TR-Dizin İndeksli Yayınlar Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12416/8652
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Article Widths and Entropy of Sets of Smooth Functions on Compact Homogeneous Manifolds(Tubitak, 2021) LEVESLEY, Jeremy; KUSHPEL, Alexander; Taş, KenanWe develop a general method to calculate entropy and n-widths of sets of smooth functions on an arbitrary compact homogeneous Riemannian manifold Md . Our method is essentially based on a detailed study of geometric characteristics of norms induced by subspaces of harmonics on Md . This approach has been developed in the cycle of works [1, 2, 10–19]. The method’s possibilities are not confined to the statements proved but can be applied in studying more general problems. As an application, we establish sharp orders of entropy and n-widths of Sobolev’s classes Wγ p ( Md ) and their generalisations in Lq ( Md ) for any 1 < p, q < ∞. In the case p, q = 1, ∞ sharp in the power scale estimates are presented.Article An Algebraic Stability Test for Fractional Order Time Delay Systems(Balikesir University, 2020) Özyetkin, Münevver Mine; Baleanu, DumitruIn this study, an algebraic stability test procedure is presented for fractionalorder time delay systems. This method is based on the principle of eliminatingtime delay. The stability test of fractional order systems cannot be examineddirectly using classical methods such as Routh-Hurwitz, because such systemsdo not have analytical solutions. When a system contains the square roots ofs, it is seen that there is a double value function of s. In this study, a stabilitytest procedure is applied to systems including ps and/or different fractionaldegrees such as s where 0 < α < 1, and αǫR. For this purpose, the integerorder equivalents of fractional order terms are first used and then the stabilitytest is applied to the system by eliminating time delay. Thanks to the proposedmethod , it is not necessary to use approximations instead of time delay termsuch as Pad´e. Thus, the stability test procedure does not require the solutionof higher order equations.Article A Behavioral Perspective on Price Convergence via Perturbed Metric Spaces with an Extended Contraction(Association of Mathematicians (MATDER), 2026) Bilazeroğlu, ŞeymaIn this study, we examine how investors update their price forecasts over time within a "perturbated metric space," which incorporates behavioral influences and market friction. Classical metric structures are inadequate when the measured distance changes with perceived deviations. Therefore, a new structure is proposed in which the measured distance is modified by perceived deviations. In this context, the existence of a fixed point is guaranteed through an extended contraction inequality, and the convergence behavior of the model is analyzed using different examples. Simulations established under different linear and nonlinear update functions demonstrate that the model can reflect both slow and fast market behaviors that reach equilibrium. The proposed approach mathematically demonstrates that investors can reach a common price expectation in the long run, even with heterogeneous psychological responses.Article A Discrete Element Method for Evaluating the Seismic Performance of Concrete Gravity Dam-Reservoir Systems Under Main Shock-Aftershock Events(Tulpar Academic Publishing, 2025) Soysal, B.F.Dams are crucial for water supply, flood prevention, and hydroelectric power generation. Often located in seismically active regions, they are vulnerable to main shock-aftershock (MS-AS) sequences, which can compromise structural integrity and hydraulic safety. Critical aspects of dam response to MS–AS events remain unclear, particularly the required rest time between successive events and threshold AS-to-MS intensity measure ratios that could serve as predictors of additional damage. This study addresses these gaps by analyzing concrete gravity dam–reservoir systems of three heights (50 m, 100 m, and 150 m) using the developed discrete element–based approach coupled with displacement/pressure-based mixed finite elements for the reservoir. Empirical rest time equations were derived from 124 as-recorded ground motions, while seismic performance under varying intensity levels was evaluated using 14 as-recorded MS–AS sequences. Damage was quantified using discrete indices of base crack length, maximum base crack width, and maximum total upstream crack width. Results indicate that AS primarily propagate existing cracks at lower intensities, whereas higher intensities generate new cracks along the upstream face, increasing crack widths by 25–30% on average. The 50 m high dam remained within the mild damage category, while taller dams occasionally reached moderate levels, posing potential seepage risks. Threshold AS-to-MS ratios for four different intensity measures were identified. These findings provide mechanistic insight into crack propagation under MS-AS events, providing practical guidance for post-earthquake dam safety assessment, inspection