC)

Anyway, "Tick, meaning "sound made by a clock" is probably first recorded 1540s; tick-tock is recorded from 1848."[11] Alansplodge (talk) 03:07, 12 January 2013 (UTC)

I once trained as an instrument mechanic. Not a lot to do with clocks, but the skills enable an instrument mechanic to repair clocks and watches, and a lot of us including me did so. I still do occaisonally. Virtually all mechanical clocks and watches have a degree of tick assymetry, however a good quality mechanism correctly adjusted will have so little assymetry the ear should not be able to detect it. Note I said "should" - more on that below.

There are a great variety of clock mechanisms, so I'll just cover a typical balance wheel mechanism. In such movements what determines the rate is oscillation of a spring (the spiral hairsping) loaded balance wheel. The mass of the wheel together with the spring elasticity sets the rate. The spring is at rest (no tension) when the wheel is in the centre position. The wheel has a pin a small distance from the axis which engages with a fork. The fork supplies energy from the escape cog. The cycle is as follows: Wheel turns turns forward, until at about 30 degrees or so until the pin hits the fork, making a sound. Initially the wheel inertia moves the fork until the escape gog trips (another sound) then the fork looses contact with the pin on one tyne and hits it with the other tyne - a relatively loud sound, and imparts energy to the wheel to keep it going. The wheel continues and the pin moves out of the fork until increasing spring tension overcomes wheel inertia - the wheel is then at maximum rotation, and starts to turn in the opposite direction. Continuing to turn, the pin again contacts the fork, making a sound, the escape cog trip, etc, in the opposite direction.

We thus see that the wheel oscillates back and forth through (typically) about 230 to 300 degrees or so. Each "tick" (correct term is "beat") actually consists of three sounds: pin hits fork, escape trip, fork hits pin. The time between the three sounds of each tick are too close together for the ear to resolve as separate impacts, but are clearly resolved in electronic clock & watch analysers. If the wheel centre position as set by the rest (zero tension) position of the hairspring is different to the centre position as determined by the position of the fork tynes, the energy imparted by the fork will be different for each rotation direction. This makes (1) the loudness of the sounds different in each direction, (2) the relative loudness of the three impacts in each "tick" different to the subsequent "tock", which affects the perceived sound quality, and 3) the degree of rotation different in each direction, which makes the time interval between "tick" and "tock" different to between the "tock" and the tick".

So, yes, especially in a worn, cheaply made, or poorly adjusted clock, the tick does sound different to the tock. And the timing assymetry is detectable by the ear, but persons not trained in clock repair tend to just perceive it as tick sounding different to tock.

The ear is very susceptable to assigning patterns to sounds, even when no pattern exists. Even with a good perfectly adjusted clock, many people will perceive every second tick to be different. This phemomena is easily demonstrated by moving you finger in time to the tocks (ie each second tick) - your brain will lock into percieving that the ticks are different to the tocks. Get a second person to, after a while, force you to change finger timing forward one tick. Many people will then re-assign what is a tick sound and what is a tock sound. Another way is to set an electronic metronome going at a fast rate without beat accentuation. Many people will, especially if told it is so, percieve ticks different to tocks, even though in an electronic metronome (don't use a traditional mechanical metronome) that is impossible.

Wickwack 120.145.74.148 (talk) 03:09, 12 January 2013 (UTC)

Antique pendulum clocks do tick-tock. They aren't symmetrical. They have a wheel with teeth that is turning in one direction. On the tick, there is this U-shaped thing that goes between the teeth at one point. On the tock it is lifted and the other side goes down in another place. I'm not sure if this accounts for the difference in sound. Bubba73 ^{You talkin' to me?} 04:06, 12 January 2013 (UTC)

Yes, that u-shaped thing interacting with the toothed wheel is the escape - not essentially different to the escape in an oscillating wheel & spring type clock. In a wheel & spring clock or watch, the escape sound is normally much quieter than the impacts of the pin and fork, so assymetry in the escape is not easily heard. However in many antique pendulum clocks, the escape is coupled to the pendulum via a flexible strip in such as way as to be silent, so the escape is the only thing you hear. In other clocks a rod arrangment was used, which makes a slight click. However, a well adjusted and correctly lubricated antique pendulum clock should still make very even ticks - don't overlook the tendency of the ear to assign a pattern as I said above. Correct adjustment and even ticking is confirmed with an analyser - essentially a clamp microphone, amplifier, and paper strip recorder - the instant of each sound (pin impacts, escape trips) is marked on a moving strip of paper, and usually the amplified sounds can be listened to in headphones. This lets you set the amplitude, symmetry, and rate very quickly and enables one to diagnose all sorts of troubles that lead to inaccuracy. Wickwack 58.170.182.38 (talk) 06:05, 12 January 2013 (UTC)

I'm not doubting Wickwack's excellent analysis, but all of the grandfather clocks I've ever heard have had a tock very different from their tick! (Sometimes a different frequency of sound, with the tock lower than the tick, as well as a different interval between them.) They probably were all old and worn and not recently adjusted. I agree that perfectly-adjusted mechanisms should have tocks identical to ticks. Dbfirs 08:58, 12 January 2013 (UTC)

If the interval between tock and tick is perceptively quite different from tick to tock, as distinct from being heard as tock sounding different to tick, your clock is very badly worn. In many antique grandfather clocks, the bearing for the U-arm is fibre. I've seen them worn down so the hole for the shaft is no longer round, but a more or less straight track several mm long. It takes 60 to 80 years of running without any clean-and-oil servicing to get that bad. I suggest locating a reputable clock repairer, as your clock is about to stop. Wickwack 60.230.222.99 (talk) 10:12, 12 January 2013 (UTC)

Yes, you are correct about the age and lack of servicing of the clock (not mine, it belonged to my uncle who oiled it occasionally -- it now belongs to my cousin who has probably had it serviced properly). And it did tend to become irregular just before it stopped. You obviously have experience of better-serviced clocks than the ones I've seen. Dbfirs 13:15, 12 January 2013 (UTC)

What is the technical name of the perceptual phenomenon that Wickwack mentioned where, hearing a series of identical even-spaced sounds, people still tend to group them metrically into pairs? μηδείς (talk) 06:50, 12 January 2013 (UTC)

