实现向IPv6过渡的NAT-PT技术

本文分析了从IPv4到IPv6过渡的三种常用机制:双协议栈技术、隧道技术和NAT-PT(网络地址-协议转换)技术,建立一个小型、简易的实验室,具体给出了NAT-PT的实现技术方法和步骤,最后通过NAT-PT网关的地址和协议转换功能成功将IPv6和IPv4数据包相互转换.     

基于NAT-PT的IPv4/IPv6转换网关的安全机制研究

基于网络地址协议转换(NAT-PT)的转换网关是目前IPv4向IPv6过渡的主要形式之一。IPv6强制实施的IPSec不能与NAT-PT协同工作。本文结合安全协议集IPSec和NAT-PT的特点,构建了一个增加安全机制的转换网关的模型。     

基于 NAT-PT 和双栈技术的 IPv6 校园网方案设计与实现

IPv6校园网规划建设及实现IPv4与IPv6资源互访已经成为新一代校园网研究需解决的问题。通过分析IPv6的原理和新特性、NAT-PT的地址转换及协议转换功能等IPv4向1Pv6过渡技术,结合校园网光缆和设备,研究使用NAT-PT和双栈技术规划部署IPv6校园网和解决校园网内IPv4与IPv6资源互访的问题,提出了符合校园网实际情况的IPv6网建设方案,实现了IPv4与IPv6资源互访。     

NAT-PT协议转换网关的设计与实现

介绍NAT-PT的技术原理,给出NAT-PT协议转换网关的概念和系统结构。根据RFC2766文档和RFC2765文档的相关说明,参照Linux内核关于IPv4／IPv6网络实现部分的源代码,设计并实现NAT-PT网关应用程序。该程序由主体模块、应用层网关模块、网络地址转换模块和协议转换模块组成。     

IPv6到IPv4的过渡

下一代的IP网络将是一个以IPv6协议族基础之上的统一IP网络,本文首先介绍IPv6协议的技术特点,以及实现IPv4协议到IPv6协议的过渡,并着重描述了IPv4向IPv6的转换的NAT-PT技术实现原理及算法.     

利用NAT-PT网关实现IPv6与IPv4网络互通

分析了NAT-PT网关的地址转换和协议转换功能,研究了NAT-PT将IPv6和IPv4数据包进行相互转换的过程。提出了一种利用NAT-PT网关实现两类主机通信的方案。     

增强的NAT-PT和IPSec兼容解决方案

分析IPv4/IPv6过渡时期NAT-PT和IPSec协议的兼容性解决方案,并基于此提出一种增强的IPSec分段保护方案,通过对IKE协议的适当改进增加了发起方对NAT-PT转换网关的发现和自动处理机制,提高了NAT-PT转换网关的透明性。性能分析显示该方案具有较好的安全性和适应性,便于过渡网络安全策略的实施。     

IPv4向IPv6的过渡策略

本文简单介绍了IPv6协议,并阐述了在现阶段IPv4与IPv6共存的情况下,IPv4向IPv6过渡的三种较为成熟的双协议栈技术、隧道技术和NAT-PT技术,最后概括了过渡策略的演进。     

基于NAT-PT的分段IPSec隧道建立技术

NAT-PT技术解决了IPv4/IPv6之间的通信问题,但是通信过程中的安全却没有得到保证。对基于NAT-PT的IPv4/IPv6网络通信原理及存在问题进行分析,并进行了IPSec安全协议的应用实施分析后,提出一种分段的IPSec安全隧道建立技术,实现在NAT-PT特殊网络环境下部署IPSec安全隧道从而保证通信数据的安全。     

一种面向智能校园网的IPv6过渡技术

本文详细分析了双栈协议、隧道技术和NAT-PT技术这三种常用的过渡机制,并通过一个IPv6实验床的建设,利用IPv6双栈协议和隧道技术过渡机制,有效地实现了校园网从IPv4向IPv6的平滑过渡。与已有的技术相比,该方法实现了IPv4和IPv6的共存及协同运行。     

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).