Wikipedia:Reference desk/Archives/Science/2010 June 17

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June 17

Lapping water

This video shows, in slow motion, a dog lapping up water. It seems that the dog drops his tongue in and bends it under itself to create a scoop. This is the opposite of what I expected. Is this the standard method that animals use to lap up water? Dismas|^(talk) 02:14, 17 June 2010 (UTC)

That was very interesting. I don't think the dog is doing it voluntarily. The structure of it's tongue must simply be shaped that way. I tried and I can't get my tongue to move that way, which is why it's different from what I would expect. It doesn't necessarily have to be the same for every animal, it's just however it's tongue is shaped. Ariel. (talk) 04:57, 17 June 2010 (UTC)

Cats lap water by absorbing the water with its tongue like a sponge if I recall correctly, but their tongues bend like ours, forward instead of backward like a dog's. Btw, is it really so surprising that a dog's tongue bends backwards? Whenever a dog is panting with its tongue sticking out, it's always drooping down. Our tongues don't do that. If you really want to be surprised, look at an Echidna's penis. It has four heads.148.168.127.10 (talk) 13:14, 17 June 2010 (UTC)

It was surprising that they intentionally move it that way. I thought the panting downward direction was simply because the tongue was hanging limp. Dismas|^(talk) 19:49, 17 June 2010 (UTC)

I've observed my pigs drinking by sticking their mouths in the water and sucking, so not like a dog at all. --Sean 15:43, 17 June 2010 (UTC)

What's also interesting (to me at least) is the reliance on suction for the dog to drink. I've had this happen to both of my dogs: they will approach the bowl, thirsty, lap it a few times, and then submerge their whole mouth in an attempt to drink, but in an effort to keep their nose dry they will be exhaling the whole time and only really succeed at making the water very bubbly. They will struggle with this for a few minutes at least until human intervention arrives. What has happened is there is a sizeable foreign object stuck in their teeth (usually a plastic bit of a chew toy) that stops them from making a clean seal around their tooth line, and they are completely unable to lap water in the normal fashion. Removing the object immediately remedies the problem. --144.191.148.3 (talk) 16:45, 18 June 2010 (UTC)

tuna as cat food

The cat food article says that fresh water fish may be deficient in thiamine so does tuna provide in abundance all of the nutrients a cat needs that is lactating? Also are lactating cats normally thin or should they be normal weight or a bit overweight? 71.100.0.224 (talk) 02:58, 17 June 2010 (UTC)

For questions such as these, it would be best to ask your local veterinarian. They will be the best people to tell you what your cat needs. Dismas|^(talk) 03:06, 17 June 2010 (UTC)

That is true only for a cat that someone might own. Strays and feral cats pose an entirely different situation since most likely the vet will start by asking when was the last time you brought her in. 71.100.0.224 (talk) 03:19, 18 June 2010 (UTC)

I would expect a lactating cat (hopefully female) to be normal weight or slightly over, owing to the weight of the milk itself. But cats aren't cows, so don't expect a bulging sack of milk. As for diet, a variety of foods is best to provide all the necessary nutrients. StuRat (talk) 03:40, 17 June 2010 (UTC)

Yes see your vet, but this page says tuna is OK for an occasional treat but not as an exclusive diet. While it seems relatively normal for lactating queens to be thinner, I'd be tempted to make sure she is getting good food and plenty of it to give her kittens the best start possible. --TammyMoet (talk) 09:57, 17 June 2010 (UTC)

If you mean pure tuna such as would be served to humans, then that definitely isn't a balanced diet for any cat, just as it wouldn't be for humans. Tuna cat food, on the other hand, has all the other things a cat needs. --Tango (talk) 11:54, 17 June 2010 (UTC)

Rigid airships vertical control

How do Rigid airships (e.g. Hindenburg) move vertically? Do they use elevators on the stabilizers, or do they use ballonets like modern blimps? --The High Fin Sperm Whale 04:15, 17 June 2010 (UTC)

According to Zeppelin (which is a much better article than the Rigid airship article), "A Zeppelin was steered by adjusting and selectively reversing engine thrust and by using rudder and elevator fins." under Principal characteristics section. --Jayron32 04:21, 17 June 2010 (UTC)

Altitude can be controlled using buoyancy. Release ballast to increase buoyancy and ascend, release lifting gas to decrease buoyancy and descend. Using aerodynamic control would work when moving, but would not work at very low airspeed. anonymous6494 04:27, 17 June 2010 (UTC)

I think I've seen a documentary saying they used ballonets. I could be wrong. It might have been about modern blimps. — DanielLC 04:56, 17 June 2010 (UTC)

Modern blimps do use ballonets, but do rigid airships? --The High Fin Sperm Whale 05:22, 17 June 2010 (UTC)

Carrying ballast is an expensive thing to do - it reduces payload and limits the amount of vertical travel you can do without running out of the stuff. Venting lifting gas is also a bad idea because it too limits your flight capabilities. These days they're using helium as lifting gas which is increasingly expensive stuff. In the days of the Zepplins, they used hydrogen - and that's really cheap. Ballonets are a much more elegant solution to the problem. Modern airships have to work with much tighter air traffic control requirements than the Zepplins did - and having the ability to change altitude cheaply, quickly and precisely is an important part of what they need to do to be cost-effective. I'd expect expect modern craft to carry some ballast and have at least the capability to vent gas for emergency situations - but I doubt they do either of those things routinely. SteveBaker (talk) 11:34, 17 June 2010 (UTC)

