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Our interview takes the form of a podcast to which we have added a short text enriched with visuals. It aims to present a work constituting the Magali Loffreda’s doctoral thesis in education (2021) about how teachers manage their educational resources. This work consisted of the editorialization of a graphic booklet produced in partnership with Solène Voegel, then a graphic designer at Okoni. The aim was to report on teachers practices around resources., Notre entretien, qui se présente sous la forme d’un podcast auquel nous avons ajouté un court texte enrichi de visuels, vise à présenter un travail constitutif de la thèse de doctorat en sciences de l’éducation de Magali Loffreda (2021) sur l’activité d’organisation des ressources éducatives par les enseignant·es. Ce travail a consisté en l’éditorialisation d’un livret graphique réalisé en partenariat avec Solène Voegel, alors graphiste chez Okoni, dans l’objectif de rendre compte des pratiques enseignantes autour des ressources.

International audience; Notre proposition interroge les connaissances mobilisées lors de la conception des ressources éducatives numériques à travers le prisme du modèle de l’expertise documentaire - qui définit quatre familles d’activités autour des ressources : concevoir, accéder, organiser et communiquer -, et à l’aune de dix-neuf entretiens d’enseignants en IUT intervenant dans les trois disciplines suivantes : Génie Biologie, Gestion des Entreprises et Administration, et Informatique. Nos analyses éclairent les facteurs influençant les prises de décision des enseignants : la référence au monde professionnel comme justification des choix didactiques et pédagogiques, et la rigueur dans le choix des sources sélectionnées. Le modèle met ainsi en évidence les relations entre pratiques informationnelles, contextes professionnels et connaissances des enseignants. Nos analyses soulignent également l’importance des contraintes de l’écosystème informationnel, qui ont une influence forte sur les pratiques informationnelles.

International audience; Notre proposition interroge les connaissances mobilisées lors de la conception des ressources éducatives numériques à travers le prisme du modèle de l'expertise documentaire-qui définit quatre familles d'activités autour des ressources : concevoir, accéder, organiser et communiquer-, et à l'aune de dix-neuf entretiens d'enseignants en IUT intervenant dans les trois disciplines suivantes : Génie Biologie, Gestion des Entreprises et Administration, et Informatique. Nos analyses éclairent les facteurs influençant les prises de décision des enseignants : la référence au monde professionnel comme justification des choix didactiques et pédagogiques, et la rigueur dans le choix des sources sélectionnées. Le modèle met ainsi en évidence les relations entre pratiques informationnelles, contextes professionnels et connaissances des enseignants. Nos analyses soulignent également l'importance des contraintes de l'écosystème informationnel, qui ont une influence forte sur les pratiques informationnelles.

The unique electronic and crystallographic structure of intermetallics is known to result inexcellent catalytic performances for selected chemical reactions. Moreover, a high structuralstability of the surface is generally assumed, even under reaction conditions, owing to thespecific bonding network of these compounds. Transition metal (TM = Fe, Co) aluminides ofthe Al13TM4 stoichiometry have previously demonstrated high activities and selectivities inpartial hydrogenation of alkynes and alkadienes [1]. Focusing on the Al13Co4(100) surface as a model catalyst for butadiene hydrogenation, the reaction conditions are predicted to modify the relatively flat surface structure identified under ultra-high vacuum, in the form of highly cohesive clusters emerging from the bulk lattice [2]. Unlike the flat one, this termination is catalytically active and fully selective. Its contrasted catalytic behavior as compared to that of the reference Al13Fe4(010) surface – which is more active but less selective – is rationalized in terms of alkene and hydrogen co-adsorption properties. The reaction mechanism on Al13Fe4(010) is elucidated thanks to microkinetic modeling [3]. This work demonstrates that a realistic description of the surface structures under reaction conditions is mandatory to the design of new-generation catalysts based on the complex topology of intermetallic surfaces.[1] L. Piccolo et al., Catalytic properties of Al13TM4 complex intermetallics [...], Sci. Technol. Adv. Mater. 20 (2019) 557[2] É. Gaudry et al., Catalytic activation of a non-noble intermetallic surface […], J. Mater. Chem. A 8 (2020) 7422[3] C. Chatelier et al., Mechanism of Butadiene Hydrogenation to Butene on Al13Fe4(010), to be submitted (2022)

International audience; The understanding of the structure and properties of γ−Al 2 O 3 supported platinum-tin catalysts in oxidizing conditions is of prominent importance for many catalytic reactions. By using density functional theory calculations and ab initio molecular dynamics simulations, we identify the adsorption sites of oxygen atoms on a Pt 10 Sn 3 /γ−Al 2 O 3 (100) cluster model and analyze its reconstruction and electronic charge redistribution. A strengthening of O adsorption is found for the cluster with respect to the Pt 3 Sn(111) surface, due to the key role of Al-Pt interfacial sites at low coverage, the ductility and the metastability of the cluster. Moreover, the ab initio ( [[EQUATION]] , T) thermodynamic phase diagrams show only minor differences between the supported Pt 10 Sn 3 and Pt 13 clusters. Both clusters are much more oxidized than their homologous Pt and Pt 3 Sn(111) surfaces, and their oxygen contents may exceed 1 ML. This suggests a stronger size effect than an alloying effect for the oxidation of the metallic nanoparticles at small size.

