question stringlengths 37 38.8k | group_id stringlengths 2 6 | sentence_embeddings listlengths 768 768 |
|---|---|---|
<p>Why does a term proportional to $\left(F,\,\tilde{F}\right)\propto Tr\left[ F_{\mu\nu}\tilde{F}^{\mu\nu}\right]$ in the Lagrangian of the pure Yang-Mills theory violate CP?</p> | g17657 | [
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<p>I need to evaluate two Grassmann integrals, one over "real" Grassmann variable another one over complex variables.</p>
<p>Lets start with the real one first :</p>
<p>The prototype we have for $n$ real Grassmann variables :</p>
<p>$$
\tag{1}\int d^n\psi \exp{[\frac{1}{2}\psi^T M\psi]} ~=~ (\det M)^{1/2}
$$</p>
<p... | g17658 | [
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<p>I am interested in why people are interested in <a href="http://en.wikipedia.org/wiki/Seiberg_duality" rel="nofollow">Seiberg duality</a>? Can it be used for something? Does it (or may it) correspond to any 'real world' physics? I don't have enough background to understand the details and I would like to know if it ... | g17659 | [
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<p>Planck's temperature is theorized to be the highest possible temperature in the universe. But, has it been reached? Or, will any object or phenomenon ever reach this absolute temperature?</p> | g17660 | [
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<p>Consider a Chern-Simons Lagrangian $\mathscr{L}=\mathbf{e}^2-b^2+g\epsilon^{\mu \nu \lambda} a_\mu\partial _\nu a_\lambda$ in 2+1 dimensions, where the 'electromagnetic' fields are $e_i=\partial _0a_i-\partial _ia_0$ and $b=\partial _1a_2-\partial _2a_1$.</p>
<p>From the Lagrangian, we obtain the classical equation... | g17661 | [
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<p>I have seen a discussion of what would happen for an ideal gas expands irreversibly and adiabatically until absolute zero degree K. The entropy change is like that:</p>
<p>Δs=Cv ln(T2/T1)+R ln(V2/V1)</p>
<p>It is impossible for T2 to be zero K in the equation and so it becomes one justification of the third law. I... | g17662 | [
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<p>I am trying to understand the physics behind a single sailed boat. I have read the following questions</p>
<p><a href="http://physics.stackexchange.com/questions/94541/sailing-against-the-wind-is-this-a-fair-model">Sailing against the wind. Is this a fair model?</a></p>
<p><a href="http://physics.stackexchange.com... | g17663 | [
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<p><a href="http://www.dailygalaxy.com/my_weblog/2013/02/the-real-universe-is-250-times-bigger-than-the-visible-hubble-volume-todays-most-popular-1.html" rel="nofollow">This article</a> claims that because the universe appears to be flat, it must be infinite. I've heard this idea mentioned in a few other places, but th... | g17664 | [
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<p>In some extensions of the Standard Model of particle physics (Supersymmetry with R-parity violation being a prominent example), the proton is allowed to decay, e.g. via $p\to e^+\pi^0$:</p>
<p><img src="http://i.stack.imgur.com/piYKh.png" alt="Feynman diagram of proton decay in a GUT"></p>
<p>While this decay is o... | g17665 | [
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<p>I'm trying to determine a lower bound for the work input necessary to make an entropy-reducing process "spontaneous" in the sense that the 2nd law is not violated.</p>
<p>For a constant temperature and volume process, I'd calculate the change in Helmholtz free energy and say ΔA = -W. When considering a non-isother... | g17666 | [
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<p>I am trying to prove when the following holds:</p>
<p>$$|a\rangle |b\rangle \langle c|\langle d| = |a\rangle \langle c| \otimes |b\rangle \langle d|$$</p>
<p>where $\otimes$ stands for tensor product and the $a,b,c,d$ are $N$ dimensional state vectors.</p>
<p>I can see that for $N=2$ it holds true for $a,b,c,d\ \... | g17667 | [
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<p>There's more gravitational force in our galaxy (and others) than can be explained by counting stars. So why not lots of dark planetery systems (ie without stars) ? Why must we assume some undiscovered and unexplained form of matter ?</p> | g832 | [
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<p>I symbolize $T$ as the time-ordered operator and $::$ as normal order symbol.
