question stringlengths 37 38.8k | group_id stringlengths 2 6 | sentence_embeddings listlengths 768 768 |
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<p>I wonder, what is content of output of zeolite-based pressure swing adsorption oxygen concentrators (both oxygen output, and exhaust output)? </p>
<p>Yes, they can produce 95% oxygen. </p>
<p>But what's the remaining 5%? Is it just argon and other noble gases, or some air contaminants could also be concentrated (... | g7127 | [
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<p>I have always taken for granted that 'the aperture of a loss-less isotropic antenna is $\dfrac {\lambda^2} {4\pi}$'. </p>
<p>On a whim, I tried to look up how this expression was derived, but so far I have not been able to find out a reference that works it out. Can someone outline the proof, or help me with any po... | g7128 | [
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<p>Extrapolation of the expansion of the Universe backwards in time using general relativity yields an infinite density and temperature at a finite time in the past.</p>
<p>If the matter contained within our galaxy were concentrated within a small radius wouldn't that lead to the entire universe being a black hole? If... | g15 | [
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<p>I am working on a concept for something and i want to make sure i understand something clearly before i start on everything else. Note, my project is more about the interactions of elements of complex systems rather than physics. Im just using this paragraph as an example, not doing a project on quantum mechanics.... | g7129 | [
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<p>When I first learned about the <a href="http://en.wikipedia.org/wiki/Depletion_force">depletion interaction</a>, my initial reaction was that it looks very similar to the Casimir effect. On making this remark to the professor, he replied somewhat mystically: "It <strong>is</strong> the Casimir effect." No further de... | g7130 | [
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<p>If light is travelling vertically upwards and I am travelling horizontally and perpendicular to light, the velocity of light in the vertical direction will get reduced. How does this happen? How does motion in x-direction cause a reduction in speed of light in y-direction ?</p>
<p>Also, in Lorentz Transformation, s... | g7131 | [
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<p>i was wondering if anyone could give an explicit calculation or show a link that shows the proof to Furry's theorem. showing how the vacuum expectation value of any odd number of electromagnetic currents vanishes. in particular the case for n=3.</p> | g7132 | [
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<p>Inspired by <a href="http://physics.stackexchange.com/questions/79089/intuitive-explanation-of-why-orbits-are-closed">this recent question</a>, I would like to understand from a more general and mathematical perspective why closed orbits are only found for the Kepler ($V(r) \sim 1/r$) or harmonic ($V(r) \sim r^2$) p... | g7133 | [
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<p>I recently came across a comment that when we push a rubber ball into water filled in a bucket, the water level rises because of the force applied by our hand (i.e. the more force we apply, the more water rises). But I do believe it's absurd, water rise occurs as a function of volume (of our hand).</p>
<p>If water... | g7134 | [
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<p>The NOVA show on the string theory have mention once that the proton and neutron will be disappear in finite amount of time, then reappearing on somewhere else. Is there any experiment have shown that this is true?</p> | g7135 | [
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<p>Could someone explain how, or at least show me a link that explicitly shows the calculation of a two-loop corrections to scalar’s two-point function
in $\varphi^4$ theory in the massless limit. </p> | g7136 | [
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<p>We are able to see this beautiful world because of light. When light gets reflected from the object, the reflected light enters our eye retina and thus we are able see that particular object from which light was reflected from. In our daily life, we see certain things which are transparent, they appear transparent b... | g7137 | [
