Home – Home – Jornals – Avtometriya 2016 number 1

The efficiency of a number of the classical methods of supervised classification of hyperspectral data is estimated by an example of discriminating the types of the underlying surface in natural and man-made areas. The minimum distance, support vector machine, Mahalanobis, and maximum likelihood methods are considered. Particular attention is paid to studying the dependence of the data classification accuracy on the number of spectral features and the way of choosing them in the above-mentioned methods. Experimental results obtained by processing real hyperspectral images of landscapes of various types are reported.

A model of image recording in the circular microscanning regime is considered. An algorithm that allows obtaining an image with a large number of samples from a set of smaller-size frames for a known path of the scanning array is proposed. Numerical simulations are performed to estimate the changes in the amplitude of a small-size object with a static position of the photodetector array and microscanning in the start/stop mode. The influence of the gap between the array elements and scanning radius on the object amplitude is studied. The final ratio of the object amplitude to the random noise level in the case of static accumulation and circular microscanning in the start/stop mode are compared for arrays with different sizes of the gap between the array elements.

This papers describes the effectiveness of textural features on the basis of gradient tensors in the problem of segmentation of images containing textures with structural redundancy. It is shown that the use of the bank of Gaussian bandpass filters in the formation of a feature space which is invariant to shifts and rotations of textures improves the performance of the segmentation algorithm. Examples demonstrating the application of textural features to the problem of segmentation with an unknown number of texture classes contained in the image are presented.

A new goodness-of-fit test constructed with the use of the interval estimation of the probability distribution function is proposed. A comparative analysis of this test with the Kolmogorov test is carried out. It is shown that it is possible to select the correct distribution function and the hypothetical function different from it so that the proposed goodness-of-fit test can have a significantly better performance than the Kolmogorov test. The presented numerical simulation results are in good agreement with the theoretical conclusions.

With regard to the problems of passive ranging, one of the modifications of the wellknown energy method for determining the range to an emitting target with partially known motion parameters on the basis of a single receiving point is developed. The problem is solved using solely the measurements of the power (amplitude) of the received signal on a predetermined time grid with no account for direction-finding data. The analytical dependences allowing for exploration of the working region of the method are obtained. An algorithm for the formation of the resulting ranging estimate in the current time taking into consideration the measurement redundancy is constructed. The results of computational experiments that confirm the possibility of practical implementation of the proposed modifications of the energy method are presented. The recommendations on the use of the results obtained in multipoint systems of passive location are given.

A problem of tracking of a group of identical objects with a variable shape and a large number of occlusions is considered. This problem is important for biology and safety systems. An algorithm of detection and tracking of biological objects on the basis of a sequence of depth images is proposed. Being tested, the algorithm provides one mistake per 193 collisions for the worst sequence.

The problem of face recognition is discussed. For this purpose, a method based on scalar perturbation functions and a set-theoretic operation of subtraction is proposed. It is shown that all surface points and the mask volume are used in the process of sample testing for more accurate identification.

A method has been developed to determine the shrinkage parameters of holographic photopolymer materials (including changes in the mean refractive index and thickness of the recording layer) during hologram recording with a measurement error acceptable for practical applications of these materials. Experimental verification of the method has proved its efficiency.

It has been shown that the problem of optimal actuator placement for adaptive square mirrors can be reduced to the analytical solution using elements of the theory of unbiased designs for the natural vibrations of a square plate with free edges. A stochastic model for the wavefront has been developed using regression analysis. Formulas are given for calculating the bias in working-out the desired optical surface geometry of an adaptive mirror.

Simultaneous crosswind and strength of atmospheric turbulence are estimated by the classical laser scintillation method and passive optical method from analysis of the light scattered by a natural or man-made topographic objects in natural daylight illumination conditions. The passive sensing method does not require artificial light sources a consists in the formation of incoherent images of topographic objects in the natural sunlight and analysis of image distortions induced by turbulence between the object and the plane of observation. The estimates of integral crosswind and index of refraction structure constant of air were compared in atmospheric experiments at the same measuring optical path by both methods. The comparison with lidar data was made. Optical measurements of integral characteristics were accompanied by independent local acoustic measurements using a sonic anemometer.

