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Ensuring Access to Safe and Nutritious Food for All Through the Transformation of Food Systems
Quantum dots based superluminescent diodes and photonic crystal surface emitting lasers
This thesis reports the design, fabrication, and electrical and optical characterisations of GaAs-based quantum dot (QD) photonic devices, specifically focusing on superluminescent diodes (SLDs) and photonic crystal surface-emitting lasers (PCSELs). The integration of QD active regions in these devices is advantageous due to their characteristics such as temperature insensitivity, feedback insensitivity, and ability to utilise the ground state (GS) and excited state (ES) of the dots.
In an initial study concerning the fabrication of QD-SLDs, the influence of ridge waveguide etch depth on the electrical and optical properties of the devices are investigated. It is shown that the output power and modal gain from shallow etched ridge waveguide is higher than those of deep etched waveguides. Subsequently, the thermal performance of the devices is analysed. With increased temperature over 170 ÂșC, the spectral bandwidth is dramatically increased by thermally excited carrier transition in excited states of the dots.
Following this, an investigation of a high dot density hybrid quantum well/ quantum dot (QW/QD) active structure for broadband, high-modal gain SLDs is presented. The influence of the number of QD layers on the modal gain of hybrid QW/QD structures is analysed. It is shown that higher number of dot layer provides higher modal gain value, however, there is lack of emission from QW due to the requirement of large number of carriers to saturate the QD. Additionally, a comparison is made between âunchirped QDâ and â chirped QDâ of hybrid QW/QD structure in terms of modal gain and spectral bandwidth. It is showed that âchirpedâ of the QD can improve the âflatnessâ of the spectral bandwidth.
Lastly, the use of self-assembled InAs QD as the active material in epitaxially regrown GaAs-based PCSELs is explored for the first time. Initially, it is shown that both GS and ES lasing can be achieved for QD-PCSELs by changing the grating period of the photonic crystal (PC). The careful design of these grating periods allows lasing from neighbouring devices at GS ( ~1230 nm) and ES (~1140 nm), 90 nm apart in wavelength. Following this, the effect of device area, PC etch depth, PC atom shape (circle or triangle or orientation) on lasing performance is presented. It is shown that lower threshold current density and higher slope efficiencies is achieved with increasing the device size. The deeper PC height device has higher output power due to more suitable height and minimal distance to active region. The triangular atom shape has slightly higher slope efficiency compared to triangular atom shape which is attributed to breaking in-plane symmetry and increase out-of-plane emission
Machine Learning Research Trends in Africa: A 30 Years Overview with Bibliometric Analysis Review
In this paper, a critical bibliometric analysis study is conducted, coupled
with an extensive literature survey on recent developments and associated
applications in machine learning research with a perspective on Africa. The
presented bibliometric analysis study consists of 2761 machine learning-related
documents, of which 98% were articles with at least 482 citations published in
903 journals during the past 30 years. Furthermore, the collated documents were
retrieved from the Science Citation Index EXPANDED, comprising research
publications from 54 African countries between 1993 and 2021. The bibliometric
study shows the visualization of the current landscape and future trends in
machine learning research and its application to facilitate future
collaborative research and knowledge exchange among authors from different
research institutions scattered across the African continent
A Decision Support System for Economic Viability and Environmental Impact Assessment of Vertical Farms
Vertical farming (VF) is the practice of growing crops or animals using the vertical dimension via multi-tier racks or vertically inclined surfaces. In this thesis, I focus on the emerging industry of plant-specific VF. Vertical plant farming (VPF) is a promising and relatively novel practice that can be conducted in buildings with environmental control and artificial lighting. However, the nascent sector has experienced challenges in economic viability, standardisation, and environmental sustainability. Practitioners and academics call for a comprehensive financial analysis of VPF, but efforts are stifled by a lack of valid and available data.
A review of economic estimation and horticultural software identifies a need for a decision support system (DSS) that facilitates risk-empowered business planning for vertical farmers. This thesis proposes an open-source DSS framework to evaluate business sustainability through financial risk and environmental impact assessments. Data from the literature, alongside lessons learned from industry practitioners, would be centralised in the proposed DSS using imprecise data techniques. These techniques have been applied in engineering but are seldom used in financial forecasting. This could benefit complex sectors which only have scarce data to predict business viability.
To begin the execution of the DSS framework, VPF practitioners were interviewed using a mixed-methods approach. Learnings from over 19 shuttered and operational VPF projects provide insights into the barriers inhibiting scalability and identifying risks to form a risk taxonomy. Labour was the most commonly reported top challenge. Therefore, research was conducted to explore lean principles to improve productivity.
