İstanbul Gedik Üniversitesi Kurumsal Akademik Arşivi
DSpace@Gedik, İstanbul Gedik 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 telif haklarına uygun olarak Açık Erişime sunar.
Güncel Gönderiler
Microstructural and mechanical characterizations of weld metal of S960QL ultra high strength steel joints obtained with different multi-pass laying techniques using GMAW
(Institute of Physics, 2024) Mert, Tolga; Gürol, Uğur; Tümer, Mustafa
15 mm thick ultra-high strength steel plates with 960 MPa yield strength were welded using different multi-pass laying techniques (i.e., stringer and weaving beads) with torch manipulation. Weld metals obtained were compared using different mechanical (i.e., micro tensile tests and Vickers hardness maps) and microstructural (i.e., optical microscope, scanning electron microscope, x-ray diffraction, electron backscatter diffraction) characterization techniques. Coarser grains and acicular ferrite were observed in weld metal obtained with the weaving pass procedure. There were hardness differences in the face and root passes of both weld metals. Yet, hardness values were 19% and 11% higher for the face and root regions of the joint obtained by stringer pass procedure, respectively. Fractographs of micro tensile test specimens revealed dimples depicting ductile network structure for both joints.
Tailored proton conductive membranes of PVdF-co-HFP: investigating the synergistic effects of ammonium tetrafluoroborate and phosphoric acid dopants on dielectric characteristics
(Institution of Chemical Engineers, 2024) Yılmazoğlu, Mesut; Abacı, Ufuk; Erdemi, Hamit; Çoban, Ozan
This study investigates the structural, thermal, and dielectric properties of pure PVdF-co-HFP matrix and its composite electrolytes, PVdF-co-HFP/NH4BF4[x], both before and after PA doping, using FTIR, SEM, TGA, and dielectric analyses. FTIR spectra reveal characteristic vibrational bands, confirming the presence of various functional groups and phases. SEM images display a smooth and homogeneous surface morphology for pure PVdF-co-HFP, while the composite electrolytes exhibit irregular dispersion of NH4BF4 salt and rougher surfaces upon PA doping. TGA analysis shows that the onset of thermal degradation occurs at approximately 370 ℃ for pure PVdF-co-HFP, while PA-doped samples demonstrate higher decomposition temperatures, exceeding 400 ℃ due to hydrogen bonding and ionic complex formation. The presence of NH4BF4 and PA doping also affects the crystallinity of the PVdF-co-HFP matrix, notably shifting the transition temperatures of the alpha and beta phases. Ionic conductivity measurements indicate that PA doping significantly enhances conductivity by increasing charge carrier concentration and facilitating ion transport. PA-doped PVdF-co-HFP/NH4BF4[10] showed the highest conductivity reaching 1.68 × 10−3 S.cm−1 at 1 MHz and 400 K. Dielectric studies reveal frequency-dependent behavior, with dielectric constant (ε') and loss (ε") showing distinct trends influenced by salt concentration and PA doping. The dielectric tangent loss (tanδ) of PA-doped PVdF-co-HFP/NH4BF4 composite membranes exhibits frequency and temperature dependence. At higher temperatures, tanδ increases with frequency, showing a resonance peak that shifts towards higher frequencies. The study elucidates the impact of PA doping on the structural, thermal, and electrochemical performance of PVdF-co-HFP/NH4BF4 composites, providing insights for their potential applications in advanced electrolyte systems.
