All Questions
230,049
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What new insights are gained in quantum information by doing tasks (e.g. creating BECs) in space?
Recently, I have seen a lot of discussion surrounding NASA and quantum technologies. Specifically, there is a paper that came out in Nature titled "Quantum gas mixtures and dual-species atom ...
- 1,100
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0
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9
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Interpretation of density wave observables
Given some Hamiltonian quantum system, one can ask questions about (expectation values of) observables. While some have an intuitive meaning, e.g. energy or magnetisation, I find it hard to grasp the ...
- 1
0
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0
answers
14
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Limiting Summation to the First Brillouin Zone
I am stuck on validating whether the procedure I am doing is correct. If we have an 'infinite' sum which looks as follows:
$$\sum_\vec{q} a(\vec{q}) $$
where $\vec{q}$ is a momentum transfer. I aim to ...
- 21
0
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0
answers
17
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What is topological about topologically ordered states?
My naive understanding based off section 4.8 of Nakahara's Geometry Topology and Physics is that topologically ordered phases are ground states that are homotopically inequivalent to other possible ...
- 59
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0
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7
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Clarifying the properties and meaning of scaling dimensions of lattice operators
I'm trying to understand scaling dimensions of lattice operators in translationally invariant critical spin chains. The main example I have in mind is the transverse field Ising model. There's a nice ...
- 1,644
-1
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1
answer
22
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Help finding mass of an object using circular motion [closed]
I am currently doing a lab where I need to find the mass of an object using uniform circular motion.
The lab goes as follows: you attach a rubber duck to a string, feed that string through a small ...
- 1
0
votes
1
answer
27
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Potential energy of a moving mass-spring system
I want to figure out the Lagrangian $\mathcal{L}(q_j, \dot{q}_j^{})$ of the arrangement given in the figure with $x$ and $u$ as generalized coordinates, respectively, the horizontal position of the ...
- 146
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0
answers
5
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Convection and the Strouhal number
Whenever I look into information about the Strouhal number, I always see it reference vortex shredding. But the Strouhal number can also be used in the context of turbulent convection where
$$
St=\...
1
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0
answers
34
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Intuition behind force components after Lorentz transormations
So if we have a body that has velocity $v_x=v$ and $v_y=0$ in reference frame $K$ and $v_x'=v_y'=0$ in $K'$. Then if we have force $\vec{F'}$ acting on that body, its components are:
$$F_x=F_x'\\ F_y=\...
1
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0
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28
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How to rotate a 3D matrix about a line by a certain degree? [closed]
Physics Ch 67.1 Advanced E&M: Review Vectors (15 of 55) Coordinate Transformation in 3-D: Ex. 2
I was watching the following video where the goal was to find the Coordinate Transformation matrix ...
- 21
1
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38
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Mechanics vs thermodynamics? [closed]
Many systems of classical interacting particles resonate predominantly at a single well-defined scale although they actually should theoretically allow for broad range of behaviours.
For example, a ...
- 635
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25
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Piecewise electromagnetic quantities. How limits of piecewise intervals transform in boosted frame?
Context
I am studying electromagnetic quantities in the framework of special relativity.
I understand that I can write the contravariant components of the four potential $A^\mu$, and that they ...
- 392
-1
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0
answers
23
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Why is mechanical advantage for a wheel and axle not consistent for all wheels and axles? [closed]
This question plagues my existence. Why is it that sometimes the ratio for wheel and axles are the radius of the wheel / radius of the axle, but other times its reversed? I researched and found that ...
-3
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0
answers
18
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Electric Circuits [closed]
I got the first part of the question right but once i short circuit the v1 source I can't seem to get it right.
- 1
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answers
16
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QED feyman graph Coordinate space doubt
So I know that there are the Feyman rules to transform mathematical equation into graphs but to me it's not too much clear when I should draw the graph vertically or horizontally i.e. how I determine ...
- 1
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1
answer
15
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Is the ray model appropriate only for spherical/planar waves?
In ray optics, light propagation is modeled using rays, i.e., curves that are perpendicular to the wavefront. In general, rays can be curved; however, if the medium is homogeneous, it follows that the ...
- 133
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1
answer
27
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Hydraulic press
Let's say I have an asymmetrical U-shaped tube, one branch is wider than the other. If I now pour some liquid into this tube, the liquid reach the same high in both branches. Then, I will cover both ...
- 733
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16
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Why is the general equation for interplanar spacing not applicable here [closed]
https://imgur.com/a/w2vXbPd
So I just got back the solutions for one of my midterms, and I'm confused by this answer. I thought the interplanar spacing was,
$$ d_{hkl}=a/\sqrt{h^2+k^2+l^2} $$ for ...
