question stringlengths 37 38.8k | group_id int64 0 74.5k |
|---|---|
<p>I'm a beginner of QFT. Ref. 1 states that </p>
<blockquote>
<p><em>[...] The Lorentz group $SO(1,3)$ is then essentially $SU(2)\times SU(2)$.</em> </p>
</blockquote>
<p>But how is it possible, because $SU(2)\times SU(2)$ is a compact Lie group while $SO(1,3)$ is non-compact? </p>
<p>And after some operation, he... | 902 |
<p>I understand what three-phase power is. But when I look at some pictures of a double-circuit-three-phase-power-line I see two or three lines close together? What is the purpose of these lines close together?
(the wires are attached by smaller wires or connectors)</p>
<hr>
<p>Is there a separate alternator for th... | 3,543 |
<p>As a mathematics graduate student whose research area lies in low-dimensional topology (more precisely, invariants of 3-dimensional topological manifolds), I heard that there exist multiple applications of this theory to theoretical physics, and moreover, that many mathematical problems in the field actually arise f... | 99 |
<p>I woke up this morning thinking about spinning discs. Could someone verify whether my reasoning below is correct?</p>
<p><strong>Problem 1</strong></p>
<p>Suppose have two identical uniform discs constrained to move in a plane. Set disc $A$ spinning about its centre of mass, clockwise viewed from above. Now collid... | 3,544 |
<p>When an index of the Kronecker-delta tensor $\delta_a^b$ is lowered or raised with the metric tensor $g_{ab}$, i.e. $g_{ab}\delta^b_c$ or $g^{ab}\delta_b^c$, is the result another <a href="http://en.wikipedia.org/wiki/Kronecker_delta" rel="nofollow">Kronecker-delta tensor</a>?</p> | 3,545 |
<p>Two observers A and B, in different initial system describe the same physical event with their particular, different space time coordinates . Let the coordinate of the event be $x^\mu$ for observer A and ${x^\prime}^\mu$ for observer B .Both coordinates are connected by means of the Lorentz transformation.
$${x^\pri... | 3,546 |
<p>I'm in grad school and notice there are no prerequisites required for QFT in the physics department. In fact, the system allows me to sign up for the course just fine as a technical elective.</p>
<p>But... my field is chemical engineering and I've only taken basic quantum mechanics. I would really love to learn m... | 3,547 |
<p>My questions are in italics. In the article [1] a dimensional regularization is presented on an electrostatic example of an infinite wire with constant linear charge density $\lambda$. It is shown that the direct computation of the scalar potential gives infinity:
$$
\phi({\bf x})
= {\lambda\over 4\pi\ep... | 3,548 |
<p>In doing a little research into natural background radiation, I came upon a table from the National Council on Radiation Protection and Measurement (NCRP). It shows that inhaled radon gas is by far the largest contributor to average annual dose equivalent from background radiation, for people living in the United St... | 3,549 |
<p>I am trying to find the potential $V$ inside a sphere using the method of image charges.</p>
<p>I have a conducting spherical shell. The charge $q$ is inside the sphere. The sphere is ungrounded and is an equipotential because it is a conductor. </p>
<p>If I place an image charge $q'$ outside the sphere, I can mak... | 3,550 |
<p>When I look at electric or magnetic fields, each of them has a constant that defines how a field affects or is affected by a medium. For example, electric fields in vacuum have a permittivity constant $ϵ_0$ embedded in the electric field expression of a point charge: $E = q/4π ϵ_0r^2$. However, if I put this point c... | 3,551 |
<p>If I look at Hooke's law as it's defined in my textbook, it looks like:</p>
<p>$F = -k\Delta s$</p>
<p>Therefore, the restoring force of an ideal spring will be proportional to the displacement from equilibrium, where $k$ will be the constant of proportionality. From this equation, I believe that it can't be said ... | 3,552 |
<p>I am having trouble understanding how centripetal force works intuitively.</p>
<p>This is my claim.</p>
<p>When I have a mass strapped on a string and spin it around, I feel the mass pulling my hand.
