question stringlengths 37 38.8k | group_id stringlengths 2 6 | sentence_embeddings listlengths 768 768 |
|---|---|---|
<p>I've seen the <a href="http://en.wikipedia.org/wiki/Wave_function" rel="nofollow">Wave Function</a> as a psi $\Psi$ $\psi$.
And always heard that the wave function is the <a href="http://en.wikipedia.org/wiki/Complex_number" rel="nofollow">Complex Number</a> as <a href="http://en.wikipedia.org/wiki/Imaginary_number"... | g12307 | [
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<p>Scattering of light by light does not occur in the solutions of Maxwell's equations (since they are linear and EM waves obey superposition), but it is a prediction of QED (the most significant Feynman diagrams have a closed loop of four electron propagators).</p>
<p>Has scattering of light by light in vacuum ever b... | g12308 | [
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<p>If the velocity is a relative quantity, will it make inconsistent equations when applying it to the conservation of energy equations?</p>
<p>For example:</p>
<p>In the train moving at $V$ relative to ground, there is an object moving at $v$ relative to the frame in the same direction the frame moves. Observer on t... | g12309 | [
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<p>When we see things around us, distant objects look smaller to our eyes than nearby objects do.</p>
<p>Is there any physics-related reason why our eyes or brain perceive things like this?</p>
<p>Or if this is purely biology issues (<-but nothing is purely biology or something like that..), can anyone briefly sho... | g12310 | [
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<p>If a ring/belt would be constructed</p>
<ul>
<li>of a sufficiently strong material</li>
<li>around the entire equator</li>
<li>at 100m height from the surface</li>
<li>assuming the land/water beneath is flat (no mountains get in the way),</li>
</ul>
<p>How would that ring behave - would it remain still, or crash a... | g12311 | [
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<p>In the documentary: "<a href="https://www.youtube.com/watch?v=fpb7NMR-XOo" rel="nofollow">Curiosity - Did God Create the Universe (on YouTube)</a>", theoretical physicist and cosmologist <a href="http://en.wikipedia.org/wiki/Stephen_Hawking" rel="nofollow">Stephen Hawking</a> states that time did not exist before th... | g12312 | [
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<p>In <a href="http://en.wikipedia.org/wiki/Vacuum_energy">wiki</a> the Vacuum Energy in a cubic meter of free space ranges from $10^{-9}$ from the cosmological constant to $10^{113}$ due to calculations in <a href="http://en.wikipedia.org/wiki/Quantum_electrodynamics">Quantum Electrodynamics</a> (QED) and <a href="htt... | g12313 | [
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<p>I am not sure if this question is appropriate for this section, but I just want to know what these type of questions are called and when do physics majors learn them?</p>
<p>These problems have to do with pulleys and constant lengths. I found the problem in an engineering dynamics course.</p>
<p>Example</p>
<p><i... | g12314 | [
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<p>As far as I know, according to quantum field theory, there are some photons that go faster than <em>c</em>, which is the speed of light in vacuum. </p>
<p>However, there seems to be a paper and a corresponding experiment that show every photon obeys the speed limit of <em>c</em>. (<a href="http://physics.aps.org/sy... | g12315 | [
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<p>Inflation was the extreme accelerating expansion of the universe, see here:
<a href="http://en.wikipedia.org/wiki/Inflation_(cosmology)" rel="nofollow">http://en.wikipedia.org/wiki/Inflation_(cosmology)</a>
It worked in a similar way to dark energy but was so strong it would easily tear atoms apart (if it wasn't far... | g12316 | [
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<p>The quantum-mechanical motion problem of an electron in electric field of the nucleus is well known. The quantum-mechanical description of electron motion in a magnetic field is also not difficult, since it needs to solve the Schrödinger equation of the form:
$$\frac{(\hat p + eA)^2} {2m} \psi = E \psi $$
But if we ... | g12317 | [
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<p>I've been trying to find a good source for what the planets look like in the infrared, specifically if viewed as a point source. I've been working with a low resolution telescope that senses in the infrared. What will a planet look like?</p> | g12318 | [
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<p>What is the experience using the <a href="http://en.wikipedia.org/wiki/Sky-Watcher" rel="nofollow">Sky-Watcher</a> Skyhawk 1145P SynScan AZ GOTO telescope and can it be recommended for a new astronomer? Is it any good?</p> | g12319 | [
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<p>Black holes were first predicted by astrophysics, then observed. Was the existence of galaxies first predicted by astrophysics, or first observed by astronomers?</p> | g12320 | [
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<p>I have just read an article about it here(<a href="http://www.greatdreams.com/2012.htm" rel="nofollow">http://www.greatdreams.com/2012.htm</a>)(Scroll to bottom). I'm just a website developer, and I really want to know if this is really true. I'm curious.</p>
