question stringlengths 37 38.8k | group_id stringlengths 2 6 | sentence_embeddings listlengths 768 768 |
|---|---|---|
<p>How can we show that the weak interaction violates the charge conjugation symmetry?</p> | g8150 | [
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<p>In the common configuration of the <a href="http://en.wikipedia.org/wiki/Hall_effect" rel="nofollow">Hall Effect</a>, why wouldn't the conductor move?
It follows the same principle of the Lorentz force or basic electric motor doesn't it?</p>
<p>I can't seem to find the difference between them...</p> | g8151 | [
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<p>The density matrix (or state matrix) is a generalization of a wave function that is able to describe incoherent superpositions of an N-state system. It is often written as a matrix and observables are calculated by taking the trace of the product of itself with the operator in question.</p>
<p>Hestenes' spinors are... | g8152 | [
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<p>How do I find the orbit of a moving point object given 3 past passing positions and the tangents at these passing positions, and given that the orbit is known to be an ellipse?</p> | g8153 | [
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<p>What are the circumstances in which neutrinos can harm humans or even kill them.?</p> | g8154 | [
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<blockquote>
<p>2 particles are constrained to move in a ring. Both particles begin moving at $t=0$ from $p=0$, each particle moving in the opposite direction of the other. It is known that they are moving at different constant velocities. Both particles pass each other (without interaction) 4 times before simultaneo... | g8155 | [
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<p>Imagine I have a long rod of metal. Let's say it's 1m long, 1cm wide and 1mm high. Now suppose I pass DC through it. But instead of running the current through lengthwise, I want to run it sidewise. That is, in ascii art:</p>
<pre><code> \/ - attach "+" here
+-------------------------------------... | g8156 | [
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<p>I am currently designing a lighting solution for Phillips as part of my university degree. However I am stuck on a small problem, as stated above. If I was to have a strip of perspex, with the sides matt and the bottom polished, would I achieve more light through the polished surface or the matt surface. And why?? <... | g8157 | [
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<p>I have a college-level understanding of Physics. A <a href="http://phys.org/news/2014-05-team-accurately-teleported-quantum-ten.html" rel="nofollow">recent study</a> from the University of Delft in the Netherlands that seems to suggest that quantum teleportation of information (as in "<em>communication of informatio... | g8158 | [
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<p>I'm confused about an exercise of a book. I understand that the units for angular velocity is $\text{rad/s}$; but I don't understand, how can I get it from the relation $\omega=\sqrt{k/m}$.</p>
<p>Solving this equation: $\omega^2=(10^4\text{ N/m})/50\text{ kg}$. From this, I get these units:</p>
<ul>
<li><p>For $\... | g8159 | [
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<p>I want to know the rate at which air will ascend above a stove element.</p>
<p>Is there some relationship between ambient air temperature, element temperature, and speed of the resulting updraft?</p>
<p>If nothing definite, is there anything approximate that I could use?</p> | g8160 | [
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<p>An electron is trapped in a one-dimensional well of width $0.132\,$nm. The electron is in the ninth excited state ($n=10$) state. What is the uncertainty in its momentum? The problem gives a hint to use the equation $\Delta{p_x}=\sqrt{(p_x^2)_{avg}}$ (the root mean square of the momentum of the particle). I know the... | g8161 | [
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<p>Unlike most <a href="http://en.wikipedia.org/wiki/Planck_units" rel="nofollow">Planck units</a> named after "Planck" such as Planck length, Planck temperature, etc, the <a href="http://en.wikipedia.org/wiki/Planck_mass" rel="nofollow">Planck mass</a> seems more closed to daily life. It is about $10^{-5}$g, same orde... | g8162 | [
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<p>I have a tank of oil at 55 degrees c. I plan to run a copper pipe 8mm in diameter (1mm thickness) into a coil 15m long inside the tank. For all purposes of assumption, the copper pipe is perfectly transferring heat across to the oil and vice-versa.</p>
<p>I have a pump of 10l/min that circulates this oil around the... | g8163 | [
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<p>Re-reading <a href="http://physics.stackexchange.com/a/33156/5265">http://physics.stackexchange.com/a/33156/5265</a>; I find myself thinking if light, being EM in the humanly visible spectrum, may possess gravity - does a magnetic field also possess gravity?</p> | g8164 | [
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<p>On page 54 of Weinberg's QFT I, he says that an element $T(\theta)$ of a connected Lie group can be represented by a unitary operator $U(T(\theta))$ acting on the physical Hilbert space. Near the identity, he says that</p>
