基于拓扑结构和节点性能的应用层组播算法

针对当前应用层组播节点具有异构性和存在传输延迟等问题,提出一种基于拓扑结构和节点性能的应用层组播算法。根据拓扑感知的方法对网络进行分层分簇,在构建组播树时考虑节点的异构性,使高性能的节点接近源节点,低性能的节点接近叶子节点。实验结果表明,该算法能提高组播树的效率,降低端到端的延迟,减小链路压力和控制开销,在大规模节点环境中有效改善组播树的性能。     

视轴稳定系统的非接触式陀螺修正技术

针对陀螺视轴稳定装置中陀螺的输出漂移误差影响视轴稳定性能的问题,提出一种利用视觉测量技术对陀螺信号进行实时修正的方法。通过在地面上共面设置的4个固定信标和载体上双焦CCD摄像机,组成单目视觉测量系统,应用四元数描述载体和大地直角坐标系间的变换关系,在此基础上采用Levenberg-Marquardt迭代算法和刚体运动学原理,推导出采用DLOSS装置实现陀螺信号修正的机理。仿真结果表明了该方法的有效性。     

效能增强的Ad hoc网络服务发现协议

针对Ad hoc网络中服务发现难度大的问题,分析当前服务发现协议的优缺点,提出一种适用于Ad hoc的服务发现协议ESDP,该协议位于应用层,采用推拉结合的模式,通过缓存、节点合作、随机回退等机制减少数据包传输,从而节省电量消耗,同时考虑设备的异构性和安全机制。网络模拟和分析表明该协议性能良好。     

一种自动监测系统异构性解决方案

文章对空气质量自动监测系统的异构性问题进行了分析与研究,提出了＂抽象设备、映射数据、虚拟协议＂的解决方案,将物理设备屏蔽在驱动一级,将抽象设备屏蔽在转换程序一级,将数据按空气质量因子分类型打包传送到组态王对应的寄存器组,实现了不同数据接口、不同数据类型以及不同传送协议下的企业信息自动化。     

北斗双星／SINS组合导航中的捷联惯导算法研究

摘要针对北斗双星／SINS组合导航系统,研究了捷联惯导的姿态和速度更新算法。将等效旋转矢量算法应用与姿态解算,消除了传统的四元数算法存在的不可交换性误差对导航精度的影响,并对速度解算中的划浆误差进行了补偿。将算法应用到北斗双星／捷联惯导组合导航系统,通过实际的跑车实验验证算法的有效性。     

Commentary on Krishnaswamy et al. - Quantifying and mapping biodiversity and ecosystem services: Utility of a multi-season NDVI based Mahalanobis distance surrogate

Remote sensing is a powerful tool for characterizing, estimating or modelling species diversity. Differences in environmental properties of different habitats should lead to differences of spectral responses, which can be detected by satellite imagery. Hence, spectral distance may be related to species diversity. Based on previous studies, Krishnaswamy et al. [Krishnaswamy, J., Bawa, K. S., Ganeshaiah, K. N., & Kiran, M. C. (2009). Quantifying and mapping biodiversity and ecosystem services: Utility of a multi-season NDVI based Mahalanobis distance surrogate. Remote Sensing of Environment.] used spectral distance to estimate species diversity. Since a noisy scatterplot of species versus spectral diversity is expected, the commonly used Ordinary Least Square regression may fail to detect trends which occur across other quantiles than the mean.Krishnaswamy et al. [Krishnaswamy, J., Bawa, K. S., Ganeshaiah, K. N., & Kiran, M. C. (2009). Quantifying and mapping biodiversity and ecosystem services: Utility of a multi-season NDVI based Mahalanobis distance surrogate. Remote Sensing of Environment.] proposed a quantile-quantile plot method as an alternative to conventional regression based approaches which are inappropriate for dependent pair-wise dissimilarity or similarity data. By this commentary I demonstrate the utility of a quantile regression technique to complement the Krishnaswamy et al. [Krishnaswamy, J., Bawa, K. S., Ganeshaiah, K. N., & Kiran, M. C. (2009). Quantifying and mapping biodiversity and ecosystem services: Utility of a multi-season NDVI based Mahalanobis distance surrogate. Remote Sensing of Environment.] graphical approach in terms of a predictive model.     

