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April 11

Torque due to gravity

http://web.mit.edu/juang/OldFiles/Public/Classes/8.012/exams/final-F02sol.pdf. For question six, the solution uses the conservation of angular momentum. But doesn't gravity exert a torque on the block? If we define our origin as the top of the cone, then r x mg isn't zero because the two aren't parallel. Thanks. 173.179.59.66 (talk) 01:33, 11 April 2010 (UTC)

The generated torque is perpendicular to the axis of rotation. Since the axis of rotation is fixed by assumption, such a torque can not change the angular momentum about that axis. Dragons flight (talk) 02:44, 11 April 2010 (UTC)

Thanks. 173.179.59.66 (talk) 05:09, 11 April 2010 (UTC)

Quantum Entanglement

Quantum entanglement can't be used to transfer information because this would violate relatvity (the data travel, if possible, would be instantanious, which would be faster than the speed of light), that part I understand. Now consider this, imagine two friends, Alice and Bob, each have a box with a particle in it. Those two particles are entangled to one amother and are in a superpositon of being the color red or blue. As soon as one of the two of them looks at their particle, decoherence will occur and the particle will be either red or blue, not both. Not only that but because the two particles are entangled, the other friends particle will become the opposite color. If Alice looks and finds hers to be red, Bobs, even though he hasn't looked yet will be blue. A soon as Bob looks he will find his to be blue and he will know that Alices must have been red. Isn't this a transfer of information? I know that Alice or Bob can't use this to transfer their own information, like one telling the other their favorite kind of pie, because the color that the particles ultimatly become when viewed is random and unpredictable. But still, isn't information still being transfer, when one looks at the color of their particle they immediatly know the color of their partners too. Wouldn't this violate relativity? Could some one please explain to me how that would be possible, am I mssing something?

The way I'd look at it is that they each already had the info on the other, they just hadn't looked at it yet. So, the info didn't travel between the two remote people at all, it was already right there in the box. StuRat (talk) 03:32, 11 April 2010 (UTC)

I agree...who needs all that funky quantum stuff? Take a matchstick, break it in half and toss each half into a box...give one box to Bob and the other to Alice (at random). Whoever opens their box and sees that they have the head of the match knows that the other person has no head on their half of the matchstick - and vice-versa. That isn't what's happening with the quantum entanglement thing (well, depending on your interpretation of quantum theory) - but the information/communication situation is indistinguishable and no laws are broken in the process. SteveBaker (talk) 03:49, 11 April 2010 (UTC)

Yeah, in this particular experiment there's nothing going on that's very interesting or problematic. Bell's theorem is that there are ways to measure the entangled particles that can't be reproduced with match sticks, but even then there's no information communicated. The test for that is, can Alice make an arbitrary yes/no decision after she and Bob part company, and then somehow let Bob figure out what her decision is faster than light. It's still impossible. Rckrone (talk) 05:25, 11 April 2010 (UTC)

What do these formulae mean?

$W={\frac {\lambda x}{d}}\,$

$v={\sqrt {\frac {T}{\mu }}}$

$\theta _{I}=\theta _{R}$

${\frac {\sin {\theta _{i}}}{\sin {\theta _{r}}}}={\frac {v_{1}}{v_{2}}}=n$

$n_{1}\sin {\theta _{1}}=n_{2}\sin {\theta _{2}}$

What do each of these various formulae mean?--Alphador (talk) 02:14, 11 April 2010 (UTC)

Welcome to the Wikipedia Reference Desk. Your question appears to be a homework question. I apologize if this is a misevaluation, but it is our policy here to not do people's homework for them, but to merely aid them in doing it themselves. Letting someone else do your homework does not help you learn how to solve such problems. Please attempt to solve the problem yourself first. If you need help with a specific part of your homework, feel free to tell us where you are stuck and ask for help. If you need help grasping the concept of a problem, by all means let us know.

MISEVALUATION--Alphador (talk) 02:56, 11 April 2010 (UTC)

You might find Snell's law a helpful article to start at. Your first equation looks like a common representation for the result of a double-slit experiment. Technically, any of these equations can mean anything, because you have not defined what the variables represent - but most of them are standard-form, standard-notation equations for some elementary optical physics. Nimur (talk) 02:44, 11 April 2010 (UTC)

And your second equation looks like uncommon notation for the frequency of a pendulum. Again, it can mean anything if you don't define v, T, and μ. Nimur (talk) 02:50, 11 April 2010 (UTC)

Thank's for the article on Snell's law, it is very helpful. I don't know what the variables stand for, that's primarily what I want to find out.--Alphador (talk) 03:04, 11 April 2010 (UTC)

You might be better off looking for more information at wherever you got those equations from. They all look like items from the waves and optics chapter of an introductory physics text. However, the symbols used in equations often vary from text to text and course to course. We could make educated guesses about what they each mean, but to be certain you'd need to know where they came from. Dragons flight (talk) 03:36, 11 April 2010 (UTC)

I do not recognize the first equation, the second equations is the speed of propagation of a wave in a vibrating string, the third one is the law of reflection, and the last two are two different ways to express Snell's law. Dauto (talk) 04:02, 11 April 2010 (UTC)

First equation could be to do with diffraction, although I would expect to see an expression involving sin(θ) on the left hand side. Gandalf61 (talk) 08:55, 11 April 2010 (UTC)

Owl species

What is the species of these owls? --Tyw7  (Talk • Contributions)   Changing the world one edit at a time! 03:02, 11 April 2010 (UTC)

• 
  Unknown owl #1
• 
  Unknown owl #2
• 
  Unknown owl#3

#2 looks like a variety of Barn Owl. --Jayron32 03:14, 11 April 2010 (UTC)

The second one is without a doubt a Barn owl (Tyto alba). The second one is maybe a Northern Saw-whet Owl (Aegolius acadicus) or a Screech-owl (Megascops)? --The High Fin Sperm Whale 03:17, 11 April 2010 (UTC)

Whale, I take it the 2nd second is really the 1st ? StuRat (talk) 03:21, 11 April 2010 (UTC)

I think the one on the left is a Little Owl -- Athene noctua, the white 'eyebrows' are the clincher. I agree that the one on the right is a Barn owl -- Tyto alba. SteveBaker (talk) 03:23, 11 April 2010 (UTC)

How about the 3rd owl? --Tyw7  (Talk • Contributions)   Changing the world one edit at a time! 04:20, 11 April 2010 (UTC)

My guess is the Great Grey Owl (Strix nebulosa). --The High Fin Sperm Whale 04:50, 11 April 2010 (UTC)

I was going with Barred Owl - but now that I look, I think I agree that it's a Great Grey Owl. SteveBaker (talk) 04:52, 11 April 2010 (UTC)

Is there a way to create a barrier to light rays that LOWERS THEIR FREQUENCY using light or energy?

I have a question.

Is there a way to create a temporary "barrier" (that does not use matter, but energy or light) that would cause all light particles that contact it to reduce in frequency —for instance, turn visible light into infrared rays, or infrared into microwaves.

And could such a "barrier" be created with energy or light waves, and not any actual physical matter? Pine (talk) 03:03, 11 April 2010 (UTC)

No - there is no such thing. SteveBaker (talk) 03:17, 11 April 2010 (UTC)

You could use gravitational redshifting. Gravitational fields contain energy, though it's not like you can just make it like you can light. Also, any form of energy will have a gravitational field, so technically that works. This only will reduce the frequency going in one direction, and will increase it if it goes the other way. — DanielLC 06:06, 11 April 2010 (UTC)

Also, there is no such thing as energy that exists by itself without associated matter or light. So by asking for a barrier made of energy but not matter you already reached the impossible, even without trying to reduce the frequency. Ariel. (talk) 07:26, 11 April 2010 (UTC)

Well, you can have energy without matter - a photon has energy, but it is a boson, whereas all matter consists of fermions. What you can't have is energy without mass (or vice versa) because of mass-energy equivalence. Gandalf61 (talk) 08:49, 11 April 2010 (UTC)

In a certain sense, you can do it with matter. Just let the light heat up an object; it will then re-radiate light at a frequency, or rather a spectrum of frequencies, determined by its temperature. If you don't let it get too hot, the bulk of that radiation will be at a lower frequency than the incoming light.

Of course this is rather indirect — it's quite unlike a frequency doubling crystal, which can be thought of much more directly as shining infrared light in and getting green light out. --Trovatore (talk) 09:30, 11 April 2010 (UTC)

Of course you can do it with matter. —Preceding unsigned comment added by 92.8.98.253 (talk) 22:21, 11 April 2010 (UTC)

Filling a volcano with water

This might sound like a strange idea but I thought I'd ask about it anyway... If you were to fill the craters of the world's volcanoes with water, what would happen? Would the cap of the volcano be kept cooler and therefore possibly stave off an eruption? And if there was a violent eruption, would the water either A) decrease the amount of ash that was ejected into the atmosphere or B) be vaporized and therefore provide the moisture necessary for that ash to rain back down sooner? Dismas|^(talk) 03:32, 11 April 2010 (UTC)

Well, if it's an active volcano, the water will likely boil away faster than you can pump it in...but eventually, I suppose, you'd make a thin insulating crust over the lava pool that might allow you to fill things up a bit. But the power of a typical volcano isn't going to be suppressed that way - either you'd end up with an explosion instead of a slow oozing of lava - or you'd maybe cause the lava to force it's way to the surface via some other route. I don't think you have a hope in hell of shutting the thing down. SteveBaker (talk) 03:40, 11 April 2010 (UTC)

Agreed. Note that many calderas already contain a crater lake. StuRat (talk) 03:43, 11 April 2010 (UTC)

Explosive volcanic eruptions (as opposed to comparatively gentle flow of lava) are directly correlated with the amount of water in the magma: more water, more explosion, since the water flashes to steam when pressure is released. Water on top of the magmatic mass would exert little cooling effect (there are submarine eruptions all the time, although explosive eruptions are suppressed in deep water by pressure). See Phreatic eruption for a discussion of the role of water in volcanism. On land, water + magma = boom. Acroterion _(talk) 03:48, 11 April 2010 (UTC)

The OP should keep in mind that the part of a volcano you can see (the mountain bit) is actually only a small part of the actual volcano. Think "iceberg". The actual structure is many orders of magnitude larger than the mountain you see at the surface; and the processes that cause an eruption occur many miles underground, and nothing you can do at the surface is going to affect it. It would be like trying to stop a bullet by placing a thimbleful of water into the barrel. --Jayron32 03:51, 11 April 2010 (UTC)

There have been some very active submarine volcanoes. Surtsey started out as a volcano 130m underwater. Kolumbo in the Aegean Sea is another example. Gandalf61 (talk) 08:42, 11 April 2010 (UTC)

Okay, so it wouldn't stave off the eruption. What about the plume of ash in the second half of my query? Dismas|^(talk) 03:53, 11 April 2010 (UTC)

No, it would just add steam and water vapor to the ash cloud. --The High Fin Sperm Whale 04:48, 11 April 2010 (UTC)

Wet ash probably will not travel as far as dry ash. The amount of ash will be the same, but it will fall down faster. Ariel. (talk) 06:51, 11 April 2010 (UTC)

I doubt even that. Any water in the caldera will be vaporized in seconds, and the mass of water that any such caldera would contain would be insignificant compared with the mass of ash. Perhaps for the first few seconds of an eruption, one might see such a wet-ash effect (and that's a very small maybe, I still doubt it will have any effect), but for the bulk of the eruption, there will be zero effect. --Jayron32 12:06, 11 April 2010 (UTC)

Water makes volcanoes worse, not better. John Riemann Soong (talk) 21:40, 11 April 2010 (UTC)

Enough water can make them better, like if they are under miles of water. Volcanoes down there rarely pose problems for those of us on the surface. StuRat (talk) 00:40, 12 April 2010 (UTC)

Water + volcano? Bad ideas. See Lahar 66.133.196.152 (talk) 09:28, 12 April 2010 (UTC)

The Cumbre Vieja volcano is already partly filled with water, increasing the risk for a potential collapse of its western flank. The Erta Ale volcano may have water surrounding its base due to sea level rise and this may initiate the rifting in the area. There are also active subglacial volcanoes underneath the West Antarctic ice sheet such as the one under Pine Island Bay, which if they erupt could have an effect on global sea levels. ~AH1^(TCU) 00:38, 15 April 2010 (UTC)

Destroying the Earth

Is there any weapon by which the entire planet Earth can be destroyed into pieces? --Galactic Destroyer (talk) 07:12, 11 April 2010 (UTC)

You probably want this website for complete and detailed instructions. Ariel. (talk) 07:20, 11 April 2010 (UTC)

No. (At least not one known to humans.) Axl ¤ [Talk] 08:07, 11 April 2010 (UTC)

I agree - the answer is "No". If you absolutely, utterly have to find a way to do it (eg, for quasi-believable fictional purposes) then I recommend the idea of using the Large Hadron Collider to make a particle called a strangelet - which has the peculiar property of changing anything it touches into another strangelet. This would result in a chain reaction that would result in the entire planet turning into a blob of strangelets about the size of a golf ball over the course of just a few minutes. However, the idea that strangelets actually exist is highly speculative and controversial - the idea that you could create one using the LHC is even more speculative and even less likely - and the idea that they would be stable enough (when not at the core of a large neutron star) to remain stable for long enough to achieve the destruction of the earth is yet more speculative than that. But, it's not currently known to be definitely impossible - and for the purposes of sci-fi, that's usually good enough! SteveBaker (talk) 14:03, 11 April 2010 (UTC)

Is it possible to change the orbit of a large comet using a space probe so that it can collide with earth? --Galactic Destroyer (talk) 16:04, 11 April 2010 (UTC)

Changing the trajectory of asteroids has been suggested before, usually to avoid an impact event but I don't see why it couldn't be used to create one as well. But even if you were to turn a near miss into an impact using a method like this, it wouldn't blow the world into little pieces. You'd need a huge body to do something like that, something closer to the size of the moon than the size of a comet, and I don't think it's feasible to make the moon smash into the earth with current technology. TastyCakes (talk) 16:26, 11 April 2010 (UTC)

Even the moon would not be enough. It might hurt people, the the earth itself will still be there in one piece. You would need something much larger, like venus. Ariel. (talk) 18:11, 11 April 2010 (UTC)

"Hurt people"? I'm pretty sure if you drop the moon on the Earth, you'd boil most of the seas and atmosphere and kill all macroscopic life. But you're right, the chunk of rock would mostly remain in one piece unless you somehow gave the moon far greater velocity than it has now. Dragons flight (talk) 18:20, 11 April 2010 (UTC)

Also see giant impact hypothesis: scientists think that the moon may have come from a collision between Earth and a Mars-sized object. It presumably had a big effect on surface conditions, but Earth is still around. Paul (Stansifer) 19:11, 11 April 2010 (UTC)

It would have turned the Earth back into a molten ball. To actually permanently blast the Earth into pieces that would never re-accumulate to form a new Earth, the object would have to be going a substantial portion of the speed of light, I'd think. StuRat (talk) 19:18, 11 April 2010 (UTC)

You'd need something of order several times the gravitational binding energy of the Earth (2×10³² J). So you'd "only" have to get a mass the size of the moon up to a few hundred km/s or so. Dragons flight (talk) 19:32, 11 April 2010 (UTC)

Would that be enough to blast all the parts of the Earth out of the solar system, in different directions ? Otherwise, if they are all left in about the same orbit the Earth has now, I'd expect them to come back together over million or billions of years. StuRat (talk) 22:51, 11 April 2010 (UTC)

Well, first, if the earth was blown into little bits, which over the next 1,000,000,000 years reformed into a planet, I would argue that it is not the same planet, especially since there would be no one left who could differentiate. Googlemeister (talk) 19:16, 12 April 2010 (UTC)

See also this discussion Count Iblis (talk) 01:28, 12 April 2010 (UTC)

Try the Illudium Q-36 Explosive Space Modulator. Are you having trouble seeing Venus? Nyttend (talk) 02:07, 12 April 2010 (UTC)

Or, you might try using a Death Star. 24.23.197.43 (talk) 07:47, 12 April 2010 (UTC)

Yes. I just finished testing a Earth Destroying Weapon yesterday and it did a very good job of the portion of the Earth which I used to test it. I need more money though to make it large enough to destroy the whole Earth. You can make an offer to lease it on my talk page and if I accept I'll provide you with the email address for my PayPal account. CHeers.

Nitrogen/neon atmosphere

According to our article on the gas neon, it is a common element in the universe. So, here's a question. Let's assume you have a planet that has an atmospheric mixture of 60% nitrogen, 20% neon and 20% oxygen at say, about 0.95 atmospheres at datum level. Would there be any impediment to human life in such an atmosphere? We're assuming "liveable" temperatures here. Googling suggests that neon poses no problems re: toxicity at Earth-like conditions, but I thought I'd ask. Thanks in advance. Peter Greenwell (talk) 09:07, 11 April 2010 (UTC)

Neon is entirely inert; even moreso than nitrogen. I suspect there would be little differnce, vis-a-vis breathability with any atmosphere that was about 20% oxygen and 80% inert gases, regardless of the identity of the inert gases, be they argon, neon, or nitrogen. --Jayron32 12:03, 11 April 2010 (UTC)

Deep ocean divers sometimes use a mixture of neon and oxygen as a Breathing gas - so we have definite knowledge that it's harmless as a replacement for Nitrogen. Since it is a 'noble gas' it won't react with anything, so that's no surprise. SteveBaker (talk) 13:48, 11 April 2010 (UTC)

However, some articles related to trimix find the presence of various amounts of nitrogen (and alternative non-oxygen gases) has some effects on, for example, High pressure nervous syndrome. Those all seem to be about reducing negative effects seen at high pressure, so it's not clear if the studies are relevant to nitrogen-content at normal atmospheric pressure (i.e., where we have evolved to live, and where our "normal" for health baselines is). DMacks (talk) 17:42, 11 April 2010 (UTC)

Right: nitrogen's not quite inert: see for example nitrogen narcosis. Interestingly, that article suggests that helium and neon are the only gasses that don't have a narcotic effect at high temperature pressure. I guess the narcotic effect is due not to the chemical reactivity of the gas (as oxygen toxicity is), but rather to the physical process of the gas dissolving in body tissue at high pressures. Huh, I learned something new today. Buddy431 (talk) 20:43, 11 April 2010 (UTC)

That should be high pressure in the second sentence. Argon#Safety does not mention its narcotic properties, should it, or is it so close to oxygen and nitrogen that it doesn't really matter? --NorwegianBlue ^talk 21:30, 11 April 2010 (UTC)

Right you are (fixed now). As for Argon, I don't think that it's typically breathed under high pressure, (as nitrogen or oxygen might be, in SCUBA equipment), so there's probably not much of a need to state that it has narcotic effects at high pressures. If the nitrogen narcosis article is right, that nearly every gas has this effect at high pressures, then it seems sort of pointless to list it for every gas, and should probably be only listed for gasses that might be breathed at high pressure. Buddy431 (talk) 22:45, 11 April 2010 (UTC)

Usually, they breathe helium and oxygen - but that makes their voices squeaky - so in some applications, they use neon and oxygen because the neon has more similar density to nitrogen and hence does not distort voices noticably. Neon is more expensive than helium though - so not many divers use it. In either case, the entire point of doing it is because those gasses DON'T dissolve in the body tissues when under pressure to the extent that nitrogen does - and hence avoids most of the problematic depressurization issues. SteveBaker (talk) 13:32, 12 April 2010 (UTC)

Nitrogen narcosis isn't a depressurization issue (the bends are though). Nitrogen narcosis happens at depth due to... well the articles not real clear on it, but it doesn't involve gasses coming out of solution, as the bends do. Buddy431 (talk) 14:16, 12 April 2010 (UTC)

Plants

Hi. Are there any plants that benefit from the use of a slice of lemon placed on top of the soil in a pot? Thanks. ~AH1^(TCU) 16:06, 11 April 2010 (UTC)

Not sure about lemon particularly but there are plants that like acidic soil (http://www.winsfordwalledgarden.com/development.aspx?Page=Acid_lovers). ny156uk (talk) 16:16, 11 April 2010 (UTC)

(edit conflict)I would think lemon juice (namely the citric acid) would make the soil somewhat more acidic, which would benefit any plant that likes acidic soil. But that would depend on the soil pH before you add the lemon, the amount of lemon you had and so on. I would suspect one slice wouldn't have much effect since they're not that acidic, but that's just a guess. TastyCakes (talk) 16:20, 11 April 2010 (UTC)

Note that the lemon slice will soon rot, and may give off a strong smell once it gets fuzzy. For this reason, you may do better to squeeze out some juice and discard the slice, at least for indoor plants. StuRat (talk) 16:25, 11 April 2010 (UTC)

What causes the strong smell? ~AH1^(TCU) 01:24, 12 April 2010 (UTC)

Mold spores ? StuRat (talk) 02:38, 12 April 2010 (UTC)

Stains

Why are stains, especially water-based ones (even for water alone), invariably darker at their perimeter, yet frequently invisible at the center?--Shantavira|^{feed me} 17:12, 11 April 2010 (UTC)

"Invariably"^{[citation needed]}--can you be more specific about what sorts of stains you are talking about--the effect of a water-based material spreading out on the surface and/or the water (and possibly stuff it in) altering the surface itself could be two different effects. For example, if I spill water on a not-water-proof painted surface, the water can dissolve the paint at the point of the drip and carry it outward as the drop expands until the water evaporates. Repeat, repeat, repeat, and now the wood winds up bare in the middle and the extra paint spread out from it. DMacks (talk) 17:26, 11 April 2010 (UTC)

I can think of several possible reasons:

1) Miniscus. Since water droplets on non-absorbent materials are curved, there's more surface area near the edges, so, when they dry, those items carried on the surface of a drop (like dust and pollen) accumulate more on the edge than in the middle.

