# Questions tagged [non-equilibrium]

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### 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-...
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### Rayleigh Benard Convection analyzed as heat engine?

The treatment I've seen for Benard convection in a textbook is to derive approximate equations of motion and then show that there is a periodic solution matching the boundary conditions. This is ...
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### How to generate a PDE from a discrete equation in a rice-pile like model?

I am reading Noise and dynamics of self-organized critical phenomena by Albert Díaz-Guilera Here, on an extension of the rice-pile model by Bak et al demonstrating self-organized criticality. Equation ...
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### Dynamical interpretation of reflecting boundary conditions in the Fokker-Planck equation

Background: For a particle driven by the dynamical equation $$\dot{x}(t) = a(x,t) + b(x)\xi(t),$$ where $\xi(t)$ is a Gaussian white noise, the probability distribution of position $x$ is governed by ...
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### Literature on non-equilibrium statistical mechanics [duplicate]

I am a graduate student, currently planning on self-studying non-equilibrium statistical mechanics. I have tried searching for literature myself, but no book/online course that I have found seems ...
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### Equation of motion of a gas's center of mass due to heating

So here's a pretty basic question that I don't know how to solve within standard thermodynamics. Let's say I have a container with a gas in it. I transfer heat, $Q$, to the gas from the bottom of the ...
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### Basis state of non-interacting fermions

I am trying to calculate the periodic dynamics of many-body systems (spin-$1/2$ $XY$) Hamiltonian, where, H_1 = \sum_{i=1}^{N-1}(\sigma^{x}_{i}\sigma^{x}_{i+1}+\sigma^{y}_{i}\sigma^{...
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### In non-equilibrium energy calculations, how do you handle negative formation enthalpies?

I'm working on some simulation software at the moment which deals with high speed flows in chemical non-equilibrium (including plasma states). When the code initially calculates total energy, it uses ...
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Textbooks treat black body radiation as radiation in thermal equilibrium with its environment (more specifically - with a black body): Planck's formula is essentially derived from the partition ...
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### Are stationarity, Markovianity and Gaussianity sufficient conditions to ensure that the random force on a Brownian particle is delta correlated?

In the Langevin model, if we make the assumption that the random force $\eta(t)$ acting on the Brownian particle is a stationary, Markovian, and gaussian process, does it automatically ensure that the ...
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### Black body vs. Thermal radiation

I am seeking clarification of the following terms: Black body radiation Thermal radiation Thermal light source At the first glance, the first two are the same thing, and they are the radiation ...
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### Canonical ensemble: what if the phase space density is not known?

In canonical ensemble, the probability is defined as $$P(E)=\frac{g(E)\exp(-E/T)}{Z},$$ and the partition function is defined as Z(T)=\int_0^{\infty}dE\,g(...
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### What happens to entropy when half the particles are removed?

Curiosity question. What happens to entropy in the following situation? A gas fills an entire container and is in equilibrium. Suddenly all particles are removed from half the container. As such, ...
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### Non-equilibrium phase transition

I have come across the term Non-equilibrium phase transition. And unfortunately I can't find any examples of such a phenomenon. What examples of nonequilibrium phase transitions are known? Are there ...
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### Is entropy maximized for steadily driven systems?

Suppose we send an electric current through a piece of metal. If we knew only the average energy and current through the sample, it would seem natural to assume the state of the sample is described by ...
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### Can we define the concept of temperature for a system in non-equilibrium steady state?

I would like to define the temperature for a system in a non-equilibrium steady-state. The standard textbooks show that the temperature is estimated by equating the internal energy of the system with ...
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### Does systems (such as the cell) far from equilibrium have to dissipate their energy? Can't they store it? Is there a physical requirement for that?

It is a well known fact in the field of non-equilibrium statistical physics that in order to maintain a system far from equilbrium, you need to drive it via an external energy source. The system uses ...
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### Equal time Keldysh Green's function and expectation value of the F operator in the continuum notation

I recently went through Field Theory of Non-Equilibrium Systems by Alex Kamenev (2011) and I wanted to understand certain points in detail. My current problem is to understand how one can calculate ...
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### Is there really an inconsistency with the original Langevin equation (as claimed in the book Nonequilibrium Statistical Mechanics - V. Balakrishnan)?

I am reading the book Nonequilibrium Statistical Mechanics by V. Balakrishnan. In chapter $17$ (page $244$) he argues that the original Langevin equation has inconsistencies and should, therefore, be ...
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### Detailed balance: What does one rigourously mean by the transition rate $dw$?

Consider (for example) non-relativistic electron-impact ionisation, in which an effectively stationary atom in state $I$ is struck by an electron of momentum ${p_1}$, producing an atom in state $J$ ...
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