面向WLAN室内定位的T检验样本容量优化方法

WLAN（Wireless Local Area Networks）室内定位已受到人们广泛的关注,而在离线指纹采集阶段常常容易造成位置指纹RSS数据采集的盲目性和不可靠性,并忽略所需采集RSS（Received Signal Strength）样本容量与定位性能的关系.为了解决这一问题,本文提出一种面向WLAN室内定位的T检验样本容量优化方法.该方法在离线阶段利用OC（Operating Characteristics）函数优化指纹数据库允许的最小RSS样本容量,而在在线阶段利用T检验方法对目标终端进行粗定位,并进而提出基于T检验的KNN（K-Nearest Neighbour）算法以完成对目标终端的精定位.此方法用有限的样本容量获得较稳定的定位性能分析结果,显著地减少了大量的人力和时间开销.     

Localization of strain in metal matrix composites studied by a scanning electron microscope-based grating method

The deformation characteristics of the metal matrix composites Ag/Ni and Al/Al₂O₃ are studied at microstructural level by a scanning electron microscope based grating method and finite element (FE) simulation. The measured strain was found to localize in narrow bands in the ductile matrix of both composites. In the case of the Al/Al₂O₃ composite, the bands are preferentially initiated in Al regions adjacent to the interface of large Al₂O₃ particles, leading to local strain maxima. The band positions found in the Ag/Ni composite are also affected by the less deformable Ni phase, but strain localization first occurs by sliding of single Ag grains sometimes located away from the Ni phase. Using a FE model of real phase geometry and measured border displacements as boundary conditions, the simulation agrees reasonably with the experiment. The differences in the case of the Al/Al₂O₃ composite are due to particle cracks and voids at the particle/matrix interface. This effect was found in the experiment but not considered in modelling. For the Ag/Ni composite the band positions agree fairly well. However, the level and gradient of strain is clearly different as the crystallographic orientation of the Ag grains was not accounted for in modelling.     

Semi-Direct Visual Odometry and Mapping System with RGB-D Camera

In this paper a semi-direct visual odometry and mapping system is proposed with a RGB-D camera, which combines the merits of both feature based and direct based methods. The presented system directly estimates the camera motion of two consecutive RGB-D frames by minimizing the photometric error. To permit outliers and noise, a robust sensor model built upon the t-distribution and an error function mixing depth and photometric errors are used to enhance the accuracy and robustness. Local graph optimization based on key frames is used to reduce the accumulative error and refine the local map. The loop closure detection method, which combines the appearance similarity method and spatial location constraints method, increases the speed of detection. Experimental results demonstrate that the proposed approach achieves higher accuracy on the motion estimation and environment reconstruction compared to the other state-of-the-art methods. Moreover, the proposed approach works in real-time on a laptop without a GPU, which makes it attractive for robots equipped with limited computational resources.     

基于Bregman散度的无线传感器网络定位

现有算法难以处理脉冲噪声,导致无线传感器网络（WSN）中节点定位精度较低,为此提出基于Bregman散度的WSN定位算法. 该算法分为2个阶段：欧氏距离矩阵（EDM）恢复阶段和坐标映射阶段. 基于EDM的自然低秩性,将EDM恢复问题转化为噪声环境下的矩阵补全问题;采用L_1,2范数显式平滑脉冲噪声,建立正则化矩阵补全模型;为了有效求解该模型,定义多元函数Bregman散度,将分裂Bregman迭代拓展到矩阵空间,结合交替最小化算法,得到EDM的估计;在此基础上,基于多维标度法对节点位置进行估计. 实验结果表明,在不同噪声条件下,该算法在保证高效性的同时,在定位精度和鲁棒性方面优于其他算法,特别是当采样率达到一定程度时,定位误差不到其他算法的1/4.     

