MS Theses

Permanent URI for this collection

Browse

Recent Submissions

Now showing 1 - 5 of 1257
  • Thesis

    Deep Compressed Sensing for THz UM-MIMO Channel Estimation

    (2024-01) Lin, Ganghui; Alouini, Mohamed-Slim; El-Atab, Nazek; Shihada, Basem; Computer, Electrical and Mathematical Science and Engineering (CEMSE) Division

    Envisioned as a pivotal technology for sixth-generation (6G) and beyond, Terahertz (THz) band communications possess the potential to satisfy the escalating demand for ultra-high-speed wireless links. While ultra-massive multiple-input multiple-output (UM-MIMO) is tempting in counteracting the exceptionally high path loss at THz frequency, the channel estimation (CE) of this extensive antenna system introduces significant challenges. The success of deep learning (DL) in various fields makes it a promising candidate for THz-band CE. In this thesis, we propose a meta-learning-based channel estimator with generative adversarial network (GAN) architecture. Instead of training a GAN that learns the channel distribution only, our proposed model also learns how to infer the channel fast during the training. Our results show significant superiority over the baseline GAN estimator and traditional estimators. Our model can achieve a 3 dB lower normalized mean squared error (NMSE) than a GAN estimator with a 98% computation reduction in the online inference stage. Our designed training loss function provides a more meaningful measure of model performance during training than GAN training with adversarial loss. Moreover, the proposed model presents super-fast training convergence and a 67% reduction in pilot length compared to the baseline GAN estimator.

  • Thesis

    Electron Tunneling in Single and Bilayer Graphene Heterojunctions

    (2024-01) Alsubhi, Sana R.; Schwingenschlögl, Udo; Elatab, Nazek; Laquai, Frederic; Physical Science and Engineering (PSE) Division

    Graphene, a crystalline two-dimensional monolayer of carbon atoms, is regarded as one of the most intriguing carbon allotropes. Owing to its distinct properties and the exceptional characteristics of its charge carriers, graphene has become a focal point for extensive theoretical and experimental research. Recent studies have revealed the experimental feasibility of creating graphene heterojunctions, which are formed by interconnecting flakes of bilayer graphene with single-layer graphene. In this thesis, we explore electron tunneling in single-bilayer heterojunctions employing a continuum model. Specifically, we investigate the influence of the terminated edge type, which can manifest as either zigzag or armchair edges, on the transport properties. Our analysis encompasses the computation of key quantities, including transmission and reflection probabilities, as well as conductance. Additionally, we introduce an electrostatic voltage as a means to provide external control over quantum transport within these heterojunctions. The results reveal the efficiency of the gate voltage controlling the quantum transport with armchair edges, while its impact on zigzag edges is notably limited. Finally, we show the effect of system geometry, particularly the width of the graphene flakes, to elucidate its role in electron tunneling characteristics. Our findings pave the way for valuable insights into quantum transport within graphene heterojunctions, offering guidance for experimental investigations and the optimization of system parameters to enhance their practical applications.

  • Thesis

    Assessment of CO2 Storage Potential in the Unayzah Formation, Central Saudi Arabia

    (2024-01) Khodayeva, Aytaj.; Alafifi, Abdulkader; Hoteit, Hussein A.; Buchem, Frans V.; Physical Science and Engineering (PSE) Division

    This study represents a comprehensive evaluation of the geological CO2 storage potential in saline aquifers of the Unayzah Formation in central Saudi Arabia. It follows the previous work of (Corrales et al., 2022) to assess the CO2 storage capacity in the Unayzah aquifers. The current study covers a more extensive region southeast of Riyadh, (303 km by 135 km), and extends its simulation of CO2 injection and monitoring over a period of 75 years and 900 years, respectively. A new 3D geocellular model for the Unayzah formation in the study area was constructed using published stratigraphic and structural data and unpublished regional data. This model was used in dynamic simulations to model the CO2 storage capacity and the regional up-dip migration of the CO2 plume towards the west. In the base case simulation, we positioned 11 CO2 injection wells 10 km east and down dip of the Nuayyim trend. The anticlinal traps in the Nuayyim trend are targeted to understand how much CO2 could be trapped in these structures assuming these fields will be depleted by the time CO2 reaches there. Each well injected 1 Mt of CO2 annually for 75 years, followed by 900 years of monitoring. The simulation shows that southern wells injected CO2 into the Unayzah C layer because of its higher heterogeneity and the CO2 plume reaches the Nuayyim field after 75 years of injection and 20 years of monitoring. Northern wells inject CO2 mainly into Unayzah A and B layers and the CO2 plume migrates more than 26 kilometers up dip and does not reach to Hawtah trend even after 900 years of monitoring. Moreover, residual and solubility trapping have a significant effect on CO2 storage as it moves up-dip to the west. Finally, the effect of hysteresis, salinity, kv/kh ratio, and injection rate on the CO2 trapping was investigated. To conclude, the Unayzah aquifer has large CO2 storage potential along the Hawtah and Nuayyim trends assuming the oil fields will be depleted by the time injected CO2 reaches anticlinal structures.

