Wikipedia:Reference desk/Archives/Science/2008 September 17

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September 17

Simulation from first principles

How complex a process can modern computers simulate from first principles in our understanding of matter? I know we don't have a complete theory of matter because of tying gravity into QM, but gravity's negligible on small scales, so let's ignore that. What sort of processes can be simulated (not modeled!) just using the Standard Model? How about a single atom splitting? A grain of sand plinking another one? The first few collisions of a nuclear explosion? What can we actually calculate with no hand waving? Is the limiting factor one of computing resources or holes in the theory which cause the results to not match reality? I hope I expressed this clearly. Thanks. --Sean 00:03, 17 September 2008 (UTC)

Let's simplify this a bit. My computer has 2Gbytes of RAM - if we stored position and momentum to double precision for each particle - plus a couple of other bytes for particle type...that kind of thing - then we need 50 bytes per particle. So we have only enough space for 42 million particles in memory. If we simulated a bunch of hydrogen atoms - those are just one proton and one electron - we'd have room for 21 million atoms. Sadly there are 6x10²³ hydrogen atoms in just one gram of gas. So we can simulate about 1/3x10¹⁶th of a gram. You could store all of the particle data on disk - that would get you a couple more orders of magnitude...but certainly anything as complicated as grains of sand are completely out of the question! We could do similar estimates based on the time to do those calculations...I'm pretty sure the results would be just as depressing. SteveBaker (talk) 04:20, 17 September 2008 (UTC)

Here is an article about an IBM/LLNL research project in 2002 that researched deformation of metals by simulating the interactions of 1 billion individual atoms - this required 10 days computing time on a supercomputer. I don't think this is quite what you mean by first principles, as each atom was modelled as an indivisible particle. If you went down to the level of fundamental particles, i.e. quarks and electrons, you would be increasing the complexity by a factor of 100 to 1,000 (strong force interactions between individual quarks must be more difficult to model than the longer-range electromagnetic interactions between atoms). So probably around 1 to 10 million atoms is the upper limit for truly "first principles" simulation with current technology (which is in the same ballpark as SteveBaker's figure). Gandalf61 (talk) 09:47, 17 September 2008 (UTC)

Even a single proton—with its three quarks interacting via the eight gluon fields, which also interact nonlinearly with each other, the whole thing subject to quantum self-interference in a phase space of uncountably many dimensions—is far too complex to simulate exactly. All simulations are approximations. I'm not sure that modern physics even has first principles. There's no axiomatic formulation of the Standard Model; the path integral that it's based on doesn't seem to be mathematically well defined, and it can only be "evaluated" using various tricks. I guess there's an analogy with the calculus, which didn't get a rigorous formulation (the epsilon-delta limit stuff) until long after Newton successfully used it to do physics. But I think it's a fairly common view among particle physicists that the Standard Model will never be formulated rigorously because it really isn't rigorous—it's nothing more than a collection of approximation techniques (for the real, unknown physics) with no "exact approximation" at the core. -- BenRG (talk) 10:56, 17 September 2008 (UTC)

OK, thanks to all for the depressing answers. I knew it was bad, but I didn't know it was that bad! --Sean 13:33, 17 September 2008 (UTC)

I think you'd be fairly horrified about the state of computational physics even at the macro scale. There are many physics engines for performing nothing more complex than Newton's laws of motion on human-scaled objects under gravity and friction. You'd think that the superbly well-understood physics on simple bodies like a dozen or so cuboids would be child's play to simulate - yet even those super-simple things are VERY hard to get right. Even the very best simulations tend to be heavily restricted in what can be done - with a horrible tendency to blow up and generate ridiculous forces and accellerations.

The problem tends to be that time is a continuous function in the real world - but inside a computer it pretty much has to be quantised at a fairly gross level (like maybe 1/100th second increments). Also, in the computer, we don't have infinite precision and precision errors can "leak" energy.

Some current software that works in this area would fail if (for example) you simply made a large stack of cubes - like a tower maybe - stack the cubes perfectly and have them all completely stationary. The collision detection code would have small roundoff errors that would make the cubes vibrate because they were bouncing up and down under gravity at distances that were at the smallest that the computer could resolve. Those vibrations would "leak" energy from nowhere into the system and the whole pile of cubes would start jiggling and bouncing at large scales until the whole pile would collapse with no external forces being applied beyond simple gravity. We're getting better at fixing those problems - but it's generally via ugly kludges that show up under all sorts of subtle special-case conditions.

SteveBaker (talk) 16:07, 17 September 2008 (UTC)

I know what you mean about the game packages. I was amazed when I learned that you can have a whole company whose only product is software to make a person's body look natural when it's falling down, but now I see those kinds of things all the time. --Sean 17:36, 17 September 2008 (UTC)

Yep - absolutely. "Ragdoll physics" are very important to many games. When the character is running around and under "intelligent" control, you can pretty much prerecord animations in a motion capture suite - but when they die and just fall to the ground, they need to behave in a physically reasonable way or it looks laughable. Since in so many games, a large fraction of the "action" entails killing people - they'd better look realistic when they die. That stuff is a pain to set up with a solid body physics package - so if you can buy a chunk of middleware that'll handle that for you - then it's worth having. SteveBaker (talk) 21:37, 17 September 2008 (UTC)