2) Diffusion. Since the water is pulled by capillary action along an absorbent material, and pulls the contaminants along with it, they tend to continue to be carried along until the water dries, and the stain thus forms at the boundary where the drying occurs.

3) Perception. In the middle you are comparing it with areas stained nearly the same amount, while, at the edge, you're comparing it with unstained areas. Thus, the edge appears to be stained more, by comparison. StuRat (talk) 17:36, 11 April 2010 (UTC)

The stain dries from the edges first. As it does, water plus dirt is pulled toward the edge to equalize the wetness. This causes more dirt to be at the edge vs. the middle. Ariel. (talk) 18:07, 11 April 2010 (UTC)

Ah, that sounds right. Thanks. Re my "invariably", see the illustration accompanying the stain article, or Google images of "water stain".--Shantavira|^{feed me} 18:56, 11 April 2010 (UTC)

Yes, it is right. It's an effect similar to the one that leads to the formation of moraines. Dauto (talk) 03:23, 12 April 2010 (UTC)

Of course, wikipedia has an article: coffee ring. Enjoy, Robinh (talk) 07:58, 13 April 2010 (UTC)

Systolic and diastolic blood pressure

Hi everyone, I know what systolic and diastolic blood pressures are but I'm not really sure what are the different factors that increase/decrease systolic and/or diastolic blood pressure. Can anyone explain to me what the factors are and a little about the mechanism behind it?

Thanks a million! :) —Preceding unsigned comment added by 116.15.143.83 (talk) 17:23, 11 April 2010 (UTC)

Our blood pressure article would be a good place to find this information, as well as specific articles related to Systolic and Diastolic parts. DMacks (talk) 17:30, 11 April 2010 (UTC)

internal balance

All life must maintain an internal balance, despite environmental changes. This is called _____. —Preceding unsigned comment added by 98.236.88.134 (talk) 20:04, 11 April 2010 (UTC)

This is called a homework question. DMacks (talk) 21:02, 11 April 2010 (UTC)

Aw, come on. We could at least tell the questioner that the word s/he seeks begins with the same four letters as "homework", and that our article Life would be a reasonable place to start looking. --NorwegianBlue ^talk 21:07, 11 April 2010 (UTC)

Or you could paste the sentence into Google, which gives the answer in about two seconds. Looie496 (talk) 21:43, 11 April 2010 (UTC)

Venus of Willendorf

Were there fat people around ~20,000 years ago? I had the impression nutrition was pretty poor for everyone, but Venus of Willendorf suggests other wise. Would she have to be a queen or something, while her minions ran around desperately trying to gather/kill enough food to feed her? Aaadddaaammm (talk) 20:10, 11 April 2010 (UTC)

From the article, clearly we don't know for sure what it was for (it's not like it came with a book of instructions). As the article notes "not a realistic portrayal but rather an idealization of the female figure"; I guess when you live in a world with naught but skinny nomad women, that's what you'd idealise. Thinking it's meant to actually display a real person is like some future people discovering images of Jessica Rabbit or Jordan and mistakenly thinking such forms could actually exist. -- Finlay McWalter • Talk 20:26, 11 April 2010 (UTC)

Even at the Last Glacial Maximum when things were at their worst, there surely would have been isolated places and times when there was way more food than people to eat it. Looie496 (talk) 21:09, 11 April 2010 (UTC)

Lol, that’s really funny when you think about it! It's not like the women you see in magazines these days are "realistic depictions of real people" either! 2000 years from now they might dig up some playboy magazines and wonder if anyone ever actually looked like that. :) Vespine (talk) 04:12, 12 April 2010 (UTC)

"Professor, it appears that AIDS was more wide-spread than we thought, as clearly all the women in this magazine are suffering from some terrible disease. Yet, somehow, they still managed to smile. Weren't our ancestors brave ?" StuRat (talk) 00:34, 12 April 2010 (UTC)

Female body shape discusses some of the cultural norms regarding female body shape in various places and at various times. --Jayron32 02:02, 12 April 2010 (UTC)

All it takes for obesity is agriculture and the social stratification that allows a few people access to excess. alteripse (talk) 10:41, 12 April 2010 (UTC)

Alteripse hit the nail on the head of what I am asking. Was there agriculture and social stratification ~20,000 years ago in Europe? Aaadddaaammm (talk) 13:28, 12 April 2010 (UTC)

Things may have changed since the last time I read anything about this, but I'm pretty sure the standard interpretation of Venus of Willendorf and similar figurines is that the depicted females are pregnant and symbolize fertility - of humankind, of earth and nature in general or both. Of course, she's also rather plump and well-fed, which was probably the ideal back then, as pointed out by others. Again, as far as I remember, Venus of Willendorf is not believed to reflect a society with social stratification but a relatively primitive and egalitarian one.--91.148.159.4 (talk) 15:23, 12 April 2010 (UTC)

To answer aaadddaaammm's first question, there was certainly no agriculture in Europe, or anywhere, in 20 000 BC. There may have been extremely limited social stratification (i.e. people who fight better get to eat more, or something), but agriculture and "civilization" won't arise until after 10 000 BC. Buddy432 (talk) 16:58, 12 April 2010 (UTC)

Interesting, so then how did people know what a fat woman looked like? Aaadddaaammm (talk) 17:27, 13 April 2010 (UTC)

Probably, there were occasional periods and areas of relative well-being, and during those periods and in those areas people stuffed themselves - until they became plump, if given the chance. Then they starved again, then they stuffed themselves again, etc.. Fortunes change. There were always reasons for some clans to have more success as hunters-gatherers than others, and hence to become fatter.--91.148.159.4 (talk) 18:53, 13 April 2010 (UTC)

Miscellaneous Meteorology

These are newbie questions, and I would appreciate answers to them, because they pertain to a piece of writing I'm working on. How does the coriolis effect work on the Thermohaline Current? I understand what it is, roughly, and I think it would determine what direction the current would turn if it hit a coastline, but I'm not sure. There's a type of wind that comes down from high mountains as the air there cools slightly and falls, and warmth is carried along. What is this type of wind? Assuming that one were to take a mountain area where there was such a wind, would increasing the absorbent ability of the rock (i.e. making it blacker) increase the heat of the area and increase the heat and strength of the wind?

Thanks. —Preceding unsigned comment added by 69.109.172.138 (talk) 21:39, 11 April 2010 (UTC)

Foehn wind such as the chinook. The effect doesn't arise from the heat of the mountains but from their height and shape. Rmhermen (talk) 00:13, 12 April 2010 (UTC)

Also take a look at Thermohaline circulation, which is influenced by the shape of coastlines in addition to wind circulation caused by pressure gradient. ~AH1^(TCU) 00:33, 15 April 2010 (UTC)

Swallowed by a whale

Has there ever been a verifiable recorded case of a human being swallowed whole by a whale, but managing to get out somehow and living to tell the tale? Except for Johah, I mean - as with many stories from the Bible, there can be considerable doubt as to whether it happened exactly as described, or if it even happened at all (and isn't just a legend or a metaphor for something else). Did it ever happen during the days when whaling was far more widespread than it is now? --95.148.104.124 (talk) 21:44, 11 April 2010 (UTC)

The only recorded story that I've heard is the James Bartley story, which is purely fiction. It has been repeated with a different character replacing James Bartley to make it a local legend to various seaports - which makes it even more fiction. -- kainaw™ 22:16, 11 April 2010 (UTC)

Does whale physiology even allow such a thing? How far into a whale could a human-sized object get? 149.169.59.6 (talk) 02:04, 12 April 2010 (UTC)

Let's think for a moment about the conditions in the whales' stomach. There is no air there. The liquid is hydrochloric acid. It's an environment that's highly tuned to digesting the very stuff your body is made of. It's REALLY hard to imagine you surviving in those conditions for more than maybe 30 seconds to a minute. So - your only chance is to hack your way through several feet of muscle, fat and super-tough blubber. Seems astronomically unlikely to me. SteveBaker (talk) 02:35, 12 April 2010 (UTC)

Answering the question about whale physiology, some guy did a LOT of research into the James Bartley story (I'm sure the guy's name/research is easy to track down on Google). I remember reading a synopsis of his story in which a biologist stated that the largest whales could swallow a man whole, but most whales could not. As for the fake story, they understand about the air and digestion. The claim was that James was swallowed while the whale was being brought aboard a whaling ship. So, he was only in there for a short time - but was still partially digested and required medical treatment. The guy who did the research tracked down the ship he supposedly fell from and talked to both the captain and his wife - both refuted the story. He went to the hospital which supposedly gave him treatment. All there refuted the story. He checked the ships logs, which had no record of a James Bartley. He even went further, but honestly, is there any reason to believe that a while swallowed a man who lived through the process? -- kainaw™ 02:57, 12 April 2010 (UTC)

As to whether it would be possible for a whale to even swallow a human whole, probably not. Most toothed whales like dolphins and orcas aren't nearly large enough to do so, and baleen whales, which look large enough, aren't apparently built right. Blue Whale#Size indicates that, while their mouths are large enough to hold something like 90 metric tonnes of food and water, their throats are only large enough to fit an object the size of a "beach ball". I suppose, if it was a small man, and if he were oriented just right, he could wiggle down there. --Jayron32 04:18, 12 April 2010 (UTC)

"...your only chance is to hack your way through several feet of muscle, fat and super-tough blubber." - or be vomitted up by the whale, which could conceivably happen in the required time frame (assuming that you could be swallowed in the first place). Mitch Ames (talk) 09:14, 12 April 2010 (UTC)

Do whales have a gag reflex, as a matter of interest? --Kurt Shaped Box (talk) 10:03, 12 April 2010 (UTC)

They do seem to spit out unwanted items. In one of the David Attenborough specials, they were filming the whales make a bubble net and then lunge for the fish at the surface. Birds were also diving for the fish, and one got swallowed. The whale spit it out, and it survived. The divers filming underwater hoped the same would happen if they got swallowed, but were lucky enough to not have to test that theory. Note that "swallowed" here probably just means "taken into the mouth", not the stomach. StuRat (talk) 16:01, 12 April 2010 (UTC)

Sperm Whale, Physeter catodon at MarineBio.org says the following.

The gullet of Physeter catodon is the largest among cetaceans; it is in fact the only gullet large enough to swallow a human.

-- Wavelength (talk) 14:32, 12 April 2010 (UTC)

Not a whale per se, but how about a Whale shark? Is it's digestive system capable of ingesting an entire human with minimal harm? Googlemeister (talk) 15:47, 12 April 2010 (UTC)

No, it's set up like a whale, to digest small food, not people. StuRat (talk) 15:55, 12 April 2010 (UTC)

According to http://mlbible.com/matthew/12-40.htm, Jesus Christ believed that Jonah had been swallowed by a sea creature.

-- Wavelength (talk) 16:30, 12 April 2010 (UTC)

A lot of people believe a lot of things that aren't true...it doesn't make them true. But I don't think we're seriously objecting to the idea that someone might somehow be swallowed by a whale - the issue is how they might possibly survive to tell the tale. SteveBaker (talk) 17:59, 12 April 2010 (UTC)

Well, the way I see it, you have three options if actually swallowed by a whale:

1. Make the whale vomit
2. Pull out your knife/machete (presuming that you have one) and try to cut your way out
3. Climb back up its oesophagus and out the mouth

2. and 3. may also work to elicit 1. I don't suppose that the whale would enjoy having a signal flare set off in its innards either.

Are you certain that there's no air present in the stomach of a whale, Steve? I mean, I know literally nothing about the digestive processes of Sperm Whales - but I always thought that stomachs in general had some sort of (presumably fucking foul) air/contents boundary. Do whales digest food quickly - or are they more like snakes, in the sense that food can sit in their stomachs for a couple of weeks before it is broken down? --Kurt Shaped Box (talk) 18:20, 12 April 2010 (UTC)

Why would there be air there? Whales swim at great depths - air in their stomachs would be a liability - if it got in there somehow, they'd probably just belch it out. If there were gases in there, I doubt it would be very breathable anyway. SteveBaker (talk) 02:45, 13 April 2010 (UTC)

Being mammals, I'd expect them to have a reasonably fast digestive system, like ours. But, of course, only the first stage of digestion is in the stomach, with the intestines doing most of the work. StuRat (talk) 01:22, 13 April 2010 (UTC)

You could buy a little time by hacking your way from the stomach into the whale's lungs - then you'd have enough air for several hours while you decide what to do next. Mitch Ames (talk)

Still - you arrive there - it's dark, there no air, you don't know which way is up and which down, your skin is probably burning from the pH 1 or 2 acid that's all around you. I doubt the stomach walls are staying still - so you don't have any kind of good footing. You probably got pretty roughed up by the whole business of being in the water, grabbed an swallowed. You'd be far too disoriented to make a serious plan. Get real - you don't stand a hope in hell! SteveBaker (talk) 02:45, 13 April 2010 (UTC)

You should probably count your senses :-) Mitch Ames (talk) 05:36, 13 April 2010 (UTC)

How about a Finding Nemo option where the individual were just inside the mouth cavity for a short period. This seems a lot more feasible. I believe in The Holy Bible, but you can't take some things literally. It is a physical impossibility that Noah harvested 2 of every terrestrial species. If Noah had that technology, ability to travel, and knowledge, he also could have orbited the earth in an awesome space station. Humankind today couldn't even come close to achieving this.--FUNKAMATIC ~talk 03:28, 14 April 2010 (UTC)

Mystery Box

Hi. In a recent lab I had, I had to determine the contents of a mystery box. I was told that there were two impedances, Z₁ and Z₂, and that in total there were 3 circuit elements (they can either be a resistor, capaictor, or inductor). Now, I was able to short the Z₂ element, which allowed my to isolate Z₁. I then added a resistor in series with Z₁ and ran an alternating current through the circuit (resistor is between input generator and Z₁. What I saw was a low-pass filter. I reasoned that this meant that there would be a capacitor in Z₁, because an RC circuit produces a low-pass filter when run through an alternating current (the voltage was measured across Z₁). Looking more closely, I saw that at high frequencies, the voltage died down to zero, but at low frequencies the voltage wouldn't reach the voltage of the generator (as would be expected if Z₁ were just a capacitor), but a value a bit lower than that.

When I was doing the lab, it struck me as very obvious that this implied that Z₁ consisted of a capacitor in parallel with a resistor. The problem is that I forget why. Can anyone help lead me in the right direction? Thanks. 173.179.59.66 (talk) 22:13, 11 April 2010 (UTC)

Alright, so I was able to answer my original question, but how would I get the capacitance with a bode plot? 173.179.59.66 (talk) 03:09, 12 April 2010 (UTC)

See the article Bode plot. Figure 1(b) and the section 3 Example describe the lowpass case. Cuddlyable3 (talk) 23:29, 12 April 2010 (UTC)

Least common cause of death

What is the least common cause of death in human history? Of course, every death is unique, with many just a variation on the same official cause, but what is the least common official cause. To qualify it further, if every human death had resulted in an autopsy, what would be the least common cause recorded on the autopsy reports. Thanks JohnnyShadow (talk) 22:38, 11 April 2010 (UTC)

The least common non-cause of death must be the case of Phineas Gage. Cuddlyable3 (talk) 09:36, 12 April 2010 (UTC)

Such a claim would be impossible to prove or conjecture on. There are likely thousands or millions of "unique" deaths, depending on how you define the "cause" of death. The graph of "cause of death" in the modern world has large numbers dying of things like heart disease and cancer and infectious disease and then a VERY long tail where all of the randomly weird causes of death lie. For example, there have been only been three people in the history of the world to be killed by exposure to the vacuum of outer space, see Soyuz 11. --Jayron32 23:09, 11 April 2010 (UTC)

Which also illustrates the problem of counting. Three cosmonauts died of exposure to outer space, but if you instead labeled those deaths as "asphyxiation" then it would be relatively common. At least one person has died by driving a big rig off the S-curve in the Oakland Bay Bridge, while many people die in traffic accidents. Many deaths can appear unique, or nearly so, if you describe them in enough detail, but there is nothing particularly special about that. Dragons flight (talk) 23:35, 11 April 2010 (UTC)

And some people would argue that we all die from the very same thing, lack of oxygen to the brain, and there are no unique deaths. Dismas|^(talk) 23:36, 11 April 2010 (UTC)

They'd very clearly be wrong. A brain reduced to a pulp by a bullet or smashed into a jelly in an explosion needs no lack of oxygen to be a very dead thing. --Tagishsimon (talk) 00:15, 12 April 2010 (UTC)

Indeed. Almost all people die from lack of oxygen to the brain. A few do die from physical trauma to the brain. --Tango (talk) 00:58, 12 April 2010 (UTC)

Not to mention that one can die from excess oxygen to the brain, as well. Like my old electronics professor said, "if it doesn't work, that means either there is a contact where there shouldn't be one, or there is no contact where there should be one". No, seriously, lack of oxygen to the brain is not the only ultimate cause of death. --Dr Dima (talk) 00:28, 12 April 2010 (UTC)

I don't think oxygen toxicity directly causes death very often. When it does, I think it is more likely to be due to damage to the lungs resulting in a lack of oxygen to the brain than the actually effects of too much oxygen in the brain (which are things like nausea and seizures). --Tango (talk) 00:58, 12 April 2010 (UTC)

Alexander Litvinenko died of a rare cause of death. Bus stop (talk) 01:03, 12 April 2010 (UTC)

That depends on how you define it. Homicide is a fairly common cause of death, and death from radiation sickness is a bit less common, but not exactly rare. If you define that more broadly as death from exposure to radioactive elements, then millions have probably died from lung cancer due to exposure to radon gas. StuRat (talk) 01:12, 12 April 2010 (UTC)

Kurt Gödel starved himself to death because of a fear of being poisoned. Count Iblis (talk) 01:19, 12 April 2010 (UTC)

Biology should be our concern. Life being a biological process, we should want to concern ourselves with that which interrupts that process, resulting in death, especially in those cases where the person is young and/or otherwise healthy. Cause of death can probably be understandably less clear in old age and/or otherwise poor overall health involving many weaknesses in the biology supporting life. Bus stop (talk) 01:30, 12 April 2010 (UTC)

I typed unusual deaths in the search box and wasn't surprised to hit a redirect: List of unusual deaths. It would have been unusual if Wikipedia didn't have something like that. See also Darwin Awards#Examples and more at http://www.darwinawards.com if you have a morbid sense of humor. PrimeHunter (talk) 01:34, 12 April 2010 (UTC)

No person has ever died because they were shot by User:Nyttend. Nyttend (talk) 02:05, 12 April 2010 (UTC)

So they all recovered from their gunshot wounds, then ? StuRat (talk) 02:33, 12 April 2010 (UTC)

No, it's just that Nyttend prefers knives.  ;-) Dragons flight (talk) 02:52, 12 April 2010 (UTC)

Apparently, two people died in a blogging accident. — DanielLC 04:42, 12 April 2010 (UTC)

You made me spray scone over my table! Vimescarrot (talk) 21:20, 12 April 2010 (UTC)

No-one has mentioned Kenneth Pinyan yet? Whoa. --Kurt Shaped Box (talk) 10:05, 12 April 2010 (UTC)

Being struck by a meteorite would probably be up there. --The High Fin Sperm Whale 18:24, 12 April 2010 (UTC)

It's hard to beat being killed by a meteorite impact, although the only recorded example involves a dog rather than a human. But my favorite story is of the Greek playwright Aeschylus, who was supposedly killed by a tortoise dropped on his head by an eagle. (Lots of people think that story is ridiculous, but it's actually pretty common for birds to drop animals with shells onto rocks to break them open, so I don't see why it couldn't have happened.) Looie496 (talk) 18:25, 12 April 2010 (UTC)

AFAIK, gulls will drop baby sea turtles onto rocks to crack them. Also, what about Soviet scientist Dr. Nikolai Ustinov? (no article?) Consumed horribly by the bioweapon that he had helped to develop and perfect after accidental exposure - and then in death, helping to advance science by becoming the source of a new, more potent strain of said bioweapon, which was named 'Variant U' by his colleagues in his honour... ---Kurt Shaped Box (talk) 18:45, 12 April 2010 (UTC)

Maybe no article because that website does not appear to be an unimpeachably reliable source. Comet Tuttle (talk) 20:05, 12 April 2010 (UTC)

Especially if he was bald. --The High Fin Sperm Whale 18:31, 12 April 2010 (UTC)

Death from laughter is surprisingly common. No more jokes on the Reference Desks, please. Comet Tuttle (talk) 20:04, 12 April 2010 (UTC)

Given the average level of funnyness of the jokes here, I don't think we have much to worry about. Buddy431 (talk) 04:48, 13 April 2010 (UTC) .

