question stringlengths 37 38.8k | group_id stringlengths 2 6 | sentence_embeddings listlengths 768 768 |
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<p><a href="http://en.wikipedia.org/wiki/%282%2B1%29%E2%80%93dimensional_topological_gravity">Pure $2+1$-dimensional gravity</a> in $AdS_3$ (parametrized as $S= \int d^3 x \frac{1}{16 \pi G} \sqrt{-g} (R+\frac{2}{l^2})$) is a topological field theory closely related to Chern-Simons theory, and at least naively seems li... | g16201 | [
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<p>I've seen in a few textbooks now a useful looking expansion procedure for determinants, but I don't understand the details of it. <a href="http://books.google.com/books?id=MWQBAQAAQBAJ&pg=PA218&lpg=PA218&dq=diagonal%20expansion%20determinant%20wick%20theorem&source=bl&ots=JFkVrVLsmI&sig=y0HYM... | g16202 | [
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<p><a href="http://www.youtube.com/watch?v=JGfynrsdaV0" rel="nofollow">Here</a> is one of the many videos on youtube showing how a cornstarch and water mixture can become very hard when put under stress. I haven't found a good explanation of why it behaves the way it does. Is there any paper that has been published on ... | g496 | [
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<p>In the first lecture of MIT's Classical Mechanics Prof. Lewin highlights the importance of uncertainties in measurements by quoting "Any measurements, without the knowledge of uncertainty is meaningless."
He measures the length of a student and an aluminium bar both in their vertical and horizontal positions respect... | g16203 | [
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<p>Why magnetic lines comes from north to south out side of the magnet </p>
<p>is any magnetic lines comes from south to north if so in which direction </p>
<p>What is the reason of magnetic lineS </p> | g16204 | [
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<p>I'm getting a bit confused when finding components of vectors and forces.</p>
<p>In problems for vectors, I've always known that if you want to get the components of a vector, you would use the following:</p>
<p><img src="http://i.stack.imgur.com/UWNQM.png" alt="enter image description here"></p>
<hr>
<p>Recentl... | g16205 | [
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<p>How would I go about creating small polarised scientific lenses?</p>
<p>Thinking 5mm by 5mm, with a light-source behind it for the purposes of reducing (polarised) surface reflection (assisted with a cross-polarised viewer).</p>
<p>Is the idea that I just need to apply magnesium fluoride; and if so, at what consis... | g16206 | [
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<p>In Griffiths' <em>Intro to QM</em> [1] he gives the eigenfunctions of the Hermitian operator $\hat{x}=x$ as being </p>
<p>$$g_{\lambda}\left(x\right)~=~B_{\lambda}\delta\left(x-\lambda\right)$$</p>
<p>(cf. last formula on p. 101). He then says that these eigenfunctions are not square integrable because </p>
<p>$$... | g16207 | [
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<p>Several years ago, New Scientist featured an article on a new theory by Stephen Hawking that involved the future having some effect or "backreaction" on the present.</p>
<p>As it would be very tedious and time consuming to root through several years of back issues to find it again, I was hoping someone might be abl... | g16208 | [
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<p>If we have equal charges located at the corners of a regular polygon, then the electric field at its center is zero. Are there other points inside a polygon where the field vanishes?