So, I want to say that the mass is trying to move away from the center of the circle, and yet centripetal force mak... | 727 |
<p>In <a href="http://en.wikipedia.org/wiki/Special_relativity" rel="nofollow">SR</a>, the interval $I$ between two spacetime events is called <em>light-like</em> if $I=0$.
Griffiths in his <em>Introduction to Electrodynamics</em> book says that [page 503],</p>
<blockquote>
<p><em>If $I=0$ we call the interval ligh... | 3,553 |
<p>I have read that we need all operators in QM to be linear to confirm the principle of superposition which is experimentally well proven. I wonder how such an experiment could be made?</p> | 100 |
<p>Consider the following Hamiltonian which describes massless Dirac fermion on the surface of a topological insulator nanowire,
$$H = -i\hbar v_{F}\left[ \partial_{x}\sigma_{x} + \frac{\sigma_{y}}{R}\left( \partial_{\phi} + i\eta\right)\right]\ \text{.}$$
The nanowire has translational symmetry in $x$-direction and $\... | 3,554 |
<p>I feel disturbed by this question: Suppose $A$ and $B$ are POVM's with respective $\sigma$-algebras $\mathcal{F}_A$ and $\mathcal{F}_B$ and outcome spaces $\Omega_A$ and $\Omega_B$. Then why can't I take the following POVM $Z = A\cdot B$ defined on $\mathcal{F}_A \otimes \mathcal{F}_B$ as the joint measure? I mean i... | 3,555 |
<p>I'm developing an app that contains a 3D scene which the user can navigate. As the user moves it gives the illusion that you are browsing a real landscape but for the illusion to work I need to know two things:</p>
<ol>
<li>How to calculate the angular sizes of all the objects relative to their distances from the o... | 3,556 |
<p>Is there any optical component in existence that uniformizes randomly pointing rays?</p>
<p><img src="http://i.stack.imgur.com/IIXrV.jpg" alt="The component (greenish-yellow) takes in random light and uniformizes it. Light is traveling from left to right"></p> | 3,557 |
<p>I understand the energy and mass can change back and forth according to Einstein. It is fluid; it can go from one to the other. So, what keeps mass from just turning into energy? Is there some force holding a subatomic particle together? What keeps mass in it's state? I hope this is not a silly question but I am clu... | 67 |
<p>I've seen plans for a pendulum oscillator water pump that is claimed to pump a large volume of water (100 gallons) from a well of 100 feet deep. The pendulum consists of a 100 pound weight raised 6 feet. A second 20 pound weight is hoisted up a pole 20 feet high. This second weight powers a mechanism which gives ... | 3,558 |
<p>How can we show that the Einstein-Hilbert action is Parity invariant? $$
S_{EH}=\int \sqrt{-g}R d^4x $$ </p> | 3,559 |
<p>We can calculate the current density $\mathbf{j}$ of the electron in Hydrogen, and it is given by:
$$
j_\phi=-e\frac{\hbar m}{\mu r\sin\theta}\left|\psi_{nlm}\left(r,\theta,\phi\right)\right|^2
$$
(<a href="http://www.phys.spbu.ru/content/File/Library/studentlectures/schlippe/qm07-05.pdf" rel="nofollow">derivation f... | 3,560 |
<p>The equations I'm using are:</p>
<pre><code>x = x + (DT * vx)
vx = vx * C
</code></pre>
<p>My DT is always 0.01 and the coefficient <code>C</code> (related to a linear drag coefficient, as mentioned in the comments) is greater than 0 and less than 1. The above will keep happening until x naturally reaches its limi... | 3,561 |
<p>Let me first say that I am not a physicist, but I am trying to make a simulation on my computer and I have the following question.</p>
<p><img src="http://i.stack.imgur.com/24umY.jpg" alt="enter image description here"></p>
