Modélisation de la vitesse de séchage du maïs

Cet article consiste à présenter un autre modèle appliqué à la détermination de la vitesse de séchage du produit hygroscopique. Ce modèle est obtenu par la ressemblance entre la cinétique chimique et la cinétique de séchage. L’intérêt de ce présent travail c’est de trouver un modèle simple, facile et fiable pour caractériser la vitesse de séchage du produit. En adoptant ce modèle, nous avons obtenu un autre modèle mathématique de la cinétique de séchage du maïs. Nous validons le modèle adopté par rapport à l’autre modèle, nous observons que les résultats sont en accords.Mots-clés : Modèle, vitesse séchage, cinétique de séchage, produitshygroscopiques, maïs

Direct overlapping effect of f orbitals for valence fluctuating materials in Kondo regime

75.20.Hr Local moment in compounds and alloys; Kondo effect, valence fluctuations, heavy fermions, 75.30.Mb Valence fluctuation, Kondo lattice, and heavy-fermion phenomena, 71.28.+d Narrow-band systems; intermediate-valence solids,

IrPd nanoalloys: simulations, from surface segregation to local electronic properties

SSCI-VIDE+ECI2D+LPIInternational audienceUsing semi-empirical modeling, namely tight-binding at different levels of accuracy, the chemical, crystallographic, and electronic structures of bimetallic IrPd nanoparticles are characterized. For the purpose, model cuboctahedral particles containing 561 atoms are considered. Atomistic simulations show that core-shell nanoparticles are highly stable, with a strong surface segregation of Pd, at least for one atomic shell thickness. Within self-consistent tight-binding calculations founded on the density functional theory, an accurate insight is given into the electronic structure of these materials which have a high potential as catalysts

Electronic structure model for single B, C or N adatoms upon graphite

An extra-orbital tight-binding scheme and a repulsive Born-Mayer model are used to determine the total adsorption energy of a 2p adatom (B, C or N) at the surface of graphite. The corresponding electronic structure of the adsorbed atom is deduced for the most stable (hollow) position. Our model allows us to exhibit an increase of the local density of states on the adatom and a decrease of charge transfer (from adatom to carbon) when going from boron to nitrogen

DFT study of BaTiO 3 (001) surface with O and O 2 adsorption

Progress of scanning tunneling microscopy (STM) allowed to handle various molecules adsorbed on a given surface. New concepts emerged with molecules on surfaces considered as nano machines by themselves. In this context, a thorough knowledge of surfaces and adsorbed molecules at an atomic scale is thus particularly invaluable. In this work, within the framework of density functional theory (DFT), we present an electronic and structural ab initio study of a BaTiO 3 (001) surface (perovskite structure) in its paraelectric phase. As far as we know the atomic and molecular adsorption of oxygen at surface is then analyzed for the first time in the literature. Relaxation is taken into account for several layers. Its analysis for a depth of at least four layers enables us to conclude that a reasonable approximation for a BaTiO 3 (001) surface is provided with a slab made up of nine plans. The relative stability of two possible terminations is considered. By using a kinetic energy cut off of 400 eV, we found that a surface with BaO termination is more stable than with TiO 2 termination. Consequently, a surface with BaO termination was chosen to adsorb either O atom or O 2 molecule and the corresponding calculations were performed with a coverage 1 on a (1×1) cell. A series of cases with O 2 molecule adsorbed in various geometrical configurations are also analyzed. For O 2, the most favorable adsorption is obtained when the molecule is placed horizontally, with its axis, directed along the Ba-Ba axis and with its centre of gravity located above a Ba atom. The corresponding value of the adsorption energy is -9.70 eV per molecule (-4.85 eV per O atom). The molecule is then rather extended since the O–O distance measures 1.829 Å. By comparison, the adsorption energy of an O atom directly located above a Ba atom is only -3.50 eV. Therefore we are allowed to conclude that the O–O interaction stabilizes atomic adsorption. Also the local densities of states (LDOS) corresponding to various situations are discussed in the present paper. Up to now, we are not aware of experimental data to be compared to our calculated results. Copyright EDP Sciences/Società Italiana di Fisica/Springer-Verlag 200773.20.Hb Impurity and defect levels; energy states of adsorbed species, 71.15.Mb Density functional theory, local density approximation, gradient and other corrections,

Intercalation of graphite and hexagonal boron nitride by lithium

Although graphite and hexagonal form of BN (h-BN) are isoelectronic and have very similar lattice structures, it has been very difficult to intercalate h-BN while there are hundreds of intercalation compounds of graphite. We have done a comparative first principles investigation of lithium intercalation of graphite and hexagonal boron nitride to provide clues for the difficulty of h-BN intercalation. In particular lattice structure, cohesive energy, formation enthalpy, charge transfer and electronic structure of both intercalation compounds are calculated in the density functional theory framework with local density approximation to the exchange-correlation energy. The calculated formation enthalpy of the considered forms of Li intercalated h-BN is found to be positive which rules out h-BN intercalation without externally supplied energy. Also, the Li(BN)3 form of Li-intercalated h-BN is found to have a large electronic density of states at the Fermi level and an interlayer state that crosses Fermi level at the zone center; these properties make it an interesting material to investigate the role of interlayer states in the superconductivity of alkali intercalated layered structures. The most pronounced change in the charge distribution of the intercalated compounds is found to be charge transfer from the planar σ states to the π states