Simulation of a Helicon plasma source using a multivariable fuzzymodel

This paper reports work on the development of an automatic control system for a Helicon plasma processing source. The lack of a definitive physical model for the plasma physics of the source and the power coupling mechanism to the plasma precludes the use of traditional control algorithms. This paper develops a fuzzy model that simulates the behavior of the plasma source using the process of genetic algorithms to identify and optimize the parameters of the fuzzy model. This type of model will eventually be used to test a fuzzy control system for the plasma source. In this work, an extensive set of experimental data was acquired where the magnetic field and input power to the plasma source were varied over a wide range while the electron number density was measured. From this learning dataset, the genetic algorithm derived the values of the parameters for the difference equation that describes the system. The fuzzy model so constructed was used to predict the behavior of the source from known input parameters. Comparing the predictions with experimental observations showed that the fuzzy model was generally able to predict the behavior of the plasma as its input parameters were varied with a precision of better than 10%     

Harmonic analysis of time-limited signals

The problem of the estimation of the harmonic content of a signal is studied. The study is limited to the class of causal signals which are the response of linear stable systems to pulse inputs. Two cases are examined: (i) the output of a system whose model has one real pole; (ii) the output of a system whose model has a complex conjugate pole pair. An analytical expression for the error that arises when using the finite Fourier transform is obtained. It is shown that the method required to deal with these two cases are sufficient to deal also with systems having many zeros and poles. The principal dependence of the error on the observation interval length is discussed, and also its dependence on other parameters, such as the ratio of the input pulse length to the observation interval length, and the position of the poles of the system model in the s-plane.     

基于模糊模型的混沌时间序列预测

对于复杂、病态、非线性动态系统，基于模糊集合的模糊模型，利用模糊推理规则描述动态系统的特性，是一种有效方法.讨论了利用模糊建模方法实现非线性系统的建模和预测.首先，利用在线模糊竞争学习方法划分输入变量的模糊输入空间，然后利用卡尔曼滤波算法估计模糊模型的参数.采用该方法对Mackey Glass混沌时间序列进行预测试验，结果表明利用本方法可以在线或者离线能对Mackey Glass混沌时间序列进行准确预测，证明了本方法的有效性. 关键词： 模糊竞争学习 混沌时间序列 卡尔曼滤波     

QKD and QDC via optical-wireless link for quantum mobile telephone network application

We propose a novel system of the simultaneous continuous variable quantum key distribution (QKD) and quantum dense coding (QDC) using a soliton pulse within the nonlinear micro-ring resonator devices. By using the appropriate soliton input power and nonlinear micro-ring parameters, the continuous signals are generated spreading over the spectrum. The polarized photons are formed by using the polarization control unit incorporating into the micro-ring system, which is allowed the different time slot entangled photon pair randomly formed. Results obtained have shown that the application of such a system for the simultaneous continuous variable quantum cryptography and dense coding within a single system is plausible, which is can be implemented within the mobile telephone hand set and networks.     

射频激励等离子体非线性效应的FDTD数值模拟

在考虑热运动、电子复合、扩散等效应后，建立电磁波与等离子体相互作用模型，验证了射频激励等离子体时产生的二次、多次谐波以及各个不同频段信号的调制现象，得到了不同激励功率、产生电子的电场阈值、电子能量等参数对电磁波频谱的影响，这对于射频激励等离子体的电路匹配、耦合器件以及等离子体天线传输、电磁兼容等设计很有帮助. 关键词： 射频 谐波 等离子体 非线性     

Input shaping and variable structure control for simultaneous precision positioning and vibration reduction of flexible spacecraft with saturation compensation

This paper treats the question of simultaneous robust attitude control and vibration suppression of orbiting spacecraft with flexible appendages. The spacecraft consists of a rigid body and two flexible appendages and the finite dimensional representation of the flexible spacecraft is assumed to be of arbitrary order. Robust nonlinear variable structure control (VSC) strategy integrated with input shaping technique is concerned for the pitch angle control and elastic vibration suppression under actuator saturation limit. More specially, the input shaper is implemented outside of the feedback loop, which is designed for the reference model and achieves the exact elimination of residual vibration; while for the feedback loop, the variable structure controller is designed to make the closed-loop system behave like the reference model with the input shaper in the presence of parametric uncertainty, external disturbances and actuator saturation. To prevent the presence of input saturation from destroying the system performance, a saturation compensator is designed as well for the variable structure attitude control system. For the synthesis of the attitude controller, only the pitch angel and its derivative are used. Simulation results are presented which show that in the closed loop, pitch angel control and elastic mode stabilization are accomplished in spite of uncertainty and external disturbance.     

