Araştırma Çıktıları | TR-Dizin | WoS | Scopus | PubMed

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Measuring Temperature Change on Photothermal Au Nanorod and Nanocage Upon Laser Irradiation
(Amer Chemical Soc, 2015) Cavusoglu, Halit; Sakalak, Huseyin; Buyukbekar, Burak Zafer; Demirel, Gokhan; Citir, Murat; Yavuz, Mustafa Selman
Broadband Low Reflection Surfaces With Silicon Nano-Pillar Square Arrays for Energy Harvesting
(2022) Tut, Turgut
In this work, optimization of the nanopillar arrays and thin films coated on silicon substrate has been investigated in order to minimize the optical reflection loss from the silicon substrate surface. Nano-pillars's height, incline angle, array properties are systematically optimized. Full field Finite Difference Time Domain method is used to simulate EM fields and calculate the reflection from the modified nanostructured substrate surfaces in 400nm-1100nm spectral range. Optimization recipe is clearly presented and it is not only useful for square arrays but for regular arrays of nano-pillars in general.
Quasi-Static Operation of 2-Axis Microscanners With AlN Piezoelectric Quad-Actuators
(Institute of Electrical and Electronics Engineers Inc., 2021) Hah, D.
Aluminum nitride (AlN) started to draw attentions as a material for piezoelectric actuation owing to its CMOS process compatibility and safeness for biomedical applications. Due to its relatively low piezoelectric coefficients, AlN-based piezoelectric actuators have been mostly operated in resonance modes, especially in optical scanning. This paper presents a novel design of a 2-axis-tilt microscanner with AlN piezoelectric quad-actuators and meander-shaped hinges for reasonable quasi-static operation. Through finite-element-method simulation, it is shown that the proposed device can have about 9 degree of optical scan angle in two dimensions with the voltage amplitude of 50 V. Lissajous scanning operation of the device is demonstrated as well via simulation. © 2021 Elsevier B.V., All rights reserved.
Citation - Scopus: 19
A Novel Feature Design and Stacking Approach for Non-Technical Electricity Loss Detection
(Institute of Electrical and Electronics Engineers Inc., 2018) Aydin, Zafer; Güngör, Vehbi Çağrı
Non-technical electricity losses continue to jeopardize economic and social well-being of many countries. In this work, we develop machine learning classifiers that can identify anomalous electricity consumption in Turkey. Starting from weekly electricity usage data, we develop new features that capture statistical and frequency domain characteristics of the customers and their consumption patterns. We analyze the effect of reducing number of feature descriptors through dimensionality reduction and feature selection techniques. To overcome the class imbalance problem, we implement several ensemble methods and compare their prediction accuracy to those of the standard classifiers. The proposed features and combining strengths of different classifiers bring significant improvements on performance metrics, which is demonstrated through detailed simulations on shopping mall sector. We anticipate that advances in this field will contribute to the economies considerably. © 2018 Elsevier B.V., All rights reserved.
Determination of Factors Affecting International Students’ Satisfaction Levels Using CHAID Analysis
(2024) Ayten, Asım Mustafa; Göver, İbrahim Hakan
Uluslararasılaşma, son zamanlarda yükseköğretim kurumları için tüm dünyada vazgeçilmez bir unsur haline gelmiştir. Yükseköğretim kurumlarında uluslararasılaşmayı sağlayan pek çok bileşen olmakla birlikte, öğrenim gördükleri ülkeye sağladıkları önemli katkılar nedeniyle uluslararası öğrenciler bu konuda diğerlerine göre daha fazla ön plana çıkmaktadır. Bu nedenle, tüm dünyada yükseköğretim kurumları uluslararası öğrenci sayılarını ve bu öğrencilerin memnuniyet düzeylerini artırma arayışındadır. Uluslararası öğrencilerin taşıdığı önemden yola çıkan bu çalışma, Türkiye’deki bir devlet üniversitesinde öğrenim gören uluslararası öğrencilerin memnuniyet düzeylerine etki eden faktörleri ortaya koymak amacındadır. Bu amaç için Orta Doğu Teknik Üniversitesinde (ODTÜ) öğrenim gören toplam 330 uluslararası öğrenciye 25 soruluk bir on-line anket uygulanmış ve anket verileri CHAID analizi ile değerlendirilmiştir. Analiz sonuçları; uluslararası öğrencilerin izlenimlerinin, öğrenim derecelerinin ve cinsiyetlerinin memnuniyet düzeyleri üzerinde önemli bir etkiye sahip olduğunu göstermektedir. CHAID analiziyle ortaya konulan bu faktörlerin dikkate alınması, yükseköğretim kurumlarına daha fazla sayıda uluslararası öğrenci çekmek amacıyla belirlenen ya da geliştirilen uluslararasılaşma stratejilerine katkısı olacaktır.
