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Öğe Comparison of preoperative and postoperative anterior segment measurements with Pentacam in horizontal muscle surgery(Wichtig Editore, 2008) Emre, S.; Cankaya, C.; Demirel, S.; Doganay, S.PURPOSE. To evaluate the effect of horizontal muscle surgery (recession or recession plus resection) on the anterior chamber parameters in patients after strabismus surgery. METHODS. The Scheimpflug of 18 eyes of 12 patients with horizontal deviations were recorded just before surgery and 1 month after surgery. The power of anterior surface of cornea in horizontal and vertical axis, thinnest corneal thickness, anterior chamber depth, anterior chamber volume, and cornea volume were analyzed. The clinical characteristics of patients, the size of the deviations, the surgical doses, and observed responses to surgery were reviewed. RESULTS. There were six male and six female patients with an average age of 11.4 years (range, 4 to 22 years). Mean preoperative deviation was 47.91 PD (range, 20 to 75 PD), eight patients had esotropia with 57.5 PD average deviation (range, 40 to 75 PD), and four patients had exotropia with 28.75 PD average deviation (range, 20 to 35 PD). Of these 18 eyes, 12 eyes had horizontal muscle recession and 6 eyes had recession plus resection surgery. At the end of 1 month, three patients were orthophoric and eight patients had residual deviations varying between 16 and 35 PD. Preoperative and postoperative comparison of the whole study group documented insignificant changes in anterior chamber parameters and in keratometer readings. However, after dividing patients into two groups-recession or recession plus resection group-only one parameter, anterior chamber volume, was significantly reduced in recession plus resection group. CONCLUSIONS. Patients with strabismus who undergo recession plus resection procedure are prone to change in anterior chamber volume. Study with larger groups and long follow-up is necessary for clearer documentation of alterations at anterior chamber parameters.Öğe THE CORNEAL BIOMECHANICAL PARAMETERS IN TYPE 1 DIABETES MELLITUS(Wichtig Publ, 2015) Dikci, S.; Genc, O.; Ekmen, R.; Tas, M.; Firat, P. G.; Demirel, S.[Abstract Not Available]Öğe Electrochemical effects and magnetic properties of B substituted LiCoO2: Improving Li-battery performance(Elsevier Science Sa, 2016) Oz, E.; Altin, S.; Demirel, S.; Bayri, A.; Altin, E.; Baglayan, O.; Avci, S.LiCo(1-x)BxO(2) (x = 0, 0.125, 0.25, 0.375, 0.5, 0.75 and 1) samples were synthesized via solid state reactions. They were characterized by SEM, X-ray powder diffraction, FTIR, Raman, electrical and magnetic measurements. XRD data show impurity phases for x >= 0.25 samples due to boron content. Based on FTIR studies, the peak position of CoO6 shifts with increasing B content. The Raman spectra of LiCoO2 shows the presence of three broad bands, indicating the possible formation of spinel structure. The effective magnetic moments of the samples were calculated using Curie-Weiss law with temperature independent term. The M-H curves of x = 0.375 and 0.5 samples show very weak hysteresis loops. Effects of boron substitution on battery performance are also investigated. x = 0.125 and x >= 0.25 samples give promising results due to their enhanced reversibility of cycling compared to pristine LiCoO2. Capacity retentions for 100 cycles for x = 0, 0.125 and 0.25 samples are 22%, 81% and 83%, respectively. (C) 2015 Elsevier B.V. All rights reserved.Öğe The electrochemical properties of V-doped Li2Ti6O13 and Na2Ti6O13 anode materials(Iop Publishing Ltd, 2019) Demirel, S.; Altin, S.Li2Ti6-xVxO13 and Na2Ti6-xVxO13 (where x = 0, 0.025, 0.05, 0.1) are prepared by conventional ion exchange method and solid-state reaction technique, respectively. According to XRD analysis, increasing V contents in the structures cause the formation of LiVO3 and LiV3O8 phases for x >= 0.025 substitutions for Li2Ti6O13 and Na4V2O7 in structure for Na2Ti6O13 x >= 0.025. It was observed two redox peaks for both undoped compositions which are related to insertion and deinsertion of Li/Na ions in the structure. The battery performances were investigated for Li2Ti6-xVxO13 and Na2Ti6-xVxO13 systems and it is found that pure Li2Ti6O13 sample has showed the capacity of 36 mAh g(-1) and 27 mAh g(-1) for 1 and 1000 cycle respectively which show better capacity fade when compared with the other anode materials. The battery performance of undoped Na2Ti6O13 sample has 40 mAh g(-1) and 34 mAh g(-1) for 1 and 1000 cycle respectively. In addition to this, the x = 0.05 V-substitution has showed 66 mAh g(-1) for the first cycle which is higher than that of the undoped sample. It was investigated the structural deformation of the cells by in situ XRD during to CV process and ex situ XRD and Raman techniques after cycling of the cells. It is predicted that the changes of the reflection planes of the crystallites/grains during to cycling of the cells may be the main reason of the decrease of the battery performance which is related to insertion and de-insertion energy of the Li-ions.