Home – Home – Jornals – Atmospheric and Oceanic Optics 2021 number 8

The dependence of limit of detection of Mg, Mn, Sr, Pb, Al, and B in aqueous solutions by femtosecond laser induced breakdown spectroscopy on the laser pulse repetition rate is studied. It is shown that at pulse repetition rates from 50 to 1000 Hz and under the same other experimental conditions, the best limits of detection for all elements are achieved at a laser pulse repetition rate of 166 Hz.

The results of comparative studies of the ratio of aerosol fractions in the surface air and snow layers chronologically linked to stratigraphically significant snowfalls are presented. Probable paths of winter air masses were reconstructed using backward trajectories calculated with NOAA HYSPLIT_4 model and gridded meteorology NCEP/NCAR Reanalysis. It is shown that the features of the formation of the winter aerosol field within the Ob-Tomsk interfluve are mainly associated with winds with a southern component.

The paper presents the results of the study of the Umov effect for large compare to the wavelength of the incident radiation nonspherical particles. The calculation was carried out for particles with maximal sizes of 100, 140, 170 and 200 microns. The results were obtained for 210 different refractive indices, the real part of which varied from 1.3 to 1.6 with a step of 0.5, the imaginary part varied from 0 to 0.1344. It has been shown that the Umov effect is fulfilled for all the particles when the imaginary part of the refractive index is less than 0.001.

The role of heat fluxes in phytoplankton production during the summer heating of Barguzin Bay of Lake Baikal was explored using mathematical modeling. The results of numerical experiments showed effects of longwave radiation and latent and sensible heat fluxes on phytoplankton growth in the upper layers. This study found that the largest concentrations of phytoplankton biomass are localized at some distance from the mouth of the Barguzin River.

The optical scheme and technical characteristics are described of an experimental setup for atmospheric studies of a possibility of compensating for aberrations of the initial wavefront of an optical beam by the aperture sensing technique based on the signal of atmospheric backscatter of radiation from an additional laser source.

The results are presented of experimental studies of a possibility of compensating aberrations of the initial wavefront of an optical beam by the aperture based on the atmospheric backscatter signal of radiation from an additional laser source at a different wavelength. It is shown that the makes it possible to reduce the beam wavefront aberrations by several times, down to 1-2 wavelengths at optimal angles of view of the scattered radiation receiver. As a result, the distortions of the intensity distribution in a beam cross section and beam divergence decrease and the power in the beam paraxial region increases.

The pressure jump method was used to determine the energy release in an apokampic discharge at various air pressures. The maximum energy release and electroluminescence in the NUV spectral range are achieved in the pressure range from 85 to 92 Torr, which roughly corresponds to the formation heights of such optical phenomena in the middle atmosphere as blue jets, starters, and giant jets. The facts found make it possible to supplement the picture of the formation of these phenomena.

An algorithm for estimating sizes of regions affected by cloudiness on the errors of retrieval the reflection coefficients of the Earth’s surface areas observed through gaps in a cloudy field is suggested. The algorithm is based on statistical simulation by the Monte-Carlo method of the process of radiation transfer through broken stochastic cloudiness. Two stochastic models of cloudy fields are considered: 1) clouds shaped as parallelepipeds and 2) clouds shaped as paraboloids. The method is tested for two fragments of actual MODIS images. It is shown that the broken cloudiness influences the error in the reflection coefficient retrieved at distances from 5-7 to 25 km from the observation point (depending on the observation conditions).

A brief description of measuring means, a free-oscillation setup with a transverse sting of the model, and test conditions is reported. A procedure for processing experimental data is described. Quasi-steady and damping aerodynamic characteristics of the pitching moment of the model in the range of Mach numbers M = 1.75-6 are obtained. A comparison of research results with calculated data, as well as with the previous experimental data obtained using the base sting is given. It was found that at M = 3-6 regular undamped oscillations of the model are excited.

