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<p>I'm wondering if it exists a composition law for the squeezing operation ? I guess so for geometric reason, since they are (generalized, and the phase is annoying of course) hyperbolic rotations of the annihilation $a$ and creation $a^{\dagger}$ operators of some bosonic modes.</p>
<p>I define the squeezing operato... | 1,308 |
<p>As an electric motor spins, the energy from the electricity is 'conducted' to the rotor by the magnetic fields. However, when the motor is stopped, the energy becomes heat and burns up to motor. What causes this heat to be formed? Is it purely generated by the current flowing through the wire or is the magnetic f... | 1,309 |
<p>Momentum is defined as
$$p = \gamma m_0 v$$
And here is another law
$$E^2=(m_0c^2)^2+(pc)^2$$
And <a href="http://www.pveducation.org/pvcdrom/properties-of-sunlight/energy-of-photon" rel="nofollow">this website</a> says the energy of a red photon is $1.9074 eV$. Also, light has a rest mass of $0$. The problem is tha... | 1,310 |
<p>To my knowledge there are three types of acceleration when a body (e.g. a rod) is moving in a circle about an axis. These are:</p>
<ol>
<li><p>Angular acceleration : this is the rate of change of angular velocity.</p></li>
<li><p>Tangential acceleration : this is the linear acceleration of the system in a tangentia... | 1,311 |
<p>When an EM wave diffracts, I can imagine that its EM field interacts with the charges in a certain obstacle thus inducing a wave behaviour on the charges of the matter that will interact with the EM of the photon.</p>
<p>However, I am having difficulty to make the analogy with matter waves. Since a matter wave is a... | 1,312 |
<ol>
<li><p>In electroweak theory, for the first generation of leptons, in the doublet
$$\psi_L=\begin{pmatrix}
\nu_{eL}\\
e_L
\end{pmatrix}$$
we assign a non-abelian charge $I=\frac{1}{2}$. Is this a Noether charge? </p></li>
<li><p>A $SU(2)$ transformation on the Lagrangian:
$$\mathcal{L}^{ferm}=i\bar\psi_R\gamma^\mu... | 1,313 |
<p>Need help doing this simple differentiation.
Consider 4 d Euclidean(or Minkowskian) spacetime.
\begin{equation}
\partial_{\mu}\frac{(a-x)_\mu}{(a-x)^4}= ?
\end{equation}
where $a_\mu$ is a constant vector and the indices are summed over since one really doesn't need to bother about upper and lower indices in flat sp... | 1,314 |
<p>There are many decorative devices, that keep a small metal sphere levitating in air by attracting it to a top electromagnetic coil while monitoring their height by optical sensors.</p>
<p>There is also the 'levitron' where a passive permanent magnet spinning top is hoovering above some permanent magnets, it's orien... | 1,315 |
<p>So I'm having problems with the double infinite potential well given by</p>
<p>$$V(x)= \left\{\begin{array}{ll}
\infty & -\infty < x < -a-b \\
0 & -a-b< x < -a \\
V_0 & -a < x < a \\
0 & a < x < a + b \\
\infty & a+b < x < \infty \\
\end{array}\right.$$</p>
<p>I ha... | 1,316 |
<p>I've heard that the big bang began in all places at once, but my physics teacher told my class that the universe was all once compressed into a single dense piece of matter. If my physics teacher is right, then did that dense piece of matter have the same mass as the entire universe now? And if it was so small and y... | 15 |
<p>By fundamental definition of a entangled system we can say that if we know the quantum state of one subsystem then we can describe the state of another subsystem.
