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        • KCI등재SCOPUS

          Pre‑calculated duty cycle optimization method based on genetic algorithm implemented in DSP for a non‑inverting buck‑boost converter

          Zafer,Ortatepe,Ahmet,Karaarslan 전력전자학회 2020 JOURNAL OF POWER ELECTRONICS Vol.20 No.1

          This study presents a pre-calculated duty cycle optimization method based on the genetic algorithm for a non-inverting buck-boost converter (NIBBC). In this method, the duty cycles are calculated via a discrete model estimation of NIBBC. Despite its high computational time requirements, this method can find solutions to problems that other methods cannot overcome due to their lack of linearity, continuity, or other features. This algorithm is developed using the TMS320F28335 digital signal processor, which is a 32-bit floating point processor operating at 150 MHz. The robustness and stability of this method at varying input voltages, loads, and parameters are then analyzed following the IEEE and IEC standards. The experimental results verify the simulation results and highlight the efficiency, power quality, wide output voltage range, and stability of the proposed method.

        • KCI등재SCOPUS

          The effect of in-plane deformations on the nonlinear dynamic response of laminated plates

          Zafer,Kazanci,Halit,S.,Turkmen 국제구조공학회 2012 Structural Engineering and Mechanics, An Int'l Jou Vol.42 No.4

          In this study, the effect of in-plane deformations on the dynamic behavior of laminated plates is investigated. For this purpose, the displacement-time and strain-time histories obtained from the large deflection analysis of laminated plates are compared for the cases with and without including in-plane deformations. For the first one, in-plane stiffness and inertia effects are considered when formulating the dynamic response of the laminated composite plate subjected to the blast loading. Then, the problem is solved without considering the in-plane deformations. The geometric nonlinearity effects are taken into account by using the von Kármán large deflection theory of thin plates and transverse shear stresses are ignored for both cases. The equations of motion for the plate are derived by the use of the virtual work principle. Approximate solution functions are assumed for the space domain and substituted into the equations of motion. Then, the Galerkin method is used to obtain the nonlinear algebraic differential equations in the time domain. The effects of the magnitude of the blast load, the thickness of the plate and boundary conditions on the in-plane deformations are investigated.

        • KCI등재SCOPUS

          Numerical investigation on the structural behavior of two-way slabs reinforced with low ductility steel

          Zafer,Sakka,R.,Ian,Gilbert 국제구조공학회 2018 Structural Engineering and Mechanics, An Int'l Jou Vol.65 No.3

          A numerical investigation of the impact of steel ductility on the strength and ductility of two-way corner and edge-supported concrete slabs containing low ductility welded wire fabric is presented. A finite element model was developed for the investigation and the results of a series of concurrent laboratory experiments were used to validate the numerical solution. A parametric investigation was conducted using the numerical model to investigate the various factors that influence the structural behavior at the strength limit state. Different values of steel uniform elongation and ultimate to yield strength ratios were considered. The results are presented and evaluated, with emphasis on the strength, ductility, and failure mode of the slabs. It was found that the ductility of the flexural reinforcement has a significant impact on the ultimate load behavior of two-way corner-supported slabs, particularly when the reinforcement was in the form of cold drawn welded wire fabric. However, the impact of the low ductility WWF has showed to be less prominent in structural slabs with higher levels of structural indeterminacy. The load-deflection curves of corner-supported slabs containing low ductility WWF are brittle, and the slabs have little ability to undergo plastic deformation at peak load.

        • KCI등재

          Relationship of Non-Dipper and Reverse-Dipper Pattern with Sleep Quality in Normotensive Patients

          Zafer,Yalım,Sümeyra,Alan,Yalım 대한수면연구학회 2020 Journal of sleep medicine Vol.17 No.1

          Objectives: It has been observed in many different populations that circadian blood pressure (BP) patterns have a significant impact on cardiovascular (CV) results. Important predictors of CV morbidity and mortality are known as non-dipper (ND) and reverse-dipper (RD) BP pattern. RD and ND patterns are frequently encountered in many normotensive patients in daily practice. Methods: The purpose of this study is to evaluate the frequency and quality of sleep, especially in normotensive young individuals, by using sleep questionnaires and to evaluate their relationship with poor BP patterns. A total of 195 normotensive patients (68 dippers, 63 ND, and 65 RD) were enrolled into this cross-sectional study. The insomnia severity index (ISI), Epworth sleepiness scale (ESS), and Pittsburgh sleep quality index (PSQI) approved questionnaires were applied to evaluate the presence and severity of sleep disorders and to determine the patient's sleep quality. Results: When dipper and ND groups were compared, significant differences were observed in ISI, ESS, and PSQI (p<0.001). Then, the study patients were re-evaluated as dipper, ND, and RD groups and seen this significant difference continued (p<0.001). Also, the sleep time was significantly different between all groups of dipper (7.23±0.11 hours), ND (6.72±0.15 hours), and RD (5.79±0.11 hours) (p<0.001). In the correlation analysis, a significant inverse relationship was observed between sleep time and all survey results (p<0.05). Conclusions: RD and ND patterns are associated with sleep quality in healthy individuals. It is necessary to evaluate patients with RD and ND BP patterns in normotensive individuals in terms of sleep disorders in detail.

