Home – Home – Jornals – Journal of Applied Mechanics and Technical Physics 2017 number 2

This paper presents a new concept for studying the spatio-temporal modes of laser generation in which several time scales coexist in the emission (one of which is related to the resonator round-trip time). The essence of the concept is that the time dependence of the intensity is investigated in two dimensions, one of which corresponds to the evolution over sequential resonator round-trips. It is shown that fiber lasers of various types, e.g., quasicontinuous lasers and passive and active mode locked pulsed lasers, has a diversity of spatio-temporal generation modes. The possibility of experimental detection of localized structures, including solitons, in fiber laser radiation is demonstrated. The prospects of the proposed approach are discussed.

A method of layer-by-layer heterodyne analysis of volume optical media is described. The results of theoretical evaluation, computer modeling, and experimental investigation of the dependence of the maximum speed of analysis of the parameters of the optical circuit and medium are given. The effect of the analysis speed on the resolution of the method for the thickness of the optical medium and on the nature of the dependence of the output signal on the depth of the studied layer is evaluated. A method for increasing the maximum scanning speed is proposed. Results are confirmed experimentally.

A method is developed to ensure precise alignment of the origin of a polar coordinate system in which the laser beam position is defined in writing diffractive optical elements with the optical blank rotation axis. This method is used to improve the accuracy of a circular laser writing system in writing large-scale diffractive optical elements in a polar coordinate system. Results of studying new algorithms of detection and correction of positioning errors of the circular laser writing system in the course of writing are reported.

The dynamics of the crystallization front induced by the temperature gradient at the upper boundary of a horizontal layer of water bounded by flat thermostatted surfaces is studied. The formation and evolution of convective structures are visualized by methods of the Hilbert optics and digital video recording. The difference in the temperatures of the upper ( T₁) and lower ( T₂) thermostats satisfies the condition T ₁ < T₂. In this system, the temperature of the cooled upper surface is an order parameter. Reaching a critical value of this parameter leads to a bifurcation phase transition from the liquid state (supercooled water) to the solid state (ice). The velocity and shape of the crystallization wave front are determined. The spatial-temporal state of the crystallization wave is found, in which the wave front shape is a line of equal velocities. The dynamic profile of the isothermal surface bounding the spatial shape of the solid phase is visualized.

The information system "Electronic Structure of Atoms" for atomic spectroscopy is proposed. Information on the size and characteristics of the website data base is given, and the database parameters are compared with reputable world analogs. Scientific data visualization tools implemented in the form of spectrograms and Grotrian diagrams in the system are considered. It is shown that the classified levels and transitions in tabular and graphical forms are presented more fully than in similar information systems. The efficiency of using the information system "Electronic Structure of Atoms" to solve various research tasks, including the analysis of the electronic structure of atomic systems, and to prepare experts is discussed.

An algorithm is proposed for processing phase images with the use of computing power of graphics processing units (GPUs) for three-dimensional geometry measurements by means of phase triangulation. It is shown that implementation of the phase image decryption algorithm on the GPU is faster by more than 100 times than on the central processing unit (CPU). Practical implementation of the proposed approach can substantially improve the performance of phase triangulation methods.

A problem of construction of a robust regulator for a nonaffine nonstationary a priori uncertain dynamic object with a delay. The quality of operation of the constructed control system is illustrated through simulations.

A new approach is proposed for detection of suspicious objects in X-ray images for security assurance. The approach is based on using the statistical model of the image for detecting anomalies. The model is designed with the use of the "bag-of-words" with context definition of the word coordinates in the image in forming the statistical pattern. It is experimentally demonstrated that this approach ensures adequate approximation of the result of detection of suspicious objects by humans.

The method of image classification with its preliminary transformation to principal components and with the use of the Hilbert-Huang transform is studied by an example of neural network classification of a hyperspectral image. The efficiency of the method is demonstrated through comparisons with traditional methods of neural network classification with the use of spectral components as attributes and principal components without involving spatial information. Radial-basis and complex neural networks are used for classification.

Interpolation methods for developing digital terrain model using geoinformation system data are considered. For this purpose, the best-known methods are analyzed: inverse distance weighting (IDW), kriging, ANUDEM, spline interpolation, the natural neighbor method, and the method based on the construction of a triangulation irregular network (TIN) model). The modeling accuracy is estimated for a terrain located between the Ui, Tara, and Irtysh Rivers in the Omsk region of West Siberia (Russia). Analysis of the results of estimating the accuracy of a digital terrain model developed using the ArcGIS 10 geoinformation system shows that the best results were obtained using spline methods and inverse distance weighting.

