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July 9

EQUATION HELP;;;

pro e can plot curvs with equations we give. I am in urgent need of the following equation.Any mathematician kindly help me..:

i need equation for a twisted pair wire(2 wires only wound in form of a helix along a circle.Such as a two

TWISTED CABLE PICTURE

The figure below shows a twisted cable .i need equation for such a twisted curve made along a helix. as such a twisted wire in form of a telephone cable.RIGHT!!

TELEPHONE CABLE

Sameerdubey.sbp (talk) —Preceding undated comment added 03:26, 9 July 2012 (UTC)

Your 2nd link doesn't work for me. If you simply want a 2D model, use a positive and negative sine wave for the two wires. For example:

Y = sin(X)/10

Y = -sin(X)/10

I divided by 10 to flatten them out a bit, you can change this if you want them flattened more or less. Let us know if you need to plot a 3D helix, and/or add thickness to the wires, or if you need to simulate 3D by having the wire in front alternate each time they cross. (However, beware that each of these changes make the implementation more complex.) StuRat (talk) 03:37, 9 July 2012 (UTC)

Thanx a lot for quick reply.However i want a 3d model.and the wires would not overlap,they are twisted actually as shown in the figure.I think this would become simpler if i think in terms of cylindrical coordinate. i forgot to mention that the helix must form a closed circle.

i am giving a link for twisted wire once again. telephoner cable

once again stating my whole proble. 1.a twisted wire(2 strands only) 2.in form of helix(like telephone cable) 3.helix must form a closed curve

actually i am trying to make 3d model for a circular core wound with twisted wire.ok plz help 203.197.246.3 (talk) —Preceding undated comment added 06:37, 9 July 2012 (UTC)

Do you want something like this: [1], but modeled in 3D ? Also, you didn't say whether you need to represent wire thicknesses, or just show the center-lines. If you do want to show the thickness, do you want a surfaced model or a solid model ? StuRat (talk) 06:51, 9 July 2012 (UTC)

If you just want the center-lines, it's just (cos kt, sin kt, t) and (-cos kt, -sin kt, t), where k is a constant proportional to how twisted you want it. If you want thickness, you could approximate it with (cos ku + r cos v, sin ku + r cos v, u) where r is the minor radius if it's not very twisted, or with (cos ku (1 + r sin v), sin ku (1 + r sin v), u + r cos v) if it is. If you want something more accurate, I'd have to think about it more, so I'd rather not until I know that's what you actually want. You could toy with that last r to make it look better. — DanielLC 20:11, 9 July 2012 (UTC)

Silicone dioxide in vitamins for hair

I have read sbout silicone dioxide in food as additives what about hair vitamins? I am researching a product sold on the internet under a company called Hair Essentials for Women. This product is being marketed to women for thinning hair or want stronger thicker hair> My concern is how safe is it in capsule form? Does it really affect the linning of our stomach? — Preceding unsigned comment added by 174.112.156.3 (talk) 04:02, 9 July 2012 (UTC)

I've never heard of silicone dioxide, are you sure you have that right ? Silicon dioxide, on the other hand, is basically sand, so I wouldn't expect it to be particularly helpful or harmful (unless inhaled). AFAIK, it's just filler, often added to dilute super sweet artificial sweeteners to get them closer to the net sweetness of sugar. StuRat (talk) 04:17, 9 July 2012 (UTC)

It is an additive used as said as a filler and to prevent powders from clumping. The danger from ground glass is mechanical. It has to be above a certain size to pose a threat of irritation. The grade used in food (like taco seasoning powder) and drugs is non-problematic. μηδείς (talk) 04:23, 9 July 2012 (UTC)

Agreed, unless it's inhaled. I also would think it would tend to grind down the teeth over the years, since it's very hard, but the capsules should avoid this (on the plus side, it might help to remove dental plaque and dental calculus when not in capsules). I also wonder if it qualifies as non-nutritive dietary fiber. StuRat (talk) 04:29, 9 July 2012 (UTC)

Yes, when I worked as a prep-cook I used to make the chili, and the ground glass would form a nice white cloud no matter how I tried to pour it. See Silicon_dioxide#Health_effects. Baking soda and salt, or even table sugar is much better if you need an abrasive to brush your teeth. No, it is definitely not fiber, fiber is absorptive. You want to keep your intake to a minimum: the poison is in the dose. μηδείς (talk) 04:49, 9 July 2012 (UTC)

I had a similar problem with cinnamon forming a cloud, but figured out a solution. I pour it directly into liquid (like applesauce), which limits the cloud size. Then, before I turn the container back upright, I put the lid on. This prevents the second cloud that comes out when the cinnamon falls back down to the bottom of the container. I try to do all this quickly, while holding my breath, and then evacuate the area, to avoid breathing any cinnamon clouds that were produced. (Anyone who has ever inhaled a cloud of cinnamon powder will appreciate why I take such precautions.) StuRat (talk) 00:29, 10 July 2012 (UTC)

Why can't the extra dimensions of M-theory be temporal?

M-theory requires 7 hidden dimensions, so why must these be spatial rather than temporal dimensions? Hcobb (talk) 12:25, 9 July 2012 (UTC)

I don't know much about this, but the importance of 9+1 dimensions in string theory is related to a special property of Spin(9,1) (see [2] at the end of the page). That property isn't shared by Spin(8,2), Spin(7,3), etc., though it is shared by Spin(8) and, I think, Spin(10,2) and so on. M-theory adds one spatial dimension to that. Don't ask me why. -- BenRG (talk) 17:41, 9 July 2012 (UTC)

environmental science

what are the different types of biomes? — Preceding unsigned comment added by Scmcforpeace83 (talk • contribs) 12:46, 9 July 2012 (UTC)

That seems like something that could be answered by reading our article entitled "biome". DMacks (talk) 12:49, 9 July 2012 (UTC)

Newton's atoms in my body

Now there's a wide spread saying that your body contains atoms that were once in [put a famous person here]'s body. Now that seems nice, and the reason they offer for this is that atoms circulate in nature and since the number of atoms in human body is huge, there are at least some atoms in our body that belong to somebody. Well, first of all, I agree that elements circulate in nature, but how long does it take for them to do so? given that some of the people they exemplify are pretty recent in history, I'm skeptical about this claim, I mean I'm sure that atoms in my body were there in the body of some prehistoric animals for sure, but individuals in recent history?! and given all the plants and animals (including people) that have ever existed, aren't there at least some individuals that didn't make it to my body? It seems a bit unlikely to me. does the "shuffling" of atoms through history happen this fast and this radically?--Irrational number (talk) 13:24, 9 July 2012 (UTC)

Water circulates much faster than solids, and air even faster than that. It is certainly plausible that most of the air you breathe contains atoms that have been around the world in relatively short timeframes. I'm not so sure how well the claim holds up in the end though. Even though we have ridiculously huge numbers of atoms in us, there are a lot more atoms in the environment that aren't currently part of any human. Just because you have something like 10^25 (for example - i made the number up) more atoms than the number of people that ever existed doesn't necessarily make it likely that at least one has come from each person. 209.131.76.183 (talk) 14:20, 9 July 2012 (UTC)

(ec)Molecules in air move as fast as the wind, recent examples of which are radioactive fallout from the Chernobyl disaster in Ukraine arriving 36 hours later in Finland and the rapidly changing area of Air travel disruption after the 2010 Eyjafjallajökull eruption. You don't have to be on this planet very long to have a high probability of sharing gas with him and her. DriveByWire (talk) 14:40, 9 July 2012 (UTC)

We did the math for this in high school. The result is pretty convincing, although we assumed for simplicity that once in the air a molecule stays in the air, and that people don't rebreathe the same molecules, and came up with an estimate of 1,000 atoms per breath having been breathed by Jesus as well. Even correcting for air molecules leaving the atmosphere and people not breathing unique molecules in every breath the number should remain well over 100. The math desk might work out a formula for you. μηδείς (talk) 17:04, 9 July 2012 (UTC)

Saying that one specific person's atoms are likely in your body is VERY different from saying that the atoms of every individual who's ever lived is in your body. Suppose that, for a random person, you're 99.999% likely to have one of his atoms. That means that for 1 million random individuals, there's only a 1 in 22,000 chance (0.99999^1000000) that you'd have an atom from every single person. --140.180.5.169 (talk) 17:32, 9 July 2012 (UTC)

Yes, but the likelihood is much, much, much, much, much much higher than 99.999%, which is merely 1/100,000. How many atoms are there in a mole, how many moles does someone breathe a day, and how many days do they live? The number that gives is incredible. Divide it by the number of liters in the atmosphere and you get molecules per liter. A helpful visualization to comprehend the numbers is to imagine a raindrop magnified to the size of the earth. The water atoms would be the size of basketballs. That's just one drop of water. μηδείς (talk) 17:40, 9 July 2012 (UTC)

I'll point out, as I do every time this topic comes up, that atoms and molecules are indistinguishable quantum particles and hence it's quite meaningless to ask whether a particular atom now is the same as a particular atom from a long time ago. It probably does make sense to talk about what fraction of yourself was formerly Newton, but it doesn't make sense to compute a probability that you have at least one former Newton atom, because all atoms are a mixture of former Newton and non-former-Newton. -- BenRG (talk) 17:56, 9 July 2012 (UTC)

You realize, of course, that your interpretation of that article ("all atoms are a mixture of former Newton and non-former-Newton") is entirely wrong. Atoms may swap outer electrons, but the electrons themselves and the nuclei of the atoms maintain their integrity excepting radioactive decay. μηδείς (talk) 18:27, 9 July 2012 (UTC)

It's not an interpretation of that article, but a true statement about quantum mechanics. If the article really says otherwise then it should be fixed. The reason that particles lose their identity when in close proximity is that every interaction has contributions from Feynman diagrams in which the particles switch places and other diagrams in which they don't. -- BenRG (talk) 19:06, 9 July 2012 (UTC)

The central point of that article is that electrons, protons, and neutrons are indistinguishable from each other because they don't have smaller identifying features. Any electron is as good as another. But under normal circumstances, nuclei simply do not flow into one another. That's Heraclitus or Deepak Chopra, not Richard Feynmann. μηδείς (talk) 19:22, 9 July 2012 (UTC)

If that's the point of the article, it's misleading. That's why we can't tell them apart, not why we know they're the same. We know they're the same because quantum states with the particles switched interfere, which only happens if they're the same state. For example, if the amplitude of state A is 0.1 and the amplitude of state B is 0.1, the probability of getting A is 0.1^2 = 0.01, and the same for B. The probability of A or B is 0.02. If the two states are the same except with two identical bosons switched, the probability of getting either state is 0.04. If they're not the same state, that's a 0.01 chance of getting A, a 0.01 chance of getting B, and a 0.02 chance of ... what exactly?

You could claim that the universe is just symmetric in such a way that any two particles have the same/opposite amplitude when switched. If you accept the Many Worlds interpretation, this would mean that you share the atoms of an equally likely alternate universe Newton. If you accept the Copenhagen interpretation, it means that any time two identical particles get entangled, they have a 50% chance of switching. Quantum entanglement has been found on relatively large scales, which would seem to imply that any action on a smaller scale would cause entanglement. The quarks in nearby atoms are constantly interacting via., among other things, their electric charges. Every time the waveform collapses, the quarks could end up in any of the nuclei. — DanielLC 19:51, 9 July 2012 (UTC)

It seems that the original poster has asked a specific question, and gotten some very ambiguous answers shrouded in debate about the appropriateness of various methodologies. ..."How long does it take" ... for a molecule to move from place to place... this is predominantly dictated by the mean free path and the drift velocity; for molecules in common substances, an answer can be determined, subject to realistic parameters. The extent to which the calculations of those parameters will require quantum-mechanics, as opposed to being suitably-well approximated by classical statistics, will depend on the type of molecule. So, for example, a very large organic carbon compound will probably behave fairly well like a classical particle (albeit one with a strange shape, moment of rotational inertia, and so forth); while an individual oxygen or hydrogen atom will probably behave in a way that is much better described using the ugly statistical formulations that quantum physics requires to accurately make predictions. For lack of a better model, and given that the OP hasn't precluded the use of a spherical cow model, it seems fair to assume that every molecule on the planet (including those inside living organic tissues) could be considered as a member particle of a gigantic Maxwellian gas, whose temperature is approximately the average surface temperature of our planet; so simply calculate the average molecular speed, and you've got an approximation for the rate of particle circulation. You can use the diffusion equation to estimate the mean distance traveled by any individual particle. Once you've got that model working, you can add in as much additional complexity as you like to correct for all of the terrible, invalid assumptions that are clearly due to such a simplistic model. If you're interested in classical statistical physics, I always recommend the red book of Statistical Physics and Thermodynamics. If you're interested in quantum mechanical statistics, there exists a plethora of very bad texts to choose from. Nimur (talk) 21:48, 9 July 2012 (UTC)

"We are star dust."

"Yes, but we're also made of dino poo." :-) StuRat (talk) 18:56, 9 July 2012 (UTC)

So we're both golden ... and brown? Clarityfiend (talk) 20:50, 9 July 2012 (UTC)

...and we've got to get our dino poo back to the garden. StuRat (talk) 21:00, 9 July 2012 (UTC)

Back to the quantum physics, can we please get a ref on how often atmospheric nuclei in different molecules at room temperature (or even the temperature of lava) can be expected actually to intermingle? In atoms per year? As for the mean free path, it is something like 10cm, travelling at 1,000kmph, at room temperature, but that is hardly relevant on the timescale since newton. Weather mixes the atmosphere pretty well on that sort of time scale. μηδείς (talk) 22:14, 9 July 2012 (UTC)

If you're using quantum physics, the answer is that they're already the same nuclei. You could mess around with the question enough to get something that looks like the sort of answer you'd expect (so long as the particles don't get too close together), but the question itself is fundamentally flawed.

If you insist on messing with it to get the sort of answer you're looking for, the atoms in your body and the atmosphere intermingle every time you eat and breathe. When you digest food, the carbon in it gets stored in fat. When you exercise, the carbon in your fat gets exhaled in CO2. The CO2 gets absorbed by plants, and gets eaten by someone else. I'm not sure exactly how long it takes to get spread around in the air, but the bottleneck is probably the time between plants getting picked and eaten. — DanielLC 05:09, 10 July 2012 (UTC)

My thinking as well; even ignoring the rather crucial issue of unique persistent identity we could still spend days just proposing metabolic, climatological, geological, and ecological factors that need to be taken into account, to say nothing of resolving them with any precision. That being said, the OP is clearly looking for a ballpark estimate -- that is, is it more likely than not? And my (half-)impressionistic take on it is that he has reason to be skeptical - the likelihood of possessing an atom from any one particular historical figure (again, assuming we ignore the indescernability principle), especially a recent figure, is probably small - if not exactly astronomically small. That's a rather unempirical answer, I know and I hope to see the math take root here for something more concrete, but I'd be surprised if even rough estimates suggest it to be likely. If we're going to try though, might I suggest A subpage? since the discussion is likely to get quite involved? Unless someone knows a reason not to create a subpage on the RefDesk. I can always copy our work over to subpage in my user space later if we aren't finished by the time this thread is archived. Snow (talk) 12:11, 10 July 2012 (UTC)

Medeis, I just want to mention that the identity question I'm talking about comes from whole nuclei swapping places, not from any process involving the constituent nucleons. The amplitude for some kind of mix-and-match rearrangement of two nuclei is vanishingly small because of the energy barrier, but there's no energy barrier to this nucleus going over there and that nucleus coming over here. They just go around each other, they don't pass through each other or teleport. Nevertheless they follow Bose-Einstein or Fermi-Dirac statistics in these processes. If they merely had the same properties (but weren't "indistinguishable" in the quantum sense) they would follow classical statistics and it would be possible to figure out which was which after an arbitrary amount of time. -- BenRG (talk) 16:30, 10 July 2012 (UTC)

So now that atoms are maintaining their identity? Before it was "all atoms are a mixture of former Newton and non-former-Newton". You have yet to make a coherent claim and provide a ref for it. μηδείς (talk) 16:39, 10 July 2012 (UTC)

Medeis, with due respect, I think you need to stop attacking BenRG's words (because, more often than not, he tends to be exactly correct); and instead, you should reacquaint yourself with exactly which quantities are known to be quantized. Those quanta describe physical parameters that are defined as "indistinguishable" according to the indistinguishability principle - because they have no other properties. Nimur (talk) 18:05, 10 July 2012 (UTC)

I never claimed that atoms of the same isotope are distinguishable based on their properties. Frankly, if BenRG wants to come here and imply how tired he is of having to correct people all the time the responsibility certainly does lie with him to make a coherent and consistent statements and to back his facts with refs. To say theoretically that two identical atoms may switch places with each other with and unspecified frequency in no way indicates that it is meaningless to say that one is breathing atomic nuclei which someone else breathed. It's an absurd claim based on a new agey wagey pseudo-grasp of science. I don't intend to comment on this any more, since it might imply I think the matter is open to argument. But I will be impressed when I see numbers and refs. μηδείς (talk) 22:52, 10 July 2012 (UTC)

I hate people like Chopra who say "quantum mechanics!" to justify whatever crap they believe in. And I don't like to call quantum mechanics weird or unintuitive because I think that's a cop out. But there is a reason that many physicists describe it that way. What I'm describing, whether it sounds strange or not, is an essential and basic feature of quantum mechanics. I don't understand what you think quantum mechanics is, if you don't think it's this. The only reference that makes sense is any introductory quantum mechanics textbook, or maybe QED (book). In QED there are Feynman diagrams like the ones I was talking about in figures 59 and 60 (pages 93 and 94) in my copy. Please don't come back and say that those diagrams don't prove anything. I'm not saying that the diagrams by themselves prove anything. I'm just trying to point you to a relevant part of the book, in case you don't want to read the whole thing.

I'm sorry I sounded testy in my first post. I was kind of testy at the time, but that's no one's fault but mine. -- BenRG (talk) 05:14, 11 July 2012 (UTC)

The reference desk has had a similar question more than once but I couldn't find it in the archives. Here is a similar off wiki discussion: [3]. Rmhermen (talk) 15:42, 10 July 2012 (UTC)

The fact that atoms are identical in QM is actually a trivial issue here (the state is a sum over permutations of the labels you assign to the atoms). What you need to do is formulate the problem in terms of a well defined correlation function. Count Iblis (talk) 17:47, 11 July 2012 (UTC)

environmental science

describe chaparral. give and describe the three types of chaparral. differentiate those three

S.C.M.C."WARFARE" (talk) 13:28, 9 July 2012 (UTC)S.C.M.C."WARFARE"

We have an article on chaparral. Read it. Then do your own homework. AndyTheGrump (talk) 13:31, 9 July 2012 (UTC)

the white whale

A friend recently visited Cook Inlet, Alaska where she saw the locally endangered Beluga. Why, she asks, is it still legal to use their eggs for caviar if they are endangered? μηδείς (talk) 17:13, 9 July 2012 (UTC)

Whales are eutherian mammals, and thus do not lay eggs. Beluga caviar is the eggs of the beluga (sturgeon), which lives in the Caspian Sea, and not in Alaska. AlexTiefling (talk) 17:16, 9 July 2012 (UTC)

According to beluga (sturgeon), this fish is "critically endangered", so I suppose the question still makes sense... -- Ed (Edgar181) 17:27, 9 July 2012 (UTC)

In terms of a worldwide ban, the article also suggests the obvious answer is correct, i.e international politics. Unfortunately (IMO) it is generally difficult to get action to protect some endangered species when a fair number of countries, particularly influental ones are against the idea. However the OP's comments are unclear. As far as I know they live in the US and their friend was obviously visiting a part of the US. According to our article and supported by [4], importing Beluga caviar has been illegal in the US since 2005 and illegal to trade in interstate commerce. It's still legal to trade intrastate it if it was imported before the ban, but it seems likely any beluga caviar that remains legally imported in the US must now be very rare and therefore very expensive whatever the state (although there is probably some variance). If the OP or their friend is aware of a source of Beluga caviar in the US that isn't so I suggest they contact the appropriate authority (FWS?) as it's likely it's illegally imported. BTW, the earlier source which despite some later statements only mentions specific bans on Beluga caviar from the Caspian and Black Sea may lead one to believe it's possible to get it from the Adriatic Sea which our article mentions as a possible habitat. But this apparently incredibly outdated source (it doesn't mention the 2005 US bans nor does it mention the 2006 CITES ban although it does support the idea international politics are making a ban difficult) [5] suggests they haven't been seen there since 1980. Nil Einne (talk) 19:00, 9 July 2012 (UTC)

What I wonder about is whether the sturgeon will be fished to extinction, or whether the fishing will stop once the price gets too expensive for the consumers to justify. ←Baseball Bugs ^{What's up, Doc?} carrots→ 09:15, 10 July 2012 (UTC)

It seems to be a veblen good, so maybe not. StuRat (talk) 16:47, 10 July 2012 (UTC)

The reason the beluga whale and the beluga sturgeon share the same word in their name is that both derive from the Russian word белуха (belukha), meaning "white". Ghmyrtle (talk) 09:40, 10 July 2012 (UTC)

Beluga caviar is not white. μηδείς (talk) 22:43, 10 July 2012 (UTC)

No, the but the fish is white(ish). 203.27.72.5 (talk) 23:16, 10 July 2012 (UTC)

Terrell rotation matrix

How do you find the matrix for Terrell rotation? I understand that Terrell rotation isn't quite linear, but I just want the first approximation. — DanielLC 19:58, 9 July 2012 (UTC)

Just apply the Lorentz transform to the nearest- and farthest- points on the object, or to any vertices you like; and fit a rotation to the transformed vertices. (If you only use two vertices, that is very straightforward). This is covered in Tipler's introductory relativity chapters, if I recall correctly; and does not require very advanced mathematics. Nimur (talk) 21:31, 9 July 2012 (UTC)

No. You'd have to calculate when and where the points crossed your past time cone. Since it's nonlinear, it would only work in the limit. Of course, the answer itself will only work in the limit for the same reason, so that's not that big a problem. You'd need four points to do it since it's not really a rotation (three if you're only doing it in two dimensions, which I am). Finally, I need an equation for it. I was hoping someone, somewhere already calculated it out. — DanielLC 04:47, 10 July 2012 (UTC)

The easiest way to understand the appearance of a "moving" object is by working in a frame where the object is at rest. Then it's just an ordinary linear perspective projection modified by aberration. I'm not sure how to write down a formula for this—I think it's easier to just understand the geometry of the situation, so you can solve any particular problem of this kind, than to memorize a complicated general formula. -- BenRG (talk) 06:00, 10 July 2012 (UTC)

I don't want to memorize it. I want to program it. — DanielLC 07:21, 10 July 2012 (UTC)

Well, what I said still applies—the appropriate formula will depend on what sort of program you want to write. If you want to visually simulate relativistic motion through a static scene, you can do that as follows: do an ordinary nonrelativistic 3D rendering of the scene onto a cube map with the camera at the player's instantaneous location, then, for each point in your final image, take a ray in that direction, modify it by the aberration formula (using the player's velocity relative to the scene), intersect it with the cube map, optionally apply some kind of color and brightness transformation, and you're done. This is the same basic approach as Fisheye Quake except that you're using the aberration formula instead of a fisheye projection. On any graphics card with programmable pixel shaders you should be able to do this in real time for an arbitrarily moving (and accelerating) player.

The relativistic aberration page only tells me how to mess with the angle. Not the distance. Come to think of it, do I do the distance the light was sent from, or would it mess with parallax and end up being closer/further than it appears? — DanielLC 20:17, 10 July 2012 (UTC)

There's no distance in aberration. It acts on rays of light, not points in spacetime. I assume you're asking because you need a value for the z buffer. If so, the easiest way is probably to pick a reference frame (such as the rest frame of the environment) and use the distance (=time) in that frame. See below. -- BenRG (talk) 02:55, 11 July 2012 (UTC)

If you're thinking more along the lines of a text-based program that solves a parametrized word problem, tell me what the word problem is and I'll come up with a formula. -- BenRG (talk) 07:53, 10 July 2012 (UTC)

My program is a relativistic shoot-em-up. It can find where it's supposed to draw a bullet or enemy, but I want to know how to warp the image properly. In principle, I could just have it check where to draw every vertex, and then attach lines from there, but this seems like a waste of processing power. — DanielLC 20:17, 10 July 2012 (UTC)

I approve of this project. :-) When I first saw Fisheye Quake I thought about doing a relativistic Quake, but never actually got around to it.

I recommend that you render each independently moving object in the way I suggested above: first render to a cube map, then apply aberration (and perhaps other effects) with a pixel shader. Here's some detail about how to do that.

• You need to keep track of a coordinate frame for each rigid object in the game (landscape, player, opponent, bullets) and a fixed background frame in which you express the dynamical position of everything. You need to know how to transform between all of these. The transformations will vary with time. All this is standard in 3D graphics, but there are two differences here. First, these are spacetime coordinate systems (x, y, z, t), and the transformations between them are Poincaré transformations (Lorentz transformations, rotations, and translations). Second, because light has a finite speed, you need to keep a historical record of coordinate transformations for each object instead of just the "current" transformation. This is complicated, but I'll assume you know how to do it. The rest is pretty easy. :-)
• To render a frame, do the following for each object other than the player:

• Find the point of intersection of the player's past light cone with the object's worldline. You mentioned that you already know how to do this. From now on when I talk about object coordinates I mean the object's historical coordinate frame at that point on its worldline.
• Transform the player's spacetime position into object coordinates.
• Render six views of the object into six square offscreen RGBZ buffers, with a 90° field of view, with the camera located at the spatial part of the transformed player position and facing in the ±x, ±y, ±z directions. This is standard 3D stuff, except that doing the lighting correctly is tricky. I'm going to ignore lighting for now.
• For each pixel on the screen:

• Find the pixel's location in player coordinates. I assume you know how to find the x, y, z coordinates. The t coordinate needs to be −sqrt(x²+y²+z²), so that the line from the player (origin) through the pixel location is a past light ray.
• Transform the player location and the pixel location into object coordinates. Find the intersection of the (spatial part of the) ray through the two of them with the cube map.
• Optionally alter the RGB value from the cube map. I'm going to ignore this for now.
• Find the point on the ray with t = Z, where Z is the Z value from the cube map (I'm treating the Z values as negative integers with 0 being the camera's location). Note that this point lies on the surface of the object. Transform the point into player coordinates (or background coordinates, or any other coordinate system you like, as long as it's the same for every object in this frame). Take the transformed t coordinate as your new Z value.
• Write the transformed RGB value and transformed Z value to the output buffer.

That's it. Note that I didn't use the aberration formula anywhere in this. All transformations are Lorentz (Poincaré) transformations. I think this makes things simpler (and faster).

If you just want the rotation, not the aberration, as you originally requested, then you can bypass the cube map and write directly to the output buffer. However I don't think it's any easier to do it this way, and it may not even be much faster (on a modern GPU). If you really want to do it, I'll work out some steps.

If you're interested in proper lighting, redshift, etc., I'll try to figure out some way of doing that. It's not easy, and may make the game hard to play.

Note that to really be relativistically correct you need to deal with the twin effect somehow. If player Alice is standing still and player Bob is circling around her, you need to freeze Bob's game occasionally to allow Alice to "catch up". It's not hard to do this correctly, but it might detract from the fun of the game. Alternatively you could slow Bob's game down, but that feels wrong to me, since it gives the wrong impression about Bob's subjective perception of time. -- BenRG (talk) 02:55, 11 July 2012 (UTC)

That's alright, Bob won't find that the handicap worries him too much. Girls are terrible at first-person shooters. 203.27.72.5 (talk) 05:35, 11 July 2012 (UTC)

A shoot 'em up is 2D, and generally single player. I am considering making a multiplayer option, mostly just because I figured out how. Shoot 'em ups commonly have a button to slow time down. I could make it so that you can slow time down until you reach your opponent's past time cone, and if you reach their future time cone, it just turns on automatically. This system would also neatly avoid network lag problems.

I suppose I probably have more than enough computing power to check each vertex individually. It's just that transforming the sprites seems simpler and more elegant. Also, that way I won't have to deal with tachyons having parts that you can't see, and other parts that you can see twice. I could limit it to slower-than-light particles only, which would get me out of all the necessary stuff to make tachyons dodgeable, not to mention the time travel paradoxes, but that would just feel like a missed moment of awesome. Especially because of the paradoxes.

I can't imagine leaving out the lighting effects. Imagine all the cool stuff you could do with them. Give a bullet a transparent infrared skull on a violet background, and it will look like a red skull when it's flying towards you, and then turn blue once you dodge it. Paint flowers on an enemy, and you can see those ultraviolet patterns on them when they fly away. Anyway, I've largely figured out how to do it. I'll just have the brightness of each color component be the brightness of the color times the visibility of that frequency at that color receptor. — DanielLC 05:35, 11 July 2012 (UTC)

In a 2D shooter the camera is effectively at infinity, which makes it of limited use to the player if you take the speed of light limit seriously. If you ignore that problem, then moving objects are simply Lorentz contracted. There's no Terrell rotation in this situation (though the Lorentz contraction can lead to an effective rotation: a line with slope 1, horizontally contracted by a factor of 2, is a line with slope 2). There's also no aberration. The redshift factor is the gamma factor of the moving object (independent of direction). There's never a blueshift. This would probably be kind of boring.

The best I can come up with for this type of game is to have the camera hovering a relatively short distance above the game field, tracking the player (perhaps simultaneously with respect to the lab frame), and filming the field with a wide-angle lens. If the game objects are 3D meshes (even though the action is 2D) then the method I described above will still work, and it will handle everything including Terrell rotation, but with a large number of independent moving objects it may be too slow. I can work out how to optimize it if this is indeed what you want to do. Lighting is still complicated.

The difficulty with Doppler shift is that there's no way to do it correctly in the RGB color model. An object colored #000000 might glow in the infrared, in which case it turns red when blueshifted, or it might not. If the shifts are small then you can probably fake it convincingly. You may also want to think about the brightening/dimming associated with aberration (I don't know if it has a name, but it's related to the headlight effect). -- BenRG (talk) 18:07, 11 July 2012 (UTC)

I suppose what I'm doing would best be described as taking the point of view from the ship, and then, without correcting for optical abberations, working out what it would look like from above. Think of it like those things they show radar images on that show how far away stuff is and in what direction as if it was a picture taken from above, even thought it was taken from right there. Also, I am not planning on using an RGB color model. I'm planning on using a (frequency, intensity) model.