Citation - WoS: 1
GIS-AHP Approach for a Comprehensive Framework to Determine the Suitable Regions for Geothermal Power Plants in Izmir, Turkiye
(Konya Teknik Univ, 2024) Koca, Kemal; Karipoglu, Fatih; Ozturk, Emel Zeray
Geothermal energy is gaining more reputation and importance around the world. Correspondingly, suitable location selection is a critical step and has become necessary for the successful installation and operation of geothermal power plants. This study investigated suitability of & Idot;zmir region, located in the Aegean part of T & uuml;rkiye, in terms of geothermal power plants applications by using the combination of Geographical Information System and Analytic Hierarchy Process. Based on the request of power plants, thirteen important criteria were evaluated under three main categories named as physical (C1), environmental (C2) and technical (C3). Moreover, expert's opinions were taken into consideration to calculate the importance of these criteria. Key results showed that & Idot;zmir was suitable for geothermal power plants. The final suitability map layer pointed out that %8.73 (1.037 km2) of total area were determined as highly suitable regions in terms of installation. In addition, the obtained suitability map layer was compared with actual geothermal power plants. Based on the comparison study, power plants in Seferihisar were moderately suitable for geothermal power plants while the location of Bal & ccedil;ova power plant was highly suitable. Regarding the suitability assessment in the present study, the location of Dikili power plants had the least suitability score.
Citation - Scopus: 5
Emotion Detection Using Multivariate Synchrosqueezing Transform via 2D Circumplex Model
(Institute of Electrical and Electronics Engineers Inc., 2018) Ozel, Pinar; Akan, Aydin; Yilmaz, Bulent; Özel, Pınar; Akan, Aydin I.; Yilmaz, Bulent
Emotion detection by utilizing signal processing methods is a challenging area. An open issue in emotional modeling is to obtain an optimum feature set to use for the classification process. This study proposes an approach for emotional state classification by the investigation of EEG signals via multivariate synchrosqueezing transform (MSST). MSST is a post-processing technique to compose a localized time-frequency representation yielding multivariate syncyrosqueezing coefficients. After obtaining these coefficients from EEG signals for 18 subjects from DEAP dataset, coefficients and self-assessment-mannequins (SAM) labels of those subjects are used for emotional state classification by using support vector machines (SVM) nearest neighbor, decision tree, and ensemble methods. The accuracy rate is 70.6% for high valence high arousal (HVHA), 75.4% for low valence high arousal (LVHA), 77.8% for high valence low arousal (HVLA), and 77.2% for low valence low arousal (LVLA) cases using SVM. © 2019 Elsevier B.V., All rights reserved.
Citation - Scopus: 1
Detection of Epileptic Seizures With Tangent Space Mapping Features of EEG Signals
(IEEE, 2021) Altindis, Fatih; Yilmaz, Bulent
Detection of epileptic seizures from EEG signals is well-studied topic for the last couple of decades. Lately, automated signal processing and machine learning methods were developed to detect epileptic seizures. However, most of the methods are tailored to subjects and require fine tuning of many parameters. In this study, we proposed to use Riemannian geometry-based signal processing method that already showed superior performance on brain-computer interface problems, to extract features. We showed that tangent space mapping features of EEG signals can be used to detect seizures with high accuracy and precision.
