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This question was inspired by Abstruse Goose :)
http://abstrusegoose.com/342
It's well known that any attempt to describe the spin (of say an electron) in terms of non-internal spatial coordinates is futile since this is just orbital angular momentum and can't take half-integral values. Spin is currently understood to ... |
Fermilab seems to have ruled out monopoles with mass less than 850 GeV, but I have seen some estimates of the mass thought to be in the order of up to $10^{18}$ GeV, which, of course, would make them undetectable in any accelerators. By 2013, the LHC is scheduled to reach up to 14 TeV. The only disputed sighting of a c... |
Quasiparticles theoretically can form braids on a 2D surface. The braids apparently are quite stable for reasonably long periods, allowing a superposition state more time before it decoheres through environmental interaction. This would be a big step in quantum computing. Has this actually been achieved or is it theory... |
Why are so many condensed matter phenomena so sensitive to impurities? In fact, quite a number of them depend upon impurities for their very existence!
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Well, it does according to this preprint for certain scales.
What would be a simple way to explain MOND to a layman?
Does it ignore mainstream physics? How much?
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Why do we have so many dualities in string theory? Is there a reason for that?
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We suppose for simplicity we have a 1D oscillator, but this is a question about the general CCR in oscillators, second quantization, quantum field theory etc.
We know coherent states form a non-orthonormal overcomplete basis.
We know they satisfy $A |\alpha>=\alpha |\alpha>$, where $|\alpha>=e^{-\frac{|\alpha|^2}{2}} ... |
Context is 1D Ising model. Metropolis algorithm is used for simulate that model. Among all possible spins configurations (states) that algorithm generates only states with the desired Boltzmann probability.
Algorithm chooses spin at random and makes a trial flip. If trial satisfies certain conditions related to Boltzm... |
How much free energy is there in the Earth-ionosphere waveguide resulting from the constant bombardment of lightning strikes all over the Earth, and how do you go about calculating an estimate for it?
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In quantum mechanics the state of a free particle in three dimensional space is $L^2(\mathbb R^3)$, more accurately the projective space of that Hilbert space. Here I am ignoring internal degrees of freedom otherwise it would be $L^2(\mathbb R^3)\otimes S$, but let's say it is not that time of the month. The observable... |
Senior physicists constantly complain they spend too much time on administration, teaching, getting grants, serving in committees, peer-reviewing articles, supervising, etc. . Do senior physicists conduct research by getting their post-docs and graduate students to do all the intensive work for them?
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Are there any projects/experiments running for the observation of topological defects (domain walls, monopoles, etc)?
Are there any past/canceled or future such projects?
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Why is there a breakdown of Kolmogorov scaling in turbulence? What causes intermittency?
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If we couple a Yang-Mills theory with a Higgs field and some quarks in the fundamental representation, we can have a Higgs phase and a confining phase. However, they are indistinguishable. The Wilson loops scale according to the perimeter law, not the area law in the confining phase because of hadronization. In the Hig... |
Baryons in quantum chromodynamics can be described as a bound state of three quarks. But they can also be described as a topological soliton of the pion field. How can both descriptions be equivalent?
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Well, the Possion bracket:
$ \{ A(q,p),B(q,p) \} \equiv \sum_{s} \left( \dfrac{\partial A}{\partial q_{s}} \dfrac{\partial B}{\partial p_{s}} - \dfrac{\partial A}{\partial p_{s}} \dfrac{\partial B}{\partial q_{s}} \right) $
is a coordinate transformation according to the words of this Wikipedia page: (link: http://en.w... |
In Physics ordinary terms often acquire a strange meaning, action is one of them. Most people I talk to about the term action just respond with "its dimension is energy*time". But what is its historial origin?
http://en.wikipedia.org/wiki/Action_(physics)#History doesn't really give much insight, as it lacks citations ... |
What happens when two D-branes annihilate? Do we get a radiation of strings?