It is called clustering illusion. See http://en.wikipedia.org/wiki/Clustering_illusion. Check also apophenia. Wickwack 60.230.222.99 (talk) 10:30, 12 January 2013 (UTC)

That's the phenomenon broadly, but I thought there was a specifically musical or perceptual term related to rhythmic phrasing. μηδείς (talk) 20:33, 12 January 2013 (UTC)

If I had time right now, I would record an antique clock's tick tock and upload it, but I don't think I will be able to for several days. Bubba73 ^{You talkin' to me?} 22:13, 12 January 2013 (UTC)

I found "grandfather clock ticking" on youtube, captured the sound, imported into sound editing software, and did a screenshot: File:Screenshot of a grandfather clock tick tock.jpg. The one on the left is the tick and the one on the right is the tock. Bubba73 ^{You talkin' to me?} 22:38, 12 January 2013 (UTC)

And File:Grandfather clock tick tock 2.jpg shows how the ticks are generally louder than the tocks. Bubba73 ^{You talkin' to me?} 03:55, 13 January 2013 (UTC)

On that one, the sound is louder about every 10th beat. It shouldn't be like that. Could be a drive train gearwheel damaged, or a badly worn bearing. Wickwack 120.145.32.87 (talk) 10:48, 13 January 2013 (UTC)

The current flu going around

Subject: The current flu going around. Question...Is there any data which indicates what the odds are of getting this current flu if one does not get vaccinated?

Thank you — Preceding unsigned comment added by 24.62.161.254 (talk) 23:35, 11 January 2013 (UTC)

It depends on how isolated you are. But it really points once again to the extreme shallowness of the modern human gene pool. Sic semper Monocultures. Hcobb (talk) 23:46, 11 January 2013 (UTC)

is the vaccine effective against this strain?--Jonharley667 (talk) 02:23, 12 January 2013 (UTC)

A very good Q. I got the flu myself, about a week before Xmas. Fortunately, I was over it by the holiday. But I want to know if the vaccine would have spared me the trouble, had I been vaccinated. StuRat (talk) 02:31, 12 January 2013 (UTC)

I was reading recently that the vaccine is believed to be 60-70% effective this year. Dragons flight (talk) 02:39, 12 January 2013 (UTC)

Thanks, but let's break it down by strain. Is the flu that's going around in the US a single strain, or multiples ? Are each of those strains included in the vaccine ? What is the chance that the vaccine will prevent you from getting each strain ? And, also, how does that 60-70% compare with previous years ? StuRat (talk) 02:47, 12 January 2013 (UTC)

As usual, there are multiple strains, but they're covered well by the vaccine as noted here: So far this season, most (91%) of the influenza viruses that have been analyzed at CDC are like the viruses included in the 2012-2013 influenza vaccine. There are graphics here on CDC's flu dashboard, showing that it's mostly influenza A/H3 (consistent with H3N2). Effectiveness of the vaccine in adults in preventing significant disease ranges from 50-70% (PMID 22252003 & PMID 22032844). -- Scray (talk) 03:25, 12 January 2013 (UTC)

serependitiously, I was just reading up on this. So: flu vaccine currently consists of an H1N1, a H3N2, and a B strain (starting in a couple of years, it will have 2 B strains). According to the CDC, the dominant strain this year can be seen to be H3N2, which has the highest mortality (most years, H1N1 is the most numerous). However, the vaccine has a pretty good fit this year:

2009 H1N1 [17]:

• All 17 2009 H1N1 viruses tested were characterized as A/California/7/2009-like, the influenza A (H1N1) component of the 2012-2013 influenza vaccine for the Northern Hemisphere.

Influenza A (H3N2) [327]:

• 325 (99.4%) of the 327 H3N2 influenza viruses tested have been characterized as A/Victoria/361/2011-like, the influenza A (H3N2) component of the 2012-2013 Northern Hemisphere influenza vaccine.
• 2 (0.6%) of the 327 H3N2 viruses tested showed reduced titers with antiserum produced against A/Victoria/361/2011.

Influenza B (B/Yamagata/16/88 and B/Victoria/02/87 lineages) [177]:

• Yamagata Lineage [118]: 118 (66.7%) of the 177 influenza B viruses tested so far this season have been characterized as B/Wisconsin/1/2010-like, the influenza B component of the 2012-2013 Northern Hemisphere influenza vaccine.
• Victoria Lineage [59]: 59 (33.3%) of 177 influenza B viruses tested have been from the B/Victoria lineage of viruses.

Gzuckier (talk) 03:29, 12 January 2013 (UTC)

StuRat's question, about whether he himself would be better off getting vaccinated cannot be answered, for the following reasons: 1) you need to account for herd immunity (http://en.wikipedia.org/wiki/Herd_immunity) - if most of the folk you come into contact with are immunised, you are protected as well. 2) your immune system can deal with almost all flu viruses even ones it hasn't seen before, if exposed at low level but not a high level. I've noticed many times if my wife comes home from work sniffly at the beginning of flu season, she may come down the next day with full symptoms, but I will remain healthy. But if I have to spend a lot of time with someone at work who is already quite sick, I'll often be sniffly a couple of days later, then get sick too - and my wife will stay healthy. 3) The flu virus currently going round may be one that your immune system has seen before. For example, a swine flu strain that caused the authorities in various counties to be very concerned a couple of years ago had little impact in Australia, mostly folk who got sick were young children. Research showed that we had been exposed to it about 10 years before. 4) the vaccine may not cover the particular virus going round. Each year the authorities make a calculated gamble on what viruses are likely to be a problem - they cannot always get it right.

A study was done by Telstra (the main phone, cable TV, and internet company in Australia) some years ago, comparing the number of days off work for vaccinated staff and non-vaccinated staff, to see if it was worthwhile to pay for the cost. It turned out there was no significant difference - however, not all staff who take sick leave are geniunely sick, also you can take time off to look after a sick wife or child, obscuring the data.