I know that in quantum field theory generally we have:</p>
<p>$$T\phi_1(x_1)\dots\phi_n(x_n)=:\phi_1(x_1)\dots\phi_n(x_n):+A$$</p>
<p>where $A$ roughly means all possible contractions. I have read a convincing proof.</p>
<p>However when... | g17668 | [
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<p>I attempted to simulate the interaction of a moving particle and a potential well in <a href="http://www.wolfram.com/mathematica/" rel="nofollow">Mathematica</a>. The particle should experience a force of -$1/r^2$, if the equation for the potential well is -$1/r$. The inputs for the <a href="http://reference.wolfram... | g17669 | [
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<p>I have been trying to reproduce a calculation (equation 4.12) in this paper <a href="http://arxiv.org/pdf/1107.2678v1.pdf" rel="nofollow">http://arxiv.org/pdf/1107.2678v1.pdf</a> by Carlip reviewing the derivation of the effective central charge of the BTZ Black Hole so that one can use the microcanonical form of th... | g17670 | [
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<p>This question came up in a computer science / robotics exam and I still don't know the solution for it. I figured out that it's classical mechanics related, so I thought this might be the best place to ask it.</p>
<blockquote>
<p>Suppose a control system is described by the equation </p>
<pre><code>C = A*x + B*d... | g17671 | [
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<p>I think I understand the basic idea of photoelectric effect but there are two things in the schematic diagram of the apparatus for the investigation of the photoelectric effect which I do not understand.</p>
<p>Firstly, the emitting electrode is connected to a positive terminal of a battery. This implies there is a... | g17672 | [
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<p>Is there any substance with bigger volumetric heat capacity than water? According to <a href="http://en.wikipedia.org/wiki/Specific_heat_capacity#Table_of_specific_heat_capacities" rel="nofollow">this table</a> water has the biggest known VHC. But I can't believe that in the 21. century we have no special material w... | g17673 | [
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<p>I have read that the night sky should have been bright because every spot should end up pointing to a star in the infinite universe but this is not the case because the universe is expanding. I am thinking if the universe cannot be expanding with speed faster than light then the dark night sky is also due to the uni... | g688 | [
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<p>As a child I remember hearing the popular paradox presented by Zeno proposing that Achilles could never catch a tortoise in a race since he would have to traverse the infinite space between himself and the tortoise. After some pondering I concluded that the obvious answer to the dilemma is that the space is not inf... | g17674 | [
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<p>Could you please help me understand what is the difference between rocket engines designed to work in air (first stage) and vacuum (later stages)? </p> | g17675 | [
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<p>Where would I look to get the most accurate experimental values of <a href="http://en.wikipedia.org/wiki/Parton_%28particle_physics%29" rel="nofollow">parton distribution functions</a> for the proton? I know these functions aren't measured <em>directly</em>, but I'd basically like to find a fit that involves recent ... | g17676 | [
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<p>I have learned in my physics classes about five different types of <a href="http://en.wikipedia.org/wiki/Mass">masses</a> and I am confused about the differences between them.</p>
<p>What's the difference between the five masses: </p>
<ol>
<li><p>inertial mass, </p></li>
<li><p>gravitational mass,</p></li>
<li><p>... | g88 | [
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<p>This question: <a href="http://physics.stackexchange.com/questions/8567/how-do-electron-configuration-microstates-map-to-term-symbols">How do electron configuration microstates map to term symbols?</a><br>
And the discussion of multielectron effects here: <a href="http://physics.stackexchange.com/questions/8483/quan... | g17677 | [
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<p>Like, if you <a href="http://www.wolframalpha.com/input/?i=volume+16+Psyche+%2F+1mm" rel="nofollow">hammered out the asteroid 16 Psyche into a 1 mm thick</a> <a href="http://en.wikipedia.org/wiki/16_Psyche#Characteristics" rel="nofollow">iron foil</a> disc telescope mirror <a href="http://www.wolframalpha.com/input/... | g17678 | [
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<p>I know that the approximation for the moment of inertia of an infinitely thin rod of mass $m$ and length $L$ spinning around an axis perpendicular to its own axis at its center is $\frac{mL^2}{3}$: </p>
<p><img src="http://i.stack.imgur.com/LVgxB.png" alt="enter image description here"></p>
<p>What happens when th... | g17679 | [
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<p>Lets consider the line element:</p>
<p>$$ds^2=dr^2+r^2[d\theta^2+\sin^2\theta d\phi^2]$$</p>
<p>There are three variables r,theta and phi.
