Nonlinear force-free coronal magnetic stereoscopy

Getting insights into the 3D structure of the solar coronal magnetic field have been done in the past by two completely different approaches: (1.) Nonlinear force-free field (NLFFF) extrapolations, which use photospheric vector magnetograms as boundary condition. (2.) Stereoscopy of coronal magnetic loops observed in EUV coronal images from different vantage points. Both approaches have their strength and weaknesses. Extrapolation methods are sensitive to noise and inconsistencies in the boundary data and the accuracy of stereoscopy is affected by the ability of identifying the same structure in different images and by the separation angle between the view directions. As a consequence, for the same observational data, the computed 3D coronal magnetic field with the two methods do not necessarily coincide. In an earlier work (Paper I) we extended our NLFFF optimization code by the inclusion of stereoscopic constrains. The method was successfully tested with synthetic data and within this work we apply the newly developed code to a combined data-set from SDO/HMI, SDO/AIA and the two STEREO spacecraft. The extended method (called S-NLFFF) contains an additional term that monitors and minimizes the angle between the local magnetic field direction and the orientation of the 3D coronal loops reconstructed by stereoscopy. We find that prescribing the shape of the 3D stereoscopically reconstructed loops the S-NLFFF method leads to a much better agreement between the modeled field and the stereoscopically reconstructed loops. We also find an appreciable decrease by a factor of two in the angle between the current and the magnetic field which indicates the improved quality of the force-free solution obtained by S-NLFFF.Comment: 9 pages, 7 figure

The Marangoni effect and translation of free non-deformable drops

A model is presented for flow caused by interface tension gradients, the so called Marangoni effect, on a free, nondeformable drop. A free drop, initially at rest, undergoes a translation motion upon the action of surface flow. The experiments carried out by injecting a drop with surfactants, which induce an interface tension gradient, are in good agreement with the theoretical model proposed

ASSOCIATIONS VEGETALES DE L’ORDRE POTENTILLO – POLYGONETALIA R. TX. 1949 DU PLATEAU ET DE LA PLAINE DU COVURLUI

Les auteurs ont identifié deux associations végétales qui n’ont pas été mentionnés encore dans cette région: Agrostietum stoloniferae Burduja et al. 1956 et Rorippo austriacae – Agropyretum repentis (Timar 1947) R. Tx. 1950. Les associations sont décrites sous l’aspect corologique, des conditions stationnelles, de la composition floristique et de la structure phytosociologique

Prédire la difficulté des requêtes : la combinaison de mesures statistiques et sémantiques

National audienceLa performance d’un Système de Recherche d’Information (SRI) est étroitement liée à la requête. Les requêtes pour lesquelles les SRI échouent sont appelées dans la littérature des « requêtes difficiles ». L’étude présentée dans cet article vise à analyser, adapater et combiner plusieurs prédicteurs de difficulté de requêtes. Nous avons considéré trois prédicteurs: un lié à l’ambiguïté des termes, un basé sur la fréquence des termes et une mesure de répartition des résultats. L’évaluation de la prédiction est basée sur la corrélation entre la difficulté prédite et la performance réelle des SRI. Nous montrons que la combinaison de ces prédicteurs donne de bons résultats. Le cadre d’évaluation est celui des collections TREC7 et TREC8 adhoc

Low polarized emission from the core of coronal mass ejections

In white-light coronagraph images, cool prominence material is sometimes observed as bright patches in the core of coronal mass ejections (CMEs). If, as generally assumed, this emission is caused by Thomson-scattered light from the solar surface, it should be strongly polarised tangentially to the solar limb. However, the observations of a CME made with the SECCHI/STEREO coronagraphs on 31 August 2007 show that the emission from these bright core patches is exceptionally low polarised. We used the polarisation ratio method of Moran and Davila (2004) to localise the barycentre of the CME cloud. By analysing the data from both STEREO spacecraft we could resolve the plane-of-the-sky ambiguity this method usually suffers from. Stereoscopic triangulation was used to independently localise the low-polarisation patch relative to the cloud. We demonstrated for the first time that the bright core material is located close to the centre of the CME cloud. We show that the major part of the CME core emission, more than 85% in our case, is H$\alpha$ radiation and only a small fraction is Thomson-scattered light. Recent calculations also imply that the plasma density in the patch is 8 10$^8$ cm$^{-3}$ or more compared to 2.6 10$^6$ cm$^{-3}$ for the Thomson-scattering CME environment surrounding the core material.Comment: 5 pages, 3 figure

Hybrid Honey Bees Mating Optimization Algorithm for Identifying the Near-Optimal Solution in Web Service Composition

This paper addresses the problem of optimality in semantic Web service composition by proposing a hybrid nature-inspired method for selecting the optimal or near-optimal solution in semantic Web Service Composition. The method hybridizes the Honey-Bees Mating Optimization algorithm with components inspired from genetic algorithms, reinforcement learning, and tabu search. To prove the necessity of hybridization, we have analyzed comparatively the experimental results provided by our hybrid selection algorithm versus the ones obtained with the classical Honey Bees Mating Optimization algorithm and with the genetic-inspired algorithm of Canfora et al