虚拟网络行为对互联网整体特性的影响

虚拟网络是一种依赖Internet基础设施所提供的传输能力，但又具有独立拓扑结构和信息传递规则的应用层网络行为逻辑网络.提出了耦合虚拟网络行为与物理节点的抽象模型，对一类典型的虚拟网络逻辑拓扑给互联网整体特性带来的影响进行了分析.研究表明在虚拟网络作用下，节点数据包排队长度存在相变特性，但相变临界点比对规则网络发生了明显左移，网络性能相对恶化.当数据包注入速率小于相变临界速率时，节点数据包排队长度不相关或短程相关；在接近临界速率处，节点数据包排队长度长程相关，幂指数H增大，网络获得更强的长程相关性.同时，在注入速率大于或等于临界速率时，虚拟网络行为使网络呈现出一致的长程相关特性.     

互联网络数据包传输的一种简单元胞自动机模型

提出了一种描述计算机互联网络数据包传输的简单元胞自动机模型,并研究了沿着网络固定路径中路由节点数据包队列长度和传输时间的统计特性.计算机仿真结果表明,根据数据包输入速率和路由节点平均最大传输速率的不同,系统存在自由流和拥塞两种相态.在自由流状态,路由节点数据包排队长度和传输时间都呈现幂律特性;在拥塞状态,路由节点数据包排队长度呈现白噪声特征,而传输时间在低频段为幂律、高频段为白噪声特征.仿真结果和已有文献和经验数据得到的结论一致. 关键词： 元胞自动机 1//f噪声 幂律 计算机网络     

复杂计算机网络中的相变和整体关联行为

利用相变的概念解释复杂计算机网络中广泛存在的幂律现象,并未考虑到网络这一复杂系统中节点之间的相互关联作用.通过一种计算机网络模型,对网络中的相变和整体关联行为进行了分析和比较.研究表明,随着负载的增加,网络节点行为的空间和时间的长程相关性逐渐增强,整体关联行为逐渐显现;在临界状态,网络负载变化的功率谱呈现1/f²的特点,而节点排队长度变化的功率谱服从1/f^α分布,其中α≤2.网络节点行为在时间和空间上的关联进一步得到说明. 关键词： 计算机网络 相变 关联 幂律     

基于局部路由策略的复杂网络拥塞控制

提出一种复杂网络上的局部路由策略,算法采用节点收缩法评估节点的重要度,发送节点根据邻居节点的重要度及网络的状态自适应地调整向邻居节点转发数据包的概率.在网络处于自由流通状态时充分发挥关键节点的优势,保证数据包快速到达目的地;在网络处于即将拥塞时分散业务,根据节点重要度准确识别网络中的关键节点,通过有效分流予以保护.仿真结果表明:在网络处于自由流通状态时,该局部路由策略能充分发挥网络中关键节点的枢纽作用,保持较低的传输时延;在网络部分关键节点出现拥塞时,该局部路由策略能有效避开拥挤严重的节点,将数据包均匀地分布在各个节点上,有效抑制网络拥塞,提高网络的容量.     

Repeat Sequences and Base Correlations in Human Y ChromosomePalindromes

利用信息论和统计学的方法并结合生物学的特征研究人类Y染色体回文序列的互信息、“n字”熵、条件熵,定量分析了回文序列的长程关联和短程关联,发现其中既存在长程关联也存在短程关联,并且它们主要是由序列中的重复序列引起的. 研究表明重复序列含量越高碱基之间的关联越强.     

手机通话网络度特征分析

手机通信数据详细记录了人们的通信行为, 成为研究人们社会关系、行为模式的重要资源. 通话号码个数、通话次数和时长是手机通信网络的基本属性. 本文在复杂网络理论基础上, 应用统计的方法研究了中国西部某城市三百余万手机用户不同节假日和工作日的 四天通话数据在不同尺度下的号码度、通话度、时长度的分布以及平均号码度、 平均通话度、平均时长度的特征.研究表明, 所有尺度下, 号码度、通话度、时长度均为幂律分布, 幂指数随尺度、日期和指标的不同而不同, 在[1.3, 4] 范围内波动.总体上, 号码度幂指数大于通话度和时长度幂指数, 入度幂指数大于出度幂指数;节假日幂指数大于相应指标的工作日幂指数, 休息时段幂指数大于工作时段幂指数;与工作日相比, 节假日的平均号码度和平均通话度较小, 平均时长度较大.揭示了绝大多数用户每日只接打1个号码的电话, 节假日期间接打电话的用户数、次数、时长减少, 但平均通话时长增大的特征. 关键词： 手机通话网络 复杂网络 度分布 通话模式     

