Nonequilibrium and Irreversibility

Probing local equilibrium in nonequilibrium fluids

“…from different modelings of boundary baths) describe equally well what seems to be the same macroscopic NESS (or MNESS in short), defined in terms of a few macroscopically smooth fields [11]. Key for this sort of nonequilibrium ensemble equivalence (which can be formally stated via the chaotic hypothesis of Gallavotti and Cohen [10]) is the notion of local thermodynamic equilibrium (LTE) [2,12], i.e. the fact that an interacting nonequilibrium system reaches locally an equilibriumlike state defined by e.g.…”

“…In this work we study a system of N ∈ [1456, 8838] hard disks of radius in a two-dimensional box of unit size L = 1, with stochastic thermal walls [35,42,43] at x = 0, L at temperatures T 0 ∈ [2,20] and T L = 1, respectively, and periodic boundary conditions along the y-direction. The stochastic thermal walls work as follows: each time a particle hits one of these walls, its velocity v = (v x , v y ) is randomly drawn from a Maxwellian distribution defined by the wall temperature…”

“…Out of equilibrium, dynamics and statistics are so intimately knotted that no general bottom-up approach exists yet (similar to equilibrium ensemble theory) capable of predicting nonequilibrium macroscopic behavior in terms of microscopic physics, even in the simplest situation of a nonequilibrium steady state (NESS) [1][2][3][4][5][6][7]. In contrast with equilibrium, the microscopic probability measure associated to a NESS (or mNESS hereafter) is a complex object, often defined on a fractal support or strange attractor, and is utterly sensitive to microscopic details as the modeling of boundary reservoirs (e.g., deterministic vs stochastic) [2,[8][9][10]. Moreover, the connection between mNESSs and a nonequilibrium analog of thermodynamic potentials is still murky at best.…”

Biology and nonequilibrium: Remarks on a paper by J.L. England

“…Crooks [1] who uses classical mechanics to describe the system M of interest and stochastic dynamics for the bath. The use of stochastic dynamics (Langevin's equation) is traditional and has proved very useful in nonequilibrium statistical mechanics (see for instance [2]), but it limits the understanding of what is physically going on (see [4], [9] for more modern views). We prefer thus an approach based on deterministic dynamics.…”

Entropy production and Fluctuation Relation in turbulent thermal convection

“…The introduction of the so-called fluctuation relation (FR) [5][6][7][8][9] has represented a remarkable result in this area of physics. The FR for nonequilibrium fluctuations reduces to the Green-Kubo and Onsager relations close to equilibrium [10][11][12][13] and represents one of the few exact results for systems kept far from equilibrium. However, a general response-theory for this kind of (nonequilibrium) systems is still to be produced.…”