Chaotic features of nuclear structure and dynamics: selected topics
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Zelevinsky, Vladimir↗
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Features of the structural states of KNbO{sub 3} single crystals before and after fast-neutron irradiation
Neutron irradiation is a unique tool for forming new structural states of ferroelectrics, which cannot be obtained by conventional methods. The inf luence of the irradiation by two doses of fast neutrons (F = 1 × 10{sup 17} and 3 × 10{sup 17} cm{sup –2}) on the structure and properties of KNbO{sub 3} single crystals has been considered for the first time. The developed method for taking into account the experimental correction to the diffuse scattering has been used to analyze the structural changes occurring in KNbO{sub 3} samples at T = 295 K and their correlations with the behavior of dielectric and nonlinear optical characteristics. The irradiation to the aforementioned doses retains the KNbO{sub 3} polar structure, shifting Т{sub Ð}¡ to lower temperatures and significantly affecting only the thermal parameters and microstructure of single crystals. Neutron irradiation with small atomic displacements provides a structure similar to the high-temperature modification of an unirradiated KNbO{sub 3} crystal.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Comparative analysis of the structural and morphological features of biogenic and synthesized goethite nanoparticles
A comparative analysis of the relationship between the morphological forms and magnetic properties of natural goethite particles from the crust of weathering of the Far East and Vietnam basalts and pure, chemically synthesized goethite particles was performed using Mössbauer spectroscopy, X-ray diffraction analysis, and scanning electron microscopy. It is shown how the shape of biogenic goethite particles affects their magnetic properties, which significantly differ from the magnetic properties of chemically synthesized samples.
36 MATERIALS SCIENCE↗
Specific Features of the Structure and Properties of High-Temperature Oxide Materials Based on Bismuth Sodium Titanate
Single-phase ceramic samples from the region of morphotropic phase boundary in the (1–x)(Na{sub 0.5}Bi{sub 0.5})TiO{sub 3–x}BaTiO{sub 3} and (1–y)[(Na{sub 0.5}Bi{sub 0.5})TiO{sub 3–x}BaTiO{sub 3}]–yBi(Mg{sub 0.5}Ti{sub 0.5})O{sub 3} systems, modified by low-melting LiF and 0.6NaCl–0.4LiF additives, have been prepared by solid-state synthesis. The effect of additives on the phase formation, structural parameters, and dielectric and ferroelectric properties of the ceramics has been studied. A decrease in the ceramic sintering temperature is found. A slight increase in the unit-cell volume upon modification of the ceramics under study by lithium fluoride and 0.6NaCl–0.4LiF additive is revealed. First-order ferroelectric phase transitions near 700–800 K have been observed. The prospects for improving the piezoelectric properties of modified ceramic samples are proved.
36 MATERIALS SCIENCE↗
Specific features of magnetic structure formation in orbitally degenerate BiMnO{sub 3} manganite
The orbital structure and magnetic ordering of the Jahn-Teller multiferroic BiMnO{sub 3} manganite have been theoretically studied. It is shown that the orbital structure depends not only on the nearest-neighbor oxygen environment of manganese ions, but also on their next-to-nearest neighbors. The orbital structure significantly influences the magnetic order that forms as a result of competition between ferromagnetic and antiferromagnetic exchange interactions.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Special features of the structure of the beta-stability line for nuclei
The mass-number (A) dependence Z{sub β}(A) for nuclei lying on the beta-stability line (BSL) is calculated for A and Z values in the ranges of A = 2–258 and Z = 1–100, respectively. The calculated values are compared with experimental data. The deviations ΔZ = Z{sub expt} − Z{sub β} are analyzed. This analysis of ΔZ reveals that there are three regions of A values in which the A dependence of ΔZ is parabolic. The possible forms of the A dependence of ΔZ are analyzed, and it is shown that the majority of nuclei belong to several parabolas simultaneously.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Growth features and spectroscopic structure investigations of nanoprofiled AlN films formed on misoriented GaAs substrates
Nanostructured aluminum-nitride films are formed by reactive ion-plasma sputtering onto GaAs substrates with different orientations. The properties of the films are studied via structural analysis, atomic force microscopy, and infrared and visible–ultraviolet spectroscopy. The aluminum-nitride films can have a refractive index in the range of 1.6–4.0 at a wavelength of ~250 nm and an optical band gap of ~5 eV. It is shown that the morphology, surface composition, and optical characteristics of AlN/GaAs heterophase systems can be controlled using misoriented GaAs substrates.