A new and intuitive method for evaluating the efficiency of the compression process in a supersonic air intake is proposed. The method is based on a comparison of the geometric compression ratio of the flow tube in the air intake under consideration with the maximum possible isentropic compression. It is shown that a higher value of the geometric compression ratio in the air intake allows obtaining higher thrust characteristics, with other conditions being identical.

The influence of ice crystals in an air flow on evolution of run-back ice on the surface of the wing model is numerically investigated for the conditions of experiment in an icing wind tunnel. The results confirm that a change in the mass of ice deposits upon introducing crystals into the flow observed experimentally is associated with absorption of some mass of ice crystals by the water film formed on the surface of a solid at low flow velocities and with film splashing at higher flow velocities. In the first case, the mass of the run-back ice increases; in the second case, it decreases.

Relations for the coefficients of transformation of disturbances to pressure oscillations for the case of long-wave disturbances of the external flow are derived from the general analytical solution of the inviscid problem of disturbance interaction with an oblique shock wave on a wedge. Numerical simulations of interaction of long-wave disturbances with a shock wave on a flat plate aligned at an angle of attack in the interval 5°- 20° for a viscous flow regime are performed. Deviations of the transformation coefficients simulated for the viscous case from the inviscid analytical solution in the long-wave approximation are calculated, and corrections for viscous-inviscid interaction in the analytical solution are obtained.

The paper describes how the acoustic impact on an impinging jet induces a maldistribution in the radial velocity field within the nearwall zone of spreading jet. The r.m.s. velocity pulsation level in the nearwall jet is lower than in the natural jet. A higher length of the laminar flow zone in a microjet was noted. The development of sinusoid-type instability facilitates a higher combustion efficiency for a propane-butane fuel mixture in the impinging microjet; this reduces the soot emission. The tests demonstrated that the zero acoustic impact makes the flame spectrum more yellow (including the flame from the nearwall zone). This testifies about deficiency of oxidizer (air) and soot presence in the combustion products. The combustion efficiency for diffusive flame in the impinging jet depends on the nozzle diameter and nozzle-target distance.

A turbulent circular jet with variable density caused by the mixing of air with gases of different densities (air, helium, and carbon dioxide) is studied. The Reynolds number is fixed for all cases: Re = 5300. Using proper orthogonal decomposition and direct numerical simulation data, a comparative analysis of the three gases under consideration is carried out. It is shown that with a decrease in the ambient gas density, the frequency of coherent structures formation drops, and the number of proper orthogonal decomposition (POD) modes necessary for constructing a low-dimensional flow model decreases.

The paper studies the transfer of angular momentum across the interface of two immiscible liquids in a closed vortex flow, generated in a stationary cylindrical container by a rotating disk, being the upper endwall of the cylinder. When the disk rotates, a centrifugal force begins to act on the upper less dense liquid, which leads to the appearance of a centrifugal circulation of the upper liquid. Since the swirling flow of the upper fluid along the sidewall moves from the rotating disk to the interface, it transfers the angular momentum to the interface, thereby swirling the lower fluid as a result of the action of viscous friction. A forced circulation of the lower fluid arises. Flow visualization and measurement of the circumferential velocity component serve to determine the regularities of the formation of a vortex flow of a denser liquid located under the interface and having no direct contact with the solid disk generating the vortex motion. The development of the centrifugal circulation of the lower liquid is found to be similar to that in a monofluid. The obtained results are of interest for further development of vortex devices and reactors that provide complex vortex motion of ingredients for mass transfer enhancement, optimization of the operation of existing units and for the design of new devices.

