98,332 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
An Deformation of Gauged STU Supergravity
Four-dimensional gauged STU supergravity is a consistent
truncation of the standard gauged supergravity in which
just the four gauge fields in the Cartan subgroup of are
retained. One of these is the graviphoton in the supergravity
multiplet and the other three lie in three vector multiplets. In this paper we
carry out the analogous consistent truncation of the newly-discovered family of
-deformed gauged supergravities, thereby obtaining
a family of -deformed STU gauged supergravities. Unlike in some other
truncations of the deformed supergravity that have been
considered, here the scalar potential of the deformed STU theory is independent
of the parameter. However, it enters in the scalar couplings in the
gauge-field kinetic terms, and it is non-trivial because of the minimal
couplings of the fermion fields to the gauge potentials. We discuss the
supersymmetry transformation rules in the -deformed supergravities, and
present some examples of black hole solutions.Comment: 31 pages. Derivation of the range of \omega corrected; discussion of
supersymmetry of solutions extended, and a reference adde
AdS Dyonic Black Hole and its Thermodynamics
We obtain spherically-symmetric and -symmetric dyonic black holes that
are asymptotic to anti-de Sitter space-time (AdS), which are solutions in
maximal gauged four-dimensional supergravity, with just one of the U(1) fields
carrying both the electric and magnetic charges . We study the
thermodynamics, and find that the usually-expected first law does not hold
unless P=0, Q=0 or P=Q. For general values of the charges, we find that the
first law requires a modification with a new pair of thermodynamic conjugate
variables. We show that they describe the scalar hair that breaks some of the
asymptotic AdS symmetries.Comment: 21 pages, typos corrected, discussion of Euclidean action adde
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