Crystal structure of the growth surface of silicon carbide obtained by sublimation

Structural study of polycrystalline silicon carbide obtained by sublimation performed via X-ray luminescence and X-ray diffraction analysis. It is shown that chemical vapor deposition of silicon carbide results in the formation of grains with the (00.1), (01.1), and (12.3) crystallographic planes parallel to the growth surface. The grains with the (00.1) growth planes are characterized by perfect structure and by red luminescence. Domains with yellow luminescence have a mosaic structure with the (01.1) and (12.3) growth planes.     

An Interval-Parameter Fuzzy Approach for Multiobjective Linear Programming Under Uncertainty

An interval-parameter fuzzy linear programming method (IFMOLP) is proposed in this study for multiple objective decision-making under uncertainty. As a hybrid of interval-parameter and fuzzy methodologies, the IFMOLP incorporates interval-parameter linear programming and fuzzy multiobjective programming approaches to form an integrated optimization system. The method inherits advantages of interval-parameter programming, and allows uncertainties and decision-makers’ aspirations to be effectively communicated into its programming processes and resulting solutions. Membership functions for both objectives and constraints are formulated to reflect uncertainties in different system components and their interrelationships. An interactive solution procedure has been developed based on solution approaches of the interval-parameter and fuzzy programming techniques, plus necessary measures for handling the multiobjective feature. A didactic example is provided in the paper to illustrate the detailed solution process. Possibilities of further improvements by seeking Pareto optimum and incorporating flexible preference within constraints are also discussed.     

Allophane: a natural gel in volcanic soils with interesting environmental properties

Volcanic (allophanic) soils are interesting in terms of the control of the greenhouse effect and the knowledge of the porous features is of importance to understand the mechanism of C and N sequestration. These soils contain a peculiar clay: allophane aggregates quite close to the synthetic mineral gels aggregates. These volcanic materials behave as gels during drying with a large irreversible shrinkage that can modify the soil physical properties. Consequently, as for silica gels, we use the CO₂ supercritical drying procedure (SD) to control the drying step and to preserve the structural and textural properties of the soils. The experimental results show that the N and C content in the soils is clearly dependent on the allophane content. We also show that the textural properties, such as specific surface area, are higher for the supercritically dried samples, compared to the classically dried samples, and SAXS results confirm the preserving effect of the SD. With these data, we propose possible effects of the specific surface area on the C and N content of the allophanic soils.     

Adsorption of fission products onto soils using a fission multitracer

The adsorption behavior of fission products to various soils was studied using a multitracer. The multitracer was prepared by neutron irradiation of ²³⁵U. Distribution coefficients of fission products were obtained for seventeen kinds of Japanese soils. It was found that zirconium, niobium, and rare earth elements show high distribution coefficients for all soil samples, however, elements like alkali metals show varied values.     

Optical Magnus effect in metamaterials fabricated from ferromagnetic microwires

In homogeneous negative phase velocity media, the Doppler and Cherenkov-Vavilov effects and the refraction and pressure of light are anomalous: they are inverse with respect to the corresponding effects in conventional media. Using the geometrical optics approximation, it is shown that the optical Magnus effect in inhomogeneous negative phase velocity media is also anomalous. The effect is demonstrated by considering a metamaterial consisting of parallel amorphous ferromagnetic microwires in a magnetic field. The metamaterial proves to be a left-handed one in the realistic region of the electromagnetic spectrum. The optical properties of such a left-handed medium can be controlled by the external magnetic field.     

New cobalt and rare earth metal tungstates CoRE<Subscript>2</Subscript>W<Subscript>2</Subscript>O<Subscript>10</Subscript>

A new family of cobalt and rare-earth metal tungstates (CoRE₂W₂O₁₀ where RE=Y, Dy, Ho and Er) were synthesized by heating in the solid-state equimolar CoWO₄/RE₂WO₆ mixtures. The obtained compounds are isostructural and crystallize in the monoclinic system. They melt incongruently in an inert atmosphere at 1494 K (CoY₂W₂O₁₀), 1523 K (CoDy₂W₂O₁₀), 1517 K (CoHo₂W₂O₁₀) and 1493 K (CoEr₂W₂O₁₀). For each CoRE₂W₂O₁₀ compound the solid product of melting is an adequate RE₂WO₆.