Citation - Scopus: 7
A Comparative Analysis on Medical Article Classification Using Text Mining & Machine Learning Algorithms
(Institute of Electrical and Electronics Engineers Inc., 2021) Kolukisa, Burak; Dedeturk, Bilge Kagan; Dedeturk, Beyhan Adanur; Gulsen, Abdulkadir; Bakal, Gokhan
The document classification task is one of the widely studied research fields on multiple domains. The core motivation of the classification task is that the manual classification efforts are impractical due to the exponentially growing document volumes. Thus, we densely need to exploit automated computational approaches, such as machine learning models along with data & text mining techniques. In this study, we concentrated on the classification of medical articles specifically on common cancer types, due to the significance of the field and the decent number of available documents of interest. We deliberately targeted MEDLINE articles about common cancer types because most cancer types share a similar literature composition. Therefore, this situation makes the classification effort relatively more complicated. To this end, we built multiple machine learning models, including both traditional and deep learning architectures. We achieved the best performance (R¿82% F score) by the LSTM model. Overall, our results demonstrate a strong effect of exploiting both text mining and machine learning methods to distinguish medical articles on common cancer types. © 2022 Elsevier B.V., All rights reserved.
Citation - Scopus: 2
Investigation of the Beneficiation of Low Grade Manganese Ores
(Chamber of Mining Engineers of Turkey maden@maden.org.tr, 2013) Bayat, Oktay; Altiner, Mahmut; Top, S.
In this study, beneficiation of low grade manganese ores was investigated by applying high intensity dry magnetic separation, MGS (Multi Gravity Separator) and flotation methods. Manganese grades of the ores were 25.65% Mn and 13.96% Mn taken from Antalya and Kayseri regions, respectively. Flotation and magnetic separation recoveries of both tested samples were low and the grades of the concentrates were less than 45% Mn. Similar results were also observed using a lab-type MGS but a concentrate could be obtained with 41.24% Mn and 78.71% recovery for manganese ores taken from Antalya region. © 2014 Elsevier B.V., All rights reserved.
Stimuli-Responsive and Self-Assembled Sericin Materials for Various Applications
(Elsevier, 2025) Arabaci, N.; Demirbas, A.; Dadi, S.; Dogan, F.; Öçsoy, I.
The silkworm cocoon's structural integrity is maintained by sericin, which acts as a sticky binding layer that envelops the fibroin fibers, effectively holding them together. In the silk industry, sericin is removed from the structure of fibroin during the degumming process in order to provide the silk's whiteness, softness, and smoothness and also to make it dyeable. Sericin, which is separated from the fibroin of the cocoon by the degumming process in the textile industry in the production of silk fabric, is discarded as waste material. This waste helps cell attachment, proliferation, and differentiation in sericin-based materials, owing to its biocompatibility, biodegradability, and bioactivity features. Due to all these specific features, sericin protein is involved in the production of various biomaterials such as films, hydrogels, scaffolds, conduits, fibers, and devices used in tissue engineering and regenerative medicine. © 2025 Elsevier B.V., All rights reserved.
Accurate Prediction of Residual Stresses in Machining of Inconel 718 Alloy through Crystal Plasticity Modelling
(2023) Bal, Burak; Cetın, Barıs; Yılmaz, Okan Deniz; Kesriklioglu, Sinan; Kapçı, Mehmet Fazıl; Buyukcapar, Ridvan
Artık gerilmelerin belirlenmesi ve değerlendirilmesi, savunma, havacılık ve otomotiv endüstrilerinde kullanılan bileşenlerin arızalanmasını önlemede çok önemlidir. Bu çalışmanın amacı, Inconel 718'in işlenmesi sırasında oluşan artık gerilmeleri doğru bir şekilde tahmin etmek için bir malzeme modeli sunmaktır. Ortogonal talaşlı imalat testleri, çeşitli kesme ve ilerleme hızlarında gerçekleştirilerek, Inconel 718'in işlenmesinden sonraki artık gerilmeler, X-Ray ışın kırınımı ile karakterize edildi. Bu süper alaşımın mikroyapısal girdilerini ticari olarak temin edilebilen bir sonlu eleman yazılımına (Deform 2D) aktarmak için bir viskoplastik kendi içinde tutarlı kristal plastisite modeli geliştirildi. Ayrıca simülasyonlar klasik Johnson - Cook malzeme modeli ile aynı işleme parametrelerinde yapıldı. Bu çalışmada elde edilen simülasyon ve deneysel sonuçlar, kristal plastisite tabanlı çok ölçekli ve çok ölçekli malzeme modelinin, mevcut modele kıyasla Inconel 718'in işleme kaynaklı kalıntı gerilmelerinin tahmin doğruluğunu önemli ölçüde geliştirdiğini ve yüzey kusurlarını en aza indirmek için kullanılabileceğini göstermiştir. Geliştirilen bu model, kesilmesi zor malzemelerin işlenmesinde yüzey kusurlarını ve üretim denemelerinin maliyetini en aza indirmek için kullanılabilir.
