5,853 research outputs found
Application of the coherent state formalism to multiply excited states
A general expression is obtained for the matrix element of an m-body operator
between coherent states constructed from multiple orthogonal coherent boson
species. This allows the coherent state formalism to be applied to states
possessing an arbitrarily large number of intrinsic excitation quanta. For
illustration, the formalism is applied to the two-dimensional vibron model
[U(3) model], to calculate the energies of all excited states in the large-N
limit.Comment: LaTeX (iopart); 10 pages; to be published in J. Phys.
Scalar Field Dark Matter: non-spherical collapse and late time behavior
We show the evolution of non-spherically symmetric balls of a
self-gravitating scalar field in the Newtonian regime or equivalently an ideal
self-gravitating condensed Bose gas. In order to do so, we use a finite
differencing approximation of the Shcr\"odinger-Poisson (SP) system of
equations with axial symmetry in cylindrical coordinates. Our results indicate:
1) that spherically symmetric ground state equilibrium configurations are
stable against non-spherical perturbations and 2) that such configurations of
the SP system are late-time attractors for non-spherically symmetric initial
profiles of the scalar field, which is a generalization of such behavior for
spherically symmetric initial profiles. Our system and the boundary conditions
used, work as a model of scalar field dark matter collapse after the turnaround
point. In such case, we have found that the scalar field overdensities tolerate
non-spherical contributions to the profile of the initial fluctuation.Comment: 8 revtex pages, 10 eps figures. Accepted for publication in PR
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Modelling the inorganic nitrogen behaviour in a small Mediterranean forested catchment, Fuirosos (Catalonia)
The aim of this work was to couple a nitrogen (N) sub-model to already existent hydrological lumped (LU4-N) and semi-distributed (LU4-R-N and SD4-R-N) conceptual models, to improve our understanding of the factors and processes controlling nitrogen cycling and losses in Mediterranean catchments. The N model adopted provides a simplified conceptualization of the soil nitrogen cycle considering mineralization, nitrification, immobilization, denitrification, plant uptake, and ammonium adsorption/desorption. It also includes nitrification and denitrification in the shallow perched aquifer. We included a soil moisture threshold for all the considered soil biological processes. The results suggested that all the nitrogen processes were highly influenced by the rain episodes and that soil microbial processes occurred in pulses stimulated by soil moisture increasing after rain. Our simulation highlighted the riparian zone as a possible source of nitrate, especially after the summer drought period, but it can also act as an important sink of nitrate due to denitrification, in particular during the wettest period of the year. The riparian zone was a key element to simulate the catchment nitrate behaviour. The lumped LU4-N model (which does not include the riparian zone) could not be validated, while both the semi-distributed LU4-R-N and SD4-R-N model (which include the riparian zone) gave satisfactory results for the calibration process and acceptable results for the temporal validation process
Phase II of the ASCE Benchmark Study on SHM
The task group on structural health monitoring of the Dynamic Committee of ASCE was formed in
1999 at the 12
th
Engineering Mechanics Conference. The task group has designed a number of analytical
studies on a benchmark structure and there are plans to follow these with an experimental program. The
first phase of the analytical studies was completed in 2001. The second phase, initiated in the summer of
2001, was formulated in the light of the experience gained on phase I and focuses on increasing realism in
the simulation of the discrepancies between the actual structure and the mathematical model used in the
analysis. This paper describes the rational that lead the SHM task group to the definition of phase II and
presents the details of the cases that are being considered
A symmetry adapted approach to vibrational excitations in atomic clusters
An algebraic method especially suited to describe strongly anharmonic
vibrational spectra in molecules may be an appropriate framework to study
vibrational spectra of Na clusters, where nearly flat potential energy
surfaces and the appearance of close lying isomers have been reported. As an
illustration we describe the model and apply it to the Be, H, Be
and Na clusters.Comment: 8 pages with 2 tables, invited talk at `Atomic Nuclei & Metallic
Clusters: Finite Many-Fermion Systems', Prague, Czech Republic, September
1-5, 199
Comment on ``Boson-realization model for the vibrational spectra of tetrahedral molecules''
An algebraic model in terms of a local harmonic boson realization was
recently proposed to study molecular vibrational spectra [Zhong-Qi Ma et al.,
Phys. Rev. A 53, 2173 (1996)]. Because of the local nature of the bosons the
model has to deal with spurious degrees of freedom. An approach to eliminate
the latter from both the Hamiltonian and the basis was suggested. We show that
this procedure does not remove all spurious components from the Hamiltonian and
leads to a restricted set of interactions. We then propose a scheme in which
the physical Hamiltonian can be systematically constructed up to any order
without the need of imposing conditions on its matrix elements. In addition, we
show that this scheme corresponds to the harmonic limit of a symmetry adapted
algebraic approach based on U(2) algebras.Comment: 9 pages Revtex, submitted February 199
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