علوم وتكنولوجيا

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    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.
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    Heritabilities, gains from selection and genetic correlations for grain yield of barley grown in two contrasting environments
    (ELSEVIER, 1995) Bouzerzour, H; Dekhili, M
    Heritabilities and variance component estimates were obtained from a set of 15 barley lines and cultivars grown for three consecutive years in two contrasting environments in the high plateaux of Eastern Algeria. Genotype × environment interactions, particularly related to seasonal effects, seriously limited selection for increased barley grain yield. Their effect was to reduce the genetic variance component, heritability estimates and genetic correlation coefficients. The results indicated that selection in a high-yielding location does not identify genotypes suitable for low-yielding environments, which are more representative of the production conditions of a low-input agriculture. Selection in low-yielding environments appears more efficient.
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    Global solutions to a system of strongly coupled reaction-diffusion equations
    (Pergamon, 1996) Kirane, Mokhtar; Kouachi, S
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    Fuzzy direct adaptive control of permanent
    (IEEE, 1998) Benmahammed, Khier; Goléa, Amar; Goléa, Noureddine
    This paper investigates the application of new fuzzy adaptive controller to the control of permanent magnet synchronous motor (PMSM) speed. The proposed controller consists of two parts: the first one, is the classical fuzzy logic controller (FLC) constituted by fimy If-TheB rules, whose inputs are the speed error and the change of speed error, and its output is the reference torque. The second part, is the adaptation mechanism, which adjusts the Fuzzy controller parameters to minimize the error between the reference speed output and the machine speed. The fumy adaptive controller PAC) can be started without prior information on the machine, and can learn and tune rapidly the fuzzy controller rules to meet the desired performance, even when the machine parameters change. A simulation studies for various operating conditions, show the superior performance of the FAC compared to PI controller.
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    Induction machine speed control
    (ECC, 1999) Goléa, A.; Goléa, N.; Kadjoudj, M.
    This paper investigates fuzzy adaptive control of induction machine (IM) speed. The proposed controller consists of two parts: the first is classical fuzzy logic controller (FLC) constituted by fuzzy If-Then rules. The second part is adaptation mechanism, which adjusts the fuzzy controller parameters in order to minimize the error between the reference speed and the machine speed. The fuzzy adaptive controller (FAC) can be started without prior information on the machine, and can learn and tune rapidly the fuzzy controller rules to meet the desired performance, even when the machine parameters change. Simulation studies for various operating conditions show the superior performance of the FAC compared to PI controller
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    Fuzzy adaptive control
    (IEEE, 2000) Goléa, N.; Benmahammed, K.; Goléa, A.
    This paper investigates a direct fuzzy adaptive control of continuous-time nonlinear systems. The proposed adaptive scheme uses a Takagi-Seguno (TS) fuzzy controller, which allows the inclusion of a priori information in terms of qualitative knowledge about the plant operating points or analytical conventional regulators (e.g., state feedback) for those operating points. Stability and robustness of this adaptive scheme are studied using the hyperstability tools. It is proven that this adaptive controller is globally asymptotically stable, and robust against external disturbance and approximation error. Fast tracking, low complexity and parameter convergence characteristics of the proposed approach are illustrated by simulation results.
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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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    Multivariable fuzzy adaptive
    (2002) Goléa, Noureddine; Goléa, Amar
    Based on Takagi-Seguno (TS) fuzzy eystems, we are used, this allows fast control update, which is limit Present a direct fuzzy model-following adaptive control for factor for L~~~~~~~ approach is used multivariable (MIMO) nonlinear systems. The use of the TS 8y6tems allows the inclusion of a priori information to establish the stability and robustness properties of the in terms of qualitative knowledge about the plant operat- proposed fuzzy adaptive scheme, in presence of approxiing peints or analytical conventional linear regulators. It is mation error, external disturbance and input gain variaproven, using Lyapunov stability, that this adaptive scheme tion, ~h~ results, for a two-li* robot model, is robust against external disturbance, approximation error and input gain variation, and achieves asymptotic tracking show that, this fuzzy adaptive control realizes a consistent of a stable reference model. The effectiveness of the pro- tracking performance under approximation error and exterposed fuzzy approach is demonstrated, by simulation, on a two-link robot model.
