Wikipedia:Reference desk/Archives/Science/2007 June 2

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June 2

Blood transfusion: what about the antibodies in the donor blood?

I read the articles about human blood groups and transfusions, and it is not clear to me why the anti-bodies in the donor blood do not cause problems in the receiver. Type O blood is the universal donor, but it contains anti-bodies against A and B. Are these anti-bodies neutralised before the blood is given to a recipient, who may well have type A, B, or AB? Or do they only work in the body of the donor? 85.180.50.3 01:49, 2 June 2007 (UTC)

In modern blood banking, the blood is centrifuged and separated into red cell concentrate and plasma. The amount of antibodies in a red cell concentrate is not sufficient to cause problems in the recipient. When whole blood of type O is transfused to a recipient of type A, a transfusion reaction may occur due to anti-A in the donor's plasma. --NorwegianBlue ^talk 13:46, 2 June 2007 (UTC)

So, for blood plasma, the compatibility rules are reversed, i.e. the universal plasma donor is type AB? 85.180.50.3 18:47, 2 June 2007 (UTC)

Correct. Plasma of blood group AB does not contain ABO antibodies. --NorwegianBlue ^talk 18:52, 2 June 2007 (UTC)

Thank you! 85.180.50.3 19:19, 2 June 2007 (UTC)

Elastic Potential Energy

I have a problem. A 80 kg block is attached to a 1.42m stretched spring at a 60 degree incline without friction and I have to find the spring constant, k. I know the equation, but the only thing missing is the actual elastic potential energy. If I have that, I can figure it out. Can anybody point me in the right direction? Thanks in advance.

How can you stretch a spring when the angle is at an incline? If anything it should compress it instead of stretching it. --antilived^{T | C | G} 04:49, 2 June 2007 (UTC)

You should be able to use Hooke's Law to find k. You're given x (1.42m). You can find F from the gravitational force, remembering you have to use trig because it's on an incline (so it's not just mg, I think you'll need to use mg sin 60 from memory). Substitute in and solve for k. --203.164.131.127 12:41, 2 June 2007 (UTC)

So the correct answer would be 358.45?

No. The correct answer must include units! --Prophys 07:48, 3 June 2007 (UTC)

358.45 Newtons then?

Nono. Read the first part of Hooke's law carefully. Also, newton should start with a small n (despite what Hooke's law says). Also something is wrong with your calculation. Check your free body diagram. Better still, check your textbook. --Prophys 11:32, 4 June 2007 (UTC)

Magnetism

Any idea how magnetic particles(magnetic force) can penetrate through ordinary matter??OR do they??Does the same apply for electric force??~~

Perhaps you mean magnetic fields and electric fields? --Reuben 07:21, 2 June 2007 (UTC)

Electric and magnetic fields are a way of transferring (mediating) force from a source to the surrounding matter. So if you have a charge, the charge has a field around it based on what force it exerts on another charge (the force here would be coulomb force).

They can pass though matter, but other magnetic dipoles or charges will change the field. One can just add (superposition) the contributions to the field from different sources.

Of course, all atoms contain charges, but they average out to be neutral (screening), so don't really have any impact. --h2g2bob (talk) 07:55, 2 June 2007 (UTC)

The question is really being asked backwards. Why would these fields be stopped by matter? Gravitational fields aren't. SteveBaker 15:23, 2 June 2007 (UTC)

Faraday cage? --Wirbelwindヴィルヴェルヴィント (talk) 19:05, 2 June 2007 (UTC)

A Faraday cage stops the magnetic field, by generating electic currents in the conductor that makes an opposing magnetic field. In most conductors the current will be dissipated over time, so a static magnetic field cannot be stopped for long by a sheet or slab of metal. Eventually it will make its way through. GB 23:54, 3 June 2007 (UTC)

Correction: A Faraday cage nullifies electric fields, not magnetic fields, although they are related, it's not the same thing. --Taraborn 21:52, 5 June 2007 (UTC)

Temperature

I have always why, when temperature is the measure of average kinetic enegry, we don't use a unit of energy, such as the joule, instead of a separate and unnecessary unit, like the kelvin.

My question is also, is it possible to use Joules, for example, to measure temperature in the same way that Kelvins are used? If so, what value do you give? The average kinetic energy of each molecule, atom, unit of volume of substance, what?

