Liste des documents
Structure, magnetic and microwave studies of mechanically alloyed powders Fe45Ni35Co20
Nanocrystalline Fe-35 wt%Ni-20 wt%Co has been prepared by using a high-energy planetary ball mill with increasing milling time from 4 to 36 h. Microstructural characterisations showed the development of an face-centred cubic nanostructured Fe-35 wt%Ni-20 wt%Co alloy with an average crystallite size of 8 nm. The magnetic investigation revealed that the nanostructures obtained from a milling time of 36 h have the highest magnetic saturation and the lowest coercive field. In addition, the hardness and the electromagnetic absorption of the Fe-35 wt%Ni-20 wt%Co alloy were found to increase with the milling time. These evolutions could be attributed to the crystallite size and the strain variations in the samples during milling. Voir les détails
Mots clés : nanostructure, magnetic, nanocristalline, Mechanical Alloying, Fe, Co
Numerical simulation study of a high efficient AlGaN-based ultraviolet photodetector
In this paper, a two-dimensional (2D) numerical simulation study of a p+-n-n+ AlGaN-based ultraviolet (UV) photodetector, which is designed to achieve true solar blindness with a cutoff wavelength of 0.31 µm, is presented. The device performance is evaluated by investigating both the current density-voltage characteristics and the spectral response (SR). The proposed structure is optimized in terms of the fundamental geometrical and doping parameters. During the simulations, it was found that the detector is sensitive to the UV rays in the 0.155-0.37 µm wavelength range and the spectral response can reach 0.156 AW-1 under a light intensity of 1 Wcm-2 at zero-bias voltage and room temperature. This SR peak value increases further under reverse bias conditions. The temperature effect on the detector SR and the impact of an explicit trap concentration located into the p+ and n-region are also investigated. The spectral response decreases for a temperature exceeding 420 K. At the same time, the SR reference values begin to be affected only for acceptor and donor trap densities that are much higher than the local (total) doping concentration. Voir les détails
Mots clés : AlGaN, Numerical simulation, Photodetector, Spectral response, Trap Density
Electroless copper deposition on epoxy glass substrate for electrocatalysis of formaldehyde
In this paper, we investigated the characteristics of a structured copper (Cu) ?lm deposited on the surface of an insulating epoxy glass (EG) substrate via a facile electroless plating process. The ?lm produced by this method was found to be of high purity and has a homogeneous microstructure consisting of an assembly of numerous aggregates that vary in size from 1 to 5 mm depending on the electroless deposition time. The electrocatalytic activity of the prepared electrode was investigated for the electrooxidation of formaldehyde using cyclic voltammetry in 0.1 M NaOH solution. Results show that formaldehyde oxidation takes place at a low potential of -0.34 V with large anodic current densities. Voir les détails
Mots clés : copper, electroless plating, Formaldehyde, Oxidation, Thin films
Computational insights about the dynamic behavior for the inclusion process of deprotonated and neutral aspirin in β-cyclodextrin
Molecular dynamics was used to study the inclusion of neutral and deprotonated aspirin into the β-cyclodextrin (β-CD) cavity. The molecular dynamic simulation allows following the time dependent behavior of the formation of the inclusion complex. For both complexes, we find a reasonable and a realistic pattern of the complexation. The calculations show a single pathway consisting of a no reversible binding process leading to the complexation of aspirin. Whereas for deprotonated aspirin it has been observed a reversible binding, in which one way leads to the binding form, and the reverse way to the unbinding form. Throughout the simulation, the penetration of aspirin (ASA) or deprotonated aspirin (ASA−) inside the cavity occurs only with a phenyl ring entering first through the wider or narrower rim. The determination of free energy using unbiased and biased simulations of the corresponding inclusion processes gives more favorable inclusion process of aspirin than deprotonated aspirin. The inclusion of the guest molecule is found deeply embedded within ASA:β-CD complex whereas it is partial in ASA−:β-CD complex. Also, the orientation A of both complexes is found more favorable of ca. 1.9 kcal/mol, and of ca. 0.8 kcal/mol, respectively for neutral and deprotonated complex. Aspirin molecule establish one H-bond between the hydrogen carboxylic atom and one oxygen atom of primary hydroxyl group of β-CD; this H-bond is detected during about 20% of the simulation period. In addition, we found that water molecules in the first solvation layer are implied with hydrogen carboxylic atom and the keto oxygen atoms within H-bonds. While, water molecules of the second solvation layer is in interact with the O1 and O2 oxygen atoms of aspirin. Accordingly, based on the obtained results we can consider that the hydrophobic/hydrophilic interactions are the most important driving forces of the complexation assisted by stabilizing H-bonds. Voir les détails
Mots clés : Aspirin, Cyclodextrin, Inclusion complexes, Molecular dynamic simulation, Umbrella sampling, Hydrogen bonding
SIMULATION STUDY OF SUPER-RESOLUTION IN HYDROPHONE MEASUREMENTS OF PULSED ULTRASONIC FIELDS
In order to carry out reliable measurements of pulsed ultrasonic fields, the use of a piezoelectric hydrophone as receiver is recommended. However, due the finite size of the receiver aperture the measured acoustic pressure is affected by spatial averaging on the surface active face. The aim of this work is to deconvolve the spatial effects of the receiver hydrophone in order to reconstruct the pulsed ultrasonic field with a better spatial resolution. Hereby, the linear pulsed pressure field radiated in water by wideband planar transducers of 19 mm diameter, with central frequencies fc=2.25 MHz and fc=15 MHz are considered. The receivers are PVDF membrane hydrophones of 25 µm - thickness with rectangular and circular apertures. The results of this study show the strong dependency of the reconstruction quality upon the signal-to-noise ratio (SNR). Generally, the quality of the reconstruction decreases with decreasing SNR. Good reconstruction quality has been obtained with correlation coefficient larger than 0.9936 when the “acquired” signals are not too much noisy (SNR=60dB). In this case, improvement of the spatial resolution by a factor of 5 and 9 respectively could be reached. The reconstruction quality depends also upon the hydrophone dimensions, the axial distance to the source, the central frequency and the spectral frequency bandwidth of the pressure pulse. Voir les détails
Mots clés : Super-resolution, spatial inverse filter, spatial Wiener filter, PVDF hydrophone, pulsed ultrasonic field, ultrasonic field reconstruction.
