Current-feedback operational amplifiers and applications

The current-feedback operational amplifier (CFOA) is a relatively new arrival in the analogue designer's tool kit. The first monolithic device was produced by Elantec Inc. in 1987 and since then it has intrigued and puzzled many. Is it really better than the conventional and well known voltage-feedback operational amplifier (VOA)? How does the CFOA differ in design? What are the applications where it performs better than the VOA and when should the VOA be used in preference to the CFOA? We attempt to give some insight into the design and performance of the CFOA and to answer these questions     

The major problems facing engineering education

Engineering education has been much studied during the past fifty years. One of the first major studies, known as the Wickenden Report in its trial version recommended that engineering education be at the graduate level. However, this was later amended to say that engineering education should be an undergraduate study, but should be followed by an internship in which one's further education would be guided by the engineering colleges, industry, and the engineering societies working together. The dilemma of engineering education has been that we have tried to combine a broad general education with some engineering in a sort of liberal science education, instead of offering professional education with a very strong technological stem. Since we have chosen the former path, we find ourselves confronted by other unresolved questions. Should we teach science or engineering practice? How much emphasis should there be on design and how much on theory and analysis? How broad should the curriculum be and how much of the humanities should it contain? How much should we depend on graduate work to train an engineer? Now in addition to these dilemmas we find ourselves confronted with the problem of finding sufficient time to cover the material considered necessary. It is obvious that many of our constraints, schedules, credits, fifty-minute periods, lectures, laboratories, and lock-step methods must be replaced by new methods and systems designed to teach more efficiently. This offers an opportunity for cooperation among industry, the colleges, and the professional societies.     

A heuristic task assignment algorithm to maximize reliability of adistributed system

Distributed systems potentially provide high reliability owing to the program and data-file redundancy possible. In many applications, high reliability is the major consideration for system design. Previous work has shown that the distribution of programs and data-files can affect the system reliability appreciably, and that redundancy in resources such as computers, programs, and data-files can improve the reliability of a distributed system. This work formulates a practical application for a reliability-oriented distributed task assignment problem which is NP-hard. Then, to cope with this challenging problem, a greedy algorithm is proposed, based on some heuristics, to find an approximate solution. The simulation shows that, in most cases tested, the algorithm finds suboptimal solutions efficiently; therefore, it is a desirable approach to solve these problems     

Teaching measuring systems beyond the year 2000

This article is an attempt to contribute to the discussion about teaching measuring systems beyond the year 2000 by answering three fundamental questions: (1) What should students at the dawn of the 21st century know about measuring systems? (2) Why should students know a systems approach to electrical measurement? (3) How should measuring systems be taught? The following gives the authors' point of view on this subject, based on 25 years of teaching various aspects of measuring systems to students of widely varying technical and cultural backgrounds     

On coupling multi-systems through data sharing

The demand for larger transaction rates and the inability of single-system-based transaction processors to keep up with demand have resulted in the growth of multi-processor-based database systems. The focus here is on coupling in a locally distributed system through multi-system data sharing in which all systems have direct access to the data. This paper addresses the following questions; i) How does a workload running on a single system today perform if migrated to a multi-system? ii) What are the multi-system locking design issues that limit multi-system performance and what is the maximum number of systems that may be effectively coupled? iii) Can alternative locking designs increase the number of systems that may be effectively coupled? Our analysis is based on traces from large mainframe systems running IBM's IMS database management system. We have developed a hierarchical modeling methodology that starts by synthesizing a multi-system IMS lock trace and a reference trace from single-system traces. The multisystem traces are used in trace-driven simulations to predict lock contention and database I/O increase in multi-system environment and to generate workload parameters. These parameters are used in event-driven simulation models to examine the overall performance under different system structures. Performance results are presented for realistic system parameters to determine the performance impact of various design parameters. Lock contention is found to be the critical factor in determining the coupling effectiveness and the effect of alternative locking design to reduce lock contention is studied. The limit on coupling is explored and the analysis indicates that, for this workload, on the order of 6 to 12 systems may be effectively coupled through data sharing, depending on system structure and locking design.     

光传输网管海量数据存储访问研究

文章主要针对光传输网管系统中网无数量急剧增长导致的网管数据库更新查询效率极低,甚至出现系统崩溃的问题,提出了一种高效的分布式数据库系统架构.该系统采用主从技术、Memcached技术与分布式数据库结合的方式,将数据分散地存储在多台独立的设备上,提高了数据的查询效率.系统容量大、可靠性高、扩展能力强,具有很强的实用性.     

