Deelrapport: Bevraging van de aanbodzijde In het kader van de DIVERSITEITSBAROMETER HUISVESTING

peer reviewe

10 um wavefront spatial filtering: first results with chalcogenide fibers

Wavefront cleaning by single-mode fibers has proved to be efficient in optical-infrared interferometry to improve calibration quality. For instance, the FLUOR instrument has demonstrated the capability of fluoride glass single-mode fibers in this respect in the K and L bands. New interferometric instruments developped for the mid-infrared require the same capability for the 8-12 um range. We have initiated a program to develop single-mode fibers in the prospect of the VLTI mid-infrared instrument MIDI and of the ESA/DARWIN and NASA/TPF missions that require excellent wavefront quality. In order to characterize the performances of chalcogenide fibers we are developping, we have set up an experiment to measure the far-field pattern radiated at 10 um. In this paper, we report the first and promising results obtained with this new component.Comment: Conference "Interferometry for Optical Astronomy II", SPIE 200

Majorana-magnon interactions in topological Shiba chains

A chain of magnetic impurities deposited on the surface of a superconductor can form a topological Shiba band that supports Majorana zero modes and holds a promise for topological quantum computing. Yet, most experiments scrutinizing these zero modes rely on transport measurements, which only capture local properties. Here we propose to leverage the intrinsic dynamics of the magnetic impurities to access their non-local character. We use linear response theory to determine the dynamics of the uniform magnonic mode in the presence of external $ac$ magnetic fields and coupling the Shiba electrons. We demonstrate that this mode, which spreads over the entire chain of atoms, becomes imprinted with the parity of the ground state and, moreover, can discriminate between Majorana and trivial zero modes located at the ends of the chain. Our approach offers a non-invasive alternative to the scanning tunneling microscopy techniques used to probe Majorana zero modes. Conversely, the magnons could facilitate the manipulation of Majorana zero modes in topological Shiba chains.Comment: 5+9 pages, 8 figures, the final published versio

Preventing plant-pedestrian collisions: Camera & screen systems and visibility from the driving position

International audienceThe issue of collisions between plant or site vehicles and pedestrians concerns numerous sectors of activity. Lack of visibility for drivers over their direct environments is one of the main causes of such accidents, which are often serious. Visibility can be improved indirectly by using camera-and-screen systems. This article gives the findings of a study on the detectability of a pedestrian by a driver using such a system in various configurations. It is thus recommended that, under the most unfavourable conditions, any pedestrian entering the danger zone be shown on the screen with at least a minimum height of 10 mm. Since the risk of non-detection is higher at the edges of the screen than at the centre, it is also recommended that the detection zone of the system cover an area extending beyond the danger zone under surveillance. Finally, since the size of the screen does not have a significant influence on detection, the choice of the screen size should be governed more by criteria regarding the fitting out of and the ergonomics of the cab or of the driving position

A catalog of reference stars for long baseline stellar interferometry

The calibration process of long baseline stellar interferometers requires the use of reference stars with accurately determined angular diameters. We present a catalog of 374 carefully chosen stars among the all-sky network of infrared sources provided by Cohen et al. 1999. The catalog benefits from a very good sky coverage and a median formal error on the angular diameters of only 1.2%. Besides, its groups together in a homogeneous handy set stellar coordinates, uniform and limb-darkened angular diameters, photometric measurements, and other parameters relevant to optical interferometry. In this paper, we describe the selection criteria applied to qualify stars as reference sources. Then, we discuss the catalog's statistical properties such as the sky coverage or the distributions of magnitudes and angular diameters. We study the number of available reference stars as a function of the baseline and the precision needed on the visibility measurements. Finally, we compare the angular diameters predicted in Cohen et al. 1999 with existing determinations in the literature, and find a very good agreement.Comment: Conference "Interferometry for Optical Astronomy II", SPIE 200

Modeling and enacting processes. Some difficulties.

Colloque avec actes et comité de lecture.This paper reports about difficulties when modeling processes. It is based on experiences gained in different contexts : virtual teams (software engineering, administration), well established virtual enterprises (embedded systems) and temporary virtual enterprises (building construction). Most of the difficulties are common to most organization types, but are more or less accurate depending on this type

Improving Raman velocimetry of laser-cooled cesium atoms by spin-polarization

We study the peformances of Raman velocimetry applied to laser-cooled, spin-polarized, cesium atoms. Atoms are optically pumped into the F=4, m=0 ground-state Zeeman sublevel, which is insensitive to magnetic perturbations. High resolution Raman stimulated spectroscopy is shown to produce Fourier-limited lines, allowing, in realistic experimental conditions, atomic velocity selection to one-fiftieth of a recoil velocity.Comment: 12 pages, 6 figures, Elsevier style, to appear in Opt. Commu

La zone hyporhéique, une composante à ne pas négliger dans l'état des lieux et la restauration des cours d'eau

Les projets de restauration des cours d'eau sont maintenant de plus en plus fréquents et ambitieux. Intégrant un grand nombre de composantes de l'hydrosystème, ils ne prennent néanmoins pas pleinement en compte sa dimension verticale et oublient souvent un compartiment fondamental, représenté par la zone hyporhéique. Cette zone constitue une seconde rivière dont l'écoulement souterrain est invisible, et dont l'existence et la fonction sont largement méconnues. Pourtant elle joue un rôle fondamental dans le maintien des processus écologiques et dans la préservation de la biodiversité du cours d'eau. Après avoir précisé les rôles du milieu hyporhéique et souligné l'effet des activités humaines qui altèrent souvent sa structure et ses fonctions, on montrera de quelle manière les projets actuels de réhabilitation pourraient être complétés grâce à l'intégration systématique de la zone hyporhéique dans leurs plans et leurs suivis de restauration. / Stream restoration projects are nowadays more and more numerous and ambitious. While they now integrate many components of hydrosystems, they are still ignoring a fundamental one, the hyporheic zone. This zone can be considered as a second river whose subsurface flow is invisible and whose functions are still poorly known. Nevertheless, the hyporheic zone plays a major role in sustaining stream ecological processes and preserving stream biodiversity. After pointing out how human activities can impair the hyporheic zone structure and function, we will show how restoration projects could be much improved by considering the hyporheic zone