70040 research outputs found
Sort by
Negotiation of unlicensed spectral resources by independent wireless network operators
Get PDFThe broadcast nature of wireless communication makes it prone to signal interference, particularly in the license-exempt part of the radio spectrum. This unlicensed spectrum is free to use with only the maximum transmit power and a few other parameters being regulated. Billions of devices operate in these frequency bands worldwide today, often in close range from each other, causing performance degradation and security concerns. Particularly in urban environments, many Independent Wireless network Operators (IWOs) vie for scarce spectral resources. One set of solutions encompasses collaboration between IWOs preceded by negotiation. The primary aim of this research is to gain understanding on how IWOs can practically negotiate and share unlicensed spectral resources in an automated manner.
The first challenge in this research is to understand what exactly is the utility that operators can negotiate on. By surveying 68 researchers, we showed that throughput and Signal-to-Interference-plus-Noise Ratio (SINR) are the two most likely candidates, with a preference for throughput. We also concluded that utility is unlikely to be homogeneous among IWOs. The second challenge is therefore to understand how a system with heterogeneous utility demands can be best modelled. For this, we investigated a use case where some or all IWOs demand Physical Layer Security (PLS) in addition to SINR. We modelled this problem as a non-cooperative game with secrecy capacity as its utility function.
By numerical analysis of the model, we evidenced that varying the transmission power is the only strategy the IWOs can apply to optimise SINR under the condition of perfect secrecy. To investigate how the model could optimise secure throughput instead of SINR, we applied a discreet event simulator emulating a real-world environment. The results indicate that IWOs can indeed practically collaborate to achieve secret wireless communications and optimise throughput using today’s equipment.
By defining a multi-dimensional utility function, we then designed a Software-Defined Wireless Network for automated negotiation and collaboration, where multiple agents are tasked with the negotiation on behalf of users. By handing over the decision-making process to the IWOs, we guaranteed the agents' engagement in the process, solving the problem that collaboration cannot be forced upon actors in unlicensed spectrum. We validated our approach by measurements in a simplified implementation based on Wi-Fi
Control of a High-speed (<50,000 rpm) Interior Permanent Magnet Synchronous Motor
Get PDFHigh-speed interior permanent magnet synchronous motors (HS-IPMSMs) play a critical role in modern industrial and automotive applications, yet their performance is often constrained by losses, parameter variations, and deadtime effects. This thesis investigates advanced field-oriented control (FOC) strategies to address these challenges, with a particular focus on improving efficiency and robustness in HS-IPMSM operation.
A comprehensive review of existing control methods highlights the limitations of conventional maximum torque per ampere (MTPA) and loss minimization control (LMC) strategies under parameter variations, particularly in the presence of core loss. To enhance system performance, an improved MTPA strategy that explicitly accounts for core loss is proposed, alongside a novel LMC method that incorporates the partial derivative of core loss resistance with respect to the d-axis current. Analytical and experimental validation on a HS-IPMSM (5kW, 50,000 rpm) demonstrate that these methods effectively reduce electrical losses. Additionally, a hybrid trajectory combining MTPA and LMC is developed to balance efficiency and torque output across varying load conditions.
Further investigation into motor parameter variations reveals their substantial impact on both MTPA and LMC performance. A systematic analysis identifies optimal parameter selection strategies, enhancing robustness in real-world applications. To overcome the limitations of polynomial-fitting-based methods, a novel Taylor-series-based approach is proposed for both LMC and MTPA control method (under torque control mode), enabling real-time adaptation to parameter fluctuations through lookup-table-based online estimation. Experimental results confirm its effectiveness in improving efficiency with negligible influence on dynamic performance.
The thesis also addresses deadtime-induced distortions, proposing a compensation technique for both static inductance measurement and real-time current control. A standstill flux-linkage-based inductance measurement method with deadtime compensation significantly improves accuracy, with results closely aligning with finite element analysis (FEA) and AC standstill test predictions. Moreover, an enhanced deadtime compensation strategy is introduced to mitigate PWM-induced current ripple, achieving substantial reductions in current ripple magnitude and total harmonic distortion (THD).
Collectively, these advancements contribute to the development of more efficient and robust control strategies for HS-IPMSMs, offering improved performance across a wide range of operating conditions. The findings provide valuable insights for the future design and optimization of high-speed motor drive systems, particularly in applications requiring high efficiency with limited computation time
Multiphysics Coupling Analysis of Indicator Gas Variations Induced by Coal Spontaneous Combustion in Longwall Goaf
Get PDFUnderstanding the self-heating behaviour and distribution patterns of indicator gases within longwall goaf is critical for preventing coal mine spontaneous combustion (sponcom). In prior studies, coal self-heating temperature and variations of gas products are often analysed independently, making it challenging to comprehensively reveal their dynamic interrelations. Moreover, the gas emission patterns observed under laboratory conditions are difficult to directly extrapolate to the field environment of a longwall goaf.
