Doctoral Theses
Permanent link for this collection
The Doctoral Theses collection contains digital copies of AUT doctoral theses deposited with the Library since 2004 and made available open access. All theses for doctorates awarded from 2007 onwards are required to be deposited in Tuwhera Open Theses unless subject to an embargo.
For theses submitted prior to 2007, open access was not mandatory, so only those theses for which the author has given consent are available in Tuwhera Open Theses. Where consent for open access has not been provided, the thesis is usually recorded in the AUT Library catalogue where the full text, if available, may be accessed with an AUT password. Other people should request an Interlibrary Loan through their library.
Browse
Recent Submissions
Now showing 1 - 5 of 1568
- ItemCompensating for Signal Saturation Due to Electrostatic Noise in Electroencephalogram (EEG) Acquisition(Auckland University of Technology, 2024) Heidarian, MahdiThe electroencephalogram (EEG) is a non-invasive tool for monitoring the electrical activities of the brain for different applications from clinical and neurological research to brain-computer interface (BCI) platforms. EEG can be acquired by different types of electrodes like wet, dry contact, and capacitive electrodes. Although wet/gel electrodes are the gold standard for EEG recording in clinical applications and for short periods of tests, they are not a preferred option during continuous daily activities and for wearable gadgets. Shortcomings of gel electrodes and the critical role of prompt response after brain stroke, have inspired researchers to design dry electrodes and try to make them more compatible with wearable EEG measurement systems. Dry EEG electrodes can record the signals through galvanic contact to the scalp skin or capacitively without a direct connection to the skin. The electrode-tissue impedance (ETI) in both types of dry EEG sensory systems is highly associated with the hair-air domain which can cause erroneous measurements due to unknown impedance characteristics of hair, the potential of having heavy motion artefacts in wearable measurement systems, and hair’s static electricity discharge through the system. These effects can potentially lead to long-term blockage and/or heavy baseline drifts in high-gain front-end dry EEG electrode circuits. The main aim of this study is to evaluate and mitigate the effect of electrostatic noise on dry EEG electrodes. To achieve this, a simulation of an active band-pass filter employing an operational amplifier (op-amp) was conducted. This filter is designed to operate within the EEG frequency band, between 0.72 Hz and 72 Hz. Recognizing the weak nature of EEG signals on the scalp, a gain of 220 was selected. In addition, a simplified lumped model representing the hair-air domain was integrated into the input stage. This model was applied to both contact and non-contact dry electrodes. To mimic electrostatic noise, the human-body model (HBM) based on the MIL-STD 833 standard was employed. This choice aimed to replicate real-world conditions, ensuring a comprehensive simulation. After evaluating the designed amplifiers in normal working conditions, simulations were completed to observe the progression from mild disruption to complete signal loss as the injected charge increased. Furthermore, the relationship between the physical properties of the hair-air domain and the duration of the signal disruption was evaluated. Moreover, to validate the simulation outcomes, the printed circuit board (PCB) layout of the simulated circuits was manufactured and tested. The experiment results are aligned with the simulation results. The electrostatic noise was injected into the circuit using a manufactured electrostatic discharge (ESD) simulator that is capable of injecting charge with MIL-STD 833 standard characteristics. Once the simulation results of destructive effects of the electrostatic noise were confirmed, compensation measures were devised and implemented on the PCBs to mitigate the impact of electrostatic charges. In dry contact electrodes, a discharge pathway was established to facilitate the dissipation of the charge. For dry non-contact electrodes, the compensation approach encompassed a detection/control unit capable of detecting saturation in the amplification stage, along with a Howland current pump, which, in combination, served to elevate the input baseline and expedite the return to normal operational conditions within a shorter timeframe. The effectiveness of these compensation strategies was subjected to testing and validation using the developed PCB layouts, and the ESD simulator. Conclusively, a homogenous human head phantom made of gelatine and covered with genuine Remy human hair was used. This setup served to assess the electrodes’ capability to replicate human hair conditions. To introduce electrostatic charges, an IMCS 2600 ESD gun was employed. Subsequently, the dry contact EEG electrode, both with and without compensation techniques, was employed to capture signals and appraise the effectiveness of the designed dissipation path. During the experiments, the signal loss occurred on the contacted EEG electrodes without the compensation strategy, although the duration was comparatively shorter than observed in the PCB circuit experiments. The compensation strategy proved effective, eliminating signal loss entirely by providing a discharge path, as confirmed by the simulation results. The results of this PhD research introduce a novel method to decrease the signal blockage duration in active dry EEG electrodes, rendering them more viable for integration into wearable biopotential measurement devices.
