Crystal structures of double calcium and alkali metal phosphates Ca10 M(PO4)7(M = Li, Na, K)

Crystal structures of double calcium and alkali metal phosphates described by the general formula Ca₁₀ M(PO₄)₇(M = Li, Na, K) have been studied by the Rietveld method. The lattice parameters are a = 10.4203(1) and c = 37.389(1) Å (for M = Li), a = 10.4391(1) and c = 37.310(1) Å (for M = Na), and a = 10.4229(1) and c = 37.279(2) Å (for M = K); sp. gr. R3c, Z = 6. The specific features of the distribution of alkali metal cations over the structure positions are discussed.     

Ion aggregation of methylpyrazinium iodide and its derivatives in crystals and in solutions of nonpolar solvents

Aggregation of methylpyrazinium iodide and its derivatives in chloroform and dichloromethane solutions was studied by EAS and ¹H NMR spectroscopy. The isopentylpyrazinium iodide ion quadruple formation constants in solutions were evaluated. Formal extinction coefficient in the outer-sphere charge transfer band maxima does not depend on the degree of aggregation in the system. A model suggested for the formation of ion quadruples in solutions was discussed in terms of the density functional theory and using the X-ray diffraction data for crystalline methylpyrazinium iodides and its derivatives.     

Effect of annealing on the structural and microwave magnetic properties of singlelayer and multilayer films of various compositions

The effect of annealing on the structure and microwave magnetic properties of composite single-layer and multilayer films is investigated. It is found that as the threshold annealing temperature is attained, the width of the FMR line increases abruptly, depending on the concentration ratio of metallic alloy and dielectric. It is shown that the FMR line broadening is also associated with the occurrence of and increase in high-frequency modes of absorption. The surfaces of annealed and unannealed films are investigated at various concentrations of metallic alloys and dielectrics using an atomic force microscope. The strong change in the magnetic characteristics after film annealing is associated with a change in surface roughness and inhomogeneity, and in the size distribution of nano- and submicron formations and their spacing.     

Numerical-analytical method for investigating the stability of the axisymmetric motion of bodies of revolution in soil media

A method for investigating the stability of the axisymmetric motion of a body of revolution in a compressible soil medium with allowance made for the nonlinear physical and mechanical properties of the soil and the effects of two-dimensional flow is presented.     

Analysis of models for calculating the motion of solids of revolution of minimum resistance in soil media

The solution of problems of searching for the optimal shape of a body when it penetrates into dense media is considered using local interaction models (LIMs) and Grigoryan's model of a soil medium in an axisymmetric formulation. A new LIM is obtained that is improved by taking account of the non-linear compressibility and shear strength in the analytical solution of a problem on the expansion of a spherical cavity. The applicability of an LIM that is quadratic with respect to the velocity in determining the forces resisting penetration of sharp bodies into soft soil is justified theoretically and experimentally and the violation of the conditions for the model to be applicable in the case of blunt bodies is established. It is shown that a solution taking account of non-linear flow effects in a two-dimensional formulation enables both the shape as well as power and kinematic characteristics of the optimal blunt bodies as they pass through soil media to be improved considerably. The ratio of the finite depths of penetration of solids of revolution into soft ground taking account of internal friction is estimated by the ratio of the coefficients in the Rankine–Resal formulae.     

Thermodynamics of a gas of deconfined bosonic spinons in two dimensions

We consider the quantum phase transition between a Néel antiferromagnet and a valence-bond solid (VBS) in a two-dimensional system of S = 1/2 spins. Assuming that the excitations of the critical ground state are linearly dispersing deconfined spinons obeying Bose statistics, we derive expressions for the specific heat C and the magnetic susceptibility χ at low temperature T in terms of a correlation length ξ(T). Comparing with quantum Monte Carlo results for the J-Q model, which is a candidate for a deconfined Néel-VBS transition, we obtain an almost perfect consistency between C, χ, and ξ. The corresponding expressions for magnon (triplet) excitations are not internally consistent, however, lending strong support for spinon excitations in the J-Q model.     

Synthesis and properties of fluorosilicon compounds for protection of cultural monuments from harmful environmental exposure

Methods for the synthesis of perfluorocarboxylic acid derivatives with reactive trialkoxysilyl groups soluble in organic and organofluorine (1,1,2-trichlorotrif1uoroethane, etc.) solvents have been developed. The contact angles of water and decalin, water absorption, resistance to freezing, and salt-resistance of limestone and plaster samples treated with these compounds were determined. Fluorosilicon organic compounds impart more hydro- and oleophobic properties to the protected surfaces than known organosilicon agents and reliably protect sculptures and architectural monuments from mold and algae deposition.     

Synthesis and thermal properties of polydimethylsiloxanes modified by decyl and methylundecylenate substituents

A series of polydimethylsiloxanes modified by long-chain hydrocarbon substituents, including those containing terminal ester groups, was synthesized. The structures of the copolymers were confirmed by the data of ¹H and ²⁹Si NMR spectroscopy. The thermal properties of the copolymers were studied by differential scanning calorimetry. The change in the behavior of the copolymers is observed at the content of modifying units is >5 mol.% and the fluidity of the polymers is retained at the content of these units <15 mol.%.     

The first conducting cationic bis-dithiolene complexes of nickel and gold

Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2158–2159, September, 1989.