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The role of Arabidopsis MAP kinase genes in biotic and abiotic stress signalling
Get PDFPlants are constantly faced with environmental stresses which trigger morphological,
physiological, biochemical, and molecular changes that can negatively affect crop
productivity. Plants detect and respond to these stresses via diverse means including
signalling pathways such as the Mitogen-activated-protein-kinase (MAPK) networks which
have shown to play a role in stress signalling, activating many stress-responsive genes
through the agency of the plant stress hormone, abscisic acid (ABA). The work in this thesis
examines the role of selected MAPK genes in abiotic and biotic stress, with novel findings
being made for MPK1 and MPK2.
It is known that MPK1 and MPK2 genes together with other MAP Kinases play a role in
pathogen stress resistance and ABA regulation. In this study their additive function in
enhancing osmotic and pathogen stress tolerance was uncovered. The observed increased
sensitivity of the mpk1/2 double mutant to exogenous ABA was attributed to the synergistic
role of MPK1 and MPK2 with MPK2 as the main contributor in the negative regulation of
the transcription factor ABI4, and also in the suppression of ABA biosynthesis although
mechanism remains to be defined fully. The results suggest that the high expression of ABI4
in mpk2 and mpk1/2 mature seeds contributed to low germination under salinity and osmotic
stresses. It was shown via gene expression of the stress responsive gene RD29A in stressed
seedlings that the A. thaliana MPK2 gene promotes salt tolerance in seedlings by acting as a
positive regulator for RD29A. MPK1 however, negatively regulated RD29A under salinity
stress, and also suppressed the ability of MPK2 to promote RD29A expression in seedlings
during osmotic stress. It was evident in this study that the same genes played different roles
under different stress conditions, this was obvious when target genes acted as negative and
positive regulators of proline and ABA respectively under osmotic stress, but not under salt
stress. Based on the above findings, coupled with results for protein-protein interactions from
the Split ubiquitin yeast-2-hybrid assay which identified upstream activators of MPK1 and
MPK3 as MKK1-, MKK2- MKK3- proteins, and MPK2 as MKK1 protein, it is hypothesised
that pathogens, salt, and/or osmotic stress may potentially be perceived through MKK1,
MKK2 and/or MKK3, to activate MPK1, MPK2 and/or MPK3 protein, during stress
signalling. These stress responses are not governed by simple linear pathways, but are
networks that might more subtly regulate the plant response to biotic and abiotic stresses.James Watt Scholarshi
Optical metasurfaces for polarization generation, detection and imaging
Get PDFLike phase and amplitude, polarization is a fundamental property of light, which can
reveal hidden information and has been used in many research fields, including material
science, medicine, target detection and biomedical diagnosis. Polarization generation,
detection and imaging are of importance for fundamental research and practical
applications. Although conventional optics can perform these tasks, it suffers from a
complex system, large volume and high cost, which cannot meet the continuing trend of
miniaturization and integration. Optical metasurfaces, the two-dimensional counterparts
of metamaterials, are planar nanostructured interfaces, which have recently attracted
tremendous interest in realizing ultrathin and lightweight planar optical devices. Optical
metasurfaces can manipulate light’s amplitude, phase and polarization in a desirable
manner, providing a new and compact platform to generate, detect and manipulate light’s
polarization. This thesis utilises optical metasurfaces to realise and experimentally
demonstrate novel optical devices for polarization generation, detection and imaging. Due
to the simplicity of the design and fabrication, this thesis is mainly focused on geometric
optical metasurfaces, which are superior to other types of metasurfaces.