International audience

The arduous modelling of reactions at heterogeneous catalysts is greatly simplified when adsorption-energy scaling relations between intermediates exist. The offset of these linear relations is structure-independent when the slope is unity and otherwise depends on the coordination number of the active sites. Here we examine the adsorption of *C, *CH, *CH2, *CH3 and *COH on five different surface sites of nine transition metals to establish their structure-sensitive scaling relations. Interestingly, we show that the scaling relations of *C (valency 4) and C-containing species with valency 3 (*CH, *COH) have peculiar structure-independent offsets. These offsets stem from the analogous bonding of those adsorbates to the adsorption sites, in spite of their dissimilar valency. We show how this result implies that reaction pathways in catalysis involving *C, *CH and *COH, for instance CO2 electroreduction to CH4, will usually have sizable thermodynamic limits imposed to their optimization. F.C.-V acknowledges funding from Spanish MICIUN RTI2018-095460-B-I00, Ramón y Cajal RYC-2015-18996 and María de Maeztu MDM-2017-0767 grants and partly by Generalitat de Catalunya 2017SGR13. We thank Red Española de Supercomputación (RES) for supercomputing time at SCAYLE (projects QS-2019-3-0018, QS-2019-2-0023, and QCM-2019-1-0034) and MareNostrum (project QS-2020-1-0012). The use of supercomputing facilities at SURFsara was sponsored by NWO Physical Sciences, with financial support by NWO. The authors also thank GENCI resources (Project 609) and PSMN in Lyon for CPU time and assistance, as well as the CPER/SYSPROD project (N° 2019-AURA-P5B) for financial support.

International audience; Highlights• We calculated radical production around gold/water nanoparticle (GNP/WNP) in water.• Calculations were performed for single keV photon absorption.• In the micrometer range, radicals are overproduced by GNP compared to WNP.• In the nanometer range, radicals are overproduced by small GNP compared to WNP due to Auger electrons.• In the nanometer range, radical production is comparable for large NP.

International audience; In a previous work, we extended and benchmarked the MDM Monte Carlo code with available data for gold metallic media irradiated by electron beams. In this paper, we worked with the aim of improving the cross sections on which our Monte Carlo simulation is based, and which are essential for an accurate description of the transport of electrons in gold. The mesoscopic potential of solid gold has been predicted, and its sensitivity toward electron emission has been evaluated. This potential was derived from the calculation of the electrostatic and atomistic potential by density functional theory and used to calculate inelastic inverse mean free path for electron transport. After integrating these results into our Monte Carlo code, we evaluated the impact of these new cross sections on yields of electron emission from solid gold irradiated by monoenergetic electron beams. We obtained a mesoscopic potential value of − 12.77 eV for our model of bulk metal gold, 27% lower than the one commonly estimated from the Fermi energy. This result impacted on the inverse mean free path for plasmon excitations with a 10% decrease for electrons in the range of 6–30 eV. Regarding electron emission yields, there was no impact of the new mesoscopic potential on the primary electron yields, but for secondary electrons, the emission yields were increased by a factor of up to two depending on the primary beam energy and thickness of the gold foil.

Teaching relies on a number of resources necessary for the preparation of lessons. The way they circulate is a challenge for those working in the field of education. The evolutions linked to the development of digital technologies also raise, in an increasingly pressing manner, the question of their organization. Our thesis studies these organizational practices. A multidimensional analytical framework articulating the macro, meso and micro levels has been developed in order to apprehend this activity by taking into account the socio-historical context in which it is deployed. It allows us to reveal the relationships and tensions between these three levels. On the theoretical level, it has been developed and enriched by the contributions of various academic works carried out in the fields of educational sciences, information and communication sciences, organizational sciences, and the history of knowledge, sciences and technologies. It has enabled us to develop a network of concepts that shed light on our subject. Methodologically, we have used this framework to conduct empirical investigations based on qualitative methodologies. These have led to the development of three corpora. Two corpuses are based on teachers' discourses. The first is the result of an ethnographic investigation in a high school. The second is based on elements of discourse from teachers’ network websites concerning the organization of resources and the mobilization of management tools. The last corpus is based on an analysis of the offer of digital tools and services for the organization of resources, or presenting functionalities dedicated to the organization of resources. Finally, we undertook the development of two glossaries to embrace the key notions and concepts used in this research. Our analyses underline the complexity of the resource organization activity. The latter is based on several actions relying on a vast hybrid tooling (paper and digital) and manifesting itself through forms of do-it-yourself. It also covers several dimensions: practical, affective, biographical and intimate. Our thesis shows that this activity, which could be thought of as trivial and secondary, plays on the contrary an important role in the process of appropriation and construction of knowledge, and that it is through this process that teachers can be ressourcefullness, and thus build and establish their legitimacy as professionals in the making and in development., L'exercice du métier enseignant s'appuie sur un certain nombre de ressources nécessaires à la préparation des cours. Leurs modes de circulation et d'appropriation constituent un enjeu pour l'ensemble des acteurs du secteur éducatif. Les évolutions en lien avec le développement du numérique posent également, de manière de plus en plus pressante, la question de la façon dont ils les organisent. Notre thèse étudie ces pratiques d’organisation. Un cadre d'analyse multidimensionnel articulant les niveaux macro, méso et micro a été construit afin d'appréhender cette activité en tenant compte du contexte socio-historique dans lequel elle se déploie. Il permet de mettre à jour les relations et tensions entre ces trois niveaux. Sur le plan théorique, il a été développé et enrichi par les apports de divers travaux menés dans les domaines des sciences de l’éducation, des sciences de l’information et de la communication, des sciences de l'organisation, et de l'histoire des savoirs, des sciences et des techniques. Il a permis d’élaborer un réseau de concepts éclairant notre sujet. Sur le plan méthodologique, nous nous sommes appuyés sur ce cadre pour mener des enquêtes empiriques reposant sur des méthodologies qualitatives. Ces enquêtes ont donné lieu à l'élaboration de trois corpus. Deux corpus s'appuient sur les discours des enseignants. Le premier est issu d'une enquête de type ethnographique dans un lycée. Le deuxième repose sur des éléments de discours de sites web de réseaux enseignants concernant l'organisation des ressources et la mobilisation d'outils de gestion. Le dernier corpus est fondé sur une analyse de l’offre d’outils et de services numériques pour l’organisation des ressources, ou présentant des fonctionnalités dédiées à l’organisation des ressources. Enfin, nous avons entrepris l’élaboration de deux glossaires pour embrasser les notions et concepts-clés utilisés dans cette recherche. Nos analyses soulignent la complexité de l'activité d'organisation des ressources. Cette dernière repose sur plusieurs actions s'appuyant sur un vaste outillage hybride (papier et numérique) et se manifestant par des formes de bricolages. Elle recouvre également plusieurs dimensions : pratique, affective, biographique et intime. Notre thèse montre que cette activité, que l’on pourrait penser triviale et secondaire, joue au contraire un rôle important dans le processus d'appropriation et de construction des connaissances, et que c'est à travers ce processus que les enseignants peuvent avoir de la ressource, et ainsi construire et asseoir leur légitimité en tant que professionnels de l'enseignement en devenir et en développement.

