Wikipedia:Reference desk/Archives/Science/2009 April 17

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April 17

free dicom viewer

Does anyone know of the best free dicom viewer out there? I want one with all of the features of Osirix, but that runs on windows. Specifically I want the following features:

-A GUI interface. -Installed from an .exe file, or other autoinstaller file. -not web based (although if you find a web based one and you can help me set it up then that's fine) -Viewer supports:

 -Regular tools: cine, zoom, magnifier, pan, windowing
 -Measuring
 -ability to compare two or more images
 -ability to colour enhance the images

- 3D mpr and post processing like OSIRIX.

It doesn't have to be open source. It just has to be free of charge. I do not need a pacs server, just a full featured radiology workstation. Please help me. I've searched google for months and come up with nothing except osirix. If there is a windows version of that i'll take it!!!!!

THANK YOU —Preceding unsigned comment added by Pilotbaxter007 (talk • contribs) 00:26, 17 April 2009 (UTC)

WTF are you screaming at us? I can't help but someone who can help out may decide not to by your ALL CAPS approach. Feel free to edit your question. -hydnjo (talk) 00:57, 17 April 2009 (UTC)

Much better, thanks. I hope someone provides a satisfactory response. -hydnjo (talk) 01:44, 17 April 2009 (UTC)

NIH top 40

Where can I find a list of the top 40 NIH funded medical schools?Tuckerekcut (talk) 00:47, 17 April 2009 (UTC)

Google? --Jayron32.talk.contribs 01:02, 17 April 2009 (UTC)

Is there another explanation for Black Holes besides being dense matter from which light cannot escape?

Has anyone considered the possibility that a black hole is simply a phenomenon produced by 2 bodies, such as galaxies, moving away from each other at a combined speed that is greater than the speed of light. For instance, our galaxy may "appear" to be a black hole to inhabitants of a neibouring galaxy which is moving in the opposite direction. Acknowledging that nothing can travel faster than the speed of light it is still possible for 2 bodies to be moving away from each other at a almost twice the speed of light. The light from either body would never reach the other thereby making them invisible to each other. Would this not produce a black hole effect?

--UncleJink (talk) 03:50, 17 April 2009 (UTC)

Actually, even if two galaxies (on different sides of us) are moving away from us at near the speed of light, an observer in either one would still be able to see the other and would not see the other galaxy as moving faster than the speed of light (see this section on relativistic addition of velocities). Additionally, even if there were a galaxy we couldn't see, it wouldn't explain black holes or look like a black hole at all. It would just be something you couldn't see. It wouldn't explain any of the Black hole related phenomena that have been observed. Someguy1221 (talk) 03:56, 17 April 2009 (UTC)

We do not "see" distant galaxies because the light is red shifted. But the fact that far off galaxies are moving away from us is observed phenomenon, not just theoretical. We can observe galaxies moving away faster than light provided that they are no so far off that their light has not reached us yet. Galaxies which are too far off are beyond our observable universe. But yes, regardless of speed of our and far off galaxy, the speed of light coming from the distant galaxy will be the same. Black Hole is region of space that is within our range of observation and we cannot see light from it because light cannot escape from Black Hole due to very high gravity. It is nothing to do with speed of observer or that of Black Hole. If light not reaching us is criteria for Black Hole, then we can say we are in enclosed inside of a black hole ( which region of non observable universe) manya (talk) 05:03, 17 April 2009 (UTC)

From special relativity we know that the speed of light is the same in all frames. Starting with two planets moving away from some central point at near light speed in opposite directions, we can change to a frame where one of the planets is stationary. In this frame, any light emitted towards an observer on the stationary planet from the moving planet will still approach the observer at 'c'. So it's still going to get there, you can't out-run light. (Also, as mentioned by Someguy, the moving planet in this frame would not exceed the speed of light itself.) 129.67.117.21 (talk) 12:27, 17 April 2009 (UTC)

It is not the case that there were many observations of black holes and a theory needed to be developed to explain them. Actually, it is entirely the other way round. Black holes were predicted to exist (or at least the possibility) from the theory of gravity, and then astronomers went out looking for them. Thus there is no question of there being any alternative explanations. Although many candidate black holes have now been identified (Cygnus X-1 being the first) it would be a very rash astrophysicist who would make the claim that their existence is established beyond all doubt. SpinningSpark 13:04, 17 April 2009 (UTC)

You don't need to change reference frames to understand why your reasoning is flawed. Say you're going to the "right" at 3/4 c and an object to your "left", that's going left at 3/4 c, emits some light toward you. The light goes to the right at c, which is faster than you're going, so it will eventually reach you. In cosmology, though, what you describe is possible, and the effect is something like a black hole turned inside out—the event horizon is still a sphere, but instead of the inside being invisible from the outside, it's the outside that's invisible from the inside (and we're inside). That's still not the same as a black hole, though—there's no way to confuse the two. -- BenRG (talk) 15:00, 17 April 2009 (UTC)

