question stringlengths 37 38.8k | group_id stringlengths 2 6 | sentence_embeddings listlengths 768 768 |
|---|---|---|
<p>I got some naive questions on the ground states of <a href="http://arxiv.org/abs/cond-mat/0506438" rel="nofollow">honeycomb Kitaev model</a> (with open boundary conditions):</p>
<p>(1) Consider a simple case that $J_x=J_y=0$, then the model reduces to $$H=J_z\sum_{z\text{ }\text{links}}S_i^zS_j^z.$$ It's obvious t... | g14730 | [
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<p>I keep reading the same phrase about the very short life time of the top quark:</p>
<blockquote>
<blockquote>
<p>Because the t-quark decays on a shorter than the characteristic QCD interaction-time it cannot hadronize. Therefore it give to possibility to be seen as a bare quark.</p>
</blockquote>
</blockquo... | g14731 | [
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<p>So, objects are certain colors because they are absorbing every color except for that one. So why is it that if I take a projector and project a blue image on a red wall, the red wall still reflects the blue image rather than absorbing the blue light? I don't know if this is considered a dumb question, but I was thi... | g14732 | [
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<p>If I have these theoretical predictions:
\begin{align}
\omega_{p_1} = 4.5132 \pm 0.0003~\text{rad/s} && \omega_{p_2} = 4.5145 \pm 0.0002~\text{rad/s}\\
\omega_{b_1} = 0.0707 \pm 0.0003~\text{rad/s} && \omega_{b_2} = 0.0700 \pm 0.0002~\text{rad/s}
\end{align}</p>
<p>And I got these experimental resul... | g14733 | [
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<p>My mom and I were in a car accident. We are ok, but I want to know how fast the car that hit us was going. We were stopped at a light. The car that hit us from behind was a big GMC SUV. Our car was a Cadillac srx and mom looked it up it weighs 4,277 pounds. Then we hit a little car in front of us at 12mph and the ai... | g14734 | [
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<p>We know that when a capacitor charges from a source $E$, it stores energy of $E=\frac{1}{2}QV $. <br> This is derived without taking into consideration any resistances present in the circuit.</p>
<p>We also know that the battery does work $W=QV$ to pump the charge $Q$.
It is explained that the remaining $\frac{1}{... | g14735 | [
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<p>This is a question regarding Francesco, section 4.3.3. In this section, he considers the two-point function
$$
S_{\mu\nu\rho\sigma}(x) = \left< T_{\mu\nu}(x) T_{\rho\sigma}(0)\right>
$$
He then goes on to claim that symmetry of the stress-energy tensor implies $$S_{\mu\nu\rho\sigma}(x) = S_{\nu\mu\rho\sigma}(x... | g14736 | [
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<p>What is the best container material for heat transfer between ice and water?</p>
<p>this is a difficult question to ask without displaying a picture of what I'm meaning.</p> | g14737 | [
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<p>Why do neutrino account for 99% of the energy release for a SN II, while it is not expected to be the case for SN Ia?</p>
<p>Is it because the densities are not high enough to induce inverse beta-decay?</p>
<p>(The question came from reading Particle Astrophysics of Donald Perkins, section 7.14.1 last paragraph (i... | g14738 | [
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<p>What is the proper format to ask debunking questions without being marked as off-topic, yet be able to step through the entire theory logically?</p>
<p>Specifically, I am looking at Wallace Kluck's claim on decuity.com that </p>
<p>"Light is an inertial particle not a wave"</p>
<p>A rotating electron is treated a... | g14739 | [
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<p>Recently, I was taught by my sir that the Acceleration of an electron of Bohr Atom is equal to its frequency. I am confused and didnt understand why it turns out to be equal</p> | g14740 | [
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<p>When a conductor <strong>that's purpose is to carry current</strong> ,is laminated to reduce eddy currents, does it affect the current capacity for that same conductor? Will it reduce the current capacity?</p> | g14741 | [
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<p>I came across a line that said "an atom of heavy element is hit with a <strong>low velocity neutron</strong>, otherwise the required reaction would not achieve result". So, why not a neutron of high velocity is successful to achieve a nuclear fission ? </p> | g14742 | [
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<p>I know the derivation of Hubble time goes something like this (I am an a-level student so this may not be the actual derivation): Two galaxy that is moving away from each other at speed v are now D distance apart assuming the time when they where together is t=0 i.e. at the Big Bang the time since the Big Bang is gi... | g452 | [
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<p>I am interested in solutions of the Schroedinger equation. For simplicity I started my studies with the $n=1$ ground state of the hydrogen atom. I was particularly interested in the higher moments of the kinetic energy operator $\mathbf{T}$. Much to my surprise I encountered serious problems as soon as I worked on t... | g14743 | [
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<p>An electric motor draws 20 Amps, when at maximum load of x.
