155 research outputs found
Blastomycosis of the spine with paraplegia
A case of blastomycosis with vertebral and visceral involvement is presented
La prévention durable des TMS : Quels freins ? Quels leviers d'action ?
L’objectif de cette recherche-action est d’éclairer, à travers des interventions dans un nombre significatif d’entreprises, les freins à une prévention durable des TMS, mais aussi les leviers d’action les plus pertinents. Le présent document constitue le rapport final de cette recherche-action
Large-scale structure of a nation-wide production network
Production in an economy is a set of firms' activities as suppliers and
customers; a firm buys goods from other firms, puts value added and sells
products to others in a giant network of production. Empirical study is lacking
despite the fact that the structure of the production network is important to
understand and make models for many aspects of dynamics in economy. We study a
nation-wide production network comprising a million firms and millions of
supplier-customer links by using recent statistical methods developed in
physics. We show in the empirical analysis scale-free degree distribution,
disassortativity, correlation of degree to firm-size, and community structure
having sectoral and regional modules. Since suppliers usually provide credit to
their customers, who supply it to theirs in turn, each link is actually a
creditor-debtor relationship. We also study chains of failures or bankruptcies
that take place along those links in the network, and corresponding
avalanche-size distribution.Comment: 17 pages with 8 figures; revised section VI and references adde
Electronic dynamic Hubbard model: exact diagonalization study
A model to describe electronic correlations in energy bands is considered.
The model is a generalization of the conventional Hubbard model that allows for
the fact that the wavefunction for two electrons occupying the same Wannier
orbital is different from the product of single electron wavefunctions. We
diagonalize the Hamiltonian exactly on a four-site cluster and study its
properties as function of band filling. The quasiparticle weight is found to
decrease and the quasiparticle effective mass to increase as the electronic
band filling increases, and spectral weight in one- and two-particle spectral
functions is transfered from low to high frequencies as the band filling
increases. Quasiparticles at the Fermi energy are found to be more 'dressed'
when the Fermi level is in the upper half of the band (hole carriers) than when
it is in the lower half of the band (electron carriers). The effective
interaction between carriers is found to be strongly dependent on band filling
becoming less repulsive as the band filling increases, and attractive near the
top of the band in certain parameter ranges. The effective interaction is most
attractive when the single hole carriers are most heavily dressed, and in the
parameter regime where the effective interaction is attractive, hole carriers
are found to 'undress', hence become more like electrons, when they pair. It is
proposed that these are generic properties of electronic energy bands in solids
that reflect a fundamental electron-hole asymmetry of condensed matter. The
relation of these results to the understanding of superconductivity in solids
is discussed.Comment: Small changes following referee's comment
The Hubbard Model at Infinite Dimensions: Thermodynamic and Transport Properties
We present results on thermodynamic quantities, resistivity and optical
conductivity for the Hubbard model on a simple hypercubic lattice in infinite
dimensions. Our results for the paramagnetic phase display the features
expected from an intuitive analysis of the one-particle spectra and
substantiate the similarity of the physics of the Hubbard model to those of
heavy fermion systems. The calculations were performed using an approximate
solution to the single-impurity Anderson model, which is the key quantity
entering the solution of the Hubbard model in this limit. To establish the
quality of this approximation we compare its results, together with those
obtained from two other widely used methods, to essentially exact quantum Monte
Carlo results.Comment: 29 pages, 16 figure
Weak Localization Effect in Superconductors by Radiation Damage
Large reductions of the superconducting transition temperature and
the accompanying loss of the thermal electrical resistivity (electron-phonon
interaction) due to radiation damage have been observed for several A15
compounds, Chevrel phase and Ternary superconductors, and in
the high fluence regime. We examine these behaviors based on the recent theory
of weak localization effect in superconductors. We find a good fitting to the
experimental data. In particular, weak localization correction to the
phonon-mediated interaction is derived from the density correlation function.
