81 research outputs found
Optical neuron using polarisation switching in a 1550nm-VCSEL
We report a new approach to mimic basic functionalities of a neuron using a 1550 nm Vertical Cavity Surface Emitting Laser (VCSEL) which is based on the polarisation switching (PS) that can be induced in these devices when subject to polarised optical injection. Positive and negative all-optical threshold operations are demonstrated experimentally using external optical injection into the two orthogonal polarizations of the fundamental transverse mode. The polarisation of the light emitted by the device is used to determine the state of the VCSEL-Neuron, active (orthogonal) or inactive (parallel). This approach forms a new way to reproduce optically the response of a neuron to an excitatory and an inhibitory stimulus. © 2010 Optical Society of America
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MixitĂ© en Education Physique et Sportive: Evolution de la motivation des Ă©lĂšves dans le cadre dâun enseignement mixte au cours dâun cycle de danse
Dans le cadre de notre formation en EPS, nous nous sommes intĂ©ressĂ©s Ă lâengagement des Ă©lĂšves dans les classes mixtes. Cette question de lâengagement dans un contexte mixte semblait important Ă nos yeux, dans un contexte dâenseignement de plus en plus en classes mixtes dans le Canton de Vaud. Il nous semblait judicieux de porter notre regard sur les variations de la motivation des Ă©lĂšves dans ce cas de figure, notamment dans les activitĂ©s fortement connotĂ©es par genre (football, danse, âŠ). La motivation en EPS a Ă©tĂ© investiguĂ©e par de nombreux auteurs. Nous avons choisi de porter la focale sur les effets Ă©ventuels du guidage de lâenseignant, du travail par petits groupes, de la crĂ©ation de sens par lâengagement des Ă©lĂšves dans un projet et de lâutilisation de la tablette numĂ©rique dans le processus dâapprentissage des Ă©lĂšves. Nous avons rĂ©alisĂ© une Ă©tude avec deux classes de 9H sur 17 leçons, dans une activitĂ© connotĂ©e fĂ©minine (danse). Nous avons procĂ©dĂ© Ă des observations, soutenues par trois focus groups et deux questionnaires (MIXEPS et ISEP). Des indicateurs ont Ă©tĂ© dĂ©finis pour mesurer les variations de motivation des Ă©lĂšves, permettant de repĂ©rer les effets potentiels des diffĂ©rentes variables : guidage de lâenseignant, travail par petits groupes, projet et utilisation de la tablette numĂ©rique. Les rĂ©sultats montrent que le guidage de lâenseignant et la mise en projet ont un impact positif sur lâĂ©volution de la motivation au cours du cycle. Il est plus difficile de conclure avec certitude que lâenseignement par petits groupes et lâutilisation de la tablette gĂ©nĂšrent une motivation plus importante. Dâun point de vue professionnel, cette Ă©tude souligne lâimportance du sens des apprentissages par le biais de la mise en projet ainsi que lâattention Ă porter sur lâĂ©volution des Ă©lĂšves afin dâadapter les formes de guidage au plus prĂšs de cette Ă©volution
Strong and weak chaos in networks of semiconductor lasers with time-delayed couplings
Nonlinear networks with time-delayed couplings may show strong and weak chaos, depending on the scaling of their Lyapunov exponent with the delay time. We study strong and weak chaos for semiconductor lasers, either with time-delayed self-feedback or for small networks. We examine the dependence on the pump current and consider the question of whether strong and weak chaos can be identified from the shape of the intensity trace, the autocorrelations, and the external cavity modes. The concept of the sub-Lyapunov exponent λ0 is generalized to the case of two time-scale-separated delays in the system. We give experimental evidence of strong and weak chaos in a network of lasers, which supports the sequence of weak to strong to weak chaos upon monotonically increasing the coupling strength. Finally, we discuss strong and weak chaos for networks with several distinct sub-Lyapunov exponents and comment on the dependence of the sub-Lyapunov exponent on the number of a laser's inputs in a network
The SWAP EUV Imaging Telescope Part I: Instrument Overview and Pre-Flight Testing
The Sun Watcher with Active Pixels and Image Processing (SWAP) is an EUV
solar telescope on board ESA's Project for Onboard Autonomy 2 (PROBA2) mission
launched on 2 November 2009. SWAP has a spectral bandpass centered on 17.4 nm
and provides images of the low solar corona over a 54x54 arcmin field-of-view
with 3.2 arcsec pixels and an imaging cadence of about two minutes. SWAP is
designed to monitor all space-weather-relevant events and features in the low
solar corona. Given the limited resources of the PROBA2 microsatellite, the
SWAP telescope is designed with various innovative technologies, including an
off-axis optical design and a CMOS-APS detector. This article provides
reference documentation for users of the SWAP image data.Comment: 26 pages, 9 figures, 1 movi
Prominence eruption observed in He II 304 Ă up to >6 Râ by EUI/FSI aboard Solar Orbiterâ
Aims. We report observations of a unique, large prominence eruption that was observed in the He II 304 Ă
passband of the Extreme Ultraviolet Imager/Full Sun Imager telescope aboard Solar Orbiter on 15â16 February 2022.
