Open Research Exeter - University of Exeter
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Mechanical Properties and Environmental Performance of Calcium Carbide Residue-Based Materials in Soil Stabilisation
No full textThis study systematically investigated three types of calcium carbide residue (CCR)-based materials for sustainable soil stabilisation, including CCR alone, CCR combined with fly ash (CCR-FA), and CCR-FA activated by a waste glass-derived alkaline activator. A series of microstructural analyses, isotropic consolidation, consolidated undrained, tank leaching, and wetting-drying cycle tests were conducted, and life cycle assessment was applied to evaluate their feasibility and sustainability. An established constitutive model was adopted to reproduce the stress-strain behaviour of stabilised soils.
The results showed that all CCR-based materials significantly improved soil strength compared to untreated soil, with alkali-activated CCR-FA developing the highest strength and lowest compressibility in early curing stages due to the formation of both C-A-S-H and N-A-S-H gels. When the consolidation pressure was between the gross yield stress and final yield stress, strength of stabilised soils significantly reduced, while consolidation pressures higher than final yield stress improved shear strength. The 28-day cured CCR-FA and alkali-activated CCR-FA stabilised soils retained high strengths following seven wetting-drying cycles, while CCR stabilised soils collapsed after only two cycles. The low concentrations of heavy metals leached from CCR-based materials demonstrated their low environmental risk. The CCR-FA stabilised soil could effectively immobilise Cu, Cr, and As, while CCR alone was more effective for Pb. The LCA results confirmed environmental advantages of CCR-based materials, particularly CCR-FA, though these benefits were influenced by waste availability and the energy source during material processing. The adopted constitutive model reasonably captured the stress-strain behaviour of 60-day cured CCR stabilised soil. Overall, these findings demonstrate the feasibility and sustainability of CCR-based materials for soil stabilisation and offer practical recommendations for their application.</p
Current Induced Magnetisation Dynamics in Ferromagnetic Nanowires
No full textFerromagnetic nanowires are functional and integral constituents in a variety of advanced technologies, including tuneable microwave devices, magnetic storage, spintronics, electromagnetic wave absorbers, noise suppressors, and biomedical applications. Their significance and popularity stem from the ability to tune both their static and dynamic magnetic responses through their geometry, dimensions, lattice parameters, material composition, magnetic anisotropy, and external fields. Arrays of magnetic nanowires can also be synthesised with high degree of uniformity and with controlled anisotropy using template assisted electrodeposition methods making them more accessible. Furthermore, metallic ferromagnetic nanowires are compatible with semiconductor fabrication techniques for integration into, for example, magnonic nanostructures and devices. Understanding the magnetisation dynamics and spin wave modes in individual and arrays of magnetic nanowires and their dependence on the nanowire and lattice material and geometrical parameters is critical for the design and tuning of magnetic devices, composites and metamaterials employing magnetic nanowires. Fabricated arrays with nanowire diameters of few nanometres or tens of nanometers support high frequency operations but are difficult to characterise and observe experimentally, which make modelling and simulation essential tools for the design and development of associated materials and devices. Modelling the magnetisation dynamics in magnetic nanowires is complex due to the rich micromagnetic energy landscape and supported resonance modes. This is made more challenging in metallic magnetic nanowires (in microwave devices and absorbers for example) which require consideration of applied and induced currents, and of electromagnetic wave interaction that produce non-uniform electromagnetic fields with different skin depths (both non-magnetic and magnetic) that control the resonance mechanism and spin-wave modes in the magnetic nanowires. Available analytical models of the magnetisation dynamics and resonance in magnetic nanowires simplify the Landau-Lifshitz-Gilbert (LLG) equation of magnetisation to arrive at closed-form solutions that limits their applicability (for example operate in the magnetostatic or exchange limits and apply to simple geometries). Numerical models offer more detail but often focus on the micromagnetic or the electromagnetic responses separately. Thus, there is a need for a numerical approach that can solve both the electromagnetic (Maxwell’s equations) and micromagnetic (LLG equation) coupled system and accurately simulate the magnetisation dynamics and fields in magnetic nanowires and arrays. Cobalt exhibits strong saturation magnetisation and pronounced magnetocrystalline anisotropy (MCA) making it a favourable material or constituent for high frequency applications. Crystallographic measurements and fabrication studies indicated that the MCA in cobalt nanowires is predominantly perpendicular to the nanowire axis, and the potential for controlling the angle of anisotropy. This control provides an additional and interesting mechanism of tuning the resonance frequency and spin-wave modes in cobalt nanowires. The effect of different angles of MCA on the dynamic response in magnetic nanowires and on resonance modes is not well understood which, again, is important for the design and tuning of microwave devices, absorbers and biomedical applications. Arrays of metallic ferromagnetic nanowires embedded in dielectric matrices, exhibit a tuneable effective electromagnetic response through external fields that is affected by the resonance properties of individual nanowires and the dipolar coupling between them. When excited by electromagnetic waves, electric fields couple with metallic magnetic nanowires and induce currents and skin effects that spatially and temporally affect the magnetisation distributions and hence resonance modes in the nanowires and arrays. There is currently lack of understanding of the effective dynamic response of arrays of metallic ferromagnetic nanowires and their effective properties arising from the complexity and scale of the problem. Current approaches focus on simplified semi-analytical models that ignore exchange or solved separately using either micromagnetics or electromagnetics (assuming a frequency dependent permeability as input). Hence there is a need for a numerical model that addresses the above challenges to model and understand the dynamic permeability in magnetic nanowire arrays to design and tune devices and metamaterials. This research and thesis establish a comprehensive transient electromagnetic - micromagnetic numerical model in finite-elements within COMSOL Multiphysics that couples the solution of Maxwell’s and LLG equations to model and simulate the magnetisation dynamics and resonance in individual and arrays of magnetic nanowires, excited by applied (axial) currents and electromagnetic plane waves. This model includes the contributions of exchange, magnetocrystalline anisotropy, magnetostatic fields and induced currents (eddy currents). This model was used to study and understand the current-induced resonance in individual, semi-infinite, two-dimensional circular cobalt nanowires with diameters in the range 10-100 nm and at different angles of uniaxial magnetocrystalline anisotropy. The individual nanowires are excited by a 70 GHz Gaussian electric current pulse applied parallel to the nanowire axis. The calculated transient magnetisation distributions and power absorption spectra indicate predominately curling mode resonance for nanowire diameters ≥ 20 nm with symmetrical radial spin-wave modes when the magnetocrystalline is parallel to the nanowire axis. The resonance frequencies and their size dependence agree with Aharoni’s exchange curling theory. Increasing the out of plane MCA angle breaks the circular symmetry and produces elliptical curling magnetisation accompanied by significant reduction in the resonance frequencies (for example from 50 GHz fundamental mode frequency in a 100 nm diameter nanowire with MCA parallel to the nanowire axis, to 15 GHz for perpendicular anisotropy). These results demonstrate the significant impact of MCA angle on resonance in ferromagnetic nanowires and the promising potential of using this anisotropy to tune the frequency response of magnetic nanowires. The finite-element electromagnetic-micromagnetic model was further applied to investigate the complex electromagnetic wave response and effective dynamic permeability of periodic, two-dimensional arrays of cobalt nanowires with diameters in the range 10-200 nm and packing fractions of 0.1, 0.3 and 0.6. The 70 GHz Gaussian electromagnetic wave source wavelength in the simulation is larger than the nanowire diameters and lattice constants and thus operating in the metamaterial limit. This enabled the extraction of the effective dynamic permeability of the array from the simulated scattering parameters. With the MCA parallel to the nanowire axis, the simulated peak frequencies in the imaginary permeability correspond approximately to a uniform mode ferromagnetic frequency for an interacting nanowire array. The imaginary permeability peaks also exhibited slight shift towards lower frequencies with increase in the magnitude of the permeability with increased packing fractions due to dipolar interactions and collective precession. The simulations also showed that the peak resonance frequencies in the permeability spectra for each packing fraction have negligible sensitivity to nanowire diameters, particularly for diameters greater than 100 nm. This is be attributed to the ≈ 50 nm magnetic skin depth in cobalt which confines the response to the circumferential region of the nanowire. Increasing the deviation of the MCA angle from the nanowire axis causes significant shift in the resonance frequencies in the