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911.
Deyue Zhang Yukun Guo Chengchun Gong Guan Wang 《Advances in Computational Mathematics》2012,36(1):3-20
The scattering of time-harmonic electromagnetic waves propagating in a homogeneous chiral environment by obstacles is studied.
The problem is simplified to a two-dimensional scattering problem, and the existence and the uniqueness of solutions are discussed
by a variational approach. The diffraction problem is solved by a finite element method with perfectly matched absorbing layers.
Our computational experiments indicate that the method is efficient. 相似文献
912.
In this paper, we investigated the Hopf bifurcation of the eXplicit Control Protocol (XCP) for the Internet congestion control system. These bifurcation behaviors may cause heavy oscillation of average queue length and induce network instability. A time-delayed feedback control method was proposed for controlling Hopf bifurcation in the XCP system. Numerical simulation results are presented to show that the time-delayed feedback controller is efficient in controlling Hopf bifurcation. 相似文献
913.
Fenglan Sun Jiancong Chen Zhi-Hong Guan Li Ding Tao Li 《Nonlinear Analysis: Real World Applications》2012,13(5):2271-2284
Finite-time consensus problems of the leader-following multi-agent systems with jointly-reachable leader and switching jointly-reachable leader are studied in this paper. Based on the graph theory, LaSalle’s invariance principle and Lyapunov stability theory, the finite-time consensus protocols are presented for the first-order and second-order leader-following systems. Some examples and simulation results are given to illustrate the effectiveness of the obtained theoretical results. 相似文献
914.
Fenglan Sun Zhi-Hong Guan Xi-Sheng Zhan Fu-Shun Yuan 《Nonlinear Analysis: Real World Applications》2012,13(5):1979-1990
This paper studies the convergence and convergence speed for the second-order and the high-order discrete-time multi-agent systems with random networks and arbitrary weights. Random networks mean that the existence of any edge is probabilistic and independent of any other edge. By introducing the agreement set, velocity control gain and high-order state control gain, some consensus protocols are provided for the discrete-time random networks. Moreover, the per-step and asymptotic convergence factors are proposed to measure the convergence and convergence speed. Some examples and simulation results are given to illustrate the effectiveness of the obtained theoretical results. 相似文献
915.
916.
917.
This paper presents an experimental investigation of adverse pressure gradient turbulent flow over two rough surfaces and a reference smooth surface. The adverse pressure gradient was produced in an asymmetric diffuser whose opening angle was 3°. The rough surfaces comprised sand grains and gravels of nominal mean diameters of 1.55 mm and 4.22 mm, respectively. The tests were conducted at an approach flow velocity of 0.5 m/s and the momentum thickness Reynolds number varied from 900 to 3000. A particle image velocimetry technique was used for the velocity measurements. Profiles of the mean velocity, turbulent intensities, Reynolds stress ratios, mixing length, eddy viscosity and the production terms were then obtained to document the effects of adverse pressure gradient (APG) on low Reynolds number rough-wall turbulent boundary layers. The results indicate that APG thickens the boundary layer and roughness sublayer. The APG and surface roughness also enhanced the production of turbulence as well as the turbulence level when compared with the smooth-wall data. 相似文献
918.
Zhi-Qiang Feng Christine Renaud Jean-Michel Cros Hongwu Zhang Zhenqun Guan 《International Journal of Solids and Structures》2010,47(17):2215-2222
The present paper is devoted to the analysis of the contact/impact problems with Coulomb friction and large deformation between two hyperelastic bodies of Gent model. The total Lagrangian formulation is adopted to describe the geometrically non-linear behavior. For the finite element implementation, the explicit expression of the incremental law of Gent model is derived. A first order algorithm is applied for the numerical integration of the time-discretized equation of motion. Efficiency and accuracy of the resulting method is illustrated on a two-dimensional static contact problem and a three-dimensional dynamic contact problem as compared with ANSYS simulations. 相似文献
919.
Field emission properties and surface structure of nickel containing amorphous carbon 总被引:1,自引:0,他引:1
G. Y. Chen J. S. Chen Z. Sun Y. J. Li S. P. Lau B. K. Tay J. W. Chai 《Applied Surface Science》2001,180(3-4):185-190
Nickel containing amorphous carbon (a-C:Ni) films have been deposited by filtered cathodic vacuum arc (FCVA) technique by introducing pure nickel into the graphite target. The field electron emission property of a-C:Ni was improved when compared to that of pure tetrahedral amorphous carbon (ta-C) by FCVA. The emission threshold field of a-C:Ni film is about 5 V μm−1, whilst the threshold field of the ta-C film is about 13 V μm−1. Raman spectroscopy suggests that the sp2 clusters in the carbon film increase both in size and number when Ni is introduced. However, the emission was found to degrade to threshold fields beyond 20 V μm−1 after the a-C:Ni film was left in ambient for a week. This observation is attributed to surface absorption of oxygen on the a-C:Ni film, as determined by X-ray Photoelectron Spectroscopy. 相似文献
920.
This paper describes an optical system for high temperature creep strain measurement using quartz optical fiber, super long working distance microscope and digital image processing techniques. In this system one end of the quartz optical fibers is arrayed in a small area on the specimen surface and the other end is illuminated by a laser beam. The fiber ends on the specimen surface form the spot array. The small optical spots on the specimen are tracked by a CCD camera and the images are processed by digital image processing software. The diameter of each quartz fiber is 100 μm and the fibers can be arrayed in a small area. The local strains are determined by measuring the variety of relative distance between two spots. Experimental results of local creep strain on the welding joints of 15CrMo and HK40 at 850°C are obtained. 相似文献