1
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0answers
39 views

Thermal AdS3 in Chern Simons

I am currently working with (2+1) gravity in Chern-Simons formulation and I have a question about thermal AdS. The way I understand that one retrieves thermal AdS is by Wick rotation and ...
1
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0answers
68 views

How much electric charge can a copper sphere, made of N atoms, contain?

If somebody wants to charge a cooper sphere made of N atoms, what is the maximum positive charge the sphere can reach? Same question about a negative charge. Source For example if the sphere is ...
1
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0answers
105 views

A bead is threaded on a frictionless vertical wire loop of radius R

The question is the very last sentence at the end of this post. In this post, I'll demonstrate how I reach to a contradiction(the conditions mentioned in conjecture 1 should be satisfied by all ...
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0answers
72 views

How is my guitar cable picking up clear radio-signals?

I've recently noticed radio-signals coming through my guitar amplifier. I'm on the top floor of a building in a densely populated city, with a clear visual path to many other buildings. My guitar ...
1
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0answers
23 views

Why do magnetic forces scale down so poorly?

Im told by experts in MEMS and nanotech that magnetic forces scale down very poorly. This is one reason we have many MEMS devices based on electric forces/electrostatics but not on magnetics. Can ...
1
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0answers
37 views

Heat Capacities ratio equal to 1

In which situations can be found the ratio between $C_{P}$ and $C_{V}$ to be equal to the unity? I have read in other places that it happens for liquids and solids because they can be assumed to be ...
1
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0answers
69 views

Is Gibbs free energy really a true energy that can be used to do work?

Gibbs energy came from the relation $$\Delta S_\text{universe}= \Delta S_\text{surroundings}+\Delta S_\text{system}\ge 0.$$ By little algebra, we can arrive at $$\Delta S_\text{universe}= \frac{-\...
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0answers
67 views

Is there a model of the universe with the transfinite (space)time?

In mathematics there is a concept of ordinal numbers where one can count to infinity and beyond. For example the least number that is greater than all the finite numbers is denoted by $\omega$. Such ...
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0answers
24 views

Do clouds of dark matter cool and contract?

If dark matter participates in the weak interaction, clouds could cool via thermal neutrino radiation...? And even if does not participate in the weak interaction, clouds should contract via ...
1
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0answers
109 views

Wen plaquette model with one kind of plaquette operator

Let us say that we modify the familiar Wen plaquette model so that only one kind of plaquette operator is in the Hamiltonian which is a product of $\sigma_z$s, what kind of topological order or state ...
1
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0answers
37 views

Question on decay constant

I have a model of the radioactivity of a target which is undergoing Neutron Spallation. The Protons are incident upon the target for approximately 200 hours. Within the model, over the course of ...
1
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0answers
38 views

Are densities only good approximations?

In a number of situations, continuous densities (e.g. for mass, electric charge, etc.) are used in calculations. However, for example, as far as I know, matter is not continuous. Also, for example, ...
1
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0answers
65 views

Why doesn't entropy get decreased in adiabatic expansion process?

I was reading the second step of Carnot cycle in which the system undergoes adiabatic expansion doing work & thus decreasing the internal energy of itself. The entropy didn't change as no further ...
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0answers
65 views

Internal resistance of a battery

It is my understanding that internal resistance of the battery is mainly due to resistance of its electrodes and electrolytes. During the charge or discharge of the battery, there's a potential drop $\...
1
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0answers
57 views

Combinatorics of fourth order feynman diagram

I am trying to calculate how many different forth order feynman loop diagrams I can produce. I know that for 2nd order it is 6x3x2 thus 3! since you start with 3 lines coming out of each vertex so 6 ...
1
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0answers
110 views

Why does hot water and cold water makes different sounds while filling a bucket from a tap

When I fill hot water in a bucket while bathing, there is a difference in the noise it makes compared to cold water. Is there any Relation between temperature of water and sound it makes during ...
1
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0answers
41 views

Poynting of EM field and group velocity

Could anyone please show me mathematically how the poynting vector of an EM field is always parallel to its group velocity? I do understand the physical reason why it has to be the case, but showing ...
1
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0answers
38 views

Reference frame question

Two examples of possible time dilation based on reference frames and acceleration: An alien ship flies into our galaxy. They watch the arms spinning (assume they are immortal and have a LOT of time ...
1
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0answers
21 views

