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

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

Article | 2016 | Scientific Reports6

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

Tığlı-Aydın, Rahime Seda | Hazer, Baki | Acar, Merve | Gümüşderelioğlu, Menemşe

Article | 2013 | Polymer Bulletin70 ( 7 ) , pp.2065 - 2082

A novel biocompatible copolymer membrane was synthesized and characterized for use in guided bone regeneration using polymeric soybean oil-g-polystyrene (PSO-g-PS) graft copolymer which was successfully obtained by free radical polymerization of styrene initiated by PSO peroxide as a macroinitiator at 80 C. Osteoblastic cellular activities of MC3T3-E1 cells on PSO-g-PS membranes with different soybean oil composition (PSO-g-PS1, PSO-g-PS2, and PSO-g-PS3) were evaluated. Nuclear magnetic resonance (1H NMR) spectra showed that PSO inclusion (mol%) was found to be 27, 69, and 51 % for PSO-g-PS1, PSO-g-PS2, and PSO-g-PS3 membranes, resp . . .ectively. Superior biocompatibility of the PSO-g-PS membranes was determined compared to polystyrene tissue culture plates (TCPS) as positive control. Cell proliferation was enhanced on PSO-g-PS2 and PSO-g-PS3 membranes compared to PSO-g-PS1 membranes (p < 0.001), and a statistically significant higher ALP value of MC3T3-E1 cells on PSO-g-PS2 membranes (p < 0.05) suggested that proliferation and differentiation of preosteoblastic on PSO-g-PS membranes were enhanced with regard to soybean oil content within the membranes. Thus, the present study suggests that PSO-g-PS2 membranes, which showed a favorable biological environment for the preosteoblastic cells, can be well suited for bone tissue engineering applications. © 2013 Springer-Verlag Berlin Heidelberg Daha fazlası Daha az

Allı, Sema | Tığlı-Aydın, Rahime Seda | Allı, Abdülkadir | Hazer, Baki

Article | 2015 | JAOCS, Journal of the American Oil Chemists' Society92 ( 3 ) , pp.449 - 458

Well-defined graft copolymers based on poly(?-caprolactone) (PCL) via poly(linoleic acid) (PLina), are derived from soybean oil. Poly(linoleic acid)-g-poly(?-caprolactone) (PLina-g-PCL) and poly(linoleic acid)-g-poly(styrene)-g-poly(?-caprolactone) (PLina-g-PSt-g-PCL) were synthesized by ring-opening polymerization of ?-caprolactone initiated by PLina and one-pot synthesis of graft copolymers, and by ring-opening polymerization and free radical polymerization by using PLina, respectively. PLina-g-PCL, PLina-g-PSt-g-PCL3, and PLina-g-PSt-g-PCL4 copolymers containing 96.97, 75.04 and 80.34 mol% CL, respectively, have been investigated . . . regarding their enzymatic degradation properties in the presence of Pseudomonas lipase. In terms of weight loss, after 1 month, 51.5% of PLina-g-PCL, 18.8% of PLina-g-PSt-g-PCL3, and 38.4% of PLina-g-PSt-g-PCL4 were degraded, leaving remaining copolymers with molecular weights of 16,140, 83,220 and 70,600 Da, respectively. Introducing the PLina unit into the copolymers greatly decreased the degradation rate. The molar ratio of [CL]/[Lina] dramatically decreased, from 21.3 to 8.4, after 30 days of incubation. Moreover, reduced PCL content in PLina-g-PSt-g-PCL copolymers decreased the degradation rate, probably due to the PSt enrichment within the structure, which blocks lipase contact with PCL units. Thus, copolymerization of PCL with PLina and PSt units leads to a controllable degradation profile, which encourages the use of these polymers as promising biomaterials for tissue engineering applications. © AOCS 2015 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

Yılmaz, Ergin | Özer, Mahmut

Article | 2013 | Physics Letters, Section A: General, Atomic and Solid State Physics377 ( 18 ) , pp.1301 - 1307

We consider a scale-free network of stochastic HH neurons driven by a subthreshold periodic stimulus and investigate how the collective spiking regularity or the collective temporal coherence changes with the stimulus frequency, the intrinsic noise (or the cell size), the network average degree and the coupling strength. We show that the best temporal coherence is obtained for a certain level of the intrinsic noise when the frequencies of the external stimulus and the subthreshold oscillations of the network elements match. We also find that the collective regularity exhibits a resonance-like behavior depending on both the coupling . . .strength and the network average degree at the optimal values of the stimulus frequency and the cell size, indicating that the best temporal coherence also requires an optimal coupling strength and an optimal average degree of the connectivity. © 2013 Elsevier B.V Daha fazlası Daha az

Kaya, Ceren | Erkaymaz, Okan | Ayar, Orhan | Özer, Mahmut

Proceedings | 2018 | 26th IEEE Signal Processing and Communications Applications Conference, SIU 2018 , pp.1 - 4

Refractive disorders are common health problems in the community and they are the most important cause of visual impairment. In this study, it was aimed to classify the individuals who have hypermetropia and myopia refractive disorders or not. For this, horizontal and vertical Electrooculogram (EOG) signal data from the right and left eyes of the individuals were used. The performance of the data was investigated by using Logistic Regression (LR), Naive Bayes (NB), Random Forest (RF) and REP Tree (RT) data mining methods. According to the obtained results, REP Tree method has shown the most successful classification performance to d . . .etect hypermetropia and myopia refractive disorders from Electrooculogram (EOG) signals. © 2018 IEEE Daha fazlası Daha az

