对称性在曲线积分和曲面积分计算中的应用

引进了函数关于点、直线与平面的奇偶性的概念,对文[1]-[4]中所给出的关于利用积分弧段与积分曲面的对称性及被积函数的奇偶性计算曲线积分与曲面积分的结果作了进一步推广,得到了一些更为一般性的结果.     

一种利用等效模型与遗传算法的动态有限元模型修正方法

为了解决现有动态有限元模型修正方法计算效率不高或者可能获得局部最优解的问题,提出了一种利用等效模型和遗传算法的动态有限元模型修正新方法.首先,在设计参数的取值范围内,根据预设的多项式模型的阶次以及自变量的个数,利用试验设计方法获得拟合响应面模型所需要的最优样本点;通过有限元分析获得样本数据,并利用回归分析获得响应面模型,从而以响应面模型逼近结构特征与设计参数之间的函数关系.然后,在遗传算法的适应度评估环节,利用响应面模型替代有限元模型计算对应于一组设计参数的结构特征,并计算遗传个体的适应度,最终通过进化获得最优解,即为修正后的设计参数.以汽车车架模型为例,对其进行有限元分析与模态试验,并利用所提出的方法进行模型修正.修正后,模态频率误差的均方值小于2%.用修改后结构的动态特性的测试结果,对修正后有限元模型的预测能力进行检验,模态频率预测误差的均方值小于2%.     

Surface reconstruction by offset surface filtering

The problem of computing a piecewise linear approximation to a surface from its sample has been a focus of research in geometry modeling and graphics due to its widespread applications in computer aided design. In this paper, we give a new algorithm, to be called offset surface filtering （OSF） algorithm, which computes a piecewise-linear approximation of a smooth surface from a finite set of cloud points. The algorithm has two main stages. First, the surface normal on every point is estimated by the least squares best fitting plane method. Second, we construct a restricted Delaunay triangulation, which is a tubular neighborhood of the surface defined by two offset surfaces. The algorithm is simple and robust. We describe an implementation of it and show example outputs.     

激光诱导聚合物表面周期性微结构的快速制备研究

采用波长355nm的紫外偏振激光，通过步进扫描法在聚酰亚胺（BDTA—MMAD）薄膜表面制备了激光诱导周期性表面微结构（LIPSS），采用原子力显微镜（AFM）分析了LIPSS图形质量及几何尺寸，考察了X、Y方向扫描速度和扫描步长等参数对LIPSS制备的影响，发现随着X方向扫描速度和Y方向扫描步长的增大，由于薄膜表面受到激光辐射累积能量降低，LIPSS图形质量明显下降。但是，在提高Y方向扫描步长的同时提高激光辐射能量，仍能在较快速度下制得规则的LIPSS结构。根据实验结果提出了实现LIPSS快速制备的优化条件，并探讨了LIPSS的形成机理。     

积分运算中几种常见错误剖析

针对多元函数积分运算中的几种常见错误,即:对被积函数及积分区域的对称性、面积分及重积分的积分区域、曲面积分的投影区域等几个方面进行了剖析,并给出几点注意事项.     

响应曲面法优化无籽刺梨多酚提取工艺研究

文章采用三因素三水平的响应曲面分析方法优选了无籽刺梨多酚的提取工艺.结果表明,提取金刺梨多酚的最佳方案为:酒精浓度72%、固液比1:13、提取时间23 min,用此条件下提取实际测得的平均提取含量为1.8117%.     

公式拟合法计算乙醇水溶液的表面吸附量

建立了乙醇水溶液的表面张力σ与浓度c的关系，由此式求出（Dσ／Dc）r，再由吉布斯吸附公式计算各浓度的表面吸附量г。所求得的г随c的变化规律与文献吻合。     

Academic boredom,approaches to learning and the final-year degree outcomes of undergraduate students

Academic boredom is a largely negative and disabling achievement-related emotion. In this mixed-methods exploration of 224 students attending a single university in England, academic boredom was found to arise at the point of course delivery, while studying at other times and during the completion of assignments for assessment. Quantitative data from the recently adapted Boredom Proneness Scale for use across the UK higher education sector (the BPS-UKHE) and the Approaches and Study Skills Inventory for Students (ASSIST), enriched with qualitative data from 10 semi-structured research interviews, indicate that those with a higher propensity towards academic boredom than others displayed the deep, strategic and surface profiles of ‘less effective learners’. This was reflected in their interest in ideas, their ability to organise resources and manage time, what they had to memorise or do to ‘get by’, their achievement motivation and their sense of purpose. As part of a greater evolving network of other contributing factors, this translated into lower final degree marks and fewer ‘good’ degree awards. Recommendations surrounding boredom mitigation and approaches to learning are suggested which warrant serious consideration. The work presented here makes an important contribution to a surprisingly neglected field of UK higher education research and the student engagement agenda.     

Effect of Shock Wave on Fabricated Anti-Blast Wall and Distribution Law Around the Wall Under Near Surface Explosion

The loads of shock wave effect on fabricated anti-blast wall and distribution law around the wall were investigated by using near surface explosion test method and FEM.The pressure-time histories and variety law on the foreside and backside of the anti-blast wall were adopted in the tests of variety of different explosion distances and dynamites,as well as in the comparison between the test and numerical calculation.The test results show that the loads of shock wave effect on the anti-blast wall were essen-tially consistent with calculation results using criterion under surface explosion when explosion distances exceed 2 m,the distribution of overpressure behind wall was gained according to variety law based on small-large-small.It is also demonstrated that the peak overpressure behind wall had commonly appeared in wall height by 1.5--2.5 multiples,and the peak overpressures of protective building behind wall could be reduced effectively by using the fabricated anti-blast wall.     

Differential response of root morphology to potassium deficient stress among rice genotypes varying in potassium efficiency

Disparity in the root morphology of six rice (Oryza sativa L.) genotypes varying in potassium (K) efficiency was studied with three K levels: 5 mg/L (low),10 mg/L (moderate) and 40 mg/L (adequate) in hydroponic culture.Morphological parameters included root length,surface area,volume and count of lateral roots,as well as fine (diameter<0.2 mm) and thick (diameter>0.2 mm) roots.The results indicate that the root growth of all genotypes was reduced under low K,but moderate K deficiency increased the root length of the efficient genotypes.At deficient and moderate K levels,all the efficient rice genotypes developed more fine roots (diameter<0.2 mm) than the inefficient ones.Both fine root count and root surface area were found to be the best parameters to portray K stress in rice.In accordance with the root morphology,higher K concentrations were noted in shoots of the efficient genotypes when grown at moderate and deficient K levels,indicating that root morphology parameters are involved in root uptake for K and in the translocation of K up to shoots.K deficiency affected not only the root morphology,but also the root ultra-structure.The roots of high-efficient genotypes had stronger tolerance to K deficient stress for root membrane damage,and could maintain the developed root architecture to adapt to the low K growth medium.