结合背景差分和显著值筛选的运动检测算法

本文为降低背景干扰,提出了一种结合背景差分和显著值筛选的运动检测方法。该方法将VIBE运动检测方法看作一个前置处理过程,用于粗定位可疑目标区域。然后在这些可疑目标区域上,提出一种基于稀疏表示和组合Lasso回归的显著值计算方法,计算可疑区域图像块的显著值。最后通过滤除显著值过小的可疑区域图像块来降低背景干扰,提高运动检测的精确度指标。在Changedetection.net的数据子集上的仿真实验结果表明,该方法的召回率和精确度指标都较高,而且平均检测耗时少。     

基于非参数特征提取的早期林火烟雾检测

提出了一种基于非参数特征提取的早期森林火灾烟雾检测方法。采用双背景模型进行运动区域检测,得到可疑烟雾区域。再利用早期火灾烟雾颜色特征和运动特性对提取的可疑运动区域进行颜色判别,对增长区域以及上升区域进行检测,排除部分干扰目标。根据提出的非参数特征提取法,计算并科学地选取可疑区域的特征量,将其输入训练好的支持向量机(SVM)进行烟雾判别。对多段视频进行测试表明,该方法能适用于复杂多变的野外环境,排除干扰,有效地检测出早期林火烟雾。     

端到端网络流量的混合估计方法(英文)

利用主成分分析法获取端到端网络流量的主要特征分量并获得其初始估计结果.为克服其初值敏感性将估计结果作为遗传算法的初始值、链路流量估计偏差作为遗传算法的适应度函数,通过构建合适的交叉和变异概率函数来控制遗传算法的交叉和变异过程.采用合适的约束迭代函数,利用遗传算法通过迭代寻优获得端到端流量的估计结果,仿真结果表明所提出的方法是可行的.     

垂直加热管内下降两相流瞬态空泡率的数学模型研究

本文提出瞬态垂直下降流动管内两相流空泡率的数学模型和其计算方法，可用来计算介质流量瞬变和加热负荷瞬变时管内各处的空泡率．为了验证模型计算的精确性，在R－12实验台架上进行了空泡率的测量，同样工况下，测量与计算结果相当一致．流量瞬变时的最大平均偏差小于13％，热负荷瞬变时小于15％．由此可认为本模型方法，可用于工程计算，尤其适用于棒束之类的复杂流道．     

基于滑速比的气水两相流气相流量计算方法研究

目前对气水两相流的分相流量的研究中,多是针对两相流总流量和液相分相流量进行,对气相分相流量的研究很少.本文利用文丘里管和含气率传感器对空气水两相流气相流量计算方法进行了研究,在均相流模型基础上考虑了滑速比因素造成的影响,探讨了两相流气相流量计算方法.结果表明,该方法相对于传统的均相流模型在计算精度上得到了显著提高.     

反射镜稳定系统的仿真与误差分析

提出一种光电稳定系统的误差分析方法。该方法建立在对稳定控制系统仿真设计的基础上,利用稳定系统刚度传递函数曲线,对各种扰动源引起的误差进行分析与计算。利用该误差分析方法,将使设计者在设计中明确应该对哪些误差进行控制,从而实验总体精度要求。最后用一具体设计实例验证本方法。     

蒙特卡罗与离散纵标耦合方法在压水堆堆腔漏束计算中的应用

为克服蒙特卡罗(MC)方法计算时间长和离散纵标(SN)方法复杂几何描述不精确的困难,采用SN-MC耦合计算流程,研究了基于蒙特卡罗方法和离散纵标方法的耦合方法。耦合方法的主要思想是根据离散纵标程序提供的中子角通量,利用接口程序计算出面源的分布概率,然后由修改后的源抽样子程序生成包括上下圆面源和圆柱面源的组合源,提供给蒙特卡罗程序进行计算分析。初步计算结果表明,该耦合方法是正确的,可用于压水堆堆腔漏束的计算分析。     

电动增压器流量特性的测定与数值分析

应用计算流体动力学方法对研制的电动增压器的压气机整机进行了三维湍流流场模拟计算.计算中对压气机实体模型进行适应性很强的非结构三角网格划分,采用Realizable κ-ε双方程湍流模型模拟时均Navier-Strokes方程.利用热线风速仪对电动增压器出口截面的流量特性进行了测定.将计算的压气机出口流量特性以及速度场分布与实验值进行比较,结果基本吻合,这对电动增压器的结构设计优化具有重要的指导作用.     

