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51.
Ze-Ping Wang 《Acta Mechanica Solida Sinica》1993,6(1):69-80
Based on meso-damage mechanics, a model of dynamic ductile damage under tensile stress is developed, in which work-hardening behavior, rate-dependent contribution and inertial effects are taken into account. Plate-impact test on pure copper under one-dimensional plane strain condition is conducted. Some significant mechanical phenomena are observed by means of microscopic observations of the spalled specimen. The mathematical model presented in this paper is incorporated in a hydrodynamic one-dimensional finite-difference computer code, to simulate the process of spallation in pure copper sample. Comparison of numerical calculations and experimental results shows that the model can describe spall damage successfully. 相似文献
52.
Yngve Willassen 《Journal of multivariate analysis》1979,9(1):138-149
The paper consists of two parts. In the first part a previous result by Solari [(1969) J. Roy. Statist. Soc. Ser. B31] for a simplified two-variable model is generalized to the multivariate case. In the second part the behaviour of the likelihood surface is clarified when we have replications of observations. 相似文献
53.
在传媒业发达的当今,动画片成为儿童认识世界的一个主要渠道,有选择地收看动画片是家庭教育的一部分。学龄前后是创造力这种复合能力培养的最佳时期。本文以一部经典作品为例,帮助家长从优化多元性格、培养观察力和想象力、保持好奇心、自主寻找答案等角度出发,甄选有益身心的动画片,让儿童在快乐中开启创造潜能。 相似文献
54.
In the paper a stochastic control problem consisting of continuously acting controls, impulse controls and stopping times of a partially observed diffusion with discounted cost functional is considered. The problem is successively approximated by time, observation, control and space discretizations to obtain finally a completely observed finite valued control problem. It is shown that the optimal strategy for the approximating problem, which can be numerically computed, is nearly optimal for the original problem 相似文献
55.
Based on the dual-wavelength high altitude detecting lidar we developed, daytime observation capability was realized in its sodium fluorescence channel by employing a Na (sodium) atomic filter and other relevant technologies. Because of the very narrow passband and very high out-of-band suppression of the Na atomic filter, the lidar echo at an 80-110 km altitude can be obtained even at noontime when background light from the sun is very strong. The capability for a 24-h continuous observation of the lidar system has been demonstrated by the preliminary observation result. This development makes the constant detection and investigation of high altitude atmosphere over the country possible. 相似文献
56.
An optimal vibration control strategy for partially observable nonlinear quasi Hamiltonian systems with actuator saturation is proposed. First,a controlled partially observable non-linear system is converted into a completely observable linear control system of finite dimension based on the theorem due to Charalambous and Elliott. Then the partially averaged It stochastic differential equations and dynamical programming equation associated with the completely observable linear system are derived by using the stochastic averaging method and stochastic dynamical programming principle,respectively. The optimal control law is obtained from solving the final dynamical programming equation. The results show that the proposed control strategy has high control effectiveness and control effciency. 相似文献
57.
作者借助于新研制的可以直接观察磨损动态过程的试验装置和扫描电镜原位观察了无润滑条件下金属滑动表面的磨损特征与变化,发现摩擦表面可以划分为真实接触区和过渡磨损区,两者的磨损机理不同,真实接触区发生的是粘着磨损,而且磨粒沿摩擦力方向有明显增大的趋势;随着真实接触区的磨损,过渡磨损区可以逐渐转变为真实接触区,而且由于磨粒增多,非磨损区也可以逐渐转变为过渡磨损区。对磨损过程中摩擦力变化的测试结果表明,当磨损表面发生粘着时的粘着力与Bowden和Tabor粘着理论计算值十分接近。 相似文献
58.
59.
The solutions of navigation observation equations for CAPS 总被引:2,自引:2,他引:0
Chinese scientists invent the navigation and positioning system based on commercial communications satellites and develop
them successfully into China Area Positioning System (CAPS). In principle, this system is different from the GPS broadcasting
satellite navigation class, where the propagation epoch of original navigation signals for pseudo-range measurement is from
a ground master control station rather than from satellite transponders. This paper addresses the establishment of the three
observation equation models for the navigation and positioning system based on communications satellites, and expresses them
identically to operator equations and optimized models. Furthermore, both algorithms of the linear solution for the observable
characteristic equation and the least-squares solution for the condition number more than 4 are discussed, with several methods
for the exact solution, such as improving the behavior of coefficient matrices, right estimation for the weighted right hand
side and selection of iteration forms of solutions, and the influence of the condition number on improving navigation and
positioning accuracy is also analyzed carefully. Hopefully, all the works would be contributive to further development of
the navigation and positioning system based on communications satellites, and be potentially valuable to other satellite navigation
and positioning systems.
Supported by the National Basic Research and Development Program of China (Grant No. 2007CB815500) 相似文献
60.
Control of melt flow during Czochralski (CZ) crystal growth by application of magnetic fields is an important technique for large-diameter (>300 mm) silicon single crystals. Melt convection under magnetic fields is an interesting problem for electromagnetic-hydrodynamics. This paper reviews the effects of a vertical magnetic field and a cusp-shaped magnetic field on melt flow during CZ crystal growth. Melt flow in vertical magnetic fields or cusp-shaped magnetic fields was investigated by the direct observation method based on X-ray radiography and by numerical simulation. The first part of this review shows the result of direct observation of molten silicon flow under magnetic fields. It also compares the results of experimental and numerical simulation. The second part shows the details of the numerical simulation of the behavior of molten silicon in magnetic fields. 相似文献