Oh dear. I'm not doing anything to remedy the situation, am I? Buddy431 (talk) 04:50, 13 April 2010 (UTC)

Backwards Ffuns video[1]. Cuddlyable3 (talk) 12:42, 13 April 2010 (UTC)

Buddy it's not the fault of your jokes, it's just the way you tell them. Cuddlyable3 (talk) 13:05, 15 April 2010 (UTC)

April 12

I know why the sky is blue...

..but why does it feel so far away? Aaronite (talk) 00:35, 12 April 2010 (UTC)

Perspective. --Jayron32 00:46, 12 April 2010 (UTC)

That was a whole lot simpler than I expected. Aaronite (talk) 01:01, 12 April 2010 (UTC)

Simple...but not true. The sky seems far away even when there are absolutely no clouds or anything. How can clear air have "perspective"? Nah. The deal is that our visual system has five ways to judge distance - in order of increasing range:

• The amount of muscle tension needed to distort the lens to form a sharp image.
• The amount by which our two eyes have to point inwards to make the two images form a single image.
• The amount by which the object moves as our heads move.
• The relative size of things whose size we know well (trees, houses, people, etc) - and that one thing is in front or behind another.
• The amount of color change due to Rayleigh/Mie scattering (far mountains look purple-ish, etc).

Things that show none of those effects appear (effectively) infinitely far away...which includes the sky. We don't see any of these 3D cues for the blue or black of the sky - we can somewhat judge the distance for clouds - but even then it's tough because we don't have "reference" for how big they should be, and they transmit and filter light rather than reflecting it. Things like sun, moon, planets and stars all appear to be infinitely far away.

SteveBaker (talk) 02:19, 12 April 2010 (UTC)

Don't forget relative brightness. But, of course, this also assumes you know the absolute brightness, to gauge the distance properly. I don't think the Moon seems infinitely far away, because it contains familiar sights, like mountains, which we can see and compare with the size of mountains on Earth. StuRat (talk) 02:30, 12 April 2010 (UTC)

Relative brightness comes under the category of color change. SteveBaker (talk) 13:18, 12 April 2010 (UTC)

How is the frequency of a wave the same as the magnitude ? StuRat (talk) 14:24, 12 April 2010 (UTC)

On computers. Using the RGB system, a pure red colour (typically 255,0,0) would presumably have the same frequency as an apparently duller red, but will have an RGB value of something like (128,0,0) and is therefore a "different colour". --Phil Holmes (talk) 15:51, 12 April 2010 (UTC)

In that example, I'd say the magnitude was decreased, but the frequency remained the same. StuRat (talk) 16:43, 12 April 2010 (UTC)

"Color" is not at all the same thing as "frequency" - if it were then "lime green" and "forest green" would be the same "color" and "pink" wouldn't be a "color" at all because it's not representable by a simple frequency - and if you were to argue that it was a color then you'd have to admit to "white" and "dark grey" being the same "color" - which is stretching the meaning of the word to breaking point! The correct word for what you are thinking of is "hue" which is the nearest approximation that our eyes can perceive to the "frequency" of the light. SteveBaker (talk) 17:52, 12 April 2010 (UTC)

I wouldn't call white, black, or gray "colors" at all. I see the problem. I'm using def 3 at Wiktionary:color, while you are using def 2. StuRat (talk) 21:29, 12 April 2010 (UTC)

I think basically the reason the sky seems so far away is that it doesn't move as you move around -- no parallax, in other words. For what it's worth, having lived in both the west and east of the USA, it has often struck me that the sky seems much farther away in the west. I expect this is somehow a result of the lower humidity. Looie496 (talk) 18:13, 12 April 2010 (UTC)

high altitude training chamber levels blood acidity

its my understanding that as the carbon dioxide levels in our blood go up so does blood acidity. many pilots go through high altitude training chambers with high levels of nitrogen to adjust to hypoxia. in a high nitrogen environment does blood acidity go up or down or stay the same? —Preceding unsigned comment added by Jonny12350 (talk • contribs) 01:07, 12 April 2010 (UTC)

High nitrogen environments can lead to the bends. I am not sure what effect, if any, it has on blood pH. --Jayron32 01:57, 12 April 2010 (UTC)

High nitrogen environments can;t cause the bends, as the nitrogen has no way of entering the bloodstream as bubbles (recall that hemoglobin, the O₂-carrying compound in RBCs, cannot bind to elemental nitrogen). @OP It may interest you to know that our atmosphere is ~80% nitrogen, and less than 20% O₂. While true that respiratory acidosis can be caused by hypoventilation (not breathing enough), a high nitrogen environment would likely have little, if any, effect on this. Acidemia is caused by an imbalance of CO₂ and O₂ in the blood; it has nothing to do with other gases in the air. --Anonymous 02:13, 12 April 2010 (UTC)

Almost totally wrong about the bends. It is caused by dissolved inert gases such as nitrogen (or helium when used in some diving mixtures). See Decompression sickness#Mechanism. Dragons flight (talk) 02:43, 12 April 2010 (UTC)

To avoid confusion, the above poster is not me. My "--Anonymous" signature is done manually and does not have parentheses as in "(UTC)". (Yeah, I know, this is what I get for being anonymous.) --Anonymous, 05:23 UTC, April 12, 2010.

But you aren't anonymous - you're User:64.231.232.179, posting from somewhere around Toronto, Canada. If you want to be anonymous, create a user account. SteveBaker (talk) 13:25, 12 April 2010 (UTC)

Don't imagine that an IP address identifies a person. I have contributed to WP from several IP addresses, all of them shared by other people. However, I am the only one posting here with the form of signature I use. --Anonymous, 18:53 UTC, April 12, 2010.

High nitrogen does not have any effect on acidity either way. And the bends are caused by high pressure, not high <any specific gas>. The high altitude effects the partial pressure of oxygen - basically oxygen is not "pushed" into the blood as effectively. The altitude training gives the body time to adjust to this by making more red blood cells and some other changes as well. The acidity of the blood is very very very carefully managed by the body, so even if the high altitude changed it, the body would adjust it to compensate. But I don't know if high altitude will have an effect on it. Ariel. (talk) 18:57, 12 April 2010 (UTC)

Decreased pressure of carbon dioxide in the atmosphere seems like it would cause more of it to diffuse out of the blood, which would raise the pH. Except blood is buffered, so you are just stressing whatever system maintains that buffer (and losing some of whatever precursors are involved)--see carbonate#Biological significance. DMacks (talk) 15:22, 13 April 2010 (UTC)

Gold

Dude, I checked the various elements and noticed that Gold has a higher density than most of the elements that are even higher on the table. What is the deal? I'm sure I can handle the scientific stuff, but give me the simple answer so I can explain it to my friends. —Preceding unsigned comment added by 68.28.104.239 (talk) 02:22, 12 April 2010 (UTC)

Density is mass per unit volume, so there are two ways to increase density of a collection of object: Make the objects heavier, or pack them closer together. In the case of gold, you rightly note that its density is higher than elements which have heavier atoms; so that leaves the second method of varying density, which is the organization of the gold atoms in the solid form. There are two effects going on, the atomic radius of gold, and the crystal lattice of the gold atoms in the solid form. Lets deal with atomic radius first.

Periodic trends#Atomic radius is some basic background, but basically heavier atoms are not automatically larger atoms in terms of volume. The gas-phase atomic radius of an element actually decreases as you move to the right along any row of the periodic table. In other words, though a gold atom is heavier than say, a cesium atom, it is also smaller in size than a cesium atom. This is because of something called effective nuclear charge. To simplify it, as you move right through a row of the periodic table, you are adding more protons to the nucleus of an atom, but you are not adding more energy levels to the electron cloud. The electrons that match those protons are added to existing energy levels, not to new energy levels, so the effect is such that the additional protons are exerting a greater pull on the outermost energy levels of the atoms to the right, making them progressively smaller and smaller in radius. If you move down in the periodic table, you add an additional energy level, which causes a large increase in radius. Thus, gold is going to be denser than elements below it on the periodic table, despite having lighter atoms. With gold, the radius is even smaller than expected because of something called the Lanthanide contraction.

Gold also has a face centered cubic crystal lattice, which is a very efficient way of packing atoms into a crystal. The face centered cubic crystal has the highest Atomic packing factor among the standard cubic crystal shapes. This means that in any given unit cell of the gold crystal, there is very little "empty space" and thus, a higher density.

Hope that helps some! --Jayron32 02:48, 12 April 2010 (UTC)

Hey, that made perfect sense to me, but my friends are lost. I sent them packing. Next time they come over, we will try to figure out something way easier. —Preceding unsigned comment added by 68.28.104.234 (talk) 02:58, 12 April 2010 (UTC)

Just tell them that the gold atoms, while lighter than atoms lower down on the periodic table, are packed together in such a way as to minimize the empty space between them. That makes a higher density than other elements whose atoms are packed together in a less efficient manner. --Jayron32 03:00, 12 April 2010 (UTC)

Thanks Jason...don't you have to teach tomorrow? —Preceding unsigned comment added by 68.28.104.244 (talk) 03:07, 12 April 2010 (UTC)

I no longer work in the classroom. I work mostly as a private tutor right now. --Jayron32 03:19, 12 April 2010 (UTC)

Hey dude 68.28.104.239, your friends may enjoy hearing Archimedes' bathtime story about the weight of a gold crown. Cuddlyable3 (talk) 09:17, 12 April 2010 (UTC)

Read this as well for more about the size of the gold atom, and how special relativity makes gold yellow. Ariel. (talk) 19:01, 12 April 2010 (UTC)

Organic crops and contamination

How can a farmer protect organic crops from being contaminated by non-organic crops? Also and more specifically, how can a farmer protect non-GMO crops from being contaminated by crops of genetically modified organisms? -- Wavelength (talk) 03:58, 12 April 2010 (UTC)

The first one is relatively easy, just don't grow your crops adjacent to a non-organic farm. I don't think crop-dusting planes are used much any more, as it's too expensive and unhealthy for the pilots and farmers. So, that leaves hand-spraying, which isn't likely to over-spray nearly so much. Chemical fertilizers aren't much of a problem, either, although a bit might blow onto adjacent farms. Only if the organic farm was downhill would major run-off be a problem.

The 2nd one is a real problem, though. If the GMO crops really are more fit, as the makers claim, then they will naturally spread to adjacent farms and displace the natural crops. The GMO companies try to stop this by making farmers destroy the seed, but there's no way to do that 100%. And, since GMO crops may look identical to their organic cousins, there's no way to remove them without genetically testing every one. Perhaps the GMO crops need to have a gene inserted which will make them fluoresce under UV light, so organic farmers can find them and remove them. StuRat (talk) 05:23, 12 April 2010 (UTC)

Actually, there's a third problem. While some genetically modified crops, like Maize, require people for fertilization, there are other crops which spread pollen via the air, or which use, say, honeybees to spread pollen. So, if my farm is certified organic, and its next to YOUR farm, which uses genetically modified crops, and your pollen drifts over to my farm (who's gonna stop it?) or the two farms are visited by the same honeybees, then what's to stop my organic crops genetic material from being contaminated by YOUR genetically modified genome? The big problem would seem to be the spread of the genetically-modified genome via pollenation. The second-generation hybrid crops can no longer be considered organic, so the organic farmer may have legal standing to sue for damages (indeed, I believe this has already happened). Its a thorny issue. --Jayron32 05:36, 12 April 2010 (UTC)

Hey, what's the big deal? About genetically modified crops, I mean? 24.23.197.43 (talk) 07:58, 12 April 2010 (UTC)

Hay ? Cuddlyable3 (talk) 09:10, 12 April 2010 (UTC)

Organic farming is more than avoidance of GMO, it relies on crop rotation, green manure, compost, biological pest control, and mechanical cultivation, with limited use of synthetic fertilizers and synthetic pesticides, plant growth regulators, livestock antibiotics and food additives. Because the harmfulness of GMOs remains disputed we may see marketing of "organically grown GMOs".Cuddlyable3 (talk) 09:10, 12 April 2010 (UTC)

Variety Genetic use restriction technology would greatly limit any second generation problems and is advocated for this reason (amongst others). Well there is a slight possibility according to an article there may be some limited spread with the sterility only becoming apparent in later generations. However they have had limited use out of concern of food security, farmers rights and other such issues. Nil Einne (talk) 20:15, 12 April 2010 (UTC)

Contamination was an issue in Monsanto Canada Inc. v. Schmeiser. -- Wavelength (talk) 14:05, 12 April 2010 (UTC)

Actually AFAIK, we don't really know what happened in that case. The farmer claims that is was accidential contamination that he wasn't aware of or something of that sort, but that was dismissed by the court, not surprising given the evidence. Either it was accidential contamination and the farmer in that case then "identified, isolated and saved" the GM seeds or the contamination part was simply untrue. P.S. Note that the article also says "While the origin of the plants on Schmeiser's farm remains unclear, the trial judge found that "none of the suggested sources [proposed by Schmeiser] could reasonably explain ..... Schmeiser's crop" Nil Einne (talk) 20:15, 12 April 2010 (UTC)

No, I mean, why would the spread of GMO crops would even be an issue at all? I mean, all of the "ordinary" crops we already grow have been subjected to a lengthy process of artificial selection, and quite a number have been crossbred with plants of some different but related species -- why would genetic engineering be any different than this "conventional" kind of crossbreeding? For example, I've never heard of people making a big fuss because the wheat we grow had been crossbred with wild rye way back when; so why is this "new" crossbreeding suddenly such a big deal? Personally, I think that this whole debate about GMO crops "contaminating" other crops is just a big tempest in a teacup. 24.23.197.43 (talk) 05:02, 13 April 2010 (UTC)

Correction: wheat was crossbred with goatgrass, not with wild rye. I stand corrected. :-) 24.23.197.43 (talk) 05:25, 13 April 2010 (UTC)

The main concern with GMO crops is that we aren't sure that all of the alterations to the genetic code of these crops are perfectly safe. The most widespread example of this in the states is "Bt corn". Bt, or Bacillus thuringiensis , is a naturally occuring soil bacteria that is used in forestry and agriculture to prevent crop damage by killing off larvae of moths and butteflies (lepidoptera). Thing is, they figured out how to splice the genes from the bacteria into good "old fashioned" corn. So...people may worry about all their pet moth collections dying off, or they might not like eating high doses of naturally occuring pesticides. Bt has proven overwhelmingly safe for humans in its historic uses, but that was before our food started making its own pesticide. I'm terrible at linking in here...but Bt has it's own page you can look up. 68.153.29.23 (talk) 07:44, 13 April 2010 (UTC)

Please see Co-existence of genetically modified and conventional crops and derived food and feed. -- Wavelength (talk) 15:19, 13 April 2010 (UTC)
[I am revising my comment. -- Wavelength (talk) 15:40, 13 April 2010 (UTC)]

Is there a term for that shimmery border you get where two vibrant colours meet?

... bright light purple spots on a bright green field for example, as on one of my daughter's dresses?

Ta Adambrowne666 (talk) 05:42, 12 April 2010 (UTC)

I know the effect you are talking about, unfortunately the article Complementary color does not discuss it. --Jayron32 05:47, 12 April 2010 (UTC)

Maybe the term that your hunting for is Chromatic aberration.--Aspro (talk) 12:15, 12 April 2010 (UTC)

Since this is a subjective observation it would be helpful if anyone can link to an image. Cuddlyable3 (talk) 08:54, 12 April 2010 (UTC)

It might be caused by the afterimage of the pattern as the motion of the eye or the subject moves it out of sync with the image, creating colored fringes. Paul (Stansifer) 12:01, 12 April 2010 (UTC)

I know why it happens in television pictures - but you're talking about "reality"?

The only thing that I can imagine that would cause such a thing with naked eye vision would be due to the fact that your eyes focus each of the three primary colors at a slightly different 'depth' - so it's hard to keep the boundaries between very pure complementary colors (green and magenta, for example) in sharp focus. Personally, I don't see a shimmery border in such cases...and I'm a little surprised to hear that you do.

On television it happens because of the way they added color to the pre-existing monochrome television standard by encoding the color on a higher frequency carrier and using the phase of the signal to encode color. When you switch the signal from green to magenta, the phase changes 180 degrees and that has the effect of producing a momentary drop in frequency that allows the color signal to briefly depress or raise the overall signal level in the 'brightness' channel - so you get either a bright or a dark vertical line where the colors change. On PAL format television, it shimmers because of the phase of the color signal being reversed on every alternate line.

SteveBaker (talk) 12:33, 12 April 2010 (UTC)

You may be seeing an iridescence effect? Comet Tuttle (talk) 13:43, 12 April 2010 (UTC)

Complementary colors "clash." Found here:

"Complementary colors are on opposite sides of the color wheel -- they are each half of a pair of contrasting colors. For example, blue is a complementary color to yellow. Green is complementary to purple and magenta. A pair of complementary colors printed side by side can sometimes cause visual vibration (clash) making them a less than desirable combination. However, separate them on the page with other colors and they can work together. Note the spelling. These are not complimentary colors. They don't always flatter (compliment) one another but they do complete (complement) each other."

