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  • (2020) Hu, Shangfeng
    Thesis
    The neural cell adhesion molecule 2 (NCAM2) is a cell adhesion molecule (CAM) of the immunoglobulin superfamily (IgCAMs). NCAM2 plays an important role in the developing and mature nervous system by regulating neurite outgrowth and synapse formation and maintenance. NCAM2 is also involved in neurodevelopmental and neurodegenerative brain disorders, such as autism spectrum disorder (ASD) and Alzheimer’s disease (AD), respectively. β-site amyloid precursor protein cleaving enzyme 1 (BACE1) is an aspartic protease, which plays a key role in AD by cleaving the amyloid precursor protein (APP) to produce the toxic Aβ peptide accumulating in brains of AD patients. Synaptic levels of NCAM2 are reduced in the hippocampus of AD patients and Aβ treated cultured hippocampal neurons. Since BACE1 activity is increased in brains of AD patients, we investigated whether there is a functional interaction between NCAM2 and BACE1. Our study shows that NCAM2 can be cleaved by BACE1 and BACE2, a homolog of BACE1. The cleavage site of NCAM2 by BACE1 and BACE2 is within the extracellular domain region, which is close to the transmembrane domain of NCAM2. The intracellular domain of NCAM2 is not required for the cleavage. Our study also shows that BACE-dependent cleavage of NCAM2 is not enhanced by Aβ. The BACE-dependent turnover of NCAM2 is higher in hippocampal than in cortical neurons possibly due to higher exo- and endocytosis of BACE1 in hippocampal neurons when compared to cortical neurons. We also found that the cell surface levels of BACE1 and the shedding of BACE1 are increased in NCAM2 knock-out neurons, whereas the total levels and endocytosis of BACE1 are not affected by NCAM2 deficiency. Taken together, our study demonstrates that NCAM2 is cleaved by BACE1 and BACE2 and regulates cell surface levels of BACE1 most likely by regulating the delivery of BACE1 to the cell surface.

  • (2020) He, Mushi
    Thesis
    When (isopropylcyclopentadienyl)rhenium tricarbonyl [(i-PrCp)Re(CO)3], i-Pr = isopropyl] is photolysed in pentane at low temperature in situ in an NMR probe, three short half-life isomers of i-PrCpRe(CO)2(pentane) were yielded as described previously. The decay rate and half-life of the isomers were measured in kinetics experiments. The chemical shifts of the i-PrCp part and pentane part of three isomers were assigned with TOCSY NMR experiments with different mixing times. Exchange processes and rates among the isomers were measured with EXSY NMR at 160 – 176 K. Possible intramolecular exchanges among pentane parts of isomers include [1,2], [1,3], [1,4] and [1,5] shifts. [1,3] shifts were found to be the fastest exchange process and rates were measured with EXSY NMR occurring with a rate of 2.8 - 4.0 s-1 at 176 K. [1,2] shifts were also observed to be occurring at an approximately 20 times slower rate and difficult to quantify. [1,4] and [1,5] shifts may be occurring slowly but could not be quantified. The lowest free energy of activation barrier for a [1,3] shift was ΔG++ = 40.3 kJ/mol, calculated with the Eyring equation. The soluble final product (i-PrCpRe)2(CO)5 was observed in NMR spectra; the minor insoluble final product (i-PrCpRe)(CO)2O(i- PrCpRe)(CO)2 was identified with mass spectrometry. Cyclohepta-1,3,5-triene molybdenum tricarbonyl (η6-C7H8)Mo(CO)3 undergoes a fluxional process. There are two protons on carbon 7 of the cyclohepta-1,3,5-triene ring ; One is Hexo, the other is Hendo. Analysis of the pattern of exchanging protons in EXSY NMR experiments at +150 °C showed directly that an intramolecular [1,5] shift of Hendo is occurring at a rate of 0.0139 ± 0.054 1/s. Exchange peaks and NOE peaks were confirmed with EXSY experiments at variable temperature, 120 -150 °C. The barrier to exchange from the EXSY NMR spectra (ΔG++ = 28.7 ± 0.4 kcal/mol) is similar to the barrier calculated using DFT. An intermolecular exchange between (η6-C7H8)Mo(CO)3 and free cycloheptatriene was also observed.