Evaluating the Impact of Sentiment Analysis on Deep Reinforcement Learning-Based Trading Strategies
(Institute of Electrical and Electronics Engineers Inc., 2024) Etcil, Mustafa; Kolukisa, Burak; Bakir-Güngör, Burcu
Portfolio optimization is a form of investment management that aims to maximize returns while minimizing risks. However, the inherent complexity and unpredictability of financial markets pose a challenge. Recent advancements in machine learning, particularly in deep reinforcement learning (DRL), offer promising solutions by enabling dynamic and adaptive trading strategies. This paper presents a comprehensive evaluation of three actor-critic-based DRL algorithms-Advantage Actor-Critic (A2C), Deep Deterministic Policy Gradient (DDPG), and Proximal Policy Optimization (PPO)-applied to portfolio optimization. These strategies were implemented in both sentiment-aware and non-sentiment-aware versions, allowing for a direct comparison of their performance. The sentiment-aware models incorporated sentiment analysis using FinBERT and knowledge graphs to measure market sentiment from financial news, while the non-sentiment-aware models relied solely on stock prices and technical indicators. Our comparative study demonstrates that incorporating sentiment analysis resulted in consistently superior risk-adjusted returns and portfolio resilience during market fluctuations compared to non-sentiment-aware strategies. © 2025 Elsevier B.V., All rights reserved.
Gain Enhancement of a mmWave Patch Antenna Array Having Limited Number of Input Ports
(Institute of Electrical and Electronics Engineers Inc., 2024) Keskin, Mehmet Ziya; Yentur, Abdulkadir; Ozdur, Ibrahim T.; Kiliç, Veli Tayfun
mmWave sensors are rapidly being used in various fields due to their low power consumption, compact size, and cost-effectiveness, particularly for applications like target detection and tracking. This study investigates the gain enhancement of a patch antenna array operating in the mmWave frequency band of 76 GHz - 81 GHz, where commercial single-chip integrated circuits are available. We analyze the S-parameters and radiation patterns of a reference antenna in detail, comparing simulation results with experimental measurements to ensure accuracy. Acknowledging the challenges posed by mmWave patch antennas, we propose a straightforward method to enhance peak gain while preserving the capabilities of the commercial patch structure. Specifically, by twinning one of the input port signals using a power divider, we increase the number of elements in the array without altering the number of input ports. Our findings suggest that this technique can increase the peak gain by 1.3 dB and narrow the beam by 4°, resulting in practical benefits such as enhanced target detection range and accuracy in radar applications while mostly preserving the functioning of the system. © 2025 Elsevier B.V., All rights reserved.
Optimal Location Determination of Electric Vehicle Charging Stations: A Case Study on Turkey's Most Preferred Highway
(2022) Gülbahar, İbrahim Tümay; Sütçü, Muhammed
Today, electric vehicles are seen as one of the most suitable and environmentally friendly alternatives to internal combustion engine vehicles. An important issue related to the dissemination of electric vehicles is the location of the vehicle charging network and specifically the optimum location selection of the charging stations. Generally, most of the studies focus on popular destinations such as city centers, shopping areas, bus stations, and airports. Although these places are often used in normal life, they can usually provide an adequate solution for daily charging needs due to the number of alternative charging stations. However, finding adequate charging stations is not possible in intercity travels especially in highways. In this paper, we proposed a decision model to determine the location of electric car charging stations in highways. We create an optimization model to decide the optimum locations for the charging stations that can meet the customer demands on the Istanbul-Ankara highway. The proposed model determines optimum charging stations that enable passengers traveling with their electric vehicles to travel in Istanbul-Ankara highway in the shortest time.
