question stringlengths 37 38.8k | group_id stringlengths 2 6 | sentence_embeddings listlengths 768 768 |
|---|---|---|
<p>Hi I've done an experiment in physics using a basic circuit. Can anybody explain how come the data logging equipment I was using continued to register a current when there isn't a positvie voltage in the circuit. </p> | g18025 | [
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<p><strong>transition probabilites</strong> of atomic systems prone to some time-varying electromagnetic field are very often calculated using <strong>perturbation theory</strong> leading to expressions including the vector potential $\mathbf{A}$. This approach seems to be very complicated and I am wondering:</p>
<blo... | g18026 | [
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<p>Why and how are electrons get excited and what happen inside an atom when electrons get excited?</p> | g18027 | [
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<p><strong>1. The problem statement, all variables and given/known
data</strong></p>
<p><em>Consider a time-dependent harmonic oscillator with
Hamiltonian</em></p>
<p>$$\hat{H}(t)=\hat{H}_0+\hat{V}(t)$$</p>
<p>$$\hat{H}_0=\hbar \omega \left( \hat{a}^{\dagger}\hat{a}+\frac{1}{2} \right)$$</p>
<p>$$\hat{V}(t)=\lamb... | g18028 | [
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<p>Say I have a charge of +q and -q on the positive and negative terminals of a battery. If I connect wires to each terminal, but don't connect the wires (essentially creating an open circuit), the charges move around to neutralize the field in the wire.</p>
<p>During this transient state, charges move around. Would t... | g18029 | [
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<p>The "theorem" that I can "just" separately deal with orthogonal quantities (like horizontal and vertical force or velocity, etc), I never found explicitly mentioned, but just implicitly in the solution of exercises. Why?</p>
<p>I do not think that this is obvious.</p>
<p>For example projectile motion exercises are... | g18030 | [
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<p>Which symmetry is associated with conservation of flux (e.g., in electromagnetism)?</p>
<p>For example, when working with Gauss's law in electromagnetism, net flux through an arbitrary volume element remains unchanged when the net charge is unchanged. </p> | g18031 | [
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<p>Background:</p>
<p>In Bose-Einstein stats the quantum concentration $N_q$ (particles per volume) is proportional to the total mass M of the system:</p>
<p>$$ N_q = (M k T/2 \pi \hbar^2)^{3/2} $$
where k Boltzmann constant, T temperature</p>
<p>Questions:</p>
<p>A) For a B-E system "entirely of Photons" - what... | g18032 | [
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<p>Maxwell derived the shape of the probability distribution of velocity of gas particles by starting with just two assumptions.</p>
<p>These are:</p>
<ol>
<li><p>The probability distribution is rotation invariant.</p></li>
<li><p>The components (of velocity of a gas particle) in the direction of the coordinate axes ... | g18033 | [
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<p>I have this assignment:</p>
<blockquote>
<p>Show that super-dense coding protocol with the key in the state
$\frac{|00⟩⟨00|+|11⟩⟨11|}{2}$ is equivalent (in a sense of
transmission rate and security) with classical one-time pad.</p>
</blockquote>
<p>I understand that super-dense coding protocol is a <em>codin... | g18034 | [
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<p>My sir started a new chapter "magnetism and matter". Sir said that iron fillings form a particular arrangement when sprinkled around a magnet. I saw the figure in my book where it was shown the arrangement of some iron fillings at a distance from the magnet. I didn't get much convinced. If a magnet, which can pull i... | g18035 | [
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<p>A two-dimensional spinless non-relativistic p+ip superfluid undergoes a quantum phase transition between the BCS (weakly-coupled) and BEC (strongly-coupled) regimes. This transition is driven by massless fermions and believed to be of the third order. Most easily it can be shown, but relating the problem to the Dira... | g18036 | [
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<p>Could anyone explain to me what "quantize" means in the following context?</p>
<blockquote>
<p>Quantize the 1-D <a href="http://en.wikipedia.org/wiki/Harmonic_oscillator" rel="nofollow">harmonic oscillator</a> for which
$$H~=~{p^2\over 2m}+{1\over 2} m\omega^2 x^2.$$</p>
</blockquote>
<p>I understand that the... | g18037 | [
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<p>Suppose we have two objects sitting on two side of a lever, and the lever also has a mass, and those objects have masses. Then how we can balance $\sum τ$?</p>
<p>This is what I have done:</p>
<p>$$\begin{multline}M_\text{heavier}\times g\times D_\text{from center to heavier} - M_\text{lighter}\times g\times D_\t... | g18038 | [
