question stringlengths 37 38.8k | group_id stringlengths 2 6 | sentence_embeddings listlengths 768 768 |
|---|---|---|
<p>On calm days, the water in the toilet looks completely still. But when it's rainy and windy out, the water looks like it moves and pulsates. Why is this?</p> | g8245 | [
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<p>I heard a saying that <a href="http://en.wikipedia.org/wiki/Exotic_R4" rel="nofollow">$\mathbb{R}^4$</a> having infinitely many differential structures which are not diffeomorphic to each other has a relationship with Yang-Mills field. Does anyone can explain it, and give me some references.</p> | g8246 | [
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<ol>
<li><p>How does one derive the superconformal algebra? </p></li>
<li><p>Especialy how to argue the existence of the operator $S$ which doesn't exist either in either the supersymmetric algebra or the conformal algebra? </p></li>
<li><p>What is the explanation of the convention of choosing If $J _ \alpha ^\beta$ as... | g8247 | [
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<p>In the photoelectric effect there is a threshold frequency that must be exceeded, to observe any electron emission, I have two questions about this.</p>
<p>I) <strong>Lower than threshold</strong>:
What happen with lesser frequency/energy photons? I mean there is no energy transferred? If some energy were transferr... | g8248 | [
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<p><img src="http://i.stack.imgur.com/WNlBP.png" alt="enter image description here"></p>
<p>In my book equation for two advanced wave which created this static wave are
$$y_1=asin{\frac{2\pi}{\lambda}(vt+x)} $$
$$y_2=asin{\frac{2\pi}{\lambda}(vt-x)} $$</p>
<p>and equation for static wave is derived by adding this two... | g8249 | [
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<p>Although clearly this force would be significantly greater with a rotating black hole, is it still possible to calculate this drag for say a satellite orbiting the Earth?</p> | g272 | [
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<p>Recently, I read in the journal <a href="http://www.nature.com/news/stephen-hawking-there-are-no-black-holes-1.14583">Nature</a> that Stephen Hawking wrote a paper claiming that black holes do not exist. How is this possible? Please explain it to me because I didn't understand what he said.</p>
<p>References:</p>
... | g763 | [
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<p>When we like to produce known forces, we know that standard weights acting vertically on a object creates a known force. Now, what are the other methods to generate forces with accuracy. It is a DIY experiment I like to do, so any apparatus which uses simple devices like coils, motors, stepper/servo motors, or simil... | g8250 | [
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<p>Say there is a satellite polar-orbiting the Earth at 600km.
How much would the satellite be dragged additionally due to dragging force?</p>
<p>Such that $$ \Omega = \dfrac{r_s \alpha r c}{\rho^2(r^2 + \alpha^2) + r_s \alpha^2 r sin^2 \theta}$$</p>
<p>such that:</p>
<p>$r_s = \dfrac{2GM}{c^2}$ is the Schwarzchild ... | g272 | [
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<p>This is a statement from Giamarchi's book on Quantum Physics in 1D:</p>
<p>"For a single-particle in a cosine potential, the slightest amount of
tunneling between two cosine minima leads to conduction bands, for
example, and restores the translational symmetry. However, our
sine-Gordon problem is a two-dimensional ... | g8251 | [
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<p>Assume "The Big Crunch" scenario (the universe will collapse to a singularity). In this case, I think of the entire universe as an isolated system; in the "Big Crunch" scenario, it seems to me gravity itself would act as the "walls" of the system, keeping all the matter and energy inside. Thus, by the second law of ... | g8252 | [
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<p>I'm a very visual learner and I would like to know if the diagram representing the Schwarzschild solution is altered at all when the torsion tensor is non zero.</p>
<p>Of particular interest - what is the graphical form of a metric with no curvature and the full range of torsion values?</p> | g8253 | [
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<p>In certain books like David Griffiths electrodynamics , he treats current as a vector in some places. Moreover certain problems like current in a strip are often dealt with by taking current components. I am having a difficult time understanding this.