A radar-like screen can show whatever it wants. Realistically it would show whatever would allow the pilot to shoot things most effectively. It certainly wouldn't show Doppler shift, for example, since that wouldn't be helpful at all. There is no "relativistically correct" thing for it to show, unless you literally want it to use its sensors to figure out what the scene would look like from above, in which case the correct thing to show is what the scene actually looks like from above. Relativity can tell you what you'll see, but it can't tell you what your point of view looks like from someone else's point of view. That doesn't make any sense. -- BenRG (talk) 21:50, 11 July 2012 (UTC)

Is [6] and Rotation matrix too simplistic? DriveByWire (talk) 15:38, 11 July 2012 (UTC)

I'm not sure what to say about the external page. It makes things much more difficult than they need to be by doing everything in the rest frame of the camera, instead of the rest frame of the object. I'm not sure how a Lorentz contraction could be visible in this two-dimensional world, where the image in the camera is just a line. The line in the camera does get shorter when the object is moving, because of the headlight effect. The interesting observation that Penrose and others made circa 1960 is that a moving sphere always has a circular outline, not (as you might expect) an oval, but you need all three spatial dimensions for that effect. Regarding the rotation matrix, the easiest way to understand the Terrell rotation is as a real rotation related to the camera's spatial location in the rest frame of the object, so a rotation matrix will work when drawing the object just as in ordinary 3D graphics. But the camera image (not the object itself) is also altered by aberration. If the object has a large angular size at the camera's location then aberration will distort straight lines into curved lines, but if the object is small then aberration will stretch or shrink the image but not distort it much. -- BenRG (talk) 18:07, 11 July 2012 (UTC)

It is false. The contraction part of Terrell rotation does not counter out Lorentz contraction, and doesn't even necessarily apply in the same direction. If an object is moving towards you, it will look longer than it really is. If it's moving away, it will look much shorter. If you want to know what it really ends up looking like, I suggest checking out Light Speed!. — DanielLC 18:41, 11 July 2012 (UTC)

Note that the description of optical aberration at http://lightspeed.sourceforge.net/about.html is wrong, which may be the reason for some of your confusion. I think that their images are probably relativistically correct, they just have the terminology wrong (and they're doing it the hard way). -- BenRG (talk) 22:31, 11 July 2012 (UTC)

Higgs boson

Is it possible to block Higgs bosons or manipulate the Higgs field in some way to reduce another particle's mass? --146.7.96.200 (talk) 21:07, 9 July 2012 (UTC)

Not at this time, nor for the conceivable future, save via the intervention of Clarkeian "magic". — Lomn 21:12, 9 July 2012 (UTC)

Is it theoretically possible? --146.7.96.200 (talk) 21:56, 9 July 2012 (UTC)

Not in any meaningful sense under present theory (see above need to invoke "magic"). — Lomn 23:00, 9 July 2012 (UTC)

From my limited understanding, it is roughly as theoreticaly possible as a perpetual motion machine. It would need to violate laws which we hold as some of the most certain laws we have. Vespine (talk) 01:20, 10 July 2012 (UTC)

Yes, and in the early universe the Higgs field was different, it was zero on average, causing the mass of particles to be zero. When the universe cooled, the Higgs field settled down at its minimum energy, which is not at zero field strength, causing particles to gain mass. Count Iblis (talk) 01:28, 10 July 2012 (UTC)

Hold on a second. If you heat a system above the electroweak unification temperature, you can no longer describe the Higgs interaction as "giving mass to the particles", but that doesn't mean it just disappears. Unless I'm seriously confused, what you get at high temperatures is a complicated interacting soup that in no way resembles a bunch of free massless particles. Technically they are massless, but technically they're massless at low temperature too.

Also—as you no doubt know but the original poster probably doesn't know—almost all of the mass of ordinary baryonic matter (the stuff we're made of) comes from the strong force binding the protons and neutrons, not from the Higgs field. Even if you could dial the Higgs field down to zero (which you can't) it would hardly make any difference in the mass of any ordinary object. It would make enough of a difference that cellular chemistry would no longer work and everybody would die, but not much of a difference numerically. -- BenRG (talk) 05:45, 10 July 2012 (UTC)

• So, do we have an article that explains which particles have mass independent of Higgs, and which would be massless with a zero (high energy) Higgs field present?
• Also, as I (don't) understand it, the Higgs is a scalar field, so the field level can only be lower or higher than it is now. If I have a majik laser pointer that shoots a big beam of very fast-moving Higgs particles, will the field in the area it lights up (before they decay) be lower or higher? Wnt (talk) 15:53, 10 July 2012 (UTC)

All of the elementary particles in the standard model, except the Higgs itself, get an effective mass through the Higgs interaction. In composite particles the binding energy and the kinetic energy of the particles also count as mass. So basically it's the elementary particles that are massless.

The Higgs boson is a wave in the Higgs field, so it alternates between higher and lower than normal. -- BenRG (talk) 04:41, 11 July 2012 (UTC)

And note that you don't need to use the Higgs field to change the mass of particles. What makes the Higgs field special is that it achieves its minimum energy state when the field strength isn't zero. This then causes particles to gain a mass in the vacuum. Then if you want to use some field to make the mass of a particle different from what it is in vacuum, you can use any field that couples to that particle. E.g. the mass of an electron in a very strong electromagnetic field is slightly different from its vacuum value. The shift of the squared mass of an electron in the beam of a laser is given by:

${\frac {\Delta m^{2}}{m^{2}}}=2\alpha \lambda _{e}\lambda \rho$

where $\alpha$ is the fine structure constant, $\lambda _{e}$ the electron Compton wavelength, $\lambda$ the wavelength of the laser beam and $\rho$ the density of photons in the laser beam. Count Iblis (talk) 01:42, 10 July 2012 (UTC)

Habitatable zone at the tip of RGB

About the tip of RGB in 7.59 billion years I was wondering where will earth-like habitable zone be located (Jupiter and Sautrn's system, or more likely Pluto)? General calcualations, yes I know Jupiter and Saturn's orbit will be further out roughly 1.7 times further out (roughly 8.8 AU and 17 AU) but the thing is the luminosity greatly increases by 3000 times. The mathematic calculations yahoo answers figure out is 3000/5.2x1.7 for Europa, and 3000/9.5x1.7 for Titan to figure out the surface condition for Europa and Titan. Is this possible at the tip of RGB, Europa can end up colder than earthlike temperature today of only -40F? I was wondering what is the coldest temperature estimate Europa may be in 7.59 billion in the future. I don't know what other calculations will work according to the tip of RGB, the star's temperature is alot cooler, if that matter.69.226.40.110 (talk) 21:09, 9 July 2012 (UTC)

I did a quick search and found this mentioned in Terraforming of Europa, alas, not with good sources that I noticed... I see [7] this talks about it reaching Mars, but it says nothing of Jupiter... of course, the huge caveat with all this is that the planetary orbits are likely to shift as the sun expands, and if so... well, just about anything can happen. Wnt (talk) 21:21, 9 July 2012 (UTC)

If humans (or our descendents) are still around in 7.59 billion years to worry about it, I suspect technology will have advanced to a level where we could just move the Earth wherever we wanted to. Although, by then, only a small portion of humanity may live on Earth (those who like to do things in the quaint, old-fashioned way). StuRat (talk) 21:30, 9 July 2012 (UTC)

For information, RGB refers to the Red Giant Branch phase of a sun's evolution. That is predicted for our Sun in about 5 billion years. DriveByWire (talk) 21:48, 9 July 2012 (UTC)

Am I not clear at the first place? I mean when sun peak the luminosity and size at the end of the giant stage at 3000 times the luminosity and when sun reaches the maximum radius of 1.0 or 1.2, could Europa at that time when sun being 3000 times brighter stay at the temperature below -40F? I don't know how to calculate that way. --69.226.40.110 (talk) 22:31, 9 July 2012 (UTC)

It wasn't clear to me what the B meant, although I knew you were talking about a red giant. StuRat (talk) 23:39, 9 July 2012 (UTC)

I meant when the sun's giant reaches its maximum size and luminosity could Europa just heat up only up to -40F where Mars surface temperature is today?--69.226.40.110 (talk) 23:46, 9 July 2012 (UTC)

Pluto will never be a habitable planet. μηδείς (talk) 02:44, 10 July 2012 (UTC)

As we've explained to you a dozen times before, nobody knows the answers to these questions. You are quoting numbers that are just the best guesses of a particular paper. There are numerous papers, all with different answers, because we're talking about what will happen in billions of years time and there is far too much uncertainty to draw any firm conclusions. Asking essentially the same question again and again is not going to change the answer. --Tango (talk) 14:59, 10 July 2012 (UTC)

What do you mean by dozen times before? How can you know it was the same person asking? — Preceding unsigned comment added by Plusanother (talk • contribs) 21:56, 10 July 2012 (UTC)

The same writing style and, essentially, the same question. It is obviously the same person. --Tango (talk) 02:13, 11 July 2012 (UTC)

To be a lot less rigorous, the habitable zone article points out that this is approximately a simple inverse-square relationship - so to make Jupiter, at 5 AU, inhabitable, you need a Sun 25 times as bright. But looking for more on this, I happened across [8], which suggests that the Sun will get less than 20 times brighter by 12.1 Gyr, at which point it starts pulsing and losing mass catastrophically and they abandoned attempts to model the results. Those authors favored a 200K water-ammonia life possibility on Titan for a few hundred million years. Of course, even 0.01 Gyr is a very long time if you happen to be a good gardener with an extensive assortment of seeds, so I wouldn't rule out the notion of some balmy paradise Jupiter moon existing for some brief span near the end. Wnt (talk) 15:45, 10 July 2012 (UTC)

Product of animal menstruation?

Recently I got into a discussion with a radical vegan and she, besides calling me cruel, inhumane, close minded, and so on, also said that I was set on eating products of animal menstruation. Although I did not understand when she said it, I believe she meant eggs. So, first does it make sense? was it really eggs? Is that normal within the vegan community to talk like that about eggs? Second, according to menstruation, it only refers to certain mammals, does any serious person talk about some form of avian menstruation? Third, is there any non-animal menstruation? OsmanRF34 (talk) 22:20, 9 July 2012 (UTC)

You can't reason with radicals, doesn't really matter what the topic is. You are right that birds don't technically menstruate, but one PART of menstruation: the expulsion of an unfertilized ovum is technically what laying an egg is, so it's not really a massive stretch IMHO to call a chicken egg a "chicken's period". But so what? My fav breakfast is chicken periods with slices of pig's arse, yum! It's an Appeal to emotion, we associate menstruation with "disgust", I personally don't know why, I think it has religious roots really, but I think in fact, there's nothing disgusting about it. In fact, mayube you could ask the vegan what she finds so disgusting about menstruation? Vespine (talk) 22:46, 9 July 2012 (UTC)

Slight technicality there Vespine, it is not pig's arse, but pig's chest. Pigs arse is still good though!! Caesar's Daddy (talk) 07:30, 10 July 2012 (UTC)

Many vegetarians are fine with milk and eggs, as no animal has to die to get those. As for your third Q, if you are asking if there are animals that don't menstruate, then yes, there are. For example, cats don't, but dogs do.

A retort you could make, if she likes honey, is to tell her that it's bee spit. Or, if she likes fruit, tell her she is eating plant ovaries. StuRat (talk) 22:53, 9 July 2012 (UTC)

Bee vomit, actually. Delicious! Ratbone58.164.228.40 (talk) 02:25, 10 July 2012 (UTC)

She was a vegan: so no animal products (which come from animal slavery, with or without killing). Veganism is all about animal rights in a very radical way.

The third point is about the redundancy: why animal menstruation? Is there something that could be called vegetable menstruation somewhere? OsmanRF34 (talk) 23:25, 9 July 2012 (UTC)

As far as "animal slavery", that's a fair characterization of factory farming, but how does she feel about "happy" free-range chickens ? StuRat (talk) 23:38, 9 July 2012 (UTC)

I don't believe vegans share your definition of slavery = factory farming and I don't believe I'll talk again with her about such topics, so my understanding might be limited. Anyway, as far as I could understand, no captivity of animals is acceptable to her: no milk, no eggs. It's not only the killing. It's the slavery. And she has the equivalent of normal people's opinion on slavery but applied to animals. Mainstream citizens do not accept slavery, even if the master treats the slaves well. So, she doesn't accept animal slavery. OsmanRF34 (talk) 00:10, 10 July 2012 (UTC)

If somebody wanted to provide me with food, housing, and medical care, and, in return, only asked something from me which I couldn't use anyway, like, say, my urine, I'd sign right up ! StuRat (talk) 19:19, 10 July 2012 (UTC)

THAT wouldn't be slavery, since someone asked you for something. That's trading. Just imagine the opposite case, if you get imprisoned, get lots of food to make you fat, health care only if it were economically viable, otherwise they let you die, and at the end they would eat your fat ass. — Preceding unsigned comment added by Plusanother (talk • contribs) 22:38, 10 July 2012 (UTC)

You seem to be talking about factory farming, but I was talking about free-range chickens raised for their eggs, which aren't imprisoned, but are free to come and go as they please. They also aren't fed so much that they get fat, since they aren't for eating, but for laying eggs. And comparing the health care they get with the lack of any in a wild bird, it seems like a good deal. StuRat (talk) 23:55, 10 July 2012 (UTC)

I would say she's talking out of her arse (if you'll pardon the expression), birds don't menstruate. I think you will find the Menstruation (mammal) article more informative. If you meet her again, tell her she's flogging a dead horse (sorry!). As for non-animal menstruation, it's the shedding of the uterine lining so, by definition, it's only possible in animals. Richerman (talk) 23:32, 9 July 2012 (UTC)

She means animal as opposed to human. I agree with Vespine's and StuRat's points. My last girlfriend that was a vegetarian would eat eggs and milk, just "nothing with eyes". And she would point out to people that she wore leather because there was no suitable substitute, but would prefer something else if it were available. Much more reasonable than telling people they were eating chicken abortions. μηδείς (talk) 23:48, 9 July 2012 (UTC)

The funny thing is, the factors that drove the evolution of brains big enough to allow us to worry about these ethical dilemmas are thought by some to include the consumption of fish and shellfish and that we later learned to cook meat. Richerman (talk) 00:01, 10 July 2012 (UTC)

Just out of curiosity, what use of leather can't be substituted with something else? Wnt (talk) 00:23, 10 July 2012 (UTC)

I suppose elegant shoes, specially men's ones, have to be of good quality leather. OsmanRF34 (talk) 00:30, 10 July 2012 (UTC)

Quality hiking shoes were her main concern. She moved to Colorado from the east coast due to her love of winter sports. μηδείς (talk) 00:47, 10 July 2012 (UTC)

What about substituting hiking for canasta? 203.27.72.5 (talk) 01:25, 10 July 2012 (UTC)

What in bloody hell would she need leather shoes to play canasta for?

Umm.....if she played canasta instead of hiking, she wouldn't need the shoes, and the cows wouldn't have to die for her hobby. 203.27.72.5 (talk) 03:04, 10 July 2012 (UTC)

The cattle are dying anyway. And the poor canasta plants? Who's thinking about their well-being? μηδείς (talk) 03:41, 10 July 2012 (UTC)

Just got to say to those claiming veganism is extemely radical, you need to check out Jainism, they won't even kill plants or bacteria. Unique Ubiquitous (talk) 01:36, 10 July 2012 (UTC)

They certainly will kill bacteria and various other microorganisms simply by having a functional immune system. 203.27.72.5 (talk) 02:04, 10 July 2012 (UTC)

I assume their religion only requires them to attempt to minimize the deaths they cause, not eliminate them entirely. I'd also assume they put more value on large animals than bacteria. StuRat (talk) 02:44, 10 July 2012 (UTC)

The immune system kills invaders, not the native flora, whose cell numbers outnumber those of your body by ten to one. μηδείς (talk) 02:49, 10 July 2012 (UTC)

Are you absolutely sure that the immune system never, ever kills any of the native flora in the body? I'm pretty sure some opportunistic infections are due to native flora that are normally kept in check by the immune system. 203.27.72.5 (talk) 03:16, 10 July 2012 (UTC)

Ah, yes. Candida albicans is a good example. 203.27.72.5 (talk) 03:19, 10 July 2012 (UTC)

It's biology, not math. Of course there are exceptions. Such organisms are like clonal colonies, in any case, not groups of unique zygotic individuals. The body does not usually kill them off entirely. I am not a Jain, but I would assume the relevant point is that you are not voluntarily going out of your way to kill bacteria which inhabit your body without invitation in the first place.

Well, my point is that regardless of what Jains might say or think or believe, they will kill a variety of things no matter what they do. 203.27.72.5 (talk) 03:44, 10 July 2012 (UTC)

Your italics sound just like my niece. You understand the difference between killing a leaf and killing an entire unique individual plant? Almost all infections are by clones, identical cells, like the leaves of plants rather than individual zygotes. μηδείς (talk) 03:53, 10 July 2012 (UTC)

I note with no little amusement how the supposedly radical vegan manages to justify using leather. It reminds me of something Mark Twain said, in the voice of Huck Finn talking about his aunt, who was always condemning smoking and drinking. "She took snuff, but that was alright, cause she done it herself." ←Baseball Bugs ^{What's up, Doc?} carrots→ 09:12, 10 July 2012 (UTC)

I think you have confused Osman's radical vegan with Medeis' vegetarian ex. AlexTiefling (talk) 09:40, 10 July 2012 (UTC)

I was actually thinking of someone I know who's a "devout" vegan who also smokes cigarettes. Go figure. ←Baseball Bugs ^{What's up, Doc?} carrots→ 14:58, 10 July 2012 (UTC)

What's the problem with that? Cigarettes are not animal products.

For most vegans, their health is at least part of the reason for their dietary choices, which makes such an unhealthy choice as smoking surprising. StuRat (talk) 17:16, 10 July 2012 (UTC)

OK, but there are also enough vegans who are vegans due to ethical reasons. It's not necessarily a contradiction. — Preceding unsigned comment added by 188.76.173.109 (talk) 18:13, 10 July 2012 (UTC)

Most vegans I know smoke all sorts of things that aren't good for their health, and I really don't finding it suprising at all. According to Hippie; "Hippies rejected established institutions, criticized middle class values, opposed nuclear weapons and the Vietnam War, embraced aspects of Eastern philosophy, championed sexual liberation, were often vegetarian and eco-friendly, promoted the use of psychedelic drugs which they believed expanded one's consciousness, and created intentional communities or communes." 203.27.72.5 (talk) 20:12, 10 July 2012 (UTC)

It's ironic that their ethics toward others apparently does not extend toward themselves. I wonder, though, if they got their wish and all "enslaved" domestic chickens were turned loose, how long would it be before canines and raptors had pretty well wiped them off the face of the earth? ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:03, 10 July 2012 (UTC)

Actually, feral chickens do quite well for themselves, although they are not caged layers. μηδείς (talk) 23:43, 10 July 2012 (UTC)

And frankly it's a poor argument for all of the excesses of the meat industry to claim that you really are just concerned with what would happen to all the poor animals if you weren't keeping them in small pens and slaughtering them. It's just not very likely that that's what's keeping you up at night. (I'm not a vegan, but I don't pretend that factory farming is anything ethical.) --Mr.98 (talk) 00:28, 11 July 2012 (UTC)

There's no question that the extreme factory farming that you're alluding to is cruelty to animals. It's a fact of life that every living thing eats and eventually gets eaten. It's good to treat domestic animals as humanely as possible or practical, up to and including the method of slaughtering. ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:58, 11 July 2012 (UTC)

We're definitely out of our league here. If someone wants to ask how it is that humans can think that we can enforce an ethical code on behalf of animals that the animals themselves have never followed toward one another and never will follow, better ask the folks at the Humanities desk... Wnt (talk) 21:32, 11 July 2012 (UTC)

July 10

What is an extended structure?

What is the precise meaning of an "extended structure" in chemistry?

I want to understand "the design and construction of extended structures"[9] in the context of adsorbents. Also "extended solids" seems to be a synonym (used in the title of a paper listed there).

From Googling, it seems to be often used in the context of large complex molecules such as DNA and melanin.

Thanks! --Chriswaterguy talk 00:47, 10 July 2012 (UTC)

Okay, no takers yet...

As far as I can work out (guess, really) it's where a material doesn't have molecules in the usual sense, but a more or less consistent, repeating structure. But that sounds like a crystal: "A crystal or crystalline solid is a solid material whose constituent atoms, molecules, or ions are arranged in an orderly, repeating pattern extending in all three spatial dimensions." That article states that there are crystals with covalent bonds, so it's not that either.

Is it a synonym for crystal, but emphasizing the importance of the structural details? With research into adsorbents, the structure is critically important; with rock salt, the internal structure isn't of so much interest for most people dealing with it. (I suspect there's more to it than this, though.) --Chriswaterguy talk 06:58, 11 July 2012 (UTC)

As far as I can see from the use of the term here and here, it refers to the structure above the unit cell level i.e. how the unit cells stack together. It looks like it would be important when there are more than one unit cell type present, since the way unit cells stack together is generally pretty obvious. From my understanding of what a unit cell is, if there are supposedly different unit cells alternating throughout the structure, then the unit cell has been incorrectly identified, and should incorporate both of the other "unit cells" into one which does simply repeat without interuption. It also seems to have a special meaning in biochemistry. 203.27.72.5 (talk) 07:27, 11 July 2012 (UTC)

Actually, look at the section "Description of crystal structures" here. It basically says that understanding the unit cells as I said above is occasionally insufficient to describe the structure, so then they talk about extended solid-state structures that have multiple unit cell types. 203.27.72.5 (talk) 07:38, 11 July 2012 (UTC)

In the context of surfaces (which I think is what you're looking at since you mention absorbents) it might mean the structure at the surface according to this paper. I suppose in that sense it's the structure "extended all the way to the edge". Here's yet another paper that defines the term in a completely different way - using it to refer to the structure incorporating charge density. From this FAQ I think it just means any rendition of the structure that shows more than one unit cell, even if they are identical and repeating. So, in summary, it means a lot of things to a lot of people even just within the field of chemistry. 203.27.72.5 (talk) 08:07, 11 July 2012 (UTC)

Thank you, that's very helpful! --Chriswaterguy talk 03:08, 20 March 2013 (UTC)

How do ants detect rain long before it arrives?

Topic says it all. ScienceApe (talk) 02:10, 10 July 2012 (UTC)

They can't. No wait, they can. Or can they? 203.27.72.5 (talk) 02:21, 10 July 2012 (UTC)

Phase IV: http://www.youtube.com/watch?v=gcjBIkS-QC4 . μηδείς (talk) 02:34, 10 July 2012 (UTC)

The simplest way, I imagine, would be to detect falling barometric pressure, like a barometer does, to predict bad weather. (This could be done with an air sac exposed to the atmosphere, which would shrink when pressure rises, and grow when it falls. I wonder if they have anything like that.) StuRat (talk) 02:39, 10 July 2012 (UTC)

Who says they can? What would you expect them to do? The black ants on my lawn can't. On the few fine days we've had this summer in the UK they build little towers of fine soil among blades of grass in which they place their pupae only for these to be washed out by a sudden shower. I know it's OR but no less reliable than some of the sites cited above. Caesar's Daddy (talk) 07:27, 10 July 2012 (UTC)

It's true that Lasius niger in the UK don't move their colonies before heavy rain but here in Thailand where the rainy season can be a serious problem for ants, it's commonplace to see entire colonies of what I assume are Paratrechina longicornis with multiple queens emigrate hours before heavy rain, often into your house, or at least off the ground. They neatly arrange the larvae and pupae into piles on higher ground or hold onto them all until the rains have finished. Then they leave. Sean.hoyland - talk 10:05, 10 July 2012 (UTC)

Fascinating, I've never heard of such a behaviour in an ant species that is not generally nomadic by nature. As to the sensory mechanism they use to perceive these oncoming events, I agree it is likely to be barometric in nature, but would not discount some form of hydrometeor perception (specifically, a level of precipitation which is noticeable to the ant well in advance of the rain that we perceive) or even temperature. I do not think an exposed air sac is likely as it is not consistent with any precursor organ or physiological structure I am familiar with in ants and many animals are believed to have barometric perception without the need for such an external feature. It's worth noting that barometric pressure would be an inconsistent mechanism for most species of ant to detect rain on the horizon since most drops in pressure do not herald rain, but in a region like Thailand the correspondence is higher than on average, meaning the mechanism would be more dependable for species living in such a context. Add in the amount of rain involved and it makes sense why these particular ants might have the capability where most others lack it. Snow (talk) 13:00, 10 July 2012 (UTC)

The sac wouldn't need to be external, just have access to external air, say via a pore. Could be like the human ear, with a membrane covering a hole. StuRat (talk) 17:10, 10 July 2012 (UTC)

How can air conditioning units be measured in BTUs?

It makes no sense to me. That's a bit like measuring a car's engine in miles. BTU is a unit of energy. Surely when one decides on an air conditioning unit / heat pump one chooses one with a certain power rating, like watts or BTU per hour or something like that. How does BTU hold any meaning? I can state that a one watt air conditioning unit can produce 100,000 BTU (provided you run it for about 30,000 hours - about three and a half years). 41.164.7.242 (talk) 07:33, 10 July 2012 (UTC) Eon

British thermal unit indicates that "BTU" in that context is used as shorthand for "BTU per hour". ←Baseball Bugs ^{What's up, Doc?} carrots→ 09:07, 10 July 2012 (UTC)

In the developed world we use kW .. :-) Electron9 (talk) 22:46, 12 July 2012 (UTC)

More is needed to evaluate an air conditioner than kw input. A good air conditioner moves more BTU/h than a poor one, with the same kw consumed. Joules output would be ok.those in the heating and cooling trade in the US have long used "tons" to describe cooling units. Edison (talk) 17:03, 13 July 2012 (UTC)

And a car's lifetime, including its engine, is typically measured in miles, at least in the United States. In the same way, aircraft engines are measured in hours of running time. Miles or hours determine the maintenance and replacement intervals. ~Amatulić (talk) 22:58, 10 July 2012 (UTC)

HIV transmission by insect

Are there any proven cases of HIV being transmitted by mosquito bite? Or by any other insect bite? I'm wondering if I'm being told duff information. -- 84.12.35.122 (talk) 08:23, 10 July 2012 (UTC)

Our article suggests that HIV cannot in theory be transmitted by a mosquito bite, because mosquitoes inject only saliva into their victims, not regurgitated blood, and HIV is not present in the insect's saliva. It suggests one potential transmission route: if a mosquito containing HIV-infected blood were to be swatted against someone's skin, the infected blood could enter the victim's body via a scratch or open wound, but it cites no known examples. Wikipedia is not itself a reliable source, but the article does cite sources. The results of a Google search on the question appear to agree that there have been no reliably documented cases of HIV infection via mosquito bite. - Karenjc 08:50, 10 July 2012 (UTC).

On any other insect bite it looks less certain to me. Bubonic plague seems to transmit with regurgitated blood from flea into host for example. Simultaneous infection with Bubonic plague (to cause the regurg) and HIV looks technically plausible? --BozMo talk 10:55, 10 July 2012 (UTC)

Unlikely, given the prevalence of fleas and not a single documented case of this happening. Mind you diseases which display such a pathology/epidemiology tend to be those which have evolved for a long time to exploit exactly that route of transfer. Bear in mind also that HIV does not survive for long outside of the human body, even when it's not being attack by the immune system of another host creature. Also note that flea bites do not usually re-introduce blood when they feed multiple times -- Y. pestis has a particular mechanism for causing the flea to regurgitate the blood during a second feeding, a mechanism HIV does not share. Snow (talk) 13:17, 10 July 2012 (UTC)

How can you document such a thing? There are probably many HIV infected people who cannot spot the origin of their infection and most of us are mostly not aware when we were beaten up by a mosquito, and even, I dare to say, some people die of AIDS without realizing it what is killed them. — Preceding unsigned comment added by Plusanother (talk • contribs) 22:01, 10 July 2012 (UTC)

Well, I wouldn't exactly say that it's outright impossible, just that such a case has never been empirically documented (or even suggested as likely in serious medical literature that I know of, though the potential of the mechanism has been explored nonethless), and that it seem unlikely given what we know about the disease's pathology and the physiology of the two host organisms. Keep in mind that HIV research is a prolific field; if this was happening it's almost certain we'd know about it (and any researcher who proved the existence of the mechanism would be propelled to life-long acclaim). Snow (talk) 00:37, 11 July 2012 (UTC)

I strongly doubt it's documentable, because given the social aspects of HIV transmission modes, there are doubtless many people who will strongly deny the usual routes of infection, but who didn't get it by mosquito. The only way we could find out would be to play with a captive population and HIV-fed mosquitoes, and I doubt we've done that even at Diego Garcia, though you never know any more. Wnt (talk) 21:28, 11 July 2012 (UTC)

Hmm, mosquito bites can transmit other viral diseases, such as dengue fever and malaria, so I'm wondering why it's so implausible that HIV can't possibly be present in mosquito saliva. ~Amatulić (talk) 23:04, 10 July 2012 (UTC)

Dengue fever and malaria are caused by protozoans which actively move into the saliva. μηδείς (talk) 23:42, 10 July 2012 (UTC)

Wrong about dengue, which is viral, was thinking of Chagas' disease. μηδείς (talk) 00:43, 11 July 2012 (UTC)

There are two layers to answering that question. First there's the proximal explanation of the mechanisms (as referenced above). But to address the issue more broadly and in terms of pragmatics, there's the explanation that the virus already has a perfectly suitable (and, unfortunately, highly efficient) mechanism for propagating itself. While technically not a living organism (depending on your definition), a virus does have a kind of evolutionary course, and each has adapted to operate in highly specific context. The balance the HIV virus has struck does not (at present) allow it to survive outside the human body for long, nor to exploit routes of infection which do not involve human-to-human contact. Developing such traits would likely require significant trade-offs for the disease which, given it's current virulence and tenaciousness, are not necessarily beneficial to it. Snow (talk) 00:48, 11 July 2012 (UTC)

So why is it so easily transmitted through sharing used needles and blood transfusions? 203.27.72.5 (talk) 00:55, 11 July 2012 (UTC)

Those are very intimate routes of transmission protected from exposure to oxygen which rips apart the viral coat of HIV almost immediately. Mosquito saliva also has anti-coagulants and digestive enzymes which destroy the virus. μηδείς (talk) 01:06, 11 July 2012 (UTC)

If HIV is destroyed on contact with oxygen, shouldn't it be destroyed in vivo as your blood passes through the lungs? 203.27.72.5 (talk) 01:22, 11 July 2012 (UTC)

Well, individual virions are constantly being destroyed by the regular metabolic processes of the body (as well as by the immune system, even in the case of AIDS), but their numbers are such that they can weather these storms, sometimes even laying relatively "dormant" in certain tissues (nervous tissue is particularly susceptible to certain viruses, for example) and then re-amassing themselves as the opportunity presents itself. Snow (talk) 01:34, 11 July 2012 (UTC)

And the transmission of infected blood of one individual into the bloodstream of another tends to be more immediate and consist of markedly larger amounts. On top of all of this, mosquitos rarely need more blood than they can consume in a single feeding; in most cases they use it to drive egg fertilization and engage in such feeding only as necessary (though some more aggressive species do use it as a more consistent means of sustenance). Snow (talk) 01:29, 11 July 2012 (UTC)

Large amounts of the virus are actually destroyed in vivo, but the blood is a buffered, supportive environment (ignoring the immune response) and keep in mind that oxygen in the blood is largely bound by hemoglobin. Also, as I said elsewhere, biology is not math, and there are exceptions. It is entirely possible HIV may have been transmitted by insect bite, just unlikely and impossible to prove after the fact. Would anyone like to volunteer as a test subject? μηδείς (talk) 01:36, 11 July 2012 (UTC)

Is it so unlikely that it's not worth doing an experiment with simian immunodeficiency virus , a couple of chimps and several hundred mosquitos? There's also this link for anyone who's interested. 203.27.72.5 (talk) 02:14, 11 July 2012 (UTC)

There is an infinite difference of scale between the yes-or-no possibility and the almost-zero likelihood of something happening. You pay me enough, I will indeed get a mosquito to infect a chimp with SIV. But if the prospect of dying of AIDS from a bugbite actually frightens you you might as well go on benzodiazepines to prevent yourself from dying of a meteor strike. μηδείς (talk) 02:33, 11 July 2012 (UTC)

Nah, the word of the CDC is good enough for me. I was just interested in the whys and hows of it all. 203.27.72.5 (talk) 04:43, 11 July 2012 (UTC)

There is no obvious reason why it would be absolutely impossible for someone to get a bit of HIV infected blood from a mosquito or tick into a scratch and catch the disease. Mosquitoes and ticks obviously have large dollops of blood in them, which could include various pathogens. The CDC says that one unit of HIV might get transmitted in 10 million mosquito bites. It isn't clear whether the "1 unit" is enough to cause an infection, but how many millions of mosquito bites take place each year? Maybe a billion in the US, if each person gets bit 3 times. But few of the mosquitoes would have had a previous partial meal on an infected person. Insect-born pathogens were shown to be the cause of numerous diseases of people and animals, but typically in models where the pathogen survives and fluorishes in the mosquito, unlike HIV. West Nile is transmitted by skeeters who have previously bitten an infected animal, and I would be much more concerned about getting West Nile from a mosquito bite. There might be a reason for governmental authorities to poo-pooh any possibility of HIV infected blood getting carried to infect a victim who gets bitten by the insect, or who swats a blood-filled insect and it enters the bite or some other scratch, since if the small possibility were shown to exist, people might demand that HIV infected persons have to dwell far away from uninfected persons. Combine a small likelihood of insect transmission, and the societal harm from restricting HIV infected persons to something like leper colonies on a remote island, and you could get unwarranted denials."Trust me, I'm from the Government and I'm here to help you" just does not resonate with credibility for many people. Edison (talk) 20:30, 11 July 2012 (UTC)

