324139 research outputs found
Sort by
Lead-tin perovskite solar cells: exploring thermal evaporation and interface engineering for improved stability and performance
No full textThis thesis explores the development of narrow-bandgap, lead-tin (PbSn), perovskite solar cells (PSCs), focusing on the enhancement of performance and stability through two fabrication techniques: solution processing and vacuum thermal evaporation. It also covers how to build, optimise, and upgrade customised evaporator design and how to optimise co-evaporation recipe of perovskites. It covers several key aspects of the fabrication process, device characterisation, and stability testing. The first chapter introduces the urgency of renewable energy, particularly photovoltaics, as a solution to global warming. The research focuses on perovskite solar cells, specifically the PbSn perovskites, which makes them ideal for tandem solar cells. Chapter two provides a theoretical foundation for the research, explaining the working principles of photovoltaic cells, and focusing on perovskite materials, their crystal structures, and bandgap tunability. It also covers the two main fabrication methods-solution processing and vacuum evaporation-highlighting the advantages and disadvantages of each. Chapter three describes all experimental methods and characterisations used throughout the entire thesis. Chapter four presents an innovation in interface engineering, introducing alumina nanoparticles buffer layer for solution-processed PbSn perovskites. This buffer layer prevents direct contact between the perovskite absorber and the top electrode, mitigating detrimental effects on device performance and stability. The applied interface improves device maximum-power-point efficiency from 10.3% to 15.3% by enhancing the conformality of the electron transport layer and reducing recombination losses. This leads to an increase in the steady-state open-circuit voltage by 0.1 V, while also enhancing overall efficiency, reproducibility, and stability, with a six-fold improvement in operational stability. Chapter five details the building and optimisation of a customised thermal evaporator, critical for achieving high-quality, reproducible thin films. Several steps that the author took to build and fine-tune an evaporator are shown in the chapter. Chapter six explains the way to optimise the co-evaporation process for PbSn perovskites. By systematically adjusting the evaporation rates of CsI, PbI2, the Sn alloy, and FAI, a reproducible recipe for high-performance PbSn PSCs is successfully developed. Additionally, the new methodology of evaporation Sn content, using the alloy of Sn (the mixture of SnI2 and SnF2) was developed by the author. The chapter also covers single SnI2 evaporation without SnF2, which showed promising results but posed reproducibility challenges. Chapter seven offers a direct comparison between solution-processed and thermally evaporated PbSn perovskites. The evaporated films demonstrate smoother, more compact structures without typical SnF2 aggregation on the surface from the solution processing. Devices fabricated using thermal evaporation show superior efficiency and stability, achieving a maximum-powerpoint efficiency of 17.01%, compared to 14.33% for solution-processed devices. The steady-state open-circuit voltage of thermally evaporated devices reaches approximately 0.8 V, surpassing the 0.74 V observed in solution-processed devices, along with a 0.04 increase in the quasi-fill factor. Stability tests under light and heat stress under open-circuit conditions reveal that evaporated PbSn devices have 4 times superior stability than their solution-processed counterparts. Overall, this thesis concludes by highlighting the potential of vacuum evaporation as a scalable, stable, and high-efficiency fabrication technique for PbSn PSCs, recommending further exploration of all-perovskite tandem applications. The thesis also advances the understanding of PbSn perovskites, focusing on thermal evaporation, interface engineering, performance enhancement, and long-term stability
Direct measurement of the attractive electrosolvation force between a pair of colloidal particles
Get PDFIn solution, electrically like-charged particles can experience a strong and long-ranged attraction that leads to the formation of stable, slowly reorganizing clusters. The attractive force underpinning this spontaneous organization process has been shown to depend on both the sign of charge of the particle and the nature of the solvent medium. The origin of the attraction has been ascribed to the preferential orientation of solvent molecules at the object-electrolyte interface. Here, we use optical imaging to directly measure the spatial profile of the potential of mean force between isolated pairs of charged microspheres. Working with particles carrying a variety of surface chemistries we find that the range of the electrosolvation attraction is substantially longer than previously held. In particular we show that particles carrying strongly anionic surface coatings composed