Nanostructured Si/SiO2 Quantum Wells

The motivation for developing light-emitting devices on an indirect transition semiconductor such as silicon has been widely discussed for Si/SiO2 nanostructures. In this chapter, we report on the fabrication of Si/SiO2 quantum-confined amorphous nanostructured films and their optical properties. The Si/SiO2 nanostructures comprising amorphous Si, SiO2, and Si/SiO2 multilayers are grown using ultrahigh vacuum radio frequency magnetron sputtering. Optical absorption coefficients of the Si/SiO2 nanostructures are evaluated with regard to tentative integrated Si thicknesses. Optical energy band gaps of the Si/SiO2 multilayer films are in accordance with the effective mass theory and described as E0 = 1.61 + 0.75d−2 eV at the Si layer-integrated thicknesses ranging from 0.5 to 6 nm. Quantum confinement effects in the Si/SiO2 nanostructures are inferred from optical transmittance and reflectance spectra. The rapid-thermal-annealed Si/SiO2 multilayer films demonstrate the intensified photoluminescence at ~1.45 eV due to the formation of nanocrystalline silicon. The temperature dependence of the nanocrystalline luminescence intensity shows the nonmonotonous behavior which is interpreted invoking the Kapoor model

Studies on the Reaction of Thorium with Graphite at High Temperatures

The reaction of thorium metal with graphite was studied in the temperature range of 900℃ to 1600℃. It was found that the reaction rate was parabolic and the activation energy for the reaction was 53 kcal/mole below 1200℃. Marker experiments showed that the growth of the carbide film was due mainly to the migration of carbon. From these results the rate determining process of the reaction seems to be the diffusion of carbon through the carbide film formed on the metal surface. Hydrocarbons, yielded by hydrolysis of the carbide film, were analysed by the gas-chromatographic method, from which the ratio of ThC/ThC_2 in the carbide film was determined. The film formed below 1200℃ was composed of ThC only. However, in the film formed above 1300℃ the ratio of ThC/ThC_2 decreased with increasing temperature. These results were confirmed by the X-ray diffraction technique. Parabolic rate constants for ThC and ThC_2 formations and apparent rate constants for the carbide film growth were obtained from the rate constant of the total carbide formation and the ThC/ThC_2 ratio in the carbide. The activation energy for the ThC_2 formation was found to be 120 kcal/mole from the results above 1300℃. The diffusion coefficient of carbon in ThC was calculated from the rate constants for the carbide formation. The amount of thorium carbide which forms in a thorium blanket of a graphite matrix fuel reactor was estimated

Phospholipids Effect on Survival and Molting Synchronicity of Larvae Mud Crab Scylla serrata

Effect of phospholipids on survival and molting synchronicity of mud crab larvae Scylla serrata were examined using Artemia enriched with five treatments of emulsion oil i.e. treatment with different level of soybean lecithin (SL) together with a level of DHA70G (referred to as DHA-SL0, 20 and 40) and treatment with SL and cuttle fish phospholipids (CPL) at 40 uL/L without DHA70G (referred to as WDHA-SL and WDHA-CPL). Survival rate, intermolt period, carapace width, and molting synchronicity were evaluated. Additionally, lipid classes and fatty acid composition of enriched Artemia were analyzed. Survival rate, intermolt period, and carapace width at the first crab (FC) stage of mud crab larvae fed DHA-SL0 to 40 were similar to that of WDHA-CPL but higher than that of WDHA-SL (P < 0.05). Moreover, mud crab larvae fed DHA-SL20, DHA-SL40, and WDHA-CPL had a significantly higher molting synchronicity index compared to that of larvae fed WDHA-SL and DHA-SL0. It can be concluded that combination of phospholipids and essential fatty acids exhibited an additive effect in improving molting synchronicity of mud crab larvae

Modeling the spectral conductivity of Al-Mn-Si quasicrystalline approximants: A phenomenological approach

The electronic structure of a quasicrystalline approximant sample is analyzed by means of a combined study of different experimental transport curves within a phenomenological approach. The main features of the obtained spectral conductivity are discussed and compared to those corresponding to icosahedral quasicrystals. Such a comparison provides interesting clues about the role of quasiperiodic order and of local atomic arrangements in the origin of unusual behaviors in the electrical conductivity and thermopower observed in complex metallic alloys

