مقـــــــــالات 2000-2010

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Browsing مقـــــــــالات 2000-2010 by Title

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    A common fixed point theorem for weakly compatible mappings in symmetric spaces satisfying a contractive condition of integral type
    (2006) Aliouche, A; Jungck, G
    In this paper, we proved a common fixed point theorem for weakly compatible mappings in symmetric spaces satisfying a contractive condition of integral type and a property (E.A) introduced in [M. Aamri, D. El Moutawakil, Some new common fixed point theorems under strict contractive conditions, J. Math. Anal. Appl. 270 (2002) 181–188]. Our theorem generalizes Theorem 2.2 of [M. Aamri, D. El Moutawakil, Common fixed points under contractive conditions in symmetric spaces, Appl. Math. E-Notes 3 (2003) 156–162] and Theorem 2 of [M. Aamri, D. El Moutawakil, Some new common fixed point theorems under strict contractive conditions, J. Math. Anal. Appl. 270 (2002) 181–188
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    A loss minimization DTC scheme for EV induction motors
    (IEEE, 2007) Haddoun, Abdelhakim; Benbouzid, Mohamed El Hachemi; Abdessemed, Rachid; Ghouili, Jamel; Srairi, Kamel
    This paper proposes a strategy to minimize the losses of an induction motor propelling an electric vehicle (EV). The proposed control strategy, which is based on a direct flux and torque control scheme, utilizes the stator flux as a control variable, and the flux level is selected in accordance with the torque demand of the EV to achieve the efficiency-optimized drive performance. Moreover, among EV’s motor electric propulsion features, the energy efficiency is a basic characteristic that is influenced by vehicle dynamics and system architecture. For this reason, the EV dynamics are taken into account. Simulation tests have been carried out on a 1.1-kW EV induction motor drive to evaluate the consistency and the performance of the proposed control approach.
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    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.
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    Approximation by polynomials with bounded coefficients
    (ELSEVIER, 2007) Zaimi, Toufik
    Let θ be a real number satisfying 1 <θ< 2, and let A(θ ) be the set of polynomials with coefficients in {0, 1}, evaluated at θ. Using a result of Bugeaud, we prove by elementary methods that θ is a Pisot number when the set (A(θ ) − A(θ ) − A(θ )) is discrete; the problem whether Pisot numbers are the only numbers θ such that 0 is not a limit point of (A(θ ) − A(θ )) is still unsolved. We also determine the three greatest limit points of the quantities inf{c, c > 0, c ∈ C(θ )}, where C(θ ) is the set of polynomials with coefficients in {−1, 1}, evaluated at θ, and we find in particular infinitely many Perron numbers θ such that the sets C(θ ) are discrete.
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    Bonding Analysis of Square-Antiprismatic and Fused Square-Antiprismatic Copper(I)-Selenium Clusters
    (Journal of Cluster Science, 2004) Zouchoune, Bachir; Fransois Halet, Jean; Yves Saillard, Jean
    The electronic structure of the Cu2(4n+2)Se4n+2(PH3)8 (n = 1–4) D4h series of model clusters has been analyzed by means of density functional theory calculations. The fused square antiprismatic structure of the metal framework is found to be always preferred over the fused cuboctahedral one because it reinforces the Cu-P bonds. Thus, the presence of the terminal phosphine ligands tends to strengthen the Cu…Cu (d10… d10) bonding by mixing bonding combinations of the vacant Cu 4s and 4p orbitals into the occupied 3d combinations. The calculations indicate that the compounds corresponding to n = 3 and 4 should be easily two-electron-reduced, leading to stable dianionic specie
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    Boundary conditions for one-dimensional Feshbach–Villars equation
    (ELSEVIER, 2000) Merad, M; Chetouani, L; Bounames, A
    We solve the one-dimensional Feshbach–Villars equation for spinless particle subjected to a scalar smooth potential. The wave function is given in terms of the hypergeometric function and via a limiting procedure, the wave functions of the step potential are deduced. Then, the appropriate boundary conditions for the step potential are deduced using the two-component form.
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    Calculation of the contact angle of a spherical surface with a bubble in flotation
    (ELSEVIER, 2009) Bouhenguel, M; Kouachi, S; Bouchemma, A
    We have developed a method for the calculation of contact angle of spherical particle in interaction with a bubble in the process of flotation. The balance of forces acting on the instantaneous TPC perimeter in the radial direction could connect the central angle α and the contact angle θ in only one equation depending on the modified Bond number Bo, which made it possible to couple this equation with the one of the contact angle in function of the linear tension. Some theoretical results are presented.
