CuAl single crystals of a low stacking fault energy have been deformed along the〈111〉 direction in an apparatus which consists of a compression machineinterfaced with an atomic force microscope. The emergence process of dislocations hasbeen in situ studied during deformation. Plasticity occurs in this material bypropagation of Shockley dislocations which generate two possible kinds of stackingfaults, extrinsic or intrinsic. The fine structure of slip lines has been investigatedby atomic force microscopy. A differentiation between these two possible twin mechanisms in this alloy is attempted. It is concluded that twinning in this materialcan not only be explained by the intrinsic stacking faults and that the contributionof extrinsic faults has to be considered.

In this paper, a simple model classically used to describe electrical behavior in conducting polymers can take into account transport properties in polyaniline dopedwith two different counter-ions and in polyaniline-polystyrene blends. Conduction isMaynly limited by hopping or tunneling between polaronic conducting clusters. When thestructural disorder is less pronounced, a metallic contribution can occur near roomtemperature in series with the hopping/tunneling one. This heterogeneous picture usedfor unblended polyaniline can be applied to explain electrical blend properties abovethe percolation threshold when conduction occurs among completely connectedpolyaniline paths. Below the percolation threshold, the model has to take into accountan additional contribution due to a hopping mechanism between large disconnectedsegments of polyaniline. It is shown that thermoelectric power reflects essentiallythe metallic behavior of the conducting clusters.

The effective electrical conductivity of a two-phase material consisting of a lattice of identical spheroidal inclusions in a continuous matrix is determined analytically. The inclusions are located at the node points of asimple-cubic lattice and the axis of rotation of each spheroid coincideswith one of the lattice vectors, such that the spheroids are aligned witheach other and with the lattice. With an electric field applied in thedirection of the rotation axes of the spheroids, the electric potential isfound by solving Laplace's equation. The solution is found by analyticallycontinuing the interstitial field into the particle domain and replacing theparticles with singular multipole source distributions. This yields anexpression for the potential in the interstitial domain as a multipoleexpansion. Using Green's theorem, it can be shown that only the firstcoefficient in this expansion is required to determine the effectiveconductivity of the composite. The coefficients are determined by applyingcontinuity conditions at the particle-matrix boundary and, in a novelapproach, this is achieved by transforming the multipole expansion into anexpansion in spheroidal harmonics. Results for spheres and prolate andoblate spheroids are compared with experimental data and previoustheoretical work, and excellent agreement is observed.

The dielectric properties of heterogeneous materials for various condensed-mattersystems are important for several technologies, e.g. impregnated polymers forhigh-density capacitors, polymer carbon black mixtures for automotive tires and currentlimiters in circuit protection. These multiscale systems lead to challenging problemsof connecting microstructural features (shape, spatial arrangement and sizedistribution of inclusions) to macroscopic materials response (permittivity,conductivity). In this paper, we briefly discuss an ab initio computationalelectrostatics approach, based either on the use of the field calculation packageFLUX3D (or FLUX2D) and a conventional finite elements method, or the use of the fieldcalculation package PHI3D and the resolution of boundary integral equations, forcalculating the effective permittivity of two-component dielectric heterostructures.Numerical results concerning inclusions of permittivity ε 1 with variousgeometrical shapes periodically arranged in a host matrix of permittivityε 2 are provided. Next we discuss these results in terms ofphenomenological mixing laws, analytical theory and connectedness. During the pursuitof these activities, several interesting phenomena were discovered that will stimulatefurther investigation.

The reflectivity of two-dimensional pyramidal absorbers and the transmittance of photonic crystals made of dielectric fibers is analyzed by means of two approaches. In the first one an integral representation of the scattered field is used and the absorbers are modeled by a stack of gratings of infinite extent. In the second approach, the absorbers and the crystal are replaced by an equivalent multilayered medium obtained by means of two homogenization methods. We assess the efficiency of these methods with respect to parameters such as the density of the gratings, their relative permittivity and the polarization of the incident wave.

A numerical scheme is presented to compute the response of a composite material to an applied field. The scheme is based onan iteration that uses a Fourier transform based projection method to compute the response of a reference material to the applied field, and a contraction mapping to relate the response of thereference material to the response of the composite material.The scheme also utilizes nested uniform grids to improve performance, and to evaluate the refinement of the grid.

The key idea of this work is application of the concept of magnetic groups and Curie's principle to the tensor description of complex and bianisotropic media. It is shown how to find the symmetry group of the media under external perturbation and to calculate the structure of the constitutive tensors starting from the symmetry of the medium. The theory may be used as a first step in the problem of new artificial material synthesis.