After going through books and dealing with problems,i think that... | g273 | [
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<p>I don't quite get the practical use of a <a href="http://en.wikipedia.org/wiki/Capacitor" rel="nofollow">capacitor</a>. The theory is fine, but in simple words please explain how, why and where capacitors are used? Is there any other equivalent circuit for capacitors? From what I have learnt capacitors are used to s... | g8254 | [
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<p>I am trying to calculate
$$Z = \int\limits_{\phi(\beta) = \phi(0) =0} D \phi\ e^{-\frac{1}{2} \int_0^{\beta} d\tau \dot{\phi}^2}$$
without transforming it to the <a href="http://en.wikipedia.org/wiki/Matsubara_frequency" rel="nofollow">Matsubara frequency space</a>, I can show that $Z = \sqrt{\frac{1}{2\pi \beta}}... | g8255 | [
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<p>If it does have a pH, I mean. Though I don't see why it shouldn't have it.</p>
<p>Both the <a href="http://en.wikipedia.org/wiki/Br%C3%B8nsted%E2%80%93Lowry_acid%E2%80%93base_theory" rel="nofollow">Brønsted-Lowry</a> and <a href="http://en.wikipedia.org/wiki/Lewis_acids_and_bases" rel="nofollow">Lewis</a> definitio... | g8256 | [
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<p>From the question "<a href="http://physics.stackexchange.com/questions/79152/why-is-the-absolute-zero-273-15">Why is the absolute zero -273.15ºC?</a>" I understood that 1°C is the 100th part of the difference of melting and boiling temperature of water (this is my high school physics, maybe there is a more accu... | g8257 | [
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<p>I am trying to find the moment of intia about its centre of a sector of a circle of radius $a$, mass $m$ and angle $\pi/3$. I have found the answer it is $\frac{1}{2}ma^2$ but originally tried a method that was unsuccessful and don't know why this is the case. This involved finding the moment of interia of element... | g8258 | [
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<p>I have a system, where there are ball bearings on the pistons that clamp the metal plate with special dents for ball bearings. The system should be precise, because it is used for microscopy. It also should be as noiseless as possible. It also should be fast, so the impact at high velocity is inevitable.</p>
<p>I'v... | g8259 | [
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<p>Is there a vibratory rate at which my hand would just pass right through the object and it could not be perceived by touch anymore?</p> | g8260 | [
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<p>Please,kindly help me; my teacher assigned me problem set, and she never went over anything about interferometers in class. Also, there is almost no information about about how to solve interferometer problems in my book. I have no idea how to set this problem up, and I have no intuition concerning how I should solv... | g8261 | [
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<p>Considering that speed increases weight and the proton is going at almost the speed of light, I would like to know how much a speeding proton would weigh in the LHC.</p> | g8262 | [
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<p>We are building an addition on our home that will allow us to build a basement home theater room with some level of flexibility regarding its size and shape. I've been reading somewhat conflicting information about room dimensions and shapes to provide optimal acoustics, and few sources seem to directly cite a scie... | g8263 | [
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<p>I'm having a little trouble with wrapping my head around a part of a method which is fairly 'new' in some fashions to me. I imagine it should be fairly obvious, but I am not seeing something at the moment.</p>
<p>Let's take the Lagrangian density to be </p>
<p>$$\mathcal{ L}={1\over{2}}\left(\mu\dot{\phi}^2-Y(\pa... | g8264 | [
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<p>I remember being in my college dorm, watching a film with a friend. His computer wasn't loud enough and we couldn't hear properly. So he took his earphones and put them on a electric guitar coil. He then plugged his guitar to his amp and voilà, we could listen through the amp.</p>
<p>Why on earth did this work? </p... | g8265 | [
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<p>Is there any interacting quantum field theory of massless fields with helicity $\pm 1$ which can be expressed entirely locally in terms of the field strength F<sub>μν</sub> with no reference to vector potentials at all? Clearly, quantum electrodynamics doesn't fall into this category. The Aharonov-Bohm effect ... | g8266 | [
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<p>For a single point mass :
$\tau=F_{t}r=ma_tr=(m r^2)\alpha = I\alpha$</p>
<p>For multiple point masses bound together : $\sum \tau_i = (m_ir_i^2)\alpha = I\alpha$</p>
<p>But how do we go from that to $I\alpha = F_tr_{app} $ (for the multiple masses case), where $r_{app}$ is the point where force is applied? That ... | g8267 | [
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<p>Are there any materials exploring intermediate levels (of any sub-subject) which give plain English descriptions along side formulas/equations//diagrams/notations?</p> | g8268 | [
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<p>I want to compute the viscosity of argon at different temperatures. What is <a href="http://en.wikipedia.org/wiki/Viscosity#Gases" rel="nofollow">Sutherland's constant</a> of argon?</p> | g8269 | [
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<p>A 6500-kg helicopter accelerates upward at 0.60 m/s² while lifting a 1200-kg car.
