精密镗削头振动模态的实验研究

通过对国产与进Ｄ的同类型精密镗削头振动模态实验研究，找出了这两种精密镗削头的固有振动频率，给出了它们的各阶动画振型图．从这一侧面解释了国产精密镗削头回转精度偏低的原因。     

CNC系统中任意三维椭圆弧的高速插补新方法

本文根据两步递归插补的思想,导出了任意三维椭圆弧高速插补的公式和算法.它是空间圆弧高速插补方法在三维椭圆弧的情况下进一步推广应用.本文最后还对插补算法进行了稳定性分析和误差分析.     

一种基于B/S的农业资源综合数据服务系统──通用农业资源数据服务系统开发设计

基于浏览器 /服务器 (B/S)结构的通用农业资源数据库系统 ,将农业统计中常用的 5 0 0多个技术指标分成三大类 ,17个小类 ,基本涵盖了农业生产和管理统计的主要领域 普通用户通过浏览器实现对数据库的组合查询或浏览 ,也可将数据文件下载 系统提供了 9种统计分析方法以及 5种预测方法 ,授权用户可进行数据文件上载 管理员通过浏览器可对数据库进行管理维护     

偏心因子数据的计算方法研究进展

从偏心因子(acentric factor)的定义出发，分析了ω数据的确定方法和获取数据的手段，评述了国内外ω计算方法的近期进展，包括对应态蒸气压关联方程法、对应态基团贡献法(CSGC)、图论法及拓扑法等，指出了各种方法的优缺点及最新的计算发展方向。     

一阶线性非齐次微分方程求解方法的讨论和一个简化的求解方法

本文证明了一阶线性非齐次微分方程y＇+P(x)·y=f(x)三个求解方法:参数变易法、积分公式、积分因子法之间的等同关系.从参数变易法中引出一个简化的积分公式.事实上此公式恰是对用参数变易法解高阶线性非齐次微分方程时对n=1的拓广.最后以实例验证此公式的简易.     

关于矩阵条件数的一些结论

本文讨论了一些矩阵范数达到极小的充要条件,其主要结果如下:1.设?为m×n实矩阵,且具有n个线性无关的列,则求?广义逆谱条件数等于1的充要条件为?=cI,其中c为正常数.2.设?为n阶非异实矩阵,则矩阵A的求逆p-范数条件数等于1的充要条件为A=cpσ,其中c为正常数,σ是置换阵,其对角元都等于 1或-1.3.设?为n阶非异实矩阵,则矩阵4的求逆F-范数条件数等于1的充要条件为?=cU,其中c为正常数,U为正交阵.     

An ERP study for the degrees of the difficulty in visual search

The present study mainly probed the relationships between ERP components and the degrees of difficulty in visual search. Three experimental and one controlled conditions were randomly selected. Results showed that the P1, N1, and P2 amplitudes and latencies had no significant differences among the three experimental and one controlled conditions, and the ERP waveforms of low perceptual load of visual search were different from that of high perceptual load. These results might indicate that the latencies and amplitudes of initial P1, N1 and P2 in high and low perceptual load conditions were almost the same. The ERP waveforms of parallel search were very different from that of serial search, and the ERP waveforms of serial search were very similar. The P3 amplitudes increased as the degrees of the difficulty in visual search decreased.     

基于改进 HAF的线性调频雷达信号参数估计

针对多项式相位信号(PPS)中的线性调频(LFM)雷达信号参数估计,通过提出频谱方差极大值准则对PPS次优参数估计方法高阶模糊度函数(HAF)进行了改进,提出了适于单分量LFM参数估计的改进HAF。首先讨论了HAF对LFM参数的估计方法及其局限性,然后提出了分段频谱方差极大值法则下LFM调频斜率估计的方法,将其与HAF相结合提出了单分量LFM参数估计的改进HAF,克服了接收信号与实际信号起点不一致性对HAF带来的影响,降低了由于HAF局限性带来的调频斜率估计误差,改善了HAF的累积误差效应。MATLAB仿真验证了改进方法较HAF的优越性。     

一个可靠指标计算公式的误差分析

对美国桥梁设计规范中计算可靠指标的一个公式进行分析,认为该公式是近似的,并指出了其近似的原因。分别采用该公式和蒙特卡罗法计算可靠指标,计算结果表明该公式的误差高达30%,远远超出工程容许范围。因此在工程上应用该公式进行可靠指标计算是不合适的。     

Picturing the moon: Hevelius’s and Riccioli’s visual debate

This article investigates the maps of the moon produced in the mid-seventeenth century by Jesuit Giambattista Riccioli (1598-1671) and Johannes Hevelius (1611-1687), whose cartographic projects competed for widespread acceptance. Although Hevelius’s Selenographia (1647) was applauded for its many detailed, self-engraved pictures of the moon, his cartography and proposed nomenclature were supplanted by Riccioli’s as offered in Almagestum novum (1651), in spite of the latter’s simplistic pictures and promotion of geocentric cosmology. Exploring this paradox through pictorial analysis, three types of images common to both Selenographia and Almagestum novum are compared, employing an analytical tool developed by Svetlana Alpers in The art of describing (1983). A focus on this debate exposes the tensions evoked by new technologies of vision and competing cultures of visual epistemology in seventeenth-century astronomy. As both selenographers grappled with questions about the role of representation and what kinds of knowledge could be generated visually, the successes and failures of their competing projects present implications for the course of visual astronomy, as well as for our understanding of the use of ‘visual technologies’ in a period of controversy.