256 research outputs found
Stochastic thermodynamics of chemical reaction networks
For chemical reaction networks described by a master equation, we define
energy and entropy on a stochastic trajectory and develop a consistent
nonequilibrium thermodynamic description along a single stochastic trajectory
of reaction events. A first-law like energy balance relates internal energy,
applied (chemical) work and dissipated heat for every single reaction. Entropy
production along a single trajectory involves a sum over changes in the entropy
of the network itself and the entropy of the medium. The latter is given by the
exchanged heat identified through the first law. Total entropy production is
constrained by an integral fluctuation theorem for networks arbitrarily driven
by time-dependent rates and a detailed fluctuation theorem for networks in the
steady state. Further exact relations like a generalized Jarzynski relation and
a generalized Clausius inequality are discussed. We illustrate these results
for a three-species cyclic reaction network which exhibits nonequilibrium
steady states as well as transitions between different steady states.Comment: 14 pages, 2 figures, accepted for publication in J. Chem. Phy
Molecular kinetic analysis of a finite-time Carnot cycle
We study the efficiency at the maximal power of a
finite-time Carnot cycle of a weakly interacting gas which we can reagard as a
nearly ideal gas. In several systems interacting with the hot and cold
reservoirs of the temperatures and , respectively,
it is known that which
is often called the Curzon-Ahlborn (CA) efficiency . For the
first time numerical experiments to verify the validity of
are performed by means of molecular dynamics simulations and reveal that our
does not always agree with , but
approaches in the limit of .
Our molecular kinetic analysis explains the above facts theoretically by using
only elementary arithmetic.Comment: 6 pages, 4 figure
Bounds of Efficiency at Maximum Power for Normal-, Sub- and Super-Dissipative Carnot-Like Heat Engines
The Carnot-like heat engines are classified into three types (normal-, sub-
and super-dissipative) according to relations between the minimum irreversible
entropy production in the "isothermal" processes and the time for completing
those processes. The efficiencies at maximum power of normal-, sub- and
super-dissipative Carnot-like heat engines are proved to be bounded between
and , and , 0 and
, respectively. These bounds are also shared by linear, sub-
and super-linear irreversible Carnot-like engines [Tu and Wang, Europhys. Lett.
98, 40001 (2012)] although the dissipative engines and the irreversible ones
are inequivalent to each other.Comment: 1 figur
Entropy and efficiency of a molecular motor model
In this paper we investigate the use of path-integral formalism and the
concepts of entropy and traffic in the context of molecular motors. We show
that together with time-reversal symmetry breaking arguments one can find
bounds on efficiencies of such motors. To clarify this techinque we use it on
one specific model to find both the thermodynamic and the Stokes efficiencies,
although the arguments themselves are more general and can be used on a wide
class of models. We also show that by considering the molecular motor as a
ratchet, one can find additional bounds on the thermodynamic efficiency
Efficiency at maximum power: An analytically solvable model for stochastic heat engines
We study a class of cyclic Brownian heat engines in the framework of
finite-time thermodynamics. For infinitely long cycle times, the engine works
at the Carnot efficiency limit producing, however, zero power. For the
efficiency at maximum power, we find a universal expression, different from the
endoreversible Curzon-Ahlborn efficiency. Our results are illustrated with a
simple one-dimensional engine working in and with a time-dependent harmonic
potential.Comment: 6 pages, 3 figure
Thermoelectric efficiency at maximum power in a quantum dot
We identify the operational conditions for maximum power of a
nanothermoelectric engine consisting of a single quantum level embedded between
two leads at different temperatures and chemical potentials. The corresponding
thermodynamic efficiency agrees with the Curzon-Ahlborn expression up to
quadratic terms in the gradients, supporting the thesis of universality beyond
linear response.Comment: 4 pages, 3 figure
Magnon-driven quantum-dot heat engine
We investigate a heat- to charge-current converter consisting of a
single-level quantum dot coupled to two ferromagnetic metals and one
ferromagnetic insulator held at different temperatures. We demonstrate that
this nano engine can act as an optimal heat to spin-polarized charge current
converter in an antiparallel geometry, while it acts as a heat to pure spin
current converter in the parallel case. We discuss the maximal output power of
the device and its efficiency.Comment: 6 pages, 4 figures, published version, selected as Editor's choic
Efficiency at maximum power of minimally nonlinear irreversible heat engines
We propose the minimally nonlinear irreversible heat engine as a new general
theoretical model to study the efficiency at the maximum power of heat
engines operating between the hot heat reservoir at the temperature and
the cold one at (). Our model is based on the extended
Onsager relations with a new nonlinear term meaning the power dissipation. In
this model, we show that is bounded from the upper side by a function
of the Carnot efficiency as . We demonstrate the validity of our theory by showing that
the low-dissipation Carnot engine can easily be described by our theory.Comment: 6 pages, 1 figur
Efficiency of a Brownian information machine
A Brownian information machine extracts work from a heat bath through a
feedback process that exploits the information acquired in a measurement. For
the paradigmatic case of a particle trapped in a harmonic potential, we
determine how power and efficiency for two variants of such a machine operating
cyclically depend on the cycle time and the precision of the positional
measurements. Controlling only the center of the trap leads to a machine that
has zero efficiency at maximum power whereas additional optimal control of the
stiffness of the trap leads to an efficiency bounded between 1/2, which holds
for maximum power, and 1 reached even for finite cycle time in the limit of
perfect measurements.Comment: 9 pages, 2 figure
Interaction of molecular motors can enhance their efficiency
Particles moving in oscillating potential with broken mirror symmetry are
considered. We calculate their energetic efficiency, when acting as molecular
motors carrying a load against external force. It is shown that interaction
between particles enhances the efficiency in wide range of parameters. Possible
consequences for artificial molecular motors are discussed.Comment: 6 pages, 8 figure
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