An illusion efect of Maxwell’s fsh-eye lens

We show that Maxwell’s fsh-eye lens can make a semi-circular perfect electric conductor look like a circular one.Such an efect can also be achieved(not perfectly)by using negative index metamaterials,but only within a single frequency.Maxwell’s fsh-eye lens,however,can work for a set of eigenfrequencies.Numerical simulations are performed to verify the efect.     

Purcell’s swimmer revisited

Purcell’s swimmer was proposed by E. M. Purcell to explain bacterial swimming motions. It has been proved experimentally that a swimmer of this kind is possible under inertial-less and high viscous environment. But we could not investigate all the aspects of this mechanism through experiments due to practical difficulties. The computational fluid dynamics (CFD) provides complementary methods to experimental fluid dynamics. In particular, these methods offer the means of testing theoretical advances for conditions unavailable experimentally. Using such methodology, we have investigated the fluid dynamics of force production associated with the Purcell’s swimmer. By employing dynamic mesh and user-defined functions, we have computed the transient flow around the swimmer for various stroke angles. Our simulations capture the bidirectional swimming property successfully and are in agreement with existing theoretical and experimental results. To our knowledge, this is the first CFD study which shows the fact that swimming direction depends on stroke angle. We also prove that for small flapping frequencies, swimming direction can also be altered by changing frequency-showing breakdown of Stokes law with inertia.     

Inverse problem for Chaplygin’s nonholonomic systems

Chaplygin’s nonholonomic systems are familiar mechanical systems subject to unintegrable linear constraints, which can be reduced into holonomic nonconservative systems in a subspace of the original state space. The inverse problem of the calculus of variations or Lagrangian inverse problem for such systems is analyzed by making use of a reduction of the systems into new ones with time reparametrization symmetry and a genotopic transformation related with a conformal transformation. It is evident that the L...     

The Level 2 Fuzzy Comprehensive Evaluation Model’s Application in 5S

Some method on the evaluation of management’s effect should be applied to 5S of manufacturing enterprises’ workshops.To improve traditional methods that are applied to evaluation of management’s effect of those enterprises,the paper applied the level 2 fuzzy comprehensive evaluation model to the new method and detailedly demonstrated the new method that based on the level 2 fuzzy comprehensive evaluation model with a practical example.In a period of production,managers can easily grasp the macroscopic effect of 5S with the new method,and then make some corresponding measures according to certain actual condition.     

结合Cannikin’s Law的离线数据增广方法研究

数据增广是提升深度学习模型性能的有效方法之一。针对多类别目标检测任务中检测性能不平衡问题,提出一种针对“短板类别”（检测性能远低于模型平均检测性能的类别）的离线数据增广方法。受Cannikin’s Law的启发,采用基于复制粘贴（copy-paste）机制的场景多样性增广方法。随机采集训练集中“短板类别”实例区域,通过相似性度量机制选取训练集中增广目标样本进行随机粘贴。为了降低随机粘贴导致的遮挡问题,采用基于自遮挡（cut-replace）机制的增广方法提升模型遮挡表达能力。通过截取样本自身区域,对特征表达最显著区域进行遮挡。实验表明,FCOS目标检测框架在PASCAL VOC数据上的平均检测精度（mean average precision,mAP）从79.10%提升到83.90%,其中短板类别更为显著,提升了20.8个百分点。在MS-COCO数据上平均检测精度提升了0.9个百分点。     

Jumarie’s修正的R-L分数阶系统的新解法

结合同伦摄动理论和Sumudu变换方法,提出了一种简单有效的摄动方法,并应用该方法求解了Jumarie’s修正的Riemann-Liouville(R-L)分数阶的方程,该方程带有分数阶的初值条件,而以前的文献中很少讨论分数阶的初值条件。结果表明该方法具有较高的精度和有效性。     

基于随机灰度图的全局Moran’s I 指数的计算与分析

全局Moran’s I指数反映了空间邻近的区域单元属性值的相似程度。该文主要编程实现了基于各个方向距离的权重矩阵的全局Moran’s I指数的计算;并基于随机生成的灰度图像设计实验,通过不同属性值的替代和权重距离的变化计算和分析全局Moran’s I指数,验证其探测聚集性的敏感程度。     

基于Ward’s方法的k-平均优化算法及其应用

通过对k-平均算法存在不足的分析,提出了一种基于Ward’s方法的k-平均优化算法。算法首先在用Ward’s方法对样本数据初步聚类的基础上,确定合适的簇数目、初始聚类中心等k-平均算法的初始参数,并进行孤立点检测、删除;基于上述处理再采用传统k-平均算法进行聚类。将优化的k-平均算法应用到罪犯人格类型分析中,实验结果表明,该算法的效率、聚类效果均明显优于传统k-平均算法。     

Performance Evaluation of Public Bus Transportation by Using DEA Models and Shannon’s Entropy:An Example From a Company in a Large City of China

The purpose of this paper is to assess the operational efficiency of a public bus transportation via a case study from a company in a large city of China by using data envelopment analysis(DEA)model and Shannon’s entropy.This company operates 37 main routes on the backbone roads.Thus,it plays a significant role in public transportation in the city.According to bus industry norms,an efficiency evaluation index system is constructed from the perspective of both company operations and passenger demands.For passenger satisfaction,passenger waiting time and passenger-crowding degree are considered,and they are undesirable indicators.To describe such indicators,a superefficient DEA model is constructed.With this model,by using actual data,efficiency is evaluated for each bus route.Results show that the DEA model with Shannon’s entropy being combined achieves more reasonable results.Also,sensitivity analysis is presented.Therefore,the results are meaningful for the company to improve its operations and management.