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Altered isotope charge distribution of acetylcholine neurotransmitter and Myasthenia Gravis
(Churchill Livingstone, 2016) Bayri, A.; Unal, S.; Altin, S.; Bulut, F.; Dayanc, B. E.
Acetylcholine (ACh) is a central neurotransmitter that is used for signal transmission among neurons. For signal transmission in neurons, a neurotransmitter must bind to its receptor in order to produce an action potential. It is known that in Myasthenia Gravis (MG) cases, autoantibodies could block this binding. In the future, the treatment of MG could be achieved via modulation of molecular interaction between ACh and acetylcholine receptor (AChR). This study suggests that if an atom on a ligand (i.e. a neurotransmitter) is replaced with its isotope, it may cause charge redistribution such as that the binding between ligand and its receptor may be improved. Hence suggesting that with replacement of atoms with their isotopes in any biologically important ligand could alter its affinity towards its corresponding receptor, which would have a wide array of applications in medicine. (C) 2016 Elsevier Ltd. All rights reserved.
Current-Voltage Measurements on a Bi2Sr2CaCu2Ox Whisker and Investigation of Its Vortex Dynamics in Self Field
(Springer, 2013) Altin, S.; Aksan, M. A.; Yakinci, M. E.; Bernstein, P.
We report current-voltage measurements carried out on a high quality Bi2Sr2CaCu2Ox whisker in a large temperature range below the critical temperature. When a perpendicular field is applied, the current-voltage curves are typical of the flux flow regime at low fields and resemble flux creep characteristics at high fields. This change, related to what is described as the critical current peak effect is associated to a transition between different vortex phases. In this contribution, we focus on the dynamics of the vortices in self field. We show that the critical current in the flux flow regime can be calculated straightforwardly taking into account inter-vortex forces only, supposing that free vortices run between pinned vortices.
Effect of Bi deficiency on grain alignment of BiPb-2223 thin film fabricated using rf sputtering process and on critical current density properties
(Taylor & Francis Ltd, 2011) Aksan, M. A.; Altin, S.; Yakinci, M. E.; Guldeste, A.; Balci, Y.
In the present study, thin films prepared as a function of the Bi concentration in the BiPbSrCaCuO system were synthesised. Thin films were fabricated using radio frequency sputtering method. Crystal structure of the films fabricated was determined from X-ray diffraction measurements. The crystal orientation was analysed by X-ray pole figure and in-plane alignment. Both X-ray diffraction and pole figure analysis revealed that crystallinity in the films decreased significantly with decreasing Bi concentration in the system. A systematic decrease in the superconducting transition temperature and hole concentration per CuO plane was obtained with decreasing Bi concentration. The J(c) values of the films were calculated using Bean formula. It exhibits a significant dependence on the magnetic field and temperature. It was found that J(c) decreased sharply with increasing applied magnetic field. The highest J(c) value was found to be 1.06 x 10(6) A cm(-2) at 10 K, which corresponded to the best flux pinning among the films fabricated.
Effect of Bi2O3 Addition on the Single-Crystal BiSrCaCuO Whisker Growth
(Springer, 2011) Altin, S.; Aksan, M. A.; Altin, E.; Balci, Y.; Yakinci, M. E.
Bi-2212 superconducting whiskers have been fabricated by annealing a melt-quenched precursor using suitable heat-treatment cycles for Bi3+x Sr2Ca2Cu3O8+delta where x=1 and 2. Approximately 1-3 mm long whiskers were fabricated for x=1 and x=2 and their physical, electrical and magnetic properties were investigated. Crystallization activation energies of the materials were calculated according to Kissinger and Augis-Bennet method using the DTA data. Microstructural changes from glass to heat-treated glass-ceramic materials at different temperatures were investigated with SEM, EDX and XRD analyses. It was observed that the structure of the whiskers has high c-axis oriented single-crystalline Bi-2212 phase. The whiskers fabricated for x=1 and 2 showed very smooth surface without cracks and dislocations. T (c) of the whiskers for x=1 and 2 were obtained to be 83.2 K and 79.8 K respectively. The change of magnetization with applied magnetic fields (M-H) was investigated at three different temperatures, 10, 20 and 40 K, and J (c mag) was determined using the Bean model.
Effect of Ce substitution on superconducting properties of Bi2Sr2Ca2Cu3O10+? system fabricated by glass-ceramic technique
(Springer, 2011) Ozturk, R.; Aksan, M. A.; Altin, S.; Yakinci, M. E.; Balci, Y.
In this study, the samples with nominal composition of Bi2-x Ce (x) Sr2Ca2Cu3O10+delta , where x=0, 0.05, 0.1, 0.2, 0.4 and 0.6, are synthesized by using conventional glass-ceramic technique. Effects of the Ce substitution on the structural/microstructural and electrical properties of the Bi-2223 system have been investigated in detail. Ce has a solid solubility limit on glassification, which is found to be x=0.2. It is seen that glassification is destroyed for the Ce substitutions above x=0.2. Further, XRD investigations showed that main phase in all the heat-treated samples is identified to be Bi-2212. From SEM-EDX investigations of heat-treated samples, it is revealed that the highly Ce-substituted samples had complex and deformed structure. It is also found that electrical properties degraded with increasing the Ce concentration. Especially in high Ce substitution level, superconductivity is destroyed and an insulating behavior is observed.
