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101.
传统的形状及位置表示模型通常是建立在低层次的无应用意义的几何拓扑元素之上,因而无法很好地支持计算机辅助设计(CAD)向实用化和智能化方向发展。本文提出了一种非数值化的基于约束的产品形位描述模型,并对该模型中存在的一些问题进行了深入的讨论。该模型符合设计人员实际设计思维与过程,同时也支持高层次产品设计信息以及产品的设计过程信息,因而为传统CAD系统向新一代实用化智能化CAD系统过渡提供了一个良好的产品形位表示模型。 相似文献
102.
Improved wetland remote sensing in Yellowstone National Park using classification trees to combine TM imagery and ancillary environmental data 总被引:6,自引:0,他引:6
The U.S. Fish and Wildlife Service uses the term palustrine wetland to describe vegetated wetlands traditionally identified as marsh, bog, fen, swamp, or wet meadow. Landsat TM imagery was combined with image texture and ancillary environmental data to model probabilities of palustrine wetland occurrence in Yellowstone National Park using classification trees. Model training and test locations were identified from National Wetlands Inventory maps, and classification trees were built for seven years spanning a range of annual precipitation. At a coarse level, palustrine wetland was separated from upland. At a finer level, five palustrine wetland types were discriminated: aquatic bed (PAB), emergent (PEM), forested (PFO), scrub-shrub (PSS), and unconsolidated shore (PUS). TM-derived variables alone were relatively accurate at separating wetland from upland, but model error rates dropped incrementally as image texture, DEM-derived terrain variables, and other ancillary GIS layers were added. For classification trees making use of all available predictors, average overall test error rates were 7.8% for palustrine wetland/upland models and 17.0% for palustrine wetland type models, with consistent accuracies across years. However, models were prone to wetland over-prediction. While the predominant PEM class was classified with omission and commission error rates less than 14%, we had difficulty identifying the PAB and PSS classes. Ancillary vegetation information greatly improved PSS classification and moderately improved PFO discrimination. Association with geothermal areas distinguished PUS wetlands. Wetland over-prediction was exacerbated by class imbalance in likely combination with spatial and spectral limitations of the TM sensor. Wetland probability surfaces may be more informative than hard classification, and appear to respond to climate-driven wetland variability. The developed method is portable, relatively easy to implement, and should be applicable in other settings and over larger extents. 相似文献
103.
Jacobo de Uña-Álvarez 《Computational statistics & data analysis》2007,51(5):2653-2669
A new model for cross-sectional lifetime data is presented. The model is based on the length-bias assumption, and it is adapted to situations in which several types of censoring may occur. The NPMLE of the survival function is derived. An EM-algorithm to approximate the NPMLE is devised. The performance of the introduced estimator is investigated through simulations. A real set of data collected as part of a study on unemployment duration in Spain is used for illustration purposes. 相似文献
104.
Joel 《Journal of Parallel and Distributed Computing》2005,65(12):1601-1606
Lee and Batcher have designed networks that efficiently merge k separately provided sorted sequences of known lengths totalling n. We show that the design is still possible, and in fact easier to describe, if we do not make use of the lengths, or even the directions of monotonicity, of the individual sequences—the sequences can be provided in a single undelimited concatenation of length n. The depth of the simplest resulting network to sort sequences that are “k-tonic” and of length n is , generalizing Batcher's 1968 results for the extreme values of k (k=2 corresponding to merging, and k=n/2 corresponding to general sorting).The exposition is self-contained and can serve even as an introduction to sorting networks and Batcher's results. 相似文献
106.
包钢医疗保险信息管理系统的构建 总被引:1,自引:1,他引:0
本文论述了包钢医疗保险信息管理系统的网络设计、应用程序功能及主要技术,并说明了应用情况及使用价值. 相似文献
107.
一种基于时间分层决策矩阵的综合评价算法 总被引:1,自引:0,他引:1
综合评价系统用四元总体(A,Z,X^(k),D)表示,其中决策矩阵X^(k)是具有对象维i,指标维j,时间维k的三维矩阵,将三维矩阵X(k)按时间划分形成m个二维矩阵,每个二维矩阵分别代表每个年度n个评价对象对应于p个指标的属性集,讨论了按时间分层决策矩阵的多指标综合评价问题,描述了按时间分层的决策矩阵的求解算法,并采用Visual Foxpro数据库语言编程实现。 相似文献
108.
计算机网络的发展日新月异。下一代计算机网络(NGN)的探讨、研究已经成为当前的潮流。下一代网络是目前电信、互联网运营商和设备厂商都在讨论的热点技术,国内外许多网络运营商都在探讨,并正在或考虑建设试验网进行更深入的研究。本文介绍了NGN的定义、主要特点、分层结构和关键技术。 相似文献
109.
We explore in this paper the efficient clustering of market-basket data. Different from those of the traditional data, the features of market-basket data are known to be of high dimensionality and sparsity. Without explicitly considering the presence of the taxonomy, most prior efforts on clustering market-basket data can be viewed as dealing with items in the leaf level of the taxonomy tree. Clustering transactions across different levels of the taxonomy is of great importance for marketing strategies as well as for the result representation of the clustering techniques for market-basket data. In view of the features of market-basket data, we devise in this paper a novel measurement, called the category-based adherence, and utilize this measurement to perform the clustering. With this category-based adherence measurement, we develop an efficient clustering algorithm, called algorithm k-todes, for market-basket data with the objective to minimize the category-based adherence. The distance of an item to a given cluster is defined as the number of links between this item and its nearest tode. The category-based adherence of a transaction to a cluster is then defined as the average distance of the items in this transaction to that cluster. A validation model based on information gain is also devised to assess the quality of clustering for market-basket data. As validated by both real and synthetic datasets, it is shown by our experimental results, with the taxonomy information, algorithm k-todes devised in this paper significantly outperforms the prior works in both the execution efficiency and the clustering quality as measured by information gain, indicating the usefulness of category-based adherence in market-basket data clustering. 相似文献
110.