If this is possible, how would I convert from Kelvin to Joules for temperature?

Thanks --Steevven1 ^{(Talk) (Contribs) (Gallery)} 03:21, 2 June 2007 (UTC)

Take a look at Boltzman constant — Kieff | Talk 03:53, 2 June 2007 (UTC)

Thanks, but I don't think I understand. Could you (or someone else) try and explain the answers to my questions such that the layman with moderate knowledge of physics could understand? Steevven1 ^{(Talk) (Contribs) (Gallery)} 04:34, 2 June 2007 (UTC)

Different kinds of materials have different thermal properties, so the amount of energy it takes to change the temperature by 1°C is not the same. This quantity is called the heat capacity (depends on how big the sample is) or specific heat (a material property). It can also change with temperature. So there's no one conversion factor between temperature and energy or energy density. That answers part of your question, but then a second part is left: why do we need both energy and temperature? The reason is that temperature tells you not just how much energy is there, but where energy will flow. If you put two blocks of different material in contact with each other, heat will always flow from the higher temperature to the lower temperature. And if the temperatures are the same, you have thermal equilibrium. So energy has the property of being conserved globally, and temperature has the property of telling you which way heat will flow. There's no one quantity that does both of those things. If you want a thermodynamic understanding of temperature, go back to the definition T = dQ/dS. It shows that entropy increases whenever heat flows from higher to lower temperature. --Reuben 05:29, 2 June 2007 (UTC)

Temperature is not simply "average kinetic energy", or even proportional to it. That is only true for ideal gases and maybe some other ideal materials. Temperature is really the tendency of a system to give up energy to its environment. In other words, it's proportional (inversely) to the relative increase in entropy (likelihood) when the energy increases a certain amount. In symbols, temperature is defined by the relationship ${\frac {1}{T}}=\left({\frac {\partial S}{\partial U}}\right)_{V,N}$ where T is the temperature, S the entropy, U the energy of the system, V the volume, and N the number of particles. So you see T cannot have the same units as energy; it has to have units of energy over entropy. If we measured entropy in some unit called the "boltzmann", temperature could be measured in kelvins per boltzmann, but that's not how it turned out historically. We measured temperature a long time before we measured entropy, so temperature is measured in kelvins and entropy is measured in joules per kelvin. —Keenan Pepper 06:52, 2 June 2007 (UTC)

Here's a good analogy from my thermodynamics textbook (Schroeder): If systems are people and energy is money, then entropy is happiness, and temperature is generosity. Almost everyone would like to have more money (i.e. has a positive temperature), but some people care more about money than others. Therefore money flows from generous people to stingy people and the overall hapiness increases (i.e. energy flows as heat from hot systems to cold systems and the overall entropy increases). —Keenan Pepper 06:56, 2 June 2007 (UTC)

Thank you all very much. I think I understand a lot better now. Steevven1 ^{(Talk) (Contribs) (Gallery)} 17:11, 2 June 2007 (UTC)

Steevven1, your question is excellent, and the answer is that it is quite possible to redefine our system of units so that temperature and energy have the same unit (i.e. setting Boltzmann's constant equal to 1): see natural units. In the same way, one can redefine the units to set other fundamental constants equal to 1. For example, doing so with the speed of light (setting c=1) means that we would measure length in time units (or vice versa). That is quite natural to do, and we do it every time we talk about lightyears. Similarly mass can be measured in energy units using E=mc², and particle physicists do this every day, for example talking about the proton mass in terms of the energy unit electron volts. Not all fundamental constants you can think of can be set to 1 at the same time, however, since there are fundamental unitless constants of Nature such as the fine structure constant. Therefore there are several different sets of "natural units" to choose from, depending on which classes of equations you want to simplify.--mglg_(talk) 20:46, 2 June 2007 (UTC)

writing technology

A CAPTCHA.

hey friends dont we have any stuff in wikipedia related to writing technology.(i dont want things on writing machines.printers etc) actuall my research is trying to concentrate completely on degree of roughness of writing surfaces and nib size of pen and then on handwriting quality obtained .

please someone help me on:

1.how to know the roughness of a paper.(i hope some tables might also work if yes then i would require the roughness of 4 to 5 varities of papers.kindly help)

2.kindly state some degrees to judge the beauty of a handwriting(if possible mathematically i.e.measurement of angles etc.).

