Wikipedia:Reference desk/Archives/Science/2008 March 22

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March 22

Automatic crossbow

Has there ever been such a device as a fully automatic crossbow? If not, is there any technical reason why not? --Kurt Shaped Box (talk) 01:14, 22 March 2008 (UTC)

Well we have an article repeating crossbow. Also take a look at Zhuge Liang#Legacy the ancient chinese supposed inventor of these.

Also this thread [1] describes unmanned automatic crossbows mounted on chariots driven by the turning chariot wheels and flung at the enemy by setting fire to the horses tails. No idea how reliable this source is, but it conjures up a wonderful picture. SpinningSpark 01:36, 22 March 2008 (UTC)

I'll test this next time I go by a stable, assuming I can find a used chariot. But what happens when the horses turn around and come running back? Maybe that's why this method of warfare didn't catch on? :) Franamax (talk) 12:27, 22 March 2008 (UTC)

Just be thankful that you weren't fighting alongside war pigs (if they ever existed). --Kurt Shaped Box (talk) 13:17, 22 March 2008 (UTC)

Why would they come running back? If someone set your arse on fire would you go back there? SpinningSpark 13:29, 22 March 2008 (UTC)

If I was on fire, I probably wouldn't be paying that much attention to where I was running. --Kurt Shaped Box (talk) 13:37, 22 March 2008 (UTC)

(e/c) Ahh, war pigs, I always wondered what Black Sabbath was going on about! SS, why would the horses keep running in a straight line? If your butt's on fire, do you keep track of directions? (Don't try this at home kids) What I was thinking of though is that they might run back towards some of the unburnt horses they were just hanging around with, horses tend to do that. And they would have kept at least one horse for the general to ride afterwards, right? Who wants to ride a smelly burnt horse? :) Franamax (talk) 13:45, 22 March 2008 (UTC)

water heater is making a whining sound

I live in a two story house. Our water heater is making a whining sound that can be heard all through the house. I'm afraid that a pipe or the water heater is going to blow and cause a terrible problem. Do you know what could be making the whining sound that has never been heard in our house before? What can we do about it?

Gas? Fueloil? Electric? Immersion? A little more detail would help. --BozMo talk 06:55, 22 March 2008 (UTC)

It sounds like you need a plumber to not only examine the water heater, butt crack this problem wide open before a serious leak occurs. StuRat (talk) 11:41, 22 March 2008 (UTC)

Googling on "water heater" whining provides many useful links. I have heard that they can make noises when there is a layer of deposits in the bottom in which water can become superheated and be forced through the deposits. It is possible that the pressure relief valve is starting to leak. I would warn you that the water heater is nothing to mess around with; when things go wrong they can go wrong big. Here is a video from Mythbusters that proves that. --Milkbreath (talk) 13:35, 22 March 2008 (UTC)

I'd amend that to "the water heater is nothing to mess around with if you don't know what you're doing". In my opinion that Mythbusters video is (like much popular entertainment) somewhat alarmist. The fact that you never hear about water heaters exploding like that in real life is good proof that, virtually all of the time, the designed-in safety mechanisms work as they're supposed to. I'm not saying it never happens, but anyone who tampers with or disables a safety device such as a T&P valve displays criminal negligence and stupidity. —Steve Summit (talk) 14:05, 22 March 2008 (UTC)

Addendum: Never? Well, hardly ever. Yikes. —scs 14:10, 22 March 2008 (UTC)

Yes, the Mythbusters are not a reliable primary source as a rule, but I watched that one, and we're seeing the true consequences of defeating the safety devices, turning the thermostat up, and then simply turning the thing on and waiting. No extra explosives or other heroic measures were used for dramatic effect. Both they and I were astonished at the violence of the event. Apparently, such explosions were commonplace before the introduction of the safety valve. --Milkbreath (talk) 14:41, 22 March 2008 (UTC)

Right. But the nice thing is, today, simultaneous failures of both the thermostat and the safety valve are exceedingly rare. I'd wager that all such failures are due to capping off of the safety valve (as in the referenced Seattle P-I article, presumably because the valve was leaking). —Steve Summit (talk) 15:16, 22 March 2008 (UTC)

