Yılmaz, Ergin | Baysal, Veli | Özer, Mahmut

Article | 2015 | Physics Letters, Section A: General, Atomic and Solid State Physics379 ( 26-27 ) , pp.1594 - 1599

We investigate the effects of time-periodic coupling strength on the temporal coherence or firing regularity of a scale-free network consisting of stochastic Hodgkin-Huxley (H-H) neurons. The temporal coherence exhibits a resonance-like behavior depending on the cell size or the channel noise intensity. The best temporal coherence requires an optimal channel noise intensity, and this coherence can be significantly increased by time-periodic coupling strength when its frequency matches the integer multiples of the intrinsic subthreshold oscillation frequency of H-H neuron. Particularly, we find the multiple-coherence resonance depend . . .ing on frequency of time-periodic coupling strength at the optimal noise intensity. We also obtain a resonance-like dependence of temporal coherence on the amplitude of time-periodic coupling strength. Additionally, we investigate the effects of average degree on the temporal coherence and find that the temporal coherence exhibits a resonance-like behavior with respect to the network average degree, indicating that the best regularity requires an optimal average degree. © 2015 Elsevier B.V. All rights reserved Daha fazlası Daha az

Uzuntarla, Muhammet | Yılmaz, Ergin | Wagemakers, Alexandre | Özer, Mahmut

Article | 2015 | Communications in Nonlinear Science and Numerical Simulation22 ( 01.Mar ) , pp.367 - 374

Vibrational resonance (VR) is a phenomenon whereby the response of some dynamical systems to a weak low-frequency signal can be maximized with the assistance of an optimal intensity of another high-frequency signal. In this paper, we study the VR in a heterogeneous neural system having a complex network topology. We consider a scale-free network of neurons where the heterogeneity is in the intrinsic excitability of the individual neurons. It is shown that emergence of VR in heterogeneous neuron population requires less energy than a homogeneous population. We also find that electrical coupling strength among neurons plays a key role . . . in determining the weak signal processing capacity of the heterogeneous population. Lastly, we investigate the influence of interneuronal link density on the VR and demonstrate that the energy needed to obtain the resonance grows with the increase in average degree. © 2014 Elsevier B.V Daha fazlası Daha az

Yılmaz, Ergin | Özer, Mahmut

Article | 2015 | Physica A: Statistical Mechanics and its Applications421 , pp.455 - 462

We study the effect of the delayed feedback loop on the weak periodic signal detection performance of a stochastic Hodgkin-Huxley neuron. We consider an electrical autapse characterized by its coupling strength and delay time. The stochastic Hodgkin-Huxley neuron exhibits subthreshold oscillations, and thus has an intrinsic time scale with the subthreshold oscillations. Therefore, we investigate the interplay of the subthreshold oscillations, coupling strength and delay time on the weak periodic signal detection. Results indicate that the delayed feedback either enhances or suppresses the weak signal detection depending on its param . . .eters, when compared to that without the feedback. The delayed feedback augments the weak periodic signal detection for the optimal values of the intrinsic noise and the coupling strength when the delay time is close to the integer multiples of the period of the intrinsic oscillations, due to the multiple resonance among the weak signal, the intrinsic oscillations, and the delayed feedback. We analyze the interspike interval histograms and show that the delayed feedback enhances or suppresses the weak periodic signal detection by increasing or decreasing the phase locking (synchronization) between the spiking and the weak periodic signal. We also show that an optimal phase locking is obtained when the delay time is close to the period of the intrinsic oscillations, leading a single dominant time scale in the spike trains. © 2014 Elsevier B.V. All rights reserved Daha fazlası Daha az

Özer, Mahmut | Ekmekçi, N. Hakan

Article | 2005 | Physics Letters, Section A: General, Atomic and Solid State Physics338 ( 2 ) , pp.150 - 154

Ion channel noise that stems from the stochastic nature of the channel has important effects on neuronal dynamics. In this context, we examine the effect of the channel noise on the time-course of recovery from inactivation of sodium channels by using a stochastic extension of the Hodgkin-Huxley model. We show that the channel noise provides both some amount of the non-inactivated channels and a smaller time-course for recovering from inactivation leading to an increased maximal sodium conductance compared to deterministic one. © 2005 Elsevier B.V. All rights reserved.

Altın, Süreyya | Demircioğlu, Nuhi | Peker, İbrahim | Altın, Ahmet

Article | 2007 | Colloids and Surfaces A: Physicochemical and Engineering Aspects306 ( 1-3 SPEC. ISS. ) , pp.14 - 21

In this study, the effects of the acceptor phase and the donor phase properties on sodium ion transport were examined in bulk liquid membrane systems. In the experiments, toluene and a mixture of toluene-dichloromethane (90-10%, v/v) containing 1 × 10-3 M DB18C6 (dibenzo18crown6) was used as the membrane. In order to examine the effects of different the acceptor phases, firstly H2SO4, HCl, HNO3, CH3COOH and distilled water were used as the acceptor phases. Furthermore, the experiments were performed by using various acid concentrations such as 2, 0.2 and 0.02 M of acids, as the acceptor phase. In the second part of the study, the ef . . .fect of donor phase on sodium ion transport was examined. For this examination, Na2SO4, NaNO3, NaOH and NaCl were applied. In order to determine the effect of the donor phase concentration, the experimentation was performed using 1.08 × 10-2, 2.17 × 10-2, 3.26 × 10-2 and 4.34 × 10-2 M concentrations of Na+ in form of NaCl. Finally, nonsteady-state kinetics was applied on all data obtained from the experiments and reaction constants (k1, k2, and k3) and the values of the Rmax, tmax, k1/k2 were calculated. Consequently, it was determined that the type and the concentration of the acceptor phase and the donor phase solutions were significant for transport efficiency in liquid membrane systems. The most efficient transport was obtained by applying 2 M H2SO4 and 2.17 × 10-2 M Na+ in form of NaCl. Besides, It was observed that there was a significant effect of the anion attached to the cation on transport efficiency. © 2007 Elsevier B.V. All rights reserved Daha fazlası Daha az