Master Degree / Yüksek Lisans Tezleri
Permanent URI for this collectionhttps://hdl.handle.net/11147/3008
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Master Thesis Effect of Random Structural Variations on the Optical Properties of Honeycomb Photonic Crystals(01. Izmir Institute of Technology, 2021) Tunçtürk, Yiğit; Sözüer, Hüseyin SamiPeriodic dielectric structures called photonic crystals(PhCs) are being used in various sensors and devices. Since PhCs are designed to operate within certain frequency ranges, accuracy in structure becomes important. During the manufacturing process, random errors in geometry can be encountered. Two types of errors come to the forefront, surface roughness and positional randomness. Once the periodic structure becomes imperfect due to random errors, calculations for the desired frequency ranges must be performed using supercells. In this thesis, effect of surface roughness and positional ran- domness on photonic density of states are investigated for both TM and TE modes in two-dimensional honeycomb photonic crystals.Master Thesis Elliptical Cavity Designs, Fabrications and Experiments To Investigate Cell Misalignment and Surface Roughness Effects(Izmir Institute of Technology, 2019) Karatay, Anıl; Yaman, FatihIn this thesis, the results of 5 different elliptical cavity designs at different cell numbers and frequencies and the fabrication and measurement of two of these are presented in order to investigate the effects of cell alignment error and surface roughness. First, a 9-cell, 3.9 GHz elliptical cavity with very poor cell-to-cell coupling is designed and the acceleration parameters are optimized. Thanks to the low cell-to-cell coupling, it is aimed to better observe possible mechanical defects and the effects of cell alignment errors in this cavity on the fundamental cavity parameters and particle-cavity interaction are investigated using CST-MWS program. In addition, the effect of surface roughness of the cavity on wake fields and impedances is among the parameters that are tried to be observed. Second, a 3-cell 2 GHz cavity and its scaled version, 3-cell 3.9 GHz cavity, are designed to demonstrate that the effects of cell misalignment were not limited to only this geometry, and similar simulations are repeated for these cavities. In the experimental part of the thesis, a 3-cell 3.9 GHz elliptical cavity with high cell-to-cell coupling is designed and fabricated with a 3D printer and made conductive by nickel and copper coating techniques. Then, the effects of cell misalignment on the quality factor and the electric field on the acceleration axis are investigated experimentally. For these processes, bead-pull measurement is utilized in addition to weak and critical coupling measurements. In the last part, a 2.45 GHz single cell aluminum cavity is fabricated, the same experiments are repeated and it is experimentally demonstrated that similar effects can also be observed with higher conductivity values.Master Thesis Investigations on Surface Electric Charge of Silica Nanoparticles With Different Surface Roughnesses(Izmir Institute of Technology, 2019) Alan, Büşra Öykü; Barışık, MuratSilica nanoparticles have been receiving more attention from diverse research areas recently due to their significant physical properties such as large pore volume and high internal surface area, colloidal stability, high biocompatibility, and tunable pore sizes. These silica nanoparticles are great candidates for drug delivery applications because they can transport a large amount of drugs into selective organs and tissues due to their high surface area and large pore volume. However, there are important drug delivery mechanisms that need to be understood properly such as cellular uptake, endosomal escape, drug loading and release, and crossing physical barriers. Physicochemical properties of nanoparticles (size, shape, surface charge, or surface chemistry) are important for understanding these mechanisms in order to develop successful drug delivery applications. This research investigates how these surface charge properties change with different particle, pore diameters, roughness structure on the nanoparticle surface, and different temperature and solution conditions. Also, we investigate how the surface charging behavior of rough nanoparticles interacts with a flat plate. Rough nanoparticles and their interactions with surfaces theoretical assumptions can be wrong and ionic distribution can show variation locally. In order to calculate ionic distribution and surface charge properties in these systems, proper equations and boundary conditions were employed. The charge regulation model was used as a boundary condition because of the electric double layer overlap effect. Results showed that there was a considerable variation on surface charge properties due to the roughness structure with different roughness and particle sizes and temperature difference.Master Thesis Optimization of Surface Roughness on a Milling Process Using Stochastic Methods(Izmir Institute of Technology, 2019) Dinç, Özcan; Artem, Hatice SeçilNowadays, milling process is one of the most widely used metal processing methods in many fields from space and aircraft to automotive industry. The surface roughness values of the workpiece in milling process vary depending on the thermal, chemical and abrasive loads that occur during cutting. Spindle speed, depth of cut and feed rate are the cutting parameters affecting the surface roughness. Hence, these parameters at the time of machining constitute an important issue. Accordingly, in this thesis optimization of surface roughness has been performed using the stochastic search methods. First, using experimental data obtained in the milling process, it was aimed to establish a regression model to determine average surface roughness equation as an objective function. The cutting parameters and average surface roughness value were considered as input and output in regression analysis, respectively. In this study, seven different mathematical models have been established and examined to carry out regression analysis. The reliability and stability of the mathematical models were investigated. The most appropriate mathematical model has been constructed and then used as an objective function for optimization. Nelder-Mead, Random-Search, Simulated Annealing, and Differential Evolution were the stochastic search algorithms to perform the optimization in the present study. In conclusion, it was found that the minimum average surface roughness value depends on spindle speed, depth of cut and feed parameters.Master Thesis Determination of the Particle Interactions -Rheology Suface Roughness Relationship for Dental Ceramics(Izmir Institute of Technology, 2007) Kes, Mürşide; Polat, HürriyetIn this study, relationship between particle interactions, rheology and surface roughness for dental ceramics was determined. For this purpose IPS Empress 2 veneer powder was chosen and characterized with XRD, SEM, EDS, Zeta Potential and Particle Size measurements.Particle interactions have been interpreted in the light of DLVO Theory for distilled water and electrolyte solutions at different concentrations (0.1, 0.25, 0.5, 0.75,1 M NaCl and CaCl2). The results indicated that interactions between particles change with electrolyte concentration and valency. Electrical Double Layer Thickness (Debye Length) compresses and Energy Barrier height decreases as electrolyte concentration and valency increase mean that there is agglomeration between particles. In order to understand the rheological properties of the system shear rate versus shear stress and shear rate versus viscosity graphs were interpreted for the same environmental conditions, distilled water and electrolyte solutions at different concentrations. It was obtained that at low electrolyte conditions particles formed agglomerates, however at high electrolyte conditions the system reached equilibrium where particles formed gel structures due to their non-Newtonian behaviour.The results obtained from rheological measurements were compared with the results obtained from AFM, profilometer and SEM measurements for the surfaces prepared with IPS Empress 2 veneer powder and it was concluded that in the presence of electrolytes (Na+ and Ca2+) surface roughness increased at low concentrations due to agglomeration of particles whereas surface roughness decreased at high concentrations most probably due to gelation in the system. Moreover, this situation was supported with contact angle measurements where contact angle mean values are high and ditributions are wide at low electrolyte concentrations while contact angle mean values are small and distributions are narrow at high concentrations