مقـــــــــالات 2000-2010

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Performance optimization of a photovoltaic induction motor pumping system
(ELSEVIER, 2004) Betka, A; Moussi, A
The performances of a photovoltaic pumping system based on an induction motor are degraded once insolation varies far from the value called nominal, where the system was sized. To surmount this handicap, an improvement of these performances by the optimization of the motor efficiency is described in this paper. The results obtained are compared with those of similar work pieces presented in the literature where the motor effeciency and air gap flux where optimized separatly. The simulation results show that the proposed system allows at the same time to combine the performances of the system with constant efficiency and the simplicity of implementation provided by the system with constant airgap flux.
Path integral treatment for a Coulomb system constrained on D-dimensional sphere and hyperboloid
(ELSEVIER, 2007) Lecheheb, A; Merad, M; Boudjedaa, T
The propagator relating to the evolution of a particle on the D-sphere and the D-pseudosphere, subjected to the Coulomb potential, was reconsidered in the Faddeev–Senjanovic formalism. The mid-point is privileged. The space–time transformations used make it possible to regularize the singularity and to bring back the problem to its dynamical symmetry SU(1, 1)
On the Electronic Structure of Distorted Cubic Rhodium Cluster Complexes Containing Bridging Germanium or Phosphorus Ligands
(Springer Science-Business Media, 2007) Zouchoune, Bachir; Yves Saillard, Jean; Francois Halet, Jean
DFT calculations show that the optimal metal valence electron (MVE) count of omnicapped cubic rhodium clusters containing more than eight terminal ligands, is 114. For such a count, a closed-shell configuration is computed with a substantial HOMO-LUMO gap. The presence of more than eight terminal ligands in the clusters favors highly distorted cubic architectures with capping ligands asymmetrically bound to the distorted metallic square faces. Removal of terminal ligands leads to the replacement of bonding M–L electron pairs by nonbonding electron pairs localized on the metal atoms, giving rise to unchanged MVE count
On a time-discretization method for a semilinear heat equation with purely integral conditions in a nonclassical function space
(ELSEVIER, 2007) Merazga, Nabil; Bouziani, Abdelfatah
In this paper, we construct a semidiscrete approximate solution to a semilinear one-dimensional heat equation subject to integral boundary conditions by means of the Rothe discretization in time method. The convergence of the approximation scheme obtained is proved, yielding the well-posedness of the problem considered.
Occurrence of the antifeedant 14,15-dihydroajugapitin in the aerial parts of Ajuga iva from Algeria
(Pergamon, 2000) Ladjel, Segni; Bondi, M.L; Lamara, K
Observer-based adaptive control of robot manipulators
(ELSEVIER, 2008) Goléa, Noureddine; Goléa, Amar; Barra, Kamel
This paper presents a fuzzy adaptive control suitable for motion control of multi-link robot manipulators with structured and unstructured uncertainties. When joint velocities are available, full state fuzzy adaptive feedback control is designed to ensure the stability of the closed loop dynamic. If the joint velocities are not measurable, an observer is introduced and an adaptive output feedback control is designed based on the estimated velocities. In the proposed control scheme, we need not derive the linear formulation of robot dynamic equation and tune the parameters. To reduce the number of fuzzy rules of the fuzzy controller, we consider the properties of robot dynamics and the decomposition of the uncertainties terms. The proposed controller is robust against uncertainties and external disturbance. Further, it is shown that required stability conditions, in both cases, can be formulated as LMI problems and solved using dedicated software. The validity of the control scheme is demonstrated by computer simulations on a two-link robot manipulator
Numerical simulation of drying under variable external conditions
(ELSEVIER, 2006)
The aim of this work is to study the drying kinetic behavior with respect to the variation of the external conditions. Diffusion model based on Ficks law is used. The heated air thermo-physical properties variation and shrinking effect are taken into consideration. The coefficient of diffusion is calculated based on experimental data and presented as a function of temperature and velocity. The numerical resolution of the mass transfer equation allows the calculation of the distribution of moisture inside the product, at any time. Sudden and progressive augmentation of temperature and velocity are simulated; the drying kinetic answers by changing its behavior with a non-instant response. Solar drying was investigated through the study of a flat air collector. The ambient air velocity considerably influenced the outlet temperature of the collector air which reverberates on the drying kinetic.