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<p>The formula for <a href="http://en.wikipedia.org/wiki/Magnetic_levitation" rel="nofollow">magnetic levitation</a> is</p>
<p>$$ B \frac{dB}{dz} = \frac{ \rho g }{\chi} $$</p>
<p>but as always, I have a hard time figuring the units in SI. The left hand side is $\mathrm{T^2 /m}$, while $\chi$ has units of $\mathrm{m^... | g7138 | [
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<p>I recall vaguely that energy is absorbed/radiated in packets called quanta. Quanta were what are now known as photons. </p>
<p>What I'm curious about - Is absorption/radiation vis-a-vis photon lossy? Do the total number of photons exactly match the energy acquired/released?</p> | g7139 | [
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<p>I understand the definitions "theorem" and "conjecture" in mathematics, but I wasn't sure for physics. I mean, if it's <em>proved</em> mathematically, it's a theorem, otherwise it's a conjecture. But for physics (i.e. when the idea is meant to correspond to a physical reality - and - can only said to 'true' if teste... | g7140 | [
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<p>As you know the equation of capillary action id given by:</p>
<blockquote>
<p>$h=\dfrac{2\gamma\cos\theta}{\rho gr}$</p>
<p>Where:</p>
<p>$h$ is the height the liquid is lifted,</p>
<p>$\gamma$ is the liquid-air surface tension,</p>
<p>$\rho$ is the density of the liquid,</p>
<p>$r$ is th... | g7141 | [
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<p>Consider a cement block of the same density as sea-water resting on the (perfectly polished) seafloor. I also assume the side-faces of the cement block are highly polished, so that no vertical hydrostatic forces can attack on them. A cable is attached to the top of the block.</p>
<p>My question ist: How much force ... | g7142 | [
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<p>I've seen the <a href="http://en.wikipedia.org/wiki/Kerr_metric" rel="nofollow">Kerr metric</a> usually presented in the Boyer-Lindquist coordinates where there is a cross term in the $d\phi$ and $dt$ term. I've done a good bit of searching and cannot find any coordinates which express the Kerr metric in an orthogon... | g7143 | [
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<p><img src="http://i.stack.imgur.com/qay6o.jpg" alt="Universe"></p>
<p>I would be interested in what people think of Fulvio Melia's <a href="http://arxiv.org/abs/1205.2713" rel="nofollow">argument</a> for a linearly expanding Universe.</p>
<p>I realize that the experimental evidence seems to be pointing to an accele... | g7144 | [
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<p>I was looking up X-Ray crystallography using Bragg's Law:</p>
<p>$2d\sin\theta = n\lambda$</p>
<p>and I can understand the values of everything except this integer value $n$.</p>
<p>As far as my research got $n$ is used to describe the atom spacing in the crystal lattice, but I don't understand how you'd express ... | g7145 | [
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<p><img src="http://i.stack.imgur.com/xtzJm.png" alt="Physics doubt"></p>
<p>In which of the following situation will the bullet of the pistol penetrate deeper in the wall? Why? Alternatively will the penetration in both cases be the same? Can you explain the concepts behind this?</p> | g7146 | [
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<p>According to equation 5.2.5 in Polchinski :-</p>
<p>$$\int d^2 \sigma~ \delta^{'}g_{ab} \times [-2(P_1 \delta \sigma)_{ab} +(2\delta w - \Delta \cdot \delta \sigma)g^{ab}]=0$$</p>
<p>The assumption here is that " Moduli correspond to variation $\delta^{'}g_{ab}$ of the metric that are orthogonal to all variations ... | g7147 | [
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<p>I pulled apart a flashlight and found a similar lens as the one shown below.</p>
<p><img src="http://i.stack.imgur.com/k4Vhh.jpg" alt="enter image description here"></p>
<p>I assume that the light starts off as a “point source” somewhere inside and the curvature and/or shape of the “lens” makes parallel wavefronts... | g7148 | [
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<p>Given formula:</p>
<p><img src="http://i.stack.imgur.com/JsywY.png" alt="enter image description here"></p>
<p>How I can use to calculate distribution of points in space, so if i choose path which contains most of the points I get path that close to "free-fall path".