Similarly, hot air balloons only use ballast in emergencies. Routinely, they climb by firing their burner and fall by waiting, but in an emergency they can drop a sandbag or two and rise much more quickly than they could otherwise. I would imagine airships do the same - if you're about to crash, you drop ballast, but otherwise you use more efficient means. --Tango (talk) 12:01, 17 June 2010 (UTC)

Rigid airships, and semi-rigid airships, have a horizontal stabilizer (although it isn't for the purpose of longitudinal stability) and a vertical stabilizer. These two surfaces are equipped with elevators and a rudder that are operated by the pilot in a manner similar to those on a fixed-wing aircraft. The airship is a very low aspect ratio airfoil so when it is inclined to the oncoming airflow it will generate aerodynamic force for the purposes of climbing and turning. These airships are likely to have ballonets for the purpose of trimming at low speed, and the ability to carry ballast to achieve neutral buoyancy, but they generally have an empennage for the purpose of height control and maneuvering when travelling at speed. Dolphin (t) 12:19, 17 June 2010 (UTC)

The Graf Zeppelin had yet another technique: it carried two different fuels for its engines. If it was desired to make the ship gradually lighter, they would burn gasoline rather than releasing ballast. The rest of the time they would burn Blau gas, which was a flammable mixture of gases almost the same density as air. Carrying the Blau gas increased the volume of the airship but meant that it could burn fuel and hardly change its weight. --Anonymous, 18:33 UTC, June 17, 2010.

Weren't the old Zeppelins able to use thrust vectoring by tilting their airframe or engines to provide a vertical component to their thrust forces? Googlemeister (talk) 18:39, 17 June 2010 (UTC)

Yes, the Zeppelins were able to generate lift by tilting the entire airship, but the amount of lift from the engines was a tiny component of the total lift generated. Because of its shape, the Zeppelin acts like an enormous wing. --Carnildo (talk) 01:47, 18 June 2010 (UTC)

Thanks. One more question: are there any modern, or plans to build, a rigid airship? --The High Fin Sperm Whale 16:51, 17 June 2010 (UTC)

See CargoLifter. Looie496 (talk) 18:53, 17 June 2010 (UTC)

Plenty of plans, but nobody's actually building one. --Carnildo (talk) 01:47, 18 June 2010 (UTC)

See aeroscraft. They are supposed to be building it soon or now. 148.168.127.10 (talk) 13:20, 18 June 2010 (UTC)

How do they test for performance enhancing drugs in an atheletes urine?

It is a known fact that the International Olympic Committee tomtoms itself as being foolproof and rigorous when it tests the samples of athletes every year as part of any International sporting event. Be it athletics, cycling, tennis or weightlifting several ( highly decorated) sportsmen have fallen from grace following positive drug tests.

Initially they cry foul only to realise their folly later.

My question is, how are these tests done and what do they actually look for in these tests? If the tests are indeed fool proof, how did Marion Jones escape the rigorous dragnet for years and only after an internal family scuffle did she come out with her confession- till she confessed she wasnt actually stripped off or detected. Agassi had also confessed last year.

What makes the cheats stay one step ahead of the testing agencies? Is there a defective testing process being used?

And hypothetically speaking if there is one Marion Jones and a Lance Armstrong out there, there could also be other undetected cases right?--Fragrantforever 10:47, 17 June 2010 (UTC) —Preceding unsigned comment added by Fragrantforever (talk • contribs)

I feel compelled to point that, despite Lance Armstrong being possibly the most tested athlete over the past 11 or so years, he has never failed a single drug test, be it urine or blood. The only person who claims he saw Armstrong injecting illegal performance enhancing drugs is Floyd Landis, who has his own agenda to pursue. --TammyMoet (talk) 11:33, 17 June 2010 (UTC)

The biggest problem is that athletes are always finding new things to take to enhance their performance, some of which are difficult to detect and perhaps not even illegal or banned. StuRat (talk) 12:25, 17 June 2010 (UTC)

it's an ongoing process, and no system is ever foolproof. Consider it as an arms race, each time a new product is developed it takes some time to develop a test to detect it. Once that test is developed some will try to find ways to evade that test, leading to a need for further testing to detect the evasions. So you see it continually escalates.

Each test will have a margin for error, so in the marginal zone athletes can legitimately challenge the results. I'm not sure which side of caution the sports authorities err on because a false positive could reasonably ruin an athletes marketability and ability to make a living.

The actual tests range from reasonably well known to highly sensitive. The most recent are the most sensitive as protecting them in this way reduces the opportunity for counter-measures to be developed.

