Percolation Centrality: Quantifying Graph-Theoretic Impact of Nodes during Percolation in Networks

A number of centrality measures are available to determine the relative importance of a node in a complex network, and betweenness is prominent among them. However, the existing centrality measures are not adequate in network percolation scenarios (such as during infection transmission in a social network of individuals, spreading of computer viruses on computer networks, or transmission of disease over a network of towns) because they do not account for the changing percolation states of individual nodes. We propose a new measure, percolation centrality, that quantifies relative impact of nodes based on their topological connectivity, as well as their percolation states. The measure can be extended to include random walk based definitions, and its computational complexity is shown to be of the same order as that of betweenness centrality. We demonstrate the usage of percolation centrality by applying it to a canonical network as well as simulated and real world scale-free and random networks. © 2013 Piraveenan et al.published_or_final_versio

Topological analysis of longitudinal networks

Longitudinal networks evolve over time through the addition or deletion of nodes and edges. A longitudinal network can be viewed as a single static network that aggregates all edges observed over some time period (i.e., structure of network is fixed), or as a series of static networks observed in different point of time over the entire network observation period (i.e., structure of network is changing over time). By following a topological approach (i.e., static topology and dynamic topology), this paper first proposes a framework to analyze longitudinal networks. In static topology, SNA methods are applied to the aggregated network of entire observation period. Smaller segments of network data (i.e., short-interval network) that are accumulated in less time compared to the entire network observation period are used in dynamic topology for analysis purpose. Based on this framework, this study then conducts a topological analysis of email communication networks of an organization during its different operational conditions to explore changes in the behavior of actor-level dynamics. © 2012 IEEE.published_or_final_versio

Efeitos da terapia ultrassônica de baixa intensidade sobre o infarto agudo do miocárdio em ratos

Introdução. O infarto agudo do miocárdio (IAM) é considerado importante causa de morbidade e mortalidade no mundo e no Brasil. Novas intervenções terapêuticas estão sendo testadas isoladas ou em associação com as já existentes com o intuito de impedir a progressão ou atenuar o remodelamento no coração infartado. Dentre elas destaca-se a aplicação do Ultra-som (US) conjunto com agentes trombolíticos. Entretanto, na aplicação da energia ultrassônica como terapêutica pós-infarto é avaliado somente o seu possível efeito como agente trombolítico, não sendo investigado a sua possível implicação no processo de cicatrização da área infartada e parâmetros funcionais cardíacos. Objetivos. Diante dessas informações, nós objetivamos avaliar os efeitos da terapia ultrassônica transtorácica não-invasiva de baixa intensidade (NITUS) sobre a morfologia e função do músculo cardíaco de ratos infartados cirurgicamente após o 5° e 30° dia. Metodologia. Ratos machos Wistar (200-250g) foram pesados e divididos aleatoriamente em oito grupos com oito animais em cada grupo. Quatro grupos de animais foram submetidos à indução do IAM através da oclusão permanente da artéria coronária descendente anterior esquerda, sendo que dois destes grupos foram sacrificados no 5° dia após o IAM e as cinco aplicações da terapia ultrassônica e os outros dois grupos foram sacrificados no 30° dia após o IAM e as 5 aplicações da terapia ultrassônica. Quatro grupos de animais foram submetidos à cirurgia fictícia (Sham), sendo que dois destes grupos foram sacrificados no 5° dia após a cirurgia fictícia e as 5 aplicações da terapia ultrassônica e os outros dois grupos foram sacrificados no 30° dia após a cirurgia fictícia e as 5 aplicações da terapia ultrassônica. Os parâmetros da terapia ultrassônica foram freqüência de 1MHz, potência de 1W/cm2, modo pulsado e tempo de aplicação de 5 minutos. Para avaliação dos parâmetros funcionais foi realizado registros hemodinâmicos de todos os grupos e após a coleta dos registros os corações foram retirados para análise morfométrica a fim de avaliar a área da cicatriz do infarto. Os corações foram cortados em 4 fatias sendo retirados 3 cortes com espessura de 8 micrômetros da terceira fatia do ápice para a base, e estes foram corados com picrosírius. Foi utilizada uma câmera de vídeo para capturar uma área que contivesse todo o corte. A imagem era capturada com a utilização do programa AMCap e após a captura, esta era arquivada. A imagem arquivada era transferida para o programa ImageJ 1.42q/java no qual era marcada a área da cicatriz. De modo semelhante, era marcada toda a área da parede ventricular, para se obter a relação entre a área da cicatriz e a área total da parede ventricular. Resultados. No que concerne aos parâmetros hemodinâmicos, observamos que 30 dias após o IAM houve redução na pressão diastólica final (PDF) (mmHg) do grupo IAM+US quando comparado com grupo IAM (15±1.9 e 26±1.4; p<0.01 respectivamente). Não houve diferença significativa na área da cicatriz do infarto entre os grupos IAM e IAM+US no 5º. dia após infarto (31.6%±3.1% e 34.5%±1.6, respectivamente). Houve redução da área da cicatriz do infarto no grupo IAM+US quando comparado ao grupo IAM (21.5%±1.4% e 26.2%±1.7%; p<0.05, respectivamente) no 30º dia após IAM. Conclusão. A terapia com US dentro dos parâmetros estabelecidos, reduziu a área da cicatriz do infarto no grupo IAM+US (30 dias) bem como manteve a PDF dentro de valores fisiológicos, provavelmente por exercer influência nas fases inflamatória, proliferativa e de remodelamento, o que favorece um aumento na velocidade da resposta inflamatória por meio da mobilização de células inflamatórias como neutrófilos, macrófagos, ao mesmo tempo em que estimulou à degranulação dos mastócitos, bem como interferiu na mobilização leucocitária

