SACM - United States of America
Permanent URI for this collectionhttps://drepo.sdl.edu.sa/handle/20.500.14154/9668
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Item Restricted Characteristics and Health Risks Associated with Fine Particulate Matter and Its Components in Two Major Cities of Saudi Arabia: A Study of Makkah and Madinah(Saudi Digital Library, 2026) ALsufayan, Yousef; Khwaja, HaiderAbstract Urban air pollution, particularly from fine particulate matter (PM₂.₅), is a growing public health concern in many rapidly urbanizing countries and regions, including Saudi Arabia. This thesis investigates the levels, sources, seasonal variations, and health impacts of PM₂.₅ in the cities of Makkah and Madinah. PM₂.₅ monitoring focused on identifying key pollutants—including black carbon (BC), trace elements (TEs), and water-soluble ions (WSIIs)—which were measured using advanced analytical techniques such as Optical Transmissometer (OT-21), Energy Dispersive X-Ray Fluorescence Spectrometry (ED-XRF), and ion exchange chromatography. Source apportionment was carried out through positive matrix factorization (PMF), elemental enrichment factor (EF) calculations, and backward air mass trajectory analysis. The study investigates PM₂.₅ concentrations at five urban sites in Makkah, including Alharam, Ar Rusayfah, Alshoqiyah, Alhajj, and Herra Hospital. Average PM₂.₅ concentrations in these sites ranged from 59.3 μg/m³ to 109 μg/m³, exceeding the World Health Organization’s (WHO) 24-hour guideline of 15 μg/m³ by factors ranging from 4.0 to 7.3. In Madinah, PM₂.₅ concentrations were lower but still exceeded international air quality standards. Average concentrations across five sites, including Al-Awali, Al-Hijra, Uhad, Bab al-Masjid, and Bagidu, ranged from 37.7 μg/m³ to 103.3 μg/m³, with higher concentrations observed in urban and high-traffic areas. Seasonal patterns show that PM₂.₅ concentrations peak in the spring due to increased traffic, construction activities, and meteorological conditions conducive to particulate accumulation, while the winter months exhibit lower concentrations, attributed to improved atmospheric dispersion. The chemical composition analysis revealed that sulfate (SO₄²⁻) was the most abundant ion, followed by ammonium (NH₄⁺) and nitrate (NO₃⁻), which together accounted for approximately 19% of the total PM₂.₅ mass. The study identified multiple sources of PM₂.₅, including combustion of fossil fuels, vehicular emissions, industrial dust, and secondary aerosols, with significant contributions from both local and long-distance transported pollutants. A key objective of the study was to quantify the impact of air pollution exposure on health by examining the association between daily PM₂.₅ concentrations and cardiopulmonary morbidity. The research linked specific PM₂.₅ constituents, including BC and TE like lead (Pb), nickel (Ni), and iron (Fe), to short-term health impacts. In Makkah, BC and Pb were significantly associated with increased hospital admissions for cardiovascular (CVD) and pulmonary diseases. These constituents serve as critical indicators of anthropogenic activity: BC primarily reflects incomplete combustion from heavy traffic and diesel engines, while Pb acts as a tracer for industrial emissions. Furthermore, these associations were particularly pronounced for inpatient admissions, suggesting that individuals with pre-existing conditions are more vulnerable to the acute effects of air pollution. The analysis also revealed that certain populations, such as middle-aged adults and females, showed greater susceptibility to PM₂.₅ exposure, possibly due to biological or behavioral factors. Women, for instance, may experience higher internal doses due to smaller airway diameters or distinct activity patterns .The short-term health risks from BC were comparable to findings from other regions with high pollution levels, such as China and North America, underscoring the need for source-specific mitigation strategies. The results of this study underscore the importance of considering the chemical composition of PM₂.