Streamlined intergalactic ship

On a very hypothetical, sci-fi basis, would it make sense for a spaceship traveling at a meaningful percentage of the speed of light to be streamlined as, at these speeds, the near vacuum of the integalactic or interstelar space is experienced as quite dense? Does that makes sense? What could we compare it to that can be intuitively understood? Thank you. 190.244.186.234 (talk) 00:36, 17 September 2008 (UTC)

Probably not. You're right that the interstellar medium would be a real issue at relativistic speeds. However, it's an issue that would have to be solved regardless of ship geometry -- you can't plan for some chunk of your ship to be constantly bombarded by hard gamma rays. As such, once you've solved the problem, it's likely a solution that can be applied across the board -- something like a Bussard ramjet would work just as well for a Borg cube as the starship Enterprise. — Lomn 02:09, 17 September 2008 (UTC)

There must be a range of speeds at which streamlining would help - and the difference in speeds between what would require streamlining and what would need yards of lead shielding could maybe be the difference between (say) 95% of the speed of light and 99%...not a great deal in terms of getting where you want to go. SteveBaker (talk) 03:09, 17 September 2008 (UTC)

There has to be some benefit from having a smaller surface area exposed to vacuum. Plus it looks much cooler (or more intimidating if you run into potential unfriendlies out there). Clarityfiend (talk)

It's sci-fi. Who cares? If you want the ship streamlined, invent some science that articulates why it needs to be that way. If you want it shaped funny, write the science some other way. It's the beauty of suspension of disbelief. --Shaggorama (talk) 07:23, 17 September 2008 (UTC)

Presumably he cares. That's why he asked. APL (talk) 20:56, 17 September 2008 (UTC)

I don't believe that there is any speed you could travel at under which conventional compressive drag would occur (but see caveat later). For that a particle you hit has to rebound into some other particle(s) and then either it or they hit your ship again before you've moved out of the way (that in you're effectively compressing the fluid before you, and that compression pushes you back). In a dense medium like water that's overwhelmingly likely to occur, but in the ultra low density environment of intergalactic space I think you'll find that the initially incident particle is so incredibly unlikely to hit another particle in the timeframe involved that you'll get no rebound and thus no "drag". [Things would be different if you C wasn't a limit, and surely at some impossible hyper-duper-C speed then you'd be hitting so many particles that the rebound probabilies became inevitabilities.] But you still have to worry about collisions, and at near-C speeds hitting even tiny motes of matter is going to be like being shot with a tank shell. Being shot by a tank shell has two demerits - momentum transfer (in this case you slow down a bit) and physical damage (it hurts). The solution, one your spaceship will need, is the same as employed by tank designers - a sloping hull. The more sloping the more glancing the blow, the less momentum you lose, and the less damage you take. I don't think Clarityfiend's concern about surface-to-vacuum would be a concern, because there's no need for that pointy "impact plow" to be filled with air or otherwise be habitable. It's a lot like the sea hull of a submarine - the submariners live in an ugly squat sausage-shaped pressure hull, which is surrounded by the elegant but unpressurised sea hull. SteveBaker's feelings regarding shielding are, however, I think well founded. Blasting around the universe at near-C is like being the projectile in a CERN experiment - all kinds of scary science impacts are going to be happening on the surface of the impact plow, giving off heat (in the plow) and gamma radiation and probably all that stangelet-blackhole-darkmatter disaster stuff that won't happen to CERN but will to you. So that's the front of your ship designed - it's got a super-pointy impact plow (maybe 2 km long and 100m in diameter) filled up with DU. After that there's a 2km pole at the end of which is your living module (where you and your chums live in a colour-coded-unitard utopia). Now for the back end. Let's face it, you're not going anywhere fast with those lefty-wefty renewable sustainable bussard organic macrame power sources; if history shows us anything, it's that to get anywhere fast you have to burn lots of evil fuel and leave a big mess. So behind your living module is another long pole, at the end of which is the propulsion module, wherein some faustian science horror occurs (bashing white holes into black holes, sacrificing bunny souls to Legba, etc.). Armed with this you can happily blast around the universe, and you can probably even bash on through planetary space, sterilizing the planets of impressed natives with the hard x radiation from your engines. Just don't try turning a corner. -- Finlay McWalter | Talk 22:28, 17 September 2008 (UTC)

Awesome! A round of applause for Finlay please!

Within the Milky Way - there are about a million particles per cubic meter...and it's almost all hydrogen and helium. But here on earth there are 2.5x10²⁵ of them per cubic meter. (That's the Loschmidt constant BTW)...so (naively) to encounter the same number of particles per second as an earthbound airplane flying at (say) 100 kph, your starship would have to be moving at 100kph x 2.5x10²⁵ / 1,000,000 - which is 2.5 x 10²¹kph - however, the speed of light is only 10⁹ kph - so at first sight, we never need streamlining.

However, as your speed approaches that of light, relativity starts to cause distances along your line of flight to become compressed - and also to increase the mass of the particles you're encountering - so that there will indeed be a speed at which the tenuous particles of deep space will seem exactly as dense as air to a regular airplane. The closer you get to the speed of light, the denser that interstellar medium becomes.

The tricky point is at that the kinetic energy these little particles release when they hit your starship depends on your velocity as well as their mass. So the energy of those collisions with the skin of your starship start to cause unacceptable amounts of damage - does that happen before or after the aerodynamics of it kick in?

