容许参数变换下曲线和曲面的几何不变量     

王恒斌  郭亚梅 《安阳师范学院学报》2013,(5):25-29

空间曲线和曲面的几何量的计算均依赖于所选参数.本文从参数变换的角度,较详细讨论了曲线的弧长、曲率、挠率及曲面上两方向的夹角、曲面的面积、曲面的曲率等都与坐标参数的选取无关.这反映了曲线与曲面的几何性质不依赖于参数的选取.  相似文献   

Positivity and quality of college life of business students: The mediating role of learning approaches     

《Studies in Educational Evaluation》2020

Drawing upon the causal agency theory, this study examined the direct and indirect (via learning approaches) links between positivity and quality of college life (QCL) of business students in a transitioning market, Vietnam. Two studies were conducted to test these relationships using structural equation modeling. Findings from study 1, based on a sample of 428 business students, showed that positivity was positively related to QCL. Further, deep learning approaches mediated the relationship between positivity and QCL. Findings from study 2, based on a sample of 416 business students, reconfirmed the role of positivity in QCL. However, the indirect relationship between positivity and QCL was not significant, demonstrating that surface learning approaches did not mediate the relationship between positivity and QCL. The findings contribute to the literature on positivity in higher education by confirming the overarching role that positivity plays, directly and indirectly (via deep learning approaches), in QCL.  相似文献   

面模型与球壳模型下的电场强度     

孟波 《安顺师范高等专科学校学报》2008,10(5):95-96

通过采用面模型与球壳模型对均匀带电球面处的电场强度的计算与分析,揭示了其场强分布与所采用的物理模型的依赖关系,指出两种模型下谈及球面处的场强均有实际意义。  相似文献   

中国月平均地表反照率的估算及其时空分布   总被引：12，自引：1，他引：12  

蔡福  祝青林  何洪林  刘新安  于贵瑞 《资源科学》2005,27(1):114-120

本文利用1948年～2003年55年平均的NCEP/NCAR(National Center for Environmental Prediction/National Center for Atmospheric Research,美国国家环境预报中心/美国国家大气研究中心)再分析辐射资料和中国10km×10km土地利用类型图,借助GIS、GrADS(Grid Analysis and Display System,网格分析与展示系统)等空间化技术,采用图形回归处理等方法建立了国家尺度的10km×10km的中国地表月平均反照率栅格图.研究表明,估算的地表反照率的季节变化十分明显:冬季(1月)最大,夏季(7月)最小,春秋季(4月和10月)次之,且秋季比春季稍大;空间分布与地理纬度、地势高低和距海远近关系很大,西部地区大于东部地区,北部地区大于南部地区,高海拔地区大于丘陵和平原地区.几种土地覆被类型反照率的估计值如下:林地、水稻和小麦地为0.17～0.23;草地为0.20～0.32;雪被为0.44～0.76;沙漠为0.35左右.总的来说,估算结果比较合理,能够较好地反映出中国地表反照率的时间、空间变化特征,也能反映多年气候平均值的特点.因此,在目前气候要素之一的多年平均的地表反照率研究较少的情况下,利用多年平均NCEP/NCAR再分析资料与土地利用类型图进行回归处理不失为是一种相对合理的方法.  相似文献   

Intersections of two offset parametric surfaces based on topology analysis     

欧阳应秀  唐敏  林军呈  董金祥 《Journal of Zhejiang University. Science. B》2004,(3)

INTRODUCTIONTheOSSI(OffsetSurface/SurfaceIntersection)problemisasub-problemofgeneralSSI.AlthoughtheOSSIproblemcanberesolvedbyapplyinggeneralSSIalgorithm,itiscomputationallyexpensiveandexhaustive.Inrecentdecades,effortshavebeenfocusedoncomputingSSIexactly,efficiently,androbustlyinageneralsetting(Abdel-MalekandYeh,1997;Changetal.,1994;BurkeandSabharwal,1996;Mullenheim,1991).Thesetechniquescanbeclassifiedmainlyintofivecategories:algebraic,latticeevaluation,marching(tracing)method,…  相似文献   

Science Letters：Mask synthesis and verification based on geometric model for surface micro-machined MEMS     

