Liste des publications
PURIFICATION OF CARBON NANOTUBES
Nanotubes have never ceased to make object of research around the world. The scientific community has high hopes on these nanomaterials seen their exceptional properties and their various applications. The as-prepared CNTs contain impurities such as metal catalysts, amorphous carbon, and multi-shelled carbon particles. These impurities must be removed to realize the intrinsic properties of the CNTs. Purification is an essential issue to be addressed. Here we present an overview of the purification of carbon nanotubes, based on two methods of purification, filtration and acid treatments. Voir les détails
Mots clés : CNTs, Filtration, acidacid treatments treatments
Enhancement of rolling bearing fault diagnosis based on improvement of empirical mode decomposition denoising method
Signal processing is a widely used tool in the field of monitoring and diagnosis of rolling bearing faults. The vibration signals of rolling bearing contain important information which can be used for early detection and diagnosis of faults. These signals are usually noisy and masked by other sources and therefore the information about the fault can be lost. In this work, we propose an enhancement of rolling bearing fault diagnosis based on the improvement of empirical mode decomposition (EMD) denoising method. This method is made to extract the useful fault signal in order to use the detection indicators such as the kurtosis and the envelope spectrum. Firstly, EMD is applied to the vibration signals to obtain a series of functions called the intrinsic mode functions (IMFs). Secondly, we present an approach based on the energy content of each mode to determine the trip point which allows selecting the relevant modes. The singular selected IMFs are determined by comparing the average energy of all the unselected IMFs with the energy of each selected IMFs; then, an optimized thresholding operation is performed to denoise these IMFs. Finally, the kurtosis and spectral envelope analysis were investigated for early detection and localization of the fault position. Different experimental data are used to validate the effectiveness of the proposed method. The obtained results showed that the proposed method is more efficient and more sensitive to the early detection and diagnosis of rolling bearing faults than the conventional denoising method. Voir les détails
Mots clés : Vibration analysis, bearing Fault diagnosis, EMD, threshold Denoising, energy, Relevant mode selection, envelope, Kurtosis
Rolling bearing fault diagnosis based on improved complete ensemble empirical mode of decomposition with adaptive noise combined with minimum entropy-deconvolution
The vibration signals provide useful information about the state of rolling bearing and the diagnosis of the faults requires an accurate analysis of these signals. Several methods have been developed for diagnosing rolling bearing faults by vibration signal analysis. In this paper, we present an improvement of the technique Complete Ensemble Empirical Mode Decomposition with Adaptive Noise (CEEMDAN), this technique is combined with the Minimum Entropy Deconvolution (MED) and the correlation coefficient to diagnose defects. First, the vibration signal was decomposed by the improved CEEMDAN decomposition into several oscillatory modes called Intrinsic Mode Function (IMF). After calculation of the correlation coefficients between the original signal and their IMFs, the modes with higher coefficients are selected as the relevant modes. Secondly, the MED technique is applied to the selected modes in order to improve the sensitivity of the scalar and frequency indicators of faults detection. Finally, kurtosis and envelope analysis are used to detect and locate the defect position. The simulation is carried out using the Case Western University data base and the results obtained show that the proposed method provides very good results for the early detection and diagnosis of defects and can efficiently extract the defective characteristics of the rolling bearing. Voir les détails
