438 research outputs found
Ultracold neutral plasma expansion in two dimensions
We extend an isothermal thermal model of ultracold neutral plasma expansion
to systems without spherical symmetry, and use this model to interpret new
fluorescence measurements on these plasmas. By assuming a self-similar
expansion, it is possible to solve the fluid equations analytically and to
include velocity effects to predict the fluorescence signals. In spite of the
simplicity of this approach, the model reproduces the major features of the
experimental data
Fluorescence measurements of expanding strongly-coupled neutral plasmas
We report new detailed density profile measurements in expanding
strongly-coupled neutral plasmas. Using laser-induced fluorescence techniques,
we determine plasma densities in the range of 10^5 to 10^9/cm^3 with a time
resolution limit as small as 7 ns. Strong-coupling in the plasma ions is
inferred directly from the fluorescence signals. Evidence for strong-coupling
at late times is presented, confirming a recent theoretical result.Comment: submitted to PR
Resource Allocation Among Agents with MDP-Induced Preferences
Allocating scarce resources among agents to maximize global utility is, in
general, computationally challenging. We focus on problems where resources
enable agents to execute actions in stochastic environments, modeled as Markov
decision processes (MDPs), such that the value of a resource bundle is defined
as the expected value of the optimal MDP policy realizable given these
resources. We present an algorithm that simultaneously solves the
resource-allocation and the policy-optimization problems. This allows us to
avoid explicitly representing utilities over exponentially many resource
bundles, leading to drastic (often exponential) reductions in computational
complexity. We then use this algorithm in the context of self-interested agents
to design a combinatorial auction for allocating resources. We empirically
demonstrate the effectiveness of our approach by showing that it can, in
minutes, optimally solve problems for which a straightforward combinatorial
resource-allocation technique would require the agents to enumerate up to 2^100
resource bundles and the auctioneer to solve an NP-complete problem with an
input of that size
Atomic wave packet dynamics in finite time-dependent optical lattices
Atomic wave packets in optical lattices which are both spatially finite and
time-dependent exhibit many striking similarities with light pulses in photonic
crystals. We analytically characterize the transmission properties of such a
potential geometry for an ideal gas in terms of a position-dependent band
structure. In particular, we find that at specific energies, wave packets at
the center of the finite lattice may be enclosed by pairs of band gaps. These
act as mirrors between which the atomic wave packet is reflected, thereby
effectively yielding a matter wave cavity. We show that long trapping times may
be obtained in such a resonator and investigate the collapse and revival
dynamics of the atomic wave packet by numerical evaluation of the Schr\"odinger
equation
Book Reviews
Although the three lectures contained in this volume are propounded as a trinity, the reader will not find in them that unity which is of the essence of a trinity, as distinguished from an aggregate of three. The author proposes a triune division of legal science, Past, Present and Future. But the first lecture deals with a particular phase of the past, the second with a remotely related phase of the present, and the last with a quite unrelated phase of the future, so that they have little in common, save the brilliance that sparkles through them all
Calorimetry of Bose-Einstein condensates
We outline a practical scheme for measuring the thermodynamic properties of a
Bose-Einstein condensate as a function of internal energy. We propose using
Bragg scattering and controlled trap manipulations to impart a precise amount
of energy to a near zero temperature condensate. After thermalisation the
temperature can be measured using standard techniques to determine the state
equation . Our analysis accounts for interaction effects and the
excitation of constants of motion which restrict the energy available for
thermalisation.Comment: 6 pages, 1 figure. Updated to published versio
Self-interference of a single Bose-Einstein condensate due to boundary effects
A simple model wavefunction, consisting of a linear combination of two
free-particle Gaussians, describes many of the observed features seen in the
interactions of two isolated Bose-Einstein condensates as they expand, overlap,
and interfere. We show that a simple extension of this idea can be used to
predict the qualitative time-development of a single expanding BEC condensate
produced near an infinite wall boundary, giving similar interference phenomena.
We also briefly discuss other possible time-dependent behaviors of single BEC
condensates in restricted geometries,such as wave packet revivals.Comment: 8 pages, no figures, to appear in Physica Script
One-particle dynamical correlations in the one-dimensional Bose gas
The momentum- and frequency-dependent one-body correlation function of the
one-dimensional interacting Bose gas (Lieb-Liniger model) in the repulsive
regime is studied using the Algebraic Bethe Ansatz and numerics. We first
provide a determinant representation for the field form factor which is
well-adapted to numerical evaluation. The correlation function is then
reconstructed to high accuracy for systems with finite but large numbers of
particles, for a wide range of values of the interaction parameter. Our results
are extensively discussed, in particular their specialization to the static
case.Comment: 19 Pages, 7 figure
- …