₅ when formulating air quality regulations. The analysis determined that sources of these pollutants in the investigated cities—specifically combustion-derived BC and metal-rich fractions—were associated with a significantly greater likelihood of the adverse health outcomes evaluated. The study finding support targeted emission control strategies, particularly in urban areas and during high-traffic periods such as the pilgrimage seasons. It also calls for stricter rules on vehicle emissions, industrial filtration, and real-time monitoring of air quality. Future research should focus on improving exposure assessment and implementing integrated mitigation strategies to protect public health and promote sustainable urban development. Keywords: PM2.5, Water soluble ions, Air quality Sources , GLM, Negative Binomial18 0Item Restricted Examining Youth Online Safety and Well-Being Through the Lens of Social Media Affordances(Saudi Digital Library, 2026) Alluhidan, Abdulmalik; Yin, ZhijunSocial media has become a fundamental part of adolescents’ lives. Yet the effect of its use on their well-being remains debatable, as prior research shows a lack of consensus, with studies identifying effects in both positive and negative directions. A key limitation in existing literature is the tendency to treat social media as a single, uniform entity when examining its risks and benefits. Much prior work has focused on how use frequency or intensity relates to outcomes, often overlooking how specific platform design components shape these outcomes. This generalized approach obscures how different platforms offer distinct patterns of engagement that may lead to varying experiences. Without accounting for these differences, it becomes difficult to identify which aspects of social media are responsible for particular risks or benefits. Understanding how the design influences user experiences is therefore critical for developing interventions that move beyond addressing harmful outcomes alone and instead target the underlying inputs and pathways that contribute to those outcomes. To address these limitations, this dissertation adopts an affordance-based approach to examine online safety and well-being among youth. Affordances refer to the perceived possibilities for action offered by a technology, including how platform features enable or constrain user behavior. In the context of social media, an affordance-based perspective helps explain how youth navigate, experience, and respond to platform design. Applying this lens moves the discussion beyond broad risk-and-benefit debates and provides a clearer conceptual framework for identifying design choices that reduce harm and support positive use. Additionally, rather than focusing on temporary characteristics such as platform popularity, this approach targets replicable technological qualities, allowing findings and interventions to remain applicable, thereby improving generalizability as platforms evolve over time. Across four studies, this dissertation first conducts a systematic literature review of prior research to develop an affordance-centered framework that maps how platform features relate to user activities, the affordances they enable, and associated benefits and risks. It then examines youth support-seeking experiences across seven social media platforms to show how affordances in different contexts shape outcomes. Next, it turns to private channels to show how conversational settings shape both youth disclosures and the responses they receive. Finally, it uses participatory co-design to translate these insights into affordance-informed recommendations for improving youth online safety and well-being.4 0Item Restricted ANALYSIS AND SIMULATION OF A FREE BOUNDARY PROBLEM MODELING TUMOR EVOLUTIONDr.Xuming Xie(Saudi Digital Library, 2025) Aldakhil, Amal; Xuming, XieThis dissertation concerns analysis and simulation of a free boundary problem modeling tumor growth. Incorporating immune cell interactions, the model consists of a coupled system of partial differential equations describing the densities of cancer cells and T-cells within a tumor region whose boundary evolves dynamically over time. A new framework is developed by assuming flux boundary conditions for both cancer cells and T-cells at the moving boundary. Using tools in the theory of Partial Differential Equations, we establish the existence, uniqueness, and global behavior of classical solutions under suitable initial conditions. To complement the theoretical results, a fully discrete numerical algorithm based on the finite difference method is derived after rescaling the problem to a fixed domain, the stability of the numerical algorithm is discussed. Numerical simulations are conducted to explore the long-term behavior of the tumor, demonstrating that the tumor may shrink or grow depending on the immune killing rate. The numerical results validate the theoretical predictions and provide deeper insights into the interplay between tumor evolution and immune response. This study contributes to the mathematical understanding of tumor-immune dynamics and highlights the critical role of immune strength in determining tumor fate, offering potential implications for immunotherapy strategies.4 0Item Restricted