question stringlengths 37 38.8k | group_id stringlengths 2 6 | sentence_embeddings listlengths 768 768 |
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<p>I am an undergrad interested in Condensed Matter Theory. Particularly topological phases and systems exhibiting topological order. A potential research advisor doing a lot of work in Symmetry Protected Topological (<a href="http://en.wikipedia.org/wiki/Symmetry_protected_topological_order" rel="nofollow">SPT</a>) Ph... | g13880 | [
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<p>(Reformulation of part 1 of <a href="http://physics.stackexchange.com/questions/741/electromagnetic-field-as-a-connection-in-a-vector-bundle">Electromagnetic Field as a Connection in a Vector Bundle</a>)</p>
<p>I am looking for a good notation for sections of vector bundles that is both invariant <em>and</em> refer... | g13881 | [
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<p>The title says it all. I think this should be a pretty simple question but I just couldn't find the answer.</p>
<p>Ok -- I'll give a bit more context to my question. I'm encountering this in the context of general relativity, when we're trying to solve for the Schwarzschild solution. We write down a metric that res... | g13882 | [
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<p>I have 2 equation describing the alternating amperage $I_1$ and $I_2$. I need to get amount of these amperages.</p>
<p>My equations:
$$I_1=10\sin(\omega t+30)$$
$$I_2=20\sin(\omega t-50)$$</p>
<p>How can i make it? I forgot. </p>
<p>Thank you.</p> | g13883 | [
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<p>In this excerpt from Griffith's quantum mechanics book:</p>
<blockquote>
<h1>THE FREE PARTICLE</h1>
<p>We turn next to what should have been the simplest case of all: the free particle [$V(x) = 0$ everywhere]. As you'll see in a momentum, the free particle is in fact a surprisingly subtle and tricky example.... | g13884 | [
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<p>I was thinking about Einstein's train and platform experiment and was wondering if a beam of light experiences throw? Let me explain, if I take a water hose and point it straight out and then swing and stop my arm, the water will for a moment go past the end of the hose in the direction I was swinging my arm... </p>... | g13885 | [
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<p>Are valence electrons in non-polar molecules localized or delocalized?</p>
<p>I'm quite confused about the whole electron localization and delocalization business.
I'd love a simplified explanation that a high-schooler can understand.</p> | g13886 | [
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<p>I was thinking about this today...</p>
<p>Is it possible for a planet to be made almost entirely of water (H20)? I'm sure that other elements would be in the mix, but I mean almost entirely made of water. Even the core. No rocky interior covered by water.</p>
<p>If so, what would the core be like? I imagine th... | g434 | [
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<p>In quantum field theories (to be relativistic, (non-)relativistic statistical or whatever), we have the powerful diagrammatic approach at our disposal. Most of the time we can not sum up all the diagrams, only a sub-class of them. I was thinking of the Hartree-Fock ones to give an example, but they are several class... | g13887 | [
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<p>In special relativity one assume that spacetime
can be locally described by 4 coordinates, so it makes
sense to model it as a 4-dimensional manifold.</p>
<p>I had the impression that it is assumed that there is an atlas of
special charts called inertial reference frames.