Can that value of current be applied even if the load was ten times less than x from a certain power source? </p> | g14744 | [
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<p>If an orifice is placed inside a pipe with a smaller diameter than the rest of the pipe, fluid will follow a curved path in order to enter the orifice, and then expand. </p>
<p>I was wondering at what distance would the diameter of the flow reach its minimum (the vena contracta) and at what distance after that woul... | g14745 | [
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<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/9898/the-density-of-clouds">The Density of Clouds</a> </p>
</blockquote>
<p>according to definition of cloud :</p>
<p>A visible mass of condensed water vapor floating in the atmosphere, typically high a... | g260 | [
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<p>From what I gather, a <a href="http://www.scholarpedia.org/article/Boltzmann_machine" rel="nofollow">Boltzmann machine</a> can be identified with a <a href="http://en.wikipedia.org/wiki/Spin_glass" rel="nofollow">spin glass</a>. Though I don't know the details yet (and would welcome any references within the last 5 ... | g14746 | [
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<p>Everybody knows that sound cant travel through space, but is really valid? Here is my scenerio:</p>
<p>Given the size of a football field's length cubed, there are two objects at two opposing sides. the walls of the vacuum are nonexistent, so the only matter that exists are the two objects. Now if the Object A were... | g14747 | [
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<p>In many books, for a linear dielectric medium in which we have Maxwell's equations and the relationships
$${\mathbf D}=\varepsilon({\mathbf x}){\mathbf E}$$
and
$${\mathbf B}=\mu({\mathbf x}){\mathbf H}$$
we find formulae for the electromagnetic energy as
$$U=\int d{\mathbf x}\frac{1}{2}({\mathbf E}\cdot{\mathb... | g14748 | [
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<p>In the derivation of Rutherford's scattering formula, for example, this one <a href="http://tinyurl.com/qxc6m6k" rel="nofollow">here</a> or this one <a href="http://www.personal.soton.ac.uk/ab1u06/teaching/phys3002/course/02_rutherford.pdf" rel="nofollow">here</a>, we conclude that:
$$\frac{db}{d\theta} < 0,$$ i.... | g14749 | [
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<p>Is there any book that provides an overview of <a href="http://en.wikipedia.org/wiki/Condensed_matter_physics" rel="nofollow">Condensed Matter Physics</a>? I have had a course in QM and statistical physics and some. I dont know anything about this field, so is there a readable introduction to this large field? One t... | g453 | [
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<p>Does the concept of strong coupling mean anything in a classical setting? If strong coupling means just an inability to apply perturbative methods to the Hamiltonian, then obviously yes, we can provide examples of "classical" systems that cannot be handled perturbatively, such as granular materials, dusty plasmas, e... | g14750 | [
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<p>In the book Quantum Gravity in 2+1 dimension by S. Carlip, in the second chapter (section 2.1), he comments that a compact 3-manifold with a flat time orientable Lorentzian metric and a purely spacelike boundary, necessarily has the topology $[0,1]\times \Sigma$, where $\Sigma$ is a closed surface that is homeomorph... | g14751 | [
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<p>The principle conservation of energy is often taken as an obvious fact, or law of nature. But it seems to me the definition of energy is far from obvious, or natural: <a href="http://en.wikipedia.org/wiki/Energy" rel="nofollow">http://en.wikipedia.org/wiki/Energy</a> lists lots of different types of energy. </p>
<p... | g14752 | [
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<p>In Coulomb's law if the relation was as if electric field intensity was to vary inversely $1/r$ with distance rather than the inverse $1/r^2$ of square of distance, would the Gauss's law still be valid? This was asked in our university tests and I'm clueless about it.</p> | g14753 | [
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<p>On the one hand, classical electromagnetism tells us that light is a propagating wave in the electromagnetic field, caused by accelerating charges. Then comes quantum mechanics and says that light consists of particles of quantized energy, $hf$. Also, now these particles are modeled as probability waves obeying Shro... | g14754 | [
