2,318 research outputs found
Heat fluctuations in Ising models coupled with two different heat baths
Monte Carlo simulations of Ising models coupled to heat baths at two
different temperatures are used to study a fluctuation relation for the heat
exchanged between the two thermostats in a time . Different kinetics
(single--spin--flip or spin--exchange Kawasaki dynamics), transition rates
(Glauber or Metropolis), and couplings between the system and the thermostats
have been considered. In every case the fluctuation relation is verified in the
large limit, both in the disordered and in the low temperature phase.
Finite- corrections are shown to obey a scaling behavior.Comment: 5 pages, 2 figures. To be published in Journal of Physics A:
Mathematical and Theoretical as fast track communicatio
Phase-ordering dynamics of binary mixtures with field-dependent mobility in shear flow
The effect of shear flow on the phase-ordering dynamics of a binary mixture
with field-dependent mobility is investigated. The problem is addressed in the
context of the time-dependent Ginzburg-Landau equation with an external
velocity term, studied in self-consistent approximation. Assuming a scaling
ansatz for the structure factor, the asymptotic behavior of the observables in
the scaling regime can be analytically calculated. All the observables show
log-time periodic oscillations which we interpret as due to a cyclical
mechanism of stretching and break-up of domains. These oscillations are dumped
as consequence of the vanishing of the mobility in the bulk phase.Comment: 9 pages, 4 figures, EPJ styl
Spinodal decomposition to a lamellar phase: effects of hydrodynamic flow
Results are presented for the kinetics of domain growth of a two-dimensional
fluid quenched from a disordered to a lamellar phase. At early times when a
Lifshitz-Slyozov mechanism is operative the growth process proceeds
logarithmically in time to a frozen state with locked-in defects. However when
hydrodynamic modes become important, or the fluid is subjected to shear, the
frustration of the system is alleviated and the size and orientation of the
lamellae attain their equilibrium values.Comment: 4 Revtex pages, 4 figures, to appear in Physical Review Letter
Hybrid lattice Boltzmann model for binary fluid mixtures
A hybrid lattice Boltzmann method (LBM) for binary mixtures based on the
free-energy approach is proposed. Non-ideal terms of the pressure tensor are
included as a body force in the LBM kinetic equations, used to simulate the
continuity and Navier-Stokes equations. The convection-diffusion equation is
studied by finite difference methods. Differential operators are discretized in
order to reduce the magnitude of spurious velocities. The algorithm has been
shown to be stable and reproducing the correct equilibrium behavior in simple
test configurations and to be Galilean invariant. Spurious velocities can be
reduced of about an order of magnitude with respect to standard discretization
procedure.Comment: Final version, to appear in Phys. Rev.
Energy and Heat Fluctuations in a Temperature Quench
Fluctuations of energy and heat are investigated during the relaxation
following the instantaneous temperature quench of an extended system. Results
are obtained analytically for the Gaussian model and for the large model
quenched below the critical temperature . The main finding is that
fluctuations exceeding a critical threshold do condense. Though driven by a
mechanism similar to that of Bose-Einstein condensation, this phenomenon is an
out-of-equilibrium feature produced by the breaking of energy equipartition
occurring in the transient regime. The dynamical nature of the transition is
illustrated by phase diagrams extending in the time direction.Comment: To be published in the Proceedings of the Research Program "Small
system non equilibrium fluctuations, dynamics and stochastics, and anomalous
behavior", Kavli Institute for Theoretical Physics China, July 2013. 40
pages, 9 figure
Switching dynamics in cholesteric blue phases
Blue phases are networks of disclination lines, which occur in cholesteric
liquid crystals near the transition to the isotropic phase. They have recently
been used for the new generation of fast switching liquid crystal displays.
Here we study numerically the steady states and switching hydrodynamics of blue
phase I (BPI) and blue phase II (BPII) cells subjected to an electric field.
When the field is on, there are three regimes: for very weak fields (and strong
anchoring at the boundaries) the blue phases are almost unaffected, for
intermediate fields the disclinations twist (for BPI) and unzip (for BPII),
whereas for very large voltages the network dissolves in the bulk of the cell.
Interestingly, we find that a BPII cell can recover its original structure when
the field is switched off, whereas a BPI cell is found to be trapped more
easily into metastable configurations. The kinetic pathways followed during
switching on and off entails dramatic reorganisation of the disclination
networks. We also discuss the effect of changing the director field anchoring
at the boundary planes and of varying the direction of the applied field.Comment: 17 pages, 11 figure
A lattice Boltzmann study of phase separation in liquid-vapor systems with gravity
Phase separation of a two-dimensional van der Waals fluid subject to a
gravitational force is studied by numerical simulations based on lattice
Boltzmann methods (LBM) implemented with a finite difference scheme. A growth
exponent is measured in the direction of the external force.Comment: To appear in Communications in Computational Physics (CiCP
Monte Carlo study of the growth of striped domains
We analyze the dynamical scaling behavior in a two-dimensional spin model
with competing interactions after a quench to a striped phase. We measure the
growth exponents studying the scaling of the interfaces and the scaling of the
shrinking time of a ball of one phase plunged into the sea of another phase.
Our results confirm the predictions found in previous papers. The correlation
functions measured in the direction parallel and transversal to the stripes are
different as suggested by the existence of different interface energies between
the ground states of the model. Our simulations show anisotropic features for
the correlations both in the case of single-spin-flip and spin-exchange
dynamics.Comment: 15 pages, ReVTe
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