Science

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  • (2022) Zhang, Qi
    Thesis
    As a dominant terrestrial ecosystem of the Earth, forest environments play profound roles in ecology, biodiversity, resource utilization, and management, which highlights the significance of forest characterization and monitoring. Some forest parameters can help track climate change and quantify the global carbon cycle and therefore attract growing attention from various research communities. Compared with traditional in-situ methods with expensive and time-consuming field works involved, airborne and spaceborne remote sensors collect cost-efficient and consistent observations at global or regional scales and have been proven to be an effective way for forest monitoring. With the looming paradigm shift toward data-intensive science and the development of remote sensors, remote sensing data with higher resolution and diversity have been the mainstream in data analysis and processing. However, significant heterogeneities in the multi-source remote sensing data largely restrain its forest applications urging the research community to come up with effective synergistic strategies. The work presented in this thesis contributes to the field by exploring the potential of the Synthetic Aperture Radar (SAR), SAR Polarimetry (PolSAR), SAR Interferometry (InSAR), Polarimetric SAR Interferometry (PolInSAR), Light Detection and Ranging (LiDAR), and multispectral remote sensing in forest characterization and monitoring from three main aspects including forest height estimation, active fire detection, and burned area mapping. First, the forest height inversion is demonstrated using airborne L-band dual-baseline repeat-pass PolInSAR data based on modified versions of the Random Motion over Ground (RMoG) model, where the scattering attenuation and wind-derived random motion are described in conditions of homogeneous and heterogeneous volume layer, respectively. A boreal and a tropical forest test site are involved in the experiment to explore the flexibility of different models over different forest types and based on that, a leveraging strategy is proposed to boost the accuracy of forest height estimation. The accuracy of the model-based forest height inversion is limited by the discrepancy between the theoretical models and actual scenarios and exhibits a strong dependency on the system and scenario parameters. Hence, high vertical accuracy LiDAR samples are employed to assist the PolInSAR-based forest height estimation. This multi-source forest height estimation is reformulated as a pan-sharpening task aiming to generate forest heights with high spatial resolution and vertical accuracy based on the synergy of the sparse LiDAR-derived heights and the information embedded in the PolInSAR data. This process is realized by a specifically designed generative adversarial network (GAN) allowing high accuracy forest height estimation less limited by theoretical models and system parameters. Related experiments are carried out over a boreal and a tropical forest to validate the flexibility of the method. An automated active fire detection framework is proposed for the medium resolution multispectral remote sensing data. The basic part of this framework is a deep-learning-based semantic segmentation model specifically designed for active fire detection. A dataset is constructed with open-access Sentinel-2 imagery for the training and testing of the deep-learning model. The developed framework allows an automated Sentinel-2 data download, processing, and generation of the active fire detection results through time and location information provided by the user. Related performance is evaluated in terms of detection accuracy and processing efficiency. The last part of this thesis explored whether the coarse burned area products can be further improved through the synergy of multispectral, SAR, and InSAR features with higher spatial resolutions. A Siamese Self-Attention (SSA) classification is proposed for the multi-sensor burned area mapping and a multi-source dataset is constructed at the object level for the training and testing. Results are analyzed by different test sites, feature sources, and classification methods to assess the improvements achieved by the proposed method. All developed methods are validated with extensive processing of multi-source data acquired by Uninhabited Aerial Vehicle Synthetic Aperture Radar (UAVSAR), Land, Vegetation, and Ice Sensor (LVIS), PolSARproSim+, Sentinel-1, and Sentinel-2. I hope these studies constitute a substantial contribution to the forest applications of multi-source remote sensing.

