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Twinning is an essential plastic deformation mechanism in hexagonal-close-packed (HCP) metals, where the number of operative dislocation slip systems is limited. Twinning plays an important role in governing the balance between strength and ductility of the materials. The {10-12} and {11-21} twinning are two commonly observed tension twins, and will be the focus of this dissertation. The nucleation and growth are the two stages of the twin formation process, understanding the mechanisms behind which facilitates the study of the mechanical properties of the HCP metals and gives guidance to the alloy design strategies.Grain boundaries and dislocation pile-ups have always been thought of as the most possible twin nucleation sites, but there is a lack of experimental evidence and theoretical understanding of the twin nucleation mechanism from a single lattice dislocation. In this dissertation, a combined experimental and theoretical study of twin nucleation from a single dislocation in HCP crystals is presented. Specifically, high-resolution transmission electron microscopy has been used to identify {11-21} twin nuclei in HCP rhenium, and provided evidence of their nucleation from a dislocation. An anisotropic elasticity model of dislocation dissociation, parametrized by density functional theory calculations, provides conditions for twinning disconnection nucleation and propagation, necessary for the {11-21} twinning mechanism to be operative. The analysis serves to advance our understanding of the origin of the unique predominance of {11-21} twinning in rhenium, which correlates with the high strength and ductility of this metal. The model also provides new insights into design strategies that may be effective in activating this twinning mode and enhancing the balance between strength and ductility in HCP alloys more broadly.This dissertation also explores twin thickening. Twin thickening requires that the twin grows normal to the K1 plane. Molecular dynamics simulations are used to investigate {10-12} and {11-21} twin thickening processes through spontaneous twinning disconnection (TD) formation under applied shear deformation with a constant strain rate, based on an embedded-atom-method potential model of Zr. The stress responses and twin boundary (TB) structure changes verify that both twins thicken through TD formation. However, the thickening process of {10-12} and {11-21} twins differ in significant ways. While {10-12} TD loops were observed to form and expand during the twin thickening process, the {11-21} TB exhibits a more structurally disordered interface throughout the simulation and no sharp boundary corresponding a {11-21} TD ‘loop’ can be recognized, i.e., the TD for this TB is structurally rough. Moreover, the {11-21} twin requires a much lower critical shear stress for twin thickening. The low critical shear stress of {11-21} twin thickening also indicates that these twins should grow easily once nucleated. To the extent that these results apply to HCP materials more generally, the promotion of {11-21} twin nucleation may be an effective way to enhance twinning deformation and twin boundary related work hardening in HCP materials, with the potential to enhance the strength and ductility combination.

The international development cooperation landscape that has been largely dominated by the OECD-DAC members since the 1960s began to change in recent years with the ‘emergence’ and growing prominence of a group of ‘new’ development partners, many of which come from the Global South. Heated debate has since been going on around the socalled ‘emerging donors’ but much of that is flawed by its DACorientation, an almost exclusive focus on the ODA form of cooperation, as well as a lack of empirical evidence. Against this context, with an intent to further the current research on the Southern development partners, this thesis selects China, one of the most representative among them, and aims to investigate the Chinese ‘development package model’ through the case of its agricultural development cooperation policy and practice in Africa. Specifically, this thesis tries to explain how China’s current ‘package model’ of development cooperation has been shaped by its own decades-long history of aid-giving and reforms. At the same time, it attempts to explore how exactly the ‘package model’ has been played out on the ground, and especially how the innovative commercial elements have been incorporated and utilized in China’s agricultural development cooperation with Africa. Lastly, the thesis examines results of this new ‘package model’ of Chinese development cooperation so far provides a systematic explanation to why the ‘implementation gap’ exists in this specific policy issue. Based on a detailed historical review, the thesis argues that China’s own identity and experiences over the past decades have played a significant role in shaping its current model, and thus balances, to certain extent, the oft-seen ‘DAC/Northern-centric’ tendency of many in observing, judging and sometimes trying to assimilate the Chinese/Southern development cooperation model(s). The thesis also gives an in-depth treatment to the ‘development package’ model through the case of Chinese agricultural cooperation with Africa and compares that with the emerging trend of ‘development PPP’ in the Northern DAC community. It thus enriches the research on Southern development partners and that on development cooperation in general which both tend to focus almost exclusively on ODA. Furthermore, the thesis fills the gap of lack of empirical evidence in the existing literature by incorporating more project-level, fieldwork based case studies on the Chinese/Southern development cooperation model(s). By doing so, the thesis also points out a series of practical problems in the implementation phase that otherwise may not be identified, and more importantly provides a systematic explanation for that ‘implementation gap’. From a theoretical perspective, in order to explain the abovementioned implementation challenges, this thesis adopts the ‘Public Policy Implementation (PPI)’ approach and establishes an analytical framework based on a ‘dialogue’ between the theoretical literature and the empirical data. It thus finds that three aspects – namely the policy per se that structures the implementation process, the policy implementer who are formally or informally mandated to carry out the policy, and the implementation environment wherein the policy is executed – have played a crucial and synergic role in accounting for the observed ‘implementation gap’ of Chinese agricultural cooperation policy in Africa; the ‘implementer’ factor, furthermore, has weighed more strongly in this regard given its potential role in remedying policy imperfections and responding to adverse environment. This ‘policy-implementerenvironment’ framework may also serve as a useful analytical tool for analysing China’s development and foreign policy implementation in other fields in Africa and explaining the implementation results.