Öğe Enhanced thermoelectric properties induced by chemical pressure in Ca3Co4O9(Elsevier Sci Ltd, 2014) Demirel, S.; Avci, S.; Altin, E.; Altin, S.; Yakinci, M. E.We report the investigation of boron substitution on structural, electrical, thermal, and thermoelectric properties of Ca-3_xBxCo4O9 (x=0, 0.5, 0.75, and 1) in the temperature range between 300 K and 5 K. X-ray diffraction studies show that the Ca3Co4O9 phase is successfully preserved as the majority phase in the x=0.5 sample despite the small size of boron ions. Electrical transport measurements confirm that B3+ substitution for Ca2+ causes an increase in resistivity due to the decrease in carrier concentration. x=0.5 sample is found to have a Seebeck coefficient of 181 mu V/K at room temperature which is similar to 1.5 times higher than that of the pure Ca3Co4O9. Our results indicate that the chemical pressure due to the large ionic radii difference between B3+ (0.27 angstrom) and Ca2+ (1 angstrom) enhances the thermoelectric properties as long as the unique crystal structure of Ca3Co4O9 is preserved. (c) 2013 Elsevier Ltd and Techna Group S.r.l. All rights reserved.Öğe Enhancement of battery performance of LiMn2O4: correlations between electrochemical and magnetic properties(Royal Soc Chemistry, 2016) Demirel, S.; Oz, E.; Altin, S.; Bayri, A.; Altin, E.; Avci, S.We report the results of a systematic investigation of structural, electrical transport, magnetic, and electrochemical properties of LiBxMn2-xO4 (where x = 0.0-1), synthesized via a one-step solid state reaction technique. We find that the parent compound (x = 0) has the non-stoichiometric Li1.05Mn2O4 phase and the B ions successfully incorporate the structure for x <= 0.5. The resistivity anomaly of the parent compound below 100 K is attributed to the antiferromagnetic correlations. The linear part of the chi(-1)-T data are used to calculate the effective magnetic moments and to determine the total number of Mn3+ and Mn4+ ions. Magnetization measurements show that Jahn-Teller active Mn3+ ions have high spin configuration. Average valance of Mn ions increases with increasing boron content. Electrochemical studies show improved capacity retention for x = 0.125 for 100 charge-discharge cycles. This improvement is attributed to subtle modifications in the structural and magnetic properties upon substitution.Öğe An enhancement ZT and spin state transition of Ca3Co4O9 with Pb doping(Elsevier Science Sa, 2015) Demirel, S.; Altin, E.; Oz, E.; Altin, S.; Bayri, A.We reported the structural, electrical, thermal and magnetic properties of Pb-doped Ca3Co4O9 in the range of 300-5 K. DTA analysis showed that the stability of the Ca3Co4O9 was increased with Pb doping. According to XRD analysis, it is found that Pb ions were successfully doped in the Ca3Co4O9 structure. The temperature of resistivity minima, T-min, increased by increasing the Pb doping level and it is seen that incommensurate spin density wave state becomes more stable with Pb doping. The enhancement of thermopower was explained that Pb doping in Ca sites caused a decrease of Co4+ fraction such that Co4+ ions transformed into Co3+ or Co2+. The room temperature ZT value of the polycrystalline sample reaches about 16 times larger value than that of the un-doped polycrystalline sample which is the promising candidate for high temperatures in the thin film applications. According to magnetic susceptibility measurement, the increase of effective magnetic moment by Pb concentration was explained by spin state transition of Co3+ from low spin to intermediate spin and high spin state together with some orbital angular momentum contribution which comes from T-5(2) term due to a decrease of the ligand field splitting energy. (C) 2014 Elsevier B. V. All rights reserved.