Methods. Observations from several vantage points â Solar Orbiter, the Solar-Terrestrial Relations Observatory, the Solar and Heliospheric Observatory, and Earth-orbiting satellites â were used to measure the kinematics of the erupting prominence and the associated coronal mass ejection. Three-dimensional reconstruction was used to calculate the deprojected positions and speeds of different parts of the prominence. Observations in several passbands allowed us to analyse the radiative properties of the erupting prominence.
Results. The leading parts of the erupting prominence and the leading edge of the corresponding coronal mass ejection propagate at speeds of around 1700 km sâ1 and 2200 km sâ1, respectively, while the trailing parts of the prominence are significantly slower (around 500 km sâ1). Parts of the prominence are tracked up to heights of over 6âRâ. The He II emission is probably produced via collisional excitation rather than scattering. Surprisingly, the brightness of a trailing feature increases with height.
Conclusions. The reported prominence is the first observed in He II 304 Ă
emission at such a great height (above 6 Râ)
Three Eruptions Observed by Remote Sensing Instruments Onboard Solar Orbiter
On February 21 and March 21 â 22, 2021, the Extreme Ultraviolet Imager (EUI) onboard Solar Orbiter observed three prominence eruptions. The eruptions were associated with coronal mass ejections (CMEs) observed by Metis, Solar Orbiterâs coronagraph. All three eruptions were also observed by instruments onboard the SolarâTErrestrial RElations Observatory (Ahead; STEREO-A), the Solar Dynamics Observatory (SDO), and the Solar and Heliospheric Observatory (SOHO). Here we present an analysis of these eruptions. We investigate their morphology, direction of propagation, and 3D properties. We demonstrate the success of applying two 3D reconstruction methods to three CMEs and their corresponding prominences observed from three perspectives and different distances from the Sun. This allows us to analyze the evolution of the events, from the erupting prominences low in the corona to the corresponding CMEs high in the corona. We also study the changes in the global magnetic field before and after the eruptions and the magnetic field configuration at the site of the eruptions using magnetic field extrapolation methods. This work highlights the importance of multi-perspective observations in studying the morphology of the erupting prominences, their source regions, and associated CMEs. The upcoming Solar Orbiter observations from higher latitudes will help to constrain this kind of study better
Understanding the enhanced synchronization of delay-coupled networks with fluctuating topology
We study the dynamics of networks with coupling delay, from which the connectivity changes over time. The synchronization properties are shown to depend on the interplay of three time scales: the internal time scale of the dynamics, the coupling delay along the network links and time scale at which the topology changes. Concentrating on a linearized model, we develop an analytical theory for the stability of a synchronized solution. In two limit cases the system can be reduced to an âeffectiveâ topology: In the fast switching approximation, when the network fluctuations are much faster than the internal time scale and the coupling delay, the effective network topology is the arithmetic mean over the different topologies. In the slow network limit, when the network fluctuation time scale is equal to the coupling delay, the effective adjacency matrix is the geometric mean over the adjacency matrices of the different topologies. In the intermediate regime the system shows a sensitive dependence on the ratio of time scales, and specific topologies, reproduced as well by numerical simulations. Our results are shown to describe the synchronization properties of fluctuating networks of delay-coupled chaotic maps
The Kuramoto model in complex networks
181 pages, 48 figures. In Press, Accepted Manuscript, Physics Reports 2015 Acknowledgments We are indebted with B. Sonnenschein, E. R. dos Santos, P. Schultz, C. Grabow, M. Ha and C. Choi for insightful and helpful discussions. T.P. acknowledges FAPESP (No. 2012/22160-7 and No. 2015/02486-3) and IRTG 1740. P.J. thanks founding from the China Scholarship Council (CSC). F.A.R. acknowledges CNPq (Grant No. 305940/2010-4) and FAPESP (Grants No. 2011/50761-2 and No. 2013/26416-9) for financial support. J.K. would like to acknowledge IRTG 1740 (DFG and FAPESP).Peer reviewedPreprin
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Density Fluctuations in a Coronal Hole
We have measured the root-mean-square (rms) amplitude of intensity ïŹuctuations, ÎI, in plume and interplume regions of a polar coronal hole. These intensity ïŹuctuations correspond to density ïŹuctuations. Using data from the Sun Watcher using the Active Pixel System detector and Image Processing on the Project for Onboard Autonomy (Proba2), our results extend up to a height of about 1.35Re. One advantage of the rms analysis is that it does not rely on a detailed evaluation of the power spectrum, which is limited by noise levels to low heights in the corona. The rms approach can be performed up to larger heights where the noise level is greater, provided that the noise itself can be quantiïŹed. At low heights, both the absolute ÎI, and the amplitude relative to the mean intensity, ÎI/I, decrease with height. However, starting at about 1.2Re, ÎI/I increases, reaching 20%â40% by 1.35Re. This corresponds to density ïŹuctuations of Îne/neâ10%â20%. The increasing relative amplitude implies that the density ïŹuctuations are generated in the corona itself. One possibility is that the density ïŹuctuations are generated by an instability of AlfvĂ©n waves. This generation mechanism is consistent with some theoretical models and with observations of AlfvĂ©n wave amplitudes in coronal holes. Although we ïŹnd that the energy of the observed density ïŹuctuations is small, these ïŹuctuations are likely to play an important indirect role in coronal heating by promoting the reïŹection of AlfvĂ©n waves and driving turbulence
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