1,021 research outputs found
Efficiency statistics at all times: Carnot limit at finite power
We derive the statistics of the efficiency under the assumption that
thermodynamic fluxes fluctuate with normal law, parametrizing it in terms of
time, macroscopic efficiency, and a coupling parameter . It has a
peculiar behavior: No moments, one sub- and one super-Carnot maxima
corresponding to reverse operating regimes (engine/pump), the most probable
efficiency decreasing in time. The limit where the Carnot bound
can be saturated gives rise to two extreme situations, one where the machine
works at its macroscopic efficiency, with Carnot limit corresponding to no
entropy production, and one where for a transient time scaling like
microscopic fluctuations are enhanced in such a way that the most probable
efficiency approaches Carnot at finite entropy production.Comment: 5+4 pages, 4 figures. Title modifie
Degree of coupling and efficiency of energy converters far-from-equilibrium
In this paper, we introduce a real symmetric and positive semi-definite
matrix, which we call the non-equilibrium conductance matrix, and which
generalizes the Onsager response matrix for a system in a non-equilibrium
stationary state. We then express the thermodynamic efficiency in terms of the
coefficients of this matrix using a parametrization similar to the one used
near equilibrium. This framework, then valid arbitrarily far from equilibrium
allows to set bounds on the thermodynamic efficiency by a universal function
depending only on the degree of coupling between input and output currents. It
also leads to new general power-efficiency trade-offs valid for macroscopic
machines that are compared to trade-offs previously obtained from uncertainty
relations. We illustrate our results on an unicycle heat to heat converter and
on a discrete model of molecular motor.Comment: 24 pages, 5 figure
Collective effects enhancing power and efficiency
Energy conversion is most efficient for micro or nano machines with tight
coupling between input and output power. To reach meaningful amounts of power,
ensembles of such machines must be considered. We use a model system to
demonstrate that interactions between tightly coupled nanomachines can
enhance the power output per machine. Furthermore, while interactions break
tight coupling and thus lower efficiency in finite ensembles, the macroscopic
limit () restores it and enhances both the efficiency and
the output power per nanomachine.Comment: 5 pages, 3 figure
Inequalities generalizing the second law of thermodynamics for transitions between non-stationary states
We discuss the consequences of a variant of the Hatano-Sasa relation in which
a non-stationary distribution is used in place of the usual stationary one. We
first show that this non-stationary distribution is related to a difference of
traffic between the direct and dual dynamics. With this formalism, we extend
the definition of the adiabatic and non-adiabatic entropies introduced by M.
Esposito and C. Van den Broeck in Phys. Rev. Lett. 104, 090601 (2010) for the
stationary case. We also obtain interesting second-law like inequalities for
transitions between non-stationary states.Comment: 4 pages, 2 figure
Work statistics in stochastically driven systems
We identify the conditions under which a stochastic driving inducing energy
changes on a system coupled to a thermal bath can be treated as a work source.
When these conditions are met, the work statistics satisfies the Crooks
fluctuation theorem traditionally derived for deterministic drivings. We
illustrate this fact by calculating and comparing the work statistics for a
two-level system driven respectively by a stochastic and a deterministic
piecewise constant protocol.Comment: 19 pages, 7 figures, 2 table
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