基于网格密度峰值聚类的实时雷达分选系统

雷达分选是雷达信号处理中的重要环节。为了解决从复杂电磁环境中准确分选出各个雷达信号的难题,提出一种新的基于网格密度峰值的数据流聚类算法,并将其应用于对雷达信号脉冲描述的实时聚类,从而进行雷达分选。该算法采用双重网格划分方式,解决传统基于网格的聚类算法中边界丢失的问题,并采用基于改进密度峰值的网格合并方式进行聚类避免将距离较近的类合并。仿真实验结果表明,该算法可以用于实时雷达分选,很好地处理了重叠严重的雷达信号,有较高的准确度和抗干扰能力。     

基于在线核聚类的雷达信号分选方法

提出一种变参数在线核聚类算法(OKCAP),将其应用于未知雷达辐射源信号分选中。OKCAP基于支持向量机的思想,采用核映射技术将数据映射到高维线性空间中进行处理,利用随机梯度下降法更新类的边界函数,且梯度下降步长和惩罚项参数可根据雷达信号动态调整,从而实现雷达辐射源信号的在线分选。仿真结果证明,该方法具有较快的聚类分选速度和较高的分选准确率。     

雷达脉内调制信号时频分布特征提取方法

针对复杂体制雷达辐射源信号分类识别问题,提出了一种基于时频分析的雷达脉内调制识别算法。首先对时频矩阵在时间域进行等间隔分区,然后通过检测区间内信号时频能量峰值提取其时频特征,最后用支持向量机实现了分类识别。该方法以信号时频能量峰值分布的差异区别不同的雷达脉内调制方式,有效降低了特征维数。仿真结果表明,该方法对雷达脉内调制具有较好高识别正确率,而且具有较强的抗干扰能力。     

雷达脉内调制方式的自动识别

为解决雷达信号分选中雷达脉内调制方式的自动识别问题,用一种新的时频图像简化算法来提取特征向量,随后利用支持向量机对提取的特征向量进行分类识别。首先从图像中提取包含有效信息的像素点,然后求出每一列像素点的中心点,最后对所有中心点进行相同长度的采样直接将图像转化为曲线,大大减少了特征维数。仿真实验结果验证了该算法对雷达信号的脉内调制方式识别具有较高正确率,并有一定的抗噪性,且在较低信噪比条件下仍然保持较高的正确率。     

一种新的ESM数据分选算法

研究获取敌方雷达辐射源数据,在识别准确性问题上,ESM数据分选在电子侦察领域有重要的作用.针对辐射源识别的正确性,采用聚类和到达角外推相结合方法实现ESM数据分选,提出一种基于支持向量机和到达角外推的ESM数据分选算法.算法根据ESM数据辐射源参数信息,用支持向量机实现ESM数据聚类,根据其参数实现分类,再将信号到达角外推,预测信号下一时刻到达角,并以最近邻域关联准则将信号方位角关联,从而实现ESM数据分选.算法有效结合了辐射源参数特征和到达角变化趋势,可在辐射源较密集的环境下实现分选.仿真结果和实际数据测试表明了算法的有效性.     

雷达信号全脉冲数据分析的极值序列分析方法(一)

针对脉冲雷达提出了一种新的雷达信号全脉冲数据分析算法——极值序列分析法。该算法能够分析雷达信号的脉冲脉幅、脉宽、到达时间、信噪比、载频、脉冲包络特征参数和脉内调制特征参数。该算法具有参数测量精度高、识别调制类型准确率高、算法速度快和存储空间小的优点。     

雷达信号全脉冲数据分析的极值序列分析方法(二)

针对脉冲雷达提出了一种新的雷达信号全脉冲数据分析算法——极值序列分析法。该算法能够分析雷达信号的脉冲脉幅、脉宽、到达时间、信噪比、载频、脉冲包络特征参数和脉内调制特征参数。该算法具有参数测量精度高、识别调制类型准确率高、算法速度快和所需存储空间小的优点。通过对该方法开发的Matlab工具箱的仿真测试，结果表明了该方法的有效性。     

一种新的未知雷达辐射源聚类分选方法

未知雷达信号的分选一直是雷达对抗情报处理中的难题。因此,提出了一种新的基于数据势场聚类的未知雷达信号分选方法。该方法无需预先指定分类数,利用信号参数之间的关联性自动进行聚类,以此达到分选的效果。同时方法适宜于处理大量数据,对噪声影响不敏感,无需先验知识支撑。最后,通过计算机仿真验证了该方法的可行性和有效性。     

