question stringlengths 37 38.8k | group_id stringlengths 2 6 | sentence_embeddings listlengths 768 768 |
|---|---|---|
<p>I understand that the fundamental representation of $U(1)$ amounts to a multiplication by a phase factor, e.g. EM. I thought that when it is extended to higher dimensional representations, it would just become a phase factor times the identity matrix.</p>
<p>Can someone explain where the hypercharge comes into the ... | g8339 | [
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<p>why do two observers measure the same order of events if we are inside the light cone?</p>
<p>(e.g. if ds^2 > 0 time order is preserved according to the class mech book I am reading, but it doesn't give any proof of this) I assume there is some simple geometrical argument I am missing</p>
<p>and analgously why do... | g8340 | [
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<p>In a common wood fire such as a campfire, is matter converted to energy or is it simply an exothermic chemical reaction and all the mass can be accounted for in the ash and soot?</p> | g8341 | [
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<p>Consider the following example:</p>
<blockquote>
<p><em>A bullet of mass 45g is fired at a speed of 220 m/s into a 5.0 kg sandbag hanging from a string from the ceiling. The sandbag absorbs the bullet and begins to swing. To what maximum vertical height will it rise? (Assuming negligent air resistance and heat lo... | g8342 | [
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<p>The abstract Weyl Algebra $W_n$ is the *-algebra generated by a family of elements $U(u),V(v)$ with $u,v\in\mathbb{R}^n$ such that (Weyl relations)
$$U(u)V(v)=V(v)U(u)e^{i u\cdot v}\ \ Commutation\ Relations$$
$$U(u+u')=U(u)U(u'),\qquad V(v+v')=V(v)V(v')$$
$$U(u)^*=U(-u),\qquad V(v)^*=V(-v)$$
It is a well known f... | g8343 | [
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<p>Given a system of two particles with spin up and down, I have troubles to understand the possible states of this system.</p>
<p>I would have normally thought, that the possible states are the tensor products of the states of each particle with one of the other.
This would have given us the states that are listed in... | g8344 | [
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<p>I have seen on this site some questions regarding the nature of gravitational-force, and the ways in which it could be interpreted. Most of them mention that the space-time fabric came into existence due to the big-bang. But I cannot understand why it came into existence during the big-bang, and had no earlier exist... | g8345 | [
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<p>My question is, <em>can the (classical) Lagrangian be thought of as a metric</em>? That is, is there a meaningful sense in which we can think of the <em>least-action</em> path from the initial to the final configuration as being the <em>shortest</em> one? Then the equations of motion would be geodesics - not in phys... | g8346 | [
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<p>I know perfectly well how to derive the magnitude of the electric field near a conductor,
$$E = \frac{\sigma}{\varepsilon_0}$$ and near a sheet of charge, $$ E = \frac{\sigma}{2\varepsilon_0} .$$</p>
<p>In fact, I can explain with clarity each step of the derivation and I understand why is one two times larger tha... | g8347 | [
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<p>I've been wondering: </p>
<p>Are there, still, some advantages, for current research, to study Newtonian gravity? I mean, not experimentally, where Newton gravity is a very good approximation to everyday phenomenon or, even, to the solar system (aside some perihelion problems, gravitational lensing, etc...) but to ... | g8348 | [
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<p>How can we construct a <a href="http://en.wikipedia.org/wiki/Tauc_plot" rel="nofollow">tauc plot</a> using data from the transmission spectra? How does one calculate the absorption coefficient for plotting tauc plots? </p> | g8349 | [
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<ol>
<li><p>Mathematically, (by mathematically I means by equations) what is path of light in the accelerating elevator?</p></li>
<li><p>What is the difference between an ordinary derivative and covariant derivative (which is used in curved geodesic)?</p></li>
</ol> | g8350 | [
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<p>I have read about the application of railguns and other ground powered launch, where there is no need to carry any propellant in the rocket.</p>
<p>I am wondering, to <strong>what velocity should the vehicle achieve to enter into the orbit of earth?</strong>
I know the orbital velocity and escape velocity calculati... | g8351 | [
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<p>I'd like to know if the sign in front of a kinetic term in QFT important. For the scalar field we conventionally write (in the $ + --- $ metric),
\begin{equation}
{\cal L} _{ kin} = \frac{1}{2} \partial _\mu \phi \partial ^\mu \phi
\end{equation}
Based on the answer given <a href="http://physics.stackexchange.com... | g8352 | [
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<p>What happens when the photon which hits a metal surface has energy equal to the work function of that surface?
$$\phi = hf$$
I realise the emitted electron will have no kinetic energy after escape, but then what does it do? Hover above the surface? Or does it have momentum from escaping? I also don't understand what... | g8353 | [
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<p>The annihilation and creation operators are given below
$$
\hat a|n\rangle=\sqrt{n}|n-1\rangle\qquad\text{and}\qquad\hat a^\dagger|n\rangle=\sqrt{n+1}|n+1\rangle
$$</p>
<p>Now I know the operator a^ is not Hermitian but as to why I'm a little confused.
