Investigation of numerical atomic orbitals for first-principles calculations of the electronic and transport properties of silicon nanowire structures

This thesis is focused on the application of numerical atomic basis sets in studies of the structural, electronic and transport properties of silicon nanowire structures from first-principles within the framework of Density Functional Theory. First we critically examine the applied methodology and then offer predictions regarding the transport properties and realisation of silicon nanowire devices. The performance of numerical atomic orbitals is benchmarked against calculations performed with plane waves basis sets. After establishing the convergence of total energy and electronic structure calculations with increasing basis size we have shown that their quality greatly improves with the optimisation of the contraction for a fixed basis size. The double zeta polarised basis offers a reasonable approximation to study structural and electronic properties and transferability exists between various nanowire structures. This is most important to reduce the computational cost. The impact of basis sets on transport properties in silicon nanowires with oxygen and dopant impurities have also been studied. It is found that whilst transmission features quantitatively converge with increasing contraction there is a weaker dependence on basis set for the mean free path; the double zeta polarised basis offers a good compromise whereas the single zeta basis set yields qualitatively reasonable results. Studying the transport properties of nanowire-based transistor setups with p+-n-p+ and p+-i-p+ doping profiles it is shown that charge self-consistency affects the I-V characteristics more significantly than the basis set choice. It is predicted that such ultrascaled (3 nm length) transistors would show degraded performance due to relatively high source-drain tunnelling currents. Finally, it is shown the hole mobility of Si nanowires nominally doped with boron decreases monotonically with decreasing width at fixed doping density and increasing dopant concentration. Significant mobility variations are identified which can explain experimental observations.

An investigation of the utilisation of health impact assessments (HIAs) in Irish public policy making

It is the aim of this thesis to investigate Health Impact Assessment (HIA) use in public policy formulation in Northern Ireland and in the Republic of Ireland. The influences affecting the use of HIAs will be examined in this study. Four case studies, where HIA has been conducted, will be used for research analysis. This includes HIAs conducted on traffic and transport in Dublin, Traveller accommodation in Donegal, a draft air quality action plan in Belfast and on a social housing regeneration project in Derry. HIA aims to identify possible intended and unintended consequences that a project, policy or programme will have on the affected population’s health. Although it has been acknowledged as a worthwhile tool to inform decision-makers, the extent to which it is used in policy in Ireland is subject to scrutiny. A theoretical framework, drawing from institutionalist, impact assessment and knowledge utilisation theories and schools of literature, underpin this study. The investigation involves an examination of the unit of analysis which consists of the HIA steering groups. These are made up of local authority decision makers, statutory health practitioners and community representatives. The overarching structure and underlying values which are hypothesized as present in each HIA case are investigated in this research. Chapters 2 and 3 outline the main literature in the area which includes theories from the public health and health promotion paradigm, the policy sciences and impact assessment techniques. Chapter 4 describes the methodology in this research which is a multiple case study design. This is followed by an analysis of the cases and then concludes with practical recommendations for HIA in Ireland and theoretical conclusions of the research.

Effect of room temperature transport vials on DNA quality and phylogenetic composition of faecal microbiota of elderly adults and infants

Background: Alterations in intestinal microbiota have been correlated with a growing number of diseases. Investigating the faecal microbiota is widely used as a non-invasive and ethically simple proxy for intestinal biopsies. There is an urgent need for collection and transport media that would allow faecal sampling at distance from the processing laboratory, obviating the need for same-day DNA extraction recommended by previous studies of freezing and processing methods for stool. We compared the faecal bacterial DNA quality and apparent phylogenetic composition derived using a commercial kit for stool storage and transport (DNA Genotek OMNIgene GUT) with that of freshly extracted samples, 22 from infants and 20 from older adults. Results: Use of the storage vials increased the quality of extracted bacterial DNA by reduction of DNA shearing. When infant and elderly datasets were examined separately, no differences in microbiota composition were observed due to storage. When the two datasets were combined, there was a difference according to a Wilcoxon test in the relative proportions of Faecalibacterium, Sporobacter, Clostridium XVIII, and Clostridium XlVa after 1 week's storage compared to immediately extracted samples. After 2 weeks' storage, Bacteroides abundance was also significantly different, showing an apparent increase from week 1 to week 2. The microbiota composition of infant samples was more affected than that of elderly samples by storage, with significantly higher Spearman distances between paired freshly extracted and stored samples (p

Sectoral impacts on the diversity of carabid beetles (Coleoptera: Carabidae) and their associated ecosystem service of biocontrol

