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Castany P.,INSA Rennes | Ramarolahy A.,INSA Rennes | Prima F.,CNRS Paris Research Institute of Chemistry | Laheurte P.,CNRS Study of Microstructures, Mechanics and Material Sciences lab | And 2 more authors.
Acta Materialia | Year: 2015

Mechanisms of superelasticity were investigated by in situ cyclic tensile tests performed under synchrotron X-ray radiation on Ti-24Nb-0.5N and Ti-24Nb-0.5O compositions of metastable β titanium alloys. Analyses of diffraction patterns acquired under load and after unloading for each cycle were used to determine the characteristics of the potential mechanisms of deformation in both alloys. The Ti-24Nb-0.5N alloy exhibits the conventional behavior of superelastic β titanium alloys. Synchrotron X-ray diffraction (SXRD) experiments proved that superelasticity is exclusively due to the occurrence of a stress-induced martensitic (SIM) transformation from the β phase to the α″ phase. The evolution of volume fraction of α″ martensite corresponds exactly to the variation of the recovery strain of the cyclic tensile curve. Conversely, the Ti-24Nb-0.5O alloy displays a non-conventional behavior. SXRD experiments showed a huge ability of the β phase to deform elastically until 2.1%. Surprisingly, a reversible SIM transformation also occurs in this alloy but starts after 1% of applied strain that corresponds to the yield point of the stress-strain curve. Although the SIM transformation occurs, the β phase simultaneously continues to deform elastically. The superelasticity of this alloy is unexpectedly due to a combination of a high elastic deformability of the β phase and a reversible SIM transformation. In both alloys, the lattice parameters of the α″ martensite evolve similarly in accordance with the initial texture of the β phase and the crystallography of the transformation. © 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Source

Costa D.,CNRS Paris Research Institute of Chemistry | Pradier C.-M.,CNRS Surface Science Lab | Tielens F.,CNRS Laboratory of Condensed Matter Chemistry, Paris | Savio L.,National Research Council Italy
Surface Science Reports | Year: 2015

Understanding the bio-physical-chemical interactions at nanostructured biointerfaces and the assembly mechanisms of so-called hybrid nano-composites is nowadays a key issue for nanoscience in view of the many possible applications foreseen. The contribution of surface science in this field is noteworthy since, using a bottom-up approach, it allows the investigation of the fundamental processes at the basis of complex interfacial phenomena and thus it helps to unravel the elementary mechanisms governing them. Nowadays it is well demonstrated that a wide variety of different molecular assemblies can form upon adsorption of small biomolecules at surfaces. The geometry of such self-organized structures can often be tuned by a careful control of the experimental conditions during the deposition process. Indeed an impressive number of studies exists (both experimental and - to a lesser extent - theoretical), which demonstrates the ability of molecular self-assembly to create different structural motifs in a more or less predictable manner, by tuning the molecular building blocks as well as the metallic substrate. In this frame, amino acids and small peptides at surfaces are key, basic, systems to be studied. The amino acids structure is simple enough to serve as a model for the chemisorption of biofunctional molecules, but their adsorption at surfaces has applications in surface functionalization, in enantiospecific catalysis, biosensing, shape control of nanoparticles or in emerging fields such as "green" corrosion inhibition. In this paper we review the most recent advances in this field. We shall start from the adsorption of amino acids at metal surfaces and we will evolve then in the direction of more complex systems, in the light of the latest improvements of surface science techniques and of computational methods. On one side, we will focus on amino acids adsorption at oxide surfaces, on the other on peptide adsorption both at metal and oxide substrates. Particular attention will be drawn to the added value provided by the combination of several experimental surface science techniques and to the precious contribution of advanced complementary computational methods to resolve the details of systems of increased complexity. Finally, some hints on experiments performed in presence of water and then characterized in UHV and on the related theoretical work will be presented. This is a further step towards a better approximation of real biological systems. However, since the methods employed are often not typical of surface science, this topic is not developed in detail. © 2015 Elsevier B.V. All rights reserved. Source