Cooperative Estimation for Coordinated Target Tracking in a Cluttered Environment

The purpose of the work in this paper is to gain insight into several fundamental questions that arise whenever a distributed multiple-vehicle control system is endowed with communication capabilities. These fundamental questions include: what data should each vehicle share?, how frequently should communication take place?, and what benefit does communication provide? These questions are evaluated with respect to a target tracking task in which multiple pursuit vehicles estimate the state of a target vehicle. This task has three main components: communication, estimation, and control. Communication takes place on a broadcast network, estimation is achieved with an Unscented Kalman Filters, and the controller is behavior-based. Simulation results show that communication always improves distributed estimate results. Which information to transmit depends on available bandwidth, and more frequent communication generally yields better estimates. Simulation results also show how coordinated control can be beneficial to target tracking in a cluttered environment.     

A view of reliability and quality measurements fortelecommunications systems

The authors present a customer (telephone company) oriented view of R&Q (reliability and quality) measurements for telecommunications systems based on Bellcore's experience and work in this area. On behalf of its clients, Bellcore has published its preliminary view of generic requirements for supplier quantification of several aspects of system reliability and quality measurement. These generic requirements are contained in Bellcore's `Reliability and Quality Measurements for Telecommunications Systems (RQMS),' TA-TSY-000929 (1989). The measurements are applicable to network switching elements (local switch, tandem, signal transfer point, service control point, packet switch, adjunct, etc.), operations systems, and transparent systems. Their scope covers system, software, hardware, firmware, and product support, and they are directed toward the system test, first office application, and general availability system life-cycle stages. Issues covered by this document are discussed in some detail     

Modelling Market-Based Decentralised Management Systems

A centralised approach to management of distributed systems works well when applied to relatively small-scale systems. As the scale grows, so do the problems of making appropriate system-wide decisions and co-ordinating their execution. As a result, large centrally managed systems tend to be ponderous and rigid. Devolving decision-making responsibility to local units means that locally appropriate responses to changed circumstances can be made rapidly. However, it is quite possible that local decisions in different elements of the system will interfere adversely. How does one co-ordinate local decisions in large systems without re-introducing central control and its associated problems? The decentralised approach adopted here is to craft the interactions between local decision-making elements (agents), in order that effective management of the overall system is an emergent result of repeated local decisions and interactions. The general solution to this problem is an ambitious long-term research goal. This paper presents some results that offer a way forward within a particular class of problem in which the interactions between agents can be modelled as sale and purchase of commodity items.     

Group Communication Using Modular Protocol Stacks

Today's distributed systems consist of many different components, making the efficient management of such systems an extremely difficult task. Group communication should provide a potential solution to make the management process more flexible. It is possible to build a group communication system based on traditional distributed technology such as CORBA (Common Object Request Broker Architecture), but efficiency is poor due to lack of support for multicast and the overhead of building groups in current commercially available products. Multicast is a key part of a future group communication architecture and although reliability is not yet supported there are workarounds which provide a solution. This paper discusses the design and implementation of reliable IP multicast protocols for group communication. One important aspect of this work is the modularisation of the protocol blocks, and the design of a modular protocol, which can be used in conjunction with other similar protocol blocks to build a communication stack for group communications, is described in detail.     

Sharing issues between FPLMTS and fixed services

Any sharing between future public land mobile telecommunication systems (FPLMTS) and fixed services must be on the basis of maintaining high reliability and performance for both services. The focus of this article is to examine the following. Can mobile and fixed systems share the same frequency band? How much unwanted signal power is received by each system from the other? How does the unwanted signal power vary as mobile users roam in an area covered by the main-beam and the sidelobes of the fixed service? What effects do the parameters of FPLMTS (transmitter power, bandwidth, etc.) and the parameters of the fixed service (antenna directivity, power, bandwidth, etc.) have on the unwanted signal power levels? How is the unwanted power level affected by the path geometry, in particular fixed service antenna height and propagation conditions (congested areas) between the mobile and fixed stations?     

Key factors in the successful application of quality functiondeployment (QFD)

In the product design and development process, quality function deployment (QFD) provides a comprehensive, systematic approach to ensure that new products meet or exceed customer expectations. This paper reports on the results of a survey of more than 400 companies in the United States and Japan using QFD. The objective of the study was to understand the key factors that result in the successful application of QFD. The research questions investigated in this study were developed both inductively from QFD case studies in the United States and Japan and deductively from the literature. Regression analysis estimates the effects of organizational characteristics, data sources, and QFD tools and techniques on QFD improvements in the product and process. The results show that QFD is most likely to have a positive impact when there is management support for QFD and new customer data specifically collected for the QFD study are used. The benefits of QFD are independent of the tools and techniques used as part of the QFD study     

复杂系统可靠性分配的层次分析法

可靠性分配是系统可靠性设计的一个重要环节,进行可靠性分配时需要对系统的各个组成部分进行全面的衡量。对复杂系统而言,一方面由于影响系统可靠性的因素有很多,并且其中一些可以进行定量的描述,一些只能定性地衡量;另一方面由于系统复杂,使得可靠性分配较为困难,所以现在的方法不能很好地解决这一问题。提出了复杂系统可靠性分配的层次分析法。并对其基本思想和过程进行了介绍,给出了计算实例,最后对该方法在实际问题中的应用提出建议。     

