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A calculation of the behavior of the conductance through resonant double barrier (n = 2 cells) and superlattice (n > 2 cells), for systems with uncoupled channels is presented. The numerical calculation was done using III and V semiconductors, such as GaAs and AlAs physical systems. Based on the Multicomponent Scattering Approach the two probe Landauer conductance and the phase time are calculated and interpreted. An oscillatory behavior of the conductance for a superlattice for uncoupled holes is observed, as we expected. This model provides evidences of the classical Hartman prediction for energies under the barrier height for uncoupled heavy and light holes, while a non linear dependence of the phase time with the barrier width, the Ramsauer -- Townsend oscillations, for energies above the barrier is observed. [ABSTRACT FROM AUTHOR]

Synthesis and conductivity characterization of the RE0.5Y0.5Ba2Cu3O7-δ (RE=Sm, Gd, Dy, Ho, Eu, Yb) superconducting materials are reported. Samples were produced by the standard solid state reaction method. The x-ray diffraction data permit to establish the crystalline appropriated distribution of rare earth and yttrium. DC resistivity measurements reveal the improvement of the critical temperature (Tc) when substitution of exact 50-50 mix of rare earth (Sm, Gd, Dy, Ho, Eu, Yb) and Yttrium is performed. The Tc was determined by the criterion of the maximum in the temperature derivative of electrical resistivity for the analyzed samples. [ABSTRACT FROM AUTHOR]