The article considers the problem of wind velocity estimation from the statistics of the integral characteristics of the images of incoherent sources in the turbulent atmosphere, namely, the received power and the bias vector of the center of gravity of the image. In the framework of the first approximation of the method of small perturbations, expressions for the mutual correlation functions of these characteristics and the bias vectors for a couple of point sources registered through a couple of receivers are derived. It is shown the correlation maxima are shifted from the origin of coordinates and the shift value depends on the wind velocity. The possibility of estimation of the vector of transverse velocity averaged over the optical path from the shape of correlation functions and shifts of correlation maxima is shown.

Coherent properties of the diffraction-free optical beams propagating in a turbulent atmosphere are studied. The problem analysis is based on solution of the equation for the second-order mutual coherence function of a field of optical radiation. The behavior of the degree of coherence of the diffraction-free (cos and fundamental Bessel) optical beams depending on parameters of the beams and characteristics of the turbulent atmosphere is investigated. It has appeared that fundamental property of diffraction-free beams is the oscillating character of coherence degree of these beams, which is shown at low levels of fluctuations in the turbulent atmosphere. At high levels of fluctuations in the turbulent atmosphere, the degree of coherence of a diffraction-free cos beam becomes closer to the similar characteristic of a plane wave, while a diffraction-free fundamental Bessel beam becomes closer to a spherical wave. The analysis of two spatial scales of degree of coherence of optical beams has shown that the integral scale of coherence degree for diffraction-free beams is more representative characteristic than coherence of radius. The integral scale of coherence degree of diffraction-free beams is practically unequivocally connected with conditions of propagation of optical radiation in a turbulent atmosphere.

Based on the numerical solution of the parabolic wave equation for the complex spectral amplitude of the wave field the propagation of a short pulsed Laguerre-Gaussian beam with femtosecond duration was studied. It has been shown that the difraction broadening of the Laguerre-Gaussian beam decreases with the pulse duration in comparison with continuous wave radiation.

In the given paper, using the Pointing vector streamlines, the effective beam width dependence on initial field distribution of axially symmetric laser beam, propagating in the turbulent atmosphere, is investigated. Spatial evolution of effective beam widths of ring-shaped laser beams, such as Laguerre-Gaussian and dark hollow beams was examined in comparison with Gaussian beams under condition that the beam power in transmitter aperture of an atmospheric optical system is the same for all laser beam modes studied in the paper. It was shown that in the case of medium-to-strong turbulence effective beam widths of high-order Laguerre-Gaussian and dark hollow beams can be less than effective beam width of a Gaussian beam in the atmosphere.

Impact of combustion phases of typical Siberian biomass on optical, microphysical, and physical-chemical properties of smoke aerosols were investigated in small-scale fires at the Large Aerosol Chamber (LAC). The comprehensive analysis has revealed the influence of combustion temperature on formation and time evolution of pine and debris emission characteristics. Size distributions and complex refractive indices in the ranges of ultrafine, fine, and coarse particles were determined from polar spectronephelometer measurements of the angular aerosol scattering. In smoldering phases, smoke is found to be weakly absorbing while mixed fires also emit strongly absorbing soot particles produced in open flaming phases. Characteristics of aerosol microstructure such as morphology and composition were analyzed. Group Soot and Organics were identified as micromarkers of Siberian biomass burning in open flaming and smoldering phases, respectively. Carbon fraction (organic and elemental carbon), chemical compounds, and water-soluble ionic fraction exhibit the strong dependence on the combustion phase. Anhydrosugar (levoglucosan) was determined in smoldering fires as the stable molecular marker of Siberian pine burning. A number of chemical compounds were found to act as specific markers of soft wood. At smoke aging in a chamber the condensation of organic and inorganic species leads to transformation of the aerosol surface chemistry and formation of the particle group rich by potassium. Thus, the complexicity and changeability of chemical composition and microstructure of atmospheric aerosol pollution during Siberian wildfires were realized.

The threshold characteristics of lasing in a layer of colloidal solution of dye Rhodamine 6G with plasmon-resonance Au nanoparticles and non-plasmon-resonance Pt nanoparticles excited by a wavelength of 532 nm are experimentally investigated. The spectral dependence of the scattering and absorption cross sections of nanoparticles of gold and platinum are calculated within the Mie theory. It is established experimentally that the addition of nanoparticles to the active medium reduces the lasing thresholds by two orders of magnitude. It is shown that the lasing threshold value is 1.5-2 times lower when adding gold nanoparticles than when adding platinum nanoparticles of the same concentration.