Their transition maps are restrictions of af... | g13888 | [
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<p>My understanding of orbital mechanics is very limited, but as I understand geostationary satellite, they stay in place by having an orbital speed corresponding to the spot they're orbiting over.</p>
<p>So my basic intuition tells me that it's not possible to have a geostationary satellite over the poles, since they... | g13889 | [
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<p>If $ϕ^† ϕ$ is invariant under $SU(2) \times U(1)$, a Phys.SE <a href="http://physics.stackexchange.com/q/71481/2451">question</a> I recently posted, then does that mean $ϕ^† ϕ$ is invariant under rotations and translations?</p> | g13890 | [
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<p>I know that in principle, the Fock state is not the same as a product state because if it were, the photons would be uncorrelated. What I don't understand is, can it be expanded in product states? </p>
<p>For example, if two photons share the same mode, is the state $|2,0\rangle$ the same as the product $|1,0\rangl... | g13891 | [
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<p>If we have a linear molecule with a dipole moment $\mu$ in a static electric field $E$, the potential is given by $V = - \langle \mu,E \rangle$. What is the appropriate equation for the potential if we have a polarizability $\epsilon_1$ along the direction of the dipole moment?</p>
<p>If anything is unclear, please... | g13892 | [
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<p>I'm trying to understand mathematically that for the free expansion of an ideal gas the internal energy $E$ just depends on temperature $T$ and not volume $V$.</p>
<p>In the free expansion process the change in internal energy $\Delta Q = \Delta W = 0$, therefore by the first law $\Delta E=0$. Energy is a function... | g13893 | [
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<p>From what I understand acceleration does not cause a force, but rather forces cause acceleration, so if I have a ball moving with CONSTANT velocity, that hits a wall, then the wall must apply a force to deflect the ball (i'am assuming no force by the ball since it is moving with constant velocity), but where does th... | g13894 | [
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<p>This is kind of an elementary question, but since i cannot find a reliable source on this i wanted to ask what is the formula for energy conversion efficiency? I know efficiency is calculated as useful energy out/energy in, but i've been reading some papers on Q-switching, and some people have used Energy(pump)/Ener... | g13895 | [
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<p>Some author(in the paper of <a href="http://dx.doi.org/10.1119/1.15862" rel="nofollow">Evolution of the modern photon</a>) mentioned that photon cannot account for the zero intensity through two crossed polarizators by 90 degree. Why so? </p> | g13896 | [
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<p>The question can be formulated as following:</p>
<p>Suppose
$$\delta \int_{t_1}^{t_2}{[p\cdot \dot{q} - H(p,q,t) ]dt} = 0$$
$$\delta \int_{t_1}^{t_2}{[P\cdot \dot{Q} - K(P,Q,t) ]dt} = 0$$</p>
<p>in which $$P = P(p,q,t), Q = Q(p,q,t)$$ is an invertible transformation.</p>
<p>Can we prove that there must exist a $... | g13897 | [
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<p>In the book by Arthur Beiser, <a href="http://www.goodreads.com/book/show/1722720" rel="nofollow"><em>Concepts of modern physics</em></a>, in the chapter LS coupling there is this image: </p>
<p><img src="http://i.stack.imgur.com/BTWyz.png" alt="enter image description here"></p>
<p><strong>QUESTION:</strong></p>
... | g13898 | [
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<p>In my investigation, tires will quickly get bald if we ride a motorcycle at high speed. Is it correct? How to explain it in physics? Does the friction increase at high speed rotation?</p>
<p>Update: The word "quickly" means that the tire gets bald with less distance traveled. </p> | g13899 | [
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<p>According to this and other similar papers, <a href="http://www.nature.com/nature/journal/v352/n6337/abs/352699a0.html" rel="nofollow">http://www.nature.com/nature/journal/v352/n6337/abs/352699a0.html</a>, adding a current-carrying path can increase the voltage drop across a circuit. What is the simplest example of ... | g13900 | [
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<p>I am imagining an unusual experiment which will require intense beams of either protons or neutrons. The experiment would work better with neutrons, but neutron sources are much <strike>weaker</strike> messier so I am considering both. I am interested in beams of almost any non-relativistic energy. I am not sure ... | g13901 | [
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<p>I was researching about the heat-death of the universe, and I was wondering if my understanding of it so far is factual to the theory?</p>
<p>However, the 3rd Law of Thermodynamics prevents the universe’s entropy from reversing because that law states that the temperature cannot equal 0 Kelvin. The heat of the univ... | g13902 | [
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<p>I was given with the position state of hydrogen atom:</p>
<p>$$
R_{21} =\left(\sqrt{\frac{1}{3}}Y^0_1 + \sqrt{\frac{2}{3}}Y^1_1\right)
$$</p>
<p>I am getting confused about getting the expectation value of energy, I know from the form that:</p>
<p>$$ R_{21} \Rightarrow n=2, l=1$$</p>
<p>according to <a href="htt... | g13903 | [
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<blockquote>
