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Article Citation - WoS: 28Citation - Scopus: 30Functionalized Polysulfide Copolymers With 4-Vinylpyridine Via Inverse Vulcanization(Elsevier Science Bv, 2019-06) Berk, Hasan; Balci, Burcu; Ertan, Salih; Kaya, Murat; Cihaner, AtillaA new series of functional polysulfide copolymers called poly(sulfur-random-4-vinylpyridine) (poly(S-r-4VP)) was synthesized via inverse vulcanization technique by ring opening polymerization of elemental sulfur in the presence of 4-vinylpyridine (4VP). The corresponding copolymers can be post functionalized by using amine group in 4VP unit to get polymers bearing various properties. Elemental sulfur was heated up to 160 degrees C and 4VP was added slowly to a clear yellowish orange colored liquid at this temperature. The reaction mixture was vitrified to form a reddish-brown polymeric material at 180 degrees C in 1 h. The products were characterized by using FTIR, NMR, and Raman spectroscopic techniques. Poly(S-r-4VP) copolymers are soluble in common solvents like dichloromethane, chloroform and tetrahydrofuran. Weight-average molecular weights of poly(S-r-4VP) copolymers with different wt% 4VP were measured by using gel permeation chromatography technique. The polysulfide copolymers with different wt% 4VP have high weight-average molecular weights with polydispersity indeces (PDI) in a range from 1.88 to 4.06 measured by gel permeation chromatography. Post functionalization of the copolymer with 50 wt% 4VP as an example was performed successfully by using alkyl bromide to get N-alkyl quaternized 4VP in polymer backbone.Article Citation - WoS: 57Citation - Scopus: 62Reliability Evaluation of a System Under a Mixed Shock Model(Elsevier Science Bv, 2019-05) Eryilmaz, Serkan; Tekin, MustafaA new mixed shock model is introduced and studied. According to the model, for two fixed critical values d(1) and d(2) such that d(1) < d(2), the system under concern fails upon the occurrence of k consecutive shocks of size at least d(1) or a single large shock of size at least d(2). The new model combines run and extreme shock models. Reliability properties of the system are studied under two cases: when the interarrival time X-i between the (i - 1)th and ith shock, and the magnitude of the ith shock Y-i are independent for all i, and when the interarrival time between the (i - 1)th and ith shock, and the magnitude of the ith shock are dependent for all i. (C) 2018 Elsevier B.V. All rights reserved.Article Citation - WoS: 5Citation - Scopus: 5Optical properties of (Ga<sub>2</sub>Se<sub>3</sub>)<sub>0.</sub><sub>75</sub> - (Ga<sub>2</sub>S<sub>3</sub>)<sub>0.</sub><sub>25</sub> single crystals by spectroscopic ellipsometry(Elsevier Science Bv, 2019-05) Isik, M.; Gasanly, N. M.; Gasanova, L.Structural and optical properties of 75 mol % Ga2Se3 - 25 mol % Ga2S3 system of single crystals were investigated by experimental techniques of x-ray diffraction (XRD), energy dispersive spectroscopy, Raman spectroscopy and ellipsometry. XRD pattern indicated that the studied compound has crystalline nature with cubic structure. Vibrational modes in the crystal were revealed using Raman spectroscopy experiments in the 90-450 cm(-1) frequency range and nine modes were observed in the spectrum. Ellipsometry measurements were utilized in the 1.2-6.2 eV range to get spectral dependencies of optical constants; complex dielectric function, refractive index and extinction coefficient. Under the light of fundamental expressions and models, refractive index and extinction coefficient spectra were analyzed to get various optical parameters of the single crystal.Article Citation - WoS: 11Citation - Scopus: 11Fabrication and Characterization of Yb/Moo<sub>3< Devices(Elsevier Science Bv, 2019-05) Al Garni, S. E.; Qasrawi, A. F.In this study we have explored some of the properties of Yb/MoO3/(C, Yb) thin films as a multifunctional optoelectronic device. While the MoO3 films which are deposited onto glass substrate are found to be of amorphous nature, the Yb metal induced the growth of orthorhombic phase of MoO3. The films are high transparent and exhibit energy band gap value of 3.0 eV which make it sensitive to light signals in the near ultraviolet range of light. In addition, the frequency dependent capacitance-voltage characteristics of