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.     

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.     

Low complexity method for spreading sequence estimation of DSSS signal in non-cooperative communication systems

It is a necessary step to estimate the spreading sequence of direct sequence spread spectrum (DSSS) signal for blind despreading and demodulation in non-cooperative communications. Two innovative and effective detection statistics axe proposed to implement the synchronization and spreading sequence estimation procedure. The proposed algorithm also has a low computational complexity with only linear additions and modifications. Theoretical analysis and simulation results show that the algorithm performs quite well in low SNR environment, and is much better than all the existing typical algorithms with a comprehensive consideration both in performance and computational complexity.     

基于有符号移位序列的零相关区互补序列集交织构造方法

提出有符号的移位序列,将移位序列分为移位和符号两部分,并基于此提出一种零相关区互补序列集的交织构造方法.该方法利用完备互补序列对作为初始序列,根据初始序列与移位序列长度的关系分2种情况构造移位序列.第1种情况,二者长度互素,分析并证明移位序列中未引入与引入1个、2个负号后新序列对相关函数的分布情况,提出当移位序列长度为3时,获得完备互补序列集的方法;第2种情况,移位序列长度被初始序列长度整除,当移位序列长度为偶数时,提出获得完备互补序列集的方法.实例仿真证明了以上构造的有效性.     

全长基因的克隆

新基因全长cDNA序列、全长DNA序列的获得常常是分子生物学工作者面临的难题。本文就克隆全长基因的各种技术如文库筛选法、各种PCR技术及新发展起来的电子克隆法等方法作一简单综述。     

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。     

无线网络中自适应阵列处理算法的性能比较

信道间干扰是无线局域网在标准制定和实用中较重要的问题,如使用OFDM技术的高速率无线局域网标准802.11a,工作在国家信息基础设施频段5GHz(许多国家无需频段许可),因此,可能出现多个用户使用相同子载波连接接入点。该类系统中,选用最大似然法进行参数估计是最优的,但计算复杂度大;选用次优但低复杂度的期望极大法作参数估计更具实用价值。在多用户使用同一载波接入时,实际仿真证实了期望极大算法可有效地抵抗信道间干扰。     

刊中刊

《科学》324卷5928号435—537页牲畜解码动物驯化是人类社会发展过程中的一个重要部分,研究人员历时6年,花费5300万美金最终破解了牛的基因组序列,可以从历史和生物学的角度对牛有了更近一步的认识。牛的基因组的破译不仅有助人们了解牛的驯化过程,提高牛肉,牛奶的质量改善人类的生活质量,还有助了解人类的疾病。     

有限维Banach空间鞅型序列关系的一个证明方法

对文献<鞅与Banach空间几何学>中有限维Banach空间鞅型序列关系的定理给出了详细地证明,并且利用此证明思路得到了任意无穷维Banach空间上渐近鞅不是依概极限鞅的反例,对比该文献,本文的方法更为简洁易懂.