Recep Tayyip Erdoğan Üniversitesi Kurumsal Akademik Arşivi
DSpace@RTEÜ, Recep Tayyip Erdoğan Üniversitesi tarafından doğrudan ve dolaylı olarak yayınlanan; kitap, makale, tez, bildiri, rapor, araştırma verisi gibi tüm akademik kaynakları uluslararası standartlarda dijital ortamda depolar, Üniversitenin akademik performansını izlemeye aracılık eder, kaynakları uzun süreli saklar ve yayınların etkisini artırmak için telif haklarına uygun olarak Açık Erişime sunar.
Güncel Gönderiler
Nonlinear receding contact mechanics of functionally graded layers for aerospace structures: a symmetry-based analytical and FEM study
(Multidisciplinary Digital Publishing Institute (MDPI), 2026) Abushattal, Ahmad; Terzi, Merve; Eyüboğlu, Ayşegül; Yaylacı, Murat; Sekban, Dursun Murat; Yaylacı, Ecren Uzun; Birinci, Ahmet
Functionally graded materials (FGMs) are widely applied in spacecraft structural design, thermal protection systems, and planetary landing mechanisms, benefiting from their ability to resist large thermal, pressure, and force gradients. To assess structural response behaviors for lander missions, docking maneuvers, and force transfer in layered aerospace structures, analyzing the contacts subjected to heavily stressed areas becomes very important. This article investigates the receding contact between a functionally graded top layer and a uniform substrate lying on a Winkler elastic foundation using the elasticity theory. An analytical approach has been validated using a finite element method (FEM) implemented in ANSYS. Comparison between the analytical solution and the FEM solution has been conducted for different stamp radii, elastic foundation stiffnesses, and ratios of shearing modulus for various realistic materials in the aerospace field. The data indicate very good convergence between the two solutions for both the length of contacts and the normal stress distribution, where differences are always below 3%. An increase in stamp radius leads to an extension of the contacts as well as a reduction in normal stresses and elevated stiffness and shearing modulus ratio contribute to smaller contacts and higher stresses. The validated methodological approach offers a realistic means for predicting force transfer mechanisms in spacecraft landing pads, multi-layer insulation panels, adaptive space structures, and functionally graded parts subjected to localized loads. This work offers predictive capabilities for space material interface design and optimization for harsh mechanical environments.
Effects of dexmedetomidine treatment after cerebral ischemia/reperfusion on apoptosis and oxidative stress: a rat model
(Multidisciplinary Digital Publishing Institute (MDPI), 2026) Kuyumcu, Mahir; Yıldızhan, Eda
Objectives: Cerebral ischemia/reperfusion (IR) injury is characterized by excessive oxidative stress and activation of apoptotic pathways, which play a central role in neuronal loss and poor neurological outcomes. Modulation of these mechanisms represents a clinically relevant strategy for neuroprotection. This study aimed to investigate the neuroprotective effects of dexmedetomidine (Dex) on oxidative stress, apoptotic signaling, and neuronal integrity in an experimental rat model of cerebral IR injury. Materials and Methods: Female Wistar rats were assigned to control, IR, and IR+Dex groups. Transient cerebral ischemia was induced for 45 min followed by 2 h of reperfusion. Oxidative stress was evaluated using serum antioxidant enzyme activities (superoxide dismutase [SOD], catalase [CAT], glutathione peroxidase [GSH-Px]), total oxidant and antioxidant status (TOS, TAS), and lipid peroxidation levels (malondialdehyde [MDA]). Apoptotic signaling was assessed by histopathological examination, transmission electron microscopy, and immunohistochemical analysis of B-cell lymphoma 2 (Bcl-2), Bcl-2-associated X protein (Bax) and apoptotic peptidase activating factor-1 (APAF-1) expression, quantitatively evaluated using QuPath with statistical comparison between groups. Bioinformatic network analysis and molecular docking were performed to explore predicted interactions between Dex and apoptosis-related proteins. Results: Cerebral IR induced a marked oxidative imbalance, characterized by reduced antioxidant enzyme activities and increased lipid peroxidation. Dex treatment partially improved antioxidant capacity and reduced oxidative stress parameters. Histopathological and ultrastructural analyses demonstrated severe neuronal degeneration following IR, whereas Dex-treated rats exhibited attenuated neuronal damage and improved ultrastructural preservation. Immunohistochemical analysis showed increased Bax and APAF-1 expression and reduced Bcl-2 expression after IR; these alterations were significantly modulated toward control levels in the IR+Dex group. Bioinformatic analysis identified apoptosis-related pathways, including apoptosis, p53 signaling, and necroptosis, as significantly enriched, while molecular docking suggested stable predicted interactions between Dex and key apoptotic regulators. Conclusions: In this experimental rat cerebral IR model, Dex exerted partial but significant neuroprotective effects by attenuating oxidative stress, modulating apoptotic marker expression, and preserving neuronal morphology. These findings support the potential role of Dex as a neuroprotective agent in ischemia-related brain injury, warranting further translational investigation.