Yb/MoO3/(C,Yb) structure display pronounced accumulation, depletion and inversion regions that nominate it for use as tunable metal-oxide-semiconductor MOS device. The physical parameters including the built in voltage, barrier height, flat band and threshold voltages of the MOS capacitors are also determined. Furthermore, the current-voltage characteristics displayed high rectification ratio that could reach 1.26 x 10(4) at biasing voltage of 0.5 V nominating the Yb/MoO3/C device for use as electronic switches. On the other hand, the impedance spectroscopy analysis in the frequency domain of 0.01-1.80 GHz, have shown that the Yb/MoO3/Yb structures are more appropriate for microwave applications than Yb/MoO3/C device. The microwave cutoff frequency for the Yb sandwiched MoO3 exceeds 140 GHz. The return loss for the Yb/MoO3/Yb reaches 26 dB at 1.8 GHz. These values are attractive as they suit microwave low/high pass band fillers.Article Citation - WoS: 7Citation - Scopus: 7In situ monitoring of the permanent crystallization, phase transformations and the associated optical and electrical enhancements upon heating of Se thin films(Elsevier Science Bv, 2019-09) Qasrawi, A. F.; Aloushi, Hadil D.In this work, the in situ structural transformations from amorphous to polycrystalline upon heating and the associated enhancements in the structural parameters of selenium thin films are studied by means of X-ray diffraction technique. The Se thin films which are grown onto ultrasonically cleaned glass substrate by the thermal evaporation technique under vacuum pressure of 10(-5) mbar exhibits structural transformation from amorphous to polycrystalline near 353 K. The films completed the formation of the structure which includes both of the hexagonal and monoclinic phases at 363 K. It is observed that the hexagonal phase dominates over the monoclinic as temperature is raised. Consistently, the thermally assisted crystallization process is accompanied with increase in the crystallite size, decrease in the microstrain, decrease in defect density and decrease in the percentage of stacking faults. The scanning electron microscopy measurements also confirmed the crystallinity of selenium after heating. The time dependent reputations of the crystallization test has shown that the achieved phase transitions and enhancements in structural parameters are permanent in selenium. Optically, the crystallization process is observed to be associated with redshift in the absorption spectra and in the value of the energy band gap. Electrically, the in situ monitoring of the electrical conductivity during the heating cycle has shown that the electrical conductivity stabilizes and exhibit a decrease in the acceptor levels from 566 to 321 meV after the crystallization was achieved.Article Citation - WoS: 24Citation - Scopus: 28Enhancing Proton Conductivity Via Sub-Micron Structures in Proton Conducting Membranes Originating From Sulfonated Pvdf Powder by Radiation-Induced Grafting(Elsevier Science Bv, 2018-01) Sadeghi, Sahl; Sanli, Lale Isikel; Guler, Enver; Gursel, Selmiye Alkan; Işıkel Şanlı, Lale; Alkan Gürsel, SelmiyeWe report here submicron-structured proton conducting poly(vinylidene fluoride)-graft-poly(styrene sulfonic acid) (PVDF-g-PSSA) membranes for polymer electrolyte membrane fuel cells (PEMFC). Highly conductive proton exchange membranes were obtained by single-step radiation grafting of sodium styrene sulfonate (SSS) to powder-form PVDF, followed by casting and subsequent solvent evaporation. The obtained submicron structure of membrane through solvent evaporation led to the arrangement of ionic channels proving increasing proton conductivity with the increase in graft level. In addition, a temperature above melting point of PVDF was used for solvent evaporation to allow melted PVDF to fill the formed pores, providing denser structure resulting in improved mechanical properties of the membranes. SSS grafting to PVDF powder was verified by NMR spectroscopy, and resultant membranes were characterized for proton conductivity, water up-take, morphology, mechanical and thermal properties, and fuel cell performance. According to preliminary tests, proton conductivities which were observed to increase with graft level were found to be around 70 mS cm(2) at 35% graft level. Thus, this led to a promising power