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November 17

Two problems involving angular motion

I do not know how to approach these problems. The first is finding the initial angular velocity/speed of a wheel that rotates 5.3 radians to a complete stop in 3.4 seconds. The second is finding the angular acceleration of a 26 centimeter thick 2.9-kilogram cylinder that has a force of 16 Newtons being applied to it. --Melab±1 ☎ 05:02, 17 November 2012 (UTC)

The first problem isn't well-defined as stated; what's missing is presumably an assumption that the wheel is subjected to a constant torque, or equivalently, that it undergoes a constant angular acceleration. This problem might be easier for you to solve with a well-chosen change in variables. Think of a movie of the decelerating wheel that's played at the same speed as it was recorded, but backwards. The movie being played backwards will still be 3.4 seconds long, and will still show the wheel rotating 5.3 radians, still at the same constant angular acceleration except for a change in sign. What constant angular accelereration will produce a rotation of 5.3 radians in 3.4 seconds? And then given that value for the constant acceleration, what will be the speed of the wheel at the end of the reversed movie? Red Act (talk) 05:59, 17 November 2012 (UTC)

The basic procedure for the second problem is to look up the cylinder's moment of inertia at List of moments of inertia, determine the torque from the equation at Torque#Moment arm formula, and then find the angular acceleration from the equation at Angular acceleration#Constant acceleration. Red Act (talk) 06:19, 17 November 2012 (UTC)

However, we are missing some geometry info on the cylinder. Is that a hollow cylinder ? If so, and it's rotating about it's axis, we need an inside radius or diameter and an outside radius or diameter. Given that we have the thickness, we could find either one, if we had the other. We also need to know if it's made of a uniform density material. The length of the cylinder is not important, since we are given the total mass (it would be, however, if we were instead given the density). And where is this force applied ? Tangent at the outer diameter ? StuRat (talk) 22:32, 17 November 2012 (UTC)

civil engineering related

why moment of inertia of a hollow circular cross-section is more than a solid circular cross-section? — Preceding unsigned comment added by 49.137.37.116 (talk) 13:14, 17 November 2012 (UTC)

The weighted average distance from centre of all small mass elements making up a thin ring is equal to its radius, but the wesighted average distance from centre of all small mass elements in a solid cylinder must obviously be less that its' radius, as elements exist from the centre outwards. However, this does not mean that the moment of inertia will be less for a solid cylinder as its' total mass will be considerably greater. See the formulae in the List of Moments of Inertia article. Floda 121.221.79.138 (talk) 13:53, 17 November 2012 (UTC)

The moment of inertia for a single point is mr^2. Turning that point into a ring, or a cylinder, doesn't matter - you still have the same mass, rotating around the same axis at the same length. But making that ring solid means you take the mass that was at distance r, and distribute it in a column from the center point (moment of inertia zero) to the full distance r. However - the distribution is not even, because there's only one point at the very center. So a small segment of the ring, when distributed toward the middle, forms a narrow triangle, with the average point in the triangle at a distance of r over the square root of 2 away from the center. Twisted any which way, the result is half the moment of inertia. Wnt (talk) 20:49, 17 November 2012 (UTC)

if the eye changes focal length to focus on an object, why isn't our visual perception like a zoom lens?

I don't notice my visual field at infinity (f=17 mm) being that much wider than my visual field at f=22mm, at the minimum focusing distance, at least not on the order that I would expect a 30% change in focal length to achieve. 71.207.151.227 (talk) 17:45, 17 November 2012 (UTC)

That's because your eyes are not cameras and your brain is not a .jpg file. Visual perception doesn't really work like a camera. Of course, the laws of optics still apply to the lenses in your eyes, but beyond that how you perceive the electrical signals that get sent from your retina to your visual cortex is very different from what any camera does, and you can't really reliably draw analogies between the two. --Jayron32 19:46, 17 November 2012 (UTC)

• In the eye, the image plane (retina) never moves in relation to the aperature (iris). Only the shape of the lens changes. Since the light moves in a relatively straight line from part of an external feature to a spot on the retina, the external feature remains about the same size. In a camera with a zoom lens, the distance from a lens to the film changes, but the lenses themselves are of solid and unalterable glass. Wnt (talk) 20:33, 17 November 2012 (UTC)

  A zoom lens is not "solid and unalterable glass," but a collection of glass lenses which changes the spacing between elements to alter the focal length. The distance of some elements to the film may change both to alter the focal length and to adjust the focus. Edison (talk) 02:11, 18 November 2012 (UTC)

  But if the focal length changes, the angle of view should change shouldn't it? A focal length is a measure of how strongly it bends rays overall, which in turn affects angle of view. It shouldn't matter by what method the focal length is changed. 71.207.151.227 (talk) 09:51, 18 November 2012 (UTC)

  • • • I think NorwegianBlue has put his finger on it, below. To rephrase, there are two variables involved — focal length and magnification. A zoom lens changes both; your eye mostly changes just the former. --Trovatore (talk) 02:32, 19 November 2012 (UTC)
• A more relevant comparison with a camera would be using manual focusing, which does not change the size of the image, but allows you to choose whether the foreground or the background should be in focus. --NorwegianBlue ^talk 22:36, 17 November 2012 (UTC)

You've only got decent vision in your fovea anyway, so width of field is sort of irrelevant. Gzuckier (talk) 02:29, 19 November 2012 (UTC)

But the question is, what solid angle of the world is represented in that image on the fovea? If you could increase the magnification of your eye, then you could reduce that solid angle, zooming in on smaller features in the world. But you can't, to any significant extent. --Trovatore (talk) 02:38, 19 November 2012 (UTC)

Doesn't a zoom lens move a heck of alot more in relation to the film than the focal point of the eye's lens in relation to the retina?

Another opportunity for me to make a pitch for the excellent book, Applied Photographic Optics. Camera optics provide a user-interface that isolates focus and zoom as distinct entities - in other words, it is possible to focus, without changing field of view; and zoom, without losing focus. Very nice, expensive camera lenses can be focused with negigible parasitic zoom because they are complex multi-element glass. In my twelve-element 70mm-300mm telephoto lens, the "zoom" is actually driving a gear system that slides several elements - to correct for some optical aberrations, and to help stay mostly focused while continuously extending the focal length over two and a half octaves. If you have a simple lens, say a single element convex magnifier-glass - and you move it relative to the image plane to provide focus - then you'll also see a very obvious zoom or magnification effect. Several multi-element lens designs are discussed in the book, portions of which are available to browse for free online. Chapter 30.2 discusses practical considerations for distortion-free telephoto zoom. Nimur (talk) 13:25, 19 November 2012 (UTC)

November 18

Where is the Heisenberg cut article?

I searched for Heisenberg cut but didn't find it. So does it exist as a subsection somewhere or is it just a dead cat? Hcobb (talk) 01:10, 18 November 2012 (UTC)

There is certainly enough information out there to create an article: see [1]. Wikipedia only exists because people no different than you created and expanded all of the articles. That is, if you find something is missing from Wikipedia, you are literally the best person in the world to add it; or you're no worse than anyone else. So, feel free to create that article! --Jayron3201:44, 18 November 2012 (UTC)

Excellent, by the way Hcobb, on creating the article. This looks like an excellent candidate for WP:DYK if you can expand it a bit! --Jayron32 12:38, 18 November 2012 (UTC)

At the moment the article is (intentionally) isolated with no inbound links, but I hope it can either serve as the main article for the subsections in other articles that it notes, or be merged into a slightly more broad article that covers the concept. If so it might well be split between Heisenberg's own writings and other contributions to the subject, and the more general concept that has been taken up by quantum computing. Hcobb (talk) 17:49, 18 November 2012 (UTC)

BTW, suppose that you did have a Heisenberg cut device, that I suppose would measure all possible quantum numbers inside a box. Say you subjected an average sized household cat to this, how big would the resulting explosion be? A chemical explosive because you've just messed up all the electron orbitals? A nuclear explosion because you've swatted all the nucleons? Or an anti-matter level explosion because you've sampled all the quark states? Hcobb (talk) 17:59, 18 November 2012 (UTC)

Based on this question and what you wrote in the new article, I think you don't understand what the cut is. The cut is the correspondence you define between quantities in a theory that you want to test and quantities that you know how to measure in the real world. To put it another way, it's the boundary at which you splice a speculative theory to a commonsense engineer's physics that everyone already accepts as true. This is a necessary part of any theory that claims to describe the real world. To a large extent it doesn't matter where you place the cut, but it needs to be at a high enough level that all the controversial physics is handled by your theory.

A nice non-quantum example is Einstein's 1905 paper on special relativity. The math of special relativity had already been worked out at that time. Einstein's only contribution was giving it an interpretation that made sense. He did that by moving the cut. Instead of assuming that distances and time intervals are things that can in principle be measured to arbitrary accuracy by sufficiently good instruments, as everyone had assumed in the past, he treated those instruments as part of the system to be modeled by the new theory. As his measurable quantities, instead of position and time, he used the time shown on a clock face when some event happens at the clock's location. The assumption that a human experimenter (his "observer", though the meaning of that term has changed since then) can read a clock face is much weaker than the assumption that an experimenter can measure true distances and times. And it turned out that the latter assumption was actually wrong.

In quantum mechanics, if you make the usual division between quantum system and measurement apparatus, the disappearance of the interference pattern in the double-slit experiment seems bizarre. If you instead do as Einstein did and make the apparatus part of the quantum system, using readings on dials as your measurable quantities, you get a much more comprehensible result: the wave function gives a classical probability for each possible readout, the collapse is just a Bayesian update, and the disappearance of the interference pattern is caused by a quantum interaction between the photon/electron and the apparatus (quantum decoherence) which couldn't be modeled when you assumed the apparatus wasn't quantum.

By the way, I've never heard the term "Heisenberg cut" before. I've seen occasional mentions of the cut between theory and experiment, but not with Heisenberg's name attached. It does get a fair number of Google hits, but I think it's an unfamiliar term to most physicists and is probably used mostly by people like Stapp (who I consider a crank). -- BenRG (talk) 21:05, 18 November 2012 (UTC)

I agree with BenRG. I've read more than a few books on atomic physics, and I've never encountered this phrase in the context of quantum physics. From a cursory glance at the references in our new article, it appears to be a sort of popular science neologism used by "physics-philosophers." Nimur (talk) 12:34, 19 November 2012 (UTC)

To be entirely fair, being quackery doesn't mean it isn't proper article fodder. It may be quackery, and if so, the article should use reliable sources to report it as such. But quackery alone is not enough of a reason to not have an article. We have articles on homeopathy and astrology; the articles both report the "internal logic" of the beliefs and also explain clearly and unambiguously that the scientific community thinks they are bullshit. I have absolutely no familiarity with the term either, but I also don't have the physics background that you two do to find sources that refute it. If the rather stubby article needs expansion, one needed route of expansion may be some explanation (properly cited) of this as a not-accepted thing. --Jayron32 13:54, 19 November 2012 (UTC)

The final reference in the article doesn't look like quackery [2] - it describes specific writings by Heisenberg in the 1930s about contextual hidden variable theory, which he considered by postulating various placements of a cut "Schnitt" between observer and observed. I'm not likely to answer this question, but at least it is a valid concept from the development of quantum mechanics. Wnt (talk) 19:12, 19 November 2012 (UTC)

Just to clarify. I'm not saying one way or the other if the concept is quackery or not. The concept could be sound science, or it could be bullshit. Being bullshit is not, of itself, however, grounds for not having an article on something. Homeopathy is unmitigated bullshit, but that doesn't mean Wikipedia doesn't have an article describing it. Which is not to say that this concept is bullshit. It may not be; just that Ben and Nimur's objections to it are not grounds for not having an article about the concept. --Jayron32 20:19, 19 November 2012 (UTC)

I am also somewhat concerned that the article currently states "there are no actual Heisenberg cuts anywhere...". That last reference describes the Heisenberg cut as an integral part of the Copenhagen interpretation, so that statement appears to assert that Copenhagen is wrong. Copenhagen is certainly not as popular as it used to be, but I do not think it has been so soundly rejected as to allow an NPOV article to assert that. --Trovatore (talk) 19:32, 19 November 2012 (UTC)

