11 research outputs found
Exact formula for currents in strongly pumped diffusive systems
We analyze a generic model of mesoscopic machines driven by the nonadiabatic
variation of external parameters. We derive a formula for the probability
current; as a consequence we obtain a no-pumping theorem for cyclic processes
satisfying detailed balance and demonstrate that the rectification of current
requires broken spatial symmetry.Comment: 10 pages, accepted for publication in the Journal of Statistical
Physic
Breaking of general rotational symmetries by multi-dimensional classical ratchets
We demonstrate that a particle driven by a set of spatially uncorrelated,
independent colored noise forces in a bounded, multidimensional potential
exhibits rotations that are independent of the initial conditions. We calculate
the particle currents in terms of the noise statistics and the potential
asymmetries by deriving an n-dimensional Fokker-Planck equation in the small
correlation time limit. We analyze a variety of flow patterns for various
potential structures, generating various combinations of laminar and rotational
flows.Comment: Accepted, Physical Review
Interaction model for magnetic holes in a ferrofluid layer
Nonmagnetic spheres confined in a ferrofluid layer (magnetic holes) present
dipolar interactions when an external magnetic field is exerted. The
interaction potential of a microsphere pair is derived analytically, with a
precise care for the boundary conditions along the glass plates confining the
system. Considering external fields consisting of a constant normal component
and a high frequency rotating in-plane component, this interaction potential is
averaged over time to exhibit the average interparticular forces acting when
the imposed frequency exceeds the inverse of the viscous relaxation time of the
system. The existence of an equilibrium configuration without contact between
the particles is demonstrated for a whole range of exciting fields, and the
equilibrium separation distance depending on the structure of the external
field is established. The stability of the system under out-of-plane buckling
is also studied. The dynamics of such a particle pair is simulated and
validated by experiments.Comment: 15 pages, 11 figures (18 with subfigures). to appear in Phys. Rev.
Transitions in the Horizontal Transport of Vertically Vibrated Granular Layers
Motivated by recent advances in the investigation of fluctuation-driven
ratchets and flows in excited granular media, we have carried out experimental
and simulational studies to explore the horizontal transport of granular
particles in a vertically vibrated system whose base has a sawtooth-shaped
profile. The resulting material flow exhibits novel collective behavior, both
as a function of the number of layers of particles and the driving frequency;
in particular, under certain conditions, increasing the layer thickness leads
to a reversal of the current, while the onset of transport as a function of
frequency occurs gradually in a manner reminiscent of a phase transition. Our
experimental findings are interpreted here with the help of extensive, event
driven Molecular Dynamics simulations. In addition to reproducing the
experimental results, the simulations revealed that the current may be reversed
as a function of the driving frequency as well. We also give details about the
simulations so that similar numerical studies can be carried out in a more
straightforward manner in the future.Comment: 12 pages, 18 figure
Noise-assisted classical adiabatic pumping in a symmetric periodic potential
We consider a classical overdamped Brownian particle moving in a symmetric
periodic potential. We show that a net particle flow can be produced by
adiabatically changing two external periodic potentials with a spatial and a
temporal phase difference. The classical pumped current is found to be
independent of the friction and to vanish both in the limit of low and high
temperature. Below a critical temperature, adiabatic pumping appears to be more
efficient than transport due to a constant external force.Comment: six pages, 3 figure
Reliability of fluctuation-induced transport in a Maxwell-demon-type engine
We study the transport properties of an overdamped Brownian particle which is
simultaneously in contact with two thermal baths. The first bath is modeled by
an additive thermal noise at temperature . The second bath is associated
with a multiplicative thermal noise at temperature . The analytical
expressions for the particle velocity and diffusion constant are derived for
this system, and the reliability or coherence of transport is analyzed by means
of their ratio in terms of a dimensionless P\'{e}clet number. We find that the
transport is not very coherent, though one can get significantly higher
currents.Comment: 14 pages, 5 figure
Force and Motion Generation of Molecular Motors: A Generic Description
We review the properties of biological motor proteins which move along linear
filaments that are polar and periodic. The physics of the operation of such
motors can be described by simple stochastic models which are coupled to a
chemical reaction. We analyze the essential features of force and motion
generation and discuss the general properties of single motors in the framework
of two-state models. Systems which contain large numbers of motors such as
muscles and flagella motivate the study of many interacting motors within the
framework of simple models. In this case, collective effects can lead to new
types of behaviors such as dynamic instabilities of the steady states and
oscillatory motion.Comment: 29 pages, 9 figure