2D and 3D polarization structures are generated based on a metalens approach. A ring
focal curve, an Archimedean spiral focal curve, and seven-segment-based decimal
numbers are experimentally demonstrated in 2D space, while a 3-foil knot, a 4-foil knot,
and a 5-foil are realized in 3D space. The geometric metasurfaces are designed based on
colour and phase multiplexing and polarization rotation, creating various 3D polarization
knots. Various 3D polarization knots in the same observation region can be achieved by
controlling the incident wavelengths, providing unprecedented polarization control with
colour information in 3D space. Novel polarization detection is experimentally
demonstrated through optical holography, light’s orbital angular momentum, and optical
ring vortex beams. The measured polarization parameters such as major axis, ellipticity,
and handedness are in good agreement with the theoretical prediction. A multifunctional
microscope is proposed and developed to image different objects, including biological
samples such as cheek cells and beef tendons. For the same sample, five images with
different optical properties are obtained on the same imaging plane, which can
simultaneously perform edge imaging, polarimetric imaging, and conventional
microscope imaging. Benefiting from the ultrathin nature, compactness and
multifunctionality of the optical metasurface devices, the integration does not excessively increase the volume of the optical system. With its promising capabilities and potential
for expandability, we believe our microscope will herald an exciting new era in
biomedical research.
The ultrathin nature of optical metasurfaces and their unprecedented capability in light
control have provided a compact platform to develop ultrathin optical devices with novel
functionalities that are very difficult or impossible to achieve with conventional optics.
The metasurface platform for polarization detection and manipulation is very attractive
for diverse applications, including polarization sensing and imaging, optical
communications, optical tweezers, quantum sciences, display technologies, and
biomedical research as well as wearable and portable consumer electronics and optics
where miniaturized systems are in high demand
Development of ultrafast laser inscribed astrophotonic components
Get PDFThe rapid development of astronomical instrumentation has been aided by many
innovative new photonic designs, which offer improvements in stability, precision, size
and cost, scalability, etc. ─ the field of astrophotonics. A powerful technique enabling
many of these astrophotonic devices, ultrafast laser inscription (ULI), creates highly
localised and controlled refractive index modification, which guides the path of light in
a very efficient manner. This thesis discusses three separate astrophotonic devices, each
with a specific application, to demonstrate the versatility of ULI.
Firstly, a reformatting device based on a photonic lantern and 3D ULI waveguide
reformatting component, transforms a multimode telescope PSF to a diffraction-limited
pseudo-slit. When used to feed a spectrograph, a significant reduction in modal noise ─
a limiting factor in high-resolution multimode fibre-fed spectrographs ─ is
demonstrated, with the potential for improved near-infrared radial velocity observations.
Secondly, a similar ULI reformatting device for an integral field unit, based on
multicore fibre with affixed microlenses, may enable the direct imaging of exoplanets
and characterisation of their atmospheres. Thirdly, a two-telescope K-band beam
combiner based on ULI directional couplers with an achromatic 3dB splitting ratio is
presented. Such a device will upgrade the stellar interferometry capabilities of the
CHARA array
The effect of audit objections on performance measures and market indicators of audited organisations – evidence from textile manufacturing sector of Pakistan
Get PDFThe purpose of this research was to investigate if the auditees respond effectively to
modified audit opinions. The study is important to judge the in-time response to audit
opinion for financial transparency, audit policy formation and remedial measures. The
population consisted of all listed textile manufacturing companies of Pakistan. The textile
sector is the largest indigenous sector with a large number of audit objections. To judge
the effectiveness of the audit opinion on audit response, various performance indicators
of the auditee are used. Three subsequent years after the audit opinion are considered to
judge the audit responses. Other influencing variables like size and age of the company,
cotton prices, yarn production, exchange rates and the export value of textiles were taken
as control variables. Additionally, any difference in audit responses between the two
textile policy regimes (2009-2013 & 2014-2017) in Pakistan was investigated. Data was
manually collected for the period 2009-2017 from the archival records of all relevant
stakeholders. Giving rise to a data set with more than one thousand observations, audit
responses were classified into three ordinal categories of good, negligible and bad
responses. A positivist research paradigm was followed to explore the research question.