Whoops, sorry, not the same ref -- I'm talking about this one. --Trovatore (talk) 19:35, 19 November 2012 (UTC)

I agree - we cannot be certain that Heisenberg cuts do not exist. They are required in some interpretations of quantum mechanics, but not in others. I have tried to make the article more NPOV. Gandalf61 (talk) 09:46, 20 November 2012 (UTC)

Voltage across an inductor

I read about the self inductance phenomenon and about the equation V=L(di/dt). But I am confused about the direction of V. My confusion is that current flowing through an inductor causes a 'back-emf', and the back emf is equal to V(or so I think). If so, shouldn't the direction of V be in the opposite of that of I? Also, in the Voltage and Current graph sketch across the inductor, I saw that the phase difference is 90 degree, but the voltage and the current are infact, in the same direction. I just don't get the fact that how V is in the same direction of the current that causes it. According to Lenz's law, it should be in the opposite direction. — Preceding unsigned comment added by 210.4.65.52 (talk) 04:17, 18 November 2012 (UTC)

Voltage doesn't have a direction; I guess you're talking about the direction of the voltage drop, which is what's meant by V. I don't know if this helps, but in the hydraulic analogy, an ideal inductor is like a heavy but frictionless paddlewheel. Its inertia opposes any attempt to either increase or decrease the current, which leads to a downstream pressure drop (positive V) or gain (negative V) in the case of a forced current increase or decrease respectively. -- BenRG (talk) 07:23, 18 November 2012 (UTC)

Another point to consider is that the induced voltage depends on the _change_ in current, not the static (DC) current. If you have a perfect inductor carrying a DC current, it won't have any voltage across it (because its DC resistance is zero). If you increase the current, the induced voltage will be in the "opposite direction" to the DC current - if you reduce it, the induced voltage will be in the "same direction". Tevildo (talk) 21:14, 18 November 2012 (UTC)

URGENT INFO NEEDED

Dear all, I need to know how thymoquinone actually acts! I mean does it pass through the cell membrane? Does it have a receptor? How does it expert its effect? attaches to a protein to change its activity? ... Any info regarding that will be appreciated. Best kukubah 04:51, 18 November 2012 (UTC) — Preceding unsigned comment added by Kukubah (talk • contribs)

PubChem is a good place to start for stuff like this (see here). Also, note the warning at the top of this page about timeliness - this really isn't the best place to ask urgent questions. Zoonoses (talk) 05:46, 18 November 2012 (UTC)

Hmmm, oddly enough I'm finding a source that the antinociception and anticonvulsant effects work via the kappa opioid receptor. [3][4] Wnt (talk) 06:04, 18 November 2012 (UTC)

When did dark energy start to dominate?

There's a graph currently on the Hubble's law article that shows universal expansion. It's hard to read the inflection point, and I don't find it mentioned in the article or any related articles.

That is to say: after inflation ended, the universal expansion was decelerating. Now it is accelerating. When was the critical time when deceleration became acceleration?

(Let's say, treating the dark energy as a cosmological constant... do other proposals imply a different critical time?) — Preceding unsigned comment added by 174.118.1.24 (talk) 08:07, 18 November 2012 (UTC)

Ignoring radiation (which only matters at early times) and assuming the universe is flat (no global curvature), the evolution of the cosmological scale factor is:

$\left({{\dot {a}} \over a}\right)^{2}=H_{0}^{2}\left(\Omega _{M}a^{-3}+\Omega _{\Lambda }\right)$

Where $a$ is the scale factor, $H_{0}$ is the current Hubble constant, $\Omega _{M}$ is the fraction of the closure density in mass (including dark mass) and $\Omega _{\Lambda }$ is the fraction of the closure density in dark energy. (See also: Lambda-CDM model)

The inflection point occurs at ${\ddot {a}}=0$.

Rewriting the above we get:

${\dot {a}}^{2}=H_{0}^{2}\left(\Omega _{M}a^{-1}+\Omega _{\Lambda }a^{2}\right)$

$2{\dot {a}}{\ddot {a}}=H_{0}^{2}\left(-\Omega _{M}a^{-2}{\dot {a}}+2\Omega _{\Lambda }a{\dot {a}}\right)$

$0=\left({{\dot {a}} \over a}\right)\left(-\Omega _{M}a^{-1}+2\Omega _{\Lambda }a^{2}\right)$

Given that ${\dot {a}}>0$ for all times since the creation of the universe, it follows that inflection occurs at:

$\Omega _{M}=2\Omega _{\Lambda }a^{3}$

$a=\left({\Omega _{M} \over 2\Omega _{\Lambda }}\right)^{1/3}$

Using current values for $\Omega _{M}$ and $\Omega _{\Lambda }$, gives $a\approx 0.57$. Which implies that the inflection occurred when the universe was about 57% of its current size. Getting the corresponding time will require integrating the equations above with respect to time, but since the expansion was roughly linear, the 57% of size is approximately 57% of time, implying that the inflection point occurred roughly 7.8 billion years after the Big Bang, or roughly 5.9 billion years ago. Dragons flight (talk) 09:36, 18 November 2012 (UTC)

Brilliant, thanks --174.118.1.24 (talk) 17:36, 18 November 2012 (UTC)

When Ω_M + Ω_Λ = 1 there's an exact solution, $a(t)=\left({\tfrac {\Omega _{M}}{\Omega _{\Lambda }}}\sinh ^{2}\left({\tfrac {3}{2}}{\sqrt {\Omega _{\Lambda }}}H_{0}t\right)\right)^{1/3}$ (copied from here). That gives $t={\frac {2\sinh ^{-1}{\sqrt {1/2}}}{3{\sqrt {\Omega _{\Lambda }}}H_{0}}}$ at the inflection point, which is about 7.1 billion years a.b.b. or 6.6 billion years ago (using parameters from here, which also give me a ≈ 0.57). -- BenRG (talk) 18:28, 18 November 2012 (UTC)

What happens if someone were to be struck by something like the Oh-My-God particle?

I mean, being hit by a 60 mph baseball is pretty painful. I mean, it was pretty unlikely for any one particular particle to have struck that particular sensor at Dugway Proving Ground, so there is likely some finite flux/second for that kind of particle. Yet there really isn't a recorded instance in history where someone suddenly suffered a severe injury (on the magnitude of a gunshot wound) suddenly and catastrophically for no reason at all. 71.207.151.227 (talk) 10:07, 18 November 2012 (UTC)

I don't think you'd notice, if as this site says, normal cosmic rays " pass through us, through our houses, through our bodies" every day, why do you think this particular form of cosmic ray would be any different? --TammyMoet (talk) 14:17, 18 November 2012 (UTC)

I think the OP was shocked by the exceptionally high energy (as I was, and the observers were). If all of that energy were absorbed by a human body, it would certainly have a significant effect on a par with a gunshot, but, fortunately for us, most of the energy is carried away by other particles without interacting significantly with the human body. Usually, damage at atomic level is not significant at cellular level, though it would be interesting to know if genetic change is caused by such particles. Perhaps they are the main driver of evolution? Dbfirs 15:35, 18 November 2012 (UTC)

Also note that 50 J is the amount of energy delivered to a typical household incandescent light bulb lit for about 1 second. That's really not that much energy from a macroscopic point of view. Dauto (talk) 16:20, 18 November 2012 (UTC)

Lesser rays are noticeable. [5] See also Cosmic ray visual phenomena. The "Oh-My-God particle" was a very rare event in the upper atmosphere and so has not been experienced yet by anyone, and until such time as it happens we can't really know what the effect would be like. Wnt (talk) 17:14, 18 November 2012 (UTC)

It could lead to a dose of a few Sievert and that can be deadly. UHECRs won't penetrate the atmosphere, hit your body and cause the equivalence of an air shower inside your body. But you can think of other ways this can theoretically happen. E.g. a cosmic ray particle can hit a dark matter particle, and that dark matter particle can then get a a similar energy. Most likely such a high energy dark matter would move through your body and the Earth, but there is then a small chance that it would interact with a nucleus in your body, giving you a potentially fatal dose of radiation. Count Iblis (talk) 17:28, 18 November 2012 (UTC)

(ec) As an aside, the detection system used (the 'Fly's Eye', a predecessor to the High Resolution Fly's Eye Cosmic Ray Detector which worked on similar principles) wasn't solely dependent on detectors on the Earth's surface, and didn't just sit and wait for a single 50-joule particle to smack into a single ground-based sensor. What the Fly's Eye picked up were showers of particles generated when a high-energy cosmic ray started to interact with the upper atmosphere; using an array of telescopes it could (literally) see these interactions by the light they produced, as collision after collision ionized atmospheric gases and generated sprays of new, fast particles that in turn triggered further ionization events. Those interactions would have occurred across several kilometers of atmosphere. To be clear, it wasn't a single *pop* and *flash* as the entire 50 joules was deposited at a single point of collision; instead, energy would be deposited along a long, branched track as the particle kicked off other fast particles produced by collisions and gradually came to rest.

In the unlikely event that such a particle did reach the Earth's surface (and a human being there) without interacting with anything else, it still wouldn't do much to a person. I don't know what the linear energy transfer rate would be for a proton in this energy regime, but I strongly suspect that the proton would emerge from the other side of your body with nearly all of its energy still intact, having deposited only a tiny, tiny faction of its 50 joules inside you. TenOfAllTrades(talk) 17:36, 18 November 2012 (UTC)

But how far does an air shower (physics) spread within a human body? Wnt (talk) 19:12, 18 November 2012 (UTC)

The density of the human body is a few thousand that of the atmosphere (at the relevant height), so you'll get a significant part of the air shower in your body (70 cm times 3000 is 2.1 km ). Count Iblis (talk) 19:48, 18 November 2012 (UTC)

The interaction length for daughter particle creation from ultrahigh energy protons is about 400 meters of air or 40 cm of water. The energy loss scale per particle is about 2-3 MeV / cm in water. If the Oh-My-God particle hit you directly, traveling vertically through you, it would have about 1.8 m to work with. So, roughly, say 3 MeV / cm * 40 cm for the initial particle + 2 * 3 MeV / cm * 40 cm for the first daughter pair + 4 * 3 MeV / cm * 40 cm for the second daughters + 8 * 3 MeV / cm * 40 cm for the third daughters + 16 * 3 MeV / cm * 20 cm for the last generation before exiting. In total, it would have deposited about 0.4 nanojoules of energy while passing through you, or roughly 0.000000001% of its energy in the 6 nanoseconds it took for the particle to enter and exit your body. You would not even notice a direct hit by such a particle. Such a particle could keep producing daughters out to the hundreds of billions. Though, even if you got him with 100 billion high energy particles, odds are you still wouldn't notice much effect. Even absorbing the full 50 J, is only an amount of heat equal to what humans produce every 0.5 seconds. 50 J is an enormous amount of energy for a single particle to have, but the energy and momentum of that particle would seem trivial to macroscopic objects like us since we are composed of roughly 7×10²⁷ atoms. Dragons flight (talk) 22:28, 18 November 2012 (UTC)

And yet the astronauts do notice being hit with ordinary cosmic rays, even to the extent that the flickering disturbs their sleep according to the source I listed, so there must be something off there? Wnt (talk) 23:10, 18 November 2012 (UTC)

In a completely dark room, after adjusting, the eyes are sensitive to light flashes with as few as about 10 photons entering the eye. That amounts to a detection limit of about 5×10⁻¹⁹ J. Hence, it's not surprising that cosmic rays crossing the eyeball can be seen, but that's because the eyes are exquisitely sensitive and not because the energy is in any bulk way significant. Dragons flight (talk) 23:59, 18 November 2012 (UTC)

I remembered as a child reading about a "scorch mark" left by the passage of a cosmic ray through an astronaut's helmet, which had much impressed me, but looking into it now, and seeing your estimate of the power released, I think that this must have been a sensationalization of something like the use of parthicle track-etch technique in "the Apollo helmet dosimetry experiment". Wnt (talk) 14:58, 19 November 2012 (UTC)

