Wide-band active variable tuning circuits

Active variable tuning circuits having a constant bandwidth or a constant Q value are described. Their resonant frequency can be varied continuously over a considerable range maintaining high performance. A generalised immittance convertor (GIC) is used as variable reactance and a new compensation technique using negative capacitance is proposed. The validity of the theory is confirmed by experiments employing ganged variable resistances as variable elements in the tuning circuits. The variable resistances are replaced by periodically switched resistances to obtain circuits which can change their resonance frequency linearly with voltage and are suited for integrated circuits. As a practical application, low frequency spectrum analysers are described.     

Design of arbitrary-phase variable digital filters using SVD-based vector-array decomposition

This paper proposes a straightforward method for designing variable digital filters with arbitrary variable magnitude as well as arbitrary fixed-phase or variable fractional delay (VFD) responses. The basic idea is to avoid the complicated direct design of one-dimensional (1-D) variable digital filters by decomposing the original variable filter design problem into easier subproblems that only require constant 1-D filter designs and multidimensional polynomial approximations. Through constant 1-D filter designs and multidimensional polynomial fits, we can easily obtain a variable digital filter satisfying the given variable design specifications. To decompose the original variable filter design into constant 1-D filter designs and multidimensional polynomial fits, a new multidimensional complex array decomposition called vector array decomposition (VAD) is proposed, which is based on two new theorems using the singular value decomposition (SVD). Once the VAD is obtained, the subproblems can be easily solved. Furthermore, we show that the VAD can also be generalized to the weighted least squares (WLS) case (WLS-VAD) for the WLS variable filter design. Three design examples are given to illustrate that the WLS-VAD and VAD-based techniques are considerably efficient for designing variable digital filters with arbitrary variable magnitude and arbitrary fixed-phase or VFD responses.     

关于变频液压调速系统的发展及应用综述

分析了传统的节流调速液压回路的不足之处，并介绍了变频液压技术的特点，指出了变频液压动力系统是一种从源头考虑功率匹配的全局型节能动力系统，它具有节能效果好、可简化液压回路、调速范围大、噪声小等优点。综述了国内外变频液压技术的发展过程、应用领域及研究现状。讨论了变频液压存在的问题，包括低速稳定性，响应的快速性．启动或换向时的平稳性，调速精度和效率等，并针对这些问题提出了多种不同的对策，最后对变频液压的发展作了展望。     

Digital Speech Interpolation for Variable Rate Coders with Application to Subband Coding

A theoretical method of evaluating degradations of variable rate coders in a multichannel digital speech interpolation (DSI) system is developed. Each of the coder outputs has a variable rate based on the algorithm. The DSI system multiplexes the outputs of these variable rate coders into a fixed bit rate channel. During periods of high activity all active users are served, but at a reduced rate depending on the demand. The degradation due to high activity is shared by all active users. This system avoids speech clipping and "freeze-out" distortion. Theoretical expressions of the system overload probability and the probability of degradation to a particular user in the DSI system are derived. Two types of variable rate coders, namely, a constant quality subband coder and a constant noise subband coder, are chosen and used as examples. Comparisons of the degradations are made between the theoretical results and computer simulated results for the two types of variable rate coders, and close agreement is observed. The theory is applicable to other variable rate coding algorithms as well. In this study, all of the simulations are made at 40 percent speech activity and the average rate of the variable rate coders is close to 16 kbits/s. Objective quality measures indicate that in a system with a trunk size larger than 40, the variable rate coder DSI system can achieve a 2:1 compression with a degradation of less than 1 dB compared to non-DSI variable rate coders. This corresponds to a total gain of 8:1 when compared to 64 kbit/s PCM.     

An Investigation of a Feedbaclk Control System for Stabilization of Microwave Radiometers

A method of stabilizing receivers for radio telescopes is discussed and shown to be capable of substantially reducing sensitivity to gain fluctuations. The system employs a variable noise source as a controlled feedback element. Such a system does not require long warm up times since the output is dependent only upon the stability of the variable noise source and reaches stabilization very rapidly. Investigations were made of a number of variable noise sources for use in the system, includlng: gas discharge tubes with variable attenuators, crystal diodes, and gas discharge tubes with variable duty cycles. Several crystal diodes were measured and the noise output was found to be linear with current for temperatures up to approximately 5000/spl deg/K. A variable noise source using a gas discharge tube with variable duty cycles to adjust the average temperature of the comparison termination of the radiometer is also discussed. Results are given for an experimental X-band system using a crystal diode as a variable noise source. For this system, a reduction of gain by 5 db had no measurable effect on the accuracy of measurement.     