Note that purple and green fall into the category of complementary colors. Bus stop (talk) 13:54, 12 April 2010 (UTC)

I'll just note that I see the effect as well, though most often where red and blue come in contact. The colours (in my experience) have to be deeply saturated and flat (no shading or borders of any kind). For some reason children's colouring books often get printed with those colours and I often see the bright red letters shaking against the blue background. Matt Deres (talk) 14:28, 12 April 2010 (UTC)

The Bank of America signs have this effect on me. This one isn't as bad as some of the ones around here (since adding white outlining around the letters reduces this issue), but does somewhat show the problem: [2]. StuRat (talk) 14:50, 12 April 2010 (UTC)

It is called scintillation. Probably it happens because even when the eyes seem to be still, they are constantly making tiny movements called microsaccades. These cause the receptive fields near the edges to fluctuate back and forth between the two colors. A similar thing happens in the so-called grid illusion. Looie496 (talk) 17:28, 12 April 2010 (UTC)

That's a likely name for the phenomenon, but that's not a useful article to point to in this case. Matt Deres (talk) 00:53, 13 April 2010 (UTC)

Good answers, all - thanks - yes, makes sense that it's due to microsaccades. Adambrowne666 (talk) 08:14, 15 April 2010 (UTC)

Biological pest control for Fruit fly

Are there any Biological pest control for Fruit fly ? --yousaf465' 08:37, 12 April 2010 (UTC)

Yes, baby chameleons. Chameleons Online--Aspro (talk) 12:03, 12 April 2010 (UTC)

One approach that has been tried is to breed a vast number of fruit flies of the same species - treating them (eg by irradiation) to make them infertile - and then to release them into the area. If you can outnumber the local (fertile) population with infertile flies (by a factor of 10 to 1, for example), you'll reduce their breeding effectiveness to near zero as the probability of a naturally born fertile male happening to meet a naturally born fertile female drops dramatically (in this case to about 1%). Since fruit flies don't live very long, their population crashes within one generation. Repeating the treatment on the (much reduced) initial population should pretty much eradicate them. SteveBaker (talk) 13:06, 12 April 2010 (UTC)

That was used to stop the spread of the Medfly. See Medfly#California_medfly_crisis. However, I'd expect people to object to releasing all those fruit flies, year after year, to combat normal fruit flies. Also, is irradiation 100% effective at sterilization ? If not, you could end up increasing their mutation rate and making them more of a threat. StuRat (talk) 14:34, 12 April 2010 (UTC)

It's pretty effective, and I've never heard of mutation being a significant problem (the odds of said mutation also being beneficial is fairly low as well). I'm not sure people would object to the released fruit flies. The only reason fruit flies are a pain is because they lay eggs in the fruit... sterile males won't do that (and they would be released over croplands anyway, so it's not like we're talking about fruit flies being dropped into your iced tea). Anyway, Sterile insect technique is the full article... --Mr.98 (talk) 14:44, 12 April 2010 (UTC)

Obviously, even a beneficial mutation won't be a problem if the irradiated flies are infertile and therefore unable to pass this wonderous gene onto the next generation. The odds of an animal happening to avoid being sterilized AND getting a beneficial mutation AND mating with a rare fertile animal are very low indeed. (Unless of course you end up with 50' tall mutant fruit flies with laser eyes and an unaccountable craving for human flesh...albeit infertile!) SteveBaker (talk) 17:42, 12 April 2010 (UTC)

Sounds something like the Drake Equation:

Nb = Ni × Ff × Fs × Fm × Fb

Nb = Number of Beneficial mutant fruit flies which reproduce
Ni = Number of surviving Irradiated fruit flies
Ff = Fraction of Ni which remain Fertile
Fs = Fraction of Ff which Successfully mate with other fertile fruit flies
Fm = Fraction of Fs which undergo a Mutation in their sex cells
Fb = Fraction of Fm where the mutation is beneficial

And, just like the Drake Eq., depending on the values you plug in, we can get zero or huge numbers. StuRat (talk) 21:22, 12 April 2010 (UTC)

...and we should probably toss in:

Fc = Probability that the beneficial gene is passed on to a given offspring.
No = Number of offspring produced from one successful fruit fly mating.
Fo = Fraction of newly hatched fruit flies surviving to maturity.

N_o and F_o might be kinda large given that we've just wiped out most of the competition for resources from other fruit fly. SteveBaker (talk) 23:53, 12 April 2010 (UTC)

Some gardening stores sell mantis ootheca for bio pest control. Mantis larvae eat fruit flies. Also, Metarhizium anisopliae or similar entomopathogenic fungi may be effective against medfly, but I don't think they are actually used against medfly. The end result of entomopathogenic fungus action is a pure Nightmare Fuel for some people, so I can imagine their commercial success may be somewhat limited. --Dr Dima (talk) 17:10, 12 April 2010 (UTC)

The usual difficulty with introducing predator species is that in many cases, the predators themselves become a pest - either eating beneficial species when they've finished consuming all of the pests - or consuming so much that they starve out other natural predators higher up the food chain (birds, for example). Hence. this is an extremely risky strategy. SteveBaker (talk) 17:42, 12 April 2010 (UTC)

True, especially when the predator is a non-native species or an apex predator. The ootheca I mentioned are of either Mantis religiosa or Tenodera sinensis. Neither is native to US, however, both are present in US in the wild since around 1900, with not much -- if any -- ill effect. It's not like releasing Africanized honeybees in America or cats/foxes/rabbits in Australia. --Dr Dima (talk) 18:55, 12 April 2010 (UTC)

Actually one of these methods will be used in melon farm.--yousaf465' 07:37, 15 April 2010 (UTC)

three phase electric energy meter

give construction, working and principle of a three phase electirc energy meter

Three-phase electric power
Electricity meter. Cuddlyable3 (talk) 23:13, 12 April 2010 (UTC)

Cholestasis in humans and animals

Hello all.

I'm currently working on a bio for toxicologist Gabriel L. Plaa. For talking about his primary research, I'm basing mostly on doi:10.3109/03602539709037571, an account by himself of his career. There's one aspect regarding his research on cholestasis I'm quite unclear about. Basically a significant interest for him was the elaboration of a protocol to detect cholestatic properties in drugs by animal test, but this was made difficult because, I think, the common lab animals (he specifically discuss rats and mentions hamsters and rabbits) are much less susceptible to cholestasis than human. Is that correct? I'd ask on that article's talk page, but it is little edited (and the article is currently rather... curt).

As an aside, has such a protocol been devised since Plaa's retirement? Since I'm no medical student, I wouldn't quite know where to look regarding the state of the art of this subject.

Thanks in avance, Circéus (talk) 12:40, 12 April 2010 (UTC)

You might find this helpful. Target organ toxicity, Volume 1; By Gerald M. Cohen. Page 102 Second paragraph down: “Foreign compounds whose administration to animals leads to intrahapatic cholestasis show some interesting specie variations.... etc., etc. “ I don't know about any successful protocols. In vitro human cell studies might be better today but even they are not definitive.--Aspro (talk) 14:39, 12 April 2010 (UTC)

It does confirm the state of the art at the time, but is not, unfortunately, really useful for current aspects fo the topic: it was published in 1986. 14:44, 12 April 2010 (UTC)

I've dug up a few refs that indicate that the issues with prediction of human hepatotoxicity based on animal models are well-known and still not solved (Chem. Biol. Interact. 150(1)115-128 doi:10.1016/j.cbi.2004.09.011), though I'd still appreciate a better informed opinion. Circéus (talk) 16:41, 12 April 2010 (UTC)

is it possible to "work off" cholesterol?

Is it possible to "work off" cholesterol? What about "after the fact" (ie when it's clogging your arteries). If you switch to a low-cholesterol diet after years of high cholesterol, do the clogs slowly undue, or are your veins and arteries difigured for life? If it IS possible to "undo" over time, Approximately what time frame are we talking about for this? Thank you. 84.153.204.187 (talk) 14:34, 12 April 2010 (UTC)

The Atherosclerosis article reports some mixed findings on this, so "maybe, a bit" seems to summarise. -- Finlay McWalter • Talk 16:00, 12 April 2010 (UTC)

The body also makes cholesterol, so even if you ate none at all, you can still have high levels simply because that's what your body wants. In general cholesterol is not absorbed particularly well, and most is created in the body, not from food. The problems are caused by a bad diet in general, not specifically eating cholesterol. Since cholesterol is (indirectly) made from fat, and fat is made from sugar (via insulin). So just eating lots of sugar can raise your cholesterol level. If you want to reduce the effects you need to fix your diet in general and not focus just on cholesterol. Ariel. (talk) 19:12, 12 April 2010 (UTC)

Or to practice regular exercise, according to our article (unsourced, though). --NorwegianBlue ^talk 17:28, 13 April 2010 (UTC)

Printing on aluminum cans

How (the process) and what (ink? something else?). 20.137.18.50 (talk) 15:24, 12 April 2010 (UTC)

This paper by someone at Coors has a section on aluminium can printing, curing, and ink-sealing. -- Finlay McWalter • Talk 15:58, 12 April 2010 (UTC)

Old television smoky exploding madness!

An old television (Ferguson TX 37340) was brought into service on 2010-04-11 at 2020 hours and after a few minutes made some loud crackly banging noises and smoke emanated from the vents at the rear. The television was quickly decommissioned and the area ventilated. The picture was apparently unaffected until the moment at which the electrical supply was terminated. What components in the television are likely to cause such noises and smoke and yet allow the television to continue operating, with sound, as it did? --92.25.206.9 (talk) 15:24, 12 April 2010 (UTC)

Persuade a responsible adult to take the back off and have a look. A coating of old (damp?) dust may have provided a conduction path from the HT circuit to the chassis. Track marks (burns) may be visible. Had it just been brought into the room from a colder place? – One should always give electrical equipment of this type, time to equalise with the ambient temperature, so that condensation (forming from the humid warm air) can evaporate.--Aspro (talk) 16:34, 12 April 2010 (UTC)

Another possibilities is insects nesting in there, which managed to short out an electrical connection. StuRat (talk) 16:40, 12 April 2010 (UTC)

As stated. high voltage arcing (perhaps across dust) could make noise and smoke. This could be around the flyback transformer. Some resistors make smoke when they fail. Capacitors sometimes are a ceramic cylinder with a roll of paper and foil inside, and arcing in it can cause the end to blow off. Failed insulation in a transformer or coil winging can cause smoke and popping noise. The problem is that things like this would usually be accompanied by disturbances in the picture. If the picture was unaffected until the end, the faults could be in the audio circuitry, where the extremely high (several kilovolt) voltage is not found, but where small problems can cause loud "crackly banging" noises from the speaker, since it could be at a level where there is yet much amplification before it reaches the speaker. Edison (talk) 18:46, 12 April 2010 (UTC)

I would also advise caution in removing the back. Old TV's often have large capacitors inside and even though the TV is physically unplugged from the wall - there is still enough energy there to give you a nasty shock or high voltage burn - maybe even kill you! I agree that the likely cause was dust & fluff inside causing the thing to arc. It may be that you got lucky and all that happened was an arc that burned up some of the accumulated fluff. Ideally, you'd want to get that stuff out of there - maybe with some gentle vacuuming - maybe with some of that aerosol "canned air" that electronics stores sell (it's not really "air") that allows you to blow the dust out of tight spaces. But like I said - avoid prodding around inside with anything metallic - and keep your fingers out of the circuitry, even if the TV is turned off and unplugged at the wall. SteveBaker (talk) 19:18, 12 April 2010 (UTC)

I had planned on waiting a week, but I couldn't and removed the back this afternoon. I found no obvious damage/burn marks. I do plan to take it outside tomorrow, weather permitting, spray with canned air duster and see if it will operate safely again. I've no need to put anything near any of the capacitors but I will be wearing rubber gloves while I take it outside and clean it. 92.25.112.212 (talk) 22:02, 12 April 2010 (UTC)

Err... in that case, this might be a good time to check your building and contents insurance policy. If you are going to leave the back off when you switch on, have the curtains draw and the lights off to see the sparks more easily... and a CO2 extinguisher to hand. Do let us know how it went. Good luck.--Aspro (talk) 18:10, 13 April 2010 (UTC)

Household dishwashing type rubber gloves would be of no particular use when dealing with a capacitor holding a charge of 10 thousand or 20 thousand thousand volts. Edison (talk) 16:19, 14 April 2010 (UTC)

How long is safe ?

Regarding a TV capacitor, how long would it take to fully discharge after it's unplugged ? A minute ? An hour ? A day ? A year ? StuRat (talk) 20:53, 12 April 2010 (UTC)

I think it depends on the circuitry and on air humidity, but I certainly wouldn't touch it for half an hour, and I would be nervous up to two hours. The capacitor will take much longer to fully discharge because voltage reduces with exponential decay, in theory never quite reaching zero. Dbfirs 22:03, 12 April 2010 (UTC)

A reference I've just read says, for HV, anywhere between days and indefinitely. Here it is. --Tagishsimon (talk) 22:08, 12 April 2010 (UTC)

It says "In the case of old TV sets using vacuum tube HV rectifiers, the leakage was essentially zero. They would hold their charge almost indefinitely.". If they're that good, maybe we need to replace the batteries in our electric cars with vacuum tubes. :-) StuRat (talk) 01:41, 13 April 2010 (UTC)

Charge isn't energy. —Preceding unsigned comment added by 92.17.233.94 (talk) 10:29, 14 April 2010 (UTC)

Nobody said it was. StuRat (talk) 18:59, 14 April 2010 (UTC)

You need the HV discharge tool, a long insulated rod (which you hold) with grounding clip wire attached. Graeme Bartlett (talk) 22:14, 12 April 2010 (UTC)

In a phenomenon which is counterintuitive, a high voltage capacitor which has been thoroughly grounded and discharged can recharge itself over time. Utility workers who lived to a ripe old age have a motto "If it ain't grounded, it ain't dead." I have been very savagely "bit" by TV set high voltage terminals quite a while after they were turned off and unplugged. Edison (talk) 01:45, 13 April 2010 (UTC)

How long after ? StuRat (talk) 13:32, 13 April 2010 (UTC)

Certainly several minutes, perhaps over an hour. A capacitor can store charge longer than that. Edison (talk) 16:17, 14 April 2010 (UTC)

I had some old 70v (4700uF ?) electrolytic capacitors that I was going to use in a power supply. The supply never got built and the capacitors were left open circuit in the cupboard for over 20 years. Recently I needed one for something and measured the voltage out of curiosity. It was about 4v! Never trust a cap to be discharged unless its shorted out and kept shorted.--79.76.250.218 (talk) 16:39, 13 April 2010 (UTC)

Assuming they were fully charged to start, and that the energy loss works like the half-life of radioactive elements, that gives us about a 14% loss per year. (If the loss was linear, it would be more like a 5% loss per year.) Either way, that sounds like a good way to store a charge long-term. StuRat (talk) 19:08, 14 April 2010 (UTC)

"Neutron-activatable elements"?.. I'm inventing terms because I don't know English well.

Hello! I have a problem with a term. I need to translate help file for our program into English. It concerns neutron-gamma spectrometry in well-logging. The closest topic I found here is Neutron activation analysis. In our program we have a list of elements that are subject to neutron activation (I, B, Al, H, Si, Ca, Fe etc.). How can I call them as a whole? Neutron-activatable elements?.. Neutron-capturing elements?.. Elements, subject to neutron activation?.. Shorter is better. For instance, I need to translate a sentence saying something like "To convert channels to energies, you must specify at least two peaks of neutron-activatable elements..." - you see, it needs a short term, and of course I can't just say "peak" because it can't be just any peak - it can't be a Compton peak or escape peak. Thanks in advance.94.41.62.121 (talk) 15:54, 12 April 2010 (UTC)

It's hard to answer your question. Perhaps something like 'detectable element' would work. You don't necessarily need to say 'neutron detectable element', since if that's what your product does it's implied. Ariel. (talk) 19:16, 12 April 2010 (UTC)

about generators

iam planning to convert mechanical energy in to electrical energy. in our daily life, in many ways ,we use many electrical devices and machines. in those, considering ideal conditions, some energy is being wasted. many devices operated by rotatory motion. so,iam planning to attach some required number of small generators.which does not affect the motion of the devise or machine non ideally. for example, arranging small generators to fan. in which the generators(4 or 6) are attached to the down rod carrying the fan, avoiding their weight on the fan. after collecting some current in to battery, fan collects current from battery and spontaneously battery is recharged. in this way we could minimise the usage of electricity. i would like to know, is it possible to construct so. and modifications i need. please give me some sugessions to plan better. thank you. iam waiting. could any one respond to me.

iam k. kumar raja. mechanical engineering(first year, b.tech), aditya engineering college, suram palem, near kakinada, india.

As near as I can tell, you're talking about getting energy from a fan by putting magnets on the shaft, and using the rotation of the magnets to generate electricity. This should work, but the law of conservation of energy means that you would lose more energy, due to the increased mass being rotated along with the fan, putting more strain on the motor. StuRat (talk) 16:31, 12 April 2010 (UTC)

I'm not sure exactly what is being asked either, but it sounds a bit like a dynamo. Perhaps that article can help you out. Matt Deres (talk) 16:42, 12 April 2010 (UTC)

Yep, StuRat is correct. Here's the problematic phrase:

attach some generators which do not affect the motion of the device

I've bolded the part that doesn't work. If the generators don't affect what they're attached to, then they're not generating anything. Conversely, if they're generating something, then they're increasing the load (and affecting the device). This is just a restatement of a perpetual motion machine, and it doesn't work. What you can do is try to make the initial device more efficient.

