Scopus İndeksli Yayınlar Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12416/8651
Browse
111 results
Search Results
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 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.Article The Ever-Evolving Dark Side Emotions of the Football Supporters: A Study on Adaptation of Schadenfreude Scale(Pamukkale University, 2025) Şener, İrge; Karapolatgil, Ahmet AnılEnjoying from others’ maleficence, defined as schadenfreude, is a common emotion among football team supporters. Based on the social identity of supporters, schadenfreude develops as part of the rivalry, which the main sources of it are ‘similarity’, ‘repeated competition’, and ‘competitiveness’. This study is aimed to understand and classify supporters’ schadenfreude reasons based on an adapted scale. For this aim, the data gathered from a questionnaire consisting of a sample of 1.163 supporters of 14 Turkish football teams is examined by SPSS in order to reveal participants’ schadenfreude and their reasons for evaluating their rivals. As a result of participants’ rivalry classifications, the most common reasons for considering a team as a rival are determined respectively as ‘image’, ‘neighborhood’, and ‘worldview difference’. Moreover, schadenfreude is mostly felt towards the archrival, and supporters would be happiest with negativities experienced by the rival team’s managers. However, damage to rival team facilities is found as an unhappy situation. The study is the first that demonstrates the relationship between schadenfreude and rivalry and proposes ‘unique incident’ and ‘feasible contingencies’ as new rivalry factors. With these factors, different perspectives on the formation and continuity of rivalry are presented.Article Citation - WoS: 10Citation - Scopus: 11Effects of Calibration Sample Size and Item Bank Size on Ability Estimation in Computerized Adaptive Testing(EDAM, 2015) Şahina, Alper; Weiss, David J.; Sahin, AlperThis study aimed to investigate the effects of calibration sample size and item bank size on examinee ability estimation in computerized adaptive testing (CAT). For this purpose, a 500-item bank pre-calibrated using the three-parameter logistic model with 10,000 examinees was simulated. Calibration samples of varying sizes (150, 250, 350, 500, 750, 1,000, 2,000, 3,000, and 5,000) were selected from the parent sample, and item banks that represented small (100) and medium size (200 and 300) banks were drawn from the 500-item bank. Items in these banks were recalibrated using the drawn samples, and their estimated parameters were used in post-hoc simulations to re-estimate ability parameters for the simulated 10,000 examinees. The findings showed that ability estimates in CAT are robust against fluctuations in item parameter estimation and that accurate ability parameter estimates can be obtained with a calibration sample of 150 examinees. Moreover, a 200-item bank pre-calibrated with as few as 150 examinees can be used for some purposes in CAT as long as it has sufficient information at targeted ability levels.