Network is considered naturally as a wide range of different contexts, such as biological systems, social relationships as well as various technological scenarios. Investigation of the dynamic phenomena taking place i...Network is considered naturally as a wide range of different contexts, such as biological systems, social relationships as well as various technological scenarios. Investigation of the dynamic phenomena taking place in the network, determination of the structure of the network and community and description of the interactions between various elements of the network are the key issues in network analysis. One of the huge network structure challenges is the identification of the node(s) with an outstanding structural position within the network. The popular method for doing this is to calculate a measure of centrality. We examine node centrality measures such as degree, closeness, eigenvector, Katz and subgraph centrality for undirected networks. We show how the Katz centrality can be turned into degree and eigenvector centrality by considering limiting cases. Some existing centrality measures are linked to matrix functions. We extend this idea and examine the centrality measures based on general matrix functions and in particular, the logarithmic, cosine, sine, and hyperbolic functions. We also explore the concept of generalised Katz centrality. Various experiments are conducted for different networks generated by using random graph models. The results show that the logarithmic function in particular has potential as a centrality measure. Similar results were obtained for real-world networks.展开更多
Theoretic and practical significance has been highlighted in the research of the roles and functions of destinations,as destinations are restricted by the spatial structure based on tourist flow network from the persp...Theoretic and practical significance has been highlighted in the research of the roles and functions of destinations,as destinations are restricted by the spatial structure based on tourist flow network from the perspective of relationship.This article conducted an empirical analysis for Tourism Region of South Anhui(TRSA) and revealed the necessity and feasibility of studying the roles and functions of destinations from tourist flow network's perspective.The automorphic equivalence analysis and centrality analysis were used to classify 16 destinations in TRSA into six role types:tourist flow distribution center,hub of tourist flows,passageway destination,common touring destination,attached touring destination,and nearly isolated destination.Some suggestions were given on suitable infrastructure construction and destinations service designs according to their functions in network.This destination role positioning was based on tourist flow network structure in integral and macroscopic way.It provided an important reference for the balanced and harmonious development of all the destinations of TRSA.In addition,this article verified the applicability of social network analysis on tourist flow research in local scale,and expanded this method to destination role and function positioning.展开更多
目的:“中枢控制器模型”理论主张大脑是运动疲劳的关键调节器,而小脑和基底节为2个主要调定点,该假说为探究运动疲劳的中枢影响机制提供了新的理论基础和研究方向,但受限于研究手段一直无法在人体中得到验证。本研究拟通过功能性磁共...目的:“中枢控制器模型”理论主张大脑是运动疲劳的关键调节器,而小脑和基底节为2个主要调定点,该假说为探究运动疲劳的中枢影响机制提供了新的理论基础和研究方向,但受限于研究手段一直无法在人体中得到验证。本研究拟通过功能性磁共振成像(functional magnetic resonance imaging,fMRI)技术探究与运动疲劳相关的大脑区域以及相应脑区之间的激活与功能连接状态,从而验证人体运动疲劳的“中枢控制器模型”理论。方法:招募20名800 m跑成绩≤2 min 3 s的男性运动员,对其进行最大摄氧量测试,根据测试结果最终遴选出相对最大摄氧量≥55 ml/(kg·min)的11名被试。实验前使用氢质子磁共振波谱(1H-magnetic resonance spectroscopy,1H-MRS)测试被试静息态脑区代谢物质的浓度;使用全脑血氧水平依赖功能磁共振成像(blood oxygen level dependent-functional Magnetic Resonance Imaging,BOLD-fMRI)测试被试静息态脑功能网络连接。随后进行递增负荷运动至疲劳实验,试达到疲劳状态后即刻进行与实验前一致的fMRI测试。结果:通过1H-MRS测试发现,运动疲劳发生后被试左侧基底节区(basal ganglia,BG)的Cho/Cr显著降低(P<0.05);通过BOLD-fMRI发现运动员递增负荷运动至疲劳后小脑(cerebellum)和初级运动区(primary motor areas,M1)、小脑和躯体感觉运动区(sensory motor cortex,SMC)、小脑和海马(hippocampus)/海马旁回(parahippocompalgyrus)之间的功能网络连接程度减弱(P<0.05)。结论:运动疲劳发生后基底节区的代谢物质下降,以小脑为中心的脑功能默认网络连接降低,基底节区和小脑可能是使人体出现运动疲劳状态的重要脑功能区,也初步验证了基底神经节和小脑作为2个监视系统来调控人体产生运动疲劳的“中枢控制器模型”理论假说。展开更多
文摘Network is considered naturally as a wide range of different contexts, such as biological systems, social relationships as well as various technological scenarios. Investigation of the dynamic phenomena taking place in the network, determination of the structure of the network and community and description of the interactions between various elements of the network are the key issues in network analysis. One of the huge network structure challenges is the identification of the node(s) with an outstanding structural position within the network. The popular method for doing this is to calculate a measure of centrality. We examine node centrality measures such as degree, closeness, eigenvector, Katz and subgraph centrality for undirected networks. We show how the Katz centrality can be turned into degree and eigenvector centrality by considering limiting cases. Some existing centrality measures are linked to matrix functions. We extend this idea and examine the centrality measures based on general matrix functions and in particular, the logarithmic, cosine, sine, and hyperbolic functions. We also explore the concept of generalised Katz centrality. Various experiments are conducted for different networks generated by using random graph models. The results show that the logarithmic function in particular has potential as a centrality measure. Similar results were obtained for real-world networks.
