Diffraction of the Plane Wave by an Impedance Cone

Some questions concerning the justification of the solution in the problem of diffraction of the plane wave by an impedance cone are discussed. The surface waves, as well as the Weyl-van-der-Pol phenomenon, are studied in the zone illuminated by reflected rays. Bibliography: 19 titles.__________Translated from Zapiski Nauchnykh Seminarov POMI, Vol. 297, 2003, pp. 191–215.     

Wave Properties of Double One-Dimensional Periodic Sheet Grating

We show that the double one-dimensional periodic sheet gratings always have waveguide properties for acoustic waves. In general, there are two types of pass bands: i.e., the connected sets of frequencies for which there exist harmonic acoustic traveling waves propagating in the direction of periodicity and localized in the neighborhood of the grating. Using numerical-analytical methods, we describe the dispersion relations for these waves, pass bands, and their dependence on the geometric parameters of the problem. The phenomenon is discovered of bifurcation of waveguide frequencies with respect to the parameter of the distance between the gratings that decreases from infinity. Some estimates are obtained for the parameters of frequency splitting or fusion in dependence on the distance between the simple blade gratings forming the double grating. We show that near a double sheet grating there always exist standing waves (in-phase oscillations in the neighboring fundamental cells of the group of translations) localized near the grating. By numerical-analytical methods, the dependences of the standing wave frequencies on the geometric parameters of the grating are determined. The mechanics is described of traveling and standing waves localized in the neighborhood of the double gratings.     

Diffraction of a Plane Discontinuos Wave in Layered Anisotropic Elastic Media

The problem of transformation of the front of a plane longitudinal shock wave by curvilinear interfaces of layered anisotropic elastic media with different mechanical properties is considered. To solve the nonlinear Snell equations, the approach based on a synthesis of the Newton method and the algorithm of parametric continuation of a solution is used. The cases of focusing and scattering of rays by convex and concave interfaces of layered composite media and by convex lenses are investigated. Numerical examples are given for various ratios between the parameters of the elastic media.     

On an Integral Equation in the Problem of Diffraction of a Plane Wave on a Transparent Circular Cone

The problem of diffraction on a transparent convex cone is studied. A uniqueness theorem is proved for the case where the cone is illuminated by a compact source. For a circular cone, the solution is obtained in the form of Kontorovich-Lebedev integrals and Fourier series expansions. A singular integral equation is deduced for the Fourier coefficients, and its regularization is carried out. Bibliography: 13 titles. __________ Translated from Zapiski Nauchnykh Seminarov POMI, Vol. 308, 2004, pp. 101–123.     

Diffraction of a Plane Electromagnetic Wave Obliquely Incident on the Edge of an Impedance Wedge: the Uniqueness of a Classical Solution

The problem on the diffraction of an electromagnetic plane wave on an impedance wedge is considered. The uniqueness of a classical solution is proved. Bibliography: 9 titles.     

Diffraction of Plane Electromagnetic Waves on a Small Obstacle Inside a Layer

The problem on the diffraction of the electromagnetic plane wave on a small obstacle in a layer is investigated. The obstacle is assumed to be a circular cylinder and its radius is small in comparison with the length of the incident wave. It is proved that the small obstacle radiates as a linear source. Its intensity is proportional to the area of a cross-section and the jumps of the dielectric and magnetic constants on the interfaces. Bibliography: 4 titles.     

Periodic Plane Waves for the Oregonator

The Oregonator is a set of differential equations proposed by R. J. Field and R. M. Noyes as a model for the oscillating chemical reaction first studied by B. P. Belousov and A. M. Zhabotinskii. In this paper it is shown that the associated diffusion equations have periodic plane waves for parameter values not covered in earlier work. This amounts to studying a singularly perturbed system when nothing is known about the stability of periodic solutions for the reduced system.     

