System size stochastic resonance in a model for opinion formation

We study a model for opinion formation which incorporates three basic ingredients for the evolution of the opinion held by an individual: imitation, influence of fashion and randomness. We show that in the absence of fashion, the model behaves as a bistable system with random jumps between the two stable states with a distribution of times following Kramer's law. We also demonstrate the existence of system size stochastic resonance, by which there is an optimal value for the number of individuals N for which the average opinion follows better the fashion.Comment: 10 pages, to appear in Physica

Dynamics and Scaling of Noise-Induced Domain Growth

The domain growth processes originating from noise-induced nonequilibrium phase transitions are analyzed, both for non-conserved and conserved dynamics. The existence of a dynamical scaling regime is established in the two cases, and the corresponding growth laws are determined. The resulting universal dynamical scaling scenarios are those of Allen-Cahn and Lifshitz-Slyozov, respectively. Additionally, the effect of noise sources on the behaviour of the pair correlation function at short distances is studied.Comment: 11 pages (including 13 figures) LaTeX file. Accepted in EPJ

Dynamical mechanism of anticipating synchronization in excitable systems

We analyze the phenomenon of anticipating synchronization of two excitable systems with unidirectional delayed coupling which are subject to the same external forcing. We demonstrate for different paradigms of excitable system that, due to the coupling, the excitability threshold for the slave system is always lower than that for the master. As a consequence the two systems respond to a common external forcing with different response times. This allows to explain in a simple way the mechanism behind the phenomenon of anticipating synchronization.Comment: 4 pages including 7 figures. Submitted for publicatio

Order parameter expansion study of synchronous firing induced by quenched noise in the active rotator model

We use a recently developed order parameter expansion method to study the transition to synchronous firing occuring in a system of coupled active rotators under the exclusive presence of quenched noise. The method predicts correctly the existence of a transition from a rest state to a regime of synchronous firing and another transition out of it as the intensity of the quenched noise increases and leads to analytical expressions for the critical noise intensities in the large coupling regime. It also predicts the order of the transitions for different probability distribution functions of the quenched variables. We use numerical simulations and finite size scaling theory to estimate the critical exponents of the transitions and found values which are consistent with those reported in other scalar systems in the exclusive presence of additive static disorder

Noisy continuous--opinion dynamics

We study the Deffuant et al. model for continuous--opinion dynamics under the influence of noise. In the original version of this model, individuals meet in random pairwise encounters after which they compromise or not depending of a confidence parameter. Free will is introduced in the form of noisy perturbations: individuals are given the opportunity to change their opinion, with a given probability, to a randomly selected opinion inside the whole opinion space. We derive the master equation of this process. One of the main effects of noise is to induce an order-disorder transition. In the disordered state the opinion distribution tends to be uniform, while for the ordered state a set of well defined opinion groups are formed, although with some opinion spread inside them. Using a linear stability analysis we can derive approximate conditions for the transition between opinion groups and the disordered state. The master equation analysis is compared with direct Monte-Carlo simulations. We find that the master equation and the Monte-Carlo simulations do not always agree due to finite-size induced fluctuations that we analyze in some detail

Steam reforming of water-soluble fast pyrolysis bio-oil: Studies on bio-oil composition effect, carbon deposition, and catalyst modifications

Bio-oils from fast pyrolysis of lignocellulosic biomass can be phase separated into a heavy water insoluble portion and a light water-soluble portion. The water-rich portion contains mainly carboxylic acids, carbohydrates, aldehydes, ketones and alcohols. This highly oxygenated water-rich portion was evaluated for production of the renewable hydrogen required for the upgrading reactions. There are certain challenges introduced due to the complexity of these mixtures. Catalyst deactivation by coking and the formation of carbon deposits are major limitations although the specific causes were previously unidentified. A bio-oil fractionating system can separate heavier components from the light-end components. This light-end fraction has shown to be better suited for hydrogen production via steam reforming at moderate temperatures generating mainly hydrogen and carbon dioxide. Due to their chemical instability the bio-oils showed evident aging leading to decreased hydrogen production potential when stored for long periods of time. Model compounds representing the water-soluble components we compared in controlled tests to find troublesome species in terms of resistance to reaction and carbon deposition tendency. Experiments were performed under kinetic control conditions at low conversions to reveal reaction characteristics while avoiding thermodynamics and transport limitations. It was found that levoglucosan, acetic acid, and furfural were the species with the highest limitation in terms of carbon deposition leading to decreased hydrogen production and lowcatalyst stability. Levoglucosan was found to decompose more easily leading to carbon deposition even in the absence of a catalyst. Acetic acid and furfural were then found to tend to coke over the catalyst but where mostly thermally stable. Acetic acid was found to be one of the most abundant and troublesome compounds in water-soluble bio-oil. Magnesium and Cobalt modified Nickel/Alumina steam reforming catalysts were tested at 460 and 650yC using acetic acid as a probe molecule. These temperatures corresponded respectively to reforming regimes where no coke removal by steam was observed and where coke removal happened at an accelerated rate as determined by temperature program oxidation. The addition of Magnesium as support modifier led to reduced coke accumulation by promoting coke gasification at 650yC, but at 460yC a different trend was observed where coke removal rate was not prevalent. A supported bimetallic Ni-Co catalyst showed a coke reduction effect at 460yC, but at 650yC it seemed to promote coke formation. When comparing the results of supported and unsupported Ni-Co catalysts the presence of an Alumina support was appeared to be necessary to achieve high hydrogen formation with decreased coking. The data suggest that a synergistic effect exists between the Ni-Co and the Alumina support, where the latter may enhance water activation contributing to the reduced coking for the bimetallic catalyst

Diversity-induced resonance in a model for opinion formation

We study an opinion formation model that takes into account that individuals have diverse preferences when adopting an opinion regarding a particular issue. We show that the system exhibits "diversity-induced resonance” [C.J. Tessone et al. Phys. Rev. Lett. 97, 194101 (2006)], by which an external influence (for example advertising, or fashion trends) is better followed by populations having the right degree of diversity in their preferences, rather than others where the individuals are identical or have too different preferences. We support our findings by numerical simulations of the model in different network topologies and a mean-field type analytical theor