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Many Phases of Accelerating Black Holes in 2+1 Dimensions
Get PDFThis thesis focuses on the study of accelerating solutions within the context of Einstein-AdS gravity in 2+1 dimensions, exploring both classical and holographic perspectives. These solutions exhibit a diverse range of phases that bear similarities to the C-metric in 3+1 dimensions while displaying certain peculiarities and novelties.
We start by describing the different classes of geometries that can be obtained from analysing the three-dimensional C-metric. After including a domain wall that acts as the external force driving the acceleration, we construct accelerating point particles and accelerating Ba\~nados--Teitelboim--Zanelli (BTZ) black holes exhibiting distinct accelerated phases depending on the energy density of the domain wall. Furthermore, we present a novel accelerating black hole that is not continuously connected with the BTZ black hole. A detailed description of the spacetimes and their embedding into AdS is presented.
From there, we investigate the boundary description of such geometries with particular emphasis on the accelerating BTZ black holes.
We find that the Fefferman--Graham prescription developed for accelerating black holes in four--dimensions leads to a holographic stress tensor that depends on the conformal freedom of the boundary metric. While this behaviour is natural, computing holographic quantities requires choosing a particular conformal representative. As an alternative, we propose that using an Arnowitt--Deser--Misner (ADM) ``radial'' decomposition offers a more suitable identification of the boundary data. Our findings reveal that the dual conformal field theory lies in a curved background being characterised by the stress tensor of a perfect fluid.
The Euclidean action is also obtained ensuring a well-posed variational principle. This requires including contributions from the internal boundaries generated when including a domain wall to the spacetime. We show that these boundary terms can be expressed in terms of the Nambu--Goto action of the domain wall which is added on top of the standard renormalised Einstein--Hilbert action for AdS.
Finally, we compute the entanglement entropy by using the fact that the solution can be mapped to Rindler-AdS where the Ryu--Takayanagi surface is easily identifiable. As the acceleration increases the accessible region of the conformal boundary decreases and therefore the entanglement entropy also decreases. This is interpreted as a process in which the dual theory loses information due to the acceleration
Investigating the antecedents and outcomes of approach- avoidance crafting: The role of paternalistic leadership and work identity
Get PDFJob crafting plays a critical role in enhancing employee well-being and performance. Designing smart jobs that facilitate employees learning and development is an important but challenging task for organizations. This thesis attempts to investigate the antecedents and outcomes of job crafting in the forms of approach-avoidance crafting (Study 1, 2 and 3) and task-, relational-, cognitive crafting (Study 2).
Study 1 (N=318) investigates the antecedents (benevolence and authoritarianism as two dimensions of paternalistic leadership) and outcomes (burnout, work engagement, OCB) of approach- avoidance crafting. Results shown benevolence was positively related to approach crafting and performance goal orientation moderates this relationship. Authoritarianism was found positively related to avoidance crafting. Approach and avoidance crafting were found related to employee outcomes. This study contributes to the research on the antecedents and outcomes of approach-avoidance crafting and provides insights into the proactive work design. Study 2 (N=104) broadens the scope of Study 1 to include individual work identity as a mediator between approach-avoidance crafting and employee proactive service performance. It also extends the job crafting theory by testing the antecedents and outcomes of task-, relational-, cognitive crafting. Results shown consistent findings with Study 1 and supported part of hypotheses of Study 2. This study is the first to directly test the relevance between job crafting and work identity. Study 3 (N=365, 82 teams) used a multilevel data to develop a comprehensive theoretical model. Results shown individual perceptions of benevolence was positively related to approach crafting, and individual perceptions of authoritarianism was positively related to avoidance crafting. Approach and avoidance crafting were both positively related to work identity. Work identity was positively related to work engagement. At team-level, team level benevolence was positively related to team approach crafting and team proactive service performance.