The simplest case would be an equilateral triangle of equal charges. I thought it would be easy to find the location of such other p... | g16209 | [
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<p>As far as I know that QM is probability-based and Feynman proposed a <a href="http://en.wikipedia.org/wiki/Quantum_computer" rel="nofollow">quantum computer</a> (QC) as an emulator for fast computation. Reading the introductory articles, I just do not get the essence of the speedup. I understand the q-bits and such ... | g16210 | [
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<p>If one graphed the volume per time of air being expelled from a common elastic balloon out of a hole of constant size relative to the balloon's surface area, would the curve of the graph be exponential or polynomial? I have neither the means to perform the experiment nor the brains to theorize, but I'm very interes... | g16211 | [
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<p>I'm watching some archived video lectures on QM in <a href="http://coursera.org" rel="nofollow">Coursera</a> given by Umesh Vazirani from UC Berkeley and I have a question regarding a Bell's experiment (I guess something close to <a href="http://en.wikipedia.org/wiki/Bell_test_experiments" rel="nofollow">this</a>) d... | g16212 | [
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<p>I am just curious that if constants in cgs units change the answer of an equation. For example, Coulomb's constant, in SI units it equals to $8.98...\times 10^9 \,\mathrm{N\,m^2\,C^{-2}}$. However in cgs units it equals to 1. I think the difference between an answer calculated with Coulomb's constant in SI units and... | g16213 | [
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<p>I am preparing for an exam, on this problem I had the opposite direction of the magnetic field.</p>
<p>A conductor-cylinder with radius R has been cut in half ($\phi \in [0,\pi]$)
A DC current $I$ runs along $\hat Z$, and can be assumed to be evenly distributed.</p>
<p>The problem is to calculate the magnetic fiel... | g16214 | [
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<p>I am preparing for an exam, on one problem my answer differ from the solution. </p>
<p>The current $i(t)=I_0e^{-\alpha t}$ runs in a long straight conductor along $\hat z$.</p>
<p>Point A,B,C,D forms a triangle.
A and B is at $L \hat x$ with a very small separation in $\hat z$ with a resistance R between.
C and D... | g16215 | [
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<p>I know that similar questions have been asked before, but none of them is exactly what I would like to know. </p>
<p>I want to have a general idea of what string theory is, without having to read several hundred pages first. So, if you had to give a short formulation of string theory, what would it be? </p>
<p>Her... | g16216 | [
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<p>I have looked online to no avail. There is two competing answers and I am curious to know which one is right.</p>
<p>Someone asked me this question. If you are traveling at the speed of light can you see your reflection in a mirror in front of you?</p>
<p>My answer to the question is no, I would figure that in o... | g586 | [
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<p>So I'm reading a text on electricity and it talks about using the integral to compute the total charge of a collection of points, which I mostly understand. But then we get to finding the electric field due to a charged collection of points and I find things that don't make sense to me. For instance, for an infini... | g16217 | [
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<p>The speed of sound in a gas may be given by the following formula,</p>
<p>$$c = (kRT)^{1/2},$$</p>
<p>where $k$ is specific heat ratio, $R$ is the gas constant and $T$ is the temperature.</p>
<ol>
<li><p>What are the limits of this formula? At very cold and very hot temperatures for instance? </p></li>
<li><p>Wou... | g16218 | [
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<p>I would like a tool which allows me to enter some paper citation, and then will begin drawing a graph, where each paper is linked to other papers that cite the original paper or are cited by it. </p>
<p>It seems like this would be a handy way to identify influential papers in a field at a glance. </p>
<p>Does an... | g16219 | [
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<p>I know that in electron guns we see in TV's and lots of other places, we have electron emitter (cold/hot W needle in the simplest case) and electrons are accelerated using lattice with high-voltage potential. </p>