This paper describes the development and implementation of a microresonator based on a semiconductor Bragg reflector and a microlens selectively positioned above a single InGaAs quantum dot (111). The microresonator constructor provides effective pumping of quantum dots and high external quantum radiation output efficiency. This microresonator can be used to create single-photon and photon-pair emitters entangled in polarization and based on single semiconductor quantum dots.

The mechanism of charge transport in MIS structures on the basis of thin hafnium and zirconium oxide films is studied. It is shown that transport in the studied materials is limited by photon facilitated tunneling between traps. From the comparison of experimental current-voltage caracteristics of MIS structures n -Si/HfO₂/Ni and n -Si/ZrO₂/Ni, the estimated, thermal, and optical energies of traps are determined. It is shown that oxygen vacancies are localization centers (traps) of charge carriers in HfO₂ and ZrO₂.

This paper demontstrates the possibility of developing a high-voltage waveguide photodetector comprised of Schottky diodes and based on a Au/Ge - Si structure with Ge quantum dots pseudomorphic to a silicon matrix, which ensures an increase in the external quantum yield and open-circuit voltage. It is shown on this photodetector that there is a great increase and broadening in sensitivity up to λ = 2.1 μm, which coincides with the main radiation range of a black (gray) body at the emitter temperatures from 1200 to 1700 ºC, practically used in thermal photogenerators. This state of the ensemble of Ge quantum dots by means of molecular beam epitaxy can be obtained only under the condition of low growth temperature (250-300 ^oC). It is established that, below the Si absorption edge, photoresponse on the photodetectors under consideration is determined by two main mechanisms: absorption on the ensemble of Ge quantum dots and Fowler emission. It is shown by the analysis of the Raman scattering spectra on the optical photons of Ge - Si structures that the quantum efficiency of photodetectors based on them in the first case is due to the degree of nonuniform stress relaxation in the array of Ge quantum dots. The photoresponse directly associated with the Ge quantum dots is manifested on Schottky diodes with a hyperfine intermediate oxide layer SiO2, which eliminates the second mechanism. In further development, the proposed photodetector architecture with pseudomorphic Ge quantum dots can be used both for portable thermal photogenerators and fiber-optic data transmission systems at wavelengths corresponding to basic telecommunication standards (λ = 0.85, 1.3, and 1.55 μm) on the basis of silicon technologies.

This paper describes the stochastic models of electron-hole recombination in inhomogeneous semiconductors in two-dimensional and three-dimensional cases, which were developed on the basis of discrete (cellular automation) and continuous (Monte Carlo method) approaches. The kinetics of the particle recombination in pure diffusion and diffusion with tunneling is studied. Certain difference between the behavior of electron-hole spatial correlations calculated by discrete and continuous models and the nature of segregation formation in three-dimensional semiconductors associated with that behavior is revealed. The comparative analysis of the simulation characteristics determined via cellular automatic and continuous recombination models is carried out.

A mathematical model is proposed and analytical solutions are constructed for the problem of the growth of a hydrate layer during contact of gas and water for two limiting regimes of gas hydrate formation, determined by mass transfer and heat transfer. Critical values are obtained for thermal parameters and for parameters that determine the flow properties of the hydrate layer (diffusion coefficient and permeability), on which the hydrate formation regime depend.

The interaction of a shock wave with turbulent flow has been experimentally investigated. The case where the shock wave formed on one end of the tube, passed through the interface between two resting gases with different densities (air-CO₂ or air-Ar), reflected from the end of the tube and interacted with turbulent mixing zone formed at the contact boundary. The Mach number of the shock wave incident on the interface in air was M ≈ 2.37-2.57. The flow field was recorded using schlieren method and high-speed video recording. It is found that after passing the mixing zone, the shock-wave front is deformed and becomes unstable.

The accuracies of measurement of the velocity field using clinical and research magnetic resonance scanners were compared. The flow velocity was measured for a fluid simulating blood in the carotid artery model connected to a programmable pump. Using phase-contrast magnetic resonance tomography, velocity distributions in the carotid artery model and were obtained and compared with the analytical solution for viscous liquid flow in a cylindrical tube (Poiseuille flow). It is established that the accuracy of the velocity measurement does not depend on the field induction and spatial resolution of the scanners.

