question stringlengths 37 38.8k | group_id stringlengths 2 6 | sentence_embeddings listlengths 768 768 |
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<p>There are a lot of videos showing the simple homopolar motors in action.
Let's look at this one: <a href="http://www.youtube.com/watch?v=6jyraFLqfqE" rel="nofollow">http://www.youtube.com/watch?v=6jyraFLqfqE</a>
It is supposed to be working due to the Lorentz force.</p>
<p>Electrons go through the magnet, deflect u... | g17843 | [
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<p>There seems to be a fairly large inconsistency in various textbooks (and some assorted papers that I went through) about how to define the Clausius-Mossotti relationship (also called the Lorentz-Lorenz relationship, when applied to optics). It basically relates the polarizability of a material to it's relative permi... | g17844 | [
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<p>The usual schematic representing the setup of Frank-Hertz experiment is the following:</p>
<p><img src="http://i.stack.imgur.com/YRuQi.gif" alt="enter image description here"></p>
<p>However, sometimes, you can see a bit different schematic:</p>
<p><img src="http://i.stack.imgur.com/7v3mT.png" alt="enter image de... | g17845 | [
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<p>So yea, if two magnets attract/repel multiple times(A LOT) will they lose their magnetism? If they don't break during the whole process?</p> | g17846 | [
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<p>2 gas flows connect and mix in a pipe.
The following is known:</p>
<p>$\dot{m_1}$; $\dot{m_2}$ - mass flow rate of the inlet gases $(\frac{kg}{s})$</p>
<p>$A_1$; $A_2$; $A_{mix}$ - the cross section of the pipes $(m^2)$</p>
<p>$\rho_1$; $\rho_2$ - the densities of the 2 gases</p>
<p>$T_1 = T_2 = T_{mix} $</p>
<... | g17847 | [
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<p>For a given gauge transformation, say, the electromagnetic field, where observable quantities aren't affected by transformations of the form
$$\mathbf{A}' = \mathbf{A} + \nabla \chi,$$
$$\phi' = \phi - \frac{\partial \chi}{\partial t},$$
$$\Psi' = \Psi \cdot \exp(\frac{iq\chi}{\hbar}).$$</p>
<p>What exactly does th... | g17848 | [
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<p>I'm working on a college project for a subject called <em>Motorcycle Engineering</em>, and in this project I'm supposed to do some reverse engineering on a MATLAB program to model the engine of the motorcycle. In this program I just came across the following expression:
$$u=h_f-RT+(c_p-R)(T-T_0)$$
where $u$ is the s... | g17849 | [
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<p>Considering the fault of any experimental evidence from LHC for supporting the supersymmetry idea until now, can we say that it is dead? Generally the people who are working on this subject say that MSSM probably is dead but we have some new extensions of it such as NMSSM. This argument seems weird a bit. Sometimes ... | g550 | [
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<p>I'm interested in purchasing a new telescope and have narrowed it down to the NexStar 6 SE vs. the Orion XT8.</p>
<p>I'd like to be able to get into astrophotography and read that having the Go-To (auto-tracking) is a must -- this would eliminate the Orion XT8. I really like the large(r) aperture of the XT8, but ha... | g17850 | [
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<p>We should all fondly remember this basic undergraduate problem: A quantum particle is incident (from the left) upon a potential barrier of height V and width L. Compute the transmission and reflection coefficients.</p>
<p>However, this isn't the full story. To completely solve the potential barrier, we need a com... | g17851 | [
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<p>It was kind of hard to miss <a href="http://en.wikipedia.org/wiki/June_2011_lunar_eclipse" rel="nofollow">the lunar eclipse this week</a>, although I didn't see it in person (<a href="http://en.wikipedia.org/wiki/Sod%27s_law" rel="nofollow">Sod's law</a> means that on every relatively major astronomical event clouds... | g17852 | [
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<p>I know the galaxies are moving away from us (faster and faster) but when we say the universe is expanding, is that really only pertaining to the galaxies expanding or is the space itself expanding? I know we don't yet know what the boundary is, but I just wanted clarification around the commonly used phrase "Univer... | g17853 | [
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<p>When a load is resting on an inclined plane, there is force $mg \sin(x)$ that's vertical to the inclined plane and force $mg \cos(x)$ horizontal to the plane acting on it like this:</p>
<p><img src="http://i.stack.imgur.com/mfCsM.png" alt="enter image description here"></p>
<p>My textbook says the weight $mg$ h... | g17854 | [
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<p>Do all celestial bodies of sufficient mass such big asteroids, moon, planets etc. have orbit such that the period of revolution is same as the sidereal period of that object (such as geostationary orbit in earth) ?</p> | g17855 | [
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<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/78/why-do-neutrons-repel-each-other">Why do neutrons repel each other?</a> </p>
</blockquote>
<p>What I mean is that the neutrons are attracted to one another via gravity, so what force keeps them from c... | g551 | [
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<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/9661/protons-repulsion-within-a-nucleus">Protons' repulsion within a nucleus</a> </p>
</blockquote>
<p>How positively charged protons remain glued to each other while they should repel each other out... | g425 | [
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<p>(v2)</p>