Best Food

If a human had to survive on just water and one other substance, what would that substance be ? —Preceding unsigned comment added by 80.5.206.57 (talk • contribs) 15:19, 22 March 2008

In order to survive as long as possible, I think it would be sodium chloride. Without it he would die pretty soon from water poisoning. Icek (talk) 15:31, 22 March 2008 (UTC)

Does cornish pasty count as a substance? Or how about earth (soil) - with earth and water you could grow your own food..87.102.16.238 (talk) 16:22, 22 March 2008 (UTC)

Guinness? Heh, I know it's probably an urban legend - but has anyone else heard it said that you can supposedly get all/most of your nutritional needs from five pints of Guinness per day? --Kurt Shaped Box (talk) 19:24, 22 March 2008 (UTC)

Much as I am always in favour of beer theories, I would go with milk, being as it is designed to do just that - provide you with all the nutrients you need to survive. SpinningSpark 21:29, 22 March 2008 (UTC)

I think a "substance" is something with a definite chemical composition, which is not true for milk, beer and the like. Icek (talk) 11:18, 23 March 2008 (UTC)

I'd go with oxygen. — DanielLC 16:30, 23 March 2008 (UTC)

Garlic for treatment of wounds

Hello, there is hearsay about usage of garlic for the treatment of wounds up to the time of WWI. For the respective WP articles, I'd need at least one account that it was official treatment. Google was no use, neither the Project Gutenberg full text search.

Do you know of a passage in a book (even fiction) where garlic was used on a wound, or its usage was recommended by an official about 100 years ago? --85.179.13.254 (talk) 17:10, 22 March 2008 (UTC)

would this help http://news.bbc.co.uk/2/hi/health/3344325.stm

Also try searching for 'allicin' if you haven't already87.102.16.238 (talk) 17:47, 22 March 2008 (UTC)

http://www.bulkherbstore.com/GM

In his book, Advanced Treatise in Herbology, Dr. Edward Shook had this to say about the valuable antibiotic properties of garlic: "The use of garlic in the 1st World War (WW1) as an antiseptic was most sensational. In 1916, the British government asked for tons of the bulbs, offering one shilling a pound for as much as could be produced. A great quantity of it was used for the control of suppuration in wounds. The raw juice was expressed, diluted with water, and put on swabs of sterilized sphagnum moss which was applied to the wounds. Where this treatment was given, it has been proved that there has never been one single case of sepsis or septic results. Consequently, the lives of tens of thousands have been saved by this one miraculous herb."

does that help87.102.16.238 (talk) 17:51, 22 March 2008 (UTC)

Can you give me the page number of that passage, please? I would like to read it myself, and see if Dr. Shook has references for that opinion. Many thanks!

To the other poster: the antimicrobial activity of garlic compounds is well established, thanks. The question is specifically about official former usage. --85.179.15.63 (talk) 07:37, 23 March 2008 (UTC)

Sorry I haven't got the page number87.102.16.238 (talk) 10:43, 23 March 2008 (UTC)

How were you able to produce that passage, then? --85.179.24.245 (talk) 15:29, 24 March 2008 (UTC)

It comes from the link he provided right before it. -Elmer Clark (talk) 00:45, 26 March 2008 (UTC)

Genetic mutation resulting in deformities of the offspring

1. In sexual reproduction, i.e., fertilization of egg by sperm, does mutation of the egg or sperm producing organs, say by means of radiation, always result in the failure of the organs to produce viable egg or sperm, i.e., egg or sperm that can result in a fertilized egg? In other words, are deformities in an offspring due to mutated egg or sperm producing organs?
2. If mutated egg or sperm producing organs are not responsible for deformities in an offspring then is mutation of the egg or sperm, say by irradiation, after they are produced and prior to fertilization responsible for deformities in the offspring?
3. If deformities do not result from mutated egg or sperm occurring after they are produced, say by irradiation, then are deformities in the offspring the result of a faulty union of egg and sperm?
4. If faulty union of egg and sperm are not responsible for deformities in the offspring then is the genetic mechanism by which deformities occur in the offspring the result of mutation of the fertilized egg after it is fertilized, by say irradiation of the fertilized egg? 71.100.1.14 (talk) 17:18, 22 March 2008 (UTC)