- 1
-1
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0
answers
13
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Help with question from Isaac Physics (Path and Phase Difference 11.5) [closed]
This question was taken from Isaac Physics Path and Phase Difference 11.5
The question states:
20 GHz microwaves pass through a pair of narrow slits 10cm apart. Calculate the fringe spacing (y when n=...
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1
vote
1
answer
59
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How do they set the clocks on spacecraft visiting several other planets
Scientists have sent spacecraft into distant space passing nearby other planets on the voyage. How do they set the clocks to adjust for kinetic time dilation (special relativity) and gravitational ...
- 4,241
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34
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Why does hysteresis even exist in ferromagnet or Ising model?
I understand the math where mean field theory gives 2 (+ and -) self-consistent magnetization values for n-dimensional Ising model when the temperature is below the critical temperature. How does this ...
- 544
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2
answers
85
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How Quantum Mechanics reconciles with Classical Mechanics?
Imagine we have to charged particles. The kinetic energy of the system is:
$$
T = \frac{1}{2}(m_1 + m_2) \mathbf{\dot{R}}_{cm}^2 + \frac{1}{2} \mu \dot{R}^2 + \frac{L^2}{2 \mu R^2}
$$
and its ...
- 1,323
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12
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Various types of correlation functions in models with random interactions
In the Ising model, spin correlations are characterized by the following correlation function
$$
C_{ij} = \langle \sigma_i\sigma_j\rangle - \langle \sigma_i\rangle\langle \sigma_j\rangle
$$
where $\...
- 4,970
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0
answers
20
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Gradient of Schwarzschild horizon
I am studying Schwarzschild horizon and badly stuck with some Math stuff
Consider the scalar field defined on Manifold by
$$
u(t,r,\theta,\phi)=(1-\frac{r}{2m})e^{\frac{r-t}{4m}}
$$
$$
du=\frac{1}{4m} ...
- 41
-2
votes
0
answers
12
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Work Done by Pseudo Force while applying Bernoulli equation with respect to the container
Why is work done by pseudo force not considered while applying Bernoulli equation with respect to the container (eg, in finding efflux velocity the container should have some acceleration due to the ...
- 1
1
vote
1
answer
30
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Conditions for ball to retrace after colliding with wall
When a ball collides to wall,what would be some conditions for it to retrace or atleast return to from where it was thrown.
When thought about it I was getting a result that ball has to collide with ...
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-5
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0
answers
24
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Problem on Gravitation about satellites [closed]
Answer Shown is option a and d.
Please tell me how
0
votes
1
answer
20
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Hinged rods concepts
Let's say we have 2 surfaces - rod and a wall which are connected with a hinge.
What I'm struggling to understand is the direction in which reaction forces at a hinge act.
Do they always act ...
1
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0
answers
68
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Does this integral actually vanish?
When doing P&S Exercise 3.4 (e), I stumbled upon the following Hamiltonian:
$$H = \frac{1}{2}\int d^3p\xi^{rT}p\sigma\xi^{s}(a^{r\dagger}_pa^s_p+a^{s\dagger}_pa^r_p),$$
where $\xi^{1,2} = (1,0)^T,(...
- 270
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0
answers
25
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Does conserved observable mean conserved expected value? [closed]
In the Schrödinger picture of quantum mechanics, an observable $O$ is conserved if it commutes with the Hamiltonian. I was thinking about what this means in an experimental setting. Is the expected ...
- 1,252
1
vote
1
answer
54
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Interpretation of classical hamiltonian $H=\frac{\vec{p}^2}{2m}-\frac{q}{2m}L_zB+\frac{q^2B^2}{8m}(x^2+y^2)$
For a particle of charge $q$ in a homogeneous magnetic field along $z$-axis, $\vec{B}=B\hat{z}$, its classical Hamiltonian is given by $$H=\frac{(\vec{p}-q\vec{A})^2}{2m}.$$ In the gauge $\vec{A}=\...
- 11.2k
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1
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50
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Why does a particle initially at rest at origin with acceleration as square of its $x$ coordinate ever move?
Consider a particle initially at rest at origin, with acceleration, $a$, such that $ a(x)=x^2 $.
Since the particle is at origin, initial acceleration would be 0. It's also at rest initially. Its $x$-...
1
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0
answers
34
views
Bending angle equation of particle in a magnetic and electric field
Using the equations for an Electric field and Magnetic field between two plates:
$$
E = \frac Vr
$$
$$
B=\frac{2I}{2\pi r}\cdot\mu_0
$$
where $V$ is plate voltage, $r$ is plate separation, $I$ is ...
