Observatoire Des Science Of Lunivers

Besançon, France

Observatoire Des Science Of Lunivers

Besançon, France
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Beyer H.F.,Helmholtz Center for Heavy Ion Research | Gassner T.,Helmholtz Center for Heavy Ion Research | Trassinelli M.,French National Center for Scientific Research | Trassinelli M.,Paris-Sorbonne University | And 48 more authors.
Journal of Physics B: Atomic, Molecular and Optical Physics | Year: 2015

The experimental investigation of quantum-electrodydamic contributions to the binding energies of inner shells of highly charged heavy ions requires an accurate spectroscopy in the region of hard x-rays suitable at a limited source strength. For this purpose the focusing compensated asymmetric Laue crystal optics has been developed and a twin-spectrometer assembly has been built and commissioned at the experimental storage ring of the GSI Helmholtzzentrum Darmstadt. We characterize the crystal optics and demonstrate the usefulness of the instrumentation for accurate spectroscopy of both stationary and fast moving x-ray sources. The experimental procedures discussed here may also be applied for other spectroscopic studies where a transition from conventional germanium x-ray detectors to crystal spectrometers seems too demanding because of low source intensity. © 2015 IOP Publishing Ltd.

Blanc N.,University Claude Bernard Lyon 1 | Diaz-Sanchez L.E.,University of Kassel | Ramos A.Y.,CNRS Neel Institute | Tournus F.,University Claude Bernard Lyon 1 | And 9 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2013

An annealing-driven transition from a chemically disordered A1-like structure to a chemically ordered L10-like phase has been revealed for size-selected CoPt clusters with diameters from 2 to 4 nm, from experiment to theory confrontation. For chemically ordered particles, atypical lattice-parameter ratios c/a are inferred. This ratio is found to be remarkably different depending on the approach used (c/a>1 from x-ray absorption at the Co K edge and c/aâ‰0.94 from the Pt dominated x-ray diffraction). A first-principles theoretical study accurately explains this astonishing feature and provides a detailed understanding of the element-specific local relaxations, which are crucial in these nanoalloys. © 2013 American Physical Society.

Hillion A.,CNRS Condensed Matter Physics Laboratory | Cavallin A.,Ecole Polytechnique Federale de Lausanne | Vlaic S.,Ecole Polytechnique Federale de Lausanne | Tamion A.,CNRS Condensed Matter Physics Laboratory | And 11 more authors.
Physical Review Letters | Year: 2013

In sharp contrast to previous studies on FeRh bulk, thin films, and nanoparticles, we report the persistence of ferromagnetic order down to 3 K for size-selected 3.3 nm diameter nanocrystals embedded into an amorphous carbon matrix. The annealed nanoparticles have a B2 structure with alternating atomic Fe and Rh layers. X-ray magnetic dichroism and superconducting quantum interference device measurements demonstrate ferromagnetic alignment of the Fe and Rh magnetic moments of 3 and 1μB, respectively. The ferromagnetic order is ascribed to the finite-size induced structural relaxation observed in extended x-ray absorption spectroscopy. © 2013 American Physical Society.

Mortillaro J.M.,Observatoire Des Science Of Lunivers | Mortillaro J.M.,Agrocampus Ouest | Schaal G.,University of Western Brittany | Schaal G.,Observatoire Des Science Of Lunivers | And 7 more authors.
Estuarine, Coastal and Shelf Science | Year: 2013

In coastal estuarine embayments, retention of water masses due to coastal topography may result in an increased contribution of continental organic matter in food webs. However, in megatidal embayments, the effect of topography can be counterbalanced by the process of tidal mixing. Large amounts of continental organic matter are exported each year by rivers to the oceans. The fate of terrestrial organic matter in food webs of coastal areas and on neighboring coastal benthic communities was therefore evaluated, at multi-trophic levels, from primary producers to primary consumers and predators. Two coastal areas of the French Atlantic coast, differing in the contributions from their watershed, tidal range and aperture degree, were compared using carbon and nitrogen stable isotopes (δ13C and δ15N) during two contrasted periods. The Bay of Vilaine receives large inputs of freshwater from the Vilaine River, displaying 15N enriched and 13C depleted benthic communities, emphasizing the important role played by allochtonous inputs and anthropogenic impact on terrestrial organic matter in the food web. In contrast, the Bay of Brest which is largely affected by tidal mixing, showed a lack of agreement between isotopic gradients displayed by suspended particulate organic matter (SPOM) and suspension-feeders. Discrepancy between SPOM and suspension-feeders is not surprising due to differences in isotopes integration times. We suggest further that such a discrepancy may result from water replenishment due to coastal inputs, nutrient depletion by phytoplankton production, as well as efficient selection of highly nutritive phytoplanktonic particles by primary consumers. © 2013 Elsevier Ltd. All rights reserved.

Pajot O.,Observatoire Des Science Of Lunivers | Vernotte F.,Observatoire Des Science Of Lunivers | Plantard C.,Observatoire Des Science Of Lunivers | Mbaye P.M.,Observatoire Des Science Of Lunivers
Electronics Letters | Year: 2012

A composite clock layout and results are presented. This apparatus combines the stability of several reference clocks for different durations. A voltage-controlled quartz oscillator is driven by a hydrogen maser clock for mid-term stability and by a caesium atomic clock for long-term stability. The best clock stability at a given averaging time is transferred to the voltage-controlled oscillator by a special control system using two commands. © 2012 The Institution of Engineering and Technology.

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