解二维柱几何输运问题的离散——配置有限元方法

本文研究了求解多群多种介质的二维柱几何中子输运问题的离散一配置方法(TCC)。该方法对时间t用Crank-Nicholson中心差分,源项采用离散纵标近似和源迭代技巧,对空间变量采用配置有限元方法。本文讨论了算法。证明了守恒性。并且证明了本方法在K=1时等价于DSN^[2]方法,因此本方法是DSN方法的高阶推广。本文还给出了数值计算结果。我们对精确解以及多个二维柱几何的临介物理问题进行了数值计算,由分析比较可见,取得了较好的结果。     

68 kA高温超导电流引线关键参数研究

主要研究68 kA高温超导电流引线的关键参数,首先,对盒式超导接头直流电阻、换热器优化和整体安全分析的方法进行研究,随后对引线进行低温性能实验,结果表明,接头直流电阻、换热器流量消耗、LOFA及Burnout时间等关键参数的计算结果与实验结果基本相符,本研究验证了关键参数计算及分析方法的准确性。     

Network traffic behaviour near phase transition point

We explore packet traffic dynamics in a data network model near phase transition point from free flow to congestion. The model of data network is an abstraction of the Network Layer of the OSI (Open Systems Interconnect) Reference Model of packet switching networks. The Network Layer is responsible for routing packets across the network from their sources to their destinations and for control of congestion in data networks. Using the model we investigate spatio-temporal packets traffic dynamics near the phase transition point for various network connection topologies, and static and adaptive routing algorithms. We present selected simulation results and analyze them.     

光弹性分组环(ORPR)节点中光分组组装算法研究

介绍了光弹性分组环(ORPR)节点模型,分析了ORPR网络中流量成型时光分组组装算法,提出一种适合ORPR网络的基于控制发送时间的光分组组装算法,给出了该算法的算法结构,并和传统的光分组组装算法做了比较。该算法通过分组发送间隔的调整,使得分组单位时间内的流量的自相似性被平滑,具有很好地抑制突发性的效果,同时,分组组装的时间门限可以被ORPR调度算法动态调整,可以适应缺乏缓存的ORPR网络的调度机制。     

On coding for reliable communication over packet networks

We consider the use of random linear network coding in lossy packet networks. In particular, we consider the following simple strategy: nodes store the packets that they receive and, whenever they have a transmission opportunity, they send out coded packets formed from random linear combinations of stored packets. In such a strategy, intermediate nodes perform additional coding yet do not decode nor wait for a block of packets before sending out coded packets. Moreover, all coding and decoding operations have polynomial complexity.We show that, provided packet headers can be used to carry an amount of side-information that grows arbitrarily large (but independently of payload size), random linear network coding achieves packet-level capacity for both single unicast and single multicast connections and for both wireline and wireless networks. This result holds as long as packets received on links arrive according to processes that have average rates. Thus packet losses on links may exhibit correlations in time or with losses on other links. In the special case of Poisson traffic with i.i.d. losses, we give error exponents that quantify the rate of decay of the probability of error with coding delay. Our analysis of random linear network coding shows not only that it achieves packet-level capacity, but also that the propagation of packets carrying “innovative” information follows the propagation of jobs through a queueing network, thus implying that fluid flow models yield good approximations.     

Optimal dynamic bandwidth allocation for complex networks

Traffic capacity of one network strongly depends on the link’s bandwidth allocation strategy. In previous bandwidth allocation mechanisms, once one link’s bandwidth is allocated, it will be fixed throughout the overall traffic transmission process. However, the traffic load of every link changes from time to time. In this paper, with finite total bandwidth resource of the network, we propose to dynamically allocate the total bandwidth resource in which each link’s bandwidth is proportional to the queue length of the output buffer of the link per time step. With plenty of data packets in the network, the traffic handling ability of all links of the network achieves full utilization. The theoretical analysis and the extensive simulation results on complex networks are consistent. This work is valuable for network service providers to improve network performance or to do reasonable network design efficiently.     

HyPASS: Design of hybrid-SDN prevention of attacks of source spoofing with host discovery and address validation

SDN (Software-Defined Networking) is a new technology that separates data and control planes; the main components of SDN are OFSwitches and Controller. The traffic flow is monitored by the SDN controller. Initially, OFSwitches lack security rules for packet handling. OFSwitch sends the packet to the controller for examination, creating control messages that favor the packet and establishing necessary flow entry. Host packets are sent to their destination, seeing only the destination host address and not the source host address. The attacker takes advantage of this situation and generates packets with forged source addresses in order to conceal his identity and perform various source address spoofed attacks such as Denial of Service (DoS), man in the middle (MiM), Distributed DoS (DDoS), and so on. This paper proposes a design for discovering hosts proactively, preparing HostTable, configuring flow entry during handshaking, and detecting and preventing source-forged attacks in Hybrid SDN. We called it HyPASS: Design of Hybrid-SDN Prevention of Source Spoofing Attacks with Host Discovery and Address Validation. We used Python for Mininet implementation and tested it on RYU and POX controllers. During the experiment, it identifies and drops 99.99% of packets with the forged source address.     

