WOS - Web of Science
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Publication 2D hybrid meshes for direct simulation Monte Carlo solvers(IOP Publishing, 2013-02-08) N Sengil; U SengilPublication 3-State Protein Secondary Structure Prediction based on SCOPe Classes(FapUNIFESP (SciELO), 2021) Sema Atasever; Nuh Azgınoglu; Hasan Erbay; Zafer AydınPublication 4G/LTE Technology For Smart Grid Communication Infrastructure(IEEE, 2015) Gozde, Haluk; Taplamacioglu, M. Cengiz; Ari, Murat; Shalaf, Hamza; Gazi University; Cankiri Karatekin University; Turk Hava Kurumu University; Turkish Aeronautical AssociationThe smart grid concept has emerged as a new trend to operate and manage the electric power systems more effective and efficient in recent years as different from centralized and distributed power systems. In this concept, the electric energy consumption is optimized by using an advanced automation system which needs more information about the power system elements from generation units to end-users and controls them in light of this information. Undoubtedly, receiving and transmitting of this information requires two-way, high speed, reliable and secure communication infrastructure. In this study, Long Term Evolution (LTE) technology and its usage in smart grid infrastructure are investigated. Additionally, the challenges for using 4G/LTE in smart grid applications are also discussed.Publication A 120 MHz fast automatic tuning CMOS active-RC lowpass filter(ELSEVIER SCI LTD, 2023) Yesil, Ercem; Zencir, Ertan; Zencir, Ertan; Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK); Turk Hava Kurumu University; Turkish Aeronautical AssociationIn this paper, a fast automatic cutoff frequency calibrating, CMOS lowpass filter with linear-in-dB tunable gain and constant in-band group delay is presented. The automatic frequency tuning (AFT) circuit can successfully tune the cutoff frequency to 120 MHz with less than 4.7% error. In-band group delay variation is handled using a capacitor process variation detection circuit (CPVD), and the overall tuning time is less than 700 ns. The design is done using STM PD-SOI 130 nm CMOS process, and the supply voltage is 1.2 V with a total power consumption of 21.7 mW. The overall filter provides a programmable linear-in-dB gain of 0.5 dB to 17.6 dB range with a cutoff tuning range of 80 to 180 MHz. The in-band group delay variation is below 500 ps with an adjacent channel ratio (ACR) of 85 dB. The spurious free dynamic range (SFDR) is over 66.6 dBc. The active area of the filter with tuning is 0.171 mm2.Publication A compact octagonal-ring monopole antenna for super wideband applications(WILEY, 2020) Okan, Tayfun; Turkish Aeronautical Association; Turk Hava Kurumu UniversityA compact monopole super wideband antenna has been designed and fabricated in this study. The proposed antenna consists of an octagonal-ring shaped patch with a stub positioned on the top right corner of it to enhance the impedance bandwidth. Further improvement is ensured by optimally shifting both the patch and feed line away from the center line, and introducing a notch on the ground plane. The fabricated antenna covers the frequency band from 2.59 to 31.14 GHz with a reflection coefficient of |S-11| <= - 10 dB. It has a bandwidth of 28.55 GHz, fractal bandwidth percentage of 169% and bandwidth ratio of 12.02:1. Omnidirectional radiation characteristics are observed over the operating bandwidth in the far-field measurements. Furthermore, the far-field radar cross section measurement of the antenna is also simulated on PC and relatively low values are obtained through the operating bandwidth. Presented antenna has a relatively small size (40 x 40 x 1.01 mm(3)) and exhibits good gain and efficiency characteristics in comparison to studies with similar bandwidth.Publication A comparative study of spreading of novel corona virus disease by ussing fractional order modified SEIR model(Elsevier BV, 2021-02) Hussam Alrabaiah; Muhammad Arfan; Kamal Shah; Ibrahim Mahariq; Aman UllahPublication A comparative study on utilizing hybrid-type nanofluid in plate heat exchangers with different number of plates(SPRINGER HEIDELBERG, 2020) Gurbuz, Emine Yagiz; Sozen, Adnan; Variyenli, Halil Ibrahim; Khanlari, Ataollah; Tuncer, Azim Dogus; Mugla Sitki Kocman University; Gazi University; Gazi University; Turk Hava Kurumu University; Turkish Aeronautical Association; Mehmet Akif Ersoy UniversityDifferent methods have been utilized to enhance the thermal efficiency of the heat exchangers (HEs). A widely used method to upgrade the thermal efficiency of HEs is upgrading the thermal properties of working fluid