Optically access a single valley in indirect semicondutors

An indirect semicondutor has an energetic minimum of its band structure at a point different from the $\Gamma$ point. But, there are multiple of them. Silicon for example has its band minimum at the ...
1
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0answers
27 views

Problems with relational quantum mechanics

Are there any theoretical issues with Rovelli's interpretation? And just from extrapolation of the macroscopic world making much more sence through Einstein's relative description, is it reasonable ...
1
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0answers
41 views

Sterile neutrino constraints (summary of results)

Constraints on sterile neutrinos come from an amazingly wide range of different sources. From astrophysical observations (review1, review2) to particle physics experiments (MiniBooNE, Daya Bay, LSND, ...
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0answers
19 views

ray tracing through a stack of flat plates

Say I want to trace rays in 3 dimensions through a stack of flat plates of various refractive indices. My rays have canonical coordinates {Q,P}. The plates are normal to the z axis, all the rays start ...
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0answers
59 views

Josephson junction exceeding the coherence length of the cooper pair

In this recent paper http://arxiv.org/abs/1504.03286, the authors present the data that they measured Fraunhofer-like diffraction pattern in a Josephson junction with graphene sandwiched between ...
1
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0answers
67 views

Bernoulli's Equation for Barotropic Flows

I'm trying to understand a derivation of Bernoilli's Equation and I'm having a hard time understanding the math behind this indentity $$ \frac{1}{\rho} \nabla p = \nabla \int \frac{\textrm{d}p}{\rho}....
1
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0answers
43 views

What does the Scattering Amplitudes tell us about the interactions of matter

I am confused as to the role of the wave function in quantum mechanics. My understanding is that the wave function/state vector is purely a algorithm or mathematical means to compute the results of ...
1
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0answers
77 views

Proof of Lagrangian

I'm having some trouble with some math on a problem for a physics class (looking for help with some partial derivatives, not an answer). Let $$L'=L+\dfrac{dF}{dt},$$ where $L$ is a Lagrangian and $F$ ...
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0answers
58 views

Creation of entangled electrons

If one obtains two entangled in polarization photons by parametric down conversion and one of them is accepted by and electron 1 and other by electron 2 - are this electrons now entangled in spin?
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0answers
20 views

Target space Lorentz symmetry of superstrings in noncritical dimensions

Is the target space Lorentz symmetry of noncritical strings ($D \neq 26$) or superstrings ($D \neq 10$) broken or is it not? Naive arguments suggest that the mentioned anomaly does not exist, since ...
1
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0answers
59 views

Argument of a Cosine function (referring to Principles of QM by R. Shankar)

On Page 72, Shankar solves the differential equation: $$ \frac{d^2}{dt^2}\langle m\rvert\psi(t)\rangle=-\left(\frac{m^2\pi^2}{L^2}\right)\langle m\rvert\psi(t)\rangle$$ as: $$ \langle m\rvert\psi(t)\...
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0answers
50 views

Where does E8 come from in M-Theory?

Where does the E8 symmetry comes from in M-Theory? For example when you compactify one of the dimensions on a line you get E8xE8 heterotic string theory. Or if you compactify 11D Supergravity ...
1
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0answers
58 views

Fraunhofer diffraction at circular aperture - integration of bessel function

I'm trying to understand the calculation here: http://en.wikipedia.org/wiki/Fraunhofer_diffraction_(mathematics)#Circular_aperture for the solution by integration, but I plain and simple fail to see ...
1
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0answers
53 views

Coupling of LC circuits

I am reading an old article in a physics journal in which the author explains that the frequency between two identical, but capacitively coupled oscillators becomes $\omega_\pm=\omega_0\sqrt{1\pm\...
1
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0answers
18 views

Conformal compactification and the use of spinors (Twistor theory)

I was reading the book from Huggett and Tod "An introduction to twistor theory" and as the book evolves they reach to the necessity to "found" a Lie derivative of a spinor respect to a conformal ...
1
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0answers
72 views

Massive Dirac model Chern number 1/2

Why is massive Dirac model have a Chern number as half? I know this is something related to anomalies. And for fermions we have half, for bosons we have integer. But I failed to find any good ...
1
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0answers
59 views

Two double slit experiments after each other

Does the act of observation forever destroy a photon or electron's wave like behaviour? What would the result be if the electron was observed, and instead of displaying the two lines or particle like ...
1
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0answers
29 views

Atmospheric Tides effect on atmospheric pressure

Regarding the atmospheric tides effect on the pressure, this answer (and the referenced sources) seem to point that such effect is very small. However, this pressure prediction graph for my hometown ...
1
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0answers
53 views

Dependence of the magneto-rotational instability (MRI) on thermal relaxation?

