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排序方式: 共有507条查询结果,搜索用时 15 毫秒
71.
Hiroki Ago Naoyasu Uehara Masaharu Tsuji Motoo Yumura Toshihiko Setoguchi 《Carbon》2006,44(14):2912-2918
Changes in the gas composition during the methane chemical vapor deposition growth of single- and double-walled carbon nanotubes over metal-supported MgO catalysts were investigated in an attempt to increase the nanotube yield. Monitoring the gas composition by gas chromatography as a function of the reaction time provides information on the activity and lifetime of the catalyst. The degree of methane decomposition, i.e., the C-H bond dissociation, was closely related to the nanotube yield, and the Fe-Mo binary catalyst exhibited a high activity. The effects of water vapor on the catalytic nanotube growth were also studied by introducing water vapor in the inlet gas. An appropriate amount of water prolonged the lifetime of the catalyst and increased the nanotube yield by 35%. 相似文献
72.
Unlike in the North Atlantic, no continuous record of anthropogenic lead (Pb) has been available in the western Pacific. We reconstructed historical changes in anthropogenic Pb on the basis of Pb isotope ratios recorded in annually-banded coral retrieved from Ogasawara Island, Japan. Whereas the predominant natural source of Pb to the surface of the western Pacific apparently is Chinese loess, anthropogenic Pb has affected the western Pacific at least since the late 19th century. From the late 19th to the early 20th century, Australian Pb used in Japan was an important source of anthropogenic Pb. During 1920-1940, Pb emitted from parts of the world other than Japan contributed somewhat to the western Pacific, and the amount of Pb imported from Australia declined. Alkyl Pb used in Japan became the main source from 1950 until the mid-1970s, when leaded gasoline began to be regulated in Japan. Since the mid-1980s, aerosols from China have been the predominant source of Pb in the western Pacific. During the 1990s, around 60% of Pb in the surface of the western Pacific was from Chinese aerosols. We also investigated the present spatial distribution and likely sources of Pb in the western Pacific by using coral samples. Enrichment in 208Pb, which is a characteristic of Pb from China, was found in all coral samples except that from Pohnpei, Micronesia, suggesting that at present anthropogenic Pb is transported to the western Pacific mainly from China via westerly winds. 相似文献
73.
Lin X Matsuya S Nakagawa M Terada Y Ishikawa K 《Journal of materials science. Materials in medicine》2008,19(2):479-484
We have reported that low-crystalline porous calcite block, which is useful as a bone substitute or a source material to prepare
apatite-type bone fillers could be fabricated by exposing calcium hydroxide compact to carbon dioxide gas saturated with water
vapor. In the present study, we investigated the effect of molding pressure on the transformation of calcium hydroxide into
calcite and the mechanical strength of the carbonated compact. Transformation into calcite was almost completed within 72 h,
however, a small amount of Ca(OH)2 still remained unreacted at higher molding pressure because of incomplete penetration of CO2 gas into the interparticle space due to dense packing of Ca(OH)2 particles. On the other hand, high molding pressure resulted in an increase in diametral tensile strength (DTS) of the calcite
compact formed. Critical porosity of the calcite block was calculated as approximately 68%. 相似文献
74.
Masayuki Imose Akihiro Ohta Yoshihiko Takano Masaru Yoshinaka Ken Hirota Osamu Yamaguchi 《Journal of the American Ceramic Society》1998,81(4):1050-1052
Mullite/Y-TZP composites in the mullite-rich region, using powders of mullite prepared via the hydrazine method and a commercially available zirconia compound (ZrO2 (2Y)), have been fabricated by sintering for 3 h at 1450°C in air. The grain sizes of mullite and ZrO2 (2Y) are changed with increased ZrO2 (2Y) content; the former decreases from 0.25 µm to 0.13 µm, and the latter increases from 0.21 µm to 0.35 µm. High strength (780 MPa) and fracture toughness (5.4 MPam1/2 ) are obtained in the 50/50 (vol%) mullite/ZrO2 (2Y) composite with 99.6% of theoretical density. 相似文献
75.
76.
Masaru Yoshinaka Ken Hirota Masayuki Ito Hiroshi Takano Osamu Yamaguchi 《Journal of the American Ceramic Society》1999,82(1):216-218
Tin(IV) oxide (SnO2 ) crystallizes at room temperature by adding hydrazine monohydrate ((NH2 )2 · H2 O) to a hydrochloric acid solution of tin, followed by washing and drying. Well-densified SnO2 ceramics (99.8% of theoretical) with an average grain size of 0.9 μm have been fabricated by hot isostatic pressing for 2 h at 900°C and 196 MPa. Their Vickers hardness and bending strength are 14.4 GPa and 200 MPa, respectively. They exhibit an electrical conductivity of 2 × 10−3 −9 × 10−3 S·cm−1 at room temperature. 相似文献
77.
78.
K.M. Neaupane T. Yamabe R. Yoshinaka 《International Journal of Rock Mechanics and Mining Sciences》1999,36(5):54
This paper describes the application of a numerical model of thermal–mechanical–fluid flow coupling system to the simulation of laboratory freezing and thawing experiments on rocks. A theoretical formulation that accommodates a linear stress–strain constitutive relationship is presented and a two-dimensional (plane stress) numerical modeling is performed based on the finite element method applied to thermo–poro–elasticity. As the primary objective of this research is to simulate the freezing and thawing process, the developed code takes into account the phase change of pore water during freezing. It is found from the numerical simulation that a relatively good prediction can be made of temperature transfer and deformation behavior within the elastic deformation limit. In some cases, however, large deformation results from the freezing processes, leading to material failure. Future research should therefore take into account irreversible and plastic effects. 相似文献
79.
町屋是日本传统的联排别墅形式,从江户时代起盛行,目前京都还保留了一些町屋.京都町屋的特征之一是狭窄的正面和被称为"鳗鱼床"(Unaginonedoko)的深处.京都现在的町屋经常被改造成商店或旅馆. 相似文献
80.
Masaharu Seguchi 《Starch - St?rke》2001,53(9):408-413
Chlorination and heat treatment of wheat flour changes the surface character of starch granules from hydrophilic to hydrophobic, and high oil binding ability of the starch granules can be observed. It was suggested that the hydrophobicity, in case of chlorination, was due to chemical modification of the starch granule surface proteins, and, in case of heat treatment, due to conformational changes of the proteins. This hydrophobicity could be also obtained by aging (233 days at room temperature). The hydrophobicity of starch granules in batter is highly related to the springiness of pancake. Heat treated wheat starch granules can encapsulate flavor through their oil binding ability. 相似文献