Microstructure of Ba1−xLaxTiO3−δ ceramics sintered by spark plasma sintering

Nano-sized Ba1−xLaxTiO3 (0.00 ≤ x ≤ 0.14) powders were prepared by a coprecipitation method and calcined at 850 °C in air. The corresponding ceramics were obtained by Spark Plasma Sintering (SPS) at 1050 °C. These ceramics are oxygen deficient and are marked as Ba1−xLaxTiO3−δ. Both powders and ceramics were characterized by X-ray diffraction (XRD) and Transmission Electron Microscopy (TEM). The effect of lanthanum concentration on the densification behavior, on the structure and the microstructure of the oxides was investigated. Average grain sizes are comprised between 54 (3) nm and 27 (2) nm for powders, and 330 (11) nm and 36 (1) nm for ceramics according to the La-doping level. Powders crystallize in the cubic (or pseudo-cubic) perovskite phase. The structure of ceramics consists in a mixture of cubic (or pseudo-cubic) and tetragonal perovskite type phases. As the lanthanum content increases, the tetragonality of the samples decreases, as well as the grain size

La différenciation pédagogique au cours du regroupement d’élèves de trois enseignantes de sciences au secondaire

Cette thèse trace une nouvelle manière d’analyser les pratiques de la différenciation pédagogique. Elle cerne le regroupement d’élèves tel qu’il se déroule dans le milieu naturel au cours d’une démarche d’investigation scientifique, une ficelle jusqu’à présent inaperçue. En effet, plusieurs recherches indiquent que les enseignants qui différencient affirment avoir recours au regroupement d’élèves en classe, sans avoir véritablement exploré ce contexte. Ainsi, cette étude de multicas décrit le déroulement des regroupements provisoires effectués par trois enseignantes de sciences du secondaire au Québec qui ne prétendaient pas différencier l’enseignement et dégage leurs conceptions à l’égard de l’hétérogénéité des groupes-élèves. Avec ce nouvel éclairage sur le concept de la différenciation pédagogique, cette recherche élabore une modélisation empirique de la différenciation intuitive dans une perspective de théorisation.This thesis presents an innovative way of analyzing the concept and practice of differentiated instruction. Through a scientific inquiry, it identifies the provisional students’ grouping in an unaltered classroom setting, an aspect which until now has not been examined. Previous research has shown that teachers who use differentiation resort to in-class grouping without having truly explored the context. Using a multi-case study, we describes the process of in-class grouping done by three science teachers at the secondary education level in Quebec who do not purposely use differentiation. Furthermore, it also unveils these teachers perceptions with regard to heterogeneity of groups formation. In a theorical perspective, and guided by our findings, this reaserch develops an empirical model of intuitive differentiation

Essaie de mesure de l’utilité de l’audit dans la gouvernance des organisations publiques

Auditing is an essential practice to ensure the proper control of operations, activities and functions within public organizations, and in result, contribute to the achievement of short, medium and long-term objectives. However, a few years ago, auditing was still a marginal practice in the Moroccan public sector, a practice that has gradually expanded following the law number 62-99 forming the financial jurisdictions code, the new constitution of 2011 and other recent managerial reforms. This article seeks to assess the usefulness of auditing in the governance of public organizations through a qualitative approach based on the Court of Accounts reports, as the main audit and control institution in the public sector. To do this, we chose to carry out a documentary study of the audit reports published following thematic audit missions done by the Court of Accounts in four ministerial departments. The results showed the importance of this audit in the transparency and governance of the public administrations studied, through the improvement of the internal control system, risks detection and the implementation of the necessary corrective actions. However, we were also able to observe that the audit alone does not resolve all the shortcomings excellently identified, which could be a logical reason to introduce a new practice in the public sector, which is more appropriate in terms of analyzing and resolving problems, notably the global diagnosis.   Keywords: Audit, public sector, management of public organizations, governance, performance. JEL Classification: M42 Paper type : Empirical researchL’audit est considéré actuellement comme une pratique indispensable pour assurer la bonne maitrise des opérations, des activités et des fonctions au sein de toute organisation notamment du secteur public, et contribuer par conséquent à la réalisation des objectifs à court, moyen et long terme. Cependant, il y a quelques années, l’audit était encore une pratique marginale dans le secteur public marocain, pratique qui s’est progressivement étendu à la suite de la loi n° 62-99 formant code des juridictions financières, de la nouvelle constitution de 2011 et des autres dernières réformes managériales. Cet article cherche à évaluer l’utilité de l’audit dans la gouvernance des organisations publiques à travers une approche qualitative sur la base des rapports de la Cour des comptes qui constitue l’organe principal de contrôle et d’audit dans le secteur public. Pour ce faire, nous avons choisi de procéder par une étude documentaire des rapports d’audit publiés à l’issue des missions d’audit thématique effectuées par la Cour des comptes auprès de quatre départements ministériels. Les résultats ont montré l’importance de cet audit dans la transparence et la gouvernance des administrations publiques étudiées par le biais de l’amélioration du dispositif de contrôle interne, l’identification des risques et la mise en place des actions correctives nécessaires. Toutefois, nous avons pu constater également que l’audit à lui seul ne permet pas la résolution de l’ensemble des insuffisances excellement identifiés, ce qui pourra être une raison logique pour l’introduction dans le secteur public d’une nouvelle pratique plus adéquate en termes d’analyse et de résolution des problèmes, notamment le diagnostic global.   Mots-clés : Audit, secteur public, management des organisations publiques, gouvernance, performance. Classification JEL :  M42 Type de l’article : Article empiriqu

