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May 9

Neanderthal genes in modern humans

I read here that I may be partially Neanderthal. What I don't understand is how it is possible that you could only have a small nonzero Neanderthal contribution to the human genome. I mean, the scientists are surprised that it seems to be as large as 1% to 4% instead of a much lower number or zero. But how can any nonzero Neanderthal contribution to someone's DNA be less than an entire chromosome? Count Iblis (talk) 00:23, 9 May 2010 (UTC)

Chromosomes come in pairs, and the two members of a pair can swap parts via the process of chromosomal crossover. After a sufficient number of generations you get a very high level of mixing, even between parts of a single chromosome. Looie496 (talk) 00:35, 9 May 2010 (UTC)

(edit conflict)I think, emphasis on that, that they are referring to the original DNA that is left in your DNA. Clearly when the Neanderthal mated with a Homo sapien, they're contributing chromosomes, but over time this DNA is going be diluted with new DNA from other Homo sapiens. I think I explained that badly. In short, the 1% is the remaining original Neanderthal DNA. Regards, --—Cyclonenim | Chat  00:37, 9 May 2010 (UTC)

Yeah, Looie explains it better. Regards, --—Cyclonenim | Chat  00:37, 9 May 2010 (UTC)

What confused me (speaking as someone who almost failed high school biology), is that since we have 46 chromosomes, I would have thought that the smallest (non-zero) amount of neanderthal DNA we could posses is 1/46th. Does this "chromosomal crossover" that Cyclonenim mentioned mean that two parents can have more than 2^46 different possible offspring? 24.68.41.132 (talk) 02:55, 9 May 2010 (UTC)

Yes. Nil Einne (talk) 08:41, 9 May 2010 (UTC)

The first-generation offspring will have 23 chromosomes that are "all-neanderthal", and 23 chromosomes that are "all-modern-human". The number of possible neanderthal chromosome combinations that the neanderthal parent could transmit to the child is a lot greater than 2²³, due to recombination between the two variants of neanderthal chromosomes that the neanderthal parent has inherited from the neanderthal grandparents. Likewise of course with the human parent. When the hybrid child grows up, and starts producing reproductive cells, there will again be recombination between the pairs of chromosomes, but now the recombination will occur between a neanderthal-derived chromosome and a modern-human-derived chromosome, resulting in chromosomes that are partly derived from neanderthals and partly derived from modern humans. If the hybrid's children continue breeding with modern humans, the neanderthal contribution to the genomes of their offspring will be diluted. However, if some of the neanderthal genes turn out to be advantageous, natural selection will ensure that these are not lost. --NorwegianBlue ^talk 09:57, 9 May 2010 (UTC)

Thanks for the answer everyone! (I should have kept biology on my high school curriculum, I guess). So, how fragmented will the Neanderthal genetic material be in the modern population? I roughly estimated this as follows. Suppose that I have a Neanderthal gene on one of my chromosomes, orginating from a hybrid that lived 60,000 years ago. Then, if I understand this article correctly, on average two genes separated by a million base pairs will have a P = 1% probability of being separated in the next generation. So, the probability of a gene that is L*10^6 basepairs away not being separated after N generations is (1-P*L)^N, which is valid for L not much larger than 1. If I take N = 3000 and equate the probability to 1/2, I find L = 0.023. So already at a distance of 23,000 basepairs there is a 50% chance of separation. Count Iblis (talk) 14:56, 9 May 2010 (UTC)

Natural selection is not random. 67.243.7.245 (talk) 15:16, 9 May 2010 (UTC)

Yes it is! SteveBaker (talk) 16:09, 9 May 2010 (UTC)

This is actually a misconception about natural selection. The process wherein DNA mutations occur is random, as is the combination of genetic information from one's parents. However, as DNA encodes physiology and behavior, these two random process have consequences in the environment, which means genetic information is subject to nonrandom processes of selection. Over time, the genes that encode for physiology and behavior that work best in a given environment persist at a greater frequency than those that don't; this is natural selection.

Bringing it to the subject at hand, this means that if any Neanderthal genetic information has environmental consequences (including those from the social environment), then there would be non-random influence on populations descending from such intermixing. For example, if the Modern-Humans who came to Europe after Neanderthals had very dark skin, then they would have difficulty producing vitamin D; relevent genetic information from the native Neanderthals, who surely would have already acquired lighter skin, would thus be favored over generations. — Ƶ§œš¹ _{[aɪm ˈfɹ̠ˤʷɛ̃ɾ̃ˡi]} 19:17, 9 May 2010 (UTC)

So a random frog mutates and gets the gene for eternal life and for being irresistable to frogs of the other sex - but is eaten by your pet cat just one hour before it reached maturity and passed this remarkable gene onto the next generation. OF COURSE IT'S RANDOM!!! SteveBaker (talk) 23:51, 9 May 2010 (UTC)

Does eternal life mean that the frog is more likely to survive and pass on its genes in this particular environment? I don't think so, but even if it did, it's not a guarantee. Advantagious changes usually only give a slight advantage over others. If natural selection were random, then there would be nothing pushing species to adapt to their environments.

Keep in mind that when there are no selective pressures on a given set of DNA, it is subject to genetic drift, which is also random. — Ƶ§œš¹ _{[aɪm ˈfɹ̠ˤʷɛ̃ɾ̃ˡi]} 01:22, 10 May 2010 (UTC)

(Edit Conflicts) But in that example, Steve, natural selection hasn't occurred, because it never had a chance to. The selection happens over generations, after one or more frogs have (semi-randomly) mutated that gene and successfully introduced it into the frog gene pool, when nature/the environment (including pet cats) operates on it (or more accurately its phenotypic expression(s)) and selects for or against it. Individual carrier frogs may well be subject to random accidents (ones not related to the genes' effects), and others to random 'good fortune', but the effects of these will average out in the gene pool as a whole, so the selection pressure on that gene is the opposite of random. Compare it to Monopoly where, although individual moves are affected by the limited randomness of dice scores (e.g. you can't score 1 or 13), a skilful player will still usually beat less skilful ones in the long run, though he/she might still be wiped out by unusual events. 87.81.230.195 (talk) 01:49, 10 May 2010 (UTC)

Steve, your frog example is not random. it is stochastic. These are two different things. Natural selection is not random. Dauto (talk) 05:38, 10 May 2010 (UTC)

I suggest you look up the word "stochastic" in the dictionary. Wiktionary provides just one meaning - it says "stochastic: Random, randomly-determined.". Randomness that tends to average out in the long run is still random. There is still always the possibility that a thousand species of genetically perfect dinosaurs get wiped out by a random meteor strike. SteveBaker (talk) 16:20, 10 May 2010 (UTC)

If, over thousands of generations, a species changes to adapt to its environment, then that change itself can't be random. At the individual level, the advantage of beneficial genes is much smaller than it is at the group level over generations. Your examples seem to assume that environment is irrelevent when it comes to fitness. In your frog example, the most advantagious genes are the ones that make frogs cat resistant. In your dinosaur example, the meteor strike has altered the environment so drastically that the genes that didn't fit the new environment didn't survive. When the environment changes drastically and none of the individuals in a species have genes that favor that environment, extinction is a lot more likely. — Ƶ§œš¹ _{[aɪm ˈfɹ̠ˤʷɛ̃ɾ̃ˡi]} 18:05, 10 May 2010 (UTC)

One thing that I think we're missing here is that Neanderthal and Modern-Human DNA would be remarkably similar to start with. Heck Chimpanzee DNA and Human DNA is about 94% identical - we'd imagine that Neanderthals and humans would be more similar than Chimps and humans. So even if we had one complete Neanderthal chromosome - we'd still only have a tiny, tiny percentage of DNA that looked different from a Neanderthal-free modern human. SteveBaker (talk) 16:09, 9 May 2010 (UTC)

To quote Wikipedia, "While unable to definitively conclude that interbreeding between [humans and Neanderthals] did not occur, analysis of the nuclear DNA from the Neanderthal suggests the low likelihood of it having occurred at any appreciable level". Source: Hayes, Jacqui (15 November 2006). "DNA find deepens Neanderthal mystery". Cosmos. http://www.cosmosmagazine.com/news/853/dna-find-deepens-neanderthal-mystery. Retrieved 18 May 2009. 

That 2006 quote is pretty irrelevant now. It relates to the same group, and the same project. The data they had aquired in 2006 did not give evidence for admixture. Today, when more data is available, it turns out that some interbreeding probably occured. --NorwegianBlue ^talk 20:21, 9 May 2010 (UTC)

Paintballing science

Where I went paintballing they sold pressurized CO₂ chambers, as well as more expensive pressurized N₂ chambers (used for firing the balls). Why would nitrogen be better than carbon dioxide? Isn't it just dependent on the pressure, which is independent of the gas used? Also, my facemask kept fogging up and I was wondering what could have been done to reduce that. But before that, I'm not too sure why it would fog up...my guess is that it fogs up because the moist air from our lungs (moist because it was raining?) hits the cold visor, causing the air to cool down which makes the water in the air condense. I'm not completely satisfied by this because the air cools down to the same temp as the surrounding air, which can hold its water without too much trouble. I was hopeing someone could help me out with this. But anyways, about preventing the fogging...I heard spitting on the visor helps, but why? Any other useful tips? Thanks. 173.179.59.66 (talk) 01:49, 9 May 2010 (UTC)

After looking at some paintball forums, it seems that the nitrogen is stored as a compressed gas, but the CO₂ is stored as a liquid. As a gas (nitrogen) expands, it gets slightly cooler, but as liquid CO₂ evaporates it gets very cold. Apparently this makes the gun cold and leads to less consistent shots. See [1].24.150.18.30 (talk) 02:27, 9 May 2010 (UTC)

As for the fogging mask, smearing a drop of saliva may work, as I know (from experience) that this is useful in SCUBA diving (I'm sure that a fogged up mask is no fun in paintball, but it can be an absolute nightmare underwater!). The fogging is caused by water vapour in your breath hitting a cold surface (the mask) and condensing into tiny droplets. My theory is that if there is already a thin layer of moisture (saliva) on the mask that is smooth enough to see through, then any drops that form from you exhaling will just become part of that layer and won't affect the light passing through. Dive shops and maybe ski stores may sell antifog lens cleaners which could help.24.150.18.30 (talk) 02:37, 9 May 2010 (UTC)

The other option is to get a better quality mask with vents to allow the moisture out (not an option for SCUBA divers, but it works well for masks used in air - I've used one for skiing and you could really tell the difference if you blocked the vents, not that I can work out why goggles that only covers your eyes, not your nose or mouth, would fog up so much...). --Tango (talk) 02:54, 9 May 2010 (UTC)

On preventing your mask from fogging up, I often see people at paintball fields putting shaving cream on their facemask lenses in order to prevent fogging. No idea what the theory behind this is or why it works, but I guess people wouldn't do it if it didn't have some degree of effectiveness. And yes, if you're serious about paintball, definitely invest in a high-quality mask with vents and anti-fog coating on the lenses. --Cerebellum (talk) 03:31, 9 May 2010 (UTC)

Smearing the visor with spit can reduce fogging because of the spit's small tendency to act as a surfactant - it prevents the condensate from forming small drops and instead it forms a uniform layer, which you can see through. Other liquids, such as shaving foam, potato juice and detergent do the same thing. The best way of reducing condensation is to use a double-layered mask, which is very common in skiing. The inner one warms up and so does not suffer from condensation. The outer one gets cold, but the warm damp air does not reach it, and so it doesn't get fogged either. Many motor-cycle helmets do the same sort of thing, often with a system called a pin lock. --Phil Holmes (talk) 09:45, 9 May 2010 (UTC)

And least anybody forgets to mention it. Wikipedia -as always- has an article. Paintball equipment.--Aspro (talk) 12:26, 9 May 2010 (UTC)

Also see Anti-fog... Cacycle (talk) 22:11, 9 May 2010 (UTC)

Thanks a bunch! 173.179.59.66 (talk) 02:05, 10 May 2010 (UTC)

Angular momentum transform

If the angular momentum of a particle about the point (x0,y0) is known, how do I calculate the angular momentum with respect to another position, say (x1,y1)? --142.151.129.67 (talk) 02:54, 9 May 2010 (UTC)

You can't. They are independent. Imagine you have a particle with mass 1kg moving in a circle of radius 1m centred at (0,0) at 1 m/s - it has a constant angular momentum around (0,0) of 1 Nms. The same particle's angular momentum around (0,1) will depend on its position in the circle, eg. when it is at (0,1) its angular momentum will be zero, when it is at (0,-1) its angular momentum will be 2 Nms. If there was a transformation from one centre to another then a constant angular momentum would have to transform into a constant angular momentum, so clearly there is no such transformation. --Tango (talk) 03:03, 9 May 2010 (UTC)

A good discussion of the mathematics of angular momentum under various coordinate transforms is given in Chapter 9.4 of Classical Dynamics of Particles and Systems ($150 at Amazon). You can probably find this book at a university library. The derivation is too complex to write here, but can be summarized: "The total angular momentum about an origin is the sum of the angular momentum of the center of mass about that origin and the angular momentum of the system about the position of the center of mass." This is closely related to the parallel axis theorem, which describes the transform of moment of inertia to other coordinate systems. I am not sure if Tango's statement above is correct - I think what he means is that the angular momentum can not be easily represented. In the case of a non-inertial coordinate system, the angular momentum will appear to not be conserved, and will be time-varying. This is one way to describe Coriolis force, for example - a "mysterious" generation of angular momentum - but all that is really happening is that we are observing conservation of momentum in a system from the viewpoint of a non-inertial frame. Nimur (talk) 02:05, 10 May 2010 (UTC)

It's not difficult to represent, it is impossible. The Coriolis force has nothing to do with it; we haven't changed reference frame. I've shown that given an angular momentum around one point I can find two situations both with that angular momentum around that point but with different angular momenta around a different point. That means you cannot determine the angular momentum around the second point without more information. --Tango (talk) 02:33, 10 May 2010 (UTC)

Tango, I think you are incorrect; what you have shown failed to take into account the Parallel Axis Theorem; in other words when you gave your circle example, you did not account for the angular momentum of the center of mass (in the new coordinate system - you moved the origin!). This is where the mysterious 2 Nms has disappeared / appeared - it should have been the angular momentum relative to the new position of the center of mass. Your derivation was incomplete, and that's why there's the inconsistency - you have performed half of the transform but forgot to transform the system's angular momentum about the center. If you decompose the vector to the center, r, into (r_a + R), where R is the vector to the new origin, and r_a is the vector to the true center of mass of the object, and then proceed with your derivation, you will find a new term in R (which describes, in your case, the orbit of the object around an arbitrary circle, and varies with time). The sum of the angular momenta from the system (M R x dR/dt) and the object's rotation (I_ar_a) will be conserved - that is the total angular momentum of the entire system. Think of Earth revolving around the sun, and also rotating on its own axis. The total angular momentum of the system is constant, but if you observe from the point of view of Earth, (which is a moving reference frame), you "forgot" to account for the angular momentum of the whole orbit. This must be accounted for by computing the center of mass for the entire system, and taking a coordinate transform to your new origin of choice. In an n-body problem, where the choice of origin is arbitrary, how else would we be able to analyze angular momentum? It is definitely possible to represent angular momentum as observed from any arbitrary origin; this is done by decomposing the angular momentum into a rotation about the new origin and a rotation about the object's center of mass. For each arbitrary origin, the numeric values of this decomposition vary. In the most general coordinate transforms (rotations and translations), we need one or more inertia tensors to describe the system, and can not drop any terms. Nimur (talk) 15:16, 10 May 2010 (UTC)

I'm talking about single particle. The centre of mass is the location of the particle and the angular momentum of the system around the centre of mass is zero. There is only one term. I don't need any theorems since I'm calculating the angular momentum for a specific system using the definition of angular momentum. --Tango (talk) 21:22, 10 May 2010 (UTC)

Unless I'm very much mistaken, isn't angular momentum defined within a plane, and not "about" anything? In which case, the question isn't very meaningful.--Leon (talk) 21:41, 10 May 2010 (UTC)

The definition of angular momentum, as given in our article, is $\mathbf {L} =\mathbf {r} \times \mathbf {p} =\mathbf {r} \times m\mathbf {v} \,,$ so given an arbitrary coordinate system, r and v are going to be different. Because we know that angular momentum is a conserved quantity, something has to account for these changes in r and v. That would be the parallel axis theorem, which is a direct consequence of the definition of angular momentum in generalized coordinates. Nimur (talk) 07:10, 11 May 2010 (UTC)

Correct, and the cross product yields a bivector, or oriented plane segment.

The parallel axis theorem allows one to determine the moment of inertia of a body about a given axis if the moment of inertia about its centre of mass is known. From this, if one knows the angular velocity about this new axis, one can furthermore calculate the angular momentum. That is not the same as being able to ascertain the angular momentum about some new point if all that is known is the angular momentum about some other.--Leon (talk) 07:44, 11 May 2010 (UTC)

That is the definition of angular momentum around the origin. The numbers I've quoted above are the magnitude of that vector (my system was planar, so there was no reason to state the direction - it is clearly perpendicular to that plane). Angular momentum is conserved - that means it stays the same if you change the time. It doesn't stay the same if you change the origin. There is clearly a relationship between the angular momentum around one point and the angular momentum around another, but that relationship depends on the details of the system in question so you can't do anything if you are just given the angular momentum. You need to be given the details of the system as well. --Tango (talk) 10:56, 11 May 2010 (UTC)

(Hope this helps) A critical oversight in much of the above is that the origin r is in an "inertial" frame, one undergoing no net force. If one considers angular momentum about the axis of rotation, that's fine, and angular momentum is constant in the absence of an external torque. However, if the origin is anything other than the axis of rotation, but the motion of particles is much as before (the same, but all translated), for the origin to remain an inertial frame (i.e. with no forces or torques acting upon it) there must be some external torque to counterbalance the torque incurred on the origin by holding the rotating body in place. Hence angular momentum of the system does not "appear" constant, though it is, we have simply neglected some forces! As an example, consider holding a stick with a spinning wheel ball held on a string, spinning about this end, at the end opposite to your hand. The wheel ball is exerting a force on your hand, and you are (presumably) counterbalancing that with some force to keep the stick in place. Make any sense?--Leon (talk) 00:37, 12 May 2010 (UTC)

Ok, let's simplify the example. Abandon all forces. We have a single particle moving at constant velocity. It has (at a given moment of time) an angular momentum around (0,0,0) of (1 Nms,0,0). What, given no additional information, is its angular momentum around (0,1,0)? Please give the actual numbers (and show your working). --Tango (talk) 16:05, 12 May 2010 (UTC)

Its angular momentum isn't "about" anything! And the general equation, $\sum _{i}\mathbf {r} _{i}\times \mathbf {p} _{i}$, is always valid providing that the assigned origin is experiencing no net force. This is a tacit assumption of the definition. So we can't "abandon" all forces. If I spin a ball on a string around my finger, the latter of which is at (0,0,0), the ball is exerting a force on my finger but not a torque, though my finger is still supplying a force to exactly counterbalance that of the string. However, imagine I spin the ball on a string, attached at one end to a pole, of which I am holding the other end, and my hand holding the pole is at (0,0,0). The force that the pole exerts on my hand is a torque in this case, and if my hand is to be kept at (0,0,0) my hand must be providing an equal and opposite torque back. Newton's laws do make assumptions about the frame of reference, and indeed he argued for an "absolute" frame of reference (I can't think of the exact line of reasoning or the exact statement, but it involved this: swish water around a bucket and take the water to be in the rest frame and calculate; you get very different results to what is observed; taking the Earth as the rest frame you get results that tie in MUCH better with experimental data).--Leon (talk) 22:12, 12 May 2010 (UTC)

It is about something. Angular momentum is all about rotations. You can't have a rotation without a centre of rotation. Usually we use the origin (that is the assumption implicit in your formula), but there is no requirement to do so (and the choice of origin is arbitrary anyway). Read the second sentence of Angular momentum - note the bit where it says "with respect to some point". When I said abandon all forces I meant assume we have a system with no forces in it, hence the particle has constant velocity (a particle travelling along a straight line will have non-zero angular momentum, as long as the line doesn't go through the point you are working with respect to). --Tango (talk) 23:35, 12 May 2010 (UTC)

Yes, we are free to use any point, any non-accelerating point. And your example is weak because the angular momentum is constant in it! You may point out that in your example angular momentum does depend on the axis of rotation, which I concede is correct, absolute momentum and absolute angular momentum are of little significance (changes wrt to time are significant, not the absolute values); if you account for those forces that mediate the rotation in my example above, the paradox dissolves.--Leon (talk) 08:04, 13 May 2010 (UTC)

However, depending on what exactly the crux of the matter is, I may be seeing your point. Yes, a choice of frame does affect the value of angular momentum calculated. This would also be true for linear momentum (try a constantly moving frame), and in both cases we would be unable to ascertain the new (angular) momentum without more data that the momenta themselves.--Leon (talk) 08:11, 13 May 2010 (UTC)

Of course the angular momentum is constant - it is a conserved quantity and I got rid of all forces that could possibly change it. There is no rotation in my example, just a particle travelling along a straight line, so there is no axis of rotation either. The angular momentum tells you what the nominal axis of rotation is (it will be perpendicular to the plane determined by the path of the particle and the point you are working wrt), rather than being determined by it. I don't understand what paradox you are talking about - there is no reason to expect angular momentum to be the same wrt different points. The crux of the matter is the OP's question, which is very clear, and you have now finally agreed that my answer was correct. I really don't understand why you were disagreeing... --Tango (talk) 10:18, 13 May 2010 (UTC)

Boiling and vapor

From my understanding, boiling a solution evacuates solely the water as vapor and causes the solutes to remain in solution. But what happens when all the solvent has been vaporized; is the solute in crystal form along the walls of the pot? My particular question relates to boiling milk. Does the water content boil off and the fats, sugars, etc. remain in solution, albeit more concentrated? What exactly is included in the steam that comes off of a pot of boiling milk? DRosenbach ^{(Talk | Contribs)} 03:19, 9 May 2010 (UTC)

Yes the steam will be mostly water. The scum left behind will be largely protein and lactose, with liquid butter fat making up the oily component. The lactose in water will form a syrup, which will boil at a higher temperature, and this will eventually caramelize. Graeme Bartlett (talk) 03:30, 9 May 2010 (UTC)

Mostly...what other than water would boil off? And when you say that the syrup will boil at a higher temp, so that would be carbohydrate in gas form? DRosenbach ^{(Talk | Contribs)} 03:32, 9 May 2010 (UTC)

The vapour consists of the compounds of the liquid in the relation to their partial pressure at the given temperature and that is depending on the vapour pressure of the compound. So at 100°C a little of the fat will be also evaporate, not enough to see it but not zero molecules. With milk I would guess that the vapour is more than 99.999% water. --Stone (talk) 08:42, 9 May 2010 (UTC)

Strictly, your original statement is not true. If we dissolve some ethanol in water and then raise the temperature of the solution, the initial vapour will be composed predominantly of ethanol with some water also. As stone says, the proportion of ethanol to water would depend on their partial pressures at the temperature the solution had been raised to. So "boiling a solution" does not evacuate "solely the water as vapour". --Phil Holmes (talk) 09:39, 9 May 2010 (UTC)

Well to start with the most volatile substances will boil out first. These would be nitrogen oxygen carbon dioxide. You would also have noticed a smell, this is also due to volatile substances that have evaporated along with the water. Graeme Bartlett (talk) 12:31, 9 May 2010 (UTC)

When you boil milk, it is almost entirely water that evaporates. If you boil it down until almost no water is left, the result is fudge -- an almost solid mass made a bit squishy by the fat content. (The fudge you buy in stores has a lot of sugar added, and usually other flavorings such as chocolate, but basic fudge is what you get by boiling the water out of milk.) Looie496 (talk) 16:07, 9 May 2010 (UTC)

Plastic&Electric kettles

from what kind of plastic are electric kettle made? —Preceding unsigned comment added by Ha-y Gavra (talk • contribs) 11:04, 9 May 2010 (UTC)

PEEK comes to mind but it is expensive.[2] More common high temp. plastics are polypropylene and POM.--Aspro (talk) 12:40, 9 May 2010 (UTC)

My kettle says >PP< which I'm pretty sure means polypropylene: the article says this is a common material to make kettles out of. 86.180.48.37 (talk) 19:45, 9 May 2010 (UTC)

Moon distance

how far is moon from the earth —Preceding unsigned comment added by 41.184.96.83 (talk) 12:54, 9 May 2010 (UTC)

384,405 km (from center to center), according to a diagram in the moon article. DRosenbach ^{(Talk | Contribs)} 13:04, 9 May 2010 (UTC)

Which makes for about 376,296 km (233,819 miles) subtracting out both sphere's radii. DRosenbach ^{(Talk | Contribs)} 12:08, 11 May 2010 (UTC)

Well, as the moon's orbit is best described by an ellipse there are a few key distances which can all be found in the first few lines of the infobox here. The apogee is the furthest distance it ever gets from Earth and the perigee the closest. Martlet1215 (talk) 16:55, 9 May 2010 (UTC)

river discharge

What is the relationship between the average discharge of a river and maximum discharge? —Preceding unsigned comment added by Amrahs (talk • contribs) 13:32, 9 May 2010 (UTC)

There isn't a relationship between those two figures. Rivers vary: maximum discharge is the largest amount of water that flows through the river in a certain amount of time, that usually happens in winter time. Average discharge is the average (usually mean) amount of water that flows through in a certain amount of time.--92.251.131.97 (talk) 14:24, 9 May 2010 (UTC)

Have you read Discharge (hydrology).--Aspro (talk) 14:30, 9 May 2010 (UTC)

National Security Guards or Special Air Service

which one according to u are better; SAS of British army and NSG of India?

thank you —Preceding unsigned comment added by 117.197.245.199 (talk) 13:37, 9 May 2010 (UTC)

Well if we compare the performance of the SAS during the Iranian embassy seige and both Iraq wars to the performance of the NSG during hte Mumbai terror attacks I think SAS is better.--92.251.131.97 (talk) 14:21, 9 May 2010 (UTC)

The Wikipedia (science) reference desk is not the place to ask for opinions. The best one can possibly do to answer this question is to attempt to list records of each service's performances in similar situations. As the activities of these organisations are largely kept secret, it is quite difficult to attempt to gather empirical evidence of any relevance. 88.90.16.140 (talk) 15:43, 9 May 2010 (UTC)

Why isn't a place to ask for opinions? Sure this isn't science it should be in humanities or misc, but we can give opinions.--92.251.131.97 (talk) 16:43, 9 May 2010 (UTC)

The reference desks were originally set up to assist people with writing articles. Our opinions don't go in the articles and so the ref desks are about facts not opinions. Theresa Knott | token threats 16:46, 9 May 2010 (UTC)

Have you read the bit at the top of the page where it says "The reference desk does not answer requests for opinions"? --Phil Holmes (talk) 17:27, 9 May 2010 (UTC)

Is there much Greek blood in southern Italians?

