Nombre total de résultats : 258
Pertinence Titre A-Z Plus récents Plus anciens
10 25 50
Année de publication

Structural, electronic properties of compounds AlAs, BAs and AlP, BP

K. BOUBENDIRA, H. Meradji, S. Ghemid, A.Boumaza, H.Meradi  (2013)
Article de conférence

We determine the structural, electronic properties of AlAs, BAs and AlP BP alloys using the full potential-linearized augmented plane wave method (FP-LAPW) within the density functional theory (DFT). The exchange-correlation potential is treated by the generalized gradient approximation (WC-GGA). The investigation on the effect of composition on lattice constant, bulk modulus and band gap shows not linear dependence on the composition. The ground state properties such as lattice constant, bulk modulus, pressure derivative of the bulk modulus are in good agreement with numerous experimental and theoretical data. For the electronic properties, we used the mBJ-LDA approximation. The bowing of the fundamental gap versus composition predicted on the composition is in a good agreement with experiment. Voir les détails

Mots clés : FP-LAPW, DFT, Ternary alloys, bands structure, bowing gap and thermodynamic propertie

Etude  thermohydraulique du comportement du bain de fusion au cours du soudage TIG

A.H. ZITOUNI, M. AISSANI, Y. Benkedda  (2012)
Article de conférence

Dans ce travail nous nous intéressons à la modélisation du comportement thermohydraulique du bain de fusion lors du soudage TIG sans métal d’apport. Pour cela, nous développons un modèle mathématique décrivant le transfert thermique couplé avec l’écoulement du fluide fondu au sein du bain fondu.Une simulation numérique (2D axisymétrique) de soudage TIG d’une tôle en acier inoxydable 304L est donc menée, en utilisant le code du calcul Comsol®4.2 basé sur la méthode des éléments finis. Les résultats montrent un bon accord avec la littérature. Voir les détails

Mots clés : Modélisation thermohydraulique, soudage TIG, Comsol®, bain de fusion

Optimization of Optical Gain in Inx Ga1-xSb/GaSb unstrained quantum well structures for detection

Said Dehimia, Aissat Abdelkaderb, Djamel Haddadc, Lakhdar Dehimid  (2015)
Article de conférence

In this paper we study the effects of In concentration, temperature, quantum well width and carrier density on optical gain for GaSb/In1-xGaxSb/GaSb untrained quantum well structures. This system was chosen as it is useful in infrared emission, finally, we introduce the optimum structure of quantum well to obtain the maximum optical gain, at room temperature and infrared emission particularly 2.3 (µm), for the use this structure in application of spectroscopic analysis of the gases specially CH4. Voir les détails

Mots clés : Quantum well, In1-xGaxSb, optical gain, laser, Detection

Reconstruction of Pulsed Ultrasonic Fields Received by a hydrophone of rectangular aperture by application of inverse methods.

W. Djerir, T. Boutkedjirt, A. Badidi Bouda  (2013)
Article de conférence

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. The output signal may also be distorted because of the frequency variations of its transfer function. The aim of this work is to deconvolve the spatio-temporal effects of the receiving chain (hydrophone, cable, oscilloscope...) in order to reconstruct the pulsed ultrasonic field with higher spatial and temporal resolution. This constitutes an inverse problem, which has been encountered in various domains of physics. The possibility of deconvolving the spatial effects has been shown for harmonic ultrasonic fields. The present contribution is a generalization of the study to pulsed ultrasonic fields. For that, three methods allowing the inversion of the aperture effect are tested 1) Wiener’s method 2), the power spectral equalization method (PSE), and 3) the maximum a posteriori method (MAP). The obtained results show that the three methods are able to reconstruct the ultrasonic field from the spatially averaged values and the quality of the reconstruction depends strongly upon the SNR, the hydrophone dimensions and the axial distance to the source. Voir les détails

Mots clés : pulsed ultrasonic fields, Wiener’s method, the power spectral equalization method (PSE), the maximum a posteriori method (MAP).


SATOUR ABIDA, Fouad Boubenider  (2007)
Article de conférence

Our work consists to study the propagation of guided waves in an isotropic solid plate, put in contact with a liquid.. To study the sensitivity of the guide when it is in the presence of a liquid, we plotted the dispersion curves of phase and group velocity, of transverse and longitudinal displacement, and the attenuation according to the product frequency-thickness. The attentive study of these curves let us to locate two particulars points, P1 and P2 on the dispersion curves for the S0 and A0 modes respectively. When the guided wave is excited under the point P1, it undergoes a maximum attenuation, and when the wave is excited under the point P2, it undergoes a less attenuation. A range of experiments was carried out to justify the theoretical forecasts. The results obtained are very satisfactory and show clearly, the sensitivity of the wave for well defined products frequency-thickness. Voir les détails

