Saudi Cultural Missions Theses & Dissertations
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Item Restricted Perovskite Solar Cells Incorporated with Processing Additives(The University of Akron, 2024) Sawwan, Hussain; Gong, XiongThe increased use of solar energy for power is anticipated to lead to the shift from traditional power sources to renewable energy sources. Photovoltaic (PV) is a promising technology due to its ability to directly convert sunlight into electricity with no pollution. Solar cells, specifically those based on metal halide perovskites (MHPs) have gained popularity recently due to their power conversion efficiency (PCE) that have increased dramatically over the past 15 years, from 3.8% to more than 26 %. The rapid development in PCE is due to the advanced features that MHPs have such as cost-effective and easy processing, high absorption coefficient, large diffusion length, and low exciton binding energy. In particular, the purpose of this study is to develop solution-processed perovskite solar cells (PSCs) by tuning film morphology and optoelectronic properties of metal halide perovskites incorporated with processing additives, thereby optimizing the performance of PSCs. To maximize the potential of perovskite, controllable crystallization is crucial for producing high-quality perovskite thin films with fewer structural defects and additive engineering is a facile and effective method among other techniques. We mainly investigated the effects of various processing additives on the MHPs based on MAPbI3 perovskite (where MA is CH3NH3) and correlate PCE in term of film morphology, crystallinity, photocurrent hysteresis, optoelectronic properties, device performance and stability of PSCs.19 0Item Restricted Effect of Light and Heavy Touch on Transtibial Amputees’ Postural Control and Weight-Bearing Asymmetry(University of Illinois Chicago, 2024) Tobaigy, Moaz; Sawers, AndrewThe objective of this thesis was to determine the effect of augmented sensory feedback and mechanical support on traumatic unilateral transtibial prosthesis users’ postural stability, neuromuscular control, and weight-bearing asymmetry during quiet stance. Our central hypothesis was that postural instability in traumatic unilateral transtibial prosthesis users is a sensory problem. To test this hypothesis 12 traumatic unilateral transtibial prosthesis users and 12 unimpaired age- and sex-matched adults were recruited, enrolled, and completed the study protocol. Participants postural stability, neuromuscular control, and weight-bearing asymmetry were assessed during quiet stance under three conditions: baseline no touch, light touch, which provides sensory feedback, and heavy touch, which provides mechanical support. Postural stability, neuromuscular control, and weight-bearing asymmetry were characterized by center of pressure mean velocity, total integrated area across select lower limb muscles, and a weight-bearing asymmetry index, respectively. In the first study of this thesis unilateral transtibial prosthesis users were found to have greater medial-lateral but not anterior-postural postural instability than age- and sex-matched adults. Importantly, this medial-lateral instability was only resolved relative to age- and sex-matched adults with mechanical support from heavy touch. In the second study we found that neither light touch (i.e., sensory) nor heavy touch (i.e., mechanical support) shifted traumatic unilateral transtibial prosthesis users’ neuromuscular control of postural stability towards proximal muscles during quiet stance. In contrast, we found that mechanical support from heavy touch significantly reduced the total muscle activity used by traumatic unilateral transtibial prosthesis users during quiet stance. In the third study of this thesis we found that despite improvements in postural stability via heavy touch, there was no accompanying reduction in weight-bearing asymmetry, suggesting that weight-bearing asymmetry is not used as a compensation to maintain stability The results of this thesis suggest that contrary to our central hypothesis postural instability in unilateral transtibial prosthesis users may be attributable to mechanical rather than sensory deficits.17 0Item Restricted The Effect of ESG on The Financial Sector(University of New Orleans, 2024-05-09) Sendi, Asaad; Kabir, Hassan MThis paper explores the intricate impact of ESG (Environmental, Social, and Governance) factors on the stability of banks across different continents, with a specific focus on distinguishing the effects on both conventional and Islamic banking institutions. Our comprehensive empirical analysis reveals a substantially positive influence of ESG activities on the stability of both types of financial institutions. Notably, after employing pooled and fixed estimator regressions, the findings highlight the significantly positive effect of lagged ESG scores on the stability of conventional and Islamic banks, signifying the potential for ESG performance to enhance their overall stability. Further examination shows that the environmental pillar score, particularly in the conventional banking sector, displays highly positive and statistically significant outcomes, emphasizing the constructive impact of environmentally responsible practices. Conversely, the social pillar exhibits a positive correlation with the z-score in the Islamic banking segment, indicating that banks actively involved in community service and social responsibility initiatives experience improved stability. In conclusion, our study underscores the transformative potential of ESG activities in positively shaping both the external perception and internal operations of banks, ultimately contributing to increased valuations and improved stability.31 0Item Restricted Influence of Variation in Mix Composition on Stability and Performance of Asphalt Mixtures(2023-05) Abu Saq, Mohammed; Kassem, EmadIncorporating Reclaimed Asphalt Pavement (RAP) in asphalt mixtures offers remarkable environmental and economic benefits. However, proper design and evaluation of asphalt mixtures with RAP are needed to ensure satisfactory performance. This study examined and proposed several methods for proper design and evaluation of asphalt mixtures with and without RAP. The first phase