Engineering

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Now showing 1 - 10 of 501
  • (2021) Dang, Bac
    Thesis
    Natural kidney filtration is a compact, multi-step filtration process which passes wastes and exceeded fluids via microscale vessels in glomerulus and tubules. The principal renal replacement therapy (RRT), commonly called dialysis, is a single-step filtration process based on diffusion to replace kidney failure. Conventional dialysis is limited in its effectiveness (not a continuous treatment), its impact on quality of life (typically requiring patients to spend several days per week in a clinic), and its cost (large systems, requiring frequent membrane replacement). This thesis is an investigation into the feasibility of using microfluidics and membrane technology to create portable alternatives to dialysis systems. It starts with a comprehensive review of the state-of-the-art in portable artificial kidneys, microfluidics, membrane science, and other related fields. An innovative, multi-step process was designed to mimic kidney filtration using two membranes; one to filter out large particles and one to remove urea and recycle water, thus mitigating the need for a dialysate system. The underlying physics (the mixing and shear stress) of the mechanisms which could enhance filtration performance at microscale was then studied. It was found that by adding microspacers into narrow-channel flows, it is possible to significantly enhance filtration. Optimized 3D-printed spacer designs (e.g., a ‘gyroid’ spacer) showed flux enhancement of up to 93% (compared to a plain channel) when using a plasma mimicking solution. The use of different blood and plasma mimicking solutions also suggested a prior step to separate large biological components (e.g., cells, proteins) is helpful to reduce cell contact and fouling in membrane filtration. The potential use of microfluidic diode valves and micropumps for pressure and flowrate regulation in the proposed small-format system was discussed. Membrane processes which mimic the filtration function of the tubules and have the potential for integration into portable systems (e.g., reverse osmosis and membrane distillation) are demonstrated to be useful potential alternatives to dialysis in toxin removal and in returning clean water to the blood stream.

  • (2021) Sun, Yu
    Thesis
    A pseudolite (PL) is a ground-based positioning system that offers flexible deployment and accurate “orbits”. The PL system can carry on the role of the GNSS to provide precise positioning for indoor users. However, there are some unusual challenges that seriously affect the performance of a PL system in precise indoor positioning. To raise PL-based positioning accuracy up to the centimeter level or higher, the use of the PL carrier phase measurement with ambiguity resolution is a unique consideration. The PL phase ambiguities are also contaminated by clock bias, multipath errors, and cycle clips. Their existence destroys the integer nature of ambiguity and impedes the pursuit of further accuracy improvement. The major contributions in this research for addressing the above-mentioned challenging issues are specified as follows: 1. The ground-based AR methods are discussed. The impact of ground-based geometry on indoor AR is researched, and the influence of linearization error is also investigated. An efficient PL-based AR method is studied and verified in the balance of gaining convenience and avoiding linearization impact. 2. The clock bias between PL transmitters can be properly handled in a way that time synchronization can be achieved with a transmitter-only PL system at low cost and simplicity. Therefore, the PL-based the ambiguities are able to be fixed to correct integers, and centimeter-level indoor precise positioning can be reliably achieved. In addition, the proposed way for time synchronization is also applicable for other ground-based systems for precise positioning purposes. 3. The stochastic model for mitigation of indoor multipath and NLOS is investigated. The experimental results demonstrate that the proposed stochastic model is superior to other existing models in indoor multipath mitigation as it is competent to suppress the multipath errors mainly caused by multipath to the smallest in both static and kinematic results, respectively. Moreover, it is also verified to be efficient for NLOS mitigation. With the proposed new stochastic model, precise point positioning is confidently expected indoors. 4. The methods for PL-based cycle slips are extensively studied and discussed. Numerical results indicate that the integer-cycle slips can be efficiently and accurately detected and corrected. The concern about PL-based cycle slip is minimized, the reliability and sustainability of PL-based precise indoor positioning can be promised.