Laboratory experiments with a first-overtone CO laser are performed to simulate a lidar system. The trace remote sensing scheme of atmospheric gases (nitrous oxide and methane) at emission lines of the pulsed first-overtone CO laser is tested using topographic target and receiving telescope. Results of the measurements of absorption of the first-overtone CO laser operating at 20 selected emission lines in gas mixtures with the gases studied at various configurations of the experimental scheme are presented.

To reconstruct the data of hydrophysical parameter observations, a model based on a neural network with the teacher has been suggested. The indices of global climate modes of the ocean-atmosphere system were applied as the model input. The processes of the model teaching and adaptation, which allow one to find the most accurate solution of the problem of modeling, is described. The comparison of modeled monthly average Danube's runoff with data of observation demonstrated their good correspondence. Missed in some years observation data on sea water transparency (depth of white disc visibility) were reconstructed. The proximity of reconstructed and observed depths of white disc visibility was noted. Some features of interannual variability of reconstructed data on sea water transparency caused by both climatic factors during 1950-1962 and changes in the chlorophyll а concentration during 1998-2010 were found.

The methodological issues and theoretical results related to determination of the boundaries of laser-hazard distances (LHD) when eyes are exposed to direct and scattered radiation produced by a laser landing system (LLS) are discussed. LHD calculation algorithms during LLS operation in field conditions are considered. LHD have been calculated for a single and a group of laser sources for a variety of weather conditions. Computer software for laser radiation dosimetry calculation during LLS operation in field conditions is suggested.

A method for finding exact solutions of the equations of gas dynamics with a linear velocity field is proposed. This method was used to find exact solutions for one submodel of the evolutionary type which was fully integrated for the case of a polytropic gas. Examples of particle motion for the obtain exact solutions are given.

Wind flows in meromictic saline lakes in which the water column does not mix to the bottom for at least one year are studied. This leads to the formation of the upper and depth layers with small density gradients, between which there is a water layer with a large density gradient. It has been shown that, depending on the density stratification and the wind speed, wind flows (in a vertical plane) of two types are possible: with one or two circulation zones. For a two-layer lake model, a criterion for the change in the wind flow regime is proposed.

This paper considers a liquid in a finite-size cylinder in which Marangoni instability occurs. The upper boundary of the liquid is free and deformable. The problem of the occurrence of convection in a cylindrical container is solved using the method of separation of variables. A homogeneous differential equation of the sixth order with constant coefficients and complex boundary conditions is obtained. In the case of monotonic perturbations, an analytical expression for critical Marangoni numbers is derived. The case of a weightless liquid in the cylinder is considered.

Thermodynamic irreversibilities generated by the combustion process are evaluated and analyzed numerically. The numerical simulation is performed for a reference case study for which experimental data are available in the literature: diffusion flame properties in a common burner configuration are studied by the Fluent software with the standard k- e turbulence model and two-step chemical reaction. The study quantifies the contribution of each mechanism to entropy generation, i.e., friction, heat conduction, species diffusion, and chemical reaction. The chemical reaction and heat conduction are found to be the major sources of entropy production. Preheating of air reduces thermodynamic irreversibilities within the combustor.

An unsteady free convective flow of a viscous fluid past an oscillating plate is considered, and the effects of entropy generation are investigated. The governing partial differential equations are normalized by using suitable transformations, and an exact solution of the problem is obtained by using the Laplace transformation technique. The expressions for the velocity and temperature are then used to compute the skin friction, Nusselt number, local entropy generation number, and Bejan number.

The effect of a vertical alternating current, electric field, and heat transfer on a peristaltic flow of a dielectric viscoelastic Oldroyd fluid is studied. This analysis involves uniform and non-uniform annuli having a mild stenosis. The analytical solutions of equations of motion are based on the perturbation technique. This technique depends on two parameters: amplitude ratio and small wave number. Numerical calculations are performed to obtain the effects of several parameters, such as the electrical Rayleigh number, temperature gradient, Reynolds number, wave number, maximum height of stenosis, and Weissenberg numbers, on the distributions of velocity, temperature, electric potential, and wall shear stress. It is found that the above-mentioned distributions in the case of a convergent tapered tube are larger than those in the case of a non-tapered one as well as a diverging tapered tube.

