The problem of bidirectionality in bianisotropic media, i.e. existence of plane eigenwaves propagating forwards and backwards along a certain direction with the same propagation factor is discussed. It is shown that bidirectionality in bianisotropic media exists for the following directions: (1) perpendicular to a plane of symmetry, (2) perpendicular to a proper axis, (3) along an improper axis, (4) parallel to an antiplane, (5) along an antiaxis of symmetry.

We have studied the effect of thickness on the structural, optical and electrical properties of In2O3:Sn (ITO) thin films. Two series of ITO thin films have been deposited onto glass substrates by DC sputtering at two partial pressures of oxygen (ppo): 4 × 10−4 and 4.75 × 10−4 mbar. Each series consists of samples with thickness ranging from 306 nm to 1440 nm. We observed a change of texture with thickness; the thinner films grow with a 〈111〉 preferred orientation; however as the thickness increased, the preferred orientation becomes in the 〈100〉 direction. The lattice constant and the grain size have also been obtained from the X-ray spectra. The energy gap, Eg, has been obtained from the transmission curve; Eg is found to decrease with increasing thickness for both series. The electrical resistivity ρ has been studied as a function of thickness, ppo and temperature (T). The temperature was varied from room temperature (RT) to 450 °C and back to RT; a hysteresis effect was observed in the ρvs.T curve. Also, a minimum in ρ was observed, in all these samples, in the temperature range 260 to 280 °C. For these temperatures, we have studied the effect of annealing time on the electrical resistivity for samples having both textures. We noted that ρ increased with annealing time and reaches a saturation value equal to the RT temperature value. Hall effect experiments were done on all these samples. The concentration n and the mobility μH were obtained. These parameters are found to be sensitive to the thickness and the texture of these films. All these results will be correlated and discussed.

Due to the fast development of microelectronics, quite an important number of the chemical aspects of component formation has been occulted. In particular just a few studies are related to thin film formation in the scope of chemical reactions and modelisation. Thermodynamics itself has been implemented rather ponctually and in an incomplete way. One of the Mayn reasons for this is that thin films are considered as standingly non equilibrium systems and that. thermodynamics, as a macroscopic science, has Maynly been considered as inadequate. Thus, we have decided to reconsider the problem of thin films formation from a strictly chemical point of view.Using a simple system (formation of silicon nitride on monocrystalline silicon), the chemical reactions have been investigated. Classical thermodynamics, though inaccurate and approximate for such systems is necessary to develop the first steps of a thermodynamical model describing the deposit formation. Using a computer program helping a global treatment of several chemical reactions confirms the conclusions obtained by classical thermodynamics. We have discussed the insufficiency of the classical model, and shown that, with respect to what was experimentally observed, it was nevertheless globally valid, and that the nitride formation should be regarded as a superposition of classical chemical reactions that occurred in "close to the equilibrium" states and globally following the classical laws of thermodynamics. Thus, we propose a model of formation for the first mono layer of Si3N4 on monocrystalline silicon which is in total agreement to experimental observations.

This study deals with the application of sliding mode control theory to induction machine fed by a PWM voltage source inverter in which the system operates in the field oriented control. Thus, after determining the decoupled model of the machine, a set of simple surfaces have been applied to a cascade structure and the associated control laws have been synthesized. Furthermore, in order to reduce chattering phenomenon, smooth control functions with appropriate threshold have been chosen. Simulation study is conducted to show the effectiveness of the proposed method and then validated by an experimental prototype.

The aim of this work consists in presenting a simple modelling (the molecular collision theory), easily usable in an industrial environment in order to predict the evolution of thermodynamical characteristics of the combustion of two-phase mixtures in a closed or a vented vessel. Basic characteristics of the modelling have been developed for ignition and combustion of propulsive powders and adapted with appropriate parameters linked to simplified kinetics. A simple representation of the combustion phenomena based on energy transfers and the action of specific molecules is presented. The model is generalized to various mixtures such as dust suspensions, liquid fuel drops and hybrid mixtures composed of dust and a gaseous supply such as methane or propane in the general case of vented explosions. The pressure venting due to the vent breaking is calculated from thermodynamical characteristics given by the model and taking into account, the mass rate of discharge of the different products deduced from the standard orifice equations. The application conditions determine the fuel ratio of the used mixtures, the nature of the chemical kinetics and the calculation of a universal set of parameters. The model allows to study the influence of the fuel concentration and the supply of gaseous additives, the influence of the vessel volume (2400ℓ ≤ Vb ≤ 250 000ℓ) and the influence of the venting pressure or the vent area. The first results have been compared with various experimental works available for two phase mixtures and indicate quite correct predictions.