As far as I know i should use square root of De... | g7149 | [
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<p><a href="http://www.youtube.com/watch?feature=player_detailpage&v=jfySIeS1XZE#t=118s" rel="nofollow">http://www.youtube.com/watch?feature=player_detailpage&v=jfySIeS1XZE#t=118s</a></p>
<p>If so, how are they created (roughly speaking). Earlier in the video he says that a laser scanned the surface of the obj... | g7150 | [
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<p>I am interested to know how the (non)existence theorems of <a href="http://en.wikipedia.org/wiki/Constructive_quantum_field_theory">constructive QFT</a> and <a href="http://ncatlab.org/nlab/show/AQFT">algebraic QFT</a> are related (or not). I have only a weak grasp of either, so I'm looking for something like a quic... | g7151 | [
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<p>When we write equations in QM, in certain places, the wave function is represented as $\psi(x,t)$, which is the wave function in position space, and in some other places, it is written as $\Psi(t)$. What is the difference between the two?</p> | g7152 | [
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<p>I was watching one of Neil Degrasse Tyson talks and there was a scientist (can't recall his name sorry) who was talking about a recent discovery: </p>
<blockquote>
<p><em>"Doubly-even self-dual linear binary error-correcting block code" has been discovered embedded within the equations of superstring theory.</em>... | g7153 | [
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<p>Weinberg on p. 287 of his QFT vol. 1 introduces the extended interaction operator:
$$
\tag 1 \hat{V}(t) \to \hat{V}(t) + \sum_{a}\int d^{3}\mathbf x \hat{o}_{a}(\mathbf x ,t)\varepsilon_{a}(x).
$$<br>
Here
$$
\hat{S} = \hat{T}e^{i\int \hat{V}(t)dt}, \quad \hat{o}_{a}(\mathbf x, t) = e^{i\hat{H}_{0}t}\hat{o}_{a}(\ma... | g7154 | [
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<p>Specifically, I am trying to roughly determine the sound produced by a ball when it hits the floor and bounces. If the ball exerts a pressure onto the floor, then certainly this pressure will go on to create a sound wave in the floor (infinite block) and the air. I was just wondering if there is any way to find the ... | g7155 | [
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<p>Suppose we have action $S[q]$ and its stationary path $q_s$, I want to find the orthonormal paths $\psi_n$ that can diagonalize the second variation of the action $S[q]$. How to do that? Thanks</p> | g7156 | [
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... |
<p>I drive a Volvo v40 with a 110hp diesel engine. It usually use 4.6L/100km.</p>
<p>If I plug my laptop which is 85W, will this change the fuel need? If so, by how much?</p> | g7157 | [
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<p>I've heard that scientist proof that viruses of the Tobacco mosaic virus could interfere with themselves. I'm referring to quantum interference-- the same as photons. Unfortunately, I couldn't find any material on this problem on the Internet , so I don't know if it's true. Viruses have a width between 20nm and 100... | g7158 | [
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<p>The question pretty much sums up what I need to know. Why is it that light only gets dispersed into a spectrum when travelling through two non-parallel sides(like a prism) and not through something like a glass slide with parallel slides.</p>
<p>And how does this experiment(an experiment conducted by Newton) explai... | g7159 | [
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<p>shouldn't be the quantization formula (in one dimension) equal to</p>
<p>$ N_{smooth}(E)+N_{osc}(E) = \oint_{C}p.dq $ ??</p>
<p>where the Oscillating term is just the correction from Gutzwiller trace formula or a sum over Orbits</p>
<p>why is just the oscillating term ignored ..</p> | g7160 | [
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<p>I have a question about the $ \hat{n} $ in this formula $\sigma = P \dot{}\hat{n}$.</p>
<p>Why do sometime in my book they get $\sigma = P \cos{\theta}$ for a sphere. Isn't $\hat{n} = r$ ? </p>
<p>And then in another problem, where $P = \cfrac{k}{r}\hat{r}$ and r = a (inner) and r = b (outer) they get $\sigma =\c... | g7161 | [
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<p>Is the holographic principle applicable everywhere, e.g. is it possible to learn everything about any whatsoever volume of space everywhere in the universe from the boundary of it or does it have to be bounded by some special feature like an event horison? And do the same thing always apply in the reverse direction ... | g7162 | [
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<p>A particle is projected from a point on level ground with a speed of $u$ meters per second and an angle of elevation $\theta$. The maximum height reached by the particle is $42$ meters above the ground and the particle hits the ground $196$ meters from its point of projection. Find the values of $\theta$ and $u$.</p... | g7163 | [
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<p>I've been reading about Cosmic Background Radiation (CMBR) lately. My understanding so far is that this is the "Noise"/"Flash" from the big bang. Assuming that information is correct, how far away is it traveling in order to reach us? The way it was described to me makes it sound as if it should be coming from th... | g10 | [