Now, to branch off a little bit, there are options along the lines of regenerative braking, which quite clearly add to the load of an axle in order to generate electricity. The distinction here, though, is that it doesn't operate concurrently with the motor -- a car does not both speed up and slow down at the same time. But this is a means of recovering some energy under limited circumstances. — Lomn 17:26, 12 April 2010 (UTC)

I'm very skeptical about this proposal. Certainly in the case of the fan, adding these small generators to the blades will make it harder to spin the fan and would result in either (a) the fan spinning more slowly and therefore being less effective or (b) consuming more electricity than your generators are able to recover. The energy you waste that way will (with 100% certainty) exceed your gains through these generators. There are a few places where wasted energy can be regained (and, as someone already mentioned, regenerative braking on motor vehicles, bicycles, etc is one of them). But in most cases, you only end up making things worse. So, sadly, I have to say that your idea is not workable. SteveBaker (talk) 17:33, 12 April 2010 (UTC)

A wind turbine is essentially a fan with magnets on the shaft to generate electricity, so if you operate your fan by allowing the wind to turn it (or even a person or animal), then maybe you could get some "free" electricity, but otherwise, as stated above, you will get less electricity out than you put in. Dbfirs 17:53, 12 April 2010 (UTC)

I don't know why the OP thinks there is a reason to add generators to a battery-powered fan. When the wind can drive the fan faster than the battery then you already have a wind turbine generator that charges the battery. Whichever of the power conversions DC-to-mechanical or mechanical-to-dc is happening there are losses, which rules out any possibility of making a perpetual motion machine by combining the two conversions. However a big wind turbine can usefully supply power enough to run a small fan. Cuddlyable3 (talk) 13:34, 15 April 2010 (UTC)

Air ducts

Why is a lot of ductwork in large HVAC systems square, whereas in things like natural gas pipes, the are circular in cross section? I would think that production costs are lower for a circular pipe, so why is HVAC square? Googlemeister (talk) 19:18, 12 April 2010 (UTC)

There is less worry for leak in HVAC; leaks are undesirable, but not disastrous or dangerous. As such, HVAC ducts can be made of cheap, lightweight, and "flimsy" material. Natural gas pipes must resist corrosion, impact damage, and pressure, so they must be constructed of sturdy pipe. Sturdy metal is easier to roll into tubing or piping than it is to create straight rectangular boxes and weld or roll a seam on each edge. "Flimsy" (by comparison) HVAC ducts do not need pressure- and impact-resistant pipe, so their shape can be whatever is easy to manufacture and install. Nimur (talk) 19:36, 12 April 2010 (UTC)

Also, a rectangular cross-section allows you to have the maximum cross-sectional area which fits in a rectangular region, such as between support beams in a wall. StuRat (talk) 20:43, 12 April 2010 (UTC)

In my house, the air conditioning ducts are circular cross-section insulated/flexible pipe where they travel through the attic space - but switch to box-section as they travel through walls and places like that. I agree with StuRat that the box-section simply fits better into the spaces available. Circular tubes use less material per unit-cross-section - and resist pressure better - but they waste a lot of volume when going through square/flat things like walls and ceilings. SteveBaker (talk) 21:32, 12 April 2010 (UTC)

Hollywood has decreed that high security buildings shall be equipped with unsecured HVAC ducts that are large enough for secret agents to creep through, with grilles that are handy for spying through and are lightly held by spring clips for covert access, especially over priceless jewels in museums. The consequencies for civilisation of people suspecting that any of this is unbelievable are too ghastly to imagine hence the need for square ductwork. Cuddlyable3 (talk) 13:52, 15 April 2010 (UTC)

Using imaging software to determine the length of a section of coiled apparatus

I want to determine the length of the highlighted portion of the tool in this photograph. I know that the total length of the tool is 130 cm. My idea was to import it into Inkscape or GIMP and then trace over it and use some tool to tell me how long the trace is, but I don't know if any such tool exists. I want to compare this flexi shaft with a number of others, because I need to drill in a rather tight place. The low-tech solution might be to print it out and use a piece of string... what's the less-low-tech solution? --92.25.112.212 (talk) 20:20, 12 April 2010 (UTC)

No need to print it out, just make it as large as possible on the screen and use a string there. Note that this wouldn't work if some parts were farther away than others, though. I tried it myself, and got that the ratio of the length of the handle to the overall length is about 1:6.2. Thus, if the overall length is 130 cm, the handle is about 21 cm long. StuRat (talk) 20:28, 12 April 2010 (UTC)

I don't know of a feature to do that in any art tools I own - but here is a way that should work:

• In a paint program like Photoshop or GIMP (which is a free download)...I'll use GIMP terminology - but if you use Photoshop, you'll know what I mean.
• Make two transparent layers over the top of the image - copy the image to both layers - delete the white background.
• Cut the image where the coiled part overlaps itself so that you have two non-overlapping sections - one in each layer.
• Erase the "handle" part whose length you wish to measure - and the bit that sticks out at the other end so you have nothing but the shaft itself, split over two layers.
• Measure the width of the shaft in pixels using the measurement tool.
• Use the "histogram" tool to figure out the percentage of pixels in the image that are not white/transparent in each of the two layers - add those two percentages and multiply by the height and width of the total image to determine the total area of the shaft of the tool.
• Divide the number of non-transparent/white pixels (which is the area of the shaft) by the width of the shaft in pixels.
• Now you know the length of the shaft in pixels.
• Measure the length of the other part of the tool (in pixels) directly using the measurement tool.
• Length of curled shaft + length of tool = 130cm - so now you know how many pixels there are per centimeter - and now you can calculate the length of the bit you're interested in.

...or do it StuRat's way with string - which is MUCH better! SteveBaker (talk) 21:20, 12 April 2010 (UTC)

Save your string. From the image the highlighted length is 14.3x the width of the cable. If that is 1cm (you CAN measure that, yes?) then the length would be 14.3cm. But you need more clearance to use the tool because the cable cannot bend sharply. Cuddlyable3 (talk) 23:01, 12 April 2010 (UTC)

If you have access to MATLAB, you can use the Image Processing Toolbox to generate a generalized 2D spatial transform and unwrap that coil. You can register the image to create a pixel-to-meters transform; this way your transform will yield a directly readable measurement of length in meters. MATLAB and the Image Processing Toolbox are unfortunately not free, and as far as I know, GNU Octave does not have free alternatives to the image processing toolbox utilities, but you can manually program those features if you have a solid grasp of image processing. Nimur (talk) 23:08, 12 April 2010 (UTC)

Thomas Edison's lab supposedly needed to determine the volume inside an early light bulb. Francis Upton, a gifted mathematician, used calculus to approximate the volume, based on the shape of the bulb and the thickness of the glass. Thomas Edison supposedly filled the bulb with sand or water and weighed it, using the density of sand to determine the volume in an analog fashion. The string/analog method and the photometric/mathematical method should agree in general in the present case. Edison (talk) 01:38, 13 April 2010 (UTC)

Instead of overcomplicating things with software and reducing accuracy in the process, why not use software to improve the accuracy of the result? Use GIMP's perspective tool to turn the image into what an overhead view would look like, then print out the result & measure with a string. --99.237.234.104 (talk) 01:29, 13 April 2010 (UTC)

The pic already shows the device head-on. StuRat (talk) 01:34, 13 April 2010 (UTC)

Thomas Edison's lab supposedly needed to determine the volume inside an early light bulb. Francis Upton, a gifted mathematician, used calculus to approximate the volume, based on the shape of the bulb and the thickness of the glass. Thomas Edison supposedly filled the bulb with sand or water and weighed it, using the density of sand to determine the volume in an analog fashion. The string/analog method and the photometric/mathematical method should agree in general in the present case. Edison (talk) 01:38, 13 April 2010 (UTC)

It seems to me that the mathematical methods should be used only in cases where the simpler method wouldn't work, like determining the volume of a battleship. This is both because the mathematical methods, being more complex than direct measurements, take longer, and have a higher probability of error. StuRat (talk) 11:25, 13 April 2010 (UTC)

Applying the mathematical methods incurs a higher probability of human error but you can't blame math for that. Cuddlyable3 (talk) 12:52, 13 April 2010 (UTC)

In the case of measuring the volume of a battleship, mathematical or analytic methods are probably prone to less error than "filling with sand and measuring the mass." You can imagine the logistics challenges associated with filling a battleship with sand, and massing it afterwards... the only way I can think to measure the mass of such a large object is using an analytic method with prior knowledge about the material properties, volume, densities, and so on. Nimur (talk) 16:25, 13 April 2010 (UTC)

Yes, and that's why I gave finding the volume of a battleship as an example of a case where a "simpler method wouldn't work". StuRat (talk) 17:14, 13 April 2010 (UTC)

Measuring the mass of a battleship is probably an accountancy problem: What is the cost of a ton of steel? What is the value of a ton of steel scrap? How much did we spend on steel? How much did we recoup from selling the left-over bits? SteveBaker (talk) 18:28, 13 April 2010 (UTC)

April 13

Problem about capacitors in series

I don't seem to understand how capacitors can be connected in series. My question requires picturing a normal circuit diagram with two capacitors connceted in series with a cell. Now, I am rather puzzled with the fact that when you just connect the capacitors, you can get an ampere reading of say 2A between the two caps...I mean the Ammeter connected in series with the two caps except that you place it between them. Like II---A---II where the II is the cap symbol and A is the ammeter. I read in a book that capacitors arent supposed to pass any current between them. That's supposedly the point. But then, how come the Ampere reading. Upon searching in Google, I cam up with something about charges, but couldnt get the picture. I need to know because I am dying with curiosity.

If you are using alternate current than there will be a current going through the capacitor. There might also be some transient current even if the current is direct. Dauto (talk) 04:56, 13 April 2010 (UTC)

It is not true that capacitors can't pass current. It isn't possible for charged particles to move across the barrier, but when the amount of charge on one face of the capacitor changes, it produces an electric field that causes movement of charges on the other side, thereby inducing a current. Looie496 (talk) 05:07, 13 April 2010 (UTC)

If electricity in a wire is like water in a pipe, then a capacitor is like an impermeable elastic membrane blocking the pipe. If you push the water in one direction with a constant pressure, the membrane will stretch until the restoring force balances the pressure, at which point the water flow will stop. The current on the far side of the membrane is always the same as the current on the near side, though—there's just a limit to how far the water can flow in total, for a given pressure. When the water is just sloshing back and forth (alternating current), there's no such limit because the membrane never stretches too far in either direction. -- BenRG (talk) 07:51, 13 April 2010 (UTC)

I like that analogy! One could extend it to explain the rules for capacitors in series and parallel, and to a warning about very high pressures (voltages) breaking the membrane. Dbfirs 08:29, 13 April 2010 (UTC)

Then you will love the Wikipedia article Hydraulic analogy. Cuddlyable3 (talk) 12:58, 13 April 2010 (UTC)

I did! It made very interesting reading. I've always thought of electricity intuitively in this way, but I've never thought of extending the analogy that far! Dbfirs 20:18, 14 April 2010 (UTC)

Wasp question (not about the insect)

Could anyone suggest some plausible reasons for a Wasp to suffer catastrophic failure? By "catastrophic" I mean severe enough to cause the engine to fail suddenly and completely during flight (as opposed to developing reduced power or gradually overheating) AND to require custom-made spares and/or a fully-equipped machine shop to repair. Any ideas, anyone? 24.23.197.43 (talk) 05:14, 13 April 2010 (UTC)

Bird strike (could it take out a piston engine?). Or Enemy Fire. Buddy431 (talk) 05:46, 13 April 2010 (UTC)

That didn't redirect to where I thought it would. I guess shooting is the closest I can find. That's really a pathetic article for an important topic. Buddy431 (talk) 05:48, 13 April 2010 (UTC)

The capitalization of "Fire" makes it a title (song title, in this case). However, Enemy fire is a redlink, I will redirect it to shooting. StuRat (talk) 09:45, 13 April 2010 (UTC)

Done. StuRat (talk) 09:45, 13 April 2010 (UTC)

Are you writing a novel or something? Avoid the word Catastrophic failure as in my book that means reduced to scape. Mechanical failure of some sort would be a good candidate. Components used in engines of that era where prone to fail unexpectedly. What you want is a failure that does not wreck the engine. A dropped vale in the cylinder head would cause the pilot to shut down the engine ASAP.

Here are a list of WASP engines photos on Wikimedia Commons.[3] There are lots of valves. Badly broken cylinder rings could be another - would cause a lot of dramatic smoke to trail from the aircraft etc., etc. A dropped valve would require the head to be removed and the old valve sleeve to be removed a new one pressed in, you need a workshop for that. From the photos I can’t tell if the valve would drop through into the cylinder but if it can, then that would damage the piston head a be a major repair job. Broken rings could score the cylinder walls and require regrinding as well as needing the piston to be removed. Again, you can’t do that sitting on the side of the tarmac. If its for a novel, then don’t get technical. Finally: I don’t know what year air worthiness certificates were introduced but the only need I have come across for a ‘custom made spare’ is when a script writer wants to get the message across to the audience that this is just another silly American B movie that lacks any credibility what's-so-ever; but if you must, here are some possible things that such an aircraft might be used for.--Aspro (talk) 08:00, 13 April 2010 (UTC)

I don't see anything wrong with giving details. Even if the audience doesn't understand them, they still "lend authenticity". As for a "custom spare", perhaps a component of the engine needs to be replaced, and no spare is readily available, so might be produced by a nearby machine shop ? This scenario might come up particularly during war, when getting the plane flying again may be critical and the normal delivery of spare parts may be interrupted by enemy action. StuRat (talk) 10:02, 13 April 2010 (UTC)

A brief comment as to why the component failed (say metal fatigue) is OK but there is that danger, that a technical explanation may lead the audience to think that this in depth information is going to turn out to be important, later on in the story. Indulge too often, and the audience can get lost with information overload. It is different for such shows as CSI: Crime Scene Investigation because there is always someone on hand, and at the right time, to ask the soppy questions, that give the investigators the opportunity to spell out for the audience, exactly how each factoid links together. However, if the OP was writing that sort of thing, he would already have the background knowledge to be able to do his own research in this area. Second point. For reasons of weight and performance, aircraft engines are built to very tight safety margins. Even in war time, critical engine parts, that might be held responsible for such a failure would be have been manufactured to such high quality standards, that it is unrealistic, that a workshop would have those engineering documents available to inform them how to do it. An airfield workshop would unlikely have suitable case hardening nor heat treatment ovens, and on so on, nor stocks of the right metal in that grade. If they need to case harden or heat treat a chisel etc., they would just use a forge. The engineer whipping off his leather belt and punching out of it a new washer for the lube system is a possibility, but that is the sort of thing that can be fixed easily and would not lead to a sudden catastrophic failure. The two conditions the OP requests thus exclude each outer, even for this era. --Aspro (talk) 11:52, 13 April 2010 (UTC)

Wrong fuel or sand in the fuel. Cuddlyable3 (talk) 13:05, 13 April 2010 (UTC)

Thank you all very much (especially Aspro). Yes, I'm planning to write a novel about a long-distance flight, and the particular scene with the engine failure is supposed to happen somewhere in Indonesia, and to lead into a comic scene where my heroine goes with a local trucker to get spares but the trucker drives so recklessly that they run off the road several times and end up having to make repairs to the truck as well. I think a dropped valve would be the best kind of engine failure in this case -- serious enough to make the engine fail at once and completely, but not so serious as to wreck it altogether. Plus, the engine would make a lot of dramatic-sounding noises at the moment of failure. (And yes, if the cylinder was one of the upward-pointing ones, then the valve would drop into the cylinder.) As far as "custom-made spares", my understanding is that they don't make Wasp engines or spares for them anymore, so any spare part that is specific to that engine and not just a generic engine spare would have to be made to order. Once again, thanks a lot to everyone, and clear skies to you! 24.23.197.43 (talk) 02:14, 14 April 2010 (UTC)

You could probably specify a broken valve spring - that would avoid the "dropping into the cylinder" thing - and it's likely that you could find a sufficiently similar spring (eg from a truck engine or something) to at least allow you to limp home. My problem is that this engine has a lot of cylinders and the failure of one valve wouldn't cause a total failure - just a loss of power. Just have the fuel line break...much more abrupt - and very certain to force a landing. Also more credible that you could find some replacement tubing. SteveBaker (talk) 18:49, 14 April 2010 (UTC)

generalising the pI = pH formula for situations where the opposing weak acid and base are of different concentrations

It dawned on me that a major shortcut for amine + carboxylic acid solutions of equal molarity was to treat them like an amino acid and therefore pH = pI = (pKa1 + pKa2) / 2. But what if they are of different concentrations? How would I modify the formula? Is there a way to "weight" the pKas? I'm guessing they wouldn't be weighted linearly? John Riemann Soong (talk) 06:54, 13 April 2010 (UTC)

Voltage Divider and a Wheatstone Bridge

The article on the wheatstone bridge uses the idea of a voltage divider to calculate the voltage across the bridge. But it seems to me that there's a problem with this approach. The equation for the voltage divider assumes that the current running through the two impedances is equal for both. However, if we consider, say, R₁ and R₂ to make a votage divider, then because there's a current across the bridge, the current across R₁ will not be the same as the current across R₂. So we can't use the voltage divider equation in this case. How, then, is the method describes in the wheatstone bridge article valid? 173.179.59.66 (talk) 08:07, 13 April 2010 (UTC)

The key point is that the position is adjusted so that the current through V_G is zero, then the current must be the same through R₁ as it is through R₂, because there is nowhere else for it to go. Think of current through (not across). Dbfirs 08:19, 13 April 2010 (UTC)

Except, from the article:

"If all four resistor values and the supply voltage ($V_{S}$) are known, the voltage across the bridge ($V_{G}$) can be found by working out the voltage from each potential divider and subtracting one from the other. The equation for this is:

$V_{G}={{R_{x}} \over {R_{3}+R_{x}}}V_{s}-{{R_{2}} \over {R_{1}+R_{2}}}V_{s}$

This can be simplified to:

$V_{G}=\left({{R_{x}} \over {R_{3}+R_{x}}}-{{R_{2}} \over {R_{1}+R_{2}}}\right)V_{s}$"

So it seems that there is a voltage across V_g, and hence a current. 173.179.59.66 (talk) 20:30, 13 April 2010 (UTC)

Er, not when the bridge is balanced (ie when the contents of tha braces equals zero) there aint.--BandUser (talk) 21:18, 13 April 2010 (UTC)

Try putting $V_{G}=0$ in your equation (the braces), and thus deriving the equation to find ${R_{x}}$: $R_{x}=(R_{2}/R_{1})\cdot R_{3}$ . Perhaps this needs to be spelled out in the article if it is being misunderstood. Dbfirs 21:48, 13 April 2010 (UTC)

From the article: "...if R1, R2, and R3 are known, but R2 is not adjustable, the voltage difference [ie V_g] across or current flow through the meter can be used to calculate the value of Rx...". So clearly, the formula presented above is used to calculate what the voltage across the bridge would be, whether or not it's balanced. Hence V_g isn't necessarily zero. 173.179.59.66 (talk) 23:08, 13 April 2010 (UTC)

This was an alternative for when the normal balancing procedure is not possible. The point of the normal balancing procedure is that it can give a very accurate result. I would question the accuracy of the "alternative" that you mention, but I haven't used it. (If you are not going to balance at all, then you might as well just use a multimeter!) Perhaps the article needs more explanation. Dbfirs 02:13, 14 April 2010 (UTC)

It's apparently a quicker method, because it's faster to read a voltmeter than to adjust a resistor. Regardless, my question still remains unaddressed: seeing as how V_g need not be zero (as the article, and hence the above formula, both assume), how is it that the approach used, that is, via voltage dividers, is valid? 173.179.59.66 (talk) 04:40, 14 April 2010 (UTC)

V_g, as a galvanometer, draws an extremely small current, so I assume that we are making a fairly accurate approximation. I have only ever used a Wheatstone Bridge in accurate mode, but I can see that for some applications, it might be more convenient to use the alternative, with good accuracy provided that the current through the galvanometer is extremely small. Our article doesn't explain how to apply the correction, but I'll leave this to an expert. Dbfirs 08:20, 14 April 2010 (UTC)

So if I understood correctly, the galvanometer will have a very high resistance to minimize the current lost, right? Originally I had thought that this must be true, but in an assigment I recently had, we were given the same layout as a Wheatstone bridge, except V_g was replaced by a regular resistor. We were then asked to find the current through this resistor. The problem is that, in the solutions, my teacher used the same method as above, by using voltage dividers. Is he wrong? 173.179.59.66 (talk) 08:32, 14 April 2010 (UTC)

No. Galvanometers are low resistance, very sensitive ammeters. For bridges with arms in hundreds of ohms region, you could take the galvo resistance to be effectively zero. I have never heard of using a bridge unbalanced for measurement of one of the arms. But if you wanted to do this I suggest using a high impedance voltmeter to measure the difference in voltage. This will draw effectively zero current and then you could work out the unknown resistor.

When you were asked to work out the current through the resistor, was the bridge balanced? If so, the answer would of course be zero. Hope this clarifies.--BandUser (talk) 17:21, 14 April 2010 (UTC)

(I think the usual arrangement is to use a galvanometer with a high series resistance to protect it, which makes it into a high impedance voltmeter if the resistance is known.) With the resistor in place of the galvanometer, I think you were just expected to use Kirchoff's circuit laws without the special Wheatstone Bridge equation that is only valid when the current through the galvanometer is zero. You might also like to read Network analysis (electrical circuits) for a general treatment. Dbfirs 19:47, 14 April 2010 (UTC)

No, the bridge was very specifically said not to be balanced. And yet, he used the voltage divider method above to get the voltage across the bridge, and divided that by the resistor value of the bridge (which was comparable to the value of the other resistors) to get the current. But from what I understand, this is a mistake, right? 173.179.59.66 (talk) 20:35, 14 April 2010 (UTC)

Plants - pinching new growth? pinching? really?