  • Thesis

    Harnessing the Potential of Beneficial Bacteria Associated with Desert-Farmed Olive Tree Plantations in Saudi Arabia

    (2023-11) Al Romaih, Sarah M; Daffonchio, Daniele; King Abdullah University of Science and Technology (KAUST); Hong, Peiying; Rosado, Alexandre; Marasco, Ramona; Biological and Environmental Science and Engineering (BESE) Division

    Plants thriving in arid environments host beneficial microorganisms and microbiomes specialised in supporting host stress resilience. Investigating such microbial communities and understanding the key abiotic and biotic factors for their recruitment and selection, it is pivotal to identify the main players in supporting plants under desert farming. In this thesis, by exploiting a straightforward yet sophisticated pilot setup that implements three reduced levels of irrigation (vs standard conditions), I investigated the response of bacterial communities associated with the rhizosphere of olive trees at the Al-Jouf olive desert farm in Saudi Arabia. I analysed how irrigation levels influence bacterial recruitment in the rhizosphere, the root-surrounding soil, and the barren soil, discerning the contributions of environment-mediated and plant-mediated drivers in shaping bacterial communities. Rhizosphere samples from stressed plants were also used to cultivate and isolate bacteria for screening their plant-promoting activities and potential as plant probiotics in desert farming. The results revealed that stressed plants recruited specific bacterial groups, including Actinobacteriota (Micrococcaceae) and Patescibacteria, respect to those enriched in non-stressed plants (i.e., Pseuodomonas). Besides their capacity to tolerate abiotic stresses (i.e., salinity, drought, and high temperature), the rhizosphere bacteria exhibited various plant growth-promoting traits, such as the production of auxin-like root-promoting hormones and nutrient solubilisation. In vivo screening using two strains with multi-plant growth-promoting traits, namely Kocuria sp. (RH27, Micrococcaceae family) and Pseudomonas sp. (RH30), induced significant modifications of the root architecture of Arabidopsis thaliana, including root hair proliferation and branching. Notably, these modifications promoted plant biomass increase mainly during stress conditions, highlighting their potential for sustaining farming under arid conditions. Ongoing experiments in a sheltered experimental olive tree field established at KAUST reveal that, although a significant increase of biomass has not been yet achieved, olive tree plants treated with RH27 and RH30 have enhanced net photosynthesis, contributing to increased C-sequestration and enhancing carbon sink potentials, thus aiding in negative CO2 feedback.

  • Thesis

    Origin of peridotites from Thurwah ophiolite (Saudi Arabia), and their potential for CO2 mineralization.

    (2023-11-23) LOPEZ, SUAREZ MARIA C; Alafifi, Abdulkader M.; Hoteit, Hussein A.; Alafifi, Abdulkader M.; Van Der Zwan, Froujke; Physical Science and Engineering (PSE) Division

    Mineral carbonation is a cost-efficient and technically feasible method for permanent CO2 disposal. Peridotites have potential for mineral carbonation due to the high reactivity of olivine and pyroxene with injected CO2-rich fluids to precipitate stable carbonates Ellis (1959), (Ellis 1963) This thesis evaluates the feasibility of carbon mineralization in the Jabal Thurwah mafic-ultramafic complex by geological mapping of the lithology and structure using aerial digital photogrammetry, field observations, and satellite images, as well as petrological, mineralogical, and geochemical analysis, including XRF, SEM-EDS, and EPMA. Field mapping confirms previous studies that Jabal Thurwah is a thrusted ophiolite consisting mainly of an ultramafic mantle section, with minor intrusive gabbros and diabase. However, it lacks the previously reported layers of sheeted dikes and pillow lavas. The mantle section was extensively serpentinized and affected by ductile shearing during obduction. We report the occurrence of rodingite in a serpentine tectonic mélange. The chemical composition of olivine and Cr-spinel from the mantle section also indicate that Jabal Thurwah is a forearc ophiolite, and its mantle section was affected by high degrees of partial melting. This study indicates the unsuitability of Jabal Thurwah for in-situ carbon mineralization due to several factors. First, most of the mantle section is completely serpentinized, therefore the low abundance of reactive olivine and pyroxene. Second, the serpentinized ultramafic rocks lack open fractures, and any fractures are completely filled by magnesite or chrysotile. Ex-situ carbonation of the serpentinite is technically possible, but unsuitable due to the health and environmental impact of mining asbestos-bearing rocks, and high cost.