The magnetic field of an annular MHD thruster made of independent superconductingmodules has been studied with analytical and numerical methods. This configurationallows to obtain large magnetized volumes and high induction levels with rapidlydecreasing stray fields. When some inductors are out of order, the thruster reMaynsstill operational, but the stray fields increase in the vicinity of the failure. Forgiven structural materials and superconductors, it is possible to determine the sizeof the conductor in order to reduce the electromagnetic forces and the peak fieldsupported by the conductors. For an active field of 10 T in a 6 m ray annular activechannel of a thruster with 24 modules, the peak field is exactly 15.6 T in theNb3Sn conductors and the structure has to sustain 108 N/m forces. The necessityto place some magnetic or superconducting shield is discussed, particularly when the thruster is in a degraded regime.

Electrical traction of vehicle needs accurate control of torque and flux. DC machinesare Maynly used but they are expensive and need heavy Mayntenance. Since some years,the use of field oriented vector control induction machines allows to fulfill the sameobjectives with lower cost. Unfortunately, they may present a decrease of their performances and an instability when their parameters vary with the temperature or the magnetic state and in the presence of converter or measurement noises. Therefore it isnecessary to design effective control laws, which are especially less sensitive to these perturbations and variations. In this work, we have undertaken the conception andthe realization of a voltage vector flux control whose inputs have been uncoupled bycompensating terms. The torque and the flux regulations are realized at two differentlevels: an internal regulation loop for stator currents, and an external one for fluxand torque. In order to achieve robust stability and performance objectives, we haveinvolved several new methods in the doMayn such as H ∞ control designed bygenetic algorithms and reduced order extended Kalman filtering in the synchronousframe. Simulations will show the method efficiency and experimental results validatethe control strategy.

This article deals with a general method for finding the equations of the dynamicresponse of a bimorphous piezoelectric structure through a variational formulation.First, a method of resolution is proposed then a general electric equivalent circuitinvolving the design parameters of the device is deduced, followed by the description ofapplication to a travelling-wave stator.

This study concerns the multiple scattering of light in random granular systems and the analysis of the image formed by the light scattered by a random medium. We developed an imagery method with high grey level resolution for visualization and analysis of the intensity profile in the backscattering spot image. We further present statistical models for the radiative transfer in granular media only involving the photon mean path length, the asymmetry factor and the absorption probability of photons. A renormalization of the photon trajectory in the medium gives a photon transport equation for anisotropic scattering and leads to an analytical expression for the intensity profile in the backscattering spot. We finally compare the results from imagery experiments with the predictions from numerical simulations and statistical models.

A study on Au/n-Si Schottky barrier diodes (SBDs) parameters with andwithout thin native oxide layer fabricated on n-type Si grown by LPE (Liquid-PhaseEpitaxy) technique has been made. The native oxide layer with different thicknesses onchemically cleaned Si surface was obtained by exposing the Si surfaces to clean roomair before metal evaporation. The native oxide thicknesses of samples D2, D3, D4 andD5 are in the form D2 < D3 < D4 ≤ D5 depending on the exposing time. It has been seenthat the value of the barrier height Φ b of samples D2 (0.64 eV), D3 (0.66 eV), D4(0.69 eV) and D5 (0.69 eV) increases with increasing the exposure time and tends tothat of the initial sample D1 (the initial sample, 0.74 eV), and thus also their I − Vcurves. Especially, the experimental results related to the exposure time of thesurfaces to clean air are close in agreement with recently results reported for theHF-treated n-Si surface during initial oxidation in air. Furthermore, it has beendetermined experimentally that ageing of the Au contacts on the oxidized epilayer Sileads to barrier height values close to those measured for Au on chemically cleanedsurfaces.

Results on the stability regions of alpha (α) to gamma (γ) transition for CO2 gas laser mixture 3He:1CO2:1N2 RF capacitative dischargeswith and without the addition of Xe are presented in terms of current, voltage andpower characteristics. Measurements have also been made of the mean electron energy,neutral gas temperature and time averaged visible emission for different electrodeseparations, frequencies and intermediate pressures. It is found that the Xe additionhas increased the neutral gas temperature and transition input power, while it hasdecreased the mean electron energy and transition voltage. The time averaged visibleemission has shown strong CO and NO emission from the discharge.

The generalized impedances allow to characterize a one-way thermal system whose two faces are accessible. From experimental measurements of the flux densities and variations in temperature in the access faces of a homogeneous material, the two generalized impedances of storage and transfer are calculated in the frequential field. The theory of the thermal quadripole enables to determine a theoretical expression of these impedances. After a sensitivity study which underlines the accessible parameters and the optimal frequency band, an optimization procedure of the setting of the ideal model of one of the two impedances on the corresponding experimental curve allows to identify the effusivity and the thermal diffusivity of material. The method is applied to the study of a sand with three water contents.