A particle possess wave-particle duality. If one experiment verify the wave nature of particle then we can not see its particle behaviour in same exp and ... | 1,317 |
<p>Although there is no standard measure of entanglement, the GHZ states </p>
<p>$|GHZ\rangle=\frac{1}{\sqrt{2}}(|0\rangle^{\otimes n}+|1\rangle^{\otimes n})$</p>
<p>are often deemed as maximally entangled states of $n$ qubits. We know by now that even separable states can exhibit correlations that are impossible in ... | 1,318 |
<p>Does the heat of vaporization of water depend strongly on the relative humidity of the gas into which it evaporates? </p>
<p>Some context: If we want to calculate the dew point of water, we find the temperature at which the <em>partial pressure</em> of the water lies on the liquid/vapor boundary of the water phase ... | 1,319 |
<p>I have some knowledge about LC circuits, like I know Maxwell's equations, the differential equations of circuit oscillator and so on. I am armed with equations to solve physical problems involving inductors and their behavior.</p>
<p>But I always need to understand things as they really are. And I can't find anythi... | 1,320 |
<p>We want to find the energy of a hydrogen atom ($Z=1$) in the ground state
$$
\psi_{100} = \frac{1}{\sqrt{\pi}}e^{-r}\ \ \ \ \ \ (\mbox{atomic units})
$$
with Hamiltonian
$$
H = -\frac{1}{2}\nabla^2-\frac{1}{r}
$$</p>
<p>Then</p>
<p>$$
\begin{align*}
\langle \psi_{100}|H|\psi_{100}\rangle &=\int_0^\infty \int_... | 1,321 |
<p>Some physical properties of water change in the presence of solutes: vapor pressure, boiling point, freezing point and osmotic pressure. In particular, these four properties are called <a href="http://en.wikipedia.org/wiki/Colligative_properties" rel="nofollow"><em>colligative properties</em></a> because they depend... | 1,322 |
<p>I´m wondering how can one get to the definition of Functional Derivative found on most Quantum Field Theory books:</p>
<p>$$\frac{\delta F[f(x)]}{\delta f(y) } = \lim_{\epsilon \rightarrow 0} \frac{F[f(x)+\epsilon \delta(x-y)]-F[f(x)]}{\epsilon}$$</p>
<p>from the definitions of Functional Derivatives used by mathe... | 1,323 |
<p>Many documentaries regarding the double slit experiment state that they only send a single photon through the slit. How is that achieved and can it really be ensured that it is a single photon?</p> | 1,324 |
<p>So, I have a camera crane that has a pivot leaving 2 distances, 0.5mts and 1.5mts respectively. Plus a small L-shaped piece of metal and the end of d2 (1.5) which holds a camera, which I suppose I have to add it to the force applied on that side. One additional variable is that there's a piece of metal attached to ... | 1,325 |
<p>When considering tabulated standard values of heat of combustion (∆H° combustion) or any other similar value, the results are reported for species in their standard states (1 bar pressure, 25°C, etc). When something combusts, however, macro state variables such as pressure and temperature change. For the tabulated v... | 1,326 |
<p>This question is regarding <a href="http://en.wikipedia.org/wiki/Noether%27s_theorem" rel="nofollow">Noether's Theorem</a> in general, but also in the application to an example. The example is:</p>
<blockquote>
<p><em>Find the conserved current for the Lagrangian</em>
$$L=\bar{\psi}(\frac{i}{2}\gamma^{\mu}\part... | 1,327 |
<p>A tank has 2000 litres of capacity (Ct). It fills at 5 l/s. It is filled with 800 l at time 0.</p>
<p>a) How many seconds will it need to fill half the tank.</p>
<p>So I did this:</p>
<p>X = time.</p>
<pre><code>5 l * X 2000L
---- = ------- - 800L
s 2
X = 200L
---------
5... | 1,328 |
<p>I'm doing some numerical Monte Carlo analysis on the 2 dimensional Ising model at the critical point. I was using the Metropolis 'single flip' evolution at first with success, though it suffers from critical slow down and makes studying large lattices unlikely possible. I'm now looking at cluster flip algorithms, sp... | 1,329 |