If we use a surface constraint like r=constant the number of
independent variables is reduced by one--now we have two independent
variables.These surfaces[corresponding to r=co... | g17680 | [
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<p>I need to make a camera lens that can easily withstand temperatures of about 1000 Fahrenheit.</p>
<p>What should I make the lens out of? </p> | g17681 | [
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<p><img src="http://i.stack.imgur.com/rwrAc.png" alt="enter image description here"></p>
<p>In the standard techniques of beam related problems, solving for moment at any cross section includes counting the torque due to shear force as well as some extra moment, which according to me should be due to the same shear fo... | g17682 | [
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<p>Consider a spherically symmetric distribution of density $\rho(r)$. We can define the mass enclosed within each radius $r$ using $\frac{dM(r)}{dr} = 4\pi r^2 \rho(r)$, with the condition that $M(r=0) = 0$.</p>
<p>The gravitational acceleration and potential can then be given as,</p>
<p>$$\begin{align}
a_g &= ... | g17683 | [
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<p>Firstly, is there a general procedure/algorithm for attacking Hamiltonians having spin-position coupling, e.g.,
$$\frac{\mathbf{\sigma_1}\cdot\mathbf{\sigma_2}}{|\mathbf{r_1}-\mathbf{r_2}|}$$</p>
<p>I do not know where to begin.</p>
<p>Secondly, I would like you to recommend a textbook which discuss such a kind o... | g17684 | [
0.001576295937411487,
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0.028835628181695938,
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0.07862836122512817,
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0.037333324551582336,
0.035293955355882645,
0.007052224595099688,
0.05738825723528862,
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-0... |
<p>It is known that the RVB states can support spin-charge separations and its elementary excitations are spinons and holons. But it seems that there are some different possibilities for the nature of the statistics of the spinons and holons. Specifically, (1) spinons are <em>fermions</em> while holons are <em>bosons</... | g17685 | [
-0.01505052950233221,
-0.01909872144460678,
0.012927505187690258,
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0.06311573833227158,
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0.04741354286670685,
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-0.04383024573326111,
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0.00019979964417871088,
-0.03510482609272003,
-0.0... |
<p>I'm not a physicist. I want to understand the macroscopic <a href="http://en.wikipedia.org/wiki/Maxwell%27s_equations" rel="nofollow">Maxwell's equations</a>. But after reading Wikipedia and other Googled stuffs, I got very confused. In particular, $D$ and $H$ have two different equations, respectively. One group i... | g17686 | [
-0.020709233358502388,
0.04243018478155136,
-0.01749638468027115,
-0.018674416467547417,
0.03752324357628822,
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0.018779270350933075,
0.010863266885280609,
0.03401041775941849,
-0.02139510214328766,
-0.027952050790190697,
0.03031310997903347,
-0.006600960157811642,
0.0... |
<p>I'd like to have something like <a href="http://bass2000.obspm.fr/download/solar_spect.pdf" rel="nofollow">this</a>, but for single atoms and with more extended range of wavelengths.</p>
<p>All I could find e.g. for hydrogen was lots of talks about Rydberg formula etc. and plots of spectrum in visible region. But I... | g17687 | [
-0.03696810081601143,
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0.042497795075178146,
0.014092547819018364,
0.05437881499528885,
0.0... |
<p>I just switched from Timberland to Adidas shoes, and noticed a horrible trait of the <a href="http://www.tactics.com/a/3s5h/9/adidas-campus-vulc-skate-shoes-black-turquoise-white-sole.jpg" rel="nofollow">Adidas tread</a>: instead of being composed of externally-protruding bumps like the Timberland, it is composed of... | g17688 | [
-0.010094485245645046,
0.039244625717401505,
0.005015513859689236,
-0.08353637158870697,
-0.018723247572779655,
0.010289392434060574,
0.08345773071050644,
0.05586816370487213,
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0.014135707169771194,
0.02726924978196621,
-0.030244193971157074,
0.04467128589749336,
0.00... |
<p>Is there a reason why plugs tend to be 110 V in America but 220 V in Europe? Is one of them better than the other?</p> | g17689 | [
0.017642995342612267,
0.030047694221138954,
0.0044387271627783775,
0.034374967217445374,
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0.022154932841658592,
-0.009069166146218777,
0.0013134246692061424,
0.034610241651535034,
0.029564503580331802,
... |
<p>I was given a problem at school: </p>
<blockquote>
<p>How much <a href="http://en.wikipedia.org/wiki/Energy" rel="nofollow">Energy</a> do we need to make a rocket of mass $m$ faster than the escape velocity so that it can travel in outer space?</p>
</blockquote>
<p>Here's how I worked:<br>
I know that the escape... | g17690 | [
-0.021057605743408203,
0.07238348573446274,
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0.007009149994701147,
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0.028097253292798996,
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0.01085420697927475,
-0.0035146716982126236,
0.04532558470964432,
0.04189196601510048,
-... |
<p>Since we know in condensed matter the lifetime of positron is about 10^-10 seconds, how do we collide positrons with electrons? How many positrons were there during the LEP experiment?</p>
<p>I know positrons can be produced in beta decays or when two photons 'collide', but do positrons exist naturally such as elec... | g17691 | [
0.08852723240852356,
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-0.03297547996044159,
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0.020632317289710045,
-0... |
<p>When water falls from some height to the ground and forms a puddle, where does most of the initial potential energy go?