Is it because they 'create' and 'annihilate' photons hence they... | g8354 | [
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<p>When I learn QFT, I am bothered by many problems in complex analysis.</p>
<p>1) $$\frac{1}{x-x_0+i\epsilon}=P\frac{1}{x-x_0}-i\pi\delta(x-x_0)$$</p>
<p>I can't understand why $1/x$ can have a principal value because it's not a multivalued function. I'm very confused. And when I learned the complex analysis, I've n... | g8355 | [
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<p>Consider the 3-dimensional Minkowski space
$$
ds^2=dt'^2-dr'^2-r'^2d\phi'^2
$$</p>
<p>Now we transform it into a rotating frame:
$$
t'=t,r'=r,\phi'=\phi+\omega t
$$</p>
<p>Then the metric becomes
$$
ds^2=(1-r^2\omega^2)dt^2-dr^2-2\omega r^2d\phi dt-r^2 d\phi^2
$$</p>
<p>Consider a static observer in the rotating ... | g8356 | [
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<p>I have studied from Griffiths, the relativistic form of momentum is
$$p = \frac{1}{\sqrt{1-\frac{v^2}{c^2}}} m_0v$$ </p>
<p>Now when I evaluate the momentum for photon, I just insert $v=c$ and $m_0=0$ and I get $p= 0/0$. How does it make sense? </p>
<p>Can you tell me that where I am wrong?</p> | g195 | [
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<p>I am attempting to validate an accelerometer. I have a triaxial accelerometer and placed it on a wheel which goes at various frequencies from 1 to 3 Hz.
Am I right in thinking that I would expect the acceleration in <em>z</em> to be 1g?</p>
<p>Then in the <em>x</em> and <em>y</em> plane I would expect a read out of... | g8357 | [
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<p>Let $\psi (x,y,z)$ be a scalar field. I found the following statement in Morse & Feshbach Methods of Theoretical Physics:</p>
<blockquote>
<p>The limiting value of the difference between $\psi$ at a point and the average value of $\psi$ at neighboring points is $-\frac{1}{6}(dxdydz)^2\nabla ^2\psi$</p>
</bloc... | g8358 | [
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<p>I'm trying to relate the concept of entropy to keeping my room clean as suggested by my high school teacher ~1993...</p>
<p>Comparing the two scenarios:</p>
<ol>
<li><p>Every day I come home and throw an empty can on the floor and every night before bed I pick it up and throw it in the trash.</p></li>
<li><p>Ever... | g8359 | [
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<p>I suppose this is also an English question, but I'll ask it here first.</p>
<p>Why does the milli- prefix mean 1/1000 when it sounds so much like million? According to the internet, this dates back to the 18-19th centuries. Did it make more sense back then? Are we stubbornly holding on to meanings from borrowed pre... | g8360 | [
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<p>I took an empty clear sphere with radius r, put some weight inside this sphere, and put in into the water. I calculate the buoyancy force as:</p>
<p>Volume of the sphere = Volume of the water displaced (Vdisplaced) = (4/3)<em>pi</em>(r^3);
Weight of the displaced water = Buoyancy force (B) = Vdisplaced * density of... | g8361 | [
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<p>Could anyone suggest where can I find absorption spectra & refractive index of Glycerol?</p>
<p>I am specifically interested in UV range, 200-400nm, everything I was able to find out was for standard conditions only...</p>
<p>Is there any software which can get these parameters through simulation?</p> | g8362 | [
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<p>When a Electron gets promoted to the conduction band from valence band (In generation) lets say for example in Silicon at room temperature.</p>
<p>Is there any way to determine (on average) how long it will last before falling back down in the hole it just left.</p>
<p>What about with a Voltage Applied?</p>
<p>Th... | g8363 | [
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<p>So we can define a particle by defining its kinetic and potential energy, knowing that we can get a wavefunction describing a particle.</p>
<p>But the kinetic energy involves motion, and motion can be described in many different frames of reference as different quantities, so is the Hamiltionian not uniquely define... | g8364 | [
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<p>A while ago, during my introductory physics course, my professor purposefully neglected to tell us about the existence of the anti-electron neutrino in beta decay; he made it an assignment(on our honor) to propose a theory to explain where the missing energy ran off to. Since I was not very experienced at the time, ... | g8365 | [
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<p>Does it make sense to say that the quantum field of a photon is exactly proportional to the photon's electromagnetic field?</p>