矿用全断面硬岩快速掘进机位姿纠偏控制系统设计

介绍矿用全断面硬岩快速掘进机及其姿态测量与控制方法.结合盾构机和悬挂掘进机姿态测量方法,提出基于激光指示仪和新型电子激光标靶的测量系统,对掘进机进行实时三维坐标测量.通过采集的俯仰角、滚动角以及水平偏航角,来推导出掘进机切口、尾部中心的坐标以及位置偏差,经过误差仿真实验表明在本测量系统下,测量精度符合施工要求.PLC根据掘进机水平和垂直偏差量对掘进机进行实时纠偏,并给出了纠偏程序实现流程和友好的人机界面设计,实现了对全断面硬岩快速掘进机姿态的准确测量与稳定控制.     

固定翼无人机的自抗扰反步控制

针对固定翼无人机姿态和速度控制中系统存在模型不确定性和外界扰动的情况,本文设计了基于扩张状态观测器的反步控制器抑制系统扰动以提高无人机的控制性能.首先建立无人机速度误差模型和姿态误差模型,其中姿态误差模型采用四元数作为变量以避免欧拉角在描述姿态时存在的奇点问题和复杂三角运算;进而设计扩张状态观测器对系统中存在的扰动进行估计,并将扰动估计值与控制器设计相结合,分别设计出姿态控制器和速度控制器来抑制扰动的影响且使无人机姿态和速度收敛到期望值.最后基于李雅普诺夫理论证明系统的稳定性.仿真结果表明,本文所设计方法能够抑制系统中存在的扰动.     

Integrating functional,social, and psychological determinants to explain online social networking usage

People involved in business are increasingly aware of the online social phenomenon and its potential as a marketing tool. Building upon the marketing, social psychology, and information system literature, this study empirically examines a set of functional determinants derived from the technology acceptance model and socio-psychological determinants drawn from the theory of reasoned action and social cognitive theory that may be responsible for the motivations of participants in online social networks. We propose a model by integrating functional, social, and psychological factors in predicting attitude and online social network usage. The survey outcomes from a cross-sectional study among 387 Facebook users in Malaysia support the hypothesised model. This study contributes by extending the cognitive learning theories in predicting online social networking usage. Particularly, this research presents a different perspective on online social networking by exploring the mediating effect of attitude and the moderating role of individual characteristics. This study demonstrates that desirable changes in the perception of functional benefits, self-efficacy, and need for cognition as well as perceptions of social pressure from significant others might lead to corresponding changes in attitude towards online social networking. Results of the study support the model efficacy and predictive ability of the proposed integrative model which may serve as a theoretical foundation for future researchers interested in examining other virtual community engagements such as blogging, online advertising, and online public relations activities.     

ADRC Law of Spacecraft Rendezvous and Docking in Final Approach Phase

This article addresses the high-precision coordinated control problem of spacecraft autonomous rendezvous and docking, which couple the relative position and attitude in the final approach phase. The coupled dynamics equations of the tracking-target spacecrafts is derived by using dual quaternions. Then, a cascade Active Disturbance Rejection Controller is proposed, by which the extended state observer and nonlinear error feedback law is designed, the virtual value on which the actual control volume tracking is calculated to ensure the finite time convergence of the relative position and attitude tracking errors in spite of parametric uncertainties and external disturbances. Finally, numerical simulations are performed to demonstrate that the proposed approaches, which can avoid the coupling effect and restrain the interference, can track the target spacecraft in a relatively short period of time, and the control precision can satisfy the requirements of docking.