Search results for "Engineering sciences"
showing 10 items of 2347 documents
Frequency Stability Measurement of Cryogenic Sapphire Oscillators with a Multichannel Tracking DDS and the Two-Sample Covariance
2018
This article shows the first measurement of three 100 MHz signals exhibiting fluctuations from 2E-16 to parts in 1E-15 for integration time tau between 1 s and 1 day. Such stable signals are provided by three Cryogenic Sapphire Oscillators (CSOs) operating at about 10 GHz, also delivering the 100 MHz output via a dedicated synthesizer. The measurement is made possible by a 6-channel Tracking DDS (TDDS) and the two-sample covariance tool, used to estimate the Allan variance. The use of two TDDS channels per CSO enables high rejection of the instrument background noise. The covariance outperforms the Three-Cornered Hat (TCH) method in that the background converges to zero "out of the box," wi…
Development of a microwave transduction gas sensor
2013
In this work, we have developed a new gas-sensing transduction based on the propagation of microwave inside a sensitive material to detect atmospheric pollutants at room temperature. First, we present a short overview of the main gas-sensing transduction in the litterature. These techniques operate in frequency ranges different from microwaves. The dielectric permittivity is the main physical parameter in the microwave transduction. The principle is based on the excitation of a sensitive material by a microwave electromagnetic field in a propagative structure. The reflected wave is specific to the excitation's frequency. It depends on the interaction between the sensitive material and the p…
Manufacturing and characterization of Al matrix composites with nano reinforcements via cold spraying
2019
This study aims at developing new routes for manufacturing Al matrix composites (AMCs) strengthened with nano reinforcements by solid-state cold spraying (CS) process. Three different AMCs including CNTs/Al, TiB2/AlSi10Mg and TiB2/7075Al were successfully fabricated by CS of the composite powders prepared using different approaches. The microstructure evolution of as-sprayed composite samples was investigated by means of different characterization methods like X-ray diffraction (XRD), scanning (SEM) and transmission electron microscopy (TEM) and electron backscatter diffraction (SEM/EBSD). The adhesion strength, tribological behaviour, corrosion properties as well as the mechanical performa…
Elaboration de céramiques transparentes Er YAG : synthèse de poudre par co-précipitation et frittage SPS
2013
Yttrium aluminium garnet (YAG, Y3Al5O12) transparent ceramics have attracted much attention since it can replace single crystals as host materials in solid state heat capacity lasers. These polycrystalline ceramics present improved mechanical and spectroscopic properties, as well as a better heat conductivity, lower fabrication costs for larger size materials. Furthermore, it is possible to reach higher doping concentrations as well a uniform distribution. Doping YAG with Erbium (Er:YAG) allows eye-safe emission at 1645nm. Moreover, a low doping rate (0.5%at.) enables upconversion process during laser operation. Conditions for transparency are amongst others, the absence of defects, a high …
Optimisation of metallic interconnects for hydrogen production by high temperature water vapour electrolysis (HTVE)
2012
The high temperature water vapour electrolysis offers a promising method for highlyefficient hydrogen production. It works as an inverse solid oxide fuel cell, using water vapourand electricity in order to produce hydrogen. A major technical difficulty related to hightemperature water vapour electrolysis (HTVE) is the development of interconnects workingefficiently on a long period. From the electrical point of view, the interconnect must have alow contact resistance with the electrodes. Indeed, it directly affects the electrochemicalconversion efficiency (water into hydrogen) and it can penalize the process. The interconnectmust present a slow oxidation kinetics and form as less as possibl…
3D acquisition system for transparent objects
2010
This thesis deals with a new automated tridimensional inspection system for transparent surfaces, based on polarization analysis. We first present an extension of the ‘Shape from Polarization’ method for transparent surfaces. After being reflected, an unpolarized light wave becomes partially linearly polarized, depending on the surface normal and on the refractive index of the media it impinges on. Hence, by measuring the polarization parameters of the reflected light, the surface normals are computed. The ambiguity concerning the normal orientation is solved here with a multispectral lighting system. Finally, the description of the whole acquisition prototype is given as well as some exper…
Contribution à la compréhension de l'influence des paramètres de formulation et de procédé sur la structure et les propriétés fonctionnelle de films …
2012
The aim of this study is the analysis of structure and transfer mechanisms through chitosan based food packaging materials with incorporated carvacrol as a model of antimicrobial active substance. Integration of composition parameters, structure, processing and drying of chitosan systems is correlated to its physico chemical and functional properties. Understanding and detailed analyses of processing parameters is crucial in production of active chitosan coatings applied on conventional materials such as polyethylene. So, the knowledge of composition and microstructure in association to environmental conditions, control the retention and the release kinetics of carvacrol from chitosan film.…
Modélisation numérique d'assemblages collés : application à la réparation de structures en composites
2013
This study is one part of a program of research with regard to the repair of composite structure with extern bonded-patches. The principal objectives of this program are, on one side, the identification of all the factors susceptible to influence the long-term performance of this type of repair, on the other, to determine the extent to which the use of such assemblage can be proved to be an optimal solution. The conception of such a system needs essentially the development of a tool of simulation and of robust prediction because various mechanisms of damage can take place in a very complex way and the final fracture of the system arise from the propagation of damage zones. This study consis…
Study of fatigue behavior of plant fiber reinforced composites : taking into account the variability of properties
2012
The present study focuses on the characterization and comparison of the quasi-static and fatigue properties of flax and glass fibre reinforced composites with an epoxy matrix. An extensive experimental campaign of fatigue tests have been performed using the measured quasi-static tension and in plane-shear properties. It appears that the static and fatigue characteristics of the glass/epoxy composites are higher than that of flax/epoxy ones with similar fibre volume fraction and lay-ups. However, due to the low density of flax reinforcements, the differences between the specific properties of the two materials are low. The measurement of the evolution of the fatigue properties has highlighte…
Détection automatique de chutes de personnes basée sur des descripteurs spatio-temporels : définition de la méthode, évaluation des performances et i…
2013
We propose a supervised approach to detect falls in home environment adapted to location andpoint of view changes. First, we maid publicly available a realistic dataset, acquired in four differentlocations, containing a large number of manual annotation suitable for methods comparison. We alsodefined a new metric, adapted to real-time tasks, allowing to evaluate fall detection performance ina continuous video stream. Then, we build the initial spatio-temporal descriptor named STHF usingseveral combinations of transformations of geometrical features and an automatically optimised setof spatio-temporal descriptors thanks to an automatic feature selection step. We propose a realisticand pragma…