基金Under the auspices of National Natural Science Foundation of China(No.41001070,40801054,40371030)
文摘Theoretic and practical significance has been highlighted in the research of the roles and functions of destinations,as destinations are restricted by the spatial structure based on tourist flow network from the perspective of relationship.This article conducted an empirical analysis for Tourism Region of South Anhui(TRSA) and revealed the necessity and feasibility of studying the roles and functions of destinations from tourist flow network's perspective.The automorphic equivalence analysis and centrality analysis were used to classify 16 destinations in TRSA into six role types:tourist flow distribution center,hub of tourist flows,passageway destination,common touring destination,attached touring destination,and nearly isolated destination.Some suggestions were given on suitable infrastructure construction and destinations service designs according to their functions in network.This destination role positioning was based on tourist flow network structure in integral and macroscopic way.It provided an important reference for the balanced and harmonious development of all the destinations of TRSA.In addition,this article verified the applicability of social network analysis on tourist flow research in local scale,and expanded this method to destination role and function positioning.
文摘目的:“中枢控制器模型”理论主张大脑是运动疲劳的关键调节器,而小脑和基底节为2个主要调定点,该假说为探究运动疲劳的中枢影响机制提供了新的理论基础和研究方向,但受限于研究手段一直无法在人体中得到验证。本研究拟通过功能性磁共振成像(functional magnetic resonance imaging,fMRI)技术探究与运动疲劳相关的大脑区域以及相应脑区之间的激活与功能连接状态,从而验证人体运动疲劳的“中枢控制器模型”理论。方法:招募20名800 m跑成绩≤2 min 3 s的男性运动员,对其进行最大摄氧量测试,根据测试结果最终遴选出相对最大摄氧量≥55 ml/(kg·min)的11名被试。实验前使用氢质子磁共振波谱(1H-magnetic resonance spectroscopy,1H-MRS)测试被试静息态脑区代谢物质的浓度;使用全脑血氧水平依赖功能磁共振成像(blood oxygen level dependent-functional Magnetic Resonance Imaging,BOLD-fMRI)测试被试静息态脑功能网络连接。随后进行递增负荷运动至疲劳实验,试达到疲劳状态后即刻进行与实验前一致的fMRI测试。结果:通过1H-MRS测试发现,运动疲劳发生后被试左侧基底节区(basal ganglia,BG)的Cho/Cr显著降低(P<0.05);通过BOLD-fMRI发现运动员递增负荷运动至疲劳后小脑(cerebellum)和初级运动区(primary motor areas,M1)、小脑和躯体感觉运动区(sensory motor cortex,SMC)、小脑和海马(hippocampus)/海马旁回(parahippocompalgyrus)之间的功能网络连接程度减弱(P<0.05)。结论:运动疲劳发生后基底节区的代谢物质下降,以小脑为中心的脑功能默认网络连接降低,基底节区和小脑可能是使人体出现运动疲劳状态的重要脑功能区,也初步验证了基底神经节和小脑作为2个监视系统来调控人体产生运动疲劳的“中枢控制器模型”理论假说。