SteveBaker (talk) 05:55, 18 September 2008 (UTC)

Actually you start to get chemical reactions between impacting particles and the hull when the energy is a few tens of eV per particle. For hydrogen, that occurs at ~50 km / s, i.e. 0.01% of the speed of light. Beyond that it is basically impossible to design a hull that wouldn't be eroded by impacting particles. The space shuttle has similar issues on re-entry (it reaches ~8 km/s during the fastest part of re-entry), and the heat shield is specifically designed to survive the partial erosion during the trip. Incidentally, and in response to Finlay, the speed of sound in the galactic medium is "only" ~100 m / s. So to the extent that traditional drag matters in an environment with extremely low pressure, it certainly should start to matter before you cross the "sound barrier", though I would expect that drag would still be pretty negligible. Dragons flight (talk) 06:41, 18 September 2008 (UTC)

Thank you all so much. Finlay your exposé was magistral. One dirty, eroded, pointy behemoth on the way. OP. 201.253.132.39 (talk) 15:04, 19 September 2008 (UTC)

Zucchini and squash

I've been growing Zucchini and squash. I've noticed that ants (and some other insects) seem to be crawling on them. They also seem to have been attacked by Leaf Miners. Are they safe to eat? 67.150.174.6 (talk) 00:58, 17 September 2008 (UTC)

As Leaf miners are in the leaves they won't affect the fruit and ants etc can be washed off. Some green conscious solutions are squirting the fruit with detergent diluted in water + garlic juice to discourage crawling insects. The stub article suggests companion planting rather than insecticide to help the miners problem. Julia Rossi (talk) 02:33, 17 September 2008 (UTC)

Just wash em off and chop em up. Unless the food looks rotten, I wouldn't be too concerned. Ants are everywhere in Brazil; if you find any in your food the locals usually just laugh it off, saying "they're good for the eyes" before chowing down. --Shaggorama (talk) 07:21, 17 September 2008 (UTC)

minimum size for a planet

Part of the definition of a planet is that it be massive enough to form a sphere. Given the type of material that makes up the bodies beyond Neptune, what would be the minimum diameter for a planet? --Halcatalyst (talk) 01:44, 17 September 2008 (UTC)

The definition of a planet is a sphere? I've got a football in the back garden, and I am pretty sure it's not a planet.--ChokinBako (talk) 11:54, 17 September 2008 (UTC)

Did this ball aggregate under its own gravity to form a sphere? Remarkable! --Scray (talk) 15:25, 17 September 2008 (UTC)

Right - so the definition specifically DOESN'T specify a minimum mass. In fact, Pluto (that famous non-planet!) is sufficiently massive to form a sphere - but it's STILL not a planet because mass isn't the only criteria. It isn't a planet because it has failed the "Clearing the neighbourhood" test. (check out Plutino to understand why not).

If we discount the "clearing the neighbourhood" bit - then perhaps your question is "How large much an object be to have sufficient gravity to pull itself into a sphere?" - (well, technically "to reach hydrostatic equilibrium" - the Earth is not a perfect sphere) then I guess there is a different answer. The trouble here is that when a body is a liquid, it takes very little gravity to do the job - if it's made of solid ice or nickel-iron, then it takes a great deal more gravitation to do the job. Consider 4 Vesta - which is a mere 530km across and is believed to have gained hydrostatic equilibrium when it was still a molten blob, but which is now a very non-spherical shape due to meteor bombardment and cannot regain a spherical shape because it's now solidified. On the other hand, Ceres is still spherical and is 950km across. So I suppose we could say that for a SOLID body - the limit is somewhere between 530km and 950km diameter - but for a liquid body, the limit is less than 530km...arguably, there is no lower limit for a liquid body because even a single water droplet assumes a spherical shape in zero g (although it is the surface tension forces that dominate in that case).

SteveBaker (talk) 03:00, 17 September 2008 (UTC)

It is very hard to say what would be the required mass, as, indeed, it depends both on the composition and on the conditions in which the said planet was formed. These things are almost impossible to predict. We don't know the internal composition of Trans-Neptunian objects, so theoretical predictions for the required mass may vary substantially. TNOs are also nearly impossible to optically observe with decent resolution, at least at the present state of technology, so we also do not know for sure which are round and which are not. It is, however, reasonable to assume, based on observations, that Eris and Sedna are round, as possibly are some smaller TNOs; (136108) 2003 EL61 is probably not round, but that may be due to its fast rotation. For the smaller objects the shape can not be determined with acceptable accuracy at present. That puts the upper limit on the required mass at the order-of-magnitude of (1-3)*10²¹ kg; but it may be lower than that. Hope this helps. --Dr Dima (talk) 03:39, 17 September 2008 (UTC)

As of today 2003 EL61 is called Haumea. Rmhermen (talk) 21:08, 17 September 2008 (UTC)

Regarding the "liquid body" suggestion - well, it is highly unlikely to find a drop of liquid in space, because it does not have enough gravity to prevent its vapor from escaping. Thus, the vapor pressure will be lower than the solid-liquid-gas triple point, and the drop will eventually boil out (or partially boil out and partially freeze - that depends on initial temperature and the final steady-state temperature). However, an aggregate of loose solid material may form a sphere at arbitrary low mass, if it remains unperturbed. That was not the original question. The original question was, as SteveBaker correctly noted, what is a smallest required mass for a compact but not spherical object with a solid surface at temperature of a few tens of Kelvin and density of a few g/cm³ to gravitationally produce enough internal pressure to be able to assume hydrostatic equilibrium. The inner parts of the object need not be solid in this process, though. They may be liquid or solid-liquid mixture due to residual heat, compression heat, radioactive decay, etc. --Dr Dima (talk) 04:05, 17 September 2008 (UTC)

