question stringlengths 37 38.8k | group_id int64 0 74.5k |
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<p>This question is motivated by <a href="http://physics.stackexchange.com/questions/98067/does-natural-unit-of-information-and-entropy-nat-play-special-role-in-the-free">this one</a>.</p>
<p>Suppose $l$ is the minimum measurable unit of length. What is entropy of a spinless particle contained in this interval?</p>
<... | 6,565 |
<p>Let's say you are in the air 500 meters above flat land and you have no parachute. Which pose - forming a sphere or spreading all extremities to make yourself as wide as possible or other - is the most appropriate to cause the highest likelihood of survival?</p>
<ol>
<li>in the air</li>
<li>right before impact</li>... | 6,566 |
<p>What is the formula we use to calculate average speed?</p> | 225 |
<p>In multi-electron atoms, the electronic state of the optically active "subshell" is often expressed in "term symbols" notation. I.e. $^{2S+1}L_J$. This presumes that the system of electrons has definite $L^2$, $S^2$ and $\mathbf{J}$ eigenstates.</p>
<p>In order to determine all the possible electronic states compat... | 6,567 |
<p>In an assignment I am given a random car with a random suspension system, and told that it is sufficient to test the safety of the car with regards to the suspension on three different sinusoidal roads.</p>
<p>The first road has an amplitude of 5 centimeters and a period of 20 meters, the second road has an amplitu... | 6,568 |
<p>Say there was some situation where you have a lot of subatomic particles interacting with each other and decided to draw (say, by joining Feynmann diagrams) those interactions- so that you got some sort of (?directed) graph... what kind of network would you obtain? Would it be scale-free? Would it be a complex netwo... | 6,569 |
<p>Imagine a bar </p>
<p>spinning like a helicopter propeller,</p>
<p>At $\omega$ rad/s because the extremes of the bar goes at speed</p>
<p>$$V = \omega * r$$</p>
<p>then we can reach near $c$ (speed of light)
applying some <strong>finite</strong> amount of energy
just doing </p>
<p>$$\omega = V / r$$</p>
<p>The... | 121 |
<p>Assume we have a conveyor scales. Which consists of scales, and motor with conveyor belt placed above, so that the boxes can be measured (weight) while moving above. What I want is to create the model of the oscillations of that scale.
The equation of the oscillations of the spring is well known for everybody.
How ... | 226 |
<p>I'm reading an article about bi layered membranes which state that for the free energy function<br>
$f(\theta) = \theta \ln \theta + (1-\theta)\ln(1-\theta) + \chi \theta (1-\theta)$</p>
<p>Where $\phi_i$ is the mole fraction of certain types of lipids in layer $i$ and $\chi$ is the energy of interaction between tw... | 6,570 |
<p>Argument: Buckling is an engineering concept that can only be applied to <strong>thin columns</strong> with <strong>compressive</strong> loading.</p>
<p>(Is it possible to) Prove the above sentence right or wrong with mathematical formulation. Emphasis on cellular and solid materials that have no concept of "thin".... | 6,571 |
<p>When Einstein started to think about gravitation, he completely created a new theory that no experiment supported. He based his reasoning, as he explained it later, on small thought experiments (Gedankenexperiment) that led him to formulate the equivalence principle. From this equivalence principle, he used the prin... | 6,572 |
<p>In the literature (<a href="http://openlibrary.org/books/OL6927036M/Vorlesungen_u%CC%88ber_mechanik" rel="nofollow">Kirchhoff G. - Mechanic (1897), Lecture 18</a> or Lamb, H. - Hydrodynamics (1879)) one can find the following analytical closed form expression for the gravitational potential of homogeneous ellipsoid ... | 6,573 |
<p>I am reading a physiology book chapter (<a href="http://rads.stackoverflow.com/amzn/click/0387983813" rel="nofollow">Mathematical Physiology, by Keener</a> --Respiration chapter) about the gas exchange between capillaries and alveoli. It seems that this gas exchange can be modeled after some simple physical relation... | 6,574 |
<p>Or would it be acceleration voltage? Acceleration sounds like it makes more sense, but my paper says accelerating.</p>
<p>What are possible ways you could go about calculating it?</p> | 6,575 |
<p>My question is vague, so I'm hoping the answers will help me ask more concrete questions and maybe produce some interesting discussion.</p>
<p>In mean field theory, say for the Ising model, we treat the magnetization $m$ as a parameter and derive the equation
$$