A probabilistic model representing a spectrum of variables and their associated uncertainty was built according to the DSS framework to evaluate the financial risk for VF projects. This enabled flexible computation without precise production or financial data to improve economic estimation accuracy. The model assessed two VPF cases (one in the UK and another in Japan), demonstrating the first risk and uncertainty quantification of VPF business models in the literature. The results highlighted measures to improve economic viability and the viability of the UK and Japan case.
The environmental impact assessment model was developed, allowing VPF operators to evaluate their carbon footprint compared to traditional agriculture using life-cycle assessment. I explore strategies for net-zero carbon production through sensitivity analysis. Renewable energies, especially solar, geothermal, and tidal power, show promise for reducing the carbon emissions of indoor VPF. Results show that renewably-powered VPF can reduce carbon emissions compared to field-based agriculture when considering the land-use change.
The drivers for DSS adoption have been researched, showing a pathway of compliance and design thinking to overcome the âproblem of implementationâ and enable commercialisation. Further work is suggested to standardise VF equipment, collect benchmarking data, and characterise risks. This work will reduce risk and uncertainty and accelerate the sectorâs emergence
DĂ©veloppement dâun systĂšme intelligent de reconnaissance automatisĂ©e pour la caractĂ©risation des Ă©tats de surface de la chaussĂ©e en temps rĂ©el par une approche multicapteurs
Le rĂŽle dâun service dĂ©diĂ© Ă lâanalyse de la mĂ©tĂ©o routiĂšre est dâĂ©mettre des prĂ©visions et des avertissements aux usagers quant Ă lâĂ©tat de la chaussĂ©e, permettant ainsi dâanticiper les conditions de circulations dangereuses, notamment en pĂ©riode hivernale. Il est donc important de dĂ©finir lâĂ©tat de chaussĂ©e en tout temps. Lâobjectif de ce projet est donc de dĂ©velopper un systĂšme de dĂ©tection multicapteurs automatisĂ©e pour la caractĂ©risation en temps rĂ©el des Ă©tats de surface de la chaussĂ©e (neige, glace, humide, sec). Ce mĂ©moire se focalise donc sur le dĂ©veloppement dâune mĂ©thode de fusion de donnĂ©es images et sons par apprentissage profond basĂ©e sur la thĂ©orie de Dempster-Shafer. Les mesures directes pour lâacquisition des donnĂ©es qui ont servi Ă lâentrainement du modĂšle de fusion ont Ă©tĂ© effectuĂ©es Ă lâaide de deux capteurs Ă faible coĂ»t disponibles dans le commerce. Le premier capteur est une camĂ©ra pour enregistrer des vidĂ©os de la surface de la route. Le second capteur est un microphone pour enregistrer le bruit de lâinteraction pneu-chaussĂ©e qui caractĂ©rise chaque Ă©tat de surface. La finalitĂ© de ce systĂšme est de pouvoir fonctionner sur un nano-ordinateur pour lâacquisition, le traitement et la diffusion de lâinformation en temps rĂ©el afin dâavertir les services dâentretien routier ainsi que les usagers de la route. De façon prĂ©cise, le systĂšme se prĂ©sente comme suit :1) une architecture dâapprentissage profond classifiant chaque Ă©tat de surface Ă partir des images issues de la vidĂ©o sous forme de probabilitĂ©s ; 2) une architecture dâapprentissage profond classifiant chaque Ă©tat de surface Ă partir du son sous forme de probabilitĂ©s ; 3) les probabilitĂ©s issues de chaque architecture ont Ă©tĂ© ensuite introduites dans le modĂšle de fusion pour obtenir la dĂ©cision finale. Afin que le systĂšme soit lĂ©ger et moins coĂ»teux, il a Ă©tĂ© dĂ©veloppĂ© Ă partir dâarchitectures alliant lĂ©gĂšretĂ© et prĂ©cision Ă savoir Squeeznet pour les images et M5 pour le son. Lors de la validation, le systĂšme a dĂ©montrĂ© une bonne performance pour la dĂ©tection des Ă©tats surface avec notamment 87,9 % pour la glace noire et 97 % pour la neige fondante
Increased lifetime of Organic Photovoltaics (OPVs) and the impact of degradation, efficiency and costs in the LCOE of Emerging PVs
Emerging photovoltaic (PV) technologies such as organic photovoltaics (OPVs) and perovskites (PVKs) have the potential to disrupt the PV market due to their ease of fabrication (compatible with cheap roll-to-roll processing) and installation, as well as their significant efficiency improvements in recent years. However, rapid degradation is still an issue present in many emerging PVs, which must be addressed to enable their commercialisation. This thesis shows an OPV lifetime enhancing technique by adding the insulating polymer PMMA to the active layer, and a novel model for quantifying the impact of degradation (alongside efficiency and cost) upon levelized cost of energy (LCOE) in real world emerging PV installations.