The MRI is the most efficient driver of turbulence in accretion discs (as measured by the effective scalar stress). The magnetic field, being properly coupled to the gas (weak coupling), connects the ...
1
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0answers
74 views

Regge trajectory and Kaluza Klein tower

The mass of hadrons in the Regge trajectory scales as $m=\sqrt{\frac{J}{\alpha}-\alpha_0}=\sqrt{\frac{n}{\alpha}-\alpha_0}\propto \sqrt{n}$, where $J=n$ is the spin of the particle (in natural units,...
1
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0answers
15 views

Optical Delay Lines

Why does the peak group delay for an add-drop ring resonator's drop port reduces to 1/4th of that of an all-pass ring resonator? Shouldn't it just be half of its value as the transit length is ...
1
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0answers
73 views

Signs of Grandi's series $1-1+1-1+1-1+1+\ldots$ in the real world?

I'm talking about the convergence of the series $1-1+1-1+1-1+1+\ldots$ to $1/2$. I was discussing with some friends (we study physics) and I argued that Cesaro summation is a fair extension of the ...
1
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0answers
39 views

Why does inter-electron distance in wire grow with acceleration?

When you have an electrically neutral wire, and apply a voltage across it, free electrons (provided by source) flow through the wire and thus an electric current is created. Assuming an ideal scenario,...
1
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0answers
31 views

How can the response at the terminal end of an infinite ladder network be solved?

In a recent post: How can the transfer function of an infinite ladder network be used to solve real world problems? I reference how one can solve the transfer function (impedance) of an infinite ...
1
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0answers
50 views

Cumulative mass & mass distribution of a disc galaxy

Hernquist has a great formula to represent the cumulative mass of a spherical galaxy (8): http://star-www.st-and.ac.uk/~hz4/contempastro/hqm.pdf 1) Is there any simple formula for disc shaped galaxy ...
1
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0answers
26 views

Can we 'dope' a fluid to make it become a superfluid?

The only element that can become a superfluid is Helium (He-3 and He-4) since it does not solidify not matter how cold it gets, hence it can reach the superfluid transition temperature whilst still a ...
1
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0answers
29 views

Force and inclined plane

An incline of mass $m_2$ can move without friction on a horizontal plane. A block of mass $m_1$ is fixed to the incline with a piece of string. How does the system move when the string is burnt? The ...
1
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0answers
40 views

The change of length of positive column in glow discharge

When I was doing the experiment of glow discharge, I lowered the voltage between electrodes and find that the length of positive column will increased quickly around a certain voltage(the interval of ...
1
vote
0answers
30 views

If a heater was turned on its' own wire, would heating of the wire cause the resistance to increase, thus the current into the heater to decrease?

I'm thinking not, because; A) It wouldn't make much sense in the real world because you'd need to avoid ever turning a heater towards its own wire, and you'd have to regulate the temperatures of any ...
1
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0answers
53 views

When a coil makes a complete turn, why is does magnetic flux double with respect to time?

EMF, $\mathcal{E}$, is equal to -d($\phi$)/dt Where $\phi$ is magnetic flux. Why is it that if from $t_1$ to $t_2$ the coil makes a complete turn and during this turn the normal vector's angle with ...
1
vote
0answers
42 views

Earth to LEO, gravity drag and potential energy

A lot of references indicate takes about 9.4 km/s of delta-v to reach LEO. https://en.wikipedia.org/wiki/Low_Earth_orbit#Orbital_characteristics The delta-v needed to achieve low Earth orbit ...
1
vote
0answers
49 views

Why doesn't a stationary wave completely destruct, instead of just at the nodes, when the waves are in fixed positions (see examples)

Example 1: I understand that two progressive waves, say π out of phase, travelling in the same direction with the same frequency and amplitude will completely destruct. This is due to the principal of ...

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