If you absorb 50 J from such a process, that would roughly be equivalent to 1 Sievert which is potentially deadly. Count Iblis (talk) 01:52, 19 November 2012 (UTC)

As I pointed out, what would actually absorbed be from a direct hit by the Oh-My-God particle is negligible. You can't capture 50 J unless it has already cascaded to roughly 100 billion lower energy particles before it reaches you and yet somehow remained confined enough to hit a single person. Dragons flight (talk) 04:46, 19 November 2012 (UTC)

Yes, although the 2 daugher particles per collisions in the beginning seems a bit low i.m.o. The COM energy here is huge... Count Iblis (talk) 19:21, 19 November 2012 (UTC)

If someone did drop dead from a cosmic ray, how would the coroner be able to tell afterwards? μηδείς (talk) 04:37, 19 November 2012 (UTC)

50 J is the energy of a 60 mph baseball. That's gotta hurt! 199.111.203.215 (talk) 04:39, 19 November 2012 (UTC)

It's the momentum of grain of salt in very light breeze. You'd never notice. Dragons flight (talk) 04:46, 19 November 2012 (UTC)

That's not what the linked article says. Is there a factor of 1000 error in a calculation? Dbfirs 07:28, 19 November 2012 (UTC)

The article is talking about kinetic energy, not momentum. --Trovatore (talk) 07:47, 19 November 2012 (UTC)

Sorry Dragons flight, and thanks for the explanation, Trovatore. I must learn to read carefully before commenting! I ought to know the difference, though anyone who has been hit with a hollow-point rifle bullet will know that energy can cause a lot of damage without carrying much momentum. Dbfirs 07:39, 20 November 2012 (UTC)

• Again, I ask, how would one know someone had been hit by one of these particles? μηδείς (talk) 18:04, 19 November 2012 (UTC)

• There will be a trail of minute trace amounts of radioactive isotopes in your body. The first part of the equivalent of the air shower in your body will be due to collisions that have so much center of mass energy that they completely shatter a nucleus to pieces. The COM energy of an incoming proton of energy E = 10^20 eV and an Iron nucleus of mass m = 52 GeV at rest is sqrt[2*10^20 eV*52 GeV + (52 GeV)^2] =3.2*10^15 eV which is hundreds of times larger than the COM energy at which the LHC can carry out collisions of nuclei to create a quark gluon plasma. Count Iblis (talk) 19:18, 19 November 2012 (UTC)

So this is apparently not something that is ever likely to be observed, but may happen all the time for all we know? μηδείς (talk) 17:31, 20 November 2012 (UTC)

You would not be aware of it if it were to happen, so you would have to describe the state of the universe where you are as a superposition containing a component with a very small amplitude where such things have happened to your body. Count Iblis (talk) 17:38, 20 November 2012 (UTC)

The Philippines and total plastic bag bans (again)

I've taken the liberty of moving this to the Humanities Refdesk. That's where you should ask questions about laws. Wnt (talk) 19:10, 18 November 2012 (UTC)

Electroshocking people

If someone is holding you and you electroshock him (with a regular electroshock weapon), can the shock pass to you? And if you apply it to his arm, does it affect his legs? Comploose (talk) 16:25, 18 November 2012 (UTC)

Not sure, but you may find some of the answers (and/or sadistic pleasure) in this Brainiac clip. - Cucumber Mike (talk) 17:47, 18 November 2012 (UTC)

Of course, unless you were insulated from them by clothing, etc. Here's a pertinent demonstration with a whole bunch of people in a row and an electric fence: [[6]]. And yess, it affects the whole body, and not just the part it's applied to. There wouldn't be much point to using one if it didn't. There designed to incapacitate the target, not just make them go "Ouch!'. Dominus Vobisdu (talk) 19:20, 18 November 2012 (UTC)

No, most regular electroshock weapons have two contacts and the current flows between the two, so others in physical contact are unlikely to feel a significant shock. If there is a voltage relative to earth (as in electric fences), then the shock can be passed through many participants. Dbfirs 07:18, 19 November 2012 (UTC)

How many people are dying in Gaza?

In response to complaints, I've taken the liberty of moving this to the Humanities Refdesk. (It's not that complicated to do this if a thread bothers people) Wnt (talk) 05:14, 19 November 2012 (UTC)

Asbestos in the WTC

Was asbestos in the WTC, and was it blown in the air, or not? Comploose (talk) 18:38, 18 November 2012 (UTC)

Typing "asbestos in world trade center" into Google got me this: [7]. It looks as though it shouldn't be too hard to find the answer among those search results. --Jayron32 19:15, 18 November 2012 (UTC)

"no asbestos" in world trade center also generates many results. Comploose (talk) 20:27, 18 November 2012 (UTC)

Many of those results aren't reliable sources (conspiracytheorists etc.). Trio The Punch (talk) 22:34, 18 November 2012 (UTC)

Yep. Read this. The NYT wrote: "Anticipating a ban, the builders stopped using the materials by the time they reached the 40th floor of the north tower, the first one to go up. ". Trio The Punch (talk) 20:12, 18 November 2012 (UTC)

Lump of fat close to the heart — in roe deer in the winter season — What is it called?

I have heard that roe deer, and other wild animals living in places with cold and snowy winters, every autumn developes a big lump of fat close to the heart.
(I presume that this somehow helps them survive through the winter season).
I want to read more about this phenomenon but: what is it called? or where might be a good place to start searching for for this?
Could you please help me?89.9.197.219 (talk) 19:33, 18 November 2012 (UTC)

Quote from Bone Marrow Fat as an Indicator of Condition in Roe Deer: "Fat reserves are generally utilised sequentially starting with the subcutaneous deposits, followed by the mesenteric, kidney and finally bone marrow fat". So I think roe deer store fat in those 4 places. Trio The Punch (talk) 20:01, 18 November 2012 (UTC)

The lump of fat by the heart would be mesenteric, but there may be a specific name for it as well. μηδείς (talk) 23:10, 18 November 2012 (UTC)

The OP is possibly referring to a dewlap (accumulation of fat under the neck or at the front of and external to the ribcage), common on hooved animals - though I didn't think deer grow noticable dewlaps. The mesentery is on the other side of the diaphram and not near the heart - Medeis is wrong again. Floda 124.182.38.51 (talk) 14:49, 19 November 2012 (UTC)

It's quite possible the OP may have meant a dewlap, although the wording of the question seemed to imply something internal. And while the mesentery holding the guts in place is often referred to as "the mesentery", mesentery tissue and its derivatives occur wherever there are organs, such as the heart, situated within the coelom. For example, cardiac messentery. The OP may be referring to epicardial adipose tissue or brown adipose tissue. Without a better explanation we can't be sure. μηδείς (talk) 17:45, 19 November 2012 (UTC)

The link provided by Medeis does not provide access to the book text. I just love posters who provide links that for this and other reasons do not support their claims. Entering "cardiac mesentery" in AltaVista does not return anything that supports the idea of live mammals having a cardiac mesentery. Possibly Medeis was thinking about the mesothelium, which has a different function and is not likely to be related to the OP's question. Floda 60.228.244.240 (talk) 01:07, 20 November 2012 (UTC)

The link works for me, perhaps it's a region issue for google books? Anyway, right or wrong, Medeis seems to be linking in good faith, to an anatomy monograph from 1906. The text does list "cardiac mesentary" in a caption for a plate, saying the diagram shows "Transverse section of a tadpole, showing ... ventral cardiac mesentary." If this is not standard usage today, then perhaps the terminology has changed in the past ~100 years... SemanticMantis (talk) 02:40, 20 November 2012 (UTC)

Ahah! Tadpoles! Organisms evolutionary less developed than mammals, and embryos, are described as having a cardiac mesentery. The ventral mesentary in mammals is not cardiac as it is after the diaphram. The book access could be a regional issue or perhps is enabled if you access from within a library?? Floda 121.215.68.108 (talk) 02:50, 20 November 2012 (UTC)

Do you even know what ventral means? It's just a direction. The heart has a ventral surface as does the brain, etc. What's referred to as the ventral mesentery in humans is the mesentery closest to the belly. (Aha!) Cardiac mesentery in adult mammals doesn't disappear, it just doesn't hold the heart in place because the heart grows to fill the pericardium. It could potentially become fatty in deer, but we still don't even know what the OP is specifically talking about. Besides your bizarre need to attack me, what for I don't know, do you have anything to add to this discussion? μηδείς (talk) 03:11, 20 November 2012 (UTC)

The ventral mesentery is mesentery closest to what is the front in humans, but this is below (in humans) the diaphram as I said. What is above/in front of the diapham as a lining is the mesothelium. Any cardiac mesentery could be described as ventral, dorsal or whatever according to standard terminology, but flexibility in terminology does not mean it actually is there. Fat occurs in the vicinity of the heart but big lumps of it (to use the OP's term) would compromise breathing. So, yes, we don't know what the OP had in mind (he was quite possibly missinformed anyway - he doesn't cite a source), but fat external to the ribcage is more likely. Do you have anything usefull to add, apart from trying to defend an unsupported opinion by personal attack? Your link doesn't count as according to SemanticMantis it is about tadpoles. You might as well claim that deer do not have diaphrams and breath via gills. Floda 121.215.68.108 (talk) 04:01, 20 November 2012 (UTC)

@ Semantic Mantis, I simply provided a copy to the first link at google that mentioned cardiac mesentery; it wasn't really meant to be relevant to the deer question as such, just to show that mesentery is a type of tissue found in relation to organs that float in the coelom, not some sort of organ that resides only in the abdomen. This article is interesting, it mentions studies of fatty female elk hearts themselves, as well as fat surrounding them on the pericardium, as well as the kidneys. They study this muscular and mesenteric fat because it is a sign of fertility. I presume they don't study bone marrow fat since it would only be lost in starving deer and subcutaneous fat since it would be a sign of obesity. Searches for "roe deer dewlap" don't seem to get any relevant hits and image searches aren't encouraging. American elk don't seem to have dewlaps either. Moose do, but they hardly seem to be fat storage organs. μηδείς (talk) 03:52, 20 November 2012 (UTC)

Again, Medeis, you have provided a link that does not support your claim. Yes, fat occurs around the heart, but the link does not even use the term mesentery, and does not in any way indicate "big lumps". Floda 121.215.68.108 (talk) 04:01, 20 November 2012 (UTC)

• From Trio The Punch we know that mesenteric fat is important in the roe deer, and Medeis referenced epicardial adipose tissue. In better-studied organisms (humans) we know that there are indeed epicardial fat deposits which share a common embryological origin with those of the mesentery.[8][9] While researchers show more interest in the pathology, this fat serves as a source of triglycerides and perhaps regulatory signals affecting the heart and arteries in subtle ways (the object of their present research). "Epicardial fat can be abundant especially in ruminants" and is absent in starving animals, and the pointed shape of the apex of the heart "can be pronounced in starving animals due to lack of epicardial fat." [10] At this point we're probably nearing the edge of what is known; roe deer are not model organisms and the amount of effort people have put in to figure out the role of epicardial fat is probably limited. I doubt that anyone has really liposuctioned it from the animals and seen what happens to their cardiovascular fitness or whatever. But you can do a lot of reading about epicardial fat in other organisms.[11] Wnt (talk) 18:06, 20 November 2012 (UTC)

Floda and Medeis, would you please both be so kind to refrain from interacting with/talking about the other person? This message is carefully worded to be as neutral as possible, but that does not mean I don't have an opinion. According to the rules of the internet you both lost the debate. Jimbo won, because he did not participate. This is not an invitation to say something like: "I'll stop talking to x because x is an idiot". There is no need to respond to this message. Thanks in advance, Trio The Punch (talk) 20:40, 20 November 2012 (UTC)

There is a need to respond. Wnt has usefully added to the discussion by a well considered post that includes links to relevent references. Where I or Medeis have or have not won any debate is perhaps of no relavence - the OP has been presented with some information, albeit some contradictory but the OP can weigh it up, and Wnt has usefully added information that should assist the OP (should he/she be interested) and anyone else in understanding just what fat occurs around the heart. Floda 120.145.137.177 (talk) 00:30, 21 November 2012 (UTC)

November 19

manual lenses in bridge cameras

Besides Fujifilm what others brands make super-zooms cameras with a lens capable of doing manual zoom and manual focus??

recently a friend was looking for a super-zoom, and showed me a canon SX – something, and it felt like a toy in my hands, and he don’t like the Fuji’s IQ,

are any Sony, Canon, or Nikon camera bridge (with a zoom around 18~30x) like the hs line of fuji??