1. Mutation is a process involving alteration of the genetic code. Now, mutation affecting the reproductive organs can lead to effects in the sperm/egg's DNA or their body, both of which can lead to offspring deformities. Now, your other question is backwards, and it's a fact that there are also deformities caused by other processes than mutation, e.g., folate deficiency of the mother, to name one.

2. Radiation can affect sperm as in my answer 1, or it can damage sperm's DNA directly. All radiation damages are highly dependent on the radiation dosage and the time when the mutation happens (like in the midst of cell dupication or such), and even then, the body has means to neutralize a good deal of such damage, provided it's healthy (no alcohol, no smoking).

4. Yes, also eggs' DNA can be damaged after eggs were produced (all human eggs are produced beforehand, anyway. That's why mothers are advised not to have children after 40 for mutation and other damage risk reasons, like Down's syndrome). -- 85.179.13.254 (talk) 17:37, 22 March 2008 (UTC)

So are you saying that a mutation in the parent before egg or sperm production or mutation in the egg or sperm after production but before fertilization or mutation after fertilization can result in a deformity or difference in an offspring? 71.100.1.14 (talk) 18:18, 22 March 2008 (UTC)

Yes, definitely. It wouldn't happen often, normally, as said, because of the body's defenses. The risk, however, is not exactly zero.

BTW, coincidentally, folate deficiency affects even males and their sperm, according to this fresh news article. --85.179.15.63 (talk) 07:32, 23 March 2008 (UTC)

Children's medicine 100 years ago.

In books such as The house at Pooh Corner or Peter Pan, children (specifically Roo and Peter respectively) are described as drinking medicine or tonic each day "to make them grow up strong". What was in these concoctions, would they have been prescribed by a doctor, an apothecary or made up at home? Zeimusu | Talk page 17:22, 22 March 2008 (UTC)

Mostly patent medicines, which really thrived in the early 20th century when both of those books were written, before any meaningful drug and advertising regulation was done. (Even today, under the guise of "natural" cures all sorts of hogwash is sold with fantastical claims, e.g. Airborne (dietary supplement). Let we think they were so stupid then, let us look at ourselves and our own propensity for such things!) --Captain Ref Desk (talk) 19:03, 22 March 2008 (UTC)

On the other hand, some of those concoctions might have helped, by providing vitamins and minerals which might otherwise be deficient in the child's diet. Cod liver oil is one such example. StuRat (talk) 21:13, 22 March 2008 (UTC)

The Smallest?

Is there a limit to how small a particle can be? Is there a point where a particle no longer MOVES to a point, but GOES to a point because it is so small that you can't be half way there?--Xtothe3rd (talk) 18:05, 22 March 2008 (UTC)

String theory is based on the idea that there is a minimum (1-dimensional) particle size, rather than zero-dimensional point particles. It isn't clear whether string theory is really going to work out physically and mathematically but yeah, that's the basic question it asks. More generally, though, there is Planck length, the smallest distance at which our physical theories make any sense. At a point much larger than that, though, the uncertainty principle keeps us from knowing whether a given particle is in a specific space or not. --Captain Ref Desk (talk) 18:53, 22 March 2008 (UTC)

However, the gravitational singularity of a black hole is a mathematical point. That is, it's infinitely small with no volume (but a definite mass). StuRat (talk) 21:07, 22 March 2008 (UTC)

Resolution of the naked eye

With my naked eye on an overcast day I can tell whether someone on a covered porch 500 feet away is wearing a black hat with a 3/4 inch white pendant or patch. How can I translate this to the resolution capability of my naked eye and compare it with a standard resolution capability for the human eye? 71.100.1.14 (talk) 18:53, 22 March 2008 (UTC)

The standard resolution capability is about one minute of arc (1/60 of a degree) which equals 0.0003 radians. For small angles, the angle in radians can be calculated by dividing the length of the object or separation of objects (perpendicular to the line of sight) by the distance. Now, if you see just one white patch on a black background that does not mean that your resolution is actually (width of the patch)/distance. What you would need is 2 white patches on a black background, and then determine the largest distance at which you can still see that it's 2 patches and not 1.

