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Öğe CO2 gas detection properties of a TIO2/Al2O3 heterostructure under UV light irradiation(Institute of Physics Publishing, 2015) Karaduman, Irmak; Demir, Mehmet; Yıldız, Dilber Esra; Acar, SelimAl/TiO2/p-Si and Al/TIO2/Al2O3/p-Si samples were prepared using the atomic layer deposition method (ALD) and their gas sensing properties were investigated. The electrical properties of the samples were studied using a two probe method in the temperature range 25-230 degrees C and at room temperature UV conditions. The TiO2/Al2O3 heterojunction sample exhibited an excellent gas sensing response to CO2 gas at room temperature and improved the effect of UV light irradiation. The results showed that heterostructures helped to improve the gas sensor properties, affected the sensing at room temperature and thus guided the design of photocatalysts. The TiO2/Al2O3 heterojunction prepared using this method can be used as a material for semiconductor gas sensors detecting poisonous gases like CO2 at room temperature with high sensitivity and selectivity.Öğe Comparison of Six Methods of Central Corneal Thickness Measurement in Healthy Eyes(2021) İçel, Erel; Karakurt, Yücel; Yılmaz, Hayati; Uğurlu, Adem; Demir, MehmetObjectives: Several methods of measuring central corneal thickness (CCT) have been compared, however, the data are still limited and conflicting. The aim of this study was to determine the agreement of CCT measurements performed in healthy eyes using ultrasound pachymetry (USP), non-contact tono/pachymetry, specular microscopy, biometry, Scheimpflug-based corneal topography, and optical coherence tomography (OCT). Methods: All of the participants underwent a complete ophthalmological examination. The CCT of all of the eyes included was measured using 6 different methods. The agreement between the methods was analyzed using the mean difference and Bland-Altman analysis based on a 95% limits of agreement. Results: A total of 64 patients with a mean age of 40.96±14.52 years (range: 20-78 years) were included in the study. The mean CCT value was 552.10±35.65 ?m, 550.40±35.55 ?m, 554.67±35.49 ?m, 545.39±34.21 ?m, 546.25±35.49 ?m, and 552.64±33.59 ?m using USP, non-contact tono/pachymetry, non-contact specular microscopy, biometry, Scheimpflugbased corneal topography, and OCT, respectively. The bias values determined by Bland-Altman plots were -1.70, -2.56, 6.71, 5.85, and -0.53 for tono/pachymetry, specular microscopy, biometry, topography, and OCT, respectively. OCT demonstrated the lowest bias compared to USP. The overall intraclass correlation coefficient was 0.961 (range: 0.945- 0.974) with a 95% confidence interval. Conclusion: All of the CCT measurements obtained using non-contact tono/pachymetry, non-contact specular microscopy, biometry, Scheimpflug-based corneal topography, and OCT were consistent with the USP measurements of healthy controls. Larger prospective studies to determine the interchangeability of different methods for CCT measurements in pathological conditions are warranted.Öğe High temperature wear behavior of the surface-modified externally cooled rolls(Elsevier B.V., 2018) Günen, Ali; Kanca, Erdoğan; Karakaş, Mustafa Serdar; Koç, Vahdettin; Gök, Mustafa Sabri; Kanca, Yusuf; Çürük, Ahmet; Demir, MehmetExternally cooled rolls of a steel plant were coated using three different surface modification techniques, namely titanizing, boronizing and borotitanizing. The grown coatings were examined using optical microscopy, scanning electron microscopy, microhardness measurements, X-ray diffraction and Raman analysis. Depending on the coating technique, a wide range of coating thicknesses and microhardness values were obtained; the highest microhardness was obtained in the titanized sample, while the greatest coating thickness was obtained in the borotitanized sample. Wear tests were performed on the untreated and coated specimens using a ball-on-disc wear tester under two different loads (1 N, 3 N) at three different temperatures (25 °C, 250 °C, 450 °C). The average friction coefficient values decreased at elevated temperatures, and increased under increased load. Temperature had a significant effect on the wear mechanism. At room temperature the effective wear mechanism was delamination, while at 250 °C and 450 °C oxidative wear was observed. All of the surface modification treatments improved the wear resistance. The highest wear resistance was observed in the borotitanized sample. © 2018 Elsevier B.V.Öğe Novel mixed ligand complexes of Co(II), Ni(II), Cu(II), and Zn(II) with 1,10-phenanthroline and acesulfame. Synthesis, structural analysis and hydrogen adsorption study(Pergamon-Elsevier Science Ltd, 2021) Sahin, Zarife Sibel; Demir, Mehmet; Yildirim, Tugrul; Yurdakul, Omer; Ali Kose, DursunFour novel metal organic framework (MOF) structures containing acesulfame (ace) and 1,10-phenanthroline (phen) ligands of Co2+, Ni2+, Cu2+ and Zn2+ metal cations were synthesized. The crystal structure analysis of three compounds (1, 2, and 3) was also performed. The structural formula for complex 4 is proposed based on spectroscopic and thermal analysis data. It has been determined that structures 1, 2, and 4 are in a distorted octahedral geometry. It has been suggested that the charge balance of the coordination sphere with 2+ is provided by two monoanionic ace ligands located outside the coordination sphere as counter-ion. In structure 3, there are two Cu-II metal cations, two phen ligands coordinated as bidentate to each metal cation and ace ligand that provides monoanionic-monodentate coordination. The Cu2+ cation has distorted bipyramidal geometry. The maximum hydrogen gas adsorption has been found 1.4575 mL/g (0.046 wt%) for the Ni complex. (C) 2021 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