  • (2022) Goyal, Rishav
    Thesis
    The Southern Hemisphere extratropical westerly winds are the strongest time-averaged surface winds on Earth, having a profound impact on weather systems, ocean circulation, Antarctic sea-ice as well as oceanic uptake of heat and carbon. The westerly winds have shown poleward intensification in the last few decades driven primarily by stratospheric ozone depletion with a secondary role played by increasing greenhouse gases. In recent years we have seen early signs of ozone recovery as a result of the Montreal Protocol. Part 1 of this thesis demonstrates that by curbing CFC emissions, the Montreal Protocol also played a critical role in mitigating future surface climate change, equivalent to approximately 25% reduction in global surface warming by 2050. A major feature of the Southern Hemisphere extratropical atmospheric circulation is its strong zonal coherence. However, there are notable zonal asymmetries embedded in the flow, with two important examples being the zonal wave 3 (ZW3) and Amundsen Sea Low (ASL). Although these features have received significant attention from the scientific community, the mechanisms responsible for their presence are still not clear. In Part 2, model experiments suggest that the ZW3 pattern is generated remotely by tropical deep convection and not by the presence of three extratropical landmasses as had previously been assumed. Quantification of ZW3 impacts requires a way to consistently characterize this variability. In Part 3, I formulate a new index for ZW3 which accounts for variability in the structure, phase and amplitude of ZW3. In Part 4, I provide evidence that in contrast to ZW3, the ASL is generated primarily by the interaction between westerly winds and Antarctic orography. Zonally asymmetric features are not only present in the mean circulation but also in the past and projected westerly wind changes in the Southern Hemisphere. These are characterized in Part 5 in reanalysis and models. Following on from this, I demonstrate in ocean model simulations that future projected zonally asymmetric atmospheric changes can drive substantial changes in the ocean circulation in the Pacific and Indian Oceans, accounting for more than 30% of the projected surface ocean warming around parts of Australia (Part 6).

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

  • (2022) Boldbaatar, Jigmidmaa
    Thesis
    Sexual conflict could play an important role in shaping spatial variation in sex ratio in facultatively parthenogenetic species. This is because if females of such species avoid mating, they can establish all-female populations via parthenogenetic reproduction. By contrast, if females cannot avoid mating (i.e., males), they reproduce offspring of both sexes and establish mixed-sex populations in the wild. In Australia, natural populations of Megacrania batesii exhibit extreme spatial variation in sex ratio, with all-female and mixed-sex populations occurring over a small scale. However, it is unclear how facultatively parthenogenetic females avoid mating and establish all-female populations. Sex-specific patterns of dispersal could play a role because, depending on whether females are mated or unmated, they could establish mixed-sex and all-female populations if they successfully disperse to new areas. However, if males invade all-female populations, they could convert these populations into mixed-sex populations via mating. In chapter one, I therefore investigated dispersal rate of females and males from a mixed-sex population and single females from an all-female population. I found that females from the all-female population were less dispersive than females and males from the mixed-sex population. I also found that dispersal was limited to movement within habitat patches. Additionally, in chapter two, I examined whether costs associated with mate guarding (which is widespread and long-lasting in M. batesii) imposes energetic costs on females (i.e., reduction in foraging rate) because guarded females carry males. If females’ foraging rates were impacted by guarding males, mate guarding could be a manifestation of sexual conflict in M. batesii. However, I found little evidence that laboratory-reared females from mixed-sex populations fed more while unpaired than while paired with males. Overall, these studies contribute insights into how sex-specific dispersal and costs of mating and guarding might contribute to sexual conflict and variation in sex ratio in natural populations of the facultative parthenogenetic species, M. batesii.

  • (2022) Zhang, Jun Ze
    Thesis
    This thesis investigates some properties of complex structures on Lie algebras. In particular, we focus on nilpotent complex structures that are characterized by a suitable J-invariant ascending or descending central series dj and dj respectively. In this thesis, we introduce a new descending series pj and use it to give proof of a new characterization of nilpotent complex structures. We examine also whether nilpotent complex structures on stratified Lie algebras preserve the strata. We find that there exists a J-invariant stratification on a step 2 nilpotent Lie algebra with a complex structure.