<p>I'm pasting the content from it:</p>
<blockquote>
... | g12321 | [
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<p>I was reading my quantum mechanics text and I have a doubt. I have the energy levels well defined for the finite square well and the author suddenly compares (I believe) those levels with the levels of the nucleon with the following phrase: "is the spacing between levels on the order of MeV for a nucleon bound in a ... | g12322 | [
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<p>Since baryons (e.g. protons, neutrons) are composite particles it should be possible to split them apart. If so, is it then possible to extract useable energy out of the splitting of baryons in analogy to nuclear fission?</p> | g12323 | [
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<p>What is latent heat of vaporization ($L_v$) in the first place? <a href="http://en.wikipedia.org/wiki/Enthalpy_of_vaporization" rel="nofollow">Wikipedia</a> seems to indicate that it is the energy used in overcoming intermolecular interactions, without taking into account at all any work done to push back the atmosp... | g12324 | [
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<p>If there is a device in which a ball is attached to a pivot by a rod of length R and it is left to oscillate by dragging it to one side so that it is completely horizontal, at any point on its decent the ball has some velocity and also has some angular velocity about the pivot. In this case is the rotational kinetic... | g12325 | [
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<p>Let $|\psi \rangle$ represents a wavefunction through and $\langle \psi |$ represent the dual<br>
vector. Now there are things such as <a href="http://en.wikipedia.org/wiki/Matter_wave" rel="nofollow">matter waves</a>, could $|\psi \rangle$ represents a matter wavefunction, (of course representation is a definition)... | g12326 | [
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<p>I need to find out how far a ball is from the predicted trajectory in 2 dimensional space and I know the start and end position of the ball in both dimensions. Along with that I know the initial velocity and the angle at which the ball was launched. </p>
<p><strong>Every single variable is known in this picture.</... | g12327 | [
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<p>Consider a generalized 1D tight-binding model (without spin) with the following Hamiltonian
\begin{equation}
\mathcal{H}\left(\{\chi_{r,r+1}\}\right)=\sum_{r}(\chi_{r,r+1}c^\dagger_rc_{r+1}+h.c.)~,
\end{equation}
and suppose that the complex number $\chi_{r,r+1}$ is a variational parameter. The $r$ index runs over a... | g12328 | [
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<p>Please forgive my ignorance, I am not a student of physics in any capacity, therefor my understanding of string theory is extremely limited to say the least. Based on the recent lack of evidence in support of SUSY at the LHC, my question is: what are the implications if Superstring theory is debunked? (again, please... | g391 | [
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<p>The question comes from a comment by Mark Rovetta on my earlier question about the <a href="http://physics.stackexchange.com/questions/55536/what-if-the-earths-core-goes-cold">Earth's core going cold</a>.</p> | g12329 | [
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<p>The phenomenon of multi-photon ionization of atoms has been studied, both theoretically and experimentally, for several decades. Intense laser beam devices are the apparatuses used for the <a href="http://en.wikipedia.org/wiki/Resonance-enhanced_multiphoton_ionization" rel="nofollow">experimental study of this pheno... | g12330 | [
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<p>A firearm relies upon some kind of explosive powder to drive the slug out of the barrel. </p>
<p>My guess however is that in space (at GEO, or higher) a firearm would be unusable due to the extremes of temperature/pressure. Secondly the powder probably would not ignite when the hammer fell.</p>
<p>Are my assumptio... | g12331 | [
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<p>We can store cold (ice), heat (i.e. hot water bag) and electrical charge (batteries). We can even "store" a magnetic field in a magnet. We can convert light into energy and then, if we want, back to light. But we can't store light in form of light in significant amounts. What is the explanation of that in physics ... | g12332 | [
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<p>I`m studying the Hamiltonian with point interaction centered in $y$ in three dimensions.
I know that the elements in the domain of the Hamiltonian are of the form
$$\psi=\phi+qG^z(\cdot-y)$$
where $G^z(x)=\frac{e^{i\sqrt{z}|x|}}{4\pi|x|}$, $q\in\mathbb{C}$ and $\phi\in H^2$. The boundary condition is
$$q=\frac{4\pi\... | g12333 | [
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<p>More specifically, how do you physically prepare the superposition of two beams of polarized light? </p>
<p>Suppose beam A and beam B, the two input beams, each have unknown polarizations.<br>
Beam C, the output beam, must be the superposition of beams A and B.<br>
How do you do it?</p>
<p>You can create an ove... | g12334 | [
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<p>That there is some form of generalized framework from which quantum mechanics follows as a certain limit?