FORCE FEEDBACK VERSUS ACCELERATION FEEDBACK IN ACTIVE VIBRATION ISOLATION

This paper compares the force feedback and acceleration feedback implementation of the sky-hook damper when it is used to isolate a flexible structure from a disturbance source. It is shown that the use of a force sensor produces always alternating poles and zeros in the open-loop transfer function between the force actuator and the force sensor, which guarantees the stability of the closed loop. On the contrary, the acceleration feedback produces alternating poles and zeros only when the flexible structure is stiff compared to the isolation system; this property is lost when the flexible modes of the sensitive payload interfere with the isolation system.     

Start-up phase plasma discharge design of a tokamak via control parameterization method

The tokamak start-up is a very important phase during the process to obtain a suitable equalizing plasma, and its governing model can be described as a set of nonlinear ordinary differential equations(ODEs). In this paper, we first estimate the parameters in the original model and set up an accurate model to express how the variables change during the start-up phase, especially how the plasma current changes with respect to time and the loop voltage. Then, we apply the control parameterization method to obtain an approximate optimal parameters selection problem for the loop voltage design to achieve a desired plasma current target. Computational optimal control techniques such as the variational method and the costate method are employed to solve the problem, respectively. Finally, numerical simulations are performed and the results obtained via different methods are compared. Our numerical parameterization method and optimization procedure turn out to be effective.     

Design of a negative group delay filter via reservoir computing approach: Real-time prediction of chaotic signals

An optimal arbitrary order filter with negative group delay is proposed for a real-time prediction of complex band-limited signals. The filter consists of a set of second-order linear dissipative oscillators and is determined by a rational transfer function with fixed poles and optimized zeros. The filter design and optimization algorithm is based on a reservoir computing approach. The predictive properties of the filter are demonstrated numerically for two chaotic model systems — the finite-dimensional Rössler system and the infinite-dimensional Mackey-Glass system, as well as for the real biological signal of the fingertip photoplethysmogram.     

Cascades of two-pole-two-zero asymmetric resonators are good models of peripheral auditory function

A cascade of two-pole-two-zero filter stages is a good model of the auditory periphery in two distinct ways. First, in the form of the pole-zero filter cascade, it acts as an auditory filter model that provides an excellent fit to data on human detection of tones in masking noise, with fewer fitting parameters than previously reported filter models such as the roex and gammachirp models. Second, when extended to the form of the cascade of asymmetric resonators with fast-acting compression, it serves as an efficient front-end filterbank for machine-hearing applications, including dynamic nonlinear effects such as fast wide-dynamic-range compression. In their underlying linear approximations, these filters are described by their poles and zeros, that is, by rational transfer functions, which makes them simple to implement in analog or digital domains. Other advantages in these models derive from the close connection of the filter-cascade architecture to wave propagation in the cochlea. These models also reflect the automatic-gain-control function of the auditory system and can maintain approximately constant impulse-response zero-crossing times as the level-dependent parameters change.     

基于expectation maximization算法的Mamdani-Larsen模糊系统及其在时间序列预测中的应用

Epanechnikov混合模型和Mamdani-Larsen模糊系统之间的对应关系被建立:任何一个Epanechnikov混合模型都唯一对应着一个Mamdani-Larsen模糊系统,在一定条件下,Epanechnikov混合模型的条件均值和Mamdani-Larsen模糊模型的输出是等价的.一个设计模糊系统的新方法被提出,即利用expectation maximization算法设计模糊系统.将设计的模糊系统应用于时间序列预测,仿真结果表明：利用EM算法设计的模糊系统比其他模糊系统精度更高,抗噪性更强 关键词： expectation maximization(EM)算法 Mamdani-Larsen模糊系统 Epanechnikov混合模型 混沌时间序列     

Prescribing Zeros and Poles on a Compact Riemann Surface for a Gravitationally Coupled Abelian Gauge Field Theory

In this paper, we study the existence of prescribed cosmic strings and antistrings realized as the static solutions with prescribed zeros and poles of the Einstein equations coupled with the classical sigma model and an Abelian gauge field over a compact Riemann surface. We show that the equations of motion are equivalent to a system of self-dual equations and the presence of string defects are necessary and sufficient for gravitation which implies the equivalence of topology and geometry in the model. More precisely, we prove that the absence of a solution with zeros and poles implies that the underlying Riemann surface S must be a flat 2-torus and that the existence of a solution with zeros and poles implies that S must be a 2-sphere. Furthermore, we develop an existence theory for solutions with prescribed zeros and poles. We also obtain some nonexistence results.The authors research was supported in part by NSF grants DMS–9972300 and DMS–9729992 through the Institute for Advanced Study.     

