大脑网络的探索进程(一)——研究特点、方法与三大类型

大脑网络是复杂的生命系统中一个最典型的复杂网络,是一类"网络的网络"。目前可从三个层次对大脑网络进行建模探索,即微观尺度(神经元)、中尺度(神经集群)、大尺度(脑区域),各层次之间相互影响、错综复杂,研究难度很大。笔者从网络科学观来评述大脑网络的探索进程、研究方法和主要类型。

脑小血管病认知功能障碍的脑网络研究

脑小血管病(cerebral small vessel disease,CSVD)是导致VCI的最常见原因,VCI起病隐匿,渐进发展,早期表现为执行和信息处理速度减慢,晚期可累及记忆、语言、视空间等多个认知领域,最终可能发展为痴呆[1-2]。CSVD导致的皮质下型VCI是最多见的VCI亚型,占VCI患病率的50%~70%,其病理机制目前仍不清楚,且缺乏特异性的治疗方法,因此早期识别、诊断和干预尤为重要[3]。VCI的诊断需依赖于多领域的神经心理学评估以及影像检查,2013年国际CSVD影像共识把新发皮质下小梗死、血管源性腔隙、血管源性脑白质高信号、血管周围间隙、脑微出血和脑萎缩作为CSV D的结构影像学标志物[4]。

磁共振扩散张量成像在青少年抑郁症中的研究进展

抑郁症是致残的主要原因之一,通常始于青春期。青少年抑郁症常导致学业失败、同伴关系不佳、行为问题、家庭及社会关系冲突,甚至自杀等不良后果,早期预防和积极有效的治疗至关重要。磁共振扩散张量成像技术能定量评价脑白质微结构,构建结构网络,可用于分析青少年抑郁症患者脑白质异常与症状、年龄、性别等临床变量的相关性。青少年抑郁症扩散张量成像研究显示,青少年抑郁症患者存在胼胝体、扣带束及钩状束等多个白质纤维束微结构异常,前额叶-纹状体环路、前额叶-边缘系统神经环路受损,且与记忆、情绪调节、奖励处理、认知加工等密切相关,与成人抑郁症中的发现一致。本研究对扩散张量成像的成像原理、数据处理方法及在青少年抑郁症中的应用进展进行简要综述,为今后的研究提供新思路。

基于深度聚类的供水管网分区构建方法研究

在供水系统管理中,分区管理是进行管网运营、压力管理和漏损控制的有效工具,其构建方法直接影响分区效能的发挥程度。然而,大多数分区方法通常未能充分考虑管网的拓扑结构与水力状态之间的复杂相互作用,所得分区方案无法充分利用现有分区设施,在实际工程应用中面临困难。鉴于此,提出了一种基于结构性深度聚类网络(Structural Deep Clustering Network,SDCN)的供水管网分区构建方法。使用SDCN有机融合管网拓扑结构和水力状态信息进行聚类分析,根据聚类结果以及管网计量设施实际情况,对孤立节点进行归类分析,提出聚类边界调整的有效计算方法,以形成最终分区方案。与两种经典的管网聚类方法相比,该方法具有更好的管网节点聚类精度,分区结果面向工程实际需求,可以为管网分区规划与建设提供有效的技术支撑。

收缩喷嘴内部流道型线对射流流场的影响

为研究收缩喷嘴内部流道形成对射流流场的气体动特性参数的影响 ,根据可压缩流体轴对称N—S方程 ,采用非结构网格和二阶精度的有限体积法 ,对不同内部流道形线的喷嘴自由射流进行数值模拟。亚声速射流采用RNGk_ε湍流模型 ,超声速射流采用S—A湍流模型 ,计算结果与实验较吻合。在亚声速流动中 ,收缩喷嘴的收缩角大小会影响其对射流的阻滞效果 ,内部流道形线设计为维多辛斯基曲线可以获得更好的流场动特性参数 ,有利于提高喷嘴的工作效率。在超声速流动中 ,喷嘴流道型线对出口膨胀波的角度与强弱影响较大 ,要根据射流的有效作用区域选择合适的喷嘴 ,才能使能量的损失最小。若要获得较佳的外部流场参数 。

Transition of plasticity and fracture mode of Zr-Al-Ni-Cu bulk metallic glasses with network structures

Effect of network structure on plasticity and fracture mode of Zr？Al？Ni？Cu bulk metallic glasses （BMGs） was investigated. The microstructures of transversal and longitudinal sections were exposed by chemical etching and observed by scanning electron microscopy （SEM）. The mechanical properties were examined by room-temperature uniaxial compression test. The results show that both plasticity and fracture mode are significantly affected by the network structure and the alteration occurs when the size of the network structure reaches up to a critical value. When the cell size （dc） of the network structure is ~3μm, Zr-based BMGs characterize in plasticity that decreases with increasingdc. The fracture mode gradually transforms from single 45° shear fracture to double 45° shear fracture and then cleavage fracture with increasingdc. In addition, the mechanisms of the transition of the plasticity and the fracture mode for these Zr-based BMGs are also discussed.

