1,652 research outputs found
Spectre negatif d'un operateur elliptique avec des conditions au bords de Robin
In this article we discuss some estimates of the number of the negative eigenvalues and their moments of energy for an elliptic operator L = L0 - V(x) defined in Hm(Rn+) with the Robin boundary conditions containing a potential W(x), in terms of some integrals of V and W
Boundary values as Hamiltonian variables. I. New Poisson brackets
The ordinary Poisson brackets in field theory do not fulfil the Jacobi
identity if boundary values are not reasonably fixed by special boundary
conditions. We show that these brackets can be modified by adding some surface
terms to lift this restriction. The new brackets generalize a canonical bracket
considered by Lewis, Marsden, Montgomery and Ratiu for the free boundary
problem in hydrodynamics. Our definition of Poisson brackets permits to treat
boundary values of a field on equal footing with its internal values and
directly estimate the brackets between both surface and volume integrals. This
construction is applied to any local form of Poisson brackets. A prescription
for delta-function on closed domains and a definition of the {\it full}
variational derivative are proposed.Comment: 26 pages, LaTex, IHEP 93-4
Spin-dependent electron dynamics and recombination in GaAs(1-x)N(x) alloys at room temperature
We report on both experimental and theoretical study of conduction-electron
spin polarization dynamics achieved by pulsed optical pumping at room
temperature in GaAs(1-x)N(x) alloys with a small nitrogen content (x = 2.1,
2.7, 3.4%). It is found that the photoluminescence circular polarization
determined by the mean spin of free electrons reaches 40-45% and this giant
value persists within 2 ns. Simultaneously, the total free-electron spin decays
rapidly with the characteristic time ~150 ps. The results are explained by
spin-dependent capture of free conduction electrons on deep paramagnetic
centers resulting in dynamical polarization of bound electrons. We have
developed a nonlinear theory of spin dynamics in the coupled system of
spin-polarized free and localized carriers which describes the experimental
dependencies, in particular, electron spin quantum beats observed in a
transverse magnetic field.Comment: 5 pages, 4 figures, Submitted to JETP Letter
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