A Bayesian Mumford–Shah Model for Radiography ImageSegmentation
This paper investigates the segmentation of radiographic images using a level set method based on a BayesianMumford–Shahmodel. The objective is to separate regions in an image that have very close arithmetic means, where a model based on thestatistical mean is not effective. Experimental results show that the proposed model can successfully separate such regions,in both synthetic images and real radiography images. Voir les détails
Mots clés : Level set
Preparation and characterization of spinel type Zn2TiO4 nanocomposite.
Zinc orthotitanate Zn2TiO4 spinel structures have been prepared by solid state reaction in two stages. First, a mixture of ZnO and TiO2 (67% anatase+33% rutile) in a molar ratio of 2:1 was mechanically milled for 6 and 18 h, at room temperature, in a high energy planetary ball mill under argon atmosphere. Next, the ball milled powders were calcined at 900°C for 2 h, pressed into pellets and then sintered for 4 h at 1100°C in air. Phase formation, microstructure, surface morphology and optical properties were characterized by X-ray di?raction, Raman scattering spectroscopy, Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy coupled with energy dispersive X-ray spectroscopy, atomic force microscopy and UV–visible spectro- photometery. The mechanical milling process for 6 h gives rise to the formation of nanocrystalline orthotitanate Zn2TiO4 (15.5%, =13.2 nm) in addition to unreacted rutile TiO2, anatase TiO2 and ZnO structures. As the milling process progresses up to 18 h, the volume fraction of Zn2TiO4 increases to about 44.5%. The sintered pellets exhibit a composite structure where about a small amount of rutile nanograins are dispersed into the Zn2TiO4 matrix. FT-IR and Raman results con?rm the biphasic character of the sintered pellets. The band gap energy is milling time dependent. It varies from 3.22 for pellet 6 h to 3.45 for pellet 18 h. Voir les détails
Mots clés : Mechanical Alloying, ZnO−TiO2 system, XRD, Raman spectroscopy, SEM
DETECTION OF BROKEN ROTOR BAR FAULT IN THE SQUIRREL CAGE INDUCTION MOTOR USING WAVELET PACKET ANALYSIS
The fault of broken rotor bars in a three phase induction motor is diagnosed by using the wavelet Packet analysis. In this paper Daubechies wavelet is selected as the wavelet base and the wavelet coefficient is obtained from the wavelet transform of current signal of the faulty induction motor. Tghe energy of wavelet components appear to be useful for detecting different electrical faults. In this paper we will study the problem of broken rotor bars Voir les détails
Mots clés : Wavelet Packet, Analysis, diagnosis fault, induction motor, broken bar
Simplified Modelling of Tandem Cold Rolling
In this paper, a calculation technique for solving the problem of regulatinginter-stand tension in a tandem cold rolling is proposed. Based on the slicesmethod, the proposed technique develops a computational model for a singlestand, and then generalizes it for five stands. The effectiveness of this technique is evaluated using experimental data acquired from tandem rolling millof IMittal steel complex of El-Hadjar-Algeria. By taking into account theelasticity of the rolls and using Newton’s method; the developed model can beused to calculate, successfully, the tensions correction of the five stands.Compared with the LAM3 software, the obtained results indicated that theproposed technique is effective and can be used to produce better performance of tandem cold rolling. Voir les détails
Mots clés : modelling, tandem cold rolling, slices method, elasticity, Newton’s method.
Core-rim structure formation in TiC-Ni based cermets fabricatedby a combined thermal explosion/hot-pressing process
TiC-Ni-based cermets were obtained by thermal explosion from different elemental mixtures(Ti, C, Ni and X, where X = Cr, Mo or W) and subsequently densified by hot-pressing under acyclic load. The whole process was performed in a single stage in the same experimentaldevice according to the following thermal and pressure procedure: a heating rate ramp up to1573 K without applying any load followed by an isothermal dwelling under a compressivecyclic load of 32 MPa. The thermal explosion synthesis occurred during the heating ramp at atemperature close to 1273 K that was practically independent of the starting nominalcomposition. The influence of different refractory elements on the chemical composition andmicrostructure of cermets was studied. SEM characterization showed that only with Mo andW, the cermets developed the characteristic core-rim structure. A high densification wasachieved, but decreased when the refractory elements were added. Nevertheless, in thesecases higher hardness values were obtained. Voir les détails
Mots clés : Cermets, Thermal explosion, Core-rim microstructure, Solid-solution carbides