- ItemCellulose-Based Surfactants: Designing Particle-Based Surfactants for Sustainable Applications(Auckland University of Technology, 2024) Tiban Anrango, Bryan AndresSurfactants are versatile chemicals used in a wide variety of everyday goods, ranging from personal care products to pharmaceuticals. Their usefulness lies in their amphiphilic nature, which makes them essential for any product where oil and water are required to mix and form a stable mixture. In 2023, their market size was valued at USD 30 billion, with expected growth of 10% by 2033. To date, the majority of the market is dominated by molecular surfactants obtained partially or wholly from the petrochemical industry. Current efforts are focused on replacing traditional surfactants with greener alternatives, especially from renewable sources, without compromising on performance. In recent decades, there has been a surge of interest in the use of solid particles as emulsifiers. The resulting oil/water mixtures are known as Pickering emulsions, and are particularly stable due to the localisation of the particles at the oil/water interface, which forms a physical barrier that prevents coalescence. The Pickering emulsifiers currently in commercial use are all particles with homogeneous wettability. However, it has been demonstrated that particles with dual wettability have the potential to decrease the interfacial energy further and act as even more effective emulsifiers. Research in this area has predominantly focused on metallic, silica, plastic, and inorganic materials. This thesis set out to investigate the synthesis of cellulose Janus nanospheres with dual wettability by the partial modification of the particle surface via the use of Pickering emulsions. Chapter 2 investigates the key parameters for the formation of hydrophilic spherical nanocellulose particles (SNC) and their partial surface functionalization with hydrophobic alkyl chains. Partial modification relied on the ability of SNCs to form oil-in-water Pickering emulsions, with the particles sitting at the oil/water interface, with one face wetted by water and the other wetted by oil. A lipophilic modifier was added to the oil phase, resulting chemical modification on a single hemisphere, allowing the synthesis of amphiphilic Janus cellulose nanospheres. One of the more significant findings to emerge from this study is that the amphiphilicity of the particles could be tuned by changing the lipophilic modifier and changing the reaction time to modify the degree of chemical modification. Furthermore, our modified particles showed enhanced surface activity compared to hydrophilic nanospheres, likely attributable to the particles’ dual affinity. Following optimisation of the reaction parameters, we demonstrated that this chemical modification improved the emulsification properties of the particles, as oil-in-water emulsions obtained with our nanospheres showed superior performance than the commercial surfactant polyoxyethylene (10) oleyl ether (Brij O10). Chapter 3 presents an alternative method of producing amphiphilic cellulose nanoparticles that involves an initial complete esterification of the cellulose surface, followed by cleavage of the esters from a single hemisphere to produce Janus particles. We found that the completely esterified particles had a high degree of substitution (higher than for the etherified particles) and were able to efficiently stabilise water-in-oil (inverse) emulsions. Prior to this study, few examples have described the use of bio-derived nanoparticles as water-in-oil Pickering emulsifiers. The partial cleavage of the esters from these nanospheres was achieved by the addition of NaOH to the water phase to achieve hydrolysis on the single hemisphere wetted by water. The degree of cleavage could be controlled by the reaction time, resulting in changes in the amphiphilic nature of the particles and their emulsification properties. Although this work was limited to the application of our particles as bio-based emulsifiers, these results highlight the potential of this partial modification methodology as a simple way to synthesise cellulose nanospheres with adjustable hydrophilic-hydrophobic balance that mimics the action of surfactants with different hydrophobic-hydrophilic balance (HLB). In addition, the synthesis of Janus particles by using Pickering emulsions to partially mask particles on the nanoscale is methodology that can be extended for the synthesis of anisotropic nanoparticles from a range of other materials.