The effect of PMMA morphology on the success of a ternary strategy was investigated, leading to device design guidelines. It was found that either increasing the weight percent (wt%) or molecular weight (MW) of PMMA resulted in an increase in the volume of PMMA-rich islands, which provided the OPV protection against water and oxygen ingress. It was also found that adding PMMA can be effective in enhancing the lifetime of different active material combinations, although not to the same extent, and that processing additives can have a negative impact in the devices lifetime.
A novel model was developed taking into account realistic degradation profile sourced from a literature review of state-of-the-art OPV and PVK devices. It was found that optimal strategies to improve LCOE depend on the present characteristics of a device, and that panels with a good balance of efficiency and degradation were better than panels with higher efficiency but higher degradation as well. Further, it was found that low-cost locations were more favoured from reductions in the degradation rate and module cost, whilst high-cost locations were more benefited from improvements in initial efficiency, lower discount rates and reductions in install costs
An investigation of the relationship between perioperative characteristics and perioperative anaesthesia on the postoperative systemic inflammatory response and clinical outcome in patients undergoing surgery for colorectal cancer
In UK, colorectal cancer (CRC) is the fourth most common cancer and the second most common cause of cancer death. Until now, surgical resection remains the cornerstone for the management of CRC in all stages, however, stress response elicit from surgery may cause different changes through multiple systems in human body including neural, endocrine, metabolic, inflammatory, and immunological changes. In addition, other perioperative factors such as volatile anaesthetic and opioids may induce the immunosuppression. There is a proportional correlation between the stress response and the magnitude of the inflammatory immune response, invasiveness, and duration of surgery. The pre-operative and post-operative status of patients are important when considering the prognosis. The systemic inflammatory response (SIR) has been recognised to correlate with tumour progression and the prognosis of CRC. An exaggerated postoperative SIR is associated with postoperative infective complications and poor survival. Several predictive markers of the SIR have been used, such as the neutrophil to lymphocyte ratio (NLR), serum C-reactive protein (CRP) level, and Glasgow prognostic score (GPS). Some evidence reported that general anaesthesia (GA) combined with regional anaesthesia (RA) are better than the single use of general anaesthesia in reducing the post-operative immuno-suppression in some degrees. Furthermore, the peri-operative inflammatory process may be affected by the choice of anaesthetic technique, with propofol reported to have anti-inflammatory effect by targeting neutrophil activity. Up to now, there is insufficient evidence to recommend any specific anaesthetic or analgesic technique for patients undergoing surgery for tumour resection based on inflammatory response, recurrence, and metastasis. The work presented in this thesis further examines the relationship between the perioperative characteristics, perioperative anaesthesia, and the postoperative systemic inflammatory response following surgery for colorectal cancer. Several preoperative medications along with anaesthesia might influence the postoperative systemic inflammatory response but the question is whether the post-operative systemic inflammatory response affected by the administration of different types of anaesthesia or not following surgery for colorectal cancer. Chapter 1 discusses the epidemiology, aetiology, carcinogenesis, risk factors of colorectal cancer, pro-carcinogenic factors, anti-carcinogenic agents, inflammation and cancer, the post-operative systemic inflammatory response, tumour staging, screening, and diagnosis of colorectal cancer. Chapter 2 discusses the treatment of colorectal cancer. Chapter 3 discusses different anaesthetic techniques and agents. Chapter 4 provides summary and aims of the thesis. Chapter 5 represents findings from a systematic review and meta-analysis about the effect of anaesthesia on the postoperative systemic inflammatory response in patients undergoing surgery. The results conclude that there was some evidence that anaesthetic regimens may reduce the magnitude of the post-operative SIR. However, the studies identified in this systematic review were heterogeneous and generally of low quality. Chapter 6 represents a retrospective cohort study about the relationship between anaesthetic technique, clinicopathological characteristics and the magnitude of the postoperative systemic inflammatory response in patients undergoing elective surgery for colon cancer. The results show that the type of anaesthesia varied over time and appears to influence the magnitude of the postoperative SIR on post-operative day 2 for those patients who underwent for open surgery but not laparoscopic surgery. Chapter 7 represents a prospective cohort study about the effect of anaesthesia on the magnitude of the postoperative systemic inflammatory response in patients undergoing elective surgery for colorectal cancer in the context of an enhanced recovery