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<p>I have hit a roadblock in my simulation, where there are 2 authors with contradicting equations on the model.</p>
<p>So I have simulated both, and drew it out for a few diameters. My dish size is 40m.</p>
<p>I am unsure which model to use for laser transmission over 40,000km from space to Earth. The more intuitive... | g14755 | [
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<p>Just what the title states.</p>
<p>Assuming identical conditions, excellent visibility -
If a 1W monochromatic light source, and a 1W non-monochromatic light source were viewed at a location in deep space, which of the two would be visible from a greater distance? </p> | g14756 | [
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<p>My possibly mistaken understanding is that <a href="http://en.wikipedia.org/wiki/Dark_energy" rel="nofollow">dark energy</a> changes with time, whereas a <a href="http://en.wikipedia.org/wiki/Cosmological_constant" rel="nofollow">cosmological constant</a> is, well, constant. What about gravitational clumping? Detec... | g14757 | [
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0.05484588071703911,
0.015... |
<blockquote>
<p>A balloon with volume 2800 m³ is heated up to 60 °C.
If the outer temperature is 12 °C and the air has a pressure of 960 hPa, what is
the density of the air inside the balloon and on the outside?</p>
</blockquote>
<p>In the solutions they used the following formula: $ \rho_1 = \rho_0 \cdot \frac{... | g14758 | [
0.017489252611994743,
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<p><a href="http://en.wikipedia.org/wiki/Ocean_thermal_energy_conversion" rel="nofollow">OTEC</a> (Ocean Thermal Energy Conversion) utilizes the temperature gradient between cold deep ocean water, and warmer water to do work. I understand the pressure in the depths may be as high as a couple of orders greater than surf... | g14759 | [
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<p>The work function of any metal is no doubt constant for it is related to electromagnetic attraction between electrons and protons. However on increasing the intensity of any light source the kinetic energy of the emitting electrons must increase, mustn't it? Let us assume there is only 1 electron in a metal surface.... | g14760 | [
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<p>I've always pictured EM radiation as a wave, in common drawings of radiation you would see it as a wave beam and that had clouded my understanding recently.</p>
<p>Illustration on the simplest level:</p>
<p><img src="http://i.stack.imgur.com/UEs0c.jpg" alt="EM wave from sun"></p>
<p>Which obviously would not make... | g14761 | [
0.0035332657862454653,
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<p>Hamilton's principle states that a dynamic system always follows a path such that its action integral is stationary (that is, maximum or minimum).</p>
<p>Why should the action integral be stationary? On what basis did Hamilton state this principle?</p> | g617 | [
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<p>I understand that an accurate determination of the bounds of the "habitable zone" for a given stellar system depends on a large number of factors, including many beyond characteristics of the parent star, such as details of planetary atmosphere and residual heat of formation, system age and dynamics, etc.; but is th... | g14762 | [
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<p>It has always bugged me that tables for water (and other) properties have the capability to look up internal energy as a function of <em>both</em> temperature and pressure. If we limit the discussion to liquid below the saturation temperature, then what is the qualitative argument to say that $u(T)$ is inaccurate a... | g14763 | [
0.0227142795920372,
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<p>Has Bose-Einstein theory been considered for dark matter?</p>
<p>The theory would explain why no measurable radiation is emitted due to zero temperature--its lack of interaction with other matter and its gravitational lensing. Yet I haven't seen it considered. Am I missing something or have I totally misunderstood ... | g14764 | [
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<p>In graphene, free electrons can have the following wavefunctions (there are other options, with minus signs in various places, but this will serve as an example): </p>
<p>$\psi(\vec{p})=A\left[\begin{array}&e^{-i\phi/2}\\e^{i\phi/2}\end{array}\right]$ </p>
<p>where $\phi=\tan(p_y/p_x)$ is the polar angle in... | g14765 | [
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<p>In all the houses of two levels where I have been, why I hear the sound from downstairs clearer when I am at the second level, than I hear sound from upstairs when I am at the first level?</p>
