6,705 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
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.
Random Walk with a Boundary Line as a Free Massive Boson with a Defect Line
We show that the problem of Random Walk with boundary attractive potential
may be mapped onto the free massive bosonic Quantum Field Theory with a line of
defect. This mapping permits to recover the statistical properties of the
Random Walks by using boundary --matrix and Form Factor techniques.Comment: 17 pages, Latex, 3 figures include
Glass Polymorphism in TIP4P/2005 Water: A Description Based on the Potential Energy Landscape Formalism
The potential energy landscape (PEL) formalism is a statistical mechanical
approach to describe supercooled liquids and glasses. Here we use the PEL
formalism to study the pressure-induced transformations between low-density
amorphous ice (LDA) and high-density amorphous ice (HDA) using computer
simulations of the TIP4P/2005 molecular model of water. We find that the
properties of the PEL sampled by the system during the LDA-HDA transformation
exhibit anomalous behavior. In particular, at conditions where the change in
density during the LDA-HDA transformation is approximately discontinuous,
reminiscent of a first-order phase transition, we find that (i) the inherent
structure (IS) energy, , is a concave function of the volume,
and (ii) the IS pressure, , exhibits a van der Waals-like loop.
In addition, the curvature of the PEL at the IS is anomalous, a non-monotonic
function of . In agreement with previous studies, our work suggests that
conditions (i) and (ii) are necessary (but not sufficient) signatures of the
PEL for the LDA-HDA transformation to be reminiscent of a first-order phase
transition. We also find that one can identify two different regions of the
PEL, one associated to LDA and another to HDA. Our computer simulations are
performed using a wide range of compression/decompression and cooling rates. In
particular, our slowest cooling rate (0.01 K/ns) is within the experimental
rates employed in hyperquenching experiments to produce LDA. Interestingly, the
LDA-HDA transformation pressure that we obtain at K and at different
rates extrapolates remarkably well to the corresponding experimental pressure.Comment: Manuscript and Supplementary Materia
Critical properties of the three-dimensional equivalent-neighbor model and crossover scaling in finite systems
Accurate numerical results are presented for the three-dimensional
equivalent-neighbor model on a cubic lattice, for twelve different interaction
ranges (coordination number between 18 and 250). These results allow the
determination of the range dependences of the critical temperature and various
critical amplitudes, which are compared to renormalization-group predictions.
In addition, the analysis yields an estimate for the interaction range at which
the leading corrections to scaling vanish for the spin-1/2 model and confirms
earlier conclusions that the leading Wegner correction must be negative for the
three-dimensional (nearest-neighbor) Ising model. By complementing these
results with Monte Carlo data for systems with coordination numbers as large as
52514, the full finite-size crossover curves between classical and Ising-like
behavior are obtained as a function of a generalized Ginzburg parameter. Also
the crossover function for the effective magnetic exponent is determined.Comment: Corrected shift of critical temperature and some typos. To appear in
Phys. Rev. E. 18 pages RevTeX, including 10 EPS figures. Also available as
PDF file at http://www.cond-mat.physik.uni-mainz.de/~luijten/erikpubs.htm
Universality in the merging dynamics of parametric active contours: a study in MRI-based lung segmentation
Measurement of lung ventilation is one of the most reliable techniques of
diagnosing pulmonary diseases. The time consuming and bias prone traditional
methods using hyperpolarized HHe and H magnetic resonance
imageries have recently been improved by an automated technique based on
multiple active contour evolution. Mapping results from an equivalent
thermodynamic model, here we analyse the fundamental dynamics orchestrating the
active contour (AC) method. We show that the numerical method is inherently
connected to the universal scaling behavior of a classical nucleation-like
dynamics. The favorable comparison of the exponent values with the theoretical
model render further credentials to our claim.Comment: 4 pages, 4 figure
Finite-size scaling at the dynamical transition of the mean-field 10-state Potts glass
We use Monte Carlo simulations to study the static and dynamical properties
of a Potts glass with infinite range Gaussian distributed exchange interactions
for a broad range of temperature and system size up to N=2560 spins. The
results are compatible with a critical divergence of the relaxation time tau at
the theoretically predicted dynamical transition temperature T_D, tau \propto
(T-T_D)^{-\Delta} with Delta \approx 2. For finite N a further power law at
T=T_D is found, tau(T=T_D) \propto N^{z^\star} with z^\star \approx 1.5 and for
T>T_D dynamical finite-size scaling seems to hold. The order parameter
distribution P(q) is qualitatively compatible with the scenario of a first
order glass transition as predicted from one-step replica symmetry breaking
schemes.Comment: 8 pages of Latex, 4 figure
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