一种基于逻辑最小项化简的非线性函数实现方法

神经网络的数字VLSI实现中,非线性激活函数是计算部件设计中的难点.区别于其他模拟近似方法,本文提出的LMN方法使用逻辑最小项化简,对查找表(即函数真值表)进行有效压缩,提炼出函数最简逻辑表达式后,可直接生成结构规整的门级电路,且除线延时外,电路只有数个门级延时.该方法使用程序实现,简化了设计过程.结果表明当定点位数小于12时,该方法在速度及误差方面具有更好的性能.     

神经网络计算部件的数字VLSI优化设计

在神经网络的数字VLSI实现中，激活函数及乘累加等计算部件是设计中的难点。区别于使用乘法器及加法器的传统方法，该文提出的LMN方法基于查找表(即函数真值表)，使用逻辑最小项化简提炼出函数最简逻辑表达式后，可直接生成结构规整的门级电路，除线延时外，电路只有数个门级延时。以非线性函数为例对该方法进行了介绍，结果表明当定点数位数较少时，算法在速度及误差方面具有更好的性能。     

基于双逻辑门级图形表示的功耗优化技术

针对现有基于传统布尔逻辑进行逻辑级功耗优化的局限性,提出逻辑函数基于传统布尔逻辑和Reed-Muller逻辑的双逻辑门级图形表示的功耗优化方法.首先在逻辑级采用简化有序二叉决策图实现逻辑函数的双逻辑表示;然后通过代数分解和布尔分解获得双逻辑门级表示,进而基于功耗成本估算进行门级功耗优化;最后实现变量级和门级的两层次的优化方法.与学术界著名的ABC和工业界最先进的工具Design Compile(DC)进行比较的实验结果表明,该方法均具有一定的优势.     

组合逻辑

2.7 代数简化在上一节中,我们看到任何组合逻辑函数都可以用两种标准形式来表达,然后用两级电路来实现标准表达式,但是,这样的电路通常并不是实现逻辑函数的最经济的方法。在下面三节中我们要讨论使逻辑函数简化或者最佳化的方法以期达到最经济的效果。“简化”意味着寻找项数最少或者字母最少的表达式。“最佳化”则是意味着寻找最能适应某些简化规定的表达式。通常,我们总是先试图使表达式的项数减到最少,然后才是字母数。这种方式相当于先减少逻辑门的数目,然后再使输入端数亦减到     

基于演化算法的奇偶校验器自动设计*

基于演化算法技术,提出一种新的设计思想,实现奇偶校验器的电路自动设计.实验证明,多目标演化算法具有较少的运算量和较高的效率,能自动设计出使用逻辑门数更少、延时更小的奇偶校验器.     

基于反向神经网络的硬件木马识别

针对侧信道、逻辑功能、逆向工程等硬件木马检测技术存在高成本、高设备要求、易受工艺噪声影响和不适用于大规模电路等问题,提出了一种基于反向神经网络的门级硬件木马识别方法。通过提取电路的门级网表特征,使用电路特征集构建全新反向神经网络,训练成门级硬件木马分类器。通过不断调整神经网络的隐藏层数和节点数,实现门级硬件木马识别,最终达到99.82%的正常电路识别率、87.83%的木马识别率和99.27%的线网准确度,在正常电路几乎完全识别的前提下,获得了较高的硬件木马识别效果。     

大电路固定极性Reed-Muller逻辑快速转换算法

针对已有的列表技术在极性转换中只能解决中小规模电路的问题,提出一种基于不相交乘积项列表技术的快速转换算法.首先将待处理的逻辑函数表示为不相交乘积项之和形式;然后通过对已有的基于最大项的列表技术进行分析和改进,使得改进后的列表技术可以实现将逻辑函数从不相交乘积项的AND?OR形式向固定极性XNOR?OR形式的Reed-Muller逻辑转化.文中算法用C编程实现,并用MCNC标准电路进行测试.实验结果表明,该算法可以快速实现大电路的极性转换,并且具有运算速度对电路的输入变量数不敏感的特点.     

演化电路的故障自修复设计与实现

为进一步提高电子系统在恶劣环境下的生存能力,对采用虚拟可重构电路(VRC)技术的演化电路进行电路自修复研究。根据VRC技术,建立一个可用于数字电路演化的门级电路模型,设计二进制的染色体编码。给出实现电路自主修复的工作流程,探讨进行电路故障诊断和修复的途径。在直流无刷电机控制电路中模拟宇宙单粒子烧毁逻辑门产生常见的SA错误,使电机不能正常运转。通过在线演化方法,绕过错误单元使得电机恢复转动。实验结果证明,使用演化方法可以有效解决电路中的SA故障,提高电路的可靠性。     

基于布尔过程论的层次化延时分析方法

芯片设计的日益复杂化和高速化对电路精确的定时特性提出了越来越高的要求。电路的延时不仅与电路的拓扑结构有关,而且还与电路的逻辑功能及输入都有密切的关系。采用Boole过程论这种统一描述数字电路的逻辑行为和时变行为的代数形式作为理论基础,提出了波形多项式偏导的概念,并用之重新定义了敏化。用偏导定义的敏化改进了解析延时模型,基于最长可敏化通路的延时建立了电路模块或子电路的延时矩阵模型,由延时矩阵模型出发提出了一种精确的电路层次化延时分析方法。最后用实验验证了文中提出的延时分析方法的有效性。     

逻辑函数的立体化简法及其实现

逻辑函数的“立体化简法”是在卡诺图化简法的思想基础上设计的一种新型逻辑函数化简方法.这种方法用逻辑函数立方体代替卡诺图,在三维立体空间进行逻辑函数的化简.卡诺图法可以方便地化简四个变量以内的逻辑函数,而立体化简法可以方便地化简六个变量以内的逻辑函数.使用CubeScape在线网站的功能可以方便地表示逻辑函数立方体,让学生直观地感受逻辑函数最小项的逻辑相邻关系,更好地理解立体化简法化简逻辑函数的原理.     

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).