simulated permeability spectra to lower frequencies with increased magnitude of the permeability, similar to the behaviour of individual nanowires. For the case of perpendicular anisotropy, two distinct frequency peaks appear in the permeability spectra. Analysis of the total power absorbed in the nanowire array revealed that the lower frequency peak corresponds to the fundamental resonance mode in the individual nanowires while the second higher frequency peak corresponds to the dipolar field contribution. Increasing the packing fraction shifts the two peaks closer to each other due to the increased dipolar coupling. The outcomes of this research provide a more detailed understanding of the dynamic response of individual and arrays of metallic ferromagnetic nanowires and establish their potential as tuneable building blocks for high-frequency metamaterial and device applications. Moreover, the numerical method here can be easily extended to three-dimensions and enable the modelling and simulation of a wide range of magnetic materials and devices.</p
Theatre and Drama in the Ptolemaic Fayum. Notes on Papyri from the Zenon Archive
No full textIntroductionSome of the documentary papyri of the Zenon archive join the much smaller number of its literary papyri in offering a snapshot of the importance of Greek culture in the daily life of Greek settlements in third-century BCE Egypt.1 In particular, P. Cair. Zen. V 59823 and P. Lond. VII 2140, with their mentions of a theatre, and P. Cair. Zen. III 59417, with its mention of a κωμῳδός, often feature in studies of the cultural landscape of Philadelphia, the Fayum and Ptolemaic Egypt more broadly.2 Moreover, P. Cair. Zen. IV 59651 has attracted attention in the same connection for the presence of an isolated line of Aeschylus on its back.3 In this paper, I will reconsider these four papyri from a material and/or textual perspective and add new elements to their interpretation and contextualisation. While many aspects remain uncertain, my aim is to reappraise this material in order to offer both new insights and further corroboration of some of the conclusions reached in their most recent reassessments,4 and thereby contribute to a more precise understanding of the cultural policies and practices of the third-century BCE Fayum.</p
Introduction: Bringing youth Into contemporary Italian television
No full textThe introduction outlines the history of Italian youth-oriented series in Italy, tracing the influence and presence of a range of styles and genres visible in contemporary output. It analyses some of the reasons for the recent international success of Italian products since the Italian launch of Netflix in 2015 and the advent of premium television outlets and on-demand platforms. It offers an overview of current literature and approaches to the topic, setting the volume in the context of current debates on transnational media, audiovisual genres, youth representation and TV audience studies. It introduces the scope and contents of the book and the rationale for its structure.</p
Mechanisms of the Composite Face Effect (CFE): Perceptual Learning Fails to Reveal the Effect in Prototype-Based Artificial Stimuli
No full textThis study investigated the role of perceptual learning in the composite face effect (CFE), which is characterized by reduced accuracy in recognizing the top half of a face when it is combined with the bottom half of another face, particularly when the composite is upright and aligned, compared to when the two halves are laterally offset (misaligned). The misalignment disrupts configural/holistic processing, affecting recognition performance. Experiment 1a (n=96) employed prototype-defined checkerboards to investigate the presence of the composite effect. The advantage of using these stimuli is that expertise can be precisely controlled. Experiment 1b (n=96) aimed to replicate the composite effect using face stimuli, serving as a control and enabling direct comparison of the effect between face and checkerboard stimuli. Both experiments employed a full design that included congruent and incongruent, aligned and misaligned composites to measure the composite effect. Results from Experiment 1a indicated that the composite effect could not be obtained with checkerboard composites, whereas Experiment 1b confirmed the robust presence of the CFE in face stimuli. Based on these findings, we can interpret that perceptual learning does not significantly contribute to the CFE.</p
Micro-component disaggregation of domestic water demands using machine learning
No full textGrowing population and rapid urbanisation have increased the pressure on water supply in many countries and regions, leading to severe water stress. The escalating impacts of water pollution and climate change are exacerbating the issue of water scarcity. Increasing water supply is generally associated with the development of water infrastructure and investment in alternative water sources. In contrast, addressing water conservation through effective household water management has become a critical issue to tackle water shortage crises.