by utilizing nanoparticles. In this study, Al(2)O(3)and CuO have been utilized to prepare Al2O3-CuO/water hybrid nanofluid. Accordingly, Al(2)O(3)and CuO nanoparticles have been mixed into the water with 1% (50:50) weight concentration. The main objective of this work is testing the prepared hybrid nanofluid in plate-type HEs (PHEs) with 8, 12 and 16 plates to determine the influence of number of plates on heat transfer improvement by hybrid nanofluid. Experimental findings of the present study demonstrated that utilizing Al2O3-CuO/water hybrid-type nanofluid in the PHE enhanced thermal efficiency notably in comparison with single-type nanofluids. Using this hybrid nanofluid increased the thermal performance in all PHEs with different number of plates. However, it is observed that increasing number of plates led to more increment in thermal performance by utilizing hybrid nanofluid. The highest increment in overall heat transfer coefficient was obtained as 12%, 19% and 20% in PHEs with eight, 12 and 16 plates, respectively. In addition, the highest enhancement in effectiveness was achieved as 10%, 11.7% and 16% in PHEs with eight, 12 and 16 plates, respectively.Publication A comparison of peptide amphiphile nanofiber macromolecular assembly strategies(SPRINGER, 2019) Dana, Aykutlu; Tekinay, Ayse B.; Tekin, E. Deniz; Tekin, Emine Deniz; Stanford University; Turk Hava Kurumu University; Turkish Aeronautical Association.Supramolecular peptide nanofibers that are composed of peptide amphiphile molecules have been widely used for many purposes from biomedical applications to energy conversion. The self-assembly mechanisms of these peptide nanofibers also provide convenient models for understanding the self-assembly mechanisms of various biological supramolecular systems; however, the current theoretical models that explain these mechanisms do not sufficiently explain the experimental results. In this study, we present a new way of modeling these nanofibers that better fits with the experimental data. Molecular dynamics simulations were applied to create model fibers using two different layer models and two different tilt angles. Strikingly, the fibers which were modeled to be tilting the peptide amphiphile molecules and/or tilting the plane were found to be more stable and consistent with the experiments.Publication A comprehensive survey on recent metaheuristics for feature selection(Elsevier BV, 2022-07) Tansel Dokeroglu; Ayça Deniz; Hakan Ezgi KizilozPublication A comprehensive survey on utilization of hybrid nanofluid in plate heat exchanger with various number of plates(EMERALD GROUP PUBLISHING LTD, 2022) Afshari, Faraz; Tuncer, Azim Dogus; Sozen, Adnan; Variyenli, Halil Ibrahim; Khanlari, Ataollah; Gurbuz, Emine Yagiz; Erzurum Technical University; Mehmet Akif Ersoy University; Gazi University; Gazi University; Turk Hava Kurumu University; Turkish Aeronautical Association; Mugla Sitki Kocman UniversityPurpose Using suspended nanoparticles in the base fluid is known as one of the most efficient ways for heat transfer augmentation and improving the thermal efficiency of various heat exchangers. Different types of nanofluids are available and used in different applications. The main purpose of this study is to investigate the effects of using hybrid nanofluid and number of plates on the performance of plate heat exchanger. In this study, TiO2/water single nanofluid and TiO2-Al2O3/water hybrid nanofluid with 1% particle weight ratio have been used to prepare hybrid nanofluid to use in plate type heat exchangers with three various number of plates including 8, 12 and 16. Design/methodology/approach The experiments have been conducted with the aim of examining the impact of plates number and used nanofluids on heat transfer enhancement. The performance tests have been done at 40 degrees C, 45 degrees C, 50 degrees C and 55 degrees C set outlet temperatures and in five various Reynolds numbers between 1,600 and 3,800. Also, numerical simulation has been applied to verify the heat and flow behavior inside the heat exchangers. Findings The results indicated that using both nanofluids raised the thermal performance of all tested exchangers which have a various number of plates. While the major outcomes of this study showed that TiO2-Al2O3/water hybrid nanofluid has priority when compared to TiO2/water single type nanofluid. Utilization of TiO2-Al2O3/water nanofluid led to obtaining an average improvement of 7.5%, 9.6% and 12.3% in heat transfer of heat exchangers with 8, 12 and 16 plates, respectively. Originality/value In the present work, experimental and numerical analyzes have been conducted