Öğe Fabrication and electrochemical properties of LiCo1-xRuxO2 cathode materials for Li-ion battery(Elsevier Science Sa, 2016) Oz, E.; Demirel, S.; Altin, S.LiCo1-xRuxO2 (where x - 0.0-0.5) are prepared by conventional solid-state reaction technique. The effect of Ru substitutions on the structural properties and electrochemical performance of LiCoO2 cathode materials is investigated in detail. The XRD analysis shows that increasing Ru content in LiCoO2 above x = 0.1 causes formation of different phases such as Li1.4RuO3, Li2Ru0.5Co0.5O3 and RuO2 which are used in the Li-ion batteries as an electrode materials. It is found in the XRD analysis that the Ru doping causes a decrease in the crystallite size which is important for improving the battery performance. The CV analysis shows that the Ru doping till x = 0.1 can produce an improvement in the performance of the cell and the capacity retention after 50 cycle is much better than that of the cell that fabricated using the pure LiCoO2. (C) 2016 Elsevier B.V. All rights reserved.Öğe Fabrication of Ca-Mn-Nb-O compounds and their structural, electrical, magnetic and thermoelectric properties(Iop Publishing Ltd, 2018) Oz, E.; Demirel, S.; Altin, S.; Altin, E.; Baglayan, O.; Bayri, A.; Avci, S.CaMn1-xNbxO3-delta (0 <= x <= 1) were synthesized by conventional solid state reaction method. The structural properties were determined by FTIR, Raman, XRD, XAS measurements. The FTIR and Raman modes change by increasing Nb content and the lattice volume increases by increasing Nb content. The solubility limit of Nb is determined as x <= 0.3 and impurity phases start to appear above this limit. The temperature dependence of the magnetization data shows an antiferromagnetic transition below 120 K for low Nb content. Increasing the Nb content causes a change in the magnetic phase from antiferromagnetic to paramagnetic. The oxygen deficiency in CaMnO3-delta may cause the formation of polaron effect which is destroyed by the Nb ions. The difference graph of XAS data for x = 0 and 0.5 show that the number of Mn3+ ions increases by increasing Nb content to maintain the charge neutrality.Öğe Growth mechanism and magnetic and electrochemical properties of Na0.44MnO2 nanorods as cathode material for Na-ion batteries(Elsevier Science Inc, 2015) Demirel, S.; Oz, E.; Altin, E.; Altin, S.; Bayri, A.; Kaya, P.; Turan, S.Nanorods of Na0.44MnO2 are a promising cathode material for Na-ion batteries due to their large surface area and single crystalline structure. We report the growth mechanism of Na(0.44)Mno(2) nanorods via solid state synthesis and their physical properties. The structure and the morphology of the Na0.44MnO2 nanorods are investigated by X-ray diffraction (XRD), scanning and tunneling electron microscopy (SEM and TEM), and energy-dispersive X-ray (EDX) techniques. The growth mechanism of the rods is investigated and the effects of vapor pressure and partial melting of Na-rich regions are discussed. The magnetic measurements show an antiferromagnetic phase transition at 25 K and the Pelf is determined as 3.41 and 3.24 mu(B) from the chi-T curve and theoretical calculation, respectively. The electronic configuration and spin state of Mn3+ and Mn4+ are discussed in detail. The electrochemical properties of the cell fabricated using the nanorods are investigated and the peaks in the voltammogram are attributed to the diffusion of Na ions from different sites. Na intercalation process is explained by one and two Margules and van Laar models. (C) 2015 Elsevier Inc. All rights reserved.Öğe High temperature thermoelectric properties of the Ca3-xBxCo4O9 system(Springer, 2013) Demirel, S.; Altin, S.; Aksan, M. A.The Ca3-xBxCo4O9 system (x = 0.0, 0.05, 0.75 and 1.0) has been prepared using the solid-state reaction technique. Structural, microstructural, transport properties (temperature dependence of resistivity, thermoelectric power) of the samples fabricated were investigated in details. The structural/microstructural investigations showed that complex and multiphase crystallographic structure was formed with the B-substitution. A decrease in the grain size was observed in the B-substituted samples. The resistivity increased with the substitution due to decrease in the grain size and weak-link among the grains. It is found that that the thermoelectric power is insensitive to the B-substitution. The highest power factor value was obtained in the x = 0.0 sample, however, it decreased in the B-substituted samples.