1,274 research outputs found
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
On the possible observational manifestation of supernova shock impact on the neutron star magnetosphere
Impact of supernova explosion on the neutron star magnetosphere in a massive
binary system is considered. The supernova shock striking the NS magnetosphere
filled with plasma can lead to the formation of a magnetospheric tail with
significant magnetic energy. The magnetic field reconnection in the current
sheet formed can convert the magnetic energy stored in the tail into kinetic
energy of accelerated charged particles. Plasma instabilities excited by beams
of relativistic particles can lead to the formation of a short pulse of
coherent radio emission with parameters similar to those of the observed bright
extragalactic millisecond radio burst (Lorimer et al. 2007).Comment: 8 pages, Astron. Lett. in pres
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
Fine structure of perturbed Laguerre-Gaussian beams: Hermite-Gaussian mode spectra and topological charge
We found that small perturbations of the optical vortex core in the
Laguerre-Gaussian (LG) beams generate a fine structure of the Hermite-Gauss
(HG) mode spectrum. Such perturbations can be easily simulated by weak
variations of amplitudes and phases of the HG modes in the expansion of the LG
beam field. We also theoretically substantiated and experimentally implemented
a method for measuring the topological charge of LG beams with an arbitrary
number of ring dislocations. Theoretical discussion and experimental studies
were accompanied by simple examples of estimating the orbital angular momentum
and the topological charge of perturbed LG beams.Comment: 16 pages, 7 figure
Bounds on positive interior transmission eigenvalues
The paper contains lower bounds on the counting function of the positive
eigenvalues of the interior transmission problem when the latter is elliptic.
In particular, these bounds justify the existence of an infinite set of
interior transmission eigenvalues and provide asymptotic estimates from above
on the counting function for the large values of the wave number. They also
lead to certain important upper estimates on the first few interior
transmission eigenvalues. We consider the classical transmission problem as
well as the case when the inhomogeneous medium contains an obstacle.Comment: We corrected inaccuracies cost by the wrong sign in the Green formula
(17). In particular, the sign in the definition of \sigma was change
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