- 11
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votes
1
answer
43
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Tension in rope and displacement of length
I have a project at home where I want to know the position of a camera.
I have two drums mounted at a fixed horizontally distance 'd' from each other. There is an encoder mounted on each drums so I ...
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0
answers
15
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Understanding Chern-Simons on non trivial manifold
I am studying abelian Chern-Simons theory on a non-trivial manifold. Could you let me know how accurate my understanding is?
Here's what I figured out:
The action of U(1) leaves the action invariant ...
- 165
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0
answers
43
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Help me clarifying this please! [closed]
When to use Q=nCpln(T2/T1) and when to use Q=nCpDeltaT? Is it something to do with the reversible process?
(I know Cp is specific heat capacity at constant pressure)
1
vote
0
answers
18
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What is the position-space form of the photon propagator in axial gauge?
I'm interested in the form of the photon propagator in position space, when expressed in an axial gauge $ n \cdot A =0$, where in the case I am interested in, $n^\mu = \{1,0,0 \dots, 0\}$ (for a $D$-...
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1
vote
0
answers
15
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Conformal mapping of Euclidean Schwarzchild ads blackhole
I have been trying to understand this for some time. given the Euclidean S-AdS black hole metric,
$$ ds^2 = f(r)d\tau^2 + \frac{1}{f(r)} dr^2 + r^2d\Omega^{2}_{D-2} $$
From what I understand this has ...
1
vote
1
answer
32
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Decay chain diffferential equation
Consider I have a decay chain $A\rightarrow B \rightarrow C$. With decay constants $\lambda_{1}, \lambda_{2}$
If I would want to find an equation relating the number of nuclei B to the decay constants,...
- 6,415
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0
answers
21
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A standard irrotational flow: is there an intuitive derivation?
It is said that a flow is irrotational if $\nabla \times \textbf{v}=0$ for the velocity profile. I know that there's a whole lot of vector calculus involved in "properly" writing the ...
- 123
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35
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Help on physics study plan [closed]
A little background
I want to self-study introductory physics, so I've read
there, Kevin put in his advice to self-study physics you can start from AP Physics 1,2 and then progress to doing the Yale ...
2
votes
2
answers
121
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Photon as a qubit
I am studying Quantum Key Distribution which relies on photonic qubits, the photon.
Indeed, this one is viewed as a qubit, that is a two state system, just like the
spin of an electron, an atom with ...
- 71
3
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answers
45
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Peskin & Schroeder Chap 7.1: Two-point correlation function in Field Strength renormalization
I have some simple questions. I was going through Peskin & Schoeder Introduction to QFT, trying to understand the two-point correlation function on interacting theory (Chapter 7.1) for the case $x^...
- 31
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0
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29
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Frequncy dependece of energy of a monochromatic wave
Using the Poynting vector expression, the energy of a plane wave if given by
$$ E_{\text{light}}=-\epsilon_{0}c\int_{t_{i}}^{t_{f}}\left|{\varepsilon}(t)\right|^{2}dt\oint_{S}\left[\left(\hat{\mathbf{...
4
votes
1
answer
140
views
Action as the integral of a differential form
I'm wondering if the action functional can be written as the integral of a differential form and if so how it relates to the Lagrangian. I tried considering in 1D the Lagrangian $L(q,v,t)$ as a ...
- 857
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1
answer
39
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Could a geomagnetic storm disrupt the functioning of nerves?
It is known that geomagnetic storms can cause power grid outages. Can they also disrupt the functioning of nerves/the nervous system?
- 21
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0
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26
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Differences in $L$ and $S$, symmetries
I have a symmetric wavefunction when $L=0$. There are a lot of proofs to see this, so I understand it.
I have a symmetric wavefunction when 2 particle of $S=1/2$ each, combine in a bound state with $S=...
- 47
-1
votes
0
answers
23
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Simple atmospheric air pressure and temperature model with velocity sinks and sources [closed]
I'm seeking to understand how to make a simplistic model for pressure, temperature and velocity in an earth-like atmosphere, given the following features:
Initially static atmosphere (zero air ...
1
vote
1
answer
78
views
Angular momentum operator in second quantization
I wanted to know what the angular momentum operator in the second quantization would look like in terms of the annihilation and creation operators.
-1
votes
1
answer
16
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Transmittance of one material through a multilayer
Good morning,
I have the transmittance and the reflectance spectrum of PET (Polyethylene terephthalate) and I also have the transmittance and the reflectance spectrum of PET + Copper (50 nm). I would ...
- 21