聚合物中长程关联能的动力学研究

本文计算采用扩展的SSH哈密顿模型,加上长程关联哈密顿量,在自然边界条件下,用绝热动力学方法研究了有限长反式聚乙炔链中平均关联能随时间的演化,计算了长程电子关联对极化子动力学的影响并计算了极化子状态下的长程关联能.结果发现,加入一个电子或空穴,平均关联能的大小随着时间呈非周期性阻尼振荡,经过一定时间后,平均关联能趋近一个恒定值,此时得到比较稳定的极化子位形.当格点增加时,长程关联能趋于恒定的时间逐渐缩短.     

二维有限能量约束下最优导航问题的理论分析

最近，Li等研究了在Kleinberg导航模型中引入总能量／l=cⅣ约束后的最优导航问题，其中4为网络中所有长程连边的长度之和，C为正常数，Ⅳ为网络节点总数．他们通过在1维和2维导航模型中的模拟结果推测，在有限能量约束下Kleinberg导航模型中按照幂律方式添加长程连边的最优幂指数应该是α=d＋1，其中d为导航模型的维数．本文在平均场理论下，建立了2维有限能量约束下的导航过程的动态微分方程，通过对该方程进行数学分析以及数值求解，从理论上证明了当网络规模足够大且总能量相对较小时，2维有限能量约束下的最优导航幂指数确实为α=3，这一结果证实了Li等之前的推测．     

混合交通流时间序列的去趋势波动分析

应用去趋势波动分析法研究交通流时间序列的复杂性,探讨了混合交通流时间序列演变行为的标度指数.根据标度指数的变化特征,进而揭示交通流时间序列所具有的长程相关性和短程相关性.通过分析发现,存在一密度ρ,当ρ₁<ρ<ρ₂时,交通流时间序列具有长程相关性;而当ρ<ρ₁或ρ>ρ₂时,交通流时间序列具有短程相关性,即密度的变化影响着标度指数的变化.另外分析了在不同慢车比率条件下时间序列的标度指数,发现慢车比率的变化 关键词： 混合交通流 去趋势波动分析 时间序列 长程相关     

基于节点相关性的网络不动点理论研究

现代复杂的通信网络内部存在着广泛的幂律现象，网络节点之间存在相关特性. 根据这种相关特性，提出了网络不动点理论. 将Banach不动点理论引入网络模型，证明了网络不动点理论的正确有效性. 证明过程是把通信网络看作由路径预测算法产生的似马尔可夫链的路由节点迭代序列形成的网络空间. 由节点相关性可知，此空间中的节点序列相对越长就越能折射出搜索的目标所在，预测准确率也会逐步增加，可以更好地进行目标定位、数据挖掘等. 通过某种路由准则的算子从源节点最终映射到的目的节点与Banach空间的不动点相对应，即为网络空间的不动点. 当网络发展到能为用户提供真正的无处不在的连接时，网络不动点理论的物理特性将非常明显. 因为网络规模越大，节点间的群体作用越显著，就越能显现网络不动点理论的物理特性. 关键词： 计算机网络 长程相关 不动点 幂律     

Adaptive local routing strategy on a scale-free network

Due to the heterogeneity of the structure on a scale-free network, making the betweennesses of all nodes become homogeneous by reassigning the weights of nodes or edges is very difficult. In order to take advantage of the important effect of high degree nodes on the shortest path communication and preferentially deliver packets by them to increase the probability to destination, an adaptive local routing strategy on a scale-free network is proposed, in which the node adjusts the forwarding probability with the dynamical traffic load (packet queue length) and the degree distribution of neighbouring nodes. The critical queue length of a node is set to be proportional to its degree, and the node with high degree has a larger critical queue length to store and forward more packets. When the queue length of a high degree node is shorter than its critical queue length, it has a higher probability to forward packets. After higher degree nodes are saturated (whose queue lengths are longer than their critical queue lengths), more packets will be delivered by the lower degree nodes around them. The adaptive local routing strategy increases the probability of a packet finding its destination quickly, and improves the transmission capacity on the scale-free network by reducing routing hops. The simulation results show that the transmission capacity of the adaptive local routing strategy is larger than that of three previous local routing strategies.     