In order for an object to be moving away from us quickly enough to be receding faster than the speed of light, it would be beyond the boundary of the observable universe. So we would never *detect* them in the first place (to do so would be to observe them as they were before they were created). ~AH1^(TCU) 01:16, 21 April 2009 (UTC)

Coriolis effect and sniping

In the game Call of Duty 4, there is a part where we have to snipe a guy 896 meters away. Our captain says that we should take 3 things into consideration: 1 Variable Humidity 2 Wind speed 3 The Coriolis effect My question is how does variable humidity and the Coriolis effect effect the bullet? You can read it here http://en.wikiquote.org/wiki/COD4#Cpt._MacMillan under Capt. MacMillan. —Preceding unsigned comment added by 116.71.49.171 (talk) 05:32, 17 April 2009 (UTC)

Wind is obious - it exerts a force on the bullet pushing it away. The coriolis effect is when the earth spins as the bullet is travelling, so by the time it hits the target, the bullet is now offline, even though it travelled perfectly straight, because the earth rotated relative to the bullet. Humidity reduces the density of the air, which will effect the total force of the wind and humidity.--155.144.40.31 (talk) 05:53, 17 April 2009 (UTC)

I haven't played the game, but I have had military training in long-distance shooting. Everyone has to do up to 500 meters and in special schools we go beyond that. Wind and humidity play a factor. The coriolis effect is brought up, but doesn't matter. The sights are set for distance to the target, taking the actual arc of the bullet into consideration. So, as you "click click click" the distance to the target, you are adjusting for the actual arc of the bullet. The main thing you do is adjust for windage (left and right) and then distance (up and down). If it is extremely humid, you add distance. Then, breath, relax, aim, steady, squeeze. In Call of Duty, do you have to adjust your sight left/right and up/down or do they have you just winging it by aiming a little up and a little off to the side? -- kainaw™ 06:33, 17 April 2009 (UTC)

I don't know about rifles, but the computerized control systems on long distance artillery (such as naval guns) do routinely make Coriolis corrections. Dragons flight (talk) 06:43, 17 April 2009 (UTC)

You don't adjust the sights in CoD4, you just aim a little off to the side. (Also, they don't really simulate the coriolis effect there at all, that's just patter. Ditto for the humidity. What matters is the wind (which is indicated by a flag nearby, so you can tell what direction it's blowing in, and how hard); the rest of it is just there to bring atmosphere to the scene. It does the trick, too.) -- Captain Disdain (talk) 10:23, 17 April 2009 (UTC)

Setting the distance isn't enough to account for the coriolis effect - you need to know what direction you are firing in as well. The maximum acceleration due to coriolis effect is velocity*angular momentum (but rotated 90 degrees). If we take a muzzle velocity of 1000m/s (and assume it doesn't slow down during travel, which isn't realistic, but nevermind) and the mean angular velocity of the Earth (from Earth's rotation) of 7.2921150 × 10⁻⁵ radians per second, we get a coriolis acceleration of about 0.07m/s². If the target was 1000m away, the bullet would take 1s to get there, resulting in a deflection of 35mm. That's a noticeable amount (although it's an overestimate in most cases), but probably far less significant than the wind. --Tango (talk) 11:15, 17 April 2009 (UTC)

You also need to know your latitude. Algebraist 11:38, 17 April 2009 (UTC)

The Coriolis effect does not exist when firing due east or due west. It has maximum effect when firing due north or due south. It has intermediate effect when firing at directions in between. – GlowWorm.

GlowWorm, that's not right. To eliminate the coriolis effect you would have to shoot paralel to the earth's axis. That would be firing along the north-south direction with an upward (or downward) inclination identical to the local latitude. If you forget about the vertical component of the coriolis force (which gets masked by gravity anyways), the coriolis effect is identical in all horizontal directions. Dauto (talk) 19:02, 17 April 2009 (UTC)

I don't see that, Dauto. If a gun is north of the equator and fires due north at a target due north of it, the gun and the target are both on the same line of longitude. During the flight of the shell the target moves to the east. So does the line of longitude. So the shell will land west of the target. This is tricky to think about. Am I wrong? – GlowWorm. —Preceding unsigned comment added by 98.16.66.104 (talk) 01:23, 18 April 2009 (UTC)

Yes, you are wrong. In the nothern hemisphere the coriolis force will deflect the bullet towards its right. If you shoot towards the north the deflection will be eastward. That happens because as it moves towards the north it is actually approachingthe earth's axis. from the equation for the speed of an object in circular motion $v=\Omega R\,$ we see that the bullet is actually moving eastward faster than the target (larger $R\,$) and that's why it appears to be deflected eastward. Dauto (talk) 05:11, 18 April 2009 (UTC)

