WOS - Web of Science
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Publication Implementation of DBSCAN Method in Star Trackers to Improve Image Segmentation in Heavy Noise Conditions(2023) Nevsan ŞENGİL; Şengil, Nevsan; Türk Hava Kurumu Üniversitesi, Uzay Mühendisliği Bölümü, Ankara, TürkiyeStar trackers are currently the most accurate sensors for determining the attitude of a spacecraft. These sensors comprise not only highly capable optical detectors and processor units but also complicated software solvers. One of the main solvers employed in star trackers is image segmentation. In this study, the aim is to develop a hybrid image segmentation method which is a combination of both global thresholding and density-based spatial clustering of applications with noise (DBSCAN) method to increase detection probability of the stars in heavy noise. Secondly, a sorting algorithm is added to list the detected stars in terms of their brightness to increase the efficiency of the star tracking algorithm. Then, this new approach and two different conventional segmentation methods are applied to the Orion star constellation image polluted with Gaussian, salt and pepper, and uneven background noises. The resulting images of these segmentation methods are compared in terms of denoising capabilities. Although computationally more expensive, the proposed DBSCAN-based hybrid method displays a background pixel recovery performance of 99.5%, compared to Otsu global thresholding and adaptive thresholding methods’ 73.5% and 79.9% recovery values, respectively. Additionally, it has been demonstrated that the sorting algorithm successfully listed the detected stars in accordance with their brightness.Publication Effect of Cutting Parameters on Surface Roughness and Cutting Forces in Hard Turning of 1.2367 Hot Work Tool Steel(Politeknik Dergisi, 2023-10-01) Sümeyye ERDEM; Mustafa ÖZDEMİR; Mohammad RAFİGHİ; Mehtap YAVUZBu çalışmada 1.2367 sertleştirilmiş (55 HRC) sıcak takım çeliğinin tornalanmasında farklı kesme parametrelerinin yüzey pürüzlülüğü (Ra) ve kesme kuvvetleri üzerindeki etkisi incelenmiştir. Bu deneysel çalışmada, deney tasarımı Taguchi metodu kullanılarak yapılmış ve kesme parametreleri olarak sabit talaş derinliği, üç farklı kesme hızı ve üç farklı ilerleme miktarı seçilmiştir. Kesme parametrelerinin yüzey pürüzlülüğü ve kesme kuvvetleri üzerindeki etkisi varyans analizi (ANOVA) yapılarak değerlendirilmiştir. Sonuçlara göre ilerleme hızındaki artışa bağlı olarak yüzey pürüzlülüğü değerinin arttığı görülmüştür. Kesme hızının ise yüzey pürüzlülük değeri üzerinde belirli bir etkisi görülmemiştir. Radyal kuvvet (Fx), teğetsel kuvvet (Fy) ve ilerleme kuvveti (Fz) üzerinde ise, en etkili parametrenin ilerleme hızı olduğu görülmüştür.Publication MANAGING EBOLA AND COVID-19 CRISES FOR AVIATION INDUSTRY: DID INDUSTRY LEARN HOW TO LEARN?(Universidad del Quindio, 2022-04-22) H.Bahar Aşcı; R.Dilek Koçak; Alper B. Dalmış; Göçmen, Firdevs DidemLearning is necessary for an organization to evolve, improve and innovate. We are all conditioned to benefit from the evident effects of our behaviors. After the first try, we do not touch the hot stove again. We are also conditioned to recognize complex scenarios and apply fast solutions. Companies are like humans and they also learn as people do. From this point of view, the aviation industry is discussed in this study beyond the learning loops approach of Agrysis which is an effective tool that encourages the kind of thought and action that is needed to transform an organization into a learning one. Turkish Airlines, EasyJet, Delta Airlines, Air China, United Airlines, China Eastern Airlines, China Southern Airlines, American Airlines, Southwest Airlines and Ryanair had chosen as the sample of this study and data collected from the annual reports of these companies was analyzed with document analysis methodology. By comparing the crisis management styles of the industry during Ebola and Covid-19 Diseases the question “did the industry learn how to learn?” tried to be answered and as a result, the study found that the way the industry responded to both crises had not gone too far from single loop learning, or in other words, the industry had only given a reaction to the actions on time and forgot every experience till the next crisis. In the end, the study discussed that single loop learning style of airline companies may be the reason for the rapid spread of those kinds of diseases all over the world.Publication Rhetorical Structure Appearances in Memoir-Type Text(Cukurova University Faculty of Education Journal, 2022-12-30) Çağrı KAYGISIZ; Nermin YAZICIWriting skill, which includes many factors and complex processes, is the linguistic skill that receives the lowest amount of support in the out-of-school social context among learning areas. Therefore, practices conducted at schools for the development of writing skills are significant. Such practices are aimed toward students gaining awareness of the functioning of the language system and producing texts that are compatible with discourse features developed in line with communicative purposes. Therefore, theories and approaches that describe how to make choices that match specific text types are an important component of writing education. This study aims to determine the appearance of the units in memoir-type texts that allow tracking the coherence relations on the text surface with the establishment of rhetorical relations between sections of text using the tools of the rhetorical structure theory and review and discuss at an academic level why these tools should be taken