Reconstruction of the fine structure of an acoustic scatterer against the distorting influence of its large-scale inhomogeneities

In the ultrasonic diagnostics of small-size neoplasms of biological tissues at the earliest stage of their development, an efficient way to eliminate the distorting influence of high-contrast or large inhomogeneities of the biological medium is to apply the iterative technique. A simple approach is proposed, which makes it possible with only two iteration steps to achieve an efficient focusing of the tomograph array. At the first step, the unknown distribution of the large-scale inhomogeneities of sound velocity and absorption over the scatterer is reconstructed, where the large-scale inhomogeneities are those whose size exceeds several wavelengths. At the second step, the fine structure of the scatterer is reconstructed against the large-scale background, which can be performed with a high accuracy owing to the evaluation of the background at the first step. The possibility of simultaneous reconstruction of the large-scale and fine structures by the noniterative Grinevich-Novikov algorithm is considered as an alternative. This algorithm reconstructs in an explicit form two-dimensional refractive-absorbing acoustic scatterers of almost arbitrary shape and strength. Taking into account the effects of multiple scattering, this algorithm provides resolution of the fine structure almost as good as that achieved in reconstructing the same structure against an undistorting homogeneous background. The results of numerical simulations of both algorithms are presented.     

Circuit-switching networks with FIFO plus justifying blockout service on infinite graphs

A class of circuit-switching open queueing networks is discussed. The main result of the paper is that if extra message flows are not too intensive and the path distribution is mainly concentrated on the paths of (graph) distance 1 (nearest neighbour connections), then the network has a unique stationary working regime, no matter how large the configuration graph of the network is. Standard properties of this regime are established such as decay of correlation and continuity.     

Aqueous Solutions of Colloidal Ruthenium: the Radiation–Chemical Preparation and Optical Absorption

The radiation-chemical reduction of Ru(III) is studied in aqueous RuCl₃ solutions containing isopropyl alcohol. In the presence of sodium polyacrylate, the stable sols of metal are formed with spherical particles 4–8 nm in diameter. The optical spectrum of nanoparticles is characterized by an increasing absorption in the UV spectral region with no maximum (₂₀₀ = 7.2 × 1030 l mol^–1 cm^–1). The colloids of ruthenium in an aqueous solution are stable in the open air.     

Reactions of Elemental Phosphorus and Phosphine with Electrophiles in Superbasic Systems: XVI. Phosphorylation of Benzyl Chloride with Elemental Phosphorus and Phosphine

The major product of the reaction of benzyl chloride with red phosphorus in the system concentrated aqueous KOH-dioxane-phase-transfer catalyst (43–95°C, Ar) is tribenzylphosphine oxide (yield up to 61%). Under similar conditions, phosphorylation of benzyl chloride with white phosphorus occurs differently, yielding dibenzylphosphine oxide as major product. Conditions are found for preparative synthesis of dibenzylphosphine from phosphine and benzyl chloride in the system KOH-DMSO.__________Translated from Zhurnal Obshchei Khimii, Vol. 75, No. 5, 2005, pp. 724–728.Original Russian Text Copyright © 2005 by Trofimov, Gusarova, Malysheva, Shaikhudinova, Belogorlova, Kazantseva, Sukhov, Plotnikova.     

Linear silver clusters in aqueous solution (clusterites): radiation-induced chemical synthesis and properties

The formation and properties of the products of the radiation-induced chemical reduction of silver ions in aqueous solutions containing sodium polyacrylate were investigated. The absorption spectra of these species exhibit a band at 290 mn and a band in the visible region. The latter shifts from 470 nm to -800 nm with time or after the addition of silver ions. The species obtained (clusterites) arc linear silver clusters bound to the carboxyl groups of the ion exchanger. The red shift of the visible band is due to the increase in their size. The mechanism of the formation and the structure of the clusterites are discussed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1429–1435, June, 1996.     

Reactions of Elemental Phosphorus with Electrophiles in Super Basic Systems: XVII. Phosphorylation of Arylalkenes with Active Modifications of Elemental Phosphorus

The example of the phosphorylation of styrene and 2-vinylnaphthalene with elemental phosphorus in the KOH-DMSO system at room or elevated temperature was used to show that the activated red phosphorus prepared from white phosphorus under ionizing radiation has a reactivity comparable with that of white phosphorus and significantly higher than that of ordinary technical red phosphorus.     

Infrared absorption and electron paramagnetic resonance studies of vinyl radical in noble-gas matrices

Vinyl radicals produced by annealing-induced reaction of mobilized hydrogen atoms with acetylene molecules in solid noble-gas matrices (Ar, Kr, and Xe) were characterized by Fourier transform infrared and electron paramagnetic resonance (EPR) spectroscopies. The hydrogen atoms were generated from acetylene by UV photolysis or fast electron irradiation. Two vibrational modes of the vinyl radical (nu7 and nu5) were assigned in IR absorption studies. The assignment is based on data for various isotopic substitutions (D and 13C) and confirmed by comparison with the EPR measurements and density-functional theory calculations. The data on the nu7 mode is in agreement with previous experimental and theoretical results whereas the nu5 frequency agrees well with the computational data but conflicts with the gas-phase IR emission results.