两子系统在周期切换连接下的振荡行为及其机理

研究了两非线性系统在周期切换连接下的分岔和混沌行为.通过局部分析,分别给出了两子系统参数空间诸如Fold分岔、Hopf分岔等临界条件,进而考虑两子系统存在不同稳态解时通过周期切换连接下的复合系统的分岔特性,给出了不同的周期振荡行为,并揭示了其相应的产生机理.指出系统轨迹可以由切换点分割成不同的部分,分别受两子系统的控制,而随参数的变化,切换点数目成倍增加,导致系统由倍周期分岔序列进入混沌.同时,在其演化过程中,虽然子系统定性保持不变,但由于切换导致的非光滑性,复合系统不仅仅表现为两子系统动力特性的简单连接,而是会产生各种分岔,导致诸如混沌等复杂振荡行为.     

非线性切换系统的动力学行为分析

建立了周期切换下的非线性电路模型,基于子系统平衡点及其稳定性分析,分别给出了其相应的fold分岔和Hopf分岔条件,讨论了子系统在不同平衡态下由周期切换导致的各种复杂行为,指出切换系统的周期解随参数的变化存在着倍周期分岔和鞍结分岔两种失稳情形,并相应地导致不同的混沌振荡,进而结合系统轨迹及其相应的分岔分析,揭示了各种振荡模式的动力学机理. 关键词： 周期切换 倍周期分岔 鞍结分岔 混沌     

分段线性电路切换系统的复杂行为及非光滑分岔机理

分析了分段线性电路系统在周期切换下的复杂动力学行为及其产生的机理. 基于平衡点分析, 给出了两子系统Fold分岔和Hopf分岔条件. 考虑了在不同稳定态时两子系统周期切换的分岔特性, 产生了不同的周期振荡, 并揭示了其产生的机理. 在不同的周期振荡中, 切换点的数量随参数变化产生倍化, 导致切换系统由倍周期分岔进入混沌. 关键词： 分段线性电路 切换系统 非光滑分岔     

切换电路系统的振荡行为及其非光滑分岔机理

探讨了周期时间开关及控制阈值下在两个Rayleigh型子系统之间切换的电路系统随参数变化的复杂动力学演化过程, 通过对子系统平衡点的分析, 给出了参数空间中Fold分岔和Hopf分岔的条件, 考察了切换面处广义Jacobian矩阵特征值随辅助参数变化的分布情况, 得到了切换面处系统可能存在的各种分岔行为, 进而讨论了系统不同行为的产生机理, 指出系统的相轨迹存在分别由周期开关和控制阈值决定的两类不同的分界点, 而系统轨迹与非光滑分界面的多次碰撞将导致系统由周期倍化分岔导致混沌振荡.     

周期切换下Rayleigh振子的振荡行为及机理

本文研究了自治与非自治电路系统在周期切换连接下的动力学行为及机理.基于自治子系统平衡点和极限环的相应稳定性分析和切换系统李雅普诺夫指数的理论推导及数值计算.讨论了两子系统在不同参数下的稳态解在周期切换连接下的复合系统的各种周期振荡行为,进而给出了切换系统随参数变化下的最大李雅普诺夫指数图及相应的分岔图,得到了切换系统在不同参数下呈现出周期振荡,概周期振荡和混沌振荡相互交替出现的复杂动力学行为并分析了其振荡机理.给出了切换系统通过倍周期分岔,鞍结分岔以及环面分岔到达混沌的不同动力学演化过程.     