<p>But the question is why doesn't this lattice slow down electrons once they passes through it?</p>
... | g16220 | [
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<p>In quantum field theory, the solution of the time evolution operator of the Schrodinger equation (in the interaction picture) is given by Dyson's series, which is used to calculate the S-matrix. Why we are still working with the non-relativistic Schrodinger equation (instead of the Klein-Gordon equation)?</p>
<p>So... | g16221 | [
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<p>Very often the energy released in large-scale events (e.g., earthquakes, meteor impacts, etc) is described in terms of some number of 'tons of TNT'. This may be all well and good for those with an intuitive sense of big explosions, but specifically, how many <em>joules</em> are there in the 'ton of TNT'? I can work ... | g16222 | [
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<p>Classically, <a href="http://en.wikipedia.org/wiki/Shot_noise">shot noise</a> observed in the signal generated by a laser incident on a photodiode is explained as being due to the quantization of light into photons, giving rise to a <a href="http://en.wikipedia.org/wiki/Poisson_process">Poisson process</a>. In quan... | g16223 | [
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<p><a href="http://quantummechanics.ucsd.edu/ph130a/130_notes/node246.html" rel="nofollow">UCSD's online QM notes</a>, as usual, starts stating that QM operators are Hermitian and says that operator $O$ elements can be computed by </p>
<p>$$O_{ij} = \langle u_j|O|u_i\rangle$$</p>
<p>The $u_i$ are eigenvectors, which ... | g16224 | [
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<p>I've just moved into my first place, and for reasons I do not condone or recommend I don't have any method of refrigeration right now. Luckily I now live very close to shops, so it isn't a big deal, but it made me think: if I really had to, what would be the most efficient way to keep food cool without using any ele... | g16225 | [
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<p>At room temperature....</p>
<p>How long will the sugar stay suspended once dissolved ?</p>
<p>What governs the rate of settling ? </p>
<p>What part does Brownian motion play ?</p>
<p><em>Sugar might be a bad example...please substitute as needed.</em></p> | g16226 | [
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<p>I have been going through some problems in Sakurai's <em>Modern QM</em> and at one point have to calculate $\langle \alpha|\hat{p}|\alpha\rangle$ where all we know about the state $|\alpha\rangle$ is that $\langle x|\alpha\rangle=f(x)$ for some known function $f$. ($|\alpha\rangle$ is a Gaussian wave packet.) Sakura... | g16227 | [
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<p>Is there any scientific experiment that can lead us to conclude we live in 3 dimensions without the premise of the conception of limited dimensions?</p>
<p>Thank you all who helped in the improvement of this question (which was not clear at first). </p> | g16228 | [
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<p>For example, the ground state of the antiferromagnetic(AFM) Heisenberg model $H=J\sum_{<ij>}\mathbf{S}_i \cdot \mathbf{S}_j(J>0)$ on a 2D square lattice is a Neel state, which is a classical order described by conventional order parameters $\left \langle \mathbf{S}_i \right \rangle$.</p>
<p>On the other ha... | g16229 | [
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<p>How, exactly, did Tycho Brahe do his measurements of (no) stellar parallax? All the descriptions of parallax that I have been able to find seem to talk about the change in position of a nearby star compared to background stars farther away, but as far as I know the Ptolemaic system assumed that the fixed stars were ... | g16230 | [
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<p>I am wondering something about the breaking of conformal symmetry: I know that it can be broken at the quantum level, anomalously, but I never encountered or heard about a model where it is broken "à la Higgs" with a potential whose true minimum would spoil this invariance (e.g. making appear a particular energy sca... | g16231 | [
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<p>Can someone show me how the Lorentz transformation can be derived from the metric equation:
$s^2=c^2t^2-x^2$</p> | g16232 | [
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<p>It is often claimed that spin-2 particles return to their previous state after $\pi$ rotation, just like spin-1/2 particles return after $4\pi$ rotation. But my calculation suggests otherwise.</p>
