Liste des publications
Enhancement of photoelectrochemical and optical characteristics using a TiO2 nanoparticles interlayer in MEH-PPV heterojunction devices
In this work, MEH-PPV+TiO 2 composite material was prepared by incorporation of titanium oxide nonoparticles (TiO 2) into poly[2-methoxy-5-(2′-ethylhexyloxy)-p-phenylenevinylene] (MEH-PPV) polymer matrix and deposited by spin coating on glass and indium thin oxide (ITO) substrates. The absorbance of various MEH-PPV composites incorporating different concentrations of TiO 2 nanoparticles shows that addition of TiO 2 improves absorption of the composites. TiO 2 and the conjugated polymer have absorption in the UV and visible regions, respectively. As a result, the composite has slightly broader absorption. In addition, absorption of the composite shows that the polymer induces a certain structuring, as evidenced by the presence of fine structures. The effect of inserting a TiO 2 nanoparticles interlayer in the MEH-PPV polymer heterojunction device on the photoelectrochemical and optical characteristics of the device has been studied. The modified device (MEH-PPV+TiO 2) shows improved photocurrent density characteristics, and increased with TiO 2 concentration. The study showed that the presence of inorganic semiconductor nonoparticles (TiO 2) in polymer film improves the optical and the photovoltaic properties of MEH-PPV, and was designed to explore new approaches to improve light-collection efficiency in polymer photovoltaic. Voir les détails
Mots clés : Hybrid composite materials, MEH-PPV, morphology, photocurrent
Effect of the austenite hot deformation on the transformation microstructural mechanics parameters of a microalloyed steel
This study was established to optimize the heat treatments - mechanical and improve the mechanical properties of microalloyed steel with Nb-Ti-V for the production of hot rolled strip. A database of the main parameters of deformation of this steel was developed by dilatometer-plastometer tests. The cooling experiments were used to simulate sequences of the industrial process. The results of these investigations used to analyze the effect of deformation parameters on the evolution of the ferritic structure and mechanical properties of steel. The conditions of rolling deformation bands must be simulated by experimental investigations in order to find a favorable microstructure while choosing the appropriate technological parameters. The microstructural evolution during hot rolling is a dominant factor for achieving the optimal properties. The chemical composition can predict the limits of the desired properties, but these limits depend significantly thermomechanical conditions imposed. A good adaptation of these conditions with the performance of the material allows for a high quality finished product. These investigations will be the basis for determining in advance of the microstructure, mechanical properties for subsequent monitoring of the industrial process. Voir les détails
Mots clés : Microalloyed steel, Austenite, hot deformation, mechanical properties, structure
Impact of the inhomogeneous structure of the active layer on the transfer characteristic of polysilicon TFT's
Recently polycrystalline silicon (pc-Si) thin film transistors (TFT's) have emerged as the devices of choice for many applications. The TFT's made of a thin un-doped polycrystalline silicon film deposited on a glass substrate by the Low Pressure Chemical Vapor Deposition technique LPCVD have limits in the technological process to the temperature <; 600°C. The benefit of pc-Si is to make devices with large grain size. Unfortunately, according to the conditions during deposition, the pc-Si layers can consist of a random superposition of grains of different sizes, where grains boundaries parallels and perpendiculars appear. In this paper, the transfer characteristics IDS-VGS are simulated by solving a set of two-dimensional (2D) drift-diffusion equations together with the usual density of states (DOS: exponential band tails and Gaussian distribution of dangling bonds) localized at the grains boundaries. The impact of thickness of the active layer on the distribution of the electrostatic potential, the effect of density of intergranular traps states and grain size on the TFT's transfer characteristics IDS-VGS have been also investigated. Voir les détails
Mots clés : Transistor TFT, 2D simulation, heterogeneous structure, Grain Size, transfer characteristic
Segmentation of welding defects using level set methods
Non-destructive testing (NDT) is a technique used in science and industry to evaluate the properties of a material without causing damage. In this paper we propose a method for segmenting radiographic images of welding in order to extract the welding defects which may occur during the welding process. We study different methods of level set and choose the model adapted to our application. The methods presented here take the property of local segmentation geodesic active contours and have the ability to change the topology automatically. The computation time is considerably reduced after taking into account a new level set function which eliminates the re-initialisation procedure. Satisfactory results are obtained after applying this algorithm both on synthetic and real images. Voir les détails
Mots clés : image segmentation, Level set, weld defects, Radiographic image
Uniaxial Anisotropic Substrate Effects on the Resonance of an Equitriangular Microstrip Patch Antenna
Using a new combined approach, the effect of the uniaxial anisotropic dielectrics on the resonant frequency and radiation field of an equi-triangular patch antenna is presented in this paper. The problem is analysed in the spectral domain using the moment method and an electric field integral equation combined with a mathematical approach. However, the dyadic Green's functions corresponding to the proposed structure are separately developed and the Fourier transform of the basis current components are calculated mathematically using 'the reference element' method. Numerical results show that the change in the resonant frequency and the radiation patterns of the antenna is due primarily to a small disturbance of the substrate's nature. Then the effect of the uniaxial anisotropic materials is a significant parameter and most essential on the microstrip antenna characterization. Voir les détails
Mots clés : Uniaxial anisotropic dielectric, moment method, spectral domain
In vitro microemboli classification using neural network models and RF signals