into account in the processes of writing education.Publication Isı Borulu-Isı Geri Kazanım Ünitesinde ZnO/Su ve ZnOAl2O3/Su Nanoakışkanları Kullanılarak Performansın İyileştirilmesi(Politeknik Dergisi, 2022-03-01) İpek AYTAÇ; Adnan SÖZENEndüstride ve birçok atık ısı tesislerinde kullanılan atık ısı geri kazanım üniteleri gerekli temiz havanın ön ısıtılmasında kullanılan sistemlerdir. Bu çalışmada ısı değiştiricisi ısı borusu olan bir ısı geri kazanım ünitesinin performansının iyileştirilmesi ve böylece çalışma sıcaklık aralığının arttırılması amacıyla oluşturulan deney düzeneği üzerinde uygulamalı bir çalışma yapılmıştır. Çalışmanın özgün yanı ısı değiştiricisi olarak kullanılan ısı borularında son yıllarda pek çok uygulama olanağı bulan nanoakışkanların kullanılması hedeflenmiştir. ZnO/Su ve ZnOAl2O3/Su nanoakışkanları ısı borusunda çalışma akışkanı olarak kullanılmış ve temel akışkan suya göre ısı geri kazanım ünitesi ısıl performansındaki iyileşme oranları belirlenmeye çalışılmıştır. Soğuk hava bölgesinde (kondenser), soğuk hava hızı 0.437m/s ve Re=7100 olduğunda ZnOAl2O3 ve ZnO nanoakışkanları için sırasıyla %90 ve %80 oranında iyileşme elde edilmiştir.Publication On the stability analysis of a fractional order epidemic model including the most general forms of nonlinear incidence and treatment function(Communications Faculty of Sciences University of Ankara Series A1 Mathematics and Statistics, 2023-10-10) Esra KARAOĞLU; Karaoğlu, EsraIn this paper, we propose to study a SEIR model of fractional order with an incidence and a treatment function. The incidence and treatment functions included in the model are general nonlinear functions that satisfy some meaningful biological hypotheses. Under these hypotheses, it is shown that the disease free equilibrium point of the proposed model is locally and globally asymptotically stable when the reproduction number $R_{0} $ is smaller than 1. When $ R_{0}>1 $, it is established that the endemic equilibrium of the studied system is uniformly asymptotically stable. Finally, some numerical simulations are provided to illustrate the theory.Publication Aircraft Selection Decision Support Model for Fleet Planning of the Low Cost Airlines(Eskisehir Osmangazi University Journal of Economics and Administrative Sciences, 2023-08-01) Cem GÜNTUT; Meriç GÖKDALAY; Gökdalay, Meriç HaticeIn this study, a decision support model was created for the aircraft type selection in the fleet planning decision of a low-cost airline and 21 sub criteria were determined for the model in five main groups as technical, economic, environmental, political and other criteria. In this decision support model, the Fuzzy TOPSIS and Fuzzy MOORA Multi Criteria Decision methods were applied, and 17 different narrow body aircraft types produced by Airbus, Boeing, Embraer, and Airbus/Bombardier aircraft manufacturers were evaluated. In the evaluation, it was found that Airbus A321NEO was the most preferable aircraft for the low-cost airline business model among the aircraft types.Publication An Economic Analysis on the Use of Resources Allocated for Defense: An Empirical Study on Turkey(Ege Akademik Bakis (Ege Academic Review), 2023-03-13) Ceyda AKTAN; Yaşar KÖSE; Emre YILMAZIn this study, the relationship between Turkey's defense expenditures and the independent variables selected as gross domestic product, foreign debt, and unemployment, in a 33-year period between 1998 and 2020, were examined using the Toda-Yamamoto causality test. According to the findings, it has been observed that there is causality from defense expenditures to gross domestic product, that is, the change in defense expenditures affects gross domestic product. Similarly, causality has been determined from defense expenditures to external debt. Therefore, it is possible to state that the change in defense expenditures will have an impact on foreign debt. In this respect, the findings are in agreement with the literature. The increase in defense expenditures will increase the production of the defense industry, the export of this production will result in a resource inflow to the country and the gross domestic product will increase. On the other hand, in some countries, defense expenditures will be financed by debt from foreign sources, which will increase foreign debt.Publication Uçak Kazaları ile Hisse Senedi ve Şirket Değeri Arasındaki İlişkilerin Belirlenmesi: Havayolu Taşıyıcısı ve Uçak Üreticisi Şirketler Üzerinde Analitik Bir Çalışma(Eskisehir Osmangazi University Journal of Economics and Administrative Sciences, 2022-04-01) Yaşar KÖSE; Ceyda AKTANÇalışmanın amacı, havayolu sektöründeki uçak kazaları ile ticari havayolu taşıyıcı şirketleri ve ticari uçak üreticisi şirketlerin hisse senedi fiyatları arasında bir ilişkinin olup olmadığının belirlenmesidir. Dünyada havayolu sektöründe yer alan havayolu taşıyıcı şirketleri ve büyük uçak üreticisi iki şirketin 2013-2020 yıllarında yaptıkları toplam 38 adet uçak kazası sonrasındaki ilk gün ve takip eden haftanın günlerindeki anormal getirileri ile kümülatif anormal getirileri analiz edildiğinde; uçak kazalarının bazılarında kazadan sonraki ilk ve takip eden 7 gün içinde gerek havayolu taşımacı şirketlerinin gerekse uçak üreticisi şirketlerin hisse senetlerinin değerlerinde genel olarak düşüş yaşanırken, bazı uçak kazalarından sonraki günlerde hisse senetleri değerlerinde değişim olmadığı veya artış yaşanmadığı görülmüştür.Publication Kalman Filtering With Linear State Equality Constraints: A Method Based on Separating Variables(Institute of Electrical and Electronics Engineers (IEEE), 2022) Habib Ghanbarpourasl; Serkan Zobar