<p>Let z axis be the axis of rotation. The matrix form of $J_z$ under the basis $\{|2m\rangle\}(m=0,\pm 1,\pm 2)$ is
$$... | g16233 | [
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<blockquote>
<p>Say a person is walking along.</p>
<p>He then jumps.</p>
<p>The person weighs $25$kg (irrelevant?).</p>
<p>Just after jumping, his velocity is 5m/s (positive is taken as up).</p>
<p>Gravity is taken as $-9.80665\text{ m/sec}^2$.</p>
<p>Using $(v_1-v_0)/g$, I know that it will ... | g16234 | [
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<p>Just what the title states</p>
<p>Some part or the other of this Globe faces approximately towards the Sun during each 24 hour period. What is the total amount of heat (in calories) incident on average during this 24-hour period?</p> | g16235 | [
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<p>Is this formula correct?</p>
<p>$$ \frac{-1}{\pi}Im\int_{0}^{\infty}\!dt~\exp(Et)\Theta (t)\exp(i \epsilon t) ~=~ \sum _{n}\delta (E-E_{n}), $$</p>
<p>$$ \Theta (t)~=~ \sum_{n}\exp(-tE_{n}) ,$$ </p>
<p>and I have used Shokhotsky's formula for the Dirac delta function </p>
<p>$$ \delta (x)~=~ \frac{-1}{\pi}Im \fr... | g16236 | [
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<p>I tried this with two 9V batteries that you can interlock easily and they heat up a lot. Why does this happen? The internal resistance of the batteries would be quite small so why would they still heat up a lot due to Joule heating?</p>
<p><img src="http://i.stack.imgur.com/KbNh9.png" alt="Circuit"></p> | g16237 | [
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<p>I am trying to work out the yearly energy production of an onshore Siemens SWT-3.0-101, hub height 94m, total height 144,5. Here is the power curve at each wind speed level worked out through a software:</p>
<p><img src="http://i.stack.imgur.com/s9yri.jpg" alt="power curve"></p>
<p>I am trying to work out the aver... | g16238 | [
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<p>I am interested in knowing what is the significance of red filter band in the study of redshift dependence of spatial orientation of galaxies?</p> | g16239 | [
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<p>I'm starting Physics, and I don't understand why the acceleration along the x-axis is zero for an object thrown near the surface of the Earth. This may be problem specific, but I wouldn't know since I am just beginning.</p> | g16240 | [
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<p>This comes from a discussion forum, where a friend of mine asked the following:</p>
<blockquote>
<p>We can see objects in space billion of light years away, right? I started wondering about that.</p>
<p>If you take 2 objects in space, the other should be able to see the other no matter what angle in degrees ... | g16241 | [
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<p>Pop-sci ST books say, "At every point of space, there is a Calabi-Yau space..." or similar. But uncertainty p. and noncommgeom say, no points in space, only planckons (not my coinage). Is 'point of space' (meaning real, not abstract/mathematical space) inexact terminology, or a category error, like "an atom of mayon... | g16242 | [
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<p>I am starting University in September, 2014. I have some knowledge already on classical mechanics as I took optional Applied Math courses (called Mechanics 1 and Mechanics 2) in my mathematics A-Level. I am also self-studying the book Classical Mechanics by Goldstein, Poole and Safko to gain a deeper understanding o... | g16243 | [
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<p>Somewhere I read that the <a href="http://en.wikipedia.org/wiki/PSR_B1913+16" rel="nofollow">Hulse-taylor binary</a> pulsar can not differentiate between competing theories assuming different speeds of gravity. Is it mathematically true in general, that the orbital decay of two orbiting bodies cannot possibly favor ... | g16244 | [
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<p>The full MSSM contains 120 parameters. In SUSY searches, one usually picks a model like MSUGRA which makes a few assumptions and only has 5 free parameters like $m_0$, $m_{1/2}$, ....</p>
<p>Now, I'm wondering if there is a way to look at supersymmetry in a more phenomenological way, and parametrize it by (low-ener... | g16245 | [
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<p><em>Every Action Has An Equal and Opposite Reaction</em> (Newton's Third Law.)</p>
<p>If this is the case, does gravity have an equal-opposing force? </p>
<p>From asking around I still haven't got a very clear answer; those who I've talked to seem to believe there isn't one - that gravity is actually a singularity... | g16246 | [