You can only conclude anything about the resolution capability of your eye from your experiment if the background around the hat was bright, and you could clearly see a pattern (e. g. along a horizontal line) of bright background - black hat - white patch - black hat - bright background. Then your resolution capability is at least ((width of the hat)/2)/distance.

If you are interested in the general calculation of the resolution of optical instruments (including eyes), you could start at Airy disc. Icek (talk) 19:22, 22 March 2008 (UTC)

To verify then at standard resolution capability for reflected ambient light then should I be able to see with a bright background a white patch on a 3.6 inch black object 500 feet away?

The Airy disc article seems to suggest that the reason I can see stars at night in the sky is due to the intensity of the light being emitted by the star attenuated by background and the distance, i.e., I can not see them when the background light is bright and I would not be able to see them at night at that distance if they were only reflecting ambient light like the moon.

Regarding the verification of standard resolution capability: Yes, but two white patches on a larger black background and a friend placing randomly one or two of the patches onto the background without you knowing whether it's one or two patches would be better.

Sorry, I'm still not clear on the size of the patches and their distances apart. Would I say start with a single patch that was so small it could not be seen and increase the size until it could be seen, then use of these patches at some relevant distance apart to determine my resolution. Is there a formula for patch size and their distance apart, the size of the black easel and the intensity of the background light?

The white patches should be just as small as possible, so your method should work. If the background is dark enough, you should see a white patch even when it is fairly smaller than the resolution limit. Take the distance between the white patches center-to-center. In principle you could compute the theoretical diffraction pattern for extended patches instead of points, but I don't think that's necessary. Icek (talk) 06:55, 25 March 2008 (UTC)

Regarding the Airy disc, yes, the intensity of the light lets you see objects that are far smaller than your resolution limit.

Interestingly, one could even go beyond the Airy limit if one used a monochromatic filter and light detecting elements far smaller than the Airy resolution limit. Then you could calculate the distribution of brightness from the diffraction pattern. But of course that is assuming that your optical instrument is nearly perfect with no stray light etc. Icek (talk) 11:59, 23 March 2008 (UTC)

hummm... is it possible that this is how in part the Hubble telescope is constructed? 71.100.1.14 (talk) 18:33, 23 March 2008 (UTC)

No. Remember that the Airy disc is an idealized model. For telescopes below the atmosphere, atmospheric turbulence causes distortions of the image (see Astronomical seeing), preventing us from reaching the Airy limit (the images can nowadays improved by adaptive optics, but currently only for long-wavelength light). The resolution of the Hubble Space Telescope is about 1/20 of a second of arc - about what you get with the Airy formula for a 2.4 m mirror at visible wavelengths. Icek (talk) 19:25, 23 March 2008 (UTC)

speed of an ant

I've clocked a frightened ant at 1 foot in 3.1 seconds and faster. This give me .32 feet per second or 116 feet per hour or .02 miles per hour. Where can I find a list of speeds for other insects? 71.100.1.14 (talk) 19:09, 22 March 2008 (UTC)

Since ants vary dramatically in size, I'd expect them to also vary dramatically in speed. This will also be true for many other insects. So, a chart listing the speed of "ants", "centipedes", "beetles", "flies", etc., would be meaningless. You'd need to list the individual species of each. StuRat (talk) 21:04, 22 March 2008 (UTC)

Okay, I have no problem with that. Even though there are vast differences in speed for even the same species (humans) there is statistics which can provide a maximum, a mean and a standard deviation. 71.100.1.14 (talk) 08:26, 23 March 2008 (UTC)

