Özer, Mahmut | Bal, Abdullah

Article | 2004 | Istanbul University Journal of Electrical and Electronics Engineering4 ( 1 ) , pp.1091 - 1104

In this paper, we investigate dynamics of voltage-gated ionic channels which are of great importance in integrating the information received by neurons. Understanding of dynamical behavior of voltage-gated ionic channels plays a major role for determining underlying mechanism of spike activity and predicting the neuronal behavior. Investigation is carried out based on Hodgkin-Huxley (H-H) mathematical formalism. Ionic channel gate model is discussed briefly. Relaxation phenomenon is studied in the gate variables. Then effects of temperature on dynamics of gate variables are examined. Finally voltage-clamped simulations are carried o . . .ut to determine their dynamic behaviors based on squid giant axon. In this paper, we investigate dynamics of voltage-gated ionic channels which are of great importance in integrating the information received by neurons. Understanding of dynamical behavior of voltage-gated ionic channels plays a major role for determining underlying mechanism of spike activity and predicting the neuronal behavior. Investigation is carried out based on Hodgkin-Huxley (H-H) mathematical formalism. Ionic channel gate model is discussed briefly. Relaxation phenomenon is studied in the gate variables. Then effects of temperature on dynamics of gate variables are examined. Finally voltage-clamped simulations are carried out to determine their dynamic behaviors based on squid giant axon Daha fazlası Daha az

Özer, Mahmut

Proceedings | 2003 | Mathematical and Computational Applications8 ( 1-3 ) , pp.71 - 78

In this study, phase-plane analysis is carried out for a simplified model of Purkinje cell dendrite in terms of voltage-gated ionic channels involved. State variables, nullclines and equilibrium points of the model are determined, and effects of ionic channel conductance and injected current on the shape of nullclines and the equilibrium points are investigated. In this study, phase-plane analysis is carried out for a simplified model of Purkinje cell dendrite in terms of voltage-gated ionic channels involved. State variables, nullclines and equilibrium points of the model are determined, and effects of ionic channel conductance and . . . injected current on the shape of nullclines and the equilibrium points are investigated Daha fazlası Daha az

Korkut, Şeyda | Kılıç, Muhammet Samet | Hazer, Baki

Article | 2019 | Asia-Pacific Journal of Chemical Engineering14 ( 6 ) , pp.71 - 78

A copolymer poly(methyl methacrylate-co-vinylferrocene) was synthesized and used for the first time in a biofuel cell design. Bioanaode enzyme glucose oxidase and biocathode enzyme bilirubin oxidase were physically immobilized onto the copolymer-modified electrodes. Characterization studies were conducted by scanning electron microscopy, carbon-13, fourier transform infrared and hydrogen-1 nuclear magnetic resonance, and cyclic voltammograms. The designed biofuel cell was operated with linear sweep voltammetry. The maximum current was at 45°C with 120 µg of polymer amount. An improved power density of 323 µW cm-2 that is higher than . . . other ferrocene-based fuel cells was obtained with 10-mM glucose at 0.4 V with the designed bioanode. © 2019 John Wiley & Sons Ltd Daha fazlası Daha az

Kılıç, Muhammet Samet | Korkut, Şeyda | Hazer, Baki

Article | 2017 | Electroanalysis29 ( 10 ) , pp.2377 - 2384

Newly synthesized poly(styrene-g-oleic amide) was coated onto a rhodium nanoparticle modified glassy carbon (GC) surface for the fabrication of horseradish peroxidase based biosensor used for hydrogen peroxide detection. The rhodium modifed electrode presented ten times higher signal than unmodified electrode even at low elecrtroactive enzyme quantity by enhancing the electron transfer rate at the applied potential of -0.65 V. The biosensor designed by under the optimized rhodium electrodeposition time exhibited a fast response less than 5 s, an excellent operational stability with a relative standard deviation of 0.6 % (n=6), an ac . . .curacy of 96 % and a large linear range between 50 µM and 120 mM for hydrogen peroxide. Detection limit and the sensitivity parameters were calculated to be 44 µM and 57 µA mM-1 cm-2, respectively by preserving its entire initial response up to the 15 days, while only 20 % of its initial response was lost at the end of one month. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinhei Daha fazlası Daha az

