Minimal LST representations of MAP(n)s: Moment fittings and queueing approximations

A Markovian arrival process of order n, MAP(n), is typically described by two n × n transition rate matrices in terms of rate parameters. While it is straightforward and intuitive, the Markovian representation is redundant since the minimal number of parameters is n² for non‐redundant MAP(n). It is well known that the redundancy complicates exact moment fittings. In this article, we present a minimal and unique Laplace‐Stieltjes transform (LST) representations for MAP(n)s. Even though the LST coefficients vector itself is not a minimal representation, we show that the joint LST of stationary intervals can be represented with the minimum number of parameters. We also propose another minimal representation for MAP(3)s based on coefficients of the characteristic polynomial equations of the two transition rate matrices. An exact moment fitting procedure is presented for MAP(3)s based on two proposed minimal representations. We also discuss how MAP(3)/G/1 departure process can be approximated as a MAP(3). A simple tandem queueing network example is presented to show that the MAP(3) performs better than the MAP(2) in queueing approximations especially under moderate traffic intensities. © 2016 Wiley Periodicals, Inc. Naval Research Logistics 63: 549–561, 2016     

基于神经网络的广义两点边值问题

在航天领域中 ,多数制导问题均可以抽象为广义两点边值问题。本文探讨了神经网络在广义两点边值问题求解中的应用。首先讨论了离线制导这一类静态两点边值问题的求解 ,在此基础上 ,对在线制导这一类动态两点边值问题进行了分析 ,并给出了有效的解决方法     

案例智能维修训练系统的设计与实现

基于案例的智能维修训练系统将智能教学系统与CBR技术结合起来应用在故障维修领域。在智能教学理论与CBR技术的支持下,围绕案例阐述了智能维修训练系统的设计和实现。给出了系统的通用体系结构;采用框架法实现知识库的设计;分析学生模型的构成并给出学生知识水平和学习能力的评估方法;针对训练策略给出其控制流程及其实现过程。这种基于案例的智能维修训练系统能有效地应用于装备的实际维修训练中。     

一种基于相位校正的InISAR图像配准新方法

针对InlSAR三维成像中的图像配准问题进行研究,从理论上推导了同一基线上两干涉天线之间图像失配准的原因,并定量分析了图像失配准量对后续干涉处理的影响.研究表明,初始时刻同一基线上两干涉天线间的波程差引起两幅ISAR图像距离方向的亚像素级失配,而成像积累时间内两干涉天线波程差的变化量则引起两幅ISAR图像多普勒方向的像...     

上转换荧光强度与激光功率的关系

为了实现较清晰双频上转换三维立体图像,对Pr3＋离子双频上转换发光进行了研究。实验中选用Pr3＋和Yb3＋：ZBLAN玻璃作为频率上转换发光材料,分析了上转换发光强度与泵浦光强度的关系,得出了实现较清晰双频上转换三维立体图像的实验条件。     

近似平面场景多视点图像拼接算法

以小型无人机对地观测为应用背景,研究了近似平面场景多视点图像拼接问题。对于已知粗略相机位姿的情况,提出一种融合相机位姿信息和图像特征点对应信息的方法,采用直接稀疏Cholesky分解方法求解拼接全局优化问题。由该方法得到的拼接结果没有全局变形,局部拼接误差也得到了明显的改善。对于相机位姿未知的情况,先采用structure-from-motion(SFM)方法恢复相机姿态和场景稀疏结构信息,再采用稀疏全局调整方法获得最终的图像变换参数。通过沙盘图像和真实的航拍图像拼接实验验证了算法的有效性。     

新型棒料高速动态跟随切割装置设计与优化

针对目前棒料高速动态切割装置支撑半径无法调整,切割精度以及刃磨刀片刃口形状无法控制的缺陷,根据切割装置切割原理,建立了切割模式、刀片数量等切割参数与支撑半径、切割误差的数学模型,并运用曲柄滑块机构设计了新型可调式支撑装置;基于空间齐次坐标变换方法构建了切割刀片刃口形状与切割直径、砂轮安装角度等刃磨参数之间的曲线方程,设计了新型可调式刃磨装置。以刀盘转速、切割误差等作为优化目标,采用MATLAB优化工具箱,对现有双刀双切烟支切割装置的切割和刃磨特性参数进行了非线性多目标优化。根据优化结果,提出了一种新型高速动态跟随切割装置设计方案,该方案采用四刀双切的切割模式。与原装置相比,新装置在切割效率不变的情况下具有更好的切割质量。最后通过仿真验证了该装置的可行性。     

Modeling of unsupervised knowledge graph of events based on mutual information among neighbor domains and sparse representation

Text event mining, as an indispensable method of text mining processing, has attracted the extensive attention of researchers. A modeling method for knowledge graph of events based on mutual information among neighbor domains and sparse representation is proposed in this paper, i.e. UKGE-MS. Specifically, UKGE-MS can improve the existing text mining technology's ability of understanding and discovering high-dimensional unmarked information, and solves the problems of traditional unsupervised feature selection methods, which only focus on selecting features from a global perspective and ignoring the impact of local connection of samples. Firstly, considering the influence of local information of samples in feature correlation evaluation, a feature clustering algorithm based on average neighborhood mutual information is proposed, and the feature clusters with certain event correlation are obtained; Secondly, an unsupervised feature selection method based on the high-order correlation of multi-dimensional statistical data is designed by combining the dimension reduction advantage of local linear embedding algorithm and the feature selection ability of sparse representation, so as to enhance the generalization ability of the selected feature items. Finally, the events knowledge graph is constructed by means of sparse representation and l₁ norm. Extensive experiments are carried out on five real datasets and synthetic datasets, and the UKGE-MS are compared with five corresponding algorithms. The experimental results show that UKGE-MS is better than the traditional method in event clustering and feature selection, and has some advantages over other methods in text event recognition and discovery.     

有限水深Kelvin源格林函数的传播特性及其应用

为探究有限水深环境下自由面兴波在远场的传播特性,应用线性水动力学的基本理论,从有限水深Kelvin源格林函数的积分表达式中提取相函数,采用同相分析法求得亚临界和超临界速度区下远场传播波系的等相线。结果表明,水深傅汝德数Fh1时远场传播波包括横波和散波两个波系,F_h1时远场波系仅由散波构成,点源兴波的影响范围可由Kelvin角的大小确定,当F_h趋近于1时Kelvin角迅速增大至90°。依据船型要素、两船相对位置和池壁几何参数,并计及船模的定常兴波经池壁反射作用后对自身和另一船模的干扰,提出了有限水深条件下并行航行两船模池壁效应的判别方法,并结合实例检查分析了某试验工况下的池壁效应。     

基于多尺度稀疏字典的SAR图像目标识别方法

针对合成孔径雷达目标识别问题,提出一种基于多尺度稀疏字典的SAR图像目标识别方法。稀疏字典选择是稀疏表示中的关键问题之一,该方法利用小波多尺度分析构造过完备稀疏字典,将训练样本图像在小波解析域中进行小波多层分解,充分利用小波多尺度分析突出图像局部特征的特点,并和过完备稀疏表示有效结合组成级联字典。通过求解测试样本相应的稀疏系数矢量并根据系数矢量中对应训练样本类别的重构误差判定目标类型。实验结果表明,该方法在识别前无需对SAR图像进行预处理,具有良好的识别效果。