Iskánder Vigoa Pérez (talk) 00:24, 19 November 2012 (UTC)

From bridge camera "With zoom ranges and sales rapidly increasing in the early 21st century, every major camera manufacturer has at least one 'super zoom' in their lineup." So, just wait and see. Or try one like the Sony NEX-some # or one of its concurrents. [12] is a good source of such information. Philoknow (talk) 16:35, 19 November 2012 (UTC)

Yes, sure, but talking about now?? There isn’t any 15-30x camera capable of manual zoom and focus… or at least manual focus?

the canon sx40 looks just like a toy wat side of my mom’s fuji hs20

my friend has family that will come to Cuba next week and he wants to exploit this opportunity

Iskánder Vigoa Pérez (talk) 19:39, 19 November 2012 (UTC)

It may help if you further explain your question. I assume many bridge cameras probably even most bridge cameras have manual focusing at lead thats what our article and many other discussions seem to suggest. Heck I think even some higher end P&S or those at the crossover point have manual focusing (I seem to recall using at least camera with it and a search also finds mention of manual focus in some P&S cameras) although it may be very hard to use due the difficult focusing on the LCD (our article mentions many bridge cameras provide a zoomed in focus square), it's ultimately primarily a software issue. But your original question makes me think you want more then simple manual focusing. Do you want manual focusing using some sort of focus ring or similar rather then adjusting a slider on screen with cursors? (Your second question also seems to reaffirm this point. Surely nearly even single non fixed zoom camera offers some sort of manual zoom even the vast majority of P&S ones. i guess some may have some sort of point to zoom or try to zoom in faces when set to potrait mode but manually zooming must be the way most people use zoom cameras. Even cameras without a zooming lens will often provide zooing controls due to 'digital zoom'. Of course the controls will often be a simple cursor or with modern touch screen controls perhaps an on screen slider.)

In any case a simple search for 'bridge camera manual focus' finds this review [13] which discussess manual focus methods in various recent bridge cameras most of which appear to have fairly high zooming levels. There are also lots of other older discussions from the same search, while many of the models may now be old you should be able to find their replacements and see what they do. Of course if you can't find anything fulfilling your requirements your best bet may be to consider a DSLR, its not clear why your focused on bridge cameras. Pricewise it's often not clear cut nowadays so I assume its a size issue but if you have special requirements you may have no choice.

Nil Einne (talk) 01:44, 20 November 2012 (UTC)

Yes, I meant a bridge camera with two rings, a focus ring and a zoom ring… (just like the Fujifilm’s HS)I recommended him to buy a d3200 and a cheap tamron18-200 (he can afford it) but he wants something larger, 20x or more…

I guess the IQ of a picture taken whit this camera/lens, at 200mm and cropped to the half will still be better than the IQ of a picture of any bridge… and making math that’s 22x or so, I told him but he wants a bridge camera with 20 x or more…

Do you know any model available right now (from canon, nikon, sony or pentax), or are the fujis the only choice?

Thanks for the answer!

Iskánder Vigoa Pérez (talk) 03:19, 20 November 2012 (UTC)

pneumonia survival rates

what was the pneumonia survival rate before antibiotics, and what is it now?--Wrk678 (talk) 01:40, 19 November 2012 (UTC)

From the article Pnemonia#Management: 10% mortality now vs 50% before antibiotics for patients who end up in the hospital. RudolfRed (talk) 02:47, 19 November 2012 (UTC)

yes but not everyone ended up is hospital back then either, so I need rates for those that died at home.--Wrk678 (talk) 03:31, 19 November 2012 (UTC)

I found this page: http://www.jci.org/articles/view/29920, which says 30-40% fatality rate. RudolfRed (talk) 04:28, 19 November 2012 (UTC)

Also note that the fatality rate may be different for different strains. StuRat (talk) 03:43, 20 November 2012 (UTC)

Element transmutation

Can iron transmute to silver?--Almuhammedi (talk) 13:40, 19 November 2012 (UTC)

Probably not. Iron is at the apex of the nuclear binding energy graph, which means that it is the hardest element to transmute out of. To put it another way, given a long enough time frame, thermodynamically the entire universe should be transmuting into iron. Nuclear fusion of smaller elements in stars produces iron as the ultimate end product, and spontaneous fission shouldn't produce any element smaller than iron. --Jayron32 13:47, 19 November 2012 (UTC)

Well sure, but that's not really the question being asked. (Strictly speaking, because of activation energy barriers associated with nuclear fusion, what you would actually get if you wait long enough is a cold, near-perfect vacuum contaminated ever-so-slightly with hydrogen, helium, and an elemental assortment enriched in stuff around the iron peak. Further, most grand unified theories predict that all 'stable' nuclei and even bare protons will eventually decay, with a half life on the rough order of 10³⁶ years. See, for instance, proton decay, ultimate fate of the universe, and future of an expanding universe.)

Energetically-unfavorable transmutation is certainly possible, and happens on a regular basis in laboratories all over the world. It also occurs in nature; on the largest scale supernova nucleosynthesis is responsible for virtually all of the heavier-than-iron elements in the universe. (One could argue on that basis, not entirely speciously, that much of the silver we have already is the result of transmutation of iron.) Whether the multiple steps required to get from iron (atomic weight around 56) up to silver (atomic weight around 107) could be carried out industrially with meaningful yields is questionable, and whether it could be done economically is doubtful in the extreme. TenOfAllTrades(talk) 15:49, 19 November 2012 (UTC)

This does not answer your question, but it is Quite Interesting. See also Synthesis of precious metals. Trio The Punch (talk) 13:53, 19 November 2012 (UTC)

It used to be that a nuclear engineer learned how to read the periodic table, suitably modified for radiochemistry. Here are some educational decay charts from Lawrence Berkeley National Lab. I know of no direct transition from iron to silver: but you can sum over the known probabilities of all possible intermediate transition probabilities and determine exactly how unlikely the transition is. Like many processes in nuclear physics, the probability of iron-to-silver transmutation is probably tiny but non-zero. For perspective, consider how much silver we have on earth, and how much hydrogen we started with in the original phase of stellar nucleosynthesis. That ought to give you a sort of intuitive idea about the scale of the probability. Start with a sun-sized blob of hydrogen, and after a few billion years, you end up with a tiny amount - maybe a few thousand tons - of silver. The probability of hydrogen transmuting to silver is very small, and yet, on a cosmological scale, even very rare events can occur. Nimur (talk) 13:59, 19 November 2012 (UTC)

Given you have a nice neutron source like a nuclear reactor you will transmute 1g of iron into a few mg of silver and a lot of other elements over time (most likely years). The whole thing will be radioactive like hell but if you wait 10 half-lifes you are save.--Stone (talk) 14:19, 19 November 2012 (UTC)

• My feeling is that most silver has originated by transmutation from iron (supernova nucleosynthesis) - but it turns out your workbench has to include the right kind of supernova, an "r-process-rich star". A second r process, to be precise. This is apparently explained in [14], but that is not an easy read! Found via [15] which is far too simple. Still... if you can do it in a supernova, then this is just a matter of engineering. :) Wnt (talk) 17:00, 19 November 2012 (UTC)

• Buy Cox's The Elements. It is one of the most fascinating and best written books I have ever read (read the reviews at the link) and available very cheap used. μηδείς (talk) 18:01, 19 November 2012 (UTC)

It would be more economically feasible to get to Ag from Cd, by irradiating stable ¹⁰⁶Cd with neutrons (producing ¹⁰⁷Cd, which undergoes electron capture to ^107mAg, which decays by IT to stable ¹⁰⁷Ag). Double sharp (talk) 06:22, 20 November 2012 (UTC)

Technically, ¹⁰⁶Cd is only observationally stable, and can theoretically decay by β⁺β⁺ to ¹⁰⁶Pd with a half-life of over 4.1×10²⁰ a, but that doesn't make any difference as the half-life is so long that the decay has never actually been observed. Double sharp (talk) 06:26, 20 November 2012 (UTC)

Is this a fallacy? Classifying people from a psychological perspective

If you classify people, mothers for example, into angry, controlling, narcissistic, envious, emotionally unavailable mothers, aren't you forcing reality into your categories, ignoring that anyone, any person, can have one of the typical behavior of each and every category above? Wouldn't that be a series of categories without typical specimen, since you'll end up pushing mothers into the category that better fits yours feelings? Philoknow (talk) 16:52, 19 November 2012 (UTC)

Hmmm... now there's an interesting psych experiment. Given well trained actors with detailed and well-selected instructions, who assemble an artificial research community (e.g. a supposed Mars mission psych test) can you induce any individual to fall into one of these types regardless of their previous personality? Wnt (talk) 17:03, 19 November 2012 (UTC)

Is that an allusion to a thought experiment that really happened or just the creation of one? Philoknow (talk) 17:04, 19 November 2012 (UTC)

Just me piggybacking on your question, sorry. Wnt (talk) 19:15, 19 November 2012 (UTC)

• A fallacy is an invalid method of reasoning from premises to a conclusion. Merely categorizing things is not a fallacy, although you may miscategorize, or categorize according to flawed categories. But those are not fallacies, they are other errors in thinking. If you personally have "mother issues" there are family counselors and psychiatrists available among other professional help. See also our list of fallacies. μηδείς (talk) 17:11, 19 November 2012 (UTC)

The mother issue is just an example I came across. But there are alternative categories for co-workers, partners, and whatever you want. How to you call this kind of errors in thinking? If you have too little evidence for them, isn't there a too-little-evidence-for-the conclusion fallacy? Philoknow (talk) 17:14, 19 November 2012 (UTC)

It would be the drawing of conclusions from application of invalid categories that might be fallacious, again, see the list and look for one that seems to cover what you are thinking of. (That's just a matter of what fallacy means--not all mistakes in reasoning are fallacies.) Perhaps you could give a more detailed example of the sort of thing you have in mind. Perhaps you mean someone who forms an immediate judgment of a person as a type of "x" and then interprets all that persons actions as being due to their being an "x" regardless of evidence? That would be stereotyping, which literally means solid (as in the sense of unchangeable) categorizing. μηδείς (talk) 17:58, 19 November 2012 (UTC)

I'd say it's a misconception, but not an error in the reasoning. For more on this check Scientific misconceptions and list of common misconceptions. OsmanRF34 (talk) 18:10, 19 November 2012 (UTC)

What is this fallacy?: Report says that college students who talk to parents at least once a week are less likely to have trouble with abusing alchohol/drugs, therefore parents should call child at least once a week. Logically I would say that the student who talks to parents once a week is already more responsible, etc. which is why they call/ talk to parents regularly.165.212.189.187 (talk) 19:11, 19 November 2012 (UTC)

To me, this seems like making a correlation equal to causation. What the name for this fallacy is, I don't know, but correlation=/= causation.128.227.105.163 (talk) 20:14, 19 November 2012 (UTC)

It would be correlation does not imply causation. --140.180.252.13 (talk) 20:14, 19 November 2012 (UTC)

The following is what Carl Jung wrote in a letter to Sigmund Freud dated 12th June 1911 : "My evenings are taken up largely with astrology. I make up horoscopic calculations in oder to find a clue to the core of psychological truth. Some remarkable things have turned up which will certainly appear incredible to you . . . . . . I dare say we will one day discover in astrology a good deal of knowledge that has been intuitively projected into the heavens". Cinquefoil (talk) 19:08, 19 November 2012 (UTC)

If we didn't "force reality into our own categories", there'd be no way to reason or talk about anything (try it.) Psychologizing as a form of argument, however (speculating about the motives/psychological causes etc as to why one's opponent hold the views they hold, and attacking the former instead of the latter) is a bad thing Asmrulz (talk) 09:17, 20 November 2012 (UTC)