一个跃变电路切换系统的振荡行为及分岔机理分析

本文研究两个非线性电路系统通过开关组成的时间切换系统的复杂振荡行为及其产生机理.利用开环运算放大器放大倍数为极大值的特性,即运算放大器总是处于正的或负的饱和状态,当输入电压从负过零变正时,输出电压从正饱和状态跃变为负饱和状态,本文选择子电路系统中的非线性部分为跃变函数.首先对两个子系统进行了稳定性分析,给出了不同参数条件下的振荡行为,然后在子系统单个参数在一定范围内变化,而其他参数保持不变的情况下,研究了切换系统的复杂振荡特征,并分析了其产生机理.由于子系统方程的非光滑性和切换带来的整个系统的非光滑性,使得整个系统的周期振荡轨迹有四个切换点,随着参数的变化,周期振荡轨线与非光滑分界面发生擦边分岔,导致周期振荡分裂成两个对称的周期振荡.并且研究了切换点位置改变对整个系统周期振荡行为的影响以及切换点处的分岔机理.     

周期切换下Chen系统的振荡行为与非光滑分岔分析

研究了不同参数Chen系统之间进行周期切换时的分岔和混沌行为.基于平衡态分析,考虑Chen系统在不同稳态解时通过周期切换连接生成的复合系统的分岔特性,得到系统的不同周期振荡行为.在演化过程中,由于切换导致的非光滑性,复合系统不仅仅表现为两子系统动力特性的简单连接,而且会产生各种分岔,导致诸如混沌等复杂振荡行为.通过Poincaré映射方法,讨论了如何求周期切换系统的不动点和Floquet特征乘子.基于Floquet理论,判定系统的周期解是渐近稳定的.同时得到,随着参数变化,系统既可以由倍周期分岔序列进入混沌,也可以由周期解经过鞍结分岔直接到达混沌.研究结果揭示了周期切换系统的非光滑分岔机理.     

非对称型簇发振荡吸引子结构及其机理分析

旨在揭示频域不同尺度耦合时非对称动力系统簇发振荡的特点及其分岔机理,并进一步揭示快子系统多平衡点共存导致的不同簇发模式及其产生原因.以经典的蔡氏振子为例,通过引入非对称控制项及周期变化的电流源,选取适当参数,构建存在频域两尺度耦合的非对称动力系统模型.当周期激励频率远小于系统的固有频率时,将整个周期激励项视为慢变参数,得到随慢变参数变化的快子系统平衡曲线及其不同的分岔点以及分岔行为.重点分析了三种不同周期激励幅值下典型的非对称簇发振荡及吸引子结构,揭示其相应的产生机理.指出外激励幅值的变化不仅会引起不同稳定平衡点吸引域的变化,也会使得慢变量穿越不同分岔点的时间间隔发生变化,导致系统产生不同形式的簇发振荡.     

分段Filippov系统的簇发振荡及擦边运动机理

本文旨在揭示非光滑Filippov系统中由频域上不同尺度耦合导致的簇发振荡行为及其产生机理.以经典的周期激励Duffing振子为例,通过引入对状态变量的分段控制及适当选取参数,使得激励频率与系统固有频率之间存在量级差距,建立了频域两尺度耦合的Filippov系统.当激励频率远小于系统的固有频率时,可以将整个激励项视为慢变参数或慢变子系统,从而得到广义自治快子系统.分析了由非光滑分界面划分的不同区域中各快子系统的平衡点及其分岔特性随慢变参数变化的演化过程.考察了两种典型参数条件下系统的振荡行为及其动力学特性,指出参数变化不仅会引起其相应子系统平衡曲线及其分岔特性的改变,也会导致不同模式的簇发振荡.同时,轨迹穿越非光滑分界面时会产生不同的动力学行为,特别是在一定参数条件下,由于运动轨迹受不同子系统的交替控制,存在着擦边运动现象,从而导致特殊形式的非光滑簇发振荡.基于转换相图及各区域中快子系统的平衡曲线及其分岔特性,揭示了非光滑分界面对系统簇发振荡的影响规律及不同簇发振荡的分岔机理.     

