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Article Citation - WoS: 2Citation - Scopus: 2Analysis of Optical Constants and Temperature-Dependent Absorption Edge of Gas0.75se0.25< Layered Crystals(Pergamon-elsevier Science Ltd, 2017) Isik, Mehmet; Gasanly, NizamiGaS0.75Se0.25 single crystals were optically characterized through transmission and reflection measurements in the wavelength range of 450-1000 nm. Derivative spectrophotometry analyses on temperature dependent transmittance spectra showed that band gap energies of the crystal increase from 239 eV (T=300 K) to 2.53 eV (T=10 K). Band gap at zero temperature, average phonon energy, electron phonon coupling parameter and rates of change of band gap energy with temperature were found from the temperature dependences of band gap energies under the light of different models reported in literature. Furthermore, the dispersion of room temperature refractive index was discussed in terms of single effective oscillator model. The refractive index dispersion parameters, namely oscillator and dispersion energies, zero-frequency refractive index, were determined as a result of analyses. (C) 2017 Elsevier Ltd. All rights reserved.Article Citation - WoS: 210Citation - Scopus: 259Impact of Cyclic Wetting-Drying on Swelling Behavior of Lime-Stabilized Soil(Pergamon-elsevier Science Ltd, 2007) Guney, Yucel; Sari, Dursun; Cetin, Murat; Tuncan, MustafaIn this study, the impact of cyclic wetting and drying on swelling behavior of lime-stabilized clayey soils has been investigated. Swelling potential and swelling pressure tests have been carried out on soil mixtures with various amounts of kaolinite-bentonite clays, and on a high plasticity clayey soil sample. The tests have been repeated after the addition of lime to the lime-treated samples in different preparation. In each cycle the tested samples were allowed air dry to their initial water content thus shrinking to their initial height, which is called 'partial shrinkage' method. The results showed that the initial beneficiary effect of lime stabilization was lost after the first cycle and the swelling potential increased at the subsequent cycles. On the other hand, the swelling potential and the swelling pressure of the untreated soil samples started decreasing after the first cycle and they reached equilibrium after the fourth cycle. (c) 2005 Elsevier Ltd. All rights reserved.Article Citation - WoS: 199Citation - Scopus: 195Existence and uniqueness of a common fixed point on partial metric spaces(Pergamon-elsevier Science Ltd, 2011) Abdeljawad, T.; Karapinar, E.; Tas, K.; Karapnar, E.In this work, a general form of the weak phi-contraction is considered on partial metric spaces, to get a common fixed point. It is shown that self-mappings S, T on a complete partial metric space X have a common fixed point if it is a generalized weak phi-contraction. (C) 2011 Elsevier Ltd. All rights reserved.Article Citation - WoS: 7Citation - Scopus: 8Some Remarks on Global Asymptotic Stability of Neural Networks With Constant Time Delay(Pergamon-elsevier Science Ltd, 2007) Singh, VimalAn elegant proof of a previously reported criterion for the uniqueness and global asymptotic stability of the equilibrium point of a class of neural networks with constant time delay is presented. The present proof yields some interesting observations. (c) 2005 Elsevier Ltd. All rights reserved.Article Citation - WoS: 11Citation - Scopus: 13A Low Band Gap Polymer Based on Selenophene and Benzobis (thiadiazole)(Pergamon-elsevier Science Ltd, 2017) Abdulrazzaq, Mohammed; Ozkut, Merve Icli; Gokce, Gurcan; Ertan, Salih; Tutuncu, Esra; Cihaner, AtillaA new derivative of benzobis(thiadiazole) based donor-acceptor-donor type monomers, namely 4,7-di (selenophen-2-yl)benzo[1,2-c;4,5-c']bis[1,2,5]thiadiazole (SeBTSe), was synthesized and its polymerization was carried out successfully via electrochemical polymerization in an electrolyte solution of 0.1 M tetrabutylammonium hexafluorophosphate dissolved in dichloromethane. The monomer SeBTSe is a deep red chromophore and it has four redox states: one oxidation, one neutral and two reduction states. The electrochemical behaviour of the corresponding polymer called PSeBTSe was studied by cyclic and differential pulse voltammetry. There is a good agreement between electrochemical (0.62-0.66 eV) and optical (0.63 eV) bandgaps of the polymer. Like the monomer, the ambipolar polymer has four redox states and electrochromic properties: gray beige at neutral state, smoky azurite at oxidized state, beige at first reduced state and dark beige at second reduced state. (C) 2017 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: 8Citation - Scopus: 9Can Fool's Gold "pyrite" Become Real Gold as a Catalyst for Clean-Energy H2 Production?