question stringlengths 37 38.8k | group_id stringlengths 2 6 | sentence_embeddings listlengths 768 768 |
|---|---|---|
<p>Suppose you have a particle in a box, and there may or may not be a Dirac delta potential somewhere in the box. How could one detect whether or not the potential is present? </p>
<p>Furthermore:
If there's more than one way to do this, what's the easiest or "cheapest"?
How long will it take?
Can it be done with cer... | g19145 | [
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<blockquote>
<p>A force field is given by $F = 3z+5$. Find the work done in moving an object in this force field along the parabola $z = t^2 + it$ from $z = 0$ to $z = 4+2i$.</p>
</blockquote>
<p><img src="http://i.stack.imgur.com/HO4ot.png" alt="enter image description here"></p>
<p>I don't understand why conjugat... | g19146 | [
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<p>I am working on a satellite simulator for a project/game and I am stuck on this one bit of physics. So far I have a satellite that revolves around earth on a 2D plane following Keplerian motion using Kepler's equation. Everything is fine and the satellite will orbit many times without problem. I can also change the ... | g19147 | [
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<p>Feshbach resonance is described with coupling of 2 systems differing in the form of potentials :- one is said to produce a bound state (in 'closed' channel) and other is to produce scattering states (in 'open' channel). The two channels are said to be coupled by another potential term. The resonance occurs where a b... | g19148 | [
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<p>Suppose we want to calculate the following matrix element.
$$
\langle \alpha |\hat{o}|\beta\rangle
$$</p>
<p>Where $\alpha$ and $\beta$ are two arbitrary basis states in a many-particle basis set, and $\hat{o}$ is an arbitrary operator.</p>
<p>If we now insert two identities, we can rewrite this as </p>
<p>$$
\in... | g19149 | [
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<p>Lord Kelvin defined the absolute temperature scale in the mid-1800s in such a way that nothing could be colder than absolute zero. Physicists later realized that the absolute temperature of a gas is related to the average energy of its particles. Absolute zero corresponds to the theoretical state in which particles ... | g19150 | [
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<p>I'm reading chapter 16 in Fluid Mechanics by Kundu. </p>
<p>It is stated (figures 16.16 and 16.17) that in a constant area duct flow with heating or friction, to go from subsonic conditions to supersonic violates the 2nd law of thermodynamics. How can that be possible? How does a fluid attain supersonic speeds in t... | g19151 | [
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<p>As far as I'm aware, the eye acts like a pinhole camera in that it inverts the image on the rentina. This makes sense as the rays converge and form a focal point that is upside down.</p>
<p>Myopia (shortsightedness) is described as the rays focusing before the retina, resulting in a blurred distance image. This wou... | g19152 | [
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<p>Looking at the radiation from the sun (T=5800K) I got a little surprise which I do not understand. </p>
<p>I first calculated the energy density u and also the number of photons per unit volume ng. From this one gets the average energy per photon:</p>
<p>$$
E_g = \frac{u}{n_g}
$$</p>
<p>Converted to a wavelength ... | g19153 | [
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<p>I'm currently working through the symmetry of the stress tensor, in relation to viscous flow. I am looking at this by examining the conservation of angular momentum equation for a material volume $V(t)$ with unit normal $\vec{n}=(n_1,n_2,n_3)$. I am having issue with applying the divergence theorem to this term</p>
... | g19154 | [
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<p>To calculate the effective coupling constants $u'_2(q)$ and $u'_4(q)$ of the effective Hamiltinian eq (4.9) of <a href="http://www.sciencedirect.com/science/article/pii/0370157374900234" rel="nofollow">this</a> paper</p>
<p>$$ H' = -\frac{1}{2}\int\limits_q u'_2(q)\sigma'_q\sigma'_{-q}
- \int\limits_{q_1}... | g19155 | [
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<p>Given a setup like: </p>
<p><img src="http://i.stack.imgur.com/SEW8T.png" alt="enter image description here"></p>
<p>Is it possible to find current and voltage through each resistors given resistor values and overall voltage (battery voltage I suppose). </p>
<p>I think $$I_0=I_A=\frac{\Delta V}{R_{total}}$$</p>
... | g19156 | [
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<p>Could you check me on this: if I'm interested in total power (summed over all frequency) of CMBR absorbed by a black body in empty space, would that be proportional to the surface of BB?</p> | g19157 | [
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<p>When I first heard people talking about using Kitaev's toric code to do topological quantum computation, I was thinking how many lines does the toric code have. Then I was told that
the "code" really represents quantum states. Later, I understood that the "code"
is the degenerate ground subspace of <a href="http://... | g19158 | [
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<p>Most descriptions of spontaneous symmetry breaking, even for spontaneous symmetry breaking in quantum systems, actually only give a classical picture.