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<p>I read a paper on solving Schrodinger equation with central potential, and I wonder how the author get the equation(2) below. <a href="http://iopscience.iop.org/0305-4470/10/6/001" rel="nofollow">Full text.</a>
<img src="http://i.stack.imgur.com/PXCtx.png" alt="a paper"></p>
<p>In Griffiths's book, it reads</p>
<p... | g16247 | [
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<p>I am not talking about mirrors, just a plain window made of glass like material. Would it be possible to allow light pass only in one direction but not the other?</p> | g777 | [
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<p>I'm looking for some good books on fractals, with a spin to applications in physics. Specifically, applications of fractal geometry to differential equations and dynamical systems, but with emphasis on the physics, even at the expense of mathematical rigor. Hope that was clear and specific enough. </p> | g16248 | [
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<p>It's not uncommon that the term 'frames per second' (sometimes abbreviated as fps or FPS) is associated with, or even equated to, the unit Hertz (Hz). I'm not exactly sure how these two concepts relate to each other.</p>
<p>The difference I can see is that SI defines Hertz as $\text{s}^{-1}$, which makes it a unit,... | g16249 | [
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<p>Using the ideas from a previous question <a href="http://physics.stackexchange.com/questions/98513/is-there-a-field-equation-which-can-reduce-into-all-three-flavors-of-spin-zero">here</a> it can be shown that if one takes the boson spin 1 stress-energy tensor of the form</p>
<p>\begin{align}
T^{\mu\nu}_{\text{spin ... | g16250 | [
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<p>In my readings I've run into this idea of an "infrared catastrophe" associated with 1/f noise. As far as I can tell it is because when you graph the periodogram of the 1/f signal you see the PSD goes to infinity as frequency goes to 0. Not sure what that means practically though. If we are talking about a sound wa... | g16251 | [
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<p>From a physics perspective, it's pretty easy to see why a a massive particle will be restricted to timelike paths, etc. but does the math guarantee that on its own or do we have to impose it? More specifically, given an arbitrary smooth Lorentzian manifold, can there be geodesics which change character from spacelik... | g16252 | [
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<p>I am attempting to model a situation, in which a sphere of some material of identifiable thermal properties is receiving heat at a constant rate. And that material is coming into equilibrium with the surrounding fluid, such that the heat it is receiving is equivalent to the heat that is going out via convection.</p>... | g16253 | [
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<p>In some cases, we can enable the Night Mode (reversing the bright and dark color of the display; such as White Text, Black Background) for the screen display.</p>
<p><a href="http://en.wikipedia.org/wiki/Liquid-crystal_display" rel="nofollow">LCD(Liquid-crystal display)</a> seems to be a common monitor display devi... | g16254 | [
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<p>So, I am quite new to CFT (and a as descriptive answer as possible would be appreciated). I want to know what uniquely defines a CFT in 2D and otherwise. </p>
<ol>
<li><p>Firstly in 2D, What defines a CFT? So I know we start with a central charge, and a set of primary fields with given conformal dimensions. What el... | g16255 | [
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<p>This feynman diagram represents the elastic proton scattering of electrons.</p>
<p><img src="http://i.stack.imgur.com/gKizX.png" alt="enter image description here"></p>
<p>The $e^-$ has an initial momentum $k$ and a final $k^\prime$.
The circle represents that the target(the proton that is) has a structure and $q$... | g16256 | [
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<p>Sometimes, mainly due to my limited knowledge of experimental modern physics, whenever I fancy and think about quantum physics, things appear really amusing and counter intuitive, and when if I don't get them resolved, I can't help but think about it all the time and waste a lot of precious time. As a part of it is ... | g16257 | [
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<p>I have a bunch of readings of a wave consisting of volts and time.
I need to calculate the frequency of the biggest wave, but i'm not sure exactly how.
