83,308 research outputs found
From the Complete Yang Model to Snyder's Model, de Sitter Special Relativity and Their Duality
By means of Dirac procedure, we re-examine Yang's quantized space-time model,
its relation to Snyder's model, the de Sitter special relativity and their
UV-IR duality. Starting from a dimensionless dS_5-space in a 5+1-d Mink-space a
complete Yang model at both classical and quantum level can be presented and
there really exist Snyder's model, the dS special relativity and the duality.Comment: 7 papge
Density oscillations in trapped dipolar condensates
We investigated the ground state wave function and free expansion of a
trapped dipolar condensate. We find that dipolar interaction may induce both
biconcave and dumbbell density profiles in, respectively, the pancake- and
cigar-shaped traps. On the parameter plane of the interaction strengths, the
density oscillation occurs only when the interaction parameters fall into
certain isolated areas. The relation between the positions of these areas and
the trap geometry is explored. By studying the free expansion of the condensate
with density oscillation, we show that the density oscillation is detectable
from the time-of-flight image.Comment: 7 pages, 9 figure
Characterisation of real GPRS traffic with analytical tools
With GPRS and UMTS networks lunched, wireless multimedia services are commercially becoming the most attractive applications next to voice. Because of the nature of bursty, packet-switched schemes and multiple data rates, the traditional Erlang approach and Poisson models for characterising voice-centric services traffic are not suitable for studying wireless multimedia services traffic. Therefore, research on the characterisation of wireless multimedia services traffic is very challenging. The typical reference for the study of wireless multimedia services traffic is wired Internet services traffic. However, because of the differences in network protocol, bandwidth, and QoS requirements between wired and wireless services, their traffic characterisations may not be similar. Wired network Internet traffic shows self-similarity, long-range dependence and its file sizes exhibit heavy-tailedness. This paper reports the use of existing tools to analyse real GPRS traffic data to establish whether wireless multimedia services traffic have similar properties as wired Internet services traffic
Black Holes in Six-dimensional Conformal Gravity
We study conformally-invariant theories of gravity in six dimensions. In four
dimensions, there is a unique such theory that is polynomial in the curvature
and its derivatives, namely Weyl-squared, and furthermore all solutions of
Einstein gravity are also solutions of the conformal theory. By contrast, in
six dimensions there are three independent conformally-invariant polynomial
terms one could consider. There is a unique linear combination (up to overall
scale) for which Einstein metrics are also solutions, and this specific theory
forms the focus of our attention in this paper. We reduce the equations of
motion for the most general spherically-symmetric black hole to a single
5th-order differential equation. We obtain the general solution in the form of
an infinite series, characterised by 5 independent parameters, and we show how
a finite 3-parameter truncation reduces to the already known Schwarzschild-AdS
metric and its conformal scaling. We derive general results for the
thermodynamics and the first law for the full 5-parameter solutions. We also
investigate solutions in extended theories coupled to conformally-invariant
matter, and in addition we derive some general results for conserved charges in
cubic-curvature theories in arbitrary dimensions.Comment: 28 pages. References adde
Security improvement of using modified coherent state for quantum cryptography
Weak coherent states as a photon source for quantum cryptography have limit
in secure data rate and transmission distance because of the presence of
multi-photon events and loss in transmission line. Two-photon events in a
coherent state can be taken out by a two-photon interference scheme. We
investigate the security issue of utilizing this modified coherent state in
quantum cryptography. A 4 dB improvement in secure data rate or a nearly
two-fold increase in transmission distance over the coherent state are found.
With a recently proposed and improved encoding strategy, further improvement is
possible.Comment: 5 pages, 2 figures, to appear in Physical Review
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