OVER-EXPRESSION OF GENE ENCODING FATTY ACID METABOLIC ENZYMES IN FISH

Eicosapentaenoic acid (EPA, 20:5n-3) and docosahexaenoic acid (DHA, 22:6n-3) have important nutritional benefits in humans. EPA and DHA are mainly derived from fish, but the decline in the stocks of major marine capture fishes could result in these fatty acids being consumed less. Farmed fish could serve as promising sources of EPA and DHA, but they need these fatty acids in their diets. Generation of fish strains that are capable of synthesizing enough amounts of EPA/DHA from the conversion of α-linolenic acid (LNA, 18:3n-3) rich oils can supply a new EPA/DHA source. This may be achieved by over-expression of genes encoding enzymes involved in HUFA biosynthesis. In aquaculture, the successful of this technique would open the possibility to reduce the enrichment of live food with fish oils for marine fish larvae, and to completely substitute fish oils with plant oils without reducing the quality of flesh in terms of EPA and DHA contents. Here, three genes, i.e. Δ6-desaturase-like (OmΔ6FAD), Δ5-desaturase-like (OmΔ5FAD) and elongase-like (MELO) encoding EPA/DHA metabolic enzymes derived from masu salmon (Oncorhynchus masou) were individually transferred into zebrafish (Danio rerio) as a model to increase its ability for synthesizing EPA and DHA. Fatty acid analysis showed that EPA content in whole body of the second transgenic fish generation over-expressing OmΔ6FAD gene was 1.4 fold and that of DHA was 2.1 fold higher (P&lt;0.05) than those in non-transgenic fish. The EPA content in whole body of transgenic fish over-expressing OmΔ5FAD gene was 1.21-fold, and that of DHA was 1.24-fold higher (P&lt;0.05) than those in nontransgenic fish. The same patterns were obtained in transgenic fish over-expressing MELO gene. EPA content was increased by 1.30-fold and DHA content by 1.33-fold higher (P&lt;0.05) than those in non-transgenic fish. The results of studies demonstrated that fatty acid content of fish can be enhanced by over-expressing gene encoding enzymes involved in fatty acid biosynthesis, and perhaps this could be applied to tailor farmed fish as even better sources of valuable human food

Studies on the β-ε Transformation in Cobalt-Nickel Alloys. II : Microstructure of Transformation Relief

The dislocation model for the mechanism of diffusion-less transformation of the f. c. c. structure β into the c. p. h. ε in cobalt-nickel alloys was studied from electron-microscopic observation of relief markings on the crystal surface formed by the transformation. It can be considered that the transformation of β into ε proceeds through the motion of half-dislocations (α/6) [121]_β, (α/6)[211]_β, and (α/6) [112]_β in the (111) plane of a f. c. c. crystal. When these half-dislocations move in all directions over the crystal surface, tilts having three different inclinations to the surface are formed, which can be estimated to be 19°28\u27, -10°2\u27 and -10°2\u27, respectively, if the surface is parallel to the (112)_β plane, while under an external stress only one type of half-dislocations similar in direction to the stress can be considered to move, and then only one sort of the tilts is preferred. These surface tilts result in the relief markings on the crystal surface. The above results predicted theoretically were confirmed by electron-microscopic observation of markings, and it was found that the width of the zone of homogeneous displacement in marking (about 0.1～1μ for 25 per cent nickel alloy) decreased slightly with decreasing nickel content, but in alloys containing less than a few per cent of nickel it decreased abruptly and in pure cobalt it was of the order of 100A

Studies on the β-ε Transformation in Cobalt-Nickel Alloys. I : Propagation Process of the Transformation

The propagation of the diffusionless transformation of the f.c.c. structure (β) into the h.c.p. structure (ε) in cobalt-nickel alloys was microscopically investigated. As the transformation proceeds, many narrow relief markings such as slip lines appeared in parallel to the {111}_β in flat free surface of the alloy. The cross section of each marking was a ridge or a valley with almost definite slopes on both sides but not symmetrical, and their inclinations were always less than 20°; its width was about 1～2μ. In pure cobalt, however, no marking was observable. The rate of growth of an ε crystal was less than ten-thousandth of that of a "Umklapp" martensite in steel, and these transformation processes are very resemble, when viewed from the growth rate, habit plane and structure of relief marking, to the "Schiebung" type of martensite in steel

Th-ThC Phase Diagram

The partial phase diagram in the Th-C system between pure Th and ThC was studied by metallographic and X-ray techniques and by measurements of electrical resistivity in quenched and slow cooled Th-C alloys. The peritectic point of the reaction, liq.+ThC⇄α-Th, was found at 16 at%C and about 1875℃ and the peritectic composition of ThC was 33 at%C. The eutectic reaction occurred at 1650℃ and its composition of α-Th and β-Th was 6.5 and <0.5 at%C, respectively. The α⇄β transformation temperature rose gradually with the carbon content up to 2.3 at%C and rose rapidly between the compositions of 2.3 and 3.7 at%C. The phase boundaries of α/ThC+α, ThC+a/ThC. ThC/ThC+ThC_2 and liq.+ThC/ThC were also established