Open Research Exeter - University of Exeter
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Earth-like exoplanets in spin-orbit resonances: climate dynamics, 3D atmospheric chemistry, and observational signatures
No full textTerrestrial exoplanets around M- and K-type stars are important targets for atmospheric characterisation. Such planets are likely tidally locked with the order of spin-orbit resonances (SORs) depending on eccentricity. We explore the impact of SORs on 3D atmospheric dynamics and chemistry, employing a 3D coupled Climate-Chemistry Model to simulate Proxima Centauri b in 1:1 and 3:2 SOR. For a
1:1 SOR, Proxima Centauri b is in the Rhines rotator circulation regime with dominant zonal gradients (global mean surface temperature 229 K). An eccentric 3:2 SOR warms Proxima Centauri b to
262 K with gradients in the meridional direction. We show how a complex interplay between stellar radiation, orbit, atmospheric circulation, and (photo)chemistry determines the 3D ozone distribution.
Spatial variations in ozone column densities align with the temperature distribution and are driven by stratospheric circulation mechanisms. Proxima Centauri b in a 3:2 SOR demonstrates additional atmospheric variability, including daytime-nighttime cycles in water vapour of +55% to −34% and ozone (±5.2%) column densities and periastron-apoastron water vapour cycles of +17% to −10%. Synthetic emission spectra for the spectral range of the Large Interferometer For Exoplanets fluctuate by up to 36 ppm with orbital phase angle for a 1:1 SOR due to 3D spatial and temporal asymmetries. The homogeneous atmosphere for the 3:2 SOR results in relatively constant emission spectra and provides an observational discriminant from the 1:1 SOR. Our work emphasizes the importance of understanding the 3D nature of exoplanet atmospheres and associated spectral variations to determine habitability and interpret atmospheric spectra
EFL Saudi learners’ beliefs about vocabulary knowledge: An exploratory study
No full textConsidering the crucial role that vocabulary has in foreign language acquisition, educators have consistently expressed concerns about how to facilitate the acquisition of vocabulary for learners. While there is a widespread agreement that beliefs have a substantial influence on learners' behavior, there has been limited research dedicated to exploring English foreign language learners (EFL) learners’ beliefs regarding vocabulary knowledge. Additionally, the study investigates vocabulary learning strategy use and explores the correlation between learners’ beliefs about vocabulary knowledge and their vocabulary strategy use.
This study employs a mixed method design to address the research gap. I collected twenty samples from a peer review task and conducted semi-structured interviews with seven students at a Saudi university. Furthermore, a questionnaire was administered to fifty-four students from another university in the same region in Saudi Arabia. The participants in the study are first-year students enrolled in the preparatory year. The results from the peer review task and semi-structured interview data were compared with the questionnaire findings to provide further insights into learners’ beliefs about vocabulary knowledge and their vocabulary learning strategy use.
The findings reveal that certain aspects of vocabulary knowledge seem to receive less attention from learners. These include concepts and referents, spelling, word associations, collocations, and constraints on use. The aspect of word association was reported as the least valued among other vocabulary aspects.
Furthermore, the main findings indicate that Saudi students use transactional and determination strategies (comprehension strategies), metacognitive, cognitive, and memory (knowledge-oriented strategies), and interactional and affective strategies (use-oriented strategies). However, the agreement on the use of individual strategies in these categories differs. The determination strategies of thinking of a similar Arabic word, associating a word with a picture, and looking up the word in an English-Arabic dictionary were the least agreed upon in their use. Also, students agreed less with the use of some memory strategies such as using semantic feature grids, semantic maps, and learning idiomatic expressions. Using flash cards, putting English labels on physical objects, and listening to a tape recording of word lists were less agreed upon among cognitive strategies. Furthermore, metacognitive strategies such as passing over unknown words when reading or listening and continuing to learn vocabulary over time reported lower agreement percentages.