Approx what % of people from southern Italy have some Greek ancestors?

Approx what % of people from the Po valley have some Celtic ancestors?

thanks--92.251.131.97 (talk) 14:19, 9 May 2010 (UTC)

Happy to help, but a little google searching goes a long way! Greeks in Italy...and still looking around for Po valley --rocketrye12 ^{talk/contribs} 15:11, 9 May 2010 (UTC)

Sorry I'm already aware of the history of greek people in Italy so that article doesn't help much, I'm asking how many actual Italian people have greek blood. —Preceding unsigned comment added by 92.251.131.97 (talk) 16:25, 9 May 2010 (UTC)

You are going to have to give a better definition of Greek blood. If you just mean a person with an ancestor who has lived in Greece in the past, the number would be almost all of them. Graeme Bartlett (talk) 21:54, 9 May 2010 (UTC)

I'm going to suggest that you **** blood. DNA sequencing is where it's at. You want to look for the allele/haplotype frequencies (or their combinations) for molecular phenotypes that tend to be particular to "Greeks" (though you're going to have to define what type of Greek -- Mycaenean, Hellenistic, etc.?) John Riemann Soong (talk) 07:28, 10 May 2010 (UTC)

I think it's rather likely that the OP is simply using 'blood' in the colloquial fashion as used in Kinship terminology to mean related by a common ancestor (i.e. genetically related) rather then literally having anything to do with blood. DNA sequencing is of course simply a method of attempting to measure this relationship. Of course you can use a blood sample for DNA sequencing although it's rare given the difficulty of taking blood compared ot other easier methods of obtaining a DNA sample like a cheek swab. Nil Einne (talk) 08:58, 10 May 2010 (UTC)

I agree. And by that definition, I'd bet on 99+% for both "celtic blood" and "greek blood" unless one defines a non-negligible threshold. --Stephan Schulz (talk) 09:16, 10 May 2010 (UTC)

travel speed in space

how fast a spaceship travel in space? —Preceding unsigned comment added by Pedfp (talk • contribs) 14:21, 9 May 2010 (UTC)

It would depend on where it's going. It would have to be going fast enough to achieve the appropriate Escape velocity.--Aspro (talk) 14:33, 9 May 2010 (UTC)

It's not necessary to reach escape velocity to escape a planet (at least not the escape velocity at the surface), as mentioned at Escape velocity#Misconception. -- BenRG (talk) 04:03, 10 May 2010 (UTC)

Are you asking, how fast can spaceships currently existing travel, or how fast could they travel, or how fast is theoretically feasible with different methods? Because it will be different for each of them. --Mr.98 (talk) 15:03, 9 May 2010 (UTC)

• The fastest manned spacecraft was Apollo 10 on it's return journey from the moon when it hit 39,900 kilometers per hour (24,791 mph) in 1969. That's also the fastest that any human has travelled.
• The fastest any human built unmanned spaceship has ever gone (and actually, is continuing to go right now) is the New Horizons probe that NASA has sent to Pluto. It is travelling at 16.3 kilometers every second which is 58,500 kilometers per hour, 10.1 miles per second or 36,400 miles per hour. It will gradually slow down as it gets closer to Pluto. The long-term fastest spacecraft are the Voyager probes - which are going fast enough to escape the sun's gravity completely - around 34,000 miles per hour.
• The fastest practical (just!) spacecraft we've ever designed would be the Project Orion nuclear bomb-powered spacecraft that in some versions would be theoretically capable of reaching about 10% of the speed of light and getting us to the nearest star in about 1000 years. An Orion-class spacecraft would (by necessity) be simply gigantic - with a massive 'pusher plate' about 20 kilometers across! You could house an entire city full of people inside - but it would be ruinously expensive to build - and if you launched it, it woudl make the area for hundreds of miles around its launchpad uninhabitable due to radioactive fallout - possibly causing a 'nuclear winter' scenario and ending life on earth in the process! However, if mankind had to leave the Earth in a hurry for some reason of impending catastrophy (a major earth-killing asteroid impact, for example) then it would perhaps be feasible to build such a thing in order to save a half million people and save some vestige of humanity for the future!
• There have been highly theoretical concepts for anti-matter powered spacecraft that would permit speeds up to 80% of light speed...but we have no idea how we could build such things in practice.
• The fastest that any spaceship (or anything else for that matter) could theoretically go is just a hair short of the speed of light...no matter how it's built or propelled, that's a "final" limit because no physical object can travel at the speed of light.

SteveBaker (talk) 15:52, 9 May 2010 (UTC)

An Orion drive's pusher plate doesn't have to be that big. According to the designs, the plate wouldn't be wider than the ship itself, and the ship's diameter can be less than 50 meters. ScienceApe (talk) 20:25, 9 May 2010 (UTC)

And it could be built in orbit or (if small enough) launched into orbit using a conventional rocket, thus avoiding radioactive fallout at ground level. 67.170.215.166 (talk) 08:22, 10 May 2010 (UTC)

The problem is that Orion only works if it is exceedingly heavy. It has to survive being pounded by nuclear weapons! Not just once - but hundreds or even thousands of times! That makes building it in orbit impractical. I suppose you could possibly build it on the moon using locally mined materials though. SteveBaker (talk) 11:49, 10 May 2010 (UTC)

Well at least an equation tells us that we'd need infinite energy to go the speed of light, but I'm not so sure. I mean I bet all the "empty space" inside atoms will turn out not to be empty at all (maybe that will solve the dark matter speculation). Science is pretty primitive even now considering what it may be in even 100 years, never mind 1,000 or if/when humans have colonized other planets.--92.251.131.97 (talk) 16:29, 9 May 2010 (UTC)

Matter not reaching the speed of light is more of a structural requirement of our current understanding of physics. It's not just an issue of taking too much energy. In order for the laws and the speed of light to be the same in all inertial frames, things just can't work such a way that matter can move like that. Rckrone (talk) 17:04, 9 May 2010 (UTC)

And dismissing what is pretty solid science on the basis that there might be a magical workaround is, well, magical thinking. It's possible that Magiconium exists and somehow allows us to break the basic rules of special relativity, but there's absolutely no good reason to think so. --Mr.98 (talk) 18:45, 9 May 2010 (UTC)

The equations of special relativity have been exceptionally well tested. When you sling material around in something like the Large Hadron Collider, you can see how it takes increasingly large amounts of energy to get asymptotically closer to lightspeed - precisely in accordance with that equation. There is no realistic possibility that the equation is wrong. Sad and annoying though it is - the speed of light is an exceptionally well researched "hard limit" that's not going to be exceeded by conventional means. We're down to "wormholes" and "warp drives" and other highly unlikely technologies that 'get around' the lightspeed limit...but those are all very dubious science and stink of wishful thinking rather than scientifically derived possibilities. SteveBaker (talk) 11:49, 10 May 2010 (UTC)

Not saying you are wrong here Steve, but the same things were said about aircraft and the speed of sound through the 20s and early 40s. Aren't all scientific principals in theory only one experiment (ok, not counting verification experiments) away from being discarded? Googlemeister (talk) 13:34, 10 May 2010 (UTC)

That was an entirely different matter. They already knew that (for example) a rifle bullet or the tip of a bull-whip could go faster than sound - the issue wasn't a fundamental one. The doubt was that an airplane could be controlled above the speed of sound. Also, they hadn't done any experiments to try this on a small scale. We've done precisely that. We've found that the amount of energy it takes to accelerate a bunch of electrons or protons from (say) 90% of the speed of light to 99% of the speed of light is less than it takes to get from 99% to 99.9% - which in turn is less than it takes to get from 99.9% to 99.99% and so on. The rate of increase exactly fits the equation. Also, the idea that an aircraft couldn't fly faster than sound was based on gut feel and untested ideas. The speed of light limit emerged from simple mathematics and solid experimental evidence - and every single subsequent experiment (and there have been an awful lot of them) has backed it up to the hilt. Nobody is saying that it's absolutely, utterly impossible that we're wrong about this - that would be unscientific - but what we can say is just how improbable it is that we're wrong given the vast pile of evidence we've amassed since the theory was put forward that precisely match the predictions it makes. It's hard to express a measure of 'believability' here...um...I would say (for example) that it is more likely that the Simulation hypothesis is true than that Special relativity is wrong. SteveBaker (talk) 22:54, 10 May 2010 (UTC)

That's a great answer, Steve, but how would traveling at .1c get you to Proxima Centauri in 1000 years? Or did you mean nearest stars? — Ƶ§œš¹ _{[aɪm ˈfɹ̠ˤʷɛ̃ɾ̃ˡi]} 19:02, 9 May 2010 (UTC)

You don't just take off from earth, turn on the hyperdrives and instantly start going at 0.1c. The Orion would slowly gain speed up to 0.1c halfway through the trip - then have to turn around and slow down to zero by the time they get to their destination. Anyway, that number came from our Project Orion article...I suppose it might be wrong. SteveBaker (talk) 23:30, 9 May 2010 (UTC)

Assuming uniform acceleration, the average speed is half the maximum speed. 4ly/0.05c=80 years. I'll go and check that article... --Tango (talk) 01:48, 10 May 2010 (UTC)

Ah, I see what happened. You took the time from the original paper and the speed from the later studies - they were different versions of the design and had different speeds. --Tango (talk) 01:51, 10 May 2010 (UTC)

I don't follow the logic behind Project Orion. The relativistic rocket equation is m ∂α/∂t = −β ∂m/∂t, where α is the ship's rapidity, m is its proper mass, β is the exhaust velocity, and t is proper time. Integrating gives m_i / m_f = e^{Δα / β}. Plugging in Δα = 0.1 (10% c) and β = 30 km/s gives m_i / m_f ~ 10⁴³⁴, i.e., you need 10⁴³⁴ times as much fuel as payload to get to that speed, or 10⁸⁶⁸ if you want to slow down again at the other end. That's assuming a perfect cylindrical explosion and perfect elastic reflection off the reaction plate. The article's source for the claim of 0.1 c is "Cosmos" by Carl Sagan, which does say "Orion and Daedalus might travel at 10 percent the speed of light"—with no source or justification, of course. In context it's easy to believe that Sagan just made the number up. The other problem with traveling at 10% c is the particles of the interstellar medium striking you at a speed of 30,000 km/sec and a rate of maybe 10,000 per square meter per second. The whole thing seems to me quite ludicrous. -- BenRG (talk) 04:03, 10 May 2010 (UTC)

Our article gives an exhaust velocity of up to 30,000 km/s, not 30 km/s. --Tango (talk) 18:10, 10 May 2010 (UTC)

You need to be careful with speeds in space - you need to specify what they are relative to. I think your Apollo 10 speed is relative to the Earth and your New Horizon's speed is relative to the Sun, so they aren't directly comparable. --Tango (talk) 21:31, 9 May 2010 (UTC)

Again, I read the numbers from their respective articles. You can check them for yourself. SteveBaker (talk) 23:30, 9 May 2010 (UTC)

I'm not saying the numbers are wrong, just meaningless without specifying the reference frame. --Tango (talk) 01:48, 10 May 2010 (UTC)

I understand perfectly what you're saying - and I agree with you 100% - I'm just asking that you don't shoot the messenger! I'm merely repeating what the respective articles say. Unless the Guinness Book of Records sets a standard for what speeds have to be relative to...all bets are off. The Earth orbits around the sun at 67,000 mph - which is more than the numbers specified for any of those spacecraft - so it's hardly an insignificant matter! FWIW, I'm pretty sure the Apollo 10 numbers are relative to the Earth where the New Horizons and Voyager numbers are relative to the Sun - but I can't tell for sure. SteveBaker (talk) 11:49, 10 May 2010 (UTC)

I think that new Stephen Hawking Into The Universe with Stephen Hawking show, where he goes on about how it may be possible for us to travel forwards in time, mentions the fastest spacecraft created. You can watch it on Youtube if you haven't seen it already, or are interested. There are three episodes. I think he mentions how fast the Voyagers are speeding out of the solar system. An awesome show, I think.--Brianann MacAmhlaidh (talk) 08:38, 10 May 2010 (UTC)

I know - I watched it on TV a few nights ago and winced when they said that. The Voyager probes have been the fastest man made spacecraft for almost 30 years and are very famous for that fact - so it's written up that way in an awful lot of books and web sites. The New Horizons spacecraft only beat their record fairly recently after some slingshot manouver or other and it will soon slow down again, leaving the two Voyagers as the 'current' fastest once more. Both Voyagers are also slowing down of course - they are still influenced by the sun's gravity, albeit feebly. It's perfectly possible that Hawking's show is out of date (when was it written?) - or simple inadequately fact-checked at the time. SteveBaker (talk) 11:36, 10 May 2010 (UTC)

What does crab use to dig a hole ?

I'd like to know what crab uses to dig a hole on a beach or muddy area. Thanks. —Preceding unsigned comment added by Srkim793 (talk • contribs) 18:29, 9 May 2010 (UTC)

I would imagine they all use the same method as this, even if their digging into river banks etc.Ghost Crab digging a hole Fort Desoto Beach, FL--Aspro (talk) 19:09, 9 May 2010 (UTC)

Invention of high blood pressure medication

I am trying to find when the first high blood pressure or hypertension medication was first developed, who developed it, was it meant to be used for this disease or was it found to be better for another. I found who invented the blood pressure test, but for life of me can't find anything on the medication. Thank you so much —Preceding unsigned comment added by 166.183.201.189 (talk) 18:43, 9 May 2010 (UTC)

Do you mean modern synthetic pharmaceutical drugs? Herbalists have used plants that achived the same effect long before the start of 'recorded' history; so that date is not available.--Aspro (talk) 19:17, 9 May 2010 (UTC)

Hypertension has only been recognized as a disease since the 19th century, so I find Aspro's assertion that it's been treated intentionally since before recorded history to be unlikely. Drugs used to treat high blood pressure are known as Antihypertensive drugs, of which there are many types. There's no history on that page, which is unfortunate. The hypertension#history article only briefly mentions a history, giving a couple of the people who first recognized that it existed. Buddy431 (talk) 19:36, 9 May 2010 (UTC)

Where did I state that they knew they where treating high blood pressure? Were the Ancient Egyptians able to explain the metallurgical science behind adding tin to copper, which enabled them to defend their empire? Or was it just obvious it was harder? Can bumble bees fly, although they are aerodynamically ill equiped to do so? --Aspro (talk) 20:08, 9 May 2010 (UTC)

Back up your assertion then. Find a natural substance used for a long time that lowers high blood pressure. Buddy431 (talk) 20:18, 9 May 2010 (UTC)

Reading both articles further, a major type of High Blood Pressure medication is ACE inhibitors. There is some History both on that page, as well as the more technical article ACE inhibitors drug design. The first article indicates that the first ones were discovered in the 1950s and 1960s, but it wasn't until 1981 that the U.S. Food and Drug Administration approved captopril for use. Buddy431 (talk) 19:42, 9 May 2010 (UTC)

According to this article: "Until the late 1940s, treatment for hypertension had been largely limited to sedatives, nitrates, or the complete surgical ligation of the sympathetic nerves running alongside the spinal cord. Over the course of the ensuing decade, four entirely new classes of antihypertensive drugs emerged in a dizzying array of branded combination preparations. Though high levels of adverse effects at initial dosages limited their widespread use, by 1958 these antihypertensives had more or less displaced surgical treatment for acute hypertensive crises." The four classes Greene identifies are ganglionic blockers (the "earliest class of specific antihypertensives"), hydralazine ("thought to neutralize an unknown “pressor substance,” is still in use today at lower dosages"), rauwolfia compounds, and veratrum alkaloids. That's all pretty much Greek to me, but the article itself is about Diuril, which was initially a diuretic, but later found to be a good anti-hypertension drug, and is credited as radically changing the way hypertension is treated (e.g. treating chronic and symptomless cases rather than just acute ones). Greene also has a book out that talks a lot about this. --Mr.98 (talk) 19:47, 9 May 2010 (UTC)

Here's another good, easily read (though unsourced) article about the history of Hypertension treatment: [3]. The site is all about high blood pressure, and looks reasonable (though I'm no medical professional). They say that Veratrum alkaloids were the first types of drugs, used as early as the 1930's, but that their effectiveness was limited (they were also quite toxic). Buddy431 (talk) 19:54, 9 May 2010 (UTC)

Another thought. Just as different herbs would be given to treat different causes of high blood pressure, so different synthetic drugs would been developed to treat those different causes too. So, perhaps you need to defocus from the major symptom, to each of the underlying causes. Let me know of what's not clear and I'll rephrase it (we don't give medical advice so I'm playing-safe here) --Aspro (talk) 19:55, 9 May 2010 (UTC)

Please back up your assertions. Hypertension's only been recognized recently, and people generally couldn't have treated a risk factor that they didn't know existed. While it's true that some high blood pressure drugs were developed from natural products (like ACE inhibitors from the venom of Bothrops jararaca), I can find no mention that these substances were used medicinally before the heavy research done starting in the 1950s. It appears that different substances were tested more or less at random in a guinea pig to find one that worked. Treating high blood pressure with straight up snake venom would have been very bad, and unless you can find a citation asserting so, I won't believe it. Buddy431 (talk) 20:16, 9 May 2010 (UTC)

“unless you can find a citation asserting so, I won't believe it.” I'm not posting here to prove to you, or anyone else. OP 166.183.201.189 has asked a question, and a good one; and I am doing what I can, to guide them to the answer that their looking for. I am 'aware' that some countries have adopted teaching methods, where students end up demanding that they get spoon fed, like some, cuckoo chick in a nest. However, if they expect regurgitated factoids from me, without context, and without doing any of the slog themselves - then can take a running jump.--Aspro (talk) 21:16, 9 May 2010 (UTC)

As soon as Google 'cardiaca' I get Motherwort, the next thing that comes to mind is kidneys, so what comes up - dandelions. Oh silly me, of course! The real reason why they recorded these things in these old books is that Dr Who left a copy of the BNF and some modern herbalists books!--Aspro (talk) 20:18, 9 May 2010 (UTC)

I'll grant you motherwort: it appears to contain a mild vasodilator that can reduce blood pressure, and it was (and is) used for heart problems (among other things). You also make a good point about diuretics (what dandelion's were used for), in that they can be used to treat hypertension. However, most modern diuretics used to treat hypertension (like Thiazide) are actually effective in lowering blood pressure even at levels below which they increase urine production. I'm sorry I was so dismissive of you, but I'd really appreciate it if you could give examples, rather than make bold assertions without backing them up. Buddy431 (talk) 20:50, 9 May 2010 (UTC)

For those that find this discussion difficult to fathom (and this should not be a discussion page but a ....). A manufacture can only get pattern protection for something that has been invented. A patted treatment can be sold for thousands of times its cost to manufacture. Even after spending millions on drug development, it still makes more money than it would if it manufactured a generic drug. So what is a manufacturing company going to do ?

As an aside: Charles Dickens died from an apoplectic fit from which he never recovered, (I only say this because I have read an original copy of the Times newspaper giving the details) . In those days, surgeons where the top rank of the medical profession but herbs were an anathema to them. --Aspro (talk) 20:43, 9 May 2010 (UTC)

Actually, physicians, not surgeons, were still "the top rank" of the medical profession in 1870. Surgical training had only become integrated into medical school a few decades earlier. The first appendectomy in England had not yet been performed and Joseph Lister was early in his career. alteripse (talk) 00:27, 10 May 2010 (UTC)

Using oil from an oil spill

Is it possible to use oil from an oil spill? I know it's mixed up with seawater and other gunk, but can't they use some chemical process to extract the oil and then refine that into petroleum products like gasoline? ScienceApe (talk) 20:19, 9 May 2010 (UTC)

Yes. They refine it and sell it like normal. Ariel. (talk) 21:40, 9 May 2010 (UTC)

When crude oil comes out the ground it is mixed up with salty water, grit and all sorts of stuff. It just costs so much more to recover and process it when it floats about on the ocean. The ancient Greeks however, found it very profitable to collect.--Aspro (talk) 21:41, 9 May 2010 (UTC)

Oil-water emulsions are routinely collected and re-refined, mostly from the water used to wash the tanks on oil tankers (which is illegal to dump into the ocean, obviously, because of toxic hazards). The oil-water mixture first has to be desalted and dewatered to prevent corrosion problems downstream -- where I work, we use electrostatic desalters to get rid of the salt, and multi-plate oil separators to separate out the water (these would also get rid of the grit). Generally, oil collected from an oilslick in the ocean (or from washing tankers) has to be desalted/dewatered in a separate unit from the oil that comes from the well, because the former contains a lot more salt and water; once desalted and dewatered, though, it can be fed to the same atmospheric distillation unit as the oil from the well. So yeah, it's very much possible to collect and refine oil from an oil spill. 67.170.215.166 (talk) 08:37, 10 May 2010 (UTC)

Why don't our severed limbs/appendages just grow back?

