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1.
2.
Toshio Kimura Hideto Kajiyama Ryuichi Yazaki Takashi Yamaguchi 《Journal of Materials Science》1996,31(15):4149-4157
The densification and microstructure development of ZnO containing Zn7Sb2O12, ZrO2, and aggregated ZnO were investigated to elucidate the effect of nondensifying inclusions on the sintering of ceramic/ceramic composites. The inclusion retarded the densification, and the degree of retardation was found to depend on the chemical species of inclusion; Zn7Sb2O12 had the largest effect, followed by ZrO2 and then aggregated ZnO last. The experimental results for aggregated ZnO was explained by the theory which predicts the generation of backstresses. The backstresses give a less significant effect on the densification. For Zn7Sb2O12 and ZrO2, the microstructure of the matrix varied with distance from an inclusion particle; much porosity was observed in the region surrounding the inclusion. Circumferential voids, which are responsible for the suppression of densification, form during the initial stage of sintering. Inclusion particles generate an anchoring effect which retards the densification of the matrix immediately surrounding the inclusion particle during the intermediate stage.Supported by the Inamori Foundation. 相似文献
3.
N Ide K Hirao Y Hata M Takeuchi M Irie I Yao M Deguchi A Toyoda H Nishioka A Mizoguchi Y Takai 《Canadian Metallurgical Quarterly》1998,243(2):634-638
In Caenorhabditis elegans, the vulval induction is mediated by tyrosine kinase receptor/Ras signal transduction pathway composed of the lin-3, let-23, and let-60 products. In addition to these gene products, the lin-2, lin-7, and lin-10 products are also implicated in this pathway. Lin-2 encodes a MAGUK and lin-7 encodes a small protein with one PDZ domain. The lin-10 product has no homology to known proteins. Here, we have cloned a rat homologue of the lin-10 product and characterized it. Rat lin-10 is ubiquitously expressed in various rat tissues and distributed in both the cytosol and membrane fractions. In brain, however, rat lin-10 is distributed only in the membrane fraction and enriched in the synaptic plasma membrane and postsynaptic density fractions. These results suggest that rat lin-10 is involved at least in synaptic functions in brain. 相似文献
4.
The role of ergosterol in yeast stress tolerance, together with heat shock proteins (hsps) and trehalose, was examined in a sterol auxotrophic mutant of Saccharomyces cerevisiae. Ergosterol levels paralleled viability data, with cells containing higher levels of the sterol exhibiting greater tolerances to heat and ethanol. Although the mutant synthesised hsps and accumulated trehalose upon heat shock to the same levels as the wild-type cells, these parameters did not relate to stress tolerance. These results indicate that the role of ergosterol in stress tolerance is independent of hsps or trehalose. 相似文献
5.
Contrasting effects of water-soluble and water-insoluble dietary fibers on bile acid conjugation and taurine metabolism in the rat 总被引:2,自引:0,他引:2
The effect of the type of dietary fiber on the bile acid and taurine metabolism was examined in rats. Diets containing 10%
of various water-soluble fibers (citrus pectin, konjak mannan, guar gum) as compared to a fiber-free diet increased biliary
excretion of total bile acids. In contrast, water-insoluble dietary fibers (cellulose, corn bran, chitin; 10% in the diets)
as well as cholestyramine (5% in the diet) considerably, decreased bile acid excretion. Water-soluble dietary fibermediated
increases in bile acid excretion were totally attributable to increases in glycine-conjugates. Thus, these fibers greatly
increased by the bile acid glycine-to-taurine ratio (G/T). Excretio of glycine conjugates decreased more than that of taurine
conjugates in rats fed various water-insoluble dietary fibers. As a results, G/T in rats fed water-insoluble fibers was significantly
lowered as compared to G/T in animals fed a fiber-free diet. Cholestyramine did not affect the G/T ratio of bile acids. Fecal
bile acid excretion and the activities of hepatic cholesterol 7α-hydroxylase (EC 1.14.13.17) in rats fed various water-soluble
dietary fibers approximately doubled as compared to the respective values for rats fed a fiber-free diet. Whereas cholestyramine
greatly increased these parameters, water-insoluble fibers did not significantly affect them. Various water-soluble fibers
decreased hepatic concentration and urinary excretion of taurine as well as the activity of hepatic cysteine dioxygenase (EC
1.13.11.20). In contrast, water-insoluble fibers considerably increased hepatic taurine concentrations and enzyme activities.
The parameters for taurine metabolism were unaffected by cholestyramine. It was suggested that the types of dietary fiber
affected hepatic taurine synthesis and thus modified bile acid glycine/taurine ratios. 相似文献
6.