  • (2020) Cho, Yongyoon
    Thesis
    The power conversion efficiency (PCE) of metal halide perovskite solar cells (PSCs) has increased from 3.8 to 25.2% in the last decade, making perovskite the most promising material for future solar cells. However, further PCE and stability improvement are important for successful commercialization. Therefore, the aim of this thesis is to investigate ways of increasing PCE and addressing instability of PSCs. Initial PCE increase has been observed during ambient storage for many PSCs. Through a series of experiments, the origin of the storage effect was attributed to a combination of i) defect reduction in perovskite, ii) conductivity increase, and iii) evolution of the highest occupied molecular orbital (HOMO) in spiro-OMeTAD. In particular, the HOMO level change was revealed to play a significant role in PCE improvement. In terms of strategy for improving PCE, a novel passivation technique was developed by forming 2D/3D perovskite thin layer using a mixture of formamidinium iodide and iso-butylammonium iodide on the perovskite layer. This technique achieved a maximum PCE of 21.7%, while simultaneously enhancing device light and moisture stability. The defect density reduction, the uniform surface coverage of the passivation material and the suppressed ion migration by bulky organic cation were found to be the key parameters for PCE and stability improvement. Storage effect was also studied for these passivated PSCs. It is found that the changed conduction band of passivated perovskite influenced the initial temporal change of PCE, suggesting the importance of interface band alignment by passivation and conductive materials. Also, despite significantly suppressed non-ideal recombination at the surface/interface by passivation, analysis of the dominant recombination revealed the need for defect reduction in bulk perovskite. Consequently, by engineering the composition of bulk perovskite layers to decrease defects, PCE of 22.2% was achieved. Finally, the effects of removing one of hole transport material (HTM) additives, 4-tert-butylpyridine (tBP) (via HTM solvent engineering) on device performance and thermal stability were investigated. The suppressed morphological change at high temperature for tBP-free HTM was the reason for thermal stability improvement. This work shows that comparable efficiencies can still be achieved without the use of the thermally unstable HTM dopant.

  • (2021) Gresham, Isaac
    Thesis
    Polymer brushes are arrays of densely surface-tethered polymer chains, and are of interest for two reasons. Firstly, they possess interfacial characteristics, such as antifouling and lubrication, that are desirable in many applications. Secondly, they are model systems that can provide additional insight into polymer behaviour due to their unique geometry. Observing the interfacial structure of these brush layers is critically important for understanding both their properties and the mechanisms driving the polymer behaviour. To date, neutron reflectometry (NR) is the only technique that can demonstrably resolve the nanoscale structure of polymer brushes. However, these diffuse interfaces produce subtle features in the reflectometry data that challenge interpretation, with typical analyses failing to quantify the derived structure's uncertainty. Furthermore, the experimental potential of this technique for the study of brushes is only just being realised. This Thesis advances NR as a tool for studying polymer brush systems by establishing a robust analysis methodology that overcomes previous hurdles and demonstrating novel experimental techniques. In both cases, poly(N-isopropylacrylamide) (PNIPAM) brushes are used as model systems. First, the polymer system is characterised through the novel observation of surface-initiated ARGET ATRP using time-resolved NR, and a study of the dry brush as a function of humidity and temperature. Second, methodologies are developed that allow for robust determination of both solvated and confined brush structures. Lastly, NR is used to elucidate the behaviour of PNIPAM brushes in complex environments. A novel confinement apparatus is used to investigate the structure of a PNIPAM brush under mechanical confinement and contrast-variation provides unparalleled insight into PNIPAM–surfactant systems. In each case, complementary techniques are essential in guiding reflectometry experiments and fully understanding the polymer system. This work develops and demonstrates techniques that enhance the study of diffuse interfaces with the NR technique. Moreover, the holistic structural examination of PNIPAM undertaken sheds new light on the phase behaviour of this ostensibly well-understood polymer and highlights its rich interaction with surfactants.

