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241.
242.
U. Reimer
H. -J. Schek
《Data & Knowledge Engineering》1989,4(4):321-352The first part of this paper introduces the basic constructs of a frame representation model and gives a formal definition for them. Subsequently the nested relational model (NF2) is described as an extension of the classical relational model to support relation-valued attributes. In the second part of this paper both models are compared with each other and a mapping of frame representation structures to NF2 structures is specified. The structural similarities between frames and NF2 relations are made clear and it is shown that their main difference is due to the type polymorphism introduced by the concept hierarchy of the frame model. This causes type collisions to occur in the strictly typed NF2 model when frames are directly mapped to NF2 structures. Two solutions to this problem are suggested and compared. The paper concludes with a reformulation of query operations of the frame model in terms of NF2 algebra operations. 相似文献
243.
Dr Joseph A. Cannataci 《AI & Society》1989,3(3):169-183
This paper examines some of the possible legal implications of the production, marketing and use of expert systems. The relevance of a legally useful definition of expert systems, comprising systems designed for use both by laymen and professionals, is related to the distinctions inherent in the legal doctrine underlying provision of goods and provision of services. The liability of the sellers and users of, and contributors to, expert systems are examined in terms of professional malpractice as well as product liability. A recurring theme indicates that legislators may be inclined to restrict possibilities of liability suits in order to avoid disincentives to the creation of expert systems. 相似文献
244.
Aseel Berglund Erik Berglund Anders Larsson Magnus Bang 《Universal Access in the Information Society》2006,4(4):300-327
The television (TV) is one of the most common entertainment devices in homes. Searching and finding TV programs is a common task and using TV guides is one way of performing this. This paper presents three studies that are focused on examining audiences’ TV habits and TV guide usage, evaluating a new concept based on linking paper and pen with TV technology, and studying the audiences’ attitudes toward and anticipated interest in the future guide. The results of our first study emphasize the value of using paper based TV guides and also identify the deficiencies. We also found indications that the advantages and disadvantages of paper-based TV guides are related to the physical properties of paper. Thus, we suggest a solution that uses digital pen and paper technology to offer a new interaction method for TV. A research system “Paper Remote”, is developed and used in the two subsequent studies. Viewers tick designated areas on the paper-based guide to perform actions such as channel switching. However, this solution is not a substitute for the remote control device. We argue that these user studies on linking digital paper to the TV for everyday information navigation illuminate the possibilities of providing innovative solutions also for home information systems also. 相似文献
245.
Shunsuke Ohashi 《Electrical Engineering in Japan》2005,150(1):71-77
Magnetic bearing using pinning force of a permanent magnet and a high‐temperature superconductor has been developed. Additional permanent magnet is introduced to increase the levitation force of the magnetic bearing. In this hybrid magnetic bearing system, levitation force is mainly given by the repulsive force of the permanent magnets, and stability for the lateral direction is given by pinning force of the superconductor. The experimental device is developed. A ring‐type superconductor and a bulk one are examined. Levitation characteristics of the hybrid magnetic bearing are measured. The bulk superconductor shows better characteristics of both levitation and lateral stability than the ring one. Levitation force of the hybrid system becomes about twice as large as that of the nonhybrid one. Although, the repulsive force of the permanent magnet decreases the lateral stability of the system, its influence becomes small by choosing an adequate position of the permanent magnets and the superconductor. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 150(1): 71–77, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10350 相似文献
246.
247.
248.
Abd El-Shafy A. Nafeh Faten H. Fahmy Essam M. Abou El-Zahab 《Solar Energy Materials & Solar Cells》2003,75(3-4):723-728
In this paper the implementation of a suggested stand-alone PV system, for maximum-power point tracking (MPPT), is carried out. Also, this paper presents a comparative study, through experimental work, between the conventional PI controller and the fuzzy logic controller (FLC) under different atmospheric conditions. The implemented system with both the PI controller and the FLC gives a good maximum-power operation of the PV array, but the tracking capability for different optimum operating points is better and faster for the case of using the FLC compared to the case of using the PI controller. 相似文献
249.
大型水轮发电机组励磁变压器参数及绝缘方式的选择--由三峡机组励磁系统投运引起的思考 总被引:1,自引:0,他引:1
结合三峡机组励磁系统的调试及投运经验,对大型水电机组静止自励系统选型中存在的一些关键性技术课题进行分析与论证,期望得出的结论有助于在大型水轮发电机组励磁系统参数选择和在提高机组运行安全、可靠性方面提供有益的借鉴。文中提出的励磁系统设计新理念仅代表个人的观点。 相似文献
250.
ZHANG Hui-juan HUI Shi-en ZHOU Qu-lan 《国际设备工程与管理》2007,12(1):36-41
The purpose of this paper is to present the flow field in the 300MW tangential firing utility boiler that used the Low NOx Concentric Firing System (LNCFS). Using the method of cold isothermal simulation ensures the geometric and boundary condition similarity. At the same time the condition of self-modeling is met. The experimental results show that the mixture of primary air and secondary air becomes slower, the average turbulence magnitude the relative diameter of the tangential firing enlarges of the main combustion zone becomes less and when the secondary air deflection angle increases When the velocity pressure ratio of the secondary air to the primary air (p2/p1) enlarges, the mixture of the secondary air and the primary air becomes stronger, the average turbulence magnitude of the main combustion zone increases, and the relative diameter of the tangential firing becomes larger. Because the over fire air (OFA) laid out near the wall has a powerful penetration, the relative diameter of the tangential firing on the section of the OFA is very little, but the average turbulence magnitude is great. When the velocity pressure ratio of the OFA to the primary air POFA/p1 increases, the relative diameter of the tangential firing on the section of the OFA grows little, the average turbulence magnitude becomes larger and the penetration of the OFA becomes more powerful. 相似文献