Sustainable modification of bitumen using waste toner and lignin
(Multidisciplinary Digital Publishing Institute (MDPI), 2026) Varli Bingöl, Başak; Fiat, Samed Oğuzhan; Genç, Ömer; Özdemir, Mehmet Emin; Yaylacı, Murat
Integrating waste materials into road infrastructure is essential for environmental sustainability and resource efficiency. This study addresses the modification of short-term-aged 50/70-penetration-grade bitumen using two sustainable additives: waste toner powder and lignin. Waste toner was added at weight percentages of 4%, 8%, 12%, and 16%, while lignin was added at 15% and 20%. Since these modifiers have individual uses, this study examines how they may strengthen the oxidized binder. It focuses on extending the lifespan of the mixture by combining industrial and bio-based polymers. The main aim was to delineate the impact of these modifiers on the physical consistency, low-temperature flexibility, and microstructural morphology of the binder. The results show that both modifiers increase binder stiffness by reducing penetration at all modification rates. The resins in the waste toner enhance the polymer matrix, and the lignin’s aromatic structure increases the elastic components, improving high-temperature stability. However, ductility tests showed a reduction in elongation capability, suggesting a brittle state at lower temperatures. Also, waste toner additive is identified as the ideal modifier for high-temperature applications. SEM analysis illuminated the mechanisms underlying these performance modifications. Both additives had homogeneous distribution and good bitumen matrix interfacial bonding at lower concentrations.
Prognostic significance of the systemic inflammation response index (SIRI) in patients with hodgkin lymphoma
(Multidisciplinary Digital Publishing Institute (MDPI), 2026) İlkkılıç, Kadir; Şen, Bayram
Background and Objectives: Interest in biomarkers reflecting the inflammatory nature of Hodgkin lymphoma (HL) is increasing. This study aimed to evaluate the prognostic significance of the Systemic Inflammation Response Index (SIRI) in patients with HL. Materials and Methods: In this study, 105 patients diagnosed with classical HL at the Hematology Clinic of Recep Tayyip Erdoğan University Faculty of Medicine between January 2015 and April 2025 were retrospectively evaluated. Patients were divided into 2 groups according to the SIRI cut-off value. Results: A high SIRI (≥3.78) was significantly associated with advanced disease stage, poor performance status, higher IPS-7 and IPS-3 scores, non-response or partial response to treatment, relapse, and increased mortality. A positive correlation was found between SIRI and IPS 7 scores (p < 0.001, rho = 0.355). In the univariate analysis for progression-free survival (PFS), hemoglobin, IPS 7 score, and SIRI were identified as prognostic factors; in the multivariate analysis, high SIRI was identified as an independent prognostic factor (p = 0.033). In the univariate analysis for overall survival (OS), age, hemoglobin, albumin, lymphocyte count, IPS 7 score, and SIRI were identified as prognostic factors; and, in the multivariate analysis, age over 45 and high SIRI were identified as independent prognostic factors (p = 0.016, p = 0.012). In the survival analysis, high SIRI levels were associated with shorter PFS and OS (p = 0.001, p < 0.001). Additionally, PFS and OS durations were shorter in patients with high IPS 7 scores (p < 0.001, p < 0.001). Conclusions: A high SIRI prior to treatment was identified as an independent prognostic factor in HL patients and was associated with shorter PFS and OS. This index may help identify high-risk patients and assist clinicians in their decision-making processes by enabling individualized risk assessment.
Meta-analysis of effectiveness of pedagogical innovations involving technology in organic chemistry education in developing students’ academic performance
(American Chemical Society, 2026) Sivrikaya, Serpil Özkurt; Çalık, Muhammet; Kurt, Sevil
Because organic chemistry asks students to use visual and spatial thinking skills (e.g., three-dimensional structures of molecules) and comprehend various chemical reactions and mechanisms, it naturally needs pedagogical innovations involving technology to result in better academic performance. However, none of the previous studies has investigated the extent to which these pedagogical innovations are effective in improving students’ academic performance of organic chemistry education. This study aims to meta-analytically assess the effectiveness of the pedagogical innovations involving technology in organic chemistry education in developing students’ academic performance. The current meta-analysis handled 26 studies as the corpus of the data retrieved from the database and manual search. The authors initially coded the studies via a template form and inserted all statistical data from a Microsoft Excel sheet into Comprehensive Meta-Analysis (CMA V2) statistics software to calculate Hedges’ g for the corpus data. The findings pointed to the large effect for the overall effect size (g = 0.973). Also, it was found that only subgroups for the use of technological tools within the moderator variable “type of pedagogical innovations involving technology” played a significant role at predicting the students’ academic performance as a result of the treatments. In light of the findings, it can be inferred that the pedagogical innovations involving technology in organic chemistry education are more effective and fruitful in developing the students’ academic performance than nontechnology-based control groups. Further, the current meta-analysis study concludes that high school (for educational level), flipped classroom (for the pedagogical models including technology), digital media (for the use of technological tools), and short-term treatment (for implementation duration) act as the most effective variables to learn organic chemistry via the pedagogical innovations. Future research should focus on other individual and moderator variables to offer more adaptive alternatives for the use of chemistry teachers and lecturers.