From what I've researched I'm thinking I need to find the largest reading (volts) and that would be my biggest wave. Then I need to search for the closes value to ze... | g16258 | [
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<p>I have a question regarding the effect of quantum mechanical operators. The definition that I'm familiar with says that an operator $A$ acts on a vector from a Hilbert space, $|\psi\rangle$, and the result is another vector, $|\psi'\rangle$:
$$A |\psi\rangle = |\psi'\rangle$$</p>
<p>However, in class I've also seen... | g16259 | [
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<p>It was originally a problem from Professor Eugene Demler's problem set.</p>
<p>Consider an SO(5) rotor model:
\begin{align}\mathcal{H}=\frac{1}{\chi} \sum_{i,ab}L_{ab}^2(i)-J\sum_{<ij>,a}n_a(i)n_a(j)+g\sum_i(n^2_1+n^2_5-n_2^2-n_3^2-n_4^2)(i).\tag{1}\end{align}</p>
<p>Here $n_a(i)$ describes the SO(5) supersp... | g16260 | [
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<p>How is a "baseline" established.</p>
<p>When an experiment is performed to verify the reliability of something like carbon dating.</p>
<p>How do we know the results we get over the period of the test is still valid for an item older than one billion years?</p> | g16261 | [
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<p>Of course for the standard configuration(i.e. two opposite charges separated by some distance), there exist higher order multipole moments. However for an ideal dipole(those dipoles associated with point mass, which means the separation is zero), are there any higher order moments? </p> | g16262 | [
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<p><img src="http://i.stack.imgur.com/ohx7t.jpg" alt=""><img src="http://i.stack.imgur.com/yLA6b.jpg" alt=""></p>
<p>Okay, so I am having a hard time wrapping my head around this. Before looking at the answer, I worked the example and got the answer only because I used dimensional analysis to get me to the right units... | g16263 | [
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<p>I know the electrons are in the spin singlet state, and the spatial part of the wave function is an S-state. </p>
<p>But that is not sufficient for it to be diamagnetic. </p> | g16264 | [
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<p>I was reading through Stephen Hawking's <a href="http://www.hawking.org.uk/space-and-time-warps.html" rel="nofollow">explanation</a> of two - dimensional space. In that he mentioned that it will be very difficult to design a living being that could exist only in 2 dimension. What are the fundamental problems ar... | g16265 | [
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<p>I'm reading about color vision and have some trouble understanding the motivation for why the <a href="http://en.wikipedia.org/wiki/Trichromacy" rel="nofollow">trichromatic theory</a> was suggested in the first place. The book I'm reading ("Psychgology: The science of mind and behavior") states:</p>
<blockquote>
... | g16266 | [
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<p>At what temperature will create <a href="http://www.google.com/search?q=temperature+amorphous+TiSi" rel="nofollow">amorphous TiSi</a>?</p>
<p>I think it's around 500 Celsius but I'm not sure.</p> | g16267 | [
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<p>I found <a href="http://news.sciencemag.org/2012/04/light-bends-itself" rel="nofollow">this article</a> and I didn't understand it. I did get that they were able to bend light to 360 degrees. </p>
<p>Does that mean if take a box that is completely empty, and shine a light into it, it will keep rotating in a circle ... | g16268 | [
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<p>The photons are completely polarized, i.e their polarization states can be expressed as $a|R\rangle+b|L\rangle$, where $|R\rangle$ and $|L\rangle$ are two helicity eigenstates of the photon. For example, the $|R\rangle$ photon is right circularly polarized and the $|H\rangle=\frac{1}{\sqrt{2}}(|R\rangle+|L\rangle)$ ... | g16269 | [
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<p>When dragging an object, there is a greater start-up force than the force it takes to keep it moving. Why is this? Why are there two different values for friction?</p> | g30 | [
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<p>What is the smallest number of Fredkin gates needed to simulate a <a href="http://en.wikipedia.org/wiki/Toffoli_gate" rel="nofollow">Toffoli gate</a>? What is the smallest number of Toffoli gates needed to simulate a <a href="http://en.wikipedia.org/wiki/Fredkin_gate" rel="nofollow">Fredkin gate</a>?</p>
<p>Where t... | g16270 | [