<p>I have a pulse profile (binned photon counts versus phase) of a star, and for each count rate I have its statistical error.</p>
<p>I want to calculate the so-called pulsed-fraction $P_{frac}=\frac{F_{max}-F_{min}}{F_{max}+F{min}}$, where $F_{max}$ and $F_{min}$ are the maximum and minimum count rates, respectively.... | 1,330 |
<ol>
<li><p>Can physical states be treated as information (strings over some alphabet)?</p></li>
<li><p>If (1) is true, isn't this a trivial conclusion that the universe can be simulated by a Turing machine or a cellular automaton or any other computational model, given that differential equations that determine the ev... | 1,331 |
<p>I have a basic enough question. Assume that one has one of those ideal see saws, i.e. the teeter-totter pivots on point source, the balance is of uniform mass etc.</p>
<p>Now assume that one places an object of mass m on one end. This will force the balance to tilt on side. Now suppose that one adds another mass of... | 1,332 |
<p>Can somebody explain to me, when the following two equations (equations 2.48 and 2.50 <a href="http://physics.usask.ca/~hirose/p812/notes/Ch2.pdf" rel="nofollow">in this document</a>) are applicable and what $\Phi_s$ and $\Phi$ actually are? The thing is, I want to find general equations that determine the field pro... | 1,333 |
<p>I am attempting to model the impact of a deformable body (clean, dry sand characterized as a continuous fluid) with flexible diaphragm (in this case a sheet of rubber). Assuming that this is a closed system (no sand escapes) do you think work-energy theorem is adequate for approximating the total force imparted on t... | 1,334 |
<p>I've bumped into the study of the $SU(N)$ theory in the <a href="http://en.wikipedia.org/wiki/1/N_expansion" rel="nofollow">large-$N$ limit</a>.
I'm wondering in which way the study of this Yang-Mills theory, can give contribution to QCD with gauge group $SU(3)$, i.e. $N=3$ Any suggestion?</p> | 1,335 |
<p>The oil, vinegar and other liquids in homemade salad dressing separate into layers after sitting for a while, making the mixture become more organized as time evolves. Why doesn't this violate the 2nd law of thermodynamics?</p>
<p>I assume that the answer is that since the separation is due to gravity, the effect ... | 1,336 |
<p>In the context of <a href="http://en.wikipedia.org/wiki/Inflation_%28cosmology%29" rel="nofollow">Inflationary Cosmology</a>, it is postulated that there was a period of shrinking <a href="http://en.wikipedia.org/wiki/Hubble_radius" rel="nofollow">Hubble Sphere</a> radius $(aH)^{-1}$.</p>
<p>$$ \frac{d}{dt} (aH)^{-... | 1,337 |
<p>Is it possible to consider the regular polygons ($n$-gons) as deformed circles and use a <a href="http://www.google.com/#q=pseudo-polar+coordinate+system" rel="nofollow">pseudo-polar coordinate system</a> to calculate their moment of inertia over its center $O$. Inasmuch as I know (I am a solid mechanics beginner), ... | 1,338 |
<p>In the US HEPA filters will remove 99.97% of particles sized 0.3 microns. In Europe HEPA filters do not have to meet this exact figure and there are different classes of HEPA filters e.g. h10(removes 85% at .3 microns, h11 removes 95% at .3 microns etc, h14 removes 99.97% etc.). </p>
<p>Suppose you have a vacuum ... | 1,339 |
<p>In <a href="http://iopscience.iop.org/1742-5468/2005/05/P05012" rel="nofollow">Spin-glass theory for pedestrians</a> by Castellani and Cavagna, the initial formula used to introduce the replica trick is written as:</p>
<p>$$\overline{\log Z}=\lim_{n\rightarrow0}\frac{1}{n}\log\overline{Z^{n}}\qquad(1)$$</p>
<p>whe... | 1,340 |
<p>I have an electric field and a certain charged particle in it that has a certain potential energy associated with it. Where does the energy go if I remove the field?</p> | 1,341 |
<p>It is well known that the orbits of Ganymede, Europa and Io are in a 4:2:1 resonance. Most online sources (including but not limited to <a href="http://en.wikipedia.org/wiki/Galilean_moons" rel="nofollow">Wikipedia</a>) say that such an <a href="http://en.wikipedia.org/wiki/Orbital_resonance" rel="nofollow">orbital ... | 1,342 |
