41 research outputs found
Multicritical Points And Reentrant Phenomenon In The BEG Model
The Blume - Emery - Griffiths model is investigated by use of the cluster
variation method in the pair approximation. We determine the regions of the
phase space where reentrant phenomenon takes place. Two regions are found,
depending on the sign of the reduced quadrupole - quadrupole coupling strength
. For negative we find Para-Ferro-Para and Ferro-Para-Ferro-Para
transition sequences; for positive , a Para-Ferro-Para sequence.
Order parameters, correlation functions and specific heat are given in some
typical cases. By-products of this work are the equations for the critical and
tricritical lines.Comment: 14 pages, figures available upon reques
On the low-temperature phase of the three-state antiferromagnetic Potts model on the simple cubic lattice
The three-state antiferromagnetic Potts model on the simple cubic lattice is
investigated using the cluster variation method in the cube and the star-cube
approximations. The broken-sublattice-symmetry phase is found to be stable in
the whole low-temperature region, contrary to previous results obtained using a
modified cluster variation method. The tiny free energy difference between the
broken-sublattice-symmetry and the permutationally-symmetric-sublattices phases
is calculated in the two approximations and turns out to be smaller in the
(more accurate) star-cube approximation than in the cube one.Comment: 4 pages REVTeX + 2 PostScript figures, to be published in Phys. Rev.
E as a Rapid Communicatio
Ordinary Percolation with Discontinuous Transitions
Percolation on a one-dimensional lattice and fractals such as the Sierpinski
gasket is typically considered to be trivial because they percolate only at
full bond density. By dressing up such lattices with small-world bonds, a novel
percolation transition with explosive cluster growth can emerge at a nontrivial
critical point. There, the usual order parameter, describing the probability of
any node to be part of the largest cluster, jumps instantly to a finite value.
Here, we provide a simple example of this transition in form of a small-world
network consisting of a one-dimensional lattice combined with a hierarchy of
long-range bonds that reveals many features of the transition in a
mathematically rigorous manner.Comment: RevTex, 5 pages, 4 eps-figs, and Mathematica Notebook as Supplement
included. Final version, with several corrections and improvements. For
related work, see http://www.physics.emory.edu/faculty/boettcher
Phase transitions in a spin-1 model with plaquette interaction on the square lattice
An extension of the Blume-Emery-Griffiths model with a plaquette four-spin interaction term, on the square lattice, is investigated by means of the cluster variation method in the square approximation. The ground state of the model, for negative plaquette interaction, exhibits several new phases, including frustrated ones. At finite temperature we obtain a quite rich phase diagram with two new phases, a ferrimagnetic and a weakly ferromagnetic one, and several multicritical points
Restoring brain function after stroke - bridging the gap between animals and humans
Stroke is the leading cause of complex adult disability in the world. Recovery from stroke is often incomplete, which leaves many people dependent on others for their care. The improvement of long-term outcomes should, therefore, be a clinical and research priority. As a result of advances in our understanding of the biological mechanisms involved in recovery and repair after stroke, therapeutic opportunities to promote recovery through manipulation of poststroke plasticity have never been greater. This work has almost exclusively been carried out in preclinical animal models of stroke with little translation into human studies. The challenge ahead is to develop a mechanistic understanding of recovery from stroke in humans. Advances in neuroimaging techniques now enable us to reconcile behavioural accounts of recovery with molecular and cellular changes. Consequently, clinical trials can be designed in a stratified manner that takes into account when an intervention should be delivered and who is most likely to benefit. This approach is expected to lead to a substantial change in how restorative therapeutic strategies are delivered in patients after stroke