This study is focused on the heat and mass transfer effects in a magnetohydrodynamic (MHD) flow of a viscous nanofluid saturating a porous medium past an exponentially radiating stretching sheet. The governing differential equations are transformed to a system of nonlinear ordinary differential equations by suitable transformations. It is noted that stratification affects the local Nusselt and Sherwood numbers.

An attempt is made to study a steady two-dimensional flow of a viscous incompressible fluid incident at some angle onto a plate lubricated with a thin layer of a power-law fluid. Similar and nonsimilar solutions of the governing partial differential equations are obtained numerically by imposing the continuity of velocity and shear stress at the interface layer between the fluid and the lubricant. The Keller box method is applied to obtain the solutions. The limiting cases for full and no-slip conditions are compared

An unsteady double diffusive mixed convection boundary layer flow over a vertically stretching sheet in the presence of suction/injection is investigated in this paper. The governing partial differential equations are reduced by applying suitable transformations to a set of nonlinear ordinary differential equations, which is solved by the Keller box method. The influence of various flow parameters on the velocity, temperature, and species concentration profiles of the fluid is studied. The effect of some problem parameters on the skin friction coefficient in the presence of suction/injection is considered

Numerical simulation was performed to study convective structures in a thin silicone oil layer heated from below, whose free surface is exposed to air flow, generating a drift current. Transformation of the basic equations to a form suitable for spectral methods is proposed. The steady flow velocity profile obtained under laboratory experiment conditions is calculated. It is shown that increasing the Reynolds number leads to the transition from the polygonal convective cells to longitudinal (elongated along the flow) rolls. The dependence of the transitional Reynolds number on the temperature on the lower boundary of the layer is obtained. The calculation results are compared with experimental data.

The structure and heat transfer in a turbulent separated flow in a suddenly expanding channel with injection (suction) through a porous wall are numerically simulated with the use of two-dimensional averaged Navier-Stokes equations, energy equations, and v²-f turbulence model. It is shown that enhancement of the intensity of the transverse mass flux on the wall reduces the separation region length in the case of suction and increases the separation region length in the case of injection up to boundary layer displacement. The maximum heat transfer coefficient as a function of permeability is accurately described by the asymptotic theory of a turbulent boundary layer.

The stability of steady convective flow in an inclined plane fluid layer bounded by ideally thermally conductive solid planes is studied in the presence of a homogeneous longitudinal temperature gradient under unstable stratification conditions where the layer is inclined so that the temperature is higher in the lower part than in the upper part. It is shown that the inclination leads to the transition from critical perturbations to long-wave helical perturbations. Stability maps of flow regimes are given for the entire range of Prandtl numbers and inclination angles corresponding to unstable stratification.

The radial angular temperature distribution in a porous medium with nonuniform permeability is investigated by numerical simulation of nonisothermal filtration of live oil taking into account the degassing heat, the Joule-Thomson effect, and the adiabatic effect. It is shown that nonuniform permeability in the wellbore zone of the porous layer leads to anomalous cooling due to intense degassing in the well-permeable zone.

Estimations of CO₂ emission and net ecosystem exchange (NEE) between atmosphere and bog surface were made in south taiga of European Russia for summer seasons of 2013-2015. Flux measurements were carried out by static chamber method every 7-10 days on 3 homogeneous in soil moisture and vegetation type experimental sites. Statistically significant distinctions of NEE and CO₂ fluxes were found between different experimental sites. It has been established that bog significance in CO₂ balance to atmosphere should be assessed with regard to the spatial heterogeneity of bogs.

The results of long-term evaluation of carbon stock and current carbon sequestration based on the example of pine-dwarf shrub-sphagnum biogeocoenoses on Vasyugan mire are given. In different climatic conditions (different years) NРP varies from 206 to 337 g C m^-2 x year^-1. An increase in intensity of carbon emissions was revealed in drier vegetation periods. Most of the carbon losses are determined by emission of carbon dioxide (the average is 61.3 g C m^-2 x year^-1, or 23.5 % of NPP). Progression of peat formation may be stated. The removal of the carbon by mire waters calculated by the mathematical model is 3.0 % of NРР with an average value of the removal of 7.9 g C m^-2 x years^-1. On the basis of the model of vertical growth of mires was calculated present-day rate of carbon accumulation from 10.3 g C m^-2 x years^-1 in polygonal mires to 51.7 g C m^-2 x years^-1 in grassy mires.