Wouldn't it also have an effect on an east-west shot? Not because it's going off target to one side or the other but because the bullet is traveling slower or faster relative to the target. So if you're shooting eastward, the target is coming at the bullet as the bullet is moving towards the target. Therefore, you don't need to aim as high. Right? Dismas|^(talk) 05:19, 18 April 2009 (UTC)

Yes, there's a second effect but your description of it is also incorrect. Due to the earth's rotation, in a referential attached to the earth's surface there is a centrifugal force. We don't notice that force because it gets included into our perception of the gravitational force as the earth itself deforms under the influence of that force becoming a little flat (Yes a small fraction of what we perceive as gravity is actually centrifugal force). If you now shoot a bullet eastward, that bullet will be rotating around the earth's axis faster than objects attached to the earth's surface, creating an extra centrifugal force. That extra centrifugal force is not included in the local gravity force and must be perceived as a new force pushing the bullet away from the earth's axis. This force has both a vertical component upwards (that is an effect in the opposite direction to the one you incorrectly described) as well as a horizontal component southward. If you shoot the bullet westwards, you get the opposite effect and end up having an extra force with components downward and northward. This effect I describe now together with the one I described earlier are included under one umbrella as the coriolis effect. If you ignore the vertical component of the coriolis effect, you will see that between the two effects there is always a force towards the right of the direction of the movement of the bullet (in the nothern hemisphere). Moreover, this horizontal component of the coriolis force turn out to have the same magnitude independently of which direction you shoot the bullet. Neat uh? Dauto (talk) 06:40, 18 April 2009 (UTC)

The vertical component of the Coriolis effect is also known as the Eötvös effect. There is a discussion of various factors affecting the ballistics of projectiles in our article on external ballistics. Gandalf61 (talk) 11:32, 18 April 2009 (UTC)

So all in all the answer to the original question is its just patter for the Game(wind is the main issue)....and after 1000m a 35mm move of the rnd should not make a diffrence as you aim center of mass. 896m shot would produce less say a 27mm move of the rnd from the center mass of a human with a >50 CAL weapon(most suited for the distance and the job) wont make the slightest diffrence to the out come of the shot the guy would be dead(see u-tube exploding people from afghanistan when hit with .50 rnds) Only James bond kills somebody from 100 miles with a head shot. 1000m is center of mass if your trying to kill/assassinate there for Coriolis effect does not really apply, unless dealing with long range artillary.

In real life, ask the instructor. Wind... of course, humidity, yes, it changes the density of the air, so the bullet will slow down, and the coriolis effect will indeed make you hit another target's head at 900m or more if they are too close. Also, is true, the best way to snipe is to do it west-east or east-west, and from a top position so you dont have to correct the vertical angle, and btw, you dont need to be a math expert to take the shot, the experience and a plastic board with some parameters/data used to adjust the scope will help on the task. Elgatoduro (talk)

How can dumb electrons be so clever?

The behavious of things like for example electrons are described by complicated maths formulas, that require a high intelligence and a good education to understand. So how come a little electron knows how to behave? They cannot have computers hidden away inside them. 78.146.249.32 (talk) 11:12, 17 April 2009 (UTC)

They don't have to think how to behave. Their behavior is guided automatically according to the laws of physics, which we are still trying to decipher. It is like we have to calculate with what velocity and initial angle an object has to be launched to reach a certain distance according to the laws of physics, but when the object is actually launched, it (the object itself) doesn't calculate in the beginning of launch how far it has to go. It has no other choice but to reach that distance because it has no control over itself, it cannot think and react. It has to obey the laws of physics. For the projectile motion, those laws are simple. For describing electrons, they become complicated and require sophisticated mathematics and high intelligence. But the analogy still holds and electron having no other choice and no control over itself has to behave the way the laws of nature demand it to. - DSachan (talk) 11:22, 17 April 2009 (UTC)

And what's the problem with saying that? Your question is like asking 'when I let go of a stone, how does it know it's supposed to fall?' It just do. Dauto (talk) 14:05, 17 April 2009 (UTC)

Thats like saying "they just do". 78.146.249.32 (talk) 12:03, 17 April 2009 (UTC)

Yes, that's exactly what he meant. You've got two alternative explanations here. 1) They just do 2) They were designed that way by someone or something that created them. But whichever it is, electrons don't need to be intelligent to do this, any more than a rock needs to be intelligent to know that it should roll downhill. DJ Clayworth (talk) 14:01, 17 April 2009 (UTC)