(Pergamon-elsevier Science Ltd, 2019) Inger, Erk; Inger, ErkThe natural, most abundant sulfide mineral of pyrite was modified using polyethyleneimine (PEI) for use as a catalyst in H-2 release reactions from NaBH4 in methanol. The catalytic performances of pyrite, pyrite-PEI, and protonated pyrite-PEI (pyrite-PEI+) were compared and the hydrogen generation rate (HGR) values of 795 +/- 26, 2883 +/- 190, and 4320 +/- 188 mL H-2/(g of catalyst x min)(-1) were measured for H-2 production from NaBH4 methanolysis. The effect of methanol:water mixture at various ratios, the amount of catalyst, the concentration of NaBH4, and temperature on H-2 production from NaBH4 in methanol catalyzed by pyrite-PEr were investigated. The activation energies for pyrite-PEI, and pyrite-PEI+ catalyzed H-2 release reactions were calculated as 47.2 and 36.8 kJ/mol, respectively. It was found that the activity % for the pyrite-PEI+ catalyst decreased to 76.2 +/- 2.7% after five consecutive uses with 100% conversion for each re-use study. Furthermore, the re-generation of pyrite-PEI+ catalyst after the 5th usage was readily ensured by HCl treatment to completely recover and further increase the activity% of the catalyst. Therefore, pyrite was shown to be a useful re-generable and economic green catalyst for H-2 production in many potential applications. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.Article Citation - WoS: 6Citation - Scopus: 8What Comes After Repression? the Hegemonic Contestation in the Gold-Mining Field in Turkey(Pergamon-elsevier Science Ltd, 2018) Ozen, Hayriye; Ozen, SukruIt is widely known that many local environmental mobilizations against resource extraction projects of trans national capital have been repressed by the use of the state force in the late-industrializing world. What is less known is the aftermath of these repressions. Do they conceal all the traces of these mobilizations and lead to naturalization of the extractive operations of transnational capital at the local spaces? We address this question by examining two subsequent local environmental mobilizations in Turkey against gold-mining MNCs. Drawing on Laclauian insights on political struggles and hegemony, we first conceptualize repression of dissent not only as the repression of dissidents or protesters, but also that of protest discourse. Then, we argue that the forceful repression of the actors of those mobilizations succeeding to articulate an appealing protest discourse can make the hegemony and domination of transnational capital at the local level highly fragile, thus providing the conditions of possibility of subsequent similar mobilizations. The protest discourse constituted through such mobilizations may sediment despite the repression of protesters and become highly influential on the discursive trajectory of subsequent mobilizations. Yet, such an influence, as we also demonstrate in this study, may not only enable subsequent movements, but also limit their hegemonic capabilities.Article Citation - WoS: 16Citation - Scopus: 16Elimination of Overflow Oscillations in Direct Form Digital Filters Using Saturation Arithmetic(Pergamon-elsevier Science Ltd, 2008) Singh, VimalA novel frequency-domain criterion for the elimination of limit cycles in a class of digital filters using saturation arithmetic is presented. An example showing the effectiveness of the present criterion is given. (C) 2008 Elsevier Ltd. All rights reserved.Article Citation - WoS: 51Citation - Scopus: 54Functionally Graded Hollow Cylinder Under Pressure and Thermal Loading: Effect of Material Parameters on Stress and Temperature Distributions(Pergamon-elsevier Science Ltd, 2018) Evci, Celal; Gulgec, MufitThis study presents an analytical solution of stresses and displacements in a long functionally graded (FGM) hollow cylinder subjected to uniform heat generation and internal pressure. Thermo-elastic material properties of FGM cylinder continuously vary in radial direction along the thickness with a power function. The temperature distribution is assumed to vary as a function of the radial coordinate and in steady state. Stress formulation approach is employed using the Airy stress function to derive the analytical solution. In the failure analysis of FGM cylinder, Coulomb-Mohr theory is applied for the ceramic phase whereas Tresca yield criterion is used for the metal phase. The stress analysis reveals that stresses in FGM cylinder decrease considerably, compared to the homogenous one, for a particular interval of material parameters. Radial displacement analysis in FGM cylinder supports the results obtained from stress analysis. (C) 2017 Elsevier Ltd. All rights reserved.