Is there any theory that has been discovered that can lead to the same predictions of QM but is not strictly QM?</p> | g12335 | [
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<p>When I ride my bike, does half of the energy go into the earth because of Newton's third law? Does the energy in the earth transfer into heat upon my brakes when I utilize them?</p>
<p>If the earth was 2000 times less massive than it is, and I applied the same energy to my pedal, would my bike move (relative to an ... | g12336 | [
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<p>I am trying to determine the contact area between a cylinder and a plane surface of two different materials so that the plane lies tangent to the cylinder. There is elastic contact between the two materials so the plane surface deforms to create a contact area around an area of the cylinder because there is a force ... | g12337 | [
0.07206471264362335,
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0.009189075790345669,
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<p>Well, this is a simple, basic and I think even silly doubt. The first time I saw the definition of momentum as $p = mv$ I started to think why this is a good definition. So I've read the beginning of Newton's Principia where he said that momentum is a measure of quantity of motion.</p>
<p>Well, this started to make... | g12338 | [
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<p>I read this in my textbook: <em>A charged particle or object is not affected by its own electric field.</em></p>
<p>Since I find this completely unintuitive and my mind is yelling "wrong! wrong! how could a particle even distinguish between its own field and the external fields?" I would really like to hear an expl... | g12339 | [
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<p>Previously, I have calculated energy spectrum for 3D isotropic turbulent flow data which is equally spaced in all three directions and then to compute the energy spectrum, one performs Fourier transform and then accumulates energy located in different wavenumber bins and then gets the ($k^{−5/3}$) slope and it all w... | g12340 | [
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<p>Is there a simple answer to this question ? see last line of this paragraph
<a href="http://en.wikipedia.org/wiki/Fermionic_condensate#Fermionic_superfluids" rel="nofollow">http://en.wikipedia.org/wiki/Fermionic_condensate#Fermionic_superfluids</a> </p> | g12341 | [
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<p>I'm studying the refraction in optics.</p>
<p>If a red light monocromatic beam of red light (700 nm) passes from air to water it becomes with a wavelenght of aprox 526 nm. </p>
<p>So, my question is: How is going to see this beam a diver? Red (700 nm) or something more like green (526 nm)? (Let's suppose that the ... | g12342 | [
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<p>In the photoelectric cell my teacher says that the electron emission from the cathode depends on the frequency of the incident photon and it doesn't depend on the light intensity (I = nhU/ta , Right?) so if the light intensity increased the photoelectric current won't change .</p>
<p>but what if this increase in t... | g12343 | [
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<p>I have a question that arised by reading <em>A Course in Modern Mathematical Physics</em> by Peter Szekeres.</p>
<p>He defines the galilean space $\mathbb{G}^{4}$ to be the space of events with a structure consisting of three elements:</p>
<ol>
<li>Time intervals $\Delta t=t_2-t_1$</li>
<li>The spatial distance $\... | g12344 | [
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<p>Last week in class we derived the formula for time dilation using light clocks and got $$t=\gamma t_0\quad \gamma=\left(1+\left(\frac vc\right)^2\right)^{-1/2}$$
So far so good. However, after class I was thinking of an alternate proof, but for some reason I got another result and I can't tell why. </p>
<p>Basicall... | g12345 | [
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<p>What is the assumption for <a href="http://en.wikipedia.org/wiki/Boltzmann_H-theorem" rel="nofollow">Boltzmann H-theorem</a>? One can derive it just from the unitarity of quantum mechanics, so this should be generally true, does it imply a closed system will always thermalize eventually? Does it apply for many-body ... | g12346 | [
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<p>After having learnt that the <a href="http://physics.stackexchange.com/questions/104216/lie-group-of-schrodinger-wave-equation">Galilean (with its central extension)</a> with an unitary operator</p>
<p>$$ U = \sum_{i=1}^3\Big(\delta\theta_iL_i + \delta x_iP_i + \delta\lambda_iG_i +dtH\Big) + \delta\phi\mathbb{\hat... | g12347 | [
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<p>As I understand, satellites and the Moon orbiting Earth are in free fall. Isn't the same true for Earth orbiting the Sun?</p>
<p>My question is then: How can the Sun's gravity affect <a href="http://en.wikipedia.org/wiki/Tidal_force" rel="nofollow">tides</a>? Aren't the molecules in the oceans in free fall relative... | g12348 | [
