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Lunar Volatile Resources and their effect on Human Exploration
No full textLunar volatiles are molecules that exist in a gaseous phase when exposed to the equatorial surface atmospheric conditions of the Moon. The shadowing effect of craters at the lunar poles allows the temperatures in the polar regions of the Moon to sustain lunar volatiles in a solid phase for extended periods of time. The National Aeronautics and Space Administration (NASA) is due to land humans on the lunar South Pole in 2026 in an attempt to examine and sample the lunar volatiles. Hence, the impact of these volatiles on human health, and changes to the geo-mechanical properties of the lunar regolith containing volatiles caused by human activities need to be understood. The research conducted within this thesis aims to bridge the knowledge gap of lunar volatiles, providing greater insights into the location of the volatiles, the impact of volatiles on human lunar activities and human health.
Hence, the research investigates the locations of volatile lunar resources for the entire Moon and their impact on human exploration and development of the Moon. Furthermore, the data obtained has been used to create a 4-dimensional thermal model for the entire Moon from the lunar surface to a depth of 2.65 metres, analysing the temperature at over 400 million data points every 2.5 hours. Using this model has enabled the identification of a combined cold trap volume of 435 km3 or 783,820 million metric tonnes of lunar regolith cold traps that could sustain long-term water ice, including over 156 individual cold traps beyond the lunar poles as close to the lunar equator as 59.8oS latitude.
The impact of changing thermal effects on the consolidation of regolith-water ice mixes that can lead to over 50% consolidation of lunar regolith was determined. Also, the calculation of the mass of the lunar volatiles that can impact human health, with 0.15 grams of lunar regolith containing volatiles in 1 cubic meter of atmosphere, is able to exceed safe airborne contaminant exposure limits
Behavioural Inference from Artificial Neural Networks in the Context of Travel Decisions
Get PDFRecent advancements in Artificial Intelligence (AI) have demonstrated its potential for accurately predicting travel behaviour. However, the lack of interpretability and inconsistency with behavioural theories limit their application in travel behaviour modelling. This PhD thesis addresses these challenges by developing novel Neural Network (NN) models that are consistent with behavioural theories and offer interpretability and identifiability.
The first phase of the research investigates how model performance changes when shifting from conventional NN models to theory-based NNs grounded in behavioural theories. Using post-hoc interpretation methods, I show that NN models that impose the independence of irrelevant alternatives constraint yield outputs aligned with behavioural expectations, while conventional NNs do not. In the second phase, the thesis introduces a novel theory-based NN model fully consistent with the random utility maximisation theory (RUM-NN) that can implement any distribution for the error components and consider correlation among them. RUM-NN is introduced in two linear and nonlinear versions. The linear version maintains a one-to-one connection with traditional discrete choice methods, while the nonlinear version expands capabilities by capturing complex relationships. RUM-NN supports diverse error term distributions which bridges AI and discrete choice modelling in a unique, interpretable framework. Using synthetic datasets and a real-world application, I demonstrate RUM-NN can replicate the performance of established econometric models such as multinomial logit and multinomial probit models, then I show it can achieve higher predictive accuracy as it allows for any error term distribution and can introduce non-linearity. The next phase extends and improves RUM-NN model to model nuanced concepts like unobserved constructs and taste heterogeneity. I further extended RUM-NN into an Integrated Choice and Latent Variable (ICLV) model which offers flexibility in error term distribution. The empirical results revealed that the proposed model outperforms ICLV in prediction accuracy and log-likelihood. Finally, the thesis addresses taste heterogeneity by proposing Mixed RUM-NN, a model that learns alternative-specific parameters as distributions and accommodates diverse assumptions about the stochastic error component. The extended version of RUM-NN outperforms the mixed logit model in prediction accuracy and goodness-of-fit measure
Reworking the Wagga Rug: how Australian retail workers make patchworks of care
No full textIn recent decades, employment has become increasingly precarious and unpredictable. For many, particularly those in the retail sector, short or split shifts and highly changeable schedules are commonplace. Formal childcare services, on the other hand, offer prebooked sessions of care, generally for a long day, and the same days every week. We have not yet solved the policy problem of how to care for the children of these workers. In fact, the challenges of providing formal childcare that is highly flexible are so great that two experimental projects in Australia failed: the Flexibility Trial and the Nanny Trial which both attempted to connect workers with non-standard hours with forms of childcare that could accommodate such irregular hours. This chapter asks how some of the lowest paid workers, those in the retail sector, manage the complexity of their childcare arrangements when they are under pressure to be highly accommodating of unpredictable employment schedules. Analysis of a national survey of members of the Shop, Distributive and Allied Employees’ Association (the SDA), an Australian union representing 230,000 retail, fast food and warehousing workers, show the complexity of the care arrangements which families use. Combining Laura Balbo’s (1992) enduringly relevant notion of mothers creating and maintaining a ‘patchwork’ of care, with a framework developed by Erika Katzman and Elizabeth Kinsella for analysing forms of work associated with organising disability care, we explore the labour of mothers managing the complex and ever-changing schedules of their employment, their partners’ employment, with their children’s care
The diversity of scleractinian corals throughout marine habitats. An exploration of the coral photoendosymbiotic spectrum.