Emboli classification is of high clinical importance for selecting appropriate treatment for patients. Several ultrasonic (US) methods using Doppler processing have been used for emboli detection and classification as solid or gaseous matter. We suggest in this experimental study exploiting the Radio-Frequency (RF) signal backscattered by the emboli since they contain additional information on the embolus than the Doppler signal. The aim of the study is the analysis of RF signals using Multilayer Perceptron (MLP) and Radial-Basis Function Network (RBFN) in order to classify emboli. Anthares scanner with RF access was used with a transmit frequency of 1.82 MHz at two mechanical indices (MI) 0.2 and 0.6. The mechanical index is given as the peak negative pressure (in MPa) divided by the square root of the frequency (in MHz). A Doppler flow phantom was used containing a 0.8 mm diameter vessel surrounded by a tissue mimicking material. To imitate gas emboli US behaviour, Sonovue microbubbles were injected at two different doses (10ll and 5ll) in a nonrecirculating at a constant flow. The surrounding tissue was assumed to behave as a solid emboli. In order to mimic real clinical pathological situations, Sonovue concentration was chosen such that the fundamental scattering from the tissue and from the contrast were identical. The amplitudes and bandwidths of the fundamental and the 2nd harmonic components were selected as input parameters to the MLP and RBFN models.Moreover the frequency bandwidths of the fundamental and the 2nd harmonic echoes were approximated by Gaussian functions and the coefficients were used as a third input parameter to the neural network models. The results show that the Gaussian coefficients provide the highest rate of classification in comparison to the amplitudes and the bandwidths of the fundamental and the 2nd harmonic components. The classification rates reached 89.28% and 92.85% with MLP and RBFN models respectively. This short communication demonstrates the opportunity to classify emboli based on a RF signals and neural network analysis. Voir les détails
Mots clés : Microemboli, Gaseous embolus, Solid embolus, RF signals, Neural Network
VIBRATION MONITORING FOR FAULT DIAGNOSIS IN ROTATING MACHINERY USING WAVELET TRANSFORM
Vibration analysis is essential in improving condition monitoring and fault diagnostics of rotating machinery. Many signal analysis methods are able to extract useful information from vibration data. Currently, the most of these methods use spectral analysis based on Fourier Transform (FT). However, these methods present some limitations; it is the case of non-stationary signals. In the present work, we are interested to the vibration signal analysis by the Wavelet Transform (WT). The WT is one of the most important methods for signal processing; it is especially suitable for non-stationary vibration measurements obtained from accelerometer sensors. The monitoring results indicate that the WT can diagnose the abnormal change in the measured data. Voir les détails
Mots clés : Vibration analysis, Fault Diagnosis, Rotating machinery, Spectral analysis, Wavelet transform
Potentials of Inx Ga1-x N photovoltaic tandems
During the past few years a great variety of multi-junction solar cells has been developed with the aim of a further increase in efficiency beyond the limits of single junction devices. In this work, the solar power conversion efficiency of InxGa1-xN based tandem solar cells was investigated. With this intention, one simulation of the spectral response and the current-voltage characteristic was carried out using a simulation program designed under ‘Visual Basic 5’ language for this reason. Our calculation indicates that the attainable efficiency can be enhanced up to 34 % and 37% for tandems with double and triple junctions respectively, obtained under 1-sun AM1.5 illumination and at ambient temperature, using realistic material parameters. A comparison has been made of our results with those of other models. Voir les détails
Mots clés : Tandem, InGaN, Spectral response, I-V characteristics
Effect of the heat treatment on the microstructural evolution of the Nickel based superlloy
The effect of heat treatment on the microstructure of cobalt-rich nickel based superalloy was studied applying scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The aim of the present work was to investigate the formation and evolution of different phases during the heat treatment of superalloy similar to Udimet 500. The presence of a relatively high volume fraction of γ’ particles in the γ matrix suggests on inefficient cooling rate during oil quenching from 1150°C. Carbides such as MC primary carbides of the type TiC and MoC as well as secondary carbides M23C6 (Cr23C6) were found in grains and at grain boundaries. Voir les détails
Mots clés : superalloy; heat treatment;, SEM and TEM; γ' particles; carbides .
Monotoring of air quality in an iron foundry(Case of NOx, SO2 , benzene and dust)
The requirements as regards ecology are imposed more and more by the legislator. The cast iron foundries,using the cupola furnace like means of fusion and several other materials for the clothes industry of the mouldsand the cores, produce a great quantity of noxious gas and dust. These polluants are discharged into theatmosphere and are very harmful for the human health of the workers and the environment bordering the sitesof production. So, our study relates to the monitoring of polluting gases such as: the so nox and btx ,2continuously during a working station by passive sensors and to measure the dust level reigning in the variousworkshops of the foundry by the method of decantation (method of bergeroff). All these pollutants are knownfor their harmful effect on human health. The strategic aims had by this study is to index the atmosphericemissions, to determine the level of the air pollution generated by the activity of a manufacturing unit ofcastings out of cast iron using like moulding the traditional process, to determine the peaks of concentration ofpolluting gases (so nox and btx), to quantify and analyze pollution by the suspended particles, to work out a2cartography of the air pollution) and to compare the values obtained relating to the current situation withlimiting values who. The results of taken measurements showed a very strong pollution reaching of the values333236.6 µg/m for benzene (c6h6), 508.2 µg/m for the dioxide of sulfur (so ) and 722.4 µg/m for oxides of2nitrogen (nox). The concentrations of dusts are in on this side limiting value of who. Their chemical analysisshowed the presence of much silica and iron. Voir les détails
Mots clés : cast iron foundry, gaseous polluant, atmosphere, dust, values who.