Information traffic in scale-free networks with fluctuations in packet generation rate

We study the information traffic in scale-free networks where the information generation rate varies with time as a periodic function. We observe that when the fluctuation in packet generation rate increases, the average transit time increases and network performance degrades. In order to improve the transportation efficiency in this situation, we propose a new routing method called mixed routing. It operates in two modes: (1) when the packet generation rate is small, the shortest paths are used to deliver the packets to the destination; (2) when the packet generation rate is large, the traffic loads in central nodes are redistributed to other non-central nodes, using the so-called efficient routing method. We find that the time shifting between the two modes is very critical for the routing performance. Consequently, we provide an efficient method to determine the critical times to shift the routing modes for achieving good network performance.     

The Effect of Queueing Strategy on Network Traffic

In recent years, the transportation system has been faced by increasing challenge in congestion and inefficiency, and research in traffic network has become a significant area of interest. In this paper, we introduce a dynamic-information-based (DIB) queueing strategy into network traffic model under the efficient routing strategy. DIB makes a packet with higher priority to be delivered if there are less packets travelling along its path from the current node to the destination. It is found that, compared with the traditional first-in-first-out (FIFO) queueing strategy, DIB can effectively balance the traffic load of the system via delaying packets to be delivered to congested nodes. Although the network capacity has no obvious changes, some other indexes which reflect transportation efficiency are efficiently improved in the congestion state. Besides, extensive simulation results and discussions are provided to explain the phenomena. The results may provide novel insights for research on traffic systems.     

Integrating network structure and dynamic information for better routing strategy on scale-free networks

We study information packet routing processes on scale-free networks by mimicking the Internet traffic delivery strategies. We incorporate both the global network structure information and local queuing information in the dynamic processes. We propose several new routing strategies to guide the packet routing. The performance of the routing strategies is measured by the average transit time of the packets as well as their dependence on the traffic amount. We find that the routing strategies which integrate both global network structure information and local dynamic information perform much better than the traditional shortest-path routing protocol which takes into account only the global topological information. Moreover, from comparative studies of these routing strategies, we observe that some of our proposed methods can decrease the average transit time of packets but the performance is closely dependent on the total amount of traffic while some other proposed methods can have good performance independent of the total amount of traffic with hyper-excellent average transit time of packets. Also, numerical results show that our proposed methods integrating network structure information and local dynamic information can work much better than the methods recently proposed in [S. Sreenivasan, R. Cohen, E. López, Z. Toroczkai, H.E. Stanley, Phys. Rev. E 75 (2007) 036105, Zhi-Xi Wu, Gang Peng, Eric W.M. Wong, Kai-Hau Yeung, J. Stat. Mech. (2008) P11002.], which only considered network structure information.     

基于改进蚁群算法的交通最优路径方法研究

本文提出一种基于改进蚁群算法的交通路径最优方法,首先根据图论的思想构建了城市交通网络模型,结合层次分析法考虑了道路长度、交叉口停滞、交通拥挤、道路容量、天气状况等五个主要因素。然后在MATLAB平台下,采用改进的蚁群算法对静态交通网络和动态交通网络分别进行最短路径的求解,最后进行了对比分析。研究结果表明,在综合考虑以上五种因素的情况下,动态交通网络下的路径最优算法能为出行者找到更准确更便捷的路线。     

Routing strategies in traffic network and phase transition in network traffic flow

The dynamics of information traffic over scale-free networks has been investigated systematically. A series of routing strategies of data packets have been proposed, including the local routing strategy, the next-nearest-neighbour routing strategy, and the mixed routing strategy based on local static and dynamic information. The capacity of the network can be quantified by the phase transition from free flow state to congestion state. The optimal parameter values of each model leading to the highest efficiency of scale-free networked traffic systems have been found. Moreover, we have found hysteretic loop in networked traffic systems with finite packets delivering ability. Such hysteretic loop indicates the existence of the bi-stable state in the traffic dynamics over scale-free networks.