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<p>When i apply high voltage (through a capacitor bank) across an aluminium foil, it gets converted into plasma. I want to simulate this process and study the properties of the plasma produced henceforth. I would then like to change my experimental parameter and see if my simulation predicts the correct output. </p>
<... | g7164 | [
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<p>First of all, I know that light does indeed travel slower in a medium like air or water, but that's because the photons are bouncing off of the medium's particles and in different directions so the light beam as a whole is slowed down (or at least that's the classical explanation I've read somewhere).</p>
<p>But my... | g7165 | [
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<p>I have started doing <em>Relativistic Quantum Mechanics</em> from <em>Greiner</em>.</p>
<p>I'm having difficulty understanding the following derivation for commutation relations (page 4):</p>
<p>$$[\hat{p}^\mu, x^\nu] = i\hbar[\frac{\partial}{\partial{x_\mu}},g^{\nu \sigma}x_\sigma]=$$
$$= i\hbar g^{\nu \sigma}\fr... | g7166 | [
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<p>As an electrical/computer engineer, I already have a relatively thorough understanding of classical electromagnetism. </p>
<p>From what I understand though, classical EM is only an approximation to quantum electrodynamics. I'm very curious about how it all <em>really</em> works though.</p>
<p>So as an ECE engineer... | g7167 | [
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<p>In Sakurai's <em>Modern Quantum Mechanics</em> (2nd ed) p.99, he says</p>
<blockquote>
<p>We know from the theory of partial differential equations that
(<em>time-independent Schrodinger equation</em>) subject to boundary
condition ($\psi(\mathbf{x}')\rightarrow 0$ as
$|\mathbf{x}'|\rightarrow\infty$) allow... | g7168 | [
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<p>I have a bottle of vodka that has a load of gold flakes suspended in it. It has been sat still for over 24 hours and the flakes are all still suspended within the liquid: they have not risen to the surface or sunk to the bottom. Any ideas as to the physics behind this? </p> | g7169 | [
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<p>I know that the electric field is zero inside a perfect conductor. However, I am here discussing non-perfect conductors. So let's suppose we have a conducting medium with conductivity $\sigma_1$ and electric permittivity $\epsilon_1$. Another conducting medium is enclosed by the first medium and this one has conduct... | g7170 | [
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<p>In scattering theory, what is a good intuitive picture to think of s-wave, p-wave or d-wave collisions ? What is their importance and what are the examples where a particular one is assumed to be the only important one and rest are taken as negligible ?</p> | g7171 | [
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<p>As a planet moves through the solar system, a <a href="http://en.wikipedia.org/wiki/Bow_shock">bow shock</a> is formed as the solar wind is decelerated by the magnetic field of the planet. Presumably the creation of this shock wave would cause drag on the planet, certainly in the direction of orbit but possibly rota... | g7172 | [
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<p>I'm doing a project (dissertation) on the mathematics of Aerofoil Theory. I wonder if I could get some advice on a possible structure. I'm new to fluid dynamics, so it's quite hard to know where to start. </p>
<p>So far I've looked at different types of flows; streamlines and velocity potentials. I've also covered ... | g7173 | [
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<p>I have a question about the most general (diff$\times$Weyl)-invariant and Poincare-invariant form of action. In Polchinski's string theory p15, there is an action for manifold without boundary
$$S_{\mathrm{p}}'= - \int_M d \tau d \sigma (-\gamma)^{1/2} \left( \frac{1}{4\pi \alpha'} \gamma^{ab} \partial_a X^{\mu} \pa... | g7174 | [
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0... |
<p>I have three questions about the BRST symmetry in Polchinski's string theory vol I p. 126-127, which happen together </p>
<p>Given a path integral
$$ \int [ d\phi_i dB_A db_A d c^{\alpha}] \exp(-S_1-S_2-S_3) \tag{4.2.3}$$
with $$ S_2 =-iB_A F^A (\phi) \tag{4.2.4}$$
$$ S_3 = b_A c^{\alpha} \delta_{\alpha} F^A(\phi) ... | g7175 | [
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<p>In a semi conductor, for an electron in valence band to transfer to conduction band, it needs energy which can be provided by applying an electric field such that a force is applied on it until it breaks free from its parent atom. Now till the time it is at rest no change in kinetic energy is there. Hence, the energ... | g7176 | [
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<p>How can I determine the focal length and position of a lens mounted in an inaccessible position inside a tube by a laboratory experiment?