<p>As I read e.g. <a href="http://physics.stackexchange.com/questions/13945/why-is-compactification-restricted-to-toroids-calabi-yau-co">in this question</a>, the nice holonomy group features of Calabi-Yau manifolds are valuable regarding supersymmetry (I suspect because it's a symmetry involving the targe... | g17856 | [
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<blockquote>
<p>Are the more recently discovered symmetries in string theory such that the theories based on mirroring geometries are absolutely the same from an observable point of view?</p>
</blockquote>
<p>I have mirror symmetry in mind, i.e. by symmetries I mean the dualities encountered in string theory.</p>
<... | g17857 | [
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<p>In the recent Spielberg/Jackson Tintin movie, there is a scene where Red Rackham and Captain Haddock's ships are fighting, and cannons are fired. The cannonball is shown at one point to go through a wave, and inflict serious damage on the other ship. I know that bullets stop in water; do cannonballs, with their gr... | g17858 | [
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<p>If I understand correctly, the distinction between semiconductors and insulators is a matter of convention? A semiconductor is basically an insulator with an (enough) narrow band gap, usually around $3$ $eV$.</p>
<p>I have a few equations used for semiconductors, will they still work for insulators? Or are they gra... | g17859 | [
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<p>I got the impression from several public lectures that, when it comes to the fine tuning problem, physicists tend to give multiverse together with anthropic principle as a plausible solution, but seldom anthropic principle alone. </p>
<p>However it seems the core of this kind of solution is really anthropic princip... | g17860 | [
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<p>Here's a question in a paper based on refraction of light. I can't seem to solve it for some reason.</p>
<blockquote>
<p>A man looks down at a fish length of 20 cm. His eye is 2m above the
surface of the water ($\mu = 4/3$) an the fish is 2m below the surface
shown in the figure. The ratio of angular width $\... | g17861 | [
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<p>I've been pursuing physics on my own, and I need something cleared up. Say I have two arbitrary objects, I have their velocities, I know when the collide, I have their normal vectors, etc. I know where a force is applied, how much, which direction(lever arm, etc). I THINK that what I'm trying to do is vector decompo... | g17862 | [
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<p>This is a bit of an abstract question so I'll try explain this as best I can from the bottom up.</p>
<p>I would like to know if it is possible to observe a sheet of fluid, much like a sheet of glass, falling completely flat and level.</p>
<p>Imagine a volume of water that is at rest on some sort of very, very fast... | g17863 | [
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<p>I am thinking if it's possible to detect Cherenkov radiation in water caused by dissolved natural potassium (KOH) in it without using photo-multipliers. </p>
<p>The main question is does 1 beta particle generate 1 photon, or multiple? Specifically, how many photons of <em>visible light</em> should I expect from 1.3... | g17864 | [
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<p>I know that this won't work but I'm asking <em>Why</em>?</p>
<p>Becuase as far as the vehicle POV - there <strong>is</strong> a force which drags him to the right.</p>
<p>Isnt $F=ma$ applies here? What is that im missing?</p>
<p><img src="http://i.stack.imgur.com/NM23U.jpg" alt="enter image description here"></p> | g552 | [
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<p>I feel this is somehow a stupid question, but I don't know the true answer. What happens to an astronaut who's floating in a spaceship in space when it begins to move? Will the astronaut not move until he smashes onto a wall in the spaceship? Or will he move with the spaceship due to gravity? Or does it depend on th... | g17865 | [
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<p>The so called consistent histories interpretation is claimed to be a correction of the Copenhagen Interpretation. One of its aim, as much as I can see is to show that observers don't have any special role and a history is represented as a sequence of projection
operators in the Heisenberg picture. It has been convin... | g17866 | [
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<p>Dirac came up with a general theory of constraints, including second-class constraints. To quantize such systems, he first computed the Dirac bracket <em>classically</em>, and only then "promoted" the classical Dirac bracket into a commutator. However, this leads to operator ordering ambiguities over and above what ... | g17867 | [
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<p>Consider some basic cosine waves of the form ${E_i} = {E_0}\cos ({\omega _i}t - {k_i}z)$ with different amplitudes, frequencies and phases. We know a combination of such waves could result in a wave which has an envelope that is traveling at a group velocity and also has a phase velocity. </p>
<p>When there are som... | g17868 | [
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<p>We need to get things into space but it costs too much. Lots of people talk about space elevators but no one talks about the skyhook idea. I'm referring to this:
<a href="http://en.wikipedia.org/wiki/Skyhook_%28structure%29" rel="nofollow">Skyhook (Wikipedia)</a>, not the thing in Batman. It is also illustrated in ... | g17869 | [
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0.0023705505300313234,
0.... |
<p><a href="http://en.wikipedia.org/wiki/Antiparticle">http://en.wikipedia.org/wiki/Antiparticle</a> says "Corresponding to most kinds of particles, there is an associated antiparticle with the same mass and opposite electric charge."