International audience; Scanning transmission electron microscopy experiments indicate that face-centered cubic (FCC) is the predominant ordered structure for Ag309 ± 7 nanoclusters, synthesized in vacuum. Historically, experiments do not present a consensus on the morphology at these sizes, whereas theoretical studies find the icosahedral symmetry for Ag309 and the decahedral shape for nearby sizes. We employ density functional theory calculations to rationalize these observations, considering both regular and defective Ag nanoparticles (281–321 atoms). The change of stability induced by the presence of defects, symmetry loss, and change of number of atoms is evaluated by the nanoparticle surface energy, which was measured previously. FCC and decahedral symmetries are found to be more favorable than icosahedral, consistent with our measurements of clusters protected from extended atmospheric exposure. In addition, an energy-free descriptor, surface atomic density, is proposed and qualitatively reproduces the surface energy data. Nonsymmetric and defective structures may be preferred over perfectly regular ones within a given size range.

International audience

International audience; The use of gold nanoparticles to enhance radiation therapy efficiency has been thoroughly investigated over the past two decades. While theoretical studies have mostly focused on physical mechanisms and dose enhancement, studies of free radical production are scarce. In this work, we investigated the primary yield of free radicals ( and ) induced by 20–90 keV monoenergetic photons, for small GNPs concentrations. Our study is based on a Monte Carlo approach which enables electron transport down to low energy, both in water and in gold. We obtained, for a gold concentration of 1 , an average chemical enhancement varying from 6 to 14%, depending mostly on the photon energy and, to a lesser extent, on the chemical species and size of the GNP. This enhancement is strongly correlated to the dose deposition enhancement, although not strictly proportional. While supporting the hypothesis that therapeutic efficiency of GNPs may not simply be explained by an overproduction of free radicals in the early stage, our simulation provides inputs for further macroscopic simulations, including cumulative track effects and potentially GNP chemical reactivity.

International audience; The unique electronic and crystallographic structure of intermetallics is known to result in excellent catalytic performances for selected chemical reactions. Moreover, owing to the specific bonding network of these compounds, a high structural stability of their surfaces is generally assumed, even under reaction conditions. Transition metal (TM = Fe, Co) aluminides of the Al 13 TM 4 stoi-chiometry have previously demonstrated high activities and selectivities in partial hydrogenation of alkynes and alkadienes. Focusing on the Al 13 Co 4 (100) surface as a model catalyst for butadiene hydrogenation, the hydrogen-rich reaction conditions are predicted-based on DFT calculations and atomistic thermodynamics-to modify the relatively flat surface structure identified under ultra-high vacuum, in the form of highly cohesive clusters emerging from the bulk lattice. Unlike the flat one, this termination presents favorable adsorption properties, able to make it catalytically active and fully selective to butenes. In addition, its contrasted catalytic behavior as compared to that of the reference Al 13 Fe 4 (010) surface-which is more active but less selective-is rationalized in terms of butadiene, butene and hydrogen co-adsorption properties. This work demonstrates that a realistic description of the surface structures under reaction conditions is mandatory to the design of new-generation catalysts based on the complex topology of intermetallic surfaces.

International audience; Functionalized gold nanoparticles are investigated by density functional theory calculations in the context of cancer radiotherapy. Several typical experimental shapes, including nanostars, nanospheres, and nanorods, are modeled by optimizing Au clusters covered by organic monolayers composed of hydrated short-chain polyethylene glycol (PEG) ligands. The PEGylation stabilizes significantly the stellation of decahedral Au54 by deforming significantly its geometry at the spikes. The higher stability of the PEG molecules adsorbed on this stellated nanocluster with respect to the more spherical icosahedral Au55 and Au79 leads to a larger energy cost to desorb them and thus a weaker propensity for the starred nanoparticle to exchange ligands with the cell membrane, in agreement with experiments. These results open interesting possibilities for advancing our understanding of the cellular uptake of gold nanoparticles.

International audience

SSCI-VIDE+ECI2D+LPI; International audience; Intermetallic compounds exhibit a high degree of structural diversity, with numerousunique structure types. Among them, complex intermetallic compounds, also known ascomplex metallic alloys (CMAs), present large periodic structures based on building blocksconsisting in highly symmetric atomic polyhedra, often displaying motifs of simplercompounds, like hierarchical replacement of atomic positions in the more elementalstructures by larger atomic clusters or cages in the complex ones. Typical clusters/cagesfound in quasicrystals include Mackay, Bergman and Tsai clusters, and a large variety ofhighly symmetric polyhedra are generally found in CMAs.The structural complexity of CMAs extends to the surface. In this talk, the relationshipbetween the three dimensional cluster-based bulk structure and the two-dimensional surfacewill be questioned in two cases: the pseudo-10fold surfaces of Al13TM4 (TM = Fe, Co)quasicrystalline approximants [1] and the low-index surfaces of the Ba8Au5.25Ge40.75 cagecompounds [2], using a combination of experimental techniques under ultra-high vacuumand theoretical calculations based on the Density Functional Theory. The focus will be onthe different mechanisms by which stable surface terminations are selected, to highlight thefactors governing the atomic and electronic properties of the observed surface.The specific atomic arrangements at the surface induced by the intrinsic cluster-based bulkstructure of CMAs are expected to affect their surface properties. This will be discussed inthe case of the pseudo-10fold surfaces of Al13TM4 compounds, in terms of their catalyticproperties [3].[1] Ph. Scheid et al., Acta Cryst. A, 75 (2019) 314-324; É. Gaudry et al., Phys. Rev. B 94 (2016) 165406; J. Ledieu et al., Phys. Rev. Lett. 110 (2013) 076102.[2] K. Anand et al., J. Phys. Chem.. C 122 (2018) 2215 and 29298.[3] L. Piccolo et al., Sci. Technol. Adv. Mater. 20 (2019) 557.