\langle\sigma_i\rangle = \tanh (\beta J dm),
$$
where... | 6,576 |
<p>If you "disobey" the constraints of the <a href="http://en.wikipedia.org/wiki/Kramers%E2%80%93Kronig_relations" rel="nofollow">Kramers-Kronig relations</a>, what happens? Do you get non-physical results?</p>
<p>I am simulating reflection and transmission off/through a slab of material. I specify the complex index o... | 6,577 |
<p>My question is mainly an engineering question. Assume I have a turbine in which I adiabatically expand compressed air. The air cools down and does work to its surroundings, which is captured by the blades of the turbine and then is transformed into rotational energy/electricity. </p>
<p>When instead I let the compr... | 6,578 |
<p>We know about some events that happen very quickly. For example, the <a href="https://en.wikipedia.org/wiki/Dielectric" rel="nofollow">dielectric</a> relaxation time is about $10^{-14}\, \mathrm{seconds}$. </p>
<p>I'm interested in other processes that switch extremely fast or or could be use as a very short tick ... | 446 |
<p>Immediately prior to becoming a supernova the core of some types of stars may suffer gravitational collapse. </p>
<ul>
<li><p>What happens to any planets in orbit around the star at the instant the mass is fully collapsed? </p></li>
<li><p>Assuming this sudden change would cause some perturbation ; how large/distan... | 6,579 |
<p><strong>(1)</strong> As we know, we have theories of second quantization for both bosons and fermions. That is, let $W_N$ be the $N$ identical particle Hilbert space of bosons or fermions, then the "many particle" Hilbert space $V$ would be $V=W_0\oplus W_1\oplus W_2\oplus W_3\oplus...$ , and further we can define c... | 6,580 |
<p>I read some where that there are three types of UV and infrared rays namely UV-A, UV-B, UV-C and near infrared, mid infrared and far infrared. Which is the most abundant among the the three in Ultraviolet and infrared radiation from sun? I mean there is a total of 1000 W per unit area illumination by sun among which... | 6,581 |
<p>In spherical coordinates the flat space-time metric takes:</p>
<p>$$ds^2=-c^2dt^2+dr^2+r^2d\Omega^2$$</p>
<p>where $r^2d\Omega^2$ come from when the signature of metric $g_{\mu\nu}$ is (-,+,+,+)?</p>
<p>what is signature of spherical metric?</p>
<hr>
<p>this is signature of spherical coordinates:
$(1,r^2,r^2\s... | 6,582 |
<p>If light is passed through two polarizing filters before arriving at a target, and both of the filters are oriented at 90° to each other, then no light will be received at the target. If a third filter is added between the first two, oriented at a 45° angle (as shown below), light will reach the target.</p>
<p>Why ... | 6,583 |
<p>New question: In string theory and QFT, do particles travel back in time? Not related to antimatter: Do they travel back and forth in time in reality or are these just interpretations of mathematical formulas used to make sense of calculations?</p>
<p>This is a different question (<a href="http://physics.stackexcha... | 6,584 |
<p>The first <a href="http://en.wikipedia.org/wiki/Chern_class" rel="nofollow">Chern number</a> $\cal C$ is known to be related to various physical objects.</p>
<ol>
<li><p>Gauge fields are known as connections of some principle bundles. In particular, principle $U(1)$ bundle is said to be classified by first Chern nu... | 6,585 |
<p>In the special relativistic action for a massive point particle, </p>
<p>$$\int_{t_i}^{t_f}\mathcal {L}dt,$$</p>
<p>why is the Lagrangian </p>
<p>$$\mathcal {L}=-E_o\gamma^{-1}$$</p>
<p>a negative number?</p> | 924 |
<p>The question concerns <a href="http://www.theepochtimes.com/n3/739183-former-nasa-physicist-disputes-einsteins-relativity-theory/?photo=2" rel="nofollow">this video</a>: </p>
<p>It says that the <a href="http://en.wikipedia.org/wiki/Gravitational_lens" rel="nofollow">Gravitational Lens</a> effect is an illusion, me... | 6,586 |
<p>I have a ball of metal about an inch in diameter and a concave disc of another metal (which is magnetic) around the ring of the disc (about $12 {\rm mm}$ in diameter). I don't know which metals they are. The ball is not magnetic on its own. That is <a href="http://en.wikipedia.org/wiki/Paramagnetism" rel="nofollow">... | 6,587 |
<p>If we are travelling with the speed of light, can we see whats behind us(like if we are moving away from earth can we able see the earth)? And how we see the things that we are approaching with speed of light? Does the things look like fast forwarding because we are moving and the source also sending photons with th... | 6,588 |
