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Utilisation des Méthodes Variationnelles et des Équations d’Évolution en Traitement d’Images

boutiche yamina (2018)
Thèse de doctorat

Le travail mené dans le cadre de cette thèse porte, essentiellement, sur la segmentation etla restauration des images par les techniques basées sur l’évolution de courbes, les equations aux dérivées partielles (EDP) et le calcul variationnel. Notre intérêt s’est porté sur la représentation implicite des courbes via les ensembles de niveaux. Plusieurs avantages découlent de l’utilisation d’une telle représentation, elle présente moins de contraintes sur la géométrie des objets à segmenter (peuvent être irréguliers c.-à-d. avec de fortes courbures). De plus, elle permet un changement automatique de la topologie en cours d’évolution.Pour amorcer ce travail, nous nous sommes penchés, en premier, sur la famille des contoursactifs paramétriques. Par la suite, nous avons étudié les contours actifs implicites basés contour et ceux basés région. Une attention particulière a été accordée aux approches basées région vu leurs multiples avantages comparé à la famille des approches basées contour. De ce fait, nous avons pu mettre en évidence les points forts et faibles des trois grandes classes des contours actifs basé région, à savoir les approches globales, locales et hybrides.Ce travail nous a mené à proposer une fonctionnelle d’énergie régissant l’évolution ducontour, combinant des statistiques locales (moyennes et variances) et des statistiques globales (moyennes), avec une hybridation à poids dynamique de ces deux termes. Aussi, la rapidité de la convergence a été significativement améliorée en nous inspirant de l’algorithme par balayage (sweeping) pour proposer un algorithme rapide d’optimisation de la fonctionnelle. Ce dernier permet de calculer l’optimum de la fonctionnelle sans avoir à passer par l’équation d’Euler-Lagrange. Ces deux points constituent l’essentiel de notre contribution dans cette thèse. Enfin, pour valider nos résultats, une étude comparative et une évaluation quantitative ont été mises en oeuvre entre le modèle proposé et les modèles les plus en vue de la familledes contours actifs basés région. Voir les détails

Mots clés : Segmentation d’images, Restauration d’images, regularisation, Approches variationnelles, Ensembles de niveaux, Statistiques locales et globales

Correlation Between the Pitting Potential Evolution and σσ Phase Precipitation Kinetics in the 2205 Duplex Stainless Steel

Mustapha DJAMA, Djaffar Saidi, Abdelaziz Kadri, Nabil KHERROUBA, Brahim MEHDI, Stéphane Mathieu, Thierry Schweitzer, IDIR Brahim  (2018)
Publication

The aim of this work is to correlate the pitting potential (Epit) evolution with the kinetics ofrphaseprecipitation in the 2205 duplex stainless steel aged at 850°C after solution treatment at 1150°C. Thepotentiodynamic polarization curves indicate a reduction of the pitting corrosion resistance with the agingtime, which is revealed by a decrease in theEpitvalues from 0.65 to 0.40 VSCE. Thus,Epitvalues are used todetermine the kinetics parameters of therphase precipitation. The experimental transformed fractionagrees well with the one calculated by using the modified Kolmogorov–Johnson–Mehl–Avrami equationwith an impingement parameterc= 0.6. Voir les détails

Mots clés : kinetic, KJMA, Pitting corrosion, otentiodynamic polarization, r phase precipitation

Isothermal and non-isothermal precipitation kinetics in Al–Mg–Si-(Ag) alloy

Oussama.Djema, Mabrouk.Bouabdallah, Riad.Badji, Amr.Saadi, Nabil.Kherrouba, Amane.Sahli  (2019)
Publication

In the present work, isothermal and non-isothermal precipitation kinetics in a 6063 aluminium alloy containing a small silver (Ag) addition have been investigated using Vickers microhardness and Differential Scanning Calorimetry (DSC) measurements respectively. Isothermal kinetics analysis showed that β'' phase precipitation obeyed the Johnson-Mehl-Avrami (JMA) model. The DSC analysis revealed that Ag addition modified the precipitation sequence in the investigated 6063 aluminium alloy through the formation of an additional metastable pre-β'' phase. An approach based on the additivity concept has been applied to the heating DSC diagrams to investigate the β'' phase precipitation. The obtained Avrami exponent values from this approach led to suggest that the β'' phase precipitation proceeded through two processes during continuous heating. The Avrami exponent value obtained at the final stage of the transformation was consistent with that obtained from the isothermal analysis, whereas the corresponding activation energy was higher than the one calculated from the isothermal analysis and Kissinger's method. It was also established that the precipitation kinetics of the β'' phase was enhanced by the formation of the precursor phase pre-β''. Voir les détails