1. See Surface metrology and Profilometer.

2. It's impossible to make a mathematical definition of beauty. That's what "subjective" means. However, if instead you want to measure legibility, simply start a human subject far away from the writing and let them approach until they can first read it. The writing that can be read from the farthest distance on average is the most legible. Make sure none of the subjects are farsighted or nearsighted and that the writing samples are all the same size. —Keenan Pepper 07:14, 2 June 2007 (UTC)

Keenan Pepper's suggestion for #2 may determine a sort of legibility, but I can imagine several alternative orthogonal metrics of legibility

• Start each reader at a fixed difference and gradually increase light-level until the text is readable.
• Change the angle of inclination of the text (start with a slant at 90 degrees and tilt towards the viewer).
• Change the context given for each letter (i.e. some text samples are random alpha-numerics, so the test is purely about character recognition; others are coherent sentences, so context can speed up the deciphering process).
• Change the ambient conditions on which the text is printed (noisy background, distortion or blurring)

Such issues are common in optical character recognition and CAPTCHAs. Nimur 01:06, 3 June 2007 (UTC)

Per the original question, surfaces are often measured in terms of maximum allowed deviation per square area. This is common in machining and in surface science. Keenan Pepper's articles will be very useful. Nimur 01:08, 3 June 2007 (UTC)

How to add wings

I've been trying on and off for the past six months to come up with a way to theoretically add wings on to an already four-legged tetrapod. In particular, I'm interested in the mechanics of how two sets of limbs could both function on the same body.

Adding wings is rather common in artwork, both in angelic-looking human characters (usually from Anime) and fantasy animals like dragons and griffins. But the wings are usually depicted as simply sprouting out of the subject's back, with no apparent skeletal or muscular structure anchoring them to the body. Or else, these structures are clearly defined, but couldn't possibly work: such as a dragon whose wings and forelimbs are both anchored to a single shoulder, the wing and possibly a second shoulderblade sprouting from a joint that is most mysteriously attached to the top of the regular foreleg's shoulderblade. Not only is the attachment point seem rather small given the fact that the wings are supposed to support all of the animal's weight in the air, there seems to be little if any room for muscles (particularly those required for the downstroke, since the forelegs are in the way), and I can't imagine how ungainly it would be for such a creature to try to run around like a normal animal, with those big bundles attached to its shoulders! It seems to be a lose-lose situation, neither set of limbs being operable in the presence of the other.

But I suspect that this is far more problematic with animals than it is with humans, since usually the animal's forelegs and wings supposedly operate at a ninety degree angle to one another. With regard to winged humans, I see only so many options:

1. Move one pair of limbs somewhere else

This doesn't seem all that easy. I guess you could move one lower on the body, but since muscles seem to need a rib cage to anchor to, you'd have to lengthen the torso, and while I don't know that it wouldn't work, it would end up looking kind of... freakish.

2. Make one pair smaller

The problem with this option is that, so far as I can tell, the pair that's made smaller probably won't be useful anymore, as in, they'd might as well not be there at all.

3. Use something other than the conventional vertebrate design

This is a very broad category. At first I was thinking insect wings, but I have no knowledge of insect wing structure, so I wouldn't know where to begin. I also thought of a Venus flytrap-type design, but it turns out that the traps react on a cellular level (would that even work for something as big as wings for a human?) and can only be operated a dozen or so times, so I guess the wings would only resemble a flytrap mechanism superficially.

Any suggestions? 71.217.121.199 07:00, 2 June 2007 (UTC)

You are perfectly right. Simply "adding" the supernumerary limbs will not readily make them functional, and is thus likely to be evolutionally detrimental. This is especially true for wings, where a very considerable modification of bone, muscle, and skin structure is required to make them at least partially functional. The tetrapod body plan is very robust, and, if anything, the ocassional reduction of the limb pair number to 1 or to 0 has happened along some evolutionary branches; but never, to my knowledge, an increase to 3 or more. (I am specifically talking about species-wide phenomena and not about sporadic mutations like this; in the latter example, as you expected, the wings are completely non-functional). As for the "suggestions" part, well, I'd start with a large robust bat, say, a Flying fox (Megachiroptera) or a noctule (Microchiroptera); depending on whether it is a frugivore or a carnivore that you wish for. Adding a second - smaller - pelvis on the same vertebral column is less "problematic" than adding wings. Have fun. Dr_Dima.