<p>Pioneer <a href="http://en.wikipedia.org/wiki/Pioneer_10">10</a> & <a href="http://en.wikipedia.org/wiki/Pioneer_11">11</a> are robotic space probes launched by the NASA in the early 1970's. After leaving our solar system, an <strong>unusual deceleration</strong> of both spacecrafts has been measured to be appro... | 6,589 |
<p>In all the literature I've seen the turbulent energy spectrum described as $E(k)$ instead of $E(L)$, i.e. as a function of a wave number not eddy size. The connection via $k=2\pi/\lambda$ is clear, but exactly what wave process is meant here. Is the idea that turbulent flow can be viewed as a superposition of waves?... | 6,590 |
<p>I've seen many science popularisation documentaries and read few books (obviously not being scientist myself). I am able to <em>process and understand</em> basic ideas behind most of these. However for general relativity there is this one illustration, which is being used over and over (image from Wikipedia):</p>
<... | 6,591 |
<p>On a quantum scale the smallest unit is the <a href="http://en.wikipedia.org/wiki/Planck_scale">Planck scale</a>, which is a discrete measure.</p>
<p>There several question that come to mind:</p>
<ol>
<li>Does that mean that particles can only live in a discrete grid-like structure, i.e. have to "magically" jump ... | 114 |
<p>If a vibrating atom can produce light why can't an alternating current of electrons do the same?</p>
<p>EDIT: When I use the term "light" I mean all EMR</p> | 6,592 |
<p>consider object A with mass $m_{A}$ and positional vector $\overrightarrow{r_{A}}$</p>
<p>object B with mass $m_{B}$ and positional vector $\overrightarrow{r_{B}}$</p>
<p>object C with mass $m_{C}$ and positional vector $\overrightarrow{r_{C}}$</p>
<p>since reference frame is inertial (assumed) so</p>
<p>$m_{A}\... | 6,593 |
<p>I am looking at the <a href="http://en.wikipedia.org/wiki/Poincare_sphere" rel="nofollow">Poincaré sphere</a> and I am trying to compute a <a href="http://en.wikipedia.org/wiki/Jones_calculus" rel="nofollow">Jones matrix</a> for a particular rotation. Specifically, I would like it to perform the following maps:</p>... | 6,594 |
<p>How are the external magnetic field intensity H, magnetisation M and the entropy related to each other? i.e. if I change the magnetic field intensity by dH what will be the change in entropy dS in terms of M. </p> | 6,595 |
<p>An isolated system $A$ has entropy $S_a>0$.</p>
<p>Next, the isolation of $A$ is temporarily violated, and it has entropy reduced $$S_b ~=~ S_a - S,\space\space\space S\leq S_a.$$</p>
<p>Is it true to say: <strong>the process of lowering entropy of a system requires work and energy?</strong></p>
<p>I am not su... | 6,596 |
<p>In <a href="http://en.wikipedia.org/wiki/Metric_expansion_of_space#Understanding_the_expansion_of_Universe" rel="nofollow">this wikipedia article</a> it is described how a beam of light, with its locally constant speed, can travel "faster than light". That is to say it travels a distance, which, from a special relat... | 6,597 |
<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/759/does-quantum-physics-really-suggests-this-universe-as-a-computer-simulation">Does Quantum Physics really suggests this universe as a computer simulation?</a> </p>
</blockquote>
<p>I know the title so... | 227 |
<p>Say we have an expression of the form:
$$
\left<0\right|:\phi(x)^2: : \phi(y)^2:\left|0\right>,
$$
where $\phi$ is some scalar field. I have heard the claim several times, that in evaluating this expression using Wick contractions, one only has to contract terms between groups of normal ordered terms. In this ... | 6,598 |
<p>I am trying to make sense of <a href="http://arxiv.org/abs/physics/0210005" rel="nofollow">arXiv:physics/0210005</a>. I am confused with the concept of information bearing degrees of freedom of a system mentioned at the very beginning. To verify the arguments of the paper, I would like to start with a 1-D quantum si... | 6,599 |
<p>Google has not been very useful in this regard. It seems no one has clearly defined terms and Kittel has too little on this. </p> | 6,600 |
<p>Hey guys I really need help on this problem.</p>
<blockquote>
<p>A ceramic slab of dimentions 5cm x 10 cm x .25 cm has to be heated to $177\,^{\circ}{\rm C}$. The ceramic slab travels on a conveyor belt traveling at $.1 \frac{m}{s}$. The slab is initially at a temperature of $18\,^{\circ}{\rm C}$ when it enters a... | 6,601 |
<p>Reading about plasmonic nanoparticles I faced the term "localised light".</p>
<p>How can one localise light? What are applications of it?</p> | 6,602 |
<p>How to calculate the area / volume of a black hole?
