IPv6无线传感器网络低功耗路由算法

为满足IPv6无线传感器网络低功耗的要求,采用适配层路由,在LOAD路由协议基础上提出一种简化的按需式路由算法。本算法采用精简的路由控制报文、路由表和路由请求表,简化了路由发现过程,优化了路由维护机制。仿真实验表明,该算法能有效的降低IPv6无线传感器网络的功耗。     

基于DSR协议的备用路由机制设计和性能评价

由于Adhoc网络中无线节点的移动性及无线信道的不稳定性,已经建立起来的源和目的节点间的路由在多媒体业务传输过程中往往会失效,重新发现路由会导致较大延迟和丢包,对实时多媒体业务传输这是不能接受的,因此需要在Adhoc网络中建立一种快速路由恢复机制以减少因路由失效引起的较大端到端的延迟和丢包。将有线网络中广泛使用的备用路由机制扩充到了无线Adhoc网络DSR路由协议上,并通过实验床上进行的户外实验,分析和评价了增加了备用路由的DSR协议在减少路由失效次数和投递率方面的性能改善。     

基于链路时间预测的移动Ad Hoc网路由

移动Ad Hoc网络是一种自组织、无基础设施的网络。而节点的自由移动促使链路频繁的断裂。为此,提出基于链路连通时间预测路由LDPR(Link Duration-Prediction-based Routing)。LDPR路由先通过节点运动信息,预测链路的连通时间。然后,再依据链路的连通时间计算路由生成时间,并选择两条路由生成时间长的路由协同传输数据,一条路由作为主路由,另一条路由作为备用路由。通过双路由机制,提高数据包的传输效率。实验数据表明,相比于传统的按需距离矢量AODV(Ad Hoc On-demand Distance Vector)路由,LDPR路由在吞吐量和端到端传输时延方面的性能得到有效改善。     

一种高效抗毁的无线自组织网络路由策略

针对在网络被毁伤以致分割后的路由重建和通信恢复问题,提出一种结合传统Ad Hoc路由和时延容忍路由的混合路由策略。采用按需选择时延容忍网络(DTN)路由的方式,使Ad Hoc路由失效后能利用DTN路由的时延容忍和网络容错能力继续路由。仿真实验结果表明,与PROPHET和AODV路由协议相比,该路由策略能在网络毁伤后快速重建路由,以保证近似毁伤前的高投递成功率,并利用局部的AODV路由缩短端到端时延。     

基于选择函数的分布式启发算法DCLC—DSF

QoS路由的DCLC单播路由（Delay-Constrained Least-Cost Unicast Routing）问题属于NP－完全问题。本文提出一种多项式复杂度的分布式启发算法DCLC－DSF。DCLC－DSF基于简单的选择函数,每个网络结点只需维持本地的状态信息：相邻链路的延时和代价度量。该算法有以下优点：1）简单性;2）动态性;3）重路由功能;4）协商功能。在最坏情况下,DCLC－DSF的消息复杂度为O（e^2）,结点的计算复杂度为O（n^2）;在稳定的网络环境下,消息复杂度为O（e）。此外,本文还给出DCLC－DSF算法有限状态机模型。仿真实验表明：DCLC－DSF算法的平均代价不精确度是最佳算法的5－8％,证明它是一种简单、精确、健壮的的启发式算法。     

移动Ad Hoc网路AODV路由协议的改进

针对移动Ad Hoc网络AODV路由协议的路由维护的缺点,提出了AODV-BR路由协议,即具有备份路由的AODV路由协议。新协议通过为网络中的连接链路增加一条备份路由提高了AODV路由维护的性能。仿真实验表明AODV-BR有效减少了网络中链路中断的数量,降低了丢包率。     

基于超节点的结构化P2P路由算法的研究

在对经典的结构化P2P路由算法研究的基础上,提出了BSNCCC(Based Super Node Cube Connect Cycle)路由算法。该算法节点维护的信息为O(1),查询步长为O(d)(节点个数N=d*2d),在充分考虑节点性能差异性的基础上,将性能好的节点作为路由过程中的主节点。模拟试验结果表明,在动态变化的P2P网络中,BSNCCC路由算法的效率优于Cycloid等算法。     

一种IP网络友好的Overlay路由机制*

现有IP网络存在不支持QoS,故障恢复速度慢等问题。作为克服或屏蔽这些缺陷的一种有效手段,Overlay网络在当前Internet上被广泛部署和应用。目前存在很多的Overlay路由结构和方法。然而在现存的多层路由中,上层Overlay网络在路由决策时通常对底层的IP网络性能和状态缺乏有效的协调和感知,致使上层Overlay路由和底层IP路由常常处于非协同、非优化工作状态,产生大量路由抖动和次优路由。为解决这些问题,提出了一种底层IP网络友好的Overlay路由机制,其基本思路为：增加Overlay网络的层感知能力,减少路由抖动增加Overlay路由的稳定性。Overlay网络根据底层IP网络的节点跳数、链路带宽、丢包率等反映底层IP网络性能的信息做出路由决策。实际网络中,通过调整Overlay网络的链路代价有效控制Overlay网络的路由决策。最后仿真结果表明：与传统双重路由（Dual Routing）相比,此IP网络友好Overlay路由机制在减少Overlay网络路由抖动,降低Overlay网络路径代价膨胀,提高Overlay网络故障恢复成功率和满足Overlay业务需求等方面有优势。     

BGP路由冲突解决方案的研究

在分析BGP路由策略冲突问题的基础上,针对当前网络传输路由层面的发展要求,提出了基于优先池机制的BGP路由冲突解决方案,将路由的稳定性加入到BGP的判决过程中,同时引入了路由的相关性概念,对基于路由信息和通信数据进行转发的BGP路由环境展开了进一步的研究。仿真结果表明,该方法能够有效地缩短BGP路由的收敛时间,从而对整体网络环境下BGP路由冲突问题的解决起到了良好的促进作用。     

基于链路中断预测的AODV路由算法研究

在移动自组网中,节点的移动导致拓扑动态变化,已经建立的路由时刻存在中断的可能,而传统的AODV路由协议中的路由修复方法开销大、时延长。针对这一问题,提出了一种基于链路中断预测的改进路由算法。该算法在链路中断之前启用备用节点,尽量避免路由修复;在链路中断后,首先在本地进行链路修复,不成功再逐层由上游节点发起路由搜索。仿真实验结果表明,与传统AODV相比控制开销降低了40%,端到端时延减少了25%,提高了网络性能。     

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).