时频等高图在旋转机械振动故障信号检测中的应用

提出用基于Morlet小波变换的时频等高图检测信号中奇异性的方法。旋转机械某些故障发生时将产生具有奇异性的非平稳信号，检没出振动信号中的奇异性对于设备状态监测和故障早期诊断很有意义。小波变换在时域和频域内同时具有局部化能力，是分析故障信号奇异性的有利工具，为旋转机械故障检测提供了新思路。文中通过对仿真的旋转机械转子各类振动突变信号进行分析，说明Morlet小波时频等高图能直观表示信号中的微弱奇异成分，可以有效提取信号中的微弱奇异特征。     

中药材栀子的X射线衍射傅立叶指纹图谱鉴定研究

为建立一种新的中药材鉴定与分析方法,我们采用粉末X射线衍射分析技术,分别对19个不同来源的栀子样品进行实验分析研究。利用粉末X射线衍射傅立叶(Fourier)指纹图谱分析方法,获得栀子与水栀子等中药材的各自对照衍射图谱和特征标记峰值。使用对照衍射图谱和特征标记峰值可以很好地区分道地中药材栀子、药材栀子变种-水栀子及地方习用品-黄花栀子。分析结果表明,粉末X射线衍射Fourier指纹图谱分析方法可以用于传统中药材的鉴定与质量控制。     

考虑应变梯度效应的低碳钢试样单向拉伸尺寸效应理论研究

采用二阶应变梯度塑性理论，得出伸长率、峰值应力后工程应力应变曲线和真应力应变曲线的解析解，结果表明三者均具有尺寸效应。将低碳钢试样的单轴拉伸简化为轴向的一维问题。采用拉伸过程中体积不变假设及平衡条件，将应变梯度引入屈服函数，得到伸长率、平均应变及真应变的解析式。理论结果完全反映伸长率与标定长度呈反比的客观事实。工程应力应变曲线尺寸效应可以在数值结果中找到佐证。拉应变局部化是三者尺寸效应的本质原因。     

基于情景感知的低交互移动双因素认证系统

针对传统双因素认证缺乏可用性的问题,本文提出了一种基于情景感知的低交互移动双因素认证系统.用户通过本系统登录网站时,除输入用户名和口令外,只需点击令牌程序的认证键即可完成认证,平均登录时间不超过5秒.同其它可用性加强的移动双因素认证系统相比,本系统能够抵抗同一环境下的攻击者,而且支持用户手机浏览器进行网站登录.最终安全分析和实验结果证实了本方法的有效性.     

一种指纹模块在考勤终端中的应用与研究

针对学生代考现象难以准确及时地发现这一问题,介绍了一种利用人体指纹生物特征实现的个人身份认证装置,该装置基于C8051F020核心处理器,嵌入光学指纹识别模块,集成了以太网络接口及相应的外围设备,使其具备单机和联网的双重工作模式和较高的安全性与可靠性、较强的适应能力.在初期的实践应用中,结果表明其具有较高的身份识别率,有利于减少学生代考现象的发生.     

Localization under anchor node uncertainty for underwater acoustic sensor networks

This paper deals with the problem of sensor node localization in the presence of uncertainty in anchor node location. Aqueous environments are prone to adverse effects of underwater currents. This adversity causes non‐negligible mobility to the anchor nodes deployed under water. Localization in the presence of uncertainty in the anchor node location is quite challenging. Also, the authors consider the ray‐bending property of underwater medium due to depth dependent sound speed, to furnish the accurate position estimate of the target node. Standard ray equations are used to model the path followed by acoustic rays in water. Maximum likelihood estimation is proposed to estimate the location of target node with uncertainty in anchor node positions and is compared with the scheme with exact knowledge of anchor node positions, and the results are reported. Monte Carlo simulation is used to assess the performance of the proposed method. Also, the Cramer‐Rao lower bound with uncertainty in anchor nodes is derived and described. Simulation results of the proposed algorithm outperform the existing algorithm with known anchor location by up to 49.4%, and hence, accuracy is improved in the proposed method.