Efficient processing of spatial joins with DOT-based indexing

A spatial join is a query that searches for a set of object pairs satisfying a given spatial relationship from a database. It is one of the most costly queries, and thus requires an efficient processing algorithm that fully exploits the features of the underlying spatial indexes. In our earlier work, we devised a fairly effective algorithm for processing spatial joins with double transformation (DOT) indexing, which is one of several spatial indexing schemes. However, the algorithm is restricted to only the one-dimensional cases. In this paper, we extend the algorithm for the two-dimensional cases, which are general in Geographic Information Systems (GIS) applications. We first extend DOT to two-dimensional original space. Next, we propose an efficient algorithm for processing range queries using extended DOT. This algorithm employs the quarter division technique and the tri-quarter division technique devised by analyzing the regularity of the space-filling curve used in DOT. This greatly reduces the number of space transformation operations. We then propose a novel spatial join algorithm based on this range query processing algorithm. In processing a spatial join, we determine the access order of disk pages so that we can minimize the number of disk accesses. We show the superiority of the proposed method by extensive experiments using data sets of various distributions and sizes. The experimental results reveal that the proposed method improves the performance of spatial join processing up to three times in comparison with the widely-used R-tree-based spatial join method.     

A tree-structured crash surrogate measure for freeways

In this paper, we propose a novel methodology to define and estimate a surrogate measure. By imposing a hypothetical disturbance to the leading vehicle, the following vehicle’s action is represented as a probabilistic causal model. After that, a tree is built to describe the eight possible conflict types under the model. The surrogate measure, named Aggregated Crash Index (ACI), is thus proposed to measure the crash risk. This index reflects the accommodability of freeway traffic state to a traffic disturbance. We further apply this measure to evaluate the crash risks in a freeway section of Pacific Motorway, Australia. The results show that the proposed indicator outperforms the three traditional crash surrogate measures (i.e., Time to Collision, Proportion of Stopping Distance, and Crash Potential Index) in representing rear-end crash risks. The applications of this measure are also discussed.     

基于Java/CORBA的GIS网上信息发布系统

在比较了当前流行的几种GIS网上信息发布系统的基础上，针对当前GIS系统的互操作问题，提出了一种基于Java/CORBA技术的GIS网上信息发布系统，这一系统充分地利用了Java语言的跨平台性，并结合CORBA分布计算框架结构实现了异构GIS平台信息的互操作性。     

Parlay‐based service provision in circuit‐ and packet‐switched telecommunications networks

The spectrum of potential value added services over Internet telephony is wide, but the current service provision solutions are inadequate or proprietary. The nature of Internet differs significantly from that of circuit switched network, however, VoIP architectures can capitalize service control architectures in the PSTN world. We describe such an architecture based on the intelligent network and the Parlay, employing distributed objects and mobile agents as enabling technologies. This architecture has been implemented in the PSTN and the Internet and it has provided a framework for service provisioning, augmenting the space of supported services. Copyright © 2004 John Wiley & Sons, Ltd.     

对美国DOT制动标准的深入研究及探讨

本文详细介绍了美国DOT制动标准的内容以及DOT制动试验的项目、方法和试验流程,并且结合笔者本人长期从事摩托车制动项目的经验,总结了DOT制动的难点和重点,以供读者参考。     

软土地层中双圆盾构法隧道的抗震分析

目前对于上海双圆盾构法隧道的抗震问题 ,尚没有成熟的方法可供利用。本文结合上海地区典型软土室内动力试验研究成果 ,采用考虑土 -结构相互作用的软土地层中地下建筑物抗震稳定分析方法 ,研究了隧道 -土体体系二维地震反应 ,并应用梁单元有限元模型研究了隧道的纵向地震反应。计算结果包括 :地震引起的隧道周围软土孔隙水应力比、震陷、动剪应力比 ,以及隧道结构的动剪应力、轴力、剪力、弯矩等。最终从地震影响角度对该隧道的优劣作了初步评价 ,为工程决策提供了重要参考依据 ,所得结论可为软土隧道抗震设计提供参考依据。     

双圆盾构隧道衬砌结构设计及参数研究

评价了盾构隧道衬砌结构设计模型及其发展现状,指出不同计算模型的特点和适用范围,通过上海地铁M8线实际工程对不同计算模型进行了分析和对比,重点讨论了双圆DOT(Double-O-Tube)盾构隧道结构计算中各种设计参数对计算结果的敏感性。研究结果表明,双圆盾构隧道结构计算中,目前常用的几种计算模型(修正惯用法、梁-弹簧模型等)都能满足工程设计的具体要求,关键在于计算参数选择的合理性和匹配性。不同的设计参数对结构计算结果的影响程度各不相同,对于中浅埋双圆盾构隧道,拱背土压力的影响不能忽略,否则计算结果将偏不安全。     

双圆盾构施工对邻近砌体建筑物影响的数值模拟

采用三维MIDAS/GTS软件,考虑建筑物-土体-隧道共同作用,模拟了双圆盾构隧道垂直穿越墙下筏基砌体结构建筑物的工况,研究隧道施工引起的建筑物附加沉降及荷载,考虑隧道水平位置及墙体层数改变的影响。分析结果表明:随着双圆盾构机穿越建筑物,建筑物的沉降量逐渐增大,完全通过以后建筑物沉降趋于稳定并略有回弹;沿隧道掘进方向的建筑物产生短期不均匀沉降,先从零逐渐增大,随后逐渐减小并趋于零;构件第一主应力最大值σ1和墙体最大剪应变均逐渐增大并趋于稳定。随着隧道轴线与建筑物轴线水平距离从零开始增大,建筑物呈现向隧道一侧倾倒的趋势,基础局部倾斜先增大、后减小;在一定范围内,σ1最大值和最大剪应变基本保持不变,超出后逐渐减小,并接近初始值。随着建筑物层数的增加,墙体最大剪应变呈线性增长,对建筑物造成轻微的损害。     

盾构法隧道双层车道布置构想

针对盾构法隧道的特点 ,根据公路建筑限界的要求 ,布置了双层车道 ,还设想了采用等直径和不等直径双连DOT盾构法隧道建造双层车道的方案。     

双圆隧道盾构推进对周围环境影响的现场监测

结合中国第一条双圆隧道工程施工,对双圆隧道盾构推进对周围环境影响的现场监测方法进行了论述.文章以双圆盾构隧道区间施工为实例给出了双圆盾构推进过程中周围土体的变形、土压力、水压力变化的监测方法与测点布置方案,据此监测方案,可以详细监测与分析盾构推进过程中周围土体的地表变形、深层土体变形及土体中的土压力、水压力的变化,从而揭示盾构推进对周围的土体环境的扰动影响规律.