Co–Mn-oxide spinel catalysts for CO and propane oxidation at mild temperature

CoxMn3−xO4 oxides (0≤x≤3) were prepared by controlled decomposition of mixed oxalates near 200 ◦C, followed by a calcination at 300 ◦C. These oxides are amorphous for x < 0.9. For higher cobalt fraction they have a cubic spinel structure and their crystallite size grows with the cobalt fraction. These materials have a large surface area; the highest values, exceeding 250 m2/g, were obtained for x≈2. The spinel oxides exhibit an outstanding catalytic activity for propane oxidation at mild temperature (20–200 ◦C). They are also active for CO oxidation at ambient temperature. This high activity was correlated both with the surface area and the cobalt concentration. The most efficient material is Co2,3Mn0,7O4, which has a better activity than cobalt oxide catalysts reported in the literature

Synthesis of highly porous alumina-based materials

γ-Alumina-based materials with high porous volume, tunable pore size, were synthesized by the addition of both PEO/PPO/PEO triblock copolymers (Pluronics® F127 and P123) and metal nitrates (Al3+, Mn2+, Cu2+) in a boehmite (AlOOH) nanoparticle hydrosol. During the subsequent thermal treatment, the surfactant was removed leaving a highly porous framework. The pore size distribution was strongly dependent on the metal nitrate added and its concentration. By this simple process it was possible to modify the porous volume in the range 0.3–2.6 cm3 g−1 and the median pore diameter in the range 5–40 nm. All these materials presented high surface areas in the range 300–500 m2 g−1. During the drying AlOOH particles aggregate to form linear objects (flat rods, laths) in order to minimize electrostatic repulsion. We think that the improvement of the textural characteristics of γ-alumina could be explained by the adsorption of copolymer on to these fiber-like objects, preventing the compact rearrangement of the boehmite nanoparticles in a compact “card-pack” microstructure during the drying. The addition of electrolytes induces a reduction of electrostatic repulsions, leading to the formation of both fiber-like objects at lower AlOOH concentration, and a 3D network by bridging these 1D objects. This bridging is reversible since the gel returns to a sol state under shearing, but polymer adsorption can prevent the full collapsing of this network during the drying step and a huge porosity can be maintained after calcination

Thermal stabilization of alumina modified by lanthanum

Transition alumina, with different La loadings, were synthesized from boehmite (AlOOH) hydrosols containing a PEO/PPO/PEO triblock copolymer (Pluronics® P123) and lanthanum nitrate. After calcination at 500 °C, the xerogels prepared from these sols have large specific surface area (≈400 m2/g) and very large porous volumes, increasing with the amount of La to reach 2.5 cm3/g for La/(La + Al) = 0.036. This material still kept a surface area close to 180 m2/g and a pore volume of 2.3 cm3/g when it was calcined at 1000 °C. However, after calcination at 1200 °C, the best textural properties (70 m2/g and 0.6 cm3/g) were observed for La/(La + Al) = 0.015. Larger La loadings led to the formation of LaAl11O18 and LaAlO3 and the detection of these mixed oxides was associated with a decrease of surface area and pore volume. The improvement of the thermal stability of these materials can be explained by the synergy of two effects: (i) the adsorption of copolymer onto fiber-like boehmite nanoparticles, preventing their compact rearrangement during the drying and maintaining a large porosity after calcination; (ii) the inhibition of the sintering process through the formation of thermally stable species between reactive surface sites (strong Lewis acid sites) and lanthanum atoms

Synthèse et caractérisation de nouveaux catalyseurs hétérogènes pour la dépollution de l'air

