687 research outputs found
Derivation of a Matrix Product Representation for the Asymmetric Exclusion Process from Algebraic Bethe Ansatz
We derive, using the algebraic Bethe Ansatz, a generalized Matrix Product
Ansatz for the asymmetric exclusion process (ASEP) on a one-dimensional
periodic lattice. In this Matrix Product Ansatz, the components of the
eigenvectors of the ASEP Markov matrix can be expressed as traces of products
of non-commuting operators. We derive the relations between the operators
involved and show that they generate a quadratic algebra. Our construction
provides explicit finite dimensional representations for the generators of this
algebra.Comment: 16 page
A computer-assisted motivational social network intervention to reduce alcohol, drug and HIV risk behaviors among Housing First residents.
BackgroundIndividuals transitioning from homelessness to housing face challenges to reducing alcohol, drug and HIV risk behaviors. To aid in this transition, this study developed and will test a computer-assisted intervention that delivers personalized social network feedback by an intervention facilitator trained in motivational interviewing (MI). The intervention goal is to enhance motivation to reduce high risk alcohol and other drug (AOD) use and reduce HIV risk behaviors.Methods/designIn this Stage 1b pilot trial, 60 individuals that are transitioning from homelessness to housing will be randomly assigned to the intervention or control condition. The intervention condition consists of four biweekly social network sessions conducted using MI. AOD use and HIV risk behaviors will be monitored prior to and immediately following the intervention and compared to control participants' behaviors to explore whether the intervention was associated with any systematic changes in AOD use or HIV risk behaviors.DiscussionSocial network health interventions are an innovative approach for reducing future AOD use and HIV risk problems, but little is known about their feasibility, acceptability, and efficacy. The current study develops and pilot-tests a computer-assisted intervention that incorporates social network visualizations and MI techniques to reduce high risk AOD use and HIV behaviors among the formerly homeless. CLINICALTRIALS.Gov identifierNCT02140359
Exactly solvable model with two conductor-insulator transitions driven by impurities
We present an exact analysis of two conductor-insulator transitions in the
random graph model. The average connectivity is related to the concentration of
impurities. The adjacency matrix of a large random graph is used as a hopping
Hamiltonian. Its spectrum has a delta peak at zero energy. Our analysis is
based on an explicit expression for the height of this peak, and a detailed
description of the localized eigenvectors and of their contribution to the
peak. Starting from the low connectivity (high impurity density) regime, one
encounters an insulator-conductor transition for average connectivity
1.421529... and a conductor-insulator transition for average connectivity
3.154985.... We explain the spectral singularity at average connectivity
e=2.718281... and relate it to another enumerative problem in random graph
theory, the minimal vertex cover problem.Comment: 4 pages revtex, 2 fig.eps [v2: new title, changed intro, reorganized
text
Meander, Folding and Arch Statistics
The statistics of meander and related problems are studied as particular
realizations of compact polymer chain foldings. This paper presents a general
discussion of these topics, with a particular emphasis on three points: (i) the
use of a direct recursive relation for building (semi) meanders (ii) the
equivalence with a random matrix model (iii) the exact solution of simpler
related problems, such as arch configurations or irreducible meanders.Comment: 82 pages, uuencoded, uses harvmac (l mode) and epsf, 26+7 figures
include
Power Spectra of a Constrained Totally Asymmetric Simple Exclusion Process
To synthesize proteins in a cell, an mRNA has to work with a finite pool of
ribosomes. When this constraint is included in the modeling by a totally
asymmetric simple exclusion process (TASEP), non-trivial consequences emerge.
Here, we consider its effects on the power spectrum of the total occupancy,
through Monte Carlo simulations and analytical methods. New features, such as
dramatic suppressions at low frequencies, are discovered. We formulate a theory
based on a linearized Langevin equation with discrete space and time. The good
agreement between its predictions and simulation results provides some insight
into the effects of finite resoures on a TASEP.Comment: 4 pages, 2 figures v2: formatting change
Meanders and the Temperley-Lieb algebra
The statistics of meanders is studied in connection with the Temperley-Lieb
algebra. Each (multi-component) meander corresponds to a pair of reduced
elements of the algebra. The assignment of a weight per connected component
of meander translates into a bilinear form on the algebra, with a Gram matrix
encoding the fine structure of meander numbers. Here, we calculate the
associated Gram determinant as a function of , and make use of the
orthogonalization process to derive alternative expressions for meander numbers
as sums over correlated random walks.Comment: 85p, uuencoded, uses harvmac (l mode) and epsf, 88 figure
Meanders: A Direct Enumeration Approach
We study the statistics of semi-meanders, i.e. configurations of a set of
roads crossing a river through n bridges, and possibly winding around its
source, as a toy model for compact folding of polymers. By analyzing the
results of a direct enumeration up to n=29, we perform on the one hand a large
n extrapolation and on the other hand we reformulate the available data into a
large q expansion, where q is a weight attached to each road. We predict a
transition at q=2 between a low-q regime with irrelevant winding, and a large-q
regime with relevant winding.Comment: uses harvmac (l), epsf, 16 figs included, uuencoded, tar compresse
Magnetic Field Behaviour of a Haldane Gap Antiferromagnet
We investigate the magnetic field behaviour of an antiferromagnetic
Heisenberg spin-1 chain with the most general single-ion anisotropy. We discuss
the regime in which the magnetic field is below the transition value. The
splitting of the Haldane triplet is obtained as a function of a field applied
in an arbitrary orientation by means of a Lancz\H os exact diagonalization of
chains of up to 16 spins. Our results are nicely summarized in terms of a
first-order perturbation theory. We explain various level crossings that occur
by the existence of discrete symmetries. A discussion is given of the electron
spin resonance and neutron scattering experiments on the compound
Ni(CHN)NOClO (NENP).Comment: 18 pages and 6 figs not included available by ftp, plain TeX,
SPhT/93-04
Time-Dependent Density Functional Theory for Driven Lattice Gas Systems with Interactions
We present a new method to describe the kinetics of driven lattice gases with
particle-particle interactions beyond hard-core exclusions. The method is based
on the time-dependent density functional theory for lattice systems and allows
one to set up closed evolution equations for mean site occupation numbers in a
systematic manner. Application of the method to a totally asymmetric site
exclusion process with nearest-neighbor interactions yields predictions for the
current-density relation in the bulk, the phase diagram of non-equilibrium
steady states and the time evolution of density profiles that are in good
agreement with results from kinetic Monte Carlo simulations.Comment: 11 pages, 3 figure
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