耦合电路中的复杂振荡行为分析

讨论了两个非线性电路适当连接后的耦合系统随耦合强度变化的演化过程.给出了两子系统各自的分岔行为及通向混沌的过程,指出原子系统均为周期运动时,耦合系统依然会由倍周期分岔进入混沌,同时在混沌区域中存在有周期急剧增加及周期增加分岔等现象.而当周期运动和混沌振荡相互作用时,在弱耦合条件下,受混沌子系统的影响,原周期子系统会在其原先的轨道邻域内作微幅振荡,其振荡幅值随耦合强度的增加而增大,混沌的特征越加明显,相反,周期子系统不仅可以导致混沌子系统的失稳,也会引起混沌吸引子结构的变化. 关键词： 非线性电路 耦合强度 分岔 混沌     

Solution-processed high-k thin films as a resistive switching for ReRAM applications

Resistive switching characteristics of solution-processed high-k thin films (HfO_x and TaO_x) were investigated for ReRAM applications. The thickness of solution-processed high-k thin films can be easily controlled by simple spin coating. We optimized the critical thickness of solution-processed HfO_x and TaO_x thin films, for reliable ReRAM operations. A similar bipolar resistive switching behavior was observed from both solution-processed and sputter-processed HfO_x films. Furthermore, it was found that the solution-processed HfO_x and TaO_x films have a uniform resistive switching characteristic. The dominant conduction of these solution-processed films is described by Ohmic conduction in the low-resistance state. On the other hand, Ohmic conduction at low voltage and Poole–Frenkel emission at high voltage dominate in the high-resistance state. It was verified that the solution-processed HfO_x and TaO_x films have superior endurance and retention characteristics. Therefore, ReRAM devices based on solution-processed high-k materials are expected to be a promising candidate, for usage of resistive memory in glass substrate or flexible substrate based electronic devices.     

Cr^4＋：YAG的可饱和吸收特性与被动Q开关性能研究

运用速率方程计算了Ｃｒ＾４＋：ＹＡＧ晶体的可饱和吸收特性参数，包括初始吸收系数，饱和吸收系数，饱和光强和损耗调制度，用Ｃｒ＾４＋：ＹＡＧ对脉冲和连续Ｎｄ：ＹＡＧ激光器进行了被动调Ｑ，在脉冲Ｎｄ：ＹＡＧ激光器上得到了８ｎｓ的调Ｑ激光脉冲，在连续Ｎｄ：ＹＡＧ激光器的调Ｑ中得到了间隔和幅度抖动小于５％的输出脉冲充列。     

Coexistence of filamentary and homogeneous resistive switching in graded WOx thin films

Reversible clockwise and counter‐clockwise resistive switching in a Pt/graded WO_x /W stack is reported. Two stable switching modes with opposite switching polarity and different electrical characteristics are found to coexist in the same memory cell. Clockwise switching shows filamentary characteristics that lead to relatively faster switching with excellent retention at high temperature. Counter‐clockwise switching exhibits homogeneous conduction with slower switching and moderate retention. The field‐induced switching reversal might be due to inhomogeneous expansion of W during thermal oxidation. Our results provide a clue to modulate the switching type in Pt/WO_x /W memory cells. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

切换系统Lyapunov指数的算法及应用

Lyapunov指数是判定系统非线性行为的重要工具,然而目前的大多算法并不适用于切换系统.在传统Jacobi法的基础上,提出了一种新算法,可以直接计算得到n维切换系统的n个Lyapunov指数.首先,根据切换面处相邻轨线的动态变化规律,从相空间几何推导出切换面处轨线变化的Jacobi矩阵;然后,对该矩阵进行QR分解,从而利用R的对角线元素实现Lyapunov指数的切换补偿;最后,将新算法应用到平面双螺旋混沌系统、Glass网络和航天器供电系统三个实例中,并将计算结果与Poincaré映射方法的计算结果进行比较,对新算法的有效性进行验证.     

光交换的原理与实现

本文详细介绍了空分、时分、波分以及各种复合形式光交换的概念和所需关键器件的原理,给出了在目前技术条件下各种光交换单元的实现方案,并比较了它们的难易程度和优缺点.     

