Multi-spectral piston sensor for co-phasing giant segmented mirrors and multi-aperture interferometric arrays

This paper presents the optical design of a multi-spectral piston sensor suitable to co-phasing giant segmented mirrors equipping the Future Extremely Large Telescopes (ELTs). The general theory of the sensor is described in detail and numerical simulations have been carried out, demonstrating that direct piston and tip-tilt measurements are feasible within accuracies respectively close to 20 nm and 10 nano-radians. Those values are compatible with the co-phasing requirements, although the method seems to be perturbed by uncorrected atmospheric seein

Reelin Controls Progenitor Cell Migration in the Healthy and Pathological Adult Mouse Brain

Understanding the signals that control migration of neural progenitor cells in the adult brain may provide new therapeutic opportunities. Reelin is best known for its role in regulating cell migration during brain development, but we now demonstrate a novel function for reelin in the injured adult brain. First, we show that Reelin is upregulated around lesions. Second, experimentally increasing Reelin expression levels in healthy mouse brain leads to a change in the migratory behavior of subventricular zone-derived progenitors, triggering them to leave the rostral migratory stream (RMS) to which they are normally restricted during their migration to the olfactory bulb. Third, we reveal that Reelin increases endogenous progenitor cell dispersal in periventricular structures independently of any chemoattraction but via cell detachment and chemokinetic action, and thereby potentiates spontaneous cell recruitment to demyelination lesions in the corpus callosum. Conversely, animals lacking Reelin signaling exhibit reduced endogenous progenitor recruitment at the lesion site. Altogether, these results demonstrate that beyond its known role during brain development, Reelin is a key player in post-lesional cell migration in the adult brain. Finally our findings provide proof of concept that allowing progenitors to escape from the RMS is a potential therapeutic approach to promote myelin repair

Étude de l'émission interstellaire a l'aide de l'étalon de Fabry-Perot

The interferometric observations already published permit the Doppler-Fizeau, effect in the faintest galactic nebulae having more than 3' apparent diameter to be obtained with a 120 cm telescope. The equivalent slit width on the sky may be 0,5" with a 195 cm teléscope. With the same instrument a new optical arrangement using a small exit pupil is able to reach nebulae of 20" apparent diameter, with an accuracy of 3 km/s. Description of a monochromatic radiation selector giving direct photographs of the nebulae in one monochromatic radiation such as Hα or [N II], with the possibility of obtaining directly the picture of the nebula in a given radial velocity. An experiment to test the continuity of the multilayers used is given.Les observations interférométriques déjà publiées permettent de mesurer l'effet Doppler-Fizeau des nébuleuses galactiques les plus faibles jusqu'à un diamètre apparent de 3', avec le télescope de 125 cm. La largeur de fente équivalente, sur le ciel, peut être de 0,5" avec un télescope de 195 cm. Avec le même instrument, un nouveau système optique, utilisant un petit trou de sortie, permet d'atteindre des nébuleuses de 20" de diamètre apparent, avec une précision de 3 km/s. On décrit un sélecteur de radiations permettant de photographier les nébuleuses en lumière monochromatique, par exemple en lumière Hα ou [N II], avec la possibilité d'obtenir directement une image de la nébuleuse pour une vitesse radiale donnée. On décrit une méthode pour contrôler l'uniformité des couches multiples utilisées

MONTAGE PÉROT-FABRY A MULTI-LENTILLES

Description d'un montage nouveau de l'étalon de Pérot-Fabry pour l'observation simultanée des régions d'émission des galaxies. Mesure de la rotation et de la recession.Describes a new design with a Fabry-Perot etalon for the simultaneus observation of emission regions in the galaxies. Measurement can be made of rotation and redshift