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<p>Consider a gedanken(=thought) experiment where I am tracking the motion of the electron in a hydrogen atom with a time resolution of (say) $\Delta t = 10^{-20}$ seconds. Further assume (for simplicity) that the proton is stationary. In quantum field theory we talk about forces carried by virtual particles. Therefore... | g18039 | [
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<p>For $a$ being positive what are the quantisation conditions for an exponential potential?</p>
<p>$$ - \frac{d^{2}}{dx^{2}}y(x)+ ae^{|x|}y(x)=E_{n}y(x) $$
with boundary conditions $$ y(0)=0=y(\infty) $$
I believe that the energies $ E_{n} $ will be positive and real </p>
<p>I have read a similar paper:</p>
<block... | g926 | [
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<p>If walking is a result of the reaction to a kick backwards to the ground (reaction being friction), it appears that it should be true that the kick will have to be less than the kinetic friction (which is less than the static friction threshold = $\mu$mg) or the acceleration will never be more than $\mu$g. What happ... | g18040 | [
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<p>As per in the title. If it turns out that neutrinos do travel faster than the speed of light, how will the success of special relativity be explained? My apologies if this has been asked before; I've just browsed through few questions, and I couldn't find one that matches (although it was slightly touched on in one ... | g18041 | [
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<p>I just finished reading Feynman's <em>Lectures on Physics</em> vol.I, §34-9: "The momentum of light". The author explains that there is a relation between the wave 4-vector $k^{\mu}$ and the energy-momentum 4-vector $p^{\mu}$ of an EM wave, namely </p>
<p>$$p^{\mu}=\hbar k^{\mu}, $$
or equivalently
$$\tag{deB}W=\hb... | g18042 | [
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<p>Question 1: What is the status of string random matrix models (~ triangulated random surfaces) with c>1?</p>
<p>In my limited search, I have just come across a few papers by Frank Ferrari (in 2000-2002) on this. But, they applied, if I understand correctly, to a few cases with some specific kind of singularities in... | g18043 | [
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<p>Assume we look at an interaction between 2 fermions</p>
<p>$V \sum_{k_i,k_j,k_m,k_n} c_{k_i}^\dagger c_{k_j}^\dagger c_{k_m} c_{k_n} \delta_k $</p>
<p>where $\delta_k$ conserves momentum. We can directly write down a few terms from the sum</p>
<p>$ ... + \underbrace{c_{k_1}^\dagger c_{k_2}^\dagger c_{k_3} c_{k_4}... | g18044 | [
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<p>Okay this is probably a stupid question but here goes: </p>
<p>We know that molecules in a liquid are attracted from all the molecules around it so there is no net attraction. Well, then how do the molecules at the surface exist because there are only molecules below it and not above it? Won't they accelerate downw... | g18045 | [
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<p>Two blocks are pulled across a frictionless surface by a $240\ N$ force, as shown in the diagram below: $60\ kg$ - - - cord - - - $20\ kg$ → $240\ N$. If the blocks are accelerating at $3\ m/s^2$ what is the tension of the cord in between the two blocks?
So I don't really have a strategic approach to this problem. ... | g18046 | [
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<p>I found a problem that says:</p>
<blockquote>
<p>Show by direct substitution that $R_{10}$ is a solution of Schrödinger's radial equation.</p>
</blockquote>
<p>AFAIK Schrödinger's radial equation is</p>
<p>$\frac{-\hbar^2}{2m}[\frac{d^2}{dr^2}+\frac{2}{r}\frac{d}{dr}-\frac{l(l+1)}{r^2}]R+E_p(r)R=ER$</p>
<p>and... | g18047 | [
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<p>I found this formula for a <a href="http://en.wikipedia.org/wiki/Polytrope" rel="nofollow">polytropic process</a>, defined by $PV^n = {\rm constant}$, in a book:</p>
<p>$$C = \frac R{\gamma-1} + \frac R{1-n} $$
where $C$ is <a href="http://en.wikipedia.org/wiki/Specific_heat" rel="nofollow">molar specific heat</a> ... | g18048 | [
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<p>In replying to a <a href="http://physics.stackexchange.com/questions/39216/why-are-we-talking-about-space-curvature-as-if-we-know-what-space-is">recent question</a> I stated:</p>
<blockquote>
<p>Gravitational waves have not been yet experimentally observed so as to have their velocity measured.</p>
</blockquote>
... | g18049 | [
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<p>A wine glass filled with water (approximately half or a quarter), when you use a wet finger and rub the top of the wine glass, the wine glass will produce a sound. I heard that it is because of the "stick and rub" effect ... Can you explain this effect or other principal that cause this sound to be produced?
how mu... | g970 | [
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<p>I was reading some QFT notes and there is one point that I don't understand, they are justifying why we need QFT saying that the number of particles is not preserved once we consider special relativity. </p>
<p>For example, if a particle is in a box of side $L$, then by Heisenberg's principle: $\Delta p \geq h/L$ a... | g18050 | [
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<p>This question is based on highly intuitive picture of the <a href="http://en.wikipedia.org/wiki/Aharonov%E2%80%93Bohm_effect" rel="nofollow">Aharonov-Bohm effect</a> (perhaps a naive one). </p>
<p>From what I have read, the current explanation of the AB effect is that although the electron passing through the two s... | g18051 | [
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<p>In a textbook, I found this relation for eigenvalues of total angular momentum:
$$(L^2)_{mn} = \langle l,m \rvert L^2 \lvert l,n\rangle = \hbar^2l(l+1)\delta_{mn}$$</p>
<p>What is the $\delta_{mn}$ refer to? The book does not explain.</p>
<p><a href="http://books.google.com/books?id=frvBRTnWpEIC&pg=PA63&lp... | g18052 | [
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-0.0108250193297863,
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0.03427482023835182,
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<p>We are looking for a publication or website that explains the Standard Model in terms of Hilbert space and Lie algebra.</p>
<p>We are reading Debnath's <em>Introduction to Hilbert Spaces and Applications</em> and Iachello's <em>Lie Algebras and Applications</em>. Is there a book or website that combines the two app... | g18053 | [
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<p>I was browsing Etsy today and came across <a href="http://www.etsy.com/listing/82376489/dice-1-die-3d-printed-steampunk-style" rel="nofollow">this</a>.</p>
<p>What tests are there to see if the dice are usable, ie, if one side isn't favored over another, and if all sides are balanced?</p>
<p>Would this just be to ... | g18054 | [
-0.008239206857979298,
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0.052759427577257156,
... |
<blockquote>
<p>Consider two non-interacting Fermions (half-integer spin) confined in
a 'box'. Construct the anti-symmetric wavefunctions and compare the
corresponding ground-state energies of the two systems; one with
particles of identical spin and the other with particles of opposite
spin.</p>
</blockquote... | g18055 | [
-0.03586921840906143,
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<p>For training students in <strong>competitive exams & physics olympiads</strong>, I want to illustrate deeper meanings in problem solving through diagrams.</p>
<p>I have my teaching material hand drawn in OneNote. I want to create some professional quality <strong>colorful diagrams</strong> that we find in <stro... | g18056 | [
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<p><a href="http://burro.cwru.edu/Academics/Astr221/StarPhys/coulomb.html" rel="nofollow">This web page</a> says that only <strong>3-10 keV of energy</strong> is required to break the Coulomb barrier for colliding hydrogen nuclei.</p>
<p>Pretty far from what originally said.</p>
<p>Is this true? Does this have someth... | g18057 | [
0.02142443135380745,
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<p>What is the simplest simulatable model giving our rotating earth its 3 circulation cells (Hadley, Ferrel, Polar)?
The model should also show 1 circulation cell if the earth's rotation were stopped (or in a case like Venus), and
no circulation at all if radiation were somehow uniform to/from the earth (instead of tru... | g18058 | [
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<p>If I have a reaction (shown below), and I'm supposed to work out what the products will be, what would the lepton neutrino $\nu$ be? e.g electron neutrino:
$$ \nu + p \to $$</p> | g18059 | [
-0.005016363691538572,
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0.038996461778879166,
0.0560992956161499,
-0.0309... |
<p>Are the telescopes really capturing these colors in deep space or are they just "artist's impression". What could make such vast space "red" or "green"?</p>
<p><img src="http://i.stack.imgur.com/qWc1Y.png" alt="deep space photo"></p> | g18060 | [
-0.009534388780593872,
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0.02030... |
<p>Can someone give an example of an one dimensional local gapped quantum lattice model with a discrete non-Abelian global internal symmetry that is spontaneously broken in the ground state? In particular, where ground states transform as an irreducible representation with dimension > 1?</p> | g18061 | [
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<p>I am aware of three apparently different forms of angular momentum: spin, orbital and macroscopic, like a spinning crystal or baseball.
Can angular momentum be transferred or converted from one of these forms to another?