to investigate the influence of using TiO2-Al2O3/water hybrid nanofluid in various plate heat exchangers. The attained findings showed successful utilization of TiO2-Al2O3/water nanofluid. Based on the obtained results increasing the number of plates in the heat exchanger caused to obtain more increment by using both types of nanofluids.Publication A Direct Numerical Simulation Study for Flame Structure and Propagation Characteristics of Multi-Jet Flames(TAYLOR & FRANCIS INC, 2023) Kiran, D.; Minamoto, Y.; Osawa, K.; Shimura, M.; Tanahashi, M.; Tokyo Institute of Technology; Turk Hava Kurumu University; Turkish Aeronautical Association; Universidad Politecnica de Madrid; Tokyo Institute of TechnologyLifted multi-jet flames of hydrogen and steam-diluted oxygen are studied using direct numerical simulations (DNS). The DNSs have been carried out for laminar and turbulent flame configurations. The simulation data are analyzed to investigate the flame and flame-base structures and the flame-base propagation in a configuration akin to a gas turbine with multiple fuel jets. The laminar flames have a tribrachial structure, although lean premixed and diffusi on flame branches collide downstream owing to preferential diffusion. The turbulent multi-jet flames have a single connected base region, whereas the laminar flames have separate bases, each of which is associated with the corresponding fuel jet. Although turbulent multi-jet flames have substantially different flame-base characteristics from laminar multi-jet flames (and conventional single-jet lifted flames), the propagation speed is similar for both conditions. The results suggest that the well-known flame-base stabilization theory can be straightforwardly applied to the multi-jet configuration, despite the turbulent flame structure's unconventional features.Publication A facile approach for the fabrication of antibacterial nanocomposites: A case study for AgNWs/Poly(1,4-Cyclohexanedimethylene Acetylene Dicarboxylate) composite networks by aza-Michael addition(PERGAMON-ELSEVIER SCIENCE LTD, 2022) Altinkok, Cagatay; Acik, Gokhan; Daglar, Ozgun; Durmaz, Hakan; Tunc, Ilknur; Agel, Esra; Istanbul Technical University; Trakya University; Turk Hava Kurumu University; Turkish Aeronautical Association; Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK)Nanotechnological improvements allow the production of new generation materials among which nanocomposite-based polymers are increasingly applied for wide variety of applications due to the demand increment of improving life quality of mankind. This article describes a simple, facile and fast route which could be adopted for the synthesis of metal nanocomposite materials with a variety of polymers. In this purpose, the cysteamine compound containing an amine (NH2) and a thiol (-SH) functional groups was incorporated onto silver nanowires (NH2-AgNWs). Next, poly(1,4-Cyclohexanedimethylene Acetylene Dicarboxylate) (PCA) possessing electron deficient internal alkyne moiety is synthesized starting from acetylene dicarboxylic acid (ADCA). Finally, one-pot aza-Michael addition is then realized between prepared NH2-AgNWs and synthesized PCA to achieve a series of cross-linked antibacterial nanocomposite networks (PCA:NH2-AgNWs = 1; 5; 10 wt%). The nanocomposites and intermediates are fully characterized by Fourier transform infrared and proton nuclear magnetic resonance (FT-IR, 1H NMR) spectroscopies, gel permeation chromatography (GPC) scanning electron microscopy (SEM), Energy-dispersive X-ray spectroscopy (EDS), thermogravimetric and differential scanning calorimetry analyses (TGA and DSC) and antibacterial test. The results reveal that the higher content of AgNWs in the network has occasioned the enhancement in thermostability and glass transition temperature. The antibacterial efficacy tests against Escherichia coli (E. coli, G) and Staphylococcus aureus (S.aureus, G +) further indicate that higher rate of inhibition is attained for nanocomposite network including 10 wt% AgNWs compared to others and pristine PCA. Consequently, a polyester based AgNWs/PCA nanocomposite with antibacterial activity has been considered as a versatile candidate for various promising nanocomposite applications.Publication A fractional dynamical model for honeybee colony population(WORLD SCIENTIFIC PUBL CO PTE LTD, 2018) Akman Yildiz, Tugba; Turkish Aeronautical Association; Turk Hava Kurumu UniversityBees are the main contributors of pollination and it is predicted that disruption of pollination causes some serious problems in economics, agriculture and ecology. It has been reported that honeybee colony collapse has