基于对数域同态滤波的时延估计算法研究

针对水声信道中窄带信号的多途时延估计问题,本文在对复倒谱时延估计方法进行研究的基础上,提出了一种基于对数域同态滤波的时延估计算法.结合复倒谱与同态滤波思想,将接收的窄带信号首先变换到对数域,然后与本地存储的信号进行谱减法,再对相减后的信号进行滤波以消除残余的信号与噪声成分,最后将其恢复到时域以获取多途时延估计.与传统的匹配滤波/相关处理以及复倒谱分析方法相比,本文算法具有时延估计精度高、噪声抑制能力较强等特点.仿真与湖试数据处理结果证明了该方法的有效性.     

基于无噪后验错误矢量信号能量的变正则因子仿射投影算法

变正则因子技术是提高仿射投影自适应算法性能的重要方法之一.由于环境噪声的影响,现有的变正则因子自适应算法收敛速度较慢且稳态误差较大,各种测量、评估误差的存在进一步恶化了算法性能.为提高自适应算法的跟踪性能,本文在分析无噪先验错误矢量、无噪后验错误矢量和额外均方错误间关系的基础上,提出通过最小化无噪后验错误矢量信号能量来推导自适应变正则因子表达式的方法.在实践应用中,该方法利用了测量噪声的统计方差特性,并提出一种更加光滑且更加容易控制的指数缩放因子评估方法.系统辨识的仿真结果表明本文方法与传统的变正则因子方法以及变步长方法相比有更快的收敛速度与更低的稳态误差.     

Learning Association Rules and Tracking the Changing Concepts on Webpages: An Effective Pornographic Websites Filtering Approach

We applied the decision tree algorithm to learn association rules between webpage’s category (pornographic or normal) and the critical features. Based on these rules, we proposed an efficient method of filtering pornographic webpages with the following major advantages: 1) a weighted window-based technique was proposed to estimate for the condition of concept drift for the keywords found recently in pornographic webpages; 2) checking only contexts of webpages without scanning pictures; 3) an incremental learning mechanism was designed to incrementally update the pornographic keyword database.     

一种针对类别数据分析的平行坐标改进方法

针对类别数据在传统平行坐标系中的映射重叠问题，提出类别统计和数据累积式偏移映射的平行坐标改进方法。该方法首先统计多维数据中的各类别数据的频次，使用直方图表示其记录数，将直方图与平行坐标相结合提出改进平行坐标。然后提出一种类别数据的数据累积式偏移算法，将映射在一点的数据均匀分布在坐标轴上的一定区域中，区域的范围根据数据记录数确定。最后设计实现可视化分析系统，通过改进平行坐标实现对数据集的筛选、条件交叉分析、类别间数据分析和维度间数据分析；通过联动视图和弦图两种方式实现每两个维度间的对比分析；通过字云显示每一维度的频次分布。案例数据集实验结果表明，该方法能在平行坐标中实现各维度中类别间的对比、各维度中记录数排序，以及对筛选数据集的分析，展示类别型数据维度间的关联关系。     

潜孔钻机湿式除尘系统的改造

潜孔钻机由于钻孔直径大、钻孔效率高等优点,在矿山开采、建筑等领域应用广泛。潜孔钻机潜孔式凿岩的实质是在轴向压力的作用下,利用冲击和回转两种力进行破碎岩石的方法,最终形成了大量的岩粉通过压缩空气沿着钻杆与孔壁之间排出孔外。潜孔钻机设计了干式除尘和湿式除尘两套系统,根据现场使用情况干式除尘系统不适合现场工况使用,湿式除尘系统由于结构设计不合理导致除尘效果不稳定。通过对湿式除尘系统结构分析总结,并对其制定了改造方案,并组织了实施,取得了良好除尘效果。     

γ-γ符合测量系统的新型前端读出电路研制

研制了一种新型前端读出电路，用于重离子治癌装置中符合测量原型系统的研究和测试。电路主要包括能量链、时间链和数据处理单元。能量链由截止频率7 MHz的抗混叠滤波器和模数转换器(ADC)组成，形成波形采样电路；时间链由高速比较器构成的定时甄别电路和时间数字转换器（TDC）组成；数据处理单元基于现场可编程门阵列(FPGA)设计实现。电路的线性度优于0.8%，噪声小于0.8 mV（RMS）。配合LaBr3单晶体条测试，能量分辨为4.5%（FWHM），在与LYSO晶体阵列配合测试时，位置映射散点图清晰。该前端读出电路性能优于CAMAC系统，具有较好的实际应用前景。     

