Structural relaxation around substitutional Cr3+ in MgAl2O4

The structural environment of substitutional Cr3+ ion in MgAl2O4 spinel has been investigated by Cr K-edge Extended X-ray Absorption Fine Structure (EXAFS) and X-ray Absorption Near Edge Structure (XANES) spectroscopies. First-principles computations of the structural relaxation and of the XANES spectrum have been performed, with a good agreement to the experiment. The Cr-O distance is close to that in MgCr2O4, indicating a full relaxation of the first neighbors, and the second shell of Al atoms relaxes partially. These observations demonstrate that Vegard's law is not obeyed in the MgAl2O4-MgCr2O4 solid solution. Despite some angular site distortion, the local D3d symmetry of the B-site of the spinel structure is retained during the substitution of Cr for Al. Here, we show that the relaxation is accomodated by strain-induced bond buckling, with angular tilts of the Mg-centred tetrahedra around the Cr-centred octahedron. By contrast, there is no significant alteration of the angles between the edge-sharing octahedra, which build chains aligned along the three four-fold axes of the cubic structure.Comment: 7 pages, 4 figure

Je communique donc je suis :: la communication non verbale de l’enseignant en contexte de classe culturellement très hétérogène

La réalité de l’enseignement a énormément changé ces dernières années. En effet, de plus en plus d’étrangers vivent en Suisse, ce qui modifie considérablement l’homogénéité culturelle des classes. Ce changement n’est pas sans conséquence sur la manière dont les enseignants conduisent leurs leçons. La présente étude, s’inscrivant dans un contexte de recherche qualitative, repose essentiellement sur la communication non verbale d’un enseignant étant dans une classe ayant un grand niveau d’hétérogénéité (plus de 30%). L’objectif de ce travail consiste à observer, par le biais d’extraits vidéo, les pratiques relevant du langage non verbal d’enseignants du primaire travaillant dans des classes culturellement hétérogènes dans le but de les identifier, de les analyser, de les comprendre et de les formaliser. À travers cette recherche, j’ai pu constater que l’identité d’une personne façonnée par ses expériences vécues va avoir beaucoup d’impacts sur la manière d’être en classe et donc sur sa façon de communiquer non verbalement. Ensuite, l’enseignant est libre de respecter ou non les coutumes de ses élèves. Sa personnalité, ses valeurs et sa sensibilité face aux différentes cultures vont effectivement jouer un rôle dans sa façon d’enseigner. Finalement, le langage non verbal n’est pas forcément privilégié dans un contexte de classe culturellement hétérogène mais il fait partie intégrante de la façon dont l’enseignant communique et transmet des messages à ses élèves, qu’ils soient de même culture ou de culture différente

From Film Archives to Digital Filmmaking: Exploring War Memories in American Documentaries

The memory of American wars has been largely influenced by iconic visuals, used either to promote patriotic cohesion behind the rationale for war or to question the motivations behind the United States military involvement abroad. War documentaries, while serving conflicting perspectives in times of war, participate in the construction of sites of memory while retrospectively engaging with war issues. Incorporating archive footage as a source of historical knowledge, these nonfiction films pr..

Structural relaxation around substitutional Cr3+ in pyrope garnet

The structural environment of substitutional Cr3+ ion in a natural pyrope Mg3Al2Si3O12 has been investigated by Cr K-edge Extended X-ray Absorption Fine Structure (EXAFS) and X-ray Absorption Near Edge Structure (XANES) coupled with first-principles computations. The Cr-O distance is close to that in knorringite Mg3Cr2Si3O12, indicating a full relaxation of the first neighbors. The local C3i symmetry of the octahedral Y site is retained during Cr-Al substitution. The second and third shells of neighbors (Mg and Si) relax only partially. Site relaxation is accommodated by strain-induced bond buckling, with angular tilts of the Si-centered tetrahedra around the Cr-centered octahedron, and by a radial deformation of the Mg-centered dodecahedra

L’Histoire terrible mais inachevée de Norodom Sihanouk, roi du Cambodge, de la Cartoucherie au pays des Khmers

En 2010, Ariane Mnouchkine missionne Delphine Cottu et Georges Bigot pour remettre en scène L’Histoire terrible mais inachevée de Norodom Sihanouk, roi du Cambodge d’Hélène Cixous avec les acteurs cambodgiens de Phare Ponleu Selpak. En 1984, au retour d’un séjour qu’elles effectuent dans un camp de réfugiés cambodgiens à la frontière thaïlandaise, Ariane Mnouchkine et Hélène Cixous décident de mettre en scène un des drames les plus effroyables de l’histoire contemporaine. Une épopée de près d..