If so, how? </p> | g18062 | [
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0.027566609904170036,
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<p>In particular I am curious if the values of the rest masses of the electron, up/down quark, neutrino and the corresponding particles over the next two generations can be defined as constant or if there is an intrinsic uncertainty in the numbers. I suppose that since there is no (as of yet) mathematical theory that p... | g18063 | [
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0.00701297540217638,
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<p>In almost all proofs I've seen of the Lorentz transformations one starts on the assumption that the required transformations are linear. I'm wondering if there is a way to prove the linearity:</p>
<p>Prove that any spacetime transformation $\left(y^0,y^1,y^2,y^3\right)\leftrightarrow \left(x^0,x^1,x^2,x^3\right)$ t... | g603 | [
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0.008752160705626011,
0... |
<p>I'm not sure if this question is for Physics SE, but I'd go ahead and ask.</p>
<p>I was wondering how the heated showers work (the ones with the hot and cold knobs).
I have always been curious and this may clear my head on the questions such as :</p>
<ol>
<li>Why is the temperature so volatile? (A slight turn to ... | g18064 | [
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0.027073414996266365,
0.03776746988296509,
-0.... |
<p>I would like to ask why the scattering matrix $S^{ab}(x)=\left\langle gluon\: b|gluon\: a\right\rangle$ can be approximated for fast particle interacting with a traget field $A^{-}$ by wilson line $S^{ab}(x)=\left[P\exp\left\{ ig\int dx^{+}T_{c}A_{c}^{-}(x^{+},x_{\perp})\right\} \right]^{ab}$</p> | g18065 | [
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0.03073059394955635,
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... |
<p>It is usually said/done in textbooks and classes that if $\Delta x$ is known then $\Delta p_x$ can be estimated using the uncertainty principle as $\Delta p_x \sim \hbar/\Delta x$.</p>
<p>But the uncertainty principle does not say that, it says $\Delta p_x\ge\hbar/\Delta x$. That means we can only set a lower bound... | g18066 | [
0.02632881887257099,
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0.014231142587959766,
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<p>This is regarding the proof of Birkhoff's theorem. A part of the proof requires one to show that the most general spherically symmetric metric can be written in the form
$$
ds^2 = -e^{2\alpha(t,r)} dt^2 + e^{2\beta(t,r)}dr^2 + r^2 d\Omega_2^2
$$
In order to show this, Carroll briefly describes how one would go about... | g18067 | [
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0.05082101747393608,
0.06394181400537491,
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0.028324246406555176,
0.021240418776869774,
0.01889062114059925,
0.025253435596823692,
-0.... |
<p>When the plate spacing is large the capacitor system is storing more energy than when it is small.</p>
<p>If one manually changes the spacing, where does the additional energy "come from" as the plate spacing increases?</p> | g18068 | [
0.0571708008646965,
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0.03494754806160927,
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0.02920... |
<p>Does requiring $\delta R=0$ on the boundary of hyper-surface create any restrictions or problems in deriving the field equations from Einstein-Hilbert Action? </p> | g18069 | [
0.008905685506761074,
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0.011233764700591564,
0.044... |
<p>This <a href="http://www.ted.com/talks/ramesh_raskar_a_camera_that_takes_one_trillion_frames_per_second.html" rel="nofollow">TED talk</a> suggests that we can now watch as a beam of light propagates through a bottle filled with water. My question is: can we use this new technology to perhaps 'see' the photon as it m... | g18070 | [
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-0.03227151557803154,
0.06080358102917671,
0.07063151150941849,
0.06433754414319992,
0.02431... |
<p>I've heard the work a few times now, the most recent in the star trek film. Is a <a href="http://simple.wikipedia.org/wiki/Gravitational_singularity" rel="nofollow">singularity</a> a real thing? If so what is it?</p> | g18071 | [
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0.013666708953678608,
0.0025565288960933685,
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0.08091577887535095,
-0.00... |
<p>Why are the colours visible only at the fringes of the light refracted through a rectangular prism?</p> | g18072 | [
0.040684375911951065,
0.029448730871081352,
0.023261427879333496,
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0.04208316653966904,
0.02878349833190441,
0.023227300494909286,
0.01583... |
<p>I would like to compare the energy requirements of the 2 following tasks:</p>
<ol>