Actually, the behavior of an individual electron is not all that complicated, the problem with the calculation of their movement comes in when you have many subatomic particles acting together and influencing each other in a non-linear fashion. Truthforitsownsake (talk) 14:08, 17 April 2009 (UTC)

Some very complex-appearing behavior can arise from very simple rules. For example, Conway's Game of Life consists solely of rules simple enough that an 8-year-old can follow them. Yet from these rules you can get crazily complex behavior which would be difficult for people to explain. That's not unique to the GoL. Other simple rulesets show similarly complicated results (see Cellular automaton). Now, I'm not claiming that the behavior of electrons is the result of emergent behavior: what I'm saying is that electrons are following what are to them very simple rules (e.g. "move to a lower energy state"), but because of how these rules are constructed and how they interact with the environment, the overall behavior of the electrons appears very complex to us and requires complex math to represent because we don't "see" the world the same way an electron does. -- 128.104.112.117 (talk) 23:47, 17 April 2009 (UTC)

Also, the electron doesn't "know" how to behave. The OP is putting the cart before the horse here. We invent mathematical equations to model the behavior of electrons. But the equations don't tell the electron how to behave, they tell US how the electron will behave. The electron would continue to do what it did even if we didn't try to figure it out... --Jayron32.talk.contribs 02:19, 18 April 2009 (UTC)

As for the cellular automata, you might also be interested in Calculating Space and digital physics. These are theories that describe our universe as similar to a cellular automaton and thereby try to explain your problem of the intelligent dumb matter. 84.174.85.135 (talk) 11:04, 18 April 2009 (UTC)

78.146, how do you behave at any given moment? You have a set of forces pulling you through life and at each instant you respond to those forces. Sometimes certain forces are stronger than others. Sometimes you do dumb things (so there goes your argument of having intelligence) - but you do those dumb things because local forces caused you to act that way. Other times you do smart things - but only because other forces drew you that way.

You are an electron, and an electron is you. You both respond to a complex set of inputs and neither of you have a "computer" (well, you have a brain, but it uses electrons to act). On a semi-related topic, see The Tao of Physics. Franamax (talk) 23:46, 18 April 2009 (UTC)

bodybuilding

hi everybody and thanks for reading this .. my question is : what are the negative results I can get from bodybuilding ? Does it have any negative effects on hormones and sperms ? —Preceding unsigned comment added by Sha9law0 (talk • contribs) 11:43, 17 April 2009 (UTC)

You should talk to an expert about that, rather than random people on the internet. If you are a member of a gym, they will probably have personal trainers that can advise you. We have an article, Overtraining, which might answer some of your questions, but don't rely on us when your health is at risk. --Tango (talk) 12:01, 17 April 2009 (UTC)

A normal and healthy human can do heavy exercise -- including bodybuilding work -- with no adverse effect on hormones or sperms. Unfortunately, many professional-level bodybuilders have cheated with anabolic steroids, which can have serious negative effects on both hormones and sperms. --Sean 14:22, 17 April 2009 (UTC)

I'd like to see some sources if you're going to make such claims. I don't deny of course that anabolic steroids seriously screw up your body and are one of the reasons many body builders suffer serious adverse effects. However while the human body is very good at compensating, it seems a fairly extreme claim to me that there will definitely no adverse effects on hormones or sperm from body building. Presuming we're talking about quite hefty body building, the exercise and diet can itself have some fairly major effects and it seems unlikely to me that these will have no effect (positive or negative) on your hormones or sperm (or for that matter other bodily functions). This doesn't mean I believe your going to go infertile from body building, simply that there's a difference between saying it will have no adverse effects and saying that it's unlikely to have extremely detrimental effects Nil Einne (talk) 22:23, 17 April 2009 (UTC)

I agree that I should have qualified what I said. I was thinking of a sensible amount of bodybuilding, but I agree that an absurd amount of bodybuilding could very well affect the sperms, for some definitions of "sensible" and "absurd". --Sean 22:47, 18 April 2009 (UTC)

Consult an exercise physiologist. Wisdom89 _{(T / ^C)} 16:46, 17 April 2009 (UTC)

If you take steroids, obviously there are tremendous negative effects. If you don't, the major negative effects probably come from the huge amounts of food you have to eat to do top-level bodybuilding, and the heavy weighting of the food toward protein. There's also a problem in that bodybuilders are sometimes so musclebound that they have difficulty doing ordinary activities. Looie496 (talk) 18:19, 17 April 2009 (UTC)

You should also consider what else you would be doing with all your time that you would be spending in the gym. Will it stop you working or ruin your social life, or stop you having time to edit Wikipedia? There are also injuries resulting from improper use of equipment. Graeme Bartlett (talk) 22:01, 17 April 2009 (UTC)

Questions on cell size and multicellularity

What limits the size of a living cell? Why don't we see (for e.g.) cells the size of a dog?

