Realization of a transfer function matrix by expanding it about a general point "a"

A technique for the realization of a transfer function matrix by its expansion about an arbitrary point "a" is proposed. The procedure does not involve any inversion to obtain the resulting quadruple [A, B, C, D].     

Automatic Contour Detection Using a "Fixed-Point Hachimura-Kuwahara Filter" for SPECT Attenuation Correction

Attenuation correction for single-photon emission computed tomography (SPECT) usually assumes a uniform attenuation distribution within the body surface contour. Previous methods to estimate this contour have used thresholding of a reconstructed section image. This method is often very sensitive to the selection of a threshold value, especially for nonuniform activity distributions within the body. We have proposed the "fixed-point Hachimura-Kuwahara filter" to extract contour primitives from SPECT images. The Hachimura-Kuwahara filter, which preserves edges but smoothes nonedge regions, is applied repeatedly to identify the invariant set-the fixed-point image-which is unchanged by this nonlinear, two-dimensional filtering operation. This image usually becomes a piecewise constant array. In order to detect the contour, the tracing algorithm based on the minimum distance connection criterion is applied to the extracted contour primitives. This procedure does not require choice of a threshold value in determining the contour. SPECT data from a water-filled elliptical phantom containing three sources was obtained and scattered projections were reconstructed. The automatic edge detection procedure was applied to the scattered window reconstruction, resulting in a reasonable outline of the phantom.     

基于what和where信息的目标检测方法

根据视觉系统两条通路理论,提出了一种基于what和where信息的目标检测方法.采用以环境为中心的where信息进行自顶向下的注意控制,指导what信息驱动的自底向上的注意.自顶向下的注意包括预注意和集中注意两个阶段,预注意依据where信息为特定目标出现与否提供先验,做出是否继续搜索的判定.集中注意的结果与what信息相结合,将注意指向目标最有可能出现的图像区域,并得到一系列样本显著区域.应用于多幅自然图像的实验结果证明了算法的有效性.     

A universal de-embedding procedure for the "on-wafer" GHz probing

A novel de-embedding procedure for "on-wafer" GHz probing is presented. The parasitic effects arising from the bond-pads are modeled generally by two-port networks. Thus, no equivalent circuit details are required. Even the transmission line effects occurring at extremely high frequencies can be taken into account in this model.<>     

A Simplified "Real Frequency" Technique Applied to Broad-Band Multistage Microwave Amplifiers

A computer-aided design (CAD) procedure, which is a new and simplified "real frequency" technique, is introduced for treating the broad-band matching of an arbitrary load to a complex generator. The method can be applied to the design of interstage equalizers for microwave amplifiers. It utilizes the measured data obtained from the generator and the load networks. Neither an a priori choice of an equalizer topology, nor an analytic form of the system transfer function, is assumed. The optimization process of the design procedure is carried out directly in terms of a physically realizable, unit normalized reflection coefficient which describes the equalizer atone. Based on the load-generator matching technique, a sequential procedure to design multistage microwave amplifiers is presented. An example is given for a three-stage, FET amplifier proceeding directly from the measured scattering parameters of the FET devices. The example is in three parts and illustrates the sequential method; that is, first a single-stage, then a two-stage, and finally the three-stage system is computed.     

Comments on "Non-iterative quality phase-gradient autofocus (QPGA) algorithm for spotlight SAR imagery"

For original paper see ibid., vol.36, no.5, pt.1, p.1531-9 (1998). The quality phase-gradient autofocus (QPGA) technique was proposed to speed up the estimation convergence of phase-gradient autofocus by selectively increasing the pool of quality synchronization sources instead of selecting the "brightest" pixels within the image. It is now found that the QPGA, with its inherent scatter "growing" concept and target-filtering procedure, is also able to focus in environments with stationary and moving targets.     

"环保"引领电视机技术新发展--浅谈我国电视机"环境标志"认证及发展

本文从一名检测技术人员的角度,首先,分析了电视机中国"环境认证"的标准以及要求,同时指出"低辐射彩电"并不等同于"环保电视";接着,针对目前电视机在中国"环境标志"认证的要求,说明详解了认证检测技术方法;最后,分析指出电视产业今后的环保技术研究方向.     

Matrix Methods for the Dynamic Range Optimization of Continuous-Time $G_{m}$- $C$ Filters

This paper presents a synthesis procedure for the optimization of the dynamic range of continuous-time fully differential $G_{m}$-$C$ filters. Such procedure builds up on a general extended state-space system representation which provides simple matrix algebra mechanisms to evaluate the noise and distortion performances of filters, as well as, the effect of amplitude and impedance scaling operations. Using these methods, an analytical technique for the dynamic range optimization of weakly nonlinear $G_{m}$- $C$ filters under power dissipation constraints is presented. The procedure is first explained for general filter structures and then illustrated with a simple biquadratic section.      

AN "E" Field Rod Antenna and Preamplifier for A.M. Field Strength Measurements

A vertical short rod antenna and preamplifier package has been developed for A.M. field strength measurements on special occasions. It is designed to interface directly with the auxiliary input of the Potomac Instruments Models FIM-21 and FIM-41 field strength meters. Some of its uses consist of noticeably greater accuracy in gathering data involved in the "talkdown" procedure, after Silliman, test and adjustment measurements during inclement weather and as a convenience in making aircraft and over-water measurements.     