L'objectif de ce travail de thèse est de synthétiser et d'optimiser de nouveaux catalyseurs hétérogènes pour la dépollution de l'air. Ces catalyseurs sont des nanomatériaux, issus d'un procédé sol/gel au voisinage de la température ambiante et en solution aqueuse. L'ajustement de certains paramètres de synthèse permet de contrôler la structure cristalline, la morphologie, la taille, la porosité et la dispersion des particules submicroniques en solution. La viscosité des suspensions ainsi obtenues étant facilement ajustable, celles-ci peuvent être déposés sur différents types de substrat pour la mise en forme de matériaux fonctionnels. Cette étude se concentre sur deux grandes familles de matériaux : les alumines mésoporeuses et les oxydes mixtes de métaux de transition. Nous avons tout d'abord synthétisé des catalyseurs à base d'alumine gamma à porosité modulable, en combinant l'utilisation de tensioactifs non ioniques (copolymères triblocs) avec l'ajout de nitrates métalliques dans un sol de nanoparticules de boehmite (AlOOH). L'élimination du tensioactif, lors du traitement thermique nécessaire à la transformation de la boehmite en alumine gamma, permet de conserver un réseau extrêmement poreux. La distribution poreuse étant intimement liée à la concentration et au type de nitrate métallique employé, il est possible d'ajuster les propriétés texturales des matériaux dans un large domaine de porosité (volume poreux : de 0,3 à 2,6 cm3/g, taille moyenne des pores : de 5 à 40 nm et surface spécifique allant de 300 à 500 m2/g). Les alumines de transition présentent une grande stabilité thermique, cependant au-delà d'une température limite (< 900°C) la structure cristalline de ces alumines de transition évolue vers l'alumine alpha (corindon), qui est la forme thermodynamiquement stable. Cette transformation s'accompagne d'une diminution drastique de la porosité et de la surface spécifique (< 1 m²/g). Nous avons montré que l'ajout de nitrate de lanthane permet de stabiliser fortement l'alumine à haute température qui peut conserver une grande porosité même après calcination à 1200°C (Sp = 80 m2/g et Vp = 0,6 cm3/g). Cette stabilisation peut être expliquée par la combinaison de deux effets, l'adsorption du copolymère sur les particules aciculaires de boehmite empêche leur réarrangement pendant le séchage et permet de maintenir un réseau poreux après calcination, et l'inhibition du frittage grâce à la formation d'espèces thermiquement stables entre les sites actifs de surface (site fortement électrophiles) et les atomes de lanthane. La deuxième partie de cette étude se focalise sur la préparation de catalyseurs à base d'oxydes mixtes à structure spinelle pour l'oxydation à basse température (< 50°C) du monoxyde de carbone (CO) et du propane (C3H8). Ces matériaux ont été préparés selon deux voies de synthèse différentes : la précipitation d'hydroxydes métalliques en milieu dilué et la précipitation d'oxalates mixtes. Dans le cas de la précipitation d'hydroxydes, afin de synthétiser des matériaux ayant une large gamme de surface spécifique et de porosité, différents paramètres ont ainsi été étudiés (pH, ajout de tensioactifs, d'oxydant) et ont conduit, pour certains, à des oxydes dont les porosités sont largement supérieures à celles reportées dans la littérature (Sp = 240 m2/g et Vp = 1,7 cm3/g). La deuxième voie de synthèse utilisée comporte deux étapes, la précipitation d'oxalates mixtes suivies de leur décomposition thermique sous pression partielle d'oxygène réduite (4%). Le contrôle précis de la réaction de décomposition, fortement exothermique, permet d'obtenir des matériaux à grande surface spécifique.The objective of this thesis is to synthesize and optimize new heterogeneous catalysts for air pollution control. These catalysts are nanomaterials produced from a sol / gel process developed at room temperature and in aqueous solution. By adjusting some key parameters of the synthesis, it is possible to control crystalline structure, morphology, size, porosity, and dispersion of the submicron particles in the solution. Sol viscosity is easily adjustable and these dispersions can be deposited on different types of substrates, which represents a significant advantage for the shaping of materials known as "functional". This study focuses on two major families of materials: mesoporous aluminas and mixed transition metal oxides. Initially, we synthesized gamma alumina based catalysts with tunable porosity, by combining the use of nonionic surfactants (triblock copolymers) with the addition of metal nitrates in a nanoparticle boehmite sol (AlOOH). The removal of the surfactant during the heat treatment required for the conversion of the boehmite to gamma alumina, keeps a highly porous network. The pore distribution is strongly dependent on the concentration and type of used metal nitrate, it is possible to tune the volume of the porous material from 0.3 to 2.6 cm3/g and the average pore size from 5 to 40 nm. In addition, all these materials have a very large specific surface area, ranging from 300 to 500 m2/g. Transition aluminas have high thermal stability, however, beyond a limit temperature (< 900°C) the crystal structure of these metastable aluminas progressively evolves to alpha alumina (corundum) which is the thermodynamically stable form. This transformation is accompanied by a drastic decrease of porosity and specific surface area (< 1 m²/g). We have shown that the addition of lanthanum nitrate can greatly stabilize transition alumina at high temperature. Indeed they can maintain a high porosity even after calcination at 1200°C (Sp = 70 m2/g and Vp = 0.6 cm3/g). This stabilization can be explained by the combination of two effects, the adsorption of the copolymer on the acicular boehmite particles prevents their rearrangement during drying and helps maintain a porous network after calcination, and the inhibition of the sintering through the formation of thermally stable species between surface active sites (highly electrophilic site) and the lanthanum atoms. The second part of this study focuses on the preparation of mixed-oxide spinel catalysts for oxidation at low temperature (< 50°C) of carbon monoxide (CO) and propane (C3H8). These materials have been prepared by two different synthetic routes: the precipitation of metal hydroxides in dilute medium and precipitation of mixed oxalates. In the case of the precipitation of hydroxides, to synthesize materials having a wide range of specific surface area and porosity, various parameters have been studied (pH, addition of surfactants, oxidizing agent) leading to preparation of oxides whose pores are much higher than those reported in the literature (Sp = 240 m2/g and Vp = 1.7 cm3/g). The second synthetic route used involves two steps, the precipitation of mixed oxalates followed by thermal decomposition under reduced oxygen partial pressure (4%). The precise control of the decomposition reaction, strongly exothermic, allows for high surface area materials. Systems giving the best conversion rates at low temperature are compositions rich in cobalt. Among them, some catalysts are capable to oxidize propane from 80°C, this exceptional performance is well above the best catalysts reported in the literature even those containing precious metals

