地月通信链路传输协议的研究与性能分析

从传输层和应用层2个角度对空间信息传输中地月通信链路可靠传输协议进行研究,基于OPNET软件开发CCSDS协议进程级模块。针对地月骨干链路场景配置TCP 、SCPS-TP、CFDP/UDP和MDP/UDP 4种可靠传输方式,并进行协议仿真与性能分析。实验结果表明,在长传播延迟、高误码率和高度不对称性前/返向信道速率的链路上,SCPS-TP协议失去了TCP增强优势,MDP协议也表现一般,而CFDP协议的可靠传输模式能较好地适应于这种环境。     

基于TCP/IP的网络通信及其运用分析

网络通信是以物理环境为运行中心的通讯方式,借助链路连接,实现多方信息的传输与交流。网络通信的高效运行必须建立在协议基础上,利用运行协议,控制网络通信。目前,网络通信的协议趋向于TCP/IP,以此来提高网络通信的速度,基于TCP/IP构建网络化的通信系统。本文结合实际工作,以TCP/IP为研究基础,分析网络通信及其运用。     

TCP/IP在“动中通”系统中的问题研究

针对"动中通"通信链路的特点,及TCP/IP协议的相关特点和算法,对TCP/IP协议在动中通链路中的几项缺陷进行了研究,并给出了可行的改进方案。     

TCP/IP在“动中通”系统中的问题研究

针对"动中通"通信链路的特点,及TCP/IP协议的相关特点和算法,对TCP/IP协议在动中通链路中的几项缺陷进行了研究,并给出了可行的改进方案。     

基于RapidIO的实时CORBA中间件实现

为了解决CORBA传统传输协议TCP/IP的时延不确定问题,提出了使用基于点对点的包交换RapidIO协议来替代TCP/IP的方法,研究了CORBA的可插拔传输协议框架,从而实现了CORBA报文在RapidIO总线上的传输。测试结果显示,基于RapidIO的CORBA实时性优于基于TCP/IP的CORBA。     

具有卫星链路的TCP/IP网络性能测量方法研究

Iternet已被广泛应用于多媒体信息的传输,但TCP/IP对于传输实时性较高的宽带业务时,质量得不到有效保证.特别在卫星链路上,通过TCP/IP传输宽带业务受到了"时延带宽积"的"瓶颈"制约,长期得不到较好应用.本文针对某专用TCP/IP网络的特殊应用背景,通过构建实验平台,确定测量内容,设计测量方法和研制测试工具等,为专用TCP/IP网络实时传输宽带业务提供试验数据.     

卫星网络传输层协议分析与改进

TCP/IP协议的成熟极大地促进了地面网络的发展,然而传统TCP/IP协议难以直接高效地应用于卫星网络.文中针对卫星网络固有的大带宽时延积、高误码率等特点以及卫星网络中UDP流的资源争用问题,深入对比分析了传统TCP协议在卫星网络中的缺点,并针对多媒体数据流引入TFRC机制,从而实现卫星网络TCP流量和UDP流量竞争情况下带宽的公平分配.实验表明:TFRC机制的引入可以有效解决流量带宽竞争问题,较好地实现卫星网络带宽的公平性.     

TCP/IP协议栈的实现方法

TCP/IP协议是互联网的核心协议,也是大多数网络应用的核心协议.介绍了TCP/IP协议栈的概念及基本工作原理,详细描述了TCP/IP协议栈的裁剪、设计和实现方案,并以单片机C8051 F340和网络控制芯片CP2200为硬件平台,设计和实现了一个面向远程工业公职领域的精简TCP/IP协议栈,包括UDP、ARP、IP及TCP等协议模块.经过精简后的协议栈代码量小,结构合理,易于移植和扩充.     

一种融合电路交换与分组交换的方法

提出了基于TCP交换技术的电路交换与分组交换融合的新方法,分析了TCP交换需要解决的主要问题,较详细的讨论了TCP交换中由IP路由协议创建与撤销电路链路的过程,边界路由器与核心路由交换机所需完成的主要功能与任务以及实现TCP交换所必须研究的关键技术.     

Modbus转以太网协议转换的研究

针对Modbus协议设备与以太网设备通讯问题,深入研究Modbus协议和TCP/IP协议通讯模式,提出一种Modbus协议和TCP/IP协议的转换方法,并在理论层次解决串行链路和以太网的数据传输速度相差很大的问题。     

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).