1,635 research outputs found
Wigner-Poisson and nonlocal drift-diffusion model equations for semiconductor superlattices
A Wigner-Poisson kinetic equation describing charge transport in doped
semiconductor superlattices is proposed. Electrons are supposed to occupy the
lowest miniband, exchange of lateral momentum is ignored and the
electron-electron interaction is treated in the Hartree approximation. There
are elastic collisions with impurities and inelastic collisions with phonons,
imperfections, etc. The latter are described by a modified BGK
(Bhatnagar-Gross-Krook) collision model that allows for energy dissipation
while yielding charge continuity. In the hyperbolic limit, nonlocal
drift-diffusion equations are derived systematically from the kinetic
Wigner-Poisson-BGK system by means of the Chapman-Enskog method. The
nonlocality of the original quantum kinetic model equations implies that the
derived drift-diffusion equations contain spatial averages over one or more
superlattice periods. Numerical solutions of the latter equations show
self-sustained oscillations of the current through a voltage biased
superlattice, in agreement with known experiments.Comment: 20 pages, 1 figure, published as M3AS 15, 1253 (2005) with
correction
Multiquantum well spin oscillator
A dc voltage biased II-VI semiconductor multiquantum well structure attached
to normal contacts exhibits self-sustained spin-polarized current oscillations
if one or more of its wells are doped with Mn. Without magnetic impurities, the
only configurations appearing in these structures are stationary. Analysis and
numerical solution of a nonlinear spin transport model yield the minimal number
of wells (four) and the ranges of doping density and spin splitting needed to
find oscillations.Comment: 11 pages, 2 figures, shortened and updated versio
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Javier ANDONEGUI GURRUCHAGA, Teología como ciencia práctica en Escoto: Acerca de la posición mediadora escotista en la problemática Filosofía-Teología del s. XIII, Pontificium Athenaeum Antonianum («Theses ad lauream», 75), Roma 1985, 96 pp., 16,5 x 23,5. [RECENSIÓN]
Bartolomé LOBO GUERRERO y Fernando ARIAS DE UGARTE, Sínodos de Lima de 1613 y 1636, estudio introductorio de José María SOTO RÁBANOS, Centro de Estudios Históricos del CSIC e Instituto de Historia de la Teología Española de la Universidad Pontificia («Tierra nueva e cielo nuevo», 11; «Sínodos americanos», 6), Madrid-Salamanca 1987, CIII + 457 pp., 17 x 24,5. [RECENSIÓN]
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