<p>How can we know that a black hole exists if it attracts both matter and light, and to prove that it exists would need to observe it?</p>
<p>It's a very common question but I don't know the answer.</p> | 16 |
<p>A fluid in a rotating bucket will take on a parabolic shape (for example of some simple derivations of this result see <a href="http://en.wikipedia.org/wiki/Bucket_argument" rel="nofollow">http://en.wikipedia.org/wiki/Bucket_argument</a>). The assumptions that play into the derivations that I've seen do not take int... | 1,343 |
<p>Why would the blood boil? Is it because of the temperature or pressure? Because I really can't figure it out. I thought space didn't have a temperature above freezing unless close to a star or the sun. But if it is the pressure how would that work?</p> | 1,344 |
<p>If you drop a glass cup on the ground, it will break and shatter into pieces. This happens all the time and is consistent with quantum mechanics. But it never happens that a shattered glass cup rearranges itself from the ground into someone's hand as a whole glass cup, even though this is also consistent with quantu... | 611 |
<p>I have a question that's been bothering me for years.</p>
<p>Given a rod of uniform mass distribution with total mass $M$ and length $L$ that lies on a horizontal table (with one end fixed to the table around which the rod is free to rotate in the horizontal plane, and a force F applied perpendicular to the rod at ... | 1,345 |
<p>Is the Laplacian operator, $\nabla^{2}$, a <a href="http://en.wikipedia.org/wiki/Self-adjoint_operator" rel="nofollow">Hermitian operator</a>? </p>
<p>Alternatively: is the matrix representation of the Laplacian Hermitian?</p>
<p>i.e.</p>
<p>$$\langle \nabla^{2} x | y \rangle = \langle x | \nabla^{2} y \rangle$$<... | 1,346 |
<p>Say you have two white noise signals with different variation amplitudes A1 and A2 as shown in this beautiful Excel graph:</p>
<p><img src="http://i.stack.imgur.com/6ASjL.png" alt="White noise signals" title="White noise"></p>
<p>Ignoring the DC offset as it's been represented here, how do you relate the amplitude... | 1,347 |
<p>For the oscillation of a torsion pendulum (a mechanical motion), the time period is given by<br>
$T=2\pi\sqrt{\frac{I}{C}}$ which is a result of the angular acceleration $\alpha=\frac{d^2\theta}{dt^2}=-(\frac{C}{I})\theta$ where $C$ is the restoring <a href="http://en.wikipedia.org/wiki/Couple_%28mechanics%29" rel="... | 1,348 |
<p>I'm dealing with a problem here and even that I'm trying to solve it i can't</p>
<p>It says:</p>
<blockquote>
<p><em>In what figures the voltmeter and ampere-meter are wrong positioned?</em></p>
</blockquote>
<p><img src="http://i.stack.imgur.com/fKKPJ.jpg" alt="enter image description here"></p>
<p>I think th... | 1,349 |
<p>I've got to calculate the thermionic emission through a diode, so I need to use <a href="http://en.wikipedia.org/wiki/Thermionic_emission#Richardson.27s_Law" rel="nofollow">Richardson's Law</a>. However, one thing's got me confused - according to the Wikipedia page:</p>
<p>$$J = A_GT^2e^\frac{-W}{kt}$$</p>
<p>I co... | 1,350 |
<p>To me, adiabatic processes are idealisation. What do people mean with statements such as: "turning off the coupling constant (in QED say) adiabatically"?</p> | 1,351 |
<p>I have often heard it said (by professional cosmologists) that if the universe is infinite, then there necessarily exist infinitely many copies of me repeated throughout.</p>
<p>The reasoning seems to be that any finite volume of space can contain at most finitely many fundamental particles existing in finitely man... | 1,352 |
<p>Consider a rollercoaster that goes down a slope:</p>
<p><img src="http://i.stack.imgur.com/94VBI.png" alt="rollercoaster"></p>