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In a lot of laymen explanations of general relativity it is implied that the four dimensions of the space-time are equivalent, and we perceive time as different only because it is embedded in our human perception to do so.
My question is: is that really how general relativity treats the 4 dimensions?
If so - what are t... |
"stability" is invoked as the justification for the axiomatic requirement that the spectrum of the generators of the translation group must be confined to the forward light-cone. The spectrum condition has pervasive, significant effects in axiomatic QFT. There seems to be no proof, however, that the spectrum condition ... |
Is there a detection method in use that can distinguish a neutrino from its anti-neutrino?
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I would like to expand on what I mean by the title of this question to focus the answers.
Normally whenever a theory (e.g. General Relativity) replaces another (e.g. Newtonian Gravity) there is a correspondence requirement in some limit. However there is also normally some experimental area where the new larger theory ... |
How does one build up an intuitive gut feeling for physics that some people naturally have? Physics seems to be a hodgepodge of random facts.
Is that a sign to quit physics and take up something easier?
Thanks for all the answers. On a related note, how many years does it take to master physics? 1-2 years for each leve... |
I just saw this "trick" where a cup of water is turned over onto a table without spilling (using a piece of cardboard. After removing the cardboard from underneath the cup, the person then removes the cup in a particular way (lifts straight up and twists) and lo and behold, the water stays in it's position as if the c... |
Some topological solitons formed from bosonic fields have fermionic statistics. Why?
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It is a question about free carrier behavior in graphene flakes. (or may be called charge confinement)
Say if we have a perfect hexagonal free standing graphene flake terminated with zigzag edges. Since there are two subatoms (let's call them A,B) in every unit cell. Edges will be terminated, let say, ABABAB (as shown ... |
In my previous question I asked how gravity can be represented as dents in space. It seems that it's a metaphor. But I wondered with spac expanding does the effect of gravity get bigger as well, I know from other questions that mass doesn't expand like the gaps between mass do although I have no idea why. So using the ... |
It is well known in racing that driving the car on the ideal "slip angle" of the tire where it is crabbing slightly from the pointed direction produces more cornering speed than a lower slip angle or a higher one.
(More explanation as requested) I'm considering two main effects on the tire when in a turn:
The tread ... |
Does magnetic propagation follow the speed of light? E.g. if you had some magnet of incredible strength and attached an iron wire that is one light year long to it, would the other end of the iron wire begin to show a magnetic field in a year, or could it possibly be faster than a year?
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I'm a bit rusty on my fluid dynamics. I'm experimenting with creating my own leaf vacuum.
How would I determine how much suction a fan creates?
Bernoulli's equation would apply correct?
I would also need a fan curve right?
Does CFM matter much when creating a vacuum?
Ultimately what I'm looking for is the Force @ in... |
Adding milk first increases the volume to heat and lowers average temerature, but adding it afterwards seems to have similar effects. How can you compare the two?
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I have a physics lab tomorrow and I would appreciate it if you could give me your opinion on whether my reasoning is correct for this situation or not:
https://i.stack.imgur.com/WMzA7.jpg
The title of the lab is hydrostatic and is roughly described in the attached pic.
We will take data using different weights to measu... |
How do I go about finding the pressure exerted on a rectangular surface in a free flowing air stream?
I wouldn't imagine that this is directly related to the airspeed / surface area, but have no idea where to start. Is there even an equation, or does one need to do some kind of FEA?
For instance a 1.2m x 2.4m metal she... |
According to the first law of thermodynamics, sourced from wikipedia
"In any process in an isolated system, the total energy remains the same."
So when lasers are used for cooling in traps, similar to the description here: http://optics.colorado.edu/~kelvin/classes/opticslab/LaserCooling3.doc.pdf where is the heat tran... |
I have a question with regard to probabilistic quantum cloning - see for example http://prl.aps.org/abstract/PRL/v80/i22/p4999_1.
It does seems like I can use the proof for no-cloning theorem to disproof the existence of equation (7) in the paper quant-ph/9704020. Do you think this is true?
