Liste des publications
Structural, optical and electrical properties of TiO2 thin films synthesized by sol–gel technique
The influence of annealing temperature on the structure, optical and electrical property of TiO thinfilms with (101) preferential orientation were deposited on glass substrates by sol–gel technique has beenstudied. As-deposited films were amorphous, and the XRD studies showed that the formation of anatase phasewas initiated at annealing temperature close to 400 °C. The grain size of the film annealed at 550 °C was about22 nm. The transmission spectra, recorded in the UV visible range reveal a relatively high transmissioncoefficient (~70%) in the obtained films. The transmittance data analysis indicates that the optical band gap (E)is closely related to the annealing temperature, an indirect band gap ranging from 3.43 eV to 3.04 eV wasdeduced. The electrical resistivity measurement that were carried out in function of the annealing temperature showed a sharp decrease in resistivity was found to be 0.0802 .cm.2g Voir les détails
Mots clés : TiO2Thin films, Annealing, DRX, anatase, Optical property, resistivity
Study of the spray to globular transition in gas metal arc welding: a spectroscopic investigation
The gas metal arc welding (GMAW) process is strongly influenced by the composition of the shielding gas. In particular, addition of CO2 increases the threshold current for the transition from unstable globular to more stable spray transfer mode. We report on the diagnostics—using optical emission spectroscopy—of a GMAW plasma in pure argon and in mixtures of argon, CO2 and N2 while operated in spray and globular transfer modes. The spatially resolved plasma parameters are obtained by applying the Abel transformation to laterally integrated emission data. The Stark widths of some iron lines are used to determine both electron density and temperature, and line intensities yield relative contents of neutral and ionized iron to argon.Our experimental results indicate a temperature drop on the arc axis in the case of spray arc transfer. This drop reduces with addition of N2 and disappears in globular transfer mode when CO2 is added. Despite the temperature increase, the electron density decreases with CO2 concentration. The highest concentration of iron is observed in the plasma column upper part (close to the anode) and for GMAW with CO2.Our results are compared with recently published works where the effect of non-homogeneous metal vapour concentration has been taken into account. Voir les détails
Mots clés : GMAW, Optical Emission Spectroscopy, Boltzmann Plot
Correlation between structural and optical properties of SiO2/TiO2multibilayers processed by sol-gel technique and applied toBragg reflectors
SiO2 and TiO2 thin layers processed by sol-gel technique have been deposited,alternatively, on glass substrates and Si (111) wafer. Dip-coatedmultibilayerswere characterized by different experimental techniques:XRD,SEM, FTIRandUV-VIS-NIR. The obtainedX-ray diffraction patterns analysishave shown that our films crystallize in anatase and rutile phases whateveris the number of bilayers and the corresponding grain sizes increasefrom 5.48 nmto 16.11 nm. The SEMmicrograph shows that our layers arehomogeneous without any visual cracks. The FTIR spectra have shownthat the vibration of Si-O-Ti bonds becomes intense by the increase in thenumber of bilayers. This increase, on the on hand, decreases the transmissioncoefficient from 4.58% to 0.55% and increases the width of the stopband shown in UV-VIS-NIR spectra. On the other hand, the band-gap decreasesfrom3.73 eV to 3.59 eV. In addition, a pseudo band-gap is locatedbetween 300 nmand 400 increasing from1.76 eVto 2.29 eV.? 2013 Trade Science Inc. - INDIA Voir les détails
Mots clés : Sol-gel;, Anatase;, Rutile;, Stop band;, Si-O-Ti;, Band-gap.
Linear Fractional Order System Identification using Adjustable Fractional Order Differentiator
In previous decades, it has been observed that many physical systems are well characterised by fractional order models. Hence, their identification is attracting more and more interest of the scientific community. However, they pose a more difficult identification problem, which requires not only the estimation of model coefficients but also the determination of fractional orders with the tedious calculation of fractional order derivatives. This study focuses on an identification scheme, in the time domain, of dynamic systems described by linear fractional order differential equations. The proposed identification method is based on the recursive least squares algorithm applied to an ARX structure derived from the linear fractional order differential equation using adjustable fractional order differentiators. The basic ideas and the derived formulations of the identification scheme are presented. Illustrative examples are presented to validate the proposed linear fractional order system identification approach. Voir les détails
Mots clés : Adjustable fractional order differentiator, Least squares method, Linear fractional differential equation, Recursive identification.
Texture, misorientation and mechanical anisotropy in a deformed dual phase stainless steel weld joint
The deformation behavior of a duplex stainless steel weld joint is studied. A detailed texture analysis shows that the increase of the deformation percentage leads to a reinforcement of all possible {hkl}〈111〉and {hkl}〈100〉 components in austenite, and of the {hkl} 〈110〉 components in ferrite for both the base metal (BM) and the heat affected zone (HAZ). In the weld metal (WM), a strong scatter of the crystallographic orientation relationship (OR) initially found in the solidification microstructure is recorded after deformation. The analysis of the Kernel Average Misorientation (KAM) distribution shows that the deformation is more concentrated in the base metal than in the other parts of the weld joint. The final mechanical behavior studied through microhardness measurement and micromechanical calculations, allows us to separate the contribution of both microstructural and textural evolution to the overall strain hardening of the weld joint. Voir les détails
Mots clés : duplex stainless steel, deformation texture, mechanical anisotropy, TIG welding
Identification of Linear Fractional Systems of Commensurate Order
The identification of fractional order systems is a more difficult problem than the integer order systems because it requires not only the estimation of the model coefficients but also the determination of the fractional orders with the tedious calculation of fractional order derivatives. This paper addresses the identification of linear fractional systems of commensurate order. The proposed identification method is based on the recursive least squares algorithm applied to a linear regression equation derived from the linear fractional order differential equation using adjustable fractional order differentiator. The proposed technique does not require a prior knowledge of the commensurate order of the fractional linear differential equation. The derived formulations of the identification scheme are presented. Illustrative examples are also presented to validate the proposed linear fractional systems of commensurate identification approach. Voir les détails
Mots clés : Least squares method, Linear fractional differential equation, Recursive identification.
