反向工程中三角网格的加工特征识别

为实现反向工程中的特征重构,提出一种在三角网格上由Morse-Smale复形转换为分割面属性邻接图进行加工特征提取的算法.首先通过移动最小二乘曲面法计算网格顶点曲率,构建曲率特性指标函数,消除因网格连接引起的误差,达到降噪的作用;然后在三角网格上建立和简化Morse-Smale复形,精确提取特征线,将网格分割为边界清晰连续的区域,并获得各区域的邻接关系;最后判断关键点和特征线的性质,将Morse-Smale复形直接转换为分割面属性邻接图进行加工特征识别.实验结果表明,该算法准确、高效,而且不需要人工干预,对于反向工程中大规模、带噪声的网格具有较好的识别效果.     

草地场景真实感模拟技术综述

草体作为自然场景的一种重要组成元素,其数量众多、覆盖范围广,因此很难实现实时绘制,大规模草地场景真实感模拟已成为计算机图形学中研究的热点和难点之一.文中对20多年来草地场景真实感模拟技术的发展情况进行综述,分别从绘制技术、LOD表达、动态模拟以及业界现状等几个方面做了比较深入的介绍,分析并比较了一些典型方法的基本原理和优缺点;最后对该领域未来的发展趋势进行了展望.     

模拟器在嵌入式软件开发中的应用实现

嵌入式系统在电子产品中的应用,加快了电子产品更新换代的速度,要想在技术竞争中立于不败之地,唯有加快应用软件开发进程,缩短产品开发周期.模拟器在嵌入式系统应用软件开发中的使用,大大简化了软件调试过程.本文基于μ C/OS-II嵌入式实时操作系统,研究开发出一款利用模拟器进行应用软件开发的多媒体播放器智能菜单,具有很大的实际应用价值,加快了产品的开发速度,增加了产品的核心竞争力.     

人体心脏的4维图像建模和参数分析

研究一种基于4维医学图像的活动形状模型方法,用于构建人类心脏的3维柔性模型并进行自动化参数分析,以得到心脏各方位的量化功能指标。首先,通过造影技术获取心脏周期内各时刻的立体图像,根据时间序列形成一组4维图像。在大量医学图像的基础上,用统计方法分析得到心脏的一般形状,局部的变化范围和分布概率密度,为人类心脏建立一个数字化的计算模型。在此基础上,针对具体病人进行图像分割和形状拟合以计算其心脏静态和动态形状参数,然后分析得到与心脏功能相关的一些重要参数。研究内容包括心脏模型的建立,心脏静态参数分析,心脏动态功能分析,疾病分析等,对病人心脏在特定时刻的每组图像生成其3维结构模型,为医生提供丰富有力的诊断和治疗依据。     

基于局部规划的三维航迹规划方法

研究飞行器航迹是选择最优航线问题,针对三维航迹规划中搜索空间大、计算时间长的问题,为缩短搜索时间,获得最优航迹,提出了一种基于A<'*>算法并结合局部规划的三维航迹规划方法.方法首先对A<'*>算法中的当前待扩展节点在局部规划空间中确定几个最有希望的扩展节点,再将其与A<'*>算法相结合,最后对局部规划算法过程中的不足,通过地形标记和加入树搜索深度惩罚做出改进,有效地减小了搜索空间,缩短了搜索时间,并在搜索过程中充分利用地形信息,使算法生成的航迹能够避开大的地形障碍,而且能够充分利用有利的地形.在实际地形数据中进行的实验表明方法能快速、有效地规划出理想优化的航迹.     

Testing the equality of proportions for correlated otolaryngologic data

In otolaryngologic (or ophthalmologic) studies, each subject usually contributes information for each of two ears (or eyes), and the values from the two ears (or eyes) are generally highly correlated. Statistical procedures that fail to take into account the correlation between responses from two ears could lead to incorrect results. On the other hand, asymptotic procedures that overlook small sample designs, sparse data structures, or the discrete nature of data could yield unacceptably high type I error rates even when the intraclass correlation is taken into consideration. In this article, we investigate eight procedures for testing the equality of proportions in such correlated data. These test procedures will be implemented via the asymptotic and approximate unconditional methods. Our empirical results show that tests based on the approximate unconditional method usually produce empirical type I error rates closer to the pre-chosen nominal level than their asymptotic tests. Amongst these, the approximate unconditional score test performs satisfactorily in general situations and is hence recommended. A data set from an otolaryngologic study is used to illustrate our proposed methods.     

Thermodynamic modeling of the Na–Al–Ti–H system and Ti dissolution in sodium alanates

Thermodynamic assessments were made to optimize thermodynamic models and parameter fits to selected experimental and first principles hypothetical predicted phase data within the Na–Al–Ti–H system. This enabled thermodynamic modeling of Ti solubility within the sodium alanates: NaAlH₄ and Na₃AlH₆, and the relative stability of Ti-bearing phases. The modeling provides insights into the role of Ti originating from Ti-based activating agents commonly referred to as ‘catalysts’ in promoting reversibility of the Na–Al–H dehydrogenation and rehydrogenation reactions under moderate temperature and pressure conditions relevant to H storage applications. Preliminary assessments were made to evaluate H solubility in bcc-Ti and hcp-Ti, and stability of the hydride δ-TiH₂. To model possible Ti dissolution in NaAlH₄ and α-Na₃AlH₆, sub-lattice models were applied. A repulsive interaction is predicted by first principles calculations when Ti is dissolved in NaAlH₄ or α-Na₃AlH₆, which becomes stronger with increasing temperature. Although Ti is virtually insoluble in NaAlH₄ or α-Na₃AlH₆, a small addition of TiCl₃ will induce a thermodynamic driving force for formation of TiH₂ and/or TiAl₃. The addition of pure Ti shows a weaker effect than TiCl₃ and leads to formation of TiH₂ only. Based on a combined interpretation of present thermodynamic modeling and prior experimental observations, the TiAl₃ and TiH₂ phases are ascribed to have a catalytic effect, not a thermodynamic destabilization effect, on the reversibility of the dehydrogenation/rehydrogenation reactions in the Na–Al–H system.     

代理服务器的组建、维护与管理技术

代理服务器是实现多个用户使用一条外网线同时访问互联网络不可缺少的组成部分,文章结合计算机网络专业课程的教学与实践,分别介绍了代理服务器的作用、配置、组建和维护与管理技术与技巧,是网络技术人才培训的一个实训项目。     

危险化学品流域污染模拟

危险化学品的流域污染关系到社会安全的重大问题.本论文二次开发CE-QUAL-W2,得突发性流域污染模型.通过建立二维水力学模型及二维水质模型,运用数值计算方法,自动计算水力学变量,快速应急模拟危险化学品造成的流域污染.同时,作者利用收集到的信息,模拟吉林双苯厂爆炸造成的松花江的流域污染,结果基本达到迅速、直观的应急反应要求,表明模型有效.     

基于重要目标区的三维地形快速渲染方法

三维地形的显示需要绘制大量的三角形网格,为了提高地形显示速度目前广泛采取了三角形网格简化技术。针对弹道导弹作战区域地形的特殊性,提出了一种基于重要目标区的网格简化方法。从BMP位图读取地形高度信息,以四叉树保存网格数据,按照区域重要性静态确定地形网格疏密程度。并采用DirectX平台,实现了导弹战区三维地形显示,提高了渲染效率。