# All Questions

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### What is the interface tension between ordered and disordered phases of the Potts model?

I read in these papers(1,2) the concept of interface tension. I can't understand its definition. I can hardly imagine there is some tension in a model. Any help will be appreciated.
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### Irreducible Representations Of Lorentz Group

In Weinberg's The Theory of Quantum Fields Volume 1, he considers classification one-particle states under inhomogeneous Lorentz group. My question only considers pages 62-64. He define states as ...
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### What is tricritical point？

Critical point is the transition temperature of a second order phase transition. But what does tricritical point mean? WIki says that a tricritical point is a point in the phase diagram of a system at ...
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### Calculating the moment inertia for a circle with a point mass on its perimeter

I want to calculate the tensor of the moment of inertia. Consider this situation: The dot represents a points mass, in size equal to $\frac{5}{4}m$. $m$ is the mass of the homogenous circle. I'm ...
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### What is the relationship between complex time singularities and UV fixed points?

In this paper it is described how the turbulent kinetic energy spectrum and the flatness (a measure for intermittency) are governed by the position of the (dominant) singularities of the solutions of ...
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### Finding surface tension of water at certain temperature and pressure

The question is: Using the Young-Laplace Equation (if applicable), find the surface tension (dynes/cm) for water at 20 degrees Celsius with 2.5 psi. Round to the nearest tenth. ...
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### How do objects change their axis of rotation?

If I hold a pencil at its end and spin it, throwing it upwards, it will spin about its end, but will soon start spinning around its center. How is this? I would draw the following torque diagram for ...
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### How would gravity change on a planet rotating around itself very fast?

Let's take a planet identical to Earth, but with rotation speed multiplied by ten thousand. What would happen with the gravity if it was spinning madly around itself? Would the centrifugal force make ...
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### What are the rainbow and ladder approximations in a solid state physics context?

All references I find talk about quarks and gluons, where I have only very limited knowledge about. From it's name (rainbow) I guess it applies to fermions coupled to bosons and we're interested in ...
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### Why does a supernova explode

This is really bugging me. When you look up some educational text about stars life, this is what you find out: Gravity creates the temperature and pressure to start fusion reactions. The fusion ...
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### Why does the comb attract the pieces of papers if they're neutral?

When we rub our hairs with a comb, and then try to attract small pieces of paper, they're attracted by the comb. The pieces of the paper were not electrified before they were attracted. Then they ...
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### Why can't we accelerate objects past the speed of light? [duplicate]

Is there any intuitive reasoning behind why there would be this universal speed limit? It just seems so arbitrary. I know that there must be things that are unknown, but what reasoning is there behind ...
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### inductance value of a single turn thin circular coil

the question may seem simple but I haven't found any fitting formula yet. The problem is the following: consider a single-turn, circular coil made of reasonably thin wire (diameter of the wire much ...
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### Gauss's Law with Moving Charges

My text claims that Gauss's Law has been proven to work for moving charges experimentally, is there a non-experimental way to verify this?
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### Consequences of compactness in physics

If we understand spacetime as a $4$-dimensional manifold $M$, from the point of view of physics what are the consquences of a subset of it being compact? My point here is simple: in math we usually ...
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### Why does compressing a piston increase the internal energy?

When we compress a piston, its total internal energy increases, however I don't understand why. As the piston compresses, the temperature should change, as the total energy density increases. As a ...
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### What would be the basis vectors for this 2D crystal structure?

In the above image, I have a 2D crystal structure. The lattice vectors are described by: a = {-1/2, -Sqrt[3]/2}; b = {1, 0}; and the location of atoms A and B ...
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### There must be free positive charges, moving oppositely to electrons for the wire with current to stay neutral

All popular expositions (e.g. these ones) of relativistic electromagnetism claim univocally that electrons in motion become more dense due to the speed. They teach that Lorentz contraction of charges ...
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### Can Increasing the Turbulence Inside a Pipeline Economically Increase Flow?

"The velocity gradient in turbulent flows is steeper close to the wall and less steep in the center of the pipe than it is for laminar flows (Blatt p.97)." Does this mean that some degree of ...
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### What happens to the electron companions of cosmic ray protons?

If primary cosmic rays are made mostly of protons, where are the electrons lost, and does this mean that the Earth is positively charged? Does the sun eject protons and electrons in equal number?
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### integrated vertex operators" in 1-loop open/closed bosonic string amplitude

This question is in reference to the first ~15 minutes of this String Theory lecture by Prof.Shiraz Minwalla, http://theory.tifr.res.in/Videos/strings28_24sep08.mp4 Can one give a reference ...
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### State emitting from an extended thermal source

This calculation is for a double slit experiment setup which is experiencing a far field radiation from an extended monochromatic thermal source. I assume the source is 1-D and it's length is $b$. ...
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### Are all points in the universe connected?

Is it true that every point in the universe is connected or could be so theoretically? If so how is this mediated? Is it through the quantum nature of the fabric of space or is it through the ...
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### Small charged sphere's motion in earth's magnetosphere?

Suppose that a spherical metal sphere with mass $m=10^{-16}kgr$ radius $R=10μm$ charge $Q=10^{-9}C$ travels with $v=c/3$ and is trapped in the earth's magnetosphere at a distance around $r = 1000km$. ...
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### A particlar normal ordering problem [duplicate]

Say we have an expression of the form: $$\left<0\right|:\phi(x)^2: : \phi(y)^2:\left|0\right>,$$ where $\phi$ is some scalar field. I have heard the claim several times, that in evaluating ...
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### What is the difference between lattice vectors and basis vectors?

Google has not been very useful in this regard. It seems no one has clearly defined terms and Kittel has too little on this.
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### Horizontal $E$-field for a charged conducting disk

For part of a simulation I am writing, I need to know the electric field emitted from a charged conducting disk. If the disk was laid out in the $x$-$y$ plane, I am interested in the field in that ...
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### How to understand the emergent special relativity in the superfluid?

The superfluid vacuum theory was proposed to understand some features of the vacuum (aether) from the emergence point of view. Although made up of non-relativistic atoms, the low-energy excitations of ...
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### Dopant concentration and changes in band gap energy

Thanks to this lovely website, I was able to pop out reasonable values for my band gap energies from a translucent material. As expected, I found a decrease in band gap energy due to my treatments. ...