二维合金系统的有序动力学研究

采用主方程方法在对概率近似下对三元fcc结构晶体在(001)方向的一个层面的有序无序动力学过程进行了研究.计算了长程序参量(LRO)和短程序参量(SRO)随时间的演化过程.在系统从完全无序态弛豫到平衡态的过程中存在各种瞬态有序相.瞬态相有着不同的特点,如序参量(LRO,SRO)瞬态相曲线形状不同等.产生它们的原因有不同的原子特征迁移时间、原子间最近邻和次近邻相互作用差异、短程相关性和长程相关性的差异对弛豫过程的影响. 关键词： 对概率近似 瞬态有序相 长程序参量(LRO) 长程相关性     

Unified index to quantifying heterogeneity of complex networks

Although recent studies have revealed that degree heterogeneity of a complex network has significant impact on the network performance and function, a unified definition of the heterogeneity of a network with any degree distribution is absent. In this paper, we define a heterogeneity index 0≤H<1 to quantify the degree heterogeneity of any given network. We analytically show the existence of an upper bound of H=0.5 for exponential networks, thus explain why exponential networks are homogeneous. On the other hand, we also analytically show that the heterogeneity index of an infinite power law network is between 1 and 0.5 if and only if its degree exponent is between 2 and 2.5. We further show that for any power law network with a degree exponent greater than 2.5, there always exists an exponential network such that both networks have the same heterogeneity index. This may help to explain why 2.5 is a critical degree exponent for some dynamic behaviors on power law networks.     

Fractal landscapes in biological systems: long-range correlations in DNA and interbeat heart intervals

Here we discuss recent advances in applying ideas of fractals and disordered systems to two topics of biological interest, both topics having common the appearance of scale-free phenomena, i.e., correlations that have no characteristic length scale, typically exhibited by physical systems near a critical point and dynamical systems far from equilibrium. (i) DNA nucleotide sequences have traditionally been analyzed using models which incorporate the possibility of short-range nucleotide correlations. We found, instead, a remarkably long-range power law correlation. We found such long-range correlations in intron-containing genes and in non-transcribed regulatory DNA sequences as well as intragenomic DNA, but not in cDNA sequences or intron-less genes. We also found that the myosin heavy chain family gene evolution increases the fractal complexity of the DNA landscapes, consistent with the intron-late hypothesis of gene evolution. (ii) The healthy heartbeat is traditionally thought to be regulated according to the classical principle of homeostasis, whereby physiologic systems operate to reduce variability and achieve an equilibrium-like state. We found, however, that under normal conditions, beat-to-beat fluctuations in heart rate display long-range power law correlations.     

Many-body correlations in the problems of electrodynamics of fluids

This paper presents a review of the theory of the many-body correlation phenomena in fluids, in which the collective character of the fluctuations is caused by the long-range interaction of electrodynamic origin. The procedure of the statistical mechanical averaging of the microscopic electrodynamic equations is developed for a classical system of the interacting polarizable molecules with a subsequent account of the molecular correlations. As a result an effective expansion for the refractive index is obtained. The dependence of the refractive index on the thermodynamic parameters near the critical point is investigated using the scaling-law asymptotics for the many-body correlation functions. A molecular theory of the multiple light scattering is suggested. A method of evaluation of the many-body any-order scattering intensity in the critical region is described. Using a resummation procedure, similar to that developed for the light propagation problem, the correlation function expansion is obtained for a classical system of charged and neutral particles, correlations due to the short-range forces are taken into account. The expansion gives series in terms of the effective “dressed” electrostatic potential containing no long-range Coulomb divergencies, nor short-range ones.     

Lévy-flight spreading of epidemic processes leading to percolating clusters

We consider two stochastic processes, the Gribov process and the general epidemic process, that describe the spreading of an infectious disease. In contrast to the usually assumed case of short-range infections that lead, at the critical point, to directed and isotropic percolation respectively, we consider long-range infections with a probability distribution decaying in d dimensions with the distance as . By means of Wilson's momentum shell renormalization-group recursion relations, the critical exponents characterizing the growing fractal clusters are calculated to first order in an -expansion. It is shown that the long-range critical behavior changes continuously to its short-range counterpart for a decay exponent of the infection . Received: 17 July 1998 / Revised: 20 July 1998 / Accepted: 28 July 1998     

Anomalously large critical regions in power-law random matrix ensembles

We investigate numerically the power-law random matrix ensembles. Wave functions are fractal up to a characteristic length whose logarithm diverges asymmetrically with different exponents, 1 in the localized phase and 0.5 in the extended phase. The characteristic length is so anomalously large that for macroscopic samples there exists a finite critical region, in which this length is larger than the system size. The Green's functions decrease with distance as a power law with an exponent related to the correlation dimension.