Liste des publications
Pipelines Corrosion Due to the Electromagnetic Pollutioncaused by the High Voltage Power Lines
This paper studies the effect of theelectromagnetic pollution caused by the high voltage powerlines on the corrosion of the buried pipeline. In this objective,the finite element method (FEM) was used to calculate themagnetic field distribution and the induced current densitiesin the buried pipeline caused by both horizontal and verticalconfiguration of the HVPL during steady state conditions. Inorder to diagnose the effect of the electromagnetic pollutionon the corrosion of the pipeline, the electrochemicalimpedance spectroscopy (EIS)measurements were used tocharacterize the corrosion polarization properties of X70 steelin simulated soil at various AC current densities. The resultsshow that, the electromagnetic pollution caused by the highvoltage power lines affect the electrochemical characteristicsof the X70 steel pipeline and accelerate the corrosion of thepipeline. Voir les détails
Mots clés : Electromagnetic pollution, high voltage power line, induced current density, X70 steel pipeline, corrosion, Finite Element Method, Electrochemical impedance spectroscopy
DFT calculations of structural magnetic and thermal properties of C15 C14 and C36 Laves phases in Fe-Nb-Zr
The Pseudo-Potential Density Functional Theory (PP-DFT) method is applied to investigate the C15, C14and C36 Laves phases within the Fe-Nb-Zr system. The lattice parameters, bulk moduli, heats of formationand magnetic moments are predicted considering various spin configurations. ZrFe2 andZr0.5Nb0.5Fe2 are found to be ferromagnetic in the C15 and C36 structures, respectively. NbFe2 is predictedto be ferrimagnetic in C36. The magnetic states dependency of these compounds on the volumecompression shows interesting magnetic transition from the low to high spin state. This transition ismore pronounced for NbFe2 and Zr0.5Nb0.5Fe2. The thermal properties of NbFe2 and Zr0.5Nb0.5Fe2 are wellpredicted by using the quasi-harmonic Debye model. The obtained linear volume expansion for ZrFe2 isin excellent agreement with the experimental value at 800 K. The vibrational entropies of the studiedalloys confirm the coexistence of the three Laves phases at high temperature. Voir les détails
Mots clés : Laves Phases, Magnetism, Thermal Properties, DFT, Quasi-harmonic Debye model
Effect Of Thickness On The Structural, Microstructural, Electrical And Magnetic Properties Of Ni Films Elaborated By Pulsed Electrodeposition On Si Substrate
We have studied the effect of thickness on the structural, microstructural, electrical and magnetic properties of Ni films electrodeposited onto nn-Si (100) substrates. A series of Ni films have been prepared for different potentials ranging from −−1.6V to −−2.6V. Rutherford backscattering spectrometry (RBS), X-ray diffraction (XRD), four point probe technique, atomic force microscopy (AFM) and vibrating sample magnetometry (VSM) have been used to investigate the physical properties of elaborated Ni thin films. From the analysis of RBS spectra, we have extracted the films thickness tt (tt ranges from 83nm to 422nm). We found that the Ni thickness, tt (nm), linearly increases with the applied potential. The Ni thin films are polycrystalline and grow with the ?111??111? texture. The lattice parameter aa (Å) monotonously decreases with increasing thickness. However, a positive strain was noted indicating that all the samples are subjected to a tensile stress. The mean grain sizes DD (nm) and the strain εhklεhkl decrease with increasing thickness. The electrical resistivity ρρ (μΩ.μΩ.cm) increases with tt for tt less than 328nm. The diffusion at the grain boundaries may be the important factor in the electrical resistivity. From AFM images, we have shown that the Ni surface roughness decreases with increasing thickness. The coercive field HCHC, the squareness factor SS, the saturation field HSHS and the effective anisotropy constant K1effK1eff are investigated as a function of Ni thickness and grain sizes. The correlation between the magnetic and the structural properties is discussed Voir les détails
Mots clés : Ni thin films; pulsed electrodeposition; structural properties; microstructure; magnetization curves; magnetic anisotropy.
