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We present results from a multiwavelength study of the blazar PKS 1954–388 at radio, UV, X-ray, and gamma-ray energies. A RadioAstron observation at 1.66 GHz in June 2012 resulted in the detection of interferometric fringes on baselines of 6.2 Earth-diameters. This suggests a source frame brightness temperature of greater than 2 × 1012 K, well in excess of both equipartition and inverse Compton limits and implying the existence of Doppler boosting in the core. An 8.4-GHz TANAMI VLBI image, made less than a month after the RadioAstron observations, is consistent with a previously reported superluminal motion for a jet component. Flux density monitoring with the Australia Telescope Compact Array confirms previous evidence for long-term variability that increases with observing frequency. A search for more rapid variability revealed no evidence for significant day-scale flux density variation. The ATCA light-curve reveals a strong radio flare beginning in late 2013, which peaks higher, and earlier, at higher frequencies. Comparison with the Fermi gamma-ray light-curve indicates this followed ~ 9 months after the start of a prolonged gamma-ray high-state—a radio lag comparable to that seen in other blazars. The multiwavelength data are combined to derive a Spectral Energy Distribution, which is fitted by a one-zone synchrotron-self-Compton (SSC) model with the addition of external Compton (EC) emission.
Results are presented of long-term monitoring at the radio telescope RATAN–600 and a model interpretation of instantaneous 1–22 GHz spectra at six frequencies for a sample of 550 compact extragalactic radio sources. The sources are selected from the Preston et al. (1985) VLBI survey and are located in the declination range from −30° to +43°. Dependence of the index of variability on frequency is analysed for different subsamples. Factors of flux density variations range from 1 to 15. A typical behaviour of spectra evolution during strong radio outbursts in various objects is recognised suggesting a common physical nature of the variability. Invoking VLBI observations in spectra–structure analysis, we find that usually more than 70% of the total emission is coming from the mas scale at frequencies higher than 5 GHz. The observed variability can be explained in the model with a relativistic jet of parsec scale in the longitudinal magnetic field or in the shock-in-jet model.
The introduction of the ragweed leaf beetle in the South of Russia in 1978–1989 was
accompanied by a number of spectacular phenomena that determined the general success of
the ragweed control and further dispersal and acclimatization of the beetles:
(i) formation of solitary population waves (SPW), characterized by an
extremely high density of the phytophage population at the narrow band of the front of a
moving wave defoliating nearly all ragweed plants, and (ii) rapid, within
5-6 generations, development of flight in the leaf beetle species that in its homeland
lost the ability to fly. We present here a demogenetic model capable of reproducing both
these phenomena, assuming that the flight ability of a phytophage population is governed
by a single diallelic locus with flight and flightless alleles that determine three
genotypes of the ragweed leaf beetle. Simulation results agree well with the practical
recommendation of retaining a high density of common ragweed in the release area in order
to provide the necessary conditions for the initial increase of the leaf beetle population
and the formation of the wave. The model confirms the earlier hypothesis that the SPW is
the key factor that determines efficiency of weed biocontrol program. We demonstrate also
that the formation of the wave has crucially accelerated the development of the beetles’
ability to fly.
Accurate alignment of the radio and optical celestial reference frames requires detailed understanding of physical factors that may cause offsets between the positions of the same object measured in different spectral bands. Opacity in compact extragalactic jets (due to synchrotron self-absorption and external free-free absorption) is one of the key physical phenomena producing such an offset, and this effect is well-known in radio astronomy (“core shift”). We have measured the core shifts in a sample of 29 bright compact extragalactic radio sources observed by Very Long Baseline Interferometry (VLBI) at 2.3 and 8.6 GHz. We report the results of these measurements and estimate that the average shift between radio and optical positions of distant quasars could be of the order of 0.1--0.2 mas. This shift exceeds the expected positional accuracy of Gaia and SIM. We suggest two possible approaches to carefully investigate and correct for this effect in order to align accurately the radio and optical positions. Both approaches involve determining a Primary Reference Sample of objects to be used for tying the radio and optical reference frames together.
The aim of this research was to study the effect of 12-minute clinical death on innate and acquired behavior, biogenic amine concentration, and the composition and quantity of neural populations in specific brain regions of white rats. The study shows that in animals during the postresuscitation period with formal restoration of neurological status, there are changes in emotional reactivity, orientation-exploration reactions, impairment of learning and memory, decrease in exercise tolerance and pain sensitivity. These processes are accompanied by alterations in serotonin and norepinephrine levels in the frontal cerebral cortex, dopamine and serotonin levels in the striatum, certain biochemical indices in blood plasma and neural loss in the CA1 sector of the hippocampus and lateral portions of the cerebellum.