<p>Say you have a uniformly charged straight wire of length $2L$ going from $-L$ to $+L$ along the $z$ axis with its midpoint located at $z=0$. What is the electrostatic potential, in cylindrical coordinates, for points in the midplane of the wire ($x,y$ plane)? From this electric potential, calculate th... | g13904 | [
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<p>When detecting radio waves in space, we use very large telescopes or arrays of telescopes. But according to QM, aren't photons point particles when measured? Does a photon with a large wavelength have a wider probability distribution with regard to where it can be expected to be detected? Is that why photons with... | g13905 | [
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<p>It is better for you to have studied "Feynman lectures on Physics Vol.3", because I cannot distinguish whether the words or expressions are what Feynman uses only or not and in order to summarize my questions here, I have to just quote the contents of the book.</p>
<p>However, one thing I notice is that "base state... | g13906 | [
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<p>Pair production is where an energetic photon on its interaction with strong electric field surrounding a nucleus produces electron-positron pair. Annihilation of matter is its converse where an electron-positron pair produces two photons on interaction with nucleus.</p>
<p>But how do these happen? I mean, Why do th... | g13907 | [
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<p>I was reading that a new type of refrigerator might reach a coefficient of performance (COP) of 10. This seems quite the achievement and the authors state that their approach might achieve a Carnot efficiency of 75%. (I could not get hold of the original source as it is a part of an expensive book series "Zimm C, Ja... | g13908 | [
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<p>If I am given a system, which I might have to describe using a generalized entropy, like the "q-deformed" Tsallis entropy, do I have to fit q from experiment or might I know it beforehand?
How do I know the parameter q and/or how can I possibly obtain the degree of non-extensitivity via experiment?
How can I measu... | g13909 | [
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0.006915535777807236,
0.06418850272893906,
0.025377750396728516,
0.016814127564430237,
-0.05734938383102417,
0.006465662736445665,
0.019309567287564278,
0.03... |
<p>I have looked around, and I will admit that I'm a bit lost on the definitions.</p>
<p><a href="http://en.wikipedia.org/wiki/Pressure" rel="nofollow">Wikipedia</a>'s opening reads:</p>
<blockquote>
<p>Pressure (symbol: P or p) is the ratio of force to the area over which that force is distributed.</p>
</blockquot... | g13910 | [
0.06553812325000763,
0.018154414370656013,
-0.03712907433509827,
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0.0470646433532238,
0.021631436422467232,
0.008446754887700081,
0.05404747650027275,
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-0.026529354974627495,
0.03337422013282776,
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0.009802903980016708,
-0.00... |
<p>Whether is it our solar system or a whole galaxy, there is usually a massive object (star or black hole) at the centre with gas and objects rotating around it. </p>
<p>The gravitational effect of the star/black hole extends uniformly (more or less) in every direction in 3d. Why does matter tend towards a single pla... | g13911 | [
0.01959049142897129,
-0.014315353706479073,
-0.0043624574318528175,
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0.0859798714518547,
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0.023557303473353386,
0.0496160052716732,
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-0.0354616679251194,
0.052885204553604126,
-0.03151081129908562,
0.04569724202156067,
0.0112138... |
<p>The stress applied on a rod is linearly proportional to its strain. But shouldn't the opposite be true? I mean if you pull particles further apart doesn't the force they apply on each other decrease because the distance between them increases? Kinda like gravity?</p> | g13912 | [
0.039525315165519714,
0.04229115694761276,
0.0015079296426847577,
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<p>Naively, I would assume that a topological invariant remains invariant under continuous deformations of whatever space the invariant belongs to. In the case of topological insulators, this space is the space of parameters characterizing the material and its environment. If we consider the magnitude of a magnetic fie... | g13913 | [
0.08018986880779266,
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0.02510356716811657,
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0.013769333250820637,
0.004446420818567276,
-0.032... |
<blockquote>
<p>A rotating charge such as the electron classically orbiting around the nucleus, will constantly lose energy in
form of electromagnetic radiation. </p>
</blockquote>
<p>I asked my teacher about how this radiation is created from the charge. My teacher said that energy is usually lost by the mechan... | g13914 | [
0.013030062429606915,
0.0165475495159626,
0.006112879142165184,
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<p>Suppose that particles of two different species, A and B, can be chosen with
probability $p_A$ and $p_B$, respectively. </p>
<p>What would be the probability (and distribution) $p(N_A;N)$ that $N_A$ out of $N$ particles are of type A? </p>
<p>I'm trying to apply the Binomial distribution here but am bothered by th... | g13915 | [
0.01812523975968361,
0.025552742183208466,
0.011099062860012054,
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0.054648205637931824,
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0.02467821165919304,