Say if I was to lose a finger, or a hand, or part of my arm or something in an accident. Why doesn't the missing part just grow back eventually, considering that the flesh and bones of our bodies have the ability to repair themselves? --95.148.104.246 (talk) 20:33, 9 May 2010 (UTC)

The body is limited in its ability to regenerate since that same ability is what leads to tumours. Finger tips often do grow back, but that's about it for humans. Some reptiles have more impressive regenerative abilities (I don't know if they have more cancer - I think they have shorter lifespans, which probably reduces the extent of the problem). There is some information on this topic here: Regeneration (biology). --Tango (talk) 21:38, 9 May 2010 (UTC)

Evolutionarily that's not strictly true. While this is one factor, a more prominent one is that it would be so unlikely for you to lose a major body part in your everyday life, so if you had genes for regeneration, it wouldn't give you enough of an advantage over people who don't so that they would be perpetuated. If you do lose a limb, you would probably die before it could regenerate (without the miracles of modern medicine, that is), so you couldn't reproduce. So evolutionarily, the major genetic changes that would allow this have no incentive to occur. 22:49, 9 May 2010 (UTC) —Preceding unsigned comment added by 68.248.227.1 (talk)

That's only true if such a trait were a "major genetic change." I think the question may be "since our cells were able to grow themselves into arms and legs once before, why can't they do so again?" I assume that there's some epigenetic explanation for why this ability is switched off after development is complete, but I don't know if that's true. — Sam 76.118.181.97 (talk) 23:05, 9 May 2010 (UTC)

Yes, it's to do with stem cells differentiating into different tissue types. In mammals, that is a one-way process. --Tango (talk) 23:15, 9 May 2010 (UTC)

I do not agree that fingertips grow back in humans. I have seen individuals who lost a fingertip and 50 years later it had not grown back even a little bit. Some non-mammals, like amphibians, can regenerate limbs. Edison (talk) 23:49, 9 May 2010 (UTC)

I said often, not always. See the article I linked to above, it has a section on finger tips. --Tango (talk) 01:39, 10 May 2010 (UTC)

Humans notably can regenerate their livers from only a part of it. Buddy431 (talk) 00:21, 10 May 2010 (UTC)

It's my understanding that humans actually have the ability to naturally regenerate limbs but this ability is lost as we age. A fetus that loses a limb can regrow it. Children under five years who lose fingertips can regrow them without trouble. After this, tissue regeneration only takes place over small distances (about 1 cm). There are ways being developed that use this natural ability to regenerate tissue to grow new organs. this video and this video talk about applying this in medicine. — Ƶ§œš¹ _{[aɪm ˈfɹ̠ˤʷɛ̃ɾ̃ˡi]} 01:10, 10 May 2010 (UTC)

Conversely however, I scratched my cheek just after I was born and it never healed even slightly! 86.7.19.159 (talk) 21:57, 10 May 2010 (UTC)

We can regenerate organs. We just have to find the correct combination of cellular signals to the turn the system back "on". It's quite about evolutionary incentives. Our liver cells are under constant daily attack from oxidants and all sorts of toxins we eat. So naturally they have been selected to regenerate quite often. John Riemann Soong (talk) 03:22, 10 May 2010 (UTC)

The primary error is in your premise -- you ask why we cannot regenerate if we can repair. They are too entirely separate things, although obviously somewhat related. It's sort of like asking "I don't understand why we can't fly if we can walk!" DRosenbach ^{(Talk | Contribs)} 14:27, 10 May 2010 (UTC)

Are vacuums in Europe more powerful than in North America?

In North America the practical limit to a household motor is 12-13 amps, i.e. 1300-1500 watts. But in Europe the voltage is higher, plus they have high amp ring circuits. So do they make the vacuums with more powerful motors? Ariel. (talk) 22:12, 9 May 2010 (UTC)

My vacuum is a Henry. A very popular brand in the UK. It has a 1200W motor and plenty of suction. I don't see why anyone would need any more. Theresa Knott | token threats 22:15, 9 May 2010 (UTC)

Things like kettles are faster boiling in Europe. My kettle's 3,100 watts. With vacuums there is little point in higher power. --Aspro (talk) 22:29, 9 May 2010 (UTC)

Wouldn't a higher power vaccum be harder to push? 68.248.227.1 (talk) 22:39, 9 May 2010 (UTC)

I don't live in Europe but of course a substanial portion of the world uses 220-240V outside of Japan, Taiwan, most parts of the Americas (some of which do use 220-240V as well) and a few other various places File:Weltkarte der Netzspannungen und Netzfrequenzen.svg and NZ isn't one of those places.

Anyway my vacuum which is this (I think) [4] is rated 2,300W. However it has a powerhead and at a guess 100-200W at least would be for that when in use. It also has adjustable power. It got good reviews from the NZ Consumer's Institute at the time I think (I didn't read them but the person who purchased it did I believe) which was about 4 years ago, I think the powerhead is good for pet hairs and the like, as well as especially dirty carpets (probably good since I don't vacuum as much as I should). See also [5].

Note that that also says "Vacuum cleaners are often promoted on the basis that more watts equals better performance. This is not true. Our tests show no relationship between performance and rated watts." [6].

I can easily find 2000W vacuums [7] [8] [9] [10] [11] [12] [13] [14] [15] [16].

Two of those are in the UK i.e. Europe, so the answer to this question is apparently some are. For the NZ ones, you can see the price of those with higher power ranges from cheap to expensive so although a primarily a gimmick, it appears many do it. And the answer to the wider but unasked question about places outside Europe with 220-240V is also some are.

Nil Einne (talk) 08:19, 10 May 2010 (UTC)

Soot

Where does the soot come from in my gas fire? —Preceding unsigned comment added by 79.76.139.1 (talk) 22:24, 9 May 2010 (UTC)

Impurities in the gas (or impurities that are picked up in the pipes or the mechanisms of the fire itself). If there is a significant amount of soot then something is wrong and you should call a gas engineer out. --Tango (talk) 22:34, 9 May 2010 (UTC)

(Edit conflict)Soot is made of small particles of carbon that cool off before they have time to burn. Soot is the same as smoke, only smoke is in the air. When you burn anything with carbon in it, whatever is left that is black is carbon that has not burned. Hope this helps, --The High Fin Sperm Whale 22:37, 9 May 2010 (UTC)

Presuming it is mostly Methane and so, it will have carbon atoms as part of its composition. The soot come from incomplete combustion of the gas.--Aspro (talk) 22:40, 9 May 2010 (UTC)

Specifically - if the gas is burning smokily and leaving soot - then there isn't enough oxygen present for complete combustion. Carbon burns in oxygen - if there is carbon left, then it couldn't find oxygen to combine with to make carbon dioxide. That's bad because it also means that there could easily be more carbon monoxide than there should be - and that's a fairly serious health risk. SteveBaker (talk) 23:22, 9 May 2010 (UTC)

"Fairly serious health risk" means you could die in a matter of hours. Jc3s5h (talk) 23:27, 9 May 2010 (UTC)

Depending on the amount of ventilation - yes, that's perfectly possible. But (for example) candle flames burn very smokily - and produce a lot of carbon monoxide too - but you don't generally have enough of them for that to be a problem. However, with the amount of fuel that a gas heater gets through - there is ample scope for problems. I think our OP should get his fire looked at by an expert - there is plenty of scope here for personal danger! SteveBaker (talk) 11:23, 10 May 2010 (UTC)

How do wheels on a cannon affect the force on the cannon ball?

Hi all,

I always thought that wheels on cannons were just the prevent the cannon from, say, ripping out ship floorboards, and that having them "robbed" the cannon ball of some of its energy, but my friend says that the cannon ball actually travels further when the cannon has wheels on it.

I have two arguments. The first is slightly less persuasive even to me: The cannon rolling back requires energy, which is taking energy away that could have gone into the ball. The answer to this is probably: if the cannon is bolted down, this energy probably just goes into changing the spin of the Earth in some minute way, or something.

My second argument is: the ball is propelled forward by expansion of the air between the ball and the back of the cannon, much like a spring pushing two things apart. If you put two marbles on either side of a compressed spring and let go, both would travel a little way. If you fixed one end down and just had one marble, the one marble would travel further when you let go. Right?

So... what's the real science? Thanks! Sam — 76.24.222.22 (talk) 22:55, 9 May 2010 (UTC)

You're right that the ball would move faster if the cannon weren't allowed to move, assuming you didn't just destroy everything. Conservation of momentum requires that when the cannon ball moves forward, something else has to be moving back with the same amount of momentum, but if that object is the Earth rather than only the cannon it will get much less energy out of the interaction (since energy is proportional to velocity squared, while momentum is linear in velocity) and the ball will receive more of it. That's really the same thing that happens with the marbles, since the fixed end of the spring is also pushing against the Earth. Rckrone (talk) 23:14, 9 May 2010 (UTC)

The primary reason for wheels on cannons is to enable the artillerymen to move them around; it's far simpler to limber a cannon than to take it all apart and carry the pieces around on waggons. Nyttend (talk) 01:40, 10 May 2010 (UTC)

The tackle on a shipboard gun carriage from the age of sail is a simple form of recoil mechanism that prevents the firing shock from tearing the ship apart. It softens the opposite reaction by spreading the force in time - otherwise, the effect on the firing ship would be similar to the cannonball hitting the opposing ship. It also brings the muzzle of a gun inboard, allowing for reloading without having to haul the gun backwards to get access to the front end of a muzzle-loading cannon. Acroterion _(talk) 01:48, 10 May 2010 (UTC)

Ok, so let's see if I get this right. Say the the cannon weighs 100 kg and the cannon ball weighs 1 kg.

• From conservation of momentum, we know that the cannon will travel at V backwards and the cannon ball will travel at 100V forward, right?

If the total energy of the explosion was 100 Joules, then

• cannon KE + cannon ball KE = 100
• {(1/2)100 * 1V^2} + {(1/2) * 100V^2} = 100
• 100 V^2 = 100
• V = 10

So the cannon ball travels forward at 10 * 100 = 1000 m/s? Is that right? And the units?

Now we bolt the cannon to the ship, so the whole thing weighs 1000kg.

• From conservation of momentum, we know that the cannon will travel at V' backwards and the cannon ball will travel at 1000V' forward, right?

If the total energy of the explosion was 100 Joules, then

• cannon KE + cannon ball KE = 100
• {(1/2)1000 * 1V'^2} + {(1/2) * 1000V'^2} = 100
• 1000 V'^2 = 100
• V' = 0.31

So the cannon ball travels forward at 0.31 * 1000 = 310 m/s?

Blah, that doesn't work. I just proved that the cannon ball goes slower when the cannon is attached the the ship. Where did I go wrong? — Sam 76.24.222.22 (talk) 03:40, 10 May 2010 (UTC)

I didn't read the whole thing, but as a general rule, you don't get accurate results in ballistics by working with energy, mainly because it's too difficult to model how much of the energy gets dissipated. --Trovatore (talk) 03:44, 10 May 2010 (UTC)

Perhaps your friend is getting it mixed up with a trebuchet, which does work better with wheels. This is because the counterweight moves back when the ball moves forward, so it results in the trebuchet moving forward more, and because the kinetic energy of the weight is more down and less backwards, causing it to throw the ball up more too. — DanielLC 05:21, 10 May 2010 (UTC)

Without commenting on the math, a gun firing a 32-lb ball weighed about 6000 lb (with another 1000 lb or so for the carriage) with a muzzle velocity of something a little less than 2000 ft/sec (sorry about the units - no metric in those days). Acroterion _(talk) 11:51, 10 May 2010 (UTC)

Little mistake, "{(1/2)100 * 1V^2} + {(1/2) * 100V^2} = 100" should have been

............................................................. (100v)^2

so the resulting v should be very small indeed. Maybe about 14 centimetres per second for the cannon, 14 metres per second for ball.

Using energy should work. Keep trying Polypipe Wrangler (talk) 10:49, 12 May 2010 (UTC)

Pitot tube pressure/height

I was reading the article on pitot tubes and I saw that the difference between static and dynamic pressures is used to calculate the airspeed on an aircraft. What I wanted to know (because it's not explained in the article) is how exactly one finds the static and dynamic pressures are measured within the tube. Some sort of spring apparatus? --130.216.46.2 (talk) 23:48, 9 May 2010 (UTC)

Pressure sensor. Ariel. (talk) 00:03, 10 May 2010 (UTC)

The static pressure is measured by the static sensor. The whole process is better explained at Pitot-static system. Dismas|^(talk) 00:41, 10 May 2010 (UTC)

It is the dynamic pressure (or impact pressure) that is relevant to the indicated airspeed of an aircraft, not the difference between static and dynamic. For a low-speed aircraft, the difference between the stagnation pressure and static pressure is called dynamic pressure. At speeds faster than about 0.3 Mach the difference between stagnation and static pressures is called impact pressure. Static pressure is conveyed by a conduit to one side of a diaphragm (ie an aneroid capsule or bourdon tube) and stagnation pressure is conveyed (from the pitot tube) to the other side. The deflection of the aneroid or bourdon is proportional to the dynamic pressure. The deflection drives the airspeed pointer, and the face of the airspeed indicator is calibrated so that it displays indicated airspeed in units of knots, km/hr, miles per hour etc. See Airspeed indicator#Operation. Dolphin (t) 03:22, 10 May 2010 (UTC)

May 10

rate for humans

What is the maximum number of calories a human could burn an hour without setting themselves on fire? (by burning I mean through exercise and by setting themselves on fire I mean with a match like some crazy protester.) 71.100.0.29 (talk) 02:15, 10 May 2010 (UTC)

I seem to recall that the highest scientifically measured metabolic rate was during tests of the Gossamer Condor, a human-powered aircraft. (Gossamer Condor and Albatross: A Case Study in Aircraft Design, AIAA, 1980). I vaguely recall numbers on the order of feeding the cyclist a 10,000-calorie-per-day diet, and working all those calories out of him by having him pedal at top efficiency for many hours each day. [17]. This was about the maximum; feeding the cyclist more sugar, or training him harder each day, did not effectively get any more energy out of him. This thesis, Human Powered Helicopter (1991, Naval Postgraduate School), has a nice plot on page 12, indicating maximum power output plotted vs. time that power can be sustained. It is feasible to sustain approximately 1.5 horsepower (or about 1000 calories-per-hour) for about one minute. It is feasible to sustain half that rate for a much longer period of time. After a few hours at ~500 calories-per-hour, though, a human's entire daily food intake would be used up; hence the research into intense super-nutrition, sugar-syrups, and so forth, for the human-powered flight. Per the OP's question, these metabolic rates are well below the autoignition temperature of a human, so through exercise alone, it is impossible for a human to ignite. Nimur (talk) 02:31, 10 May 2010 (UTC)

I've personally burned 1000 calories in an hour running on a treadmill, if the numbers were accurate, and I was nowhere close to a top-level athlete. Note however that the calories the body burns do not equal the power output of the person -- well over half of it goes into waste heat. My understanding is that somebody like Lance Armstrong during a race will burn over 1500 calories per hour for at least a couple of hours. Looie496 (talk) 03:29, 10 May 2010 (UTC)

I would not believe what the treadmill says unless you have an oxygen mask on. There is a factor of ten in unknowns which they are guessing. Ranulph Fiennes has been quoted as saying that racing in the artic you lose weight on 8000 calories a day but you cannot metabolise more than this. He quotes 15000 calories output but beware trying to match the performance of someone who cut off his own finger-tips... --BozMo talk 11:41, 10 May 2010 (UTC)

What do you mean by 'There is a factor of ten in unknowns which they are guessing.'? What unknowns, and why a factor of ten? --22:07, 10 May 2010 (UTC)87.114.95.229 (talk) signed too late—Preceding unsigned comment added by 87.114.95.229 (talk) 22:06, 10 May 2010 (UTC)

Mystery Plant

Hello! I am hoping there are some botanists here who can shed some light on this plant for me. (pun not intended.) This plant has recently come into my possession, and the prior owner was just as clueless as I am. I am hoping to find out what species this plant is, or at least it's family, so I can best take care of it. Any help is much appreciated. (A few more images are available if needed.) ^Avicenna_sis @ 04:25, 10 May 2010 (UTC)

It is definately a type of succulent plant, likely a member of the Crassulaceae family. My best guess is this is a Crassula, likely a Jade plant or some similar. You might want to search through various genera and species of the Crassulaceae family to find a good match, if the Jade plant isn't it... --Jayron32 04:41, 10 May 2010 (UTC)

You might, in the absence of an answer here, like to try Flikr. Accounts are free and they have a group especially for unidentified plants (craftily called "What plant is that")[18]which I can confirm provides an excellent and quick service. Whatever it is it needs much more light than it is (or has been) receiving. It definitely looks etiolated. Caesar's Daddy (talk) 06:17, 10 May 2010 (UTC)

This is some variety of Echeveria, possibly E. elegans. Here [19]is a photo of several varieties of which the one at front centre look like yours but is in a normal form and not drawn up from lack of light. Richard Avery (talk) 19:59, 10 May 2010 (UTC)

russia

why are many (not all) russia drunks? —Preceding unsigned comment added by Tom12350 (talk • contribs) 04:36, 10 May 2010 (UTC)

. Do you have any evidence that Russians are more prone to alcholism than people of other cultures? There are stereotypes of Russians as such, but there's lots of bullshit stereotypes out there, many of which have zero basis in fact. Russians drink, but so don't people from other countries. --Jayron32 04:46, 10 May 2010 (UTC)

Alcoholism in Russia happens to be a redirect to the "Russia" section of the Binge drinking article, and that section states that Russian binge drinking is basically on par with most other European countries. It doesn't specifically discuss alcoholism in Russia. Comet Tuttle (talk) 05:27, 10 May 2010 (UTC)

The Russians seem to think alcoholism is a "national calamity" (Pravda, 2006) and a "national disaster" (RIA Novosti, 2010). This article says "Consuming on average 32 pints of pure alcohol per person per year, Russians are among the heaviest drinkers in the industrialized world." According to this academic commentary, "Alcohol, as a central component of life in Russia, has been commented on, by Russians and by travellers from other countries, since at least the tenth century AD." Fee fi fo fum, I smell the blood of a new article, but I don't have time today. Clarityfiend (talk) 06:04, 10 May 2010 (UTC)

Aren't the Irish the biggest drunks of all? :-) 67.170.215.166 (talk) 08:43, 10 May 2010 (UTC)

I discussed this in a conversation with one Irish and one Russian friend of mine. I think the conclusion was that Irish drink more, but Russians drink harder. Vimescarrot (talk) 09:45, 10 May 2010 (UTC)

I'll drink to that. Cuddlyable3 (talk) 18:29, 10 May 2010 (UTC)

but why —Preceding unsigned comment added by Tom12350 (talk • contribs) 19:15, 10 May 2010 (UTC)

My unsourced, inexpert take on it: Drinking has been deeply ingrained in Russian culture for centuries and therefore more or less accepted. In modern times, Russia, and the Soviet Union before it, were dreary places for the masses, so they drank as an escape. Clarityfiend (talk) 19:57, 10 May 2010 (UTC)

Another possible reason would be the extremely cold climate, which would encourage some people to drink hard liquor in order to "keep warm" (a potentially dangerous practice that can in some cases lead to hypothermia or even death). FWiW 67.170.215.166 (talk) 02:03, 13 May 2010 (UTC)

Where can I find paid gigs to be a guinea pig for a medical experiment within 150 miles of Manhattan, KS? (With room & board included?)

Now you see, I've heard about willing members of society becoming the subjects of medical experiments where a medical school tests prototype drugs and/or experimentally new medical procedures on any willing participant.

I think nowadays would be a good time to start becoming a medical test subject. However, it must be within reasonable distance (~150 miles) of Manhattan, KS, with local lodging also paid for by the medical school or whatever medical research lab is doing these experiments.

So could someone help me find these gigs? In whatever links you give, be sure it'll also give the amounts each test subject will be paid for each experiment (or time-period of these sets of experiments).

For those of you who are about to ask me to just Google it, I already did, and the results were not at all helpful.

--Let Us Update Wikipedia: Dusty Articles 06:39, 10 May 2010 (UTC)

It seems highly unlikely you could support yourself with such a "career", most medical test subjects receive a very small honorarium for participating in the test; usually enough to cover travel expenses and maybe give you enough cash for a night on the town (say, $50-$100). Many will also pay for medical expenses should any complications arise. I can't think of a single lab that would cover room and board, nor would it likely be possible to participate in enough tests to live off of. Many tests may be mutually exclusive, and most require you to have a medical condition first, and already be under the treatment of a doctor. For example, if they were testing a radical new cancer treatment, it would do you no good if you don't have cancer. Also, some tests you participate in may preclude you from participating in other tests. There are some paid testing where they do take "anyone off the street" who volunteers for the test, but these are so unreliable, rare, and poorly paid that I can't imagine you supporting yourself on such a gig. --Jayron32 06:48, 10 May 2010 (UTC)

There is the NASA bed rest study, where they do provide room and board, except you have to stay in a bed without getting up. If you are interested: https://bedreststudy.jsc.nasa.gov/ Ariel. (talk) 07:24, 10 May 2010 (UTC)

I'm a unit assistant for a clinical trials unit at my University hospital. We board test subjects for a week, and offer taxis/rides into town. We pay them 300 dollars / wk and they get 15/dollars a day for meals via hospital vouchers. But yeah, there are conditions or predispositions we target. John Riemann Soong (talk) 07:25, 10 May 2010 (UTC)

If you can stretch your travel radius to Wales and don't mind getting the sniffles, consider signing up at the Common Cold Research Centre. Cuddlyable3 (talk) 10:02, 10 May 2010 (UTC)

Flexing axe heads

I split a fair bit of wood (not commercial, just for home), often with a standard axe and a sledge hammer. The complete book of self sufficiency says one thing you should not do is hit the back of a stuck axehead with a sledge hammer, using it as a splitting wedge. The book says doing this will break the axe handle but I find the tempation to do so irresistable when the axe sticks in a tough log. And the book is right, it breaks the axe handle (not at once but over a few hours misuse), AFAICT not because the sledge hammer ever hits the wood but apparently because the heavy steel axe head deforms enough under the strike of an eight pound sledge hammer to damage the wooden handle in the middle of it (??is that possible). The bit of the handle inside the axe head pulverises, leaving the rest of the handle intact (so I can plane off and put the axe head back on a couple of inches lower. So what's the deflection mode of the axe head and can I do anything to stop the damage to the handle? This particular bad habit is a great time saver. What if a cut the handle so it had a top and bottom gap and was held by the sides? Or put in a piece of rubber or something? Any ideas? --BozMo talk 10:26, 10 May 2010 (UTC)

As an aside, you can get splitting wedges (basically a wide axe-head without a shaft). If the axe gets stuck in the log-end, then tap the wedge into the wood in the crack you've made, free the axe, tap the wedge in a bit more to secure it, then whack it with the sledge hammer. CS Miller (talk) 10:45, 10 May 2010 (UTC)

Thanks I have a splitting wedge but I need to get through logs in a matter of a few seconds and collecting a wedge from where it landed, putting it into a log, tapping with a smaller hammer, wriggling out the axe and then moving the wedge centrally and then hitting it with a big hammer takes ages compared to 50% one strike 50% two strike with an axe and hammer --BozMo talk 10:49, 10 May 2010 (UTC)

Based on what I know about axes and hammers (which is not that much), the sledge puts the back side of the ax blade under compression, causing the hollow channel in the blade that holds the handle in place to flex ever so slightly in the direction of the blow, and to put a bending stress on the handle, which eventually cracks from material fatigue. But hey, I could be wrong about this, no? As far as what you can do about it, cutting the handle so that it's only held by the sides is a very bad idea -- it will just let the ax-head wobble and maybe lead to a major accident. One possible solution would be to get an ax with a handle made of some ductile material (not rubber, but some kind of hard plastic could work), or machining a broad groove in the handle where it passes through the ax-head and putting a sleeve of hard rubber on it, then putting the ax-head back on so that it rests on that sleeve. Another alternative would be an all-metal ax, like a tomahawk or something. FWiW 67.170.215.166 (talk) 10:57, 10 May 2010 (UTC)

(ec) I don't think it's because the axe-head is deforming and breaking the handle - I think it's because of the inertia of the handle. When you hit the head, it moves very abruptly - the unyielding metal of the hammer and the head mean that when the fast-moving hammer hits the stationary head, the axehead has to accelerate from zero to something like half the speed of the hammer head in the very short amount of time over which the two can deform. The acceleration is likely to be hundreds of g's - which is then (more gradually) reversed as the axe is slowed down again by its passage through the wood that you're chopping and is again stationary. Meanwhile - that LONG axe-handle has to follow along. The end that's attached to the axe-head has to accelerate just as the head does - but the center of mass of the handle is roughly halfway along it - so the inertia of the handle acts a long way away - so it has lots of leverage - and the result will be all sorts of really nasty forces propagating along the handle...enough (evidently) to weaken, and eventually break it.