For extremely good reason. The Government, being run by big business, does not help anyone other than its own constituent bourgeoisie. Whoop whoop pull up ^{Bitching Betty | Averted crashes} 21:15, 11 July 2012 (UTC)

While they might not be always 100% truthful, they are here to help. Edison even pointed out that the only reason for downplaying the truth is to strike a balance between the "likelihood of insect transmission, and the societal harm from restricting HIV infected persons to something like leper colonies on a remote island". If the CDC says it's not worth worrying about, I'm not going to worry about it. But for interests sake I wanted to know just how unlikely it was. 203.27.72.5 (talk) 22:03, 11 July 2012 (UTC)

There probably is a risk of insect being a vector transmission path. The problem is how to scientifically document a transmission mechanism with low probability, long (10y) incubation time, and where the victim may not even beaware of the insect bite in question, nor would any experiment be ethical. As for the truth factor in authorities, just consider that they have other priorities than yourself! Take rather a look at the mechanism involved rather than any "we know better" from authorities. Kitchen knifes and salads is another path. Heard of any restaurants with guaranteed HIV free staff lately? So: does the blood sucked up by the mosquito present an infection risk (for HIV)?, can it be pushed into a person be smacking it? can viruses migrate from the blood into the saliva? Any data where the number of viable viral particles is measured would be interesting. And can't be THAT hard to establish. Then probabilities can be calculated. Electron9 (talk) 00:25, 12 July 2012 (UTC)

Well, it's not as if the issuehasn't been studied. (Those are just a few amongst scores that treat the issue that I found in a cursory search). You're quite right that incubation periods often muddle the issue some for any disease, but that doesn't researchers can't determine a given vector as impossible for a given virus based solely on what they do know about the pathophysiology involved. Or even on strong epidemiological evidence; one of those examples I included in this post points out that if mosquito were capable of transmitting the disease then you wouldn't see as striking a trend on the age-range of new infections -- barring infections by transfusion and mother-to-child, almost all new cases excluded the very young and the very old, for obvious reasons, but if mosquitos were transmitting the disease, their dispersed selection of targets would not allow this to be the case. Now, this might not be satisfying to those who might argue that it could still have happened just a handful of times, but puttign together statistical evidence (bearing in mind the massive numbers involved) and a number of different findings as regards the pathology of the disease and the physiology of the carriers, it's about as certain as anything gets in medical science. As to the disease being transmitted by someone prepping a salad, that's obviously unrealistic and if there are indeed kitchens that go out of their way to not hire personnel with HIV, and then are foolish enough to advertise the fact, you can probably expect to see some discrimination lawsuits on the matter in the near future (and the plaintiffs will almost certainly win too, if we're talking about any country in the English speaking west here). Even if you meant that the HIV-infected individual cut themselves then I still don't see it happening. First off, consuming anything less than ounces of infected blood is probably not likely to cause infection (unless you had a large open cut in the mouth or somewhere else in the upper digestive tract). Second, its unlikely a salad with any amount of blood on it is going out to a customer and three -- don't eat your salad if it comes with blood on it! Snow (talk) 09:28, 12 July 2012 (UTC)

What about a HIV positive teppanyaki chef? 101.173.170.146 (talk) 10:47, 12 July 2012 (UTC)

Hah! Well, if your teppanyaki chef is stabbing himself, you're taking your life into your own hands being so close to him regardless. Snow (talk) 12:11, 12 July 2012 (UTC)

Actually, those references you cite have a case of mumble. "Extremely low or nonexistent", "extremely unlikely", aren't actually answers as to whether one case has ever occurred. They're practical answers for everyday living; still, if you run into someone who claims to have experienced an Immaculate Infection, they deserve to be given the benefit of the doubt. Because it's biology, and you never really know. Speaking of which, if a chef serves up his own testicles, [10] even if properly cooked, what are the odds that a piece of viral RNA or integrated DNA can become transfected into a vulnerable epithelial cell. Hmmm.... (but then again, he wasn't in one of the risk groups! Wnt (talk) 13:26, 12 July 2012 (UTC)

Hard facts would be for each mg of blood sucked up by the mosquito there is N number of infectious viruses. And the same number for the saliva. Then a probability for N number of viruses to cause an infection. No need for transmission experiments, except for letting one mosquito to suck. The rest just lab work (BPL-4?). Electron9 (talk) 22:43, 12 July 2012 (UTC)

Things with vanishingly small probability do happen from time to time, like someone a few years ago surviving a rabies infection, or a full term baby delivered healthy from an ectopic pregnancy, or a train derailment recently in Illinois causing a train and railroad bridge to fall on a couple driving under the bridge in their car, killing them, or someone winning the lottery twice, or a girl getting HIV from a dentist's drill, or a 5 year old girl, Lina Medina, giving birth to a healthy baby. In the case of the OP's question, it would likely take experiments with simians and infected mosquitoes, similar to the experiments proving mosquito transmission of Yellow Fever, but public policy issues as outlined above would likely prevent any researcher getting government funding for such iron clad research, and we are left with probability calculations and poo-poohing by the government. If someone claimed they got HIV from an insect bite, no one would believe them. It would be like a girl claiming she must had gotten pregnant from sperm in the public swimming pool, or got VD from a toilet seat. Edison (talk) 20:19, 12 July 2012 (UTC)

Oh Japan, what are we ever going to do with you? The best part of that article has got to be the reporter wearing a surgical mask and a dazed expression that seems to say "Where did my life take this turn? I was supposed to be a journalist..." or maybe "Really!? we're doing this now? I've gotta get that work visa." Heh. Snow (talk) 20:41, 12 July 2012 (UTC)

Evolution of the four fundamental forces

I seem to recall there was a section in my physics book that gave a timeline of when the four forces evolved. Which came first, and when, etc. Is there any article here that gives a timeline? ScienceApe (talk) 11:44, 10 July 2012 (UTC)

Chronology_of_the_universe#Very_early_universe ? --BozMo talk 12:10, 10 July 2012 (UTC)

The "orthodox" sequence is that gravity separated first, followed by the strong force, and finally the weak force separated from the electromagnetic force when the Higgs mechanism gave rest mass to W and Z bosons but not to photons - see this timeline. But as of now only the final one of these three phase transitions is understood in any detail - different sources give different answers about the timing and mechanism of the first two, with varying amounts of speculation. And if you add supersymmetry breaking to the mix, that complicates the picture even more. Gandalf61 (talk) 12:15, 10 July 2012 (UTC)

Infant eye glasses

I know that with toddlers who can at least talk, they do vision tests with symbols of things like boats and houses, but I've seen infants barely able to crawl with glasses. How can doctors ascertain the visual acuity of someone who can't tell you what they're seeing because they haven't acquired any language higher than "bbbbb whaa whaa abababa"? 20.137.18.53 (talk) 12:16, 10 July 2012 (UTC)

The glasses could be used to correct a squint: NHS link. Brammers (talk/c) 12:51, 10 July 2012 (UTC)

It is possible to measure the roundness of the eyeball using modern equipment. This will indicate astigmatism, which can bee corrected using glasses. --TammyMoet (talk) 13:53, 10 July 2012 (UTC)

There is an instrument called a “Retinoscope” which we use to shine a light into the toddler’s eye from a distance of about 17 inches. We can interpret the reflection that comes back from the back of the toddlers retina into the pupil area. As we move the instrument from side to side, the reflected light we are watching will move either in the same direction as our instrument or in the opposite direction. This tells us whether we are dealing with nearsightedness or farsightedness. The speed of motion of the reflected light is an indication of how much prescription power will be required. In a seasoned practitioner’s hands we are able to very precisely determine how much and what power is required without asking the toddler a single question. We do the same with adults who can’t communicate or are illiterate or can’t speak the same language, as in third world countries where in some instances on field trips no communication is possible at all. It’s pretty neat. Dr. Dhavid Cooper DriveByWire (talk) 14:18, 10 July 2012 (UTC)

The illiterate part doesn't make sense. At the eye doctor, they never actually ask me to read the letters, in any case, they just ask which is clearer. Now, when I get a driver's license, then I have to read the letters, because there they want proof that I can see clearly, but even there, they could substitute symbols like houses and dogs and ice cream cones. As far as people who don't speak the language, all they need to communicate is "better" or "worse", which could be a thumbs up and thumbs down. StuRat (talk) 16:55, 10 July 2012 (UTC)

Going back over 20 years when I was an adult literacy tutor, I taught a young man who wore bottle-end glasses but who still couldn't see you unless he stood right up close to you. He was more or less unable to read, and over about 18 months we worked on that. One day he walked in to class with new glasses, which were much thinner, and he didn't stand right next to me. What had happened was that he'd finally been able to read the letters and texts the optician had been giving him during his eye test, and the prescription was exactly what he'd needed - for the first time ever. --TammyMoet (talk) 19:01, 10 July 2012 (UTC)

If his eye doctor had simply asked when it looked clearer, rather than ask him to read the letters, the whole problem could have been avoided. It seems that some eye doctors need to be retrained. I suspect that, to avoid embarrassment, the student had faked being able to read, and, once he guessed the letters correctly, continued to say them that way, even as they got blurrier with stronger lenses. The eye doctor should also switch the letters used at each increment, if asking people to read them, to avoid such deception. StuRat (talk) 19:10, 10 July 2012 (UTC)

Tammy has pulled your leg, Stu. Quite apart from the fact that anybody with even half a brain would sooner or later, and most likely very much sooner, discover for himself whether the prescribed specs were right (if like me, you need a different prescription for reading than for distance, you probably do what I do - if I am reading and want to look at a clock some distance away, I just hold my reading specs a couple of cm forward off my nose - that changes the effective power by about 2 diopters and matches my distance prescription), the optometrist would have had to be a complete moron. Usually they check by homing in on the correct prescription from different directions. If you give wrong answers (as naughty children sometimes do) they soon detect it. Whenever I have had my eyes checked, the optometrist has first used a retinoscope to quickly get a rough idea, then uses the big-E chart to fine-tune.

I must correct some misconceptions however. It is not sufficient for the optometrist to ask "which is clearer?" The preception of what is clearer can differ from that which is best read. The patient may have the impression that the letters on the chart are their clearest, yet a small change in lens power of cylinder axis may improve his accuracy in reading the letters, particularly if he is getting specs for the first time. Usually what they do is ask "Which is better - first or second? (changes setting, pauses, changes setting back again) second or first?". then as it gets pretty good, they change to asking "Please read the 2nd last line." or similar. Then they distract you, change setting again, - and what do you know, one of those fine print letters seems to have changed!

Also, just because someone you know suddenly rocks up with lenses noticeably thicker or thinner, it DOES NOT necessarily mean they have radically changed prescription. It could be that he/she has changed to lense material of different refractive index. Spectacle shops these days tend to push the newer high-index lenses for cosmetic reasons, but the high-index materials have poorer colour dispertion. Wickwack60.230.208.161 (talk) 02:37, 11 July 2012 (UTC)

When you talk about "eye doctors", are they optometrists or opthamologists? 203.27.72.5 (talk) 22:10, 10 July 2012 (UTC)

Presumably an optometrist, if his only vision issue was that he needed glasses. StuRat (talk) 02:15, 11 July 2012 (UTC)

Infants are resolute about throwing off eyeglasses that do not help their vision. DriveByWire (talk) 14:20, 10 July 2012 (UTC)

I'm betting an infant would also throw off a pair of glasses frames with no lenses at all just because the plastic is touching their temples. 20.137.18.53 (talk) 17:57, 10 July 2012 (UTC)

They don't throw off glasses that let them see properly, when they couldn't previously, in my experience. It's kind of amazing to watch, because you'd expect them to not tolerate something on their face like that, but clearly if their vision is bad enough they are just pleased to be able to see properly.

Also, Wickwack, opticians aren't always so good at spotting the naughty children. I knew a child who lied on their eye test to get glasses (this soon came out after the novelty wore off). She was a particularly bright child, so maybe she gamed the eye test particularly well? But then I also know a naughty child who deliberately showed up to a school eye test without their (powerful) glasses on, so that the optician got very excited about how this child had slipped through the net, and the child's parents got a very strange letter home. Perhaps I know unusually determined naughty children? 86.164.62.161 (talk) 02:31, 14 July 2012 (UTC)

You can just compare their reactions without needing them to speak. If they ignore a toy, they probably can't see it clearly enough to realise it is something interesting. So you change the lenses until they show interest in the toy, at which point you know they can see it. --Tango (talk) 15:03, 10 July 2012 (UTC)

What's the street value of testogel?

Testogel, which I will not link as it is merely a redirect, is a form of testosterone that comes as sachets of gel, the idea being that someone with low testosterone can apply it to themselves. It is prescription medication meant either for hypogonadism or for FtM transexuals.

However it could also be used by body builders as it is an anabolic steroid. What is the street value of a pack of 30 x 50mg sachets of it? Egg Centric 13:37, 10 July 2012 (UTC)

Where are you? Is the purchase you ask about illegal? DriveByWire (talk) 14:26, 10 July 2012 (UTC)

I'm not interested in making any purchase - or indeed making any sale. I am legally prescribed testogel and being on the isle of man it costs me £3.65 a month (as any prescribed drug does). I was just interested in what the street value of it is as I enjoy boasting about that sort of thing in pubs (I am also prescribed another drug that has a much higher street value, incidentally, but that is irrelevant to this question). Egg Centric 17:38, 10 July 2012 (UTC)

You can order steroids legally via US webshops. Count Iblis (talk) 15:29, 10 July 2012 (UTC)

It's a bit hard to accurately assign a street value, even for a given location. A crack head that wants it might not be able to pay much of anything, or might offer a stolen stereo, whereas the token party-girl rich lawyer's daughter might pay a few quid, not realising that it can be so easily obtained legally. Oh, and purely out of interest, is yours prescribed for hypogonadism or FtM transexualism? 203.27.72.5 (talk) 22:02, 10 July 2012 (UTC)

It's just me or do other people also find it funny that the OP is on the Isle of Man? Plusanother (talk) 00:04, 11 July 2012 (UTC)

Surely 84,000 dooinneyyn(?) all have to be somewhere. That's not including Moddey Dhoo who can chase a greater number of cats than available tails. DriveByWire (talk) 15:13, 11 July 2012 (UTC)

Mick Jagger (a popular singer m'lud) has called for all drugs to be legalised on the Isle of Man. It seems that Narcotics Anonymous meetings are held at St. Joseph's Catholic Church, Douglas, Isle of Man. DriveByWire (talk) 22:29, 10 July 2012 (UTC)

Domestic wiring

I formatted this as a new question. DriveByWire (talk) 14:24, 10 July 2012 (UTC)

Which wire is used in domestic wiring? — Preceding unsigned comment added by Nikhilbdvg (talk • contribs) 14:17, 10 July 2012 (UTC)

Depends on the load and the local electrical code. In the U.S. most common is 3-wire 14 gauge for 15 amp circuits. You also see 12 gauge for 20 amp circuits for heavier loads (large appliances, a/c, etc.) Rmhermen (talk) 14:34, 10 July 2012 (UTC)

There are various kinds of domestic wiring. Suggest you read the article.--Shantavira|^{feed me} 15:40, 10 July 2012 (UTC)

'Non-metallic-dry' or NMD is the common wire used for woodframe in Canada. Most only count the insulated conductors though so 14/2 NMD would be 14 guage, (15 amp), black, white and bare ground. 14/3 has a red. Don't use heat trace cable though. I heard about a guy that stole a bunch of wire from work and wondered why is walls got warm and none of his stuff worked very well.--Canoe1967 (talk) 18:29, 10 July 2012 (UTC)

Why wasn't there fusion in the early evolution of the universe?

The strong nuclear force existed only a few fractions of a second after the Big Bang, and only a few fractions of a second later protons formed. So what was stopping the universe from undergoing fusion at around this time since presumably the required heat and pressure was present? 148.168.40.4 (talk) 16:01, 10 July 2012 (UTC)

According to the article, most helium-4 in the universe is thought to trace back to fusion "shortly after the Big Bang". See Big Bang nucleosynthesis. From 3 to 20 minutes after the Big Bang, protons and neutrons were stable, but fusion was still possible. Wnt (talk) 16:11, 10 July 2012 (UTC)

Too much heat and pressure was present. It's basically the same reason why million-degree-Celsius steam does not condense into ice. Looie496 (talk) 16:13, 10 July 2012 (UTC)

Wnt is right. There was fusion during the Big Bang nucleosynthesis. 203.27.72.5 (talk) 21:57, 10 July 2012 (UTC)

Yes, but, as Wnt said, not until around the 3 minute mark. The OP was asking about fractions of a second after time zero. The answer is that it was simply too hot for fusion then -- if anything fused together for an instant, something would slam into it and break it apart an instant later. Looie496 (talk) 22:58, 10 July 2012 (UTC)

It's an interesting question, and I don't really know enough to answer. But my understanding from the article is that first the quark-gluon plasma cooled down, but even then proton-antiproton pairs were being produced spontaneously at 10^-6 second, maybe later. So you don't have the situation where a cooling quark-gluon plasma would spit out intact iron nuclei because they're the most stable degradation product; they'd get hit instantly by antiparticles (indeed, almost always would contain antiparticles...) and be blown apart. At the latest point, right before the pairs stop being produced, there should only have been enough energy to make single nucleons, not alpha and anti-alpha pairs and such. After that, Looie's answer applies. I assume three minutes is when there was too little energy left to knock helium atoms apart, and twenty was when there was too little left to knock them together. (For comparison, consider how high temperatures favor production of nitrogen oxides, and lower but not too low temperatures resolve them to nitrogen and oxygen in a catalytic converter) Wnt (talk) 13:17, 12 July 2012 (UTC)

Electromotive force in an unclosed circuit

Even if an electric circuit is unclosed, the source of voltage continues to work — and the energy that would move the charges in the circuit, had the circuit been closed, is still there.

What resists the emf in an unclosed circuit? Intuitively, the gap in the circuit can be viewed as a resistor with infinite resistance that would imply infinite energy loss, had the current not been zero. But Ohm's and Joule's laws are abstractions. What's their physical sense at the ends of the gap, in terms of individial charge carriers (e.g. electrons)?

And what happens in the circuit, in the immediate vicinity of the gap, in the first moments after it is closed (e.g. by connecting wires or flipping a switch), enabling the flow of current? How do the charges flow and how does the information that the circuit was closed propagate from the gap to the circuit as a whole? - Sikon (talk) 16:53, 10 July 2012 (UTC)

Close circuit: electrons bounce back. Open circuit: electrons stop bouncing back. 188.76.173.109 (talk) 18:16, 10 July 2012 (UTC)

The free electrons have nowhere to go, so stay in the wire, until connected to another wire, then they flow into it. The charge in the wire (modeled by the percentage of free electrons) is equal to that of the source, say the battery terminal, so all flow stops. StuRat (talk) 18:25, 10 July 2012 (UTC)

At the level of the electrons, its best to analyse the situation using electric potentials and the "lines of force" along the gradient of the potential. The electric potential at a point is a measure of the energy at that point due to electrons and protons around it attracting and repelling any charge placed there. In a conductor like a metal, if no current is flowing, the potential all over its surface is the same; the electrons which are free to move jostle around so that no point is more crowded than another.

When a switch is open, the two metal contacts are at slightly different potentials - one is more crowded with electrons than the other. However, the electrons are bound to the surface of the metal (because of the metal nuclei) and it takes some energy for them to escape -either as free electrons or by jumping onto the air molecules and forming ions. If the voltage (electron overcrowding/shortage) is low enough, no electrons can escape from one surface to another. If the voltage is sufficiently high some of them will break out of their bonds and move between the metal and the air molecules. These air ions will zoom away from the metal surface, gaining speed as they are repelled and smash into more air molecules as they go to the other metal surface. In short order you will have a white hot stream of ions and electrons tearing across the gap. This is a spark.

As soon as the gap is closed, electrons from the more crowded side flow into the less crowded metal. (The electric field from these new electrons travels to all corners of the universe at the speed of light. But this field of course dies of as 1/distance-squared with the constant of decay depending on dielectric shielding by things in the way.) These electrons push the electrons around them, who in turn push the electrons around them and so on, letting the electrons at the far end of the wire flow out. In most wires, the electrons are packed so tightly and can move so rapidly that the effect is instantaneous. The time taken for the bunched-electron wave of information to travel down a line can be significant if you turn the switch on and off fast enough- for example in radio transmission.Staticd (talk) 19:01, 10 July 2012 (UTC)

We answered a similar question about Surface charges on an open circuit recently. DriveByWire (talk) 21:45, 10 July 2012 (UTC)

What causes a material to reflect light and why does light travel slower through matter than vacuum?

• What causes some materials to reflect light (metals for example)?
• What causes different materials to have different refractive index (i.e. light waves travel at different speed through it)?

85.230.137.182 (talk) 18:46, 10 July 2012 (UTC)

The article Refractive index gives a microscopic explanation of the slowing of light. DriveByWire (talk) 21:52, 10 July 2012 (UTC)

Light speed is around 186,000 miles per second in a vaccuum, or some such. I wonder, what is the slowest speed that light has ever been measured - and whether it's possible to slow it down even more. ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:59, 10 July 2012 (UTC)

See slow light. 203.27.72.5 (talk) 23:07, 10 July 2012 (UTC)

That's a different kind of slowness than the refractive-index aspect. DMacks (talk) 03:09, 11 July 2012 (UTC)

Not being a scientist, I didn't totally follow the article, but it basically answered my question. ←Baseball Bugs ^{What's up, Doc?} carrots→ 05:50, 11 July 2012 (UTC)

There is a touching story about a scientist who invented a slow glass through which light takes over a year to pass. He tested panes of the glass in his house and afterwards spent many days in the garden, occasionally looking up and waving. The explanation is that his wife had died the previous year. DriveByWire (talk) 14:33, 11 July 2012 (UTC)

That sounds like Light of Other Days by Bob Shaw. Gandalf61 (talk) 14:49, 11 July 2012 (UTC)

The reflection in a metal is basically because it conducts electricity. The electromagnetic wave in the light causes electric current to run on the surface of the metal. An electric field cannot exist parallel to the metal surface, and yet the light wave would normally have one. The net result of this is another light wave that bounces off in just the right direction for a reflection with the phase altered to cancel out that electric field. Graeme Bartlett (talk) 08:26, 11 July 2012 (UTC)

That sounds utterly wrong to me. I'm pretty sure that EMR does not induce a current in metal that it is incident on. This would also imply that all conductive materials are reflective, which they aren't. And what's so special about the visible spectrum in all of this anyway? Why should x-rays not induce a current in metals and reflect throught that mechanism if visible light does? 101.173.85.81 (talk) 09:26, 11 July 2012 (UTC)

Certainly currents are induced (in a perfect conductor, they are only surface currents); see also penetration depth. The visible spectrum is special because at higher frequencies the electric currents induced fail to precisely match the phase of the incident radiation, so absorption results instead; see also plasma frequency. --Tardis (talk) 13:20, 11 July 2012 (UTC)

Specular reflection#Explanation and Fresnel equations. DriveByWire (talk) 14:40, 11 July 2012 (UTC)

See the article on Plasmons--78.150.236.161 (talk) 19:52, 11 July 2012 (UTC)

Mysterious behavior of high-speed projectiles

Is it possible that a bullet (gun-shot) fired from a high-velocity rifle (say M-16 etc.) instead of entering the human head, orbit around it, breaking it's move-in-a-straight line rule and enter the skull from back side (opposite side , not available to gunner ) i.e. changing it's course of movement. If yes, then what laws of physics make it possible ? 124.253.91.183 (talk) —Preceding undated comment added 21:27, 10 July 2012 (UTC)

Unless the gun is actually firing very small, maneuverable rockets, no. What made you ask the question? Someguy1221 (talk) 21:32, 10 July 2012 (UTC)

I know it sounds idiotically strange ! I am asking this question because it has happened... — Preceding unsigned comment added by 124.253.91.183 (talk) 21:38, 10 July 2012 (UTC)

If so then you have already answered your own question "Is it possible....[?]". The article Orbit equation gives the physical laws that govern a gravitational orbit. I think it impossible to satisfy them with practical values for the bullet mass, head mass and bullet tangential velocity. The value of Escape velocity would surely be exceeded. Might the incident have actually been an accident with a Boomerang? DriveByWire (talk) 22:11, 10 July 2012 (UTC)

The 5.56 NATO round fired by AR-15 family rifles was known as the tumbler during the Vietnam war due its strange terminal ballistics. After striking flesh the bullet would move in counter-intuitive directions leading to exit wounds where you wouldn't expect them. A vet once told me a story about seeing a dead VC with a single entry wound near his navel, and a single exit wound near his collar bone. 203.27.72.5 (talk) 21:53, 10 July 2012 (UTC)

Intriguing. Do you happen to have a source or remember if they determined the compositional elements of the rounds that caused this uncommon ballistic profile? I'd be very interested in studying the issue since our current article on the round does not make mention of it (though it does note an unusually high degree of fragmentation for the round's mass and profile). Was the issue prevalent with regard to the M-16 or particular firing modes? Snow (talk) 00:18, 11 July 2012 (UTC)

No reliable sources, but here is a forum thread that basically confirms the same story my vet friend told me. As the posters note, having the centre of mass towards the rear increasing the chance of tumbling on contact with a medium denser than air. 7.62x39 are even worse. They often start to tumble end over end without impact with anything. You know this is happening when your bullet holes look like this. 203.27.72.5 (talk) 00:46, 11 July 2012 (UTC)

Thanks for the link (and actually there does seem to be some decent literature linked to there). And yeah, that explanation seems consistent with the yaw and accuracy issues that are noted on our 5.56 NATO article. I wonder how much the tumbling itself contributes to the fracturing or if they are better characterized as both the result of the round's center of mass. I'll peruse the literature and see if I can't find a way to note this behaviour as a brief mention in the relevant articles. Thanks again! Snow (talk) 01:03, 11 July 2012 (UTC)

I suspect that you are merely confusing the entrance and exit wounds. While, typically, the entrance wound is smaller than the exit would, that's not always the case. StuRat (talk) 22:08, 10 July 2012 (UTC)

That sounds like an element of a conspiracy theory, namely one related to the JFK assassination. Plusanother (talk) 22:07, 10 July 2012 (UTC)

A bullet found on Connally's hospital gurney, and two bullet fragments found in the presidential limousine, were ballistically matched to a 6.5 × 52 mm Italian Carcano M91/38 bolt-action rifle found on the 6th floor of the Texas Book Depository. The M16 fires a different 5.56×45mm cartridge, and there were not many M16's around on November 22, 1963. Obviously the existence of an M16 bullet that can fly backwards in space and time, and leave no trace, is exactly the kind of secret that a conspiracy of the CIA, the KGB, the American Mafia, the Israeli government, FBI director J. Edgar Hoover, sitting Vice President Lyndon B. Johnson, Cuban President Fidel Castro, anti-Castro Cuban exile groups and the Federal Reserve won't reveal. DriveByWire (talk) 22:46, 10 July 2012 (UTC)

You forgot the Rothschild and Rockefeller families and the Bilderberg Group. They are into this too, pushing the ropes from behind the scene. Plusanother (talk) 23:09, 10 July 2012 (UTC)

I've talked about gunshot wounds with a lawyer at some length, some time ago, and one point he emphasized rather emphatically is that bullets can behave extremely unusually once inside the human body. It's not weird physics, it's the fact that ammunition does not always have sufficient force to break out of the body at all points, and will hit various hard and soft things inside the body, and can do weird things like follow bones (get shot in the arm, exit wound out the leg, was one example the lawyer had seen). No weird physics there — just chaotic movement and complex systems. So, just a priori, I wouldn't rule it out, though it doesn't seem especially likely. But given enough gunshot wounds... --Mr.98 (talk) 00:23, 11 July 2012 (UTC)

There's also a simple ricochet, where the bullet could bounce off an object behind the target, say a tree, and hit the target from the rear. This could be the entire bullet, or just a fragment, if it shatters when hitting the first object (more likely if it first hit a rock). StuRat (talk) 00:29, 11 July 2012 (UTC)

Mystery solved? In all seriousness, OP, this behaviour is inconsistent with the basic physical principals we'd expect to be at work here - as noted by others above, the gravitational influence of the mass of the head upon the bullet would be miniscule compared to its forward velocity of the round -- nor could atmospheric resistance account for such a radical arc in said trajectory. Snow (talk) 01:16, 11 July 2012 (UTC)

Weirder yet was the soldier that got shot though his privates during the civil war. The musketball carried on and hit a female civilian in the abdomen and she got pregnant from it. I think they got married after the war when they figured out what happened.--Canoe1967 (talk) 15:50, 11 July 2012 (UTC)

Never happened. Someguy1221 (talk) 16:02, 11 July 2012 (UTC)

It did happen, it was Dilbert, a robot, a cow, and some aliens, though. μηδείς (talk) 16:34, 11 July 2012 (UTC)

But wasn't Dilbert getting shot at from the rear anyway? [11]--Aspro (talk) 23:03, 11 July 2012 (UTC)

I saw a murder trial in which someone killed a man with two shots to the head from a 32 caliber pistol. One round entered under the scalp on the side of the head, and tunneled around from the side of the head to the back of the skull, where it lodged in the neck muscles, but unlike the OPs incident, it did not proceed to break through the skull in the back, but at least it ended up in the right spot to do so if it still had sufficient velocity and tumbled the right way. Edison (talk) 20:18, 11 July 2012 (UTC)

July 11

Dangerous Good Classification

I've been asked to determine the amount of soluble lead in a mixture of minerals in order to work out its Dangerous Goods Classification. The method is predefined and straight forward, but I'm trying to work out for my own interest how the results of this test enable us to classify the mixture. I'm told that if the concentration of soluble Pb exceeds 5% of the dry mass, then the material is a Class 6.1: Poison. But that class is actually defined as having an oral toxicity of equal to or less than 200mg/Kg in an animal. So I don't see how the 5% number is anything more than an arbitrary cut off. Does anyone have any idea how this works, or better yet actual experience with classifying class 6 dangerous goods? 203.27.72.5 (talk) 04:39, 11 July 2012 (UTC)

Well, the higher the percentage of lead, the less you'd need to consume to be poisoned. Presumably more toxic substances would be considered poisonous in lower percentages, so the total amount you would need to consume to be poisoned is the same in both cases. I'm not sure why they chose 5%, though. They must have some idea in mind of how much a person (a toddler, a person with pica, etc.) might reasonably consume. StuRat (talk) 05:47, 11 July 2012 (UTC)

It's not lead as such though. It's soluble lead. Total lead doesn't even come into it (and it's well over 50% for many of these materials). Is there a known LD50 of "soluble lead" of around 10mg/kg? 203.27.72.5 (talk) 05:55, 11 July 2012 (UTC)

Looking at a variety of material safety data sheets, it does seem that the LD50 for aqueous lead is ~10mg/kg in rodents. The precise number varies wildly depending on precisely how the lead has been solubilized. The most lethal forms of lead appear to be those bound to organic compounds. Acute LD50s are missing from MSDSs for simple lead salts, although they include doses that cause illness over time, which is actually quite low. Someguy1221 (talk) 07:41, 11 July 2012 (UTC)

Can you tell me what compounds you're refering to so I can look up the MSDSs? This is most definitely an inorganic lead species, most likely a mixture of PbS, PbSO4 and maybe some oxides. 101.173.85.81 (talk) 09:22, 11 July 2012 (UTC)

Heavy metals accumulate in tissue, so you can't use LD50 here. "CDC considers a blood lead level of 10 μg/dL to be a level of concern for children. EPA limits lead in drinking water to 15 μg per liter."[12] This is not medical advice. You should consult a trained professional toxicologist for your question. 71.212.249.178 (talk) 17:03, 11 July 2012 (UTC)

Actually telling the poster how to categorize a good for shipping isn't medical advice, it's legal advice - still, unfortunately, beyond our purview. However, it sounds like the OP is asking for an explanation of the reasoning behind this rule, not help in figuring out and applying it. My assumption is that the 5% figure is by weight, and so the rule tells you how much soluble lead there is in a given weight shipped. If what's being considered is how much lead will leach into the soil around a crash scene if firefighters hose down the burning package, then I suppose that's sort of reasonable if you're considering the fire as being of some set size in terms of mass. If it's the damage done if the stuff pours out of a hole in the package and a kid skateboarding around the company's loading dock face-plants into a pile of it ... less so, but anything more realistic might be too bureaucratically challenging for all involved. Wnt (talk) 18:25, 11 July 2012 (UTC)

To clarify, I'm not the one working out the dangerous goods classification. I'm just providing data to someone, who is passing that data to someone who is working it out. As Wnt said, I'm just interested in how they got the 5% figure from the actual definition. The LD50 is prescibed in the definitions, so if you want to argue that it's not important and we should look at chronic toxicity, take it up with the United Nations Economic and Social Council. It looks like Someguy hit on it above, but I'm still waiting for him to let me know what compounds he looked at the MSDSs for. You don't need to assume that the 5% figure is by weight, I gave that in the statement of the question "5% of the dry mass". And leaching into soils, etc. sounds more like criteria for Class 9: Environmentally hazardous material (although the wikipedia article on that is a bit vague). I don't think specific, plausible scenarios come into it really. It's "just how toxic is it?", not "how likely is it that some one will eat it?". 203.27.72.5 (talk) 20:36, 11 July 2012 (UTC)

Bell / clapper

I have a long case grandfather clock which chimes in a rather tinny way. How can I improve its voice? Kittybrewster ☎ 11:02, 11 July 2012 (UTC)

Such clocks need regular cleaning and lubrication, but there are fragile parts and delicate adjustments so don't just attack it with oil or WD40. You could cause a lot of damage if you're not careful. Having said that, before calling a professional I would visually inspect the mechanism to ensure it is clean and that the hammer(s) and gong(s) (it's unlikely to be a bell and a clapper) are moving smoothly and not fouling anything. The hammer should only touch the gong momentarily, not come to rest on it. If there is a pad on the hammer it might need replacing.--Shantavira|^{feed me} 11:44, 11 July 2012 (UTC)

On this page you can hear grandfather clock chimes and identify your own, probably the Westminster chimes. Here is a video that shows the chiming mechanism of an (unspecified) grandfather clock receiving attention. If yours is like this, check that the tubular bells hang freely. Other videos on the linked YouTube page give insights into other types of clocks. DriveByWire (talk) 14:16, 11 July 2012 (UTC)

You may also have spiderwebs, dust bunnies, or even a crack in one of the noise making parts.--Canoe1967 (talk) 15:42, 11 July 2012 (UTC)

Can you identify what's wrong with the sound ? Different sounds may indicate different problems:

1) Short decay: If the sound quickly stops, this could be a sign that it just needs cleaning, as all that dust may dampen the sound. Or, perhaps the gong is attached to something which absorbs the sound too quickly, like wood. This could be the result of a poor repair job.

