A parametric antenna for hydrophysical research on long-distance paths

This work considers the capabilities of a hydroacoustic antenna based on principles of nonlinear acoustics to perform hydrophysical studies on long-distance paths. The antenna is described and results from initial experiments at sea are reported. The antenna is installed at a depth of 40 m at the site of investigations by the Hydrophysical Institute, Abkhazia Academy of Sciences. At a pumping frequency of 20 kHz, it allows the medium to be probed in the 300–3000 Hz range of parametric radiation on long-distance routes. The sharp directional pattern (2° angular resolution) of the broadband parametric radiation ensures single-mode excitation of the marine waveguide throughout the frequency band. Generation of a specific signal by a parametric antenna provides conditions for using the frequency dispersion of the velocity of acoustic signal propagation in the marine waveguide to compress the signal as it travels along a long-distance path.     

Reactions of polyfluoroalkenylsulfenyl chlorides with carbonyl compounds

Polyfluorinated 1-fluoroalk-1-enylsulfenyl chlorides react with ketones RCOCH₂R′ to give unsaturated sulfides. The latter undergo smooth cyclization into 2-alkylidene-1,3-oxathioles in the presence of BF₃·NEt₃. Published inIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1770–1773, October, 2000.     

Molecular simulation of gas hydrate nanoclusters in water shell: Structure and phase transitions

Gas hydrate nanoclusters surrounded by water shells are studied by the molecular dynamic method. Hydrates of methane (sI structures) and krypton (sII structures), as well an ice nanocluster in a supercooled water shell, are considered. The main attention was focused on studying the local structure and phase transitions. Variations in local partial densities with an increase in temperature are monitored. Melting points of nanosized samples of gas hydrates are determined using caloric curves. Additional information on the behavior of the considered systems is obtained from the temperature dependences of diffusion coefficients and the Lindemann criterion. Two-phase transitions are revealed for gas hydrate nanoclusters. The first phase transition at 210 K can be assigned to the melting of the ice shell. The second transition at 230–235 K is identified as the phase transition in the hydrate core. The melting of ice cluster is observed at 215 K, which corresponds to the melting point of bulk crystal upon the use of the SPC/E water model.     

Convenient method of synthesis of Cp2TaH3

Modified method for preparation of Cp₂TaH₃ by reaction between TaCl₅, CpNa, and LiAlH₄ in dimethoxyethane is described: The yield of Cp₂TaH₃ is 25 %.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2050–2051, October, 1995.     

Increase in the fatigue durability of stainless steel by electron-beam surface treatment

The structure, phase composition and dislocation substructure of 20Cr23Ni18 steel subjected to electron-beam treatment and subsequent multicycle fatigue loading until destruction were studied by scanning and transmission electron microscopy. It was shown that electron-beam treatment with an energy density of 20 J/cm² increases the fatigue durability by a factor of 2.1. The cause of steel fatigue destruction is analyzed and a way of further increasing the fatigue durability is proposed.     

Trifluoromethyl-containing cumulated 1,3-oxathiols and 1,4-oxathians

In the course of acid catalysis, ortho-(1-trifluoromethylvinylthio)phenols cyclize into benzo-1,3-oxathiols, and on treatment with aqueous alkali — into benzo-1,4-oxathians. The characteristic features of these transformations and the oxidative reactions of oxathians were studied.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1625–1630, July, 1991.     

Modeling the solvation shell of complexes in solution for quantum chemical calculations of electronic spectra

A procedure that allows for solvation effects is suggested; it is designed for quantum chemical calculations of the electronic spectra of complex compounds. Based on Monte Carlo (MC) simulation of the solvation shell one can calculate the electrostatic potential created by the solvation shell at the sites of all atoms of the complex; appropriate corrections are added to the diagonal elements of the Fock matrix and to the matrix elements of the Hamiltonian in the configuration interaction method. The method suggested has been implemented based on the semiempirical (CINDO) version of the CI (configuration interaction) technique and tested on the following compounds: [Ru(NH₃)₅(py)]²⁺, [Ru(NH₃)₅(pyz)]²⁺, [Ru(bpy)(CN)₄]^2?, [Ru(NO)(py)₄-NC-Ru(py)₄(CN)]³⁺.     

Uranium hexafluoride reduction with hydrogen atoms

The simulation of uranium hexafluoride reduction to uranium tetrafluoride by hydrogen and fluorine in flow has demonstrated that the high-capacity thermochemical atom generators designed for continuouswave chemical lasers are promising for the industrial implementation of the continuous reduction process. Two variants of the reduction process are suggested: one uses a generator of H atoms and the other uses a generator of F atoms.