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排序方式: 共有2783条查询结果,搜索用时 218 毫秒
211.
212.
A friction stir processing (FSP) technique has been developed for use with aluminum and magnesium alloys, with the goal of high-strain-rate processing. In this study, we treat the microstructures of aluminum samples, of three levels of purity, manipulating their grain sizes, making them finer, using FSP. Grain sizes decreased with an increase in the Zener-Hollomon parameter, at all purity levels. However, the recrystallized grain of FSP-ed ultra-high-purity (99.999%) aluminum was particularly large, compared to the grain sizes of lower-purity (99% and 99.99%) aluminum, when subjected to the same processing conditions. The grain size reached a certain minimum value at high-strain-rates of processing, which we report for each purity level herein. 相似文献
213.
Toru Ikegami Tomotake Morita Shunichi Nakayama Hideyuki Negishi Dai Kitamoto Keiji Sakaki Yasunori Oumi Tsuneji Sano Kenji Haraya Hiroshi Yanagishita 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2009,84(8):1172-1177
BACKGROUND: Pervaporation employing ethanol‐permselective silicalite membranes as an alternative to distillation is a promising approach for refining low‐concentration bioethanol solutions. However, to make the separation process practicable, it is extremely important to avoid the problems caused by the adsorption of succinate on the membrane during the separation process. In this work, the pervaporation of an ethanol fermentation broth without succinate was investigated, as well as the influence of several fermentation broth nutrient components. RESULTS: Candida krusei IA‐1 produces an extremely low level of succinate. The decrease in permeate ethanol concentration through a silicone rubber‐coated silicalite membrane during the separation of low‐succinate C. krusei IA‐1 fermentation broth was significantly improved when compared with that obtained using Saccharomyces cerevisiae broth. By treating the fermentation broth with activated carbon, bioethanol was concentrated as efficiently as with binary mixtures of ethanol/water. The total flux was improved upto 56% of that obtained from the separation of binary mixtures, compared with 43% before the addition of activated carbon. Nutrients such as peptone, yeast extract and corn steep liquor had a negative effect on pervaporation, but this response was distinct from that caused by succinate. CONCLUSION: For consistent separation of bioethanol from C. krusei IA‐1 fermentation broth by pervaporation, it is useful to treat the low nutrient broth with activated carbon. To further improve pervaporation performance, it will be necessary to suppress the accumulation of glycerol. Copyright © 2009 Society of Chemical Industry 相似文献
214.
Solution of linear systems in arterial fluid mechanics computations with boundary layer mesh refinement 总被引:1,自引:1,他引:0
Murat Manguoglu Kenji Takizawa Ahmed H. Sameh Tayfun E. Tezduyar 《Computational Mechanics》2010,46(1):83-89
Computation of incompressible flows in arterial fluid mechanics, especially because it involves fluid–structure interaction,
poses significant numerical challenges. Iterative solution of the fluid mechanics part of the equation systems involved is
one of those challenges, and we address that in this paper, with the added complication of having boundary layer mesh refinement
with thin layers of elements near the arterial wall. As test case, we use matrix data from stabilized finite element computation
of a bifurcating middle cerebral artery segment with aneurysm. It is well known that solving linear systems that arise in
incompressible flow computations consume most of the time required by such simulations. For solving these large sparse nonsymmetric
systems, we present effective preconditioning techniques appropriate for different stages of the computation over a cardiac
cycle. 相似文献
215.
216.
Kenji Arata Nobutaka Takeuchi Masaru Yoshinaka Ken Hirota Osamu Yamaguchi 《Journal of the American Ceramic Society》1997,80(8):2168-2170
Continuously graded MoSi2 -ZrO2 (2Y) materials with high density (97.5% of theoretical) have been fabricated by uniaxial wet-molding, followed by hot pressing (1000°C/1 h/30 MPa) and hot isostatic pressing (1400°C/2 h/196 MPa). Their composition profiles are greatly influenced by the viscosity of mixed solutions of glycerin and ethanol used as a dispersion medium; a linear compositional gradient from MoSi2 /ZrO2 (2Y) 70/30 to 20/80 mol% is obtained from the solution (50/50 vol%) with a viscosity of 20 mPa s. Vickers hardness (Hv) and fracture toughness (KIC) increase from 9.7 to 12.4 GPa and from 5.1 to 12.5 MPa m1/2, respectively, with increasing ZrO2 (2Y) composition. 相似文献
217.
