A statistical analysis of the kinetics of chain-branching chemical reactions with quadratic chain termination

Analytical and numerical simulations of stochastic phenomena in the kinetics of chain-branching reactions with linear and quadratic chain termination during fast changes in external conditions that cause sharp transitions of the governing parameter through the critical point were studied. A statistical analysis was performed based on nonlinear stochastic differential equations of Langevin type for the concentration of active species and on the corresponding Fokker-Planck equations for the probability distribution function of the concentration of these species. An expression for the statistical distribution of the induction period of the reaction and its mean and variance were calculated from an approximate analytical solution. The time evolution of the probability density function of the concentration of active species was presented graphically.     

Ferrite and high-temperature superconductor targets for sputtering

A method is described of preparing targets for sputtering, which involves the use of plasma deposition of respective powders onto a cooled metal plate. It is demonstrated that the use of plasma technology enables one to produce, in a controlled atmosphere, intricately shaped ceramic targets characterized by a highly uniform composition and by reliable mechanical and thermal contact of the resultant coating with the holder plate. Experiments are performed on the sputtering of targets to prepare polycrystalline ferrite films for magnetooptical applications and epitaxial films of high-temperature superconductors.     

Evolution of the optical properties and the electrical resistivity of CaMnO3 during the substitution of Mo for Mn ions

The reflectance, the optical density, and the optical conductivity spectra of CaMn_{1 ? x} Mo _x O₃ (x ≤ 0.07) polycrystals are studied over a wide spectral region. The substitution of Mo⁶⁺ ions for Mn⁴⁺ ions leads to a strong decrease in the first high-energy phonon band, which is related to vibrations in the MnO₆ octahedron. The appearance of band-type charge carriers is detected in CaMn_{1 ? x} Mo _x O₃ with x ≤ 0.04, and carrier localization is observed in CaMn_0.93Mo_0.07O₃. This localization increases at T < 160 K, i.e., during the transition from the paramagnetic to the antiferromagnetic state with orbital ordering and a monoclinic structure. The optical conductivity spectrum of CaMn_0.93Mo_0.07O₃ exhibits a strong shift of fundamental absorption bands, which is associated with a change in the band structure because of a decrease in the splitting of the 3d levels of Mn in the crystal field.     

Determination of Mercury by Nondispersive Atomic Fluorescence Spectrometry

A nondispersive atomic fluorescence spectrometer for the determination of mercury by the cold-vapor technique has been developed. The conditions for mercury vapor generation in a hydride generator (the concentration and volume of the reagents, reaction and purge times, and argon flow rate) are optimized for fluorescence measurements. An algorithm is proposed for the calculation of the analytical signal that leads to an increase in the signal-to-noise ratio by a factor of 3 as compared to the conventional procedure. On the basis of the results obtained, procedures for the determination of mercury in soil and semolina samples are developed with a detection limit of 60 pg and RSD = 10%. The accuracy of the determinations is verified by an analysis of standard reference samples of soil and semolina.     

Optical properties of the Cr<Subscript>5</Subscript>S<Subscript>6</Subscript> single crystal

Results of the investigation of optical density spectra of Cr₅S₆ single crystals in the infrared region have been presented. A comparative analysis of the temperature dependences of the magnetization and the light absorption has been performed. Physical mechanisms to explain the specific features of the spectral and temperature dependences of the optical density have been proposed.     

Magnetoreflection of light in CoFe<Subscript>2</Subscript>O<Subscript>4</Subscript> magnetostrictive spinel

The reflection and magnetoreflection of natural light within the infrared spectral range is studied in single crystals of CoFe₂O₄ ferrimagnetic ferrite spinel. Correlation between the reflection of light and magnetoelastic characteristics of this spinel is found. It is shown that the most significant magnetic-field-induced changes in the magnetoreflection of the spinel occur near the fundamental absorption edge and within the range of the phonon spectrum.