Liste des publications
Degradation of plastic pipe surfaces in contact with an aggressive acidic environment
olyethylene (PE) pipes transporting water are vulnerable to aggressive agents which are able to diffuse through buried plasticpipes causing oxidative degradation. The latter may occur as a result of a spontaneous chemical reaction with atmospheric oxygen or as an induced oxidizing reaction with disinfectant agents (i.e. chlorine or hypochlorous acid ions) which are commonly added to municipal water supplies for public health reasons. Basically, PE pipes surfaces undergo undesired oxidation reactionswhenever they are in contact with adverse external environments and/or when conveying fluids which tend to modify internal pipe wall structure. In this work, the effects of distilled water and diluted hydrochloric acid at different concentrations on the external and internal surfaces of a high density polyethylene (HDPE-100) pipe are studied. The measured parameters are roughness and hardness in order to appreciate surface quality variances in as-received and degraded materials. Initially the outer surface is rougher than the inner’s one but in contact with distilled water, the external surface roughness increased by 6% although the internal face of the tube revealed a small decrease (<5%). When exposed to hydrochloric acid, pipe roughness (μm) showed a substantial increase as a function of increasing medium concentration. Crystallinity (χ in %) measurements confirmed the gap between outer (51.55%) and inner (61.31%) surfaces indicating that degradation has taken place at the structural level when HDPE was in contact with such aggressive agents. On the other hand, it is revealed that after exposure to oxidizing environments, crystallinity dropped by approximately one third when compared to as-received material; therefore reducing resistance to fracture and subsequently pipe lifetime. Voir les détails
Mots clés : polyethylene pipe; environment; distilled water; diluted hydrochloric acid; degradation; surface roughness; hardness; crystallinity.
Water quality of the plain of El-Hadjar wilaya of Annaba (Northeast Algeria)
The region of El- Hadjar is known for its diversity of industries that stretch of the steel industry to the food and materials processing. Industrial and domestic waste is channeled into streams Oued Seybouse is its major tributary Oued Meboudja, both flanked with major industrial areas. Pollution of surface and groundwater has become a particular problem of interest for health and environmental conservation. This study aims to physico- chemical characterization of waters in this area using 11 sampling points covering the entire area of a spread on rivers and plains of El Hajar). The results are expressed in terms of concentrations of the various pollutants such as nitrate, nitrite and chloride in a first step. The physico -chemical parameters were recorded over a period of seven months during 2009 and relate to salinity, conductivity, pH, Eh ... It was found that the region is moderately polluted following the accepted standards. The data are correlated with industrial and agricultural activity in the region. The study is in the process of being completed by a water quality map of the entire region with the concentrations of hydrocarbons and heavy metals. The evolution of these parameters will develop a policy for the preservation of the environment that is needed in these times. Voir les détails
Mots clés : pollution, environment, surface water, groundwater quality, physical and chemical analysis, environmental policy, El- Hajar.