Overall, this thesis enriches the understanding of the antecedents and outcomes of job crafting. It indicates important directions for future research and outlines practical recommendations on nurturing employee job crafting, together with promoting employee well-being, citizenship behavior and proactive performance
THE UK BIRTH CENTRE POSTNATAL EXPERIENCE: ROOM FOR IMPROVEMENT?
Get PDFIntroduction: Postnatal care is one of the most neglected areas of maternity care and inadequate postnatal care has consequences for maternal recovery, breastfeeding initiation and continuation, and parent-infant relationships. Little is known about the experience of in-patient postnatal care for those giving birth within an alongside midwife-led unit in the UK. Evolutionary medicine has been used in the past to develop interventions to support evolved maternal-infant biology within clinical postnatal settings. This research aimed to trial an evolutionary-informed intervention (an in-bed bassinet), to improve parent-infant closeness, to facilitate responsive parent-infant care and to understand the experiences of families receiving postnatal care within a UK alongside midwife-led unit.
Methods: Families (n=33) who gave birth to their first infant in an alongside birth centre in the North East of England were randomly allocated either an in-bed bassinet or a standalone bassinet for their in-patient postnatal stay. Video was used to observe caregiver-infant interactions throughout the postnatal stay and assess the influence of bassinet allocation on breastfeeding, parent-infant contact, maternal sleep, and staff presence. Of those who participated, analysable data for 31 participants was collected. Following participation semi-structured interviews were conducted with a subsample of participants (n=25) to understand the acceptability of the bassinet and gather feedback on their postnatal experiences.
Results: There were no statistically significant differences between those allocated an in-bed bassinet versus a standalone bassinet for breastfeeding duration, frequency, or rate per hour. Mothers who were allocated an in-bed bassinet touched their infants significantly more than those allocated a standalone bassinet (p = 0.04), there was no significant difference in maternal or other caregiver holding, maternal sleep or staff presence. Regression analyses indicated that breastfeeding duration throughout the analysed period was associated with time spent in any bassinet (b=-0.213 (95%CI -0.40, -0.03)), prenatal intention to breastfeed (b=39.185 (95% CI 3.158, 75.213)) and maternal education (b=49.757 (95%CI 2.158, 97.357)).
Reponses to the intervention were influenced by families need for rest, recovery, responsiveness, and safety throughout the postnatal period. Both bassinets influenced these themes in different ways, depending on maternal condition following birth and parental values. Overall families appreciated that the in-bed bassinet facilitated responsiveness and allowed them to closely observe their infants. The bassinets did present difficulties with parental rest and unique safety concerns.
Conclusion: The results of this research indicate that the postnatal environment at the study site was hindering maternal postpartum recovery and breastfeeding initiation. Based on the results of the present study this thesis proposes the concept of ‘midwife-led postnatal care’ that upholds the philosophy of midwife-led care throughout the entire peripartum period
Design and optimisation of THz and mm-wave components for communications
Get PDFThis thesis proposes millimetre-wave (mm-wave) and terahertz (THz) components that can be used in highly integrated systems. These components have been designed for low cost and ease of manufacture using traditional manufacturing techniques, such as printed circuit board (PCB) printing and microlithography. The proposed frequency regions pose unique challenges, including high water-vapor attenuation [1] and the need for micro-scale components. This can limit the achievable power transfer, thereby lowering the signal-to-noise ratio (SNR) associated with components. Components have therefore been highly optimised for power efficiency to compensate for this.
A genetic algortihm (GA), Agenoria, written and revised by the author throughout this work, is presented that can optimise a variety of passive mm-wave and THz components. This uses pre-written FDTD software, Lucifer, which was previously designed in-house, to simulate component performance. A GA is chosen, as compared to other numerical methods, they are more likely to scale well to THz frequencies due to being able to optimise within many constraints at once. The challenge of manufacturing at the micrometre scale can be avoided by specifying constraints such as minimum feature size.
