13506 research outputs found
Sort by
Quantum optics with 87Rb vapour in the hyperfine Paschen-Back regime
Get PDFWe present experimental studies of quantum optics with Rb vapour in the hyperfine Paschen-Back (HFPB) regime. We use a \SI{0.6}{\tesla} magnet to enter the HFPB regime, where, for Rb, the atomic transitions are separated by more than their Doppler width. This allows us to create clean 3- or 4-levels systems, which we model simply and effectively by solving the Lindblad master equation. We study electromagnetically induced transparency in a V configuration in the HFPB, where we see large, clean absorption and corresponding transmission features. We model the system, and use the model to understand the role of coherence in the features seen. We carry out seeded four-wave mixing in a double ladder scheme (5S--5P--5D), both in and out of the HFPB regime, and compare the two regimes. The simplicity of the system in the HFPB regime allows us to model the system to understand the features we see in the experimental spectra. We convert our seeded FWM into spontaneous FWM, which we use to produce pairs of heralded single photons. We find the zero-field regime to be more efficient for the production of these pairs, and measure , demonstrating that this is a single photon source. Throughout, we make use of lens cavity etalon filters, which we commission, characterise and compare to atomic line filters. We investigate fine structure changing collisions, which transfer atoms between 5P states, and can be a significant source of noise for quantum optics experiments in thermal vapours. We deduce that these are Rb-buffer gas collisions, measure the spectra of the fluorescence produced after a collision, and use the resolved spectra of the HFPB regime to determine that the nuclear spin magnetic quantum number, , is preserved in these collisions
The implications and impact of artificial intelligence, big data and HR analytics in HRM: A critical analysis of EU enterprises
Get PDFThis study offers a critical evaluation of HR analytics. Specifically, the ideas and concepts surrounding HR analytics, such as what is HR analytics, the development of HR analytics in organizations and how it may impact organizational performance. To advance and answer these research questions, this study relied on systematic reviews, logistic regression, interaction effect analysis, and interviews with the European Company Survey (ECS) to assess the interrelationship between HR analytics and organizational factors. Based on the findings, certain key areas are addressed. Firstly, research question 1 has succeeded in developing a more systematic and coherent definition of HR analytics and artificial intelligence in HR. It has also successfully identified some factors that influence the use of HR analytics in organisations. In particular, the results of study two found that factors such as firm age, firm size, the complexity of the firm process and the type of variable pay systems have been shown to be key indicators of why certain companies use HR analytics while others do not. Furthermore, the results for study three also provided a bigger picture of how organizational factors might be the reasons for explaining firms’ financial returns when examining the relationship between variables. In particular, factors such as employee motivation, the use of HR analytics, and variable pay systems are also believed to be critical in determining which factors affect a company’s financial returns. In addition, the study provides additional knowledge for five specific areas in analytics and artificial intelligence in HR, namely firm characteristics, challenges, key reasons to adopt HR software, new trends and user traits
Understanding Landscape and Ice Sheet Evolution in the Gamburtsev Subglacial Mountains, East Antarctica, using Ice Sheet Surface Mapping
Get PDFLandscapes buried beneath the Antarctic Ice Sheet preserve information about the geologic and geomorphic evolution of the continent both before and during the wide-scale glaciation that began roughly 34 million years ago. Throughout this time, some areas of the ice sheet have remained cold-based and non-erosive, preserving ancient landscapes remarkably intact. The Gamburtsev Subglacial Mountains in central East Antarctica are one such landscape, maintaining evidence of tectonic, fluvial and glacial controls on their distinctly alpine morphology. The central Gamburtsevs have previously been surveyed using airborne ice-penetrating radar, however, many questions remain as to their evolution and their influence on the East Antarctic Ice Sheet, including where in the region to drill for a 1.5-million-year-long ‘Oldest Ice’ core. In this thesis, new maps of the planform geometry of the Gamburtsev Subglacial Mountains are derived from satellite remote sensing datasets of the ice sheet surface, based on the relationship between bed roughness and ice surface morphology. Automated and manual approaches to mapping were tested and validated against existing radar data and elevation models. Manual mapping was more effective than automated approaches at reproducing bed features observed in radar data, but a hybrid approach is suggested for future work. The maps produced here show detail of mountain ridges and valleys on wavelengths significantly smaller than the spacing of existing radar flightlines, and mapping has extended well beyond the confines of existing radar surveys. Morphometric analysis of the mapped landscape reveals that it constitutes a preserved (> 34 Ma) dendritic valley network, with some evidence for modification by topographically-confined glaciation prior to ice sheet inception. The planform geometry of the landscape is a significant control on locations of basal melting, subglacial hydrological flows, and the stability of the ice sheet over time, so the maps presented here may help to guide decisions about where to search for Oldest Ice
The effect of soil bunds as Natural Flood Management features on soil water chemistry and hydraulic conductivity
Get PDFNature-based solutions to flooding have drawn growing attention in recent years as climate change models predict a significant increase to flood-risk in the UK and around the world. The lack of systematic empirical evidence to support Natural Flood Management (NFM) initiatives still presents a key barrier to the widespread implementation of NFM techniques.
