The design of a solid state trip system for nuclear power plants

In this paper, a new nuclear safety system has been devised that promises a great reduction in the unavailability of conventional systems of compatible arrangement. Four principal design approaches are combined to realize this improvement.The first is the employment of solid state devices throughout the system for achieving not only a much faster system response, but also a better reliability. The second involves the application of sequential redundancy, so that the effective system operation can be maintained by a standby unit in the event of a failure in the principal system.The third approach employs the concept of cellular automata in failure detection and switching functions. Finally, the fourth design approach provides an automatic shift from 2 out of 3 to 2 out of 2, whenever a channel is rejected.     

Feedback control of the nuclear magnetization state: experimental results

In a previous paper (Proc. Soc. Magn. Reson. Med., San Francisco, CA, USA, 1991), the authors investigated feedback control of the nuclear magnetization state. This strategy facilitates the optimization of the pulse parameters during the imaging sequence. In this work, results from a series of experiments used to test the theoretical predictions are presented. Two groups of experiments were performed using a commercial imager and a small sample of distilled water. In the first group of experiments the control objective is to regulate the magnetization orientation to a constant reference angle. The results show that a closed-loop system produces the desired orientation. In contrast, an open-loop input results in an appreciable error between desired and measured orientation. A second group of experiments shows that a closed-loop system can force the magnetization orientation to track a desired trajectory. In both groups, the closed-loop experimental and simulation results are in excellent agreement. The application of feedback control to MRI and spectroscopy is discussed.     

Feedback control of the nuclear magnetization state: modeling and control design

Magnetic resonance (MR) images are obtained by observing the fluctuations in nuclear magnetization produced by sequences of RF pulses and applied magnetic field gradients. The design of a pulse sequence is based on the expected response of the nuclear magnetization. Currently, all pulse sequence parameters are loaded into the pulse programmer before the start of the sequence and remain unchanged until the completion of the sequence. A fundamentally different approach is considered, whereby the sequence parameters are adjusted between successive RF excitation pulses. In this manner, the nuclear magnetization is regulated to a desired state by using measurements of the magnetization to adjust the amplitude and duration of the RF pulses. Feedback control of the nuclear magnetization state may be advantageous in certain types of MR experiments, for example those requiring a repeated spin-echo or gated MR image acquisition. As a first step in developing this approach a simple scheme for regulating the angle between the bulk magnetization and the axis applied static magnetic field is presented. The behavior of the closed-loop system is explored using computer simulations.     

细胞的核膜及核孔的微细结构

核膜是真核细胞的重要特征之一。核膜将细胞内的空间分隔为两个不同的区域 ,即细胞核和细胞质。细胞核储存遗传物质 ,为控制细胞生命活动的中心。细胞质内分布着内质网、高尔基体和线粒体等细胞器 ,执行细胞各种生命功能。核膜由内核膜和外核膜构成 ,核孔是由内、外核膜融合产生的圆环形结构。核膜把细胞核与细胞质隔离开 ,使其互不干扰地执行各自的功能。核孔的重要作用是介导细胞核与细胞质之间的物质转运。可采用各种光镜和电镜技术对核膜和核孔进行观察与研究。首先使用的喹啉蓝荧光染剂ＤｉＯＣ6(3)处理生活的大肠癌培养细胞ＣＣＬ187,…     

The globalization of nuclear weapons

What is it like to live in a world in which the materials and technology for making nuclear weapons are freely traded? We are in the midst of finding out. Earlier this year, investigators determined that Pakistani scientist A.Q. Khan sold some of the technologies he used to build Pakistan's nuclear bomb to several governments that had long sought atomic bombs, including Iran and Libya. Clearly; the threat of the "casual" use of nuclear weapons and of nuclear terrorism has been catapulted from the abstract to the alarmingly concrete. For the right price, an entire weapon might be obtainable on the black market. Only intensive, imaginative diplomacy and a massive demonstration of collective will on the part of the worldwide community can avert this nuclear catastrophe in the making. Sadly, both are in short supply today.     

