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Article Citation - WoS: 40Citation - Scopus: 52Variable Structure Control of a Class of Uncertain Systems(Pergamon-elsevier Science Ltd, 2004) Efe, MÖ; Ünsal, C; Kaynak, O; Yu, XHThis brief paper proposes a method for tuning the parameters of a variable structure controller. The approach presented extracts the error at the output of the controller and applies a nonlinear tuning law using this error measure. The adaptation mechanism drives the state tracking error vector to the sliding hypersurface and maintains the sliding mode. In the simulations, the approach presented has been tested on the control of Dulling oscillator and the analytical claims have been justified under the existence of measurement noise, uncertainty and large nonzero initial errors. (C) 2003 Elsevier Ltd. All rights reserved.Article Citation - WoS: 14Citation - Scopus: 19Electrochemistry of nickel(II) complexes with N,N'-bis(3,5-di-tert-butylsalicylidene)polymethylenediamines(Pergamon-elsevier Science Ltd, 2005) Özalp-Yaman, S; Kasumov, VT; Önal, AMThe electrochemical oxidation of several N,N'-polymethylenebis(3,5-di-tert- butylsalicylaldiminato)nickel(II) complexes, Ni(L-x), has been studied by cyclic voltammetry and in situ UV-Vis spectroscopy in DMF Cyclic voltammograms of Ni(L-x) (x = 1-4) complexes displayed two-step oxidation processes under nitrogen gas atmosphere. The first oxidation peak potentials of all the Ni(II) complexes corresponds to the reversible one-electron oxidation process of the metal center, yielding Ni(III) species. EPR spectrum of the electrolysis solution was recorded after one electron transfer at liquid nitrogen temperature also confirms the formation of [Ni-III (L-3)](+) species (g(x) > g(y) > g(z)) with a (2)A(1)(d(z)(2))(1) ground state. Upon addition of pyridine to one electron oxidised solutions a new penta coordinated species, [Ni-III(L-3)Py](+) (g(perpendicular to) > g(parallel to), a(parallel to)(N-14) = 8 G), was produced. The second oxidation peak of the complexes was assigned as the ligand based oxidation, generating a coordinated phenoxy radical species. (c) 2005 Elsevier Ltd. All rights reserved.Article Citation - WoS: 7Citation - Scopus: 9Properties of Boron Doped Ti-Ba Superconductors(Pergamon-elsevier Science Ltd, 2003) Kayed, TSThe effects of boron doping on the formation and properties of the Tl-based superconductors have been studied. Up to 10 wt.% boron has been added to the oxides having the nominal composition, Tl1.8Ba2Ca2.2Cu3Ox, by the usual solid-state reaction method. Boron additions in the range 0.8-1.0% increase the fraction of the Tl-2223 phase and significantly improve the critical temperature of the samples. Higher amounts of boron additions eliminate the Tl-2223 phase, reduce the fraction of Tl-2212 phase and cause separate non-superconducting phases to be formed. The formation of non-superconducting phases does not allow us to obtain pure Tl-2212 phase. (C) 2002 Elsevier Science Ltd. All rights reserved.Article Citation - WoS: 5Citation - Scopus: 5Electrochemical Polymerization of 4-Allylanisole(Pergamon-elsevier Science Ltd, 2001) Cihaner, A; Testereci, HN; Önal, AMElectrochemical polymerization of 3-allylanisole (4AA). via constant potential electrolysis, has been investigated in acetonitrile using two different supporting electrolytes. Redox behavior of the monomer was also studied in the same solvent-electrolyte couples at room temperature. Electrochemical polymerization of the monomer yielded insoluble polymer films on the electrode surface, which bears a very low conductivity, together with the low molecular weight polymers in the bulk of the solution. The decrease in the monomer concentration, during the electrochemical polymerization. was monitored by taking the cyclic voltammogram of the electrolysis solution. The effect of temperature on the rate of electrochemical polymerization was: also studied. The polymers were characterized by taking the H-1-NMR and FTIR spectra. Molecular weight of the soluble polymer was determined by vapor pressure osmometry. Thermal analysis of the polymer film and soluble polymer were done by DSC. (C) 2001 Elsevier