The influence of the stagnation temperature of the accelerating gas flow and that of nozzle travel speed on the deposition efficiency are studied when depositing single Cu-coating tracks by the cold spray technique. The experiments performed clearly show that the nozzle traverse speed substantially affects the value of measured deposition efficiency: the higher is the nozzle traverse speed, the lesser the measured deposition efficiency turns out to be at all other things being identical. Such a behavior can be explained by the fact that the first impacts of particles onto the substrate do not lead to their adhering to the surface and, hence, to coating deposition. It is known that, before the coating starts to grow, it is necessary for the substrate surface to be subjected to a sufficient number of particle impacts. This preparatory stage is called the activation stage, or the delay (induction) stage of the deposition process. It is shown for the first time that the specific (per unit area) mass of the powder consumed at the activation stage depends on the stagnation temperature of the accelerating gas flow: the higher is the stagnation temperature, the lower is the specific mass consumed.

The heat-induced variations in material properties for a layered glass-metal composite material were studied for the case of induction heating and the subsequent composite annealing of the sample. A cylindrical sample of the composite (outer metal cylinder covering the glass cylinder) was used in our experimental study. This sample is an imitation of a brittle rock under a high stress. The simulation complexity originates from superposition of the glass point transition within the glass layer, induction heating for the whole sample, and heat radiation from the external metallic surface. Structural and mechanical relaxation processes in glass are calculated using the Boltzmann-Volterra superposition and the Tula-Naraiswami-Mazurin-Moynihan (TNMM) model based on introducing a structural temperature as an additional parameter. The paper offers a mathematical model and a simulation method for calculating the temperature field and material properties distributions during the composite production process. The simulation results are presented for various regimes of heating and for glass-metal composite properties. This approach is useful for evaluating the operation modes of the glass layer annealing and for estimating the evolution of laminated composite materials.

The development of a convective flow after sudden heating of a vertical wall that laterally bounds a layer of ethyl alcohol in a system consisting of vertical layers of alcohol and air, separated by a thin metal partition, is studied numerically in a conjugate problem statement. The equations of thermogravitational convection in the Boussinesq approximation, written in variables of temperature, vortex, and stream function, are solved by the finite element method. The development of unsteady hydrodynamic and thermal boundary layers on all four vertical walls is studied. The temperature fields in liquid, gas and in a vertical partition are calculated. The features of the development of the spatial form of the flow and unsteady conjugate convective heat transfer between the layers of liquid and gas affect significantly the unsteady temperature fields and temperature gradients in a thin metal partition. The maximum temperature gradients in the partition appear at the initial stage of flow development.

Based on the known calculated and experimental data on distribution of temperature and gas compositions near the flame front in jets, it is shown that the nature of a change in the total enthalpy during combustion of mixed and unmixed reagents depends on the molecular properties of gases to different extents, but in the same way. Systems with Lewis numbers less than one have a maximum in the enthalpy profile; if the Lewis number is greater than one, a minimum appears near the flame front. Data on heat fluxes associated with thermal conductivity and diffusion are obtained. It has been found that during combustion of unmixed reagents, the heat flux carried by diffusion is an order of magnitude less than the flux carried by thermal conductivity. For mixed reagents, the heat fluxes carried by diffusion and thermal conductivity exceed the heat fluxes in the flame of unmixed reagents.

Transient processes are experimentally investigated at the initial stage of heat and mass transfer with steam absorption on the surface of 57.8% water solution of lithium bromide in a bath with a diameter of 70 mm. The experiments were carried out both with a pure solution and with a solution where n -octanol surfactant was added. It is shown that with a sharp steam pressure increase in the volume above the surface of an absorbing solution, local temperature inhomogeneities are generated on the solution surface. The growth rate of these inhomogeneities is proportional to the growth rate of the steam pressure. It was found that, in contrast to the solution without surfactant, where convective flow is observed only during a short time interval after steam supply to the absorber, in a fixed layer of water LiBr solution with surfactant addition, there is stable thermocapillary convection in the near-surface layer of solution during absorption. It is shown that for variable bottom topography, there can be space-localized zones, where the temperature on the solution surface is determined by the shape of bottom topography.

