基于时间反转理论及压电阵列技术的损伤图像监测方法

结构损伤的监测、定位和辨识技术是结构健康监测研究中一个热点,也是当前研究的难点之一.针对结构损伤图像辨识研究的难点,分析了时间反转聚焦原理,结合压电阵列技术,提出了基于时间反转聚焦方法的板结构损伤图像监测方法,并进行了实验验证研究.实验结果表明该方法能较为有效地表征损伤特征和范围,实现简单,有助于结构健康监测的实用化.     

基于圆形压电阵列的主动Lamb波损伤成像监测研究

对主动Lamb波结构健康监测中的压电阵列技术进行了研究。分析了传统的矩阵式压电阵列在应用中存在的问题,基于回声式原理研究设计了圆形压电阵列方法,分析了该方法的特点和信号采集过程,结合时间反转成像技术,实现对损伤的监测,实验结果表明:该方法能克服传统矩阵式压电阵列在应用中存在的监测范围、信号监测能力差异等问题,最后分析了圆形压电阵列还存在的问题。     

无方向数据采集的相控阵结构健康监测研究

超声相控阵结构健康监测过程中由于按角度扫描的数据采集持续时间长,结构损伤前后采集的数据易受环境和结构变化的影响,针对这一问题,提出无方向数据采集的相控阵结构健康监测成像定位方法。基于相控阵方法,对采集后数据根据发射和接收过程进行时间延迟的计算,然后将监测结果进行二维成像。该方法在玻璃纤维复合材料板结构上的实验研究证明,采用无方向数据采集的相控阵结构健康监测方法能够精确监测结构中损伤并对损伤进行清晰成像;并且该方法可以大大缩短监测时间,从而使监测过程不受环境条件变化的影响,为超声相控阵监测方法的工程化奠定基础。     

航空运输集装托盘脱胶监测的概率成像方法

为了提高航空运输集装托盘使用的安全性与经济性,针对航空运输集装托盘脱胶监测技术的空白,提出了一种基于损伤概率成像方法的航空运输集装托盘脱胶监测方法.该方法首先使用损伤散射信号包络损伤因子计算方法求取各激励-传感通道上的损伤因子,然后使用损伤概率成像方法获取被监测区域的结构损伤概率图像,最后使用概率坐标加权算法计算出航空运输集装托盘脱胶的位置坐标.自制了一块试件对该方法进行了实验验证.实验结果表明:基于损伤概率成像方法的航空运输集装托盘脱胶监测方法可以对航空运输集装托盘脱胶进行不依赖信号传播速度的成像定位,定位误差不大于2 cm.     

基于声表面波技术的导弹健康管理系统研究

针对现有导弹诊断健康管理系统仅适用于电子分系统（部件）的局限性，提出一套面向弹上电子类设备和弹体结构材料的整弹健康管理系统。重点进行了基于稀疏阵列的导弹壳体材料声表面波健康监测方法研究。根据阵列的几何位置及超声信号的渡越时间进行超声成像，实现弹体材料中损伤的定位检测。同时，通过实验研究了弹体材料中声表面波的各向异性传播特性，对成像方法中的波速进行了修正。在此基础上，将该方法应用于典型弹体试件的（硅纤维复合板）健康监测实验中。结果表明，基于稀疏阵列的声表面波技术可以实现弹体试件中损伤成像及定位检测。研究工作为导弹整弹健康管理提供了一种可行的方案。     

基于碳纳米管薄膜电学成像的复合材料结构损伤识别研究

随着纳米技术的飞速发展,碳纳米管因其良好的自感应能力逐渐被应用在结构健康监测领域.提出将碳纳米管薄膜布置在复合材料结构表面作为智能感知层,结合电学成像方法,根据碳纳米管薄膜边界电压值的变化,重建损伤引起的电导率变化分布图像,以确定损伤情况.为提高电学成像效果,采用基于L1范数正则化的最小二乘法重建电导率变化分布,并利用L曲线法选取适当的正则化参数,结合内点法进行反演.搭建了电学成像测试系统并进行了实验研究,实验结果验证了本文所提出方法的可行性和有效性.     

