Browsing by Author "Çelik E."

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    Artificial neural network-based prediction technique for wear loss quantities in Mo coatings
    (2006) Çetinel H.; Öztürk H.; Çelik E.; Karlik B.
    Mo coated materials are used in automotive, aerospace, pulp and paper industries in order to protect machine parts against wear and corrosion. In this study, the wear amounts of Mo coatings deposited on ductile iron substrates using an atmospheric plasma-spray system were investigated for different loads and environment conditions. The Mo coatings were subjected to sliding wear against AISI 303 counter bodies under dry and acid environments. In a theoretical study, cross-sectional microhardness from the surface of the coatings, loads, environment and friction test durations were chosen as variable parameters in order to determine the amount of wear loss. The numerical results obtained via a neural network model were compared with the experimental results. Agreement between the experimental and numerical results is reasonably good. © 2006 Elsevier B.V. All rights reserved.
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    Comparison of amiodarone and propafenone for maintenance of stable sinus rhythm after bipolar radiofrequency ablation combined with a mitral valve procedure in patients with mitral valve disease and persistent atrial fibrillation
    (Baycinar Medical Publishing, 2015) Beşir Y.; Gökalp O.; Yetkin U.; Çelik E.; Iner H.; Lafçi B.; Tetik O.; Gürbüz A.
    Background: This study aims to examine the effects of amiodarone versus propafenone for maintenance of stable sinus rhythm after left atrial bipolar radiofrequency ablation combined with a mitral valve procedure in patients with mitral valve disease and persistent atrial fibrillation. Methods: The study included 75 patients (29 males, 46 females; mean age 66,8±7.4 years; range 54 to 82 years) who underwent left atrial bipolar radiofrequency ablation combined with mitral valve surgery between July 2008 and July 2010. Patients were divided into three groups of 25: propafenone group (group 1), amiodarone group (group 2), and control group (group 3). Atrial fibrillation patients with slow ventricular response were excluded from the study. Results: Data was collected at preoperative period, during surgery, prior to discharge from hospital, and at 3, 6, and 18 months after discharge. Patients from all groups were followed for 18 months. In group 1, the number of patients in sinus rhythm was 22 at discharge, 20 at three months, and 21 at six and 18 months. In group 2, the number of patients in sinus rhythm was 18 at discharge, 13 at three months, 15 at six months, and 16 at 18 months. In group 3, the number of patients in sinus rhythm was 16 at discharge, 11 at three months, 12 at six months, and 14 at 18 months. Group 1 had a statistically significantly higher rate of stable sinus rhythm. No hospital mortality was observed in any group. Conclusion: This study revealed that propafenone was more effective than amiodarone in maintenance of stable sinus rhythm at the postoperative period in patients who underwent bipolar radiofrequency ablation combined with a mitral valve procedure.
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    Structural and optical properties of SrAl2O4: Eu2+/Dy3+ phosphors synthesized by flame spray pyrolysis technique
    (Elsevier B.V., 2019) Gültekin S.; Yıldırım S.; Yılmaz O.; Keskin İ.Ç.; Katı M.İ.; Çelik E.
    In this study Sr0.985Al2O4:0.005Eu2+/0.01Dy3+ luminescent materials with long afterglow and high intensity were synthesized by flame spray pyrolysis (FSP) method for the first time. Precursor solution was divided into two separate part. One of the parts was used FSP process, the other one was dried to simulate sol-gel process. Thermal properties and organic content of FSP derived particles and dried gel were compared using DTA-TG and FTIR devices. FSP derived particles were sintered in argon medium at 1200 oC. Phase and elemental analysis of the final phosphors were carried out by X-Ray Diffraction (XRD) and X-Ray Photo electron Spectroscopy (XPS) measurements. Scanning electron microscopy (SEM) images were obtained to observe particle morphology. Optical properties of phosphor were determined by Photoluminescence (PL), thermoluminescence (TL) and radioluminescence (RL) measurements. The emission spectra of Sr0.985Al2O4:0.005Eu2+/0.01Dy3+ were composed by a green band at 525 nm at room temperature when it was excited by 350 nm light, assigned to anomalous luminescence originated by Eu2+ and Dy3+ in the host lattice. There were estimated peaks at around 90, 130, 170 and 200 oC under the main glow curve in the sample irradiated by X-ray and He-Ne laser (λexc = 632 nm). RL spectrum of Sr0.985Al2O4:0.005Eu2+/0.01Dy3+ powders have four distinct emission peaks at around 527 nm, 576 nm, 667 nm, 753;nm and a comparatively weak emission band at about 846 nm. © 2018 Elsevier B.V.
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    Synthesis and characterizations of sol–gel derived LaFeO3 perovskite powders
    (Springer, 2020) Çoban Özkan D.; Türk A.; Çelik E.
