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991.
992.
InGaAs quantum dots formed in tetrahedral-shaped recesses on GaAs (111)B grown by metalorganic chemical vapor deposition 总被引:1,自引:0,他引:1
Yoshiki Sakuma Masashi Shima Yuji Awano Yoshiro Sugiyama Toshiro Futatsugi Naoki Yokoyama Kazuhito Uchida Noboru Miura Takashi Sekiguchi 《Journal of Electronic Materials》1999,28(5):466-480
Novel semiconductor quantum dots (QDs), grown in tetrahedral-shaped recesses (TSRs) formed on a (111)B GaAs substrate, are
described from both material science and device application points of view. After explaining the fabrication procedure for
TSRs, growth of InGaAs QDs and their optical properties are explained. It is revealed that an InGaAs QD of indium-rich chemical
composition is formed spontaneously at the bottom of each TSR. The mechanism of the QD formation is discussed in detail. It
is proved from magneto-photoluminescence that the QDs actually have optical properties peculiar to zero-dimensional confinement.
Several experimental results indicating excellent growth controllability of the QDs are presented. Finally, recent challenges
to apply the QDs to electronic memory devices are reported. Two kinds of devices, where the position of individual QD is artificially
controlled, are proposed for the first time and the preliminary experimental results are explained. 相似文献
993.
Modeling of inclusion removal in a tundish 总被引:6,自引:0,他引:6
Mathematical models have been developed to predict the removal of alumina inclusions from molten steel in a continuous casting
tundish, including the effects of turbulent collisions, reoxidation, flotation, and removal on the inclusion size distribution.
The trajectories of inclusion particles are tracked through the three-dimensional (3-D) flow distribution, which was calculated
with the K-ɛ turbulence model and includes thermal buoyancy forces based on the coupled temperature distribution. The predicted distributions
are most consistent with measurements if reoxidation is assumed to increase the number of small inclusions, collision agglomeration
is accounted for, and inclusion removal rates are based on particle trajectories tracked through a nonisothermal 3-D flow
pattern, including Stokes flotation based on a cluster density of 5000 kg/m3 and random motion due to turbulence. Steel samples should be taken from as deep as possible in the tundish near the outlet
and at several residence times after the ladle is opened, in order to best measure the Al2O3 concentration entering the submerged entry nozzle to the mold. Inclusion removal rates vary greatly with size and with the
presence of a protective slag cover to prevent reoxidation. The random motion of inclusions due to turbulence improves the
relatively slow flotation of small inclusions to the top surface flux layer. However, it also promotes collisions, which slow
down the relatively fast net removal rates of large inclusions. For the conditions modeled, the flow pattern reaches steady
state soon after a new ladle opens, but the temperature and inclusion distributions continue to evolve even after 1.3 residence
times. The removal of inclusions does not appear to depend on the tundish aspect ratio for the conditions and assumptions
modeled. It is hoped that this work will inspire future measurements and the development of more comprehensive models of inclusion
removal. These validated models should serve as powerful quantitative tools to predict and optimize inclusion removal during
molten steel processing, leading to higher quality steel. 相似文献
994.
Takeo Ushiki Mo-Chiun Yu Kunihiro Kawai Toshikuni Shinohara Kazuhide Ino Mizuho Morita Tadahiro Ohmi 《Microelectronics Reliability》1999,39(3):327
The effects of ion species/ion bombardment energy in sputtering deposition process on gate oxide reliability have been experimentally investigated. The use of xenon (Xe) plasma instead of argon (Ar) plasma in tantalum (Ta) film sputtering deposition for gate electrode formation makes it possible to minimize the plasma-induced gate oxide damage. The Xe plasma process exhibits 1.5 times higher breakdown field and five times higher 50%-charge-to-breakdown (QBD). In the gate-metal sputtering deposition process, the physical bombardment of energetic ion causes to generate hole traps in gate oxide, resulting in the lower gate oxide reliability. The simplified model providing a better understanding of the empirical relation between the gate oxide damage and the ion-bombardment energy to gate oxide in gate-metal sputtering deposition process is also presented. 相似文献
995.
