# Questions tagged [non-equilibrium]

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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 ...
20 views

### How do you determine the Pull Direction for a GROMACS umbrella sampling simulation to generate the most accurate free energy value?

I am trying to calculate the free energy between a protein and aptamer using GROMACS. Literature has indicated that one of the best way to do so is by performing an umbrella sampling MD simulation ...
1 vote
29 views

### Detailed derivations about Mode Coupling Theory (MCT)

I am currently reading two articles related to mode coupling theory (MCT) and I am stuck in evaluating some ensemble averages, since there is no detailed derivations given. Moreover, the two ...
44 views

### What is an good book to study classical non-equilibrum thermodynamics? [duplicate]

I am a physics student who has just started my master's program and am taking a course on classical non-equilibrium thermodynamics. I am looking for a book that can help me learn this subject. Are ...
1 vote
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### Application of Schwinger-Keldysh formalism in various topics except cosmology

I want to find some theories or models on Schwinger-Keldysh formalism (in-in formalism) focusing on flat spacetime in terms of correlation functions. For example, I know there are many applications ...
26 views

### Is it possible for a droplet to condense in the middle (bulk rather than boundary) of the vapor without impurity?

As a rule of thumb, vapor condensation usually happens at the interface between the system and the heat reservoir. Now, according to my analysis below, it is the only way for vapor to condense, which ...
74 views

### A question on relaxation time approximation

I was learned that the form of collision term in relaxation time approximation is set to be: $$\left (\frac{\partial f}{\partial t}\right)_c=-\frac{f-f^0}{\tau}$$ in with $f^0$ is local equilibrium ...
105 views

### A problem in solving a PDE of the time-ordered Green function

In the article written by Jauho in 2006 Introduction to the Keldysh nonequilibrium Green function technique, I've tried to operating with whether $g_{k\alpha}^t$ or $g_{k\alpha}^{-1}$ from right to ...
23 views

### Spontaneous emission as dissipation and fluctuation

Suppose we have some sort of medium and we want to build an effective theory of light inside. Of course we want to calculation the dielectric constant, which in turn is determined by the ...
34 views

### If a system lies in a non-equilibrium state initially, and there are two possible equilibrium final states. How does the system evolve? [closed]

This should be the area of non-equilibrium thermodynamics. The system is in a non-equilibrium state and after a long time it will evolve into an equilibrium state. But now we have two possible final ...
1 vote
32 views

### Can the Keldysh occupation function have a zero for bosons or a pole for fermions?

In the Keldysh framework for nonequilibrium dynamics of quantum systems we learn that there are essentially two Green's functions that characterize a system: the retarded Green's function $G^R(\omega)$...
1 vote
152 views

### Electrostatics of non-equilibrium situations

In footnote 1 of Chapter 13 of Ashcroft and Mermin, they remark that The only case we shall discuss in which the local equilibrium distribution is not the uniform equilibrium distribution (13.1) (...
1 vote
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### Distinguishing between equilibrium and non-equilibrium distributions?

Suppose a physical system is described by some effective double-well potential landscape with fluctuation-driven motion along this landscape. If we watch the system for a sufficiently long time and ...
1 vote
47 views

### Boltzmann equation for Lennard-Jones particles?

In the Vlasov variant of Boltzmann equation, the Coulomb pair forces are included via the force term that appears as the prefactor of the derivative of the density with respect to velocity. In that ...
175 views

### Deriving diffusion coefficients from Newtonian mechanics of Lennard-Jones phases?

The diffusion coefficient is known in the traditional physical literature as an empirical parameter of Fick's law. Here the observation is that spatial gradients of densities are suppressed by a rate ...
59 views

### From Newtonian mechanics to Boltzmann (or statistical) mechanics

Classical mechanical systems observable on a dynamical scale are subject to Newton's laws. In this case, knowledge of the Hamiltonian allows us to minimize energy taking into account inertia. This ...
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1 vote
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### Higher order (order > 2) derivatives of free energy - higher cumulants in statistical mechanics

The first derivatives of free energies generally give relationships between thermodynamic conjugate pairs, like entropy $S$ & temperature $T$ pressure $P$ & volume $V$ and so on. The second ...
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### Condition for spontaneity of a non-equillibrium statistical system

