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81.
刚性圆板自由落体在水面上的冲击压力 总被引:2,自引:0,他引:2
本文对一个刚性圆板自由落体在水面上的冲击过程建立了比较精确的理论模型,并建立了相应的数值格式。计算结果与已有的实验结果符合良好,通过计算进一步给出了下落质量和下落高度对冲击压力峰值的影响。 相似文献
82.
非接触型光外差轮廓仪 总被引:1,自引:0,他引:1
本文介绍一种纳米级非接触型高精度光外差轮廓仪,它是基于普通光路的光外差干涉仪。工件表面被两束有微小频差的激光束所照射,其中一束经聚焦后用作测量光探针来扫描工件表面,另一束则用作参考光束。两束光经表面反射后产生干涉。测量信号和参考信号的相位差与表面的微不平值成正比。仪器的横向分辨率为2μm,高度分辨率为1 nm,它不需要对试样作大范围的调整,且可用试样自身作参考面。信号经光电转换后由微型计算机进行处理,它能快速完成测量、计算、显示及打印出各种参数和曲线。 相似文献
83.
Demir H.V. Jun-Fei Zheng Sabnis V.A. Fidaner O. Hanberg J. Harris J.S. Jr. Miller D.A.B. 《Semiconductor Manufacturing, IEEE Transactions on》2005,18(1):182-189
This work reports an easy planarization and passivation approach for the integration of III-V semiconductor devices. Vertically etched III-V semiconductor devices typically require sidewall passivation to suppress leakage currents and planarization of the passivation material for metal interconnection and device integration. It is, however, challenging to planarize all devices at once. This technique offers wafer-scale passivation and planarization that is automatically leveled to the device top in the 1-3-/spl mu/m vicinity surrounding each device. In this method, a dielectric hard mask is used to define the device area. An undercut structure is intentionally created below the hard mask, which is retained during the subsequent polymer spinning and anisotropic polymer etch back. The spin-on polymer that fills in the undercut seals the sidewalls for all the devices across the wafer. After the polymer etch back, the dielectric mask is removed leaving the polymer surrounding each device level with its device top to atomic scale flatness. This integration method is robust and is insensitive to spin-on polymer thickness, polymer etch nonuniformity, and device height difference. It prevents the polymer under the hard mask from etch-induced damage and creates a polymer-free device surface for metallization upon removal of the dielectric mask. We applied this integration technique in fabricating an InP-based photonic switch that consists of a mesa photodiode and a quantum-well waveguide modulator using benzocyclobutene (BCB) polymer. We demonstrated functional integrated photonic switches with high process yield of >90%, high breakdown voltage of >25 V, and low ohmic contact resistance of /spl sim/10 /spl Omega/. To the best of our knowledge, such an integration of a surface-normal photodiode and a lumped electroabsorption modulator with the use of BCB is the first to be implemented on a single substrate. 相似文献
84.
Jun Rong Li Jun Wang Jia Rui Xu Ming Qiu Zhang Min Zhi Rong Qiang Zheng 《Composites Science and Technology》2006,66(16):3126-3131
The authors of this paper synthesized a series of amphiphilic triblock copolymers of polystyrene-b-poly(ethylene glycol)-b-polystyrene (PS-PEG-PS) having different PEG/PS ratios with nearly identical molecular weights of the entire copolymers. The interfacial interactions in the composites consisting of carbon black and the copolymers can thus be tailored. When these conducting composites are exposed to certain solvent vapors, their electrical resistances greatly increase, showing the gas sensitivity. The present work indicated that this switching behavior is controlled by the structural relaxation of the composites because matrix swelling acts as the main mechanism. The response time has been correlated with absolute temperature by Arrhenius equation, and the estimated activation energy reflects mobility of the fillers involved in the solvent induced expansion of the surrounding polymer. Therefore, by using the gas sensibility of the conductive composites, the structure evolution of the composite materials in solid state and the effect of filler/matrix interfacial interaction on the relaxation property of the matrix polymer has been inspected. It was found that lower activation energy represents stronger interfacial interaction in case good solvent of the matrix was used for the test. 相似文献
85.
