Liste des documents
Reconstruction of Pulsed Ultrasonic Fields Received by a hydrophone of rectangular aperture by application of inverse methods.
In order to carry out reliable measurements of pulsed ultrasonic fields, the use of a piezoelectric hydrophone as receiver is recommended. However, due the finite size of the receiver aperture the measured acoustic pressure is affected by spatial averaging. The output signal may also be distorted because of the frequency variations of its transfer function. The aim of this work is to deconvolve the spatio-temporal effects of the receiving chain (hydrophone, cable, oscilloscope...) in order to reconstruct the pulsed ultrasonic field with higher spatial and temporal resolution. This constitutes an inverse problem, which has been encountered in various domains of physics. The possibility of deconvolving the spatial effects has been shown for harmonic ultrasonic fields. The present contribution is a generalization of the study to pulsed ultrasonic fields. For that, three methods allowing the inversion of the aperture effect are tested 1) Wiener’s method 2), the power spectral equalization method (PSE), and 3) the maximum a posteriori method (MAP). The obtained results show that the three methods are able to reconstruct the ultrasonic field from the spatially averaged values and the quality of the reconstruction depends strongly upon the SNR, the hydrophone dimensions and the axial distance to the source. Voir les détails
Mots clés : pulsed ultrasonic fields, Wiener’s method, the power spectral equalization method (PSE), the maximum a posteriori method (MAP).
ELECTROCHEMICAL STUDY OF THE INHIBITORY EFFICACY OF TWO SCHIFF BASES SYNTHESIZED TOWARDS THE CORROSIONOF STEEL IN CONCRETE.
Corrosion of Reinforcement is a major factor limiting the life of reinforced concrete buildings. The steel in concrete can corrode when many aggressive substances penetrate into the pores of concrete containing oxygen. Various methods exist to pr otect the steel against corrosion. These methods include the use of corrosion inhibitors which is a means of protection very easy and effective. The research on the protection of steel against corrosion showed that a large number of inhibitors are organic species containing in their structure elements such as nitrogen, oxygen and sulfur. Schiff bases whose applications are very numerous are recently used and the results are very satisfactory in the solution simulating the pore water in interface (frame / concrete). For this and for the same purpose, we synthesized, characterized and st udied the inhibitory power of two Schiff bases and their initial products of synthesis: • 1, 2-dehydroacetic acid ethylene diamine (H2 L1) ; • 1, 2-dehydroacetic acid amino naphtol (H2 L2) ; • Dehydroacetic acid (DHA) • 3-amino -2-Naphtol (Amine) towards the corrosion of construction steel. The elect rochemical parameters and characteristics of the corrosion were determined by cyclic voltammetry exploiting Tafel curves by Volta Masters 4 software. The study of the corrosion inhibition by these organic compounds has led to the conclusion that they have high level of inhibition rate. Compounds (H2 L1) and (H2L2) which are original and their starting materials of synthesis show an inhibition rate close to 70% at a concentration of 10-6M for each of them in the concrete environment after four months. After seven months of immersion of rebar in concrete, the results of mechanical tests show that the compound (H2L1) improves the mechanical strength of the concrete structure but DHA affects it. This behavior can be explained by the formation of bonds between metal sites and the free electron pairs of oxygen and nitrogen. The results confirm that the structure of these heterocyclic compounds do not affect the effectiveness of inhibition of corrosion of steel in concrete. Voir les détails
Mots clés : Schiff bases, corrosion, inhibitor, concrete, 1, 2-dehydroacetic acid ethylene diamine, 2-dehydroacetic acid amino naphtol, DHA, 3-amino -2-Naphtol
ELABORATION DE COUCHES MINCES DE ZnO A FAIBLES PERTES OPTIQUES PAR PROCEDE SOL-GEL