The smallest "round" astronomical object known has a diameter of about 400 km. The largest object known not to be round also is about 400 km in diameter. (One is a moon of Saturn and one a moon of Neptune, I think - too lazy to look up their names.) So the minimum diameter seems to be around 400 km. See also dwarf planet candidate.--Roentgenium111 (talk) 21:26, 21 September 2008 (UTC)

Sebaceous gland

Apparently, a Pimple is when the Sebaceous_glandSebaceous Gland blocks usually from the skin thickening or something. However a Sebaceous_cystSebaceous cyst is the same. Is there any explanation for this? —Preceding unsigned comment added by 70.89.49.205 (talk) 03:36, 17 September 2008 (UTC)

A pimple is always infected whereas a sebaceous cyst need not be. The latter are larger and located deeper in the subcutaneous tissue whereas pimples are more superficial. --Scray (talk) 12:52, 17 September 2008 (UTC)

Gasoline/alcohol mixture

The other day as I was filling up my truck, I noted that the pump had "may contain up to 10% ethanol" on it. If I remember my high school science, alcohol burns cleaner than gasoline. So my question is twofold: first, what would be the optimum mixture of gasoline/ethanol to get the most efficient and clean burn? 10%? 25%? 50%? Second (local moonshine laws notwithstanding), could one simply add ethanol to their gasoline tank(i.e. mix it with the gasoline) and still run their vehicle? Can a gasoline engine run on "pure ethanol?" OK. My queery was three fold. :) Thanks —Preceding unsigned comment added by 216.154.17.110 (talk) 03:49, 17 September 2008 (UTC)

Ethanol#As a fuel says that Brazilian gasoline contains 25% ethanol and over 20% of cars there can run on 100% ethanol, using ethanol-only and flexible-fuel engines. Clarityfiend (talk) 04:35, 17 September 2008 (UTC)

Don't take Clarityfiend's comment as meaning that you can just pour everclear in your car and go for a drive. Cars that run on 100% ethanol have engines that were designed to accept ethanol as their primary fuel. Gasoline engines can tolerate some ethanol in the fuel mixture, but only so much. If you want to run your car on ethanol, you'll need to convert your engine. In Brazil, alcohol is cheap because of how much sugarcane they produce, so ethanol is available at most gas stations. I'm gonna guess that's not the case where you live, so you may want to stick with the gas/ethanol mixture from the pump. --Shaggorama (talk) 07:16, 17 September 2008 (UTC)

Ethanol produces a little less energy per gallon than gasoline - and in small doses, most modern cars tolerate it quite well. However, older cars suffer because ethanol dissolves rubber - which does bad things to rubber fuel lines. Ethanol also conducts electricity quite well (gasoline does not) - so some fuel pumps and fuel gauges that are immersed inside the gas tank will short out and fail. However, fixing those kinds of things isn't difficult. The most significant change that most engines need is to have their engine management computer adjusted (perhaps reprogrammed) to deal with the different mixture control you need in order to optimise performance. The biggest problem in Brazil is that their cars are generally poorly converted from gasoline to run on ethanol - and for some reason, their converted engines don't start well on ethanol. Hence most cars there have a small gas tank and a switch on the dash that lets you switch between gasoline and ethanol. So you put the switch into the gasoline position, start the engine - and when it gets up to operating temperature, you switch over to ethanol.

Most cars that claim to be able to run on Ethanol here in the USA are actually only able to run on "E85" - which is a mixture of 85% ethanol and 15% gasoline. I believe that E15 (15% ethanol 85% gas) is what we're currently limited to with "normal" cars. E100 is available only in a few countries - I know Brazil is one...I believe there are a handful of others.

I restore classic cars - and for me, even E15 is a major problem because some of my cars are old enough (1960's) to have rubber seals and rubber hoses all over the place - and running on E15 is going to gradually kill my cars. Rumors of having E25 in US gas stations is pretty worrying. I can usually replace those rubber parts with modern plastic seals and steel hoses - but then they won't be "authentic" or "original" anymore...sigh.

SteveBaker (talk) 13:13, 17 September 2008 (UTC)

Ethanol also preferentially absorbs atmospheric and liquid water, which I think may cause problems. A little bit is good, it will form an azeotrope with the contaminant water in the bottom of your fuel tank; but lots of it will start absorbing water from the air too. Franamax (talk) 09:00, 18 September 2008 (UTC)

Light

Is there a material that changes opacity/scatters more or less light when subject to electric field? How is that effect called? —Preceding unsigned comment added by 89.201.134.211 (talk) 03:51, 17 September 2008 (UTC)

Take a look at the Electro-optic effect with an affect called electroabsorption. Graeme Bartlett (talk) 04:57, 17 September 2008 (UTC)

Liquid crystals can be made to do that - what they do is to change the plane of polarization of the light when you apply a voltage to them - so if you stick a sheet of polarizing film in front or behind the liquid crystal, you can effectively block light or allow it through using small voltages. This is how all manner of displays work - everything from digital watches to flat screen TV's. SteveBaker (talk) 12:59, 17 September 2008 (UTC)

Some other designs of liquid crystals don't rotate polarization but instead become turbid under the application of an electric field. These are used in those windows that magically become translucent and then transparent again (as seen in The Sum of All Fears, although that may be a CGI effect and also at Disneyworld's Star Tours warm-up show). For more information, see our not-so-hot Dynamic Scattering Mode article.