ALR (talk) 12:30, 17 June 2010 (UTC)

You are forgetting about drugs that simply increase the concentration of something that already exists naturally in the body. Athletes simply claim "I just naturally have a high level". Another class is something that is metabolized very very fast, those are hard to detect since they leave no residue, so you have to try to measure their effects instead of the drug directly. But hard training can cause similar effects, and now you have to try to distinguish. For example a drug that increases red blood cell count - the only way to tell was that the new ones are a bit smaller than the regular ones. There was another drug that they proposed using carbon isotope testing - apparently the ratio of the drug was slightly different from the naturally produced one (I don't think they ever did test for it, and it's one that is currently undetectable). Ariel. (talk) 20:54, 17 June 2010 (UTC)

The specific instances that you mention fit into the general case that I've talked about. The naturally high defence is essentially a marginal case argument, hence some debate around where the thresholds for sanction lie.

As you illustrate, no system is inherently foolproof, there are always ways around the testing, the challenge is for the testers to keep up with that.

ALR (talk) 22:57, 17 June 2010 (UTC)

True, but it does raise questions about the rationale for the ban in the first place. Why is it fairer for an athlete to have a naturally high level of something, than for him to eat some of it? One possible answer is that the athlete's biological makeup is part of what the competition tests, which is certainly true — but then why shouldn't women compete on an equal basis against men? (Which of course in practice means no more women in most sports; exceptions would be some of the ones judged on aesthetics, and some ultra-endurance events.) --Trovatore (talk) 02:33, 18 June 2010 (UTC)

I would see the argument around why artificial performance enhancement is banned as very different from the debate about how artificial enhancement is detected. The former is a philosophical and ethical argument, the latter science and technology implementation.

Any time that one takes science and applies it to the real world there are ambiguities around thresholds and scope for practitioner interpretation discretion and challenge.

ALR (talk) 09:52, 18 June 2010 (UTC)

To be sure, it's a different argument. To my mind, though, it illustrates one of the reasons that the argument for banning them is not convincing. --Trovatore (talk) 10:22, 18 June 2010 (UTC)

To answer the first question, I believe that they inject it (the urine sample, after a bit of preparatory work) into a HPLC to look for the actual drug or one of the metabolites. The presence of a drug can be confirmed by comparing with a known sample, or through a MS detector to verify the molecular weight.Pmdove (talk) 02:40, 18 June 2010 (UTC)

The samples are tested for a wide range of contaminants, so a number of different tests are carried out on different segments of the sample.

ALR (talk) 09:52, 18 June 2010 (UTC)

Alumin(i)um

Is the correct spelling "aluminum" or "aluminium"? --76.77.139.243 (talk) 13:13, 17 June 2010 (UTC)

Aluminium#Present-day_spelling. Aaadddaaammm (talk) 13:14, 17 June 2010 (UTC)

Aluminium. But if you are American you are allowed to spell it incorrectly. DuncanHill (talk) 13:18, 17 June 2010 (UTC)

The IUPAC recognizes both as valid alternatives, but prefers aluminium. On the other hand, they only recognize "Sulfur" as the correct English language spelling of the element with an atomic number of 16. Must be some sort of American bias, and all that. Buddy431 (talk) 17:29, 17 June 2010 (UTC)

What do they say for c(a)esium? DMacks (talk) 18:19, 17 June 2010 (UTC)

From our Caesium article, both are accepted, but "caesium" is preferred. Similar to alumin(i)um I guess - British is preferred, but American is acceptable. Buddy431 (talk) 21:02, 17 June 2010 (UTC)

In the case of aluminium, given a choice, it doesn't make sense to use "um" when the "ium" form is used in 81 of 117 element names (uranium, plutonium, vanadium, potassium, sodium, magnesium, calcium, and strontium, etc). There are, however, just 4 elements that have just 'um' (lanthanum, platinum, molybdenum and tantalum). There are 8 elements that end with "on", 3 with "gen" and 5 with "ine" and 17 with no particular ending. The choice to spell sulphur with an 'f' is a part of a general spelling simplification to replace 'ph' with 'f' because they sound the same and 'f' is simpler (although Phosphorus is still using 'ph' because US spelling rules are no more uniform than those of the rest of the English-speaking world!) SteveBaker (talk) 18:44, 17 June 2010 (UTC)

On the contrary, aluminum is the more etymologically- and historically-correct spelling. It is derived from the Latin alumina, by changing feminine to neuter. The original spelling was alumium, (from "alum"), which also would have been fine, but no one uses that these days so it's not really in contention.

Beyond etymology, aluminum was also the choice of the discoverer, Humphrey Davy; discoverers' choices generally carry some weight. Unfortunately "an anonymous contributor to Quarterly Review, a British political-literary [!] journal" made the rather unfounded suggestion to add the "i", and it stuck right of the Pond. --Trovatore (talk) 18:53, 17 June 2010 (UTC)

If you are in England (and I presume most other English speaking places), "aluminium" is correct. If you are in America "aluminum" is correct. In fact, the only reason that I know that it is spelled differently (or, in response to DuncanHill, incorrectly) in England is that I have relatives there. Falconus^{p t c} 20:59, 17 June 2010 (UTC)

No incorrect or correct way; it is just the inconsistencies of English spelling. But for chemistry, the IUPAC name is recommended. --Chemicalinterest (talk) 11:33, 18 June 2010 (UTC)

