LEARNING CAUSAL GRAPHS OF NONLINEAR STRUCTURAL VECTOR AUTOREGRESSIVE MODEL USING INFORMATION THEORY CRITERIA

Detection and clarification of cause-effect relationships among variables is an important problem in time series analysis. Traditional causality inference methods have a salient limitation that the model must be linear and with Gaussian noise. Although additive model regression can effectively infer the nonlinear causal relationships of additive nonlinear time series, it suffers from the limitation that contemporaneous causal relationships of variables must be linear and not always valid to test conditional independence relations. This paper provides a nonparametric method that employs both mutual information and conditional mutual information to identify causal structure of a class of nonlinear time series models, which extends the additive nonlinear times series to nonlinear structural vector autoregressive models. An algorithm is developed to learn the contemporaneous and the lagged causal relationships of variables. Simulations demonstrate the effectiveness of the nroosed method.     

Evidence for self-organized criticality in unscheduled downtime data of equipment

How to reduce downtime and improve availability of the complex equipment is very important. Although the unscheduled downtime（USDT） issues of the equipment are very complex, the self-organized criticality（SOC） is the right theory to study complex systems evolution and opens up a new window to the investigation of disasters, such as the sudden failure of the equipment. Firstly,SOC theory and its validation method are introduced. Then an SOC validation method for USDT of the equipment is proposed based on the above theory. Case study is done on bottleneck equipment in a factory and corresponding data pre-process work is done. The rescaled-range（R/S） analysis method is used to calculate the Hurst exponent of USDT time-series data in order to determine the long-range correlation of USDT data on time scale;at the same time the spatial power-law characteristic of USDT time series data is studied. The result shows that the characteristics of SOC are revealed in USDT data of the equipment according to the criterion of SOC. In addition, based on the characteristics of SOC,the overall framework of the prediction method for major sudden failure of the equipment is proposed based on SOC.     

基于隐藏马尔可夫模型的干扰抑制技术

研究了DS(direct sequence)扩频系统中基于隐藏马尔可夫模型HMM(hide Markov models)的干扰抑制技术，简要引述了算法原理，着重给出了该算法的改进方案和在具体干扰条件下的系统性能仿真。研究表明，该算法由于能够对干扰信号进行准确估计，因而减小了对有用信号的损伤，可以获得更好的抗干扰性能。通过减小复杂度的措施，可以用于实际系统，这对于应用DS扩频系统的短波通信和卫星通信，增强抗干扰能力具有重要意义。     

60Co-γ射线辐照对月季“蜻蜓”的诱变效应及突变体ISSR分析

为培育花色独特、栽培品质优良的新型蓝色月季,使用⁶⁰Co-γ射线对月季“蜻蜓”进行辐照处理,并设置40,50,60 Gy三个剂量梯度.月季“蜻蜓”辐照产生的诱变效应表现为：(1)辐照处理均会对植株造成一定的损伤和产生抑制生长效应,且高剂量辐照处理的植株在生长过程中,出现生长点或老叶叶尖枯死、新叶生长缓慢、新芽不再萌发、植株根部萎蔫且出现腐烂发黑现象;(2)突变体在花型、花色、花期、花瓣等花部形状上与对照组(CK)存在较大差异,具体表现在突变体的最大花径增大或缩小、花色改变、花期缩短、花瓣数量和花瓣形态改变.采用简单重复序列区间扩增多态(ISSR)分子标记技术及非加权组平均法(UPGMA)对辐照处理的月季“蜻蜓”材料进行遗传多样性和亲缘关系聚类分析,发现月季“蜻蜓”经过辐照诱变之后遗传物质有不同程度的突变.以上结果为培育优质蓝色月季品种奠定了基础.     

基于超螺旋精度提升机制的OFDM网络信道噪声消除算法

为解决当前OFDM网络信道噪声消除算法难以规避信道中的窄带莱斯噪声,且抗信道衰落能力不强,以及信道间普遍存在严重的频率干涉问题,提出了一种基于超螺旋精度提升机制的OFDM网络信道噪声消除算法.首先,根据各个传输子信道具有差异化的频率载波特性,将传输子信道等价为接收背景中的接收点,从而构建了超螺旋接收结构,有效消除不同传输子信道间存在的频率干扰特性,降低信道窄带莱斯噪声对信号预发射过程的衰落影响;随后,基于角度识别方式进行锐-钝识别,并结合拐点思想,采用序列重排技术,将待发射信号进行消波处理,并进行自旋精度提升,从而提高了其抗窄带莱斯噪声的性能.仿真实验表明:与常见的超高频精度自适应机制(UHF adaptive,UHFA)、共线度自旋精度提升机制(the degree of accuracy of collinear spin,DACS)相比,本文算法与理想状态下的OFDM功率谱密度曲线最为接近,具有更高的信号增益水平与更低的信道误码率.     

5·12汶川地震在武都区造成灾害的特点分析

5·12汶川地震引发了崩塌、滑坡、泥石流和地裂缝等次生地质灾害．经过对武都区地质灾害应急排查,确定地质灾害隐患点516处,其中由地震引发新的灾害占87．8％．通过运用GIS技术手段对灾害点综合分析,发现这次地震在武都区造成的灾害具有一定的规律性．通过灾害点具体现象和理论相结合分析了3种灾害特点的成因,为以后抗震减灾提供一些技术参考和理论依据．     

高能级强夯在大厚度黄土地区应用研究

用强夯处理湿陷性黄土地基的主要目的是消除湿陷性并提高其承载力,目前规范中只有8500kN·m能级以下的有效深度预估值,而15000kN·m的高能级强夯在大厚度湿陷性黄土地区的应用在国内尚属首次．通过工程实例介绍了其试夯情况和深达15m的处理效果,为今后的类似工程提供了参考依据．     

正交约束PARAFAC的DS-CDMA盲接收机

根据平行因子(PABAFAC)模型,研究多用户DS-CDMA系统的盲检测算法.利用DS-CDMA系统中扩频码正交或近似正交的性质,提出了一种基于正交约束PARAFAC(OC-PARAFAC)的DS-CDMA盲接收机,给出了正交约束情况下三线性分解的克拉美-罗界的解析表达式.实验表明正交约束三线性最小二乘(OCTALS)算法在处理DS-CDMA信号时比传统的TALS算法具有更低的克拉美-罗界.与传统的PARAFAC接收机相比,OC-PARAFAC接收机改善了误码率性能,具有更快的收敛速度.     

Jacobi符号在数论中的应用

Jacobi符号是数论中的重要工具.通过具体实例,讨论了利用Jacobi符号判断有理数是否是整数、求解不定方程、判断递归序列是否是平方数的基本方法.     

有向图谱半径的上界

本文利用矩阵理论, 给出了用图的出度序列表示的简单有向图的谱半径的可达上界, 同时还刻画了达到上界的极图.