Oxygen non-stoichiometries in (Th0.7Ce0.3)O2−x

Oxygen non-stoichiometry in (Th_0.7Ce_0.3)O_2−x oxide solid solutions was investigated from the viewpoint of Ce reduction. The oxygen non-stoichiometry was experimentally determined by means of thermogravimetric analysis as a function of oxygen potential at 1173, 1273 and 1373 K. Features of the isotherms of oxygen non-stoichiometry in (Th_0.7Ce_0.3)O_2−x similar to those in oxygen non-stoichiometric actinide and lanthanide dioxides were observed. The oxygen non-stoichiometry in (Th_0.7Ce_0.3)O_2−x was compared with those of CeO_2−x and (U_0.7Ce_0.3)O_2−x. It was concluded that the Ce reduction has some relation to defect forms and their transformations in the solid solutions.     

Radical-initiator-Induced solid-state polymerization of butadiyne nanocrystals in water and their dispersion stabilization

Butadiyne nanocrystals in water are usually polymerized by UV or gamma-ray irradiation to give polydiacetylene (PDA) nanocrystals. In this study, we confirmed that solid-state polymerization of 1,6-di(N-carbazolyl)-2,4-hexadiyne (DCHD) and 5,7-dodecadiyn-1,12-diyl bis[N-(butoxycarbonyl-methyl)carbamate] (4BCMU) could be stimulated by water-soluble radical initiators. The radical initiators used were potassium peroxodisulfate, three kinds of azo-type compounds and a redox initiator. In all cases, the solid-state polymerization was confirmed by color change into blue indicating that PDA modified by the radical residues at the end was formed. However, nanocrystal cohesion occurred especially when the concentration of the initiators was high or the dispersion was kept for a long time. In order to improve the dispersion stability, two kinds of surfactants, i.e., sodium dodecyl sulfate (SDS) or dodecyltrimethylammonium chloride (DTMAC), were added to the DCHD nanocrystal aqueous dispersion. As a result, when anionic SDS was added, the solid-state polymerization of nanocrystals proceeded without coagulation and quantitative conversion was confirmed for all initiators. Cationic DTMAC has no effect on dispersion stabilization. PDA nanocrystal surfaces in water are negatively charged in nature and electric interaction of nanocrystals with the cations results in decrease of surface charge and aggregation of nanocrystals.     

High copy number mutants derived from Corynebacterium glutamicum cryptic plasmid pAM330 and copy number control

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Ultrafast nonlinear optical effect in CdTe-doped glasses fabricated by the laser evaporation method

The laser evaporation method is an attractive technology to synthesize composite materials. We tried to apply the laser evaporation method on fabrication of CdTe-doped glasses for the first time. CdTe microcrystallites embedded in SiO₂ films were confirmed by transmission electron microscope images. The third-order nonlinear susceptibility χ⁽³⁾ and the decay time τ of CdTe-doped glasses were measured by three-beam forward type degenerate four-wave mixing. The maximum value of χ⁽³⁾ was estimated 4.2 x 10^-7 esu when the absorption coefficient was 6000 cm^-1. From the limitation of pulse duration of 5 ps, τ was not exactly measured but imagined to be shorter than 10 ps, which was much faster than the other semiconductor-doped glasses ever reported. The figure of merit defined as χ^(3)/τ is probably larger than 7.     

Capillary rise properties of porous mullite ceramics prepared by an extrusion method using organic fibers as the pore former

Porous mullite ceramics with unidirectionally oriented pores were prepared by an extrusion method to investigate their capillary rise properties. Rayon fibers 16.5 μm in diameter and 800 μm long were used as the pore formers by kneading with alumina powder, kaolin clay, China earthen clay and binder with varying Fe₂O₃ contents of 0, 5 and 7 mass%. The resulting pastes were extruded into cylindrical tubes (outer diameter (OD) 30–50 mm and inner diameter (ID) 20–30 mm), dried at room temperature and fired at 1500 °C for 4 h. The bulk densities of the resulting porous ceramics ranged from 1.31 to 1.67 g/cm³, with apparent porosities of 43.2–59.3%. The pore size distributions measured by Hg porosimetry showed a sharp peak at 10.0 μm in the sample without Fe₂O₃ and at 15.6 μm in the samples containing Fe₂O₃; these pores, which arose from the burnt-out rayon fibers, corresponded to total pore volumes ranging from 0.24 to 0.34 ml/g. SEM showed a microstructure consisting of unidirectionally oriented pores in a porous mullite matrix. Prismatic mullite crystals were well developed on the surfaces of the pore walls owing to the liquid phase formed by the Fe₂O₃ component added to color the samples. The bending strengths of the tubular samples ranged from 15.6 to 26.3 MPa. The height of capillary rise, measured under controlled relative humidities (RH) of 50, 65 and 85%, was greater in the ceramics containing Fe₂O₃ than in those without Fe₂O₃, especially in the thinner samples. The maximum capillary rise reached about 1300 mm, much higher than previously reported. This excellent capillary rise ability is thought to be due to the controlled pore size, pore distribution and pore orientation in these porous mullite ceramics.     

Cytochrome b5-like hemoprotein/cytochrome b5 reductase complex in rat liver mitochondria has NADH-linked aquacobalamin reductase activity

Rat liver mitochondrial NADH-linked aquacobalamin reductase was characterized to clarify its enzymological properties. Most of the enzyme was solubilized with 10 g/L Triton X-100 from rat liver mitochondrial membranes. The elution behavior of the solubilized enzyme was identical to that of NADH-cytochrome c reductase (b-type cytochromes/cytochrome b5 reductase complex) during DEAE-Sepharose Fast Flow column chromatography. By mixing both purified cytochrome b5-like hemoprotein (outer membrane-cytochrome b) and cytochrome b5 reductase, cob(II)alamin was formed from aquacobalamin and NADH. These results provide evidence that the outer membrane-cytochrome b/cytochrome b5 reductase complex has the activity of the NADH-linked aquacobalamin reductase in rat liver mitochondria. Some properties of the NADH-linked aquacobalamin reductase were studied using the function of rat liver mitochondrial membranes. The specific activity (109.5 +/- 14.3 nmol.min-1.mg protein-1) of the enzyme was shown under physiological conditions (pH 7.1 at 40 degrees C). The optimal pH and temperature for activity were 7.1 and 40 degrees C, respectively. The apparent Km values were 41.9 mumol/L for aquacobalamin in the presence of 0.2 mmol/L NADH and 14.4 mumol/L for NADH in the presence of 0.1 mmol/L aquacobalamin. The enzyme was specific for aquacobalamin, because cyanocobalamin could not be reduced by the enzyme.