Cc,Cs, and parasitic correction in quadrupole probe-forming lenses

Approximate expressions are derived for the second and third order aberrations of a quadrupole doublet, allowing for aberrations intrinsic to fields of perfect symmetry, for parasitic aberrations of imperfect symmetry, and for compensating multipole lenses. Five third-order coefficients are found, and expressed in terms of four octopole strengths and the first-order parameters of the doublet as determined by its dimensions. For compensation of third-order aberrations of achromatic quadrupole/octopole lenses, either skew octopole lenses are required externally, or lenses with more than 8 poles are required coincident with the quadrupoles. If an octopole lens is added between the quadrupoles of the achromatic doublet, the spherical aberration of a condenser lens may be compensated. Such a Cs and Cc compensated quadrupole doublet is suitable for use as a probe-forming lens in focused ion beam systems and ion microscopes.     

Derivative Form of Off-axis Aberration Correction Surface and Its Application in Solar Energy Concentration

By using the derivative method, we obtained the same result with that of the previous work of Chen et al. in 2006. Different from the integral form, the derivative form of the surface expression published in this paper is derived from differential equation and based on the theory of non-imaging focusing heliostat proposed by Chen et al. in 2001. The comparison of the derivative form of fixed aberration correction surface has been made with that of integral form surface as well as that of spherical surface in concentrating the solar ray.     

人眼像差校正仪视网膜动态稳像研究

针对人眼无意识的抖动导致图像位置在眼底成像设备上无规律变化而无法有效观察指定区域的问题,提出了一种视网膜图像实时动态稳像算法.该算法依据图像匹配理论,在图像探测的同时引入图像有效区域实时"计算-移位".利用时间上相邻的视频序列图像近似对应于眼底同一位置的特点,通过"采集-运算"找到当前采集图像的中心区域.把当前图像的中心区域与第一帧采集图像的中心区域进行相关匹配,获取当前视网膜图像相对第一帧图像抖动的偏移方向和偏移量,然后把当前图像移位,循环执行此过程,并剔除无法匹配的图像,使得屏幕上的图像始终是在同一个位置的静态图像.实验证明:本文提出的算法解决了自适应眼底成像设备在对视网膜细胞观测时因为人眼自然抖动而造成的图像不稳定问题;解决了人眼在可见光波段的激光照明下受到较强刺激而无法长时观测的问题,实现了细胞和微血管同平台同算法观测;是采用拼接技术实现大视场图像的前提.     

低温实验冷库数据采集和控制系统设计

针对一座小型实验低温冷库自行开发了实用的数据采集和控制系统,能够满足低温冷库日常的数据采集,实现计算机的自动控制以及对冷库运行危险的报警.文中在对已形成的低温冷库自动采集和控制系统思想基础上,进一步探讨和论证其方便性、实用性.本系统是基于VB6.0为开发平台,使读者更容易理解,也使试验人员可以顺利地操控并进行试验.应用...     

Theory of paraxial lateral aberrations of electrostatic imaging electrostatic electron optics based on asymptotic solutions and its verification

In imaging electron optics, study of geometrical lateral aberrations of third order and paraxial lateral aberrations of second order has traditionally been paid more attention to, but the existence of paraxial chromatic aberrations of third order and paraxial chromatic aberrations of magnification of third order was almost ignored, and the general form of paraxial lateral aberration has not been studied theoretically.In the present paper, the paraxial lateral aberrations expressed in general form have been derived emphatically on the basis of asymptotic solutions of paraxial equation. The relationship between the coefficients of asymptotic solutions has been investigated, which proves that the coefficients of asymptotic solutions are related each other. Through a bi-electrode electrostatic spherical concentric system model, two special solutions expressed by asymptotic solutions and accurate solutions in a bi-electrode electrostatic spherical concentric system have been deduced, and the paraxial lateral aberrations have been verified and tested, in which the aberration coefficients are solved by asymptotic solutions of paraxial equation. Result completely proves that the approach based on asymptotic solutions to solve the paraxial lateral aberrations are practicable and accurate enough. The paraxial chromatic aberration of magnification of third order and the paraxial chromatic aberration of third order have been firstly derived, and the Recknagel-Artimovich formula of paraxial chromatic aberration of second order which possess an greatest part in the whole paraxial lateral aberrations has been deduced and confirmed. A simple and clear form for expressing paraxial lateral aberrations of imaging electron optics is suggested for practical use. Results of the present paper will have theoretical value for aberration theory of imaging electron optics and practical significance for the design of image tubes.     