Wickwack 120.145.74.148 (talk) 03:45, 12 January 2013 (UTC)

Answering the original question, I know someone who went went for a holiday in the US and got the flu in the last days they were there, but on the whole, I expect the odds of most New Zealanders getting it in the next four months or so is quite low and I'm reasonably sure most health authorities don't recommend the vaccine in general for us. Now once our influenza season starts things will start to change (although whether it can be called 'The current flu going around' may be debatable). Nil Einne (talk) 13:06, 12 January 2013 (UTC)

Is there any benefit to getting the same flu shot twice? I am looking for real statistics or sources, thanks. μηδείς (talk) 06:46, 12 January 2013 (UTC)

I know you asked for stats or sources, but I'll be surprised if there are any, for the following reason: Whenever I have had a flu shot, the nurse asks 3 questions: 1) Are you allergic to chickens? 2)have you already had a flu shot this year? and, 3) do you currently have flu symptoms or suspect you may be coming down with flu? If you answer is yes to any one, you don't get a shot. This is how it works in Australia, I assume other countries are the same. Wickwack 60.230.222.99 (talk) 10:02, 12 January 2013 (UTC)

Lack of substantial benefit from repeated influenza vaccination was established in adults a long time ago, e.g. 1977, 1987 and compelling evidence for multiple-dose vaccination of older adults has not emerged. The situation is different for children (6 months to 8 years) who have never been vaccinated previously - for them, two doses are recommended (by the US ACIP) to establish immunity PMID 14986252 (thereafter, annual vaccination is adequate). -- Scray (talk)

To answer the OP's OQ, the Examiner website (which I can't link to because WP thinks it's spam) has an article on the new strain which is sweeping America. One of the links on the page may have the exact statistics for him. --TammyMoet (talk) 12:26, 12 January 2013 (UTC)

To get past that spam blocking here, do a google search for the title of the article you are looking to link to, let's say "Flu outbreak worsens, causing vaccine shortage in some areas". Then cut out the address location that shows your google results, of which the article you want should be the first hit and post it like this. (Open this up in the edit box to see what I have done. μηδείς (talk) 19:06, 12 January 2013 (UTC)

UPDATE: I seem to have contracted the flu again. I assume I'm now immune to the strain I caught before Xmas, so this must be a new strain, right ? I was fully recovered for a couple weeks, so it seems unlikely it's the original strain making a comeback. I guess I need to get a flu shot next year. StuRat (talk) 00:43, 13 January 2013 (UTC)

There's multiple shit going around, Stu. I have had the same bacterial sinus infection since Halloween with three courses of antiobiotics, a few days respite each time, and the same symptoms over and over, the worst being a post-nasal drip that causes me to be nauseous from the phlegm. All my intimates have caught this from me, my lover and mother (not the same person) having gotten over it, my father having had it worse than I did (and now taking a very heavy round of mopsiflopsicin to cure it), and my nephews having developed it after they left my parentses after Christmas. It's thoroughly miserable, with some vomitting by me, dad, and one of the boys. But it's not the flu, which I haven't had in over a decade. Are you sure you have had the flu and the same flu twice? μηδείς (talk) 03:49, 13 January 2013 (UTC)

This is getting a little too personal - please remember that this desk is for science questions (not discussion of personal medical maladies). -- Scray (talk) 04:12, 13 January 2013 (UTC)

January 12

Apophis 2029 and satellites

This talks about the 2029 Apophis close approach and it possibly hitting satellites. To me, that chance is so small that is is nothing to worry about. But is it massive enough to alter the orbits of (geosynchronous) satellites? Bubba73 ^{You talkin' to me?} 02:23, 12 January 2013 (UTC)

At 325 meters across, no. --Guy Macon (talk) 06:36, 12 January 2013 (UTC)

Satellites that must maintain an accurate station (this includes geosynchronous and GPS satellites) will have manoeuvring thrusters to adjust for any drift from the desired position. Far more substantial disturbances than a gravitational disturbance from a mass zipping rapidly past will be within the correction capacity of such thrusters. The question would more likely be a matter of whether the disturbance can be detected at all. — Quondum 11:08, 12 January 2013 (UTC)

Also note that the Earth would be deflected just like the satellite (although both by an amount too small to detect). The satellite would only be deflected slightly more since it is presumably closer. StuRat (talk) 01:07, 13 January 2013 (UTC)

Thank you

Resolved

Bubba73 ^{You talkin' to me?} 01:01, 13 January 2013 (UTC)

Mali

How come the french are fighting Islamists in Mali here http://www.bbc.co.uk/news/world-africa-20991719 but are not fighting them in Syria?--Jonharley667 (talk) 03:16, 12 January 2013 (UTC)

Lots of reasons. They're 100% Islamist in Mali and in control of a large territory. In Syria, they're only one of a number of rebel factions. You can't even pinpoint where they are. Nor does France want to be seen supporting an evil dictator. Clarityfiend (talk) 03:57, 12 January 2013 (UTC)

One reason is that the Mali government has asked for aid in the conflict, whereas the Syrian government would likely be the opposing force were French forces to intervene. In this comparison it is easier to ally with an already formed government that has reasonably close ties to the people (Mali), than to attempt to side with very factional rebels against a more singular government (Syria). In addition, the scale of conflict is much different. The death toll and size of military forces in the Syrian conflict unquestionably dwarfs that of the conflict in Mali, if our entries on the subjects are correct. 2012-present Northern Mali Conflict, Syrian Civil War Lord Arador (talk) 03:59, 12 January 2013 (UTC)

Plus, as Clarityfiend has already noted, France is officially in opposition to the Syrian government(e.g. [12])), while in support of the Syrian Malian government. If France were to be on any side, militarily, in Syria it would be against the Assad government, not for it, and the Assads are definitely not Islamists. In Mali, they support the Government, so it's fairly easy to take a stand there with troops. --Jayron32 04:22, 12 January 2013 (UTC)

Did you mean to say the French both support and oppose the Syrian government ? StuRat (talk) 04:29, 12 January 2013 (UTC)

So corrected. Good catch. --Jayron32 05:08, 12 January 2013 (UTC)

My point was that the french (and others) are actively helping and arming Islamist rebels in Syria. --Jonharley667 (talk) 04:52, 12 January 2013 (UTC)

Do you have any sources for that ? StuRat (talk) 04:57, 12 January 2013 (UTC)

Well, it's true: [13] But so what? Why should France (or any nation or person or anything else) be ruled by arbitrary and incidental similarities in their policies. The French support the anti-government forces in Syria (which contain some Islamist groups), while they support the Mali government (which is fighting a different Islamist group). What would be the problem with those two positions? --Jayron32 05:07, 12 January 2013 (UTC)

