193 research outputs found
Granular Brownian Motors: role of gas anisotropy and inelasticity
We investigate the motion of a wedge-shaped object (a granular Brownian
motor), which is restricted to move along the x-axis and cannot rotate, as gas
particles collide with it. We show that its steady-state drift, resulting from
inelastic gas-motor collisions, is dramatically affected by anisotropy in the
velocity distribution of the gas. We identify the dimensionless parameter
providing the dependence of this drift on shape, masses, inelasticity, and
anisotropy: the anisotropy leads to a dramatic breaking of equipartition, which
should easily be visible in experimental realizations.Comment: 5 pages, 4 figure
Fluctuating Currents in Stochastic Thermodynamics II. Energy Conversion and Nonequilibrium Response in Kinesin Models
Unlike macroscopic engines, the molecular machinery of living cells is
strongly affected by fluctuations. Stochastic Thermodynamics uses Markovian
jump processes to model the random transitions between the chemical and
configurational states of these biological macromolecules. A recently developed
theoretical framework [Wachtel, Vollmer, Altaner: "Fluctuating Currents in
Stochastic Thermodynamics I. Gauge Invariance of Asymptotic Statistics"]
provides a simple algorithm for the determination of macroscopic currents and
correlation integrals of arbitrary fluctuating currents. Here, we use it to
discuss energy conversion and nonequilibrium response in different models for
the molecular motor kinesin. Methodologically, our results demonstrate the
effectiveness of the algorithm in dealing with parameter-dependent stochastic
models. For the concrete biophysical problem our results reveal two interesting
features in experimentally accessible parameter regions: The validity of a
non-equilibrium Green--Kubo relation at mechanical stalling as well as negative
differential mobility for superstalling forces.Comment: PACS numbers: 05.70.Ln, 05.40.-a, 87.10.Mn, 87.16.Nn. An accompanying
publication "Fluctuating Currents in Stochastic Thermodynamics I. Gauge
Invariance of Asymptotic Statistics" is available at
http://arxiv.org/abs/1407.206
Fluctuating Currents in Stochastic Thermodynamics I. Gauge Invariance of Asymptotic Statistics
Stochastic Thermodynamics uses Markovian jump processes to model random
transitions between observable mesoscopic states. Physical currents are
obtained from anti-symmetric jump observables defined on the edges of the graph
representing the network of states. The asymptotic statistics of such currents
are characterized by scaled cumulants. In the present work, we use the
algebraic and topological structure of Markovian models to prove a gauge
invariance of the scaled cumulant-generating function. Exploiting this
invariance yields an efficient algorithm for practical calculations of
asymptotic averages and correlation integrals. We discuss how our approach
generalizes the Schnakenberg decomposition of the average entropy-production
rate, and how it unifies previous work. The application of our results to
concrete models is presented in an accompanying publication.Comment: PACS numbers: 05.40.-a, 05.70.Ln, 02.50.Ga, 02.10.Ox. An accompanying
pre-print "Fluctuating Currents in Stochastic Thermodynamics II. Energy
Conversion and Nonequilibrium Response in Kinesin Models" by the same authors
is available as arXiv:1504.0364
Comment on "A test-tube model for rainfall" by Wilkinson M., EPL 106 (2014) 40001
This paper is a comment to M Wilkinson, EPL 106 (2014) 40001, arXiv:1401.4620
[physics.ao-ph,cond-mat.soft], which draws conclusion from our data that are at
variance with our observations
Impurity-induced step interactions: a kinetic Monte-Carlo study
A one-dimensional continuum description of growth on vicinal surfaces in the
presence of immobile impurities predicts that the impurities can induce step
bunching when they suppress the diffusion of adatoms on the surface. In the
present communication we verify this prediction by kinetic Monte-Carlo
simulations of a two-dimensional solid-on-solid model. We identify the
conditions where quasi one-dimensional step flow is stable against island
formation or step meandering, and analyse in detail the statistics of the
impurity concentration profile. The sign and strength of the impurity-induced
step interactions is determined by monitoring the motion of pairs of steps.
Assemblies containing up to 20 steps turn out to be unstable towards the
emission of single steps. This behavior is traced back to the small value of
the effective, impurity-induced attachment asymmetry for adatoms. An analytic
estimate for the critical number of steps needed to stabilize a bunch is
derived and confirmed by simulations of a one-dimensional model.Comment: 9 pages, 8 figure
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