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Probing the Mode of Action of eW5 - A Small Molecule Plant Growth Promoter
Get PDFThe work described in this thesis cover two distinct areas of chemistry. The primary body of this thesis looks at a small molecule N-(2-aminoethyl)naphthalene-1-sulfonamide (named eW5, 1) which has been shown to promote various aspects of plant growth (Volume I, Chapters 1-4). Plant hormonal pathways control almost every aspect of plant development and growth. Small molecules can selectively perturb these highly complex and interconnected pathways and have thus demonstrated to be effective tools for the study of plant hormonal signalling. In order to determine the mode of action of eW5, two lines of research were undertaken and are described in the thesis. In the first approach, target identification of 1 was initiated by SAR studies that showed that C–4 substituents were viable, indicating viable incorporation of a photoaffinity tag. Three synthetic approaches towards a chemical probe were explained–ultimately affording N-{2-[2-({4-[(2-aminoethyl)sulfamoyl] naphthalen-1-yl}oxy)ethoxy]ethyl}-3-tert-butyl-N-(pent-4-yn-1-yl) benzamide hydrochloride (145) which was shown to retain the growth promoting abilities of 1. A complementary approach using a genetic screen of EMS mutants was also employed to identify the causative gene mutation for eW5-resistance.
In the second aspect of the thesis (Volume II), two separate studies on Ir catalysed aromatic C–H activation are described. The development of the transformation of C–H bonds to form organoboron compounds has allowed for the formation of highly functionalised aromatics and late-stage functionalisation of compounds, making it of significance to the fields of natural product synthesis and medicinal chemistry. In the first of these studies, tandem Ir catalysed borylation – Suzuki-Miyaura cross coupling to 2-halo nicotinates was developed to afford trifunctional pyridines. Fluoro-aromatics represent another interesting class of substrates and as such, the second report describes a systematic study on the regioselectivity of Ir catalysed borylation. It was shown that the fluorine substitution pattern and the boron source were able to alter the standard steric controlled regioselectivity subtly yet distinctly in various substrates
Exploring excimeric interactions in mono- and dinuclear cyclometallated platinum(II) complexes for deep-red/near-infrared emission
Get PDFThe work described in this thesis is concerned with the development of new molecular materials that emit deep-red or near-infrared (NIR) light upon excitation. Molecules that emit efficiently in these regions of the electromagnetic spectrum are important in a variety of security, technological, and biological applications. The focus is on platinum-containing molecules, the key role of the metal being to enhance spin-orbit coupling and thus facilitate the formally forbidden emission from triplet states that is necessary to produce efficient devices. A range of platinum(II) complexes with cyclometallating ligands have been synthesised and their photophysical properties studied. The luminescence both from isolated molecules and from species comprised of two or more molecules has been evaluated, with the aim of establishing reliable strategies for tuning the emission further into the NIR.
Chapter 2 describes complexes featuring symmetric, tridentate N^C^N-coordinating ligands and one monodentate ligand, X. Organic light-emitting diodes (OLEDs) fabricated using some of these complexes as the emissive layer display NIR electroluminescence through the formation of aggregates. The identity of X is found to influence the aggregation: the change from X = Cl to I is accompanied by a 4-fold increase in the external quantum efficiency (EQE) of the device, whilst X = SCN red-shifts the emission to λELmax = 940 nm, apparently the longest-wavelength emission reported to date for a device employing a non-porphyrinic platinum(II) complex.
The work of Chapter 3 introduces related complexes featuring asymmetrically-substituted N^C^N ligands: it establishes that the wavelength of the unimolecular emission tends to follow that of the corresponding parent symmetric complex of lowest excited-state energy. Complexes of ligands that incorporate 3-substituted isoquinoline are found to have a particularly high propensity to excimer formation, whilst 4-trifluoromethylpyridine ligands lead to a red shift in the emission, both unimolecular and excimer/aggregate.
Chapters 4 and 5 focus on the strategy of covalently linking two complexes through a rigid xanthene scaffold, with a view to facilitating their face-to-face interaction. Complexes with tridentate and bidentate ligands are discussed in the two chapters, respectively. They mostly display broad, long-wavelength emission at all concentrations in solution, likely arising from intramolecular excimers, with impressive quantum yields ranging from 0.11 to 0.61. The interactions are further favoured using a second xanthene to generate “molecular squares” which display purely excimeric emission.