Multinomial logistic regression in SPSS was applied to model the associations
statistically between the audit opinions and audit responses. The main outcomes of this
study were (1) time is needed to allow good responses effectively (2) severity of audit
opinions is associated with better audit response and (3) mixed results for two textile
policies in terms of audit responses. The research has several limitations, most notably
that financial performance measures lack precision and that no account has been made of
the variation in the performance of individual audit firms. Nevertheless, the research is a
substantial contribution to knowledge and applied practices. The outcome of this study
supports the value of the audit and the need for appropriate managerial interventions to
address the issues raised. The research has demonstrated that how effective response to
audit opinion can positively impact performance. The insights are useful for regulators to
improve decision-making for the credibility of the audit process. Textile companies may
enhance their financial transparency and sustainability through effective and in-time audit
responses
The role of structural inheritance and far field tectonism for the evolution and prospectivity of the Northern North Sea Basin
No full textAbstract currently unavailable. Please refer to PDF. Restricted access until 01.08.2024
The design, synthesis and application of 4,7-Diarylbenzo[c][1,2,5]thiadiazole photocatalysts
Get PDFThe debate surrounding climate change and global resource consumption has stimulated
discussion within the chemical community about sustainable methods for enabling
chemical transformations. Among the various avenues of research, photocatalysis has
been identified as an attractive sustainable option as it would allow society to make use
of light as an abundant resource that is not environmentally damaging. Current state of
the art photocatalysts tend to be based on iridium and ruthenium polypyridyl complexes.
However, the cost and low natural abundance of the metals they contain is not compatible
with the long term environmental sustainability that modern photocatalysis is striving
towards. Organophotocatalysts have been identified as a promising solution to this
problem as they are derived from more abundant chemical feedstocks, making them far
cheaper to synthesise and allowing for better long-term sustainability.
In addition to natural pigments and organic dyes, various organic π-conjugated
electron donor-acceptor (D-A) systems, comprising of electron-rich donor and electron-deficient acceptor groups connected through delocalised π-conjugated structures, have
been investigated as organophotocatalysts. The benzo[c][1,2,5]thiadiazole (BTZ) group
is an example of a strongly electron withdrawing group that has mainly been researched
for photovoltaic systems although some promising photocatalysis has already been
investigated with this moeity.
Four different methods for utilising BTZ photocatalysts are presented in this
thesis. The first of these was a conventional homogeneous approach to photocatalysis,
whereby a series of structurally similar molecular BTZ photocatalysts were synthesised
to optimise their photophysical and optoelectronic properties towards a test photoredox
reaction. Secondly, photocatalysts were appended to the upper-rim of calix[4]arenes to
investigate using their ability to form host-guest complexes to facilitate photocatalysis.
The third and fourth regimes involve the use of two different polymer systems by either
chemically incorporating the BTZ group into conjugated porous polymers or by trapping
molecular photocatalysts within solution cast thin films of intrinsically microporous
polymers
The Urban Systems Abstraction Hierarchy : a resilience tool to capture cascading flood exposure
Get PDFFloods are increasing in both frequency and intensity under climate change. Research
has shown that people who are socially vulnerable are more exposed to flood risk. Worse
is that flood disadvantage that exists today is projected to continue in the future: it is
stubborn. Current approaches are not working sufficiently well to unblock this stubborn
disadvantage. Something new is required. A fresh perspective to flood exposure is
offered in this thesis. Flood exposure is nested within the wider urban environment
through the development of a systems tool – the Urban Systems Abstraction Hierarchy –
to quantify how tangible flood exposure cascades through complex system interactions to
impact longer-term resilient outcomes. Resilience concepts are applied to navigate the
tool and interpret its quantitative results. The thesis provides a theoretical contribution to
understanding how flood resilience concepts are currently perceived and applied within
flood risk management. It provides a methodological contribution to capture these new
resilience insights in a tool. It provides a practical contribution by identifying the
interactions which can help cities withstand, absorb or adapt to flood exposure, enabling
transformative resilience strategies.Engineering and Physical Sciences Research Council (EPSRC) funding
Investigation into multiple melt spin recycling cycles of Poly(ethylene terephthalate) (PET)
No full textPolyethylene terephthalate (PET) is one of the most common fibres used in textiles due
to its good mechanical properties. PET bottles are often recycled into fibres for clothing;
however, very few PET based textiles are recycled in a closed loop process to make new
textiles. The simplest form of recycling is mechanical, but this results in a degradation of
properties and often requires the addition of virgin material. Although the loss of
properties is well known no data could be found to quantify this decrease. Therefore, a
study was undertaken to determine the change in the properties of PET filaments as a
result of multiple recycling cycles. In order to recycle the filaments they had to be cut to
less than 5 mm sections to pass through the extruder. If sections were longer, they would
become entangled and would not pass through the extruder evenly. Filaments were
extruded and recycled four times. The load at maximum extension was seen to decrease
exponentially with the recycling cycle which was believed to be a result to chain scission.
