认知无线电中基于状态转移概率的感知时隙优化算法

为了在感知性能与系统传输效率之间对感知时隙长度进行有效折衷,在对授权信道当前分别为"占用"和"空闲"状态时的感知时隙长度与状态转移概率之间的关系进行分析的基础上,提出了一种基于授权信道状态转移概率预测的感知时隙长度优化算法。该算法能够保证在感知过程中始终用最小的感知时隙长度来满足系统对感知性能的最低要求,以最大化认知系统的能量效率与传输效率。     

压力容器定期检验中应优先选用超声方法检测埋藏缺陷

分析了压力容器埋藏缺陷存在的特点,比较了不同检测方法最适用的对象,提出压力容器定期检验时应优先选用超声波方法对埋藏缺陷进行检测.     

Asymptotic results for Fourier‐PARMA time series

Periodically stationary times series are useful to model physical systems whose mean behavior and covariance structure varies with the season. The Periodic Auto‐Regressive Moving Average (PARMA) process provides a powerful tool for modelling periodically stationary series. Since the process is non‐stationary, the innovations algorithm is useful to obtain parameter estimates. Fitting a PARMA model to high‐resolution data, such as weekly or daily time series, is problematic because of the large number of parameters. To obtain a more parsimonious model, the discrete Fourier transform (DFT) can be used to represent the model parameters. This article proves asymptotic results for the DFT coefficients, which allow identification of the statistically significant frequencies to be included in the PARMA model.     

电动力绳索系统的周期解求解及其稳定性分析

摘 要：对运行在倾斜圆轨道上的电动力绳索系统的动力学特性进行了分析研究。首先建立了系统的动力学模型,分别采用摄动法及推广后的数值算法求得系统的基本周期解,并运用所给数值算法中的稳定性判据分析了周期解的稳定性,得出该系统周期运动不稳定的结论。最后进行仿真验证,结果表明在摄动量较小时,两种求解算法得到的周期解基本相同,但当摄动量较大时,摄动法求得的周期解发生了畸变,不理想此时通常借助数值算法加以求解;仿真结果同样证实了所得周期解的不稳定特性。     

变速移动荷载下轨道结构动力响应解析解研究

为了研究列车进出站对周围环境的振动影响,推导了轨道结构在变速移动荷载作用下动力响应的解析解形式。首先以Duhamel积分为基础,应用动力互等定理,得到了变速移动荷载作用下,半无限弹性空间体上任意点动力响应的一般表达式;然后在该式的基础上,针对轨道结构的周期性特点,将荷载沿钢轨的移动问题转化为拾振点以轨枕间距为周期向反方...     

Influence of parallelogram cells in the axial behaviour of fibrous composite

Effective longitudinal shear moduli closed-form analytical expressions of two-phase fibrous periodic composites are obtained by means of the asymptotic homogenization method (AHM) for a parallelogram array of circular cylinders. This work is an extension of previous reported results, where elastic, piezoelectric and magneto-electro-elastic composites for square and hexagonal arrays with perfect contact were considered. The constituents exhibit transversely isotropic properties. A doubly period-parallelogram array of cylindrical inclusions under longitudinal shear is studied. The behaviour of the anisotropic shear elastic coefficients is studied for several cell geometry arrays. Numerical examples and comparisons with other theoretical results demonstrate that the present model is efficient for the analysis of composites in which the periodic cell is rectangular, rhombic or a parallelogram. The effect of the arrangement of the cells on the shear effective property is discussed. The present method can provide benchmark results for other numerical and approximate methods.     

通信信号的单通道盲分离和码元序列盲估计

针对被单根天线接收的多个通信信号的单通道盲分离问题,提出了一种新算法.该算法利用各个通信信号的周期性差异和波形差异,应用过采样技术和高阶统计量分析技术来构造适用于独立分量分析的多通道混合模型,从而将多信号盲分离问题转化成波形和码元序列的估计问题.仿真证实了新算法的可行性和优越性.     

基于光纤陀螺的转台周期性误差抑制方法

为抑制测角系统周期性测量误差对光电跟踪系统速度平稳性和成像效果的影响,采用光纤陀螺系统建立误差模型和误差补偿器,对系统进行误差补偿控制。首先,对测角系统测量结果中含有周期性误差的机理进行分析,建立了周期性测角误差的数学模型;其次,采用高精度光纤陀螺建立了一套基于傅里叶理论的角度测量误差模型采集系统,并通过七个步骤提取了测角误差模型的具体表达式;然后,根据提取的测角误差表达式,分四个步骤对系统周期性误差进行补偿控制。最后,通过跟踪成像实验来验证控制补偿的有效性。实验结果表明,跟踪速度误差的最大值降低到0.04 ()/s,比未补偿控制时降低了8倍左右,满足光学成像系统速度误差小于0.1 ()/s的要求,条纹成像效果得到了明显改善。     

Circle Chart for the Monitoring of Maxima in Periodic Processes

An important process characteristic is process maxima as it is often an important quality or performance parameter. Such measurements often play a vital role in process analysis and have to be monitored carefully. In this paper, we consider the problem of monitoring process maxima when the process exhibits a kind of periodicity. A circle chart for periodical process maxima with or without seasonal patterns monitoring is developed and studied, by modeling the process maxima using the extreme value distribution. Mean normalization is applied for periodic process monitoring with seasonal patterns to facilitate comparison between different sections and periods. The average cycle run length is proposed to measure charting efficiency. Copyright © 2014 John Wiley & Sons, Ltd.     

考虑桥墩-水平梁间弹簧接头的周期性高架桥平面内振动能量带分析

对无限多跨周期性高架桥结构的周期单元含一个桥墩、二个水平梁及三个连接弹簧,据Bernoulli-Euler梁及Bloch理论,推导具有水平梁-梁、水平梁-桥墩间弹簧接头传递矩阵,建立周期性高架桥结构平面内振动能量带特征方程。据该模型采用数值算例考察桥墩-水平梁刚度比、接头弹簧刚度等对周期性高架桥结构能量带分布特征影响。计算结果表明,具有水平梁-梁、水平梁-桥墩间弹簧接头的周期性高架桥结构发生平面内振动时,高架桥结构中存在与轴向压缩、横向剪切及弯曲振动对应的三类晶格波,即衰减较快且沿高架桥结构传播距离较短、只在某些频域能传播、除较小频率时难以传播外其它较宽频域均能传播。分析结果表明,高架桥结构设计时须保证结构基本主频不能落在较小频率区域,否则极易引起振动波能量集中,造成结构破坏。随周期性高架桥结构水平梁刚度、水平梁-梁接头弹簧刚度增大,沿高架桥结构传播的晶格波衰减会减慢,振动波能量沿高架桥结构会传播更远。