Envelope transient simulation of nonlinear electronic circuits using multi-rate Runge-Kutta algorithms

Time-step integration is a popular technique commonly used for the envelope transient simulation of an electronic circuit. However, many kinds of circuits are characterized by widely separated time scales, which lead to significant computational costs when numerically solving its differential systems. Even so, this situation can be exploited in an efficient way using multi-rate methods, which integrate system components with different step sizes. In this paper two multi-rate Runge-Kutta schemes are studied and tested in terms of computational speed and numerical stability. The results for linear stability analysis here obtained are much more coherent with the characteristics of the methods than the ones previously presented in [6]

Magnetic-field effects in defect-controlled ferromagnetic Ga_{1-x}Mn_xAs semiconductors

We have studied the magnetic-field and concentration dependences of the magnetizations of the hole and Mn subsystems in diluted ferromagnetic semiconductor Ga_{1-x}Mn_xAs. A mean-field approximation to the hole-mediated interaction is used, in which the hole concentration p(x) is parametrized in terms of a fitting (of the hole effective mass and hole/local moment coupling) to experimental data on the Tc critical temperature. The dependence of the magnetizations with x, for a given temperature, presents a sharply peaked structure, with maxima increasing with applied magnetic field, which indicates that application to diluted-magnetic-semiconductor devices would require quality-control of the Mn-doping composition. We also compare various experimental data for Tc(x) and p(x) on different Ga_{1-x}Mn_xAs samples and stress the need of further detailed experimental work to assure that the experimental measurements are reproducible.Comment: RevTeX 4, 3 two-column pages, 4 colour figures; to appear in J Appl Phy

Biologia de Allograpta exotica (Wiedemann), Taxomerus lacrymosus (Bigot) (Diptera: Syrphidae) e de Nephaspis hydra Gordon (Coleoptera: Coccinellidae), predadores de ovos e ninfas da mosca-branca, Bemisia tabaci (Gennadius) biótipo B (Hemiptera: Aleyrodidae).

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Variação fenotípica em acessos de açaizeiro (Euterpe oleracea Mart.) para caracteres relacionados à produção de frutos.

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