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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. Source


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. Source


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. Source


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. Source


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. Source

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