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<p>I read the related answer to whether photons have size, and the answer seemed to be it depends. If a Photon, or a rather an E&M wave has a magnetic and electric field, should things be able to feel this? I know electrons do get 'sloshed' in these fields, but what is the range of influence of a photon? How much ... | g16271 | [
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<p>I am trying to implement Takens' correlation dimension for noisy time series formula given in Eq (8) in (Estimation of the dimension of a noisy attractor. Schouten JC, Takens F, van den Bleek CM Physical Review E, vol 50, number 3, 1994) . The actual derivation and explanation is given in <a href="http://download.sp... | g16272 | [
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<p><code>Question</code>:</p>
<blockquote>
<p>An electron and positron are moving in opposite directions, and are in the spin singlet state. Two Stern-Gerlach machines are orientated in some arbitrary direction; one along unit vector $\hat{s}_1$ (which measures the electron's position) and one along unit vector $\ha... | g16273 | [
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<p>If you have two magnets (not in contact) and then put a non-magnetic object in between the two magnets, does that decrease the attraction/repulsion between the two magnets?</p>
<p>It seems that it wouldn't, because, if it would, then you could allow two magnets to attract each other, then put an object in between b... | g16274 | [
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<p>I've read this <a href="http://physics.stackexchange.com/questions/76743/index-raising-and-lowering-how-does-it-work">related question</a>, though it didn't satisfy me; I hope this complements it. I know that if I contract a covariant tensor ${A_{\alpha\beta}}$ with a vector ${B^\beta}$, I get some other covector ${... | g16275 | [
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<p>I was wondering whether or not a slide in a slide projector acts as light diffuser? So when I have a light source that does not have a parallel beam on the slide can I expect that the other side of the slide is illuminated with a Lambertian of similar reflectance?</p>
<p>I am wondering this because I want to know i... | g16276 | [
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<p>I am not physics in training so if anything is unclear please request clarification.</p>
<p>I have a set of objects to be placed on a line, linked with springs of known lengths (L) and stiffnesses (K). I want to solve the equilibrium positions of each object (x).</p>
<pre><code>o---------o--------------o
x0 ... | g16277 | [
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<p>One suggestion for explaining superluminal neutrinos (assuming for the sake of argument that the OPERA results should hold up) is that the neutrinos have taken a route through extra dimensions, with an appropriate metric of the form $\mathrm{d}s^2=-\mathrm{d}t^2 + f(r)\mathrm{d}x^2 + \mathrm{d}r^2$. This would be co... | g16278 | [
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<p><img src="http://i.stack.imgur.com/cvSGd.png" alt="wave equation question"></p>
<p>I am having trouble understanding the boundary conditions.</p>
<p>From the solutions, the first is that $D_1(0, t) = D_2(0, t)$ because the rope can't break at the junction.</p>
<p>The second is that $\dfrac{\partial D_1}{\partial ... | g16279 | [
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<p>I am confused. Could someone kindly explain what's going on in this question?</p>
<blockquote>
<p>A particle of mass $m$ and charge $e$ moves in the $x,y-$ plane. There is a constant magnetic field $B$ that points in the $z$ direction. Initially the particle has energy $\gamma m$ in the rest frame of the observer... | g16280 | [
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<p>This question is inspired from reading Mitchell Porter's nice answer <a href="http://physics.stackexchange.com/a/64437/2751">here</a> to a question asking why supersymmetry should be expected naturally. Among other things, he explains that since weak scale supersymmetry comes a bit under pressure now, theorists coul... | g16281 | [
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<p>Eastern European swimming pools are often brown tinted water. i was told it was the color of the chemical to keep the pools clean, but who knows. These pools did not smell unsanitary and may have even been the result of original brown listerine. May be it was just iron from a natural spring. The pool was still trans... | g16282 | [
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<p>What is the difference between the process in which energy converts to matter and the process in which it converts to antimatter? In colliders, for instance, is the product (either being the matter or the antimatter counterpart of a specific particle) solely a result of angular momentum conservation (given that this... | g16283 | [