I'm new to this whole horticulture thing. I'm starting easy, with an avocado seed. It's got roots and I expect a shoot soon. I've read that if you don't want a 10 foot tall tree with 2 leaves at the top you should "pinch off" new growth every once in a while to encourage it to expand outwards rather than upwards. My question concerns the exact action - am I really just... cutting off the top of my plant? This seems rather barbaric. Is there a special way to cut it? 59.46.38.107 (talk) 09:14, 13 April 2010 (UTC)

Pinching is just that, taking your thumb and fingernail and nipping out the shoot. Wait until it gets to a manageable height and then take out the growing tip. If you're growing tomatoes, this process is called "stopping" and will result in more fruit. I've never grown an avocado so I can't vouch for it in this circumstance. This article [4] has more detail on the process and its results. --TammyMoet (talk) 09:49, 13 April 2010 (UTC)

Take note, the reason these jungle plants have a big seeds is so that they have the energy reserve to shoot up above the deep shade, given by the thick ground level foliage of the forest floor, until they reach sufficient light to sustain them further. It will bolt skywards given half a reason to. An indoor room give the same light level reading on a camera as the jungle floor. Pinch the top bud out as suggested. You could leave it outside during the day. As your new to this, set an alarm clock to ring in the early evening, so that you remember to bring it back inside, so as to avoid any frost damage. Avocados are cheap, so experiment. --Aspro (talk) 10:27, 13 April 2010 (UTC)

You don't need to lop off the entire top of the plant, all you need to do is eliminate the terminal buds (buds at the top/end of the seeding) by "pinching" them off. Let's say your avocado seedling is now a meter tall and growing straight up without branching. If you cut off the group of buds at the top of the seedling (at the end of the growing season) it will stop growing straight up next year . Instead the seeding will start sending branches off to the sides from a set of buds lower down the seeding (usually next to the leaves). These side branches will grow diagonally upwards the next season. When you think these side branches have grown high enough (2-3 meters?), you can then pinch or cut off the terminal buds of these branches. This process goes on and on and on until you have the tree with the high and form you want. The article "Pruning" may help. Sjschen (talk) 18:45, 13 April 2010 (UTC)

marine animals that have evolved from land animals.

Sir,Madam. I was thinking about the structure and movement of various marine animals, and got to wondering, is the upwards and downwards movement of the tail section of certain species whales and dolphins for instance, indicative of species that have returned from the land to the sea. bearing in mind the propensity of fish to move their tail sections from left to right. Yours Truly John Walshe.

I don't think that's a hard-and-fast rule, as there are marine animals not evolved from land animals which use the up-and-down motion, too, such as rays. There are also land animals, like snakes, which use a side-to-side motion. However, the up-and-down motion does facilitate sticking ones head (or just blow-hole) out of the water to breath, and only marine mammals need to do that, so there is some link. StuRat (talk) 11:06, 13 April 2010 (UTC)

I suppose the up-and-down motion of walking on land translates into up-and-down swimming in sea; the reason marine snakes, lizards and newts swim side-to-side like eels would then be that they crawl partly side-to-side on land as well. What about the ichthyosaurs, does anyone know how they swam? --91.148.159.4 (talk) 15:22, 13 April 2010 (UTC)

Considering that their tail fins were vertically oriented, I'd say it's much more likely that they used the fish style of side-to-side motion. Matt Deres (talk) 16:50, 13 April 2010 (UTC)

True. Well, I suppose this can be connected to the fact that they evolved not from dinosaurs (dinosaurs had developed the capacity to walk up-and-down pretty much like modern land mammals do), but from more archaic reptiles that presumably still crawled with partial side-to-side movement like lizards. Thus, one may say that while the implication "terrestrial origin -> walking -> up-and-down swimming" does exist, it only holds in those lineages where "proper" up-and-down walking has already been developed in the first place, and this took quite some time to develop in terrestrial animals. Penguins are another telling example - unlike ichthyosaurs, they do not originate from crawling reptiles but, ultimately, from walking ones (specifically from dinosaurs), so their swimming is primarily up-and-down oriented, as in marine mammals.--91.148.159.4 (talk) 18:42, 13 April 2010 (UTC)

Shrimp

The horizontally oriented tails of marine mammals developed from side-by-side hind legs, so there's a connection there. Fish on the other hand developed without any tie to what anatomy worked on land. Rckrone (talk) 17:46, 13 April 2010 (UTC)

Actually, looks like I'm wrong with regard to cetaceans and manatees whose tail fins are just tails. So scratch that. However, the Marine_mammal#Adaptations section touches on what 91.148.159.4 said about swimming and walking motions. Rckrone (talk) 17:58, 13 April 2010 (UTC)

Bear in mind that most "flat" fish evolved from bottom-feeding fish that habitually lay on their sides and whose eyes and various other body parts migrated to make that a permanent thing. Looked at like that, they are flapping their tails "from side to side" - but they are swimming on their sides so it looks like they are flapping up and down. SteveBaker (talk) 18:05, 13 April 2010 (UTC)

Dawkins addressed this very point in "Greatest Show on Earth" and he agrees with the premise suggested by the OP. it is the orientation of the mammalian spine that gives the up and down "galloping" motion in aquatic mammals. I think rays do not flex their spine up and down to swim, they use their laterals. And steve above is also correct. Also land snakes and lizards didn't evolve a mammalian spine so I don't see why the fact they walk side to side has anything to do with aquatic mammals. Another extremely interesting thing about land/sea migration is that it looks like some turtles/tortoises migrated from the sea to the land not just once but twice! Sea to land, back to sea and to land again! Including the ancestral fish to amphibian migration, that means they've been from sea to land three times! Vespine (talk) 22:29, 13 April 2010 (UTC)

Well the spine and the way of walking change together, one is a means for the other. But I don't think it's only a mammalian thing; as I said, I think that there are animals other than mammals that have adapted to swim, and that swim not laterally like fish, but mostly up-and-down. Penguins evolved from birds, which walk on land, and (swimming) shrimp evolved, perhaps, from bottom-walking crustaceans - although admittedly both seem to use their limbs more than fish and cetaceans usually do.--91.148.159.4 (talk) 22:57, 13 April 2010 (UTC)

Well that's exactly the point, penguins evolved to walk on land too but do not use their spine for swimming so they are a bit of an "inbetween" and shrimp don't have spines so they don't really count. I do agree with you that a spine which bends vertically is not THE definitive indicator of mammalian origins in an aquatic animal, but it is one of the very strong indicators. Along with things like lungs and bone structure. Vespine (talk) 00:20, 14 April 2010 (UTC)

Sure, no doubt about mammalian origins. The OP was about a connection between tail movement orientation and terrestrial origins in general, not only mammalian origins, so I was trying to say that the connection between walking and up-and-down swimming in a broad sense may hold not only in mammals. I'm conjecturing that dinosaurs' and birds' spines have also become sufficiently re-oriented to make vertical oscillation easier than lateral one. Of course, I could be wrong - I don't understand the underlying anatomy well enough, and I don't really have examples: it's true that penguins don't seem to rotate their bodies for swimming very much anyway, so it may have been too far-fetched of me to draw them into the picture. On the other hand, there may be some examples with swimmers that have a background as sea-bottom walkers: for example lobsters swim by flipping their tails up and down more or less like marine mammals (source in hidden text). Shrimp and crayfish use limb-like structures, but they also flip their tails like lobsters ((source in hidden text)). The flat ends of their tails are also horizontally flat, as in marine mammals. --91.148.159.4 (talk) 14:25, 14 April 2010 (UTC)

Primaeval woodland in the UK

Is there are woodland or forest left in the UK that is truely wild and has never ever been planted or cultivated? Even ancient woodlands such as the New Forest were planted centuries ago. Thanks 78.147.232.11 (talk) 12:25, 13 April 2010 (UTC)

According to episode three Man Made Britain of Britain From Above - which I've just (20 minutes ago) watched - the answer is pretty much no. Mitch Ames (talk) 13:51, 13 April 2010 (UTC)

Depends what you mean by "never ever been planted or cultivated". The wood at the bottom of my garden (Brandon Wood, Warwickshire) is an ancient woodland, mentioned as such in the Doomsday Book. But no tree in there seems to be more than about 150 years old. This could be because the trees have been harvested over the ages, and that might mean the woodland has been "cultivated". Also a woodland which contains pollards - that has been "cultivated", but it could date from "time immemorial". I beg to differ with Mitch, however, in that the Caledonian forest seems to be a remnant of the post-glacial coniferous forest which covered the British Isles after the last Ice Age. --TammyMoet (talk) 15:22, 13 April 2010 (UTC)

Caledonian Forest 89.240.34.241 (talk) 22:34, 13 April 2010 (UTC)

In a case like this, I wonder how great a role something like the Little Ice Age can play in skewing the results. I'm not a climatologist, but it seems to me that you'd have a hard time finding a section of forest that had existed continually for, say, a thousand years when you have temperature changes that great, lasting for so long. Matt Deres (talk) 16:44, 13 April 2010 (UTC)

300 years is a blink of an eye when talking about great trees such as oaks! --TammyMoet (talk) 19:07, 13 April 2010 (UTC)

Not if it gets so cold that it causes the tree to die or even if the climate shift is enough to curtail the growth of saplings in favour of more cold-hardy species. More philosophically, there's the possibility of a variation of the "Ship of Theseus" - is it still the same forest if the oaks survive, but the beeches and poplars are replaced with, say, birches and evergreens? Matt Deres (talk) 20:20, 13 April 2010 (UTC)

I've seen numerous oaks younger than that develop rot to the center and basically die of old age. Edison (talk) 16:14, 14 April 2010 (UTC)

What I should have said was, is there any land in the UK that has never been cultivated, managed, or planted? Unless its bare rock, its probably going to be a forest, climax community and all that. I understand that Britain would naturally be covered in wild forest but at various times all of it (or nearly all?) has been cultivated or cleared by man. 89.240.34.241 (talk) 21:32, 13 April 2010 (UTC)

Places such as Rothiemurchus, Abernethy and Glen Affric are remnants of the Caledonian Forest of which according to our article only 1% remains (but that 1% should fit your requirement).213.160.108.26 (talk) 22:25, 14 April 2010 (UTC)

Gravity, friction and mass.

Would you please explain what is conflict in my logic based on my understanding of the laws of physics between statement number 1 and statement number 2. I suspect my knowledge of physics is flawed and I would welcome guidance.

Statement 1.

Two bodies(say a sphere) of identical size and shape are dropped at the same time from the same height. One sphere is filled with lead and the other sphere is filled with feathers. Both spheres will hit the ground at the same time.

Statement 2.

The same two spheres are each placed on identical skateboards and set off at the same time down an identical slope. The sphere filled with lead will pass the sphere filled with feathers.

If gravity is a constant accelerating force what is the explanation for the outcome of statement number 2 ?

Thank you.

86.12.198.101 (talk) 14:44, 13 April 2010 (UTC)

That's so easy. The coefficient of friction is not the same for every force applied. This is obvious if you think about what happens when you try to push with your pinkie a balloon versus a lead ballast of the same shape. In an "idealized" environment (where the physicist assumes zero friction) you can push each of them just as easily. Or maybe not, since they have inertia. What do I know, I'm just a useless hack. 84.153.214.140 (talk) 14:58, 13 April 2010 (UTC)

Statement 1 is true in an idealized setting without air resistance or other friction. Statement 2 is false in this setting (with no friction, the skateboard will behave like a sled - but see below).

Statement 2 is true in most realistic settings with friction.

However, there is an idealized setting in which both are true: No air resistance and rolling resistance, but perfect friction between skateboard wheels and slope. In this case, the potential energy of the system (proportional to the mass of the skateboard and the sphere) is converted into kinetic energy (corresponding to forward motion and proportional to the mass of the system) and rotational energy of the skateboard wheels (which is independent of the weight of the system). In the heavier system you need a smaller proportion of energy to make the wheels spin, so a larger part is kinetic energy, hence it goes faster. --Stephan Schulz (talk) 15:05, 13 April 2010 (UTC)

(edit conflict) Statement 1 is only true in vacuum. Otherwise air resistance will have an effect. For substances with such different densities as lead and feathers, air resistance will be a significant factor. In Statement 2 air resistance will have an even bigger effect, as the effective force acting on each skateboard and sphere parallel to the slope is less than its weight; it is weight x sin(θ) where θ is the angle between the slope and the horizontal. Gandalf61 (talk) 15:08, 13 April 2010 (UTC)

The problem here is that the two parts of the question make different kinds of assumptions. In effect, we have a spherical cow and a goat-shaped goat. In the first case, the questioner has seen fit to ignore the effects of air resistance - which would otherwise result in the lead ball hitting the ground before the feather-filled ball. But in the second case, friction with the track and between the axles and the wheels has not been ignored, because if it had then both skateboards would arrive at the end of the track at the same time. So this is really an issue of missing/unstated assumptions. If we were told (for example) that these two experiments were being carried out on the moon (no air resistance - but plenty of friction) then we might reasonably understand what the questioner had in mind...but without that context, we don't know what we're supposed to ignore and what we required to take into account.

The question is greatly confused by the fact that we're specifically told that the feathers are packed into a ball the exact size and shape of the lead ball. If we're supposed to be ignoring air resistance then why bother saying that? The usual assumption in this kind of question is that if such details are stated, then they are relevant. SteveBaker (talk) 17:48, 13 April 2010 (UTC)

Not quite, see my comment above. There is a reasonable abstraction (no friction, no air-resistance, but perfect no-slip wheels of finite moment of inertia) where you can have this result. --Stephan Schulz (talk) 18:13, 13 April 2010 (UTC)

Its like rolling two cylinders down an inclined plane, only this time it's the skateboard wheels that are absorbing the energy. The same thing would happen on the moon, so air resistance isn’t the prime factor.--Aspro (talk) 18:22, 13 April 2010 (UTC)

... and if you take the spheres off the skateboards and just roll them down the slope, then the lead sphere will still win (assuming the spherical shell is more dense than the feathers). There was a similar question on an Oxford Entrance examination in the 1960s. If you want the feathers to win, then you have to put less lead inside the other sphere and suspend it at the centre with light spokes. Dbfirs 21:12, 13 April 2010 (UTC)

Oxford Entrance examination of the 1960s??? Are these practical experiments preformed any more? I have read, just this month, that the modern school system only trains pupils to pass exams, instead of providing an education. There are many questions asked 'here' which seem to confirm that education (and the insight that it can provide) is a thing of the past. Can we get these school fees reimbursed? They have not delivered the goods.--Aspro (talk) 21:59, 13 April 2010 (UTC)

BTW: Just to be fully correct, the lead ball will hit the ground (slightly) before the feather one. It is not true that everything falls at the same speed, but rather it is approximately true. On earth the difference is not measurable, but it is there. To the OP: do not let this confuse you - most of the time the approximation is correct and should be used. Ariel. (talk) 02:40, 14 April 2010 (UTC)

I think I know why you think think that, and if yes, I had a major discussion with my high-school teacher about it. Both bodies are attracted towards the common center of mass, and the heaver ball makes the Earth move faster...right? Or wrong? --Stephan Schulz (talk) 07:40, 14 April 2010 (UTC)

Well, let's be a little careful about that. He who lives by the nit-pick must also die by the nit-pick! We know that $F=G{\frac {m_{1}m_{2}}{r^{2}}}$ - the force exerted on each body (both the ball and the earth) is proportional to the product of the two masses. However, the acceleration due to that force is given by A = F / m ...and the acceleration is what we care about here. So the acceleration of the ball depends only on the mass of the earth because its own mass cancels out...and the same is true of the acceleration of the planet...it depends only on the mass of the ball. So yes, the earth does move by the most microscopic amount imaginable in the direction of the ball due to the balls' own (insanely puny) gravitational field. If you drop the lead ball, it'll hit the ground a vanishingly small amount of time sooner than if you had dropped the feathery ball. But (and this is the point where your nit-pick fails!) if you drop both balls at the same time (as this experiment stipulates) - then even at this microscopic level of nit-picking, they still land together since the earth is being accelerated simultaneously by both balls. (Unless you drop the balls on opposite sides of the planet or something - but then our uber-nit-picker would invoke relativity and we'd have to ask what "simultaneous release" means for widely separated objects moving in different directions.) The balls themselves both experience the exact same accelerations. But in any case, the numbers involved are vastly too small to matter and I strongly urge our OP to studiously ignore this part of the thread because it's very, very, silly! SteveBaker (talk) 18:42, 14 April 2010 (UTC)

Homosexuality and Pedophilia

Hello, I don't want to do politics, so please don't do either, I was just wondering if there are any studies inverstigating links or relations between homosexuality and pedophilia. Again, no polemics, no political (in)correctness, just studies, please. Thank you very much. --Lorem ipsum dolor sit amet (talk) 18:00, 13 April 2010 (UTC)

Yes. This review article from 2007 should contain some relevant references. --NorwegianBlue ^talk 18:48, 13 April 2010 (UTC)

To clarify, this link is about childhood victims of homosexual paedophilia becoming homosexuals as adults, not about homosexuals being likely to commit paedophiliac acts (I'm clarifying, because there were some recent questions about the latter in connection to a statement by some papal spokesman).--91.148.159.4 (talk) 19:01, 13 April 2010 (UTC)

Not a study but I shall contribute a logical argument: how could homosexuality be any more related to pedophilia than various fetishes, such as shoe fetish, or even heterosexuality? Pedophilia itself is a sexual orientation, just like verious fetishes.--92.251.147.169 (talk) 18:51, 13 April 2010 (UTC)

See yesterday's thread at Wikipedia:Reference Desk/Humanities#Homosexuality = Paedophilia? Studies?. Comet Tuttle (talk) 20:23, 13 April 2010 (UTC)

Is pedophilia normal?--79.76.163.157 (talk) 23:18, 13 April 2010 (UTC)

What do you think? Look up the definition of "normal" and try to fit paedophilia into any of those definitions. I'll be surprised if you are left with any ambiguity after this exercise. Vespine (talk) 00:23, 14 April 2010 (UTC)

I detect that are implying that the answer is clearly abnormal, however it depends on the definition you take. Here are two, from WordWeb v5.0:

1. (psychology) being approximately average or within certain limits in e.g. intelligence and development - this make both homosexuality and pedophilia abnormal

2. In accordance with scientific laws - this makes both homosexuality and pedophilia normal

Abnormality says nothing about the potential harm to individuals nor what remedies (e.g. convince society that homosexuality is acceptable vs aversion therapy for homosexuals) are appropriate. An IQ of 150 is abnormal. It says nothing useful. 78.148.114.247 (talk) 00:56, 14 April 2010 (UTC)

Well, no, you're arguing semantics, I specifically said to look up the various definitions. Normal can also mean "(of a solution) containing one equivalent weight of the constituent in question in one litre of solution." but it's hardly relevant, just like "in accordance to scientific laws" is not relevant in this context either. dictionary.com normal has that definition at 4(b) of natural occurrence. google normal does not even have that definition. If the question was "is a society with paedophiles normal?" I'd say you might have an argument, but is being a paedophile normal? I think is clear cut. Vespine (talk) 01:23, 14 April 2010 (UTC)

Well if you use the definition "of natural occurrence" (is being a paedophile a/of natural occurence) then perhaps although it depends what you mean by 'natural occurrence'. If you mean innate then I think the answer is may be. As we've discussed many times before on the RD, the word natural is very fussy and it would seem difficult to argue conclusively any behaviour that occurs isn't natural. Well unless you believe in God and/or the devil in which case you could certain behaviours only come from God and/or the devil and these aren't natural but that isn't a particularly scientific answer. Nil Einne (talk) 01:58, 14 April 2010 (UTC)

Is being a homosexual normal? 78.148.114.247 (talk) 01:53, 14 April 2010 (UTC)

