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Arrayed LiDAR signal analysis for automotive applications
Get PDFLight detection and ranging (LiDAR) is one of the enabling technologies for advanced
driver assistance and autonomy. Advances in solid-state photon detector arrays offer
the potential of high-performance LiDAR systems but require novel signal processing
approaches to fully exploit the dramatic increase in data volume an arrayed detector
can provide.
This thesis presents two approaches applicable to arrayed solid-state LiDAR. First, a
novel block independent sparse depth reconstruction framework is developed, which
utilises a random and very sparse illumination scheme to reduce illumination density while improving sampling times, which further remain constant for any array
size. Compressive sensing (CS) principles are used to reconstruct depth information
from small measurement subsets. The smaller problem size of blocks reduces the
reconstruction complexity, improves compressive depth reconstruction performance
and enables fast concurrent processing. A feasibility study of a system proposal for
this approach demonstrates that the required logic could be practically implemented
within detector size constraints. Second, a novel deep learning architecture called
LiDARNet is presented to localise surface returns from LiDAR waveforms with high
throughput. This single data driven processing approach can unify a wide range
of scenarios, making use of a training-by-simulation methodology. This augments
real datasets with challenging simulated conditions such as multiple returns and
high noise variance, while enabling rapid prototyping of fast data driven processing
approaches for arrayed LiDAR systems.
Both approaches are fast and practical processing methodologies for arrayed LiDAR
systems. These retrieve depth information with excellent depth resolution for wide
operating ranges, and are demonstrated on real and simulated data. LiDARNet is
a rapid approach to determine surface locations from LiDAR waveforms for efficient point cloud generation, while block sparse depth reconstruction is an efficient method to facilitate high-resolution depth maps at high frame rates with reduced power and memory requirements.Engineering and Physical Sciences Research Council (EPSRC
Tailored quantum light for photonic quantum technologies
Get PDFPhotonic quantum technologies rely on the deterministic preparation of qubits encoded in quantum states of light: advances in this field are therefore contingent
with the development of reliable photon sources. In this Thesis, I address this challenge presenting a novel and versatile approach to single-photon generation based
on nonlinearity engineering in parametric down-conversion. By tailoring the effective nonlinearity of a crystal, this scheme enables access to the spectral degree
of freedom of photonic qubits with unprecedented precision, and translates into a
number of different applications based on the manipulation of the biphoton spectral/temporal properties. A thorough theoretical and numerical description of such
approach is provided and paired with experimental benchmarks conducted in three
main experiments. The first experiment tackles the single-photon spectral purity
problem in down-conversion sources: pure photons are in fact required for achieving perfect two-photon interference, a keystone of most quantum protocols. The
second experiment demonstrates the feasibility of nonlinearity engineering to produce tailored entanglement encoded in the spectrum of biphoton states. Finally, the
third experiment certifies the compatibility of this technique with different degrees
of freedom, demonstrating hyperentanglement of spatially and spectrally structured
quantum light. In conclusion, this Thesis stands as a cookbook for designing simple
yet flexible and highly-efficient single-photon sources based on tailored parametric
down-conversion processes
The nature of the relationship between strategic management and corporate taxation : the use of strategic management by the UK tax practitioner in corporate taxation
Get PDFTax is a critical function in any organisation. In most developed countries, it is common
for an organisation to pay nearly a fifth of its annual profit to the tax authorities before
distributing value to shareholders. Suppose the primary goal of the organisation is to add
value for shareholders. In that case, the expectation is that it will be strategic with its tax
planning to achieve and sustain a competitive advantage. To accomplish this aim, the
organisation can choose from several different strategic management theories and
models. This variety leads to fragmentation in academia. Similarly, research in corporate
taxation also lacks integration due to the different backgrounds of scholars. This
commonality between the two subjects may explain why there is limited literature on the
nature of the relationship between strategic management and corporate tax strategy.
This research investigates three pertinent research questions. Is there a relationship
between strategic management and corporate tax planning? Does an integrated strategic
management framework show a relationship between strategic management and
corporate taxation? Does the tax practitioner act strategically in corporate tax planning?
A pragmatic paradigm is adopted using an interpretive research method with document
analysis, questionnaire, and interview techniques.
A defined, integrated framework of strategic management is established after an
extensive review of the strategic management literature. The framework consists of the
design, planning and positioning schools with the resource-based view and dynamic
capabilities with creative action. This framework facilitates collecting empirical data
from the tax strategy documents of the one hundred largest listed organisations in the UK (FTSE 100) and interviews and questionnaires with seventeen senior tax practitioners.