Second thought: a False Vampire Bat may be a better carnivore template (compared to a noctule). Remember that scaling in size is not straightforward, as different properties (wing area, muscle and bone strength, body mass, energy consumption, cooling rate) depend on different powers of linear size of the animal. Cheers, Dr_Dima.

Sounds good! Thanks for the help. :D 71.217.121.199 17:14, 2 June 2007 (UTC)

This is the sort of puzzle that should be very interesting to solve when Spore comes out. -- Phoeba Wright^OBJECTION! 20:43, 2 June 2007 (UTC)

No, figuring out when Duke Nukem Forever will follow is the more interesting puzzle to solve when Spore comes out.

On a less flippant note, Spore is a game, not a simulation, so it's unlikely you'll gain much insight in the "real" problem by solving it in Spore -- if there's a problem to solve at all, and you won't just click to add wings and see your creature take flight. 82.95.254.249 21:25, 2 June 2007 (UTC)

Forever is the release date. This is common knowledge now, really.

I know it's not a total simulation, and it's probably possible to make a skeleton that would be impossible to have exist in real life, but then, we don't have dragons walking around we can experiment on -- Phoeba Wright^OBJECTION! 06:36, 3 June 2007 (UTC)

You could try to staple wings to a Komodo dragon, but I'm not hopeful about the results. 82.95.254.249 14:45, 3 June 2007 (UTC)

Couldn't the wings be added to the back of the shoulder blades :) There seems to be enough room there for muscles :) And if the shoulder muscles went along the wing instead of around its base, they would fit in easier :) Or you could look at flying four legged animals, which tend to have their 'wings' between their arms and their legs :) HS7 14:47, 3 June 2007 (UTC)

What flying four-legged animals? I'd have looked at removing a pair of legs from a flying insect shape, but it might not work scaled up. Skittle 21:57, 3 June 2007 (UTC)

Presumably Hidden secret means animals such as flying squirrels or flying frogs. For other such animals see flying and gliding animals. In my opinion, the most likely avenue for any sort of sustained flight involves evolution of the ribs to create wings, similar to the gliding membranes of draco lizards. - AMP'd 22:17, 3 June 2007 (UTC)

Ah, '!flying'. Skittle 22:35, 4 June 2007 (UTC)

I've been playing with the same idea for a while now. When I draw a griffin or dragon or the like, I attach the wings in the place of the forelegs (arms) and attach the "new" forelegs at the opposite end or midpoint of the ribcage, essentially adding another wishbone/clavicle. It can look almost natural if you're careful about how you place things, though obviously the insertions for the muscles would get quite complicated. Adding the wings at the midpoint or ventral end of the ribcage looks more balanced, but actually seems less natural to me since the wings are the limbs that would require the most muscle while the forelegs could essentially act as a balance when on the ground - pseudo-forelegs would even work. Matt Deres 00:09, 4 June 2007 (UTC)

Yes I did mean that, I know its not really flying, but you could change it so it is :) I thought about this problem a few weeks ago, although I was trying to do it without changing the original shape too much :) The best way I have found is to have the wing bones attached to the back of the shoulder blades, held in place by tendons and muscles instead of bones :) This might work, and would avoid trying to rearrange every other part of the animal around the wings :) Sorry If Ive repeated myself a bit, but I wanted to add more without just changing my original answer :) HS7 19:18, 4 June 2007 (UTC)

Model it after insects? Gzuckier 17:33, 5 June 2007 (UTC)

DoD carbon emissions

How much carbon dioxide does the U.S. military emit? 75.35.115.68 10:11, 2 June 2007 (UTC)

Not so much since they went nuclear. Bendž|Ť 10:50, 2 June 2007 (UTC)

Hahahahaha! 81.93.102.185 11:16, 2 June 2007 (UTC)

That would be a hard question to answer with any accuracy. Even if you came up with a rough estimate based on tanks, trucks, planes, boats, etc., there'd be a lot of other variables to take into consideration. --24.147.86.187 00:29, 3 June 2007 (UTC)

The first problem that comes to mind, is "how much extra carbon dioxide would be emitted if all military personnel were suddenly converted to civilians." Many who currently use mass-transit or live on-base would suddenly become commuters.