of DNA or phospholipid bilayers display long-range attraction. We further find that the length scale governing the decay of the attractive force can depend on the properties of the interacting particles. This contrasts with the canonical expectation that the screening length governing the interaction of charged particles in solution depends exclusively on the properties of the intervening electrolyte medium. The observations point to significant departures from current thinking, and the likely need for a model of interactions that accounts for the molecular nature of the solvent, its interfacial behaviour, and spatial correlations. Finally, a strong and long-ranged attraction mediated by anionic matter constituting lipid membranes and chromatin could carry far-reaching implications for organization and structure formation in biology
Detecting changes in along-path HF propagation during the April 2024 total solar eclipse with radio amateurs and low-cost instrumentation
Get PDFThe total solar eclipse of April 8, 2024 presented a uniquely favorable circumstance for radio science. The Moon’s shadow passed near Canadian time standard station CHU, which transmits in the high frequency (HF, i.e., 3–30 MHz) band. It was therefore possible to observe signal changes due to shifting ionospheric conditions along the path of the eclipse by using CHU as a signal of opportunity. In under 3 months, our undergraduate team developed and deployed low-cost instrumentation to record CHU for timing and amplitude analysis. 18 units were distributed across 6 locations roughly aligned with the eclipse path. Each unit contained a radio recorder which retained time traceability to UTC via GPS time synchronization, allowing capture of the CHU signal with no unbounded error beyond the 50 µs sampling interval. Seven units captured changes in the received signal during the eclipse, most notably a tenfold increase in the signal strength at 7.85 MHz for a unit in Little Rock, AR. Its timing suggests a one-hop propagation path reflecting in the ionosphere over Cleveland, OH. The stations were deployed to and maintained by volunteers contacted through the amateur radio and citizen science community. This campaign demonstrates the accessibility and effectiveness of research using low-cost instrumentation and the power of citizen science
Improving the medical school experience for students from widening participation backgrounds: setting the scene for an action research approach
Get PDFIntroduction: In the UK, the medical profession has long drawn its ranks from the most privileged in our society. Widening participation (WP) is a policy agenda that aims to increase representation and support students from underrepresented groups to access higher education. The Medical Schools Council (MSC) has committed to increasing access for students from lower socioeconomic groups through reforms in outreach and admissions policies. New medical schools have also opened with strong commitments to WP. However, despite broader admissions, limited attention has been given to the experiences and support needs of WP students during their medical school years. This study examines both student and faculty perspectives and prioritises recommendations to enhance WP student experience, with the aim of answering the following research questions: 1. What are the lived experiences of WP students during their time at medical school, and how do they make sense of the barriers and supports that shape their wellbeing, belonging and progression? 2. How do medical educators articulate their understanding of the challenges faced by WP students and of institutional responses? 3. Which interventions to enhance WP student experience, do students and faculty reach consensus on, for implementation by medical schools? Methodology: This study employed a participatory approach, informed by the principles of action research. This methodology was selected to advance beyond descriptive accounts of disadvantage by positioning students and educators as co-researchers. Thematic analysis was conducted using a reflexive approach. Data collection included the following components: • 20 WP students and faculty took part in interviews and workshops, these included: o Semi-structured interviews with nine WP students from Aston and Oxford University. o Workshops and interviews with 11 faculty and clinical educators across UK institutions. • A two-round Delphi study involving 51 participants (40 faculty and 11 WP students) was conducted to develop consensus recommendations. Results and Discussion: The Interviews and workshops identified the following themes: Theme A: Barriers before and during medical school - Sub-theme A1: Pre-admission Barriers and their Legacy - Sub-theme A2: Economic and Structural Constraints on Student Experience - Sub-theme A3: Uneven Academic Preparation - Sub-theme A4: Belonging, Identity and Social Experience Theme B: Educator Perspectives on institutional responsibilities and support for WP students - Sub-theme B1: Recognising Structural Constraints The Delphi process consolidated