Mots clés : vibration signal, rolling bearing fault, complementary ensemble empirical mode decomposition, coefficient correlation, minimum entropy deconvolution, Kurtosis, Envelope analysis
Temperature Evolution, Microstructure and Mechanical Properties of Heat-Treatable Aluminum Alloy Welded by Friction Stir Welding: Comparison with Tungsten Inert Gas
Friction Stir Welding (FSW) is a solid-state welding technique that can join material without melting the plates to be welded. In this work, we are interested to demonstrate the potentiality of FSW for joining the heat-treatable aluminum alloy 2024-T3 which is reputed as difficult to be welded by fusion techniques. Ther eafter, the FSW joint is compared with another one obtained from a conventional fusion process Tungsten Inert Gas (TIG). FSW welds are made up using an FSW tool mounted on a milling machine. Single pass welding was applied to fabricated TIG joint. The comparison between the two processes has been made on the temperature evolution, mechanical and microstructure behavior. The microstructural examination revealed that FSW weld is composed of four zones: Base metal (BM), Heat affected zone (HAZ), Thermo-mechanical affected zone (THAZ) and the nugget zone (NZ). The NZ exhibits a recrystallized equiaxed refined grains that induce better mechanical properties and good ductility compared to TIG joint where the grains have a larger size in the welded region compared with the BM due to the elevated heat input. The microhardness results show that, in FSW weld, the THAZ contains the lowest microhardness values and increase in the NZ; however, in TIG process, the lowest values are localized on the NZ. Voir les détails
Mots clés : Friction Stir Welding, tungsten inert gaz, aluminum, microstructure
Modeling and Simulation of Biaxial Strained P-MOSFETs: Application to a Single and Dual Channel Heterostructure
The objectives of this work are focused on the application of strained silicon on MOSFET transistor. To do this, the impact and benefits obtained with the use of strained silicon technology on p-channel MOSFETs are presented. This research attempt to create conventional and two-strained silicon MOSFETsfabricated from the use of TCAD, which is a simulation tool from Silvaco. In our research, two-dimensional simulation of conventional MOSFET, biaxial strained PMOSFET, and dual-channel strained P-MOSFET has been achieved to extract their characteristics. ATHENA and ATLAS have been used to simulate the process and validate the electronic characteristics. Our results allow showing improvements obtained by comparing the three structures and their characteristics. The maximum of carrier mobility improvement is achieved with the percentage of 35.29 % and 70.59 % respectively, by result an improvement in drive current with the percentage of 36.54 % and 236.71 %, and reduction of leakage current with the percentage of 59.45 % and 82.75 %, the threshold voltage is also enhanced with the percentage of 60 % and 61.4%. Our simulation results highlight the importance of incorporating strain technology MOSFET transistors. Voir les détails
Mots clés : Biaxial strain, CMOS technology, SILVACO-TCAD, Strained silicon layers
Structural and magnetic properties of FeCuNi nanostructured produced by mechanical alloying
We investigated the magnetic, morphological, and structural properties of FeCuNi. The powder alloy iselaborated by mechanical alloying process for 10 h with varying the Cu content. The aims of this workare to study the effect of Ni/Cu ratio on the magnetic and microstructure properties. The crystallite sizedecreases with the increase of Ni. The reduction of crystallite size proceeds slowly until 17 nm for 30% ofNi. Coercivity and saturation magnetization increases from 105.4 Oe, 122.568 emu/g to 156.77 Oe,140.679 emu/g respectively caused by the increase of the concentration of Cu and dislocation densityas well as the decrease of the crystallite size Voir les détails
Mots clés : FeCuNi nanostructured, Mechanical Alloying, MEB, DRX, VSM
Optoelectronic properties of the new quaternary chalcogenides Zn2CuInTe4 & Cd2CuInTe4: ab-initio study.
