43 research outputs found
Soliton ratchets
The mechanism underlying the soliton ratchet, both in absence and in presence
of noise, is investigated. We show the existence of an asymmetric internal mode
on the soliton profile which couples, trough the damping in the system, to the
soliton translational mode. Effective soliton transport is achieved when the
internal mode and the external force are phase locked. We use as working model
a generalized double sine-Gordon equation. The phenomenon is expected to be
valid for generic soliton systems.Comment: 4 pages, 4 figure
DNA transport by a micromachined Brownian ratchet device
We have micromachined a silicon-chip device that transports DNA with a
Brownian ratchet that rectifies the Brownian motion of microscopic particles.
Transport properties for a DNA 50mer agree with theoretical predictions, and
the DNA diffusion constant agrees with previous experiments. This type of
micromachine could provide a generic pump or separation component for DNA or
other charged species as part of a microscale lab-on-a-chip. A device with
reduced feature size could produce a size-based separation of DNA molecules,
with applications including the detection of single nucleotide polymorphisms.Comment: Latex: 8 pages, 4 figure
Accumulating Particles at the Boundaries of a Laminar Flow
The accumulation of small particles is analyzed in stationary flows through
channels of variable width at small Reynolds number. The combined influence of
pressure, viscous drag and thermal fluctuations is described by means of a
Fokker-Planck equation for the particle density. It is shown that in the limit
of vanishing particle size a uniform particle distribution is always approached
in the long time limit. For extended spherical particles, conditions are
specified that lead to inhomogeneous densities and consequently to particle
accumulation and depletion. Hereby the boundary conditions for the particle
density play a decisive role: The centers of spherical particles must keep the
minimal distance of their radius from the fluid boundaries. The normal
components of the forces acting on the sphere then may assume finite values
which are diffusively transported into the bulk of the fluid.Comment: final version, accepted by Physica
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
Control of Current Reversal in Single and Multiparticle Inertia Ratchets
We have studied the deterministic dynamics of underdamped single and
multiparticle ratchets associated with current reversal, as a function of the
amplitude of the external driving force. Two experimentally inspired methods
are used. In the first method the same initial condition is used for each new
value of the amplitude. In the second method the last position and velocity is
used as the new initial condition when the amplitude is changed. The two
methods are found to be complementary for control of current reversal, because
the first one elucidates the existence of different attractors and gives
information about their basins of attraction, while the second method, although
history dependent, shows the locking process. We show that control of current
reversals in deterministic intertia ratchets is possible as a consequence of a
locking process associated with different mean velocity attractors. An
unlocking efect is produced when a chaos to order transition limits the control
range.Comment: to be published in Physica A - 11 pages - 10 figure
Disorder Induced Diffusive Transport In Ratchets
The effects of quenched disorder on the overdamped motion of a driven
particle on a periodic, asymmetric potential is studied. While for the
unperturbed potential the transport is due to a regular drift, the quenched
disorder induces a significant additional chaotic ``diffusive'' motion. The
spatio-temporal evolution of the statistical ensemble is well described by a
Gaussian distribution, implying a chaotic transport in the presence of quenched
disorder.Comment: 10 pages, 4 EPS figures; submitted to Phys. Rev. Letter
Brownian motion exhibiting absolute negative mobility
We consider a single Brownian particle in a spatially symmetric, periodic
system far from thermal equilibrium. This setup can be readily realized
experimentally. Upon application of an external static force F, the average
particle velocity is negative for F>0 and positive for F<0 (absolute negative
mobility).Comment: 4 pages, 3 figures, to be published in PR
Brownian motors: noisy transport far from equilibrium
Transport phenomena in spatially periodic systems far from thermal
equilibrium are considered. The main emphasize is put on directed transport in
so-called Brownian motors (ratchets), i.e. a dissipative dynamics in the
presence of thermal noise and some prototypical perturbation that drives the
system out of equilibrium without introducing a priori an obvious bias into one
or the other direction of motion. Symmetry conditions for the appearance (or
not) of directed current, its inversion upon variation of certain parameters,
and quantitative theoretical predictions for specific models are reviewed as
well as a wide variety of experimental realizations and biological
applications, especially the modeling of molecular motors. Extensions include
quantum mechanical and collective effects, Hamiltonian ratchets, the influence
of spatial disorder, and diffusive transport.Comment: Revised version (Aug. 2001), accepted for publication in Physics
Report