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

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

Article | 2016 | Scientific Reports6 , pp.1091 - 1104

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

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

Özer, Mahmut | Graham, Lyle J. | Erkaymaz, Okan | Uzuntarla, Muhammet

Article | 2007 | NeuroReport18 ( 13 ) , pp.1371 - 1374

Cortical neurons in-vivo operate in a continuum of overall conductance states, depending on the average level of background synaptic input throughout the dendritic tree. We compare how variability, or fluctuations, in this input affects the statistics of the resulting 'spontaneous' or 'background' firing activity, between two extremes of the mean input corresponding to a low-conductance (LC) and a high-conductance (HC) state. In the HC state, we show that both firing rate and regularity increase with increasing variability. In the LC state, firing rate also increases with input variability, but in contrast to the HC state, firing re . . .gularity first decreases and then increases with an increase in the variability. At high levels of input variability, firing regularity in both states converge to similar values. © 2007 Lippincott Williams & Wilkins, Inc Daha fazlası Daha az

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

Article | 2016 | Science China Technological Sciences59 ( 3 ) , pp.364 - 370

An autapse is an unusual synapse that occurs between the axon and the soma of the same neuron. Mathematically, it can be described as a self-delayed feedback loop that is defined by a specific time-delay and the so-called autaptic coupling strength. Recently, the role and function of autapses within the nervous system has been studied extensively. Here, we extend the scope of theoretical research by investigating the effects of an autapse on the transmission of a weak localized pacemaker activity in a scale-free neuronal network. Our results reveal that by mediating the spiking activity of the pacemaker neuron, an autapse increases . . .the propagation of its rhythm across the whole network, if only the autaptic time delay and the autaptic coupling strength are properly adjusted. We show that the autapse-induced enhancement of the transmission of pacemaker activity occurs only when the autaptic time delay is close to an integer multiple of the intrinsic oscillation time of the neurons that form the network. In particular, we demonstrate the emergence of multiple resonances involving the weak signal, the intrinsic oscillations, and the time scale that is dictated by the autapse. Interestingly, we also show that the enhancement of the pacemaker rhythm across the network is the strongest if the degree of the pacemaker neuron is lowest. This is because the dissipation of the localized rhythm is contained to the few directly linked neurons, and only afterwards, through the secondary neurons, it propagates further. If the pacemaker neuron has a high degree, then its rhythm is simply too weak to excite all the neighboring neurons, and propagation therefore fails. © 2016, Science China Press and Springer-Verlag Berlin Heidelberg 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

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

Özer, Mahmut | Provaznik, Ivo

Article | 2005 | JOURNAL OF THEORETICAL BIOLOGY233 ( 2 ) , pp.237 - 243

The precise form of the rate constant functions of ion channels is very crucial for reproducing the electrophysiological behavior. Therefore, how well they account for experimental data plays an important role in the behavior of the model. In this study, we derive kinetic coefficients of activation and inactivation gates in ion channels by Onsager reciprocity theorem for an ensemble of gating particles, and propose that the obtained kinetic coefficients can be used as a comparative tool for the empirical validity of fitted rate constant functions to experimental data. We also illustrate its applicability based on the activation and . . .inactivation kinetics of T-type calcium channel in thalamic relay neurons. We show that the shape of the steady-state curve by itself seems to be a poor indicator of the functional form of the rate functions, but the time constant curves reflect considerable variation depending on the particular form of the rate functions, and that the kinetic coefficients related to the time constants provide a powerful tool to determine the empirical validity of the fitted rate constants. (C) 2004 Elsevier Ltd. All rights reserved Daha fazlası Daha az

Altan, Aytaç | Köksal, Kerem | Hacıoğlu, Rıfat

Article | 2017 | Karaelmas Fen ve Mühendislik Dergisi7 ( 1 ) , pp.218 - 227

Bu çalışmada, görsel çizgi (rota) takibi için İnsansız Hava Aracı (İHA) üzerinde bulunan 3 eksenli yalpanın dış bozucu etki altında model öngörülü denetimi gerçekleştirilmektedir. İHA ile görsel çizgi takibi için Tanjant Vektör Alan Kılavuz (TVAK) yöntemi kullanılmaktadır. Dış ortam ve kapalı ortamda yapılan testlerde, ön tanımlaması yapılan çizginin görüntü işleme algoritmalarıyla tespiti ve sonrasında TVAK yöntemi kullanılarak rota takip işlemi gerçekleştirilmektedir. İHA’nın alçak ve yüksek irtifa uçuşlarında rota takibi başarım oranları deneysel olarak gözlemlenmektedir. Elde edilen sonuçlar PID denetime sahip yalpadan elde edil . . .en veriler ile karşılaştırılmaktadır. Dış bozucu etki altında TVAK yöntemi ile rota takibi için İHA üzerindeki 3 eksenli yalpanın MPC denetiminde PID ile denetime göre başarılı sonuçlar elde edilmektedir. In this study, Model Predictive Control (MPC) is performed under the external disturbance effect of the 3-axis gimbal on the Unmanned Aerial Vehicle (UAV) for visual line tracking. The Tangent Vector Fields Guide (TVFG) method is used for visual line tracking with UAV. In the tests performed in the outdoor and indoor environments, the pre-defined line is detected with the image processing algorithms and then the line tracking process is performed using the TVFG method. The visual line tracking success rates in the low and high altitude of UAV flight are observed experimentally. The obtained results are compared with data obtained by the gimbal having PID control. The successful results are obtained with MPC control according to PID control of 3 axis gimbal on UAV under external disturbance for visual line tracking using TVFG method Daha fazlası Daha az

