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

Article | 2019 | Asia-Pacific Journal of Chemical Engineering14 ( 6 )

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

Akbuğday, Burak | Yılmaz, Ergin

Proceedings | 2019 | TIPTEKNO 2019 - Tip Teknolojileri Kongresi

Obstructive sleep apnea defined as a medical condition caused by loss of muscle tone in upper airway dilator muscles. There are various treatment methods exist for this condition both invasive and non-invasive, but they all have their weaknesses and strengths. Electrical stimulation method seems to be the most promising non-invasive method in terms of efficiency and adherence rate. This study introduces a low-cost, easy-to-use and wireless novel device to treat obstructive sleep apnea based on electrical stimulation method. The developed device uses an accelerometer to track respiration and apnea episodes and when an apnea episode i . . .s detected delivers a small electric current to dilator muscles to make them regain their muscle tone, thus treating obstructive sleep apnea. The device also communicates with a smartphone application to keep a recording of respiration and apnea data to enable further studying of data by medical professionals and researchers. © 2019 IEEE Daha fazlası Daha az

Palabaş, Tuğba | Gürleyen, Hatice Hilal | Uzuntarla, Muhammet

Proceedings | 2019 | TIPTEKNO 2019 - Tip Teknolojileri Kongresi

It is known that activity is terminated abruptly as a result of strong synchronization in bistable neuron populations when there is sufficient current stimulation. The aim of this study is to investigate the effect of ion channel blocking on the phenomenon of spontaneous termination of ongoing activity in the bistable neural network connected by excitatory chemical synapses using stochastic Hodgkin-Huxley (H-H) equations. The obtained results show that significant changes in the dynamics of neurons occur due to the blocking of potassium ion channels at different rates depending on the coupling strength. As the coupling of synaptic i . . .nteraction increases, the synchronization between neurons increases and the activity terminates. Simulation results showed that sodium ion channels are not effective on this phenomenon. © 2019 IEEE Daha fazlası Daha az

Çilli, Salih | Çalım, Ali | Uzuntarla, Muhammet

Proceedings | 2019 | TIPTEKNO 2019 - Tip Teknolojileri Kongresi

Vital functions in living organisms occur through changes in electrical activity. These activities consist of brain rhythms with different frequencies that exhibit oscillatory behavior and can be monitored by local field potentials or EEG recordings. The synchronization of neural activity underlies the emergence of these rhythmic waves, which are of great importance in the nervous system. In this study, the effects of changes in intrinsic mechanisms and intercellular communication, that are constituting neural activity, on the synchronization of neuron pair which is composed of two nerve cells and connected with different types of s . . .ynaptic junction were investigated in a biologically meaningful way. The obtained results showed that the excitability, synaptic and ionic conductivity levels are crucial for neurons to synchronize. It has also been found that the noise caused by the stochastic nature of the ion channels is an auxiliary biological component to achieve synchronization. © 2019 IEEE Daha fazlası Daha az

Uzuntarla, Muhammet

Article | 2019 | Neurocomputing367 , pp.328 - 336

We study the firing behavior of bistable neurons that are coupled by both electrical and chemical synapses, constituting a hybrid coupled population. We use stochastic Hodgkin–Huxley model neurons for the dynamics of individual bistable units within the population and the connectivity is implemented with a scale-free network topology which is a widely used network paradigm in theoretical studies of neural circuits. By analyzing the electrical activity of both whole population and individual neurons, it is shown that population mean firing rate exhibits a non-monotonic behavior in the space of electrical and chemical coupling strengt . . .hs. We identify dynamical mechanisms that shape such non-monotonic spiking behavior and show that different types of population spiking patterns can emerge by fine-tuning the coupling strengths of electrical and chemical synapses. Furthermore, we map the transitions between observed dynamical states in the parameter space of interest depending on the level of individual neuron bistability, existence probability of a synapse type and intrinsic ion channel noise. © 2019 Elsevier B.V Daha fazlası Daha az

Uzuntarla, Muhammet | Torres, Joaquin J. | Çalım, Ali | Barreto, Ernest

Article | 2019 | Neural Networks110 , pp.131 - 140

We observe and study a self-organized phenomenon whereby the activity in a network of spiking neurons spontaneously terminates. We consider different types of populations, consisting of bistable model neurons connected electrically by gap junctions, or by either excitatory or inhibitory synapses, in a scale-free connection topology. We find that strongly synchronized population spiking events lead to complete cessation of activity in excitatory networks, but not in gap junction or inhibitory networks. We identify the underlying mechanism responsible for this phenomenon by examining the particular shape of the excitatory postsynaptic . . . currents that arise in the neurons. We also examine the effects of the synaptic time constant, coupling strength, and channel noise on the occurrence of the phenomenon. © 2018 Elsevier Lt Daha fazlası Daha az

