Home – Home – Jornals – Flora and Vegetation of Asian Russia 2017 number 4

The results of the development of vertical-cavity surface emitting lasers based on Al_xGa_1-xAs and In_yGa_1-yAs solid solutions are presented. Developed lasers demonstrate stable single-mode operation at a wavelength of 794.9 nm and 894.6 nm, which offers the prospects of their applications in miniature quantum frequency standards operating at the transition 5S_1/2→5P_1/2 of ⁸⁷Rb and ¹³³Cs atoms.

The mechanisms of surface transformation during annealing of epi-ready InP (001) substrates in a flux of arsenic molecules have been studied in situ by reflection high-energy electron diffraction. The effect of the annealing temperature and the arsenic flux on the processes of removing oxides from the InP surface, which occur as a result of thermal decomposition and chemical interaction of oxides with arsenic, has been studied.

The analysis of the processes of generation of the second harmonic in the layers of CdTe, CdxHg_1-xTe and the substrate from GaAs heterostructure Cd_xHg_1-xTe/CdTe/ZnTe/GaAs orientation (013) is carried out. Measurements of the azimuthal dependence of the signals of the second harmonic in comparison with the calculated data obtained during the numerical modeling of the ideal crystal for a given orientation near the cut (013) were carried out. It is shown that the substrate and epitaxial layers after cultivation have a reversal of the orientation plane, which was for substrates of GaAs +8 and -3 angular degrees from the ideal plane (013), for layers of heterostructures - up to 8 angular degrees from the orientation of the substrate, which has a weak dependence on the composition in thickness. The observed reversals of the orientation plane depend on the discrepancy between the parameters of the lattice of the conjugated materials of the heterostucture Cd_xHg_1-xTe /CdTe/ZnTe/GaAs. The recorded increase in noise with the minimums of azimuthal dependence of the second harmonic signal in the layers of Cd_xHg_1-xTe is due to the presence of disoriented microsicts.

The action of quantum wells design and specific features of their manufacturing technology on the performance and maximum modulation depth of optical shutters based on quantum wells A₃B₅ predestinated for mode locking of NIR lasers is analyzed.

The problem of in situ temperature control during the growth of epitaxial layers of CdHgTe by molecular beam epitaxy is considered. Various approaches to solving the problem using spectroscopic ellipsometry are proposed. They are based on the temperature dependence of the optical constants spectra of the CdTe buffer layer and the growing CdHgTe layer. The results of experimental testing of these methods are presented, which show that the temperature measurement accuracy is several degrees, and the sensitivity reaches fractions of a degree. At the stage of stationary growth, it is possible to determine the change not only in temperature, but also in the composition of the growing layer from the ellipsometric spectra.

The issues related to the development and manufacturing single photon detector based on single-photon avalanche photodiodes (SPAD) InP/InGaAs/InP, operating in Geiger mode on telecommunications wavelength 1550 nm are discussed. A description of the SPAD design is given. The method of obtaining the InP/InGaAs/InP heterostructure by molecular-beam epitaxy, methods of manufacturing SPAD chip by planar technology, features of selective doping with zinc p-regions in the InP layer and developed electronic schemes for measurement main parameters of SPAD are described. Preliminary results of measurements SPAD parameters are presented.

The antireflection properties of coatings composed of subwavelength-sized dielectric SiGe particles grown on Si(100) substrates using the dewetting phenomenon are studied. The average particle size was set by the amount of deposited Ge and varied in the range from 0.2 to 1.4 μm. The excitation of magnetic and electric resonances in the SiGe particles led to a decrease in reflection by approximately 60%, depending on the average particle size, in comparison with the reflection of the Si surface not covered with particles. The broad particle size distribution provided the antireflection properties over a wide spectral range, in which small particles produced a stronger antireflection effect than large particles. Numerical simulation has shown that for particles on a substrate, the efficiency of excitation of magnetic and electric resonances strongly depends on the ratio of the height of the particles to the size at their base.

The use of the vacuum photodiode with two semiconductor electrodes for studying the multialkali photocathode (MP) photoemission properties was demonstrated in this work. The photoluminescence and quantum efficiency spectra were studied; the high-resolution energy distribution curves for the MP were obtained for the first time. The measurements were performed under illumination of the MP in the spectral range of 400-950 nm and the temperature range of 90-300 K. Using the data obtained the conclusion, that the MP is a photocathode with effective negative electron affinity, was made. The properties of the solar element based on the vacuum photodiode were studied.