A Modular Integration of SAT/SMT Solvers to Coq through Proof Witnesses

International audienceWe present a way to enjoy the power of SAT and SMT provers in Coq without compromising soundness. This requires these provers to return not only a yes/no answer, but also a proof witness that can be independently rechecked. We present such a checker, written and fully certified in Coq. It is conceived in a modular way, in order to tame the proofs' complexity and to be extendable. It can currently check witnesses from the SAT solver ZChaff and from the SMT solver veriT. Experiments highlight the efficiency of this checker. On top of it, new reflexive Coq tactics have been built that can decide a subset of Coq's logic by calling external provers and carefully checking their answers

Stable Constrained Dynamics

International audienceWe present a unification of the two main approaches to simulate deformable solids, namely elasticity and constraints. Elasticity accurately handles soft to moderately stiff objects, but becomes numerically hard as stiffness increases. Constraints efficiently handle high stiffness, but when integrated in time they can suffer from instabilities in the nullspace directions, generating spurious transverse vibrations when pulling hard on thin inextensible objects or articulated rigid bodies. We show that geometric stiffness, the tensor encoding the change of force directions (as opposed to intensities) in response to a change of positions, is the missing piece between the two approaches. This previously neglected stiffness term is easy to implement and dramatically improves the stability of inextensible objects and articulated chains, without adding artificial bending forces. This allows time step increases up to several orders of magnitude using standard linear solvers

Multifarious Hierarchies of Mechanical Models for Artist Assigned Levels-of-Detail

International audienceWe present a new framework for artist driven level of detail in solid simulations. Simulated objects are simultaneously embedded in several, separately designed deformation models with their own independent degrees of freedom. The models are ordered to apply their deformations hierarchically, and we enforce the uniqueness of the dynamics solutions using a novel kinetic filtering operator designed to ensure that each child only adds detail motion to its parent without introducing redundancies. This new approach allows artists to easily add fine-scale details without introducing unnecessary degrees-of-freedom to the simulation or resorting to complex geometric operations like anisotropic volume meshing. We illustrate the utility of our approach with several detail enriched simulation examples