Atlant (talk) 18:28, 17 September 2008 (UTC)

Crickets Chirping

I have a cricket chirping LOUDLY just outside my bedroom window. It's driving me nuts! How long will this likely go on? Weeks? Months? 168.103.225.108 (talk) 04:28, 17 September 2008 (UTC)jmic

I suggest bug spray. Those with more compassion for nature might suggest waiting a few hours. I think it is unlikely that the cricket will stay there for too long. Plasticup ^T/C 05:29, 17 September 2008 (UTC)

If you have a tape recorder, record the cricket chirping. Play it back from a safe distance away from the house; the cricket will eagerly jump towards you. --Kjoonlee 07:22, 17 September 2008 (UTC)

Outdoors, it may eventually go away - but if one gets indoors, it can be absolutely maddening. They are smart enough to stop chirping when you walk around nearby and it's almost impossible to figure out where they are in the room. They also seem to live for weeks without food before they finally "just die already" and stop the incessant racket. We've resorted to bug spray in desperation. SteveBaker (talk) 12:55, 17 September 2008 (UTC)

Lucky you don't live near rice fields. I get billions of frogs banging away all night during the mating season. Nothing I can do about them! (By 'banging away' I mean shouting, trying to attract a mate, not actually what I just said....).--ChokinBako (talk) 14:15, 17 September 2008 (UTC)

You don't have to live near rice fields. Here in New England, "peepers" will keep you up if you're sensitive to that sort of thing. Presumably, they're saying the same thing as their rice-loving cousins, but with a Bahstahn accent.

Atlant (talk) 22:19, 17 September 2008 (UTC)

How does business units monetize their AR with bank and what are the criteria to be met?

Every BU sells some goods on credit, however to meet their working capital demands, they need to influx money which they borrow from Financial institutions. The question is what is the process of Monetizing the Receivable? How is that different from Leverage? What are the nitigritties of monetization of the AR?

Answers will be highly appreciated.

Thanks —Preceding unsigned comment added by 203.201.226.253 (talk) 07:15, 17 September 2008 (UTC)

I only hear Crickets_Chirping in response to your question on this Science desk. Maybe Wikipedia:Reference_desk/Miscellaneous would be a better place to ask? --Scray (talk) 12:47, 17 September 2008 (UTC)

I think you're describing an example of an Asset-based loan. Basically, if the borrower pledges its accounts receivable as security for the loan, it will pay a lower interest rate. Also see Factoring (finance), which is basically a sale of AR. Btw, RD/H is probably better. Zain Ebrahim (talk) 13:43, 17 September 2008 (UTC)

H2O mixed with CO2

If the molecular weight of the first is 18 and of the second is 117, shouldn't CO2 go down?Mr.K. (talk) 12:10, 17 September 2008 (UTC)

Density is not determined by molar mass. --Scray (talk) 12:44, 17 September 2008 (UTC)

...and if you doubt that - think about how liquid water is denser than steam - and how ice floats on liquid water because it's less dense. All of those things are H2O - but they vary immensely in density. SteveBaker (talk) 12:51, 17 September 2008 (UTC)

Note that the exception to the above is if both are gases. If you're talking steam, then you're correct -- but a steam/CO₂ mix is an uncommon scenario. — Lomn 12:53, 17 September 2008 (UTC)

What about exhaust from burning hydrocarbons? (admittedly these will commonly be mixed with nitrogen and other gases) AlmostReadytoFly (talk) 13:37, 17 September 2008 (UTC)

Ummm, 12+16+16=4844? And yes CO2 is denser than H2O (Avogadro's law and all that) but when mixed, the molecules are moving around really fast (speed of sound), so, in usual circumstances, they're very well mixed. Saintrain (talk) 14:37, 17 September 2008 (UTC)

Yes, I meant CO2 is 44. Actually Co2 is 117....Mr.K. (talk) 15:28, 17 September 2008 (UTC)

What's Co2? 2 x ⁵⁹Co = 118? Or something else? Saintrain (talk) 16:24, 17 September 2008 (UTC)

The isotopes of cobalt range in atomic weight from 50 u (50Co) to 73 u (73Co).Mr.K. (talk) 17:29, 17 September 2008 (UTC)

Co₂·⁺ is actually observed in the mass spectrum of many dicobalt complexes. It's not very abundant, so the 118 m/z signal for that fragment composed of the most common isotopes is probably the only one that's commonly seen. DMacks (talk) 17:10, 22 September 2008 (UTC)

Yup, it's always about density if the materials don't mix and it's also about diffusion and intermolecular attraction if they do. As a kid, I was always confused why humid air rises ("water is heavier than air!"). Except it's not liquid water vs (gaseous) air, but rather water vapor compared to air. Water weighs 18 g/mol, air is mostly nitrogen, which weighs 28 g/mol. A mole of any gas has approximately the same volume, so now it's obvious that the less dense water would tend to rise compared to the more dense air. DMacks (talk) 14:52, 17 September 2008 (UTC)

The humid air tends to be warmer, too? --Scray (talk) 15:02, 17 September 2008 (UTC)

Yes, but backwards. As air cools, the net amount of condensation will increase (taking water out of the air and depositing all over my car). Say, rather, that warmer air will tend to have more humidity. Matt Deres (talk) 20:31, 17 September 2008 (UTC)

Shards of pottery

I have noticed that in all of the pictures of exposed Terra Preta, such as Amazon Pit with Scientists the shards of pottery lie spaced and horizontal at various depths as if individually placed and them covered as opposed to piles with shards at different angles, as one might find in a garbage heap or Midden. From this I assume the use of the shards is intentional but for what purpose? 71.100.15.15 (talk) 14:22, 17 September 2008 (UTC)

