32,062 research outputs found
Influence of Anomalous Dispersion on Optical Characteristics of Quantum Wells
Frequency dependencies of optical characteristics (reflection, transmission
and absorption of light) of a quantum well are investigated in a vicinity of
interband resonant transitions in a case of two closely located excited energy
levels. A wide quantum well in a quantizing magnetic field directed normally to
the quantum-well plane, and monochromatic stimulating light are considered.
Distinctions between refraction coefficients of barriers and quantum well, and
a spatial dispersion of the light wave are taken into account. It is shown that
at large radiative lifetimes of excited states in comparison with nonradiative
lifetimes, the frequency dependence of the light reflection coefficient in the
vicinity of resonant interband transitions is defined basically by a curve,
similar to the curve of the anomalous dispersion of the refraction coefficient.
The contribution of this curve weakens at alignment of radiative and
nonradiative times, it is practically imperceptible at opposite ratio of
lifetimes . It is shown also that the frequency dependencies similar to the
anomalous dispersion do not arise in transmission and absorption coefficients.Comment: 10 pages, 6 figure
Elastic Light Scattering by Semiconductor Quantum Dots
Elastic light scattering by low-dimensional semiconductor objects is
investigated theoretically. The differential cross section of resonant light
scattering on excitons in quantum dots is calculated. The polarization and
angular distribution of scattered light do not depend on the quantum-dot form,
sizes and potential configuration if light wave lengths exceed considerably the
quantum-dot size. In this case the magnitude of the total light scattering
cross section does not depend on quantum-dot sizes. The resonant total light
scattering cross section is about a square of light wave length if the exciton
radiative broadening exceeds the nonradiative broadening. Radiative broadenings
are calculated
Effects of the low lying Dirac modes on excited hadrons in lattice QCD
Chiral symmetry breaking in Quantum Chromodynamics is associated with the low
lying spectral modes of the Dirac operator according to the Banks-Casher
relation. Here we study how removal of a variable number of low lying modes
from the valence quark sector affects the masses of the ground states and first
excited states of baryons and mesons in two flavor lattice QCD.Comment: 6 pages, 2 figures. Contribution to proceedings of "Excited QCD
2012", May 6-12, 2012, Peniche, Portuga
Effect of the Spatial Dispersion on the Shape of a Light Pulse in a Quantum Well
Reflectance, transmittance and absorbance of a symmetric light pulse, the
carrying frequency of which is close to the frequency of interband transitions
in a quantum well, are calculated. Energy levels of the quantum well are
assumed discrete, and two closely located excited levels are taken into
account. A wide quantum well (the width of which is comparable to the length of
the light wave, corresponding to the pulse carrying frequency) is considered,
and the dependance of the interband matrix element of the momentum operator on
the light wave vector is taken into account. Refractive indices of barriers and
quantum well are assumed equal each other. The problem is solved for an
arbitrary ratio of radiative and nonradiative lifetimes of electronic
excitations. It is shown that the spatial dispersion essentially affects the
shapes of reflected and transmitted pulses. The largest changes occur when the
radiative broadening is close to the difference of frequencies of interband
transitions taken into account.Comment: 7 pages, 5 figure
More effects of Dirac low-mode removal
In previous studies we have shown that hadrons, except for a pion, survive
the removal of the lowest lying Dirac eigenmodes from the valence quark
propagators. The low-modes are tied to the dynamical breaking of chiral
symmetry and we found chiral symmetry to be restored by means of matching
masses of chiral partners, like, e.g., the vector and axial vector currents.
Here we investigate the influence of removing the lowest part of the Dirac
spectrum on the locality of the Dirac operator. Moreover, we analyze the
influence of low-mode truncation on the quark momenta and thereupon on the
hadron spectrum and, finally, introduce a reweighting scheme to extend the
truncation to the sea quark sector.Comment: 7pages, 4 figures. Proceedings of the 31st International Symposium on
Lattice Field Theory, July 29 - August 3, 2013, Mainz, German
Transmission of a Symmetric Light Pulse through a Wide QW
The reflection, transmission and absorption of a symmetric electromagnetic
pulse, which carrying frequency is close to the frequency of an interband
transition in a QW (QW), are obtained. The energy levels of a QW are assumed
discrete, one exited level is taken into account. The case of a wide QW is
considered when a length of the pulse wave, appropriate to the carrying
frequency, is comparable to the QW's width. In figures the time dependencies of
the dimensionless reflection, absorption are transmission are represented. It
is shown, that the spatial dispersion and a distinction in refraction indexes
influence stronger reflection.Comment: 8 pages,8 figures with caption
Principals of the theory of light reflection and absorption by low-dimensional semiconductor objects in quantizing magnetic fields at monochromatic and pulse excitations
The bases of the theory of light reflection and absorption by low-dimensional
semiconductor objects (quantum wells, wires and dots) at both monochromatic and
pulse irradiations and at any form of light pulses are developed. The
semiconductor object may be placed in a stationary quantizing magnetic field.
As an example the case of normal light incidence on a quantum well surface is
considered. The width of the quantum well may be comparable to the light wave
length and number of energy levels of electronic excitations is arbitrary. For
Fourier-components of electric fields the integral equation (similar to the
Dyson-equation) and solutions of this equation for some individual cases are
obtained.Comment: 14 page
Quantum critical behaviour of the plateau-insulator transition in the quantum Hall regime
High-field magnetotransport experiments provide an excellent tool to
investigate the plateau-insulator phase transition in the integral quantum Hall
effect. Here we review recent low-temperature high-field magnetotransport
studies carried out on several InGaAs/InP heterostructures and an InGaAs/GaAs
quantum well. We find that the longitudinal resistivity near the
critical filling factor ~ 0.5 follows the universal scaling law
, where . The critical exponent equals ,
which indicates that the plateau-insulator transition falls in a non-Fermi
liquid universality class.Comment: 8 pages, accepted for publication in Proceedings of the Yamada
Conference LX on Research in High Magnetic Fields (August 16-19, 2006,
Sendai
The identification of wheat genetic resources with high dietary fiber content
The quality properties of different variety mixtures and composite cross populations were studied with the aim of identifying genotypes with high dietary fiber content and to cultivate and examine the effect of these components on the end-use quality. Based on the results of a Europe-wide trial, we could detect two populations and variety mixtures which had significantly higher total (TOTAX) and water extractable arabinoxylan (WEAX) content, than most of the studied genotypes, with positive effect on the human health. These populations/mixtures are promising dietary fiber resources and suitable not only for organic but also for conventional farming, especially in Central Europe. The seeds of the best population (Mv Elit CCP) was multiplied to supply it for interested farmers in Hungary in the frame of the European trial on organic heterogeneous materials
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