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<p>In GR, it's usually taken for granted - or as a definition - that the time measured by an observer's clock is related to the geometry in a very simple way, $d\tau^2 = |ds^2|$. This is easy enough to see in some simple contexts, like special relativity, but it might not be obvious in general spacetimes.</p>
<p>In pr... | g12349 | [
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<p>I have a lattice with Lattice Vectors $(\vec{t}_1,\vec{t}_2,\vec{t}_3)$ which are NOT orthogonal in general.<br>
How can I identify the atoms/unit cells that belong to a plane - that is normal to a given direction.<br>
I do recognise that the lattice might not be periodic in ANY direction - only specific ones. </p>... | g12350 | [
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<p>A beam $\displaystyle 3m$ long with fixed support on one end and hinge on the other end is subjected to a uniform load of $10\ kN/m$. What is the maximum shear of this beam?</p>
<p>The solution is this one:</p>
<p>$\displaystyle Max.Shear = \frac{5\omega{L}}{8}=\frac{5\left(10\right)\left(3\right)}{8}=18.75\ kN$</... | g12351 | [
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<p>In Caroll's Spacetime and Geometry, page 227, he says that from the Schwarzschild metric, you can see than from inside a black hole future events all lead to the singularity. He says you can see this because for $r<2GM$, t becomes spacelike and r becomes timelike. I don't understand his reasoning though. Why does... | g12352 | [
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0.002228... |
<p>Let's have the potential $U = -V_{0}$ for $|x| \leqslant a$ and $U = 0$ for $|x| > a$.
The stationary Dirac equation for bound states gives
$$
tg(\frac{p_{2}a}{\hbar}) = \frac{2\Gamma}{1 - \Gamma^{2}}, \qquad (1)
$$
where
$$
\Gamma = \frac{p_{1}}{p_{2}}\frac{E + mc^{2} + V_{0}}{E + mc^{2}}, \quad p_{1}c = \sqrt{m... | g12353 | [
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0.0517... |
<p>I recently spend some time on cooking and I'm curious about the time evolution of the temperature of the water. I did some experiment and the temperature is of the form
$$ T = 100 \mathrm{^\circ C} + (T(t_0) - 100 \mathrm{^\circ C}) e^{-k(t - t_0)} $$
for some positive constant $k$ somehow (for example, see <a href=... | g12354 | [
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0.... |
<p>After all, it <em>does</em> change direction when reflection occurs. So shouldn't it also accelerate? And since the acceleration cannot increase the speed of light, mustn't it slow down?</p> | g658 | [
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<p>As we know, there are two distinct <a href="http://en.wikipedia.org/wiki/Graphene#Electronic_properties" rel="nofollow">Dirac points</a> for the free electrons in <a href="http://en.wikipedia.org/wiki/Graphene" rel="nofollow">graphene</a>. Which means that the energy spectrum of the 2$\times$2 Hermitian matrix $H(k_... | g12355 | [
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0.03284242004156113,
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0.010726475156843662,
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-0.... |
<p>Suppose you know that a qubit is either is in state $|+\rangle$ with probability $p$ or in state $|-\rangle$ with probability $1-p$. If this is the best you know about the qubit's state, where in the Bloch sphere would you represent this qubit?</p> | g12356 | [
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<p>I found the freefall motion equation which describes terminal velocity of a falling body, but I can't find a similar equation for a vehicle subject to constant traction force, so I tried determining it by myself, but resulting equation is not plausible, as it shows dozens of seconds needed for a 1600 kg vehicle to g... | g12357 | [
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<p>I am a little confused, from the first law of thermodynamics (energy conservation)</p>
<p>$$\Delta E = \delta Q - \delta W $$</p>
<p>If the amount of work done is a volume expansion of a gas in, say a piston cylinder instrument at constant pressure,</p>
<p>$$\Delta E = \delta Q - pdv$$</p>
<p>Here $p$ is the con... | g12358 | [
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... |
<p>I am taking an introductory class in seismology, but have some difficulties understanding the logic behind the formula used to calculate the time it takes for a refracted wave to return to the surface from which it was sent out originally. </p>
<p>So, say we have a seismic wave sent out from a horizontal layer. We... | g12359 | [
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<p>I have a sample of U-238 of which my Geiger counter detects beta activity at 700 events per second. Based on the counter's efficiency of 98.6% for U-238, the activity would be about 710 becquerels, I think. Here I am going off of my understanding based on explanations from many different people.</p>
<p>From here I ... | g12360 | [