  • (2021) Ye, Zile
    Thesis
    Oxygen vacancy and surface area of the ceria nanoparticles are two major factors that contribute on the catalytic performance. Doping is one of the most commonly applied and also one of the most effective way to improve the performance of nanoceria. Different types of dopants can effectively change the physical/chemical properties of the synthesized nanoparticles. Iron can effectively increase the specific surface area of nanoceria and increase the oxygen vacancy concentration. Copper can induce the crystal growth as nucleating agent and increase the oxygen vacancy concentration at high dopant concentration. A copper-iron codoped system was designed to increase both of the specific surface area and oxygen vacacy concentration for the nanoceria. Two major effects of the dopants on crystal growth are kinetics and equilibrium. Kinetics is controlling the nucleation and distribution of the dopants. At low dopant level, the low distribution density of dopants effectively hinders the crystal growth. With increasing dopant concentration, the distribution density of the dopants increases, allows them to act as nucleation agent, significantly increase the crystal growth. And eventually, the oversaturated dopant reverses the trend of growth again. Structural changes are controlled by the equilibrium, where iron acting as acceptor of the Frenkel defect, forming substitutional solid solution with ceria, increases the oxygen vacancy concentration, results in the structural destabilisation. And copper acting as donor, stabilising the structure as nucleating agent. After iron reaches its solubility limit, copper may become the acceptor (substitutional), stabilising and destabilising the codoped system at the same time. By adjusting the dopant concentration, allows the oxygen vacancy concentration and the specific surface area of the codoped nanoceria to be increased.

  • (2021) Chu, Nicholas
    Thesis
    Mistletoes exert a pervasive influence over many aspects of an ecosystem but the positive effects of mistletoe have historically been underappreciated. This is because of the nature of mistletoes as hemiparasites, and how an overabundance of mistletoe can debilitate the functioning of its host. However, different host species respond to different mistletoe infections in different ways. In this thesis, I sought to understand more about the functional role of the pale-leaf mistletoe (Amyema maidenii) that parasitises mulga trees (Acacia aneura) in arid zone Australia. Firstly, I used the host quality hypothesis as a framework to evaluate the relative abundance of the pale-leaf mistletoe in mulga trees. Secondly, I conducted an experimental mistletoe removal study to test the theory that mistletoes can influence the microclimate of its host, thereby facilitating habitat use of a free ranging animal. The first study revealed that mistletoes aggregate on taller mulga trees, where the negative effects of mistletoe infection are more likely to occur. In the experimental removal study, my results evidence a novel pathway for how mistletoes can modulate the microclimate beyond its own physical structure, creating a distinctly cooler understorey microclimate at the host-scale. In trees where mistletoe was present, kangaroos (red kangaroo – Osphranter rufus) also preferentially rested beneath these trees when compared to trees where mistletoe was removed. I conclude that the pale-leaf mistletoe is an important constituent within arid zone Australia but this is likely mediated by different mechanisms. Results from my first study suggest that the pale-leaf mistletoe may have an important negative role as they aggregate on taller trees, thereby increasing the likelihood that they may debilitate the functioning of taller host trees. On the other hand, results from the second study provides further support for the theory that mistletoes function as a keystone resource, structuring species interactions and positively influencing ecosystem functioning. More broadly, results from the second study emphasise the prevalence of positive interactions within ecological communities and how they can occur in unexpected ways and between organisms that never come into direct contact.

  • (2020) Qu, Bolin
    Thesis
    Photocatalysis as an efficient and green solution to produce highly efficient and renewable energy H2 has attracted more attention recently. Among many photocatalyst materials, perovskite oxides have shown high efficiency and excellent stability under light irradiation due to their unique crystal structures and electronic properties. SrTiO3 as one of the perovskite oxides is a promising photocatalyst because of its low cost, high photochemical stability, and catalytic efficiency. However, the wide band gap of SrTiO3(3.2eV) makes it active only under UV light irradiation instead of visible light which means more harsh reaction conditions and more energy consumption. Therefore, it is a big challenge for modifying SrTiO3 to improve photocatalytic performance. In this work, a hydrothermal method was used to synthesize pristine SrTiO3 nano-cubic particles with high crystallinity. Then a novel strategy is applied through creating more oxygen vacancies and doping with chromium in the pristine SrTiO3 to improve photocatalytic performance respectively. A molecular dynamic simulation method was first used to investigate the oxygen vacancies diffusion mechanism for a better understanding of experimental directions. The simulation part concludes that creating more oxygen vacancies and elevate the temperature would increase the oxygen vacancies diffusion in SrTiO3. Then, the annealing method was used to create oxygen vacancies mixing SrTiO3 with strong reductant NaBH4 in the tube furnace with Argon gas flow. After creating more vacancies in SrTiO3, H2 production efficiency has been improved for three times. For the doping chromium part, a similar method has been used to synthesize cubic Cr-doped SrTiO3 nanoparticles. The colour of the product turns to yellow-green and the analysis of energy dispersive X-ray spectroscopy and inductively coupled plasma concludes that Cr element doped in SrTiO3 successfully. It is observed that the degree of crystallization of the products increased with increasing reaction time according to the XRD result. UV-visible spectroscopy indicates that the band gap of Cr-doped SrTiO3 is 2.30eV, much lower than pristine SrTiO3 of 3.32eV. Photocatalytic performance efficiency of Cr-doped SrTiO3 is eight times better than pristine SrTiO3, three times better than annealing SrTiO3.