According to the classical picture, spontaneous symmetry breaking can only happen for non-linear systems. Classical linear systems, such as Harmonic oscillators, ca... | g19159 | [
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<p><img src="http://i.stack.imgur.com/pW1vD.gif" alt="enter image description here"></p>
<p>In the above Alpha decay reaction, we get thorium by the alpha decay of uranium with an alpha particle. But we also get energy of amount Q by this process. And according to my course books, this Q energy comes from E = mc2 i.e.... | g19160 | [
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<p>Let's deal specifically with a two-level system. I understand that ``coherence'' is due to the off-diagonal elements in the density matrix $\rho(t) = \sum_{i}|\psi_i(t)\rangle p_i\langle\psi_i(t)|$ for the system (generally written for mixed states). Entanglement can be measured by finding the eigenvalues $p_i$ of t... | g19161 | [
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<p>I have a question regarding the force a band places on an object. Say I have a rubber band wrapped around 2 pegs at a certain distance, and at that distance I know the pounds of force per inch it is pulling at. For example, if the pegs are placed such that the band is stretched to 52 inches, the force the bands ap... | g19162 | [
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<ol>
<li><p>Quarks combine to form composite particles called hadrons, the most stable of which are protons and neutrons, the components of atomic nuclei. Due to a phenomenon known as color confinement, quarks are never directly observed or found in isolation.</p></li>
<li><p>Color confinement, often simply called conf... | g19163 | [
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<p>According to Kepler's law of planetary motion, the earth revolves around the sun in an elliptical path with sun at one of its focus.
However,
according to general theory of relativity,
the earth revolves around the sun in the curved space and it revolves in a circular path.</p>
<p>Which is correct? Does the plan... | g587 | [
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<p>I mean if I am in a room totally closed to light. If I switch on a torch for a second then switch it off. So will the inside of room be always bright?</p> | g588 | [
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<p>I am a glassblower, and I would like to trap smoke in a glass bubble, my hope is to create an infinitely lingering smoke inside.</p>
<p>Is this possible?</p> | g19164 | [
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<p>When we rub two glass rods with their respective pieces of silk cloth, the two glass rods would repel each other. What if we rub the glass rod against the other glass rod? Will they repel each other? Or they only get charged when they are rubbed by silk cloth? </p> | g19165 | [
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<p>I have got this all down pat:</p>
<p>1.Collision with a moving particle excites an atom.</p>
<p>2.This causes an electron to jump to a higher energy level.</p>
<p>3.The electron falls back to its original energy level, releasing the extra energy in the form of a photon.</p>
<p>Here are a few questions:</p>
<p>H... | g19166 | [
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<p>With the heat engine</p>
<p><img src="http://i.stack.imgur.com/ulLxt.png" alt="enter image description here"></p>
<p>we have an ideal gas working the substance. I want to show that the efficiency of this heat engine is</p>
<p>$$\eta = 1 - \frac{1}{\gamma}\frac{\bigg(\frac{V_3}{V_1}\bigg)^\gamma - \bigg(\frac{V_2... | g19167 | [
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<p>According to Huygens principle, if we consider any point of the primary wave fronts, each point is the source of secondary disturbance. If the point size we consider tends to zero, the number of points on that wave front which enters the slit tends to infinity. Thus, if we consider the slit how much ever small, we m... | g19168 | [
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<p>Can a positron beam be used to cut through metal?</p> | g19169 | [
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<p>I googled the sentence in the title of this question and found the famous experiment by
Wu <em>et al</em> demonstrating that electrons in weak decay are emitted ``in the direction of motion of a left-handed screw rotating with the nuclear spin''.</p>
<p>This show that: asymmetry in decay -> parity violation.</p>
... | g19170 | [
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<p>I know that I can calculate the probability distributions of $x$ and $p$ from the <a href="http://en.wikipedia.org/wiki/Wigner_quasiprobability_distribution" rel="nofollow">Wigner quasiprobability distribution</a>, and I can calculate the probability distributions of other operators by calculating their eigenstates,... | g19171 | [
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<p>One of the pertinent questions about many body systems that causes me much wonder is why the solar system is so stable for billions of years. I came across the idea of "resonance" and albeit an useful concept, it hardly explains the long stability of the solar system. Normally an N body problem with inverse square m... | g19172 | [