Please help.</p> | g7177 | [
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<p>I'm working through some problems for a QM exam and I've realised I don't really understand the concept of parity of solutions. I'm looking at a simple finite potential well problem: $$V(x)=0, \quad |x|>d$$
$$V(x) = V_0 \quad |x|<d$$
where $V_0$ is positive. I'm looking at bound states, so that $0<E<V_0$... | g7178 | [
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0.02853364497423172,
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<p>Does anybody know how to implement the WKB approximation for the two-dimensional Schrodinger equation with a harmonic oscillator potential:</p>
<p>$\frac{1}{2}\Biggl[-\biggl(\frac{\partial^2}{\partial x^2}+\frac{\partial^2}{\partial y^2}\biggr)+x^2 + y^2 + 2xy\Biggr]\Psi(x,y) = E\Psi(x,y)$</p> | g7179 | [
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<p>I still don't really understand what contextuality means in reference to quantum mechanics. If someone could give a clear definition that would be great. It sounds like it means you can't always relate the state of a system to its wavefunction or something? That confuses me since it seems to violate quantum mecha... | g7180 | [
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<p>I'm confused with the Gauss' Law to calculate the electric field for two coaxial cylindrical conductors of finite length.</p>
<p>I know that we can use the Gauss' Law to calculate the electric field for two coaxial cylindrical conductors of INFINITE length, but I don't see why we can use the Gauss' Law for the one ... | g7181 | [
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<p>Classically, we obtain the equations of motion by finding a path which has an action that is stationary with respect to small changes in the path. That is the path for which:</p>
<p>$\delta S =0$</p>
<p>Scaling the action by a constant should therefore do nothing. However, some books seem to consider the overall... | g7182 | [
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<p>If water is introduced in a container maintained at 20 °C in vacuum conditions, a gaseous phase will appear and the pressure will stabilize at the vapour pressure for the given temperature inside the container. So far so good.</p>
<p>Now imagine the experiment is repeated but instead of vacuum conditions, the water... | g7183 | [
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0.0328... |
<p>Using Fujikawa's path integral treatment of the triangle diagram, one can show that</p>
<p>$$\mathrm{Tr} \gamma^5 = \int d^4 x\ \partial_{\mu}j^{\mu} $$</p>
<p>Where $j^{\mu}$ is the Noether current of $U(1)_A$. Thus, the $U(1)_A$ anomaly can be traced to to fact that the trace of $\mathrm{Tr} \gamma^5 \neq 0$ a... | g7184 | [
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<p>Hi guys I'm currently trying to solve a mock exam for an exam in a few days and am a bit confused by the solutions they gave us for this exercise:</p>
<p>Exercise:</p>
<blockquote>
<p><em>A solid is composed of N atoms which are each localized at points in a lattice. Excursions about the equilibrium position of ... | g7185 | [
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<p><code>Question</code>: Show that the radial wave function for the hydrogen atom are orthogonal with no exceptions.</p>
<p><code>Attempt</code>:
We know that the wave function for the hydrogen atom is orthonormal; that is,</p>
<p>$$\langle\psi_{nml}\mid \psi_{n'm'l'}\rangle=\delta_{nn'}\delta_{mm'}\delta_{ll'}$$</... | g7186 | [
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<p>I understand how the mechanism of spontaneous symmetry breaking works, and why it produces Goldstone bosons (for global symmetries) and massive gauge bosons (for local ones).</p>
<p>However, I'm confused as to why we identify Goldstone bosons as we do. Take the linear sigma model for example. Why do we say that the... | g7187 | [
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<p>Specifically, my question is:
Should one expect energy quantization for a particle in the following potential well?
