1,370 research outputs found
Crossed Andreev effects in two-dimensional quantum Hall systems
We study the crossed Andreev effects in two-dimensional
conductor/superconductor hybrid systems under a perpendicular magnetic field.
Both a graphene/superconductor hybrid system and an electron gas/superconductor
one are considered. It is shown that an exclusive crossed Andreev reflection,
with other Andreev reflections being completely suppressed, is obtained in a
high magnetic field because of the chiral edge states in the quantum Hall
regime. Importantly, the exclusive crossed Andreev reflection not only holds
for a wide range of system parameters, e.g., the size of system, the width of
central superconductor, and the quality of coupling between the graphene and
the superconductor, but also is very robust against disorder. When the applied
bias is within the superconductor gap, a robust Cooper-pair splitting process
with high-efficiency can be realized in this system.Comment: 10 pages, 10 figure
Ballistic Thermal Rectification in Asymmetric Three-Terminal Mesoscopic Dielectric Systems
By coupling the asymmetric three-terminal mesoscopic dielectric system with a
temperature probe, at low temperature, the ballistic heat flux flow through the
other two asymmetric terminals in the nonlinear response regime is studied
based on the Landauer formulation of transport theory. The thermal
rectification is attained at the quantum regime. It is a purely quantum effect
and is determined by the dependence of the ratio
on , the phonon's frequency.
Where and are respectively the
transmission coefficients from two asymmetric terminals to the temperature
probe, which are determined by the inelastic scattering of ballistic phonons in
the temperature probe. Our results are confirmed by extensive numerical
simulations.Comment: 10 pages, 4 figure
Key-point Detection based Fast CU Decision for HEVC Intra Encoding
As the most recent video coding standard, High Efficiency Video Coding (HEVC) adopts various novel techniques, including a quad-tree based coding unit (CU) structure and additional angular modes used for intra encoding. These newtechniques achieve a notable improvement in coding efficiency at the penalty of significant computational complexity increase. Thus, a fast HEVC coding algorithm is highly desirable. In this paper, we propose a fast intra CU decision algorithm for HEVC to reduce the coding complexity, mainly based on a key-point detection. A CU block is considered to have multiple gradients and is early split if corner points are detected inside the block. On the other hand, a CU block without corner points is treated to be terminated when its RD cost is also small according to statistics of the previous frames. The proposed fast algorithm achieves over 62% encoding time reduction with 3.66%, 2.82%, and 2.53% BD-Rate loss for Y, U, and V components, averagely. The experimental results show that the proposed method is efficient to fast decide CU size in HEVC intra coding, even though only static parameters are applied to all test sequences
A Vertically Resolved MSE Framework Highlights the Role of the Boundary Layer in Convective Self-Aggregation
Convective self-aggregation refers to a phenomenon in which random convection
can self-organize into large-scale clusters over an ocean surface with uniform
temperature in cloud-resolving models. Previous literature studies convective
aggregation primarily by analyzing vertically integrated (VI) moist static
energy (MSE) variance. That is the global MSE variance, including both the
local MSE variance at a given altitude and the covariance of MSE anomalies
between different altitudes. Here we present a vertically resolved (VR) MSE
framework that focuses on the local MSE variance to study convective
self-aggregation. Using a cloud-resolving simulation, we show that the
development of self-aggregation is associated with an increase of local MSE
variance, and that the diabatic and adiabatic generation of the MSE variance is
mainly dominated by the boundary layer (BL). The results agree with recent
numerical simulation results and the available potential energy analyses
showing that the BL plays a key role in the development of self-aggregation. We
further present a detailed comparison between the global and local MSE variance
frameworks in their mathematical formulation and diagnostic results,
highlighting their differences.Comment: 50 pages, 2 tables, 12 figures, submitted to the Journal of the
Atmospheric Science
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The evolution of vortex tilt and vertical motion of tropical cyclones in directional shear flows
Recent studies have demonstrated the importance of moist dynamics on the intensification variability of tropical cyclones (TCs) in directional shear flows. Here, we propose that dry dynamics can account for many aspects of the structure change of TCs in moist simulations. The change of vortex tilt with height and time essentially determines the kinematic and thermodynamic structure of TCs experiencing directional shear flows, depending on how the environmental flow rotates with height; i.e., in a clockwise (CW) or counter-clockwise (CC) fashion. The vortex tilt precesses faster and is closer to the left-of-shear (with respect to the deep-layer shear), with smaller magnitude at equilibrium in CW hodographs than in CC hodographs. The low-level vortex tilt, and accordingly more low-level upward motions are ahead of the overall vortex tilt in CW hodographs, but are behind of the overall vortex tilt in CC hodographs. Such the configuration of vortex tilt in CW hodographs is potentially favorable for the continuous precession of convection into the up-shear region, but in CC hodographs is unfavorable. Most of the upward motions within a TC undergoing CW shear are concentrated in the down-shear-left region, whereas those in the CC shear are located in the down-shear-right region. Moreover, the upward (downward) motions are in-phase with positive (negative) local helicity in both CW and CC hodographs. Here we present an alternative mechanism that is associated with balanced dynamics in response to vortex tilt to explain the coincidence and also the distribution variability of vertical motions, as well as local helicity in directional shear flows. The balanced dynamics could explain the overlap of positive helicity and convection in both moist simulations and observations
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