Construction and Validation of a Hybrid Lumbar Spine Model For the Fast Evaluation of Intradiscal Pressure and Mobility

International audienceA novel hybrid model of the lumbar spine, allowing fast static and dynamic simulations of the disc pressure and the spine mobility, is introduced in this work. Our contribution is to combine rigid bodies, deformable finite elements, articular constraints, and springs into a unique model of the spine. Each vertebra is represented by a rigid body controlling a surface mesh to model contacts on the facet joints and the spinous process. The discs are modeled using a heterogeneous tetrahedral finite element model. The facet joints are represented as elastic joints with six degrees of freedom, while the ligaments are modeled using non-linear one-dimensional elastic elements. The challenge we tackle is to make these different models efficiently interact while respecting the principles of Anatomy and Mechanics. The mobility, the intradiscal pressure, the facet joint force and the instantaneous center of rotation of the lumbar spine are validated against the experimental and theoretical results of the literature on flexion, extension, lateral bending as well as axial rotation. Our hybrid model greatly simplifies the modeling task and dramatically accelerates the simulation of pressure within the discs, as well as the evaluation of the range of motion and the instantaneous centers of rotation, without penalizing precision. These results suggest that for some types of biomechanical simulations, simplified models allow far easier modeling and faster simulations compared to usual full-FEM approaches without any loss of accuracy

Dépistage du Syndrome d'Apnées Obstructives du Sommeil et évaluation du risque cardiovasculaire à l'officine (implication du pharmacien et perspectives d'application)

La loi HPST reconnaît aux pharmaciens d officine la possibilité d exercer de nouvelles missions, dont le dépistage de certaines pathologies. Le pharmacien, par son accessibilité et ses compétences, semble idéalement positionné pour mener à bien ce type d action. Cependant, la conjoncture économique étant difficile pour le secteur, la mise en place du dépistage non rémunéré présente un risque pour l entreprise officinale. C est dans ce contexte que le projet Pharma-SAS a été développé. Cette étude consiste à mettre en place le dépistage du syndrome d apnées obstructif du sommeil (SAOS) par le pharmacien, au comptoir de l officine ainsi que l évaluation du risque cardiovasculaire chez certains des sujets inclus. Le SAOS constitue le principal trouble respiratoire lié au sommeil. Il correspond à l obstruction partielle ou totale des voies respiratoires supérieures pendant le sommeil, à l origine d apnées ou d hypopnées. Cette maladie touche près de 5 % de la population, elle est responsable de nombreuses complications cardiovasculaires et d une nette dégradation de la qualité de vie. Au niveau clinique, le SAOS se caractérise par une somnolence diurne et des ronflements associés parfois à des pauses respiratoires. Ces symptômes, facilement identifiables, permettent un dépistage aisé réalisable à l aide d un simple questionnaire. 214 sujets ont été inclus dans l étude Pharma-SAS et parmi eux, 71 sujets ont été décrits à haut risque de SAOS. A notre connaissance, seulement 4 des sujets dépistés à haut risque de SAOS ont effectué l examen diagnostic. Un diagnostic de SAOS a ainsi été vérifié chez 3 de ces patients qui sont actuellement traités par pression positive continue.GRENOBLE1-BU Médecine pharm. (385162101) / SudocSudocFranceF

Anatomy Transfer

Characters with precise internal anatomy are important in film and visual effects, as well as in medical applications. We propose the first semi-automatic method for creating anatomical structures, such as bones, muscles, viscera and fat tissues. This is done by transferring a reference anatomical model from an input template to an arbitrary target character, only defined by its boundary representation (skin). The fat distribution of the target character needs to be specified. We can either infer this information from MRI data, or allow the users to express their creative intent through a new editing tool. The rest of our method runs automatically: it first transfers the bones to the target character, while maintaining their structure as much as possible. The bone layer, along with the target skin eroded using the fat thickness information, are then used to define a volume where we map the internal anatomy of the source model using harmonic (Laplacian) deformation. This way, we are able to quickly generate anatomical models for a large range of target characters, while maintaining anatomical constraints