Onur, Tuğba Özge | Carlson, Johan E. | Svanström, Erika | Hacıoğlu, Rıfat

Article | 2017 | Erzincan Üniversitesi Fen Bilimleri Enstitüsü Dergisi10 ( 1 ) , pp.138 - 147

Elastik dalgalar, sadece gaz ve sıvılarda değil aynı zamanda katılarda da yayılırlar. Katılar, sıvı ve gazlarda olmayan form elastisitesine sahip olduğundan, katıların elastik özellikleri farklıdır. Bu nedenle, sadece boylamsal dalgalar değil aynı zamanda diğer dalgalar da katılarda yayılabilir. Katı içinde yayılan dalgalar kullanılarak hedefin konumu hakkında bilgi edinilebilir. Bu çalışmada ince düzlemlerde tek transdüktör kullanılarak ultrasonik dalga yayılımının modellenmesi yapılarak, uyarlamalı algoritma ile hedef uzaklığı kestirilmektedir. Elde edilen sonuçlarda, modellenen dalga yayılımında ultrasonik dalganın hızı ile birli . . .kte zaman gecikmesi uyartım noktasının sensöre olan uzaklığı ile ilintili olduğu için, uyarlamalı algoritma ile darbe cevabı başlangıç noktası belirlenerek hedef konumunun tespit edilebildiği görülmektedir. Elastic waves propagate not only in gases and liquids but also in solids. The elastic properties of solids are different since they have form elasticity which liquids and gases don't have. Because of this reason, not only longitudinal waves but also other waves can propagate in solids. Waves propagating in solids can be used to get information about target location. In this paper, modelling of ultrasonic wave propagation in thin plates is investigated by using a single transducer and target distance is estimated with adaptive algorithm. According to the obtained results, it can be seen that target location can be estimated by detecting the starting point of the impulse response with adaptive algorithm since the delay along with the velocity of ultrasound wave in the modelled wave propagation is related to the distance between the excitation point and sensor Daha fazlası Daha az

Onur, Tuğba Özge | Carlson, Johan E | Svanström, Erika | Hacıoğlu, Rıfat

Article | 2019 | Iranian Journal of Science and Technology - Transactions of Electrical Engineering43 ( 3 ) , pp.405 - 413

This paper demonstrates how flexural wave propagation in a thin plate can be modeled by estimating the combined effect of the excitation source signal and the impulse response of the ultrasonic sensor. The wave propagation in the plate is modeled using the wave equation for the flexural wave mode. A theoretical model for flexural wave propagation in thin plates has been derived, and it has been compared with measurements excited by tapping gently on the surface. The combined effects of the excitation source signal and the impulse response of the low-cost piezoelectric sensor are modeled using finite-impulse response and/or infinite- . . .impulse response filters. Thereafter, the performances of the selected filters are compared on estimating the wave propagation in a thin quartz glass plate. Results indicate that the most accurate estimation of wave propagation has been obtained using a linear phase filter which attributes all dispersions to the flexural wave. © 2018, Shiraz University Daha fazlası Daha az

Onur, Tuğba Özge | Hacıoğlu, Rıfat

Article | 2017 | Turkish Journal of Electrical Engineering and Computer Sciences25 ( 2 ) , pp.939 - 949

We investigated adaptive algorithms for a Hammerstein block structure in which a static nonlinear block and dynamic linear block are cascaded. The approach considered here is to use generalized orthonormal basis functions in a Hammerstein block structure by using xed pole lter banks. We applied the normalized least mean square approach to the developed adaptive algorithm in order to acquire Hammerstein block structure parameters. Performance comparison of the proposed approach was investigated considering convergence speed and parametric complexity for acoustic echo cancellation application. The results indicated that in the develop . . .ed algorithm along with appropriate selection of xed poles, the algorithm convergences faster and less parametric complexity is provided when compared to direct adaptive Hammerstein algorithms with IIR and FIR linear blocks. We investigated adaptive algorithms for a Hammerstein block structure in which a static nonlinear block and dynamic linear block are cascaded. The approach considered here is to use generalized orthonormal basis functions in a Hammerstein block structure by using xed pole lter banks. We applied the normalized least mean square approach to the developed adaptive algorithm in order to acquire Hammerstein block structure parameters. Performance comparison of the proposed approach was investigated considering convergence speed and parametric complexity for acoustic echo cancellation application. The results indicated that in the developed algorithm along with appropriate selection of xed poles, the algorithm convergences faster and less parametric complexity is provided when compared to direct adaptive Hammerstein algorithms with IIR and FIR linear blocks Daha fazlası Daha az