A new hyperchaotic system and its linear feedback control

This paper reports a new hyperchaotic system by adding an additional state variable into a three-dimensional chaotic dynamical system, studies some of its basic dynamical properties, such as the hyperchaotic attractor, Lyapunov exponents, bifurcation diagram and the hyperchaotic attractor evolving into periodic, quasi-periodic dynamical behaviours by varying parameter k. Furthermore, effective linear feedback control method is used to suppress hyperchaos to unstable equilibrium, periodic orbits and quasi-periodic orbits. Numerical simulations are presented to show these results.     

简易混沌振荡器的混沌特性及其反馈控制电路的设计

研究了一个新的简易混沌振荡电路系统的稳定性和混沌特性,从理论上推导了该混沌振荡电路系统的稳定和混沌的条件,并对该系统进行了精确反馈线性化控制.最后,通过电路仿真实验和硬件实验验证了理论分析的准确性.     

Time-delay feedback control in a delayed dynamical chaos system and its applications

The feedback control of a delayed dynamical system, which also includes various chaotic systems with time delays, is investigated. On the basis of stability analysis of a nonautonomous system with delays, some simple yet less conservative criteria are obtained for feedback control in a delayed dynamical system. Finally, the theoretical result is applied to a typical class of chaotic Lorenz system and Chua circuit with delays. Numerical simulations are also given to verify the theoretical results.     

随机参数Duffing系统中的随机混沌及其延迟反馈控制

研究了谐和激励下含有界随机参数Duffing系统(简称随机Duffing系统)中的随机混沌及其延迟反馈控制问题.借助Gegenbauer多项式逼近理论，将随机Duffing系统转化为与其等效的确定性非线性系统.这样，随机Duffing系统在谐和激励下的混沌响应及其控制问题就可借等效的确定性非线性系统来研究.分析阐明了随机混沌的主要特点，并采用Wolf算法计算等效确定性非线性系统的最大Lyapunov指数，以判别随机Duffing系统的动力学行为.数值计算表明，恰当选取不同的反馈强度和延迟时间，可分别达到抑制或诱发系统混沌的目的，说明延迟反馈技术对随机混沌控制也是十分有效的. 关键词： 随机Duffing系统 延迟反馈控制 随机混沌 Gegenbauer多项式     

Vacancy growth and migration dynamics in atomically thin hexagonal boron nitride under electron beam irradiation

Atomically thin hexagonal boron nitride (h‐BN) is investigated using aberration‐corrected ultra‐high resolution electron microscopy under 80 kV electron beam. This study focuses on the in situ formation, growth and migration of vacancies in h‐BN. This study also reveals interaction dynamics of edges and vacancies with adatoms and molecules under the electron beam. According to this investigation, boron monovacancies migrate through their second neighbor to reduce the surface energy of the membrane. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Nonlinear feedback control of a novel hyperchaotic system and its circuit implementation

This paper reports a new hyperchaotic system by adding an additional state variable into a three-dimensional chaotic dynamical system. Some of its basic dynamical properties, such as the hyperchaotic attractor, Lyapunov exponents, bifurcation diagram and the hyperchaotic attractor evolving into periodic, quasi-periodic dynamical behaviours by varying parameter k are studied. An effective nonlinear feedback control method is used to suppress hyperchaos to unstable equilibrium. Furthermore, a circuit is designed to realize this new hyperchaotic system by electronic workbench (EWB). Numerical simulations are presented to show these results.     

平均电流控制型Boost功率因数校正变换器中的中频振荡现象分析

基于输入电压可用其有效值代替以及电感电流与输出电压的波动频率远低于变换器开关频率的假设,建立了用于描述平均电流控制型Boost PFC变换器动力学行为的小信号模型,研究了该变换器中的中频振荡现象问题,揭示了系统发生中频振荡现象的内在物理机理,并给出了系统发生中频振荡现象的参数边界.研究结果表明,该非线性现象不同于已发现的快尺度不稳定性现象和慢尺度不稳定性现象,其主要特征是其振荡频率介于交流输入电压线频率和开关频率之间.最后,电路实验结果证实了理论分析的正确性. 关键词： 中频振荡 平均电流控制 Boost功率因数校正变换器 小信号模型     