The study also reported that there are correlations between learners’ beliefs about vocabulary knowledge and their vocabulary learning strategy use. Learners who value various aspects of vocabulary knowledge, such as pronunciation, spelling, word parts, word associations, concepts and referents, and form and meaning, are likely to engage in determination and transactional strategies. There is a significant correlation between learners' beliefs about the importance of word associations, collocations, and register with memory and metacognitive strategies. Also, there is a noteworthy correlation between learners' beliefs about the importance of word associations, collocations, and pronunciation with affective and interactional strategies. Overall, this study broadens the understanding of learners’ beliefs about vocabulary knowledge and highlights the importance of developing a well-rounded view of vocabulary knowledge. These and other pedagogical implications were discussed
The Ramifications of Political Events in the Workplace
No full textThis thesis examines how political identity and contextual factors, such as power status and numerical status, shape coworker interactions and employee well-being. Three interconnected studies were conducted during significant electoral events in the US, Canada, and Australia to investigate these relationships. The first study, using data from the 2020 US Presidential Election, found that shifts in power status affect coworker interactions, influencing both harmful and helpful behaviors. The second study, based on data from the 2022 Australian Federal Election, explored the interplay among political identity, power status, and numerical status. The results indicated that power status interacts with numerical status to shape coworker interactions, with effects varying based on political identity. Specifically, a “double status effect” was identified, where holding both power and numerical majorities or minorities amplifies or mitigates certain behaviors. The third study focuses on employee well-being in two parts. The first, using data from the 2020 US Presidential Election, revealed that positive treatment from outgroup coworkers mediates the effect of power status on well-being. The second, using data from the 2021 Canadian Federal Election, highlighted the importance of numerical status on well-being. It showed that voters in the numerical majority within their workgroup reported better well-being than those in the numerical minority, even when holding power minority status. This suggests that being in the numerical majority may buffer against the negative effects of political disappointment. Collectively, these studies highlight the complex interplay between political identity, power dynamics, and numerical status in shaping coworker interactions and employee well-being
Understanding Time Through Ovid's Metamorphoses
No full textThe main subject matter of this thesis is the nature of time. It will explore the concept via an analysis of its representation in Ovid’s Metamorphoses, an epic poem about change which displays a deep understanding of the many ways time can be organised and experienced. In this thesis, I will demonstrate that the arguments and accumulated knowledge relating to time and human temporal experience found in a broad range of disciplines, such as ancient and modern philosophy, psychology, and the natural and social sciences, are also discernible in Ovid’s ancient poem, which uses its figurative power to reflect upon the underlying cosmological structures that underpin its fictional world. I will begin by examining how the Metamorphoses provides time with its own discernible structure before considering the concept in relation to some of the Metamorphoses’ most important poetic themes. The first of these relates to power relationships and the abuse of power: how the powerful deploy their own and other people’s temporality to exert control over the powerless or less powerful. The second focuses on change and identity formation, specifically how metamorphosis alters the spatio-temporal properties of those who undergo drastic transformation into other entities, as well as the degree to which the original human can survive the process of change. The third theme discussed in this thesis in relation to time involves memory and storytelling: how characters can expand their temporal horizons through the stories they tell about themselves and other people, in relation to past and future. This thesis should therefore advance the existing scholarship on the Metamorphoses by providing a comprehensive account of how time is represented in Ovid’s poem in all of its major facets. But it will also consider how the Metamorphoses can contribute to the ongoing interdisciplinary discussion on time and temporal experience more generally
An evaluation of the peer group influences on physical activity (PA) levels in children and adolescents: a systematic review and meta-analysis
No full textAbstract
Title: An evaluation of the peer group influences on physical activity (PA) levels in children and adolescents: a systematic review and meta-analysis.
Background:
Non-communicable diseases (NCD) are the greatest cause of mortality and morbidity worldwide, with great economic and personal costs. NCDs can be defined as chronic conditions that can be life changing or life limiting and there are various risk factors, including modifiable behaviours, such as smoking, unhealthy diet excessive alcohol and physical inactivity (PI).
PI is recognised as being a key contributor to NCD's and despite the World Health Organisation (WHO) producing global guidelines for PA back in 2010, the problem of PI is still increasing. Adolescents have been identified as the most inactive of all age groups, with only one in four meeting WHO guidelines. Research has shown that health behaviours that are developed in childhood, including those for PA, are often carried over into adulthood. Therefore, it is essential to address this problem in children and adolescents, to prevent inactive adults of the future. Various factors have been shown to influence PA levels, with the social influences of parents and peer group, thought to be dominant. This systematic review aimed to review the peer group influences on PA in children and adolescents.
Study Design:
A systematic search was carried out using the databases Embase, Medline, AMED, PsychINFO, Global Health, Scopus, CINAHL and Web of Science. 1074 titles were retrieved for screening against set inclusion and exclusion criteria, by 2 reviewers. 78 studies we retained for full text review and 25 studies entered the systematic review. The studies were assessed for risk of bias using the QATSDD appraisal tool and then data were extracted for analysis against a set framework. A combination of meta-analysis and narrative analysis were used to analyse the data.
