2,136 research outputs found
Equilibrium vortex formation in ultrarapidly rotating two-component Bose-Einstein condensates
Equilibrium vortex formation in rotating binary Bose gases with a rotating
frequency higher than the harmonic trapping frequency is investigated
theoretically. We consider the system being evaporatively cooled to form
condensates and a combined numerical scheme is applied to ensure the binary
system being in an authentic equilibrium state. To keep the system stable
against the large centrifugal force of ultrafast rotation, a quartic trapping
potential is added to the existing harmonic part. Using the Thomas-Fermi
approximation, a critical rotating frequency \Omega_c is derived, which
characterizes the structure with or without a central density hole. Vortex
structures are studied in detail with rotation frequency both above and below
?\Omega_c and with respect to the miscible, symmetrically separated, and
asymmetrically separated phases in their nonrotating ground-state counterparts.Comment: 7 pages, 7 figure
Bending-wave Instability of a Vortex Ring in a Trapped Bose-Einstein Condensate
Based on a velocity formula derived by matched asymptotic expansion, we
investigate the dynamics of a circular vortex ring in an axisymmetric
Bose-Einstein condensate in the Thomas-Fermi limit. The trajectory for an
axisymmetrically placed and oriented vortex ring is entirely determined,
revealing that the vortex ring generally precesses in condensate. The linear
instability due to bending waves is investigated both numerically and
analytically. General stability boundaries for various perturbed wavenumbers
are computed. In particular, the excitation spectrum and the absolutely stable
region for the static ring are analytically determined.Comment: 4 pages, 4 figure
Turbulence generation in homogeneous particle-laden flows
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76730/1/AIAA-1998-240-706.pd
Investigation of Lab Fire Prevention Management System of Combining Root Cause Analysis and Analytic Hierarchy Process with Event Tree Analysis
This paper proposed a new approach, combining root cause analysis (RCA), analytic hierarchy process (AHP), and event tree analysis (ETA) in a loop to systematically evaluate various laboratory safety prevention strategies. First, 139 fire accidents were reviewed to identify the root causes and draw out prevention strategies. Most fires were caused due to runaway reactions, operation error and equipment failure, and flammable material release. These mostly occurred in working places of no prompt fire protection. We also used AHP to evaluate the priority of these strategies and found that chemical fire prevention strategy is the most important control element, and strengthening maintenance and safety inspection intensity is the most important action. Also together with our surveys results, we proposed that equipment design is also critical for fire prevention. Therefore a technical improvement was propounded: installing fire detector, automatic sprinkler, and manual extinguisher in the lab hood as proactive fire protections. ETA was then used as a tool to evaluate laboratory fire risks. The results indicated that the total risk of a fire occurring decreases from 0.0351 to 0.0042 without/with equipment taking actions. Establishing such system can make Environment, Health and Safety (EH&S) office not only analyze and prioritize fire prevention policies more practically, but also demonstrate how effective protective equipment improvement can achieve and the probabilities of the initiating event developing into a serious accident or controlled by the existing safety system
Spontaneous Crystallization of Skyrmions and Fractional Vortices in the Fast-rotating and Rapidly-quenched Spin-1 Bose-Einstein Condensates
We investigate the spontaneous generation of crystallized topological defects
via the combining effects of fast rotation and rapid thermal quench on the
spin-1 Bose-Einstein condensates. By solving the stochastic projected
Gross-Pitaevskii equation, we show that, when the system reaches equilibrium, a
hexagonal lattice of skyrmions, and a square lattice of half-quantized vortices
can be formed in a ferromagnetic and antiferromagnetic spinor BEC, respetively,
which can be imaged by using the polarization-dependent phase-contrast method
Transcritical flow of a stratified fluid over topography: analysis of the forced Gardner equation
Transcritical flow of a stratified fluid past a broad localised topographic
obstacle is studied analytically in the framework of the forced extended
Korteweg--de Vries (eKdV), or Gardner, equation. We consider both possible
signs for the cubic nonlinear term in the Gardner equation corresponding to
different fluid density stratification profiles. We identify the range of the
input parameters: the oncoming flow speed (the Froude number) and the
topographic amplitude, for which the obstacle supports a stationary localised
hydraulic transition from the subcritical flow upstream to the supercritical
flow downstream. Such a localised transcritical flow is resolved back into the
equilibrium flow state away from the obstacle with the aid of unsteady coherent
nonlinear wave structures propagating upstream and downstream. Along with the
regular, cnoidal undular bores occurring in the analogous problem for the
single-layer flow modeled by the forced KdV equation, the transcritical
internal wave flows support a diverse family of upstream and downstream wave
structures, including solibores, rarefaction waves, reversed and trigonometric
undular bores, which we describe using the recent development of the nonlinear
modulation theory for the (unforced) Gardner equation. The predictions of the
developed analytic construction are confirmed by direct numerical simulations
of the forced Gardner equation for a broad range of input parameters.Comment: 34 pages, 24 figure
Selective interlayer ferromagnetic coupling between the Cu spins in YBa Cu O grown on top of La Ca MnO
Studies to date on ferromagnet/d-wave superconductor heterostructures focus
mainly on the effects at or near the interfaces while the response of bulk
properties to heterostructuring is overlooked. Here we use resonant soft x-ray
scattering spectroscopy to reveal a novel c-axis ferromagnetic coupling between
the in-plane Cu spins in YBa Cu O (YBCO) superconductor when it
is grown on top of ferromagnetic La Ca MnO (LCMO) manganite
layer. This coupling, present in both normal and superconducting states of
YBCO, is sensitive to the interfacial termination such that it is only observed
in bilayers with MnO_2but not with La Ca interfacial
termination. Such contrasting behaviors, we propose, are due to distinct
energetic of CuO chain and CuO plane at the La Ca and
MnO terminated interfaces respectively, therefore influencing the transfer
of spin-polarized electrons from manganite to cuprate differently. Our findings
suggest that the superconducting/ferromagnetic bilayers with proper interfacial
engineering can be good candidates for searching the theorized
Fulde-Ferrel-Larkin-Ovchinnikov (FFLO) state in cuprates and studying the
competing quantum orders in highly correlated electron systems.Comment: Please note the change of the title. Text might be slightly different
from the published versio
Stationary wave patterns generated by an impurity moving with supersonic velocity through a Bose-Einstein condensate
Formation of stationary 3D wave patterns generated by a small point-like
impurity moving through a Bose-Einstein condensate with supersonic velocity is
studied. Asymptotic formulae for a stationary far-field density distribution
are obtained. Comparison with three-dimensional numerical simulations
demonstrates that these formulae are accurate enough already at distances from
the obstacle equal to a few wavelengths.Comment: 7 pages, 3 figure
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