That source only says that France is supporting the Syrian National Coalition. The SNC's president if a "moderate Islamist", but his views, although hardly enlightened by Western standards, are very different from those of Ansar Dine or al-Qaeda. Also, the SNC's vice presidents are prominent democratic activists (according to our article), one of whom is a secular feminist. The SNC is much more accurately described as an anti-Assad and pro-democracy coalition, not an Islamist coalition. --140.180.240.178 (talk) 07:17, 12 January 2013 (UTC)

This article about a recent Syria attack http://www.bbc.co.uk/news/world-middle-east-20984142 says the attack was led by the jihadist groups al-Nusra Front, Ahrar al-Sham and the Islamic Vanguard which are Al Qaeda groups, the same groups france is fighting in Mali. It's not just "some" Islamist groups they are a major force in Syria right now.--Jonharley667 (talk) 07:20, 12 January 2013 (UTC)

This article http://www.brisbanetimes.com.au/world/rebels-linked-to-alqaeda-set-to-take-syrian-airbase-20130111-2cl7s.html says the the Al Nusra Front makes up 30 to 40 per cent of the rebels in all of Syria. --Jonharley667 (talk) 07:28, 12 January 2013 (UTC)

The same groups France is fighting in Mali? Nonsense. The main groups who were fighting the government of Mali (until they started fighting each other) are the National Movement for the Liberation of Azawad (they want an independent homeland for the Tuareg people), and Islamist groups Ansar Dine and the Movement for Oneness and Jihad in West Africa. None of those groups have anything to do with Syria.

Right now, Northern Mali is facing this. --Guy Macon (talk) 07:40, 12 January 2013 (UTC)

My point is they are both Islamist, Al Qaeda groups, both in Mali and Syria. --Jonharley667 (talk) 08:03, 12 January 2013 (UTC)

No, you specifically said that "al-Nusra Front, Ahrar al-Sham and the Islamic Vanguard are groups France is fighting in Mali." No. They aren't.

Your new, revised claim is still dead wrong. Ansar Dine is not an Al Qaeda group. They are Sufi, Al Qaeda is Sunni and thinks Suffis are heritics. The National Movement for the Liberation of Azawad is not an Al Qaeda group. They are Tuareg separatists, and Al Qaeda doesn't give a rat's ass about the Tauregs. Movement for Oneness and Jihad in West Africa did break off from Al-Qaeda in the Islamic Maghreb, (which is a purely African group) but there is no real evidence that Al-Qaeda in the Islamic Maghreb is part of Al-Qaeda, or in any way connected with any group outside of Mali and Algeria. They share a certain ideological affinity with Al-Qaeda, but in their literature and speeches they talk about getting inspiration from Seku Amadu and El Hadj Umar Tall, not from Osama bin Laden. Saying they are "the same groups" goes against all the available evidence. They don't even speak the same language! Syrians speak Arabic and Malians speak Bambara, and French.

I get a feeling that you are not very familiar with the wide variety of unconnected or loosely connected militant groups in the near east and western Africa. I hear Wikipedia has a lot of information on the subject... --Guy Macon (talk) 10:53, 12 January 2013 (UTC)

I think your in denial that France is supporting terrorism in Syria.--Jonharley667 (talk) 00:07, 13 January 2013 (UTC)

I know that science means "knowledge", which is potentially limitless in its scope, but this type of question is much better suited to the (In-)Humanities Desk, some of whose denizens never visit here. -- Jack of Oz ^[Talk] 03:32, 13 January 2013 (UTC)

You asked why France opposes the Malian Islamists but not the Syrian opposition and got plenty of good answers, despite asking on the wrong desk. It's obvious now that you're just trying to push your own views. You've come to the wrong place for that. --140.180.240.178 (talk) 12:21, 13 January 2013 (UTC)

Measuring sleep deprivation while on prescription stimulants

What methods can be used to measure short-term sleep deprivation or its effects on traffic safety, when the subject cannot fall asleep due to caffeine and/or prescription stimulants (ruling out the Epworth sleepiness scale or the multiple sleep latency test)? Any that can be self-administered? NeonMerlin 04:04, 12 January 2013 (UTC)

I suppose there are any number of tests that could be used, like saying the alphabet backwards. Normally used as a drunk driving test, you might also fail if you're sleep deprived. StuRat (talk) 04:11, 12 January 2013 (UTC)

As an example, testing the effects of sleep deprivation versus the effects of drunkenness on driving ability has been done using a "reaction time" test in some instances. You could probably download for free, or use online, any of a variety of "reaction time" type tests. They have valid uses even if they're quite primitive - in the 1990s the RAF used a very simple computer program of this nature to screen applicants for training as a pilot. --Demiurge1000 (talk) 14:04, 12 January 2013 (UTC)

Human evolution

Why did human beings, along with many other species, evolve to have males stronger than females? --Yashowardhani (talk) 08:09, 12 January 2013 (UTC)

It's by no means universal. Many insects, for example, have the reverse. However, in humans and many other mammals, pregnant females are rather incapacitated, so not much able to go hunting or fight. Thus, a gender-based separation developed, where men did most of the hunting and fighting, and women did things which could still be done while pregnant, like gathering and processing foods, making clothes, raising children, etc. With this division of labor, it makes sense for men to be bigger and stronger, since those are more important for hunting and fighting. (Also keep in mind that tens of thousands of years ago, women spent most of their short lives either pregnant or nursing.) StuRat (talk) 08:41, 12 January 2013 (UTC)

You've shown that it's not necessary for women to be strong, but is it advantageous for them to be weak? If so, why? If not, what is it that made women weak, if it wasn't natural selection? --140.180.240.178 (talk) 10:10, 12 January 2013 (UTC)

Energy cost. Male humans need to eat more calories than females. Wickwack 60.230.222.99 (talk) 10:23, 12 January 2013 (UTC)

Agree. With starvation a constant threat, there had to be a good reason to justify excess energy expenditure. StuRat (talk) 00:38, 13 January 2013 (UTC)

