28,361 research outputs found
Maximal-entropy random walks in complex networks with limited information
J.G.-G. was supported by MICINN through the Ramon y Cajal program and by grants FIS2008-01240 and MTM2009-13848
Soliton attenuation and emergent hydrodynamics in fragile matter
Disordered packings of soft grains are fragile mechanical systems that loose
rigidity upon lowering the external pressure towards zero. At zero pressure, we
find that any infinitesimal strain-impulse propagates initially as a non-linear
solitary wave progressively attenuated by disorder. We demonstrate that the
particle fluctuations generated by the solitary-wave decay, can be viewed as a
granular analogue of temperature. Their presence is manifested by two emergent
macroscopic properties absent in the unperturbed granular packing: a finite
pressure that scales with the injected energy (akin to a granular temperature)
and an anomalous viscosity that arises even when the microscopic mechanisms of
energy dissipation are negligible. Consistent with the interpretation of this
state as a fluid-like thermalized state, the shear modulus remains zero.
Further, we follow in detail the attenuation of the initial solitary wave
identifying two distinct regimes : an initial exponential decay, followed by a
longer power law decay and suggest simple models to explain these two regimes.Comment: 8 pages, 3 Figure
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
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
Finite sampling effects on generalized fluctuation-dissipation relations for steady states
We study the effects of the finite number of experimental data on the
computation of a generalized fluctuation-dissipation relation around a
nonequilibrium steady state of a Brownian particle in a toroidal optical trap.
We show that the finite sampling has two different effects, which can give rise
to a poor estimate of the linear response function. The first concerns the
accessibility of the generalized fluctuation-dissipation relation due to the
finite number of actual perturbations imposed to the control parameter. The
second concerns the propagation of the error made at the initial sampling of
the external perturbation of the system. This can be highly enhanced by
introducing an estimator which corrects the error of the initial sampled
condition. When these two effects are taken into account in the data analysis,
the generalized fluctuation-dissipation relation is verified experimentally
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.
Computing the -coverage of a wireless network
Coverage is one of the main quality of service of a wirelessnetwork.
-coverage, that is to be covered simultaneously by network nodes, is
synonym of reliability and numerous applicationssuch as multiple site MIMO
features, or handovers. We introduce here anew algorithm for computing the
-coverage of a wirelessnetwork. Our method is based on the observation that
-coverage canbe interpreted as layers of -coverage, or simply
coverage. Weuse simplicial homology to compute the network's topology and
areduction algorithm to indentify the layers of -coverage. Weprovide figures
and simulation results to illustrate our algorithm.Comment: Valuetools 2019, Mar 2019, Palma de Mallorca, Spain. 2019. arXiv
admin note: text overlap with arXiv:1802.0844
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