An improved car-following model with consideration of the lateral effect and its feedback control research

A car-following model is presented, in which the effects of non-motor vehicles on adjacent lanes are taken into ac- count. A control signal including the velocity differences between the following vehicle and the target vehicle is introduced according to the feedback control theory. The stability condition for the new model is derived. Numerical simulation is used to demonstrate the advantage of the new model including the control signal; the results are consistent with the analytical ones     

Novel automatic control for the optimum optical gain and phase differences in SOA-MZI wavelength converter: Theory and experiment

We have proposed, simulated, and experimentally verified the novel automatic control method and apparatus to automatically adjust and constantly maintain the optimum optical gain and phase differences in order to achieve the automatically optimized semiconductor optical amplifier (SOA)-Mach-Zehnder interferometer (MZI) wavelength converter (WC) with wide input power dynamic range (IPDR) and maximum extinction ratio (ER). Our automatic control algorithm is proposed through the results of simulation and its validity is confirmed through the experiment.     

Modified coupled map car-following model and its delayed feedback control scheme

A modified coupled map car-following model is proposed, in which two successive vehicle headways in front of the considering vehicle is incorporated into the optimal velocity function. The steady state under certain conditions is obtained. An error system around the steady state is studied further. Moreover, the condition for the state having no traffic jam is derived. A new control scheme is presented to suppress the traffic jam in the modified coupled map car-following model under the open boundary. A control signal including the velocity differences between the following and the considering vehicles, and between the preceding and the considering vehicles is used. The condition under which the traffic jam can be well suppressed is analysed. The results are compared with that presented by Konishi et al. (the KKH model). The simulation results show that the temporal behaviour obtained in our model is better than that in the KKH model. The simulation results are in good agreement with the theoretical analysis.     

Liu混沌系统的线性反馈同步控制及电路实验的研究

研究了新型混沌系统——Liu混沌系统的同步控制问题，基于Liu混沌系统的混沌特性，采用线性反馈控制方法，给出了实现Liu混沌系统同步的控制参数取值范围，数值仿真和电路实验证实了该方法的有效性. 关键词： Liu混沌系统 线性反馈控制 混沌同步 电路     

受迫Holmes-Duffing系统安全域分形及时滞速度反馈控制

以受迫Holmes-Duffing系统为研究对象, 对系统施加时滞速度反馈控制, 研究周期激励引起的系统安全域的分形侵蚀及时滞速度反馈对分形侵蚀安全盆的控制作用. 利用Melnikov函数法给出时滞受控系统的安全盆的边界分形条件. 再以时滞量为变参数, 运用四阶Runge-Kutta方法和点映射方法数值研究了时滞对受控系统安全盆的影响规律. 结果表明在弱反馈下, 时滞量的增大能够提高安全盆边界分形的阈值, 从而抑制安全盆的分形侵蚀. 说明时滞速度反馈能够有效抑制系统的安全盆侵蚀.     

功率超声设备频率振幅自动控制研究

本文根据差动变量器桥式电路补偿电学臂的原理，采用锁相环（PLL）及模拟乘法器等技术，进行功率超声设备频率振幅自动控制，结果表明，这种控制方法具有频率跟踪范围宽，负载知应能力强及系统性能稳定等功效。     

Bifurcations and chaos control in discrete small-world networks

An impulsive delayed feedback control strategy to control period-doubling bifurcations and chaos is proposed. The control method is then applied to a discrete small-world network model. Qualitative analyses and simulations show that under a generic condition, the bifurcations and the chaos can be delayed or eliminated completely. In addition, the periodic orbits embedded in the chaotic attractor can be stabilized.     

光束控制系统热效应与球差对激光光束质量的影响

采用Strehl比、桶中功率、β参数和束宽描述远场光束质量，研究了光束控制系统热效应和球差对远场激光光束质量的影响.用四维仿真程序作了详细计算，给出了数值计算结果并进行了物理分析.研究表明，传输通道的热效应和正球差会使远场光强分布扩展，可聚焦能力下降，光束质量变差.有意义的是，当激光发射功率达到一定值时，合适选取负球差会在几何焦面得到比无球差时更高的峰值光强和更好的可聚焦能力.但在以前的工作中，由于焦移，类似的结论是在实际焦面上得出的.非线性热晕的存在是其物理原因，对此用数值计算例子作了说明. 关键词： 高功率激光 热效应 光束控制系统 球差