892 research outputs found
Quark mass density- and temperature- dependent model for strange quark matter
It is found that the radius of a stable strangelet decreases as the
temperature increases in a quark mass density-dependent model. To overcome this
difficulty, we extend this model to a quark mass density- and temperature-
dependent model in which the vacuum energy density at zero baryon density limit
B depends on temperature. An ansatz is introduced and the regions for the best
choice of the parameters are studied.Comment: 5 pages, 4 figure
Entropic Interactions in Suspensions of Semi-Flexible Rods: Short-Range Effects of Flexibility
We compute the entropic interactions between two colloidal spheres immersed
in a dilute suspension of semi-flexible rods. Our model treats the
semi-flexible rod as a bent rod at fixed angle, set by the rod contour and
persistence lengths. The entropic forces arising from this additional
rotational degree of freedom are captured quantitatively by the model, and
account for observations at short range in a recent experiment. Global fits to
the interaction potential data suggest the persistence length of fd-virus is
about two to three times smaller than the commonly used value of .Comment: 4 pages, 5 figures, submitted to PRE rapid communication
Shifts and widths of collective excitations in trapped Bose gases by the dielectric formalism
We present predictions for the temperature dependent shifts and damping
rates. They are obtained by applying the dielectric formalism to a simple model
of a trapped Bose gas. Within the framework of the model we use lowest order
perturbation theory to determine the first order correction to the results of
Hartree-Fock-Bogoliubov-Popov theory for the complex collective excitation
frequencies, and present numerical results for the temperature dependence of
the damping rates and the frequency shifts. Good agreement with the
experimental values measured at JILA are found for the m=2 mode, while we find
disagreements in the shifts for m=0. The latter point to the necessity of a
non-perturbative treatment for an explanation of the temperature-dependence of
the m=0 shifts.Comment: 10 pages revtex, 3 figures in postscrip
Dielectric formalism and damping of collective modes in trapped Bose-Einstein condensed gases
We present the general dielectric formalism for Bose-Einstein condensed
systems in external potential at finite temperatures. On the basis of a model
arising within this framework as a first approximation in an intermediate
temperature region for large condensate we calculate the damping of low-energy
excitations in the collisionless regime.Comment: 4 pages, no figures, RevTe
Quasinormal Modes in three-dimensional time-dependent Anti-de Sitter spacetime
The massless scalar wave propagation in the time-dependent BTZ black hole
background has been studied. It is shown that in the quasi-normal ringing both
the decay and oscillation time-scales are modified in the time-dependent
background.Comment: 8 pages and 7 figure
Properties of excitations in systems with a spinor Bose-Einstein condensate
General theory in case of homogenous Bose-Einstein condensed systems with
spinor condensate is presented for the correlation functions of density and
spin fluctuations and for the one-particle propagators as well. The random
phase approximation is investigated and the damping of the modes is given in
the intermediate temperature region. It is shown that the collective and the
one-particle excitation spectra do not coincide fully.Comment: 5 pages, 1 figur
Geometry of the extreme Kerr black holes
Geometrical properties of the extreme Kerr black holes in the topological
sectors of nonextreme and extreme configurations are studied. We find that the
Euler characteristic plays an essential role to distinguish these two kinds of
extreme black holes. The relationship between the geometrical properties and
the intrinsic thermodynamics are investigated.Comment: Latex version, 10 page
Dirac Cosmology and the Acceleration of the Contemporary Universe
A model is suggested to unify the Einstein GR and Dirac Cosmology. There is
one adjusted parameter in our model. After adjusting the parameter
in the model by using the supernova data, we have calculated the gravitational
constant and the physical quantities of , and by using the present day quantities as the initial conditions and
found that the equation of state parameter equals to -0.83, the
ratio of the density of the addition creation and the
ratio of the density of the matter including multiplication creation, radiation
and normal matter at present. The results are self-consistent
and in good agreement with present knowledge in cosmology. These results
suggest that the addition creation and multiplication creation in Dirac
cosmology play the role of the dark energy and dark matter.Comment: 13 pages, 8 figure
UK export performance research - review and implications
Previous research on export performance has been criticized for being a mosaic of autonomous endeavours and for a lack of theoretical development. Building upon extant models of export performance, and a review and analysis of research on export performance in the UK for the period 1990-2005, an integrated model of export performance is developed and theoretical explanations of export performance are put forward. It is suggested that a multi-theory approach to explaining export performance is viable. Management and policy implications for the UK emerging from the review and synthesis of the literature and the integrated model are discussed
Quasi-Quantum Groups, Knots, Three-Manifolds, and Topological Field Theory
We show how to construct, starting from a quasi-Hopf algebra, or
quasi-quantum group, invariants of knots and links. In some cases, these
invariants give rise to invariants of the three-manifolds obtained by surgery
along these links. This happens for a finite-dimensional quasi-quantum group,
whose definition involves a finite group , and a 3-cocycle \om, which was
first studied by Dijkgraaf, Pasquier and Roche. We treat this example in more
detail, and argue that in this case the invariants agree with the partition
function of the topological field theory of Dijkgraaf and Witten depending on
the same data G, \,\om.Comment: 30 page
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