Agenoria is tested on a series of planar patch antennas with varying frequency responses. The first is a broadband antenna, optimised between 100 GHz and 5.0 THz, where 79% of the spectrum shows some improvement. The second antenna is optimised for a single peak at 1.0 THz. The evolved antenna’s simulated power output is considerably higher than that of the reference case, with an improvement at 1 THz of 267%. The third antenna is a dual peak antenna, with peaks optimised at 1.0 THz and 1.2 THz showing a 4,510% and 250% improvement on the reference case from the first generation.
One candidate antenna design, the broadband antenna, was then fabricated and experimentally verified, both in-house by the author. Due to the extremely broadband nature of the antenna, it was not possible to validate the simulated performance across the entire frequency range. Therefore, the verification was completed at a frequency band of 0.8 THz to 1.0 THz, within the optimised range. A vector network analyser (VNA) with two bidirectional VDI WR 1.0 frequency extenders with high-gain horn antennas operating between 0.75 THz and 1.10 THz was used for testing. The antenna transmission and angular dependence was measured and found to concur with simulated results for both the evolved antennas and a reference plain patch antenna. Feedline losses were investigated using the experimental set-up shown in Figure 61. The calculated loss of the microstrip line, connecting the antenna pairs, is 0.79 ± 0.06 dB/mm, which shows promisingly low losses. The combination of these antenna measurements verifies the simulation output within the region 0.8 THz to 1.0 THz. This provides strong evidence that the simulations would match experimental results across the entire simulated range.
In addition, a simple modulation platform for THz communications has been developed to be used in conjunction with WR1.0-VNAX frequency extenders. This consists of an on-off switching board, designed and simulated for a 12.3 GHz carrier wave, corresponding to the RF input of the extender modules, and a power detector board, designed for the LO output of the extenders. These components were designed using traditional techniques, such as transmission line theory, and optimised using Keysight Advanced Design System (ADS) Method of Moments (Momentum) electromagnetic simulator.
The power detector was successfully designed and fabricated in house. It was characterised, and a clear peak seen between 310 and 320 MHz, of 1.38 V at 314 MHz. This PCB was then used in the characterisation of the on-off keying capabilities of the VNA and extender heads. The switch was found to work best at 10 kHz but can modulate the VNA 12.3 GHz input at frequencies between 1 Hz and 1 MHz.
A series of frequency multipliers and mixers were also produced. The frequency multipliers were designed and simulated in the 10 to 30 GHz frequency range. Simulations consistently showed a strong third harmonic while others were successfully filtered by on-chip microstrip filters. However, the preliminary experimental results show a stronger effect of the filter output due to tolerances than had been predicted.
The frequency mixers were designed for two consecutive frequency ranges. The low frequency mixers, combining 2 GHz and 1.685 GHz signals, had a measured output power of -42.3 dBm at 0.315 GHz, where the mixer is optimised for. A mid-frequency mixer, designed to combine frequencies of 20 GHz and 18 GHz to produce a 2 GHz output signal, produced an output power of -45.8 dBm at the optimised frequency
When the shaking stops: an evaluation of post-earthquake rehabilitation of the Kasthamandap in Hanumandhoka Durbar Square
Get PDFThe Kasthamandap, a historic timber pavilion, and eponym of Kathmandu, collapsed during the Gorkha Earthquake that struck central Nepal on 25th April 2015. The reconstruction was completed in 2021. The aim of the thesis is to map and evaluate the longitudinal success of heritage rehabilitation approaches focused on a single monument in Kathmandu, the Kasthamandap, and the extent to which each intervention altered and transformed linkages with its communities. The thesis investigates the communities involved with the Kasthamandap before, during and after the Gorkha Earthquake, under the five main categories of users, urban community, authorities, custodians and those providing a broader significance to the monument. The research was carried out through interviews and consulting secondary sources, accompanying the four-year reconstruction of the monument.