2) If you are hearing multiple strikes instead of one, then either the hammer is hitting more than once or the gong is hitting something else.

3) Out of tune: Likely because the mass of the gong is off. Again, this could be due to a poor repair job, say if they attached it with a different fastener than the original.

4) Buzzing: Could indicate a crack in the gong, in which case it would need to be replaced (they could try repairing it, but it will probably never sound quite right). StuRat (talk) 17:58, 11 July 2012 (UTC)

Perhaps I have misdescribed it. It has one bell which has one kicker whch has no pad on it. Kittybrewster ☎ 11:46, 13 July 2012 (UTC)

Can you remove the bell easily? If you hang it buy a string and hit it with similar metal as the hammer then you may be able to tell if the wrong sound comes from the bell or the way it is mounted in the clock. The mounting may be worn out or damaged, the bell may be touching something or have dust/cracks etc. Was there a pad at one time possibly?--Canoe1967 (talk) 17:29, 14 July 2012 (UTC)

Ant evolution question

First and foremost I want to make it clear that I accept evolution as a fact. Just have a specific question about it.

I heard that ants evolved from wasps and that certain traits such as stingers which they inhereted from wasps do show up in certain species of ants. So if this is true, it stands to reason that the genes that code for those stingers should be homologous to the genes that code for the stingers on wasps. My question is, are they in fact homologous? My other question is, are ant wings also coded by homologous genes that code for wasp wings? 148.168.40.4 (talk) 14:52, 11 July 2012 (UTC)

Our article Ant says "Ants evolved from a lineage within the vespoid wasps.", so what you heard is apparently true. I don't know the answers to your questions for sure, but I would take it that pretty well all insect wings are homologous, and I would think the stings are too. But you need to be careful about your terminology. When you say "are ant wings also coded by homologous genes", this is a misleading simplification: a structure as complicated as a wing will be coded by a huge number of genes, many of which will also control other things quite unrelated to wings. I'm sure there are particular genes without which wings will not form at all, but that does not mean that those particular genes 'code for wings'. --ColinFine (talk) 16:12, 11 July 2012 (UTC)

The only way the genes wouldn't be homologous would be if the structures were lost entirely and then reevolved from scratch. Even then, if they still existed, the same genes might be used over again to form the new structures. In this case the animals are so closely related and the structures so conserved there is no question of their not being homologous. μηδείς (talk) 16:27, 11 July 2012 (UTC)

Nesting for clarity, not replying to Colin, heh

I don't know if there have been any attempts at mapping ant or wasp genomes and comparing them (AFAIK, only fruit flies have been studied that extensively), but yes they are. We don't need to examine their genes to know that they are homologous every time (since we're not even that savvy yet at identifying specific genes). Most of the times comparative morphology and developmental morphogenesis is more than enough. See our articles for Body plan, Hox genes, and Evolutionary developmental biology. In the same way that human and chimpanzee hands are obviously homologous, so are ant and wasp (and other Hymenoptera) wings and stingers (and legs, and eyes, and jaws, etc.).

Note that despite popular misconception, ant "stings" are from the abdomen, not from bites. And these stings can range from being delivered by piercing or being sprayed directly at an opponent. Nevertheless, both ant and wasp stings come from the same structure also present in other insects, albeit highly modified - the ovipositor. And they still function as such in some species.

Wings are a special case as they can evolve to be suppressed partially or wholly during development by genetic or environmental "switches". A phenomenon known as polymorphism (as in human sexual dimorphism). In most ants polymorphism is exhibited by "castes" where sterile female workers and soldiers are all wingless while the fertile queen and males are winged (at least temporarily). In wasps, some extreme examples are in the family Mutillidae, better known as velvet "ants", whose females are wingless and resemble ants while the males remain winged. Same thing with the chalcid wasps, whose males may sometimes even be neotenic, retaining wingless worm-like forms with the sole purpose of mating with females before the females leave the hosts.

Rest assured, like Colin said above, all wings of all insects (not just ants and wasps) are homologous, even in cases where the wings may be reduced to only one pair (with the hindwing having evolved into knob-like balancing structures known as halteres in Diptera, or the forewings being modified into protective armored coverings known as elytra in Coleoptera) or absent altogether. See also Insect wing (particularly the section on its evolution and morphogenesis).

Lastly, all ants today evolved from a single ancestor, but you must understand that like how humans did not evolve from chimps, ants as well did not evolve directly from modern wasps. Instead they both share a common wasp-like ancestor. The ancestors of ants, wasps, and bees diverged from each other at around 160 million years ago. Ancestors of eusocial ants and wasps in turn diverged from each other at around 140 to 110 million years ago. The oldest known ant fossil is the Cretaceous Sphecomyrma freyi preserved in amber from ~80 million years ago. Like its name suggests, it was more like a "wasp-ant" in that though it was indisputably an ant (possessing the metapleural gland unique to ants) it also exhibited characteristics which are undeniably from wasp-like ancestors (which includes a retractable sting, among others).-- OBSIDIAN†SOUL 16:27, 11 July 2012 (UTC)

List of sequenced animal genomes#Protostomia - Several insects have had their genomes sequenced, including several ants and wasps. Unique Ubiquitous (talk) 16:34, 11 July 2012 (UTC)

There's a certain amount of philosophy involved in homology, and so peculiar details emerge. For example, Diptera and Strepsiptera both have a pair of wings, they both probably have the vast majority of the controlling genes in common... problem is, one has forewings and the other has hindwings, with the others greatly reduced. So if you look into the genetics you'll find Ultrabithorax has different effects on these wings, even though at first glance it looked like a homologous network. Evolution does that a lot, and not always in ways you can see - it can duplicate a gene, use two copies for a while, then one lineage gets one copy and the other gets the other and you're left scratching your head trying to figure out why the genes diverged from one another so much sooner than the animals you're studying. Wnt (talk) 18:15, 11 July 2012 (UTC)

Regarding 'ant "stings" are from the abdomen, not from bites', I suppose it can be a bit of both e.g. Oecophylla majors haven't retained a functional sting but they do bite and spray the bite with acid from the end of their abdomen. It looks like this after a few seconds. Sean.hoyland - talk 18:53, 11 July 2012 (UTC)

The fantastic "helmets" of treehoppers are actually a third "wing" pair

I meant that the bite itself is not the one delivering the venom, as most people seem to have the misconception that the venom glands are located at the ant's mandibles like in snake fangs.

The bite-and-spray behavior is actually the norm in formic acid-spraying ants (formicines) when dealing with larger animals. While in others, like some myrmicines (e.g. fire ants and bulldog ants) and the primitive ponerines (e.g. trap-jaw ants), they only bite (if at all) to gain a foothold, while injecting the venom (not spraying, though the organs responsible are both derived from ovipositors) with functional stingers. The venom of the latter two subfamilies are also more similar to venom used by wasps, and are often extremely painful and in some cases medically significant.

Also, in addition to Wnt, there's also an ancestral third wing pair attached to the first segment of the thorax, which has since been lost in most modern insect body plans. It reappeared among treehoppers as their "helmets" (see picture). Insects, like most higher animals (including humans) are derived from repetitive body segments that later became modified and/or fused as they evolved to become more specialized (traces of that is evident in our embryonic stages). Ancestral insects therefore actually had one pair of "wing" appendages for each body segment (though they were not wings then, of course). They were eventually suppressed by Hox genes (like the previously mentioned Ultrabithorax) for all body segments except two, which eventually became used for flight. Except for treehoppers, apparently, which somehow broke the mold. And given that a third pair was more or less superfluous when it reappeared, evolution got creative with it instead. :P -- OBSIDIAN†SOUL 22:22, 11 July 2012 (UTC)

Air Conditioning

Regarding energy usage to cool a home, are the following two situations equivalent?

• 1 Outdoor temperature = 80º and indoor thermostat & temperature = 72º
• 2 Outdoor temperature = 81º and indoor thermostat & temperature = 73º hydnjo (talk) 15:09, 11 July 2012 (UTC)

No, but many methodologies will consider them "approximately" equal. We have an article on degree days, which links to many related concepts. Nimur (talk) 15:29, 11 July 2012 (UTC)

Both situations have an 8º differential so if they are not equivalent then which will require more energy to maintain? hydnjo (talk) 17:15, 11 July 2012 (UTC)

I suspect that the lower temperatures will require ever so slightly more energy, considering that to go from 8 degrees above absolute zero down to absolute zero would require an infinite amount of energy. StuRat (talk) 17:46, 11 July 2012 (UTC)

True. See Carnot engine for the formula, which is indeed based on a ratio of temperatures in kelvins. That formula describes how much energy you can extract by reversing the process, which for a perfect air conditioner is theoretically equivalent. A specific, real air conditioner, with real coolant with a real boiling point, will act differently from that, however, and I can't tell you how. Wnt (talk) 18:01, 11 July 2012 (UTC)

In general, engines work at higher efficiency in a lower ambient temperature, so the air conditioner working in 81 degree weather is slightly less efficient. The inside temperature change gives the target amount of energy which has to be spent, which simply requires it run a certain amount of time, and is not relevant to the efficiency of the engine sitting in the unchanging heat outside the window. Strictly speaking, the heat capacity of air does change by a very small amount, so the amount of energy needed to be expended will differ as the cooler air has a higher heat capacity. This is no where near the difference you run into at the heat of condensation of the boundary conditions of solidification or absolute zero. There is no way to calculate which is greater, the better efficiency or the greater work at the lower temperature, without the specifics. But my gut feeling is the difference in efficiency will be higher, given most air conditioners are inefficient, and it will take more input energy to cool from the higher temperature. μηδείς (talk) 20:08, 11 July 2012 (UTC)

• Think the answer here lays in the laws of Thermodynamics. As one learns when at school: it is easier to add heat to something that is already hot than to something that is cold – thus the revers is true also. So, as the temperatures drops (regardless of ∆t remaining constant) the efficiency must drop. Ergo, case 1... “Outdoor temperature = 80º and indoor thermostat & temperature = 72º” will require more energy to maintain the same temperature differential (∆t) than case two. --Aspro (talk) 22:35, 11 July 2012 (UTC)

I think, Aspro, you might be thinking about the heat of fusion of ice, which much requires more energy to melt a solid liter of ice entirely to water at a constant 32 degrees than to raise a liter one degree from 32 degrees to 33. There is no law that says it is easier to heat hot things than cold ones. That being said, according to Thermal efficiency air conditioners aren't strictly rated by efficiency, since they are not heat engines. μηδείς ([{User talk:Medeis|talk]]) 01:50, 12 July 2012 (UTC)

No. I said what I meant.--Aspro (talk) 01:53, 14 July 2012 (UTC)

Case 1 (80/72) is essentially the more efficient for refrigerative airconditioning. This is partly because of the charecteristics of compressors and refrigerant fluids, and partly because the saturation moisture contaent of air is less at lower temperatures - saturation conditions exist at the evaporator, thus less work is done removing moisture at lower temperatures. Manaufacturers of compressors provide curves of efficiency vs evaporator and vs condensor temperatures in their application datasheets - these always show greater efficiency at lower temperatures. However, in practice you can get some anomallies as the compressor is normally cycled on and off by the thermostat. Each time the compressor is started, it works inefficiently for a while until refrigerant conditions are stabilised. Ratbone58.167.247.229 (talk) 02:05, 12 July 2012 (UTC)

The genesis of this question lies in my wife's insatiable desire to lower our A/C thermostat a degree or two (over which I have no control) and my energy conscious self's justification that its the same as though the outdoor temperature (also over which I have no control) had risen a degree or two. Thanks all for your thoughtful responses, I guess should find something more profound to worry about :-) hydnjo (talk) 23:09, 12 July 2012 (UTC)

In which case you asked the wrong question. Lowering the cooled space temperature further below the outside temperature will always increase your electricity consumption. Figures typical of domestic airconditioners having a COP of around 2.5 and using a common refrigerant: With an outside temperature of 80 F and decreasing the internal temperture from 72 F to 70 F will increase the amount of heat to be shifted by (80 - 70)/(80 - 72) i.e., an increase of 25%. To do this, electricity consumption will have to rise, but not quite 25%, as the lower evaproator temperature will increase efficiency - electricity consumption will rise about 23% or so. Now, if the set point is left at 70 F, and the outside temperature drops to 78 F, the amount of heat to be shifted drops back to the same amount as before. However, the lower condensor temperature also improves efficiency, so electricity consumption will fall a bit more than 25% - it will now drop about 27%, so your electricity consumption will be about 96% of the 80/72 case (not counting anomallies due to cycling). Ratbone124.178.45.153 (talk) 10:06, 13 July 2012 (UTC)

Ratbone, he didn't ask the wrong question. He understands that lowering the thermostat increases energy consumption. He's just rationalizing it by saying that it would have been the same if the outside air temp increased by the same amount. His question was just about whether or not that logic is actually correct. 203.27.72.5 (talk) 22:35, 13 July 2012 (UTC)

Well stated but I prefer intellectualizing ;-) hydnjo (talk) 01:42, 14 July 2012 (UTC)

Ratbone, no I don't think so. The question I posed was Out > In = 80º > 72º vs 81º > 73º. In both cases the outdoor temperature is 8º warmer than the indoor temperature. I arbitrarily chose both the outdoor ∆t = 1º and the Out > In ∆t = 8º for illustration and ease of calculation. hydnjo (talk) 13:14, 13 July 2012 (UTC)

Neutralize soap?

What's the most effective way to neutralize liquid soap that has been spilled inside a rucksack (unwashable) ..? Electron9 (talk) 18:44, 11 July 2012 (UTC)

Does 'unwashable' mean it can't get wet or can't handle the punishment of a machine? If it can handle warm water you could just soak it until the soap dissolves and dilutes. The warmer the water the faster it will work. You could try dry cleaning but that may be a cost issue. If there is perfume in the soap that may last longer but should go away by September when school starts.--Canoe1967 (talk) 18:57, 11 July 2012 (UTC)

It means it should not be put in a machine because the water protection may suffer. And the protection may have chemical components that I don't want in the machine. So I thought about something chemically better than plain hot water. Electron9 (talk) 20:33, 11 July 2012 (UTC)

In that case, you can go ahead and machine wash it, then spray it with water-proofing agent after it dries. (You should be able to buy that at a shoe store.) StuRat (talk) 20:36, 11 July 2012 (UTC)

Does unwashable mean unsoakable and unrinsible? 71.212.249.178 (talk) 19:07, 11 July 2012 (UTC)

I'd first physically remove as much as possible, with a sponge. Then soak it, say in the tub. You may need to drain the water and replace it several times, until you stop seeing suds. Tumble dry on low heat. (If you literally have a rucksack that falls apart if it gets wet, on the other hand, then throw it out and get a better one.) StuRat (talk) 19:11, 11 July 2012 (UTC)

If it has leather parts you may wish to treat those with leather water-proofing, etc. first. Can you get a manual for your pack or a similar one that says how to treat the leather?

The number one best chemical to neutralize soap is water. Think about it. What other kind of substance could you imagine that isn't it self going to be a pain (or require water) to remove? Vespine (talk) 22:51, 11 July 2012 (UTC)

To answer your hypothetical, an oil-based substance may be appropriate, especially if the rucksack is leather. Special leather oils are good for leather, and any greasy substance in sufficient quantity will neutralize a soap. I don't recommend blindly attempting this solution in the example at hand, though. BigNate37_(T) 22:54, 11 July 2012 (UTC)

Make sense as soap decomposes flesh which protect itself with.. oil. The question is then what amount and type of oil. The rucksack is made with textile. Electron9 (talk) 04:05, 12 July 2012 (UTC)

If it's textile, then just use water. Otherwise you'll need soapy water to get the oil off it anyway. 203.27.72.5 (talk) 04:11, 12 July 2012 (UTC)

Why are commercial aircraft round?

Couldn't all the Boeings and Airbuses be less like a cylinder and more flat? It seems to me that lots of space gets lot due to this cylindrical form. OsmanRF34 (talk) 22:15, 11 July 2012 (UTC)

A round cross-section is the strongest shape, anything ovular would require stronger materials to achieve the same structural integrity. This may be the reason they are round: to minimize structural mass. Granted, I am not an aerospace engineer, nor close to it. BigNate37_(T) 22:28, 11 July 2012 (UTC)

It's not just structural integrity, but also the ability to stand the overpressure of maintaining close to one atmosphere at a height where ambient air pressure is only ~20% of normal. --Stephan Schulz (talk) 22:32, 11 July 2012 (UTC)

How is the ability to tolerate overpressure any different to structural integrity? 203.27.72.5 (talk) 22:39, 11 July 2012 (UTC)

Is that why combat aircraft pilots are often seen to be using a breathing apparatus? I.e., to allow the cockpit to have less of a pressure differential without affecting the pilot, because they are too small to be perfectly round? BigNate37_(T) 22:36, 11 July 2012 (UTC)

Note that they are not perfectly round and are slightly oval in shape. The Embraer E-170 for example is 3.35m high and 3.01 meters wide. 203.27.72.5 (talk) 22:38, 11 July 2012 (UTC)

Wide-body aircraft like the Boeing 747 and Airbus A380 are far from round. 203.27.72.5 (talk) 22:49, 11 July 2012 (UTC)

Cross-section comparison of Airbus A380 and Boeing 747-400

— Preceding unsigned comment added by 203.27.72.5 (talk) 22:51, 11 July 2012 (UTC)

They're shaped like beer cans for the same reason. Hcobb (talk) 22:41, 11 July 2012 (UTC)

I'd question two premises. One, I highly doubt much space is wasted at all in a modern jet liner. There's an incredible amount of stuff that gets packed into that cylinder. Two, it's not really "space" that is the issue anyway, it's more about weight. Anything that "looks" like wasted space is probably required for access. Don't forget that just about every single component in the plane must be able to be inspected and replaced if required at some stage, so packing everything as tight as possible to save "space" doesn't sound like a great idea for more then one reason. Vespine (talk) 22:47, 11 July 2012 (UTC)

Just to second what Vespine said, those "wasted" spaces are filled with things like ballasts and fuel tanks that can take just about any shape you like. The space in a modern airliner is used with efficiency you're not likely to see anywhere else, unless you happen to be flying a bit higher. 203.27.72.5 (talk) 23:01, 11 July 2012 (UTC)

Actually, to slightly contradict part of what Vespine said, space is a major issue in addition to weight. Drag is (generally speaking) inversly proportional to density, so unused "wasted" space (if it actually existed) would lower the average density of the aircraft and increase drag. This is obviously all from an initial design of the aircraft perspective. I'm not suggesting that existing aircraft could fill in those gaps with extra passengers' luggage to reduce drag :). 203.27.72.5 (talk) 23:22, 11 July 2012 (UTC)

I didn't say aircraft are cylindrical, just like a cylinder. Another point: there is less wasted space because commercial aircraft combine cargo (not related to the passengers flying in it) with passengers as best as it gets. But if it were more flat in the y-axis, you could reduce the cargo space and put more people into it. The resulting aircraft would look more like a big wing (and you could have shorter wings). It's clear to me that there are lots of calculations and reasons for the shape that aircraft have, but I'd be happy with a couple of hints. OsmanRF34 (talk) 23:30, 11 July 2012 (UTC)

Something else to consider is the comfort factor in each seat. In the Airbus 380 diagram above, it looks like tall outside passengers on the upper deck will have their necks bent by the fuselage wall. Passenger comfort alone would dictate a rounded square cross section be used, but anyone who has ever been on an airplane can attest that passenger comfort is obviously only a minor concern. StuRat (talk) 23:53, 11 July 2012 (UTC)

Well maybe not anyone. To quote one airline passenger, "If you travel as much as we do you appreciate the improvements in aircraft design of less noise and more comfort – provided you don't travel in something called economy class, which sounds ghastly." 203.27.72.5 (talk) 00:49, 12 July 2012 (UTC)

Size of Earth's orbit last 2000 years

Has the size of the Earth's orbit around the Sun changed significantly in the last 2000 years, as this article says? Bubba73 ^{You talkin' to me?} 22:58, 11 July 2012 (UTC)

See Earth's orbit. But here's the spoiler: no it hasn't. 203.27.72.5 (talk) 23:02, 11 July 2012 (UTC)

Thanks. I thought that it hadn't changed that much in 2000 years, but I don't see anything in that article addressing it. Bubba73 ^{You talkin' to me?} 23:26, 11 July 2012 (UTC)

The paper that is described by that Daily Mail article is freely available here. The Daily Mail article is misleadingly worded. Even though the Earth's orbit has not changed significantly, the precession of the Earth's axis combined with the elliptical shape of its orbit has caused a small change in the distance from the Sun during June-July-August, and that's the change that the authors invoke to account for their data. Looie496 (talk) 23:26, 11 July 2012 (UTC)

(See our article on Milankovitch cycles for more information.) Looie496 (talk) 23:35, 11 July 2012 (UTC)

Airliner cabin air

Does the air in an airliner cabin recirculate, or is there some mechanism to exchange it with outside air without losing the cabin pressure? 203.27.72.5 (talk) 23:14, 11 July 2012 (UTC)

Humans exhale carbon dioxide (and depending on the in-flight meals... other gases too). This has to be got rid of so stale air gets bleed off. Therefore, air can not be recirculated. The banning of smoking also meant that the amount new air added to the cabin could be reduced -thus saving the costs of pressurizing greater amounts of air to keep the interior atmosphere agreeable. To save more costs, they also reduced (in the last decade), the cabin pressure – but to the detriment of passengers suffering from emphysema and other medical conditions that low air pressure can aggravate. To counter the possible resulting in-flight emergencies from this new practice, some air-lines are now carrying portable automatic heart defibrillators on board -as if to say – we endeavour to take great care of our customers as always. I don't know what is better – a twenty cents cheaper ticket or free electric shocks.Also, On some air-line carriers you might also notice a very odd smell wafting over you. [13]--Aspro (talk) 23:42, 11 July 2012 (UTC)

Ah, are you sure about the trend in cabin pressure? The sources I've looked at seem to suggest the opposite. (See, for example, cabin pressurization.) The new Boeing 787 and Airbus A380 have effective cabin altitudes of 6000 ft and 5000 ft, respectively, significantly lower than the 7000-8000 ft seen on older aircraft. I suspect that you may be the victim of similar misconceptions about the quality of cabin air today versus a decade or two ago. The amount of air supplied per passenger hasn't changed much over the last forty years; if anything, the banning of smoking aboard aircraft has made the air cleaner for everyone: [14]. TenOfAllTrades(talk) 00:18, 12 July 2012 (UTC)

moved from my talk page: 'Hello Aspro. On 11 July you replied to a question asked at Wikipedia:Reference desk/Science. The question related to Airliner cabin air. See your diff. Your answer included the following statements:

The banning of smoking also meant that the amount new air added to the cabin could be reduced -thus saving the costs of pressurizing greater amounts of air to keep the interior atmosphere agreeable. To save more costs, they also reduced (in the last decade), the cabin pressure – but to the detriment of passengers suffering from emphysema and other medical conditions that low air pressure can aggravate. To counter the possible resulting in-flight emergencies from this new practice, some air-lines are now carrying portable automatic heart defibrillators on board.

To support your answers you supplied a link to a website that discusses spraying of insecticides on airliners. See your diff. I have looked at that website but found nothing to support the statements I have pasted above.

I have also looked at the Wikipedia article on Cabin pressurization but I found no information of the kind you gave in your answer. It looks to me like you have used the opportunity given by this question to respond with some of your original research. It looks to me very much like your own conspiracy theory, or someone else’s conspiracy theory to which you have enthusiastically subscribed.

Wikipedia’s reference desks are intended as places where Users from around the world can ask serious questions and receive high-quality answers. I think your answer was a very poor one so I ask that, in future, if you can’t find the answer using the resources of Wikipedia or some other reliable published source, don’t answer the question. Certainly don’t use the reference desks as vehicles for your own original research or your favourite conspiracy theory. Before I write anything more I am interested in whatever comment you wish to make about my criticism. Dolphin (t) 01:07, 12 July 2012 (UTC)

To both above comments: The reference to insecticides was an aside for those that did not know about this practice -not support to my previous post. I could have mentioned other forms of chemical contaminations but they tend not to be intentional. Second. During the Second World War the Science aviation Aviation Medicine. recognised that above 6,000 feet, air crews need to breath oxygen and above 10,000 ft it became mandatory. So with the introduction of passenger airlines with pressured cabins, the design specifications called for 6,000 ft also (whether airline operates choose to use this capability to the full is a matter of economics). This was long before the introduction of the Dreamliner and A380. However, when fuel costs shot up, many airline sort to save costs by manually reducing the cabin pressures and volume exchange. Here is a resent discussion on what cabins pressure ought to be. [15], [16]. “Respiratory benefits and costs of returning to the 30% higher outside air ventilation rates and 8% higher cabin pressures of the 1960s and 1970s are outlined (emphasis mine). [17]. Maintaining cabin pressure come at no small cost over the operating life of an aircraft, therefore Boeing’s have designed the Dreamliner so that the air exchange can be matched to the exact number of passengers on each flight. The figure of 8,000 feet is the acceptable maximum and OK for a fit person – some airlines however have been suspected of maintaining lesser cabin pressures. See:APPENDIX 4: Major destinations exceeding 2438 m (8000 ft) [[18]] Note: This was not an exhaustive list . This is not OR on my part but recounting worries that have been brought to my attention by friends who have had reason to to battle with their management in the air transport industry. With more people flying more frequently, these problems are increasing. Added to that, is the inconvenient times when one's plane gets diverted, due to a medical emergency suffered by another passenger. https://docs.google.com/viewer?a=v&q=cache:07VuQ4uYGoMJ:www.hkcem.com/html/publications/Journal/2003-3/p191-196.pdf+bmj+aricraft+emerhentcy&hl=en&pid=bl&srcid=ADGEESiu-XlD7QAT1c4RklFueboncLuqEzpTDzFFf379IB9VFwvbCUYG09O7DK9aDp969-UdpgAX7LfMvWvV3HEE3pekdoKvi1r_CP3ikGna_Bc6fZRXrbKSdBMO9PSXPERrf1F3L07f&sig=AHIEtbTbx9TzLUNnlKv02lj46hyVQa0uKw

Air travel is now incredibly safe due to the development of regulations encouraging good practice but blind trust in believing that accountants can run the airlines alone and go along with believing every reassurance the PR department coughs up , is not something your air aircrew on your next flight maybe happy to go along with – after all, they often have to deal with life and death decisions and in the worst cast scenario -more likely hit the ground before you do. --Aspro (talk) 17:07, 13 July 2012 (UTC)

Without wanting to get too much in to this discussion, I don't really get the relevence of 'appendix 4'. If you visit a destination with an altitude greater then 8000 feet, of course you should expect to experience cabin 'pressuration' greater then 8000 feet by the end of the journey. This source [19] cited by the same source with the appendix 4 does cite a range up to 8,915 feet although it's from 1988 and mentions the higher crusing altitude of more modern aircraft as a factor for lower pressurations (I didn't look at the source only the abstract).

In terms of the rest of the stuff, even one of your sources seems to support the idea that new aircraft are designed to be able to maintain maximum cabin pressurations of 6000 feet through long haul flights which older aircraft were generally not. While you're correct it's not clear airlines will use this, I haven't seen anything from your sources suggesting there has been a recent reduction in cabin pressuration.

One of the sources does suggest things were better in the 60s or 70s but both your earlier and more recent comments seem to suggest this as a recent thing as well. Notably if your read that source (well I only skimmed through it), it seems to suggest the difference from the 60s-70s was the inability of aircraft from that time to recirculate air which was done for cost reasons. It does mention a trend through increasing recirculated air. (It mentions there are some advantages to the passenger from increasing recirculated air but from the abstract I guess they concluded the disadvantages outweighed the advantages.) More importantly since I'm only really addressing the cabin pressuration comment, it also seems to suggest that the changes from earlier are because of the increased cruise altitude and you'll need stronger airframes etc to allow high pressuration at the higher cruise altitudes. To this extent, you're correct it's a cost issue but this doesn't really seem to be the manner you were referring to. Notably although I only skimmed through it, while having lower cabin pressurations obviously saves costs, I didn't notice any suggestion there was a concern airlines were raising pressuration to save cost beyond that dictated by the cruising altitude and airframe. The source is from 2002 so I guess lack info one the recent aircraft like the 787 or A380 which sound like the sort of thing they were referring to that would be needed.

As a final point unless I missed it none of the sources mention any recent changes in cabin pressuration levels beyond that from the newer aircraft.

As to what you've heard from the industry, I can't comment on that although I admit I'm somewhat dubious about things heard in the 'industry' which no one else seems to know. I would at least expect these to show up in non-RS (forums etc) and probably even the odd RS. (I'm not saying they don't exist, simply that without them I don't find your claim particularly credible.)

