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      • KCI등재

        Distribution of neuroendocrine cells in the small and large intestines of the mole-rats (Spalax leucodon)

        Ali Bayrakdar,Mine Yaman,Ramazan Ilgün 한국통합생물학회 2015 Animal cells and systems Vol.19 No.5

        In this research, we aimed to determine the regional distribution and relative frequency of immunoreactive (IR) endocrine cells of ghrelin, glucagon, somatostatin–14 (SOM–14), neuropeptide Y (NPY), calcitonin-gene-related peptide (CGRP), insulin and galanin in small and large intestines of mole-rats (Spalax leucodon) by using immunohistochemical staining methods. For this purpose, small and large intestine regions of six adult mole-rats were used as material. In the small and large intestines of mole-rats (S. leucodon), ghrelin, glucagon, SOM–14, NPY and CGRP were identified at various frequencies, but insulin and galanin were not detected in this study. Ghrelin-IR cells were only observed in the small intestine. In addition, the existence of positive staining in the cells was decreased while passing from duodenum to ileum. Glucagon-IR cells were mainly detected in the small intestine regions and colon. SOM–14-IR cells were detected throughout the small intestines with a lesser frequency. NPY-IR cells were also detected in the small and large intestines at various frequencies but not in cecum and rectum. CGRP-IR cells were scarce in duodenum and jejunum, but their numbers increased from ileum to colon. In conclusion, the present study revealed the existence and distributions of neuropeptide-secreting endocrine cells in small and large intestines of mole-rats (S. leucodon).

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        The statistical optimization of bacterial cellulose production via semi-continuous operation mode

        Ali O¨ zhan Aytekin,Deniz Dilan Demirbag,Tug˘c¸e Bayrakdar 한국공업화학회 2016 Journal of Industrial and Engineering Chemistry Vol.37 No.-

        Bacterial cellulose (BC) is highly pure and has a higher crystallinity and molecular weight than plantcellulose. Therefore, BC can be used in many different areas such as biotechnology, pharmaceutical,cosmetics. Because of the price of BC, the productivity of BC is an important parameter for industrial scaleapplications. In this study, BC was produced in static culture using a semi-continuous operation mode;the conditions were optimized using response surface methodology (RSM). The collected BC wascharacterized by Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM),and tensile strength. Optimization parameters were selected as glucose concentration, surface area/volume ratio, surface area and incubation day intervals. The optimum values for incubation dayintervals, volume changing ratios, glucose concentrations and surface area/volume ratios were 7 days,66%, 50 g/L and 1.22 cm 1, respectively. BC productivity reached 0.284 g/L/day under optimalconditions, while the model equation proposed 0.289 g/L/day. RSM is essential for determining theoptimum values of parameters for BC production compared with the one-variable-at-a-time method. The semi-continuous operation mode is alternative and a good candidate for the industrial scaleproduction of BC.

      • KCI등재

        Non-preemptive Queueing Model of Spectrum Handoff Scheme Based on Prioritized Data Traffic in Cognitive Wireless Networks

        Muhammed Enes Bayrakdar,Ali Çalhan 한국전자통신연구원 2017 ETRI Journal Vol.39 No.4

        In this study, a non-preemptive M/G/1 queueing model of a spectrum handoff scheme for cognitive wireless networks is proposed. Because spectrum handoff gives secondary users an opportunity to carry on their transmissions, it is crucially important to determine the actions of primary users. In our queueing model, prioritized data traffic is utilized to meet the requirements of the secondary users. These users’ packets are categorized into three different priority classes: urgent, real-time, and non-real time. Urgent data packets have the highest priority, while non-real time data packets have the lowest priority. Riverbed (OPNET) Modeler simulation software was used to simulate both reactive and proactive decision spectrum handoff schemes. The simulation results were consistent with the analytical results obtained under different load and traffic conditions. This study also revealed that the cumulative number of handoffs can be drastically decreased by exploiting priority classes and utilizing a decent spectrum handoff strategy, such as a reactive or proactive decision-based strategy.

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