22,831 research outputs found
Time Evolution In Macroscopic Systems. II: The Entropy
The concept of entropy in nonequilibrium macroscopic systems is investigated
in the light of an extended equation of motion for the density matrix obtained
in a previous study. It is found that a time-dependent information entropy can
be defined unambiguously, but it is the time derivative or entropy production
that governs ongoing processes in these systems. The differences in physical
interpretation and thermodynamic role of entropy in equilibrium and
nonequilibrium systems is emphasized and the observable aspects of entropy
production are noted. A basis for nonequilibrium thermodynamics is also
outlinedComment: 28 page
Entropy and Entropy Production in Some Applications
By using entropy and entropy production, we calculate the steady flux of some
phenomena. The method we use is a competition method, , where is system entropy, is entropy production and
is microscopic interaction time. System entropy is calculated from the
equilibrium state by studying the flux fluctuations. The phenomena we study
include ionic conduction, atomic diffusion, thermal conduction and viscosity of
a dilute gas
The Principle of Minimal Resistance in Non-Equilibrium Thermodynamics
Analytical models describing the motion of colloidal particles in given
velocity fields are presented. In addition to local approaches, leading to well
known master equations such as the Langevin and the Fokker-Planck equations, a
global description based on path integration is reviewed. This shows that under
very broad conditions, during its evolution a dissipative system tends to
minimize its energy dissipation in such a way to keep constant the Hamiltonian
time rate, equal to the difference between the flux-based and the force-based
Rayleigh dissipation functions. At steady state, the Hamiltonian time rate is
maximized, leading to a minimum resistance principle. In the unsteady case, we
consider the relaxation to equilibrium of harmonic oscillators and the motion
of a Brownian particle in shear flow, obtaining results that coincide with the
solution of the Fokker-Planck and the Langevin equations
A linear nonequilibrium thermodynamics approach to optimization of thermoelectric devices
Improvement of thermoelectric systems in terms of performance and range of
applications relies on progress in materials science and optimization of device
operation. In this chapter, we focuse on optimization by taking into account
the interaction of the system with its environment. For this purpose, we
consider the illustrative case of a thermoelectric generator coupled to two
temperature baths via heat exchangers characterized by a thermal resistance,
and we analyze its working conditions. Our main message is that both electrical
and thermal impedance matching conditions must be met for optimal device
performance. Our analysis is fundamentally based on linear nonequilibrium
thermodynamics using the force-flux formalism. An outlook on mesoscopic systems
is also given.Comment: Chapter 14 in "Thermoelectric Nanomaterials", Editors Kunihito
Koumoto and Takao Mori, Springer Series in Materials Science Volume 182
(2013
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