基于3G网络和CAN总线的汽车远程控制系统设计

针对传统汽车远程控制系统时延高、安全性差等问题,提出了新的远程控制方案,实现了远程服务器通过车载控制终端对车载网络中各节点设备的远程控制;在远程服务器与车载控制终端通信过程中采用3G网络、TCP协议和AES加密,降低了系统的通信时延,提高了系统的可靠性和安全性;车载控制终端与各节点设备采用CAN总线网络进行通信,实现了对各节点的有效控制;经过测试,系统能很好地满足远程服务器对车门窗、车灯、报警器和发动机等节点设备远程控制时延和安全性的要求,各节点响应快,可靠性高,具有较强的实时性和良好的扩展性。     

机器人关节通信总线系统的建模与验证

高速串行现场总线Controller Area Network （CAN）被广泛部署到机器人通信系统中.而服务机器人任务具有并发性和高实时性的特点,因此如何根据总线协议规范和应用需求精化设计模型,保证系统设计的正确性和实时性要求,避免设计阶段的漏洞十分必要.针对传统方法的局限性,本文提出使用形式化方法对基于CAN现场总线型控制系统进行建模分析.首先对系统进行模型抽象和形式表达;其次进行形式建模和自动验证,在UPPAAL中实现主控制器、关节控制器、收发器、仲裁器和CAN总线的时间自动机模型;最后对机器人通信系统进行正确性验证和实时性分析.实时性分析发现随着总线上关节节点数的增多,低优先级节点的最坏仲裁时延的增长速率加大,针对这个问题在形式模型中加入了改进的动态优先级策略.实验结果表明部署动态优先级策略后不仅减小了低优先级节点的仲裁时延而且还可以加大CAN总线的节点负载量,为系统设计提供有效的指导和参考.     

CAN总线实时性研究及改进

随着CAN总线控制网络的复杂化,单段网络上的控制节点数目增多而且网络带宽利用率要求日益提高,这使得总线上属性优先级低的数据传输延时增加;提出了一种动态时分CAN的设计思想,理论上给出了不同属性数据帧传输的最大时延;解决CAN现场总线在网络带宽利用率高时,数据传输的实时性问题,尤其是保证了低优先级信息的实时性;而且,相对于TF—CAN具有更好的灵活性;实验结果证嘲;同属性的数据时延都得到了减少,尤其是属性优先级低的数据;验证了设计思想,证明了协议的可行性。     

基于CAN总线的轮询通信系统设计

针对传统CAN总线通信系统基于仲裁发送机制所存在的通信通道易堵塞、实时性、可靠性差问题,设计了CAN总线节点轮询通信系统。系统CAN总线通信机制为采用主从控制下的节点轮询方式。最后,通过实验完成了CAN轮询通信测试,结果表明,CAN通信实时性高,整机运行稳定、可靠。     

基于CAN总线网络控制系统中的时延分析及对策

网络时延严重影响网络控制系统的实时性和稳定性.分析CAN总线网络控制系统时延的构成,针对给定的网络控制系统模型,给出系统稳定性与网络时延之间的数学关系式,并讨论了网络负载率对网络时延,系统稳定度的影响.采用基于时间触发方式的CAN总线信息调度方案,结果表明,该调度方法消除了CAN总线系统由于总线冲突而引起的时延.计算机仿真及实验表明,相比于事件触发方案,基于时间触发的CAN总线网络调度方案使系统性能得到明显改善.     

基于CAN总线的数据臂通信设计

针对数据臂的多电机驱动、多传感器信息采集的特点,提出了一种基于CAN总线的数据臂通信方案.通过CAN总线将上位机与下位机各关节测控节点相连,实现系统的分布式测量与控制;在此基础上,制定了适合于模块化结构数据臂通信要求的CAN总线协议,以协调总线上的信息流,从而减小总线冲突仲裁所需时间.该系统的数据传输准确率高、实时性好、工作性能稳定、连线简单,能够满足数据臂对实时性、可靠性等性能的要求.     

改进型 CAN 总线协议的实时性研究

目前,CAN 总线广泛应用于实时控制系统,其实时性对系统的安全性和可靠性产生很大影响.为了提高 CAN 总线的实时性,文中系统分析了 CAN 总线协议特点,提出减少标识符、增加数据位等改进措施,降低其数据帧自身开销,对CAN 协议进行改进.最后对改进型协议的帧利用率进行了分析,并通过将改进型协议应用于一个消息集,得到了消息集的最坏响应时间.实验结果表明,改进型协议在提高帧利用率的同时,缩短了消息的最坏响应时间,从而提高了 CAN 总线通信的实时性.     

CAN控制系统的时延分析及混合算法

在车载控制器局域网络(CAN)总线的通信中,消息之间的碰撞及低优先级消息的等待时延过长严重影响了通信的稳定性和实时性。通过对CAN控制系统中的消息时延分析,确定排队等待时间是影响通信的关键因素,结合改进的共享时钟算法和动态ID序列算法,提出一种共享ID序列混合算法。将节点消息按ID序列发送,减少消息在同一时刻碰撞,消除消息的排队等待时延,从而提高网络的实时性和稳定性。仿真结果表明,该算法能够避免消息的碰撞,增强消息的确定性,有效改善网络性能。     

改进型CAN总线协议的实时性研究

目前,CAN总线广泛应用于实时控制系统,其实时性对系统的安全性和可靠性产生很大影响。为了提高CAN总线的实时性,文中系统分析了CAN总线协议特点,提出减少标识符、增加数据位等改进措施。降低其数据帧自身开销,对CAN协议进行改进。最后对改进型协议的帧利用率进行了分析,并通过将改进型协议应用于一个消息集,得到了消息集的最坏响应时间。实验结果表明,改进型协议在提高帧利用率的同时,缩短了消息的最坏响应时间,从而提高了CAN总线通信的实时性。     

基于CAN总线的凿岩机器人分布式控制系统设计

分析了凿岩机器人控制系统的构成,针对集中控制方式的缺点,提出了分布式控制系统的方案.分配了CAN总线智能节点及其功能,设计了适合于凿岩机器人实时性要求的CAN总线用户协议.提出了各智能节点的通信设计要求,以协调总线上的信息流,减小总线冲突仲裁所需时间.     

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).