The paper presents the experiments on irradiation of the yttrium oxide powder target with a relativistic electron beam and evaporative production of yttrium oxide nanopowder. The phase and chemical consistence, specific surface and particles geometry of nanopowder was studied. A model of mass productivity of nanopowder vs. input e-beam power was tested qualitatively. The effect of continuous operation of setup on the filter catching capacity was studied. A phenomenon of a tubular-shaped structure growing from the hot targeting point toward the electron beam direction was described.

The solubility of heavy alkali metals in liquid lithium was investigated at temperatures from the melting point of Li to ~1200 K by the method of gamma-raying of liquid samples by a narrow beam of gamma radiation. Even at high temperatures, the solubility of K, Rb, and Cs in liquid lithium has been found to be very insignificant. The potassium content in the lithium-rich phase is 0.2 at. % at 850 K and 3.4 at. % at 1212 K. The solubility of rubidium in liquid lithium, within the measurement error, is zero at temperatures from 453 K (melting point of Li) to 800 K and reaches only 0.5 at. % at 1172 K. Cesium is practically insoluble in liquid lithium up to a temperature of 1150 K.

The propagation of a flame over the surface of a liquid fuel deposited on a substrate with low thermal diffusivity has been studied. It has been shown that this system-fuel and substrate - is not thermally thin. Heat transfer in front of the flame edge due to the motion of the liquid under the temperature gradient in the liquid layer (the Marangoni effect) has been analyzed. Estimates of temperature gradients in the condensed phase, the thickness of the liquid fuel layer in front of and below the flame front are given. The velocity of the diffusion flow of the fuel in the gas phase at the flame edge is estimated. It is shown that the temperature gradient along the surface of the liquid film determines the velocity of the film and the rate of diffusion of the evaporated fuel to the flame edge.

The initial (linear) stage of the development of rotating transverse detonation waves in a flat-radial annular combustion chamber is determined and simulated. The problem of linear mode stability of the cylindrical front of Chapman-Jouguet deflagration combustion in a radially diverging subsonic flow with a small Mach number in the presence of perturbation waves of the flow entropy is solved. The steady flame front is described by discontinuity of the gas-dynamic parameters provided that the combustion products are in chemical equilibrium. It is revealed that the flame front is unstable for some types of small perturbations of the main flow of the combustible mixture and the flame front. Instability is determined under the condition of a constant flow rate in the mixture injection system. The spatial forms of oscillations and perturbation waves of the combustion front in the annular combustion chamber are obtained by numerical and analytical methods.

Zero-dimensional computations of nanosecond-order ignition using a nanosecond discharge are performed with two constraints. The effects of these constraints are assessed to study the experimental rapid pressure change properly at the initial stages. The computations are carried out with the following constraints: constant internal energy and volume (U&V) and constant enthalpy and pressure (H&P), revealing differences between the two solutions. As the pressure remains constant under the H&P constraint, the total number density of all species decreases during ignition. In this case, O radicals are less generated and consumed. The progression of all reactions and temperatures increases under the H&P constraint less intensely than under the U&V constraint. Significant differences are found between the results calculated under the U&V and H&P constraints. Therefore, large discrepancies with real phenomena can be caused if the loss due to pressure reduction is not treated well.

Provision of stability of the operation process in solid-propellant rocket motors is an integral aspect of engine design and operation. The present paper describes a numerical and experimental method of determining the linear stability of the operation process in a solid rocket motor with an axisymmetric combustor. The method is based on solving a linearized system of equations that describe the dynamics of solid propellant combustion products in the frequency domain. The values of acoustic conductivity of the solid-propellant combustion region obtained in a pulse T-burner are used as the boundary conditions. Verification of the method is performed on the basis of numerical and experimental data obtained for six model engines. Results of stability computations for the operation process in an engine with a large aspect ratio operating on a metallized propellant are reported.