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<p>I know there's lots of questions that address similar situations, (<a href="http://physics.stackexchange.com/questions/92144/batteries-connected-in-parallel">Batteries connected in Parallel</a>,
<a href="http://physics.stackexchange.com/questions/107661/batteries-and-fields">Batteries and fields?</a>,
<a href="http:... | g12361 | [
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0.016... |
<p>I'm actually interested in cases of cross-discipline data re-use.</p>
<p>I know that the <a href="http://lasco-www.nrl.navy.mil/lasco.html" rel="nofollow">SOHO/LASCO coronographs</a> are used for <a href="http://sungrazer.nrl.navy.mil/" rel="nofollow">comet finding</a>, that solar telescopes were used to get inform... | g12362 | [
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<p>Reading / viewing up on how jet engines work, <a href="http://youtu.be/p1TqwAKwMuM?t=9m02s" rel="nofollow">this video</a> explains at the 9:02 mark that, for turbofan engines, ".. it is more aerodynamically efficient to have a lot of air moving relatively slowly rather than a little air moving relatively quickly." I... | g12363 | [
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<p>A professor told me that most physicists assume that all identical fermions are in completely orthogonal states. If that is true, then does that mean that that the total wave function is highly localized for a closed box of a huge number of electrons? I get confused between when your supposed multiply wavefunctions ... | g12364 | [
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<p>Almost all of the <strong>orbits of planets</strong> and other celestial bodies <strong>are elliptical</strong>, <strong>not circular</strong>. </p>
<p>Is this due to <a href="http://www.astro-tom.com/technical_data/why_elliptical.htm">gravitational pull</a> by other nearby massive bodies?
<strong>If this was the ... | g973 | [
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<p>I am having a discussion with my coworkers. Does anyone know what is the wavelength of turquoise color and whether it is closer to green or blue when comparing their wavelengths ? </p> | g12365 | [
0.005551822017878294,
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0.041874274611473083,
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0.017227936536073685,
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0.04124535992741585,
0.07659774273633957,
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0.0391... |
<p>I have some trouble in the interpretation of the <a href="http://en.wikipedia.org/wiki/Weakly_interacting_massive_particles" rel="nofollow">WIMP</a> cross-section annihilation versus their mass.</p>
<p><img src="http://www.quantumdiaries.org/wp-content/uploads/2012/07/XENON100_2012.png" alt="Graph"></p>
<p>I under... | g12366 | [
0.018557416275143623,
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0.03890451043844223,
0.0465024933218956,
0.047480031847953796,
0.06270217150449753,
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0.01522933878004551,
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0.052719030529260635,
-0.... |
<p>so apologies if this is a silly question...</p>
<p>In the type 1 see saw model we add extra Majorana fermions to our model. These fermions have to be total gauge singlets in order to have a Majorana mass term and thus trigger the see saw mechanism.</p>
<p>In a supersymmetric model we add gauge singlet superfields ... | g12367 | [
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0.020655110478401184,
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0.051381971687078476,
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0.04667138308286667,
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0.0061425198800861835,
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0.031551700085401535,
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<p>If a ball hits the floor after an acceleration then why does it bounces lower? I mean the Energy is passed to the floor then why does the floor give back less Energy?</p> | g12368 | [
0.1233217641711235,
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<p>I was thinking about the following thought experiment, but wasn't sure about its outcome.</p>
<p>Suppose there is a black-hole and I enter it with a partitioned box containing two different gases on either side. After passing, the event horizon the radius of a black-hole increases as I added mass to the system (?).... | g12369 | [
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0.06174971163272858,
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0.004654348362237215,
0.006031284108757973,
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<p>I need help with the following problem, please help me get started as I do not know where to begin with</p>
<p>One spherical raindrop is falling in the atmosphere. Mass of the raindrop increases proportional with it's area. There's no counterpoise in it's move. I should show that radius of a rain drop is increasing... | g12370 | [
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0.014045355841517448,