    In this study, LaFeO3 perovskite powders were prepared via the sol–gel method in two different annealing temperatures (500 and 850 °C-according to DTA/TG results) for use in dye-sensitized solar cell applications. The thermal, structural, microstructural, particle size, optical and magnetic properties of the samples were characterized by differential thermal analysis (DTA)/thermogravimetric analysis (TG), Fourier transforms infrared spectrometer (FTIR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), particle size analysis (PSA), UV–Vis spectrometer and vibrating sample magnetometer (VSM). Our XRD findings show that the as-synthesized powders have an excellent crystallinity, and Scherrer’s Equation is used for the estimation of crystallite sizes (within 26–29 nm). Samples were analyzed to reveal the valence states of elements through XPS. Survey scan XPS spectra and high-resolution XPS spectra of La-3d5 and Fe-2p for LaFeO3 samples are given. SEMs employed to observe surface morphologies of all xerogel and ceramic perovskite powder materials and SEM images were verified with PSA results. UV–Vis spectrometer analysis results show that the optical bandgap values (Eg) as measured on both particles were found 2.42 eV. In addition to all analyses, the powders show ferromagnetic behavior, and VSM analyses are used to determine ferromagnetic properties. These results, especially low bandgap, make LaFeO3 powders possible to further increase the performance and efficiency of perovskite-based cells. © 2020, Springer Science+Business Media, LLC, part of Springer Nature.
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    Synthesis and characterization of sol–gel derived LaFe0.5Mn0.5O3 perovskite powders for dye-sensitized solar cell applications
    (Springer, 2022) Çoban Özkan D.; Türk A.; Çelik E.
    In the present work, structural, microstructural, thermal, magnetic and optical properties of LaFe0.5Mn0.5O3 prepared perovskite powders were exclusively compared for processing temperatures for applications of dye-sensitized solar cells. In this framework, LaFe0.5Mn0.5O3 perovskite powders were synthesized with the sol–gel method at 500 °C and 850 °C (according to DTA/TG results). They were characterized through DTA/TGA (Thermogravimetric and Differential Thermal Analysis), FTIR (Fourier Transformed Infrared Spectroscopy), XRD (X-Ray Diffractometer), XPS (X-Ray Photoelectron Spectroscopy), PSA (Particle Size Analysis), SEM (Scanning Electron Microscopy), VSM (Vibrating Sample Magnetometer) and UV–Vis Spectrometer. In line with the obtained results, ferroelectric perovskite powders were successfully produced. These powders have crystallite sizes of 27.38–35.74 nm, bandgap values of 1.19–0.93 eV, particle sizes of 28–358 nm and ferromagnetic properties. In addition to the effect of synthesis temperature on LaFe0.5Mn0.5O3 synthesis with these characterization processes, it was found that the production of sustainable and applicable dye-sensitized solar cells using LaFe0.5Mn0.5O3 powders can be useful as innovative and futuristic approaches. © 2022, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.
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    Factors Affecting Recurrence and Survival in Stage IIA Colon Cancer Patients
    (S. Karger AG, 2024) Erciyestepe M.; Selvi O.; Dinç G.; Öztürk A.E.; Aydın O.; Sonuşen Ş.D.; Güneş T.K.; Avcı T.; Vatansever S.; Çelik E.; Atcı M.M.
    Introduction: Our study delves into the intricate interplay of risk factors and the strategic selection of adjuvant therapy, scrutinizing their influence on recurrence and survival outcomes in stage IIA (T3N0M0) colon cancer patients. Materials and Methods: The study examined the medical records of patients who underwent surgery for stage IIA colon cancer. Identification of stage IIA (pT3N0M0) colon cancer involved a comprehensive review of postoperative clinical records and histological reports. Parameters such as demographic data, tumor characteristics, microsatellite instability status, tumor locations, recurrence risk factors, preoperative carcinoembryonic antigen levels, and adjuvant treatments were systematically evaluated. Results: In our study involving 220 patients, 138 were male (62.7%), with a median age of 62 years and a median body mass index of 25.1 kg/m2. In the patient group without risk factors, no statistically significant difference was detected in disease-free survival (DFS) rates between those who received treatment and those who did not (p = 0.546). DFS rates of patients with >1 risk factor were statistically significantly lower than those with a single risk factor (p = 0.017). In patients with >1 risk factor, the DFS of those who did not receive adjuvant treatment was significantly lower than those who received adjuvant treatment (p < 0.001). In the patient group with recurrence, when adjuvant treatments were considered, recurrence was significantly higher in the group receiving capecitabine (p = 0.01). Conclusion: The decision for adjuvant chemotherapy in stage IIA colon cancer patients involves careful consideration of various parameters and risk factors. The evolving landscape of research may refine recommendations, ensuring optimal treatment outcomes while minimizing unnecessary toxicity. © 2024 S. Karger AG, Basel.