I profess no special knowledge here, but would it be possible that the method of excavation favored retention of horizontal shards? Wouldn't pottery shards tend to be somewhat level in a pile anyway? --Scray (talk) 15:13, 17 September 2008 (UTC)

As you can see in the photo there are no piles. Individual pots could be represented but neither the pieces or the pots are one on top the other but rather spread out. If dumped with other garbage and trash the pieces would have a tendency to angle. 71.100.15.15 (talk) 21:55, 17 September 2008 (UTC)

Even within a midden, many of the pieces will horizontal. Let's look at the process involved (yes, I have been trained in archaeology): whether the shard gets tossed into a midden or simply gets left in the walkway or falls through floorboards in more modern sites, the pieces will come to rest just as you'd expect - lying flat. As dust, dirt (and in the case of middens, decomposing food) comes to build up on top the pieces, the effect of making the shards horizontal increases. Where you see vertical shards is when the midden is so full of something dumped all at once that there's no time for each piece to "find its level" or where a larger piece has been broken post deposition with enough dirt and junk around it to support it standing upright. Trying to leave pieces in that way intentionally would be time-consuming and a little pointless (as you alluded to) and would not likely fool a trained archaeologist for long. (On that last point, leaving those bits in place, even with them hanging like that, is the mark of someone who's doing the dig in a very thorough, "by the book" manner). Matt Deres (talk) 16:31, 17 September 2008 (UTC)

Terra preta seems to be more of an engineered soil than a garbage dump. It may be reasonable to expect that the potsherds would be systematically laid - if there was cultural knowledge on how to produce terra preta. Since this soil seems widespread in the presumptive area of cultural knowledge and has high productivity, the possibility remains that there was a defined and careful formula for how to make terra preta. Franamax (talk) 08:46, 18 September 2008 (UTC)

What weighs one centigram?

What are some common objects that weigh one centigram?

--80.148.22.232 (talk) 15:12, 17 September 2008 (UTC)

A large grain of sand. --Scray (talk) 15:16, 17 September 2008 (UTC)

A raindrop. (Assuming about 3 to 4mm diameter). SteveBaker (talk) 15:51, 17 September 2008 (UTC)

Might want to tell your friends about that Orders of magnitude (mass) page. Just a few days ago, someone from your same IP asked a very similar question...would be good for everyone to learn about the solution to this type of question rather than just the specific answer to a specific metric-prefix. DMacks (talk) 16:13, 17 September 2008 (UTC)

Why does depression affect concentration?

I've been told that trouble concentrating is a symptom of depression. So I've been wondering if depression's affect on concentration is a chemical symptom or something psychological, does anyone know why concentration is affected by depression? —Preceding unsigned comment added by Mr.K. (talk • contribs) 16:27, 17 September 2008 (UTC)

IMO the short answer is that the effect is "both" chemical and psychological. The longer answer is that they are the same thing, just seen from a different point of view. Wanderer57 (talk) 17:06, 17 September 2008 (UTC)

pls help me with these question

--203.199.213.67 (talk) 17:03, 17 September 2008 (UTC) this book became a minor internet phenomenon when it was reviewed by users of a forum some of whom described it as genrebreaking master piece,while others mentioned that they found it better than the davinci code.another claimed it may cure insomnia,while somebody stated that it provided him with the phone no. of his future wife,pls tell me what is this all about?

It could be anything - those are pretty generic comments that people routinely make about any number of books (other than the phone number bit - that's the only real clue, but I don't recognise it). You would be better off on the miscellaneous or entertainment desks, though - this isn't a science question. --Tango (talk) 18:21, 17 September 2008 (UTC)

Or Humanities... some of those folks appear to read books now and then. (BTW, where are you getting these claims from? That might be a clue.) -- Coneslayer (talk) 18:27, 17 September 2008 (UTC)

The Secret?Avnas Ishtaroth _{drop me a line} 01:35, 18 September 2008 (UTC)

It may cure insomnia? Doesn't exactly sound like a rave review. BTW, are you the same person who asked this [1] or is this question going around for some reason? As for the future wife thing, maybe this guy [2] can help you Nil Einne (talk) 09:16, 18 September 2008 (UTC)

Doesn't exactly sound like a serious question, either. --68.166.144.211 (talk) 12:16, 18 September 2008 (UTC)

Keep in mind that "better than The DaVinci Code " is not much of a standard. --- OtherDave (talk) 12:46, 18 September 2008 (UTC)

over the counter medicatons

what over the counter medications contain benzoylecgonine?? —Preceding unsigned comment added by 24.17.22.80 (talk) 18:13, 17 September 2008 (UTC)

According to this, small amounts of cocaine are found in Health Inca Tea which can be purchased without a prescription. I guess that doesn't answer your question, but it's another way that benzoylecgonine might show up in the body. The article also says that cocaine is sometimes an ingredient for topical medications from ears/nose/throat doctors. Cocaine is metabolized into benzoylecgonine in the body, so it doesn't seem likely that benzoylecgonine would be a component of OTC medications. —Preceding unsigned comment added by 98.210.62.147 (talk) 20:55, 17 September 2008 (UTC) it's a serious question from a quiz which claims it to be wiki proof.anyway,thank u!! —Preceding unsigned comment added by 203.199.213.67 (talk) 08:41, 19 September 2008 (UTC)

Copper Sulphate

Copper sulphate is a white powder as a solid compound. Yet, when dissolved in water, why is its solution blue? Luthinya (talk) 20:37, 17 September 2008 (UTC)

When dehydrated (by heating for example), copper sulphate is white or grey. When it absorbs water, it turns bright blue. There are photos and more information in the article Copper(II) sulfate, for example in the section "Chemistry education". Wanderer57 (talk) 20:59, 17 September 2008 (UTC)

Needles in your thigh

I hope I've managed to ask this question in a way that makes it clear that I'm not asking for medical advice. If not, please delete the question.