The relationship of a community to a specific monument, such as the Kasthamandap, is determined by its interaction and positioning with other associated and, often contesting, communities. With political and social change over time, the relationship between individuals and groups and the monument changes. Natural disasters, such as earthquakes which cause physical damage to the monument, can be catalysts for changes in the relationships of the various community groups with the monument.
Communities do not belong to a single homogeneous entity with clearly defined needs and aspirations; and, therefore, it is necessary for these communities to negotiate amongst themselves as to how best to address issues concerning their livelihood, collaboration and identity. The negotiations that went into the reconstruction of a historic monument, the Kasthamandap, have been presented in this study. By understanding and recognising these dynamics, it may be possible to improve community consultation and engagement in Nepal’s rehabilitation procedures in the future
A New Era for Direct Detection Experiments: Probing New Neutrino Physics at Dark Matter Detectors with Solar Neutrinos
Get PDFDark matter direct detection experiments are about to hit a complex obstacle - the irreducible background of solar neutrinos. While this will complicate the search for dark matter, it will usher in the beginning of a new search for beyond Standard Model neutrino physics. However, the use of solar neutrinos as a signal of novel physics in these detectors is still in its infancy. To further explore the potential of next-generation and far-future direct detection experiments in this vein, we consider how deviations in the solar neutrino rate can be used as an indirect probe of new physics in the neutrino sector. We consider beyond Standard Model extensions that can serve as solutions to the present tension in the muon's anomalous magnetic moment, as well as the more general framework of neutrino non-standard interactions. In all cases, we find that future direct detection experiments will be able to either probe as-yet unconstrained new neutrino physics or provide us with information complementary to dedicated neutrino experiments.
We conclude that direct detection experiments are poised to become key players in the field of neutrino physics, contributing to a compelling research mission beyond their search for dark matter
International spillovers of US unconventional monetary policy to emerging market economies
Get PDFThis paper analyses whether US unconventional monetary policy (UMP) shocks contribute to the global financial and macroeconomic conditions in EMEs. Using global VAR models, we assessed the possible effects of US UMP on financial and macroeconomic conditions in EMEs and documented the credit channels through which potential spillovers occur, focusing on cross-border portfolio flows. We found that US UMP leads to an increase in bond outflows, in turn, the rise of inflows to EMEs results in a significant response by financial variables, indicating that US UMP generates sizable spillovers by financial terms in EMEs. While these results represent commonalities within a country, there is evidence of cross-country heterogeneity. The magnitude of spillovers depends on the EMEs' trade integration, exchange rate regime, and financial market development. The results of this thesis suggest that EMEs’ policymakers could mitigate their financial vulnerability to US UMP by fostering flexibility of exchange rates as well as domestic financial market development, while such policy might reduce long-run growth
Characteristics of Supraglacial Channels and Drainage Networks on Antarctic Ice Shelves
Get PDFSupraglacial channels that flow on ice shelves can store and transport large volumes of meltwater to various locations (e.g., moulins, lakes, crevasses) during the melt season, so they play an important role in glacial hydrology and ice shelf stability. However, the current understanding of supraglacial channels is limited, especially the underlying processes and the controls on their development and variability. This study uses multiple remotely sensed data including satellite imagery and Digital Elevation Models (DEMs) to measure supraglacial channels in Antarctica. Five contrasting ice shelves around the margin of the Antarctic Ice Sheet are chosen as the study sites – Bach, Nansen, Nivlisen, Riiser-Larsen and Roi Baudouin ice shelves. Supraglacial lakes and channels are mapped by automatic delineation method during the melt season in 2020 and 2022, and key fluvial metrics are calculated, e.g., number, length, width, depth, sinuosity, bifurcation ratio, orientation, slopes and drainage density. Extensive supraglacial lakes and channels were observed on all five Antarctic ice shelves during the peak of the melt season and most were interconnected to form a total of 119 channel networks at different scales. The results demonstrate that: (ⅰ) supraglacial channel networks often occurred in areas with low elevations and near grounding lines, (ⅱ) supraglacial channel networks on different ice shelves exhibited different drainage patterns and hydromorphic characteristics, (ⅲ) the surface topography and structural glaciology of ice shelves affected the distribution of the supraglacial channel network. Future work could focus on long-term observation of supraglacial channels and exploring the applicability of terrestrial river-related research methods (e.g., hydrological modelling) to supraglacial channels
MLM Diffusion: Generating Globally-Consistent High-Resolution Images from Discrete Latent Spaces
Get PDFContext/Background: Creating deep generative models capable of generating high-resolution images
is a critical challenge for modern deep learning research, with far-reaching impacts in domains such
as medical imaging and computer graphics. One method that has recently achieved great success in
tackling this problem is probabilistic denoising diffusion. However, whilst diffusion models can generate
high quality image content, key limitations remain in terms of high computational requirements.
