基于Pro/ENGINEER的液压挖掘机设计集成与轻量化分析

本文分析了Pro／ENGINEER三维参数化设计流程，结合液压挖掘机的模型和组成特点，对其在参数化设计、装配与运动仿真、有限元分析与结构优化、轻量化设计等方面进行了深入剖析。通过此流程，可以提高液压挖掘机的设计效率，降低设计时间。文中完全摒弃了偏重参数化设计的思想，而是以液压挖掘机的实际问题为核心，该方案也适用于其他类似工程机械设备的研发。     

一种支持软件资源可信评估的框架

提出了一种支持软件资源可信评估的框架,并分析了该框架涉及到的技术,如证据收集、证据信任管理和可信评估等.阐述了该框架在北京大学软件资源库中的设计决策和实现方案,并给出一个详尽的实例分析.     

挖掘机摇臂机构运动仿真设计

本文以挖掘机摇臂机构为例,探讨在Pro／ENGINEER软件环境下,对挖掘机摇臂机构进行虚拟装配、运动仿真及动态分析,为挖掘机概念样机设计、制造方案的设计评估提供有效参考数据,从而提高其设计开发效率。     

挖掘机摇臂机构运动仿真设计

本文以挖掘机摇臂机构为例,探讨在Pro/ENGINEER软件环境下,对挖掘机摇臂机构进行虚拟装配、运动仿真及动态分析,为挖掘机概念样机设计、制造方案的设计评估提供有效参考数据,从而提高其设计开发效率。     

基于本体的主题爬虫的研究

主题网络爬虫是专业搜索引擎的重要组成部分,设计了一种基于本体的主题爬虫框架,使用领域本体来描述爬行主题,采用关键词提取技术确定网页主题,提出了基于领域本体的网页相关度计算的公式,实践证明基于本体的主题爬虫对网页提取的准确率大大提高。     

网络拓扑层次化安全评估综合熵权算法

提出了一种网络拓扑层次化安全评估框架, 并基于该框架设计了一种安全评估过程中风险因素权重计算方法. 该方法在传统的层次分析法的基础上进行了改进, 引入熵权法的概念并进行修正, 在实际运用过程中其计算结果更加合理, 为网络安全态势评估奠定良好基础.     

基于移动学习的学科主题学习资源设计研究

移动学习作为一种新型的学习方式正成为研究热点,而基于移动学习的学科主题学习资源相对缺乏。本文阐述了移动学习的概念及特点、主题学习、学科主题学习资源的理论基础,分析了基于移动学习的学科主题学习资源设计的基本原则,最后构建了基于移动学习的学科主题学习资源的设计框架。     

集成式房屋框架信息建模法的研究

以集成式房屋为研究对象,提出了集成式房屋的框架信息建模(FIM)方法。该方法融合了BIM与制造业设计建模方法,结合了自顶向下、参数化及模板建模等技术。并运用实例验证了集成式房屋的框架信息建模法的有效性,大大缩短了传统集成式房屋设计研发周期。     

面向企业信息化的数据质量评估研究

数据质量问题是企业信息化过程中面临的一项重要挑战,但针对数据质量评估的研究还缺乏足够的重视.文中从数据质量定义出发,阐述了数据质量的各个不同维度及其评估指标的确定,在对比分析已有成果的基础上给出了主观、客观两种评估方法,通过引入SOA上下文的可重用服务思想,设计了一种数据质量评估的服务框架,基于该框架对输入输出、流程管理、自动化评估等服务进行了阐述,并使用Web Services服务组件的形式实现了所有的功能需求.     

基于遗传算法的电路故障诊断超参数优化算法框架

针对基于SVM的模拟电路故障诊断中诊断参数的调节是通过试凑法或按照全局最优的原则确定的,没有考虑实际诊断要求,无法进行各诊断环节参数同时调整优化的现状。提出一种适应度模型用于遗传算法参数寻优,把实际电路诊断要求量化成参数指标引入模拟电路故障诊断的优劣评估中;建立了基于遗传算法的电路诊断模型参数闭环寻优框架,对诊断系统的各部分参数优化进行整体度量,并分析了参数搜索算法的收敛性。通过实例诊断分析了闭环故障诊断参数寻优框架下各部分的参数制定对决策的影响,说明了建立的闭环故障诊断模型参数寻优框架和搜索算法的有效性和实用性。     

Improving the performance of focused web crawlers

This work addresses issues related to the design and implementation of focused crawlers. Several variants of state-of-the-art crawlers relying on web page content and link information for estimating the relevance of web pages to a given topic are proposed. Particular emphasis is given to crawlers capable of learning not only the content of relevant pages (as classic crawlers do) but also paths leading to relevant pages. A novel learning crawler inspired by a previously proposed Hidden Markov Model (HMM) crawler is described as well. The crawlers have been implemented using the same baseline implementation (only the priority assignment function differs in each crawler) providing an unbiased evaluation framework for a comparative analysis of their performance. All crawlers achieve their maximum performance when a combination of web page content and (link) anchor text is used for assigning download priorities to web pages. Furthermore, the new HMM crawler improved the performance of the original HMM crawler and also outperforms classic focused crawlers in searching for specialized topics.     

