Chimera-like states in modular neural networks

Chimera states, namely the coexistence of coherent and incoherent behavior, were previously analyzed in complex networks. However, they have not been extensively studied in modular networks. Here, we consider a neural network inspired by the connectome of the C. elegans soil worm, organized into six interconnected communities, where neurons obey chaotic bursting dynamics. Neurons are assumed to be connected with electrical synapses within their communities and with chemical synapses across them. As our numerical simulations reveal, the coaction of these two types of coupling can shape the dynamics in such a way that chimera-like states can happen. They consist of a fraction of synchronized neurons which belong to the larger communities, and a fraction of desynchronized neurons which are part of smaller communities. In addition to the Kuramoto order parameter ?, we also employ other measures of coherence, such as the chimera-like ? and metastability ? indices, which quantify the degree of synchronization among communities and along time, respectively. We perform the same analysis for networks that share common features with the C. elegans neural network. Similar results suggest that under certain assumptions, chimera-like states are prominent phenomena in modular networks, and might provide insight for the behavior of more complex modular networks

No charge reversal at foam film surfaces after addition of oppositely charged polyelectrolytes?

The present work deals with control of the stability of ionic surfactant (tetradecyl trimethyl ammonium bromide) foam films by the addition of oppositely charged polyelectrolytes. In the two cases of low and high polyelectrolyte concentrations, a common black film is formed. This is due to an electrostatic repulsion (in the latter case, according to the hitherto assumption) caused by a charge reversal at film surfaces at high polyelectrolyte concentration. But what happens around the nominal isoelectric point (IEP), where the net charge of the whole film is close to zero? Is a Newton black film formed or does the film break? Disjoining pressure isotherms show a strong reduction in stability close to the IEP. The comparison between surface tension and elasticity measurements and disjoining pressure isotherms leads to a surprising conclusion: The stability of foam films seems not to be dominated by the net charge of the polyelectrolyte/surfactant complexes at the surface, which was the former hypothesis, but by the overall net charge of the film

Modulating coherence resonance in non-excitable systems by time-delayed feedback

We propose a paradigmatic model system, a subcritical Hopf normal form subjected to noise and time-delayed feedback, to investigate the impact of time delay on coherence resonance in non-excitable systems. We develop analytical tools to estimate the stationary distribution and the time correlations in nonlinear stochastic delay differential equations. These tools are applied to our model to propose a novel quantity to measure coherence resonance induced by a saddle-node bifurcation of periodic orbits