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<p>The cosmic microwave background that we observe uniformly around us is usually explained by assuming that our universe is the surface of a four dimensional sphere. That way the uniformity makes sense since there is no center. My question is if this is true then what is the explanation that describes the fact that th... | g13916 | [
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<p>I understand a problem like this has already been asked, but I have not found an answer that makes it clear. A force is applied to a box on a table(lets ignore friction), and the box moves with some constant velocity. In this case, acceleration is equal to zero. The net force does not. How can we explain this?</p>
... | g13917 | [
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<p>While studying thermal physics at school, I have been taught that solids simply have more potential energy than the liquids and gases. Note that it was said that this potential energy is due to the intermolecular bonds between the atoms. However, my intuition makes me doubt this, why would there be more potential en... | g13918 | [
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<p>I am having trouble with the meaning of the $k$ vectors in an energy diagram.
If I want to populate some band, let say using a laser, what will be the significance of $k$?
Does it correspond to the polarization angle with respect to particular planes? </p> | g13919 | [
-0.045215677469968796,
0.00004785677811014466,
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0.03966866061091423,
0.04051811993122101,
0.0021820631809532642,
0.05593487247824669,... |
<p>The free energy, $F$ of a thermodynamic system at a given temperature $T$, is defined as,
\begin{equation}
e^{-\beta F} = \mathcal{Z} = \sum_{\{configuration\}} e^{-\beta E(configuration)
}
\end{equation}
where $\beta = 1/k_BT$ and $E$ is the energy of a certain configuration.</p>
<p>Now my question is:</p>
<p><s... | g13920 | [
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0.004075655713677406,
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0.006838588044047356,
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... |
<p>Find your average speed if you go 15m/s for 1000 m and then 30m/s for 1000 m</p>
<p>I understand that average speed is total distance / total time. The distance for this problem would be 2000m travelled. How would I figure out the total time?</p> | g13921 | [
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<p>consider you are in a train that moves with a speed of $c/4$. A bulb is hanged from the ceiling. A light beam leaves the bulb downward. Exactly under the bulb on the floor is a detector. According to the principle of relativity the light will not strike the detector in the reference frame of a non-moving observer (... | g13922 | [
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<p>Some planetary orbits occasionally can appear to move backwards to an observer on the Earth? </p>
<p>Does anyone know concise, clear, web-based visualizations, animations or tutorials that clearly show how this might come about?</p>
<p>I have difficulties imagining it "in my head". A link to an animated solar syst... | g13923 | [
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<p>I can't understand something about emissivity. Emissivity is defined as the ratio of the radiant energy of an object, to radiant energy of blackbody at a temperature $T$. So, The vegetation has approximate emissivity of $0.99$ and concrete smaller than this like $0.95$. But in thermal images vegetation appears dark... | g13924 | [
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0.00702206464484334,
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-0.0095... |
<p>I am writing a lab report for class on PNMR experiment that we did. <em>How come in this experiment we don't worry about the electron spins in our sample?</em> Aren't the electrons affected by the PNMR machine as much as the protons? Isn't there electron proton spin interactions? For some reason, the lab only talks ... | g13925 | [
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0.00... |
<p>I am not comparing <em>passive</em> gravitational mass with rest inertial mass. Is there an evidence in Standard Model which says that <em>active</em> gravitational mass is essentially mass assigned by Higgs mechanism.</p> | g13926 | [
0.035815853625535965,
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<p>With the discovery of the Higgs Boson, some have been calling it the <a href="http://www.theatlantic.com/technology/archive/2012/07/why-the-higgs-boson-discovery-is-disappointing-according-to-the-smartest-man-in-the-world/259468/" rel="nofollow">end of experimental particle physics for our generation</a>, due to the... | g13927 | [
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0... |
<p>Maybe some of my assumptions here are basically wrong, but isn't it true that</p>
<ul>
<li>pion is the "mediator" for the strong force field. </li>
<li>the quantum field theory basically says that there are no fields, instead all forces are caused by interchanging of mediator particles all the time.</li>
</ul>
<p>... | g13928 | [
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0.017685... |
<p>We know that in high temperature, resistivity in metals goes linearly with temperature. As temperature is lowered, resistivity goes first as $T^5$ due to "electron-phonon" interaction, and then goes as $T^2$ as temperature is further lowered due to "electron-electron" interactions. </p>
<p>My question is, is there ... | g13929 | [
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0.... |
<p>Let's have generating functional in path integral form for gauge $SU(n)$ theory with interaction:
$$
\tag 1 Z[J] = \int DB D\bar{\Psi}D\Psi D\bar{c}Dc e^{iS}.