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<p>I encountered this term <strong>a uniform RVB spin-liquid state</strong> in some <a href="http://prb.aps.org/abstract/PRB/v65/i16/e165113" rel="nofollow">articles</a>, for example, see the paragraph under Eq.(29) on page 9 in this <a href="http://prb.aps.org/abstract/PRB/v65/i16/e165113" rel="nofollow">paper</a>.</p... | g12371 | [
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<p>Background:
I'm a legal MMJ patient and I've been looking into water pipers/bongs recently. I understand that this question can be a little controversial but where I live this is all legal as long as you have the proper prescription. Last few years there has been quite a lot of "scientific" bongs that has been hitt... | g12372 | [
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0.0424887053668499,
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<p>I'm trying to simulate by finite elements method Maxwell equations for a current carrying wire. My 3d geometry consists of a cylinder and a box containing it. I will use a mixed formulation and Nedelec's elements introducing a vector potential. I'm in a magnetostatic regime. At the end of the simulation I would like... | g12373 | [
0.014037474058568478,
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0.020280946046113968,
0.008994988165795803,
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... |
<p>When we're dealing with problems in electrostatics (especially when we use Gauss' law) we often refer to electric <a href="http://en.wikipedia.org/wiki/Field_line">field lines</a> density which is inversely proportional to radius in case of a single point charge (all field lines are directed radially). My question m... | g333 | [
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0.06346984952688217,
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<ol>
<li><p>Does the equivalence principle imply that there is some fundamental difference between acceleration due to gravity and acceleration by other means (because there is no way to 'feel' free fall acceleration for a uniform gravitational field)? </p></li>
<li><p>Does General Relativity allow you to describe the... | g12374 | [
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0.0073022786527872086,
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0.006619828287512064,
0.002231850754469633,
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0.008530869148671627,
0.03... |
<p>Imagine two electrons $A$ and $B$ at rest.</p>
<p>Electron $B$ is at a vertical distance $r$ above electron $A$.</p>
<p>Let us assume that the electrons are constrained to move on horizontal rails.</p>
<p>At time $t=0$ I give electron $A$ a horizontal acceleration $a$ for a time interval $\Delta t$.</p>
<p>At ti... | g12375 | [
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<p>I'm looking for primer material on the modelling the physics of liquids. In particular I want to make a small simulation (I'm a programmer by profession) of throwing ink at a board, much like this.</p>
<p><a href="http://www.pond5.com/stock-footage/670934/ink-splatter.html" rel="nofollow">http://www.pond5.com/stock... | g12376 | [
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0.025023940950632095,
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0.04639917239546776,
... |
<p>Regarding general relativity:</p>
<ul>
<li>What is the physical meaning of the Christoffel symbol ($\Gamma^i_{\ jk}$)?</li>
<li>What are the (preferably physical) differences between the Riemann curvature tensor ($R^i_{\ jkl}$), Ricci tensor ($R_{ij}$) and Ricci scalar ($R$)? For example why do the Einstein equatio... | g12377 | [
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<p>I am currently learning about simple harmonic motion.
In a book I am reading it says frequency of kinetic energy is twice the frequency of velocity for a harmonic oscillator by showing velocity vs time graph and KE vs time graph</p>
<p>What I think it means to say is that kinetic energy reaches its maximum value 2 ... | g12378 | [
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0.018224257975816727,
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<p>I need to know this for my project- "power generation using the pressure applied on a keypad of a mobile electronic device". How much pressure does it take to displace a single electron off its crystal structure so that it is suitable for generating piezo-electricity?</p> | g12379 | [
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<p>Lately I have been reading a lot about the discovery of the Higgs boson and it got me thinking, what is the potential application of this particle? I mean can the Higgs Boson change our world the way the discovery of the electron has?</p>
<p>For example: The Higgs Boson is what gives all other particles mass, could... | g392 | [
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0.020281784236431122,
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0.033117... |
<p>As it is getting warmer here by the minute I was asking myself:</p>
<p><strong>Are there materials, that are black (in th visible range) but reflect (most) invisible light?</strong></p>
