2,323 research outputs found
Exactly-solvable models of proton and neutron interacting bosons
We describe a class of exactly-solvable models of interacting bosons based on
the algebra SO(3,2). Each copy of the algebra represents a system of neutron
and proton bosons in a given bosonic level interacting via a pairing
interaction. The model that includes s and d bosons is a specific realization
of the IBM2, restricted to the transition regime between vibrational and
gamma-soft nuclei. By including additional copies of the algebra, we can
generate proton-neutron boson models involving other boson degrees of freedom,
while still maintaining exact solvability. In each of these models, we can
study not only the states of maximal symmetry, but also those of mixed
symmetry, albeit still in the vibrational to gamma-soft transition regime.
Furthermore, in each of these models we can study some features of F-spin
symmetry breaking. We report systematic calculations as a function of the
pairing strength for models based on s, d, and g bosons and on s, d, and f
bosons. The formalism of exactly-solvable models based on the SO(3,2) algebra
is not limited to systems of proton and neutron bosons, however, but can also
be applied to other scenarios that involve two species of interacting bosons.Comment: 8 pages, 3 figures. Submitted to Phys.Rev.
Quantum multifractality as a probe of phase space in the Dicke model
We study the multifractal behavior of coherent states projected in the energy
eigenbasis of the spin-boson Dicke Hamiltonian, a paradigmatic model describing
the collective interaction between a single bosonic mode and a set of two-level
systems. By examining the linear approximation and parabolic correction to the
mass exponents, we find ergodic and multifractal coherent states and show that
they reflect details of the structure of the classical phase space, including
chaos, regularity, and features of localization. The analysis of
multifractality stands as a sensitive tool to detect changes and structures in
phase space, complementary to classical tools to investigate it. We also
address the difficulties involved in the multifractal analyses of systems with
unbounded Hilbert spacesComment: 14 pages, 7 figure
Spiral Defect Chaos in Large Aspect Ratio Rayleigh-Benard Convection
We report experiments on convection patterns in a cylindrical cell with a
large aspect ratio. The fluid had a Prandtl number of approximately 1. We
observed a chaotic pattern consisting of many rotating spirals and other
defects in the parameter range where theory predicts that steady straight rolls
should be stable. The correlation length of the pattern decreased rapidly with
increasing control parameter so that the size of a correlated area became much
smaller than the area of the cell. This suggests that the chaotic behavior is
intrinsic to large aspect ratio geometries.Comment: Preprint of experimental paper submitted to Phys. Rev. Lett. May 12
1993. Text is preceeded by many TeX macros. Figures 1 and 2 are rather lon
Square patterns in Rayleigh-Benard convection with rotation about a vertical axis
We present experimental results for Rayleigh-Benard convection with rotation
about a vertical axis at dimensionless rotation rates in the range 0 to 250 and
upto 20% above the onset. Critical Rayleigh numbers and wavenumbers agree with
predictions of linear stability analysis. For rotation rates greater than 70
and close to onset, the patterns are cellular with local four-fold coordination
and differ from the theoretically expected Kuppers-Lortz unstable state. Stable
as well as intermittent defect-free square lattices exist over certain
parameter ranges. Over other ranges defects dynamically disrupt the lattice but
cellular flow and local four-fold coordination is maintained.Comment: ReVTeX, 4 pages, 7 eps figures include
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