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
Crystal-length optimization in 681-nm pumped Tm:YAG and Tm:LuAG lasers: from low threshold to SESAM Q-switching
(Elsevier, 2026) Kaya, Fatma; Bilici, Hatice; Sumpf, Bernd; Demirbaş, Ümit; Beyatliı Ersen
We systematically quantify how crystal length governs efficiency, tuning bandwidth, and passive Q-switching in 681 nm tapered-diode-laser (TDL) pumped Tm:YAG (1.5 at.%) and Tm:LuAG (2 at.%) oscillators. By scanning four lengths (3, 5, 7, and 9 mm), we identify a three-way trade-off among pump absorption, quasi-three-level reabsorption, and length-dependent passive loss. In continuous-wave (CW) operation, maximum extraction occurs at 7 mm in both hosts, while the minimum absorbed lasing thresholds are obtained with the 3 mm crystals (35–45 mW). In the experiments, instantaneous slope efficiencies reach 60% (Tm:YAG) and 52% (Tm:LuAG), corresponding to photon-quantum efficiencies of 1.78 and 1.54. Using an intracavity quartz birefringent filter, we achieve >220 nm of continuous tuning and reproducible two-color operation; in Tm:LuAG, the longest crystals impose a short-wavelength cutoff (below ∼1.92 μm), so shorter lengths are required for full spectral access. Passive Q-switching with a SESAM is strongest for 7 mm Tm:LuAG, producing 1.36 μs pulses with 1.2 W peak power. These results establish crystal-length selection rules for compact, red-pumped 2 μm sources balancing efficiency, tunability, and passive Q-switching.
A research on melting, energy storage, and entropy generation in a vertical shell-tube latent heat storage system with different fin models and laminar flow regimes
(Elsevier Masson s.r.l., 2026) Gürsoy, Emrehan
This numerical study investigates the melting time, energy storage, and second-law efficiency of a latent heat thermal energy storage (LHTES) system consisting of a vertical shell and tube heat exchanger using aluminium metal foam (MF) and fins with different geometries. RT58 paraffin wax phase change material (PCM) was used as the heat storage material, and heat input to the system was provided by hot water flowing through the inner tube in a laminar regime (Re = 1000 and 2000) and T inlet = 358 K. Rectangular, triangular, and parabolic fin models with the same total surface area were compared under different fin lengths. The analyses were carried out using the enthalpy-porosity approach and the Darcy–Brinkman–Forchheimer model. The results show that fin geometry and dimensions are decisive factors in PCM melting time, energy storage capacity, and entropy generation (EnG). While rectangular fins provided the shortest melting time, parabolic fins stood out with a more homogeneous melting profile and lower overall EnG performance. The best performance was obtained with the longest parabolic fin (P3) model. This model provided 4-19% lower thermal EnG compared to other geometries. Re = 2000 significantly shortened the full melting time of the PCM by increasing heat transfer compared to Re = 1000. The results show that the combined use of MF and fins in vertical shell and tube LHTES systems increases energy storage efficiency and reduces thermodynamic irreversibilities.
Twelve-month smoking cessation outcomes following immediate referral in people who smoke with chronic airway diseases: a randomized study
(BioMed Central Ltd, 2026) Karadoğan, Dilek; Telatar, Tahsin Gökhan; Kaya, İlknur; Atlı, Siahmet; Kabil, Neslihan Köse; Marım, Feride; Akgün, Metin
Background: Tobacco cessation support remains underutilized in routine care for patients with airway diseases such as asthma and COPD. In this multicenter randomized trial (NCT05764343, registration date: 2023-03-01), we previously reported that immediately scheduled appointments to smoking cessation clinics improved access and quit rates at 1-week and 3-month follow-ups. The present study evaluated whether these effects were sustained at 12 months. Methods: This prospective, parallel-arm, multicenter randomized trial included 397 adult people who smoke diagnosed with asthma, COPD, or bronchiectasis. Participants were allocated to either usual support (brief advice only) or immediate support (brief advice plus an appointment scheduled at a smoking cessation clinic). Smoking status was assessed by telephone at 12 months. Self-reported quitters were invited for exhaled carbon monoxide (CO) testing. The primary outcome was continuous abstinence at 12 months, analyzed on an intention-to-treat basis. Results: Of 397 randomized patients, 330 (83.1%) completed the 12-month follow-up, with similar loss to follow-up between groups. In the intention-to-treat analysis, the 12-month smoking cessation rate was significantly higher in the immediate support group compared with the usual support group (20.7% vs. 11.6%, p = 0.019). Among non-quitters, quit attempts, smoking cessation clinic admission, and pharmacotherapy use were significantly more common in the immediate support group (p < 0.05). Conclusion: Immediate scheduling of smoking cessation clinic appointments resulted in significantly higher 12-month quit rates compared to usual care. These findings support the integration of proactive referral strategies into routine management of patients with chronic airway diseases.