<p>$U(T(\theta)) = 1 + i\theta^a t_a + \frac{1}{2}\theta^a\theta^bt_{ab} + ...$</p>
<p>Wein... | g8165 | [
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<p>This question is dedicated to Martin Fleischmann (1927-2012).</p>
<p>When a molecule is adsorbed on a metal surface, the Raman scattering amplitude from the molecule is enhanced. According to <a href="http://en.wikipedia.org/wiki/Surface_enhanced_Raman_spectroscopy" rel="nofollow">Wikipedia</a>, the downconversion ... | g8166 | [
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<p>It seems a positive cosmology constant behaves like a negative pressure. However, the positive cosmology constant cause a expanding universe. So I am puzzling about this: </p>
<p>A negative pressure cause a expanding universe?</p>
<p>To me, it is easy to imagine the positive pressure cause expanding just like gas.... | g8167 | [
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<p>Suppose there is a material with heavy nuclei attached on its surface, presumably binded by the outer shell electrons. Now, the surface is exposed to a cold positron gas, which annihilates against some of these outer shell electrons.</p>
<p>What might happen with the heavy nuclei? do they have to become free from t... | g8168 | [
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<p><img src="http://i.stack.imgur.com/YH1BH.png" alt="enter image description here"></p>
<p>What happens? we have 2 Generators and 2 intensities, when I2 and I3 come together (they have opposite sides ) what happens?</p>
<p>I tried writing down the voltage relations but I'm stuck because I don't know what intensity s... | g8169 | [
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<p>I'm taking a graduate physics class.
I usually sit at the front and madly scribble down everything the teacher writes....
But the professor also publishes his notes on the internet.
I find it sometimes difficult to understand what is going on in class . Often the problem is that I am spending most of my time scribbl... | g8170 | [
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<p>I always thought that the microcanonical partition function would measure the number of states that correspond to some fixed energy. Despite, I found in this paper (equation 3.4) that we integrate over all configurations that have an equal or lower energy than some fixed number $E$. Does this make sense to you?</p>
... | g8171 | [
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<p>What is the difference between these laws?
Which law is more useful?
When to use <a href="http://en.wikipedia.org/wiki/Ampere%27s_Law" rel="nofollow">Ampere's law</a> and when to use <a href="http://en.wikipedia.org/wiki/Biot%E2%80%93Savart_law" rel="nofollow">Biot-Savart law</a>?</p> | g8172 | [
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<p>Whilst observing a lighthouse, I noticed that I could only see the cone of light reflected in the water when the lighthouse light was directly pointed at me. At all other points, I could just about see the cone of light in the air, but no light was visible on the water. Why is this the case?</p>
<p><strong>NB:</str... | g8173 | [
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<p>Can someone explain me the purpose of auxiliary lens in microscope. </p>
<p>The specification says:</p>
<pre><code>Eyepiece: Extra wide field 10x Eyepiece w Spectacle Correction 30mm Ocular
Objective 0.7-45x , Auxiliary 2x
</code></pre>
<p>And the manufacturer claims that it is having magnification of 90X. Is it... | g8174 | [
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<p>I've come across the <a href="http://en.wikipedia.org/wiki/Onsager_reciprocal_relations#Abstract_formulation" rel="nofollow">Onsager reciprocal principle</a>. It's almost clear, except for <strong>thermodynamic conjugate quantities</strong> - what's that, physical meaning (except the formal definitions: $X_i = -\fra... | g8175 | [
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<p>Scott Aaronson asked a very deep question at <a href="http://physics.stackexchange.com/q/39383">Hawking radiation and reversibility</a> about what happens if black hole evolution is reversed thermodynamically. Most of the commenters missed his point entirely. Of course it's overwhelmingly improbable statistically to... | g8176 | [
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<p>Is it possible for two spheres (a & b) to have an inelastic collision with BOTH the total linear and angular momentum preserved? I'm doing some physics simulation of some spheres attracting each other like gravity and and a initial net angular momentum making them spin around a center. I want to have inelastic c... | g8177 | [
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<p>I have a series of waves that I would like to compare to one another. The measurements are two-dimensional with time on the x-axis and an intensity measurement on the y-axis. </p>
<p>I'd like some way of quantifying how different each wave is to the other. Is there a technique to do what I am looking for? </p> | g8178 | [
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<p>Why can the hyperon $\Omega^{-}$ not decay by strong interaction? It seems that strangeness must be violated, but why is it the only way?</p> | g8179 | [
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<p>Asume we have a particle sitting at the point A(0,0) in a gravitational field.
