The influence of structural and electrical parameters of the pyroelectric phase on the pyroelectric properties of a polymer-pyroelectric ceramic composite

The influence of structural and electrical parameters of the pyroelectric phase on the pyroelectric properties of composites based on poly(vinylidene fluoride), vinylidene fluoride-tetrafluoroethylene copolymer (F-42), and pyroelectric ceramics of the lead zirconate titanate family with different structures is investigated. It is revealed that the pyroelectric coefficient of the composite is determined by the reorientation polarization and the mobility of domains in the pyroelectric ceramic phase, which depend on the homogeneous parameter of the spontaneous strain of the perovskite cell.     

Investigation of non-steady-state centeally symmetric filtration of a liquid in closed heterogeneous media

This paper is the final stage in a study of the properties of the non-steady-state filtration of a homogeneous liquid towards a central well with a hemispherical end face in heterogeneous media with a dual porosity, consisting of hemispherical regions set one inside the other with different values of the medium parameters [1, 2]. Exact solutions are found for the problems of the decrease in seam pressure as a function of time and distance, as well as of the time change in output of a well with a hemispherical end face operating at a fixed flow rate, or at a fixed end face pressure, respectively, in closed heterogeneous media. The effect of the magnitudes of the heterogeneous media parameters on the change in their production process indicators is established on the basis of numerical calculations.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 3, pp. 98–104, May–June, 1976.     

Centrally symmetrical filtration of liquid in cracked porous media with a hemispherical supply contour

The motion of a homogeneous liquid in a well with a hemispherical face is studied for the case of transient, spherically radial filtration in cracked porous media comprising mutually superposed hemispherical regions with different crack permeabilities, having a supply contour in the outer hemispherical region. Using a Laplace integral transformation with respect to the time variable, the systems of differential equations describing the filtration of liquid in these media are solved for zero initial and corresponding boundary conditions. Exact solutions are obtained for the reduction in stratal pressure with time and distance, and also for the changes taking place in the output of a well operating under conditions of specified face pressure. On the basis of corresponding numerical calculations, the influence of the parameters of the cracked porous strata and the radius of the surface containing the supply contour on the indices of the production process is established.     

On sharp estimates of the convergence of double Fourier–Bessel series

The problem of approximation of a differentiable function of two variables by partial sums of a double Fourier–Bessel series is considered. Sharp estimates of the rate of convergence of the double Fourier–Bessel series on the class of differentiable functions of two variables characterized by a generalized modulus of continuity are obtained. The proofs of four theorems on this issue, which can be directly applied to solving particular problems of mathematical physics, approximation theory, etc., are presented.