Both rural and urban areas in the North Pennine Hills in Northeast England have historically been substantially affected by flooding. This study focused on a small-scale pilot installation of five earth bunds designed as temporary storage units for flood water in the upper catchment of the River Wear in Weardale. An upscaled installation of such features on a larger spatial scale may have a significant impact on reducing flood-risk by slowing down flood flows. To assess the effectiveness of the bunds, water sensors were installed in each of the five bunds to record the frequency of flood storage. Changes in soil hydraulic conductivity were measured throughout the study period (December 2021 to June 2022) to assess changes in infiltration capacity as a measure of bund construction quality. Finally, the chemistry of soil water was analysed through Inductively Coupled Plasma Mass Spectrometry (ICP-MS), to establish whether the bunds can act as filters for pollutants in a catchment suffering from heavy metal contamination with possible implications to water quality improvements.
Due to instrument malfunction, no data was recorded on the frequency with which the bunds acted as active storage features. No evidence was found for the bunds’ ability to act as sinks for heavy metals, although the data are not conclusive. Hydraulic conductivity measurements found no variation across the five bunds, nor across different areas of each bund, suggesting the bund structure remains stable through time and does not vary in quality. Further research is required to corroborate these results, with more extensive sampling and over a longer time scale
“You're like a salesman or a saleswoman, you're trying to sell that person exercise”: How the socioeconomic position of an area influences General Practitioners’ engagement with physical activity as a treatment pathway for mild to moderate mental health conditions
Get PDFOverview: Mental health problems affect one in four people in the UK (Farmer and Dyer, 2016). Socioeconomic position (SEP) has impacted both lifestyle and the quality of general healthcare (Office of National Statistics, 2016). This study was the first to specifically explore how the socioeconomic area of a General Practitioner’s (GP’s) practice, impacts the use of physical activity (PA) as a treatment for mental health conditions. It aimed to: (i) Explore GPs’ experiences of physical activity and other provisions for mental health, in their local area; (ii) Understand perceived problems regarding access to physical activity to support mental health; and (iii) Understand how existing socioeconomic inequalities may impact the mental health treatment approach of GPs.
Methodology: Participants (n=6) were recruited using convenience sampling. The inclusion criteria for this study were that GPs had to be based in England and currently working in general practice. The participants represented different socioeconomic areas, allowing comparison and contrast across findings. Interviews focused on the provision of and access to mental health treatment pathways, barriers that GPs encountered and the healthcare inequalities that exist. A reflexive thematic analysis was undertaken (Braun and Clarke, 2019).
Results: The first theme, ‘Precedence of pharmaceutical and psychological approaches as treatment pathways’, focused on the growing mental health cases that GPs are experiencing. There were narrow treatment options for GPs, despite acknowledgement of PA benefits. The ‘Insufficient implementation of PA schemes’ theme identified perceived problems with PA schemes and the multifaceted reasons for patients’ lack of engagement. The SEP was perceived to influence the GPs’ and patients’ attitudes to treatment pathways. The ‘Complexity of barriers to PA for GPs and patients’ theme outlined difficulties that lead to restricted PA engagement, with COVID-19 exacerbating these. There was also inadequate interaction between GPs and stakeholders.
Conclusion: GPs working in lower socioeconomic areas experienced greater difficulties in referring and engaging patients in PA; challenges were complex and differed across localities. Findings highlight a training need around PA for GPs who work in higher socioeconomic status areas and a need for improved communication between GPs, external healthcare professionals, providers and patients
X-ray Imaging Studies of Topological Magnetism
Get PDFThis thesis applies resonant soft x-ray scattering techniques to the study of single crystal lamellae hosting topological magnetic states. In particular, imaging methods are used to examine exotic magnetisation textures whose properties are affected by their topology. These include investigating magnetic skyrmions, anti- skyrmions, reports of biskyrmions, and the identification of a surface spiral state, previously theorised to exist in chiral helimagnets.