(g=9.81) It is going to move along some path to the point B(a,b) Where a>0 and b<0.
What is the curve the particle needs to be moving at to arrive at B in the
least time possible?</p>
<p>(Fastest curve between two points. )</p>
<p><... | g6 | [
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<p>I have read the paper "Steady state entanglement between hybrid light-matter qubits", <a href="http://arxiv.org/abs/0711.1830" rel="nofollow">arXiv:0711.1830v2</a>.
There, writers obtained density operator in matrix form after solving steady state equation (13). I want to know how one can trace out polaritonic degre... | g8180 | [
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... |
<p><img src="http://upload.wikimedia.org/wikipedia/commons/b/ba/Feynman_EP_Annihilation.svg" alt=""></p>
<p>I am having some trouble understanding this fenyman diagram, it seems to indicate that the electron produces the positron, as the arrow of the positron is pointing from the electron.</p>
<p>Additionally the arr... | g8181 | [
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<p>It's pretty straight-forward to visualise <em>second-order non-linear optical mixing processes</em> in which two waves of frequencies $\omega_{1}$ and $\omega_{2}$ mix up to generate new waves of different frequencies.</p>
<p>For example the sum-frequency generation:
<img src="http://i.stack.imgur.com/hnoco.jpg" al... | g8182 | [
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... |
<p>This question is the continuation of the <a href="http://physics.stackexchange.com/questions/90200/einstein-action-and-the-second-derivatives">following one</a>. I still don't understand why $(1)$ may be set to zero. This refers to the zero value variations of metric and its derivatives on the infinitely far surface... | g8183 | [
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<p>I'm looking to improve my understanding of quantum superposition. Consider the two-slit setup, where $|A\rangle$ is the state of the electron at the source, $|z\rangle$ is the state at some point on the detector, and $|S_{1}\rangle$ and $|S_{2}\rangle$ are the states at the two slits. As I understand it, the probabi... | g8184 | [
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<p>At one point, I decided to make friends with the low-lying spectrum of QCD. By this I do not mean the symmetry numbers (the "quark content"), but the actual dynamics, some insight.</p>
<p>The pions are the sloshing of the up-down condensate, and the other pseudoscalars by extending to strangeness. Their couplings a... | g8185 | [
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<p>If I'm sitting in the den with my door slightly cracked, I can hear my wife washing dishes in the kitchen down the hall. But why can't I also 'see' images of her washing dishes if, say, I looked up on my wall? </p>
<p>Broken down:</p>
<ol>
<li>Sound waves bounce off things. </li>
<li>Light waves bounce off things... | g186 | [
0.020581230521202087,
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<p>What is the difference between <a href="http://en.wikipedia.org/wiki/Work_%28thermodynamics%29" rel="nofollow">work</a> in thermodynamics and <a href="http://en.wikipedia.org/wiki/Work_%28physics%29" rel="nofollow">work</a> in mechanics?</p> | g8186 | [
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<p>QFT says that all particles are indistinguishable from one-another [1]. That is, take a proton from cosmic ray from a supernova a billion light-yeas away, and compare it to a proton that just got smashed out in the LHC, and they are indistinguishable from one-another. Replace either with the other, and nothing will ... | g8187 | [
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<p>In Special Relativity, the spacetime interval between two events is $s^2 = -(c{\Delta}t)^2+({\Delta}x)^2+({\Delta}y)^2+({\Delta}z)^2$ giving the Minkowski metric $\eta_{\mu\nu}=\text{diag}(-1, 1, 1, 1)$. What is the justification for making time have a negative coefficient, and how closely is that related to the 2nd... | g8188 | [
