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(2021)ThesisImprovements in liquid lithium-ion battery electrolytes using of metal organic frameworks (MOFs) as a functional decoration on polymer membrane separators were investigated using a combination of experimental and theoretical methods. Zirconium-based MOF UiO-66 was introduced to the polymer support using the mixed matrix membrane (MMM) method. The method allowed the one-step manufacture of a robust, mechanically pliable polymer-MOF membrane composite of high MOF loading. MOF-MMMs imparted improved electrochemical behaviours such as a widened potential operating window, near-unity transference number, and increased presence of solid electrolyte interphase (SEI) components crucial to battery performance. Density functional theory (DFT) calculations were also performed to provide insights regarding electrolyte solvation in the presence of MOF. A simple dip-coating technique was utilised to modify the surface of the MOF-MMMs with polydopamine (PDA) for further improvement of the electrochemical properties. Increased transference numbers, as well as stability during rate cycling, were observed with the resulting PDA-MMM owing to the improved electrode/electrolyte interface. However, surface analyses using x-ray photoelectron spectroscopy (XPS) showed that there are reduced amounts vital SEI components compared to the original MOF-MMM support. The last section further explores the versatility of UiO-66 and tackled the preparation of gel polymer electrolytes (GPEs) decorated with UiO-66 via phase inversion technique. Using the phase inversion method, the fabricated GPE contained pores from both polymer substrate and the intrinsic pores of the 3D nanomaterial for improvement of electrochemical properties. It was demonstrated in this work that the MOF GPE is equally inert and suitable in ether or carbonate-based electrolytes. Overall, this study demonstrated the versatility of UiO-66 metal organic frameworks for use as a functional nanofiller for electrolyte membranes. With the use of inexpensive membrane fabrication methods, the composites obtained are viable for lithium-metal battery applications. Similarly, insights drawn can provide a springboard towards future study of MOF-based electrolytes.
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(2021)ThesisKesterite Cu2ZnSnS4 (CZTS), having the Earth-abundant and environment-benign constituents, and stable structure, is regarded as a promising thin-film photovoltaic material. However, the current power conversion efficiency (PCE) of CZTS solar cells is far below the commercialization-viable level. One of the main issues restricting the efficiency is the severe Shockley-Read-Hall (SRH) recombination at the highly defective CdS-buffer/CZTS-absorber heterointerface and within the CZTS absorber layer, giving rise to a large open circuit voltage (Voc) deficit. This thesis aims to mitigate the SRH recombination within the CdS/CZTS heterojunction by novel post-deposition treatment technologies to facilitate the passivation of the local defects. Firstly, the ultrathin intermediate stannic oxide (SnO2) layer was introduced at the CZTS/CdS heterointerface via a solution method. The employment of this layer enabled the effective passivation of the heterointerface, resulting in higher Voc, fill factor (FF) and thus PCE. Secondly, we applied our in-house developed moisture-assisted post-deposition annealing (MAPDA) treatment to modify the heterojunction by manipulating the trace element distributions. This technology enabled Na and K depletion in the CZTS film, which, in turn, facilitated the spontaneous Cd diffusion during the chemical bath deposition process for CdS buffer layer, driving a significant improvement in device performance. The heterojunction modification is attributed to the remarkable mitigation of local deep-level defect and the creation of the preferrable shallow acceptor copper vacancies. Peak efficiency at 9.40 % was obtained using the combined MAPDA and heterojunction air annealing (HJA) treatments, which further optimized the elemental distributions within the heterojunction region. Finally, the nanoscale optoelectronic characterization techniques, including Kelvin probe force microscopy (KPFM) and conductive-atomic force microscopy (C-AFM) were applied to investigate the impact of excess Na and K at the CZTS surface. The significant enhancement of quasi-Fermi level splitting and effective alleviation of SRH recombination through the combined MAPDA and HJA treatments were also revealed by surface photovoltage (SPV) analysis through KPFM. These technologies with first-hand novelty explore new defect passivation routes in kesterite solar cells, which can also be widely applied to other thin-film solar cells.