Recommended — by IUPAC, I suppose. I imagine IUPAC does some good things, but their silly pronouncements on naming should just be ignored, as with those of most similar organizations. There is no particular value to spelling uniformity anyway. --Trovatore (talk) 21:08, 18 June 2010 (UTC)

Yech yah orr write un da losst puent Neel Une (tuke) 00:24, 19 Juun 2010 (UTC) (P.S. For those who can't be bothered working out what I said: "Yes you are right on the last point" Nil Einne (talk) 09:50, 19 June 2010 (UTC))

Well, that's just incomprehensible gibberish — obviously not what I was talking about. I'm talking about organizations that reprehensibly attempt to impose uniformity on usage rather than letting it evolve naturally. In English, we do not have, and will never permit, an equivalent of the Academie Francaise, and anything that looks like it needs to be smacked down. --Trovatore (talk) 00:53, 19 June 2010 (UTC)

Ah jaast speel isa divareent then ya, neh nid fah spilung uunafurmehtey liik yeah saeed. Ey min, us nah deeferent fruum waat yeah raykommund, reit? Sah nuh prubelum, yersah?

Yersa raaaght nah went Academie Francaise teel meah huaw tah speeel. Sah eye spiila huw ey wint end evuilvi niitarally fuum ward teh wurd. Yeeh pliise jan muh ta smuk duan ill whu teh muah huw teh spoel!

Ensadentohleh, isa hiupy yeah feelaw dah derskaveruh inuh Aanited Setaytes ov Umareyka liekeh Nipponium. Uoh waat...

Niil Innuh (tuuk) 09:31, 19 Juon 2010 (UTC)

In attempting to defend the indefensible, you're just being silly. --Trovatore (talk) 18:37, 19 June 2010 (UTC)

According to The Collins English Dictionary ISBN 978-0-00-778980-1, it is spelt; aluminium, and defined as a light silvery-white coloured metal that does not rust. However, I was of the opinion that it can react with air and weather and "chaff", which I would call "rust". Who is right? MacOfJesus (talk) 23:25, 20 June 2010 (UTC)

Aluminum indeed oxidizes in air, but forms a resistant oxide film rather than flakes of rust; this film then stops further oxidation and prevents the metal from rusting through. The term "chaff" refers to thin strips of aluminum foil used as a radar decoy. 67.170.215.166 (talk) 04:34, 21 June 2010 (UTC)

Metals used by the human body

What metals are used by the human body? (For example, iron is used in hemoglobin.) --76.77.139.243 (talk) 13:26, 17 June 2010 (UTC)

See Composition of the human body#Elemental composition. TenOfAllTrades(talk) 13:40, 17 June 2010 (UTC)

Plasma weapons

If you had a weapon that shot a stream of plasma at a target, could you use magnetic fields to change the plasma's direction if the target moved? --76.77.139.243 (talk) 13:31, 17 June 2010 (UTC)

Magnetic fields allow you to manipulate plasma, so sure, in principle, you could. However, there are drawbacks. First, as far as I can tell from a quick search, nobody is working on a "stream of plasma" weapon. Instead, plasma-based weaponry is generally related to generating powerful lasers. Second, magnetic fields lose strength exponentially with distance. To direct the stream of plasma at any significant distance, then, you're talking about needing far more energy than the plasma itself has -- so why not just use that energy as the weapon? — Lomn 14:45, 17 June 2010 (UTC)

You wouldn't just need magnetic fields to change the direction, you would need them to keep the stream contained. A stream of plasma would spread out very quickly without something to stop it. Unfortunately, the magnetic field required would be so strong that every iron object nearby would be pulled towards you very fast. --Tango (talk) 16:56, 17 June 2010 (UTC)

Looks like an ideal weapon to me. Targets the right person... --Stephan Schulz (talk) 16:59, 17 June 2010 (UTC)

It's not going to "target the right person" any better than a grounded-in-reality laser would. — Lomn 17:27, 17 June 2010 (UTC)

I think you may have misinterpreted Stephan's comment :-) --Trovatore (talk) 20:16, 17 June 2010 (UTC)

Ah, yes. I think I see now. — Lomn 20:33, 17 June 2010 (UTC)

An electric field might work better. Ariel. (talk) 20:58, 17 June 2010 (UTC)

They're the same thing, just in a different frame of reference. What's a magnetic field for the gun will be an electric field for the plasma (or a combination of the two). --Tango (talk) 21:47, 17 June 2010 (UTC)

A static electric field. It falls by r^2 (not r^5 like a magnet), and will not attract every metal object in the room. Ariel. (talk) 22:29, 17 June 2010 (UTC)

So which system do they use for the lightsaber? 67.170.215.166 (talk) 04:46, 20 June 2010 (UTC)

According to Tanmay Vachaspati (from classroom), gluons are used in a lightsabre (since they're the only self-interacting fundamental-force particle). SamuelRiv (talk) 08:10, 20 June 2010 (UTC)

Very interesting; the only part that I don't get is, how do they manage to get a gluon field outside of the nucleus? 67.170.215.166 (talk) 02:05, 22 June 2010 (UTC)

papers

can i use a extra long roller with regular size papers ?