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<p>Suppose we have an atom with several energy levels (e.g. an hydrogen), and it is hit by photons. </p>
<p>I know that in order to have the atom change energy levels, the photon must have an energy level precisely equal to the energy difference of the two levels.</p>
<p>What happens if the photon has more energy tha... | g8189 | [
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<p>If two light rays start simultaneously in the space from exactly opposite ends in opposite direction that is separated by a distance of 600000 km in a way they meet at the mid point (300000 km from source), then:</p>
<ol>
<li><p>How much time it will take to meet the front most photon of one ray to meet the front m... | g8190 | [
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<p><img src="http://i.stack.imgur.com/k0rQo.png" alt="enter image description here"></p>
<p>M1 slides down a frictionless ramp and collides with M2 They both compress the spring. How far is the spring compressed? What is the final velocity of M1 on the rebound up the ramp?</p>
<p>I was thinking if its possible to loo... | g8191 | [
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<p>I know this is probably some basic math once you have the figures, but my Google-fu is failing me.</p>
<p>Say I have <strong>5 pounds of air</strong>. Air meaning, the typical composition of the atmosphere of Earth. And by 5 pounds I mean the weight of the mass of the air, not it's pressure or anything like that.</... | g8192 | [
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<p>Visible light diapason is 400 - 700 nm which is 1.43 - 2.5 Mhz.</p>
<p>If using an antenna I would broadcast steady sinusoidal wave in this range, why the EM emitted by the antenna are not visible?</p>
<p>Suppose the power source for antenna in a range of Kilo or Mega watts</p> | g8193 | [
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<p>I'm given this commutator:
$$\left[PXP,P\right]$$
Being $P\psi=-i\hbar\partial_x\psi$, and $X\psi=x\psi$</p>
<p>I've solved it in two ways, the first one is just aplying the commutator to some function $\psi$ and see what I get. My final result is:
$$\left[PXP,P\right]=-i\hbar^3\partial_{xx}$$
The second one is usi... | g8194 | [
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<p>If you were to build an upright machine that had a rod fitted into a ball bearing at the base and was secured to another rod at the top of the initial rod extending perpendicularly. To which you attached a magnet, and around this machine you also placed several upright rods containing magnets that would push/pull th... | g8195 | [
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<p>If you consider the damping force is friction like in:
<img src="http://i.stack.imgur.com/4JAFJ.jpg" alt="enter image description here"></p>
<p>then the force should be $$F=\mu N$$ where $\mu$ is the coefficient of kinetic friction. Why then is the damping force assumed to be linearly dependent on velocity?</p> | g8196 | [
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<p>I've seen force defined in special relativity as the rate of change of 4-momentum</p>
<p>$$ {\bf{F}} = \frac{d {\bf{p}}}{dt} $$</p>
<p>Can anyone comment on the following derivation of that relation? </p>
<p>Take one dimension of space. If I'm moving with 4-velocity ${\bf U}(t) = \frac{d{\bf x}}{d \tau}$, then I'... | g8197 | [
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<p>Obviously this is impossible in relativity; however, if we ignore relativity and use only Newtonian mechanics, is this possible? How (or why not)?</p> | g8198 | [
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<p>I know that $0 \,\mathrm{K}$ cannot be reached, this is discussed <a href="http://physics.stackexchange.com/q/32830/">here</a> and <a href="http://physics.stackexchange.com/q/81589/">here</a>.</p>
<p>But, why is it such an important statement? </p>
<p>I mean, there are many properties which will never be zero, lik... | g8199 | [
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<p>For flat FLRW cosmology, we can write down two Friedman equations and one matter equation:</p>