<p>At the higher level it has speed $v_0$, then it goes down a slope and at the end it has speed $v_0 + \Delta v$. The carriage is not powered and has negligible friction. </p>
<p>So by c... | 1,353 |
<p>I am confronted with the following scaling equation (in Laplace domain if that matters):</p>
<p>$\tilde\psi(s) = a \tilde\psi(s/b)$</p>
<p>I know the answer is such that $\tilde\psi(s) \sim s^{\beta} K(s)$ where $\beta = \ln a/\ln b$ and I don't really care what K is. I'm not sure if the functions $\tilde\psi(s)$ ... | 1,354 |
<p>M. Mezard, G. Parisi and coworkers have written about replica symmetry and its breaking in spin glasses, structural glasses, and hard computational problems.</p>
<p>I am just getting acquainted with this literature. Where are the best places to start understanding replica symmetry?</p>
<p>Can anyone here explain ... | 1,355 |
<p>I have searched for an answer to this question on physics SE but I have not seen a question in which it is addressed properly. Please let me know if there is an answer already.</p>
<p>My question briefly is, is the uncertainty principle a technical difficulty in measurement OR is it an intrinsic concept in Quantum ... | 1,356 |
<p>Mass and Energy can warp space-time around them, but that doesn't answer what space-time is, what is space?</p> | 1,357 |
<p>I'm doing experiments that require using a big, thin, contrast grid, for example 1 black pixel and then 1 white pixel alternately. </p>
<p>I've met with a few DLP projectors and in each of them I had to manually adjust <strong>clock adjustment/phase adjustment.</strong> If I didn't do so, image was flickering or h... | 1,358 |
<p>The problem that got me thinking goes like this:- </p>
<blockquote>
<p><em>Find $dp/dx$ where $p$ is the probability of finding a body at a random instant of time undergoing linear shm according to $x=a\sin(\omega t)$. Plot the probability versus displacement graph. $x$=Displacement from mean.</em> </p>
</bloc... | 1,359 |
<p>I am confused on <a href="http://en.wikipedia.org/wiki/Bra%E2%80%93ket_notation" rel="nofollow">bra-ket notation</a> in quantum mechanics. My professor says that a ket is an eigenfunction of some operator. However, for some time now I thought a ket could represent a general wavefunction. Obviously any wavefunction s... | 1,360 |
<p>So I am dealing with the following hamiltonian, and the following perturbation:
$$H=-\mu B_0\sigma_z$$
$$V=\mu B_1(\cos(\omega t)\hat x-\sin(\omega t)\hat y)\cdot{\bf \sigma}$$
I am asked for the probability that the spin will go from ground state at time 0 to the excited state at time t using first order time depen... | 1,361 |
<p>I don't fully understand what would happen if we could travel at the speed of light. But I saw somewhere here that it would mean events happen out of order. But why is this a problem. It is said that cause has to happen before the effect, but why does this have to be linear? </p>
<p>And why is it that the speed of ... | 137 |
<p>I'm a computer scientist that likes to read about math and physics occasionally. A local author at a nearby aviation center brought bernoulli's flight equations into question.</p>
<p>It was clear enough logic, but I didn't understand all the math involved. He basically said that the lift equations don't account for... | 17 |
<p>I'm taking a solid state course, and is currently on the subject of dielectrics. In one of the sections, concerning "Impurities in Dielectrics" the books says:</p>
<p><em>"Impurities can also be used to make insulators conductive, exactly like doped semiconductors. Donor or acceptor levels have to lie close to the ... | 1,362 |
<p>As far as I know, since the earth is spinning, centrifugal force should be throwing you off the earth. However, gravity counteracts that by being a stronger force. So if you stood an object with the exact mass and size of earth, but it wasn't spinning, would you perceive gravity to be stronger?</p>
<p>If this is tr... | 18 |
<p>I have just begun studying quantum field theory and am following the book by Peskin and Schroeder for that.