Impact depth

This article gives the formula for the impact depth as derived by Newton. How can it be derived? The article gives a sketch but doesn't have the details. 65.92.7.202 (talk) 16:59, 19 November 2012 (UTC)

The key criteria from it are "impactor carries a given momentum. To stop the impactor, this momentum must be transferred [...] to the material (mass) directly in front of the impactor, which will be pushed at the impactor's speed. If the impactor has pushed a mass equal to its own mass at this speed, its whole momentum has been transferred to the mass in front of it and the impactor will be stopped." Write the equation for the momentum of the projectile; substitute a function of the the projectile's density and length for the mass term. Do the same for the target material. Set them equal to each other (conservation of momentum) and solve for...whatever. DMacks (talk) 18:39, 19 November 2012 (UTC)

Iron Dome

Is the Patriot missile much worse or expensive than the Iron dome? If the Israelis find the rockets from the Palestinians so disturbing, why didn't they have lots of Iron Domes? According to the article they are not prohibitively expensive. If you compare them to a land incursion they are quite cheap. Philoknow (talk) 17:24, 19 November 2012 (UTC)

It's a different job. Patriot defends against long range missiles which descend on the target at very high speeds. Iron dome defends against short range threats, which approach at relatively low speeds. Israel's equivalent of Patriot is Arrow (Israeli missile). -- Finlay McWalterჷTalk 17:40, 19 November 2012 (UTC)

According to the article, some Israelis do think Iron Dome systems are too expensive. --Demiurge1000 (talk) 17:51, 19 November 2012 (UTC)

"too expensive" comparing to a Palestinian Quassam rocket. OsmanRF34 (talk) 18:13, 19 November 2012 (UTC)

Iron Dome is a new system. It still has some problems and is still in development. In the future they will likely have many more of them. Ruslik_Zero 18:54, 19 November 2012 (UTC)

It already successfully intercepts at least 70% of the rockets launched against populated areas (as much as 90% according to the Jerusalem Post). 24.23.196.85 (talk) 07:01, 20 November 2012 (UTC)

Universal milling machine or turret milling machine....

Hi I want to know which type of milling machine has better accuracy universal or turret milling machine. — Preceding unsigned comment added by 117.219.148.78 (talk) 19:31, 19 November 2012 (UTC)

A turret mill is generally less rigid. However, how accurately you machine any workpiece is dependent on so many factors I would not like to make a claim either way. If the job is done with the correct approach, the machines are adequately looked after, correct speeds and tools used, there is no reason why any properly designed machine tool should not be used at an accuracy determined by the machinist's available measuring instruments. Wickwack 120.145.142.95 (talk) 01:29, 20 November 2012 (UTC)

November 20

What's the solution to Haldane's dilemma?

Haldane's dilemma (edit | talk | history | protect | delete | links | watch | logs | views)

I read the article and still don't understand. Sagittarian Milky Way (talk) 03:23, 20 November 2012 (UTC)

The article doesn't seem to provide a great or simple overview of the topic, but from what I understand, the "dilemma" is due to some people's interpretation that a mathematical model can be used to make a vague and nonquantitative prediction in contradiction to observations. It seems to me that the "resolution" is not to trust the flawed mathematical formulation, because it makes vaguely incorrect predictions. Where are you getting stuck? Lots of scientists have designed models, or created mathematical equations, that turned out to be wrong. Even more scientists have produced proper, accurate models, that are misunderstood and misused by others to make erroneous claims. Perhaps you'd do better to ignore the "dilemma" and simply read our better article about population genetics.Nimur (talk) 05:23, 20 November 2012 (UTC)

I'll read that, tomorrow. Interesting I'm sure. Sagittarian Milky Way (talk) 07:05, 20 November 2012 (UTC)

Yup: from my understanding of the article, the 'solution' is that the dilemma never existed in the first place: Haldane was making assumptions that don't accord with real genetic/evolutionary processes, so his conclusions were invalid. AndyTheGrump (talk) 05:31, 20 November 2012 (UTC)

• See [16]. The number of mutational changes that occur really is much greater than the number that become fixed - most of the time, random mutations are neutral mutations. There is also the truncation selection, which I would say is relevant in so-called "junk DNA" - a concept which is now growing old, but which at least accurately reflects the point that regulatory sequences are prone to constant fine-tuning and there are a bazillion different ways to get the same effect. (You can have a 6 base pair motif that isn't exact anywhere in a fairly loose region of DNA and the outcome may work out to be the same pattern of regulation) So it doesn't really matter how evolution serves you up a "strong COMT promoter" or a "weak COMT promoter", depending on whether warriors or worriers are doing better against the hyenas this season. There's no need for fixation of one precise change because there are so many ways to strengthen or weaken the binding of a particular protein to the promoter. Wnt (talk) 05:35, 20 November 2012 (UTC)

Well then the article should say that then. It's actually very simple. You're left with the impression that a resolution hasn't been found in 55 years despite extremely embiggened knowledge of genetics and the fact that scientists like explaining things. Besides "we know which side is correct" (the fossil record/radioisotopic dating/genetics and all that) (which is not mentioned by the way).

Hey, are there any other paradoxes which we know/knew which side is correct but don't know why? Sagittarian Milky Way (talk) 07:01, 20 November 2012 (UTC)

The article clearly needs work but it seems to accurately report that the dilemma is no real dilemma. For example right in the LEDE it says:

Contrary to creationist claims, Haldane's dilemma is of no importance in the evolutionary genetics literature

....

Haldane stated at the time of publication "I am quite aware that my conclusions will probably need drastic revision", and subsequent corrected calculations found that the cost disappears. He had made an invalid simplifying assumption which negated his assumption of constant population size, and had also incorrectly assumed that two mutations would take twice as long to reach fixation as one, while sexual recombination means that two can be selected simultaneously so that both reach fixation more quickly. The creationist claim is based on further errors and invalid assumptions

Nil Einne (talk) 14:35, 20 November 2012 (UTC)

As far as I can see just having had a quick look there is a basic flaw in that in reality the main competitors for an individual in a species are other members of that species. They do not normally compete with nature, they compete with each other. Thus his rate of death does not matter much normally when the environment is only changing slowly. Of course all bets are off nowadays that humans are around and killing everything in sight but catastrophes like that aren't the norm. Dmcq (talk) 10:12, 20 November 2012 (UTC)

And when rapid change occurs, populations do become extinct. Antibiotics wouldn't be much use if that wasn't the case. Millions of populations of bacteria are destroyed before one becomes resistant. In the section Origin of the term "Haldane's Dilemma" it says if an environmental change occurs that necessitates the rather rapid replacement of several genes if a population is to survive, the population becomes extinct. That's not a dilemma, that's reality. Ssscienccce (talk) 01:39, 21 November 2012 (UTC)

Bear pig

What animal is equally related to a bear and a pig?GeeBIGS (talk) 05:47, 20 November 2012 (UTC)

What do you mean "Equally related"? I'm not sure I follow your question... --Jayron32 05:53, 20 November 2012 (UTC)

Did they have a common ancestor? What did it look like? Similar to anything extant today?GeeBIGS (talk) 05:56, 20 November 2012 (UTC)

Ah. It would have to be a pretty old ancestor. Taxonomically speaking, the smallest grouping that both bears and pigs share is the clade Laurasiatheria. I'm not entirely sure what the nearest common ancestor for that clade is, but it's got to be a long time ago, among mammals. --Jayron32 06:08, 20 November 2012 (UTC)

What would a hybrid possibly look like?GeeBIGS (talk) 06:00, 20 November 2012 (UTC)

I don't know that bears and pigs are genetically close enough to hybridize. Most hybrids need to share a genus, usually. Bears and pigs don't even occupy the same order (Carnivora vs. Artiodactyla). --Jayron32 06:08, 20 November 2012 (UTC)

You can answer many questions of this type pretty easily on Wikipedia (I haven't looked for any recent updates on NCBI). Look up bear. Look up pig. Look up class, order, etc in the table at right. Both are mammals; the bear is order Carnivora, the pig is order Artiodactyla. Now look those up and you'll see both of these are in superorder Laurasiatheria. Now - look for anything in Laurasiathera that is not in Carnivora or Artiodactyla (well, Cetartiodactyla and Ferae, once you look at the tree) - that gets you Perissodactyla, any odd-toed ungulate, as a potential answer, though as the branch is unresolved in the taxonomy shown it's still possible it's closer to one or the other. Oh, and yes -- the way you phrase the question, anything more distantly related also qualifies, plants, yeasts, sea urchins etc. But looking for the closest animal equally related to both is the more interesting question. :) Wnt (talk) 06:09, 20 November 2012 (UTC)

I am satisfied with a tapir for now.GeeBIGS (talk) 06:20, 20 November 2012 (UTC)

It's an entirely invalid assumption to just pick an animal from a separate order (tapir) but within the same superorder/class and assume that it's related with equal distance from both starting point. And furthermore, the OP jumps from asking what the actual equally related animal is to what would a possible hybrid look like -- these may very well be two totally different things, because closest same relateness might have very little to do with outward appearance (phenotype). DRosenbach ^{(Talk | Contribs)} 13:55, 21 November 2012 (UTC)

Depending on who asked the question, the answer they were looking for may have been Al Gore. But taxonomically, Jayron is right. However the earliest Laurasiathere certainly did not look like a Tapir, and probably looked more like a rat or an opossum. μηδείς (talk) 17:28, 20 November 2012 (UTC)

GeeBIGS—you ask the question, "What would a hybrid possibly look like?" Is the question what actual animal a possible hybrid would look like? Or is the question what nonexistent animal a "hybrid" would look like? I believe there is software that makes an image metamorphose into another image. It does so over many steps. One of the middle steps would be a credible transitional animal between bear and pig. Bus stop (talk) 17:39, 20 November 2012 (UTC)

An attempt at this research was reported 2008-4-1.[17] Of course, this is discredited; it would be unethical to use cells from a bear.[18] Wnt (talk) 18:18, 20 November 2012 (UTC)

Earlier, unconfirmed reports had existed for almost two years at that point. --Jayron32 19:32, 20 November 2012 (UTC)

Kidding aside, I'm loath to rule out the possibility of such a hybrid, even at the genetic level. Our article on polyploidy introduces me to the curious case of the Plains viscacha rat, which has been proposed as a recent polyploid. Research into the animal might reveal mechanisms by which dosage compensation for the duplicated genome could have succeeded. If you have a means for polyploids to survive, then it becomes feasible for bear-pig fusion nuclei to survive, except for some relatively narrow mechanisms of reproductive isolation which conceivably could be worked out in cell culture of some embryonic stem cell precursors. In the long term bottom line, there is no theoretical reason why bears and pigs can't be cleanly hybridized; it is strictly a technical problem (though a substantial one) and when push comes to shove you could build a synthetic combination up gene by gene if you had to. By comparison, there was no logical reason why somatic cell cloning ever had to be possible; that was dumb luck/excessive simplicity in evolution. Wnt (talk) 22:40, 20 November 2012 (UTC)

A bear is about as closely related to a pig as a person is to a rabbit. Good luck with that. μηδείς (talk) 23:53, 20 November 2012 (UTC)

Someone once crossed an owl with a goat, don'cha know. ←Baseball Bugs ^{What's up, Doc?} carrots→ 06:36, 21 November 2012 (UTC)

Any such attempt would be certain to make both the owl and the goat rather cross, although I have seen the occasional old goat with owl eyebrows: [19]. :-) StuRat (talk) 07:23, 21 November 2012 (UTC)

Hmmm... evidently you've never heard of the famous hootin' nanny. ←Baseball Bugs ^{What's up, Doc?} carrots→ 21:00, 21 November 2012 (UTC)

How can I separate mixture of water and ammonia?