To address these challenges, this study integrates Multiphysics coupled modelling with experimental analysis. Firstly, a Multiphysics coupling model is developed to represent the interactions among solid, gas, and thermal processes within the goaf. This model systematically investigates the coupling mechanisms between temperature and gas distributions during coal self-heating, along with their spatiotemporal evolution characteristics. Based on this model, a coal oxidation model incorporating gas products of C2H4 and C2H6 as sponcom gas indicators is introduced, informed by laboratory experimental results. By integrating these two models, this research comprehensively explores the relationships among temperature, gas concentrations, and coal properties during sponcom. The results demonstrate that temperature gradients drive the migration and accumulation of indicator gases, and the sponcom process exhibits a pronounced localisation trend. Combined experimental and numerical simulation findings elucidate the coupling laws governing temperature fields and gas distributions, providing a scientific basis for optimising gas monitoring systems and enhancing the accuracy of identifying coal sponcom.
In summary, this thesis establishes an integrated coal sponcom model that captures the coupled evolution of temperature fields and indicator gas behaviours. By revealing the dynamic correlation between temperature variations and gas concentration patterns, it provides a theoretical basis for optimising the layout of gas and temperature monitoring systems, particularly enhancing the placement of Tube Bundle Systems and other gas detection devices. These findings offer practical guidance for improving early warning accuracy and understanding indicator gas evolution during sponcom development, with direct implications for advancing mine safety management
Catalytic nanomedicine via modulating ROS homeostasis for disease treatment
No full textReactive oxygen species (ROS) including singlet oxygen (1O2), hydroxyl radical (·OH), hydrogen peroxide (H2O2), and superoxide anion (O·-2) are fundamental products generated from essential oxidation and reduction reactions in organisms. Due to the critical role of ROS homeostasis as the regulator to maintain cellular metabolism, modulation of aberrant ROS level using catalytic nanoparticles has emerged as a promising strategy for disease treatment. This nanoparticle-based catalytic approach has demonstrated many merits in safety and efficacy owing to confined therapeutic effect at the target and avoiding off-target drug release. The primary tactics for ROS-mediated disease treatments fall into two categories: elevating ROS levels to induce tumour eradication and scavenging overexpressed ROS to rescue damaged cells.
This thesis summarizes recent advance in therapeutic modalities utilizing ROS regulation through endogenous chemicals and external stimulations, including elevated level of H2O2 in the tumour microenvironment, external light irradiation, and ultrasound trigger, and discusses underlying shortcomings and prospects. In Chapter 3, oxygen-deficiency rich molybdenum carbide MXene nanostructures (MoOx@Mo2C) are developed for controllable ROS production to eradicate drug-resistant pathogen under ultrasound stimulation. Both in vitro and in vivo evaluations show elimination of pathogens with negligible cytotoxicity. In Chapter 4, an anticancer platform utilizing a nanobiohybrid (GSAu) composed of non-pathogenic bacteria, Geobacter sulfurreducens (GS), with in-situ biosynthesized Au nanoparticles have been established, achieving tumour inhibition by consuming endogenous H2O2 to produce lethal ·OH for safe and efficient cancer therapy. In Chapter 5, leveraging the reductive nature of GS, a ROS scavenging modality was constructed to alleviate atherosclerosis symptoms. The key findings and perspectives are presented in Chapter 6
Cyber Evaluation and Management Toolkit (CEMT): A threat-focused, model-based approach to assessing the cyberworthiness of cyber-physical systems to facilitate informed decision-making
Get PDFEnsuring the cyberworthiness of complex cyber-physical systems is a critical component of designing modern military capabilities. The requirement to ensure the mission systems are resilient to cyber attacks and able to operate safely and effectively within a contested cyber environment is widely articulated, but the path to achieving that requirement efficiently and effectively is less clear. Our initial hypothesis, based on a survey of the available literature, identified that a model-based approach that focused on detailed modelling of adversarial threats could produce assessments that were both sufficiently detailed and intuitive to decision makers, but existing model-based approaches were unable to satisfactorily meet these objectives.
A new model-based approach, the Cyber Evaluation and Management Toolkit (CEMT), was developed to address the gaps in the literature, and early prototypes of this approach were evaluated via face validity trials using generic case studies that surveyed expert respondents within the Australian Defence enterprise. Promising results to these face validity trials paved the way for field research and an implementation trial that applied the CEMT to the assessment and evaluation of the cyberworthiness of a complex military capability within the Royal Australian Navy (RAN). Stakeholders involved in the implementation trial responded to surveys to gather data on the efficiency, effectiveness and user satisfaction of our new approach as a tool for assessing the cyberworthiness of a complex cyber-physical system.