<p>\begin{align}
\bar{\Psi}
=
\dfrac{\bar{E}+i\bar{B}}{\sqrt{\int (E^2+B^2)dV}}
\end{align}</p> | g8366 | [
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<p>I've been studying Bagger & Giannakis paper on the SuperHiggs Mechanism found <a href="http://arxiv.org/abs/hep-th/0502107v1" rel="nofollow">here</a>. </p>
<p>The paper shows how SUSY is broken by a $B_{\mu\nu}$ gauge field background restricted to $T^3$ in $M^7\times T^3$ Compactification of the heterotic stri... | g8367 | [
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... |
<p>Let's say I've got an Earth-like planet with no atmosphere: it's just a barren ball of rock. I want to live there, but I don't like domes, so instead I'm just going to dig a big hole and let gravity keep the air in.</p>
<p>How deep a hole do I need?</p>
<p>According to a chart I found, the density of the atmospher... | g8368 | [
-0.008261095732450485,
0.039074525237083435,
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0.011690453626215458,
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0.08723677694797516,
0.034744374454021454,
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0.005556275602430105,
-0.008336697705090046,
0.014030144549906254,
... |
<p>I do not remember when, but a while a ago I was told that for a spring with stiffness $k$ and a mass $m$, the equation $-kx = ma$ never holds. (assume a horizontal spring)</p>
<p>So if I was given a problem like this:</p>
<blockquote>
<p>You pull a mass $m$ attached to a spring with stiffness $k$ to the right of... | g8369 | [
0.08650653809309006,
0.05431438609957695,
0.02259928546845913,
0.019343391060829163,
0.034654345363378525,
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0.01171932928264141,
0.015914766117930412,
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-0.020833266898989677,
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0.03698372468352318,
-0.00... |
<p>Considering how low the power density is at the sun's core, I seem not to be able to expect what would happen to matter in case it was thrown inside the sun's core.
For example, let's assume an Earth-like planet is placed at the center of the Sun's core, and with the power density of 276.5 $watts$/$m^3$ which is ver... | g8370 | [
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0.014083866961300373,
0.018720952793955803,
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... |
<p>WHAT I KNOW: </p>
<p>classical computers store information in bits which can either be 0 or 1, but in quantum computer the qubit can store 0 , 1 or a state that is the superposition of these two states.
Now when we make a "measurement" (to determine the state of qubit), it changes the state of qubit, collapsing it ... | g8371 | [
0.005668359808623791,
0.044468045234680176,
0.00869126245379448,
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0.02728503756225109,
0.028808120638132095,
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-0.04064108431339264,
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0.007771719247102737,
0.006099293939769268,
0.0... |
<p>This assignment is about the one dimensional harmonic oscillator (HO).
The hamiltonian is just as you know from the HO, same goes for the energies, but I get that the wavefunction of the particle, at $t = 0$, is given by:</p>
<p>$\psi \left( x,\,\,t=0 \right)=A\left( {{\phi }_{0}}\left( x \right)+2i{{\phi }_{2}}\le... | g8372 | [
0.02976306714117527,
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0.04452250525355339,
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0.04504074528813362,
0.05799861252307892,
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0.015646526589989662,
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0.04318665340542793,
-0.06434852629899979,
0.0322... |
<p>If two balls collide (elastically) and there is no friction between them, will their angular momentum change after the collision?</p> | g8373 | [
0.07868107408285141,
-0.030313577502965927,
0.02984905242919922,
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0.04503243789076805,
0.037994757294654846,
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-0.030582807958126068,
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-0.0017577280523255467,
... |
<p>I understand that we can prove that for any process that occurs in an isolated and closed system it must hold that</p>
<p>$$\Delta S\geq0$$</p>
<p>via <a href="http://en.wikipedia.org/wiki/Clausius_theorem" rel="nofollow">Clausius' theorem</a>. My question is, how can I prove this in a mathematical way?</p> | g8374 | [
0.06080007925629616,
0.02893132157623768,
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0.014038936235010624,
0.04488430544734001,
