Nombre total de résultats : 278
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Ultrasonic device calibration for estimation of retained austenite in tool steel

Faci, Y, Abbas, a, Mebtouche, A.  (2005)

High percent of retained austenite in tool steel involve ill-fated effects as cracks. It is very important to control it. Ultrasonic device can be calibrated by using of ultrasonic velocities measurements. The variation of the velocities in tool steel as function of the rate of austinite is very small and require measurements with high accuracy. The calibration method is very simple and need neither mathematical methods nor simulations. Voir les détails

Mots clés : • Martensite, • Retained austenite, • Ultrasound longitudinal velocity, • Ultrasound transversal velocity

Performance analysis of a Pt/n-GaN Schottky barrier UV detector

F. Bouzid, L. Dehimi, F. Pezzimenti  (2017)

The electrical and optical characteristics of an n-type gallium nitride (GaN) based Schottky barrier ultraviolet (UV) detector, where a platinum (Pt) metal layer forms the anode contact, have been evaluated by means of detailed numerical simulations considering a wide range of incident light intensities. By modeling the GaN physical properties, the detector current density-voltage characteristics and spectral responsivity for different (forward and reverse) bias voltages and temperatures are presented, assuming incident optical power ranging from 0.001 to 1 Wcm-2. The effect of defect states in the GaN substrate is also investigated. The results show that, at room temperature and under reverse bias voltage of -300 V, the dark current density is in the limit of 2.18×10-19 Acm-2. On illumination by a 0.36-µm UV uniform beam with intensity of 1 Wcm-2, the photocurrent significantly increased to 2.33 Acm-2 and the detector spectral responsivity reached a maximum value of 0.2 AW-1 at zero-bias voltage. Deep acceptor trap states and high temperature strongly affected the spectral responsivity curve in the considered 0.2 µm to 0.4 µm UV spectral range. Voir les détails

Mots clés : Gallium nitride, Schottky barrier, ultraviolet detector, photocurrent, responsivity, Temperature


Article de conférence

Copper oxide thin films were deposited by a low-cost and simple spray pyrolysis technique on glass substrate at 485°C, The aqueous copper nitrate Cu(NO3)2,6H2O with the different concentrations (0.1 M , 0.3M) used as a source of copper. The structural, morphological, and optical properties of the CuO thin films were studied by X-ray diffraction (XRD), Scanning electron microscopy (SEM), UV-vis-spectrophotometer. The X-ray diffraction patterns confirm the presence of CuO phases with preferential orientation along (-111), (111). The optical direct gap energy for Copper oxide calculated from optical absorption measurement is 2.82 eV , which is quite comparable with the report value Voir les détails

Mots clés : Copper oxide, Spray pyrolysis, Thin films

Numerical simulations of the electrical transport characteristics of a Pt/n-GaN Schottky diode

Fayçal Bouzid, Fortunato Pezzimenti, Lakhdar Dehimi, Mohamed L. Megherbi, Francesco G. Della Corte  (2017)

In this paper, using a numerical simulator, we investigated the current-voltage characteristics of a Pt/n-GaN thin Schottky diode on the basis of the thermionic emission (TE) theory in the 300 to 500 K temperature range. During the simulations, the effect of different defect states within the n-GaN bulk with different densities and spatial locations is considered. The results show that the diode ideality factor and the threshold voltage decrease with increasing temperature, while at the same time, the zero-bias Schottky barrier height (Φb0) extracted from the forward current density-voltage (J-V) characteristics increases. The observed behaviors of the ideality factor and zero-bias barrier height are analyzed on the basis of spatial barrier height inhomogeneities at the Pt/GaN interface by assuming a Gaussian distribution (GD). The plot of apparent barrier height (Φb,App) as a function of q/2kT gives a straight line, where the mean zero-bias barrier height ( ) and the standard deviation (σ0) are 1.48 eV and 0.047 V, respectively. The plot of the modified activation energy against q/kT gives an almost the same value of and an effective Richardson constant A* of 28.22 Acm-2K-2, which is very close to the theoretical value for n-type GaN/Pt contacts. As expected, the presence of defect states with different trap energy levels has a noticeable impact on the device electrical characteristics. Voir les détails

Mots clés : Gallium nitride, Schottky barrier, diode, Temperature


A. Saihia, L. Sayad, H. MERADI  (2017)

Grounds movements are considered a natural hazard, some of which have, over time, significant slow movements.Significance of these dynamic effects involves a risk which generates human and material damage. Policymakers musttake this issue into account in their permanent security organization program. Some landslides exhibit a function of time,significant slow movements. They are assigned to a behavior of clay materials mechanism caused by the variation ofgeotechnical properties. The effects of water seepage in wet periods generally linked to the viscous nature of claymaterials are causes primarily .They can also be related to the variation modeling parameters. The land slip site is locatedat the road CW16 Seraidi -Chétaibi, (Annaba, Algeria) area with an annual rainfall of more than 700mm. Analysis of theslope stability is carried out using several methods of deformation calculation of the natural ground state. In our case weuse a plastic Mohr Coulomb from supported models. The project proposes to examine the different causes using theexample of Cam Clay. The project will examine the different causes using the example of Cam Clay; elasticvisco plasticmodel with time (SSCM: Soft Soil Creep Model) set in a finite element program Plaxis. This technique can show us howdifferent behavioral assumptions can describe the slow movements of a slope. A comparison will be made with the MohrCoulomb (MC). Voir les détails

Mots clés : Mohr Coulomb, slip, numerical modeling, plaxis, cam clay, elasticvisco plastic model

Eddy current characterization and Magnetic properties of iron alumina nanostructured alloy

Ahmed Benyahia, Abderrahmane YOUNES, Mohammed Khorchef, Rabah ABDELKADER, Mourad ZERGOUG  (2017)
Article de conférence

The mechanical alloying technique has been used to synthesis iron alumina nanostructred powder in a high energy planetary ball-mill PM400. Electromagnetic and magnetic characterizations of the powders was investigated by eddy current and vibrating sample magnetometer, the impedance, the coercivity and saturation magnetization of the iron alumina mixtures changes in function of x% (wt). Voir les détails

Mots clés : iron alumina, electromagnetic and magnetic properties, Eddy Current, VSM.

