Directional emission of stadium-shaped micro-lasers

The far-field emission of two dimensional (2D) stadium-shaped dielectric cavities is investigated. Micro-lasers with such shape present a highly directional emission. We provide experimental evidence of the dependance of the emission directionality on the shape of the stadium, in good agreement with ray numerical simulations. We develop a simple geometrical optics model which permits to explain analytically main observed features. Wave numerical calculations confirm the results.Comment: 4 pages, 8 figure

Inferring periodic orbits from spectra of simple shaped micro-lasers

Dielectric micro-cavities are widely used as laser resonators and characterizations of their spectra are of interest for various applications. We experimentally investigate micro-lasers of simple shapes (Fabry-Perot, square, pentagon, and disk). Their lasing spectra consist mainly of almost equidistant peaks and the distance between peaks reveals the length of a quantized periodic orbit. To measure this length with a good precision, it is necessary to take into account different sources of refractive index dispersion. Our experimental and numerical results agree with the superscar model describing the formation of long-lived states in polygonal cavities. The limitations of the two-dimensional approximation are briefly discussed in connection with micro-disks.Comment: 13 pages, 19 figures, accepted for publication in Physical Review

Experimental stabilisation of 2D vortex patterns using time-dependent forcing

Experimental results of the effect of time-periodic and "chirped" (electro-magnetic) forcing on vortex patterns in shallow-water-layer flows are presented. Analogously to vibrational control, the use of a time-periodic forcing results in stabilisation of otherwise unstable vortex patterns. Chirped frequency forcing yields self-organising patterns that are different from those in stationary and periodically forced experiments. The results are shown to be consistent with theoretical analysis of 2D Taylor-Green vortices, i.e. unstable analytical solutions of the 2D Navier-Stokes equation. These results imply that, compared to the more often analysed stationary forced flows, time-varying forcing can stabilise different vortex patterns in shallow-water-layer flows

Elliptic Flow Analysis at RHIC with the Lee-Yang Zeroes Method in a Relativistic Transport Approach

The Lee-Yang zeroes method is applied to study elliptic flow ($v_2$) in Au+Au collisions at $\sqrt{s}=200A$~GeV, with the UrQMD model. In this transport approach, the true event plane is known and both the nonflow effects and event-by-event $v_2$ fluctuations exist. Although the low resolutions prohibit the application of the method for most central and peripheral collisions, the integral and differential elliptic flow from the Lee-Yang zeroes method agrees with the exact $v_2$ values very well for semi-central collisions.Comment: 4 pages, 4 figure

Hard and soft probe - medium interactions in a 3D hydro+micro approach at RHIC

We utilize a 3D hybrid hydro+micro model for a comprehensive and consistent description of soft and hard particle production in ultra-relativistic heavy-ion collisions at RHIC. In the soft sector we focus on the dynamics of (multi-)strange baryons, where a clear strangeness dependence of their collision rates and freeze-out is observed. In the hard sector we study the radiative energy loss of hard partons in a soft medium in the multiple soft scattering approximation. While the nuclear suppression factor $R_{AA}$ does not reflect the high quality of the medium description (except in a reduced systematic uncertainty in extracting the quenching power of the medium), the hydrodynamical model also allows to study different centralities and in particular the angular variation of $R_{AA}$ with respect to the reaction plane, allowing for a controlled variation of the in-medium path-length.Comment: 5 pages, 4 figures, Quark Matter 2006 proceedings, to appear in Journal of Physics

Day ahead solar forecasting applied to an insular site

Paper presented to the 3rd Southern African Solar Energy Conference, South Africa, 11-13 May, 2015.Some small territories, like islands and isolated areas, actually experience a high penetration rate of PV inside a small electricity grid. Moreover, the high amplitude fluctuations of PV outputs can destabilize the grid stability. In order to avoid the risk of blackout, some countries set up regulatory limits of PV integration. In this context, the forecasting of the PV output is necessary for the supply-demand balance and for the increase of the penetration rate of PV. Previous works on this topic were mainly done for large-scale continental grids. Due to the small scale of the climatic phenomena, forecasting the solar irradiance in insular territories addresses new issues. In order to cope with specific plant operations, forecasts must be provided with different granularities and horizons. In this work, we will focus on day ahead forecasts with an hourly granularity. Dayahead forecasts are produced for scheduling of resources and commitment of units of production. This paper presents a comparison of two post processing models. A Model Output Statistics (MOS) and an Artificial Neural Network (ANN) are applied to the IFS (Integrated Forecast System) forecasts for the insular site of Saint-Pierre in Reunion Island. The small scale of the climatic phenomena requires to set up these post processing methods differently than in the continental areas.cf201

Machine learning techniques for short term solar forecasting

Paper presented to the 3rd Southern African Solar Energy Conference, South Africa, 11-13 May, 2015.In this work, we propose a benchmarking of supervised machine learning techniques (neural networks, Gaussian processes and support vector machines) in order to forecast the Global Horizontal solar Irradiance (GHI). We also include in this benchmark a simple linear autoregressive (AR) model as well as a naive model based on persistence of the clear sky index. The models are calibrated and validated with data from Reunion Island (21.34°S ; 55.49°E). The main findings of this work are, that for hour ahead solar forecasting, the machine learning techniques slightly improve the performances exhibited by the linear AR and the persistence model. These nonlinear techniques start to outperform their simple counterparts for forecasting horizons greater than one hour.dc201

Hydrodynamics at RHIC -- how well does it work, where and how does it break down?

I review the successes and limitations of the ideal fluid dynamic model in describing hadron emission spectra from Au+Au collisions at the Relativistic Heavy Ion Collider (RHIC).Comment: 8 pages, 4 figures. Invited talk presented at Strange Quark Matter 2004 (Cape Town, Sep. 15-20, 2004). Proceedings to appear in Journal of Physics