<p>Let's consider that we have three free charges that somehow can change their charge in t... | 3,562 |
<p>Given the formula</p>
<p>$$\frac{{\Delta}(KE)}{KE_i}=\frac{(KE_f-KE_i)}{KE_i}=\frac{-M}{(m+M)}$$</p>
<p>Now I know these that the conservation of momentum is always applicable. Also I understand that</p>
<p>$$KE=\frac{1}{2}mv^2$$
and
$$p=mv$$
When trying to solve it I get
$$\frac{m_2(v_2)^2}{m_1(v_1)^2}-1$$</p>
... | 3,563 |
<p>Say I have a hollow cylinder and I wanted to strap it down to the bed of a truck. I would tension the strap on one end, and it would exert a force on the cylinder. My intuition tells me that the strap would crush the hollow cylinder down toward the truck bed, but when I think about it, there are inward forces perpen... | 3,564 |
<p>Looking directly at a welder is dangerous because large amounts of UV light is produced. What makes this light? Is it electrons from the current that excites metal atoms, and these atoms sends out UV light? Or does the extreme heat have anything to do with this?</p>
<p>Is it dangerous to look directly at a nail bei... | 3,565 |
<p>I know that I can use conservation of energy to find the velocity of a particle at a point when it's travelling in a vertical circle by saying</p>
<p>$$mgr(1-\cos{\theta})=\frac{1}{2}mv^2$$</p>
<p>then rearranging to get $v=\sqrt{2gr(1-\cos{\theta})}$</p>
<p>But I want to see this done 'the long way' using newton... | 3,566 |
<p>I have tried this question every way I can think but in the equation for particle $L$ $g$ cancels every time. Could someone show me how to do it correctly or tell me what I am doing wrong. Thanks,</p>
<p>The Question:</p>
<blockquote>
<p>A string with negligible mass passes over a smooth pulley V with a
part... | 3,567 |
<p>I am reading Berkeley Physics Course, Volume 2 (Electricity and Magnetism
by Edward M. Purcell).</p>
<p>I am in chapter $3$ pg $92$, and the book discusses conductors.</p>
<p>The following is from the book:</p>
<p>Because the surface of a conductor [in Fig $3.2$] is necessarily
a surface of constant potential, th... | 3,568 |
<p>Is "second quantization" means system wich can contain variable, unknown, superposed and otherwise uncertain number of qubits?</p>
<p>Can "second quantized" system contain 0.5% of 1 qubit and 95% of 2 qubits?</p>
<p>Does this mean that quantum field state cannot be described with quantum computer with fixed number... | 3,569 |
<p>I have the transformation law of the Lorentz group for Pauli matrices:
$$
\tag 0 (\sigma^{\mu})_{a \dot {a}}{'} = \Lambda^{\mu}_{\quad \nu} N_{a}^{\quad c}(\sigma^{\nu})_{c \dot {c}}(N^{-1})^{\dot {c}}_{\quad \dot {a}},
$$
where
$$
N_{a}^{\quad c} = 1 + \frac{1}{2}\omega_{\mu \nu}\sigma^{\mu \nu}, \quad N^{\quad \d... | 3,570 |
<p>An answer to the question <a href="http://physics.stackexchange.com/q/133301/25794">If we could build a neutrino telescope, what would we see?</a> contains a <a href="http://apod.nasa.gov/apod/ap980605.html">link to a neutrino image of the sun </a> by the Super-Kamiokande neutrino detector. </p>
<p><img src="http:/... | 3,571 |
<p>In quantum optics, the output from a laser is modelled using a coherent state; what are some orders-of-magnitude for the complex parameter (usually denoted $\alpha$) of the coherent state corresponding to real laser fields used in experiments?</p> | 3,572 |
<p>I am somewhat confused about this topic. </p>
<p>It is usually explained how magnetic fields avoid breaking time reversal symmetry by the example of a field produced by a circulating charge current - run time backwards, the current direction is reversed and so is the field.</p>