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0.09068158268928528,
0.04180590435862541,
0.054... |
<p>I am looking into the decay of a $\Phi$-meson decaying into $K^+$, $K^-$. My problem is, the $\Phi$-meson has a total angular momentum of 1 and the two Kaons have a total angular momentum of 0. On the first glance this seems to be a violation of the angular momentum conservation law.</p>
<p>I tried to explain it to... | g8375 | [
-0.006281137466430664,
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0.021731702610850334,
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0.012347990646958351,
0.05816838517785072,
0.04376578703522682,
0.0360969603061676,
0.007426396943628788,
-0.016793938353657722,
-0.02056637965142727,
0.011... |
<p>If space itself is expanding, then why would it have any effect on matter (separates distant galaxies)? </p>
<ul>
<li><p>Space is "nothing", and if "nothing" becomes bigger "nothing" it's still a "nothing" that shouldn't interact with matter in any way (it doesn't have mass, energy, etc).</p></li>
<li><p>Gravity do... | g56 | [
0.054240547120571136,
0.045744284987449646,
0.02243674546480179,
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0.02721848525106907,
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0.007878429256379604,
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-0.11746178567409515,
0.07234152406454086,
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0.... |
<p>If I'm correct a quark can change color by emitting a gluon. For example a blue up quark $u_b$ can change into a red up quark by emitting a gluon:
$$u_b \longrightarrow u_r + g_{b\overline{r}}$$
(Here, the subscript indicates color and $\overline{r}$ means anti-red). This is needed to keep the color balance (left ha... | g8376 | [
0.010748818516731262,
0.048590224236249924,
0.019795216619968414,
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0.09538818895816803,
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-0.007292755413800478,
0.010076313279569149,
0.09843181073665619,
0.009340477176010609,
0.03... |
<p>The Higgs boson propagator can be written $$\frac{1}{p^2-m^2+\Sigma(p^2)}$$. If we take $p^2=m_P^2$ the physical mass, we get $m_P^2=m^2-\Sigma(m_P^2)$. Now, if $\Sigma\sim \Lambda^2$, we get $m^2\sim\Lambda^2+m_P^2$.</p>
<p>It had assumed that the mass correction from fermion loops was positive, but from this it a... | g8377 | [
0.03979520499706268,
0.0058999136090278625,
0.0082247881218791,
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0.02109818533062935,
0.0272796880453825,
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0.05207701027393341,
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0.012223426252603531,
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0.009415038861334324,
0.013042951934039593,
0.073350... |
<p>Assuming it is possible in principle to entangle the degrees of freedom of the event horizons of two black holes, and that this is something that can be done, either after the black hole is formed, or only by careful preparation before collapse. </p>
<blockquote>
<p><strong>Question:</strong> Could exist a physic... | g8378 | [
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0.021840408444404602,
0.022946277633309364,
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... |
<p><a href="http://physics.stackexchange.com/questions/80773/the-example-of-relativity-of-simultaneity-given-by-einstein/80776#80776">This answer</a> to a recent question related to <a href="http://archive.org/details/relativitythespe00einsuoft#chapters.8.and.9" rel="nofollow">Einstein's thought-experimental definition... | g8379 | [
0.04302186518907547,
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0.03739086911082268,
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0.086216501891613,
0.05506151169538498,
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-0.002307346323505044,
0.00863... |
<p>This is quite embarrassing to ask, but I haven't done a fluid flow calculation in a very long time and when you don't use it, you lose it!</p>
<p>I have a natural gas pipeline that I want to purge of air with natural gas. It's a 3" and 4" line totalling about 6,600 feet. I'll be injecting natural gas into the lin... | g8380 | [
0.03937314450740814,
0.028086591511964798,
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0.012732678093016148,
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0.008934654295444489,
0.03581605851650238,
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-0.005014390219002962,
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0.017004692927002907,
-0.008583365008234978,
-0... |
<p>We have a long, cylindrical wire carrying a constant current I in an inertial frame. At a distance of R from the center of the wire, the magnitude of magnetic field is $μI/2πR$.
