Theory for the spatiotemporal dynamics of domain walls close to a nonequilibrium Ising-Bloch transition

© 2015 American Physical Society. We derive a generic model for the interaction of domain walls close to a nonequilibrium-Bloch transition. The universal scenario predicted by the model includes stationary Ising and Bloch localized structures (dissipative solitons), as well as drifting and oscillating Bloch structures. Our theory also explains the behavior of Bloch walls during a collision. The results are confirmed by numerical simulations of the Ginzburg-Landau equation forced at twice its natural frequency and are in agreement with previous observations in several physical systems.Peer Reviewe

Nonlocality-induced front interaction enhancement

We demonstrate that nonlocal coupling strongly influences the dynamics of fronts connecting two equivalent states. In two prototype models we observe a large amplification in the interaction strength between two opposite fronts increasing front velocities several orders of magnitude. By analyzing the spatial dynamics we prove that way beyond quantitative effects, nonlocal terms can also change the overall qualitative picture by inducing oscillations in the front profile. This leads to a mechanism for the formation of localized structures not present for local interactions. Finally, nonlocal coupling can induce a steep broadening of localized structures, eventually annihilating them.Comment: 4 pages, 6 figure

Fluctuations and correlations in the polarization patterns of a Kerr medium

We study correlations among different components of the spectrum of the light intensity field close to a pattern forming instability associated with the polarization of the light field. In particular we find strong correlations between opposite wave vectors of critical wave number and anticorrelations of the zero wave number and the critical one. These anticorrelations are a manifestation of nonlinear critical fluctuations of the polarization of light.Financial support from the European Union TMR network QSTRUCT -Project No. FMRX-CT96-0077! and from DGICYT Project No. PB94-1167 Spain is acknowleged.Peer Reviewe

Role of the phase in the identification of delay time in semiconductor lasers with optical feedback

We consider a semiconductor laser with external optical feedback operating at a regime for which the delay time signature is extremely difficult to identify from the analysis of the intensity time series, using standard techniques. We show that such delay signature can be successfully retrieved by computing the same quantifiers from the phase, the real or the imaginary part of the field, even in presence of noise. Therefore the choice of the observable is determinant for parameter identification.Financial support from the Ministerio de Ciencia e Innovacion (MICINN), Spain, and the Fondo Europeo de Desarrollo Regional under projects FIS2007-60327 [Física Interdisciplinar de Sistemas Complejos (FISICOS)] and TEC2009-14101 [Delay-Coupled Diode Lasers for Photonic Applications (DeCoDicA)] and by the European Commission (EC) Project PHOCUS (FP7-ICT-2009-C- 240763) is acknowledged. R. M. Nguimdo also acknowledges fellowship BES-2007-14627 under the FPI program of MICINN.Peer reviewe

Theory of collective firing induced by noise or diversity in excitable media

5 pages.-- PACS numbers: 05.45.Xt, 05.40.-a, 02.50.-r.-- Final full-text of the paper available at: http://dx.doi.org/10.1103/PhysRevE.75.016203.Large variety of physical, chemical, and biological systems show excitable behavior, characterized by a nonlinear response under external perturbations: only perturbations exceeding a threshold induce a full system response (firing). It has been reported that in coupled excitable identical systems noise may induce the simultaneous firing of a macroscopic fraction of units. However, a comprehensive understanding of the role of noise and that of natural diversity present in realistic systems is still lacking. Here we develop a theory for the emergence of collective firings in nonidentical excitable systems subject to noise. Three different dynamical regimes arise: subthreshold motion, where all elements remain confined near the fixed point; coherent pulsations, where a macroscopic fraction fire simultaneously; and incoherent pulsations, where units fire in a disordered fashion. We also show that the mechanism for collective firing is generic: it arises from degradation of entrainment originated either by noise or by diversity.The authors acknowledge financial support by the Ministerio de Educación y Ciencia (Spain), FEDER Contract Nos. FIS2004-5073, FIS2004-953, BFM2001-0341 and the EU NoE BioSim (LSHB-CT-2004-005137)

Mismatch-Induced Bit Error Rate in Optical Chaos Communications Using Semiconductor Lasers With Electrooptical Feedback

8 pages, 8 figures.We analyze the influence of parameter mismatch between emitter and receiver systems on the bit error rate of an optical chaos communication scheme. Intensity hyperchaos is generated in the system by semiconductor lasers with electro-optical feedback. We find analytical predictions for the dependence of the bit error rate with the amplitude of the various mismatches and the statistical properties of the hyperchaotic carrier. A good concordance is found with numerical and experimental results.This work was supported in part by the European Commission through the research project OCCULT under Contract IST-2000-29683, in part by the the MEC (Spain) and FEDER under Projects FIS2004-00953 (CONOCE2), BFM2001-0341-C02-02 (SINFIBIO), and TIC2001-4572-E, and in part by a research grant from the Govern de les Illes Balears.Peer reviewe

Secondary bifurcations of hexagonal patterns in a nonlinear optical system: alkali metal vapor in a single-mirror arrangement

12 pages.-- PACS nrs.: 89.75.Kd, 42.65.Sf, 47.54.+r, 47.20.Ky.Secondary bifurcations of hexagonal patterns are analyzed in a model of a single-mirror arrangement with an alkali metal vapor as the nonlinear medium. A stability analysis of the hexagonal structures is performed numerically. Depending on the wavenumber of the hexagons different instabilities are predicted. Some of them take place at a finite wavenumber and result in the formation of structures with twelve spatial modes. These structures are compared with those observed experimentally.The authors acknowledge financial support from the European Science Foundation (PHASE network). D.G. and P.C. acknowledge financial support from MCyT (Spain, projects "Acciones Integradas" Grant Nos. HA98-29, PB97-0141-C02-02, BFM2001-0341-C02-01, and BFM2000-1108). E.G.W., T.A. and W.L. acknowledge financial support by the Deutsche Akademische Austauschdienst (Acciones Integradas) and by the Deutsche Forschungsgemeinschaft.http://dx.doi.org/10.1103/PhysRevE.69.036205Peer reviewe

Web Interface for Generic Grid Jobs, Web4Grid

For a long time grid has been used practically only by large projects which can afford to have fine-tuned sophisticated interfaces for the researchers involved on these projects. Grid has the potential to be a key instrument for a wide variety of scientific topics which require to perform many calculations, for example to explore complex system dynamics as function of parameters. The reduced size of the research groups and the diversity of problems makes unsuitable to develop specific interfaces in most of the instances while the cumbersome grid shell commands are a barrier that requires a significant amount of determination to overcome. Web4Grid interface is intended to be a user-friendly web where grid users can submit their jobs and recover the results on an automatic way. Besides the interface provides the capability to monitor the existing jobs and to check the (local) grid status (load, number of free cores available, ...). Web4Grid interface does not require specific grid usage training nor any knowledge about the middleware behind it

Logical operations with Localized Structures

We show how to exploit excitable regimes mediated by localized structures (LS) to perform AND, OR, and NOT logical operations providing full logical functionality. Our scheme is general and can be implemented in any physical system displaying LS. In particular, LS in nonlinear photonic devices can be used for all-optical computing applications where several reconfigurable logic gates can be implemented in the transverse plane of a single device, allowing for parallel computing.Comment: 11 pages, 6 figure