Do prokaryotic cells show multicellularity? I know they form colonies, but do individual cells show division of labor/specialization? If not, why not? —Preceding unsigned comment added by 121.241.167.100 (talk) 12:56, 17 April 2009 (UTC)

One thing that limits cell size is the way that cells function. Cells require a large surface area to volume ratio. Now while technically, you could still have very massive cells with the same surface area to volume ratio, the structure would be such that the cell would pull itself apart from gravity. 65.121.141.34 (talk) 13:25, 17 April 2009 (UTC)

¡Grande!

Cells can get bigger than a dog! A Hypselosaurus egg (which, assuming it's like modern eggs, is a single cell) could reach a foot in length, larger than the dog at right. You could probably find an ostrich egg bigger than some dogs. And even the biggest dog has a nerve cell that runs from the tip of its tail to its brain, which is pretty long, if not "big". Also, see the discussion regarding division of labor here. --Sean 14:38, 17 April 2009 (UTC)

I do not believe that large eggs are just one cell. I think thats a myth. For one thing, they would have terrible problems with the celluar equivalent of respiration, as their volume to surface area ratio would be very much different from a normal cell. 78.149.194.28 (talk) 18:26, 17 April 2009 (UTC)

To clarify the common misconception. Ova, that is the female gamete colloquially known as "eggs" are a single cell. Actual eggs, certainly are NOT. No ova I know of are larger than microscopic for any species. The largest cells are still likely nerve cells, as mentioned, there have been some documented to be several feet long; even given their thinness, that still makes them quite sizable. --Jayron32.talk.contribs 19:34, 17 April 2009 (UTC)

That's interesting, Jayron32. So, you're saying that our article, which you cited, propagates this misconception in saying, "The ovum is the largest cell in the human body, typically visible to the naked eye without the aid of a microscope or other magnification device". Maybe you could clarify? --Scray (talk) 20:40, 17 April 2009 (UTC)

Also, from our Egg (biology) article, "The 1.5 kg ostrich egg contains the largest existing single cell currently known...". Seems we really have a contradiction here. --Scray (talk) 20:44, 17 April 2009 (UTC)

Yeah, OK, so the human ova is a bit larger than microscopic. But really, only a bit. And the canard that an egg is a single cell misrepresnts what a cell is. It doesn't have organelles, it doesn't contain a cell nucleus or anything like that. Its basically a big sac of amniotic fluid and surrounding a smaller sac of nutrients to provide fuel for the growing embryo. Our article is actually probably wrong here. It calls avian and reptilian eggs "zygotes" That makes no sense. If the zygote develops into the embryo, then why is the egg still here?!? So yes, I will buy that the ovum is the largest cell in the body. But a chicken egg is still not a "cell", unless you redefine what a cell is to mean "everything that a cell is, and eggs too". --Jayron32.talk.contribs 02:15, 18 April 2009 (UTC)

So are you saying you believe that an egg lacks organelles and a nucleus? --Scray (talk) 03:48, 18 April 2009 (UTC)

I just re-read your comment, and realize that you're specifically referring to the avian/reptilian yolk and albumin as lacking a nucleus and organelles. All right, I'll agree with that as a generalization. BTW, "ova" is plural, "ovum" is singular. --Scray (talk) 03:57, 18 April 2009 (UTC)

Another note: Caulerpa may be the largest cell by surface area; it's multinucleated. By longest dimension, the largest cell may be the neuron of the giant squid. --Scray (talk) 04:19, 18 April 2009 (UTC)

One more note: the Squid giant axon (not specific to giant squid - it's just a giant axon) can be 1 mm in diameter - a diameter easily visible to the naked eye; with a length that can be measured in meters, this is a huge cell. --Scray (talk) 16:40, 18 April 2009 (UTC)

The article correctly states not that an egg is a single cell, but instead it states that the ostrich egg contains the largest known single cell. So, tell me Jayron, If the yolk of the egg is not that cell, where's the cell? Dauto (talk) 04:55, 18 April 2009 (UTC)

To clarify I interpreted big as weight, and dog as a standard medium sized dog. 65.121.141.34 (talk) 16:08, 17 April 2009 (UTC)

As to division of labour, there is the awesome dictyostelium - but it's a eukaryote. :( As far as the "why not" bit goes, I'm not sure that lack of a nuclear membrane is the defining factor in how cell specialization works, it comes down in the end to appropriate communication. Perhaps prokaryotes don't adopt this strategy because they've never had to? There are many paths to evolutionary success. I can't think of any definitive (published) reason why a prokaryote couldn't do the same thing. Interesting question though - there's my whole afternoon shot now! :) Franamax (talk) 20:38, 17 April 2009 (UTC)