Mots clés : 6063 aluminium alloy, Ag addition, Precipitation kinetics, JMA model, Additivity concept

Effect of solution treatment on the microstructure, micromechanical properties, and kinetic parameters of the β → α phase transformation during continuous cooling of Ti-6Al-4V titanium alloy

Nabil KHERROUBA, Denis CARRON, Mabrouk BOUABDALLAH, Riad BADJI  (2019)
Publication

The aim of this study is to examine the effect of solution treatment temperature (STT) on the microstructure, the micromechanical properties, and the kinetic parameters of the β → α phase transformation during continuous cooling of the dual phase titanium alloy Ti-6Al-4V. Increasing the STT from 1050 °C to 1200 °C delays the formation of the α phase during cooling and increases the value of its activation energy. The microstructural analysis reveals the emergence of αW platelets from protuberances on the αGB / αW interface. The investigation of the morphology of the αW platelets reveals the presence of ledges on their longest side showing a sharp extremity. The micromechanical properties determined by nanoindentation and microhardness tests are almost insensitive to the cooling rate but are strongly affected by the STT; the higher the STT, the lower the overall microhardness of the Ti-6Al-4V alloy. In addition, the STT affects the microhardness and the Young’s modulus of both α and β phases differently; when the STT increases, the microhardness and the Young’s modulus of the α phase decrease whereas those of the β phase increase. Voir les détails

Mots clés : Ti-6Al-4V, solution treatment, ledge mechanism, interface instability, Nanoindentation, partitioning

Structural, Electronic and Mechanical Properties of C14-Mg 2 RE(RE=Eu, Er, Tm, Yb and Lu) Laves Phases: A DFT Study

A. Zahague, B. Lagoun, A. Legris, R. Besson, L. Rabahi, D. Bradai  (2019)
Publication

The Pseudo-Potential Density Functional Theory (PP-DFT) method is applied to investigatethe structural, electronic and mechanical properties of C14-Mg 2 RE Laves phases, with RE being Eu,Er, Tm, Yb and Lu. The predicted cell parameter and c/a ratio of each compound are in good agreement with experimental and theoretical results. Moreover, the studied alloys exhibit a metalliccharacter, which is attributed to the presence of Mg atoms in the C14 Laves phase. Also, theformation of C14-Mg 2 RE is found to be controlled by the hybridisation between Mg p states and RE-d and f states. From a mechanical property analysis, the studied alloys are found to be mechanicallystable. The Mg 2 Lu compound exhibits higher ductility, while Mg 2 Er exhibits the smallest one.Finally, Mg 2 Yb is found to be more anisotropic than other phases. Voir les détails

Mots clés : A DFT calculations, B Magnesium based Laves phases, C Density Functional Theory (DFT), D Mechanical properties, E Electronic properties

Nitriding effect on structural stability and magnetic properties of FeAl alloys:DFT study

Ismahane Berrached, Lyacine RABAHI, Malika Gallouze, Abdelhafid Kellou  (2019)
Publication

Using the DFT calculations, the phase stability, structural deformation and magnetic momentof Fe-riche FeAl alloys in presence of different percents of nitrogen were calculated. Theformation enthalpy of these Fe-Al alloys indicates that N preferred the octahedral site than thesubstitution one. Significant changes occur in this energy, affected by N and Fe contentcausing local distortions. From 25 at.% N, the phenomenon of saturation appeared and thesubstitution takes place. The addition of 6 at.% N stabilizes Fe 9 Al 7 and Fe 10 Al 6 . The presenceof N atom leading to decrease the total magnetic moment of FeAl nitride when the magneticorder is antiferromagnetic between N and Fe atom. This magnetic moment increased by theferromagnetic coupling between Fe and N, thus increasing the Fe local magnetic moment andthe magneto-volume effect. Voir les détails

Mots clés : Nitriding, Magnetic Properties, Structural Stability., FeAl Alloys, DFT

Comparative investigation of the Ni and the Fe effect on the structure andmechanical response of a WC-W-Ni hardmetal obtained by infiltration

H. Bouchafaa, D. Miroud, S. MATO, Z. Boutaghou, B. Cheniti, F.J. PÉREZ, G. ALCALÁ  (2019)
Publication

In the present work, and in order to enhance the efficiency of drilling tools for the oil and gas industry, theinfluence and performance of Ni and Fe during spontaneous infiltration on a WC-W-Ni composite materialmechanical behaviour was addressed. Solid-state activity of Fe and Ni during infiltration exhibits partial dissolution in the metallic binder. The chemical affinity between Fe and Ni, provided by the Fe powder and thebinder respectively, derived on the formation of the (Fe, Ni) solid solution and FeNi3 intermetallic precipitates inthe particle/matrix diffusion region, with a hardness (12 GPa) close to that of WC and high elastic modulus (230 GPa). Furthermore, the diffusion of Fe to the matrix leads to the formation of sub-micrometer precipitatesof α-Fe with some (Ni, Mn) in solid solution and of Ni3Sn with a small amount of Cu dissolved, driving to anincrease of about 30% in its elastic modulus, and without appreciable effect in the hardness observed. Voir les détails

