Influence of oxygen partial pressure on properties 12zsolid solutions

The annealing of YBa₂Cu_zO_7−δcompounds (2.5 ≤ z ≤ 3.5) in oxygen flow (at temperature of synthesis and following fast cooling) leads to: (i) a reduction in homogeneity range; (ii) decreasing of copper content influence on superconducting properties of samples; (iii) considerable decreasing of ΔT_cvalue as a result of cation and anion vacancies order.     

Photoluminescence of GeO<Subscript>2</Subscript> films containing germanium nanocrystals

Germanium nanocrystals were formed in a GeO₂ film during the process of germanium monoxide gas-phase deposition onto a sapphire substrate and studied by photoluminescence (PL) and Raman scattering spectroscopy. A PL peak in this heterosystem was observed in the visible region at room temperature. The sizes of Ge nanocrystals were estimated from the position of a Raman peak corresponding to scattering by localized optical phonons in germanium. The PL peak position calculated with allowance for the electron and hole size quantization in Ge nanocrystals coincides well with the experimentally observed position of this peak.     

Structure and superconducting properties of Bi2Ba2−xMxCuO6+δ

The effect of oxygen nonstoichiometry and barium cation substitution on the structure and superconducting properties of Bi₂Ba_2−xM_xCuO_{6 +δ}(M = Sr, Ru, Rh, Pd, In, Sb or Pb;xchanged from 0 to 0.2) were studied. The cation-substituted samples annealed in oxygen flow contain a superconducting phase withT_c^initnear 95 K.     

Effect of Coupling between Rotational and Translational Brownian Motions on NMR Spin Relaxation: Consideration Using Green Function of Rigid Body Diffusion

Using the Green function of arbitrary rigid Brownian diffusion (Goldstein,Biopolymers33, 409–436, 1993), it was analytically shown that coupling between translation and rotation diffusion degrees of freedom does not affect the correlation functions relevant to the NMR intramolecular relaxation. It follows that spectral densities usually used for the anisotropic rotation diffusion (Woessner,J. Chem. Phys.37, 647–654, 1962) can be regarded as exact in respect to the rotation–translation coupling for the spin system connected with a rigid body.     

Relationship between (micro)structure and functional (photocatalytic and adsorption) properties of anatase–mordenite nanocomposite

Research on Chemical Intermediates - Anatase–mordenite nanocomposite was synthesized in&nbsp;situ and characterized by X-ray diffraction analysis, Brunauer–Emmett–Teller...     

Lithium experiment on solar neutrinos to weight the CNO cycle

The measurement of the flux of beryllium neutrinos with an accuracy of about 10% and CNO neutrinos with an accuracy of 20–30% will enable one to find the flux of pp neutrinos in the source with an accuracy better than 1% using the luminosity constraint. The future experiments on νe^? scattering will enable one to measure with very good accuracy the flux of beryllium and pp neutrinos on the Earth. The ratio of the flux of pp neutrinos on the Earth and in the source will enable one to find with very good accuracy a mixing angle θ_⊙. A lithium detector has high sensitivity to CNO neutrinos and can find the contribution of the CNO cycle to the energy generated in the Sun. This will be a stringent test of the theory of stellar evolution and combined with other experiments will provide a precise determination of the flux of pp neutrinos in the source and a mixing angle θ_⊙. The work on the development of the technology of a lithium experiment is now in progress.     

Physical substantiation of the lithium experiment

The lithium detector is highly efficient for measurement of CNO neutrino flux. The application of the equation of solar luminosity balance provides a possibility of determination of the total pp-neutrino flux with an uncertainty of approximately 1% if the neutrino flux from CNO cycle is measured with an uncertainty of 30%. This is possible if the measurement uncertainty of the total neutrino capture rate by lithium is 10%, which can be reached using a detector with a mass of 10 t during 5 years. As a rule, experiments with solar neutrinos are carried out for 10 years and longer.     

Structure and mechanical properties of foils made of nanocrystalline beryllium

The phase composition and structural features of (45–90)-μm-thick foils obtained from nanocrystalline beryllium during multistep thermomechanical treatment have been established using electron microscopy, electron diffraction, electron backscattering diffraction, and energy-dispersive analysis. This treatment is shown to lead to the formation of a structure with micrometer- and submicrometer-sized grains. The minimum average size of beryllium grains is 352 nm. The inclusions of beryllium oxide (ВеО) of different modifications with tetragonal (sp. gr. P4₂/mnm) and hexagonal (sp. gr. P6₃/mmc) lattices are partly ground during deformation to a size smaller than 100 nm and are located along beryllium grain boundaries in their volume, significantly hindering migration during treatment. The revealed structural features of foils with submicrometer-sized crystallites provide the thermal stability of their structural state. Beryllium with this structure is a promising material for X-ray instrument engineering and for the production of ultrathin (less than 10 μm) vacuum-dense foils with very high physicomechanical characteristics.     

Kinetics of fluorination of metallic molybdenum with elementary fluorine

The kinetics of the heterogeneous reaction of metallic molybdenum with elementary fluorine under conditions close to those used in actual technological practice at a concentration of fluorine in the gas mixture equal to 20–50 vol % was studied. The kinetic parameters were evaluated using the Arrhenius equation. A regression equation was obtained using the statistical method of experimental design for practical calculations of the rate of fluorination of metallic molybdenum with elementary fluorine. This equation makes it possible to calculate the fluorination rate at any point of the factor space, at fluorine concentrations of 30–50 vol % and initial temperatures of 250–350°C.Translated from Zhurnal Prikladnoi Khimii, Vol. 77, No. 12, 2004, pp. 1950–1955.Original Russian Text Copyright © 2004 by Rybakov, Seredenko, Orekhov, Mironov.     

Cryo-Electron Tomography Studies of Cell Systems

Crystallography Reports - Cryo-electron tomography is a powerful tool for determining the three-dimensional structures of macromolecular complexes in their natural environment. The minimization of...