13,406 research outputs found
Spectrum of turbulent Kelvin-waves cascade in superfluid helium
To explain the observed decay of superfluid turbulence at very low
temperature, it has been proposed that a cascade of Kelvin waves (analogous to
the classical Kolmogorov cascade) transfers kinetic energy to length scales
which are small enough that sound can be radiated away. We report results of
numerical simulations of the interaction of quantized vortex filaments. We
observe the development of the Kelvin-waves cascade, and compute the statistics
of the curvature, the amplitude spectrum (which we compare with competing
theories) and the fractal dimension.Comment: 32 pages, 22 figure
Topological defect motifs in two-dimensional Coulomb clusters
The most energetically favourable arrangement of low-density electrons in an
infinite two-dimensional plane is the ordered triangular Wigner lattice.
However, in most instances of contemporary interest one deals instead with
finite clusters of strongly interacting particles localized in potential traps,
for example, in complex plasmas. In the current contribution we study
distribution of topological defects in two-dimensional Coulomb clusters with
parabolic lateral confinement. The minima hopping algorithm based on molecular
dynamics is used to efficiently locate the ground- and low-energy metastable
states, and their structure is analyzed by means of the Delaunay triangulation.
The size, structure and distribution of geometry-induced lattice imperfections
strongly depends on the system size and the energetic state. Besides isolated
disclinations and dislocations, classification of defect motifs includes defect
compounds --- grain boundaries, rosette defects, vacancies and interstitial
particles. Proliferation of defects in metastable configurations destroys the
orientational order of the Wigner lattice.Comment: 14 pages, 8 figures. This is an author-created, un-copyedited version
of an article accepted for publication in J. Phys.: Condens. Matter. IOP
Publishing Ltd is not responsible for any errors or omissions in this version
of the manuscript or any version derived from it. The definitive
publisher-authenticated version is available online at
10.1088/0953-8984/23/38/38530
Remote sensing in Iowa agriculture: Identification and classification of Iowa's crops, soils and forestry resources using ERTS-1 and complimentary underflight imagery
There are no author-identified significant results in this report
Influence of FK 506 (tacrolimus) on circulating CD4 <sup>+</sup> t cells expressing cd25 and cd45ra antigens in 19 patients with chronic progressive multiple sclerosis participating in an open label drug safety trial
We have taken the opportunity of a clinical trial of the potential efficacy and safety of FK 506 (tacrolimus) in chronic progressive multiple sclerosis (MS) to examine the influence of this potent new immunosuppressant on circulating T-lymphocytes in an otherwise healthy non-transplant population. Peripheral blood levels of subsets of CD4+ T lymphocytes expressing the activation molecule interleukin-2 receptor (p55 α chain; CD25) or the CD45RA isoform were determined sequentially in 19 patients that were treated continuously with oral FK 506 (starting dose 0.15 mg/kg/day) for 12 months. No significant change in the proportion of circulating CD25 + CD4+ cells was observed over the study period in which the mean trough plasma FK 506 level rose from 0.3 ±0.2 to 0.5 ±0.4 ng/ml. There was also no significant effect of FK 506 on the percentage of CD45RA + CD4 + cells in the peripheral blood at 12 months compared with pretreatment values. Analysis of a subgroup of 7 patients, who showed a sustained reduction in CD25 + CD4+ cells and a reciprocal increase in CD45RA* CD4 * cells for at least 6 months after start of treatment, did not reveal any difference in disability at one year compared with the treatment group as a whole. The side effects of FK 506 were mild and the overall degree of disability estimated by the mean Kurtzke expanded disability status scale (EDSS) score or the ambulation index did not deteriorate significantly in the 19 patients studied over the 12 months of FK 506 administration. © 1994 Informa UK Ltd All rights reserved: reproduction in whole or part not permitted
Uncovering Bugs in Distributed Storage Systems during Testing (not in Production!)
Testing distributed systems is challenging due to multiple sources of nondeterminism. Conventional testing techniques, such as unit, integration and stress testing, are ineffective in preventing serious but subtle bugs from reaching production. Formal techniques, such as TLA+, can only verify high-level specifications of systems at the level of logic-based models, and fall short of checking the actual executable code. In this paper, we present a new methodology for testing distributed systems. Our approach applies advanced systematic testing techniques to thoroughly check that the executable code adheres to its high-level specifications, which significantly improves coverage of important system behaviors. Our methodology has been applied to three distributed storage systems in the Microsoft Azure cloud computing platform. In the process, numerous bugs were identified, reproduced, confirmed and fixed. These bugs required a subtle combination of concurrency and failures, making them extremely difficult to find with conventional testing techniques. An important advantage of our approach is that a bug is uncovered in a small setting and witnessed by a full system trace, which dramatically increases the productivity of debugging
Magnetic vortex-antivortex crystals generated by spin-polarized current
We study vortex pattern formation in thin ferromagnetic films under the
action of strong spin-polarized currents. Considering the currents which are
polarized along the normal of the film plane, we determine the critical current
above which the film goes to a saturated state with all magnetic moments being
perpendicular to the film plane. We show that stable square vortex-antivortex
superlattices (\emph{vortex crystals}) appears slightly below the critical
current. The melting of the vortex crystal occurs with current further
decreasing. A mechanism of current-induced periodic vortex-antivortex lattice
formation is proposed. Micromagnetic simulations confirm our analytical results
with a high accuracy.Comment: 12 pages, 11 figure
Anomalous translational velocity of vortex ring with finite-amplitude Kelvin waves
We consider finite-amplitude Kelvin waves on an inviscid vortex assuming that
the vortex core has infinitesimal thickness. By numerically solving the
governing Biot-Savart equation of motion, we study how the frequency of the
Kelvin waves and the velocity of the perturbed ring depend on the Kelvin wave
amplitude. In particular, we show that, if the amplitude of the Kelvin waves is
sufficiently large, the perturbed vortex ring moves backwards.Comment: 6 pages, 5 figures, v2: minor changes, v3: typos correcte
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