and
<a href="http://physics.stackexchange.com/questions/23100/what-is-anti-matter">Wh... | g17870 | [
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<p>I'm a little confused about matter waves and especially interference.</p>
<p>$\lambda = h/p$</p>
<p>The denominator is momentum and is thus reliant on mass. If we assume that the property holds for particles only, then I run into some problems with constituent "particles". What I mean by that are objects normall... | g17871 | [
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0.03016... |
<p><strong>Scenario:</strong> a spaceship is travelling at a high fraction of $c$. The interstellar gas and CMB radiation has blueshifted significantly and we are facing a possible melting of the front radiation shield!</p>
<p>but the ship has good radiator area in the back so there might be a significant temperature ... | g17872 | [
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<p>Assume you are moving 10 meters in 10 seconds northward. What is the acceleration?. </p>
<p>Using this equation: $a = (v_f - v_o)/\Delta(t)$ and filling it in with this data: $v_f=1$ which comes from $10$ $m/10s=1m/s$, $v_o=0$ because we are starting at a speed of $0$ and $t=10$ because that's how long it tooks. We... | g17873 | [
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<p>Do ideal gases have a certain potential energy at a certain temperature?</p> | g553 | [
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<p>The wave equation in $3$ dimensions is simply:</p>
<p>$$\nabla^2\psi = \dfrac{1}{v^2} \dfrac{\partial^2}{\partial t^2}\psi,$$</p>
<p>and the intuition behind this is that at each point of space with coordinates $(x,y,z)$ with have some quantity oscilating there. If it's a sound wave what is oscilating are molecule... | g17874 | [
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<p>In standard LFL theory, the effect mass of quasiparticle is different from the composite Fermion's mass. It seems that this is no longer true in Chiral case (e.g. a finite density system with interacting massless left handed fermions)?
What is Landau's FL theory for chiral Fermions?
Thanks!</p> | g17875 | [
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<p>The s-d interaction Hamiltonian is as fellows</p>
<p>$H_I=Js.S$, J is the coupling strength. </p>
<p>We focus on the antiferromagnetic case, where $J>0$.</p>
<p>According Anderson's poor man's scaling, the renormalized coupling strength $J$ increases as the band width $D$ decreases. Anderson originally did the... | g17876 | [
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<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/50015/confusion-on-quantum-field-theory">confusion on quantum field theory</a> </p>
</blockquote>
<p>Are field quanta infinite in extent as stated in Art Hobsons paper? What does this even mean? I've not... | g554 | [
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<p>I want to prove that pair production (electron-positron) cannot happen in complete vacuum. This is why I obeyed conservation of energy and got equation:</p>
<p>$$h \nu = m_e c^2 \Bigl[ \gamma(v_1) + \gamma(v_{2})\Bigl]$$</p>
<p>I did the same for conservation of momentum and got an equation which is different:</p>... | g17877 | [
0.05567779764533043,
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<p>Is it possible to write an arbitrary density matrix $\hat{\rho}$ in the following form ? </p>
<p>$$\hat{\rho} ~=~ \frac{1}{N} \sum_{\ell=1}^N \left|x_{\ell}\right\rangle \left\langle x_{\ell}\right|,$$</p>
<p>where $\left\{\left|x_{\ell}\right\rangle\right\}_{\ell = 1}^{N}$ are normalized states (but not necessari... | g17878 | [
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0.04595482721924782,
... |
<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/50015/confusion-on-quantum-field-theory">confusion on quantum field theory</a> </p>