increased dramatically for some time in different parts of the world. In order to investigate the causes of colony collapse, we establish a fractional multi-order honeybee colony population model. Two different models with Caputo and Caputo-Fabrizio differentiation operators have been compared. We justify the existence and uniqueness of the solution. Stability analysis has been presented. We find the numerical values of the fractional order (p,q) so that the numerical results are close to the experimental findings more than the integer-order case.Publication A fuzzy approach for the reviewer assignment problem(PERGAMON-ELSEVIER SCIENCE LTD, 2014) Das, G. Sena; Gocken, Tolunay; Turkish Aeronautical Association; Turk Hava Kurumu University; Adana Alparslan Turkes Science & Technology UniversityAssignment of experts to project proposals is a significant task for funding agencies which have to assess the potential value of the research and development (R&D) projects through peer review. The problem is known as reviewer assignment problem and has real-world applications in funding agencies, conferences and research journals. Given a set of experts and a set of proposals; the problem can be defined as assigning the most suitable experts to the proposals under some constraints, which are generally encountered by funding agencies. In this study, a fuzzy model is offered to solve the reviewer assignment problem. The objective of the model is to maximize the total matching degree of assigned experts under some constraints such as cost of forming a panel and the size of a panel. The matching degrees are defined using linguistic variables to denote the expertise of each expert with respect to each proposal. The fuzzy mathematical model, which also takes into account different constraints related to the problem, is solved via the selected fuzzy ranking methods namely; the signed distance method and the method of ranking fuzzy numbers with integral value. The solution of an example problem - inspired from a real-life situation with both of the mentioned methods revealed the effectiveness of the solution approach. It is believed that the use of the offered fuzzy approach could improve the accuracy of the decisions made by funding agencies. (C) 2014 Elsevier Ltd. All rights reserved.Publication A fuzzy logic-based stabilization system for a flying robot, with an embedded energy harvester and a visual decision-making system(Elsevier BV, 2023-09) Abdullatif Baba; Basil Alothman; Baba, AbdullatifPublication A Generic, Multi-Period and Multi-Partner Cost Optimizing Model for Cloud-Based Supply Chain(IGI GLOBAL, 2016) Akyuz, Goknur Arzu; Rehan, Mohammad; Turkish Aeronautical Association; Turk Hava Kurumu University; Atilim UniversityCloud technology in a multi-enterprise, collaborative context is one of the most promising topics at IT-Supply Chain (SC) intersection. Cloud comes with well-proven advantages and cost savings; enabling collaboration and business intelligence. Cloud transition is still on-going with individual enterprise-level transitions. However, collaborative paradigm dictates that entire network well-being is to be considered over enterprise-level concerns. Thus, handling the transition of a single enterprise is not sufficient for strategic network leverage. Planning and managing across multiple enterprises is required, taking into consideration various cost items and budget constraints. In this study, a multi-period multi-partner cost-optimizing model is developed for network-level management of cloud transition for a SC. The model produces an optimal transition plan, indicating timing of the transition for each partner to obtain the maximum cost savings across network over a specified planning horizon. The model proposed is generic, flexible and customizable for different sectors/settings.Publication A High-Speed Fully Differential Telescopic Op-Amp for Active Filter Designs in V2X Applications(WORLD SCIENTIFIC PUBL CO PTE LTD, 2022) Barin, Furkan; Zencir, Ertan; Zencir, Ertan; Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK); Turkish Aeronautical Association; Turk Hava Kurumu UniversityIn this paper, an ultra-wideband fully differential two-stage telescopic 65-nm CMOS op-amp is presented, which uses low-voltage design techniques such as level shifter circuits and low-voltage cascade current mirrors. The designed op-amp consists of two stages. While the telescopic first stage provides high speed and low swing, the second stage provides high gain and large swing. Common-mode feedback circuits (CMFB), which contain five transistors OTA and sensing resistors, are used to set the first-stage