An efficient reliability evaluation method for industrial wireless sensor networks

Aimed at the difficulties in accurately, comprehensively and systematically evaluating the reliability of industrial wireless sensor networks （WSNs）, a time-evolving state transition-Monte Carlo （TEST-MC） evaluation method and a novel network function value representation method are proposed to evaluate the reliability of the IWSNs. First, the adjacency matrix method is used to characterize three typical topologies of WSNs including the mesh network, tree network and ribbon network. Secondly, the network function value method is used to evaluate the network connectivity, and the TEST-MC evaluation method is used to evaluate network reliability and availability. Finally, the variations in the reliability, connectivity and availability of these three topologies are presented. Simulation results show that the proposed method can quickly analyze the reliability of the networks containing typical WSN topologies, which provides an effective method for the comprehensive and accurate evaluation of the reliability of WSNs.

SIMULATION AND PERFORMANCE ANALYSIS OF NETWORK ON CHIP ARCHITECTURES

The network on chip（NoC）is used as a solution for the communication problems in a complex system on chip（SoC）design.To further enhance performances,the NoC architectures,a high level modeling and an evaluation method based on OPNET are proposed to analyze their performances on different injection rates and traffic patterns.Simulation results for general NoC in terms of the average latency and the throughput are analyzed and used as a guideline to make appropriate choices for a given application.Finally,a MPEG4 decoder is mapped on different NoC architectures.Results prove the effectiveness of the evaluation method.

Vulnerability analysis of multimodal transport networks based on complex network theory

To explore the structural characteristics and vulnerability of multimodal transport networks,this study identifies the structural characteristics of a multimodal transport network on the basis of the complex network theory.Key nodes are clarified from the analysis of the structural characteristics.The characteristic path length and percentage of the largest subgraph are applied to analyze the vulnerability of the multimodal transport network after random and intentional attacks on the nodes.The network of a multimodal transport company is taken as an example in the empirical analysis.Results show that with more than ten nodes under a random attack,the percentage of the largest subgraph is less than 20%,and the characteristic path length is less than 2.The same performance is observed for more than seven nodes under an intentional attack.The multimodal transport network is more vulnerable under an international attack against key nodes.The results of the topology and node failure under random or intentional attacks would support the management of the multimodal transport network.Suggestions for the emergency transportation organization of enterprises under attacks are proposed accordingly.These suggestions should help improve network invulnerability and recovery from node failure.

Analysis on Refinery System as a Complex Task-resource Network

Refinery system, a typical example of process systems, is presented as complex network in this paper. The topology of this system is described by task-resource network and modeled as directed and weighted graph, in which nodes represent various tasks and edges denote the resources exchanged among tasks. Using the properties of node degree distribution, strength distribution and other weighted quantities, we demonstrate the heterogeneity of the network and point out the relation between structural characters of vertices and the functionality of correspond- ing tasks. The above phenomena indicate that the design requirements and principles of production process contrib- ute to the heterogeneous features of the network. Besides, betweenness centrality of nodes can be used as an impor- tance indicator to provide additional information for decision making. The correlations between structure and weighted properties are investigated to further address the influence brought by production schemes in system con- nectivity patterns. Cascading failures model is employed to analyze the robustness of the network when targeted at- tack happens. Two capacity assignment strategies are compared in order to improve the robustness of the network at certain cost. The refinery system displays more reliable behavior when the protecting strategy considers heteroge- neous properties. This phenomenon further implies the structure-activity relationship of the refinery system and provides insightful suggestions for process system design. The results also indicate that robustness analysis is a _promising applicat!on of methodologies from complex networks to process system engineering..

A statistical end-to-end performance model for networks with complex topologies

Network calculus provides new tools for performance analysis of networks, but analyzing networks with complex topologies is a challenging research issue using statistical network calculus. A service model is proposed to characterize a service process of network with complex topologies. To obtain closed-form expression of statistical end-to-end performance bounds for a wide range of traffic source models, the traffic model and service model are expanded according to error function. Based on the proposed models, the explicit end-to-end delay bound of Fractional Brownian Motion（FBM） traffic is derived, the factors that affect the delay bound are analyzed, and a comparison between theoretical and simulation results is performed. The results illustrate that the proposed models not only fit the network behaviors well, but also facilitate the network performance analysis.

Average Range and Network Synchronizability

The influence of structural properties of a network on the network synchronizability is studied by introducing a new concept of average range of edges. For both small-world and scale-free networks, the effect of average range on the synchronizability of networks with bounded or unbounded synchronization regions is illustrated through numerical simulations. The relations between average range, range distribution, average distance, and maximum betweenness are also explored, revealing the effects of these factors on the network synchronizability of the small-world and scale-free networks, respectively.