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(2022)ThesisModern power systems are facing growing penetration of renewable distributed generation (DG) in active distribution networks (ADNs), mainly driven by energy transition, decarbonization and economic benefits. However, renewable DG such as wind turbine and solar photovoltaic (PV) characterize fluctuating and intermittent output power as well as non-dispatchable attributes. Also, the renewable generation cannot fully align with load consumption, resulting in a supply-demand energy mismatch. To address uncertainties of renewable DG and improve renewable energy utilization efficiency, battery energy storage systems (BESSs) are considered as a promising technology for renewable integration in power systems. Thus, this thesis focuses on the optimal allocation and operation of BESS in highly distributed energy resource (DER)-penetrated ADNs. Firstly, a robustly optimal allocation method for BESSs is developed to alleviate power unbalance and voltage rise, thus improving the PV hosting capacity of ADNs. Considering random locations and capacities of the distributed rooftop PVs, future PV installations are regarded as uncertainties, which provides a new perspective on hosting capacity improvement. Secondly, for energy management, a two-stage coordinated method of day-ahead demand response and BESS is developed to minimize the total operating cost. Considering the limited BESS capacity and time-coupling of state of charge (SoC) during the scheduling, an SoC interval management method is proposed to improve BESS dispatch efficiency from the whole-day perspective. Thirdly, this SoC interval management is integrated into an adaptive BESS dispatch method for unbalanced microgrid operation. The corresponding optimization problem is solved by a hybrid interval-robust optimization method. Fourthly, different ownerships of DERs also bring challenges to microgrid energy management. A transactive energy sharing approach between a microgrid operator and multiple DER-aggregators is developed with a distributed coordination framework. A two-settlement internal transactive energy market is proposed to support this energy sharing. The uncertainties in the above methods are properly modelled and addressed by different optimization methodologies. The proposed methods have been successfully demonstrated and compared with existing works. The results verify their high efficiency and robustness against uncertainties.
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(2021)ThesisWith the rapid development of optical fiber technology, fiber loss has been greatly reduced in spectral region from 1200 nm to 1700 nm. To date, only limited spectral range (approximately 100 nm or 20% of the total 500 nm band between 1200 nm and 1700 nm band) has been commercially utilized, since erbium-doped fiber amplifier (EDFA) is the only commercially available optical fiber amplifier working within 1520 nm to 1620 nm. Therefore, developing wideband and flat-gain fiber amplifiers operating the whole or the EDFA uncovered spectral region of 1200 nm to 1700 nm, has been pursuing for higher capacity photonic networks. Bismuth and Erbium co-doped Fibers (BEDFs), due to near infrared (NIR) broadband luminescence, are regarded as promising gain media towards developing wideband and flat-gain fiber amplifier covering entire range of available bands between 1200 nm and 1700 nm. There are various bismuth active centers (BACs) responsible for different NIR luminescence bands and the formation of BACs is closely correlated with fiber core compositions, fabrication, and post-draw processing. To develop efficient BEDFs lasers/amplifiers, the higher BACs concentration is needed, and high unsaturable losses needs to be further reduced. In this thesis, post-draw thermal and optical processing and effects on performance of BEDFs are studied, exploring potential post-draw processing methods to improve the BEDFs performance. The BEDFs demonstrated in this thesis were manufactured in National Fiber Facility at University of New South Wales (UNSW). Research works, outcomes and original findings from this PhD study are briefly summarized in the following. (1) Presented an overview of the development of BEDFs (2) Presented a review of the post-draw thermal and optical processing on BDFs/BEDFs (3) Studied and identified thermal effects on BAC-Si activation and background loss in BEDFs (4) Investigated and achieved BAC-Si activation on thermal quenching in BEDFs (5) Investigated and achieved loss reduction on thermal annealing in 3D silica lithography BEDFs (6) Studied and found the relation between BAC-Si photobleaching and Al2O3 doping concentrations in BEDFs (7) Studied and found the dependence of cut-off wavelength on temperature in BEDFs