<li><p>Total energy to evaporate 1 litre of water at normal atmospheric pressure at normal temperature?</p></li>
<li><p>Total energy to compress air into a 1 litre container so that the compressed air had a mass of 1kg? What air pres... | g18073 | [
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0.0350361131131649,
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-0.05588266998529434,
-0.014807011000812054,
0... |
<p>Well i had seen a toy, which i till date don't know was it battery powered or not? and also could it be used to actually create energy (I know that it is not possible but whats the problem?)</p>
<p><strong>Structure</strong> of a toy: Imagine a toy man having magnets at his feet, he is fixed to an axle and can just... | g18074 | [
0.006304938346147537,
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-0... |
<p>How far can we extend the formalisms on <a href="http://en.wikipedia.org/wiki/Quantum_mechanics" rel="nofollow">quantum mechanics</a> (QM) to <a href="http://en.wikipedia.org/wiki/Quantum_field_theory" rel="nofollow">quantum field theory</a> (QFT)? In particular,</p>
<ol>
<li><p>How is a Fock space $\mathcal{F}$ di... | g18075 | [
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-0.06197020411491394,
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-0.07055073976516724,
-0.00800283718854189,
0.02... |
<p>I'm trying to read <a href="http://www.cs.princeton.edu/courses/archive/fall05/frs119/papers/feynman85_optics_letters.pdf" rel="nofollow" title="Quantum Mechanical Computer">Quantum Mechanical Computer</a> and to implement the CCNOT logical gate with Mathematica.</p>
<p>Since i wish to use the SWITCH implementation... | g18076 | [
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0.010957436636090279,
0.015507950447499752,
0.040362510830163956,
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-0.... |
<p>I heard and read couple of times reference to a certain identity in conformal field theory (maybe specific to two dimensions). The identity relates the trace of stress-energy tensor to the beta functions of all the operators in the simplest way:
$$T^{\mu}_{\mu} = \sum_{i}\beta({\cal{O_i}}){\cal{O_i}}$$
It's an opera... | g18077 | [
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0.0076861027628183365,
-0.0230... |
<p>I am trying to recast a problem I am working on in terms of Lagrangian mechanics. I am in the following situation. Suppose I have a function $f:X \rightarrow \mathbb{R}$ (a field). In the its simplest case, I am studying constant functions. Since $X$ is an open ball, this is the same as studying:
$$ \nabla f = 0.... | g18078 | [
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-0.0209751445800066,
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0.030014462769031525,
0.018529726192355156,
-0.03... |
<p>I figure that at large enough distances, the potential field of an ion is just the Coulomb potential for its net charge. But what happens at scales comparable to the ion's Bohr radius? Could there be, for example, some sort of screening effect from the electron shell that changes the potential? (depending on what th... | g18079 | [
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0.03357613831758499,
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<p>From a real world perspective each dimension in the 3-D Cartesian System can be represented by an axis that is perpendicular to 2 other axes. I read somewhere else that the effect of ${\sqrt {-1}}$ is to reorient data 90 degrees on the "imaginary" axis. I guess my question is this: What role ( if any) does ${\sqrt... | g560 | [
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0.02494189701974392,
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-0.05... |
<p>In my text book, it is given : </p>
<blockquote>
<p>One calorie is defined as the amount of heat required to raise the temperature of water from 14.5 °C to 15.5 °C.</p>
</blockquote>
<p>I found out in wikipedia that this is actually the definition of 15 °C calorie. </p>
<p>I want to know that as temperature inc... | g18080 | [
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<p>This is a fairly basic question but is something that I've never properly understood. If you have a cavity with perfectly reflecting walls, I understand that there are obviously frequencies which generate standing waves but I'm not sure I understand why they are the only frequencies which need to considered. What ha... | g18081 | [
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0.019297003746032715,
0.0009373308275826275,
0.043769... |
<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/2175/is-it-possible-for-information-to-be-transmitted-faster-than-light">Is it possible for information to be transmitted faster than light?</a> </p>
</blockquote>
<p>we know that speed of light is an un... | g4 | [
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0.0380498468875885,
-0.... |