However, in general, I think the per-capita use of fossil fuels is higher in the military than in normal civilian life, because the military tends to operate more heavy equipment and aircraft (per capita). Nimur 00:56, 3 June 2007 (UTC)

Except, perhaps for the navy. Nuclear powered submarines and aircraft carriers ought to be emitting a lot less CO2 than (say) a supertanker or a cruise ship. SteveBaker 13:26, 4 June 2007 (UTC)

The navy is still mostly destroyers, crusiers and other smaller ships that do not have nuclear rectors. Nuclear power is mostly used for giving extramely long mission endurance, by removing the need to refuel. This helps Aircraft carriers stay at sea for months potentially for years, and Submarines can also stay under water indefinatly. Czmtzc 18:07, 4 June 2007 (UTC)

I've researched this in the past and one can get firm numbers for the amount of fossil fuels the US department of defense purchases annually. My recollection is that it came to something like 1-2% of the total for the US as a whole. So altogether it isn't all that impressive. Though for perspective, less than 1 in 1000 people is in the military, so it follows that the average soldier is consuming ~10 times as much fossil fuel as the average civilian. Dragons flight 08:53, 5 June 2007 (UTC)

Please cite your sources; I disagree with your "1 in 1000 people" statistic per United States Army, which states that the army alone employs over 1 million Americans. This is approximately "1 in 300" or about 0.3% of the US population; and it does not even count the other branches. According to this White House statistic from 2005, "Number of Employees: 2.3 million Military (Active, Reserve, and Guard) and almost 700,000 Civilian" which roughly equates to 1 in 100. Nimur 16:54, 5 June 2007 (UTC)

Marsh Acidity

I collected water samples at the inlet, body, and outlet of a freshwater marsh, and found that pH drops as one moves downstream. How can this be explained? The pH values were, respectively, 7.0, 6.5, and 5.0. Thanks. -- Sturgeonman 15:11, 2 June 2007 (UTC)

Can you describe for us in detail how you collected the samples and performed the measurements? (Sampling method, container size and type, approximate water depth, pH meter type, pH calibration method.) TenOfAllTrades(talk) 17:31, 2 June 2007 (UTC)

ok, I took water samples in a glass bottle at a relatively shallow inlet, body, and outlet of a freshwater marsh. I then used Microbe-lift pH strips to test the ph. I did this test twice, on two different days, and got the same results. In my project, I want to prove that marshes filter out pollutants, but this part of my data isn't helping. Maybe it could be because the marsh is surronded by schist, a non-alkaline rock?-- Sturgeonman 19:30, 2 June 2007 (UTC)

Is the marsh full of decaying plant material, and does decay produce carbonic acid? I know that in agricultural fields it does, requiring lime to be added to "sweeten" the soil from time to time if a lot of organic material has decayed and been incorporated in the soil. Could acid rain be a factor? Edison 22:01, 2 June 2007 (UTC)

Also, you have not defined what it means to "filter out pollutants." Many pollutants have neither acidic nor basic characteristics. Have you got any system to specifically measure pollutants in consideration? A lot of stream-watch kits will have a few pre-made chemical tests to determine nitrate levels, sulfite levels, dissolved oxygen, and so forth, which is at least a broader assay than just pH. Nimur 22:53, 2 June 2007 (UTC)

Yep, it could be due to the buffering capacity (or lack thereof) of the surrounding rock and soil. If the river were running through (for example) limestone rock or soil before it reached the marsh, the carbonate content of the limestone would tend to raise the water's pH.

The breakdown of plant matter may also release a number of mildly acidic compounds (like tannins) that would lower the pH of the marshwater. TenOfAllTrades(talk) 16:19, 3 June 2007 (UTC)

If the march is very reducing and full of sulphur, then as the water racts with oxygen it could be forming sulphuric acid. This happens with mine waste water often. Is the water in your marsh black and smelly? GB 06:58, 4 June 2007 (UTC)

Dolomitic Conglomerate

I saw this rock type on a geology map, but I have no idea what it is (not to mention its properties), and I couldn't find much about it on Wikipedia. I mainly want to know whether or not this rock type is permeable and porous. Thanks! —Preceding unsigned comment added by 82.33.108.169 (talk • contribs)

The adjective, dolomitic, tells you that the cement holding the conglomerate together is mostly dolomite. Alone, this will not tell you whether it is porous or permeable; many dolomitic rocks are, but by no means is every dolomite porous, and those that are may or may not be permeable. You need to look at the rock, or find a description that includes those properties. Cheers Geologyguy 18:13, 2 June 2007 (UTC)

Thanks!