无线结构健康监测传感器网络中的时间序列同步算法

现有的无线传感器网络时间同步算法的同步精度较低,无法满足分布式结构损伤检测系统的要求.文章提出一种基于最小化序列能量差的时间同步算法.该算法通过比较传感器节点在不同时刻记录的采样信号序列,采用比较能量差的方法进行时间序列自同步.经过理论分析及多次实验证明,采用该方法的同步精确度符合无线结构健康监测系统对时间同步精度要求.     

基于时间反转聚焦的声发射源定位算法

声发射检测可以判断损伤的活性和严重性而被广泛应用,但对损伤位置仍没有更准确的定位方法。提出一种基于时间反转理论的声发射源准确定位的方法。根据声发射被动监测的特点,研究采用时间反转聚焦方法使声发射信号能量叠加放大,提高信号的信噪比,并分析推导了具体损伤声源信号时间反转聚焦增强过程;利用时间反转对声发射源的自适应聚焦能力,重建信号传播波动图,通过信号聚焦显示出损伤声源位置和区域;最后通过数值仿真对该方法进行验证,仿真结果表明能有效提高损伤声源信号的能量,能够对检测区域的信号重建,并通过显示准确给出损伤声源位置,定位精度较常规时差定位法有较大提高。     

基于随机森林的桁架结构损伤程度预测

为适应桁架结构健康监测技术的发展,进一步优化桁架结构损伤程度预测效果,提出一种基于随机森林的桁架结构损伤程度预测算法。算法建立并优化桁架结构损伤数据库,对多个损伤信号分量提取频域特征,通过孤立森林算法和缺失森林算法对数据库进行异常检测和数据补全,并采用主成分分析法对其进行特征降维。经实验验证,算法能够针对不同损伤程度的桁架结构敏感度做出有效判定,与极端随机树、AdaBoost、Bagging等回归算法相比,均方误差显著降低,为桁架结构健康监测提供了有效的预测手段。     

桥梁结构的未标记模态特征稀疏编码深度学习监测*

由于建筑物结构健康问题大部分是累积性损害,很难被检测到,实际结构和环境噪声的复杂性使得结构健康监测更加困难,并且现有方法在训练模型时需要大量的数据,但是实际中对于数据的标记是很复杂的。为克服该问题,通过配备无线传感器网络,并采用稀疏编码实现桥梁结构健康监测,然后通过大量未标记实例在实现特征提取基础上进行稀疏编码算法训练,实现数据维度压缩和无标记数据预处理。其次,利用深度学习算法实现桥梁结构健康监测类别预测,同时基于线性共轭梯度对Hessian优化进行改进,利用半正定高斯-牛顿曲率矩阵替换不确定Hessian矩阵,进行二次目标组合,以实现深度学习算法效率提升;实验结果表明,所提深度学习桥梁结构安全检测算法实现了环境噪声稀疏编码水平下的高精度结构健康监测。     

Only connect: teaching, technology and telesis

Abstract This paper describes an approach to the design of interactive multimedia materials being developed in a European Community project. The developmental process is seen as a dialogue between technologists and teachers. This dialogue is often problematic because of the differences in training, experience and culture between them. Conditions needed for fruitful dialogue are described and the generic model for learning design used in the project is explained.     

European Community policy and the market

Abstract This paper starts with some reflections on the policy considerations and priorities which are shaping European Commission (EC) research programmes. Then it attempts to position the current projects which seek to capitalise on information and communications technologies for learning in relation to these priorities and the apparent realities of the marketplace. It concludes that while there are grounds to be optimistic about the contribution EC programmes can make to the efficiency and standard of education and training, they are still too technology driven.     

一种自适应子融合集成多分类器方法

融合集成方法已经广泛应用在模式识别领域,然而一些基分类器实时性能稳定性较差,导致多分类器融合性能差,针对上述问题本文提出了一种新的基于多分类器的子融合集成分类器系统。该方法考虑在度量层融合层次之上通过对各类基多分类器进行动态选择,票数最多的类别作为融合系统中对特征向量识别的类别,构成一种新的自适应子融合集成分类器方法。实验表明,该方法比传统的分类器以及分类融合方法识别准确率明显更高,具有更好的鲁棒性。     

Avoiding semantic and temporal gaps in developing software intensive systems

Development of software intensive systems (systems) in practice involves a series of self-contained phases for the lifecycle of a system. Semantic and temporal gaps, which occur among phases and among developer disciplines within and across phases, hinder the ongoing development of a system because of the interdependencies among phases and among disciplines. Such gaps are magnified among systems that are developed at different times by different development teams, which may limit reuse of artifacts of systems development and interoperability among the systems. This article discusses such gaps and a systems development process for avoiding them.     