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(2021)ThesisRecent innovations in the area of liquid crystals have led to the development of passive electro-optic liquid crystal transducers that enables a new approach to compact, monolithic, and even portable Q-switched and mode-locked lasers. My Ph.D. study concentrates on the liquid crystal cells with a thin gap filled with nano-scale pitch ferroelectric smectic-C* liquid crystals, of which the molecular arrangement can be continuously deformed by the electric fields, giving rise to the "deformed helix" mode of operation. The deformation of molecular helical structure gives rise to the electric field controlled birefringence and orientation of the optical axis, which illustrates the possibility of using the liquid crystal modulator as an active intracavity loss modulator in laser applications. This thesis presents the basic liquid crystal physics, design, modeling approaches, and characterisation of liquid crystal modulator in great detail for readers to understand its basic principles. To theoretically study its performance when applied to the 1 µm Q-switched lasers, the numerical model was developed. The numerical model predicted that the pulse width can be reduced to 17 ns and the peak power can be enhanced to 1.15 kW, when the absorbed pump power, the external optical loss, and the temperature are optimised. To utilise this novel technique in the industry, the University of New South Wales, Macquarie University, and Lastek started the collaboration for the development of a commercial prototype of compact actively Q-switched lasers in 2017. Later, the operation wavelength range was extended further to 1.88 µm in Tm3+-doped ZBLAN waveguide chip lasers. The experimental results demonstrated that the shortest pulse duration was around 31 ns, which provided the peak power of 1.3 kW at the repetition rate of 200 Hz. Additionally, all-in-one fibre lasers operating at 1.55 µm were designed and experimentally developed in an all-fibre setup. The proposed all-in-one fibre lasers support CW, Q-switched, AM, and FM mode-locked operation modes, and the mode can be easily switched by applying different electrical signals. The simulation and experimental results illustrate the feasibility of utilising liquid crystal modulators in lasers, nonlinear applications. Additionally, utilising this novel optical technology for the development of the new generation of neural interfaces, that can record activation potentials at different positions, is another ambitious goal to achieve in the future.
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(2022)ThesisCRISPR/Cas9-based gene editing is no doubt among the most intensively studied topics in bio-related fields in the recent decade, and certain new programmable Cas nucleases have been exploited recently for the development of a variety of biological tools far beyond gene editing, particularly for biosensor development. Although CRISPR/Cas-based biosensing has brought about a revolution in the area of nucleic acid diagnostic with their superior performances, its advantages were challenged when attempting to expand towards a broader range of non-nucleic acid targets. The currently reported methods for non-nucleic acid targets has successfully demonstrated the versality of CRISPR/Cas components in combining with other biosensing elements, however, combining these elements without proper optimization or controllable bioreaction environments could also bring additional variable factors into the system, hence potentially leading to compromised sensitivity or overall increase of system complexity. In this project, two novel CRISPR/Cas12a-based biosensing systems have been developed to realise simple, sensitive and universal non-nucleic acid detections. Both of these systems are established on a standard 96-well plate format, similar to the widely used ELISA diagnostic approach. The first system utilised an aptamer as its recognition molecule for rapid detection of two small proteins with fM-level sensitivity within 1.5 hours. In the second system, antibody was used as a recognition molecule, allowing to draw on a huge pool of commercially available antibodies to support its universality. This system exhibits ultra-high sensitivity down to 1 fg/mL (aM-level) for the detection of two protein targets. With these two successfully developed CRISPR/Cas12a-based non-nucleic acid biosensing systems, the universality and feasibility to deal with two practical bio-detection scenarios was investigated. The antibody-based system with minor modifications was directly used as a ready-to-use sensitivity enhancer onto a commercial IFN-γ ELISA kit, which resulted in a 2-log increase in sensitivity without changing its original protocol. Then, a similar modification strategy was used to re-direct the antibody-based system to detect whole pathogenic microorganism, Cryptosporidium parvum oocyst. Without the need for specialised instruments, the results show a successful detection of this pathogen with single oocyst sensitivity and capable of applying in challenging environmental samples. All these results serve as successful demonstration of the great potential in CRISPR/Cas-based biosensing technology to achieve affordable, translatable, and deployable solutions for various clinical, industrial and research diagnostic needs.
