Sound field of normal modes in a stratified medium with a plane-parallel stream

Expressions for the sound field and radiated power of a pointwise harmonic source in a stratified medium with a plane-parallel stream are presented and discussed.Institute for Physics of Microstructures, Russian Academy of Sciences, Nizhny Novgorod. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 38, Nos. 1–2, pp. 122–126, January–February, 1995.     

Method for calculating the monochromatic field in a layered medium

An approximate method is proposed for calculating the monochromatic field described by the wave equation in a layered medium. The method is based on the use of the equivalent propagation constant and makes it possible to reduce the computation time as compared to other methods based on the strictly dynamic approach. The range of correct application of the method is estimated for the problems for which the exact solution is known.     

A method of calculating the Green’s function for a layered medium

A method of calculating the Green’s function for the Laplace equation is suggested. This method is based on the use of properties of the special Bessel and Struve functions. An example of calculations is given. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 70–76, July, 2007.     

High-Q oscillations in a layered elastic medium

Conditions of the existence of long-lived acoustic resonances that occur in a layered medium because of its oscillation with low damping factors are considered. A priori theoretical estimates relating the distribution of resonance frequencies in the complex plane to the parameters of inhomogeneity of the layered system are obtained. A scheme of resonance calculations in numerical modeling is described. Examples of geophysical media with long-lived resonances are presented.     

Propagating modes of a lens-like medium

The wave equation for a weakly guiding medium having a cylindrical symmetry and parabolic index distribution has been solved exactly. Simple power series are obtained for the field distributions of the modes, which illustrate the type of fields that will be found in graded core fibres away from the core cladding discontinuity. These results are discussed and compared to the modes predicted for other types of fibres.     

Buildup of an electron-photon avalanche in a layered medium with a random-distributed density

This is a study concerning the buildup of an electron—photon avalanche in a medium with a random-distributed density. The formulas derived here describe the avalanche characteristics, averaged over fluctuations of the medium, in terms of the corresponding avalanche characteristics for a medium with a deterministically distributed density. Numerical results are shown pertaining to an avalance in the atmosphere.     

Localization of vibrational modes in a layered lattice with diagonal and off-diagonal disorder

This paper discusses the possibility of weak localization of the phonon modes in a nonideal harmonic crystal lattice whose separate layers are weakly coupled to each other. An expression is obtained for the diffusivity tensor. The role of inverse coherent scattering processes is studied. It is established that, when such processes occur under conditions of strong diagonal disorder in the region of relatively low frequencies, where the dispersion law of the phonon modes exhibits two-dimensional properties, substantial renormalization of the diffusivity can take place. The paper analyzes the situation that occurs under conditions of off-diagonal disorder when resonant-scattering impurity centers are present in the lattice. The question of the possible nature of the low-temperature plateau in the thermal conductivity of the complex crystals BSCCO and BSYCO is discussed. Zh. éksp. Teor. Fiz. 113, 930–954 (March 1998)     

Surface acoustic oscillations in a periodically layered medium

The existence of surface acoustic waves at the interface between a periodically layered and a homogeneous half-space is predicted. The reason for the arisal of such waves is the violation of the transnational symmetry pertinent to the periodic structure. The properties of the surface waves at a free boundary and a boundary with an elastic half-space are considered.     

Resonance modes of layered ferromagnets in a transverse magnetic field

Intensities and positions of resonance lines are calculated for the ferromagnetic resonance spectra of multilayer ferromagnetic films in a magnetic field oriented normally to the film surface. It is shown that the positions of spectral lines depend on the number of ferromagnetic layers, while the line intensities are determined by the phase shift between the oscillations of the magnetic moments of neighboring layers. A qualitative comparison is carried out between the results of calculations and the spectra observed in experiments.     

Calculation of a quasi-stationary field in the layered medium

A method of calculating the field of a single point charge in a layered medium is suggested. The method makes it possible to simplify the computational formulas for the potential. The solution of the problem employs the properties of Bessel and Struve functions. The results apply to a wide class of problems solvable in terms of Green’s function.     

Propagation of elastic waves in a nonideal layered medium

The peculiarities of propagation of acoustic excitations through an imperfect 1D superlattice are studied in the virtual crystal approximation. The dependence of the lowest acoustic band gap of a nonideal (disordered in composition) two-sublattice 1D phonon crystal on the concentration of impurity layers is simulated numerically.