So while quantising the Klein Gordon field, we Fourier expand the field and then work only in the momentum space. What is the need for this expansion?</p> | 1,363 |
<p>First thing I've been wondering is how the gravitational field is emitted. Matter emits gravitational waves, and I guess that those waves travel at around the speed of light. If that's not the case, please direct me to something that explains that.<br>
For now I'll assume that this emits a waves that travels at the ... | 876 |
<p>Recently I read an interesting article about <a href="http://en.wikipedia.org/wiki/Negative_temperature" rel="nofollow">negative temperature</a>. I was puzzled because I thought before that <a href="http://en.wikipedia.org/wiki/Temperature" rel="nofollow">temperature</a> has definite meaning in thermodynamics: it te... | 1,364 |
<p>I have been wondering about the axiom of choice and how it relates to physics. In particular, I was wondering how many (if any) experimentally-verified physical theories require axiom of choice (or well-ordering) and if any theories actually require constructability. As a math student, I have always been told the ax... | 1,365 |
<p>Well this is pretty noobish question and I am not sure how to ask.<br />
When We talk we don't talk in an uniform frequency. Then how can one measure frequency of ones sound/voice ? <br />
I am asking this cause several times I've heard people to say this is his/her frequency of voice. Is this a vague term ? or it h... | 1,366 |
<p>I've tried to find the moment of inertia of a cylinder rotating about an axis parallel to its base (i.e about the 'End diameter') as one can see <a href="http://hyperphysics.phy-astr.gsu.edu/hbase/icyl.html" rel="nofollow">here</a> . But when I checked my results with different references ,I've found that it's incor... | 1,367 |
<p>The partition function of a dipole in an electric field is a well-known problem, analytical solvable (nice integral, can be calculated with pen and paper), for example in the Langevin treatment of paramagnetism.</p>
<p>I'm right now looking at a classical quadrupole in an electric field. This looks very different, ... | 1,368 |
<p>spin-0 is massive or massless?
How does we separate the massive and massless degrees of freedom for spin-2?
What is the partially massive?</p> | 1,369 |
<h2>Definitions / Background</h2>
<p>In LTE, Kirchoff's law for radiation holds:</p>
<p>$$ \frac{j_{\nu}}{\alpha_{\nu}} = B_{\nu} (T) $$</p>
<p>where $j_{\nu}$ is the specific radiative emissivity, $\alpha_{\nu}$ is the monochromatic radiative absorption, and $B_{\nu} (T)$ is the Planck function evaluated at the tem... | 1,370 |
<p>A purely phase-modulated signal has no power modulation. This is obvious enough if you look at the time series, but I'd like to "see" it in the frequency domain.</p>
<p>In physical terms, if we take a laser beam and apply phase modulation via an electro-optic modulator and then send this beam to a photodiode, we w... | 1,371 |
<p>Suppose i try to derive the most generic Dirac-like equation (that is, as factors of first-order expression in momenta and mass operator where we allow coefficients that are associative, don't necessarily commute to each other, but they commute with the space-time degrees of freedom)</p>
<p>Usually the Dirac equati... | 1,372 |
