Showing papers by "Grenoble Institute of Technology published in 1997"

A new small-angle X-ray scattering instrument on the French CRG beamline at the ESRF multiwavelength anomalous scattering/diffraction beamline (D2AM)

Abstract: A new small-angle X-ray scattering instrument has been set up on the D2AM-ESRF beamline. This modular instrument, which has the capacity to handle different sample environments (variable temperature and pressure), is designed for easy wavelength changes, i.e. for anomalous-scattering studies. This paper describes its design and discusses in some detail its positioning and alignment with respect to the focusing optics. The mirrors were found to be a major source of diffuse scattering, which was eliminated by rearrangement of the slit positions and refocusing of the optics. The present configuration yields a high flux (10~°photons s -~) and allows measurements down to q = 0.005 ~-1.

On the influence of dislocations on precipitation in an Al-Zn-Mg alloy

Abstract: The influence of predeformation on the precipitation and on the resulting mechanical properties in an Al-Zn-Mg alloy was studied using a combination of complementary experimental techniques, namely transmission electron microscopy, differential scanning calorimetry, small-angle X-ray scattering and microhardness. The thermomechanical treatment was designed to show a significant effect of deformation on the precipitation process. It was observed that the presence of dislocations during precipitation promoted fast nucleation of the equilibrium η phase in the η 2 orientation instead of nucleation of the η' phase with subsequent transformation to η 1 and η 4 outside dislocations. The large growth rate of precipitates lying on dislocations provoked a growing precipitate-free zone around dislocations. This resulted in a lower value of peak hardness and a faster overall coarsening kinetics.

Interfacial reactions and diffusion during the thermal oxidation of titanium in water vapour

Abstract: L'oxydation, a 850°C, du titane dans la vapeur d'eau, beaucoup plus rapide que dans l'oxygene, progresse par transport d 'ions hydroxydes substitutionnels dans TiO 2 depuis l'interface externe jusqu'a l'interface interne. L'hydrogene libere a cette interface se dissout majoritairement dans le metal, stabilisant la phase β-Ti dans laquelle le transport d'oxygene est tres rapide. Ce phenomene fait apparaitre en quantite notable, au moins en debut de reaction, des oxydes de degres inferieurs (Ti 3 O 5 , Ti 2 O 3 ) a l'interface metal-couche de corrosion.

Misfit Dislocations in Limited Inhomogeneous Media: A Review

Abstract: Elastic fields of translation and misfit dislocations (resp. TD's and MD's) are investigated for two types of inhomogeneous materials.

Utilisation des statistiques d'ordre supérieur pour l'analyse d'images texturées

Abstract: In signal processing, High Order Statistics (H.O.S) are more and more used for complex applications such as blind sources separation. In image processing, textures analysis is an application domain where it would be interesting to use H.O.S. The objective of this article is to point out the main advantages and drawbacks of a texture caracterisation by H.O.S. comparing to a classical caracterisation by cooccurrence matrices.

Estimation rapide de vitesse à base de triades de filtres de Gabor

Abstract: The frequential methods for motion estimation in image sequences provide good optical flows, but are reputed to require intensive calculations. We present a new frequential method based on four monodimensional motion estimation. Each 1D estimation is realized by directly combining the energetic responses of a triad of spatiotemporal Gabor filters. This model has two fundamental properties : it represents an important link in the processing chain of the visual system, and it constitutes a fast and efficient algorithm.

Décorrélation de sources large bande en traitement d'antenne actif à haute résolution

Abstract: High resolution eigenstucture-based techniques for signal sources localization are known to be ineffective in the presence of highly correlated signals. This is even worse for active methods, i.e. when the received signal is composed of time-delayed ampitude-weighted replicas of a single signal, the emitted one. In order to avoid such difficulties, a technique which enables high resolution active methods to correctly localize all signal sources irrespective of their correlation is presented here.

Thermal oxidation resistant surface alloys processed by laser alloying on Z38CDV5 ferritic steel

Abstract: Des alliages de surface ont ete elabores sur un acier ferritique faiblement allie (Fe - 0,38% C - 5% Cr - 1% Si - 0,8% Mo - 0,5% V, pourcentages massiques) par irradiation laser assurant la fusion et la dissolution d'un predepot. Tous les predepots utilises (silicium, nitrure de silicium Si 3 N 4 ou carbure de chrome Cr 3 C 2 ) ont permis, apres optimisation, d'obtenir des alliages de surface dont l'oxydation dans l'oxygene entre 850 et 950°C fournit une couche protectrice de Cr 2 O 3 . La remarquable tenue en cyclage thermique semble resulter de la diffusion essentiellement anionique dans cet oxyde.

Non-linear representations, sensor reliability estimation and context-dependent fusion in the audiovisual recognition of speech in noise.

Abstract: The paper involves the recognition of French audiovisual vowels at various signal-to-noise ratios (SNRs). It deals with a new non-linear preprocessing of the audio data which enables an estimation of the reliability of the audio sensor in relation to SNR, and a significant increase in the recognition performances at the output of the fusion process.

Silver‐Gold Alloys Prepared by Pulse Plating Modeling of the Chemical Composition

Abstract: The individual and simultaneous deposition of silver and gold from low cyanide concentration solutions showed two regions in the potentiodynamical j-E curves. At low overpotentials, these processes take place through adsorbed species while at high overpotentials the normal diffusional region is observed. Then, when pure silver and gold deposits are prepared by galvanostatic pulse plating, the presence of adsorbed species cannot be disregarded. This phenomenon prevails and has an important effect when silver and gold are simultaneously deposited by pulse plating. Therefore, the chemical composition of the alloys is described by a model in the activation region while another model was deduced for the diffusional region. The models take into account typical parameters of pulse plating and were developed by application of the statistical experimental design methodology.

Optical interference effects in noncoherent all-optical networks for signal processing

Abstract: Optical delay-line networks are investigated for electrical signal filtering applications. Results concerning the microwave frequency response of some basic structures such as unbalanced Mach-Zehnder interferometers and ring resonators based on fiber-optic components are briefly summarized. We report the microwave performance of some integrated unbalanced Mach-Zehnder interferometers fabricated in glass by a silver ion-exchanged process. These devices can be used as microwave notch filter in the 1.5 GHz - 15 GHz range. At the resonance frequencies, a rejection depth of over 30 dBe was obtained. Furthermore, we focus on the interference effects of the light carrier which can occur, even in the incoherent regime, when basic structures are cascaded in order to perform complex filtering responses. These include the role of optical phase shift and polarization dependence. A new transfer matrix analysis is introduced for modeling the microwave response of cascaded devices showing good agreement with experiments.

Détection et contrôle par filtrage adaptatif des zones de frontière dans des images multitexturées

Abstract: The classical balance in automatic segmentation of images is the formation of regions and the detection of frontiers. In the case of textured images, this dual processing is realised in a multidimensional space described by the way of the textures features. Here, the considered features are the energies computed through a bank of oriented band pass filters (2D Gabor filter) and then locally spatially integrated. The spectral characteristics of the frontier areas are studied to derive a simple regularisation mechanism where it is possible to both decrease the incertitude in the localisation of a frontier and keep a good formation of homogeneous regions. This is done by an adaptive spatial integration of the feature energies.