<p>But what about the moment associa... | 3,573 |
<p>My car has proximity sensors to help me park. I've noticed that when motorcycles whiz past me the proximity alarm goes off. I originally though that the motorcycles were just too close, but now I have observed that that isn't the case; cars or other road uses at a similar distance and speed do not set off the sens... | 3,574 |
<p>Does the subadditivity (and <a href="http://en.wikipedia.org/wiki/Strong_Subadditivity_of_Quantum_Entropy" rel="nofollow">strong subadditivity</a>) of quantum entropy hold for infinite dimensional quantum systems as well? Unfortunately the books in my hand give proof for finite dimensional cases only and I could not... | 3,575 |
<p>There is some porous dielectric membrane with strictly vertical cylindrical pores. I would like to find theoreticaly optical transmission spectra of this membrane, depending on the bulk material optical dispersion, radius and height of cylindrical pores and the distance between their centers.</p>
<p>In result I wa... | 3,576 |
<p>If we have two inertial frames $S$ and $S'$ and $S'$ is moving to the right w.r.t. $S$ with a velocity $v$. Suddenly $S$ undergoes negative acceleration (no longer being inertial) and after some time the acceleration stops when the frame has reversed its velocity. How much will be the time difference between two, pr... | 3,577 |
<p>I want to make a finite element analysis of a cold airflow through warmer pipes. In particular I want to see how the pipes cool down and the air heats up, as it travels through the pipes. Wich are the equations and boundary conditions that I have to consider?</p>
<p>I assume that the velocity field is already given... | 3,578 |
<p>Is there any good software for construction optical path's in geometrical optics. More specifically I want features like:</p>
<ul>
<li><p>draw $k \in \mathbb{N}$ objects $K_1,\dots,K_n$ with indices of refraction $n_1,\dots,n_k$ and light sources $l \in \mathbb{N}$ light sources $L_1,\dots,L_l$</p>
<p>-- draw for ... | 812 |
<p>Can we say that we are crystals because just like crystals we are made up of very small unit (cell) making up almost the same shape (our body) everywhere.</p> | 3,579 |
<p>Why massless particles have zero chemical potential?</p> | 93 |
<p>I made a metal cylinder that is the <strong>SAME</strong> size as my 400g propane cylinder (picture: <a href="https://2ecffd01e1ab3e9383f0-07db7b9624bbdf022e3b5395236d5cf8.ssl.cf4.rackcdn.com/Product-800x800/7a66c8cb-d697-4680-9321-fcb73ede75c9.jpg" rel="nofollow">here</a>). I want to transfer <strong>ALL</strong> (... | 3,580 |
<p>This refers to the discussion about <a href="http://en.wikipedia.org/wiki/Gravitational_wave" rel="nofollow">gravitational waves</a> for the YouTube video <em><a href="http://www.youtube.com/watch?v=RzZgFKoIfQI" rel="nofollow">LIGO Gravitational Wave Observatory</a></em>.</p>
<p>I have two questions:</p>
<ol>
<li>... | 3,581 |
<p>When using the ray trace methodology to solve a given thin lens question, does the arrow (commonly used as the example object when tracing) represent the literal height of the object or the perceived height of the object relative to the lens? Refresher image below:
<img src="http://boson.physics.sc.edu/~rjones/phys1... | 3,582 |
<p>I am in grade 10.
I have developed an interest in physics but unfortunately I do not know/ have not studied calculus yet as my school board does not recommend it in grade 10.