There are several sources on the internet that list the speed of various animals. A published list is in Natural History Magazine, March 1974, The American Museum of Natural History; and James G. Doherty, general curator, The Wildlife Conservation Society. That list is reproduced here. A compendium that compares the collates reported in various sources for the speeds of a range of animals is points 730-745 here. IBangMyHead (talk) 12:18, 23 March 2008 (UTC)

71.100.1.14, your last two speed figures are a factor of 10 too low. We wouldn't want the ref desk to be sued by someone who was outrun by an ant. --Heron (talk) 13:16, 23 March 2008 (UTC)

These figures are based on 1 foot in 3 seconds. I originally named then "Darters" but they are an invasive species which I have forgotten the name of now. They may be moving along at 1 inch per second or less foraging and then when frightened dart off at 3 to 4 inches per second - too fast to follow with them a finger to give them a good smash. 71.100.1.14 (talk) 08:37, 24 March 2008 (UTC)

As Stu said, it really depends on the species. Of the large Old World ants, Cataglyphis ants run pretty damn fast, easily over 10 cm/s, maybe as much as 20 cm/s. Messor and Camponotus are slower, several cm/s is probably the limit. Smaller ants are around 1 cm/s or less. However, these are just my non-scientific observations, so you should definitely NOT use them as a reference. As for other insects - please be more specific, then we (the Ref Desk) will probably be able to help. Cheers, --Dr Dima (talk) 15:26, 23 March 2008 (UTC)

I'm not real sure but these look allot like Argentine ants. 71.100.1.14 (talk) 20:53, 24 March 2008 (UTC)

Fixed previous link. Pallida  Mors 04:43, 25 March 2008 (UTC)

Why are you frightening ants to measure their speed?

The fabric of space

Did Einstine say that his math would not work unless space was actualy something. In other words, space could not simply be an empty void that matter exists in but an actual physical thing. e.g. "fabrick of space and time" I read somewhere that he called it ether.

You may be interested in general relativity and spacetime. — Matt Eason ^{(Talk • Contribs)} 20:40, 22 March 2008 (UTC)

For Einstein, space and time are bound together inextricably—you cannot reasonably talk about one without talking about the other (you cannot measure space without time, you cannot measure time without space, and you cannot talk about what you cannot measure—a few of Einstein's fundamental axiomatic realizations), and the composition of space affects the way in which time is perceived (and thus, because of relativity, the way time operates itself, as there is no time outside of space). So instead of space and time we have "spacetime".

It is not the same thing as the luminiferous aether, which was an earlier theory that Einstein rejected.

To elaborate a bit: it is not so much that empty space is not "empty" (that is, devoid of matter), it is that the idea of "space" itself is a geometrical construct, and it is more flexible than one might normally assume. The presence of any mass at all, for example, deforms spacetime, and the result is the effect that we call "gravity". We slide along this deformation in spacetime without even realizing it, towards the center of large masses, in this case, the planet Earth, along the path of least resistance.

Hopefully that will clarify things a little bit—I've oversimplified things a bit but I don't think I've committed any major errors. --Captain Ref Desk (talk) 20:40, 22 March 2008 (UTC)

Where is the centre of the universe?

If the universe is continually expanding outward in every direction, then where is the point from which it is expanding? That must be where the big bang occurred? But where is it, say, in relation to our earth? Are we nearer to the centre of the universe or the "edge" of it? As you will have guessed, I am not a science person. Kaiwhakahaere (talk) 20:34, 22 March 2008 (UTC)

Without knowing the shape of the universe, it is not possible to define a center. And further, there are possible shapes to the universe for which there is no geometric center. Also, there is no position in space "where the big bang occurred." The big bang occurred everywhere. To explain how that might be possible, think of the expansion of the universe. When we look at distant galaxies, we notice that the speed at which the galaxy is receding is directly proportional to its distance from us (Hubble's law), and this seems consistent in every direction. That is, almost everything is moving away from us, and we seem to be at the center of it all. However, this observation would be true no matter which galaxy we were in. It would subsequently be true that if we were to run time backwards, we would see everything rushing towards us and the density of matter/energy would increase towards infinity as we approached the big bang, and this observation would be the case no matter which galaxy we were in! Thus, each galaxy can equally claim that is the central point of expansion, and thus it is probably untrue that an actual "center of the universe" exists anywhere, and it is certainly untrue that the big bang occurred at one point. Someguy1221 (talk) 21:08, 22 March 2008 (UTC)