This paper deals with the two dimensional (2-D) infrared photonic crystal slab with an air-bridge structure featuring defect waveguides in which the optical propagation properties were obtained by measurements of transmission spectra. 3-D finite-difference time-domain (FDTD) simulations have revealed the appearance of four defect propagation modes for the band structure and transmission spectra in the air-bridge slab. These defect modes were experimentally identified in the measured transmission spectra. 相似文献
86.
Yu Zheng Haiyi Zhang Li Zhao Liujing Wei Xingyuan Ma Dongzhi Wei 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2008,83(10):1409-1412
BACKGROUND: 2,3‐Butanediol (2,3‐BD) is a valuable chemical that can be biosynthesized from many kinds of substrates. For commercial biological production of 2,3‐BD, it is desirable to use cheap substrate without pretreatment, such as starch. However, there have been few reports on the production of 2,3‐BD directly from starch. RESULTS: In this work, gene malS coding for α‐amylase (EC 3.2.1.1) precursor was inserted into plasmid pUC18K, and secretory over‐expression of α‐amylase was achieved by engineered Klebsiella pneumoniae. The extracellular recombinant amylase accelerated the hydrolyzation of starch, and one‐step production of 2,3‐BD from starch was carried out by engineered K. pneumoniae. A 2,3‐BD concentration of 3.8 g L?1 and yield of 0.19 g 2,3‐BD g?1 starch were obtained after 24 h fermentation. CONCLUSION: The one‐step production of 2,3‐BD from starch was achieved by secretory over‐expression of amylase in K. pneumoniae. This would simplify the process and reduce the production cost considerably by enabling use of starch with minimal pretreatment. Copyright © 2008 Society of Chemical Industry 相似文献
87.
Distributed Rule-Regulated Spectrum Sharing 总被引:2,自引:0,他引:2
Lili Cao Haitao Zheng 《Selected Areas in Communications, IEEE Journal on》2008,26(1):130-145
Dynamic spectrum access is a promising technique to use spectrum efficiently. Without being restricted to any prefixed spectrum bands, nodes choose operating spectrum on-demand. Such flexibility, however, makes efficient and fair spectrum access in large-scale networks a great challenge. Prior work in this area focused on explicit coordination where nodes communicate with peers to modify local spectrum allocation, and may heavily stress the communication resource. In this paper, we introduce a distributed spectrum management architecture where nodes share spectrum resource fairly by making independent actions following spectrum rules. We present five spectrum rules to regulate node behavior and maximize system fairness and spectrum utilization, and analyze the associated complexity and overhead. We show analytically and experimentally that the proposed rule-based approach achieves similar performance with the explicit coordination approach, while significantly reducing communication cost. 相似文献
88.
电信运营企业重组后,中国电信业具有广阔的市场前景.文章分别从知识营销、定位营销、服务营销等方面阐述了电信业务营销的基本思路.同时,分析了在营销的整个过程中的多种营销技巧. 相似文献
89.
90.
Zhi‐Long Ye Min Lu Yan Zheng Ya‐Hong Li Wei‐Min Cai 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2008,83(11):1541-1550
BACKGROUND: Food waste generally has a high starch content and is rich in nutritional compounds, including lipids and proteins. It therefore represents a potential renewable resource. In this study, dining‐hall food waste was used as a substrate for lactic acid production, and response surface methodology was employed to optimise the fermentation conditions. RESULTS: Lactic acid biosynthesis was significantly affected by the interaction of protease and temperature. Protease, temperature and CaCO3 had significant linear effects on lactic acid production, while α‐amylase and yeast extract had insignificant effects. The optimal conditions were found to be an α‐amylase activity of 13.86 U g?1 dried food waste, a protease activity of 2.12 U g?1 dried food waste, a temperature of 29.31 °C and a CaCO3 concentration of 62.67 g L?1, which resulted in a maximum lactic acid concentration of 98.51 g L?1 (88.75% yield). An increase in inoculum size would be appropriate for accelerating the depletion of initial soluble carbohydrate to enhance the efficiency of α‐amylase in dining‐hall food waste fermentation. CONCLUSION: A suitable regression model for lactic acid production was developed based on the experimental results. Dining‐hall food waste was found to be a good substrate for lactic acid fermentation with high product yield and without nutrient supplementation. Copyright © 2008 Society of Chemical Industry 相似文献