(a) What is the lift force exerted by the air on the rotors?<br>
(b) What is the tension in the cable (ignore its mass) that connects the car to the helicopter?</p> | g8270 | [
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<p>I should preface this by admitting that my physics background is rather weak so I beg you to keep that in mind in your responses. I work in mathematics (specifically probability theory) and a paper my adviser asked me to read dealt with a discrete approximation to the random Schrödinger operator $\Delta + V(x,\omeg... | g8271 | [
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<p>Relativistic mass $\displaystyle m(v)=\frac{m_o}{\sqrt{(1-(v/c)^2}}$ </p>
<p>$m_o$ = mass of object measured at rest<br>
$c$ = speed of light ($3\times 10^8\;m/s$)<br>
$v$ = speed</p>
<p>If the total relativistic energy of an object is given by $E=mc^2$, then find the second-order Taylor approximation of $E(v)$. ... | g8272 | [
0.06035472825169563,
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<p>Framework</p>
<p>If there was a cable constructed at the equator about the circumference of the Earth, and if this cable had sufficient strength to remain intact while erect, call this tensile strength T.</p>
<p>Question</p>
<p>With a rocket, could you launch the cable from the surface of the Earth without exceed... | g8273 | [
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<blockquote>
<p>A thin plank of mass $M$ and length $l$ is pivoted at one end. The plank is released at 60$^{\circ}$ from the vertical. What is the magnitude and direction of the force on the pivot when the plank is horizontal?</p>
</blockquote>
<p>I have a doubt: does the pivot exert an upwards force on the plank w... | g8274 | [
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<p><a href="http://earthtech.org/publications/davis_STAIF_conference_2.pdf" rel="nofollow">The Alcubierre Warp Drive in Higher Dimensional
Spacetime</a> (H. G. White & E. W. Davis), among other sources, proposes that the x-axis symmetry paradox for Alcubierre-style warp drives can be resolved by interpreting the w... | g8275 | [
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<p>Let me first believe that the ${\cal N}=2$ Landau-Ginzburg theory does in the IR flow to a non-trivial fixed point and that if the potential is of the form $\Phi ^k$ then the central charge of the CFT at that fixed point is indeed $3(1-\frac{2}{k})$. </p>
<ul>
<li><p>Given the above, how does it somehow obviously f... | g8276 | [
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<p>What don't we know about how electricity and/or magnetism works?</p> | g8277 | [
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-... |
<p>What is the connection between Planck's constant and gravity? Why is the Planck scale the natural scale for quantum gravity? I would have though the scale would be related to G, not h. </p> | g8278 | [
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<p>The quark composition of the neutral pion ($\pi^0$) is $\frac{u\bar{u} - d\bar{d}}{\sqrt{2}}$. What does this actually mean?</p>
<p>I think it's bizarre that a particle doesn't have a definite composition. There's a difference of 2 MeV between the quark masses and I don't understand how this can be ignored. If I we... | g8279 | [
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<p>If you push a bar magnet inside a solenoid, a current is produced. But why is that? I mean, the wire is being moved <em>along</em> the magnetic field, so taking the cross product:</p>
<p>$\vec{F} = I\vec{V}\times\vec{B} = I|\vec{V}||\vec{B}|\sin\theta\hat{n}$</p>
<p>Here, the angle between the velocity of the char... | g8280 | [
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<p>Sometimes I may come up with an equation in mind, so I want to search for the related material. It may be the case that I learn it before but forget the name, or, there is no name for the equation yet. In this case, I may be able to recall a reference book. Searching in Internet can be a fast way though.</p>
<p>How... | g8281 | [
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<p>Suppose you take a loop of string and place it on the surface of a liquid, the string should become taut due to surface tension. How would you be able to calculate the tension in the loop of string?</p>
<p>My main difficulty in solving this problem is the direction in which surface tension force act on the thread -... | g8282 | [
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<p>I understand that in electrostatics all charges are 'static' due to equal forces acting upon them. This then leads to the fact that the arising electric field must be perpendicular to the metals surface at the surface. What i don't understand is what force is counteracting the electric field. I have read that there ... | g8283 | [