Is there a corresponding mathematical function such as rotating $1/x$ around the $x$-axis or likewise to find the volume? </p> | 6,603 |
<p>For a simulation, I want to compute the path that light follows near a black hole.</p>
<p>Non-relativistically, a massive point particle in a central newtonian gravitational field follows either an ellipse, a parabola, or a hyperbola. Is the same true relativistically for light around a black hole? A problem I see ... | 6,604 |
<p>I know there may be missing information, but my question is really simple and yet I haven't found an answer to it. To make things easy, let's assume we have a $40×40×40$ cm oven that we want to keep its temperature at $200$ degrees Celsius using natural gas. How much energy per second is consumed to achieve this?</p... | 6,605 |
<p>Imagine two laser beams A and B are released at the same moment to bounce between two mirrors, A was moving and B was at rest, doing the calculations I found that for a person at rest B would reach the upper mirror before A because in his frame of reference A travels less distance. but for another person in the sam... | 6,606 |
<p>The <a href="http://en.wikipedia.org/wiki/Vis-viva_equation" rel="nofollow">proof</a> of the vis-viva equation of orbital mechanics found on wikipedia looks, in my opinion, somewhat convoluted and unenlightening. Considering the simplicity and importance of the vis-viva equation, is there a shorter or more insightf... | 6,607 |
<p>Lately I'm reading about surface enhanced fluorescence. In many articles I can see that <a href="http://en.wikipedia.org/wiki/Fluorophore" rel="nofollow">fluorophores</a> are called "dipoles". Is it because that they can be modelled by a vibrating electric dipole? Or maybe they are all chemical dipoles?</p> | 6,608 |
<p>I saw the following way of derivation of Maxwell equations: author starts from Lorentz transformations for the 3-vector of force, then he applies them for the Coulomb law, after that gets the Lorentz force law with expressions for $\mathbf E $ and for $\mathbf B$ fields, then he takes curl and divergence and, finall... | 6,609 |
<p>I am studying the Fujikawa method of determining the chiral anomalies in a $U(1)$ theory. As we know the basis vectors selected are the eigenstates of the Dirac operator. One of the reasons given is that the eigenstates diagonalize the action which is needed for determining an exact quantity such as Ward-Takahashi i... | 6,610 |
<p>Through what I learned from school, frequency $f=\frac1T$ while $T$ is the period. However, things get harder in college where there are non-periodic signal. That means they have no period or their period is extended to infinity but they still have frequency. How can they have frequencies even there is no period to ... | 6,611 |
<p>This theory has bugged me ever since my first physics class on the subject. If this (<a href="http://en.wikipedia.org/wiki/Kinetic_theory" rel="nofollow">http://en.wikipedia.org/wiki/Kinetic_theory</a>) is true, it leads me to a few weird conclusions.</p>
<p>Opening the rear window in a pickup truck at 10 m/s doesn... | 6,612 |
<p><strong>If any equations are there ,for split the light particle, means
that i have a 1m length of light just consider that in that who can i
split the light particle into 1/2 m length Pls tell</strong> </p> | 6,613 |
<p>While watching a <a href="http://en.wikipedia.org/wiki/Schlieren_photography" rel="nofollow">Schlieren</a> video of a <a href="https://www.youtube.com/watch?v=4CR22kpG3ig" rel="nofollow">hand clapping</a>, I noted a very distinct difference between a sound wave and a puff of air, which were both created by a hand cl... | 6,614 |
<p>I am reading the original paper by Bondi, van der Berg and Metzner (<a href="http://rspa.royalsocietypublishing.org/content/269/1336/21" rel="nofollow">link</a>) regarding gravitational waves in asymptotically flat axisymmetric spacetimes. In the introduction, he makes the following comment - </p>
<blockquote>
<p... | 6,615 |
<p>Suppose we have a material point. If it is moving from position $X_0$ with initial velocity $V_0$ and constant acceleration $A$, then from elementary physics course I remember that its movement is described by the equation</p>
<p>$$X(t) = X_0 + V_0t + At^2/2.$$</p>
