小孔径扩散焊质量检测用超声换能器的研制

为了提高超声成像系统的分辨率,研制了用于检测双金属转子复合层扩散焊连接质量的超声换能器.论文提出了用声程相等的概念来设计超声传感器的聚焦,详细介绍了其制作工艺,并利用数字动态光弹仪器对超声换能器的聚焦声场进行了验证.制作的换能器中心频率为10 MHz,波列只有两个周期,在实际的检测中可分辨0.5 mm当量的缺陷.     

基于洛伦兹力机理的电磁超声周向导波传感器研制

在分析基于洛伦兹力机理的电磁超声周向导波检测原理的基础上,通过实验方式研究传感器参数对检测信号幅值的影响,根据实验结果确定了传感器参数.设计并制作了电磁超声周向导波传感器.对所研制的传感器进行性能测试,结果表明:该传感器能检测出Φ3.2 mm的通孔缺陷.     

弹性层中的SH板波传播特性及电磁超声激励方法的研究

研究水平剪切波(Shear Horizontal,简称SH波)的传播特性及激励接收方法对该波在无损检测和声弹性技术范围内的工程应用有着重要的价值.首先,SH波在弹性层中传播的多模态、频散特性在文中作了详细的分析,同时重点研究了电磁超声技术在非铁磁性材料波导中产生SH波的探头结构和基础理论,并以试验的方法验证了其部分电声特性,结果表明,SH板波具有其他类型波所没有的独特特性,而电磁超声技术在SH波的激励接收方面有着很大的优势.     

电磁超声换能器优化设计与板状结构损伤成像应用研究

提出了一种用于板状结构损伤成像的虚拟电磁超声换能器EMAT(Electromagnetic Acoustic Transducer)阵列.由螺旋线圈和圆柱形永磁铁组成的电磁超声换能器可以通过洛伦兹力在铝板中有效地激发低频散和高幅值的单一S0模态兰姆波.实验研究了电磁超声换能器配置参数(如激发频率,螺旋线圈外径、螺旋线圈内径和提离距离)对S0模态兰姆波性能的影响.另外,将接收电磁超声换能器移动到用于接收兰姆波的多个预定义位置来构建虚拟传感器阵列,实验研究了阵元间距和阵元数量对成像结果的影响.结果表明,通过相控虚拟聚焦成像方法,虚拟电磁超声换能器阵列的成像结果与实际损伤位置吻合良好.     

桩柱周期分布的平板中SH波的传播特性分析及其在聚焦透镜设计中的应用研究

本文首先建立求解水平剪切波(即SH波)在桩柱周期分布的板中传播的理论模型,计算其带隙结构,并与有限元仿真的结果进行对比,验证该理论模型的准确性.在此基础上,应用此模型研究桩柱高度对最低阶水平剪切波(即SH0)的影响,发现随着桩柱高度的增加,SH0的相速度降低.基于桩柱高度与相速度的敏感特性,设计了一款可实现SH0聚焦的透镜,并进行相关的仿真分析,研究该透镜的适用范围和聚焦效果.研究结果表明,该透镜聚焦位置准确,聚焦能量高,且在不改变结构的情况下在一定频率范围内均可实现聚焦功能,从而为能量收集、超声医学、无损检测、吸声降噪等应用提供新的思路.     

增强SH波电磁超声传感器信号的方法与实验

电磁超声传感器技术作为一种非接触无损测量方法,可用于恶劣工况的无损检测,尤其是可以实现水平剪切(SH)波的激励和接收。基于磁致伸缩效应的常规SH波电磁超声传感器信号较弱,为得到较强SH信号,改善信噪比,提出了一种增强电磁超声传感器信号的方法。该方法是在主永久磁铁闭合磁路上施加辅助永久磁铁,提高电磁超声线圈下部构件磁化强度,从而增强信号。实验证明:此方法可以使信号得到明显增强,并且有助于提高缺陷检测能力。     

电磁超声换能器线圈设计与提高换能效率研究

提出了一种提高电磁超声换能器EMAT(Electromagnetic Acoustic Transducer)换能效率的方法,首先,在COMSOL Multiphysics软件中建立了电磁超声无损检测激发探头有限元模型,然后研究了电磁超声换能器中双层叠加螺旋线圈的基板厚度、铜箔厚度以及提离距离对换能效率的影响.结果表明:减小基板厚度以及提离距离,增加线圈铜箔厚度可以提高EMAT换能效率.最后通过实验进行验证,仿真结果与实验基本一致.     

大作用距离超声波传感技术研究

研制了谐振频率为24.5 kHz的新型气介超声测距传感器,其作用距离超过了32 m.该传感器是由径向-厚度耦合谐振模式的超声波换能器、推挽变换器和具有高信噪比的时间-增益可变接收器所组成的.其中,作为超声波发送器的推挽变换器能够为阻抗为475 Ω的换能器负载提供峰-峰值超过400 V的交变电压.建立了基于NI 6024E数据采集控制卡和PC机的超声波测距平台,采用超声波发送信号与回波信号的包络相关来估计声波的射程时间,提高了超声波测距系统的鲁棒性.     

基于AlN的压电MEMS超声换能器阵列

针对目前超声换能器机电耦合系数较低的问题,本文设计了一种以氮化铝(AlN)为压电材料的微机电系统(MEMS)超声换能器阵列以提高机电耦合系数.在COMSOL Multiphysics中用模态分析确定了超声换能器工作在一阶模态下有最大的声场输出,并给出了其声场传播示意图.通过对超声换能器在工作状态时的应力分析,计算出当上...     

弯曲振动超声换能器在陆地自主车上的应用

因为作用距离较短,所以超声波传感器一般用于机器人低速运行在静态环境中进行的短距离测量,无法作为高速行驶陆地自主车的前视传感器来使用.为解决问题,根据超声换能器功率高、频率低时,发射的超声波衰减慢、传播距离远的原理,基于能改善传统压电换能器和磁致伸缩换能器的声匹配、提高气介式超声换能器辐射声功率及效率的弯曲振动换能器,研制了一种高功率、低频率、作用距离远的超声传感器,其波束角为9°,最大作用距离可超过35m,经实验测定,超声传感器在最大量程处测量数据稳定、指向性强,完全能够满足在高速行驶的陆地自主车进行远距离测距的要求.     

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.