these findings, resulting in consensus on institutional policies and interventions. Top priorities included annual reviews of financial support, mentorship programmes linking WP students with faculty or senior peers, and comprehensive postgraduate career guidance. Students placed a higher emphasis on career progression and opportunities for paid healthcare-related roles than faculty, underscoring the importance of integrating the student voice in policy design. Conclusion: Although WP has improved access to medical education, students from lower socioeconomic backgrounds continue to encounter structural barriers. A participatory approach led to the consensus on interventions to be prioritised by medical schools to support WP students. By incorporating student and faculty perspectives, this study provides evidence-based recommendations to inform institutional practice and national policy
Global multi-ancestry genome-wide analyses identify genes and biological pathways associated with thyroid cancer and benign thyroid diseases
Get PDFThyroid diseases are common and highly heritable. We performed a metaanalysis of genome-wide association studies from 19 biobanks for five thyroid diseases: thyroid cancer, benign nodular goiter, Graves' disease, lymphocytic thyroiditis, and primary hypothyroidism. We analyzed genetic association data from ~2.9 million genomes and identified 313 known and 570 novel independent loci significantly linked to thyroid diseases. We discovered genetic correlations between thyroid cancer, benign nodular goiter, and autoimmune thyroid diseases (rg=0.16-0.97). Telomere maintenance genes contributed to benign and malignant thyroid nodular disease risk, whereas cell cycle, DNA repair and damage response genes were associated with thyroid cancer. We proposed a paradigm explaining genetic predisposition to benign and malignant thyroid nodules. We found PRS associations with thyroid cancer risk of structural disease recurrence, tumor size, multifocality, lymph node metastases, and extranodal extension. PRS identified individuals with aggressive thyroid cancer in a biobank, creating an opportunity for genetically-informed population screening
Meanings and practices of solidarity in global health: a qualitative investigation - study protocol
Get PDFIntroduction: Solidarity in global health is often invoked as an ethical imperative to guide responses to global health challenges. Its meanings and practices across diverse contexts, however, remain under-explored. Deepening an understanding of how solidarity is conceptualised, enacted and perceived by a diverse array of actors within the global health ecosystem is crucial to advancing meaningful and measurable application of this commitment in global health. Methods and analysis: This qualitative study uses interpretive research methodology to explore perspectives on solidarity among key global health stakeholders: community-level leaders in civil society organisations working on global health issues; research institute directors in the Global South; and individuals with experience of funding decision-making with major global health funding and agenda setting organisations (‘global health influencers’). Data will be gathered through semi-structured interviews and analysed using inductive and deductive reflexive thematic analysis, to identify patterns and differences in how these global health stakeholders recognise and define solidarity or its absence in their day-to-day work, while remaining attentive to conceptual tensions, participant interpretations of solidarity that may be unfamiliar to our team, and our role as researchers in shaping what we register and emphasise as significant in our reporting of findings. Ethics and dissemination: Ethics approval was obtained from the Western University Health Sciences Research Ethics Board (HSREB) in Ontario, Canada # 2024-123965-87873 and the Ethics Committee for the Humanities, University of Ghana # ECH 163/23–24 and University of Oxford, Oxford Tropical Research Ethics Committee (OxTREC) waiver dated 10 April 2024. Study results will be submitted for peer-reviewed publication. Results will also be summarised in an open access report and presented at various stakeholder meetings and in online webinars. Protocol registration: The final protocol was registered with Open Science Framework on 28 October 2023. View only link: https://osf.io/gryp5/?view_only=8baff435a35847f09a342408d38ee35b
Impact of socio-economic and political factors on global COVID-19 vaccine coverage: an empirical study