Masaru Kaieda Taichi Samukawa Takeshi Matsumoto Kazuhiro Ban Akihiko Kondo Yuji Shimada Hideo Noda Fumiki Nomoto Koutaro Ohtsuka Eiji Izumoto Hideki Fukuda 《Journal of Bioscience and Bioengineering》1999,88(6):627
A new enzymatic method of synthesizing methyl esters from plant oil and methanol in a solvent-free reaction system was developed. It is anticipated that such plant oil methyl esters can be used as a biodiesel fuel in the future. Lipase from Rhizopus oryzae efficiently catalyzed the methanolysis of soybean oil in the presence of 4–30 wt% water in the starting materials; however the lipase was nearly inactive in the absence of water. The methyl ester (ME) content in the reaction mixture reached 80–90 wt% by stepwise additions of methanol to the reaction mixture. The kinetics of the reaction appears to be in accordance with the successive reaction mechanism. That is, the oil is first hydrolyzed to free fatty acids and partial glycerides, and the fatty acids produced are then esterified with methanol. Although R. oryzae lipase is considered to exhibit 1(3)-regiospecificity, a certain amount of 1,3-diglyceride was obtained during the methanolysis and hydrolysis of soybean oil by R. oryzae lipase solution. Therefore, the high ME content in the reaction mixture is probably attributable to the acyl migration from the sn-2 position to the sn-1 or sn-3 position in partial glycerides. 相似文献
996.
The photonic transport network requires wavelength routing management and this function can be achieved by employing optical switch connection supervision. The authors propose a supervision method that uses a simplified optical spectrum analyzer and describe the development of an optical switching board employing this method. The supervision method also enables the optical switching board to control the optical power automatically and this equalizing function is demonstrated 相似文献
997.
H Suzuki S Kawai T Aizawa K Kato S Sunayama R Okada H Yamaguchi 《Canadian Metallurgical Quarterly》1999,33(1):198-205
OBJECTIVES: This study was designed to determine whether coronary vasospasm in patients with variant angina pectoris (VAP) may produce focal organic lesions at the site of vasospasm that would contribute to disease progression. BACKGROUND: Recent clinical angiographic and experimental studies have demonstrated the potential role of vasospasm in the worsening of organic coronary stenosis. METHODS: We studied histologically the coronary plaques obtained at atherectomy in 202 patients with moderate to severe coronary stenosis. This population included 22 patients with VAP, 100 patients with chronic stable angina and 80 patients with restenosis following angioplasty or atherectomy. Diagnosis of VAP was based on both the clinical feature of angina at rest associated with ST elevation and a positive response to acetylcholine provocation test. RESULTS: The most common histological appearance in 92% of patients with stable angina was hypocellular fibroatheromatous plaques, whereas neointimal hyperplasia was the characteristic feature of the plaque observed in 90% of patients with restenosis. The coronary specimens at the site of spasm in 15 of the 22 patients (68%) with VAP demonstrated intimal injuries such as neointimal hyperplasia (15), thrombus formation (2), and intimal hemorrhage (3). Neointimal hyperplasia was significantly more common in the patients with VAP as compared with those with stable angina (68% vs. 8%; p < 0.0001). A rapid progression of organic stenosis within three years was angiographically found in 5 of the 22 patients with variant angina. In all five cases, neointimal hyperplasia was the main contributor to the worsening of the organic lesion at the site of spasm. These histological findings in patients with VAP extremely resembled those in restenosis. Except for vasospasm, no factors significantly predicted the presence of neointimal formations in primary coronary lesions. CONCLUSIONS: Coronary vasospasm may provoke vascular injury that leads to the formation of neointima in VAP patients similar to that seen with restenosis. Coronary spasm may thus play a key role in the rapid coronary stenosis progression in certain patients with VAP. 相似文献
998.
板状碳酸钙和高纯氧化镁合成工艺的研究 总被引:1,自引:1,他引:0
论述了以白云石为原料合成板状碳酸钙和高纯氧化镁的方法,由单因素实验和多因素的正交实验,了各种因素对产品的影响,确定了适宜操作条件,产品的晶型、白度和纯度等质量标准,此工艺特点是用白石为资料同时生产板状碳酸钙和高纯氧化癣。 相似文献
999.
Mineral oils are still predominant as base oils for lubricating greases, although increased numbers of greases have been developed with synthetic oils because of their good performance properties, including thermal/oxidation stability, low‐temperature fluidity, and plastics compatibility. Long life under high‐temperature conditions and good low‐temperature fluidity are required of greases used in bearings of engine electrical components. As many plastics are used in place of metals for the purpose of weight saving, synthetic hydrocarbon greases are used that do not have adverse effects on plastics. Various other special synthetic greases are also in use depending on specific requirements, such as conductivity and vacuum conditions. The properties and applications of various synthetic greases are discussed here. 相似文献
1000.