Des couches minces d’oxyde de zinc (ZnO) synthétisées par procédé sol-gel à partir de l’acétate de zinc dissous dans une solution d’éthanol avec des concentrations de 0.5M,0.6M, 0,7M et 0,8M ont été déposées par la méthode du trempage-retrait "dip-coating" sur des substrats en verre. Les propriétés structurales, morphologiques et optiques des couches minces ont été étudiées en utilisant la diffraction des rayons X (DRX), lamicroscopie à force atomique (AFM), la transmission optique et la spectroscopie des lignes de modes "m-lines". Les différents résultats obtenus montrent la présence de la phase hexagonale de ZnO avec une orientation préférentielle selon la direction (002 )pour tous les échantillons. Les spectres de transmission optique dans le domaine UV-visible indiquent des transmissions supérieures à 70% pour l’ensemble des couches déposées. Les guides d’ondes planaires élaborés sont monomodes et présentent des pertes optiques relativement faibles de 0,8 à 1,5 dB/cm comparées à celles rapportées dans la littérature. Voir les détails
Mots clés : sol-gel, Couches minces ZnO, Guides d’ondes, Pertes optiques
EFFECT OF SOL CONCENTRATION ON OPTICAL PROPOERTIES OF SOL-GEL THIN FILMS FOR PHOTONIC APPLICATIONS
In this work, effect of zinc acetate concentration on ZnO thin films dip-coated on glass substrates has been investigated. As a starting material, zinc acetate dehydrate was dissolved in a mixture of ethanol and monoethanolamine solution with a sol concentration of 0.5, 0.6, 0.7, and 0.8 mol. L–1. The samples were characterized by X-Ray Diffraction (XRD) and the results clearly demonstrate that all the obtained films display a ZnO hexagonal wurtzite structure with a strong preferential orientation of the (002) direction. The thickness of the all samples was measured to be about of 350 nm by a Profilometer. The Roughness Mean Square (RMS) extracted from the Atomic Force Microscopy (AFM) images of the ZnO thin films surfaces show a small roughness value. It was estimated about of 6 nm for the thin film synthesised with a sol concentrationof 0.7M . The optical transmission spectra in the UV-Visible domains indicate transmission values greater than 70% for all of the deposited layers . They also show that increasing the concentration, the maximum transmission exceeds 90% for all layers and moves towards longer wavelengths. For concentrations of 0.5 and 0.6 M, the best transmission is in the visible region, while for concentration of 0.7 to 0.8 M, it is maximal in the IR one. We also find that the optical gap is dependent on the concentration. It has a maximum value for a concentration of 0.7M. Voir les détails
Mots clés : sol-gel, ZnO thin films, optical properties, Photonic applications
Effects of annealing on the structural and optical properties of ZnO thin films synthesis by spin-conting
Zinc oxide thin films were deposited on microscope glass substrate by spin-coating method,from a precursor solution containing zinc acetate dissolved in methanol. ZnO thin films were obtained after preheating the spin coated thin films at 300 °C for 3 min after each coating. The films, after the deposition of the 9-layer, were annealed in air at various temperatures of 400 °C, 500 °C and 600 °C for 2 h for complete oxidation. The structural and optical properties of ZnO films were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), UV-visible and photoluminescence techniques in order to observe the influence of thermal annealing. XRD analysis revealed that the annealed ZnO thin films consist of single phase ZnO with wurtzite structure and show the c-axis grain orientation. Increasing annealing temperature increased the c-axis orientation and the crystallite size of the films. FESEM analysis of annealed thin films has shown a completely different surface morphology behavior. UV-vis has shown that the films were highly transparent with average transmission exceeding 80% in the visible range (400–800 nm). The measured optical band gap values of the ZnO thin films were around 3,24-3,28 eV. Photoluminescence spectra revealed the intensity of UV emission (NBE) increased with the annealing temperature. Voir les détails
Mots clés : Spin-coating, Zinc oxide, Annealing, optical properties
Ultra-wideband CPW Antenna Integrated with Narrow Band Dielectric Resonator