- ItemHospitality in Tang Dynasty China (618 – 907)(Auckland University of Technology, 2024) Zhang, QingyiHospitality has played a significant role throughout human history, yet there is a lack of interest and understanding of its history in both academic and industrial spheres. This phenomenon is particularly intriguing considering that hospitality has become a crucial economic pillar in many countries, while the fundamental values of opening a door and welcoming guests, inherited from our ancestors, seem to be forgotten. In China, this phenomenon is especially thought-provoking. Although the hospitality industry in contemporary China has adopted Western models and management experiences, it has overlooked the rich historical knowledge of hospitality practices deeply rooted in its own culture. To fill this knowledge gap, this study explored the phenomenon of hospitality during the Tang dynasty in Chinese history, uncovering historical facts to remind people of the profound role historical reflection plays in the development of hospitality and human society. This research focused on the Golden Age of Chinese history: the Tang dynasty (618 – 907). The Tang dynasty was characterised by political stability, economic prosperity, and a flourishing culture. It established a relatively enlightened political system, implemented the imperial examination system, and facilitated economic prosperity through thriving trade and a robust infrastructure. Culturally, the Tang dynasty witnessed the emergence of many outstanding literary figures and painters, leaving behind a rich cultural legacy. Moreover, the Tang dynasty's openness and inclusiveness facilitated extensive exchanges with neighbouring countries and regions, contributing to the integration of Eastern and Western civilisations and profoundly influenced global politics and culture. In the Tang dynasty, hospitality emerged as an integral part of people's lives and a vibrant and colourful aspect. Exploring hospitality in such a socio- cultural context facilitates observations of a mature form of hospitality in Chinese history, providing a foundation for further research in the field. To closely observe hospitality in the lives of Individuals in the Tang dynasty, this study relied on the analysis of Tang Dynasty notes. The Tang Dynasty notes, typically recorded by individuals, contain personal observations, experiences, and thoughts, with folklore and anecdotes collected from Tang society, covering various aspects of politics, society, culture, and customs. Through a thematic analysis within the Interpretivism research paradigm, this study systematically explored Tang Dynasty notes to understand the Individuals in the Tang dynasty's hospitality activities. The study revealed widespread participation in hospitality activities across various social strata in the Tang dynasty. Participants dynamically constructed the roles of hosts and guests based on their various social identities, motivations, and purposes. Hospitality activities in the Tang dynasty exceeded stereotypical impressions, serving not only basic functions such as providing food, accommodation, and beverages but also fulfilling experiential and social functions. Consequently, hospitality became a vital avenue for the production, distribution, consumption, and reproduction of social resources and interpersonal relationships in Tang dynasty society. Beyond its diverse content, hospitality in the Tang dynasty embodied a spirit of mutual existence, co- construction, and co-enjoyment between hosts and guests, with a deeper focus on the well-being of both parties and the overall harmony of society. Exploring hospitality in the Tang dynasty not only prompts reflection on contemporary hospitality practices but also underscores the critical role of hospitality in fostering interpersonal interactions and social harmony.
