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Development of a time-resolved photoluminescence imaging system using a compressed sensing approach
Get PDFIn this work, a novel measurement technique for time-resolved photoluminescence (TRPL) imaging of semiconductors is developed using a compressed sensing approach. TRPL provides crucial insights into the charge carrier lifetimes of semiconductor materials, which directly reflect material quality and influence the efficiency of electron-hole recombination processes—key factors in the performance of devices such as solar cells and LEDs. However, conventional TRPL techniques are limited in their ability to efficiently capture high spatial resolution data, often requiring slow, point-by-point measurements that are time-intensive and unsuitable for large or non-uniform samples. The compressed sensing method developed in this work overcomes these limitations by enabling simultaneous measurement of multiple spatial points, reducing the number of measurements required while maintaining high-resolution imaging and accuracy.
The first part of the thesis develops a comprehensive simulation framework for compressed sensing TRPL measurements, beginning with simple 1D models and expanding to complex simulations in both the spectral and temporal domains. The simulation follows a statistical approach, integrating key factors such as photon pile-up and noise to ensure realistic modelling of experimental conditions. A reconstruction algorithm is also developed to handle the high-dimensional data generated from compressed sensing TRPL, forming the foundation for the design and implementation of the experimental system. The simulation results show that in some cases, as few as 2% of measurements can be sufficient compared to conventional methods, demonstrating the effectiveness of compressed sensing.
The second part of this thesis focuses on the design and construction of a TRPL measurement system, specifically developed for imaging semiconductor samples with emission in the near-infrared (NIR) spectral range using a raster scanning approach. The experimental system was setup using 640 nm pulsed laser for excitation and two photomultiplier tube detectors, allowing detection between 700-1600 nm. Point measurements were conducted on cadmium telluride (CdTe) and copper indium gallium selenide (CIGS) samples, while full raster-scan measurements were performed on CdTe. These experiments demonstrated the system’s capability but highlighted challenges such as laser light leakage and divergence of the laser beam.
In the final part of the thesis, the experimental system is modified, to demonstrate a proof-of-concept compressed sensing TCSPC imaging system for acquiring TRPL maps of semiconductor materials and devices. The TRPL imaging results obtained using the compressed sensing approach are compared with those acquired through a conventional point-by-point method over the same excitation area. The feasibility of this methodology is clearly demonstrated, highlighting reductions of 50% or more in measurement acquisition time. Additionally, the benefits and challenges of the experimental prototype system are presented and thoroughly discussed, laying the groundwork for further improvements in system design and application.
Overall, these results provide a pathway toward an improved approach to TRPL imaging, with the first example of a compressed sensing TRPL system. While this thesis primarily focuses on photovoltaic applications, the findings are applicable to other wavelengths and material systems. Future work can build on this foundation to overcome the remaining limitations and further enhance the technique's capabilities
Compiler-hardware co-design in High-Level Synthesis
Get PDFHigh-Level Synthesis (HLS) simplifies the hardware design process by generating specialized hardware directly from an algorithmic software description. Current HLS tools work well on regular code, but are suboptimal on irregular code with data-dependent memory accesses and control-flow. This is because they follow a Finite State Machine with Datapath (FSMD) model of computation, which requires the compiler to schedule operations statically at compile time, failing to adapt to runtime conditions. A Dynamic Dataflow (DDF) model of computation in HLS augments each functional unit with additional scheduling logic that enables dataflow scheduling at runtime, naturally adapting to the unpredictable conditions in irregular codes. However, the resulting hardware generated by DDF HLS uses more area and produces longer critical paths than necessary, because every operator in the circuit is scheduled dynamically, even if only a few exhibit irregular behavior.
