On the nature of the processes occurring in silver doped SiO<Subscript>2</Subscript> films under heat treatment

The processes taking place on air-heating of SiO₂−Ag⁺ films and xerogels produced from the SiO₂ sols of different pH (3.7 or 9.5) were investigated. Silver nanoparticles 10–40 nm in size tolerant to oxidation at temperatures above 600 °C were found to be formed in the systems whatever the pH value of the starting sol. SiO₂ crystallization giving the cristobalite phase in the temperature range from 500 to 800 °C was shown to proceed only in the films produced from the acidic sol, while in those formed from the alkali one SiO₂ remained amorphous. A mechanism by which the formation of Ag nanoparticles and the cristobalite phase occurs in the films at the oxidative conditions is suggested.     

Niobium (V) peroxocomplexes as a catalyst of oxidation of methylphenylsulphide by hydroperoxide

The electrospray ionization-mass spectrometry (ESI-MS) method has been used for determination of the structure of niobium peroxocomplexes. The formation of mono- and bisperoxocomplexes has been established. These complexes contain Schiff bases and 8-quinolinol as ligands. Trisperoxocomplexes are formed when pyridine and 1,10-phenanthroline are used. Peroxocomplexes with Schiff bases as ligands has shown a high activity as catalysts in the methylphenylsulphide oxidation.     

Investigation of the structural aspects in the formation of optical properties of the GeO2-Eu2O3-Ag nanosystem

The structural characteristics of the 95GeO₂-5Eu₂O₃, 94.9GeO₂-5Eu₂O₃-0.1Ag, and 99.9GeO₂-0.1Ag xerogels annealed in air at the temperature T _an = 850°C have been studied using X-ray diffraction and small-angle neutron scattering. It has been established that the significant change in the relative intensity of the ⁷ F ₀ → ⁵ L ₆ and ⁷ F ₀ → ⁵ H ₆ luminescence excitation bands of Eu³⁺ ions upon introduction of silver correlates with the decrease in the characteristic sizes of polydisperse clusters formed during annealing. The character of the changes in chemical bonds in the system due to the clustering and their role in the formation of optical properties have been analyzed.     

Surface-ionization mass spectrometry of acetylcholine halides

The surface ionization of acetylcholine iodide has been investigated mass-spectrometrically. It has been shown that surface-ionization mass spectrometry with the successive use of catalytically active and catalytically passive ionizers (ion emitters) permits a highly sensitive and reliable identification of micro amounts of acetylcholine molecules, including those present in complex mixtures.U. A. Arifov Institute of Electronics, Academy of Sciences of the Republic of Uzbekistan, Tashkent, fax (371) 162 87 67. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 70–74, January–February, 1998.     

Formation of Silver and Copper Nanoparticles upon the Reduction of Their Poorly Soluble Precursors in Aqueous Solution

The possibility of preparing silver and copper sols with a concentration of disperse phase of 10^–3 mol/l upon the reduction of poorly soluble precursors (AgI, CuI) is studied. It is established that reduction of AgI proceeds according to the solid-state mechanism with the formation of smaller Ag particles and is kinetically retarded because of the formation (on the AgI surface) of a silver shell, thus hindering the access of the reductant to AgI. The reduction of copper iodide occurs through the solution with the formation of Cu nanoparticles, the sizes of which are comparable to those of the initial iodide particles, and is limited only by the CuI dissolution rate.     

Instability of the magnetization reversal front in superconductors with a nonlinear anisotropic current-voltage characteristic

The instability of a magnetic flux flow in a system of vortices and antivortices in superconductors with a power (exponent m) anisotropic current-voltage characteristic was studied theoretically. It was shown that instability arose even at a comparatively weak anisotropy of the current-carrying properties of a superconductor if m?1. The dispersion equation determining the dependence of the increment of instability growth on the wave number was derived and analyzed.     

Anisotropic origin of the bending instability of the flux-antiflux interface in type-II superconductors

The physical nature of the macroturbulence in vortex matter in YBCO superconductors is investigated by means of a magneto-optic study of the instability in a single crystal prepared especially for this purpose. The instability develops near those sample edges where the oppositely directed flow of vortices and antivortices, guided by twin boundaries, is characterized by the discontinuity of the tangential component of the hydrodynamic velocity. This fact indicates that the macroturbulence is analogous to the instability of fluid flow at a surface of a tangential velocity discontinuity in classical hydrodynamics and is related to the anisotropic flux motion in the superconductor.     

Integral representation of a class of univalent functions

We refine and generalize a result of V. A. Zmorovich on the integral representation of a class of univalent functions which are convex in some direction. We prove that all function of the class being considered can be approximated by a Schwarz-Christoffel integral of a special form belonging to the same class.Translated from Matematicheskii Zametki, Vol. 19, No. 1, pp. 41–48, January, 1976.     

Facile Transformation of the Hydroxy‐Substituted Oxathiacrown Ethers

9(12)‐Hydroxy‐dithia‐13(16)‐crown‐4(6)‐ethers have been prepared by the condensing an oligoethylene glycol dithiol with 2,3‐dibromo‐1‐propanol. Methods of oxidation, halogenation, amination, and esterification of the 9‐hydroxythiacrown ether, producing corresponding oxathiacrown ether derivatives in good yields, have been developed. Cyclic destruction has not been found in the studied reactions. The change of the oxathiamacrocyclic ring size in the course of the halogenation and amination reactions was revealed.