Showing papers by "Université de Sherbrooke published in 1968"

Electrical properties of glass microelectrodes

Abstract: The electrical characteristics of a glass microelectrode can be designated as a parallel resistance and capacitance in series with a source of dc voltage. Measurement of these parameters depends upon the following factors: concentration, ionic species, pH, and the hydrostatic pressures of the electrolyte solutions inside the microelectrode and surrounding its tip. The physicochemical mechanism underlying microelectrode resistance and tip potential is interpreted as interaction of the surface charges of the glass and the conductivity of the solution inside the microelectrode. Methods for recording microelectrode resistance and tip potential, a method for filling microelectrodes at room temperature, and the automatic recording of microelectrode and tip potential are descried.

Correlation and Magnetic Effects in Narrow Energy Bands. II

Abstract: Correlation and magnetic effects in narrow bands are studied using a generalized self-consistent cluster treatment of the narrow-band Hamiltonian. Here the dynamics consists of electron hopping between nearest-neighbor sites and Coulomb interaction between electrons on the same site and nearest-neighbor sites. In the simpler case, where the neighbor interactions are neglected, i.e., the Hubbard model, the environment of the cluster is regarded as a particle reservoir, one for each spin. Hopping between the cluster and reservoirs is described by fermion source terms. It is required that the thermodynamic average of the particle currents of each spin within the cluster equal the corresponding particle exchange between cluster and reservoir. Electron motion in the system is examined for varying ratios of the strength of the hopping to the intrasite Coulomb repulsion. A discontinuous transition from an antiferromagnetic insulator to a metal is found under dynamical conditions close to those predicted by Hubbard and Kemeny. The effect of the intersite Coulomb interaction on the transition is next studied. These added terms are seen greatly to influence the transition and the magnetic properties of the cluster.

A General Solution for the Shortest Acquisition Time in Type-II Phase-Lock Loops

Abstract: A general solution to the synthesis of an optimum control that minimizes the acquisition time in type-II phase-lock loops is presented. The result is applied to a loop with a sinusoidal phase detector and to a loop with a multilinear phase detector.