有限精度下混沌扩频序列的性能分析

本文研究了不同精度对Chebyshev映射混沌扩频序列相关特性的影响.首次提出了有限精度门限值的概念,给出了有限精度门限值与序列长度的数学关系式;研究和分析了精度低于有限精度门限值时混沌迭代初值的选取对序列相关特性的影响,并给出了初值选取的准则.本文的研究结果为混沌映射扩频序列的应用研究提供了参考依据.     

当代欧洲的城市设计观

笔者在西欧主要城市考察之后，结合国外同行在城市中心区建设中的作法，对他们在城市设计领域中的一些重要的价值观念、设计手法进行了探讨。     

计算机辅助卡诺图化简逻辑

随着电子技术的迅速发展,卡诺图已经成为逻辑设计中常用的一种数学工具。由于卡诺图形象、直观,能把各种复杂的逻辑函数用图形表示出来。因此,卡诺图在电子技术中得到了广泛的运用。在数字电路中,逻辑函数的表示方法有:真值表,函数表达式,逻辑图以及卡诺图。卡诺图的人工化简逻辑函数历来为试凑法,无一定规律可循,繁琐而且易出错。而用计算机辅助卡诺图来化简逻辑函数的方法将克服人工算法的缺点,使化简更方便有效。     

基于身份的电子邮件系统

1984年,为了简化密钥管理并取消公钥证书的使用,Shamir提出了基于身份的密码学概念.在这种密码学模式下,用户的身份信息如用户的名字、Email地址或者IP地址可以直接用作用户的公钥.文章基于三个开放源码库:GNU Multiple Precision(GMP)、OpenSSL和IBE库,设计并实现了一个基于身份的电子邮件系统.该系统具有邮件加密、解密、签名、验证功能.     

长株潭城市群公示语现状分析及对策研究

长株潭城市群＂两型＂社会建设离不开良好的语言环境。在实地考察的基础上,结合语用学理论,通过对所收集的长株潭城市群公示语资料进行研究,分析了长株潭城市群公示语的现状,探讨了该地区公示语翻译中的问题,并提出了相应的对策。     

河涌污染治理生态恢复技术的研究进展

随着经济的快速发展,大量污染物排入河涌导致河涌水体污染问题日趋严重。采取有效的技术措施治理河涌污染势在必行。结合近年来国内外河涌治理的研究成果,综述了河涌治理中生态恢复技术的原理和特点,并指出今后研究方向。     

Bars on blocks: A cellular automata model of crime and liquor licensed establishment density

Criminologists have extensively researched the problems generated by licensed establishments. Violent offending and disorderly behavior resulting from pubs, taverns, dance clubs and bars are of particular interest to this field of study. The relative density of these liquor establishments has been found to be associated with the level of violence and disorder in surrounding areas. A complex systems approach can be used to further understand the dynamic interplay between licensed establishments, violent offending and disorder, and urban planning decisions. The model presented here utilizes cellular automata as the mathematical framework to view the varying impact of liquor licensing density on crime. This study uses a sample of liquor establishments and crime data from the City of Vancouver in British Columbia. The cellular automata model incorporates transition rules which govern the change of city blocks from low-risk blocks to high-risk blocks. The results represented by a 50 × 50 cellular grid show that high-risk blocks multiply when liquor licenses are grouped. Two scenarios are presented to contrast the impact of grouping high-risk blocks which contain more liquor establishments and dispersing such blocks. A third scenario demonstrates how increasing the positive influence in a grouped scenario stops high-risk blocks from taking over the entire grid. Future iterations of this model will incorporate census data, public transportation data, land use data and entertainment districts from other cities to further analyze the effect of licensed establishments on the distribution of crime.     

GPS与数字地图的匹配研究

GPS测量得到的是WGS-84中的地心大地坐标,而在车辆导航等方面通常使用平面地图坐标。如何实现其中的转换,一直是GPS和GIS集成中所关心的问题。该文介绍了GPS定位原理、我国常用的大地坐标系、高斯投影、从GPS定位结果至平面坐标的转换模型等。同时提出了实现GPS数据与数字地图的匹配,并实时显示车辆行驶轨迹的方法。