As the title suggests: Is there any condition, which can determine the spontaneity of a non-equilibrium statistical system? If it is a "thermodynamic" system, we can calculate its $\Delta G$ ...
1 vote
156 views

### Can first order transitions accidentally have continuous free energy derivatives

Obviously if you define a first order phase transition as having a discontinuity in the first derivative of the free energy then the answer is no, but I'm asking about if the following situation would ...
119 views

### Turbulence, Euler equations and equipartition of energy

Recently the user CBBAM asked about the inviscid limit in turbulence and the relation between Navier-Stokes equations and Euler equations when $\nu \to 0$. There I pointed out that Onsager proposed ...
1 vote
81 views

### Langevin equation with hydrodynamic interaction

We know Langevin equation in the presence of an external applied force is given by, $$m\frac{dv(t)}{dt} = -\gamma v(t) + \eta(t) + \vec{F}$$ where $\eta(t)$ is delta correlated stationary white ...
79 views

### A charged conductor NOT in electrostatic equilibrium -- still an equipotential surface?

It is well known that "the surface of any charged conductor in electrostatic equilibrium is an equipotential surface" (Serway/Jewett; emphasis mine). I haven't found a good answer online for ...
1 vote
108 views

### Can Fokker-Planck operator be turned into a hermitian operator?

We know that Fokker-Planck equation can be written as(with proper boundary and initial condition) $$\frac{\partial p(v,t)}{\partial t} = Lp(v,t)$$ where $L$ is known as the Fokker-Planck operator ...
69 views

### Understanding the Markovian and Gaussian approximations in Brownian motion

I am trying to understand in the original derivation of Brownain diffusion, where does the assumption of Markovian and Gaussian nature factor in. In Albert Einstein's original work on Brownian motion ...
341 views

### What is the entropy associated with a diffusion process?

Is it possible to calculate entropy from the solution of a diffusion equation(with natural boundary conditions) by using the formula of Shanon entropy? Could anyone help me to understand the entropic ...
555 views

### Is diffusion a nonequlibrium process?

We know that the diffusion equation can be viewed as the continuum limit of a discreet unbiased random walk. My question is the following: Is diffusion (or an unbiased random walk) a non-equilibrium ...
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### Is it possible to define concepts like free energy in the diffusion process?

How does the idea of free energy (which we derive from the canonical partition function) fit in the domain of non-equilibrium processes like diffusion?
1 vote
76 views

### What does it mean for $\omega$ to not be "real" in practice?

I am reading about landau damping and the author states that $\omega$ is never real (due to collisions). https://cds.cern.ch/record/1982428/files/377-404%20Herr.pdf \begin{equation} 1 + \frac{\...
190 views

### Is there a steady state for two conductors at different temperatures connected to a battery?

In order to understand better nonequilibrium statistical physics I came up with the following thought experiment. I wonder what are the requirements to obtain a steady state. Let us consider two ...
279 views

### What is the meaning of an entropy current?

Imagine some kind of thermoionic device, where electrons jump off a metal in vacuum due to a fixed temperature bath and in the presence of a bias voltage. In a steady state regime (and quasi-...
72 views

### Onsager's hypothesis: why is true that correlations decay with increasing time?

I am studying from Chandler's book (Introduction to Modern Statistical Mechanics) the fluctuation-dissipation theorem. Before introducing it, the book states something without really demonstrating it. ...
86 views

### What are good references to understand how Cooper pairs transport charges in superconductors?

I am trying to get a deep understanding of superconductors (in the BCS treatment) and I am now focusing on a detailed description of charge flow in superconductors. I have managed to find some partial ...
1 vote
61 views

### (Detailed) Fluctuation Theorems/Relations and their implied symmetry

I'm currently reading up on non-equilibrium statistical mechanics, in particular so-called fluctuation theorems or fluctuation relations. In Section 3.1.2 of arXiv:1205.4176, the author introduces the ...
228 views

### How can an object on top of a Norton dome start to move?

The Norton dome is a dome-shaped surface in a gravity field on the top of which a symmetrical object is placed in perfect balance. According to Newtonian determinism, the object will remain in balance ...
Suppose we have a time-independent Hamiltonian operator $\hat{H}$ of some system. We know that we can express the canonical partition function of said system as $z = \text{Tr}(e^{\beta\hat{H}})$ for ...