- Item‘Oli ‘Ula: Housing the Kronfeld Collection Through Moving-Image Practice(Auckland University of Technology, 2024) Parr, EmilyBetween the late 19th and early 20th centuries, the Kronfeld Collection was assembled by my great-great-grandparents, Gustav and Louisa Kronfeld, a Jewish merchant and a Samoan matriarch. As European empires expanded throughout Moana Oceania and settler and Indigenous worlds collided, the taonga, measina, and treasures travelled to ‘Oli ‘Ula, the Kronfeld family home in Tāmaki Makaurau Auckland. The ‘oli tree, once cultivated in Sāmoa, has fragrant red flowers; ‘ula can mean necklace, joyful, or red. The name ‘Oli ʻUla, likely given to the house by Louisa, is suggestive of these red flowers, or a garland of them. Encircled by this symbolic garland, the taonga, measina, and treasures of the Collection adorned the walls of the house. Later, they entered Aotearoa New Zealand’s public museums. This practice-based research digitally ‘houses’ selected taonga and measina from the Collection through moving-image artworks. Utilising Māori Marsden’s ‘woven universe’ (2003) and Epeli Hau‘ofa’s ‘sea of islands’ (1994) as relational frameworks, the project extends Moananui notions of the house into the digital realm. The thesis proposes that whakapapa (genealogy) and vā (relational space) are forms of provenance, and that enlivening the systems of relation of museum collections is critical in transforming their futures. Retracing the Collection’s movements to understand the forces that propelled them, the research addresses imperial collecting practices in Moana Oceania and looks to ancient reciprocal networks through which treasures circulated. Engaging Lana Lopesi’s concept of ‘Moana Cosmopolitanism’ (2021) and related notions of roots and routes, the project considers the future of the Kronfeld Collection and imagines decolonial museum ecologies. The practice enacts the reciprocity of the gift, generations later, and brings the Collection ‘into the light.’ Through archival research and moving-image practice, this project develops a tuitui (sewing, threading, binding) methodology, linking the reparative nature of sewing the fabric of the universe (Marsden, 2003) with Paul Tapsell’s metaphor connecting taonga, stitching, and the flight of the tūī (1997). The artworks, articulated as ‘cosmospheres,’ render taonga and measina as three-dimensional point clouds, and immerse them in kaleidoscopic moving-image ‘lifeworlds.’ The research proposes that through tuitui, the rendering of ancestral treasures using contemporary technologies might offer a form of repair within a woven universe.
- ItemA Spiking Neural Network Architecture for Localizing Event-Trigger Indoor Moving Sound Sources(Auckland University of Technology, 2024) Roozbehi, ZahraImagine being blindfolded in a room and hearing a voice fading and moving around. How do we track the sound's origin and distance, and how do we distinguish what is being said? What computational methods and techniques exist for addressing this problem? Sound source localization refers to acoustic methods and technology for determining sound source in a three-dimensional space. However, existing methods struggle in real-world scenarios with background noise and multiple moving sound sources. In the domain of real-time applications, researchers continue to face challenges in sound source tracking and classification. The aim of this thesis is to introduce and evaluate a novel approach based on spiking neural networks to address the challenge of sound localization in dynamic environments. We present the adaptive resonance theory-based reservoir spiking neural network (ART-rSNN) and demonstrate its application in real-time, multi-source sound detection and classification. Extensive simulations comparing our approach with other conventional machine learning models reveal that these models have some problems in categorizing and detecting sound events with multiple sources in real-time in comparison to our approach. The ART-rSNN can dynamically and autonomously adjust its neuron configuration based on received sound cues. This dynamic characteristic enables it to concentrate computation exclusively in the vicinity of estimated sound sources – a departure from static methods. Overall, our framework handles the challenges of spatio-temporal data analysis required for this task while demonstrating adaptability in managing changing acoustic environments. What sets our work apart is its reliance on the measured power of sound without necessitating prior spatial sound source data for supervised learning. This distinctive feature improves the performance of our approach, especially in scenarios where other deep-learning approaches struggle to handle multiple sound sources using only time-domain raw signals. In conclusion, the dynamic adaptability of our ART-rSNN, coupled with its performance in noisy environments and multi-source scenarios, positions it as a promising advancement in the field of AI-based approaches to sound localization and classification.