Evolutionary robotics in high altitude wind energy applications

Recent years have seen the development of wind energy conversion systems that can exploit the superior wind resource that exists at altitudes above current wind turbine technology. One class of these systems incorporates a flying wing tethered to the ground which drives a winch at ground level. The wings often resemble sports kites, being composed of a combination of fabric and stiffening elements. Such wings are subject to load dependent deformation which makes them particularly difficult to model and control. Here we apply the techniques of evolutionary robotics i.e. evolution of neural network controllers using genetic algorithms, to the task of controlling a steerable kite. We introduce a multibody kite simulation that is used in an evolutionary process in which the kite is subject to deformation. We demonstrate how discrete time recurrent neural networks that are evolved to maximise line tension fly the kite in repeated looping trajectories similar to those seen using other methods. We show that these controllers are robust to limited environmental variation but show poor generalisation and occasional failure even after extended evolution. We show that continuous time recurrent neural networks (CTRNNs) can be evolved that are capable of flying appropriate repeated trajectories even when the length of the flying lines are changing. We also show that CTRNNs can be evolved that stabilise kites with a wide range of physical attributes at a given position in the sky, and systematically add noise to the simulated task in order to maximise the transferability of the behaviour to a real world system. We demonstrate how the difficulty of the task must be increased during the evolutionary process to deal with this extreme variability in small increments. We describe the development of a real world testing platform on which the evolved neurocontrollers can be tested

A role for detailed assessment of hippocampal function in studies of Alzheimer’s Disease

The hippocampus is one of the first cortical regions to exhibit Alzheimer’s Disease (AD) pathology. The spatially-related firing of hippocampal place cells provides the cellular basis for spatial memory, and this is impaired relatively early in AD, yet few studies examine place cell activity in AD mouse models. Furthermore, current spatial navigation paradigms for rodents are not suited to tracking the progressive impairment seen in AD. This project aimed to address these gaps; the results provide initial support for the hypothesis that AD pathology disrupts hippocampal function which manifests as altered place cell activity and spatial behaviour. Chapter 3 outlines experiments validating a novel behavioural test of hippocampal function, the ‘Honeycomb Maze’, specifically designed to overcome the limitations of other tasks. Wild-type rats and mice rapidly learnt to navigate to a hidden goal, and a lesion study demonstrated the key contribution made by the hippocampus. Task difficulty was scalable through altering maze parameters, with difficult choices exhibiting a greater reliance on hippocampal processing. The findings suggest the Honeycomb Maze provides a reliable means of assessing hippocampal function in rodents and is well suited for application to studies of AD. Chapter 4 provides an in-depth characterisation of hippocampal pyramidal cell activity in an APP knock-in model of AD. Electrophysiological recordings were performed in the left CA1 subregion of four 15-month-old, freely moving, APPNL-G-F mice and four age-matched wild-type controls. Significantly fewer APPNL-G-F pyramidal cells exhibited spatial firing, and deficits were present in rate and temporal coding of spatial information. APPNL-G-F spatial cells had lower spatial information content, larger place fields, reduced phase-locking to the theta rhythm of the local field potential, and a reduction in theta phase precession. Despite the small sample size, a positive correlation was identified between amyloid β plaque burden and pyramidal cell spatial information in APPNL-G-F mice

Development of whole-heart myocardial perfusion magnetic resonance imaging

Myocardial perfusion imaging is of huge importance for the detection of coronary artery disease (CAD), one of the leading causes of morbidity and mortality worldwide, as it can provide non-invasive detection at the early stages of the disease. Magnetic resonance imaging (MRI) can assess myocardial perfusion by capturing the rst-pass perfusion (FPP) of a gadolinium-based contrast agent (GBCA), which is now a well-established technique and compares well with other modalities. However, current MRI methods are restricted by their limited coverage of the left ventricle. Interest has therefore grown in 3D volumetric \whole-heart" FPP by MRI, although many challenges currently limit this. For this thesis, myocardial perfusion assessment in general, and 3D whole-heart FPP in particular, were reviewed in depth, alongside MRI techniques important for achieving 3D FPP. From this, a 3D `stack-of-stars' (SOS) FPP sequence was developed with the aim of addressing some current limitations. These included the breath-hold requirement during GBCA rst-pass, long 3D shot durations corrupted by cardiac motion, and a propensity for artefacts in FPP. Parallel imaging and compressed sensing were investigated for accelerating whole-heart FPP, with modi cations presented to potentially improve robustness to free-breathing. Novel sequences were developed that were capable of individually improving some current sequence limits, including spatial resolution and signal-to-noise ratio, although with some sacri ces. A nal 3D SOS FPP technique was developed and tested at stress during free-breathing examinations of CAD patients and healthy volunteers. This enabled the rst known detection of an inducible perfusion defect with a free-breathing, compressed sensing, 3D FPP sequence; however, further investigation into the diagnostic performance is required. Simulations were performed to analyse potential artefacts in 3D FPP, as well as to examine ways towards further optimisation of 3D SOS FPP. The nal chapter discusses some limitations of the work and proposes opportunities for further investigation.Open Acces

Solidification behavior of high nitrogen stainless steels and establishment of a one-dimensional heat transfer framework