$$
Here
$$
S = S_{YM}(B, \partial B) + S_{M}(\Psi , D\Psi) + S_{ghosts} + \int d^{4}x \left[-\frac{1}{2\alpha}(\partial_{\mu}B^{\mu}_{a})^{2} + \sum_{\varphi}... | g13930 | [
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0... |
<p>If a thin sheet of some material in which a slit is cut is immersed in a liquid and removed, a liquid film (bridge) stays in the slit. Is it possible to calculate the shape of the film if the properties of the liquid and the dimensions of the slit are known?</p> | g13931 | [
0.038963232189416885,
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<p>What is wrong with this form of the <a href="http://en.wikipedia.org/wiki/Electromagnetic_induction" rel="nofollow">Maxwell-Faraday equation</a>?</p>
<p>$$\oint \vec{E}\ \partial \vec l= \bigcirc \hspace{-1.4em} \int \hspace{-.6em} \int \frac{\partial \vec B}{\partial t}$$</p>
<p>"Line integral of the electric fie... | g13932 | [
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0.0... |
<p>I have three questions about electromagnetic waves and was wondering whether anybody here could comment on these things:</p>
<p>Wikipedia says that there are no longitudinal EM waves, although TM and TE waves exist. How can I see that an EM wave can never be purely longitudinal?</p>
<p>Does it always hold that the... | g13933 | [
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0.0648434... |
<p>A $Z_2$ gauge theory with Ising matter field on a 2-dimensional square lattice has the Hamiltonian</p>
<p>\begin{equation}
H=-t\sum_{\vec r,j}\sigma_j^x(\vec r)-g\sum_{\vec r}\sigma^z_1(\vec r)\sigma^z_2(\vec r)\sigma^z_3(\vec r)\sigma^z_4(\vec r)-\lambda\sum_{\vec r}\tau^x(\vec r)-\mu\sum_{\vec r,j}\tau^z(\vec r)\... | g13934 | [
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0.0... |
<p>Context is 1D Ising model. Metropolis algorithm is used for simulate that model. Among all possible spins configurations (states) that algorithm generates only states with the desired Boltzmann probability. </p>
<p>Algorithm chooses spin at random and makes a trial flip. If trial satisfies certain conditions relate... | g13935 | [
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<p>I have been asked to find a way to calculate the amount of time that a flight takes during night time.</p>
<p>So far, I have the departure latitude and longitude and the time of takeoff, the arrival latitude and longitude and the time of landing. I can easily calculate the sunset and sunrise time at the departure l... | g13936 | [
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<p>Why do we have so many dualities in string theory? Is there a reason for that?</p> | g13937 | [
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<p>We suppose for semplicity to have a 1D oscillator, but this is a question abaout the general CCR algebra in oscillators, second quantization, quantum field theory etc.
We know coherent states are a non orthonormal base and are a overcomplete base.