A detailed comparison between the lattice Boltzmann method and the finite element method is presented for an incompressible steady laminar flow and heat transfer of a power-law fluid past a square cylinder between two parallel plates. Computations are performed for three different blockage ratios (ratios of the square side length to the channel width) and different values of the power-law index n covering both pseudo-plastic fluids (n<1) and dilatant fluids (n>1). The methodology is validated against the exact solution. The local and averaged Nusselt numbers are also presented. The results show that the relatively simple lattice Boltzmann method is a good alternative to the finite element method for analyzing non-Newtonian fluids.

This paper presents the results of experimental and numerical studies of heat transfer and swirling pulsating flows in short low-temperature heat pipes whose vapor channels have a conical nozzle shape. It has been found that as the evaporator of the heat pipe is heated, pressure pulsations occur in the vapor channel starting at a certain threshold value of the heat power, which is due to the start of boiling in the evaporator. The frequency of the pulsations was measured, and their dependence on the superheat of the evaporator was determined. It is found that in heat pipes with a conical vapor channel, pulsations occur at lower evaporator superheats and the pulsation frequency is greater than in heat pipes of the same size with a standard cylindrical vapor channel. It is shown that the curve of the heat-transfer coefficient versus heat load on the evaporator has an inflection corresponding to the start of boiling in the capillary porous evaporator of the heat pipe.

Nonlinear vibrations in a closed system of coupled nonlinear oscillators are studied using acetylene type molecules as an example. A criterion for the stable existence of long-lived vibrational states - local modes - in one of the oscillators is obtained. It is shown that the disappearance of a local mode, as well as its appearance, proceeds abruptly, and the mechanism of stabilization of these excitations is due to the presence or absence of internal resonances of an oscillatory system such as any polyatomic molecule. Energy values needed to excite vibrations in which local modes can appear are determined. It is shown that calculation results agree with experimental data.

This article presents a new asymptotic method to predict dynamic pull-in instability of nonlocal clamped-clamped carbon nanotubes (CNTs) near graphite sheets. Nonlinear governing equations of carbon nanotubes actuated by an electric field are derived. With due allowance for the van der Waals effects, the pull-in instability and the natural frequency-amplitude relationship are investigated by a powerful analytical method, namely, the parameter expansion method. It is demonstrated that retaining two terms in series expansions is sufficient to produce an acceptable solution. The obtained results from numerical methods verify the strength of the analytical procedure. The qualitative analysis of system dynamics shows that the equilibrium points of the autonomous system include center points and unstable saddle points. The phase portraits of the carbon nanotube actuator exhibit periodic and homoclinic orbits.

This papers the results of the numerical and analytical study of natural and quasinatural bending-gravitational oscillations of a circular elastic ice plate floating on the liquid surface and frozen to a cylindrical vertical support. In the framework of the theory of long waves in shallow water for limited and unlimited reservoirs, the dependence of natural and quasinatural frequencies of the geometrical parameters of the oscillation region is studied.

The model of generalized micropolar magneto-thermoelasticity for a thermally and perfectly conducting half-space is studied. The initial magnetic field is parallel to the boundary of the half-space. The formulation is applied to the generalized thermo-elasticity theories of Lord and Shulman, Green and Lindsay, as well as to the coupled dynamic theory. The normal mode analysis is used to obtain expressions for the temperature increment, the displacement, and the stress components of the model at the interface. By using potential functions, the governing equations are reduced to two fourth-order differential equations. By numerical calculation, the variation of the considered variables is given and illustrated graphically for a magnesium crystal micropolar elastic material. Comparisons are performed with the results predicted by the three theories in the presence of a magnetic field.

The lattice Boltzmann method is employed to simulate heat transfer in the flow past three arrangements of elliptical and circular cylinders under an isothermal boundary condition. The lattice Boltzmann equations and the Bhatnagar-Gross-Krook model are used to simulate two-dimensional forced convection at 30 ≤ Re ≤ 100 and Pr = 0.71. Pressure distributions, isotherms, and streamlines are obtained. Vortex shedding maps are observed in detail for several cases. The present results are in good agreement with available experimental and numerical data.