<p>Now, my question is, what is the equation of t... | 228 |
<p>The light traveling a 3 lake km/sec, but Pls tell me how can a control the speed of light, means can limit the speed like 2 lake km/sec are 1 lake km/sec </p>
<p>Pls tell me equation</p> | 6,616 |
<p>Given a black hole of some size, say $10^8$ solar masses, how can the size of its sphere of influence of light be calculated?</p>
<p>To clarify, ultimately I'd like to be able to calculate the apparent angle of a black hole's lensing effects, as viewed from some distance.</p>
<p>(I'm no physicist, so I might be ma... | 6,617 |
<p>How would I figure the needed pressure differential to freeze water inside a cooler using ambient air? I am assuming that the combined gas law would apply here and that the formula P1•V1/T1=P2•V2/T2 would provide the answer. My understanding is that by lowering the pressure I could effectively lower the temp as well... | 6,618 |
<p>I have measured the total activity from a radioactive sample during an experiment by counting the number of decays happening in 3 seconds intervals. I got data as:</p>
<p>Time bin: 0 1 2 3 4 5 6 7 ... <br>
Count number: 307 294 257 246 250 216 186 169 ...</p>
<p>Now I want to curve fit an exponential $ae^{bt}$ to ... | 6,619 |
<p>I'm trying to calculate the initial velocity $v_0$ and angle $\theta$ for a given destination $(x, y)$ with a launch height of $y_0$. Obviously there will be a set of pairs of velocity and angle that will pass through the destination point. This set is given by
$$ \left\{(v_0,\theta) \middle|y = - \frac{g}{2 v_0^2 \... | 6,620 |
<p>I was laying on my bed, reading a book when the sun shone through the windows on my left. I happened to look at the wall on my right and noticed this very strange effect. The shadow of my elbow, when near the pages of the book, joined up with the shadow of the book even though I wasn't physically touching it. </p>
... | 6,621 |
<p>I am trying to prove that the momentum $p_x$ operator is Hermitian, my approach is the following</p>
<p>$$<p_x>~=~\int \Psi^*(\vec{r},t)[-ih\frac{\partial}{\partial x}]\Psi(\vec{r},t)\, d^3r.$$</p>
<p>I try to do integration by parts but I cannot resolve the differential, as the integration is in respect to ... | 6,622 |
<p>Please bear with this experimentalist trying to understand the subtleties of TIs in what may well be imprecise language. I appreciate that one can deduce the topological trivial or non-trivial nature of a filled band for particular crystalline structures by virtue of $(-1)^{\nu_0} = \Pi \delta_i$ taken over the <a h... | 6,623 |
<p>I want to know how a ceramic transparency is mostly affected by the pores, grain boundary, second phases etc. present inside of it, but the major contribution is due to the pores. </p>
<p>Let's consider the glass slab with an air gap between them. It is still transparent.</p>
<p>Hence: how can simple pores make ce... | 6,624 |
<p><strong>Edit 26/Sept/13: Fixed Typo in potential</strong></p>
<p>I'm solving the following (seemingly simple) quantum-mechanical problem in <em>four spatial dimensions</em>. In natural units ($\hbar^2/2m=1$), the Schrödinger equation reads:</p>
<p>$$
\Big[-\nabla^2-\frac{24 R^2}{(\mathbf{x}^2+R^2)^2}\Big]\psi(\ma... | 6,625 |
<p>I want to solve the TISE of a particle of charge $q$ and mass $m$ in a one dimensional triangular potential, with an infinitely high potential wall at $x = 0$, i.e.</p>
<p>$$\hat{H}=-\frac{\hbar^2}{2m}\frac{\partial^2}{\partial x^2}+V(x),$$
with</p>
<p>$$V\left(x\right)=\begin{cases}qEx&{\rm if}\,x>0 \\
... | 6,626 |
<p>What I want:
I have a rubber rope which is $5m$ in length when not stressed and is able to stretch about $100\%$ (to $10m$ long). I want to accelerate a constant mass horizontally, which has negligible friction. I'd like to have a function that tells me the velocity of the mass dependent on time, so for instance vel... | 6,627 |
<p>In light-front QFT, in the Minkowski space, we define a hypersurface, $\Sigma_+ : x^3+ x^0 = 0 $. How can I write its parametric equations? </p> | 6,628 |
<p>How much energy is derived from the full process from hydrogen-1 fused into helium-4? Including all the sub-reactions (H1 into Deuterium, etc).</p> | 6,629 |
<p>In a typical photon experiment the photon is depicted as moving across the page, say from right to left.