like the roller seen here

http://www.ryomagazine.com/july/rollers.htm

but i cant get the extra long papers

Can't see why not, though you might find the ends turn out a little more loosely packed. It might help if you were to put in something at one end (say, a spare filter or two) to reduce the free 'rolling' space to regular size. 87.81.230.195 (talk) 13:57, 17 June 2010 (UTC)

Yes you can. You can even stick two or more papers together to make a longer one using the detached sticky part from another paper.83.100.250.191 (talk) 14:29, 17 June 2010 (UTC)

You'll probably get a bit of tobacco sticking out from each end, but just pinch it off with your fingers and put it back in the tin or the pouch – that's what I do rolling by hand ;-) Physchim62 (talk) 22:55, 17 June 2010 (UTC)

Antimatter

Chemically, antimatter behaves the same as matter. So could you make the antimatter version of an explosive and use it in a bomb? When the bomb detonated, it would release the energy from the explosion, and then the debris would explode again when it contacted the surrounding matter. --76.77.139.243 (talk) 16:51, 17 June 2010 (UTC)

If you could make the appropriate antimatter, then yes, that would work. However, the extra energy from the chemical reaction would be negligible compared to the energy from the matter/antimatter anihillation, so there is really no point. If you can make that much antimatter and preserve it, then just turn off the magnetic containment (or whatever) and let it touch some matter. There is no point making an explosive out of it. --Tango (talk) 17:01, 17 June 2010 (UTC)

The energy released by electrons going from some higher energy orbital to a lower energy one is really miniscule compared to the energy released by matter-antimatter destruction. Think of comparing a pressure cooker exploding versus a propane tank exploding. John Riemann Soong (talk) 17:01, 17 June 2010 (UTC)

What about if you made anti-uranium and made an atomic bomb out of it? --76.77.139.243 (talk) 17:03, 17 June 2010 (UTC)

That would only add about 0.04% to the explosion. Much more than the chemical reaction, but still not worth it. To anticipate your next question: nuclear fusion would add about 0.3% - still not worth it. --Tango (talk) 17:09, 17 June 2010 (UTC)

No I don't think it would add anything to the explosion. In a fission reaction the small amount of energy liberated comes from fissionable matter that converted to energy. In other words, matter that could have been simply annihilated with normal matter anyway. If we assume annihilation energy is 100% efficient, then you can never surpass that. Conservation of energy dictates that. Fissioning antimatter, then annihilating the products won't yield a greater blast than annihilating the input materials in the first place with equal amounts of normal matter. 148.168.127.10 (talk) 17:18, 17 June 2010 (UTC)

There's really no reason to do this. If you have the ability to make antimatter in large quantities, an antimatter weapon itself is going to be explosive enough. Adding the extra step of spreading the antimatter around first is not going to change the explosive output, I don't think. It might change the character of the explosion, at most, but even then, I am kind of dubious that it would matter (hyuk hyuk) a whole lot, in practical terms. --Mr.98 (talk) 17:10, 17 June 2010 (UTC)

Such a bomb would add absolutely no energy whatsoever to the explosion. When energy is released from a substance in any way, including the breaking and reforming of chemical bonds, the mass decreases according to E=MC². So you'd get a (comparitively tiny) bit more energy from the chemical explosion, but the antimatter-matter explosion would result in a tiny bit less energy being released. In fact, because you'd be involving less read matter in the explosion, the net result would be that less energy overall would be released! The same goes with using anti-uranium; by turning some of the antimatter mass directly into energy, you'd involve less real matter and get (slightly) less energy released. Mr. 98 is probably correct that it would probably change the character of the explosion, but from a pure energy standpoint, it's a losing proposition. Buddy431 (talk) 17:22, 17 June 2010 (UTC)

What I had in mind by suggesting a difference in character is something analogous to a thermobaric weapon. --Mr.98 (talk) 17:35, 17 June 2010 (UTC)

I think it might actually make a difference. Not in terms of energy but in terms of practicality. An anti matter bomb only works if it touches matter - but if it explodes it pushes away all the matter, significantly reducing the yield - especially if some of the anti-matter goes into space. By spreading it around first you make more matter available. Ariel. (talk) 21:03, 17 June 2010 (UTC)

I think the main difficulty here is that the antimatter is sufficiently explosive in small quantities that what one really ends up making in such a situation is just a series of antimatter bomblets or MIRVs or what have you. It's essentially a question of whether a number of "small" antimatter bombs is more effective than one "large" one. The former is undoubtedly true just based on the nature of explosions (five small nukes destroys more surface area effectively than the same material in one large nuke, because the explosion is spherical and thus the volume increases a lot quicker than the surface area). But if extraordinarily tiny (say, on the order of a gram or so) of antimatter produces around a nuke's worth of explosive anyway, you aren't really going to be blowing one piece into many smaller pieces with explosives, you're really just talking about a reentry vehicle with ten antimatter bombs on it to begin with. (Aside from the difficulties of trying to blow apart antimatter and not have it just react with the air.) --Mr.98 (talk) 21:39, 17 June 2010 (UTC)