Suppose probabilistic quantu... |
While reading a paper I ran into this particular way of writing a $\cal{N}=3$ fields (in a theory with $N_f$ hypermultiplets) that I couldn't relate to anything I had seen before in the text-books (typically Weinberg's) The claim is that $q^{Aa}$ and $\psi_{\alpha}^{Aa}$ are scalar and fermions such that $a,b$ are $SU(... |
I have often seen diagrams, like this one on Wikipedia for a thin convex lens that show three lines from a point on the object converging at the image. Do all the other lines from that point on the object that pass through the lens converge at the same point on the image?
*Updated question: * to say, "from that point o... |
I would like to migrate this Math Question into physics. The question is:
Are there conjectures in Physics which have been disproved with extremely large counterexamples? If yes, i would like to know some of them.
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Can a functional derivative be calculated if we have a function of more than one variable?
The functional derivative of, for example, $F[b(x)]=e^{\int_0^{x'} dx a(x,y) b(x)}$ is
\begin{equation}
\frac{\delta F[b(x)]}{\delta b(z)} = a(z,y) e^{\int_0^{x'} dx a(x,y) b(x)}
\end{equation}
But what about if there it's a fu... |
Given a certain running pace uphill, I want to be able to determine an equivalent pace running with no elevation change. Assumptions: similar effort in both cases (say for example running at 90% max heart rate), ignore wind, slope is constant for simplicity, ignore physiological and bio-mechanical factors, weight of th... |
A light modifier that is commonly used in studio photography is a honeycomb grid.
It narrows the beam of light to a circle with soft edges, as it can be seen here:
My question is: how is this happening?
A small reporter flash has a rectangular shape, if you place a rectangular shaped grid on it, it produces a "soft... |
I have been told (not sure if it is true), that mirror (and glass) do not allow to pass the electromagnetic signals of mobile signals.
but for a standard mirror what type of wave can pass through it?
thanks
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Consider the well known demonstration of diffraction by a narrowing slit.
(See for example the demonstration at the 30 minute mark of this lecture at MIT by Walter Lewin)
It is my (possibly mistaken) understanding that the light emerging after the slit becomes substantially slimmer than one wavelength is polarized.
Thi... |
I heard on a podcast recently that the supermassive black holes at the centre of some galaxies could have densities less than water, so in theory, they could float on the substance they were gobbling up... can someone explain how something with such mass could float?
Please see the below link for the podcast in questio... |
Do you know where can I find simple diagram (solid, liquid, gas) for for oxygen?
EDIT: I made a mistake. I wanted oxygen instead of water. sorry.
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Can anyone give a brief overview of what a wimpy particle is?
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ABS systems work by allowing a tire to continue to rotate rather than "locking-up" (stop turning) due to loss of traction with the road surface. A rotating tire can influence the direction of the car, a "locked-up" tire has no directional influence.
This also gives the tire more traction than a fully "locked-up" tire... |
In my country it is a big business now, to sell "water structuring facilities". Promoters telling that after passing through them the water obtaining fantastic abilities basing on the fact that "water can keep information coded in molecular domains, chained by weak hydrogen bonds". This "structured" water is a panacea ... |
So I wonder if it is any how possible to build laser at home. A powerful one to melt brick.
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The force of gravity is constantly being applied to an orbiting object. And therefore the object is constantly accelerating. Why doesn't gravity eventually "win" over the object's momentum, like a force such as friction eventually slows down a car that runs out of gas? I understand (I think) how relativity explains ... |
Suppose we have a lens with known focal length and are using the thin lens approximation. Is it possible to determine how an arbitrary beam of light will be deflected by it? Or, is it the case that there are multiple kinds of thin lenses, and so more information is required. I'm asking this question just so I can solve... |
Phase transitions are often detected by an order parameter - some quantity which is zero in the "disordered" phase, but becomes non-zero when order is established. For example, if the phase transition is accompanied by a breaking of a global symmetry, an order parameter can be any quantity which transforms non-triviall... |
This question is inspired by another one about the simplest model of topological insulator, where 4tnemele showed a nice two band model in the answer.