The impact of different telerehabilitation methods on peripheral muscle strength and aerobic capacity in COPD patients: a randomized controlled trial
(Multidisciplinary Digital Publishing Institute (MDPI), 2024) Ataç, Amine; Pehlivan, Esra; Karaahmetoğlu, Fulya Senem; Özcan, Zeynep Betül; Çınarka, Halit; Çörtük, Mustafa; Baydili, Kürşad Nuri; Çetinkaya, Erdoğan
Lung diseases have profound effects on the aging population. We aimed to hypothesize and investigate the effect of remote pulmonary telerehabilitation and motor imagery (MI) and action observation (AO) methods on the clinical status of elderly chronic obstructive pulmonary disease (COPD) patients. Twenty-six patients were randomly assigned to pulmonary telerehabilitation (PtR) or cognitive telerehabilitation (CtR) groups. The programs were carried out 3 days a week for 8 weeks. The 6-min walk test (6MWT), modified Medical Research Council dyspnea score, blood lactate level (BLL), measurement of peripheral muscle strength (PMS), and electromyography activation levels of accessory respiratory muscles were the main outcomes. There was a statistically significant improvement (p < 0.05) in both groups in the 6MWT distance and in secondary results, except for BLL. Generally, in the mean muscle activity obtained from the electromyography measurement after the program, there were statistically significant increases in the PtR group and decreases in the CtR group (p < 0.05). There was a statistically significant increase in PMS in both groups. An active muscle-strengthening program has the same benefits as applying the muscle-strengthening program to the patient as MI and AO. CtR can be a powerful alternative rehabilitation method in respiratory patients who cannot tolerate active exercise programs.
Investigating ultra-thin rGO coated ZnO core-shell structures in MOS devices: electrical/dielectric characteristics and relaxation mechanism
(Elsevier Ltd, 2024) Kırkbınar, Mine; İbrahimoğlu, Erhan; Demir, Ahmet; Çalışkan, Fatih
The study focused on the relaxation and polarisation mechanisms of Al/(rGO:ZnO core–shell)/pSi/Al MOS structures. For this purpose, the rGO:ZnO core–shell structures were synthesised by sol–gel procedures and coated on pSi by spin-coating. The structures were characterized as chemical, morphological and micro-structural using FESEM-EDS, AFM, XRD and Raman analysis. Additionally, the capacitance (C), conductance (G/ω), dielectric permittivity (ε′ and ε″), loss factor(tanδ), electric modulus(M′ and M″) of the samples were successfully examined by DS over the wide range of frequencies (100 Hz-1 MHz) for determining dielectric parameters. Three distinct regions were visible on the C-V and C-ω plots: accumulation (−4 to 0 V), depletion (0 to 2 V), and inversion (2 to 4 V). Two relaxation times (10-4s-10-7s) were obtained in ε′-V and ε′-ω graphs between 1–100 kHz (region 1) and 100 kHz-1 MHz (region 2). The relaxation times were according to the Maxwell-Wagner and dipolar polarisation mechanism. As a result, the capacitive effect was observed and the equivalent RC circuit obtained from the Cole-Cole diagrams allowed the samples to be used in energy storage or different electronic applications.
Proton conductivity and dielectric studies on chitosan/polyvinyl alcohol blend electrolytes: synergistic improvements with ionic liquid and graphene oxide
(Elsevier B.V., 2024) Yılmazoğlu, Mesut; Okkay, Hikmet; Abacı, Ufuk; Çoban, Ozan
This study investigates the impact of ionic liquid, 1-methylimidazolium tetrafluoroborate (IL) and graphene oxide (GO) on the performance of chitosan/polyvinyl alcohol (CS/PVA)-based composite electrolytes. Fourier-transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) confirm the successful incorporation of IL and GO, affecting the structural and morphological properties of the electrolytes. Thermogravimetric analysis (TGA) reveals enhanced thermal stability in GO-doped samples, with increased residual weight at high temperatures, while IL addition leads to higher initial weight loss due to its hygroscopic nature. Ionic conductivity measurements demonstrate that the CS/PVA/IL-GO(4.0) composite achieves the highest proton conductivity of 1.76 × 10−3 S/m at 300 K and 1 MHz, surpassing other samples and aligning with top values reported in literature. Dielectric studies show a significant increase in dielectric constant to 9.55 × 104 at 300 K and 20 Hz for CS/PVA/IL-GO(4.0), attributed to enhanced dipole alignment and polarization effects. The loss tangent analysis indicates the shortest relaxation time of 2.07 × 10−4 s for CS/PVA/IL-GO(4.0), correlating with its superior proton conductivity. These findings highlight the potential of CS/PVA/IL-GO electrolytes for advanced energy storage and conversion applications, suggesting further research into GO dispersion and long-term stability for optimized performance in practical devices.