prioritization, and incorporating sequential seismic effects into design and emergency planning. © 2025 by the Author.Article W-Band RCS Prediction of Small Objects: Comparing Two Widely Used Methods with Experimental Validation(Gazi Univ, 2025) Kara, Ali; Aydın, Elif; Yardım, Funda Ergün; Sezgin, Deniz; Ergun Yardim, FundaThis paper compares the accuracy of Shooting and Bouncing Rays and Electric Field Integral Equation methods for Radar Cross Section prediction of small objects at 77-81 GHz band. Existing studies on RCS prediction methods often lack comprehensive comparisons between computational and experimental results, particularly for small objects measured with a 77 GHz radar. This study addresses this gap by presenting an in-depth analysis of both simulation and measurement data. In this work, three targets with varying geometries and materials were measured with a frequency modulated continuous wave radar and simulated using Ansys HFSS and CST Studio Suite. The measurements were performed with a commercial off-the-shelf (COTS) frequency modulated continuous wave radar operating at 77-81 GHz. This study aims to emphasize the importance of considering both efficiency and accuracy when opting for an RCS prediction method. Overall, the outcomes of both methods have largely demonstrated good alignment. It has been noted that, while Shooting and Bouncing Rays method offers promising time-saving advantages, Electric Field Integral Equation method remains a valuable tool for complex geometries where precise results are crucial.Article Citation - WoS: 2Citation - Scopus: 2An Alternative Mean Reversion Test for Interest Rates(Central Bank Republic Turkey, 2018) Ozel, Ozgur; Ilalan, DenizA number of empirical studies assert that interest rates are governed by unit root processes rejecting any form of reversion to a long term mean by resorting to certain tests, among which the Augmented Dickey Fuller (ADF) is the most widely used one. In this study, we propose an alternative testing methodology that can be applied along with ADF test, in the sense that there are times where it can capture stationarity when the other fails to do so. Moreover, our test has more power than ADF test. As an application to real-data, we consider 10-year US and Turkish T-bond rates. (C) 2017 Central Bank of The Republic of Turkey. Production and hosting by Elsevier B.V.Article ISAR Imaging of Drone Swarms at 77 GHz(TÜBİTAK Scientific & Technological Research Council of Turkey, 2025) Coruk, Remziye Busra; Kara, Ali; Aydin, ElifThe proliferation of easily available, internet-purchased drones, coupled with the emergence of coordinated drone swarms, poses a significant security threat for airspace. Detecting these swarms is crucial to prevent potential accidents, criminal misuse, and airspace disruptions. This paper proposes a novel inverse synthetic aperture radar (ISAR) imaging technique for high-resolution reconstruction of drone swarms at 77 GHz millimeter wave (mmWave) frequency, offering a valuable tool for military and defense antidrone systems. The key parameters affecting down-range and cross-range resolution (0.05 m), ultimately enabling the generation of detailed ISAR images are discussed. Here, we create diverse scenarios encompassing various swarm formations, sizes, and payload configurations by employing ANSYS simulations. To enhance image quality, different window functions are evaluated, and the Hamming window is selected due to its highest peak signal-to-noise ratio (PSNR) (16.3645) and structural similarity (SSIM) (0.9067) values, ensuring superior noise reduction and structural preservation. The results demonstrate that the effectiveness of high-resolution ISAR imaging in accurately detecting and characterizing drone swarms pave the way for enhanced airspace security measures.Article Integrating the Seljuk Cultural Layer Into Contemporary Life: The Case of Niğde Historic City Center(Istanbul Univ, Research Inst Turkology, Dept Art History, 2025) Yavaşcan, Emel Efe; Urak, Zehra GedizGünümüz tarihî kent merkezleri, yer altı ve yer üstündeki tarihî izleriyle, kültürel zenginlikleri ve özgün kimlikle8 rinin yanı sıra, “yerin ruhu”nu yansıtan kentsel hafıza alanlarıdır. Çok katmanlı bu tarihî kent merkezleri, kültür varlıklarının fiziksel ve işlevsel eskimesi, sosyo8kültürel ve ekonomik doku bozulmaları, koruma problemleri vb. sorunlarla giderek çöküntü yerleri hâline gelmektedir. Bu sorunları barındıran Niğde kentinde yapılmış koruma uygulamalarında, kentin yer altında ve yer üstünde bulunan katmanlarının dikkate alınmamış olması çalışmada problem olarak belirlenmiştir. Kentli tarafından tepe olarak algılanan çalışma alanı uzun zamandır çöküntü alanı niteliğindedir. Çalışmanın amacı, Niğde Tarihî Kent Merkezi’nin Selçuklu Dönemi’ne ait tarihî katmanını analiz etmek, haritalan8 dırmak ve bu katmanı çağdaş koruma uygulamalarına entegre etmeye yönelik öneriler geliştirmektir. Araştırma verileri, kentin tarihî gelişiminde en belirleyici dönemin Selçuklu Dönemi olduğunu göstermektedir. Bu