The effect of Mo addition on the microstructure and Jc properties of MgB2 tapes fabricated by PIT method
(Elsevier Science Sa, 2008) Bayazit, E.; Altin, S.; Yakinci, M. E.; Aksan, M. A.; Balci, Y.
We investigated the effect of Mo addition to MgB2/Ag tapes fabricated by the ex situ PIT method. The heat treatments were carried out at 600 degrees C for 24 h under At atmosphere. The structural development, microstructures, superconducting properties and critical current density were characterized by means of XRD, SEM, M-T and M-H measurements. XRD and SEM studies indicated that Mo, not reacting with matrix of MgB2, was formed. The T-c of the tapes decreased in all the addition levels. The maximum J(c) value was obtained to be 1.2 x 10(5) A cm(-2) at 10 K for pure MgB2 tape. Decrease of J(c) was observed with increasing the Mo concentration. The J(c)-H characteristics of the tapes were decreased by the addition of Mo. This is considered to be due to the reduced flux-pinning force in the material. (C) 2007 Elsevier B.V. All rights reserved.
Effects of In-situ and Ex-situ Heat-Treatment Procedures on the Transport Properties of the MgB2 Superconducting Thin Films Fabricated by Ultrasonic Spray Pyrolysis (USP) System
(Springer, 2011) Yakinci, M. E.; Aydogdu, Y.; Aksan, M. A.; Balci, Y.; Altin, S.
Superconducting MgB2 thin films have been prepared using Ultrasonic Spray Pyrolysis (USP) system. 2.4 MHz USP system and various solutions which contain different Mg, B and de-ionized water and LAPSA concentrations and gas atmospheres were used to obtain 500 nm to 1.0 mu m thick MgB2 films. Some of the films produced were heat treated in-situ in the spraying chamber during deposition and some of them were annealed ex-situ in the tube furnace under Mg vapor. T (c) and T (zero) of the samples were obtained to be 39.5 K and 37.4, 39.5 and 37.0 for ex-situ and in-situ prepared films, respectively. The highest critical current density was obtained to be 4.12x10(6) A cm(-2) for ex-situ annealed films and 4.01x10(6) A cm(-2) for in-situ produced films. The result obtained indicated that the ex-situ preparation method provides improvement in the transport and magnetic properties.
Effects of SnO on growth and physical properties of BSCCO whiskers
(Maney Publishing, 2010) Altin, S.; Aksan, M. A.; Balci, Y.; Yakinci, M. E.
Superconductor whiskers doped with SnO have been fabricated by annealing a melt quenched (Bi2Sn1)-223 precursor using suitable heat treatment cycles. Approximately 5 mu m thick, 90 mu m wide and 5 mm long whiskers were fabricated, and their physical, electrical and magnetic properties were investigated. Crystallisation activation energies of glass phase fabricated were calculated to be 390 kJ mol(-1) using Kissinger method based on the differential thermal analysis data. The T-c value of the whiskers was found to be 94 K from M-T measurement. The magnetisation of whiskers before superconducting transition increased with decreasing temperature, and after superconducting transition, the magnetisation of whiskers decreased, from positive to negative, due to the diamagnetic nature of superconductivity. The change on magnetisation dependence of applied magnetic fields (M-H) showed that whiskers have paramagnetic-diamagnetic multiphase structure.
Electrical and optical properties of ZnO-Fe2O3-SiO2 composite prepared by SOL-GEL method
(Amer Inst Physics, 2007) Canbay, C. Aksu; Altin, S.; Aydogdu, A.; Aydogdu, Y.; Yakinci, E.
The semiconductor composite was prepared from ZnO, Fe2O3 and SiO2 transition metal oxides by sol-gel method. The surface morphology of the prepared samples were investigated by scanning electron microscopy (SEM). The activation energies of the samples in the extrinsic and intrinsic regions were found as 0.75 eV and 0.77 eV for ZFS-1 and 0.22 eV and 0.32eV for ZFS-2. The value of the optical band gap of the composite samples were calculated from the absorption coefficient depending on photon energy. The optical band gap of the samples were found as 1.60 eV and 1.70 eV for ZFS-1 and ZFS-2, respectively.
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.
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.
Elucidating the optimized P2 type Na0.67Mn1-xCuxO2 cathode active material via operando XAS
(Elsevier Science Sa, 2023) Altin, S.; Altundag, S.; Altin, E.; Vanpoucke, D. E. P.; Avci, S.; Ates, M. N.