Finally, in Chapter 5, a series of novel dinuclear platinum compounds is presented that feature bidentate N^C-coordinating ligands. The emission wavelengths are influenced both by structural modifications of the N^C moiety and by intramolecular excimeric interactions, the most red-shifted of which has λPLmax of 777 nm
Theories Beyond the Worldline
Get PDFStandard quantum field theories usually have high energy divergences which render them unacceptable as a complete theory of nature. Such divergences arise from the nature of point particle excitations. This thesis looks to go beyond such frameworks. We begin by asking the general question: what possible modifications of point particle theories are there which might give them desirable properties such as finite and well-behaved amplitudes at high energies? We use the worldline formalism to construct modifications to worldline theories which have a tower of internal states propagating along the worldline, mimicking the behaviour of string oscillator modes. We argue that string theory itself can be regarded as a special case. We show that this class of theories shares similar interesting properties with string theory, and can also be used to analyse aspects of string theory itself. We then move on to focus on the phenomenology of string theory. We study a particular compactification of type I string theory, with the aim of constructing a model with a small but positive cosmological constant which has supersymmetry broken at a high scale. Such models usually suffer stability problems, but we will show that there is a class in which all moduli are either stabilised or flat up to exponentially suppressed terms. These models could be useful starting points for constructing either truly stabilised de Sitter minima, or perhaps as providing a quintessence scenario
Exploring the properties of hot haloes around simulated galaxies
Get PDFThe existence of hot, accreted gaseous coronae around massive galaxies is a central prediction of galaxy formation models in the ΛCDM cosmology. While observations now confirm that extraplanar hot gas is present around late-type galaxies, the origin of the gas is uncertain. We investigate the origin and properties of the hot gas that surrounds galaxies in the cosmological hydrodynamical EAGLE simulations. In summary, we find that haloes of Milky Way-mass and above host hot, accreted atmospheres as predicted by White & Frenk (1991). However, supernovae heated gas (feedback) in the innermost region of the halo typically dominates the X-ray emission.
Modern hydrodynamical simulations model various physical processes in the real Universe; however, many are included using 'subgrid models'. Although subgrid models have successfully modelled feedback effects, it remains unclear if, and by how much, the differing implementations affect other halo properties. This thesis uses 'zoom-in' simulations of a Local Group-like region evolved with both the Auriga and Apostle galaxy formation models. We find that feedback processes can be classified into two broad categories: 'ejective' and 'preventative', and future observations may constrain these two regimes.
The large dynamic mass range makes it computationally expensive to run simulations of galaxy formation. Therefore, we explore the basis function expansion technique (BSE), which can efficiently approximate the potential of a simulated galactic halo. We demonstrate that the Herquinst-Ostriker BSE can successfully reproduce the orbits of particles taken from n-body simulations. We also describe two further developments, including the addition of a thin, time-dependent disc and a method to model massive satellite galaxies within the halo efficiently
Testing the use of biomarkers to trace organic carbon in a small rural catchment in the U.K
Get PDFrham University MRes thesis
Kathryn Ruth Melvin
Abstract
Testing the use of biomarkers to trace organic carbon in a small rural catchment in the U.K
The interaction between climate change and the carbon cycle on land is a pressing topic that is frequently discussed within both academia and government. Extensive research has been undertaken into organic carbon export in forested river systems, including estimating the organic carbon (OC) fluxes transported towards, and deposited in, the ocean. However, the origins of carbon transported by smaller, anthropogenically-modified river systems that are widespread in the UK are more poorly constrained. A novel approach to trace the source and pathway of OC is to use biomarkers – identifiable organic compounds that can be linked to the biological processes that formed them. This approach has been widely applied to reconstruct past environmental change and climate, but has recently been recognised as having promise to trace OC transport in rivers. In this thesis, the biomarker method was applied to a small river catchment to explore if this analysis could better constrain the origins, types and transfer of OC, furthering knowledge of the importance of catchment and fluvial process in a wider context. This thesis focuses on the River Esk in the North York Moors. The River Esk has been studied extensively because of the geology and the varied land use, from peatlands to agricultural and small forest areas, so that this catchment provides varied land uses and has the potential input of distinct OC sources which can be identified using the biomarker method. River sediments collected using a time-integrated sampling method were used to explore spatial patterns. Further work and the inclusion of more seasonal data would add even more information that is missing in this area of study. It was concluded that the use of biomarkers gave additional information when trying to understand river processes. All sample sites using biomarker analysis gave data consistent with what would be typically expected for the surroundings. An interesting difference was observed in two of the sample sites, where the biomarkers indicated an aged fossil signal. A human influence was confirmed as both sites were major sites in the iron industry in the 1800s
The Law, Politics and Practice of ‘Never Again’: Guarantees of Non-Recurrence in Transitional Justice
Get PDFEnsuring non-recurrence of mass human rights violations has been a central goal of transitional justice (TJ) since its foundations. Recent developments in international TJ policy have transformed the goal that violations should happen ‘Never Again’ into guarantees of non-recurrence (GNRs), a norm of legal origin. In TJ scholarship, GNRs have since emerged as both a pillar of TJ, comprised of distinct practices of predominantly institutional reform, and an overall objective that frames the pillars of TJ. As a result, GNRs remain ambiguous, normatively flexible, and generally unexplored in the burgeoning TJ scholarship. This thesis sets out to provide conceptual clarity to the content, characteristics and position of GNRs in transitional justice by empirically investigating conceptualisations and practices of GNRs in post-conflict Bosnia and Herzegovina (BiH). Underpinned by structuration theory, the thesis treats TJ as a primarily ideational structure, a global, discursive force that carries a set of well-established tenets prescribing how past violence and injustice should be dealt with and how non-recurrence should be achieved. The thesis examines two core questions. Firstly, how GNRs are understood and practiced by transitional justice actors in BiH and, secondly, how transitional justice as a structure influences these domestic conceptualisations and practices.