<p>Does sound travel upward more easily than downward?</p>
<p>Do the architectures of houses matter much?</p> | g14766 | [
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<p>From my experiments with measuring how fast a coin falls, I have consistently measured a faster falling rate for a coin that flips as it falls.</p>
<p>As an example, a coin dropping on its edge from height of $45 \:\rm{cm}$ hits the ground $20 \:\rm{ms}$ later than a flipping coin falling from the same height.</p>
... | g14767 | [
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<p>From my point of view, it seems that a soldier armed with a <strong>full metal plate armor</strong> was almost invulnerable at the time their opponents yielded swords, spears or bows. I understand that it couldn't be the case, but I'm not sure about the physics behind it.</p>
<p>More specifically:</p>
<ol>
<li><p>... | g14768 | [
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0.04748862236738205,
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0.004451673943549395,
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<p>How can I prove that in the static spacetime, the extrinsic curvature of hypersurface $t=constant$ is zero? My efforts all are failed. Any hint would be greatly appreciated.</p> | g14769 | [
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<p>I have a problem regarding computation of spin connection in the case where One or more dimension is compactified. For example if we take a $D+1$ dimensional bosonic string action and write the $D+1$ dimensional metric in terms of $D$ dimensional fields,and we want to compute the spin connection then how to exactly ... | g14770 | [
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<p>When a ball moves to the right, friction acts to oppose the motion, in other words, to the left. However, when a car travels around a bend, the friction acts in the perpendicular direction to the car's velocity and provides the centripetal force. I just cannot understand why friction would act in that direction.</p>... | g950 | [
0.0520523265004158,
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<p>I would like to know why scientists try to use deuterium and tritium for <a href="http://en.wikipedia.org/wiki/Fusion_power" rel="nofollow">fusion</a> and not just the ordinary <a href="http://en.wikipedia.org/wiki/Isotopes_of_hydrogen" rel="nofollow">isotope of Hydrogen</a> ${}^1H$? </p> | g14771 | [
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... |
<p>According to this calculator <a href="http://www.abecedarical.com/javascript/script_collision1d.html" rel="nofollow">http://www.abecedarical.com/javascript/script_collision1d.html</a> when low mass object hits high mass object it is reflected gaining opposite velocity almost the same as initial velocity. </p>
<p>If... | g14772 | [
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<p>My question is the following: if we had the trajectory of a particle eventually reaching a point of a rotation axis $ \vec{u} $ (take that as being the z-axis for convenience) by an angle $ s $, would Noethers Theorem still give a conserved quantity?</p>
<p>More specifically (let me go through the calculations and... | g14773 | [
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... |
<p>Suppose the linear size of everything is doubled overnight. Can you test the statement by measuring sizes by a meter stick? Can you test it by using the fact that the speed of light is a universal constant and has not changed? What will happen if all the clocks in the universe start running at half speed?</p> | g454 | [
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<p>I am studying magnetism and I am curious as to what happens in a transformer that has its secondary output wires connected through a circuit versus one that doesn't.</p>
<p>My main questions (in the case of the unconnected secondary) are:</p>
<p>Is there more or less resistance on the primary?</p>
<p>Are there eq... | g14774 | [
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<p>Question #1: Why does speed have nothing to do with inertia?</p>
<p>Question #2: If a car hits a steel wall and stops, where did the momentum go?</p> | g14775 | [
0.08354546129703522,
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<p>I'm curious to know this. Neglect air friction and imagine a bullet that were shot normal to the Earth's surface, from the Equator. I will have to consider the Coriolis effect and so I expect the path of the bullet will follow a spiral rather that a straight line (relative to Earth's centre). The gravity will reduce... | g14776 | [
