# All Questions

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### Number of microstates of discretized paths

Let us consider a square grid, which has been rotated by 45deg. On this grid we deﬁne a path, the directed polymer, which starts at the origin ($t = 0$) and extends in the positive $t$-direction (at ...
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### Can energy be defined as the most fundamental particle which exists in different forms as protons, electrons etc

What we see all the different forms of matter around is just a form of energy. Why can't this energy be the most fundamental particle. Given dust can turn into a star and then emit all sorts of ...
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### Industry application of computational quantum mechanics?

I was wondering if anybody knew of an industry application of computational quantum mechanics. For example, the efficient placement of circuit elements on a PCB is in part motivated by classical FDTD ...
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### CP-violation in SUSY QED?

I have just gone through the exercise of constructing the supersymmetrized QED action. In the end, I get a reasonable action which matches literature. But after a little analysis, I find that the ...
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### Trouble following the Saclay method (spectral representation of thermal Green functions)

Note: I just answered my own mathematical question by writing it up, but I thought I'd share it anyway in case someone else has a similar difficulty. :) I'm still left with my real physical question: ...
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### The theory of strings stretching between intersecting D-branes

I am trying to understand various aspects of intersecting D-branes in terms of the gauge theories on the worldvolume of the D-branes. One thing I'd like to understand is the worldvolume action for ...
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### Component of force field tangent to a curve

I recently had to solve the following problem: A force $F=10\hat x- 8\hat y$ is applied to an object that is constrained to travel towards increasing values of x along the path defined by $y=x^2$ ...
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### How to evaluate spin operators in second quantization for spin symmetry-broken Slater determinants?

Suppose we have the following Slater determinant: $$| \Psi \rangle = \prod \limits_{i,i'} a^+_{i\alpha} a^+_{i'\beta} | \rangle$$ where $a^+_{i\alpha}$ creates an electron ...
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### Second law of Newton for variable mass systems

Frequently I see the expression $$F = \frac{dp}{dt} = \frac{d}{dt}(mv) = \frac{dm}{dt}v + ma,$$ which can be applied to variable mass systems. But I'm wondering if this derivation is correct, ...
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### comparing torque and 0-60 speed in cars

Im looking a two cars, both are the same model but ones got a 2.0L turbo petrol engine and ones got a 3.0L turbo diesel engine. These are the full specs 2.0L Petrol 3.0L Diesel what im ...
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### What does it mean that Einstein's equations are hyperbolic-elliptical?

I says on Wolfram MathWorld that Einstein's field equations are a set of "16 coupled hyperbolic-elliptic nonlinear partial differential equations". What does it mean that the equations are hyperbolic-...
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### Dimensional transmutation in Gross-Neveu vs others

Firstly I don't know how generic is dimensional transmutation and if it has any general model independent definition. Is dimensional transmutation in Gross-Neveau somehow fundamentally different ...
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### Senior High School work on Doppler measurements

Sorry this question is really vague- as a result I'm very confused. Perhaps you can help me make sense of it. "Radar measurements: Construct a space-time diagram of the radar tracking of an asteroid ...
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### Deriving the Sommerfeld expansion by contour integration (Le Bellac p. 277)

In Le Bellac's statistical physics book he derives the Sommerfeld expansion by a contour integral. The idea is to expand integrals of the type \$I(\beta)\equiv \int_{0}^{\infty}d\epsilon\, \frac{\...
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### wave-particle duality

I have been trying to understand "wave-particle duality" and other cases related to it. I am currently a college level student. I have few question which I am not getting answers clearly. In double ...
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### Frequency Of Light [closed]

I am confused on few topics... What is meant by "Frequency of Light"? Does the Photon(s) vibrate, that is known as its frequency? If the Photons vibrate, then they have a specific frequency, then ...
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### origin of magnetic field in a permanent magnet [closed]

I have a simple question. I hope I don't get a stupid answer. Where does the magnetic field of a permanent magnet comes from AND why is it permanent (are we dealing with perpetual motion)? This is ...
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### Which are the best introductory books for topology, algebraic geometry, differential geometry, manifolds, etc, needed for string theory? [duplicate]

Which are the best introductory books for topology, algebraic geometry, differential geometry, manifolds, etc, needed for string theory?
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### Does the metal foam “whiffleball” orbital reentry idea make any sense?

Planetary Resources is a company speaking publicly about mining near Earth asteroids for resources. I'm interested the physicality of a claim they make in a video here: http://www.youtube.com/watch?...
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### What is the height of the electron orbits of an atom?

What are the heights of the electron orbits of an atom? (How far apart are the energy levels of the electron relative to the center of the atomic nucleus?) How fast do electrons move in their orbits?

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