The galvanomagnetic effects in new diluted magnetic semiconductors
SnxTe:Yb were studied to build the energy level diagram under
variation of the alloy composition and establish the connection between the
parameters of electronic structure and magnetic properties. It was found
that the Hall coefficient increases almost by order of magnitude with
increasing the temperature. As tin content decreases, while the ytterbium
concentration grows, the hole concentration decreases by several times. The results are explained by assuming a formation of an
ytterbium-induced deep defect level in the energy spectrum of the alloys,
which moves up to the top of the valence band with increasing the ytterbium
concentration and pins the Fermi level within the valence band at
sufficiently high impurity content. The hole concentration vs. ytterbium
content dependence was used to calculate the energy position of the Fermi
level in the frame of two-band dispersion law and to determine the position
of Yb level in the alloys. The diagram of the charge carrier energy spectrum
under varying the alloy composition was built.
Photoluminescence (PL) of nanocrystalline Si (nc-Si) assemblies formed by thermal crystallization of amorphous Si/SiO2 and SiO/SiO2 superlattices (SLs) has been investigated at different temperatures and excitation conditions. The low temperature resonant PL spectroscopy reveals phonon-assisted excitonic recombination. At room temperature the samples formed from a-SiO/SiO2 SLs possess relatively high PL quantum yield (∼ 1%). The PL transients have non-exponential decay, which indicates the exciton energy transfer in nc-Si ensembles. The excitonic energy of Er-doped nc-Si SL structures can be almost completely transferred to Er ions incorporated in SiO2 matrix that results in a strong emission line at 0.81 eV.
The synthesis of nc-Si by reactive evaporation of SiO and subsequent thermal induced phase separation is reported. The size control of nc-Si is realized by evaporation of SiO/SiO2 superlattices. By this method an independent control of crystal size and density is possible. The phase separation of SiO into SiO2 and nc-Si in the limit of ultrathin layers is investigated. Different steps of this phase separation are characterized by photoluminescence, infrared absorption and transmission electron microscopy measurements. The strong room temperature luminescence of nc-Si shows a strong blueshift of the photoluminescence signal from 850 to 750 nm with decreasing crystal size. Several size dependent properties of this luminescence signal, like decreasing radiative lifetime and increasing no-phonon transition properties with decreasing crystal size are in good agreement with the quantum confinement model. Er doping of the nc-Si shows an enhancement of the Er luminescence at 1.54 μm by a factor of 5000 compared to doped SiO2 layers. The decreasing transfer time for the nc-Si to Er transition with decreasing crystal size can be understood as additional proof of increasing recombination probability within the nc-Si for decreasing crystal size.
The origin of anomalous birefringence of grossular–andradite (grandite) garnets from skarns in Mali and Russia was considered. The crystals had complex superposition of two phenomena: mismatch compositional strain (stress birefringence) and growth ordering of atoms (growth dissymmetrization). Study of the crystals using several experimental techniques (optical microscopy, microprobe analysis, X-ray diffraction topography and X-ray single crystal diffraction) as well as calculations of anomalous birefringence has confirmed this hypothesis. Depending on the crystal composition and growth conditions, the relative magnitude of each phenomenon controls the various optical effects. As a result one can see two groups of crystals which are found to have fundamentally different anomalous optical properties: crystals with low (<0.001) and high (0.001–0.015) values of birefringence. The spatial distribution of birefringence within each group is different and this fact is related to different mechanisms causing optical anomalies: stress birefringence and growth dissymmetrization for these two groups, respectively.
We report on luminescence hole burning experiments, which prove that radiative recombination between quantum confined states is the only viable model for the mechanism of the light emission from porous silicon. We find that more than 90% of the luminescence originates from quantum confined states inside the Si nanocrystals.
Polarization memory effect in the porous Si photoluminescence is studied. The anisotropy of the linear polarization degree is found in the samples etched with polarized light-assistance. The effect is explained by the anisotropie in plane distribution of the elongated Si crystallites. Under resonant optical excitation four-fold anisotropy of the photoluminescence polarization, linked to the crystalline axes of the bulk Si substrate, is observed.
Photoluminescence saturation under intense CW optical excitation and optical degradation of photoluminescence from porous Si are studied. The anisotropy of the luminescence is observed under intense linearly polarized illumination at room temperature and after polarized light induced degradation at low temperature. The Auger process is shown to be responsible for these observations.
We present a detailed photoluminescence excitation study of the optical transitions in GaN. This technique is employed to distinguish between band-to-band excitation and exciton contribution to the formation of the free exciton, bound exciton, violet and yellow photoluminescence bands. We show the dominant role of the Fröhlich polar intraband scattering in the formation of the free exciton states. We demonstrate that bound exciton states in a large extent are created by the capture of the free excitons by shallow impurities as well as by phononassisted resonant excitation of the bound exciton states. The capture of the free carriers excited in the band continuum is a main excitation source for the violet and yellow bands. However, distinct A- and C-exciton resonances are detected in the excitation spectra of the violet and yellow emission bands.
The yellow Luminescence in GaN centered at 2.2 eV has been studied in various epitaxial layers grown by MOVPE on sapphire and by the sandwich sublimation methode on 6H-SiC substrates. The photoluminescence and optically detected magnetic resonance results can be consistently explained by a recombination model involving shallow donors and deep donors.
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