Diffraction image of screw dislocations in X-ray section topography methods

X-ray diffraction patterns in a thin crystal are investigated by numerical simulation and experimental section topography for the case when the screw dislocation axis is parallel to the dislocation vector. The strongly distorted region near the dislocation core is found to operate like an X-ray mirror wheninteracting with an X-ray wave field in a scattering triangle; i.e., new wave fields appear in the new scattering triangles in the strong distortion region where the crystal departs from the reflecting position, and the coherent interaction of the new fields with the old leads to the formation of a complex X-ray image. Superposition of these waves, taking into account their phases, is found to result in a large variety of defect images.     

Optimization of ocean acoustic monitoring systems

We formulate and solve certain problems of the optimal amplitude-phase tuning of antenna complexes that emit and receive acoustic signals in inhomogeneous ocean-type waveguides.     

Raman scattering spectroscopy of inclusions of carbon in Al<Subscript>2</Subscript>O<Subscript>3</Subscript> films and its solid solutions with HfO<Subscript>2</Subscript>

We apply Raman scattering spectroscopy to study the nature of carbon inclusions in Al₂O₃ and (HfO₂) _x (Al₂O₃)_{1 ? x} films deposited using volatile complex compounds. Raman spectra of the films under investigation contain D and G vibrational modes, which indicate that carbon clusters of the sp ² configuration tend to form in the films. We estimate the size of clusters from the integrated intensity ratio I _D /I _G and find it to be in the range of 14–20 Å. The content of hydrogen in carbon clusters is calculated from the height of the photoluminescence pedestal and is found to vary from 14 to 30 at % depending on the regime of the film’s synthesis.     

Holographic nanocomposites for recording polymer-nanoparticle periodic structures: I. General approach to choice of components of nanocomposites and their holographic properties

We studied polymerizable nanocomposites for obtaining polymer-nanoparticle periodic structures by a holographic method. A general approach to choosing components of composites is developed that ensures a maximal contrast and high efficiency of structures for different types of nanoparticles. We found that the optimal monomeric component of a nanocomposite is a combination of single- and multifunctional monomers with substantially different reactivities. In this case, the low-reactivity monomer should posses a low viscosity, be a good solvent for nanoparticles, and have a low thermodynamic affinity to the polymer network formed upon the polymerization of the high-reactivity monomer. We developed a holographic composition based on known commercially produced monomers that ensures the formation of highly efficient periodic structures for nanoparticles of different types. We described the holographic properties of obtained nanocomposites, as well as parameters of bulk gratings recorded in them.     

Behavior of ascorbic acid in hetero- and homophase chain-radical oxidation processes

Initiated hetorophase oxidation of cumene with oxygen was examined in the presence of ascorbic acid in a wide concentration range.     

Base-free aerobic oxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid over Pt/C catalysts synthesized by pulse alternating current technique

The Pt/C catalysts with various Pt content (5-30 wt%) synthesized via electrochemical pulse alternating current technique have been evaluated for the base-free aerobic oxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid. The higher Pt content in the catalyst (30 wt%) provides the product yield up to 65% upon performing the process in concentrated (～0.1 M) aqueous solutions of the substrate.     

X-ray diffraction in a uniformly bent crystal in reflection geometry

The features of the intensity distribution over the exit surface of a uniformly bent crystal have been investigated in reflection geometry. Experiments have been performed using thin-layer heterostructures Si_(1−x)Ge _x /Si. For heterosystems, internal stresses induced in the film and substrate lead to an elastic bending of the whole system. The section topographs exhibit deformation interference fringes. It is important that the contrast of this interference pattern is almost one order of magnitude higher than the contrast in the case of Bragg scattering in a perfect crystal. The observed interference pattern depends on the radius of bending of the crystal. As the bending radius increases, all maxima shift toward the basic Bragg peak. Correspondingly, all distances between the interference fringes decrease. It has been shown that the positions of intensity maxima do not depend on the sign of the crystal bending. For a negative sign of the radius of the crystal bending (positive strain gradient), the integrated intensity increases. The results of the numerical simulation of the diffraction images agree well with the experimental topographs. A comparison of the numerical simulation of the interference pattern with the experimental topographs makes it possible to exactly determine the radius of the crystal bending (4%). The formulas describing the positions of interference maxima as a function of the bending radius of the sample have been obtained using the results of the numerical simulation of the experiment.     

Hematoside with 8-O-methyl-N-glycolylneuraminic acid from the starfishLinckia laevigata

A ganglioside was isolated from the starfishLinckia laevigata, and its structure was elucidated by chemical methods, mass spectrometry, and enzymatic hydrolysis with neuraminidase. The ganglioside is a hematoside containing 8-O-methyl-N-glycolylneuraminic acid, 8-O-Me-Neu5Gc-α2→3-Gal-β1→4-Glc-β1→1-Cer. The lipid part of the ganglioside consists of unsubstituted fatty acids (the major component is palmitic acid) and C_18∶1-iso-sphingenine.     

Following screened perturbations in an elastic medium with a thin layer

The result of the calculation of the field of a longitudinal wave which has passed through an elastic layer is studied and the character of the propagation of different phases of this wave is determined.Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Matematicheskogo Instituta im V. A. Steklova AN SSSR, Vol. 165, pp. 159–165, 1987.     

Direct soft photon production inK + p andπ + p interactions at 250 GeV/c

Inclusive production of direct soft photons is studied inK ⁺ p andK ⁺ π interactions at 250 GeV/c. Total cross sections, Feynman-x and transverse momentum distributions of direct γ's are presented. The measured cross sections are several times larger than expected from QED inner bremsstrahlung, indicating the presence of an anomalous soft photon source. The model of Lichard and Van Hove, based on the “cold quark-gluon plasma” picture, agrees with the data.