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Ab initio investigations of the electronic structures and chemical bonding in LiCo6P4 and Li2Co12P7
No full textInternational audienceThe electronic structures of the metal-rich phosphides LiCo6P4 and Li2Co12P7 were studied by DFT calculations. Both phosphides consist of three-dimensional [Co6P4] and [Co12P7] polyanionic networks which leave hexagonal channels for the lithium atoms. COOP data show strong Co-P and Co-Co bonding within the polyanions. The lithium atoms have trigonal prismatic phosphorus coordination. Total energy calculations indicate stability upon de-lithiation towards the Co6P4 and Co12P7 substructures
Decentralized Localization Using Fingerprinting and Kernel Methods in Wireless Sensor Networks
No full textInternational audienceSensors localization has become an essential issue in wireless sensor networks. This paper presents a decentralized localization algorithm that makes use of radio-location fingerprinting and kernel methods. The proposed algorithm consists of dividing the network into several zones, each of which having a calculator capable of emitting, receiving and processing data. By using radio-information of its zone, each calculator constructs, by means of kernel methods, a model estimating the nodes positions. Calculators estimates are then combined together, leading to final position estimates. Compared to centralized methods, this technique is more robust, less energy-consuming, with a lower processing complexity
Localisation par fingerprinting et méthodes à noyaux dans les réseaux de capteurs sans fil
No full textInternational audienc
Board of Directors and Bank Performance: Beyond Agency Theory
No full textInternational audienceBy integrating agency, stewardship and resource–dependency perspectives, this paper associated three characteristics of the board of directors - outside directors, insiders' equity ownership and leadership duality (Executive Officer also being the Chairman of the Board) - with bank's financial performance in Lebanon. Using a panel model, and after controlling for endogeneity problems, we examined 54 listed and unlisted banks from 2005 to 2010. Our results implied that the presence of outside directors on the board and the leadership duality have no statistical impact on performance. It seems that severe regulations by the Lebanese monetary authority act as an external governance mechanism. On the contrary, insiders' ownership promotes convergence of the interests of managers/shareholders and shapes the performance of banks. Our findings may well urge Lebanese bankers and regulators towards further development and implementation of governance practices to enhance the performance and the stability of one of the pillars of the Lebanese economy
A parallel proximal splitting method for disparity estimation from multicomponent images under illumination variation
No full textInternational audienceProximal splitting algorithms play a central role in finding the numerical solution of convex optimization problems. This paper addresses the problem of stereo matching of multi-component images by jointly estimating the disparity and the illumination variation. The global formulation being non-convex, the problem is addressed by solving a sequence of convex relaxations. Each convex relaxation is non trivial and involves many constraints aiming at imposing some reg- ularity on the solution. Experiments demonstrate that the method is efficient and provides better results compared with other approaches
Contraintes structurales et dimensionnement en fatigue de jonctions tubulaires soudées
No full textWOSInternational audienceLes jonctions tubulaires, fréquemment employées dans l'industrie offshore, sont soumises en service à des contraintes résultant de chargements élémentaires de traction-compression, flexion dans le plan et flexion hors plan. Ce travail porte sur l'analyse des recommandations classiquement utilisées pour le dimensionnement en fatigue des jonctions soudées lors de l'application de sollicitations combinées. Plus particulièrement, il a porté sur l'étude du comportement en fatigue d'une jonction soudée en T soumise à un chargement de type flexion déviée. Tout d'abord, sur le plan numérique, par la réalisation d'un modèle éléments-finis et la mise en œuvre de méthodes telles que celle proposée par l'IIS, puis, sur le plan expérimental, à travers la réalisation d'essais de fatigue sur ce type de jonctions. Les comparaisons essais/calculs ont montré que l'application de ce type de recommandations ne s'avérait pas systématiquement sécuritaire. Aussi, une démarche visant à prendre en compte le caractère multiaxial des contraintes en pied de cordon de soudure a été mise en œuvre afin de compléter les recommandations visant au dimensionnement des jonctions tubulaires soudées
Mobilité d'un réseau de capteurs sans fil basée sur les méthodes à noyau