Results:
The meta-analysis showed a weak positive correlation between children and adolescents PA levels and the PA levels of their peers. It also identified a weak positive correlation between children and adolescents PA levels and peer support for PA. There was, however, a large degree of statistical heterogeneity and so these results must be viewed with caution. It is also recognised that the complexities of the number of potential variables imparting influence in observational studies, including individual, social, geographical and socioeconomic, means that finding a suitable statistical model to predict which influence is producing which effect, is challenging.
Narrative analysis identified significant contradiction, regarding the nature and magnitude of peer group influence. However, the dominant theme across the review, showed that enjoyment and socialisation processes were consistently considered a factor in increased PA participation. The social aspects of peer interaction should therefore be prioritised in interventions to encourage healthy PA behaviour.
Conclusion:
The PA of children and adolescents is largely influenced by the enjoyment factor of socialising with peers, and this understanding should inform the development of an intervention to address PI. Statistically significant findings were inconsistent and appeared influenced by type and complexity of the statistical model used, so a greater understanding of how to effectively analyse observational data is needed.
Systematic review registration: Prospero CRD4202225976
Smart Nanoparticles and Complex Light-Matter Interactions for Single-Molecule Sensing: Investigating Multifunctional Molecular Sensing and Metal-Atom Catalysis on Gold Nanoparticles at Single Molecule Level
No full textThis thesis investigates the use of Whispering Gallery Mode (WGM) sensors for studying molecular interactions and catalytic processes at the single molecule level, focusing on engineered plasmonic nanoparticles. The research addresses key challenges in developing a real-time single-molecule sensing platform by controlling molecular interactions between analyte molecules and gold nanorod’s surface influenced by small buffer molecules while also advancing catalytic reactions of sub-kD molecules through integrating experimental
techniques and theoretical analysis. Molecular dynamics (MD) simulations and Density Functional Theory (DFT) calculations are often used to predict interactions at short timescales and determine binding energies. However, no single-molecule sensor is capable of real-time kinetic validation of these predictions. This gap limits the advancement of nanomaterials in applications such as chem-/bio-sensing and catalysis. Therefore, this thesis presents WGM sensors as a promising platform to bridge this gap by providing real-time, label-free analysis of molecular interactions. The first part of the study probes the multifunctional (phosphate, carboxylate, amine) molecules ( l1kDa), like glyphosate, binding to gold nanoparticles under different buffer conditions. The research focuses on how buffer molecules, acting as ligands, influence binding dynamics and interaction kinetics. The WGM sensor is used to monitor these interactions in real-time, while complementary DFT calculations offer a molecular-level understanding of the observed phenomena. Also, the study explores how small buffer molecules impact molecular binding and stability, investigating how these effects change by changing pH and buffer composition. This approach not only validates DFT predictions but also emphasises the significant role of small molecules, such as buffers or ligands, in influencing the binding kinetics of analytes, which is crucial for designing real-time sensors. The second part of the thesis shifts the focus to catalytic reactions on platinum-modified gold nanorods (Pt@AuNRs), exploring how nanoscale catalyst distribution influences catalytic performance. The WGM sensor is used to monitor the reduction of azobenzene via localised formic acid dehydrogenation at the catalytic site, offering detailed insights into reaction pathways and kinetics at the single-molecule level. The study investigates
the impact of Pt loading, from atomic-scale deposition to layered growth, revealing how
the architecture of catalytic sites affects performance. Additional experiments involving
carbon monoxide poisoning and varying formic acid concentrations confirm the critical role of active Pt sites. Bulk analytical techniques like UV-Vis spectroscopy, Raman spectroscopy, and HPLC-MS further validate the catalytic processes observed in the WGM platform, supported by DFT simulations.
