Optical fractionation of an ensemble of impurity molecules with respect to the magnitude of the piezochromic effect

A method of hole burning in the 0-0 band of the impurity-absorption spectra of polymers and glasses is suggested. This method is selective not only with respect to the transition energy, but also with respect to the magnitude of the piezochromic effect. It is shown that, in combination with the modulation of the wavelength of probe radiation, this method makes it possible to determine the contribution of the impurity molecules with a specified magnitude of the piezochromic effect to the total absorption and luminescence of a sample. This circumstance allows one to study experimentally the correlation of the piezochromic effect with other characteristics of impurity molecules.     

Search for the emission of π<Superscript>0</Superscript> mesons from the neutron-induced fission of <Superscript>235</Superscript>U nuclei

A nuclear-reactor experiment on the search for the emission of neutral pions from the neutron-induced fission of ²³⁵U nuclei has been carried out. To this end, an experimental setup for searching for the emission of π⁰ mesons with high sensitivity to this process has been designed and produced. This setup consisted of two Cherenkov total-absorption spectrometers for the detection and measurements of the energy of two gamma-ray photons from π ⁰-meson decay. The spectrometers were placed at the exits of two coaxial horizontal experimental channels. To protect the detectors from low-energy β and γ rays and neutron fluxes, 3.5-m-long water filters were situated in the channels. To reject the cosmic background, large-area scintillation counters operating in the anticoincidence mode were placed over each spectrometer. The energy and time resolution of the spectrometers, as well as the efficiency of detecting charged particles by scintillation counters, were tested on the secondary electron beam of the Tomsk electron synchrotron Sirius. Runs of measurements of the effect on the operating reactor (duration of 805 h) were alternated with runs of measurements of background on the stopped reactor (duration of 403 h). Statistical processing of the experimental results yields an upper limit of ≤5.3×10 ^?12 with a 90% confidence level for the probability of the emission of neutral pions from the neutron-induced fission of ²³⁵U nuclei. This result and results of other works carried out with sources of spontaneously fissioning ²⁵²Cf nuclei show that the probabilities of the emission of π⁰ mesons from spontaneous fission and fission induced by fission-spectrum neutrons are equal to each other.     

Growth of Sb-Bi gradient single crystals

The growth conditions and structural quality of Sb-Bi gradient single crystals with Bi content from 2 to 18 at %, grown by the Czochralski method with solid phase feed, are investigated. Bi distribution in the crystals along their pulling direction are studied by electron probe microanalysis and the change in the interplanar spacing is analyzed by double-crystal X-ray diffraction. It is established that the pulling rate and feed mass affect the Bi distribution in Sb-Bi single crystals.     

Thermal-performance evaluation of coolant passages with staggered arrays of pin fins

Three-dimensional laminar forced convection including steady-periodic transition is investigated up to periodic-chaotic transition in the fully developed region of coolant passages with staggered arrays of pin fins. Comparative examples concern overall pressure losses and heat transfer characteristics of circular, square and elliptical pins made of nickel and copper. In the numerical model, transient conjugate heat transfer is assumed and space periodicities in pressure, velocity components and temperatures are taken into account. In the range of operative conditions investigated, overall friction factors increase almost linearly with the Reynolds number, while the increase of overall Nusselt numbers with the Reynolds number is characterized by two slope changes connected with the onset of streamwise vortices, and the shedding of transverse vortices, respectively. The use of copper, instead of nickel, increases the overall Nusselt number with all shapes, but is particularly beneficial to the elliptical section. Square pins are characterized by the highest values of friction factors, but are also the best performers as far as convection enhancing is concerned. The reverse is true for the elliptical pins which are characterized by the lowest values of friction factors, but are the worst performers as far as convection enhancing is concerned. On the basis of overall performances, the elliptical pins made of copper are the best choice, at least in the upper range of Reynolds numbers investigated.     

Adsorption of the Cu<Superscript>2+</Superscript> ions from aqueous solutions on the active carbon oxidized with hydrogen peroxide and impregnated with nitrogen-containing compounds

Adsorption of the copper ions from aqueous solutions, benzene, and water on the active carbon obtained by chemical activation from walnut shells was studied. The active carbon was additionally oxidized with hydrogen peroxide and then impregnated with nitrogen-containing compounds. As a result of impregnation with melamine, a secondary porosity is formed within the oxidized active carbon, leading to an increase in the specific surface of the sorbent. A modified carbon surface is heterogeneous, and the carbons themselves exhibit catalytic activity in the oxidation of luminol and decomposition of hydrogen peroxide.     

Synthesis and structure of nanocrystalline La0.50Ba0.50MnO3

Nanocrystalline manganite La_0.50Ba_0.50MnO₃ was synthesized by the soft-chemical method. For this purpose, the sol-gel method was modified and improved. A trihydric saturated alcohol, e.g., glycerol, was suggested as a new organic matrix. The crystal structure of the composite was studied by X-ray powder diffraction at room temperature. A La_0.50Ba_0.50MnO₃ powder annealed in air at T = 500°C is characterized by a perovskite-like cubic structure with the unit-cell parameter a = 3.869 Å. The chemical composition of the sample was studied by electron-probe X-ray microanalysis. The La: Ba: Mn cation ratio in the material was 1: 1: 2. The surface topography was examined with a scanning electron microscope. The crystallite size was ～30 nm. The dependence of the crystal structure and the surface topology on the annealing temperature was studied. The high-temperature treatment in air resulted in the growth of larger, micrometer-size, crystallites.