Between the second and third recycling a large change in elongation at break occurred.
Recycling also increased the young’s modulus of the filaments, showing that re-extrusion
increases the brittleness of the filaments. This was seen to be most prevalent between the
second and third recycling (appears to be a cliff edge effect) as filaments could no longer
be drawn. This was seen for both bottle and film grade PET. Recycling was seen to affect
the colour of the extruded filaments; with each cycle they became more yellow and
opaque. The time between extrusion and drawing was identified as an important variable
due to physical ageing. Recycled filaments and filaments of the lower grade were found
to be more susceptible to physical ageing than virgin filaments of a higher grade. The
study also incorporated modified clay into the filaments in an attempt to mitigate the loss
of mechanical properties. The PET pellets were ground into powder to aid mixing with
clay. The resultant fibres were then tested however, due to incomplete mixing no
statistically significant change in mechanical properties could be seen
Equations in groups, formal languages and complexity
Get PDFWe study the use of EDT0L languages to describe solutions to systems of equations in various classes of groups. We show that solutions to systems of equations
with rational constraints in virtually abelian groups can be expressed as EDT0L
languages. We also study the growth series of these solutions. In addition, we show
that the class of groups where solutions can be described using EDT0L languages
is closed under direct products, wreath products with finite groups and passing to
finite-index subgroups, using standard normal forms in each of the constructions.
Using these operations together, we show that the solutions to systems of equations,
when expressed as suitable quasi-geodesic normal forms, in virtually direct products of hyperbolic groups, including dihedral Artin groups, can be described using
EDT0L languages. We conclude by showing that single equations in one variable in
the Heisenberg group can also be expressed using EDT0L languages, with words expressed in Mal’cev normal form. Proving this requires us to first show that solutions
to quadratic equations in the ring of integers are EDT0L
Dissipative solutions to the stochastic Euler equations
Get PDFWe study the three-dimensional incompressible Euler system subject to stochastic forcing. We develop a concept of dissipative martingale solutions, where the nonlinear terms
are described by general Young measures. We construct these solutions as the vanishing
limit of solutions to the corresponding stochastic Navier-Stokes equations. This requires
a refined stochastic compactness method incorporating the generalised Young measures.
As a main novelty, our solutions satisfy a form of the energy inequality which gives rise
to the weak-strong uniqueness result (pathwise and in law). A dissipative solution coincides (pathwise and in law) with a strong solution as soon as the later exists.
Furthermore, we extend our results to the compressible Euler system. Here we introduce the concept of stochastic measure-valued solutions to the compressible Euler system describing the motion of a temperature-dependent inviscid fluid subject to stochastic
forcing, where the nonlinear terms are described by defect measures. These solutions
are weak in the probabilistic sense (probability space is not given a ‘priori’, but part of
the solution) and analytical sense (derivatives only exists in the sense distributions). In
particular, we show that existence and weak-strong principle (i.e. a weak measure-valued
solution coincides with a strong solution provided the later exists), hold true provided
they satisfy some form of energy balance. Finally, we show the existence of Markov selection to the associated martingale problem
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