Science Ltd. All rights reserved.Article Citation - WoS: 21Citation - Scopus: 21Special Standard Static Space-Times(Pergamon-elsevier Science Ltd, 2004) Dobarro, F; Ünal, B; Debarro, FernandoEssentially, some conditions for the Riemannian factor and the warping function of a standard static space-time are obtained in order to guarantee that no nontrivial warping function on the Riemannian factor can make the standard static space-time Einstein. (C) 2004 Elsevier Ltd. All rights reserved.Article Citation - WoS: 42Citation - Scopus: 41Synthesis and Characterization of Mg2b2<(Pergamon-elsevier Science Ltd, 2005) Qasrawi, AF; Kayed, TS; Mergen, A; Gürü, MMagnesium borate of the form Mg2B2O5 has been prepared and its structural and thermal properties were studied using X-ray diffraction and differential thermal analysis. An investigation of the electrical and optical properties of Mg2B2O5 system has been carried out. The electrical resistivity of the sample was measured in the temperature range of 170-400 K. The data analysis revealed an extrinsic nature of the conductivity with two impurity levels located at 0.13 and 0.71 eV in the temperature ranges of 170-230 K and 240-400 K, respectively. The optical transmission and reflection was recorded at 300 K in the incident photon energy range of 3.0-6.0 eV. The absorption coefficient data analysis revealed an indirect optical energy band gap of 4.73 eV. In addition, two impurity levels located at 3.43, and 4.49 eV were observed in the absorption spectra. (c) 2005 Elsevier Ltd. All rights reserved.Article Citation - WoS: 28Citation - Scopus: 10Electrical Conductivity and Hall Mobility in P-Type Tlgase2 Crystals(Pergamon-elsevier Science Ltd, 2004) Qasrawi, AF; Qasrawı, Atef Fayez Hasan; Gasanly, NM; Qasrawı, Atef Fayez Hasan; Department of Electrical & Electronics Engineering; Department of Electrical & Electronics EngineeringSystematic dark electrical conductivity and Hall mobility measurements have been carried out in the temperature range of 200-350 K on p-type TlGaSe2 crystals. The analysis of the temperature-dependent electrical conductivity and carrier concentration reveals the extrinsic type of conduction with an acceptor impurity level located at 0.33 eV, and donor and acceptor concentrations of 9.0 x 10(15) and 1.3 x 10(16) cm(-3), respectively. A hole and electron effective masses of 0.520m(0) and 0.325m(0), respectively, with a donor to acceptor compensating ratio of 0.69 are also being identified. The Hall mobility is found to be limited by the hole-phonon short-range interactions scattering with a hole-phonon coupling constant of 0.17. (C) 2004 Elsevier Ltd. All rights reserved.Article Citation - WoS: 37Citation - Scopus: 39A New Refined Form of Jordan's Inequality and Its Applications(Pergamon-elsevier Science Ltd, 2006) Özban, AY; MathematicsA new refined form of Jordan's inequality [D.S. Mitrinovic, Analytic Inequalities, Springer-Verlag, 1970; F. Yuefeng, Jordan's inequality, Math. Mag. 69 (1996) 126] is proved and an application of it, together with some numerical results, are given. (C) 2005 Elsevier Ltd. All rights reserved.Conference Object Citation - WoS: 1The Generalized Divergence Theorem and Its Application To Harmonic Maps(Pergamon-elsevier Science Ltd, 2001) García-Río, E; Kupeli, DNA survey of divergence theorems in semi-Riemannian geometry is made. The generalization of a divergence theorem to vector fields along a map is given in semi-Riemannian geometry and an application of it is made in Riemannian geometry to obtain some sufficient conditions for a map to be harmonic.Article Citation - WoS: 3Instability Intervals of a Hill's Equation With Piecewise Constant and Alternating Coefficient(Pergamon-elsevier Science Ltd, 2004) Guseinov, GS; Karaca, IYIn this paper, we obtain asymptotic formulas for eigenvalues of the periodic and the semiperiodic boundary value problems associated with a Hill's equation having piecewise constant and alternating coefficient. As a corollary, it is shown that the lengths of instability intervals of the considered Hill's equation tend to infinity. (C) 2004 Elsevier Ltd. All rights reserved.
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