The results of the implementation trial generally supported the claim that the CEMT was both an efficient and effective tool for assessing cyberworthiness, and the overall user satisfaction of the tool was high – especially in comparison to extant approaches. The results also identified that the CEMT facilitated informed decision making with respect to cyber risk.
These results support our initial hypothesis that threat-informed, model-based approaches can be used to systematically assess the cyberworthiness of complex cyber-physical systems and present that assessment in a manner that is intuitive and understandable to decision makers. The CEMT provides a strong example of such an approach and further development of the tool could lead to an operationalised capability for assessing the cyberworthiness of complex cyber-physical systems
Unravelling Mechanisms and Enhancing Hydrogen Storage in Porous Silicon: A Multifaceted Approach
No full textThis thesis presents a comprehensive investigation into the potential of porous silicon (pSi) as a hydrogen storage material, encompassing both pSi powders and thin films. The research successfully demonstrated room-temperature hydrogen absorption and desorption in metal-doped pSi, a significant advancement compared to many other porous materials necessitating cryogenic conditions.
A key focus of the research was the optimization of pSi fabrication processes. For pSi powders derived from Al-Si alloy, the study systematically investigated the impact of etchant combinations, milling parameters, and doping processes on hydrogen storage capacity. The findings underscored the importance of using less oxidizing etchants like HCl and carefully controlling secondary corrosion conditions with HNO3 to achieve enhanced surface area and optimal hydrogen storage capacity. Additionally, the positive influence of ball milling on surface area and hydrogen storage was demonstrated, revealing the intricate relationship between milling parameters and structural properties. The hydrogenation mechanism in pSi powder was elucidated through combinations of advanced characterization techniques, including neutron scattering and in-situ measurements, confirming the chemisorptive nature of hydrogen interaction and highlighting the catalytic role of dopants.
In terms of pSi thin films, the research focused on refining the fabrication route to improve yield and production rates. The influence of hydrofluoric acid concentration on morphology and crystal structure was meticulously examined. Incorporating Pd and Pt dopants into pSi thin films led to substantial enhancements in hydrogen storage capacity, particularly at room temperature. Furthermore, neutron scattering experiments, utilising techniques such as Small-Angle Neutron Scattering (SANS), provided critical insights into the hydrogenation mechanism of pSi thin films, revealing the interplay between hydrogen and the pSi structure.
Overall, this thesis contributes significantly to advancing pSi-based hydrogen storage technologies. The findings not only deepen our understanding of the material's fabrication, characterization, and hydrogenation behaviour but also highlight the potential of pSi as a viable and efficient hydrogen storage material, paving the way for its future implementation in clean energy applications
Reconstructing Late Pleistocene Atmospheric Radiocarbon using Subfossil New Zealand Kauri (Agathis australis)
Get PDFAbrupt and extreme climatic and environmental changes punctuated the late Pleistocene period (80,000 to 11,650 years ago), preceding the relatively stable Holocene. Proxy-climate records demonstrate instability during this last glacial period, offering valuable insights into future climate variability. To fully exploit these proxy records, robust geochronological frameworks are necessary to align global ice-marine-terrestrial datasets. Detailed records of cosmogenically-produced atmospheric radiocarbon enable precise correlations of 14C in terrestrial and marine sequences and 10Be in ice core records.
Subfossil New Zealand kauri (Agathis australis) trees buried in bogs across Northland, New Zealand, provide the potential for a high-precision radiocarbon calibration curve extending over the full range of radiocarbon dating (55,000 years). Due to their longevity and preservation, subfossil kauri substantially contribute to radiocarbon calibration across the late Pleistocene, not just in the Southern Hemisphere but globally. The preserved samples also offer a unique opportunity to reconstruct atmospheric radiocarbon and climate-carbon dynamics on multi-millennial timescales with annual resolution.
Here, I investigate a new subfossil kauri archive from Waipu and Finlayson Farms, including five floating tree-ring chronologies covering a discontinuous 6,000 year period, with radiocarbon dates ranging from 22,000 to 49,000 years BP. Focusing on a selected floating chronology, five dendrochronologically crossdated and radiocarbon-dated tree-ring series were analysed across three laboratories. The bi-decadally resolved Waipu-Finlayson calibration sequence was compared to two established calibration datasets and wiggled-matched, resulting in a final span of 28,000-31,000 years cal BP. This atmospheric radiocarbon record provides significant insights into the alignment and fluctuations of terrestrial and marine proxy records during this period. Of particular interest, this timeframe coincides with a slowdown of the Atlantic Meridional Overturning Circulation (AMOC) and the Heinrich 3 iceberg discharge event from the Laurentide Ice Sheet.
