GaN films grown by vapor-phase epitaxy in a hydride-chloride system on Si(111) substrates with AlN buffer sublayers

Oriented GaN layers with a thickness of about 10 μm have been grown by hydride-chloride vaporphase epitaxy (HVPE) on Si(111) substrates with AlN buffer layers. The best samples are characterized by a halfwidth (FWHM) of the X-ray rocking curve of ω_θ = 3–4 mrad. The level of residual mechanical stresses in AlN buffer layers decreases with increasing temperature of epitaxial growth. The growth at 1080°C is accompanied by virtually complete relaxation of stresses caused by the lattice mismatch between AlN and Si.     

Phase Stability of the A2Cu3O4X2 (A = Alkaline-Earth; X = Halogen) System

Stability of A ₂ Cu ₃ O ₄ X ₂ (A = Sr, Ba; X =Cl, Br) of the 2342 phase with the Cu ₃ O ₄ plane, which is composed of the Cu(1)O ₂ and extra Cu(2) sublattices, has been studied in the temperature range between 600 °C and 950 °C. Polycrystalline samples of the composition Sr _2–x Ba _x Cu ₃ O ₄ Cl _2–y Br _y were prepared by the solid-state reaction method. From the powder x-ray diffraction analysis, we have made the phase diagram (x vs. y vs. heat-treatment-temperature). It has been found that the 2342 phase becomes stable with increasing x and y at high heat-treatment-temperatures instead of a mixture of CuO and the A ₂ CuO ₂ X ₂ (2122) phase with the CuO ₂ plane. These results can be explained in terms of the structural matching between the Cu ₃ O ₄ plane and the A ₂ X ₂ layer.     

Elucidation of the effect of welding speed on melt flows in high-brightness and high-power laser welding of stainless steel on basis of three-dimensional X-ray transmission in situ observation

This research was performed with the objective of clarifying the effect of welding speed on melt flows during melt-run welding of SUS304 stainless steel plates with a 6-kW power laser beam on the basis of three-dimensional X-ray transmission in situ observation. As welding speed increased from 25 to 250 mm/s, three kinds of welds characterized by porosity formation and no defects or underfilling due to spatters were produced. The average and the maximum values of measured melt flow velocity were 3 and 10 times higher than the welding speed, respectively. Two kinds of circulation flows at the inlet or the tip of a keyhole were confirmed to control heat transfer in a molten pool. It was found that the circulation flows were so sensitive to the welding speed that bubbles resulting in porosity or spatters were often formed. According to X-ray observation of the formation of spatters with tungsten carbide (WC) tracers, as the melt flow rose along the keyhole wall, the velocity was accelerated from 0.24–0.54 m/s near the keyhole inlet. Consequently, the melt flows made the convex surface behind the keyhole grow higher, resulting in spattering.     

Domestic energy-use pattern by the households: A comparison between rural and semi-urban areas of Noakhali in Bangladesh

An explorative survey was carried out on rural and semi-urban households to find out the energy consumption pattern with respect to socio-demographic and geographic factors in Bangladesh by using stratified random sampling technique. The study revealed that 100% of the households used biomass, 98% kerosene, 61% electricity, 23% LPG and 5% candle in the rural areas. In the semi-urban areas, 100% of the households used electricity, candle and natural gas, 60% kerosene and 13% petrol. Households’ mean expenditure for total energy was US$ 5.34 (SE, 0.43) with total income US$ 209.84 (SE, 6.69) month^-1 in the rural areas, while it was US$ 6.20 (SE, 1.35) in the semi-urban areas with the total income US$ 427.76 (SE, 24.19) month^-1. This study may be a useful baseline information to energy policy makers in Bangladesh.     

Independent Control of Low-Energy Resonant States and Polaron States by the Zn-Doping and the Structural Transition in La2−x Sr x CuO4 and La2−x Ba x CuO4 (x=0.11)

The superconductivity depression mechanisms at x≈1/8 in La_2−x Ba _x CuO₄ and Zn substitution in La_2−x Sr _x CuO₄ were investigated by Raman scattering. About 80% of low-energy electronic states are two-dimensional at x≈1/8 and form the Fermi arc around (π/2,π/2). The low-energy states are composed of the resonant peak relating to the insulator–metal transition and the polaron states of the B _3u phonons. Zn substitution depresses the resonant peak, while the LTT structure depresses the polaron states. The superconductivity is suppressed if one of them is reduced.     

Preparation and properties of Cu-grafted transparent TiO2-nanosheet thin films

Transparent TiO₂ nanosheet thin films were prepared using layer-by-layer method with poly(diallyldimethylammonium chloride) as a counter polymer. The possibility of photocatalysis by the light in the long wavelength range was examined by grafting Cu on the film. Photocatalytic decomposition activity for gaseous 2-propanol under UV illumination without light for electron excitation of TiO₂ nanosheet was increased by Cu grafting, suggesting that the interfacial charge transfer mechanism is effective also for nanosheet films.     

Overseas oil-development policy of resource-poor countries: A case study from Japan

Japan, currently the world's third largest oil consumer, depends on imports for almost all of its oil needs. Owing to this high level of dependence, Japanese citizens as well as the economy have historically been vulnerable. In the past, certain incidents caused by the interruption of oil imports have resulted in fatal damages to the country. In order to reduce these risks, the Japanese government has supported overseas exploration and development activities of the domestic upstream oil industry, which has not proven as successful as expected. This paper presents the experiences, policies, and the structure of Japan's attempts to increase the share of domestic oil needs met by development activities. While conducting this study, both internal and external constraints were encountered. In addition to the lack of domestic oil reserves, factors including the institutional design of cooperation between government and private industries, the early history of the upstream industry, the target area of overseas development, and the changing environment have created impediments toward achieving the targets. In 2006, Japan again set a new target for doubling the ratio of self-developed oil in its total imports by 2030, and will face challenges in clearing the above-mentioned hurdles.