A range of tools for disaggregating water consumption into end-use levels have been developed in the recent years. Many of these studies involve the intrusive approaches, for example, installing sensors at individual water appliances in the household, to collect accurate water end-use data. However, due to cost and privacy concerns, non-intrusive methods are preferred in many cases. Developing non-intrusive method requires high-quality water end-use information, which enables the accurate separation between water end-use types. This study aims to develop and evaluate an effective machine learning-based method for disaggregating household water end-uses. A variety of machine learning algorithms and input features for disaggregation processes have been investigated, evaluated, and discussed in this research.
The water end-use disaggregation requires high-resolution water consumption data (typically at intervals of less than a minute) to enable the extraction of detailed water consumption patterns. Devon, a coastal county in the United Kingdom, is the study area for this research. The water utility in the study area offers access to diverse water consumption datasets, collected via pulse interval loggers and automated meter reading (AMR) meters. The resolution of the water consumption data available in the area ranges from 30-minute intervals to recordings of each litre used. To support the disaggregation process, the research also presents the labelling process of each type of water end-use, along with the deployment of online household water consumption survey.
The water end-use disaggregation can be broadly divided into two main components, segmenting water consumption data into end-use events and classifying these events with appropriate labels. The first part of the research
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involves the process of data collection, cleaning and water end-use segmentation. The second part presents the development and evaluation of machine learning methods, including k-nearest neighbours, Random Forest and Artificial Neural Networks, using both physical features and time series patterns of water end-use events. The results from evaluating various machine learning models and input features combinations indicate that Random Forest is a promising method for further research, especially when combing physical features with time series patterns. The final part integrates the models developed for detecting each type of water end-use, as introduced in separate chapters, and applies the integrated model to a wider range of households within the study area.
Based on the results from both detection of separate water end-uses and the application of the integrated model, several key findings from this research are summarised as follows: machine learning algorithms may perform differently depending on the specific type of water end-use, indicating that the selection of suitable algorithms is important for improving water end-use classification accuracy; the similarity of water end-use time series patterns proves to be an effective input feature, especially when labelled water end-use data is scarce. A small number of typical water end-use patterns can serve as reference samples for measuring similarity with unlabelled water end-uses. These reference samples function as cluster centroids, with similarity measured as the distance between each end-use and these central patterns. This approach can be applied when multiple patterns exist for a single water end-use type, allowing similarity to be used as an input feature for the training of water end-use disaggregation model alongside physical features, which may show limitations in capturing the water usage variability.</p
Molls, Madams, and Masterminds: Challenging Perceptions of Women in Organised Crime in Late Nineteenth and Early Twentieth Century USA.
No full textThis thesis examines perceptions of women in organised crime which emerged during the post-civil war period through to the early twentieth century. The political atmosphere of the United States had an unparalleled impact on organised crime discourse. Though women were a major part of political and societal developments, perceptions of women in organised crime are often simplified and they have experienced significant levels of exclusion from organised crime narrative. Through its investigation into perceptions of women in organised crime during this period, this thesis demonstrates how those perceptions have solidified into contemporary thinking about organised crime. Consequently, crime discourse still focuses on gendered differences in crime which cannot be fully supported.
