7,497 research outputs found
Micromagnetic simulations of sweep-rate dependent coercivity in perpendicular recording media
The results of micromagnetic simulations are presented which examine the
impact of thermal fluctuations on sweep rate dependent coercivities of both
single-layer and exchange-coupled-composite (ECC) perpendicular magnetic
recording media. M-H loops are calculated at four temperatures and sweep rates
spanning five decades with fields applied normal to the plane and at 45
degrees. The impact of interactions between grains is evaluated. The results
indicate a significantly weaker sweep-rate dependence for ECC media suggesting
more robustness to long-term thermal effects. Fitting the modeled results to
Sharrock-like scaling proposed by Feng and Visscher [J. Appl. Phys. 95, 7043
(2004)] is successful only in the case of single-layer media with the field
normal to the plane.Comment: 7 pages, 14 figure
KINEMATICS OF ASSISTED AND RESISTED SPRINTING AS COMPARED TO NORMAL FREE SPRINTING IN TRAINED ATHLETES
The purpose of this study was to examine the kinematics of sprinting under assisted (or overspeed) and resisted conditions as compared to normal sprinting during the acceleration and top-speed phases of a sprint. SIX volunteer subjects completed 3 trials of each of 4 conditions: assisted sprinting (AS); free sprinting (FS); resisted sprinting (RS); and, sprint start (SS). One trial per subject per condition was randomly selected for kinematic analysis. Video (60 Hz) was collected in the sagittal plane for two full strides and analysed in 2D using an 8-point, 6-segment model with APAS software. Statistical analysis found no significant differences between AS and FS for any kinematic parameters. No significant differences were found between RS and SS for any kinematic parameters. AS differed significantly (
Dynamics of a tunable superfluid junction
We study the population dynamics of a Bose-Einstein condensate in a
double-well potential throughout the crossover from Josephson dynamics to
hydrodynamics. At barriers higher than the chemical potential, we observe slow
oscillations well described by a Josephson model. In the limit of low barriers,
the fundamental frequency agrees with a simple hydrodynamic model, but we also
observe a second, higher frequency. A full numerical simulation of the
Gross-Pitaevskii equation giving the frequencies and amplitudes of the observed
modes between these two limits is compared to the data and is used to
understand the origin of the higher mode. Implications for trapped matter-wave
interferometers are discussed.Comment: 8 pages, 7 figures; v3: Journal reference added, minor changes to
tex
The Peierls substitution in an engineered lattice potential
Artificial gauge fields open new possibilities to realize quantum many-body
systems with ultracold atoms, by engineering Hamiltonians usually associated
with electronic systems. In the presence of a periodic potential, artificial
gauge fields may bring ultracold atoms closer to the quantum Hall regime. Here,
we describe a one-dimensional lattice derived purely from effective
Zeeman-shifts resulting from a combination of Raman coupling and radiofrequency
magnetic fields. In this lattice, the tunneling matrix element is generally
complex. We control both the amplitude and the phase of this tunneling
parameter, experimentally realizing the Peierls substitution for ultracold
neutral atoms.Comment: 6 pages, 5 figure
Dual-species quantum degeneracy of potassium-40 and rubidium-87 on an atom chip
In this article we review our recent experiments with a 40K-87Rb mixture. We
demonstrate rapid sympathetic cooling of a 40K-87Rb mixture to dual quantum
degeneracy on an atom chip. We also provide details on efficient BEC
production, species-selective magnetic confinement, and progress toward
integration of an optical lattice with an atom chip. The efficiency of our
evaporation allows us to reach dual degeneracy after just 6 s of evaporation -
more rapidly than in conventional magnetic traps. When optimizing evaporative
cooling for efficient evaporation of 87Rb alone we achieve BEC after just 4 s
of evaporation and an 8 s total cycle time.Comment: 8 pages, 4 figures. To be published in the Proceedings of the 20th
International Conference on Atomic Physics, 2006 (Innsbruck, Austria
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