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Reinoso J.A.,Spanish University for Distance Education (UNED) | Zamora-Munt J.,Campus University Illes Balears | Masoller C.,Polytechnic University of Catalonia
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2013

We present a numerical study of the pulses displayed by a semiconductor laser with optical feedback in the short-cavity regime, such that the external cavity round-trip time is shorter than the laser relaxation oscillation period. For certain parameters there are occasional pulses, which are high enough to be considered extreme events. We characterize the bifurcation scenario that gives rise to such extreme pulses and study the influence of noise. We demonstrate intermittency when the extreme pulses appear and hysteresis when the attractor that sustains these pulses is destroyed. We also show that this scenario is robust under the inclusion of noise. © 2013 American Physical Society.

Galve F.,Campus University Illes Balears | Pachon L.A.,National University of Colombia | Zueco D.,University of Zaragoza
Physical Review Letters | Year: 2010

Decoherence due to contact with a hot environment typically restricts quantum phenomena to the low temperature limit, kBT/ω1 (ω is the typical energy of the system). Here we report the existence of a nonequilibrium state for two coupled, parametrically driven, dissipative harmonic oscillators which, contrary to generalized intuition, has stationary entanglement at high temperatures. This clarifies the role of temperature and could lighten the burden on quantum experiments requiring delicate precooling setups. © 2010 The American Physical Society.

Gonzalez-Avella J.C.,Campus University Illes Balears | Cosenza M.G.,University of Los Andes, Venezuela | Eguiluz V.M.,Campus University Illes Balears | San Miguel M.,Campus University Illes Balears
New Journal of Physics | Year: 2010

We study the collective behavior of non-equilibrium systems subjected to an external field with a dynamics characterized by the existence of non-interacting states. Aiming at exploring the generality of the results, we consider two types of model according to the nature of their state variables: (i) a vector model, where interactions are proportional to the overlap between the states, and (ii) a scalar model, where interactions depend on the distance between states. The phase space is numerically characterized for each model in a fully connected network and in random and scale-free networks. For both models, the system displays three phases: two ordered phases, one parallel to the field and another orthogonal to the field, and one disordered phase. By placing the particles on a small-world network, we show that an ordered phase in a state different from the one imposed by the field is possible because of the long-range interactions that exist in fully connected, random and scale-free networks. This phase does not exist in a regular lattice and emerges when long-range interactions are included in a small-world network. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.

Martinez-Garcia R.,Campus University Illes Balears | Calabrese J.M.,Smithsonian Conservation Biology Institute | Hernandez-Garcia E.,Campus University Illes Balears | Lopez C.,Campus University Illes Balears
Geophysical Research Letters | Year: 2013

Regular vegetation patterns in semiarid ecosystems are believed to arise from the interplay between long-range competition and facilitation processes acting at smaller distances. We show that, under rather general conditions, long-range competition alone may be enough to shape these patterns. To this end we propose a simple, general model for the dynamics of vegetation, which includes only long-range competition between plants. Competition is introduced through a nonlocal term, where the kernel function quantifies the intensity of the interaction. We recover the full spectrum of spatial structures typical of vegetation models that also account for facilitation in addition to competition. Key Points Spatial vegetation model only considering long-range competition for water. The model does not consider short-range facilitation. Patterns in the system are determined by the kernel competition function. ©2013. American Geophysical Union. All Rights Reserved.

Hernandez-Carrasco I.,Campus University Illes Balears | Lopez C.,Campus University Illes Balears | Hernandez-Garcia E.,Campus University Illes Balears | Turiel A.,CSIC - Institute of Marine Sciences
Ocean Modelling | Year: 2011

Much of atmospheric and oceanic transport is associated with coherent structures. Lagrangian methods are emerging as optimal tools for their identification and analysis. An important Lagrangian technique which is starting to be widely used in oceanography is that of finite-size Lyapunov exponents (FSLEs). Despite this growing relevance there are still many open questions concerning the reliability of the FSLEs in order to analyse the ocean dynamics. In particular, it is still unclear how robust they are when confronted with real data. In this paper we analyze the effect on this Lagrangian technique of the two most important effects when facing real data, namely noise and dynamics of unsolved scales. Our results, using as a benchmark data from a primitive numerical model of the Mediterranean Sea, show that even when some dynamics is missed the FSLEs results still give an accurate picture of the oceanic transport properties. © 2010 Elsevier Ltd.