  • (2022) Ayshan, Han
    Thesis
    Video game trailers are an effective promotional form of intermediation that enables audiences to navigate and engage with old and new media. Although video game trailers function as advertisements designed to sell a game, they are also stories that provoke social media commentary and debate. Trailers aim to draw the viewer in, convey sound and imagery, and evoke an involuntary reaction of excitement and awe. In this thesis, I will be using the games Fallout 4, Watch Dogs 2, and Assassin’s Creed: Syndicate. In the case studies, I investigate how viewers make sense of the promotional and storytelling aspects of video game trailers. I examine how video game trailers have the potential to arouse emotions and interest before viewers even play the game. Trailers provide an insight into the basic gameplay, not only into the gameplay but also into the story and the characters (protagonists and antagonists). They show audiences the video game theme genre and provide the viewer with a visual and auditory tool to entice possession. This project explores these themes, showing how video game trailers have an inherited cinematic quality but also how trailers actually spend little time presenting actual gameplay. There is a clear connection with movie trailers, teasing the events that will take place in the game and asking the player what will happen next. In this study, I used the methods of narrative analysis and textual analysis to analyse comments from YouTube, Facebook, and a survey of video gamers. The textual analysis of the trailers raises questions of representation and authenticity. In this research, I identified an incongruity between the representation of the core features of a game and the promotion of those features in the trailer. The narrative analysis of the trailers focused on storytelling and emplotment in the trailers. A key theme that has emerged from the analysis is that superheroes engage in vigilantism, a justifiable form of self-administered violence. Gamers may feel at ease with the violence used to correct perceived injustices. There is potential for gamers to consider the moral grey area of vigilante violence and romanticised vigilantism. With their enhanced ability to simulate complex interactive narratives for actual and simulated authenticity, video games offer a sophisticated engagement with players that contributes significantly to their widespread and universal support. The role of culturally created characters in the experience of playing a video game helps stimulate philosophical research. I explore whether normative audience expectations can speed up the development of cultural expectations about the relationship between the player and the narrative of the game and its audience. In this context, I examine case study video game trailers and ask what it means to revise our understanding of the relationship between power, law, and morality while playing the game. I examine and critique how the narrative, and thus the mechanics of a specific game, shapes our understanding of connection, power, law, or morality; I contend that prestige reflects normative privilege and law.

  • (2022) Chou, Yu-Hsiang
    Thesis
    The traditional ITO-based transparent conductive films and electrodes have been widely applied in many fields and used in various electronics in the past decades. However, its brittle property and costly manufacturing process limit the development of ITO for next-generation electronic devices, which need the features of light weight, flexibility, and low cost. Silver nanowires have attracted considerable attention from researchers among many candidates due to their outstanding electrical, mechanical, and optical properties. Many synthesis methods of AgNWs have been demonstrated recently, but there are still some parameters that are unclear and need further investigations. In this thesis, one-step solvothermal synthesis of AgNWs has been studied and explored. AgNWs with a high aspect ratio (~2000) were successfully obtained by using this method. The morphology of AgNWs was significantly affected when tuning the different factors, including the heating temperature of PVP dissolution, the molar ratio of PVP/AgNO3, the molecular rate of PVP, and the concentration of ionic assistants. Moreover, another latest modified polyol method, the Maillard reaction process, has also been introduced and researched in this thesis. The ultra-long AgNWs (~100 μm) were successfully generated through the Millard reaction method using ammonium chloride and glucose as reacting agents of MRPs. Effects of experimental parameters such as reaction time and pressure environment on the morphology of AgNWs have also been investigated. Besides, the extra salt additive (NaBr) was employed to see if the NW diameter would become thinner to achieve the high aspect ratio AgNWs. The NW diameter was greatly reduced when the molar ratio of NH4Cl/ NaBr was at 40:1; however, a large amount of Ag nanoparticles were generated, which could significantly affect the overall performance of AgNWs. The AgNWs-based TCFs were fabricated in this project. With the help of annealing post-treatment, TCFs with low sheet resistance (~22 Ω/sq) and high transmittance (86%) were prepared using the high aspect ratio AgNWs. In addition, the AgNWs were applied to the electrochemical reduction of CO2 to syngas and showed the potential of syngas production. Nevertheless, more factors and studies need to be carried out to improve the Faradic efficiency of syngas production.

