Browsing by Author "Alzahrani, Yasser"

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Acomprehensive study of amyloid-beta kinetics and mechanism influenced by metal ions, chelation therapy, and inhibitor drugs in the treatment of Alzheimer’s disease
(Saudi Digital Library, 2025) Alzahrani, Yasser; Yarahmadian, Shantia
Alzheimer's disease (AD) is a progressively developing neurological condition leading to cognitive and behavioral decline. The cause of AD is still unknown. Pathologically, hypotheses such as impaired neurotransmission, oxidative stress, metal ions, and amyloid-beta (A$\beta$) aggregation are vital contributors to AD's pathophysiology. Recent research focuses on treatments targeting the brain's A$\beta$ polymer deposits, commonly seen as amyloid plaques. Chapter 1 introduces AD, dissertation goals, and its outline. Chapter 2 provides a detailed scientific background on the pathophysiology of AD and key hypotheses from the literature and reviews recent drug treatment research. Chapter 3 aims to develop intuitive mathematical models to elucidate AD treatment with inhibitory drugs. These models clarify the complex kinetics of A$\beta$ formation and drug interactions. We discuss two categories of drugs: first, anti-inflammatory drugs (NSAIDs), which act as monomer inhibitors of A$\beta$ aggregation, and second, drugs that directly interact with A$\beta$ aggregated polymers. We initially analyze each drug independently and then assess their combined effects. Our numerical simulations demonstrate that the first type of drug reduces the equilibrium state value of aggregated filaments, whereas the second model of drug exhibits even greater efficacy in reducing the equilibrium state value of aggregated filaments. Furthermore, we conduct simulations of the simultaneous application of both drugs. The results are compared with the experimental data. Chapter 4 presents a novel and rigorously validated mathematical model to investigate the kinetics of ($A\beta$) aggregation in the presence of biologically relevant metal ions, chelating agents and inhibitor drugs. The model captures the microscopic reaction mechanisms that exist in the dynamics of $A\beta$ and explicitly accounts for the catalytic roles of copper, zinc, and iron ions, key contributors to the formation of neurotoxic plaques in AD. Clearly, our framework integrates dual therapeutic strategies: (i) metal chelation therapy, which binds and neutralizes free metal ions, and (ii) direct inhibition of $A\beta$ aggregation. Simulations in a variety of kinetic regimes reveal how each intervention modulates aggregation pathways, independently or synergistically. These studies focus on developing and analyzing mathematical models that describe the aggregation of $A\beta$ with and without metal ions under different inhibitor drugs and chelation treatment.
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PARAMETRIC STUDY FOR JET IMPINGEMENT HEAT TRANSFER ENHANCEMENT USING DIFFERENT ROUGHNESS ELEMENTS
(2023-08) Alzahrani, Yasser; Han, Je Chin
Gas turbines are utilized for a variety of industrial applications, such as electric power generation (large land-based gas turbines), driving compressors and pumps, and providing thrust for aircraft propulsion (jet engines). To maximize the engine’s efficiency, the rotor inlet temperature (TIT) needs to continuously increase beyond its current maximum of 1700 oC, which is far beyond the softening limit of turbine blades and vanes at 1000 oC. Thus, the cooling of hot gas path components is vital to prevent component failure due to thermal stress. Over the past decades, turbine cooling technologies have rapidly advanced. Regions under critical heat loads from the combustor gases, such as the leading edge of rotating blades and the leading edge and mid-cord regions of stator vanes, require aggressive. Jet impingement is commonly used in these areas. Jet impingement cooling provides a very high local heat transfer rate at the expense of a high pressure loss penalty. Further enhancement of jet impingement heat transfer has been achieved by introducing roughness elements to the target surface. Therefore, continued research to evaluate the performance of different roughness elements is necessary. In this dissertation, experimental investigations on the heat transfer, crossflow, and discharge coefficients in a rectangular impingement channel roughened with pin-fins, strip-fins, orW-shaped ribs were conducted using a steady-state, copper plate experimental method. The experimental study was supplemented by numerical flow field visualizations using ANSYS Fluent software to better understand the complex flow behavior. This parametric study examines the associated effects of varying the following key parameters: jet Reynolds number (Rejet = 10k – 70k), jet-to-target surface spacing (z/d = 3 and 6), pin-fin height (H/d = 1.5 and 2.75), strip-fin height (H/d = 1.5 and 2.75), and W-rib pitch (P/e = 18, 9 and 6). The results revealed important information regarding the heat transfer performance of each investigated configuration. Experimental results showed that all channel configurations have similar discharge coefficients, which decrease at a higher rate beyond Rejet = 50k when increasing the height of pin-fin or strip-fin, the number of W-rib rows, or the jet-to-target surface spacing. Additionally, the pressure drop in the impingement channel increases with the addition of roughness elements. The results indicated that the heat transfer augmentation from increasing fin height or number of W-ribs is less than the augmented surface area. Therefore, it is recommended to optimize the height and position of installed roughness elements for best heat transfer performance. Furthermore, the numerical results demonstrated highly non-uniform velocity distributions at the near-target surface regions, signifying non-uniform heat transfer. The highest heat transfer enhancement was obtained in the narrow impingement channel with long strip-fins.
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