The effect of the ratio of the components of mixtures of nickel (II) oxide with titanium on the modes and rate of combustion of compositions based on them has been studied. It is found that under normal conditions, a change in the mass content of nickel oxide from 75 to 30 % leads to a natural change in combustion modes: fire flame, a multi-stage mode, and a self-oscillating mode with periodic stripping of combustion products from the burning surface. It is shown that the maximum burning rate of such mixtures (82 mm/s) is achieved at an equal mass ratio of nickel oxide and titanium. In condensed combustion products of a mixture of nickel oxide with titanium, Ti₂Ni intermetallic and Ni₂Ti₄O _x double oxide identified.

The stages of chemical transformation in the combustion wave of an exothermic Fe₂O₃/Al/AlN mixture in nitrogen atmosphere is studied using an original method for terminating a combustion front. It is revealed that, in a stoichiometric Fe₂O₃/6Al mixture diluted with 35 % (wt.) AlN, the combustion front stops following the combustion of a 30 ÷ 40-mm mixture column. The zones of a stopped combustion wave are investigated by the local analysis methods. It is shown that the alumothermal reduction of iron (III) oxide to iron aluminide proceeds in stages via the formation of a (FeAl) _x O _{ydouble oxide having varying chemical composition. The final synthesis products include aluminum oxynitride, iron aluminide, and unreacted aluminum nitride.}

Mathematical models constructed in the macroscopic approximation are used to perform a theoretical study of volume and wave synthesis in a hybrid mixture consisting of nonactivated and activated powders of the same composition. Synthesis dynamics depending on the proportion of activated powder at different values of the preliminary mechanical activation parameters is considered. Analytical formulas are obtained for approximate estimates of the temperature and time of synthesis in nonactivated and activated compositions.

A model for synthesizing a composite during combustion is proposed and numerically investigated. It is assumed that a set of chemical transformations can be described by a kinetic scheme with two total parallel reactions. One of the reactions corresponds to the matrix synthesis, and the other one to the inclusion synthesis. It is taken into account that the mixture components melt in a certain temperature range rather than at a fixed melting point. The possibility of the reaction front propagation in a self-oscillating mode is shown. The critical values of the parameters that separate the stationary and self-oscillating modes of the reaction front propagation are revealed. Computational results in extreme cases correspond to known theoretical concepts.

This paper presents the results of an experimental study of shock compression of titanium hydride TiH₂ and the deuterides of zirconium ZrD₂, tantalum TaD_0.8, and titanium TiD₂, TiD_1.6, and TiD_1.1 in the pressure range 30 ÷ 220 GPa. The synthesis of titanium and zirconium deuterides from titanium and zirconium powders and tantalum deuterides from tantalum rods is described. The Hugoniots of deuterides and hydrides were determined using the well-known reflection method. Shock-wave compression was performed using shock-wave generators with explosive charges of different power. A description of the obtained experimental data using simple equations of state is proposed.

Results of numerical simulations of fracture of titanium and aluminum nanocrystals by the molecular dynamics are reported. The nanocrystals are subjected to uniaxial tension in a wide temperature range (300 ÷ 1 270 K). It is demonstrated that tension of titanium nanocrystals heated to temperatures above 0.7 of the melting temperature in a non-stressed nanocrystal first leads to a phase transition from the crystalline to liquid state, followed by their fracture. This effect is not observed in the case of tension of the aluminum nanocrystal.

The influence of the velocity of compact metal projectiles of spherical and cylindrical shapes on the size of craters formed in steel targets of different strength was studied in the velocity range 2 ÷ 10 km/s by numerical simulations using two different computing systems. The behavior of the materials of the projectile and target is described using a model of a compressible elastoplastic medium with a constant yield point. The materials of projectiles are copper, titanium, and tantalum. The mass and velocity of projectiles are specified assuming that their kinetic energy is constant. It is found that the dependences of the crater depth on the velocity of projectiles with a constant kinetic energy have a maximum point, and the volume of craters decreases monotonically with increasing velocity.

