1,495 research outputs found
Mesoscopic dynamical differences from quantum state preparation in a Bose-Hubbard trimer
Conventional wisdom is that quantum effects will tend to disappear as the
number of quanta in a system increases, and the evolution of a system will
become closer to that described by mean field classical equations. In this
letter we combine newly developed experimental techniques to propose and
analyse an experiment using a Bose-Hubbard trimer where the opposite is the
case. We find that differences in the preparation of a centrally evacuated
trimer can lead to readily observable differences in the subsequent dynamics
which increase with system size. Importantly, these differences can be detected
by the simple measurements of atomic number.Comment: 5 pages, 4 figures, theor
Persistent current formation in a high-temperature Bose-Einstein condensate: an experimental test for c-field theory
Experimental stirring of a toroidally trapped Bose-Einstein condensate at
high temperature generates a disordered array of quantum vortices that decays
via thermal dissipation to form a macroscopic persistent current [T. W. Neely
em et al. arXiv:1204.1102 (2012)]. We perform 3D numerical simulations of the
experimental sequence within the Stochastic Projected Gross-Pitaevskii equation
using ab initio determined reservoir parameters. We find that both damping and
noise are essential for describing the dynamics of the high-temperature Bose
field. The theory gives a quantitative account of the formation of a persistent
current, with no fitted parameters.Comment: v2: 7 pages, 3 figures, new experimental data and numerical
simulation
Direct imaging of a digital-micromirror device for configurable microscopic optical potentials
Programable spatial light modulators (SLMs) have significantly advanced the
configurable optical trapping of particles. Typically, these devices are
utilized in the Fourier plane of an optical system, but direct imaging of an
amplitude pattern can potentially result in increased simplicity and
computational speed. Here we demonstrate high-resolution direct imaging of a
digital micromirror device (DMD) at high numerical apertures (NA), which we
apply to the optical trapping of a Bose-Einstein condensate (BEC). We utilise a
(1200 x 1920) pixel DMD and commercially available 0.45 NA microscope
objectives, finding that atoms confined in a hybrid optical/magnetic or
all-optical potential can be patterned using repulsive blue-detuned (532 nm)
light with 630(10) nm full-width at half-maximum (FWHM) resolution, within 5%
of the diffraction limit. The result is near arbitrary control of the density
the BEC without the need for expensive custom optics. We also introduce the
technique of time-averaged DMD potentials, demonstrating the ability to produce
multiple grayscale levels with minimal heating of the atomic cloud, by
utilising the high switching speed (20 kHz maximum) of the DMD. These
techniques will enable the realization and control of diverse optical
potentials for superfluid dynamics and atomtronics applications with quantum
gases. The performance of this system in a direct imaging configuration has
wider application for optical trapping at non-trivial NAs.Comment: 9 page
Dynamic and Energetic Stabilization of Persistent Currents in Bose-Einstein Condensates
We study conditions under which vortices in a highly oblate harmonically
trapped Bose-Einstein condensate (BEC) can be stabilized due to pinning by a
blue-detuned Gaussian laser beam, with particular emphasis on the potentially
destabilizing effects of laser beam positioning within the BEC. Our approach
involves theoretical and numerical exploration of dynamically and energetically
stable pinning of vortices with winding number up to , in correspondence
with experimental observations. Stable pinning is quantified theoretically via
Bogoliubov-de Gennes excitation spectrum computations and confirmed via direct
numerical simulations for a range of conditions similar to those of
experimental observations. The theoretical and numerical results indicate that
the pinned winding number, or equivalently the winding number of the superfluid
current about the laser beam, decays as a laser beam of fixed intensity moves
away from the BEC center. Our theoretical analysis helps explain previous
experimental observations, and helps define limits of stable vortex pinning for
future experiments involving vortex manipulation by laser beams.Comment: 8 pages 5 figure
Integrating TV/digital data spectrograph system
A 25-mm vidicon camera was previously modified to allow operation in an integration mode for low-light-level astronomical work. The camera was then mated to a low-dispersion spectrograph for obtaining spectral information in the 400 to 750 nm range. A high speed digital video image system was utilized to digitize the analog video signal, place the information directly into computer-type memory, and record data on digital magnetic tape for permanent storage and subsequent analysis