<img src="http://i.stack.imgur.com/qhXAW.png" alt="potential"></p>
<p>More generally, how can one tell whether or not energy should be discrete/quantized just by looking at the potential function?</p... | g7188 | [
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<p>A simple question about wormholes: What happens if a large object is pushed through a much smaller wormhole? For example, what happens if I push an elephant through a palm-sized wormhole? My intuition is that depending on the magnitude of the force applied, either a part of the elephant is ripped out, or the elephan... | g7189 | [
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<p>I have the following problem on my homework. The actual problem has numbers, but I figure using symbolic notation will help me understand the concept in the long run.</p>
<p>A block of mass $M$ is launched by a spring of negligible mass and constant $K$ along a frictionless surface. Prior to launch the spring is co... | g7190 | [
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<p>I have read so many forums on this and I still do not understand and it's affecting my ability to move forward with learning physics right now.</p>
<p>Imagine the following scenario: a person on a frictionless surface pushes on a stationary object. Both the person and the object have the same mass. I understand tha... | g7191 | [
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<p>Kirchhoff's loop/current rule is just law of conservation of energy and Kirchhoff's junction rule is just law of conservation of charge.So, I think that these can be applied to any circuits unlike Ohm's law. Is there any exceptions? </p> | g7192 | [
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<p>I'm studying the Simple Harmonic Motion, and I am hesitant about, how to get mass values for infinite period?</p>
<ul>
<li>When mass is 0.</li>
<li>When mass is infinite.</li>
</ul>
<p>With $\tau=2\pi/\sqrt{k/m}$. </p> | g7193 | [
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<p><a href="http://en.wikipedia.org/wiki/Eratosthenes">Eratosthenes</a> famously observed that the suns rays were perpendicular to the ground in one location, yet non-perpendicular to the ground at a location some miles to the north. On the assumption that the sun's rays are all parallel, this means the earth is round ... | g7194 | [
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<blockquote>
<p>A sailboat is moving at a constant velocity. Is work being done by a net external force acting on the boat?</p>
</blockquote>
<p>The answer key is "No" according to the work energy theorem about work is done when there is a change in final and initial velocity. But if I use Work = Force x displacemen... | g7195 | [
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<p>Problem: A bungee-cord jumper is on a bridge that is $y_1$ above water level $y_2$.
The bungee cord obeys Hooke's law with spring constant $k$ and has a relaxed length $L$
The jumper stops before reaching the water, what height is her feet above the water at this point $d$?</p>
<blockquote>
<p>I define the positi... | g7196 | [
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<p>In MTW, p. 398, "Box 16.4 (continued)", there's an interesting sketch (which can also be seen on<br>
<a href="http://www.pma.caltech.edu/~ph236/yr2008/readings/MTW_Chapter16.pdf" rel="nofollow">p. 15 of this excerpt (www.pma.caltech.edu/~ph236/yr2008/readings/MTW_Chapter16.pdf)</a>.<br>
(It's not the only sketch of ... | g7197 | [
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<p>Dirac equation is $i \hbar \gamma^\mu \partial_\mu \psi - m c \psi = 0 $</p>
<p>To show its Lorentz invariance, we convert spacetime into $x'$ and $t'$ from $x$ and $t$ and then</p>
<p>$( iU^\dagger \gamma^\mu U\partial_\mu^\prime - m)\psi(x^\prime,t^\prime) = 0$</p>
<p>The question is, how does one show from the... | g7198 | [
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... |
<p>I'm doing an exercise on vertex operators in the CFT book by Di Francesco & al.; exercise 9.2 p.329 :</p>
<p>Using mode expansion show that: $$\langle\tilde{\phi(z)}\tilde{\phi(w)}\rangle= - \text{ln} \;(1-\frac{w}{z})$$</p>
<p>I managed to complete the calculation but I'm bothered by the fact that the right ... | g7199 | [
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<p>I have person weighing spring scale. I live in Japan where the house has wood floors which deflect significantly under weight. I weighed my self in the bathroom and in the tiled bath area. The difference was 2.5 kilograms greater in the bath area but it could still be affected by possibly an angled floor or deflecti... | g7200 | [
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<p>Suppose that two matrices $A$ and $B$, representing real($\mathbb{R}$) physical quantity, can be multiplied commutatively with each other; i.e. $AB =BA$. However, each matrix cannot be multiplied commutatively with other matrices all the time (obviously). If two matrices represent physical quantity, can they be stat... | g7201 | [