基于混合核函数的雷达辐射源信号识别

针对单核函数支持向量机性能的局限性问题,提出将多项式核函数与高斯核函数构建成一种混合核函数支持向量机,并将其应用于雷达辐射源信号识别。将信号的常规参数与脉内特征参数作为输入特征,通过仿真实验,证明了算法的有效性,并比较了不同权值对于分选效果的影响。     

雷达辐射源信号符号化脉内特征提取方法

提出一种对雷达辐射源信号进行符号化分析的雷达辐射源信号脉内特征提取方法,该方法能够从信号中快速有效地提取定量信息。将符号化过程中反映信号自相关特性的采样时延和反映信号调制规律特性的香农熵作为脉内特征。通过对7种雷达辐射源信号仿真实验和数据分析表明:提取的样本特征在低信噪比(0~5 dB)情况下具有很好的抗噪性和可聚类性,同时算法计算简单快捷,能够简化分类器的设计,故有利于工程应用。     

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。     

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.     

Editorial: Special issue on recent advances in hybrid control theory and applications

正The demands of a rapidly advancing technology for faster and more accurate controllers have always had a strong influence on the progress of automatic control theory.In recent years control problems have been arising with increasing frequency in widely different areas,which cannot be addressed using conventional control techniques.The principal reason for this is the fact that a highly competitive economy is forcing systems to operate in regimes where     

Information for Authors

正Aim The Journals of Zhejiang University-SCIENCE(A/B/C)areedited by the international board of distinguished Chinese andforeign scientists,and are aimed to present the latest devel-opments and achievements in scientific research in China andoverseas to the world’s scientific circles,especially to stimulateand promote academic exchange between Chinese and for-eign scientists everywhere.     

Enhancing a leaf radiative transfer model to estimate concentrations and in vivo specific absorption coefficients of total carotenoids and chlorophylls a and b from single-needle reflectance and transmittance

The relative concentrations of different pigments within a leaf have significant physiological and spectral consequences. Photosynthesis, light use efficiency, mass and energy exchange, and stress response are dependent on relationships among an ensemble of pigments. This ensemble also determines the visible characteristics of a leaf, which can be measured remotely and used to quantify leaf biochemistry and structure. But current remote sensing approaches are limited in their ability to resolve individual pigments. This paper focuses on the incorporation of three pigments—chlorophyll a, chlorophyll b, and total carotenoids—into the LIBERTY leaf radiative transfer model to better understand relationships between leaf biochemical, biophysical, and spectral properties.Pinus ponderosa and Pinus jeffreyi needles were collected from three sites in the California Sierra Nevada. Hemispheric single-leaf visible reflectance and transmittance and concentrations of chlorophylls a and b and total carotenoids of fresh needles were measured. These data were input to the enhanced LIBERTY model to estimate optical and biochemical properties of pine needles. The enhanced model successfully estimated reflectance (RMSE = 0.0255, BIAS = 0.00477, RMS%E = 16.7%), had variable success estimating transmittance (RMSE = 0.0442, BIAS = 0.0294, RMS%E = 181%), and generated very good estimates of carotenoid concentrations (RMSE = 2.48 µg/cm², BIAS = 0.143 µg/cm², RMS%E = 20.4%), good estimates of chlorophyll a concentrations (RMSE = 10.7 µg/cm², BIAS = − 0.992 µg/cm², RMS%E = 21.1%), and fair estimates of chlorophyll b concentrations (RMSE = 7.49 µg/cm², BIAS = − 2.12 µg/cm², RMS%E = 43.7%). Overall root mean squared errors of reflectance, transmittance, and pigment concentration estimates were lower for the three-pigment model than for the single-pigment model. The algorithm to estimate three in vivo specific absorption coefficients is robust, although estimated values are distorted by inconsistencies in model biophysics. The capacity to invert the model from single-leaf reflectance and transmittance was added to the model so it could be coupled with vegetation canopy models to estimate canopy biochemistry from remotely sensed data.     

Mr. Twinn’s bombes

This article discusses the history and design of the special versions of the bombe key-finding machines used by Britain’s Government Code & Cypher School (GC&CS) during World War II to attack the Enigma traffic of the Abwehr (the German military intelligence service). These special bombes were based on the design of their more numerous counterparts used against the traffic of the German armed services, but differed from them in important ways that highlight the adaptability of the British bombe design, and the power and flexibility of the diagonal board. Also discussed are the changes in the Abwehr indicating system that drove the development of these machines, the ingenious ways in which they were used, and some related developments involving the bombes used by the U.S. Navy’s cryptanalytic unit (OP-20-G).