</blockquote>
<p>I asked are field quanta infinite in extent and I keep getting back that its the probabibility distrib... | g554 | [
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... |
<p>Just a quick question if I may.</p>
<p>The Poynting vector, or the energy flux density, is given by:</p>
<p>$\mathbf{S} = \frac{1}{\mu_{0}}(\mathbf{E} \times \mathbf{B})$</p>
<p>So it's the cross product between the $\mathbf{E}$-field and $\mathbf{B}$-field. So depending on the direction of the fields, the Poynti... | g17879 | [
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<p>The speed of sound in the ocean is given by</p>
<p>$$c_s(\theta,z) = 1450 + 4.6\theta - 0.055\theta^2 + 0.016z$$</p>
<p>$\theta$ is the temperature in degrees celcius, and $z$ is the depth. In a simplified model, $\theta$ is constant at 10$\,^\circ $C for the part of the ocean above the "themocline". The thermocli... | g17880 | [
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0.02... |
<p>What is the dependence of the beta function of pure $SU(N_\text{c})$ Yang-Mills theory on the number of colors? I guess
$$\mu\frac{dg_\text{YM}}{d\mu}=-\beta_0N_\text{c}g_\text{YM}^3-\beta_1N_\text{c}^2g_\text{YM}^5-\beta_2N_\text{c}^3g_\text{YM}^7-\cdots\,,$$
with the appropriate constants $\beta_0,\beta_1,...$, as... | g17881 | [
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0.009503391571342945,
0.009815596975386143,
0.... |
<p>I'm building a bridge out of balsa-wood strips for school, and wanted some advice. These are the specifications:</p>
<ul>
<li>Height: 2 to 6 in</li>
<li>Length: 12 inches, plus 1-3 inches on each side resting on tables</li>
<li>Width: 2 +- 1/16 in at the base</li>
<li>Weight: <= 50 g</li>
</ul>
<p>The objective... | g17882 | [
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0.013136651366949081,
0.045573264360427856,
0.005463792011141777,
-0.0... |
<p>I have a fluid flowing through a pipe in the ocean and there is heat transfer from the ocean to the fluid in the pipe. I prepared a simulation and the results show that if I increase the mass flow rate of the fluid through the pipe then the heat transfer rate to the fluid increases and the outlet temperature increas... | g17883 | [
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<p><strong>I noticed that <code>v</code> [in step (2.5)] is not the same as the terms from the first formula, even if they are related..</strong></p>
<p><strong>I tried to understand how did he reach to this step:</strong></p>
<p><img src="http://i.stack.imgur.com/weOqQ.jpg" alt="enter image description here"></p>
<... | g17884 | [
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0.05052896589040756,
0.04578157886862755,
-0.... |
<p>Electricity and magnetism was unified in the 19th century, and unification of electromagnetism with the weak force followed suit, bringing into play the electroweak force.</p>
<p>I've been told that unifying these with the strong force is likely to be far easier than unifying them with gravity, albeit still very ha... | g17885 | [
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0.0361... |
<p>I am a mathematician and am originally from the math side of stackexchange. I want to model the behaviour of a drop of ink diffusing in water. I dont want to simply use the diffusion equation $u_t(\mathbf{x},t)=D \triangledown^2u(\mathbf{x},t) $ because firstly it will produce a diffusion of the ink completely symme... | g17886 | [
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0.02949819527566433,
0.0023070569150149822,
0.05643728747963905,
0.0... |
<p>I need to prove that the <a href="http://en.wikipedia.org/wiki/Intrinsic_parity" rel="nofollow">intrinsic parities</a> of a particle and antiparticle with spin zero are the same. Can I prove that by an argument that operator of $P$-inversion commutes with charge conjugation operator for the spin-zero particle?