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<p>When looking at the <a href="http://pdg.lbl.gov/" rel="nofollow">PDG</a>, there is a difference between the 'running' and the 'current' quark masses.</p>
<p>Does anyone know which is the difference between these two?</p> | g19173 | [
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... |
<p>Consider the action functional</p>
<p>$S[z;t_1,t_2]=\int_{t_1}^{t^2}[g(z,\bar{z})\dot{z}\dot{\bar{z}}]^{\frac{1}{2}}dt$</p>
<p>with $z(t)$ a complex path with end points $z_i=z(t_i),\; i=1,2$. $g(z,\bar{z})$ is a positive real function on $H=\{z\in C: Im(z)>0\}$.</p>
<p>After some easy questions the exercise a... | g19174 | [
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0.050993070006370544,
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-0.0374... |
<p>Here is my understanding of Schrödinger's equation and wave functions: (I'm considering the time independent equation.)</p>
<blockquote>
<p>The equation takes in values of energy as an input and, being a differential equation, gives functions as outputs. These functions correspond to the different orbitals.</p>
... | g19175 | [
-0.03168044611811638,
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-0.02324693277478218,
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0.05314704775810242,
0.03159338980913162,
0.0044... |
<p>I'm trying to recreate some work that a professor explained to me in his office, specifically deriving the free particle propagator going from $(y,0)$ to $(x,T)$ using the Feynman Path Integral. I'm trying to reproduce $$K(x,T;y,0) = \sqrt{\frac{m}{2\pi i\hbar T}}\mathrm{exp}[\frac{im(x-y)^2}{2\hbar T}]$$Here's what... | g19176 | [
0.04663439095020294,
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0.005149560980498791,
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0.016942040994763374,
0.020954841747879982,
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0.038422007113695145,
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0.03975536301732063,
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0... |
<p>If you have a field which value is just Gaussian noise plus a constant do you call it <a href="http://en.wikipedia.org/wiki/Isotropy" rel="nofollow">isotropic</a>?</p>
<ul>
<li>there is no preferred direction</li>
<li>however it is not "the same" in all directions if "the same" means "constant"</li>
</ul>
<p>The q... | g19177 | [
0.03701429069042206,
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0.042900245636701584,
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0.019891882315278053,
-0.00027119091828353703,
-0.... |
<p>So, I was reading about this Dragon V2 and it has got touch controlled screens, but screen might be unreadable for pilots because of engine vibrations and whatnot. I came across this comment on reddit.</p>
<p><em>"I read an article on the SLS/Orion. They had a problem with vibrations making screens unreadable. It w... | g19178 | [
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0.013388155959546566,
0.0010359225561842322,
0.071964... |
<p>Let's say you live at a moderate (temperate, in today's terms) latitude during the last glacial maximum. You're probably in some kind of steppe or taiga biome, even though you're at 40 degrees north, and you've never known hot weather. If you're outside on a sunny summer day, would you still get a suntan/sunburn lik... | g19179 | [
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<p><strong>The Problem</strong><br>
For a small mass a distance $R_i$ away from the center of the Earth, how long would it take for the object to fall to the surface of the Earth, assuming that the only force acting upon the object is the Earth's gravitational force?</p>
<p><strong>Relevant Information</strong><br>
Th... | g755 | [
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0.009314678609371185,
0.03422165289521217,
0.00... |
<p>Let $C$ be a cuboid (rectangular parallelepiped) with edges of lengths $a < b < c$. </p>
<p>Consider an axis that passes through the centers of two opposite faces of $C$. There are three such axes, one passing through the centers of the $a$–$b$ faces, one through the centers of the $a$–$c$ faces, and one thro... | g644 | [
0.0752219557762146,
0.05257994309067726,
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-0.07035... |
<p>I want to check if I correctly understand polarization.</p>
<p>Considering a single photon travelling in vacuum, it can only be polarized linearly under the same direction at any time, right?</p>
<p>When we talk about circular polarization, or unpolarized light, we are talking about sums of linearly polarized phot... | g19180 | [
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0.0210666935890913,
0.0025208136066794395,
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... |
<p>The position of an object moving along X-axis is given as $X=a+bt^2$ where $a=8.5\,\mathrm m$, $b=2.5\,\mathrm {m/s^2}$ and $t$ is measured in seconds. What is it's velocity at $t=0$ and $t=2.0$ s? What is the average velocity between $t=2.0s$ s and $t=4.0$ s?</p>
<p>I have no idea what to do. I have seen this in n... | g19181 | [
0.05373154208064079,
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0.016676077619194984,
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0.05586943030357361,
0.04038501903414726,
-0.0... |
<p>How does a body acquire charge or get charged up?
