Liste des publications
Resonant Frequency of Tunable Microstrip Ring Antenna Printed on Isotropic or Uniaxially Anisotropic Substrate
In this study, the resonant frequency of annular ring microstrip resonator with uniaxial anisotropic substrate and air gap layer is analyzed. The cavity model for simple ring microstrip antenna is extended with some modifications for the tunable geometry taking into account the anisotropy inthe layer. The theoretical resonant frequency results are in very good agreement with the experimental results reported elsewhere. The air gap tuning effect on the resonant characteristics is also investigated for fundamental and higher order modes. Voir les détails
Mots clés : Microstrip, Ring Antenna
Resonance of High Tc Superconducting Microstrip Patch in a Substrate-Superstrate Configuration
The effect of a protecting dielectric superstrate on the resonance of a high Tc superconducting microstrip patch is investigated. The analysis approach is based on the spectral-domain method of moments in conjunction with the complex resistive boundary condition. The complex surface impedance of the superconducting thin film is determined using London’s equation and the two-fluid model of Gorter and Casimir. Numerical results show that the resonant frequency of the high Tc superconducting rectangular patch decreases monotonically with increasing superstrate thickness, the decrease being greater for high permittivity loading. Voir les détails
Mots clés : Resonance, Microstrip antenna, Superstrate
Synthesis, characterization of cesium and cobalt substitutedwells–Dawson heteropolyoxotungstates salts and their photocatalytic applications
Heteropoly compounds in the solid state are ionic crystals (sometimes amorphous) consisting of large polyanions, cations, water of crystallization, and other molecules. Heteropolyacids (HPAs) have several advantages as catalysts. On the one hand, they have a very strong Brønsted acidity, especially the cobalt and cesium salts; on the other hand they are exhibiting fast reversible multielectron redox transformations under mild conditions. The cobalt and cesium salts of wells–Dawson HPAs were synthesized and characterized using elemental analysis and spectroscopic techniques (31P-NMR, FT-IR).The wells–Dawson anions possess the ability to accept or release electrons through an xternal potential or upon exposure to UV radiation (photochemical reactions). The catalytic tests of these salts were investigated on phenol degradation where the UV photodegradation of acidified aqueous solutions (pH = 2) were studied in a batch photoreactor under ambient temperature and continuous circulation of phenol solution. The results reveal high catalytic activity for two HPAs, the best catalyst is the salt of cesium; where the presence of cesium improves significantly both the photcatalytic activity and the selectivity to oxalic acid. Voir les détails
Mots clés : Characterisation Heteropolyacids Dawson- Type, Cesium, Cobalt Photo Catalysis
Influence of heat treatment condition on passivity of titaniumaluminum-vanadium alloy in sodium chloride solution
Corrosion of Ti6Al4V was study with different heat treatments in3,5% NaCl solution by electrochemical measurements, includedpotenthiodynamic polarization curves, linear polarization resistance(LPR) measurements and electrochemical impedance spectroscopy(EIS), in order to focus on exploring the effect of annealing on theelectrochemical response in a quantitative manner. The samples wereprepared in the state of the art; heat treatments were applied at fourdifferent temperatures of 550, 750, 950 and 1100°C. Themicrostructure of samples has been studied using the opticalmicroscopy and the mechanical properties have been evaluated suchas microhardness HV. The electrochemical test show that the corrosionrates of treated samples at temperature equal or more then 750 ° C;are much better for the untreated sample. Although, the corrosionproduct on the surface is identified as titanium dioxide by XRD in allsamples. Voir les détails
Mots clés : Ti6Al4V, corrosion, heat treatment, Corrosion product, XRD
Morphology and Photoelectrochemical Characterization of MEH-PPV/PCBM Composite Film Doped with TiO2 Nanoparticles
Poly[2-methoxy-5-(20-ethylhexyloxy)-p-phenylenevinylene] (MEH-PPV), [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) and titanium dioxide (TiO2) nanoparticles (n-type) were dissolved, mixed and deposited by physical methods (spin-coating) on indium tin-oxide (ITO) substrate. The incorporation of the titanium dioxide nanoparticles changed the morphology and increased the roughness of polymers film (MEH-PPV/PCBM), and the photocurrent density of the composite (MEH-PPV/PCBM +n-TiO2) was higher than that of single MEH-PPV/PCBM film. The study showed that the presence of n-TiO2 particles in the polymeric film improves the photoelectrochemical properties of MEH-PPV/PCBM composite. Voir les détails
Mots clés : Photocurrent density, Electrochemical property, Hybrid coating, Conducting Polymer, titanium dioxide, Organic nanostructures
Bearing fault diagnosis based on feature extraction and condition classification
Bearing fault diagnosis has attracted significant attention over the past few decades. It consists of two major parts: vibration signal feature extraction and condition classification for the extracted features. In this paper, feature extraction from faulty bearing vibration signals is performed by a combination of signal's time-varying statistical parameters and features obtained through the preprocessing of the vibration signal samples using Db2 discrete wavelet transform at the fifth level of decomposition. In this way, an 8-dimensional vector of the vibration signal feature is obtained. After feature extraction from vibration signal, the support vector machine (SVM) was applied to automate the fault diagnosis procedure. To improve the classification accuracy for bearing fault prediction, particle swarm optimization (PSO) is employed to simultaneously optimize the SVM kernel function parameter and the penalty parameter. The results have shown feasibility and effectiveness of the proposed approach. Voir les détails