I would like to know the correct term (for googling purposes) for a specific type of treatment that I've been subjected to. The treatment consists of a physiotherapist putting needles into trigger points in the iliotibial tract, supposedly for releasing tension in the muscles attached to it, for treating iliotibial band syndrome (yes, I've been running too much, too often, too fast, and increased the distance too soon). Sensing my scepticism, she assured me that it had nothing whatsoever to do with acupuncture. The treatment is given as a supplement to excersises that aim to stretch the lilotibial tract, and excersises that aim to strengthen the gluteal muscles. My questions are:

• what search terms will give me the most relevant hits for this treatment on google?
• ditto on pubmed?
• do we have a page on this treatment?
• is anyone aware of placebo-controlled studies on this treatment, for iliotibial band syndrome or other similar conditions?

Thanks, --NorwegianBlue ^talk 20:52, 17 September 2008 (UTC)

Do they run an electric current through the needles or just poking you with needles? --antilived^{T | C | G} 06:23, 18 September 2008 (UTC)

Sorry, should have mentioned that. This time, needles and no current. Next time, they're planning to run an electric current through. --87.54.16.18 (talk) 06:42, 18 September 2008 (UTC) (NorwegianBlue not logged in, from a hotel PC)

This sounds a lot like electro-stimulation. Myo-stimulation is not uncommon, they have a weight-loss deal that does the same sort of thing, only from the surface. The difference is skin penetration, which will dramatically lower the overall electrical resistance. You haven't mentioned the proposed penetration depth or voltage, and we're not able to adequately judge either. Asking for controlled study ref's is bordering on medical advice, or at least opens the possibility of POV's creeping in - which is part of the medadvice stricture, really. You might be better to ask your practitioner for references from the Medical Review Board which approved the procedure. Get some good names and numbers, then we can search the heck out of it. Franamax (talk) 08:20, 18 September 2008 (UTC)

Quote?

I need a good quote on technology, that has enough information to cite it fully in MLA. Can anyone help? I can't seem to find anything useful with google. —Preceding unsigned comment added by 99.237.213.17 (talk) 21:58, 17 September 2008 (UTC)

One Charles Lindberg goes "I have seen the science I worshiped, and the aircraft I loved, destroying the civilization I expected them to serve." I find it pretty fitting as a technology/sociology quote, though perhaps if you're thinking more positive-impacts it wouldn't be any good. ny156uk (talk) 22:28, 17 September 2008 (UTC)

What kind of "good" quote? Pro-technology? Anti-technology? Something else? Straightforward? Cryptic? Interesting? It would help us a lot if you would give some description of what it was to be used for and what you need it to be "useful" for. "Technology's essence is nothing technological," was Heidegger's classic take on it. --98.217.8.46 (talk) 23:32, 17 September 2008 (UTC)

There are so many great quotes to choose from. But I'd have to go with: "Any sufficiently advanced technology is indistinguishable from magic." - Arthur C Clarke.

Or maybe: "For a successful technology, reality must take precedence over public relations, for Nature cannot be fooled." - Richard P. Feynman

May I also recommend our sister site "http://en.wikiquote.com" - type "Technology" into the search box...enjoy! SteveBaker (talk) 05:05, 18 September 2008 (UTC)

Side note: enjoy Wikiquote while you can, it might be gone soon. Franamax (talk) 08:04, 18 September 2008 (UTC)

Actually, I kinda doubt that'll happen. Getting consensus to dump all that work by all those people would be tough. Consider that every single significant contributor to WikiQuote will vote "No" - and not too many others will vote at all. The proposal is to delete the site entirely - which would also require agreement from all of the various different language WikiQuotes - some of whom have already agressively cleaned-house (eg the French and German sites). Getting cross-language consensus is a non-starter. The Wikimedia foundation lawyer has already weighed in with a statement that he considers all of WikiQuote to fall within "fair use" on the grounds that there are MANY commercial books of quotations that are not prosecuted for copyvio's - and WikiQuote is a non-profit which puts them even further from the law.

What's much more likely is that WP:SOFIXIT will apply and they'll set up more reasonable guidelines to sharply limit the number of fan-cruft quotes from TV shows and movies. Some "quotes" for episodes of (for example) "The Simpsons" are more like whole pages out of the script and certainly start to fall into the "copyvio" category rather than the "fair use" bin! A compromise in which the fan-cruft gets nuked and new rules are set up to stop it from coming back are much more likely to get acceptance than simply wiping out years of work by hundreds of people. Something as simple as "No more than three quotes per film or TV episode." would solve 99% of the complaints.

But those of us who find the site useful (I certainly do) need to keep an eye on the discussion there and be prepared to express our views should it ever come to a vote.

