196 research outputs found
Nonlinear emission dynamics of a GaAs microcavity with embedded quantum wells
The emission dynamics of a GaAs microcavity at different angles of
observation with respect to the sample normal under conditions of nonresonant
picosecond-pulse excitation is measured. At sufficiently high excitation
densities, the decay time of the lower-polariton emission increases with the
polariton wavevector; at low excitation densities the decay time is independent
of the wavevector. The effect of additional nonresonant continuous illumination
on the emission originating from the bottom of the lower polariton branch is
investigated. The additional illumination leads to a substantial increase in
the emission intensity (considerably larger than the intensity of the
photoluminescence excited by this illumination alone). This fact is explained
in terms of acceleration of the polariton relaxation to the radiative states
due to scattering by charge carriers created by the additional illumination.
The results obtained show, that at large negative detunings between the photon
and exciton modes, polariton-polariton and polariton-free carrier scattering
are the main processes responsible for the filling of states near the bottom of
the lower polariton branch.Comment: 10 pages, 6 figures. This is an author-created, un-copyedited version
of an article accepted for publication in Journal of Physics: Condesed
Matter. IOP Publishing Ltd is not responsible for any errors or omissions in
this version of the manuscript or any version derived from i
PREVALENCE AND CAUSES OF IRON DEFICIENCY IN INFANTS
Purpose: To evaluate the prevalence of iron deficiency in infants, to identify the factors causing them.Materials and Methods: Completed questionnaires 1052 lactating mothers, to determined the level of hemoglobin in 948 infants, serum ferritin, serum iron, total iron binding capacity of serum (n=60), the concentration of iron in breast milk (n=62).Results: The prevalence of anemia in infants in region was 6 times higher than the official statistics (349.2/1000 vs. 52,9/1000). Iron status was higher in exclusively breast-fed in first 6 mo, but the incidence of anemia in 9 mo old infants was independent of the type of feeding. Anemia in infants contributed of antenatal factors (prematurity, threat of abortion, utero-placental dysfunction), (p<0.05). Infants older 6 mo has a decrease level of serum iron (5,6 μmol/L vs. 15,0 μmol/L, р=0,04). The level of iron in breast milk was independent on the mother’s intake, iron supplementation during pregnancy and lactating.Summary: The development of iron deficiency in infants contributes to antenatal factors and low level of iron in breast milk
A case report of dopa-responsive dystonia in a young woman
Dopa-responsive dystonia (DRD) is a rare progressive genetically heterogenous disorder with pediatric onset. DRD is 3 times as prevalent in women than in men. This article reports a clinical case of DRD in a young female presenting with paraparesis, foot dystonia (more pronounced in the right foot) and pronounced walking impairment, who was admitted for emergency treatment to a Neurology Unit. Based on the additional tests, which included a levodopa trial and Sanger sequencing, the patient was diagnosed with DRD. Levodopa caused a considerable improvement of the symptoms. The article describes the clinical features of the disease, talks about its differential diagnosis, genetic predisposition and treatment strategy. © 2020 Pirogov Russian National Research Medical University. All rights reserved
Dynamics of spatial coherence and momentum distribution of polaritons in a semiconductor microcavity under conditions of Bose-Einstein condensation
The study was supported by the Russian Foundation for Basic Research (project nos. 12-02-33091, 13-02-12197, and 14-02-01073) and the Presidium of the Russian Academy of Sciences. The work of V.V.B. was supported in part by a scholarship of the President of the Russian Federation.The dynamics of spatial coherence and momentum distribution of polaritons in the regime of Bose-Einstein condensation in a GaAs microcavity with embedded quantum wells under nonresonant excitation with picosecond laser pulses are investigated. It is shown that the establishment of the condensate coherence is accompanied by narrowing of the polariton momentum distribution. At the same time, at sufficiently high excitation densities, there is significant qualitative discrepancy between the dynamic behavior of the width of the polariton momentum distribution determined from direct measurements and that calculated from the spatial distribution of coherence. This discrepancy is observed at the fast initial stage of the polariton system kinetics and, apparently, results from the strong spatial nonuniformity of the phase of the condensate wavefunction, which equilibrates on a much longer time scale.Publisher PDFPeer reviewe
Addressing the exciton fine structure in colloidal nanocrystals: the case of CdSe nanoplatelets
We study the band-edge exciton fine structure and in particular its
bright-dark splitting in colloidal semiconductor nanocrystals by four different
optical methods based on fluorescence line narrowing and time-resolved
measurements at various temperatures down to 2 K. We demonstrate that all these
methods provide consistent splitting values and discuss their advances and
limitations. Colloidal CdSe nanoplatelets with thicknesses of 3, 4 and 5
monolayers are chosen for experimental demonstrations. The bright-dark
splitting of excitons varies from 3.2 to 6.0 meV and is inversely proportional
to the nanoplatelet thickness. Good agreement between experimental and
theoretically calculated size dependence of the bright-dark exciton slitting is
achieved. The recombination rates of the bright and dark excitons and the
bright to dark relaxation rate are measured by time-resolved techniques
Modeling of Spiking-Bursting Neural Behavior Using Two-Dimensional Map
A simple model that replicates the dynamics of spiking and spiking-bursting
activity of real biological neurons is proposed. The model is a two-dimensional
map which contains one fast and one slow variable. The mechanisms behind
generation of spikes, bursts of spikes, and restructuring of the map behavior
are explained using phase portrait analysis. The dynamics of two coupled maps
which model the behavior of two electrically coupled neurons is discussed.
Synchronization regimes for spiking and bursting activity of these maps are
studied as a function of coupling strength. It is demonstrated that the results
of this model are in agreement with the synchronization of chaotic
spiking-bursting behavior experimentally found in real biological neurons.Comment: 9 pages, 12 figure
Mode locking of hole spin coherences in CsPb(Cl, Br)3 perovskite nanocrystals
The spin physics of perovskite nanocrystals with confined electrons or holes is attracting increasing attention, both for fundamental studies and spintronic applications. Here, stable lead halide perovskite nanocrystals embedded in a fluorophosphate glass matrix are studied by time-resolved optical spectroscopy to unravel the coherent spin dynamics of holes and their interaction with nuclear spins of the 207Pb isotope. We demonstrate the spin mode locking effect provided by the synchronization of the Larmor precession of single hole spins in each nanocrystal in the ensemble that are excited periodically by a laser in an external magnetic field. The mode locking is enhanced by nuclei-induced frequency focusing. An ensemble spin dephasing time of a nanosecond and a single hole spin coherence time of T2 = 13 ns are measured. The developed theoretical model accounting for the mode locking and nuclear focusing for randomly oriented nanocrystals with perovskite band structure describes the experimental data very well
NANOSTRUCTURAL ANALYSIS IN COMPARATIVE ESTIMATION OF DEGENERATIVE CHANGES IN INTERVERTEBRAL DISK
By atomic force microscopy we realized the research of anatomic material represented by the fragments of tissue of intervertebral disks of different stages of degenerative process. The researches were carried out with help of probe nanolaboratory with videomicroscope Ntegra Prima. As the result we obtained direct experimental data that proves some theoretical investigation that hadn't had. visual proves
- …