$$
\h... | g17887 | [
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<p><strong>Background</strong></p>
<p>I'm new to physics and math. I stopped studying both of them in high-school, and I wish I hadn't. I'm pursuing study in both topics for personal interest. Today, I'm learning about acceleration as a step toward understanding force, and then related concepts (power, work, etc.)</p>... | g17888 | [
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0.02263168804347515,
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0.030387... |
<p>The universe expanded from nothing, right? And black holes may be a "gate" to parallel universes, is it possible that stars that is being sucked in by black holes in our universe may be the origin of the energy in another universes "big bang"? Is there any theories that explains that?</p> | g17889 | [
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0.026306921616196632,
0.026706919074058533,
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0... |
<p>I've seen people estimate the Bohr radius using the uncertainty principle by assuming that
$$\Delta x \sim r$$
and
$$\Delta p \sim p$$</p>
<p>then $$p \approx \frac{\hbar}{r}$$</p>
<p>Using this assumption will give the Bohr radius when minimizing the Hamiltonian.</p>
<p>They didn't however justify their original... | g17890 | [
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0.003959986846894026,
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0.0... |
<p>This probably doesn't fit into the realm of regular questions ; it is more of an applied rather than theory/math question ...</p>
<p>Anyway, I'm curious whether a metre diameter speaker fitted over a manhole may dislodge any blockage using the principle of resonance. Obviously blockage would be best dislodged at a ... | g17891 | [
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0.040499769151210785,
0.01602115109562874,
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0.020... |
<p>I know about and believe to understand the general wave equation based Kirchhoff diffraction formula, which in the Fraunhofer limit leads to a farfield complex wave function by Fourier transforming the complex wave function of the incident beam in the aperture.</p>
<p>I believe it should be possible to describe thi... | g17892 | [
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0.0740048885345459,
... |
<p>A bit of background helps frame this question. The question itself is in the last sentence.</p>
<p>For his PhD thesis, Richard Feynman and his thesis adviser John Archibald Wheeler devised an astonishingly strange approach to explaining electron-electron interactions without using a field. Their solution was to tak... | g17893 | [
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0.02301967144012451,
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0.02696... |
<p>The theory I've recently come to postulates that:</p>
<ol>
<li><p>The volume of space filling the universe is finite and is constantly growing, thus the boundaries of the universe are constantly expanding.</p></li>
<li><p>The expansion of the universe's boundaries is caused by light that is converted into fresh spa... | g17894 | [
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0.065... |
<p>Since the electric field inside a conductor is zero that means the potential is constant inside a conductor, which means the "inside" of a conductor is an equipotential region. </p>
<p>Why books conclude also that, the surface is at the same potential as well?</p> | g17895 | [
0.04327484220266342,
0.01882544532418251,
0.006461697164922953,
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0.009... |
<p>In electromagnetism books, such as Griffiths or the like, when they talk about the properties of conductors in case of electrostatics they say that the electric field inside a conductor is zero.</p>
<p>I have 2 questions: </p>
<ol>
<li><p>We know that conductors (metallic) have free electrons which randomly moves ... | g474 | [
0.05300527811050415,
0.04199599474668503,
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0.06692559272050858,
0.07020844519138336,
0.005711894482374191,
0.027816899120807648,
-0.05424943193793297,
-0.010522962547838688,
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0.011010169982910156,
0.013198385946452618,
-0.03... |
<p>Evolution is a principle in biology, whereby organisms evolve their ability to replicate and multiply in numbers over successive generations. From a computational point of view, the organisms employ a common programming (DNA, RNA, etc.) and runtime environment (cell biology). This evolution has eventually evolved a ... | g17896 | [
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0.017891164869070053,
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0.... |
<p>In <em>Quantum field theory</em> by Lewis H. Ryder, a <a href="http://en.wikipedia.org/wiki/Supermultiplet" rel="nofollow">supermultiplet</a> is mentioned with no explanation as to what one is.</p> | g17897 | [
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<p>Recently I watched a documentary about Io, a moon around Jupiter. Io has volcanic activity even though it is small and can't retain heat well because gravity from Jupiter and a nearby moon cause it to sort of speed up from the opposing gravitational pulls, causing heat, when they are all lined up.</p>
<p>My questio... | g17898 | [