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    Common fixed point theorems of Gregus type for weakly compatible mappings satisfying contractive conditions of integral type
    (ELSEVIER, 2007) Djoudi, A; Aliouche, A
    We prove a common fixed point theorem of Gregus type for four mappings satisfying a contractive condition of integral type in metric spaces using the concept of weak compatibility which generalizes Theorem 2 of [A. Djoudi, L. Nisse, Gregus type fixed points for weakly compatible mappings, Bull. Belg. Math. Soc. 10 (2003) 369–378] and other papers. We prove also common fixed point theorems of Gregus type using a strict contractive condition of integral type, a property (E.A) and a common property (E.A) introduced by [M. Aamri, D. El Moutawakil, Some new common fixed point theorems under strict contractive conditions, J. Math. Anal. Appl. 270 (2002) 181–188] and [W. Liu, J. Wu, Z. Li, Common fixed points of single-valued and multi-valued maps, Int. J. Math. Math. Sci. 19 (2005) 3045–3055], respectively.
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    Common fixed point theorems of Gregus type for weakly compatible mappings satisfying generalized contractive conditions
    (ELSEVIER, 2008) Aliouche, A
    We prove a common fixed point theorem of Gregus type for four mappings satisfying a generalized contractive condition in metric spaces using the concept of weak compatibility which generalizes theorems of [I. Altun, D. Turkoglu, B.E. Rhoades, Fixed points of weakly compatible mappings satisfying a general contractive condition of integral type, Fixed Point Theory Appl. 2007 (2007), article ID 17301; A. Djoudi, L. Nisse, Gregus type fixed points for weakly compatible mappings, Bull. Belg. Math. Soc. 10 (2003) 369–378; A. Djoudi, A. Aliouche, Common fixed point theorems of Gregus type for weakly compatible mappings satisfying contractive conditions of integral type, J. Math. Anal. Appl. 329 (1) (2007) 31–45; P. Vijayaraju, B.E. Rhoades, R. Mohanraj, A fixed point theorem for a pair of maps satisfying a general contractive condition of integral type, Int. J. Math. Math. Sci. 15 (2005) 2359–2364; X. Zhang, Common fixed point theorems for some new generalized contractive type mappings, J. Math. Anal. Appl. 333 (2) (2007) 780–786]. We prove also a common fixed point theorem which generalizes Theorem 3.5 of [H.K. Pathak, M.S. Khan, T. Rakesh, A common fixed point theorem and its application to nonlinear integral equations, Comput. Math. Appl. 53 (2007) 961–971] and common fixed point theorems of Gregus type using a strict generalized contractive condition, a property (E.A) and a common property (E.A).
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    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.
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    DKP Equation with Smooth Potential and Position-Dependent Mass
    (International Journal of Theoretical Physics, 2007) Merad, M
    The Duffin–Kemmer–Petiau (DKP) equation for spin 0 and 1 with smooth potential and position dependent- mass is solved. The solution is given in terms of the Heun function. The step case for potential and mass are deduced as a limiting case. The boundary conditions are also discussed
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    DKP particle in time-dependent field
    (CZECHOSLOVAK JOURNAL OF PHYSICS, 2006) Merad, M; Bada, H; Lecheheb, A
    We present the solution of Duffin–Kemmer–Petiau (DKP) equation of spin 0 and 1 in the case of the time-dependent mass in the presence of a time-dependent linear scalar field. Calculation is carried out analytically, the wave functions are then deduced for both cases and are connected respectively to the auxiliary equations. The adiabatic approximation is deduced and reveals that in this study we have an obvious absence of the geometrical amplitude factor.
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    Dynamic strategy based fast decomposed GA coordinated with FACTS devices to enhance the optimal power flow
    (ELSEVIER, 2010) Mahdad, Belkacem; Bouktir, T; Srairi, K; EL Benbouzid, M
    Under critical situation the main preoccupation of expert engineers is to assure power system security and to deliver power to the consumer within the desired index power quality. The total generation cost taken as a secondary strategy. This paper presents an efficient decomposed GA to enhance the solution of the optimal power flow (OPF) with non-smooth cost function and under severe loading conditions. At the decomposed stage the length of the original chromosome is reduced successively and adapted to the topology of the new partition. Two sub problems are proposed to coordinate the OPF problem under different loading conditions: the first sub problem related to the active power planning under different loading factor to minimize the total fuel cost, and the second sub problem is a reactive power planning designed based in practical rules to make fine corrections to the voltage deviation and reactive power violation using a specified number of shunt dynamic compensators named Static Var Compensators (SVC). To validate the robustness of the proposed approach, the proposed algorithm tested on IEEE 30-Bus, 26- Bus and IEEE 118-Bus under different loading conditions and compared with global optimization methods (GA, EGA, FGA, PSO, MTS, MDE and ACO) and with two robust simulation packages: PSAT and MATPOWER. The results show that the proposed approach can converge to the near solution and obtain a competitive solution at critical situation and with a reasonable time.