What is the magnitude of magnetic field in another inertial frame moving at a certain speed opposite to the direction of electric current? ... | g8381 | [
0.034042518585920334,
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0.08657262474298477,
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0.05477446690201759,
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0.014704403467476368,
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0.032595615833997726,
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-0... |
<p>I ran into a bit of physics yesterday, and couldn't understand the physics at work. I've been scouring the Internet, but haven't found the answer yet. I'm guessing there's a basic principle I'm misinterpreting or ignorant of.</p>
<p>Basically, the sewer backed up into my house. Among other points of entry, water fl... | g8382 | [
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0.0806952714920044,
0.04745106026530266,
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-0.07124024629592896,
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0.0245490912348032,
0.09222424030303955,
0.02159287... |
<p>Suppose we have a disc with a hole, when computing moment of inertia of this about the disc's centre. Why do we subtract the moment of inertia of the removed part from the moment of inertia of complete disc? </p> | g8383 | [
0.0705837607383728,
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0.046659257262945175,
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0.089881032705307,
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0.024708421900868416,
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-0.03... |
<p>$\vec F=m\vec a$ ,for moving object with 10 $km/s$ in a constant manner ,where acceleration is zero. ie No force on object ?</p>
<p><a href="http://www.physicsforums.com/showthread.php?t=622711" rel="nofollow">http://www.physicsforums.com/showthread.php?t=622711</a></p> | g275 | [
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0.00048112813965417445,
0... |
<p>Water on earth has been theorized to have come through comets trapped inside crystals. But why wouldn't that water evaporate on impact, and wouldn't the atmosphere at that time allow the vapours to escape Earth?</p>
<p>Also, what is the current scientific opinion of the validity of this theory ?</p> | g8384 | [
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0.016893556341528893,
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0.012897202745079994,
0.008667401038110256,
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0.0309183057397604,
0.004229... |
<p>Why do we need to use the sign convention again in the mirror equation while solving numericals when we know we have already used a convention while deriving the mirror equation? The question is not about the importance of sign conventions but why do we need to use the sign conventions twice? Doesn't the equation al... | g8385 | [
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0.061723146587610245,
0.052736084908246994,
0.060... |
<p>We know that near a massive object, light's wavelength and frequency changes, but its speed remains same. I'd like to know how it is possible for frequency to change, unless we change the light source? </p> | g8386 | [
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0.066749706864357,
0.07111000269651413,
0... |
<p>I am not sure if I understand spin operators correctly. Given a two spin system in state $|++\rangle$ and an operator $S = S^{(1)} + S^{(2)}$</p>
<p>Then I have</p>
<p>$$
S_z |++\rangle
= (S^{(1)}_z + S^{(2)}_z) (|\tfrac{1}{2}, \tfrac{1}{2}\rangle \otimes |\tfrac{1}{2}, \tfrac{1}{2}\rangle)
= (S_z|\tfrac{1}{2}, \... | g8387 | [
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0.015077147632837296,
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0.02500920370221138,
0.009930496104061604,
0.0016... |
<p>Does a black body (imagine like a square of solid black-body-matter) thermally conduct well at room temperature?</p> | g8388 | [
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0.05812952667474747,
0.008640582673251629,
0.0... |
<p>There's a question on my homework about the process $e^{-} e^{+} \rightarrow \tau^{+} \tau^{-}$. Specifically, it is claimed that the minimum energy required of the colliding positron and electron beams is slightly less than twice the $\tau$ mass, and I am asked to explain this deviation and compute it. In the conte... | g8389 | [
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0.008733589202165604,
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0.012577406130731106,
0.032725367695093155,
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0.01776069775223732,
0.02573149837553501,
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0.02371109277009964,
0.00... |
<p>In the Schrödinger equation in the position representation
$$
i\hbar\frac{\partial}{\partial t}\Psi(x,t)
~=~[\frac{-\hbar^2}{2m}\nabla^2+V(x,t)]\Psi(x,t),
$$
is the potential $V(x,t)$ an operator acting on $\Psi$ or merely a scalar?</p> | g8390 | [
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0.0022377129644155502,
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0.0008520139963366091,
0.04528546333312988,
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0.05492331087589264,
0.026756197214126587,
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0.014446026645600796,
0.008355436846613884,
0.02051795832812786,
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0... |
<p>I found this solid-solid transformation in wikipedia. <a href="http://en.wikipedia.org/wiki/Phase_transition#Types_of_phase_transition" rel="nofollow">http://en.wikipedia.org/wiki/Phase_transition#Types_of_phase_transition</a>
Please tell me what it is?
It's present in types of phase transition in wiki.</p> | g8391 | [
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-0... |
<p>Type I superstring theory is unoriented, and it seems that it needs to be so in order to exist. </p>
<p>Now, we always have open-closed duality, that connects at least the ultraviolet sector of a theory with the infrared sector of another, so in principle we should have some oriented open strings coming from it, by... | g8392 | [
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0.007992350496351719,
0.024434875696897507,
0.02... |
<p>I have a gravity-related question. I am programming an orbit simulator. I have everything up and running, but I would like to render the smaller body's orbital path (the larger body is fixed). To do this, I need the parametric equations for the body's position for any given time (i.e. I need an $x(t)$ and $y(t)$ fun... | g8393 | [
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0.07978444546461105,
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0.014585812576115131,
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-0.010879982262849808,
-0.0033239643089473248,
-0.0027227408718317747,
0.021913329139351845,
... |
<p>Suppose you are doing an experiment to determine the work function of a metal.
You get $KE_1$, $\nu_1$ and $KE_2$, $\nu_2$.