Effects of Fe substitution by Nb on physical properties of BaFeO3: A DFT + U study
The structural, electronic, magnetic and thermal properties of BaFe1xNbxO3 perovskites oxides are investigatedusing the Density Functional Theory (DFT). The Generalized Gradient Approximation (GGA) andon-site Hubbard potential corrections (GGA + U) are considered. According to the formation energiesand phonon spectra, the stoichiometric BaFeO3 and BaNbO3 oxides have a stable cubic phase. The GGA+ U calculations show a half metallic behavior of BaFeO3 with a large exchange splitting, in agreementwith previous experimental and theoretical works. The Fe substitution by Nb for x = 0.5 leads to a surprisinginsulating ground state. The values of the band gap is 0.40 eV and 1.84 eV using GGA and GGA + U,respectively. For x = 0.875 and x = 1, the corresponding alloys are metallic and non-magnetic, while forx = 0.5 and x = 0.625 the antiferromagnetic ground state is found using GGA + U. For the remaining Nbcompositions a half metallic character is noticed with a ferromagnetic state. The quasi-harmonicDebye model is successfully applied to study the temperature evolution of lattice parameters and bulkmoduli for different Nb compositions. Voir les détails
Mots clés : BaFe1-xNbxO3 perovskites, Structural properties, Magnetic moments, Density Functional Theory, GGA + U, Quasi-harmonic Debye model
Reliability Index of HDPE Pipe Based on Fracture Toughness
his work presents a contribution to evaluate the reliability of a high density polyethylene (HDPE) pipe using the PHIMECA Software. The critical stress intensity factor (KIC) is adopted as a criterion to the maximum limit of a numerically calculated KI. The reliability index β is obtained using failure probability and a mechanical model. It is found that at lower KIC, no safe domain for actual service pressures existed while for moderate and higher values of KIC (above 3.5 MPa.√m); the β design index is reached and even exceeded. In terms of increasing crack length, β decreased systematically for all toughness cases supporting the idea that reliability and fracture toughness designate similar properties for service life or material resistance to cracking. For a KIC=5 MPa.√m, the pipe is considered safe when crack length is below 370μm. Finally, it is shown that SDR basis is a reasonable and conservative design approach for plastic pipes. Voir les détails
Mots clés : HDPE pipe, critical stress intensity factor, crack length, SDR, reliability index, PHIMECA software
Modelling of a Cd1−xZnxTe/ZnTe Single Quantum Well for Laser Diodes
In this paper, the carrier density, temperature and quantum well width effect have been investigated for the optical gain for a Cd1−xZnxTe/ZnTe Zinc-blend strained quantum well structure. The device emits laser radiations in green–yellow–orange. Our results showed that the optical gain significantly increases with the increasing of the carrier density. It also increases with the decreasing of the Zn concentration, the well width and the temperature. In addition, the optimal threshold current density values were determined for three alloy compositions as 0.7, 0.8 and 0.9. Voir les détails
Mots clés : Quantum wells diode laser gain CdZnTe optoelectronics
Modeling and simulation of ZnxCd1-xTe/ZnTe quantum well structure for laser applications
In this work, we modeled and simulated aZnxCd1-xTe/ZnTe based single quantum well structure. We have taken into account the effect of carrier density, alloy composition, temperature and wells width on the optical gain as well as threshold current density. The use of ZnTe as a barrier leads to the improvement of the carrier confinement such as Qc (83%)/Qv (17%). Then, we have optimized the quantum well structure that allows obtaining a threshold current density Jth = 500 A/cm2. This study allowed us to achieve laser diodes VCSEL quantum well reliable and emitting around 0.740 μm. Voir les détails
Mots clés : Quantum well Semiconductor laser Gain ZnCdTe Optoelectronics
Micrographic Image Segmentation using Level SetModel based on Possibilistic C-MeansClustering
Image segmentation is often required as afundamental stage in microstructure material characterization.The objective of this work is to choose hybridization betweenthe Level Set method and the clustering approach in order toextract the characteristics of the materials from thesegmentation result of the micrographic images. Morespecifically, the proposed approach contains two successivenecessary stages. The first one consists in the application ofpossibilistic c-means clustering approach (PCM) to get thevarious classes of the original image. The second stage isbased on using the result of the clustering approach i.e. oneclass among the three existing classes (which interests us) asan initial contour of the level set method to extract theboundaries of interest region. The main purpose of using theresult of the PCM algorithm as initial step of the level setmethod is to enhance and facilitate the work of the latter. Ourexperimental results on real micrographic images show thatthe proposed segmentation method can extract successfully theinterest region according to the chosen class and confirm itsefficiency for segmenting micrographic images of materials. Voir les détails
Mots clés : Level set, clustering approach, micrographic images;, image segmentation.
Fast algorithm for hybrid region-based active contours optimisation
Active contours are usually based on the optimisation of energy functionals that are built to attract the curve towardsthe objects' boundaries. This study describes a hybrid region-based active contours technique that uses global means to definethe global fitting energy and local means and variances to define the local fitting energy. The optimisation of the functional isperformed by applying a sweeping-principle algorithm, which avoids solving any partial differential equation and removes theneed for any stability conditions. Furthermore, sweeping-principle algorithm is not based on the computation of derivatives,which allows using a binary level set function during the minimisation process instead of the signed distance function,consequently this removes the need for the distance regularisation term, avoiding its subtle side effects and speeding up theoptimisation process. Successful and accurate segmentation results are obtained on synthetic and real images with a significantgain in the CPU execution time when compared with the minimisation via the commonly used gradient descent method. Voir les détails
Mots clés : image segmentation
Pulsed eddy current signal analysis of ferrous and non-ferrous metals under thermal and corrosion solicitations
Most metals endure in contact with ambient air, liquids or other metals the phenomena of oxidation. The kinetics of the corrosion can be significant and destroy the metal. The marine corrosion or soil affects many materials, more than ever if it touches the pipeline, ship hulls or buried pipes. The investigation of NDT methods to predict corrosion behavior can be a rational solution to prevent from this kind of industrials problems.Eddy current and pulsed eddy current (PEC) are proposed as a powerful Nondestructive Testing and Evaluation (NDT&E) technique. The application of this kind of technique in the industrial domain is used in detection of the defects, particularly in the determination of corrosions information contained in the received signal gives the possibility allow to use the PEC in the Non Destructive Evaluation of materials that can be analysed. The work in this papers explain the behaviour of the eddy current, pulsed Eddy Currents and various electromagnetic parameters in the analysed samples. We have showed in this work that all microstructure modifications of the samples were detected and can be quantified by Pulsed eddy current measurements. Modifications of the microstructure obtained by air cooled, quenched and corroded samples in aluminium, heat treatment changement in mild steel were evaluated by PEC. Voir les détails
Mots clés : pulsed eddy current (PEC), ), lift off variation, corrosion