62,500 research outputs found
Universality of BSW mechanism for spinning particles
Ba\~nados (BSW) found that Kerr black holes can act as particle
accelerators with collisions at arbitrarily high center-of-mass energies.
Recently, collisions of particles with spin around some rotating black holes
have been discussed. In this paper, we study the BSW mechanism for spinning
particles by using a metric ansatz which describes a general rotating black
hole. We notice that there are two inequivalent definitions of center-of-mass
(CM) energy for spinning particles. We mainly discuss the CM energy defined in
terms of the worldline of the particle. We show that there exists an
energy-angular momentum relation that causes collisions with
arbitrarily high energy near-extremal black holes. We also provide a simple but
rigorous proof that the BSW mechanism breaks down for nonextremal black holes.
For the alternative definition of the CM energy, some authors find a new
critical spin relation that also causes the divergence of the CM mass. However,
by checking the timelike constraint, we show that particles with this critical
spin cannot reach the horizon of the black hole. Further numerical calculation
suggests that such particles cannot exist anywhere outside the horizon. Our
results are universal, independent of the underlying theories of gravity.Comment: 8 pages, 1 figure
Changes of Kondo effect in the junction with DIII-class topological and -wave superconductors
We discuss the change of the Kondo effect in the Josephson junction formed by
the indirect coupling between a one-dimensional \emph{DIII}-class topological
and s-wave superconductors via a quantum dot. By performing the
Schrieffer-Wolff transformation, we find that the single-electron occupation in
the quantum dot induces various correlation modes, such as the Kondo and
singlet-triplet correlations between the quantum dot and the -wave
superconductor and the spin exchange correlation between the dot and Majorana
doublet. Moreover, it plays a nontrivial role in modifying the Josephson
effect, leading to the occurrence of anisotropic and high-order Kondo
correlation. In addition, due to the quantum dot in the Kondo regime, extra
spin exchange correlations contribute to the Josephson effect as well.
Nevertheless, if the \emph{DIII}-class topological superconductor degenerates
into \emph{D}-class because of the destruction of time-reversal invariance, all
such terms will disappear completely. We believe that this work shows the
fundamental difference between the \emph{D}- and \emph{DIII}-class topological
superconductors.Comment: 10 pages, 3 figures. Any comment is welcom
Acceleration computing process in wavelength scanning interferometry
The optical interferometry has been widely explored for surface measurement due to the advantages of non-contact and high accuracy interrogation. Eventually, some interferometers are used to measure both rough and smooth surfaces such as white light interferometry and wavelength scanning interferometry (WSI). The WSI can be used to measure large discontinuous surface profiles without the phase ambiguity problems. However, the WSI usually needs to capture hundreds of interferograms at different wavelength in order to evaluate the surface finish for a sample. The evaluating process for this large amount of data needs long processing time if CPUs traditional programming is used. This paper presents a parallel programming model to achieve the data parallelism for accelerating the computing analysis of the captured data. This parallel programming is based on CUDATM C program structure that developed by NVIDIA. Additionally, this paper explains the mathematical algorithm that has been used for evaluating the surface profiles. The computing time and accuracy obtained from CUDA program, using GeForce GTX 280 graphics processing unit (GPU), were compared to those obtained from sequential execution Matlab program, using Intel® Core™2 Duo CPU. The results of measuring a step height sample shows that the parallel programming capability of the GPU can highly accelerate the floating point calculation throughput compared to multicore CPU
Planning and Design Strategies for Sustainable Urban Development
In order to create high impact low-carbon architecture it is necessary to address issues at the urban scale. This paper reviews methods adopted in the UK, Hong Kong and America and develops a series of themes that should be incorporated in modern city development strategies to produce green and sustainable outcomes. These are concerned with: planning policies and building regulations; neighborhood and site planning; and building design. Underlying themes which must be incorporated are connected to: building façade, systems design and operation; energy demand and supply; transportation systems; water supply and use; and wastes/pollution issues. To achieve success a number of support mechanisms are needed including strategic and infrastructure development, implementation of assessment frameworks, and the distribution of information and knowledge to stakeholders. The themes are compared to recent developments in the city of Kunming and proposals for future applications are explored
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