260 research outputs found
Collective stochastic resonance in shear-induced melting of sliding bilayers
The far-from-equilibrium dynamics of two crystalline two-dimensional
monolayers driven past each other is studied using Brownian dynamics
simulations. While at very high and low driving rates the layers slide past one
another retaining their crystalline order, for intermediate range of drives the
system alternates irregularly between the crystalline and fluid-like phases. A
dynamical phase diagram in the space of interlayer coupling and drive is
obtained. A qualitative understanding of this stochastic alternation between
the liquid-like and crystalline phases is proposed in terms of a reduced model
within which it can be understood as a stochastic resonance for the dynamics of
collective order parameter variables. This remarkable example of stochastic
resonance in a spatially extended system should be seen in experiments which we
propose in the paper.Comment: 12 pages, 18 eps figures, minor changes in text and labelling of
figures, accepted for publication in Phys. Rev.
Active elastic dimers: Cells moving on rigid tracks
Experiments suggest that the migration of some cells in the three-dimensional
extra cellular matrix bears strong resemblance to one-dimensional cell
migration. Motivated by this observation, we construct and study a minimal
one-dimensional model cell made of two beads and an active spring moving along
a rigid track. The active spring models the stress fibers with their
myosin-driven contractility and alpha-actinin-driven extendability, while the
friction coefficients of the two beads describe the catch/slip bond behavior of
the integrins in focal adhesions. In the absence of active noise, net motion
arises from an interplay between active contractility (and passive
extendability) of the stress fibers and an asymmetry between the front and back
of the cell due to catch bond behavior of integrins at the front of the cell
and slip bond behavior of integrins at the back. We obtain reasonable cell
speeds with independently estimated parameters. We also study the effects of
hysteresis in the active spring, due to catch bond behavior and the dynamics of
cross-linking, and the addition of active noise on the motion of the cell. Our
model highlights the role of alpha-actinin in three-dimensional cell motility
and does not require Arp2/3 actin filament nucleation for net motion.Comment: 13 pages, 9 figure
Lower order and higher order entanglement in hyperfine manifold modeled as a four-wave mixing process
Possibilities of generation of lower order and higher order intermodal
entanglement in 87Rb 5S-5P-5D hyperfine manifold are rigorously investigated
using Sen-Mandal perturbative technique by showing the equivalence of the
system with the four-wave mixing (FWM) process. The investigation has revealed
that for a set of experimentally realizable/relevant parameters we can observe
lower order and higher order intermodal entanglement between pump and signal
modes, signal and idler modes, and idler and pump modes in a FWM process
associated with the 87Rb 5S-5P-5D hyperfine manifold. In addition, trimodal
entanglement involving pump, signal and idler modes is also reported.Comment: 12 pages, 5 figure
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