# All Questions

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### Topological Insulators: is HgX a special case?

I got confused by reading this article: Francois Virot, Roland Hayn, Manuel Richter, and Jeroen van den Brink. “Engineering topological surface-states: HgS, HgSe and HgTe.” arXiv preprint ...
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### Converting heat into energy

I'm currently building a custom desk. In this desk I will also build-in a small part with a custom electronic panel to provide power to USB devices. As my gaming pc generates a lot of heat and the ...
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### Total momentum and crystal momentum of electron in lattice

Consider a 1D lattice with distance between $\mathrm{atoms} = a$ and length of lattice $L$. Also consider the nearly free electron model and that the electron does not interact with the ...
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### Relativity velocity problem [on hold]

In the laboratory frame, two observers A and B are moving along the sides of an equilateral triangle with equal speeds c/2 as shown in the figure. The speed of B as measured by A will be- a) √3 ...
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### A question on relative relativistic velocities [on hold]

A body moving at 0.500c with respect to an observer disintegrates into two fragments that move in opposite directions relative to their center of mass along the same line of motion as the original ...
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### Help me out, Please [on hold]

For a configuration of charges and currents confined within a volume V, show that ∫Jdτ = dp/dt where p is the total dipole moment. (Hint: Evaluate ∫∇.(xJ) dτ (at const. ...
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### Noether's theorem in the realm of superfluids

In 1969 Keith Moffat showed helicity conservation for ideal fluids such as liquid Helium. This work is proving seminal in our understanding of turbulent flows and viscous fluids. In the case where ...
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### How do you define a reversible path for general processes?

The equation $dS = \frac{\delta Q}{T}$ is only defined for a reversible path. Given a irreversible path we typically calculate the entropy by choosing a reversible path from the same initial to final ...
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### Which surface to use in Ampere's law?

In calculating the current enclosed by an Amperian loop, one must, in general evaluate an integral of the form $$I_\text{encl} = \int \mathbf{J}\cdot\mathrm{d}\mathbf{a}$$ The trouble is, there are ...
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### Does velocity or acceleration cause time dilation?

What causes time dilation? Acceleration or velocity? I've seen multiple comments on this forum that assert velocity is the cause, but that doesn't seem right to me. You can't have velocity without ...
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### Logarithmic intensity formula factor?

In formulae for sound intensity and sound pressure, there is a logarithm part for the logarithmic increase of the quantity we're studying, and also a numerical factor 10 or 20 depending on the ...
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### Too small error on the calculus of wavelenght

I have this function: $$\lambda=d \sin(\arctan(\frac{x}{z}))$$ and I want to find its absolute error. $d$ is a constant ($10^{-6}$), $x =(0.716 \pm 0.001)$ m, and $z=(1.000 \pm 0.001)$ m. For the ...
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### How are anyons possible? (another version)

I know that this question has been submitted several times (especially see How are anyons possible?), even as a byproduct of other questions, since I did not find any completely satisfactory answers, ...
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### QFT Literature recommendation [duplicate]

Before answering, please see our policy on resource recommendation questions. Please try to give substantial answers that detail the style, content, and prerequisites of the book or paper (or ...
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### Measuring spin direction by means of coherent light?

Let us assume that we have the ferromagnetic surface where all atoms have the same direction of spins. And we can interact with the single atom in such lattice. Is it possible to measure the ...