In this paper, an ultra-wideband (UWB) patch antenna integrated with dielectric resonator is proposed for cognitive radio applications. The patch antenna is fed by coplanar waveguide (CPW) line, consists of a rectangular monopole having an elliptical base, and operates from 2.6 to 12 GHz. The proposed structure integrates a narrow band rectangular dielectric resonator antenna (RDRA) for operation. The RDRA operates at 5.8 GHz and is excited through an aperture inserted in the UWB patch antenna that is considered as a ground plane. The electromagnetic analysis is carried out using CST microwave studio and HFSS software. The numerical results, obtained from simulation, are given and compared in terms of S parameters and radiation patterns. Voir les détails
Mots clés : Integrated antenna, coplanar waveguide (CPW) line, rectangular dielectric resonator antenna (RDRA)
EMPIRICAL MODE DECOMPOSITION BASED SUPPORT VECTOR MACHINES FOR MICROEMBOLI CLASSIFICATION
The classification of circulating microemboli, in the bloodstream, as gaseous or particulate matter is vital for selecting appropriate treatment for patients. Until now, Doppler techniques have shown some limitations to determine clearly the nature of circulating microemboli. The traditional techniques are largely based on the Fourier analysis. In this paper we present new emboli detection method based on Empirical mode decomposition and support vector machine using Radio Frequency (RF) signal instead of Doppler signals. Voir les détails
Mots clés : classification, Microemboli, Radio Frequency signals, Empirical Mode Decomposition, ultrasound.
Photovoltaic array modeling and MPPT using artificial neural network.
The good operation of a photovoltaic system depends on weather conditions such as illumination and temperature, because for example in a mobile station powered by a photovoltaic source, power supplied by the photovoltaic generator fluctuates when changing direction or during passage in poorly sunny, In other words, a good photovoltaic system is where the power delivered by the photovoltaic generator is maximum whatever the conditions. In the present work, we will precede first time modeling of solar cells by neural networks, then, we will use this approach to track the point of maximum power regardless of the location of use and operating conditions.; ; ; ; . Voir les détails
Mots clés : signal diode model, modeling, photovoltaic array, Neural Network, MPPT
Propagation characteristics of Chirped Vector Soliton in optical fibers with variable coefficients
In this work we study the propagation characteristics of chirped vector solitons in optical fiber systems with variable coefficients by using the compact split step Padé scheme (CSSPS). The numerical simulations show that the chirped managed vector soliton with different perturbations maintains its characteristics during propagation along the polarization maintaining optical fiber. Voir les détails
Mots clés : vector soliton, chirped soliton, optical fibers, compact split step Padé scheme, coupled higher-order nonlinear Schrodinger equations, temporal waveform.
Inhibition de l’acier A304 par le copolymère, polybithiophène/polymethyl-2furanne – Etude en milieu sulfurique
Cette présentation, consiste en l’utilisation de copolymères comme inhibiteurs de corrosion. Ces copolymères ont été obtenus à partir de deux monomères le bithiophène (Bth) et le methyl-2furanne (MeF). L’étude a été effectuée en utilisant la technique de voltampérométrique cyclique (VC) et spectroscopie électrochimique d'impédance (EIS). Ce copolymère a été synthétisé en milieu acétonitrile/ LiClO4 0.1M, contenant les deux monomères à des concentrations 0.01M sur une électrode d’acier inoxydable A304. Les films de copolymères (Polybithiophène et Poly methyl-2furanne) obtenus sur l’acier, sont analysés en milieu acide sulfurique (H2SO4 1N). Les courbes de Tafel et les diagrammes d’impédance ont montré que le copolymère obtenu peut servir d’inhibiteur de corrosion. Ceci a été justifié par un déplacement des potentiels et une diminution des courants de corrosion, et par une augmentation du diamètre de la boucle capacitif observée aux hautes fréquences. Voir les détails
Mots clés : copolymères, bithiophène, methyl-2furanne, corrosion