可变温红外探测器中测杜瓦设计

介绍了一种中测变温杜瓦装置(简称变温杜瓦),可实现多个温度条件下(60～300 K)连续测试芯片性能.与传统的中测液氮杜瓦相比,变温杜瓦体积较小,可与制冷机耦合,从而实现多个温度可调.另外,将变温杜瓦的框架部件设计为可拆卸结构,既可以兼容多种规格的芯片,又提高了芯片性能的封装效率.通过试验测试,变温杜瓦组件芯片衬底区域...     

时变质量梁系统的振动主动控制研究

为了保证机械臂运动的高精度、准定位,采用主动控制技术降低结构的干扰振动是一项迫切而紧急的任务。该文以含变质量构件的弹性梁系统为对象,开展变质量弹性结构的振动特性研究和振动主动控制研究。使用模态叠加法推导了粘贴有压电片的变质量-柔性梁组合结构的控制方程,通过仿真获得变质量弹性梁系统的振动特性和运动规律。然后设计反馈控制器对质量增大系统和质量减小系统进行了振动主动控制,并采用时频分析技术分析了控制效果。仿真结果表明,变化的质量在引起系统振动频率改变的同时,还引起了一个附加的阻尼。在变质量时变系统的共振频率区间,通过反馈控制可有效抑制结构的振动。     

A New Monolithic Variable Capacitor

A method of realizing monolithic variable linear circuit elements ispresented. The method exploits monolithic variable gain amplifiers tomodify the values of passive integrated devices. The technique describedherein realizes floating true two-terminal variable elements. A theoreticalanalysis of a variable capacitance cell is performed as a prelude to apractical design producing capacitances in the range of 4 pF to 30 pF. Theresults of theoretical analyses are compared to SPICE [1] simulations of thesubject cell, prototype circuit results are presented, and performancelimitations are discussed.     

Loss minimization in scalar-controlled induction motor drives withsearch controllers

Loss minimization in scalar-controlled induction motor drives (IMD) with search controllers (SC) is investigated. The problems arising when the input power is used as the controlled variable are described. It is proved that better results are achieved if the stator current is used as the controlled variable     

一种两阶段变量选择的LIBS定量分析方法

使用机器学习方法结合激光诱导击穿光谱(Laser Induced Breakdown Spectroscopy,LIBS)进行定量分析,变量选择的结果直接影响最终的定标模型.现有的变量选择方法多存在需要先验知识、计算量庞大等问题,因此提出一种两阶段变量选择方法.第一阶段为排序阶段,以皮尔逊相关系数r为排序准则快速排除与...     

Low-Complexity Design of Variable Bandedge Linear Phase FIR Filters With Sharp Transition Band

This paper presents a very low-complexity design of variable bandedge linear phase finite-impulse-response (FIR) filters with fixed sharp transition width. The idea is to first decompose the input signal into several channels in the frequency domain. The channel(s) involved with the transition band of the variable filter due to the variation of the bandedge is (are) shaped to produce the required transition band, and then summed up with the channels involved with the passband of the variable filter to produce the required frequency response. The proposed variable filter has extremely low complexity when the transition band is sharp, if compared with other techniques such as the Farrow structure. It is possible that the computational complexity of the variable filter is even lower than that of a corresponding fixed filter with the same transition width and ripple specifications implemented in its direct form.      

A new switching surface sliding-mode speed control for inductionmotor drive systems

In this paper, a sliding-mode speed controller based on a new switching surface is proposed for induction motor systems. With this variable structure control switching surface, the exponential stability is guaranteed for the speed servo control and insensitivity to uncertainties and disturbances are obtained as well. Moreover, an adaptive variable structure speed control is studied to relax the need for the bound of disturbance in variable structure control. The insensitivity or robustness of the proposed method for general speed servo systems is maintained, and the dynamic performances are improved as well. Finally, the validity of proposed scheme is demonstrated by computer simulations and experimentations     

简述变压变频电源期间核查的方法

期间核查也称为运行检查或中间核查.测量设备在两次校准或检定之间的时间间隔内,多次使用适当技术校核方法进行检查,以确保测量设备在"服役"期间一直维持良好状态的活动.变压变频电源作为实验室的重要仪器,其输出数据的准确性直接关乎到后续受试设备的各项工作指标,所以需要对变压变频电源进行期间核查以确保其有精确的输出.     

非定态路径测试问题的分析与一种转换算法

测试数据生成中使用静态分析法的主要问题之一是难以处理程序变量的不确定性.本文对软件测试数据生成中的变量"不确定"问题进行了分析,认为该问题的实质是程序中变量本身的符号不确定性和程序的动态性,根据这个思路提出非定态路径、变符号变量、程序状态变量等概念,并将问题进行了形式化的描述,证明了非定态路径约束解空间可进一步划分为多个子空间.在此结论的基础上,本文给出了一个将非定态路径测试转换为定态路径测试的算法,对非定态路径测试问题的理论分析和解决途径进行了有益的尝试.     