Based on the example of Krivoye Lake (North Karelia) dependence of productivity of lake ecosystems on geographical, climatic conditions, and drainage terrestrial production is described in the form of dynamic mass-balance model. A model algorithm is presented. It has been concluded that at natural interannual fluctuations of nutrient loads and owing to absence of anthropogenic influence Krivoye Lake has been keeping the status of oligotrophic waterbody over more than 40 years.

The results of study of the ratio of hydrothermal (temperature and precipitation) conditions and ecological spectrum of the flora of vascular plants of the Tom river basin are presented. On the basis of the calculated coefficients of linear correlation between average monthly temperature data and sediments and environmental groups of model basins, it was found that the influence of the main parameters of hydrothermal regime (temperature and precipitation) on the plains and in the mountains, in varying degrees, affected the ecological spectrum of the flora. Hydrothermal conditions of the cold period of the annual cycle have the greatest impact on environmental features.

Historical changes in distribution of animals in European Russia are of permanent interest to specialists. To this end information contained in the Economic Notes to the General Land Survey of the Russian Empire (XVIII-XIX centuries) is of particular importance. The article presents the first results of the data analysis of mammalian fauna in the boreal forests of European Russia. The data are contained in a systematic sampling arranged on the basis of the Economic Notes and cover 7 provinces, 32 counties, and 377 specific dachas. There are 1774 animals mentioned (21 names of animals (species), 10 families and 5 orders). A comparison of distribution of certain species the most characteristic and significant for boreal forests in XVIII-XIX centuries and at the present time has been made.

The site of open shallows of the Volga Reach in the Rybinsk Reservoir (Volga) subjected to impact of common heron colonies was studied in 2009-2011. Some changes in phytoplankton community composition typical of water trophic level rise were noticed. Floristic wealth reduction along with increase in biomass due to phytophlagellates - cryptophytes, euglenales, dinophytes and chrysophytes, as well as flagellar forms of green algae were registered at the heronries. Changes in phytoplankton communities were temporary and connected with herons nesting period, which allows to treat the studied site as “traumatic” ecotone.

Traphic relationships were examined for macroinvertebrates and fish inhabiting St. Petersburg methane seep (Central part of lake Baikal, ~1400 m depth). The analyses of the values of carbon and nitrogen stable isotopes showed that all animals associated with the seep were heterotrophs with different feeding strategies, symbiotrophs were absent. Seep enimals consumed combined food with different portion of methane derived carbon ranged from 2.7 to 89 %. The average values of the δ¹³С varied from -26.2 ‰ (in benthopelagic amphipods) to -64.5 ‰ (in gastropods). The trophic food web of the methane seep consisted of filter feeders (pelagic amphipods TP 1.9), detritophages (gastropods TP 2.2 and burrowing amphipods TP 2.1), polyphages (nectobenthic and bentho-pelagic amphipods TP 2.8-3.2), and predators (flat worms TP 3.6-4.2 and cottoid fish TP 3.0-3.8). Animals occupying the similar trophic positions differed significantly in the δ¹³С values and utilized partly overlapping different food components.

The aim of the current study was to assess synergistic effect of thermal stress, pollution and parasitic infestation on the activity of antioxidant enzymes (peroxidase, catalase, and glutathione-S-transferase) in different populations of the wide-spread species of pulmonate mollusk Lymnаea stagnаlis distributed in the Belarus Republic water bodies. It has been shown that the combined influence of anthropogenic effect and parasitic infestation on the one hand and experimental hyperthermia coupled with the parasitic invasion on the other hand affect the activity of peroxidase. The combined impact of parasitic infestation and contamination of the reservoir leads to the change of the catalase activity. No significant correlations between the studied factors and the activity of glutathione-S-transferase were found. The simultaneous exposure to elevated temperature, pollution and infectiousness of mollusks does not affect the activity of the studied enzymes.

The research was conducted in the southern part of the forest-steppe zone of West Siberia (Novosibirsk oblast’). The spatial-temporal structure of the spider community was studied at the continuous chain of habitats (180 m long) from the central part of small birch-aspen forest to the center of meadow site. We applied two sampling methods which completed each other: pitfall trapping and hand separating soil samples. Over 5000 specimens of spiders from 83 species and 14 families were collected during 2007-2008. Spiders are most abundant in June and less abundant in July. Representatives of different families are maximally abundant in different sites: Lycosidae and Gnaphosidae mainly in the forest, and Philodromidae - in the solonetz meadow. The distribution of diversity and abundance of spiders and carabids through the habitat gradient is generally similar. This is controversial compared to the spatial interactions of these two groups of predatory arthropods in extreme ecosystems: in Arctic and near saline lakes. Niche distinguishing between carabid and spider species is not only topical. It includes use of different strata of vegetation, various seasonal activity and trophic specialization.