Here we report on the structural and electrochemical properties of P2-type Na0.67Mn1-xCuxO2 (where x = 0.20-0.50) via various techniques. X-ray diffraction (XRD) reveals a reduction of the unit cell volume upon substitution of Cu elucidated through detailed Rietveld analysis. The cyclic voltammetry (CV) behavior is also affected by the Cu substitution indicating new redox reactions stemming from Cu substitution. Galvanostatic cycling measurements at room temperature show that when x = 0.35 in a P2-type Na0.67Mn1-xCuxO2 cathode active material, the best electrochemical performance is obtained. The Na-ion diffusion rate is found to be strongly dependent upon the environmental temperature. Changes in the valence state and the local structures of P2-type Na0.67Mn1-xCuxO2 during the charge/discharge are in-vestigated through the operando X-ray absorption spectroscopy (XAS) technique. (c) 2022 Elsevier B.V. All rights reserved.
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.
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.
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.
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.
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.
Fabrication of Cr doped Na0.67Fe0.5Mn0.5O2 compounds and investigation of their structural, electrical, magnetic and electrochemical properties
(Springer, 2019) Altin, E.; Altundag, S.; Altin, S.; Bayri, A.
The main purpose of the study is to investigate the battery properties behind the electrical and magnetic properties. The first part of the study is about the fabrication of Cr-doped Na0.67Fe0.5Mn0.5O2 and the structural properties of the powders, which were investigated by XRD, EXAFS, FTIR and Raman Spectroscopy. Temperature-dependent resistivity measurements showed that room temperature resistivity values increased with Cr-ion content and all samples show an exponential decrease with increasing temperature. The magnetic properties of the Cr-doped samples were investigated, and it was found that the Cr ions strongly affected the magnetic structure of the samples. The second part of the study is about battery performance using the samples as cathode materials. Hence, CR2032 coin cells were fabricated by using the Cr-doped samples and the CV measurements showed that a high level doping of Cr ions in the structure prevented Na diffusion in the cells. The obtained CV graphs were discussed from the viewpoint of lattice dynamics. The EIS and cycling properties showed that Cr-ions in Na0.67Fe0.5Mn0.5O2 decrease of the capacity fade of the cells.
Fabrication of NdCeCuO and effects of binding agents on the growth, micro-structural and electrical properties
(Elsevier Science Bv, 2011) Altin, S.; Aksan, M. A.; Turkoglu, S.; Yakinci, M. E.
NdCeCuO superconducting samples were fabricated using ethyl alcohol, acetone and ethylenediaminetetraacetic acid (EDTA) as binding agents. For evaporation of binding agents, the samples were heat treated at 1050 degrees C for 24 h and then at 950 degrees C for 6-48 h under argon atmosphere to obtain the superconducting phase. The best superconducting performance was found in the sample heat treated at 1050 degrees C for 24 h and then 950 degrees C for 12 h which was fabricated by using acetone as binding agent. The T(c) and T(0) value was found to be similar to 25 K and 23.4 K, respectively. Grain size in the samples fabricated was calculated using Scherer equation and SEM data. It was found that grain size strongly depends on the binding agents and heat treatment conditions. Some cracks and voids on the surface of the samples were observed, which influences the superconducting and electrical transport properties of the samples. (C) 2011 Elsevier B.V. All rights reserved.
Fabrication of single crystalline Bi-2212 whisker with addition of Sb2O3 into the Bi2Sr2Ca2Cu3Ox system and their thermal, structural and superconducting properties
(Elsevier, 2011) Altin, S.; Aksan, M. A.; Yakinci, M. E.
Single crystalline Bi-based superconducting whiskers have been fabricated from a melt quenched Bi2SbSr2Ca2Cu3Ox. precursor using suitable heat treatment cycles. Whiskers fabricated in this study have 6-15 mu m thickness, 60-95 mu m width and 1-3 mm length. Crystallization activation energy of the material fabricated was calculated to be 609 kJmol(-1) by Kissinger method. Structural and micro-structural changes with the heating treatment cycles were analyzed by XRD and SEM-EDX. It was found that whiskers have pure c-axis oriented single crystalline Bi2Sr2CaCu2Ox (Bi-2212) phase with very smooth surface and without cracks and dislocations. Sb ions did not diffuse directly to the structure of whiskers. But Sb ions added to the system caused to decrease the number of whiskers. Temperature dependence of resistivity was analyzed along both the a- and c-axis. The superconducting transition temperature. To of the whiskers was found to be 93.8 K for the a-axis resistivity and 90.9 K for the c-axis resistivity, respectively. The transport critical current density, integral(trans)(c) was found as 2.6 x 10(5) A/cm(2) at 10 and 1.1 x 10(5) at 70 K. Magnetization hysteresis (M-H) was investigated at three different temperatures (10, 20 and 30 K). Magnetic critical current densities, integral(mag)(c), of whiskers were determined using the Bean's Model. (C) 2011 Elsevier Masson SAS. All rights reserved.

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