13,173 research outputs found
Robustness of onion-like correlated networks against targeted attacks
Recently, it was found by Schneider et al. [Proc. Natl. Acad. Sci. USA, 108,
3838 (2011)], using simulations, that scale-free networks with "onion
structure" are very robust against targeted high degree attacks. The onion
structure is a network where nodes with almost the same degree are connected.
Motivated by this work, we propose and analyze, based on analytical
considerations, an onion-like candidate for a nearly optimal structure against
simultaneous random and targeted high degree node attacks. The nearly optimal
structure can be viewed as a hierarchically interconnected random regular
graphs, the degrees and populations of which are specified by the degree
distribution. This network structure exhibits an extremely assortative
degree-degree correlation and has a close relationship to the "onion
structure." After deriving a set of exact expressions that enable us to
calculate the critical percolation threshold and the giant component of a
correlated network for an arbitrary type of node removal, we apply the theory
to the cases of random scale-free networks that are highly vulnerable against
targeted high degree node removal. Our results show that this vulnerability can
be significantly reduced by implementing this onion-like type of degree-degree
correlation without much undermining the almost complete robustness against
random node removal. We also investigate in detail the robustness enhancement
due to assortative degree-degree correlation by introducing a joint
degree-degree probability matrix that interpolates between an uncorrelated
network structure and the onion-like structure proposed here by tuning a single
control parameter. The optimal values of the control parameter that maximize
the robustness against simultaneous random and targeted attacks are also
determined. Our analytical calculations are supported by numerical simulations.Comment: 12 pages, 8 figure
Reducing Cascading Failure Risk by Increasing Infrastructure Network Interdependency
Increased coupling between critical infrastructure networks, such as power
and communication systems, will have important implications for the reliability
and security of these systems. To understand the effects of power-communication
coupling, several have studied interdependent network models and reported that
increased coupling can increase system vulnerability. However, these results
come from models that have substantially different mechanisms of cascading,
relative to those found in actual power and communication networks. This paper
reports on two sets of experiments that compare the network vulnerability
implications resulting from simple topological models and models that more
accurately capture the dynamics of cascading in power systems. First, we
compare a simple model of topological contagion to a model of cascading in
power systems and find that the power grid shows a much higher level of
vulnerability, relative to the contagion model. Second, we compare a model of
topological cascades in coupled networks to three different physics-based
models of power grids coupled to communication networks. Again, the more
accurate models suggest very different conclusions. In all but the most extreme
case, the physics-based power grid models indicate that increased
power-communication coupling decreases vulnerability. This is opposite from
what one would conclude from the coupled topological model, in which zero
coupling is optimal. Finally, an extreme case in which communication failures
immediately cause grid failures, suggests that if systems are poorly designed,
increased coupling can be harmful. Together these results suggest design
strategies for reducing the risk of cascades in interdependent infrastructure
systems
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