<p>Is there any way a pure math guy can get his rigorous math fix while simultaneously moving fusion research forward? Is fusion simply too complicated to take a pure math approach? What open math questions are there pertaining to fusion?</p> | g18082 | [
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<p>By definition Ricci Tensor is a Tensor formed by contracting two indices of Riemann Tensor. Riemann Tensor can be visualized in terms of a curve, a vector is moving and orientation of the initial and final vector. However, the operation of contraction of indices which give rise to Ricci Tensor doesn't give any visua... | g18083 | [
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<p>Does inducing a current in a wire result in any changes in the strength of a permanent magnet? Specifically, what would the results of the following controlled experiment be? </p>
<p>You set up two alternators that each simply consist of a permanent magnet located inside a stationary loop of wire as depicted <a hre... | g18084 | [
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<p>I am looking at the solutions that my professor put up and I feel that he did something wrong. Here is the question and I will give my stab at the solution so you can see why I think that it is wrong.</p>
<p>A straight fin is fabricated of aluminum alloy with conductivity of 185 $\frac{W}{mK}$ with a base thickness... | g18085 | [
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<p>When we calculate Riemann Tensor for different curvature we have lots of components. However, there are many components that are zero. How can we argue, based on the symmetry of connection , that those elements are zero? </p>
<p>For example if I am calculating the Riemann Tensor of $S^2$ sphere, I get only one non ... | g18086 | [
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<p>I hope this a question that can be answered and isn't too vague. I'm also only after a very rough answer.</p>
<p>I'm adding a small amount (~500mL) of sugar solution into a carboy with a much larger volume of water (~20L).<br>
I don't particularly want to stir it in very much because there is a lot of sediment that... | g18087 | [
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<p>Water drops kept on different surface evaporate after a few minutes. How can I reduce the rate of evaporation of these drops? Can I add some additives which suppress evaporation?</p> | g18088 | [
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<p>I have probably very naive question.</p>
<p>In case of CARS microscopy <a href="http://en.wikipedia.org/wiki/Coherent_anti-Stokes_Raman_spectroscopy" rel="nofollow">http://en.wikipedia.org/wiki/Coherent_anti-Stokes_Raman_spectroscopy</a> we have $ω_{pr}+ω_{p}-ω_{S}$, how can we have minus $ω_S$?
In fluorescent mic... | g18089 | [
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<p>Consider a time-independent potential: $V(x)$. Then, it is usually stated that
$$
\Psi(x,t)=\rho(x)\exp{\left(-\frac{i}{\hbar}Et\right)}
$$
is the general form of a solution of the Schrodinger equation
$$
i\hbar \partial_t\Psi=H\Psi
$$. Why is this the case?</p> | g18090 | [
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<p>In the context of quantum mechanics via path integrals the normalization of the propagator as</p>
<p>$$\left | \int d x K(x,t;x_0,t_0) \right |^2 ~=~ 1$$</p>
<p>is incorrect. But why?</p>
<p>It gives the correct pre-exponential factor for the free particle and the incorrect one for the harmonic oscillator.</p>
<... | g18091 | [
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<p>I am not asking why it occurs, but what it is. Everything understood is something.</p>
<p>Something would entail the existence of a property, whether or not tangible.</p>
<p>We know photons exist, but we know they are subatomic particles.</p>
<p>Speaking on states and matter, is gravity matter? Does it have state... | g18092 | [
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<p>That Voyager and several other spacecraft have had anomalous changes in speed is known. According to the news reports, the differences are unsettling. But just how large are these anomalies really? Are they 'way down there' at the levels of computational precession? Or, if I understood how to calculate them, could I... | g18093 | [
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... |
<p>When I read the Wiki about <a href="http://en.wikipedia.org/wiki/Legendre_transformation" rel="nofollow">Legendre transformation</a>, there is a statement</p>
<blockquote>
<p>The Legendre transformation is an application of the duality relationship between points and lines.</p>
</blockquote>
<p>What's the meanin... | g18094 | [
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0.025524519383907318,
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<p>I'm looking at some gamma spectroscopy calibration data, produced by a known source (semi known... the source was last calibrated 2006...) </p>
