6,734 research outputs found
Different Facets of Chaos in Quantum Mechanics
Nowadays there is no universally accepted definition of quantum chaos. In
this paper we review and critically discuss different approaches to the
subject, such as Quantum Chaology and the Random Matrix Theory. Then we analyze
the problem of dynamical chaos and the time scales associated with chaos
suppression in quantum mechanics. Summary: 1. Introduction 2. Quantum Chaology
and Spectral Statistics 3. From Poisson to GOE Transition: Comparison with
Experimental Data 3.1 Atomic Nuclei 3.2 The Hydrogen Atom in the Strong
Magnetic Field 4. Quantum Chaos and Field Theory 5. Alternative Approaches to
Quantum Chaos 6. Dynamical Quantum Chaos and Time Scales 6.1 Mean-Field
Approximation and Dynamical Chaos 7. ConclusionsComment: RevTex, 25 pages, 7 postscript figures, to be published in Int. J.
Mod. Phys.
A multistream model for quantum plasmas
The dynamics of a quantum plasma can be described self-consistently by the
nonlinear Schroedinger-Poisson system. Here, we consider a multistream model
representing a statistical mixture of N pure states, each described by a
wavefunction. The one-stream and two-stream cases are investigated. We derive
the dispersion relation for the two-stream instability and show that a new,
purely quantum, branch appears. Numerical simulations of the complete
Schroedinger-Poisson system confirm the linear analysis, and provide further
results in the strongly nonlinear regime. The stationary states of the
Schroedinger-Poisson system are also investigated. These can be viewed as the
quantum mechanical counterpart of the classical Bernstein-Greene-Kruskal modes,
and are described by a set of coupled nonlinear differential equations for the
electrostatic potential and the stream amplitudes.Comment: 20 pages, 10 figure
A Note on the Toda Criterion for Interacting Dipole-Quadrupole Vibrations
The Toda criterion of the Gaussian curvature is applied to calculate
analytically the transition energy from regular to chaotic motion in a
schematic model describing the interaction between collective dipole and
quadrupole modes in atomic nuclei.Comment: Latex, 9 pages, 2 figures (available upon request), to be published
in Modern Physics Letters
Energy Level Quasi-Crossings: Accidental Degeneracies or Signature of Quantum Chaos?
In the field of quantum chaos, the study of energy levels plays an important
role. The aim of this review paper is to critically discuss some of the main
contributions regarding the connection between classical dynamics,
semi-classical quantization and spectral statistics of energy levels. In
particular, we analyze in detail degeneracies and quasi-crossings in the
eigenvalues of quantum Hamiltonians which are classically non-integrable.
Summary: 1. Introduction; 2. Quasi-Crossing and Chaos; 3. Molecular
Spectroscopy; 4. Nuclear Models; 4.1 Zirnbauer-Verbaashot-Weidenmuller Model;
4.2 Lipkin-Meshow-Glick Model; 5. Particle Physics and Field Theory; 6.
Conclusions.Comment: 26 pages, Latex, 9 figures, to be published in International Journal
of Modern Physics
Load distribution in small world networks
In this paper we introduce a new model of data packet transport, based on a
stochastic approach with the aim of characterizing the load distribution on
complex networks. Moreover we analyze the load standard deviation as an index
of uniformity of the distribution of packets within the network, to
characterize the effects of the network topology. We measure such index on the
model proposed by Watts and Strogatz as the redirection probability is
increased. We find that the uniformity of the load spread is maximized in the
intermediate region, at which the small world effect is observed and both
global and local efficiency are high. Moreover we analyze the relationship
between load centrality and degree centrality as an approximate measure of the
load at the edges. Analogous results are obtained for the load variance
computed at the edges as well as at the vertices.Comment: 6 pages, 5 figures. Included in conference proceedings International
Conference PhysCon 2005 August 24-26, 2005, Saint Petersburg, RUSSI
Spectral Statistics in Large Shell Model Calculations
The spectral statistics of low--lying states of shell nuclei are studied
by performing large shell--model calculations with a realistic nuclear
interaction. For isotopes, we find deviations from the predictions of the
random--matrix theory which suggest that some spherical nuclei are not as
chaotic in nature as the conventional view assumes.Comment: 9 pages, LaTex, 3 figures available upon request, to appear in
Proceedings of the V International Spring Seminar on Nuclear Physics, Ed. by
A. Covello (World Scientific
Large Shell Model Calculations for Calcium Isotopes: Spectral Statistics and Chaos
We perform large shell model calculations for Calcium isotopes in the full fp
shell by using the realistic Kuo-Brown interaction. The Calcium isotopes are
especially interesting because the nearest-neighbour spacing distribution P(s)
of low-lying energy levels shows significant deviations from the predictions of
the Gaussian Orthogonal Ensemble of random--matrix theory. This contrasts with
other neighbouring nuclei which show fully chaotic spectral distributions. We
study the chaotic behaviour as a function of the excitation energy. In
addition, a clear signature of chaos suppression is obtained when the
single-particle spacings are increased. In our opinion the relatively weak
strength of the neutron-neutron interaction is unable to destroy the regular
single-particle mean-field motion completely. In the neighbouring nuclei with
both protons and neutrons in valence orbits, on the other hand, the stronger
proton-neutron interaction would appear to be sufficient to destroy the regular
mean-field motion.Comment: Latex, 7 pages, 2 postscript figures, to be published in the
Proceedings 'Highlights of Modern Nuclear Structure', S. Agata sui due Golfi
(italy), Ed. A. Covello (World Scientific
Development and application of analytical and statistical techniques for the non-invasive monitoring and analysis of cultural heritage
Characteristics of Candida isolates from patients with diabetes mellitus.
The present research has investigated the molecular characterization of oral yeasts in healthy individuals from different dental clinical settings in the United Kingdom, and patients from the UK and Italy who were affected by diabetes mellitus (DM) to determine the impact of DM upon candidal infection of the mouth. In the present study of patients with DM from the UK and Italy a lower than expected incidence of oral candidal infections (7/249, 2.8%) was observed. The presence of oral yeasts and genotypic diversity of C. albicans was also not influenced by DM. There was no significant difference between the presence of oral yeasts in Italian and UK DM patients. However, more (p=0.04) C. dubliniensis isolates were found in non-DM individuals. Higher levels of Candida adhesion to fibronectin-coated paramagnetic beads were observed in isolates from DM patients. Isolates from patients with low oral yeast loads adhered significantly (p=0.0T) more than those from patients with high oral yeast loads. In general, there was no difference in proteolytic activity of isolates from DM or control patients. Candida isolates from UK DM patients had significantly greater in vitro resistance to azole antifungal agents (miconazole p<0.0001 fluconazole p=0.02 ketoconazole p=0.01) than those from Italian DM patients. In addition, C. albicans isolates from all examined patients were more susceptible to fluconazole (p=0.0008) and miconazole (p=0.01) than non-C. albicans strains. PCR fingerprinting and subsequent phylogenetic analysis revealed that C. albicans isolates from UK DM patients were the most diverse (p<0.0001) in comparison to those from Italian DM patients or from healthy subjects. Finally, it was observed that the activity of a rat IgM monoclonal anti-idiotypic antibody (mAbKlO) and a synthetic decapeptide (KP) had a significant dose- dependant fungicidal activity upon a wide spectrum of C. albicans and non-C albicans isolates from patients with and without DM
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