In conclusion, this thesis highlights the importance of local environmental changes around plasmonic nanoparticles in influencing both molecular binding and catalytic reactions on engineered smart nanoparticles. The research establishes the WGM sensor platform as a versatile and advanced tool for single-molecule studies, offering a deeper understanding of interaction mechanisms and catalytic efficiency. The findings provide valuable insights into the rational design of nanomaterials, pushing the boundaries of single-molecule science and enabling targeted applications in biosensing, catalysis, and material science
Unveiling the Photophysical and Triboelectric Properties of Novel 2D Materials
No full textTransformative innovations in nanotechnology have led to the integration of two-dimensional (2D) materials into a diverse range of technologies, including but not limited to photovoltaics, transistors, reinforced composites, and biosensors. The development of these advanced materials holds immense promise, with extensive work dedicated to their synthesis, optoelectronic characterisations, and environmental applications. This thesis begins by investigating the optoelectronic properties of novel 2D perovskites, a family of crystalline materials characterised by the structure ABX3, highlighting their promising applications in sensing and high-resolution imaging technologies. Subsequently, the research delves into the development of more eco-friendly and scalable lead-free perovskites, which exhibit exceptional performance as photodetectors. Building on the demonstrated efficiency of these innovative materials, the direction shifts towards prioritising the use of renewable resources and the development of biodegradable, self-powered technologies. This includes the introduction of bio-sourced beeswax designed for a simple yet high-performing encapsulation method, aimed at improving the stability of these sensitive 2D materials. The encapsulation enables the otherwise deteriorating perovskites to survive submerged underwater for an extended period and withstand highly corrosive liquids. This biodegradable beeswax was further applied to develop self-sensing graphene-based textile triboelectric nanogenerators. The dynamic molecular interactions and the hydrophobic nature of beeswax provide intrinsic thermal healing, water-repellent, and self-cleaning properties, ensuring functionality under bending and humid environments. The fabricated devices operate as flexible, lightweight, self-powered sensors for low-frequency wearable applications and can also function as energy harvesters for environmental noise and vibrations. These innovations represent a stepping stone in reducing the technological environmental impact by leveraging on natural raw materials as active element for energy harvesting, paving the way to a sustainable technological development by mankind
Optical and Thermal Performance Enhancement of Ultra-High Concentrator Photovoltaic Thermal (CPV/T) System
No full textThe use of highly efficient photovoltaic (PV) material can achieve high conversion
power outputs. III-V multi-junction solar cells with efficiencies of >35% are rarely
deployed in a conventional panel due to the extreme cost. Concentrator photovoltaics
present a solution by pairing these highly efficient solar cells with relatively
inexpensive, non-imaging optics. Maximising the solar concentrator factor within these
systems presents advantages and challenges; the added heat flux over the receiver can
damage the solar cells, however the addition of a cooling system can prevent this and
allow further energy capture. Optimisation of such a system at the maximum achievable
concentration factor yields information on the performance limits of the technology,
which will require further research before widespread commercialisation can begin.
Thus, this research focuses upon ultra-high (UH) concentrator photovoltaics (CPV).
The research within this thesis is focused on the exploration and experimental
demonstration of a concentrated photovoltaic thermal (CPV/T) system. Specifically,
the performance of the system is enhanced through the development of a heat sink for
cooling and capture of thermal energy, in addition to maximising the concentration
factor using cell bonded tertiary optical elements. A simulative theoretical modelling
approach is developed using an iterative solver within COMSOL Multiphysics. At each
stage of experimental analysis, this model is validated with real-world data allowing an
in-depth understanding of the electrical and thermal performance of the system. After
a comprehensive review of the literature within the field, it was noted that there was a
notable lack of extended outdoor experimental analysis for CPV/T systems.
Furthermore, concentration factor had inconsistent definitions, often based primarily
around the geometric ratio of optic to solar cell active area, rather than the irradiance
distribution.
The cooling system is designed to focus the convective heat transfer at the point where
the highest heat flux is generated by the irradiance profile. Different geometries and
materials are considered, leading to the design of the serpentine-based heat sink which
successfully maintained low PV cell temperatures. These are experimentally tested
indoors with a solar simulator and under real-world outdoor conditions, allowing
evaluation of the accuracy of indoor analyses in predicting true performance. The
ii
maximum cell temperature is consistently below 70℃ and the cell efficiency is
successfully kept above 36%. Converging channel geometries are also theoretically
analysed using the validated simulative approach. Under realistic conditions with
consistent manufacture tolerance, they were unable to improve system performance,
giving more depth to the potentially misleading results of previous literature studies.
The effect of partial shading of optics is also experimentally investigated and analysed
further using the validated simulative model. By comparing the distributions of
irradiance over the solar cell a relationship between the net electrical efficiency and the
thermal stress generation is found. Thermal stress reduces the system lifetime and
hence, must be minimised. In some cases, a favourable trade-off can be found, with
thermal stress reductions of 5-10%, causing electrical exergetic efficiency losses of
<3.5%. This yields important information regarding the multi-objective relationship
between system lifetime and specific focal image design.
Finally, to push toward the limit of potential UH-CPV technology, various cell-bonded
optic materials are experimentally evaluated within the concentrator optic with a newer
model of solar cell. Different refractive indexes could unlock smaller focal images at
the cost of higher absorption and reflective losses. Using Sylgard-184 as the cell-
bonded optic material, the highest effective concentration achieved was a , of
1475.9 suns, with a corresponding a geometric concentration of ~6,560 suns.