<p>My question is, looking at for example <a href="http://www.nucleide.org/DDEP_WG/Nuclides/Co-57_tables.pdf" rel="nofollow">http://www.nucleide.org/DDEP_WG/Nuclides/Co-57_... | g18095 | [
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<p>I would really like to understand Higgs-Englert’s discovery that earned them the 2013 physics Nobel prize. I tried reading <a href="http://prl.aps.org/abstract/PRL/v13/i9/p321_1" rel="nofollow">their work</a>, but understood nothing of it unfortunately.</p>
<p>The reason why I’m asking here is because, unfortunatel... | g18096 | [
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<p>In theory, could pure sound be lethal? How loud would it have to be? Also, which events are the loudest in the universe, and how loud are they? I'm confining attention to events which occur regularly, e.g. starquakes. </p> | g18097 | [
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<p>It seems to be commonly accepted that the Big Bang occurred roughly 13.7 billion years ago. My question is what is the meaning of the year in this context?</p>
<h2>When I type <a href="https://www.google.com/search?q=year%20definition" rel="nofollow">year definition</a> into google, it returns this:</h2>
<p><img ... | g18098 | [
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0.022... |
<p>I am currently learning Quantum mechanics on a slightly advanced level. I am curious in knowing if there are Linear Operators (Linear Maps) in the Hilbert Space (finite dimensional ones) that don't have isomorphic with Matrices? In those case are there any other representations that we can choose?</p> | g18099 | [
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... |
<p>In this post let $U$ be the universe considered as a manifold.</p>
<p>From what I gather we don't really have any firm evidence whether the universe is closed or open. The evidence seems to point towards it being open but closedness is within the error range of present data.</p>
<p>However, this seems to be an awf... | g18100 | [
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0.04451766610145569,
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0.004451144486665726,
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0.013248068280518055,
0.... |
<p>For simplicity I'll consider only gravity, but in general this question only applies to conservative forces.</p>
<p>As per my understanding, the way one gets to the equation for gravitational potential energy is this:</p>
<p>$(1)$ $\ddot{r}=-\frac{MG}{r^2}$ is given experimentally</p>
<p>$(2)$ $KE=\frac{1}{2}m\do... | g18101 | [
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0.009451311081647873,
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0.0156591534614563,
0.0439230315387249,
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0.0029068400617688894,
-0.002... |
<p>Can one morph a wire by electrical current into a shape different than static shape at beginning? As in the beginning shape being in a spiral, then when electrical energy is passed through the wire it becomes straight. When the current is shut off it would return to a spiral shape as in the beginning form. OR vise v... | g18102 | [
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<p>Consider a quantum system in thermal equilibrium with a heat bath. In determining the density operator of the system, the usual procedure is to maximize the von Neumann entropy subject to the constraint that the ensemble average of the Hamiltonian has a fixed value.</p>
<p><strong>What justifies this assumption?</... | g18103 | [
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0.0350978821516037,
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0.05587952584028244,
0.04118414595723152,
0.079... |
<p>I got confused by reading this article:</p>
<blockquote>
<p>Francois Virot, Roland Hayn, Manuel Richter, and Jeroen van den Brink. “<a href="http://arxiv.org/abs/1306.0999" rel="nofollow">Engineering topological surface-states: HgS, HgSe and HgTe</a>.” arXiv preprint arXiv:1306.0999 (2013).</p>
</blockquote>
<p>... | g18104 | [
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0.013778848573565483,
-0.014995542354881763,
0.01235610619187355,
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0.02689306251704693,
-... |
<p>I'm currently building a custom desk. In this desk I will also build-in a small part with a custom electronic panel to provide power to USB devices.</p>
<p>As my gaming pc generates a lot of heat and the panel will generate some too, I was thinking about doing something with this heat. I read <a href="http://physic... | g18105 | [
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0.0026750233955681324,
0.017129158601164818,
-0.07654014974832535,
... |
<p>In relativistic quantum field theories (QFT),</p>
<p>$$[\phi(x),\phi^\dagger(y)] = 0 \;\;\mathrm{if}\;\; (x-y)^2<0$$</p>
<p>On the other hand, even for space-like separation</p>
<p>$$\phi(x)\phi^\dagger(y)\ne0.$$</p>
<p>Many texts (e.g. Peskin and Schroeder) promise that this condition ensures causality.