<p>(1) $H^2=\frac{8 \pi G}{3} \rho$</p>
<p>(2) $\frac{\ddot{a}}{a} = -\frac{4 \pi G}{3} (\rho +3p)$</p>
<p>(3) $\dot{\rho} = -3 H (\rho +p)$</p>
<p>It is well known that, given an equation of state, (1)+(3) implies (2)... | g8200 | [
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0.03528444096446037,
0.0292... |
<p>The initial velocity is 14 m/s the final velocity is 0. The distance is 9.0 m and the time is 1.5 s. When solving for the acceleration, why do I get different values when using different kinematic equations?</p>
<p>$x = v_i t + \frac{1}{2} a t^2 \rightarrow a = -11.2 \frac{m}{s^2}$</p>
<p>$v_f = v_i + a t \r... | g8201 | [
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<p>I am trying to read up some review articles about Majorana physics in topological material, but I am not really familiar with the condensed matter terminology (with condensed matter in general I should say) since I come from a high-energy background, so I come across quite a lot of vocabulary and visualization issue... | g8202 | [
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<p>I am working on solving the equation of motion for a particular system. It has been a long time since I've worked with matrix equations and need help in simplifying the following:</p>
<p>$\frac{d}{dt}$$(I_G\omega)$ + $\omega \times(I_G\omega)$ + $My\times [(−\dot\omega\times y)$−$\omega \times (\omega \times y)]$ =... | g8203 | [
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<p>There is a system of N particles. They interact and are bound together with a binding energy Eb (or potential energy). To characterize the system there are multiple terms</p>
<ul>
<li>Energy per particle Eb(N)/N</li>
<li>Energy of a particle leaving the cluster Eb(N) - Eb(N-1)
Can I call this evaporation energy?</l... | g8204 | [
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0.09649787843227386,
... |
<p>I have a one BHP water pump, the water pressure of a coiled hose connected to the water pump output side was not that great. Would an unwound water hose produce greater water pressure? [Friction Losses?]</p>
<p>Thanks,
Alan</p> | g8205 | [
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<p>I need to know if I understand this point.</p>
<p>The factor of HZZ vertex in the SM Lagrangian is half the value of the Feynman rule which appears in Diagrammatica.</p>
<p>When I calculate the decay of Higgs into 2 Z, I have to integrate over only half the phase space, because the two Z's are identical.</p>
<p>S... | g8206 | [
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0.05917... |
<p>Can you recommend books or papers that highlight or discuss extensively, or at least more than average, the similarites/differences between phase space and Hilbert space? I am primarily interested in physics, not mathematics, but am willing to look at good math books also.<br>
For all I know, this might be one of t... | g8207 | [
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<p>Let's say we have two identical spinning flywheels, that have arbitrary geometry, and are made of copper. </p>
<p>Now we apply some heat energy at the center point of flywheel A, causing it to slow down a bit, because some mass was added into it. </p>
<p>And we apply a force, but no torque, at the center of flywh... | g8208 | [
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0.024261312559247017,
0.0113... |
<p>I can model this interaction as Zee does in "Quantum field theory in a nutshell". In chapter I.4 section "from particle to force" he uses two delta functions for the source. The integral gives $E=-\frac{1}{4\pi r}e^{-mr}$</p>
<p>I consider $J=\delta^{(3)}(x-x_1)-\delta^{(3)}(x-x_2)$.
Im assuming that this represent... | g8209 | [
0.025959601625800133,
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<p>Is it only necessary a human consciousness? A measurement device?
Can it be said that any of them cause the wave function collapse?</p> | g75 | [
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<p>As the title says, what would be non-ergodic processes that occur in statistical physics?
