HIV传播的动态混合无标度网络生成算法

研究人类免疫缺陷病毒(HIV)的传播机理,提出一种HIV传播中基于配置模型的动态混合无标度网络生成算法。根据HIV在男性和男性、男性和女性之间的传播规律分别构造同性和异性无标度网络,将其放在同一系统中形成混合传播网络,并添加网络的动态变化特性,以反映真实社会网络的演化过程。基于配置模型的复杂网络生成算法可快速、灵活和鲁棒地生成给定网络尺寸和幂律度分布指数的复杂网络,而且网络中的边可断开和重连,弥补了经典 BA 模型的不足。仿真结果表明,该算法能正确、有效地反映HIV混合传播网络的特性。     

注射吸毒人群HIV动态分层Agent网络传播模型

基于配置模型建立一个静脉注射吸毒人群HIV传播的动态分层Agent复杂网络模型,用于模拟HIV在现实共用针具吸毒网络中的传播。在该模型中,共享吸毒网络中的个体分为core层、inner层和outer层,对应吸毒人员中的高危人群、中等危险人群和一般危险人群。网络中层内连接较强,而层间连接较弱,由可调概率矩阵控制。网络中的人群总数可以变化,节点间的连边可以断开和重连,网络具有动态特性。网络中的个体Agent中包括了感染、病程发展以及自愿咨询与检测、国家的免费治疗和免费针具交换等干预政策对个体行为改变、病程和传播的影响机制。仿真实验结果表明,该模型能正确反映不同危险行为层的吸毒人群网络中HIV传播的特点。     

二部无标度网络上病毒传播模型和免疫策略研究

针对计算机网络上的病毒传播问题,提出一种二部无标度网络,其节点分为客户机和服务器两类。在二部无标度网络上应用易感-感染-易感(SIS)传播模型,采用率方程的方法研究二部无标度网络上病毒的状态转移和临界行为,得出客户机感染密度与服务器感染密度的关系式。在SIS模型的基础上利用免疫策略,针对相同的网络拓扑和病毒传播模型,分析比较免疫策略的免疫功能,并给出支持理论结果的数值模拟,结果验证了随机免疫、节点度免疫与相识点免疫策略都具有防御病毒传播的功能,并且防疫能力依次增强。     

无标度网络中考虑个体重视的传染病传播研究

分析传染病传播动力学行为是复杂网络研究的基本问题之一,现有的传染病传播模型研究没有充分考虑到传染病传播过程中人为因素的影响,即易染个体在传染病传播过程中的行为反应。针对以上问题提出了一种改进的无标度网络中具有个体重视的SIR传染病传播模型。利用平均场理论方法,分析了所提模型的动力学行为。研究了在无标度网络中具有个体重视的易染个体的比例和个体重视度对传染病传播的影响。理论分析和数值模拟结果表明,增大具有个体重视的易染个体的比例和增加易染个体的重视度,可以有效地改善传染病的传播阈值、传播的速度和爆发的规模。     

具有社团结构的加权网络的病毒传播研究

文中根据Barrat等提出的BBV网络的建模思想,考虑网络社团结构特性,构建一种具有社团结构的加权无标度网络模型,利用SI传染病模型,研究该网络模型中权值增长系数和网络社团强度对病毒传播行为的影响。结果表明,权值增长系数增大时,病毒由感染源社团扩散到其他社团的时间变长,进而抑制了网络中的病毒传播。另外,研究还表明,在加权无标度网络中,较弱的社团强度能抑制病毒的传播,这与无权网络中的结论正好相反。     

基于加权网络的僵尸网络传播模型研究

主要研究不同网络拓扑下的僵尸网络Botnet传播行为,重点研究基于两种加权网络下的僵尸网络传播特性。基于经典加权网络(BBV网络)的演化规则,在随机权重的基础上,提出随机增量的加权演化模型;通过模型仿真,发现基于随机加权的网络与其它两种网络拓扑下僵尸网络相比,表现出更强的健壮性,这与建模时的理论分析完全一致。仿真结果表明,与无标度网络下的传播模型相比,基于加权网络的传播模型更符合僵尸网络在实际网络中的传播特性。     

基于Agent动态网络的疾病传播模型

提出一个基于Agent动态网络的疾病传播模型,研究疾病在人群中传播扩散的动态过程。在扩展疾病传播的SIR模型基础上,利用不同的个体状态描述各阶段病情。在二维规则网络上,通过增加个体自主移动性构建动态社会网络,并考虑个体异质性和所采取的防护措施对疾病传播的影响。仿真结果表明,该模型较好地反映了动态社会网络和个体适应性行为对疾病传播的影响,并与实际情况基本保持一致。     

个体特征对在线社会网络中信息传播的影响

为研究个体特征对在线社会网络中信息传播的影响,结合个体特征、社会加强和信息属性,提出一个简单的信息传播模型。在传播模型中主要考虑记忆效应、社会加强、信息属性和个体特征这4个因素,并根据服从均匀分布与幂律分布的个体在规则网络、WS小世界网络、BA无标度网络上传播信息的能力,对此进行仿真实验,同时在Facebook上进行实证研究。结果表明,不论哪种情况下,信息的传播速度遵循BA无标度网络最快,规则网络最慢的规律,规则网络的稳定时间也最长。Facebook的传播图与BA网络的结果图类似。     

加权局域网络上的病毒传播行为研究

病毒传播问题的研究一直是国际上科学家所关注的焦点,但是在加权局域网络中的病毒传播研究却是空白。由于实际存在的网络很大一部分是加权局域网络,因此研究了一种特定加权局域网络中的传播行为。采用病毒传播的SI模型,令病毒的传播速度和网络的连接权重正相关。对加权局域网络中病毒传播行为的研究表明：加权局域网络的无标度性质和加权局域世界性质对病毒的传播有深刻的影响。由于加权局域网络能够很好地反应实际世界,因此该研究具有很广的应用背景。     

考虑个体警觉行为的双层网络流行病传播模型

流行病传播过程中常伴随个体意识信息的扩散,然而目前关于流行病与意识信息关系的研究大部分未考虑意识信息在传播过程中对个体接触行为的影响。提出一种基于个体警觉状态的双层网络流行病传播模型。建立下层物理接触网络描述流行病的传播,构建上层信息扩散网络描述流行病传播中信息扩散,根据个体的行为偏好和警觉性设计警觉个体避免与非警觉个体接触、警觉个体避免与警觉个体接触两种接触行为策略,并在BA-BA、BA-WS和WS-WS 3种双层网络中模拟两种行为策略对流行病传播的影响。仿真结果表明,该模型中两种个体警觉行为策略通过调节警觉性参数均能有效降低流行病感染规模并提高流行病爆发阈值,从而抑制流行病在人群中传播。     

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).