  • (2020) Sarmiento, Czar Jakiri
    Thesis
    The Philippine Height System (PHS) modernisation is driven by recent advances in geodetic technology and the Philippines’ need to be geodetically responsive to natural disasters. Aspects of the shift from a levelling-based system to a GNSS and gravimetric geoid-based system, being a cost-effective modernisation strategy for developing countries, were investigated. This thesis expands available scientific literature for the International Height Reference System/Frame (IHRS/F) development of the International Association of Geodesy (IAG), and the PHS modernisation efforts of the National Mapping and Resource Information Authority (NAMRIA). Three elements of a modern PHS were studied. 1. The engineering implications of the new Philippine Geoid Model (PGM). 2. The temporal variability of the geoid and benchmarks with focus on the effects of tropical hydrology. 3. The PHS relationship to the IHRS/F. An evaluation of the new Technical University of Denmark (DTU-Space) and NAMRIA-developed PGM, was done to provide a quality baseline for managing the progression and limitations of a gravimetric geoid-based height system for the country. Statistical measures show that points clustered in the southern latitudes and eastern longitudes have relatively higher residuals due to geodynamic and hydrologic activity. It is concluded that a localised PGM can be used for third order applications. Tropical effects on the reference frame and the geoid were examined. Displacements were analysed by estimating tidal and non-tidal loading for selected Philippine active geodetic stations using rain sensor data, local geologic information and ground validation. The mean dynamic topography (MDT) was also investigated. DTU10, VM500-ph and RADS-ph were compared with GNSS-geoid MDTs (GNSS-PGM2016.66, GNSS-EIGENGL05C). A nationwide scale, low-resolution Philippine vertical ground motion map inferred from Sentinel-1A scenes from January 2015 to December 2019 was also produced. Estimations confirm the intensity of land motion in the eastern and southern part of the country. Using Gravity Recovery and Climate Experiment (GRACE) temporal models, large variations for two IHRS/F-proposed Philippine stations were computed and show coincidence with high rainfall records. A causality relationship between high rainfall and geoid variation, however, is inconclusive. Lastly, a novel way of characterising local height systems relationship for the IHRS/F that takes into account the non-homogenous states of geodetic development within a developing, archipelagic country is introduced. Recommendations for a modernised Philippine Height System were made as a result of this study.

  • (2020) Morsalin, Sayidul
    Thesis
    Electrical insulation of high voltage (HV) power equipment plays essential roles in sound functioning and reliability of power systems. Examining the insulation condition through various diagnostic testings such as dielectric response (DR) and partial discharge (PD) measurements may be able to reveal the presence of defects and degradations in the insulation. Very low frequency (VLF- 1 Hz or lower) applied voltage has emerged as a promising diagnostic tool as it significantly reduces the required reactive power from the test supply. However, the existing interpretation knowledge at conventional power frequency (PF) 50 Hz cannot be directly applied to understand test results in the VLF range. This is the main motivation of the research which explores the dielectric behaviours and associated physical processes under VLF excitation. For dielectric response, experimental studies were carried out on short sections of medium voltage service-aged cross-linked polyethylene (XLPE) cables to diagnose the bulk insulation condition, such as the measurement of dissipation factor, polarisation and depolarisation current, frequency domain spectroscopy, activation energy etc. Experimental results show that dielectric behaviours of electric insulation are influenced by several factors including the excitation frequency, voltage amplitude, ambient temperature, dipolar processes (e.g. conduction and polarisation) etc. An empirical physical model describing the loss-factor measurement based on well-known dipolar theories is developed and verified by experimental results. Different partial discharge processes (e.g. cavity, surface and corona) are also investigated at both VLF (0.1 Hz) and 50 Hz applied voltage. Measurement results are presented with the phase-resolved image and show that discharge characteristics (inception voltage, magnitude and repetition rate) are strongly dependent on the applied frequency. Based on the finite element analysis (FEA) method, a dynamic model to simulate the discharge behaviours in the cavity or on the degraded surface is developed to examine the frequency dependence. The main contributions of this research include the measurement and modelling of both the dielectric response and partial discharge in electrical insulation. The research findings provide valuable information to understand the diagnostic characteristics at very low frequency excitation.