Öğe Jc enhancement and flux pinning of Se substituted YBCO compound(Springer, 2013) Yakinci, Z. D.; Gokhfeld, D. M.; Altin, E.; Kurt, F.; Altin, S.; Demirel, S.; Aksan, M. A.Y-2/3 Se1/3Ba2Cu3Ox compound was fabricated by using solid state fabrication technique. Optimum heat treatments conditions for Y0.77Se0.33Ba2Cu3Ox were investigated. It was determined that the XRD results of these samples were similar to Y-123 phase with some impurities. Magnetization dependence of applied magnetic fields was measured in the range of 0-9 T at 10-50 K. The symmetric and asymmetric M-H loops were obtained for the samples. Magnetization loops obtained from measurements were successfully described by the extended Valkov-Khrustalev model. The temperature and applied magnetic field dependencies of magnetization of sample were estimated and critical current density of samples was calculated by Bean model and pinning force of samples was calculated by using Lorentz force. It is found from critical current density values that Se additions were acted as a pinning center which increased critical current density.Öğe Low temperature electrical and thermal transport properties of the Ca3-xSbxCo4O9 system(Springer, 2012) Demirel, S.; Aksan, M. A.; Altin, S.In this study, the Ca3-xSbxCo4O9 (x = 0.0, 0.5, 0.75 and 1.0) system was fabricated using solid-state reaction technique. From the XRD analysis, it was found that increase of the Sb concentration in the system caused formation of impurity phases and therefore a distortion in the main lattice. The SEM-EDX results showed that the grain size reduced with increasing Sb in the Ca3Co4O9 system. The resistivity, rho, value increased with increasing the Sb-content and insulating behavior was obtained as the temperature was decreased. The samples fabricated have positive thermoelectric power, S, value, suggesting that holes are dominant charge carriers in the samples. S value decreased with decreasing the temperature. The Fermi energy, E-F , and the carrier concentration, n, decreased by the Sb-substitution. The Sb-substitution caused a decrease of thermal conductivity, kappa which is due to reduction of the phonon thermal conductivity, kappa(ph,) in the system. Figure of merit, ZT, value decreased significantly due to strongly increase in rho. The impurities, defects and distortion with substitution of Sb are responsible for large variation on electrical and thermal transport properties.Öğe Low Temperature Magnetic Behavior of Ca3Co4Ox Polycrystalline Material(Springer, 2013) Demirel, S.; Altin, S.; Aksan, M. A.Misfit layered Ca3Co4O9 samples have been fabricated by solid-state reaction method. X-ray diffraction analysis showed that the samples have the c-axis oriented monoclinic structure. The temperature dependence of the DC magnetization of the sample fabricated was investigated in an applied field of 2000 Oe. Magnetization of the sample increased smoothly down to 20 K, then increased rapidly with decreasing temperature, suggesting a transition to the ferrimagnetic phase. M-H analysis indicated a paramagnetic behavior between 20 and 300 K and hysteretic effect below 20 K which corresponds to paramagnetic-ferrimagnetic phase transition. The ferrimagnetisms are most likely caused by interlayer coupling between the Ca2CoO3 and CoO2 subsystems in unit cell.Öğe Magnetic and microstructural properties of LiCrO2.Cr2O3 system by doping of the boron ions(Springer, 2015) Demirel, S.; Oz, E.; Bayri, A.; Altin, S.In this study, we reported the structural, electrical and magnetic properties of B-doped LiCrO2.Cr2O3 system by boron doping. XRD pattern of the samples showed that the boron ions were substituted with Cr ions in both lattices and the volume of the cells were decreased by increasing boron content. The particle size and strain calculations were performed by using XRD pattern and it is found that the particle sizes were not changed much by boron doping but the strain were increased by increasing boron in the samples. The susceptibility of the undoped sample shows two different phase behavior with decreasing temperature and it is found that the magnetic properties of Cr2O3 were dominant at room temperature to 100 K and the peak at 62 K was due to the LiCrO2 phase. It should be noted that the boron doping were caused the decrease of the room temperature susceptibility and the antiferromagnetic interactions were destroyed by boron incorporation of the lattice.