Scopus İndeksli Yayınlar Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12416/8651
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Article Vessel Segmentation in MRI Using a Variational Image Subtraction Approach(Tubitak Scientific & Technological Research Council Turkey, 2014) Nar, Fatih; Saran, Ayse Nurdan; Saran, MuratVessel segmentation is important for many clinical applications, such as the diagnosis of vascular diseases, the planning of surgery, or the monitoring of the progress of disease. Although various approaches have been proposed to segment vessel structures from 3-dimensional medical images, to the best of our knowledge, there has been no known technique that uses magnetic resonance imaging (MRI) as prior information within the vessel segmentation of magnetic resonance angiography (MRA) or magnetic resonance venography (MRV) images. In this study, we propose a novel method that uses MRI images as an atlas, assuming that the patient has an MRI image in addition to MRA/MRV images. The proposed approach intends to increase vessel segmentation accuracy by using the available MRI image as prior information. We use a rigid mutual information registration of the MRA/MRV to the MRI, which provides subvoxel accurate multimodal image registration. On the other hand, vessel segmentation methods tend to mostly suffer from imaging artifacts, such as Rician noise, radio frequency (RF) inhomogeneity, or partial volume effects that are generated by imaging devices. Therefore, this proposed method aims to extract all of the vascular structures from MRA/MRI or MRV/MRI pairs at the same time, while minimizing the combined effects of noise and RF inhomogeneity. Our method is validated both quantitatively and visually using BrainWeb phantom images and clinical MRI, MRA, and MRV images. Comparison and observer studies are also realized using the BrainWeb database and clinical images. The computation time is markedly reduced by developing a parallel implementation using the Nvidia compute unified device architecture and OpenMP frameworks in order to allow the use of the method in clinical settings.Article The Lebesgue Constants on Projective Spaces(Tubitak Scientific & Technological Research Council Turkey, 2021) Kushpel, AlexanderWe give the solution of a classical problem of Approximation Theory on sharp asymptotic of the Lebesgue constants or norms of the Fourier-Laplace projections on the real projective spaces P-d (R). In particular, these results extend sharp asymptotic found by Fejer [2] in the case of S-1 in 1910 and by Gronwall [4] in 1914 in the case of S-2. The case of spheres, S-d, complex and quaternionic projective spaces, P-d(C), P-d(H) and the Cayley elliptic plane P-16 (Cay) was considered by Kushpel [8].Article Sustainable Development Solutions Network (SDSN) Reports Between 2018 and 2023: Malmquist Index Analysis for the Performance of OECD Countries(Wiley, 2026) Kalemci, R. Arzu; Unsal, Mehmet Guray; Alp, Ihsan; Celik, Busra Agan; Dalkilic, Altay Ogulcan; Agan Celik, BusraIn 2015, the United Nations (UN) adopted the 17 Sustainable Development Goals (SDGs), calling for urgent action to end poverty, reduce inequality, and secure a sustainable future. Within this global agenda, the commitment of the Organization for Economic Co-operation and Development (OECD) is particularly significant given its institutional capacity and international influence. This study examines Sustainable Development Solutions Network (SDSN) reports for 2018-2023 using the Malmquist Productivity Index (MPI) as an alternative performance measurement tool. The MPI allows assessment of annual changes in total factor productivity and efficiency differences across OECD members. Rather than directly measuring absolute progress toward the SDGs, the analysis evaluates relative efficiency dynamics among countries in transforming sustainability-related indicators over time. The results provide comparative insights into how OECD countries improve or deteriorate in their relative sustainability performance within the observed period. The results show that OECD countries display uneven progress, with some improving while others stagnate or decline, and reveal persistent disparities in efficiency and productivity. By providing a dynamic and comparative evaluation, the study contributes to quantitative SDG monitoring and offers insights for policymakers seeking to enhance sustainable development strategies.Article Singular Dirac Systems in the Sobolev Space(Tubitak Scientific & Technological Research Council Turkey, 2017) Ugurlu, EkinIn this paper we construct Weyl's theory for the singular left-definite Dirac systems. In particular, we prove that there exists at least one solution of the system of equations that lies in the Sobolev space. Moreover, we describe the behavior of the solution belonging to the Sobolev space around the singular point.Article Simheuristic Framework for Optimizing Urban Mobility at Signalized Roundabouts(DAAAM International Vienna, 2026) Gokce, M. A.; Qadri, S. S. S. M.; Oner, E.Managing high traffic volumes and traffic congestion at signalized intersections remains a critical urban challenge. Appropriate traffic signal timing (TST) and phase sequencing are essential for ensuring smooth traffic flow. This study presents a microscopic simulation-based heuristic optimization (Simheuristic) framework using the Genetic Algorithm (GA) for optimizing the TST of Four-Legged Two-stops Signalized Roundabouts (FLTSR). The framework is tested using the actual traffic flow through a microscopic simulation model developed in Simulation for Urban Mobility (SUMO). Within this framework, the integrated GA searches for the green TSTs to minimize vehicular queue lengths, while SUMO is used to evaluate those timings. Additionally, four different phase sequence settings are evaluated to find the efficient configuration. The proposed approach is benchmarked against Webster's method and the existing TST plan. In the best-case scenario, the proposed framework improves vehicular flow by mitigating the average time loss, average waiting time, and the average number of vehicles in a queue at the FLTSR up to 35.83 %, 51.91 %, and 50.97 %, respectively, compared to the current setting. (Received in November 2025, accepted in January 2026. This paper was with the