Physical and photo-electrochemical characterizations of ZnO thin films deposited by ultrasonic spray method: Application to HCrO4−photoreduction
ZnO thin films, prepared by ultrasonic spray onto glass substrate, crystallize in the wurtzite structure. The XRD pattern shows preferential orientation along the [0 0 2] direction. The films deposited at 350 consist of 60 nm crystallites with an average thickness of ∼150 nm and SEM images show rough surface areas. The gap increases with increasing the temperature of the substrate and a value of 3.25 eV obtained for films deposited at 350?C. ZnO is nominally non-stochiometric and exhibits n-type conduction because of the native defects such as oxygen vacancies (VO) and/or interstitial zinc atom (Zni) which act as donor shallows. The conductivity is thermally activated and obeys to an exponential type law with activation energy of 57 meV and an electron mobility of 7 cm2V−1s−1. The capacitance-voltage (C−2measurement in acid electrolyte (pH ∼ 3) shows a linear behavior with a positive slope, characteristic N-type conduction. A flat band potential of −0.70 VSCE and a donors density of 5.30 × 1016cm−3are deter-mined. The Nyquist plot exhibits two semicircles attributed to a capacitive behavior with a low density of surface states within the gap region. The centre is localized below the real axis with a depletion angle of 16?ascribed to a constant phase element (CPE) due to the roughness of the film. The energy band diagram assesses the potentiality of ZnO films for the photo-electrochemical conversion. As application, 94% of chromate (3.8 × 10−4M) is reduced after 6 h under sunlight (AM 1) with a quantum yield of 0.06%and the oxidation follows a first order kinetic. Voir les détails
Mots clés : ZnO, thin film, Ultrasonic spray, Photo-electrochemical, Chromate, Sunlight
Influence of niobium on the hardening phenomenon and wear in the manganese steel \(12% Mn\) destined for the railway
This study relates to the manufacture of austenitic manganese steel for the heartswitching crossings of railways in all industrial countries where heavy loads are movedby rail. This steel is characterized by a high surface hardness service yard caused by thephenomenon of hardening. According to the microstructure formed after quenching, thetransformation of austenite into martensite during working, determine the operating life.The rate of transformation of austenite into martensite can force a compromise betweenductility and wear resistance of the steel in order to withstand large forces without breaking.The objective of this study is to improve the resistance to abrasion and friction to cast stateand after heat treatment by the addition of niobium. This study permitted to develop a newshade of manganese steel can be integrated into the production of heart of railway switcheswith better lifecycle. Voir les détails
Mots clés : manganese steel, effect of niobium, hardening, wear.
Analysis and Mitigation of the Interference Between High Voltage Power Line and Buried Pipelines
Analysis of electromagnetic interference between high voltage overhead power transmission lines and nearby gas/oil pipeline has been a topic of growing interest for many years. When pipelines are located in shared row with power lines, the pipeline can incur high induced voltages and currents due the AC interference. The induced voltage on pipeline can be dangerous for operator to touch the pipeline as well as pipe corrosion can result from AC discharge. This research evaluates and analyzes the electromagnetic interference effects on oil and gas buried pipelines created by the nearby high voltage transmission lines. The aim is to evaluate the AC corrosion likelihoods of pipelines and suggest proper mitigation solutions. Voir les détails
Mots clés : AC interference, Induced Voltages, Electric Power Transmission Lines, pipeline, AC Corrosion, cathodic protection, soil resistivity
Ultrasonic Flaw Detection in Composite Materials Using SSP-MPSD Algorithm
Due to the inherent inhomogeneous and anisotropy nature of the composite materials, the detection of internal defects in these materials with non-destructive techniques is an important requirement both for quality checks during the production phase and in service inspection during maintenance operations. The estimation of the time-of-arrival (TOA) and/or time-of-flight (TOF) of the ultrasonic echoes is essential in ultrasonic non-destructive testing (NDT). In this paper, we used split-spectrum processing (SSP) combined with matching pursuit signal decomposition (MPSD) to develop a dedicated ultrasonic detection system. SSP algorithm is used for Signal-to-Noise Ratio (SNR) enhancement, and the MPSD algorithm is used to decompose backscattered signals into a linear expansion of chirplet echoes and estimate the chirplet parameters. Therefore, the combination of SSP and MPSD (SSP-MPSD) presents a powerful technique for ultrasonic NDT. The SSP algorithm is achieved by using Gaussian band pass filters. Then, MPSD algorithm uses the Maximum Likelihood Estimation. The good performance of the proposed method is experimentally verified using ultrasonic traces acquired from three specimens of carbon fibre reinforced polymer multi-layered composite materials (CFRP). Voir les détails
