https://hdl.handle.net/20.500.12619/45456 Mon, 13 Apr 2026 19:28:06 GMT 2026-04-13T19:28:06Z https://hdl.handle.net/20.500.12619/45557 Evaluation of key mechanical design properties and mechanical characteristic features of advanced Bi-2212 ceramic materials with homovalent Bi/Ga partial replacement: Combination of experimental and theoretical approaches M. B. Turkoz; Y. Zalaoglu; Turğay, Tahsin; Öztürk, Oğuzhan; B. Akkurt; G. Yildirim This study models the variations in the key mechanical design properties and mechanical characteristic features of Ga substituted Bi-site Bi-2212 ceramics prepared within the different molar ratios of x = 0.000, 0.005, 0.010, 0.030, 0.050, 0.100 and 0.300 with the assistant of available theoretical approaches; namely, Meyer's law, proportional sample resistance, elastic/plastic deformation, modified proportional sample resistance model, Hays Kendall and indentation-induced cracking methods for the first time. The mechanical modeling parameters are gathered from the microhardness (Vickers) experimental tests performed at various applied loads interval 0.245 N-2.940 N. The results provide that the key mechanical design features improve systematically with the augmentation of trivalent Bi/Ga partial replacement level up to x = 0.05 due to the rapid decrement in the main structural problems; namely, the grain orientations, lattice strains, distortions, dislocations, grain boundary interaction/coupling problems, crack-initiating and crack-producing omnipresent flaws in the advanced Bi-2212 ceramic system. Accordingly, the optimum Ga inclusions strengthens the mechanical durability towards the applied stress due to the increased stabilization in the durable tetragonal phase. After the critical substitution amount of x = 0.05, the mechanism turns reversely, and the general mechanical characteristic features including the stiffness, mechanical durability and strength degrade remarkably. Additionally, the mechanical modeling results demonstrate that the Bi/Ga impurity leads to vary positively the quality of standard indentation size effect (ISE) feature until x = 0.05, beyond which the excess Ga additives damage seriously ISE feature of Bi-2212 inorganic compounds. Besides, the indentation-induced cracking (IIC) model is noticed as the best method to describe the true microhardness parameters of Bi/Ga substituted Bi-2212 compounds for the mechanical characterization. Tue, 01 Jan 2019 00:00:00 GMT https://hdl.handle.net/20.500.12619/45557 2019-01-01T00:00:00Z https://hdl.handle.net/20.500.12619/45558 Effect of homovalent Bi/Ga substitution on propagations of flaws, dislocations and crack in Bi-2212 superconducting ceramics: Evaluation of new operable slip systems with substitution M. B. Turkoz; Y. Zalaoglu; Turğay, Tahsin; Öztürk, Oğuzhan; G. Yildirim This study defines a strong methodology between the mechanical performance behaviors and formation possible operable slip systems in the crystal structure of Bi-2212 superconducting phase with trivalent Bi/G substitution with the aid of Vickers hardness tests exerted at various indentation load intervals 0.245 N-2.940 N. It is found that the mechanical performance behaviors improve regularly with the increment in the trivalent Bi Ga partial substitution level up to the value of x = 0.05 due to the formation of new operable slip system. Namely, the optimum gallium (Ga) impurities serve as the strain fields and associated forces for the interaction of dislocations within the different orientations with each other to impose the surface residual compressive stresses orienting favorably the superconducting grains. Thus, the propagation of dislocations, flaws and cracks divert in the crystal structure. On this basis, the presence of optimum Ga impurity in the Bi-2212 crystal syster strengthens the mechanical strength, critical stress, resistance to the plastic deformation, stiffness and durabilit nature. Moreover, the experimental results advance in-depth understanding of fundamental links between th porosity and Young's moduli of elasticity founded on the impurity level and applied test loads. It is observed that in case of the optimum level of x = 0.05 the propagation of flaws, dislocations and cracks proceed along the transgranular regions instead of the intergranular regions as a consequence of improvement in the durabl tetragonal phase. On the other hand, the excess Ga content level in the polycrystalline Bi-2212 system results i the augmentation in the stress raisers, crack surface energy and crack-initiating flaws, activating the stress-induced phase transformation. Tue, 01 Jan 2019 00:00:00 GMT https://hdl.handle.net/20.500.12619/45558 2019-01-01T00:00:00Z https://hdl.handle.net/20.500.12619/45560 Interaction between precious metals price and Islamic stock markets Tuna, Gülfen Originality/value - The author would like to emphasize that this article is second to examine precious metals and Islamic stock markets in literature. Tue, 01 Jan 2019 00:00:00 GMT https://hdl.handle.net/20.500.12619/45560 2019-01-01T00:00:00Z https://hdl.handle.net/20.500.12619/45559 PREDICTION OF WATER QUALITY IN RIVA RIVER WATERSHED Öz, Nurtaç; Topal, Bayram; Halil Ibrahim Uzun The Riva River is a water basin located within the borders of Istanbul in the Marmara Region (Turkey) in the south-north direction. Water samples were taken for the 35 km drainage area of the Riva River Basin before the river flows into the Black Sea at 4 stations on the Riva River every month and analyses were carried out. Changes were observed in the quality of water from upstream to downstream. For this purpose, the spatial and temporal variations of water quality were investigated using 13 water quality variables with the ANOVA test. It was observed that COD, DO, S and BOD were important in determining the spatial variation. On the other hand, it was found out that all the variables were effective in determining the temporal variation. Moreover, the correlation analysis which was carried out in order to assess the relations between water quality variables showed that the variables of BOD-COD, BOD-EC, COD-EC, BOD-T and COD-T were correlated and the regression analysis showed that COD, TKN and NH4-N explained BOD and BOD, NH4-N, T and TSS explained COD by approximately 80 %. Consequently, the Artificial Neural Network (ANN), Decision Tree and Logistic Regression models were developed using the data of training set in order to predict the water quality classes of the variables of COD, BOD and NH4-N. Quality classes were predicted for the variables by inputting the data of testing set into the developed models. According to these results, it was seen that the ANN was the best prediction model for COD, the Decision Tree for BOD and the ANN and Decision Tree for NH4-N. Tue, 01 Jan 2019 00:00:00 GMT https://hdl.handle.net/20.500.12619/45559 2019-01-01T00:00:00Z