On the use of permanent symmetric scatterers for ship characterization

The symmetric scattering characterization method (SSCM) has been recently introduced for high-resolution characterization of certain targets under coherent conditions. SSCM is based on the Poincare/spl acute/ sphere representation, which supports a high-resolution decomposition of symmetric target scattering, as well as assessment and validation of the backscatter coherence. In this paper, the SSCM is investigated for ship characterization using Convair-580 polarimetric synthetic aperture radar (SAR) data. It is shown that the target Poincare/spl acute/ parameters permit identification of dominant scatterers with a significant symmetric scattering component. The polarization orientation angle of these quasi-symmetric scatterers is used to derive an estimate of the ship's pitch angle, under certain conditions. The effect of SAR system focus setting errors and Doppler centroid mistracking on the SSCM performance is investigated. It is shown that the SSCM is sensitive to the system focus setting and Doppler centroid shift. The first-order effects of these errors can be removed prior to the application of the SSCM method.     

On the zeros of discrete-time linear periodic systems

Discrete-time linear periodic single-input/single-output (SISO) systems having uniform relative degree are considered. A closed-form expression of the blocking input is derived and exploited to obtain a computationally advantageous characterization of the structural zeros. Indeed, it suffices to compute the eigenvalues of a suitably defined (n × n) matrix, wheren is the system order. It is shown that, in contrast to the general case studied in previous papers, the number of zeros of linear periodic SISO systems with uniform relative degree is always time invariant and equal to the difference between the system order and the relative degree. The new characterization is also used to provide a simple expression for the zeros of linear periodic systems described by input-output difference equations.This paper has been partially supported by MURST Project Model Identification, System Control, Signal Processing.     

A self-test and dynamics characterization circuit for MEMS electrostatic actuators

This paper presents a high-bandwidth capacitance estimation and driving circuit especially tailored for its use with MEMS electrostatic actuators. The circuit can be integrated as a part of a system comprising an electrostatic actuator to provide self-testing and failure prediction capabilities and also as a simple and low-cost actuator dynamics characterization system capable of measuring both periodic and non-periodic movements.     

周期序列DSSS系统抗CW干扰性能分析

在简要论述按传统的基于标准高斯近似(SGA)假设得到的DSSS系统抗单音连续波(CW)干扰性能分析结果的基础上,推导出CW干扰经周期序列DSSS系统相关解扩处理产生的符号判决变量中干扰分量的数学表达式,对周期序列DSSS系统抗CW干扰的实际性能进行了理论分析与仿真。结果表明,周期序列DSSS系统在CW干扰下符号判决变量中的干扰分量呈现固定电平或单频波动,并不近似于标准高斯分布,周期序列DSSS系统抗CW干扰的实际性能与基于SGA假设的分析结果完全不同,其误码性能不仅与干信比、干扰频偏和相位密切相关,还与具体的扩频序列有关。     

Minimum rate sampling and reconstruction of signals with arbitraryfrequency support

We examine the question of reconstruction of signals from periodic nonuniform samples. This involves discarding samples from a uniformly sampled signal in some periodic fashion. We give a characterization of the signals that can be reconstructed at exactly the minimum rate once a nonuniform sampling pattern has been fixed. We give an implicit characterization of the reconstruction system, and a design method by which the ideal reconstruction filters may be approximated. We demonstrate that for certain spectral supports the minimum rate can be approached or achieved using reconstruction schemes of much lower complexity than those arrived at by using spectral slicing, as in earlier work. Previous work on multiband signals have typically been those for which restrictive assumptions on the sizes and positions of the bands have been made, or where the minimum rate was approached asymptotically. We show that the class of multiband signals which can be reconstructed exactly is shown to be far larger than previously considered. When approaching the minimum rate, this freedom allows us, in certain cases to have a far less complex reconstruction system     

半导体激光器混沌相位共轭反馈控制方法

提出了半导体激光器混沌相位共轭反馈(PCF)控制方法,建立了相位共轭反馈控制条件下激光器电流激发混沌的物理模型,发现其混沌控制物理机制是相位共轭反馈影响改变了激光器非线性增益和线宽增强因子特性,控制了系统的动力学行为及频率特性,其影响程度与反馈系数、延迟时间和光线宽增强因子等有关。数值模拟结果表明,在不同强度的光反馈下,通过调节相位共轭反馈光的延迟时间可以控制混沌激光到周期态、双周期态、多周期态等;发现相位共轭反馈控制特点是反馈光场和输出激光处于相干增强状态去实现混沌控制,且能控制实现激光器功率增强的周期脉冲输出。     

引进产品贮存可靠性试验评价方法探讨

提出了一种基于性能退化的贮存加速试验和元器件贮存寿命特征检测分析相结合的方法来进行引进产品电子部件贮存可靠性试验评价研究,并介绍了贮存加速退化试验和寿命特征检测的有关方法。     