Duplex stainless steel (DSS) has excellent corrosion resistance and mechanical properties due to its dual-phase structure. The solidification process is the key to determining the structure of materials, and an in-depth investigation of solidification can help us better understand the properties of materials. The melting and solidification processes of S32101 DSS were investigated using high temperature confocal microscopy (HTCM)

Identification of the degradation mechanisms of organic solar cells:active layer and interfacial layers

Organic Solar Cells (OSCs) represent a photovoltaic technology with multiple interesting application properties. However, the establishment of this technology into the market is subject to the achievement of operational lifetimes appropriate to their application purposes. Thus, comprehensive understanding of the degradation mechanisms occurring in OSCs is mandatory in both selecting more intrinsically stable components and/or device architectures and implementing strategies that mitigate the encountered stability issues. Inverted devices can suffer from mechanical stress and delamination at the interface between the active layer, e.g. poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PCBM), and the hole transport layer, e.g. poly(3,4-ethylenedioxythiophene):poly(p-styrene sulfonate) (PEDOT:PSS). This work proposes the incorporation of a thin adhesive interlayer, consisting of a diblock copolymer composed of a P3HT block and a thermally-triggerable, alkyl-protected PSS block. In this context, the synthesis of poly(neopentyl p-styrene sulfonate) (PNSS) with controlled molar mass and low dispersity (Ð ≤ 1.50) via Reversible Addition-Fragmentation chain Transfer (RAFT) polymerisation has been extensively studied. Subsequently, Atomic Force Microscopy (AFM) was explored to characterise the thermal deprotection of P3HT-b-PNSS thin layers to yield amphiphilic P3HT-b-PSS, indicating that surface deprotection prior to thermal treatment could occur. Finally, structural variation of the alkyl protecting group in PSS allowed reducing the thermal treatment duration from 3 hours (P3HT-b-PNSS) to 45 minutes for the poly(isobutyl p-styrene sulfonate) (PiBSS) analogous copolymer. Another critical issue regarding the stability of OSCs is the sunlight-driven chemical degradation of the active layer. In the study herein, the combination of experimental techniques and theoretical calculations has allowed identification of the structural weaknesses of poly[(4,4’- bis(2-ethylhexyl) dithieno [3,2-b:2’,3’-d]silole)-2,6-diyl-alt-(4,7-bis(2-thienyl)-2,1,3-benzothiadiazole)-5,5’-diyl], Si-PCPDTBT, upon photochemical treatment in air. Additionally, the study of the relative photodegradation rates in air of a series of polymers with systematically modified backbones and/or alkyl side chains has shown no direct correlation between chemical structure and stability. It is proposed instead that photostability is highly dependent on the crystalline character of the deposited films. Furthermore, it was verified that photostability of blends based on these polymers is dictated by the (de)stabilising effect that [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) has over each polymer. Finally, a multiscale analysis on the degradation of solar cells based on poly[4,4' bis(2- ethylhexyl) dithieno[3,2-b:2',3'-d]silole)-2,6-diyl-alt-[2,5 bis(3 tetradecylthiophen 2-yl)thiazole[5,4-d]thiazole)-1,8-diyl] and PCBM, indicated that by judicious selection of device layers, architectures, and encapsulation materials, operational lifetimes up to 3.3 years with no efficiency losses can be successfully achieved

The Quotative System of Nigerian English

This thesis explores the ways speakers of Nigerian English (NE) re-create their own speech and the speech of others in narrative discourse using different quotatives. Research on English quotatives largely concentrated on the spread of quotatives in native varieties (e.g. American English, Barbieri, 2007; British English, Buchstaller, 2006; Scottish English, Macaulay, 2001; New Zealand English, Buchstaller & D’Arcy, 2009; Australian English, Winter, 2002; Canadian English, Tagliamonte & D’Arcy, 2004), whereas non-native varieties have received notably less attention. Therefore, this thesis presents an account of the acquisition and spread of quotatives in NE, which is a non-native variety. The study is based on naturally occurring data collected from 180 participants during sociolinguistic interviews conducted at different locations in Nigeria. The primary focus is on be like, say, tell, and zero quotatives on the grounds of their high frequency in my data. The study adopts Schneider’s (2007) Dynamic Model of Postcolonial Englishes to examine the emergence and development of NE, and Variationist Sociolinguistics (Labov, 1963, 1966; Trudgill, 1974; Tagliamonte, 2012) for the analysis of the quotatives. The analysis is based on a mixed-methods approach that relies on both quantitative and qualitative analyses. The quantitative analysis was conducted using Rbrul (Johnson, 2009). The discourse analytic qualitative method was employed in the qualitative analysis mainly to address the question of how and why different quotatives have specific discourse-pragmatic functions in performed narratives. While investigating how users of NE differ from other varieties of English in their use of quotatives, the study explores how the speaker’s choice of the different quotatives is conditioned by both linguistic (the content of the quote, grammatical person of the quotative, and tense/time reference of the quotative) and social (age, sex, regional origin, and social class) factors. The findings from this thesis show that there is a change in the development of quotative expressions in NE, which has a strong place in the way Nigerians recreate speech in narrative conversations. The findings demonstrate that a marked change in NE with respect to quotatives lies in be like use and how this quotative form offers an alternative way of introducing direct speech, which seems on the same model as say, tell, and other traditional quotative forms. In sum, this thesis offers insight into understanding the mechanisms of linguistic change and how the English quotative system has been adapted in NE.Doktorgradsavhandlin