Öğe Structural properties and electrochemical performance V-doping Li2Ti3O7 and Li4Ti5O12 anode materials(Springer, 2019) Demirel, S.; Altin, S.Li2Ti3-xVxO7 and Li4Ti5-xVxO12 (x=0-0.1) are successfully fabricated using the conventional solid-state reaction technique. The battery performance of the cells showed that the highest capacity of Li2Ti3-xVxO7 was obtained for the sample of x=0.025 which has 153mAh/g and 123mAh/g for 1 and 1000, respectively. In addition to this, the best capacity of the cell of Li4Ti4.5V0.5O12 was found as 202mAh/g for the first cycle and it was decreased to 194mAh/g for 1000 cycles. To understand the capacity fade mechanism, we performed ex situ structural experiments and it is found that the unit cell of the crystalline phase is directly affected to battery performance. We concluded that in this study the V-substituted samples have a potential for next-generation battery fabrication since it may cause the increase of the stability of the cells.Öğe Structural, magnetic, electrical and electrochemical properties of SrCo02.5, Sr9Co2Mn5O21 and SrMnO3 compounds(Elsevier Sci Ltd, 2017) Demirel, S.; Oz, E.; Altin, S.; Bayri, A.; Baglayan, O.; Altin, E.; Avci, S.SrCo1-xMnxO3-d (0 <= x <= 1) were synthesized by conventional solid state reaction method. We found that Mn substitution hinders the decomposition of carbonate at 900 degrees C and increases the synthesis temperature of SrCo1-xMnxO3-d to 1200 degrees C. Three different main phases emerge as the Mn content is increased; SrCoO2.5, Sr9Co2Mn5O21 and SrMnO3. Structural properties of the samples were investigated by Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, x-ray diffraction (XRD) and scanning electron microscopy (SEM). Valance states of the transition metal (TM) ions were estimated based on lattice parameters and ionic radii of TM ions. High temperature resistivity measurements show hysteresis upon heating and cooling and is attributed to oxygen release without any endothermic/exothermic activity. The spin configurations of Co and Mn ions in SrCoO2.5, Sr9Co2Mn5O21. and SrMnO3 were estimated by Curie-Weiss fitting of X-T curves. Electrochemical measurements show two anodic/cathodic peaks indicating two main types of oxygen sites in the unit cell.Öğe Synthesis of Na2Ti3O7 nanorods by a V-assisted route and investigation of their battery performance(Royal Soc Chemistry, 2020) Altin, S.; Demirel, S.; Oz, E.; Altin, E.; Hetherington, C.; Bayri, A.; Avci, S.We report the V-assisted synthesis of Na2Ti3O7 nanorods via a conventional solid state reaction technique. Energy dispersive X-ray spectroscopy (EDS) mapping showed that V-ions are not incorporated into the main structure of the nanorods but rather V behaves as a flux agent during the growth of the nanorods. The cyclic voltammetry (CV) analysis of the samples shows changes in the redox peaks as a function of V content. Our detailed ex situ X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray absorption spectroscopy (XAS) analyses after 1000 cycles show that the degradation mechanism is the formation of various titanium oxide impurity phases which inhibits the Na-ion diffusion.Öğe Synthesis of ultra-thin nanobristles of Na-Mn-O compounds and their magnetic and structural properties(Elsevier Sci Ltd, 2016) Oz, E.; Demirel, S.; Altin, S.; Bayri, A.; Avci, S.Boron substituted Na0.44MnO2 nanorods were synthesized via conventional solid state reaction technique. Optimum synthesis temperature of the nanorods is determined as 750 degrees C. As the temperature increases, the nanorods start merging each other. As the boron content increases, amount of nanorods decrease due to the emergence of impurity phases. 12.5% boron substitution (x=0.25 in NaMn2-xBxO4 nominal composition) into Mn site striggers the formation of ultra-thin nanobristles on the surface of the nanorods. These nanobristles disappear completely in x=0.75 sample. We attribute the formation of these nanobristles to the increase in the internal energy upon increase in the unit cell volume. (C) 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved.Öğe Thermal and mechanical properties of La-Al-Sb alloys(Springer, 2014) Altin, E.; Oz, E.; Demirel, S.; Erdem, M.We fabricated La-Al-Sb alloy by arc melter system and the fabrication conditions were described in detail. Microstructural analyses were performed and it was found that LaSb, Al11La3 Al4La, AlLa3 and Sb phases formed for different heat treatment conditions. The resistivity results showed the metallic and semiconducting type behavior depending on heat treatment temperatures. The thermal-conductivity measurement was performed in the range of 2-300 K and the data were analyzed by the sum of lattice and carrier components. The linear temperature dependence of thermo power indicates metallic type characteristic of the samples. The micro-hardness values of the phases in the samples were analyzed and it was found that there are two different hardness regions in the samples.