THE IMPACT OF YOUTUBE INFLUENCERS ON CONSUMER PURCHASE INTENTION AND ENGAGEMENT IN SAUDI ARABIA(Saudi Digital Library, 2026) Alqahtani, Abdullah; Fei, XueThis study examines the influence of YouTube influencers' characteristics and content attributes on consumers' purchase intention and engagement in the Saudi Arabian context. Grounded in Source Credibility Theory and interpreted through the Elaboration Likelihood Model (ELM), the study employs a quantitative approach using survey data collected from 402 participants. The findings reveal differentiated effects across the two outcome variables. Initially, Perceived Trustworthiness and Perceived Expertise were not significant predictors of either purchase intention or consumer engagement. However, after introducing the control variables (age, gender, and social media use), gender significantly predicted purchase intention, and Perceived Trustworthiness became a significant predictor of purchase intention. In addition, Perceived Attractiveness and Perceived Homophily significantly influenced consumer engagement, but did not affect purchase intention, indicating that they enhance relational and interactive responses rather than direct purchasing behavior. Conversely, Perceived Influencer–Product Congruence significantly influenced purchase intention but not consumer engagement, highlighting the importance of perceived fit and authenticity in shaping behavioral outcomes. Notably, Perceived Informative Value emerged as the only variable that significantly influenced both purchase intention and consumer engagement, underscoring its central role in the effectiveness of YouTube influencer content. Overall, the findings refine the application of Source Credibility Theory to YouTube influencer marketing and demonstrate how different influencer characteristics and content attributes operate through distinct persuasive mechanisms, as explained by the Elaboration Likelihood Model. The study also provides practical implications for developing more effective influencer marketing strategies in Saudi Arabia.13 0Item Restricted Teacher's Perceptions of AI Tools in English Academic Writing Instruction(Saudi Digital Library, 2026) Alotaibi, Najla; Zhang, TerrenceThis research examines university-level instructors' perceptions of generative artificial intelligence (AI) applications, such as ChatGPT, in teaching academic writing. The study explores instructors' perceptions, interpretations, and adaptations regarding the challenges and opportunities of AI integration in their classes. This research relies on semi-structured interviews to examine how teachers use AI in their writing classes, their concerns about originality and academic integrity, and how they are adjusting their pedagogical practices to incorporate AI. The findings show that although teachers believe AI can enhance students' learning, they are also concerned about overreliance on technology and its impact on students' critical thinking. The study provides insights into the evolving role of AI in writing pedagogy and offers practical implications for incorporating AI into educational institutions without compromising academic integrity.6 0Item Restricted PhD Dissertation(Saudi Digital Library, 2026) Almalki, Faris Abdullah; Cortes, DanielLow back pain can originate from the facet joint, which is innervated by the medial branch of the dorsal rami in the lumbar spine. One of the modalities used to treat facet joint pain is the use of radiofrequency ablation (RFA) of the medial nerve. Since this nerve supplies both facet joints and multifidus muscles, applying RFA will not only alleviate facet joint pain but also adversely affect the multifidus muscle. The multifidus muscle has an essential role in maintaining spinal stability. Activation of the multifidus muscle during different movements affects the pressure within the lumbar intervertebral discs. Therefore, its function is interrelated with the biomechanics of the spine. Denervation after RFA can significantly alter the normal mechanics of the spine, which in turn can lead to or worsen degeneration in spinal tissues such as the intervertebral disc and surrounding ligaments. The goal of this study is to evaluate the impact of the RFA procedure on the biomechanics of the spine. To achieve this, first, force-dependent kinematics simulations of different torso movements were performed to quantify the changes in joint forces and vertebral rotations that occur after denervation of the multifidus. These changes were found to be significant, especially after bilateral ablation compared to unilateral ablation. These results were used to evaluate changes in stresses and strains in