Mots clés : Lamb waves; generation; attenuation; dispersion curves


A. Satour et F. Boubenider  (2007)
Article de conférence

The object of this work consists to study the feasibility of a liquid level sensor using the A0 Lamb wave mode. This sensor is made of a vertically one meter and thirty plate of stainless steel in which one, an A0 Lamb wave mode is generated. To perfect the sensor, we have to choose the good material, the thickness of the plate and the vibration mode of the wave. To do that, we have plot the phase and group velocity curves, the transversal and longitudinal displacements versus the product frequency x thickness. The curves interpretation enables to visualize the best target point for the excitation energy on a suitable guided wave mode at a suitable frequency; this point is called the operating point. When the chosen mode is generated, the echo from the reflexion at the guide-water interface is easily detected by the transmitter-receiver transducer and can be worked efficiently. Voir les détails

Mots clés : : Lamb waves modes; Guided waves; sensor; level

Study of the spray to globular transition in gas metal arc welding: a spectroscopic investigation

Flavien Valensi, Stéphane Pellerin, Quentin Castillon, Amar BOUTAGHANE, Krzysztof Dzierzega, Sylwia Zielinska, Nadia Pellerin, Francis Briand  (2013)

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

Theoretical model and experimental investigation of current density boundary condition for welding arc study

Amar BOUTAGHANE, Khedidja Bouhadef, Flavien Valensi, Stéphane Pellerin, Y. Benkedda  (2011)

This paper presents results of theoretical and experimental investigation of the welding arc in Gas Tungsten Arc Welding (GTAW) and Gas Metal Arc Welding (GMAW) processes. A theoretical model consisting in simultaneous resolution of the set of conservation equations for mass, momentum, energy and current, Ohm’s law and Maxwell equation is used to predict temperatures and current density distribution in argon welding arcs. A current density profile had to be assumed over the surface of the cathode as a boundary condition in order to make the theoretical calculations possible. In stationary GTAW process, this assumption leads to fair agreement with experimental results reported in literature with maximum arc temperatures of ∼21 000 K. In contrast to the GTAW process, in GMAW process, the electrode is consumable and non-thermionic, and a realistic boundary condition of the current density is lacking. For establishing this crucial boundary condition which is the current density in the anode melting electrode, an original method is setup to enable the current density to be determined experimentally. High-speed camera (3000 images/s) is used to get geometrical dimensions of the welding wire used as anode. The total area of the melting anode covered by the arc plasma being determined, the current density at the anode surface can be calculated. For a 330 A arc, the current density at the melting anode surface is found to be of 5 × 107 Am−2 for a 1.2 mm diameter welding electrode. Voir les détails

Mots clés : Gas Tungsten Arc Welding, GTAW, Gas Metal Arc Welding, GMAW, spectroscopie

LTE Experimental Validation in a Gas Metal Arc Welding Plasma Column

Flavien Valensi, Stéphane Pellerin, Amar BOUTAGHANE, Krzysztof Dzierzega, Nadia Pellerin, Francis Briand  (2011)

During gas metal arc welding (GMAW), the plasma obtained has a rich composition and some hypothesis are often made for modelling, in particular the local thermodynamical equilibrium (LTE) state of the plasma. It is then important to study its validity domain, as it is also needed for plasma parameters determination.The plasma was investigated using optical emission spectroscopy. The electron temperature and density were determined from Stark width measurements, independently of the plasma equilibrium state, and compared to the excitation temperature obtained using the Boltzmann plot (BP) method. The welding experiments were made at arc current of 330 A, with pure argon as shielding gases. The LTE is verified in the core region of the plasma, for about one half of the column radius in the arc lower part. Voir les détails

Mots clés : GMAW, Optical Emission Spectroscopy, Boltzmann Plot, Sola method, LTE

Plasma diagnostics in gas metal arc welding by optical emission spectroscopy

Flavien Valensi, Stéphane Pellerin, Amar BOUTAGHANE, Krzysztof Dzierzega, Sylwia Zielinska, Nadia Pellerin, Francis Briand  (2010)

The plasma column in a metal inert gas welding process is investigated by optical emission spectroscopy and high-speed imaging. The concentration and repartition of iron vapours are measured and correlated with the plasma and electrode geometric configuration. Plasma temperatures and electron densities are also measured for each studied position in the plasma. The temperatures are calculated using two different methods, allowing validation of the local thermodynamic equilibrium state of the plasma. The results show a maximum temperature of 12500K in the upper part of the arc, away from the arc axis. The iron concentration reaches a maximum of 0.3% close to the anode and strongly decreases along both the vertical and radial directions.The plasma thermophysical properties, calculated from this plasma composition, are then discussed regarding the metal transfer mode. Voir les détails

Mots clés : GMAW, Optical Emission Spectroscopy, Boltzmann Plot, Sola method, LTE