We know them are given from $A |\alpha>=\alpha |\alpha>$. wher... | g13938 | [
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... |
<p>Well, it does according to <a href="http://arxiv.org/abs/1102.3913" rel="nofollow">this preprint</a> for certain scales.</p>
<p>What would be a simple way to explain MOND to a layman?</p>
<p>Does it ignore mainstream physics? How much?</p> | g13939 | [
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<p>Why are so many condensed matter phenomena so sensitive to impurities? In fact, quite a number of them depend upon impurities for their very existence!</p> | g13940 | [
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0.04118476063013077,
-0.018446721136569977,
0.02... |
<p>Why, if the Schwarzschild metric is a vacuum solution ($T_{\mu\nu}=0$) , do textbooks state that $T=\rho c^{2}$ when approximating Poisson's Equation from the Einstein Field Equations? </p>
<p>Thank you.</p> | g13941 | [
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<p>Just what the title states; and this isn't an original question ...</p>
<p>On full-moon, moonlight is almost as bright as mid-dawn ; yet there is hardly any colour visible. This is not the case with sunlight. </p>
<p>I'm curious to know why this is the case</p> | g13942 | [
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0... |
<p>I'm having a problem starting and solving the following problem:</p>
<p><img src="http://i.stack.imgur.com/QX76Y.png" alt="Fluid Mechanics"></p>
<p>My attempt at the solution was to realize you need to balance the upward forces with those of the downward forces in which case you have a buoyant force, for the upwar... | g13943 | [
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<p>The S-matrix of superstring theory will have finitely many massive particles which decouple in the asymptotic future/past and massless particles like gravitons, photons and dilatons. Typically, there will be an infinite number of massless "soft quanta". In the far future/past, all of these dressed particles will dec... | g13944 | [
0.020601628348231316,
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<p>Exactly what paper by W. Pauli introduced the idea for the existence of a neutrino and how was its existence confirmed experimentally (who did that and in what paper)?</p> | g13945 | [
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<p>I was told by my professor that the current in a purely LR Circuit with at initial state (JUST after closing the switch) is zero. Can you please help me understand why it that so? </p> | g13946 | [
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<p>I am designing a LED dimmer using software-controlled Pulse Width Modulation, and want to know the minimum PWM frequency that I must reach to make that LED dimming method indistinguishable from variable DC current.</p>
<p>To dim to X% power, the led will be fully on for X% of the PWM period, and fully off for the r... | g13947 | [
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0.005492975935339928,
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<p>I shine laser line in front of one side of multimode optical fibre.Light coming out of other side is projected into wall.Whether the intensity pattern seen on wall is same as the mode of propagation of light pattern drawn on text books?</p> | g13948 | [
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<p>I have a few basic questions about the Pauli-Lubanski spin 4-vector S.</p>
<ol>
<li><p>I've used it in quantum mechanical calculations as an operator, that is to say each of the components of S is a matrix operator that operates on an eigenvector or eigenspinor. But my question is about the utility of S in a classi... | g13949 | [
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<p>This is my first question on the Physics portion of Stack Exchange. I was hoping to get some light on the topic of gravity. I don't have much background knowledge of physics so I might as well start here.</p>
<p>I have a few planet and gravity related questions:</p>
<p><strong>1).</strong> Does planetary gravity... | g13950 | [
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<p>According to Faraday's law, changing magnetic flux induces an electric field. Is that electric field always circular? </p> | g13951 | [
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<p>Look at <a href="http://www.modernrelativitysite.com/chap11.htm" rel="nofollow">equation 11.2.17 in this page</a>. The expression is:</p>
<p>$$ T = 10^{-5} \text{K m} \frac{\xi}{\frac{GM}{c^2} \lbrace \frac{GM}{c^2} + \xi \rbrace - e^2 }$$</p>
<p>where</p>
<p>$$ \xi = (r_s^2 - a^2 - e^2)^{1/2}$$</p>
<p>and the u... | g13952 | [
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0.021879... |
<p>I encountered a physics problem which inquired about a ball rolling inside a parabolic bowl (i.e. a bowl where any cross section through the vertex would make a parabolic shape given by $y = kx^2$). The ball was to be released from some initial height $z_0$ and allowed to roll back and forth inside the bowl.</p>
<p... | g13953 | [
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<p>I really need some assistance setting up this problem. any assistance would be a Godsend:</p>
<p>a uniform heavy chain of length <code>a</code> initially has length <code>b</code> hanging off of a table. The remaining part of chain a - b, is coiled on the table. Show that if the chain is released, the velocity of t... | g13954 | [
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<p>I found recently that water fills a bottle quicker through only observation if I hold the tube away from the filling water than if I leave the tube inside the bottle. why does that happen? does potential energy have anything to do with this? <img src="http://i.stack.imgur.com/VUXJU.jpg" alt="enter image description ... | g13955 | [
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<p>If I were on one side of the room and moved at the speed of light to the other side of the room, to an observer it would appear that I teleported. If time stops at that speed, it would be instantaneous but we know that light is not instantaneous (see light years).