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<p>I've noticed that one can obtain D-terms either by integrating a vector superfield (the vector multiplet) over superspace or by integrating a Kahler potential over superspace. In both cases we get functions of the D-auxiliary field (albeit different functions) that contribute to the Lagrangian density. A subsequent ... | g17899 | [
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0.06880892813205719,
0.0... |
<p>I know that two functions which describe the state of a particle in an infinite square (on interval $-d/2<x<d/2$) well are like: </p>
<p>\begin{align}
\psi_{even}&= \sqrt{\frac{2}{d}}\sin\left(\frac{N\pi x}{d}\right)\quad N=2,4,6\dots\\
\psi_{odd} &= \sqrt{\frac{2}{d}}\cos\left(\frac{N\pi x}{d}\right)... | g17900 | [
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0.02279767580330372,
-0.010... |
<p>If I insert a piece of glass between two objects carrying different charges, would they <em>still</em> attract?</p>
<p>If they attract, does the piece of glass affect the force of attraction and is there any formula explaining the decrease of this force ? Also If they don't attract, Why..?</p> | g17901 | [
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<p>I have a series of vectors (current speeds) based on an ENU (East North Up) system. I would like to estimate the current speed of the water headed in a specific direction.</p>
<p>In this example I am interested in isolating the water flowing in the direction of 150 degrees, and am looking at the best way to calcula... | g17902 | [
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<p>Okay, so Jupiter, Saturn, et. al are gas giants. I understand that they have large gassy atmospheres, which, due to the pressure would eventually become more and more dense as one approaches the center of the planet. <a href="http://physics.stackexchange.com/questions/25918/falling-into-saturn-or-jupiter-would-we-... | g17903 | [
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<p>If we consider the 126 Higgs-like boson as a pseudo-Nambu-Goldstone boson, what are the experimental fingerprints of that case? What are the main differences, in a purely effective field theory approach and/or "new physics" scenario with respect to the fundamental and boring Standard Model Higgs (take it as a neutra... | g17904 | [
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<p>Say I have an object that starts falling from rest at 2 m/s<sup>2</sup>. Its total displacement and velocity at the end of every second should look something like this:</p>
<pre><code>t d v
1 2 2
2 6 4
3 12 6
4 20 8
</code></pre>
<p>At the end of the first second, it should have accele... | g17905 | [
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<p>Say I have a bucket of fuel that can produce 150J of energy by combustion. No matter what frame of reference an observer or the bucket of fuel is in, since the configuration of molecules stay the same, the amount of energy produced by complete combustion of the fuel would be 150J.</p>
<p>Say I have a spaceship trav... | g17906 | [
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<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/36303/introduction-to-ads-cft">Introduction to AdS/CFT</a> </p>
</blockquote>
<p>Since my question in a similar topic was deleted, I'll ask away and hope ppl won't come here telling me: this was already ... | g555 | [
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<p>I'm looking at the following problem from "Physics 3" by Halliday, Resnick and Krane (4th edition):</p>
<blockquote>
<p>The armature of a motor has 97 turns each of area 190 cm² and rotates in a uniform magnetic field of 0.33 T. A potential difference of 24 V is applied. If no load is attached and friction is neg... | g17907 | [
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<p>Are scalars starting at around 1300 MeV analogous to some kind of sound in the vacuum glue? </p>
<p><a href="http://physics.stackexchange.com/q/13458/9082">Background</a>:<br>
There are scalars starting at around 1300 MeV which are probably some combination of glue-condensate sloshing around and quark-condensate ... | g17908 | [
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0... |
<p>i mean given a system with a conserved Energy in one dimension</p>
<p>$$ E= \frac{p^{2}}{2m}+V(x) $$</p>
<p>then the 'solution' to this problem is implicitly given by</p>
<p>$$ t(x)= \frac{1}{2m} \int_{0}^{x}\frac{du}{\sqrt{E-V(u)}} $$</p>
<p>so apparently from this equation we could know all the quantities $ p(... | g17909 | [
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0.00... |
<p>I am thinking about some topological field theories, and I am wondering when one can say that the stationary phase approximation (ie. a sum of the first-order variations about each vacuum) is exact.</p>
<p>I am looking perhaps for conditions on how the space of vacua is embedded into the space of all field configur... | g17910 | [
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<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/48311/physical-explanation-for-capacitive-circuit">Physical explanation for capacitive circuit</a> </p>
</blockquote>
<p>We say that in capacitive circuit, the voltage and current are out of phase. Curre... | g556 | [
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0... |
<p>Unfortunately, I missed a few lectures on four-vectors and I am pretty confused on how to go about solving the below question. I would be extremely grateful for any responses or solutions to enlighten my knowledge on four-vectors.</p>
<blockquote>
<p>In a particular frame of reference a particle with 4-velocity $... | g17911 | [
