Evaporation maps for ternary non-ideal liquid mixtures

This thesis deals with the evaporation of non-ideal liquid mixtures using a multicomponent mass transfer approach. It develops the concept of evaporation maps as a convenient way of representing the dynamic composition changes of ternary mixtures during an evaporation process. Evaporation maps represent the residual composition of evaporating ternary non-ideal mixtures over the full range of composition, and are analogous to the commonly-used residue curve maps of simple distillation processes. The evaporation process initially considered in this work involves gas-phase limited evaporation from a liquid or wetted-solid surface, over which a gas flows at known conditions. Evaporation may occur into a pure inert gas, or into one pre-loaded with a known fraction of one of the ternary components. To explore multicomponent masstransfer effects, a model is developed that uses an exact solution to the Maxwell-Stefan equations for mass transfer in the gas film, with a lumped approach applied to the liquid phase. Solutions to the evaporation model take the form of trajectories in temperaturecomposition space, which are then projected onto a ternary diagram to form the map. Novel algorithms are developed for computation of pseudo-azeotropes in the evaporating mixture, and for calculation of the multicomponent wet-bulb temperature at a given liquid composition. A numerical continuation method is used to track the bifurcations which occur in the evaporation maps, where the composition of one component of the pre-loaded gas is the bifurcation parameter. The bifurcation diagrams can in principle be used to determine the required gas composition to produce a specific terminal composition in the liquid. A simple homotopy method is developed to track the locations of the various possible pseudo-azeotropes in the mixture. The stability of pseudo-azeotropes in the gas-phase limited case is examined using a linearized analysis of the governing equations. Algorithms for the calculation of separation boundaries in the evaporation maps are developed using an optimization-based method, as well as a method employing eigenvectors derived from the linearized analysis. The flexure of the wet-bulb temperature surface is explored, and it is shown how evaporation trajectories cross ridges and valleys, so that ridges and valleys of the surface do not coincide with separation boundaries. Finally, the assumption of gas-phase limited mass transfer is relaxed, by employing a model that includes diffusion in the liquid phase. A finite-volume method is used to solve the system of partial differential equations that results. The evaporation trajectories for the distributed model reduce to those of the lumped (gas-phase limited) model as the diffusivity in the liquid increases; under the same gas-phase conditions the permissible terminal compositions of the distributed and lumped models are the same.

Piezoelectric energy harvesting using blood-flow-like excitation for implantable devices

The goal of this research is to produce a system for powering medical implants to increase the lifetime of the implanted devices and reduce the battery size. The system consists of a number of elements – the piezoelectric material for generating power, the device design, the circuit for rectification and energy storage. The piezoelectric material is analysed and a process for producing a repeatable high quality piezoelectric material is described. A full width half maximum (FWHM) of the rocking curve X-Ray diffraction (XRD) scan of between ~1.5° to ~1.7° for test wafers was achieved. This is state of the art for AlN on silicon and means devices with good piezoelectric constants can be fabricated. Finite element modelling FEM) was used to design the structures for energy harvesting. The models developed in this work were established to have an accuracy better than 5% in terms of the difference between measured and modelled results. Devices made from this material were analysed for power harvesting ability as well as the effect that they have on the flow of liquid which is an important consideration for implantable devices. The FEM results are compared to experimental results from laser Doppler vibrometry (LDV), magnetic shaker and perfusion machine tests. The rectifying circuitry for the energy harvester was also investigated. The final solution uses multiple devices to provide the power to augment the battery and so this was a key feature to be considered. Many circuits were examined and a solution based on a fully autonomous circuit was advanced. This circuit was analysed for use with multiple low power inputs similar to the results from previous investigations into the energy harvesting devices. Polymer materials were also studied for use as a substitute for the piezoelectric material as well as the substrate because silicon is more brittle.

Infant nutrition and the gut microbiota

Establishment of the intestinal microbiota commences at birth and this colonisation is influenced by a number of factors including mode of delivery, gestational age, mode of feeding, environmental factors and host genetics. As this initial establishment may well influence the health of an individual later in life, it is imperative to understand this process. Therefore, this thesis set out to investigate how early infant nutrition influences the development of a healthy gut microbiota. As part of the INFANTMET project, the intestinal microbiota of 199 breastfed infants was investigated using both culture-dependent and culture-independent approaches. This study revealed that delivery mode and gestational age had a significant impact on early microbial communities. In order to understand host genotype-microbiota interactions, the gut microbiota composition of dichorionic triplets was also investigated. The results suggested that initially host genetics play a significant role in the composition of an individual’s gut microbiota, but by month 12 environmental factors are the major determinant. To investigate the origin of hydrogen sulphide in a case of nondrug- induced sulfhemoglobinemia in a preterm infant, the gut microbiota composition was determined. This analysis revealed the presence of Morganella morganii, a producer of hydrogen sulphide and hemolysins, at a relative abundance 38%, which was not detected in control infants. Following on from this, the negative and short term consequences of intrapartum antibiotic prophylaxis exposure on the early infant intestinal microbiota composition were demonstrated, particularly in breast-fed infants, which are recovered by day 30. Finally, the composition of the breast milk microbiota over the first three months of life was characterised. A core of 12 genera were identified amongst women and the remainder comprised some 195 genera which were individual specific and subject to variations over time. The results presented in this thesis have demonstrated that the development of the infant gut microbiota is complex and highly individual. Clear alterations in the intestinal microbiota establishment process in C-section delivered, preterm and antibiotic exposed infants were shown. Taken together, long-term health benefits for infants, particularly those vulnerable groups, may be conferred through the design of probiotic and prebiotic food ingredients and supplements.