Efficient Finite-Difference Time-Domain Modeling of Driven Periodic Structures and Related Microwave Circuit Applications

The sine–cosine method for the finite-difference time-domain-based dispersion analysis of periodic structures is extended to incorporate the presence of nonperiodic wideband sources. A new formulation of this method is presented to clearly demonstrate that it can be employed for the characterization of periodic structures over a broad bandwidth. Moreover, its coupling with the array-scanning technique enables the incorporation of nonperiodic sources, thus enabling the fast characterization of driven periodic structures in the time domain via a small number of low-cost simulations. The convergence, accuracy, and efficiency of the proposed method is demonstrated with its application to the analysis of a negative-refractive-index transmission-line “perfect lens” and the successful comparison of simulated with experimental results. Finally, a modified version of this method is proposed for the accelerated simulation of microwave circuit geometries printed on periodic substrates.      

Decomposition of posterior alpha rhythm

The classical posterior alpha rhythm has been decomposed into regular and irregular components using orthogonal transformation. A periodicity generator is considered, which has three characteristic control parameters: the periodicity, the amplitudes or scaling factors and the pattern associated with successive periodic segments. The regular component is shown to be equivalent to an oscillator or periodicity generator whose parameters are dynamically varying and, thus, producing both amplitude- and frequency-modulation. The irregular component is devoid of such modulating behavior. Electroencephalogram signals from normal, maniac and epileptic subjects are studied. Through analytic signal-based analysis, it is shown that for the regular component, healthy brain possesses universal scaling behavior, whereas heterogeneous scaling or absence of universality is observed for the diseased brain.     

Fundamentals of Fast Simulation Algorithms for RF Circuits

Designers of RF circuits such as power amplifiers, mixers, and filters make extensive use of simulation tools which perform periodic steady-state analysis and its extensions, but until the mid 1990s, the computational costs of these simulation tools restricted designers from simulating the behavior of complete RF subsystems. The introduction of fast matrix-implicit iterative algorithms completely changed this situation, and extensions of these fast methods are providing tools which can perform periodic, quasi-periodic, and periodic noise analysis of circuits with thousands of devices. Even though there are a number of research groups continuing to develop extensions of matrix-implicit methods, there is still no compact characterization which introduces the novice researcher to the fundamental issues. In this paper, we examine the basic periodic steady-state problem and provide both examples and linear algebra abstractions to demonstrate connections between seemingly dissimilar methods and to try to provide a more general framework for fast methods than the standard time-versus-frequency domain characterization of finite-difference, basis-collocation, and shooting methods     

Periodic replacement when minimal repair costs depend on the age and the number of minimal repair for a multi-unit system

A policy of periodic replacement with minimal repair at failure is considered for the multi-unit system which have the specific multivariate distribution. Under such a policy the system is replaced at multiples of some period T while minimal repair is performed at any intervening component failures. The cost of a minimal repair to the component is assumed to be a function of its age and the number of minimal repair. A simple expression is derived for the expected minimal repair cost in an interval in terms of the cost function and the failure rate of the component. Necessary and sufficient conditions for the existence of an optimal replacement interval are exhibited.     

Periodic replacement when minimal repair costs depend on the age and the number of minimal repairs for a multi-unit system

A policy of periodic replacement with minimal repair at failure is considered for a multi-unit system which has a specific multivariate distribution. Under such a policy the system is replaced at multiples of some period T while minimal repair is performed for any intervening component failure. The cost of a minimal repair to the component is assumed to be a function of its age and the number of minimal repairs. A simple expression is derived for the expected minimal repair cost in an interval in terms of the cost function and the failure rate of the component. The necessary and sufficient conditions for the existence of an optimal replacement interval are found.     

System for deep venous thrombosis detection using objective compression measures

A system for objective vessel compression assessment for deep venous thrombosis characterization using ultrasound image data and a sensorized ultrasound probe is presented. Two new objective measures calculated from applied force and transverse vessel area are also presented and used to describe vessel compressibility. A modified star-Kalman algorithm is used for feature detection in acquired ultrasound images, and objective measures of vessel compressibility are calculated from the detected features and acquired force and location data from the sensorized probe. A three-dimensional shape model of the examined vessel that includes compressibility measures mapped as colors to its surface is presented on the user interface, as well as a virtual representation of the image plane. The compressibility measures were validated using expert segmentation of healthy and diseased vessels and compared using paired t-tests, which showed a significant difference between healthy and diseased cases for both measures. 100% sensitivity and specificity were obtained for both measures. The system was implemented in real-time (16 Hz) and evaluated using a tissue phantom and on healthy human subjects. Sensitivity was 100% and 60%, while specificity was 97% for both measures when implemented. The initial results for the system and its components are promising.     