Vacuum Cleaners and Fine Dust as an Explosive Hazard

Why doesn't the fine dust collected in a vacuum bag, combined with the increased temperatures that the vacuum bag experiences during normal operation, create an explosive hazard? - MSTCrow 17:34, 2 June 2007 (UTC)

Conventional explosives need a chemical reaction to take place. Usually this means combining an oxidizer and a fuel in a combustion reaction, then limiting the volume to increase temperature and pressure. All these conditions are usually what are considered "explosive" - dust has very little to do with it. If for some reason, the fine dust and the nominal temperature increase resulted in a severe pressure shockwave, that would be an explosion; but that almost always requires chemical combustion. Nimur 18:20, 2 June 2007 (UTC)

Nimur, you missed what MSTCrow was heading at, namely the possibility of a dust explosion. I'd say it's a good question, and I only can guess that maybe, the kind of dust one finds on the floor of one's home is less combustible than things like flour. (Flour is the standard example for a "dust explosive". If you try to set fire to a bowl of flour, you won't succeed. But blow it in the air with just the right unlucky flour-to-air mixing ratio and a single spark will cause a major explosion. Such accidents, often fatal, are not too uncommon to happen in bakeries; though they now have precautions, of course.) Simon A. 18:46, 2 June 2007 (UTC)

The German wikipedia entry de:Staubexplosion mentions that house dust can indeed cause an explosion. They say that dust can accumulate in the plenum of a suspended ceiling and cause and explosion in case of a fire, which the spreads a fire in a single room through the whole floor. But a fire from below is much hotter, of course, than the insides of a vacuum cleaner, which is, after all, continuously cooled by the sucking air stream. Simon A. 18:52, 2 June 2007 (UTC)

The inside of a vacuum heats up due to engine heat. That's why it ejects hot air and the filtration bag becomes noticeably warm. The ambient temperature is increased. I'd also add that the vacuum generates an electro-static charge. Or at least plastic ones (except for the motor) do so. - MSTCrow 19:39, 2 June 2007 (UTC)

"But blow it in the air with just the right unlucky flour-to-air mixing ratio and a single spark will cause a major explosion."... Really? Maybe it's just my skepticism acting up. This sounds like pseudoscience. Nimur 22:45, 2 June 2007 (UTC)

Try telling that to the workers of a custard powder factory that exploded when the fine powder was accidentally released and exploded.[1] Indeed, one of the rules at flour preparation factories is that all chutes must be grounded, because the flour flowing down a plastic pipe can generate huge levels of static electricity that can then arc to nearby metal objects and explode the dust released by the flour. Laïka 23:23, 2 June 2007 (UTC)

Also, Nimur must never have seen the physics/chemistry lab demo in which a fine dust of lycopodium spores is blown into the air and ignited. It makes a huge, impressive ball of flame. Afterwards, everyone thinks the powder must have been especially explosive (they often ask "Where can I get some of that?"), but really you could do it with flour or sawdust or anything organic, as long as the dust is fine enough. —Keenan Pepper 00:17, 3 June 2007 (UTC)

This dust explosion safety guide has a lot of useful information about the physics behind them. My guess is that it is either: 1. not enough heat for ignition and/or 2. bad dust-to-air ratio (these are related issues — if there is a bad dust-to-air ratio the ignition energy required goes up very high, it has to be within certain tolerances). All that being said there does appear to be a market for explosion proof industrial-sized vacuum cleaners but I can't immediately tell if they are "explosion proof" because they won't have explosions inside them or if they won't set off explosions in dangerous environments. --24.147.86.187 00:26, 3 June 2007 (UTC)

Rescind. In light of these new facts, I rescind my previous skepticism. It's pretty weird, but apparently it is a known phenomenon. Nimur 00:53, 3 June 2007 (UTC)

