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Öğe Analysis of Poly (2-Hydroxyethyl Methacrylate)-co-Poly (4-Vinyl Pyridine) Copolymers [COP2,4] Irradiated: an EPR study(POLISH ACAD SCIENCES INST PHYSICS, 2016) Ceylan, Y.; Aydogmus, H. Yumurtaci; Usta, K.; Usta, A.; Ceylan, N.; Yilmaz, H.Poly(2-hydroxyethyl methacrylate)-co-poly(4-vinyl pyridine) and poly(HEMA)-co-poly-(4-VP) copolymers were synthesized by free radical polymerization. K2S2O8 was used as an initiator. Chain lengths of the copolymer was changed by varying the monomer/initiator ratio. These polymers have molarites of 2.6 and 2.1 respectively and are called COP2 and COP4. The samples were exposed to gamma rays at room temperature. After irradiation, the EPR spectra of COP2 and COP4 were recorded between 120 K and 450 K. From the temperature dependence of the line intensity, it was concluded that unpaired spin concentration in the irradiated samples has been changing with temperature. A theoretical study, presented in this report, was aimed to test success of the machine learning methods and to select the best learning method.Öğe Comparative Study of Influences of Gamma Rays on Calix[4]Arene and 25,27-di(4-Nitrobenzyl)-26,28-Dihydroxycalix[4]Arene: EPR Study(POLISH ACAD SCIENCES INST PHYSICS, 2017) Ceylan, Y.; Usta, K.; Ceylan, N.; Usta, A.; Koc, Y.In the present study, calix[4]arene and its derivate 25,27-di(4-nitrobenzyl)-26,28-dihydroxycalix[4]arene were irradiated for 72 hours by Co-60 gamma rays at dose rate of 0.720 kGy/h. These irradiated samples were analyzed by EPR method and it was found that one type of radical was produced in calix[4]arene, and two type of radicals were produced in 25,27-di(4-nitrobenzyl)-26,28-dihydroxycalix[4]arene. The measurements were performed in the temperature range of 273-400 K using x-band EPR spectrometer. It was observed that the spectra, obtained from two samples, have very weak temperature dependence. Hyperfine and g parameters were calculated for two samples.Öğe An EPR Study on Radiation-Induced 2-(piperidin-1-ylmethyl) phenol Single Crystal(POLISH ACAD SCIENCES INST PHYSICS, 2016) Usta, K.; Ceylan, Y.; Usta, A.; Ceylan, N.; Aras, E.For the assessment of irradiation influence on 2-(piperidin-1-ylmethyl) phenol single crystals (C12H17NO), electron paramagnetic resonance measurements were carried out on the samples exposed to Co-60 radiation at dose values of 22.8, 45.6 and 68.4 kGy at room temperature. Electron paramagnetic resonance signals were not observed in non-irradiated sample and in samples irradiated at dose values of 22.8 and 45.6 kGy. The electron paramagnetic resonance measurements were performed on the single crystals. This irradiated single crystal was rotated in steps of 10 degrees. One type of radical center was found. The average values of g and hyperfine constant of the detected radiation damage center were calculated from experimental spectra as follows: g = 2.0052, A(H) = 0.74 mT.Öğe An EPR study on radiation-induced 4-hydroxyphenyl-acetic acid polycrystalline(ELSEVIER SCIENCE BV, 2015) Ceylan, Y.; Usta, K.; Usta, A.; Aydogmus, H. Yumurtaci; Guner, A.To determine of irradiation effect on 4-hydroxyphenyl-acetic acid polycrystalline, electron paramagnetic resonance (EPR) measurements were carried out. Two samples were used, which were given dose of 22.8 and 49 kGy by gamma rays using Co-60-source. EPR signals were not observed from irradiated sample, taken dose of 22.8 kGy. The measurements were performed on the sample, absorbed dose of 49 kGy, at the temperature between 120 K and 450 K. The two radical structures were suggested within experimental error. Though the radicals are identical, it was determined that they have different EPR parameters. It was observed that the intensities of the EPR spectra were to be dependent on the temperature. Also, in this study, it was aimed to test success of the machine learning methods to select the best method can be implemented theoretically. (C) 2015 Elsevier B.V. All rights reserved.Öğe An ESR Study on 2,4 Diaminotoluene Exposed to Gamma Rays and Application of Machine Learning(POLISH ACAD SCIENCES INST PHYSICS, 2016) Ceylan, Y.; Usta, K.; Aydogmus, H. Yumurtaci; Usta, A.; Ceylan, N.; Aras, E.The polycrystals of 2,4 diaminotoluene were produced by slow evaporation of solvent. The polycrystalline samples were exposed to Co-60 gamma rays with dose rate of 0.950 kGy/h, at room temperature, for 12, 24, 48, and 72 hours. The electron paramagnetic resonance measurements were carried out on these samples in the temperature range between 298 K and 400 K. No electron paramagnetic resonance signal was observed in the samples irradiated for 12, 24, 48 hours. Two types of radicals were detected using ESR spectrometer in the sample irradiated for 72 h. These radiation damage centers were called RI and RII. The average values of g and the hyperfine coupling constant were calculated. This study also investigates the potential usage of machine learning methods and aims to test the success of these methods and to select the best method.Öğe Evaluation of Antioxidant Activity, Phytochemicals and ESR Analysis of Lavandula Stoechas(POLISH ACAD SCIENCES INST PHYSICS, 2015) Ceylan, Y.; Usta, K.; Usta, A.; Maltas, E.; Yildiz, S.The antioxidant activity of phytochemicals and of the methanolic extract of Lavandula stoechas was evaluated by beta-carotene-linoleate bleaching, DPPH radical scavenging, ferric reducing/antioxidant power (FRAP). The obtained results were compared with antioxidant activities of synthetic antioxidants, such as BHT and BHA. The highest antioxidant activity of the extract was observed by DPPH radical scavenging assay, which was 84.45 +/- 5.1 % at 1 mg ml(-1). Rutin, rosmarinic acid, and caffeic acid were main phenolics in the extract. The total phenolic content of the methanolic extract of Lavandula stoechas was found to be 105.5 +/- 2.7 mg gallic acid equivalent (GAE). Electron spin resonance (ESR) measurements were also performed on the samples. Free radicals were determined by ESR method. g value was found to be 2.0034 for the Lavandula stoechas; 2.0052 for quercetin.Öğe In Vitro Analysis of AHPlus and MM-Seal by ESR and Thermoanalytical Methods(POLISH ACAD SCIENCES INST PHYSICS, 2015) Ceylan, Y.; Usta, A.; Usta, K.; Cobankara, F. Kont; Yildirim, C.; Birey, M.The free radicals and their concentration in resin materials may impact biocompatibility and polymerization properties of dental materials. The aim of this study was to determine whether there are free radicals and to obtain useful information about thermal stability of materials using electron spin resonance (ESR) spectroscopy, TGA (Thermogravimetry Analysis) and DTA (Differential Thermal Analysis) methods. Epoxy resin-based sealers AHPlus and MM-Seal samples, freshly mixed and set, were prepared to be analysed with ESR and thermal methods. The free radicals were found in dental materials. As radical concentration in AHPlus have changed very slowly, the concentration in MM-Seal have decreased dramatically. Also, MM-Seal was found to decompose in three steps with the increasing temperature, while decomposition of the AHPlus occurred in two steps.