What surprises me is that some sledge hammers also have long handles - how come the sledge-hammer's handle doesn't break for the same reasons?

I understand that using a splitting wedge slows you down - but not as much as a broken axe handle. This job is simply going to take longer than you thought.

SteveBaker (talk) 11:16, 10 May 2010 (UTC)

You could be right but only that it is the acceleration. The deceleration afterwards must be the same as normal use hence the sledge handle is ok. hmm.—Preceding unsigned comment added by BozMo (talk • contribs)

As far as I know, the primary reason for not striking the back of an axe with the hammer is avoiding dangerous splinters. Never hit steel on steel. I think you might do well to invest into a heavy rubber mallet - that should be easier on your tools and easier on your eyes, and it can be used with your current work flow (although you may need a few more blows). --Stephan Schulz (talk) 11:50, 10 May 2010 (UTC)

The OP needs a Log splitter. Cuddlyable3 (talk) 18:27, 10 May 2010 (UTC)

Curiously I did look into it but actually the better ones used by farmers are screw head ones which our article does not even mention, run off a tractor engine and they cost a couple of thousand dollars. For my 6 or 7 metre tonnes of logs a year thats an overkill. The cheaper hydraulic ones like in the WP article seem to be okay for dealing with small diameter plantation wood or a coppice but hopeless when you have big hardwood logs which comes from falling trees in an old garden, and the very big hydraulic ones are hopelessly expensive for light use. So axe it is and it looks like I will go with Steve's advice. All aerobic anyway. --BozMo talk 19:38, 10 May 2010 (UTC)

Another way to split wide logs is to aim your axe so that the near end of axe's blade lands at the near end of log. Then on your second swing, aim the axe so that the near end of the blade hits just after the crack you've made. Hopefully the two cracks will join and the axe will go all the way through. CS Miller (talk) 20:07, 10 May 2010 (UTC)

You can get axes with toughened heads suitable for being whacked with a hammer. I'll have a sniff about and if I can find a link to such will post it here. DuncanHill (talk) 22:17, 10 May 2010 (UTC)

• OK, what you need is a splitting maul. The blade is shaped for efficient splitting (a felling axe has a different profile, and will be less effective for splitting). The poll is toughened, so it can be used as a sledge or should be OK to use a sledge on it. Try a good manufacturer such as Gränsfors Bruks [20]. DuncanHill (talk) 22:23, 10 May 2010 (UTC)

The technique I was taught was that when the axe gets stuck, rotate the axe handle 180 degrees, lift the whole thing up and strike the base block with the axe head lowest. If you are strong this often splits the wood. Polypipe Wrangler (talk) 10:57, 12 May 2010 (UTC)

Calculating the velocity of a cannon ball and cannon

Hi all,

I was trying to work out the velocity that a cannon ball and cannon would have after the cannon is fired in my question above (How do wheels on a cannon affect the force on the cannon ball?), but I think I failed. Can someone help?

Suppose we have a 1kg cannon ball and a 100 kg cannon. Suppose the explosion of the gunpowder provided 100 Joules, and that this was transformed perfectly into the KE of the cannon and cannon ball. How fast would the cannon ball move?

Thanks a lot, — Sam 76.24.222.22 (talk) 11:39, 10 May 2010 (UTC)

Conservation of energy: 1/2*(1kg)*(vb)^2+1/2*(100kg)*(vc)^2=100J

Conservation of momentum: 1*vb+100*vc=0

vc=-vb/100

1/2*(1kg)*(vb)^2+1/2*(100kg)*(-vb/100)^2=100J

1/2*(1kg)*(vb)^2+1/2*(100kg)*(-vb)^2/100^2=100J

(1/2*(1kg)+1/2*(100kg)/100^2)*(vb)^2=100J

vb=sqrt(100J/(1/2*(1kg)+1/2*(100kg)/100^2))=14.0719509m/s

vc=-0.140719509m/s 157.193.175.207 (talk) 13:46, 10 May 2010 (UTC)

edited to correct sign error 157.193.175.207 (talk) 13:48, 10 May 2010 (UTC)

(ec) I won't do your homework for you, but the key to this problem is conservation of energy and momentum. Since you can probably assume that both quantities are initially zero, you know the final energy is 100 J, and the final momentum is zero. You can work from there to find the velocities. anonymous6494 13:51, 10 May 2010 (UTC)

Interesting. So it seems from my calculations that, while it certainly makes a difference if the cannon is big and heavy, it doesn't make a huge difference

Using a cannon weight of 10kg, we get vb=sqrt(100J/(1/2*(1kg)+1/2*(10kg)/10^2)) = 13.48 m/s
Using a cannon weight of 100,000kg, we get vb=sqrt(100J/(1/2*(1kg)+1/2*(100000kg)/100000^2))=14.14m/s

Is that right? So in answer to my earlier question, bolting the cannon directly to the ship, so that the weight of the cannon would be equal to the entire weight of the ship, would make the cannon balls travel slightly faster, but not a lot. So putting wheels on the cannons (for which there are a bunch of other reasons) doesn't rob very much energy from the cannon balls. Is that right? — Sam 63.138.152.189 (talk) 14:31, 10 May 2010 (UTC)

You could just put blocks behind the wheels and move them when you want to reload and have the best of both worlds. Googlemeister (talk) 15:41, 10 May 2010 (UTC)

I didn't check the math but the conclusion seems right. The ratio of kinetic energies each of the two objects gets is the inverse of the ratio of their masses. So for a 10kg cannon, the cannon ball is already getting most of the total energy (10/11 of it). Rckrone (talk) 17:16, 12 May 2010 (UTC)

Solubility of nickel chromate

Does nickel chromate react with hydrochloric acid when it dissolves, or does it just dissolve? Another related question is: Is chromic or hydrochloric acid stronger? You only have to answer one of these. --Chemicalinterest (talk) 11:40, 10 May 2010 (UTC)

Question 1) Depends on how you define "react" and "dissolve". If nickle and chromium ions cannot coexist in solution together, then it seems unlikely that the presence of excess hydronium or chloride would effect the situation. If you are trying to make an insoluble salt dissolve, then something sort of complexation is probably needed, much like how at VERY high pH's, soluble copper hydroxide complexes form which can cause Cu(OH)₂ to redissolve as the Cu(OH)₄^2- ion. The only lewis base in your proposed system would be the chloride ion, so I would suspect that, if it DOES dissolve, you are creating NiCl₄^2-, which is a complex ion attested to in the Nickel(II) chloride article. For Question 2) Chromic acid is not a compound which readily exists either isolated or in water. Stable "chromic acid" generally only works as a mixture of chromate (or dichromate) salts and a strong acid such as hydrochloric or sulfuric; and the strength of these chromic acid solutions probably depends on the strength of the co-acid present. From the point of view of Arrhenius theory, there is no acid which can be "stronger" than HCl anyways; it dissociates extensively in water; since acid strength is a measure of % dissociation, no acid may be stronger than HCl, though several "tie" it in terms of acid strength. --Jayron32 13:48, 10 May 2010 (UTC)

There is: No acid dissociates 100% in water. But does it react with HCl, i.e. to form Cl₂, or does it just dissociate and dissolve? According to my anionic activity theory: Ni²⁺ is higher up on a standard reduction potential chart than H⁺. If chromic acid is stronger, than the Ni²⁺ will stay with the chromate, causing no reaction. If hydrochloric acid is stronger, the H⁺ ion will take the chromate, forming chromic acid. I know some people don't like my idea of ions in solution "sticking" together, but that is what my opinion of anions is. --Chemicalinterest (talk) 14:29, 10 May 2010 (UTC)

(edit conflict with below) My Table of standard reduction potentials shows that Cl₂ is a (slightly) better oxidizer than chromate (or dichromate, whatever), which, if we believe that, means that the Cl^- will not be oxidized to Cl₂. As to your first question specifically, look at Nickel Chromate, where it says it dissolves in an HCl solution, forming a "yellow solution". This is, as Jayron says, likely to be Ni(Cl)₄^2-: see here. Finally, Chromic acid is weird (as Jayron points out), so it doesn't really make sense to talk about it in the sense of a normal acid. Usually it's used as a strong oxidizing agent, rather than as an acid. The article makes is unclear as to what species is actually in solution, (Chromium trioxide vs. H₂CrO₄), but it really doesn't matter. Buddy431 (talk) 15:21, 10 May 2010 (UTC)

Look, dude, you can't just invent your own acid-base theory. Science doesn't work like that. What inadequate hole in the existing theory are you trying to plug? Not the least of which is that your theory doesn't work, as it presupposes the existance of things which do not exist. You keep insisting that substances which exist in water simply do not; like a week ago when you kept trying to find discrete NaCl particles floating in water. Lets see if we can dispense with some of the multitude of misconceptions in the above proposal you have. Regarding HCl's dissociation in water: Insofar as there is no perfection in the universe, yes, nothing is 100%. However, insofar as we must use measuring devices to detect things, there is no way to measure the amount of discrete HCl particles in water, so it is as functionally close to 100% dissociated as we need it to be. One can make comparitive gas-phase measurements of acid strength between acids, but any acid which has a higher aqueous-phase pKa than hydronium is effectively 100% dissociated in water, so it is completely moot to decide on strength between, say, HCl and H₂SO₄. Compare the pKa of water (14) with the pKa of Hydrochloric Acid (-7). That's a difference of 21 pKa units, or a difference in equilibrium constant of 10²¹. That means that at a 1 molar concentration of HCl, we have something on the order of SQRT (6 x 10²³/10²¹) or about 25 molecules of HCl per liter. There is absolutely no way that this is not as close to 100% dissociated as you need it to be. Secondly, the reduction potential chart has NOTHING TO DO WITH ACID-BASE STRENGTH. There's just no way that the oxidation/reduction relationship between hydrogen and nickel and chromate and chloride has anything to do with how they will react in an acid-base sense. You are completely ignoring things like coordination chemistry, complex ion formation, lewis theory, stuff like that, all well established and functioning parts of chemistry. You can't just have an opinion about anions "sticking" together, with no experimental proof, and then act like this is somehow a "valid" theory. You're just making shit up, and that isn't really what science is all about!!! --Jayron32 15:06, 10 May 2010 (UTC)

(ec) Make sure you don't base any further predictions on a model that is your opinion which contradicts reality. Even in college, we make all sorts of approximations and "known to be not quite correct" explanations, but we know when we are "not correct". Things might work well in a few limited cases, so we are very careful not to apply those things outside of their correct realm. In normal (not many-molar concentration) solutions, strong electrolytes like HCl are so dissociated there's no reason to consider the few molecules that are bound. In a water solution of two strong acids, neither takes the H⁺...the H⁺ is solvated by the water (as H₃O⁺) because water is a stronger base than the anion from any strong acid and there is like 55 molar concentration of water in glass of water (vs only a few molar at most concentration of the counter-anions). DMacks (talk) 15:08, 10 May 2010 (UTC)

With react I mean a redox reaction. I can demonstrate the anionic activity series by analyzing the reaction of barium chloride and copper sulfate. Since sulfuric acid is a stronger acid than hydrochloric acid, the cation of a more reactive metal will take the stronger acid, forming barium sulfate. Sodium acetate is reacted with hydrochloric acid. Since sodium is the cation of a more reactive "metal" according to the standard electrode potential page, the hydrogen will bond with the acetate, forming acetic acid and sodium chloride. Calcium hydroxide and sodium carbonate react to form sodium hydroxide and calcium carbonate. Because carbonic acid is stronger acid than water, then calcium must be expected to bond with carbonate because it is higher up on the standard electrode potential chart (not the activity series). This anionic theory is just a helpful way to predict whether certain salts will react or not. It really concerns precipitates though, not reactions in which all four of the salts are soluble, the reactants and the products. --Chemicalinterest (talk) 19:37, 10 May 2010 (UTC)

What I mean by sticking together is that, like in the reaction of barium chloride and copper sulfate, the barium kicks the chloride out and takes sulfate, leaving copper chloride. Essentially, the copper chloride exists since the Ba²⁺ and SO₄^2- ions are out of solution. --Chemicalinterest (talk) 19:40, 10 May 2010 (UTC)

The copper chloride doesn't exist. What exists is discrete copper ions and discrete chloride ions. You are confusing a notational convenience (like writing CuCl_{2 (aq)}) with actual reality. Let's take your theory, and show where it doesn't work: If I mix Lead(II) acetate and sodium perchlorate, I would get absolutely no precipitate. This is despite the fact that a) acetic acid is weaker than perchloric acid and b) lead is higher up on the standard reduction potential table. Using either your "which acid is stronger" theory OR your "standard reduction potential" theory, that one doesn't fit. I can find any random number of mixtures which will not work; that you have found some random ones that coincidentally do means nothing. --Jayron32 20:16, 10 May 2010 (UTC)

OK, your example had several fallacies: None of these (lead(II) acetate, sodium perchlorate, sodium acetate, and lead(II) perchlorate) is insoluble. Second, sodium is higher up on the standard reduction potential than lead. So sodium would keep perchlorate. It doesn't really apply when all of the products are soluble though. As you said, compounds don't exist as discrete ions. --Chemicalinterest (talk) 00:29, 11 May 2010 (UTC)

"I can demonstrate the anionic activity series by analyzing the reaction of barium chloride and copper sulfate. Since sulfuric acid is a stronger acid than hydrochloric acid". You're not going to get very far in validating your hypothesis if aren't even using correct data for your fundamental example: hydrochloric acid pKa=−8 vs sulfuric acid pKa=−3. DMacks (talk) 20:47, 10 May 2010 (UTC)

Here is a question: Do stronger acids displace weaker acids from weaker acid salts? Does hydrochloric acid displace acetic acid from sodium acetate? Does hydrochloric acid displace boric acid from sodium borate? Does sulfuric acid displace hydrofluoric acid from calcium fluoride? Does sulfuric acid displace hydrochloric acid from sodium chloride? If it does, then hydrochloric acid is weaker than sulfuric acid. --Chemicalinterest (talk) 00:29, 11 May 2010 (UTC)

The answer to your first three examples is "yes": hydrochloric acid will create acetic, hydrofluoric, and boric acid from the appropriate salts. This is because those three are "Weak acids", and do exist as single species in water. However, the answer to your last question (hydrochloric and sulfuric acid in water) is NO. Both of those are "Strong acids" that will completely dissociate in water: there will not exist either HCl molecules, nor H₂SO₄ molecules, in the water. Instead, there will exist H₃O⁺, Cl^-, and HSO₄^-. I think your confused about "acid strength" and the table of standard reduction potentials. An acid-base reaction is not an oxidation-reduction reaction. The trouble is, many acids are also oxidizing agents: so called "oxidizing acids" (that should be an article. Edit: and now it is!). That is, the anion acts as an oxidizing agent stronger than the H⁺. These include nitric acid, chloric acid, Chromic acid, and to a lesser extent sulfuric acid, among others. While they may seem similar, the "strength" of an acid refers to it's ability to dissociate, not it's strength as an oxidizing agent. Many highly oxidizing acids are also strong acids: nitric, perchloric, and sulfuric, for example, so it's easy to confuse the two different properties. Buddy431 (talk) 04:27, 11 May 2010 (UTC)

See Hydrogen chloride#Laboratory methods: they produced hydrogen chloride from sulfuric acid by its reaction with sodium chloride. (But can sulfuric acid be produced from hydrochloric acid?) --Chemicalinterest (talk) 10:49, 11 May 2010 (UTC)

I see. What they're doing is taking dry sodium chloride (i.e. salt) and adding concentrated sulfuric acid to it. The HCl is then released as a gas (where it's usually called "hydrogen chloride" rather than "hydrochloric acid"). You couldn't do the same with sulfuric acid only because sulfuric acid isn't volatile: it won't bubble out as a gas. Additionally, sulfuric acid can be prepared as a nearly pure liquid, while hydrochloric acid, when a liquid, always exists as a solution. So if you tried adding even the most concentrated hydrochloric acid to a sulfate, you would just dissolve the sulfate and get an acidic solution. Buddy431 (talk) 14:55, 11 May 2010 (UTC)

@ChemicalInterest: I don't want to sound whiney here, but why don't you and John Riemann Soong just exchange email addresses and be done with it? I for one have used up all my Good Faith, and am getting quite fed up with what appears to be constant use of W:RD instead of your local classroom resources and library and learning how to do basic research on your own... DaHorsesMouth (talk) 01:00, 12 May 2010 (UTC) What is the ref desk for then? Asking questions about things that puzzle you. --Chemicalinterest (talk) 22:21, 12 May 2010 (UTC)

I'm searching for the name of a possible "fallacy"

I've seen an article here on Wikipedia, but cannot remember the name. I've just searched the list of fallacies, but could not find it there. It is about a scenario when the situation is getting worse, nearly everyone knows about it and about possibilities to avoid it, but they don't do anything against it because that would lead to short-term loss of comfort or competitiveness... so they doom themselves on the long term. There was a name for this, and even scientific game theory -related explanations, if I remember correctly. --131.188.3.21 (talk) 12:10, 10 May 2010 (UTC)

I think you may somewhat misremember the tragedy of the commons. The problem there is not a loss of comfort or competitiveness (albeit that might be a result of cooperative action), but that at any time the optimal individual behavior is to stress the commons as much as possible, even if that leads to a degradation that's bad for everyone. The two standard ways out of this are to privatize the commons (hard to do with oceans or the air, for example), or to enforce rational behavior from all participants via regulation with punishment. --Stephan Schulz (talk) 12:44, 10 May 2010 (UTC)

Thanks, but I know this dilemma, and think this is not the one I'm looking for. This is about acting to max out one's own benefit and disregarding the common goals. What I'm searching for is when, for example, decision makers could solve a situation (or at least keep it from worsening) but refuse to act out of fear that the temporary loss of comfort might make them lose power or not win the next election. --131.188.3.20 (talk) 13:03, 10 May 2010 (UTC)

Sounds a lot like Prisoners dilemma. Googlemeister (talk) 13:16, 10 May 2010 (UTC)

Not at all. I'm sorry if that sentence was not clear enough, but by "This is about acting to max out one's own benefit and disregarding the common goals" I meant the example given above (tragedy of the commons) was about it, but that's not the one I'm looking for. --131.188.3.21 (talk) 13:30, 10 May 2010 (UTC)

I think the kind of situation our OP is thinking about is like if you had an oil leak on your car. You can either spend $10 to top up the oil once a week - or $300 to fix the problem properly. On any given week, topping up the oil is easiest and cheapest - but over a year, you've spent $520 and a dozen visits to the store to buy oil and 52 x 10 minutes = 8 hours of your time dealing with it...when you could have spent $300 and 6 hours and fixed it properly. Sadly, I don't know of a convenient name for this behavior. It's very similar to the tragedy of the commons...but not exactly that. How about "short term thinking" - or "horizon thinking"? SteveBaker (talk) 15:20, 10 May 2010 (UTC)

Drifting off topic, but I'm not sure those terms best describe your scenario, Steve. You might be well aware of the long term disadvantage of repeatedly topping up, but simply not have $300 available for the better solution, a sort of individual variation on the Poverty trap.

Re the OP's question, Endowment effect isn't quite what is described but is perhaps related. 87.81.230.195 (talk) 15:53, 10 May 2010 (UTC)

It might be that my memory is failing me, but I still think I've seen an article about it here on Wikipedia. I think the examples were more politically oriented, for example decision makers avoiding to do something just because they fear their ratings will drop, or that society itself became to value its comfort too much and let things get worse over time. --131.188.3.20 (talk) 16:13, 10 May 2010 (UTC)

The situation you described reminds me of groupthink. Vranak (talk) 16:28, 10 May 2010 (UTC)

Is there a name for the fallacy of believing that all fallacies have names? --Tagishsimon (talk) 16:33, 10 May 2010 (UTC)

Or the fallacy that all forms of wrong-mindedness are indeed fallacies. Vranak (talk) 17:17, 10 May 2010 (UTC)

I'm just searching for an article I've once seen. It might not even have "fallacy" in its name, because I already searched that list. --131.188.3.21 (talk) 16:50, 10 May 2010 (UTC)

You are describing a situation like a Nash equilibrium in mathematical game theory. This is where any change in strategy by any player (competitor) will produce (short-term) losses. In such a situation, people tend to do nothing, even though this may be bad for all parties. Staecker (talk) 17:16, 10 May 2010 (UTC)

I'm surprised we don't have an article on the monkey trap. The monkey puts its hand into a transparent jar to grab the bait, but can't withdraw its clenched fist from the jar; it would have to let go of the food in order to free itself, but refuses to do so. It "prefers" to remain trapped.--Shantavira|^{feed me} 08:15, 11 May 2010 (UTC)

I think you might be looking for dynamic inconsistency. Maedin\^talk 11:36, 11 May 2010 (UTC)

Physical fitness, health, and running

I've tried looking online for advice on general physical health and fitness, but I find pretty much nothing that I could consider to be a reliable source - they're all either:

• People trying to sell something, or
• People who have learned everything from people trying to sell them something.

So I've turned to the Wikipedians for some fitness advice. I'm considering going running, twice a week (my current fitness regime consists of sitting in front of my computer every day). Now, most websites seem to recommend doing it more than that, but they mention doing it specifically to increase things like muscle development, endurance, etc. Thing is, I'm not interested in any of that - I just want to live a little longer (and maybe get some free endorphins); I want to be healthier for no more reason than to be healthier. A friend told me that, if that was the case, I may as well just walk the same distance instead.

So; is running twice a week enough to achieve anything? Is walking really just as good (and what's the difference)? And why is it so hard to find objective sources for this kind of info? Vimescarrot (talk) 12:47, 10 May 2010 (UTC)

There is no way to predict what your optimal training regime should be. There are some important guidelines that you should stick to, though. If you are older than 35 years old and you have not been physically active since a very long time, then you should not start any intensive physical activity like running straight away. You should then start with walking and then very gradually build up your fitness over the course of several months by gradually increase walking pace and duration, before you start intensive physical training like running. Even then, it is advisable to check with your doctor before you switch to running.

Even if you are younger than 35, it is still advisable to start with walking. This is because the frequency and duration of trainings are important. If you are not fit, there is no way you could run for half an hour, five times per week. But it is likely that you can start with brisk walking every other day for 30 minutes. As your fitness level improves, you can replace one of these brisk walking trainings by a jogging exercise. Some time later you can replace all the brisk walking excercises by jogging exercises. At that time you can also replace one of the jogging exercises with running.

This gradual increase in intensity has the advantage that when exercising you get can interpret the feedback your body gives you better. If you were to start running straight away, then you may get out of breath after 2 minutes. You don't have yet developed any feeling to adjust your pace to the right level. Most people in this situation tend to run way too fast.

