基于多级子空间投影的侧扫声呐底混响抑制

底混响是侧扫声呐进行沉底静态小目标探测时的主要背景干扰,针对此问题提出了一种基于多级二分奇异值分解BSVD子空间投影的底混响抑制方法.该方法首先对接收信号构造二阶Hankel矩阵,通过矩阵的奇异值确定混响子空间,然后利用正交子空间投影抑制回波信号中的底混响,最后根据所选级数对回波信号进行多级正交子空间投影,并用otsu...     

主动声纳的时频盲分离算法研究

主动声纳目标探测中,水雷等浅海安静型小目标声散射回波受海洋环境干扰严重,影响对目标特征的准确提取与识别,探测可靠性低.针对上述问题,研究一种结合形态学滤波的时频域盲分离算法,根据主动声纳回波中目标与混响的时频特征差异,设计形态学结构元的几何结构,滤除与目标谱不重叠的混响及互项干扰,再利用波形聚类方法优化与目标谱重叠的混响干扰,突出目标亮点的时频谱线,得到目标声散射的自项时频信息,最后获得目标亮点的时频域解混矩阵,分离出目标声散射信号.数值仿真结果表明,结合形态学滤波的时频域盲分离算法,提高了目亮点信号的信混比.     

随机共振在水声信号检测中的应用

海洋混响是水声信号目标检测中的主要干扰之一,克服混响干扰一直足水声信号处理的一个重要课题.如何在混响背景中有效地进行水声信号目标的检测?为了解决着一问题,引入了随机共振的方法.首先,在随机共振的原理基础上,给出了利用随机共振原理检测微弱周期信号的基本方法,并对方法进行了分析与验证.然后,将方法应用于以模拟混响为背景干扰的水声信号的检测中,仿真结果进行了分析,证明了方法的可行性.     

混响背景下的距离扩展目标的GLRT检测

研究浅海混响背景下距离扩展目标的检测问题,由于海洋环境的干扰,影响信号检测效果.为此,提出了一种混响背景下的广义似然比双门限检测器(DHGLRT-RE).首先利用自回归(AR)模型对混响进行建模,利用估计的AR系数对混响进行预白化处理得到近似的白噪声环境,然后在近似白噪声背景下利用GLRT双门限检测器对目标进行检测.第一门限筛选出信噪比较高的待测距离单元,将对应的检测统计量非相干累加与第二门限进行比较,从而检测目标的有无.仿真结果说明,提出的检测器在混响背景下提高了对距离扩展目标的检测概率.     

海底混响的空时模型及仿真

研究海底混响特性问题,海底混响是声纳设备在浅海海域进行水下探测、通信和导航中遇到的主要干扰信号.为了有效识别水中混响特征,提出了一种海底混响模型,用仿真软件为实现抗混响提供较完整的依据.采用划分散射单元,得到包含相位信息、多普勒频移信息等主要影响混响形成具有空时特性的海底混响模型,能广泛适用于各种阵列,并推导了任意阵型的阵列信号输出模型,采用带通采样技术在matlab上进行仿真,结果表明,实现了混响模型的瞬时值和包络值的概率密度分布、频谱、空时特性等.表明了仿真特性能够为抗混响研究提供依据.     

运动基阵的混响信号仿真研究

研究建立混响信号的模型,针对水声混响信号来源于水中大量的随机散射体的散射,并对抗混响信号的研究提供保证.为适用于水声实时仿真系统中的混响环境,保留混响信号所具有的统计特征实现仿真混响信号,提出了基于FIR及IIR滤波器设计的实现方法,从而提供了一种适用于半实物仿真的实时混响信号实现方法,通过对比仿真条件下IIR滤波器设计实现混响信号的效果进行仿真.结果表明,采用滤波器设计实现的仿真混响信号与随机点散射累积实现的混响信号统计特征一致,但混响信号生成速度明显快于后者,为实验混响模型提供了依据.     

三维成像声呐目标回波建模仿真及分析

针对三维成像声呐成像及后续图像处理背景下存在实际场景数据难获取的问题,提出海底混响场景下实际目标建模模型和回波信号仿真的方法.文章首先建立了浅海楔形海底的线状目标回波模型,然后基于射线声学混响模型,采用信道卷积法推导得到理想环境下的回波信号以及浅海环境混响干扰下的回波信号,最后对回波信号进行三维波束成像和三角网重建,并...     

水下目标的声纳回波数据仿真

对水下静态小目标的声纳回波信号进行了仿真研究。针对水下静态小目标中典型的圆柱壳体加球冠形头部的结构,建立了该类目标声纳回波信号的亮点模型,以及声纳系统走航探测时的动态数据模型。在计算仿真数据时,将模型化的目标回波数据与真实的水声背景混响数据相融合,更真实的模拟实际情况。通过与湖海试实验结果的对比,该模型仿真效果良好,可以为声纳信号处理、水下目标识别等方面的研究提供支持。     

浅海主动声呐空时自适应混响抑制方法

混响伴随着主动声呐系统发射信号而产生的干扰,当声呐平台有一定的运动速度时,不同方位对应的混响具有不同的多普勒频移,使得混响在频域范围内形成一定带宽的干扰,与信号频谱发生混叠,采用常规的运动平台自身运动补偿技术单纯地从频域抑制混响效果很不理想。针对该问题,采用一种空时自适应处理方法利用混响空时分布特性,在最小化干扰的约束条件下求得自适应加权系数,使目标信号不受损失同时有效地抑制混响。通过仿真结果证明了该方法的有效性。     

主动声纳阵的混响仿真及检验

研究海洋混响的干扰检验问题,由于真实的混响数据信息难获取,混响仿真中不能体现声纳信号形式、平台运动、海洋环境的问题,针对传统方法不能准确检验混响情况,提出了一种基于HODGKISS单元散射理论的海洋混响的阵列模型,把过去单一阵元的混响仿真推广到整个阵列的混响仿真,并考虑了发射波形、发射信号形式、声纳平台运动以及海洋环境等参数,使仿真条件尽量接近真实环境.最后,通过仿真比较瞬时值和包络概率密度分布、空时二维谱几个方面的特性,实验证明了模型及混响仿真结果的准确性和有效性.     

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.