New designs for graded refractive index antireflection coatings
(ELSEVIER, 2005) Mahdjouba, A; Zighed, L
The incessant progress in thin layers technology, especially the graded index inhomogeneous dielectrics, allows the realization of antireflection coatings (ARCs). Graded refractive index silicon oxynitrides are deposited by electron cyclotron resonance plasma-enhanced chemical vapor deposition (ECR-PECVD) controlled in situ by monochromatic ellipsometry. While avoiding the complexity of the classical multilayer ARCs, graded coatings permit to obtain the same performances, or furthermore to improve solar cells efficiency. A theoretical model, validated by confrontation to ellipsometric spectra, and reflectance measurements were used to optimize different suggested profiles. Calculation predicts an enhancement of photogenerated current exceeding 45% and a weighted reflectance (between 300 and 1100 nm) around 5.6%. On texturized surfaces, these ARCs should enhance short-circuit current by 52.79%.
Neo-clerodane diterpenoids from teucrium polium SSP.Aurasianum
(Pergamon, 1994) Ladjel, Segni; Laamara, Kadour; Pais, Mary
five neo-clerodane diterpenes were isolated from the aerial parts of Teucrium polium ssp. aurasianum. One was known (teumicropodine) and the others were new 3-deacetylteumicropodine,3,20-bis-deacetylteupyreinidine, 6,20-bis-deacetylteupyreinidine and 3,6,20-tri-deacetylteupyreinidine. Their structures and absolute stereochemistry were elucidated by spectral and correlation techniques.
Towards formalizing web service composition in maude’s strategy language
(2010) Merouani, Hamza; Mokhati, Farid; Seridi-Bouchelaghem, Hassina
WS.BPEL 2.0 (Web Services Business Process Execution Language) commonly known as BPEL for short, is currently the de-facto standard language to represent the behavior of web services composition. It offers the possibility to specify the behavior of business processes in two ways: executable and abstract business processes. An abstract business process defines a business protocol that describes the ordering of messages to be sent and received to or from a web service. An executable process, which is the focus of this paper, defines the execution order of a set of activities, the partners involved in the process, the messages and the events exchanged between partners. BPEL suffers, in fact, from a lack of standard formal semantics. This weakness can lead to inconsistencies, ambiguities, and incompleteness within the developed models. We present, in this paper, a novel approach for formalizing web service composition as an executable formal specification described in the Maude language Strategy, a recent extension of Maude. The formalization process is accomplished in two steps: (1) translating the BPEL description in an extension of UML 2.0 called UML-S “UML for Services” and (2) translating the UML-S graphical description generated to Maude’s strategy language.
Social web services discovery
(2010) Metrouh, Abdelmalek; Mokhati, Farid
Over the past few years, an exceptional interest has been taken in the area of Service-Oriented Computing. Particularly, a remarkable effort has been made in the context of Web service discovery, a very important and active research domain. In fact, the number of Web services has grown rapidly and the task of their discovery resting on standards, UDDI and ebXML becomes more and more difficult. The most proposed approaches for Web services discovery focused on the description of Web services themselves and neglect their interaction with each other. In this paper, we use the concepts of social networking, the principles of recommender systems and Web services communities, in the context of Web 2.0, introduced in our previous work to significantly reduce this task. The obtained results seem promising.