Aims: This thesis investigates new techniques to overcome the computational cost requirements that
currently limit generative diffusion models. Specifically, this thesis focuses on training deep learning
models to model and sample from discrete latent spaces that can be used to generate high-resolution
images
Method: This thesis introduces a novel type of diffusion probabilistic model prior capable of generating discrete latent representations of high-resolution images by utilising bidirectional transformers. The
quality and diversity of images generated by these models are then evaluated and compared quantitatively and qualitatively to other similar models, before other interesting properties are also explored.
Results: The proposed approach achieves state-of-the-art results in terms of Density (LSUN Bedroom:
1.51; LSUN Churches: 1.12; FFHQ: 1.20) and Coverage (LSUN Bedroom: 0.83; LSUN Churches: 0.73;
FFHQ: 0.80), and performs competitively on FID (LSUN Bedroom: 3.64; LSUN Churches: 4.07; FFHQ:
6.11) whilst also offering significant advantages in terms of computation time.
Conclusions: Through the use of powerful bidirectional transformers and discretised latent spaces, it
is possible to train a discrete diffusion model to generate high-quality, high-resolution images in only
a fraction of the time required by continuous diffusion probabilistic models trained on the data space.
Not only are these models faster to train and sample from, they also only require a single NVIDIA
2080ti GPU with 11GB of RAM for successful training and achieve state-of-the-art results in terms of
generated image quality and diversit
Understanding Youth Image-Based Sexual Abuse: The Role of Context and Police Discretion
Get PDFThere has been much written about youth image-sharing and particularly ‘sexting’ over the years. Academics have explored different facets of these experiences including the role of consent, its gendered nature and proximity to relationship abuse. However, even with these investigations, there is a need to identify and understand harmful image-sharing in more depth, specifically, what is described in this research as youth image-based sexual abuse. Using knowledge about child sexual abuse images and image-based sexual abuse, this thesis intends to explore in more detail how youth image-based sexual abuse is experienced, focusing in on two themes, context, and police discretion. A mixed methods approach was utilised, including an analysis of Freedom of Information responses from Police forces in England and Wales and semi-structured interviews. Findings collated from the Freedom of Information responses provided details on different youth image-based sexual abuse offences, including the gender and age of victims and suspects. A total of 26 participants were interviewed, 18 police officers of different ranks and 8 practitioners, whose professions ranged from specialist sex and relationships educators to youth workers. The interviews shed light on the complexities of youth image-based sexual abuse, such as which cases are encountered by police and practitioners, what challenges are presented as well as how decision-making is navigated. Further themes were identified when quantitative and qualitative findings were analysed collectively, such as the impact of the situational and individual context on youth image-based sexual abuse, the degree to which police discretion is applied thematically throughout these cases, and the many challenges which police, practitioners and young people face. This thesis makes an original contribution by examining in depth the nature of youth image-based sexual abuse, as well as highlighting the influence policing and police discretion has
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