arXiv subjects

Alexandre Rosas

Publications and source records attributed to Alexandre Rosas.

25 records · Page 2Linked to original sources

arXiv2003

Pulse Propagation in Chains with Nonlinear Interactions

Pulse propagation in nonlinear arrays continues to be of interest because it provides a possible mechanism for energy transfer with little dispersion. Here we show that common measures of pulse dispersion might be misleading; in strongly anharmonic systems they tend to reflect a succession of extremely narrow pulses traveling at decreasing velocities rather than the actual width of a single pulse. We present analytic estimates for the fraction of the initial energy that travels in the leading pulses. We also provide analytic predictions for the leading pulse velocity in a Fermi-Pasta-Ulam beta-chain.

cond-mat.soft↗

arXiv2003

Self-Similarity in Random Collision Processes

Kinetics of collision processes with linear mixing rules are investigated analytically. The velocity distribution becomes self-similar in the long time limit and the similarity functions have algebraic or stretched exponential tails. The characteristic exponents are roots of transcendental equations and vary continuously with the mixing parameters. In the presence of conservation laws, the velocity distributions become universal.

cond-mat.stat-mech↗

arXiv2003

Pulse Dynamics in a Chain of Granules With Friction

We study the dynamics of a pulse in a chain of granules with friction. We present theories for chains of cylindrical granules (Hertz potential with exponent $n=2$) and of granules with other geometries ($n>2$). Our results are supported via numerical simulations for cylindrical and for spherical granules ($n=5/2$).

cond-mat.stat-mech↗

arXiv2003

Dynamics of Two Granules

We study the dynamics of two particles that interact only when in contact. In this sense, although not in every particular, the interactions mimic those in granular materials. The detailed solution of the dynamics allows an analysis of the backscattering behavior of the first particle and of the energy dissipation in the system as a function of various parameters.

cond-mat.stat-mech↗

arXiv2002

Multifractal analysis of DNA walks and trails

The characterization of the long-range order and fractal properties of DNA sequences has proved a difficult though highly rewarding task due mainly to the mosaic character of DNA consisting of many interwoven patches of various lengths with different nucleotide constitutions. We apply here a recently proposed generalization of the detrended fluctuation analysis method to show that the DNA walk construction, in which the DNA sequence is viewed as a time series, exhibits a monofractal structure regardless of the existence of local trends in the series. In addition, we point out that the monofractal structure of the DNA walks carries over to an apparently alternative graphical construction given by the projection of the DNA walk into the $d$ spatial coordinates, termed DNA trails. In particular, we calculate the fractal dimension $D_t$ of the DNA trails using a well-known result of fractal theory linking $D_t$ to the Hurst exponent $H$ of the corresponding DNA walk. Comparison with estimates obtained by the standard box-counting method allows the evaluation of both finite-length and local trends effects.

cond-mat.stat-mech↗

arXiv2001

The Random Field Ising Model on Hierarchical Lattices I: Phase Diagram and Thermodynamics

The phase diagram and the thermodynamics of the random field Ising model (RFIM) defined on a family of diamond hierarchical lattices of arbitrary dimension and scaling factor $b=2$ is investigated. The phase diagram is studied considering the flow of the renormalized joint probability distributions of couplings and fields. A continuous (Gaussian) and a discrete (delta-bimodal) initial symmetric probability distributions for the random fields with variance $H_{0}$ are particularly considered. The thermodynamics properties (energy, specific heat and magnetization) are obtained by an exact recurrence procedure and analyzed as function of the temperature and the random field. Close and above the paramagnetic-ferromagnetic transition evidences of the formation of rare but large field induced correlated clusters of reversed spins are observed. For all studied properties no strong qualitative distinct behavior is found whenever the continuous or the discrete distribution of random fields are considered.

cond-mat.dis-nn↗

arXiv2001

The Random Field Ising Model on Hierarchical Lattices II: Ground State Critical Properties

The ground state critical properties of the Random Field Ising Model (RFIM) on the diamond hierarchical lattice are investigated via a combining method encompassing real space renormalization group and an exact recurrence procedure. The local magnetization and the nearest neighbors pair correlation function are exactly calculated. The fixed-point joint probability distribution of couplings and local fields are numerically obtained and analyzed, indicating that the critical behavior of the model is governed by the zero temperature disorder fixed point. The critical exponents associated with the order parameter and correlation length are estimated showing an universal behavior regarding the choice of the initial probability distribution for initial local fields being the symmetric continuous Gaussian or discrete delta-bimodal.

cond-mat.dis-nn↗