Adaptive support vector machine-based surface qualityevaluation and temperature monitoring. Applicationto billet continuous casting process
A method for surface quality evaluation and tem-perature monitoring of the billet in continuous casting isconsidered in this paper. This method uses the differencebetween the measured and the filtered temperature comput-ed using an adaptive support vector machine method. Thetemperature field, measured by an infrared camera, is affect-ed by an important noise called calamine (a metal oxidegenerated during the cooling process). The quality of thebillet ’ s surface temperature is connected to the secondarycooling behavior, and therefore an evaluation of the cala-mine effect is needed. Methods such as soft sensing andadaptive support vector machine are used for a global eval-uation of calamine intensity on the monitored area of thebillet in continuous casting. This kind of approaches isapplied in continuous casting process for constructing acomplementary condition monitoring system, which allowsan online calamine evaluation. Simulation results, based onthe measured surface temperature and the adaptive supportvector machine analysis, showed that this new combinedapproach is easily implementable and gives good resultswhen applied online. Voir les détails
Mots clés : Continuous casting . Surface billet casting . Infrared temperature measurement . Adaptive support vector machine (ASVM) . Process and quality evaluation
Improvement of photoelectrochemical and opticalcharacteristics of MEH-PPV using titaniumdioxide nanoparticles
The use of bulk heterojunctions can increase the ef?ciency of exciton dissociation inpolymer-based photovoltaics. We prepared and characterized bulk heterojunctions ofpoly[2-methoxy-5-(20-ethylhexyloxy)-p-phenylenevinylene] (MEH-PPV) and titaniumdioxide nanoparticles deposited by spin coating on indium tin oxide substrates. Thesurface morphology of the MEH-PPVþTiO2 composite ?lms revealed that addition ofTiO2 nanoparticles increased the ?lm roughness. The effect of TiO2 nanoparticles on thephotoelectrochemical and optical characteristics of MEH-PPV polymer heterojunctionswas studied. Addition of TiO2 nanoparticles improved the absorbance of MEH-PPVcomposite ?lms. Moreover, the photocurrent of the composite devices increased withthe TiO2 nanoparticle concentration. These observations provide an insight into newapproaches to improve the light collection ef?ciency in photoconductive polymers Voir les détails
Mots clés : Organic–inorganic compounds MEH-PPV Morphology Photoelectrochemical properties
Inferential sensor – Based adaptive principal componentsanalysis for mechanical properties prediction and evaluation
This paper is concerned with a method for on-line quality prediction and evaluation ofmechanical properties in metal testing. This method uses an Adaptive Principal ComponentAnalysis (APCA) as a multi predictor of different sub-models defining the mechanical prop-erties such as constraints limits and elongation. The PCA technique, characterized by itsmultivariate component, is strongly recommended to model a multi-input-multi-outputsystem. The complex system is generally known as a non-linear and unsteady state pro-cess. The PCA method is a linear projection. To adapt it and to improve the prediction accu-racy, a variant of this method is considered based on iteratively using a specific algorithm.This kind of approaches is applied for constructing an inferential model, which allows areliable and accurate predictor. Simulation results, based on the measured and computeddata using the above-cited method, show that the proposed approach is easily implement-able and give an accurate prediction. Voir les détails
Mots clés : Soft sensor, Mechanical testing, Adaptive principal component analysis, Uncertainties evaluation
Analysis of High Tc Superconducting Rectangular Microstrip Patches over Ground Planes with Rectangular Apertures in Substrates Containing Anisotropic Materials
A rigorous full-wave analysis of high superconducting rectangular microstrip patch over ground plane with rectangular aperture in the case where the patch is printed on a uniaxially anisotropic substrate material is presented. The dyadic Green’s functions of the considered structure are efficiently determined in the vector Fourier transform domain. The effect of the superconductivity of the patch is taken into account using the concept of the complex resistive boundary condition. The accuracy of the analysis is tested by comparing the computed results with measurements and previously published data for several anisotropic substrate materials. Numerical results showing variation of the resonant frequency and the quality factor of the superconducting antenna with regard to operating temperature are given. Finally, the effects of uniaxial anisotropy in the substrate on the resonant frequencies of different TM modes of the superconducting microstrip antenna with rectangular aperture in the ground plane are presented. Voir les détails
Mots clés : Anisotropic material, Anisotropic substrates, Dyadic green's functions, Operating temperature, Rectangular aperture, Rectangular microstrip patch, Superconducting microstrip antennas, Uniaxially anisotropic substrate