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<p>I learned that a quantum system has an "overall state", a vector in a Hilbert space. That Hilbert space can be decomposed in a basis of "basic states". For example if in the Universe there is only a free electron with its own spin, and I pick an axis $z$, there is an infinite basis of "position+spin", let's say $|(0... | g8284 | [
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<p>I've been looking at LIGO figures for <a href="https://dcc.ligo.org/public/0002/T0900288/003/AdvLIGO%20noise%20curves.pdf">gravitational wave sensitivity here</a> and it seem to be displayed in an adimensional strain ratio (which I assume that is more or less equivalent to metric perturbation $h_{\mu \nu}/g_{\mu \nu... | g8285 | [
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<p>We have 12 different 'notes' per octave on a musical keyboard. They are set up so that every 'note' (A, B,C etc) is a second harmonic of the same 'note' in the next higher octave. With this ratio in place, it seems that everything on a keyboard should be divided up into equal groups of 2,3,4 or 6. However, the ke... | g8286 | [
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<p>While travelling in the train on the sunset, I have noticed the strange phenomenon. The shadows of the lonely trees and lampposts, that stay along the railroad, are moving on the wall in the same direction as the train. I tried my artist talents to express the situation as a picture:</p>
<p><img src="http://i.stack... | g8287 | [
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<p>What I mean by effective in the question refers to the time and space requirements for sending information over a quantum communications channel. Having read "Mike and Ike" but doing no independent research on the question, my initial impression is that a channel using an effect from quantum field theory e.g. quantu... | g8288 | [
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<p>Ignoring for the moment the experimental necessity of eliminating the gluon singlet state, the nine "raw" gluon color components form two quite distinct sets. The first set consists of the six (color,anti-other-color) components:</p>
<blockquote>
<p>$r\overline{g}$, $r\overline{b}$, $g\overline{b}$, $g\overline{r... | g8289 | [
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<p>I'm trying to recall some fact that I learned in my college materials science class, where we learned concepts like stress vs. strain. </p>
<p>I remember that materials like metal have a breaking point, and if an applied stress produces a force higher than the breaking point, the metal will break. Or something like... | g8290 | [
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<p>I've played with this idea for years, and haven't really been able to eliminate it. So, perhaps someone here can point to simple experimental evidence that would do so.</p>
<p>Here's the issue: Antimatter of course annihilates ordinary matter, but the more precise statement is that antiparticles annihilate <em>the ... | g8291 | [
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<p>If we have a kilometer long million slit light source and make an observation on a slit at one of the ends, will the interference pattern fully collapse or partially collapse? is there any delay in the propagation of the collapse or is the collapse instant?</p>
<p>Link to multiple slits.</p>
<p><a href="http://hyp... | g8292 | [
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<p>Consider two bodies orbiting each other.</p>
<p>As the Universe expands would the distance between them increase?</p>
<p>Most people say that a gravitationally bound system will not expand with the Universe. They say that such a system is not described by the FRW solution.</p>
<p>But surely one could consider two... | g8293 | [
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<p>According to the scalar Field theory we write Lagrangian as $$\mathcal{L}=\frac{1}{2}\partial^\mu \phi \partial_\mu \phi -\frac{m^2}{2}\phi^2 -\frac{\lambda}{4!}\phi^4 \tag {1}$$
What I want to do is to get a equation of solitary wave (solition) from the above Lagrangian which will lead for solving many solitary pr... | g8294 | [
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<p>I know the <a href="http://en.wikipedia.org/wiki/Richter_magnitude_scale" rel="nofollow">Richter magnitude scale</a> is often used for measuring the strength of earthquakes. At the same time, explosive/destructive releases of energy are often quoted in equivalent amounts of TNT. Is there some way to relate these two... | g8295 | [