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<p>If you have an electron moving in empty space, it will be represented by a wave packet. But packets can spread over time, that is, their width increases, with it's uncertainty in position increasing. Now, if I throw a basketball, why doesn't the basketball's packet spread as well? Wouldn't that cause its uncertainty... | g14777 | [
0.04629393294453621,
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0.03214946761727333,
-0.00358... |
<p>While a treatment of electron spin can be found in any introductory textbook, I've noticed that the electron's magnetic field seems to be treated classically. Presumably this is because a quantum treatment of the electromagnetic field would venture into the much more difficult topic of quantum electrodynamics. Howev... | g14778 | [
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<p>I am trying to get a better understanding of the definition of temperature at the subatomic level. I have a background in molecular biology with some college physics, but no deep quantum mechanics background.</p>
<p>Everything I've found on the web (Wikipedia, Google Scholar) seems to use 'temperature' very loosely... | g14779 | [
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0.006195435766130686,
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... |
<p>Could someone please explain this equation $$M\bf {\ddot{r}}=-\nabla \phi$$
Where $\bf r$ is a position vector and $\phi$ is the potential function.
Could someone brief explain the potential function and tell me why we've got <strong>minus sign</strong> before the nabla operator?</p> | g14780 | [
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<p>Wikipedia says yes but on Newtonian arguments. From general relativistic point of view Moon is not rotating but moving along geodesic trajectory. And like parallel transport of a vector (pointing to the direction of motion) on a surface of a sphere along equator, from outside it seems like rotation. So, would Moon s... | g14781 | [
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<p>We have two identical massive metal spheres at the same temperature at rest in free space. Both have an identical charge and the Coulomb force [plus the black-body radiation pressure if the temperature is non-zero] exactly counteracts the gravitational force between them, resulting in no net forces on either object... | g14782 | [
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<p>This concerns the famous two-slit experiment. Electrons or photons or your favorite particle, doesn't matter. As we all know, the attempt to detect which slit the quanta pass through leads to loss of the diffraction pattern. </p>
<p>The interesting part of the experiment is describing what happens when neither ... | g14783 | [
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<p>Can someone please explain to me what <a href="http://www.google.com/search?as_q=&as_epq=euler+density" rel="nofollow">Euler Density</a> is? I have encountered it in <a href="http://en.wikipedia.org/wiki/Conformal_anomaly" rel="nofollow">Weyl anomaly</a> related issues in various articles. Most of them assumes t... | g14784 | [
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<p>After watching this video:</p>
<p><a href="http://www.youtube.com/watch?v=j1jIjx0XF_U" rel="nofollow">http://www.youtube.com/watch?v=j1jIjx0XF_U</a></p>
<p>The experience is made with a speaker that generates a sound wave or mechanic wave. Can you use this to establish a link to <a href="http://en.wikipedia.org/wi... | g414 | [
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<p>In various articles (I am here talking about specially the ones related to string theory etc.) I have seen the discussion on density and distribution of eigenvalues. I want to know why do we use them (why are they important to consider in some calculation, how to construct them), if there's any physical significance... | g14785 | [
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0.04906388372182846,
-0.001943178242072463,
-0.04104529693722725,
0.04316294193267822,
0.007132641039788723,
0.043797142803668976,
0.02706662379205227,
-0.014103556051850319,
-0.0030239662155508995,
0.008807351812720299,
-0.04453658685088158,
0.0890713557600975,
0.061... |
<p>Is it possible to find the true anomaly of an object in a Kepler orbit given the orbital period of the object, the orbital eccentricity and the time? Assuming a two body system and the mass of the orbiting body is negligible.</p>
<p>I'm doing this computationally so I'd like to be able to place an object on an orbi... | g14786 | [
0.021960550919175148,