For power applications, AlGaAs/GaAs heterojunction bipolar transistors (HBT's) were found to present high efficiency and linearity at high density RF power. We report power performances in S-band of a 6 × 60 µm2 one emitter finger HBT fabricated in our laboratory. At 1.8 GHz, when tuned for maximum efficiency, each transistor delivered a CW output power of 0.5 W (150 kW/cm2) and a power-added efficiency of 62% and 80% in class AB and C operation respectively. The physical model based on technological and measured parameters incorporates temperature dependence for most of its parameters. It has been easily used to analyse DC and RF power characteristics in class AB mode and to determine input and output optimum matching cells. Good agreement between simulated and experimental results support the validity of the model.

Dans une première partie nous avons développé un modèle d'analyse pluridisciplinaire qui établissait les dépendances fonctionnelles entre les variables de conception et les performances magnéto-électro-thermiques d'un moteur brushless à aimants permanents. Dans cet article nous décrivons une procédure de dimensionnement adaptée à la conception de la machine alimentée à fréquence variable sous faible tension. L'objectif est d'intégrer la dynamique du convertisseur électronique dès la phase initiale du dimensionnement, au même titre que les spécifications électromécaniques et thermiques. La procédure est gérée par une méthode d'optimisation déterministe de type Programmation Quadratique Séquentielle. Elle intègre l'influence du convertisseur au moyen de deux spécificités : la première consiste à évaluer les fonctions du problème d'optimisation sur la base du module d'analyse pluridisciplinaire ; la deuxième permet de contrôler l'évolution du dimensionnement au travers de variables d'optimisation dont la liste inclut les consignes de la commande en courant du convertisseur. Les difficultés d'optimisation liées au mode de fonctionnement discret du convertisseur sont discutées au regard du calcul de la sensibilité du couple électromagnétique envers la consigne de courant du convertisseur ; une méthode est proposée pour assurer la robustesse de la procédure en présence du convertisseur. L'application porte sur le dimensionnement d'un moteur à aimants permanents de type “brushless trapézoïdal" destiné à la traction d'un scooter électrique ; l'évolution de la structure optimale avec le degré de complexité du module d'analyse est mise en évidence.

The unsteady forced convection involved in incompressible laminar boundary-layer over a semi-infinite plate is investigated. Initially, a steady state convective heat transfer with constant plate temperature or constant plate heat flux is established between the plate and the flow. By differential method, we study the thermal effect on this first state of a positive or a negative sudden change in either the plate temperature or plate heat flux. Numerical solution of differential equations is obtained for the whole transient from the initial steady state to the final one. Detailed results of the effect of the wall conditions change on the transient process are given for the fluids encountered in the usual applications (0.6 ≤ Pr ≤ 100). An exponential law of the instantaneous heat coefficient is deduced as function of Pr in the said Prandtl number range.

In this paper, a mathematical model of the mechanical behaviour of prosthetic blood vascular structures is analysed when taking into account effects of finite deformations, residual stresses which can be induced by fabrication processes and the composite nature of the material constituting those structures. The case of particular applied strains, viewed as arising during surgical manipulation and implying axial and circular shear stresses, is also studied. The resulting distribution of stresses within the wall shows large gradients which can be reduced when the effects of adequate pre-existing initial stresses are present.

Due to technical errors, the figures have been badly printed. We publish entirely the article herein, sincerely apologizing to the authors for the unpleasant inconvenience.

We present a set of complementary experimental and numerical tools for studying miscible fluid displacements in porous media with large scale heterogeneities. Experiments are realized in transparent 2D Hele-Shaw cells allowing optical observations and in 3D packings of glass beads with an acoustical technique for imaging fluid displacements. Permeability heterogeneities are modeled by spatial variations of either the local aperture of the Hele-Shaw cell or the diameter of the grains used in the packing. The Hele-Shaw cell model provides high resolution maps of the invasion front location at regular time intervals and of the flow lines: the velocity field is determined by combining these informations. Acoustical images of relative concentration distributions in the 3D packing are in agreement with Hele-Shaw cell data and can be obtained in a broader range of experimental situations. Such experiments realized with a stabilizing density contrast between invading and displaced fluids demonstrate a strong reduction of the front width at low flow velocities, a similar reduction is obtained at high velocities with a stabilizing viscosity contrast. The technique is also applicable to study fluid displacements in natural opaque media. Numerical simulations by a Boltzmann lattice technique using a Stokes-like diffusive term to smooth out the effect of permeability discontinuities provide complementary informations. They are shown to give similar results as experiments for same flow parameter values and to allow for a fast exploration of a broad range of fluid properties and flow situations.