Mots clés : Metal matrix composites, Liquid-solid reactions, Precipitation, powder metallurgy, diffusion, mechanical properties

TiO2 doped with nickel thin films Properties

H. Dehdouh, M-C. BENACHOUR, R. Bensaha, M. Zergoug  (2018)
Article de conférence

Thin films of un-doped and Ni-doped TiO2 were synthesized by the sol–gel dip-coating technique and deposited on glass substrates, for different annealing temperatures (from 400 °C to 500 °C). The X-rays diffraction and Raman show the formation of anatase phase, we also notice that doping with Ni influence the intensity of anatase peaks and decreases of grain sizes (from 24.3 to 15.23 nm). The nanostructure Ni-doped TiO2 thin films was observed AFM, which shows that the elaborated films are smooth and dense with Rms values of about 3 nm. The calculate values of refractive index of thin films increases from 2.22 to 2.38, and reduction in transmittance and band gap with the increase in the nickel concentration. Vibrating sample magnetometer results of un-doped TiO2 thin films reveal a ferromagnetic behavior at room temperature with Ms = 0.67 10-4 emu and low content of nickel doping leads to an enhancement of the saturated magnetic moment Ms =1.11 10-3 emu. Voir les détails

Mots clés : Ni-doped TiO2, sol-gel, Thin films, TiO2 properties

Structural modification, photoluminescence, andmagnetic property enhancement with Er3+ doping,of sol–gel TiO2 thin films

Heider DEHDOUH, Rabah Bensaha, Mourad ZERGOUG  (2017)
Publication

Nanocrystalline undoped and Er3+ doped TiO2 thin films were prepared by sol–gel dip-coatingtechnique onto glass substrates. Post-deposited films were annealed at 450 °C for 1 h. Differentialscanning calorimetric analysis showed that undoped film crystallization occurred at 339 °C, whileit appears at lower temperature for Er:TiO2. X-ray diffraction and Raman spectroscopy resultsindicate that the films crystallize only into anatase phase, and the crystallite size decreases from24.3 to 21.16 nm with increasing Er3+ doping ratio. The photoluminescence (PL) spectra arecomposed of two broad peaks at 520–570 nm and 640–680 nm assigned to (2H11/2, 4S3/2)–4I15/2 and4F9/24I15/2 transitions of Er3+ ions, respectively. PL emission intensities increase gradually raisingthe erbium doping ratio. Vibrating sample magnetometer results of undoped TiO2 thin films reveala ferromagnetic behavior at room temperature and erbium doping leads to an enhancement of thesaturated magnetic moment (Ms). Voir les détails

Mots clés : TiO2 doped Er3+, Sol–gel, Photoluminescence, Magnetic Properties

Elaboration and characterization of ITO electrode modi?ed bytransition metal dispersed into polyaniline thin ?lms

Oua?a Belgherbi, Dalila Chouder, M.A. Saeed  (2018)
Publication

This work presents the characteristics of composite materials thin ?lms of polyaniline (PAni) andnickel (Ni) particles deposited onto indium tin oxide (ITO) substrate. The electropolymerizationof aniline was performed in acidic medium by potentiodynamic methods. The nickel particleswere electrochemically deposited on the surface of PAni/ITO by reducing metal ions (Ni) usinga potentiostatic method from a separate solution. The e?ect of applied potential as well as immersingtime of complexation on the amount of nickel dispersed was investigated. Di?erentcharacterization techniques were employed to study the electrochemical behavior and surfacecharacteristics of the Ni-PAni/ITO thin ?lms such as Electrochemical Impedance Spectroscopy(EIS), Cyclic Voltammetry, Fourier Transform Infrared Spectroscopy (FTIR), UV–visSpectroscopy, Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM).The morphology of the obtained composites shows a uniform dispersion of nickel particlesonto the polyaniline matrix and reveals that the immersing times of complexation has a signi?cante?ect on the amount of incorporated particles. The impedance spectroscopy study revealsthat the conductivity of the composite ?lm increases with the amount of nickel incorporated.UV–vis and FTIR results con?rm the presence of PAni and Ni particles on theelectrode surface. Voir les détails

Mots clés : polyaniline, Electro-polymerization, Nickel particles, Chronoamperometry, Materials composites