Assessment in primary education in Ireland

This doctoral study examines assessment in primary education in the Republic of Ireland. The nature and purpose of assessment offer an insight into the values which are prioritised by an education system. In 2011, in the Republic of Ireland, the Department of Education and Skills (DES) published a strategy aiming to improve standards of literacy and numeracy. The document, entitled, Literacy and numeracy for learning and life: the national strategy to improve literacy and numeracy for children and young people 2011-2020, contains improvement targets as measured by standardised tests. It also mandates the increased use of standardised tests in primary education, and directs that aggregated scores should be reported to both Boards of Management and the DES. The study is framed by the theoretical perspectives of Michel Foucault and Pierre Bourdieu. Both of these commentators examine social policy and practice in an effort to provide insight into the history and operation of social institutions. This study is especially influenced by Foucault’s archaeology and genealogy of knowledge, and his notion of governmentality. It is also particularly cognisant of Bourdieu’s thoughts on habitus, doxa and capital. The study contains reviews of literature in the areas of assessment, assessment policy, and assessment policy in Ireland. These reviews highlight current debate in each of these areas while also grounding this debate in an historical context. The dissertation contains four empirical sections. 1) It analyses policy documents prepared in the development of the published strategy as well as investigating the strategy itself. In so doing it is aware of the burgeoning influence of pan-national bodies on policy development. 2) A number of high profile policy makers were interviewed as part of the study and their views are interpreted in light of the findings of the literature reviews. 3) The perspective of teachers was sought through a questionnaire survey. This gathered data on these teachers’ views on the purpose of assessment as well as their actual practice. 4) Finally, children were also included as participants in this study. They were interviewed in focus groups and encouraged to contribute drawings as well on their views of assessment in primary school. Literacy and numeracy for learning and life is seen as a seminal document in Irish education. This study is significant in its analysis of original data from high profile policy makers, including two Ministers for Education and Skills. It is also significant in its inclusion of the perspectives of primary school pupils. Finally, the study considers the nature and role of assessment in a holistic manner by including the views of policy makers, teachers and pupils. The study notes that policy development in Ireland underwent a change in the preparation of Literacy and numeracy for learning and life and that international influences, while present, are also mediated to suit the local context. It also highlights a lack of clarity in the definition of assessment in primary education and argues that there is a lack of balance in the approaches that are prioritised. The study demonstrates that teachers are impacted by the strategy but that they also change it by focusing on their own concerns while using assessment tools. The children provide compelling evidence of the impact of assessment on the learner. The study shows how assessment tools (and school subjects) are valued with differing levels of importance by a variety of stakeholders.

Development of InAlN HEMTs for space application

This thesis investigates the emerging InAlN high electron mobility transistor (HEMT) technology with respect to its application in the space industry. The manufacturing processes and device performance of InAlN HEMTs were compared to AlGaN HEMTs, also produced as part of this work. RF gain up to 4 GHz was demonstrated in both InAlN and AlGaN HEMTs with gate lengths of 1 μm, with InAlN HEMTs generally showing higher channel currents (~150 c.f. 60 mA/mm) but also degraded leakage properties (~ 1 x 10-4 c.f. < 1 x 10-8 A/mm) with respect to AlGaN. An analysis of device reliability was undertaken using thermal stability, radiation hardness and off-state breakdown measurements. Both InAlN and AlGaN HEMTs showed excellent stability under space-like conditions, with electrical operation maintained after exposure to 9.2 Mrad of gamma radiation at a dose rate of 6.6 krad/hour over two months and after storage at 250°C for four weeks. Furthermore a link was established between the optimisation of device performance (RF gain, power handling capabilities and leakage properties) and reliability (radiation hardness, thermal stability and breakdown properties), particularly with respect to surface passivation. Following analysis of performance and reliability data, the InAlN HEMT device fabrication process was optimised by adjusting the metal Ohmic contact formation process (specifically metal stack thicknesses and anneal conditions) and surface passivation techniques (plasma power during dielectric layer deposition), based on an existing AlGaN HEMT process. This resulted in both a reduction of the contact resistivity to around 1 x 10-4 Ω.cm2 and the suppression of degrading trap-related effects, bringing the measured gate-lag close to zero. These discoveries fostered a greater understanding of the physical mechanisms involved in device operation and manufacture, which is elaborated upon in the final chapter.