In order to exploit the fundamental properties of the new tellurides quaternary diamond-like structure Zn2CuInTe4 and Cd2CuInTe4, first principles investigation in the frameworkof the Full-Potential LAPW scheme have been carried out for that purpose. We used theWu and Cohen generalized gradient approximation (GGA-WC) to calculate the optimizedstructure that corresponds to the global minima of the energy. Enthalpy of formation showsthat the most stable structures are the relaxed ones. The EV-GGA and the TB-mBJ approx-imations were also used for electronic and optical properties. The equilibrium electronicparameters found are in good agreement with the previous results. The real and thecient, theopt imaginary parts of the dielectric function, the refractive index, the extinction coeffiicalconductivity, the absorption coefficient, the loss function and the reflectivity are reviewedin the large spectral range of photon energy. The present study demonstrates a variety ofnovel electronic and optical properties, which make these compounds highly promising foroptoelectronic materials. Voir les détails
Mots clés : DFT, Quaternary tellurides, Enthalpy of formation, band gap, Absorption coefficient
First principles investigation of optoelectronic properties ofZnXP2 (X = Si, Ge) lattice matched with silicon for tandemsolar cells applications using the mBJ exchange potential
II-IV-V2 materials are attractive compounds for optoelectronic, photonic and photovoltaicapplications due to their valuable ternary chemistry. A primary technological challengein photovoltaics is to find and develop a lattice matched efficient material to be usedin combination with silicon for tandem solar cells. ZnSiP2 and ZnGeP2 chalcopyrites arepromising semiconductors that could satisfy these criteria. Particularly, ZnSiP2 is known tohave bandgap energy of∼2 eV and a lattice mismatch with silicon of 0.5%. In this work, thefirst principle calculations have been performed to investigate the structural, electronic andoptical properties of ZnSiP2 and ZnGeP2 in chalcopyrite structure within the Full Potential-Linearized Augmented Plane Wave (FP-LAPW) method based on the Density FunctionalTheory (DFT) as implemented in WIEN2K code. The local Density approximation (LDA) ofPerdew and Wang was used as exchange-correlation potential to calculate the structuralproprieties. Furthermore, the recently modified Becke-Johnson (mBJ) functional of Tranand Blaha was also employed to compute the electronic and optical properties in order toget best values of the band gap energy and some better degree of precision. The complexdielectric function, the complex refractive index, reflectivity, absorption coefficient, and theoptical conductivity were calculated to illustrate the linear optical properties of both compoundsZnSiP2 and ZnGeP2. At last, the obtained results indicate that ZnSiP2 and ZnGeP2are attractive materials in optoelectronic devices especially as a lattice matched materialwith silicon for tandem solar cells applications. Voir les détails
Mots clés : FP-LAPW, mBJ, Chalcopyrite, Electronic band structure, Linear optical properties
Optical study of cubic, and orthorhombic structures of XCaCl3 (X = K, Rb) compounds: Comparative Ab initio calculations
The study predicts the optical properties of cubic and orthorhombic structures of XCaCl3 (X = K, Rb) perovskite compounds through electronic band structure computation within the framework of density functional theory (DFT). The ground state functions are computed employing full potential linearized augmented plane wave (FP-LAPW) method. Improved band gap values and the electronic as well as optical properties were calculated by Tran and Blaha modified Becke–Johnson (mBJ) functional. The studied compounds’ density of states reveals that Cl-p states dominate the valence band. To understand the optical properties, and predicting the optically isotropic nature of these materials, the real and imaginary parts of dielectric function, refractive index, absorption coefficient, and energy loss spectra are plotted. The present study shows a great potential utilization in ceramic scintillators. Voir les détails
Mots clés : DFT, FP-LAPW, Perovskites, Optical parameters, Scintillators
Aeroelastic analysis of the air foil bearings in steady state
In recent decades, turbomachinery has known a special development with the aim of lightening rotating components of machinery and preserving the environment all for improving operating performances. The key elements in the turbomachinery are the air foil bearings that support rotors rotating at high speeds. In this paper, we are interested in the aero-elastic study of air foil bearing in stationary régime. The deformable structure contains a corrugated foils (bumps) fixed on a top-foil rigid which forms with rotor and air an elasto-aerodynamic contact. Numerical modeling was developed based on the Reynolds equation and an elastic deformation model of the bump depending on aerodynamic pressure, bump geometry and its mechanical proprieties. This problem non-linear is resolved using finite difference discretization and Newton-Raphson method. Finally, the calculations show the pressure distribution and field of film thickness as well as other fluid-structure interaction characteristics due to the functional conditions. Voir les détails
Mots clés : air bearing, aero-elastic, foil structure, film thickness, charge capacity