Get PDFCoral reefs are vital ecosystems that support extensive marine biodiversity and provide essential ecosystem services. However, the ongoing impacts of anthropogenic climate change, particularly increasing sea-surface temperatures, are reshaping coral reef systems globally, driving an increased focus on key reef-building species. Much of the research to date has concentrated on dominant tropical coral species and their associated symbioses with photosynthetic dinoflagellates of the family Symbiodiniaceae, and its subsequent break down in response to increasing sea surface temperatures. This has resulted in significant knowledge gaps surrounding the broader diversity of the Anthozoa. Approximately half of scleractinian (hard) coral species either do not maintain a symbiotic relationship with Symbiodiniaceae, or their symbiosis with Symbiodiniaceae is considered to be variable, yet these species are significantly and comparatively understudied. Further, the limited species diversity and biogeographic scope of current coral studies have led to broad generalisations and significant research gaps. This has hindered our understanding of the diversity, complexity, and flexibility of coral photoendosymbiosis across species and marine habitats. This thesis therefore seeks to highlight the complexity and variability of coral photoendosymbiosis and presents scleractinian coral diversity as a spectrum ranging from photoendosymbiotic to aphotoendosymbiotic species. This research focuses on historically understudied marine ecosystems, including sub-tropical and temperate habitats, where more variable environmental conditions often promote unconventional or variable photoendosymbiosis, or the absence of photoendosymbiosis. Within this thesis, I systematically map the literature (1967-2021) on corals without or with variable photoendosymbiosis (482 publications) to find significant data deficiencies regarding their biodiversity, function, and response to anthropogenic stressors. Building on these knowledge gaps, I investigate corals within the understudied sub-tropical lagoonal reef system of Norfolk Island to demonstrate the presence of unconventional photoendosymbioses. I find that white or pale colour morphs of the genera Platygyra and Paragoniastrea comprise approximately 20% of their population at Norfolk Island and maintain photophysiological function, underscoring that visual coral health assessments alone are not sufficient for some coral genera at high latitudes. This thesis also examines a species of blue Montipora at Norfolk Island, demonstrating that the photosynthetic function and Symbiodiniaceae densities of colonies vary with seasonal temperature changes, highlighting photoendosymbiotic variability in high-latitude environments. The first characterisation of Symbiodiniaceae species from corals of Norfolk Island is also reported, with blue Montipora sp. found to predominantly associate with Cladocopium genotypes. Lastly, I detail the biogeography, fundamental biology, and ecology, of an aphotoendosymbiotic cup-coral genus, Culicia, within the temperate waters of New South Wales, Australia. This research shows the high prevalence of cryptic coral species within Australia’s temperate marine ecosystems and reports unique coral spawning events to occur in Sydney Harbour and across temperate New South Wales from early to mid-summer. This thesis further demonstrates that focusing on corals within underexplored marine ecosystems, and the diverse photoendosymbiotic relationships they encompass, will likely reveal a wealth of previously overlooked diversity, offering valuable insights into coral biology, ecology, and future projections for the Anthozoa beyond the limitations of traditional tropical research
Introduction
No full textThe introduction addresses questions about Kant’s access to Stoic philosophy and other matters about Stoicism in his immediate intellectual context. After this biographical and historical contextualisation, the individual chapters are introduced
Mapping Ventral Striatopallidal Circuitry and Synaptic Plasticity in Appetitive Behaviour
No full textThe ventral striatopallidal system, comprising nucleus accumbens shell (AcbSh) and ventral pallidum (VP), is a key player in appetitive behaviour. Input from medial prefrontal cortex (mPFC) and projections to lateral hypothalamus (LH) contribute to its roles in drug-seeking and relapse. Although the broad connectivity between the four structures is well-established, much cellular and synaptic detail is lacking. The precise circuitry organisation and possible behaviour-evoked neuroadaptations in cortico-accumbal synapses are poorly understood. This thesis addressed these gaps. Opsin-assisted circuit-mapping demonstrated three disynaptic pathways through the ventral striatopallidal network: AcbSh → VP → LH, mPFC → AcbSh → LH, mPFC → AcbSh → VP. AcbSh innervation of LH-projecting VP neurons was primarily from D1-expressing neurons. Dual retrograde tracing identified VP-projecting and LH-projecting AcbSh neurons as separate subpopulations. Electrophysiology recordings taken at two behavioural timepoints showed distinct presynaptic plasticity at cortico-accumbal synapses of