International audience; Solvated gold nanoparticles have been modeled in the fluxional regime by density functional theory including dispersion forces for an extensive set of conventional morphologies. The study of isolated adsorption of one water molecule shows that the most stable adsorption forms are similar (corners and edges) regardless of the nanoparticle shape and size, although the adsorption strength differs significantly (0.15 eV). When a complete and explicit water solvation shell interacts with gold nanoclusters, metastable in vacuum and presenting a predominance of (100) square facets (ino-decahedra Au55 and Au147), these nanoparticles are found unstable and transform into the closest morphologies exhibiting mainly (111) triangular facets and symmetries. The corresponding adsorption strength per water molecule becomes independent of shape and size and is enhanced by the formation of two hydrogen bonds on average. For applications in radiotherapy, this study suggests that the shapes of small gold nanoparticles should be homogenized by interacting with the biological environment.

International audience; The metal cluster size in supported metal catalysts impacts the oxidation state of the metal atoms, coordination capability, and finally the catalytic activity-especially when the number of atoms becomes countable. The correlation between metal oxidation state and its catalytic consequences for ultrafine Pt was studied for photocatalytic overall water splitting using a Pt/SrTiO 3 (photo)catalyst. A distinctive change in catalytic behavior and oxidation state was observed below 100 Pt-atom clusters at ~2 nm. Combining density functional theory (DFT) and experimental characterizations including X-ray absorption spectroscopy (XAS), X-ray photoelectron spectroscopy (XPS), and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), the smaller Pt clusters obtained by the surface organometallic route (under 100 Pt atoms) were predominantly oxidized and selectively performed photocatalytic water splitting selectively without activation of the water-forming back-reaction from H2 and O2. When the Pt clusters obtained by classical impregnation were larger than 2 nm, they remained metallic (Pt 0) and were active for both water splitting and the competing thermal water formation back reaction. In addition, Pt 0 clusters are poisoned in the presence of CO, whereas highly dispersed ultra-fine oxidized Pt clusters are insensitive to CO. This paper presents evidence of ultrafine PtOx (below approximately 2 nm clusters) that are insensitive to coordination of various gas identities (H 2 , O 2 , CO), resulting in efficient and selective photocatalytic overall water splitting.

Statistical mechanics and transition-state theory have been used to investigate the diffusion kinetics of gold and copper atoms on pristine and various reduced surfaces of rutile TiO2 (110). A DFT+U approach has been employed to calculate potential energy maps and to evaluate the required diffusion activation barriers. The role of the support reducibility has been examined on the adsorption properties (optimal structures, energetics, and spin polarization) and diffusion kinetics, especially for the reduced support presenting a single subsurface oxygen vacancy. This approach has allowed us to demonstrate key discrepancies between Au and Cu atoms and to sketch out a comparative scenario for the early-stage nucleation of Au and Cu nanoparticles on the various surface states of TiO2 (110).

International audience; Many discourses emphasize the great educational potential of digital technologies. These technologies can renew both the activities carried out with students, the management of their learning paths, working methods, etc. In theory, this will be beneficial for education. But the evolution of these technologies in the field of education does not necessarily lead to idyllic results. In reality, the changes observed in these areas are slow and are based on very localized, rarely convergent, and often incomplete. Several elements are likely to determine the uses of computer technologies: the strategies of publishers and links with «EdTech» companies; political choices (in terms of curricula, equipment, examinations, etc.); materials (tablets, smartphones, etc.); educational resources, their modes of production and exchange, the place of free educational resources; changes in national and European legislation about digital matters. In this paper, we will try to show how the French publishing landscape and access to educational resources is currently undergoing important changes, starting from a configuration where textbooks are central to sketch out the current situation, where the supply of online digital resources seems to open up alternatives. We will rely in particular on the case of a portal of resources financed by the Ministry of National Education and published by consortia bringing together publishers and EdTech structures.; Muchos discursos destacan el gran potencial educativo de las tecnologías digitales. Estas tecnologías pueden renovar tanto las actividades realizadas con los alumnos, como la gestión de sus itinerarios de aprendizaje, métodos de trabajo, etc. En teoría, esto sólo puede ser beneficioso para la educación. Pero la evolución de estas tecnologías en el campo de la educación no conduce necesariamente a resultados idílicos. En realidad, los cambios observables en estas áreas son lentos y se basan en cambios muy localizados, raramente convergentes y a menudo incomplesos. Es probable que varios elementos determinen el uso de las tecnologías informáticas: las estrategias de los editores y los vínculos con las empresas de technología educativa; las opciones políticas (en términos de programas, equipos, exámenes, etc.); los materiales (tabletas, teléfonos inteligentes, etc.); los recursos educativos, sus modos de producción e intercambio, el lugar de los recursos educativos gratuitos; los cambios en la legislación digital nacional y europea. En este texto, trataremos de mostrar cómo el panorama editorial francés y el acceso a los recursos educativos están experimentando actualmente cambios importantes, partiendo de una configuración en la que el manual es fundamental para esbozar la situación actual, donde la oferta de recursos digitales en línea parece tomar el relevo. Nos basaremos en particular en el caso de un portal de recursos financiado por el Ministerio de Educación Nacional y publicado por consorcios que agrupan a editores y estructuras de empresas de technología educativa. Palabras clave: Tecnologías Educativas; Portales, Recursos; Libros de texto; Profesores. Las obras se publican en RELATEC bajo una licencia Creative Commons Reconocimiento-NoComercial-SinObraDerivada 4.0 International (CC BY-NC-ND) Revista Latinoamericana de Tecnología Educativa, 16(2)