Inorganic thermoelectric materials: A review

Thermoelectric generator, which converts heat into electrical energy, has great potential to power portable devices. Nevertheless, the efficiency of a thermoelectric generator suffers due to inefficient thermoelectric material performance. In the last two decades, the performance of inorganic thermoelectric materials has been significantly advanced through rigorous efforts and novel techniques. In this review, major issues and recent advancements that are associated with the efficiency of inorganic thermoelectric materials are encapsulated. In addition, miscellaneous optimization strategies, such as band engineering, energy filtering, modulation doping, and low dimensional materials to improve the performance of inorganic thermoelectric materials are reported. The methodological reviews and analyses showed that all these techniques have significantly enhanced the Seebeck coefficient, electrical conductivity, and reduced the thermal conductivity, consequently, improved ZT value to 2.42, 2.6, and 1.85 for near-room, medium, and high temperature inorganic thermoelectric material, respectively. Moreover, this review also focuses on the performance of silicon nanowires and their common fabrication techniques, which have the potential for thermoelectric power generation. Finally, the key outcomes along with future directions from this review are discussed at the end of this article.     

基于修正 RSSI 值的四边形加权质心定位算法

在利用接收信号强度指示(RSSI)对无线传感器网络中的未知节点进行定位时,RSSI 值易受环境的影响导致定位误差, 为此提出基于 RSSI 测距修正的四边形加权质心定位算法(QWCRC)。 先对来自同一锚节点的多个 RSSI 值进行卡尔曼滤波,得 到修正的 RSSI 值,致使测距尽可能的接近真实距离;再采用四边形加权定位对未知节点进行定位,同时利用最小二乘法进行辅 助定位,此算法对于相邻锚节点圆不相交的情况给出新的解决方案。 实验结果对比表明,改进的算法相比较于四边形加权质心 算法(QWC)和 RSSI 测距修正的三角形加权算法(TWCRC),在锚节点数目 5×5 和噪声强度为 0 dbm 时,定位精度可分别提升 87. 14%和 35. 51%。     

Improvements in small-scale standardized testing of geotextiles used in silt fence applications

Silt fence have been used as a means for intercepting and treating construction site stormwater runoff prior to offsite discharge for well over 30 years. Standard small-scale testing methodologies for evaluating the filtering component of silt fence installations have failed to mimic realistic flows and sediment loadings commonly seen in field applications. To address these issues, this study evaluated the performance capabilities of two nonwoven and three woven silt fence geotextiles using an innovative testing methodology and a newly developed small-scale testing apparatus. The overall intent for conducting the evaluations was to develop a deeper understanding of effluent flow rates, sediment retention capabilities, and water quality impacts associated with geotextile fabrics. Results suggest that effluent flow rates of nonwoven geotextiles are on average 43% lower than woven materials, which results in extensive upstream retention times of impounded stormwater for nonwoven materials. Sediment retention results indicate that nonwoven geotextiles have an average sediment retention rate of 97% while woven geotextiles average 91%. Finally, water quality analyses suggest that the primary means for turbidity reductions rely on the process of sedimentation during the 30-min test period (i.e., 46% reduction) and filtration during the 90-min dewatering period (i.e., 19% reduction).     

New version of continuous–discrete cubature Kalman filtering for nonlinear continuous–discrete systems

For nonlinear continuous–discrete systems, this paper elaborates a new accurate implementation of continuous–discrete cubature Kalman filter (CD-CKF). As the main contribution of this work, the new Kalman prediction stage begins by integrating the nonlinear continuous model for all the cubature sample vectors; the prior estimate state and covariance prediction are based on the weighted statistics of these integrated cubature sample vectors and the Gauss–Legendre approximation scheme. The new square root form CD-CKF is also derived and accurately implemented by combining with the modified variable stepsize NIRK. As the advantages of proposed approach, the complicated and error-prone processes of solving covariance differential equation or calculating derivatives are avoided, while the positive semi-definiteness of prior error covariance are numerically guaranteed. Simulations of traffic control scenarios further confirm the new approach’s superior filtering performance in both reliability and accuracy.