***** To join INSNA, visit http://www.insna.org ***** Barry Wellman _______________________________________________________________________ S.D. Clark Professor of Sociology, FRSC NetLab Director Department of Sociology 725 Spadina Avenue, Room 388 University of Toronto Toronto Canada M5S 2J4 twitter:barrywellman http://www.chass.utoronto.ca/~wellman fax:+1-416-978-3963 Updating history: http://chass.utoronto.ca/oldnew/cybertimes.php _______________________________________________________________________ Robustness and modular structure in networks , arXiv Abstract: Many complex systems, from power grids and the internet, to the brain and society, can be modeled using modular networks. Modules, densely interconnected groups of elements, often overlap due to elements that belong to multiple modules. The elements and modules of these networks perform individual and collective tasks such as generating and consuming electrical load, transmitting data, or executing parallelized computations. We study the robustness of these systems to the failure of random elements. We show that it is possible for the modules themselves to become isolated or uncoupled (non-overlapping) well before the network falls apart. When modular organization is critical to overall functionality, networks may be far more vulnerable than expected. *  Robustness and modular structure in networks, James P. Bagrow, Sune Lehmann, Yong-Yeol Ahn, 2011/02/24, arXiv:1102.5085  http://arXiv.org/abs/1102.5085 _________________________________________________________________ 10. Explosive Synchronization Transitions in Scale-free Networks , arXiv Excerpt: The emergence of explosive collective phenomena has recently attracted much attention due to the discovery of an explosive percolation transition in complex networks. In this Letter, we demonstrate how an explosive transition shows up in the synchronization of complex heterogeneous networks by incorporating a microscopic correlation between the structural and the dynamical properties of the system. *  Explosive Synchronization Transitions in Scale-free Networks, Jesus Gomez-Gardenes, Sergio Gomez, Alex Arenas and Yamir Moreno, 2011/02/23, arXiv:1102.4823  http://arXiv.org/abs/1102.4823 _________________________________________________________________ 12. General coevolution of topology and dynamics in networks , arXiv Abstract: We present a general framework for the study of coevolution in dynamical systems. This phenomenon consists of the coexistence of two dynamical processes on networks of interacting elements: node state change and rewiring of links between nodes. The process of rewiring is described in terms of two basic actions: disconnection and reconnection between nodes, both based on a mechanism of comparison of their states. Different rewiring rules can be expressed in this scheme. We assume that each process, rewiring and node state change, occurs with its own probability, independently from the other. The collective behavior of a coevolutionary system is characterized in the space of parameters given by these two probabilities. As an application, for a voterlike node dynamics we find that reconnections between nodes with similar states lead to network fragmentation. The critical boundaries for the onset of fragmentation in networks with different properties are calculated on this space. We show that coevolution models correspond to curves on this space, describing coupling relations between the probabilities for the two processes. The occurrence of network fragmentation transitions are predicted for diverse models, and agreement is found with some earlier results. *  General coevolution of topology and dynamics in networks, J.L. Herrera, M.G. Cosenza, K. Tucci, J.C. González-Avella, 2011/02/17, arXiv:1102.3467  http://arXiv.org/abs/1102.3467 _________________________________________________________________ 15. Prosperity is associated with instability in dynamical networks , arXiv Abstract: Social, biological and economic networks evolve with recurrent fragmentation and re-formation, often explained in terms of external perturbations. We show that these phenomena can be a direct consequence of imitation and endogenous conflicts between 'cooperators' and 'defectors'. We employ a game-theoretic model of dynamic network formation, where prosperous individuals are more likely to be selected as role-models by newcomers who imitate their strategies and their connections. We find that cooperators promote well connected highly prosperous networks and defectors cause the network to fragment and lose its prosperity; defectors are unable to maintain the highly connected networks they invade. Once the network is fragmented, it can be reconstructed by a new invasion of cooperators. We observe that prosperity is associated with instability: cooperation is most productive when it is unstable. *  Prosperity is associated with instability in dynamical networks, Matteo Cavaliere, Sean Sedwards, Corina E. Tarnita, Martin A. Nowak, Attila Csikász-Nagy, 2011/02/24, arXiv:1102.4947  http://arXiv.org/abs/1102.4947 _________________________________________________________________ 15.01. Two wrongs do not make a right: The initial viability of different assessment rules in the evolution of indirect reciprocity , Journal of Theoretical Biology Excerpt: Indirect reciprocity models are meant to correspond to primitive moral systems, in which individuals assess the interactions of third parties in order to condition their cooperative behavior [...] Here, I present a general analytical model of indirect reciprocity and show that the class of assessment rules which positively judges a refusal to help scofflaws cannot invade a population of defectors, whereas the other class can. *  Two wrongs do not make a right: The initial viability of different assessment rules in the evolution of indirect reciprocity, Panchanathan K, February 2011, DOI: 10.1016/j.jtbi.2011.02.009, Journal of Theoretical Biology, in Press * Contributed by  Segismundo  http://dx.doi.org/10.1016/j.jtbi.2011.02.009 _________________________________________________________________ _____________________________________________________________________ SOCNET is a service of INSNA, the professional association for social network researchers (http://www.insna.org). 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