Nuclear reactions between oxygen isotopes

Elastic and inelastic cross sections have been measured for the system ¹⁶O + ¹⁷O at c.m. energies from 12.5 to 15.5 MeV, and for ¹⁶O + ¹⁸O at c.m. energies from 12 to 20 MeV, at angles between 60° and 125°. Position-sensitive detectors were employed, using the kinematic coincidence technique. The data have been analyzed with particular attention to the contributions of multiple-exchange processes.     

Asymptotic expansions of eigenvalues and eigenfunctions for elliptic boundary-value problems with rapidly oscillating coefficients in a perforated cube

We consider spectral boundary value problems of Steklov, Neumann, and Dirichlet types for second-order elliptic operators with ε-periodic coefficients in a perforated cube; the coefficients of the differential equations are assumed to satisfy some symmetry conditions. Complete asymptotic expansions with respect to the small parameter ε are constructed for eigenvalues and eigenfunctions of the said problems. Bibliography: 24 titles. Translated from Trudy Seminara imeni I. G. Petrovskogo, No. 17, pp. 51–88, 1994.     

Hydrogen production from water by visible light using zinc porphyrin-sensitized platinized titanium dioxide

The rate of H₂ evolution from aqueous suspensions of Pt/TiO₂ with deposited zinc porphyrin in the presence of an electron donor (EDTA, triethanolamine, ascorbic and oxalic acids) during irradiation by visible light (λ > 520 nm) was optimized with respect to the concentrations of platinum, zinc porphyrin and electron donor. The relationship between the rate of hydrogen evolution and pH has a maximum at pH 4–5 for EDTA, ascorbic and oxalic acids, as does the adsorption of these donors on TiO₂. In the case of triethanolamine, H₂ production increases sharply in alkaline solutions when the triethanolamine molecules are deprotonated. The photostability of the photosensitizer increases on the semiconductor. Turn-over numbers for the zinc porphyrins varied from 50 for water-soluble zinc porphyrin up to 150–185 for water-insoluble sensitizers.     

SINGLET OXYGEN INDUCES FRANK STRAND BREAKS AS WELL AS ALKALI- AND PIPERIDINE-LABILE SITES IN SUPERCOILED PLASMID DNA

A covalently closed, circular, supercoiled plasmid was exposed to singlet oxygen by a separated-surface sensitizer. For each exposure, the quantity of single oxygen entering the DNA target solution was estimated by its oxidation of histidine. After singlet oxygen exposure, some DNA samples were treated to disclose occult lesions. Agarose gel electrophoresis was then used to resolve the unrelaxed supercoils from the relaxed circular and linear species, and all bands were quantitated fluorometrically. Exposure of supercoiled plasmid DNA to singlet oxygen induced frank DNA strand breaks, alkali-labile sites (pH 12.5, 90 degrees C, 30 min), and piperidine-labile sites (0.4 M, 60 degrees C, 30 min), all in a dose-dependent manner. Yields of alkali-labile and piperidine-labile sites ranged from one to four times the frank strand break yield. Replacement of buffered H2O by buffered D2O as the DNA solvent for singlet oxygen exposures increased DNA lesion yields by a factor of 2.6 (averaged over lesion classes). Our data for the detection of frank strand breaks is at variance with published results from studies in which singlet oxygen was derived from a thermolabile endoperoxide dissolved in the DNA solution.     

Intramolecular Polycomplexes Formed by Dextran-Grafted Polyacrylamide: Effect of the Components Molecular Weight

Graft copolymers of Polyacrylamide-g-Dextran were synthesized using ceric-ion-initiated solution polymerisation technique. It is shown that the macromolecular parameters of these copolymers and their molecular structure strongly depend on the molecular weight of the Dextran part.     

Some new fundamental properties of GaN single-crystal films on SiC and sapphire substrates

Il Nuovo Cimento D - The reflectance spectra of GaN/6H-SiC, films and the absorption spectra of GaN/Al2O3 films were studied and several fundumental parameters of GaN-energy positions of exciton,...     

Structure and growth morphology of RF-sputtered superthin niobium films

Superthin niobium films of 3 to 35 Å thickness prepared by radio-frequency sputtering have been studied by modern X-ray methods, such as reflectometry, fluorescence analysis and grazing beam structure analysis. It has been shown that the films were polycrystalline and consisted of several layers of niobium oxides and solid solution Nb O. Two simple models were used to describe erly stages of film growth. In the stage of island growth the complete oxidation of Nb to Nb₂O₅ is inevitable. Beginning from effective thickness ∼ 5 Å the deposited film becomes continuous, and further, layer-by-layer growth takes place.