International audience; Many discourses emphasize the great educational potential of digital technologies. These technologies can renew both the activities carried out with students, the management of their learning paths, working methods, etc. In theory, this will be beneficial for education. But the evolution of these technologies in the field of education does not necessarily lead to idyllic results. In reality, the changes observed in these areas are slow and are based on very localized, rarely convergent, and often incomplete. Several elements are likely to determine the uses of computer technologies: the strategies of publishers and links with «EdTech» companies; political choices (in terms of curricula, equipment, examinations, etc.); materials (tablets, smartphones, etc.); educational resources, their modes of production and exchange, the place of free educational resources; changes in national and European legislation about digital matters. In this paper, we will try to show how the French publishing landscape and access to educational resources is currently undergoing important changes, starting from a configuration where textbooks are central to sketch out the current situation, where the supply of online digital resources seems to open up alternatives. We will rely in particular on the case of a portal of resources financed by the Ministry of National Education and published by consortia bringing together publishers and EdTech structures.; Muchos discursos destacan el gran potencial educativo de las tecnologías digitales. Estas tecnologías pueden renovar tanto las actividades realizadas con los alumnos, como la gestión de sus itinerarios de aprendizaje, métodos de trabajo, etc. En teoría, esto sólo puede ser beneficioso para la educación. Pero la evolución de estas tecnologías en el campo de la educación no conduce necesariamente a resultados idílicos. En realidad, los cambios observables en estas áreas son lentos y se basan en cambios muy localizados, raramente convergentes y a menudo incomplesos. Es probable que varios elementos determinen el uso de las tecnologías informáticas: las estrategias de los editores y los vínculos con las empresas de technología educativa; las opciones políticas (en términos de programas, equipos, exámenes, etc.); los materiales (tabletas, teléfonos inteligentes, etc.); los recursos educativos, sus modos de producción e intercambio, el lugar de los recursos educativos gratuitos; los cambios en la legislación digital nacional y europea. En este texto, trataremos de mostrar cómo el panorama editorial francés y el acceso a los recursos educativos están experimentando actualmente cambios importantes, partiendo de una configuración en la que el manual es fundamental para esbozar la situación actual, donde la oferta de recursos digitales en línea parece tomar el relevo. Nos basaremos en particular en el caso de un portal de recursos financiado por el Ministerio de Educación Nacional y publicado por consorcios que agrupan a editores y estructuras de empresas de technología educativa. Palabras clave: Tecnologías Educativas; Portales, Recursos; Libros de texto; Profesores. Las obras se publican en RELATEC bajo una licencia Creative Commons Reconocimiento-NoComercial-SinObraDerivada 4.0 International (CC BY-NC-ND) Revista Latinoamericana de Tecnología Educativa, 16(2)

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Polymer electrolyte membrane fuel cells have been studied for more than three decades as promising clean energy converters for automotive applications. However, improving their durability and reducing the catalyst cost (platinum loading) are ongoing challenges. Alloys are often proposed as an alternative solution which combines a good catalytic activity toward the oxygen reduction reaction and a decreased platinum content. In this work, we address density functional theory calculations for the formation of water and hydrogen peroxide on three different Pt3Ni(111) alloy model surfaces: bulk-truncated, Pt-skin, and Pt-skeleton terminations, in comparison with Pt(111). From a low-coverage Gibbs free energy analysis, the prediction of the activity order between all the catalysts agrees with electrochemical measurements: Pt-skin > Pt-skeleton > Pt(111) > bulk-truncated Pt3Ni(111). The superior activity of Pt-skin has been explained in terms of thermodynamic and kinetic properties and through an energy decompos...

The metal–support interaction on the chemical reactivity is illustrated here by density functional theory calculations for the hydrogenation of crotonaldehyde on Pt13 clusters deposited on CeO2(1 1 1). Adsorption of crotonaldehyde on the supported cluster is globally strengthened, compared to Pt(1 1 1), both on top of the cluster and at the interface with ceria. The activation barriers of the first and the second hydrogenation steps at both C C and C O bonds are consequently increased, but particularly at C O on top of the cluster, with respect to Pt(1 1 1). In contrast, the hydrogenation at C O is far easier at the interface with ceria, which underlines the key role of the support. The considered model shows a preferential route toward the formation of the saturated aldehyde, in contrast to the measurements. This study paves the way to advanced theoretical models with larger nanoparticles supported on reduced ceria in realistic conditions of environment.

International audience; Predicting the reaction mechanism of water and hydrogen peroxide formation on a platinum catalyst is a crucial step toward the understanding of the corresponding selectivity in polymer electrolyte membrane fuel cells. In this perspective, the environment of the catalytic active site should play an important role; however, its explicit description at the atomic scale is an ongoing challenge for theoretical approaches. In this study, we propose to model three effects of the environment: surface hydroxyl coverage, temperature, and reactant pressure. A detailed investigation of the reaction mechanism of water and hydrogen peroxide formation on a platinum surface is reported on the basis of density functional theory (DFT) calculations and Gibbs free energy diagrams. In standard conditions of reaction (1 atm and 353 K), the selectivity toward water and hydrogen peroxide depends on the competition between two reaction paths (molecular oxygen direct dissociation and hydrogenation), which can be tuned by the partial coverage of OH intermediate. At a low coverage of 1/12 ML, the catalyst activity is expected to be low due to a preferential but activated direct oxygen dissociation. When the OH partial coverage increases, the hydroperoxyl route becomes favorable, hence leading to hydroxyl and water by the nonactivated OOH dismutation. The direct oxygen dissociation and the whole reaction mechanism are sensitive to the hydroxyl partial coverage. Our gas/metal model opens the way to new elementary mechanisms in the presence of aqueous electrolyte and electric field that would explain how water can be produced at the beginning of the reaction (at low coverage).