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<p>I am reading a material about the degree of freedom for linear n-atom molecule and nonlinear n-atom molecule. Here is my analysis for a diatomic molecule, if there are two atoms, we have to use 3 coordinates to describe the translational motion, 2 coordinates about the rotation and 1 for vibration, so total will be ... | g8296 | [
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<p>Are Cartan structural equations equivalent to Einstein's equations
$$G_{\mu\nu}=T_{\mu\nu}$$
and why (in the case of torsionless geometries, of course)? Does it also apply with a non-null cosmological constant?</p> | g8297 | [
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<p>Why are the charges of atoms in a molecule not invariant under the rotations of the molecule? </p>
<p>My intuition is that the charges should not change under the rotation of the molecule, because their relative positions do not change. But I was told that they can change. </p> | g8298 | [
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<p>Does the <a href="http://en.wikipedia.org/wiki/General_topology" rel="nofollow">general topology</a> of Minkowski space-time change under a Lorentz transformation? Open balls in $\mathbb{R}^{4}$ (with the standard topology) are not invariant under Lorentz transformations. Does this mean for example that observers in... | g8299 | [
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<p>I know that standing waves in a simple harmonic system occur when the "echo" of a wave overlaps completely with the original wave at a certain point in time, doubling the amplitude. And then, because both waves have the same speed and frequency but opposite direction, they move away from eachother until they cancel ... | g8300 | [
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<p>Suppose a plasma has characteristic frequency $\omega_p$. Since </p>
<p>$$n = \sqrt{\left(1-\frac{\omega_p^2}{\omega^2}\right)} $$</p>
<p>For $\omega<\omega_p$, the refractive index will be imaginary - which corresponds to absorption of light.</p>
<p>For $\omega > \omega_p$, the refractive index will be rea... | g8301 | [
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<p>Does wavelength change with distance? How do they know that the change in wavelength can only be caused by the change of speed of the object to the observer? What about noises, distortions, and interferences as the light moves away from the source to the observer? Or perhaps it travelled through some unknown medium ... | g8302 | [
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<p>In Peskin's QFT book page 294, he formally addressed the quantization of EM field,</p>
<blockquote>
<p>$$propagotor_{EM}=\frac{-ig_{\mu\nu}}{k^2+i\epsilon}$$
Now that we have the functional integral quantization method at our command, let us apply it to the derivation of this expression.<br>
Consider the func... | g8303 | [
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0... |
<p>I'm wondering on what principles Noether's theorem foots. More precisely:</p>
<p><em>The action is a functional on the fields only. Why do we consider then variations of the space time too? In principle careful considerations, however, seem to untangle them as special field variations. So what's going on here truly... | g8304 | [
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<p>What is the rigorous justification of <a href="http://en.wikipedia.org/wiki/Wick_rotation" rel="nofollow">Wick rotation</a> in QFT? I'm aware that it is very useful when calculating loop integrals and one can very easily justify it there. However, I haven't seen a convincing proof that it can be done at the level of... | g8305 | [
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<p>The universe is expanding in the 3 spatial dimensions, could it not also be expanding in time dimension. In other words, are we stuck in 3 dimensions because we are riding the "bow wave" of the big bang in the time dimension, stuck on a 3d plane perpendicular to our world lines in spacetime? Think of a 3d-printer, a... | g274 | [
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<p>I've been struggling with a detail in Second Quantization which I really need to clear out of my head. If I expand the S-matrix of a theory with an interaction Hamiltonian $ H_I(x) $ then I have</p>
<p>$$ S - 1= \int^{+\infty}_{-\infty} d^4x\, H_I(x) + \int^{+\infty}_{-\infty} \int^{+\infty}_{-\infty} d^4 x\, d^4 ... | g8306 | [
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<p>If one travels in a spaceship at speed V, the time elapsed for the traveller relative to an observer on earth is dilated by,</p>
<p>$$ t' = t(1 - v^2/c^2)^{1/2} $$</p>
<p>Does this mean that a space traveller, who gradually accelerated to a speed very close to the speed of light can then travel 10 billion light ye... | g8307 | [
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<p>I want to know how to calculate the normal modes from a Lagrangian.