You must be the universe's fastest typist! Or our locations are actually coming together rather than moving apart! Only 34 seconds after I hit my save page button you posted a reply. And a great reply it was too. Tks. Kaiwhakahaere (talk) 21:15, 22 March 2008 (UTC)

I suspect this was a prepared answer, which took me longer than 34 seconds to read. 71.100.1.14 (talk) 08:32, 23 March 2008 (UTC)

It was 34 minutes, not seconds. -- BenRG (talk) 19:42, 23 March 2008 (UTC)

The big bang is more like a balloon being blown up than an explosion. The big bang happened everywhere - it was an expansion of the distances between things. So if everything in the universe were on the surface of a balloon while it was expanding very quickly, that would sort of be like the big bang. Quantumelfmage (talk) 05:49, 24 March 2008 (UTC)

Leap from a burning building

A question I posted above (Wikipedia:Reference desk/Science#Free falling human body) prompted this follow-up thought. If your house / apartment building is on fire, and you have to jump out the window ... what are some rules of thumb you should observe? In other words, what's the "best" way to jump out? And is there any relevance to what story up you are in the house / apartment building? Or is that essentially irrelevant? In other words, if I was very high up (on the 10th or 20th or 100th floor), would / should my jumping strategy be different than if I was not so high up (on the second or third floor)? Also, what are some considerations a person should factor into making a good decision to "should I jump or should I not?" Ultimately, if you were the Chief of the Fire Department and had to write a "how to manual" for people who find their homes on fire, what would be the best advice in these scenarios described? Thanks. (Joseph A. Spadaro (talk) 21:28, 22 March 2008 (UTC))

From a second floor window, you can break your fall with a "parachute roll" without any serious injury if you are properly trained. A paratrooper friend I used to know used to do this regularly as a party trick after we had been drinking (warning: don't try this at home). I have also read (sorry, forgot where) of a base jumper whose chute failed after jumping off a building at a great height. He managed to keep his fall under terminal velocity by grabbing the ledge on every floor as he went down. The fall is too fast to be able to actually hold on but it slowed him down enough to survive. Multiple fractures in both arms from hitting the ledges and broken legs on landing but he did survive (don't try this at home either). And now you mention it, I do have a "how to" book on surviving worst case scenarios - I'll see if I can find it. SpinningSpark 21:47, 22 March 2008 (UTC)

Thanks for the reply. It would be helpful to know what the term "parachute roll" means ...? Thanks. (Joseph A. Spadaro (talk) 22:15, 22 March 2008 (UTC))

Well, if the building really had been on fire the book would have been completely useless as it took too long to find - note to publisher: you need to embed an emergency siren in the spine so it can be located quickly. So anyway, it lists several falling scenarios, the closest to your question is "How To Jump From A Building Into A Dumpster" (dumpster = skip in UK). They recommend tucking in your head and bringing your legs around so that you are laying on your back. They say the reason for this is that the body tends to be thrown into a V on landing. If you land on your stomach this will break your back. Also, try not to leap outwards as this will carry you away from your aiming point. I would also repeat - don't try this at home - there's a lot that can go wrong with this one. If you miss the dumpster, you hit concrete. If you nearly miss the dumpster you might hit your head or your back on the edge - worse than hitting the concrete. If the dumpster is full of building rubble (what else would be in it? they are only full of empty cardboard boxes in the movies) then you may as well have aimed for the concrete. SpinningSpark 22:25, 22 March 2008 (UTC)