It is shown that weak localization has a strong influence on both the
phonon-mediated interaction and the electron-phonon interaction, which leads to
the universal correlation of and resistance ratio.Comment: 16 pages plus 3 figures, revtex, 76 references, For more information,
Plesse see http://www.fen.bilkent.edu.tr/~yjki
General Formula for the Thermoelectric Transport Phenomena based on the Fermi Liquid Theory: Thermopower, Nernst Coefficient, and Thermal Conductivity
On the basis of the linear response transport theory, the general expressions
for the thermoelectric transport coefficients, such as thermoelectric power
(S), Nernst coefficient (\nu), and thermal conductivity (\kappa), are derived
by using the Fermi liquid theory. The obtained expression is exact as for the
most singular term in terms of 1/\gamma_k^* (\gamma_k^* being the quasiparticle
damping rate). We utilize the Ward identities for the heat current which is
derived by the local energy conservation law. Based on the derived expressions,
we can calculate various thermoelectric transport coefficients within the
framework of the Baym-Kadanoff type conserving approximation. Thus, the present
expressions are very useful for studying the strongly correlated electrons such
as high-Tc superconductors, organic metals, and heavy Fermion systems, where
the current vertex corrections are expected to play important roles. By using
the derived expression, we calculate the thermal conductivity \kappa in a
free-dispersion model up to the second-order with respect to U. We find that it
is slightly enhanced due to the vertex correction for the heat current,
although the vertex correction for electron current makes the conductivity
(\sigma) of this system diverge, reflecting the absence of the Umklapp process.Comment: 22 pages, 11 figures; accepted for publication in PR
Active Brownian Particles. From Individual to Collective Stochastic Dynamics
We review theoretical models of individual motility as well as collective
dynamics and pattern formation of active particles. We focus on simple models
of active dynamics with a particular emphasis on nonlinear and stochastic
dynamics of such self-propelled entities in the framework of statistical
mechanics. Examples of such active units in complex physico-chemical and
biological systems are chemically powered nano-rods, localized patterns in
reaction-diffusion system, motile cells or macroscopic animals. Based on the
description of individual motion of point-like active particles by stochastic
differential equations, we discuss different velocity-dependent friction
functions, the impact of various types of fluctuations and calculate
characteristic observables such as stationary velocity distributions or
diffusion coefficients. Finally, we consider not only the free and confined
individual active dynamics but also different types of interaction between
active particles. The resulting collective dynamical behavior of large
assemblies and aggregates of active units is discussed and an overview over
some recent results on spatiotemporal pattern formation in such systems is
given.Comment: 161 pages, Review, Eur Phys J Special-Topics, accepte
Does plasmid-based beta-lactam resistance increase E. coli infections: Modelling addition and replacement mechanisms
Infections caused by antibiotic-resistant bacteria have become more prevalent during past decades. Yet, it is unknown whether such infections occur in addition to infections with antibiotic-susceptible bacteria, thereby increasing the incidence of infections, or whether they replace such infections, leaving the total incidence unaffected. Observational longitudinal studies cannot separate both mechanisms. Using plasmid-based beta-lactam resistant E. coli as example we applied mathematical modelling to investigate whether seven biological mechanisms would lead to replacement or addition of infections. We use a mathematical neutral null model of individuals colonized with susceptible and/or resistant E. coli, with two mechanisms implying a fitness cost, i.e., increased clearance and decreased growth of resistant strains, and five mechanisms benefitting resistance, i.e., 1) increased virulence, 2) increased transmission, 3) decreased clearance of resistant strains, 4) increased rate of horizontal plasmid transfer, and 5) increased clearance of susceptible E. coli due to antibiotics. Each mechanism is modelled separately to estimate addition to or replacement of antibiotic-susceptible infections. Fitness costs cause resistant strains to die out if other strain characteristics are maintained equal. Under the assumptions tested, increased virulence is the only mechanism that increases the total number of infections. Other benefits of resistance lead to replacement of susceptible infections without changing the total number of infections. As there is no biological evidence that plasmid-based beta-lactam resistance increases virulence, these findings suggest that the burden of disease is determined by attributable effects of resistance rather than by an increase in the number of infections
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