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Archived Theses
Nano ilacin tümörlü dokuya mikrokabarcik ile taşinimi
This dissertation explores the dynamics of spherical and nonspherical microbubble oscillations in microvessels and their implications for ultrasound-mediated therapeutic applications. The study focuses on microvessel properties, an aspect often neglected in the literature, and their impact on microbubble oscillation and stability. Simulations were conducted across various vessel and bubble properties and acoustic field parameters to analyze their effects on the resulting bubble surface area and shear stress on the microvessel wall where high shear stress values cause tissue damage (> 800 Pa). In particular, the maximum shear stress reaches 30 kPa with an acoustic field pressure of 1.5 atm at 8 MHz. The maximum bubble surface area should be 900 µm2 at resonance for Newtonian liquid, which affects the drug loading capacity and diffusion rate. Different constitutive models are applied to examine the effects of blood's non-Newtonian properties. For the bubble shell, Neo-Hookean model replaces simpler linear models, revealing significant deviations; for example, the difference between linear and nonlinear shell models reaches 60% when the pressure amplitude reaches 2.5 atm. In the literature, most studies use complex models, whether necessary or not. However, in this dissertation, a parametric range is obtained, where simple models can be used to prevent unnecessary long code runs. These insights provide a foundation for optimizing ultrasound-mediated drug delivery by carefully tuning bubble characteristics and acoustic settings to maximize therapeutic efficacy while minimizing potential vascular injury. The model also includes bubble-bubble interactions to determine the minimum distance to prevent collapse. Near resonance, this distance is found to be 12 µm. Contour maps for different shell and acoustic field properties are obtained to show where the ultrasound-mediated bubble application is safe or unsafe for the treatment application. Here, three criteria are considered: bubble surface area, wall shear stress, and distance between bubbles.
DMA verilerinin viskoelastik ana eğriye dönüştürülmesi ve Prony serisi bulunması
This thesis details the process of converting Dynamic Mechanical Analysis (DMA) data of a viscoelastic material at different temperatures into a master curve. The methodology involves shifting DMA data based on the Williams-Landel-Ferry (WLF) universal constants and iteratively adjusting the shift to construct a continuous master curve. A Prony series is then fitted to the master curve, providing insights into the relaxation modulus at various temperatures. For the iteration a numerical method has developed using MATLAB. This process involves a comparison between the numerical iteration and the manual shifting using excel which is a criterion for the numerical iteration. Fitting Prony series is executed using MATLAB algorithms, for this instance Least Squares Algorithm is used. The developed numerical method is verified by comparing the results to those predicted from a Finite Element Analysis of a brain tissue subjected to compression loading.
Düşük enerjili elektron demet kesim sistemi
A new electron accelerator, Rhodotron, has been designed and constructed at Boğaziçi University Kandilli Detector, Accelerator, and Instrumentation Laboratory (KAHVELab). Rhodotron accelerator accepts an electron beam with a bunch length of at most 1 ns. Therefore, a chopper system is needed to accomplish 1 ns or less electron bunch from 1 μs electron bunch. This master's thesis aims to design a chopper system to bunch electrons for the Rhodotron accelerator.
İnsansız hava araçları için düşük güçlü hafif tek girişli çok çıkışlı sentetik açıklık radarı sisteminin geliştirilmesi
Unmanned Aerial Vehicles (UAVs) are essential tools across various fields due to their flexibility, mobility, and cost-effectiveness. Integrating advanced radar systems into UAVs, however, poses challenges in power efficiency, payload weight, and real-time processing. This thesis presents a lightweight, low-power Single Input Multiple Output (SIMO) Frequency-Modulated Continuous Wave (FMCW) radar system tailored for UAVs. Initially, Stepped Frequency Continuous Wave (SFCW) radar was explored for its high resolution and subsurface sensing capabilities, but its limitations in speed and real-time processing led to the adoption of FMCW radar. The proposed system achieves real-time range and velocity measurements critical for UAV operations. Key features include multiple receiver channels for enhanced resolution and GPU-based computation for efficient SAR imaging. Extensive testing validated the radar's 50 cm range resolution and detection of objects up to 100 meters. The system's superior power efficiency and adaptability address existing UAV radar limitations, enabling applications such as obstacle detection, terrain mapping, and environmental monitoring. Future directions include algorithmic refinements, hardware miniaturization, and sensor integration.