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    Effect of acidity and metal content on the activity and product selectivity for n-decane hydroisomerization and hydrocracking over nickel–tungsten supported on silica–alumina catalysts
    (ELSEVIER, 2005) Rezgui, Y; Guemini, M
    Ni–W/silica–alumina based catalysts with different nickel and tungsten concentration (nickel ranging from 12 to 17% and tungsten ranging from 8 to 30%) were prepared by sol–gel method. The BET, temperature-programmed desorption of ammonia (TPDA) and inductively coupled plasma-atomic emission spectroscopy (ICP-AES) techniques were used to characterize the prepared solids. Afterwards, the catalysts were screened for activity and selectivity in the hydroconversion of n-decane. Under the experimental conditions, yields of isomers as well as cracking products were a function of both metal content and amount of acid sites. Up to 15% Ni content, nickel increased isomerization selectivity, afterwards, the catalytic selectivity decreased. Moreover, the higher the amount of medium acid sites present on the catalyst, the higher its activity and its deactivation.
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    Effect of pretreatment conditions on the catalytic performance of Ni-Pt-W supported on amorphous silica-alumina catalysts
    (ELSEVIER, 2008) Rezgui, Y; Guemini, M
    Activation procedures of Ni-W-Pt based catalysts, prepared by means of a hybrid technique: sol–gel and incipient wetness impregnation, were investigated in terms of their activity in reaction of n-hexane isomerization in a continuous fixed-bed quartz reactor operating at atmospheric pressure, by changing operating conditions such as time on stream, SiO2/Al2O3 and H2/n-hexane ratios. This study aims to understand the effects of the pretreatment conditions, such as calcination and reduction temperature, over some properties of these catalysts and to analyze the relationship between the metal content, the acidity (strength) of the samples and their catalytic performance. The chemical composition of the prepared solids have bas characterized by inductively coupled plasma-atomic emission spectroscopy (ICP-AES), their specific surface areas were measured using BET method, while their reduction behavior was characterized by temperature-programmed reduction and their acidity was assessed by means of ammonia temperature-programmed desorption. The collected data revealed that both BET surface areas and catalytic activity as well as surface acidity of these solids are strongly dependent on their pretreatment conditions. Besides, the reduction behavior of the prepared materials was related to nickel and platinum amounts, the higher the concentrations of these species the easier the reducibility of the samples. On the other hand, it was found that all (NixPty) catalysts deactivate with time on stream, with the conversion remaining steady after 100 min. Moreover, the obtained results on (Ni12Pt0,4)AC catalyst showed that the SiO2/Al2O3 ratio and H2 partial pressure affect isomerization selectivity positively while opposite effect was observed for activity (conversion). In addition, the main products in n-hexane hydroconversion were found to be monobranched isomers which dominate all practical conversions and their formation increases together with that of multibranched ones. Besides, the cracked products are not produced in significant amounts until about 30% conversion.
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    Effects of co- and counter-swirl on the droplet characteristics in a spray flame
    (ELSEVIER, 2008) Hadef, R; Lenze, B
    This paper reports measurements of droplet characteristics and flow field in a spray flame with inner and outer swirling air streams. The spatial distribution of droplet characteristics produced by the burner’s airblast atomizer was measured using dual-phase Doppler anemometry (PDA). The spray flame was operated near the lean blow-out limit at two flow conditions: co-swirling (flow rotation in the same direction) and counter-swirling (flow rotation in opposite directions). In both cases, the flame exhibited a U-shaped form and was marked by a large central recirculation zone. Based on the measurements of the droplet velocity components, differences between both configurations appeared for the counter-rotational setup mainly in the near burner region, where the decrease of total swirl causes deeper penetration of the droplets from the inner duct into the combustion chamber, resulting in a much more homogeneous distribution than the other one. The droplet size in terms of the Sauter mean diameter (SMD) shows little variation in the change of the direction swirl condition. Application of counter-swirl results in more turbulent droplet motion.
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    Electronic structure of bis-azepine transition-metal complexes
    (ELSEVIER, 2010) Farah, Sara; Bouchakri, Naïma; Yves Saillard, Jean
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