I make the T (kinetic energy matrix) and U (potential energy matrix), and then I calculate the determinant of $|T-\omega ^2 U|$ (with omega as the angular speed). This way I find the $\omega$'s but I dont know how to find the normal modes.
Are they ... | g8308 | [
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<p>Let's have <a href="http://en.wikipedia.org/wiki/Wick%27s_theorem" rel="nofollow">Wick's theorem</a> in following form:
for fields
$$
A_{i}(x) ~=~ A_{i}^{+}(x) + A_{i}^{-}(x),
$$
where first summand contains creation operator and the second contains destruction one, is a fair to say
$$ \tag{1}
T(A_{1}...A_{n}) ~=~ ... | g8309 | [
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<p>In non-relativistic QM, the position of a particle is an observable. In QFT, fields are the observables. However, particles must have some sort of position, otherwise we wouldn't see pictures like the ones below. What is the (linear, Hermitian) operator that describes what we are observing?</p>
<p>I've tried consid... | g8310 | [
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<p>I would like to know if Archimedes law take in equation the lack of matter. Fluid density at 1. An object with density of 0 (or near 0) is put in liquid, it's fixed. The external sphere where liquid is inside is fixed too. The lack of matter change the attraction in all the sphere itself, no ? Density change with de... | g8311 | [
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<p>Recently I saw some videos of non-newtonian (shear-thickening) fluids like corn starch mixed with water(sometimes known as oobleck), where the fluid is placed on top of a speaker cone and starts to create odd shapes as it becomes thicker in some places.
Now I wondered what would happen in the following situation:</p... | g8312 | [
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<p>If a body is resting on the ground, the Normal force equals its weight. If I keep putting another body on top of it, eventually the body will start moving into the ground until the new Normal equals the total weight of the body. I can add more weight on top and the body will move further into the ground. So it appea... | g8313 | [
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<p>Recently a "U" shaped scratch appeared on my car's front tire. It looks like someone rolled past a curb and scraped it. This has led me to the following problem:</p>
<p>Generate a plot (ideally polar) of a scratch pattern on a tire given tire radius and the ground height of a protrusion. Assume the protrusion is a ... | g8314 | [
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<p>After Apollo 11 first landed on the Moon in 1969, there have been conspiracy theories that this never really happened and that it was all a hoax. In 2010 NASA released photos from its Lunar Reconnaissance Orbiter (LRO) mission of some landing sites which showed both a lunar lander and footprints (as dark trails).</... | g822 | [
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<p>As the title explains, </p>
<ol>
<li>How does a comet form?</li>
<li>What are the elements, what is a comet composed of? </li>
<li>Why didn't they become part of planets, moons or asteroids?</li>
</ol> | g8315 | [
0.0389445461332798,
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<p>I am a newbie in water system design but I am currently faced with the exact situation below on my land, and I need to know whether gravity alone is sufficient in order to fill Tank 2 from Tank 1, as I already experienced backflow.</p>