Myxobacteria form "swarms" that travel together. This is the closest that prokaryotes come to "division of labour". Axl ¤ [Talk] 17:30, 18 April 2009 (UTC)

From McGraw-Hill's Encyclopedia of Science & Technology: "The largest known single cells of a living animal are the mature ova of the ostrich and the shark Chlamydoselache, which are about 3 in. (8 cm) in diameter." Axl ¤ [Talk]

Bullet into wood

Suppose I shoot a bullet into a block of wood, knowing the velocity and mass of that bullet. How could I estimate the final resting position of the bullet? What other information would I need to know? 58.6.129.205 (talk) 13:42, 17 April 2009 (UTC)

I don't know the exact answer to your question, I'll leave that to our resident physicists, but I think you'd need to know the distance of the wood from the initial position of the bullet (in the gun), and the strength of the wood involved. Both these factors would have a large role to play in how far the bullet can penetrate the wood. Regards, --—Cyclonenim | Chat  13:54, 17 April 2009 (UTC)

(ec)Our article on Penetration (weapons) sadly doesn't provide any information. This webpage [1] gives an equation by the 19th century French engineer Jean-Victor Poncelet, and a calculator to plug your own numbers into, which may be of use (Note that one of the users of the page spotted an error in the Java script for the calculator, hard to tell if it's been fixed). I presume that the various constants quoted would vary depending on the type of wood, orientation of the grain etc. Mikenorton (talk) 14:05, 17 April 2009 (UTC)

Looking again at those constants, C₀ looks like compressive strength and C₁ must be the density of the material. Mikenorton (talk) 14:25, 17 April 2009 (UTC)

One questionably-useful data point from personal experience. A plain old lead round-nose .22LR round will penetrate a 2x4 of plain old lumber (I think probably pine, but I'm not sure.) However a 2x4 of weather treated wood will stop the same bullet. Clearly, the density and strength of the wood is a factor. Also consider bullet shape and cross-section. A smaller, more pointed bullet will penetrate most materials better than a bigger, blunter bullet. This sounds like one for Mythbusters- I imagine trying to estimate this is more complicated than simply performing some tests. Friday (talk) 14:09, 17 April 2009 (UTC)

PS. (I mean penetrate the short way, not the long way. I don't remember trying it the other direction.) And the poster above brings up a good point about grain orientation- if a bullet can slip in between things, this is going to take less energy out of it than having to blast through things. Friday (talk) 14:11, 17 April 2009 (UTC)

Pressure-treated lumber is often a lot wetter than non-PT stuff, which I imagine accounts for the difference you saw. --Sean 14:48, 17 April 2009 (UTC)

My dad said (WP:OR) that a 22 long would go an inch and a half into the end of a 2x4, farther than I would have supposed. I know that a 22 LR will penetrate seasoned 1x lumber (something over 3/4 inch thick: very old boards) and richochet around inside the building a couple of times, from shooting at an unoccupied farm outbuilding I owned, so it did not have the velocity to penetrate the 1x board on the far side of the building. Milage may vary depending on muzzle velocity, distance to target, mass and jacketing of bullet, and type of wood, grain orientation,angle of impact, and seasoning of the wood. Snipers, assassins, CSIs and police must have some empirical data. Edison (talk) 16:06, 17 April 2009 (UTC)

Myth Busters had a show where they shot a gun into a box of jello. Maybe you can find a re-run somewhere. 76.97.245.5 (talk) 10:36, 20 April 2009 (UTC)

Paradox

One of my friends asked me this, and i just can't figure it out. Somebody please help me!! Proof that unicorns exist
For me to prove that unicorns exist, it is enough if i prove that there exists at least a single existing unicorn(possibly a more stronger statement). so there are 2 cases

1. There exists an existing unicorn
2. There exists no existing unicorn

But how can an existing unicorn not exist ? So statement 2. is false, so statement one has to be true. Therefore, unicorns exist. —Preceding unsigned comment added by Rkr1991 (talk • contribs) 15:19, 17 April 2009 (UTC)

I don't think there's a paradox so much as a silly phrase. What is the distinction between "unicorn" and "existing unicorn"? If you strip that word, then the choices of "at least one unicorn exists" and "no unicorns exist" is quite clear. In this specific case, it looks like "existing" is used to mean living. Again, though, swap the word and there's no contradiction. — Lomn 15:25, 17 April 2009 (UTC)

You almost convinced me! Nice. Isn't the joke based on a shift from "there exists no existing unicorn" to "there exists a non-existing unicorn", that is not exaclty the same statement. pma (talk) 15:42, 17 April 2009 (UTC)