I read that and am wondering if we and push that to one dimension.
For example, by analogy to the graphene case, if we have a Hamiltonian in 1D (say x) as $H(k_x)=(k_x-k... |
I was interested to read the answers to the other Many-Body Problem questions on this site and was left with one nagging question of my own. What does the Many-Body Problem reveal about reality and our attempt to understand it? To explain: if the solutions we find to this problem are in the form of lengthy iterative ex... |
Our observable universe, or a subregion of our universe many times larger than the observable universe, originated from inflating from a very tiny inflationary patch. Being so small, the initial entropy has to be bounded by a very small value. But everything in our universe originated from that tiny patch after inflati... |
If you look at most published articles, or those on the preprint server, you find the vast majority of articles have more than one authors. Are collaborations needed to be productive in physics? In other fields like math, single author articles are the norm.
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One model for confinement in quantum chromodynamics is the Savvidy vacuum. This is a spontaneous symmetry breaking of color gauge symmetry by the gauge fields. The vacuum is divided into Savvidy domains. Is this process hidden by confinement?
L.Motl: I erased one "d" from Savvidy - everywhere. Link to Savvidy vacuum ad... |
It seems that virtual photons also exist in vacuum. So the precise question is:
What is the additional virtual photon density due to the electric field of a unit charge?
Or: How many virtual photons per volume are found around a unit charge?
The answer will depend on distance, but what are the exact numbers?
|
Consider the quantum state teleportation protocol of Bennett et. al.
How does one prove that this protocol would never violate the conservation of energy? At the face of it, it doesn't seem to be something obvious, as the various measurements, communications, rotations etc. don't seem to be able to account for the diff... |
I will begin my research on AdS/CMT, however I find AdS/CMT is only a phenomelogical method, so I want to know can AdS/CMT give some results the condensed matter physicists can not give, or even predict some unseen exotic matter states?
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If we can think about the universe as a wave function then many particles should be entangled with many other particles in the universe. The obvious question arises why we don't see those entanglements in everyday circumstances. One standard explanation given is those entanglements average out and cancel so we can igno... |
My question refers to an overview of the biggest stars we know: http://farm5.static.flickr.com/4138/4820647230_faba1c9f3b_o.jpg
Why are some of those blue?
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Seiberg traced the nonrenormalization of supersymmetric theories to holomorphicity of the superpotential in chiral superspace. However, this overlooks the fact that with a different number of supersymmetric generators, supersymmetry can be real or symplectic, instead of complex. But yet, even for those cases, we still ... |
How can I find the magnetic interference of a stationary $35000 \ \mathrm{kg}$ block of $100\%$ pure iron would have on a magnetic compass and what the drop off rate of the interference would be?
So if said $35000 \ \mathrm{kg}$ block of iron was $1 \ \mathrm{m}$ away from the compass, $100\ \mathrm{m}$ away, or $10... |
This is about continuity equation. What does the last integral mean?
$$\frac{\mathrm{d}Q_V}{\mathrm{d}t}=\iiint_V \mathrm{d}^3x \,\frac{\partial\rho}{\partial t}=-\iiint_V\! \mathrm{d}^3x\,\operatorname{div}\,\mathbf{j}=-\iint\limits_{\partial V}\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\;\;\;\subset\!\supset \mathbf j\;\cdot\m... |
First of all, what is the mathematical relationship between measured linewidth (usually in units of magnetic field) and spin relaxation time? I see papers talk about spin relaxation times in terms of linewidths but I have no idea how to correlate the size of the linewidth to an actual time.
Second, is the measured lin... |
Why does an object with smaller mass hits the ground at same time compared to object with greater mass? I understand the acceleration due to gravity of earth will be same but won't the object with greater mass will fall faster?