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<p>In my textbook, it says that when $L$ is a matrix that represents real($\mathbb{R}$) physical quantity, $L^2$ represents non-negative real physical quantity. What would be the proof of this?</p> | g7202 | [
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<p>I have been reading Hawking's 'A Brief History of Time' and it has gotten me thinking about Einstein's theory of relativity, in that it assumes that an object must have infinite mass if it is to be traveling at the speed of light (please correct if I'm wrong in my beginner's knowledge of physics).</p>
<p>But, do li... | g7203 | [
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0.036... |
<p>Taking off from the Rutherford-Bohr model,</p>
<p><img src="http://i.stack.imgur.com/R8c0f.png" alt="Rutherford-Bohr model"><br>
<strong>Figure 1.</strong> <em>Rutherford-Bohr model.</em></p>
<p>when an electron absorbs energy (from light, heat, or otherwise) it jumps to a higher energy level, or shell. Then when ... | g7204 | [
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<p>Why is the amount of energy transferred to a driven mechanical oscillator largest when the drive frequency is the same as the natural frequency of the oscillator? Why are they exactly out of phase by π/2?</p>
<p>Clarifying example experimental setup: <a href="http://av.ph.tum.de/Experiment/1000/Grafik/b1605.gif" r... | g7205 | [
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<p>I am coding in c++ and am computing the position of an orbiting body as a function of time.</p>
<p>Everything is almost working. I have a nice elliptical orbit. Except, my orbiting body speeds up as it moves away from the "sun" and slows down as it approaches it.</p>
<p>The best way I can describe it is that it's ... | g7206 | [
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<p>I've found several articles discussing experimental evidence of a deuterium state of densities over $140 \textrm{ kg}/\textrm{cm}^3$:</p>
<ul>
<li><p>F. Winterberg. Ultradense Deuterium. <a href="http://arxiv.org/abs/0912.5414" rel="nofollow">arXiv</a>.</p></li>
<li><p>Shahriar Badiei, Patrik U. Andersson, Leif Hol... | g7207 | [
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<p>Which is the model that best shows the relationship between velocity and distance: </p>
<ul>
<li>$v \propto d$</li>
<li>$v \propto d^2$</li>
<li>$v^2 \propto d$</li>
<li>$v^2 \propto d^2$</li>
</ul>
<hr>
<p>What I think is from: </p>
<p>$$v=at \Rightarrow t=\frac{t}{a}$$</p>
<p>Then substitute into: </p>
<p>$$... | g7208 | [
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<p>In the The Emperor's New Mind book. While author explains why classical physics fails to explain our universe, says:</p>
<blockquote>
<p>The root cause of these is that two kinds of physical object must
coexist: particles, each described by a small finite number (six) of
parameters (three positions and three ... | g7209 | [
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<p>How can compactifying IIA (non-Chiral) and IIB (Chiral) Superstring on $T^2$ (2-torus) gives rise to ($2$ dual descriptions of) the same $\mathcal N = 2$ supergravity in $8$ dimensions? I don't see it. Could you please explain it to me or recommend me some literature to read about it? </p>
<p>Thank you! </p> | g7210 | [
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<p>While standing on a planet its gravitation force is noticeable and manifests only through the normal force, e.g. if jupiter had rocky surface, standing on the surface will apply about 2.5 times more force than when standing on earth. However sky diving on earth and on jupiter (without atmosphere) would apply the sam... | g7211 | [
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<p>Why are white holes the same thing as black holes in quantum gravity? Their Penrose diagrams in semiclassical gravity are utterly different.</p> | g7212 | [
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<p>Can vortices be self-sustaining?</p>
<p>I suppose vortices in water are not self sustaining, since they need constant supply of water at speed i.e. kinetic energy. But is the same case applicable to space time vortices? like wormholes?? or do they need some energy source for sustenance?</p>
<p>Please try to give a... | g7213 | [
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<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/10933/why-do-we-say-that-the-earth-moves-around-the-sun">Why do we say that the earth moves around the sun?</a> </p>
</blockquote>
<p>I should preface by stating that I'm not a physicist and my knowledge... | g205 | [
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<p>Since a <a href="http://en.wikipedia.org/wiki/Pulse_tube_refrigerator" rel="nofollow">pulse tube cooler</a> is basically a Stirling engine without moving parts running "in reverse", does that imply that when I keep the cold end at ambient temperature and apply heat to the hot end, I get pressure oscillations? Or do ... | g7214 | [