GaAs被动调Q兼输出耦合Nd∶YVO4激光特性研究

利用可饱和吸收半导体GaAs作为被动调Q元件和FP输出耦合镜,实现了半导体激光器(LD)抽运Nd:YVO4激光调Q运转,获得脉宽度为47ns,重复频率为1183kHz,平均功率为430mW,光束质量为M2=113的TEM00激光基横模输出,调Q抽运阈值为1700mW.并数值求解了含有GaAs被动调Q兼输出耦合的速率方程,分析了GaAs被动调Q机理以及脉宽宽度、重复频率、平均功率随抽运速率、腔长的变化关系,理论与实验结果相一致.为多功能综合型微型调Q固体激光器提供了简单有效的方法. 关键词： 被动调Q 输出耦合 GaAs     

Impact of magnetic surface anisotropy on the precessional switching of magnetization in Pt-alloy nanofilms

Precessional switching of magnetization in CoPt and FePt nanofilms is investigated by solving the Landau–Lifshitz–Gilbert (LLG) equation analytically and numerically. Switching in these films occurs only above a critical value of the magnetic field, and it further depends on the magnetocrystalline anisotropy and saturation magnetization of the film. The presence of magnetic surface anisotropy in these films reduces the switching time significantly. Also, the switching time in the case of Pt-alloys of Co and Fe is low compared to that in the case of pure Co and Fe films.     

Nanoscale imaging of ferroelectric domain and resistance switching in hybrid improper ferroelectric Ca3Ti2O7 thin films

Hybrid improper ferroelectrics have their electric polarization generated by two or more combined non-ferroelectric structural distortions such as the rotation and tilting of Ti-O octahedral in Ca₃Ti₂O₇ (CTO) family. In this work, we prepared different thickness CTO thin films on Pt substrates by pulsed laser deposition, and investigated their ferroelectric polarization reversal and the current transport properties by using the piezoresponse force microscopy and conducting atomic force microscopy, respectively. It is found that the CTO films exhibit clear ferroelectric domain switching and ferroelectric resistance switching behaviors, and the maximum resistive ratios of CTO film reaches ∼1750. These results demonstrate that hybrid improper ferroelectrics CTO films are promising materials for being employed in non-volatile memory and logic devices.     

Dynamical behaviors of a system with switches between the Rssler oscillator and Chua circuits

The behaviors of a system that alternates between the R¨ossler oscillator and Chua＇s circuit is investigated to explore the influence of the switches on the dynamical evolution.Switches related to the state variables are introduced,upon which a typical switching dynamical model is established.Bifurcation sets of the subsystems are derived via analysis of the related equilibrium points,which divide the parameters into several regions corresponding to different types of attractors.The dynamics behave typically in period orbits with the variation of the parameters.The focus/cycle periodic switching phenomenon is explored in detail to present the mechanism of the movement.The period-doubling bifurcation to chaos can be observed via the doubling increase of the turning points related to the switches.Furthermore,period-decreasing sequences have been obtained,which can be explained by the variation of the eigenvalues associated with the equilibrium points of the subsystems.     

Method of state code matrixes in the realization of optical switching using Perfect Shuffle

Based on the Left Perfect Shuffle (LPS) optical communication network constructed by cascade multi-stage LPS interconnection, using Looping algorithm, any arbitrary sequence of the input signals can be realized. However, instead of obtaining the simultaneous state codes of the same level node switches through mathematical analytical expressions directly, only routing tags of each channel can be obtained through mathematical analytical expressions so as to draw out topological chart of the network to obtain the state codes implied in the chart. Thus, the states of the switches cannot be directly programmed and controlled by computer in practical application. In this paper, based on the Looping algorithm, a method of stage code matrixes is presented to resolve this problem. By using the method, the simultaneous state codes of the same level’s four node switches can be directly obtained, which is convenient for the computer to provide controlled signals needed to finish the permutation for each node switch. The method of stage code matrixes provides further theoretical basis for the realization of optical switching by integration of Perfect Shuffle and high-speed optical switches.