Sound, heat, surface tension, or motion of the earth?</p> | g17692 | [
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0.... |
<p>Why change of magnetic flux with the time through a coil induces current in it?
Please tell me that what happen to charge in the coil if the magnet or electromagnet wave around this? Also, why a constant magnetic flux does not induces current?</p> | g17693 | [
0.04307512566447258,
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0.06408735364675522,
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0.049560... |
<p>It's known that positive mass bends space-time to create a curvature. But if something had negative mass what would it do? Make it flat or like a crest?</p> | g17694 | [
0.03222723305225372,
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0.07146096974611282,
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<p>My question isn't how they receive the energy to jump, but why. When someone views an element's emission spectrum, we see a line spectrum which proves that they don't exist outside of their orbitals (else we would see a continuous spectrum). Electrons can be released in the form of beta decay, thus proving that th... | g472 | [
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0.0707269087433815,
-0.... |
<p>Helicity operator in Dirac equation is given by
$$H=\frac{\vec{S}\times \vec{P}}{P^{2}}$$
This operator commutes with dirac hamiltonian.We can also define a helicity(with same form) operator in case of Schroedinger equation.Which will commute with Schroedinger hamiltonian and have eigenvalue $\frac{1}{2}$ or $-\fra... | g17695 | [
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0.010910398326814175,
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0.00353082362562418,
0.... |
<p>Coulomb's law is used to calculate the electrical attraction between 2 charged particles, what formula do I use to calculate an electrical attraction magnitude between 2 plates? Let's assume the first plate holds a charge of +3x10^-4 coulombs and the other one holds the same negative amount of charge (-3x10^-4), bot... | g17696 | [
0.08814265578985214,
0.035407256335020065,
0.0020354115404188633,
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0.05597526207566261,
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0.038955528289079666,
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0.044265683740377426,
0.015297246165573597,
0.0731051042675972,
-0.01673172600567341,
0.00986... |
<p>I read it news that:</p>
<blockquote>
<p><a href="http://www.popsci.com/science/article/2013-04/stephen-hawking-says-we-have-get-rock-within-1000-years" rel="nofollow">Hawking Gives Humans 1,000 Years to Escape Earth</a></p>
</blockquote>
<p>How did he arrive at this figure? Whats gonna make human race extinct i... | g17697 | [
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0.008000105619430542,
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0.022807303816080093,
0.03900871053338051,
0.0... |
<p>For fixed temperature the concentration of a gas dissolved in a solution is directly proportional to the gas pressure $p$, i.e. $c_s (T,p) = f(T)p$. Since $H_2$ only dissolves in metals as single atoms this law needs to get modified to: $c_s(T,p) = f(T) \sqrt{p}$, which is what I want to show. This is what I've got ... | g17698 | [
-0.00011045764404116198,
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0.04508278891444206,
0.02704665996134281,
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0.00866599939763546,
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0.050940848886966705,
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... |
<p>I was always puzzled by this fact.</p>
<p>A uniform cube has a sphere-shaped inertia ellipsoid. The sphere has a higher symmetry then the cube. </p>
<p>Is there any deep reason or implication behind it?</p> | g17699 | [
0.06369779258966446,
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0.007085172459483147,
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0.006718559190630913,
0.000649276829790324,
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<p>Resistance is $\frac{V}{I}$, and we get the unit $\Omega$. </p>
<p>Another unit is $\frac{W}{A^2}$. How do you derive that unit?</p> | g17700 | [
0.03498280048370361,
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0.022009121254086494,
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0.04616442695260048,
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<p>I want to simulate the vibration transmission between two colliding objects.