I am not talking about the method through which it gets charged up, but does every atom contain things that make a body charge up?
If we talked about the process by which a body gets charge, how does it happen?</p> | g19182 | [
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0.019595012068748474,
0.04244861751794815,
-0.018884... |
<p>I recently saw a video on Youtube about a <a href="http://en.wikipedia.org/wiki/Perpetual_motion" rel="nofollow">perpetual motion</a> machine. Here is the link:</p>
<p><a href="http://www.youtube.com/watch?v=OS1KXMsE2qk" rel="nofollow">http://www.youtube.com/watch?v=OS1KXMsE2qk</a></p>
<p>It's on <a href="http://w... | g19183 | [
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0.028066212311387062,
0.004404387436807156,
0.00... |
<p><img src="http://i.stack.imgur.com/QTGeQ.gif" alt="A picture showing Young's Double Slit experiment"></p>
<p>I was wondering what would happen to the fringe pattern displayed on the screen if the first slit (as shown in the picture), which is also known as "single slit", was made a bit wider. I read it in my book. ... | g19184 | [
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0.043... |
<p>Why is it true that <a href="http://en.wikipedia.org/wiki/Anyons" rel="nofollow">anyons</a> can have angular momentum taking any real value? Why aren't they restricted to the $j(j+1)$ integer values most are familar with?</p> | g19185 | [
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... |
<p>I was just studying meteorology and had a doubt about the motion of meteors towards earth.</p>
<p>Can a meteor be stopped while it is still under under the gravitational influence of Earth? As far as I know some meteors are very bulky and their motion towards the Earth's surface is with a huge magnitude of momentum... | g19186 | [
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0.005384247284382582... |
<p>Sometime when I see the sky I see that the cloud-layers go to different ways. But how is it possible?</p> | g19187 | [
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<p>Recently it has been studied non-abelian anyons in some solid-state systems. These states are being studied for the creation and manipulation of qubits in quantum computing.</p>
<p><strong>But, how these non-abelian anyons can arise if all particles involved are fermions?</strong></p>
<p>In other words, how electr... | g19188 | [
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<p>I'm making a lab report where I've used a Helmholtz coil and a magnet to find Earth's magnetic field intensity in the area by relating the frequency of oscillation of the magnet when a certain current is going through the coil, using the equation:</p>
<p>$$ f^2 = \frac{μ_o}{4π^2m_i} \left(\frac{8\mu_0N}{5^{3/2}R}I ... | g19189 | [
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0.000... |
<p>Well let's start off with that I'm not a physicist but I'd like some thoughts on something I came across in my hometown.</p>
<p>This guy:</p>
<p><img src="http://i.stack.imgur.com/G3U6R.jpg" alt="enter image description here"></p>
<p>Is it possible that due to the electrical charge of magnets this guy can make th... | g19190 | [
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<p>I have a question about the Lagrangian-formalism; they state that the holonomic constraints are expressed as:</p>
<p>$$f_\alpha(x_1,y_1,z_1,...,x_n,y_n,z_n,t) = 0 $$ where $\alpha = 1,...,L$ </p>
<p>They state now that these constraints may not contain irrelevant information. They express this by saying:
$$rank(\f... | g19191 | [
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0.02778038941323757,
0.0026378598995506763,
0.01... |
<p>I learned that the force from magnetic fields does no work. However I was wondering how magnets can be used to pick up pieces of metal like small paperclips and stuff. I also was wondering how magnets can stick to pieces of metal list a refrigerator? </p> | g484 | [
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... |
<p>I'm trying to read through a paper which explains the following about Universal Extra Dimensions (UED) vs <a href="http://en.wikipedia.org/wiki/Large_extra_dimension" rel="nofollow">ADD models</a>:</p>
<blockquote>
<p>The new feature of the UED scenario compared to the brane world is
that since there is no bran... | g19192 | [
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0.02583555318415165,
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0.036991510540246964,
... |
<p>While studying the Heat Equation, I got stuck in a statement in my book. It says:</p>
<blockquote>
