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  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             fax:+1-416-978-3963
   Updating history:

  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. *

[12] Robustness and modular structure in networks, James P. Bagrow, Sune 
Lehmann, Yong-Yeol Ahn, 2011/02/24, arXiv:1102.5085 [12]


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.

* [14] Explosive Synchronization Transitions in Scale-free Networks, Jesus
Gomez-Gardenes, Sergio Gomez, Alex Arenas and Yamir Moreno, 2011/02/23,


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.

* [16] General coevolution of topology and dynamics in networks, J.L. 
Herrera, M.G. Cosenza, K. Tucci, J.C. González-Avella, 2011/02/17, 


15. Prosperity is associated with instability in dynamical networks , 

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.

* [20] 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 [20]


  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 

* [21] 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 [22] Segismundo


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