Association of pectoralis major muscle cross-sectional area and mean density on chest CT with mortality in elderly COVID-19 patients: sex and side differences
(BioMed Central Ltd, 2026) Uzun, Ali Yavuz; Konak, Egemen; Altıntaş, Serra; Üçüncü, Yılmaz; Aktepe, Rıza; Kalkan, Ömer Faruk; Özyaşar, Ali Faruk
Background: COVID-19 is a disease that primarily affects the lungs and may follow a fatal course. The aim of this study was to investigate whether there are differences in the cross-sectional area and mean density of the pectoralis major (PM), an accessory respiratory muscle, between survivors and non-survivors with COVID-19, with analyses performed according to sex. Materials and methods: This retrospective study included a total of 201 patients aged 65 and over who were admitted to a tertiary healthcare center between March 2020 and May 2021. Patients with confirmed COVID-19 diagnosis by PCR and radiological evidence of pulmonary involvement on chest CT were included in the study, while patients with imaging artifacts that could affect measurements were excluded. The cross-sectional area and mean density of the right and left pectoralis major muscles were measured on axial CT images at the sternal angle level using 3D Slicer software. Results: Of the 201 patients, 103 (51.2%) died. In the overall cohort, PM CSA (cross-sectional area) and density did not differ significantly between survivors and non-survivors. However, sex-stratified analyses revealed that female survivors had significantly greater right and left PM CSA compared to non-survivors (p = 0.015 for both), whereas in male patients, left PM density was significantly higher in survivors (p = 0.011). Lymphopenia and elevated NLR, AST, LDH, CRP, and D-dimer were also associated with mortality (p < 0.05). Conclusion: PM muscle measurements on chest CT showed some sex-related differences between survivors and non-survivors in elderly COVID-19 patients. Lower PM CSA in women and lower PM density in men were observed in univariable analyses. However, these parameters were not independently associated with mortality after adjustment. Therefore, PM muscle assessment on routine chest CT may provide additional but limited prognostic information.
Thyroid hormone changes after tumor necrosis factor inhibitor therapy in euthyroid patients with rheumatic diseases
(BioMed Central Ltd, 2026) Kızılkaya, Bayram; Mercantepe, Filiz; Vekic, Jelena; Cüre, Osman; Klisic, Aleksandra
Background/aim: Tumor necrosis factor-alpha (TNF-α) plays a central role in chronic inflammatory diseases. Anti-TNF agents are widely used in rheumatological conditions; however, their association with thyroid hormone parameters in patients without pre-existing thyroid disease remains incompletely understood. This study aimed to evaluate changes in thyroid hormone profiles during anti-TNF therapy in euthyroid patients with rheumatic diseases. Methods: In this retrospective study, 98 patients diagnosed with rheumatoid arthritis, ankylosing spondylitis, or Behçet’s disease without known thyroid disease were evaluated. Thyroid function tests, including thyroid-stimulating hormone (TSH), free triiodothyronine (fT3), and free thyroxine (fT4), anti-thyroid peroxidase (anti-TPO) antibodies, inflammatory markers such as C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR), and metabolic parameters were assessed at baseline and after 3 and 6 months of anti-TNF therapy. Results: Anti-TNF therapy was associated with significant reductions in inflammatory markers (CRP and ESR, p < 0.01). A modest decrease in fasting glucose levels and an increase in high-density lipoprotein cholesterol (HDL-C) were observed during follow-up (p = 0.024 and p = 0.044, respectively). TSH and fT4 levels remained stable over time, whereas a gradual increase in fT3 levels was observed (p < 0.01). No significant changes were detected in anti-TPO antibody levels. Conclusions: Among euthyroid patients with rheumatic diseases, predominantly rheumatoid arthritis and ankylosing spondylitis, anti-TNF therapy was associated with stable thyroid function parameters. The observed increase in fT3 levels may reflect reduced inflammatory burden rather than direct thyroidal effects. These findings support the thyroid safety of anti-TNF agents while highlighting potential links between inflammation control and peripheral thyroid hormone conversion.