distinct AcbSh subpopulations. Presynaptic depression of mPFC input to VP-projecting AcbSh neurons was observed in animals who self-administered alcoholic beer; this may facilitate downstream VP pathways that promote appetitive seeking. Notably, the magnitude of presynaptic depression predicted alcohol-seeking during reacquisition, demonstrating a mechanistic link between circuit-specific plasticity and relapse propensity. Presynaptic potentiation of mPFC input to LH-projecting AcbSh neurons was detected in animals that experienced social isolation and longer duration of dietary restriction, regardless of self-administration history; it suggests sensitivity to stress in the mPFC → AcbSh → LH circuit branch. This thesis advances our understanding of the organisation of ventral striatopallidal circuits and the synaptic changes associated with appetitive behaviour and relapse, providing novel insights that may inform targeted therapeutic strategies for treating maladaptive reward behaviours
Fuelling the Delirious Brain: Investigating Cerebral Glucose Metabolism and a Randomised Controlled Trial of Intranasal Insulin
No full textBackground
Delirium affects 25% of older hospitalised adults and is independently associated with cognitive impairment, accelerated dementia, longer hospital stays, admission to nursing home and death. Despite this, the underlying pathophysiology of delirium remains poorly understood, and there are no licensed treatments. Studies of cerebrospinal fluid suggest altered cerebral glucose metabolism is a feature of delirium. This thesis aimed to further investigate cerebral glucose metabolism during delirium and determine if intranasal insulin could improve clinical outcomes.
Methods
This thesis comprises a literature review, neuroimaging studies, and a clinical trial. The literature review summarised emerging evidence of cerebral energy insufficiency - due to impaired glucose transport, utilisation, or regulation - as a contributor to delirium. However, it remains unclear whether cerebral hypometabolism reflects delirium itself, acute illness, or underlying neurodegenerative disease. To explore this further, fluorodeoxyglucose positron emission tomography (FDG-PET) was conducted for the first time in older patients with delirium but without dementia and compared to both acutely unwell controls and outpatients with mild Alzheimer’s disease. As insulin receptors are widely expressed in the brain and insulin acts as a neuromodulator and can increase cerebral glucose uptake, the potential of intranasal insulin as a treatment for delirium was explored with a randomised placebo-controlled trial in 100 older hospitalised patients with delirium.
Results
In the FDG-PET study, patients with delirium (but no dementia) exhibited regional cerebral hypometabolism compared to acutely unwell controls, involving the bilateral thalami, right superior frontal, right posterior cingulate, right inferolateral anterior temporal, and left superior parietal cortices (p<0.05). The severity of regional hypometabolism was found to correlate with both delirium severity and cognitive performance. Compared to patients with mild Alzheimer’s disease, delirium was characterised by relatively greater subcortical hypometabolism, particularly in the thalami, suggesting distinct neural substrates. No differences were observed in the posterior cingulate cortex, indicating potential overlap in this region. In the clinical trial, intranasal insulin did not significantly reduce the duration of delirium (median days [IQR]: insulin: 4.8 [2.9, 9.2] vs control: 6.8 [4.0, 9.8], HR 0.7, 95% CI 0.43 to 1.15; p=0.16). However, it was associated with shorter hospital length of stay (median days insulin: 7.9 [4.6,14.5] vs control: 12.9 [7.8, 17.4], HR 0.56, 0.35-0.89; p=0.014). In addition, an age-related effect was observed with reduced delirium duration in participants aged ≤88 years, whereas no response was observed in older participants.
Conclusion
This thesis provides new evidence that altered cerebral glucose metabolism is a feature of delirium and that thalamic hypometabolism may underlie distinguishing clinical manifestations such as inattention and altered arousal. While intranasal insulin did not reduce overall delirium duration, it was associated with shorter hospital length of stay suggesting broader benefits that warrant further examination. Together, these findings support cerebral glucose metabolism as both a mechanistic driver and a promising target for delirium intervention
Applications of Wet-Dry Cycling in the Prebiotic Synthesis of Aminooxazolines – Key Intermediates for Ribonucleotides
No full textContemporary investigations of origins of life chemistry often follows the now widely studied RNA world hypothesis. To provide support for the RNA world, investigations into prebiotic RNA synthesis have been ongoing since the second half of the 20th century. This approach has since led to many prebiotically plausible chemical syntheses which result in ribonucleotides crucial for RNA formation. Many challenges in prebiotic RNA synthesis still remain, however, such as the need for step-wise addition of reagents and highly specific reaction environments.
