656 research outputs found
Meanfield treatment of Bragg scattering from a Bose-Einstein condensate
A unified semiclassical treatment of Bragg scattering from Bose-Einstein
condensates is presented. The formalism is based on the Gross-Pitaevskii
equation driven by classical light fields far detuned from atomic resonance. An
approximate analytic solution is obtained and provides quantitative
understanding of the atomic momentum state oscillations, as well as a simple
expression for the momentum linewidth of the scattering process. The validity
regime of the analytic solution is derived, and tested by three dimensional
cylindrically symmetric numerical simulations.Comment: 21 pages, 10 figures. Minor changes made to documen
Consequence of superfluidity on the expansion of a rotating Bose-Einstein condensate
We study the time evolution of a rotating condensate, that expands after
being suddenly released from the confining trap, by solving the hydrodynamic
equations of irrotational superfluids. For slow initial rotation speeds,
, we find that the condensate's angular velocity increases rapidly
to a maximum value and this is accompanied by a minimum in the deformation of
the condensate in the rotating plane. During the expansion the sample makes a
global rotation of approximately , where the exact value depends on
. This minimum deformation can serve as an easily detectable
signature of superfluidity in a Bose--Einstein condensate.Comment: 4 pages, 3 figures, submitted to PR
Peri-implant bone remodeling after total hip replacement combined with systemic alendronate treatment: a finite element analysis
In order to decrease the peri-implant bone loss during the life-time of the implant, oral use of anti-osteoporosis drugs (like bisphosphonates) has been suggested. In this study, bone remodeling parameters identified from clinical trials of alendronate were used to simulate the effect of those drugs used after total hip arthroplasty on the peri-implant bone density. Results of the simulation show that the oral administrated drugs increase bone density around the implant and decreases, at the same time, the micromovements between the implant and the surrounding bone tissue. Incorporation of drug effect in numerical studies of bone remodeling is a promising tool especially to predetermine safe bisphosphonate doses that could be used with orthopedic implants
Direct observation of the phonon energy in a Bose-Einstein condensate by tomographic imaging
The momentum and energy of phonons in a Bose-Einstein condensate are measured
directly from a time-of-flight image by computerized tomography. We find that
the same atoms that carry the momentum of the excitation also carry the
excitation energy. The measured energy is in agreement with the Bogoliubov
spectrum. Hydrodynamic simulations are performed which confirm our observation.Comment: Letter, 5 figure
How plate positioning impacts the biomechanics of the open wedge tibial osteotomy; a finite element analysis
A numerical model of the medial open wedge tibial osteotomy based on the finite element method was developed. Two plate positions were tested numerically. In a configuration, (a), the plate was fixed in a medial position and (b) in an anteromedial position. The simulation took into account soft tissues preload, muscular tonus and maximal gait load.The maximal stresses observed in the four structural elements (bone, plate, wedge, screws) of an osteotomy with plate in medial position were substantially higher (1.13-2.8 times more) than those observed in osteotomy with an anteromedial plate configuration. An important increase (1.71 times more) of the relative micromotions between the wedge and the bone was also observed. In order to avoid formation of fibrous tissue at the bone wedge interface, the osteotomy should be loaded under 18.8% (approximately 50 kg) of the normal gait load until the osteotomy interfaces union is achieved
Stable and unstable vortices in multicomponent Bose-Einstein condensates
We study the stability and dynamics of vortices in two-species condensates as
prepared in the recent JILA experiment (M. R. Andrews {\em et al.}, Phys. Rev.
Lett. 83 (1999) 2498). We find that of the two available configurations, in
which one specie has vorticity and the other one has , only one is
linearly stable, which agrees with the experimental results. However, it is
found that in the unstable case the vortex is not destroyed by the instability,
but may be transfered from one specie to the other or display complex
spatiotemporal dynamics.Comment: 4 EPS figures, now features a three-dimensional stud
Collective oscillations of a classical gas confined in harmonic traps
Starting from the Boltzmann equation we calculate the frequency and the
damping of the monopole and quadrupole oscillations of a classical gas confined
in an harmonic potential. The collisional term is treated in the relaxation
time approximation and a gaussian ansatz is used for its evaluation. Our
approach provides an explicit description of the transition between the
hydrodynamic and collisionless regimes in both spherical and deformed traps.
The predictions are compared with the results of a numerical simulation.Comment: 6 pages, revtex, 2 figures include
Off-axis vortices in trapped Bose condensed gases: angular momentum and frequency splitting
We consider non centered vortices and their arrays in a cylindrically trapped
Bose-Einstein condensate at zero temperature. We study the kinetic energy and
the angular momentum per particle in the Thomas Fermi regime and their
dependence on the distance of the vortices from the center of the trap. Using a
perturbative approach with respect to the velocity-field of the vortices, we
calculate to first order the frequency shift of the collective low-lying
excitations due to the presence of an off-center vortex or a vortex array, and
compare these results with predictions which would be obtained by the
application of a simple sum-rule approach, previously found to be very
successful for centered vortices. It turns out that the simple sum-rule
approach fails for off-centered vortices.Comment: 11 pages, LaTeX, 3 figures. Perturbative approach adde
Excitations of a Bose-Einstein condensate in a one-dimensional optical lattice
We investigate the low-lying excitations of a stack of weakly-coupled
two-dimensional Bose-Einstein condensates that is formed by a one-dimensional
optical lattice. In particular, we calculate the dispersion relations of the
monopole and quadrupole modes, both for the ground state as well as for the
case in which the system contains a vortex along the direction of the lasers
creating the optical lattice. Our variational approach enables us to determine
analytically the dispersion relations for an arbitrary number of atoms in every
two-dimensional condensate and for an arbitrary momentum. We also discuss the
feasibility of experimentally observing our results.Comment: 16 pages, 5 figures, minor changes,accepted for publication in Phys.
Rev.
- âŠ