<p>We have seen that the combination of variables $\displaystyle \frac{x}{\sqrt{Dt}}$ is not only invariant with respect to parabolic dilations but also dimensionless. <strong>It is then natural to check if there ar... | g19193 | [
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<p>The formula relating current to back emf is $V-E=IR$ where $V$ is the source pd and $E$ is the back <a href="http://en.wikipedia.org/wiki/Electromotive_force" rel="nofollow">Emf</a>. Thus it can be seen that as the back emf increases the current decreases. But what is the implication of the power ($PV$) delivered ac... | g19194 | [
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<p>This question is related to Planck units (also called natural units, absolute units or God's units).
I'm wondering which constant is the most fundamental and should be normalized to 1. I would like as much explanation as possible please.</p> | g19195 | [
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0.004301... |
<p>Consider this <img src="http://i.imgur.com/ko1D4aX.jpg" alt="this"> picture.
Integrating over this infinitesimal box gives the following equivalencies:</p>
<p>$$\int_{\Delta V} d^3r~{\rm div} \vec{E}(\vec{r}) = \int_{S(\Delta V)} d\vec{f} \cdot \vec{E}(\vec{r}),$$ </p>
<p>which for $\Delta x \rightarrow 0$ gives ... | g19196 | [
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0.0019891911651939154,
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<p>If a planet is spinning east to west and there is a satellite spinning from west to east...</p>
<p>Can the satellite travel at a speed sufficient to make the planet appear, from the vantage point of the satellite, to be rotating from west to east?</p>
<p>What kind of calculations could be made to determine that sp... | g19197 | [
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-0.0331844... |
<p>There was this question that i saw in a book and it also had an answer given.</p>
<p>The Question was:</p>
<blockquote>
<p>If there were only one type of charge in the universe, then:</p>
<ul>
<li>$\phi = \oint \boldsymbol{E}\cdot \partial\boldsymbol{A} \neq 0 $ on any surface. </li>
<li>$\phi = \oint ... | g19198 | [
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<p>Upon looking at some radiation levels higher than Microwaves, I have come across "<a href="http://en.wikipedia.org/wiki/Terahertz_radiation" rel="nofollow">Terahertz radiation</a>". According to the article, there are numerous ways to generate such radiation, and that brings questions to me.</p>
<p>My confusion lay... | g19199 | [
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... |
<p>Consider a compound pendulum pivoted about a fixed horizontal axis, illustrated by the force diagram on the right:</p>
<p><img src="http://i.stack.imgur.com/aInsV.gif" alt="image was taken from hyperphysics.phy-astr.gsu.edu/hbase/pend.html#c4 "></p>
<h2>#</h2>
<p>Okay, I can't figure out where the normal force on... | g19200 | [
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-0.008342049084603786,
... |
<p>Assume that there is the following $T-H$ phase diagram with the constant pressure lines.</p>
<p><img src="http://i.stack.imgur.com/IsC28.gif" alt=""></p>
<p>Which is greater preasure? The preasure drops as we move to lower temperatures (i.e. from top to bottom)?</p>
<p>How constant pressure lines are on the water... | g19201 | [
0.017125727608799934,
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0.017... |
<p>I have this rather mathematical question about the calculation of the partial derivative of a potential energy function given by:</p>
<p>$$U(x_i)=\frac{1}{2}\sum_{i,j}\frac{\partial^2U(0)}{\partial x_i\partial x_j} x_ix_j.$$
Or if we use $b_{ij}$ for the Hessian : $$U(x_i)=\frac{1}{2}\sum_{i,j}b_{ij}x_ix_j.$$</p>
... | g19202 | [
0.06883629411458969,
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0.011533910408616066,
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<p>A hollow cylinder (radius $R$) is rolling against the wall at angular speed $\omega$. The coefficient of friction between the cylinder and the wall(ground) is $\mu$. After how many rotations the cylinder will stop rotating?</p>
<p>So I figured I need to find the time taken for cylinder to stop moving, and that woul... | g19203 | [
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<p>In the context of Confocal Microscopy literature state, "spatial rejection of out of phase light".Is that mean only light which is pass through the pinhole is used and the rest is blocked ?</p> | g19204 | [
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<p>There are two types of dirac equations:
$(p_\mu\gamma^\mu - m)\Psi(x) = 0$ and $(p_\mu\gamma^\mu + m)\Psi(x) = 0$.
