1,219 research outputs found
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 () in Au+Au
collisions at ~GeV, with the UrQMD model. In this transport
approach, the true event plane is known and both the nonflow effects and
event-by-event 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 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 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 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
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