Liste des publications
Large scale and facile synthesis of Sn doped TiO2 aggregates usinghydrothermal synthesis
Sn doped TiO2 aggregates have been successfully prepared via one pot hydrothermal technique. Differentmethods were used to characterize prepared Sn doped TiO2 aggregates such as DRX, XPS, N2 adsorption (BET),FEGSEM and UV –Vis spectroscopy. It was illustrated that the size, the morphology and the phase of preparedTiO2 aggregates is strongly influenced by the amount of added Sn doping. In addition, it was demonstrated thatthe prepared aggregates properties is influenced by the synthesis temperature. Furthermore, it was shown thatthe prepared Sn doped TiO2 aggregates are of high crystallinity. The influence of added Sn dopant amount on theoptical and structural properties of the prepared Sn doped TiO2 aggregates have been investigated. Voir les détails
Mots clés : Hydrothermal, Sn doping, TiO2, Nanoparticles assembly, optical properties
Electrocatalytic oxidation of ascorbic acid at polypyrrole thin film incorporating palladium particles
In this paper, we report a simple sensing strategy for electrochemical determination of ascorbicacid (AA) using a combination of polypyrrole (PPy) thin film and palladium particles composites deposited onto n-doped silicon (Si) substrate. A two-step electrochemical process was employed to synthesize the composite films: At first, PPy film (average thickness 200 nm) was electro-generated on Si substrate from an organic solution of the pyrrole under galvanostatic conditions. Secondly, palladium particles were electrodeposited on PPy/Si surface from a separate solution by chronoamperometry technique. The surface morphology analysis of the obtained composites shows a uniform dispersion of palladium particles onto the polymer matrix and reveals that the electrodeposition time has a significant effect on the amount and size of the incorporated palladium particles. The electrochemical reactivity of the Pd–PPy/Si-modified electrodes towards the oxidation of AA was studied by cyclic voltammetry method in 0.1 M, pH 7.0 phosphate buffer solution. The oxidation current was proportional to the concentration of AA in the range of 0.5–10 mM with a detection limit of 0.2 mM. Voir les détails
Mots clés : ascorbic acid, composite, electrocatalysis, Electropolymerization, palladium, Polypyrrole
Fast Level Set Algorithm for Extraction and Evaluation of Weld Defects in Radiographic Images
The classification and recognition of weld defects play an important rolein weld inspection. In this paper, in order to automate inspection task, we proposean aide-decision system. We believe that to obtain a satisfied defects classificationresult, it should be based on two kinds of information. The first one concerns thedefects intensity and the second one is about its shape. The vision system containsseveral steps; the most important ones are segmentation and feature computation.The segmentation is assured using a powerful implicit active contour implementedvia fast algorithm. The curve is represented implicitly via binary level set function.Weld defect features are computed from the segmentation result. We have computedseveral features; they are ranked in two categories: Geometric features (shapeinformation) and Statistic features (intensity information). Comparative study, onsynthetic image, is made to justify our choice. Encouraging results are obtained ondifferent weld radiographic images. Voir les détails
Mots clés : Code generation, State machine, Radiographic inspection, image segmentation, Level set, Region-based models, Features computation
Estimated life time in an HDPE pipe with a semi-elliptical defect under internal pressure
High density polyethylene has been widely used in marine and gas transportation, storm sewers, culverts and city drainage system. Compared with other conventional pipes, it has its own advantages, such as, chemical and corrosion resistance, toughness, flexibility, easy splicing and consequent easy handling and installation. In this paper, and in order to predict the remaining lifetime of a pipe having a defect and subjected to internal pressure, it is necessary to estimate KI stress intensity factor during the propagation of the crack. The finite element method is used to assess the values of the stress intensity factor of an axially oriented semi-elliptical crack located at the inner surface of an HDPE pipe. The crack configuration is described by the relative wall thickness (t/R), the relative crack depth (a/t) and the crack aspect ratio (a/c). The lifetimes presented are discussed according to the size of the crack and the stress intensity factor in each case. Voir les détails
Mots clés : HDPE pipe, Crack, rupture, Finite Element Method FEM, stress intensity factor, Lifetime
Amorphous SiC/c-ZnO-Based Quasi-Lamb ModeSensor for Liquid Environments
The propagation of the quasi-Lamb modes along a-SiC/ZnO thin composite plates wasmodeled and analysed with the aim to design a sensor able to detect the changes in parametersof a liquid environment, such as added mass and viscosity changes. The modes propagation wasmodeled by numerically solving the system of coupled electro-mechanical ?eld equations in threemedia. The mode shape, the power ?ow, the phase velocity, and the electroacoustic couplingef?ciency (K2) of the modes were calculated, speci?cally addressing the design of enhanced-coupling,microwave frequency sensors for applications in probing the solid/liquid interface. Three modeswere identi?ed that have predominant longitudinal polarization, high phase velocity, and quitegood K2: the fundamental quasi symmetric mode (qS0) and two higher order quasi-longitudinalmodes (qL1 and qL2) with a dominantly longitudinal displacement component in one plate side.The velocity and attenuation of these modes were calculated for different liquid viscosities andadded mass, and the gravimetric and viscosity sensitivities of both the phase velocity and attenuationwere theoretically calculated. The present study highlights the feasibility of the a-SiC/ZnO acousticwaveguides for the development of high-frequency, integrated-circuit compatible electroacousticdevices suitable for working in a liquid environment. Voir les détails
Mots clés : Lamb Modes, Amorphous SiC, Coupling configurations, sensors, viscous liquids
Engineering modeling of wear profiles in tooth flank of polyamidespur gears
The present paper is a contribution in developing an engineering model expressing the evolution of tooth flank wear in polyamide spur gears as a function of number of cycles. The method is based on first observing the behavior of wear on tooth flanks in real test conditions. Then progressive flank wear profiles are plotted in order to sort out the corresponding fitting curves together with the associated mathematical equations. The general engineering model controlling the evolution of wear profile is found of the form of quadratic equation where the variable is the circular thickness of a tooth at a given depth from the top land of the tooth. The respective parameters of the engineering wear equation are determined as a function of number of revolutions of the spur gear. A wear correction parameter kw is added in order to catch up the measuring errors when plotting the wear profile curves using the proposed engineering wear model for spur gears. The data are in good agreement with that obtained from experimental measurements. Voir les détails
Mots clés : polyamide, Spur gear, wear, Tooth flank, lubrication
Reliability estimation of pressurized API 5L X70 pipeline steel under longitudinal elliptical corrosion defect.