36 MATERIALS SCIENCE↗
Features of Electronic Structure of Intermetallic Compounds CeNi{sub 4}M (M = Fe, Co, Ni, Cu)
The evolution of the electronic structure of CeNi{sub 4}M (M = Fe, Co, Ni, Cu) intermetallics depending on the type of nickel substitutional impurity is explored. We have calculated band structures of these compounds and considered options of substituting one atom in nickel 3d sublattice in both types of crystallographic positions: 2c and 3g. The analysis of total energy self-consistent calculations has shown that positions of 2c type are more energetically advantageous for single iron and cobalt impurities, whereas a position of 3g type is better for a copper impurity. The Cu substitutional impurity does not change either the nonmagnetic state of ions or the total density at the Fermi level states. Fe and Co impurities, on the contrary, due to their considerable magnetic moments, induce magnetization of 3d states of nickel and cause significant changes in the electronic state density at the Fermi level.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Morphology and chemistry of probable VLS /vapor-liquid-solid/-type of whisker structures and other features on the surface of breccia 15015,36
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Carter, J. L.↗
Some features of the structure of the tropical tropopause
Statistics of the minimum saturation humidity mixing ratio are extracted from 2500 radiosonde ascents in the tropics (10 N to 10 S) and in the region of the Asian summer monsoon. Two periods of approximately 20 days are examined, one in the northern winter and one in the northern summer. The relation of the observations to an hypothesis, proposed by A. W. Brewer in 1949, of mass exchange between troposphere and stratosphere is briefly discussed.
Atticks, M. G.↗
Structural and stratigraphic features and ERS 1 synthetic aperture radar backscatter characteristics of ice growing on shallow lakes in NW Alaska, winter 1991-1992
Changes in Earth Remote-Sensing Satellite (ERS) 1 C band synthetic aperture radar (SAR) backscatter intensity (sigma(exp 0)) from ice growing on shallow tundra lakes at three locations in NW Alaska are described. Ice core analysis shows that all lakes on the coast at Barrow the ice, whether floating or frozen to the bottom, includes an inclusion-free layer overlying a layer of ice with tubular bubbles oriented parallel to the direction of growth. The clear ice may also be overlain by a discontinuous layer of bubbly snow ice. Backscatter is low (-16 to -22 dB) at the time of initial ice formation, probably due to the specular nature of the upper and lower ice surfaces causing the radar pulse to be reflected away from the radar. As the ice thickens during the autumn, backscatter rises steadily. Once the ice freezes to the lake bottom, regardless of the presence of foward scattering tubular bubbles, low backscatter values of -17 to -18 dB are caused by absorption of the radar signal in the lake bed. For ice that remains afloat all winter the ice-water interface and the tubular bubbles combine, presumably via an incoherent double-bounce mechanism, to cause maximum backscatter values of the order of -6 to -7 dB. The sigma(exp 0) saturates at -6 to -7 dB before maximum ice thickness and tubular bubble content are attained. A simple ice growth model suggests that the layer of ice with tubular bubbles need be only a few centimeters thick midway through the growth season to cause maximum backscatter from floating ice. During the spring thaw a previously unreported backscatter reversal is observed on the floating and grounded portions of the coastal lakes but not on the lakes farther inland. This reversal may be related to the ice surface topography and wetness plus the effects of a longer, cooler melt period by the coast. Time series of backscatter variations from shallow tundra lakes are a record of (1) the development of tubular bubbles in the ice and, by association, changes in the gas content of the underlying water and (2) the freezing of ice to the bottoms of the lakes and therefore lake bathymetry and water availability. SAR is also able to detect the onset of lake ice growth in autumn and the initiation of the spring thaw and thus has potential for monitoring high-altitude lake ice growth and decay processes in relation to climate variability.
