367 research outputs found
Molecular motor with a build-in escapement device
We study dynamics of a classical particle in a one-dimensional potential,
which is composed of two periodic components, that are time-independent, have
equal amplitudes and periodicities. One of them is externally driven by a
random force and thus performs a diffusive-type motion with respect to the
other. We demonstrate that here, under certain conditions, the particle may
move unidirectionally with a constant velocity, despite the fact that the
random force averages out to zero. We show that the physical mechanism
underlying such a phenomenon resembles the work of an escapement-type device in
watches; upon reaching certain level, random fluctuations exercise a locking
function creating the points of irreversibility in particle's trajectories such
that the particle gets uncompensated displacements. Repeated (randomly) in each
cycle, this process ultimately results in a random ballistic-type motion. In
the overdamped limit, we work out simple analytical estimates for the
particle's terminal velocity. Our analytical results are in a very good
agreement with the Monte Carlo data.Comment: 7 pages, 4 figure
Modeling friction: From nanoscale to mesoscale
The physics of sliding friction is gaining impulse from nanoscale and
mesoscale experiments, simulations, and theoretical modeling. This Colloquium
reviews some recent developments in modeling and in atomistic simulation of
friction, covering open-ended directions, unconventional nanofrictional
systems, and unsolved problems.Comment: 26 pages, 14 figures, Rev. Mod. Phys. Colloquiu
Saltatory drift in a randomly driven two-wave potential
Dynamics of a classical particle in a one-dimensional, randomly driven
potential is analysed both analytically and numerically. The potential
considered here is composed of two identical spatially-periodic saw-tooth-like
components, one of which is externally driven by a random force. We show that
under certain conditions the particle may travel against the averaged external
force performing a saltatory unidirectional drift with a constant velocity.
Such a behavior persists also in situations when the external force averages
out to zero. We demonstrate that the physics behind this phenomenon stems from
a particular behavior of fluctuations in random force: upon reaching a certain
level, random fluctuations exercise a locking function creating points of
irreversibility which the particle can not overpass. Repeated (randomly) in
each cycle, this results in a saltatory unidirectional drift. This mechanism
resembles the work of an escapement-type device in watches. Considering the
overdamped limit, we propose simple analytical estimates for the particle's
terminal velocity.Comment: 14 pages, 6 figures; appearing in Journal of Physics: Condensed
Matter, special issue on Molecular Motors and Frictio
Cracklike Dynamics at the Onset of Frictional Sliding
We propose an elasto-plastic inspired friction model which incorporates
interfacial stiffness. Steady state sliding friction is characterized by a
generic nonmonotonic behavior, including both velocity weakening and
strengthening branches. In 1D and upon the application of sideway loading, we
demonstrate the existence of transient cracklike fronts whose velocity is
independent of sound speed, which we propose to be analogous to the recently
discovered slow interfacial rupture fronts. Most importantly, the properties of
these transient inhomogeneously loaded fronts are determined by steady state
front solutions at the {\em minimum} of the sliding friction law, implying the
existence of a new velocity scale and a "forbidden gap" of rupture velocities.
We highlight the role played by interfacial stiffness and supplement our
analysis with 2D scaling arguments.Comment: 4 pages, 2 figure
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