Suchergebnisse

We use statistical tools to characterize the response of an excitable system to periodic perturbations. The system is an optically injected semiconductor laser under pulsed perturbations of the phase of the injected field. We characterize the laser response by counting the number of pulses emitted by the laser, within a time interval, ¿T, that starts when a perturbation is applied. The success rate, SR(¿T), is then defined as the number of pulses emitted in the interval ¿T, relative to the number of perturbations. The analysis of the variation of SR with ¿T allows separating a constant lag of technical origin and a frequency-dependent lag of physical and dynamical origin. Once the lag is accounted for, the success rate clearly captures locked and unlocked regimes and the transitions between them. We anticipate that the success rate will be a practical tool for analyzing the output of periodically forced systems, particularly when very regular oscillations need to be generated via small periodic perturbations ; The work of B.G. and S.B. was conducted within the framework of the project OPTIMAL granted by the European Union by means of the Fond Européen de développement regional, FEDER. C.M. and J.T.-A. acknowledge support from the Spanish Ministerio de Ciencia, Innovacion y Universidades (PGC2018-099443-B-I00 ). C.M. also acknowledges partial support from ICREA ACADEMIA, Generalitat de Catalunya and a visiting professor fellowship of CNRS (France). J.T. also acknowledges partial support from the European Commission through the European Fund of Regional Development (FEDER), Convocatoria Excellencia KTT-UPC 2019 (Spain). ; Peer Reviewed ; Postprint (author's final draft)

This work proposes a new wave-period estimation (L-dB) method based on the power-spectral-density (PSD) estimation of pitch and roll motional time series of a Doppler wind lidar buoy under the assumption of small angles (±22 deg) and slow yaw drifts (1 min), and the neglection of translational motion. We revisit the buoy's simplified two-degrees-of-freedom (2-DoF) motional model and formulate the PSD associated with the eigenaxis tilt of the lidar buoy, which was modelled as a complex-number random process. From this, we present the L-dB method, which estimates the wave period as the average wavelength associated to the cutoff frequency span at which the spectral components drop off L decibels from the peak level. In the framework of the IJmuiden campaign (North Sea, 29 March–17 June 2015), the L-dB method is compared in reference to most common oceanographic wave-period estimation methods by using a TriaxysTM buoy. Parametric analysis showed good agreement (correlation coefficient, ρ = 0.86, root-mean-square error (RMSE) = 0.46 s, and mean difference, MD = 0.02 s) between the proposed L-dB method and the oceanographic zero-crossing method when the threshold L was set at 8 dB. ; This research was funded by the Spanish Government and EU Regional Development Funds, ARS project PGC2018-094132-B-I00 and ACTRIS-IMP project GA-871115. The European Institute of Innovation and Technology (EIT), KIC InnoEnergy project NEPTUNE (call FP7) supported the measurement campaigns. The Generalitat de Catalunya—AGAUR funded doctoral grant 2020 FISDU 00455 by A. Salcedo-Bosch. CommSensLab-UPC is an Excellence Unit (MDM-2016-0600) funded by the Agencia Estatal de Investigación, Spain. ; Peer Reviewed ; Postprint (published version)

It is known that the retrieval of aerosol extinction and backscatter coefficients from lidar data acquired through so-called total-power channels – intended to measure the backscattered power irrespective of the polarization – can be adversely affected by varying depolarization effects produced by the aerosol under measurement. This effect can be particularly noticeable in advanced multiwavelength systems, where different wavelengths are separated using a system of dichroic beam splitters, because in general the reflection and transmission coefficients of the beam splitters will be different for fields with polarization parallel or perpendicular to the incidence plane. Here we propose a setup for multiwavelength aerosol lidars alleviating diattenuation effects due to changing depolarization conditions while allowing measure linear depolarization. ; This work has been supported by the following projects and grants: European Union 7th Framework Programme grant agreement No. 262254 (ACTRIS), Spanish Ministry for Economy and Competitiveness grants TEC2012-34575 and UNPC10-4E-442, and by the Catalan Agency for Support to Universities and Research (AGAUR) grant 2014 SGR 583. ; Peer Reviewed ; Postprint (published version)