<p>Please have a look at this image:</p>
<p><img src="http://img819.imageshack.... | g8316 | [
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0.03357871621847153,
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... |
<p>Frequently I see the expression
$$F = \frac{dp}{dt} = \frac{d}{dt}(mv) = \frac{dm}{dt}v + ma,$$
which can be applied to variable mass systems.</p>
<p>But I'm wondering if this derivation is correct, because the second law of Newton is formulated for point masses. </p>
<p>Furthermore if i change the inertial frame... | g8317 | [
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0... |
<p>I understand that it can't be placed anywhere on the radius because it doesn't vary with it ( and so of course it doens't make sense to place it anywhere else on the plane), but why do we place it there?</p>
<p>I undertand all the advantages that came <em>after</em>
$$\vec v = \vec\omega\times\vec r$$
$$\vec a = \... | g8318 | [
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0.0008437270298600197,
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<p>Suppose we have the following Slater determinant:
\begin{equation}
| \Psi \rangle = \prod \limits_{i,i'} a^+_{i\alpha} a^+_{i'\beta} | \rangle
\end{equation}
where $a^+_{i\alpha}$ creates an electron in state $i$ with spin $\alpha$ and, in general, $i \neq i'$. I want to evaluate $\langle \Psi | S^2 | \Psi \rangle$ ... | g8319 | [
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0.03320341929793358,
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0.03... |
<p>I recently had to solve the following problem:</p>
<blockquote>
<p><em>A force $F=10\hat x- 8\hat y$ is applied to an object that is constrained to travel towards increasing values of x along the path defined by $y=x^2$ and $z=0$. Find the component of $F$ that is tangent to this path at the point $(2,4,0)$.</em>... | g8320 | [
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0.06426001340150833,
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0.02212994545698166,
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0.03621959686279297,
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<p>We all know that light travels in straight a line, which can be proved by pinhole imaging as in the picture shown :
<img src="http://i.stack.imgur.com/lNIN3.png" alt="pinhole camera"></p>
<p>But when I'm doing this little experiment with an apple, no matter how I change the distance between the object and the pinho... | g8321 | [
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0.026798022910952568,
... |
<p>Why the absorption cross section in direct dissociation process is wide and structureless while the absorption cross section in the predissociation process is structured and containing lines which are normally Lorentzian in shape?</p> | g8322 | [
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<p>Almost every time somebody talks about atoms, at some point they mention something like this:</p>
<blockquote>
<p>If we remove the spaces between the atoms and atomic components, we can fit the solar system in a <a href="http://en.wikipedia.org/wiki/Thimble">thimble</a>.</p>
</blockquote>
<p>Or</p>
<blockquote>... | g8323 | [
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0.022808168083429337,
0.05536342412233353,
-0.03591395914554596,
-0.0019468372920528054,
-0.01... |
<p>I am learning the differential form of <a href="http://en.wikipedia.org/wiki/Gauss%27s_law">Gauss Law</a> derived from the divergence theorem.