  • (2020) Yan, Yitao
    Thesis
    The rapid development of technology has made the design, monitoring and data storage of large-scale, complex interconnected systems possible. These efficient and economical interconnected systems come with a price: the complex dynamics due to convoluted interconnections make the effective control of such a system incredibly difficult. The behaviour of the subsystems in a network is vastly different than that when it is not, and the inherent uncertainties due to modelling errors may be amplified as a result of the strong interactions. Furthermore, the ability to collect and process large amount of data leads to the paradigm shift from model-centric description to data-centric description or hybrid model/data description of a system. These challenges necessitate the need for a unified foundation for the control of complex systems that is able to admit descriptions of systems not only limited to the conventional differential/difference models. Motivated by these challenges, this thesis aims to develop such a framework for the distributed control of an interconnected system using the behavioural systems theory. As a theory that focuses on analysing the dynamics of the external variables and places the trajectories admissible within the system as the central role of describing a dynamical system, it is perfect for the construction of a platform that unifies various classes of systems and is effective in the analysis of interconnections. The framework is eventually set up as a completely representation-free structure, allowing for free choice of representations for the systems according to the specific needs. Algorithms for several representation structures are also provided. For the case where the subsystems are represented as linear time-invariant differential systems while the global requirements are specified as H-infinity type conditions, the control design follows a two-step algorithm. Firstly, the behaviours of the subsystems, the (to-be-designed) controllers as well as the global requirements are all represented as dissipative dynamical systems with quadratic supply rates, from which the (to-be-determined) controller supply rates can be found. Secondly, parametrisations of the supply rates are carried out to search for linear time-invariant representations for the controllers. Algorithms for subsystems with various types of parametric uncertainties are given to add robustness to the controllers. The resulting framework deals with interconnections, uncertainties in the subsystems and disturbance attenuation simultaneously. For the general framework, neither the subsystems nor the controllers have prescribed representations. The behaviours of the subsystems are denoted by their respective sets of trajectories and interconnections are interpreted entirely as variable sharing instead of signal flows. Furthermore, the network of an interconnected system is also defined as a dynamical system with its own behaviour, leading to a generic, scalable and flexible representation of the interconnected behaviour. From this structure, necessary and sufficient conditions for the existence of the controller behaviours can be given and all distributed controller behaviours can be constructed explicitly. This framework unites various representations and descriptions of the features of dynamical systems as behaviours, thereby allowing for the formation of a hybrid platform for the analysis and distributed control generically and systematically.

  • (2020) Holland, Sophie
    Thesis
    Anaerobic microbial metabolism of dichloromethane (DCM; CH2Cl2), quaternary amines, and methanol has important implications for carbon and nitrogen cycling in oligotrophic environments and the atmospheric flux of climate-active trace gasses. A novel, strictly anaerobic member of the Peptococcaceae family, strain DCMF, is the dominant organism in a DCM-fermenting enrichment culture (DFE) and one of very few known bacteria capable of fermenting DCM to the innocuous end product acetate. Long read, whole genome sequencing provided a single, circularised 6.44 Mb chromosome for strain DCMF, which contains 5,772 predicted protein-coding genes including an abundance of MttB superfamily methyltransferases. Genomic comparison of anaerobic, DCM-degrading bacteria provided a relatively small core genome, including the Wood-Ljungdahl pathway. Strain DCMF is the first non-obligate anaerobic DCM-degrading bacterium. Genomic, physiological and proteomic experiments confirmed that it is an anaerobic methylotroph, able to metabolise DCM, methanol, and methyl groups from quaternary amines via the Wood-Ljungdahl pathway. The quaternary amine choline was converted to glycine betaine, which was demethylated to sarcosine with a glycine betaine methyltransferase, then reductively cleaved to methylamine and acetate. Methanol (via a methanol methyltransferase) and DCM were fermented to acetate. Comparative proteomics revealed a methyltransferase system that was significantly more abundant in cells grown with DCM than glycine betaine. The novel, putative DCM methyltransferase genes are highly conserved between anaerobic DCM-degrading bacteria. Genomic and physiological evidence support placement of strain DCMF in a novel genus, for which we propose the name ‘Candidatus Formamonas warabiya’. Cohabiting bacteria in the DFE community have persisted despite repeated attempts to isolate strain DCMF, yet strain DCMF-free enrichments demonstrated that most are unable to utilise DCM, quaternary amines, or methanol. Five MAGs were generated from the long-read sequencing data and a metaproteogenomic approach suggested that the cohabiting organisms persist in the culture via necromass fermentation, i.e. oxidation of carbohydrates, proteins, and sugars released from expired strain DCMF cells. The DFE culture is a long-term stable-state community that highlights interactions between foundation species and supporting bacteria, as well as important pathways of carbon and nitrogen cycling.

