Browsing by Author "Asiri, Mohammed"

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An investigation of a novel method for the diagnosis of osteoporosis using quantitative ultrasound
(Exeter University, 2024) Asiri, Mohammed; Knapp, Karen; Fulford, Jonathan; Strain, David
Rationale: The rising global prevalence of osteoporosis and its significant financial and healthcare costs have prompted a revaluation of existing diagnostic procedures, mostly focused on dual-energy X-ray absorptiometry. Despite its popularity and usefulness, DXA has downsides that include radiation exposure, high prices, restricted availability in developing countries, and erroneous findings impacted by body fat composition. These limitations have led to the development of alternative diagnostics. Radiofrequency echographic multi-spectrometry (REMS) is a new method that uses ultrasound and advanced algorithms to evaluate bone health. However, its broad use and validation in varied therapeutic situations remain obstacles. Method: The precision error rate was measured to assess the ability of REMS to provide precise measurements. Seven operators scanned 61 participants' femur and lumbar spines to measure inter- and intra-operator reproducibility. Short-term precision tests were performed on 15 subjects, 10 continuing for medium- and long-term evaluations. Another 168 men and women were recruited to have REMS and DXA scans of the lumbar spine and femur. This set-up tested REMS' reliability and capacity to distinguish fracture patients. The study also compared REMS readings with DXA results in diabetes as a disease affecting bone density. A subset of 23 participants was scanned for abdominal fat thickness measurement to explore the influence of fat on REMS measurements. Finally, a survey assessed the acceptability of participants with REMS technology and examined how body composition affects measurement accuracy. Results: REMS had a better precision error rate than DXA in evaluating bone density in the lumbar spine and femur. REMS performed better in femoral evaluations than in the spine, in reasonable agreement with DXA and may detect osteoporosis and discriminate bone health states. Fracture risk prediction was more sensitive with DXA. The survey showed a negligible effect of body composition on the REMS measures and favourable participant approval. Despite these promising results, the study stressed the necessity to validate REMS in under-represented populations and diverse clinical settings. Conclusion: This Ph.D. project showed the promise of REMS as a novel osteoporosis diagnostic tool, highlighting its strengths and weaknesses. Based on the findings, REMS technology could potentially serve as a primary or supportive tool in the diagnosis and management of osteoporosis. Further research is essential to refine its diagnostic accuracy and efficacy in different demographics and clinical contexts. Expanding the evidence base will solidify the role of REMS in osteoporosis care.
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Computational Study of Crossflow Patterned Hollow Fiber Vacuum Membrane Distillation
(Saudi Digital Library, 2025) Asiri, Mohammed; Alparslan, Oztekin
Large Eddy Simulations (LES) were conducted to investigate transport phenomena in hollow fiber Vacuum Membrane Distillation (VMD) modules. Most previous studies have investigated VMD, where the feed flow is in the same axial direction and the boundary layers remain attached to the membranes, resulting in a gradual decline in driving force and a decrease in flux toward the outlet. A crossflow-patterned hollow fiber module (HF-VMD), in which the feed enters across the bundle, moving orthogonal to the fibers from top to bottom, is considered in this research. Key performance indicators included permeate flux, temperature polarization coefficient (TPC), and concentration polarization coefficient (CPC). The results demonstrate that crossflow geometry outperforms parallel flow, enhancing flux by nearly 40% while suppressing polarization. Medium to high packing densities (50–75%) provide an effective balance between compact module design and stable flux, as indicated by the merit number. Increasing the Reynolds number improved mixing and mass transfer, peaking at Re = 1500 by 35%. A higher feed temperature was confirmed as the dominant driver of vapor transport, boosting flux by more than 55% at 353 K compared to 333 K. In contrast, extending the module length degraded performance by 14% due to accumulated polarization. Overall, this dissertation advances the understanding of heat and mass transfer in HF-VMD systems and provides practical guidelines for module optimization using high-resolution LES simulations. The findings identify crossflow HF-VMD modules as a promising pathway for next-generation desalination technology, particularly for large-scale applications.