$${\rm div}~ \vec{E} =\frac{\rho}{\epsilon_0}.$$
So far in my study of math and physics, the word "differential" has been associated with a infinitesimal change in a value (... | g8324 | [
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0.048456039279699326,
-0.004... |
<p>This is spawned from a comment at the answer to <a href="http://physics.stackexchange.com/questions/82487/confusion-about-a-lemma-on-the-time-constraint-of-an-adiabatic-evolution-arxiv">one of my previous questions</a>.</p>
<p>Someone suggested to me that claiming the following statement might be NP-hard. Could any... | g8325 | [
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0.014001716859638691,
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0.014577355235815048,
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... |
<p>Does Gravity / curved space cause rotation?</p>
<p>Meaning, if a spaceship is heading not directly toward Earth, but slightly off to one side, and when finally being close to the Earth it falls into earth orbit, does the spaceship continue to point in the same directions as it was when approaching the earth, or doe... | g8326 | [
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0.01370270736515522,
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0.009607... |
<p>I am reading the book "Lecture notes on Electron Correlation and Magnetism" by Patrik Fazekas.</p>
<p>It says, "The ground state (of Heisenberg FM model) is not unique. We have just found that the system has the maximum value of the total spin $S_{tot}= LS$. $S^{z}_{tot} = LS $ state which is maximally polarized in... | g8327 | [
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-0.... |
<p>for those that combine Homology group and some form of Kadanoff scheme for coarse graining on a lattice, am I having a good argument when saying this:
(practical thinking now)
1. I obtain the Homology groups for a lattice space, I do some coarse graining on it, everything looks fine
2. I go to the cohomology. Cohomo... | g8328 | [
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0.0... |
<p>I acknowledge that this question is quite trivial. But in the lattice jargon, what does a $N$-sites lattice mean?</p>
<ul>
<li>it's a lattice $N\times N$ or</li>
<li>it's a lattice with $N$ vertices? </li>
<li>another option perhaps.</li>
</ul>
<p>From the context I cannot infer it. I just know that $N$ is quite l... | g8329 | [
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0.022622674703598022,
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... |
<p><img src="http://i.stack.imgur.com/DDuwM.png" alt="Hydrogen atom"></p>
<p>After seeing this photograph and reading this article : <a href="http://io9.com/the-first-image-ever-of-a-hydrogen-atoms-orbital-struc-509684901" rel="nofollow">The First Image Ever of a Hydrogen Atom's Orbital Structure</a></p>
<p>I was re... | g8330 | [
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0.09218127280473709,
-... |
<p>I apologise in advance if this question doesn't appeal to the advanced questions being asked in this Physics forum, but I'm a great fan of the Stack Exchange software and would trust the answers provided here to be more correct than that of Yahoo! Answers etc.</p>
<p>A car is travelling with a constant speed of 80k... | g8331 | [
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<p>I'd like to keep a container of potable water in my car for when I get stuck, but in the winter it gets cold enough for bottled water to freeze.</p>
<p>I can't put salt in it, because then it won't be drinkable anymore (or at least, will make my condition worse if I do drink it), and I can't mix it with alcohol in ... | g8332 | [
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<p>I've heard that turning on faucets to a slight drip will prevent pipes from freezing, but I've never understood why this is the case. Can anyone out there help me to understand? Thanks!</p> | g8333 | [
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<p>I've always heard that watering plants if the temperature goes a few degrees below freezing will help prevent them from freezing, but I've never quite understood the physics behind it. Can you guys help me to understand this a bit better? Thanks!</p> | g8334 | [
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<p>This is a second question (in what will probably become a series) in my attempt to understand LQG a little. In the <a href="http://physics.stackexchange.com/questions/2407/give-a-description-of-loop-quantum-gravity-your-grandmother-could-understand">previous question</a> I asked about the general concepts behind LQG... | g8335 | [
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... |
<p>Two magnets with Iron truncated cone or pyramid: Frustrum</p>
<p><strong>How much low inclination can the truncated cone or pyramid: Frustrum be made,
without non homogeneous lines of magnetic field coming out from the sides ?????????</strong>
<img src="http://I.stack.imgur.com/IqOxV.png" alt="Cone_Inclination"></p... | g8336 | [
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<p>Let me look at the Hamiltonian of a charged particle in a plane in a constant magnetic field ($\vec{B}$) pointing upwards - then in usual notation it is,</p>
<p>$$\hat{H} = \frac{1}{2m}\biggl(\hat{p} + \frac{e}{c}\hat{A}(\hat{r})\biggr)^2$$</p>
<p>To convert this in a Feynman-path-integral language, I pick say a g... | g8337 | [
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<p>This is a common point of argument on internet forums. I think it is fairly well established theoretically that there is a very small amount of mass converted to energy in an exothermic chemical reaction. Has this ever been observed experimentally? </p>
<p>If not, how far off is our current experimental state of th... | g8338 | [
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