基于卷积型原理的时空样条元

结构动力分析是工程设计中的重要组成部分,传统动力分析不能全面反映动力初值特征,而Gurtin变分原理则被认为是目前唯一能全面反映动力初值特征的变分原理.本文以Gurtin变分原理为基础,空间和时间上同时采用样条元,建立了计算梁的动力初值问题的样条元法。算例表明, 与现有的分析方法相比,本文具有更高的精度。     

计算机集成制造系统中的仿真技术

经验和分析表明,仿真技术已成为 CIMS 设计、分析、运行和鉴定的有力工具.另一方面,CIMS 中仿真技术的应用对仿真技术的发展也提出了新的挑战,从而必将进一步推动仿真技术自身的发展和完善.本文主要包括以下几部分内容:(1)概述面向 CIMS 的仿真建模方法学:包括常用的面向进程和事件的建模、Petri 网、Petri 网与知识基组合方法及面向对象建模方法等;(2)对仿真语言面向 CIMS 的发展提出了若干建议;(3)将并发工程概念引入仿真领域,提出一种并发仿真工程环境新建议;(4)讨论了知识系统与仿真技术的结合,给出了作者开发的 FMS 专家系统实例,并进一步讨论了其应用现状及存在的问题;(5)阐述了仿真优化技术在 CIMS 仿真中的作用以及有待解决的问题;(6)讨论了 CIMS 中的嵌入式仿真技术.     

设置障碍物密闭容器内气体爆炸数值模拟

运用均相反应流时均方程组、湍流模型k-ε、EBU-Arrhenius燃烧模型和SIMPLEC算法,对密闭容器二维空间内丙烷-空气的爆燃过程进行数值求解。计算结果反映了障碍物对火焰阵面、速度场、流场、爆炸压力以及爆炸强度的影响,得到了爆炸压力和爆炸强度与可燃气体摩尔分数之间的关系。     

如何加强设计阶段工程造价的有效控制

简述了工程造价控制的概念意义,分析了设计阶段的工作现状及存在的问题,针对设计阶段工程造价的有效控制提出了几点建议,并对其进行了详细阐述,从而有效地控制工程造价。     

STFT与SOPC技术相结合实现高速跳频图案的识别与跟踪

本文根据频率跟踪式干扰的基本原理,提出一种基于短时傅里叶变换 (STFT)的高速跳频图案的识别与跟踪方案,并采用可编程芯片系统 (SOPC)技术进行了硬件实现。理论分析与实测结果表明,该系统实现 1024点的STFT仅需 84μs,可对 10 000跳 /秒以下的高速跳频图案实时识别与跟踪。     

空时分组码的自适应调制

本文讨论了空时分组码的自适应调制技术.在接收端分集合并后的等效信道模型下,通过对自适应STBC信道容量的讨论证明了随着天线数的增加,自适应调制的重要性降低.之后针对二发一收的低价分集系统,讨论了其STBC基础上的自适应调制技术,同时给出了离散功率离散速率自适应调制区间端点的封闭解.     

轧机万向接轴铜滑块的铸造

介绍轧机万向接轴铜滑块的铸造生产工艺。实践证明 ,本工艺方案铸造的铜滑块质量完全合格     

Changes in carotenoid intake in the United States: the 1987 and 1992 National Health Interview Surveys

OBJECTIVES: To assess the changes in carotenoid intake between 1987 and 1992 among US adults by sociodemographic characteristics and high-risk groups for chronic disease; and to identify the dietary sources of specific carotenoid intake. DESIGN: A food frequency questionnaire (FFQ) was collected from a representative sample of respondents to the 1987 and 1992 National Health Interview Surveys throughout two calendar quarters. Black and white adults, 18 to 69 years old, participated in 1987 (n = 8,161) and 1992 (n = 8,341). METHOD: FFQ data were matched and linked to the US Department of Agriculture-National Cancer Institute carotenoid food composition database for analysis. STATISTICAL ANALYSIS: Mean differences in carotenoid intake over time were compared by sociodemographic characteristics and region of the country, after adjustment for sampling weights in a multiple linear regression model. RESULTS: Mean intake of the carotenoid lutein declined among white women (18%), among adults aged 40 to 69 years (16%), among persons with 9 to 12 years of education (11%), among nondrinkers (18%), among drinkers of 1 to 6 alcoholic drinks/ week (7%), among smokers (former smokers by 11%, current smokers by 7%, and never smokers by 9%), among income groups (< $20,000 by 7%, > or = $20,000 by 9%), and residents in the south and northeast (by 13% each, respectively). Mean intake of the carotenoid lycopene increased among white men (9%), among adults aged 18 to 39 years and aged 40 to 69 years (by 5% and 6%, respectively), among those with 13 years of education or more (12.5%), among alcohol drinkers (by 10% and 7% for 1 to 6 vs 7 or more drinks/week, respectively), among former and current smokers (by 6% each), among those with incomes > or = $20,000 (8%), and among residents in the west (16%) and midwest (5%). All differences described were statistically significant (P < .01). APPLICATION: The decline in lutein intake (from dark green leafy vegetables), particularly in white women, may have public health implications as a result of the recognized inverse association between carotenoid intake and disease risk.