20,067 research outputs found
Hydrodynamic mean field solutions of 1D exclusion processes with spatially varying hopping rates
We analyze the open boundary partially asymmetric exclusion process with
smoothly varying internal hopping rates in the infinite-size, mean field limit.
The mean field equations for particle densities are written in terms of Ricatti
equations with the steady-state current as a parameter. These equations are
solved both analytically and numerically. Upon imposing the boundary conditions
set by the injection and extraction rates, the currents are found
self-consistently. We find a number of cases where analytic solutions can be
found exactly or approximated. Results for from asymptotic analyses for
slowly varying hopping rates agree extremely well with those from extensive
Monte Carlo simulations, suggesting that mean field currents asymptotically
approach the exact currents in the hydrodynamic limit, as the hopping rates
vary slowly over the lattice. If the forward hopping rate is greater than or
less than the backward hopping rate throughout the entire chain, the three
standard steady-state phases are preserved. Our analysis reveals the
sensitivity of the current to the relative phase between the forward and
backward hopping rate functions.Comment: 12 pages, 4 figure
Single-Photon Generation from Stored Excitation in an Atomic Ensemble
Single photons are generated from an ensemble of cold Cs atoms via the
protocol of Duan et al. [Nature \textbf{414}, 413 (2001)]. Conditioned upon an
initial detection from field 1 at 852 nm, a photon in field 2 at 894 nm is
produced in a controlled fashion from excitation stored within the atomic
ensemble. The single-quantum character of the field 2 is demonstrated by the
violation of a Cauchy-Schwarz inequality, namely , where describes detection of two events
conditioned upon an initial detection , with
for single photons.Comment: 5 pages, 4 figure
The Dependence of Dynamo -Effect on Reynolds Numbers, Magnetic Prandtl Number, and the Statistics of MHD Turbulence
We generalize the derivation of dynamo coefficient of Field et al
(1999) to include the following two aspects: first, the de-correlation times of
velocity field and magnetic field are different; second, the magnetic Prandtl
number can be arbitrary. We find that the contributions of velocity field and
magnetic field to the effect are not equal, but affected by their
different statistical properties. In the limit of large kinetic Reynolds number
and large magnetic Reynolds number, -coefficient may not be small if
the de-correlation times of velocity field and magnetic field are shorter than
the eddy turn-over time of the MHD turbulence. We also show that under certain
circumstances, for example if the kinetic helicity and current helicity are
comparable, depends insensitively on magnetic Prandtl number, while if
either the kinetic helicity or the current helicity is dominated by the other
one, a different magnetic Prandtl number will significantly change the dynamo
effect.Comment: 44 pages, 4 figures, to appear in ApJ (vol. 552
Towards experimental entanglement connection with atomic ensembles in the single excitation regime
We present a protocol for performing entanglement connection between pairs of
atomic ensembles in the single excitation regime. Two pairs are prepared in an
asynchronous fashion and then connected via a Bell measurement. The resulting
state of the two remaining ensembles is mapped to photonic modes and a reduced
density matrix is then reconstructed. Our observations confirm for the first
time the creation of coherence between atomic systems that never interacted, a
first step towards entanglement connection, a critical requirement for quantum
networking and long distance quantum communications
Adhesion of surfaces via particle adsorption: Exact results for a lattice of fluid columns
We present here exact results for a one-dimensional gas, or fluid, of
hard-sphere particles with attractive boundaries. The particles, which can
exchange with a bulk reservoir, mediate an interaction between the boundaries.
A two-dimensional lattice of such one-dimensional gas `columns' represents a
discrete approximation of a three-dimensional gas of particles between two
surfaces. The effective particle-mediated interaction potential of the
boundaries, or surfaces, is calculated from the grand-canonical partition
function of the one-dimensional gas of particles, which is an extension of the
well-studied Tonks gas. The effective interaction potential exhibits two
minima. The first minimum at boundary contact reflects depletion interactions,
while the second minimum at separations close to the particle diameter results
from a single adsorbed particle that crosslinks the two boundaries. The second
minimum is the global minimum for sufficiently large binding energies of the
particles. Interestingly, the effective adhesion energy corresponding to this
minimum is maximal at intermediate concentrations of the particles.Comment: to appear in Journal of Statistical Mechanics: Theory and Experimen
Maximally Symmetric Minimal Unification Model SO(32) with Three Families in Ten Dimensional Space-time
Based on a maximally symmetric minimal unification hypothesis and a quantum
charge-dimension correspondence principle, it is demonstrated that each family
of quarks and leptons belongs to the Majorana-Weyl spinor representation of
14-dimensions that relate to quantum spin-isospin-color charges. Families of
quarks and leptons attribute to a spinor structure of extra 6-dimensions that
relate to quantum family charges. Of particular, it is shown that 10-dimensions
relating to quantum spin-family charges form a motional 10-dimensional quantum
space-time with a generalized Lorentz symmetry SO(1,9), and 10-dimensions
relating to quantum isospin-color charges become a motionless 10-dimensional
quantum intrinsic space. Its corresponding 32-component fermions in the spinor
representation possess a maximal gauge symmetry SO(32). As a consequence, a
maximally symmetric minimal unification model SO(32) containing three families
in ten dimensional quantum space-time is naturally obtained by choosing a
suitable Majorana-Weyl spinor structure into which quarks and leptons are
directly embedded. Both resulting symmetry and dimensions coincide with the
ones of type I string and heterotic string SO(32) in string theory.Comment: 17 pages, RevTex, published version with minor typos correcte
Direct strain and elastic energy evaluation in rolled-up semiconductor tubes by x-ray micro-diffraction
We depict the use of x-ray diffraction as a tool to directly probe the strain
status in rolled-up semiconductor tubes. By employing continuum elasticity
theory and a simple model we are able to simulate quantitatively the strain
relaxation in perfect crystalline III-V semiconductor bi- and multilayers as
well as in rolled-up layers with dislocations. The reduction in the local
elastic energy is evaluated for each case. Limitations of the technique and
theoretical model are discussed in detail.Comment: 32 pages (single column), 9 figures, 39 reference
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