Latin America goes wireless via satellite

The authors address the following questions. What does the current growth of the satellite market really mean for Latin America? What are the plans to cover the region with satellite systems? How will they impact the Latin American economy and more particularly its satellite industry? Is Latin America going satellite by itself and is it managing wireless implementation via satellite to the best of its interests? Is Latin America looking for its role in the globalization of the world? Is it possible and healthy to think about regional or subregional models to lead Latin America wireless via satellite as well as its own means? Should Latin America be considered only a market, and nothing more? How will these questions be answered? To deal with these issues, currently “fashionable” satellite applications such as direct to home (DTH) and direct broadcast satellite (DBS), as well as rural and mobile communications, are approached from the marketing, legal, and regulatory points of view, including the “sleeping” plan for the broadcasting satellite service in Region 2     

New options and insights for survivable transport networks

This article is devoted to a selection of recent topics in survivable networking. New ideas in capacity design and ring-to-mesh evolution are given, as well as a systematic comparison of the capacity requirements of several mesh-based schemes showing how they perform over a range of network graph connectivity. The work provides new options and insights to address the following questions. How does one evolve from an existing ring-based network to a future mesh network? If the facilities graph is very sparse, how can mesh efficiency be much better than rings? How do the options for mesh protection or restoration rank in capacity requirements? How much is efficiency increased if we enrich our network connectivity? We also outline p-cycles, showing this new concept can realize ring-like speed with meshlike efficiency. The scope is limited to conveying basic ideas with an understanding that they could be further adapted for use in IP or DWDM layers with GMPLS-type protocols or a centralized control plane     

Engineering layoffs: facts and myths

Being `technically vital,' proficient in a hot speciality, or retrained does not guarantee a job in today's market. This report recounts problems faced by laid-off engineers. Through their eyes, it also addresses such questions as: how successful has keeping technically vital been in making these individuals immune to layoffs? What hot new job areas have they found or not found? How well does the defense-to-commercial conversion appear to be working? In this article the case studies are highly personal views. Nonetheless, the experiences of these engineers suggest that, at least in certain contexts in today's work world while some commonly believed assumptions may be facts, others are myths     

Finite series-expansion reconstruction methods

Series-expansion reconstruction methods made their first appearance in the scientific literature and in the CT scanner industry around 1970. Great research efforts have gone into them since but many questions still wait to be answered. These methods, synonymously known as algebraic methods, iterative algorithms, or optimization theory techniques, are based on the discretization of the image domain prior to any mathematical analysis and thus are rooted in a completely different branch of mathematics than the transform methods which are discussed in this issue by Lewitt [51]. How is the model set up? What is the methodology of the approach? Where does mathematical optimization theory enter? What do these reconstruction algorithms look like? How are quadratic optimization, entropy optimization, and Bayesian analysis used in image reconstruction? Finally, why study series expansion methods if transform methods are so much faster? These are some of the questions that are answered in this paper.     

Distributed object‐oriented switching system software platform design

Key technologies are presented and evaluated for establishing a distributed object‐oriented switching system platform. This platform is based on CORBA, which can enhance software productivity and system scalability and is thus widely used in the information technology field. Conditions and requirements specific to switching systems, such as very high‐performance and non‐stop operation, are analysed and mapped to the main elements of CORBA. How to deploy and bind objects so as to minimize the processing load is clarified. Mechanisms that guarantee system reliability (saving calls in service when a system failure occurs and avoiding the spread of faults) are also presented. Evaluation of the number of dynamic program steps for systems using fully compliant CORBA, improved CORBA, and a proprietary high‐speed object‐request broker (ORB) shows that constructing a communication switching system by using the high‐speed ORB approach is sufficient, but CORBA‐compliant approaches should be used to provide an interoperable interface for communicating with external compliant systems. Copyright © 2001 John Wiley & Sons, Ltd.     

军工网络安全模拟仿真系统可信度研究

军工网络安全模拟仿真系统是一个多层次、多方面、多步骤的仿真系统。通过对系统进行VV＆A分析,结合层次分析法（AHP）的决策思想,把与仿真可信度有关的评估元素通过划分层次后并计算权重,建立起一种复杂仿真系统可信度评估的综合算法模型,最终得到整个军工网络安全模拟仿真系统的可信度。根据所得到的量化可信度结果,证明该系统具有一定的科学性。     

The CRT in phototypesetting systems

Rapidity and flexibility in photo-offset printing are synonymous with computer-driven CRTs. Yet, designing such a system has its problems. One big consideration is beam deflection linearity. Another is resolution. Reproduction accuracy resolved, design alternatives remain: Should the CRT be step-scanned or scanned continuously (as for television)? How much of the tube should be used? What should the absolute motion of the film be with respect to the generated motion of the characters? Naturally, there are tradeoffs.