Theoretical relations that optimize the design of the microbolometric elements of the FPA providing an improvement in its operating speed are presented. The requirements for the parameters of the elements and the materials used for its manufacture are formulated, which provide a fundamental opportunity to minimize the thermal relaxation time of a bolometric sensor in order to increase the frame frequency of the FPA. The results of their modeling are presented, which make it possible to optimize the design and its implementation using modern technological processes for the formation of microbolometric elements with high operating speed, taking into account the requirements of specific applications.

The design of microcavity for single quantum dot based emitters has been developed. The microcavity consists of semiconductor distributed Bragg reflector and microlens, fabricated by selective oxidation of gradient Al_XGa_1-XAs layer. The microcavity demonstrates high level of external quantum efficiency up to 70%. This microcavity can be used in the development of a single quantum dot based single photon emitters or emitters of entangled photon pairs.

Photoluminescence of structures with multiple GaN/AlN quantum wells grown by molecular beam epitaxy has been investigated. Calculated dependence of the quantum well photoluminescence band peak energy on the thickness of the GaN layer has been compared with experiment for various ratios of the thicknesses of the GaN and AlN layers. The thicknesses of the GaN and AlN layers were determined by transmission electron microscopy. The calculations of the photoluminescence band peak energy were carried out in the 6-band kp-approximation taking into account spontaneous and piezoelectric polarizations. According to the calculation results, the slope of the dependence of the emission energy on the GaN layer thickness decreases with increase in the ratio of the GaN layer thickness to the AlN layer thickness, in accordance with decrease in the electric field in the GaN layer. In quantum wells of sufficiently large thickness the observed photoluminescence band peak energy is higher than the calculation result for undoped structures due to unintentional doping of the quantum wells, which leads to screening of the built-in electric field.

A comprehensive study of monolayers of molybdenum disulfide MoS₂, formed on a silicon substrate using Raman scattering (RS), photoluminescence (PL), was carried out in comparison with the data of atomic force microscopy (AFM). Maps of the distribution of the Raman scattering intensity by optical phonons and exciton PL from monolayer MoS2 films were constructed. The dependences of the frequencies of the fundamental vibrational modes of MoS₂ (A_1g and E_2g) on the thickness of monolayer coatings were obtained. An enhancement of the Raman mode of the optical phonon of silicon by a bilayer of molybdenum disulfide was found. A hypothesis on the interference enhancement of Raman scattering of light by phonon modes of silicon is proposed.

This article is dedicated to the famous physicist, founder of the School of acousto-electronics and acousto-optics, corresponding member of the Russian Academy of Sciences, Sergey Vasilyevich Bogdanov in connection with the centenary of his birth (2.08.1921-14.02.2017).

Fundamental research of basic creating mosaic focal plane arrays (MFPAs) allowed to optimize the prototype of mosaic technology with decreasing "blind zones". At the same time, minimal damage areas are provided at the edges of the crystals after separating the wafers with the achievement of minimum gaps between crystals of adjacent submodules up to a value of no more than 2-3 microns for different determining materials. The parameters of infrared MFPAs are investigated depending on the wavelength of the maximum spectral characteristic of the photosensitivity of multilayer structures with quantum wells, on the pitch of quantum well photodetectors and on the format of submodules. In a series of the proposed variants of technological prototypes, the "blind zones" of the MFPA are optically overlapped and the ultimate, 100%, image-conversion efficiency is provided. The mosaic technology is one of the fundamental principles of achieving ultra-high dimension of the MFPAs with maximum image-conversion efficiency.

The paper proposes algorithms that allow to increase the efficiency of parallel programs execution on high-performance computer systems, in particular, when solving problems of modeling physical processes. The developed algorithms are focused on reducing the execution time of collective operations for computer systems with SMP/NUMA node architecture in standard MPI libraries. The developed read-write blocking algorithms increase the efficiency of synchronization of access to shared memory, relative to the algorithms used in the Open PMIx library.

The results of experimental studies of the features of formation and path propagation of high-intensity light channels under conditions of distortions of the initial profile of a high-power femtosecond laser radiation beam are presented. The distortions are introduced by amplitude modulation of the laser beam with the help of masks. The use of amplitude masks allows generation of a preset number of high-intensity light channels and their controllable filamentation mainly at short (tens of meters) distances of radiation propagation in air.