Listen here (for your friend). A contradictory object does not exist, but also, any object that does not exist may well have a contradictory property: this can be harmlessly assumed, for it does not exist. A contradictory property for a non-existent object is, of course, existence. Therefore a non-existent object enjoys the property of existence, so it exists pma (talk) 16:23, 17 April 2009 (UTC)

Assuming you don't just have a fetish for horses with strange frontal growths, you chose to discuss unicorns because they are objects which by definition do not exist. Any proposition in which they exist is wrong before it leaves the unicorn paddock. --Sean 16:42, 17 April 2009 (UTC)

Take it from me. If unicorns existed, my wife would own one. Paradox resolved.--UncleJink (talk) 16:43, 17 April 2009 (UTC)

A silly play with words does not a paradox make. Said that, who is to say that unicorns do not exist? Any animal with one horn fits the bill. Dauto (talk) 17:19, 17 April 2009 (UTC)

It's pretty nonsensical. "Existing" is just an adjective - it's like "Blue" or "Pointy" - if I put the phrase "existing unicorn" in quotes then either there is an "existing unicorn" or there is no "existing unicorn" - which is clearly a true statement - just like either there is a "blue unicorn" or there is no "blue unicorn". But in any case - even with your interpretation - the two sentences are only "obviously true" when you interpret "existing" like you'd say "blue". Otherwise I can make paradoxes all day long by saying things like:

Either:

1. There are pink unicorns ...or...
2. There are green dragons

That's not a paradox - it's a set of statements that are simply false. So if you insist on this rather crazy interpretation of "existing unicorn" then you simply invalidated the entire statement by turning it into "Either unicorns exist or unicorns exist"...which is false. SteveBaker (talk) 17:41, 17 April 2009 (UTC)

This sounds a little like a play on the Black Swan Problem? Though I could be wrong as i don't fully understand why their statement is supposed to be a paradox. I could sort of read it similar to the Rumsfeld statement about there being known knowns and known unknowns, and unknown unknowns? (http://www.brainyquote.com/quotes/quotes/d/donaldrums148142.html). But at least Rumfeld's made a bit of sense. 17:55, 17 April 2009 (UTC)

I would say this is clearly a play on the ontological argument for the existence of God. It runs: Define God as a being that is best in every way. Clearly it is better for God to exist than not to exist. Therefore God exists. Vast tracts of philosophy have been written to argue about the validity of this argument. Looie496 (talk) 18:14, 17 April 2009 (UTC)

Me too, I thought to the logic-ontologic trick, but in fact it's not exactly the same... It seems to me that this one is more linguistic than logic.--pma (talk) 20:02, 17 April 2009 (UTC) As to Rumsfeld I thi(self censored).

Rumsfeld was a monst(self censored) but I think he made an very perceptive point and got screwed over for it. There really are known-unkowns and unknown-unknowns! Now, the context of his pontification, that was incredibly (self censored) and dismissive of (self-censored) and repugnant to every (self-censored). I do appreciate that contribution to world thought though, flawed as its presentation may have been. Franamax (talk) 20:55, 17 April 2009 (UTC)

Surely nonexistence is purer and thus arguably "better" than existence. —Tamfang (talk) 23:03, 23 April 2009 (UTC)

To offer a poor paraphrasing of Kant: "existence is not a predicate". There's a discussion of this kind of argument in a religious setting here[2]. 163.1.176.253 (talk) 23:17, 17 April 2009 (UTC)

Sorry, of course this has been mentioned before by Looie496. Right here. 163.1.176.253 (talk) 23:26, 17 April 2009 (UTC)

This is discussed in one of the Smullyan books but I'm too lazy to look up which one even though I have them at home. Sorry. – b_jonas 18:30, 18 April 2009 (UTC)

I think this is a case of Equivocation. A classic example:

1. Nothing is better than eternal happiness.
2. A ham sandwich is better than nothing.
3. Therefore, a ham sandwich is better than eternal happiness.

The problem is that two different meanings of "nothing" are equated. I think the same thing is happening in your example, where two related but separate meanings of "existing" are being equated. The first "exists" in context means "the concept which follows has veracity", whereas the second "existing" means "is present in a tangible form". Stated slightly differently, the "There exists" in "There exists no existing unicorn" is an idiomatic phrase meaning "There is such a thing as a ...", with the "no" modifying the verb: The sentence "There exists no happy clown" means "There is no such thing as a happy clown". If we use that rephrasing, the "paradox" becomes:

1. "There is such a thing as an existing unicorn"
2. "There is no such thing as an existing unicorn"

This phrasing completely resolves the paradox. The use of "exists" instead of "is such a thing as" is a snowjob on the part of the paradox writer. -- 128.104.112.117 (talk) 23:09, 20 April 2009 (UTC)

statement 2 is true: there exists no existing (imaginary) unicorns. statement 1 is false Osip7315 (talk) 04:44, 28 December 2009 (UTC)

positron behavior

dear sir

what will happen when we put a positron in an electrostatic field?