<p>Furthermore, I asked myself <strong>what fraction of heat could be kept</strong> away using this material in daylight.</p>
<p... | g12380 | [
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<p>There are many electromagnetic structures used in microwave engineering and EM devices. For example, <a href="https://en.wikipedia.org/wiki/Patch_antenna" rel="nofollow">patch antennas</a>, metamaterials made from unit cells, etc.</p>
<p>When they design structures like patch antennas, <a href="https://en.wikipedia... | g12381 | [
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<p>Alright, we know that copper is a diamagnetic material, which has paired electrons. These paired electrons have different spin. I'm specifically interested in what is going on with the electrons in a copper coil, when creating an induced current with a magnet.</p>
<p>1 Question:</p>
<p>"Can you break the bond betw... | g12382 | [
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<p>If the electron flow in a magnet is say from South pole to North pole, then I can understand why you can't put the two north ends of magnets together, as the two flows of electrons repel each other.</p>
<p>But then why can't I put the two south pole ends of a magnet together? If the electrons flow out the North po... | g12383 | [
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0.03618735447525978,
0.014894691295921803,
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<p>The Boyer-Lindquist coordinate coordinate of the Kerr Solution is
$$
ds^2=\left(1-\frac{2Mr}{\Sigma}\right)dt^2+\frac{4Mar\sin^2\theta}{\Sigma}dtd\phi - \frac{\Sigma}{\Delta}dr^2-\Sigma d\theta^2-\left(r^2+a^2+\frac{2Ma^2r\sin^2\theta}{\Sigma}\right)\sin^2\theta d\phi^2
$$</p>
<p>Let
$$
K=\frac{\partial}{\partial t... | g12384 | [
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0.02110896445810795,
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0.012206405401229858,
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0... |
<p><img src="http://i.stack.imgur.com/IkDmz.jpg" alt="enter image description here"></p>
<p>here two reversible engines working between same temperature(1-a-b-c-a ;2- a-b-c-d-a),by carnot's theorem they will have same efficiency, but i could not understand from figures as the out put (closed area) of 1st one is less t... | g12385 | [
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<p>What is the difference between motional EMF = $-vBL$ , and Faraday's law of induction $\displaystyle\mathcal{E} = \left|\frac{d\Phi_B}{dt}\right|$?
Aren't they the same?
What is the relation of Lorentz force to motional EMF? </p> | g12386 | [
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<p>Leonid Levin said, "Exponential summations used in QC require hundreds if not millions of decimal places accuracy. I wonder who would expect any physical theory to make sense in this realm." See <a href="https://groups.google.com/forum/m/#!msg/sci.physics.research/GE5cz3xefCc/e0eh34MZGdwJ" rel="nofollow">https://gro... | g12387 | [
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<p>So, I've been enjoying reading a lot of helpful posts, but now, I found myself in the need of asking something.</p>
<p>I have a hard time grasping the general concept of electricity / how the relation between the movement of electrons and energy corresponds.</p>
<p>But so far I've reach this conclusion / guess:</p... | g12388 | [
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<p>I have recently been trying to refresh my memory on the Quantum Field Theory I learned 25 years ago while getting my Ph. D. At the time I did not study Chern-Simons modifications to QFT Lagrangians. Can someone point me to some good notes on the topic? I really want to understand the "utility" of those terms. Why do... | g393 | [
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<p>Would the following work?</p>
<p>Imagine one would</p>
<p>1) create a straight 4000 km long tube (at ground level), following the curvature of the Earth, wide enough to hold a pod the size of an aircraft cabin;</p>
<p>2) remove the air in front of the pod and make sure it accelerates to a speed of 28000 kph.</p>
... | g12389 | [
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<p>After seeing <a href="http://physics.stackexchange.com/questions/106808/why-is-jumping-into-water-from-high-altitude-fatal/106814#106814">this answer</a> claiming that displacing matter "In a very short time", "no matter whether the matter is solid, liquid, or gas" (even though he concludes that falling from a high ... | g12390 | [
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<p>Consider the case of a tidally locked planet: its axis of rotation must be perpendicular to the plane of its revolution around the parent star. Therefore, no <a href="http://en.wikipedia.org/wiki/Precession" rel="nofollow">precession</a>.</p>
<p><strong>It is possible for a planets to have a precession period that ... | g12391 | [
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<blockquote>