Uzuntarla, Muhammet | Cressman John R. | Özer, Mahmut | Barreto, Erenest

Article | 2013 | Physical Review E - Statistical, Nonlinear, and Soft Matter Physics88 ( 4 ) , pp.1 - 4

We investigate inverse stochastic resonance (ISR), a recently reported phenomenon in which the spiking activity of a Hodgkin-Huxley model neuron subject to external noise exhibits a pronounced minimum as the noise intensity increases. We clarify the mechanism that underlies ISR and show that its most surprising features are a consequence of the dynamical structure of the model. Furthermore, we show that the ISR effect depends strongly on the procedures used to measure it. Our results are important for the experimentalist who seeks to observe the ISR phenomenon. © 2013 American Physical Society.

Kaya, Ceren | Erkaymaz, Okan | Ayar, Orhan | Özer, Mahmut

Proceedings | 2017 | 2017 Medical Technologies National Conference, TIPTEKNO 20172017-January , pp.1 - 4

'Diabetes Mellitus (Diabetes)' is a disease based on insulin hormone disorders secreted from the pancreas gland. Clinical findings find out that diabetes causes some diseases in vital organs. 'Diabetic Retinopathy' is one of the most common eye diseases based on diabetes, and it is the leading cause of visual loss resulting from structural changes in the retinal vessels. Recent researches show that signals from vital organs can be used to diagnose diseases in the literature. In this study, the features of horizontal and vertical Video-Oculography (VOG) signals from right and left eye are used to classify non-proliferative and prolif . . .erative diabetic retinopathy disease. 25 statistical features are obtained using discrete wavelet transform with VOG signals from 24 subjects. Feature selection is performed using C4.5 decision tree algorithm from 25 features obtained. The statistical features obtained from C4.5 decision tree and discrete wavelet transform are applied as input to artificial neural networks and the classification performance of the 'Diabetic Retinopathy' disease are compared according to these two methods. Our results show that feature selection by C4.5 decision tree algorithm (96.87%) provides better classification performance than feature extraction with discrete wavelet transform (93.75%). © 2017 IEEE Daha fazlası Daha az

Erkan, Yasemin | Özer, Mahmut | Yılmaz, Ergin

Proceedings | 2017 | 2017 MEDICAL TECHNOLOGIES NATIONAL CONGRESS (TIPTEKNO) , pp.1 - 4

Astrocytes are star-shaped glia cells and the most common cell type in the human brain with neurons. Astrocytes fulfill many functions in human brain. Providing support to the cells of the blood-brain barrier, balancing the extracellular ion concentration, supplying nutrients to the nerve tissue, and controlling the development of nerve cells are some of these tasks. In this study, the effects of calcium (Ca') ion concentration oscillations occuring in astrocytes on the neuron firing dynamics are investigated. When the obtained results are examined, it is observed that the production rate of insole 1,4,5-triphosphate (IP3), which is . . . an agent that triggers calcium release from the resoruces in astrocytes, and the degradation time of that within the cell are important effects on the spike production dynamics of the neuron in contact with astrocyte. It is determined that neurons without any stimulation continue to produce spikes through calcium oscillations in the astrocytes, at high IP3 production rates and longer IP3 degradation times Daha fazlası Daha az

Çalım, Ali | Ağaoğlu, Şükriye Nihal | Uzuntarla, Muhammet

Proceedings | 2017 | 2017 25th Signal Processing and Communications Applications Conference, SIU 2017 , pp.1 - 4

Vital functions which take place in the brain are accomplished through synchronized neural activities between interconnected neuronal populations. In healthy and unhealthy nerve system, rhythms in different frequencies can be recognized as they are responsible for neural synchronization. Despite this, in the case of global synchronization where oscillation power is the maximum, as observed in epileptic seizures, neural activity can terminate. In this study, effects of neural network characteristics synchronization emerges from on activity termination are computationally investigated. Stochastic Hodgkin-Huxley (H-H) equations are use . . .d in the simulations. The results show that synchronization increases when neurons have high synaptic conductance and due to this, strong synaptic current neurons exposed to terminates the firings. © 2017 IEEE Daha fazlası Daha az

Baysal, Veli | Yılmaz, Ergin | Özer, Mahmut

Article | 2017 | Istanbul University - Journal of Electrical and Electronics Engineering17 , pp.3081 - 3085

In this paper, the effects of autapse, a kind of synapse formed between the axon or soma of a neuron and its own dendrite, on the transmission of weak signal are investigated in scale-free neuronal networks. In the study, we consider that each neuron has an autapse modelled as chemical synapse. Then, a weak signal that is thought to carry information or an unwanted activity such as virus is applied to all neurons in the network. It is seen that the autapse with its small conductance values can slightly increases the transmission of weak signal across the network when the autaptic time delay is equal to the intrinsic oscillation peri . . .od of the Hodgkin-Huxley neuron. Interestingly, when the autaptic time delay becomes equal to half of this intrinsic period or its integer multiples the autapse can prominently blocks the weak signal transmission. Also, as the autaptic conductance is increased the weak signal transmission is completely impeded by the autapse with its proper auatptic time delays. One consider that the weak signal is an unwanted or virius threatening the whole network, this autaptic mechanism is an efficient way to protect the network from attacks Daha fazlası Daha az