Showing papers by "Jorge Eduardo Macías-Díaz published in 2010"

Activity pattern detection in electroneurographic and electromyogram signals through a heteroscedastic change-point method

Abstract: In this work, we propose a heteroscedastic method in the detection of activity patterns of electroneurographic and electromyogram signals involved in rhythmic activities of nerves and muscles, respectively. The electric behavior observed in such signals is characterized by phases of activity and silence. The beginning and the length of electrically active and electrically silent phases in a signal allow us to quantitatively analyze the changes and the effects on a rhythmic activity produced by experimental changes. In order to distinguish between these two phases, signals are assumed to be a sample of a time-dependent, normally distributed random variable with non-constant variance, and that the determination of the variance at each point allows us to determine in which phase is the signal. The parameters of the model are determined by means of an iterative process which maximizes the log-likelihood under the proposed model. Moreover, we apply our method to the determination of the activity phases and silence phases in sequences of experimental and synthetic electroneurographic and electromyogram signals. The results obtained with synthetic data show that the method performs well in the determination of these activity patterns. Finally, the study of particular signals simulated under a generalized autoregressive conditional heteroscedasticity model suggests the robustness of the method with respect to the assumption of independence.

Positivity-preserving methods for a linearised Fisher–KPP equation with consistency properties in the energy domain

Abstract: We present some non-standard, finite-difference schemes to approximate positive solutions of a modified Fisher–KPP equation that appears in the study of population dynamics. The methods are consistent order , and they provide non-negative approximations for any choice of non-negative initial profile. Associated with each technique, we present an energy scheme that consistently approximates the energy of the system. The methods are validated against known analytical solutions for an initial-boundary-value problem and an initial-value problem, and a Neumann stability analysis is carried out in detail; moreover, a comparison with respect to a standard, higher-order method reveals that our methods are more stable and more accurate when positivity restrictions are to be observed. The stability of our methods – even in the presence of discontinuities – is numerically revealed after examining the propagation of Heaviside fronts.

Two-inductor Boost Converter Start-up And Steady-state Operation

Abstract: In this work, an isolated DC/DC twoinductor boost converter is proposed. The topology is able to start up and operate in steady-state at any output level within 0V to 400V. The current and voltage characteristics make this topology suitable for applications where the relationship between input current and output voltage is too long, such as applications in hybrid electric vehicles (HEVs). In order for its operation to be possible at any output level, two auxiliary windings were added. These auxiliary windings were included to ensure that the startup current does not rise to a higher level, as opposed to other isolated boost converters where the start-up current level is high. The design of the converter and a detailed analysis are given; an experimental 200W prototype is presented to validate the converter operation and its design.

On the propagation of binary signals in a two-dimensional nonlinear lattice with nearest-neighbor interactions

Abstract: In this work, we use a computational technique with multiple properties of consistency in order to approximate solutions of a bounded β-Fermi–Pasta–Ulam lattice in two space dimensions subject to harmonic driving in two adjacent boundaries. The processes of nonlinear supratransmission and infratransmission are employed in order to propagate binary signals in the medium by means of a suitable modulation of the driving amplitude.

A generalization of Osgood's test and a comparison criterion for integral equations with noise

Abstract: In this work, we prove a generalization of Osgood's test for the explosion of the solutions of initial-value problems We also establish a comparison criterion for the solution of integral equations with noise, and provide estimations of the time of explosion of problems arising in the investigation of crack failures where the noise is the absolute value of the Brownian motion

An Alternative Proof of Hill's Criterion of Freeness for Abelian Groups

Abstract: In this note we provide a different proof of Hill's criteria of freeness for abelian groups. Our proof hinges on the construction of suitable G(@0)- families of subgroups of the links in Hill's theorem and, ultimately, on the construction of such a family of pure subgroups of the group itself.