Qualitative data is collected and reviewed through thematic and content analysis using
NVivo software. Where appropriate, quantitative data is presented to support the
qualitative evidence. An iterative approach is adopted for reviewing the tax strategy
documents, helping to refine the data and improve the approach to interviews.
The findings of the research show that tax practitioners are strategic in formulating the tax
strategy. Therefore, the contribution to theory is that the research demonstrates that strategic
management and corporate tax are aligned by analysing tax strategy using various
interconnected strategic management concepts. The research concludes that tax strategy
follows the commercial strategy and is both deliberate and emergent depending on the
organisation's size and nature.
The research contributes to practice by developing a strategic management tool kit for the tax
practitioner to use in tax planning. The use of an integrated framework allows the tax
practitioner to consider critical themes in strategic management. The paper advocates a
checklist, which addresses the fundamental questions that the tax practitioner should consider
for each theme. By embracing the integrated framework of strategic management and using it
when formulating the organisation's tax strategy, the tax practitioner will ensure that the tax
strategy is aligned with the organisation's commercial objectives
Bayesian computation in imaging inverse problems with partially unknown models
Get PDFMany imaging problems require solving a high-dimensional inverse problem that is
ill-conditioned or ill-posed. Imaging methods typically address this difficulty by regularising the estimation problem to make it well-posed. This often requires setting
the value of the so-called regularisation parameters that control the amount of regularisation enforced. These parameters are notoriously difficult to set a priori and
can have a dramatic impact on the recovered estimates. In this thesis, we propose
a general empirical Bayesian method for setting regularisation parameters in imaging problems that are convex w.r.t. the unknown image. Our method calibrates
regularisation parameters directly from the observed data by maximum marginal
likelihood estimation, and can simultaneously estimate multiple regularisation parameters. A main novelty is that this maximum marginal likelihood estimation
problem is efficiently solved by using a stochastic proximal gradient algorithm that
is driven by two proximal Markov chain Monte Carlo samplers, thus intimately combining modern high-dimensional optimisation and stochastic sampling techniques.
Furthermore, the proposed algorithm uses the same basic operators as proximal optimisation algorithms, namely gradient and proximal operators, and it is therefore
straightforward to apply to problems that are currently solved by using proximal optimisation techniques. We also present a detailed theoretical analysis of the proposed
methodology, and demonstrate it with a range of experiments and comparisons with
alternative approaches from the literature. The considered experiments include image denoising, non-blind image deconvolution, and hyperspectral unmixing, using
synthesis and analysis priors involving the `1, total-variation, total-variation and
`1, and total-generalised-variation pseudo-norms. Moreover, we explore some other
applications of the proposed method including maximum marginal likelihood estimation in Bayesian logistic regression and audio compressed sensing, as well as an
application to model selection based on residuals
Managing the energy trilemma : a paradigmatic approach to the optimisation of utility-scale hybridised PVPG/CSP with integrated energy storage for the supply of baseload renewable energy in South Africa
Get PDFThe largest single renewable energy resource in South Africa, is arguably
that of solar power with the best solar resource found in the Northern Cape
Province with ongoing research into finding innovative ways of harvesting
and storing the solar resource, using cost-effective solutions that can be
expanded into utility-scale solar base load electrical power production units.
Two of the more recent and most innovative solar technologies are
Concentrated Solar Power (CSP) Generation and solar Photovoltaic Power
Generation (PVPG) together with Integrated Energy Storage Solutions
(CSP-IESS and PVPG-IESS) all of which have been established as viable
and feasible renewable energy technologies.
As part of managing the Energy Trilemma (Affordability, Reliability and
Sustainability) in the Optimisation of Base Load Power Production from
Renewable Solar Energy it is proposed to model and optimise a stand-alone
PVPG facility, to model and optimise a PVPG-IESS facility, to model and
optimise a CSP-IESS facility and lastly to model and optimise a Hybrid
PVPG IESS-CSP IESS facility whilst continuously optimising all options in
terms of the Energy Trilemma.