Accounting for surface coordination The exploration of heterogeneous catalysts using first-principles calculations can be daunting because the large number of atoms and possible surface geometries. Calle-Vallejo et al. describe a simpler metric for assessing optimal reactivity: a weighted average of surface coordination that includes second-nearest neighbors (see the Perspective by Stephens et al. ). The calculations identified three approaches for introducing cavity sites into the platinum(111) surface to improve its performance for the oxygen reduction reaction used in fuel cells. Science , this issue p. 185 , see also p. 164

The search for improved heterogeneous catalysts is an important but difficult task. Scaling relations between the adsorption energies of reaction intermediates greatly facilitate the computational design of catalysts. However, this methodology does not currently incorporate structure sensitivity and hence cannot describe adequately the overall activity of realistic catalyst particles and extended surfaces with several facets, edges and apices. Here, we generalize scaling relations by examining twelve different low-index, stepped and kinked surfaces of nine transition metals. This allows us to quantify the effect of the adsorption-site geometry on these relations, ensures a full prediction of their parameters, and helps in identifying intrinsic thermodynamic restrictions to the performance of catalysts. The resulting fully predictable, structure-sensitive scaling relations are a step towards the long-sought rational design of multifaceted catalytic particles. Such a design can now target not only the chemical nature of active materials but also the actual geometry of their active sites.

Understanding the selectivity of the oxygen reduction reaction, especially the formation of water versus hydrogen peroxide in fuel cells, is an ongoing challenge in electrochemistry, surface science and catalysis. In this study, we propose a comprehensive thermodynamic analysis of the reaction intermediates for the formation of water on Pt(111). Density functional theory calculations of all the elementary steps linking hydroxyl and hydroperoxyl surface species with water and hydrogen peroxide have been performed at low (1/12 ML, ML = monolayer) and high (1/4 ML) coverages. The reaction energy variation for the two competing elementary events (molecular oxygen dissociation and hydroperoxyl formation) is strongly coverage-dependent. For the direct dissociation, an increase is observed at low coverage with respect to the usual high coverage picture. The stability of the reaction intermediates is investigated from thermodynamic diagrams. At 353 K and a total pressure of 1 atm, water and hydroxyl surface species are expected to compete for adsorption on Pt(111).

Platinum is a prominent catalyst for a multiplicity of reactions because of its high activity and stability. As Pt nanoparticles are normally used to maximize catalyst utilization and to minimize catalyst loading, it is important to rationalize and predict catalytic activity trends in nanoparticles in simple terms, while being able to compare these trends with those of extended surfaces. The trends in the adsorption energies of small oxygen- and hydrogen-containing adsorbates on Pt nanoparticles of various sizes and on extended surfaces were analyzed through DFT calculations by making use of the generalized coordination numbers of the surface sites. This simple and predictive descriptor links the geometric arrangement of a surface to its adsorption properties. It generates linear adsorption-energy trends, captures finite-size effects, and provides more accurate descriptions than d-band centers and usual coordination numbers. Unlike electronic-structure descriptors, which require knowledge of the densities of states, it is calculated manually. Finally, it was shown that an approximate equivalence exists between generalized coordination numbers and d-band centers., F.C.V., P.S., and D.L. acknowledge EU funding through the PUMA MIND contract (Call FCH‐JU‐2011‐1, Code SP1‐JTI‐FCH‐2011.1.3, Project 303419). We thank IDRIS and CINES (project 609, GENCI/CT8) and PSMN for CPU time and assistance. J.I.M. acknowledges support from CSIC and ESF through the JAEDoc program. J.M.G.L. acknowledges support from MINECO (FIS2012‐30996) and the ReLiable project funded by the DCSR (11‐116792).

This report, corresponding to a project funded by The Francophone Universitary Agency (AUF). It aims at presenting a synthesis regarding the current state of the reflection in 2014 about francophone digital resources for education in sub saharian Africa., Ce texte s'inscrit dans un travail de veille scientifique effectué à la demande de l'Agence universitaire de la Francophonie (AUF). Le projet a notamment eu pour enjeu la construction d'une vision prospective, nécessaire à l'élaboration de projets pérennes. Le présent rapport concerne spécifiquement l'édition scolaire numérique.

International audience; This combined experimental and theoretical study aims at understanding why surface hydroxyl groups may enhance catalytic reactivity of MgO surfaces in basic catalysis, whereas hydroxyls are weakly deprotonating groups. We investigated that reactivity enhancement in the catalytic conversion of 2-methyl-but-3-yn-2-ol (MBOH). Reaction kinetics was experimentally determined on partially hydroxylated MgO: active sites were saturated with the reactant and catalyzed its conversion with an activation energy of 85 kJ·mol–1. Reaction pathways were calculated over fully hydroxylated, partially hydroxylated, and dehydroxylated MgO surfaces by means of first-principles simulations. To highlight the effect of reactant coverage, we also calculated the reaction pathway on MgO precovered with MBOH molecules. The results show that the surface OH groups generated by dissociative adsorption of water induce a lowering in the activation energy barriers when they keep a bare Mg2+-O2– pair available in the vicinity for MBOH to adsorb and react. Interestingly, OH groups do not directly interact with MBOH converting on the surface, but they modify the basic properties of the vicinal bare Mg2+-O2– pair on which MBOH adsorbs and converts. A similar effect is predicted when MBOH converts on a bare Mg2+-O2– pair in the vicinity of a second adsorbed MBOH molecule. The beneficial effect of coadsorbates on the reactivity of active sites is analyzed by means of a thermodynamic model and an electronic structure analysis.