CRY4BA ve CRY11AA ile etkileşen Asya kaplan sivrisineği proteinlerinin insektisit mekanizması
The Asian tiger mosquito (Aedes albopictus) is a mosquito species native to Southeast Asia that has now spread across Türkiye. Given its vector potential and remarkable ability to colonize various environmental conditions, Ae. albopictus is considered one of the most significant invasive mosquito species globally. Under experimental conditions, this mosquito species has demonstrated the potential to transmit four dengue serotypes, yellow fever, chikungunya, Ross River virus, and at least 22 other arboviruses. Consequently, preventing the spread of invasive mosquitoes necessitates the use of environmentally friendly pesticides that are species-specific and have minimal impact on non-target organisms. In this study, we aimed to investigate the larvicidal effects of Cry4Ba and Cry11Aa toxins, which are among the most effective biopesticides for targeting Aedes species. Furthermore, we sought to identify the receptors for Cry4Ba and Cry11Aa toxins to elucidate their mechanisms of action in Ae. albopictus. Despite the critical role of toxin-receptor interactions in Cry toxin efficacy, the receptors that interact with Cry toxins in Ae. albopictus have not yet been characterized. Our findings revealed that two alkaline phosphatases, a vacuolar-type ATPase subunit B, and a maltase-like receptor serve as functional receptors for Cry4Ba and Cry11Aa in Ae. albopictus larvae. Additionally, we demonstrated that the susceptibility of mosquito larvae to Cry toxins is influenced by the downregulation of these receptor gene expressions using RNA interference. These results provide new insights into the mechanisms of Cry toxin action and may contribute to developing more effective mosquito management strategies.
İyonik sıvı elektrolitlerin lityum-kükürt batarya performansı üzerindeki etkisininmodellenmesi
The lithium-sulfur (Li-S) battery is a promising future technology as an energy storage system due to its cost-effectiveness, high theoretical capacity, and energy density. However, fully understanding the complex electrochemical mechanisms remains a significant challenge for further advancement and commercial feasibility. Design parameters of Li-S cells, especially the ones regarding the electrolyte, can significantly impact their performance. In this thesis, a zero-dimensional electrochemical model is established to highlight the impact of electrolyte design parameters. The (Yan, Yin, Guo, & Wan, 2014) (Yan, Yin, Guo, & Wan, 2014) the active reaction area, initial voltage, shuttle and precipitation constants, standard potentials, exchange current densities, C-rate, and the electrolyte-to-sulfur (E/S) ratio is investigated. Simulations were performed using Fortran programming language to illustrate discharge and charge profiles. The impact of the E/S ratio on the discharge and charge profiles is investigated by altering the electrolyte volume in the cell in the model. An increase in the discharge capacity is expected with an increase in the E/S ratio. However, the model is unable to predict this trend. In addition, a sensitivity analysis was performed to see the dependence of the results on the selected model parameters regarding electrolyte design; this way, the impact of ionic liquid electrolyte design on the performance can be captured implicitly. An increase in the exchange current densities causes almost no change in the cell voltage and capacity for all three stages of redox reactions in the model. The changes in discharge and charge profiles are also negligible in terms of the changes in active reaction area and initial voltage parameters. Nevertheless, the influence of the shuttle constant on cell performance is significant; the capacity decreases significantly with increasing the shuttle constant. The model cannot reflect the effect of C-rate as mass transfer is neglected in a zero-dimensional model. In conclusion, a zero-dimensional model is utilized to investigate the impact of electrolyte design parameters through sensitivity analysis. It is successful in predicting the influence of certain parameters. The effect of the electrolyte quantity on battery performance is not observable in the suggested model.