Parachute Roll. I don't think this is used very much anymore, but in the days when parachutes were a lot less controllable it was necessary to break you fall to avoid broken ankles. Basically, it is bending at the knees to absorb some of the shock as your feet touch down and at the same time falling to one side and turning that motion into a roll as your body hits the ground to dissipate even more of your kinetic energy. Practice from standing on the ground at first and then steadily increasing heights. SpinningSpark 22:35, 22 March 2008 (UTC)

Parachute Landing Fall. 152.16.59.190 (talk) 06:11, 26 March 2008 (UTC)

One important thing to do from the 2nd or 3rd story is to hang from the ledge first, to lower your distance to the ground as much as possible, before you jump. Also aim for something relatively soft, like dirt or a bush or an awning. StuRat (talk) 06:32, 23 March 2008 (UTC)

Wow, I would have never thought of that ... but, yes, it makes perfect sense. Thanks. (Joseph A. Spadaro (talk) 18:51, 24 March 2008 (UTC))

How To Survive a 47-Story Fall Make sure you land on your feet. Gzuckier (talk) 19:00, 25 March 2008 (UTC)

Non-pop popcorn

After a nice meal i decided to have some popcorn with my beer and meaningless wikipedia-surfing. I poured the corn into the kettle and went back to my computer, waiting for the first pop. however, no pop occurred, and instead i smelt fire and when I turned around I saw thick smoke from the kettle. The corn had simply started burning instead of popping like usual - ruining the kettle in the process... I was thinking afterwards that I had put to small an amount of oil in the kettle, but after reading the popcorn article it seems that they should pop at a certain temperature, oiled or not. the next batch of popcorn (from the same bag) went fine. this is a slightly odd question, but has anyone got an idea why this might have occurred?

Did you adjust the temperature? Maybe the first lot was too high. Julia Rossi (talk) 03:10, 23 March 2008 (UTC)

Also, wikipedia surfing is never meaningless. Your knowledge increases, your eyesight deteriorates. Live long and prosper. --Dr Dima (talk) 15:54, 23 March 2008 (UTC)

off the top of my head; popping requires moisture trapped within the kernel; burning instead of popping suggests the kernels were dehydrated; if the next batch from the same bag was Ok, then my guess would be that the heating process was a little slow and the kernels dried out before getting to 212 degrees F. Gzuckier (talk) 18:55, 25 March 2008 (UTC)

How the brain processes visuals

I believe that this is a Science question ... or, rather, questions. (Question 1) When we look at a drawing of, say, Charlie Brown (or any cartoon) ... that picture in no way looks like a real human being 8-year-old boy. So, what "tricks" our brain when we see these animations to "accept" that they are people? That question was hard to word, but I hope someone catches my drift. (Question 2) We look at drawings, pictures, paintings, and visuals all the time. What exactly "distinguishes" these normal visuals from what we call "optical illusions"? In other words, in a given optical illusion, it might say: "Do you see a man or a mouse?". Some people can see the man, some the mouse, and some both. Why is that? And what exactly makes that visual different for our brain to process than when we look at a "normal" (unambiguous) visual (like my high school yearbook photo or the Iwo Jima photo)? Thanks. (Joseph A. Spadaro (talk) 22:24, 22 March 2008 (UTC))

While a cartoon face doesn't look anything like a particular human face, it is very close to looking like the Prototype Theory or average face. At a low level, we might analyze Charlie Brown's nose as a half-circle, but there is a top-down mechanism in the brain that makes us recognize it as a nose because it is in the context of a face. Each of Charlie's features do not have enough detail on their own to assert themselves as facial features, but in the context of a prototypical face and prototypical features, we can place them. So at a fine-grain, low level, high detail level, Charlie Brown's face does not look like a face, but at a high level, wholistic, gestaltic level, it does look like a face, and top-down mechanisms make us accept it as a face.