        • KCI등재SCOPUS

          Simultaneous biosynthesis of reduced graphene oxide-Ag-Cu2O nanostructures by lichen extract for catalytic reduction of textile dyes

          Zafer,Çıplak,Bengü,Getiren,Ceren,Gökalp,Ceren,Atila,Dinçer,Atila,Yıldız,Nuray,Yıldız 한국화학공학회 2020 Korean Journal of Chemical Engineering Vol.37 No.12

          Metal/metal oxide nanostructures based reduced graphene oxide (LrGO-Ag, LrGO-Cu2O, LrGO-Ag-Cu2O) nanocomposites were obtained via green method using Cetraria islandica (L.) Ach. lichen extract. Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy (TEM), scanning electron microscope energy-dispersive X-ray spectroscopy (SEM–EDX), ultraviolet-visible (UV-Vis) spectroscopy, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were performed to analyze the prepared nanostructures. The results indicated that the nanocomposites were synthesized effectively and Ag-Cu2O nanoparticles with the mean diameter of 27nm were well dispersed on the LrGO. The conversion of methylene blue (MB) to Leuco Methylene Blue (LMB) and 4-Nitrophenol (4- NP) to 4-Aminophenol (4-AP) was performed by biosynthesized catalysts in the presence of NaBH4. The reaction rate of LrGO-Ag-Cu2O nanocomposite during 4-NP and MB reduction was found as 0.0026 s1 and 0.0497 s1, respectively. The LrGO-Ag-Cu2O nanocomposite showed superior catalytic performance for the reduction of both textile dyes.

        • KCI등재SCOPUS

          Reliability-based assessment of damaged concrete buildings

          Zafer,I.,Sakka,Ibrahim,A.,Assakkaf,Jamal,S.,Qazweeni 국제구조공학회 2018 Structural Engineering and Mechanics, An Int'l Jou Vol.65 No.6

          Damages in concrete structures due to aging and other factors could be a serious and immense matter. Making the best selection of the most viable and practical repairing and strengthening techniques are relatively difficult tasks using traditional methods of structural analyses. This is due to the fact that the traditional methods used for assessing aging structure are not fully capable when considering the randomness in strength, loads and cost. This paper presents a reliability-based methodology for assessing reinforced concrete members. The methodology of this study is based on probabilistic analysis, using statistics of the random variables in the performance function equations. Principles of reliability updating are used in the assessment process, as new information is taken into account and combined with prior probabilistic models. The methodology can result in a reliability index β that can be used to assess the structural component by comparing its value with a standard value. In addition, these methods result in partial safety factor values that can be used for the purpose of strengthening the R/C elements of the existing structure. Calculations and computations of the reliability indices and the partial safety factors values are conducted using the First-order Reliability Method and Monte Carlo simulation.

        • KCI등재후보

          Influence of Crown Margin Design on the Stress Distribution in Maxillary Canine Restored by All-Ceramic Crown

          Zafer,Ozer,Cem,Kurtoglu,Amirullah,M.,Mamedov,Ekmel,Ozbay 대한치의학회 2015 Journal of korean dental science Vol.8 No.1

          Purpose: To investigate the influence of crown margin design on the stress distribution and to localize critical sites in maxillary canine under functional loading by using three dimensional finite element analysis. Materials and Methods: The bite force of 100 N, 150 N, and 200 N was applied with an angulation of 45° to the longitudinal axis of tooth. Six models were restored with IPS e.max (Ivoclar Vivadent, Schaan, Liechtenstein) with a different margin design. With lingual ledge and various thicknesses, three different core ceramics were designed in each model. Result: In the core ceramic, the maximum tensile stresses were found at the labiocervical region. In the veneering ceramic the maximum tensile stresses were found at the area where the force was applied in all models. Conclusion: Shoulder and chamfer margin types are acceptable for all-ceramic rehabilitations. A ledge on the core ceramic at cervical region may affect the strength of all-ceramic crowns.

        • KCI등재SCOPUS
        • KCI등재SCOPUS

          Volume ratio and pressure drop on hydraulic dynamic pressure calibration system

          Afaqul,Zafer,Sanjay,Yadav,Arif,Sanjid,Lalit,Kumar,Raman,Kumar,Sharma 대한기계학회 2017 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.31 No.8

          The calibration of a pressure transducer that works in dynamic conditions is an unavoidable challenge. To address this challenge, an experimental setup has been designed and developed to simultaneously generate and calibrate the dynamic pressure. The system mainly comprises a pressure chamber that accommodates a step pressure generator and test chamber with a quick open valve and pressure sensor under calibration. Accordingly, an aperiodic type of step pressure generator with a quick open valve is particularly designed. This instrument can generate a positive step pressure with a rise time of up to 11 ms and a negative step pressure with a fall time of up to 12 ms within a working pressure range from the atmospheric pressure to 200 MPa. The volume ratio of the test chamber to the pressure chamber and its effect on pressure drop is critical in such systems. The effect of volume ratio on the dynamic performance parameters, namely, rise/fall time, is explored and inferences for optimizing these parameters are derived. A mathematical model for pressure drop in the test chamber has been developed and validated to precisely determine the magnitude of the step pressure input. Lastly, the experimental study of the effect of volume ratio on pressure drop has been conducted to diminish the pressure drop, thereby minimizing the uncertainty.

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