Here $p$ are the momentum operators.</p>
<p>The fermion propagator is defined in the equation $(p_\mu\gamma^\mu - m)S_F(x-x') = \delta(x-x')$. This equation can be easily solved in momentum space:
$$S_... | g19205 | [
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0... |
<p>Working with the Wikipedia definition of the Bekenstein bound:</p>
<p>$S \leq \frac{2 \pi R k_bE}{\hbar c}$</p>
<p>$2\pi R \ $ is $m^2$</p>
<p>$k_b$ is $\frac{J}{K}$</p>
<p>$E$ is $J$</p>
<p>$\hbar$ is $J*s$</p>
<p>$c$ is $\frac{m}{s}$</p>
<p>$\frac{m^2 \frac{J}{K} J}{(Js \frac{m}{s})} = m \frac{J}{K}$</p>
... | g19206 | [
0.01925078220665455,
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<p>In Optical Coherence Tomography, Broader bandwidth/low coherence light sources are used. Is it only because to increase the resolution or are there any other reasons?
What will happen if we use a high coherence source ? </p> | g19207 | [
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<p>I am looking for an equation that gives me the potential energy of the interaction between two parallel dipoles. </p> | g19208 | [
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<p>According to <a href="http://en.wikipedia.org/wiki/Neutrino_oscillation#Theory" rel="nofollow">Wikipedia</a></p>
<blockquote>
<p><em>Neutrino oscillation arises from a mixture between the flavor and mass eigenstates of neutrinos. That is, the three neutrino states that interact with the charged leptons in weak in... | g728 | [
0.024482082575559616,
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<p>If I know that the index of refraction of a given substance is 1.4 for the average wavelength (say 550 nm), and I would like to know what is the index of refraction with a wavelength of 832 nm, how would I go about computing this? I'm not looking for an exact solution, just a rough estimate that is better than 1.4<... | g19209 | [
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<p>Which experiments prove atomic theory?</p>
<p>Sub-atomic theories:</p>
<ol>
<li><p>atoms have: nuclei; electrons; protons; and neutrons.</p></li>
<li><p>That the number of electrons atoms have determines their relationship with other atoms. </p></li>
<li><p>That the atom is the smallest elemental unit of matter -... | g19210 | [
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<p>I've been reading about supernovae for a while, and I noticed how incredibly fast their shockwave and remnants travel shortly after the explosion. So I thought about how this would affect the earth if one happened nearby.</p>
<p>I know that the earth's atmosphere already protects us from cosmic rays which I think h... | g19211 | [
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<p>I'm trying to learn how to do a many-body path integral for <strong>both fermions and bosons</strong>, and I'm stuck. I'm following Altland and Simons - Condensed Matter Field Theory, chapter 4. On page 167, equation 4.27 is</p>
<p>\begin{equation}
Z = \int \prod_{n=1}^N d(\bar{\psi}^n,\psi^n) e^{-\delta \sum_{n=0}... | g19212 | [
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<p>How does $t=0$ transform into $t - vx/c^2 = 0$ if a frame of reference is moving as given in <a href="http://www.lecture-notes.co.uk/susskind/special-relativity/lecture-1/lorentz-transformations/" rel="nofollow">here</a>?</p>
<p>It seems that the relativistic transformation is given by
$$ \begin{bmatrix}
x' \\
ct'... | g19213 | [
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<p>I can only boast of my passion for science and not of any credentials. I ask because I am curious, and it is not the type of question one can easily Google! What if the key to discovering and unlocking the secrets of dark matter and energy lie in the <a href="http://en.wikipedia.org/wiki/Island_of_stability" rel="no... | g19214 | [
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0.00221066502854228,
... |
<p>What does it mean to say that 2 fields are coupled? More generally, what does "coupling" mean?</p> | g19215 | [
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<p>Goodmorning everybody,
I have to run a numerical simulation of a Bose-Einstein condensate on a rotating disc. Now, my problem is that I became suspicious about the equation I'm using, since the final result I obtain is not what I expected. First of all, the Gross-Pitaevskii equation (in a z-axis symmetrical trap) fo... | g19216 | [
