切削数据库的最新研究进展

<正>1引言自1964年美国开发第一个切削数据库CUTDA-TA以来,经过近半个世纪的发展,切削数据库的理念已全面拓展。将计算机应用技术的最新成果与之结合,全面渗透到工程应用的各个领域。本文阐述最新计算机技术成果应用到切削数据库开发的最新进展情况。     

A Comparative Study of Urban Planning System Between Wuhan and Macao

This paper makes a comparative study of urban planning system between Wuhan and Macao,including the legislation system,administration system,and operation system of planning.Meanwhile,it also explores how to improve the current planning systems.     

Analytic expressions for a function occurring in diffraction theory

Simple expressions are derived for the Maliuzhinets (integral) function which arises in connection with diffraction by an impedance wedge. The given expressions allow the computation of the function with remarkable accuracy throughout the entire complex plane for any exterior wedge angle.     

脉冲取样锁相环的相位噪声传递特性

本文阐述的是把振荡器的频率稳定问题,区分为:决定振频参量变化引起的频率变化,振荡系统中电噪声对已产生振荡信号的调制。讨论了受到电噪声调制的信号经取样保持后的变化,得到了包含这一变化的取样锁相环的闭环传递函数,揭示了取样锁相环具有对参考信号相位噪声全不通、对VCO相位噪声全通的特性。     

英国移动通信市场的竞争和管制

目前英国是移动通信领域竞争比较充分的国家，英国的消费者以欧洲最低的费用享受着高质量的电信服务。英国电信管制局（OFTEL）通过对消费者享受到的竞争成果、消费者行为、市场结构和供应商行为这四组指标的分析来衡量英国的移动通信市场竞争态势，从而调速管制措施。目前OFTEL对移动通信市场的关注点包括SIM卡锁定、国际温游、价格透明、号码携带和短消息业务所带来的潜在性的问题。     

瑞典电信市场综述

瑞典于1993年5月颁布电信法，由此建立许可证制度。1996年，修改后的电信法对电信运营商实行不对称管制，只对占有市场主导地位的企业进行严格的监控。1997年7月，瑞典政府再次修改电信法，目的在于使之与欧盟的管制框架保持一致，增加了很多关于许或证持有者的责权规定，在固定业务市场，作为传统运营商的国有Telia公司占有绝对优势，其次是Tele2。Telia Mobile,Tele2 Mobil,Europolitan和Tele8 Kontakt是提供移动通信业务的4家运营商。     

卫星测控站射频接收系统EMC设计与测试

本文以卫星测控站为例,介绍了卫星测控站和卫星通信地面站接收系统EMC的设计与测试方法,并给出了测试结果。     

Higher order impedance and absorbing boundary conditions

Traditionally, generalized impedance boundary conditions (GIBCs) have been used to model dielectrics and coated surfaces, and absorbing boundary conditions (ABCs) have been used to simulate nonreflecting surfaces. The two types have the same mathematical form and, in most instances, a higher order condition involving higher order field derivatives has a better accuracy. We demonstrate that there is a close connection between the two and this enables us to use a systematic method which is available for generating GIBCs of any desired order to derive new two- and three-dimensional ABCs. The method is applicable to curvilinear/doubly-curved surfaces and examples are given. Finally, curves are presented that quantify the accuracy of two-dimensional ABCs up to the fourth order, and show how higher order ABCs can improve the efficiency of large scale partial differential equation (PDE) solutions     

Infants' recognition of contour-deleted figures

Infants' recognition of contour-deleted figures was investigated in four experiments using a habituation procedure. The results indicate that 12-month-old infants could recognize line drawings of figures that were missing 33%, 50%, or even as much as 66% of their contour. This was so whether the contour-deleted versions were used on habituation or on test: Intact figures were recognized after habituation to contour-deleted exemplars, and in most cases contour-deleted ones were recognized after habituation to the intact figure. The single failure appeared to be due to difficulty in discriminating between two extremely impoverished test stimuli. Findings from the final experiment, in which infants recognized complements of contour-deleted stimuli but not scrambled versions, suggested that they fill in the gaps of the contour-deleted figures so as to create a figural whole.