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Citation - WoS: 2
Citation - Scopus: 2
On the q-bernstein Polynomials of Piecewise Linear Functions in the Case q > 1
(Pergamon-elsevier Science Ltd, 2013) Kaskaloglu, Kerem; Ostrovska, Sofiya
The aim of this paper is to present new results related to the approximation of continuous functions by their q-Bernstein polynomials in the case q > 1. The first part of the paper is devoted to the behavior of the q-Bernstein polynomials of piecewise linear functions. This study naturally leads to the notion of truncated q-Bernstein polynomials introduced in the paper. The second part deals with the asymptotic estimates for the norms of the m-truncated q-Bernstein polynomials, in the case where both n and q vary. The results of the paper are illustrated by numerical examples. (C) 2012 Elsevier Ltd. All rights reserved.
Citation - WoS: 3
Instability Intervals of a Hill's Equation With Piecewise Constant and Alternating Coefficient
(Pergamon-elsevier Science Ltd, 2004) Guseinov, GS; Karaca, IY
In 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.
Citation - WoS: 28
Citation - Scopus: 34
Enhancement of Direct Methanol Fuel Cell Performance Through the Inclusion of Zirconium Phosphate
(Pergamon-elsevier Science Ltd, 2017) Ozden, Adnan; Ercelik, Mustafa; Ozdemir, Yagmur; Devrim, Yilser; Colpan, C. Ozgur
Nafion/zirconium hydrogen phosphate (ZrP) composite membranes containing 2.5 wt.% ZrP (NZ-2.5) or 5 wt.% ZrP (NZ-5) were prepared to improve the performance of a direct methanol fuel cell (DMFC). The influence of ZrP content on the Nafion matrix is assessed through characterization techniques, such as Thermogravimetric Analysis (TGA), X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Electrochemical Impedance Spectroscopy (EIS), and water uptake measurement. Performance testings of the DMFCs based on these composite membranes as well as commercial Nafion (R) 115 membrane were performed using a computer aided fuel cell test station for different values of cell temperature (40 degrees C, 60 degrees C, 80 degrees C, and 100 degrees C) and methanol concentration (0.75 M, 1.00 M, and 1.50 M). Characterization studies indicated that incorporation of ZrP into polymer matrix enhanced the water uptake and proton conductivity values of Nafion membrane. The results of the performance tests showed that the Membrane Electrode Assembly (MEA) having NZ-2.5 provided the highest performance with the peak power density of 551.52 W/m(2) at 100 degrees C and 1.00 M. Then, the performances of the MEAs having the same NZ-2.5 membrane but different cathode catalysts were investigated by fabricating two different MEAs using cathode catalysts made of Pt/C-ZrP and Pt/C (HiSPEC (R) 9100). According to the results of these experiments, the MEA having NZ-2.5 membrane and Pt/C (HiSPEC (R) 9100) cathode catalyst containing 10 wt.% of ZrP exhibited the highest performance with the peak power density of 620.88 W/m(2) at 100 degrees C and 1.00 M. In addition, short-term stability tests were conducted for all the MEAs. The results of the stability tests revealed that introduction of ZrP to commercial (HiSPEC (R) 9100) cathode catalyst improves its stability characteristics. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
Citation - WoS: 12
Citation - Scopus: 16
The Laplace Transform on Isolated Time Scales
(Pergamon-elsevier Science Ltd, 2010) Bohner, Martin; Guseinov, Gusein Sh.
Starting with a general definition of the Laplace transform on arbitrary time scales, we specify the Laplace transform on isolated time scales, prove several properties of the Laplace transform in this case, and establish a formula for the inverse Laplace transform. The concept of convolution is considered in more detail by proving the convolution theorem and a discrete analogue of the classical theorem of Titchmarsh for the usual continuous convolution. (C) 2010 Elsevier Ltd. All rights reserved.
Citation - WoS: 9
Citation - Scopus: 9
Nonoscillation and Oscillation of Second-Order Impulsive Differential Equations With Periodic Coefficients
(Pergamon-elsevier Science Ltd, 2012) Ozbekler, A.; Zafer, A.
In this paper, we give a nonoscillation criterion for half-linear equations with periodic coefficients under fixed moments of impulse actions. The method is based on the existence of positive solutions of the related Riccati equation and a recently obtained comparison principle. In the special case when the equation becomes impulsive Hill equation new oscillation criteria are also obtained. (C) 2011 Elsevier Ltd. All rights reserved.
