CEA Grenoble

Grenoble, France

CEA Grenoble

Grenoble, France
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Ravanat J.-L.,CEA Grenoble
Free Radical Research | Year: 2012

Emphasis is placed in that review article on a detailed description of the different chromatographic analytical methods that were developed for measuring cellular levels of oxidatively generated DNA lesions. The different methods are critically reviewed taking into account the advantages and limitations of the assays. Particular attention is focused on possible causes of over-or underestimation that may explain at least partly the wide range of cellular levels of lesions and in particular 8-oxo-7,8-dihydro-2′-deoxyguanosine reported in the literature. In that respect a chronological presentation of the main significant developments is provided and appears to be of particular interest to follow the technical and methodological improvements performed over the years. Finally, future possible progresses in terms of both specificity and sensitivity are presented. © 2012 Informa UK, Ltd.

Absorption spectra of liquid water at various temperatures in the whole IR region (0<ν̃<4000cm-1) are obtained from ATR spectra recorded in the mid-IR region combined with absorption spectra measured in the FIR region. They can be accurately decomposed over two independent spectra. The spectra of the two kinds of H2O (D2O) molecules they suppose are defined as fulfilling spectroscopic constraints and as being in accordance with thermodynamic values. Their enthalpy difference He - Hg is found equal to 11.8 kJ mol-1 for ordinary water and 12.2 kJ mol-1 for heavy water. H2O (D2O) molecules of lower enthalpies Hg, greater than the enthalpy of H 2O or D2O molecules in ices by 1.3 kJ mol-1, display vibrations that resemble those of H2O (D2O) molecules in ice. Molecules with enthalpies He reorient without breaking their H-bonds as He appears greater than the potential barrier for rotations around their symmetry axes. © 2011 Elsevier B.V. All rights reserved.

Tenchine D.,CEA Grenoble
Nuclear Engineering and Design | Year: 2010

Sodium cooled fast reactors have been developed in France for nearly 50 years with successively Rapsodie, Phenix and Superphenix plants. Thermal hydraulic challenges have progressively increased with the power and the size of the reactors. After Superphenix stop in 1997, the thermal hydraulic activity on sodium cooled fast reactors was drastically reduced for about 10 years. Nowadays, the so-called Astrid prototype developed in France in the frame of Generation IV deployment requires thermal hydraulic inputs to support the design and safety studies. This paper aims at summarizing the main thermal hydraulic challenges in sodium cooled fast reactors, on the basis of the past experience. Numerical and experimental tools used in the French Atomic Energy Commission (CEA) are briefly presented. The improvement on numerical simulation is emphasized with some examples of recent computations. Of course, this review is not a comprehensive one as it is mainly based on the author experience. The items covered in this paper are the subassembly, the core, the upper plenum, the lower plenum, the decay heat removal, the gas entrainment and the piping. Heat exchanger thermal hydraulics is also briefly mentioned. Several experimental and computed results are presented as simple illustrations without quantitative information on the data. © 2010 Elsevier B.V. All rights reserved.

Camp C.,CEA Grenoble | Pecaut J.,CEA Grenoble | Mazzanti M.,CEA Grenoble
Journal of the American Chemical Society | Year: 2013

The new homoleptic ate U(III) siloxide [K(18c6)][U(OSi(O tBu)3)4] 2 was prepared in 69% yield by reduction of [U(OSi(OtBu)3)4] 3 with KC 8. The reaction of the neutral U(III) siloxide complex [U(OSi(O tBu)3)2(μ-OSi(OtBu) 3)]2 1 with adamantyl azide leads to the isolation of the dinuclear U(VI) imido complex [U2(NAd)4(OSi(O tBu)3)4] 4. The X-ray crystal structure shows the presence of a "cation-cation interaction" between the two [U(NAd)2]2+ groups. In contrast the reactions of 2 with the trimethylsilyl and adamantyl azides afford the U(V) imido complexes [K(18c6)][U(NSiMe3)(OSi(OtBu)3)4] 5-TMS and [K(18c6)][U(NAd)(OSi(OtBu)3)4] 5-Ad pure in 48% and 66% yield, respectively. The reaction of 2 with CsN3 in THF at -40 C yields a mixture of products from which the azido U(IV) complex [K(18c6)][U(N3)(OSi(OtBu)3)4] 7 and the μ-nitrido diuranium(V) complex [KU(μ-N)(OSi(OtBu) 3)]2 8 were isolated. The crystal structure of 8 shows the presence of a rare U2N2 core with two nitrido atoms bridging two uranium centers in a diamond-shaped geometry. In contrast, the reaction of 1 with CsN3 affords the diuranium(IV) complex Cs{(μ-N)[U(OSi(OtBu)3)3]2} 9 presenting a nitrido ligand bridging two uranium and one cesium cations. These results show the importance of the coordination environment in the outcome of the reaction of U(III) with azides. © 2013 American Chemical Society.

