Understanding the implications of view update policies

Database views are traditionally described as unmaterialized queries, which may be coincidentally updatable according to some fixed criteria. One of the problems in updating through views lies in determining whether a given view modification can be correctly translated by the system. To define an updatable view, a view designer must be aware of how an update request in the view will be mapped into updates of the underlying relations. Furthermore, because of side effects, the view designer must also be made aware of the effects of isolated updates back into the view.To address this problem, we present a general algorithm that predicts the effects of arbitrary mapping policies. Given an update policy, this algorithm indicates whether a desired update will, in fact, occur in the view and describes all possible side effects it may have, documenting the conditions under which they occur. The algorithm subsumes the results obtained by other view design tools, and generalizes their use to encompass a larger class of views.This work was supported in part by grant A9292 from the Natural Sciences and Engineering Research Council of Canada and by scholarship 200 398/80 from Conselho Nacional de Desenvolvimento Cientifico e Tecnologico-CNPq, Brasil.     

高码速率QPSK解调载波恢复的原理与仿真

QPSK调制解调是高码速率数传系统的关键技术,载波恢复环和位定时技术的性能直接影响解调的性能。论文重点研究了一种改进型COSTAS环和并行处理技术,并在高码速率下通过System View进行系统仿真,仿真结果表明,载波恢复方法具有较好的误码率性能及抗噪声性能高等优点。     

基于MVC的医院信息管理系统设计与开发

近些年随着互联网技术的不断更新,医疗资源也加速了信息化。医院信息化作为一种解决传统医疗问题弊端的方法,也获得了大量的关注。本文基于模型 视图 控制器(model view controller)设计了开放式医院信息管理系统医疗网站,其使用Java语言,Mysql做为后台数据库。完成了系统的前台设计和数据库的设计,最后经测试具有一定可靠性和稳定性。     

基于DEM的GIS地形分析的实现方法研究

基于DEM,并结合实际系统的建立工作,探讨了实现GIS中高精度且实用有效地形分析功能的主要方法和步骤,以及相应的辅助手段。     

虚拟实景对象建模与表现

虚拟对象是指物体的数字化外观仿真模型,与基于图形的虚拟对象相比,基于图像的虚拟对象具有绘制速度与物体复杂度无关、实时性强、可轻易达到相片级的视觉表现效果以及建模简单等特点,在许多领域都具有广泛的应用前景.传统的基于图像的虚拟对象建模需已知相机参数或图像深度信息,建模繁琐复杂.针对该问题,提出一种可实用的基于图像的虚拟对象简化模型--虚拟实景对象,对该模型建模只需围绕待建模物体周围采集一圈实景图像,无需已知相机参数或图像深度信息,表现时则采用视图合成方法来合成未采集图像视点的虚拟视图,从而实现对物体的连续自由观察.实验结果表明,该方法不仅建模过程简单,而且可以实现对虚拟对象的360度连续自由操纵.     

Bilayer representation for three dimensional visual communication

This paper proposes a bilayer representation of scene consisting of foreground and background. It uses two layers to represent foreground and background, respectively. Unlike previous layer-based approaches, both layers cover the whole region instead of interested regions. Based on the bilayer representation, bilayer stereo matching, view synthesis approach and foreground/background separation algorithm are developed for three dimensional visual communication. They all consist of two steps: recovery of disparity fields of both layers and composition of these disparity fields; synthesis of images of both layers and composition of these images; computation of two layer costs and separation of foreground and background. Experimental results demonstrate that both high quality and high efficiency are achieved by above approaches. They meet the requirements of desktop-based three dimensional visual communication.     

Joint video/depth rate allocation for 3D video coding based on view synthesis distortion model

Joint video/depth rate allocation is an important optimization problem in 3D video coding. To address this problem, this paper proposes a distortion model to evaluate the synthesized view without access to the captured original view. The proposed distortion model is an additive model that accounts for the video-coding-induced distortion and the depth-quantization-induced distortion, as well as the inherent geometry distortion. Depth-quantization-induced distortion not only considers the warping error distortion, which is described by a piecewise linear model with the video power spectral property, but also takes into account the warping error correlation distortion between two sources reference views. Geometry distortion is approximated from that of the adjacent view synthesis. Based on the proposed distortion model, a joint rate allocation method is proposed to seek the optimal trade-off between video bit-rate and depth bit-rate for maximizing the view synthesis quality. Experimental results show that the proposed distortion model is capable of approximately estimating the actual distortion for the synthesized view, and that the proposed rate allocation method can almost achieve the identical rate allocation performance as the full-search method at less computational cost. Moreover, the proposed rate allocation method consumes less computational cost than the hierarchical-search method at high bit-rates while providing almost the equivalent rate allocation performance.     

浅析时空观变化及其对建筑学的影响

本文对近代以来三种主要的时空现作了分析,简要阐述了绝对-相对主义时空观,康德-后康德时代时空观、信息-后信息时代时空观对建筑学的影响。是后提出后信息时代建筑学被卷入＂个人主义＂与＂总体性制度＂ 的矛盾而激发新的活力。     

View factor calculation using the Monte Carlo method for a 3D strip element to circular cylinder

The discussion includes the application of the Monte Carlo method to determine view factor for the plate including strip elements to circular cylinder as a case in heating and cooling processes in material processing. The results involving the relationships between different discretization schemes, number of rays used for the view factor calculation, CPU time and accuracy are presented. The analysis also displays the differences between the numerical results obtained and analytical solutions for the 20, 30 and 45 element discretized figures and for (30⁴), (50⁴) and (70⁴) rays per element. The results obtained from the Monte Carlo solution indicate that smaller elements require more effort to obtain an accurate view factor.     

重庆园林地域特色研究刍议

在对重庆园林进行广泛深入的调查研究和分析比较的基础上,本文第一次概括出重庆园林的地域特色,即:其文化内涵特色表现为历史纪念园林,其景观构成特色表现为自然山水园林,其社会归属特色表现为城镇公共园林。其中山顶园林、巨石园林和城镇公共园林是重庆园林对中国园林的独特贡献。本文认为,重庆园林所蕴涵的雄阔气象、自然风格和公共精神,将成为中国园林开创新境界的强劲动力。