Nil Einne (talk) 08:46, 14 July 2012 (UTC)

So, is it that some of it recirculates and some is bled off and replaced? And how does the mechanism work that replaces it? It must be some sort of compressor I take it. Does it work a bit like a ramjet or is it just a normal air compressor? 203.27.72.5 (talk) 00:35, 12 July 2012 (UTC)

The turbine engines that drive modern airplanes are giant air compressors. Air is bled from the compressor stage of the engine and cooled in a heat exchanger; and then it is fed into the cabin, both to keep it pressurized and to replace air that is vented from the cabin in the interests of eliminating carbon dioxide, moisture and odours. Some older airplanes, such as the Vickers Viscount, obtained their air for ventilation and pressurization from blowers - mechanical compressors attached to the engine. Dolphin (t) 00:45, 12 July 2012 (UTC)

Depends on the cut off line on the word 'modern'. Pressurizing cabins from the engines, can and has lead, to contamination from the engine oils. Example: www.corporatewatch.org/?lid=3073 . The Boeing Dreamliner for instance, now gets round this by going back to the old system of having a competently separate compressor. “In the no-bleed architecture, electrically driven compressors provide the cabin pressurization function, with fresh air brought onboard via dedicated cabin air inlets.” Page 8 of www.google.com/url?sa=t&rct=j&q=dreamliner+cabin+pressure+compressor&source=web&cd=6&ved=0CFkQFjAF&url=http%3A%2F%2Fwww.boeing.com%2Fcommercial%2Faeromagazine%2Farticles%2Fqtr_4_07%2FAERO_Q407_article2.pdf&ei=rvQBUN29O8mv0QW8zPm2Bw&usg=AFQjCNHiysW9sKHOkLeY75TjbSylFq8BxA&cad=rja --Aspro (talk) 23:13, 14 July 2012 (UTC)

Thanks. 203.27.72.5 (talk) 00:58, 12 July 2012 (UTC)

Resolved

July 12

derivation of the kintetic theory equation

Hello.

My question is related to the derivation of the equation pv=1/3nMwC^2. Most of the derivations I have seen assume that the average time between colisions, t, is 2l/Vx when l is the length of the cube. When assuming this, you actually assume that each molecule travel from one wall to the other wall at constant velocity without any clashes with other molecules. this is an unlikely assumption, yet those derivations do succeed. my quastion is - why? and where can i find more rigorous and accurate derivation?

I am sorry for my poor english...

Thanks in advance, 94.159.137.4 (talk) —Preceding undated comment added 06:54, 12 July 2012 (UTC)

Isn't the assumption really that the collisions with other particles are elastic? If it does elastically collide with any other particle, it transfers momentum which that particle then in turn transfers to the wall after exactly the same amount of time has expired. This results in the same net effect for the wall, so the predicted pressure is exactly the same. 203.27.72.5 (talk) 07:41, 12 July 2012 (UTC)

I thought about this interpretation, but I don't think it's true. It would be true only when moving particle collides with a static particle. Think about collision between two particles with same mass and opposite X-component velocity - They both would be stopped. 94.159.137.4 (talk) —Preceding undated comment added 09:20, 12 July 2012 (UTC)

If they stopped, the kinetic energy would be destroyed; so they can't stop as long as energy is conserved. Imagine two billiard balls colliding head on. They don't stop, they bounce back in opposite directions. 101.173.170.146 (talk) 09:34, 12 July 2012 (UTC)

Yes, you are right, my fault. Yet I would be happy to see a rigorous derivation. 94.159.137.4 (talk) —Preceding undated comment added 09:51, 12 July 2012 (UTC)

On matters of mathematical rigour, I'm the last one that should be commenting, but is the derivation at Kinetic_theory#Pressure_and_kinetic_energy adequate? 101.173.170.146 (talk) 10:56, 12 July 2012 (UTC)

No, because of reasons I wrote above. You can see this thread in physicsforums.com, which explains the problem clearly (especially on "loom91"'s notes), yet no complete answer was given. 94.159.137.4 (talk) 11:32, 12 July 2012 (UTC)

A more accurate derivation can be found in the book: "Fundamentals of Statistical and Thermal Physics", by F. Reif, secion 7.13 page 278 and further. It starts with the heuristic derivation, followed by an exact calculation. Note that in the heuristic derivation the formula you get contains the square of the average speed, while in the exact calculation, you get the correct expression containing the average of the squared velocity. Count Iblis (talk) 17:33, 12 July 2012 (UTC)

Thank you! perhaps it's good idea to write in Kinetic_theory#Pressure_and_kinetic_energy that the derivation which described in the article (and in many academic textbooks...) is not an accurate one. 94.159.137.4 (talk) 06:22, 13 July 2012 (UTC)

It's not inaccurate. Simply assume that the Volume of the box is so small that the chances of a collision between particles happening before the particle reaching the wall is negligible. Then build a larger box by stacking the smaller boxes side by side and removing the walls between the boxes (Which has no effect in the pressure). Dauto (talk) 15:47, 13 July 2012 (UTC)

Oughterlony immunodiffusion

My question concerns the interpretation of Oughterlony immunodiffusion which I think it, the content in Wikipedia, can make people misunderstand some good points. For example Ag A contains two epitopes so called X and Y while Ag B contains epitope Z, if both Ags react with the mixed Ab which contains anti-X, anti-Y and anti-Z, the result should come out without any relationship (of identity, partial identity or non identity). Is that right? I think this technique was created before immunologist really understand about antigenic determinants. It originally is for study the relationship of each class of antibody. The content in the web can make people understand that the two Ags which are not relate to one another still give a result of non-identity. — Preceding unsigned comment added by 110.164.187.222 (talk) 12:05, 12 July 2012 (UTC)

You never posted an exact title as requested at Wikipedia:New contributors' help page/questions#Interpretation of Oughterlony's technique. Is this about Ouchterlony double immunodiffusion? I'm not qualified to discuss the topic. PrimeHunter (talk) 12:10, 12 July 2012 (UTC)

As explained at Precipitin, the antigen must be multivalent - if there's just one epitope per antigen, then it will react with an antibody, but it won't form a large gel-like complex; you'll have two dead-end epitopes stuck to one monomer antibody (four to IgE, ten to IgM - see antibody. I think F(ab')2 fragments are OK, but don't try to use Fab fragments. ;) ). Antibodies and antigens will ignore those that are not matches, so if you have two unrelated multivalent antigens, each should find its own favorite antibodies and form complexes with them somewhere or other, but ignore the other antibodies. That means that you could have multiple white lines, or even white lines crossing one another. Mix in a little bit of the right fluorescent antibody (or apply it to the gel afterward) and you could mark which is which in pretty colors if you want. Wnt (talk) 13:38, 12 July 2012 (UTC)

This is a minor point, Wnt, but where you mention the 4-valency of IgE, I think you meant sIgA. -- Scray (talk) 04:25, 13 July 2012 (UTC)

Thanks for spotting that! Wnt (talk) 21:12, 13 July 2012 (UTC)

looking for a chart

from organogenesis

hi! i'm a biology student, taking a course in comparative anatomy. i am looking for a chart [or something similar], which will: show the origin of the organs [what came from the mesoderm, ectoderm, etc.], and maybe even more- like what originated in the neural crest.

thanks! — Preceding unsigned comment added by 212.76.110.252 (talk) 16:10, 12 July 2012 (UTC)

You should read the relevant articles. Also check out embryogenesis and organogenesis, whic is a stub, but which has the picture I posted. You'll probably do better with a google image search. μηδείς (talk) 16:41, 12 July 2012 (UTC)

do you have any idea which key words i should use? i am looking for something with more details- like the somits.

thanks again... — Preceding unsigned comment added by 212.76.110.252 (talk) 16:48, 12 July 2012 (UTC)

Well, to begin with, see somites... but admittedly, that's not the image you want yet... Wnt (talk) 18:07, 12 July 2012 (UTC)

You should really just fool around with searches like "organ mesoderm", etc., at google images. You will immediately get hundreds of choices to browse through, rather than one at a time from us. μηδείς (talk) 18:56, 12 July 2012 (UTC)

Lasers

Wavelengths of the visual spectrum

Is the blue-violet laser stronger than the green one ? ( We are talking about pointers )124.253.89.189 (talk) 16:52, 12 July 2012 (UTC)

According to laserpointersafety.com, a violet pointer is more dangerous than a blue one, which is in turn much more of a hazard than a green one. Clarityfiend (talk) 17:11, 12 July 2012 (UTC)

What about this one. Is it exactly blue or violet ? Last time this very vendor fooled me into buying a three AAA battery laser (green) which he claimed is powerful enough to light up a matchstick ( It doesn't, though it does produce a slight sensation of heat on skin ) — Preceding unsigned comment added by 124.253.89.189 (talk) 17:51, 12 July 2012 (UTC)

The page you linked says the exact opposite of that. They seem to be specifically talking about the danger of temporary blinding/distraction, not permanent eye damage, which is why they scale it by the eye's sensitivity to each frequency (it's most sensitive to green). And they are talking about lasers of the same power. -- BenRG (talk) 02:02, 13 July 2012 (UTC)

On the colour spectrum, the higher-frequency colours have higher energy. Lower wavelengths means higher frequencies means higher energy. This is also why red is less harmful to your night vision than green. BigNate37_(T) 18:50, 12 July 2012 (UTC)

This isn't strictly true; red light does not affect your night vision as much because rod cells (responsible for low-light vision) are less responsive to higher wavelengths; the chart in that article shows they are most sensitive to blue-to-green wavelengths. -RunningOnBrains^(talk) 19:52, 12 July 2012 (UTC)

I stand corrected. BigNate37_(T) 22:21, 12 July 2012 (UTC)

Higher frequencies have higher energy per photon, not per laser beam. It's the power that matters, not the color. -- BenRG (talk) 02:02, 13 July 2012 (UTC)

If you want to get an answer that makes any practial sense, you will have to qualify what you mean by "strong". The energy of the light is highest at violet and lowest at red with everything else falling in between per the spectrum in the picture above. The power of the various laser pointers is not dependent on the colour of the laser, but rather on its design. The power output in watts may be stated on the laser pointer itself or on the packaging. If you're wanting to know which will heat something up the most (i.e. which will come closest to igniting that match head) that will be the one with the highest power output. My intuition is telling me that you're not going to find a battery powered pocket laser pointer that can acutally do that though. 203.27.72.5 (talk) 01:59, 13 July 2012 (UTC)

Timeline for noticeable adverse effects from 100% recirculated commercial airline cabin air

The post above ("Airliner cabin air") got me thinking (I don't know why, but I had just assumed that airline cabin air was recirculated, at least to a large extent, which I now realize is pretty daft).

Let's take for the sake of this example a modern Boeing 767-300 outfitted with a 2-class cabin, and a full passenger capacity of 269 people. Assuming that there is NO exchange of air, and that the 100% of the air is continually recirculated, how long would it take for enough oxygen to be depleted such that some passengers will begin to experience adverse effects from the lack of oxygen? How long would it take for the majority of the passengers to lose consciousness or even die due to the lack of oxygen? --Zerozal (talk) 17:06, 12 July 2012 (UTC)

As for how long before it becomes uncomfortable, that's just a few minutes. Between lower oxygen, higher carbon dioxide and other gases, high humidity, and high temperature, it's hard to know just what makes it "stale", though. The various factors can also affect each other, like high temp and humidity causing people to emit more body odor, making the air quality quickly worsen. StuRat (talk) 17:27, 12 July 2012 (UTC)

Talking of cabin pressure in aircraft and it's effect upon humans, is it possible to get rid of hijackers by suddenly lowering the pressure ? It will cause all humans in cabin to lose consciousness (without causing any permanent damage upon them). Later all can be revived easily by bringing pressure to normal. But by that time hijackers would be nicely bound and gagged, and their toys taken away...124.253.89.189 (talk) 18:09, 12 July 2012 (UTC)

It doesn't make much sense to me. Whatever people have to deal with the terrorist, would need a mask and oxygen tank. And the terrorists could also have a mask and oxygen tank (smuggled into the plane in the same way they smuggled the weapons). Besides that, cockpit doors are reinforced nowadays, and pilots are trained not to cave in. Any terrorist without a bomb won't cause much harm. 79.148.233.179 (talk) 18:20, 12 July 2012 (UTC)

Stu enjoys posting on this forum - pity he doesn't check his facts first.

During most of the flight, the passengers are at rest. According to http://ep.physoc.org/content/64/3/205.full.pdf the rest oxygen consumption of an average fit humnan is 0.263 Litres/min A 767-300 has a cabin volume of length ~49 m, 4.72 width, with a half-circle profile. Allowing for volume occupied by seats, luggage racks, etcx, the internal volume is approx 880 m³. 269 average humans, taking the density as roughly that of water, occipies a volume of 65 litres each, or a total of 18 m³. So the volume of air in the cabin is 880 - 18 - 862 m³. Air is 21% oxygen, and 767's pressurise to 80% of sea level value. so that's 145 m³ of oxygen. 269 passengers at 0.263 l/min gives a total oxygen consumption of 0.0708 m³/min. So the passengers consume in the order of 0.05% of the available oxygen per minute, or about 3% each hour.

Humans at rest are perfectly comfortable at an altitude of about 3,000m - at that height, the pressure is ~70% of sea level. So the comfort limit is reached after about 3 hours is the cabin is 100% recirculated.

However, its more complex than that. Each m³ of oxygen consumed is replaced by a m³ of CO₂. It happens that the mammilian breathing system automaticllay regulates, but our internal sensor does not sense oxygen, it senses CO₂. So the CO₂ breathed out will cause everyone to breath harder, without them necessarily noticing it. This will completely maintain blood oxygen at saturation level for much longer than the 3 hours calculated by oxygen consumption. This principle is used in gas fire suppression (eg Inogen) in computer and server rooms - when a fire is detected, a mixture of inert gasses and CO2 is pumped in, to force oxygen out and reduce it to about half the normal level - that causes most fires to go out. The CO₂ causes any people to just breath deeper, so they are not harmed.

It also happens that humans gradually starved of oxygen don't feel discomfort - they just get sleepier and sleepier, until they are unconscious.

The overall implication is that you needn't worry about aircraft fresh-air delivery failure. Cabin oxygen will considerably outlast the fuel. You will have landed long before it is a safety issue.

Sudenly dropping cabin presure to disable terroists is a bad idea. It can only work if you disable the automatic oxygen mask system. Humans will take some time, 10 minutes or more, to loose consciousness, but they WILL suffer all manner of medical problems from tissue rupture, getting hit be objects flying about, and cardiac arrest if they have any latent cardiac issues.

Ratbone124.178.45.153 (talk) 10:56, 13 July 2012 (UTC)

I never claimed that oxygen levels alone caused discomfort after a few minutes, I listed several factors. Also, you mentioned that people breath harder as carbon dioxide goes up. I agree, but also think this makes you feel uncomfortable, as do the temperature, humidity, odors, etc. Having been on a plane parked on the tarmac without any air circulation, I can tell you it gets uncomfortable quickly. StuRat (talk) 06:41, 14 July 2012 (UTC)

It also looks like you made a math error. 49 m length by 4.72 m width, with a half-circle profile (assuming the other half to be the luggage compartment, etc.), gives me a volume of 428 cubic meters, not 880 (LπR²/2 = (49π(4.72/2)²)/2 = 428), and this is before subtracting volume for seat, overhead bins, and, of course, people. StuRat (talk) 07:02, 14 July 2012 (UTC)

And you've also failed to take into account people with diminished lung/heart function, etc., who may become uncomfortable due to oxygen deprivation (hypoxia) far sooner than healthy individuals. There's even discussion of requiring higher air pressure in the cabin, in order to protect such people: [20]. StuRat (talk) 07:15, 14 July 2012 (UTC)

I think StuRat was still right that it would be uncomfortable after a few minutes though, no so much from the lack of oxygen, but more from the humidity and temperature building up causing it to feel stifling. I suppose there might be an unstated assumption that with no air exchange the air con is also broken though. If the passengers were aware of it, I'm sure many would feel uncomfortable instantly. 203.27.72.5 (talk) 20:19, 13 July 2012 (UTC)

Actually, if the cabin was just well air conditioned, it sounds like it would be better without outside air coming in. According to Ratbone there's no real negative side effects from the lower oxygen levels. Getting drowsy from the carbon dioxide would help you get to sleep and pass the time and it should keep annoying kids less active; kind of like a primitive hypersleep. In the event of a crash the LEL of fuel air mixtures would be higher. The pilot and crew would still need some extra oxygen from somewhere, but that seems a lot easier to do than the whole cabin. 203.27.72.5 (talk) 02:33, 14 July 2012 (UTC)

Carbon dioxide, if anything, would make you breath harder, then hyperventilate. I believe it's carbon monoxide which makes you drowsy, and, if it did, you'd be in danger of dying. Lucky for us very little CO should occur in the airplane cabin, unless there's a fire. StuRat (talk) 06:44, 14 July 2012 (UTC)

Let's look at Stu's claims in turn:-

1. Experince of plane on tarmac. This is not relavent to the OP's question, as he asked about 100% recycling of air, not complete shutdown of aircon. With no air moved past your face, you will notice distress a lot quicker even if temperature and humidity are the same. Note that some people have an irrational discomfort in enclosed places when things go wrong. I have experienced people claiming they are running out of oxygen after a 10 minutes or so in a stuck elevator - complete nonsence. I too have been stuck in a powered down airliner for about 30 minutes - air quality was not a problem, but being annoyed with the boredom and delay certainly was.

2. Math error. Yes, I forgot to divide by 2 to allow for the cargo hold not being part of the available air. This means that oxygen would be down to comfort limit in about 1 hour 20 min, not 3 hours as I said. But don't forget the raised CO2 will cause the passengers to automatically breather deeper.

3. Folk with diminished health. The experience of airlines over many years is that slow air quality change almost never causes problems. This is as you would expect, as humans have considerable lung over-capacity at rest, and CO2 drives breathing depth to maintain blood oxgen at stautation level. In other words, in stale air you breath deeper but still well below breathing capacity, and as blood oxygen is still saturated, the heart doesn't see any difference.

4. Rising humidity. I had some difficulty finding a simple definitive reference for human moisture evolution rates at rest (plenty of refrences for exercising sportspersons), but figures range from 0.01 kg/hr to 0.022 kg/hr for an averge sized human at rest at 25 C. We drink about 1 litre a day when not working, but most goes to make urine, the remainder breathed out and sweated. We can expect an aircraft with aircon working but with no fresh air induction to bring humidity down to 40% REL. Accoding to my stadard ASHRAE pschrometry chart, this means a moisture load of 0.0065 kg per kg of air, and a n air density of 0.85. This equates to 2.7 kg of moisture in the cabin space. Assume each person evolves 0.015 kg/hour, and a confort limit of 70% REL, which has a moisture load of 0.011 kg/kg. This means that the comfort limit with 269 humans will be reached in 30 minutes. But, wait, there's more: All those bodies will generate heat, as perhaps the sun shining on the hull. So teh aircon will remove this heat, and removing heat from air by means of passing it over a cold plate always means condensation. This will considerable extend the 30 minite time toi discomfort, perhaps even indefinitely.

5 Raised temperatures. Since the OP's question did not required aircon to be completely shut down, there is no reason for temperature to rise. However, an aircraft at crusining altitude is passing thru very cold air, so the issue is not critical.

6 Diference between CO and CO2. Both make you sleepy. Neither cause discomfort. Recovering from CO is a serious problem though.

Conclusion: While I made a calculation error, my opinion still stands: Stu is wrong, lack of fresh air in an airliner is not of any critical importance. Ratbone121.215.69.8 (talk) 11:34, 14 July 2012 (UTC)

1) You misread my response again. I did not say "complete shutdown of aircon", as you claim. I said there was a lack of "air circulation", not "aircon". It was actually quite a cold night, and the plane was ice cold to begin with, so no cooling was needed, at least not for the time we were on the tarmac. I've also had a similar experience in well insulated houses, where, without any air circulation, a roomful of people quickly becomes "stuffy". StuRat (talk) 20:20, 14 July 2012 (UTC)

3) You still seem to be talking about normal, healthy people when you say things like "humans have considerable lung over-capacity at rest". People with certain health problems are already right at the limit, with little over-capacity to draw on, and the link I provided shows a dramatic increase in deaths during flights, likely due to changing demographics leading to more unhealthy aging baby boomers on planes. It can be argued that such people shouldn't fly, or should have portable oxygen generators with them if they do, but people aren't always aware of their health problems until they have a crisis. StuRat (talk) 20:14, 14 July 2012 (UTC)

4) You haven't included your sources or the details of your math, so I have no way to check your work this time. However, it looks like you admit that, without any air conditioning, humidity will become uncomfortable in 30 minutes. That seems about right. However, note that you don't always start out at the comfortable 40% relative humidity you used in your figures. If the plane just took off, it may very well have higher humidity, due to having had the doors open while loading passengers. And, if it then sat on on the tarmac full of passengers waiting for clearance, where they don't seem to run any fans or air conditioning, then moisture will have built up even further. So, you want to bring in fresh, dry air quickly, once in flight, to reduce this humidity level. StuRat (talk) 21:00, 14 July 2012 (UTC)

5) You can't assume that flying through cold air significantly cools the plane interior, without any air exchange. An airplane, especially a large one, has a low surface-to-volume ratio, and they also tend to have insulation in the lining of the fuselage, as you don't want ice building up and periodically melting amongst the wires and such. Solar heating can also be significant, especially when flying above the clouds. StuRat (talk) 20:31, 14 July 2012 (UTC)

6) High carbon dioxide does cause discomfort, in that it creates the feeling that you need to breath. If you are already breathing heavily and still feel more of a need to breath, this is quite distressing. See "Use of carbon dioxide for euthanasia" (or animals), which states "research suggests that it is highly aversive and causes distress in many animal species" [21] StuRat (talk) 20:33, 14 July 2012 (UTC)

So why provide it at all? Why not just seal the cabin and use that air for the duration of the flight? It would have the advantages I listed above, plus reduce costs (according to Aspro in another thread), and according to what you said, would not cause any major issues. BTW, for what it's worth I don't think anything that StuRat said was relevant to what the OP asked, since the question was "how long until adverse effects?" which was further qualified by "how long until a majority of the passengers to lose consciousness or even die" and StuRat just talk about discomfort, so calling him out several logical leaps later when he's talking about a plane that was delayed on the tarmac seems a bit pointless. 203.27.72.5 (talk) 11:43, 14 July 2012 (UTC)

I took "how long until adverse effects?" to be a separate question from "how long until a majority of the passengers to lose consciousness or even die?", and considered discomfort to be an adverse effect. Note that discomfort can also lead to real medical problems, like panic attacks, hyperventilation, etc. StuRat (talk) 20:23, 14 July 2012 (UTC)

Good qestion. I'm not competent on the design/engineering of aircraft, however I do know a thing or 2 about aiconditioning of buildings. So, a few points: (1) It is quite difficult to completely seal things. In the aircon industry, there is a rule of thumb that 5% of air fed from aircon outlets should be fresh air from outside - this implies that 5% is leaving the building somewhere, otherwise pressure would rise. Nobody makes specific provision for this - leakage thru builing fabic and doors is generally very much more than sufficient. (2) I said that lack of fresh air is not critical. That does not imply it isn't desirable, especially on a long flight. That's a matter of other sorts of body odours as Stu said. Even though I am not a expert on aircraft, I do know that they do not fully pressurise (to save a bit of money on making a strong cabin). This implies a level of venting to outside anyway. Fully sealing the cabin might impoise structural safety risks if systems fail in flight. Ratbone60.230.211.9 (talk) 13:03, 14 July 2012 (UTC)

It may be of benefit to explain better how breathing works. The body breaths in response to CO2 as I said. However it is oxygen that the tissues need. We have evolved a breating system that in controlling CO2 maintains blood oxygen at saturation level - that is each red cell holds all the oxygen until reaching capillaries, becasue the lungs are ventilated at a rate a little faster than saturation requires. This has the following implications for persons at rest:-

1. If the level of oxygen in the air is reduced, CO2 remaining constant, you will feel distressed quite readily. It is a situation that evolution has not provided for.

2. If the level of CO2 (normally only about 0.03% by vol) is raised, all other gasses remaining the same, you'll breath deeper, even though you don't need to, and you won't have any discomfort up to quite high levels of CO2.

3. If oxygen level is reduced while simulaneously replacing it with CO2, you'll automatically breath deeper and blood oxygen levels will remain at saturation level, up to extreme levels where a limit is imposed by finite lung capacity.

4. If you are working physically very hard, the situation changes. With reduced oxygen pressure, your lungs may not have sufficient capacity to maintain blood oxygen at saturation level.

Do not confuse low oxygen with high CO2. The effects are different.

Interestingly, flushing the lungs with pure oxygen can kill. With near zero CO2 the chest does not move, and blood oxygen level will then fall.

Ratbone58.170.170.23 (talk) 15:33, 14 July 2012 (UTC)

Let me add some clarifications (note that I didn't say that Ratbone is wrong and frequently posts wrong answers):

"Interestingly, flushing the lungs with pure oxygen can kill", but not at sufficiently reduced pressure. At a low enough pressure 100% oxygen is fine. It's the partial pressure of oxygen in the air which is important, and that depends both on the oxygen concentration and the overall pressure.

"With near zero CO2 the chest does not move, and blood oxygen level will then fall." If you mean zero CO₂ in the air, then that's not true, since it's carbon dioxide in the lungs which matters, and that is the sum of the CO₂ inhaled from the air and that produced by the body. StuRat (talk) 20:08, 14 July 2012 (UTC)

Middle Eastern climate

Why is the Middle East so hot and dry even in areas that aren't in a rain shadow? --146.7.96.200 (talk) 18:38, 12 July 2012 (UTC)

Much of North Africa and the Middle East was once covered in forests. These were killed in Neolithic times by slash-and-burn farmers, and the soils were destroyed by overfarming and overgrazing by goats. See Deforestation#Prehistory. See also Cedars of Lebanon for a tree which was once quite widespread in the Middle East. With the soils destroyed, little local surface water remained to support a local rain cycle. The eastern US, for example, is very far from the Gulf of Mexico and the Pacific where its weather often originates. But there is enough retained local surface water that evaporation that occurs in Pennsylvania can fall as rain in New Jersey. Iraq is not going to get much rain that originates as evaporation in Jordan. μηδείς (talk) 18:52, 12 July 2012 (UTC)

This effect is also reinforced by the fact that the Middle East is in the Horse latitudes, where large-scale atmospheric subsidence (sinking of air) caused by the Hadley circulation suppresses large-scale rainfall. It's a major reason why much of Australia is desert as well.-RunningOnBrains^(talk) 19:58, 12 July 2012 (UTC)

It's a bit lumpy, though. The Azore High (semipermanent) really hits Saragasso Sea-NW India hard with the desert stick. Parts of Eurasia east enough get a respite, though (the monsoon, nearby ocean, and Himalayan "lid" probably helps, though). Miami, Cuba, and Taiwan would be Saharic on the other coast. Sagittarian Milky Way (talk) 22:56, 12 July 2012 (UTC)

Large continents, at that latitude, will tend to be dry. Much of the change in the climate is just the continuation of a geological cycle, where we've been slowly coming out of an ice age. The forested version of the Middle East was only possible at the tail end of that ice age. StuRat (talk) 02:58, 13 July 2012 (UTC)

The difference between Joshua Tree National Park and the Negev, of Central Asia and the Iowa plains, or of the Dust Bowl and the current drought, is soil quality, not rainfall. Of course rainfall matters hugely. But without overgrazing and the loss of soil the greater Middle East would be retain water and be greener than it is today. The connection between goats and deforestation is widely remarked upon. See also our article on deforestation during the Roman period]. μηδείς (talk) 04:07, 13 July 2012 (UTC)

why are IAU constellations biased towards the West?

Why do they not include any Asian, Arabic, African or Native American constellations? The Arabs advanced astronomy while Europe lingered in the Dark Ages, yet none of their culture is credited in modern astronomy. The Chinese constellations are extensive, more so than the Greek ones. Why are modern astronomers so racist? 76.104.28.221 (talk) 20:00, 12 July 2012 (UTC)

It depends on who you listen to: In India, for example, a lot of people use the traditional names (as do I). At the end of the day, "A rose by any other name would smell as sweet". Lynch7 20:13, 12 July 2012 (UTC)

See Astronomical naming conventions#Names and boundaries of constellations. The short answer is probably that when the scientific community adopted a consistent naming system for constellations, it was dominated by 'the West'. Note that as currently defined, the entire sky is divided into constellations, and adding 'new' ones would involve redefining the boundaries of old ones. In scientific terms, constellations are arbitrary and meaningless anyway. Regarding the Arabic influence on more meaningful concepts within astronomy, the traces of it are prominent however in the naming of stars: See Aldebaran, Altair, Algol, Betelgeuse, Deneb, Rigel, Vega etc - or simply see List of Arabic star names for them all. When you look into the night sky, if a star has a recognised name at all, the name was most likely first given by a speaker of Arabic. As for the suggestion that modern astronomers are racist, I suggest you do a little research before making such unfounded assertions - astronomy is a science practised worldwide by people of all nationalities and ethnicities, contrary to the implications of your posting. AndyTheGrump (talk) 20:35, 12 July 2012 (UTC)

I strongly agree with Andy. The conventions themselves aren't racist; both the constellation names and the star names reflect the prior dominance of different cultures in the subject. AlexTiefling (talk) 21:31, 12 July 2012 (UTC)

Racist? I wasn't aware there was a constellation called Judeus Rapax or a star called Delta Labiorum Nigri. (Most major star names are in the Arabic language of course.) Perhaps the issue here is not respect for tradition but euphemism, neologism, political correctness and the narcissism of youth? μηδείς (talk) 22:09, 12 July 2012 (UTC)

As others have noted, the constellations are an anachronism, their status reflected by their anachronistic naming system that was set some centuries ago. Star names, where they are significant enough to have proper names, are almost all Arabic. Only the lesser stars that didn't warrant names have binomial Latin titles. Modern star catalogs use alphanumerical designations, which can't have "racist" connotations at all (assuming the use of the Latin alphabet and Arabic numerals is satisfactory). Acroterion (talk) 15:29, 13 July 2012 (UTC)

I'll also note that in modern times the naming of astronomical bodies has become much more diverse: Makemake (dwarf planet), Haumea (dwarf planet) and List of geological features on Titan provide examples. A Latin grammar and terminology has been retained, and since there haven't been any imperial Romans for some time, few have objected. Besides, they were running out of Roman and Greek deities, Shakespearean characters and the like. I'll also note that many features on the far side of the Moon have Russian names, since the Soviets sent the first probes that saw the far side. They therefore had dibs. Star Names: Their Lore and Meanings is an interesting read, as long as you don't take Allen's discussions of Chinese and Mesopotamian naming too seriously. See here [22] for a critique and more bibliographic material. Acroterion (talk) 15:39, 13 July 2012 (UTC)

The names of the constellations are simply traditional, not anachronistic. There's no difference between that and the names of the continents, the elements, or the days of the week for that matter. Renaming them would be ridiculous, and is the sort of things that happens when you get dictatorial regimes, such as with the French Revolutionary calendar. How often would they have to be renamed to keep current? With every new graduating regime, or every new graduating college class? Leave if open to unending RfC? μηδείς (talk) 22:46, 13 July 2012 (UTC)

Are anachronistic and traditional mutually exclusive? I didn't think he was suggesting that we update the names either, just that their use now is anachronistic (and a result of tradition). 203.27.72.5 (talk) 23:43, 13 July 2012 (UTC)

My choice of words could have been more clear: as others note, it's more like a tradition that's been maintained for an astronomical subject that nowadays has little meaning when you can just program coordinates into your telescope and have it find the feature on its own, rather than needing to recognize the patterns of the stars to find things in the night sky, so anachronism and tradition can certainly coexist. Acroterion (talk) 01:29, 14 July 2012 (UTC)

Constellations are useful for more than aiming a telescope though. Not everyone depends on constant GPS positioning to navigate. Rmhermen (talk) 04:46, 14 July 2012 (UTC)

archaism or even atavism might be closer to what I imagine you mean than anachronism. —Tamfang (talk) 05:24, 14 July 2012 (UTC)

By the way, List of Arabic star names has a lot of what looks like junk in the "Meaning" column. There's a page somewhere, isn't there, to ask for help from someone who knows Arabic to clean it up? —Tamfang (talk) 05:24, 14 July 2012 (UTC)

No, none of these other terms than tradition or convention has the appropriate sense. Anachronism is used for a representation of a more modern fact in an inappropriately ancient context, like painting Sodom as if it were a renaissance Dutch city. An atavism is an either morally or biologically primitive avatar in modern times, like cannibalism, a person born with a human tail; but there is nothing inherently primitive (as opposed to simply old) about greco-roman culture. They had republics, democracies, atomism, evolution, and everything else we have except electricity and nuclear physics. Archaism implies the intentional use of a dead form. But there is a constant tradition of greco-roman mythology in the West. This is not the adoption of some style that has been dead for centuries,, but the retention of a tradition that has been alive in film and literature as recent as Kevin Sorbo and Lucy Lawless. Everything in our language and culture has a past, even if it is Lady Gaga referencing Radio Gaga. The word the has a past. Should we make up a new language from scratch every year because it was used by our dead relatives, and is therefore from the last Saeculum? μηδείς (talk) 05:30, 15 July 2012 (UTC)

Dark Energy as the Quantum Error Correcting Code of the Universe

Given the Holographic principle and that information can not be removed from the Universe as a whole, the "boundary" of the Universe must be smooth and expanding. If there is always exactly enough Dark energy to maintain the Universe as a Flat space then the dark energy is acting as a Quantum Error Correcting Code to pad the history of the Universe onto its "boundary".