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0.039048124104738235,
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0.037142861634492874,
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0.00... |
<p>I repair electrical motors in a workshop and sometimes I must repair permanent magnet DC motors and other motors that use permanent magnets. I need to specify type of permanent magnet (Ferrite or Alnico or rare earth, etc.) by a simple method. Is there a way to do this?</p> | g17912 | [
0.030834650620818138,
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0.010193034075200558,
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0.02188877947628498,
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<p>Suppose we have a quantum mechanical system, which is well described by its wave function in r-representation $\Psi$. We are interested in the properties of an observable, say the kinetic energy $T$. So we let the kinetic energy operator act on the wave function, multiply the result by Psi and integrate over spatial... | g17913 | [
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0.04427621513605118,
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0.026458734646439552,
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0.030652720481157303,
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<p>While focusing on resolutions to the <a href="http://physics.stackexchange.com/questions/38005/what-are-cosmological-firewalls">Firewall controversy</a>, and the possible implications of the Higgs field as it relates to the issue, the <a href="http://arxiv.org/abs/hep-ph/0204154" rel="nofollow">possibility of using ... | g17914 | [
0.020649826154112816,
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0.02079358510673046,
0.09532... |
<p>In a theoretical physics homework problem, I have to show the following:
$$\partial_\nu T^{\mu\nu} = - j_\nu F^{\mu\nu}$$</p>
<p>Where $T$ is the Energie-Momentum-Tensor, $j$ the generalized current and $F$ the Field-Tensor. We use the $g$ for the metric tensor, I think in English the $\eta$ is more common.</p>
<p... | g17915 | [
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0.0... |
<p>I'm wondering what the dielectric constant or permittivity of metals is --particularly copper. Do metals have an infinite permittivity?</p> | g17916 | [
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0.0050513045862317085,
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0.019198046997189522,
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0.03849282115697861,
-0.019943857565522194,
-... |
<p>Is the motion of a simple <a href="http://en.wikipedia.org/wiki/Pendulum" rel="nofollow">pendulum</a>, a <a href="http://en.wikipedia.org/wiki/Simple_harmonic_motion" rel="nofollow">simple harmonic motion</a>? It stops vibrating after sometime.</p> | g17917 | [
0.08999458700418472,
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0.006548849865794182,
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0.00830092467367649,
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<p>While dealing with General Sigma models (See e.g. Ref. 1)</p>
<p>$$\tag{10.67} S ~=~ \frac{1}{2}\int \! dt ~g_{ij}(X) \dot{X^i} \dot{X^j}, $$ </p>
<p>where the Riemann metric can be expanded as, </p>
<p>$$\tag{10.68} g_{ij}(X) ~=~ \delta_{ij} + C_{ijkl}X^kX^l+ \ldots $$
The Hamiltonian is given by, </p>
<p>$$ H... | g17918 | [
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0.0181584395468235,
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0.03892635554075241,
0.010562301613390446,
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0.030382759869098663,
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0.052050016820430756,
0.026198873296380043,
0.01... |
<p>Will gravitational waves of cosmological origin be weaker or stronger (higher amplitude $h \simeq\Delta L/L$) than those created from astrophysical sources?</p>
<p>I'm having a real hard time finding the amplitude of cosmological gravitational waves (from inflation and from cosmic defects (strings etc.)) in terms o... | g17919 | [
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0.03412053361535072,
0.00587046891450882,
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0.0237... |
<p>Just saw <a href="http://www.youtube.com/watch?v=4dRJ7fyH_nk" rel="nofollow">this cool video</a> from Plymouth University, which I actually found through <a href="http://blog.matthen.com/" rel="nofollow">Matthen's blog</a>.</p>
<p>They fill a plastic bottle with liquid nitrogen, screw the cap on, drop it in a bucke... | g17920 | [
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0.043697744607925415,
-0.001... |
<p>This is in reference to a pasteurization discussion on a homebrewing forum.</p>
<p>I have four closed bottles which will explode if containing too much pressure. Two of them are 50% full (<strong>A</strong> and <strong>B</strong>), and two of them are 75% full (<strong>C</strong> and <strong>D</strong>).</p>
<p>I... | g17921 | [
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0.0006066043861210346,
-0.031... |
<p>The superficial degree of divergence for a diagram is defined as the power of $k$ in the nominator minus the power of $k$ in the denominator. It is written to be
equal to $4\times$ (number of loops)$ - $(number of internal Fermion lines)$ - 2 \times $(number of internal Boson lines). </p>
<p>Why i... | g17922 | [
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-0.... |
<h1>Step 1</h1>
<p>Let me formulate the problem to convey my notation.