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I guess it's not a very educated question, but I never quite understood why spacecrafts have to shoot up and can't just reach space by simply continuing an upwards ascent like an airplane.
|
Are there any known uses of modeling with elastic fractals in current physical applications? (Especially uses concerning with self-similarity)
|
When something falls down, potential energy is transformed into kinetic one. Furthermore, you can attach a pulley and extract some energy (like in an aljibe), for example with a dynamo... If the object fall in a deep well, we can extract more energy, till the object reach downhole..
But what if we could have a "bottoml... |
Broadly speaking how do ideas of leading singularities and Grassmanian help in curing infrared divergences when calculating N=4 scattering amplitudes? My understanding is that one gets infra red divergences because the external gluon momenta becomes collinear with the the loop momenta. I am confused as to what Nima's a... |
Many physics papers now have dozens of authors per paper. Experimental physics may have multi-organizational and multi-country contributing staffs, but I'd guess that most of the names don't contribute a word or equation to a paper, yet they get individual authorship credit.
My question is who determines the author lis... |
I seem to be missing something basic.
I've been trying to get a simple orbital simulation working, and my two objects are Earth around the Sun.
My problem is this. I placed the Earth at 93M miles away from the Sun, or 155M km.
As I understand it, the orbital velocity of something at 155M km from the Sun is:
$$v = \sqr... |
Are Bloch equations (which describe the evolution of macroscopic magnetization) empirical? If so, under what assumptions do they hold?
$$\frac {d M_x(t)} {d t} = \gamma (\mathbf{M} (t) \times \mathbf {B} (t) ) _x - \frac {M_x(t)} {T_2}$$
$$\frac {d M_y(t)} {d t} = \gamma (\mathbf{M} (t) \times \mathbf {B} (t) ) _y - \f... |
What percentage of physics PhDs leave physics to become quantitative analysts, work in computer science/information technology or business? Is physics that bad that so many people leave? Was it worth it?
|
Let's consider rotating charged ring. Theoretically mass of this ring has no limit as rotation speed increases. So what about magnetic moment of the ring? Is it limited by the value of speed of light?
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From the "no hair theorem" we know that black holes have only 3 characteristic external observables, mass, electric charge and angular momentum (except the possible exceptions in the higher dimensional theories). These make them very similar to elementary particles. One question naively comes to mind. Is it possible th... |
There's some constant relating to electrons that also has the same value as the speed of light. What is it, what is the value, and how are they related?
EDIT: Is it the fine-structure constant?? Are there any other similar constants? If you posted that answer before, you shoulda left it (to the person who deleted their... |
Will a CFL light bulb and an incandescent light bulb, in separate respective closed systems, produce exactly the same amount of overall temperature increase over time?
Assume you have two identical closed systems with gray walls, with a system input of 20 watts of power each.
EDIT added for clarity: (On the packaging ... |
I am confused about the current and voltage. My intuitive example would be that of a pipe of say water. The diameter of the pipe determines the amount of water flowing per second but the pressure is comparable to voltage. Am I right?
And what is the difference between voltage source and current source? In what class ou... |
To put it bluntly, weather is described by the Navier-Stokes equation, which in turn exhibits turbulence, so eventually predictions will become unreliable.
I am interested in a derivation of the time-scale where weather predictions become unreliable. Let us call this the critical time-scale for weather on Earth.
We cou... |
I've only learned about to use kinematics equation when solving projectile problems but today i came across the following equations. where does they come from?