Finding seeds to bootstrap focused crawlers

Focused crawlers are effective tools for applications requiring a high number of pages belonging to a specific topic. Several strategies for implementing these crawlers have been proposed in the literature, which aim to improve crawling efficiency by increasing the number of relevant pages retrieved while avoiding non-relevant pages. However, an important aspect of these crawlers has been largely overlooked: the selection of the seed pages that serve as the starting points for a crawl. In this paper, we show that the seeds can greatly influence the performance of crawlers, and propose a new framework for automatically finding seeds. We describe a system that implements this framework and show, through a detailed experimental evaluation, that by providing crawlers a seed set that is large and varied, they not only obtain higher harvest rates but also an improved topic coverage.     

主题网络爬虫研究综述

网络信息资源呈指数级增长,面对用户越来越个性化的需求,主题网络爬虫应运而生。主题网络爬虫是一种下载特定主题网页的程序。利用在采集页面过程获得的特定信息,主题网络爬虫抓取的页面都是与主题相关的。基于主题网络爬虫的搜索引擎以及基于主题网络爬虫构建领域语料库等应用已经得到广泛运用。首先介绍了主题爬虫的定义、工作原理;然后介绍了近年来国内外关于主题爬虫的研究状况,并比较了各种爬行策略及相关算法的优缺点;最后提出了主题网络爬虫未来的研究方向。关键词：     

网络爬虫性能研究

受到学习模型爬虫的启发,主题爬虫结合网页内容和链接信息来估计网页对给定主题的相关性,得到两个新型的爬虫变种。新型爬虫强调的不仅是有学习相关网页内容的能力,而且有引向相关网页的能力,并且在查找特定主题方面的能力有质的提高。     

The Viúva Negra crawler: an experience report

This paper documents hazardous situations on the Web that crawlers must address. This knowledge was accumulated while developing and operating the Viúva Negra (VN) crawler to feed a search engine and a Web archive for the Portuguese Web for four years. The design, implementation and evaluation of the VN crawler are also presented as a case study of a Web crawler design. The case study tested provides crawling techniques that may be useful for the further development of crawlers. Copyright © 2007 John Wiley & Sons, Ltd.     

Mercator: A scalable,extensible Web crawler

This paper describes Mercator, a scalable, extensible Web crawler written entirely in Java. Scalable Web crawlers are an important component of many Web services, but their design is not welldocumented in the literature. We enumerate the major components of any scalable Web crawler, comment on alternatives and tradeoffs in their design, and describe the particular components used in Mercator. We also describe Mercator's support for extensibility and customizability. Finally, we comment on Mercator's performance, which we have found to be comparable to that of other crawlers for which performance numbers have been published.     

Petri net modules in the transformation-based component framework

Component-based software engineering needs to be backed by thorough formal concepts and modeling techniques. This paper combines two concepts introduced independently by the two authors in previous papers. On one hand, the concept of Petri net modules introduced at IDPT 2002 in Padberg [J. Padberg, Petri net modules, Journal on Integrated Design and Process Technology 6 (4) (2002) 105–120], and on the other hand a generic component framework for system modeling introduced at FASE 2002 in Ehrig et al. [H. Ehrig, F. Orejas, B. Braatz, M. Klein, M. Piirainen, A generic component concept for system modeling, in: Proceedings of FASE ’02, Lecture Notes in Computer Science, vol. 2306, Springer, 2002]. First we develop a categorical formalization of the transformation based approach to components that is based on pushouts. This is the frame in which we show that Petri net modules can be considered as an instantiation of the generic component framework. This allows applying the transformation based semantics and compositionality result of the generic framework to Petri net modules. In addition to general Petri net modules we introduce Petri net modules preserving safety properties which can be considered as another instantiation of pushout based formalization of the generic framework.     

Learning support environments: Rationale and evaluation

In this paper we argue that existing understanding of human cognition has much to offer the design of instructional systems and materials, and that new technologies, such as hypertext, in harness with traditional techniques, provide opportunities for extending the mapping of cognitive principles to instructional design. Following a review of types of knowledge, cognitive styles and strategies within a CAL framework, the advantages of learning support environments over other CAL approaches are discussed. Such environments are presented as extensions to hypertext which incorporate various generic features for learning applications. The need for evaluation of learning which is dynamic and internal to the learning tasks is stressed.     

A Generic P/T Net Model and Framework for Concurrent Integrated Design and Planning of Electromechanical Assemblies

This paper describes a new unified formal modeling framework based on generic place/transition nets (PTNs) for concurrent integrated design and planning of electromechanical assemblies. First, a generic PTN model is defined as an abstract (meta)class of all types of PTNs. Then, an integrated object modeling framework is proposed for capturing and representing information and knowledge in the assembly design and planning processes based on the defined generic PTN modeling language and formalisms. The proposed integrated assembly model with the generic PTNs can uniformly represent the causal relations at the assembly level, the operation level, and the feature-based single-part level through the data abstraction of components and connectors on various levels of integrated assembly design and planning. An assembly model compatible with the STandard for the Exchange of Product model data (STEP, officially ISO 10303) is also built with the generic PTNs. To validate the proposed modeling framework, a prototype system has been developed, and a case study on gearbox assembly design and planning is provided.