In this thesis, we propose a closer compiler-hardware co-design to make the HLS of irregular codes more efficient. We make four significant contributions. First, we show how the FSMD computational model can be extended with DDF behavior without having to schedule the entire circuit dynamically. This is achieved by letting the compiler discover sources of irregularity that prevent efficient static scheduling and by decoupling the original code into multiple FSMD instances along the discovered sources of irregularity. Second, we show how a compiler can automatically generate a Decoupled Access/Execute (DAE) architecture to enable efficient out-of-order dynamic memory scheduling in HLS, and we show how a compiler can automatically parametrize hardware structures, such as a Load-Store Queue (LSQ), to maximize throughput at minimal area usage. Third, we introduce compiler support for speculation in DAE architectures with two algorithms: one that speculates memory requests in the access program slice, and another that poisons mis-speculations in the compute slice, all without the need for mis-speculation recovery or synchronization. And finally, we show that a close compiler-hardware co-design can enable new optimization opportunities by presenting dynamic loop fusion. This novel technique is able to fuse the execution of sibling loops dynamically at runtime by resolving inter-loop memory dependencies in a hardware structure parametrized by the compiler. To enable dynamic loop fusion, we introduce a new hardware-optimized program-order schedule inspired by polyhedral compilers and we exploit the concept of monotonically non-decreasing address expressions—a larger class of functions than affine expressions required in static loop fusion. Our FPGA-based experiments show that our four contributions consistently result in at least an order of magnitude area-delay improvement over state-of-the-art HLS tools on irregular codes
Kaleidoscope: An exploratory study to support children’s progression in and through the Capabilities during primary school education
Get PDFThe image above, [p. ii] encountered in my history textbook when I was 15 years old, has remained etched in my memory. Although the context escapes me, I remember writing the words 'Born free, in chains to be', and wondering if any of us are ever free. I never imagined that, almost four decades later, I would find myself actively working to broaden an individual's opportunity to be free by exploring ways of enhancing their choices and opportunities through a consideration of personal potential and capacities.
The inspiration for this Dissertation stems from an integration of personal and professional experiences. As shared above, my 15 year old self wondered about freedom, and this thought, together with feelings of not really belonging to this world, periodically revisit me like old and unwelcome acquaintances. During my EdD studies, I questioned the reliance on standardised tests in literacy and numeracy to gauge a child's educational progress. I was reminded of the quote from the TV show The Prisoner, 'I am not a number, I am a free man', and the responding derisory laugh from the interrogator. This concern was heightened by an interaction with a seven year old student that I share in Chapter One. It is my belief that an educator's view of a child should mirror a kaleidoscope, a dynamic whole that changes with every interaction. The purpose of education is to nurture children's development so that their personal kaleidoscope evolves in a manner that maximises their potential for a flourishing life in a flourishing world. This belief influenced my time as a special education teacher when I developed skills based individualised programmes for children with complex needs, programmes unavailable through Irish education policy. I was privileged to receive encouragement from our school inspector who engaged in discussions about this approach and advised me to broaden its reach, prompting my EdD journey
Attending to the stories of displaced women: A portrait painter’s perspective
Get PDFThis thesis traces the ethical and conceptual connections between Simone Weil’s account of attention and my artistic practice of attention through portrait paintings of displaced women. I have adopted a practice-led approach whereby the philosophical reflections are intricately informed by the contemplative, prayerful traditional painting methods that I have embraced. The research journey has been inductive, and the key themes have emerged gradually, mirroring the painting process itself. Alongside Simone Weil, I draw upon Adriana Cavarero’s concept of inclination and narratability and Luce Irigaray’s luminous writings on the phenomenology of art, silence, listening and prayer.
The thesis begins with an in-depth analysis of the ethics of representation. I begin with considering the dominant tropes in contemporary portrayal of refugees in the media and the history of portraiture painting and iconography. Drawing insights from figures including Emmanual Levinas, Jean-Luc Marion and Weil I consider the transformative potential of portrait painting as an ethical practice, transcending tendencies to reify or reduce 'the other’ and cultivating a culture of encounter and ethical engagement. These ethical concerns situate the research and foreground the relational approach that I embrace to both my portraiture painting practice and to the participatory art workshops with women from displaced and asylum-seeking communities. I gently seek to offer an approach to arts practice with and by women from displaced communities, that offers a space of space of care, reverent time-taking, deep listening and attention-giving.
The exegetical chapter shines a light upon the traditional, prayerful painting methods and techniques that I have embraced, drawn from iconography and early Renaissance sacred art. Painting a portrait is a gesture of inclined attention towards the irreducible mystery of the other, in solidarity, mutual respect and love. The thesis concludes with a reflection upon the value of the exhibitions of the portraits, specifically in political contexts, in creating the space for what Weil describes as an ‘interval of hesitation’. The work of art is a sacralising act that makes possible a more expansive encounter with the other and offers itself as an interval of wonder and transcendence, gesturing towards something of enduring significance. As such, this thesis endeavours to shines a light upon the reparative, restorative and mystical potential of a work of art. I contend that a reverential, relational approach to the portrait encounter as a gift of attention is possible
Reclaiming public infrastructure: Public power New York and the struggle for energy democracy
Get PDFThis thesis explores how privatised public services and infrastructures can be reclaimed as part of a democratic transformation of the local state. The increasing privatisation of essential services and infrastructures has led to concerns about the erosion of democratic control and accountability, creating a need to understand how these can be re-embedded within democratic, public frameworks. Using the Public Power New York (PPNY) coalition’s campaign to pass the Build Public Renewables Act (BPRA) as a case study, this research investigates how a social movement can actively constitute and advance a project for energy justice and democracy. In this, demonstrating the potential for grassroots movements to catalyse broader political projects and foster democratic transformation of local governance structures.