Attempts were carried out to enhance the surface hydrophilicity of poly(L ‐lactide), that is, poly(L ‐lactic acid) (PLLA) film, utilizing enzymatic, alkaline, and autocatalytic hydrolyses in a proteinase K/Tris–HCL buffered solution system (37°C), in a 0.01N NaOH solution (37°C), and in a phosphate‐buffered solution (100°C), respectively. Moreover, its chain‐scission mechanisms in these different media were studied. The advancing contact‐angle (θa) value of the amorphous‐made PLLA film decreased monotonically with the hydrolysis time from 100° to 75° and 80° without a significant molecular weight decrease, when enzymatic and alkaline hydrolyses were continued for 60 min and 8 h, respectively. In contrast, a negligible change in the θa value was observed for the PLLA films even after the autocatalytic hydrolysis was continured for 16 h, when their bulk Mn decreased from 1.2 × 105 to 2.2 × 104 g mol?1 or the number of hydrophilic terminal groups per unit weight increased from 1.7 × 10?5 to 9.1 × 10?5 mol g?1. These findings, together with the result of gravimetry, revealed that the enzymatic and alkaline hydrolyses are powerful enough to enhance the practical surface hydrophilicity of the PLLA films because of their surface‐erosion mechanisms and that its practical surface hydrophilicity is controllable by varying the hydrolysis time. Moreover, autocatalytic hydrolysis is inappropriate to enhance the surface hydrophilicity, because of its bulk‐erosion mechanism. Alkaline hydrolysis is the best to enhance the hydrophilicity of the PLLA films without hydrolysis of the film cores, while the enzymatic hydrolysis is appropriate and inappropriate to enhance the surface hydrophilicity of bulky and thin PLLA materials, respectively, because a significant weight loss occurs before saturation of θa value. The changes in the weight loss and θa values during hydrolysis showed that exo chain scission as well as endo chain scission occurs in the presence of proteinase K, while in the alkaline and phosphate‐buffered solutions, hydrolysis proceeds via endo chain scission. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1628–1633, 2003 相似文献
7.
Poly(l-lactide) (i.e. poly(l-lactic acid) (PLLA)) and poly(d-lactide) (i.e. poly(d-lactic acid) (PDLA)) and their equimolar enantiomeric blend (PLLA/PDLA) films were prepared and the effects of enantiomeric polymer blending on the thermal stability and degradation of the films were investigated isothermally and non-isothermally under nitrogen gas using thermogravimetry (TG). The enantiomeric polymer blending was found to successfully enhance the thermal stability of the PLLA/PDLA film compared with those of the pure PLLA and PDLA films. The activation energies for thermal degradation (ΔEtd) were evaluated at different weight loss values from TG data using the procedure recommended by MacCallum et al. The ΔEtd values of the PLLA/PDLA, PLLA, and PDLA films were in the range of 205-297, 77-132, and 155-242 kJ mol−1 when they were evaluated at weight loss values of 25-90% and the ΔEtd value of the PLLA/PDLA film was higher by 82-110 kJ mol−1 than the averaged ΔEtd value of the PLLA and PDLA films. The mechanism for the enhanced thermal stability of the PLLA/PDLA film is discussed. 相似文献
8.
9.
Hideto Matsuyama Kentarou Hayashi Taisuke Maki Masaaki Teramoto Noboru Kubota 《应用聚合物科学杂志》2004,93(1):471-474
Microporous high‐density polyethylene (HDPE) and low‐density polyethylene (LDPE) hollow fiber membranes were prepared from polyethylene–diisodecyl phthalate solution via thermally induced phase separation. Effect of the polyethylene density on the membrane structure and performance was investigated. The HDPE membrane showed about five times higher water permeability than the LDPE membrane because it had the larger pore and the higher porosity at the outer membrane surface. The formation of the larger pore was owing to both the initial larger structure formed by spinodal decomposition and the suppression of the diluent evaporation from the outer membrane surface due to the higher solution viscosity. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 471–474, 2004 相似文献
10.
Phase separation rate during porous membrane formation by immersion precipitation was investigated by light scattering in a polyimide/N‐Methylpyrrolidone (NMP)/water system. In the light scattering measurement, plots of scattered intensity against scattered angle showed maxima in all cases, which indicated that phase separation occurred by a spinodal decomposition (SD). Characteristic properties of the early stage of SD, such as an apparent diffusion coefficient Dapp and an interphase periodic distance Λ, were obtained. The growth process of Λ was also followed by light scattering. The growth rate had the same tendency as Dapp when water content in the nonsolvent bath and the polymer concentration in the cast solution were changed. The pore size of the final membrane increased with decreasing water content, which was opposite to the tendency of Λ growth rate. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 292–296, 2003 相似文献