  • (2022) Han, Nathan Thomas
    Thesis
    Stimuli generated by a person’s own willed actions generally elicit a suppressed neurophysiological response than physically identical stimuli that have been externally generated. This phenomenon, known as sensory attenuation, has primarily been studied by comparing the N1, Tb and P2 components of the event-related potentials (ERPs) evoked by self-initiated vs. externally generated sounds. Sensory attenuation has been implicated in some psychotic disorders such as schizophrenia, where symptoms such as auditory hallucinations and delusions of control have been conceptualised as reflecting a difficulty in distinguishing between internally and externally generated stimuli. This thesis employed a novel paradigm across five experiments to investigate the role of agency and contingency in sensory attenuation. The role of agency was investigated in in Chapter 2. In Experiment 1, participants watched a moving, marked tickertape while EEG was recorded. In the active condition, participants chose whether to press a button by a certain mark on the tickertape. If a button-press had not occurred by the mark, then a tone would be played one second later. If the button was pressed prior to the mark, the tone was not played. In the passive condition, participants passively watched the animation, and were informed about whether a tone would be played on each trial. The design for Experiment 2 was identical, except that the contingencies were reversed (i.e., pressing the button prior to the mark led to a tone). The results were consistent across the two experiments: while there were no differences in N1 amplitude between the active and passive conditions, the amplitude of the Tb component was suppressed in the active condition. The amplitude of the P2 component was enhanced in the active condition in both Experiments 1 and 2. These results suggest that agency and motor actions per se have differential effects on sensory attenuation to sounds and are indexed with different ERP components. In Chapter 3, we investigated the role of contingency in sensory attenuation while using a similar ticker-tape design in Chapter 2. In the Full Contingency (FC) condition, participants again chose whether to press a button by a certain mark on the tickertape. If a button-press had not occurred by the mark, a sound would be played (one second later) 100% of the time (Experiment 3). If the button was pressed prior to the mark, the sound was not played. In the Half Contingency (HC) condition, participants observed the same tickertape; however, if participants did not press the button by the mark, a sound would occur 50% of the time (HC-Inaction) while if the participant did press the button, a sound would also play 50% of the time (HC-Action). In Experiment 4, the design was identical, except that a button-press triggered the sound in the FC condition. The results were consistent across both Experiments in Chapter 3: while there were no differences in N1 amplitude across the FC and HC conditions, the amplitude of the Tb component was smaller in the FC condition when compared to the HC-Inaction condition. The amplitude of the P2 component was also smaller in the FC condition compared to both the HC-Action and HC-Inaction conditions. The results suggest that the effect of contingency on neurophysiological indices of sensory attenuation may be indexed by the Tb and P2 components, as opposed to the more heavily studied N1 component. Chapter 4 also investigated contingency but instead used a more ‘traditional’ self-stimulation paradigm, in which sounds immediately followed the button-press. In Chapter 4, participants observed a fixation cross while pressing a button to generate a sound. The probability of the sound occurring after the button-press was either 100% (active 100) or 50% (active 50). In the two passive conditions (passive 100 and passive 50), sounds generated in the corresponding active conditions were recorded and played back to participants while they passively listened. In contrast with the results of Chapter 3, the results of Chapter 4 showed both the classical N1 suppression effect, and also an effect of contingency of the N1, where sounds with a 50% probability generated higher N1 amplitudes compared to sounds with 100% probability. In contrast, Tb amplitude was modulated by contingency but did not show any differences between the active and passive conditions. The results of this study suggest that both sense of agency and sensory contingency can influence sensory attenuation, and thus should be considered in future studies investigating this theoretically and clinically important phenomenon.

