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Effet des conditions de broyage sur les propriétés structurales et magnétiques des nanomatériaux FeAl élaborés par mécanosynthèse
No full text148 p. : ill. ; 30 cmDes poudres nanocristallines (Fe0.8Al0.2)100-xSix et (Fe0.75Al0.25)100-xSix ont été élaborées par mécanosynthèse à l'aide d'un vario-broyeur planétaire innovant " pulverisette 4 " à haute énergie. La formation des composés ainsi que les propriétés physiques ont été étudiées en fonction du pourcentage de silicium, x, (x = 0, 5, 10, 15 et 20 at%) en utilisant les techniques de Diffraction des rayons X (DRX), Microscopie Electronique à Balayage (MEB), analyse des rayons X par Dispersion d'Energie (EDX) , Spectroscopie MÀssbauer et magnétométrie à échantillon vibrant (VSM). Les micrographies MEB des poudres des deux séries montrent que leurs particules se présentent sous forme d'agglomérats qui possèdent une forme lamellaire pour les alliages sans silicium puis prennent progressivement une forme arrondie accompagnés d'un affinement dans leurs tailles avec l'augmentation de pourcentage de Si. L'analyse EDX a montré que la composition finale de chaque échantillon est très proche de sa composition nominale ainsi que l'absence de contamination. L'affinement des spectres de DRX obtenus a révélé la formation de la solution solide désordonnée monophasé pour chaque échantillon des deux séries, en raison de l'occupation aléatoire des sites de la maille conventionnelle (cc) de À-Fe par les atomes d'Al et de Si. Cet affinement a aussi montré que l'augmentation de la teneur en Si dans les deux séries d'alliages a pour effet de diminuer linéairement le paramètre de maille. D'autre part, la taille moyenne des grains, (nm), décroît pour les deux séries mais d'une manière différente. L'analyse des spectres MÀssbauer, collectés à 300 K, correspondant aux échantillons des deux séries (Fe0.8Al0.2)100-xSix et (Fe0.75Al0.25)100-xSix confirme les résultats obtenus par la DRX pour ce qui concerne la formation de la solution solide FeAl et Fe(Al, Si) après 72 h de broyage. De plus, elle a fournit des informations supplémentaires, que la DRX n'a pas pu révéler, sur l'existence de différents environnements magnétiques pour les atomes de fer et la formation des phases non ferromagnétiques. Les courbes d'hystérésis, prises à 300 K, de tous les échantillons des deux séries montrent que tous les alliages sont des matériaux magnétiques dou
الأليات الدستورية لتأثير رئيس الجمهرية على البرلمان في النظام الدستوري الجزائري الحالي
No full textص. 12
Improved Cuckoo Search Algorithm for Document Clustering
No full textEfficient document clustering plays an important role in organizing and browsing the information in the World Wide Web. K-means is the most popular clustering algorithms, due to its simplicity and efficiency. However, it may be trapped in local minimum which leads to poor results. Recently, cuckoo search based clustering has proved to reach interesting results. By against, the number of iterations can increase dramatically due to its slowness convergence. In this paper, we propose an improved cuckoo search clustering algorithm in order to overcome the weakness of the conventional cuckoo search clustering. In this algorithm, the global search procedure is enhanced by a local search method. The experiments tests on four text document datasets and one standard dataset extracted from well known collections show the effectiveness and the robustness of the proposed algorithm to improve significantly the clustering quality in term of fitness function, f-measure and purity
ترشيد النفقات العمومية بالبلديات في الجزائر : دراسة حالة بلديتي تيجلابين وبودواو في ولاية بومرداس
No full text(149 ص.
Compressive behaviour of concrete elements confined with GFRP-prefabricated bonded shells
No full textγ-Ray irradiation effect on GdBO3/silica:Ce3+ composite prepared by sol gel method
No full textSamples of GdBO3 doped with Ce3+ embedded in amorphous silica matrix were obtained by sol gel process and heat-treat at 1000°C for 2h in argon atmosphere. After elaboration, the samples were irradiated with γ-rays using cobalt (60Co) source in the dose range from 1 to 5kGy. The irradiation effect of γ-rays on structural and optical properties of the synthesized samples were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transforms infrared spectroscopy (FTIR) and photoluminescence spectroscopy. XRD and TEM-EDS results reveal that γ-ray irradiation reduces the crystallite size from 55nm to 30nm. It is found from FTIR study that the absorption bands intensity assigned to structural groups containing BO4 and BO3 units as well as the banding of Si-O-Si bond increases with γ-ray dose up to 4kGy. While photoluminescence measurements show that the emission bands attributed to the 5d→4F transition of Ce+3 ion intensity decreases, it is still significant even after irradiation to a dose of 5kGy. From this results it is concluded that the γ-ray irradiation up to a dose of 5kGy improve the structural and morphological quality of the synthesized GdBO3/silica: Ce3+ without altering significantly its luminescence properties
A comparative structural and magnetic study of Fe100-xPdx(x=15, 20 and 36) thin films deposited on Si (100) and glass substrates
No full textVarious structural and magnetic characterization techniques have been used to investigate Fe100-xPdx (x=15, 20 and 36) thin films deposited onto silicon and glass substrates, by thermal evaporation technique. X-ray diffraction analysis shows the presence of supersaturated solid solution with bcc structure for Pd concentrations of 15% and 20%. However, for 36% of Pd, in addition to the supersaturated α-FePd (bcc) phase, another disordered FePd3 phase with fcc structure is present. At 20 at% Pd, the magnetic characterization shows a saturation of the bcc (α-FePd) phase and the appearance of the fcc phase. The correlation between the structure and magnetic properties allows us to compare the two substrates effects on deposited thin films. As results, the measurements indicate that the grain size D, the thin film thickness and the d(110) spacing significantly affect the magnetic coercivity HC. The Fe-Pd alloys deposited on a monocrystalline Si (100) and glass substrate show that the coercivity HC is given by the random anisotropy model. & 201
Analysis of cavitating flow through a venturi
Get PDFA dynamical study of a bubbly flows in a transversal varying section duct (Venturi), is modeled by the use of the mass and momentum phases equations, which are coupled with the Rayleigh-Plesset equation of the bubbles dynamics. The effects of the throat dimension and the upstream void fraction on flow parameters are investigated. The numerical resolution of the previous equations set let us found that the characteristics of the flow change dramatically with upstream void fraction. Two different flow regimes are obtained: a quasi-steady and a quasi-unsteady regimes. The former is characterized by a large spatial fluctuations downstream of the throat, which are induced by the pulsations of the cavitation bubbles. The quasi-unsteady regime corresponds to flashing flow in which occurs a bifurcation at the flow transition between these regimes. This transition occurs at Rc 4.3 which corresponds to s 4.710-3. An analytical expression for the critical bubble size at the flashing flow point is also obtained and compared with theoretical dat
Dynamic detection of anomalies in crowd's behavior analysis
No full textThe analysis of the human behavior from video is a wide field of the vision by computer. In this work we are interested in the analysis of the crowd behavior and its entities in a dense scene. These scenes are characterized by the presence of a great number of people in the camera's field of vision. A major problem is the development of an autonomous approach for the management of a great number of anomalies which is almost impossible to carry out by operators. We present in this paper a new approach for the anomalies detection very dense scenes relaying on the speed of both the individuals and the whole group. The various anomalies are detected by switching in a dynamic way between two approaches: the artificial neurons networks "ANN" for the management of group anomalies of people, and the Density Based Spatial Clustering of Application with Noise "DBSCAN" in the case of entities. For more robustness and effectiveness, we introduced two routines that serve to eliminate the shades and the management of occlusions