Tilted x-ray holography, in conjunction with micromagnetic simulations and Lorentz transmission electron microscopy measurements, was performed on the uniaxial ferromagnet (Mn1−xNix)0.65Ga0.35 (x = 0.5) to reveal that previous reports of biskyrmions, a bound pair of opposite chirality skyrmions, likely misidentified topologically trivial magnetic bubbles. We show that pseudo-tomographic imaging methods can map the topology of the magnetic bubbles formed, and our simple model structure can be used to account for previous experimental observations without the need to invoke an exotic bound-state texture. Further x-ray holography measurements on lamellae of the archetypal chiral helimagnet FeGe show that, in a thickness regime inaccessible to many other common magnetic imaging techniques, a previously theorised stacked spiral spin state can be stabilised.
Small angle x-ray scattering measurements confirm the existence of this stacked spiral spin state in lamellae of Cu2OSeO3 and its presence was used to inform skyrmion-skyrmion interaction potentials in the context of melting transitions undergone by the skyrmion lattice. We find that skyrmion lattice melting is mediated by the proliferation of topological defects through the lattice, in a two step transition. The skyrmions behave as a condensed ensemble of particles and we present evidence consistent with a grain boundary theory of melting. This is in contrast to a previous study, which reports the skyrmion lattice melts according to KTHNY theory. We theorise that differing concentrations of skyrmions in the systems can reconcile this difference, in line with recent Monte Carlo simulations, and propose a future experiment to conclusively test the melting phase transition. Magnetic skyrmions confined in lamellae are shown to provide a rich environment for the study of two dimensional phase transitions, with a field-tunable interaction potential.
Finally, scanning transmission x-ray microscopy and x-ray ptychography are used to investigate lamellae of the inverse Heusler system Mn1.4PtSn, a system with the appropriate symmetry to host antiskyrmions. By utilising high-resolution x-ray ptychography, we find previous reports of helimagnetism in the system have misidentified nanoscale ferromagnetic stripe domains, leading to inconsistent estimations of the material parameters. In addition to antiskyrmion bubbles, we identify the coexistence of topologically trivial bubbles and elliptical skyrmions. Micromagnetic simulations, performed with empirically calculated material parameters support these observations
Engendering Life: String Objects as a Model of Process, Pattern, and Praxis in Melanesia
Get PDFIn this thesis, I show that string objects materialize and instantiate social organizing principles in Melanesia. In this region, objects like string figures, bilum bags, and fishing nets are vehicles for thought, where mind and material unite to create a multivalent and interactive model of social and temporal relations. Due to the prevalence and universality of string practices in the region, this model is available to everyone. Social and temporal relations become apparent due to the understanding that string objects possess ‘processuality,’ that the materials of string objects, their (re-)production, and (re-)use are constantly in flux rather than in a state of stasis. Through processuality, string objects convey the relations and circumstances in which desired outcomes should be achieved, prefiguring patterns, processes, and operational sequences which are then instantiated in the social framework. I show that the cognitive and physical processes of string objects in the microcosm make abstract concepts concrete and achievable in social practice by reproducing the same pattern through different levels of social life. I therefore explore how other social activities such as tuber gardening and sexual reproduction produce social cohesion and stability in a similar way to string objects. I argue that string objects are a vehicle through which social actors can conceive of the patterns and processes necessary to sustain life in the macrocosm. Through the coalescence of differentiated and reciprocal labor, string objects make evident the conditions necessary for productivity and efficacy in the social system. In conclusion, I assert that string objects contribute to fundamental understandings of social life in Melanesia
Music, ‘Sternhold and Hopkins’s’ Metrical Psalms, and the Inculcation of Protestantism in England, c.1547-1590