authors 1 month for 1 revision.)Article Revealing Fractional Effects in an Asymmetric Two-Dimensional Oscillator through Variational Mechanics(SAGE Publications Ltd, 2026) Baleanu, Dumitru; Defterli, Ozlem; Asad, Jihad; Jajarmi, Amin; AlShaikh Mohammad, Noorhan F.The present study is an application of a generalized Lagrangian-Hamiltonian approach to the analysis of an asymmetric two-dimensional harmonic oscillator with the use of the Caputo fractional derivative. Fractional Euler-Lagrange and Hamiltonian equations were systematically developed and then solved numerically using a predictor-corrector version of the Adams-Bashforth-Moulton method. The results show that decreasing the value of the fractional order (alpha) generates a form of memory-based damping within the system that transforms the classical closed orbits of phase space into spiral inward trajectories and causes the total energy of the system to decrease according to a power law, regardless of whether there are any dissipative forces in the system. It was demonstrated that both the degree of coupling and the degree of asymmetry can cause the system to lose energy at different rates and to have different amounts of attenuation in each direction. It was also demonstrated that the model provides a smooth transition to classical conservative behavior as alpha approaches unity, which confirms the physical validity of this representation. This demonstrates that fractional variational mechanics provides a consistent and physically meaningful way to describe the transition from conservative to dissipative behavior for coupled oscillating systems that are governed by memory and non-local effects.Article Outputs Bounds for Linear Systems with Repeated Input Signals: Existence, Computation and Application to Vehicle Platooning(Tubitak Scientific & Technological Research Council Turkey, 2018) Schmidt, Klaus Werner; Saglam, Harun BugraThis paper investigates the effect of repeated time-limited input signals on the output excursion of stable, linear time-invariant systems. It is first shown that the maximum norm of the output signal remains bounded if the repeated input signals are separated by a nonzero dwell time. Then a novel method for computing a tight bound on the output signal norm is proposed. The setting of the paper is motivated by a vehicle platooning application, where vehicles repeatedly open/close gaps in order to perform lane changes. The developed method analyzes driving safety by computing a bound on the spacing error between vehicles when performing repeated open/close gap maneuvers.Article Messaging Brand Experience: Brand Ethicality, Brand Trust, Brand Attitudes(Taylor & Francis Ltd, 2026) Ozsacmaci, Bulent; Kilic, Tamer; Dursun, Tolga; Celik, SuleymanMessaging applications (e.g. WhatsApp/Telegram/Signal-type platforms) have become high-frequency touchpoints within integrated marketing communications. This study examines how the brand experience of messaging applications translates into brand attitudes through two parallel mechanisms: perceived brand ethicality and brand trust. We theorize that ethicality and trust serve as communication signals that arise from interface-level design and governance choices, such as plain-language privacy notices, granular consent flows, visible encryption and reliability cues, and third-party assurances. Using survey data from active messaging users, we validated the measurement model via CFA and tested a parallel-mediation structure with bootstrapped indirect effects. Results indicate that messaging brand experience exerts a positive direct effect on brand attitudes and significant indirect effects through both brand ethicality and brand trust, confirming that persuasion in messaging hinges on credibility and transparency signals embedded in the journey. Robustness checks across alternative specifications support these findings. Theoretically, the paper integrates behavioural foundations of persuasion with corporate communication by reframing governance artefacts as source/message credibility cues that shape ethical inferences and risk reduction. Managerially, the results recommend making ethical and reliability signals salient within messaging flows, aligning privacy-by-default language with value propositions, and orchestrating assurance elements across channels to improve attitudes and downstream performance.Article Finite Biorthogonal Polynomials Suggested by the Finite Orthogonal Polynomials Mnp,Qx(Wiley, 2026) Guldogan Lekesiz, EsraConstructing a biorthogonal structure from scratch, that is, defining a biorthogonal pair is quite tough. Because here the orthogonality must be established between two different sets. There are four known univariate biorthogonal polynomial sets, suggested by Laguerre, Jacobi, Hermite and Szeg & odblac;-Hermite polynomials, in the literature. In this paper, we derive for the first time a pair of finite univariate biorthogonal polynomials suggested by the finite univariate orthogonal polynomials . The corresponding biorthogonality relation and some useful relations and properties, including differential equation and generating function, are presented. Further, a new family of finite biorthogonal functions is obtained using Fourier transform and Parseval identity. In addition, we compute the Laplace transform and fractional calculus operators for the new biorthogonal polynomial set .Article Exploring undefinedIundefined in Research: Reflexivity through a Lacanian Lens(Routledge Journals, Taylor & Francis Ltd, 2026) Canbolat, FaziletThis article explores reflexivity through a Lacanian lens, emphasizing the divided nature of the subject and the role of the unconscious in shaping reflexive practices. It examines the limitations of traditional definitions of reflexivity, which often focus on the self or ego, and offers a Lacanian perspective centered on the subject and the Borromean knot. By highlighting the roles of academic norms and expectations, language, ideal images, and unconscious forces, the article argues that reflexivity involves not only a dynamic negotiation between the researcher's subjectivity and academic structures but also the interplay of the imaginary, symbolic, and real dimensions of subjectivity. It also emphasizes how language exposes the often-overlooked real dimension within reflexivity.