Nonlinear force-free models for the solar corona I. Two active regions with very different structure

With the development of new instrumentation providing measurements of solar photospheric vector magnetic fields, we need to develop our understanding of the effects of current density on coronal magnetic field configurations. The object is to understand the diverse and complex nature of coronal magnetic fields in active regions using a nonlinear force-free model. From the observed photospheric magnetic field we derive the photospheric current density for two active regions: one is a decaying active region with strong currents (AR8151), and the other is a newly emerged active region with weak currents (AR8210). We compare the three-dimensional structure of the magnetic fields for both active region when they are assumed to be either potential or nonlinear force-free. The latter is computed using a Grad-Rubin vector-potential-like numerical scheme. A quantitative comparison is performed in terms of the geometry, the connectivity of field lines, the magnetic energy and the magnetic helicity content. For the old decaying active region the connectivity and geometry of the nonlinear force-free model include strong twist and strong shear and are very different from the potential model. The twisted flux bundles store magnetic energy and magnetic helicity high in the corona (about 50 Mm). The newly emerged active region has a complex topology and the departure from a potential field is small, but the excess magnetic energy is stored in the low corona and is enough to trigger powerful flares.Comment: 11 pages, 11 figure

Embedded real-time monitoring using SystemC in IMA network

Avionics is one kind of domain where prevention prevails. Nonetheless fails occur. Sometimes due to pilot misreacting, flooded in information. Sometimes information itself would be better verified than trusted. To avoid some kind of failure, it has been thought to add,in midst of the ARINC664 aircraft data network, a new kind of monitoring

Magnetic Field and Turbulence in Sunspots

We study the local variations of η0 and ξ (Milne-Eddington model) which are necessary in order to bring in agreement three independent determinations of the total field H, obtained from simultaneous observations of the two lines λ 5250,2 Fe I and λ 5225,5 Fe I. The distribution of the broadening as a function of field direction is consistent with the motions induced by hydromagnetic waves.</jats:p

Automated Management of Complex Systems

Les avancées technologiques réalisées ces dernières décennies ont permis un accroissement considérable des performances des matériels informatiques et des réseaux de données. De nombreux secteurs d’activité ont bénéficié de ces avancées en utilisant l’informatique et les réseaux pour accroître leur productivité et offrir des services à forte valeur ajoutée. Ces bouleversements ont amené à interconnecter un nombre très important d’équipements et de fonctions, et à construire ainsi des systèmes de plus en plus complexes. La gestion de ces systèmes est devenue, de ce fait, extrêmement difficile sans l’assistance d’outils informatiques.Ce mémoire décrit les travaux de recherche que j’ai menés depuis vingt ans sur la gestion automatisée de systèmes dans trois secteurs d’activité : les télécommunications, les data centers, et l’avionique. Chacun de ces secteurs a des spécificités qui influent sur la gestion des systèmes correspondants, mais on note néanmoins de nombreuses similitudes sur les principes de leur gestion. Le mémoire présente les résultats de différentes études concernant la configuration d’un système, sa supervision, sa sécurité, et sa sureté de fonctionnement. Une analyse comparative identifie les domaines de gestion qui sont les plus avancés dans chacun des secteurs d’activité. De là, plusieurs transferts technologiques sont proposés pour permettre d’améliorer la gestion de systèmes dans chaque secteur d’activité, en profitant des avancées réalisées dans les autres secteurs.Technological advances in recent decades have led to a considerable increase in performance of computer hardware and data networks. Many industrial sectors have benefited from these advances in using computers and networks to increase productivity and offer value-added services. These changes have led to interconnect a large number of equipments and functions, and thus to build increasingly complex systems. The management of these systems has become, therefore, extremely difficult without the support of computer tools. This paper describes the research that I have done for twenty years on the automated management systems in three industrial sectors: telecommunications, data centers, and avionics. Each of these sectors has specific characteristics that influence the management of the corresponding systems, but there are nevertheless many similarities on the principles of management. The paper presents the results of different studies on system configuration, supervision, security, and safety. A comparative analysis identifies management areas that are the most advanced in each of the industrial sectors. From there, several technology transfers are proposed to help improve the management systems in each sector, taking advantage of advances in other areas

Major Effects of Line Asymmetries in Solar Magnetic Field Measurements from Simultaneous Multi-Wavelength Observations

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THEMIS Telescope: Prospects in High Resolution Magnetic Field Observations

AbstractThe THEMIS telescope will provide high resolution observations of the solar vector magnetic field. We present some capabilities of this instrument, concerning the polarization analysis, the correlation tracker and the two spectrographs. THEMIS is expected to come into operation in 1995–1996.</jats:p