253 research outputs found
Quantum Dynamics with Bohmian Trajectories
We describe the advantages and disadvantages of numerical methods when
Bohmian trajectory-grids are used for numerical simulations of quantum
dynamics. We focus on the crucial non crossing property of Bohmian
trajectories, which numerically must be paid careful attention to. Failure to
do so causes instabilities or leads to false simulations.Comment: 17 pages, 18 figures; some typos corrected, 4 figures added, some
paragraphs extended, source code extende
Effective Dynamics of a Tracer Particle Interacting with an Ideal Bose Gas
We study a system consisting of a heavy quantum particle, called tracer
particle, coupled to an ideal gas of light Bose particles, the ratio of masses
of the tracer particle and a gas particle being proportional to the gas
density. All particles have non-relativistic kinematics. The tracer particle is
driven by an external potential and couples to the gas particles through a pair
potential. We compare the quantum dynamics of this system to an effective
dynamics given by a Newtonian equation of motion for the tracer particle
coupled to a classical wave equation for the Bose gas. We quantify the
closeness of these two dynamics as the mean-field limit is approached (gas
density ). Our estimates allow us to interchange the thermodynamic
with the mean-field limit.Comment: 27 pages, typos corrected, a few more explanations adde
Dynamics of Sound Waves in an Interacting Bose Gas
We consider a non-relativistic quantum gas of bosonic atoms confined to a
box of volume in physical space. The atoms interact with each other
through a pair potential whose strength is inversely proportional to the
density, , of the gas. We study the time evolution of
coherent excitations above the ground state of the gas in a regime of large
volume and small ratio . The initial state of
the gas is assumed to be close to a \textit{product state} of one-particle wave
functions that are approximately constant throughout the box. The initial
one-particle wave function of an excitation is assumed to have a compact
support independent of . We derive an effective non-linear equation
for the time evolution of the one-particle wave function of an excitation and
establish an explicit error bound tracking the accuracy of the effective
non-linear dynamics in terms of the ratio . We conclude
with a discussion of the dispersion law of low-energy excitations, recovering
Bogolyubov's well-known formula for the speed of sound in the gas, and a
dynamical instability for attractive two-body potentials.Comment: 42 page
Remarks on the derivation of Gross-Pitaevskii equation with magnetic Laplacian
The effective dynamics for a Bose-Einstein condensate in the regime of high
dilution and subject to an external magnetic field is governed by a magnetic
Gross-Pitaevskii equation. We elucidate the steps needed to adapt to the
magnetic case the proof of the derivation of the Gross-Pitaevskii equation
within the "projection counting" scheme
Derivation of the time dependent Gross-Pitaevskii equation without positivity condition on the interaction
Using a new method it is possible to derive mean field equations from the
microscopic body Schr\"odinger evolution of interacting particles without
using BBGKY hierarchies.
In this paper we wish to analyze scalings which lead to the Gross-Pitaevskii
equation which is usually derived assuming positivity of the interaction. The
new method for dealing with mean field limits presented in [6] allows us to
relax this condition. The price we have to pay for this relaxation is however
that we have to restrict the scaling behavior to and that we have
to assume fast convergence of the reduced one particle marginal density matrix
of the initial wave function to a pure state
Effective non-linear dynamics of binary condensates and open problems
We report on a recent result concerning the effective dynamics for a mixture
of Bose-Einstein condensates, a class of systems much studied in physics and
receiving a large amount of attention in the recent literature in mathematical
physics; for such models, the effective dynamics is described by a coupled
system of non-linear Sch\"odinger equations. After reviewing and commenting our
proof in the mean field regime from a previous paper, we collect the main
details needed to obtain the rigorous derivation of the effective dynamics in
the Gross-Pitaevskii scaling limit.Comment: Corrected typos, updated reference
Linear programming approach for solving stochastic control problem on networks with discounted transition costs
Секция 10. Теоретическая информатикаThe infinite horizon stochastic control problem on network with expected total discounted cost optimization criterion is studied. A linear programming approach for solving this problem on networks is developed. Moreover, a polynomial tim
Mean-Field Dynamics: Singular Potentials and Rate of Convergence
We consider the time evolution of a system of identical bosons whose
interaction potential is rescaled by . We choose the initial wave
function to describe a condensate in which all particles are in the same
one-particle state. It is well known that in the mean-field limit the quantum -body dynamics is governed by the nonlinear Hartree
equation. Using a nonperturbative method, we extend previous results on the
mean-field limit in two directions. First, we allow a large class of singular
interaction potentials as well as strong, possibly time-dependent external
potentials. Second, we derive bounds on the rate of convergence of the quantum
-body dynamics to the Hartree dynamics.Comment: Typos correcte
In vitro cell compatibility and antibacterial activity of microencapsulated doxycycline designed for improved localized therapy of septic arthritis
OBJECTIVES: For the treatment of septic arthritis in large animals, the local application of antibiotics as a slow release system may be an appropriate means to reach high local bioactivity and low systemic side effects and drug residues. In this study, doxycycline microspheres were developed and tested in vitro for their drug-release properties, suitability for intra-articular application and antimicrobial activity. METHODS: The development of a slow release system was achieved by microencapsulation of the drug into poly(lactide-co-glycolide) microspheres by a novel ultrasonic atomization method. Drug elution was evaluated from microspheres dispersed in elution medium at pre-defined time points by HPLC. Joint-tissue compatibility was tested on cultured bovine synoviocytes by evaluating the expression of pro-inflammatory cytokine mRNA and the production of nitric oxide (NO). Finally, the antimicrobial activity of the released antibiotic was assessed with gram-negative and gram-positive bacteria exposed to release medium sampled at days 1, 7 and 12 after microsphere suspension. RESULTS: An adequate size of the microspheres, sufficient stabilization of doxycycline in aqueous environment and drug release (25 mg microspheres in 4 mL medium) above MIC for bacteria usually isolated in bovine and equine joints were obtained over 15 days. Although the cytokine mRNA expression reflected the excellent tissue compatibility, the results with NO yielded contradictory results. Antimicrobial tests of the release medium proved to match perfectly the activity of non-encapsulated, free doxycycline as reported in the literature. CONCLUSIONS: The newly developed doxycycline delivery system achieved the target specifications and is ready for in vivo testin
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