共振条件下椭圆方程的两个非零解

研究共振条件下的一类椭圆边值问题,利用临界点理论中的Morse理论方法,通过计算零点和无穷远处的临界群,根据Morse不等式,得到该方程两个非零解的存在性.     

正交试验联用星点设计-效应面法优化西瓜皮总黄酮提取工艺研究

以总黄酮得率为指标,采用正交试验联合星点设计-效应面法考察乙醇体积分数、提取时间和固液比对西瓜皮总黄酮提取工艺的影响。结果表明正交试验确定最佳提取工艺为30倍量90％乙醇,提取3次,每次120min;星点设计一效应面法确定最佳提取工艺为14.22倍量71.17％乙醇,提取3次,每次48.25min。通过星点设计-效应面法优选的工艺合理可行,且比正交试验设计法更为准确。     

表面肌电图在人体运动研究中的应用

肌肉运动时会有微小的生物电变化，表面肌电图作为一种无创的检测方法来检测这种生物电变化。运动时肌电图的振幅、频率等指标均会产生相应的变化，而且这些变化与运动方式、运动状态、肌肉疲劳密切相关。     

伊犁新垦区土地利用和地形对表层土壤养分变异性的影响

本文基于野外实测剖面数据,借助于数理统计方法探讨了采样点尺度上土地利用和地形因子（海拔、坡度和坡向）对伊犁新垦区表层土壤有机质、全氮、全磷和全钾含量分布特征的影响。结果表明：①土地利用类型对表层土壤的有机质、全氮和全磷有显著性影响,而对全钾的影响不显著;②不同地形因子对表层土壤养分要素影响的显著性各异。4种养分含量与海拔呈极显著正相关,在500～600m梯度平均含量均最低,600～700m梯度波动范围均最大;有机质、全氮和全钾在高海拔梯度的平均含量高于低海拔的含量,全磷的平均含量随着海拔升高呈倒U型分布;③有机质和全氮与坡度呈显著正相关,3°以上的平均含量显著高于3°以下;在坡度〈1.82°时,4种养分含量的波动范围最大;④全磷与坡向呈显著负相关;阴坡的各种养分因子的平均含量不同程度的高于阳坡的含量;除全钾外,各种养分因子在阳坡的波动范围均大于阴坡的范围;⑤土地利用类型与地形条件的交互作用对表层土壤养分含量存在影响。在不同地形条件下,不同土地利用类型间的表层土壤养分含量高低情况存在差异,表现在较高海拔、较大坡度和阴坡上中覆被草地的有机质含量明显高于农田和低覆被草地,而在较低海拔、较小坡度和阳坡上则情况相反。     

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.     

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,…