If this is correct, what sort of test could be made for the adjustment of dark energy to "fit around" the mass content of the Universe? Hcobb (talk) 23:15, 12 July 2012 (UTC)

I gather from the use of terms in quotation marks that you might be aware that the definitions of the words you are using might not be clear to readers. I am not sure of your hypothesis so I can't help you test it. 71.212.249.178 (talk) 01:07, 13 July 2012 (UTC)

Well one of your hypotheses is that space is flat. You can test that. See if a cube with a side ten times longer has a thousand times the volume. Graeme Bartlett (talk) 11:40, 13 July 2012 (UTC)

The dark energy has a constant density in all cosmological eras. It doesn't adjust to the distribution of other matter. The continued spatial flatness of the universe is a prediction of general relativity, independent of the exact nature of the mass/energy. We don't know anything about the boundary of the cosmos (except that, if you believe ΛCDM, its future boundary is a 3-sphere—but that's a spacelike surface that can't expand or otherwise change with time, and it's probably a bad idea to believe ΛCDM). Quantum error correcting codes have nothing to do with your question. -- BenRG (talk) 15:26, 13 July 2012 (UTC)

July 13

Gravitational potential energy

Hi, Potential energy#General formula gives a formula for the the gravitational potential energy of a system of two masses. What is the generalised formula for a system containing an arbitrary number of masses? 86.179.115.69 (talk) 02:16, 13 July 2012 (UTC)

The link you provided tells you how to do it; "Given this formula for U, the total potential energy of a system of n bodies is found by summing, for all ${\frac {n(n-1)}{2}}$ pairs of two bodies, the potential energy of the system of those two bodies." 203.27.72.5 (talk) 02:34, 13 July 2012 (UTC)

Oh thanks, I do apologise, I did not read far enough. 02:40, 13 July 2012 (UTC) — Preceding unsigned comment added by 86.179.115.69 (talk)

term meaning

what is the meaning of the term-'dextrocardia' ? — Preceding unsigned comment added by Akshay15628 (talk • contribs) 03:21, 13 July 2012 (UTC)

Dextrocardia might be somewhat relevant. StuRat (talk) 03:34, 13 July 2012 (UTC)

Testing for an Alzheimer's gene

This article says this: "The catch is that a genetic test for the protective mutation is illogical, since it's so rare, experts said. In order to determine if an individual has the gene, doctors wouldn't be able to detect it."

Can someone explain this to me? It seems self-contradictory. Dismas|^(talk) 04:13, 13 July 2012 (UTC)

It seems like they really messed up their writing. I suspect they meant to say something like this:

"The catch is that performing a genetic test for the protective mutation is a poor use of resources, since it's so rare." StuRat (talk) 04:21, 13 July 2012 (UTC)

The article is full of apparent typos that change the meaning of what's written e.g. "Genetic test for the gene would(n't?) make sense on account of its scarcity", "The mutation appears to slow the production of the beta-amyloid protein, which has long (been?) considered a cause of Alzheimer's.". 203.27.72.5 (talk) 04:30, 13 July 2012 (UTC)

I submitted a post telling them how bad this article is. I suggest anyone who agrees do the same, so they will clean up their act. StuRat (talk) 05:00, 13 July 2012 (UTC)

Great idea for scientists to email religious websites to ask them to clean up their act. Could take a while though. Meanwhile I would tend to avoid religious websites if I wanted reliable medical information.--Shantavira|^{feed me} 08:33, 13 July 2012 (UTC)

I've found that even web pages with a systemic bias (religious sites, politcal sites, sites trying to sell you something) tend not to be biased when talking about subjects not relevant to their bias. In this case, the existence of a particular testing method for a disease says nothing about the existence or non-existence of God, so they have no reason to intentionally use bad logic, let alone bad English. On the contrary, if they can provide excellent, unbiased articles on subject not related to their bias, this may give them more credibility on those subjects they care about most. So, I believe they will make an effort to improve their articles, if we point out the problems to them. StuRat (talk) 18:22, 13 July 2012 (UTC)

One situation where this sort of thing might make sense is when the condition is so rare that the false positive rate for the test exceeds the actual positive rate for the condition. I think there's a name for the statistical conundrum that results... Staecker (talk) 11:42, 13 July 2012 (UTC)

It's an example of a base rate fallacy, and more specifically it's the false positive paradox. Equisetum (talk | contributions) 17:14, 13 July 2012 (UTC)

To clarify, it is of course only a base rate fallacy if you fail to factor in the base rate (incidence of the mutation in this case) into the false positive rate of the test, if you do factor it in and conclude that the test isn't worth doing because of it that's the false positive paradox. The sentence of the article seems to me that it may have been written by someone who has had these concepts explained to them, but hasn't understood them. Equisetum (talk | contributions) 17:31, 13 July 2012 (UTC)

I think the main reason a test wouldn't make sense would be that the test could only predict the absence of Alzheimer's disease, so a positive result would not call for any different action than a negative result. The only value of a test would be to give some reassurance to 1% of the population. Looie496 (talk) 18:53, 13 July 2012 (UTC)

Thanks all! Dismas|^(talk) 07:24, 14 July 2012 (UTC)

Does gravity remove space?

Let's say there is a small universe that is finite but unbounded (a closed universe), and this universe is filled perfectly evenly with particles. Will gravity pull the particles together, effectively removing space and making the universe smaller, or will gravity tug equally in all directions, keeping the particles where they are and maintaining the universe's size? Goodbye Galaxy (talk) 15:13, 13 July 2012 (UTC)

I would say that it displaces space which is what a gravitational field is: the displacement of space by the massive object. The gravity is the force of the space "trying" to get back to its rightful place in the lattice. They will coalesce in the center unless there is something to keep the outer particles in equillibrium with the central ones, right?165.212.189.187 (talk) 15:19, 13 July 2012 (UTC)

Your question does not provide enough information. What are the initial conditions? Is that universe expanding? What's the density of matter? Dauto (talk) 15:29, 13 July 2012 (UTC)

Right. Let's say no dark energy, no cosmological constant. It begins completely static. Density is very light (no need to take other forces other than gravity into account). Goodbye Galaxy (talk) 15:35, 13 July 2012 (UTC)

Yes, space will get smaller. This is the big crunch scenario. -- BenRG (talk) 15:43, 13 July 2012 (UTC)

OK, in this scenario, what if you took a spaceship and travelled "out" away from the center before the gravity was strong enough to prevent it. Would the spaceship avoid the big crunch?165.212.189.187 (talk) 19:19, 13 July 2012 (UTC)

I wouldn't think so. I'm no physicist here, but I would think several things. 1) In such a universe, a spaceship couldn't exist. 2) If such a spaceship did exist for the sake of the question, I would thing that once the ship reached the terminal boundary, it's engines would no longer be operating within the laws of physics. In fact, once crossing the terminal boundary, it is possible the ship would disintegrate because the forces that construct matter would no longer apply. Just a guess. I would think that you are assisted to the edge by the gravitational pull of the outer matter in equal balance to the pull from the inner matter. As you approach the edge, the draw will become increasingly stronger as you put more cosmic matter behind you that at some point the draw toward the center will overcome any sort of thrust you could generate. So for example, if Earth is the center and the moon is the outer edge, there is a point between them where they will null each other out. As you approach the moon, it will assist you to fight the Earth's pull. But at some point once you pass the moon, it's gravity and Earth's gravity will work against you.--v/r - TP 19:59, 13 July 2012 (UTC)

So you are saying that black holes arent the only cosmic body that can have an escape velocity greater than the speed of light?? Like if you find yourself on the "wrong" side of a giant supercluster.165.212.189.187 (talk) 20:23, 13 July 2012 (UTC)

If you consider that the universe consists of black holes, wouldn't that make sense? Again, I am not at all even educated in this area, I'm just putting a little layman's logic toward the problem. Although, let's consider the possibility that you can escape gravity. Do the forces (gravity, electromagnetic, weak, and strong) exist outside of the universe? My guess is that if particles such as the Higgs Boson cannot escape gravity, then the forces that give matter mass and ultimately the force that holds matter together would not exist beyond the terminal barrier. So you'd essentially disintegrate. If you were to escape that terminal barrier, you'd fall apart atomically and the resultant matter would fall back inside of the terminal barrier. Infact, I'd make a guess that you'd get less than a nanometer outside of the terminal barrier before this happened. Or, you could even theorize that the terminal barrier is exactly where this effect would happen. So upon reaching the barrier is where your atoms would break apart and essentially turn back toward the universe.--v/r - TP 20:41, 13 July 2012 (UTC)

None of it works, 165. If you are assuming the Universe is finite, then it has no center to move away from. The "boundaries" of the universe that have been mentioned here are not things that can be physically crossed by people. To give an awful analogy, it would be like trying to escape the earth by moving far enough along its surface. Someguy1221 (talk) 20:53, 13 July 2012 (UTC)

The OP started by stating that the question was about a unbounded universe (That is one without a boundary) and then he asked if it is possible to scape such universe (That is to reach its boundary). Do you see the contradiction now? Dauto (talk) 21:12, 13 July 2012 (UTC)

I understood it as that space is unbounded but cosmic matter is. The OP is postulating a hypothetical universe here and asking what would exist beyond the expansion of the universe.--v/r - TP 21:15, 13 July 2012 (UTC)

165.* and TParis, I assume the original question was about a universe that's spatially a 3-sphere or some other shape with a finite area but no boundary, so there's nowhere to escape to. The traditional "closed universe" in cosmology is in that category. If instead you have a finite region of stationary noninteracting matter surrounded by an infinite vacuum, the matter will collapse to a black hole, but the surrounding vacuum won't go away, and you can escape to it if you start early enough. -- BenRG (talk) 21:24, 13 July 2012 (UTC)

thanks Ben that is what I meant68.83.98.40 (talk) 22:05, 14 July 2012 (UTC)

Btw. The head question does not match the example it's like two different qs.??68.83.98.40 (talk) 00:42, 15 July 2012 (UTC)

MTT assay in vivo

Important and Urgent

Hi everyone I need to urgently know if MTT assay can be applied to tumor (in vivo) samples. If yes, how? what's the procedure and are there any protocols for it?

Then I need to know what options and methods I have to study angiogenesis in my tumor sections (in vivo).

how about cell viability? how should I check that in in vivo samples?

I would greatly appreciate if you can help me with that ASAP.

Regards everyone Siq3939 (talk) 16:00, 13 July 2012 (UTC)

If this is genuinely important, you should not be relying on random people on the internet for it. If, on the other hand it is homework, you need to show that you have attempted to do it for yourself before anybody here will help you, other than pointing you to articles such as angiogenesis and MTT assay. --ColinFine (talk) 17:04, 13 July 2012 (UTC)

And if it is genuinely urgent, you should not post a request somewhere where nobody has an obligation to respond immediately. It may be important, but if it's on this page, it isn't urgent. ~Amatulić (talk) 17:55, 13 July 2012 (UTC)

It is unlikely that a color coded reagent can be used in vivo, but if you have surgical access to the tissue, why not biopsy and use the extracted tissue in vitro? 71.212.249.178 (talk) 05:20, 15 July 2012 (UTC)

mole as a fundamental SI unit

The seven SI base units and the interdependency of their definitions

Why is mole considered one of 7 fundamental SI units?Its just a number and no physical significance. — Preceding unsigned comment added by 49.244.157.192 (talk) 17:01, 13 July 2012 (UTC)

You're not the first to ask this. See Mole (unit)#The Mole as a unit. --ColinFine (talk) 17:07, 13 July 2012 (UTC)

While that section says that it is different from "fundamental units" like the meter and the second, that is actualy also up for debate. A case can be made that physics is fundamentally dimensionless and therefore there are no units at all that have any physical significance whatsoever. Count Iblis (talk) 17:53, 13 July 2012 (UTC)

I agree that the mole is not a particularly fundamental unit. And the candela isn't fundamental either. But as Count Iblis said above, A strong case can be made that none of the base units are fundamental. Dauto (talk) 18:43, 13 July 2012 (UTC)

Isn't it a derived unit? I thought it was defined as the number of ¹²C atoms in 12g of pure ¹²C, and as such requires gram to be defined so it can be derived. 203.27.72.5 (talk) 21:24, 13 July 2012 (UTC)

Actually, I think the mistake here is that the SI system includes any such notion as a "fundamental unit". The SI Units are divided into base units and derived units. The mole is considered a base unit. Looking at the definitions of the base units, most of them have other units in their definitions; meters has seconds, second has kelvins, ampere has kilograms, seconds and meters, kelvin has moles, moles has kilograms, and candela has seconds, meters and kilograms. The only one that doesn't need antoher unit in its definition is kilogram, which is defined by a prototype. I'm a bit confused myself now as to why they have to have two groupings, since the kilogram is the only truly base unit. 203.27.72.5 (talk) 21:39, 13 July 2012 (UTC)

I fail to see how seconds have Kelvins in its definition and how Kelvins have moles in its definition. Dauto (talk) 02:55, 14 July 2012 (UTC)

The definition of kelvins refers to "water". It then goes on to define what water is using an isotopic ratio stated in a molar fraction. Similarly, the definition of seconds refers to a caesium atom at 0K (ok, so you could just as easily say "at absolute zero", but apparently they choose not to and take the more confusing route). 203.27.72.5 (talk) 03:13, 14 July 2012 (UTC)

(ec)By that logic, a meter is a derived unit, as it's the distance traveled by light in 1/299,792,458 of a second, and as such requires the second to be defined. My understanding is that being a derived unit is not so much that the definition depends on other units, but the definition (and dimensionality) is wholly specified by other units. For example, a Watt is entirely equivalent in unit and dimensionality to kg⋅m2⋅s⁻³. However that fails for the mole and the meter, as although other units are involved in their definition, there's a physical reference involved (either carbon or light) which transforms both the size and the kind of the measurement being referenced. -- 205.175.124.30 (talk) 21:51, 13 July 2012 (UTC)

That makes sense, but I still don't see how ampere is then a base unit as I can't see how any physical reference is in that definition. Or is there a reference to the physical nature of current that I'm not seeing? 203.27.72.5 (talk) 22:19, 13 July 2012 (UTC)

For "the constant current that will produce an attractive force of 2 × 10^–7 newton per metre of length between two straight, parallel conductors of infinite length and negligible circular cross section placed one metre apart in a vacuum", the physical reference is the two conductors and the electromotive force between them. Granted, it's not all that realizable of a physical reference, but it's still something more than a pure mathematical manipulation of quantities, as you get with watts or newtons. Anyway, the emphasis is not so much on "physical reference", but rather on the transformation of kind. An ampere measures current, which is substantially different type of quantity than "newton per metre per metre" or any such rearrangement of the units in the definition. In contrast, a newton is a kg⋅m/s² - both in size and in quality. Force is intrinsically nothing more than a mass through an acceleration. - Note this is highly dependent on point of view of "kind". As mentioned above, one could argue that the theory of relativity means that space and time are really the same thing with the speed of light being a conversion factor. With that sort of outlook, the definition of the meter seems superfluous, and the meter is simply a non-decimal rescaling of the (light-)second. However, for most purposes we still draw a distinction between space and time (e.g. make a distinction between seconds and light-seconds), so view a space-unit to be distinct from a time-unit. -- 205.175.124.30 (talk) 23:57, 13 July 2012 (UTC)

Yes, physics can in fact be interpreted as not requiring units at all. But even if we decide not to do that, and keep the meter, Kelvin, etc... as the metric system does, there is still the fact, as the OP clearly stated, that a mol is just a number, not a physical quantity at all. Dauto (talk) 02:49, 14 July 2012 (UTC)

A mol is not just a number. Avagadro's number is just a number. A mol is an amount of particles. Just like a kilogram is an amount of mass, a meter is an amount of distance and a second is an amount of time. 203.27.72.5 (talk) 02:56, 14 July 2012 (UTC)

Equivalently, a mole is the conversion-ratio between the molecular property under consideration (like mass, or electric charge), and the quantity of molecules in the sample. If we decided to standardize a unit of mass other than the gram, we would need to standardize a different Avogadro constant to count the number of particles in a sample of unit-mass. And if we decided on a unit of charge other than the coulomb, we would similarly need a different value for the conversion factor between the fundamental charge and the unit-charge. If you study the mole in the context of electrostatics, you'll see it pop up a lot in the mass to charge ratio experiments, where it's again used as a unit-conversion-factor between "bulk" charge and elementary charge; in fact, historically, electric charge measurement was the first context in which an accurate value for N_A was measured. If I recall, it was Michael Faraday who made this connection; and if you read his works, you'll find that he's notorious for using an abundance of strange units. I haven't the slightest idea how he metered out a "grain of water", let alone how he "acidulated" it. His other unit of choice was the Leyden jar. Five-eighths of an inch of zinc converts to about... 800,000 Leyden jars. I bring this up not only because it's humorous, ... but because a genius experimentalist like Faraday was able to extract fundamental physical properties, even when his experimental setup was quantified with totally arbitrarily-selected units. Nimur (talk) 17:50, 14 July 2012 (UTC)

A grain of water is pretty easy. See grain (unit). Grains are still used pretty extensively with small arms ammunition. 203.27.72.5 (talk) 20:44, 14 July 2012 (UTC)

The usefulness of knowledge of Higgs Boson etc.

Physicists have spent countless billions on colliders and other projects to confirm the existence of this boson and other particles and fields comprising the Standard Model. Earlier nuclear research up through the 1940's produced nuclear weapons, atomic power, and nuclear medicine. Has anything useful in everyday life come from this more recent research, as opposed to the earlier findings that atoms can yield energy by fission or fusion? A large body of findings in physics might well be expected to yield improved ways to generate, transmit, convert or store energy, improve transportation or communication, diagnose or treat disease, grow or preserve food, provide fresh water, make rayguns or spaceship drives or other sci-fi staples, defend against various menaces, transmit or store information, do faster computations, or do astronomy. So far, has it amounted to anything more than an interesting challenge and a lucrative career for a great many physicists? By comparison, look how quickly electricity and electromagnetism became useful in everyday life after 1800 when the Voltaic pile was announced, or how quickly we got x-rays and radio following on the work of Bequerel and Hertz in the late 19th century. Have futurists or scientists outlined even in the most general ways how any of this new science might lead to anything useful? How can a "Theory of Everything" be "Useful for Nothing" except prying more research funding from the world's taxpayers. Edison (talk) 22:15, 13 July 2012 (UTC)

A more comprehensive understanding of particle physics could send fusion research in new directions. It would take a few decades or longer before the conclusions are fully realized though. This isn't the first time that there's been a question like this on here. 203.27.72.5 (talk) 22:46, 13 July 2012 (UTC)

"By comparison, look how quickly electricity and electromagnetism became useful in everyday life after 1800 when the Voltaic pile was announced..." About 80-120 years? μηδείς (talk) 22:53, 13 July 2012 (UTC)

Electrical telegraphs were in use much earlier. 203.27.72.5 (talk) 23:01, 13 July 2012 (UTC)

Yes, there were useful electrical and electronic devices around before 1920. By 1811 Davy demonstrated the arc light. He and Faraday used electricity to isolate severl newly discovered elements. Water was decomposed in the first year. There were extremely powerful electromagnets, magnetic telegraphs, motors and generators within 40 years, with new and useful devices every decade. Is the "PET scan" and particle beam used in hospitals actually a result of the particle physics research program, as some articles touting the benefits of the LHC imply? Our article does not say it came from modern particle physics research. The positron was demonstrated in the 1930s and the cyclotron used to make the tagging chemical radioactive also dates to the 1930's. Other claims are that we will get all this spinoff from the tools they perfect to make the LHC work, like better magnets and computers. This is like "The Apollo Program gave us Tang," not a convincing argument, since a food lab could also give us Tang, a magnet lab could engineer magnets without a LHC, and IBM or equivalent are always working on faster computers for competitive purposes. "Getting us from 21st to 23rd century science" is one valid reason, but some sizzle would be nice. (Ways in with clearly understood particle physics could lead to a quantum computer the size of a candy bar, more powerful than a university supercomputer of today, costing less than an Ipod, or an electric car battery with a 500 mile range and a 10 minute recharge time, or the ability to beam power to a spacecraft engine.) Edison (talk) 23:31, 13 July 2012 (UTC)

Telegraphs were hardly "everyday" use, and that the arc light was demonstrated was of no use before electrification. Not that I expect higgsbosoning people will happen any time soon. μηδείς (talk) 00:17, 14 July 2012 (UTC)

Just because they weren't used by everyone everyday doesn't mean they didn't effect everyday life, like for example the newspapers getting information much faster and publishing it for you to read. 203.27.72.5 (talk) 00:28, 14 July 2012 (UTC)

Yes, which people on the frontier downloaded and read every morning while brewing their mail-order espresso. See the relevant articles, gotcha, and yeah, whatever. Fully half the US was electrified by...1925. Even the first transatlantic telegraph cable took til 1858. We can continue this debate in five decades. μηδείς (talk) 03:14, 14 July 2012 (UTC)

No Edison, there are no known real world applications yet for the Higgs boson. Particle physics has had a fundamental role for our understanding of the world including Cosmology, Astrophysics, Astronomy and such, but these areas of knowledge don't have many practical applications either. Nor has space exploration. Sad will be the day when we start questioning those areas of knowledge foe their lack of practical applications. Dauto (talk) 03:20, 14 July 2012 (UTC)

I hate to break it to you Dauto, but that day came the very first time a theoretical physicist asked for funding. If you want money to do something, you can't be surprised when someone asks why that thing is worth doing. 203.27.72.5 (talk) 03:34, 14 July 2012 (UTC)

"No applications yet" ignores the actual question,which dealt with identified possible benefits from all this expensive knowledge(aside from "There will be spinoff") with 10,000 bright scientists sucking up a billion dollars a year for the past and future many years. In the 1700's electrical experimenters noted that static electricity could create light, by causing a glow in an evacuated tube containing mercury vapor, and that the discharge of a Leyden jar could make a small wire incandescent before it melted (thus cueing the thoughtful reader to a future ability of electricity to provide fluorescent and incandescent light, respectively). Eighteenth century electrical researchers also noted that an insulated wire could carry information swiftly to a remote location, even though they only had static electricity's ability to attract or repel a pith ball at the remote end of the wire as a demonstration. Someone's curiosity about "Areas of knowledge" does not automatically justify billions of tax dollars, when they might be as justifiably spent on astronomy, space probes to other planets, archeology, genomics, oceanography, entomology, paleontology, , cognitive psychologyand myriad other areas of research with their own hungry scholars seeking funding. Just as Meitner's work led to the atom bombing of Japan, governments possibly envision exotic new weapons to be derived from a better understanding of particle physics ("Screw with us and we'll pop a black hole on you" or whatever) Surely somehow this expensive and hard-won knowledge might be envisioned as having some application in a few decades, by scientisis working in the field, by science writers, or by futurists. The areas of energy production, transmission, and storage as well as information storage and transformation, and computation seem like possibilities, with possible use in medical diagnosis and treatment, besides the whole sci-fi panoply of spaceship propulsion, deathrays. wormholes, etc. If one had asked a thoughtful researcher such as Faraday or Henry in the 1820's what a complete understanding of electromagnetism might produce, they might have forecast radios, motors, telegraphs, generators , and electric propulsion, rather than sputtering pompously and indignantly "HOW DARE YOU inquire as to the practical implications of research which I find interesting!" Edison (talk) 04:10, 14 July 2012 (UTC)

Did you ever play the real time strategy game Rise of Nations? In the game you can build various big structures called Wonders (just like in Age of Empires). The wonders all come with specific advantages. The Kremlin makes spies, the Statue of Liberty has economic advantages and the space program lets you see the entire map (i.e. spy satellites). But the supercollider costs a shit load and both fixes the price of goods at the market to a lowish level makes other research instantaneous. That makes no sense and I think it just reflects the fact that there are no tangible benefits to having one so they just made something up. 203.27.72.5 (talk) 04:35, 14 July 2012 (UTC)

Edison, as far as I can tell you created this thread as an excuse to soapbox, so I don't think you should sputter indignantly about other people getting on the soapbox and saying things you don't like. -- BenRG (talk) 06:03, 14 July 2012 (UTC)

Please assume good faith. It amazes me that no one has responded with any links to discussions of how a thorough knowledge of particle physics could lead to useful devices down the road. All I've seen is vilification and ridicule for daring to ask the question. Edison (talk) 20:28, 14 July 2012 (UTC)

Here's a link that might interest you. It's Peter Higgs saying that he can't think of any practical significance for the discovery of the particle that bears his name. Here are my favourite quotes; "It’s around for a very short time. It’s probably about a millionth of a millionth of a millionth of a millionth of a second. I don’t know how you apply that to anything useful," "It’s hard enough with particles which have longer life times for decay to make them useful. Some of the ones which have life times of only maybe a millionth of a second or so are used in medical applications," "How you could have an application of this thing which is very short lived, I have no idea." And yet at the same press release he apparently still said that the government is not "investing" enough money. 203.27.72.5 (talk) 23:56, 14 July 2012 (UTC)

Here is another link to an article from the University of Warwick's Knowledge Centre that says, "The investment in CERN has paid off tremendously, as developments in superconducting magnets in the LHC have led to medical applications, detector technologies have been applied to, for example, homeland security, and advances in computing and networking have become something that we all rely on in our daily lives." 203.27.72.5 (talk) 00:13, 15 July 2012 (UTC)

The basic fact is true that the high investments in particle physics have not made commensurate direct technological returns in the area of particle physics, either militarily or civilian.

But this spending was never intended to do so. The physicists like to pretend that the governments of the world spent on this money on particle physics because they discovered that knowledge was inherently valuable. (Robert R. Wilson justified Fermilab along these lines.) But this is not why the government funded this science. The US government in particular was interested in creating a "reserve labor force" of highly-trained technical people in this country — the idea was that if you train a million Ph.D.s in physics, then some large fraction of those people will be siphoned off into practical applications (nuclear reactor engineering, nuclear weapons development, rocketry, lasers, microchips, etc.) that actually are of interest. Funding big particle accelerators was a way to keep the big physicists happy and to get them to start training up large numbers of students. And the more scientists and engineers you have, the more likely that your nation is going to be the one who discovers the Next Big Thing. (We tend to see scientific discoveries as the random Einstein or Newton born into our generation, which isn't something you can really plan for, but the truth is that nearly all the normal, non-revolutionary progress in science and technology are done by just very smart people who, for whatever reason, decided not to become lawyers or bankers or doctors. The progress of science is better seen as a product of the size and funding of the scientific community rather than the number or quality of geniuses.)

It was not just about wonder weapons, of course, though those were the spur for the post-WWII and (especially) post-Sputnik boom in American physics. There are plenty of "mundane" physics advances in the Cold War period — transistors, microchips, lasers, etc. — which played an incredible role in the American war machine. (And have had side-effects for the civilian side as well. I recall seeing somewhere a graphic which traced how many of the technologies behind the iPod originated from labs doing government-funded research.) It's also much larger than the field of physics — the same pattern was applied to oceanography, for example, which is one of the great Cold War sciences that most people don't realize got almost all of its funding from defense sources and created a bank of knowledge primarily interested in topics that would be of interest to people who develop nuclear submarines.

This, anyway, is one thread of argument in the history of science (see, e.g. Chandra Mukerji, A Fragile Power: Scientists and the State, Princeton UP, 1990). The notion of the reserve labor force was at times quite explicit in US science planning. Non-coincidentally, the minute the Cold War ended, the US started to drastically reduce its support of fundamental physics, famously with the cancellation of the Superconducting Super Collider. But if you're asking, is there a wonder-weapon-style payoff to funding particle physics? Not really, not since the early Cold War/late-WWII. (Even the H-bomb, which might be a plausible candidate, owes its development less to funding of particle physics than it does computing.) But I think you're incorrect in assuming that was the goal. --Mr.98 (talk) 14:42, 14 July 2012 (UTC)

A very good answer. It keeps thousands of smart folks doing physics research, as opposed to selling insurance, or being parasites living in their parents' basements. Even if the Standard Model is as lacking in practical applications as a thorough history of 17th century snuff boxes or a debate over how many angels could dance on the head of a pin, some of the 10,000 physicists might have a serendipitous moment and come up with the device, theory, or discovery which saves the human race from disaster. Years ago, when I was interviewing for jobs, the word was that IBM wanted to hire every promising computer scientist or engineer

they could and put them to work on some harmless or promising project, because they might come up with something which would yield profits, but at least they wouldn't develop something good for a competitor. Edison (talk) 01:41, 15 July 2012 (UTC)

Also other spin offs that wouldn't(unlikely) to of been discovered without particle physics is proton therapy in the cure for cancer, as why would any think that firing high energy subatomic particles into the body would be better at killing cancer cells, and leaving healthy cells alone, would be better than medicines. If you know what you want to discover, you will only discover what you set out to discover. You will never get a paradigm shift.Dja1979 (talk) 16:09, 14 July 2012 (UTC)

Proton beam therapy sounds like a very useful technology for treating some cancers, proposed by Wilson in 1946, using the cyclotron, invented in the early 1930's. I can't see how it is a product of the billions spent since the early 1950s to find the various particles in the Standard Model. Spinoffs as the benefit sounds like the "NASA gave us Tang" pseudo-justification. Edison (talk) 01:26, 15 July 2012 (UTC)

Since the invention of agriculture, most people are free to do useless things. However, people engaging in these useless activities have to pretend that what they do is useful to get a share of the food they need to survive. Count Iblis (talk) 16:38, 14 July 2012 (UTC)

And sometimes critical scientific discoveries were made by people intending to do nothing of the sort. Transposons were discovered because Barbara McClintock wanted to know why corn sometimes had spotted kernels. RNA interference was independently discovered in plants and animals because researchers wanted to know, in the first case, if they could make prettier flowers; and in the second case why this one particular gene, lin-4, could function wh clamile being so darn tiny. Someguy1221 (talk) 02:22, 15 July 2012 (UTC)

"Keep this generation's Feynmans and Henrys in the lab, and they might happen upon something interesting and useful" is not at all a silly reason to do this basic research, along with moving us toward 23rd century science, Startrek, and all that. But I was hoping for something like "When we learn how gravity is modulated by the Higgs boson, it might be possible to build a shield against gravity." An article last year claimed that confirmation of the Higgs would "literally shake the very foundation of our understanding of the Universe we live in." How can that not have any implications whatsoever for our technology, near or far term? Quantum physics, by comparison, led to the Tunnel diode, a useful device which would not work per classical physics, and quantum physics is claimed to have promise for future powerful quantum computers. Michio Kaku has claimed that this research could shed light on antimatter engines, teleportation, and invisibility. Is this credible? How might it work? Edison (talk) 02:48, 15 July 2012 (UTC)

If in the past scientists had only studied matters where practical "payoffs" were noticeably likely before the study began, I suspect that a lot of useful discoveries would either not yet have been made or would have occurred much later than they did.

