Features of the Jahn-Teller transition in Ni1 − x Co x Cr2O4 solid solutions

The structure of Ni_{1 ? x} Co _x Cr₂O₄ solid solutions has been investigated by synchrotron X-ray powder diffraction in the temperature range of 90–350 K for compositions x = 0, 0.005, 0.01, 0.015, 0.02, 0.1, 0.5, and 0.8, and their structures have been refined using the Rietveld analysis. The T-x phase diagram for solid solutions in the studied range of temperatures and concentrations has been constructed based on the obtained data. The revealed structural phase transitions have been explained from the viewpoint of the crystal field theory and the Jahn-Teller cooperative effect. Distortions of polyhedra, which are the cause of the structural phase transition, have been evaluated. The applicability of the Landau phenomenological theory and the possibility of using the magnitude of spontaneous strains as the order parameter have been discussed.     

Peculiarities of the microstructure of a nanoscale modification of η-TiO2

Samples with nanoscale η-TiO₂ phase have been obtained by sulfate and modified sulfate methods and are characterized by a complex of techniques: X-ray diffraction, electron diffraction, small-angle X-ray scattering (SAXS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy, and X-ray energy-dispersive analysis. The effect of sample formation conditions on the size and shape of crystallites, content of the amorphous component in the samples, and their elemental composition has been established. A significant change (depending on the synthesis conditions) in the parameters of the diffraction reflection with d ～ 17–21 Å (intensity and interplanar spacing d, Å), pronounced for η-TiO₂, is revealed. This change is most likely related to the variation in the content of water molecules in the interlayer space of η-TiO₂ structure and/or the change in crystallite shape.     

Extreme shockwave systems in problems of external supersonic aerodynamics

The stationary shockwave systems (the sequences of shocks, isentropic expansion and compression waves), which arise at a planar supersonic flow of perfect inviscid gas around the bodies are investigated theoretically. The domains of the existence of shockwave systems under consideration are found analytically and numerically for the model problems of supersonic aerodynamics (the flow around a single plate, the plate with the frontal shield, polygonal profiles), the parameters of systems are determined, which provide the extrema of the force and thermal loadings as well as of the aerodynamic coefficients of streamlined bodies.     

Channeling of Auroral Kilometric Radiation During Geomagnetic Disturbances

JETP Letters - The electromagnetic fields measured on the ERG satellite are presented and their comparative analysis with measurements on the WIND satellite is carried out. The possibility of...     

Assessment of Subgrid-Scale Models for Decaying Compressible MHD Turbulence

Large eddy simulation method is formulated for study of compressible magnetohydrodynamic turbulence and assessment of different subgrid-scale models as applied for decaying case is performed. The filtered equations of compressible magnetopause using the mass-weighted filtering operation are obtained. Mass-weighted filtered equations for large-scale turbulent component comprise subgrid-scale terms and five models for closure of the subgrid-scale terms are suggested. In present paper the obtained results of numerical computations for large eddy simulation are compared with the results of direct numerical simulation of three-dimensional compressible magnetohydrodynamic turbulence. Assessment of five subgrid-scale models of large eddy simulation for MHD flows is fulfilled. The comparisons between large eddy simulation and direct numerical simulation are carried out regarding the temporal evolution of the global quantities kinetic and magnetic energy, cross helicity and the spectra of kinetic and magnetic energy.     

Viscoelastic vibrations of a triangular plates

The problem of stationary vibrations of a viscoelastic equilateral triangular plate is treated. The vibrations are caused by the action of a uniformly distributed load which varies harmonically and by the motion of the simply supported boundary of the plate as a rigid body which vibrates at the same frequency. The level lines of the vibration amplitude are studied and the graphs of the amplitude distribution along the height of the triangle are given.     

Synthesis of Polycrystalline CdSiP2 in a Gradient Temperature Field

Russian Physics Journal - A procedure for the synthesis of a CdSiP2 compound from the initial elementary components in a gradient thermal field has been developed. The phase and chemical...     

Auroral Kilometric Radiation as a Diagnostic Tool for the Properties of the Magnetosphere

JETP Letters - Auroral kilometric radiation is used as a tool for the remote diagnostics of processes in the Earth’s magnetosphere. Using satellite data and the spectrum of fluctuations of...