The present article discusses the current theoretical problem of the dissection of thicknesses of frozen Quaternary formations for the purpose of reconstructing the history of their development, stratigraphy and mapping. This justifies the utilization of the cryofacies and cryoformation methods. Cryolithostratigraphy is discussed as a new branch of science at the junction of cryolithology and climatostratigraphy. The concepts of “cryofacies”, “cryogenic contact”, “cryogenic formation” are defined; distinctive types of cryofacies cryostratigraphy and cryogenic contacts are highlighted. A range of cryolithological studies from the primary dissection of frozen thicknesses to the solution of cryolithostratigraphic problems is proposed. The relationship between cryolithostratigraphy and paleocryolithostratigraphy is revealed.

On the basis of experimental studies, an assessment of the influence of air temperature and weather type on the heat-shielding properties of the moss cover has been given. It has been revealed that in sunny weather with light cloudiness, the highest temperature of the soil surface under 1 cm thick moss is almost by 13 °С higher than under 5 cm thick moss, while in cloudy weather that difference is 3 °С. The measurements has demonstrated that for the period of 06.07 to 08.08.2016, the average temperature of the 70 cm thick soil layer under the 5 cm thick moss cover was by 1.5 °C lower than that under the 1 cm thick one.

The shrinking in mountain ranges caused by climate change worldwide today leads to periglacial lakes formation in the areas of degrading glaciation. The lifetime of moraine-dammed lakes is ephemeral on the geological time scale. They are characterized by dynamic instability and are prone to outbursts. Degradation of moraine dams often results in catastrophic outbursts. Generally, these floods are followed by mudflows. Thus, glacial outburst floods and mud floods cause significant damage to the infrastructure and populated localities in the mountain foothills. In this study, we present the stages of formation and evolution of a periglacial water body on the example of Lake Nurgan (Tsambagarav, northwestern Mongolia). Based on the results of the comprehensive field research, we have described the transgressive, regressive and post-regressive phases of the periglacial reservoir evolution.

A method for surface cooling of frozen foundations has been proposed. It includes heat insulation through the soil surface and a unit for forced circulation of a refrigerant. The latter is used only in summer during the entire period of operation of the structure. The method has important advantages in comparison with the known methods of surface cooling: a) a seasonally thawed layer can’t be formed at any time of the annual cycle and the cooling impulse enters the ground base throughout the entire calendar year; b) in urban conditions, the use of a machine cooling method (instead of seasonally operating cooling systems) is quite reasonable since it does not require significant space for its implementation. Analysis of the results of temperature fields calculating demonstrates quick cooling of the ground base: for all calculation options, the temperature at the depth of zero annual amplitude in the second year of operation reaches a value corresponding to hard frozen state of most of the soils. The decrease becomes even more significant in the third year of operation. The calculation results are rather weakly dependent on the distance between the cooling elements of the applied cooling system within the considered range of variation of that value (from 0.7 to 1.0 m).

Analysis of the glacier surges during 2015-2020 in the western parts of Peter the First Ridge, Pamir, is carried out based on the interpretation of images taken from the International Space Station, as well from Landsat, RapidEye and Sentinel satellites. It is established that massive ice blocks breaking off from glaciers and their rapid descent down the valley is not unique for that region. The damage caused to human economic activity as a result of the investigated glacier surges is described. Periods of pulsation of some glaciers are determined.

The article reflects the main milestones of the scientific activity of A.G. Skvortsov, Candidate of Technical Sciences, a renowned specialist of the ECI TyumSC of SB RAS. Andrey Georgievitch is a specialist in the field of seismoacoustic researches of shallow sections. He is the author of original methods of seismic exploration, successfully used both in the cryolithozone and beyond it.

On June 4, 2021, Stanislav Alekseevich Laukhin, a recognized specialist in Quaternary geology of the North of Russia, professor of the Department of Engineering Geology of the GGF MGRI, Doctor of Engineering Sciences, an unusually purposeful and tireless person, passed away.