Some people and organizations in the world have enormous amounts of discretionary funds. (See for example our list of most expensive paintings which shows the fortunes that have been spent on some famous paintings). If you were one of those incredibly fortunate individuals or organizations with more money than you could spend on projects that seemed likely to have "payoffs", it might well make sense to invest some of that fortune into research which had no apparent payoff on the grounds that, given your enormous resources, the cost is negligible and, secondly, that although the potential for a "payoff" was miniscule, the possibility that a payoff if one occurred might be enormous. CBHA (talk) 03:08, 15 July 2012 (UTC)

PS I don't mean to suggest that spending huge amounts of money on art is unwise. CBHA (talk) 03:08, 15 July 2012 (UTC)

I will. Someguy1221 (talk) 03:31, 15 July 2012 (UTC)

Deflecting photons with electricity or magnetism

Is it possible to change the path of electromagnetic radiation with either an electric firld or a magnetic field? i read that when a white laser passes through air that ionizes the atoms which then keep the white light from disintegrating into its composite rays. --Melab±1 ☎ 22:51, 13 July 2012 (UTC)

That's how the Large_Hadron_Collider works. It uses magnets to control the direction of photons.--v/r - TP 22:59, 13 July 2012 (UTC)

No it doesn't. It controls the path of charged particles though. 203.27.72.5 (talk) 23:02, 13 July 2012 (UTC)

Photons have no charge, so basically no it's not possible. But light does behave very strangely in the presence of a very powerful magnet. 203.27.72.5 (talk) 23:04, 13 July 2012 (UTC)

My bad, I've been reading "proton" as "photon" all over that article by mistake. Big "uh duh" moment for me right now.--v/r - TP 23:07, 13 July 2012 (UTC)

I found a previous question about the same thing and it gave this relevant reference. 203.27.72.5 (talk) 23:17, 13 July 2012 (UTC)

The effect arises due to virtual electrons, it causes non-linear corrections to Maxwell equations, see here. The effective electric permittivity tensor and magnetic permeability tensor and the index of refraction for a region of a constant magnetic field,are given here. Count Iblis (talk) 23:53, 13 July 2012 (UTC)

Does the bending of light produced by refraction have anything to do with electrcity? --Melab±1 ☎ 00:14, 14 July 2012 (UTC)

See Refractive_index#Microscopic_explanation. 203.27.72.5 (talk) 00:59, 14 July 2012 (UTC)

You can always desribe a bending effect by an effective refractive index. Light passing through a magnetic field in vacuum will bend slightly, as I pointed out above (because Maxwell's equations are not exact, there are nonlinear corrections), this can be described as if vacuum with a magnetic field is a medium with a refractive index. The formulas are given in the last link I gave above. Count Iblis (talk) 15:22, 14 July 2012 (UTC)

Why does the linearity of electromagnetism mean light cannot be bent by electric or magnetic fields, if electromagnetism was not linear what else could it be (more specific than non-linear), and if electromagnetism were non-linear how would electric or magnetic fields bend light? --Melab±1 ☎ 04:01, 14 July 2012 (UTC)

One effect of linearity is that you can just add two things and the result will be consistent eg f(a+b)=f(a)+f(b). This means that with the Maxwell's equations that if you have light doing one thing, and light doing something else, then it can also do both at once. So a light beam going left through a strong magnetic field going up, will still be a light beam going left and unaffected. However there are materials that you can introduce that can give non linear effects, eg Pockels effect, Kerr effect, and Magneto-optic Kerr effect. Graeme Bartlett (talk) 04:33, 14 July 2012 (UTC)

I know what linearity is but I do not understand how it relates to electricity or magnetism interacting with light. If light was non-linear what specfic terms exist that fall under the category of non-linearity? Quadratic? Sinusoidal? --Melab±1 ☎ 23:05, 14 July 2012 (UTC)

The early and mid 19th century researcher Michael Faraday, after documenting the conversion of electricity to magnetism and vice versa, sought a "unified field theory" tieing in light with magnetism. He found that a powerful magnetic field caused a rotation of the plane of polarization of light. Edison (talk) 04:52, 14 July 2012 (UTC)

Order of treatment in cancer

According to what order are the elements for treating cancer (amputate/operate, chemotherapy, radiotherapy) applied? I have the impression that it's normally in the order that I cite above, but don't have any source for that. OsmanRF34 (talk) 23:22, 13 July 2012 (UTC)

Completely depends on the individual case and type of cancer in question. Assuming we're only talking about solid tumors, the position of the cancer will strongly determine whether or not an operation has a high likelyhood of success. Radiation also has risks that are specific to different areas of the body. The brain is not readily damaged by radiation but is pretty difficult to operate on. In many cases all three are used to treat one cancer. Non-solid tumor cancers (like leukemia) are obviously totally different again. 203.27.72.5 (talk) 23:31, 13 July 2012 (UTC)

I know somebody who is currently in radiotherapy and is expecting surgery after the radiotherapy is over. They refused chemotherapy, but that would also have been before the surgery. --ColinFine (talk) 23:54, 13 July 2012 (UTC)

Chemo would normally come after the op too, to clear up any cells that the operation might have missed. 203.27.72.5 (talk) 23:59, 13 July 2012 (UTC)

The order in which chemo, radiation, surgery, and adjunct treatment is as much dependent on the limitations imposed by the ethics of medical trials as anything. For instance, the order in most breast cancer is: sugery, then chemo, then radition, and then adjuct hormone treatment for the following 5 years. When my wife got breast cancer in 1997, we read up on it - that was the order of treatment then, but leading researchers suspected that it would be better to do chemo first. The trouble is, surgery was in the early days the only option. Then in the 1920's they introduced radiotherapy. Trials showed that radiotherapy after surgery improved survival rates. Nobody was game to do trials before surgury, as this would put patients at risk. The same happened when chemo was invented in the late 1940's. Today, the norm for breast cancer is still operate-chemo-radiotherapy-hormone therapy. However, with bowel cancer, the operation is very complex and difficult, and up until the invention of TME & J-pouch techniques in teh 1990's very uncertain in outcome. So ethics of testing chemo first was acceptable - sure enough, it turns out that chemo and radiation given concurrently before operating is far batter. So, until recently, the norm for bowel cancer was chemo+radiation, then operate, then follow up chemo. There is no hormone treatment applicable for bowel cancer. With the development of TME operating technique, the chances in earley cancer of cancer cells remaining is very low, so it is normal to omit follow-up chemo. Whether or not operate first is also influenced by whether tumours can ve detected before they become metastatic (spreading to other parts of the body). Wickwack120.145.53.163 (talk) 04:57, 14 July 2012 (UTC)

July 14

Cognitive biases and predictions of the end of Moore's Law

Do any purely psychological explanations exist behind why the various forms and corrolaries of Moore's Law consistently continue for longer than experts predict, making it an exception to the usual optimistic bias of technology predictions? NeonMerlin 00:13, 14 July 2012 (UTC)

Are you asking why the experts are too pessimistic? Or are you asking whether Moore's Law is an illusion? I don't see how to make the question make sense if it doesn't mean one or the other. Looie496 (talk) 00:18, 14 July 2012 (UTC)

Judging by the word any I take it he means both. 203.27.72.5 (talk) 00:25, 14 July 2012 (UTC)

Because the serious limits don't start to become evident until 2016-2022? 71.212.249.178 (talk) 00:38, 14 July 2012 (UTC)

And the reason for that is intense competition pressure. To stay on top of the game, semiconductor companies continually make huge investment in research, so that each technical bottleneck is broken just in time to keep Moore's Law in place. The rate of Moore's Law is determined by the cost of research and time-to-market http://en.wikipedia.org/wiki/Time_to_market. Both are relatively constant, hence Moore's Law is fairly constant. The explanation is not psycological, its commercial. Ratbone124.182.22.24 (talk) 01:28, 14 July 2012 (UTC)

I think the point is that that's what they always say. The supposed end of Moore's law is always just around the corner when the "serious limits" start to kick in, yet in 50 odd years it's never actually happened. 203.27.72.5 (talk) 01:14, 14 July 2012 (UTC)

The optimistic bias in technological predictions is just a lack of imagination on our part. When asked to imagine what the world will look like in the future, we might say something like "cancer will no longer be a problem". If we're pressed as to how that will happen, it's usually the most obvious hyped up area of research today, like genetic thearpy or nano-robots or something like that. History has shown us that we will probably be blindsided by some unforseen breakthough and after that we'll think it was obvious and wonder why we didn't think of it sooner. We don't have the android technology seen in the 1979 film Alien, but in that film, the computers were all using a text based operating system and had tiny CRT monitors. It's easy to think of technology giving us stuff like interstellar travel and life-like robots, but thinking of the more subtle things that take incremental advances but improve our lives by so much requires more imagination than we have. The advances won't be the ones that we think they'll be, but they'll still be awesome, and that's reflected in genuine, objective measurements of technological advances, like with Moore's law. 203.27.72.5 (talk) 01:26, 14 July 2012 (UTC)

"in that film, the computers were all using a text based operating system and had tiny CRT monitors. " Not only that, but it made a sound each time a character appeared on the screen! And the speed was about 10-20 characters per second. Bubba73 ^{You talkin' to me?} 03:30, 14 July 2012 (UTC)

And no doubt the text was far larger than on any real screen. This is a common trope in movies and TV, as a person reading small, monochrome text on a screen, in silence, just isn't very interesting to watch. StuRat (talk) 04:32, 14 July 2012 (UTC)

And often the font on the screen would be OCR-A font, which makes no sense. Bubba73 ^{You talkin' to me?} 04:39, 14 July 2012 (UTC)

From memory StuRat, no it wasn't like that because it wasn't important that the viewer actually read the text, it was just lines of text scrolling over the screen much like an old execution of autoexec.bat on a 486 running windows 3.1. 203.27.72.5 (talk) 05:46, 14 July 2012 (UTC)

I can beat the Alien example. An original Outer Limits episode featured a future video phone, with a cord, and ... wait for it ... a rotary dial. :-) StuRat (talk) 02:15, 14 July 2012 (UTC)

Ha. That's hilarious. And realistically, how much has a video phone conversation changed our lives vs wireless telecommunications and reliable buttons? But no one is going to marvel at how much CGI went into making a futuristic button. Audiences wouldn't have even understood what was going on if they saw a movie that depicted the use of a modern mobile phone back when Outer limits was on TV.203.27.72.5 (talk) 02:24, 14 July 2012 (UTC)

I think they would have. After all, the Dick Tracy two-way wrist radio (introduced January 13, 1946, with video added in 1964) had buttons, going way back. StuRat (talk) 03:15, 14 July 2012 (UTC)

Did he get spammed by Jamba!, or MMS pictures of evidence to his client using the intergrated camera? Did it have a visible antenna? Did he lose reception in underground carparks, or have no coverage in a major metropolitan area? 203.27.72.5 (talk) 03:23, 14 July 2012 (UTC)

The D'Arsonval meter movement is rather funny: [23] (at the bottom). We still use that on car speedometers and gauges, though. The speaker also looks like something from a 1960's console TV. The screen does seem to use some type of flat screen technology, at least not a CRT. StuRat (talk) 04:02, 14 July 2012 (UTC)

Can Cannabis grow in the Colorado high country?

9000+ feet, Rocky Mountains. I was walking through an open meadow near a popular golf course and noticed Cannabis looking plants growing in bunches within a large circle of area. According to the rather confusing Cannabis article, "The leaves have a peculiar and diagnostic venation pattern that enables persons poorly familiar with the plant to distinguish a Cannabis leaf from unrelated species that have confusingly similar leaves (see illustration)"—first of all, what illustration?! Okay, next, the picture to the right of the paragraph sure looks like what I saw. What "unrelated species" are there that I may be confusing this with? If this is Cannabis, does that mean someone threw some seeds there as a joke or something? Thanks! Reflectionsinglass (talk) 02:58, 14 July 2012 (UTC)

Is this a real question or just a lead up to a Rocky Mountain High joke ? StuRat (talk) 03:17, 14 July 2012 (UTC)

In case it's meant as a serious Q, let me take a stab at it: Cannabis grows like a weed, hence the name. Not sure if it grows at that altitude, but, if so, maybe some hippie spilled some seeds out of his baggie, and that's all it took.

The illustration they meant was the one to the right. Here's the full-sized version: [24].

Doing some web searches, it does appear to grow at high altitudes, but 8750 feet is the highest point I saw listed explicitly. Here's a couple sites I found: [25], [26]. StuRat (talk) 04:11, 14 July 2012 (UTC)

Wild cannabis isn't that rare of a weed in NA, but no one cares because the weed version is worthless to smoke, just like the vast majority of plants we eat, plant breeders have dramatically improved the quality of cannabis that is cultivated. The "hippie" bit is uncalled for, please keep your stereotyping to yourself. Unique Ubiquitous (talk) 05:03, 14 July 2012 (UTC)

The wikipedia article must need a visit from the PC police too then, since it says that the movement is known for experimentation with drugs. 203.27.72.5 (talk) 05:37, 14 July 2012 (UTC)

Sure, but it does not follow that those who use or grow the drugs are hippies. It has never been the case that only hippies smoked pot, and the vast majority of pot smokers today are not hippies. I would be more worried that someone is intentionally growing them up there — which can be a dangerous thing to interact with depending on who is growing it. When you see a stand of marijuana growing, consider that that's somebodies money growing out there. --Mr.98 (talk) 15:15, 14 July 2012 (UTC)

Fair enough, but what's "NA". Namibia ? Netherlands Antilles ? StuRat (talk) 05:06, 14 July 2012 (UTC)

What's the reference to "grows like a weed, hence the name" about, Stu? The etymology has nothing to do with weeds, as far as I can see. -- ♬ Jack of Oz ♬ ^{[your turn]} 05:12, 14 July 2012 (UTC)

Do you not use the slang word "weed" in Australia, for cannabis ? StuRat (talk) 05:28, 14 July 2012 (UTC)

I'm pretty sure JoO is aware of the slang word, they're just saying the etymology of the slang word has nothing to do with cannabis growing like a weed. Whether or not this is true I can't say, I had trouble any reliable sources most appear to discuss othe things like the word marijuana or pot. Nil Einne (talk) 05:49, 14 July 2012 (UTC)

Sorry, of course I know it as "weed". I misinterpreted Stu's comment, which I read to mean that the name "cannabis" was from some presumably Latin or Greek word meaning "weed". My bad. But in checking out the etymology, I did discover it's cognate with the word "canvas". That had never occurred to me, but it makes a lot of sense. -- ♬ Jack of Oz ♬ ^{[your turn]} 06:24, 14 July 2012 (UTC)

NA = North America. What else, StuRat? OsmanRF34 (talk) 05:26, 14 July 2012 (UTC)

OK, a bit non-specific, though. I listed two possible more specific meanings. StuRat (talk) 05:28, 14 July 2012 (UTC)

Which of the three contains the region mentioned in the title of this section? —Tamfang (talk) 06:08, 14 July 2012 (UTC)

People often reply to questions on one part of the world with answers on how things work in their own part of the world. StuRat (talk) 06:30, 14 July 2012 (UTC)

In order that we may answer your questions within wwikipedia ref desk guidelines, please explain at the ref desk discussion board thread on this post why you cannot see the illustration in the article you searched to the right of the text you mentioned. Please upload an image there so we may help you identify the plant, although, do be aware that people have been shot for trespassing on someone's weed patch. Please explain there what evidence you have that someone has planted these plants as a joke so that we can evaluate it, rather than speculate and debate upon it. (Comment added by User:Medeis (μηδείς), who, by omitting their name, implies that their opinion is that of everyone here, when it is really only theirs. StuRat (talk) 05:09, 14 July 2012 (UTC))

From our article it appears that some people have described ditch weed as a separate species, though I haven't reviewed the evidence; whatever it is called, it was used fairly widely for routine purposes of landscaping and preventing erosion even during the early days of Prohibition. Apparently law enforcement still goes to great lengths to seek out and exterminate such plants, though they are suited for little but genuinely medicinal or perhaps textile use. Wnt (talk) 05:14, 14 July 2012 (UTC)

I do not believe it can grow there. Cannabis needs lots of warmth and light. OsmanRF34 (talk) 05:23, 14 July 2012 (UTC)

Light isn't a problem at elevation. If anything, they get more light, especially UV. Warmth could be a problem, though. StuRat (talk) 05:26, 14 July 2012 (UTC)

Perhaps I should have elaborated. "Ditch weed", according to our article, is Cannabis ruderalis, and is hardier than the other species. Wnt (talk) 11:10, 14 July 2012 (UTC)

How can law enforcement distinguish between wild useless cannabis and smokable cannabis? Do they look different enough? OsmanRF34 (talk) 05:33, 14 July 2012 (UTC)

I doubt if they bother, but just destroy anything that looks like it. StuRat (talk) 05:56, 14 July 2012 (UTC)

Cannabis sativa grows wild in the UK, and throughout Western Europe. According to my wild flowers book it is native and not introduced. I dare say it is a common escape from cultivation (hemp). It's said that the plants have little or no pharmacological content, not sure if that is because of the variety or because of the growing conditions. Illegal cultivators in the UK use greenhouses or artificial lighting. The UK police have no interest at all in wild hemp, as far as I know. Itsmejudith (talk) 17:08, 14 July 2012 (UTC)

Thanks to all the responses. The plant is growing on private property owned by a resort, which owns the golf course as well. So there's no fear of being shot. I also assume that a pot farm would look more like that scene in the film Without a Paddle, with lots of land dedicated to these plants than just the few bunches I found. I'll bring a plant inside and compare it to the photograph in the article. The way the sentence with the phrase "see illustration" is worded, I was looking for an illustration showing the different types of plants that can be confused with cannabis. I might post a photograph of these plants as well and post a link here. Reflectionsinglass (talk) 21:31, 14 July 2012 (UTC)

Question about Big Bang theory.

Transcluded from the Miscellaneous reference desk. 203.27.72.5 (talk) 06:05, 14 July 2012 (UTC)
the Big-Bang theory is telling that the universe was originated about 13.75 billion years ago from a tiny ball with infinite density and temperature when the ball blasted with a big bang. according to the theory the universe is expanding like a balloon. My questions are:-

1. where that 'tiny ball' was? kept over something? floating some where? or hanging over something?

2. where forom that 'tiny ball' came?

3. who had created that tiny ball?

4. how is it possible that a very 'tiny ball'had so much of matter that a universe of billion galaxies with billion stars are containing?

5. If the universe is expanding then there must be one starting point and one ending point or an edge, then what is there out of the edge?

— Preceding unsigned comment added by 117.201.102.48 (talk) 04:39, 14 July 2012 (UTC)

Wouldn't the Science Desk be a better place to ask science Q's like this ? StuRat (talk) 04:46, 14 July 2012 (UTC)

4) Since matter can have an infinite density, as in the singularity in a black hole, there's no reason the entire universe couldn't fit into a tiny point. StuRat (talk) 04:48, 14 July 2012 (UTC)

You might enjoy Ned Wright's cosmology tutorial.

There was probably never a time of infinity density and temperature; big bang cosmology doesn't require that, and it doesn't seem very likely. Cosmic inflation is the best known attempt to explain the origin of the initial very dense state, but there isn't enough evidence to be sure that it's right. It isn't necessary for the expanding region to have an edge, though it could. Other than that, the answer to the questions is "nobody knows (yet)". -- BenRG (talk) 06:31, 14 July 2012 (UTC)

Your questions make assumptions that the universe "before" the big bang and "outside" it have properties like the universe we know today. But depending on the particular theory, these assumptions may be false (which is why I have put those words in quotes). For example, one common theory about the Big Bang (famously presented by Stephen Hawking is that "before the Big Bang" is like "South of the South Pole". So our experience is that wherever we are on the planet there is something to the South of us; but if we go to the South Pole, our experience (our assumption) breaks down: there is no "South" there. In the same way, Hawking suggests, at the Big Bang there is no "before". On that theory, your questions 2 and 3 do not make sense, as they contain erroneous presumptions. --ColinFine (talk) 08:42, 14 July 2012 (UTC)

(ec) I thought the idea was that since all of space was contained within the big bang--there was no "place" outside it. So it makes no sense to ask "where" it happened. It happened "everywhere". Isn't this supposedly why the Cosmic microwave background radiation is found everywhere? And, perhaps I'm wrong, but isn't the big bang also supposed to be the origin of time itself? If so it would make no sense to ask about "before" or "what caused" it, right? Pfly (talk) 08:45, 14 July 2012 (UTC)

(5) An expansion does not imply that there will not be a contraction. In other words, the expansion may go on forever - or it may not. It may contract. It may oscillate between expansion and contraction. We simply don't know. Our universe may be a bubble in an even bigger universe - or it may not. I'm reminded of one of Haldane's quotes: "The universe is not only stranger than we imagine, it is stranger than we can imagine". We can gather information and see what that information leads us to, but to suggest that we know the answers to your questions is arrogant at this point in time. Doesn't stop us theorising, of course, and shouldn't stop you asking! --TammyMoet (talk) 08:53, 14 July 2012 (UTC)

Blood test after getting infected by HIV....

We cannot give medical advice
The following discussion has been closed. Please do not modify it.
I had only oral sex with a prostitute before 3 months but now I fear that it might have infected me from HIV as I had some rashes on my genitals and perhaps she also had bleeding gums........ Now I want to clear my doubt that either I got infected or not. I heard somewhere that HIV will not show up in blood test so early after getting infected, so what is right time for blood test. — Preceding unsigned comment added by 14.140.235.82 (talk) 06:19, 14 July 2012 (UTC) Wikipedia does not give medical advice. See a doctor, or other appropriate medical practitioner. AndyTheGrump (talk) 06:22, 14 July 2012 (UTC) See a physician. If you can not afford a physician, is there a free clinic in your area? Furthermore, Diagnosis of HIV/AIDS#Rapid or point-of-care tests also does not constitute medical advice. 71.212.249.178 (talk) 06:33, 14 July 2012 (UTC) The OP has not asked for medical advice regarding us diagnosing or treating his condition. He has asked how soon a positive HIV test shows up after infection. The answer is that it may take very little time or more than a year. See HIV_test#Window_period. μηδείς (talk) 05:39, 15 July 2012 (UTC)

Do Sounds Played at the Same Time Add?

If you play two sounds at the same time will the resulting sound wave be the sum of the two individual ones? I'm guessing no since a sound wave that is a constant would not sound like anything and you can add two sine waves to get this. Then again, going from the graph of a sound wave to what it sounds like has always been a point of confusion for me. Thank you for any help:-) 209.252.235.206 (talk) 09:02, 14 July 2012 (UTC)

Yes, they add (the wave equation governing sounds is a linear equation). You can have cancellation of sound waves (for example when you hear a beat). —Kusma (t·c) 09:09, 14 July 2012 (UTC)

Yes, if they are exactly the same sounds, in phase with each other, and both arrive at the listener at the same time, then, as you said "the sine waves will add". However, if they are out of phase, either from being produced at slightly different times, or being at different distances from the listener, they can actually cancel each other out (see noise cancellation). Note that when they do add, twice the amplitude of sound wave does not mean it's twice as loud. See decibel. StuRat (talk) 09:13, 14 July 2012 (UTC)

Thank you very much:-) 209.252.235.206 (talk) 09:39, 14 July 2012 (UTC)

You're welcome. I will mark this Q resolved. StuRat (talk) 09:59, 14 July 2012 (UTC)

Resolved

You marked it resolved prematurely, Stu. You have repeated a common fallacy. Consider two independent sound sources (meaning each has its own arbitary waveform and phase): One sound source imparts x watts of acoustic power to the environment and the other y watts. Since energy cannot be created or destoyed, there is x+y watts of acoustic power in the environment. However, the amplitude [the amount of air displacement, or the distance a freely suspended surface (a la a microphone diapham or an eardrum) will move] is proportional to the square root of the acoustic power, just as the voltage in an electric device is proportional to the square root of the power. Two sound sources being indentical in all respects except being out of phase cannot just cancel, as this would mean energy destroyed. What happens is cancellation occurs in some directions and reinforces to double strength in others, the directions being a function of the spacing and phase of the two sources. In other words, the sound becomes directional - analogous to the common use in radio broadcasting to use two or more carefully spaced antennas to provide directional coverage. This principle is also used in concert sound reinforcement - indentical loudspeakers fed with indentical program are "stacked" to beam the sound into the audience and not waste it to the sky. Complete cancellation can only occur if the two sound sources occupy the exact same point in space - a rather theoretical concept. Ratbone121.215.69.8 (talk) 10:12, 14 July 2012 (UTC)

That's consistent with what I said, where I mentioned them both adding and cancelling, listing cancelling due to "being at different distances from the listener". Obviously the two sources wouldn't be at different distances from all possible listeners, and there the sounds don't cancel. The noise cancellation article I linked to explains the details. As for the math, I linked to the decibel article, which explains the relationships between power level, volume, etc. StuRat (talk) 10:24, 14 July 2012 (UTC)

Transcluded to Ratbone's now created talk page. 203.27.72.5 (talk) 11:09, 14 July 2012 (UTC)

BTW, since you misspelled it 3 times in your post, let me point out that it's "identical" not "indentical". StuRat (talk) 10:24, 14 July 2012 (UTC)

You should know by now, Stu, that I do lnkow how to spoll, but I am a shockinkg typist. Ratbone121.215.29.47 (talk) 12:20, 14 July 2012 (UTC)

Either there's an error in your logic or you just weren't clear on what you meant Ratbone, but where you said "Two sound sources being indentical in all respects except being out of phase cannot just cancel, as this would mean energy destroyed" it sounds like you're saying that being in phase is an intrinsic property of the two sound sources. It's not the sources, but rather the waves that are either in or out of phase, and that depends on the location i.e. they're in phase at point A, out of phase at point C, and somewhere in the middle at point B. 203.27.72.5 (talk) 10:29, 14 July 2012 (UTC)

This is probably just a comment on my english, but the wording I used is entirely standard in electronics and acoustics. Engineers talk of sources being "in phase", "out of phase" etc, without implying that waves will be the same relative phase everywhere in space, a phenomena which you have clearly appreciated. Ratbone121.215.29.47 (talk) 12:20, 14 July 2012 (UTC)

Ah, yes, well I'm not an accoustics engineer, so I wouldn't know about their standard technical jargon. Thanks for clearing that for me. 203.27.72.5 (talk) 13:06, 14 July 2012 (UTC)

"Two sound sources being indentical in all respects except being out of phase cannot just cancel, as this would mean energy destroyed": well, they'd have to be in exactly the same place, and the energy will be zero at all times since no wave is actually emitted. —Kusma (t·c) 10:33, 14 July 2012 (UTC)

Correct. Ratbone121.215.29.47 (talk) 12:20, 14 July 2012 (UTC)

Two sources producing the same sounds in phase would be indentical, 180^o out of phase, outdentical. Everything else would be inbetweenical. Clarityfiend (talk) 22:37, 14 July 2012 (UTC)

Back to the OP's question, yes, the sound wave will be the sum of the component waves at the point considered. But the perceived sound will depend on the context and history, see Helmholtz's On the Sensations of Tone as a Physiological Basis for the Theory of Music. μηδείς (talk) 05:49, 15 July 2012 (UTC)

Black Holes and Dark Energy/Matter

If I'm not mistaken, I believe that the existence of black holes was early in the 20th century without the involvement of either dark energy or dark matter. Likewise, the more recent 'proof' that black holes actually exist (based on the velocity of stars orbiting around the unseen black hole) is not dependent on dark matter or energy either.

How does the existence of dark energy and dark matter effect our understanding of black holes?Honeyman2010 (talk) 11:01, 14 July 2012 (UTC)

There is theory about objects called MACHOs that could include black holes and is meant to explain dark matter. It's essentially been disproven though. Dark matter and black holes are believed to be unrelated. 203.27.72.5 (talk) 11:06, 14 July 2012 (UTC)

Agreed; there is no close relation or connection between the three concepts. Black holes were known to be a theoretical consequence of general relativity long before any evidence of their actual existence was found, and indeed the observational evidence for black holes is still somewhat indirect and not totally conclusive. Dark matter and dark energy are names for possible mechanisms explaining puzzling astronomical observations (the galaxy rotation problem and the accelerating universe respectively), but the details of these mechanisms are not completely understood. The similarity in names, each involving black/dark, is partly coincidence and partly lack of imagination on the part of physicists/cosmologists. Gandalf61 (talk) 11:23, 14 July 2012 (UTC)

Thanks for the answers, but my confusion does not stem from the similarity of the words "black" and "dark". My question seems logical since black holes represent infinite gravity, and dark matter and dark energy are thought to comprise perhaps 80% of the matter in the universe. Surely some interaction cannot be so summarily dismissed. Also, would the recent discovery of the Higgs (a scalar) and dark energy (thought to be a scalar) not suggest the possibility of a link? And, finally, if Unification is ever realized through String Theory (perhaps pushed along now with the Higgs), or some other preocess, would that bear on my question? Thanks Honeyman2010 (talk) 12:16, 14 July 2012 (UTC)

The article on MACHOs explains why it is unlikely that dark matter has anything to do with black holes. Also, you should read the article on black holes, as you seem to have some misconceptions about them. They do not have infinite gravity. According to general relativity they contain a point called a singularity that has infinite density. Their mass is finite and they may have other characteristics that define them (see no hair theorem). 203.27.72.5 (talk) 12:44, 14 July 2012 (UTC)

Please see Talk:Dark matter#Draft table. 71.212.249.178 (talk) 21:51, 14 July 2012 (UTC)

Polyvinyl fluoride and PubChem name. A little confusion.

Hello, I looked up polyvinyl fluoride in PubChem Compound and got struck. For polymers, PubChem Compound shows only the monomers. However in this case it shows fluoroacetylene instead of fluoroethylene. (i.e; fluoroethyne instead of fluoroethene). Why? And in Pubchem Substance, it is more confusing to me. Can you help me please? Your comments are always welcome. They have got it almost right for polyvinyl chloride. (For reference you may look CAS and CHEBI:)Vanischenu m^Talk 12:34, 14 July 2012 (UTC)

I don't think the answer is too exciting. It looks like they're just plain old wrong. Should be an alkene, not an alkyne. 203.27.72.5 (talk) 13:01, 14 July 2012 (UTC)

It's quite unfortunate that this occurred at a trusted site. Thank you for your kind reply. I will mark this question as resolved then.