It's not hard to understand: When things burn in air, the rate at which they burn depends on the ratio of the volume of the object to it's surface area. If you think about wood, you know can't easily set light to a 6" thick log with a match - you might manage to set light to a thin twig but it wouldn't burn very fast - you can set light to thin wood shavings or paper and they burn very quickly - and if you set light to sawdust (while it's floating around in the air), it burns so quickly that it's almost like an explosion. For powders that are even finer than sawdust (like flour), then the stuff literally does explode. SteveBaker 13:23, 4 June 2007 (UTC)

Is it literally exploding, where it will blow things apart, or is it just a rapid combustion? --Falconus^{p t c} 17:41, 4 June 2007 (UTC)

Explosions are fundamentally nothing more than rapid combustions. Combustion generally causes solids or liquids to become gaseous, increasing in pressure, which in turn leads to an increase in volume, equalizing the pressure. Go through this process fast enough and the pressure is sufficient to "blow things apart". — Lomn 19:19, 4 June 2007 (UTC)

So flour can produce enough pressure to cause damage, or is it just the heat? (You might be able to tell that I haven't taken chemistry yet)--Falconus^{p t c} 20:45, 4 June 2007 (UTC)

Dust explosion at the old Bird's custard factory (in England) blew a wall off. So yes. That's why there are so many precautions in place in industry concerning dust explosions. Apparently, a mixture of flour and TNT can explode with more force than straight TNT of equivalent mass. As to the hoover, I assume the reason it doesn't explode is because it doesn't get hot enough. It would need to reach the ignition point for the dust, and I assume that would be quite high. Possibly a spark in the bag could cause problems. Skittle 22:33, 4 June 2007 (UTC)

Alright, thanks. --Falconus^{p t c} 02:41, 5 June 2007 (UTC)

grain elevators blow up all the time due to the grain dust and random sparks. Also, re lycopodium, that's the stuff they used to use for flashes in the early days of photography. You know, in the civil war movies when the guy holds up the big trough of stuff that goes flash. Gzuckier 17:35, 5 June 2007 (UTC)

Actually, Gzuckier, those flashes used magnesium powder, as Flash (photography) will tell you. --mglg_(talk) 17:53, 5 June 2007 (UTC)

The light bulb in the vaccuum cleaner I was using came loose. A spark from the bulb as it was loosened by vibration and suctioned from its socket, ignited the dust. It a large enough explosion to blow apart my vaccuum, damage my left eardrum and spray the room with glass shards from the tiny bulb. —Preceding unsigned comment added by 71.94.83.133 (talk • contribs) 01:03, 7 August 2007

cost of power transmission infrastructure?

Does anyone happen to know where to find the cost of this? I've been googling it for quite some time and I haven't turned up anything. Thanks Coolotter88 20:09, 2 June 2007 (UTC)

Do you mean installation or maintenance costs? - MSTCrow 20:40, 2 June 2007 (UTC)

U.S utilities traditionally filed rate cases with their state commerce commission in which they stated how much money they had spent on "plant" and were given a legally mandated return on investment. More recently, there is competition allowed and they are in some places forced to buy power at market rates. They are also required to let others use their transmission lines to "wheel" power to internal customers such as industries and municipalities with their own distribution systems. There were battles over what should be included and what should not (imprudent construction of nuke plants that were not yet needed due to slackened load growth, for instance). Thus in the files of state utility commissions or commerce commissions should be such data. It costs money to build a generator, sucstation, transmission line etc. I have seen files in archives going back to the 19th century with details of every pole and transformer. The federal government in the US (Federal Energy Regulatory Coimmission) collects and reports on such expenditures as well as plant cost, and tabulations for a number of years are found at [2]. Of course there are accounting standards to bring in depreciation. There are many industry magazines which you can find in a university library of a school with an electrical engineering department. [3] gives annual expenses for transmission, distribution, depreciation etc for major US utilities. Edison 21:56, 2 June 2007 (UTC)

Earwig identification

Hi. I've captured and scanned an earwig, and I wonder if anybody can help figure out which species it is. It's 5/8" (16mm) in length, including forceps and antennae.

It doesn't seem to be Forficula auricularia, and the next most common species around here is Euborellia annulipes, but the pictures I find of those aren't a good match. Maybe I've got an immature earwig, with features not fully developed? Any help would be appreciated. -GTBacchus^(talk) 21:20, 2 June 2007 (UTC)

whatsthatbug.com is good for this kind of query. --TotoBaggins 21:43, 2 June 2007 (UTC)