We know that $KE = h\nu - W$ but when you solve the simultaneous equations, we have a $h$ slightly different from the textbook value.</p>
<p>Question: In such a situation should you</p>
<o... | g8394 | [
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0.039671704173088074,
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0.017836911603808403,
0.0009421015856787562,
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0.030961083248257637,
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0.0362744964659214,
0.010193808004260063,
0... |
<p>I'm currently taking an introduction to Solid State Physics class, and is now on the subject of superconductivity (SC). Currently I'm reading about the BCS theory, and how this works on a microscopic scale. I then get presented with this picture (Electron-Phonon Interaction):</p>
<p><img src="http://i.stack.imgur.c... | g8395 | [
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0.07069680094718933,
-0.031107936054468155,... |
<p>To external fields(H, - H) not equal to each other are acting on that material. <strong>Based on the hysteresis loop</strong> what would be the result?
The hysteresis area of that materials is very narrow(i.e easy to magnetize & demagnetize) H = 1000 A/m and, - H = 500 A/m. I know they are both vectors so it wou... | g8396 | [
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<p>I am trying to determine the self-inductance of a toroidal coil of mean radius $R$ with $N$ loops of radius $a$ with a current $I$ flowing within them.</p>
<p>I have calculated the magnetic field by noting that it must be in the circumferential direction (i.e. in the $\hat{\boldsymbol{\theta}}$ direction) and then ... | g8397 | [
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<p>What does <a href="http://www.google.com/search?as_q=&as_epq=smooth+dynamical+system" rel="nofollow">smooth dynamical system</a> mean? It is the title of a paper I am supposed to read in non linear systems.</p> | g8398 | [
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<p>Ok, this is definitely a silly question and is partly inspired by the last 20 minutes or so of the film <em>The Avengers</em>, so look to that if you can't picture the situation.</p>
<p>In the film a portal is opened up above new york, to somewhere in deep space. I.e. from an area where the gravitational field is e... | g8399 | [
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<p>We know that Spin is described with $SU(2)$ and that $SU(2)$ is a double cover of the rotation group $SO(3)$. This suggests a simple thought experiment, to be described below. The question then is in three parts: </p>
<ol>
<li><p>Is this thought experiment theoretically sound? </p></li>
<li><p>Can it be conducted e... | g8400 | [
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0.04530772939324379,
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... |
<p>I am having some troubles trying to classify a modified photon gas into which phase transition it belongs (if it really is a phase transition).</p>
<p>First of all, it is a photon gas that interacts with an external electric field, so the q-potential (from the grand canonical ensemble) depends on the external field... | g8401 | [
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<p>I'm thinking equivalence principle, possibilities of unbounded space-time curvature, quantum gravity ...</p> | g8402 | [
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<p>Pre-face: My step-father and I were turning the heat down on the water heater. He demonstrated that touching the ground wire doesn't shock you.</p>
<p>My understanding is that the ground wire doesn't have current unless the case of a short-circuit, or over-abundance of energy. The wire also has very little resistan... | g8403 | [
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<p>Although they have never been observed, theoretically gluons can exist outside of the nucleus of an atom in the form of a "glue ball". Since the predominant mechanism of Higgs creation at the LHC was observed to be a gluon-gluon interaction (with various virtual particles playing out in the conversion), what are th... | g8404 | [
0.03408048301935196,
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<p>I'm aware that electron pair-production from a single photon requires the presence of matter — say some large nucleus — able to absorb momentum, as in the process
\begin{align}
N \gamma \rightarrow N e^- e^+
\end{align}
where $N$ represents the nucleus. My question is, how would one represent this process with a Fe... | g8405 | [
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0.0075... |
<p>I know that recent advances in technology are doing amazing things with very low amounts of electricity, with RFID being one of the most familiar examples, but I'm not very familiar with the principles involved. It makes me wonder: is it possible (with current technology, not "is it theoretically possible?") to use... | g8406 | [
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<p>Is there a good way to directly measure a moment of inertia of the Earth, or say, other planet?</p> | g8407 | [
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... |
<p>What state is <a href="http://en.wikipedia.org/wiki/Fire" rel="nofollow">fire</a>? Solid, Liquid or Gas or Plasma? </p>
<p>I was just roaming around when this question popped out of my mind. In what state is FIRE? </p> | g276 | [
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<p>Do magnets redshift light? </p>