Depending on your age, you may be able to get into a 5 times per week running routine within perhaps half a year or one year. So, the short term goal should actually be to get fit enough to be able to train intensively. I have been excercising at a five times per week half an hour fast running routine for many years now, and all I can say is that the results are very good. Count Iblis (talk) 14:21, 10 May 2010 (UTC)

I agree with that advice. Walking for 20 minutes every evening is better than running for 40 minutes twice a week. Get a dog...they won't let you forget or duck out of your training schedule! SteveBaker (talk) 15:14, 10 May 2010 (UTC)

If you want to improve your general fitness then you need to do something that gets your heart rate up. It doesn't need to be very strenuous, as long as it increases your heart rate a bit. If you don't do much exercise at all now then a brisk walk would probably do it. I think the usual advice is that you should do it for about 30 minutes three times a week as the minimum to be effective. If you want more detailed advice then you could join a gym - they will usually have trainers that will help you put together a training regime (or you can hire a freelance trainer for a session or two). --Tango (talk) 15:25, 10 May 2010 (UTC)

If you want an exercise programme that wasn't designed to extract money from you, consider the Royal Canadian Air Force plans 5BX (for men) or XBX (for women), which were published in an inexpensive paperback by Penguin Books titled Physical Fitness from 1964. Note that, as our articles say, some of the exercises involved are now thought not to be ideal if performed unsupervised, but the programmes' general outline might be useful to you. 87.81.230.195 (talk) 15:44, 10 May 2010 (UTC)

Actually, when we had this conversation, I meant walk once a day or something, because we had been talking about certain inconveniences Vimes has of running every day and there only really being the option to do it twice a week. --KägeTorä - (影虎) (TALK) 17:45, 10 May 2010 (UTC)

Having fluctuated all my life between periods of intense physical activity and periods of torpor, I disagree about walking being better than running. Running even once a week is far more useful to your heart, lungs, energy level, and weight than any amount of walking (unless you walk up steep hills), especially if you can work up to covering five miles at a moderately brisk pace. Looie496 (talk) 22:24, 10 May 2010 (UTC)

Thanks for the responses, everyone. Vimescarrot (talk) 05:45, 11 May 2010 (UTC)

methane hydrate ignition

Would heating methane hydrates to 25C cause them to ignite or detonate if they are at 150 bara pressure and surrounded by water, or would they just melt? Googlemeister (talk) 15:28, 10 May 2010 (UTC)

No. They can't ignite/detonate without a source of oxygen...and there isn't one because you're underwater. Since you're obviously thinking about the gulf oil spill - I should point out that the oil that's coming out of the well-head is up at 150C - so if heat was enough, it would already have exploded! They might melt with the heat of oil collected beneath the dome - but that doesn't seem to be happening. The water down there is extremely cold! SteveBaker (talk) 15:35, 10 May 2010 (UTC)

Yeah, I was wondering why they couldn't rig their collector unit with electric heating or something since it looks like the methane hydrates are forming and blocking their pipe. I mean it's not like putting that in would be cheap, but its got to be cheaper then their clean up costs. Googlemeister (talk) 15:39, 10 May 2010 (UTC)

I believe they considered pumping hot water into it to do that - but the problem is that the thing filled up so quickly that now it's bouyant! This thing is the size of a three storey house and it's made of steel and concrete...it takes a LOT of ice to make something that big and heavy (200 tons!) bouyant! SteveBaker (talk) 16:23, 10 May 2010 (UTC)

The different in density between oil and water over 1.5 km height all the way up the pipe has got a lot of buoyancy... but they should have thought of that. --BozMo talk 17:22, 10 May 2010 (UTC)

I'm sure they knew that - that's the reason the thing had to weigh 200 tons! But the clathrate buildup was evidently either not expected or not expected to be so serious. SteveBaker (talk) 22:39, 10 May 2010 (UTC)

Evian bottle ring

whats the ring at the top after you take off the cap off made out of on Evian water bottles made of of ? it dosent feel like plastic it feels like acrylic or something. it gets like sticky and leaves a gross residue on your hands after its been open for a day or 2 or if it gets wet. just that ring thou not the whole bottle. heres a pic of a bottle. im taking about the part circled in red. (make sure you click to maximize the pic size)

http://img96.imageshack.us/img96/5116/water1i.jpg —Preceding unsigned comment added by Tom12350 (talk • contribs) 20:45, 10 May 2010 (UTC)

It's just a part of the cap - when you get an unopened bottle of water, it's attached to the cap - as you unscrew the cap, you break the connection between ring and cap. This is done so that you can tell that the water bottle hasn't been tampered with. I don't understand why it would leave a residue or anything though. SteveBaker (talk) 22:34, 10 May 2010 (UTC)

It's made of polypropylene. And water should not affect it at all. So I don't know what the residue you mention is. Ariel. (talk)

how do u know its made from that? the ring feels like a differnt material than the cap —Preceding unsigned comment added by Tom12350 (talk • contribs) 02:58, 11 May 2010 (UTC)

It'll feel weaker and smoother different because it's not as thick and it doesn't have the cap's structure keeping it rigid, or the grooves for grip. If the cap was as smooth as the ring, you'd never be able to grip it to open it. Vimescarrot (talk) 05:47, 11 May 2010 (UTC)

If you examine one, you'll see that it's moulded as an integral part of the cap, and you break the link between them when you open the bottle. It's therefore made from the same material as the cap. If it gets sticky and disgusting over time, you may like to think about whether you ever drink from the bottle directly, and leave a residue of your mouth on th ring? --Phil Holmes (talk) 09:06, 11 May 2010 (UTC)

Can Crusher

For my science class I have to build an aluminum can crusher. It has to crush cans consistently, into a thin piece of metal. It has to be based on a simple machine. I'm debating between dropping a piece of wood onto the can from a height, and using a pulley to keep it up until I need it to drop, and using a lever to crush it. Which one would work better? I'm planning to build it using wood, but if anyone has a better idea, I'd be open to it, and the same with another idea for the concept of the machine.

tl;dr version: What's the best way to build a can crushing machine?

RefDeskAnon (talk) 21:11, 10 May 2010 (UTC)

Well, I would expect a lever would be faster to reset after you crush a can. Googlemeister (talk) 21:13, 10 May 2010 (UTC)

Very true. RefDeskAnon (talk) 21:51, 10 May 2010 (UTC)

"Which one would work better" depends on a jillion variables (weights, distances, acceptible cost, etc.). It's a science class, you say? Do the experiment! Pick an approach, build it an test it. Change it a little to see if it gets better or worse. Each test doesn't have to be the fully built machine, just the key parts. How high a drop does it take to crush? How well can you aim from that distance? How long a lever does it take to crush? How well can your materials tolerate that much force? etc. DMacks (talk) 21:15, 10 May 2010 (UTC)

The problem is that the project is due pretty soon, and I still need to get the wood. But I hadn't thought of just doing the key parts. Thanks, both of you. Any more ideas would be appreciated. RefDeskAnon (talk) 21:51, 10 May 2010 (UTC)

I just stomped the can flat with my boot, very fast, no special tools needed. Nowadays the recyclers don't care. Graeme Bartlett (talk) 22:02, 10 May 2010 (UTC)

I actually have a can crusher - it bolts to the wall, has a hopper for the cans and a large vertical lever that pushes on a plunger to crush the can end-to-end. Of course the classy "science fair" way to do it would be to "pinch" them like this! SteveBaker (talk) 22:31, 10 May 2010 (UTC)

How are you planning on building your lever? The strength of that could offer some creative options. Dropping the wood seems the easiest option but basically that's it, you drop the wood and hope it's heavy/fast enough to crush the can. —Preceding unsigned comment added by 87.114.95.229 (talk) 22:43, 10 May 2010 (UTC)

Measuring the least amount of weight you need to reliably crush a can would be a part of the science in this. Do experiments with a variety of cans. Do some math - figure out the most weight you needed to crush each can so you know which kind are toughest. Then plot graphs of the amount by which the can gets shorter for a given amount of weight. That will allow you to decide the point at which adding more weight doesn't make much difference to how much the can gets crushed. Machines that my son and I built for science fairs that required dropping something in a controlled way benefitted from using a few feet of 2" or 3" PVC pipe (buy it from any DIY store). This guides the weight precisely onto the target and helps you to always drop it from the same height in a repeatable way that gets you more reliable data. Once you have the data - you can think how to build the machine. (How about a weight on the end of a pendulum arm that swings down and crushes a can laid horizontally in front of the bottom-most part of the swing? You could raise the weight by pulling on a lever mounted to the top of the pendulum.) SteveBaker (talk) 01:01, 11 May 2010 (UTC)

In case you didn't already Google for "Can Crusher", you could look at this web site has a bunch of different can crushers for sale. (The one I have is this one). SteveBaker (talk) 01:04, 11 May 2010 (UTC)

A lever will work a LOT better than dropping a weight. An average person with a lever can easily impart 1000 pounds of force on something. You are unlikely to get anywhere near that by dropping something. (You might have a bit of an impact force, but that will only dent the can, you need longer duration force to crush it totally.) Ariel. (talk) 03:52, 11 May 2010 (UTC)

... and avoid using soft wood for the part in contact with the can. If it has to be wood, use a hardwood, but metal would be better. Dbfirs 07:52, 11 May 2010 (UTC)

Use a car? Polypipe Wrangler (talk) 11:02, 12 May 2010 (UTC)

Or one of these babies. 67.170.215.166 (talk) 02:05, 13 May 2010 (UTC)

Do wormholes violate the 2nd 1st law of thermodynamics?

I know wormholes are theoretical, but lets assume they are real for the purposes of a thought experiment.

Lets take two mouths of a wormhole. Mouth A and Mouth B. Mouth B is stationary, but you accelerate Mouth A to 99% the speed of light. Now any object you send into Mouth B will come out of Mouth A and should now be moving at 99% the speed of light as well right? Unless Mouth A slows down as a result of accelerating the object, wouldn't this be a violation of the 2nd 1st law of thermodynamics since the object would have been accelerated without energy being conserved. ScienceApe (talk) 22:00, 10 May 2010 (UTC)

Are you sure you're talking about the second law? You don't seem to mention entropy anywhere in your thought experiment, so I don't really see how the second law comes into play. --Trovatore (talk) 22:03, 10 May 2010 (UTC)

Indeed, I think ScienceApe probably means the first law. The second law is also a problem with wormholes, though (they mess with causality, since one end can be time dilated relative to the other, allowing time travel). --Tango (talk) 22:05, 10 May 2010 (UTC)

These are the kinds of reason why very few people think that wormholes are 'real'...and even if they are, what their properties might be. One rather likely possibility is that you can't actually move them...or perhaps one end cannot move with respect to the other (so they both have to move together). If those kinds of restrictions are imposed then there is there still a problem with either thermodynamics or time travel? SteveBaker (talk) 22:23, 10 May 2010 (UTC)

That might fix it, I'm not sure how it would work, though. You can't say the ends can't move, since that would require everything in the universe to stay still since motion is relative. Not move relative to each other might be manageable, but I'm not sure how. Wormholes simply not lasting long enough for anything to pass through them is quite likely, if you can't get rid of them all together. --Tango (talk) 22:48, 10 May 2010 (UTC)

I was thinking that you might not be able to move them...because there is no way to grab a hold of them - or that there is no way to apply forces to them maybe. Since they are "connected" it seems somewhat plausible that you might not be able to move one end without also moving the other. Dunno - I think it's vastly more likely that the either don't exist - or are too narrow to allow things to pass through them - or (as you say) that they have such a short life that it's irrelevent...I dunno...they just seem like so much wishful thinking with zero evidence behind them. SteveBaker (talk) 01:09, 11 May 2010 (UTC)

I never understood why people (ScienceApe: you are not the only one) assume that if one end of the wormhole is moving and the other stationary the object sent inside would take on the properties of the exit hole. If the exit hole is moving, then the exit location would constantly change, but the exit velocity of the object traveling inside it wouldn't. Unless you assume the object is bouncing off the walls of the wormhole (like water in a tube), but then by traveling in it you are slowing down the wormhole. Also, a two dimensional wormhole entrance (like the opening of a pipe) has problems with conservation of momentum. You can cause an object to change direction, which violates that law. I think if a worm hole exists, it would have to be three dimensional - meaning you can enter it from any direction, and you leave in the same direction, with the same velocity you entered. Ariel. (talk) 01:38, 11 May 2010 (UTC)

The equivalence principle implies that you can't put these sorts of restrictions on ends of a wormhole. Any object, including a wormhole mouth, can be manipulated by gravitational tugging, and there's no way for the wormhole to "compensate" for that. Given both ends of a wormhole, I think you can always create a closed causal loop by luring them along worldlines of different lengths. Pipe-like wormholes like the one in Star Trek: Deep Space 9 are unrealistic even by wormhole standards. I think some people are misled by illustrations like this into thinking that black holes are "flat". It's actually the accretion disc that's flat. -- BenRG (talk) 09:28, 11 May 2010 (UTC)

Well Ariel if what you are saying is true, then time travel should also be impossible with wormholes. In any case, if the object that leaves the mouth isn't traveling at the same speed as the mouth that would be like stepping off of a car moving at 200 mph, as if you were stepping off of a stationary car. I don't really think that's true. ScienceApe (talk) 01:21, 12 May 2010 (UTC)

Yes. No time travel. I don't believe it's possible in principle at all, but more specifically not with wormholes either. I had a thought. Say you poke a long stick through a wormhole. So now you have one end of the stick stationary, and the other moving. Now grab the moving stick and try to stop it. What happens to the wormhole? Do you slow down the wormhole, because you are slowing down the stick? If so, then their's your answer: the energy comes from the energy containing in the motion of the wormhole. If the wormhole does not slow down, then what happens to the stick? Ariel. (talk) 07:52, 12 May 2010 (UTC)

Yes I meant 1st law, my bad. I'll change the topic name. ScienceApe (talk) 22:32, 10 May 2010 (UTC)

Energy, as we classically understand it, is not globally conserved in general relativity. Instead a compound entity, the stress-energy-momentum pseudotensor is conserved. In essence this says that you can change the total energy in the universe if and only if you change the configuration of space-time as you do it. So, yes, if you accelerate matter through your wormhole then there must be a counter-reaction in the wormhole itself, presumably causing it to slow down. Dragons flight (talk) 01:26, 11 May 2010 (UTC)

ScienceApe, by changing what you've written previously you're making some of the responses to your question appear nonsensical. I've changed it so that your old version appears, crossed out, next to your new version - hope you don't mind - it just makes the contributors who responded look slightly less foolish. Vimescarrot (talk) 05:40, 11 May 2010 (UTC)

May 11

Minimum energy for brute force attack

In the article for Brute force attack it says

The so-called Von Neumann-Landauer Limit implied by the laws of physics sets a lower limit on the energy required to perform a computation of ln(2)kT per bit erased in a computation, where T is the temperature of the computing device in kelvins, k is the Boltzmann constant, and the natural logarithm of 2 is about 0.693

So how can the minimum energy required be 0.693? 0.693 is just a number. Shouldn't it has a unit of J? 139.130.1.226 (talk) 00:22, 11 May 2010 (UTC)

The Boltzmann constant has units of J K⁻¹. Looie496 (talk) 00:27, 11 May 2010 (UTC)

Also, it is easy to see that this limit can be violated, so it is not a fundamental limit at all. Count Iblis (talk) 01:40, 11 May 2010 (UTC)

That paper seems like a meaningless moving of the goalposts. If their bit reservoir is thermal then their bit-clearing protocol doesn't work. Whatever is forcing the reservoir into a non-thermal state ought to be treated as part of the system. To put it another way, a reservoir of N bits each with an independent probability p of being zero contains N (1 + p log p + (1−p) log (1−p)) bits of known value. Their "erasure" protocol swaps the memory bit with a known bit from the reservoir, which just foists the erasure off on whatever device is replenishing the known bits in the reservoir. (And if nothing is replenishing the bits then the reservoir might as well be treated as part of the demon's internal RAM.) The only way to get p ≠ ½ in a thermal state is to have an energy difference between 0 and 1, which takes us back to square one. Maybe I'm missing something. -- BenRG (talk) 08:42, 11 May 2010 (UTC)

I'm not a mathy guy but it seems to me you are completely misreading the sentence. It's saying that "the natural logarithm of 2 is about .693". Which is true. It's not saying that the total energy required is .693; it's still defining all of the variables. The next sentence discusses the actual energy that this equation would imply (in joules and gigawatts and etc.). --Mr.98 (talk) 13:27, 11 May 2010 (UTC)

Help required with this code

Hey! Can anyone please explain me this matlab code for uniform quantization?

computer code

%quantize_uniform.m (Fig.4.1) % gives boundary vector b, quantization level vector c, % mean-square quantization error(MSQE) clear, clf %Gaussian probability density function of x pdf='exp(-(x-m).^2/2/sigma^2)/sqrt(2*pi)/sigma'; %pdf='exp(-(x-m).^2/2/sigma^2)'; xf=inline(['x.*' pdf],'x','m','sigma'); f=inline(pdf,'x','m','sigma'); m=0; sigma=1; % Mean and variance of the random variable x b0=-3; bN=3; % Given least/greatest value of the random variable x for N=5:6 % the number of quantization intervals delta=(bN-b0)/N; b=b0+[0:N]*delta; msqe=0; %Mean-Square Quantization Error for i=1:N %centroid of each interval tmp1=quad(xf,b(i),b(i+1),0.01,[],m,sigma); tmp2=quad(f,b(i),b(i+1),0.01,[],m,sigma); tmp=tmp1/tmp2; c(i)=tmp; x2f=inline(['(x-tmp).^2.*' pdf],'x','m','sigma','tmp'); msqe=msqe+quad(x2f,b(i),b(i+1),0.01,[],m,sigma,tmp); end b,c x=b0+[0:1000]*(bN-b0)/1000; N1=N+1; %ind0=find(x<b(1)); x(ind0)=b(1)*ones(size(ind0)); %left-most interval %indN=find(x>b(N1)); x(indN)=b(N1)*ones(size(indN)); %right-most interval y(find(x<b(1)))=c(1); y(find(x>=b(N1)))=c(N); for i=1:N y(find(b(i)<=x&x<b(i+1)))=c(i); end subplot(2,2,N-4), plot(x,y) %quantization graph hold on, grid on fx=feval(f,x,m,sigma); %probability density ftn plot(x,fx,'r:') axis([-3 3 -3 3]) msqe end

Thanks in advance.--111.68.97.146 (talk) 04:11, 11 May 2010 (UTC)

I've taken the liberty of formatting your source-code as MATLAB code and fixing some mis-leading indentation. This code runs two separate trials, with 5 and 6 quantization intervals, seeking to quantize a function. It appears that the quantization intervals are designed to be non-uniform width - but uniform in the number of inputs that get binned into that interval, based on an input probability distribution function. The code then demonstrates this by computing the quantization intervals (results are stored in the vector c), and applying it to quantize the input function, then plotting the results. Such quantization (with non-uniform intervals) makes optimum use of the number of bits stored, but at the expense of complexity and (deliberate) variable precision of each interval. The hard part was noting what "uniform" refers to. In this case, what is uniform is not the width of the interval, but the probability that a given input will bin into that interval. Nimur (talk) 10:35, 11 May 2010 (UTC)

Lasso Physics

Okay, so this is a homework question, but I've managed to get an answer myself that I wanted to confirm here. If I'm wrong, then hopefully you can identify where I made my error. The question goes as follows:

A thin loop of mass M and radius R is suspended from a string through a point on the trim of the hoop (the setup looks like a lariat trick/lasso). If the support is spun with a high angular velocity ω, the hoop will spin with its plane nearly horizontal and its center nearly on the axis of the support (the support here refers to what the string is attached to). The sring makes an angle α with the verticle.

• (a) Find approximately the small angle β between the plane of the hoop and the horizontal.
• (b) Find approximately the radius of the circle traced out by the center of mass around the vertical axis.

Here are the answers I found. If I'm wrong, let me know and I'll provide my reasoning so that you can perhaps let me know where I've made any incorrect assumptions. For (a), I got β = g/(Rω²), and for (b) I got r = √(Mgtanα/ω). 173.179.59.66 (talk) 07:21, 11 May 2010 (UTC)

Can you clarify what you mean by "the support is spun". Do you mean the support is twisted like a drill? And the whole setup is rigid? Or do you mean spun like a lasso is spun - i.e. the loop makes a circle, and the string (support) traces out a cone shape? Ariel. (talk) 09:43, 11 May 2010 (UTC)

The former, but the cone opens downward. 173.179.59.66 (talk) 16:08, 11 May 2010 (UTC)

Upon further reflection I believe the answer to (a) may be β=g/(Rω² - gtanα). 173.179.59.66 (talk) 21:23, 11 May 2010 (UTC)

Can a continent be subducted?

Is it possible for one continent to be subducted beneath another? As far as I can tell from Geology of India, India has slowed down a lot since colliding with Asia, but what will is likely to happen in the future? Will it simply stop eventually or end up disappearing altogether? I've checked plate tectonics, plate reconstruction and obduction but can't find any information. Continental collision looks to be the place to look but doesn't make it clear what the ultimate fates of the continents are. 131.111.30.21 (talk) 09:17, 11 May 2010 (UTC)

"Clean" subduction of an oceanic plate under a continental plate - because oceanic crust is much denser than the continent.