I have a copy of fundamentals of physics, <a href="http://www.google.com/search?as_q=halliday+resnick+walker" rel="nofollow">Halliday Resnick ... | 3,583 |
<p>As Galaxies travel through the universe, how do they orient? </p>
<p>And, does this orientation apply to stars and their satellites?</p>
<p>that is to ask if the movement of a galaxy or star is perpendicular to its satellites and its rotation.. </p>
<p>One might even compare this proposed action to that of a torn... | 3,584 |
<p>I read somewhere that part of Minkowski's inspiration for his formulation of Minkowski space was Poincare's observation that time could be understood as a fourth spatial dimension with an imaginary coefficient.</p>
<p>Clearly, taking the Euclidean norm of the vector $$(i \Delta t, \Delta x, \Delta y, \Delta z)$$ gi... | 3,585 |
<p>The strong force acting between quarks and responsible for holding protons together is 100 times stronger than the electromagnetic force. How come the nuclear binding energy derived from the strong force is millions time stronger than chemical energy. (rather than 100 times)</p> | 3,586 |
<p>I wish to understand <a href="http://arxiv.org/pdf/1008.0654v2.pdf">the statement in this paper more precisely</a>:</p>
<blockquote>
<p>(1). Any 3d Topological quantum field theories(TQFT) associates an inner-product vector space $H_{\Sigma}$ to a Riemann surface $\Sigma$. </p>
</blockquote>
<p>-</p>
<blockquote... | 3,587 |
<p>A simple boost in the $x$ direction is given by:
$$ \Lambda = \begin{pmatrix}
\cosh(\rho) & \sinh(\rho) & 0 & 0 \\
\sinh(\rho) & \cosh(\rho) & 0 & 0 \\
0 & 0 & 1 & 0 \\
0 & 0 & 0 & 1 \\
\end{pmatrix} $$</p>
<p>Which get linearized to the following transformation:
$$
x... | 3,588 |
<p>I have a doubt about how double slit experiment is made.</p>
<p>Let's think about the perforated wall, what are the requirement for it?</p>
<p>Can a photographic plate could be used as a wall ?</p>
<p>I see a problem here, as a photographic plate serve also as a detector, then the single photon experiment could e... | 3,589 |
<p>Hubble's law states that $v=Hx$</p>
<p>Age of the universe is calculated by $T= \frac{x}{v} = \frac{1}{H}$</p>
<p>but the velocity is not constant; it changes with distance, so I think that this equation cannot be applied because simply the velocity is NOT uniform</p>
<p>$v$ should have been replaced with $\frac{... | 3,590 |
<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://physics.stackexchange.com/questions/9354/question-about-time-dilation">Question about Time Dilation..</a> </p>
</blockquote>
<p>I have a question about special relativity which was bothering me for a while now. I know that as one approache... | 101 |
<p>Is there a good chance that gravitational waves will be detected in the next years?</p>
<p>Theoretical estimates on the size of the effect and the sensitivity of the newest detectors should permit a forecast on this.</p> | 357 |
<p>After spending hours understanding what exactly Black Body radiation and Ultraviolet catastrophe is, I cannot help myself asking what was the reason that make scientists such as Wilhelm Wien and Max Planck to study Black Body Radiation at the first place? What intrigue them to study a hypothetical situation? What th... | 3,591 |
<p>Given the Hubble slow-roll parameters $\epsilon=-\frac{\dot{H}}{H^{2}}$ and
$\eta=\frac{\dot{\epsilon}}{H\epsilon}$, can they assume negative values? For inflation to occurr they are required to be small but what about their sign?