of this study developed and evaluated several compaction indices as well as measured mechanical properties of asphalt mixtures prepared with RAP. The main objective of this phase is to identify methods that can be used to detect changes in mix composition (e.g., change in RAP content, binder content, binder grade, etc.) during production. The change in mix composition may adversely affect the performance of asphalt mixtures. For example, the use of higher percent of RAP or lower binder content than specified may result in stiffer mixes that are prone to fatigue cracking leading to premature failure of asphalt pavements. A mathematical model was developed to calculate a parameter called Gyratory Stability (GS) from the compaction curve data specific to the Pine Superpave gyratory compactor. The GS is the summation of shear energy increments exerted on the sample during compaction. The GS describes the ability of asphalt mixtures to resist rutting, and it can be determined during the mix design stage using the gyratory compaction data. In addition, this study examined the sensitivity of various compaction and stability indices including GS, construction densification index (CDI), locking point (LP), workability energy index (WEI), and laboratory compaction index (LCI) to changes in mix composition (e.g., RAP content, RAP source, binder content, binder grade, etc.). Such indices can be used as quick, indirect indicators of variation in mix production when placed in the field. The results demonstrated that GS, construction densification index (CDI), and laboratory compaction index (LCI) were sensitive to the binder content; however, all the compaction indices were less sensitive to the change in the RAP content and binder grade. The GS and CDI decreased with the increase in binder content while the LCI increased with the increase in binder content which indicates less energy is needed for compaction. There were fair correlations between the rut depth and both GS and CDI; however, the LCI showed better correlation with the rut depth. There is a need to evaluate and implement a balanced (engineered) mix design concept for asphalt mixes prepared with high RAP content to ensure that such mixtures have adequate resistance to cracking and rutting. Increasing the amount of RAP in asphalt mixtures offers environmental benefits and cost savings. This study demonstrated that the mix design of asphalt mixtures with 50 percent RAP can be optimized by increasing the binder content to improve the cracking resistance. The results demonstrated the improvement on the cracking resistance when increasing the binder content which indicates the importance of implementing the balance mix design when incorporating RAP materials in asphalt mixes. Furthermore, this study examined the sensitivity of various cracking performance indicators to the change in mix composition as well as the variability and correlation between different performance indicators. The results demonstrated that the Indirect Tensile (IDT) modulus (IDTModulus) and Indirect Tensile (IDT) strength (IDTStrength) were able to capture the change in binder content, binder grade, and RAP content. These two parameters can be used to assess the variation in mix composition during field production and operations. The second phase of this study focused on the development of a regression model to predict the IDT load-displacement curve which is used to calculate many monotonic cracking performance indicators to assess the performance of asphalt mixtures. The cracking performance indicators include IDTStrength, fracture energy (Gf), WeibullCRI, IDEAL-CTIndex, Cracking Resistance Index (CRI), and Flexibility Index. This study examined the effect of mix composition on the IDT load-displacement curve and developed statistical regression model to describe the curve. Asphalt mixtures with different compositions (e.g., binder grade, binder content, aggregate gradations) were prepared and tested using the IDT. The IDT regression model includes parameters that describe mix composition and properties such as binder content, aggregate gradation, complex shear modulus and phase angle of asphalt binders. The results of the proposed model correlated well with the experimental measurements. The monotonic cracking performance indicator calculated from the model also had strong correlations to the ones calculated from the measured IDT load-displacement curve. The proposed model can be used as a tool to check the preliminary performance of the asphalt mixtures during the mix design stage and mix composition can be adjusted to improve its performance (e.g., adjust binder grade, binder content, gradation, etc.). The last phase of this study further developed a Multi-Stage Semi-Circular Bending Dynamic Test (MSSD) that has been recently proposed by the researchers at University of Idaho. The MSSD was found to overcome the limitations associated with using monotonic testing when evaluating the cracking performance of samples extracted from the field. The dynamic testing simulates the repeated traffic loading applied on asphalt pavements in the field; therefore, the dynamic testing provides accurate assessment of fatigue cracking performance. The MSSD applies a fixed loading sequence to test different asphalt mixture samples including laboratory-prepared samples and field cores. The MSSD test was conducted with testing equipment that did not measure the crack opening and collected a limited number of data points which limited the analysis of the test results. There is a need to further develop the MSSD test and use an advanced system with enhanced capabilities that would enable the researchers to collect more data for advance the analysis of the test results. The MSSD results demonstrated that mixtures with higher density (less air voids) exhibited better resistance to cracking or longer fatigue life. In addition, the results clearly demonstrate the limitations of monotonic cracking performance indicators to assess the cracking resistance of asphalt mixture samples with different air void. Caution should be exercised when using the IDT test. Finally, the correlation between the revised MSSD parameters and original MSSD parameters was found to have a strong relationship with R2 of 0.83 and 0.96, respectively.15 0