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0.0... |
<p>This is a problem in Hartle's "GRAVITY":</p>
<p>Consider the functional</p>
<p>$$S[x(t)]= \int_{0}^{T} \left[\left(\frac{dx(t)}{dt}\right)^2 + x^2(t)\right]\text{ }dt$$</p>
<p>Find the curve $x(t)$ satisfying the conditions:</p>
<p>$x(0)=0$, and $x(T)=1$, </p>
<p>i.e make $x(t)$ an extremum, and find its extrem... | g19217 | [
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0.0... |
<p>Two related questions:</p>
<ol>
<li><p>Small object of mass $m$ is falling into the supermassive black hole of mass $M$. What is the maximal kinetic energy can be acquired by the small object, from the point of view of an observer whose frame of reference is at rest near event horizon?
Can it exceed $(M+m)c^2$?<... | g19218 | [
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<p>I'd like to build a small Peltier cell cooled cloud chamber.</p>
<p>The cold surface would be a copper sheet with a surface of 200x200 millimeters.</p>
<p>Is there a way to even guess the cooling power needed to bring the copper sheet below -30°C ?</p> | g19219 | [
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<p>The way I learned it from practicing Fourier analysis and signal processing besides quantum mechanics, is that Energy conservation cannot be achieved in short time scales, and that limits energy conservation in Quantum mechanics.</p>
<p>In other words: <em>Energy conservation is limited by the Heisenberg uncertaint... | g19220 | [
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<p>The “interacting wind” model of planetary nebulae is based on the idea that the white dwarf phase of stellar evolution is preceded by a red giant phase. A fast wind from the hot white dwarf overtakes the more slowly moving red giant wind and the region of interaction forms a shell of material which is driven outward... | g19221 | [
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<p>A relativistic moving particle, e.g. muon $\mu^+$, described by its four-momentum vector $p_\mu$, charge $e$ and with a given spin polarization, ${\bf S}=(S_x,S_y,S_z)$, decays into three particles, e.g. $\mu^+\to\nu_\mu e^+\bar{\nu}_e$.</p>
<ul>
<li>How does one determine the spin polarizations of decay products? ... | g19222 | [
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<p>See <a href="http://en.wikisource.org/wiki/The_Principles_of_Mathematical_Physics#The_Principle_of_Relativity."><em>The Principle of Relativity</em></a> here: <a href="http://en.wikisource.org/wiki/The_Principles_of_Mathematical_Physics"><em>The Principles of Mathematical Physics</em></a>. This was written by Poinca... | g19223 | [
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<p>First thing first, I'm looking to implement this within a multiplayer videogame as a "special" skill or powerup, but, I'm willing to build it upon a physics based explanation/theory.</p>
<p>The question may be misleading due to my language gap and lack of knowledge in physics, in that case, I'd be thankful if you'd... | g19224 | [
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<p>I need to do some calculation to find out whether my design works. I may use oil/water/air in my pneumatic cylinder (or you can call it hydraulic cylinder). Assume I have just a cylinder and I put oil into the chamber to raise a weight. My question is how much of volume will reduce when the weight is x kg (Let assum... | g19225 | [
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<p>In <a href="http://arxiv.org/abs/1207.3497" rel="nofollow">arXiv:1207.3497</a> - <em>4D partition function on $S^1 \times S^3$ and 2D Yang-Mills with nonzero area</em>, Yuji Tachikawa explains the partition function for an 4d $\mathcal{N}=2$ sigma model on $S^3 \times S^1$ with target $T^*G_{\mathbb{C}}=G \times \ma... | g19226 | [
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-0.03068... |
<p>I have a little doubt about a force being or not conservative. Well, as I understood, some forces cannot be expressed as exterior derivative of some scalar potential because the work done by the force is path dependent, in other words, it's not possible to determine the work based only on some value at the end point... | g19227 | [
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<p>When a mass(metal ball) lands on the end of a trampolne bed, the mass is displaced towards the centre of the trampoline. I have read about the energy changes and forces involved in a trampoline but can't find any information about this aspect. I'm guessing it has something to do with a spring always trying to return... | g19228 | [