  • (2020) Liu, Yang
    Thesis
    The antireflection (AR) coatings are of technological importance for applications in optical, electrochemical and sensing devices, however, good performance is restricted to the precise control of the nanoscale structure to suppress the reflection. The applied structures that have been investigated so far are featured by porosity, surface pattern and gradient distribution in the refractive index, but they remain a challenge in large scale fabrication. In this work, an investigation of highly uniform and porous silica AR coating has been systematically presented, and the recent advances of AR technology have also been summarized, including the basic principles of antireflection and its possible applications. A systematic study was carried out to investigate the effect of catalyst and aging time on silica particle size and distribution. It was found that the silica particle size can be tailored well between 9.8 to 91.0nm by the control of the ammonia catalyst ratio. Moreover, to determine the optimal size based on the sol-gel process, a comparative study of the particle effect on the AR properties was undertaken. Where capillary stress was determined to be the dominating factor of the particle assembly, and the refractive index of silica coating was adjusted from 1.16 to 1.47. Based on the current mechanisms of the antireflection and theoretical calculations, two sizes of silica sphere (56.2 and 91.0 nm in diameter) were selected as the main component of the AR coating layer. A peak transmittance achieved 99.57% at the wavelength of 550nm with an average of 98.18% over the visible range (380-800nm). Furthermore, the combination of nano porous AR coatings and the surface pattern on the solar cell covered glass showed vast improvement in the glass transmission efficiency over a wide-angle of incidence ranging from 0 to 68°. The enhancements in the photovoltaic system output efficiency are ≈ 2.5%, as estimated by a comprehensive calculation considering the net effect from transmission spectra, the AM1.5 solar radiation spectrum and silicon solar cell external quantum efficiency spectrum. A freeze test and accelerated weathering stability test showed the strong resistance of the AR coatings which suggests great potential for commercial applications.

  • (2020) Weng, Zhaoyue
    Thesis
    A metastable phase of magnesium hydride was prepared and investigated for solid state hydrogen storage. The magnesium hydride has a high theoretical hydrogen storage capacity (7.6 wt.%) but also a high dehydrogenation temperature of more than 300˚C due to its high enthalpy. Its metastable phase γ-MgH2 showed the possibility to overcome this challenge. In this project, magnesium nickel alloy was used for the catalyst effect of nickel. The samples were hydrogenated at 3.7 MPa & 350˚C under hydrogen atmosphere. Then the original α-MgH2 was converted to γ-MgH2 through ultra-high-pressure compression (4 GPa). 2.7 wt.% of γ-MgH2 was detected by X-Ray Diffraction (XRD) analysis and refinement, indicating phase transformation happened at ultra-high pressure. The dehydrogenation properties were revealed with Sieverts instrument and XRD. The samples were heated to different temperatures (100ºC, 200ºC, 300ºC and 400ºC) under vacuum with a discontinuous heating process. γ-MgH2 was found to start dehydrogenation at ~80˚C and reach a near fully decomposition at 200˚C (only 0.1 wt.% remained). The weight loss of γ-MgH2 due to dehydrogenation was calculated to be 0.8 wt.% at 100˚C and 4.5 wt.% at 200˚C. The dehydrogenation temperature of γ-MgH2 is much lower than 400˚C for the original α-MgH2. Also, the change of other phases under ultra-high-pressure compression in the samples were revealed and discussed in this project. Compression under different parameters to achieve a higher content of γ-MgH2 and a cycle test were also carried out. These properties revealed the potential and excellent properties of γ-MgH2 as a future hydrogen storage material.