In an optical illusion like the one you described, there are neural mechanisms that force us to settle on one interpretation of an ambiguous image (usually because it is the best interpretation). But the illusionary image is constructed so that neither interpretation is clearly better, so our perception switches back and forth. So the parts of your brain are getting confused and reporting inconsistent output to the part of your brain which isn't sure whether to call it a mouse or a man. So we call it an illusion. Quantumelfmage (talk) 05:43, 24 March 2008 (UTC)

Makes sense. Then, as a corollary question ... how come sometimes I cannot "see" the alternative image until someone directly points it out exactly to me? And how come sometimes I can never "see" the alternative picture, even when someone directly points it out exatly to me? Thanks. (Joseph A. Spadaro (talk) 05:53, 24 March 2008 (UTC))

I believe that we see things as other things due to our ability to handle symbolic logic. That is, to define one thing as representing another. This is important in human communication. The cartoon may only be recognized because, in our past, we have used pictures drawn in dirt with a stick to represent people, and those who could understand had a survival advantage. I doubt if a dog could recognize a cartoon as representing a person or dog, as they lack the ability to use symbolic logic. StuRat (talk) 06:07, 23 March 2008 (UTC)

Unfortunately, we do not have much of an article for associative memory, and it's a shame. I will write one if I have time this week. For the time being, a really lousy short explanation. Objects (visual objects in particular, but any sensory or conceptual objects in general) that we encounter in real life are often incomplete, poorly resolved, or somewhat different from their "standard" form. Yet, we recognize them very reliably. The underlying neural circuitry is usually called an "associative memory" network. The network has many "familiar" or "memorized" states corresponding to familiar objects or notions; these are called attractors. Any incomplete or inaccurate input to such a network (an observed object) brings the network into an attractor state which is usually rather similar to the observed object; this is recognition. Human face, or human shape, are some of the most important visual objects in the evolutionary sense, so we tend to see human shapes even in some definitely inanimate or non-human objects (see Pareidolia). So recognizing a manga or comics character, even super deformed, is really not surprising at all. And, besides, there is also a "symbolic logic" aspect which Stu mentioned: basically, we all drew pretty schematic pictures in kindergarden, at least at first; yet they were quite easy to decipher, in most cases :) . Hope this helps. --Dr Dima (talk) 15:12, 23 March 2008 (UTC)

Thanks for Question 1 (Charlie Brown). And (Question 2): We look at drawings, pictures, paintings, and visuals all the time. What exactly "distinguishes" these normal visuals from what we call "optical illusions"? In other words, in a given optical illusion, it might say: "Do you see a man or a mouse?". Some people can see the man, some the mouse, and some both. Why is that? And what exactly makes that visual different for our brain to process than when we look at a "normal" (unambiguous) visual (like my high school yearbook photo or the Iwo Jima photo)? Thanks. (Joseph A. Spadaro (talk) 20:10, 23 March 2008 (UTC))

Could physicians work as epidemiologists?

Dear Wikipedians:

My dad graduated from a non-American medical school with a MD in public health. Instead of treating patients, he works in a non-American CDC like organization doing body check-ups for primary/secondary school students and does preventive medicine propaganda in the community and also writes out a few research papers per year on the statistics of the prevalence of various diseases in the community, results of the student body checkups, etc.

I am wondering if this qualifies my dad as an epidemiologist? And is it reasonable for physicians to work as epidemiologists?

Thanks.

76.68.9.59 (talk) 22:26, 22 March 2008 (UTC)

I could be wrong, but I don't think you need to be licsenced to work as an epidemiologist. I think that it is like many occupations, if you DO it then you ARE it. (By the way, this belief has gotten me into some arguments. I believe, for example, if you studied chemistry, but don't do chemistry, you are not a chemist). ike9898 (talk) 01:48, 23 March 2008 (UTC)

There's nothing that necessarily disqualifies a physician as working as an epidemiologist, but usually epidemiologists have very rigorous training in statistics and experiment methodology, which may or may not be part of the general med school/public health education. --Captain Ref Desk (talk) 22:49, 23 March 2008 (UTC)

There are masters and Ph.D programs for epidemiology. An allopatric medical degree is not required. Wisdom89 _{(T / ^C)} 06:24, 24 March 2008 (UTC)

if he has a degree in public health and writes a few statistical-type papers a year, he's an epidemiologist. Gzuckier (talk) 18:53, 25 March 2008 (UTC)