The first experience of using the differential spectroscopy technique DOAS for retrieving the total ozone content (TOC) from measurements of the ground-based UV spectrometer UFOS is considered. Examples of spectra recorded by UFOS and similar spectral equipment are presented. Test calculations of TOC with the use of DOAS are performed based on the UFOS measurements for several days at the Voeikovo station. The resulted TOC values are compared with independent ground-based and satellite measurements. The TOC calculations systematically differ from independent data, which can apparently be eliminated by means of a more accurate adjustment of the DOAS algorithm to the problem conditions and UFOS parameters.

The absorption spectrum of a natural sample of carbon dioxide has been recorded in the 4350-4550 cm^-1 wavenumber range with a Bruker IFS 125HR spectrometer and a 30 m multipass gas cell with a White-type optical system. The spectrum was recorded with a spectral resolution of 0.02 cm^-1 at a pressure of 306 mbar, a temperature of ~ 301.7 K, and a path length of about 1058 m. That, along with 9800 interferograms, allowed attaining a sensitivity of 10^-9 cm^-1. The positions and intensities of 453 spectral lines of 17 bands of 5 carbon dioxide isotopologues (¹²C¹⁶O₂, ¹³C¹⁶O₂, ¹⁶О¹²C¹⁸O, ¹⁶О¹³C¹⁸O, and ¹⁶О¹³C¹⁷O) were measured. The 33303-02201, 41104-02201, and 41104-10002 bands of the principal isotopologue ¹²C¹⁶O₂ and the 31103-00001 band of both ¹³C¹⁶O₂ and ¹⁶О¹²C¹⁸O isotopologues were recorded for the first time. The measured line positions and intensities are compared with the values from the HITRAN2020 database.

The effects of selective and non-selective absorption by atmospheric molecules on the characteristics of radiation scattered by atmospheric aerosol in the presence of organic compounds in the latter are analyzed. The wavelengths at which the backscattered signal exceeds the total absorption are determined.

A simple and convenient form of the vibrational-rotational kinetic energy operator for symmetric molecules of the A₂B₂ type in polyspherical orthogonal coordinates is proposed. A feature of the proposed approach is the symmetry of the kinetic energy operator with respect to the permutation of the coordinates of two groups of atoms (AB) and the ease of applying contraction of wave functions. A variational calculation of the lower vibrational-rotational energy levels of the acetylene molecule has been made. The energy levels calculated in this work are compared with other sources.

The frequency behavior of spectral contributions from initial, central, and “final” sections of the power-law structure function to the spectral density of a stationary random process is considered. Their oscillating alternating-sign frequency character is demonstrated. As the frequency increases, the rate of decrease in the absolute values of these contributions approaches the inversely proportional dependence. Simple analytical approximated relationships describing the frequency behavior of the spectral contributions are suggested and analyzed. They are recommended for wide practical use. The application of the obtained relationships for more complex composite power-law functions is considered.

A change in the air composition during the transition from the troposphere to the stratosphere is investigated on the basis of aircraft sounding data. Distribution of eight gases, dispersion and chemical composition of aerosol is analyzed. It is shown that at the intersection of the tropopause, the concentrations of N₂O, CO, and CH₄ sharply decrease, while of O₃ and NO₂ and the counting concentration of aerosol, on the contrary, increase. In the elemental composition, Si dominates the tropopause; in the ion, SO₄^2-. Terrigenous elements Al, Cu, and Fe are dominated in the troposphere; and among ions, a set of several compounds varies with region. Noticeably different particle dispersions are also identified.

A large-scale comprehensive study of the composition of the troposphere of the Russian Arctic was carried out in September 2020 onboard the TU 134 “Optic” aircraft laboratory. The results of the study of the spatiotemporal variability of aerosol and black carbon (BC) concentrations are considered. The airborne sensing data were used for the analysis of general and particular features of the spatial variability of vertical profiles of aerosol and BC concentrations. The columnar BC concentrations in the arctic and subarctic latitudes were obtained.

