Home – Home – Jornals – Advanced Search

The CO₂ absorption was measured in the 7 000 and 8 000 cm^–1 region. Calculations of the absorption coefficient were performed using the asymptotic line wing shape theory. Line contour parameters were associated with the classical potential governing the center–of–mass motion and with the quantum potential of two interacting molecules. They were found from fitting the calculated absorption coefficient to experiment. The calculated coefficient values agree well with the measured data. According to the line wing theory the absorption in the band wings is due to the wings of the strong lines of adjacent band. With these assumptions experimental and calculated data on the CO₂ absorption coefficient in the band wings in the 7 000 and 8 000 cm^–1 regions can provide information on the line shape at frequency detunings from several tens to several hundreds of half-widths. The results obtained support the hypothesis that line shape parameters in the line wings related to the transitions with the same initial state appear to be close to each other. Deviations from the Lorentzian contour are defined for a set of CO₂ bands. The former are found to be different for the wings of different bands.

The behavior of the degree of coherence of a coherent vortex Bessel optical beam propagating in a turbulent randomly inhomogeneous medium is theoretically considered. The influence of an optical vortex on the degree of coherence of the Bessel beam in a randomly inhomogeneous medium is studied. The analysis is based on the solution of the equation for the second-order mutual coherence function of optical beam field. On the basis of this solution, the behavior of the module of the second-order mutual coherence function (a degree of coherence), the vortex Bessel beam field is investigated. It is shown that at low levels of fluctuations in the turbulent atmosphere, in the central part of a two-dimensional field of the degree of coherence of vortex Bessel beams, the ring dislocation is formed; the number of rings is equal to value of a topological charge of an optical beam. The structure of a ring dislocation of the degree of coherence of vortex Bessel optical beams in turbulent atmosphere is studied in detail. For this purpose, two characteristics of the ring dislocation are introduced: the spatial coordinate and width of a ring. The influence of parameters of an optical beam (a cross-section wave number and a topological charge) and atmospheric turbulence (a coherence radius of a plane optical wave) on these characteristics of the ring dislocation of the degree of coherence of a vortex Bessel optical beam is considered.

A closed system of equations for calculating the drift of an inertial heavy granule in an inhomogeneous velocity field of the carrier fluid is derived by the Krylov—Bogolyubov method of averaging over fast oscillations of velocity. Exact analytical solutions are presented and compared with the results of the numerical solution of the equations of granule motion. The influence of the granule inertia, acceleration of mass forces, and frequency of oscillations on the granule dynamics in an inhomogeneous oscillating velocity field of the fluid is studied.

This paper, presents the results of comparison of theory and laboratory experiment for simulation of the wavy flows resulting from dam break on a sudden change in the rectangular cross–sectional area of a channel whose width is greater upstream than downstream. Exact self–similar solutions containing an heuristic parameter dependent on the total energy of the flow lost on the sudden change in cross–sectional area were obtained using the first approximation of the spatially one–dimensional theory of shallow water. It is shown that theoretical solutions agree quite well with the results laboratory experiments on the possible types of waves, the their propagation velocity, and asymptotic depth values behind their fronts.

The causes of bed instability in a sandy bed channel are analyzed using a formula of sediment transport rate containing no phenomenological parameters. The sediment transport rate is uniquely determined by the normal and shear stresses on the bed and the slope of the bed surface. Using a linear model, it is shown that the only factor responsible for bed instability is perturbations of the normal bed pressure regardless of their nature.

Problems associated with the development of a propulsive device of the flapping wing type are discussed. Specific features of an unsteady flow around such a wing and the influence of its geometric parameters and the law of wing flapping on the thrust force and hydrodynamic efficiency are analyzed. Formulas for calculating the thrust force at high Strouhal numbers are derived. Some configurations of propulsive devices and possible applications are considered.

The process of moisture extraction from unhusked Korean rice is modeled with the use of a diffusion model. The diffusion coefficient is determined, which makes it possible to reconstruct the dynamics of the moisture distribution in a cylindrical sack filled by rice. It is demonstrated that the results of calculations performed for different values of the initial humidity are in reasonable agreement with experimental data obtained in the case of drying of unhusked rice in an acousto–convective drier. Results testifying to significant intensification of acousto–convective drying as compared to natural drying are obtained.

It has been shown experimentally and theoretically that the equations of the Rabotnov kinetic theory of creep with a scalar damage parameter can be used to describe the deformation (up to fracture) of metallic materials in creep without restrictions on the creep strain and energy dissipation at the moment of fracture. In finding the functional dependences in the equations of creep and damage, the damage parameter is determined by the amount of normalized specific energy dissipation in the process of material creep under the necessary condition of similarity of the initial creep curves for constant stresses and temperatures in the normalized variables.

A two-dimensional problem of deformation of a layer of a viscoelastic material glued to a solid base by a traveling wave of shear stress is solved. Analytical expressions for two shear compliance components corresponding to two surface displacement components are obtained. It is shown that the dimensionless compliance components depend only on the viscoelastic properties of the material, the ratio of the wavelength to the layer thickness λ / H, and the ratio of the wave velocity to the propagation rate of shear vibrations V/C_t⁰. Data on the dynamic compliance in the ranges 0.2 < λ / H < 60.0 and 0.2 < V/C_t⁰ <5.0 are given. It is established that, in the range 1.5 < λ / H < 5.0, the normal component of the shear compliance decreases sharply. Diagrams of the phase shift of the displacement components relative to the phases of the applied oscillatory shear stresses and diagrams of displacements and shifts of their phases over the thickness of the viscoelastic layer are presented.

An experimental study of plastic deformation zones in the vicinity of stress concentrators found a deviation of the shapes of plastic zones at the crack tip from the shapes obtained using conventional models. Moreover, the systems of bands of slip lines observed in the experiment and predicted by linear fracture mechanics are significantly different. Mathematical modeling of the propagation of plastic zones based on a finite element numerical solution of the equations of deformable solid mechanics was performed with the framework of the theory of large elastoplastic deformations. The basis of the mathematical model is the hypothesis that the structural heterogeneity of the material has a substantial effect throughout the volume of the test sample on the formation of plastic bands. Nonuniformity of the yield strength of the material is specified as a checkerboard distribution and as a system of horizontal and vertical bands. The results of the numerical calculations are compared with the experimental data, and it is shown that they are in qualitative agreement.