<p>Suppose we have an extremely powerful magnet (say the size of the Sun) and we have a smaller paramagnetic material above it (say. Titanium Brick which is indestructible) . Due to magnetic attraction it will fall toward the big magnet. </p>
<p>Now suppose that when it hits the ... | g8408 | [
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<p>Suppose you know everything about Quantum Field Theory, but nothing about the very specific interactions and particles which exist in our real word.</p>
<p>Which physical or mathematical principles could be used to reduce the infinite number of possibilities of QFT, to finish with some class of theories, in which ... | g8409 | [
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<p>I can understand that animals need some battaries to run. But, we learn that plants serve like batteries for animals because they accumulate the sun energy in the first place! You can eat them or burn to extract the accumulated energy. This means that they consist of structures that they want to blow-up and disinteg... | g8410 | [
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<p>Space isn't a perfect vacuum and I wonder how an image of a galaxy can travel billions of years without becoming diffused by photon collisions with space matter?</p> | g8411 | [
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<p>I am unable to visualize any case where angular momentum and angular velocity of an object are not parallel.</p> | g8412 | [
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0.0250... |
<p>Say there is $\hat{J} = \exp[-i \hat{p} l/ \hbar]$ and $\hat{U}= \exp[-i\hat{H}t/ \hbar]$, where $\hat{H}$ is time-independent. </p>
<p>Can we say anything about $[\hat{J},\hat{U}]$? Is it zero? How do we show this? </p>
<p>For example if $\hat{H} = \hat{p}^2 /2m + m\omega^2 \hat{x}^2/2$.</p> | g8413 | [
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<p>I want to know the properties and the behavior of the gapless excitation for the traditional <a href="http://en.wikipedia.org/wiki/Bose%E2%80%93Einstein_condensate" rel="nofollow">BEC</a>s. Could you give me some idea or references about this? </p> | g8414 | [
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<p>For rigid body we need to know position of three points and their velocities to determine everything. So that would make 12 DOF. Why do text books say it has six DOFs?</p> | g8415 | [
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<p>If my understanding of wormholes is correct, anything that moves into a wormhole can be transported from one region of space-time to another. Consider a situation where an object of mass $m$ in space at $(x_1,y_1,z_1)$ and time $t_1$ travels through a wormhole and appears at $(x_2,y_2,z_2)$ in a distant future time ... | g8416 | [
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<p>I know I should have listened to my teacher in physics class but I didn't. I need help on a thing I am trying to do for a game.</p>
<p>I want to be able to calculate Gravity pushing down on a object over a certain amount of time. (I want the object to slow down to a stop and then go back down due to gravity).</p>
... | g8417 | [
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<p>I was drawing a diagram and trying to resolve all the forces. It seems to me that because of gravity, centrifugal force will produce a sort of "dragging" motion along the surface of the earth. The centrifugal force is quite small (I got around 2.5 N at the equator). This force is easily neutralized by friction. Is t... | g18 | [
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<p>Long ago, I realized this: (super)string theory can NOT give a well-defined/unique prediction of why the electron (muon, tau) or the neutrino (any flavor) masses have the masses we measure. String theory can NOT give a concrete prediction of any SM particle mass (even resonances like the Higgs and other particles). ... | g8418 | [
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0.0245... |
<p>There are the eddy currents in thin circular copper plate thickness h and radius a, in a harmonic magnetic field which is perpendicular to plate and the effect of auto-induction is negligible. Now we must get average heat generated on it.</p>
<p>As I said, I have final equation, but how do you get to this eqution. ... | g8419 | [
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<p>In an ideal situation, we can use a simple formula to determine the velocity at which a body revolves around a massive body at a particular distance. I was wondering if there is an intuitive way to understand the motion of a body influenced by two other massive bodies (say the moon being influenced by the earth and ... | g8420 | [
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0.00871... |
<p>There seems to have some (deep) relation between <a href="http://ncatlab.org/nlab/show/Seiberg-Witten+theory" rel="nofollow">Seiberg-Witten theory</a> and <a href="http://en.wikipedia.org/wiki/Superconductivity" rel="nofollow">superconductivity</a>. e.g. <a href="http://www.ams.org/journals/bull/2007-44-03/S0273-097... | g8421 | [
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0.... |
<blockquote>
<p>A chip has a thermal resistance of 0.007 K/J s and thermal capacitance
of 1.6 J/K. You give it an impulse of heat equal to 100 J. How long
does it take for the chip to cool to within 10% of the ambient
temperature?</p>
</blockquote>
<p>I understand that I have to implement Newton's Law of Cooli... | g8422 | [