I use a Finite Element Model to simulate the vibration on each object, but
I haven't found any good mathematical model to transfer the vibration between
two FEM models that collided and keep in contact. </p>
<p><img src="http://i.stack.im... | g17701 | [
0.09143788367509842,
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0.011005259118974209,
0.002631682436913252,
0.0447104312479496,
0.0... |
<p>A ventilator fan mounted on the wall of an air tight room(except for an air intake with a given cross sectional area) is blowing air out of the room. If air displacement rate of the fan is given(CFM or m3/hr), is it possible to calculate the pressure differential that it can create between inside the room and outsid... | g17702 | [
0.03552207350730896,
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0.053528010845184326,
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0.006906903814524412,
0.031177861616015434,
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<p>A uniform rod of mass $m$ and length $l$ is pivoted at point O. The rod is initially in vertical position and touching a block of mass M which is at rest on a horizontal surface. The rod is given a slight jerk and it starts rotating about point O. This causes the block to move forward. The rod loses contact with t... | g17703 | [
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<p>Consider a system of two entangled harmonic oscillators. The normalised ground state is denoted by $\psi_0(x_1,x_2)$.</p>
<p>The reduced density matrix of the second oscillator is given by: </p>
<p>$$\rho_2 = \int_{-\infty}^{+\infty} dx_1 \int_{-\infty}^{+\infty} dx_2 \int_{-\infty}^{+\infty} dx_2' \,\psi_0(x_1, x... | g17704 | [
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0... |
<p>In a curved $(3+1)$ dimensional spacetime with metric components $g_{\mu \nu}$, the covariant derivative of a $4$ vector $\mathbf V = (V^0, \vec V)$ is given by
$$\nabla_\mu~ V^\mu = \frac{1}{\sqrt{-g}}\partial_\mu (\sqrt{-g}~V^\mu).$$</p>
<p>I expect that this relation can also be used to derive the expression fo... | g17705 | [
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0.014800206758081913,
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<p>I have a question that I would like to ask here since I'm not an expert or any near to that.
Actually I just came up with this question when I was watching The fabric of cosmos.
I couldn't find where I can ask this kind of question. So hopefully this is the right place.</p>
<ul>
<li>What is the "background" of mul... | g17706 | [
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0.020469466224312782,
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0.002446820493787527,
0.07270659506320953,
0.02... |
<p>I'm trying to understand the Einstein Field equation equipped only with training in Riemannian geometry. My question is very simple although I cant extract the answer from the <a href="http://en.wikipedia.org/wiki/Stress%E2%80%93energy_tensor">wikipedia page</a>:</p>
<p>Is the "stress-energy" something that can be... | g17707 | [
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0.04598300904035568,
0.03963717818260193,
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0.027506906539201736,
0.060349464416503906,
-0.07... |
<p>I was just watching a program on television showing how the method they use at the National Ignition Facility to attempt to achieve fusion is to fire extremely powerful lasers at a small pellet of fuel sitting in a vacuum at the center of a large 10 m diameter sphere. To people familiar with the design of the setup ... | g17708 | [
0.002619135193526745,
0.045277319848537445,
0.00443956907838583,
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0.009682731702923775,
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0.08358241617679596,
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-0.01575375162065029,
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0.040740203112363815,
... |
<p>The original paper proposing quantum key distribution protocol (now known as <a href="http://en.wikipedia.org/wiki/BB84" rel="nofollow">BB84</a>):</p>
<ul>
<li>Charles H. Bennett, Gilles Brassard, <a href="http://dx.doi.org/10.1016/j.tcs.2011.08.039" rel="nofollow">Quantum cryptography: Public key distribution and ... | g17709 | [
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0.04010545089840889,
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0.045911215245723724,
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<p>While I know that accelerating charges produces EM radiations (at least in lots of cases), most discussion about this matter only focuses on <i>which kind of situation</i> will emit EM radiations and which does not, with very little mention of the intuition behind this physical phenomenon.</p>
