核磁共振陀螺反馈环路中滤波器的影响研究

为了分析核磁共振陀螺中129Xe自旋振荡器的振幅和频率特性,建立了相应的半经典模型,其中分别采用密度矩阵和经典电磁理论描述核自旋系综和反馈系统。然后,根据自激振荡的自洽条件推导了用于描述自旋振荡器的振荡方程。进一步,利用旋转波近似和慢变振幅近似将振荡方程化简为自洽方程组,它由分别用于描述自旋振荡器振幅和频率的振幅方程和频率方程构成。基于上述自旋振荡器的半经典模型,研究了带通滤波器对自旋振荡器振幅和频率的影响。仿真结果表明,对核磁共振陀螺的典型参量,反馈环路设计不当导致的自旋振荡器频移可达亚μHz。该研究对提高基于自旋振荡器的核磁共振陀螺性能具有一定的参考价值。     

机器人光纤激光焊接TC4钛合金的工艺研究

采用机器人光纤激光焊接系统,进行了厚度为1.8 mm幅面为100 mm×200 mm的TC4钛合金激光焊接试验。为确保焊缝的质量,设计了一套气路保护装置。研究了激光功率、焊接速度、离焦量和保护气体流量等参数对焊接质量的影响,获得了优化焊接工艺参数:激光功率850~900 W、焊接速度0.7~0.9 m/min、离焦量-0.8~-0.5 mm。     

面向IPTV的H.264高清编码视频质量评估

高清晰度视频质量能够有效提升IPTV的业务体验,但是高清视频对编码速率和网络条件的要求都很高.本文在IPTV环境下,基于H.264编码技术,对不同码率下的高清编码视频进行了主观质量评测.为在现阶段IPTV网络环境下开展高清视频业务提供有效的技术参考.     

AlGaN/GaN HEMT器件小信号等效电路参数值的提取

利用国际通用的ColdFET以及宽带小信号提取方法对AlGaN/GaN HEMT器件进行小信号参数的提取,用仿真软件ADS(advanced design system)建立HEMT小信号等效电路模型,并对参数值进行优化.可快速提取器件的小信号参数并给予工艺一些反馈和指导.     

TiO2/activated carbon fibers photocatalyst: Effects of coating procedures on the microstructure, adhesion property, and photocatalytic ability

In order to more easily separate TiO₂ photocatalyst from the treated wastewater, TiO₂ film was immobilized on the surface of activated carbon fibers (ACFs) by employing two kinds of coating procedures, dip-coating, and hydrothermal treatment. The effects of coating procedures on microstructure of TiO₂-coated ACFs (TiO₂/ACFs), such as morphology, porous property, crystal structure, and light absorption characteristics were investigated in detail. The adhesion property between TiO₂ film and ACFs was evaluated by ultrasonic vibration, and the photocatalytic activity of TiO₂/ACFs was tested by the photocatalytic decoloration of methylene blue solution. The results show that hydrothermal treatment presented many advantages to obtain high-performance TiO₂/ACFs photocatalyst in comparison with dip-coating. Hydrothermal treatment could improve the binding property between TiO₂ films and ACFs, which endowed the as-obtained TiO₂/ACFs photocatalyst with improved reusable performance, and TiO₂/ACFs synthesized by hydrothermal treatment presented higher photocatalytic activity.     

Hopf bifurcation analysis in a fluid flow model of Internet congestion control algorithm

This paper focuses on the Hopf bifurcation analysis of some classes of nonlinear time-delay models, namely fluid flow models, for the Internet congestion control algorithm of TCP/AQM networks. Using tools from control and bifurcation theory, it is proved that there exists a critical value of communication delay for the stability of the network. When the delay passes through the critical value, the system loses its stability and a Hopf bifurcation occurs. Furthermore, the stability of the bifurcation and direction of the bifurcating periodic solutions are determined by applying the normal form theory and the center manifold theorem. Finally, some numerical examples are given to verify the theoretical analysis.     

A Distributed Management Method Based on the Artificial Fish-Swarm Model in Cloud Computing Environment

Recently, there are some problems in the centralized management, such as centralized management, heavy burden, excessive number of virtual machine migration, lack of mutual cooperation mechanism between nodes, can’t adapt to the cluster of change. The existing distributed management methods exist between the nodes have less cooperation mechanism and only simple communication, quality of service is no obvious improvement, system can save energy consumption is not obvious. According to the behavior characteristics of the fish, this paper presents an artificial fish to achieve mutual cooperation of nodes in the distributed management method.