Cayron C.,CEA Grenoble
Acta Materialia | Year: 2011

Grain boundary engineering (GBE) aims at optimizing the properties of face centred cubic materials with low stacking fault energy by creating a high content of special twin boundaries. Quantifying twinning and its parameters, such as the twin related domains (TRDs) and the related ∑3n special grain boundaries, is thus of prime importance for GBE. A method is presented in detail to treat the electron backscatter diffraction (EBSD) maps. The TRDs are automatically reconstructed, the twinning chain trees of the TRDs are determined and represented with fractal graphs, and the ∑3n grain boundaries are identified up to order n = 12. New parameters, such as the numbers of grains (Ng), the lengths of the longest chain (LLC), the twinning polysynthesism (p) and twinning anisotropy (a) factors, are also calculated. Examples have been given for two nickel superalloys, a silicon ingot, a cadmium telluride film, and a copper thin film. © 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Cayron C.,CEA Grenoble
Acta Crystallographica Section A: Foundations of Crystallography | Year: 2013

A 'one-step' theory based on Pitsch distortion is proposed to explain the continuity between the orientations of the Kurdjumov-Sachs (KS), Nishiyama-Wassermann (NW) and Pitsch variants observed on the electron backscatter diffraction pole figures of martensitic alloys. The Pitsch distortion respects the hard-sphere packing of the iron atoms and implies the existence of a neutral line along the close-packed direction [110]γ = [111]α. Its principal strains are 0, -5.7 and 15.5%, well below the +12, +12 and -20% values of the Bain distortion. At the nucleation step, the distortion generates martensite that continuously deforms the austenitic matrix. Martensite continues to grow in Pitsch orientation inside the deformation field of the surrounding austenite to reach KS and NW orientations in reference to the bulk austenite. Some experimental results reported in the literature are revisited, such as the {225}γ habit planes, the sometimes observed 'twins' at the midrib, the formation of butterfly martensite, and the effect of prior plastic deformation of austenite on the transformation temperature and on variant selection mechanisms. © 2013 International Union of Crystallography Printed in Singapore - all rights reserved.

The microstructure of sulfonated poly(ether ether ketone) (sPEEK) membranes was investigated by combining small-angle neutron and X-ray scattering techniques (SANS and SAXS) for large and low water contents, respectively. The ion-exchange capacity, the water content and the nature of the counterion were varied for a better understanding of the membrane microstructure. SAXS and SANS contrast variation experiments reveal a significantly more complex structure than it is commonly believed with a delicate balance of the contrasts. At low water content, the structure can be depicted by the presence of small ionic clusters and larger more or less connected core-shell domains between crystallites for low values of the sulfonation degree. The first step of the swelling process corresponds to the filling without significant structural changes of the porosity created by the solvent evaporation during the casting process. The second step is associated with a major structural reorganization induced by a large increase of the membrane water content over a small range of temperature. This reorganization is attributed to an ionic domain percolation on a large scale. The third step corresponds to the swelling of lamellar ionic domains around the crystallites as revealed by the study of the dilution laws and of the structure of sPEEK ionomer dispersions. The sizes of the ribbon-like polymer particles were determined. They do not depend linearly with the membrane ion content suggesting a nonhomogeneous distribution of the ionic groups along the polymer chain during the sulfonation process associated with the semicrystalline nature of the polymers. Finally, the effect of the degradation in oxidative media on the membrane structure is shown to correspond to an increase of the membrane water content. © 2013 American Chemical Society.

Pfalz J.,Friedrich - Schiller University of Jena | Pfannschmidt T.,Friedrich - Schiller University of Jena | Pfannschmidt T.,CEA Grenoble
Trends in Plant Science | Year: 2013

The plastid transcription machinery can be biochemically purified at different organisational levels as soluble RNA polymerase, transcriptionally active chromosome, or nucleoid. Recent proteomic studies have uncovered several novel proteins in these structures and functional genomic studies have indicated that a lack of many of these proteins results in chlorotic phenotypes of varying degree. The most severe cases exhibit complete albino phenotypes, which led to the conclusion that the proteins that were lacking had important regulatory roles in plastid gene expression and chloroplast development. In this opinion article, we propose an alternative model in which the structural establishment of a transcriptional subdomain within the nucleoid represents an early developmental bottleneck that leads to abortion of proper chloroplast biogenesis if disturbed. © 2012 Elsevier Ltd.

Mineev V.P.,CEA Grenoble
Physical Review B - Condensed Matter and Materials Physics | Year: 2013

The current in noncentrosymmetric metals in the normal and superconducting states is found within the frame of linear response theory. In line with the usual terms corresponding to diamagnetic response, the Landau diamagnetism, and the Pauli paramagnetism, the general expression contains also terms corresponding to the spatial dispersion specific for a medium without space parity. This so-called gyrotropic current is calculated in the zero-frequency case in the infrared frequency region. The static gyrotropic current yields a negligibly small correction to the London magnetostatics in a superconductor without inversion center, whereas the high-frequency response produces the natural optical activity revealed in the Kerr effect. The magnitude of the Kerr angle in the infrared frequency region is proved to be in a reasonable agreement with the recently reported observations of the Kerr effect in the pseudogap phase in several different high-Tc materials. © 2013 American Physical Society.

An automatic method to colorize and quantify the classical Pitsch, Kurdjumov-Sachs, Greninger-Troiano and Nishiyama-Wasserman orientation relationships in the electron backscatter diffraction maps of martensitic/bainitic steels is detailed. Automatic analysis of variant grouping is also presented. The method was applied to low and high carbon steels, and to iron-nickel Widmanstätten meteorites. Many results of recent literature are confirmed. In low carbon steels the individual laths exhibit continuous orientation gradients between the classical orientation relationships, and the laths tend to be grouped by close-packed plane (morphological) packets. A crystallographic scenario describing the formation of the packets is proposed on the base of the one-step model. When the carbon content increases, the orientation spreading is reduced; and martensite tends to form plate groups and burst configurations. In iron-nickel meteorites, the centimeter long Widmanstätten laths do not exhibit continuous orientation gradients but are constituted of subgrains with uniform orientation relationship; the kamacite grains in the plessite regions are grouped into Bain zones, probably due to a recrystallization during the slow cooling of the meteorites. © 2014 Elsevier Inc.

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