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0.011301752179861069,
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0.022497743368148804,
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-0.... |
<p>I read in a book that at low temperature the hydrophobic effect (for example) is entropic but at high temperatures it is enthalpic. I thought that entropy should decrease at very low temperatures. Hypothetically, can you even have entropic effects at absolute zero?</p> | g14787 | [
0.022295266389846802,
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<p>I apologize if electro-optic material is not the correct word.</p>
<p>As I understand it, when an electric field is applied to an electro-optic material, the index of refraction changes in proportion to the applied field.</p>
<p>What is happening to the structure of the material for this to occur?</p> | g14788 | [
0.06508726626634598,
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<p>Recently I'm studying PSG and I felt very puzzled about two statements appeared in Wen's <a href="http://prb.aps.org/abstract/PRB/v65/i16/e165113" rel="nofollow">paper</a>. To present the questions clearly, imagine that we use the Shwinger-fermion $\mathbf{S}_i=\frac{1}{2}f_i^\dagger\mathbf{\sigma}f_i$ mean-field me... | g14789 | [
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<p>I barely know anything about optics, so I could use some help about how to go about solving this problem. </p>
<p>If I have a ray of light at a certain height from the optical axis, propagating at an angle, and the distance it travels before it comes in comes in contact with a mirror, can I find the angle and heigh... | g14790 | [
0.0039296927861869335,
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<p>I was trying to understand how paper batteries work and came across some explanations saying that the paper battery can also behave like a supercapacitor on account of its ability to discharge and to produce bursts of peak energy.</p>
<p>Why is a normal battery unable to do the same thing?</p> | g14791 | [
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<p>I have a 1D gas made of $N$ particles placed in a harmonic potential well, so the Hamiltonian is:</p>
<p>$$ \mathcal H = \sum_{j=1}^N \left ( \frac{p_j^2}{2m} + \frac{1}{2}m\omega^2 x_j^2 \right )$$</p>
<p>The first part of the exercise asked me to find the canonical partition at temperature $T$ if the particles a... | g14792 | [
0.012172588147222996,
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<p><a href="http://www.physics4all.com/schrodingers-cat-sort-of-explained-by-perimeter-institute-physicists/" rel="nofollow">Erwin Schrödinger’s famous thought experiment's video</a> presented by Perimeter Institute for Theoretical Physics. From this video can we conclude that , in a macroscopic label we can not have ... | g14793 | [
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<p>I have a question regarding the well known fact that General Relativity is not a conformal invariant theory or to put it in other words about the fact that it is conformal variant:</p>
<p>What are the physical assumptions in General Relativity about the gravitation that make the resulting formulation of gravity to ... | g14794 | [
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<p>According to <a href="http://en.wikipedia.org/wiki/List_of_particles" rel="nofollow">http://en.wikipedia.org/wiki/List_of_particles</a>, the list of elemetary particles includes more than 30 particles (bottom of the page). Does the Standard Model explain (if yes, then how) how many of elementary particles we should ... | g14795 | [
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<p>Suppose we have
$$\rho=p_1\rho_1+p_2\rho_2$$
Where $\rho_1$ and $\rho_2$ are density matrices with $p_1+p_2=1$</p>
<p>I'm trying to show this is also a <a href="http://en.wikipedia.org/wiki/Density_matrix" rel="nofollow">density matrix</a> </p>
<p>If we let
$$\rho_1=\sum_i^n p_{\psi_i} |\psi_i \rangle \langle\ps... | g14796 | [
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<p>So I was sitting and looked at a street lamp outside my house.</p>
<p>It is an ordinary lamp that looks something like that: <img src="http://i.stack.imgur.com/0KVsN.png" alt="enter image description here"></p>
<p>This lamp emits white light and it is about 20 meters from my house. It was very dark outside and the... | g14797 | [
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0... |
<p>Is the time of the collapse of the wave function empirical?</p>
<p>Suppose there is a very long von Neumann chain of observations of a quantum system. Suppose also practically irreversible decoherence happens very early along the chain. We can have an entire class of models parameterized by the point along the chai... | g14798 | [
-0.024190861731767654,
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<p>In the paper <a href="http://arxiv.org/abs/1004.5489" rel="nofollow">arXiv:1004.5489</a> The origin of the hidden supersymmetry, the author use {Qa,Qa}={Qb,Qb}=2H, {Qa,Qb}=0 for N=2 hidden SUSY, which is different from what I was taught: {Qa,Qa}={Qb,Qb}=0, {Qa,Qb}=2H. I think they are controversially different. Is a... | g14799 | [
0.04910905286669731,
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<p>I'm asking in terms of physics. Can powerful magnetic induction rearrange spins of my body in such way I will die? How? </p>
<p>Or maybe it can rip all iron from me, which would make my blood cells useless? How many teslas should such magnet have? Are there other ways to kill people with magnetic induction only? </... | g14800 | [
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0.019118258729577065,
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-0.0497... |
<p>I'm interested in how the <a href="http://en.wikipedia.org/wiki/Skin_effect" rel="nofollow">Skin Effect</a> and the <a href="http://en.wikipedia.org/wiki/Proximity_effect_(electromagnetism)" rel="nofollow">Proximity Effect</a> interact with each other. </p>
<p>From what I can understand:</p>
<ul>
<li>The Skin Effe... | g14801 | [
0.03397316485643387,
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0.0177... |
<p>Recently-ish, I stumbled across <a href="http://www.archive.org/stream/Galaxy_Magazine_Volume_16_Number_5_/IA_Galaxy_Magazine_Volume_16_Number_5_#page/n71/mode/2up">an interesting short story</a> (by way of <a href="http://scifi.stackexchange.com/q/59555">Science Fiction & Fantasy Stack Exchange</a>) where a soc... | g14802 | [
0.009330208413302898,
0.01975773088634014,
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0.023909546434879303,
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0.05424471199512482,
... |
<p>Massive heat wave here and I don't have an air conditioner. I was investigating how commercial air conditioners work and to my surprise found that they use merely evaporation rather than a compressor/radiator cycle like fridges.</p>
<p>I have this fan on my desk so I did a quick test by putting a plastic shroud aro... | g14803 | [
0.006514828652143478,
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<p>In lieu of recent research showing the possibility of obtaining the Bose-Einstein condensate Nq, in certain polymers is there any statistical mechanical way of figuring out the frequency with which the condensate would happen at random in say certain small regions of space with high gravitational fields ie stars, bl... | g14804 | [
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<p>In an organic semiconductor, what is the average distance travelled by an exciton up to recombination? How is this value related to the morfology / structure of the organic semiconductor?</p> | g14805 | [
-0.058324385434389114,
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<p>I went to school one day, so I thought I was able to get this simple one.. but it looks like I'm not anymore. :(</p>
<p>One lonely little spaceship is resting into space. It has a small fuel capacity that it suddently burns to run away and finally reaches a speed $v$. Its tank is now empty, its kinetic energy $E = ... | g14806 | [
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<p>Permittivity is a function of frequency from an existing EM wave. But permittivity in some ways describes how a wavelength of light interacts with a metal. Certain wavelengths, sense different densities of electrons more than others. </p>
<ol>
<li><p>Can I modify the permittivity of a conductor, by applying a curr... | g14807 | [
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... |
<p>In Griffiths <em>Introduction to electrodynamics</em> it is said that Newton's third law is not valid in electrodynamics, but, in the example given, the it does not consider the retarded values for the fields and looks at the contradiction only on the magnetic force.</p>
<p>Just putting the books example: Two posit... | g14808 | [
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<p>A question on <a href="http://biology.stackexchange.com/q/21076/6166">Biology SE</a> got me thinking, ignoring <a href="http://biology.stackexchange.com/a/21092/6166">weight naturally lost during the night</a>, <em>"Do we weigh less in the morning?"</em></p>
<p>During the night, the sun is above us, and the earth b... | g455 | [
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0.042... |
<p>So the universe is expanding, rather space is expanding. By expanding we mean space is coming into existence at all points. </p>
