8,273 research outputs found
Non-monotonous crossover between capillary condensation and interface localisation/delocalisation transition in binary polymer blends
Within self-consistent field theory we study the phase behaviour of a
symmetric binary AB polymer blend confined into a thin film. The film surfaces
interact with the monomers via short range potentials. One surface attracts the
A component and the corresponding semi-infinite system exhibits a first order
wetting transition. The surface interaction of the opposite surface is varied
as to study the crossover from capillary condensation for symmetric surface
fields to the interface localisation/delocalisation transition for
antisymmetric surface fields. In the former case the phase diagram has a single
critical point close to the bulk critical point. In the latter case the phase
diagram exhibits two critical points which correspond to the prewetting
critical points of the semi-infinite system. The crossover between these
qualitatively different limiting behaviours occurs gradually, however, the
critical temperature and the critical composition exhibit a non-monotonic
dependence on the surface field.Comment: to appear in Europhys.Let
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
Effective temperature of active matter
We follow the dynamics of an ensemble of interacting self-propelled motorized
particles in contact with an equilibrated thermal bath. We find that the
fluctuation-dissipation relation allows for the definition of an effective
temperature that is compatible with the results obtained using a tracer
particle as a thermometer. The effective temperature takes a value which is
higher than the temperature of the bath and it is continuously controlled by
the motor intensity
Monte Carlo Simulations of an Extended Feynman-Kikuchi Model
We present Quantum Monte Carlo simulations of a generalization of the
Feynman-Kikuchi model which includes the possibility of vacancies and
interactions between the particles undergoing exchange. By measuring the
winding number (superfluid density) and density structure factor, we determine
the phase diagram, and show that it exhibits regions which possess both
superfluid and charge ordering.Comment: 10 pages, 15 figure
Confinement Effects in Antiferromagnets
Phase equilibrium in confined Ising antiferromagnets was studied as a
function of the coupling (v) and a magnetic field (h) at the surfaces, in the
presence of an external field H. The ground state properties were calculated
exactly for symmetric boundary conditions and nearest-neighbor interactions,
and a full zero-temperature phase diagram in the plane v-h was obtained for
films with symmetry-preserving surface orientations. The ground-state analysis
was extended to the H-T plane using a cluster-variation free energy. The study
of the finite-T properties (as a function of v and h) reveals the close
interdependence between the surface and finite-size effects and, together with
the ground-state phase diagram, provides an integral picture of the confinement
in anisotropic antiferromagnets with surfaces that preserve the symmetry of the
order parameter.Comment: 10 pages, 8 figures, Accepted in Phys. Rev.
Majority-Vote Model on a Random Lattice
The stationary critical properties of the isotropic majority vote model on
random lattices with quenched connectivity disorder are calculated by using
Monte Carlo simulations and finite size analysis. The critical exponents
and are found to be different from those of the Ising and
majority vote on the square lattice model and the critical noise parameter is
found to be .Comment: 4 pages, 6 figure
Effect of long range forces on the interfacial profiles in thin binary polymer films
We study the effect of surface fields on the interfacial properties of a
binary polymer melt confined between two parallel walls. Each wall attracts a
different component of the blend by a non-retarded van der Waals potential. An
interface which runs parallel to the surfaces is stabilized in the center of
the film. Using extensive Monte Carlo simulations we study the interfacial
properties as a function of the film thickness, the strength of the surface
forces and the lateral size over which the profiles across the film are
averaged. We find evidence for capillary wave broadening of the apparent
interfacial profiles. However, the apparent interfacial width cannot be
described quantitatively by a simple logarithmic dependence on the film
thickness. The Monte Carlo simulations reveal that the surface fields give rise
to an additional reduction of the intrinsic interfacial width and an increase
of the effective interfacial tension upon decreasing the film thickness. These
modifications of the intrinsic interfacial properties are confirmed by
self-consistent field calculations. Taking account of the thickness dependence
of the intrinsic interfacial properties and the capillary wave broadening, we
can describe our simulation results quantitatively.Comment: to appear in J.Chem.Phy
Ising analogue to compact-star matter
By constructing an Ising analogue of compact-star matter at sub-saturation
density we explored the effect of Coulomb frustration on the nuclear liquid-gas
phase transition. Our conclusions is twofold. First, the range of temperatures
where inhomogeneous phases form expands with increasing Coulomb-field strength.
Second, within the approximation of uniform electron distribution, the limiting
point upon which the phase-coexistence region ends does not exhibit any
critical behaviour. Possible astrophysics consequences and thermodynamical
connections are discussed.Comment: 4 pages, 3 figure
Yang-Lee zeroes for an urn model for the separation of sand
We apply the Yang-Lee theory of phase transitions to an urn model of
separation of sand. The effective partition function of this nonequilibrium
system can be expressed as a polynomial of the size-dependent effective
fugacity . Numerical calculations show that in the thermodynamic limit, the
zeros of the effective partition function are located on the unit circle in the
complex -plane. In the complex plane of the actual control parameter certain
roots converge to the transition point of the model. Thus the Yang-Lee theory
can be applied to a wider class of nonequilibrium systems than those considered
previously.Comment: 4 pages, 3 eps figures include
Work-distribution quantumness and irreversibility when crossing a quantum phase transition in finite time
The thermodynamic behavior of out-of-equilibrium quantum systems in finite-time dynamics encompasses the description of energy fluctuations, which dictates a series of the system's physical properties. In addition, strong interactions in many-body systems strikingly affect the energy-fluctuation statistics along a nonequilibrium dynamics. By driving transient currents to oppose the precursor to the metal-Mott-insulator transition in a diversity of dynamical regimes, we show how increasing many-body interactions dramatically affect the statistics of energy fluctuations and, consequently, the extractable work distribution of finite Hubbard chains. Statistical properties of such distributions as its skewness with its impressive change across the transition can be related to irreversibility and entropy production. Even for slow driving rates, the quasi quantum phase transition hinders equilibration, increasing the process irreversibility, and inducing strong features in the work distribution. In the Mott-insulating phase, the work fluctuation-dissipation balance gets modified with the irreversible entropy production dominating over work fluctuations. Because of this, effects of an interaction-driven quantum phase transition on thermodynamic quantities and irreversibility must be considered in the design of protocols in small-scale devices for application in quantum technology. Eventually, such many-body effects can also be employed in work extraction and refrigeration protocols on a quantum scale
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