3,275 research outputs found
Impurity-assisted Andreev reflection at a spin-active half-metal-superconductor interface
The Andreev reflection amplitude at a clean interface between a half-metallic
ferromagnet (H) and a superconductor (S) for which the half metal's
magnetization has a gradient perpendicular to the interface is proportional to
the excitation energy and vanishes at [B\'{e}ri
{\em et al.}, Phys.\ Rev.\ B {\bf 79}, 024517 (2009)]. Here we show that the
presence of impurities at or in the immediate vicinity of the HS interface
leads to a finite Andreev reflection amplitude at . This
impurity-assisted Andreev reflection dominates the low-bias conductance of a HS
junction and the Josephson current of an SHS junction in the long-junction
limit.Comment: 12 pages, 2 figure
Andreev reflection at half-metal-superconductor interfaces with non-uniform magnetization
Andreev reflection at the interface between a half-metallic ferromagnet and a
spin-singlet superconductor is possible only if it is accompanied by a spin
flip. Here we calculate the Andreev reflection amplitudes for the case that the
spin flip originates from a spatially non-uniform magnetization direction in
the half metal. We calculate both the microscopic Andreev reflection amplitude
for a single reflection event and an effective Andreev reflection amplitude
describing the effect of multiple Andreev reflections in a ballistic thin film
geometry. It is shown that the angle and energy dependence of the Andreev
reflection amplitude strongly depends on the orientation of the gradient of the
magnetization with respect to the interface. Establishing a connection between
the scattering approach employed here and earlier work that employs the
quasiclassical formalism, we connect the symmetry properties of the Andreev
reflection amplitudes to the symmetry properties of the anomalous Green
function in the half metal.Comment: 13 pages, 4 figure
Сравнительная морфофункциональная оценка различных способов диссекции печеночной паренхимы
Проведена оценка морфофункционального состояния печени до и после резекции с применением различных методов диссекции печеночной паренхимы. Показано, что при выполнении обширных резекций печени целесообразно применение методик ультразвуковой, струйной диссекции или методики "clamp crushing".Проведено оцінку морфофункціонального стану печінки до і після резекції із застосуванням різних методів дисекції печінкової паренхіми. Показано, що під час виконання обширних резекцій печінки доцільним є використання методики ультразвукової, струменевої дисекції або методики "clamp crushing".The morphofunctional state of the liver before and after resection using different methods of dissection of liver parenchyma are assessed. It is shown that at large resections of the liver it is reasonable to use the methods of ultrasound, stream dissection or "clamp crushing" technique
Exact Energy-Time Uncertainty Relation for Arrival Time by Absorption
We prove an uncertainty relation for energy and arrival time, where the
arrival of a particle at a detector is modeled by an absorbing term added to
the Hamiltonian. In this well-known scheme the probability for the particle's
arrival at the counter is identified with the loss of normalization for an
initial wave packet. Under the sole assumption that the absorbing term vanishes
on the initial wave function, we show that and , where denotes the mean
arrival time, and is the probability for the particle to be eventually
absorbed. Nearly minimal uncertainty can be achieved in a two-level system, and
we propose a trapped ion experiment to realize this situation.Comment: 8 pages, 2 figure
Flow-Field Investigation of Gear-Flap Interaction on a Gulfstream Aircraft Model
Off-surface flow measurements of a high-fidelity 18% scale Gulfstream aircraft model in landing configuration with the main landing gear deployed are presented. Particle Image Velocimetry (PIV) and Laser Velocimetry (LV) were used to measure instantaneous velocities in the immediate vicinity of the main landing gear and its wake and near the inboard tip of the flap. These measurements were made during the third entry of a series of tests conducted in the NASA Langley Research Center (LaRC) 14- by 22-Foot Subsonic Tunnel (14 x 22) to obtain a comprehensive set of aeroacoustic measurements consisting of both aerodynamic and acoustic data. The majority of the off-body measurements were obtained at a freestream Mach number of 0.2, angle of attack of 3 degrees, and flap deflection angle of 39 degrees with the landing gear on. A limited amount of data was acquired with the landing gear off. LV was used to measure the velocity field in two planes upstream of the landing gear and to measure two velocity profiles in the landing gear wake. Stereo and 2-D PIV were used to measure the velocity field over a region extending from upstream of the landing gear to downstream of the flap trailing edge. Using a special traverse system installed under the tunnel floor, the velocity field was measured at 92 locations to obtain a comprehensive picture of the pertinent flow features and characteristics. The results clearly show distinct structures in the wake that can be associated with specific components on the landing gear and give insight into how the wake is entrained by the vortex at the inboard tip of the flap
How many young star clusters exist in the Galactic center?
We study the evolution and observability of young compact star clusters
within about 200pc of the Galactic center. Calculations are performed using
direct N-body integration on the GRAPE-4, including the effects of both stellar
and binary evolution and the external influence of the Galaxy. The results of
these detailed calculations are used to calibrate a simplified model applicable
over a wider range of cluster initial conditions. We find that clusters within
200 pc from the Galactic center dissolve within about 70 Myr. However, their
projected densities drop below the background density in the direction of the
Galactic center within 20 Myr, effectively making these clusters undetectable
after that time. Clusters farther from the Galactic center but at the same
projected distance are more strongly affected by this selection effect, and may
go undetected for their entire lifetimes. Based on these findings, we conclude
that the region within 200 pc of the Galactic center could easily harbor some
50 clusters with properties similar to those of the Arches or the Quintuplet
systems.Comment: ApJ Letters in pres
Sympathetic Cooling of Mixed Species Two-Ion Crystals for Precision Spectroscopy
Sympathetic cooling of trapped ions has become an indispensable tool for
quantum information processing and precision spectroscopy. In the simplest
situation a single Doppler-cooled ion sympathetically cools another ion which
typically has a different mass. We analytically investigate the effect of the
mass ratio of such an ion crystal on the achievable temperature limit in the
presence of external heating. As an example, we show that cooling of a single
Al+ with Be+, Mg+ and Ca+ ions provides similar results for heating rates
typically observed in ion traps, whereas cooling ions with a larger mass
perform worse. Furthermore, we present numerical simulation results of the
rethermalisation dynamics after a background gas collision for the Al+/Ca+
crystal for different cooling laser configurations.Comment: Made Graphics black & white print compatible, clarified abstract and
summar
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