This is the science reference desk. We can talk about probabilities and perhaps evolutionary causes and maybe even biochemical and/or genetic causes. But words like "natural" and "normal" are not things that science can help you with. They are terms without solid meanings. We can't perform some kind of scientific test for "natural-ness" or "normality". This is a matter for society to decide. This question belongs on the "humanities" reference desk - and it's already been asked there. So unless someone can answer the actual question we've actually been asked ("Are there any studies relating these two facets of human behavior?") let's end this thread and direct readers and contributors to the correct place to discuss it. SteveBaker (talk) 02:07, 14 April 2010 (UTC)

Actually, true pedophiles (those whose primary sexual interest is prepubescent children) often don't prefer one gender over the other. It's the fact that a child IS A CHILD that attracts them. They are attracted to the way children look (i.e., the lack of adult secondary sexual characteristics is what turns them on) and think. Most pedophiles find some children more attractive than others, but what makes a particular child special may have as much to do with age and physical characteristics as with gender. Like people of more acceptable sexual orientations, a pedophile may have a "type." Gentlemen prefer blondes, women like guys who are tall/dark/handsome, and so forth - that doesn't mean that "preferring blond women" is a sexual orientation in its own right or anything other than an individual preference. An adult who chooses to act on an attraction to a person whose body is sexually mature but who is below the age of consent is another matter. Male homosexual culture, probably even more than our culture already does, idolize the beauty of youth, and as homosexuals are already existing for the most part outside of mainstream society, it may be easier for them to ignore the taboo on sexual involvement with a minor. So there may be cultural link or relation between homosexuality and sexual involvement with post-pubescent minors, but actual sexual involvement is a behavior. Attraction is involuntary, and although culture has an influence, biology is a huge factor in attraction. Are gay men more turned on by teenage boys than straight men are by teenage girls (whether either of them admit to or act on that attraction or not)? I doubt it. 71.104.119.240 (talk) 06:31, 14 April 2010 (UTC)

• Vatican Statement Regarding Comments by Card. Bertone
  • Interview with Scicluna --88.66.204.235 (talk) 17:12, 14 April 2010 (UTC)

Of course by definition, no perversions are normal. Maybe thats how we define perversions. Some perversions are legal (eg homosexuality), some are not (eg pedophilia). Other countries have different rules. Lawsin different countries are somewhat arbitrary. Morals are something defined by the religion you follow.--BandUser (talk) 00:09, 15 April 2010 (UTC)

Making my own tubular steel shelving in needed dimensions

I like this shelf but its dimensions render it inapplicable to my situation. I could buy some tubular steel or aluminium, but then what - how would I attach the ends to a plate in a way that didn't look messy? I'd like something that looks similar to the one in that picture (all-metal). I have a soldering iron and a weird little handheld butane thing I bought years ago and lost the instructions for - I remember it said something about brazing. Also, there are some putty things available where you mix two putties together and they react and harden after a period to a metal sort of bond (for fixing pipes etc). Anyone got any suggestions? --78.148.114.247 (talk) 22:18, 13 April 2010 (UTC)

You didn't link to a picture - so it's hard to guess what you have in mind. Soldering or brazing steel or aluminium tubing is a difficult and skilled process. You might want to consider using screw-fit plumbing fittings - then spray-paint it matte black or something. Take a trip to the plumbing section of your local DIY store and you'll be sure to find ready-made parts that can basically be screwed or even epoxied together to make a stiff framework - you'll even find parts that would be useful for feet and other bits and pieces. The "putty" stuff you are thinking of is called "Epoxy putty" - and that might well be all you need. If you are really itching to use the butane torch, you'd want the kind of copper plumbing fittings that have solder already applied inside the joints. That would be a much easier way to connect copper tubing - but it's not suitable (or even available) for steel or aluminium tubing. SteveBaker (talk) 23:37, 13 April 2010 (UTC)

Oh, right, thanks here is the image. I'd like it in this matt aluminium/steel finish. One possibility might be to cut off one of the sections with a multitool and then use a grinding wheel to neaten it? Most of all, I like this particularly cheap one but I can fathom no way that this would look neat after I had attacked it with a multitool. 78.148.114.247 (talk) 23:51, 13 April 2010 (UTC)

Ah - I see. Well, in the case of the one on eBay, instead of cutting off the tube that runs along the front edge of the shelf (leaving ugly, raw cut edges on the front ends of the support tubes). I would cut off the last tube at the BACK of the pipe and relocate the brackets forward one row...but everything depends on how those brackets are fixed. If they are just screwed into place - then it's easy - but if they are welded or molded on there - that wouldn't work. SteveBaker (talk) 02:22, 14 April 2010 (UTC)

Two methods:

• Buy the tubes, and flat metal for the sides, then connect them by buying long threaded dowels. Drill holes in the flat metal, put the dowels through the tubes and metal, then attach a nut on each side and tighten. Then use your multitool to trim the dowel right down to the nut. For extra reliability buy loctite threadlocker, use blue if you plan to take it apart or red if you want it permanent.

• Get short wooden dowels exactly the size of the inside of the pipe. If necessary make them using a hole saw. About 2 inches long. Glue them to the side metal, then glue the pipes onto them. For extra strength drill a hole in the metal and put a wood screw (sheet metal actually - you want a flat bottom on the head, not a cone like a typical wood screw) through the metal and into the wood.

Ariel. (talk) 02:31, 14 April 2010 (UTC)

April 14

Pressure

What is the general direction of a low pressure center as it moves across the US? Lamb99 (talk) 00:58, 14 April 2010 (UTC)

The trade winds in the US blow from west to east. As a side note weather forecasts in the US are more accurate further from the west coast because of this. Ariel. (talk) 02:44, 14 April 2010 (UTC)

They are called westerlies. The trade winds go from east to west and are over the tropics. Dauto (talk) 03:01, 14 April 2010 (UTC)

The term Ariel was trying to think of was prevailing winds. The trade winds and the westerlies are two instances of prevailing winds. --Anonymous, 05:15 UTC, April 14, 2010.

Hmm, and the map in those articles makes it look as though the trade winds do blow in the US. I've added a comment to the trade winds talk page. --Anonymous, 05:40 UTC, April 14, 2010.

Strong low pressure systems over the US can also travel northward due to ridging within its warm sector, southward due to cold Arctic air, or even retrograde westward in a counter-clockwise loop. We've seen all three of those this year, satellite archives here. ~AH1^(TCU) 23:42, 14 April 2010 (UTC)

Research influenced by funding source

I frequently read about research studies sponsored by companies or industries with a special interest, in which the conclusions of the study invariably support the position of the sponsor. A recent example that comes to mind is the FDA's 2008 finding that bisphenol A in plastics is perfectly safe, citing chemical industry studies while ignoring independent research that reached other conclusions.

What is this phenomenon called, where the conclusions of a study are pre-biased according to the sponsor's interests? I thought there might be an article on it somewhere, but all I can find is one sentence in Selection bias#Related issues. ~Amatulić (talk) 05:28, 14 April 2010 (UTC)

In general, that type of thing is called a conflict of interest. Note that the lab may do everything legit, but the company hiring them can still twist the results, by suppressing info found contrary to their business interests and highly publicizing info helpful to their business. To do this, they require the lab to sign a nondisclosure agreement before they are funded, which states that any info learned belongs to the funding company, and the lab has no right to release it independently. The same company might fund many studies at several labs, and pick and choose to find those that support their position. StuRat (talk) 05:36, 14 April 2010 (UTC)

As someone from the other side of the pond, I find it astonishing how often government decisions are the result of influence by commericial interests, rather than the public good. 89.242.91.98 (talk) 09:38, 14 April 2010 (UTC)

Research has shown that people are unaware of the factors that affect their decisions. I recommend Influence: Science and Practice for everyone. To the point, even if everything is on the up and up researchers will still be affected by their sponsors, but they may genuinely deny it. It's human nature. Imagine Reason (talk) 14:21, 14 April 2010 (UTC)

The specific question of the FDA (and other agencies) is often referred to as regulatory capture. --Mr.98 (talk) 14:33, 14 April 2010 (UTC)

Interesting replies, but not quite what I'm looking for. Doing some googling, the correct term appears to be "funding bias". Since such an article doesn't exist on Wikipedia, maybe I'll write one sometime.

I found some academic papers using this term, although the most accessible is this economist's blog article, which uses more specific terms "funding outcome bias" and "funding publication bias":

Anders Sandberg (2007-01-14). "Supping with the Devil". OvercomingBias.

Also, this paper on funding bias related to health effects on cell phone use doesn't any term to describe the phenomenon, although it refers to another paper that uses the term "sponsorship bias". ~Amatulić (talk) 18:20, 14 April 2010 (UTC)

Another source of bias is coming to a conclusion prior to examining the data, then using data evidence to support that pre-stated conclusion. This method is technically not science. ~AH1^(TCU) 23:48, 14 April 2010 (UTC)

Metal in the microwave?

The microwave in my house has a metal rack in it, in the chamber where the food cooks. How does this work without doing damage? I've brushed my hand on the rack after the microwave had been running for ten minutes or so, and it was hot, but not nearly so hot as a spoon I left in the microwave for two or three minutes. Is this some special kind of metal? Please explain! 71.104.119.240 (talk) 05:54, 14 April 2010 (UTC)

I found patent #4455467 which talks about it. It seems that the rack is designed to try to hide in the cold spots of the microwave, but also that the rack is simply large enough to absorb the heat. Ariel. (talk) 09:11, 14 April 2010 (UTC)

IIT QUESTION

A LARGE FLASK FITTED WITH A STOP COCK IS EVACUATED AND WEIGHED, ITS MASS WAS FOUND TO BE 134.57gm. IT IS THEN FILLED TO A PRESSURE OF 735mm AND THEN RE-WEIGHED , ITS MASS IS FOUND TO BE 137.456gm THE FLASK IS THEN FILLED WITH WATER AND WEIGHED AGAIN, ITS MASS IS NOW 1067.9gm. ASSUMING IT IS AN IDEAL GAS CALCULATE MOLECULAR MASS OF GAS.

    FORMULAE THAT COULD BE USED IS OF A REAL GAS EQUATION i.e :-
    
                    PV=RnT
         where:- P = PRESSURE
                 V = VOLUME
                 R = CONSTANT[0.0821]
                 n = NO. OF MOLES
                 T = TEMPERATURE
—Preceding unsigned comment added by 122.173.31.193 (talk) 06:17, 14 April 2010 (UTC) 

Don't use all caps. StuRat (talk) 06:20, 14 April 2010 (UTC)

Please do your own homework.

Welcome to the Wikipedia Reference Desk. Your question appears to be a homework question. I apologize if this is a misinterpretation, but it is our aim here not to do people's homework for them, but to merely aid them in doing it themselves. Letting someone else do your homework does not help you learn nearly as much as doing it yourself. Please attempt to solve the problem or answer the question yourself first. If you need help with a specific part of your homework, feel free to tell us where you are stuck and ask for help. If you need help grasping the concept of a problem, by all means let us know. StuRat (talk) 06:20, 14 April 2010 (UTC)

As a hint, you're given the pressure, you can get the volume from the amount of water and the density of water, and you've probably been told the temperature (or can assume room temperature). You can now solve for the number of moles. With this and the mass of the gas, you can calculate the molecular (molar) mass. Good luck. -- 140.142.20.229 (talk) 20:43, 14 April 2010 (UTC)

Even harmonics in Electrical power lines

It is generally said that only ODD harmonics are present in electrical supplyand odd harmonics are only dealt with -- My question is "Why EVEN harmonics are not present OR why it is not a problematic issue? —Preceding unsigned comment added by 170.38.136.2 (talk) 06:21, 14 April 2010 (UTC)

That's not a generally true statement. Harmonics are typically caused by some type of distortion; certain types of distortion favor amplification of even or odd harmonics. For example, see Triangle wave vs. Square wave to compare the frequency spectra. If your distortion caused the time-domain waveform to look more like a triangle wave (rising and falling during non-negligible periods), you would see more energy in odd harmonics. In general, a signal distorted by an arbitrary, general nonlinear distorting system will spread its energy to many frequencies, including even-harmonic, odd-harmonic, and non-harmonic frequencies. Nimur (talk) 15:35, 14 April 2010 (UTC)

Gravity, friction and mass II

Would you please explain what is conflict in my logic based on my understanding of the laws of physics between statement number 1 and statement number 2. I suspect my knowledge of physics is flawed and I would welcome guidance.

Statement 1.

Two bodies(say a sphere) of identical size and shape are dropped at the same time from the same height. One sphere is filled with lead and the other sphere is filled with feathers. Both spheres will hit the ground at the same time.

Statement 2.

The same two spheres are each placed on identical skateboards and set off at the same time down an identical slope. The sphere filled with lead will pass the sphere filled with feathers.

If gravity is a constant accelerating force what is the explanation for the outcome of statement number 2 ?

Thank you.

86.12.198.101 (talk) 08:42, 14 April 2010 (UTC)

You seem to have asked the samed question here yesterday, and you got several very detailed responses (see Wikipedia:Reference desk/Science#Gravity, friction_and_mass. above). Do you have a follow-up question ? Gandalf61 (talk) 08:54, 14 April 2010 (UTC)

To summarise briefly (just in case you missed the answer in the detail of the discussion), resistances will have an effect, but even if you ignore all resistance, skateboard wheels carry energy proportional to the square of speed, and this energy comes from gravity through the loss in height. A lighter sphere will have less energy to lose, so a bigger proportion will go to the wheels and less will be available for linear speed.

If the spheres were sliding down a frictionless slope with no air resistance, then they would slide at the same speed. Dbfirs 19:27, 14 April 2010 (UTC)

Memory

Today, I realized that it is easier for me to remember the name of a person if I say it out loud at least once with focused attention, rather than simply writing it down and forgetting about it. Is there something to this in the recall process, or is it simply an idiosyncrasy? Why would I be able to better recall a name spoken out loud rather than recalling a note with the name written on it? Viriditas (talk) 09:31, 14 April 2010 (UTC)

I don't know of a name for what you're describing, but I'd say it's not an idiosyncrasy. It's a common suggestion that if you want to remember the names of the people you meet, you want to address them by their names in your conversations with them. Apparently saying their names aloud helps you remember their names. A related phenomenon I've observed is that if you don't know how to pronounce a word or name, it's very difficult to remember it. So vocalizing a word seems to play a role in helping you recall it. --98.114.98.221 (talk) 11:21, 14 April 2010 (UTC)

This is often called Salience (neuroscience) --Digrpat (talk) 14:46, 14 April 2010 (UTC)

Salience, yes, thank you. That was the word I was looking for. Viriditas (talk) 20:36, 14 April 2010 (UTC)

It might be that vocalizing the name develops procedural memory of the name, as opposed to declarative memory. Paul (Stansifer) 17:55, 14 April 2010 (UTC)

Interesting. But, isn't learning a name and saying it more of a declarative memory task? And isn't writing down a name, regardless of the information, a procedural task? I don't think about much when I'm writing, I just do it. Viriditas (talk) 20:36, 14 April 2010 (UTC)

about science

how to study science more easily?  (Unsigned comment added by Sharook (talk • contribs) 15:36, 14 April 2010 (UTC))

It usually helps to have a solid grasp of basic mathematics; depending on how quantitative your scienctific inquiries are, math generally helps. Are you looking for references to books or websites, or do you want some practical study tips? Nimur (talk) 15:38, 14 April 2010 (UTC)

It is "easier" with a gifted instructor who cares whether you learn, and with a good textbook. It is "easier" to become skilled at the math portion of science if you do lots of well chosen problem sets, and that process seems to work best in a group setting, where each contributes. It is also "easier" though not easy, if the learning is as experiential as possible, with good labs and demonstrations. In "bad" labs the emphasis is all on achieving results which are "correct" with a degree of precision greater than the equipment and time provided readily allows, leading to a temptation to "drylab" or fudge results. Edison (talk) 16:11, 14 April 2010 (UTC)

I think it helps if you understand WHY some technique or formula is important rather than learning it 'cold'. It also helps immensely if you choose to learn just because you love the subject. I don't know how old you are - but I was really turned on to science through The Feynman Lectures on Physics (a set of three text-books) which are intended for kids in their final year or two of high school or their first year or two of college. Feynman was the consummate scientist. If you need inspiration, find any biography of him (there are MANY) and be amazed by how he treated subjects as diverse as how to pick up women in bars, how to eradicate ants from his kitchen and how to travel to Tuva with a scientific viewpoint - and had fun doing it. SteveBaker (talk) 18:11, 14 April 2010 (UTC)

Practicing with more scientific experiments can also make science more interesting. ~AH1^(TCU) 23:30, 14 April 2010 (UTC)

how does the nitrate reduction test work in microbiology?

I'm really really annoyed at my TAs because they seem to avoid organic chemistry explanations like the plague ... they say they can't help me with explaining why one test gives what colour and by what mechanism. OMG. So ... I was hoping someone here could tell me. Supposedly Zn(0) acts like a catalyst(?), but I'm a bit suspicious of people using this term. I rather suspect the zinc actually gets consumed. John Riemann Soong (talk) 16:25, 14 April 2010 (UTC)

We're talking about the nitrate reductase test? DMacks (talk) 17:32, 14 April 2010 (UTC)

Here's a fuller explanation than we have in the article. The test is to see if bacteria have the capability of respiring using NO₃^- in the absence of oxygen. The bacteria are grown in tubes containing media containing NO₃^-. The test to see if they are capable of such reduction is a specific test for NO₂^-. NO₂^- turns reddish purple in the presence of N, N dimethyl-1-naphthylamine and sulfanilic acid. If the bacteria have reduced NO₃^- to NO₂^-, and no further, the color change will be apparent. But if there is no color change, the bacteria may be incapable of NO₃^- reduction, or they may have reduced NO₃^- to NO₂^-, and then further reduced the NO₂^- to N₂ or other intermediates. So we distinguish between these two possibilities by adding zinc to the colorless media. Under acidic conditions, zinc catalyzes the reduction of NO₃^- to NO₂^-. So if there is NO₃^- present in the colorless media, adding zinc will produce the color change and indicate that the bacteria incubated in that medium were incapable of NO₃^- reduction. If addition of the zinc to the colorless media does not produce a color change, it means that NO₃^- is not present, and that therefore the bacteria incubated in that tube were capable of NO₃^- reduction. - Nunh-huh 00:33, 15 April 2010 (UTC)

Thanks! I kinda knew some of that already. What I am really interested in is the organic chemistry of it and the mechanism by which zinc "catalyses" the reduction. What even supplies the electrons? What gets oxidised in the reaction? Are we using metallic zinc, or the Lewis acid catalyst Zn2+? How many steps and intermediates does the reaction go through? It seemed to me that a sulfonic acid was quite oxidised already. Does the napthylamine become a nitro compound and become an aromatic dye? John Riemann Soong (talk) 00:56, 15 April 2010 (UTC)

OK, I currently suspect the napthylamine becomes an amino-napthoquinone, which shows up as red. Can anyone confirm my suspicion? Thanks. John Riemann Soong (talk) 00:58, 15 April 2010 (UTC)

Using earwax to test purity of water

I remember, as a child, being told on a wilderness survival course that you could test the purity of water by putting earwax in it. If the wax floated, the water was contaminated; if it sank, it was safe to drink. We were solemnly told not to clean our ears out in the week before a wilderness trip, and to always have a cotton bud in our survival kit.