Designing economic np control charts: A programmed simulation approach

This paper presents control charts models and the necessary simulation software for the location of economic values of the control parameters. The simulation program is written in FORTRAN, requires only 10K of main storage, and can run on most mini and micro computers. Two models are presented - one describes the process when it is operating at full capacity and the other when the process is operating under capacity. The models allow the product quality to deteriorate to a further level before an existing out-of-control state is detected, and they can also be used in situations where no prior knowledge exists of the out-of-control causes and the resulting proportion defectives.     

The development of robot art

Going through a few examples of robot artists who are recognized worldwide, we try to analyze the deepest meaning of what is called “robot art” and the related art field definition. We also try to highlight its well-marked borders, such as kinetic sculptures, kinetic art, cyber art, and cyberpunk. A brief excursion into the importance of the context, the message, and its semiotics is also provided, case by case, together with a few hints on the history of this discipline in the light of an artistic perspective. Therefore, the aim of this article is to try to summarize the main characteristics that might classify robot art as a unique and innovative discipline, and to track down some of the principles by which a robotic artifact can or cannot be considered an art piece in terms of social, cultural, and strictly artistic interest. This work was presented in part at the 13th International Symposium on Artificial Life and Robotics, Oita, Japan, January 31–February 2, 2008     

Explanation and prediction: an architecture for default and abductive reasoning

Although there are many arguments that logic is an appropriate tool for artificial intelligence, there has been a perceived problem with the monotonicity of classical logic. This paper elaborates on the idea that reasoning should be viewed as theory formation where logic tells us the consequences of our assumptions. The two activities of predicting what is expected to be true and explaining observations are considered in a simple theory formation framework. Properties of each activity are discussed, along with a number of proposals as to what should be predicted or accepted as reasonable explanations. An architecture is proposed to combine explanation and prediction into one coherent framework. Algorithms used to implement the system as well as examples from a running implementation are given.     

Three Process Perspectives: Organizations, Teams, and People

This paper provides the author's personal views and perspectives on software process improvement. Starting with his first work on technology assessment in IBM over 20 years ago, Watts Humphrey describes the process improvement work he has been directly involved in. This includes the development of the early process assessment methods, the original design of the CMM, and the introduction of the Personal Software Process (PSP)^SM and Team Software Process (TSP){^SM}. In addition to describing the original motivation for this work, the author also reviews many of the problems he and his associates encountered and why they solved them the way they did. He also comments on the outstanding issues and likely directions for future work. Finally, this work has built on the experiences and contributions of many people. Mr. Humphrey only describes work that he was personally involved in and he names many of the key contributors. However, so many people have been involved in this work that a full list of the important participants would be impractical.     

基于复小波噪声方差显著修正的SAR图像去噪

提出了一种基于复小波域统计建模与噪声方差估计显著性修正相结合的合成孔径雷达(Synthetic Aperture Radar,SAR)图像斑点噪声滤波方法。该方法首先通过对数变换将乘性噪声模型转化为加性噪声模型,然后对变换后的图像进行双树复小波变换(Dualtree Complex Wavelet Transform,DCWT),并对复数小波系数的统计分布进行建模。在此先验分布的基础上,通过运用贝叶斯估计方法从含噪系数中恢复原始系数,达到滤除噪声的目的。实验结果表明该方法在去除噪声的同时保留了图像的细节信息,取得了很好的降噪效果。     

How do children do mathematics with LOGO?

Abstract  This paper considers some results of a study designed to investigate the kinds of mathematical activity undertaken by children (aged between 8 and 11) as they learned to program in LOGO. A model of learning modes is proposed, which attempts to describe the ways in which children used and acquired understanding of the programming/mathematical concepts involved. The remainder of the paper is concerned with discussing the validity and limitations of the model, and its implications for further research and curriculum development.