does positron behave like an electron or as proton?

if we put an electron and positron together. do they attract each other or repel?

please give confirm answer.

thank you

anant ranjan —Preceding unsigned comment added by Ranjan.anant (talk • contribs) 18:08, 17 April 2009 (UTC)

Positrons have positive electric charge (hence the name) and will therefore attract electrons. Dauto (talk) 18:15, 17 April 2009 (UTC)

In an electrostatic field, a positron will not move in the same way as either an electron or a proton. It will feel the same force as a proton, but because it's a lot lighter than a proton, it will move along a different path. Looie496 (talk) 18:59, 17 April 2009 (UTC)

And as the antiparticle counterpart to an electron, a positron will annihilate when it encounters an electron (as does the electron). So you get a (comparatively) big boom. — Lomn 19:01, 17 April 2009 (UTC)

Super long leg hair

File:SmartseLeg hair.jpg

A close up shot of the hair in question with normal hairs for comparison

I have one 10cm long leg hair (not quite a world record, see here) why has this one hair grown so long? It's a lot thinner and whiter than my other leg hairs. Any ideas? Smartse (talk) 19:26, 17 April 2009 (UTC)

It's possible that it was ingrown at one point. In order to pierce the skin, it added more keratin.130.127.99.54 (talk) 20:11, 17 April 2009 (UTC)

I've added a photo in the hope it helps. Smartse (talk) 16:29, 18 April 2009 (UTC)

I've got a very fine, long, white hair on the side of my forehead, which I doubt was ingrown at any time. It grows back after plucking. --Kjoonlee 17:13, 18 April 2009 (UTC)

Redox reactions and Lewis Acids & Bases

If an oxidizing agent gains electrons, does that make it a Lewis Acid? Similarly, if a Lewis Base donates an electrons, is it also a reducing agent?130.127.99.54 (talk) 20:16, 17 April 2009 (UTC)

Not really. A Lewis Acid-Base reaction is a covalent bond formation reaction. And its a specific kind of covalent bond formation reaction. Remember that a chemical bond consists of two electrons. Under most reactions, one usually thinks of each atom on either side of the bond donating one electron to make a two-electron bond. Kind like this:

X• + •Y → X—Y

However, in a Lewis Acid-Base reaction, in the formation of the new bond, BOTH electrons come from one of the reactants. Thus, a Lewis Acid-Base reaction always looks like this:

A + :B → A—B

In this case, the A is the "acid" and the B is the "base". A Bronsted-Lowery acid-base reaction is thus a special case of the Lewis reaction, where A is ALWAYS the H⁺ ion. But the more general Lewis Acid-Base reaction encompases a whole lot of other scenarios, such as the following reaction:

F₃B + :NCl₃ → F₃B—NCl₃

In this case, the boron compound is "electron deficient", that is it has an empty orbital, or if you prefer, less than a full octet, which makes it an ideal "lewis acid". The nitrogen compound has a spare, unbonded pair of electrons, which makes it an ideal "lewis base". The thing about this is, unlike other acid-base theories, Lewis theory doesn't even deal with "H⁺" ions at all.

Now, redox reactions involve the transfer of electrons from one element to another, without necessarily forming any new bonds. For example, if you add say a piece of magnesium metal to a solution containing Copper (II) ions, you will get the following redox reaction to occur spontaneously, forming magnesium ions and copper metal:

Mg_(s) + Cu²⁺_(aq) → Mg²⁺_(aq) + Cu_(s)

No new covalent bonds have formed. What happened here is that two electrons were transfered from the magnesium to the copper. So you see, though both types of reactions involve the rearangement of electrons in some way, they are very different sorts of reactions. Actually, EVERY chemical reaction involves the rearrangement of electrons in some way, so these two types of reactions are not all that unique in that regard. I hope this makes a little more sense. You may want to read Lewis acids and bases and Redox for more on these processes in general. --Jayron32.talk.contribs 02:07, 18 April 2009 (UTC)

Nephilim

Is this real or is it photoshopped?

http://www.luisescobarblog.com/wp-content/uploads/2008/06/nephilim-skeleton.jpg

--Threebears2000 (talk) 23:22, 17 April 2009 (UTC)

It's a well-known fake. Looie496 (talk) 23:48, 17 April 2009 (UTC)

And a poorly done one too. Look at where the light is falling on the skull - only the front part is bright, the top and sides are in shadow. Now look at the shadow of the guy right next to it - the sun is falling on his back - so the skull should be brightly lit from it's right side...and it's not. SteveBaker (talk) 20:04, 19 April 2009 (UTC)