高压变频器配套用移相整流变压器

高压变频调速技术作为通用节能技术加以重点推广，多重化技术是目前高压变频器的一项重要技术，多绕组移相整流变压器是实现该项技术的一个不可缺少的元件，通过移相可以消除整流、逆变、变频等一系列变流过程中所产生的谐波对电网的污染。     

Determinants of Corporate R&D Investment: An Empirical Study Comparing Korea's IT Industry with Its Non‐IT Industry

In our study, we extracted the market, finance, and government factors determining R&D investment of individual firms in the IT industry in Korea. We collected the financial data of 515 individual firms belonging to IT and non‐IT industries between 1980 and 1999 from the Korea Investors Service's database and investigated the empirical relationship between the factors using an ordinary regression model, a fixed effects model, and a random effects model. The main findings of our study are as follows: i) The Herfindahl Index variable representing the degree of market concentration is statistically insignificant in explaining R&D expenditures in the IT manufacturing industry. ii) Assets, which is used as a proxy variable for firm size, have a positive and statistically significant coefficient. These two results suggest that the Schumpeterian Hypothesis may be only partially applied to the IT manufacturing industry in Korea. iii) The dividend variable has a negative value and is statistically significant, indicating that a tendency of high dividends can restrict the internal cash flow for R&D investment. iv) The sales variable representing growth potential shows a positive coefficient. v) The subsidy as a proxy variable for governmental R&D promotion policies is positively correlated with R&D expenditure. This suggests that government policy has played a significant role in promoting R&D activities of IT firms in Korea since 1980. vi) Using a dummy variable, we verified that firms reduced their R&D investments to secure sufficient liquidity under the restructuring pressure during Korea's 1998 and 1999 economic crisis.     

Dual Estimation of Fractional Variable Order Based on the Unscented Fractional Order Kalman Filter for Direct and Networked Measurements

The paper is devoted to variable order estimation process when measurements are obtained in two different ways: directly and by lossy network. Since the problem of fractional order estimation is highly nonlinear, dual estimation algorithm based on Unscented Fractional Order Kalman filter has been used. In dual estimation process, state variable and order estimation have been divided into two sub-processes. For estimation state variables and variable fractional order, the Fractional Kalman filter and the Unscented Fractional Kalman filter have been used, respectively. The order estimation algorithms were applied to numerical examples and to real fractional variable order inertial system realized as an analog circuit.     

复高斯变量的二次型的特征函数

在研究分集的相关文献中，复高斯变量是经常用来分析分集问题的，但由于计算较难而令人望而生畏。文中针对经常出现在文献中的循环复高斯变量，采用求矩函数的方法对它进行分析研究，给出了从简单的复高斯变量到n维联合复高斯变量的二次型特征函数，矩函数，最后采用求联合矩的方法，给出了相关循环复高斯变量的二阶矩。该联合矩可以用于研究移动通信中相关与非相关的分集技术，而且，该分析过程也可供研究者参考。     

Realization of 2-D Variable IIR Digital Filter Structures with a Small Amount of Calculations for Coefficient Update

This paper proposes 2-D variable IIR digital filter structures with a small amount of calculations for coefficient update. The proposed realization method uses the 2-D parallel allpass structure derived from the separable denominator 2-D filter as the prototype structure for 2-D variable digital filters. In order to reduce the amount of calculations, all the redundant first-order complex allpass sections are combined by modularization of the variable structure. Furthermore, we can realize a very compact variable structure with a minimal number of first-order complex allpass sections by combining complex allpass sections with their complex conjugate allpass sections. Comparison of the calculation loads of the variable structures is presented to demonstrate that the amount of calculations for coefficient update of the proposed variable structure is far less than that of the original and the modular variable structure.     

Variable neural networks for adaptive control of nonlinear systems

This paper is concerned with the adaptive control of continuous-time nonlinear dynamical systems using neural networks. A novel neural network architecture, referred to as a variable neural network, is proposed and shown to be useful in approximating the unknown nonlinearities of dynamical systems. In the variable neural networks, the number of basis functions can be either increased or decreased with time, according to specified design strategies, so that the network will not overfit or underfit the data set. Based on the Gaussian radial basis function (GRBF) variable neural network, an adaptive control scheme is presented. The location of the centers and the determination of the widths of the GRBFs in the variable neural network are analyzed to make a compromise between orthogonality and smoothness. The weight-adaptive laws developed using the Lyapunov synthesis approach guarantee the stability of the overall control scheme, even in the presence of modeling error(s). The tracking errors converge to the required accuracy through the adaptive control algorithm derived by combining the variable neural network and Lyapunov synthesis techniques. The operation of an adaptive control scheme using the variable neural network is demonstrated using two simulated examples