Thanks in advance.</p> | 3,592 |
<p>I was wondering if someone can explain why E is the way it is in cases 2,3,4 in page 9 of these <a href="http://www.maths.gla.ac.uk/~drf/courses/mhd/lect4.pdf" rel="nofollow">notes</a> ?</p>
<p>In case 2 "Short Circuit", do I just have to assume that for a perfect conductor E = 0 for short circuit ?</p>
<p>I don't... | 3,593 |
<p>It is well know that planewaves are a complete basis for solutions to the wave equation. Let us assume a 2D space, and at fixed temporal frequency, the equation reduces to the Helmholtz equation. In cylindrical coordinates, the most appropriate solutions are the two kinds of Hankel functions, representing outgoing a... | 3,594 |
<p>When two tuning forks stand near one another and one is excited, the other rings as well. When high notes are struck on a piano, lower notes are also heard. If I understand correctly, this is called <a href="http://en.wikipedia.org/wiki/Sympathetic_resonance" rel="nofollow">sympathetic resonance</a>.</p>
<p>What ... | 3,595 |
<p>Consider a supersonic plane (mach 2) aproaching a stationary sound source (e.g a fog horn on a boat).</p>
<p>If I understand it correctly, the passengers in the plane can hear the sound twice. First at a 3 times higher frequency, and then (after they passed the source) a second time at normal frequency but backward... | 3,596 |
<p>My son who is 5 years old is asking me a question about how the earth moves around the sun. What answer should I give him?</p> | 3,597 |
<p>I'm working on an article about propagators from int. representations of Green`s functions for several N-dimensional potential(all this is done in an N-dimensional Euclidian space). Potentials like the free-particle, harmonic oscillator, Coulomb and Poschl-Teller. I started from the radial equation which is satisfie... | 3,598 |
<p>I'm looking at Kopfermann H., Ladenburg R., Nature, 122, 338-339 (1928) and it appears Ladenburg in Ladenburg R., Z.Physik, 4, 451-468 (1921) was the first to discover the phenomenon of "negative dispersion" and/or "negative absorption" which is at the basis of the laser theory. That idea is present in as early as ... | 3,599 |
<p>Consider a field redefinition
$$
\phi \rightarrow \phi' = \phi+\lambda \phi^2
$$
Find the Feynman rules for this theory and work out the $2\rightarrow 2$ scattering amplitude at tree level (The result should be zero).</p>
<p>$$
\mathcal{L}_0 = -\frac{1}{2}(\partial^\mu \phi \partial_\mu \phi + m^2 \phi^2) \implies ... | 3,600 |
<p>In perspective of thermodynamics,a person can survive a temperature of twenty degrees Celsius in air, but a person cannot survive in water with same temp.(it's not because he can't breathe) why is that in perspective of thermodynamics??</p> | 3,601 |
<p>I have this graph of a gas:</p>
<p><img src="http://i.stack.imgur.com/DMQlN.jpg" alt="gas graph"></p>
<p>Now, I need to calculate work of it, based on ABCD cycle of changes (that's a bit confusing to me, do I calculate AB, BC, CD separately?). How do I do it?</p>
<p>Also, how can I calculate heat of this gas need... | 3,602 |
<p>When water freezes continuous translational symmetry is broken. When a metal becomes superconducting, what is the symmetry that gets broken?</p> | 3,603 |
<p>I realize that the question a rather large paradox, but I do wonder if such a thing were true what would happen. Assuming that neither of these "objects" can be destroyed by each other. </p> | 3,604 |
<p>Please explain from:
mathematical point of view "laws of mathematics", and, physical point of view "laws of physics"? Or is there any bound on number of dimensions?</p> | 3,605 |
<p>A system of solar panels are fixed on top of a large water tank of height $40m$ and area $10m^2$. Atmospheric pressure is $100kPa$. What is the pressure at the bottom of the tank? The density of water is $\rho =1000kg/m^3$ and $g=10m/s^2$.</p>
<pre><code>a 10kPa
b 1000kPa
c 2000kPa
d 200kPa
e 1kPa
</code></pre>
<p... | 3,606 |
<p>Connes's noncommutative geometry program includes an <a href="http://www.alainconnes.org/docs/einsymp.pdf">approach to the Standard Model</a> that employs a noncommutative extension of Riemannian metric. In recent years I've heard physicists say that this approach does not hold significant interest in the physics co... | 3,607 |
<p>Prove <a href="http://en.wikipedia.org/wiki/Biot%E2%80%93Savart_law" rel="nofollow">Biot-Savart law</a>, assuming that
$$\vec{A}=\frac I c\int \frac{d\vec{L}}{r}$$
$$\vec{B}=\nabla\times \vec{A}$$
Any hint on what to do next?</p> | 3,608 |
<p>The collision term in the Boltzmann equation can be derived from the BBGKY hierarchy. </p>
<p><a href="http://en.wikipedia.org/wiki/BBGKY_hierarchy" rel="nofollow">Wikipedia</a> says:</p>
<blockquote>
<p>In statistical physics, the BBGKY hierarchy [...] is a set of equations describing the dynamics of a system o... | 3,609 |
<p>How do I calculate the angle of Inclination for a specific location on the Earth? The only Information I've got is the longitude and latitude in degree, so I do not understand. I now <code>I=arctan(Z/H)</code> if I have three components <code>X(=north), Y(=east) and Z(=down=vertical intensity)</code>.