Not sure if boiling or freezing works--124.172.170.234 (talk) 06:39, 20 November 2012 (UTC)

Probably neither directly; ammonia as a gas is hard to seperate out by distillation. Instead, acidify the solution careful to the equivalence point, with (for example) hydrochloric acid. This should allow you to distill the water off from the resultant ammonium chloride. --Jayron32 06:50, 20 November 2012 (UTC)

If it's a reasonably concentrated solution, there's a pretty high vapor pressure of ammonia over the solution especially when warmed (see ammonium hydroxide, and in general you can boil some ammonia out (see ammonia#Properties. But the answer really depends really what the questioner's goal is (actually "separate the two components" vs "get some pure water from it" vs "get some pure ammonia from it"). Jayron's got the right start for the old industrial process (see ammonia#Synthesis and production). DMacks (talk) 08:36, 20 November 2012 (UTC)

Apparently ammonia and water don't form an azeotrope [20] - it is theoretically possible to do the distillation. But the relative ease with which ammonia can be converted to solid with HCl and back to gas with CaO means that it's not worth the trouble. Wnt (talk) 22:48, 20 November 2012 (UTC)

9th period

Are there any relativistic predictions for the 9th period of the PT (Z > 172), just as there are for the 8th (Pyykkö's)? (Note that Z = 173 is not actually predicted to be an end of the PT anymore – see Periodic table.)

Double sharp (talk) 07:16, 20 November 2012 (UTC)

• Is the table you linked the Pyykkö model?--Jasper Deng (talk) 07:23, 20 November 2012 (UTC)
  • Yes. Double sharp (talk) 07:46, 20 November 2012 (UTC)
    • Well, that model seems to make some predictions about some otherwise-period-8 elements being in the 9th period as in this table. I don't know of any predictions for other elements in the 9th period.--Jasper Deng (talk) 23:47, 20 November 2012 (UTC)
      • I wouldn't really call it period 9 – they're filling 9s and 9p_1/2 only because these are relativistically stabilized and have energies closer to that of 8p_3/2. Are there any predictions past Z > 172? Double sharp (talk) 05:13, 21 November 2012 (UTC)

How much more diverse would the species be if we hadn't gone through the Toba catastrophe?

Some alleles were lost forever, right? But I mean, how much more freaking diverse do you want the human race to be? Would we start having elf ears or white hair at youth or tribes with very strong bonds without ritual circumscision that only like making love? Would the rarer traits like Zulu veins or Sarah Baartman's anterior be more common? Perhaps some more blood types or major histocompatibility complexes or body odors? And about how close are we to filling the a full subspecies of genetic diversity? Not much, maybe? How much of the Homo sapiens genetic field is extinct? Sagittarian Milky Way (talk) 07:44, 20 November 2012 (UTC)

I am not sure which I find more troubling, your fear of elves or of people who like sex. μηδείς (talk) 17:17, 20 November 2012 (UTC)

(ec) As a first point, the idea that the Toba supereruption caused a genetic bottleneck doesn't get much support nowadays -- there was very likely a major bottleneck, but much earlier than that. In any case, genetic diversity does not necessarily show up as overt physical differences. For example, pygmies in West Africa show a considerably higher level of genetic diversity than a group of randomly chosen Europeans. Generally, though, if you want to see the effects of diversity, look at sub-Saharan Africa -- that's where diversity is greatest. Looie496 (talk) 17:19, 20 November 2012 (UTC)

The article on Toba doesn't seem as deinitive as you are. Rmhermen (talk) 19:11, 20 November 2012 (UTC)

I didn't think I was being all that definitive, but, well, the article hasn't really kept up with events. The Toba eruption is pretty clearly dated to about 70000 years ago. It has recently become clear that the rate of human genetic change is about half as high as the value that was used for a long time (PMID 22965354), and when you revise dates accordingly, the numbers don't even come close to working out. Looie496 (talk) 19:32, 20 November 2012 (UTC)

Stop talking about my anterior please. Sarah Baartman (talk) 18:02, 20 November 2012 (UTC)

(!) μηδείς (talk) 23:45, 20 November 2012 (UTC)

Someone's confused about what anterior means. ←Baseball Bugs ^{What's up, Doc?} carrots→ 20:58, 21 November 2012 (UTC)

[21] Sarah Baartman (talk) 21:21, 21 November 2012 (UTC)

free electrons per atom

How do you calculate ab initio the number of free electrons per atom. For example, Tin is found in both the +2 and +4 oxidation states. Which ones do you use for a resistivity or a mean free path calculation? However, for graphite, based on what I know about organic chemistry, it would be 6 pi electrons per six carbons, or 1. (Yet carbon is frequently found in a +4 oxidation state, like carbon dioxide). Which oxidation states do you use in the context of electrons being on the scale of the fermi velocity? 71.207.151.227 (talk) 11:04, 20 November 2012 (UTC)

Help! This is urgent. Why is it so hard to find such a list of such simple values on the internet? 71.207.151.227 (talk) 11:12, 20 November 2012 (UTC)

A better question might be, why do you think oxidation numbers have anything to do with the number of free electrons in a solid? The Fermi energy, by itself, tells you the effective density of free electrons. See for example this discussion [22]. There is also a table of Fermi energies / velocities [23]. Dragons flight (talk) 11:27, 20 November 2012 (UTC)

I'm supposed to calculate the Fermi velocities ab initio, so that won't do. 71.207.151.227 (talk) 11:57, 20 November 2012 (UTC)

You can calculate Fermi energy / free electron density from the resistivity, if you know that. What are you allowed to use, cause oxidation states probably aren't going to be what you want. Dragons flight (talk) 12:06, 20 November 2012 (UTC)

heat capacity of a plasma

What's the model for the heat capacity of a plasma? Is C_P still C_V + R? Are there lattice vibrations in a plasma? 71.207.151.227 (talk) 11:55, 20 November 2012 (UTC)

A plasma is generally approximated as a gas of partially or fully ionized nuclei superimposed with a gas of free electrons. There is no lattice in a plasma. Dragons flight (talk) 12:29, 20 November 2012 (UTC)

Isolated systems

Do true thermodynamically isolated systems occur in biology? If not, what about anywhere in the natural world? Are even closed systems possible in biology? I've heard an egg could be. — Preceding unsigned comment added by 94.116.147.229 (talk) 15:56, 20 November 2012 (UTC)

No, entirely isolated systems do not exist, they are a theoretical concept that can however be used as an approximation of a naturally occurring system in some cases. The only exception is the universe itself, because it by definition contains all matter and energy in existence, so that excludes the possibility of external interaction. And yes, an egg for all practical purposes can be considered a closed system, though I think that very small particles like hydrogen molecules could leak through the shell. - Lindert (talk) 16:13, 20 November 2012 (UTC)

Read Thermodynamic system#Isolated_system and Isolated system. Sarah Baartman (talk) 16:38, 20 November 2012 (UTC)

If an egg was a closed system, you wouldn't be able to hard-boil it! Remember, a closed system doesn't just prevent transfer of matter, but of heat/energy as well. 209.131.76.183 (talk) 18:37, 20 November 2012 (UTC)

No, that's an isolated system. A closed system can exchange energy but not matter. --Jayron32 19:30, 20 November 2012 (UTC)

Actually an egg is not a closed system at all, the chicks inside breathe through the shell. There are thousands of microscopic pores through which carbon dioxide and oxygen are transported. I couldn't find that information in our wiki article after a brief search. Vespine (talk) 01:02, 21 November 2012 (UTC)

Fuel consumption of engines

For small engines the fuel consumption is measured in g/kWh. If we multiple the SFC with the energy density of the fuel (44.4MJ/kg for gasoline in this case) we get the following expression: 300 g/kWh * 44400MJ/g = 13MJ/3.6MJ. Since the units cancel out we get a ratio, and it appears to be the inverse of the efficiency of the engine. My question is: is this actually the inverse of the efficiency? I double checked my work and everything seems correct but I'm having a hard time convincing myself that calculating the efficiency is as simple as a single multiplication.A8875 (talk) 16:29, 20 November 2012 (UTC)

Sounds pretty right, why would you expect it to be more complex? Efficiency is simply how much total energy is converted to usable energy. You have total energy on one side (the fuel) and usable energy on the other (the engine output). The hard part might have been calculating the g/kWh in the 1st place, but that's been done for you. Vespine (talk) 00:54, 21 November 2012 (UTC)

Your calculation is perfectly valid, and the answer you obtained is not unreasonable (equiv to ~ 27%). Note that when looking up the energy density of fuels it is customary to use the Low Heat Value and not the High Heat Value, as a gasoline engine does not condense the H₂O vapour in the exhaust. 44.4 MJ/kg is a reasonable value for gasoline LHV. Some people who have studied the otto air cycle formula in a physics course expect gasoline engines to have an efficiency around 50% as predicted by the otto formula. However, practical gasolines engines are nearer 25% due to a great many factors such as non-zero combustion time, heat loss to coolant, friction, etc. Keit 60.230.228.87 (talk) 00:57, 21 November 2012 (UTC)

Thanks, you two. I double checked my math a dozen times but still wasn't sure so I thought I'd get some expert opinion. I'm liable to making dumb mistakes, especially on fundamental concepts like this one.A8875 (talk) 01:11, 21 November 2012 (UTC)

There are a obvious error in your calculation, 300 g/kWh * 44400MJ/g should probably read 300 g/kWh * 44400 J/g. The result seems OK. Gr8xoz (talk) 16:27, 21 November 2012 (UTC)

Momentum transfers

I have absolutely no clue how to solve this type of problem. How do I figure out velocities after a collision or before it from the equation $m_{1}u_{1}+m_{2}u_{2}=m_{1}v_{1}+m_{2}v_{2}$? This in in one dimension. --Melab±1 ☎ 16:44, 20 November 2012 (UTC)

Conservation of energy, or if it isn't conserved you need to specify an additional condition (e.g if the masses stick to each other after the collision that imples a relation between the velocities after the collision). Count Iblis (talk) 17:13, 20 November 2012 (UTC)

It is a totally elastic collision and the masses are not necessarily equal. I'm looking for the general solution. I tried solving for $v_{1}$ but that did not work. --Melab±1 ☎ 17:18, 20 November 2012 (UTC)

m1 u1 + m2 u2 = m1 v1 + m2 v2

Totally inelastic collision: v1 = v2, so we have:

v1 = (m1 u1 + m2 u2)/(m1 + m2)

Count Iblis (talk) 17:25, 20 November 2012 (UTC)

But it can't be known for sure that $u_{1}=u_{2}$ or that $m_{1}=m_{2}$. It could be that $u_{1}\neq u_{2}$ or $m_{1}\neq m_{2}$ or both. --Melab±1 ☎ 17:34, 20 November 2012 (UTC)

If the collision is totally inelastic, then the velocities after the collision are the same. Count Iblis (talk) 17:42, 20 November 2012 (UTC)

You can't solve for two variables if you only have one equation. This problem can't be solved without more information. Looie496 (talk) 17:44, 20 November 2012 (UTC)

Well, the problem I am working with only gives me the masses and their velocities prior to colliding. It is an elastic collision. They don't stick together. --Melab±1 ☎ 17:45, 20 November 2012 (UTC)

Have a look at Elastic_collision#One-dimensional_Newtonian. There are worked examples. You have TWO equations, one for conservation of momentum (which you wrote), and another for conservation of energy (which you did not). Using both, you can solve for new velocities, regardless of how the initial masses and velocities compare. The algebra can get rough, but our article also describes a nice trick of changing the frame of reference, so that one of the initial masses has zero velocity. SemanticMantis (talk) 17:56, 20 November 2012 (UTC) P.S. I have no Idea what Iblis is thinking above. Of course the velocities can be different after collision...

It did say inelastic at one point. I guess my edit got through after his. So does the $x_{1}$ and $x_{2}$ on that page equal $u_{1}t$ and $u_{2}t$, respectively? Even still, I can't understand it. --Melab±1 ☎ 18:05, 20 November 2012 (UTC)

Apologies, I misread "elastic" for "inelastic". In that case, you have conservation of energy, but it is not recommended to use the equation for energy conservation, because the algebra then gets messy. Instead, you work in the center of mass frame where the total momentum is zero. Suppose we are in the center of mass frame, then the energy of two particles with momenta p1 and p2 with masses m1 and m2 is given by:

E = p1^2/m1 + p2^2/m2 = (p1^2) (1/m1 + 1/m2)

because in the center of mass p1 = -p2. Energy conservation thus implies that the magnitude of the momentum of the partices is the same before and after the collision.