Optimization of Passively Repetitively $Q$-Switched Three-Level Lasers

A generalized model of a passively repetitively $Q$-switched three-level laser is presented. The method for evaluation of the small-signal gain coefficient and the dissipative losses of a three-level laser is shown. To demonstrate the use of this optimization procedure, it was applied to a microchip laser generating 1.5- $mu$m radiation. The model may be expanded for a four-level laser by replacing the calculation of the small-signal gain coefficient.      

Comments on "A lower bound for the variation of a band-limited random process"

It is pointed out that the bound recently derived by Pyati and the bound of Papoulis can be obtained from the first two iterations through a procedure for developing ever tighter bounds. A bound that is tighter than Pyati's is derived from the third iteration through the procedure.     

建设独具特色的"计算机控制"精品课程

"计算机控制系统"课程是一门与国际先进大学相关课程接轨、适应航空航天和机器人等运动体控制的工程应用需求、适应本科生和研究生的专业基础教学要求的专业基础课程。该课程在内容上突出"快变系统精确建模与控制"、"模拟系统数字化实现"等,突出高速运动体的精确测量与控制技术。同时建设了一套实验体系,针对本科生、研究生的不同知识基础实行分层次、分类别组织实验的教学计划;授课同时撰写了多本"计算机控制系统"精品教材,分别由北航、高教和清华出版社出版,各版教材增加了工程应用例题和习题,为课程教学打下了基础。     

Printed S-Band 4 $times$ 4 Nolen Matrix for Multiple Beam Antenna Applications

A Nolen matrix design method is proposed as an asymptotic singular case of a recent Blass matrix design algorithm. The procedure is illustrated by a 4 $times$ 4 Nolen matrix, which design is centred at 2.2 GHz, with the amplitude and phase output excitation laws of a Butler matrix using 90 $^{circ}$ hybrids. Simulation and measurement results are presented in this paper.      

Media-intensive data communications in a "desk-area" network

The VuNet is a "desk-area" network where small switches are distributed throughout the work area, and multimedia devices usually found in the workstation are put on the network. This architecture has several advantages including distributed switching and the ability to share multimedia devices across a workgroup.<>     

"Bipolar-mode" transistors on a voltage-controlled scheme

A buried-gate vertical JFET (BVFET) operated under forward gate bias shows saturating or nonsaturating drain current characteristics simply by Changing the channel cross section area. BVFET with a proper channel cross section has similar characteristics to a "bipolar-mode" SIT (BSIT) or a depleted base transistor (DBT). A generalized picture is derived relating these forward-biased JFET's to the conventional bipolar transistor (BPT). Analysis of BVFET has proved that the operation of BSIT is completely the same as that of BPT with its base voltage controlled. The current saturation mechanism is discussed in detail in this paper.     

Control of a multijoint manipulator "Moray arm"

We introduce a multijoint manipulator that was named "Moray arm", which is a slider-integrating multijoint manipulator, where a powerful slider is installed at the base of the arm. The Moray arm emulates the motion of a Moray, thus, allowing it to easily enter a narrow space while avoiding obstacles. To elucidate the features of the Moray arm, we present new control methods named "Moray drive" and "two-degrees-of-freedom (2-DOF) Moray drive". The Moray drive control generates rotating motion of the joints in synchronization with linear motion of the slider while restricting the arm on the trajectory. The 2-DOF Moray drive control reduces the control problem of the hyper DOFs to the simple one of 2-DOFs: one of the control variables signifies the linear combination of the objective initial and final postures of the arm, while another expresses the amount of the pull-out-displacement when pulling the arm out of the housing. The properties of Moray arm controlled by Moray drive or 2-DOF Moray drive are described. Based on the 2-DOF Moray drive control, we also propose an obstacle avoidance scheme for the "Moray arm" to perform a pick-and-place task while avoiding the existing static obstacles in environment. The scheme is based on the posture space analysis and generates the obstacle collision-free trajectory in the posture space. From the simulation result, we conclude that the Moray arm controlled by the proposed schemes gives great possibility for the hyper-redundant manipulator to perform applications such as maintenance of nuclear reactors, collection of lumps of existing manganese under sea, and care of patients.     

Future Management Theory: A "Comparative" Evolution to a General Theory

Eleven existing management theory streams can be reduced to four concurrently and sequentially developing ones. Past and present evolutionary developments in management theory indicate that a future "general theory" probably can result from a "comparative" analysis and synthesis in the present decade, utilizing the management process theory as a comparative base.     

Comments on "Charge density in a conducting medium"

An alternate development of a relaxation time for free charge in conducting media, presented in the referenced letter, is questioned here. It is shown that the equations of the alternate development actually lead to the well-known "classical" time constant ε/σ. Several instances of apparently questionable reasoning in the referenced letter are commented upon.     

Facts and Fancies About a Posteriori "Wiener" Filtering

A posterior "Wiener" filtering is an estimation technique that has gained renewed interest in recent years, particularly in evoked potential studies. However, several misconceptions appear to exist with respect to the theory and its applicability. The purpose of this paper is to clarify these aspects and to explain the method in a comprehensive manner. Finally, the use of a more powerful time-varying filtering technique is recommended.     

A triggerable latch using a "Hybrid-mode" MOSFET bistable circuit

The potentialities which result from exploiting both types of conduction mechanism (majority and minority carriers) possible with an insulated-gate FET are exemplified in the design of a simple "hybrid-mode" regenerative circuit constituting a triggerable latch, which is switched on following the closure of two contacts and switched off via a separate input. The circuit is TTL-logic compatible and useful for such applications as touch-sensitive switching.