Coffinet S.,CNRS Transfers and Interactions in Hydrosystems and Soils | Huguet A.,CNRS Transfers and Interactions in Hydrosystems and Soils | Williamson D.,IRD Montpellier | Fosse C.,CNRS Paris Research Institute of Chemistry | Derenne S.,CNRS Transfers and Interactions in Hydrosystems and Soils
Organic Geochemistry | Year: 2014

Glycerol dialkyl glycerol tetraethers (GDGTs) are membrane lipids of high molecular weight and include the isoprenoid GDGTs (iGDGTs) produced by Archaea and the branched GDGTs (brGDGTs) produced by unknown bacteria. Several indices have been developed to describe the relationship between GDGT distribution and environmental parameters: the TEX86 (tetraether index of tetraethers consisting of 86 carbons), based on the relative abundances of iGDGTs, and the MBT (methylation index of branched tetraethers) and CBT (cyclisation ratio of branched tetraethers), based on the relative abundance of brGDGTs. For soils, most studies have focused only on the relationship between brGDGT distribution and environmental parameters, without examining the iGDGT distribution. We have analysed both brGDGT and iGDGT distributions and determined GDGT-derived proxies along an altitudinal transect at Mt. Rungwe, Tanzania. MBT/CBT-derived temperature values were found to correlate linearly with altitude (R2 0.75), as observed before for the other altitudinal transects investigated. The MBT/CBT-derived temperature lapse rate along Mt. Rungwe (0.7°C/100m) was similar to the in situ measured one and was consistent with results obtained previously for an altitudinal gradient in the same region at higher altitude. This confirms the robustness of the MBT/CBT as a paleoelevation proxy in East Africa. In addition, a linear correlation (R2 0.50) between TEX86 and altitude was observed, likely reflecting the effect of the adiabatic cooling of air with altitude on iGDGT distribution. This suggests that TEX86 might be used to track temperature change in terrestrial settings, in addition to the MBT/CBT indices. © 2014 Elsevier Ltd. Source

Monte M.,CSIC - Institute of Catalysis | Munuera G.,University of Seville | Costa D.,CNRS Paris Research Institute of Chemistry | Conesa J.C.,CSIC - Institute of Catalysis | Martinez-Arias A.,CSIC - Institute of Catalysis
Physical Chemistry Chemical Physics | Year: 2015

Catalysts based on combinations of copper and cerium oxides are interesting alternatives to noble metal ones for processes involved in the production/purification of hydrogen produced from hydrocarbons or biomass like the water-gas shift or the preferential oxidation of CO reactions. Active sites for such processes have been proposed to correspond to reduced species formed at the interface between both oxides. The present work provides direct evidence of reduced copper species located at the interface and observed during the course of near-ambient XPS experiments performed over samples of copper oxide supported on ceria nanospheres and nanocubes subjected to interaction with CO at different temperatures. The analysis of XPS results is based on DFT+U calculations employed as a complementary method for the analysis of redox properties of the catalysts and core-level shifts produced upon such redox changes. Differences observed in interfacial redox properties as a function of the ceria support morphology appear to be most useful to explain catalytic properties of this type of system for mentioned processes. © the Owner Societies 2015. Source

Arcadi A.,University of LAquila | Pietropaolo E.,University of LAquila | Alvino A.,University of Rome La Sapienza | Michelet V.,CNRS Paris Research Institute of Chemistry
Beilstein Journal of Organic Chemistry | Year: 2014

The scope and limitations of gold-catalyzed tandem cycloisomerization/ fluorination reactions of unprotected 2-alkynylanilines to have access to 3,3-difluoro-2-aryl-3H-indoles and 3-fluoro-2-arylindoles are described. An unprecedented aminoauration/oxidation/ fluorination cascade reaction of 2-alkynylanilines bearing a linear alkyl group on the terminal triple bond is reported. © 2014 Arcadi et al; licensee Beilstein-Institut. Source

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