Epilepsy is one of the most severe neurological disorders. However, the detailed molecular mechanism in triggering epileptic seizures is still unclear. Nitric oxide (NO) is a versatile neurotransmitter in the brain; it acts as a messenger and antiplatelet aggregation agent in the cerebral vasculature. Peroxynitrite (ONOO-), a cytotoxic compound, can be easily produced by the diffusion-controlled reaction between NO and superoxide anion (O2·-).This study used a nanomedical approach to elucidate the role of NO and ONOO- in epileptic seizures. The nanomedical approach involving a system of nanosensors (diameter 200~300nm) has been used to measure directly in vivo release of NO and ONOO- in the brains of Sprague-Dawley (SD) rats during the process of pilocarpine-induced epileptic seizure events. Seizure events were simultaneously monitored by electroencephalography (EEG). Pilocarpine stimulated both NO and ONOO- production in the brain. The ratio of NO to ONOO- concentration ([NO]/ [ONOO-]) that reflected the balance between NO and ONOO- shifted with time. Epileptic seizures were observed only at the relatively low ratio of [NO]/ [ONOO-]. The latency, duration, and frequency of seizure events have also been influenced by the balance between NO and ONOO-.

With the rapid development of technology, the need for novel materials and state-of-theart devices is growing fast. Complex oxides which have strongly correlated electrons are favorable candidates for materials industry, due to their rich phase diagrams and multiple functions. Especially, ferroelectric oxides is very promising materials in the industry for storage, due to their bistable polarization states triggered by external electrical field. This thesis is centered on ferroelectric oxides, analyzing their lattice structures and investigating the interface of ferroelectrics and other complex oxides to examine the potential of the heteostructures in the application in electronic devices. The most notable feature of ferroelectric oxides is their reversible spontaneous polarization, which is strongly related to the lattice distortion in the crystal. In chapter 2, we report a neutron diffraction study of NaNbO3 [sodium niobate], to comprehensively understand the origin of ferroelectricity. We find that the structure evolves six phases from 930K to 15K in long-range, while only three real ground states are detected at short-range. We then study the ferroelectric/manganites heterostructures and explore its potential in the application in field effect transistors and ferroelectric memories. In chapter 3, we first describe the insulator-to-metal phase transition is realized in La0.8Sr0.2MnO3 [strontium doped lanthanum titanate oxides] under the field-effect of the ferroelectric Pb(Zr0.2Ti0.8)O3 [lead titanate oxides] layer. Moreover, we find that the interfacial transition plays a very crucial role in the tunneling electroresistance effect (TER) of the heterostructures. In chapter 4, we test the similar function at the interface of ferroelectrics and cuprates. We describe that the epitaxial strain and oxygen stoichiometry both lead to substantial changes in superconducting properties and these two factors are strongly coupled. And we demonstrate that the interface superconductivity is achieved in overdoped cuprates La1.6Sr0.4CuO4 [strontium doped lanthanum cuprate oxides] under field effect, with high Meissner volume and Tc [superconducting transition temperature] around 15K. Therefore, our results provide deep understanding on ferroelectric materials and open more opportunities for their application.