Erkan, Yasemin | Saraç, Zehra | Yılmaz, Ergin

Article | 2019 | Nonlinear Dynamics95 ( 4 ) , pp.3411 - 3421

By virtue of recent developments in brain measurement technology, it is now recognized that information processing in brain includes not only neurons but also astrocytes. For this reason, to illustrate the effects of astrocyte on information processing in neuronal systems, we research the weak signal detection performance of the Hodgkin–Huxley neuron under the effect of astrocyte. It is found that the weak signal detection performance of the neuron exhibits the stochastic resonance phenomenon depending on noise intensity, where the presence of astrocyte with an optimal coupling strength significantly increases the detection performa . . .nce of the neuron when compared the one without astrocyte. The obtained results also reveal that there is an optimal weak signal frequency ensuring the best detection performance. Besides, we show that the colored noise exhibits a better performance than white Gaussian noise on improving the weak signal detection capacity of the neuron; moreover, the weak signal detection performance of the neuron demonstrates a resonance-like dependence on the correlation time of the noise. Finally, we investigate the effects of calcium channel noise. Although the calcium channel noise generally reduces the weak signal detection performance of the neuron, the optimal coupling strength warranting the best detection performance critically depends on its intensity. © 2019, Springer Nature B.V Daha fazlası Daha az

Baysal, Veli | Saraç, Zehra | Yılmaz, Ergin

Article | 2019 | NONLINEAR DYNAMICS97 ( 2 ) , pp.1275 - 1285

Chaotic Resonance (CR), whereby the response of a nonlinear system to a weak signal can be enhanced by the assistance of chaotic activities that can be intrinsic or extrinsic, has recently been studied widely. In this paper, the effects of extrinsic chaotic signal on the weak signal detection performance of the Hodgkin-Huxley neuron are examined via numerical simulation. The chaotic signal has been derived from Lorenz system and is injected to neuron as a current. Obtained results have revealed that the H-H neuron exhibits CR phenomenon depending on the chaotic current intensity. Also, we have found an optimal chaotic current intens . . .ity ensuring the best detection of the weak signal in H-H neuron via CR. In addition, we have calculated the maximal Lyapunov exponent to determine whether the H-H neuron is in chaotic regime. After determining the state of the neuron, we have shown that the H-H neuron can be able to detect the weak signal even if it is in the chaotic regime. Finally, we have investigated the effects of chaotic activity on the collective behavior of H-H neurons in small-world networks and have concluded that CR effect is a robust phenomenon which can be observed both in single neurons and neuronal networks Daha fazlası Daha az

Korkut, Şeyda | Göl, Saliha | Kılıç, Muhammet Samet

Article | 2019 | Electroanalysis , pp.1275 - 1285

A biosensor based on conductive poly(pyrrole-co-pyrrole-2-carboxylic acid) [Poly(Py-co-PyCOOH)] copolymer film coated gold electrode was developed for the quantitative phosphate determination. Enzyme pyruvate oxidase was immobilized chemically via the functional carboxylated groups of the copolymer. The potential to be applied which is deficiency of phosphate biosensor studies for precise phosphate detection was clarified by using differential pulse voltammetry technique. Performance of the sensing ability of the biosensor was improved by optimizing cofactor/cosubstrate concentrations, polymeric film density and pH. The biosensor sh . . .owed a linearity up to phosphate concentration of 5 mM, operational stability with a relative standard deviation (RSD) of 0.07 % (n=7) and accuracy of 101 % at -0.15 V (vs. Ag/AgCl). Detection limit (LOD) and sensitivity were calculated to be 13.3 µM and 5.4 µA mM-1 cm-2, respectively by preserving 50 % of its initial response at the end of 30 days. It's performance was tested to determine phosphate concentrations in two streams of Zonguldak City in Turkey. Accuracy of phosphate measurement in stream water was found to be 91 %. © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinhei Daha fazlası Daha az

Ağaoğlu, Şükrüye Nihal | Çalım, Ali | Hövel, Philipp | Özer, Mahmut | Uzuntarla, Muhammet

Article | 2019 | Neurocomputing325 , pp.59 - 66

We investigate the phenomenon of vibrational resonance (VR) in neural populations, whereby weak low-frequency signals below the excitability threshold can be detected with the help of additional high-frequency driving. The considered dynamical elements consist of excitable FitzHugh–Nagumo neurons connected by electrical gap junctions and chemical synapses. The VR performance of these populations is studied in unweighted and weighted scale-free networks. We find that although the characteristic network features – coupling strength and average degree – do not dramatically affect the signal detection quality in unweighted electrically . . .coupled neural populations, they have a strong influence on the required energy level of the high-frequency driving force. On the other hand, we observe that unweighted chemically coupled populations exhibit the opposite behavior, and the VR performance is significantly affected by these network features whereas the required energy remains on a comparable level. Furthermore, we show that the observed VR performance for unweighted networks can be either enhanced or worsened by degree-dependent coupling weights depending on the amount of heterogeneity. © 2018 Elsevier B.V Daha fazlası Daha az