Explorando el metagenoma del suelo antártico como fuente de nuevas enzimas adaptadas al frío y elementos génicos móviles

A partir de muestras de suelo antártico se obtuvo la metagenoteca PP1. Esta fue sometida a análisis funcionales y genotípicos para el aislamiento de nuevas enzimas adaptadas al frío con potenciales aplicaciones, y para la detección de elementos génicos asociados a la movilización de genes, respectivamente. Por tamizaje fenotípico se detectaron 14, 14, 3 y 11 clones productores de lipasas/esterasas, proteasas, amilasas y celulasas, respectivamente, con actividades máximas aparentes de 35 °C para las amilasas y lipasas, y de 35-55 °C para las celulasas, tal como se observó para otras enzimas adaptadas al frío. Sin embargo, una celulasa parece ser compatible con enzimas mesófilas, las que usualmente se mantienen activas hasta por sobre 60 °C. Este hecho probablemente esté asociado a un comportamiento psicrotolerante en los suelos antárticos. La metagenómica permite acceder a una nueva miríada de productos metabólicos con potenciales beneficios para aplicaciones biotecnológicas e industriales. Se detectaron los genes tipo intI y tnp por PCR, y sus productos génicos deducidos tuvieron identidades del 58 al 86 % y del 58 al 73 % con secuencias conocidas, respectivamente. Dos clones, BAC 27A-9 y BAC 14A-5, parecen presentar organizaciones sintéticas únicas, lo cual sugiere la existencia de rearreglos génicos probablemente debidos a divergencias evolutivas dentro del género o facilitados por la asociación de elementos de transposición. La evidencia de elementos génicos relacionados con el reclutamiento y la movilización de genes en ambientes extremos como la Antártida refuerza la hipótesis sobre el origen de algunos genes diseminados por elementos móviles entre los microorganismos asociados al ser humano.Metagenomic library PP1 was obtained from Antarctic soil samples. Both functional and genotypic metagenomic screening were used for the isolation of novel cold-adapted enzymes with potential applications, and for the detection of genetic elements associated with gene mobilization, respectively. Fourteen lipase/esterase-, 14 amylase-, 3 protease-, and 11 cellulase-producing clones were detected by activity-driven screening, with apparent maximum activities around 35 °C for both amylolytic and lipolytic enzymes, and 35-55 °C for cellulases, as observed for other cold-adapted enzymes. However, the behavior of at least one of the studied cellulases is more compatible to that observed for mesophilic enzymes. These enzymes are usually still active at temperatures above 60 °C, probably resulting in a psychrotolerant behavior in Antarctic soils. Metagenomics allows to access novel genes encoding for enzymatic and biophysic properties from almost every environment with potential benefits for biotechnological and industrial applications. Only intI- and tnp-like genes were detected by PCR, encoding for proteins with 58-86 %, and 58-73 % amino acid identity with known entries, respectively. Two clones, BAC 27A-9 and BAC 14A-5, seem to present unique syntenic organizations, suggesting the occurrence of gene rearrangements that were probably due to evolutionary divergences within the genus or facilitated by the association with transposable elements. The evidence for genetic elements related to recruitment and mobilization of genes (transposons/integrons) in an extreme environment like Antarctica reinforces the hypothesis of the origin of some of the genes disseminated by mobile elements among "human-associated" microorganisms.Fil: Berlemont, Renaud. Universite de Liege; BélgicaFil: Pipers, Delphine. Universite de Liege; BélgicaFil: Delsaute, Maud. Universite de Liege; BélgicaFil: Angiono, Federico. Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica. Departamento de Microbiología, Inmunología y Biotecnología; ArgentinaFil: Feller, Georges. Universite de Liege; BélgicaFil: Galleni, Moreno. Universite de Liege; BélgicaFil: Power, Pablo. Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica. Departamento de Microbiología, Inmunología y Biotecnología; Argentina. Universite de Liege; Bélgica. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay; Argentin

Validation of a novel microradiography device for characterization of bone mineralization

International audienceIn order to simplify bone mineralization measurements, a system using radiographic films has been updated with a digital detector. The objective of this paper was to validate this new device. Technologies and physical phenomena involved in both systems (radiographic films and digital detector) are different. The methodology used to compare the two systems was based on image quality and assessed on two main parameters: contrast to noise ratio and spatial resolution. Results showed that the contrast to noise ratio was similar between the two systems, provided that acquisition parameters were optimized. With regard to spatial resolution, a magnification factor of at least 4 or more was required to achieve the same resolution as films. A final validation was also shown on a real image of a bone sample. The results showed that both systems have similar image quality performances, and the system using digital detector has several advantages (easier to use than films, no consumables and faster acquisition time)

X-ray Linear Dichroism in cubic compounds: the case of Cr3+ in MgAl2O4

The angular dependence (x-ray linear dichroism) of the Cr K pre-edge in MgAl2O4:Cr3+ spinel is measured by means of x-ray absorption near edge structure spectroscopy (XANES) and compared to calculations based on density functional theory (DFT) and ligand field multiplet theory (LFM). We also present an efficient method, based on symmetry considerations, to compute the dichroism of the cubic crystal starting from the dichroism of a single substitutional site. DFT shows that the electric dipole transitions do not contribute to the features visible in the pre-edge and provides a clear vision of the assignment of the 1s-->3d transitions. However, DFT is unable to reproduce quantitatively the angular dependence of the pre-edge, which is, on the other side, well reproduced by LFM calculations. The most relevant factors determining the dichroism of Cr K pre-edge are identified as the site distortion and 3d-3d electronic repulsion. From this combined DFT, LFM approach is concluded that when the pre-edge features are more intense than 4 % of the edge jump, pure quadrupole transitions cannot explain alone the origin of the pre-edge. Finally, the shape of the dichroic signal is more sensitive than the isotropic spectrum to the trigonal distortion of the substitutional site. This suggests the possibility to obtain quantitative information on site distortion from the x-ray linear dichroism by performing angular dependent measurements on single crystals