sebeple çalışma kapsamında bu katman odak alınmıştır. Ayrıca, diğer tarihî katmanların da korunarak günlük yaşama kazandırılmasına katkı sağlamak, bu çalışmanın bir diğer hedefidir. Bu bağlamda, Selçuklu Dönemi’ne ait yer üstü ve yer altı değerlerinin sürdürülebilir korunmasına yönelik öneriler geliştirilmiştir.Article Erken Cumhuriyet Dönemi Koruma ve Eğitim Vizyonuna Dair Bir Belge: Antikiteler ve Tarihi Eserlerden Derslerde Nasıl İstifade Edileceği Hakkında Andıç(Hacettepe University, 2025) Önge, M.Public consciousness for the conservation of the cultural heritage had been one of the most significant problems of Turkey hitherto. The founders of the republic, the intellectuals and the statesmen, who knew that the ignorance is the major cause of this problem, proposed the use of the cultural heritage of all types in the history lessons as the course material. This practice took place in the curriculum of the schools for the first time in 1926. In order to define its method better, a guidebook with the title “The Memorandum on the Usage of Antiquities and Historical Artifacts in the Courses”, is published in 1935, addressing the teachers. This guidebook, which was strangely named as “memorandum”, focuses on the idea of creating heritage conservation awareness in the public by making school age teenagers understand and embrace their cultural heritage. In this context, being completely different from the present-day authoritarian attitudes, the memorandum should be accepted as a significant document, which define a conservation attitude socializing heritage conservation by public education. This document also contains the evidences, which are related to the changes in terminology for defining cultural heritage in Türkiye, with respect to the changing attitudes and ways of understanding. Although it is not known how it had emerged, it is very probable that the memorandum was a part of the series of developments relating cultural heritage conservation in Türkiye, during the 1930’s. The memorandum text was consisting of twenty-four articles. The teachers were being instructed on how they are going to use the cultural heritage of all kinds in the courses, how they are going to make the cultural heritage meaningful for the students and make them enjoy the cultural heritage. It is noteworthy that the text contains application proposals like homework on the cultural heritage examples and establishment of school museums. Although the memorandum is an outdated document, the topics in it have timeless special importance. Therefore, the memorandum can be accepted as the expression of a cultural heritage attitude beyond its age. In this study, it is aimed to carry out extensive research on the memorandum. The memorandum is analyzed with respect to the heritage conservation related developments of its period and its importance is discussed in terms of its relation to present day conservation attitudes. In addition to being valuable as a document describing the conservation approaches of the early Republican Period, it has been revealed that the memorandum is up-to-date in terms of its content and an expression of the willing approach to conservation of its period. This study is prepared by using written and live sources. © 2025, Hacettepe University. All rights reserved.Article Citation - Scopus: 4Working Memory Functions in Autism Spectrum Disorder: a Review(Association for Clinical Psychology Research, 2021) Çağlar, E.; Kaynak, H.Autism spectrum disorder, one of the most common neurodevelopmental disorders, is a lifelong condition, especially with difficulties in social communication, limited interest, and repetitive behavior. Working memory, as a basic executive function, is a cognitive process also associated with impulse control, inhibition, organization, mental flexibility, focusing on one's attention, planning, responding to new situations, initiating and monitoring actions, problem solving, and goal-directed behaviors. Studies suggest that working memory impairments are associated with repetitive behaviors, and the risk for academic failure observed in autism spectrum disorder, and other neurodevelopmental disorders. From this point of view, working memory deficits are often found in neurodevelopmental disorders, especially in autism spectrum disorder. In the current study, following an introduction to autism and working memory, working memory functions associated with autism spectrum disorder were reviewed in detail. In this context, brain imaging studies highlighting the importance of frontal lobe functions, links between repetitive behaviors and working memory, and age differences in working memory functions were summarized. Next, working memory deficits in other neurodevelopmental disorders, such as attention defi-cit/hyperactivity disorder and pervasive developmental disorder were discussed in comparison with autism. Finally, the conclusion part of the current review tried to provide a contribution to future studies. © 2021 Association of Clinical Psychology Research.