Engineering

Publication Search Results

Now showing 1 - 10 of 105
  • (2022) Li, Yi
    Thesis
    CRISPR/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.

  • (2022) Kia, Layla
    Thesis
    Timber 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.

  • (2022) Chen, Yuhui
    Thesis
    Ride-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.

  • (2022) Gnanasekera, Manaram
    Thesis
    Unmanned 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.

  • (2022) Xie, Zhouzun
    Thesis
    The 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.

  • (2022) Cao, Jun
    Thesis
    This thesis focuses on the development and applications of magnetic resonance electrical properties tomography (MREPT), which is an emerging imaging modality to noninvasively obtain the electrical properties of tissues, such as conductivity and permittivity. Chapter 2 describes the general information about human research ethics, MRI scanner, MR sequence and the method of phase-based MREPT implemented in this thesis. Chapter 3 examines the repeatability of phase-based MREPT in the brain conductivity measurement using balanced fast field echo (bFFE) and turbo spin echo (TSE) sequences, and investigate the effects of compressed SENSE, whole-head B_1 shimming and video watching during scan on the measurement precision. Chapter 4 investigates the conductivity signal in response to short-duration visual stimulus, compares the signal and functional activation pathway with that of BOLD, and tests the consistency of functional conductivity imaging (funCI) with visual stimulation across participants. Chapter 5 extends the use of functional conductivity imaging to somatosensory stimulation and trigeminal nerve stimulation to evaluate the consistency of functional conductivity activation across different types of stimuli. In addition, visual adaptation experiment is performed to test if the repetition suppression effect can be observed using funCI. Chapter 6 explores if resting state conductivity networks can be reliably constructed using resting state funCI, evaluates the consistency of persistent homology architectures, and compares the links between nodes in the whole brain. Chapter 7 investigates the feasibility of prostate conductivity imaging using MREPT, and distinctive features in the conductivity distribution between healthy participants and participants with suspected abnormalities.

  • (2022) Zulkifli, Muhammad Yazid Bin
    Thesis
    Zinc-azole-based metal organic frameworks (MOFs) have been demonstrated to exist in a wide variety of structural states, with applications in different fields such as gas separation. In this dissertation, we explore the phase control and dynamics of zinc-azolebased MOFs in crystalline, liquid, and glassy states. We first study ZIF-7 phase control using mechanochemical synthesis. Ammonium nitrate was found to be a good catalyst in mechanochemical ZIF formation, with the usage of DMF and H2O favouring ZIF-7-I and ZIF-7-III formation, respectively. New phases of ZIF-7 variations not accessible using the solvothermal method were also obtained mechanochemically indicating the possibility of a new mechanochemical synthesis route. The mechanochemical ZIF-7 mixed matrix membrane (MMM) demonstrates good CO2- based selectivity improvements. Next, we demonstrate the formation of a new meltable zinc-azole framework (ZnCP) with liquid crystal behaviour by the addition of orthophosphate. ZnCP was able to melt at a low temperature while retaining and orienting its crystallinity into transparent liquid, thus showing promising use in optical-based applications. This material can also be obtained using a top-down approach by adding phosphoric acid to ZIF-7. Controlling phosphoric acid incorporation results in different melted ZnCP particle ratios, which was explored as a gas separation membrane. We then explore the effect of silver (Ag) composite presence on the thermal dynamics of another zinc-azole framework (ZIF-62). The benzimidazole amount within the Ag-doped ZIF-62 structure affects its thermal conversion, forming either Ag-doped ZIF-zni or Agdoped ZIF glass. The thermal dynamics of Ag-doped structures were explored using both in-situ (thermal) and ex-situ techniques. Both Ag-doped phases were demonstrated to have good MMM separation improvements for CO2 and light hydrocarbon, indicating the accessibility of the silver composite. Lastly, a quick demonstration of new methods (dip and spin coating) to process ZIF-62 and ZIF-62 composite successfully forms continuous particle dispersion, allowing the formation of a continuous glass layer. Different compositions such as sandwiched structure and layer by layer were explored, with advantages outlined. The novelty of this dissertation lies within the exploration of new synthetic methods and thermal dynamics to form structurally diverse zinc-azole MOFs which will be beneficial in the understanding of phase transformations in MOFs