Any suppositions here are likely to be incomplete if not backed up by research. With that disclaimer, I'll add another factor that is likely to be a contributor to the differences between the sexes in humans, this being sexual selection (see also Sexual selection in human evolution). Just as male birds of some species display very different and gaudy plumage as a result of choice of mating partner made by the females, sexual partner selection in humans can result in such differences. Since women often get to choose their breeding partners (including quite frequently through infidelity), there is a strong selection factor based on the average female preferences. A further factor is direct competition for mates, which in humans and many other mammals favours strong men because they can beat the competition to a pulp (but more normally just send them packing). The bulk of selection in humankind did not occur under the modern state-imposed nonviolence. To some extent selection for strong women is thus absent (women are more often prizes to be won than opponents to be vanquished, and they reproduce whether they're enslaved or free). Male sexual preferences also play a role, based on the premise that the offspring of powerful men will have a greater survival probability, and powerful men get to choose their breeding partners. I consider this to be a likely explanation for the not-so-functional curves and bumps that women have, largely absent in other species. — Quondum 10:55, 12 January 2013 (UTC)

I don't consider sexual selection itself to be an answer. That is, there must be some underlying reason why human males want big breasts on their females, whereas other species don't. In this case, I believe the reason proposed for women having large breasts all the time is that it's an age marker, making it obvious when a woman is of childbearing age. (Since some women are quite short, height alone is not a good indicator.) Facial hair on males served a similar purpose. (Body hair wouldn't be as useful, after the invention of clothing.) In other species, there are color changes, etc., which serve the same function. StuRat (talk) 00:37, 13 January 2013 (UTC)

See Sexual dimorphism. Humans are at the low end of sexual dimorphism as far as primates are concerned, much more like bonobos than gorillas. This I believe is taken to mean that there is some polygamy but it is not the norm to have harems and have to defend them like gorillas do. Dmcq (talk) 13:34, 12 January 2013 (UTC)

God! Are you guys biologists? Anyway, thanks a lot for your answers. Although I have one more question- Are (human) males superior than females in intelligence as well? I read somewhere that men have larger neurons but women have more numerous neurons, so you can't really tell who's more brainy. Is that correct? --Yashowardhani (talk) 14:06, 13 January 2013 (UTC)

See the IQ section of Sex and psychology]. Have you ever won an argument with a woman ;-) Dmcq (talk) 14:43, 13 January 2013 (UTC)

Modern neurobiology thinking is that it is not the number of neurons that determines intelligence, but the number of interconnections between neurons. The size of neurons (mass or volume) seems to be unimportant.

Pure OR here, but decades of interracting with males and females, at home, office staff at work, and professionals (male and female) and managers at work has taught me that females are not more or less intelligent than males, but they ARE different:-

• Females often think faster than males, but they do not think as deeply, even when they are engineers or managers working on complex engineering or management questions.
• Females claim they are better at multi-tasking. They are more comfortable multi-tasking, but at the cost of not performing any particular task as well.
• Females are more comfortable following laid down rules. In a large engineering organisation, rules, guidelines, and policies must be set for staff to follow. However, no rulebook or policy document can cover all situations, as the author(s) cannot anticipate everything or predict the future. It is part of the role of profesional Engineers to recognise when given circumstances are something the rule/policy author did not anticipate, and decide that an exception should be made. Females, who are otherwise very capable Engineers, are never entirely comfortable with this - they tend to follow the rules just because they are the rules, even when the outcome will be sub-optimum. I've had to council female Engineers on this - I have never needed to explain it to males.
• For males, the tendency is that outcome is important; for females the tendency is that process is important.
• Females have a different negotiating style to males. Males instinctively try to go for a win-win agreement; they try to see the other's point of view. Females tend to go for a win/lose or give/take agreement; they try to assert dominance. Males compromise to secure happiness on both sides; females compromise if and only if they want to grant a favour or make the other party feel good, and they see that as a cost or investment.
• Males are more atuned to logic; females are more atuned to who feels what emotion.

Wickwack 120.145.32.87 (talk) 16:02, 13 January 2013 (UTC)

A question about Ions

Hello wonderful helpers and angels :)

How could it be that some Ions are positively charged (+) or negatively charged (-) if the number of their atom's Electrons & Protons, is always the same?

In other words, if to get Pos charge we need to add protons, and to get Neg charge we need to take out electrons, how could this be even possible if their number is in all cases equal?

Please give me the simplest and shortest answer you can, thanks. — Preceding unsigned comment added by 79.180.108.146 (talk) 12:34, 12 January 2013 (UTC)

Ionization always involves the adding and removing of electrons, not protons, because the protons are bound up in the nucleus. (I'm sure someone will be along shortly to explain about nuclear processes, but we'll ignore those for now, as they're not reversible.) So an atom that becomes a positively charged ion of the same element does so by losing a number of electrons equal to the positive charge, and one that becomes a negatively charged ion does so by gaining the appropriate amount of electrons. AlexTiefling (talk) 13:01, 12 January 2013 (UTC)

(edit conflict):The article to which you link explains it all. It is not possible to make an ion (of the same element) by adding a proton. A positive ion occurs when the atom loses an electron (usually because it has one or more in an outer "orbit" not as closely attracted as those in the inner shells, though experts might quibble with my simplistic explanation). Negative ions occur when an atom gains a spare electron (usually because its outer shell has one or more electrons needed to make it complete). Dbfirs 13:05, 12 January 2013 (UTC)

well, i assume that in some cases, there is a limit to the number of atoms that could be added to an atom. thank you! — Preceding unsigned comment added by 79.180.108.146 (talk) 14:13, 12 January 2013 (UTC)

Here are the basic rules on atoms:

1) If you change the number of protons, it becomes a new element.

2) If you keep the number of protons the same, and change the number of neutrons, it becomes a different isotope of the same element (some of which are radioactive).

3) If you keep the number of protons the same, and change the number of electrons, it becomes a different ion of the same element (meaning it has a positive or negative charge).

Note that 2 and 3 are not mutually exclusive, so you can have different ions of different isotopes of the same element. StuRat (talk) 00:25, 13 January 2013 (UTC)

Science behind dry hair

Hi. I overheard some people talking about their hair. One person said their hair was very "dry" because they washed and blowdried it every day. They knew it was "dry" because if they ever let it dry (after washing) on its own, without using the hairdryer, it remained wet for hours.

Another person responded that their hair had been a similar state, but after using moisturizing shampoo and a salon hair oil treatment, their hair became less "dry" and they could prove it because if they let it dry (after washing) on its own, it became dry in half an hour.