  • (2020) Masand, Natasha
    Thesis
    DNA cytosine methylation is an important epigenetic modification that plays a key role in gene expression. DNA methylation has been shown to be involved in numerous processes, including X-chromosome inactivation in mammals, retrotransposon silencing, genomic imprinting, carcinogenesis and the regulation of tissue specific gene expression during development. Gene expression is tightly regulated via DNA methylation (5mC) and the aberrant expression of meiotic genes in mitotic cells via CpG promoter hypomethylation has been proposed to cause cancer. Cancer/Testis Antigens (CTAs) are a group of genes that encode tumour specific antigens and are expressed in the testis, certain cancers but not in normal post-natal somatic tissues. CpG island methylation and histone modifications appear to play a role in the epigenetic regulation of CTA expression, however, very little is known about their functions in vivo. A widely studied but poorly understood question to date is the mechanisms behind aberrant CTA reactivation in cancer. Given that 5mC mediated gene repression has been found to exist in vertebrate genomes and CTAs have also been identified to be a subset of highly evolutionarily conserved genes, it is critical to understand the role of 5mC mediated CTA silencing in vertebrates. By gaining a deeper understanding into the mechanisms behind this highly conserved pattern of gene repression on a specific subset of genes, we would be able to identify methods to prevent aberrant gene expression. In this study, I analysed publicly available whole genome bisulfite sequencing (WGBS), RNA-seq and chromatin immuno-precipitation followed by massively parallel sequencing (ChIP-seq) data of developing embryonic and adult somatic tissue of 3 vertebrate species to elucidate the evolutionary epigenetic regulation of CTAs in vertebrate genomes. Integrative WGBS, RNA-seq and ChIP-seq analysis revealed that CTAs are evolutionarily conserved in zebrafish, mice and humans and mechanisms of their epigenetic regulation are also conserved. I observed that histone modifications could potentially serve as an indicator of the methylation status of CTA gene promoters and that the expression of CTAs was inversely related to gene promoter 5mC levels. I demonstrate that CTAs when over-expressed cause embryonic lethality in zebrafish and the same genes are aberrantly hypomethylated at their CpG islands in a subset of human cancers. Overall, my work shows that CTAs are epigenetically regulated in an evolutionarily conserved manner and possibly via a conserved transcription factor, ETS1, that is expressed both in embryonic and cancerous tissue.

  • (2020) He, Tengyue
    Thesis
    Intrinsic metal halide perovskite single crystal has attracted intensive attention in recent years due to its excellent optoelectronic properties. Also, controlled doping of metal halide perovskite with metal ions is a feasible way to adjust its optoelectronic properties. However, only a few metal ions (Bi3+, Fe3+, Sn2+) doping of lead halide perovskite single crystal works were reported. Here, we employed a low-temperature high-molarity crystallization (LTHMC) method to synthesize high-quality monovalent Ag ions doped CH3NH3PbBr3 single crystals. Ag+incorporation leads a 160 meV reduction on the bandgap of Ag-doped single crystals, while significant PL quenching was observed. P type behaviour of Ag-doped CH3NH3PbBr3 single crystals and enhancement on conductivity and carrier concentration were confirmed by Hall effect measurement. Space-charge limited current methods was adopted to obtain the mobility of various doping levels samples. Compared with pristine single crystal, the mobility of Ag-doped single crystal exhibits a near sixfold enhancement. Moreover, photodetector based on Ag-doped single crystal was fabricated, exhibiting better performance than undoped counterpart. This project manifests the successful introduction of silver ions in perovskite crystals while retaining the host lattice structure, presenting an effective path for adjusting the optoelectronic properties of perovskites.

  • (2022) Zhao, Runqing
    Thesis
    Emerging modes of air transport such as autonomous airport shuttle and air taxi are potentially efficient alternatives to current transport practices such as bus and train. This thesis examines bus shuttle service within an airport and air metro as two examples of network design. Within an airport, the bus shuttle serves passengers between the terminals, train stations, parking lots, hotels, and shopping areas. Air metro is a type of pre-planned service in urban air mobility that accommodates passengers for intra- or inter-city trips. The problems are to optimise the service, and the outputs including the optimal fleet size, dispatch pattern and schedule. Based on the proposed time-space networks, the service network design problems are formulated as mixed integer linear programs. The heterogeneous multi-type bus fleet case and stochastic demand case are extended for the airport shuttle case, while a rolling horizon optimisation is adopted for the air metro case. In the autonomous airport inter-terminal bus shuttle case, a Monte Carlo simulation-based approach is proposed to solve the case with demand stochasticity, which is then further embedded into an "effective" passenger demand framework. The "effective" demand is the summation of mean demand value and a safety margin. By comparing the proposed airport shuttle service to the current one, it is found that the proposed service can save approximately 27% of the total system cost. The results for stochastic problem suggest estimating the safety margin to be 0.3675 times of the standard deviation brings the best performance. For the second case, the service network design is extended with a pilot scheduling layer and simulation is undertaken to compare the autonomous (pilot-less) and piloted service design. The results suggest that an autonomous air metro service would be preferable if the price of an autonomous aircraft is less than 1.6 times the price of a human-driven one. The results for rolling horizon optimisation suggest to confirm the actual demand at least 45 minutes prior to departure. Based on data from the Sydney (Australia) region, the thesis provides information directly relevant for the service network design of emerging modes of air transport in the city.