Vision-Guided Flame Control Using Fuzzy Logic and Neural Networks

This paper presents an application of fuzzy and neural network techniques to a vision-guided closed loop control for stationary luminous flames. The image processing technique is used to analyze and identify the process states. Fuzzy control strategy avoids the difficulty in establishing a mathematical model for an ill-defined process. Expert knowledge and training patterns can be incorporated into fuzzy rules, which are represented in the form of neurons. The use of a neural network makes it easy to increase the number of control parameters and provides the system the possibility to adjust its performance automatically.     

On the location of poles of Ruelle's zeta function

We discuss examples of one-dimensional lattice spin systems of classical statistical mechanics whose generalized zeta function has all its poles and zeros on the real axis. The close relation between certain hyperbolic dynamical systems and these spin systems lets one expect that this is also true for some of the dynamical systems. In fact, we have found several one-dimensional expansive systems, among them the Gauss map whose zeta functions have their zeros, respectively their poles, on the real axis. Such a behaviour is closely related to the spectral properties of the sytems transfer operator which in the cases considered is a positive nuclear operator in a Banach space of holomorphic functions. We formulate a general conjecture concerning the spectrum of this class of operators.     

Chua混沌系统的一种模糊控制器设计——LMI法

研究了Chua混沌系统的稳定控制问题.采用模糊动态模型逼近非线性混沌系统,将非线性混沌系统模糊化为局部线性模型.用Lyapunov稳定性理论设计出,确保模糊动态模型全局渐近稳定的控制器.再用线性矩阵不等式的凸优化方法求出模糊控制器的参数.仿真验证了方案的有效性.模糊控制器简单,规则少. 关键词： Chua混沌系统 模糊动态模型 线性矩阵不等式     

Engineering the nonlinear phase shift

We treat the nonlinear phase shift response in the weak perturbation limit as a linear digital filter that can be synthesized into the values of its poles and zeros and mapped onto an optical architecture. This procedure results in a significant enhancement in the nonlinear sensitivity with a response that is robust to frequency changes within the filter passband. A precompensation technique can be used to reduce distortions under strongly driven nonlinear operation to achieve a larger phase shift. We also show that nonlinear sensitivity improves with increasing filter group delay and can be increased within constant linear bandwidth by use of higher-order filters.     

Impulsive control for Takagi--Sugeno fuzzy model with time-delay and its application to chaotic system

A control approach where the fuzzy logic methodology is combined with impulsive control is developed for controlling some time-delay chaotic systems in this paper. We first introduce impulses into each subsystem with delay of the Takagi--Sugeno (TS) fuzzy IF--THEN rules and then present a unified TS impulsive fuzzy model with delay for chaos control. Based on the new model, a simple and unified set of conditions for controlling chaotic systems is derived by the Lyapunov--Razumikhin method, and a design procedure for estimating bounds on control matrices is also given. Several numerical examples are presented to illustrate the effectiveness of this method.     

Excitation of the half-frequency of the input signal in theresponse of an antenna immersed in a plasma

The nonlinear response of a cylindrical monopole antenna immersed in a steady-state collisionless magnetic-field-free plasma and driven by a single-frequency RF source is investigated. The thickness of the ion sheath surrounding the antenna is controlled by a DC bias applied to the latter. It is found that at frequencies of the driving signal close to twice the frequency of a sheath wave resonance, the 1/2-subharmonic is excited, provided that the input power level is sufficiently high. The dependence of this process on the sheath thickness and on the electron plasma density is studied in the vicinity of several sheath wave resonances. This nonlinear effect is interpreted as a parametric excitation due to the periodic modulation of the sheath thickness, and hence its capacitance, by the applied RF signal. A similar effect can be obtained by replacing the antenna-sheath-plasma structure in the measuring circuit by a variable capacitance diode. A numerical analysis of the differential equation describing the current waveform in a microwave network modeling the antenna-sheath-plasma system is presented. It confirms the fact that a periodically modulated capacitance embedded in a linear circuit is responsible for the observed excitation of the half-frequency of the input signal     

基于模糊树模型的混沌时间序列预测

应用模糊树模型,对混沌时间序列进行建模和预测.该方法可以根据建模数据在空间中的分布信息,基于二叉树结构自适应划分输入空间,得到模糊子空间,在与叶节点对应的子空间上建立线性函数作为模糊规则的后件,用隶属度函数将各分片线性函数光滑连接,最后得到一个精度比较高的非线性映射.通过对Mackey-Glass、Lorenz和Henon混沌时间序列的建模和预测研究,仿真结果表明,该方法具有建模精度高、运行速度快、泛化能力强、预测步数多、适用范围广等优点. 关键词： 模糊树模型 混沌时间序列 预测