21,408 research outputs found
Allowed charge transfers between coherent conductors driven by a time-dependent scatterer
We derive constraints on the statistics of the charge transfer between two
conductors in the model of arbitrary time-dependent instant scattering of
non-interacting fermions at zero temperature. The constraints are formulated in
terms of analytic properties of the generating function: its zeroes must lie on
the negative real axis. This result generalizes existing studies for scattering
by a time-independent scatterer under time-dependent bias voltage.Comment: 5 pages, no figures, corrected misprints and minor changes in version
Factorization of quantum charge transport for non-interacting fermions
We show that the statistics of the charge transfer of non-interacting
fermions through a two-lead contact is generalized binomial, at any temperature
and for any form of the scattering matrix: an arbitrary charge-transfer process
can be decomposed into independent single-particle events. This result
generalizes previous studies of adiabatic pumping at zero temperature and of
transport induced by bias voltage.Comment: 13 pages, 3 figures, typos corrected, references adde
Resonant acousto-optics in the terahertz range: TO-phonon polaritons driven by an ultrasonic wave
The resonant acousto-optic effect is studied both analytically and
numerically in the terahertz range where the transverse-optical (TO) phonons
play the role of a mediator which strongly couples the ultrasound and light
fields. A propagating acoustic wave interacts with the TO phonons via
anharmonic channels and opens band gaps in the TO-phonon polariton energy
dispersion that results in pronounced Bragg scattering and reflection of the
incoming light. The separation in frequency of different Bragg replicas, which
is at the heart of acousto-optics, allows us to study the resonant
acousto-optic effect in the most simple and efficient geometry of collinear
propagation of electromagnetic and ultrasonic waves. The acoustically induced
energy gaps, Bragg reflection spectra, and the spatial distribution of the
electric field and polarization are calculated for CuCl parameters, in a wide
range of frequencies and intensities of the pumping acoustic wave. Our results
show drastic changes in terahertz spectra of semiconductor crystals that opens
the way for efficient and accessible manipulation of their infrared properties,
by tuning the parameters of the acoustic wave.Comment: 20 pages, 14 figure
Origin of the inner ring in photoluminescence patterns of quantum well excitons
In order to explain and model the inner ring in photoluminescence (PL)
patterns of indirect excitons in GaAs/AlGaAs quantum wells (QWs), we develop a
microscopic approach formulated in terms of coupled nonlinear equations for the
diffusion, thermalization and optical decay of the particles. The origin of the
inner ring is unambiguously identified: it is due to cooling of indirect
excitons in their propagation from the excitation spot. We infer that in our
high-quality structures the in-plane diffusion coefficient is about 10-30cm^2/s
and the amplitude of the disorder potential is about 0.45meV.Comment: 4 pages, 3 figure
Effect of 6-day hypokinesia on oxygen metabolism indices in elderly and senile subjects
After a strict 6 day confinement to bed of elderly and senile subjects the oxygen supply of the subcutaneous cellular tissue was impaired, and the intensity of its tissue respiration was somewhat reduced. The vacat-oxygen of the blood and urine, the coefficient of incomplete oxidation, and the oxygen deficiency in the organism were increased
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