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0.010... |
<p>I understand that a particle approaching a finite potential barrier with $E < V_0$, there still is a probability of finding the particle on the other side of the barrier due to quantum tunneling.</p>
<p>My question is, since the wavefunction is nonzero inside the barrier region, is it possible to actually make a... | g855 | [
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0.04197141155600548,
-0.002555039245635271,
0.029284561052918434,
0.04749978706240654,
-0.023471856489777565,
-0.009426935575902462,
-0.037818484008312225,
0.0011879379162564874,
0.0035490989685058594,
0... |
<p>This is a followup to a <a href="http://physics.stackexchange.com/questions/67525/gaseous-fission-has-it-even-been-demonstrated-experimentally"><strong>prior question</strong></a> I asked about gaseous nuclear fission. What is the lowest nuclear fuel density required to initiate fission? This is critical for a gas ... | g7215 | [
-0.015290677547454834,
0.0368269719183445,
0.01654573529958725,
0.03000527061522007,
0.015303676947951317,
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0.06488138437271118,
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-0.017187392339110374,
-0.0286... |
<p>Assume we have a "somewhat" ideal voltage source like a DC power supply powered by mains. Take just one terminal and form a conductive path between it and earth ground. Assuming that no conductive path exists going back to the power plant ground spike, and a fuse isn't blown, wouldn't a huge amount of current flow i... | g7216 | [
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0.08719493448734283,
0.00016608562145847827,
0.022184230387210846,
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0.04780399799346924,
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-0.06927791237831116,
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0.006370534189045429,
0.001609642873518169,
... |
<p>Is there any physical matter which won't appear on x-ray i.e. invisible matter?
I think I learnt at university that all phsyical matter appears on x-ray and there is no matter that can be invisible. Is this true? For instance, does dark matter and antimatter appear on x-ray or what technology is used to prove that t... | g960 | [
0.0833127349615097,
0.037980373948812485,
0.05004332959651947,
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0.04333590716123581,
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-0.02280016802251339,
0.08447428047657013,
0.04874535650014877,
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-0.057507958... |
<p>How can one calculate the mass of air inside a tyre, given a particular tyre size; a pressure, in $kPa = \frac{1000kg}{m\cdot s^2}$; and assuming room temperature, and normal air composition? I can't quite work out what part of the equations I'm missing to remove the $s^2$ component.</p>
<p>I realise that surface/v... | g7217 | [
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0.05921788513660431,
0.03624297305941582,
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0.04354477673768997,
0.02138603664934635,
-0.024647707119584084,
0.025322670117020607,
-0.0... |
<p>Is travel through stable macroscopic wormholes between remote points of spacetime going to be possible in a definitive theory of gravity, be it string theory or something beyond it?</p>
<p>Physicists level of understanding about the holographic principle and AdS/CFT correspondence has improved significantly and con... | g7218 | [
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0.00... |
<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/39616/what-is-the-physical-interpretation-of-force-times-area">What is the physical interpretation of force times area?</a> </p>
</blockquote>
<p>If force times area has any physical meaning, what would ... | g244 | [
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0.051326487213373184,
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0.02934897504746914,
-0.05589687079191208,
-0.005260156467556953,... |
<p>I'm working on a classical mechanics problem in which the problem states that a particle of mass $m$ moves in a central field of attractive force of magnitude:</p>
<p>$$F(r, t) = \frac{k}{r^2}e^{-at}$$</p>
<ul>
<li>$r$ is the distance from the force center,</li>
<li>$t$ is time,</li>
<li>and $k$, $a$ are constants... | g7219 | [
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0.0021526142954826355,
-0... |
<p>Consider a system of N quantum mechanical particles described on Hilbert spaces $\mathcal{H}_1,...,\mathcal{H}_N$ and with Hamiltonians $H_1,...,H_N$. The Hamiltonian operator $H_1$ acts on the Hilbert space $\mathcal{H}_1$ etc. These particles are non-interacting if the Hamiltonian of the system can be written as t... | g7220 | [
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0.0131191061809659,
-0.04787905514240265,
0.0... |
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