<p>The question: <em>The gauge pressure in your car tires is $2.60 * 10^5 N/m^2$ at a temperature of $35.0°C$ when you drive it onto a ferryboat to Alaska. What is the gauge pressure later, when the temperature has dropped to −28°C? Assume that the volume has not changed. Answer needed in atm.</em> </p>... | g12392 | [
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0.03445037826895714,
0.016073962673544884,
0.016553083434700966,
-0.005403263960033655,
-0.0... |
<p>In Kinetic Theory, one studies the evolution of a system of $N$ particles interacting with each other. We use the notation $\boldsymbol{w}_{i}$ to describe the coordinates in phase-space of each particle. Liouville's Equation gives the incompressible evolution of the $N-$Body distribution function</p>
<p>$$f^{(N)} ... | g12393 | [
0.02976221591234207,
-0.005314785521477461,
0.001859729876741767,
-0.03632827475667,
0.046242855489254,
0.06299955397844315,
0.029561880975961685,
0.014885157346725464,
-0.01101780030876398,
-0.004044554196298122,
-0.05895860493183136,
0.03501148149371147,
0.0015542709734290838,
0.01653433... |
<p>The 115 GeV ATLAS Higgs with enhanced diphoton decays has <a href="http://motls.blogspot.com/2011/05/atlas-at-94pb-diphoton-hysteria-goes.html">gone away</a> but there are several other recent tantalizing hints relevant for particle physics, namely</p>
<ul>
<li><a href="http://motls.blogspot.com/2011/05/cogent-sees... | g12394 | [
-0.02196340635418892,
0.01528517622500658,
-0.012586641125380993,
-0.05756654962897301,
0.06389954686164856,
0.017318272963166237,
0.02904127724468708,
0.05909975245594978,
-0.005216019693762064,
-0.0305066779255867,
-0.014609179459512234,
0.0011664126068353653,
0.0457301028072834,
-0.0224... |
<p>This posting is regarding the recent confirmation of the DAMA results that might be due to underlying differences in proton and neutron cross section with the dark matter particles, which reflect on the differences between Xenon and Germanium detectors</p>
<p>in the early days of particle physics, neutrinos were di... | g12395 | [
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0.004703125916421413,
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0.00855971034616232,
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0.00554003706201911,
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0.01478207390755415,
-0.00... |
<p>I know the absorption/extinction equations in nanoparticle physics should be:
$$Q_{abs}=\frac{1}{2}\mathbf{Re}\int \mathbf{J}_{tot}\cdot\mathbf{E}_{tot}^\ast dV=\frac{\omega}{2}\mathbf{Im}(\epsilon)\int|\mathbf{E}_{tot}|^2dV$$
also, for the extinction, it reads:
$$Q_{ext}=\frac{1}{2}\mathbf{Re}\int \mathbf{J}_{tot}\... | g12396 | [
0.03841230273246765,
0.0007585596758872271,
-0.01122811809182167,
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0.07527580857276917,
0.04860004410147667,
0.03850607946515083,
0.02915501967072487,
0.004159311763942242,
0.05587369203567505,
-0.033308472484350204,
0.028978122398257256,
0.031490571796894073,
0.00553... |
<p>It is known that <a href="http://en.wikipedia.org/wiki/Kepler%27s_laws_of_planetary_motion" rel="nofollow">Kepler's laws of planetary motion</a> can be derived from <a href="http://en.wikipedia.org/wiki/Newton%27s_laws_of_motion" rel="nofollow">Newton's laws of motion</a> and his <a href="http://en.wikipedia.org/wik... | g12397 | [
0.005500842351466417,
0.06332916021347046,
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0.07654030621051788,
0.020595740526914597,
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0.0037633520551025867,
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-0.... |
<p>In <a href="http://projecteuclid.org/download/pdf_1/euclid.cmp/1104178138" rel="nofollow">Witten's paper</a> <em>Quantum Field Theory and the Jones Polynomial</em>, he mentioned that:</p>
<blockquote>
<p>Geometers have long known that (via de Rham theory) the self-dual and anti-self-dual Maxwell equations are rel... | g12398 | [
0.025448542088270187,
-0.00557940686121583,
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0.07297475636005402,
0.01611820049583912,
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0.049824308604002,
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0.006541053298860788,
0.012410182505846024,
0.005552189... |
<p>Use Gauss’s Law to prove that the electric field anywhere inside the hollow of a charged
spherical shell must be zero.</p>
<p>My attempt:</p>
<p>$$\int \mathbf{E}\cdot \mathbf{dA} = \frac{q_{net}}{e}$$</p>
<p>$$\int E \ dAcos\theta = \frac{q_{net}}{e}$$</p>
<p>$$E \int dA = \frac{q_{net}}{e}$$</p>
<p>$E\ 4\pi ... | g12399 | [
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0.02860349602997303,
0.010794511996209621,
-0... |
<p>This might be a really silly question, but I don't understand it. </p>
<p>In finding the electric field due to a thin disk of charge, we use the known result of the field due to a ring of charge and then integrate the relation over the complete radius. But I had a problem in the derivation, as follows:</p>
<p>We a... | g12400 | [
0.0807400643825531,
-0.03023655340075493,
-0.02419726736843586,
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-0.03985840827226639,
-0.005991524085402489,
-0.0... |
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