<p>Recently I'm tryin... | g219 | [
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0.05832316353917122,
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0.03130454570055008,
0.024598687887191772,
0.024361995980143547,
0.04085576... |
<p>About the eyes I know that it requires for gauging distance as in Modern 3D cameras have two sensors. And two ears for sound source localization using differences in levels and timing (But not yet two microphones in mobile phones/other devices). What about other organs? Even not all organs are in pair. If it is abou... | g17710 | [
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0.028943045064806938,
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0.0009992189006879926,
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0.0021231172140687704,
-0.05042365565896034,
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0.01945429854094982,
... |
<p>Could someone remind me of the formula for potential function for a system consisting of 2 coaxial tubes maintained at a fixed potential difference and the in between medium has uniform conductivity $c$? (I have forgotten how to calculate these things, have been a long time since high school!) </p> | g17711 | [
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0.020029636099934578,
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0.04631652683019638,
-0.017997877672314644,
0.0... |
<p>I have learned Lagrange's equation, and we have Lagrangian defined as $$L=T-V$$ My question is why Lagrangian is defined like this rather than other format such as $T+V$ or something else. </p> | g547 | [
0.1067696139216423,
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0.00932919792830944,
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0.03431722894310951,
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-0.05814981833100319,
0.02328748255968094,
0.07597597688436508,
0.07841475307941437,
0.04936078... |
<p>This is a question that astronomers get asked by the public regularly, and I'm curious to see how others respond.</p> | g17712 | [
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-0.057894766330718994,
0.059435758739709854,
0.020736103877425194,
0.01704440452158451,
-0.01... |
<p><a href="http://en.wikipedia.org/wiki/Pluto" rel="nofollow">Pluto</a> has been designated a planet in our solar system for years (ever since it was discovered in the last century), but a couple of years ago it was demoted.</p>
<p>What caused this decision? And is there a chance that it could be reversed?</p> | g17713 | [
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<p>We were discussing super-critical fluids with a colleague and as were thinking about different thought-experiments, it occurred to me that you cannot really have only liquid in a piston in a real situation. I want to make sure I'm not missing something. Are there liquids which have zero vapor pressure under certain ... | g17714 | [
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<p><a href="http://en.wikipedia.org/wiki/Metric_expansion_of_space" rel="nofollow">Wikipedia says</a>: </p>
<blockquote>
<p>Metric expansion is a key feature of Big Bang cosmology and is modeled mathematically with the FLRW metric. This model is valid in the present era only on large scales (roughly the scale of gal... | g17715 | [
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<p>Here is the full problem:</p>
<p><img src="http://i.stack.imgur.com/DD5Dy.png" alt="enter image description here"></p>
<p>I was able to prove the given expression; but the interpretation part is giving me a bit of trouble. Here is my interpretation:</p>
<p>The average acceleration in $(a,b)$, is given by: $\frac{... | g17716 | [
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<p>I am having trouble in demonstrating that under SU(2) transformations the adjoint representation of SU(N) transforms as one spin 1, 2(N-2) spin $\frac12$ and singlets. I am trying to demonstrate it from $N \otimes \bar{N} = 1 + A$ where $A$ is the adjoint representation; and the fact that an N vector of SU(N) decomp... | g17717 | [
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<p>In my scant spare time I'm building an Asteroids game. You know - a little ship equipped with a pea shooter and a bunch of asteroids floating around everywhere waiting to be to blown up. But, I wanted to add a little twist. Wouldn't it be cool if Newtonian gravity was in effect and you could do thinks like enter int... | g17718 | [
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<p><img src="http://img526.imageshack.us/img526/2593/49699289.jpg" alt="">!</p>
<p>I pretty much had what the solutions had, but we disagreed with one thing, a minus sensitive sign. </p>