Etude de l’effet des conditions de polarisation sur le mode de relaxation principale (α) du PLA par la technique des courants thermostimulés (CTS)

A.BOUAMER, N. Benrekaa  (2017)
Article de conférence

Dans ce travail nous nous sommes intéressé à l’étude de l’influence des conditions de polarisation (champ et température), sur le mode de relaxation principal(α) du polylactic acide (PLA) par la technique des courants thermo-stimulés (CTS). L’influence du champ électrique se traduit parune augmentation linéaire de l’intensité du thermocourant relatif au mode α ainsi que celle de la polarisation totale de ce pic, affirmant ainsi le caractère dipolaire de la relaxation. L’élévation de la température de polarisation conduit à une augmentation progressive de l’intensité et de la polarisation jusqu’à saturation au voisinage de la transition vitreuse. Les énergies d’activations évaluées par la méthode des demi-hauteurs, augmentent pour des températures de polarisation inférieures à 70°C, puis rejoignes un palier de saturation. Un tel résultat est dû à un processus thermiquement activé et à une distribution du temps de relaxation. La température de transition vitreuse Tgaugmente avec la vitesse de chauffage. Ce résultat confirme la nature cinétique de la transition vitreuse. Voir les détails

Mots clés : Transition vitreuse, relaxation, PLA, CTS.

Amorphous SiC/c-ZnO-Based Quasi-Lamb ModeSensor for Liquid Environments

Cinzia Caliendo, Muhammad Hamidullah, Farouk LAIDOUDI  (2017)

The propagation of the quasi-Lamb modes along a-SiC/ZnO thin composite plates wasmodeled and analysed with the aim to design a sensor able to detect the changes in parametersof a liquid environment, such as added mass and viscosity changes. The modes propagation wasmodeled by numerically solving the system of coupled electro-mechanical ?eld equations in threemedia. The mode shape, the power ?ow, the phase velocity, and the electroacoustic couplingef?ciency (K2) of the modes were calculated, speci?cally addressing the design of enhanced-coupling,microwave frequency sensors for applications in probing the solid/liquid interface. Three modeswere identi?ed that have predominant longitudinal polarization, high phase velocity, and quitegood K2: the fundamental quasi symmetric mode (qS0) and two higher order quasi-longitudinalmodes (qL1 and qL2) with a dominantly longitudinal displacement component in one plate side.The velocity and attenuation of these modes were calculated for different liquid viscosities andadded mass, and the gravimetric and viscosity sensitivities of both the phase velocity and attenuationwere theoretically calculated. The present study highlights the feasibility of the a-SiC/ZnO acousticwaveguides for the development of high-frequency, integrated-circuit compatible electroacousticdevices suitable for working in a liquid environment. Voir les détails

Mots clés : Lamb Modes, Amorphous SiC, Coupling configurations, sensors, viscous liquids


A. Badidi Bouda, R. Halimi, A. Mebtouche, W. Djerir  (2011)
Article de conférence

In this paper we are proposing an experimental study of the effect of low alloy steels carboncontent on the velocity and propagation attenuation coefficient of the ultrasonic waves inthese materials. We have observed simple relations between the velocities and theattenuations according to the carbon content. The same observations can be made for theYoung modulus. These results, in conformity with the theory, show the possibility ofcharacterizing the carbon content by a nondestructive method: ultrasounds. In parallel wehave studied the effect of some heat treatments such as hardening, annealing andquenching on velocities and attenuations. The results obtained show a correlation betweenheat treatments and ultrasonic parameters. This opens ways to a more complete and nondestructive characterization of steels by ultrasonic methods. Voir les détails

Mots clés : carbon content, velocity propagation, attenuation coefficient, ultrasonic methods, steel.


A. Badidi Bouda, R. Halimi, A. Mebtouche, W. Djerir  (2008)
Article de conférence

In this paper we propose an experimental study of the steel grains size effect on the shiftfrequency of the ultrasonic waves being propagated in this material. By suitable heat treatment on samples resulting from the same bar, we have obtained identical samples butwith different mean grains sizes. We have then measured the ultrasonic shifts frequency after propagation in the material. The results obtained show a direct effect on the meangrains sizes on the ultrasonic frequency. These results, in conformity with the theory, showthe possibility of characterizing a material grains size by a nondestructive method:ultrasounds.It is known that a material characterization is possible through the measurement of someultrasonic parameters such as propagation velocities and attenuation coefficients. Wepropose a method which exploits the frequency and whose measurement is easy. Theseresults open way to a more inclusive and nondestructive characterization of materials byultrasounds. Voir les détails

Mots clés : ultrasonic frequency, propagation velocities, attenuation coefficients, nondestructive characterization