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991.
Zhao Z Adenwalla SD Ketterson JB Sarma BK 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》1989,36(5):481-484
A technique is proposed for measuring the group velocity of sound by a frequency-modulated (FM) continuous wave (CW) technique. Detailed calculations are presented, showing that V(g)=(deltaomega(m)/deltaphi)d , where V(g), deltaomega(m), deltaphi, and d are, respectively, the group velocity, change of modulation frequency, phase change of the received signal detected by a biphase lock-in amplifier, and the distance traveled by the sound. The approach has the advantage of high resolution compared to the conventional time-of-flight measurement technique. 相似文献
992.
我国古典园林论著,现在常见的有计成的《园冶》、李笠翁的《一家言居室器玩部》以及明人程荩臣的《清闲供》书中的《小蓬莱》共三种,其余零星散见于古人笔记的不计。《清闲供》一书,计有不同内容的短篇十四篇,《小蓬莱》谈造园艺术,只是书中的一项内容,全文短。《清闲供》毫无现实的积极意义,经过时代的淘汰更失去其效用,成为了糟粕。 相似文献
993.
994.
995.
本文提出一种用“整体浇注法”制做三维牙——颌骨光弹性模型的新方法,即用价格便宜的石膏做阴模,先制出与真实牙几何相似的牙光弹性模型和模拟牙周膜的乳胶套,将它们粘接好,然后将其放入颌骨石膏阴模的适当位置,浇入环氧树脂混合液,用“二次固化法”进行固化,即可制成三维牙——颌骨整体光弹性模型。此法能保证模型与实物的严格几何相似和牙周的边界条件相似,使实验精度大大提高且工艺简单、成本低。 相似文献
996.
The surface structure of the oxidized and ammonia dissolved MoO3/-Al2O3 samples and the adsorption characteristics of the sulfided samples were investigated by Laser Raman Spectroscopy (LRS) and Low Temperature Infrared Spectroscopy (LTIR) techniques.It was verified that there were two kinds of coordinated unsaturated Mo sites (denoted as MoA(CUS) and MoB(CUS)) on the surface and the precursors of MoA(CUS) and MoB(CUS) were Mo(O) and Mo(T), respectively. It was also concluded that MoA(CUS) sites could adsorb NO and CO, while MoB(CUS) could adsorb CO only. The surface concentration of MoA(CUS) might be far smaller than that of MoB(CUS). 相似文献
997.
A fundamental analysis of phase aberration correction techniques which use speckle brightness-based image equality factors (QFs) to iteratively reduce phase errors is presented. Phase aberration arises from the spatial inhomogeneity of acoustic velocity in human tissue and degrades the performance of diagnostic ultrasonic imaging systems. A theoretical analysis is presented indicating that the mean speckle brightness decreases with root-mean-square (RMS) phase error. A general definition of QFs is given using the probability of error as a criterion of performance. The QF is optimized through minimization of the probability of error under different conditions. The analysis provides a theoretical framework for the current correction technique using QFs under a variety of conditions, and is a useful tool to evaluate new QFs and correction techniques. 相似文献
998.
C. W. Zhu G. Y. Zhao V. V. S. Revankar V. Hlavacek 《Journal of Materials Science》1992,27(8):2211-2217
After analysing different plasma processes, we have designed and developed a 14kW d.c. plasma unit for generating ultrafine powders. Experiments to characterize the torch demonstrated that it is possible to operate the plasma unit over a wide range of conditions without losing its discharge stability. Temperature distribution profiles were determined radially as well as axially in the reaction chamber, and the efficiency of the torch was calculated for a fixed power input. Ultrafine powders of Ta, Mo and W were synthesized, and size and size distribution obtained. The particle size was found to be 0.03–0.1 m, with a perfect spherical shape. The analysis of the samples is discussed. 相似文献
999.
Summary Byzantine Agreement is important both in the theory and practice of distributed computing. However, protocols to reach Byzantine Agreement are usually expensive both in the time required as well as in the number of messages exchanged. In this paper, we present a self-adjusting approach to the problem. The Mostly Byzantine Agreement is proposed as a more restrictive agreement problem that requires that in the consecutive attempts to reach agreement, the number of disagreements (i.e., failures to reach Byzantine Agreement) is finite. Fort faulty processes, we give an algorithm that has at mostt disagreements for 4t or more processes. Another algorithm is given forn3t+1 processes with the number of disagreements belowt
2/2. Both algorithms useO(n
3) message bits for binary value agreement.
Yi Zhao is currently working on his Ph.D. degree in Computer Science at University of Houston. His research interests include fault tolerance, distributed computing, parallel computation and neural networks. He obtained his M.S. from University of Houston in 1988 and B.S. from Beijing University of Aeronautics and Astronautics in 1984, both in computer science.
Farokh B. Bastani received the B. Tech. degree in electrical engineering from the Indian Institute of Technology, Bombay, India, and the M.S. and Ph.D. degrees in electrical engineering and computer science from the University of California, Berkeley. He joined the University of Houston in 1980, where he is currently an Associate Professor of Computer Science. His research interests include software design and validation techniques, distributed systems, and fault-tolerant systems. He is a member of the ACM and the IEEE and is on the editorial board of theIEEE Transactions on Software Engineering. 相似文献
1000.