Absolute stability of axisymmetric perturbations in strongly magnetized collisionless axisymmetric accretion disk plasmas.

This Letter presents a kinetic description of low-frequency and long-wavelength axisymmetric electromagnetic perturbations in nonrelativistic, strongly magnetized, and gravitationally bound axisymmetric accretion-disk plasmas in the collisionless regime. The analysis, carried out within the framework of the Vlasov-Maxwell description, relies on stationary kinetic solutions which allow for the simultaneous treatment of nonuniform fluid fields, stationary accretion flows, and temperature anisotropies. It is demonstrated that these stationary configurations are actually stable against axisymmetric kinetic instabilities of this type.

Congestion phenomena on complex networks.

We define a minimal model of traffic flows in complex networks in order to study the trade-off between topological-based and traffic-based routing strategies. The resulting collective behavior is obtained analytically for an ensemble of uncorrelated networks and summarized in a rich phase diagram presenting second-order as well as first-order phase transitions between a free-flow phase and a congested phase. We find that traffic control improves global performance, enlarging the free-flow region in parameter space only in heterogeneous networks.