Bong Mo Park Kenji Kitamura Yasunori Furukawa Yangyang Ji 《Journal of the American Ceramic Society》1997,80(10):2689-2692
The relationships between cracking and mechanical twinning, and between ferroelectric polarization and mechanical twinning, in stoichiometric LiNbO3 were investigated in the present study. Three sets of mechanical twins crossed one another, and the crossed points of those twins provided preferred sites for the nucleation of cracks. Mechanical twins of LiNbO3 revealed a head-to-tail arrangement of ferroelectric polarization, and complicated polarization states were observed at the crossed points. Some possible mechanisms of crack nucleation and propagation are proposed in this paper. 相似文献
218.
The infrared chemiluminescence spectra of CO2 formed during steady-state CO+NO reaction over Pd(110) indicated that the temperature of the bending vibrational mode was much higher than that of the antisymmetric one at higher surface temperatures such as 800–850 K. Especially, in the high temperature range, more vibrationally excited CO2 was formed from CO+NO reaction than CO+O2 reaction. On the basis of the result, we propose the model structure of reaction intermediates for CO2 formation in CO+NO reaction, which is different from that in CO+O2 reaction. 相似文献
219.
This paper reports the preparation of highly mesoporous carbon membranes, which are obtained by the pyrolysis of sol-gel derived mesoporous polymer membranes using resorcinol and formaldehyde (RF). Two series of RF carbon membranes were prepared by changing the resorcinol to catalyst molar ratio. The nitrogen adsorption-desorption measurement shows that the RF carbon membranes possess a well-developed mesoporous structure with controlled pore diameters of 5.48 nm and 13.9 nm. The helium and nitrogen permeances of both RF carbon membranes were independent of the feed pressure, indicating that there was no contribution of viscous flow and the membranes are initially crack-free. The gas permeation result showed that the dominant mechanism of gas transport through both the RF carbon membranes is Knudsen diffusion. With regard to the permeation of condensable gases such as CH4 and CO2, it was observed that the surface flow also contributes to the total permeation. 相似文献
220.
Hideshi Suzuki Masahiro Ogawa Kenji Hironaka Kunio Ito Hisakazu Sunada 《Drug development and industrial pharmacy》2001,27(9):951-958
Nifedipine is a poorly water soluble drug that demonstrates low bioavailability. In a previous study, a coground mixture of nifedipine with sodium deoxycholate (DCNa), a bile salt, immediately produced colloidal particles when dispersed in water. In this study, the effect of the weight fraction of DCNa, grinding time, dissolution media, and storage conditions on colloidal particle formation in solution was investigated. The coground mixture was prepared with a vibration rod mill, and its solid state was characterized using powder X-ray diffraction. A laser diffraction particle size analyzer was used to determine the particle size distribution curve in water. The size of particles formed in solution decreased with an increase in the weight fraction of DCNa and grinding time. A nifedipine-DCNa (1 : 2 w/w) mixture coground for 30 min was used in the experiments. Colloidal particle formation from the coground mixture was also observed in dissolution media of water and a pH 6.8 buffer solution at 37°C. Most precipitates passed through a filter with a pore size of 0.8 μm, but the particle size distribution in water was different from that in the pH 6.8 buffer solution. DCNa exhibited not only micellar solubilization for drug crystals, but also a retarding effect on drug crystal growth in a supersaturated solution. The latter effect could serve to form colloidal particles in solution. When stored under 75% relative humidity at 40°C for 1 month, the amorphous coground mixture crystallized, and the particle size in water markedly increased. Therefore, the weight fraction of DCNa, grinding time, dissolution media, and humidity during storage influence the dissolution characteristics of nifedipine from a coground mixture. 相似文献