soft tissues of the spine. To create an anatomical representation of the spine for both female and male populations, statistical shape models of the vertebrae were developed from a collection of computed tomography images. Finally, a finite element model was developed and validated using the statistical shape models and the forces and angular changes from the force-dependent kinematics model. The finite element analysis (FEA) showed that RFA alters the stress distribution in the intervertebral disc, increasing the risk of disc degeneration. This approach may elucidate the effect of RFA on the intervertebral disc.3 0Item Restricted EXPERIMENTAL INVESTIGATION OF FLOW DYNAMICS IN A 9×9 HELICAL CRUCIFORM FUEL BUNDLE USING TIME-RESOLVED PIV(Saudi Digital Library, 2026) ALLowaimi, Mohammed Habeeb A; Hassan, Yassin AThe Helical Cruciform Fuel (HCF) rods proposed by Lightbridge are intended to enhance the power density of both existing and newly constructed Light Water Reactors (LWRs). Unlike conventional cylindrical rods, the HCF design incorporates axially twisted cruciform-shaped fuel rods. This distinctive geometry provides a self-supporting feature, as the rods make contact and support one another at every 90-degree twist, thereby eliminating the need for spacer grids. In addition, the design improves coolant mixing and allows for a more efficient packing arrangement of the fuel rods, both of which have the potential to increase overall reactor performance. To evaluate these potential advantages, this study proposes a detailed experimental investigation of the flow dynamics within a 9×9 HCF bundle. At present, there is a lack of high-fidelity experimental databases addressing flow behavior in such bundle configurations, especially across multiple flow regimes. The planned investigation will employ a matched index of refraction (MIR) facility in conjunction with Time-Resolved Particle Image Velocimetry (TR-PIV) at two Reynolds numbers: 350, and 7,000. Four measurement planes will be examined: the centered plane, the between-rods plane, the through-rods plane, and the near-wall plane. The analysis will extract first- and second-order flow statistics from the TR-PIV data, including mean velocity distributions, velocity magnitude, turbulent kinetic energy (TKE), root-mean-square velocity fluctuations, vorticity, and Reynolds shear stress. Additionally, power spectral density (PSD) analysis will be performed to evaluate the frequency distribution of streamwise and spanwise velocity fluctuations, enabling identification of dominant spatial frequencies and turbulent flow patterns. The outcome of this work will be a valuable high-quality experimental database for the 9×9 HCF bundle. These results will not only address a significant gap in literature but will also provide essential benchmark data for future computational fluid dynamics (CFD) simulations of advanced nuclear fuel designs40 0Item Restricted Assessment of Dimensional Accuracy, Color Stability, Wear Resistance Against Zirconia, and Relining Tensile Strength in Conventional, Milled, and 3D Printed Complete Dentures: An In Vitro Comparative Analysis(Saudi Digital Library, 2026) Shihata, Hamza; Muftu, AliObjective: This study comprehensively evaluated the properties of complete denture materials fabricated via Stratasys Poly-Jet 3D printing, Ivotion subtractive milling, and conventional heat-polymerized methods. The investigation focused on four key performance aspects: accuracy, resilient denture reline bond strength, color stability, and wear resistance. Materials and Methods: Denture samples were fabricated following each manufacturer's recommended fabrication technique. Accuracy was assessed using root mean square deviation from reference STL files across whole dentures, intaglio surfaces, and teeth regions, with baseline and post-aging measurements. Tensile bond strength of Pac-Dent resilient denture reline on denture bases was measured under standardized load. Color stability denture bases and teeth shade materials was examined by immersion in staining media (toluidine blue, coffee, tea), with color changes quantified using benchtop spectrophotometer per ISO 7491 standards. Wear was simulated over 250,000 cycles against glazed and polished Katana zirconia antagonists, with surface wear quantified using weigh before and after the test. Results: Stratasys 3D-printed dentures demonstrated superior initial accuracy with mean ± SD RMS deviations of 96.8 ± 11.7 µm compared to 584.8 ± 22.4 µm for Ivotion milled (p < 0.001). Tensile bond strength of Pac-Dent soft liner was consistent among groups (conventional: 1.01 ± 0.94 MPa; milled: 0.94 ± 0.94 MPa; 3D-printed: 0.88 ± 0.73 MPa) with no statistical significance (p = 0.781). Ivotion milled bases exhibited the greatest color stability, maintaining ΔE below clinically acceptable thresholds after staining, whereas 3D-printed bases had significantly higher discoloration, particularly with tea (ΔE 6.20 ± 2.60 for pink bases) and with coffee (12.16 ± 4.07 for tooth shade) , p < 0.001). For wear test, conventional denture material experienced significantly greater weight loss than both milled (p = 0.009) and 3D printed (p = 0.032) materials. Conclusion: Printing with Stratasys technology provides Accuracy compared to milling method using this particular workflow. Pac-Dent resilient denture reline material adheres reliably across fabrication types. Ivotion milled denture bases currently offer superior color stability and wear resistance, though 3D printing continues to evolve with improving material properties. These findings provide a comprehensive evaluation to guide clinical material selection and inform the integration of advanced digital denture fabrication workflows.11 0Item Restricted Engineering PEG-b-PPS Bicontinuous Nanospheres for Mycobacterial Lipid Antigen Delivery and CD1-Restricted T Cell Response(Saudi Digital Library, 2026) Almunif, Sultan; Scott, Evan ABicontinuous nanospheres (BCNs) are self-assembled polymer nanostructures with interconnected aqueous channels that enable co-loading of hydrophilic and hydrophobic cargo, making them attractive candidates for vaccine and drug delivery. A key barrier to their broader application has been limited control over BCN size and size distribution. This dissertation establishes a scalable approach to engineer poly(ethylene glycol)-b-poly(propylene sulfide) (PEG-b-PPS) BCNs with tunable size using a multi-inlet vortex mixer (MIVM) flash nanoprecipitation strategy. Structural characterization confirms that bicontinuous internal morphology is maintained across the engineered size range. This work further defines how BCN size and morphology contribute to biological identity, demonstrating that early protein adsorption differs between BCNs and bilayer polymersomes, while in vivo biodistribution is governed predominantly by particle size. These principles are applied to vaccine design by encapsulating the mycobacterial lipid antigen mycolic acid (MA) with defined adjuvant combinations, leveraging BCN multi-loading to evaluate how innate cues shape MA-specific responses. Although Mycobacterium tuberculosis (Mtb) infection elicits immune responses to both protein and lipid antigens, lipid antigen-based vaccination strategies remain underexplored. To address this, PEG-b-PPS BCNs co-encapsulating MA and the protein antigen Ag85B were formulated and benchmarked against Bacillus Calmette-Guérin (BCG) vaccination. MA-Ag85B-BCN vaccination elicits both MA- and Ag85B-specific responses; however, MA-driven T cell activation remains detectable up to 6 months post-vaccination, whereas Ag85B-specific T cell responses were not detected at this time point. A similar long-lasting MA-associated activation pattern is observed after BCG vaccination. Together, these studies connect scalable BCN engineering to biological performance and demonstrate BCN dual-loading as a rational strategy to deliver lipid-protein antigen combinations and shape CD1-restricted T cell responses relevant to tuberculosis vaccination.16 0Item Restricted SAUDI VISION 2030: A SUMMATIVE EVALUATION OF TOURISM (INVESTMENT AND REVENUE)(Saudi Digital Library, 2026) Alotaibi, Nada; Johnny, B. GilleylenSaudi Arabia’s dependence on oil revenues has made its economy vulnerable to fluctuations in global energy markets. To address this challenge, Saudi Vision 2030 was introduced to diversify the economy and strengthen non-oil sectors, particularly tourism. The tourism sector has been identified as a key driver of economic diversification, investment attraction, and employment creation. This study evaluates the performance of Saudi Arabia’s tourism sector within the framework of Vision 2030, focusing on tourism investment and revenue generation. Using a quantitative cross-sectional design, the research analyzes secondary data from 2006 to 2023 on tourist arrivals, tourism investment, tourism spending, and tourism employment. Descriptive and inferential statistical techniques, including time-series analysis, t-tests, and ANOVA, were applied to assess differences before and after the implementation of Vision 2030. The findings indicate significant growth in tourist arrivals, tourism investment, and tourism spending, suggesting that the tourism sector is progressing toward supporting economic diversification and achieving Vision 2030 objectives.14 0