By integrating diverse theoretical perspectives and empirical findings, this research offers a comprehensive analysis of how social movements can reclaim infrastructure and broaden political imaginaries toward more just and democratic futures. A novel theoretical framework integrates a range of concepts, following Cindi Katz’s emphasis on minor theory to introduce queer theory as an interlocutor to Nancy Fraser’s dimensions of justice.
The thesis reveals anti-democratic tendencies inherent in the technocratic and often hidden spaces of neoliberal governance. Furthermore, it demonstrates how energy infrastructure can broaden political imaginaries and foster different types of engagement with the local state. The research underscores the importance of understanding social movements as messy, evolving entities that continuously transform and are transformed by their engagement with the state, positioning queerness as an affective solidarity essential to sustaining social movements.
Empirically, the thesis contributes to literature on urban social movements and the local state, providing original insights into the dynamics of social movement organising in struggles
for energy democracy. Methodologically, it highlights the adaptive nature of research design in response to external challenges, such as the Covid-19 pandemic, and the resultant deeper understanding of social movement dynamics through qualitative research conducted in virtual spaces
Navigating mutual fund market: investor behavior, climate change exposures, and biodiversity in mutual funds
No full textAbstract not currently available
The impact of blockchain technology implementation on supply chain collaboration
No full textAbstract not currently available
Improving efficiency and performance of rotary regenerative heaters: computational fluid dynamics-based optimisation of heat transfer plates
Get PDFThis study presents a comprehensive investigation into the enhancement of thermal and aerodynamic performance of heat storage plates within rotary regenerative heaters through computational fluid dynamics (CFD) simulations and optimisation techniques.
Rotary regenerative heaters are critical in industrial applications, especially in the power generation and process industries, where they recover waste heat from exhaust gases to enhance overall system efficiency. This process ensures that the industrial applications are as efficient as possible. There is a continual demand to improve thermal performance and efficiency to meet ever-tightening stringent energy efficiency and emission reduction goals.
This PhD project focuses on optimising the aerodynamic and thermodynamic performance of the heat storage plates, or elements, within a rotary regenerative heater using advanced CFD modelling techniques, geometric optimisation, sensitivity analysis and novel innovation of integrating delta winglet vortex generators.
The initial phase involved the development of a CFD model, which was validated against experimental data from a physical test rig. This model successfully predicted the heat transfer and pressure drop performance of 3 different element profile designs, ensuring that the model was robust and accurate, and could therefore be utilised as a “virtual test rig” for continued experimentation.
Subsequently, using the validated CFD model, a geometrical optimisation was performed on the flat notched crossed style element profile. Key geometric parameters – pitch between notches and radius of notches – were altered and tested following a Latin Hypercube design of experiments methodology, and the heat transfer and pressure drop performance was measured at each configuration. A Kriging surrogate model was generated from the input variables and results, and a multi-objective pattern search function found a predicted increase in heat transfer of 7.3% and a reduction in pressure drop of 2.3%. The predicted optimal configuration was tested using the CFD model and it was confirmed that the prediction was accurate to within 1%.
A sensitivity analysis was conducted to ensure the optimised element geometry was suitable for manufacture and to assess the effect of the manufacturing tolerances on the performance of the element. The analysis was conducted using a Box-Behnken design of experiments and kriging surrogate model. The results confirmed that the optimal design maintained an improvement over the baseline design, with the worst-case scenario showing higher performance over the original element geometry, affirming its suitability for manufacture and integration into real-world applications.
To further augment the element performance, vortex generators were studied. Delta winglet type vortex generators were added to the optimised element design. These aerodynamic devices improve performance by generating longitudinal vortex structures that disrupt thermal boundary layers and promote turbulent mixing, leading to enhanced convective heat transfer. The chosen delta winglet configuration involved winglets angled opposed to the notches, with the intention of directing flow towards this area to enhance the existing flow effects generated by the notches. An optimisation scheme was carried out on the winglets, focusing on the length, angle of attack and distance from front of plate variables. A further 1% improvement in both heat transfer and friction factor was established.
The findings highlight the efficacy of combining CFD simulations with optimisation techniques to optimise heat transfer plates, ultimately leading to reasonable enhancements in the efficiency and effectiveness of rotary regenerative heaters
Development and applications of assembly theory-based molecular complexity analysis
No full textAbstract not currently available
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