Analysis of Scheduled Latency Insensitive Systems with Periodic Clock Calculus

Originally the Latency Insensitive Protocols (LIP) were invented to make a system elastic to the interconnect latencies using handshaking signals such as ‘valid’ and ‘stall’. Such protocols require extra signals leading to area overhead and may affect throughput of the system. To optimize away some of these overheads, scheduled LIPs were proposed which replaced the complex handshake control blocks by a central scheduling scheme. One can view a scheduled LIP based design as a system where within each strongly connected component of the system, the modules and the relay stations are scheduled by activation signals. These activation signals can be thought of as infinite sequence of ‘1’s and ‘0’s. If such sequences are periodic, one can view them as periodic clocks. Given the advances in periodic clock calculus in the synchronous programming context, in this paper, we analyze the LIP scheduling problem within the framework of periodic clock calculus. Such analysis provides straight forward algorithms to compute the throughput of scheduled LIP based systems. Within this framework, we also propose a method to synthesize fractional synchronizers. Fractional synchronizers are used to equalize cycles with different throughputs. Our method can determine the numbers and the scheduling sequences of such fractional synchronizers using the periodic clock calculus. In addition, we provide a static estimation of the required fractional synchronizers based only on the system’s structure which is fast and accurate.     

Noise Tolerance Assessment and System Design Discussion of a Saturable-Absorption-Based All-Optical 2R Regenerator

This letter presents the cascadability assessment and the noise tolerance characterization of an all-optical 2R regenerator based on saturable absorption and nonlinear effects in fiber. The impact of optical signal-to-noise ratio on the 2R regenerator performance is shown, and a regenerator characterization technique that can be used for system design and engineering is discussed.     

Worst-case stability analysis of switching regulators using thestructured singular value

A method to assess the effect of component tolerances on the stability of closed-loop switching regulators is given. Use of μ, the structured singular value, is made which obviates the need for time-intensive Monte Carlo simulation runs and also guarantees the assessment of the worst-case condition of the system. Furthermore, through the use of newly developed software routines for μ, the effect of up to 100 uncertainties may be taken into account. The analysis procedure entails isolating component value uncertainties Δ from the nominal system M. Subsequent determination of μ for this Δ-M structure enables a robustness assessment to be made for the system under study. A procedure which considers uncertainties in inductor, capacitor, and resistance values is given which enables reduction of a switching regulator system to Δ-M form. An example is given of a regulator design for which an assessment is made of the allowed component tolerances which guarantees a lower limit of the phase margin     

Periodic Conductivity as a Mechanism for Cardiac Stimulation and Defibrillation

This study examines the distribution of the transmembrane potential in the periodic strand of cardiac muscle established by configurations of sources similar to those arising during extracellular stimulation and defibrillation, during intracellular stimulation, and during propagation of action potential. The closed-form solution indicates that during extracellular stimulation with large current and during defibrillation, the periodic component of the transmembrane potential is very important. We postulate that this periodic component causes the depolarization or defibrillation in cardiac muscle, which is different from the depolarization mechanism for a continuous fiber. On the other hand, during propagation and intracellular stimulation, the periodic component only slightly modifies the monotonic decrease of the transmembrane potential, which suggests that the mechanism of propagation in discrete structures may be similar to that of the continuous fiber.     

Potential distribution in three-dimensional periodic myocardium. I.Solution with two-scale asymptotic analysis

The use of two-scale asymptotic analysis allows development of a model of the steady-state potential distribution in three-dimensional cardiac muscle preserving the underlying cellular network. The myocardium is modeled as a periodic structure consisting of cylindrical cells embedded in extracellular fluid and connected by longitudinal and side junctions. The method is applicable to cardiac muscle of arbitrary extent since the periodicity of the tissue is dealt with analytically, and thus numerical computations require no more resources than a continuous volume conductor problem. The asymptotic analysis approach reveals that the potential in a periodic myocardium consists of two components. The large-scale component provides the baseline for the total solution and can be determined from the anisotropic monodomain model associated with the original periodic problem. The method provides the formula for calculating the conductivity of the equivalent monodomain model on the basis of cell geometry and conductivity distribution in the cardiac tissue. The small-scale component reflects the periodicity of the underlying structure and oscillates with periods determined by the dimensions of cardiac cells. The magnitude of these oscillations depends upon the gradient of the large-scale component. During stimulation with extracellular electrodes, the small-scale component determines both the shape and the magnitude of the transmembrane potential, while the influence of the large-scale component is negligible. Hence, the small-scale component merits closer attention in pacing and defibrillation studies, especially since the model based on two-scale asymptotic analysis provides an effective means of its computation.     

Calculation of steady-state response of linear system to periodic sampled signal

A Z transform theorem is derived which yields the steady-state component of the response of a linear time-invariant system to a periodic signal sampled at a rate which is a multiple of the signal frequency. Wider applications of the theorem are discussed.