Many textbooks do not really cover <a href="http://en.wikipedia.org/wiki/Ergodicity" rel="nofollow">ergodicity</a> really well so I ask this question. I can't suddenly remember any non-ergodic process in physics..</p> | g8210 | [
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0.0668579638004303,
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<p>We know that this strange behavior is there but I am not to able grasp, how do we know it exists? Have we ever tried any experiments confirming this? Do we make use of this?</p> | g8211 | [
0.03376356512308121,
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<p>If you have a board, say a standard 2x4 of finite length, where one end is fixed in a cement wall and the other end is free, and you begin adding weight to the free end until it breaks, where will the board break? Assume the board is made of typical wood and it is perpendicular to the wall in which it's affixed.</p>... | g8212 | [
0.05634780600667,
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<p>When playing woodwind instruments, e.g., flute, if one blows harder, the sound will be one octave higher. Even harder gives even higher overtones. Does anyone know why?</p> | g270 | [
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<p>I'm attempting to follow a proof that the commutator of two Killing vectors is itself a Killing vector. The source that I've posted is from my course notes.</p>
<p><img src="http://i.stack.imgur.com/F5R5p.png" alt="Question"></p>
<p>I've highlighted the part I'm stuck on. I've been working on this question for qui... | g8213 | [
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<p>In the movie Gravity, two characters are dangling from the international space station by a long tether. I've previously wondered exactly how you could calculate the tidal forces that act on an object connected to another object in orbit. </p>
<p>I think I've got most of a solution... the <a href="http://en.wiki... | g8214 | [
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<p>How did they take photos of Jupiter - I mean Jupiter is illuminated and that's a lot of light to produce. Am I missing something, and there was some sort of dark photo technology used, or was there simply enough light from Sun to begin with? Or is this photo a fake? </p>
<p><img src="http://i.stack.imgur.com/wwJOv.... | g8215 | [
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<p>Say we have a hollow conducting sphere (with some finite thickness).
If this object has an excess charge amounting to +Q coulomb, and there is no extra electric field in the surroundings (due to other charges), how will the charge be distributed?</p>
<p>Intuitively it seems that the charge will be symmetrically di... | g8216 | [
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<p>Given the distance among stars (the most massive objective in the space) is so huge, the difference of order of magnitude is about 7.
And also, since gravity is such a weak force, how is it likely for gravity to shape <a href="http://en.wikipedia.org/wiki/Galaxy" rel="nofollow">galaxy</a> the way it is?
Would it ma... | g8217 | [
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<p>In <a href="http://books.google.com/books/about/Modern_Supersymmetry_Dynamics_and_Dualit.html?id=799ss7qTGlQC" rel="nofollow">Modern Supersymmetry</a>, John Terning, on pgs 151, and 153 performs a so called 'reliable' instanton calculation when dealing with the ADS superpotential 'since the gauge group is completely... | g8218 | [
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<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/20752/electrodynamics-textbook-that-emphasizes-applications">Electrodynamics textbook that emphasizes applications</a> </p>
</blockquote>
<p>I am a graduate student in applied mathematics and I am lookin... | g271 | [
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<p>Moreover, how can you make your voice productive? for example, using it to light an LED, charge a battery, purificating water, growing plants in a more efficient way. I want to do a project that involves using my singing voice to achieve something. </p> | g8219 | [
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<p>From the Dirac equation in gamma matrices, we know that $$\gamma^i=\begin{pmatrix}
0 & \sigma^i \\
-\sigma^i & 0
\end{pmatrix}$$ and $$\gamma^0=\begin{pmatrix}
I & 0 \\
0 & -I
\end{pmatrix}$$
Now what do we understand by this operation $\gamma^0 \gamma^{\mu \star}\gamma^0 =\gamma^{\mu T}$</... | g8220 | [
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<p>I am very interested in Thermodynamics, but though it is easy to find good books and information about classical thermo, it seems that is not the same for non-equilibrium thermodynamics. I would like to know what important discoveries (theoretical or practical) has the non-equilibrium thermo has made, and what thing... | g8221 | [