The following biomarkers of oxidative stress: catalase (CAT), glutathione-S-transferase (GST), glutathione and reductase (GR) activities as well as malondialdehyde and reduced glutathione content and heavy metal concentrations (HM) were studied in Dreissenа polymorpha tissues. Mussels were collected on three sites located in the Rybinsk reservoir differing in the levels of anthropogenic load: more polluted sites 1 and 2 and relatively clean site 3. Mussels from sites 1 and 2 had higher concentrations of HM and their response to pollutants’ action was manifested in increased processes of LPO, activation of CAT and elevated level of GHS.

The distribution of bioorganic components and compounds of anthropogenic and mixed origin in the sediments of freshwater lake Black and salt one Tus (Khakasiya) was studied by the method of gas chromatography-mass spectrometry. The contribution of major sources of organic matter to the bottom sediments was evaluated. It was found that the formation of the composition of the bottom sediments was mainly due to compounds of biogenic and mixed origin. The sites with high concentration of contaminants: pyrogenic and oil hydrocarbons and izoalkilbenzols - possible products of surfactants degradation were revealed.

The present work is performed to study the effect of heat generation on fully devel-oped flow and heat transfer of micropolar fluid between two parallel vertical plates. The rigid plates are assumed to exchange heat with an external fluid by convection. The governing equations are solved by using Crank–Nicolson implicit finite difference method. The effects of governing parameters such as transient, heat generation, mi-cropolar parameter, Prandtl number, Biot number, and Reynolds number on the veloc-ity and temperature profiles are discussed. It is found that the presence of heat generation enhances the velocity and temperature of the micropolar fluid at the middle of the channel.

The nonlinear problem of non-stationary heat conductivity of the layered anisotropic heat-sensitive shells was formulated taking into account the linear dependence of thermal-physical characteristics of the materials of phase compositions on the tem-perature. The initial-boundary-value problem is formulated in the dimensionless form, and four small parameters are identified: thermal-physical, characterizing the degree of heat sensitivity of the layer material; geometric, characterizing the relative thick-ness of the thin-walled structure, and two small Biot numbers on the front surfaces of shells. A sequential recursion of dimensionless equations is carried out, at first, using the thermal-physical small parameter, then, small Biot numbers and, finally, geome-trical small parameter. The first type of recursion allowed us to linearize the problem of heat conductivity, and on the basis of two latter types of recursion, the outer asymptotic expansion of solution to the problem of non-stationary heat conductivity of the layered anisotropic non-uniform shells and plates under boundary conditions of the II and III kind and small Biot numbers on the facial surfaces was built, taking into account heat sensitivity of the layer materials. The resulting two-dimensional boundary problems were analyzed, and asymptotic properties of solutions to the heat conductivity problem were studied. The physical explanation was given to some aspects of asymptotic temperature decomposition.

The growth rate of the liquid contact layer may be influenced by an electric current at contact melting. Depending on the direction, the electric current speeds up or slows down the liquid layer growth in comparison with the diffusion regime (no-current mode). It is shown that if the current flowing in the "accelerating" direction is de-creased inversely proportional to the square root of time, the time law of the liquid layer growth will be identical to the diffusion mode. The proposed pseudo-diffusion mode is implemented for the bismuth-indium system at 75°C. Results of calculations of the mobility and the effective charge of the melt ions are presented.

Solidification of liquating silicate magmatic melts may lead to formation of rare earth mineral deposits. By the example of quasi-binary system SiO₂–Sc₂O₃, the processes of cooling and directional solidification of the melt in an intrusive chamber have been studied, and velocities of the phase fronts and the width of the phase separation field have been calculated. Using the fluctuation approach, the physical and mathematical model of the formation and growth of dispersed phase in the continuous cooling of liquating melt was developed, and the conditions of incorporating the dispersed inclu-sions by solidified matrix phase were determined. The proposed model allows obtain-ing quantitative estimates of the size and number of inclusions per unit of hardened rock, depending on the solidification conditions and the initial chemical composition of the melt.