A gram of a solid is much smaller than a gram of air, you'll have a hard time getting it all to react at once. And the initial burst will push even more air away. It might either cycle with multiple pulses, or reach a steady state where it sort of "glows/burns". I wish it was possible to test this, maybe it can be simulated with different size grains of antimatter in air. Any graduate students here looking for a project? Ariel. (talk) 22:34, 17 June 2010 (UTC)

There are no grains of antimatter available for testing. This page mentions an efficiency of about 10⁻¹⁰ for making antiprotons at CERN; this means that making one milligram of antihydrogen would take about 10¹⁰ · 10⁻³ g · c² = 9×10²⁰ joules, which is about twice the world's total annual energy consumption. Heavier elements would add another huge power of 10 to that. -- BenRG (talk) 00:08, 18 June 2010 (UTC)

Sorry, when I said simulated I meant computer simulation. Ariel. (talk) 01:56, 18 June 2010 (UTC)

Ariel, what you're saying makes no sense. Either way the whole thing explodes and that is that. Dauto (talk) 05:09, 18 June 2010 (UTC)

As has been said, there is no use whatsoever in making explosive compounds from antimatter; the energy is no larger or smaller. For that matter (pun not intended), it would probably be easiest to use a simple antiplasma for an antimatter-based explosive. Plasma can easily be confined magnetically, and being a fluid, it will react with normal matter more or less at once. A solid block of antimatter would probably "sizzle" like a drop of water on a hot plate (albeit many orders of magnitude more violently) before all of the mass is used up, with the explosion at the edge pushing normal matter away. Moreover, an antiplasma bomb could in theory be as simple as vacuum tank containing a large, shaped electromagnet, with the antiplasma confined inside its field. Detonation is as easy as cutting the magnet's power; when the confinement is broken and the first particles touch the chamber wall, it goes boom. --Link ^(t•c•m) 11:42, 18 June 2010 (UTC)

help with Gaussian fitting and airy disks

Don't know whether this belong in math or in science...

We are tracking some nanoparticles by DIC microscopy but they appear much bigger than they already are because of the diffraction limit. We kinda know how approximately big the particles are (less than 20 nm) but of course they appear around 200-300 nm big.

So as a little assignment during 'downtime', my supervisors (who are busy) have told me I can estimate the centre of the airy disk via some sort of Gaussian method and using least squares regression, down to subpixel resolution. I want to start with a 2D fitting for one image, and hopefully 3D fitting for a stack of images taken with z-scanning. Of course, the z-resolution is considerably poorer than xy resolution so the particles (if they are spheres) and up looking like elongated ellipsoids instead.

Help??? Where do I start?

(and I do suppose it is impossible to estimate 'real size' and real boundaries via Gaussian methods?)

John Riemann Soong (talk) 16:58, 17 June 2010 (UTC)

That's a pretty challenging problem, and a lot depends on the special features of your data. One place to start might be by reading the "Modeling of data" chapter of Numerical Recipes in C or one of the other Numerical Recipes books. Looie496 (talk) 17:45, 17 June 2010 (UTC)

My supervisor told me there was an already well-established method that I just had to adapt -- it was basically an extension of nonlinear regression to three dimensions. Then again, he's a PRC postdoc student just looking for his big break, so I guess many things seem simple to him.

Also, I guess I don't need to estimate size from Gaussian methods -- I realise there's a possible approach by looking at the absorbance pattern as we scan the input light across various frequencies and use that to estimate surface energy and from that the size of the particle. John Riemann Soong (talk) 18:08, 17 June 2010 (UTC)

Also it's pretty good if I can start with 2D regression of one image rather than a stack. It'd be somewhere I can start. John Riemann Soong (talk) 18:12, 17 June 2010 (UTC)

The bottom line is that there are many algorithms available, and it's unlikely that you will be able to figure out which one your supervisor has in mind without asking. For what it's worth, here is a recent review of issues and approaches in this area. Looie496 (talk) 18:44, 17 June 2010 (UTC)

A brute force, simplistic approach is take an image I( x, y ) and compare to a Gaussian distribution $G(x,y;x_{0},y_{0},I_{0},\sigma )={I_{0} \over 2\pi \sigma ^{2}}e^{-{{(x-x_{0})^{2}+(y-y_{0})^{2}} \over 2\sigma ^{2}}}$, where fitting a point corresponds to a local minimum of $\chi ^{2}(x_{0},y_{0},I_{0},\sigma )=\int \int (I(x,y)-G(x,y;x_{0},y_{0},I_{0},\sigma ))^{2}dxdy$. As a practical matter, one can usually use simple heuristics to isolate local neighborhoods containing approximately only one particle which will improve the computational efficiency of the approach. Dragons flight (talk) 23:27, 17 June 2010 (UTC)

Well my supervisor did give me a few hints... so I know this is the approach to use. Suppose I've already isolated a neighbourhood with a single point. How do I find the parameters that will give me least squares regression for this surface?