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Exploring the Properties and Stabilisation of Nanoscale Metal Cluster/Overlayer Architectures
(Saudi Digital Library, 2026) Asiri, Mohammed; Ebendorff-Heidepriem, Heike
The shift from fossil fuels to renewable energy sources is a major focus in the global effort to reduce CO2 emissions, with photocatalytic hydrogen production being a promising approach for harvesting energy from sustainable energy sources. Photocatalysts absorb energy from sunlight to drive the water splitting reaction, producing H2. The deposition of a co-catalyst, such as noble metal clusters, can modify and improve the efficiency of the photocatalyst. Metal clusters, consisting of only a few atoms, have gained attention as co-catalysts due to their unique electronic and catalytic properties. However, maintaining their size and stability is challenging, as they tend to agglomerate into larger particles, losing their unique properties. Another challenge is the occurrence of the back reaction during photocatalysis, when H2 and O2 react to form water on the co-catalyst surface. The back reaction reduces the efficiency of photocatalytic water splitting. Atomic Layer Deposition (ALD) of thin metal oxide overlayers on cluster-modified photocatalysts offers a strategy to stabilise the clusters and suppress the back reaction. The self-limiting nature of ALD allows for deposition of an ultrathin overlayer with a controllable thickness. This thesis investigates how ALD-AlOx overlayers can be used to preserve the integrity of noble metal clusters, particularly Au clusters. It is examined how an ALD-AlOx overlayer grows on the surface of a photocatalyst formed by depositing Au clusters on TiO2 surfaces, as well as the distribution and stability of the clusters on the TiO2 surface before and after the ALD overlayer. The growth of ALD-AlOx overlayers on Au101/TiO2 was investigated as a model photocatalyst system to understand how the overlayer grows on the Au clusters and the TiO2 substrate. The investigation determines the overlayer thickness after applying several ALD cycles on a planar TiO2 substrate. The study demonstrated that the ALD-AlOx resulted in evenly deposited overlayers for the system of Au101/TiO2 with a slight tendency to be thicker on the Au cluster than on the TiO2. The layer thicknesses were found to be 2.0 Å, 3.5 Å, and 5.5 Å for 1, 5, and 10 ALD cycles, respectively. A comprehensive study of the stability of Au9(PPh3)8(NO3)3 deposited onto TiO2 by depositing an ultrathin overlayer of ALD-AlOx at various deposition temperatures, 25 °C, 100 °C, 150 °C, and 200 °C was conducted. It was found that ALD-AlOx stabilised Au9 clusters on the TiO2 surface across various temperatures. Notably, the phosphine ligands desorb during the ALD overcoating process at elevated temperatures, while the Au9 cores remained protected beneath the AlOx overlayer. The ALD-AlOx overlayer on Au metal clusters on TiO2 was studied by a combination of microscopic and spectroscopic techniques. It was revealed that the Au101 clusters were distributed randomly across the entire TiO2 surface. The roughness of the Au101/TiO2 system increases as the Au concentration increases, while ALD overcoating smooths the clusters, as the roughness was found to decrease, indicating a uniform coating on clusters by forming thicker overlayers on interstitial regions between clusters. This work provides an understanding of the role of ALD-AlOx overlayer on the stabilisation of Au metal clusters on TiO2 as a photocatalyst model system, with direct relevance of designing and improving photocatalytic water splitting for green hydrogen production.
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Identification of groundwater flow patterns and barriers in aquifers
(Saudi Digital Library, 2025) Asiri, Mohammed; Shelyag, Sergiy; Miller, Tony
The use of inverse methods has been increasing in hydrology. Numerical methods can help identify groundwater barriers and flow patterns in an aquifer, which can reduce errors when comparing the exact and estimated solutions. This thesis uses the method of characteristics (MOC) to identify transmissivity T in an area of abnormal region. From Darcy’s law for steady-state groundwater flow, we start with a one-dimensional case, which helps us consider what may and may not be in the two-dimensional case. Then we use the 2D case to calculate the stream function and find that the gradient of the stream function is orthogonal to the gradient of the head, and we use this when calculating the stream function everywhere. We use MODFLOW to generate head data for the known distribution T and to estimate T under different inflow examples. MOC gives a stable solution and can help identify the area of low T without requiring smoothness of the T distribution.
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Identifying Indicators of Compromise Against Cyber-Attacks in Industrial Control Systems
(Saudi Digital Library, 2026) Asiri, Mohammed; Saxena, Neetesh
Industrial Control Systems, indicators of compromise, forensic readiness, threat intelligence, SCADA, Cyber-Physical Systems.
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Systematic Review of Antihistamine Prescribing Guidelines for Insomnia in Adults: A Comparative Study between the UK and Saudi Arabia Professional Practices
(University of Exeter, 2024) Asiri, Mohammed; AL-Azzawi, Amad; Rhodes, Shelley
Background: This systematic review examines the guidelines for prescribing antihistamines to adult patients with insomnia in the UK and Saudi Arabia. It highlights the professional differences between the UK's National Institute for Health and Care Excellence (NICE), which emphasizes non-pharmacological treatments and patient safety, and the less stringent, pharmacologically inclined guidelines in Saudi Arabia, influenced by cultural and regulatory factors. Aim: The study aims to evaluate and compare the professional guidelines for prescribing antihistamines to adult patients with insomnia in the UK and Saudi Arabia, assessing their impact on patient safety and clinical outcomes, and identifying the factors influencing these practices. Methods: A thorough literature search was performed in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, utilizing databases such as PubMed, Scopus, Web of Science, and the Cochrane Library. The review included randomized controlled trials (RCTs), cohort studies, and cross-sectional studies that examined the effectiveness and safety of antihistamines in treating insomnia in adult patients within these regions. Systematic data extraction focused on key study characteristics such as study design, drug used, dosage, and main findings. Results: The review identified significant differences in prescribing practices between the two regions. UK guidelines are robust, advocating for initial non-pharmacological interventions, while Saudi guidelines are noted for their lack of specificity, potentially leading to inconsistent prescribing and increased risks for adult patients. The distinct roles of pharmacists in each region also reflect differing approaches to medication dispensing and management. Conclusion: The findings highlight the need for Saudi Arabia to refine its clinical guidelines to align more closely with evidence-based practices like those in the UK to enhance patient safety and treatment efficacy. Both countries could benefit from enhanced professional education and stricter regulatory oversight to improve antihistamine prescribing practices for treating insomnia in adults.
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