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    Indirect fuzzy adaptive control
    (IEEE, 2002) Goléa, Noureddine; Goléa, Amar; Kadjoudj, Mohamed
    A new fuzzy indirect adaptive controller for continuous-time nonlinear systems, with a poorly understood dynamics, is developed. The proposed adaptive scheme uses a single Takagi-Seguno (TS) fuzzy model with few parameters to learn, which results in low implementation complexity and a fast learning rate. In addition, the use of TS fuzzy model permits the inclusion of a priori knowledge about the piant dynamics in terms of exact mathematical models or qualitative information. Using the hyperstahility approach, it is proved that this adaptive controller is globally asymptotically stable, and achieves asymptotic tracking of a stable reference model. The performance of the developed approach is illustrated with simulation results.
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    Indirect fuzzy adaptive control
    (IEEE, 2002) Goléa, Noureddine; Goléa, Amar; Kadjoudj, Mohamed
    A new fuzzy indirect adaptive controller for continuous-time nonlinear systems, with a poorly understood dynamics, is developed. The proposed adaptive scheme uses a single Takagi-Seguno (TS) fuzzy model with few parameters to learn, which results in low implementation complexity and a fast learning rate. In addition, the use of TS fuzzy model permits the inclusion of a priori knowledge about the piant dynamics in terms of exact mathematical models or qualitative information. Using the hyperstahility approach, it is proved that this adaptive controller is globally asymptotically stable, and achieves asymptotic tracking of a stable reference model. The performance of the developed approach is illustrated with simulation results.
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    Multivariable fuzzy adaptive
    (2002) Goléa, Noureddine; Goléa, Amar
    Ba~ed on Takagi-Seguno (TS) fuzzy eystems, we are used, this allows fast control update, which is limit Present a direct fuzzy model-following adaptive control for factor for L~~~~~~~ approach is used multivariable (MIMO) nonlinear systems. The use of the TS 8y6tems allows the inclusion of a priori information to establish the stability and robustness properties of the in terms of qualitative knowledge about the plant operat- proposed fuzzy adaptive scheme, in presence of approxiing peints or analytical conventional linear regulators. It is mation error, external disturbance and input gain variaproven, using Lyapunov stability, that this adaptive scheme tion, ~h~ results, for a two-li* robot model, is robust against external disturbance, approximation error and input gain variation, and achieves asymptotic tracking show that, this fuzzy adaptive control realizes a consistent of a stable reference model. The effectiveness of the pro- tracking performance under approximation error and exterposed fuzzy approach is demonstrated, by simulation, on a two-link robot model.
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    Stable indirect fuzzy adaptive control
    (Elsevier, 2003) Goléa, N.; Goléa, A.; Benmahammed, K.
    This paper investigates new fuzzy model-based observer adaptive control for multi-input multi-output continuous-time nonlinear systems. The proposed adaptive scheme uses Takagi–Seguno (TS) fuzzy models to estimate the plant states and dynamics. Using stability arguments, it is shown that the proposed scheme is globally asymptotically stable. The observation and tracking errors are shown to converge asymptotically to zero, despite the presence ofexternal disturbances and approximation errors. The performance ofthe developed approach is illustrated, by simulation, on two-link robot model.
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    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.
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    Fuzzy approximation based model reference
    (IEEE, 2003) Goléa, Noureddine; Goléa, Amar; Kadjoudj, Mohamed
    Based on the universal approximation eapability of the Takagi-Seguno (TS) fuzzy systems, we present a solution to the model reference control of continuous-time nonlinear systems problem. Using the assumption that a fuzzy model exists for the considered nonlinear systems class, a direct TS fuzzy adaptive controller is designed to achieve the tracking objective. It is not required to estimate the fuzzy model, only its existence assumption is required. It is proved, using Lyapunov stability tools, that this adaptive scheme is asymptotically stable and the tracking error converges to zero. Simulation results illustrate the proposed algorithm performance.
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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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    Fatigue life prediction of welded box structures
    (Springer Science,Business Media New York, 2004) Zedira, H; Boumaza, A; Gilgert, J
    The objective of this study is to predict fatigue life of metal welded boxes. Experimental results of fatigue life are satisfactory predicted using an analytical scheme based on the volumetric approach.
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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.