Also, this is less of a priority, but often nanorods like to form aggregates of several particles ... can Gaussian methods be used to locate all their centres in such a case? John Riemann Soong (talk) 15:24, 18 June 2010 (UTC)

Your task is to fit the parameters of the Airy disk formula to your data. In the general case you can use gradient descent, but if you have extra information, you may be able to simplify things by eliminating some or all parameters. For example, if you are sure you have the whole disk, then the center of mass must be where the particle is located. The variance of the disk may give you another parameter. Knowing the characteristics of the lens may give you another. Regarding the second question, the viability depends on how far apart the centres are. If they are closer than the size of the central part of the Airy disk, it's very difficult. If not -- well, you basically have to use some sort of crude deconvolution to figure out how many objects there are and approximately where they are, then use some version of gradient descent to iteratively improve the parameter values. Looie496 (talk) 22:05, 18 June 2010 (UTC)

IP Address

How to trace the computer that has actually transfer my money from my acct from BANK OF INDIA ramakrishnapuram to its branches at Mumbai. —Preceding unsigned comment added by 117.195.209.175 (talk) 17:13, 17 June 2010 (UTC)

Ask the bank, or get a court or the government to order the bank to tell you. Otherwise the only way is to hack into the bank's computer network. Banks don't make that kind of information available to the public. Looie496 (talk) 18:47, 17 June 2010 (UTC)

EMP

How do you protect from an EMP? --76.77.139.243 (talk) 19:17, 17 June 2010 (UTC)

Faraday cage, although anything with an antenna is toast.

ALR (talk) 19:37, 17 June 2010 (UTC)

So stuff with an antenna can be hit through a Faraday cage? Why? --75.25.103.109 (talk) 20:17, 17 June 2010 (UTC)

A faraday cage will protect stuff inside it, however if you have something that needs an antenna, data comms kit or similar, the faraday cage will also prevent it working as it prevents the signals getting through. So you need to breach the faraday cage with the antenna, which provides a path inside.

Catch 22. You can put a sacrificial filter in between the antenna and the equipment that will protect the equipment, but the filter would need replaced afterwards.

ALR (talk) 20:29, 17 June 2010 (UTC)

You need to be in the centre of teh faraday cage to be fully shielded (see shell theorem) at the edges you aren't. EMP isn't the same as high voltage; from which the device does always protect.83.100.250.191 (talk) 20:55, 17 June 2010 (UTC)

Isn't an EMP a pretty low frequency? Faraday cages don't protect against low frequency magnetic fields - you need Mu-metal. Ariel. (talk) 21:07, 17 June 2010 (UTC)

Nuclear electromagnetic pulses have multiple phases. The most damaging phase for moderate scale equipment is the E1 pulse, which is extremely fast (faster than a lightning pulse). It's a "pulse", so it isn't really high or low frequency as is it non-repeating, but for the purposes of Faraday cages it acts like a high frequency signal. The subsequent E3 phase of a nuclear EMP is relatively low-frequency, but its effects are similar to a geomagnetic storm and hence generally only of concern to large scale electrical infrastructure. Dragons flight (talk) 22:19, 17 June 2010 (UTC)

The same kind of devices that can protect against a lightning hit can help lightning arrester, or surge filter. Using vacuum tubes instead of semiconductors can be of assistance too. Graeme Bartlett (talk) 07:14, 18 June 2010 (UTC)

In practice no system is going to protect from everything, the theoretical faraday cage and cages in practice are quite different things. As soon as one is using electronic or electrical equipment inside an enclosure one needs to consider power supply in, communications in and out, cooling either through chilled water, forced air or air circulation. Each of these has an impact on the effect of the cage, although each one also has mitigations; sacrificial filters, wire mesh across vents etc.

ALR (talk) 11:00, 18 June 2010 (UTC)

Some other methods of protection, short of cages, include shielding all wires and keeping the lengths as short as possible (as longer wires develop more of a charge), and simply using components in the circuit with more of an ability to withstand surges. StuRat (talk) 13:18, 18 June 2010 (UTC)

Screening of cables is putting them in a cage

ALR (talk) 15:48, 18 June 2010 (UTC) CEng MIET

Of course, one strategy to protect devices from a nuclear-detonation-induced EMP is to deny the nuclear device the opportunity to emit an EMP by destroying the incoming warhead with an interceptor or several dozen interceptors before it initiates a nuclear reaction. Nimur (talk) 18:08, 19 June 2010 (UTC)

(where) do humans fit in?

For a project I need to know two major differences between humans and animals two for chordates, two for mammals, and two for primates. Any advice? —Preceding unsigned comment added by 69.17.115.101 (talk) 22:29, 17 June 2010 (UTC)

I'm afraid we won't do your homework for you. As long as you know what chordates, mammals and primates are, you shouldn't have too much trouble (it gets harder as you go along, of course - there are loads of really obvious differences between humans and other chordates). One point I'll make - the way you word the question makes me wonder if you are aware that humans are primates, all primates are mammals and all mammals are chordates. Presumably your project involves differences between humans are either some other members of that group, or most other members. And presumably you are meant to come with different qualities for each group (since the differences between humans and other primates are also differences between humans and other mammals/chordates). --Tango (talk) 22:35, 17 June 2010 (UTC)

