An evaluation of transaction management issues in mobile real-time database systems

Ankara : The Department of Computer Engineering and Information Science and Institute of Engineering and Science Bilkent University, 1998.Thesis (Master's) -- Bilkent University, 1998.Includes bibliographical references leaves 56-58.Kayan, ErsanM.S

Bio-reduced GO/Pd nanocomposite as an efficient and green synthesized catalyst for hydrogen evolution reaction

*Balun Kayan, Didem ( Aksaray, Yazar )In this work, we introduced a green methodology for the production of palladium (Pd) decorated reduced graphene oxide (rGO), using an endemic plant of Onosma malatyana Binzet (OMB) root extract for the first time and used it as an electrocatalyst for hydrogen evolution reaction (HER) in aqueous acidic media. Benefiting from the synergetic effect between rGO and Pd nanoparticles, the as-prepared bio-reduced GO/Pd (bio-rGO/Pd) nanocomposite exhibits a remarkable performance towards HER when the results compared with the bio-rGO and bio-rPd nanocomposite. The HER overpotential at a current density of 10 mA cm−2 for bio-rGO/Pd was only 0.17 V. The Tafel slope of the bio-rGO/Pd nanocomposite film obtained from the HER polarization curves exhibits 154 mV dec−1, showing that the process is limited by the Volmer reaction step. In addition, the bio-rGO/Pd nanocomposite electrode also showed an outstanding stability after a long-term potential cycling measurement. It possesses a high synergetic effect, low charge transfer resistance and considerable electrochemical surface area. The all obtained results demonstrated that the bio-rGO/Pd will be a promising green synthesized HER catalyst

Noise Effect on Forecasting

The lack of regulation and liquidity in crypto money markets causes higher volatility compared to other financial markets. This situation increases the noise in price change. The high noise and random walk create a problem that cannot be explained by traditional stochastic financial methods. For this reason, a multi-layered deep learning model with an additive attention layer, which uses a single observation in 10-day sequences, was used in this study. Different transformations are used to reduce the noise of the closing values. As a result of the comparisons made between different approaches, it has been revealed that exponential moving averages, to be used as the value to predict, give better results than other conversions and estimation of the original price, since they explain the price better than simple moving averages and reduce the noise of the original price.IEEE,TUBITAK BILGEM,TurkcellWOS:001062571000045Conference Proceedings Citation Index – Science - Conference Proceedings Citation Index – Social Science & HumanitiesProceedings PaperUluslararası işbirliği ile yapılmayan - HAYIREkim2023YÖK - 2022-2

An easily fabricated palladium nanocatalyst on magnetic biochar for Suzuki-Miyaura and aryl halide cyanation reactions

Biochar is a carbon-rich solid, the surface of which is covered with a high density of functional carbonyl, hydroxyl and carboxylic acid groups. In this work, palladium nanoparticles were embedded on magnetic biochar and a new reusable and environmentally-friendly catalyst was developed and applied for the promotion of Suzuki-Miyaura C-C coupling and cyanation reactions. The high-carbon (77%), low-ash content (5.8%) and the relatively high surface area (266 m(2) g(-1)) of pine tree biochar (PTB) suggested that it might be highly suitable as a catalyst substrate. The Fe3O4-Pd-biochar nanocomposite was successfully characterized using SEM, TEM, EDX, FT-IR, BET and XRD. Its catalytic role was initially evaluated using p-NO2C6H4I as a model reactant (for both types of reactions) and later for the production of biaryls and benzonitriles from a wide range of aryl halides under mild reaction conditions. Biaryls and benzonitriles were characterized using GC-MS. In the case of the Suzuki-Miyaura reaction, the optimum yield of 98% was obtained with a catalyst concentration of 0.04 mol%, microwave irradiation of 400 W, and a residence time of 5 min, using K2CO3 as the base. With respect to the cyanation reaction, dimethylformamide, Na2CO3 and 6 h were the optimum solvent, base and reaction duration, respectively. Subsequently, the nanocatalyst showed excellent catalytic activity in both reactions, achieving >88% yields in most cases, regardless of the aryl iodide or bromide used and the type of substitution

Preparation and application of Fe-modified banana peel in the adsorption of methylene blue: Process optimization using response surface methodology

Banana peel was used as the feedstock for the preparation of a magnetic adsorbent for the adsorption of methylene blue (MB) in aqueous solutions. The Fe-modified banana peel was characterized by surface and spectrometric methods. The Box-Behnken design (BBD) was used for determining the conditions of each experimental run and optimization of adsorption was achieved through response surface methodology. The R2, adjusted R2, and predicted R2 coefficients of the employed BBD model were determined as 0.9820, 0.9686, and 0.9182, respectively, indicating a high level of agreement between the experimental data and the proposed theoretical model. The optimum MB adsorption of 91.89% was achieved at an adsorption time of 50 min, temperature of 45 °C, adsorbent dosage of 2.5 g and MB concentration of 5 mg L−1. Equilibrium was achieved in 48 min. The most influential process parameter was the adsorbent dosage, whereas the impact of time, MB concentration and temperature was considerably smaller. The Langmuir Qmax value of 28.1 mg g−1 compared favorably to respective values from other published adsorbents

Fe-modified hydrochar from orange peel as adsorbent of food colorant Brilliant Black: process optimization and kinetic studies

Çatlıoğlu, F. N. ( Aksaray, Yazar )Abstract: The main aims of this work were to produce and characterize Fe-modified hydrochar from orange peel waste, optimize the adsorption through response surface methodology, investigate the role of treatment time, dye concentration, adsorbent dose and temperature, and determine the dominant mechanisms through kinetics analysis. Orange peel waste was hydrothermally carbonized at 200 °C for 8 h, and the hydrochar was embedded with magnetite nanoparticles. The composite adsorbent was characterized through spectrometric and surface analytical methods. Subsequently, analysis of variance was used to design the experimental runs, propose a polynomial equation describing the adsorption process and finally optimize the adsorption conditions. The results indicated that 99% removal can be theoretically achieved at the following conditions: dye initial concentration of 6.08 mg/L, treatment time of 26.30 min, temperature of 44.79 °C and adsorbent concentration of 2.27 g/L. The dominant factors were the dye and adsorbent concentration, whereas time and temperature variations had a much lesser impact. Among examined models, the Langmuir model showed a better match to the experimental data. The maximum monolayer adsorption capacity was determined as 10.49 mg/g. The mechanism of interaction was largely based on surface chemisorption between the dye and adsorbent. Fe-modified hydrochar exhibited a positive adsorption behavior, and it was shown that a new valorization option for orange peel waste is available. This option may follow other valorization pathways, such as isolation of biologically active molecules, therefore offering a complete solution to this type of waste. Graphic abstract: [Figure not available: see fulltext.