Firth W.J.,University of Strathclyde | Paulau P.V.,Campus University Illes Balears
European Physical Journal D | Year: 2010

Separation into spectral and nonlinear complex-eigenvalue problems is shown to be an effective and flexible approach to soliton laser models. The simplest such model, a complex Ginzburg-Landau model with cubic nonlinearity, has no stable solitonic solutions. We show that coupling it to a resonant linear system is a simple and general route to stabilization, which encompasses several previous instances in both space- and time-domains. Graphical solution in the complex eigenvalue plane provides valuable insight into the similarities and differences of such models, and into the interpretation of related experiments. It can also be used predictively, to guide analysis, numerics and experiment. © EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2010.

Soriano M.C.,Campus University Illes Balears | Van Der Sande G.,Vrije Universiteit Brussel | Fischer I.,Campus University Illes Balears | Mirasso C.R.,Campus University Illes Balears
Physical Review Letters | Year: 2012

Can different or even identical coupled oscillators be completely uncorrelated and still be synchronized? What can be concluded from the absence of correlations or even mutual information in networks of dynamical elements about their connectivity? These are fundamental and far-reaching questions arising in many complex systems. In this Letter, we address these two questions and demonstrate in simple and generic network motifs that synchronized behavior in the generalized sense can be realized and constructed such that no correlations and even negligible mutual information remain. Our findings raise new questions, in particular, whether and to what extent indirect connections are being underestimated, since the related collective behavior and even synchronization are less likely to be detected. © 2012 American Physical Society.

Porte X.,Campus University Illes Balears | Soriano M.C.,Campus University Illes Balears | Fischer I.,Campus University Illes Balears
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2014

Semiconductor lasers with delayed feedback exhibit two fundamentally different dynamical states: weak and strong chaos. We characterize experimentally the mechanism for the emergence of strong chaos. Based on these insights, we demonstrate similarity properties for long delays, i.e., similar dynamics for different pump currents when adjusting the feedback strength. For different delay times, even the same time- and amplitude-rescaled version of the dynamics can be generated. Using a simple rate-equation model, these properties can be corroborated. The results have major consequences for the characterization and tailoring of the dynamics for applications. © 2014 American Physical Society.

Carro A.,Campus University Illes Balears | Toral R.,Campus University Illes Balears | San Miguel M.,Campus University Illes Balears
Journal of Statistical Physics | Year: 2013

We study a model for continuous-opinion dynamics under bounded confidence. In particular, we analyze the importance of the initial distribution of opinions in determining the asymptotic configuration. Thus, we sketch the structure of attractors of the dynamical system, by means of the numerical computation of the time evolution of the agents density. We show that, for a given bound of confidence, a consensus can be encouraged or prevented by certain initial conditions. Furthermore, a noisy perturbation is added to the system with the purpose of modeling the free will of the agents. As a consequence, the importance of the initial condition is partially replaced by that of the statistical distribution of the noise. Nevertheless, we still find evidence of the influence of the initial state upon the final configuration for a short range of the bound of confidence parameter. © 2012 Springer Science+Business Media New York.

Giorgi G.L.,Campus University Illes Balears
Physical Review B - Condensed Matter and Materials Physics | Year: 2010

The occurrence of parity-time reversal (PT) symmetry breaking is discussed in a non-Hermitian spin chain. The Hermiticity of the model is broken by the presence of an alternating, imaginary, transverse magnetic field. A full real spectrum, which occurs if and only if all the eigenvectors are PT symmetric, can appear only in presence of dimerization, i.e., only if the hopping amplitudes between nearest-neighbor spins assume alternate values along the chain. In order to make a connection between such system and the Hermitian world, we study the critical magnetic properties of the model and look for the conditions that would allow to observe the same phase diagram in the absence of the imaginary field. Such procedure amounts to renormalizing the spin-spin coupling amplitudes. © 2010 The American Physical Society.

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