The overarching claim of the thesis is that GNRs should be understood as a complex cycle, a non-hierarchical web of connected and sequenced processes in continuous practitioners’ engagement with the ideas found within the structure of TJ as well as the effects of past implementations of these ideas. Three principal arguments support this claim. First, practitioners in BiH re-contextualise the content of the norm of non-recurrence and are only seldomly influenced by existing international legal and policy frameworks in how they conceptualise GNRs. Second, transitional justice maintains persuasive power to shape many ideas considered as GNRs by the practitioners and how they are put to practice. Third, the tension between TJ’s malleability and adherence to legalism creates practical obstacles for the practices of the contextualised GNRs due to which they remain largely under-realised in BiH
Scrapbooking the Everyday Scaffolding of Sexual Violence: Making Sense of ‘Rape Culture’
Get PDFFeminist attention to the cultural causes of sexual violence has assumed many forms and debates, with the concept of ‘rape culture’ taking hold in the 1970s and being reinvigorated today. This thesis explores these debates to arrive at its unique conceptualisation of the ‘everyday scaffolding’ of sexual violence. Everyday scaffolding refers to the discursive practices – situated and material ways in which knowledges are formed – through which sexual violence becomes possible and intelligible. Designing an innovative research practice of scrapbooking, this thesis establishes these scaffolds in the lives of its participant scrapbookers; twenty-three adults with unwanted sexual experiences and one UK Rape Crisis centre. Scrapbooking involves saving, organising and sharing ‘scraps’ from everyday life, a potentially enjoyable, therapeutic and consciousness-raising practice.
Paying attention to queer, post-structuralist and feminist new materialist thinkers, this research organises scraps from participants’ books and relevant literatures into four scaffolds. Firstly, ‘Conflation and Marginalisation’: where the bringing together and confusing of often contentious sexual matters naturalises and obscures sexual violence, as does the drawing of different boundaries to separate sexual violence out. Secondly, ‘Spectacularisation’: discursive practices by which sexual violence is constituted as a spectacle, a dramatic event cut out from everyday life, with particular audiences in mind. Thirdly, ‘Catching Out’: discursive practices which establish a ‘truth’ beneath a ‘lie’ in need of unmasking, connecting sexual violence to all manner of ‘corrective’ activities. Finally, ‘Weaponisation’: sexual violence as a means towards particular and harmful ends; to further divisive politics, to facilitate sexual access, and to naturalise ‘vulnerability’. These four scaffolds are presented in order to both name and change sexual violence in ways which work with the ambiguity and potentiality of the everyday, the necessity for continuum-thinking and the reality of the research’s own performative involvement in the worlds or ‘rape cultures’ it claims to make sense of
The Quality of Accruals: Lender Side Evaluation of Borrowers, Covenant Analysis, and Current Evaluation Trends.
Get PDFDebt Covenant Hypothesis states that managers of borrowing firms may act in an opportunistic manner to avoid a potential breach of loan covenants set by lenders. Following evidence of earnings manipulation from prior research, this research analyses whether lenders can evaluate the exposure to risk and managerial opportunism, processing available information related to the borrowers. Earnings can be decomposed into cash flows and accrual components; where cash flows relate to the movement of tangible liquid assets and are less prone to manipulation, discretion can be exercised by firm management over the treatment of accruals. This research tests the accrual component of earnings for consistency and quality. If lenders are sophisticated users of financial information and take all the information in a borrower’s earnings into account, a negative (positive) relationship is expected between the quality of accruals of the borrower, and tightness of minima (maxima) based financial covenant thresholds and slack
A Consideration of Cooperative Learning to Enhance Pre-service Teachers’ Achievement in Tertiary English as a Foreign Language (EFL) Classrooms in Thailand
Get PDFCooperative learning has become a popular instructional practice around the world. It requires students working together in small groups to help support each other in maximising their own learning as well as that of others to accomplish a shared goal. A cooperative learning method, especially, Student Teams Achievement Divisions (STAD) developed by Slavin (1982) was implemented in the study. The study investigated the effectiveness of cooperative learning to enhance the English achievement of EFL (English as a foreign language) students in tertiary teacher education in Thailand. It also examined participants’ attitudes towards cooperative learning.
