Numerical modeling of the reflection coefficients for the plane sound wave reflection from a layered elastic bottom

The matrix method and its numerical realization are considered in calculating the complex reflection coefficients and refraction indices of plane sound waves for geoacoustic models of the ocean bottom in the form of homogeneous elastic (liquid) absorbing layers overlying an elastic halfspace. In calculating the reflection coefficients at high frequencies or in the presence of a large numbers of sedimentary layers, a passage from the Thomson-Haskell matrix approach to the Dunkin-Thrower computational scheme is performed. The results of test calculations are presented. With the aim of developing resonance methods for the reconstruction of the parameters of layered elastic media, the behavior of the frequency-angular dependences of the reflection coefficient are studied for various geoacoustic bottom models. The structure of the angular and frequency resonances of the reflection coefficients is revealed. The dependence of the structure (the position, width, and amplitude) of two types of resonances on the parameters of the layered bottom is considered.     

Crystalline fullerene deuteride C60D24: Spectral investigation

X-ray diffraction patterns, infrared and x-ray photoelectron spectra, and electron energy-loss spectra are obtained for fullerene deuteride C₆₀D₂₄ prepared by treating solid C₆₀ with D₂ gas. It is established that the deuteride is a polycrystalline powder with an fcc lattice (a ₀=14.55 Å). The product of thermal decomposition of the deuteride consists mainly of fullerene molecules separated by a distance much greater than in the initial fullerite.     

Localized Excitons in the Spectrum of Optical Absorption of Zinc Oxide Doped with Manganese

Physics of the Solid State - The results of the study of optical absorption and EPR signals of single crystals of zinc oxide doped with manganese are presented. A broad impurity absorption band...     

Monoclinic centers of rare-earth <Emphasis Type="Italic">S</Emphasis> ions in yttrium orthoaluminate crystals

The ESR spectrum of Gd³⁺ and Eu²⁺ monoclinic centers, which substitute for yttrium ions in YAlO₃ crystals doped with europium and zirconium, has been investigated. Parameters of the fine structure of these centers are determined. The hyperfine-interaction parameters are determined for the centers with ¹⁵¹Eu isotope, and the hyperfine structure of the centers with ¹⁵³Eu isotope is discussed.     

Regular step systems on clean Si(<Emphasis Type="Italic">hhm</Emphasis>)7 × 7 surfaces

The preparation conditions and atomic structure of regular step systems on clean Si(hhm) surfaces are studied. Regular single- and triple-step structures with different periodicities have been fabricated in ultrahigh vacuum using various heat treatment procedures. The atomically resolved scanning tunneling microscopy data demonstrate several stable triple-step configurations on vicinal Si(hhm) surfaces.     

Local atomic structure of niobates and titanates from X-ray absorption spectroscopic data

The local atomic structure of PbTiO₃, BaTiO₃, and KNbO₃ perovskite-type crystals and K _x Na_{1 ? x} NbO₃ solid solutions in different phases is investigated using the angular dependence of the pre-edge structure of the Ti and Nb K X-ray absorption spectra and the EXAFS data. In noncubic phases, a considerable deviation of the local structure from the structure determined from diffraction data is observed only for the tetragonal phase of the BaTiO₃ crystal. It is revealed that, in the cubic phase of niobates, the niobium atoms are characterized by significant displacements from the centrosymmetric positions along the threefold axes, so that they are close in the magnitude and the direction to the displacements in the low-temperatures rhombohedral phases.     

Luminescence spectra of solid xenon excited by volume discharge

The luminescence spectra of solid xenon excited by a volume discharge are studied for the first time. The majority of the energy is emitted in the VUV spectral region due to the radiative decay of excitons. A specific feature of the spectra in the UV and visible regions is the complete absence of lines belonging to neutral excited particles (one-center Xe* and two-center Xe ₂ ^* excitons) and to diatomic Xe ₂ ⁺ ions. Numerous lines of the Xe⁺ ion are shifted by 0.1–0.3 nm with respect to their positions in the gas; the larger the shift, the stronger the distortion of the line shape. Based on the data obtained, a mechanism by which solid xenon is excited and ionized by fast drifting electrons is proposed.