Usually, oceanic crust subducts, because it is denser than continental crust. In the case where two continental crust zones are colliding, as in India, the two plates have comparable density, so neither is "easily" forced down relative to the other. Eventually, given enough geological time, it seems plausible that some continental crust might be forced downward, but it would be a lot messier, with more deformation of both plates, than your typical picture of a nice, contiguous sheet as you see in the classic diagrams. In the short term, the deformation of the plates results in the Himalayan orogeny zone - more of an inelastic deformation of both plates than a clean subduction. Nimur (talk) 09:34, 11 May 2010 (UTC)

Followup - this letter from the journal Nature, The possible subduction of continental material to depths greater than 200 km (2000), puts a little bit more quantitative spin on the problem. The continental crust has to overcome a density gradient, so it can only be forced downward if the collision gives enough energy and downward momentum to the continent to overcome its buoyant force. (The momentum-, energy-, and time-scales for these sort of inelastic collisions are all huge). This letter indicates some geochemical and mineralogical observations that might put some bounds on how deep continental crust can be forced down. They claim continental crust has been subducted to depths of "150 km", and up to 300 km using "indirect observations". This paper, The Himalayan Arc: large-scale continental subduction, oroclinal bending and back-arc spreading (1986), which I'm having a hard time finding a PDF of, might be of interest. They seem to suggest that paleomagnetic data indicate a rotation and subduction of the entire Indian subcontinent. This paper, Cenozoic Volcanism in Tibet: Evidence for a Transition from Oceanic to Continental Subduction, presents geochemical evidence for subduction. They present the idea that, in India, the only two ways to relieve the strain are continental subduction (India goes under Asia), or convective thinning (India "melts" from the bottom up, and its continental crust is slowly absorbed back into the asthenosphere). Their claim is that the geochemical evidence suggests subduction. Nimur (talk) 09:39, 11 May 2010 (UTC)

Cheers for that, one reason I was asking was because I wondered if any continents have disappeared in the past - reconstructions of plate movements often look like they have big gaps in them making me wonder if other continents have been subducted, taking all their fossils with them. I guess we'll never be able to tell. Try this DOI link it gives me a pdf of the paper you couldn't find. Gotta love that someone modelled the collision with plasticene! 131.111.30.21 (talk) 10:25, 11 May 2010 (UTC)

I, Ant

I've been killing a lot of ants recently. A) Are ants certain to be too tiny-brained to have any sense of self? B) Would a modern computer be capable of mimicing an ant brain in real time? Although I expect the ant-brain circuitry has not been perfectly mapped yet. 78.146.87.143 (talk) 11:26, 11 May 2010 (UTC)

List of animals by number of neurons says that ants have 10000 to 100000 neurons, certainaly a modern PC could do a fair job of simulating that --Digrpat (talk) 11:41, 11 May 2010 (UTC)

Brains are funny things. So funny that there are guidelines as to what does and what does not deserve the moniker, and the central control of insect nervous systems are called ganglia as opposed to a brain for a reason. I don't have first hand knowledge of every organism type, but I believe that invertebrates as a group are said to have ganglia as opposed to brains -- this could very well be incorrect, though. It's likely that rules and regulations of what we term psychology do not traverse into the realm of invertebrates in any sense other than instinct and the like (except for some exceptions, such as high level cephalapods, etc.) DRosenbach ^{(Talk | Contribs)} 11:54, 11 May 2010 (UTC)

It might be possible with the computational power we have (but keep in mind that a neuron is more complex than a node in an artificial neural network), but I've never heard of any research that has even started mapping out insect central nervous systems (I bet this is because it's impossible with current technology), and we understand so little about the way that brains work that simulating an ant is an impossible dream for now. Paul (Stansifer) 14:00, 11 May 2010 (UTC)

Any animal that is physically capable of biting itself (as an ant is) needs to have enough self-recognition to prevent that from happening. Ants can do a lot more than that: they can distinguish ants belonging to their own colony from ants belonging to other colonies. The ant system for passing chemical messages is quite sophisticated. Their brains are small but they pack a lot of computation into that tiny space. Looie496 (talk) 14:56, 11 May 2010 (UTC)

When we think of how to get a universal computer to do something like determine when not to bite something, or how to distinguish some detected creature from another, it often ends up being very hard to do. Now consider if you had to make a device that wasn't universal, but instead had only one task to do (like tell you if a room is light or dark). This sort of specialized device can exist in nature, too, so it's not always fair to compare a computer to anything that demonstrates some level of intelligence. Consider, as a more direct example, the recent work being done on calculations at the atomic level: this article is about how we can use an iodine molecule to perform a fairly sophisticated math equation in a very short amount of time. Are we going to replace a general purpose CPU in a computer with a single iodine molecule any time soon? Its utility, while amazing, is incredibly narrow. --Jmeden2000 (talk) 15:27, 11 May 2010 (UTC)

As to A, it's really not possible to say without you yourself being an ant. They do not take kindly to harassment though, so I think that qualifies them for (very tiny and minor) personhood. Vranak (talk) 15:21, 11 May 2010 (UTC)

One method used to see whether something has a sense of self is to show it a mirror - if it recognizes that this is a reflection then this is meant to be proof that the creature has a sense of self (rather than the more obvious proof that the creature has a sense of 'mirrors'). Do this with ants. If they can't recognize themselves, stomp away! :) --KägeTorä - (影虎) (TALK) 15:50, 11 May 2010 (UTC)

That seems like a rather limited assessment. Apparently blind people have no sense of self, either! --Mr.98 (talk) 16:37, 11 May 2010 (UTC)

The actual experiment that KageTora is referring to here is a lot more complex than that - but it's certainly flawed. Animals like Bats that "see" with sonar may well not recognize that they are even looking at a bat because it has the wrong three dimensional curvature, etc. Dogs are often the same - most (but not all) dogs are really unimpressed by their own reflection in a mirror...presumably because it doesn't smell anything like a dog. On the other hand, birds are completely taken in by mirrors - we had a Red Cardinal in our backyard a few years ago who evidently thought that his own reflection was another male impinging on his terratory - and spend weeks and weeks battering himself against the window trying to scare himself off. If the reaction to the mirror itself is so variable, it's hard to say that an ant that fails the test is somehow lacking a sense of "self" - when the lack of pheromones coming from the reflection mean that the reflection doesn't seem like an ant at all - self or otherwise. It would be like saying that humans are not self-aware because we cannot recognize the smell from a vial of our own sweat as being our own...a dog would find that test pretty convincing! SteveBaker (talk) 17:04, 11 May 2010 (UTC)

Exactly the point I was trying to make - that the mirror experiment is designed from a very human perspective and cannot tell us much if anything about the existence or lack of a creature's sense of self. --KägeTorä - (影虎) (TALK) 17:22, 11 May 2010 (UTC)

Just FYI, it would seem that the European Magpie (ref in article) is aware that the bird in the mirror is its own reflection. I'm not exactly sure if it's the same for some of the larger parrot species (e.g. macaws, African Greys) - but some of them do certainly seem to become aware with time that the reflection is not another bird - in a way that say, Budgerigars or Cockatiels do not. --Kurt Shaped Box (talk) 17:19, 11 May 2010 (UTC)

E.O. Wilson's recent piece in the New Yorker, "Trailhead" explores, to some extent, the question of what ants "think" about. It's labeled as a work of fiction, appropriately, but given that Wilson is probably the world's foremost expert on ants, it is safe to assume that it is rooted pretty heavily in fact. His ant is basically a "programmed" creature—it does not think in a way that is analogous with humans (or mammals), though it is not "dumb". I don't know what a "sense of self" is supposed to mean in a scientific setting but I don't see much evidence for ants having one. They are instinctual automatons, albeit ones that can learn and do rather complicated things:.

If the Trailhead Colony could not understand the history of its own species, how much did it understand of its current condition? How could it make the right decisions for survival? In fact, the Trailhead Colony knew a great deal. Worker ants are far more than automated specks running around on the ground. Even with a brain one-millionth the size of a human’s, an ant can learn a simple maze half as fast as a laboratory rat, and remember the directions to as many as five different destinations when she forages away from the nest. After exploring a new terrain, a worker can integrate all the seemingly haphazard twists and loops she made and, amazingly, return to the nest in a straight line. She can learn and recall the special odor of the colony to which she belongs. The Trailhead Colony, when all the learning and thought of its workers came together, was very smart, by insect standards—and, with the unifying power of its Queen lost and its population growth plummeting, it needed to call on that group intelligence to regain its balance.

Which goes along with a lot of what Wilson has long said about ants—the colony, taken as a superorganism, is really the unit to be worried about, not the individual ant. --Mr.98 (talk) 16:37, 11 May 2010 (UTC)

Better yet, consider the whole ant colony as a being. An individual ant is just a cell of it: drop a chemical that means "I'm dead" on one ant, and all the others will quickly carry it out to the "burial place/dump". It hurries back to the nest, and the whole process is repeated again and again, the carriers never realizing that the kicking and is not quite dead. I doubt that individual ant are capable of learning anything. I'm curious weather someone can give counterexamples. --131.188.3.20 (talk) 17:10, 11 May 2010 (UTC)

I am getting the sense that underneath a lot of this discussion is a desire to throw all of ant-kind into the bin marked 'unremarkable', 'unworthy' and the like. Well I for one think they are pretty cool creatures, and would not advise harming them out of hand. At least not the innocent small black kind we get in the Pacific Northwest. Fire ants, bullet ants, and so on -- different story perhaps. Which leads me to ask 78 - are the ants bothering you by their presence alone? Is it an inherent dislike? Or are they making predations onto your territory? Eating your precious sugar, burrowing into the woodwork and so on? Vranak (talk) 18:02, 11 May 2010 (UTC)

It's remarkable how these sorts of discussions tend to evolve. The OP asks whether ants might have a sense of self, and a dozen replies later, without the OP having said anything more, they are being accused of disliking and disrespecting ants. Looie496 (talk) 18:25, 11 May 2010 (UTC)

Well he says he's been killing a lot of them lately. If that's not disrespect, well I guess it's sheer indifference. Vranak (talk) 18:28, 11 May 2010 (UTC)

Fox's diet

Do foxes eat weasels?Jameslpeterson (talk) 11:28, 11 May 2010 (UTC)

Weasels' main predators are raptors, but foxes would eat weasels. DRosenbach ^{(Talk | Contribs)} 11:56, 11 May 2010 (UTC)

Pitta bread and heat

Why is pitta bread so hot to the touch after coming out of the toaster? I'm assuming it has something to do with the air pocket inside it, but would like a proper explanation. Your regular slice of toast, for example, doesn't even get remotely near as hot. Hammer Raccoon (talk) 12:59, 11 May 2010 (UTC)

The air pocket sounds reasonable. I'd also think the texture and density have a lot to do with it. Pita bread is denser than standard toast (thus carrying more energy at a given temperature), but perhaps more importantly, has a reasonably solid surface. When you pick up a piece of toast, most of the surface is actually exposed air pockets, which can quickly cool (and which make a good insulator anyway). Contrast with pita, where all you touch is hot bread. — Lomn 13:20, 11 May 2010 (UTC)

Mostly agree with Lomn, but also consider that steam will get trapped inside those air pockets, while toast's open structure will allow more of the steam to escape. Same mechanism, it's just that steam holds an awful lot of heat. Matt Deres (talk) 13:31, 11 May 2010 (UTC)

In addition to more moisture in the pita. A pita is also much denser than a piece of white bread. the more holes the more heat dissipates quicker. The denser it is the more heat it retains.165.212.189.187 (talk) 14:24, 11 May 2010 (UTC)

Before jumping to a conclusion about steam, I'd like to pose a question — is the pita hotter, or does it just seem hotter? In other words (and Lomn's implicitly response touched on this) is there a difference in the heat conductivity and heat transfer properties of pita bread versus regular toast? If the pita can transfer energy to your fingers more rapidly (due to greater density, differences in water content, more surface in contact with your skin, or what-have-you) it will feel hotter even if it is at the same surface temperature as the toast. Consider the perceived 'hotness' of the air in an oven with the perceived temperature of a metal rack inside the oven — similar temperature, but very different heat transfer properties.

Incidentally, if you're curious about the effects of the air pocket inside, you can repeat the experiment with the pita sliced in half (across its diameter) so that the inner pocket is unsealed. TenOfAllTrades(talk) 14:27, 11 May 2010 (UTC)

Read our articles on specific heat and humours. I am not going to put two and two together for you, for fear of angering the locals, but if you reflect on what emotional personality a representative sample of a cross section of Americans are statistically likely to attribute to an anthropomorphic cartoon representation of pita bread and a piece of toast, respectively, and how this relates to the two articles, I think you will find yourself no nearer to, and perhaps even inexorably estranged from the answer you seek. 92.224.204.126 (talk) 14:34, 11 May 2010 (UTC)

... what? Nimur (talk) 10:32, 12 May 2010 (UTC)

My experience is that when you pick up a toasted pita, it's hard to avoid squeezing it a bit, which causes steam to come out, and it is the steam that burns you if you aren't careful. Looie496 (talk) 14:59, 11 May 2010 (UTC)

The flat surface of pita transfers heat efficiently to your fingertips, especially since heat causes a little vegetable oil to migrate out to the surface. Vranak (talk) 15:19, 11 May 2010 (UTC)

Thanks for the responses everyone! Very informative. Hammer Raccoon (talk) 17:25, 11 May 2010 (UTC)

Giant King Grass

when i search for giant king grass, the article under wikipedia does not appear but a totally unrelated article. —Preceding unsigned comment added by 75.172.158.69 (talk) 13:25, 11 May 2010 (UTC) :The help desk might be a better place to ask your question. --Chemicalinterest (talk) 13:34, 11 May 2010 (UTC

Giant King Grass is a red link. Page 8 of this presentation says that China Giant King Grass is a hybrid between elephant grass and another grass. Miscanthus giganteus is also a hybrid between two species, but I'm not sure if it shares all the characteristics in the presentation about CGKG. If someone can find more information (there is none on google scholar) a redirect should be made to a relevant article (maybe just to Miscanthus if nothing else can be found. 131.111.30.21 (talk) 14:41, 11 May 2010 (UTC)

This says that Giant King Grass is a trademark, that's why we won't be able to find out what actual species it is a hybrid of. Probably shouldn't have an article yet as most info looks like press releases but maybe a redirect to Miscanthus wouldn't go a miss. 131.111.30.21 (talk) 14:48, 11 May 2010 (UTC)

PoCl₂ oxidation

This is purely out of curiosity. In the polonium dichloride article, it says that polonium dichloride reacts with nitric acid to form a dark red solution and a flaky white precipitate of unknown composition. This may be the reaction: 4 HNO₃ + 6 PoCl₂ → 2 H₂O + 4 NO + 3 PoCl₄ + 3 PoO₂ Any suggestions whether it is or not? --Chemicalinterest (talk) 13:32, 11 May 2010 (UTC)

The statement is referenced to a 1955 article in J. Chem Soc. Did you check out that article? It may have more info in the article. Furthermore, there are analytical techniques which are commonplace now which were unavailible in 1955. A simple literature search may turn up more recent studies on polonium halide salts where the nitric acid reaction has been more thoroughly analyzed. --Jayron32 16:35, 11 May 2010 (UTC)

A quick google taught me that PoCl₄ is a yellow solid that seems to be fairly water-soluble (or susceptible to hydrolyis) and eaily forms soluble complexes. The Po⁺²/Po⁺⁴ electrode potential is 1.1 V (0.72 V in HCl as an ion complex) and Po⁺⁴/Po⁺⁶ 1.5 V. How does that fit with your proposal of nitric acid oxidizing Po⁺² to Po⁺⁴? DMacks (talk) 17:01, 11 May 2010 (UTC)

I wrote polonium dichloride. I have the paper in front of me and it states:

The dichloride dissolves readily in dilute hydrochloric acid to a pink solution which rapidly autoxidises to the quadrivalent state and is immediately oxidised by hydrogen peroxide or chlorine water. Addition of potassium hydroxide solution to this solution gives a dark brown precipitate (solubility 1.4 mg. of ²¹⁰Po/l.) which may be the hydrated bivalent oxide or hydroxide and which is very rapidly oxidised to the quadrivalent state. With 0.1N-nitric acid it gives a dark red solution and then rapidly a white flocculent precipitate, the composition of which is not known.

Make of that what you will.

Ben (talk) 17:46, 11 May 2010 (UTC)

Name of plant, please

I remember a plant which had curved narrow grey twigs. It would sit in a cupboard for years and on being brought out, put in a bowl and given some water, would come back to life. Named something like a Judea plant or a Lebanon plant. Kittybrewster ☎ 18:12, 11 May 2010 (UTC)

Could it be any of our Resurrection plants? Dbfirs 18:16, 11 May 2010 (UTC)

Brilliant and spot on. Anastatica. Kittybrewster ☎ 18:21, 11 May 2010 (UTC)

Fissile elements used nuclear reactors

What elements apart from uranium and plutonium are used, or could be used, to supply energy? Does plutonium require a different kind of reactor than uranium? Do other elements require different reactor set-ups? Thanks--92.251.166.171 (talk) 18:29, 11 May 2010 (UTC)

It is possible to run a molten salt reactor with the thorium fuel cycle, which uses a thorium/uranium fuel cycle. -- Finlay McWalter • Talk 18:38, 11 May 2010 (UTC)

But it's still uranium that's providing the power. The thorium absorbs neutrons produced by the fission of U-235 and creates U-233, which could then be used for generating more power. The thorium itself is not fuel, but it can be turned into fuel. --Mr.98 (talk) 22:27, 11 May 2010 (UTC)

In principle, any element that's radioactive (which is most of them - if you pick the right isotopes) could hypothetically be used to power a nuclear reactor of some kind. But the problem is that the radioactive isotopes of some elements are so rare that you can't obtain them in nature, others have such spectacularly short half-lives that even if you could find them, they'd be gone within milliseconds - and yet others have such a long half-life that they give up their energy too slowly to be useful and can't create the desired self-sustaining reactions. If you could find a source of (for example) Mercury's isotope ¹⁹⁴Hg, it's radioactive, it has a half life of 450 years and the byproduct is gold! Sadly, the only way to get ¹⁹⁴Hg is to make it by irradiating some gold...so we're not likely to see any mercury reactors around in the near future! You most certainly do need different reactors for different nuclear fuels - but the reactor isn't the biggest part of a nuclear power plant - so perhaps the cost to refit one to a different type of fuel might not be horrific. SteveBaker (talk) 20:17, 11 May 2010 (UTC)

Correct me if I'm wrong (I know very little nuclear physics) but from our nuclear reactor article a reactor sustains a nuclear chain reaction by definition, for an ordinary fission reactor (as opposed to a fusion reactor) this would surely mean that the fuel would need to be either fissile or fertile, rather than simply radioactive. An atomic battery on the other hand could hypothetically use any radioactive isotope.131.111.185.68 (talk) 22:20, 11 May 2010 (UTC)

Steve, using random radioactive elements for heat is not the same thing as powering a nuclear reactor. You need fissile materials if you are going to have an actual chain reaction. Yes, if you had ungodly quantities of very radioactive materials you could get the waste heat off of them like in an RTG but that won't be efficient for large-scale power production. There are very different principles behind such designs. An RTG is not a nuclear reactor. --Mr.98 (talk) 22:27, 11 May 2010 (UTC)

I agree, Steve is confusing RTGs and nuclear reactors. --Tango (talk) 23:03, 11 May 2010 (UTC)

See the article fissile. Basically it is just uranium and plutonium, but you can use the neutrons created (say, from U-235 fissions) to breed other isotopes of uranium or plutonium. As for different reactor designs... yes, basically. Different fuels behave differently. Different reactor designs are optimized towards specific types of fuels, and some won't work if you put in the wrong fuel. Some reactor designs are more flexible; reactors that use LEU can also use MOX fuel in many cases. But you can't just mix-and-match willy-nilly. --Mr.98 (talk) 22:27, 11 May 2010 (UTC)

There are other elements with fissile isotopes (eg. Curium), but I believe they are all synthetic, which means they are only available in small quantities. If you want enough for a significant nuclear reaction, you are going to have to go with either uranium or plutonium. --Tango (talk) 23:03, 11 May 2010 (UTC)

Actually, looking a little closer: Fast-neutron reactors use transuranics beyond plutonium as "fuels" in a the sense that they breed them and then fission them. Apparently these are known as the minor actinides. That's interesting to know. --Mr.98 (talk) 01:37, 12 May 2010 (UTC)

Chalcogenide reduction potential

It seems that chalcogenides (oxide, sulfide, selenide, telluride, polonide) become stronger reducing agents the bigger the molecules get. Oxide is very weak, sulfide is moderately weak, and telluride is quite strong. Is there a pattern? --Chemicalinterest (talk) 20:34, 11 May 2010 (UTC)

Try looking at their electronegativities, there may be a correlation. Oxygen is the most electronegative, which makes it very difficult to remove electrons from it (as a reducing agent, it would have to donate electrons to some other species) and hence is not a very good reducing agent.24.150.18.30 (talk) 22:22, 11 May 2010 (UTC)

What about calaverite, a gold telluride? Presumably it contains gold in the +1 oxidation state and tellurium in the -2 oxidation state. I thought that since telluride is such as strong reducing agent (see sodium telluride, where it is oxidized by oxygen readily) and gold(I) is such a strong oxidizing agent, that gold telluride would be extremely unstable, possible even explosive. Why is it found naturally though? Normally very reactive chemicals are not found in the earth's crust. Thanks. --Chemicalinterest (talk) 22:51, 11 May 2010 (UTC)

It is quite possible that the gold is not in the +1 oxidation state, nor is the Te in the -2 oxidation state. Things like sodium chloride may be considered to have very ionic character, with the sodium and chlorine atoms each having an almost full positive and negative charge respectively. The transition metals, and those elements down near the bottom of the periodic table behave differently, and I suspect that in this case there will be some metallic bonding, or even some covalent character given that tellurium is a semimetal. The electron rich atoms (Te2-) can donate electrons (or electron density, it doesn't have to be a whole number of electrons) to the electron poor atoms, resulting in a decrease in the charge separation. Effectively, you could have Au^(+0.5)₂ Te^(-1), or some variation which makes the tellurium less of a reducing agent and gold less of an oxidizing agent. This should show that the reducing ability of 'telluride' (or anything else in the series) is dependent on the the actual chemical species and not just on the fact that there is tellurium present. Take a look at our Wikipedia page on Bonding in solids: [21].24.150.18.30 (talk) 23:36, 11 May 2010 (UTC)

Zintl phase might be a good point to start.--Stone (talk) 15:47, 12 May 2010 (UTC)

I was always told that group VIA (16) elements tend to form compound with a -2 oxidation state. Tellurium doesn't seem to do that readily. Only oxide commonly does it. Group VA (15) elements are supposed to have a -3 oxidation state, but the elements are not predominately -3. Nitrides are not easily formed, phosphides are reactive, arsenides, antimonides, bismuthides are rare. It doesn't seem like there is much periodicity in the groups. --Chemicalinterest (talk) 16:07, 12 May 2010 (UTC)

Identify drill bits

On this page is a selection of drill bits. On the bottom right of the image are some bits that look like flat-head screwdrivers with points shooting out of the centre. What are they? --78.148.181.99 (talk) 21:18, 11 May 2010 (UTC)

Wood bits (that is to say, bits for drilling holes in wood). DuncanHill (talk) 21:21, 11 May 2010 (UTC)

See Drill bit#Spade bit. DuncanHill (talk) 21:23, 11 May 2010 (UTC)

Psychological term for the "deification" recently deceased people get?

When someone dies, especially someone young, you are almost certain to hear others describing them as wonderful, so talented, having had limitless potential, etc etc etc. Suddenly, in death, each individual's traits become a long list of superlatives. Clearly, there are people to which not all of these things really apply - and their surviving relatives & friends (to me) seem rather caught up in the moment. Is there a psychological term for this process of instantly forgetting all the negative qualities of a person and thinking of them as some sort of perfect angel once they die? 61.189.63.174 (talk) 22:30, 11 May 2010 (UTC)

I don't want to be a psychologist, but you sound like you are upset, it might help to talk to someone in person, rather than over the internet. But to answer your question: From [22]: "The Talmud contains advice for those who deliver the eulogy. Its aim should be to call attention to the achievements of the deceased. A little exaggeration was felt to be in order. In a eulogy, it is permitted to imply that the deceased was rather more generous and pious than he really was, but the kind of insincere praise which everyone present knows to be false must be avoided. One talmudic rabbi said to a man well known as a gifted eulogizer: "Give warm expression to your feelings when you eulogize me for I shall be present there." And [23] ".... give the deceased a little more credit than they deserve. The Taz (Rabbi David Segal, 1586-1667) was troubled by this apparently disingenuous leniency. In his landmark commentary on the Shulchan Aruch, he offered several possible reasons as to why embellishment may be permitted in a eulogy. Firstly, he warned that if we were forced to stick to the plain truth without any exaggeration at all, zealous people would be overly cautious. They would stint in their praise of their loved ones; shortchanging them of the praise they had deserved. He also pointed out that even in the most intimate relationships, there is so much that goes unsaid. None of us can be aware of every good deed that someone else did during their life, so we have to leave a margin of error to account for the many private acts of kindness that they may have done. Finally, he suggests that good people deserve credit for their good intentions even if these were never fulfilled, for had they only known the infinite value of a good deed they would certainly have done it. When speaking of our dead relatives, we can afford to be generous." I don't think people actually forget, so there is no specific term like what you are looking for (not that I know of anyway), but people prefer to focus on the good. Ariel. (talk) 00:00, 12 May 2010 (UTC)

Seems like a perfectly reasonable question to me (have you noticed that every single British soldier killed in Afghanistan has been a hero? Not one of them was an ordinary bloke who only signed up to escape the dole.) Anyway, the general concept is de mortuis nil nisi bonum. DuncanHill (talk) 00:07, 12 May 2010 (UTC)

Recently in Australia, Carl Williams was fondly remembered at his funeral with "touching" eulogies, before being buried in his imported gold casket.. I mean he was still a human being with a (ex)wife and kids.. I suppose kids could grow up to hate their parents, but even scumbags can love their kids and be nice to them and be fondly remembered by them, even if they were hated by everyone else, that's all it would take. I think the effect you are thinking of is related to cognitive dissonance theory, not sure what it would be specifically. Mourning for the dead is instinctive, you have to really really hate someone not to mourn them when they die. So mourning for someone and the fact that they were (sometimes/often) a big jerk would cause cognitive dissonance, so to justify it you would gloss over and forget anything unpleasant and only remember the great things about them. Vespine (talk) 01:35, 12 May 2010 (UTC)

Yeah, it's called don't speak ill of the dead. It's not a psychological pathology, it's called having respect for others. Vranak (talk) 13:55, 12 May 2010 (UTC)

There are worlds of difference between respecting someone, not speaking ill of them, and piling superlatives on a person just because they've croaked. Only this last thing is the point of the question and it's a reasonable one. So we don't speak ill of the dead (not that it's going to bother them now, is it?); why add false praise? It's a bit like what goes on when someone retires ("John worked tirelessly to improve grommet margins .2% above expectations over his forty years at this company...") - especially sports and media figures ("Howard Cosell was the greatest TV broadcaster in the history of the medium and I don't mind saying so now that the son-of-a-bitch is finally off the air..."). You can be respectful without completely throwing away your objectivity. Matt Deres (talk) 16:34, 12 May 2010 (UTC)

In many or most cases, eulogies, or eulogy-like words, are spoken by people who had some relationship to the deceased, or at least knew the person, when they were alive. There is a tendency to speak well of such a person, because you genuinely miss their good qualities, and their bad qualities are understood to no longer be a presence. Bus stop (talk) 16:49, 12 May 2010 (UTC)

I disagree with the OP's statement that grieving is the "process of instantly forgetting all the negative qualities". We could question the assumption that people delivering eulogies actually believe what they are saying. They may knowingly stretch the truth because they thought it was socially acceptable or prescribed behavior. If this is true, this behavior would be a case of Observational learning122.169.152.60 (talk) 18:00, 12 May 2010 (UTC)

I'd normally not repeat myself but I think you guys totally missed my point. Most of the stuff you are saying like "why add false praise?" and "bad qualities are understood to no longer be a presence" seem to me to be very well explained by cognitive dissonance theory. Mourning someone while at the same time remembering all the bad things they did would cause dissonance. To resolve the dissonance you either not mourn them, which is hard to do since mourning is such a primitive reaction, so you justify away any negative views you might have had and exaggerate the good things they did. This would predict that the nastier someone is, the more people would have to exaggerate the good things they did to justify their mourning. This is one of those strange "counter intuitive" things that happens which is otherwise difficult to explain. Obviously there would be a tipping point where you can no longer justify the nasty person and the option of not mourning them becomes easier, this would happen much sooner for someone who totally hated the person to begin with, but a lot later for the person's children or parents. Vespine (talk) 22:30, 12 May 2010 (UTC)

Just a side note, to eulogise is, by definition, to speak well of - [24] Adambrowne666 (talk) 22:01, 12 May 2010 (UTC)

Common magnets

Are the common magnets found in shower curtains, speakers, etc. ceramic magnets? They crack easily. If they are ceramic, do they just contain barium/strontium carbonates and iron oxides, as the article says? They dissolve in hydrochloric acid slowly with minimal bubbling to form a yellow solution, which gets more orange after time. It seems like iron oxide, then cobalt oxide. The yellow could be nickel oxide dissolving then reacting to form NiCl₄^2-, which is yellow. Any thoughts? --Chemicalinterest (talk) 22:46, 11 May 2010 (UTC)

Ferrite magnet is your article on this. They are cheap without exotic rare earth elements. Graeme Bartlett (talk) 11:09, 12 May 2010 (UTC)

Why the reddish color when they are placed in hot hydrochloric acid? Barium chloride is colorless, strontium chloride is colorless, and iron chloride is either light green or yellow. Do they have cobalt oxides in them? --Chemicalinterest (talk) 13:00, 12 May 2010 (UTC)

You should be able to precipitate the barium or strontium by adding sodium sulfate. To distinguish coblat and iron, ammonium thiocyanate causes a blue or red colour. Iron thiocyanate complex can be removed by adding fluoride, to form FeF₆^3- ion in preference. You need to read about Analytical chemistry, Bead test (which need a lot of work) and Qualitative inorganic analysis. Prospectors are very interested to tell if a mineral contains cobalt, so you can mimic what they do, ferrite is an artificial mineral. Graeme Bartlett (talk) 22:12, 12 May 2010 (UTC)

May 12

Nernst equation for reaction 2A+ + B ----> B2+ + A2

Take maybe, Ag+ and Zn(0) ...