<p>$\sum W = \Delta K$</p>
<p>$\int_0^{-s} - ks^2 ds = \frac{ks^3}{3} = \frac{1}{2}m(v^2-4^2)$</p>
<p>Rearranging, I get $v^2 = 4... | g17719 | [
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<p>The lubricant is needed only on the hair surface? How can the blade cut the slippery surface?</p>
<p>Why does soap make shaving with razor less painful?</p> | g17720 | [
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<p>From high school, I remember that Aluminium has 13 electrons and thus has an unpaired electron in the 3p shell. This should make Aluminium magnetic. However, the wiki page of Aluminium says its non-magnetic at one place(with a citation needed tag though) and at another place says it's paramagnetic. Doing a google se... | g17721 | [
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<p>In a cylindrical chamber with a high diameter-to-height ratio; a fluid is tangentially injected. there is an axial exit to the cylinder.</p>
<p>how do I determine if the vortex so formed is laminar or turbulent? what parameter will indicate this?</p>
<p>(this is a simulation; so I can measure whichever velocity/tu... | g17722 | [
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<p>Is there such a thing as an extension of <a href="http://www.edwardtufte.com/bboard/q-and-a-fetch-msg?msg_id=0003oo" rel="nofollow">Feynman diagrams</a> into three dimensions?</p>
<p>Canonical Feynman diagrams use one space and one time dimension to visualize processes involving elementary particles in space-time. ... | g17723 | [
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<p>100% of the energy from the sun is reflected back into space, it's just shifted from a low-entropy state to a high-entropy state, and from a high frequency (ultraviolet) to a low frequency (infrared). But does the total number of photons change as a result? Are there more low frequency photons, then, in order to mak... | g17724 | [
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<p>I am trying to find the angle needed for a projectile to pass-through a given point.</p>
<p>Here is what I do know:</p>
<ul>
<li>Starting Point $(x_0,y_0)$</li>
<li>Velocity</li>
<li>Pass-through point $(x_1, y_1)$</li>
</ul>
<p>I also need to incorporate gravity into the equation. Anyone have any ideas? I haven'... | g17725 | [
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<p>Recently I red an article "Surface Enhanced Fluorescence". It is a topical review by Emmanuel Fort and Samuel Gresillon.
Here it is:
<a href="http://turroserver.chem.columbia.edu/surfaceplasmons/pdf/53_JPD_41_1_2008_SEFSRev.pdf" rel="nofollow">http://turroserver.chem.columbia.edu/surfaceplasmons/pdf/53_JPD_41_1_200... | g17726 | [
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<p>Why is it true that we can deduce that Einstein's GR equations coupled with Maxwell's EM equations may be written in the form $$R_{ij}=C(F_{ik}F_j^{\,\,k}-{1\over 4}g_{ij}F_{mn}F^{mn})$$
without knowing EM?</p>
<p>I wonder if it's a degree of freedom thing. Please enlighten! Thanks.</p> | g17727 | [
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<p><strong>Intent:</strong> Not looking to make-up something, I seek explanations which are possible to duplicate</p>
<p><strong>Description of Phenomenon:</strong> The halved side of the bubble would be horizontal to Earth's surface, and the bowl shape would be closer to the ground. </p>
<p><strong>Image of Shape (... | g17728 | [
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<p>This is a technical question about equation (2.42) of the original paper <a href="http://ccdb5fs.kek.jp/cgi-bin/img/allpdf?198810152" rel="nofollow">[KS]</a> of the Kazama-Suzuki construction. I think the authors did a simple substitution $\tilde{J}^a=\hat{J}^a-\frac{i}{k}f_{a\bar{b}\bar{c}}j^{\bar{b}} j^{\bar{c}}$ ... | g17729 | [
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<p>There is an equation that relates energy $E$, angular momentum $L$ and other constants and variables to find $\left(\frac{dr}{d\tau}\right)^2$ in a plane.
$$\left(\frac{dr}{d\tau}\right)^2=\frac{E^2}{m^2c^2}-\left(1-\frac{2GM}{c^2r}\right)\left(c^2+\frac{L^2}{m^2r^2}\right)$$
So, $\frac{dr}{d\tau}$ is:
$$\frac{dr}{d... | g17730 | [
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<p>I don't remember anything from school, so please what do you say about the title?</p> | g223 | [
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<p>Imagine this scenario: I have 2 objects in vacuum without any force exerted upon them not even a possible gravitational force between them.
Now if one of them gets a gravitational or magnetic force, how long from the moment the object gained this force to the other object to be affected by it?