Exponentially Decreasing Solutions of Diffraction Problems on a Rigid Periodic Boundary

Mathematical Notes -     

再论各向异性平面弹性中的一个周期接触问题——纪念李国平院士吴新谋教授诞辰100周年

该文对下面的一个弹性接触问题进行了再讨论.一列周期排列刚性压头压入一个各向异性弹性半平面的边界上,并有摩擦力存在, 求应力平衡.此问题在文献[1, 2]中曾讨论过并求出其解.但解法似不完全确切.该文将它进行修正从而获得精确解的封闭形式.     

Diffraction by an Acoustic Grating Perturbed by a Bounded Obstacle

An original approach to solve 2D time harmonic diffraction problems involving locally perturbed gratings is proposed. The propagation medium is composed of a periodically stratified half-space and a homogeneous half-space containing a bounded obstacle. Using Fourier and Floquet transforms and integral representations, the diffraction problem is formulated as a coupled problem of Fredholm type with two unknowns: the trace of the diffracted field on the interface separating the two half-spaces on one hand, and the restriction of the diffracted field to a bounded domain surrounding the obstacle, on the other hand.     

Diffraction of Plane Waves on Bodies of Different Types

The problem on the diffraction of plane waves on compact domains and on an arbitrary cone is considered. The method of moving a point source to infinity for the solution of such diffraction problems is justified. Bibliography: 4 titles.     

On the Korn Inequalities on Thin Periodic Frames

Korn-type inequalities for thin periodic structures of period and width h() with h() 0 are presented. Periodic meshes, three-dimensional road structures, and three-dimensional box structures are considered. A particular attention is paid to structures with the so-called critical width when 0$$ " align="middle" border="0"> .     

Identification for a Nonlinear Periodic Wave Equation

This work is concerned with an approximation process for the identification of nonlinearities in the nonlinear periodic wave equation. It is based on the least-squares approach and on a splitting method. A numerical algorithm of gradient type and the numerical implementation are given. Accepted 14 January 2001. Online publication 20 June 2001.     

Diffraction of the Electromagnetic Wave on a Small Obstacle of Elliptic Form in a Layer

The problem on the diffraction of the electromagnetic plane wave on a small obstacle included in a layer is investigated. The obstacle is assumed to be an elliptic cylinder whose diameter and focal distance are small in comparison with the length of the incident wave. It is proved that the small obstacle radiates as a point source, and its amplitude is proportional to the area of the cross-section and the jumps of the dielectric and magnetic constants on the interfaces. Bibliography: 5 titles.     

入射平面电磁波两类球面波函数展开式的等价性证明

入射平面电磁波的球面波函数展开是求解不同圆球结构的平面波散射问题的重要工具,相关文献分别利用场的坐标分解和矢量势法得到了入射平面波的球面波函数的两种不同形式的展开式.利用偏微分方程边值问题解的存在唯一性定理,给出了这两种展开式的等价性的一个简洁的解析证明,并进行了数值验证.     

Diffraction of Plane Elastic Waves with Vertical Polarization on a Small Obstacle in a Layer

The problem on the diffraction of elastic plane waves with vertical polarization on a small obstacle (elastic inhomogeneous inclusion) inside a layer is investigated. The layer is situated on an elastic half-space. A three-layer model of isotropic elastic media is considered. The obstacle is assumed to be a circular cylinder with radius that is small in comparison with the length of the incident wave. The polarization of the incident wave is assumed to be orthogonal to the axis of the cylinder. The diffractional addition on the small obstacle to the reflected wave in an elastic layer is proved to have a larger order than the order of the first term with respect to the parameter , where is the wave number, r is the distance between the obstacle and the observation point. The small obstacle generates a cylindrical wave the intensity of which is proportional to the area of the cross-section of the obstacle and to the jumps of the square velocities in the layer and in the obstacle. Bibliography: 6 titles.     

Diffraction of the Fundamental Waveguide Wave on an Inductive Cylinder in a Rectangular Waveguide

Computational Mathematics and Modeling - We apply the integral equation method to the diffraction of a waveguide wave on an impedance inductive cylinder in a rectangular waveguide. The...