The velocity of the center of mass is

u* = (m u1 + mu2 )/(m1+m2)

The initial velocities in the center of mass system are thus:

u1' = u1 - u*

u2' = u2 - u*

The two momenta in the center of mass frame are

p1 = m1 u1'

and

p2 = m2 u2'

they are equal in magnitude and they add to zero, so p1 = -p2

This means that after the collision, the momenta reverse sign, so particle 2 will get the momentum that particle 1 had and vice versa. So, we have:

m1 v1' = p2 = m2 u2' = m2 (u2-u*) ---->

v1' = m2 (u2-u*)/m1

The velocity of particle 1 after the collision in the original frame is thus:

v1 - u* = m2 (u2-u*)/m1 ------>

v1 = u* + m2 (u2-u*)/m1

Count Iblis (talk) 18:13, 20 November 2012 (UTC)

Or, if you want to avoid using the center of mass solution, you can use the energy conservation (not as messy as Count Iblis implied). Start with the energy conservation

m1 u1^2 + m2 u2^2 = m1 v1^2 + m2 v2^2

and rearrange the terms as

m1 (u1^2 - v1^2) = m2 (v2^2 - u2^2)

Open each parenthesis as a product of two factors

m1 (u1 - v1)(u1 + v1) = m2 (v2 - u2)(v2 + u2) (Equation 1)

use the momentum equation

m1 u1 + m2 u2 = m1 v1 + m2 v2

rearranged as

m1 (u1 - v1) = m2 (v2 - u2) (Equation 2)

to substitute the factors m1 (u1 - v1) into the equation 1 above and get

m2 (v2 - u2)(u1 + v1) = m2 (v2 - u2)(v2 + u2)

which simplifies to

u1 + v1 = u2 + v2 (Equation 3)

Equations 2 and 3 above now form a set of linear equations that can be easily solved.

Dauto (talk) 19:00, 20 November 2012 (UTC)

Recycling 10, 20, or 30 year old paper

Hello, I have some old documents in boxes, and these papers are probably 10, 20, or 30 years old. I intend to recycle all of these documents, and I was wondering, can they even reuse the fibers from paper that old? 2A02:AF8:1:3500:0:0:0:9868 (talk) 21:30, 20 November 2012 (UTC)

Yep. They have different grades of paper and know which fibers can be used for which grade. Trio The Punch (talk) 23:25, 20 November 2012 (UTC)

Area of land required to feed working horses on arable farm

I have seen somewhere a statistic indicating the proportion of the cropped area (ie excluding fallow) of a typical arable farm (worked by horse power) which was required to grow the crops required to feed the horses working the farm, the point of interest being that the introduction of tractors powered by fossil fuels led (in addition to general improvements in labour productivity) to release of that land for production of crops for sale off the farm. Does anybody know what that proportion was? (I am interested in comparing it with the proportion of bio-ethanol (or similar) produced from land worked by a tractor which would be required to power the tractor.)Peter MacLaren (talk) 21:41, 20 November 2012 (UTC)

This is a very interesting and very difficult question! There is certainly no general, one-size-fits-all answer, but I will be interested to hear other responses. You can google around a bit, and see estimates at that are several orders of magnitude apart. The land needed to sustain a horse depends on how hard it's worked, what crops is grown, what the soil type is and the biome. These will restrict the plants, growing seasons, and general agricultural biodiversity and cropping systems available. Are you interested only in the horse, or do the humans have to survive off the farm too? You might be interested in 40 acres and a mule, or Three acres and a cow (the implied agricultural estimates, not the politics). Your more general question is currently the subject of intense research, funded by many governments and corporations. For starters, check out Life cycle analysis.

This does not directly answer the question, but when Ford were selling the original Fordson farm tractor back in the 1920's, the sales kits provided to dealers by Ford compared the economics of the tractor against the use of horses for ploughing, reduced after explanation to a dollar for dollar comparison. This was somtimes published in Ford's advertising, so try searching in old farm magazines. Quite likely old farm magazines and manuals from the 1920's (when tractors were competing not so much against each other but with horses) have the information you want. National Libraies usually have them, some have converted them to PDF and put them on line. I have an old Fordson manual somewhere that has a summary of the comparison - if I remember where I put it, I'll post again. Keit 60.230.228.87 (talk) 01:08, 21 November 2012 (UTC)

Page 3 of my Fordson Model F (1916) tractor owner's manual has the following text under the heading Horse and Horseless Farming:-

The harness and whiffletrees for an eight-horse team cost more than a Fordson Tractor. Yet the eight won’t do more work.

The eight horses cost double the price of the Fordson, and that at the (current) low price of horses.

Grooming eight horses once a day at 15 minutes a horse takes two hours. Watering and feeding, another hour. Harnessing and Un-harnessing, hitching up and unhooking, leading from barn to implement, etc., take yet another hour. Four hours’ work has been lost without expenditure of any energy in productive work.

A Fordson can be filled with water, fuel and oil, and thoroughly gone over in half an hour.

A Fordson can be worked continuously day and night through all the seasons of plowing, seeding, haying, harvesting.

Horses cannot be humanely worked more than eight hours in the heavier operations or ten in the lighter.

Fordsons are not troubled with flies, heat or hard ground. Horses suffer terribly and die in appalling numbers when hard worked on hard land in hot weather.

A Fordson can do all that horses can do, as well as horses can do it and belt work besides.

It takes a few hours to make a Fordson.

It takes three years’ time and three years’ care (some horsemen say five years) to make a work horse. At any time in those three years the colt may die and be a total loss.

A Fordson eats only when it is engaged in productive work.

Horses eat 365 days a year.

A Fordson makes every acre of the farm a source of profit.

An eight-horse team withdraws 40 acres from the farm’s return to feed itself.

The following section titled "Plowing Acreage and Speed Data" goes on to explain how to calculate how much land you can plow per 10 hour day. For the Forson Model F, it works out to be 7.6 acres for typical conditions - the implication is that an 8-horse team would do less. On Page 7 it says that with a "special seeding machine", a Fordson can plant corn at 3 hours per acre and bale 30 tones of hay per day, and that if necessary in rush periods a Fordson can be worked (presumably with 2 or more drivers) day and night, whereas horses must be allowed time for feeding and sleeping etc. Thus, you can consider that under rush circumstances (eg getting work done before the rains come) a Fordson does the work of 24 horses, which require 120 acres for feed.

On Page 8 it says a Fordson all up (depreciation, fuel, oil, wages for driver, etc) cost a farmer $0.95 (this is 1916 data don't forget, based on tractor purchase price $880, horse $150, both have a working life of ~5000 hours) to plow an acre, whereas a horse team will cost $1.46 to plow an acre, and confirms that an 8 horse team will in 8 hours (not counting time to feed and harrnes) do the same plowing work as a Fordson in 10 hours (not counting the 0.5 hour daily fueling and checking).

Modern tractors could be expected to considerably outperform a 1916 Fordson, and last very considerably longer than 5000 hours.

Keit 121.221.74.211 (talk) 15:17, 21 November 2012 (UTC)

• I wonder how common eight-horse teams were though. Two or four-horse teams seem to have been more often used. Perhaps some advertising sleight-of-hand here. Rmhermen (talk) 21:03, 21 November 2012 (UTC)

I also, now that I think about it, have an enginneering textbook that gives data on the thermodynamic efficiency of animals (ie calorific value of food eaten vs mechanical power output) - I will post again later. You could compare this with the calorific value of crops converted to engine fuel and teh efficiency of engines (typically ~40% for diesel engines) Keit 121.221.74.211 (talk) 15:55, 21 November 2012 (UTC)

November 21

Automated mini boats

Currently in the Gaza Strip, which is subject to a sea blockade, but also in many far-flung archipegaloes where the labor of hiring a person to make the ship may outweigh the tiny amount of cargo needed for a few residents, I would think that there would be an economic incentive for tiny ships that use GPS to carry cargoes to predetermined rendezvous points.

Now, it does occur to me that a scale model ship with a scale model boiler and a scale model screw probably ought to make only a proportionally reduced distance in a given amount of time, with fuel tanks proportional to its mass, and that therefore it should not be economical, or even possible to carry the fuel; ships are huge for a reason.

Nonetheless, model yachting using the wind exists, and the wind is, if anything, more powerful in regard to the scale vessel.

Is it possible that well-designed but very inexpensive automated model yachts could be mass produced to carry the food and medicine Gazans need past any blockade? (at least, until the Israelis have similarly tiny drone ships to attack them...) Wnt (talk) 00:15, 21 November 2012 (UTC)

Technologically speaking it's definitely possible, unmanned boats have successfully crossed the pacific[24][25]. However Palestinians may or may not have the financial or industrial power to maintain such a fleet. A8875 (talk) 01:22, 21 November 2012 (UTC)

I could see the Israelis building tiny unmanned gunboats to sink those teeny ships. Or better yet little galleys ("Ramming speed!").Clarityfiend (talk) 02:46, 21 November 2012 (UTC)

I see we have an article Liquid Robotics about these. From the site they crossed 3200 miles in 4 months, or just over 1 mph, which should be fast enough by the Lilliputian scales of the Israeli conflict. Unfortunately the site doesn't give any clear indication of the cost or even the payload of these things, so I'm still not sure how practical the idea is. Wnt (talk) 03:39, 21 November 2012 (UTC)

could probably be remote controlled via a satphone or such, assuming cell service doesn't reach out to sea that far.

this brings up one of my favorite hobbyhorses; military conflict today (as in the herein mentioned conflict) is awfully destructive and deadly, to civilians as well as combatants. yet, people seem to want it anyway. I suggest instead we go back to WWI era naval battles, with huge dreadnaughts blasting away at each other far enough offshore to be safe, but close enough for spectators. could even be a profitable entertainment. the catch being, they are unmanned, and operated by remote control. fills in that niche between football (soccer) hooliganism and thermonuclear destruction that we as a species seem to so dearly crave. Gzuckier (talk) 18:33, 21 November 2012 (UTC)

See Naval Warfare at Peasholm Park, Scarborough. Alansplodge (talk) 19:16, 21 November 2012 (UTC)

Pork v Chicken

Which would be more dangerous to do? Eat raw chicken or to eat raw pork? My friend claims eating raw chicken would be worse, but I would have guessed pork would be more dangerous. Which would be more likely to kill you or cause very serious illness? Rabuve (talk) 09:14, 21 November 2012 (UTC)

The only health risk mentioned in our Chicken (food) article is salmonella, which is normally not fatal in healthy adults. Undercooked pork, on the other hand, is known to carry Trichinosis, tapeworm and other nasties in addition to Salmonella. Rojomoke (talk) 11:24, 21 November 2012 (UTC)

The USDA maintains a website, Is It Done Yet?.gov, with the intent to inform the public about healthy and safe handling of meat and poultry. Neither pork nor chicken are safe to eat raw. Outside the realm of normal, safe, and healthy food preparation, if we wanted to answer your question, we'd need a clearer definition of "danger" and a method to compare different levels of danger. Statistically, more pork in your average grocery store has an infection of some type. According to the NIH and the USDA, in 1943, one in six Americans was infested with trichina worm as a result of uncooked or undercooked pork (trichinae fact sheet from USDA). So, from that perspective, though the statistic is grossly out of date, it's also grossly factual evidence that more pigs have worms, by the numbers, than percentage of chickens carrying contagious Salmonella bacteria. And yet, an argument can be made in either direction: salmonella is either more- or less- dangerous, if you get it, than trichinosis - even though different sources claim that you're more- or less- likely to contract it. Welcome to the world of quantitatively analyizing difficult and ambiguous data! So, is a more dangerous disease that is less likely to occur more or less dangerous? Nimur (talk) 14:18, 21 November 2012 (UTC)

The age of those stats is a huge caveat; the pork industry is much more regulated than it was 70 years ago. Due in part to pork's bad name, the industry made a huge effort to clean up the image and quality of the meat (cf. "The Other White Meat") to the point where guys like Alton Brown advocate cooking pork chops to medium rare - something that would be unheard of back in the 40s and 50s (I still can't get my elderly mom to cook them to less than "briquette"). I'd much sooner down a piece of undercooked pork than chicken, though obviously different pieces have different risk factors. Matt Deres (talk) 15:42, 21 November 2012 (UTC)

Every Tuesday I eat Mett and this is a very common here. So with proper veterinary oversight over the production raw pork does not cause any harm. It is common for decades and there is no significant illnesses or death atributed to raw pork consumption here in Germany.--Stone (talk) 20:51, 21 November 2012 (UTC)

Why don't they just test if cellphones actually do cause interferences in airplanes?