<p>Get up off the plane of the ecliptic by a couple of million miles. Look back at the Sun and watch the Earth's orbit in time-lapse for a few centuries. The orbit is an ellipse tilted at 23.5 degrees from the ecliptic. Hold station with the Sun as it rotates about the galactic center.</p>
<p>Question: Does that tilte... | 1,373 |
<p>A positive pion is an up and an anti-down. A negative pion is a down and an anti-up. What's a pion with an electrical charge of 0?</p> | 1,374 |
<p>I am hoping that someone can clarify this for me.</p>
<p>With these equations. (Boltzmann Law) and radius of Radius of star how does surface temp scale with mass</p>
<blockquote>
<p>$R _x \approx R_\bigodot (\frac{M_x}{M_\bigodot})^.5$ </p>
<p>$L _x \approx L_\bigodot (\frac{M_x}{M_\bigodot})^3.5$ </p>
... | 1,375 |
<p>The title says it all but I will add some details. I believe that interference takes place only in waves which are parallel to each other. See the picture to understand what I mean by parallel.</p>
<p><img src="http://i.stack.imgur.com/omkAt.png" alt="enter image description here"></p>
<p>We see that in the image ... | 1,376 |
<p>How do we calculate the expectation value for speed? I have heard that we must first calculate the expectaion value for kinetic energy. Someone please explain a bit what options do we have.</p> | 1,377 |
<p>In differential geometry and general relativity space is said to be flat if the Riemann tensor $R=0$. If the Ricci tensor on manifold $M$ is zero, it doesn't mean that the manifold itself is flat. So what's the geometrical meaning of <a href="http://en.wikipedia.org/wiki/Ricci_curvature" rel="nofollow">Ricci tensor<... | 1,378 |
<p>Since we see the <a href="http://en.wikipedia.org/wiki/New_moon" rel="nofollow">new moon</a> at least once in a month when the Moon gets in between of the Sun and the Earth during the evening ( and as far as I know if this happens during the day, you'll get to see a <a href="http://en.wikipedia.org/wiki/Solar_eclips... | 110 |
<p>The formula for calculating the center of mass is</p>
<p>$$ r_{center} = \frac{m_1 \cdot r_1 + m_2 \cdot r_2}{m_1+m_2} $$</p>
<p>Why can't I use it to calculate the barycentre of two planets?</p>
<p><img src="http://i.stack.imgur.com/KVVK5.png" alt=""></p>
<p>I understand how to use ratios to approach this probl... | 1,379 |
<p><strong>Groundhog Day Update, 2014</strong></p>
<p>The simple and dumb way to ask my main question is this: If something like a neutron start goes sailing by at very close to the speed of light, say fast enough to double its total mass-energy, do you "feel" the energy it is carrying as gravity as it passes by?</p>
... | 1,380 |
<p>I'm trying to diagonalize the Hamiltonian for a 1D wire with proximity-induced superconductivity. In the case without a superconductor it's all fine. However, with a superconductor I don't get the correct result for the energy spectrum of the Hamiltonian in</p>
<blockquote>
<p>Tudor D. Stanescu and Sumanta Tewar... | 1,381 |
<p>This is a question I have been asking myself for some time since the following technique is often used in the nonlinear dynamics community, but never managed to get an answer why it could be applied.</p>
<p>In symplectic mechanics, consider a dynamical system with no rigid body movements (all eigenvalues are non-ze... | 1,382 |
<p>How does:</p>
<p>$$L \cdot\frac{dL}{dt} = \frac{1}{2}\frac{d(L^2)}{dt}$$</p>
<p>where <strong>L</strong> is a vector (I dunno how to make it bold in the equation).
How do they reach to this right hand side equation?
