Du maître d’école à l’instituteur, Jacques Gavoille

Tout corps social a une histoire et s’inscrit dans l’histoire. C’est le projet de ce livre de Jacques Gavoille que de nous donner à comprendre celle, complexe, foisonnante et passionnante, de la naissance du corps des instituteurs, devenu la figure mythique de l’école républicaine en France. L’originalité de l’étude tient à son objet et à sa méthode. L’auteur a pris le parti d’étudier de façon minutieuse et systématique les dossiers personnels des instituteurs et des institutrices d’un départ..

XANES determination of chromium oxidation states in glasses: comparison with optical absorption spectroscopy

The oxidation state of chromium in glasses melted in an air atmosphere with and without refining agents was investigated by Cr K-edge X-ray Absorption Near-Edge Structure (XANES) and optical absorption spectroscopy. A good agreement in the relative proportion of Cr(III) and Cr(VI) is obtained between both methods. We show that the chemical dependence of the absorption coefficient of Cr(III) is less important in XANES than in optical absorption spectroscopy. The comparison of glasses melted under different conditions provides an indirect assessment of the molar extinction coefficient of Cr(VI) in glasses

EXAFS study of rubidium-doped single-wall carbon nanotube bundles

International audienceThe local structure around the rubidium ions inserted in single-wall carbon nanotube bundles (Rb-doped SWCNT) is studied by Rb K-edge extended x-ray-absorption fine structure (EXAFS). The dependence of the local order around the rubidium ions is investigated as a function of the time of doping (i.e., as a function of the stoichiometry of the sample). The first coordination shell of the rubidium ions, related to the distance between rubidium and the first nearest-neighboring carbon atoms, has a clear time doping dependence. Comparison between ab initio simulations of the EXAFS spectra and experimental data questions the interstitial site (between three tubes) as the preferential insertion site in SWCNT bundles. The results indicate that the rubidium ions are mainly located inside the tubes and around the bundles. The results are in good agreement with combined x-ray and neutron diffraction experiments performed on the same samples

Comparison of durability indicators obtained by Non Destructive Testing methods to monitor the durability of concrete structures

International audienceThis paper deals with the use of non destructive testing methods (NDT) to assess indicators of concrete durability and mechanical properties of reinforced concrete structures. On site, NDT methods based on electromagnetic or ultrasonic wave propagation (such as radar, impact echo, ultrasonic transmission deviceÉ) are used because they are more or less sensitive to water content and mechanical properties depending on the method. It has been shown, in a former project [1, 2], that the NDT results called Òobservablesî are linked to mechanical and durability indicators (YoungÕs modulus, compressive strength, porosity and saturation degree). Meanwhile, the relationship between observables and indicators depends on the concrete mix design. A calibration protocol is then proposed to get this relationship for the right mix of the reinforced structure studied by using a minimal number of cores. The cores are non-destructively characterised in laboratory or used to determined reference indicators by standardised destructive methods. The aims of this paper are first to present the ND calibration protocol on cores and then to validate this proposed calibration protocol. To achieve this goal, some NDT results obtained on site and on the corresponding core are compared and durability indicators deduced from NDT calibration are compared with reference durability indicators

Identification of inhomogeneous concrete cover by non-contact ultrasonic method

International audienceConcrete cover degradation is induced by aggressive agents in ambiance, chemicals, moisture, or temperature variations. Due to this degradation concrete becomes inhomogeneous and usually a thin surface layer appears with porosity and elastic modulus different than the properties of deeper sound concrete. Therefore the on-site nondestructive evaluation of concrete cover is important to monitor the integrity of concrete structures and prevent their irreversible damage. In this paper the methodology applied by the classical technique used for ground structure recovery called Multichannel Analysis of Surface Waves (MASW) is used as the NDT tool to characterize the thickness and elastic modulus of concrete cover. The procedure consists in generation and reception of surface waves within the required frequency band, using the non-contact transducers which scan evaluated profiles. Then the phase velocity dispersion characteristic V(f) is extracted, and concrete cover is characterized using as the proposed velocity gradient. The dispersion characteristics are exploited by the inversion software in order to obtain the variation of shear wave velocity as a function of depth

Comparaison expérience/calcul par association de courbes

Nous nous intéressons à une méthode de comparaison entre les résultats de calculs numériques et des vérités terrains qui nous sont présentés comme des courbes planes fermées. Nous réalisons une mise en correspondance des deux formes en nous fondant sur les distances entre leurs points. De cette mise en correspondance nous déduisons une mesure de l'écart entre les deux courbes. En définissant une fonction de coût sur l'espagne produit des deux intervalles de paramétrages, nous introduisons une nouvelle méthode qui, à partir d'une initialisation convenable, fournit une bijection réalisant l'association des deux paramétrisations. Notre initialisation est obtenue en utilisant un chemin minimal (par rapport à la fonction de coût) et notre association est recherchée comme une somme de fonctions presque sûrement croissantes. Nous montrons une application de notre méthode pour la déformation de courbes

Thermal destruction of chiral order in a two-dimensional model of coupled trihedra

We introduce a minimal model describing the physics of classical two-dimensional (2D) frustrated Heisenberg systems, where spins order in a non-planar way at T=0. This model, consisting of coupled trihedra (or Ising-$\mathbb{R}P^3$ model), encompasses Ising (chiral) degrees of freedom, spin-wave excitations and $\Z_2$ vortices. Extensive Monte Carlo simulations show that the T=0 chiral order disappears at finite temperature in a continuous phase transition in the 2D Ising universality class, despite misleading intermediate-size effects observed at the transition. The analysis of configurations reveals that short-range spin fluctuations and $\Z_2$ vortices proliferate near the chiral domain walls explaining the strong renormalization of the transition temperature. Chiral domain walls can themselves carry an unlocalized $\Z_2$ topological charge, and vortices are then preferentially paired with charged walls. Further, we conjecture that the anomalous size-effects suggest the proximity of the present model to a tricritical point. A body of results is presented, that all support this claim: (i) First-order transitions obtained by Monte Carlo simulations on several related models (ii) Approximate mapping between the Ising-$\mathbb{R}P^3$ model and a dilute Ising model (exhibiting a tricritical point) and, finally, (iii) Mean-field results obtained for Ising-multispin Hamiltonians, derived from the high-temperature expansion for the vector spins of the Ising-$\mathbb{R}P^3$ model.Comment: 15 pages, 12 figures, 1 tabl