  • (2020) Wu, Chenyu
    Thesis
    Photo-controlled polymerisation uses a photo-excited photocatalyst (PC) to reversibly and deactivate the propagating species. Under regulation by light, photo-controlled polymerisation features temporal control, spatial control, sequence control and high level of selectivity/orthogonality between different systems, leading to a range of applications in advanced macromolecular synthesis such as surface patterning, 3D/4D printing, polymeric micelles, multiblock antimicrobial polymers with precise sequences and architectures. All these unique features of photo-controlled polymerisation are largely dependent on properties and functionalities of PCs. Traditionally, the selection and discovery of appropriate PCs rely heavily on a trail-and-error approach, where extensive experimental screening is needed to identify desired candidates. To reduce costs and circumvent the challenges in laborious experimental work, a rational design strategy emerged where a new PC in application to a photo-controlled polymerisation system can be designed based on understanding of the structure-property-performance relationships. This dissertation aims to enable and streamline a general fully computer-guided rational strategy of designing an efficient and functional PC for a commonly used photocontrolled polymerisation technique, namely photoinduced electron/energy reversible addition-fragmentation chain transfer (PET-RAFT) polymerisation. This thesis starts from using naturally evolved Chl a with various functional substituents and investigating its photocatalytic performance and functionalities in PET-RAFT polymerisation. General orientations for the design of PET-RAFT PCs were inspired from this natural design. On top of this, comprehensive structure-property-performance relationships were established at the quantum chemical level as guiding principles for rational PC design of PET-RAFT polymerisation, by combining experimental and computational studies on a library of halogenated xanthene dyes. Finally, by implementing the most cutting-edged quantum chemical software packages, the fully computer-guided strategy of functional PC design for PET-RAFT polymerisation was enabled based on broadened structure-property-performance relationships. As an example, an efficient pH-switchable organic PC was designed. Application of this rationally designed PC in PET-RAFT polymerisation resulted in the first organocatalysed pH and light dual-gated controlled polymerisation.

  • (2020) Moradi, Marjan
    Thesis
    Millimeter wave networks promise to offer ultra-fast internet download speed, but the access points or base stations must always align the beams precisely to client devices. Efficient beam alignment for mobile users therefore is considered one of the most challenging problems facing millimeter wave networks. Existing approaches that use in-band beam alignment suffers from long alignment delays and low communication performance, especially when large number of mobile clients are connect to the access point. In this research, we explore the benefits of out-of-band inaudible sound assisted beam alignment to reduce the outage probability, thereby improving the performance gain of antenna in millimeter wave beamforming. In particular, this thesis makes three fundamental contributions. First, we analytically study the beam alignment performance of 802.11ad in the presence of multiple devices while rotating with an applicable angular velocity. We come up with a probabilistic model for required number of beacon intervals to complete antenna training in multi-users scenario for 802.11ad. Second, we propose to take advantage of inaudible sound as a side channel to detect the direction of client and assist beam alignment in millimeter wave access points. Using a combination of experimental and simulation analysis of the inaudible sound spectrum available in typical mobile phones, we demonstrate that the use of 50 Hz and 50 ms sound chirps with an array of two microphones provide efficient and reliable detection of direction. Moreover, we design a filtering approach using FDM channel access to correctly assign the sound source corresponding to the estimated angle on the receiver side. Third, we conduct a comprehensive simulation in order to evaluate the performance of the proposed sound assisted beamforming on the gain of antenna. \deleted{Initially, the proposed analytical model is validated by the developed simulation platform.} We show that our proposed algorithm achieves a significant 11 dB average gain of antenna for AP with 64 antenna sectors serving 10 users moving with walking speed of two different mobility model compared with IEEE 802.11 ad. This improvement is the result of using the proposed contention-free out-of-band sound channel to remove the existing contention-based channel access for beam alignment. We believe that our findings in this thesis shed new light on the fundamental benefits of out-of-band beamforming in crowded millimeter wave network.