I have a matrix $A$ which is hermitian - and is diagonalisable by a transformation
$$ U_A A\,\,U_A^{-1} = A_{diag}$$</p>
<p>Now the matrix is changed, using the small parameter $\lambda$. Therefore,
$$ A \rightarrow A-\lambda B $$ where $B$ can ... | g17923 | [
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0.008349447511136532,
-0.03469695895910263,
0.07468871772289276,
-0.013919358141720295,
... |
<p>I recently came in a work-group discussion where I think some concepts are misused. After seeking for scientific articles on the subject I have found that part of the problem is definition (what exactly is a LOD and how should we define it). But I cannot find a legitimate argument for a negative LOD when measuring a... | g17924 | [
0.04283488541841507,
-0.019185010343790054,
-0.006960407365113497,
-0.0328691229224205,
-0.008238197304308414,
0.020837439224123955,
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0.0060976287350058556,
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-0.07415606826543808,
0.02940305508673191,
0.03354817256331444,
0.021780982613563538,
0.01... |
<p>In the periodic table of the elements, only a few of the elements are gases at standard temperature and pressure. Those elements include the noble gases some of the halogens, and a few of the elements next to them, i.e. oxygen and nitrogen.</p>
<p>So why are these elements gases?</p> | g17925 | [
0.034972622990608215,
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0.000045924829464638606,
0.06244200840592384,
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-0.024147620424628258,
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0.04560525342822075,
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<p>I've heard the claim that some aspects of string theory are used to improve Monte-Carlo simulations of lattice QCD, for example by people working at the LHC.
I know a bit about Monte-Carlo methods in lattice QCD, but have no idea of how string theory ideas are applied to QCD at all, so I'd like to ask for </p>
<ul>... | g17926 | [
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0.021854547783732414,
-0.00517211714759469,
0.09781302511692047,
0.06780654191970825,
0.01... |
<p>I'm trying to calculate the new temperature of an object when the air temperature around it changes, given a period of time.</p>
<p>Basically I get periodic readings from an air temperature sensor in a refrigerator. In some cases these readings are every 5 minutes, in others every 1 minute, so the time between read... | g17927 | [
0.020541492849588394,
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0.0... |
<p>I'm trying to understand a step in <a href="http://arxiv.org/abs/1104.2661" rel="nofollow">arXiv:1104.2661</a>. Equation 3.4 reads,
\begin{equation}
\frac{1}{\Gamma(2\epsilon)}\int_{-i\infty}^{i\infty}\frac{d\omega}{2i\pi}\frac{(-t)^\omega}{(-s)^{2-\epsilon+\omega}}\Gamma^2(\omega+1)\Gamma(2-\epsilon+\omega)\Gamma(-... | g17928 | [
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0.03304365649819374,
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0.012393093667924404,
-0.01... |
<p>Topological entanglement entropy (<a href="http://arxiv.org/pdf/cond-mat/0510613.pdf" rel="nofollow">http://arxiv.org/pdf/cond-mat/0510613.pdf</a>, <a href="http://arxiv.org/abs/hep-th/0510092" rel="nofollow">http://arxiv.org/abs/hep-th/0510092</a>) is usually calculated for surfaces with boundary. How would it look... | g17929 | [
0.01190235000103712,
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0.009783584624528885,
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0.0312669612467289,
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0.01847432367503643,
0.04112984612584114,
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0.04189860820770264,
-0.02847... |
<p>How can an object that's not accelerating cause another stationary object to move in a collision? This website: <a href="http://www.physicsclassroom.com/Class/momentum/U4l2a.cfm" rel="nofollow">http://www.physicsclassroom.com/Class/momentum/U4l2a.cfm</a>, says that a "rightward <strong>moving</strong>" 7-ball experi... | g17930 | [
0.04981960728764534,
0.031236562877893448,
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0.08268851041793823,
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0.009603164158761501,
-0.... |
<p>Leon Crux invented the concept of interlocking archimedes spirals that eventually led to the <a href="http://en.wikipedia.org/wiki/Scroll_compressor" rel="nofollow">scroll compressor</a> but intended it to be used as a rotary steam engine. However technological limitations of his day prevented the rotary steam engin... | g17931 | [
0.01880682073533535,
0.03571409732103348,
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0.001... |
<p>If gravity is a curvature of space time, and the event horizon is the collapse of this curvature on itself, then if the blackhole gets more matter after it is formed we should see no effect at all (i.e. increased gravity field) outside the event horizon, apart from the effect of matter collapsing before entering the... | g215 | [
0.014591659419238567,
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0.021766623482108116,
0.013714964501559734,
0.0377400778234005,
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-0.012388143688440323,
-0.042630888521671295,
0.02538881078362465,
0.... |
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