79 research outputs found
Maximum power operation of interacting molecular motors
We study the mechanical and thermodynamic properties of different traffic
models for kinesin which are relevant in biological and experimental contexts.
We find that motor-motor interactions play a fundamental role by enhancing the
thermodynamic efficiency at maximum power of the motors, as compared to the
non-interacting system, in a wide range of biologically compatible scenarios.
We furthermore consider the case where the motor-motor interaction directly
affects the internal chemical cycle and investigate the effect on the system
dynamics and thermodynamics.Comment: 19 pages, 22 figure
Efficiency at maximum power of motor traffic on networks
We study motor traffic on Bethe networks subject to hard-core exclusion for
both tightly coupled one-state machines and loosely coupled two-state machines
that perform work against a constant load. In both cases we find an
interaction-induced enhancement of the efficiency at maximum power (EMP) as
compared to non-interacting motors. The EMP enhancement occurs for a wide range
of network and single motor parameters and is due to a change in the
characteristic load-velocity relation caused by phase transitions in the
system. Using a quantitative measure of the trade-off between the EMP
enhancement and the corresponding loss in the maximum output power we identify
parameter regimes where motor traffic systems operate efficiently at maximum
power without a significant decrease in the maximum power output due to jamming
effects.Comment: 9 pages, 9 figures, submitted to Phys. Rev.
Heat fluctuations and fluctuation theorems in the case of multiple reservoirs
We consider heat fluctuations and fluctuation theorems for systems driven by
multiple reservoirs. We establish a fundamental symmetry obeyed by the joint
probability distribution for the heat transfers and system coordinates. The
symmetry leads to a generalisation of the asymptotic fluctuation theorem for
large deviations at large times. As a result the presence of multiple
reservoirs influence the tails in the heat distribution. The symmetry,
moreover, allows for a simple derivation of a recent exact fluctuation theorem
valid at all times. Including a time dependent work protocol we also present a
derivation of the integral fluctuation theorem.Comment: 27 pages, 1 figure, new extended version, to appear in J. Stat. Mech,
(2014
Bound particle coupled to two thermostats
We consider a harmonically bound Brownian particle coupled to two distinct
heat reservoirs at different temperatures. We show that the presence of a
harmonic trap does not change the large deviation function from the case of a
free Brownian particle discussed by Derrida and Brunet and Visco. Likewise, the
Gallavotti-Cohen fluctuation theorem related to the entropy production at the
heat sources remains in force. We support the analytical results with numerical
simulations
Sisyphus Effect in Pulse Coupled Excitatory Neural Networks with Spike-Timing Dependent Plasticity
The collective dynamics of excitatory pulse coupled neural networks with
spike timing dependent plasticity (STDP) is studied. Depending on the model
parameters stationary states characterized by High or Low Synchronization can
be observed. In particular, at the transition between these two regimes,
persistent irregular low frequency oscillations between strongly and weakly
synchronized states are observable, which can be identified as infraslow
oscillations with frequencies 0.02 - 0.03 Hz. Their emergence can be explained
in terms of the Sisyphus Effect, a mechanism caused by a continuous feedback
between the evolution of the coherent population activity and of the average
synaptic weight. Due to this effect, the synaptic weights have oscillating
equilibrium values, which prevents the neuronal population from relaxing into a
stationary macroscopic state.Comment: 18 pages, 24 figures, submitted to Physical Review
Pathways of mechanical unfolding of FnIII10: Low force intermediates
We study the mechanical unfolding pathways of the domain of
fibronectin by means of an Ising--like model, using both constant force and
constant velocity protocols. At high forces and high velocities our results are
consistent with experiments and previous computational studies. Moreover, the
simplicity of the model allows us to probe the biologically relevant low force
regime, where we predict the existence of two intermediates with very close
elongations. The unfolding pathway is characterized by stochastic transitions
between these two intermediates
Equilibrium-like fluctuations in some boundary-driven open diffusive systems
There exist some boundary-driven open systems with diffusive dynamics whose
particle current fluctuations exhibit universal features that belong to the
Edwards-Wilkinson universality class. We achieve this result by establishing a
mapping, for the system's fluctuations, to an equivalent open --yet
equilibrium-- diffusive system. We discuss the possibility of observing dynamic
phase transitions using the particle current as a control parameter
Shape fluctuations and elastic properties of two-component bilayer membranes
The elastic properties of two-component bilayer membranes are studied using a
coarse grain model for amphiphilic molecules. The two species of amphiphiles
considered here differ only in their length. Molecular Dynamics simulations are
performed in order to analyze the shape fluctuations of the two-component
bilayer membranes and to determine their bending rigidity. Both the bending
rigidity and its inverse are found to be nonmonotonic functions of the mole
fraction of the shorter B-amphiphiles and, thus, do not satisfy a
simple lever rule. The intrinsic area of the bilayer also exhibits a
nonmonotonic dependence on and a maximum close to .Comment: To appear on Europhysics Letter
Current fluctuations in systems with diffusive dynamics, in and out of equilibrium
For diffusive systems that can be described by fluctuating hydrodynamics and
by the Macroscopic Fluctuation Theory of Bertini et al., the total current
fluctuations display universal features when the system is closed and in
equilibrium. When the system is taken out of equilibrium by a boundary-drive,
current fluctuations, at least for a particular family of diffusive systems,
display the same universal features as in equilibrium. To achieve this result,
we exploit a mapping between the fluctuations in a boundary-driven
nonequilibrium system and those in its equilibrium counterpart. Finally, we
prove, for two well-studied processes, namely the Simple Symmetric Exclusion
Process and the Kipnis-Marchioro-Presutti model for heat conduction, that the
distribution of the current out of equilibrium can be deduced from the
distribution in equilibrium. Thus, for these two microscopic models, the
mapping between the out-of-equilibrium setting and the equilibrium one is
exact
Work and heat probability distributions in out-of-equilibrium systems
We review and discuss the equations governing the distribution of work done
on a system which is driven out of equilibrium by external manipulation, as
well as those governing the entropy flow to a reservoir in a nonequilibrium
system. We take advantage of these equations to investigate the path phase
transition in a manipulated mean-field Ising model and the large-deviation
function for the heat flow in the asymmetric exclusion process with
periodically varying transition probabilities.Comment: Contribution to Proceedings of "Work, Dissipation, and Fluctuations
in Nonequilibrium Physics", Brussels, 200
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