To me it is counterintuitive that "dry" hair stays wet and moisturized hair dries quickly. I'd like to understand the science going on here - why does the hair remain wet or not? The hair article didn't help. Thanks! 184.147.123.169 (talk) 14:58, 12 January 2013 (UTC)

"Dry" hair has had its oils stripped, oils being hydrophobic, or water-repellant. Long "dry" hair then tends to retain water like wet mop strands, while moisturized hair will let water drip off freely like rain off a duck's back. μηδείς (talk) 18:57, 12 January 2013 (UTC)

Imagine a stack of thick towels. We will call these the "dry towels". Pour a few gallons of water on them and then measure how long it takes for the stack to dry.

Now imagine that you repeat the experiment, but first you soak the stack of dry towels in oil. We will call these the "Moisturized towels". Pour a few gallons of water on them (most of which beads up and rolls off) and then measure how long it takes for the stack to dry ("Dry" meaning "no water"). --Guy Macon (talk) 19:04, 12 January 2013 (UTC)

Now imagine you have to pay food-waste specialists to come haul away those ruined towels!  :) μηδείς (talk) 20:27, 12 January 2013 (UTC)

Do Identical twins have the same type of DNA and if so,why their behavior is different?

I have heard identical twins have the same type of DNA. So, if it is, why they don't have the same behavior?--Ganesh Mohan T (talk) 16:24, 12 January 2013 (UTC)

Behaviour is not determined by DNA. Roger (talk) 16:33, 12 January 2013 (UTC)

Behavior is not solely determined by DNA. (Nature versus nurture; gene–environment interaction; heritability; behavioural genetics; and especially on point, twin study and Minnesota Twin Family Study.) TenOfAllTrades(talk) 16:38, 12 January 2013 (UTC)

See the difference between wikt:determine and wikt:influence. Roger (talk) 16:48, 12 January 2013 (UTC)

As a general bit of research advice, it's not always wise to rely on an incomplete, wiki-based project to fully cover any particular topic; the breadth of a word's definition and usage often exceeds that which has made it into Wiktionary. Do you have anything to say that's actually relevant to the original poster's question? TenOfAllTrades(talk) 17:08, 12 January 2013 (UTC)

The above are right to point out that genetic determinism (in its strictest sense) is a fallacy, but it's also interesting to consider epigenetic differences. A famous study (Fraga et al., 2005) showed that epigenomes grow increasingly disparate between individuals with age, even monozygotic twins. Besides, even at the DNA level monozygotic twins may have differing copy-number variation Jebus989^✰ 17:49, 12 January 2013 (UTC)

Twins have the same DNA, meaning that aside from mutations and mitochondrial DNA, their DNA have the same sequence of base pairs. All organisms on Earth have the same "type" of DNA, meaning they use the same base pairs and have the same base-pair-to-amino-acid encoding scheme. --140.180.240.178 (talk) 20:11, 12 January 2013 (UTC)

Why would the mitochondrial DNA of (identical) twins be different (aside from mutations)? - Lindert (talk) 00:31, 13 January 2013 (UTC)

So, What really controls the behavior of an organism? Do DNA have any effect on the behavior?Ganesh Mohan T (talk) 09:19, 13 January 2013 (UTC)

a wormhole is two black holes?

I'm a little bit confused about this topic.how can be a wormhole two black wholes, as it is said that if we enter one mouth of the wormhole then we come from other mouth of the wormhole.if both the mouths are black holes then how can an object entering through one can come out of other hole.because nothing can escape from black hole's attraction force, everything is attracted by it then how come any thing come out of it.my doubt is if both the mouths are black holes then both of them will attract matter and all of this will be piled up at the center then how will any thing come out? — Preceding unsigned comment added by 202.65.149.230 (talk) 17:04, 12 January 2013 (UTC)

You may wish to read white hole. Brambleclawx 19:03, 12 January 2013 (UTC)

I'm reminded of CatDog. :-) StuRat (talk) 00:11, 13 January 2013 (UTC)

Some other possibilities, besides a white hole:

1) Time travel. The mass comes out at some other place and time, perhaps the Big Bang.

2) Evaporation. Black holes do very slowly evaporate, so the mass will eventually come back out that way.

3) The mass travels to a parallel universe where it comes out in either white holes or a Big Bang there.

4) No such thing as wormholes (the mass just stays in the black hole).

Note that none of these are particularly promising for the sci-fi idea of a space ship travelling around our universe. If anything makes it back out, it's probably just subatomic particles. StuRat (talk) 00:15, 13 January 2013 (UTC)

Realistically, there is no evidence to suggest that a black hole is functionally a hole in normal terms at all. It's a singularity - a point in space with no properties except mass (and possibly rotation). Anything falling into a black hole just adds its own mass to that of the hole, which will eventually shed it again through Hawking Radiation. AlexTiefling (talk) 11:14, 13 January 2013 (UTC)

large quasar group

hi, as to the recent news on 1/11/13, im curious as to any informed opinion on the matter. How could something 4x bigger than expected, and contrary to scientifically accepted givens exist, I would appreciate any response,,thank you..--Ozzie10aaaa (talk) 19:24, 12 January 2013 (UTC)

I second the user's question, what sort of informed comment can we get toward describing this object (only the one paper?) objects similar to it, and the theories about such objects and how this one violates it? I know we have several informed people here on astronomy. Unfortunately I am not one of them. μηδείς (talk) 20:52, 12 January 2013 (UTC)

Large as this thing is - it's still only a tiny dot of light. We can't measure it directly - everything has to be very indirect. You have to use spectrometry to figure out where the brightest parts of the spectrum are - then use redshift to estimate the speed at which it is moving relative to us - then use hubble expansion to estimate the distance to the object - then (knowing the nature of the object), compare the brightness to other objects of a similar type to get an idea of size. It's very easy for one of those many assumptions to go awry - so there is always scope for some other data to come along and radically alter the results. SteveBaker (talk) 00:13, 13 January 2013 (UTC)

Here is the discovery paper, and it's pretty readable. SteveBaker is almost completely wrong, which is highly unusual for him. The LGQ is not a tiny dot of light; it actually consists of 73 quasars spread across 15 degrees of the sky. The complete 3D distribution of these quasars can be gotten just by measuring their redshifts, and at a redshift of 1.3, that's a very easy measurement by spectroscopic standards. It's true that Hubble's law (or more precisely, the Friedmann equations) are needed to convert redshift into distance, but the relevant cosmological parameters have been nailed down to within 1%, and hardly anyone believes the calculated distance could be off by a factor of 2-4.