Citation - WoS: 44
Citation - Scopus: 45
Carbon Nanotube-Graphene Supported Bimetallic Electrocatalyst for Direct Borohydride Hydrogen Peroxide Fuel Cells
(Pergamon-elsevier Science Ltd, 2021) Uzundurukan, Arife; Akca, Elif Seda; Budak, Yagmur; Devrim, Yilser
At present study, carbon nanotube-graphene (CNT-G) supported PtAu, Au and Pt catalysts were prepared by microwave-assisted synthesis method to investigate the direct liquid-fed sodium borohydride/hydrogen peroxide (NaBH4/H2O2) fuel cell performance. Prepared catalysts were characterized by TGA, XRD, TEM, ICP-OES, cyclic voltammetry and rotating disc electrode (RDE) voltammetry. The catalysts were tested in a single NaBH4/H2O2 fuel cell with 25 cm(2) active area to evaluate fuel cell performance. The effects of temperature and fuel concentration on fuel cell performance were examined to observed best operating conditions. As a result of direct NaBH4/H2O2 fuel cell experiments, maximum power densities of 139 mW/cm(2), 125 mW/cm(2) and 113 mW/cm(2) were obtained for PtAu/CNT-G, Au/CNT-G and Pt/CNT-G catalysts, respectively. PtAu/CNT-G catalyst showed the enhanced NaBH4/H2O2 fuel cell performance, which was higher than the Pt/CNT-G catalyst and Au/CNT-G catalyst at 50 degrees C. The enhanced NaBH4/H2O2 performance can be attributed to synergistic effects between Pt and Au particles on CNT-G support providing a better catalyst utilization and interaction. These results suggest that the prepared PtAu/CNT-G catalyst is a promising anode catalyst for NaBH4/H2O2 fuel cell application. (c) 2020 Elsevier Ltd. All rights reserved.
Citation - WoS: 34
Citation - Scopus: 41
Development of a Personalized Thermal Comfort Driven Controller for Hvac Systems
(Pergamon-elsevier Science Ltd, 2021) Turhan, Cihan; Simani, Silvio; Akkurt, Gulden Gokcen
Increasing thermal comfort and reducing energy consumption are two main objectives of advanced HVAC control systems. In this study, a thermal comfort driven control (PTC-DC) algorithm was developed to improve HVAC control systems with no need of retrofitting HVAC system components. A case building located in Izmir Institute of Technology Campus-Izmir-Turkey was selected to test the developed system. First, wireless sensors were installed to the building and a mobile application was developed to monitor/ collect temperature, relative humidity and thermal comfort data of an occupant. Then, the PTC-DC algorithm was developed to meet the highest occupant thermal comfort as well as saving energy. The prototypes of the controller were tested on the case building from July 3rd, 2017 to November 1st, 2018 and compared with a conventional PID controller. The results showed that the developed control algorithm and conventional controller satisfy neutral thermal comfort for 92 % and 6 % of total measurement days, respectively. From energy consumption point of view, the PTC-DC decreased energy consumption by 13.2 % compared to the conventional controller. Consequently, the PTC-DC differs from other works in the literature that the prototype of PTC-DC can be easily deployed in real environments. Moreover, the PTC-DC is low-cost and user-friendly. (c) 2021 Elsevier Ltd. All rights reserved.
Citation - WoS: 45
Citation - Scopus: 50
Investigations on Microstructural Changes in Machining of Inconel 100 Alloy Using Face Turning Experiments and 3d Finite Element Simulations
(Pergamon-elsevier Science Ltd, 2016) Arisoy, Yigit M.; Guo, Changsheng; Kaftanoglu, Bilgin; Oezel, Tugrul
Nickel-base IN100 alloy is a choice of material for components requiring high strength at elevated temperatures. Machining processes applied to these components affect the microstructure, grain size, and microhardness of the finished surface. This research investigates the effects of tool micro-geometry, coating, and cutting speed on the microstructural changes during machining. 3D customized finite element simulations have been performed to predict the average grain size by implementing modified temperature dependent flow softening based material and Johnson-Mehl-Avrami-Kolmogorov crystallization models. Simulation predictions on the average grain sizes, phase fractions, and resultant microhardness are compared against experimental measurements revealing good agreements. (C) 2016 Elsevier Ltd. All rights reserved.
Citation - WoS: 173
Fixed Point Theory for Cyclic Weak Φ-Contraction
(Pergamon-elsevier Science Ltd, 2011) Karapinar, Erdal; Karapınar, Erdal; Karapınar, Erdal; Mathematics; Mathematics
In this manuscript, the notion of cyclic weak phi-contraction is considered. It is shown that a self-mapping T on a complete metric space X has a fixed point if it satisfied cyclic weak phi-contraction. (C) 2010 Elsevier Ltd. All rights reserved.
Citation - WoS: 52
Citation - Scopus: 69
Quadruple Fixed Point Theorems for Nonlinear Contractions
(Pergamon-elsevier Science Ltd, 2012) Karapinar, Erdal; Nguyen Van Luong
The notion of coupled fixed point is introduced by Gnana-Bhaskar and Lakshmikantham. Very recently, the concept of tripled fixed point was introduced by Berinde and Borcut. In this manuscript, a quadruple fixed point is considered and some new related fixed point theorems are obtained. We also give some examples to illustrate our results. (c) 2012 Elsevier Ltd. All rights reserved.

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