Modeling laser-induced incandescence of soot
(Springer-Verlag, 2007) michelsen, A; liu, F; Hadef, R
We have performed a comparison of ten models that predict the temporal behavior of laser-induced incandescence (LII) of soot. In this paper we present a summary of the models and comparisons of calculated temperatures, diameters, signals, and energy-balance terms. The models were run assuming laser heating at 532 nm at fluences of 0.05 and 0.70 J/cm2 with a laser temporal profile provided. Calculations were performed for a single primary particle with a diameter of 30 nm at an ambient temperature of 1800 K and a pressure of 1 bar. Preliminary calculations were performed with a fully constrained model. The comparison of unconstrained models demonstrates a wide spread in calculated LII signals. Many of the differences can be attributed to the values of a few important parameters, such as the refractive-index function E(m) and thermal and mass accommodation coefficients. Constraining these parameters brings most of the models into much better agreement with each other, particularly for the low-fluence case. Agreement among models is not as good for the high-fluence case, even when selected parameters are constrained. The reason for greater variability in model results at high fluence appears to be related to solution approaches to mass and heat loss by sublimation.
Discrete event simulation of embedded systems from graphical notations
(IEEE, 2010) Boutekkouk, Fateh; Benmohammed, Mohamed
In this paper, we present our approach for discrete event simulation of embedded systems. In our case, embedded systems are modelled via UML diagrams with some extensions. From UML diagrams a discrete event simulation model is generated. We use the latter model to estimate system performance.
Measurements of droplets characteristics in a swirl-stabilized spray flame
(ELSEVIER, 2005) Hadef, R; Lenze, B
Experiments have been performed in a kerosene airblast atomized spray flame where the fuel supply is sandwiched between two coswirling air streams. A phase-Doppler particle sizing system was used to measure fuel droplet size, velocity and turbulent kinetic energy of droplets and gas as well as the fuel volume flux within the combustor for two values of air preheat temperature, 200 C and 400 C. The results reveal that a small liquid fuel exists in the centre of the combustor and due to larger droplets with the swirl effect; the droplets characteristics (velocity and turbulent kinetic energy) did not follow the gas ones. Based upon these measurements, an optimum swirl number will exist with every atomization and burner arrangement of a liquid-fuelled flame associated and will be different from that associated with the corresponding gas-fuelled flame. The investigated atomizer shows a marked influence of the inlet air temperature on the measured droplet size which may be attributed to the design of the internal airflow, promoting prompt atomization at the dominant atomization mode.
Isomerization of n-heptane over Ni–WOx/SiO2–Al2O3 catalysts
(2003) Rezgui, Y; Guemini, M; Tighezza, A
Isomerization of n-heptane over Ni–WOx/Al2O3–SiO2 catalysts was carried out in a continuous flow fixed-bed reactor under atmospheric pressure. The first part of this study deals with the preparation of two series of catalysts (A and B) by the sol–gel method, while the second part deals with the isomerization of n-heptane. The principal objective of this study was to choose the catalyst giving the best isomer yield (diand tri-branched ones) with optimum reaction conditions (reaction temperature, reduction temperature and time on stream). From the results obtained, the optimum nickel content was found to be 15 wt% and it seems that the incorporation of tungsten (B series) leads to a significant enhancement in the activity of the prepared catalysts. After running on stream for 100 min, the catalyst with 15% nickel and 10% tungsten (B4 catalyst) gives the best results (29% conversion and 70% selectivity) at 250 8C.
UML modeling and formal verification of control/data driven Embedded Systems
(IEEE, 2009) Boutekkouk, Fateh; Benmohammed, Mohamed
In this paper, we present our approach for UML based modeling of control/data driven Embedded Systems. In our case application is presented as a network of hierarchic data driven and control driven tasks that communicate via abstract channels. Hardware platform is modeled as UML structure diagram. Mapping of application on hardware platform is modeled through UML constraints. From UML models, a Maude specification is generated. We use this formal specification to formally validate system functionality against some undesirable properties and to estimate system power consumption at a high level of abstraction.