Get PDFPurpose: This study seeks to explore the COVID-19 vaccine coverage across various countries by delving into its connections to seven vital indicators, these include the Human Development Index (HDI), Gross National Income (GNI) per capita, health expenditure, Internet usage, political stability, absence of violence and their correlation with the vaccine coverage. Measures: This study utilized a wealth of information from three valuable and publicly accessible data sources, such as Our World in Data, the World Bank, and the WHO database as of 20 March 2023. We then employed correlation analysis, linear regression, and structural equation modeling to examine the intricate relationships between various indicators and vaccine coverage, illuminating patterns at both national and continental levels. Results: Our comprehensive research unveiled that on an average countries around the world achieved a 54.5 ± 24.61% of COVID-19 vaccine coverage rate. Six of the seven indicators emerged to have positive correlation with the COVID-19 vaccine coverage, and they are the HDI, individuals using the internet, current health expenditure, political stability and absence of violence/terrorism, total cases per million people, and the total deaths per million people. Among these, HDI stood out as the strongest correlated indicator, and conversely, the percentage of rural population emerged as a negatively correlated indicator in relation to the vaccine coverage. Conclusions: These findings illuminate the formidable challenges associated with the quest for achieving universal vaccine coverage. In the future to address various pandemics globally, these insights emphasize the critical need for developing targeted strategies, fostering international collaboration and implementing comprehensive approaches to ensure that vaccines are fairly and equitably distributed and ultimately foster global immunity
What farmers think about using crop biotechnology to boost photosynthesis in rice and potato
Get PDFBoosting crop photosynthesis holds promise for meeting the needs of a growing population in a warming climate. However, improving photosynthesis with crop biotechnology is a new prospect for farmers and other key agrifood stakeholders, who will determine the success of such pioneering plant breeding initiatives. We conducted focus groups with 62 participants in four countries to understand farmer and agrifood stakeholder perspectives towards the aim of boosting photosynthesis through biotechnology in rice and potato, two of the world’s most important crops. We found farmers were positive towards the benefits of boosting photosynthesis, although the relative importance of improving yield was debated – water and radiation use efficiency were less contested and linked to more sustainable agriculture. Farmer concerns centered on balancing the competing agronomic and market demands that new varieties would bring. Farmers in the low-income countries had few concerns about the use of biotechnology and anchored their understanding in existing biotechnology crops, such as Golden Rice in the Philippines and Bt Brinjal in Bangladesh. Farmers in Europe and industry stakeholders were more apprehensive about biotechnology crops for several reasons that were rooted in the perceived opinion of consumers and supermarkets towards biotechnology
Studying adaptation at the invisible scale
Get PDFIn order to understand adaptation by natural selection, it is necessary to observe organisms in their natural habitat. For this reason, the field of behavioral ecology, which specializes in testing adaptive explanations for biological observations, is dominated by research on larger multicellular animals such as insects, mammals, fish, and birds. The vast majority of modern life sciences, however, is concerned with the study of cells, genes, and molecules, which are often impossible to observe directly in nature. This severely compromises our ability to complement mechanistic understand of traits of interest with adaptive understanding. This matters because only the theory of adaptation can provide an explanation for why biology operates in the way that it does, why it varies across individuals and species, a formal tool for making predictions about the future. The good news is that technological advances are creating new opportunities for understanding cellular and subcellular traits as the products of natural selection
Contrasting features of papillary and chromophobe renal cell carcinoma revealed by whole genome sequencing
Get PDFThe identification of cancer drivers is a cornerstone to delivery of precision oncology. So far sequencing of renal cell cancer (RCC) has largely been confined to the clear cell subtype of RCC. In contrast, sequencing analyses of the less common forms of RCC, papillary RCC (pRCC) and chromophobe RCC (ChRCC), have so far been limited. We analysed whole genome sequencing data on 164 tumour-normal pairs from the Genomics England 100,000 Genomes Project, providing a comprehensive, high-resolution map of copy number alterations, structural variation, and key global genomic features, including mutational signatures, intra-tumour heterogeneity and analysis of extrachromosomal DNA formation. Our research establishes correlations between genomic alterations and histological diversification and the extent to which genetically-mediated immune escape contributes to the development of these RCC subtypes. Implications: We demonstrate the distinctive genetics which characterises pRCC and ChRCC and how this information has the potential to inform patient treatment and clinical trials