一种有效的车辆网络路由协议

研究车辆网络中的路由问题,提出一种有效的路由协议。利用秘书问题的思想,该路由协议可以有效地选择对哪些车辆进行消息拷贝,因而提高发送成功率。基于真实车辆行驶数据的仿真实验表明,相比较其它方法,本文提出的路由协议可以实现更高的发送成功率。     

基于投递概率预测的DTN高效路由

在延迟容忍网络中,基于配额的多拷贝路由通过对消息拷贝数量的限制来控制开销,如何在控制开销的前提下尽可能提高消息投递成功率是其需要解决的关键问题.文中首先分析了提高消息投递成功率的配额分配策略,然后据此提出一种基于投递概率预测的配额路由算法.该路由算法根据节点的本地信息预测到其它节点的投递概率,在复制消息时,根据节点间投...     

一种间歇性连接移动网络自适应路由协议

为提高间歇性连接移动网络的消息发送效率,提出一种基于移动自组网OLSR协议的自适应路由协议ARPBO。ARPBO在网络连通时通过OLSR协议快速转发消息;在网络中断时对OLSR协议进行扩展,从消息发送节点的局部连通网络中有效选择下一跳节点,然后通过延迟容忍网络的"存储-携带-转发"机制转发消息。实验结果表明,该路由协议能够在网络存在间歇性连接时获得较高的传递成功率和较低的传递时延。     

基于公交系统的异构车载网路由协议

现有的车载网路由协议通常只利用车载网的单一特性进行路由设计,造成消息投递率过低或延迟过高。为此,提出一种整合专用短程通信与长期演进技术的异构车载网多属性决策路由协议。该协议在整合长期演进技术的基础上,以公交车辆与公交车站作为骨干网络,使用多属性决策的方法进行路由选择。仿真结果表明,与基于位置信息的贪婪边界协调者路由以及基于公交系统的距离向量路由相比,该协议能够有效地提高消息投递率并降低消息延迟。     

基于可靠最小跳数场的路由协议研究

无线传感器网络的路由协议是一个研究热点。基于最小跳数的路由能够保证网络内部最小的消息包数量，协议容易实现，应用范围很广。本文从提高网络的数据发送成功率出发，提出了一种基于可靠最小跳数场的路由协议，详细介绍了可靠最小跳数场的建立过程以及路由的实现方法。TinyOS操作系统下的模拟实验证实了协议的正确性。     

车联网中一种有效的资源共享方法

针对车联网的资源共享问题进行研究,提出一种有效的资源共享方法ERS。ERS的目标是提高资源共享的成功率、减小资源共享的延迟、减小通信代价,以及提高发送效率。为了实现这些目标,ERS设计四个策略,包括查询策略、回复策略、资源的替换策略、收到资源的告知策略。基于真实的车辆行驶数据来进行仿真实验。仿真实验结果表明,相比较其他两种方法,ERS实现较高的资源共享成功率、较低的延迟、较低的通信代价和较高的发送效率,因此是车联网中一种有效的资源共享方法。     

一种基于复杂网络理论的移动自组网路由算法研究*

针对移动自组网中节点之间数据包发送成功率不高、路由开销大和包平均延时长等问题,提出了一种基于复杂网络理论的移动自组网路由算法。在该算法中,路由发现基于路由消息在邻域范围的相互借阅,若持续时间在网络平均路由发现时间范围内,则采取动态随机路由,考核跳级数是否满足复杂网络理论的条件来选择以最少跳级数或者最短路径为指标的最优路径建立路由,否则采取位置路由,采取方向最有益的最优路径建立路由。实验分析表明,即使节点稀疏时该路由算法仍具有很好的包发送成功率和包平均延时,其综合性能优于OLSR协议和AODV协议。     

基于稳定路径的MAODV协议改进

移动Ad Hoc网络组播路由协议MAODV中,组播树在节点移动速度较快的情况下会频繁重构,使得路由开销、传输时延显著增大。针对基于邻居节点变化率的稳定路径选择方法,提出一种新的节点邻居变化率的检测机制,不需要周期性地发送Hello消息,并在此基础上设计和仿真实现了基于稳定路径的MAODV协议SP-MAODV,新协议选择的路径稳定性好且跳数小。最后从数据分组传输成功率、路由开销、平均端到端时延和时延抖动四个方面对两个协议进行了仿真比较,结果表明SP-MAODV协议减少了路径中断概率,提高了协议性能。     

基于社会组的高投递率机会网络路由协议

针对现有的基于社会组的机会网络路由协议（SGBR）存在中继节点的选择和消息副本数量的分配不合理的问题,提出了基于社会组的高投递率机会网络路由协议（SGBRHDR）。SGBRHDR协议是一种采用分布式划分社会组的多副本路由协议。在社会组内,节点依据平均关系强度值决定相遇节点是否成为转发节点;在社会组间,节点依据相遇节点所在的社会组活跃性大小分配消息副本数量。采用ONE工具对SGBRHDR协议进行了仿真,仿真结果表明：与SGBR协议相比,SGBRHDR协议减小了消息平均端到端时延的同时,消息投递成功率提高了18%。     

无人机自组网中基于Q-learning算法的及时稳定路由策略

无人机自组网凭借其抗干扰能力强、适用于复杂地形、智能化程度高和成本较低的优点,近年来受到广泛关注,该网络中路由协议的设计与优化一直是核心研究问题。针对无人机自组网中因节点快速移动造成节点本地存储的路由未及时更新而失效的问题,提出一种基于Q-learning算法的动态感知优化链路状态路由协议(DSQ-OLSR)。该协议首先充分考虑了无人机自组网节点高速移动的特点,在选取多点中继(MPR)节点时添加了链路稳定性和链路存在时间这两个指标,使得选出的MPR节点集更稳定、合理;其次,结合Q-learning算法对TC消息的发送间隔进行自适应调整,使得在网络拓扑变动较小时增大TC发送间隔以减小控制开销,而在拓扑变动较大时减小TC发送间隔用于达到快速感知并构建网络拓扑的要求,进而实现数据的及时路由。仿真结果表明,与DT-OLSR协议相比,该协议在端到端时延、吞吐量、成功率和网络生存时间性能上分别提高了12.61%、9.28%、7.69%和5.86%,由此验证了其有效性。     

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).