Yılmaz, Ergin | Özer, Mahmut | Baysal, Veli | Perc, Matjaž

Article | 2016 | Scientific Reports6 , pp.2377 - 2384

We study the effects of electrical and chemical autapse on the temporal coherence or firing regularity of single stochastic Hodgkin-Huxley neurons and scale-free neuronal networks. Also, we study the effects of chemical autapse on the occurrence of spatial synchronization in scale-free neuronal networks. Irrespective of the type of autapse, we observe autaptic time delay induced multiple coherence resonance for appropriately tuned autaptic conductance levels in single neurons. More precisely, we show that in the presence of an electrical autapse, there is an optimal intensity of channel noise inducing the multiple coherence resonanc . . .e, whereas in the presence of chemical autapse the occurrence of multiple coherence resonance is less sensitive to the channel noise intensity. At the network level, we find autaptic time delay induced multiple coherence resonance and synchronization transitions, occurring at approximately the same delay lengths. We show that these two phenomena can arise only at a specific range of the coupling strength, and that they can be observed independently of the average degree of the network. © The Author(s) 2016 Daha fazlası Daha az

Korkut, Şeyda | Kılıç, Muhammet Samet | Uzunçar, Sinan | Hazer, Baki

Article | 2016 | Analytical Letters49 ( 14 ) , pp.2322 - 2336

A carboxylated poly(styrene-b-isoprene-b-styrene) triblock copolymer was synthesized for the construction of an enzymatic fuel cell. Glucose oxidase and bilirubin oxidase were chemically immobilized via the carboxylated functional groups of the polymer. The enzymatic fuel cell working electrodes were modified with graphene to accelerate the electron transfer rate of the system. Essential design and operational parameters were carefully optimized for improving the power of the enzymatic fuel cell. A power density of 20 µW cm-2 with only 4 µg of immobilized bilirubin oxidase was generated from 30 mM glucose at 0.72 V. The improved enz . . .ymatic fuel cell was tested in a plant leaf. A power density of 14 nW cm-2 was generated with glucose produced by photosynthesis reactions conducted during 30 min in the leaf. © 2016, Taylor & Francis Group, LLC Daha fazlası Daha az

Özer, Mahmut

Article | 2004 | NeuroReport15 ( 9 ) , pp.1451 - 1455

We previously formulated dynamics of ion channel gates by the path probability method. In this study, we apply that theoretical approach to derive the activation rate kinetics of T-type calcium channel in thalamic relay neurons. We derive explicit expressions of the forward and backward rate constants and show that the proposed rate constants accurately capture form of the empirical time constant, and that they also provide its saturation to a constant value at depolarized membrane potentials. We also compare our derivations with linear and nonlinear thermodynamic models of rate kinetics obtained from the same calcium channel, and s . . .how that it is possible to capture saturation of the time constant for the depolarized membrane potentials by the only proposed rate constants. © 2004 Lippincott Williams & Wilkins Daha fazlası Daha az

Erem, Fundagül | İnan, Mehmet | Karakaş Budak, Barçın | Certel, Muharrem

Article | 2020 |

The aim of this study was to purify and characterize the peptidase of Bacillus amyloliquefaciens (Fukumoto) (strain FE-K1) isolated from ropey bread. Peptidases were purified from crude enzyme solution by affinity chromatography with an efficiency of 25 % and a purification coefficient of 1.53. The optimum pH of partially purified peptidase (PPPase) solution was determined as 7.5 and the peptidases retained approximately 90 % of their initial activity in the pH range 7.0-8.5 following incubation at 37°C for 2 h. The optimum temperature for the PPPase was 60°C. The approximate molecular weight of the PPPase was determined as 36 kDa. . . .Inactivation of the PPPase in the presence of O-FEN and EDTA showed them to be metallopeptidases and 5 mM of K+1 and 5 mM of Mn+2 ions increased the enzyme activity by 4 % and 6.15 %, respectively. The presence of Hg+2, Fe+3 and SDS (0.1-1.0 % w/v) caused inactivation whereas the enzyme retained most of its activity in the presence of 0.1-1.0 % (v/v) Triton X-100, Tween 20 and Tween 80 and 1-20 % (v/v) xylene, ethanol, acetone and acetonitrile. Characterization of the PPPase revealed the enzyme as a neutral serine metallopeptidase compatible with some organic solvents and surfactants Daha fazlası Daha az

