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.     

Quantum terahertz electrodynamics and macroscopic quantum tunneling in layered superconductors

We derive a quantum field theory of Josephson plasma waves (JPWs) in layered superconductors, which describes two types of interacting JPW bosonic quanta (one heavy and one lighter). We propose a mechanism of enhancement of macroscopic quantum tunneling (MQT) in stacks of intrinsic Josephson junctions. Because of the long-range interaction between junctions in layered superconductors, the calculated MQT escape rate Gamma has a nonlinear dependence on the number of junctions in the stack. We show that the crossover temperature between quantum and thermal escape increases when increasing the number of junctions. This allows us to quantitatively describe striking recent experiments in Bi2Sr2CaCu2O8+delta stacks.     

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.     

Synthesis and extraction properties of oxathiacrown compounds containing benzyl groups

8-Benzyl-1.4-dioxa-7,10-dithiacyclododecane and 11-benzyl-1,4,7-trioxa-10,13-dithiacyclopentadecane were obtained by the interaction of (2,3-dibromo-1-propyl)benzene with 1,8-dimercapto-3,6-dioxaoctane and 1,11-dimercapto-3,6,9-trioxaundecane. The extracting ability of the obtained compounds has been studied in relation to Sr²⁺ and Pb²⁺ ions from aqueous solutions in the presence of anions of various degrees of hardness with determination of the metal content by a radiometric method. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 244–249, February, 2006.     

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.     

Measurement of the ground state 2n pickup probability for 28Si+68Zn and its role in sub-barrier fusion enhancement

The ground state and excited state transfer yields for the 2-neutron pickup channel in the ²⁸Si+⁶⁸Zn system have been measured explicitly. The recoil mass separator at the nuclear Science Centre, New Delhi was used for the measurement. A NaI(T1) detector was used for detecting the deexcitation γ’s from the transfer products. The kinematic coincidence technique was employed for the transfer measurement. Simplified coupled channels calculations show that out of all transfer channels the major contribution to the sub-barrier enhancement comes from the ground state 2 neutron pickup channel with a ground state Q-value of+1.83 MeV.     

Fission fragment angular distributions in 16O+181Ta

Time of flight and energy of fission fragments were measured using pulsed beam. Fission fragment mass and energy integrated angular distributions were extracted. Fission fragment anisotropy was explained in the framework of saddle point model.