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<p>Let's imagine that we have a tridimensional metal object of infinite size, and decide to calculate the resistance between two arbitrary points. How would we go about doing this?</p>
<p>I have thought of two possibilities for calculating this, the first one being an adaptation of the conductivity (S/m) using the Pyt... | g8222 | [
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<p>I googled in vain and found nothing. I am surprised. Maybe somebody knows about videos of Julian Schwinger available on Internet?</p> | g8223 | [
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<p>I'm currently reading about complex geometry in order to get a feeling of how to determine the Hodge numbers, e.g. of certain orbifold constructions. Since I'm a physicist with no deeper mathematical knowledge in algebraic geometry and complex geometry, I apologize for the following possibly trivial questions. </p>
... | g8224 | [
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<p>If a cable used to power something is exposed to a radioactive source will it over time make the entire cable radioactive? </p> | g8225 | [
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<p>I came across the term <em>generalized free field</em> in a paper recently but I don't know its definition. Google leads to other papers which take it for granted and use it without defining it. It appears that O.W. Greenberg introduced the term in the paper <em>Generalized free fields and models of local field theo... | g8226 | [
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<p>$^{17}_8 O$ <a href="http://ie.lbl.gov/toi/nuclide.asp?iZA=80017" rel="nofollow">quoted here</a> has a spin of 5/2 and parity of +1 for the ground state, I agree with this, the unpaired neutron is in the $1d_{1/2}$ state so l = 2, spin = 5/2.</p>
<p>Now I want to figure out the spin an parity of the first two excit... | g8227 | [
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0.04077491536736488,
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<p>I want to prove that $^{38}Ar$ is stable with respect to $\beta$ decay, that $^{38}Cl$ decays by $\beta^-$ and that $^{38}K$ decays by $\beta^+$.</p>
<p>I know from Googling that this is true, and I also know that $^{38}Ar$ has the highest binding energy for mass number 38, thus its definitely stable with respect t... | g8228 | [
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<p>Suppose there are only two hydrogen atoms in the entire universe. Suppose further that they are both situated at the very limits of the cosmos, equally distant. Would they exert an attractive force on one another? </p> | g8229 | [
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<p>One of the unsolved problems I still have is measuring temperature in furnace at 700-1100C range (I need some +-0.1% repeatability and +-1% precision).</p>
<p><strike>Obviously, contact thermometers are quite rare & expensive for this range, everything I was able to find is rated at 450-500C max (especially as ... | g8230 | [
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<p>Consider an Einstein solid with quantized energy values $U=q\epsilon$ and $N$ oscillators. I calculated some values of an Einstein solid numerically through a function in R (at the bottom of the post). In an exercise I'm supposed to estimate $\epsilon$. </p>
<p>Apparently the answer is that I can estimate it by sho... | g8231 | [
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0.029573... |
<p>Related post : <a href="http://physics.stackexchange.com/questions/62858/derricks-theorem">Derrick’s theorem</a></p>
<p>Consider a theory in D spatial dimensions involving one or more scalar fields $\phi_a$, with a Lagrangian density of the form $$L= \frac{1}{2} G_{ab}(\phi) \partial_\mu \phi_a \partial^\mu \phi_b... | g8232 | [
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<p>I have an issue with 2D acoustic wave field modelling.</p>
<p>In order to estimate the energy propagation direction of an acoustic wave I use Poynting vectors $S$ which can be described by</p>
<p>$$
\vec{S} = - \dot{p} \nabla p
$$</p>
<p>where $p$ is the pressure field, $\dot{p}$ represents the time derivative of... | g8233 | [
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<p>Using a tennis ball as an example object, if one ball weighs 1 ounce and the other is 2 ounces, and both are struck at 100 mph on the same trajectory, would there be any difference in the deceleration rate between the 2 different mass balls? (All other things about the two balls being equal). For instance, would the... | g8234 | [
