Tool wear criterion,tool life,and surface roughness during high-speed end milling Ti-6Al-4V alloy

The objective of the present research is to investigate the relationship among tool wear, surface topography, and surface roughness when high-speed end milling Ti-6Al-4V alloy, and also to define an optimal flank wear criterion for the cutting tool to integrate tool life and the surface roughness requirements of the finish milling process. An annealed Ti-6Al-4V alloy was selected as the workpiece material, undergoing end milling with uncoated carbide inserts. The flank wear of the insert was observed and measured with the toolmaker＇s microscope. To examine machined surfaces, 3D surface topography was provided by the white light interferometer, and the arithmetical mean roughness （Ra） was calculated with the WYKO Vision32 software. The flank wear increases with cutting time, and the maximal flank wear is set as the flank wear criterion. As the cutting process progresses, tool wear is the predominant factor affecting the variation of surface roughness. According to the plots for the tool wear propagation and surface roughness variation, an optimal flank wear criterion can be defined which integrates the tool life and the surface roughness requirements for the finish milling process.     

容许参数变换下曲线和曲面的几何不变量

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.     

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

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.     

面模型与球壳模型下的电场强度

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。     

中国月平均地表反照率的估算及其时空分布

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.     

自由曲面的平面展开

1　Introduction　PlanardevelopmentofacurvedsurfaceisbroadlyusedinCAGDandCAD .Accordingtotheirdevelop ment ,surfacesaredividedintodevelopablesurfacesandnon developablesurfaces .Mostofcurvedsurfacesarenon developable ,butbroadlyusedinengineering ,suchasaircraftwings ,laminaofturbine ,fluidsur face .Howeverthedesignandhandlingofcurvedsur faceareverydifficult.Inordertopredigestthecom plexityofdesign ,planardevelopingisintroduced .Non developablesurfacescannotbedevelopedontoaplanewithoutstretch…     

Intersections of two offset parametric surfaces based on topology analysis

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,…     

NURBS曲面拟合算法及应用

对NURBS(非均匀有理B样条)曲面的拟合算法和利用"权值"局部修改NURBS曲面的方法进行了研究,运用OpenGL技术实现了NURBS曲面的虚拟显示,通过血管的表面重建实验,验证了NURBS曲面拟合算法的正确性。     

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

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…     

Multifractal analysis of surface EMG signals for assessing muscle fatigue during static contractions

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.