Liste des documents
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
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
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
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
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
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