Microstructure of single-phase cobalt and manganese oxide spinel Mn3−xCoxO4 ceramics

This paper reports microstructural studies of single-phase Mn3−xCoxO4(0.98 ≤ x ≤ 2.93) spinel ceramics using transmission electron microscopy(TEM) and energy dispersive X-ray spectroscopy (EDX). These ceramics were obtained by conventional sintering or by spark plasma sintering(SPS) of powders prepared by thermal decomposition of coprecipitated oxalate precursors. For x < 1.78 or x ≥ 1.78, the monophasic ceramicscorrespond respectively to quadratic (Q) or cubic (C) spinel structure. The ferroelastic character of the structural phase transition from C to Qis highlighted by specific microstructural features. The effect of chemical composition and heat treatment conditions on the microstructure andessentially on the presence and the characteristics of twins were investigated. The coherent twin interfaces are parallel to (1 1 2) planes in the Qcell. Twins can correspond to: tweeds, single lamellae (widths: 5–306 nm) arranged parallel to each other, large lamellae (widths: 69–928 nm)internally twinned and sometimes arranged in cyclic forms (triangular shapes)

Structural characterization of dense reduced BaTiO3 and Ba0.95La0.05TiO3 nanoceramics showing colossal dielectric values

BaTiO3−x and Ba0.95La0.05TiO3−x nanoceramics showing colossal permittivity values have been characterized. While starting powders are of cubic symmetry, X-ray and Neutron Diffraction techniques and Raman Spectroscopy measurements show that the one-step processed ceramics obtained by Spark Plasma Sintering (SPS) contain cubic and tetragonal phases. Rather large oxygen deficiency determined in such ceramics by Electron Micro Probe analysis and Electron Energy Loss Spectroscopy analyzes is explained by the presence of Ti3+, as evidenced by X-ray Photoelectron Spectroscopy measurements. Transmission Electron Microscopy and High Resolution Transmission Electron Microscopy show that these ceramics contain 50–300 nm grains, which have single-domains, while grain boundaries are of nanometer scale. Colossal permittivity values measured in our dense nanoceramics are explained by a charge hopping mechanism and an interfacial polarization of a large number of polarons generated after sample reduction in SPS apparatus

Influence of Oxygen Substoichiometry on the Dielectric Properties of BaTiO3-δNanoceramics Obtained by Spark Plasma Sintering.

Oxygen-deficient BaTiO3-d nanoceramics were prepared by spark plasma sintering. Partially reduced raw nanopowders led to unusual dielectric properties. A short postsintering treatment was performed to reach a high er/tan d, which makes them attractive for industrial applications such as low-frequency capacitors. Surprisingly, our ceramics also remained black even after annealing for 5 days at 850°C in air, indicating the presence of barriers against oxygen diffusion. This exceptional behavior in pure barium titanate was consistent with a core–shell structure made of semiconductive grains and insulating grain boundaries, due to the presence of Ti3+/Ti4+ and oxygen vacancies

L’exil intérieur ou l’identité perdue dans l’œuvre de Ghassan Salhab

Je me souviens d'être entré dans la ville en 1982, en pleine invasion israélienne. J’avais déjà un rapport amour-haine avec Beyrouth où j’avais toujours été accueilli comme un émigrant parce que je parlais mal l’arabe. Je me permets à mon tour d’être exigeant avec ce Liban qui fut longtemps fantasmatique pour moi. Aujourd’hui, je comprends enfin que cette distance me libère et me permet d’aller plus facilement que d’autres vers les questions de mémoire et de lutte contre l’oubli. Il est impos..