In achieving this objective, this researcher aims to use live data drawn from
the current project site initiative in a ‘Case Study’ underpinned by elements
from the ‘Scientific Method’, where appropriate. The research furthermore
will be supported by literature studies pertaining to CSP-IESS and PVPG IESS technologies executed under the auspices of specialist studies
focussed on the scoping of a Utility Scale Hybridised Solar Power
Generation Park (USHSPGP) in South Africa underpinned by management
of the Energy Trilemma
Bioprospecting of novel thraustochytrids from Scotland for high value compounds
Get PDFThraustochytrids are marine microheterotrophs and important producers of many
industrially relevant compounds such as docosahexaenoic acid (DHA),
eicosapentaenoic acid (EPA), extracellular enzymes, carotenoids, and proteins. Despite
their growing importance in recent years, there is currently very limited data regarding
the biodiversity and biotechnological potential of Scottish strains.
The project aimed to isolate novel thraustochytrids from a temperate climate of Scotland
and to screen them for the production of biotechnologically relevant compounds. To
achieve this, twenty thraustochytrids were isolated from the Scottish saltmarshes and
screened for the presence of lipids, extracellular enzymes, total proteins, antimicrobial
agents, and biosurfactants by the adoption of the sulfo-phospho colorimetric assay,
substrate digestion plates, Bradford assay, disc diffusion assay, and emulsification
assay, respectively.
The results showed a relative abundance of thraustochytrids in the Scottish coastal
regions as well as established a reliable method of their isolation from this area.
Moreover, the study confirmed the ability of thraustochytrids to produce many
important hydrolyzing enzymes including chitinase, cellulase, and amylase. Isolated
thraustochytrids were also able to synthesize emulsifying agents, an ability that has
never been reported before. Overall, the results here show that isolated thraustochytrids
produce a variety of biotechnologically relevant compounds with the potential to
contribute to key biotechnological sectors
A Lean Six Sigma maturity model for higher education institutions (HEIs)
Get PDFLean Six Sigma (LSS) is a continuous improvement methodology that aims to
reduce the costs of poor quality, improve the bottom-line results and create value
for both customers and shareholders. LSS has been deployed in organisations in
a variety of sectors and cultures for more than two decades. However, its
implementation in higher educational institutions around the world has only just
begun to emerge. Furthermore, there is a lack of any empirical evidence to
support any successful deployment of LSS in higher educational institutions when
addressing the key challenges faced by these institutions today.
Therefore, the purpose of this research is to investigate the current status of Lean
Six Sigma (LSS) in UK higher educational institutions and subsequently develop
a Lean Six Sigma Maturity Model which can be used to assess their current level
of LSS maturity and help these institutions develop action plans and strategic
objectives to successfully build maturity in LSS.
The study is based on a Taguchi styled systematic literature review of papers that
were published on LSS in higher education in high ranking journals in the field of
LSS, academic leadership and other specialist journals, from 2000 to 2020. A
descriptive survey via a questionnaire was conducted in the second phase of the
data collection process and semi-structured interviews were conducted in the
third phase. Based on the literature review and the findings of the empirical
research, a Lean Six Sigma Maturity Model for higher educational institutions was
developed and tested on a mix of UK and International higher educational
institutions, along with a sample of Master Black Belts from industry. The results
of the empirical study show a lack of maturity in LSS, that UK institutions are in
the early stages of implementation, and that these institutions have only recently
started to recognise the importance of LSS to their organisation. Therefore a
maturity model for this new emerging sector is vital for its success in developing
its approach to deploying LSS and will become the basis for future work and
publication by the author
Generation of deep ultra-violet pulses in hollow capillary fibres
Get PDFFemtosecond pulses in the deep ultraviolet region (DUV, 200-400 nm) are in high
demand for time-resolved studies in several fields of research such as quantum chemistry (UV photoelectron spectroscopy), material sciences (lithography in semiconductors, polymers) and biology (protein analysis, DNA sequencing, cell imaging). When
combined with external polarization control, they can provide excellent tools for chiral
molecule analysis and ultrafast magnetism studies.
A well-established route for the generation of linearly polarized pulses in the DUV has
been via frequency up-conversion in bulk materials such as nonlinear crystals or gases.
However, the former suffer from limited transmission range, narrow phase-matching bandwidths and low intensity damage thresholds while the latter require high-peak power and
provide low frequency up-conversion efficiencies. For circularly polarized pulses in the
DUV, an additional stage for polarization conversion is required, commonly implemented
by using phase retarders in the ultraviolet. This induces unwanted dispersion that compromises ultra-short duration and achromatic phase retardation.