  • (2022) Peterson, Lindsay
    Thesis
    The light sources in a scene can drastically affect the pattern of intensities falling on the retina. However, it is unclear how the visual system represents the light sources in a scene. One possibility is that a light source is treated as a scene component: an entity that exists within a scene and interacts with other scene components (object shape and object reflectance) to produce the retinal image. The aim of this thesis was to test two key predictions arising from a perceptual framework in which light sources and the objects they illuminate are considered to be scene components by the visual system. We begin examining the first prediction in Chapter 3, focusing on the role of a dynamic shape cue in the interaction between shape, reflectance, and lighting. In two psychophysics experiments, we show that the visual system can "explain away'" alternative interpretations of luminance gradients using the information provided by a dynamic shape cue (kinetic depth). In subsequent chapters, the research focus shifts to the second prediction, investigating whether multiple objects in a scene are integrated to estimate light source direction. In Chapter 4, participants were presented with scenes that contained 1, 9, and 25 objects and asked to judge whether the scenes were illuminated from the left or right, relative to their viewpoint. We found that increasing the number of objects in a scene worsened, if anything, discrimination sensitivity. To further understand this result, we conducted an equivalent noise experiment in Chapter 5 to examine the contributions of internal noise and integration to estimates of light source direction. Our results indicate that participants used only 1 or 2 objects to judge light source direction for scenes with 9 and 25 objects. Chapter 6 presents a shape discrimination experiment that required participants to make an implicit, rather than explicit, judgement of light source direction. Consistent with the results reported in Chapters 4 and 5, we find that shape discrimination sensitivity was comparable for scenes containing 1, 9, and 25 objects. Taken together, the findings presented here suggest that while object shape and reflectance may be represented as scene components, lighting seems to be associated with individual objects rather than having a scene-level representation.

  • (2022) Chen, Yimeng
    Thesis
    In recent years, the source of airport revenue has significantly changed. Accordingly, many airports have adjusted their strategies and focused on increasing retail revenue to improve financial sustainability. However, the literature review in this thesis identified two knowledge gaps: (1) empirical analyses on the effects of airport terminal design on retail revenue, and (2) application of general consumer shopping behaviour models to airport retail development. A two-step approach was developed. First, passenger shopping behaviour models were constructed based on two datasets collected at a case study airport: (1) eye-tracking data identified four types of passenger shopping behaviour—completely planned shoppers, partially planned shoppers, unplanned shoppers, and non-shoppers; (2) passenger questionnaire/interview data provided demographic and travel-related data to construct behaviour models. Second, the validity of the behaviour models was tested through an agent-based simulation model (ABSM) against the collected data. Next, the ABSM was used to examine the combined effects of passenger-related factors and terminal-related factors on retail revenue using five scenario studies. The results of the two-step approach revealed several significant findings. First, the passenger mix significantly affects retail revenue. Second, retail revenue could increase by 30% if passengers’ ‘visual distance’ was increased. Although passengers have limitations in their physical visual distance, it could be increased by providing information on retail offerings to passengers (e.g. interactive floor maps, mobile apps to provide retail information). Third, a 1% increase in dwell time could result in a 1.06% increase in retail revenue. Fourth, a sub-optimal terminal layout design could lead to a USD 57 million loss in potential annual retail revenue. Finally, adopting a centralised terminal layout could lead to a 7% increase in retail revenue. This thesis highlights the potential economic benefits of a well-designed terminal with a retail focus. In addition, this thesis demonstrates the feasibility and the potential of the proposed two-step approach in improving the existing retail configuration within airport terminals while maintaining the aeronautical functions. In conclusion, future terminal design guideline could be improved by adopting the two-step approach in designing a more retail-friendly terminal, which will contribute to the financial sustainability of the airport business.