So I'm curious what the difference between traveling... | g13956 | [
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<p>I am in undergraduate quantum mechanics, and the TA made an off-hand comment that currently no one knows how to describe fundamental particles with spin > 1 without supersymmetry. I was curious and tried to look up info on this, and wikipedia does make some comments about troubles with spin 3/2
<a href="http://en.w... | g13957 | [
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<p>I know from Carroll that the integration in GR is basically a mapping from n-form to the real number. And it's given that </p>
<p>$$d^nx=dx^0\wedge\ldots\wedge dx^{n-1}=\frac{1}{n!}\epsilon_{\mu_1\ldots\mu_n}dx^{\mu_1}\ldots dx^{\mu_n}$$</p>
<p>Now, I have an expression that is given in spherical coordinate system... | g13958 | [
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<p>I am reading <a href="http://www.ocr.org.uk/download/sm/ocr_13461_sm_gce_unit_g484_csa_m.pdf">a document</a> and in answer to the question <strong>State Newton’s second law of motion</strong> the candidate answers that <strong>The force acting on an object equals the rate of change of momentum of the object.</strong... | g13959 | [
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<p>In many books the $\phi^4$ model can produce a topological soliton called kink. Are they right? In the case of sine-Gordon model you can have a topological soliton due to you can express the Lagrangian in terms of two scalar fields taking values in a circle. As the field is constrained on a manifold the model could ... | g13960 | [
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<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/8441/what-is-a-complete-book-for-quantum-field-theory">What is a complete book for quantum field theory?</a> </p>
</blockquote>
<p>I am looking for good books that deal with Quantum Field theory starting... | g282 | [
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<p>I learned about the coronal discharge, and the common explanation is because the electric field is strong where radius of curvature is small. But I haven't found anything yet that explains why electrons like to crowd at the peaks, and and escape from the holes. </p>
<p>My intuition suggests electrons try to distrib... | g13961 | [
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<p>I have read <a href="http://en.wikipedia.org/wiki/Closure_phase" rel="nofollow">this page</a> on closure phase and could not understand the following:
\begin{align}
\psi_1 & = \phi_1 + e_B - e_C \\
\psi_2 & = \phi_2 - e_B \\
\psi_3 & = \phi_3 - e_C.
\end{align}
If the error in $\phi_3$ is $e_C$ and the e... | g13962 | [
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<p>What is the theoretical difference between the physical elementary interaction that causes an e+ to attract an e− when they exchange a virtual photon? Why is this exchange different from an e-e- scattering (which produces repulsion)?<br>
This question is related to but more specific than the recently posted <a href=... | g13963 | [
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<p>Suppose we have a spacecraft just inside the event horizon of a black hole, struggling to escape, but slowly receding into it. Another (bigger) black hole expands until its event horizon includes the spacecraft as well. This pulls both the black hole and space-craft into itself. As the spacecraft is closer to the se... | g444 | [
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<p>I'm currently reading papers about the effect of repeated measurements, such as <a href="http://prl.aps.org/abstract/PRL/v90/i6/e060401" rel="nofollow">"Purification through Zeno-Like Measurements"</a>, <a href="http://arxiv.org/abs/quant-ph/0301026" rel="nofollow">arXiv:quant-ph/0301026</a> (DOI: 10.1103/PhysRevLet... | g13964 | [
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<p>Consider a ring of radius $R$, and charge density $\rho$. What will be the potential energy of the ring in its self field?</p>
<p>The best I can do:
$$dq = \rho R \cdot \, d \alpha $$</p>
<p>$$E_p = 2 \pi R \cdot 2 \int_{0}^{\pi - \delta \alpha} \frac{\rho^2 R^2}{r(\alpha)} \, d\alpha$$</p>
<p>where</p>
<p>$$r(\... | g13965 | [
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-0.03882... |
<p>Most of the literature says that for a quenched average over disorder, an average over the log of the partition function must be taken:</p>
<p>\begin{equation}
\langle \log Z \rangle,
\end{equation}</p>
<p>while for the annealed average, it's</p>
<p>\begin{equation}
\langle Z \rangle.