The probabilistic approach is the best way to give realistic answers for design and maintenance and it is considered as a powerful decision-making tool. In the present paper, assessment of the failure probability of corroded pipeline subjected to internal pressure is estimated by using the first order reliability method (FORM). Measurements of defect dimensions have been achieved changed into collected by using ultra sound inspection probe through a 75-km pipeline portion on one of the main Algerian high pressure gas transportation that has been in service for 30 years. The sensitivity analyses have been carried out on random variables to identify the importance of the parameters within the reliability mechanical model. The modified B31G code has been coupled as a mechanical model, with Rackwitz optimization algorithm by using PHIMECA Software. The limit state function resumes the difference between the pipeline burst pressure and the pipeline operating pressure. The aim of the present work is to make in evidence the competitive importance of pressure service, wall thickness and the defect depth with regards to defect length and to determine the influence of the coefficients of variation on the failure probability and the remaining life of the pipeline. A diagram based on the reliability index results is proposed to predict the pipeline degradation and it can be used as a decision tool for maintenance program. Voir les détails
Mots clés : corrosion, Failure probability, Coefficient of variation, Modified ASME B31G
Correlation between defect depth and defect length through a reliability index when evaluating of the remaining life of steel pipeline under corrosion and crack defects.
Despite the various engineering models existing for lifetime investigation of hydrocarbon steel pipelines under localized corrosion and crack defects there is still a lack of information about the correlation between the two main parameters characterizing the geometrical defect model, depth and length. So the aim of the present work is a contribution in evaluating the remaining life of the pipeline using reliability analysis in order to correlate the two parameters through one common parameter, the reliability index. As a first step, the investigation is carried out on four standard and well established engineering models; Irwin, SINTAP, ASME B31G and Modified ASME B31G methods, aiming to coordinate results given by each of the four models. The potential defect depth and length correlation through a reliability index can be used as a decision-making tool to give realistic answers for replacing and/or repairing a tube subjected to internal pressure and on which flaws of different depths and lengths have been detected from inspection of a pipeline after few years of service. Voir les détails
Mots clés : corrosion, Defect, Reliability, Correlation, Sensitivity
FINITE ELEMENT MODELING OF GROUND MOVEMENT ON THE ROADCW16 SÉRAIDI -CHÉTAIBI (ANNABA, ALGERIA)
Grounds movements are considered a natural hazard, some of which have, over time, significant slow movements.Significance of these dynamic effects involves a risk which generates human and material damage. Policymakers musttake this issue into account in their permanent security organization program. Some landslides exhibit a function of time,significant slow movements. They are assigned to a behavior of clay materials mechanism caused by the variation ofgeotechnical properties. The effects of water seepage in wet periods generally linked to the viscous nature of claymaterials are causes primarily .They can also be related to the variation modeling parameters. The land slip site is locatedat the road CW16 Seraidi -Chétaibi, (Annaba, Algeria) area with an annual rainfall of more than 700mm. Analysis of theslope stability is carried out using several methods of deformation calculation of the natural ground state. In our case weuse a plastic Mohr Coulomb from supported models. The project proposes to examine the different causes using theexample of Cam Clay. The project will examine the different causes using the example of Cam Clay; elasticvisco plasticmodel with time (SSCM: Soft Soil Creep Model) set in a finite element program Plaxis. This technique can show us howdifferent behavioral assumptions can describe the slow movements of a slope. A comparison will be made with the MohrCoulomb (MC). Voir les détails
Mots clés : Mohr Coulomb, slip, numerical modeling, plaxis, cam clay, elasticvisco plastic model
Numerical simulations of the electrical transport characteristics of a Pt/n-GaN Schottky diode
In this paper, using a numerical simulator, we investigated the current-voltage characteristics of a Pt/n-GaN thin Schottky diode on the basis of the thermionic emission (TE) theory in the 300 to 500 K temperature range. During the simulations, the effect of different defect states within the n-GaN bulk with different densities and spatial locations is considered. The results show that the diode ideality factor and the threshold voltage decrease with increasing temperature, while at the same time, the zero-bias Schottky barrier height (Φb0) extracted from the forward current density-voltage (J-V) characteristics increases. The observed behaviors of the ideality factor and zero-bias barrier height are analyzed on the basis of spatial barrier height inhomogeneities at the Pt/GaN interface by assuming a Gaussian distribution (GD). The plot of apparent barrier height (Φb,App) as a function of q/2kT gives a straight line, where the mean zero-bias barrier height ( ) and the standard deviation (σ0) are 1.48 eV and 0.047 V, respectively. The plot of the modified activation energy against q/kT gives an almost the same value of and an effective Richardson constant A* of 28.22 Acm-2K-2, which is very close to the theoretical value for n-type GaN/Pt contacts. As expected, the presence of defect states with different trap energy levels has a noticeable impact on the device electrical characteristics. Voir les détails
Mots clés : Gallium nitride, Schottky barrier, diode, Temperature