How do you use the Nernst equation when the donor species and the receiving species give and receive a different amount of electrons? I've tried looking up examples online, but the websites are being obnoxious and giving nice examples like Cu(II) and Zn(II). I'm trying to figure out how you would figure out the reaction quotients (for the ln Q) term when say, Ag+ is oxidising Cu(0) to Cu(II), or Cr(VI) oxidises Fe(II) to Fe(III) and becomes Cr(III) in the process.

Do you set up separate Nernst equations for each half-cell, or write a Nernst equation for the whole reaction? Sometimes they seem to give different results (because of where z gets applied). John Riemann Soong (talk) 00:48, 12 May 2010 (UTC)

You balance the equation, and then use the appropriate cooeficients in the equilibrium value in the Nernst equation. So, for example, say I have silver ions being reduced and copper being oxidized to copper(II). I would write:

2Ag⁺_(aq) + Cu_(s) → 2Ag_(s) + Cu²⁺_(aq).

In this case, n=2, and

K = [Cu²⁺_(aq)] ⁄ [Ag⁺_(aq)]².

I hope that helps; be feel free to ask if you're still confused. Buddy431 (talk) 05:41, 12 May 2010 (UTC)

Controlled criticality accident?

Back a few weeks ago I went on a tour of the TRIGA Mark II nuclear reactor at Kansas State University, they said something about they could do controlled supercriticality or something of the sort, and they had a picture of a nearly-blinding burst of either Cherenkov radiation or some other bright blue-white light, similar to this except extremely bright. How does this (what I'm assuming is a) controlled criticality accident work? Ks0stm ^(T•C•G) 02:55, 12 May 2010 (UTC)

If it is controlled and intentional, than it is not an accident. 174.58.105.234 (talk) 04:29, 12 May 2010 (UTC)

That's not exactly what I was asking... Ks0stm ^(T•C•G) 04:30, 12 May 2010 (UTC)

Like you guessed it's Cherenkov radiation. All they do is remove some of the moderators. The reactor then starts "running", and the Cherenkov radiation happens automatically. It's not really a criticality accident - it's just the normal operation of the reactor. With the moderators you can dial the reactor up and down. A criticality accident and the normal running of a reactor are just different levels of the same thing. Prompt critical is a good article about the difference between the various levels of criticality. Ariel. (talk) 09:29, 12 May 2010 (UTC)

Just noting that you are confusing the control rods with the moderator. They are not the same thing. Control rods control the reaction rate. Moderators change the properties of the neutrons (e.g. slow down fast neutrons, because slow neutrons work better with certain types of reactor fuels). You don't remove the moderator while a reactor is running—it's just part of the reactor core. You can remove control rods (to increase the reaction rate). --Mr.98 (talk) 13:45, 12 May 2010 (UTC)

A nuclear reactor has to go critical to work. Graeme Bartlett (talk) 10:49, 12 May 2010 (UTC)

It's called "pulsing". It's a neat thing you can do with TRIGAs specifically:

The prototype TRIGA (Training, Research, Isotopes, General Atomics) nuclear reactor was commissioned on General Atomics' then new site on May 3, 1958. Known as the TRIGA Mark I reactor, it was originally licensed to operate at a power level of 10 kilowatts, but was soon upgraded to 250 kilowatts. This little reactor, because of its inherently safe features, could also be rapidly "pulsed" to power levels of over 1000 megawatts after which (and without any outside intervention) it would return, in a few thousandths of a second, to a safe low power as a result of the effect of the ubiquitous warm neutrons. This original TRIGA, designated as a nuclear historic landmark because it pioneered the use of unique, inherently safe capabilities in nuclear reactors, operated successfully until 1997, when it was permanently shut down because of its age. The pulsing feature of UZrH fueled reactors, first demonstrated in this prototype TRIGA at General Atomics, are standard among many TRIGA reactors, and special designs of pulsed TRIGA's in use today routinely achieve power levels of 22,000 MW to test the safety of fuels for nuclear power reactors.[25]

Basically you can pull out all of the control rods, it will get supercritical, but because of the way a TRIGA is set up, it will quickly and automatically stop the reaction. (The reason it works is that TRIGA fuel is made so that the hotter it gets, the worse it is at sustaining nuclear reactions. So it basically won't be able to melt down—the more it reacts, the more it automatically starts to correct itself. It's a good thing for a research reactor though it wouldn't work for a power reactor.) Google "TRIGA pulse" and you'll find a lot of pages on it (though most are fairly technical). There are a number of YouTube videos of TRIGAs doing this, including one of the reactor which you toured. --Mr.98 (talk) 13:34, 12 May 2010 (UTC)

There are a number of videos of such pulses on Youtube. --Sean 13:53, 12 May 2010 (UTC)

Awesome, thanks Mr.98 and Sean, that's what I was looking for. That seems to be what they were describing on the tour, and that video of the pulse actually is the KSU reactor. Thanks! Ks0stm ^(T•C•G) 00:39, 13 May 2010 (UTC)

Bomb bays

How many, if any, internal bomb bays do the F-15 Eagle, F-15E Strike Eagle, F-16 Fighting FalconF/A-18 Hornet, and F/A-18E/F Super Hornet have? --The High Fin Sperm Whale 04:58, 12 May 2010 (UTC)

All of the articles list only the number and configuration of Hardpoints on the aircraft, leading me to believe that none of them have internal bays. Beach drifter (talk) 05:08, 12 May 2010 (UTC)

Al four designs date before the stealth time and at that time a multi role jet was designed that way. Stealth design makes internal bays for bombs and rockets necessary to reduce radar reflections.--Stone (talk) 05:23, 12 May 2010 (UTC)

Interesting question, but I agree with Beach drifter & Stone. I believe that only bombers of that 'vintage' carried weapons(bombs) internally. The fighters would have internal cannon/guns. FYI the F-105 Thunderchief had hardpoints and an internal bomb bay. See Specifications(Armament)
* Bomb bay has something to say about the issue,"Notable exceptions are the F-101, F-102 and F-106 interceptor aircraft, all of which had bomb bays" Where they carried their missiles. It seems they had NO external hardpoints. I thought some of the fighters you mentioned could carry weapons 'semi-recessed' into the fuselage, but can't find any mention on Wikipedia.--220.101.28.25 (talk) 08:20, 12 May 2010 (UTC)

The F-102 and F-106 each had two hardpoints (one under each wing) for drop tanks, but carried all their missiles inside the fuselage. The F-101 had a missile bay in the fuselage, but could also carry missiles (notably the oversized Genie missile) semi-recessed under the fuselage. FWiW 67.170.215.166 (talk) 02:14, 13 May 2010 (UTC)

I can confirm that neither F15, F16 or F18 have internal bomb bays (I've built flight simulators for all three!). You see them on stealthy planes like the F117 and F22 because the weapons themselves are not stealthy and you'd spot the aircraft on radar if it had them mounted externally. SteveBaker (talk) 15:00, 12 May 2010 (UTC)

External weapons

How do having missiles and bombs carried externally on a stealth aircraft compromise its stealth? How does the radar pick them up? Thanks.--116.71.46.255 (talk) 15:11, 12 May 2010 (UTC)

Radar works by sending out radio waves and seeing what bounces back. When the signal is returned it indicates there's an object in that direction. A stealth aircraft minimize the ability of radar to detect it by being shaped in such a way that most of the radio waves that hit it get reflected off in a different direction than they came from, which means they'll never return to the radar antenna. If you stick objects on the outside, they mess up that shape. The radar will hit these external objects and reflect back to the antenna and make the plane's presence apparent. See also Stealth_aircraft#Detection. Rckrone (talk) 16:45, 12 May 2010 (UTC)

The other important factor is that stealth aircraft are often coated with materials that absorb radar. These coatings are incredibly expensive, so the military doesn't apply them to bombs and missiles. --Carnildo (talk) 01:44, 13 May 2010 (UTC)

Vulcans, Romulans and Remans

In the Star Trek universe, these three races are all related. Vulcans are the original race with those who would become Romulans leaving the planet (about 5000 years ago) to find their own planet somewhere "out there." Eventually, they do. Surprizingly, we are also introduced to Remans (who live on the sister planet to the Romulans). What does not make sense to me is the significant differences in the appearances of the three races. Given that it is only 5000 years from when the Romulans left Vulcan to the "present" day Trek universe (and an even shorter time for the Reman off shoot), is this enough time to effect the changes we see (especially with the Romulans and Remans)? If I left Earth, travelled to another planet that could sustain me, would my decendents look that much different than those who remained on Earth? —Preceding unsigned comment added by 99.250.117.26 (talk) 05:14, 12 May 2010 (UTC)

I think the underlying question then should be - how much can the external characteristics of a population of humans change in 5,000 years? - I think that's a very interesting question, and I look forward to reading the properly sourced responses! 218.25.32.210 (talk) 06:03, 12 May 2010 (UTC)

It's quite easy to change appearance in a few dozen generations with a breeding programme, as we do with breeds of dog! Dbfirs 07:57, 12 May 2010 (UTC)

QI claims that dogs are unique in that respect - domestic cats don't have anywhere near the variation that dogs do. So they say. 212.219.39.146 (talk) 09:50, 12 May 2010 (UTC)

It is believed that dogs do not originate entirely from a single species, i.e. certain closely related dog-like species from different parts of the world were mixed-in after they became domesticated, which may account for some of the extra variations. Another example of huge changes in physical appearance is of course, the domestic pigeon, a favourite of Darwin. 210.254.117.185 (talk) 10:18, 12 May 2010 (UTC)

Remember this is a work of fiction, anything is possible. However there could be a mutation that makes part of the gene expression very variable, or part of the genome very mutable. So radical changes are possible within a species or over a few generations. Graeme Bartlett (talk) 10:48, 12 May 2010 (UTC)

How different are Vulcans and Romulans anyway? They don't appear to be that different in looks, from what I remember just a slightly thicker eye area. Humans vary in eye fold shape too, but are still the same species. Ariel. (talk) 11:06, 12 May 2010 (UTC)

Also see founder effect. 131.111.185.68 (talk) 11:15, 12 May 2010 (UTC)

Have you seen the differences between the Klingons in the original series compared to those in the next generation? That was like 50-100 years difference, so perhaps alien species are really good at changing their appearances in short time scales in the star trek universe. Googlemeister (talk) 13:35, 12 May 2010 (UTC)

Ahem! "We do not discuss this with outsiders!" --Stephan Schulz (talk) 15:26, 12 May 2010 (UTC)

(edit conflict) That was due to a failed genetic experiment, not evolution. Vimescarrot (talk) 15:32, 12 May 2010 (UTC)

First of all, I agree that since Trek is science fiction, they use a certain amount of "literary license" in the story line. Also, the difference in the appearance between a Vulcan and a Romulan is is significantly less than between either of them and Remans. Even here on Earth, the variations between the various races is fairly negligble and, if I understand a National Geographic special I recently watched, took place over many thougsands of years (i.e. 100,000 +). So, I guess I am wondering just how much change one could expect given the relatively short timespan between the people leaving Vulcan and finding Romulus and Remus . . . so as someone earlier stated in rephrasing the question: how much can the external characteristics of a population of humans change in 5,000 years? —Preceding unsigned comment added by 69.77.185.91 (talk) 13:57, 12 May 2010 (UTC)

I think the Founder effect, as linked to above, is the most likely explanation for the descendants of colonists being significantly different from the parent population. The Memory Alpha article on Remus [26] says that the Remens may be descendants of Romulans, but could also be a separate species. The latter certainly seems more likely. --Tango (talk) 14:21, 12 May 2010 (UTC)

5000 years is typically more than 150 generations. A lot can change in that time. Out of Africa is only ~10 times farther back. The Americas have only been populated for ~15000 years. --Stephan Schulz (talk) 15:37, 12 May 2010 (UTC)

To add to the confusion of the origin of the Remans, there are several novels that outline their Vulcan/Romulan origins (i.e. some Romulans betrayed other Romulans who were living on Remus at the time, marooned them there and made slaves of them.)Somehow, the harsh conditions resulted in an appearance significantly different from their Romulan/Vulcan origins - I guess this is what happens when literary liciense goes too far . . . —Preceding unsigned comment added by 69.77.185.91 (talk) 14:46, 12 May 2010 (UTC)

Jumping

If I want to jump up into the air at 5.4 m/s relative to the ground after one second, do I have to apply an acceleration of 5.4 m/s² (just the Delta-v) or an acceleration of 15.2 m/s² (Delta-v plus defeating 1 g of Earth gravity)? --213.229.148.222 (talk) 08:34, 12 May 2010 (UTC)

If you start at rest (relative to the Earth) and accelerate at a constant rate (relative to the Earth) and after one second your velocity (relative to the Earth) is 5.4 m/s then, by definition, your rate of acceleration (relative to the Earth) is 5.4 m/s². But the constant force required to produce this acceleration is m(g + 5.4) N. Gandalf61 (talk) 08:56, 12 May 2010 (UTC)

It is more likely that your acceleration will be impulse-like, because you can only apply a meaningful force while your feet are in contact with the ground. Because you are not a point-particle, you can continue to change your momentum even in mid-air, but for simplification, consider that effect "negligible." So, if you want to jump off the ground with an initial velocity of 5.4 m/s (which would be pretty darned fast for a human jump), you would undergo an "instantaneous" acceleration (rather, a very abrupt acceleration lasting a few milliseconds or tens of milliseconds), as your legs and knees and feet execute the momentum transfer. It seems reasonable that this acceleration might be as high as 2 or 5 g - in other words, 20 or 50 m/s², but would only last a brief instant. Then, you would have no additional acceleration other than the constant acceleration of gravity, and your jump would slow and you would follow a parabola trajectory until you land on the ground. Since you wanted to have a velocity of 5.4 m/s after one second, you need a much higher initial velocity - we can calculate what that might be using basic physics, but it's safe to say "impossible for a human to jump that fast." Nimur (talk) 10:14, 12 May 2010 (UTC)

The relevant equation is: v = u + a.t where v is your velocity, a is your acceleration, t is the time and u is your initial velocity. There are two 'phases' to your motion and we have to resolve them separately. The first phase is when you start pushing off the ground with some acceleration - the second is when your feet leave the ground and you are in free-fall. However, since gravity slows you down during this second phase, the fastest you'll ever be moving upwards is the instant your feet leave the ground. So that means we know some of the numbers in this equation: v must be 5.4ms^-1, u is zero, but 'a' and 't' are unknowns. Since we have an equation with two unknowns, there must be an infinite number of possible solutions. A very short but very fast acceleration or a more prolonged but gentler one would do. So we need more information...and we have that...the length of your legs. So we can use another equation: d = u.t + 1/2 a.t² (d is 'distance travelled' - the other things are the same as in the previous equation). We know 'd' (the difference in your body height when squatted and when fully extended at the point your feet leave the ground), u is still zero, and we still don't know 'a' and 't'. But now we have two equations with two unknowns and we can solve for that.

When you do that, you get: a = v²/2d. How long are your legs? If we guess ~1 meter then the acceleration is something like 14.6 ms^-2...that's about 1.5g.

The tricky part of your question is about the nature of acceleration versus gravity. Your acceleration is whatever it is - gravity is a force, and your net acceleration is determined by F=m.a (F is the total force, m is your mass, a is the acceleration). To get the desired acceleration (by solving the previous pair of equations) you need to divide the force applied by your leg muscles MINUS the force due to gravity - and divide by your mass.

Of course this is all an approximation - I'm assuming that the force applied by your muscles is the same throughout the jump - which it won't be - and the calculation should really be done separately for your body, your upper and lower legs and your feet because (for example) your feet don't start to accelerate until the very last part of the jump...but in terms of figuring out whether this is even possible, the simplified version of the math is probably good enough.

SteveBaker (talk) 14:53, 12 May 2010 (UTC)

Oh - poop - I forgot that you said "after 1 second" - that makes things more complicated...v=ut + at², we know that u is zero, t is 1 and v is 5.4 so a is 5.4ms^-1 - which is much less acceleration than before - but because d = u.t + 1/2 at², you'd have to be accelerating to the desired speed over a distance of 2.7 meters - which you can't do because your legs aren't that long! So now you'll have to leave the ground at a higher speed - before the 1 second time limit is up and allow gravity to slow you down so that you hit that precise speed at the desired time. SteveBaker (talk) 20:53, 12 May 2010 (UTC)

Experiments in making LCDs

I've been reading about ways of making various display technologies at home, and I came across this video: http://www.tricklife.com/view.php?id=1049 which claims to be instructions on how to make an LCD using a battery, a magnet, water, and sugar. Unfortunately the video is corrupted or something, and it only plays the first 30 seconds. Is anyone familiar with this method? I'm a bit suspicious since I see no polarizing material. Are there any other methods for making something similar? I'd be happy with a single "pixel"-like thing which demonstrates the principle. Internet searches were no help, but maybe my google-fu is weak. —Preceding unsigned comment added by 69.196.132.120 (talk) 08:58, 12 May 2010 (UTC)

Modern LCDs are made using an electroactive polymer that has the property of changing its optical polarization when voltage is applied. Such molecules are not commonplace, though there are many with at least a weak effect. I think it is impractical to make any of these using "kitchen chemistry" - certainly, you need more than just sugar and a battery. For example, MBBA is one such molecule with the electrooptical properties that would make an LCD display possible. 4-Cyano-4'-pentylbiphenyl is a bit more modern, and here is how to make it - but again, hardly something you can do with sugar and a battery. Cholesteryl oleyl carbonate is a biological / organic liquid crystal, but I don't think that it can be made with kitchen ingredients either (our article says it can be found in some hair dyes). I also do not believe that it can be used as the active element in an LCD screen - I think it is more useful during the processing stages. Nimur (talk) 10:19, 12 May 2010 (UTC)

As an aside - an awful lot of those YouTube (and other) "science videos" where someone purports to do something quite amazing with common kitchen chemistry are faked. This is really, really annoying - if there were one category of Internet nastiness that I could wave away with a magic wand...that would be it! SteveBaker (talk) 14:28, 12 May 2010 (UTC)

Thanks for your answers. I eventually found this question on instructables which refers to this video in which Tim Hunkin (hosting The Secret Life of Machines) uses some liquid crystal he got from a lab/manufacturer. I think I'm going to see how well it works to extract the liquid from some displays I have (the black+grey displays in calculators, watches, etc). Failing that, I'll see if anyone will send me some. 75.119.253.30 (talk) 17:30, 12 May 2010 (UTC)

colorblind cuttlefish and camouflage

Since cuttlefish are supposedly colorblind, how are they able to change their own color to match their surroundings? 210.254.117.185 (talk) 10:13, 12 May 2010 (UTC)

There is no requirement that an animal can perceive every aspect of its own actions; for example, humans have a capability to emit odors that they can not smell, and regularly emit infrared radiation that they can not see. The extent to which the cuttlefish is aware of its own colorful pattern may be limited. The color-change reflex is controlled to some extent by the chromatophores themselves, and not by a central "perceptive" nervous system response. Nimur (talk) 10:25, 12 May 2010 (UTC)

So the chromatophore's themselves have some sort of color-sensitive receptor?? 210.254.117.185 (talk) 13:01, 12 May 2010 (UTC)

. You say, "the color-change reflex is controlled to some extent by the chromatophores themselves, and not by a central "perceptive" nervous system response", but the article you linked says "it has been demonstrated that the background adaptation process is vision dependent (it appears the animal needs to be able to see the environment to adapt to it)". --Sean 15:00, 12 May 2010 (UTC)

Would you believe I asked this same exact question on here two years ago? #Cuttlefish_wants_to_cuddle. --Mr.98 (talk) 13:39, 12 May 2010 (UTC)

Cool, that's helpful. Thanks for fishing that out (lol). I'm reminded of the fact that many colorblind people can tell the difference between colors, but are simply unable to name them. Apparently because color is processed multiple times in the brain, and we are only conscious of it once, though there are residual effects of being able to see color below consciousness. I wonder if cuttlefish as well may be aware of color on a different level, though I guess that depends on how they were determined to be "colorblind" in the first place, i.e. if they have the hardware or not. 210.254.117.185 (talk) 14:03, 12 May 2010 (UTC)

I don't think your perception of colorblindness is correct. There are many varieties of colorblindness - relating to the four kinds of receptors we have in our eyes (Red, Green, Blue and "Brightness"). Colorblindness entails one or more of those kinds of receptor being either weak or non-existant. In cases where red, green and blue sensors are all missing - then the person can only see brightnesses - just like looking at an old black-and-white movie on TV. In those cases, it's not a question of being unable to "name" the colors - those people live in a world entirely devoid of color. In other cases (like my son - who has a 'weak green' detector), the person is able to see and name almost all of the colors - except for those that are distinguished by subtle differences in the color range of the defective sensor. My son can easily see and name green, red, yellow and orange - as well as cyan, blue and magenta. BUT (and this is how we found out he was colorblind) can't tell the difference between the very pure red of the LED on a Nintendo Wii that's turned off - and the orange when it's in standby. The difference is evidently a really subtle change in the amount of green light - and his weak green sensor simply can't tell him which is which. He manages perfectly well in 99% of the cases where color perception is important...but does have the annoying habit of leaving his Wii in standby mode instead of turning it off!