Investigation of laminar pressurized flames for soot model validation using SV-CARS and LII
(ELSEVIER, 2005) Hadef, R; Geigle, Klaus Peter; Michael, S
Quasi-simultaneous measurements of temperature and soot volume fraction in pressurized and atmospheric flames are presented. A dual-flame burner concept yielded stable laminar flames for a variety of equivalence ratios, pressures, and fuels, and permitted the investigation of flames without the influence of soot oxidation. A CARS-based technique (shifted vibrational CARS) for temperature measurements, which offers high accuracy over the entire relevant temperature and soot concentration range, is described. Comparison of temperature measurements in the nonsooting part of a laminar diffusion flame at atmospheric pressure by SV-CARS and conventional N2 Q-branch CARS yielded excellent agreement. This new technique was applied to quasi-1D laminar flames with soot concentrations up to 10 ppm and pressures up to 5 bar. The temperature profiles measured in these flames were combined with soot concentration measurements using LII; calibration and correction for signal trapping yielded quantitative soot volume fraction data. The temperature and soot concentration data were combined to generate a comprehensive dataset for the validation of an improved kinetic soot model for the prediction of soot formation in premixed combustion at elevated pressure.
A neural network-based approach to motion estimation with discontinuities
(IEEE, 2008) Berkane, Mohamed; Clarysse, Patrick
A new neural network-based approach is proposed to estimate motion hierarchy in image sequences taking into consideration motion discontinuities. The network consists in an input layer, an intermediate layer and an output layer. In order to estimate the most likely displacement at each pixel, we have transposed the block matching approach into the neural network approach and add mechanisms to detect motion discontinuities. Information redundancy allows for parallel processing in view of real-time complex motion estimation tasks. Preliminary tests on synthetic and real images are very promising.
Hydroisomerization of n-decane over Ni–Pt–W supported on amorphous silica–alumina catalysts
(ELSEVIER, 2010) Rezgui, Y; Guemini, M
A series of NiPtW/silica–alumina catalysts (wt.%: Ni, 12–17; W: 10, Pt: 0.1–1) were prepared via a hybrid method: sol–gel and incipient wetness impregnation and characterized by inductively coupled plasmaatomic emission spectroscopy (ICP-AES), BET, temperature-programmed desorption of ammonia (NH3- TPD), pyridine adsorption followed by FTIR and TPO techniques. On these catalysts, n-decane hydroisomerization was carried out under the following conditions: fixed bed reactor, atmospheric pressure, temperature ranging from 150 to 300 8C, weight hourly space velocity of 4 h1 and molar hydrogen/hydrocarbon ratio of 5. Pt was found to promote activity and stability, the effect being optimal for 0.2 wt.% Pt. Isomers and cracking products yields were a function of both metal (Ni and Pt) content and conversion. Whatever n-decane conversion, monobranched isomers were found to be predominant. Besides, up to 10% conversion, the cracked products were not produced in significant amounts. For a time on stream of 100 min, the best results (47% conversion and 56% isomerization selectivity) were obtained at 250 8C over the catalyst containing 12% Ni, 10% W and 0.2% Pt).
Verifying UML diagrams with model checking
(IEEE, 2007) Mokhati, Farid; Badri, Mourad; Gagnon, Patrice
We present, in this paper, a framework supporting a formal verification of UML diagrams using the Maude language. The approach considers both static and dynamic features of object-oriented systems. We focus, in particular, on UML class, state and communication diagrams. The formal and objectoriented language Maude, based on rewriting logic, supports formal specification and programming of concurrent systems, as well as model checking. The major motivations of this work are: (1) bind together the UML notation and the Maude language (2) preserve the coherence in object-oriented systems description, (3) use model checking techniques to support formally their verification process. The generated Maude specifications, from the considered UML diagrams, are validated by simulation and model checking. The approach is illustrated using a concrete case study.

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