Distance travelled
Time of flight
Angle of reach
|
Given that my previous question, namely "What is the number density of virtual photons around a unit charge?" has no precise answer, here is a more precise wording:
What is the virtual photon spectral density due to the electric field of a unit charge at rest (or, better, its difference with respect to the no-field cas... |
Assuming the correctness of QM: Would the size of such a computer be smaller than the observable universe? If it were to represent all available information in the universe it seems that it's minimal necessary size would relate to a black hole of a certain mass. Would this lead us to believe this theoretical quantum co... |
suppose I have an electrostatic potential which I expand in spherical harmonics via
$$\sum_{l,m} A^l_m r^n P_l^{|m|}(\cos \theta) e^{im\varphi}$$
and I know that the field has cubic symmetry. Is there something I can say about the coefficients $A^n_m$? I ask because this would be the case for the crystal field in a cub... |
How and from where does a mathematician learn physics from a mathematical stand point? I am reading the book by Spivak Elementary Mechanics from a mathematicians view point. The first couple of pages of Lecture 1 of the book summarizes what I intend by physics from a mathematical stand point. I wanted to find out what ... |
Decades ago I was in a physics Ph.D. program, made a hash of things, and quite rightly was dropped from the program. Since then I've had a very satisfying career as a computer programmer, and picked up an M.S. in Applied Math. I'm currently working in a bioinformatics research lab, and really enjoying myself.
I think I... |
I am a beginner in this quantum-mechanics stuff. I understand the quantum eraser only from an experimental view. So I didn't understand the formalism that describes the quantum eraser. But what does the experiment tells us? Does the photon know that there is somebody watching it? And this is why it behaves in another w... |
If I place a compass over a wire(such that the wire is positioned north-south) with charge flowing through it, and it points northeast, how can I determine the direction of the electron current flowing through the wire?
|
What are some good books for learning the concepts of Kinematics, Newton laws, 2D Motion of Object etc.?
|
Do we take gravity = 9.8 m/s² for all heights when solving problems?
|
I'm sure a simple question.
I have a video of me jumping off a cliff into a river. I want to calculate how high it is. I know my weight, acceleration due to gravity of course, and I can get the time it took to hit the water.
Can I calculate (albeit roughly) how high the cliff was?
Cheers,
Tim.
|
Let the supersymmetry transformations for the chiral multiplet $(z_k,\psi_{kL},f_k)$ be,
$\delta z_k = 2i \bar{\alpha} \psi_{kL}$
$\delta \psi_{kL} = D_\mu z_k \gamma ^\mu \alpha_R + f_k \alpha_L$
$\delta f_k = 2i\bar{\alpha} \gamma^\mu D_{\mu} \psi_{kL} - 2ie\bar{\alpha}\lambda _R z^k$
Similarly let the gauge multipl... |
How does the following brief thought experiment fail to show that general relativity (GR) has a major problem in regards to black holes?
The full thought experiment is in my blog post. The post claims that GR violates its own equivalence principle at the horizon of a black hole. The principle says that the laws of phys... |
I would like to hear the best arguments for and against the Many Worlds interpretation of QM.
|
I am trying to model a system in which cubes of about 2 cm in size are floating in a circular water thank of about 30 cm in diameter. The cubes move around under the influence of the fluid flow induced by four inlets that point toward the center of the tank, and are located at the positions $0$, $\pi/2$, $\pi$, and $3\... |
What needs to be the case for a dynamical system with a continuous flow to exhibit chaos? It looks like 1D systems with a continuous flow can't exhibit chaos. Are two dimensions enough or do you need more? I was just thinking about what sort of phase portraits you could have in two dimensions, and it's not immediately ... |
From the gauge field $A_\mu$ and the QED lagrangian we can derive maxwell's equations in terms of electric and magnetic fields. Are there any situations where similar derivations using the other gauge fields like $W^{\pm}_{\mu}$, $Z_\mu$ or the gluon fields, e.g. $curl W$ could become useful?
edit: reformulated for cla... |
I am looking for a good source on group theory aimed at physicists. I'd prefer one with a good general introduction to group theory, not just focusing on Lie groups or crystal groups but one that covers "all" the basics, and then, in addition, talks about the specific subjects of group theory relevant to physicists, i.... |
How can I derive the Einstein's relation $D=k_{b}TB$, where $D$ is the diffusion coefficient and B is the mobility coefficient, from the concept of osmotic pressure?
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