pathway. The results show that there was a modest but an independent association between regional anaesthesia (RA) and a lower magnitude of the postoperative SIR. Chapter 8 represents the relationship between pre-operative medications, the type of anaesthesia and post-operative sequelae in patients undergoing surgery for colorectal cancer. The results show that there was no association between the preoperative administration of aspirin, statins and ACE inhibitors and anaesthesia. Chapter 9 represents the relationship between nutritional status, anaesthetic approach, and peri-operative characteristics of patients undergoing surgery for colorectal cancer. The results show that there was no significant association between measures of nutritional status and anaesthetic approach. Chapter 10 represents the relationship between opioid administration, type of anaesthesia and clinicopathological characteristics in patients undergoing surgery for colorectal cancer. The results show that opioid administration was independently associated with both anaesthetic and operative factors. Chapter 11 represents the main findings of the thesis and some recommendation for a future work
Cost-effective non-destructive testing of biomedical components fabricated using additive manufacturing
Biocompatible titanium-alloys can be used to fabricate patient-specific medical components using additive manufacturing (AM). These novel components have the potential to improve clinical outcomes in various medical scenarios. However, AM introduces stability and repeatability concerns, which are potential roadblocks for its widespread use in the medical sector. Micro-CT imaging for non-destructive testing (NDT) is an effective solution for post-manufacturing quality control of these components. Unfortunately, current micro-CT NDT scanners require expensive infrastructure and hardware, which translates into prohibitively expensive routine NDT. Furthermore, the limited dynamic-range of these scanners can cause severe image artifacts that may compromise the diagnostic value of the non-destructive test. Finally, the cone-beam geometry of these scanners makes them susceptible to the adverse effects of scattered radiation, which is another source of artifacts in micro-CT imaging.
In this work, we describe the design, fabrication, and implementation of a dedicated, cost-effective micro-CT scanner for NDT of AM-fabricated biomedical components. Our scanner reduces the limitations of costly image-based NDT by optimizing the scanner\u27s geometry and the image acquisition hardware (i.e., X-ray source and detector). Additionally, we describe two novel techniques to reduce image artifacts caused by photon-starvation and scatter radiation in cone-beam micro-CT imaging.
Our cost-effective scanner was designed to match the image requirements of medium-size titanium-alloy medical components. We optimized the image acquisition hardware by using an 80 kVp low-cost portable X-ray unit and developing a low-cost lens-coupled X-ray detector. Image artifacts caused by photon-starvation were reduced by implementing dual-exposure high-dynamic-range radiography. For scatter mitigation, we describe the design, manufacturing, and testing of a large-area, highly-focused, two-dimensional, anti-scatter grid.
Our results demonstrate that cost-effective NDT using low-cost equipment is feasible for medium-sized, titanium-alloy, AM-fabricated medical components. Our proposed high-dynamic-range strategy improved by 37% the penetration capabilities of an 80 kVp micro-CT imaging system for a total x-ray path length of 19.8 mm. Finally, our novel anti-scatter grid provided a 65% improvement in CT number accuracy and a 48% improvement in low-contrast visualization. Our proposed cost-effective scanner and artifact reduction strategies have the potential to improve patient care by accelerating the widespread use of patient-specific, bio-compatible, AM-manufactured, medical components
Interactive Sonic Environments: Sonic artwork via gameplay experience
The purpose of this study is to investigate the use of video-game technology in the design and implementation of interactive sonic centric artworks, the purpose of which is to create and contribute to the discourse and understanding of its effectiveness in electro-acoustic composition highlighting the creative process. Key research questions include: How can the language of electro-acoustic music be placed in a new framework derived from videogame aesthetics and technology? What new creative processes need to be considered when using this medium? Moreover, what aspects of 'play' should be considered when designing the systems? The findings of this study assert that composers and sonic art practitioners need little or no coding knowledge to create exciting applications and the myriad of options available to the composer when using video-game technology is limited only by imagination. Through a cyclic process of planning, building, testing and playing these applications the project revealed advantages and unique sonic opportunities in comparison to other sonic art installations. A portfolio of selected original compositions, both fixed and open are presented by the author to complement this study. The commentary serves to place the work in context with other practitioners in the field and to provide compositional approaches that have been taken
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