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991.
992.
A theoretical analysis is made of the relative intensity noise (RIN) in tunable two- and three-section distributed Bragg reflector (DBR) lasers by taking into account the actual frequency dependence of the Bragg reflector. The RIN is shown to depend significantly on the tuning current, especially at low frequencies and for low and moderate values of the grating coupling coefficient. For high values of this coefficient the dependence is insignificant when the tuning is performed through the DBR section, in accordance with the experimental results recently reported. The RIN spectrum is more significantly affected, however, when the phase control current in the three-section device is used for tuning. 相似文献
993.
Kenneth L Cooke JoséM Ferreira 《Journal of Mathematical Analysis and Applications》1983,96(2):480-504
The purpose of this note is to study the exponential stability for the linear retarded functional differential equation , where the delay function r(θ) ? 0 is continuous and η(θ) is of bounded variation on the interval [?1, 0]. It is shown that the spectral limit function for the equation above has a continuous dependence on the pair (η, r). The set of all functions of bounded variation η for which the equation above is exponentially stable for every delay function r, the so-called region of stability globally in the delays, is a cone. Therefore for a fixed r, the set of all η which make our equation exponentially stable, that is, the region of stability for the delay function r, contains a cone. A discussion of the characterization of these regions of stability, as well as of the largest cone contained in each region of stability for a fixed delay function r, is given. Some remarks are made with respect to a similar question for the equation , where A is a real n by n matrix, μ(θ) is bounded variation on [?1, 0] and r(θ) as before. Several examples illustrate the results obtained. 相似文献
994.
The density of states for electrons bound to Na+ impurities inside the inversion layer at the semiconductor-insulator interface of an MOS structure is calculated as a function of impurity concentration. The impurity potential is considered unscreened and the electrical quantum limit is assumed. A simple one-electron Hamiltonian is used and the disorder is treated through a cluster calculation. It is shown that the impurity band has a considerable bandwidth for impurity concentrations in a range of the experimental regime (this result agrees with the experimental findings of Hartstein and Fowler), and that the upper Hubbard band stands well above the lower band at very low concentration (in rough agreement with recent calculation done by Phelps and Bajaj on D? state). 相似文献
995.
C. E. Ferreira A. Martin C. C. de Souza R. Weismantel L. A. Wolsey 《Mathematical Programming》1996,74(3):247-266
We investigate the problem of partitioning the nodes of a graph under capacity restriction on the sum of the node weights
in each subset of the partition. The objective is to minimize the sum of the costs of the edges between the subsets of the
partition. This problem has a variety of applications, for instance in the design of electronic circuits and devices. We present
alternative integer programming formulations for this problem and discuss the links between these formulations. Having chosen
to work in the space of edges of the multicut, we investigate the convex hull of incidence vectors of feasible multicuts.
In particular, several classes of inequalities are introduced, and their strength and robustness are analyzed as various problem
parameters change. 相似文献
996.
A simple method to estimate the effects of the self- -consistency on the calculation of the electronic structure of molecule and crystals is proposed. This procedure is based on the charge transfer between the constituent atoms and is intended to avoid much computational effort. Numerical results are presented for GaAs. 相似文献
997.
Ferreira C.M. Alves L.L. Pinheiro M. Sa A.B. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1991,19(2):229-239
A kinetic study of low-pressure microwave discharges in Ar, He, and O2 is carried out using electron-transport parameters and rate coefficients derived from solutions to the Boltzmann equation, together with the continuity and transport equations for the charged particles, taking into account stepwise-ionization processes. The Boltzmann equation is solved over a wide range of the applied frequency, ω/2π, but assuming that the angular frequency ω>τ e-1, with τe, denoting the characteristic time for electron-energy relaxation by collisions. The formulation provides discharge characteristics for the maintenance field and for mean absorbed power per electron in the three gases, which are shown to agree satisfactorily with experimental data obtained from surface-wave discharges. It is shown that such an agreement would not always be obtained without consideration of the role played by stepwise-ionization processes in sustaining the discharge 相似文献
998.
Fernando Ferreira 《Archive for Mathematical Logic》1994,33(4):283-289
Summary We introduce a class of models of the bounded arithmetic theoryPV
n
. These models, which are generated by their tally part, have a curious feature: they have end-extensions or satisfyB
n
b
only in case they are closed under exponentiation. As an application, we show that if then the polynomial hierarchy does not collapse.This work was partially supported by project 6E92 of CMAF (Portugal) 相似文献
999.
Gastão A. Braga S. J. Ferreira F. C. Sá Barreto 《Journal of statistical physics》1994,76(3-4):819-834
We obtain rigorous upper bounds for the critical temperature associated with second-order phase transitions of the two-dimensional spin-1 BEG model for real values ofK andD coupling constants and forJ0. We use some correlation equalities and inequalities to show the exponential decay of the two-point function characterizing the disordered phase. 相似文献
1000.