And what is the difference between <strong>||L||</strong> and <strong>|L|</strong> ?</p> | 1,383 |
<p>Given von Neumann equation
$$\frac{d}{dt} \rho(t) = -i [H, \rho(t)] = -i e^{-iHt}[H, \rho(0)]e^{iHt}.$$</p>
<p>If we know that $[H, \rho(0)] \neq 0$, how do we prove in details the solution of von Neumann equation will never be stabilized, i.e. $$\lim_{t\to\infty}\frac{d}{dt} \rho(t) \neq 0~?$$ </p> | 1,384 |
<p>Could anyone give me a brief explanation why multilayer OLEDS as more efficient than single layer OLEDs? What other advantages exist for multilayer OLEDs over single layer OLEDs?</p> | 1,385 |
<p>The gas mileage of my vehicle tends to improve the more I have been driving on the interstate on that tank of gas - if I go through a tank of gas without at any point driving on the interstate, I will typically get 24-26 MPG, but when I have driven almost exclusively on the interstate, I will typically get 26-29 MPG... | 1,386 |
<p>I learned how to sweat a pipe today from my father. If you're not familiar with the process, <a href="http://www.popularmechanics.com/home/skills/4213319" rel="nofollow">this</a> might help.</p>
<p>One thing that jumps out at me is this line (from the above link, as well as my father's explanation)</p>
<blockquot... | 1,387 |
<p>Does an object's kinetic energy increase, decrease, or stay constant when it reaches <a href="http://en.wikipedia.org/wiki/Terminal_velocity" rel="nofollow">terminal velocity</a> while falling? </p> | 1,388 |
<p>Length of a dipole antenna according to antenna theory should be lambda/2 for best reception. I am just curious about the outcome when length of dipole antenna >> lambda. Impedance will be zero in such a case and there will be no signal received. Is it correct?</p> | 1,389 |
<p>I have seen the term topological charge defined in an abstract mathematical way as a essentially a labeling scheme for particles which follows certain rules. However I am left guessing when trying to explain what physical properties of a system lead to the need to introduce this new type of "charge." </p>
<p>If it ... | 1,390 |
<p>If I have a complex voltage $V_z$ is real voltage $V$ (i.e. the voltage used in the normal ohms law and the voltage we normally talk about) always given by $V=Re(V_z)$. Does the same apply to current? and if it is not the case how do we find $V$ from $V_z$?</p> | 1,391 |
<p>Assume you are sliding down a steep hill. Is it safer to go down with your back against the hill or the front of your body against the hill? I assumed that since the surface area of your body which is touching the hill is about the the same regardless of which way you are going down, it won't make a difference. Is t... | 1,392 |
<p>This question is entirely on tensorial notation in Wald's General Relativity. When specifying the properties of the Riemann tensor on pg39, he states:</p>
<p>$R_{[abc]}^{\quad \ \ \ d} = 0$</p>
<p>and</p>
<blockquote>
<p>For the derivative operator $\nabla_a$ naturally associated with the metric, $\nabla_a g_{b... | 1,393 |
<p>I was looking at the derivation of drift velocity of free electrons in a conductor in terms of relaxation time of electrons. </p>
<p>Here a metallic conductor XY of length $\ell$ is considered and having cross sectional area A. A potential difference $V$ is applied across the conductor XY. Due to this potential dif... | 1,394 |
<p>What does the neutrino particles follow- Dirac or Majorana Statistics?</p> | 1,395 |
<p>A superposition of two probability wave creates standing wave. Well, that is convincing. Dose waves described by schrodinger's equation have other properties of wave? like reflection, refraction, polarization ect.</p> | 1,396 |
<p>I am trying to understand the gravitational sphere of influence (<a href="http://en.wikipedia.org/wiki/Sphere_of_influence_%28astrodynamics%29" rel="nofollow">SOI</a>), but all I get by searching is the formula that you can find on Wikipedia, that is</p>
<p>$$ r_{SOI} = a \left( \frac{m}{M} \right)^{2/5} $$</p>
<p... | 1,397 |
<p>As the resistance of a circuit goes down, the power increases because the current increases, assuming constant voltage. Why is this? I feel like resistance and current are inversely proportional, so lowering one should just raise the other, and power should stay relatively constant. What is it about power that makes... | 1,398 |
<p>I was thinking how far can I hear sound coming from a concert. Today I was walking at night and I could hear sound from somewhere very far. I started following the sound but sound used to disappear momentarily and then reappear. I went atleast 2 miles but could not find where it was coming from. </p>
<p>Now I am re... | 1,399 |
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