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(2022)ThesisTimber construction is rapidly evolving towards high-rise and high-tech. The demand for mid- to high-rise buildings using engineered timber can be attributed to its high structural efficiency and mitigation of carbon dioxide emissions. However, due to the relatively low mass density and stiffness characteristics of timber, lateral load resistance is often the governing criteria for design. Restrictive design regulations, limited education and lack of innovation has seen the development of multi-storey timber structures mimic that of traditional steel and concrete buildings. This has led to the full potentials of timber as a construction material, and timber structures as an architectural form, not to be realised. In this research, an efficient structural system consisting of a timber-steel hybrid exoskeleton is proposed and tested. Specifically, composite timber-steel encased columns and steel-timber buckling restrained braces (STBRB). Experimental testing of composite timber-steel encased columns subjected to concentric and eccentric loading indicates significant stiffness and load carrying enhancement (over 100% in some cases) compared to bare timber columns with intermediate to stocky slenderness. Analytical models based on the principles of structural mechanics and simplified bilinear elastoplastic relationship accurately predicted the load carrying capacity and offers a simple method of analysis which can be used in practice. Detailed nonlinear 3D finite element (FE) simulations of the columns are developed and verified against the experimental results using ABAQUS software. Based on the experimental, analytical, and numerical results, the behaviour of composite timber-steel encased columns is found to be significantly influenced by the ratio of steel strength to timber strength (Asfsy/Atfcm) as well as knots/imperfections, particularly in low-grade wood. Cyclic tests representative of seismic actions on steel-timber buckling restrained braces (STBRB) have demonstrated stable hysteretic energy dissipation and a cumulative inelastic ductility capacity (CID) beyond the requirements prescribed in AISC 341. STBRBs with steel collars placed at the critical ends of the casings demonstrated the highest ductility and energy dissipation. The results from the study showcased the proposed system as a feasible and sustainable alternative to conventional concrete/steel BRBs.
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Modeling ride-sourcing and public transport services in a multi-modal network with multi-class users(2022)ThesisRide-sourcing services are rapidly spreading around the world. The ride-sourcing service refers to a point-to-point on-demand ride service operated by various companies, which organize and coordinate drivers using their vehicles to provide passengers with ride services. How ride-sourcing services and public transport are interacting with each other and thus yielding system-wide impacts have not received sufficient attention. This thesis extends the literature by proposing multi-class, multi-modal traffic assignment models to optimize the transport system with the presence of ride-sourcing and public transport services. The first part of the thesis develops a stylized model with a simple network with single origin-destination pair in order to analytically examine the mode choice behavior of travelers and the operation strategies of a public transport operator and a ride-sourcing operator. In such a multi-modal system, users may travel by bus, train, or ride-sourcing service. In particular, we develop a tractable bi-level model that quantifies the user equilibrium travel choices in the lower-level, where the travel choice equilibrium can be formulated as a variational inequality problem, and optimizes the operation strategies of the public transport operator that aims to minimize total system cost and the ride-sourcing operator that aims to maximize its profit in the upper-level. The existence and uniqueness of the multi-modal travel choice equilibrium are also analyzed. How the operation decision variables might affect users' mode choices and system performance is investigated both analytically and numerically. The second part of the thesis extends the stylized model to a general network model, which includes also solo-driving, and multiple OD pairs to depict a more realistic problem setting. The general network model is applied on a case study in the context of Sydney. The existence and uniqueness are also investigated for the general network model. The method of Frank-Wolfe combined with diagonalization is applied to generate numerical solutions, and illustrate the analytical observations and generate further understanding. The results show that the total system cost can be reduced while the profit of the ride-sourcing company can be increased under appropriate operating strategies of the public transport operator and the ride-sourcing operator.