Analyzing and Modeling Real-World Phenomena with Complex Networks: A Survey of Applications

The success of new scientific areas can be assessed by their potential for contributing to new theoretical approaches and in applications to real-world problems. Complex networks have fared extremely well in both of these aspects, with their sound theoretical basis developed over the years and with a variety of applications. In this survey, we analyze the applications of complex networks to real-world problems and data, with emphasis in representation, analysis and modeling, after an introduction to the main concepts and models. A diversity of phenomena are surveyed, which may be classified into no less than 22 areas, providing a clear indication of the impact of the field of complex networks.Comment: 103 pages, 3 figures and 7 tables. A working manuscript, suggestions are welcome

Emergence of Genetic Coding: an Information-theoretic Model

Peer reviewe

Origins of scaling in genetic code

“The original publication is available at www.springerlink.com” Copyright SpringerThe principle of least effort in communications has been shown, by Ferrer i Cancho and Sol´e, to explain emergence of power laws (e.g., Zipf’s law) in human languages. This paper applies the principle and the informationtheoretic model of Ferrer i Cancho and Sol´e to genetic coding. The application of the principle is achieved via equating the ambiguity of signals used by “speakers” with codon usage, on the one hand, and the effort of “hearers” with needs of amino acid translation mechanics, on the other hand. The re-interpreted model captures the case of the typical (vertical) gene transfer, and confirms that Zipf’s law can be found in the transition between referentially useless systems (i.e., ambiguous genetic coding) and indexical reference systems (i.e., zero-redundancy genetic coding). As with linguistic symbols, arranging genetic codes according to Zipf’s law is observed to be the optimal solution for maximising the referential power under the effort constraints. Thus, the model identifies the origins of scaling in genetic coding — via a trade-off between codon usage and needs of amino acid translation. Furthermore, the paper extends Ferrer i Cancho – Sol´e model to multiple inputs, reaching out toward the case of horizontal gene transfer (HGT) where multiple contributors may share the same genetic coding. Importantly, the extended model also leads to a sharp transition between referentially useless systems (ambiguous HGT) and indexical reference systems (zero-redundancy HGT). Zipf’s law is also observed to be the optimal solution in the HGT case.Peer reviewe

Evolutionary stable strategies in networked games: the influence of topology

Evolutionary game theory is used to model the evolution of competing strategies in a population of players. Evolutionary stability of a strategy is a dynamic equilibrium, in which any competing mutated strategy would be wiped out from a population. If a strategy is weak evolutionarily stable, the competing strategy may manage to survive within the network. Understanding the network-related factors that affect the evolutionary stability of a strategy would be critical in making accurate predictions about the behaviour of a strategy in a real-world strategic decision making environment. In this work, we evaluate the effect of network topology on the evolutionary stability of a strategy. We focus on two well-known strategies known as the Zero-determinant strategy and the Pavlov strategy. Zero-determinant strategies have been shown to be evolutionarily unstable in a well-mixed population of players. We identify that the Zero-determinant strategy may survive, and may even dominate in a population of players connected through a non-homogeneous network. We introduce the concept of ‘topological stability’ to denote this phenomenon. We argue that not only the network topology, but also the evolutionary process applied and the initial distribution of strategies are critical in determining the evolutionary stability of strategies. Further, we observe that topological stability could affect other well-known strategies as well, such as the general cooperator strategy and the cooperator strategy. Our observations suggest that the variation of evolutionary stability due to topological stability of strategies may be more prevalent in the social context of strategic evolution, in comparison to the biological context

Local assortativeness in scale-free networks

The level of assortative mixing of nodes in real-world networks gives important insights about the networks design and functionality, and has been analyzed in detail. However, this network-level measure conveys insufficient information about the local-level structure and motifs present in networks. We introduce a measure of local assortativeness that quantifies the level of assortative mixing for individual nodes in the context of the overall network. We show that such a measure, together with the resultant local assortativeness distributions for the network, is useful in analyzing network's robustness against targeted attacks. We also study local assortativeness in real-world networks, identifying different phases of network growth, showing that biological and social networks display markedly different local assortativeness distributions to technological networks, and discussing the implications to network design