多维多阶调制格式产生方案的比较研究

随着带宽需求的不断增长,多维多阶调制格式成为目前研究的热点.文章对8PSK(3阶相移键控)、8QAM(3阶正交调幅)和16QAM(4阶正交调幅)的实现方式从原理和拓扑结构上进行了综合性的比较研究.使用已商用的调制器件,通过串行或串并混合的结构配置,可以得到8PSK、8QAM和16QAM的调制光信号;而使用并行结构的配置...     

A generalized higher order finite-difference time-domain method and its application in guided-wave problems

In this paper, a (2M,4) scheme of the finite-difference time-domain (FDTD) method is proposed, in which the time differential is of the fourth order and the spatial differential using the discrete singular convolution is of order 2M. Compared with the standard FDTD and the scheme of (4, 4), the scheme of (2M, 4) has much higher accuracy. By choosing a suitable M/spl ges/2, the (2M, 4) scheme can arrive at the highest accuracy. In addition, an improved approximation of the symplectic integrator propagator is presented for the time differential. On the one hand, it can directly simulate unlimited conducting structures without the air layer between the perfectly matched layer and inner structure; on the other hand, it needs only a quarter of the memory space required by the Runge-Kutta time scheme and requires one third of the meshes in every direction of the standard FDTD method. By choosing suitable meshes and bandwidth M, our scheme not only retains higher accuracy but also saves memory space and CPU time. Numerical examples are provided to show the high accuracy and effectiveness of the proposed scheme.     

Facial Expression Recognition Based on Spatial and Channel Attention Mechanisms

Wireless Personal Communications - Microarray-based gene expression profiling is an emerging method to predict, classify, diagnose and to treat cancer efficiently. The characteristics of this...     

Bi2SiO5 Doping Concentration Effects on the Electrical Properties of SrBi2Ta2O9 Films

In this paper, we investigated the microstructure and electrical properties of Bi₂SiO₅ (BSO) doped SrBi₂Ta₂O₉ (SBT) films deposited by chemical solution deposition. X-ray diffraction observation indicated that the crystalline structures of all the BSO-doped SBT films are nearly the same as those of a pure SBT film. Through BSO doping, the 2Pr and 2Ec values of SBT films were changed from 15.3 μC/cm² and 138 kV/cm of pure SBT to 1.45 μC/cm² and 74 kV/cm of 10 wt.% BSO-doped SBT. The dielectric constant at 1 MHz for SBT varied from 199 of pure SBT to 96 of 10 wt.% BSO-doped SBT. The doped SBT films exhibited higher leakage current than that of non-doped SBT films. Nevertheless, all the doped SBT films still had small dielectric loss and low leakage current. Our present work will provide useful insights into the BSO doping effects to the SBT films, and it will be helpful for the material design in the future nonvolatile ferroelectric memories.     

Key-Attributes-Based Ensemble Classifier for Customer Churn Prediction

Recently, it has been seen that the ensemble classifier is an effective way to enhance the prediction performance. However, it usually suffers from the problem of how to construct an appropriate classifier based on a set of complex data, for example, the data with many dimensions or hierarchical attributes. This study proposes a method to constructe an ensemble classifier based on the key attributes. In addition to its high-performance on precision shared by common ensemble classifiers, the calculation results are highly intelligible and thus easy for understanding. Furthermore, the experimental results based on the real data collected from China Mobile show that the key-attributes-based ensemble classifier has the good performance on both of the classifier construction and the customer churn prediction.     

液体运载火箭启动过程气枕压力变化分析

以氦气瓶贮气闭式控制增压系统启动过程气枕压力变化规律为研究对象,讨论了增压系统响应时间、不同初始气枕容积、不同发动机流量启动加速性对启动过程气枕最小压力的影响。分析结果表明:对于大中型液体运载火箭,如能有效控制增压系统响应时间,使用较小的初始气枕容积即可保证启动过程发动机入口压力要求及贮箱载荷条件要求,可有效提高箭体结构效率。     

基于二维极化特征的PolSAR图像决策分类

决策树模型在极化SAR数据分类中有着极大的应用价值,既能描述分类结果的极化散射机制,又能获得较好的分类精度。但在对散射机制相似的地物进行分类时,由于经典决策树模型的节点采用的是单个特征,分类精度不理想。因此,该文提出了节点采用2维特征的方法,即在特征集相同的前提下,每次取两个特征组成特征矢量用于节点,提高了经典决策树难以区分的地物的分类精度;并且利用分类结果的混淆矩阵准确定位了导致分类误差的节点,进而对节点进行有针对性的反馈调整,进一步提高了指定地物的分类精度。利用AIRSARFlevoland数据验证了该方法的有效性,并结合极化特征描述了Flevoland地区多种植被的极化散射机制。      

水平路径上多帧湍流退化图像重建

为了重建水平路径上远距离成像系统获取的湍流退化图像,提出去除形变和振铃的分块多帧盲反卷积方法.首先按采集的顺序将图像序列分成若干图像组,通过B-spline基函数配准方法去除非等晕块之间的形变,第二步通过基于块的时域融合算法去除等晕块间的振铃,得到衍射受限的湍流退化图像,最后将所得的多帧图像进行频域重建,复原高质量图像.实验表明,所提出的算法适合于水平路径上获取的退化图像的重建,得到较高的主观视觉图像质量.     

计算机控制电气传动系统实验教学改革

数字控制技术在电气传动领域应用越来越广泛,为使学生掌握以计算机为核心的数字控制技术,培养计算机应用的能力,本文主要介绍了计算机引入直流调速教学实验系统的改革尝试。     

1.06μm激光半主动制导的目标与大气环境模型

文中给出了一种用于估算１．０６μｍ激光半主动制导兵器引头最大捕获距离的简单实用的模型,此模型由激光的大气环境传输子模型、目标子模型和目标获取子模型组成,将１．０６μｍ激光复杂的大气传输特性做了现象化、简单化和解释化的处理,指出影响传输特性和捕获距离的重要因素是大气中的气溶胶含量,而气溶胶含量对激光的衰减作用依赖于它的颗粒大小的分布和浓度,同时也考虑了降雨和降雪量对激光传输衰减系数的影响。在目标子模