International audience; Density Functional Theory (DFT) calculations show on two examples how catalytic reactivity qualitatively depends on the environment of the active sites. The example of butadiene selective hydrogenation to butenes on Pt or Pd first illustrates how alloying this catalytically active metal with a non- or less reactive elements (Sn or Au, respectively) allows weaker catalyst–molecule interactions and favors the desorption of butenes. It also shows that, from this weakening of the interactions, new reaction pathways are opened and non-selective pathways through a metallacycle intermediate are disadvantaged. Both effects concur on PtSn for an improved selectivity in butenes, while on the PdAu alloy, the gain in selectivity is explained mainly by the easier butene desorption. The dehydrogenation of ethanol on Rh and Pt surfaces shows how co-adsorbates, as water solvent molecules, can interfere with the catalytic elementary steps, assisting OH bond breaking and disadvantaging Csingle bondH dissociation. The balance between these two effects is metal dependent. Ethanol interacts by a strong H-bond with the H2O pre-covered surface, in a more stabilizing way than for the simple adsorption on the bare metal. The surface H2O (or surface-OH) complex can hence be seen as the true active site for the reaction. It is hence important to include the influence of the environment, from the surface part or from the reactant part, for an accurate modeling of heterogeneous catalytic reactions.

International audience; The growth of platinum on non-reduced CeO2 (111) surface is studied by means of calculations based on the density functional theory. Particles of increasing size are formed on the oxide surface by incorporating the platinum atoms one by one until multilayer films are obtained. The main conclusion is that platinum atoms tend to maximize the number of metallic bonds and to approach the situation of the bulk, hence preferring films to particles, particles to isolated atoms, and a three-dimensional growth to a two-dimensional one. The supported particles and the films exhibit a contraction of the Pt–Pt distances, with respect to those of the Pt bulk, in order to match the ceria lattice. The density of states projected on the filmsurfaceplatinum atoms shows important differences in shape and energy (lower d-band center) compared to the Pt(111) reference surface, which could be the major reason for the observed changes in catalytic reactivity when deposited particles are compared with single crystal surfaces.

International audience; In this work we present a multiscale theoretical methodology that scales up ab initio calculated data into elementary kinetic models in order to simulate Polymer Electrolyte Membrane Fuel Cells (PEMFC) transient operation. Detailed Density Functional Theory (DFT) calculations are performed on a model Pt(1 1 1) surface to determine the elementary kinetic rates of the Oxygen Reduction Reaction (ORR) mechanism at a Pt-based PEMFC cathode. These parameters include the effect of surface coverage on the activation barriers and are implemented into a Mean Field model describing the behavior of the electric field and charge distribution at the nanoscale interfacial vicinity to the catalyst, which is in turn coupled with microscale and mesoscale level models describing the charge and reactants and water transport phenomena across the cell. The impact of two possible ORR mechanisms on the simulated i–V curves is investigated: a first route connected with the dissociative adsorption of molecular oxygen on Pt(1 1 1), a second route related to the formation and the transformation of OOH surface species. The similarities and differences of the associated calculated i–V responses for each of these routes and the consequences on the interpretation of electrochemical observables at the cell level are discussed.

International audience; Understanding the nature of the adhesion of an organic liquid on a metal surface is of paramount importance for elucidating the stability and chemical reactivity at these complex interfaces. However, to date, the morphology, layering and chemical properties at organic liquid metal interfaces have been rarely known. Using semi-empirical dispersion corrected density functional theory calculations and ab initio molecular dynamics simulations, we show that carbon tetrachloride and ethanol films confined to a platinum surface alter their intrinsic properties and exhibit interfacial reactivity. A few interface carbon tetrachloride (ethanol) molecules adsorb dissociatively (molecularly) on platinum thanks to the surrounding medium. The adsorption strength of the interfacial molecules is consequently increased in the condensed phase as compared to the gas phase. This remarkable effect is rationalized by an interaction energy decomposition model and an electrostatic potential analysis.

2 Dupont, C. Delbecq, F. Loffreda, D. Jugnet, Y.; An experimental evaluation, under realistic conditions, of the catalytic properties of a Pt3Sn(1 1 1) model catalyst in CO oxidation under excess of hydrogen is reported in this study. From a structural point of view, two different surface terminations are available in this alloy, viz. (2 x 2) and (root 3 x root 3)R30 degrees, differing by their tin concentration and Pt-Sn local structural arrangements in the uppermost layers, thus offering specific active sites for the reaction to proceed. In this study, mass spectrometry and polarization modulation infrared reflection absorption spectroscopy measurements (PM-IRRAS) have been performed at near ambient pressure on both surfaces of the alloy and compared to those obtained on Pt(1 1 1) used as a reference. The presence of hydrogen promotes the rate of CO oxidation on the three surfaces. The influence of tin is remarkable, increasing the catalytic activity of Pt atoms by one order of magnitude. With the exception of CO, no other species such as formyls or carbonates are observed on the surface by IR spectroscopy in the range of temperature (293-425 K) investigated. (C) 2010 Elsevier Inc. All rights reserved.