Why ... | g18106 | [
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0.0... |
<p><img src="http://i.stack.imgur.com/e6LmR.png" alt="Phys Problem, ">
I tried to do this problem by taking the derivative and it did not get me the right answer. I also tried the Vdv=Ads integration and could not get the right answer. Please Help</p> | g18107 | [
0.028609540313482285,
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0.01611432246863842,
-0.00858... |
<p>Fast everyone knows the relation $E = mc^2$ but I still ask me, which units the relation has.</p>
<p>$c$ is the velocity of light. It means, a constant, isn't it? We therefore just have the relation $E = \text{constant} \times m$</p>
<p>Ok, nice to know the mass and the energy are directly proportional. But the ... | g18108 | [
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0.00755283422768116,
0.0... |
<p>According to the definition of Black-body, it absorbs all of the wavelength irradiates on it. A recent material <a href="http://www.physics4all.com/its-not-black-its-super-black/" rel="nofollow">absorbs 96.4%</a> visible light rays. Therefore , can we say that it is the most closest (ideal) blackbody? </p> | g561 | [
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0.01734599471092224,
0.0061319... |
<p>I was reading about growing single crystals and I'm a little confused about this -</p>
<p>In most crystal growing processes, a "seed crystal" is used, and the rest of the material crystallizes <em>on</em> the seed crystal (for example the <a href="http://en.wikipedia.org/wiki/Czochralski_process">czochrlaski proces... | g18109 | [
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<p>Let me explain better: from what I understand neutrinos are so pervasive they are literally everywhere. And since they have such a tiny electric charge they barely interact with anything and cannot be "removed" or "shielded" from an area in order to take a measurement of light speed in their absence. However, all th... | g18110 | [
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0.03739474341273308,
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0.042698707431554794,
0.011675965040922165,
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... |
<p>I have absorbance values for blood plasma. Absorbance was measured in range of 380 – 600 nm every 5 nm ending up with absorbance values for 45 wave lengths. I was browsing through literature, and I came across chromacity coordinates (XYZ) and this seems to be a very convenient way of summarizing data about color in ... | g18111 | [
0.06120133027434349,
-0.02358720824122429,
0.021527303382754326,
-0.03639398515224457,
0.026094792410731316,
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0.02388673834502697,
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0.014209231361746788,
0.006099322345107794,
0.021809909492731094,
0.012500036507844925,
0.042... |
<p>Suppose we have a block of mass $M$ and we are moving it up a curve, very slowly ($a=0$). The surface is not smooth, and coefficient of friction is $\mu=\mu_s=\mu_k$.</p>
<p>To move the block we apply a force $F$ to the block tangential to the surface(on which the block is, at that time). If we take the angle of sl... | g18112 | [
0.04713389277458191,
0.07373452186584473,
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0.018429288640618324,
-0.005552846007049084,
-0.028143245726823807,
0.0002690092660486698,
-0.... |
<p>I am continuing to brush up my statistical physics. I just want to gain a better understanding. I have gone through the <a href="http://www.nyu.edu/classes/tuckerman/stat.mech/lectures/lecture_4/node1.html" rel="nofollow">derivation of the classical virial theorem</a> once more. I have thought about it, googled it a... | g18113 | [
0.04617923125624657,
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0.0045791128650307655,
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0.0020528254099190235,
... |
<p>I'm reading Sternberg's Group Theory and Physics. I have a question about chapter 1.2 Homeomorphisms.</p>
<hr>
<p>Background:</p>
<p>A Lorentz Metric is defined as $||{\bf x}||^2=x_0^2-x_1^2-x_2^2-x_3^2$</p>
<p>And a Lorentz Transformation $B$ as one which satisfies $||B{\bf x}||^2=||{\bf x}||^2$</p>
<p>Identif... | g18114 | [
0.02090662531554699,
0.002649620408192277,
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0.021670518442988396,
0.01605246774852276,
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-0.008305732160806656,
-0.029840711504220963,
0.07243510335683823,
0.005673246458172798,
0.0... |
<p>$x''+\gamma x'+w_0^2x=0$</p>
<p>That is the general equation for <a href="http://en.wikipedia.org/wiki/Damping" rel="nofollow">damped</a> harmonic motion. What is the term or name that describes $\gamma$?</p>
<p>Is it called the damping constant? I know its the ration between the resistive coefficient $b$ and mass... | g18115 | [
0.04869486019015312,
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0.08064902573823929,
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0.07880361378192902,
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0.07072663307189941,
0.0034601439256221056,
-0.... |
<p>I would be grateful if somebody could help me brining the <strong>parity operator</strong> and the <strong>particle exchange operator</strong> together.</p>
<p>Suppose, there is a two-proton system, where one proton is sitting at $+r$ on the $x$-axis, one is sitting at $-r$, as shown in the figure.</p>
<p><img src... | g18116 | [
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-0.... |
<p>I've read about the idea that buckyballs and other nanostructures could be used to hold drugs and things until they reach certain places in the body and then get released.</p>
<p>So I was wondering, if you created a buckyball in air, so that some molecules that are in air (such as oxygen and nitrogen) were inside t... | g18117 | [
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<p>This was discussed in an answer to a <a href="http://physics.stackexchange.com/questions/1898/do-photons-gain-mass-when-they-travel-through-glass">related question</a> but I think that it deserves a separate and, hopefully, more clear answer.</p>
<p>Consider a single photon ($\lambda$=532 nm) traveling through a pl... | g18118 | [
0.027007699012756348,
0.042536720633506775,
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0.06965659558773041,
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0.024938736110925674,
0.0680096223950386,
-0.023791102692484856,
-0... |
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