Erem, Fundagül | İnan, Mehmet | Certel, Muharrem

Article | 2018 |

In this study, it was aimed to optimise the extracellular peptidase production of Bacillus amyloliquefaciens FE-K1, previously isolated from ropy wholemeal bread, by using response surface methodology (RSM) based on central composite design (CCD). The temperature (20-45°C), initial pH of the enzyme production medium (pH 5-9) and inoculation level (1-5%, v/v) were used as the factors for RSM, and the fermentation time was determined for each trial separately. Results showed that the optimum peptidase production occurred at 33.4°C, pH 6.62 and 2.3% inoculation. It was determined that the fermentation time was only 7h, the crude enzyme . . . had a peptidase activity of 49.17U/mL and a specific activity of 504.77U/mg under the optimised conditions Daha fazlası Daha az

Korkut, Şeyda | Uzunçar, Sinan | Kılıç, Muhammet Samet | Hazer, Baki

Article | 2016 | Instrumentation Science and Technology44 ( 6 ) , pp.614 - 628

A novel continuous flow biosensor based on gold nanoparticles and poly(propylene-co-imidazole) was developed for the online determination of p-benzoquinone. The amperometric response was measured as a function of p-benzoquinone concentration at an applied potential of -50 mV. The hydrogen peroxide concentration was optimized and fixed at 1 mM in samples. The mass transfer resistance of the copolymer film was minimized, and the flow cell was regenerated quickly at 1 mL/min. The resulting device provided good analytical performance based on a linear dynamic range from 5–100 µM, a short response time of 3 s, a detection limit of 3.3 µM . . ., excellent repeatability with a relative standard deviation of 0.82%, long-term stability of 95% after four weeks, and an accuracy of 105%. The gold nanoparticles enhanced the electron transfer rate on the electrode. The apparent Michaelis-Menten constant was 4 mM, showing that the enzyme retained catalytic specificity and provided high activity for p-benzoquinone. © 2016, Taylor & Francis Daha fazlası Daha az

Korkut, Şeyda | Uzunçar, Sinan | Kılıç, Muhammet Samet | Hazer, Baki

Article | 2019 | Instrumentation Science and Technology47 ( 1 ) , pp.1 - 18

A new amperometric urea biosensor based on gold nanoparticle embedded poly(propylene-co-imidazole) was developed for the determination of urea. The urease adsorbed on the polymeric film catalyzed the hydrolysis of urea to ammonium and bicarbonate ions and the ammonium was then electrooxidized on the gold electrode with the aid of gold nanoparticles at +0.2 V versus Ag/AgCl using differential pulse voltammetry. The biosensor provided a linear current response to urea concentration from 0.1 to 30 mM, a detection limit of 36 µM, a relative standard deviation of 2.43% (n = 18), and excellent storage stability, as the current decrease wa . . .s only 3% after 75 days. The operation of the biosensor was evaluated by the analysis of municipal sewage wastewater collected from the inlet pipe of the treatment plant of Zonguldak City in Turkey. The effects of possible interferants were also characterized. © 2018, © 2018 Taylor & Francis Daha fazlası Daha az

Özer, Mahmut

Article | 2012 | Yükseköğretim ve Bilim Dergisi2 ( 1 ) , pp.10 - 13

Son yıllarda dünya genelinde sayıları üç milyonun üzerinde olan uluslararası öğrencileri kendi ülkelerinin yükseköğretim kurumlarına alabilmek için ülkeler kıyasıya rekabet etmektedirler. Uluslararası öğrenciler, artık yükseköğretim sistemleri ve kurumlarının uluslararasılaşma boyutlarının en önemli göstergelerinden birisini oluşturmaktadır. Bu bağlamda, yükseköğretim sistemimiz ve kurumlarımızın bu göstergesinin ne durumda olduğunun tespiti, oldukça büyük bir genişleme yaşayan yükseköğretim sistemimiz açısından büyük önem arz etmektedir. Bu çalışmada, ülkemizdeki uluslararası öğrencilerin durumu ele alınmaktadır There are over thre . . .e million international students worldwide, and in recent years higher education institutions compete with each other in order to receive these students to their institutions. International students are now one of the most important indicator of the internationalization of the higher education systems and institutions. In this context, the detection of the status of this indicator in our higher education system and institutions is of great importance as our higher education system shows a large expansion. This study, discusses the status of international students in our countr Daha fazlası Daha az