371 research outputs found
Fourier's Law from Closure Equations
We give a rigorous derivation of Fourier's law from a system of closure
equations for a nonequilibrium stationary state of a Hamiltonian system of
coupled oscillators subjected to heat baths on the boundary. The local heat
flux is proportional to the temperature gradient with a temperature dependent
heat conductivity and the stationary temperature exhibits a nonlinear profile
Convergence of the Linear Delta Expansion in the Critical O(N) Field Theory
The linear delta expansion is applied to the 3-dimensional O(N) scalar field
theory at its critical point in a way that is compatible with the large-N
limit. For a range of the arbitrary mass parameter, the linear delta expansion
for converges, with errors decreasing like a power of the order n in
delta. If the principal of minimal sensitivity is used to optimize the
convergence rate, the errors seem to decrease exponentially with n.Comment: 26 pages, latex, 8 figure
A new improved optimization of perturbation theory: applications to the oscillator energy levels and Bose-Einstein critical temperature
Improving perturbation theory via a variational optimization has generally
produced in higher orders an embarrassingly large set of solutions, most of
them unphysical (complex). We introduce an extension of the optimized
perturbation method which leads to a drastic reduction of the number of
acceptable solutions. The properties of this new method are studied and it is
then applied to the calculation of relevant quantities in different
models, such as the anharmonic oscillator energy levels and the critical
Bose-Einstein Condensation temperature shift recently investigated
by various authors. Our present estimates of , incorporating the
most recently available six and seven loop perturbative information, are in
excellent agreement with all the available lattice numerical simulations. This
represents a very substantial improvement over previous treatments.Comment: 9 pages, no figures. v2: minor wording changes in title/abstract, to
appear in Phys.Rev.
Green-Kubo formula for heat conduction in open systems
We obtain an exact Green-Kubo type linear response result for the heat
current in an open system. The result is derived for classical Hamiltonian
systems coupled to heat baths. Both lattice models and fluid systems are
studied and several commonly used implementations of heat baths, stochastic as
well as deterministic, are considered. The results are valid in arbitrary
dimensions and for any system sizes. Our results are useful for obtaining the
linear response transport properties of mesoscopic systems. Also we point out
that for systems with anomalous heat transport, as is the case in
low-dimensional systems, the use of the standard Green-Kubo formula is
problematic and the open system formula should be used.Comment: 4 page
Structure and magnetism of self-organized Ge(1-x)Mn(x) nano-columns
We report on the structural and magnetic properties of thin Ge(1-x)Mn(x)films
grown by molecular beam epitaxy (MBE) on Ge(001) substrates at temperatures
(Tg) ranging from 80deg C to 200deg C, with average Mn contents between 1 % and
11 %. Their crystalline structure, morphology and composition have been
investigated by transmission electron microscopy (TEM), electron energy loss
spectroscopy and x-ray diffraction. In the whole range of growth temperatures
and Mn concentrations, we observed the formation of manganese rich
nanostructures embedded in a nearly pure germanium matrix. Growth temperature
mostly determines the structural properties of Mn-rich nanostructures. For low
growth temperatures (below 120deg C), we evidenced a two-dimensional spinodal
decomposition resulting in the formation of vertical one-dimensional
nanostructures (nanocolumns). Moreover we show in this paper the influence of
growth parameters (Tg and Mn content) on this decomposition i.e. on nanocolumns
size and density. For temperatures higher than 180deg C, we observed the
formation of Ge3Mn5 clusters. For intermediate growth temperatures nanocolumns
and nanoclusters coexist. Combining high resolution TEM and superconducting
quantum interference device magnetometry, we could evidence at least four
different magnetic phases in Ge(1-x)Mn(x) films: (i) paramagnetic diluted Mn
atoms in the germanium matrix, (ii) superparamagnetic and ferromagnetic low-Tc
nanocolumns (120 K 400 K) and
(iv) Ge3Mn5 clusters.Comment: 10 pages 2 colonnes revTex formatte
Ergodic properties of quasi-Markovian generalized Langevin equations with configuration dependent noise and non-conservative force
We discuss the ergodic properties of quasi-Markovian stochastic differential
equations, providing general conditions that ensure existence and uniqueness of
a smooth invariant distribution and exponential convergence of the evolution
operator in suitably weighted spaces, which implies the validity
of central limit theorem for the respective solution processes. The main new
result is an ergodicity condition for the generalized Langevin equation with
configuration-dependent noise and (non-)conservative force
Impact of human bladder cancer cell architecture on autologous T-lymphocyte activation
To investigate the influence of tumor cell architecture on T-cell activation, we used an autologous human model based on 2 bladder tumor cell lines as targets for cytotoxic tumor-infiltrating lymphocytes (TILs). These tumor cell lines were grown in vitro as either standard 2-dimensional (2D) monolayers or 3-dimensional (3D) spheroids. T-cell activation was determined by measuring the production of three major cytokines (tumor necrosis factor, granulocyte/macrophage colony-stimulating factor and interferon-gamma), known to be secreted by most activated TILs. Changes in the architecture of target cells from 2D to 3D induced a dramatic decrease in their capacity for stimulating TILs. Interestingly, neither TIL infiltration nor MHC class I, B7.1 costimulatory or lymphocyte function-associated factor-3 adhesion molecule downregulation played a major role in this decrease. These findings demonstrate that tumor architecture has a major impact on T-cell activation and might be implicated in the escape of tumor cells from the immune system
Electron scattering mechanisms in fluorine-doped SnO2 thin films
Polycrystalline fluorine-doped SnO2 (FTO) thin films have been grown by ultrasonic spray pyrolysis on glass substrate. By varying growth conditions, several FTO specimens have been deposited and the study of their structural, electrical, and optical properties has been carried out. By systematically investigating the mobility as a function of carrier density, grain size, and crystallite size, the contribution of each physical mechanism involved in the electron scattering has been derived. A thorough comparison of experimental data and calculations allows to disentangle these different mechanisms and to deduce their relative importance. In particular, the roles of extended structural defects such as grain or twin boundaries as revealed by electron microscopy or x-ray diffraction along with ionized impurities are discussed. As a consequence, based on the quantitative analysis presented here, an experimental methodology leading to the improvement of the electro-optical properties of FTO thin films is reported. FTO thin films assuming an electrical resistivity as low as 3.7 center dot 10(-4)Omega cm (square sheet resistance of 8 Omega/square) while retaining good transmittance up to 86% (including substrate effect) in the visible range have been obtained. (c) 2013 AIP Publishing LLC
A meaningful expansion around detailed balance
We consider Markovian dynamics modeling open mesoscopic systems which are
driven away from detailed balance by a nonconservative force. A systematic
expansion is obtained of the stationary distribution around an equilibrium
reference, in orders of the nonequilibrium forcing. The first order around
equilibrium has been known since the work of McLennan (1959), and involves the
transient irreversible entropy flux. The expansion generalizes the McLennan
formula to higher orders, complementing the entropy flux with the dynamical
activity. The latter is more kinetic than thermodynamic and is a possible
realization of Landauer's insight (1975) that, for nonequilibrium, the relative
occupation of states also depends on the noise along possible escape routes. In
that way nonlinear response around equilibrium can be meaningfully discussed in
terms of two main quantities only, the entropy flux and the dynamical activity.
The expansion makes mathematical sense as shown in the simplest cases from
exponential ergodicity.Comment: 19 page
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