Mots clés : Condition monitoring, Discrete wavelet transform, Roller Bearing, Particle Swarm Optimization, Statistical parameters, Support vector machine
Short-term HDPE pipe degradation upon exposure to aggressiveenvironments
Natural gas and drinkable water are regularly transported by underground polyethylene pipenetworks in urban and rural areas. The interaction between materials such as high density polyethylene(HDPE) and contact environments is a critical factor which strongly influences pipe behaviour for short andlong terms. The aim of this study is to establish separate effects of H2SO4, a mixture of toluene–methanoland distilled water on the mechanical properties of HDPE pipes. Two testing geometries representing thepipe wall are considered: (1) orthogonally machined filaments and (2) ASTM standard specimens. Tensiletests are carried out on both specimen types using a computer controlled Zwick machine. It is observedthat chemical environments degrade mechanical properties causing a structural weakening especially thosespecimens exposed to organic solvent and acid. For instance, filaments show a reduction in elastic modulusof 64% after 7 days of exposure to toluene and methanol. Compared to standard specimens, the obtainedproperties are much higher indicating that geometry has an effect on the measured values. Fluctuationsin mechanical properties are most probably caused by cristallinity gradients all the way through the pipewall. This type of results allowed establishing the linear relationship between the elastic modulus and theyield stress and is intended to contribute to a better understanding of properties heterogeneity effects whenexposed to unfavourable environments. Voir les détails
Mots clés : polyethylene pipe, environmental stress effect, short-term degradation, yield stress-Young’s modulus correlations, failure strain, OIT
Fusion-based shape descriptor for weld defect radiographic image retrieval
Content-based image retrieval with relevance feedback plays nowadays an important role in several machine vision applications. In this paper, such a system is proposed for weld radiograms in radiographic testing, with the aim of searching from the overall image database, interactively with the radiograph expert, discontinuities similar to some common weld defect types such as crack, lack of penetration, porosity, and solid inclusion. Therefore, shape features characterizing efficiently these defect indications are required. Two shape descriptors are proposed: a shape geometric descriptor (SGD) consisting of a set of invariant shape geometric measures chosen on the basis of their relationships with the weld defect classes and a generic Fourier descriptor (GFD) known for its discrimination powerfulness for planar filled objects. To improve the weld defect retrieval results, we propose a new fusion-based shape descriptor. The idea of the fusion strategy is to examine the compactness and the rectangularity measures in SGD and derive a criterion permitting the design of a new descriptor f(GFD,SGD) able to better discriminate, particularly, between the problematic defect classes of crack and lack of penetration. Experiments conducted on weld defect image database show the strength of the proposed hybrid descriptor compared to GFD and SGD, simply or hierarchically concatenated or used separately. Voir les détails
Mots clés : Radiographic testing, weld defect, CBIR, SGD, GFD, f(GFD, SGD)
Theoretical prediction of the structural, electronic,and thermal properties of Al1-xBxAs ternary alloys
First-principles calculations are performed to study the structural, electronic, and thermalproperties of the AlAs and BAs bulk materials and Al1-xBxAs ternary alloys using the fullpotential-linearized augmented plane wave method within the density functional theory.The structural properties are investigated using the Wu–Cohen generalized gradientapproximation that is based on the optimization of total energy. For band structurecalculations, both Wu–Cohen generalized gradient approximation and modified Becke-Johnson of the exchange-correlation energy and potential, respectively, are used. Thedependence of the lattice constant, bulk modulus, and band gap on the composition x wasanalyzed. The lattice constant for Al1xBxAs alloys exhibits a marginal deviation from theVegard's law. A small deviation of the bulk modulus from linear concentration depen-dence was observed for these alloys. The composition dependence of the energy band gapwas found to be highly nonlinear. Using the approach of Zunger and coworkers, themicroscopic origins of the gap bowing were detailed and explained. The quasi-harmonicDebye model was used to determine the thermal properties of alloys up to 500 K. Voir les détails
Mots clés : Band structures, First principle calculations, Ternary alloys, Thermal Properties
Task Performance Evaluation for Supervisory Control Systems
Integrated multi-modal Supervisory Control Systems (ISCS) are a new generation ofcomplex and synergistic Human-Machine Interaction Systems (HMIS). This paper deals withmulti-modal interaction and control applied to Human Robot Systems (HRS). A task performanceevaluation technique dedicated for multi-modal interaction and control is proposed. It enablescomparison of task performance carried out by using different selection of control modes or bydifferent operators. Objective and subjective performance measures are defined.Based on the Analytical Hierarchy Process method (AHP) which takes into account qualitative andquantitative attributes and criteria, a task performance evaluation technique has been proposed forsupervisory systems which enables multimodal interaction modes .Experimental results have been carried out and some preliminary results will be presentedconcerning parallel cable-based manipulators. Voir les détails
Mots clés : Task performance evaluation, human factors, Analytical Hierarchy Process, Adaptive supervisory control, Multi-modal interaction, Cable-based robots, Graphical-user interface.