How can firms in the UK be encouraged to create more value? A discussion and review paper
This paper investigates how firms in the UK might be encouraged to create more value through strategic innovation. Our approach is an integrative one, drawing on both the extant literature - covering the value chain, innovation and the low skill/low quality equilibrium debate - and the two systematic reviews completed by the AIM Scholars - covering promising practices and networks. In the paper we argue that there are three basic strategies that firms can adopt to create more value through strategic innovation: Increasing efficiency and effectiveness through the adoption of better practices; Innovating to produce products or services that generate more revenue — through either higher prices or larger volumes — but realised while remaining at the same position in the value chain. Fundamentally changing position in the value chain and moving to a position where the products and services that are being delivered inherently generate more value. We contend that increased value is likely to be created if firms adopt one or more of these three strategies. However, adoption is likely to represent significant challenges to management. Such challenges are linked to the levels of firm competency and their ability to construct, acquire and communicate knowledge during the innovation and subsequent implementation process. Addressing these challenges form the basis of our policy and research implications
Quantitative acoustic models for superfluid circuits
We experimentally realize a highly tunable superfluid oscillator circuit in a
quantum gas of ultracold atoms and develop and verify a simple lumped-element
description of this circuit. At low oscillator currents, we demonstrate that
the circuit is accurately described as a Helmholtz resonator, a fundamental
element of acoustic circuits. At larger currents, the breakdown of the
Helmholtz regime is heralded by a turbulent shedding of vortices and density
waves. Although a simple phase-slip model offers qualitative insights into the
circuit's resistive behavior, our results indicate deviations from the
phase-slip model. A full understanding of the dissipation in superfluid
circuits will thus require the development of empirical models of the turbulent
dynamics in this system, as have been developed for classical acoustic systems.Comment: 12 pages, 9 figure
Individualization of piperacillin dosing for critically ill patients: Dosing software to optimize antimicrobial therapy
Piperacillin-tazobactam is frequently used for empirical and targeted therapy of infections in critically ill patients. Considerable pharmacokinetic (PK) variability is observed in critically ill patients. By estimating an individual's PK, dosage optimization Bayesian estimation techniques can be used to calculate the appropriate piperacillin regimen to achieve desired drug exposure targets. The aim of this study was to establish a population PK model for piperacillin in critically ill patients and then analyze the performance of the model in the dose optimization software program BestDose. Linear, with estimated creatinine clearance and weight as covariates, Michaelis-Menten (MM) and parallel linear/MM structural models were fitted to the data from 146 critically ill patients with nosocomial infection. Piperacillin concentrations measured in the first dosing interval, from each of 8 additional individuals, combined with the population model were embedded into the dose optimization software. The impact of the number of observations was assessed. Precision was assessed by (i) the predicted piperacillin dosage and by (ii) linear regression of the observed-versus-predicted piperacillin concentrations from the second 24 h of treatment. We found that a linear clearance model with creatinine clearance and weight as covariates for drug clearance and volume of distribution, respectively, best described the observed data. When there were at least two observed piperacillin concentrations, the dose optimization software predicted a mean piperacillin dosage of 4.02 g in the 8 patients administered piperacillin doses of 4.00 g. Linear regression of the observed-versus-predicted piperacillin concentrations for 8 individuals after 24 h of piperacillin dosing demonstrated an r2 of > 0.89. In conclusion, for most critically ill patients, individualized piperacillin regimens delivering a target serum piperacillin concentration is achievable. Further validation of the dosage optimization software in a clinical trial is required. Copyrigh
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