As for the OP's question, the honest answer is that nobody knows for sure, but it seems to violate the cosmological principle. That's the whole point of the paper--if the quasar group was perfectly consistent with theory, there would be no point in publishing the paper in the first place. The paper does note, however, that similar evidence of gigaparsec structure had been found in the past: "Evidence for Gpc-scale correlations of galaxies has been presented by [...] Hutsem ́kers et al. (2005), who found that the polarisation vectors of quasars are correlated on Gpc-scales. Similarly, the existence of cosmic flows on approximately Gpc-scales (e.g. Kashlinsky et al. 2010), regardless of their cause, is itself implying that the universe is not homogeneous." There's also statistical anomalies in the cosmic microwave background--see CMB cold spot.

Medeis asked a much more complicated question, but I'll try to answer it. The cosmological principle says that the universe is homogenous and isotropic at large scales--in other words, that if you zoom out enough, it looks uniform. All the structure we see today, according to standard cosmology, comes from random temperature fluctuations in the early universe. These fluctuations, which we can see directly in the cosmic microwave background, translate to slight overdensities and underdensities of matter. The overdense regions collapse gravitationally, creating the large-scale structure of the universe. There should be a size limit to this large-scale structure, because at a certain distance from an overdense region, the gravity from that region is too weak to have much effect. The size limit is called the "End of Greatness", which is described in our article on large-scale structure, and there's abundant evidence from the CMB and from galaxy surveys that it exists. What the size limit actually is, however, is not simple to calculate, because it depends on how matter collapses gravitationally to form structure. Clowes et al. uses the results from Yadav et al., who ran a N-body simulation for the entire universe to calculate what the size limit should be if the universe were homogenous at large scales, and the result was 370 Mpc. This suggests one reason that a gigaparsec-long LGQ might be possible: the simulation is flawed. Clowes et al. discuss this in their paper: "Of course, history and, most recently, the work of Park et al. (2012) indicate that one should certainly be cautious on the question of homogeneity and the cosmological principle. The Sloan Great Wall (Gott et al. 2005) and before it, the Great Wall (Geller & Huchra 1989) — was seen as a challenge to the standard cosmology and yet Park et al. (2012) show that, in the “Horizon Run 2” concordance simulation of box-side 10 Gpc, comparable and even larger features can arise, although they are of course rare." If you were to ask for my opinion on the most likely explanation--and keep in mind I'm far from an expert--I'd say the simulation's assumptions were too restrictive, and a more realistic simulation, combined with more rigorous statistical analysis (the Clowes et al. paper has no statistical analysis at all), will show the huge-LGQ does not violate the cosmological principle. --140.180.240.178 (talk) 02:01, 13 January 2013 (UTC)

That was very clear, IP 140. I wish I had realized that this is meant to be a violation of "the cosmological principle" which is simply a heuristic, and in no way any sort of law of physics, as opposed to an actual violation of cosmological principles. The report of that latter in the press made it sound like some known physical law would constrain "structures" of a certain size to be physically impossible due to physical laws, not just statistically unlikely pending actual observation. μηδείς (talk) 03:03, 13 January 2013 (UTC)

thank you for your very good explanation,,,,,,,,,,,"TO IMAGINE IS EVERYTHING"-Albert Einstein..--Ozzie10aaaa (talk) 15:30, 13 January 2013 (UTC)

Oriole question

Does anyone happen to know exactly how does the Northern Oriole carve up a Monarch butterfly prior to eating it? Does it just tear out and consume the insides while leaving the rest of the bug more-or-less intact, or does it first rip off (and discard) the bug's wings and/or head as well? Also, do orioles make the Monarch a regular part of their diet, or do they only eat it when there's nothing else left to eat? (And while we're at it, after consuming a Monarch, does the Northern Oriole tend to have a craving for something sweet to get rid of the awful taste?) 24.23.196.85 (talk) 21:28, 12 January 2013 (UTC)

They cut it with teen-weeny knife and fork, and drench it with ketchup. ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:02, 12 January 2013 (UTC)

No, seriously! It says in the article on the Monarch butterfly: "Overwintering monarchs in Mexico are often preyed upon by black-headed grosbeaks, which are immune to that toxin. Other birds, such as orioles and jays, have learned to eat only the thoracic muscles and abdominal contents because these contain less poison than the rest of the body." (Emphasis mine.) 24.23.196.85 (talk) 22:07, 12 January 2013 (UTC)

I remember having seen movies (real moving projected film that occasionally burst into flame) in elementary school of birds tearing the wings off butterflies before eating them. They didn't linger on which part of the innards, though. μηδείς (talk) 03:39, 13 January 2013 (UTC)

Thanks! You've just confirmed my original hunch -- that the bird would first rip the wings off and discard them, because those are the worst-tasting parts of all (in the case of the Monarch and some others, in any case). But will birds like the Northern Oriole or the American Robin eat a Monarch at all if there are other insects available? 24.23.196.85 (talk) 04:15, 13 January 2013 (UTC)

Black swallow-wort

It says in the article on Black swallow-wort that an infestation of this weed can cause a decrease in bird population. My question is, how? Have they figured out any kind of causative mechanism, or is there only a positive correlation at this time? 24.23.196.85 (talk) 22:00, 12 January 2013 (UTC)

Well, the article says that it's this plant is an invasive species that crowds out other plants. That would obviously reduce populations of insects and other animals that have evolved to live in the crowded-out plants - and that in turn will reduce populations of higher species that pray upon them. If the plant crowds out grasses (as our article kinda suggests) - then maybe there could maybe be no grasshoppers left there either. So birds that like to eat grasshoppers will be forced to go elsewhere. I don't know whether it's grasses, grasshoppers and grasshopper-eating-birds that are being lost in this case - but you can be sure there will be some other food-chain that's getting broken here. Worse still, with an invasive plant species, the insects that have evolved to live on those plants probably didn't get introduced along with them - so to there may not be so many insects of any kind there - and that would reduce the population of insectivorous birds even if they are able to eat other kinds of insect. SteveBaker (talk) 00:30, 13 January 2013 (UTC)