Is it instantaneous? I... | g837 | [
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<p>Let's say you have a lamp pointed at a wall, in a dark room with no other light source, if you turned off that lamp <h1> Would the wall still be visible for any amount of time?</h1></p> | g17731 | [
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<p>A clock has negative charges -q, -2q, -3q,...., -12q fixed at a the position of the corresponding numerals on the dial. The clock hands do not disturb the electric net electric field due to pont charges. At what times does the hour hand point in the direction of the electric field at the centre of the dial?</p> | g17732 | [
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<p>Now consider parallel rays travelling towards the convex lens. After emerging they get converged at the focus. Won't this lead to interference between light rays? Practically it should but I would like to know why this does not happen.</p>
<p><img src="http://i.stack.imgur.com/bwiBG.jpg" alt="http://www.passmyexams... | g17733 | [
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<p>Infinitesimal rotations commute and every finite rotation is the composition of infinitesimal rotations which should logically mean they also commute; but they don't. Why?</p> | g17734 | [
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<p>It is fairly easy using basic special relativity to arrive at the conclusion that the magnetic force effect on nearby charges of wires carrying currents on nearby charges is only due to the length contraction in certain inertial frames from the point of view of charges, which gives rise to a perceived change in char... | g17735 | [
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<p>Everyone knows Temperature gradient is a vector quantity having direction from cold to hot.My confusion: why is temperature gradient vector if its direction is always fixed (as in the case of pressure) (Don't say that it is because it follows vector law of addition,I am searching for more concrete answer...)</p> | g17736 | [
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<p>Our body of course exchanges some atoms with environment every day however are there some of atoms which stay with us a life time? </p> | g17737 | [
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<p>In <a href="http://en.wikipedia.org/wiki/Perturbation_theory_%28quantum_mechanics%29" rel="nofollow">perturbation theory</a> perturbed eigenstates expanded by unperturbed eigenstates, but we know when the system perturbed its Hilbert space altered and hence its basis changed, then we can't state this basis spans the... | g17738 | [
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<p>Just what the title indicates. </p>
<p>Is a <a href="http://en.wikipedia.org/wiki/Supernova" rel="nofollow">supernova</a> over instantaneously? Or, does the (for want of a better word) explosion continue for a while? What is/are the order of timescales involved?</p>
<p>EDIT: Following the posted replies/comments I... | g17739 | [
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<p>How to intuitively think of energy stored in a magnetic/electric field?</p>
<p>Kindly answer in a bit simple terms without referring to mathematics.</p> | g17740 | [
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<p>String theory takes quantum mechanics and tries to make it compatible with gravity. If it turns out to be a theory of everything then would it explain why our world is described by the laws of quantum mechanics? </p>
<p>I want to understand if the laws of quantum mechanics are the only logical possibility for a low... | g17741 | [
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-0.01111193560063839,
-0.014198... |
<p>Is it by gravity? How could gravity produce a repulsive force?</p> | g548 | [
0.09012117236852646,
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0.0013078323099762201,
0.009760192595422268,
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<p>Sen 2013 says,</p>
<blockquote>
<p>...we apply Euclidean gravity to compute logarithmic corrections to the entropy of various non-extremal black holes in different dimensions [...] For Schwarzschild black holes in four space-time dimensions the macroscopic result seems to disagree with the existing result in loop... | g17742 | [
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0.0143346171826124... |
<p>This is a kind of silly question, that mostly goes unanswered: are gravitons detatched from the objects they act on, like photons in free space.</p>
<p>Maybe gravity or gravitons are collected by mass (including black holes), as they are collected by the curve in spacetime caused by the mass. The origin of graviton... | g17743 | [
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0.... |
<p>Can anyone explain me what is cyclic integral and give me some instructions how to show that there exist cyclic integral for Lagrangian<br>
$$L~=~\frac{1}{2}ma^2{\dot {\theta}}^2+\frac{1}{2}ma^2{\dot {\phi}}^2\sin^2\theta+mga\cos\theta?$$ </p> | g17744 | [
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0.0592... |
<p>The idea is to collect sunlight over a large area, and concentrate it down to the nano scale.<br>
For the sake of discussion lets say you concentrate all the light you collect down to 1000 nanometers (1µm).</p>
<p>Questions is... how much surface area sunlight would you need to collect and focus to 1µm, in order to... | g17745 | [
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0.0... |
<p>I have the following physics problem. </p>
<p>In the figure below, a stationary block explodes into two pieces L and R that slide across a frictionless floor and then into regions with friction, where they stop. Piece L, with a mass of 2.0 kg, encounters a coefficient of kinetic friction $μ_L$ = 0.40 and slides to ... | g17746 | [
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<p>I'm reading a paper which states that</p>
<blockquote>
<p>Neutron star binary merger rate at redshift $z$ per unit observer time
interval per unit volume is $\dot{n}_{m} = \dot{n}_{0} (1+z)^{2}
(1+z)^{\beta}$, where $\dot{n}_{0}$ is the local neutron star binary
merger rate per unit volume, $(1+z)^2$ account... | g17747 | [
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0.017324144020676613,
0.04924... |
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