1,697 research outputs found
Semiclassical Green Function in Mixed Spaces
A explicit formula on semiclassical Green functions in mixed position and
momentum spaces is given, which is based on Maslov's multi-dimensional
semiclassical theory. The general formula includes both coordinate and momentum
representations of Green functions as two special cases of the form.Comment: 8 pages, typeset by Scientific Wor
Symmetry Decomposition of Chaotic Dynamics
Discrete symmetries of dynamical flows give rise to relations between
periodic orbits, reduce the dynamics to a fundamental domain, and lead to
factorizations of zeta functions. These factorizations in turn reduce the labor
and improve the convergence of cycle expansions for classical and quantum
spectra associated with the flow. In this paper the general formalism is
developed, with the -disk pinball model used as a concrete example and a
series of physically interesting cases worked out in detail.Comment: CYCLER Paper 93mar01
Some observations on the assessment of preventive technologies
The articles in this issue of the International Journal of Technology Assessment in Health Care (IJTAHC) have explored the assessment of preventive health technologies. When considered together, these technologies provide an interesting contrast with the health care technologies that are usually evaluated on these pages. Disease prevention and its twin, health promotion, are usually practiced on a well population. Thus, many persons have the technology applied to them but only a fraction of these would have acquired the condition being prevented. Often the intervention is applied to populations rather than to individuals. The unit cost for preventive technologies is usually far less than that of diagnostic or therapeutic technologies. However, when multiplied by the larger population to be involved in the prevention program, the total costs can be considerable. In concluding this section on prevention, we would like to examine some of the larger areas of difference between preventive and other health technologies illustrated by the papers assembled her
Spectral Statistics: From Disordered to Chaotic Systems
The relation between disordered and chaotic systems is investigated. It is
obtained by identifying the diffusion operator of the disordered systems with
the Perron-Frobenius operator in the general case. This association enables us
to extend results obtained in the diffusive regime to general chaotic systems.
In particular, the two--point level density correlator and the structure factor
for general chaotic systems are calculated and characterized. The behavior of
the structure factor around the Heisenberg time is quantitatively described in
terms of short periodic orbits.Comment: uuencoded file with 1 eps figure, 4 page
Ab-initio Gutzwiller method: first application to Plutonium
Except for small molecules, it is impossible to solve many electrons systems
without imposing severe approximations. If the configuration interaction
approaches (CI) or Coupled Clusters techniques \cite{FuldeBook} are applicable
for molecules, their generalization for solids is difficult. For materials with
a kinetic energy greater than the Coulomb interaction, calculations based on
the density functional theory (DFT), associated with the local density
approximation (LDA) \cite{Hohenberg64, Kohn65} give satisfying qualitative and
quantitative results to describe ground state properties. These solids have
weakly correlated electrons presenting extended states, like materials or
covalent solids. The application of this approximation to systems where the
wave functions are more localized ( or -states) as transition metals
oxides, heavy fermions, rare earths or actinides is more questionable and can
even lead to unphysical results : for example, insulating FeO and CoO are
predicted to be metalic by the DFT-LDA..
Berry phase in graphene: a semiclassical perspective
We derive a semiclassical expression for the Green's function in graphene, in
which the presence of a semiclassical phase is made apparent. The relationship
between this semiclassical phase and the adiabatic Berry phase, usually
referred to in this context, is discussed. These phases coincide for the
perfectly linear Dirac dispersion relation. They differ however when a gap is
opened at the Dirac point. We furthermore present several applications of our
semiclassical formalism. In particular we provide, for various configurations,
a semiclassical derivation of the electron's Landau levels, illustrating the
role of the semiclassical ``Berry-like'' phas
Semi-classical analysis of real atomic spectra beyond Gutzwiller's approximation
Real atomic systems, like the hydrogen atom in a magnetic field or the helium
atom, whose classical dynamics are chaotic, generally present both discrete and
continuous symmetries. In this letter, we explain how these properties must be
taken into account in order to obtain the proper (i.e. symmetry projected)
expansion of semiclassical expressions like the Gutzwiller trace
formula. In the case of the hydrogen atom in a magnetic field, we shed light on
the excellent agreement between present theory and exact quantum results.Comment: 4 pages, 1 figure, final versio
Periodic orbit quantization of a Hamiltonian map on the sphere
In a previous paper we introduced examples of Hamiltonian mappings with phase
space structures resembling circle packings. It was shown that a vast number of
periodic orbits can be found using special properties. We now use this
information to explore the semiclassical quantization of one of these maps.Comment: 23 pages, REVTEX
Increasing d-wave superconductivity by on site repulsion
We study by Variational Monte Carlo an extended Hubbard model away from half
filled band density which contains two competing nearest-neighbor interactions:
a superexchange favoring d-wave superconductivity and a repulsion
opposing against it. We find that the on-site repulsion effectively
enhances the strength of meanwhile suppressing that of , thus favoring
superconductivity. This result shows that attractions which do not involve
charge fluctuations are very well equipped against strong electron-electron
repulsion so much to get advantage from it.Comment: 4 pages, 3 figure
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