非旋波近似下类克尔介质中“单模光场-受激三能级原子”系统的光子统计演化分析

本文研究了非旋波近似下类克尔介质对“单模光场-受激三能级原子”系统的光子统计演化特性的影响.数值计算的结果表明:类克尔介质的作用直接影响着受激辐射场的平均光子数< n(t) >的Rabi振荡的幅度和频率;而虚光场的影响则表现为受激辐射场的量子噪音,它与激发场强的变化及场与介质的耦合程度密切相关.另外,本文还对< n(t)>进行了频谱分析,结果发现该非线性系统存在着一系列高次谐波;并且,各高次谐波成分和振幅的变化情况完全依赖于激发场强及与介质的耦合程度.     

Numerical study of chaotic oscillations in the electron beam with virtual cathode in the external non-uniform magnetic fields

In this Letter the results of theoretical investigations of the chaotic microwave oscillator based on the electron beam with a virtual cathode are presented. Nonlinear non-stationary processes in these electron systems are studied by means of numerical analysis of 2.5D model. It was discovered that the non-uniform external magnetic field value controls the dynamical regime of oscillations in the virtual cathode oscillator. The processes of the chaotization of output microwave radiation are described and interpreted from the point of view of the formation and interaction of electron structures (bunches) in the electron beams. The numerical results have shown that the investigated electron system with virtual cathode could be considered as a promising controlled source of wideband chaotic oscillations in the microwave range.     

Searching for a near neighbor particle in DSMC cells using pseudo-subcells

LeBeau et al. (2003) [4] introduced the ‘virtual-subcell’ (VSC) method of finding a collision partner for a given DSMC particle in a cell; all potential collision partners in the cell are examined to find the nearest neighbor, which becomes the collision partner. Here I propose a modification of the VSC method, the ‘pseudo-subcell’ (PSC) method, whereby the search for a collision partner stops whenever a ‘near-enough’ particle is found, i.e. whenever another particle is found within the ‘pseudo-subcell’ of radius δ centered on the first particle. The radius of the pseudo-subcell is given by δ = Fd_n, where d_n is the expected distance to the nearest neighbor and F is a constant which can be adjusted to give a desired trade-off between CPU time and accuracy as measured by a small mean collision separation (MCS). For 3D orthogonal cells, of various aspect ratios, d_n/L ≈ 0.746/N^0.383 where N is the number of particles in the cell and L is the cube root of the cell volume. There is a good chance that a particle will be found in the pseudo-subcell and there is a good chance that such a particle is in fact the nearest neighbor. If no particle is found within the pseudo-subcell the closest particle becomes the collision partner.     

虚拟机在多媒体教室管理中的应用探讨

虚拟机技术的发展近年来已经越来越成熟,并在教学中得到了广泛的应用.结合实际的工作经验,就虚拟机在多媒体教室计算机系统管理中的应用作了探讨性的研究,分析研究了虚拟机的特点及利用虚拟机软件解决多媒体教室计算机系统管理中的若干问题.     

基于VLAN的策略路由的应用

简单介绍虚拟局域网(VLAN)及策略路由的概念,详细介绍在Linux下VLAN及策略路由的实现.根据具体问题并结合实例详细介绍在Linux下如何将二者结合解决实际问题.     

Integrated structure and control design for mechatronic systems with configuration-dependent dynamics

This paper considers the optimal design of mechatronic systems with configuration-dependent dynamics. An optimal mechatronic design requires that, among the structural and control parameters, an optimal choice has to be made with respect to design specifications in the different domains. Two main challenges are treated in this paper: the non-convex nature of the optimization problem and the difficulty in modeling serial machines with flexible components and their embedded controllers. The optimization problem is treated using the direct design strategy which considers simultaneously structural and control parameters as variables and adopts non-convex optimization algorithms. Linear time-invariant and gain-scheduling PID controllers are addressed. This methodology is exploited for the multi-objective optimization of a pick-and-place assembly robot with a gripper carried by a variable-length flexible beam. The resulting design tradeoffs between system accuracy and control efforts demonstrate the advantage of an integrated design approach for mechatronic systems with configuration-dependent dynamics.     

A Reliable Multicast Routing Protocol Based on Recovery Points and FEC in Mobile Ad-hoc Networks

Multicasting is an essential service for mobile ad-hoc networks. A major challenge for multicasting in mobile ad-hoc networks (MANETs) is the unstable forwarding path. This work presents a reliable multicasting protocol for mobile ad-hoc networks. A virtual backbone is used as a shared structure for multiple sessions. A lost packet recovery scheme is developed for reliable packet transmission, called the Recovery Point (RP) scheme. The RP scheme maintains the data packets received from the source for recovering lost packets for its downstream RPs. In addition, we combine the Forward Error Correction (FEC) technology with our RP scheme to enhance the reliability of our RP scheme. A mergence scheme for RP is also proposed to avoid excessive control overhead. Our RP and FEC based scheme can be used to improve the reliability and efficiency of the traditional non-acknowledged multicasting approach. Experiments were conducted to evaluate the proposed multicasting scheme. The results demonstrate that our scheme outperforms other schemes in terms of packet delivery ratio and multicast efficiency. Furthermore, the simulation results also demonstrate that our approach is stable in networks with high mobility.

基于虚拟仪器的变速箱加载综合实验台的研究

针对传统变速箱试验台检测精度低、能量消耗大、成本高、只能恒载荷加载的不足之处,提出了新颖节能的“交流发电,直流回馈”电封闭变速箱加载综合试验台。引入虚拟仪器技术对试验台进行自动监控与管理,实现试验台的远程测控。在检测技术的基础上将电封闭式节能加载技术、模糊控制技术与虚拟仪器技术相结合,致力于开发新型变速箱加载综合试验台,对变速箱进行综合性能测试。     

基于FPGA的精密时间间隔测量仪设计

介绍一种基于FPGA的精密时间间隔测量仪的研制过程。精密时间间隔测量仪是应科学试验中高可靠性、高精密度和多通道等测量要求而研制的。精密时间间隔测量仪以PXI接口为平台设计成为虚拟仪器,一个PXI系统可插多个精密时间间隔测量仪板卡,每个板卡可对1个起始通道与8个停止通道的脉冲信号进行时间间隔测量,同时测量停止脉冲的脉冲宽度。精密时间间隔测量仪以FPGA为测时核心,利用锁相环倍频和时钟分相技术,测量分辨力可达到1ns,测时范围可达10ns-10ms。