Local adaptive transmit power assignment strategy for wireless sensor networks

A distributed local adaptive transmit power assignment (LA-TPA) strategy was proposed to construct a topology with better performance according to the environment and application scenario and prolong the network lifetime.It takes the path loss exponent and the energy control coefficient into consideration with the aim to accentuate the minimum covering district of each node more accurately and precisely according to various network application scenarios.Besides,a self-healing scheme that enhances the robustness of the network was provided.It makes the topology tolerate more dead nodes than existing algorithms.Simulation was done under OMNeT++ platform and the results show that the LA-TPA strategy is more effective in constructing a well-performance network topology based on various application scenarios and can prolong the network lifetime significantly.

Bidirectional Clone Node Model of Optimizing Performance of Structured P2P Overlay Network

In order to reduce the maintenance cost of structured Peer-to-Peer (P2P),Clone Node Protocol (CNP) based on user behavior is proposed.CNP considers the regularity of user behavior and uses the method of clone node.A Bidirectional Clone Node Chord model (BCNChord) based on CNP protocol is designed and realized.In BCNChord,Anticlockwise Searching Algorithm,Difference Push Synchronize Algorithm and Optimal Maintenance Algorithm are put forward to increase the performances.In experiments,according to the frequency of nodes,the maintenance cost of BCNChord can be 3.5%～32.5% lower than that of Chord.In the network of 212 nodes,the logic path hop is steady at 6,which is much more prior to 12 of Chord and 10 of CNChord.Theoretical analysis and experimental results show that BCNChord can effectively reduce the maintenance cost of its structure and simultaneously improve the query efficiency up to (1/4)O(logN).BCNChord is more suitable for highly dynamic environment and higher real-time system.

Research on Testing Technologies of Network System in Smart Substations

The network structures of smart substations and the characteristics of industrial Ethernet switches are analyzed.The testing technologies of network systems based on smart substations are specifically elaborated.A viewpoint is proposed that special testing policy&method of smart substation networks should be followed,so that the results can reveal the real network data exchange performance of the whole station.This view ensures the safety and stability of smart substations and lays a foundation for future upgrades and expansions.

Estimation of Data Transfer Routes Fractal Dimension in Large Scale Networks

The article is devoted to the evaluation of fractal properties of routing data in computer large scale networks. Implemented the study of percolation network topological structures of large dimension and made their transformation into fractal macrostructure. An example of calculating the fractal dimension of the data path for the boundary of the phase transition between the states of network connectivity. The dependence of the fractal dimension of the percolation cluster on the size of the square δ-cover and conductivity value network of large dimension. It is shown that for the value of the fractal dimension of the route dc ≈ 1.5, network has a stable dynamics of development and size of clusters are optimized with respect to the current load on the network.

Agent-Based Simulation for Analyzing Network Formation with Learning Dynamics

In game theoretic context, it is assumed that the decision maker has the extraordinary skills of reasoning and calculation. This assumption is called ＂perfect rationality＂. A player with perfect rationality can solve complex problems without making mistakes. However, recently, many studies have restricted this rationality or the structure of game. These restrictions are called ＂bounded rationality.＂ The authors also focus on bounded rationality, but with learning dynamics and complex networks. A complex network covers a wide area. Currently, a wide range of studies have not only investigated network formation and the characteristics of a formed network, but also analyzed situations where a network is already provided. In addition, in an analysis using game theory, a prisoners＇ dilemma type game was used to investigate how a change in the network structure would affect the players＇ relationships Therefore, our model employs decision makers with learning dynamics and describes the interaction of decision makers as a network. The purpose of this study is to examine the behavior of the decision maker with learning dynamics and the formation of networks by the interaction of decision makers through an agent-based simulation.

Estimation of half-wave potential of anabolic androgenic steroids by means of QSER Approach

The quantitative structure-property relationship(QSPR) of anabolic androgenic steroids was studied on the half-wave reduction potential(E1/2) using quantum and physico-chemical molecular descriptors. The descriptors were calculated by semi-empirical calculations. Models were established using partial least square(PLS) regression and back-propagation artificial neural network(BP-ANN). The QSPR results indicate that the descriptors of these derivatives have significant relationship with half-wave reduction potential. The stability and prediction ability of these models were validated using leave-one-out cross-validation and external test set.

Topological Properties of Complex Networks with Different Types of Nodes

Nodes play different roles or have different functions in many natural and social networks.In this paper,a simple model with different types of nodes and deterministic selective linking rule is proposed.The structural properties by theoretical predictions are investigated that the given model exhibits a power-law distribution.

A self-organized locator obtaining method driven by local minima

The scalability of routing architectures for large networks is one of the biggest challenges that the Internet faces today.Greedy routing,in which each node is assigned a locator used as a distance metric,recently received increased attention from researchers and is considered as a potential solution for scalable routing.In this paper,LMD—a local minimum driven method is proposed to compute the topology-based locator.To eliminate the negative effect of the " quasi" greedy property—transfer routes longer than the shortest routes,a two-stage routing strategy is introduced,which combines the greedy routing with source routing.The greedy routing path discovered and compressed in the first stage is then used by the following source-routing stage.Through extensive evaluations,based on synthetic topologies as well as on a snapshot of the real Internet AS(autonomous system)topology,it is shown that LMD guarantees 100%delivery rate on large networks with low stretch.