Biomedical subjects

Roberto Artuso

Publications and source records attributed to Roberto Artuso.

6 recordsLinked to original sources

PubMed2005

Delocalized and resonant quantum transport in nonlinear generalizations of the kicked rotor model.

We analyze the effects of a nonlinear cubic perturbation on the delta-kicked rotor. We consider two different models, in which the nonlinear term acts either in the position or in the momentum representation. We numerically investigate the modifications induced by the nonlinearity in the quantum transport in both localized and resonant regimes and a comparison between the results for the two models is presented. Analyzing the momentum distributions and the increase of the mean square momentum, we find that the quantum resonances asymptotically are very stable with respect to nonlinear perturbation of the rotor's phase evolution. For an intermittent time regime, the nonlinearity even enhances the resonant quantum transport, leading to superballistic motion.

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PubMed2005

Anomalous deterministic transport.

We present a series of results on deterministic transport in chaotic system, obtained in the framework of periodic orbits theory. The emphasis is on intermittent systems, where deviations from complete chaos may induce anomalies on the asymptotic moments' growth.

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PubMed2003

Effects of a nonlinear perturbation on dynamical tunneling in cold atoms.

We perform a numerical analysis of the effects of a nonlinear perturbation on the quantum dynamics of two models describing noninteracting cold atoms in a standing wave of light with a periodical modulated amplitude A(t). One model is the driven pendulum, recently considered by D.A. Steck, W.H. Oskay, and M.G. Raizen [Science 293, 274 (2001)], and the other is a variant of the well-known kicked rotator model. In absence of the nonlinear perturbation, the system is invariant under some discrete symmetries and quantum dynamical tunneling between symmetric classical islands is found. The presence of nonlinearity destroys tunneling, breaking the symmetries of the system. Finally, further consequences of nonlinearity in the kicked rotator case are considered.

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PubMed2003

Anomalous transport: a deterministic approach.

We introduce a cycle-expansion (fully deterministic) technique to compute the asymptotic behavior of arbitrary order transport moments. The theory is applied to different kinds of one-dimensional intermittent maps and Lorentz gas with an infinite horizon, confirming the typical appearance of phase transitions in the transport spectrum.

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PubMed2002

Nonlinearity effects in the kicked oscillator.

The quantum kicked oscillator is known to display a remarkable richness of dynamical behavior, from ballistic spreading to dynamical localization. Here we investigate the effects of a Gross-Pitaevskii nonlinearity on quantum motion, and provide evidence that the qualitative features depend strongly on the parameters of the system.

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PubMed2000

Spectral properties and anomalous transport in a polygonal billiard.

We analyze a class of polygonal billiards, whose behavior is conjectured to exhibit a variety of interesting dynamical features. Correlation functions are numerically investigated, and in a subclass of billiard tables they give indications about a singular continuous spectral measure. By lifting billiard dynamics we are also able to study transport properties: the (normal or anomalous) diffusive behavior is theoretically connected to a scaling index of the spectral measure; the proposed identity is shown to agree with numerical simulations. (c) 2000 American Institute of Physics.

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