Antireflective coatings were shown to improve performance slightly but had limited
application due to the required hardness of the optic material. To the knowledge of the
authors, this is the highest experimental solar concentration factor reported thus far in
the scientific field
Where does enriched rare earth element mineralisation in the regolith of carbonatites come from? An investigation focused on two contrasting examples – Zandkopsdrift and Glenover
No full textThe process of deep, lateritic weathering leading to the enrichment of rare earth elements (REE) within the regolith overlying carbonatites is well recognised as a means to develop an economic deposit of these elements. The extractable REE are commonly hosted in monazite – a REE phosphate which forms an important accessory mineral crystallising from the igneous carbonatite melt. What is unclear is how much of this monazite is primary – i.e. igneous and inherited into the regolith as residual grains – or has crystallised rather as a neoformed mineral alongside others in the regolith within different zones, at different times, but under the ambient conditions of low temperature, climate driven chemical weathering. Furthermore, does this enrichment process need pre-existing enrichment in the REE content of the fresh rock, or is the process of chemical weathering acting on carbonate rock sufficient to produce the scale of enrichment necessary to make a potentially economic deposit? Two natural laboratories – (i) the Zandkopsdrift carbonatite aillikite complex, and (ii) the Glenover carbonatite pyroxenite complex – have been used to investigate this process. Detailed studies of the textural, mineral and chemical aspects of weathered material are contrasted with samples of fresh rock sourced from previous drilling programmes. Petrographic studies and especially the use of SEM study has been highlighted as invaluable for this type of research and these techniques are highly recommended early on in any similar study. Destruction of apatite through gradual replacement by monazite is recorded at Zandkopsdrift, while at Glenover neoformed monazite grains form together with secondary apatite under supergene conditions. In both examples much of the REE in the regolith is now hosted by supergene monazite and demonstrates that, if sufficient phosphorus is available, monazite will be the dominant REE mineral that will form under these conditions. These findings are discussed and further contrasted with recent exploration studies of the Cummins Range pyroxenite carbonatite complex in Australia, where monazite is present. These conclusionshave further been applied to devise a model of REE enrichment accompanied by regolith collapse that could be utilised in exploration. In this model initial breakdown of sulphide minerals through oxidation is regarded as a necessary prerequisite to provide the extremely acidic groundwater needed to dissolve carbonate minerals and primary REE-bearing minerals such as apatite, REE-fluorocarbonates and monazite. This reaction is further accelerated by the presence of multiple and microcrystalline intrusion related fractures within the carbonatite which allow groundwater ingress. During this style of weathering the progressive removal of Ca, Sr and especially Mg from the carbonate minerals with concomitant progressive release of Mn, REE, Ba, and Fe – in that order - occurs. The loss of mass through this style of weathering results in karst development the common collapse of the upper parts of the regolith revealed as a topographic depression. The recognition of these geomorphological features on a number of scales may assist in the identification of deeply weathered carbonatites with related regolith with an enhanced potential for concentration of REE mineralisation
WASP-121 b’s transmission spectrum observed with JWST/NIRSpec G395H reveals thermal dissociation and SiO in the atmosphere
No full textWASP-121 b has been established as a benchmark ultrahot Jupiter, serving as a laboratory for the atmospheric chemistry and dynamics of strongly irradiated extrasolar gas giants. Here, we present and analyze WASP-121 b's transmission spectrum observed with NIRSpec G395H on board the James Webb Space Telescope and find evidence for the thermal dissociation of H2O and H2 on the planet's permanent dayside. Additionally, we detect SiO at a statistical significance of 5.2σ, which is compatible with chemical equilibrium in the atmosphere. Constraining the abundance of SiO and abundance ratios between silicon and volatile atoms in WASP-121 b's atmosphere could help discriminate between possible migration histories of the planet. The three-dimensional nature of thermal dissociation on WASP-121 b's dayside and of recombination on its nightside, however, poses a challenge to constraining molecular abundances and elemental abundance ratios from the transmission spectrum. To account for this, we implemented an atmospheric model in the NEMESIS framework that splits the planet's atmosphere into dayside and nightside. A retrieval applying our atmospheric model to WASP-121 b's transmission spectrum favors a higher H2O abundance on the nightside than on the dayside, demonstrating the impact of hemispheric heterogeneity when attempting to constrain WASP-121 b's bulk H2O inventory