density of 250 mW/cm(2) at 650 mA/cm(2).Article Citation - WoS: 77Citation - Scopus: 82Δ-Shock Model Based on Polya Process and Its Optimal Replacement Policy(Elsevier Science Bv, 2017-12) Eryilmaz, SerkanShock models are of great interest in engineering reliability. Among the others, the delta-shock model has been widely studied in the literature. In this model, the system breaks down due to the arrivals of two successive shocks which are too close to each other. That is, the system fails when the time between two consecutive shocks falls below a fixed threshold delta. In the literature, the delta-shock model has been mostly studied by assuming that shocks arrive according to a renewal process so that the interarrival times between shocks are independent and identically distributed. In the current paper, we consider the case when the shock arrival process is described by a Polya process which has dependent interarrival times. In particular, we obtain survival function and mean lifetime of the system and study the optimal replacement policy for the delta-shock model based on Polya process. (c) 2017 Elsevier B.V. All rights reserved.Article Citation - WoS: 4Citation - Scopus: 4On Success Runs in a Sequence of Dependent Trials With a Change Point(Elsevier Science Bv, 2018-01) Eryilmaz, SerkanLet {X-i}(i=1)(n) be a sequence of n dependent binary trials such that the first n(1) in {X-i}(i=1)(n) are of type 1 and follow an exchangeable joint distribution denoted by L-1, and the last n2 elements in {X-i}(i=1)(n) are of type 2 and follow an exchangeable joint distribution denoted by L-2, where n(1) + n(2) = n. That is, the trials within the same group are exchangeable dependent, and the trials in different groups are dependent in a general sense. The exact distributions of the number of success runs of length k in {X-i}(i=1)(n) are obtained under nonoverlapping and at least schemes. (C) 2017 Elsevier B.V. All rights reserved.Article Citation - WoS: 35Citation - Scopus: 39Metric-Like Spaces To Prove Existence of Solution for Nonlinear Quadratic Integral Equation and Numerical Method To Solve It(Elsevier Science Bv, 2018-01) Hazarika, Bipan; Karapinar, Erdal; Arab, Reza; Rabbani, MohsenThe purpose of this paper is to obtain some common fixed point results for two mappings satisfying various contractive conditions in metric-like spaces. These results extend some previous results in the literature, since the condition under which the operator admits common fixed points is more general than the others in literature. Therefore, several well known results are generalized. As an application we use these results to existence of solution for nonlinear quadratic integral equation. To credibility, we apply modified homotopy and Adomian decomposition method to find solution of the above problem with high accuracy. (C) 2017 Elsevier B.V. All rights reserved.Article Citation - WoS: 6Citation - Scopus: 7Al/Cdse Resonant Tunneling Thin Film Transistors(Elsevier Science Bv, 2017-02) Qasrawi, A. F.; Kayed, T. S.; Elsayed, Khaled A.An Al/CdSe/GaSe/C thin film transistor device was prepared by the physical vapor deposition technique at a vacuum pressure of 10(-5) mbar. The x-ray diffraction measurements demonstrated the polycrystalline nature of the surface of the device. The de current-voltage characteristics recorded for the Al/CdSe/C and Al/CdSe/GaSe/C channels displayed a resonant tunneling diode features during the forward and reverse voltage biasing, respectively. In addition, the switching current ratio of the Al/CdSe/C increased from 18.6 to 9.62x10(3) as a result of the GaSe deposition on the CdSe surface. Moreover, the alternating electrical signal analyses in the frequency range of 1.0 MHz to 1.8 GHz, showed some remarkable properties of negative resistance and negative capacitance spectra of the AVCdSe/GaSe/C thin film transistors. Two distinct resonance-antiresonance phenomena in the resistance spectra and one in the capacitance spectra were observed at 0.53, 1.04 and 1.40 GHz for the Al/CdSe/C channel, respectively. The respective resonating peak positions of the resistance spectra shift to 0.38 and 0.95 GHz when GaSe is interfaced with CdSe. These features of the thin film transistors are promising for use in high quality microwave filtering circuits and also for use as ultrafast switches.