Yes I have read mobile phones on aircraft and I have watched that old MythBusters episode, but why can't the FAA just test if cellphones actually do interfere with communication signals? According to the article, one theory is that the lack of testing is for cost reasons, and that to save money, it should be airlines doing the experiments. But are such tests really expensive? And why can't they just tweak the communication tools of the aircraft in such a way that cellphones can't interfere with the signals? Narutolovehinata5 ^tccsdnew 11:26, 21 November 2012 (UTC)

As I understand it, the main reason they don't let you use your phone on the plane has nothing to do with safety; it's because the telecoms don't like it. It confuses their equipment to have you moving so quickly from one cell to another. But I don't have a ref. --Trovatore (talk) 11:32, 21 November 2012 (UTC)

Another safety factor is the potential for assault and battery by other, irritated passengers who would have to listen to it. ←Baseball Bugs ^{What's up, Doc?} carrots→ 12:29, 21 November 2012 (UTC)

The general issue has been discussed many, many times before on the RD, you likely want to read these discussions. However generally speaking, and our article reflects this, article communications systems are designed to be very robust and resist all sorts of interference. It is however difficult to completely prevent any possibility of interference and the small possibility of interference is one reason why there is general reluctance to allow such equipment, as both airlines and regulators tend to be very risk adverse. As I said, it's only one reason arguably only a small one, there are plenty of other reasons for any bans. Note that with the recent development of picocells on planes, airlines are started to get interested in deploying these and testing their usage together with phones sufficiently to satisfy regulators. This shouldn't be surprising, there's little incentive for airlines to pay for testing mobile phone network usage on planes when they generally won't work very well anyway when still trying to communicate with ground based equipment given the speeds involved and so the actual interest and advantage to their customers (passengers) is unclear and may be even a negative (since given the problems, there's a fair chance many of those who do try will be the sort of people to annoy other passengers). Far better to just ban them and avoid any possible risk (beyond that caused by the small number left on inadvertedly or intentionally) as well as any cost needed for testing. When they are providing a service to their customers, one which they're probably going to get paid for, that's a different matter. Nil Einne (talk) 12:49, 21 November 2012 (UTC)

In a general aviation aircraft, flying under the auspices of "Part 91," the pilot may permit you to use your cell phone if he/she believes it won't interfere with the aircraft operation: 14 CFR §91.21(b)5, prohibitions on operating a device do not apply to "Any other portable electronic device that the operator of the aircraft has determined will not cause interference with the navigation or communication system of the aircraft on which it is to be used." Aircraft operated for commercial passenger flights typically are conducted in compliance with much more stringent safety and legal regulations (Part 121), and numerous other restrictions imposed by the corporate office and its insurers. Aircraft operating outside the U.S. comply with other countries' safety regularions. On those flights, electronic devices may be prohibited for many reasons, including the fact that some devices do interfere with radio communication and navigation. If you'd like to try for yourself, place a mobile phone next to an airband scanner, and wait for a few minutes until you start hearing the clicking. It's sporadic, but it can audibly interfere with the VHF and UHF airband. This is only one of the more obvious types of interference phenomena, and it is easily demonstrable and repeatable in the safety of your home. Other more pathological types of interference also exist, and most pilots of commercial airlines do not enjoy testing their knowledge of RF circuit theory while operating large aircrafts. Nimur (talk) 13:19, 21 November 2012 (UTC)

For rules to work, rules need to be kept simple. Now imagine one person on an airliner is using a cellphone - not much of a problem. Now imagine all the passenger in a large airliner have their cellphones in use. To conserve battery energy, cellphones measure the incomming signal from the network. If the signal is strong (as it would be if you are close to a cellphone network site), the cellphone replies with a weak signal. If the network signal is weak (indicating your phone is far from the nearest network site) the phone responds by transmitting a strong signal. The aircraft may be on the limit of the range, so all cellphones transmit at full power - hundreds of them. And the metal skin of the aircract acts somewhat like the walls of a microwave oven (faraday cage) and keeps a lot of the energy within the plane. Not only might it interfere with aircraft systems, hundreds of cellphones all going at once at full power in a confined space could well be a health hazard. And, not the least important, you might not hear aircrew safety announcements. Note that cellphones when switched on communicate with teh network even when calls are not in progress.

Some airlines are investigating a means of allowing cellphones in flight. By using an onboard cell base, the phones can be instructed to use minimum power, and the onboard base relays to a telco ground station. There may be a method to restrict the number of cellphones in use, and breaking in with aircrew announcements. Floda 120.145.142.32 (talk) 13:21, 21 November 2012 (UTC)

A decade or two or three ago, some airlines (or maybe some types of planes) had telephones embedded in the seatback in front of you. You could place calls on them at any time. It wasn't cheap. It was several dollars a minute. But if you really, really needed to make a call, it was worth it. Does anyone know if any airlines or airplanes still use those? ←Baseball Bugs ^{What's up, Doc?} carrots→ 20:53, 21 November 2012 (UTC)

Dot matrix printing on irregular surfaces

Please direct me to an image, or better yet, video showing how they get dot matrix printing (e.g., expiration/use-by dates) on such irregular surfaces as the sides of milk jugs (sometimes, even on the narrow handle) or juice bottles with embossed lettering or designs made in the bottle surface. If such labeling is actually printed on flat sheets of plastic before it is even formed in the bottle/jug forming machinery, please provide proof of that. Thanks. 20.137.2.50 (talk) 14:25, 21 November 2012 (UTC)

Inkjets used for labelling (often called "coding") have a long "throw distance" - the distance at which they can eject an ink stream and still produce a coherent image. This commercial coder has a throw distance of 90mm - so that allows you to label all kinds of things, without actually touching them. That allows printing on all kinds of complicated surface shapes, and printing on delicate things like eggs. A long throw coding printer is unlike an inkjet for printing on flat paper, which has a throw distance of a few mm. -- Finlay McWalterჷTalk 14:41, 21 November 2012 (UTC)

Although a lot of things that might appear to have been printed have in fact been inscribed with a laser (e.g.) It's common for plastic bottles to be inscribed this way, and in some cases packaging is made with a dual-layer panel ready for inscription - the laser burns off the top layer revealing the lower layer, which is of a contrasting colour. -- Finlay McWalterჷTalk 14:47, 21 November 2012 (UTC)

The article section Batch coding machine#Non contact coding type has a link to this video of an inkjet coding machine in operation. See also Laser engraving. Red Act (talk) 16:39, 21 November 2012 (UTC)

Thanks. What was the series of words you two typed into whatever search engine you used to arrive at the sources you did. Teach a man to fish? 20.137.2.50 (talk) 17:38, 21 November 2012 (UTC)

I started with the Inkjet printer article, which has a link to Batch coding machine in the "See also" section. And then the Batch coding machine article contains a link to Laser engraving (via the Laser marking redirect) in the "Non contact coding type" section. Red Act (talk) 18:49, 21 November 2012 (UTC)

Why are space probes so slow?

Why are space probes so slow? For example, the NASA webpage at http://voyager.jpl.nasa.gov/mission/fastfacts.html gives the speed of the Voyager probes as about 3 to 4 AU/year. That's a tiny fraction of the 173 AU/day of the speed of light. Given that nuclear reactors can operate for years without refueling in naval nuclear propulsion, why can't we just attach a nuclear reactor to a probe, and then have it continually accelerate the probe to around 99.9%+ of the speed of light? If we could do that, then with constant acceleration and deceleration, we'd be able to reach Alpha Centauri, 4.37 light-years away, in about 9 years, less than a decade! :) —SeekingAnswers (reply) 19:01, 21 November 2012 (UTC)

It is not that space probes are actually slow, they can be traveling at kilometers per second, it is that space is so big. Graeme Bartlett (talk) 20:37, 21 November 2012 (UTC)

Even with a nuclear reactor you get not to 99.9% The amount ov energy you need is more like 10 tonnes of antimater and 10 tonnes of matter and a conversion into acceleration than a spaceprobe with 10kg. You will cover the distance to Alpha Centauri in a few decades or hudreds of years. --Stone (talk) 20:46, 21 November 2012 (UTC)

Has anyone figured out the optimal speed that such an object could be pushed, to where it's pretty fast but doesn't burn out its fuel too soon and doesn't approach the light-speed-infinite-mass dilemma? Or maybe it's already doing that? ←Baseball Bugs ^{What's up, Doc?} carrots→ 20:49, 21 November 2012 (UTC)

It depends what you mean by "optimal". I imagine the obvious choice would be to optimise the ratio of acceleration over rate of fuel consumption, but I'm sure there are other definitions of "optimal" in this case (like travelling the maximum possible distance with a given amount of fuel). I may just be wrong and the two may be equal, but the question is very interesting indeed. -Anagogist (talk) 21:08, 21 November 2012 (UTC)

To use energy for propulsion one must also have reaction mass; one must propel some matter backwards in order to get a forward reaction. Submarines propel seawater, aircraft air, but a spacecraft in a vacuum has to carry, and expend, its own reaction mass. Various means of electrically powered spacecraft propulsion make efficient use of reaction mass. -- Finlay McWalterჷTalk 20:51, 21 November 2012 (UTC)

There are a lot of concepts, but the ion propulsion took decades to come out of the lab. There is no big interest to go to Alpha Centauri if alot in the solar system is still to be done. A high speed probe into the Oort cloud might be the farthest we will go in the next generation. For that electric probulsion or solar sails or Electric sailmight be enough.--Stone (talk) 21:05, 21 November 2012 (UTC)

• Even if the Voyager probes could have gone faster, their trajectories and hence their speed was geared towards visiting all the planets they could. Little point to go faster and not fly by anything interesting. μηδείς (talk) 21:25, 21 November 2012 (UTC)

Vitamin K

Somewhere inthe recesses of my memory I recall hearing that the jewish people circumsized their sons on the 8th day because of the high level of Vitamin K at that time. Knowing that vitamin K is associated with coagulation - it seems plausible. But, is there something to vaidate this "memory"? Thanks! ---- — Preceding unsigned comment added by 24.153.163.210 (talk) 19:52, 21 November 2012 (UTC)

How would the ancients know about Vitamin K? ←Baseball Bugs ^{What's up, Doc?} carrots→ 20:47, 21 November 2012 (UTC)

I vagely remember it was the time of fastest blood clotting in the baby. Graeme Bartlett (talk) 21:00, 21 November 2012 (UTC)

That, they might know. It would be interesting to find out if that's the real reason, or if it's just a happy (so to speak) coincidence. ←Baseball Bugs ^{What's up, Doc?} carrots→ 21:28, 21 November 2012 (UTC)

LED bulb

how can I light a led bulb by the ic 7403 on project board — Preceding unsigned comment added by 117.194.125.67 (talk) 19:57, 21 November 2012 (UTC)

quad 2-input NAND gate with open collector outputs, you will ahve to limit the current for the LED by using a suitable resister for the voltage in your circuit and the current required by the LED, else you may melt it. Graeme Bartlett (talk) 21:04, 21 November 2012 (UTC)

UN hypocritical

why does the UN condemn this http://www.bbc.co.uk/news/world-africa-20427549 but supports the Syrian rebels. I don't see much difference other than most of the syrian rebels are terrorists who came from Iraq, which the UN now wants to arm. --Wrk678 (talk) 22:29, 21 November 2012 (UTC)