Get PDFThis thesis argues that the congregational or collective singing of metrical psalms was one of the principal means through which ordinary men, women and children negotiated the religious changes that shook sixteenth-century England. The thesis argues that these otherwise ‘voiceless’ individuals (those who, while using their voices to sing, lacked agency within their parish community, and are thus largely silent in the sources) shaped both the practice and corpus of texts and tunes to fit their preferences, and in doing so shaped both the speed and spread of Protestantism’s introduction into England, making its arrival and its ideas more palatable for themselves. To study fully the singing of metrical psalms, however, historians must appreciate the musical element which lies at the heart of this phenomenon. Without doing so, they miss some of the central reasons for its popularity and success. This thesis, therefore, establishes a framework through which historians can use music as a historical source, analysing it as it was heard by contemporaries. Drawing on the work of scholars from fields as diverse as music, theology, philosophy, and poetry, the thesis introduces three approaches which form the central pillars for this framework. Adopting this framework allows us to gain a fresh understanding of the surviving sources, revealing that the singing of metrical psalms may represent the most significant means through which the otherwise ‘voiceless’ came to accept Protestantism. The thesis also argues that the singing of metrical psalms was both more widespread and less controversial than scholars have previously understood, especially during the overlooked Edwardine and Marian periods. During Elizabeth I’s reign, in large part due to the experience of music and the agency of the otherwise ‘voiceless’, metrical psalmody firmly and quickly established itself first in London, then further afield, becoming an immovable element in congregational worship
Untangling topoisomerase inhibition by ParE toxins of Mycobacterium tuberculosis; a biochemical, structural, and phylogenetic approach
Get PDFMycobacterium tuberculosis (Mtb), the causative agent of TB, remains a threat to global health with recent efforts towards its eradication being reversed in the wake of the COVID-19 pandemic. Increasing resistance to gyrase targeting second-line fluoroquinolone (FQ) antibiotics indicates the necessity to develop both novel therapeutics and our understanding of Mtb growth during infection. ParDE type toxin-antitoxin systems may lie at this intersection, with ParE toxins targeting gyrase as responsive elements to both host-associated and drug-induced stress during infection. Here we present biochemical and biophysical analyses exploring the ParE1 and ParE2 poisoning of Mtb gyrase, trapping cleavage complexes potentially via a contrasting mechanism to FQ antibiotics. We also propose a novel mechanism of post-translational ParE1 toxin release and system activation via complex remodelling, a potential first in the field. We show the ParE2 toxin to be closely related to the RelE toxin family via phylogenetic analyses and as part of a collaboration with the Genevaux group (Toulouse, France) present the crystal structure of the Mtb RelBE1 complex. We highlight differences in the RelE1 toxin which may contribute to alternate and novel mechanisms of toxicity employed by Mtb RelE toxins, all three of which are upregulated during infection. Altogether, this study combines a range of techniques to better our understanding of three TA systems important to the adaptability of Mtb. We lay the foundations for future work focussing on the molecular basis of Mtb ParE and RelE toxicity through biochemical, biophysical, and structural studies
The role of the periplasmic Cu metallochaperone AccA in metalating the Cu-dependent nitrite reductase AniA in Neisseria gonorrhoea
Get PDFNeisseria gonorrhoeae (the gonococcus) respires nitrite (NO2-). This process requires the nitrite reductase, AniA, which contains T1- and T2Cu in its active sites. We have characterised AccA, a PCuAC homologue with an extended His- and Met-rich C-terminal domain, as a likely periplasmic Cu- binding metallochaperone that metalates AniA.
In this study, biochemical examination of purified AccA and site-directed variants confirms that it binds one Cu(I) atom with femtomolar affinity in the conserved 2 His, 2 Met binding site. The C-terminal domain binds Cu(II) with picomolar affinity, although precise ligands remain unknown. Gonococcal strains lacking AccA or any conserved His and Met residue in AccA fail to grow and reduce NO2-. This phenotype is reversed when Cu(II) salts are supplemented in the growth medium. These results suggest that, in the absence of AccA, AniA is expressed as an apo-enzyme, but is re-metalated if the periplasmic buffered Cu pool increases. Interestingly, gonococcal strains lacking the C-terminal domain of AccA show reduced growth and NO2- consumption only in the presence of the Cu(I) chelator BCS, suggesting a role during Cu starvation.
Cu-transfer experiments using purified proteins confirmed AccA metalates both Cu sites in AniA with metal coordinated by both the Cu primary and C-terminal Cu binding sites. However, the C-terminal tail was required for metalation of the T2-site. AniA is expressed as a monomer and Cu binding induces protein trimerisation. This may offer an alternative role of why AccA is required to metalate AniA in vitro.
This work raises questions regarding the thermodynamics and kinetics of how metalloproteins acquire Cu from the buffered cellular pool via metallochaperones
Data sources:
Access Repository Dashboard
Do you manage Open Research Online? Become a CORE Member to access insider analytics, issue reports and manage access to outputs from your repository in the CORE Repository Dashboard! 👇