The electrochemical determination of oxygen ion diffusion coefficients in La0.50Sr0.50CoO3−y: Experimental results and related properties

Results of an electrochemical method for the determination of oxygen ion diffusion coefficients D_O^2? in porous pellets of La_0.50Sr_0.50CoO_3?y are presented. Log D_O^2? can be expressed as log D_O^2?=?(2.3±0.2) 10³/T?(6.6±0.6) cm² s^?1. The activation energy E_a for the diffusion process equals 44 kJ mol^?1. Further the related electrochemical measurement and the adjustment of the oxygen deficiency y are described. At 75°C the following empirical Nernst relation between the electrode potential E (vs. a Pt/H₂ (1 atm) electrode in the same solution) and Δy is found: E=627–108 ln (Δy + 0.0054) mV. (Δy=y?y₀; y₀=mole fraction of vacancies at the reversible O₂ potential of 1190 mV). The use of La_0.50Sr_0.50CoO_3?y as a solid solution electrode in practical storage cells seems to be excluded for thermodynamic and kinetic reasons.     

Sur la stabilité thermique des étalons analytiques.iv

In this fourth article on standards the authors have plotted the thermolysis curves and ascribed the infrared absorption spectra of 12 substances in the solid state. These substances can be used in various instances for making standard solutions for chemical analysis.     

Asymptotic modeling of linearly piezoelectric slender rods

The piezoelectric thin plate modeling already derived by the authors is extended to rod-like structures. Two models corresponding to sensor or actuator behavior are obtained. The conditions of existence of non-local terms in the limit models are discussed. To cite this article: T. Weller, C. Licht, C. R. Mecanique 336 (2008).     

Efficient resolution of profen ethyl ester racemates by engineered Yarrowia lipolytica Lip2p lipase

Enzyme-catalyzed enantiomer discrimination is still a great challenge for the development of industrial pharmaceutical processes. For the resolution of ibuprofen, naproxen and ketoprofen racemates, three major anti-inflammatory drugs, only lipases from Candida rugosa present a high selectivity if solvent and surfactant use is discarded. However, their catalytic activities are too low. In the present work, we demonstrate that the lipase Lip2p from the yeast Yarrowia lipolytica has a higher catalytic activity than C. rugosa lipases to hydrolyze the ethyl esters of ibuprofen, naproxen and ketoprofen, but its selectivity is not sufficient [E = 52 (S); 11 (S) and 1.5 (R) respectively]. The enantioselectivity was further improved by site-directed mutagenesis, targeted at the substrate binding site and guided by molecular modelling studies. By investigating the binding modes of the (R)- and (S)-enantiomers in the active site, two amino acid residues located in the hydrophobic substrate binding site of the lipase, namely residues 232 and 235, were identified as crucial for enantiomer discrimination and enzyme activity. The (S) enantioselectivity of Lip2p towards ethyl ibuprofen esters was rendered infinite (E ? 300) by replacing V232 by an A or C residue. Substitution of V235 by C, M, S, or T amino acids led to a great increase in the (S)-enantioselectivity (E ? 300) towards naproxen ethyl ester. Finally, the variant V232F enabled the efficient kinetic resolution of ethyl ketoprofen ester enantiomers [(R)-enantiopreference; E ? 300]. In addition to the increase in selectivity, a remarkable increase in velocity by 2.6, 2.7 and 2.5 times, respectively, was found for ibuprofen, naproxen and ketoprofen ethyl esters.     

Cosmogenic neutrinos and gamma rays

We describe the photoproduction interactions of ultrahigh energy protons on the universal photon backgrounds and the production of very high-energy neutrinos and γ-rays in such interactions. We compare the production in propagation in the microwave background to that in the extragalactic background light. The propagation of heavy nuclei is discussed only briefly. We show the extreme models for cosmogenic neutrino production and the limits set on them by different experiments.     

On a distributed derivative model of a viscoelastic bodySur un model de corps viscoélastique de dérivé distribué

We study a viscoelastic body, in a linear stress state with fractional derivative type of dissipation. The model was formulated so that it takes into account, with a weighting factor, all derivatives of stress and strain between zero and one. We derive restrictions on the model that follow from Clausius–Duhem inequality. Several known constitutive equations are derived as special cases of the model proposed here. Two examples are discussed. To cite this article: T.M. Atanackovic, C. R. Mecanique 331 (2003).     

Critère de fatigue polycyclique pour des matériaux anisotropes : application aux monocristauxA high cycle fatigue criterion for anisotropic materials: application to single crystals

The high-cycle fatigue criteria based on a macroscopic–mesoscopic scale interpretation, initiated by Dang Van, were used essentially for polycrystalline materials. In the existing criteria the material isotropy at both mesoscopic and macroscopic scales plays a key role. The purpose of this paper is to revisit the macroscopic to mesoscopic fatigue approach taking into account the material anisotropy and some results obtained by Bui. The possible applications are some anisotropic steels or monocrystalline structures such as stitanium turbine blades. To cite this article: F. Cano et al., C. R. Mecanique 332 (2004).     

On the thermal anisotropy affecting transfers in a multilayer porous mediumSur l'effet de l'anisotropie thermique sur les transferts dans un milieu poreux multicouches

An analytical model for studying double-diffusive natural convection within a multilayer anisotropic porous medium is developed and validated with respect to a direct numerical silmulation. The studied domain is composed of two horizontal porous layers where the lower one is thermally anisotropic and is submitted to a uniform horizontal heat flux and a vertical mass flux. The assumption of parallel flow is validated and the effect of anisotropy on dynamic transitions is investigated. To cite this article: R. Bennacer et al., C. R. Mecanique 332 (2004).     

Modified fixed point algorithm in fluid–structure interactionAccélération avec des conditions de transpiration d'un algorithme de point fixe en interaction fluide–structure

In this work, we address the numerical solution of some non-linear problems arising in the time discretization of fluid–structure interaction problems with fully implicit schemes. At each time step, we have to solve a highly non-linear coupled system, since the fluid domain depends on the unknown displacement of the structure. We propose a modified fixed-point algorithm which combines the Block-Gauss–Seidel iterations with a transpiration formulation. Numerical experiments show the great improvement in computing time with respect to the standard method. To cite this article: S. Deparis et al., C. R. Mecanique 331 (2003).     

Réduction a priori de modèles thermomécaniquesAn a priori model reduction method for thermomechanical problems

A model reduction method is proposed for finite element models. A previous computation of the state of the structure is not necessary. Residuals defined over the entire time interval and the Karhunen–Loève method provide basis functions. A non-incremental algorithm, from the LATIN method, is used to compute this basis functions. Because of the non-incremental feature, the reduced order model is representative for a large evolution of the state of the structure. To cite this article: D. Ryckelynck, C. R. Mecanique 330 (2002) 499–505.