High-resolution microwave frequency dissemination on an 86-km urban optical link

We report the first demonstration of a long-distance ultra stable frequency dissemination in the microwave range. A 9.15 GHz signal is transferred through a 86-km urban optical link with a fractional frequency stability of 1.3x10-15 at 1 s integration time and below 10-18 at one day. The optical link phase noise compensation is performed with a round-trip method. To achieve such a result we implement light polarisation scrambling and dispersion compensation. This link outperforms all the previous radiofrequency links and compares well with recently demonstrated full optical links.Comment: 11 pages, 5 figure

Effets des infrasons sur l'homme

Comite: Bruit et vibrationsSIGLEAvailable from Centre de Documentation Scientifique et Technique, CNRS, 26 rue Boyer, 75971 Paris Cedex 20 (France) / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

The Student Nitric Oxide Explorer

The Student Nitric Oxide Explorer (SNOE) is a small scientific spacecraft designed for launch on a Pegasus™ XL launch vehicle for the USRA Student Explorer Demonstration Initiative. Its scientific goals are to measure nitric oxide density in the lower thermosphere and analyze the energy inputs to that region from the sun and magnetosphere that create it and cause its abundance to vary dramatically. These inputs are energetic solar photons in the EUV and X -ray spectral regions, and energetic electrons that are accelerated into the polar regions, where they cause auroral disturbances and displays. Both of these phenomena are aspects of solar variability; thermospheric nitric oxide responds to that variability and in turn determines key temperature and compositional aspects of the thermosphere and ionosphere through its radiative and chemical properties. The SNOE ( snowy ) spacecraft and its instrument complement is being designed, built, and operated entirely at the University of Colorado, Laboratory for Atmospheric and Space Physics (CU/LASP). The spacecraft is a compact hexagonal structure, 37 high and 39 across its widest dimension, weighing approximately 220 Ibs. It will be launched into a circular orbit, 550±50 km altitude, at 97.5° inclination for sun-synchronous precession at 10:30-22:30 solar time. It will spin at 5 rpm with the spin axis normal to the orbit plane. It carries three instruments: An ultraviolet spectrometer to measure nitric oxide altitude profiles, a two-channel ultraviolet photometer to measure auroral emissions beneath the spacecraft, and a five-channel solar soft X-ray photometer. The spacecraft structure is aluminum, with a center platform section for the instruments and primary components and truss work to hold the solar arrays. Power is regulated using switched arrays and a partial shunt. The attitude determination and control system uses a magnetometer, two torque rods, and two horizon crossing indicators to measure spin rate and orientation. Attitude control is implemented open-loop by ground commands. The command and data handling system is implemented using a single spacecraft microprocessor that handles all spacecraft and communications functions and instrument data. The communications system is NASA compatible for downlink using the Autonomous Ground Services station at Poker Flat; all mission operations, data processing, and analysis will be performed using a project operations control center (POCC) at the LASP Space Technology Research building

Validite des methodes d'evaluation de la qualite des isolements aux bruits aeriens entre logements

SIGLECNRS-CDST / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Secrets des champs ou le potentiel du végétal

Les plantes cultivées ont un potentiel inouï. Elles sont capables de mettre en oeuvre des stratégies efficaces pour se développer, se nourrir et se défendre. Serons-nous à la hauteur de leur potentiel ? Ce film illustre sans opposition ni polémique la manière dont les plantes cultivées s’associent, coopèrent, communiquent et cohabitent avec les êtres vivants qui les entourent : les insectes, les champignons du sol, et les autres plantes. Les recherches scientifiques et paysannes récentes ouvrent des pistes d’innovations pour l’agriculture, éclairées par l’expérience de Marc Dufumier, agronome émérite. Du maraîchage à l’agroforesterie, en bio comme en agriculture de conservation, ce sont finalement les pratiques des paysans qui permettent d’activer le potentiel du vivant pour l' agriculture

Le bruit des deux roues, caracteristiques particulieres qui pourraient expliquer certaines reactions subjectives

SIGLECNRS RP 185 (1693) / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc