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991.
The three-dimensional axisymmetric elastodynamic response of a penny-shaped crack embedded in an infinite elastic solid subjected to a pair of transient concentrated forces is investigated. The forces are applied on the symmetry axis perpendicular and symmetric to the crack surfaces, including the special case when the forces act precisely on the crack surfaces. A time-domain boundary integral equation method is applied for computing the crack-opening displacement and subsequently the time dependence of the dynamic stress intensity factors. Numerical calculations are carried out for various geometry parameters and the results are discussed. It is found that the location of the applied concentrated forces inducing the highest dynamic stress intensity factors differs from that producing the highest static values. 相似文献
992.
The communicating finite state machines can exchange messages over bounded FIFO channels. In this paper, a new technique, called reverse reachability analysis, is proposed to detect deadlocks on the communication between the communicating finite state machines. The technique is based on finding reverse reachable paths starting from possible deadlock states. If a reverse reachable path can reach the initial global state, then deadlock occurs. Otherwise the communication is deadlock-free. The effectiveness of the technique has been verified by some real protocols such as a specification of X.25 call establishment/clear protocol and Bartlet's alternating bit protocol. 相似文献
993.
Novel algorithmic features of multimedia applications and advances in VLSI technologies are driving forces behind the new multimedia signal processors. We propose an architecture platform which could provide high performance and flexibility, and would require less external I/O and memory access. It is comprised of array processors to be used as the hardware accelerator and RISC cores to be used as the basis of the programmable processor. It is a hierarchical and scalable architecture style which facilitates the hardware-software codesign of multimedia signal processing circuits and systems. While some control-intensive functions can be implemented using programmable CPUs, other computation-intensive functions can rely on hardware accelerators.To compile multimedia algorithms, we also present an operation placement and scheduling scheme suitable for the proposed architectural platform. Our scheme addresses data reusability and exploits local communication in order to avoid the memory/communication bandwidth bottleneck, which leads to faster program execution. Our method shows a promising performance: a linear speed-up of 16 times can be achieved for the block-matching motion estimation algorithm and the true motion tracking algorithm, which have formed many multimedia applications (e.g., MPEG-2 and MPEG-4). 相似文献
994.
The electromigration phenomenon has been one of the most intriguing physical problems in the semiconductor device reliability. The models to explain the phenomenon are here revised, together with the influence of materials and their microstructure. The various measuring techniques are described, including the design of special test patterns, and statistical data analysis is briefly reviewed. 相似文献
995.
997.
几何设计约束的表示与满足问题研究 总被引:3,自引:1,他引:2
对于智能CAD系统来说,具有解决几何设计约束的功能是重要的。本文提出了一种面向对象的几何设计约束表示方法,它可以通过两种方式来表达。文中给出了一个约束传播算法,用于解决约束满足问题。 相似文献
998.
本文采用离散滑模变结构控制方法,针对机器人提出了一种滑模变结构——PI控制方案,给出了该控制方案滑模存在条件及控制器设计方案。该控制器将离散滑模变结构控制和PI控制两者的优点有机地结合起来,理论分析和仿真结果表明该控制器能使机器人在各种复杂非线性动力学情况下具有良好的性能指标。这种控制器输出切换小,可以投入应用。 相似文献
999.
自韧Si3N4陶瓷的显微结构及其性能研究 总被引:4,自引:0,他引:4
利用热压的方法制得室温断裂韧性和抗弯强度分别为11.2MPa·m ̄(1/2)、823MPa,高温(1350℃)断裂韧性和抗弯强度分别为23.9MPa·m ̄(1/2)、630MPa的自韧Si_3N_4陶瓷。研究了显微结构和力学性能之间的关系。结果表明:玻璃相的含量、β-Si_3N_4的长径比等对性能有重要影响。分析了自韧Si_3N_4陶瓷的增韧机理,通过SEM明显观察到Si_3N_4中存在裂纹偏转、分支和β-Si_3N_4拔出现象。 相似文献
1000.
VF Ferrario L Marzona C Sforza A De Pol A Miani AE Bertelli A Forabosco 《Canadian Metallurgical Quarterly》1993,15(1):37-48
A model of human neonatal ovary is presented, derived from morphometric, evaluations carried out on left ovaries removed from five full-term neonates with a 46, XX karyotype, free from malformations of the genital apparatus. According to this model, the gonad can be represented by a triaxial ellipsoid with a central medullary core surrounded by a cortical stratum of constant thickness. The germinal population, consisting of follicles and primitive cortical tissue, occupies the cortex, intermingled with the interstitium or stroma. In the cortex it is then possible to describe an outer layer formed by primitive cortical tissue, and an inner portion occupied by follicles. The primary and secondary follicles fill the portion near the medulla and the primordial ones are contained in the middle and outer zones. Since the variability observed among ovaries is slight, we can propose a mean model of neonatal ovary in which the spatial relationships among the different components, the total number of follicles and their position in the cortex can be calculated. 相似文献