Using a new method for determining the parameters of wind turbulence from the spectra of the vertical wind speed measured by a pulsed coherent Doppler lidar (PCDL), an experiment was carried out in 2020 on the coast of Lake Baikal as part of the study of turbulence and internal gravity waves (IGW) in the atmospheric boundary layer (ABL). The article presents the results of this experiment and analyzes the spectra and lidar estimates of the variance of the vertical wind speed and the turbulent energy dissipation rate obtained from the measurements of the Stream Line PCDL in the presence of a low-level jet and IGW in the ABL.

In this work, we examine the transport of combustion aerosol into the stratosphere in summer 2019, when numerous wildfires occurred in Siberia, Canada, and Alaska. According to lidar observations carried out in Tomsk at the stratospheric lidar station of IAO SB RAS in August 2019, distinct layers of aerosol scattering were detected in the lower stratosphere. The analysis of back air mass trajectories calculated on the basis of satellite radiometric information about fires in the Northern Hemisphere and CALIPSO lidar data allows a conclusion that the aerosol layers observed were formed by the combustion products of fires in Siberia transported into the stratosphere.

Different methods for measuring random wavefront tilts are considered. Possibilities of measuring the Fried parameter by the differential method in turbulence sensing and adaptive optics problems are determined. Comparative measurements of the level of turbulence along a horizontal path were carried out by two optical methods: (1) with a differential turbulence meter and (2) a passive method based on image jitter measurements with a high-speed digital video camera mounted at a small astronomical telescope and real-time processing algorithms. Possible differences in the measurement results are discussed. Patterns of the evolution of the convective motion of a medium inside a volume are derived in terms of the velocity field and scalar temperature and pressure fields on the basis of numerical solution of the system of Navier-Stokes equations. Ways of developing a wavefront sensor which ensures high-precision phase measurements in both Kolmogorov and non-Kolmogorov turbulence are suggested.

A method of ultraviolet radiation dosimetry based on recording the photostimulated transition Mn³⁺ + e^– → Мn²⁺ in ultrafine MgO with a periclase crystal structure is described. The observed effect is associated with the photosensitivity of transition metal impurity ions. The intensity of the electron paramagnetic resonance (EPR) signal of Mn²⁺ ions can be used as a measure of change in the valence state of Mn impurity ions in MgO lattice. The possibility of recording a photostimulated transition by the EPR is proposed to be used in the development of a passive integrating ultraviolet detector (UV detector). The applicability of the new UV detector for assessing the ultraviolet transparency of snow cover is shown. The possibility of its use for monitoring the ultraviolet radiation on the Earth's surface in the framework of studies of the stability of tundra ecosystems in the conditions of depletion of the stratospheric ozone layer in the Arctic is discussed.

This study aims to implement a numerical scheme in order to find the eigenvalues of the Dirichlet-to-Neumann semigroup. This can be used to check its positivity for non-circular domains. This generalized scheme is analyzed after studying the case of the unit ball, in which an explicit representation for the semigroup was obtained by Peter Lax. After analyzing the generalized scheme, we checked its convergence through numerical simulations that were performed using FreeFem++ software.

In this paper, we study a nonlinear integro-differential Volterra equation with a fractional Caputo derivative. Based on techniques derived from a study of classical Volterra equations, namely Picard's iterative sequence and the product integration method, we propose a complete analytical and numerical study of this equation. Our study is closed by the development of two numerical examples.

We analyse red refinements of tetrahedral partitions and prove that the measure of degeneracy of some produced tetrahedra may tend to infinity if refinements are constructed in an inappropriate way. The maximum angle condition is shown to be violated in these cases as well.

The work considers problem of reconstruction of differential equations parameters, describing anomalous diffusion processes, on the base of known solutions. As a tool, is used the variational interpolation method elaborated by the authors earlier. The reconstruction time-dependence of diffusivity and determination of fractional time- and space-derivatives order in anomalous diffusion equation is demonstrated. There is shown a possibility of sufficient accuracy with insignificant computational expanses.

In this paper, we consider P ²₀- P ¹ mixed finite element approximations of a class of nonlinear parabolic equations. The backward Euler scheme for temporal discretization is used. Firstly, a new mixed projection is defined and the related a priori error estimates are proved. Secondly, optimal a priori error estimates for pressure variable and velocity variable are derived. Finally, a numerical example is presented to verify the theoretical results.