The promise of nuclear power

Discusses the early enthusiasm for nuclear power from 1945-1957, commercial development from 1957-1975 and the climate of public opposition in the light of accidents in the nuclear industry from 1975-2000. Prospects for the future are assessed     

The role of electronic controls for future automotive mechatronic systems

The merging of electronics and mechanical actuators for automotive applications is driven by environmental and societal influences, customer wants, quality/reliability, and value. Cost-effective mechatronics is made possible by the continuing improvements in the underlying enabling technologies. This paper examines the technology enablers as they influence automotive control systems, and then explores the impact of environmental, customer, and societal drivers as they affect control systems.     

The state of user-centered design practice

This publication contains reprint articles for which IEEE does not hold copyright. You may purchase this article from the Ask*IEEE Document Delivery Service at http://www.ieee.org/services/askieee/     

The state of Japan's military art

The issues surrounding an arrangement that allows Japanese codevelopment and coproduction of an advanced version of the F-16 fighter jet, known as the FSX project, are examined. US opposition to the FSX project arises from fears that the project will help Japanese companies compete effectively against the United States' civil aircraft industry. Another charge is that Japanese companies may be eyeing the export market in military weapons. The nature of the Japanese defense industry is discussed, and the state of its technology is assessed. The likely impact of the FSX project on the US is considered     

我国互联网安全状况分析

随着互联网在中国的快速发展,中国六大经营性互联网和四大非经营性互联网都先后建成并投入使用。据CNNIC统计,到2001年6月30日止,中国互联网上网用户数达到了2650万左右,上网计算机约1002万台。目前,互联网用户中有ISDN(2B+D)用户93.8万、专线上网用户48.8万。中国拥有如此庞大的互联网用户和基础     

国外超大规模集成电路的生产状况

介绍了国外超大规模集成电路的发展趋势,列举了21世纪需要研究的7类集成电路新技术。阐述了超大规模集成电路在武器装备中的作用,美、欧、日、韩今后的发展对策及其集成电路生产厂的主流产品与生产状况。     

Theorem on nonoptimal controls

It is indicated that it is possible to give an evaluation of performances for nonoptimal controls derived from a restricted class of optimal problems.     

自我控制的神秘LED

自从30多年前LED发明以来,其发光效率稳步上升,增加转换效率是在两个方向上实现的。某些高亮度、高效率LED表现出有显著的光伏作用,如惠普的HLMP-EG30- NR000就是一款封装在透明外壳中     

The state of the art in interplanetary Internet

Developments in space technologies are enabling the realization of deep space scientific missions such as Mars exploration. Interplanetary (IPN) Internet is expected to be the next step in the design and development of deep space networks as the Internet in the space. However, there are significant challenges to be addressed for the realization of this objective. This article captures the current state of the art and open research challenges, and intends to motivate researchers around the world to tackle these challenging problems and help realize the IPN Internet.     

Pension plans: The state of the art

The effect of termination of employment on pension benefits has become a matter of grave concern to engineers and scientists in the United States, particularly to those in the professions served by IEEE. In many cases during the postwar years, the decision to transfer from one employer to another has been a voluntary act of the professional worker and he could measure the cost of losing future pension benefits against the advantages of taking a new job. But within the last two years, a major change has occurred in the space and defense industries and their suppliers, which are so largely dependent upon government support of scientific and engineering work. In addition to discussing current pension practices in the United States, this report includes a review of activities by societies in this field, and the limitations imposed by legal and economic forces.     

Gas-discharge displays: The state of the art

The physics of the cold-cathode gas discharge is reviewed, with emphasis on such display-related aspects as the visible light output and the use of priming as a method of moving the light-emitting site through the display. Displays used for numerics, alphanumeric characters, and computer graphics are described, with attention being given both to commercially available units and to those which are still in the laboratory. Attempts to produce gas-discharge TV displays are reviewed. Such related problems as drive circuitry and overall system cost are discussed, with emphasis on considering the entire display system, including all the required power supplies and drive-circuit components.