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Öğe An exergy analysis of a concentric tube heat exchanger using hBN-water nanofluids(Inder Science Publishers, 2021) Budak Ziyadanoğulları, Neşe; Perçin, SüleymanThis study investigated the effects of using nanofluids prepared with hexagonal boron nitride (hBN) nanoparticles on the thermal performance and pressure drop of a concentric tube heat exchanger. Experiments were carried out with water-hBN nanofluids for stable, dispersed, 0.01%, 0.1% and 1% volume concentrations, at different flow rates and Reynolds numbers under parallel and counter-flow conditions. When the experimental results were examined, the exergy loss was higher in the parallel-flow heat exchanger compared to the counter-flow heat exchanger. The highest exergy loss value was obtained for distilled water at the highest Reynolds number (Re = 8,700) for parallel flow operation at 170 W. The exergy loss of water at the highest Reynolds number (Re = 8,700) for parallel flow operation increased by 15.7%, 24.8% and 49.8% for hBN-water concentrations of 0.01%, 0.1% and 1%, respectively. Exergy loss of water at the highest Reynold number (Re = 8,700) for counter flow operation increased by 11.3%, 17.3% and 29.2% for hBN-water concentrations of 0.01%, 0.1% and 1%, respectively. When evaluating the exergy analysis of the system, exergy losses due to pressure drops were negligible for both flows (parallel and counter).Öğe New voltammetric strategy for determination and electrochemical behaviors of metformin by pencil graphite electrode in the NaOH(Indian Chemical Society, 2020) Altunkaynak, Yalçın; Yavuz, Ömer; Levent, AbdulkadirMetformin(MET), an oral antidiabetic drug commonly used in the treatment of diabetes, is a drug that increases insulin sensitivity in the biguanide group [1]. MET shows its pharmacological effect by lowering the glucose level in the blood. In the literature research, there are studies using electrochemical techniques for the analysis of MET in biological fluid and drug forms[1-6]. In this study, the electrochemical properties of MET, one of the drugs used in the treatment of diabetes, were performed using a pencil graphite electrode in NaOH (0.1 M) solution. This compound was recorded with an irreversible and diffusion controlled adsorption oxidation peak at approximately +1.28 V by cyclic voltammetry. With square wave stripping voltammetry, it was observed that the peak current signals of MET in the concentration range of 2.76-24.8 µM in 0.1M NaOH solution increased linearly. At a concentration of 2.76 µM (n = 9), the limit of detection and relative standard deviation were calculated as 9.03 nM (1.495 ngmL-1 ) and 3.25 %, respectively. This method has been successfully applied for MET analysis in pharmaceutical preparations and urine samples without any separation.Öğe Plantago major protective effects on antioxidant status after administration of 7,12-dimethylbenz(a)anthracene in rats(Asian Pacific Organization for Cancer Prevention, 2011) Oto, Gökhan; Ekin, Suat; Özdemir, Hülya; Demir, Halit; Yaşar, Semih; Levent, Abdulkadir; Berber, İsmet; Kaki, BarışAim: The present study was designed to evaluate effects of Plantago major extract on oxidative status in Wistar albino rats administrated 7,12-dimethylbenz(a)anthracene (DMBA). Methods: Rats were divided into three equal groups of 6 animals each: Group 1 controls, group 2 treated with DMBA (100 mg/kg, single dose) and group 3 receiving the DMBA and the aqueous extract at 100 mg/kg/d for 60 days. Results: Significant decrease in catalase (P<0.05), carbonic anhydrase (p≤0.01), reduced glutathione (GSH) (P<0.01) and total protein (P<0.01) values was observed in the DMBA group compared with the healthy controls and DMBA + Plantago major groups. Conclusion: The results suggest preventive effects of Plantago major on DMBA induced oxidative damage in Wistar albino rats that might be due to decreased free radical generation.Öğe Archaeozoological study of a unique Late Neolithic pitfrom Tepecik-Çiftlik, central Turkey(Anthropozoologica, 2019-08-16) Gündem, Can YumniThe absence of written evidence from prehistoric periods makes it difficult to understand the origins of sacrifice or offering ceremonies. Archaeological finds from prehistoric periods are the only solid evidence for these acts and rituals. One probable case of animal sacrifice or offering in the Neolithic period has been found at the site of Tepecik-Çiftlik Höyük in central Turkey. This study is focused on a single unique pit, which contained only animal bones and was found in an open space. The contents clearly indicate that this pit can not be interpreted simply as mixed kitchen garbage since an almost complete cattle skeleton as well as sixteen left front leg remains from sheep were placed in the pit after a social, or more specifically, ritual act. Similar pit with similar content was found neither in the close region to Tepecik-Çiftlik nor within Anatolia. The main aim of this study is to introduce a special archaeological find group, those were left after certain prehistoric activity.Öğe The characteristic diode parameters in Ti/p-InP contacts prepared by DC sputtering and evaporation processes over a wide measurement temperature(World Scientific, 2017-06) Ejderha, Kadir; Asubay, Sezai; Yıldırım, Nezir; Güllü, Ömer; Türüt, Abdülmecit; Abay, BahattinThe titanium/p-indium phosphide (Ti/p-InP) Schottky diodes (SDs) have been prepared by thermal evaporation and DC magnetron sputtering deposition. Then, their current-voltage (I-V) characteristics have been measured in the sample temperature range of 100-400K with steps of 20K. The characteristic parameters of both Ti/p-InP SDs have been compared with each other. The barrier height (BH) values of 0.824 and 0.847 at 300K have been obtained for the sputtered and the evaporated SDs, respectively. This low BH value for the sputtered SD has been attributed to some defects introduced by the sputtered deposition technique over a limited depth in to the p-type substrate. The BH of the evaporated and sputtered diodes has decreased with the standard deviations of 58 and 64mV obeying to double-Gaussian distribution (GD) in 220-400K range, respectively, and it has seen a more sharper reduction for the BHs with the standard deviations of 93 and 106 mV in 100-220K range. The Richardson constant values of 89.72 and 53.24A(Kcm)-2 (in 220-400K range) for the evaporated and sputtered samples, respectively, were calculated from the modified ln(I0/T2)-q2σs2/2k2T2 vs (kT)-1 curves by GD of the BHs. The value 53.24A(Kcm)-2 for the sputtered sample in high temperatures range is almost the same as the known Richardson constant value of 60A(Kcm)-2 for p-type InP.Öğe Determination of trace metal and mineral levels in the tobacco and cigarette samples using by FASS(Chemical Society of Pakistan, 2013-04) Levent, Abdulkadir; Yardım, Yavuz; Demir, CengizCigarettes and tobacco products are consumed in large amounts by human beings in the world. Also, tobacco is one of the most important agricultural products in Turkey. The accumulation of heavy metals in tobacco leaves in accordance with a possible risk of transferring them to people by smoke is well known. This study was carried out to estimate trace metal and mineral levels in tobacco and cigarettes from Eastern and South-eastern Anatolia, Turkey. The analysis was done by flame atomic absorption spectrometry using dry ashing or wet digestion. Results obtained are in agreement with data reported in the literature.