A Parametric Study for Drilling High Quality Holes on Glass Fiber Composites
(2022) Yilmaz, Cagatay; Kesriklioglu, Sinan
The objective of this study is to investigate the effect of cutting parameters on the qual- ity of holes drilled in a glass fiber reinforced thermoset polymer with the delamination factor defined as the ratio of intended hole diameter to the diameter of the maximum area which contains both hole and delaminated area. For this purpose, Taguchi's L9 or- thogonal array was used to design the experiments and optimize the drilling parameters. 5 mm twist drill bits were used to drill the holes at various feeds and spindle speeds. The maximum diameters on the inlet and outlet sides of the holes drilled into the composite plates were then measured with an optical microscope to analyze the influence of the drilling parameters on the machining damage. The smallest delaminated area on the front and back sides of the composite plate was achieved with the lowest feed (0.05 mm/rev) for the drilling parameters used in this study. Even though the spindle speed was increased from 318 rpm to 2930 rpm at a constant feed of 0.05 mm/rev, it reduces the maximum diameter on the front and back sides by 9 μm and 266 μm, respectively. The obtained results showed that the material removal rates in the drilling of the glass fiber reinforced thermoset polymers can be increased significantly by setting the optimized process pa- rameters without adversely affecting the hole quality.
Barriers in Sustainable Lean Supply Chain Management: Implementation in SMEs
(Ege Univ, Fac Economics & Admin Sciences, 2025) Takci, Ebru; Ada, Erhan; Kazancoglu, Yigit
As the world undergoes significant transformations in various domains, including technology, energy supply and communication, the idea of sustainability has become a significant issue. This study investigates the barriers to Sustainable Lean Supply Chain (SLSC) management within Small and Medium-Sized Enterprises (SMEs) and explores the structural interrelationships among these barriers. A comprehensive literature review was carried out to recognize critical elements relevant to the research topic, resulting in the identification of fifteen specific elements that account for 85% of the barriers in SLSC management. The DEMATEL method was used to evaluate the significance and influence levels of these factors. Furthermore, structured in-depth interviews were conducted with ten experts representing sectors that constitute 85% of the SMEs operating in Kayseri Organized Industrial Zone (OIZ), Turkey, including metal products, furniture, plastic packaging, construction materials, textiles and food. The findings reveal that strategies represent the most significant barrier to SLSC management in SMEs. The barriers were analyzed in two dimensions: influencing and influenced factors. The primary influencing factor identified was laws, standards, regulations, and legislation while the most significant influenced factor was found supply and suppliers. The study concludes with findings and actionable recommendations for practitioners and decision-makers.
Testing a Metacognitive Regulation Approach for Judgment of Satiation: Might Hunger and Fullness Not Be the Polar Opposites of the Same Dimension
(2020) Güzel, Mehmet Akif; Güngör, Duygu
Despite the existence of several cognitive influences, metacognitive factors on eating and satiation still remain unclear. Therefore, we investigated a relatively recent metacognitive regulation approach and its measurement method in a lab-experiment.Participants (N=216) were shownphotografsof varying portions of common lunch foods (selected after a separate study, N=94) and asked to makepredicted judgmentsof satiation (JOS) for each via considering their actual hunger levels and whilst imagining other bodily states (e.g., extremely hungry and completely full). Differencescalculated between observed-JOS and their reference scores -thosepresumed to yield accurate matches for the cases-produced either deviances or none at all (discordant-or concordant-JOS). Hungry-group yielded significantly lower concordant-JOS percentage than full-group regardless of portion size, indicating a clearercognitive tendency to lose control over consumption when being hungry than satiated. Critically, full-group could notimagine extreme hunger as hungry-group whereas hungry-group imagined complete fullness just as full-group did, suggesting that whilst hunger was not an obstacle to imagine fullness,fullness hindered the ability to imagine hunger. These findingssuggestthathunger and fullness mightnotbe the polar opposites on the very same dimension, which would, for instance,reveal a need to revisit the treatments of eating disorders accordingly.