0.06787055730819702,
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<p>I've been struggling with this question all morning, yet I get the feeling the answer is frightfully simple. </p>
<p>If Orion appears upside down in the Southern Hemisphere and the right way up in the Northern Hemisphere, what does it look like in equatorial countries such as Kenya, Colombia, and Ecuador, bearing i... | g8423 | [
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<p>Ancient Greek astronomer Aristarchos who lived around 300 BC found a method to compute the Eart-Sun distance by applying geometry. </p>
<p><a href="http://www.youtube.com/watch?v=7ne0GArfeMs" rel="nofollow">In this video about the cosmic distance ladder</a>, at 26:30, Terence Tao explains that Aristarchos was basic... | g8424 | [
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... |
<p>Let us pretend for a moment that there are two identical planets that are exactly opposite their star from each other and are the same distance from said star. (This would make them, at all times, double the distance from their star apart from each other.)</p>
<p>Would they, under the definition of a planet, be con... | g8425 | [
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<p>I'd like to understand the physics of dynamic light scattering experiment. In particular I want to understand the basic relation between relaxation time $\tau_q$ and the diffusion coefficient $D$:</p>
<p>$\tau_q=(q^2 D)^{-1}.$</p>
<p>I suppose that more or less the following steps are necessary:</p>
<p>1) Calcula... | g8426 | [
-0.00743173249065876,
0.03528246283531189,
-0.026221824809908867,
0.01930609904229641,
0.04340054839849472,
0.006914518773555756,
0.06458484381437302,
-0.0029577831737697124,
-0.011880215257406235,
-0.014355089515447617,
-0.008633648045361042,
0.058985982090234756,
0.06472685188055038,
-0.... |
<p>Using a <a href="http://www.fluke.com/fluke/usen/electrical-test-tools/thermometers/fluke-62.htm?PID=56096" rel="nofollow">Fluke 62 Mini Infrared Thermometer</a> today on a stainless steel pipe with coolant I noticed that it gives incorrect temperature readings. There is a temperature sensor inside the coolant say... | g8427 | [
0.09107493609189987,
-0.10710518807172775,
0.016209525987505913,
-0.04537712410092354,
0.030940525233745575,
-0.0012122816406190395,
0.040800437331199646,
0.018170736730098724,
-0.03603726252913475,
-0.019845565780997276,
0.005020480137318373,
0.06547006219625473,
-0.01065109483897686,
-0.... |
<p>It's a physics club for undergraduates (first three years of university); I'm looking for projects idea that aren't too obvious like a small rocket or an electromagnet (school projects) but also not too advanced. Since most members know Newtonian mechanics, electrostatics & magnetostatics and some simple notions... | g8428 | [
-0.012734399177134037,
0.029223915189504623,
-0.007042465265840292,
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-0.003796336939558387,
0.0977478101849556,
0.047250162810087204,
0.05984020233154297,
0... |
<p>Once day, I talked to my Prof. about Computational Physics and he showed me his work. I'm quite surprised that why Prof. use C++ for computation because C++ quite complicated. I heard he talked about memory talk about pointer. Why didn't he use Python or Java that more easier? no need to manage memory no need to bus... | g8429 | [
0.0362699031829834,
0.04241206869482994,
0.01612204872071743,
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0.005770272109657526,
-0.0005221875617280602,
0.020159222185611725,
0.0... |
<p>Well the following question I really struggle to find an answer</p>
<blockquote>
<p>A thin lens creates an image of an object with magnification -3. A
second identical lens is positioned very close to the first lens such
that the distance between the two lenses can be neglected. What is the
magnification wi... | g8430 | [
0.04754660278558731,
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0.018454913049936295,
0.010965578258037567,
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0.04207029938697815,
0.052495282143354416,
... |
<p>My book starts section 2.2 like this:</p>
<p><img src="http://i.stack.imgur.com/obS89.png" alt="enter image description here"></p>
<p>Equation 1.1 is this:
$$q_x=-k\frac {\partial T}{\partial x}$$</p>
<p>As you can see in the picture I posted, my book says that one can go from equation 1.1 to equation 2.1 by inte... | g8431 | [
0.035182543098926544,
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0.007844103500247002,
0.0523027665913105,
0.00775... |
<p>I've always been not so bad in mathematics, but I'm terribly bad at physics. For me, abstract concept are totally understandable, but when it come to reality, I'm lost !</p>
<p>So, for my job, I need to understand something.</p>
<p>I have an object, travelling during $t_o$ on a distance $d_o$.</p>
<p>It has an in... | g8432 | [
0.06924890726804733,
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-0.0... |
<p>I am studying quantum statistical mechanics from the mathematician's perspective. I don't quite understand what the duality formula for entropy is <em>really</em> saying (or why there is a "duality"). </p>
<p>If $A$ is an $n\times n$ Hermitian (self-adjoint, diagonalizable) matrix, then $$S(A)=\sup\bigl[{\operatorn... | g8433 | [
-0.026333192363381386,
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0.02051909826695919,
0.05364849045872688,
-0.04... |
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