9,750 research outputs found
Second-Order Dynamics in the Collective Evolution of Coupled Maps and Automata
We review recent numerical studies and the phenomenology of spatially
synchronized collective states in many-body dynamical systems. These states
exhibit thermodynamic noise superimposed on the collective, quasiperiodic order
parameter evolution with typically one basic irrational frequency. We
concentrate on the description of the global temporal properties in terms of
second-order difference equations.Comment: 11 pages (plain TeX), 4 figures (PostScript), preprint OUTP-92-51
Spontaneous creation of discrete breathers in Josephson arrays
We report on the experimental generation of discrete breather states
(intrinsic localized modes) in frustrated Josephson arrays. Our experiments
indicate the formation of discrete breathers during the transition from the
static to the dynamic (whirling) system state, induced by a uniform external
current. Moreover, spatially extended resonant states, driven by a uniform
current, are observed to evolve into localized breather states. Experiments
were performed on single Josephson plaquettes as well as open-ended Josephson
ladders with 10 and 20 cells. We interpret the breather formation as the result
of the penetration of vortices into the system.Comment: 5 pages, 5 figure
Soliton Staircases and Standing Strain Waves in Confined Colloidal Crystals
We show by computer simulation of a two-dimensional crystal confined by
corrugated walls that confinement can be used to impose a controllable
mesoscopic superstructure of predominantly mechanical elastic character. Due to
an interplay of the particle density of the system and the width D of the
confining channel, "soliton staircases" can be created along both parallel
confining boundaries, that give rise to standing strain waves in the entire
crystal. The periodicity of these waves is of the same order as D. This
mechanism should be useful for structure formation in the self-assembly of
various nanoscopic materials.Comment: 22 pages, 5 figure
Parametric ordering of complex systems
Cellular automata (CA) dynamics are ordered in terms of two global
parameters, computable {\sl a priori} from the description of rules. While one
of them (activity) has been used before, the second one is new; it estimates
the average sensitivity of rules to small configurational changes. For two
well-known families of rules, the Wolfram complexity Classes cluster
satisfactorily. The observed simultaneous occurrence of sharp and smooth
transitions from ordered to disordered dynamics in CA can be explained with the
two-parameter diagram
Static and Dynamic Critical Behavior of a Symmetrical Binary Fluid: A Computer Simulation
A symmetrical binary, A+B Lennard-Jones mixture is studied by a combination
of semi-grandcanonical Monte Carlo (SGMC) and Molecular Dynamics (MD) methods
near a liquid-liquid critical temperature . Choosing equal chemical
potentials for the two species, the SGMC switches identities () to generate well-equilibrated configurations of the system on
the coexistence curve for and at the critical concentration, ,
for . A finite-size scaling analysis of the concentration susceptibility
above and of the order parameter below is performed, varying the
number of particles from N=400 to 12800. The data are fully compatible with the
expected critical exponents of the three-dimensional Ising universality class.
The equilibrium configurations from the SGMC runs are used as initial states
for microcanonical MD runs, from which transport coefficients are extracted.
Self-diffusion coefficients are obtained from the Einstein relation, while the
interdiffusion coefficient and the shear viscosity are estimated from
Green-Kubo expressions. As expected, the self-diffusion constant does not
display a detectable critical anomaly. With appropriate finite-size scaling
analysis, we show that the simulation data for the shear viscosity and the
mutual diffusion constant are quite consistent both with the theoretically
predicted behavior, including the critical exponents and amplitudes, and with
the most accurate experimental evidence.Comment: 35 pages, 13 figure
Comparison of Dissipative Particle Dynamics and Langevin thermostats for out-of-equilibrium simulations of polymeric systems
In this work we compare and characterize the behavior of Langevin and
Dissipative Particle Dynamics (DPD) thermostats in a broad range of
non-equilibrium simulations of polymeric systems. Polymer brushes in relative
sliding motion, polymeric liquids in Poiseuille and Couette flows, and
brush-melt interfaces are used as model systems to analyze the efficiency and
limitations of different Langevin and DPD thermostat implementations. Widely
used coarse-grained bead-spring models under good and poor solvent conditions
are employed to assess the effects of the thermostats. We considered
equilibrium, transient, and steady state examples for testing the ability of
the thermostats to maintain constant temperature and to reproduce the
underlying physical phenomena in non-equilibrium situations. The common
practice of switching-off the Langevin thermostat in the flow direction is also
critically revisited. The efficiency of different weight functions for the DPD
thermostat is quantitatively analyzed as a function of the solvent quality and
the non-equilibrium situation.Comment: 12 pages, introduction improved, references added, to appear in Phys.
Rev.
Interfacial friction between semiflexible polymers and crystalline surfaces
The results obtained from molecular dynamics simulations of the friction at
an interface between polymer melts and weakly attractive crystalline surfaces
are reported. We consider a coarse-grained bead-spring model of linear chains
with adjustable intrinsic stiffness. The structure and relaxation dynamics of
polymer chains near interfaces are quantified by the radius of gyration and
decay of the time autocorrelation function of the first normal mode. We found
that the friction coefficient at small slip velocities exhibits a distinct
maximum which appears due to shear-induced alignment of semiflexible chain
segments in contact with solid walls. At large slip velocities the decay of the
friction coefficient is independent of the chain stiffness. The data for the
friction coefficient and shear viscosity are used to elucidate main trends in
the nonlinear shear rate dependence of the slip length. The influence of chain
stiffness on the relationship between the friction coefficient and the
structure factor in the first fluid layer is discussed.Comment: 31 pages, 12 figure
On the Symmetry of Universal Finite-Size Scaling Functions in Anisotropic Systems
In this work a symmetry of universal finite-size scaling functions under a
certain anisotropic scale transformation is postulated. This transformation
connects the properties of a finite two-dimensional system at criticality with
generalized aspect ratio to a system with . The symmetry
is formulated within a finite-size scaling theory, and expressions for several
universal amplitude ratios are derived. The predictions are confirmed within
the exactly solvable weakly anisotropic two-dimensional Ising model and are
checked within the two-dimensional dipolar in-plane Ising model using Monte
Carlo simulations. This model shows a strongly anisotropic phase transition
with different correlation length exponents parallel
and perpendicular to the spin axis.Comment: RevTeX4, 4 pages, 3 figure
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