http://dspace.beu.edu.tr:8080/xmlui/handle/123456789/13544 2026-05-14T16:03:31Z http://dspace.beu.edu.tr:8080/xmlui/handle/123456789/16759 COMPARISON OF UV-PHOTOCATALYTIC AND INTRINSIC ANTIFUNGAL ACTIVITY OF TIO₂ NANOPARTICLES AGAINST CANDIDA TROPICALIS KÜCE ÇEVİK, Pınar This study aimed to evaluate the antifungal activity of titanium dioxide nanoparticles (TiO₂ NPs) against Candida tropicalis ATCC 750 under dark and UV light activation conditions. Anatase-phase TiO₂ nanoparticles were applied to C. tropicalis suspensions at four concentrations (125, 250, 500, and 1000 µg/mL) and four exposure times (15, 30, 45, and 60 min). Experiments were performed under two conditions: a dark environment and UVA irradiation (365 nm, 15 cm distance). Antifungal activity was assessed by colony counting at the end of each exposure period, and both log reduction and percentage reduction values were calculated. The combination of UV irradiation and TiO₂ nanoparticles demonstrated significantly higher antifungal activity compared to the dark condition. Under UV activation, complete elimination (100% mortality, >2.48 log reduction) was achieved at 45 minutes with 1000 µg/mL TiO₂ and at 60 minutes with 500 µg/mL. In contrast, under dark conditions the maximum reduction observed was 0.84 log (85.7%) at 1000 µg/mL after 60 minutes, and complete elimination was not obtained at any concentration. The UV-only group showed a limited antifungal effect, with only 0.27 log reduction (46.7%) after 60 minutes. Overall, the photocatalytic activity of the UV-activated TiO₂ system was approximately nine times stronger than the effect of UV irradiation alone. These findings demonstrate that UV-activated TiO₂ nanoparticles exhibit strong photocatalytic antifungal activity against C. tropicalis and can achieve complete elimination at sufficiently high concentrations. Therefore, TiO₂ nanoparticles may represent a promising alternative antifungal strategy for infections caused by C. tropicalis, particularly in cases where antifungal resistance is increasing. 2026-01-01T00:00:00Z http://dspace.beu.edu.tr:8080/xmlui/handle/123456789/16758 EVALUATING METEOROLOGICAL EFFECTS ON WIND TURBINE PERFORMANCE: ANOMALY ANALYSIS AND ENERGY LOSS QUANTIFICATION YÜKSEK, Gökhan This study investigates how ordinary atmospheric conditions induce systematic deviations from the nominal manufacturer's power curve of a modern wind turbine using a residual-based comparative power curve analysis. The approach directly compares theoretical power values with turbine-level SCADA measurements. It evaluates the difference between predicted and measured power as a continuous indicator of relative underperformance rather than as a classified anomaly. The dataset comprises wind speed, wind direction, air density, ambient temperature, cloud cover, solar irradiance, and measured electrical power from a Nordex N117/3600 wind turbine over a full annual period, complemented by temporally synchronized atmospheric data. Power residuals are analyzed as functions of wind speed and paired meteorological variables to reveal recurring deviation patterns and their physical context. The cumulative integration of positive residuals indicates an annual energy production loss of approximately 244,481 kWh, demonstrating that small but persistent power-curve departures accumulate into a substantial long-term deficit. The results show that performance deviations concentrate primarily in the partially loaded operating region and are strongly associated with variations in air density and wind regime. At the same time, temperature and radiative variables play a secondary role. The main contribution of this study is the presentation of a physically interpretable, residual-based performance deviation analysis that links power curve departures directly to atmospheric conditions and quantifies their cumulative energy impact without relying on predictive models or formal anomaly detection algorithms. 2026-01-01T00:00:00Z http://dspace.beu.edu.tr:8080/xmlui/handle/123456789/16757 DERIVING THE ERROR OF TIME FILTERED LEAPFROG SCHEME VIA MODIFIED EQUATIONS GÜZEL, Ahmet The leapfrog (LF) scheme is a cornerstone of numerical weather prediction and largescale atmospheric modeling due to its computational efficiency and ability to preserve the amplitude of pure oscillations during long integrations. However, the three-timelevel nature of the LF method introduces a parasitic computational mode that can grow over time and contaminate physical solutions. Traditionally, the Robert-Asselin (RA) filter has been employed to suppress this mode, but it inadvertently damps the physical mode, reducing the LF scheme's formal accuracy from second to first order. This research provides a rigorous mathematical analysis of modern time filters—specifically the Robert Asselin (RA), Robert Asselin Williams (RAW), and higher-order Robert Asselin (hoRA) filters— using the method of modified equations to evaluate phase and amplitude errors. By solving the linear system for each filtered scheme, we derive equivalent linear multistep methods and their corresponding two-term modified equations. Our findings confirm that the RAW filter significantly mitigates the physical mode damping of the RA filter, recovering second-order accuracy when parameters are optimally tuned (e.g., 𝛼� = 0.53). Furthermore, the hoRA filter demonstrates even higher performance, attaining second-order accuracy generally and third-order accuracy for the specific choice of 𝛽� = 0.4. Numerical tests on the oscillation equation validate these theoretical derivations, showing that the hoRA filter yields the lowest amplitude and phase error magnitudes compared to the RA and RAW alternatives. 2026-01-01T00:00:00Z http://dspace.beu.edu.tr:8080/xmlui/handle/123456789/16756 LIGHTWEIGHT-FOCUSED STRUCTURAL OPTIMIZATION OF A TROLLEYBUS MOTOR MOUNTING BRACKET USING A TAGUCHIFEM APPROACH ÖZCAN, Ahmet The increasing use of electric buses and trolleybuses in urban transportation requires the redesign of local structural components to achieve both lightweight performance and structural durability. In this context, the present study investigates the structural behavior and sheet-thickness optimization of a motor mounting bracket for a 12-m trolleybus using a combination of the Taguchi L9 orthogonal design method and finite element simulations. The analyses were conducted under quasi-static loading conditions assuming linear elastic material behavior, and boundary conditions representing the reaction forces transmitted from the traction motor to the chassis. Three geometric design parameters base sheet thickness, side sheet thickness, and stiffener sheet thickness were examined at three levels. Equivalent stress, displacement, safety factor, and mass were evaluated as response parameters, and the S/N ratio and ANOVA techniques were used to quantify parameter sensitivity and contribution to the variance of the mass response. The results indicate that the base sheet thickness is the dominant parameter governing the lightweighting performance of the bracket, while the side and stiffener sheets have comparatively lower influence. The optimum thickness configuration was identified as 5–4–5 mm, yielding a 15.5% mass reduction with respect to the 6–6–5 mm reference design while maintaining a safety factor above 3.18. The findings demonstrate that the Taguchi–ANOVA–FEM approach provides an effective decision-support framework for early-stage design of bracket-type structural components in electric bus traction systems. Moreover, the methodology is compatible with manufacturable design constraints and can be extended to multi-objective formulations including durability and fatigue performance in future studies. 2026-01-01T00:00:00Z