Resolved

Vanischenu m^Talk 19:26, 14 July 2012 (UTC)

Genetic difference between Africans

Is it true that the genetic difference between two different ethnic groups in Africa like say the Hutu and the Zulu people is comparable or even greater than the genetic difference between a given black guy and a given white guy? ScienceApe (talk) 16:07, 14 July 2012 (UTC)

I found this:

Interestingly, both autosomal and X-linked sequence data show higher DNA variation within Africans than between Africans and Eurasians, contrary to the general observation of lower within-population than between-population differences in population genetics. This finding implies that Africans differ on average more among themselves than from Eurasians. Thus, with the exception of many minor unique variants, the nucleotide diversity in Eurasians is essentially a subset of that in Africans, as suggested by the observation that both Y-linked and autosomal haplotypes found outside of Africa were often a subset of the collection of haplotypes found in Africa. Our finding is more in agreement with the out of Africa model of human evolution than with the multiregional model because it is consistent with the view that modern humans originated in Africa and that a smaller subset of this population later migrated to other parts of the world. During and after the migration some variants would have been lost and, as the separation time is still short, non-Africans have not yet acquired many high-frequency variants, though they might have derived some variants from indigenous archaic populations in Asia and Europe. For these reasons, the genetic differences between non-Africans and Africans are on average smaller than the genetic differences within Africans.
(Yu et al. (2002). "Larger Genetic Differences Within Africans Than Between Africans and Eurasians". Genetics. 161, 269-274)

Which basically means yes. I don't know specifically about Hutu or Zulu genetic differences, but the latter study includes several Bantu peoples (of which the Hutu are genetically very close to) and the Zulu people. However, it also includes the !Kung, which belong to the Khoisan-speaking peoples; and two of the African pygymy peoples, the Aka of the Mbenga group and an unspecified member of the Mbuti group. The latter peoples are the most genetically diverse of the human populations on the planet, so depending on what you mean by "African" it can be skewed one way or another. Most people tend to separate the Khoisan group and the pygmies from other African populations, which in turn are separated from the more recent ethnic Arabs in North Africa (not included in study). Also note that "Eurasians" in this case refers to European (both Western and Eastern) and Middle Eastern human populations, though the sample group for them is composed purely of Europeans.-- OBSIDIAN†SOUL 17:29, 14 July 2012 (UTC)

This should not be surprising, under the the recent African origin of modern humans theory. (It is only surprising if you are fooled into thinking that superficial differences like skin color, hair type, and eye folds are actually indicative of deep genetic differences.) Imagine Africa as a big pool of genetic diversity. Spurs are flung out of it relatively recently in human history. These spurs migrate all over the place. But they are still just spurs of some initial African population — by and large, the initial Africans stay in Africa. So there would still be more diversity there than elsewhere. See also, Founder effect: populations that leave necessarily have less genetic diversity than the place they left. Such is my quite lay understanding of it, anyway. --Mr.98 (talk) 17:36, 14 July 2012 (UTC)

On an interesting note, given the historic trends of racism. The non-African population genetically closest to African populations are Eurasians. The farthest are the dark-skinned and curly-haired Melanesian Oceanians and Australian Aborigines. Just goes to show how phenotypes can be quite misleading.-- OBSIDIAN†SOUL 17:40, 14 July 2012 (UTC)

On the example of Hutu and Zulu, both groups have origins in the Bantu expansion, so that might not be the best example to use. Of course the genetic difference between two individuals depends on the specific individuals. "A given black guy and a given white guy" is too vague to be very meaningful. Pfly (talk) 03:34, 15 July 2012 (UTC)

Name for numbers in chemical notation?

Is there an overarching, dedicated name for the numbers in chemical notation indicating quantity of atoms in a molecule. For example it would refer to the numbers, collectively as a class, in water and ozone: the 2 in H₂O, and the 3 in O₃?--108.46.98.134 (talk) 16:47, 14 July 2012 (UTC)

I just looked quickly at some of our articles on formulas. They don't seem to name them though. They are just a ratio of the moles of the elements I think. Scholars may have named them at one point. If they haven't then I move that they be called 'Canoe ratio integers'.--Canoe1967 (talk) 17:50, 14 July 2012 (UTC)

Chemical formula is one link. There are more links in the article.--Canoe1967 (talk) 18:02, 14 July 2012 (UTC)

Ha! It feels like they should have a name. I want to use it in a sentence in something I am writing but I can make do. However, I'll check back for further answers.--108.46.98.134 (talk) 18:02, 14 July 2012 (UTC)

Stoichiometric_coefficient#Stoichiometric_coefficient seems to be it. I was wrong as usual.--Canoe1967 (talk) 18:04, 14 July 2012 (UTC)

Nope. That is the big number in front to count the number of molecules in a reaction.--Canoe1967 (talk) 18:09, 14 July 2012 (UTC)

Maybe not but "stoichiometric" is a great word to know.--108.46.98.134 (talk) 18:18, 14 July 2012 (UTC)

I think the numbers (and symbols) surrounding chemical symbols are informally known as "indices" (sing. "index", of course). See this. The number specifying the number of atoms of an element seems to be rather unimaginatively known as the "right subscript" from its relative position (see Chemical symbol).

Then there's also the Greek numerical prefixes (which must be differentiated from the Latin numerical prefixes used for temporarily naming new elements), mono-, di-, tri-, tetra-, penta-, etc. (e.g. H₂O (water) is dihydrogen monoxide; O₂ (molecular oxygen) is dioxygen; O₃ (ozone) is trioxygen)

And lastly, there's the terms monatomic, diatomic, triatomic, etc. But these refer to the number of atoms in a molecule, not the number of atoms of an element in a molecule (e.g. H₂O is triatomic, so is CO₂)-- OBSIDIAN†SOUL 18:25, 14 July 2012 (UTC)

Could it safely be called the 'proportional integer suffix' type thing?--Canoe1967 (talk) 18:33, 14 July 2012 (UTC)

A single Oxygen atom is roughly more than twice the radius of a Hydrogen atom. And Hydrogen is 1/16th the relative atomic mass of Oxygen of course... so "proportional" doesn't exactly fit. :P How about just "number of atoms of an element in a molecule", heh.-- OBSIDIAN†SOUL 18:52, 14 July 2012 (UTC)

'quantitative integer suffix'? I am just trying to think of a ten dollar phrase for a 2 bit number is all.--Canoe1967 (talk) 19:00, 14 July 2012 (UTC)

What's wrong with just calling it the "subscript" ? StuRat (talk) 19:05, 14 July 2012 (UTC)

I was assuming the OP wanted a fancier term is all.--Canoe1967 (talk) 19:47, 14 July 2012 (UTC)

"atomic quantity subscripts" 71.212.249.178 (talk) 21:53, 14 July 2012 (UTC)

Even IUPAC called it just as subscripts at the very sacred Golden book, the Gold Book (online version). See empirical formula. You will be disappointed to see molecular formula.
Simply, it represents the number of an atom or a species in one molecule of the compound under consideration. This is really an amazing question! Vanischenu m^Talk 23:48, 14 July 2012 (UTC)

Our Chemical formula calls them quantity subscripts. 71.212.249.178 (talk) 02:33, 15 July 2012 (UTC)

Making graphite out of wood

How can you make it? Is that technically too difficult? What happens to wood if you just put a lot of pressure into it? OsmanRF34 (talk) 17:35, 14 July 2012 (UTC)

Can you make graphite out of wood? You can certainly make charcoal out of wood, which is another form of carbon, but isn't strictly speaking graphite. Synthetic graphite is not made from wood. --Mr.98 (talk) 17:44, 14 July 2012 (UTC)

Graphite#Uses_of_synthetic_graphite has methods. That is a sub-section of the graphite article above. I would think it is more a matter of cost than difficulty. They may use it to get purer forms as well.--Canoe1967 (talk) 17:57, 14 July 2012 (UTC)

My reading of that section led me to conclude that synthetic graphite is made of Silicon carbide, not wood. --Mr.98 (talk) 18:20, 14 July 2012 (UTC)

The natural creation section says "....a result of the reduction of sedimentary carbon compounds during metamorphism." I would assume some of that was wood. It could possibly be made from wood in a lab but would probably involve more steps?--Canoe1967 (talk) 18:43, 14 July 2012 (UTC)

Right, but doesn't that probably take like millions of years? --Mr.98 (talk) 19:36, 14 July 2012 (UTC)

Yes it would probably have to be a generation lab then?--Canoe1967 (talk) 19:50, 14 July 2012 (UTC)

Wood is a very complex substance made largely of cellulose, a sugar, when dry. Charcoal is what is made be heating wood in a reducing environment, not graphite, which is made of sheets of carbon, not amorphous carbon. μηδείς (talk) 02:19, 15 July 2012 (UTC)

When I was about 10, I was given a chemistry set (something you don't see nowadays). This led me, as it did with a lot of boys, to figure out how to make gunpowder and other sorts of explosives. I aslo had a burner that used alchohol as a fuel, burning it via a wick. I found that placing a cold plate (thin pice of metal) in the top part of the flame produced copious quantities of very pure graphite in powder form adhering to the cold plate. It works on test tubes containing water too. Keit58.169.240.198 (talk) 02:16, 15 July 2012 (UTC)

That's called soot. It's not graphite. μηδείς (talk) 02:51, 15 July 2012 (UTC)

Actually, your method (or the approximate reaction scheme behind it anyway) sounds like what these researchers are doing. 203.27.72.5 (talk) 02:50, 15 July 2012 (UTC)

Well, there you go; you could make graphite from wood by first destructively distilling it to make wood alcohol, burning it and reducing the hot CO/CO₂ with a metal. Not too efficient, but there you go. 203.27.72.5 (talk) 02:27, 15 July 2012 (UTC)

Hey wait, I didn't read that part about it working on (presumably glass) test tubes. Medeis is right. It was just soot. 203.27.72.5 (talk) 03:17, 15 July 2012 (UTC)

Yes, the black stuff on the cold plate is soot. But what is soot? In this case, almost entirely carbon with a bit of hydrocarbon. Not the same as soot from other sources such as wood. What's carbon precipitated when not heated to sublimation? Why, graphite! Keit121.221.5.163 (talk) 04:02, 15 July 2012 (UTC)

What is soot, you ask? Well, it's a mixture of hydrocarbons and amorphous carbon. Amorphous carbon is a bit of a misnomer because it's actually a mixture of graphitic and diamond-like carbon. There's no reason to think that the soot you made when you were 10 had a particularly high graphite content. Why do you think the hydrocarbon and diamond-like carbon content was low? 203.27.72.5 (talk) 04:49, 15 July 2012 (UTC)

You could just make charcoal as per above and then heat that to ~3000°C to make graphite, as is mentioned under Graphite#Electrodes. 203.27.72.5 (talk) 03:20, 15 July 2012 (UTC)

How to get graphite out of wood: Buy a bunch of pencils, split them open, and take out the graphite "leads". :-) StuRat (talk) 02:35, 15 July 2012 (UTC)

Nope - that's part graphite and part clay. Keit121.221.5.163 (talk) 04:02, 15 July 2012 (UTC)

Do algae like or even need darkness once in a while?

If algae (in my case I'm very interested in growing Spirulina) are grown in a Photobioreactor using artificial light instead of direct sunlight, it seems obvious you'd have the highest yield when the light is always on. Evolutionary, though, algae are used to having at least a few hours of "rest" during the night. If you'd supply 24/7 light, could you be halting some important processes from happening? Joepnl (talk) 21:15, 14 July 2012 (UTC)

Yes and no. Please see photosynthesis. 71.212.249.178 (talk) 21:57, 14 July 2012 (UTC)

Judging by how close to the poles algae are known to thrive, I think the assumption that in nature they wouldn't be exposed to light 24/7 is incorrect. 203.27.72.5 (talk) 22:17, 14 July 2012 (UTC)

Ok, some algae (or may be all) possibly like 24/7 light. But to be more precise: I'm only referring to algae (like Spirulina) that only survive in high temperature areas and so have had millions of years of being able to "sleep" at least 6 hours a day and possibly have developed some good or even vital use for that period.

@71.212.249.178 from that article I can't see the reason why algae would or could need darkness? Joepnl (talk) 22:49, 14 July 2012 (UTC)

I was guessing yes on "like" and no on "need" for the tropical varieties you are interested in, but μηδείς's answer below is better, especially if you judge "like" strictly by growth rate. 24/7 sunlight for tropical algae isn't likely to cause enough metabolic stress on them to make their growth rate much less than twice that of 12 hours per day sunlight. 71.212.249.178 (talk) 02:25, 15 July 2012 (UTC)

Some higher plants need a period of darkness or red light to bloom. See photoperiodicity. There are photosynthetic reactions that proceed in the dark, see dark reactions. I am unaware of any metabolic need for darkness. μηδείς (talk)

dark reactions: "Despite its name, this process occurs only when light is available." photoperiodicity is about seasons whereas growing algae is about "seasons" with a duration of perhaps 24 hours or even less. What I'm looking for is research that says "Spirulina (dietary supplement) contains a lot less beta-carotene in a 24/7 light situation, compared to Spirulina that had 20 minutes / hour darkness. Joepnl (talk) 13:18, 15 July 2012 (UTC)

What color skin did the earliest humans have?

I know of the theory stating that ancient humans migrated out of Africa, but there's something about it I don't quite understand. Would the earliest humans have had black or white skin? I'm just trying to figure out if Europeans descended from black humans, or if the black skin tone was something that evolved later in Africans to cope with the sunlight. I'm just trying to understand this better. Thank you for any and all information. InforManiac (talk) 23:18, 14 July 2012 (UTC)

Black skin would have come first, as this is important to living in Africa, or any place with bright sunlight, without getting skin cancer (clothes, hats, sunscreen, and spending most of our time indoors now serve that purpose). Europeans and (north) Asians later developed lighter skin, since, with less sunlight, skin cancer was less of a concern, and lack of UV light to synthesize vitamin D became more of an issue (vitamin D supplements now lessen this concern). StuRat (talk) 23:22, 14 July 2012 (UTC)

Thank you. That's kind of what I assumed, but I just wanted to double check. Thanks again. InforManiac (talk) 23:25, 14 July 2012 (UTC)

OK, I will mark this Q resolved. StuRat (talk) 23:27, 14 July 2012 (UTC)

Actually, the idea that skin color derived as an adaptation to protect against sunlight is an outdated but still common misconception held in increasingly low regard by researchers. Rather, like most phenotypical variation between the races, it is believed to have been (at least much more) the result of sexual selection, rather than natural selection. However, Stu is correct that the original Homo Sapiens sapiens were dark skinned. For the OP, I know of a couple of very good resources on this subject (and the general outwardly physical divergences of the races that are very accessible to even non-experts, if you're interested. Note: I've removed the resolved tag since I do not believe an accurate and full answer was given and expect further discussion to be forthcoming. Snow (talk) 00:28, 15 July 2012 (UTC)

I don't understand. Why would people in tropical climates prefer dark-skinned mates, people in temperate climates prefer medium-skinned mates, and people in arctic climates prefer light-skinned mates ? StuRat (talk) 00:58, 15 July 2012 (UTC)

They don't; it's an incremental process; people tend to prefer (but not necessarily to exclusion) mates who look like those they grew up around. This does not just apply to skin color; when you look at married couples, you find they tend to have very similar characteristics in the shape and relative size of many facial features which are counter-intuitive when you look at the overall span of human variation (things like the length of the earlobe, the width of the bridge of the nose, ect.). This and a whole ton of other well evidenced mechanisms have led a strong consensus that the differentiation of light-skinned people (and different phenotypes in general) started from random mutations (as all adaptions do, whether based in natural or sexual selection) which developed slowly thereafter. That's a cursory explanation that needs a lot more extension, I know, and I hate to bring it up and then dash out just when I got your curiosity up, but as I'm short on time and it will have to wait until later -- will comment further by tomorrow at latest, my apologies! Snow (talk) 01:16, 15 July 2012 (UTC)

That seems to just be saying that people with ancestors in hot climates having dark skin and those in cold climates having white skin is complete coincidence. That's not a very compelling argument. StuRat (talk) 02:14, 15 July 2012 (UTC)

comment: The primary driving factor for dark skin was probably not skin cancer, which likely wouldn't affect you until after you had children, but the fact that UV destroys folic acid (vitamin B9) in the blood, leading to spinal bifida in pregnant women. That is, an inappropriate level of melanin in either direction leads to deformities in children.

Also, chimps have pale or at least blotchy skin. Black skin wouldn't be necessary as long as we had hair or lived in the forest, but the earliest common ancestor to humans most likely did not live in the forest, and was very likely much less hairy than modern Europeans. — kwami (talk) 23:53, 14 July 2012 (UTC)

Why would the earliest common ancestor to humans be "very likely much less hairy than modern Europeans" ? --Demiurge1000 (talk) 00:50, 15 July 2012 (UTC)

See aquatic ape hypothesis. 203.27.72.5 (talk) 01:25, 15 July 2012 (UTC)

Europeans seem to be an outlier. Looking across the most divergent genetic lineages, most have very little body hair. The other famous outlier are the Ainu, also a northern (= cold, and not the environment of our common ancestors) people. — kwami (talk) 02:49, 15 July 2012 (UTC)

I don't think this can be answered without speculation. No harm in that, so long as what is written comes from good scientific thinking, and preferably excellent sources. Has this been studied and written about by notable, suitably qualified anthropologists or similar? We also need to moderate the original question, and suggest that black and white are not the only, diametrically opposed options. There's a lot of other shades out there. HiLo48 (talk)

Of course there a lot of other shades out there. I'm just trying to figure out, generally speaking, how humanity's skin tone started and where along the line things changed. I mean, when humanity was starting in Africa, was skin tone dark and subsequently got lighter in other areas? Or did humanity's skin start out lighter, but got darker in Africa as time progressed? I thought StuRat provided me with a good answer, and I still think his answer maybe very good. I am a little confused by the conflicting opinions though. In regards to the other shades that you mentioned, File:Homo_heidelbergensis_(10233446).jpg is one of them. I just want to get a loose understanding of what happened. InforManiac (talk) 03:47, 15 July 2012 (UTC)

As far as accessible and widely well-regarded sources go, Jared Diamond wrote extensively on this subject matter in the The Third Chimpanzee, I seem to recall. That's an excellent book, by the way, that I recommend to anyone who is looking for a primer on early human prehistory and development, especially as regards animal precursors to our uniquely human traits and our later differentiations as a species. As for more technical sources, I will add some a bit later, as well as a deeper discussion of why the "trait that evolved to protect against sunlight" hypothesis is considered dubious by contemporary researchers -- would do it now but afraid I'm just out the door! Snow (talk) 00:54, 15 July 2012 (UTC)

One bad case of sunburn in Africa would make you lion fodder. The evolution of pale skin, blond hair, and blue eyes can be attributed to sexual selection. There is a pretty universal trend for females to be paler than males. μηδείς (talk) 02:13, 15 July 2012 (UTC)

Dark skin in a sunless climate causes rickets. That's a strong selective force. Since we tan, you wouldn't get bad sunburn in Africa with pale skin, you'd just get really leathery as you age. AFAIK, the preference for pale skin is a product of hierarchical societies, and presumably would not apply to foraging populations like our common ancestors: pale skin means you spend time indoors and therefore have not had a peasant's life of outdoor labor. (Men don't want to be dark for the same reason; ditto the preference for long fingernails.) I'd like to see a study that women are actually paler than men, accounting for time spent in the sun. — kwami (talk) 02:47, 15 July 2012 (UTC)

There's Sex_differences_in_humans#Skin_and_hair and at google. μηδείς (talk) 03:00, 15 July 2012 (UTC)

@InfoManiac: Anatomically modern humans would have started out with the dark skin typical of Africans, Dravidians, Negritos, Melanesians (New Guineans) and Australian aborigines. Whites and Orientals show different mutations in the melanin genes leading to differently pale yellow and pink skins. From Race_(human_classification): "Scientists discovered a skin-lighting mutation that partially accounts for the appearance of Light skin in humans (people who migrated out of Africa northward into what is now Europe) which they estimate occurred 20,000 to 50,000 years ago. The East Asians owe their relatively light skin to different mutations.[62]"μηδείς (talk) 04:16, 15 July 2012 (UTC)

Thank you. I was just thinking about that. About a year or so ago, I was reading a news article about an African family, and a couple of the children had a certain albino mutation. I understand that there is more than one kind of albinism in humanity. But anyway, a few children of black Africans looked as European as could be. I don't remember the eye color, but instead of the hair being white, it was light blond. InforManiac (talk) 04:29, 15 July 2012 (UTC)

The Washington Post article cited for that claim basically backs up what StuRat said in the beginning about the vitamin D (but just makes hints about black skin being a defense from the sun). It also mentions potential sexual selection, so maybe there's not really a consensus on that part of the issue. 203.27.72.5 (talk) 04:35, 15 July 2012 (UTC)

Nautrally brown and blond hair also occurs among Melanesians and some Australian aborigines (though the allele responsible is different to that of Europeans). And both groups as well as the now mostly extinct Ainu are among the hairiest of the human populations. Same with epicanthic folds which actually also exist natively in Scandinavian, Northern Slavic, and Celtic Europeans as well as Khoisan-speakers of Africa. Nasal bridges vary considerably as well, being predominantly low in East Asians but high in most Native Americans, despite being descendants of the latter. And neanderthals were about as phenotypically varied as modern humans in terms of hair color at least.-- OBSIDIAN†SOUL 07:20, 15 July 2012 (UTC)

I'd like to see a ref that aborigines can have naturally blonde hair. I really can't imagine that. 203.27.72.5 (talk) 07:55, 15 July 2012 (UTC)

Picture of a Vanuatu Melanesian kid at right. And here's an Indigenous Australian young man with reddish blond hair and a kid with brown hair. Plenty more pictures on the net if you want. And here's an online article by Canadian anthropologist Peter Frost which mentions it: "Why Do Europeans Have So Many Hair and Eye Colors?" (note: Frost is the most famous proponent of the sexual selection origin of modern human phenotypes mentioned by Snow earlier); and one study: Abbie & Adey (1953). "Pigmentation in a central Australian tribe with special reference to fair-headedness". American Journal of Physical Anthropology. 13, 3:339–360. -- OBSIDIAN†SOUL 12:02, 15 July 2012 (UTC)

As a (white) Australian who has thru work met a large number of aborigines, I'm very skeptical of this. Meeting a full blood aboriginal with blond hair has not happened. The photo Obsidian posted is of Rowan McNamarra, a noted Australian child actor. In the movie Sampson & Delila, he appeared with blond hair, and in all movie promotional photos and movie associated pics he has blond hair. But in other photos he appears to have black or dark brown hair. Its worth noting that the film was about folk living with no hope. It is very common for such people to be mixed race. Full bloods tend to have more pride and self-worth - it may be that the film people had his hair dyed for that reason - the film, light on dialog as the character portrayed by Rowan is severely brain damaged from gasoline sniffing, is full of visual cues and symbology probably completely lost on non-Australians, and mostly lost on Australian white audiences. The text is a very old text. In my State, Western Australia, there is a group originating from the Carnarvon area amomgst whom blond hair is very common, and their facial appearance is a little different to other aboriginal groups. It was only recently (~20 years ago as I recall) that it was proved that a Dutch ship was wrecked on the coast about 300 years before white settlement, and surviving sailors were accepted by the locals and intermarried. That's where the blond hair came from. Samson & Delila, a low budget film acted, directed, and produced almost entirely by aboriginals was an absolutely excellent film by the way. Wickwack124.178.177.175 (talk) 13:17, 15 July 2012 (UTC)

@StuRat, Arctic dwelling people, Inuit and Eskimo are not light skinned. For the most part they are slightly darker than the average European. In the spring, for obvious reasons, the face and arms, if exposed, tend to get very dark. CambridgeBayWeather (talk) 12:10, 15 July 2012 (UTC)

July 15

CIELAB color coordinates

In the CIE Lab color space colors are represented by three parameters - lightness (L*) and a* and b* channels (the * is there to prevent confusion with the related Hunter Lab color space). L* is restricted to between 0 and 100 but the a* and b* channels, which may be positive or negative, are more complicated. Some references state they don't have a theoretically defined minimum or maximum value but note that certain combinations do not produce reaalizable colors. Others state that the minimum and maximum values depend on the color space being worked in - for instance this really gorgeous pdf explains that in the a* and b* channels are restricted to -100 to +100 if working in the CMYK space, but states that larger values can be attained in other spaces. On the other hand, this online color converter - if you inspect the javascript "under the hood" - restricts the a* and b* channels to -128 to +127. What I've not found anywhere is an explanation of how the limits on a* and b* vary, why it's exactly ±100 for the CMYK space ("by definition" is the obvious answer, but I've not seen it stated explicitly elsewhere and it isn't in the wiki article), or in general what magnitude of value is certain to be unrealizable (it's not obvious to me why that javascript only uses about ±128, but I can understand it's intuitively pointless stretching to ±500). Where could this information be found? ManyQuestionsFewAnswers (talk) 02:28, 15 July 2012 (UTC)

The article claims that its 2nd external link has "explanations" for the parameters. I think the first page of [27] may do a better job for you. You probably know that an 8-bit byte representing a signed integer has the range [-128, 127] while humans are more likely to use [-100, 100] for familiarity reasons. 71.212.249.178 (talk) 05:13, 15 July 2012 (UTC)

Thanks that's a nice link. Yes, the -100 and +100 (or -128 and +127) are obviously not completely arbitrary. But while that document has a very clear explanation of the conversion process, better than the Wiki article, I can't see an answer to my original question about what are the a* and b* co-ordinates' theoretical and practical limits (if such a distinction is meaningful!). It is clear that the human gamut extends substantially beyond a* or b* = ±100 (you can see that on this document on the diagrams from page 27 onwards) even if the CMYK space doesn't, and there are imperceptible "colors" beyond that gamut. From the diagrams it looks like b* can go above 130 and still lie in the human gamut so long as a* is approximately -30, and I can't discern where the lower boundary for b* or the boundaries for a* would lie. ManyQuestionsFewAnswers (talk) 13:35, 15 July 2012 (UTC)

Blood agents

According to page 72 of A Laboratory History of Chemical Warfare Agents, blood agents like hydrogen cyanide have a similar toxic mechanism to carbon monoxide. In this previous question, StuRat and Ratbone agreed that carbon monoxide poisoning is essentially painless; it just causes drowsiness, unconsiousness and then death. Yet the wikipedia article on blood agents cites "Blood Agents" by C. J. Walsh to claim that cyanide causes "...violent convulsions and a painful death that can take several minutes." So if they both work by the same mechanism, why is one painful and the other painless? 203.27.72.5 (talk) 05:43, 15 July 2012 (UTC)

This is outside my field, but I note that carbon monoxide posioning works by cripling the function of haemoglobin in the red cells of the blood (see http://en.wikipedia.org/wiki/Carbon_monoxide_poisoning), whereas cyanide posioning works by interfering with tissue cell mitochondria, and this would immediately affect brain cells (see http://en.wikipedia.org/wiki/Hydrogen_cyanide). So the mechanisms are not similar - they are completely different. This does directly contradict what Ledgard says on pages 72, 73. So I googled. See authoritative reference: http://emedicine.medscape.com/article/832840-overview#a0104 - this agrees with Wikipedia that hydrogen cynanide stuffs up mitochondria and gives details of how it does so. It is very well known, even amongst lay people, that CO affects red cells. Ratbone121.215.146.212 (talk) 10:36, 15 July 2012 (UTC)

Outside your field, but hit the spot none the less. Thanks very much Ratbone! 203.27.72.5 (talk) 11:01, 15 July 2012 (UTC)

Resolved

Yet another Higgs question

How many percent of physicists believed, prior to the recent discovery, that the Higgs boson would not be found by the LHC? How many percent believed that it didn't exist at all? It seems to me that although testing the claims of existing theories is important in science, the Standard Model's prediction of the Higgs is kind of like me predicting that the Sun will rise tomorrow. If it doesn't rise, that will be an earth-shattering discovery, but few people seriously expect it to not rise. Is this a valid characterization of the Higgs boson, or am I way off? --140.180.5.169 (talk) 06:40, 15 July 2012 (UTC)

The Higgs is necessary if the Standard Model is correct. But we already know it's at best flawed, so there is no general theoretical requirement for the Higgs tto exist. — kwami (talk) 07:30, 15 July 2012 (UTC)

Apparently the discovery of the Higgs boson cost Stephen Hawking a $100 bet. 203.27.72.5 (talk) 07:21, 15 July 2012 (UTC)

I don't get it. The particle has not been confirmed to have the behaviour expected of the Higgs, so why has Hawking admitted defeat? — kwami (talk) 07:26, 15 July 2012 (UTC)

Because he's noble in defeat. And because he's reasonably sure that if it turns out later they've discovered some unpredicted particle and the Higgs is still at large, then he will still be able to get his money back from the other guy. 203.27.72.5 (talk) 07:43, 15 July 2012 (UTC)

Preserving body part for future genetic sequencing

How do I preserve a part of myself as of today so that it can be genetically sequenced when technologies become cheaper, more available, and more reliable? Also, is it possible to sequence the skeletal remains of a person? Many thanks. 180.254.88.42 (talk) 08:00, 15 July 2012 (UTC)

The bone marrow could be sequenced, until decayed, which, depending on conditions, could be under a year or up to several thousand years. The easiest way to preserve your DNA would be to pull a hair, with the root, seal it in a sterile container, and freeze it. Be sure to label it. StuRat (talk) 08:46, 15 July 2012 (UTC)

A researcher in my lab stores stuff in an ethanol water mixture on the field and in the lab for Later DNA sequencing. Don't know the ratio though.Staticd (talk) 11:02, 15 July 2012 (UTC)

Sticky robots

My son has got a bathtub toy which consists of robot shaped parts that stick to the tiles when wet. The parts are very lightweight and made of some foamy material. I was wondering about the physics behind it. Explanations can be as technical as necessary. Thanks. bamse (talk) 08:03, 15 July 2012 (UTC)

Can you provide more details? Maybe the brand so we can google it and see what you're refering to? I'm just having a hard time imagining it looks like, not having any kids (or their toys) myself. 203.27.72.5 (talk) 08:23, 15 July 2012 (UTC)

Could it contain tiny suction cups ? They tend to work much better when wet. StuRat (talk) 08:42, 15 July 2012 (UTC)

I guess these are robot-shaped versions of the more common foam bathtub letters (sample ad). The adhesion mechanism is probably a mixture of static cling (as used in vinyl decals) and soap residue. Unfortunately our article on static cling is poor, and doesn't even attempt to explain how static cling decals work. --Heron (talk) 09:39, 15 July 2012 (UTC)

Does static cling work on wet objects ? StuRat (talk) 09:41, 15 July 2012 (UTC)

Cling wrap certainly does work with wet food products, so I guess it might. 203.27.72.5 (talk) 09:50, 15 July 2012 (UTC)

Be careful not to confuse cling wrap with static cling. Cling wrap sticks by means of adhesive additives (see madsci.org [28] and [29]), while static cling is a purely electrostatic effect. --Heron (talk) 11:17, 15 July 2012 (UTC)

Hmmm...my physics lecturer said once that cling wrap was the only example of a useful purpose of static electricity in everyday life. Looks like he was confused. 203.27.72.5 (talk) 11:24, 15 July 2012 (UTC)

Lightning captured in nuclear explosion photograph

I came across this popular image shown in many topics related to nuclear weapons. I have noticed there is wierd lightning on the center of the picture, connecting ground and skies, and I can't manage to find out what caused it. What is that lightning ?

http://en.wikipedia.org/wiki/File:Upshot-Knothole_GRABLE.jpg

95.105.133.125 (talk) 08:57, 15 July 2012 (UTC)

vertical smoke flares which are used to observe the shock wave --Digrpat (talk) 09:07, 15 July 2012 (UTC)

Thanks, I tought it's lighning :D — Preceding unsigned comment added by 95.105.133.125 (talk) 09:41, 15 July 2012 (UTC)

Name the Lamp - please!

Yeah, that's a ... humh ? A Gooseneck lamp !

What is the English word for this office lamp with a "swan neck" backbone (you can move it in any direction - and it stays). Grey Geezer 09:30, 15 July 2012 (UTC) — Preceding unsigned comment added by Grey Geezer (talk • contribs)

The bendy bit is called a gooseneck, so the lamp is called a gooseneck lamp. --Heron (talk) 09:34, 15 July 2012 (UTC)

I have a floor lamp like that, and just call it the "adjustable lamp". StuRat (talk) 09:35, 15 July 2012 (UTC)

I'd call it a gooseneck lamp as well. Though I'm not sure what this has to do with science. Dismas|^(talk) 09:45, 15 July 2012 (UTC)

Gooseneck - sure! Thanks! Case closed. Grey Geezer 10:39, 15 July 2012 (UTC) — Preceding unsigned comment added by Grey Geezer (talk • contribs)

Strength training

What are the advantages and disadvantages of classic weights/resistance training with cardio vs circuit training? 176.27.222.99 (talk) 13:03, 15 July 2012 (UTC)