Suppose we were actually able to witness such an experiment, from the side (to position of reader to a page).
If the photon is actually moving from left to right can I, standing at 90 degrees to the motion, see ... | 6,630 |
<p>What are the quantum mechanisms behind the emission and absorption of thermal radiation at and below room temperature? If the relevant quantum state transitions are molecular (stretching, flexing and spin changes) how come the thermal spectrum is continuous? What about substances (such as noble gases) which don't fo... | 6,631 |
<p><em>[insert obligatory statement of my lack of knowledge in physics]</em></p>
<p>Alright, so we have all seen the movies where someone gets blasted out of the airlock on their starship, or their suit decompresses while on a space walk. The poor schmoe usually either decompresses so violently that blood is oozing ou... | 6,632 |
<p>Given some observable $\mathcal O \in \mathcal H$ it is simple to construct a CP (completely positive) map $\Phi:\mathcal{H}\mapsto \mathcal{H}$ that conserves this quantity. All one has to observe is that
$$ \text{Tr}(\mathcal O \, \Phi[\rho]) = \text{Tr}(\Phi^*[\mathcal O] \rho).$$
Therefore, if we impose $\Phi^*[... | 6,633 |
<p>I need to find the possible values of energies and impulses of virtual photon emitted by real electron. I don't understand how to compute it (look to the text below). </p>
<p>Let's introduce the free electron. Then let's use the frame in which it is at rest. </p>
<p>So the laws of energy-momentum conservation take... | 6,634 |
<p>Quantization of gravity (general relativity) seems to be impossible for spacetime dimension D >= 4. Instead, quantum gravity is described by string theory which is something more than quantization (for example it introduces an infinite number of fields). More direct approaches to quantization of gravity have failed ... | 6,635 |
<p>Does the PV regulator breaks SUSY? </p>
<p>Take for instance the 1-loop (top/stop loops) correction to the Higgs squared-mass parameter in the MSSM, and you'll get something like, </p>
<p>$$\delta m^2_{h_u} = - 3Y_u^2/(4 \pi^2) m_{\tilde{t}}^2 ln (\frac{\Lambda_{PV}^2}{m_{\tilde{t}}^2})$$ </p>
<p>Where, $\Lambda_... | 6,636 |
<p>The traditional (not taking into account phasor addition or complex addition) application of Kirchoff Voltage law, i.e. $\Sigma\Delta V=0$ along a loop, does not work for AC circuits. We can sum the voltage drops to zero if we take into account their phase differences. But at some particular time, no matter what the... | 6,637 |
<p>I hope this is the right forum to ask this question. Is there a material (preferably thin, like a membrane) that changes its local conductivity (by that I mean the permeability for an electric field; I hope it's the right term) upon excitation with light or heat? I have no idea where to start my search for something... | 6,638 |
<p>It seems as though I've come across a rather unusual conclusion that could either simply be a misinterpretation or a contradictory discovery. I seem to have found a way to utilize the Heisenberg Uncertainty Principle (HUP) to our benefit to communicate faster than the speed of light (FTL). I am aware of many proposa... | 6,639 |
<p><a href="http://www.google.com/search?q=haldane+conjecture">Haldane's conjecture</a> states that the integer spin antiferromagnetic Heisenberg chains have a gap in the excitation spectrum. However, the dispersion relation of the antiferromagnetic spin wave is $\omega_k\sim k$ in the long wave length limit, meaning t... | 6,640 |
<p>Relativity of Simultaneity seems to be about OBSERVING two events simultaneously (please correct me if I am wrong). </p>
<p>However, as long as the two events are separated by a distance (any distance) then two observers (in the same frame) cannot agree that they happen simultaneously unless they are equidistant fr... | 6,641 |
<p>The water-gas phase transition is said to be similar to the ferromagnetic-paramagnetic phase transition (same set of critical exponents = same universality class). In the former case the order parameter is the difference in the densities, while in the latter it is the magnetization density.</p>
<p>In the magnetic c... | 6,642 |
<p>According to <a href="http://www.ted.com/talks/jeremy_kasdin_the_flower_shaped_starshade_that_might_help_us_detect_earth_like_planets" rel="nofollow">this TED talk by Jeremy Kasdin,</a> Nasa is planning to spend $1bn on a "Starshade" project, where a giant flower shaped metal eclipser 20 meters wide is placed 50k ki... | 6,643 |