The paper presents the algorithm of exponential transformation (biasing) and its randomized modification with branching of a Markov chain trajectory for solving the problems of gamma-ray transport in an inhomogeneous medium. These algorithms were applied to a maximum (majorant) cross-section method or the Woodcock tracking which is extremely efficient for the simulation in an inhomogeneous medium. On an example of gamma-ray transport through a thick water slab containing a random amount of air or Al balls, the numerical study of the above algorithms in comparison with the standard simulation algorithm is performed.

In the present work, a numerical scheme is constructed for the approximation of a class of Volterra integral equations of the convolution type with highly oscillatory kernels. The proposed numerical technique transforms the Volterra integral equations of the convolution type into simple algebraic equations. By an inverse transform the problem is converted into an integral representation in the complex plane, and then computed by a suitable quadrature formula. The numerical scheme is applied for a class of linear and nonlinear Volterra integral equations of the convolution type with highly oscillatory kernels, and some of the obtained results are compared with the methods available in the literature. The main advantage of the present scheme is the transformation of a highly oscillatory problem to a non-oscillatory and simple problem. So a large class of a similar type of integral equations having kernels of a highly oscillatory type can be very effectively approximated.

In April 2017, the steppes mycobiota of the “Rostov” strict nature reserve and its environs were studied. Th ere are 75 species have been identified, of which 85 % belong to class Basidiomycota, and 15 % to Ascomycota. One species ( Cheilymenia dennisii ) firstly mentioned for Russia, eight species are first indicated for Rostov province, and 20 are new for the nature reserve. Among Basidiomycota, the largest groups are “aphyllophoroid” (29 species), “agaricoid” (17) and “gasteroid” (14). A number of species have been identified ( Polyporus rhizophilus , Gastrosporium simplex , Geastrum campestre , etc.) included in several Red Data Books of the steppe regions of Russia. A large number of rare and indicative species of fungi found in the “Rostov” state nature reserve characterizes this territory as an important site for the conservation of the steppe mycobiota of Eurasia.

Taxonomic studies were conducted in the largest herbarium collections in Russia (ALTB, IRK, KFTA, LE, LECB, MW, MHA, MOSP, NS, NSK, PERM, PGFA, SVER, TK, VBGI, VLA) and abroad (BM, E, EWH, G, K, KB, P, SNU, W, WU, Z), which allowed to continue the typification of names in the genus Primula L. The lectotype (LE01024083), synthype (LE01024084) of P . macrocalyx Bunge and lectotype of P . maximowiczii Regel (LE01032003 ) were determinated.

The ways of preserving 46 Siberian species of the genus Viola L. are presented. It is established that 98 % of species are protected under natural conditions (specially protected natural territories and lists of Red Books) or in introductory centers. The possibilities of recovery of natural populations are considered.

On the basis of revision of herbarium SASY (Yakutsk) a review of species of the genus Castilleja Mutis ex L. f., growing in Republic of Sakha (Yakutia) is made. Herbarium collections reliably confirmed the occurrence on the territory of the Republic of Sakha (Yakutia) of 9 species of Castilleja and 2 species ( C. caudata (Pennell) Rebr. and C. elegans Malte) are given on the basis of literature data. In the result of morphological features analysis and characteristics of distribution of yakut species materials were identified which were described as new species C. galaсtionovae E.G. Nikolin and new variety - C. rubra (Drob.) Rebr. var. multicaulis E.G. Nikolin. Key for determination of species and data on their distribution in Yakutia are presented.

Veronica serpyllifolia ssp. serpyllifolia is a plant with a daily rhythm of fl owering and obligate autogamy, which retained some of the features entomophilous character in the structure of the flowers. Adichogamy and self-compatibility provide the contact autogamy.

Classification and ecologo-coenotic analysis results of alders of the Altai-Sayan Mts. is presented according to the Braun-Blanquet approach. Communities belong to four associations, three of them ( Doronico altaici-Duscheki etum fruticosae , Bergenio crassifoli-Duschekietum fruticosae and Athyrio distentifoliae-Duschekietum frutico sae ) is included in the class Mulgedio-Aconitetea (alliance Trollio asiaticae-Crepidion sibiricae , order Trollio- Crepidetalia sibiricae ) and association Carici iljinii-Duschekietum fruticosae ) is included in the class Loiseleu rio-Vaccinietea (alliance Empetro-Betulion rotundifoliae , order Betuletalia rotundifoliae ).