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(2022)ThesisUnmanned aerial vehicles (UAV) usage is constantly on the increase. Future skies have a risk of being congested with busy UAVs assisting humans in many different ways. Such congestion could lead to aerial collisions. To avoid disastrous situations, potential for aerial collisions should be addressed. Avoiding aerial collisions has been reported in various different ways in the literature. Out of all the ways available in the literature, collision cones have the ability to predict a future collision beforehand with a low computational burden. Many variants of the collision cone approach have been proposed for various different collision avoidance tasks in past research. However, avoiding a collision will have an effect on the total mission time. In spite of the large volume of past work, time-efficient collision avoidance has not been examined extensively in collision cone literature. This research presents methodologies to avoid aerial collisions in a time-efficient manner using the collision cone approach. The research in this thesis has considered all possible scenarios including heading change and speed change, to avoid a collision. The heading based method was mathematically proven to be time-efficient than the other methods. Initially, 2D collision avoidance methodologies are presented; however, in extreme cases, 3D collision avoidance is necessary and 2D methods have been extended to address 3D collisions. The proposed heading based method was compared with other works presented in the literature and validated with both simulations and experiments. A Matrice 600 Pro hexacopter is used for the collision avoidance experiments.
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(2022)ThesisThe polydisperse solid-liquid system has been practised in many chemical engineering applications. A fundamental understanding of complex multi-phase flow with a wide particle size distribution (PSD) in the system is beneficial for process control and reactor optimisation, yet the currently existing numerical models, including conventional computational fluid dynamics - discrete element method (CFD-DEM), fail to capture the cross-scale inter-phase/particle interactions. Accordingly, multi-resolution models are developed in this thesis for the high-fidelity simulation of polydisperse solid-liquid systems. 1) A smoothed volume distribution model (SVDM) is first developed based on the unresolved CFD-DEM framework, with the capability of simulating the polydisperse solid-liquid system with a coarse-to-fine particle size ratio of up to 20. Via studying the migration of fine particles in suspension flow through a packed bed of coarse particles, the migration mechanism of fine particles is proposed and the inherent fundamental of clusters are elucidated. Via investigating the bed hydrodynamics in a bi-disperse solid-liquid fluidised bed (SLFB), the segregation and mixing mechanisms of particles in solid-liquid systems are illuminated. Via quantifying the solid transportation behaviours during the rapid filtration of dual-media filters, a probabilistic model is derived and verified for predicting clogging performance. This work establishes an effective framework to handle complex polydisperse solid-liquid systems. 2) Two acceleration methods (i.e., coarse-grained method and machine learning method) are studied, with the capability of simulating solid-liquid systems with improved computational efficiency at spatial and temporal scales, respectively. The coarse-grained method is employed to simulate large-scale particulate systems for unveiling the sedimentation mechanism of particles in water. The machine learning method is used to predict mixing and segregation behaviours in a solid-liquid system. This work provides an efficient method to predict granular flow behaviours in solid-liquid systems. 3) Further, a hybrid CFD-DEM model combining the resolved and unresolved CFD-DEM frameworks is originally developed, with the capability of simulating the polydisperse solid-liquid system with unlimited coarse-to-fine particle size ratios, for the first time. A resolved part obtains the fluid details around each coarse particle without extra models using fine grids (i.e., grid size to particle diameter ratio, lm/dp < 1/10), an unresolved part describes the fluid-fine particle interactions with empirical correlations using coarse grids (lm/dp > 3), and a semi-resolved part denotes the medium particle behaviours with a kernel-based approximation using medium grids (1/10 < lm/dp < 3). This work delivers a novel idea for modelling cross-scale solid-liquid flow and has the potential application to any polydisperse solid-liquid systems. This thesis represents collection of a suite of innovative numerical works of polydisperse particulate flows in solid-liquid systems and provides a range of numerical tools for understanding and optimising polydisperse solid-liquid flow systems.