No full textInternational audienceLes réseaux de capteurs sans fil ont reçu une attention considérable au cours de la dernière décennie en raison de leur faible coût, de la facilité de leur déploiement et de leur aptitude à être employés pour des techniques de surveillance efficaces. Le présent article propose des schémas de mobilité qui permettent d'améliorer le suivi d'un phénomène physique. A cette fin, les méthodes à noyaux permettent de construire un modèle local pour chaque capteur, dans lequel l'entrée du modèle est la position géographique du capteur et la sortie est l'estimation de la quantité physique à mesurer. Nous montrons que les méthodes à noyaux fournissent un cadre élégant à ce problème d'estimation. Cela nous permet de définir des schémas de mobilité des capteurs pour améliorer l'efficacité des modèles, de façon à minimiser l'erreur d'approximation. Ainsi, plusieurs techniques d'optimisation sont-elles proposées en tenant compte de la première et de la seconde dérivée de l'erreur d'approximation. Les expérimentations réalisées dans ce cadre, visant à estimer la diffusion d'un gaz, montrent la pertinence de la méthode proposée
Numerical simulation of coherent turbulent structures and of passive scalar dispersion in a canopy sub-layer
No full textInternational audienceThis study deals with the problem of turbulent atmospheric boundary-layer flow over a forest canopy. Numerous previous works showed that this flow presents more similarities with a mixing-layer flow than with the standard boundary-layer flow. In this paper, this problem was studied for homogeneous canopies, using large eddy simulation (LES). The numerical results reproduced correctly the various steps of development of this flow: the appearance of a first generation of coherent structures resulting from the development of a primary Kelvin-Helmholtz instability, the reorganization of these structures, by vortex pairing and kinking, the development of a secondary instability and the formation of horseshoe vortices. Then, the process of transport of a passive scalar from a forest canopy into a clear atmosphere was studied in two cases, i.e., when the passive scalar concentration at the surface foliage is either constant or time-varying. Even though this small difference has little influence on the concentration patterns, the results showed that it can significantly affect the concentration magnitude as well as the dynamics of the total concentration in the atmosphere
Biosynthesis and Characterization of Bacterial Cellulose Produced by a Wild Strain of Acetobacter spp.
No full textInternational audienceMany advances in nanomaterials synthesis have been recorded during the last 30 years. Bacterial cellulose (BC) produced by bacteria belonging to the genera Acetobacter, Rhizobium, Agrobacterium, and Sarcina is acquiring major importance as one of many eco-friendly materials with great potential in the biomedical field. The shape of BC bulk is sensitive to the container shape and incubation conditions such as agitation, carbon source, rate of oxygenation, electromagnetic radiation, temperature, and pH. The challenge is to control the dimension and the final shape of biosynthesized cellulose, by the optimization of culture conditions. The production of 3D structures based on BC is important for many industrial and biomedical applications such as paper and textile industries, biological implants, burn dressing material, and scaffolds for tissue regeneration. In our work, wild strains of Acetobacter spp. were isolated from homemade vinegar then purified and used for cellulose production. Four media of different initial viscosity were used. Cultures were performed under static conditions at 29°C, in darkness. The dimensions and texture of obtained bacterial cellulose nanofibers were studied using scanning electron microscopy (SEM). X-ray diffraction (XRD) showed that the biosynthesized material has a cellulose I crystalline phase characterized by three crystal planes. fourrier transform infrared spectroscopy (FTIR) data confirmed the chemical nature of the fibers. Thermo-gravimetric analysis (TGA) showed that BC preserves a relatively superior non-degradable fraction compared to microcrystalline cellulose
Colloque: Savoirs de Frontières: Image, oralité et écriture
No full textColloque: Savoirs de Frontières: Image, oralité et écritureThe primary purpose of this conference is to highlight the links, sometimes invisible, between the image, the orality and and the writing in a multidisciplinary perspective. An open and common space for researchers from different specialties will be the place to share experiences and practices, without restriction or partitioning. Speaking about orality and writing in a world dominated today by images and new technologies may seem simplistic. However, the image, although sovereign hardly exist without words, as demonstrated in so many films. Conversely, poetry can not be understood without an intimate relationship with the imagination of the receiver and often generates images, mental or otherwise, of great richness.Le but premier de ce colloque est de valoriser les liens, parfois invisibles, entre l'image, l'oralité et l'écriture dans une perspective multidisciplinaire. Un espace ouvert et commun aux chercheurs de spécialités différentes permettra de partager des expériences et des pratiques, sans restriction ou cloisonnement. Parler aujourd'hui d'oralité ou d'écriture dans un monde dominé par l'image et les nouvelles technologies peut sembler réducteur. Pourtant, l'image, bien que souveraine, peine à subsister sans les mots et les paroles, comme le démontrent si bien les nombreux films qui se ressourcent des légendes et des mythes ancestraux et qui les réinventent dans un langage contemporain. Inversement, la poésie ne peut se concevoir sans un rapport intime avec l'imaginaire de son récepteur et engendre souvent des images, mentales ou autres, d'une grande richesse