This thesis aims to challenge what is passively accepted about women in organised crime and reassess the place of women in the organised crime narrative. Central to this aim is the consideration how narrative was, and is, often crafted to help achieve certain political goals, often allowing evidence to be deliberately overlooked.
Using case studies of individual women, this work will illuminate wider themes that are important to the study of the relationship between gender and organised crime. This approach will show how studies of organised crime can be strengthened by approaching the topic on a case-by-case basis. The experiences of these women express how gender wreaked havoc with how criminal women were viewed, and that gender had a great, and in many cases the greatest, influence in dictating how women were condemned. It will point out that the way in which organised crime is understood has been informed by gender in ways which are not often considered.
At its core, this thesis aims to demonstrate that women had greater involvement and influence in organised crime than has been generally argued and that women should therefore take a more central role in narratives of organised crime.</p
Beyond problemistic search: a contingency perspective on organizational response to performance feedback
No full textUsing the behavioral theory of the firm, we develop a contingency perspective of organizational search. Based on an analysis of the risk preference and learning needs of high- and low-performing organizations, we propose that low-performing, risk-tolerant organizations benefit most from searching across boundaries for new knowledge. Conversely, high-performing, risk-averse organizations benefit from internal searches to refine existing routines. We tested these propositions using a regression discontinuity design, analyzing New York City public schools’ responses to academic performance signals. Our empirical results largely support our propositions, enriching the understanding of organizations’ adoption of different search strategies in response to performance signals.</p
BOWIE-ALIGN: Exploring degeneracies in the muted transmission spectrum of the aligned hot Jupiter NGTS-2b with NIRSpec/G395H.
No full textWe present the first atmospheric observation and characterisation of the aligned, 1468 K hot Jupiter, NGTS-2b, with one JWST NIRSpec/G395H transit. These observations complete the GO 3838 observing campaign of the BOWIE-ALIGN program, which aims to investigate the link between hot Jupiter atmospheric composition and formation history through the atmospheric analysis of planets orbiting F stars that are aligned and misaligned with the host stellar spin axis. The 2.84–5.18 µm spectrum shows weak absorption features attributed to H2O and CO2 absorption, which our free chemistry retrievals fit with posteriors that converge on high mean molecular weight solutions attained through significant H2O mixing ratios. By comparing our results to interior modelling, we show that some of these solutions exceed the 43.5× solar upper limit we obtained from our interior structure models. Such solutions are likely due to cloud-metallicity degeneracies and insufficient wavelength coverage to resolve them. We show that, in the case of our observations, the likelihood distribution of H2O abundances is flat and uninformative, such that our retrievals are biased by the prior. Additionally, our statistically favoured atmospheric solution contains absorption from SO. The chemical abundances retrieved with this model are likely not astrophysically feasible and we demonstrate that the presence of SO is driven by only two data points. Our equilibrium chemistry retrievals hint at a subsolar C/O ratio and supersolar metallicity; however, we find wide posterior distributions that extend to solar values.</p
Translating autoimmune genetic risk scores into improved prediction and classification of disease
No full textThe clinical translation of established genetic risk for type 1 diabetes is hindered by a lack of standardisation and understanding of disease heterogeneity. This thesis aims to address these issues by utilising genetic risk scores (GRS) to enhance type 1 diabetes prediction, differential diagnosis, and mechanistic classification. The lack of genetic risk score standardisation typically arises due to their complex generation and use of proxies within missing data. In chapter 2, we address measurement inconsistency by developing the GRS2x model and the open-source PRSedm Python package, enabling reproducible and standardised polygenic risk calculation across array and whole-genome sequencing data. GRS2x demonstrated strong discriminatory performance in European populations, with utility in trusted research environments and ability to generate scores for other traits. Current autoantibody screening recommendations for type 1 diabetes would not be applicable for individuals diagnosed at </p