Organizational growth and hierarchical change in formal structure

Three hypotheses about aggregate change in organizational size (measured as number of employees) and formal structure over time are tested: (1.) the frequency of hierarchical change is higher at lower levels of hierarchy; (2.) periodic pressures for organizational change are translated into periodic changes in organizational size; and (3.) changes in size are more readily translated into increases in structure at lower levels of hierarchy. These hypotheses are tested by using spectral analysis to decompose the variance in the time series of size and structure. The implications of the confirmation of these hypotheses for organizational change over time are discussed.     

可调聚类系数加权无标度网络建模及其拥塞问题研究

针对实现网络特征的真实情况,提出了一类可调聚类系数的加权无标度网络模型,该模型能够重现现实网络权重和节点度呈幂律分布的统计特性．特别是聚类系数与度之间的非线性关系,恰好符合某些现实网络聚类系数与度之间的平头关系特征．最后研究了可调聚类系数加权网络模型中的拥塞问题．采用基于强度优先传递的局部路由策略,分析了网络中的流量传输问题．     

Evaluating the AS-level Internet models: beyond topological characteristics

A surge number of models has been proposed to model the Internet in the past decades. However, the issue on which models are better to model the Internet has still remained a problem. By analysing the evolving dynamics of the Internet, we suggest that at the autonomous system (AS) level, a suitable Internet model, should at least be heterogeneous and have a linearly growing mechanism. More importantly, we show that the roles of topological characteristics in evaluating and differentiating Internet models are apparently over-estimated from an engineering perspective. Also, we find that an assortative network is not necessarily more robust than a disassortative network and that a smaller average shortest path length does not necessarily mean a higher robustness, which is different from the previous observations. Our analytic results are helpful not only for the Internet, but also for other general complex networks.     

Enhancement of scale-free network attack tolerance

Despite the large size of most communication and transportation systems,there are short paths between nodes in these networks which guarantee the efficient information,data and passenger delivery;furthermore these networks have a surprising tolerance under random errors thanks to their inherent scale-free topology.However,their scale-free topology also makes them fragile under intentional attacks,leaving us a challenge on how to improve the network robustness against intentional attacks without losing their strong tolerance under random errors and high message and passenger delivering capacity.Here we propose two methods (SL method and SH method) to enhance scale-free network’s tolerance under attack in different conditions.     

无尺度网络自适应管理策略

针对建立在随机网络模型上的传统网络管理中所存在的数据采集流量偏大、同步采集发生率高等管理性能问题,提出一种适合无尺度网络的自适应网络管理策略,该策略可以通过对比被管网元地位度量阈值,动态探测被管网元在网络中所处的地位,根据网元所处地位不同自动调整数据采集周期.实验证明,这种策略在不降低网络管理功效前提下,能够减少需采集的网络管理数据,并避免了数据采集的同步,从而提高网络管理的性能.     

一种基于点和边差异性的网络结构熵

熵是反映网络异构性的重要指标. 由于只是关注网络结构中"点"或"边"的单一作用,基于度分布和度相对值的两种传统熵在刻画网络结构特征时均存在缺陷. 文章综合考虑"点"和"边"差异性,定义一种新的网络结构熵,并对规则网络、随机网络和无标度网络等结构熵进行理论分析和仿真实验. 结果表明,这种新网络结构熵可以更有效地反映网络的结构特征,尤其是对于稀疏网络及星型网络的结构差异解释更为合理. 关键词： 均匀网络 无标度网络 熵     

Failure in Complex Social Networks

A class of inhomogenously wired networks called “scale-free” networks have been shown to be more robust against failure than more homogenously connected exponential networks. The robustness of scale-free networks consists in their ability to remain connected even when failure occurs. The diffusion of information and disease across a network only requires a single contact between nodes, making network connectivity the crucial determinant of whether or not these “simple contagions” will spread. However, for “complex contagions,” such as social movements, collective behaviors, and cultural and social norms, multiple reinforcing ties are needed to support the spread of a behavior diffusion. I show that scale-free networks are much less robust than exponential networks for the spread of complex contagions, which highlights the value of more homogenously distributed social networks for the robust transmission of collective behavior.     

基于平均场理论的微博传播网络模型

微博是在通过用户关注机制建立的用户网络上分享实时信息的社交平台,而微博消息主要通过用户的转发行为使消息在用户网络上传播.掌握微博消息的传播机制,对研究微博上舆论谣言的传播、产品推广等具有指导作用.本文通过对微博传播网络的结构分析来探索微博传播过程,利用新浪微博数据,建立微博传播网络,分析该网络的生成机制,使用平均场论的方法,推导微博传播网络的度分布模型.实验结果表明:微博传播网络的度分布是时间相依的,在特定时间下网络的度分布服从幂律分布.     

基于综合故障的无线传感器网络无标度容错拓扑模型研究

针对无线传感器网络实际应用中遇到的环境损毁和能量耗尽的问题,本文首先对网络综合故障进行建模,获取满足综合故障容忍能力和网络生命期双重需求的网络节点度和节点度上限值的取值规律,并结合由无标度特征导出的两者关系,从而求得最优节点度上限值,最终引入关于节点度上限值的适应度函数,提出了容忍环境损毁和能量耗尽综合故障的无标度容错拓扑演化模型.仿真实验结果表明,该模型演化生成的无标度拓扑对环境损毁和能量耗尽具有较好的容错性,并能够有效地延长网络生命期.     

Structure Learning of \mbox{PM}_{2.5} Distribution Using Sparse Graphical Models

We consider the structure learning problem of the \mbox{PM}_{2.5} pollution data over 31 provincial capitals in China. Specifically, we make use of the graphical model tools to study the hubs and the community structures of the \mbox{PM}_{2.5} pollution networks. The results show that the hubs in the \mbox{PM}_{2.5}pollution networks are always seriously polluted cities, and the \mbox{PM}_{2.5} pollution networks have significant community structures which consist of cities which in some sense can be regarded as blocks with similar cause of pollution. In view of the results, we suggest that the government should strengthen the effort to treat the seriously polluted areas and western China areas. Moreover, the management of the \mbox{PM}_{2.5} pollution should be region-dependent.