Case study on distributed and fault tolerant system modeling based on timed automata

This article presents the modeling of a distributed fault-tolerant real-time application by timed automata. The application under consideration consists of several processors communicating via a Controller Area Network (CAN); each processor executes an application that consists of fault-tolerant tasks running on top of an operating system (e.g. OSEK/VDX compliant) and using inter-task synchronization primitives. For such a system, a model checking tool (e.g. UPPAAL) can be used to verify the complex time and logical properties formalized as safety or bounded liveness properties (e.g. end-to-end response time considering an occurrence of a fault). The proposed model reduces the size of the state-space by sharing clocks measuring the execution time of the tasks.     

Mountain c-regressions method

Since Quandt [The estimation of the parameters of a linear regression system obeying two separate regimes, Journal of the American Statistical Association 53 (1958) 873-880] initiated the research on 2-regressions analysis, switching regression had been widely studied and applied in psychology, economics, social science and music perception. In fuzzy clustering, the fuzzy c-means (FCM) is the most commonly used algorithm. Hathaway and Bezdek [Switching regression models and fuzzy clustering, IEEE Transactions on Fuzzy Systems 1 (1993) 195-204] embedded FCM into switching regression where it was called fuzzy c-regressions (FCR). However, the FCR always depends heavily on initial values. In this paper, we propose a mountain c-regressions (MCR) method for solving the initial-value problem. First, we perform data transformation for the switching regression data set, and then implement the modified mountain clustering on the transformed data to extract c cluster centers. These extracted c cluster centers in the transformed space will correspond to c regression models in the original data set. The proposed MCR method can form well-estimated c regression models for switching regression data sets. According to the properties of transformation, the proposed MCR is also robust to noise and outliers. Several examples show the effectiveness and superiority of our proposed method.     

Detecting wind disturbance severity and canopy heterogeneity in boreal forest by coupling high-spatial resolution satellite imagery and field data

Wind disturbance events can impact spatially heterogeneous patterns in vegetation structure and disturbance severity in forested landscapes. Characterizing these patterns in forested ecosystems with remote sensing data has been a persistent challenge as variation in severity may be heterogeneous at fine spatial scales. Yet the degree and pattern of disturbance severity are an important influence on successional dynamics. This study explored how spectral and textural characteristics of high-spatial resolution IKONOS imagery reflected patterns of disturbance severity across a windstorm damaged, 121-km² area of the Boundary Waters Canoe Area Wilderness (BWCAW) in northeastern Minnesota, USA. In this study, spectral and spatial features of high-spatial resolution (1-m panchromatic and 4-m multispectral) IKONOS satellite imagery from a single post-disturbance date are coupled with field observations of disturbance within 0.045-ha field plots to access the potential for empirically modeling disturbance severity across this heterogeneous landscape within the BWCAW. Combining textural and spectral features led to a multiple regression model that explained 68% of the variance, and predicted disturbance severity equally well for ground data not included in the model development. The results suggest the utility of combining spatial and spectral data for detecting differences in forest structure caused by ecological processes such as disturbance.     

交换式局域网ARP欺骗嗅探技术研究

网络嗅探技术作为解决网络安全问题的技术之一,对于网络故障判断和网络信息化管理具有重大意义。传统的共享式网络嗅探有很大的局限性,无法在交换式网络下实施嗅探操作。通过分析网络嗅探、ARP协议和数据包捕获等相关技术,结合交换式局域网的拓扑结构,提出一种采用ARP欺骗技术对用户数据进行监听的方法;利用其设计开发了一套局域网嗅探系统,使被嗅探主机本该发送给网关的数据包流经嗅探主机。功能和性能测试验证了其实用性和有效性。     

无线局域网WPS安全性分析

介绍了wi—Fi联盟的WPS标准并给出了对应的攻击方法——暴力破解攻击,使用CPN对WPS协议及改进协议进行形式化分析并证明AP限制重新发起连接认证的次数为3次时,原协议可完全被攻破而给出的改进协议成功概率仅约为3／10^8。     