International audience; Reaction pathways have been explored with periodic DFT calculations in order to understand the origin of the high selectivity for the hydrogenation of 1,3-butadiene on the Pt2Sn/Pt(1 1 1)-(√3 × √3)R30° surface alloy. The adsorption structures of butadiene, 1- and 2-butenes and all the intermediate species have been studied. Compared to the reference catalyst Pt(1 1 1), there is a change both in geometries and in relative energies: for instance, the best adsorption mode of butadiene is cis 1,4-di-σ-2,3-π, while it is trans 1,2,3,4-tetra-σ on Pt(1 1 1). On the alloy, all the adsorption energies are reduced compared to pure platinum, and the adsorption structures implying many Ptsingle bondC bonds are more destabilized. The different pathways leading to partial hydrogenation products (1-butene, 2-butene) or other intermediate surface species (1,3- and 1,4-metallacycles) have been explored. The first hydrogenation step is clearly preferred at a terminal carbon, and the further hydrogenation to 1-butene has by far the lowest barrier. Other pathways exhibit larger activation barriers, particularly those leading to metallacycles, which is the key to explain the high selectivity to butene, in contrast to Pt(1 1 1). The role of tin is dual: a role of site blocking that forces unselective pathways to adopt distorted, high-energy transition states and a role of ligand that weakens the molecular adsorption and allows decoordination of double bonds prior to the hydrogenation, which decreases the energy barriers for the selective pathway to butene.

Open source software adoption in the embedded systems domain is gaining growing interest within the european industrial and academic communities due to the significant benefits it brings in terms of flexibility and cost reduction.Nonetheless, scepticism about open source as a viable option to support critical business functions still holds, since its decentralized and distributed development model makes quality evaluation and assessment hard to achieve. This paper reports the SHARE project experience, aimed at facilitating and promoting the use of open source software in the embedded systems industry. Performed activities, proposed methodology and achieved results are presented, along with lessons learned to exploit for enabling further initiatives in the next future.

Dupont, Celine Jugnet, Yvette Delbecq, Francoise Loffreda, David; The activation of oxygen reduction reaction fascinates numerous scientists in the fields of heterogeneous catalysis, electrochemistry and surface science. Indeed, oxygen dissociation is considered usually as the rate determining step of several reactions on conventional platinum catalysts. From combined experimental and theoretical approaches, we demonstrate comprehensively how tailored platinum-tin alloy surfaces allow to go beyond this chemical limitation. Near-ambient pressure kinetic measurements show the outstanding capacity of the Pt3Sn(111) single-crystal surfaces for carbon monoxide oxidation. The apparent activation energy is almost twice lower on the platinum-tin surface than on pure platinum catalyst. The theoretical analysis based on density functional theory calculations supports the idea that oxygen dissociation is never the rate determining step on these alloy surfaces since the corresponding rates calculated at room temperature always outstrip those of carbon monoxide oxidation. The influence of surface tin content and oxygen coverage on the activity is addressed in details. The mediatory role of tin in the alloy is elucidated on the basis of a charge transfer analysis. (C) 2010 Elsevier Inc. All rights reserved.

International audience; By employing high-resolution electron energy loss spectroscopy (HREELS), temperature-programmed desorption (TPD), and low-energy electron diffraction (LEED), we have studied the adsorption and thermal decomposition of crotonaldehyde (2-butenal) on Pt(111) as well as Pt3Sn/Pt(111) and Pt2Sn/Pt(111) surface alloys. In order to understand the adsorption structures and the vibrational properties, an extensive theoretical study of the possible adsorption geometries and vibrational spectra on the three considered surfaces has been carried out using density functional theory (DFT). A careful analysis of the variety of possible adsorption configurations of crotonaldehyde allowed structural identification by correlating their vibrational fingerprints with the measured HREELS peaks. The mixed phases of crotonaldehyde formed on the model catalysts turned out to be even more complex than those we found in previous studies for prenal. The set of stable configurations identified by combination of HREELS with DFT consists of η2, η3, and η4 flat adsorption structures, which exhibit adsorption energies from −69 to −80 kJ/mol. Nonetheless, the thermal decomposition measured with TPD and the general adsorption behavior show similarities to prenal and acrolein. Starting from a strongly adsorbed state on Pt(111) at low temperatures, crotonaldehyde decomposes at temperatures close to 300 K. On the surface alloys, a high-coverage phase with structures of low hapticity such as η2-diσ(CC) is measured at low temperatures (∼160 K), and a low-coverage situation of high hapticity η2, η3, and η4 configurations is formed at higher temperatures (∼200 K). On Pt3Sn/Pt(111), two energetically competitive η1-top-E-(s)-trans-OSn forms cannot be excluded at low temperatures.

The surface restructuring of Pt(3)Sn(111) induced by oxygen chemisorption is examined by means of density-functional theory calculations. Molecular and atomic oxygen chemisorption is investigated on the two available terminations of the bulk alloy--(2 x 2) and (square root(3) x square root(3))R30 degrees--these two surfaces differing by the tin content and the nature of chemical sites. An extensive geometric, energetic, and vibrational analysis is performed including the influence of oxygen coverage in the case of atomic adsorption. For molecular adsorption, regular structures have been obtained for both surfaces with a clear effect of tin on the stability of the adsorption forms. In contrast, for atomic adsorption, two oxygen chemical states are found. In particular, a peculiar surface restructuring, involving the formation of a network of SnO(2) species, appears for large oxygen coverage. However the two terminations present discrepancies for the restructuring mechanism all along the oxygen coverage increase. All these results are supported by a systematic vibrational analysis.

The adsorption and thermal decomposition of the α,β-unsaturated aldehyde prenal (3-methyl-2-butenal) have been studied on Pt(111), the Pt3Sn/Pt(111) and Pt2Sn/Pt(111) surface alloys, and the corresponding terminations of the Pt3Sn(111) bulk alloy by means of high-resolution electron energy loss spectroscopy (HREELS), temperature-programmed desorption (TPD), and low-energy electron diffraction (LEED). By comparing the experimental results with extensive theoretical calculations of the multitude of possible adsorption configurations of prenal using density functional theory (DFT), the adsorption configurations actually present on all model catalysts have been identified. This approach, thus, reveals a new way to identify complex, multifunctional molecules adsorbed on model catalyst surfaces. On Pt(111), prenal is strongly adsorbed and decomposes at approximately 300 K. By the aid of density functional theory (DFT), five flat-lying adsorption structures of η2, η3, and η4 hapticity, which exhibit similar adso...