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<p>This question concerns the Dirac equation and the $4\times4$ $\gamma$-<a href="http://en.wikipedia.org/wiki/Gamma_matrices" rel="nofollow">matrices</a>. The task is to prove that a similarity transformation of the standard $\gamma$-matrix conserves the commutation relation</p>
<p>$$
\{\gamma^\mu,\gamma^\nu\} ~=~ 2... | g8235 | [
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... |
<p>I have numerically integrated the (reduced) homogeneous equation of a damped harmonic oscillator in order to see how the error propagates.</p>
<p>$$\frac{d^2 X}{d\phi^2} + \frac{1}{Q}\frac{dX}{d\phi}+X(\phi) = 0$$
where $\phi = 2 \pi \tau$ and $\tau$ is the reduced time</p>
<p>In the process I have also extracted ... | g8236 | [
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<p>I took an empty bottle and placed it on the floor, then tilted the bottle to one side such that the the displacement caused a disturbance in its balance but not enough to completely tilt it over. The bottle started oscillating back and forth. But as the time passed and the amplitude of oscillation decreased (as expe... | g8237 | [
0.08179522305727005,
0.004852202720940113,
0.00404771976172924,
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0.0702163353562355,
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-0.038588881492614746,
-0.02184273488819599,
-0.017393311485648155,
0.025903522968292236,
0.0394... |
<p>I have the flat FLRW metric,</p>
<p>$$ ds^2=-dt^2+a(t)^2(dx^2+dy^2+dz^2) $$
and a geodesic $\gamma(s)=(t(s),x(s),y(s),z(s))$ with parameter $s$. Two of the Killing vectors of the metric are $ \partial_x$ and $\partial_y$ which give rise to the constants of motion $ a^2\dot x$ and $ a^2 \dot y $ respectively. This ... | g8238 | [
0.03535376116633415,
-0.03887630254030228,
-0.04307498410344124,
-0.02947402559220791,
0.04993181675672531,
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-0.07689794152975082,
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<p>I am referring to this very famous paper. <a href="http://arxiv.org/abs/hep-th/9806087" rel="nofollow">http://arxiv.org/abs/hep-th/9806087</a></p>
<ul>
<li>I am referring to equations 20 and 27 and 28. Anyone can help derive them? </li>
</ul>
<hr>
<p>I vaguely think that they substituted equation 9 in the bulk pa... | g8239 | [
0.026533622294664383,
0.002114973496645689,
-0.03545200824737549,
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0.040906742215156555,
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0.03961491584777832,
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0.003127521136775613,
-0.0675203800201416,
0.01085933018475771,
0.06820058077573776,
-0.0432... |
<p>At this point in this documentary about the history of electricity: <a href="https://www.youtube.com/watch?v=oPnS2WO2_0k&t=4m40s" rel="nofollow">https://www.youtube.com/watch?v=oPnS2WO2_0k&t=4m40s</a> the guy says the Maxwell calculations predicted the generation of certain types of waves, when there is a ch... | g8240 | [
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0.014721869491040707,
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0.02258925698697567,
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0.02... |
<p>Does the current acceleration of universe imply that our universe is open?
If the universe is closed, from the <a href="http://en.wikipedia.org/wiki/Friedmann_equations" rel="nofollow">Friedmann's equation</a>, the acceleration of universe wouldn't be possible, would it be? (Of course, except for the very earlier ti... | g8241 | [
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0.039724018424749374,
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0.0... |
<p>A book on Quantum Mechanics by Schwinger states, "A unitary operator can be considered to be a complex valued function of a Hermitian operator."</p>
<p>Please give a hint on how to prove this assertion.</p> | g8242 | [
0.026639748364686966,
-0.02577347680926323,
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0.008527451194822788,
0.036699328571558,
0.001366873737424612,
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0.04156706482172012,
0.02981964871287346,
-0.02371804602444172,
-0.055912431329488754,
0.022309649735689163,
-0.006777851842343807,
0.021... |
<p>Is there any equation that calculates the $C_d$ value in the formula of air drag ?
$$F_d = \rho C_d v^2 A$$
I have found that there are tables for this constant but I am looking for the equation that evalutes it.</p> | g8243 | [
0.01972261816263199,
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0.023700235411524773,
0.051363505423069,
0.02054... |
<p>In a table fan, the blades move around in circular way and we feel air/wind when sitting on front of it. How does this happen?</p> | g8244 | [
0.031013811007142067,
0.0030474013183265924,
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0.06433996558189392,
-0.003033291781321168,
0.0... |
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