<p>I currently have a very limited knowledge of how radiation works etc, but while sat in class the other day, one question occurred to me that even my teacher could not answer.</p>
<p>We have been learning about alpha, beta and gamma radiation. I know that alpha is positive and that makes perfect sense. However, when... | 6,644 |
<p>If I knew the exact value of constant centripetal force and the <strong>average velocity</strong> of an object travelling around a circle for time $t$, would that be enough information to determine the final positon of an object? What I mean is what if I had another object, at the same initial position and with iden... | 6,645 |
<p>My professor said that the $k_BT$ displacement in the energy levels of the band electrons is due to the space-thermal displacement of the potential of the ion host. I think that this displacement is due to the thermal fluctuations of the electromagnetic field coupled to the electron charge.</p>
<p>Who is right?</p> | 6,646 |
<p>Is there any phenomenon where the 'wave description' of the electron's motion is not applicable?</p>
<p>The reason for this question is to find out if there are any situations were quantum wave theories fail. If not, it seems that the Everett's multiworld analysis as described by Coleman, <a href="http://media.phys... | 6,647 |
<p><img src="http://i.stack.imgur.com/orT7X.png" alt="enter image description here"></p>
<p>In the left side example of cantilever brakes, how do I find the tension in strings DE and DC, in terms of T. According to me applying force balance equations, horizontal and vertical forces should be zero</p>
<p>i.e. $T_{DE} ... | 6,648 |
<p>As any light reflected or emitted from objects inside a black hole (if it is possible to be there) does not leave the event horizon and comes back inside, would it be like seeing yourself?</p>
<p>What I mean is that would the light we might emit/reflect return to our eyes and make us sort of look at ourselves? </p... | 6,649 |
<p><a href="http://en.wikipedia.org/wiki/Turbulence" rel="nofollow">Wikipedia</a> states that </p>
<blockquote>
<p><em>Turbulent flow is chaotic. However, not all chaotic flows are turbulent.</em></p>
</blockquote>
<p>Someone give a picture for that?</p> | 6,650 |
<p>Assuming you have container with heat insulation (something like boiler).<br>
You can store water at any temperature <strong>below 100°C</strong>. At these conditions, you can drill a hole into container and <strong>store water at air pressure</strong>.<br>
But when you heat water to tempertature <strong>over 100°C<... | 6,651 |
<p>Need help in understanding the direction of magnetic force in the magnetic field!Totally confused by directions.</p>
<p>Why is it that magnetic force is perpendicular to the direction of magnetic field and velocity of charged particle.
Why is it(force) not in the same direction as the magnetuc field</p> | 6,652 |
<p>I know that if two air bubbles which are formed inside a liquid are somehow joined using something (say a small tube), then, as the bubble with the larger radius has less pressure and the one with the smaller radius has more air pressure, air will flow to the larger bubble from the smaller bubble as the excess press... | 6,653 |
<p>I do not have much experience on this but if an atom has some electrons around nucleus and the atom itself it is moving at some speed does that affect the distribution of electrons around?</p>
<p>I am presuming that the interaction between the nucleus and electrons has a constant speed $c$. Anything I found so far... | 6,654 |
<p>Is the classical doopler effect for light shift equal to $1-v/c$ exact or an approximation of a classical formula? I know that it is an approximation of the relativistic formula, but what was the corresponding classical formula? I ask this because in Einstein's On the Electrodynamics of moving bodies he derives $\sq... | 6,655 |
<p>It's easy for me to imagine that if we brake the front wheel then there is a chance that I'll flip.</p>
<p>On the other hand if I brake the back wheel, there is no way it'll happen no matter how fast I brake.</p>
<p>But whether I brake the front wheel or back wheel, the force I've added is a backward force at the ... | 6,656 |
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