So there are many possible kinds of colorblindness - of different degrees of rareness and impediment. But I don't think any of them are cases where the person can distinguish the colors but not name them. For that to be the case, we'd be talking about some kind of brain problem - not colorblindness. SteveBaker (talk) 14:24, 12 May 2010 (UTC)

Some types of colorblindness are caused by brain problems -- the term used is "central colorblindness" or more formally cerebral achromatopsia. The inability to name colors is called color anomia; it may or may not go together with inability to distinguish colors. As you say, though, a person with color anomia but not color agnosia would not usually be considered colorblind. Looie496 (talk) 15:56, 12 May 2010 (UTC)

Yes, I was referring to something like color anomia, not true colorblindness like SteveBaker's son seems to experience with some types of green. So basically it's possible that the colorfish could be color "unaware", though their body reacts to color at a lower level of conciousness (or maybe I should call it "nervousness"), where the cuttlefish doesn't need to be aware of the differences. But, I have to disagree partly with the fact that color agnosiacs are not considered colorblind, because surely there are many inflicted with central colorblindness that simply assume their are physically colorblind, and are never tested properly for their "brain problems". Note: most of what I've read concerning such conditions comes from the writings of Ramachandran, who also describes a condition in which the patient believes they are blind, and can't pass any vision tests, but yet is able to put keys in slots and open doors when ordered to do so, due to their "central blindness". 219.102.220.188 (talk) 00:48, 13 May 2010 (UTC)

survival instinct

Why does the survival instinct exist? What made inanimate matter in the primordial soup want to survive? — Preceding unsigned comment added by Yourmindisthesceneofthecrime (talk • contribs) 13:32, 12 May 2010 (UTC)

If they sunk back into the ooze then we wouldn't be here asking questions and postulating hypotheses. The question is the answer. Vranak (talk) 13:48, 12 May 2010 (UTC)

In a random genetic mix - those that didn't have the "want to survive" genes didn't survive - and those that did have the "want to survive" genes survived. Hence every living thing from that point onward had the "want to survive" genes. If for some reason (mutation, perhaps) a new kind of lifeform appeared that had a defective or missing "want to survive" gene - it would rapidly die out. Hence, evolution favors the present situation.

The precise abiogenesis step that took us from "inanimate matter" to "living thing" is not well understood yet (although there are some excellent hypotheses out there). However, it seems likely that a self-reproducing molecule simply formed from random chemical reactions in the early Earth. That molecule (being able to reproduce) was too simple to "want" anything - but it did reproduce. Since there would be random errors in the copying process, things like "genes" would soon appear - and the molecules that were better able to reproduce would succeed and the molecules that did a terrible job would cease to be around in large numbers. Now you have molecules that are progressively better and better at surviving...it's a bit of a stretch to say that they "want" to survive...but then: Does a bacterium "want" to survive - or is it merely "able" to survive?

SteveBaker (talk) 14:11, 12 May 2010 (UTC)

The Selfish Gene by Richard Dawkins is a great book for discussion of questions like this. Looie496 (talk) 16:34, 12 May 2010 (UTC)

Evolution

I was looking at the plants in my garden today, and I thought why is there so many different types of plants, different shapes, trees grass ferns weeds etc. Plants should evolve to best suite the environment yes? So why don't they all look the same? --ame —Preceding unsigned comment added by NettleSpors (talk • contribs) 13:42, 12 May 2010 (UTC)

I have three answers:

Firstly: Gardens are very artificial things. Go out into a nearby forest and look at the natural setup. Now you find that the plants are much less varied. The reason for that is that people have gone out to far distant habitats all around the world - looking for striking and unusual plants to sell to people who plant gardens. Those plants are not at all well-adapted to the environment where they now find themselves - which is why you have to weed (to shut out more effective - but ugly - plants from competing with yours), water, feed, trim and prune...it's also why you have plants that die without producing offspring and have to be replanted.

Secondly: Evolution is a complicated process. Just as animals can evolve different lifestyles within a single habitat (there are herbivores that exploit plants and carnivores that exploit the herbivores) - so plants may evolve to make a living by being tall and getting high enough to grab the maximum sunlight, or to cope with less sunlight and live on the forest floor. There are many possible 'niches' within a given habitat - and there are a whole lot of different strategies that can server to perpetuate a species. Each niche produces a different-looking plant.

Thirdly: Evolution is a complicated process!! If one plant was used to living in dry grasslands and another had adapted to living in a swamp - and something in the landscape changes to make the whole area become a moist forest - then both kinds of plant have to evolve to living in that new situation. However, they will end up looking different because evolution can only work with what it's got. The dry grassland plant may lose it's adaptation to need less water - and gain the ability to work with less light - but it can still be a "grass-like" plant. The wetland plant evolves the other way - gaining the ability to work with less water. The resulting plants may well be dramatically different - yet equally able to survive. Do that enough times - and you have a wild variety of shapes and forms.

SteveBaker (talk) 14:02, 12 May 2010 (UTC)

Not sure about "Go out into a nearby forest and look at the natural setup. Now you find that the plants are much less varied." What about rainforests? They're are far more diverse than any garden I've ever seen! We should have an article on the maintenance of biodiversity as that is effectively what you are asking - why isn't there an optimum species for each environment and why are there still so many species? It's a hotly debated topic in plant ecology _{(useless article!!)}. There are a couple: unified neutral theory of biodiversity _{(a pretty horrible article though)} and Intermediate Disturbance Hypothesis. This might be of interest (I think the link is free). Broadly speaking I agree with Steve's point that evolution is very complicated - we can't ever really hope to understand it and it doesn't work in a controlled, linear, deliberate or obvious manner! There is a suggestion that species create more species since each one creates new ecological niches for other species (a bit of a circular argument however). That's the basis of this paper which suggests that the diversification of angiosperms (flowering plants) allowed ferns to diversify. Another driver of this may be the Janzen-Connell effect - basically plants may be less likely to survive near their parents due to increased risk of disease and herbivory and because they will use resources (light and nutrients) similarly and this creates space for more species to establish. It's also worth noting that the environment is constantly changing, if one optimum species evolved it would soon go extinct once the environment changed. Even within a species, individuals differ in their ability to withstand a drought and this applies even more so between species (can't find any free papers about this). In an extreme drought (or fire - because some species are adapted for it whereas others are not) some individuals die whereas others survive. All in all this keeps plenty of plants alive, they're more resistant to mass extinctions than animals too as they will happily sit out poor conditions as seeds or spores. Make any sense? 131.111.30.24 (talk) 15:04, 12 May 2010 (UTC)

Niche differentiation is worth a read too and this (and the paper) suggests that we are making the conditions for one species to dominate. Also linked to Steve's first point, moving all those plants around for gardens means they can escape and become invasive species. Some people use the term Homogenocene (as in homogenous) for what may occur in the future (or is happening now) if our actions continue to cause a mass extinction and the world is populated by far fewer species. 131.111.30.24 (talk) 15:27, 12 May 2010 (UTC)

Darwin called it the principle of diversion. In Origin of Species he wrote "We know that it has been experimentally shown that a plot of land will yield a greater weight, if cropped with several species of grasses, than with two or three." This perfectly illustrates the reason why life would tend to diversify rather then homogenize. Vespine (talk) 22:12, 12 May 2010 (UTC)

Funny you should say that, I've got a whole lecture in front of me written to answer whether Darwin was right regarding that exact quotation. It's basically very hard to conduct a good experiment to test it as there are so many uncontrollable variables. Some experiments have found an effect but as the species richness increases the probability of having highly productive species increases, therefore making it more likely that the more diverse systems are more productive. A study at the Cedar Creek Ecosystem Science Reserve found that more diverse plots are more resistant to drought (in terms of the percentage biomass lost) and that they regained their biomass more quickly. But the plots were differentially fertilised, when nitrogen is added, diversity decreases and it also affects root allocation since the plants need fewer roots to acquire equal nitrogen, consequently they are more susceptible to drought as they can't access water! A reanalysis showed that in actual fact, biomass and species richness did not correlate at all. An observational study of Swedish islands found that some ecosystem processes actually decrease with increased diversity. What does this all mean? Things are a lot more complicated than we tend to realise! _{Shout if you want some links to papers}

Vespine you say "This perfectly illustrates the reason why life would tend to diversify rather then homogenize" but what does a single species gain from being in a more productive ecosystem? I'd argue the opposite since herbivory is more likely to occur there. Your point sounds slightly Gaian, as attractive and reasonable a hypothesis that it is, I can't seem to think of a mechanism by which it could work. 86.7.19.159 (talk) 22:50, 12 May 2010 (UTC) (same as 131)

I'm struggling to understand what you are actually trying to say. "Things are a lot more complicated than we tend to realize!" I completely agree, I tend to include that as a unspoken disclaimer in a discussion regarding just about anything really. Of course there must still be a balance. I don't think saying that "increased biodiversity in some places decreases some eco processes" is contrary to anything I said at all. I don't doubt there would be a point where an ecosystem is more or less optimally diversified; obviously having a million species in a square yard of soil isn't going to be optimal.. The question as I read it was why is there 20 species of grass instead of 2. The question "why is there 20 species instead of 40" would lead to a different answer. Secondly, I think this is committing a logical fallacy but humor me for a second: Extrapolate what would happen if there was a "perfect" form and every living thing was striving to evolve to it, in my opinion the flaw in that premise is patently obvious, but that's essentially what the question is asking.. As for "but what does a single species gain from being in a more productive ecosystem?" I think the question it self is absurd, by very definition "more productive" means there is some benefit, if there was nothing to gain it would not be "more productive". Vespine (talk) 00:15, 13 May 2010 (UTC)

By "Things are a lot more complicated" I guess I was meaning that there is never one simple explanation for anything, and this is particularly true in ecology. Whilst at first appearance, increased biodiversity would appear to always be a good thing, when you start to look at it more closely it gets more complicated. You're right that it's obvious why there is no optimum form for everywhere but at the same time we don't have one single way of explaining why there is so much diversity in tropical forests. I stand by the fact that a single plant species doesn't gain from being present in a more productive ecosystem and that there is no inherently good thing about a productive ecosystem. It is beneficial for a single species to be productive as they can produce more seed, but I don't see why it would be better for all the species (please correct me if I am wrong!). Ecosystems could be far more productive than they are, see Miscanthus giganteus as an example, but for whatever reason they aren't. It's worth mentioning intercropping and push-pull technology as situations where a more diverse system in agriculture is more productive than a monoculture. In these situations the species complement each other and I imagine that this also occurs in nature to some degree. 131.111.30.21 (talk) 09:19, 13 May 2010 (UTC)

Going back to the OP, we should also have mentioned that the plants in your garden have been bred selectively to look different by us and this is responsible for the amazing forms you see. 131.111.30.21 (talk) 09:19, 13 May 2010 (UTC)

It's called interspecies dependency. Tigers aren't tigers without a few boars around. Vranak (talk) 02:49, 13 May 2010 (UTC)

Nose hair

How come men's nasal hair starts to grow out of the nose around age 40-45? I understand why puberty causes changes in hair growth, but is there some related hormonal trigger that men experience in their 40s that makes nose hair grow long? Citefixer1965 (talk) 15:24, 12 May 2010 (UTC)

Don't forget ear hair. Deor (talk) 15:29, 12 May 2010 (UTC)

This Straight Dope article addresses both. I've searched for more information myself - it sounds like we don't know! Don't forget eyebrows either! Maybe someone with medical knowledge can explain, my guess would be that it'll be due to changing hormonal balance (testosterone maybe). 131.111.30.24 (talk) 15:43, 12 May 2010 (UTC)

The Neoteny theory proposes that we are a primate foetus that has become sexually mature. As we age more traits similar to a juvenile chimpanzee appear. Like increased hairiness and larger ears. --Digrpat (talk) 17:37, 12 May 2010 (UTC)

Most hair follicles in the body have androgen receptors of various sensitivities. The most sensitive area of skin to respond to even early and mild rise of testosterone is the pubic area, which is why that is usually the first place that hormonal hair grows at puberty. Second is the axillae, which is often the second place that androgenic hair grows at puberty. In other words one can rank all the areas of the human body where the hair thickness changes in response to androgens. There are several dimensions to hormonal hair growth: androgen receptor sensitivity and density, androgen levels, and duration of androgen levels. In addition to the hormonal effects, the obviousness of the hair depends on the density of hair follicles per square cm of skin, and on the darkness of the hair and paleness of the skin. So areas like nostrils and ears will respond to androgens with hair growth, but only after prolonged elevation of androgens (i.e., later in life). We arbitrarily consider puberty to end with reproductive fertility and achievement of adult height but our bodies continue to change in response to various hormones throughout our lives. alteripse (talk) 02:13, 13 May 2010 (UTC)

Volume of air in lungs

Why is the volume of air that we breathe in slightly larger than the volume of air we breathe out? —Preceding unsigned comment added by 138.16.32.88 (talk) 17:11, 12 May 2010 (UTC)

Seems dubious to me. Why do you believe that is true? Looie496 (talk) 17:19, 12 May 2010 (UTC)

CO₂, O₂ and N₂ gases aren't going to be kept in your body so the volume of gas going in should be identical to the volume leaving. More CO₂ than O₂ will leave your body, though, because O₂ is converted to CO₂ in respiration. Regards, --—Cyclonenim | Chat  17:22, 12 May 2010 (UTC)

The O₂ we take in and CO₂ we let out don't necessarily have to be in balance. It depends on the ratio of carbon and oxygen in what's being broken down. For carbohydrates they should be roughly balanced, but breaking down fats would take a lot more outside oxygen per carbon I think, which would make the volume being breathed in larger. On the other hand, your out going breath probably has more water vapor in it unless it's really humid out, which would work the other way. I don't have any idea what the magnitudes of either of these effects would be. Rckrone (talk) 17:47, 12 May 2010 (UTC)

That's correct, it's called the respiratory ratio. This is one of the few free sources I can find. For pure carbs it is 1 as they have the formula CH2O but for fats with almost no O it is 0.7. We burn about half and half normally so ours is 0.85. Since exhaled air is only about 4% CO₂ this variation can't make a great deal of difference to the volume of air. 86.7.19.159 (talk) 19:28, 12 May 2010 (UTC)

PV=NRT, so if the air being breathed out is warmed by its trip through the respiratory passages and lungs, its volume will be larger exhaled, even if the same number of molecules are present. The amount of water vapor in exhaled air is likely larger than in inhaled, meaning N is also likely to be larger. Edison (talk) 18:23, 12 May 2010 (UTC)

I assume it takes more energy to breathe in than to breathe out (relaxation of muscles?), so the extra effort required might give the impression of being "larger". 219.102.220.188 (talk) 05:01, 13 May 2010 (UTC)

Dark energy & dark matter

what relationship does dark energy and dark matter have with each other? —Preceding unsigned comment added by 165.212.189.187 (talk) 17:25, 12 May 2010 (UTC)

we infer their existence from the study of astronomy. —Preceding unsigned comment added by 122.169.152.60 (talk) 18:12, 12 May 2010 (UTC)

Oh, I understand. —Preceding unsigned comment added by 165.212.189.187 (talk) 18:13, 12 May 2010 (UTC) what relationship does dark energy and dark matter have with each other? —Preceding unsigned comment added by 165.212.189.187 (talk) 18:14, 12 May 2010 (UTC)

First, have you read our articles on dark energy and dark matter? We're not really sure what they are, as we can't directly observe them (that's the "dark" in the name), and proposed indirect observations aren't universally recognized as being valid. Our article on the Lambda-CDM model of cosmology lays out in short form what physical effects are believed to be the result of dark matter and dark energy. As for the relationship between the two, though, the first response is a fairly good one. We infer the existence of both, and as we don't really know what either of them truly are, we can't compare them much further. — Lomn 19:15, 12 May 2010 (UTC)

(edit conflict) :There is probably very little relationship between them (less than between ordinary energy and ordinary matter). Dark matter was so-called because we can't see it. Dark energy was so-called because "dark" came to mean "mysterious", not because it has any connection with dark matter. Then Dark flow was named for the same reason. It is still possible that none of them really exist, but we will need a very clever "theory of everything" to explain the effects without them. Dbfirs 19:18, 12 May 2010 (UTC)

... so does E still = MC², when the M is the mass of dark matter? Can we hope for a dark matter atomic bomb in future wars? Adambrowne666 (talk) 21:48, 12 May 2010 (UTC)

If it really is mass matter, then yes, E still = mc². But that doesn't tell you how to actually perform that conversion, and for something as elusive and non-interacting as dark matter may be, that may not be possible. -- Finlay McWalter • Talk 22:08, 12 May 2010 (UTC)

E=mc² is always applicable. Dauto (talk) 22:30, 12 May 2010 (UTC)

But it doesn't mean you can make atom bombs out of everything. Technically if you converted the mass of your foot into pure energy it would blow a city all to hell. The thing is, you can't make that conversion directly, generally speaking. Nuclear fission and fusion are something of the exception as they allow you to actually convert a significant (but still small) amount of mass into energy in a useful and deliberate way. --Mr.98 (talk) 22:37, 12 May 2010 (UTC)

Agreed. The dark matter bomb idea is complete nonsense. Dauto (talk) 22:44, 12 May 2010 (UTC)

That's what makes it a good idea. Adambrowne666 (talk) 23:43, 12 May 2010 (UTC)

Being nonsense makes it a good idea? Are you talking about reallity or science fiction? Dauto (talk) 23:56, 12 May 2010 (UTC)

I'm more interested in why we should be "hoping" for more powerful weapons of mass destruction in the next war... --Tango (talk) 01:00, 13 May 2010 (UTC)

Yeah, sorry - wasn't being clear - I just like silly ideas, and yes, I'm talking science fiction. When I wrote it, I was being playful, but of course that doesn't necesserily come across in this context. Adambrowne666 (talk) 01:00, 13 May 2010 (UTC) - and hope was used playfully too - but maybe we should hope for it - I'm imagining a WIMP bomb that sends out a huge burst of completely undetectable energy that not only leaves buildings intact, like the neutron bomb, but also has completely no effect on any life forms.

Is dark matter out there or in here?

The dark matter article is very good, but I still wonder where the stuff is. Is it out there in space - the connective tissue of the large-scale structure of the universe - or is it all-pervading? Is there some here in my room, or do I have to go farther afield to not see it?

Thanks Adambrowne666 (talk) 21:44, 12 May 2010 (UTC)

It's very possibly everywhere, or distributed with some structure. We don't know what it is (and to be honest we don't really know that it exists), and we can't (well, maybe) detect it. If dark matter exists, and if it consists of WIMPs, then there might very well be bunches of it drifting ineffectually through you right now; there are, after all, heaps of other particles that really do exist travelling through you, to similarly little effect. -- Finlay McWalter • Talk 21:55, 12 May 2010 (UTC)

The best candidate we have for dark matter are weakly interacting massive particles (WIMPs) in which case gazillions of them went through your body during the time it took you to read this post. Dauto (talk) 22:27, 12 May 2010 (UTC)

Gazillions? No. The "M" in WIMP is for massive. If the WIMP scale is somewhere in the range 1 - 1000 GeV, as often assumed, then the universal density is of order 1 per m³. Similarly, because they are massive, they would be relatively slow moving (on astronomical scales anyway). The density should increase in deep gravity wells, like galaxies and star systems, but the number passing through any person in any instant would still be relatively small. Dragons flight (talk) 01:43, 13 May 2010 (UTC)

Actually the local dark matter density is close to $\rho \sim 0.3GeV/cm^{3}\,$ and with a tipical speed of $v\sim 270km/s\,$ we get a flux of $\phi \sim {\frac {100GeV}{m_{NEUTRALINO}}}\times 10^{5}cm^{-2}s^{-1}$ which can easily put the number of neutralinos passing through a human in the range of 100 million per second. Dauto (talk) 02:55, 13 May 2010 (UTC)

"Massive" in physics doesn't mean "very big", it just means "has mass". There is no requirement for them to be moving slowly, apart from being slower than the speed of light. --Tango (talk) 10:22, 13 May 2010 (UTC)

Thanks both of you for v prompt and useful answers Adambrowne666 (talk) 01:08, 13 May 2010 (UTC)

And if the dark matter is neutrinos with mass then the number passing through a human may be about a trillion times more. Graeme Bartlett (talk) 09:14, 13 May 2010 (UTC)

May 13

Superconductors

What is the application of the diamagnetic nature of a superconductor?117.204.4.192 (talk) 09:04, 13 May 2010 (UTC)

Genetic predisposition to food types

Could an individual have a tendency, from birth, to like or dislike certain types of common foods? I believe the answer is yes, but I'm not sure where to go to find the research, if it exists. Personally, I've found myself drawn to certain types of foods throughout my life for no rhyme or reason, even foods I've never tried before. And it's not just the smell or presentation of the food, but something else altogether. Viriditas (talk) 09:09, 13 May 2010 (UTC)

Appetite, Pica (disorder) talk on this topic somewhat. Graeme Bartlett (talk) 09:17, 13 May 2010 (UTC)

There is much research now on what shapes our food preferences. The dominant factors are feeding practices of mothers early in life. Genetic factors play a very small role. The rare but notable exceptions are the rare genetic diseases in which particular foods cause immediate adverse reactions, like fructose intolerance. alteripse (talk) 10:38, 13 May 2010 (UTC)

The article on taste mentions large genetic variability to detecting some types of bitterness. I've seen suggestions that preferences to some vegetables is affected by this. Try more on google (genetic bitter vegetable etc). 88.112.56.9 (talk) 10:59, 13 May 2010 (UTC)

Using heat pumps instead of cooling towers

Would it be possible to use heat pumps to cool the water produced by power stations instead of having cooling towers and generate more electricity using the hot water produced, whilst also getting rid of an eyesore? If not why not? 131.111.30.21 (talk) 10:25, 13 May 2010 (UTC)

Heat pumps are working the wrong way round, using energy to move heat, whereas in a power station we want the transfer of heat to produce energy. Graeme Bartlett (talk) 11:30, 13 May 2010 (UTC)

What you can do is a combined heat/power process, where the "lost" heat is used for home heating and hot water. This is reasonably widespread in some European cities (it's extremely hassle-free, as you don't have to have your own burners and fuel supply), and has a number of other advantages. --Stephan Schulz (talk) 11:53, 13 May 2010 (UTC)

Also, a heat pump moves heat - so what are you going to do with the heat you just moved to cool the water? You'd need a cooling tower ..... Ariel. (talk) 12:04, 13 May 2010 (UTC)

Geographic center of USA

A quote from Geographic center of the contiguous United States.

In 1918, the Coast and Geodetic Survey found this "center" by balancing on a point a cardboard cutout shaped like the U.S.

Which map projection was used for the cardboard? Has anyone calculated the center taking into account the shape of the Earth? (Igny (talk) 10:33, 13 May 2010 (UTC))

Computer PSU

Hello people, I wanted to know if a computer PSU works like any other PSU? I know the AC current is put to a high frequency, and then transformed (thats why the transformers(there are more for the different voltages)can be that small), but my question is does all the power go thru these small trasnformers?So basically the Voltage is transformed by the transformers, am I right ? Or do newer models have a different technology?

Thank you and excuse my english

DST —Preceding unsigned comment added by DSTiamat (talk • contribs) 12:19, 13 May 2010 (UTC)

Does the article Switching power supply help? Ariel. (talk) 12:45, 13 May 2010 (UTC)

I have read the article, but I cannot find an answer to my question, does all the power go through these transformers?