<p>Is that an equal rate of expansion everywhere?</p>
<p>Now the expansion does not over come the force holding matter together, planetary systems, galaxies even galactic clusters to som... | g456 | [
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0.00... |
<p>Lets say you have a cylinder of length L, radius R, and mass M. How fast will it accelerate a mass of mass M2 that is entering the "throat" of the cylinder, considering the effects of gravitoelectromagnetism?</p>
<p>By Gravitoelectromagnetism, I'm specifically talking about the effect where a spinning body will pul... | g457 | [
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-... |
<p>Can you have a resistance less than one? Is this allowed? I've only ever seen circuits with one ohm resistance at least.</p> | g14809 | [
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0.0... |
<p>If $1 / H_0 $ is about 14 billion years, then what happened when the universe was half its current age?</p>
<p>Is the empirically determined $H_0$ supposed to have been twice its current value?</p>
<p>And when the universe is twice its current age is Hubble's parameter half its current value?</p>
<p>That would pr... | g452 | [
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... |
<p>Thermodynamical definition of <a href="http://en.wikipedia.org/wiki/Entropy" rel="nofollow">entropy</a> $$S(p)=-\int p\ln p~dx$$ is defined only on equilibrium system. But why can't we use it for non-equilibrium system? Is there a well-accepted definition for it? </p> | g14810 | [
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<p>Suppose you're analyzing some 3 dimensional object of any sort of shape, and this object explodes from some internal force (e.g, like a grenade). How would you go about determining the average number of fragments that the shape would be broken up into upon the explosion created by this internal force? </p> | g14811 | [
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<p>I was reading a bit of Landau and Lifshitz's Mechanics the other day and ran into the following part, where the authors are about to derive the kinetic energy of a free particle. They use the fact that the Lagrangian of this particle must be the same (or at most, differ by the total time derivative of a function of ... | g14812 | [
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<p>Newton's second law of motion states that $f = ma$. However, in this equation, theoretically there could be a value of $f$ and $m$ that results in an acceleration that is enough to push an object past the speed of light. In my case I have a value of newtons that is large enough (I think) to accelerate an object past... | g14813 | [
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<p>I am still unclear what the hamilitonian of a quantized field is, but what I do know is the hamilitonian of the boson field is defined as
\begin{align}
H_{\text{boson}} &=& \frac{1}{2}\sum_{\mathbf{k},\mu=-1,1} \hbar \omega_{\mathbf{k},\mu}
\Big({a^\dagger}^{(\mu)}(\mathbf{k})\,a^{(\mu)}(\mathbf{k}) + a^{(\m... | g14814 | [
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<p>The concept of orbital velocity tells us that there must be a minimum velocity for a satellite to revolve around earth and the velocity should be such that the gravitational force of earth provides centripetal acceleration to that velocity. So how is it that even a stationary body like an astronaut outside his space... | g14815 | [
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<p>My question is a follow-up to <a href="http://physics.stackexchange.com/questions/80773/the-example-of-relativity-of-simultaneity-given-by-einstein">this question about simultaneity</a>. I would have posted it as a comment to the replies for that question, but I wasn't allowed to.</p>
<p>When Resnick introduces rel... | g14816 | [
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<p>I've noticed that we have so-called 'black' clothes everywhere, I haven't seen so far any piece of clothes that would be <strong>really</strong> black, it's always some kind of lighter black.</p>
<p>For instance, if you take a 'black' shirt then put some water on it, the stain will look even darker.</p>
<p>Why is ... | g14817 | [
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<p>Can anyone recommend a good reference for classical electrodynamics that goes over <a href="http://en.wikipedia.org/wiki/Maxwell%27s_equations_in_curved_spacetime" rel="nofollow">electrodynamics in curved spacetime</a> that doesn't assume much knowledge of GR -- that is it builds up the tensor calculus and GR princi... | g14818 | [
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