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<p>I've been banging my head against a wall trying to figure out what I'm sure is a very simple problem. I want to solve the Kronig Penney model for a superlattice, which is just a normal periodic 1D potential, except the potential wells extend into all space in the directions perpendicular to the perodicity, like so:<... | g16284 | [
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<p>The tubular Feynman diagrams in string theory, unlike the usual Feynman diagrams in QFT, is <em>assumed</em> to represent scattering amplitudes, rather than <em>derived</em> from algebraic expressions of perturbative expansions in the case of QFT. Peculiar features of the tubular diagrams include the fact that there... | g16285 | [
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<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/12140/why-does-every-thing-spin">Why does every thing spin?</a> </p>
</blockquote>
<p>So why would the earth, or any planet for that matter, rotate along an axis? I know of no force which could come into... | g231 | [
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<p>I think of building a <a href="http://en.wikipedia.org/wiki/Tesla_turbine" rel="nofollow">Tesla turbine</a> out of old hard drives.</p>
<p>Now I wonder how to cut ventilation holes in the platters.</p>
<p>On the internet there are a lot of different attempts on that matter. A lot of people cut 3 arcs of 60° somewh... | g16286 | [
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<p>With a distribution function of the form $f=f_{0} + \vec{v} \cdot \vec{g}$, one can obtain the current density. My question is about $\vec{g}$; we assume a general solution to $\vec{g}$ of the form $\vec{g}= \alpha \vec{E}+\beta \vec{B} + \gamma(\vec{B} \times \vec{E}) $. By substitution into $$\frac{\mu}{c}(\vec{v}... | g16287 | [
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0.0... |
<p>A condensate of open strings with both ends attached to the same D-brane can be equivalent to a displacement of the D-brane with no open string condensate.</p>
<p>A solution to the D-brane Born-Infeld action gives rise to a semi-infinite string extension which is entirely equivalent to an open string with one end a... | g16288 | [
0.010056177154183388,
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<p>What happens if different size atoms meet? We've just created anti-helium, I think. What if one atom of anti-helium collided with one atom of iron. Would some of the iron be left over as a new element?</p> | g16289 | [
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<p>My physics teacher explained the difference between voltage and current using sandwiches. Each person gets a bag full of sandwiches when they pass through the battery. Current = the number of people passing through a particular point per unit time. Voltage = the (change in) number of sandwiches per person. In a p... | g16290 | [
0.04682958871126175,
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<p>What does it mean when we say that the CMBR is mostly gaussian? What are non-gaussianities in CMBR? How does evaluation of 3-point correlation functions of the inflaton field tells us that there is non-Gaussianity?</p> | g16291 | [
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<p>In projectile motion, what does it mean for the motion along the $x$ and $y$ axis to be independent?</p>
<p>This question is referring to the concept of projectile motions.</p> | g16292 | [
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<p>It is common knowledge among the educated that the Earth is not exactly spherical, and some of this comes from tidal forces and inhomogeneities but some of it comes from the rotation of the planet itself. The deformation from the rotational effect makes it more oblate spheroid-like, or as I would prefer, "like a pa... | g129 | [
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0.07824455946683884,
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<p>This is question from I.E. Iredov's General Physics:</p>
<blockquote>
<p><em>$1.22$ : The velocity of a particle moving in the positive direction of the $x-axis$ varies as $v = α \sqrt x$, where $α$ is a positive constant. Assuming that at the moment $t = 0$ the particle was located at the point $x = 0$.</em></p... | g16293 | [
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<p>What is the best way to focus (sun)light using flat mirrors? My goal is to start a fire. Cutting the mirrors is easy.</p> | g16294 | [
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0.05136372521519661,
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0.04111924767494202,
-0.0125461... |
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