SteveBaker (talk) 15:09, 18 September 2008 (UTC)

Blood as an indicator of pain

I get the impression that my brain is 'hardwired' to associate blood/bloodyness with pain. My question is: How good a correlation is it? If I cut myself shaving or get a nosebleed it doesn't hurt yet it can look pretty brutal. If I get a nasty cut it can really hurt but not cause much blood. Is it just a failing in my brain that causes the association (a failing in everyone's brain?) or is blood (and blood volume) a good indicator of pain/danger? Obviously lots of blood loss is a bad thing so that's why i'm thinking "yes". ny156uk (talk) 22:28, 17 September 2008 (UTC)

I would not expect this to be strongly hard-wired, since humans are omnivores and fresh bloody meat was no doubt something to celebrate, at some point in our history at least. --Scray (talk) 00:11, 18 September 2008 (UTC)

I would say that the greater association is the appearance of blood with an expectation of pain. This may be learned/reinforced from childhood - if you show up covered in blood, your parents adopt a somewhat odd response, what with the screaming and "oh you poor thing" reactions. Evolution will also program you to be more aware of your own pain sensations when you see flowing blood, you have a compelling interest to be sure it's not your own. That said, I tend to get more supreme pain from paper cuts and that grass with the sharp edges (ragged cuts) whereas I've clean-cut myself to the finger-bone and been quite clinical about the affair. Franamax (talk) 07:59, 18 September 2008 (UTC)

It may be worth mentioning that dense sensory innervation does not directly correspond to dense blood vessel spacing - that is, the areas of your body which are empirically most sensitive to pain/touch are not always the ones with the most blood flowing to them. For example, you don't really have the capacity to isolate a pain sensation to specific sub-areas of your lung or spleen, but those areas would hemorrhage pretty profusely if you were wounded in them. Conversely, the finger-tips and tongue are incredibly innervated, so a paper-cut or biting/scalding your tongue can be excruciating (even though it's a "minor" wound with minimal blood flow). Nimur (talk) 15:24, 18 September 2008 (UTC)

It hurt more when I broke my arm (no blood) than when I popped certain zits (blood). Bleeding is caused by breaking the skin. Pain is caused by any number of different things, including burning, freezing, percussion, broken bones, pinching, etc. None of those would cause any bleeding, but they can all be quite painful. — DanielLC 15:52, 18 September 2008 (UTC)

I think it's also worth noting that a paper cut only irritates the nerves, while a stab wound, for instance, cuts through and kills some nerves, hence why a paper cut hurts persistently (not to say a stab wound doesn't).CalamusFortis 20:59, 18 September 2008 (UTC)

Cell-biology experiments outside the cell

Is there an umbrella term to describe experiments performed outside the cell in the same way that in vitro describes those outside the complete body? ----Seans Potato Business 23:38, 17 September 2008 (UTC)

Perhaps cell-free is the term you're looking for (e.g. cell-free transcription/translation systems). By the way, ex vivo is used for experiments done outside the body, too - the distinction between that and in vitro is subtle. --Scray (talk) 00:05, 18 September 2008 (UTC)

We have a Cell-free_system page! --Scray (talk) 00:06, 18 September 2008 (UTC)

The problem with cell-free system is that it's typically used only where the process in question is usually assumed to take place inside a cell, and the author wants to explicitly flag to the reader that something special is going on. ('Cell-free translation system', per your comment, is a good example.) In vitro is often used to describe 'test tube'-type experiments outside cells as well as for experiments in petri dishes; the specific sense will vary from field to field and is usually (but unfortunately not always) clear from context. In describing in vitro experiments that take place inside cells, I've sometimes seen in cellulo used. (The term gets a few thousand Google hits, and is even showing up on PubMed now, in peer-reviewed research.) There's no opposite term I'd feel comfortable using in formal writing, however in casual conversation I've heard ex cellulo—usually accompanied by finger quotes and slightly raised eyebrows. TenOfAllTrades(talk) 01:50, 18 September 2008 (UTC)

Agreed on all accounts. For the OP's question, I wonder if the Community would accept extracellular and dispense with the pretend Latin? Seems simple and clear to me (lack of sophistication obvious, I suppose). --Scray (talk) 03:13, 18 September 2008 (UTC)

My concern with extracellular is that (in my experience, at least) it implies that cells are present, but the reaction or process just happens to be happening outside the cell membrane. A word like acellular might be a little better (emphasizing the absence of cells) but I don't think I've run across it being used that way in the wild. TenOfAllTrades(talk) 03:54, 18 September 2008 (UTC)

Agreed. Acellular if no cells are present in the same container, extracellular if they are present. --Scray (talk) 03:59, 18 September 2008 (UTC)

I'll agree with all that, but if an experiment is carried out with no functional cells present to modulate the reaction, either intra- or extra-, wouldn't it be called, I dunno, chemistry? Franamax (talk) 07:45, 18 September 2008 (UTC)

Sorry if you meant this to be a rhetorical question, but I'll bite. Ultimately, with or without cells, it's all chemistry, right? And it's all physics? However, when macromolecules are involved, interacting in complex ways we don't (fully) understand, it's generally called biochemistry, molecular biology, biophysics, etc. The distinctions among these are somewhat arbitrary, at least in practice. --Scray (talk) 10:45, 18 September 2008 (UTC)

Outside the cell, but still inside the body? I'd go with extracellular, if you want to specifically emphasize that it's outside the cell. If you aren't trying to belabor the "outside the cell" point, it's still just in vivo - "in life". Outside both the cell and body is in vitro (with or without the italics, as your style guide dictates.) -- 128.104.112.147 (talk) 18:56, 18 September 2008 (UTC)