李建华刘玉生  高曙明 《浙江大学学报(A卷英文版)》2005,6(9):1007-1010

INTRODUCTION When designers develop microelectromechani- cal system (MEMS) devices with the traditional ap- proach, they should devise the mask-layouts and fabrication process instead of the function and shape of the MEMS device. The geometric model of the MEMS device is then derived based on the simulated fabrication according to the devised mask layout and the process. This is analogous to generating a geo- metric model from the NC tool paths in the macro world. Obviously it is uni…  相似文献   

Multifractal analysis of surface EMG signals for assessing muscle fatigue during static contractions   总被引：1，自引：0，他引：1  

WANG Gang REN Xiao-mei LI Lei WANG Zhi-zhong 《浙江大学学报(A卷英文版)》2007,8(6):910-915

This study is aimed at assessing muscle fatigue during a static contraction using multifractal analysis and found that the surface electromyographic （SEMG） signals characterized multiffactality during a static contraction. By applying the method of direct determination ofthef（a） singularity spectrum, the area of the multifractal spectrum of the SEMG signals was computed. The results showed that the spectrum area significantly increased during muscle fatigue. Therefore the area could be used as an assessor of muscle fatigue. Compared with the median frequency （MDF）--the most popular indicator of muscle fatigue, the spectrum area presented here showed higher sensitivity during a static contraction. So the singularity spectrum area is considered to be a more effective indicator than the MDF for estimating muscle fatigue.  相似文献   

Intersections of two offset parametric surfaces based on topology analysis     

欧阳应秀  唐敏  林军呈  董金祥 《浙江大学学报(A卷英文版)》2004,5(3):259-268

Conventional methods for solving intersections between two offset parametric surfaces often include iteratively using computationally expensive SSI (surface/surface intersections) algorithm. In addition, these methods ignore the relations between the intersection curves of parametric surfaces with different offset distances. The algorithm presented in this paper, makes full use of the topological relations between different intersection loops and calculates intersection loops with the help of previously calculated intersection loops. It first pre-processes two parametric surfaces to obtain the characteristic points, called topology transition points (TTPs), which can help in the subsequent finding of the topologies of the intersection curves. Then these points are categorized into several distinct groups, and we can determine the calculation strategy for searching initial points by analyzing the properties of these TTPs on the surfaces. Hence, all intersection curves can be marched from initial points by the tracing algorithm. The proposed algorithm could calculate intersection curves robustly and effectively, and has been tested to be capable of overcoming the degenerate conditions such as loop and singularities leaking that occur frequently in conventional algorithms. Project supported by the National Research Foundation for the Doctoral Program (No. 2000033554) of Higher Education of China and the Natural Science Foundation of Zhejiang Province, China (No. 6001107)  相似文献   

河西地区内陆河流域地表水资源及动态趋势分析   总被引：1，自引：0，他引：1  

杜虎林高前兆李福兴 《资源科学》1996,18(2):44-54

河西地区是甘肃省主要经济地区之一，是国家下世纪初大规模开发大西北的纽带与依托。河西地区未来的经济发展规模，在很大的程度上取决于本地区水资源的承载能力。本文对河西地区内陆河流域天然地表水资源进行了计算和评价；对天然地表径流的变化特征进行了分析；并对河西地区>河西地区、内陆河流域、地表水资源、变化特征、动态过程、趋势预测  相似文献   

土壤和建筑材料表面氡析出率对室内氡浓度的影响     

贺小凤  王国胜  符适 《深圳信息职业技术学院学报》2011,(3):62-67

采用监测数据可靠的RAD7测氡仪,选择深圳市某平房为研究对象,检测到平房周围为土壤氡低背景区,且土壤表面氡析出率较大,约为房间内水泥地板的2倍,说明土壤是室内氡的最大来源;而水泥地板表面氡析出率较瓷砖地板大,约为瓷砖地板的4倍。铺有水泥地板的房间室内氡浓度大于铺有瓷砖地板的房间,这是由于水泥地板表面氡析出率较大。因此,为了减少室内氡浓度,应该尽可能选择表面氡析出率低的材料铺设地板,并保持开窗通风。  相似文献