  • (2022) Wang, Shuangyue
    Thesis
    Two-dimensional transition metal dichalcogenide (TMD) nanocrystals (NCs) exhibit unique optical and electrocatalytic properties. However, the growth of uniform and high-quality NCs of monolayer TMD remains a challenge. Until now, most of them are synthesized via solution-based hydrothermal process or ultrasonic exfoliation method, in which the capping ligands introduced from organic solution often quench the optical and electrocatalytic properties of TMD NCs. Moreover, it is difficult to homogeneously disperse the solution-based TMD NCs on a substrate for device fabrication since the dispersed NCs can easily aggregate. Here, we put forward a novel CVD method to grow closely-spaced TMD NCs and explored the growth mechanism and attempts on the size control. Their applications acting as electrocatalysts and adhesion layer for Au film deposition have been also well displayed. Through the whole chapters of this thesis, the following aspects are highlighted: 1. MoS2 and other TMD nanocrystals have been grown on the c-plane sapphire. The surface oxygen vacancies determine the density of TMD nanocrystals. The MoS2 nanocrystals demonstrate excellent hydrogen evolution reaction and surface-enhanced Raman scattering performance owing to the abundant edges. 2. Deep insights into the growth of MoS2 nanograins have been explored. The surface step edges and lattice structures of the underlying sapphire substrates have a significant influence on the growth behaviors. The step edges could modulate the aggregation of MoS2 nanograins to form unidirectional triangular islands. The Raman spectra of MoS2 demonstrate a linear relationship with the crystal size of MoS2. 3. The orientation of sapphire substrate has an of importance effect on the critical size of MoS2 nanocrystals. The MoS2 nanocrystals have the smallest size on the r-plane sapphire, besides, the MoS2 on r-plane sapphire demonstrates the sintering-resistance feature, which is attributed to the edge-pinning effect when MoS2 edges are anchored on the sapphire surface. 4. The MoS2 nanocrystalline layer was utilized as the adhesion layer for Au film depositing on a sapphire substrate. The Au films on MoS2 displayed superior transmittance and electrical conductivity as well as outstanding thermal stability, which lay in the strong binding of Au film with MoS2 nanocrystalline layer.

  • (2022) ZHANG, Qianyi
    Thesis
    To improve the imaging specificity for accurate diagnosis, nanoparticle-based contrast agents have been developed for magnetic bioimaging modalities including magnetic resonance imaging (MRI) and magnetic particle imaging (MPI). MPI, providing positive contrast, low tissue background (high signal-to-noise ratio) and unlimited tissue penetration depth, has great promise to become clinical imaging tool. Constructing the nanoprobe tailored for MPI based on its inherent properties is critical to achieve its potential. Tumour-targeted delivery of imaging nanoprobes also provides a versatile approach for precision diagnosis of diseases. MRI, owing to its excellent soft tissue sensitivity, high spatial resolution, and lack of ionizing radiation, has been considered as one of the imaging modalities to explore the imaging specificity. Our group has previously developed a tumour microenvironment-sensitive MRI contrast agent that can be further improved by increasing tumour cell targeting and tumour tissue penetration. Surface engineering of nanoparticles offers a critical strategy to improve tumour-targeting capacities of nanoprobes. Improvements to the efficacy of targeted nanoprobes have been intensively explored and much of this work centres on developing reliable and efficient surface functionalization strategies. Herein, in this thesis, various nanoparticles and surface modification approaches have been developed to improve imaging specificity for precision imaging diagnosis. Developing novel and promising nanoprobes based on their inherent properties and different surface modification strategies highlighting on nanoparticle engineering and emerging coating techniques has been described and discussed in this work.

  • (2022) Wang, Xiaoyi
    Thesis
    With the rapid growth of space technology, space robots play a critical role in on-orbit servicing missions, such as assembling, repairing, refueling, and transporting missions. Space robots can autonomously carry out on-orbit missions, avoiding dangerous and expensive tasks for astronauts. Unlike ground robots with fixed bases, the coupled dynamics between the free base and the manipulator of space robots need to be considered. Compared with single-arm space robots, dual-arm space robots can implement more complex tasks with a higher probability of success. Therefore, the modeling, motion control, hybrid position/force control, and post-capture control of a dual-arm space robot are investigated and presented in this thesis. The mathematical models of dual-arm space robots are developed by considering the reaction wheels (RWs) in the base. The kinematic model is constructed by the Generalized Jacobian Matrix (GJM). The dynamic models are inferred by the Newton-Euler method and the Lagrangian method, which are used in different application scenarios. The motion control of the two manipulators is used to implement a novel strategy to approach a defunct spinning target in space. By the nonlinear model predictive controller (NMPC), the end-effectors can track and plan smooth trajectories to approach and synchronize with a defunct spinning target. Meanwhile, the base attitude is regulated by the RWs to be stable at zero. The hybrid position/force control is applied to the dual-arm space robot to conduct contact operations. Novel capture and on-orbit assembly strategies are investigated. With the model uncertainties of the space robot, a robust sliding mode controller (SMC) is developed for better robust performance than the conventional computed torque controller. Furthermore, the unknown inertial parameters of the target can be precisely estimated during the capture phase. When a space robot and a target are rigidly connected during the post-capture phase, they form a combined system. The combined system can be stabilized to rest status by the space robot. The space robot can also release the target at the desired velocity. The proposed modeling, capturing of a spinning target, on-orbit assembling, and post-capturing processes are validated in the numerical simulations, which show the feasibility and effectiveness. The proposed work will improve the accuracy and efficiency of space robot technology.