\end{equation}</p>
<p>But a... | g13966 | [
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<p>To be clear, this example can't apply to the Solar System, since the barycenter is within the Sun, similarly the Earth/Moon system's barycenter is within the Earth.</p>
<p>But, given a system of gravitationally attacting masses revolving about a barycenter that is not contained within any of the masses, i.e. a bary... | g13967 | [
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<p>I want to know more about optimising an air gap between two surfaces, such as window panes or a building's walls.</p>
<p>I was taught that as a general rule, a 6cm air gap is the optimum. Any larger and convection counters the effectiveness. But something tells me this is hardly an accurate figure!</p>
<p>Can anyo... | g13968 | [
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<p>I recently studied Laplace's equation and numerical methods for solving it, and so I'm trying to simulate an electron gun.</p>
<p><img src="http://i.stack.imgur.com/Mwsk2.png" alt="Schematic of an electron gun"></p>
<p>(assuming cylindrical symmetry on the Wehnelt, anode, and beam.) The setup is simple. The filame... | g13969 | [
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0.007966127246618271,
0.... |
<p>When a shuttle is in orbit, it is essentially rotating around the "centre" of the Earth at a great speed. So why does there seem to be no centrifugal force sticking them to the 'ceiling' of the shuttle?</p>
<p>Is it because the shuttle is not actually being rotated around a point but rather continuously falling or ... | g13970 | [
0.01697402074933052,
0.03964134305715561,
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<p>Can Heisenberg's Uncertainty principle be rewritten in terms of energy density</p>
<p>writing
$$\Delta E \Delta T \geqslant \hbar/2$$
in factors of energy density
$\Delta \sigma \text{ }= \frac{3\Delta E}{4\pi r^3}$</p>
<p>I get
$$\Delta \sigma \frac{3\text{$\Delta $T}}{4\pi r^3} \geqslant \hbar/2$$</p>
<... | g13971 | [
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<p>If you consider big bang. According to that What's left at the center of universe where the Big bang occured?</p> | g13972 | [
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0.012913... |
<p>I know that the relativistic formulae for energy and momentum are:</p>
<p>$E = \gamma mc^2$ and $\textbf{p} = \gamma m\textbf{v}$;</p>
<p>Can we derive these formulae?</p>
<p>If yes, where from?</p> | g13973 | [
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<p>Consider the following operator $\hat{x}=i\hbar \frac{\partial}{\partial p}$.</p>
<p>I am trying to show that the eigenfunctions of $\hat{x}$ are not square-normalizable. I am interested in doing so since theoretically, we notice that the eigenfunction of the momentum operator $\hat{p}=\frac{\hbar}{i}\frac{\partial... | g13974 | [
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0.... |
<p>When a single-tone continuous modulating signal modulates a sinusoidal carrier, isn't the modulated wave periodic? If so, can't we apply fourier series and determine the harmonic frequency components instead of finding the frequency components using fourier transform?</p> | g13975 | [
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0.... |
<p>What are proven procedures for preparing a part that comes fresh out of the workshop for ultra-high vacuum (UHV) and extremely-high vacuum (XUV)? </p> | g13976 | [
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0.017193952575325966,
0.006708681117743254,
-0.... |
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