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<p>I was watching a video on Youtube by Brian Greene, "the illusion of time."<a href="http://www.youtube.com/watch?v=j-u1aaltiq4" rel="nofollow">http://www.youtube.com/watch?v=j-u1aaltiq4</a></p>
<p>In that video, he introduces to me the idea of a "brane," or a slice of the universe at specific points in time. And the... | g19229 | [
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<p>I explained to someone I know about General Relativity (as much as I know).</p>
<p>He said that he didn't see how it could be correct.</p>
<p>He argued:</p>
<p>How is 4-dimensional space-time space different to 3-dimensional space? he doesn't agree that as that because the 4-dimensional space-time is only differe... | g19230 | [
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<p>In a certain lecture of Witten's about some QFT in $1+1$ dimensions, I came across these two statements of regularization and renormalization, which I could not prove, </p>
<p>(1) $\int ^\Lambda \frac{d^2 k}{(2\pi)^2}\frac{1}{k^2 + q_i ^2 \vert \sigma \vert ^2} = - \frac{1}{2\pi} ln \vert q _ i \vert - \frac{1}{2\... | g19231 | [
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<p>When one does string compactification on a Calabi-Yau 3-fold. The parameters in Kähler moduli and complex moduli gives the scalar fields in 4-dimensions. It is claimed that the Kähler potentials of the CY moduli space gives the kinetic terms of the scalar fields in 4d. Could anyone let me know why?</p>
<p>I know th... | g19232 | [
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0.03... |
<p>Could someone explain why the Specific Heat Capacity (SHC) of dry air is 1.005kJ/kg.K whereas the accepted SHC for ventilation air is quoted 1.300kJ/kg.K?
Assuming the air for the ventilation calc’s is humid say 60RH @20°C it is estimated that there would be about 8.8g/kg of moisture in the air. [Using the psychrom... | g19233 | [
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<p>An <a href="http://en.wikipedia.org/wiki/EPR_paradox" rel="nofollow">EPR quantum experiment</a> can be explained by instantaneous collapse of the wave function regardless of the distance separating a pair of entangled particles. But do we have the certainty that the process is really instantaneous? If not, what is t... | g19234 | [
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0.004337263759225607,
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<p>Where and how is the entropy of a black hole stored?</p>
<p>Is it around the horizon? Most of the entanglement entropy across the event horizon lies within Planck distances of it and are short lived. </p>
<p>Is it stored near the singularity? How can you pack so much information in such a small region?</p>
<p>Can... | g19235 | [
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0.023905815556645393,
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... |
<p>I know that charge conjugation exchanges the creation (or annihilation) operators of the particles with those of the anti-particles and therefore merits the name charge conjugation. </p>
<p>However, if operated on the single electron Dirac plane wave $u(p)$ it results in v(p) and vice-versa. For me, however, $v(p)$... | g19236 | [
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<p>I have a question regarding how to extract probability from an overlap integral. Specifically, I am calculating the probability of a particle in a bound state in a delta potential $V=-\alpha \delta(x)$ ($\alpha$ is positive) remaining in a bound state after $V$ changes strength to $V=-\beta \delta(x)$. I am able to... | g19237 | [
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<p>Can somebody help me out with the intermediate details of eqn. (2.5) in this paper? </p>
<blockquote>
<p>Generalized gravitational entropy. Aitor Lewkowycz and Juan Maldacena. <a href="http://arxiv.org/abs/1304.4926" rel="nofollow">arXiv:1304.4926</a>.</p>
</blockquote>
<p>Is the Euler $\psi$ function appearing ... | g19238 | [
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0.00553579768165946,
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0.031184818595647812,
0.07163715362548828,
-0.036... |
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