基于GeoSOT剖分编码的多尺度空间信息区域包含关系计算方法

针对现阶段不同层次空间信息缺乏联系的问题,提出了一种基于剖分编码的多尺度空间信息间区域包含关系计算方法。首先,以GeoSOT剖分框架为组织基础,在不同尺度层上,以剖分面片作为基本单元组合表示地理对象,依据对象表达多尺度剖分编码模型将地理对象赋予剖分编码。然后,提出了基于剖分编码的区域包含关系计算方法,并给出了算法实现的具体流程。进一步采用剖分信息树状结构对空间信息进行统一管理,为剖分体系下组织与管理不同层次的空间信息提供了一种有效的解决思路。     

四川九寨沟地震区芦苇海危岩崩塌成因机理分析

2017年8月8日,九寨沟地震诱发了景区芦苇海区域约 2. 7×104 m3危岩体发生崩塌,在2018 年汛期该区域又产生约 3×104 m3的二次崩塌,损失巨大。目前,崩源区仍有约 2×104 m3 的危岩体仍悬而未掉,潜在风险高,故需要深入研究芦苇海危岩崩塌的特征和致灾机理。通过现场详查、无人机及 GIS 等手段,对芦苇海危岩崩塌的基本特征、失稳过程及成因机理有了初步认识。研究发现,芦苇海危岩崩塌失稳历经“坡表局部崩塌－顶部危岩带变形－撞击坡表－碎屑流”四个阶段,平均运动速度达 29. 94 m /s,崩落块石到达坡脚的概率约为 87%。同时,多次失稳主要受内因及外因综合影响,由于斜坡对地震的放大效应,岩体受加速度影响显著,产生震动拉裂或抛射; 而震裂的岩土体在后续强降雨的触发下,沿优势结构面向南西侧临空面发生二次崩滑。     

贺兰山东麓雨洪水利用研究

宁夏贺兰山东麓实施山洪截潜工程拦蓄雨洪水,采取扬水灌溉、库井结合、水权转换、供给水产养殖等方式充分利用雨洪水资源。实践表明,拦蓄后的雨洪资源达到了灌溉水质标准,可使农作物及生态绿化适时灌溉,水产养殖丰产增收,生态旅游稳步发展,雨洪水资源化利用已成为干旱区解决水资源短缺的重要途径,为城市生态环境建设及经济社会全面发展提供水资源保障。     

宁夏引黄灌区干渠直开口出流流态及流量分析

宁夏引黄灌区干渠直开口(斗口)结构是闸门加涵洞的结合体,水流通过闸孔在涵洞中呈现极为复杂的流态,有自由出流、淹没出流以及有压管流流态,并且交替变化。通过试验提出,当闸后某断面水深较小,且下游水深小于水跃的第二共轭水深时,可以按自由出流计算流量;当此水深小于或等于涵洞高度,且下游水深大于水跃的第二共轭水深时,可以按淹没出流计算流量;当此水深大于涵洞高度,且下游水深大于水跃的第二共轭水深时,可按有压管流计算流量。同时,提出了相应的流量计算公式,可供工程设计和管理使用。     

锚杆格构梁支护中格构梁最优悬臂长度讨论

为了探索格构梁的悬臂长度对格构内力的影响,采用数值试验的方法,提出最优悬臂长度概念,并讨论了最优悬臂长度取值与锚杆格构梁系统各参数之间的关系。结果表明：格构梁跨距、地基变形模量是影响最优悬臂长度的主要因素;在边坡工程中,格构梁悬臂段的长度取0.30倍跨距可以优化格构梁的内力分布,从而节约工程造价。以三峡库区巴东县沿江路大坪段边坡锚杆格构支护系统为例,介绍了最优悬臂段在该工程中的应用情况。