(edit conflict) Humans are animals, primates, mammals, chordates, etc. Hence there are no major differences. If you want to identify ways that humans are different from other members of the same taxanomic group, then one could come up with a variety of possibilities, though most would probably relate to human intelligence in some way. Dragons flight (talk) 22:39, 17 June 2010 (UTC)

In addition to the intelligence thing (speech, language, make tools etc) - the other biggy (with a few exceptions eg ostrichs) - is walking upright.83.100.250.191 (talk) 00:19, 18 June 2010 (UTC)

Sorry - I have to disagree on every one of those points:

1. Tools is definitely busted. Many animals use tools. Several birds will use small rocks to break open snail shells. There are fish that cut and use leaves to hide beneath when swimming in shallow water so as to avoid surface predators. Chimpanzees cut twigs and remove leaves to make tools that they can poke into anthills to get the ants out to eat. Tool use - and even tool manufacture is far from unique to humans.
2. Speech is a little more tricky. Wiktionary defines speech as "the ability to...use vocalizations to communicate". Plenty of animals communicate using sound. Birds sing to attract mates and mark territory. Whales and elephants keep their pod/herd together using vocalizations. My dog barks to tell me about intruders and whines at the back door when he wants to go outside for a pee. He has at least three or four distinctly different barks for everything from pain to warnings to frustration. Humans are not unique in using speech.
3. Language is even more tricky. Are the songs of whales "language"? They certainly have complex but fairly recognizable structures. But 'body language' is widely used throughout the animal kingdom. Again, my dog indicates that he wants to play by using a 'play bow' - where he rests the front his body on the ground with his hind end up in the air. Tail wagging comes in at least three forms - there is a wide side-to-side wag where the tip of the tail hits the flanks - which means "Welcome". There is also a circular motion which means "Happiness" and a slower side-to-side motion that means "Curiosity". I'm sure there is more to it than that - but that's enough to tell me that these are "words" in a gestural language. The dance of a honey bee is a language - the orientation of the dance tells you compass direction to newly found sources of nectar and the speed of the dance indicates distance.
4. Walking on two legs - clearly busted. Almost all birds do it all the time (not just ostriches) - so did many dinosaurs (think of T.Rex, for example). Gibbons run across the ground on two legs...so do kangaroos, springhares...there are lots of examples.

However, there is something specifically unique about human language: It seems likely though that no animals other than humans are able to use 'grammar'. This is what turns language from a mere series of words ("Play", "Welcome", "Danger!", etc) into open ended statements...we can put together words like "Dangerous Play" and convey the idea that playing is somehow a bad idea right now...but my dog can't use any combination of his play-bow and a danger bark to impart that idea. If he needs to express something new, he has to 'invent' a new word. He learned to push the end of his leash where it was hanging by the front door with his nose to say "It's time for walkies!" - and even after we moved the leash someplace else, he still goes to the same place by the front door and makes the same gesture - but without the leash being there...it's a new "word" in his gestural language. But in human languages, there are essentially no concepts which words cannot describe given enough time without the need to invent new words. Even with Basic English (which comprises just 850 words), it's quite possible to say pretty much anything you want. Wikipedia's Simple English encyclopedia has 60,000 articles - and is written almost exclusively with a 1000 word vocabulary. But even with a restricted set of words, our language is completely open-ended.

But the language of my dog is strictly limited to the number of body gestures and vocalisations he can make. He has "Words" but no "Grammar". If you do a Google search for "Animal Grammar", the few scientific studies you find are all pretty much negative about animal abilities in this regard.

SteveBaker (talk) 05:20, 18 June 2010 (UTC)

Similar to SteveBaker's comments on grammar is the inability of animals to express an abstraction. Even animals which can use complex language, such as higher primates like chimps and orangutans, lack the ability to express ideas or concepts in the abstract or hypothetical. A chimp can express a desire in the concrete, in that it can say "I want a banana", but it could not say, or likely even understand, an idea like "Maybe tomorrow I would like a banana, even if I do not today." Higher primates can be trained to use rudimentary grammar in their constructed language systems, usually they cannot constuct language to express ideas which are not firmly concrete. --Jayron32 05:38, 18 June 2010 (UTC)

For a cellular approach to differentiating humans from other animnals, see karyotype. Gandalf61 (talk) 08:28, 18 June 2010 (UTC)

I find it funny and little bit sad that we still try to differentiate our species with such highfalutin and complicated concepts like language, art, tool-use, etc. Those are inappropriate markers - it's the kind of thing philosophers come up with then they try to get involved in biology. The article needed here is anatomically modern human; the differences between humans and their closest living (chimpanzees) and extinct (Neanderthals) relatives comes down to the same kind of boring stuff used elsewhere in biology - dentition, skull morphology, etc. Matt Deres (talk) 13:38, 18 June 2010 (UTC)

Oh, sure! Absolutely. I'm merely pointing out that the classical 'markers' such as speech, tool use, tool creation, fighting wars...and a whole host of other things like that...have all been disproved as we find animals doing each of those things. Grammar is the only simple test I could imagine that wouldn't entail looking at the detailed biology - but looking at the biology is much more likely to produce certain answers than the more holistic approaches of looking at various skills an behaviors.