Chapter 1 of this thesis reviews prebiotic ribonucleotide syntheses, starting with seminal pathways established by Sanchez and Orgel using pentose aminooxazoline intermediates. The Powner-Sutherland pathway expands on Orgel and Sanchez’s work in particular by synthesising the pentose aminooxazolines from 2-aminooxazole and glyceraldehyde. Carell group’s unified pathway that utilises wet-dry cycles to produce purine and pyrimidine ribonucleotides is also examined. Finally, Fahrenbach and coworkers demonstrate that 2-aminooxazole can be synthesised directly from NaCN using radiolysis and wet-dry cycles in a continuous reaction network without the stepwise addition of reagents is reviewed. The continuous synthesis of the pentose aminooxazolines by Fahrenbach and coworkers, however, was not demonstrated. Fundamental challenges faced in these prebiotic ribonucleotide syntheses and strategies to overcome them are discussed. Chapter 1 also provides context for the experiments carried out in Chapter 2, i.e., prebiotic synthesis of pentose aminooxazolines using wet-dry cycles.
In Chapter 2, I investigate wet-dry cycles as a method to extend Fahrenbach and coworkers’ continuous radiolytic reaction network towards the synthesis of pentose aminooxazolines. Wet-dry cycles were found to enable pentose aminooxazoline synthesis even when starting from solutions containing excess sodium cyanide. Glyceraldehyde forms a cyanohydrin with HCN, inhibiting its reactivity. The dry-down process liberates glyceraldehyde from the cyanohydrin through excess HCN evaporation, affording its reaction with 2-aminooxazole to form pentose aminooxazolines. Experiments were conducted to optimise various reaction conditions (pH, dry-down temperature and pressure) for pentose aminooxazoline production. Detailed mechanistic investigations using NMR spectroscopy and mass spectrometry, revealed the formation of aldonic acid and 2-aminooxazole hydrate side products that lesson pentose aminooxazoline yields. The yields of pentose aminooxazolines (arabinose and ribose derivatives) determined by quantitative 1H NMR spectroscopy using DMSO as a standard to be ~1–2 (0.5–1% yield) mmol after wet-dry cycling under reduced pressure at 65 °C. The yields increased significantly to 15% using ambient pressure dry-down at 65 °C. The optimal yield observed in these experiments was 19% when the wet-dry cycle was conducted at 25 °C.
Chapter 3 (Future Work) uses the knowledge gained from Chapter 2 to propose protocols to synthesise pentose aminooxazolines in a radiolytic context starting from NaCN as the only carbon feedstock. Two sets experiments are proposed based on Fahrenbach and coworkers original radiolytic network. The first set of experiments aim to maximise the yield of pentose aminooxazolines starting from radiolysis and dry-down of solutions of 2-aminooxazole and glycolaldehyde, and the effect of radiation dose, excess cyanide concentration, pH and dry-down temperature on the final yield are suggested to be examined. The second set of proposed experiments will then use these optimised parameters for constructing a continuous radiolytic network for synthesising pentose aminooxazolines by employing multiple rounds of radiolysis and wet-dry cycling starting with NaCN as its only carbon feedstock. This proposed experiment is an extension upon the previous radiolytic network demonstrated by Fahrenbach and coworkers in order to yield pentose aminooxazolines. The proposed pathway would also have no stepwise addition of chemicals apart from NaCN after radiolysis, thus making the desired pentose aminooxazolines easier to achieve in a prebiotic scenario compared to previous works which all required specific timing for the addition of reagents and highly specific environments. Achieving this aim would provide a “one-pot” continuous pathway with simple reagents easily obtainable on prebiotic Earth
Electrochemically Stimulated Autofluorescence of Indium Tin Oxide Surface: The Implications for Fluorescence Microscopy
No full textElectrochemical fluorescence microscopy using indium tin oxide (ITO)-coated glass surfaces is increasingly employed in single-molecule and surface-based imaging. Although ITO typically exhibits low autofluorescence, here we report that under specific conditions, it can induce significant background fluorescent signal. Specifically, when exposed to light with wavelengths below 560 nm, in the presence of oxidative potentials (>0 V) and cysteamine-containing buffer at alkaline pH (8.19–10.75), a localized photoelectrochemical reaction occurs. This reaction leads to the formation of a surface-bound fluorescent species whose intensity increases over time. The rate of this emission growth depends on three key variables: shorter illumination wavelengths accelerate the process; more positive applied potentials enhance emission intensity; and higher laser power further increases the rate. We propose a mechanism in which the ammonium ion form of cysteamine (2-ammoniumethanethiolate) interacts with the ITO surface, bonding to surface oxygen atoms and thiolate groups reacting to form disulfide bridges with other thiolates groups, making cystamine. This effect presents a potential source of background in experiments involving extended ITO illumination, such as electrochemically modulated single-molecule localization microscopy. Researchers using ITO under these conditions should be aware of this phenomenon to avoid misinterpretation of fluorescence signals