But then, how ... | 3,610 |
<p>It seems I am stuck with a (at a first sight) trivial problem. </p>
<p>It's from the <em>"Quarks and Leptons" (Halzen, Martin)</em> book page $141$, where one considers the following integral: </p>
<p>$$\tag{1} T_{fi} = -i\int \!d^4x \, J_0^A(t_A,\vec{x}_A)\,J_0^B(t_A,\vec{x}_A)\frac{1}{|\vec{q}|^2}. $$
In equatio... | 3,611 |
<p>my question concerns the kinematics of 2 to 2 particle scattering. I refer to Peskin and Schroeder eq.17.59 going from this expression</p>
<p>$\frac{d^3\sigma}{dy_3dy_4dp_T}=x_1f_1(x_1)x_2f_2(x_2)\;2p_T\frac{d\sigma}{d\hat{t}}(1+2\to3+4)$</p>
<p>to this</p>
<p>$\frac{d^4\sigma}{dy_3dy_4d^2p_T}=x_1f_1(x_1)x_2f_2(... | 3,612 |
<p>In <a href="http://en.wikipedia.org/wiki/Quantum_mechanics" rel="nofollow">Quantum mechanics</a> , a <a href="http://en.wikipedia.org/wiki/Quantum" rel="nofollow">quantum</a> of energy called <strong>Quanta</strong> is origin of everything.</p>
<blockquote>
<p>In physics, a quantum (plural: quanta) is the minimu... | 507 |
<p>I am new to electron spectroscopy. I have a basic question regarding the molecular transition. I have learned about the states $\Sigma_g^+$ $\Pi_g$.. etc electronic states. But I could never find in any books the states like $a^3B_2$, $b^3A_2$ and $A^1A_2$ states! For example, I am attaching a part from from the pag... | 3,613 |
<p><img src="http://i.stack.imgur.com/nk6qd.png" alt="parabolic profile"></p>
<p>How do I compute the velocity field around the parabolic body using Navier-Stokes? I want to solve it like Poiseuille's law. </p>
<p>I have no slip at the wall boundary and a free shear layer at the boundary between the parabola and the... | 3,614 |
<p>Do static charge in a strong insulator flow to a weaker insulator when both stay in contact with each other? For example, when an insulator weaker than air placed in a medium of air, would the static charges on the insulator be absorbed to the air slowly and finally the insulator becomes neutral? If so then what is ... | 3,615 |
<p>I am a math grad student who would like to learn some classical mechanics. The caveat is I am not to interested in the standard coordinate approach. I can't help but think of the fields that arise in physics are actually sections of vector bundles (or maybe principal bundles) and would love an approach to classical ... | 277 |
<p>I have always wondered about applications of Algebraic Topology to Physics, seeing as am I studying algebraic topology and physics is cool and pretty. My initial thoughts would be that since most invariants and constructions in algebraic topology can not tell the difference between a line and a point and $\mathbb{R}... | 99 |
<p>I've seen several popular reports of a new count of low-mass stars in elliptical galaxies (<a href="http://www.usatoday.com/tech/science/space/2010-12-01-dwarf-stars_N.htm" rel="nofollow">here's one</a>).</p>
<p><strong>Edit:</strong> Pursuant to several correct comments I've changed the title to agree with the act... | 3,616 |
<p>I saw this equation today when calculating energies of photons of different frequencies, and noticed that the change in energy is a product of plank's constant and frequency. $$\Delta e = h * \nu $$ but what is the change in energy with respect to? since a change would be having some initial state $ e_f - e_i$ e sub... | 3,617 |
<p>In a <a href="http://physics.stackexchange.com/questions/134533/measuring-more-accurately-the-distance-of-remote-galaxies">previous question</a>, one issue was related to the potential energy