output to a known value. The designed two-stage telescopic operational amplifier has 41.04 dB lower frequency gain, 1.81 GHz gain-bandwidth product (GBW) and 51.9 degrees phase margin under 5 pF load capacitance. The design consumes a total current of 11.9 mA from a 1.2-V supply voltage. Presented fully differential two-stage telescopic op-amp by using low-voltage design techniques is suitable for active filter in vehicle-to-everything (V2X) applications with 120 mu m x 55 mu m layout area.Publication A Hybrid Hesitant Fuzzy Model for Healthcare Systems Ranking of European Countries(MDPI AG, 2022-11-16) Ahmet Aktas; Billur Ecer; Mehmet KabakRanking several countries on a specific area may require the consideration of various factors simultaneously. To obtain a ranking of countries, the development of analytical approaches, which can aggregate opinions of a group of people on various criteria, is essential. The main aim of this study was to propose such a ranking approach for European countries in terms of healthcare services. To this end, a hybrid group decision-making model based on Hesitant Fuzzy Linguistic Terms Set (HFLTS) and Hesitant Fuzzy Technique of Order Preference by Similarity to Ideal Solution (HF-TOPSIS) is presented in this study. Importance degree of indicators were determined by the HFLTS-based group decision-making approach, and then HF-TOPSIS was used to obtain the rank of countries. According to the results obtained by the proposed model, Austria, Sweden and Finland are the best European countries in terms of healthcare services. Moreover, two comparative analyses, one for the utilization of different hesitant fuzzy distance measures in HF-TOPSIS and one for the ranking of countries obtained by utilizing TOPSIS, return some variations in country rankings. While Austria remained the best country for all distance measures in the hesitant fuzzy environment, Luxemburg was found to be the best for the deterministic case of TOPSIS.Publication A Hybrid Supplier Evaluation Model for Personal Protective Equipment Procurement to Healthcare Employees(SPRINGER NATURE SWITZERLAND AG, 2022) Kabak, Mehmet; Aktas, Ahmet; Park, Claire Su-Yeon; Gazi University; Turkish Aeronautical Association; Turk Hava Kurumu University; University of AlbertaHealthcare workers face the risk and the danger of contracting several infectious diseases. In order to prevent from the risk of being infected by blood, contact, respiratory droplets, etc., healthcare workers need to use Personal Protective Equipment (PPE). Because of the increasing demand for quality PPE after COVID-19 pandemic, it is important for healthcare institutions to determine the best supplier. Evaluation of suppliers is a complex decision, which contains a number of alternative suppliers and conflicting criteria. The conflicts between supplier evaluation factors require institutions to make a compromise choice among alternative suppliers. Therefore, the main aim of this study is to develop an analytic supplier evaluation model for PPE procurement to healthcare institutions. To that end, a hybrid multi-criteria decision making (MCDM) model based on Analytic Hierarchy Process (AHP) and VIse Kriterijumsa Optimiz acija I Kompromisno Resenje (VIKOR) is proposed. A case study for surgical mask procurement to a hospital is presented to demonstrate the applicability of the proposed model. The application results show that the proposed model is a useful decision support tool for PPE procurements to policy-makers of healthcare institutions.Publication A Low Power, Low Phase Noise, 11.8 GHz LC-VCO in 65 nm CMOS for 5G NR Based C-V2X Applications(WORLD SCIENTIFIC PUBL CO PTE LTD, 2022) Kayanselcuk, Toprak; Zencir, Ertan; Zencir, Ertan; Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK); Turkish Aeronautical Association; Turk Hava Kurumu UniversityAn 11.8-GHz low-power, low phase noise, 65-nm CMOS LC-VCO for V2X communication standards is presented in this work. To achieve low-phase noise performance to fulfill the 5G NR C-V2X standards, several adjustments are made to the conventional LC-VCO topologies. These adjustments are briefly explained in this work. Presented VCO consumes 3.046 mA current from a 1.2-V power supply. It has -116.13 dBc/Hz phase noise at 1 MHz offset and tuning range between 11.64 GHz and 11.94 GHz. A frequency divider circuit is designed and implemented to the presented VCO to satisfy the frequency spectrum of V2X radio access technologies. To the best of authors' knowledge, this work is the first VCO implemented at 11.8 GHz in a 65-nm CMOS process with the reported phase noise number for 5G NR C-V2X applications.