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

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

Article | 2016 | Scientific Reports6 , pp.71 - 78

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

Köksal, Kerem | Surucu, Dilek | Surucu, Murat | Hacıoğlu, Rıfat

Proceedings | 2014 | 2014 22ND SIGNAL PROCESSING AND COMMUNICATIONS APPLICATIONS CONFERENCE (SIU) , pp.646 - 649

In this study, it is aimed to follow a visual route by an Unmanned Aerial Vehicle (UAV). The recognition of the predetermined line by using image processing algorithms and the process of following the route by using the method of Tangent Vector Field Guidance (TVFG) have been performed in indoor and outdoor experiments. UAV's following the correct route has been ensured by calculating the deflection caused by some factors such as wind and light which adversely affect the flight of UAV. In Vector Field Guidance method, the direction angles calculated by using the vector fields that will follow the line-shaped guide path are used. Whe . . .n the path to be followed has more than one direction instead of a single straight line, it is divided into sections which consist of straight lines, and by prioritizing these lines, the most dominant line is followed. In this study, it is aimed to provide a dynamic model by considering the tracking errors. As a result of the process adopted, UAV's autonomous flight is achieved by using the visual inputs and TVFG method, and the external disturbing factors are investigated Daha fazlası Daha az

Altan, Aytaç | Bayraktar, Köksal | Hacıoğlu, Rıfat

Proceedings | 2016 | 2016 24th Signal Processing and Communication Application Conference, SIU 2016 - Proceedings , pp.1433 - 1436

In this stuidy, the position information from ultrasound sensors on UAV related to floor gallery mine passed through the filter, it is aimed to control the position of simultaneously creating the optimum environmental map. The simultaneous in galleries made mapping, mine the data of air to the designated central monitoring system with real-time location information is transmitted to the ventilation system, which is intended to more effectively work in the mines. The gallery maps which simultaneous location and mapping information obtained by UAV Extended Kalman Filter algorithms processed were obtained experimentally. © 2016 IEEE.

Karasu, Seçkin | Altan, Aytaç | Saraç, Zehra | Hacıoğlu, Rıfat

Proceedings | 2017 | 2017 25th Signal Processing and Communications Applications Conference, SIU 2017 , pp.1433 - 1436

In this study, the wind speed prediction model is created that gives a minimum error for different hidden layer neuron numbers and delay step numbers. Using the one-minute time series, the prediction of the next wind speed is performed with the NAR neural network model. The predicted values of wind speed obtained are compared with predicted values of wind speed obtained with filter methods. For different window functions and lengths, wind speed prediction is made using filters with different weight coefficients. For the number of hidden layer neurons is 14 and the number of delay steps is 10, MAE, MSE and RMSE values are calculated . . .as 0.0315, 0.0019, 0.0445, respectively, with NAR neural network. It is seen that the proposed method for the wind speed dataset has a higher prediction performance than thefilter methods. © 2017 IEEE Daha fazlası Daha az

Onur, Tuğba Özge | Hacıoğlu, Rıfat

Proceedings | 2017 | 2017 25th Signal Processing and Communications Applications Conference, SIU 2017 , pp.1433 - 1436

Reverberation and multipath propagation afîect the accuracy of time of flight (TOF) estimation in confined underwater medium. In this paper, time delay has been estimated by obtaining the transmitted signal and first echo signal from measured signal acquised by using a wideband transducer with 5 MHz central frequency. Cross-correlation (CC) and generalized cross-correlation (GCC) methods have been applied to the obtained signals and their performances have been compared. The results show that GCC method has better performance for time delay estimation in confined underwater medium where multipath propagation and reverberation are se . . .vere. © 2017 IEEE 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

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

Onur, Tuğba Özge | Hacıoğlu, Rıfat

Proceedings | 2016 | 2016 24th Signal Processing and Communication Application Conference, SIU 2016 - Proceedings , pp.821 - 824

In this paper, two different methods are suggested in order to provide image enhancement in ultrasonic B-mode imaging. By obtaining RF data from two different phantom used to form B-mode image, their spectral characteristics were observed. Then by forming RF envelope from obtained data, conversion of envelope to color image is provided. Logarithmic compression and histogram equalization methods found in literature are used to improve image quality. From the results obtained, it is observed that both algorithms are effective based on the intended use when they are applied individually. © 2016 IEEE.

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