of cosmic structures. This raised in particular the question of
whether these structures are gravitationally bound.</p>
<p>I... | 3,618 |
<p>Yes in a recent paper I have derived Lorentz force from Maxwell equations. This is available at <a href="http://cpb.iphy.ac.cn/EN/abstract/abstract52454.shtml" rel="nofollow">http://cpb.iphy.ac.cn/EN/abstract/abstract52454.shtml</a>
best wishes</p> | 3,619 |
<p>Very basic question.... I know that GAMESS can be used to compute localized molecular orbitals, using for example Boys equation; how does one use the program to get the resulting coefficients used to mix the basis functions. </p> | 3,620 |
<p>I heard that at Quantum level events can happen out of order making causality invalid. Thus the future can happen in present and the present in the future. Is this true?</p> | 3,621 |
<p>What is the speed of a car going v=1.000 mile per hour in SI units? You can do each conversion separately. Use the facts that 1mile=1609 meters and 1hour=3600 seconds.
Express your answer in meters per second to four significant figures.</p>
<p>Okay first I set the problem to the right conversions.
I do this</p>
<... | 3,622 |
<p>You see the poles of a magnet on every magnet picture, and they are said to be in the direction of magnetic field lines, but what does that mean? Is the number of electrons different on one side of the magnet? If electrons only repel each other how do they act like magnets?</p> | 3,623 |
<p>I was reading some <a href="http://physics.stackexchange.com/search?q=postselect%2a">questions here</a>. </p>
<p>I couldn't understand what it means by postselection.</p>
<p>What is postselection? What is its use/significance? Where did it came from? </p> | 3,624 |
<p>Feynman says in his book "QED" that the square root of the fine structure constant is the probability for a charged particle to emit a photon. But for which wavelength? Or is it an average over all wavelengths? </p>
<p>Note: I meant <em>virtual</em> photon, and I meant a stable charged particle, like the electron. ... | 3,625 |
<p>Did anyone ever heard about this?I've never seen any serious physicist talk about "mass fluctuations".</p>
<p>Here is the man in his own words: <a href="http://www.intalek.com/Index/Projects/Research/woodward1.pdf" rel="nofollow">http://www.intalek.com/Index/Projects/Research/woodward1.pdf</a></p>
<p>And what abou... | 3,626 |
<p>What is the underlying reason that the same pairs of conjugate variables (e.g. energy & time, momentum & position) are related in <a href="http://en.wikipedia.org/wiki/Noether%27s_theorem" rel="nofollow">Noether's theorem</a> (e.g. time symmetry implies energy conservation) and likewise in QM (e.g. $\Delta E... | 3,627 |
<p>Is there a convention for chemical symbols of mu-mesic atoms, at least for ones bound to light atomic nuclei?</p> | 3,628 |
<p>When listing energies for the purposes of keeping track of conservation, or when writing down a Laplacian for a given system, we blithely intermix mass-energy, kinetic energy and potential energy; they are all forms of energy, they all have the same units, and so this looks OK. For example, in the LHC, turning kinet... | 3,629 |
<p>Position is relative, as it depends on the reference frame. We usually visualize the sun at the center of the solar system. BUT, we can also visualize the Earth at the center of the solar system, with the sun orbiting around it and the planets orbiting around the sun. Therefore, shouldn't we be theoretically be a... | 102 |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.