Mots clés : Non-Destructive testing, Ultrasonics, Carbon fibre, Defects, Signal processing
Ultrasonic flaw detection using threshold modified S-transform
Interference noising originating from the ultrasonic testing defect signal seriously influences the accuracy of the signal extraction and defect location. Time–frequency analysis methods are mainly used to improve the defects detection resolution. In fact, the S-transform, a hybrid of the Short time Fourier transform (STFT) and wavelet transform (WT), has a time frequency resolution which is far from ideal. In this paper, a new modified S-transform based on thresholding technique, which offers a better time frequency resolution compared to the original S-transform is proposed. The improvement is achieved by the introduction of a new scaling rule for the Gaussian window used in S-transform. Simulation results are presented and show correct time frequency information of multiple Gaussian echoes under low signal-to-noise ratio (SNR) environment. In addition, experimental results demonstrate better and reliable detection of close echoes drowned in the noise. Voir les détails
Mots clés : Flaw detection, Ultrasonic signal, Time–frequency signal analysis, Modified S-transform
Modeling of InGaN / GaAs Photovoltaic Tandem with GaAs/AlAs Bragg Mirror Rear Surface Reflector
In this work, a parametric study of a dual junction tandem based on In0.53Ga0.47N on GaAs has been carried. In order to obtain reflection of unabsorbed photons from the bottom of the device, Bragg reflectors (BR) composed of GaAs/AlAs, with appropriate thicknesses, was placed in the rear surface of the GaAs sub-cell. With this intention, the current-voltage curves are calculated for different front recombination velocities and the influence of the bottom cell thickness on efficiency has been studied. The results of simulation show that the structure’s efficiency can attain 29% under 1-sun AM1.5 illumination, for a front recombination velocity value of 1e3cm/s and 10μm bottom cell thickness. This efficiency will decrease with increasing the operating temperature. Voir les détails
Mots clés : Bragg Reflector, Carrier Lifetimes, Recombination Velocity, Efficiency, Temperature
Propagation of Lamb waves in an immersed periodically grooved plate: Experimental detection of the scattered converted backward waves
Guided waves propagation in immersed plates with irregular surfaces has potential application to detection and assessment of the extent, depth and pattern of the irregularity. The complexity of the problem, due to the large number of involved parameters, has limited the number of existing studies. The simplest case of irregularities of practical interest is the two-dimensional corrosion profile. Even this case is in general so complex, that one can extract several amplitude dominant periodic surfaces only by using a Fourier spectrum of the surface. Guided waves in plates, with one or both free surfaces having periodic perturbations of different shapes, have been presented in specialized literature. In this paper is studied the propagation of Lamb waves in an aluminum plate with a periodic grooved surface on only one side and immersed in water. The interaction between an incident Lamb wave and the grating gives rise to retro-converted waves. Preliminary numerical simulation by the finite element method is performed in order to obtain key parameters for the experiments. It is shown that retroconverted waves radiating into the water are detectable although their amplitudes are small. The phonon relation is verified for the leaky Lamb modes. The damping coefficients of the leaky Lamb modes in the grooved immersed plate are evaluated. Voir les détails
Mots clés : Liquid–solid interfaces, Rough plate, Periodic grating, Lamb waves, Converted modes
L’impact d’une Charge Fortement Capacitive Sur la Qualitédu Filtrage d’un FAP Contrôlé Par un Filtre Multi-VariableHautement Sélectif
This article is devoted to the depollution of the electrical supply networks by shunt active power filter (SAPF). We start by studying a self tuning filter (STF) based on Concordia transformation. This transformation is based on the extraction of the references of harmonic currents in the Concordia axis to compensate network harmonic and by consequence, improve the quality of power system. Next, we present the influence of a strongly capacitive load on the quality of the filtering of a SAPF controlled by a STF approach. This influence is validated by numerical simulations under Matlab-Simulink environment of a system of power PD3 a diode debited in a strongly capacitive load this results prove the major influence of this types of load in filtering quality. Voir les détails
Mots clés : SAPF, harmonic, STF, System of Power PD3, Quality of Energy, Strongly Capacitive Load, Concordia transformation