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Yayın A path loss model for link budget analysis of indoor visible light communications(Istanbul Univ-Cerrahpasa, 2021-05) Miramirkhani, FarshadIn the context of beyond 5G indoor communication systems, visible light communications (VLC) has emerged as a viable supplement for existing radio frequency based systems and as an enabler for high data rate communications. However, the existing indoor VLC systems are limited by detrimental outages caused by fluctuations in the VLC channel gain because of user mobility. In this study, we proposed a tractable path loss model for indoor VLC that reflects the effect of room size and coating material of surfaces. We performed an extensive advanced ray tracing simulation to obtain the channel impulse responses within a room and presented a path loss model as a function of distance, room size, and coating material through curve fitting. In addition, path loss parameters such as the path loss exponent and the standard deviation of the shadowing component were determined. The simulation results indicate that path loss is a linear function of distance, path loss exponent is a function of room size and coating material, and shadowing follows a log normal distribution.Yayın Surface modification of titanium using BSA-Loaded chitosan and chitosan/gelatin polymers(Springer Berlin Heidelberg, 2016-10) Önder, SakipThe integration of titanium-based implants with the surrounding bone tissue needs to be improved to increase their service life. This work presents a surface modification technique to increase the osteointegration of titanium implants. The studies were conducted in three main steps: (i) surface modification of titanium using bovine serum albumin (BSA)-loaded chitosan and chitosan/gelatin polymers, (ii) studies of BSA release from these surfaces, (iii) effect of porosity and polymer composition on osteoblast cell proliferation. TiO2 and COOH groups were formed on titanium surfaces. Then, chitosan and chitosan (C)/gelatin (G) with various ratios (G:C = 0.5:1, 1:1, 1:0.5) were mixed with BSA and fixed to the surface via carbodiimide chemistry (EDC/NHS). After the immobilization process, samples were exposed to either air or freeze-drying. Characterization studies were conducted using Fourier transform-infrared spectroscopy and scanning electron microscopy. Finally, BSA release studies in phosphate-buffered saline (0.1 M, 37 °C) and cell (osteoblast) proliferation studies using MTS assay were conducted. BSA-loaded porous structures were obtained on chitosan- and chitosan/gelatin-containing surfaces after freeze-drying, while smooth surfaces were obtained after air-drying. The BSA release rate was directly correlated with increasing gelatin amount in the chitosan/gelatin coatings. MTS analysis was not conclusive because of the absorption properties of polymer coatings. However, absorbed color density in chitosan/gelatin (G:C = 1:1) polymers under freeze-drying conditions was more dominant, indicating better cell proliferation. This method may be used to release growth factors for controlled cell proliferation and differentiation or for the local delivery of antimicrobial drugs to prevent contamination during implementation in hard tissue applications.