Citation - WoS: 1
Citation - Scopus: 2
Vision-Based Autonomous Aerial Refueling
(Amer Inst Aeronautics & Astronautics, 2022) Erkin, Tevfik; Abdo, Omer; Sanli, Yilmaz; Celik, Harun; Isci, Hasan
Aerial refueling tasks are very challenging due to the high risk of aircraft close proximity. Currently, within the drogue-probe method, the receiver aircraft pilot manages the refueling task in accordance with the tanker aircraft pilot. Therefore, autonomous aerial refueling is still an unaccomplished task for aircrafts. In this paper, a fully automated aerial refueling procedure based on digital visual inspection is proposed. A nonlinear dynamic model of receiver aircraft is derived to track the motion of drogue. In order to control the receiver aircraft affected by tanker aircraft vortex during approach, and ensure the receiver aircraft to automatically track and dock the tanker aircraft, an autopilot system that considers visual sensing of drogue motion is designed. The receiver aircraft is controlled by the autopilot system via translational motion of tanker aircraft projected by a cameramounted on the receiver aircraft. Thanks to this vision-based controllers, the need of tanker aircraft positioning is denied since camera projection has the capability of perception of three-dimensional direction of tanker aircraft. In order to test the autopilots include vision-based controllers and algorithms, the vision-based autonomous aerial refueling is operated under presence of turbulence and vortex. Finally, the simulation results demonstrate that the proposed guidance-navigation-control system achieve aerial refueling autonomously, and make it feasible and realizable for aircrafts.
Eğitimde Üstbilişsel Düzenleme Envanteri: Öğretmen Versiyonu’nun (EÜDE: Öğretmen-Kendi ve Öğretmen-Sınıf) Geliştirilme Çalışması
(2023) Basokcu, Oguz; Güzel, Mehmet Akif
Sayısız araştırma, öğretmen ve öğrencilere ait bilişsel ve üstbilişsel süreçlerin öğrencilerin akademik başarısında kritik bir rol oynadığını göstermektedir. Çalışma öncelikle öğretmenlerin kendi, öğrencilerin kendi ve öğretmenlerin öğrencilerinin bilişine dair üstbilişsel hedef, izleme ve kontrol süreçlerini içeren “eğitimde çok düzeyli bir üstbilişsel düzenleme modeli” önermeyi amaçlamıştır. İkinci olarak, önerilen model çerçevesinde “eğitimde üstbilişsel düzenleme envanteri (EÜDE)”nin öğretmenin kendi bilişini ve öğretmenin sınıfının bilişini üstbilişsel olarak düzenlediği boyutlara ait sırasıyla, “öğretmen-kendi” ve “öğretmen-sınıf” formlarının oluşturulması amaçlanmıştır. Alan yazındaki ilgili envanter ve ölçeklerden yararlanarak ve projedeki araştırmacılar tarafından eklenerek oluşturulan anket maddeleri, 5., 6. ve 7. sınıf öğrencilerine çeşitli branşlarda eğitim veren toplam 2055 öğretmene çevrimiçi olarak üç aşamada uygulanmıştır. İlk uygulamada, 483 öğretmen “öğretmen-kendi” ve “öğretmen-sınıf” boyutlarına ait toplam 169 maddeyi 5’li Likert ölçeği üzerinden değerlendirmiştir. İlk uygulama sonunda seçilen 25 “öğretmen-kendi” ve 32 “öğretmen-sınıf” düzeylerine ait madde, ikinci uygulamadaki 790 öğretmen tarafından derecelendirilmiştir. Açımlayıcı faktör analizi sonuçlarına göre belirlenen 18’er “öğretmen-kendi” ve “öğretmen-sınıf” düzeylerine ait madde ise, üçüncü aşamadaki 782 öğretmen tarafından derecelendirilmiş ve elde edilen verilere doğrulayıcı faktör analizi uygulamıştır. Her iki faktör analizi sonuçlarına göre iki formda yer alan üstbilişsel “hedef”, “izleme” ve “kontrol” alt boyutlarına ait maddeler belirlenmiştir. Güvenirlik ve faktör analizleri sonuçları geliştirilen envanterin ölçmek istediği örtük yapıyı güvenilir ve geçerli şekilde ölçtüğünü göstermiştir.

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