35,566 research outputs found
Modified Renormalization Strategy for Sandpile Models
Following the Renormalization Group scheme recently developed by Pietronero
{\it et al}, we introduce a simplifying strategy for the renormalization of the
relaxation dynamics of sandpile models. In our scheme, five sub-cells at a
generic scale form the renormalized cell at the next larger scale. Now the
fixed point has a unique nonzero dynamical component that allows for a great
simplification in the computation of the critical exponent . The values
obtained are in good agreement with both numerical and theoretical results
previously reported.Comment: APS style, 9 pages and 3 figures. To be published in Phys. Rev.
Perturbative evolution of far off-resonance driven two-level systems: Coherent population trapping, localization, and harmonic generation
The time evolution of driven two-level systems in the far off-resonance
regime is studied analytically. We obtain a general first-order perturbative
expression for the time-dependent density operator which is applicable
regardless of the coupling strength value. In the strong field regime, our
perturbative expansion remains valid even when the far off-resonance condition
is not fulfilled. We find that, in the absence of dissipation, driven two-level
systems exhibit coherent population trapping in a certain region of parameter
space, a property which, in the particular case of a symmetric double-well
potential, implies the well-known localization of the system in one of the two
wells. Finally, we show how the high-order harmonic generation that this kind
of systems display can be obtained as a straightforward application of our
formulation.Comment: 14 pages, LaTeX, 2 figures, acknowledgments adde
Neutrinoless double-beta decay. A brief review
In this brief review we discuss the generation of Majorana neutrino masses
through the see-saw mechanism, the theory of neutrinoless double-beta decay,
the implications of neutrino oscillation data for the effective Majorana mass,
taking into account the recent Daya Bay measurement of theta_13, and the
interpretation of the results of neutrinoless double-beta decay experiments.Comment: 22 page
Recursive partitioned inversion of large (1500 x 1500) symmetric matrices
A recursive algorithm was designed to invert large, dense, symmetric, positive definite matrices using small amounts of computer core, i.e., a small fraction of the core needed to store the complete matrix. The described algorithm is a generalized Gaussian elimination technique. Other algorithms are also discussed for the Cholesky decomposition and step inversion techniques. The purpose of the inversion algorithm is to solve large linear systems of normal equations generated by working geodetic problems. The algorithm was incorporated into a computer program called SOLVE. In the past the SOLVE program has been used in obtaining solutions published as the Goddard earth models
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