This thesis focuses on the experimental generation of high-energy, ultrashort DUV
pulses with controlled polarization using two alternative frequency up-conversion techniques in hollow capillary fibres; four-wave mixing and resonant dispersive wave emission. Using the first technique, record-breaking energy conversion efficiency up to 50%
and large spectral bandwidths in the DUV with high pulse energy are demonstrated with
linear polarization. This scheme is then extended to achieve direct generation of DUV
pulses with circular polarization without the need for dispersive optics in the UV. Using
resonant dispersive wave emission, high energy, circularly polarized pulses tunable across
the DUV are generated when driven by circularly polarized 800 nm pulses.
These studies allow to experimentally verify the polarization-induced dynamics with
respect to fundamental science such as the angular momentum conservation and the energy scaling of nonlinearity. Although this work is focused on DUV generation, the same
techniques can be applied to other spectral regions such as the vacuum-ultraviolet (VUV,
100-200 nm) and the mid-infrared (mid-IR, 3-8 µm) by proper selection of the driving
frequencies, and can be scaled up in output energy using larger fibre systems
Developing a Public Private Partnerships (PPP) framework for implementing road maintenance projects in South African rural communities
Get PDFSouth Africa's rural communities struggle with three main problems: lack of skills, low private
sector investment, and poor infrastructure, which further undermines private investment in
those communities. Even those with necessary skills lack opportunities to develop and deepen
their skills fully. Consequently, their ability to become more competitive in the employment
market is undermined. Skilled workforce and sustainable enterprises are the bedrock of any
effort towards sustainable rural development. This study investigates the extent to which road
maintenance activities contribute to skills transfer and enterprise development, with the aim of
developing a simplified PPP (Public-Private Partnership) framework for rural road
maintenance.
The study used a qualitative research approach that employs personal and focus group
interviews. Data was analysed using content and thematic analysis. The current PPP framework
is not conducive to skill transfers and enterprise development through road maintenance
projects. Overall, this study concludes that a small-scale PPP framework is indeed feasible,
provided the cost of the transactions is lower. The study recommends that government should
use the proposed framework from this research to bring about rural skills transfer and enterprise
development. This study focused only on rural road maintenance; hence, this may influence
the generalisability of the results to other sectors or service categories. Furthermore, this
research explicitly focused on the South African PPP framework
Ti:sapphire frequency combs for dual-comb distance metrology
Get PDFThis thesis presents research developing Ti:sapphire lasers for applications in precision
absolute distance metrology. Dual Ti:sapphire frequency combs were developed and
characterised, each typically generating 64 fs pulses at a wavelength of 780 nm and a
pulse repetition rate of 513 MHz. Electronic phase stabilisation using f-to-2f
interferometry and direct pump power modulation achieved phase slips of 234 mrad
(124 mrad) for the carrier-envelope offset frequencies of the probe (local-oscillator) comb
in observation times of 1 second. The comb mode spacings were stabilised with cavity
length feedback, achieving a phase noise of 4 mrad in one second for each laser.
The developed Ti:sapphire dual-comb system was evaluated for distance
metrology. When both combs were fully locked, absolute distance metrology was
demonstrated for distances of up to 1.6 m, corresponding to ambiguity ranges of up to
order 6. Time-of-flight precision of < λ/4 was achieved in an averaging time of 1 s,
allowing handover to interferometric precision, which achieved a precision of 2 nm after
an averaging time of 4 s. Cross-calibration of distance measurements using a
100-nm-precision delay stage allowed a direct measurement of the group velocity of air
to an uncertainty (0.0026%) consistent with values from established atmospheric
dispersion models. Modifying the repetition-rates of probe and local-oscillator combs was
shown to potentially extend the effective ambiguity range up to 12.385 km.
Methods of reducing the cost and complexity of a Ti:sapphire comb were explored
by constructing a Ti:sapphire frequency comb directly pumped by 462 nm and 520 nm
laser diodes. The laser was modelocked using a commercial saturable absorber and
generated 90 mW average power. Using piezoelectric feedback to the laser cavity length,
and current modulation of one of the pump diodes, the laser was fully phase-stabilised to
achieve the first example of a directly diode-pumped Ti:sapphire laser with fully
stabilised repetition rate and carrier envelope offset frequencies. This comb achieved a
phase slip of 860 mrad for the 10 MHz carrier envelope offset frequency and 54 mrad for
the 79 MHz repetition frequency, each over 1 second. Pulses with durations of 54 fs were
generated at a central wavelength of 803 nm. Single walled carbon nanotubes were
explored as potential saturable absorbers. A device was fabricated using spin coating and
was shown to achieve modelocking at pump powers as low as 545 mW
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