Jeffries, M. O.↗
Waveguide Modes in a Planar Graphene–Dielectric Thin-Layer Structure
Particular features of waveguide propagation of modes in a planar structure that consists of alternating layers of a dielectric and graphene are investigated. Within the effective-medium approximation, dispersion relations are obtained for symmetric and antisymmetric waveguide modes. Based on their numerical analysis, the frequency dependences of the propagation and decay constants, of the group and phase velocities, and of the energy flux carried by waveguide modes are constructed. The influence of the fraction of graphene in the structure on the behavior of waveguide modes is analyzed.
77 NANOSCIENCE AND NANOTECHNOLOGY↗
Compressive strain in Lunae Planum-shortening across wrinkle ridges
Wrinkle ridges have long been considered to be structural or structurally controlled features. Most, but not all, recent studies have converged on a model in which wrinkle ridges are structural features formed under compressive stress; the deformation being accommodated by faulting and folding. Given that wrinkle ridges are compressive tectonic features, an analysis of the associated shortening and strain provides important quantitative information about local and regional deformation. Lunae Planum is dominated by north-south trending ridges extending from Kasei Valles in the north to Valles Marineris in the south. To quantify the morphometric character, a photoclinometric study was undertaken for ridges on Lunae Planum using the Davis and Soderblom. More than 25 ridges were examined between long. 57 and 80 deg, lat. 5 to 25 deg N. For each ridge, several profiles were obtained along its length. Ridge width, total relief, and elevation offset were measured for each ridge. Analyses are given.
Plescia, J. B.↗
Stacbeam - An efficient, low-mass, sequentially deployable structure
Design features of the stacking triangular articulated compact beam (Stacbeam) as a candidate truss structure for GEOS spacecraft solar power arrays are explored. Solar arrays of increasing size require folding, noninterfering structures, minimal thermal effects, slow and controlled deployment, and a high aspect ratio. The Stacbeam consists of a triangular batten frame perpendicular to the beam axis, three longerons attached at the corners of the batten frame and mounted parallel to the beam axis, and three diagonals to provide shear and torsional stiffness. Locking hinges are installed at the midpoint and ends of each longeron and at the midpoint and ends of each diagonal. The material is graphite/epoxy composite with a 120 GPa modulus and a 1500 kg/sq m density. Successful vertical deployment on the ground has been effected with a prototype deployer, together with horizontal cantilever in a fully deployed configuration.
Adams, L. R.↗
Novel multilayer TiO 2 heterojunction decorated by low g-C 3 N 4 content and its enhanced photocatalytic activity under UV, visible and solar light irradiation
In this paper, we used a facile ball milling, microwave radiation and heating treatment method to achieve the surface modification of TiO 2 with low g-C 3 N 4 concentration, and a multilayer heterojunction composite with TiO 2 as the main part and g-C 3 N 4 as the modification agent was obtained. The obtained materials were analyzed by several characterizations to get information on their chemical composition, crystalline structure, vibrational features and optical properties. The photocatalytic performance was evaluated by degradation of rhodamine B (RhB) and methylene blue (MB) under UV, visible and direct solar light irradiation. Its photocatalytic activity was enhanced depended on the novel structure of g-C 3 N 4 /TiO 2 hybrid and the special Z-scheme electron-hole transfer model of multilayer heterointerfaces. The material preparation and structural features could be useful for the design and development of other photocatalysts with high photocatalytic activity.
54 ENVIRONMENTAL SCIENCES↗
Multi-device cooling structure having assembly alignment features
A single device having both thermal and alignment features is provided to mechanically align and more efficiently cool multiple heat generating components. The device includes one or more thermal structures and assembly alignment features, in which the one or more thermal structures make thermal contact with a plurality of heat generating components. The assembly alignment features control the positions of the heat generating components during assembly of the heat generating components onto a common substrate.
42 ENGINEERING↗