Karşılaştırmalı öğrenme ve geniş dil modellerinin biyomedikal bilgi çıkarılmasında kullanılması
As the volume of human knowledge grows at an extraordinary rate, it is becoming progressively challenging to fully comprehend and utilize the vast array of information available, even within a specialized domain. The field of Biomedicine exemplifies this, with thousands of research papers published each year contributing new insights about species, diseases, and chemicals. Such growth has created an overwhelming need for effective Information Retrieval systems, coupled with Natural Language Processing techniques, to enable the extraction and use of relevant data at a scale beyond human capacity. Effective Information Retrieval in Biomedicine demands an understanding of published research at a granular level, which involves solving several interconnected challenges. For each Biomedical abstract, it is necessary to recognize entities, normalize these entities with standardized identifiers, and extract relationships between different types of entities. These tasks facilitate a structured representation of knowledge and make complex Biomedical information more accessible for scientific and clinical appli- cations. In this study, we investigate and enhance the performance of an existing normal- ization tool, BioNEN [1], by incorporating Contrastive Learning techniques. We ex- plore the integration of dictionaries, Contrastive Learning, and Large Language Models (LLMs) to improve entity recognition, and we examine the use of LLMs for extracting relationships between entities. The result is a streamlined tool designed to identify and normalize entities in Biomedical abstracts and to effectively extract relationships, thereby enabling advancement of Biomedical Information Retrieval systems
Çentikli kompozit yapıların bölgesel güçlendirme optimizasyonu ile mekanik özelliklerin iyileştirilmesi
A composite structure is gravely weakened if a cutout is needed for functional purposes. Instead of uniformly increasing the thickness of the whole structure, locally reinforcing the region around the notches is a much more effective way of increasing the load-bearing capacity of a notched structure. The objective of this study is to find the optimum design of reinforcing layers placed around the hole in a composite laminated plate to maximize its ultimate strength with minimum use of reinforcing material. The ultimate failure load is determined using a progressive damage model based on the Puck failure criterion and the material property degradation method. Finite element (FE) models are developed to obtain the structural response of the plate under tension, compression, or pin loading. The optimum local reinforcement design is found using a modified simulated annealing algorithm, which is a reliable stochastic global search algorithm. A multi-objective optimization scheme is adopted, in which the objective function includes both the ultimate strength and the reinforcement weight so that the ultimate strength can be maximized with minimum use of material. The optimization variables are chosen as the fiber-orientation angles and the size of the reinforcing layers. Optimizations are performed for different configurations of local reinforcements to determine the most effective way of placing the reinforcing layers. Significant improvements in the strength are obtained with minimal added mass through optimization. The findings of this study have significant implications for enhancing the design of notched composite structures.
Yüksek frekanslı integraller ve saçılım problemlerinde uygulamaları
Highly oscillating integrals have drawn interest since the early stages of real and complex analysis. Their role in scattering theory, optics, fluid dynamics and many other applications increased this interest, and in the early 2000s study of numerical computation of such integrals leaped forward. Several methods are proposed for numerical methods, which we briefly compare in the thesis. In this thesis we survey the Filon-Clenshaw-Curtis quadrature for highly oscillating integrals with algebraic and logarithmic singularities and oscillators with stationary points. In that matter, several algorithms are developed and error analysis is presented. The algorithms utilize the advantageous properties of Filon-Clenshaw-Curtis quadrature compared to previously proposed numerical methods. Numerical experiments which investigate extreme cases show the accuracy and stability of the proposed quadrature rule.
Turbopompa sisteminin RPM düzenlemesi için kullanılacak oransal tahliye vanasının modellenmesi ve testi
Launch vehicles use pump-fed pressurization systems, and the energy to drive the pump can be obtained in various ways. Small rockets may use electric motors, but larger liquid rocket engines often use gas generator cycles, where the turbine is driven by pre-combustion chamber products. In this study, a novel PID controller system has been proposed in which the hot gas resulting from the combustion of a hybrid rocket motor or cold gas resulting from pressurized tank is regulated before entering the turbine, similar to the turbochargers in cars. Due to the characteristics of the hybrid rocket used in the hot gas generator, the energy produced decreases over time, and therefore the system produces more energy during operation than the turbopump system requires. The required amount of the produced gas is directed to the turbopump system and the rest is exhausted using a proportional wastegate. The excess energy produced ensures that RPM stays constant during pressure fluctuations in the combustion chamber. The proposed system employs a closed-loop control strategy, where feedback from the turbine speed is measured with a distance sensor and this feedback is used to adjust the wastegate position and maintain the desired RPM. In this study, modeling and characterization of the proportional wastegate were conducted, and a turbine speed sensor was developed using a proximity sensor. System was modeled in MATLAB Simulink, and control algorithm was developed. Then, tests were conducted with both hot and cold gas generators to validate the system's performance. Both simulation and test results demonstrate that the proposed control system can effectively regulates the turbopump speed within a desired range, even under disturbances.