Dependence of Vacuum Electrical Breakdown Field and Field Enhancement Factor on the Number of Apertures Drilled in Small Electrodes

Dark current based on field emission current is considered to be a factor causing the vacuum electrical breakdown between multiaperture acceleration grids in the JT‐60 negative ion source. In this paper, we focus on field enhancement factor, which is a key parameter of field emission from the electrode. Vacuum breakdown testing for small‐sized electrodes simulating the multiaperture acceleration grids of the negative ion source was performed. We found the field enhancement factor and breakdown field for multiaperture electrodes, and we investigated the dependence of each parameter on the number of apertures. The results revealed that an increase in the average field enhancement factor after the end of conditioning resulting from an increase in the number of apertures led to a decrease in the dielectric strength of the multiaperture electrodes.     

Role of Water Vapor in Crystallite Growth and Tetragonal-Monoclinic Phase Transformation of ZrO2

The role of water vapor in crystallite growth and the tetragonal-to-monoclinic phase transformation of ZrO₂ was studied using three specially prepared samples: an ultrafine powder of monoclinic ZrO₂ obtained by hydrolysis of ZrOCI₂, an aggregated powder of tetragonal ZrO₂ obtained by thermal decomposition of Zr(OH)₄ under reduced pressure, and an ultrafine powder of tetragonal ZrO₂ obtained by thermal decomposition of zirconyl acetate dispersed in caramel. The samples were heat-treated up to 1000°C in dry and wet atmospheres saturated with water vapor at 90°C. It was found that water vapor markedly accelerated crystallite growth for both monoclinic and tetragonal ZrO₂ and facilitated the tetragonal-to-monoclinic phase transformation. Water vapor increases surface diffusion and thus enhances crystallite growth and decreases surface energy, which leads to stabilization of the tetragonal phase.     

EIGENVECTOR METHOD IN MULTICRITERIA OUTRANKING RELATIONS

Most complex decision problems involve conflicts among multiple criteria and uncertain and imprecise data. The (fuzzy) outranking relation model that was introduced by Roy can tackle such complex situations. The present paper proposes a new ranking procedure based on the eigenvector in multicriteria outranking relations. The properties of the eigenvector method in ordinary outranking relations are investigated. Then, the eigenvector method is compared to that of qualification by several examples. Finally, we compare the eigenvector method with the distillation method in ELECTRE III in fuzzy outranking relations. The results of the two methods did not exhibit significant differences. The eigenvector method turns out useful, because it can promote a complementary viewpoint.     

Effects of Bismuth Sesquioxide on the Characteristics of ZnO Varistors

The nonlinearity of ZnO varistors is significantly influenced by the Bi₂O₃ and Sb₂O₃ contents, as well as by the phase composition of the Bi₂O₃. Degradation of the current-voltage characteristics due to the applied voltage is not always lowered by the β—γ transition of the Bi₂O₃ phase. Lattice parameter determinations and stress analyses suggest that the Bi₂O₃-rich phase in multigrain junctions causes mechanical strain at the grain boundary which may play an important role in the current-voltage characteristics of ZnO varistors.     

ESTIMATION OF DAILY INTAKE OF FOUR KINDS OF TRIHALOMETHANE BY JAPANESE HOUSEWIVES

Duplicate portions of the daily meals consumed by 30 housewives were collected for 3 consecutive days in the cities of Nagoya and Yokohama in Japan.
Meals were analyzed for chloroform, bromodichloromethane (BDCM), chlorodibromomethane (CDBM) and bromoform by using a purge-trap procedure. The average concentration (and the range) of these four kinds of trihalomethane in each of the 24 h duplicate meals were, chloroform 19.6±18.1 ppb(n.d.-106.8 ppb), BDCM 0.3±0.3 ppb(n.d.-1.7 ppb), CDBM 0.1±0.2 ppb(n.d.-0.6 ppb) and bromoform 0.5±1.3 ppb(n.d.-8.1 ppb).
The mean daily dietary intake of the four kinds of trihalomethane by housewives were, chloroform 40.0±25.4 μg, BDCM 0.6±0.5 μg, CDBM 0.3±0.3 μg and bromoform 0.9±1.3 μg.     

Synthesis of bismuth-based high-Tc superconducting fibres by using sodium alginate as a polyelectrolyte

The thermal pyrolysis processes and solid-state reactions in the synthesis of bismuth-based high-Tc superconducting fibre obtained by using sodium alginates are studied. This alginate is a polyelectrolyte and has not only an excellent ion-exchange property but also a gelation to synthesize long fibrous precursors. We first determined the optimum conditions to promote ion-exchange of this polyelectrolyte which yields high contents of metal ions in the precursor. The thermal pyrolysis of a precursor was studied by DTA and IR absorption. On the basis of the DTA and XRD, the solid-state reactions associated with the formation of the 2 2 1 2 phase were revealed. Our method can be applied easily to synthesize Ag-sheathed fibre having an improved tensile strength. This revised version was published online in November 2006 with corrections to the Cover Date.     

Abalone (Hariltis discus): Seasonal Variations in Chemical Composition and Textural Properties

Seasonal changes in adenosine 5′-triphosphate, total free amino acids, and total oligopeptides in abalone meat were analyzed. Levels were higher in summer and lower in winter. In both seasons, the most abundant free amino acid was taurine followed by arginine, glycine, glutamine, and glutamic acid. The largest peptide-bond amino acid was glutamic acid + glutamine. The collagen content decreased in summer and increased in winter. The breaking stress values of the meat were low in summer and high in winter, indicating that summer abalone would be more tender. Scanning electron microscopy revealed the collagen network was more compact in winter.