The study began with a structured review of existing empirical studies to establish whether STAD could be a promising method to use in developing English proficiency in EFL and ESL (English as a second language) contexts. The review also helped identify the challenges and barriers to implementing the method and informed the primary research in terms of achievement tests, instructor training, time allowance for team study and material preparation. The review and synthesis of 28 studies revealed several beneficial suggestions regarding cooperative learning implementation in normal educational settings. However, the credibility of the overall evidence was weak, with most studies involving key methodological flaws.
To examine the effectiveness of the method, a cluster randomised controlled trial (RCT) at the university level was used. The participants were 13 instructors and 614 students from 13 universities (forming 13 clusters). A total of eight universities that agreed to participate in the intervention were randomly assigned to experimental and control groups with four universities in each group. Another five universities agreed to complete the pre-test and post-test and are described in this thesis as an additional comparison group. The participating instructors were 13 Thai university instructors of English language from 13 Rajabhat Universities in Thailand. Their students were first-year pre-service teachers who were majoring in English in the Faculty of Education. The trial was carried out in one term consisting of 16 class sessions. The research instruments consisted of two parallel standardised English achievement tests, two attitude questionnaires (teacher and student) and classroom observations with ad hoc interviews.
The results showed that the use of cooperative learning in tertiary EFL classrooms in Thailand is feasible. In terms of attitudes, both instructors and students were generally positive towards cooperative learning and supported its activities.
Students in the treatment group did slightly better (ES = +0.09) when compared to all comparator groups. However, when considering the randomised experimental and control groups, the control group improved their post-test score (+0.26) while the experimental group declined (-0.20). Overall, cooperative learning showed no clear benefit for students’ English language achievement.
The process evaluation revealed the key factors that facilitated the implementation were teacher training and support, preparation and availability of teaching resources and materials, teachers’ positive attitudes and the duration of cooperative learning instruction. Some barriers were also found, including students’ negative attitudes, inappropriate classroom settings and facilities, and instructors’ workload.
Unfortunately, since the study was carried out during the COVID-19 pandemic, none of the universities were able to complete the course of 16 classes as planned. The number of classes students could meet in their normal classroom conditions was approximately 8 to 12. Different modes of lesson delivery (face-to-face, online and hybrid) were also reported. A replication of the study is needed for a more accurate assessment of the STAD method.
Both the structured review and the cluster RCT suggest no strong evidence that the cooperative learning method, namely STAD, led to improved pre-service teachers’ English language achievement in Thailand. However, this does not necessarily mean the method does not work. The lack of impact might be due to the challenges faced in the delivery of the intervention during the pandemic. This was compounded by the lack of complete randomisation used in the study. It is, therefore, difficult to draw more definite conclusions about the effectiveness of STAD. It might be wise to conduct further robust evaluations involving a large number of educational institutions before any considerable investment can be made to introduce this method in higher education institutions in Thailand. In the meantime, there may be other approaches with a more promising evidence base which may enhance students’ English language achievement
'Climate justice' as adaptation of the human
Get PDFGrounded in a methodology of discourse analysis, semi-structured interviews and participant-observation, this thesis examines ‘climate justice’ as a discourse articulating with other discourses, deploying certain imaginative geographies, and enfolding fundamental questions of power, race and identity in the ‘international’. In a break with accounts that take a prescriptive or essentialist approach to ‘climate justice’, I argue that Judith Butler’s conception of performativity is a framework allowing a full appreciation of the heterogeneity and contingency of ‘climate justice. My first argument appraises the liberal ‘international’ as a racialised order of governance’. Specifically, it argues that ‘climate justice’ – in context-specific instances - embodies and perpetuates whiteness, understood as an historically and geographically differentiated form of signifying power. From here, I argue that some ‘climate justice’ discourses embodying ‘international climate whiteness’, which I understand as an historically contingent form of power that operates through a cluster of institutional arrangements, discourses and affects that serve the reproduction of a liberal international order. In my second argument, I demonstrate how the ‘most vulnerable’ are positioned as a mobilising device on whose behalf the less-vulnerable are to demand ‘action’ from their political representatives. Moreover, I argue that a primary instrument for the securing of this moral economy is the idea of a ‘new narrative’ of climate change; one that reframes it as a ‘people-centred’ as well as an ‘environmental’ issue. Third and final, I argue that over the past ten years, there has been a shift in international climate policy discourse towards seeing climate change in ‘human’ as opposed to simply ‘environmental’ terms. Further, I go beyond this observation to argue that an analysis of ‘climate justice’ discourse allows us to see how the ‘human’ - and humanism - are in the process of adapting to climate change
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