An analytical solution of the problem of electrochemical machining of metals by a curvilinear cathode tool with allowance for a discontinuous function that describes the dependence of the current efficiency on the current density is obtained. According to the hydrodynamic itnerpretation, the original problem reduces to the problem of the theory of ideal fluid flows with a free surface. It is demonstrated that the use of the proposed dependence of the current efficiency on the current density ensures the existence of three domains on an unknown treated surface; these domains have different laws of the distribution of the charge fraction spent on metal dissolution. Results calculated for various particular cases are presented.

This paper presents a synergetic model that can be used to describe the boundary friction of two atomically smooth solid surfaces separated by an ultrathin lubricant layer. The model is constructed using the Lorenz equations, which are parameterized by shear stresses, shear strains, and the lubricant temperature. Given the spatial heterogeneity of these parameters, it is shown that a structure with two types of domains is formed during friction on the contact plane. Time dependences of the fractal dimensions of the domain distributions over the contact plane are calculated, and it is shown that there exists a time when the fractal dimensions take minimum values. During the evolution, the system tends to a homogeneous state in which the entire contact area is subjected to constant shear stresses which determine the relative velocity of motion of the friction blocks.

Dependences of the drag and lift force coefficients of a magnetized sphere in a hypersonic rarefied plasma flow on the angle between the plasma flow velocity and the intrinsic magnetic induction vector of the body are obtained in a wide range of the ratio of the magnetic pressure to the plasma flow pressure. It is shown that by changing the orientation of the magnetic field vector of the body and the incoming flow velocity, it is possible to control the dynamic interaction in the plasma--body system, namely, to decelerate and accelerate the magnetized sphere in the rarefied hypersonic plasma flow.

A physicochemical model of generation of nonequilibrium molecular radiation in the vacuum ultraviolet (VUV) spectral range behind the shock wave in air for shock wave velocities of 4.5 to 9.5 km/s is developed. Experimental results obtained in a shock tube in investigations of photoionization of air ahead of the shock wave front are used for verification of the numerical model of VUV radiation in the wavelength range from 85 to 105 nm. Model calculations show that nonequilibrium VUV radiation arises in a very thin high-temperature layer behind the shock wave front and is affected by the presence of electrons.

The problem of the impact of an elongated solid body with a flat bottom on a thin layer of an ideal incompressible liquid is considered in the case where the horizontal component of the body velocity is substantially greater than its vertical component. The initial stage of the impact is studied in which the a priori unknown contact area between the body and the liquid is rapidly expanding. The loads on the body are determined by the plane section method. The method of matched asymptotic expansions is used to determine the position and size of the contact spot in each section. The coupled problem is solved: the liquid flow due to the motion of the body and the body motion itself are determined simultaneously. A system of integrodifferential equations was obtained and used for numerical investigation of the body motion under the action of hydrodynamic loads, and the hydrodynamic pressure distribution over the contact spot was determined.

A boundary layer flow of a non-Newtonian fluid in the presence of nanoparticles is examined. The flow is caused by a vertical stretching sheet. Convergence of the solution obtained is checked. The values of velocity, temperature, skin friction, and Nusselt number in the boundary layer are obtained.

The flow in a channel with a backward-facing step and a rib mounted upstream of the step and generating flow disturbances is studied experimentally by the method of particle image velocimetry. It is demonstrated that mounting of a single rib leads to deformation of the profiles of the mean streamwise velocities and turbulent fluctuations. The effect of the position and height of a single rib on the recirculation region behind the backward-facing step is analyzed. Reduction of the recirculation region size behind the step in the case of flow reattachment upstream of the step is validated.

This paper presents a new accurate solution of the Navier -Stokes equations in the Boussinesq approximation that describes the thermocapillary advective flow in a slowly rotating horizontal layer of incompressible liquid with free boundaries. Such a flow emerges in the case of linear temperature distribution over horizontal coordinates or in the case of heat flux distribution on the layer boundaries. The influence of the Taylor, Marangoni, Grashof, and Biot numbers on the flow and temperature velocity profiles is studied.