Thanks! So the most likely mechanism is simple food deprivation, right? 24.23.196.85 (talk) 04:17, 13 January 2013 (UTC)

Mottaphobia

Is mottaphobia (what the hell, no article even though Nicole Kidman suffers from this condition?) more common in men or in women? 24.23.196.85 (talk) 22:14, 12 January 2013 (UTC)

Try Mottephobia - though it just redirects a short section in Moth. AndrewWTaylor (talk) 22:19, 12 January 2013 (UTC)

Thanks! So, does anyone happen to know whether it's more common in men or women? 24.23.196.85 (talk) 22:25, 12 January 2013 (UTC)

Phobias aren't really broken down into fears of each specific kinds of object - words like "mottaphobia" are largely made up on the spot by who-knows-who. As far as science is concerned, phobias are really only split into three kinds (irrational fears relating to people and social situations, agoraphobia and a fear of things like animals). The latter is called "a specific phobia" - and that's what this irrational fear of moths would come under. Our article on "specific phobias" says that "women are twice as likely to suffer from specific phobias as men". Fear of moths is obviously just a special case of Entomophobia...and our article on that subject points out that all "specific" phobias have similar causes. So I strongly believe that your answer is "women" - by about two to one. SteveBaker (talk) 00:14, 13 January 2013 (UTC)

Thanks! That's just what I wanted to hear.  :-) 24.23.196.85 (talk) 02:47, 13 January 2013 (UTC)

Our phobia article seems to back up Steve, but it seems very odd to me that claustrophobia is not mentioned here. I would think that would be by far the most common one (article says 5-7% incidence). And agoraphobia is called out separately? I thought agoraphobia was considered a subset of claustrophobia (the fear is not of open spaces, as often described, but rather of being hemmed in by a crowd and unable to escape). Maybe they're doing the reverse, counting claustrophobia as a subset of agoraphobia? --Trovatore (talk) 07:22, 13 January 2013 (UTC)

I thought agoraphobia was an umbrella word that meant insuperable anxiety/panic in a public place. In my experience of treating people with this particular phobic condition the level of anxiety usually relates to the person's perceived distance to safety, most commonly their home. As the condition presents in subtly different ways with distinct problem areas for different individuals I cannot understand the value of all this specific defining. Richard Avery (talk) 08:35, 13 January 2013 (UTC)

Do I understand that you're a psychiatrist or clinical psychologist? If so you'd know much better than I would. Can you explain the apparent omission of claustrophobia from the tripartite schema Steve reports, which does seem to correspond to what our article says? I don't see claustrophobia as either one relating to people and social situations, or one relating to things like animals. If anything, I'd have thought agoraphobia would be "relating to people and social situations". --Trovatore (talk) 09:05, 13 January 2013 (UTC)

I was a mental health nurse in my younger days and discovered that it does not require high powered techniques to help anyone to come to terms with a phobia. I have no reference for the scheme to which you refer but I have seen so much written about phobias and their cause and cure. Guess what? Much of it was rubbish, exaggeration or journalistic puff. OR warning! From my experience of both carrying out desensitisation of phobic people and discussing cases with colleagues, the classification has less to do with the therapy strategy than the patient's history and subjective response. If academics or others want to spend time naming different classes of phobias and finding names for specific phobias (some of which are either non-existent, unique or as rare as chickens teeth) then good karma. But I always preferred to concentrate on the individual client and their life. Best. Richard Avery (talk) 15:22, 13 January 2013 (UTC)

melting point

why melting point of magnesium show a deviation from regular trend in group iiA? — Preceding unsigned comment added by 119.160.126.98 (talk) 23:06, 12 January 2013 (UTC)

This sounds like a homework question. Can you give a link to that groups' article at wikipedia, so we know you have read what we have available? μηδείς (talk) 00:01, 13 January 2013 (UTC)

January 13

Polarization of light

Why partially polarized light produce glaring ? 106.209.16.55 (talk) 04:18, 13 January 2013 (UTC)

If I understand your question correctly, you've got it a little bit backwards: Partially polarized light doesn't produce glare. Rather, glare tends to be partially polarized. That's because it's reflected off of pavement, cement, the surface of water, et cetera, and those things differentially reflect incoming light of different polarization. That's why polaroid lenses are effective — they preferentially block the light that gets reflected from those surfaces, while passing the light polarized the other way. About half the light that you want to see is polarized the other way, so the brightness of the things you want to see is enhanced compared to that of the glare. --Trovatore (talk) 07:51, 13 January 2013 (UTC)

See section "Polarization by Scattering" of this. Here, it mentions Polarization by scattering is observed as light passes through our atmosphere. The scattered light often produces a glare in the skies. I want to know - Is there any relation between partially polarized light and glaring ? What means 'partially polarized light' ? 106.215.0.3 (talk) 10:49, 13 January 2013 (UTC)

Iron man

are all the technologies mention in the article currently possible? Or do we have to spend more money on research to get there? — Preceding unsigned comment added by 65.128.142.118 (talk) 07:40, 13 January 2013 (UTC)

Pretty much none of that technology exists. The prices are therefore completely fictional. Some things are just pure fantasy, such as the never-really-explained arc reactor and how the suit magically saves Tony from being squashed by extreme G-forces. Someguy1221 (talk) 08:42, 13 January 2013 (UTC)

See [14]. A perfect recipe for Stark purée. Sagittarian Milky Way (talk) 10:35, 13 January 2013 (UTC)

At least a helmet with heads-up display is possible. StuRat (talk) 09:07, 13 January 2013 (UTC)

Tuatara - a third eye in humans too?

Having recently seen my first tuatara, the New Zealand reptile with a third eye on the top of its head, it has set me wondering about the many religions eg. Hinduism, which claim a third eye for humans,somewhere between the eyebrows or on the forehead. Has anyone ever found please, the remotest trace of such an eye in any species rather more closely related to me than the tuatara? With thanks. — Preceding unsigned comment added by 109.12.63.220 (talk) 10:58, 13 January 2013 (UTC)

The relevant articles are at parietal eye (the biological concept) and third eye (the mystical concept). The two are not related, so far as I can tell. Matt Deres (talk) 14:23, 13 January 2013 (UTC)