This thesis aimed to provide an understanding of how human-induced changes in the economic sectors of agriculture and transport affect carabid diversity, potential carabidmediated biocontrol and predator-pest interactions. The research involved both observational and manipulative laboratory and field-based studies. Observational research consisted of two large-scale investigations of (1) the impact of Miscanthus and oilseed rape production (n=45) and (2) the impact of horticultural and ecological based landscaping of roadside verges (n=64). This research is the first record of carabid diversity, potential biocontrol and community assemblage with respect to bioenergy crop production and roadside landscaping in an Irish context and it is also an important addition to the limited knowledge of carabid populations in these ecosystems internationally. Manipulative work involved the examination of the role predator identity, diversity and biomass play in the suppression of pollen beetle larvae (an economically damaging insect pest of oilseed rape in Europe), using a novel experimental design called ‘simplex’. To complement this research, an additional field study on the impact of low and high oilseed rape pesticide management on carabid species richness and abundance, and crop yield, was also conducted. This research is a great contribution to the existing understanding of what constitutes the important components of predator biodiversity and expands the knowledge of the usefulness of carabid predators in the context of pollen beetle larvae control. In particular, the work shows that the abundance or biomass of beetles has an effect that is far larger than the effect of diversity on the capacity of beetles to consume prey. In turn, the field study showed that pesticide applications had little impact on yield, or carabid richness, but that carabid abundance/biomass declined drastically. The work provides compelling evidence that management practices erode the useful components of biodiversity that are essential for the delivery of biocontrol services.

Climate and energy scenarios for Ireland to 2050 using the Irish TIMES energy systems model

Due to growing concerns regarding the anthropogenic interference with the climate system, countries across the world are being challenged to develop effective strategies to mitigate climate change by reducing or preventing greenhouse gas (GHG) emissions. The European Union (EU) is committed to contribute to this challenge by setting a number of climate and energy targets for the years 2020, 2030 and 2050 and then agreeing effort sharing amongst Member States. This thesis focus on one Member State, Ireland, which faces specific challenges and is not on track to meet the targets agreed to date. Before this work commenced, there were no projections of energy demand or supply for Ireland beyond 2020. This thesis uses techno-economic energy modelling instruments to address this knowledge gap. It builds and compares robust, comprehensive policy scenarios, providing a means of assessing the implications of different future energy and emissions pathways for the Irish economy, Ireland’s energy mix and the environment. A central focus of this thesis is to explore the dynamics of the energy system moving towards a low carbon economy. This thesis develops an energy systems model (the Irish TIMES model) to assess the implications of a range of energy and climate policy targets and target years. The thesis also compares the results generated from the least cost scenarios with official projections and target pathways and provides useful metrics and indications to identify key drivers and to support both policy makers and stakeholder in identifying cost optimal strategies. The thesis also extends the functionality of energy system modelling by developing and applying new methodologies to provide additional insights with a focus on particular issues that emerge from the scenario analysis carried out. Firstly, the thesis develops a methodology for soft-linking an energy systems model (Irish TIMES) with a power systems model (PLEXOS) to improve the interpretation of the electricity sector results in the energy system model. The soft-linking enables higher temporal resolution and improved characterisation of power plants and power system operation Secondly, the thesis develops a methodology for the integration of agriculture and energy systems modelling to enable coherent economy wide climate mitigation scenario analysis. This provides a very useful starting point for considering the trade-offs between the energy system and agriculture in the context of a low carbon economy and for enabling analysis of land-use competition. Three specific time scale perspectives are examined in this thesis (2020, 2030, 2050), aligning with key policy target time horizons. The results indicate that Ireland’s short term mandatory emissions reduction target will not be achieved without a significant reassessment of renewable energy policy and that the current dominant policy focus on wind-generated electricity is misplaced. In the medium to long term, the results suggest that energy efficiency is the first cost effective measure to deliver emissions reduction; biomass and biofuels are likely to be the most significant fuel source for Ireland in the context of a low carbon future prompting the need for a detailed assessment of possible implications for sustainability and competition with the agri-food sectors; significant changes are required in infrastructure to deliver deep emissions reductions (to enable the electrification of heat and transport, to accommodate carbon capture and storage facilities (CCS) and for biofuels); competition between energy and agriculture for land-use will become a key issue. The purpose of this thesis is to increase the evidence-based underpinning energy and climate policy decisions in Ireland. The methodology is replicable in other Member States.