基于共享库的数据集成方案改进

基于共享数据库的方案是现在高校进行数据集成普遍采用的模式.但随着全局业务的增多,这种方案不可避免地会遇到共享数据库性能瓶颈的问题.从有效利用业务数据库、降低共享数据库业务压力出发,在研究了已有的改进方案之后,对基于共享数据库方案的框架进行改进,提出了一个同时使用共享数据库模式和中介模式,能够进行负载均衡的新的数据集成框架模型.对模型的优劣性进行了分析.     

基于XML虚拟数据库的异构数据源集成模型研究

解决企业数据源异构需要一种公共的数据源模型给用户提供统一的用户视图,XML以其所具有的自描述性、灵活性、强大的数据交换能力等优势克服了其他数据模式的缺点.结合当前数据集成方面的技术,提出了一种基于XML虚拟数据库的异构数据源集成模型,该模型很好地解决了异构数据源集成方面存在的一系列问题,并从数据模型和数据交换上阐述了该模型的可行性.剖析了该模型中的模式集成、异构数据集成视图、全局查询等.介绍了该模型在中国石油QHSE信息系统中的成功应用.     

基于Web Service技术的MOM安全性模型

Web Service作为一门新兴的技术,在中间件技术中有广阔的应用前景.但是,现有的Web Service安全传输方案,不适用于应用层的消息安全保护.因此,这种结合方式将会为消息中问件系统带来安全隐患,无法保证消息中间件的安全消息传递.文中提出了一个基于Web Service技术的合理的中间件模型.并结合消息中问件的特点,在分析Web服务安全技术的基础上,进一步提出了消息中间件的安全传输模型,同时阐述了保证SOAP消息安全传输的基本方法.设计了平台无关的实现方式以体现出应用的透明性.     

Development of the technical capabilities needed to build and position a prepolarization coil for a magnetic resonance imaging magnet

An experiment to show that a magnetic resonance imaging (MRI) magnet could be assembled around a patient, and used as part of a prepolarization system in which substantial transient forces are applied to parts of it, is described. The paper describes the circumstances that develop as a result of the application of the large transient fields used in this type of study, and outlines the reason for the tolerances that are permissible on the alignment of the system components. It then describes a test rig used to evaluate how the various problems might be overcome, and reports on the performance achieved with this rig. On the basis of this work, it appears that a system could be developed that would allow the application of these methods in clinical MRI.     

Back to the future: brake reaction times for manual and automated vehicles

Rear-end collisions are often quoted as being a major cause of road traffic accidents. In response to this, a great deal of ergonomics research effort has been directed towards the analysis of brake reaction times. However, the engineering solution has been to develop advanced systems for longitudinal control, which, it is argued, will mitigate the problem of rear-end collisions. So far, though, there have been few empirical studies to determine how brake reaction times will be affected by such vehicle automation. This paper presents a literature review summarizing the current state of knowledge about driver responses in non-automated vehicles. The review covers driver factors, vehicle factors and situational factors. Following the review, some empirical data are presented from a driving simulator experiment assessing brake reaction times of skilled and unskilled drivers under two different levels of automation. When compared to previous data gathered during manual driving, there seems to be a striking increase in reaction times for these automated conditions. Implications for the design and safety of automated vehicle systems are discussed.     

Visual lobe shape and search performance for targets of different difficulty

In quantitative models of visual search it has usually been assumed that visual lobe area shape was sufficiently regular to be approximated by a circle or ellipse. However, the irregularities in visual lobe shapes that have been found in studies involving extensive lobe mapping have suggested that lobe shape may have important implications for visual search performance and for the accuracy of mathematical models used for performance prediction. However, no systematic research on the relationship between the shape aspect of visual lobes and search performance seems to have been carried out and no comparisons of visual lobe shape characteristics under the effect of target difficulty have been reported. The current study was conducted to achieve two major objectives in two experiments. Experiment 1 used two different targets (letter 'O' and letter 'Y') to map the visual lobes of subjects in order to provide a systematic and quantitative comparison of lobe shape characteristics and experiment 2 was to investigate the correlation of visual lobe shape characteristics with visual search time under the effect of target difficulty. The visual lobes of 28 subjects were mapped on 24 imaginary and regularly spaced meridians originating from the centre of the visual field to resemble the full field mapping situation. Five categories of shape indices, viz. roundness, boundary smoothness, symmetry, elongation and shape regularity were investigated. The results of this study demonstrated that the visual lobe shapes of subjects elongate horizontally with medium level of roundness, high levels of boundary smoothness, symmetry and regularity for an easy target (O) against a homogeneous background of 'X's. When a difficult target (Y) was used, the visual lobes of the subjects were still elongated horizontally but to a smaller extent and with a low level of roundness, medium level of boundary smoothness and regularity and a similar high level of symmetry to the easy target. Moreover, significant correlations between shape indices and visual search time were found, suggesting mathematical models for predicting search time should not merely rely on area but also should consider visual lobe shape indices. Finally, a universal mathematical model containing several visual lobe shape indices was developed, which was applicable in the prediction of visual search time for a range of similar search tasks.     

增强现实技术在虚拟演播室系统中的应用

虚拟演播室是虚拟现实技术和视频合成技术相结合的产物,其场景是计算机生成的三维场景,由于人们对虚拟场景和复杂度的无限要求,使得场景的实时显示十分困难,使用基于图像的绘制技术构造虚拟空间能够较好地解决这个问题。在虚拟演播室中,演员需要与三维运动虚拟物体进行交互,运用增强现实技术,可以将三维虚拟物体与基于图象绘制的虚拟场景融合在一起。     

虚拟空间会议系统中视频合成技术的研究与实现

虚拟空间会议系统能够把所有与会者合成同一个虚拟会场中,从而构造一个能提供无缝的会场环境,眼神接触、凝视感知等普通多媒体会议系统不具备的虚拟协同工作环境。VST系统是我们刚刚完成的一个虚拟空间会议系统。视频合成技术是其实现的关键技术之一。本文介绍了VST系统中视频合成技术的研究与实现。     

一种基于区间约束的折半查找算法

针对变化范围很大而又相对稳定的查找对象,给出一种基于区间约束的折半查找算法。当后一个查找对象在前一个查找对象附近时,在最坏状态和平均状态下,该算法与标准的折半查找算法比较,其查找长度元旦显著减少,而且代价很小。此算法适合用于类似过程控制中的对低频信号的实时查有处理,并在国家级新产品WPJ－3微机频率事故记录装置和WQP－4微机频率继电器中得到了成功的应用。