Diffusion rayleigh : Influence de la température sur ‘L'aile collisionnelle’ des liquides moléculaires

The purely numerical computation of defect induced properties in polymers currently in use is time consuming since symmetry arguments cannot be exploited. Within the framework of Lifshitz's Green Function method, symmetry arguments well known from the treatment of chemical defects may be used for conformational defects, too, to reduce the computational work drastically.

With this objective in mind, conformational defects are classified with respect to their local symmetry in a single polyethylene (PE) chain and, for irregular PE skeletons, the defect matrix is set up in terms of appropriate symmetry states. The defect matrix of a gauche position in an otherwise transplanar PE backbone is explicitly given and the projected densities of states of this system are calculated. The applicability of optical selection rules, obtained from local symmetry, to bulk PE is briefly discussed.     

Etude théorique de la durée de vie radiative du triplet métastable de quelques composés carbonylés

Les paramètres de phosphorescence (force d'oscillateur et durée de vie), sont déterminés théoriquement pour quelques composés carbonylés (formaldéhyde, benzaldéhyde, acétophénone, propiophénone, 2,4,5-triméthylbenzaldéhyde, et 3,4-diméthylacétophénone). La fonction d'onde de l'état singulet fondamental est obtenue à l'aide d'un calcul SCF utilisant la méthode CNDO/S de Del Bene et Jaffé. Les fonctions d'onde, les énergies et les moments de transition dipolaire électrique S_I ←S ₀ et T_J ←T ₁ sont déterminés à l'aide d'une interaction portant sur des configurations mono et diexcitées par rapport à l'état singulet fondamental.

Les paramètres de phosphorescence sont calculés en utilisant une approximation monocentrique et monoélectronique de l'opérateur hamiltonien de couplage spin-orbite. Cette approximation est justifiée par la comparaison des résultats obtenus avec les valeurs expérimentales, compte tenu de la concordance entre les conditions d'expérience et les hypothèses de calcul.     

Etude spectrale d'une famille d'opérateurs non-symétriques intervenant dans la théorie des champs de reggeons

In this paper, we study a few spectral properties of a non-symmetrical operator arising in the Gribov theory. The first and second section are devoted to Bargmann's representation and the study of general spectral properties of the operator: $$\begin{gathered} H_{\lambda ',\mu ,\lambda ,\alpha } = \lambda '\sum\limits_{j = 1}^N {A_j^{ * 2} A_j^2 + \mu \sum\limits_{j = 1}^N {A_j^ * A_j + i\lambda \sum\limits_{j = 1}^N {A_j^ * (A_j + A_j^ * )A_j } } } \hfill \\ + \alpha \sum\limits_{j = 1}^{N - 1} {(A_{j + 1}^ * A_j + A_j^ * A_{j + 1} ),} \hfill \\ \end{gathered}$$ whereA* _j andA _j ,j∈[1,N] are the creation and annihilation operators. In the third section, we restrict our study to the case of nul transverse dimension (N=1). Following the study done in [1], we consider the operator: $$H_{\lambda ',\mu ,\lambda } = \lambda 'A^{ * 2} A^2 + \mu A^ * A + i\lambda A^ * (A + A^ * )A,$$ whereA* andA are the creation and annihilation operators. For λ′>0 and λ′²≦μλ′+λ². We prove that the solutions of the equationu′(t)+H _{λ′, μ,λ} u(t)=0 are expandable in series of the eigenvectors ofH _λ′,μ,λ fort>0. In the last section, we show that the smallest eigenvalue σ(α) of the operatorH _{λ′,μ,λ,α} is analytic in α, and thus admits an expansion: σ(α)=σ₀+ασ₁+α²σ₂+..., where σ₀ is the smallest eigenvalue of the operatorH _{λ′,μ,λ,0}.     

Effets comparés des impuretés de terres rares sur la résonance ferrimagnétique et la relaxation nucléaire dans le grenat de fer et d’yttrium

The anomalous properties of impure yttrium iron garnet are related to the susceptibilities of the rare earth ions which it contains. The susceptibilities are calculated assuming a slow relaxation. It is shown that the success of the theory of “slow relaxation” requires the existence of a coupling between the transverse magnetization of the iron lattice on the one hand, and components of the magnetic moments of the rare earth ions, with non zero diagonal matrix elements, on the other hand. The temperature variations of the ferrimagnetic linewidth and the nuclear relaxation time are compared.     

Étude théorique des transferts couplés de chaleur et de masse lors de la désorption du couple zéolithe 13X-eau

A mathematical model based on scale changing has been established, in order to study heat and mass transfers in a zeolithe bed during water desorption. The model has been solved numerically by the finite-volume method, for the case of two-dimensional transfers. The numerical simulation is used to present the time-space evolution of the solid temperature, the pressure and the moisture content in the reactor and to determine the sensitivity to some parameters (heating temperature, outlet temperature, heat coefficients and reactor geometry). The effects of the particle diameter, the kinetic constant of desorption as well as the effective thermal conductivity are discussed.     

Theorie statistique des alliages metalliques binaires liquides a l'aide d'une methode de groupes de sites—Analyse de l'ordre local: II. Application a des alliages présentant une courbe d'enthalpie libre de mélange dissymétrique par rapport à la concentration

The model proposed in the preceding article is modified as to explain the non-symmetry of the enthalpy of mixing. Studied alloys are supposed to be compound-forming alloys so that the local order is modified. The structure of the compound is assumed to be A₃B.     

Commande floue et thermique du bâtiment. Proposition d'une loi de chauffe adaptée à la régulation des bâtiments de type tertiaire à occupation discontinue

Fuzzy control and thermal properties of buildings: proposition of a heating law fitting the regulation of tertiary buildings with intermittence. In this article, we start with a general presentation of thermal regulation in buildings and of fuzzy logic applied to the control. Then, thanks to the numerical simulation of a building, we show why regulators based on the use of a straight line heating law are not adapted to the practice of intermittence. The command law we propose is based on fuzzy control. It takes into account both the exterior temperature and the thermal state of the building we estimate by means of the same function whatever the building. Simulating the opening of a window, we show that the closing degree of the regulation loop is very weak. The inference system incorporates constraints upon the conclusions which allow to do an off-line learning from the second week (respect of the open-loop) without any risk of obtaining an aberrant power because of a non-learned rule. The regulation we obtain limits considerably the disfunctioning caused by the open-loop control with intermittent regime. We conclude upon the interest of fuzzy control as regards to the temperature regulation of complex dynamic systems.