Reframing Chinese animation: from classicism to postmodernism in post-1949 non-commercial Chinese animated films

This thesis focuses on Chinese non-commercial animated films produced from 1949 to date, with the aim of remapping and reframing Chinese animation in the light of existing theories, critiques, and frameworks drawn from studies in animation, film, and screen media. I suggest that Chinese animation has experienced three aesthetic transformations since 1949, primarily influenced by traditional Chinese culture, by Western modernist art and literature and, most recently, by postmodernism, respectively. Thus, the research traces and thoroughly investigates these three distinctive phases of Chinese animation in chronological order, from the classical period (1950s– 1980s) to modernism (1980s–2000s) and postmodernism (after 2000s). More in detail, I first rethink and re-evaluate the success of classical Chinese animation and the Chinese school of animation and, at the same time, I explore the influence of the political situation of the time on Chinese animation. Through careful analysis of A Da (1934–87) and other Chinese animators’ practices and theory, then, I argue that a remarkable modernist transformation took place in Chinese animation between the 1980s and 2000s, mainly driven by Western modernism and the Chinese “cultural fever” movement. Finally, through a discussion of the latest non-commercial animations produced after 2005, and especially those of Bu Hua (1973– ), for the first time I classify and theorize contemporary Chinese animations within a postmodern framework. By reframing existing views and broadening the scope of the analysis to encompass new areas and frameworks, this thesis aims to provide the reader with a comprehensive and systematic understanding of post-1949 Chinese animation and to offer an original contribute to scholarship, also working as a starting point for further research in this area.

MOVPE growth and characterization of Al(Ga)N and InAlN/AlGaN quantum wells for UV LED applications

The study of III-nitride materials (InN, GaN and AlN) gained huge research momentum after breakthroughs in the production light emitting diodes (LEDs) and laser diodes (LDs) over the past two decades. Last year, the Nobel Prize in Physics was awarded jointly to Isamu Akasaki, Hiroshi Amano and Shuji Nakamura for inventing a new energy efficient and environmental friendly light source: blue light-emitting diode (LED) from III-nitride semiconductors in the early 1990s. Nowadays, III-nitride materials not only play an increasingly important role in the lighting technology, but also become prospective candidates in other areas, for example, the high frequency (RF) high electron mobility transistor (HEMT) and photovoltaics. These devices require the growth of high quality III-nitride films, which can be prepared using metal organic vapour phase epitaxy (MOVPE). The main aim of my thesis is to study and develop the growth of III-nitride films, including AlN, u-AlGaN, Si-doped AlGaN, and InAlN, serving as sample wafers for fabrication of ultraviolet (UV) LEDs, in order to replace the conventional bulky, expensive and environmentally harmful mercury lamp as new UV light sources. For application to UV LEDs, reducing the threading dislocation density (TDD) in AlN epilayers on sapphire substrates is a key parameter for achieving high-efficiency AlGaNbased UV emitters. In Chapter 4, after careful and systematic optimisation， a working set of conditions, the screw and edge type dislocation density in the AlN were reduced to around 2.2×108 cm-2 and 1.3×109 cm-2 , respectively, using an optimized three-step process, as estimated by TEM. An atomically smooth surface with an RMS roughness of around 0.3 nm achieved over 5×5 µm 2 AFM scale. Furthermore, the motion of the steps in a one dimension model has been proposed to describe surface morphology evolution, especially the step bunching feature found under non-optimal conditions. In Chapter 5, control of alloy composition and the maintenance of compositional uniformity across a growing epilayer surface were demonstrated for the development of u-AlGaN epilayers. Optimized conditions (i.e. a high growth temperature of 1245 °C) produced uniform and smooth film with a low RMS roughness of around 2 nm achieved in 20×20 µm 2 AFM scan. The dopant that is most commonly used to obtain n-type conductivity in AlxGa1-xN is Si. However, the incorporation of Si has been found to increase the strain relaxation and promote unintentional incorporation of other impurities (O and C) during Si-doped AlGaN growth. In Chapter 6, reducing edge-type TDs is observed to be an effective appoach to improve the electric and optical properties of Si-doped AlGaN epilayers. In addition, the maximum electron concentration of 1.3×1019 cm-3 and 6.4×1018 cm-3 were achieved in Si-doped Al0.48Ga0.52N and Al0.6Ga0.4N epilayers as measured using Hall effect. Finally, in Chapter 7, studies on the growth of InAlN/AlGaN multiple quantum well (MQW) structures were performed, and exposing InAlN QW to a higher temperature during the ramp to the growth temperature of AlGaN barrier (around 1100 °C) will suffer a significant indium (In) desorption. To overcome this issue, quasi-two-tempeature (Q2T) technique was applied to protect InAlN QW. After optimization, an intense UV emission from MQWs has been observed in the UV spectral range from 320 to 350 nm measured by room temperature photoluminescence.