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Saidane S.,National School in Computer Science | Babai M.Z.,BEM Bordeaux Management School | Korbaa O.,MARS Research Unit | Korbaa O.,Higher Institute of Computer science and Communication Techniques of Hammam Sousse
Computers and Industrial Engineering | Year: 2013

In this paper, we propose a new method for determining the optimal base-stock level in a single echelon inventory system where the demand is a compound Erlang process and the lead-time is constant. The demand inter-arrival follows an Erlang distribution and the demand size follows a Gamma distribution. The stock is controlled according to a continuous review base-stock policy where unfilled demands are backordered. The optimal base-stock level is derived based on a minimization of the total expected inventory cost. A numerical investigation is conducted to analyze the performance of the inventory system with respect to the different system parameters and also to show the outperformance of the approach that is based on the compound Erlang demand assumption as compared to the classical Newsboy approach. This work allows insights to be gained on stock control related issues for both slow and fast moving stock keeping units. © 2013 Elsevier Ltd. All rights reserved. Source


Souissi M.,Higher Institute of Computer science and Communication Techniques of Hammam Sousse | Schmerber G.,CNRS Institute of Genetics and of Molecular and Cellular Biology | Derory A.,CNRS Institute of Genetics and of Molecular and Cellular Biology | El Jani B.,University of Monastir
Journal of Magnetism and Magnetic Materials | Year: 2012

Metal organic chemical vapor deposition (MOCVD) has been used to grow vanadium-doped GaN (GaN:V) on c-sapphire substrate using VCl 4 as the V source. The as-grown GaN:V exhibited a saturated magnetic moment (M s) of 0.28 emu/cm 3 at room temperature. Upon high-temperature annealing treatment at 1100 °C for 7 min under N 2 ambient, the M s of the GaN:V increased by 39.28% to 0.39 emu/cm 3. We found that rapid thermal annealing leads to a remarkable increase in surface roughness of the V-doped GaN as well as the electron concentration. The annealing also leads to a significant increase in the Curie temperature (T C), we have identified Curie temperatures about 350 K concluded from the difference between the field-cooled and zero-field-cooled magnetizations. Structure characterization by x-ray diffraction indicated that the ferromagnetic properties are not a result of secondary magnetic phases. © 2012 Elsevier B.V. All rights reserved. Source


Souissi M.,Higher Institute of Computer science and Communication Techniques of Hammam Sousse | Bouzidi M.,Higher Institute of Computer science and Communication Techniques of Hammam Sousse | El Jani B.,Higher Institute of Computer science and Communication Techniques of Hammam Sousse
Journal of Crystal Growth | Year: 2012

We have investigated the annealing effect of V-doped GaN (GaN:V) epitaxial layers grown on sapphire by metal organic chemical vapor deposition (MOCVD). The film was annealed at a temperature of 1075 °C for 30 min in N 2 ambient after growth. The structural, surface morphology and optical properties of GaN:V films were studied by high resolution X-ray diffraction (HRXRD), atomic force microscope (AFM) and photoluminescence (PL). The results show that the annealing makes for the destruction in the crystal quality and surface morphology. After thermal annealing, the photoluminescence (PL) measurement showed a reduction of the blue luminescence (BL) band observed in GaN:V at room temperature (RT). The phenomenon is attributed to vanadium diffusion or to the V-related complex dissociation. Near-band-edge (NBE) peak exhibited a red shift after 1075 °C anneal. This is due to the decrease in the level of strain. In the infrared region, we observed the emergence of the line 0.93 eV accompanied by a decrease in the intensity of the 0.82 eV emission. Their possible origins are discussed. © 2011 Elsevier B.V. All rights reserved. Source

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