Is there any scientific logic behind this? To me it now seems plainly wrong. I can see that certain things - salt, for example - would affect the density of the water. But there must surely be all sorts of bacteria which could contaminate water without affecting its ability to support earwax, never mind the obvious flaw that however pure your water was to begin with, it's now got earwax in! --OpenToppedBus - Talk to the driver 16:41, 14 April 2010 (UTC)

Seems entirely bogus to me. As you say - there are a wide variety of factors that could affect the density of the water (not least, temperature) that wouldn't affect your health - and contaminants at the level of a few parts per million that could kill you that would have an utterly negligable effect on density. There is no way this could work. I suspect this was a variety of snipe hunt to persuade kids not to wash their ears before the trip. SteveBaker (talk) 17:58, 14 April 2010 (UTC)

I agree that it sounds silly. Perhaps the logic behind it has to do with the amount of air dissolved in the water. Water with no air in it would be denser, I believe, perhaps causing the Q-tip to float, and this would indicate a lack of plant life, and also wouldn't support many types of animal life, some of which may be harmful to human health. So that may be where the idea came from. However, drinking water just because earwax floats in it is a really bad idea. Just assume it's unsafe and boil it or decontaminate it via another approved method. StuRat (talk) 18:48, 14 April 2010 (UTC)

wielding

what are the sparks from wielding? are they super heated metal filings? —Preceding unsigned comment added by Jonny12350 (talk • contribs) 17:06, 14 April 2010 (UTC)

Yes, they are little burning pieces of metal. By the way, that's 'welding'. Hope this helps, --The High Fin Sperm Whale 17:56, 14 April 2010 (UTC)

decarboxylation and reduction of pyruvate

Why do these steps in fermentation not yield ATP? I imagine a dicarbonyl is quite electronically strained given the repulsion between the two carbonyl carbons. Furthermore, the reduction of acetaldehyde into ethanol AFAIK is exothermic. John Riemann Soong (talk) 17:32, 14 April 2010 (UTC)

"This tape will self-destruct in five seconds"

What kinds of technologies exist that can make a message self-destruct after it has been heard? Hemoroid Agastordoff (talk) 18:31, 14 April 2010 (UTC)

If it's on computer, just erasing all copies would do the trick. The usual self-destructing casette tape shown on spy shows appears to start a small fire when the tape completes. This would be easy to do in the tape recorder, by ejecting it into a fireproof compartment containing something like match heads, striking them, and having the plastic cassette case catch fire from that. Making the tape itself self-destruct, without help from the player, would require some fancier engineering, and would also destroy the player and maybe set the house on fire. A more realistic way to blank out the tape quickly might be to subject it to a strong electro-magnet. StuRat (talk) 18:37, 14 April 2010 (UTC)

With computers it actually gets trickier unless you are talking about extremely specialized technology. There are a lot of places in a computer's memory that information can reside, and in theory it wouldn't be too hard to hijack a message-delivering program that was trying to delete itself (deny the program the permissions to delete itself, for example). --Mr.98 (talk) 18:46, 14 April 2010 (UTC)

The ultimate form of this is quantum cryptography, where, in theory, the message is physically destroyed (the quantum state is changed) upon observation. This means that no matter what one might want to do with the original version of the message, it is technically gone. --Mr.98 (talk) 18:46, 14 April 2010 (UTC)

Old fashioned way might be to make the tape of a flammable plastic and tight wrap white phosphorous into the tape five second further down the spool than the message. You would have to wrap it un an inert atmosphere but exposed to air when the tape ran on the P would start burning and set off the tape. Or on an iPod record Captain Beaky and His Band immediately after the message forcing the listener involuntarily to smash the iPod up into small pieces... --BozMo talk 19:07, 14 April 2010 (UTC)

If the listener can be trusted to destroy the tape, it could just end "Please destroy this tape within five seconds". If the listener can't be trusted, then it becomes a Digital Rights Management problem of a sort, and there's no secure way to do it because of the analog hole: that is, the listeners could just be recording the audio with a different tape recorder onto a non-self-destructing tape. In that case BozMo's solution is really the only thing that works, although I would suggest "I'm Sad the Goat Just Died Today" by The Frogs, which is so astonishingly unmusical that the destination recorder might shred the tape in protest. Or, if you're working with video, I once saw a DVD player break down thirty minutes into Max Hell Frog Warrior. Paul (Stansifer) 21:03, 14 April 2010 (UTC)

They actually did that (the first thing) in one episode. Phelps played the tape while on a rooftop and instead of the usual self-destruct notice it ended with "Please dispose of this tape in the usual manner". There was a chimney next to him and he dropped it into that to incinerate it. --Anonymous, 21:55 UTC, April 14, 2010.

I picture it dropping safely into a pile of cold ashes, only to be retrieved by the enemy, thus blowing the whole plan. StuRat (talk) 22:17, 14 April 2010 (UTC)

A message on some edible paper provides an easy way to dispose of it. StuRat (talk) 22:19, 14 April 2010 (UTC)

Physics - Safer Car

2004 Ford Crown Victoria - Police Interceptor (16 mpg) does not have Crumple zones.

Does that mean it is safer for me to drive in that?

Weight - 4157 lbs for a Sedan (Dinosaur Car aka Traditional Sedan)

Frontal Driver Rating - 5/5 Frontal Passenger Rating - 5/5 Side Driver Rating - 4/5 Rollover 2 Wheel Drive Rating - 5/5

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2004 Chevrolet Impala (20 mpg) - I think has Crumple zones.

Frontal Driver Rating - 5/5 Frontal Passenger Rating - 5/5 Side Driver Rating - 4/5 Rollover 2 Wheel Drive Rating - 4/5

Just wondering which car to buy from the Police car Auction.

Weight - 3446 lbs

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A little more information regarding the Crown Victoria which I don't understand whether is a liability or advantage during a crash:

As one of the few remaining passenger cars with body-on-frame construction (that's why it doesn't have Crumple Zones?), it is rugged, and enables repairs after minor accidents without the need to straighten the chassis – an important benefit for a car frequently used by police forces for PIT maneuvers, a maneuver in which the back left or back right corner of a fleeing vehicle is gently pushed with the front left or front right corner of the chase vehicle, disrupting tire adhesion on the fleeing vehicle with the goal of causing the fleeing vehicle to rotate and decelerate.

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I would like to have bought the Safest Car on the market right now, which is Lexus 2010 with all the new electronic safety features that take it one step towards driver-less cars. Or the Ford Taurus 2010 which has the most of the new electronic features safety features. But I am not able to afford a brand new car, let alone a "Luxury Car" such as the Lexus.

I don't need all the space afforded by the car. But because on the road there are Pick-up Trucks/SUVs/Sport Utility vehicles it makes it necessary to buy a heavier car. But I don't think buying a Pick up truck is safer, because it is more prone to roll-overs. It will be mostly only 1 person using the car i.e. no passengers or luggage.

I think people who buy very small cars - Smart Cars/Honda Fit for a higher mpg are foolish, as they will suffer severe injuries or even death if they crash with the big vehicles mentioned above (or even for that matter a mid-size vehicle like Corolla).

Since I don't have a blank cheque to pay for Gas like Police departments, I am considering 2004 Chevrolet Impala vs. 2004 Ford Crown Victoria. These are cars that are part of most police fleet, with Crown Victoria having a 80% market share.

The Crown Victoria sedan 16 mpg has a lower mpg than a Dodge Caravan SUV which is 18 mpg.

--33rogers (talk) 19:10, 14 April 2010 (UTC)

Well, in the UK the Lexus's selling point is that they combine luxury car features with family car prices. When I was buying a new car a couple of years ago, it was a little (say 15%) dearer than Toyota or Honda, but lots (say 30%) cheaper than BMW or Audi. So don't write it off. Lexus have been producing cars for some time so why not look for a used model? --TammyMoet (talk) 19:22, 14 April 2010 (UTC)

Read Driver-less_cars#Driver-assistance section, then you will see that all new safety features only the "Luxury Cars" of 2009/2010 have them, with the exception being the Taurus.--33rogers (talk) 19:37, 14 April 2010 (UTC)

Crumple Zones are a safety feature. All else being equal, you want them in your car. Of course, they make the car harder to repair after an accident, but If I have to have unrepairable damage, I'd rather it be to my car's frame and not to my own. APL (talk) 19:25, 14 April 2010 (UTC)

If nothing else changed, a car with crumple zones would be safer, in general. However, the Crown Vic is a larger car, which also gives you more distance, and thus time, to decelerate the passengers during a crash, as well as the more mass working to push smaller cars out of the way in an accident. So, which car is actually safer, I can't say. I suggest looking up the safety stats for each. StuRat (talk) 19:31, 14 April 2010 (UTC)

Just thinking, Would it be easier to maneuver a mid-size car like the Chev Impala, to prevent a crash in the first place? Should that be also a factor to consider in the decision making process? --33rogers (talk) 19:42, 14 April 2010 (UTC)

Yes, all things being equal, a smaller car will have a smaller turning radius, and otherwise be more maneuverable. However, safety features like anti-lock brakes and traction control may have a greater effect than vehicle size. StuRat (talk) 20:19, 14 April 2010 (UTC)

Regarding Crumple Zones, my theory is this: a car with crumple zone will absorb more impact of the forces in a crash? Whereas the other car Crown Vic, which has no crumple zone, will be deflecting most of the crash force impact to the other car, thus being more safer? --33rogers (talk) 19:46, 14 April 2010 (UTC)

No - folding crumple zones transfer the energy into the car - thus, away from the passengers. The car has the distance of the crumple zone in order to slow down...It's like having a few feet of brakes before the collision. Vimescarrot (talk) 19:52, 14 April 2010 (UTC)

Agreed. StuRat (talk) 20:19, 14 April 2010 (UTC)

Flashing of white tail by alarmed animals

I disturbed a Muntjac deer by the side of the road, and as it ran away it raised its short tail showing a very visible white 'signal', just as a rabbit would. When it stopped with a lowered tail it almost disapeared as the colour of its fur matched that of the floor of the wood, and if I had not seen it moving earlier I would never have noticed it.

What is the evolutionary purpose of the white tail signal? It would make it much easier for a predator (or hunter) to see it and follow it, so more likely to be eaten. How could it have evolved? I'm not sure it would even help the relatives of the alarmed animal (and hence pass on those genes even if the target animal was killed) as its running away ought to be enough to tell them to be alert. 78.149.114.89 (talk) 19:44, 14 April 2010 (UTC)

May be there was a young fawn near by that you did not notice because you had your attention atracted to the white tail? 169.139.217.79 (talk) 19:49, 14 April 2010 (UTC)

I think the idea is this:

1) The predator starts to chase they prey.

2) The prey, knowing it has been spotted, raises the tail, as there's no point in hiding now.

3) The predator fixates on the easy to see tail during the chase.

4) The prey then lowers the tail, while changing direction, stopping or otherwise hiding it's position.

5) Had the predator been tracking some other part of the prey, it might have kept it in sight, but, having tracked the tail, which is no longer visible, it loses sight of the prey animal long enough for it to escape.

From the deer's behavior, it sounds like you got the standard anti-predator treatment, which seemed to work properly. As far as the deer is concerned, it just saved itself from being eaten by you. StuRat (talk) 19:55, 14 April 2010 (UTC)

This is common in many animals - not the 'broken wing' behavior certain birds use to draw predators away from their nests. the evolutionary advantage is that a predator has a much lower chance of catching an animal that is alert to its presence, so any animal that is aware of the predator and can attract its attention lowers the risks to nearby (unaware) prey animals at minimal risk to itself. --Ludwigs2 20:17, 14 April 2010 (UTC)

I'm not sure I would have seen it running away without its raised tail, so that knocks out the logical sequences suggested above. 78.149.114.89 (talk) 22:30, 14 April 2010 (UTC)

Not really, that just means you aren't as good of a predator (at least as far as eyesight goes) as the deer thought you were. StuRat (talk) 00:32, 15 April 2010 (UTC)

Mainly because he was not a predator (he wasn't hunting was he?), but the deer didn't know that. 169.139.217.77 (talk) 01:20, 15 April 2010 (UTC)

Cryptorchidism in patients with 5-Alpha-Reductase Deficiency. [?]

I have several questions concerning people with 5-Alpha-Reductase Deficiency. The wikipedia article says that (in childhood) they are often raised as girls because their external genitals are indistinguishable from those of natal females. At puberty, however, they are identified as boys due to —among other sex characteristics— their clitorises growing into (very small) penises and their testes descending.

My first question deals with the location of said testes in a post-pubertal man with 5aRD: How far below his abdomen are said testes located (vis-á-vis a typical, adult man)? I've tried finding images of people with 5aRD —both men and children— but thus far have come up fruitless.

Also, are patients with 5aRD more likely to develop testicular torsion, cancer, and other maladies as a result of this condition? Or is there some other factor that I'm failing to take into consideration?

May these individuals be benefitting from the action of superficial veins (notably, the Great Sapphenous Vein) providing blood to their testes cooler than arterial or deep-vein blood? Has anybody looked into this? Where may one find articles and pictures of this fascinating condition? Pine (talk) 20:48, 14 April 2010 (UTC)

Cat and dog repeller

Does anyone know of any way to repel cats and dogs (and even deer) from moving vehicles on a 50 kilometres per hour (31 mph) or less road? I've seen so many cats, dogs, and deer hit on this road, I'm wondering if there's something I can affix to my car to give the little critters a fighting chance. Thanks. Viriditas (talk) 20:58, 14 April 2010 (UTC)

Do you mean to lessen the blow if you hit them, or to make it less likely they'll get hit at all? If it's the second i'm not sure there's much you could do yourself, but protective fencing would help, also more 'openess' would probably help too - I find that mostly it's animals coming out of bushes and straight onto the road is a common cause (though Pheasants do seem to be constantly suicidal no matter what you do to try stop it). ny156uk (talk) 21:53, 14 April 2010 (UTC)

Yes, I often run down peasants pheasants. StuRat (talk) 22:00, 14 April 2010 (UTC)

Those big spotlights on the roof, like on a redneck's truck, would probably give them more warning at night. However, you might cause traffic accidents and they might be illegal. StuRat (talk) 21:58, 14 April 2010 (UTC)

You could also make more noise, say by keeping the windows down and radio on. But, again, this would annoy the neighbors. Perhaps a sound that only cats and dogs could hear would be in order. StuRat (talk) 22:02, 14 April 2010 (UTC)

They make lots of products similar to these specifically for deer. I've heard some town councils in areas with deer/car problems encourage people to install them. Beach drifter (talk) 23:03, 14 April 2010 (UTC)

a little explanation Beach drifter (talk) 23:04, 14 April 2010 (UTC)

(Edit Conflict) In my experience (with deer, badgers, etc. in the New Forest, other Hampshire and Southern English locales, and in Scotland), the best way to minimize/avoid impacts is to drive slowly and very carefully, keep a constant lookout, and slow down or stop whenever necessary. Animals tend not to understand, or rapidly get accustomed to, traffic noises both usual and unusual, and extra noise-making mechanisms would be extremely irksome for local human inhabitants, should there be any in earshot. Deer in particular are apt to be dazzled by lights and and freeze (hence the illegal hunting method of lamping), and also react unpredictably to traffic, sometimes leaping into a vehicle's path at the last second; cats are also prone to this. Of course, driver caution is enhanced in the New Forest because within its boundaries all animals (including the numerous free-roaming ponies and cattle) have automatic right of way and it is a fineable offense to hit one whatever the circumstances.

Within ten miles of my own house, in the Forest of Bere, I have had at times to slow down or stop for mice, weasels, partridges, owls (who like sitting on the median line), rabbits, (domestic) cats, fox cubs (adults tend to get out of the way) badgers, deer, and what appeared to be a juvenile puma (duly reported to the Big Cats in Britain Society - what, no Wiki article?). 87.81.230.195 (talk) 23:08, 14 April 2010 (UTC)

Bear locomotion

While bears run... how do they land with their feet? heel first or toes/front part first? --Belchman (talk) 21:47, 14 April 2010 (UTC)

Mastering crystallography

Within a week, I need to master crystallography, with emphasis on X-ray crystallography, because my 4th year biochem final exam will be heavily based on crystallography. The exam will test concepts as well as applications like doing some simple calculations involving space groups, coordinates, etc. Will it be possible to master the topic within that time frame? My plan is to read the book "X-ray crystallography made crystal clear" twice while taking notes. But I found that some pages are hard to understand due to heavy mathematics. For someone like me with only Calculus 1 and 2 background to fully understand crystallography, what other better, more easily-accessible resources or webpages are there to help you master crystallography? Thanks. —Preceding unsigned comment added by 142.58.132.157 (talk) 21:55, 14 April 2010 (UTC)

See Main Page - Online Dictionary of Crystallography. -- Wavelength (talk) 23:09, 14 April 2010 (UTC)

doctors dont wear gloves

why dont doctors dont wear gloves? example http://www.youtube.com/watch?v=NMxqzZW2Z8c&feature=channel

they never do —Preceding unsigned comment added by Jonny12350 (talk • contribs) 22:32, 14 April 2010 (UTC)

The naive thought is that bare hands are always dirty and gloved hands are always sterile. But it's not always like that. Obviously a gloved hand can be dirty if it has touched something dirty. Similarly, hands can stay relatively sterile if they are washed properly and don't come into contact with anything after cleaning. An ungloved hand also can better feel nuances that a gloved hand could miss, which might be important for certain types of examination. OK maybe not for proctology exams.

Gloves also have another purpose, to protect doctors from contagions. However, a gloved hand can still be rubbed in the eyes, spreading disease to the doctor, just like bare hands. So it may come down to the only advantage of gloves being that they serve to remind the doctor not to touch his hands to anything he shouldn't. Instead, maybe a few shock treatments would make that lesson permanent. :-) StuRat (talk) 23:02, 14 April 2010 (UTC)

Wearing gloves is in most cases offers only a source of false security for the real purpose intended because they are not replaced at the appropriate time. Have you not seen restaurant workers continue to wear their gloves to protect their hands from soil when dumping trash or even cleaning the rest room? Washing hands is therefore the preferred method since one will do it more likely than replacing gloves to keep their own hands clean. 71.100.8.49 (talk) 22:53, 14 April 2010 (UTC)

Further, doctors always wash their hands upon entering any room, and after touching just about anything. Beach drifter (talk) 22:57, 14 April 2010 (UTC)

I have a disgusting story about rubber gloves. There was a janitor at a hospital who was apparently mentally retarded. They made him wear gloves when tossing out the garbage, some of which was medical waste. He then went to the cafeteria, with his gloves still on, and handled all the food at the salad bar, such as eggs, looking for "just the right one". In his mind, since he was wearing gloves, his hands were clean, so it was OK to touch the food. He was reprimanded. StuRat (talk) 00:29, 15 April 2010 (UTC)

Fractals and the structure of the brain

Is there an article or reference for any coverage or discussion of fractal based structure of the brain. As I recall by using certain chemical procedures to process the tissues of the brain a network structure is revealed that mimics either fractal analysis of blood flow through healthy or through cancerous tissue. 71.100.8.49 (talk) 22:48, 14 April 2010 (UTC)

Birds riding thermals

Why is it that some bird species can use thermals to go really high up into the sky whilst other birds appear to be completely unable? I've seen hawks and gulls riding thermals but I don't think that I've ever seen something like a pigeon, or a duck, or a starling doing the same. —Preceding unsigned comment added by 95.148.104.4 (talk) 22:52, 14 April 2010 (UTC)

Birds like hawks, vultures, pelicans, and so on have much larger wings to take advantage of rising air current, and also have a need to be spending time high in the sky, that is how they find food. A pigeon has neither the wing area nor the desire or need to soar. Beach drifter (talk) 22:59, 14 April 2010 (UTC)

Also, large birds can't fly by flapping alone, that uses too much energy when you're that big. StuRat (talk) 23:04, 14 April 2010 (UTC)

The peregrine falcon, a large bird, can use thermals to get to high altitudes then dive down by taking advantage of their weight and gravity at extremely high speeds to catch prey. ~AH1^(TCU) 23:26, 14 April 2010 (UTC)

A couple of years ago I saw a flock of geese rising on a thermal. I've only seen it the one time, and it must have been a hell of a thermal, because geese normally have to work pretty hard just to stay in the air. Looie496 (talk) 01:17, 15 April 2010 (UTC)