The Waipu-Finlayson calibration sequence captures a critical period of change, offering insights into future climate-carbon dynamics. It highlights the considerable potential of ancient kauri as a world-class paleo-archive from the Southern Hemisphere that will contribute to future iterations of the international 14C calibration curve
Smart WiFi Sensing for Network and Environmental Awareness
Get PDFThe rapid growth of WiFi-capable Internet-of-Things (IoT) devices has connected the world. With the ubiquity of WiFi transmissions around, numerous research has shown that these WiFi-capable IoT devices can be leveraged like radars to sense the environment through the use of WiFi Channel State Information (CSI). However, our literature survey reveals that existing attempts at WiFi CSI sensing primarily focus on detecting changes caused by direct human or object movements, while little attention has been given to changes caused by the underlying network and environmental factors. To address this gap, this thesis explores the potential of WiFi sensing techniques for network traffic, environmental occupancy and thermal environment monitoring by CSI extracted from the same WiFi stream, integrated onto an autonomous WiFi sensing architecture.
As WiFi CSI are extracted from users' network activities, this thesis begins by demonstrating that CSI can be used to distinguish the underlying network traffic types that generate WiFi signals originally. Notably, we propose a novel WiFi CSI processing technique for Network Traffic Classification (NTC), which is evaluated under different environmental setups and wireless interference scenarios to verify its robustness.
After demonstrating WiFi CSI-based network awareness, we pivot to environmental occupancy sensing as the foundation for our subsequent physical environment sensing attempts. Building on existing CSI-based human activity monitoring efforts, we show that CSI can be used to monitor occupancy levels in an effective yet lightweight fashion, timely for COVID-19 containment efforts. Uniquely, we show the possibility to implement an occupancy threshold detection using binary classifications. We also show that CSI-based occupancy monitoring can be extended to challenging outdoor scenarios.
Thereafter, we focus on expanding the capabilities of WiFi CSI-based environmental sensing. In a pioneering attempt, we show that WiFi CSI can be used to detect temperature changes in the ambient environment, and thus, detecting the onset of anomalous temperature changes caused by fire incidents.
Lastly, we aim to integrate the versatile network and environmental awareness applications of WiFi CSI-based sensing into a single, autonomous platform that can support the versatile CSI sensing using commercially off-the-shelf IoT devices with the potential for scalability. In summary, this thesis significantly expanded the depth of WiFi CSI-based sensing capabilities, addressing the gap in existing WiFi CSI sensing research
Hospital Sustainability - using data and technology to improve the value of care
Get PDFThe overarching aim of this thesis is to strengthen the evidence base and to identify opportunities to support sustainability in hospital care for paediatrics. This thesis helps to understand how leveraging healthcare technology could improve value of care in two key areas. First, reducing low value care (LVC) by using an Electronic Medical Record (EMR) to direct clinicians away from unnecessary care, and second, exploring opportunities to transition care from hospital-based to home-based.
The first part of this thesis analyses the impact of multi-faceted interventions designed to reduce unnecessary care for infants with bronchiolitis. Bronchiolitis is the most common reason for hospitalisation in infants. By reducing unnecessary chest xrays (CXR) and bronchodilators, infants experience less radiation, spurious results, unnecessary antibiotic therapy, discomfort and side effects. Such reduction can lead to substantial savings to the hospital. The comparative effect of multi-faceted interventions with and without an EMR intervention is reported in Chapters 2 and 3. The results highlight the importance of robust analysis and demonstrate a lack of impact on CXR reduction, once accounting for confounding variables. Conversely, with the additional EMR alert for bronchodilator use, a significant reduction in prescribing is observed. The conclusions are two-fold; that false attribution to interventions may occur if confounding variables are not considered and the addition of an EMR intervention appears effective.
The importance of EMR interventions is further tested in Chapter 4. By using time series analysis and a cost calculation we measure the impact of four EMR interventions designed to reduce LVC in common paediatric conditions/tests. The results support EMR interventions being a cost-saving and effective method to reduce low value care. Chapters 5 and 6 focus on efficient use of hospital beds by exploring the possibility of shifting treatment to Hospital-In-The-Home (HITH) among infants with bronchiolitis. HITH benefits the child by avoiding the stress of hospital and reduces disruption to family and the financial costs of travel and carer leave. First, a systematic review of existing literature demonstrates home oxygen for bronchiolitis is a safe, feasible and cost-saving model. Expanding on this foundational literature, caregiver attitudes to receiving care at home are explored, and the potential impact on in-hospital bed-days modelled. The findings suggest transition to the home would require augmentation of caregiver health literacy and would result in a significant improvement in bed access and hospital flow.
The combination of these projects provides opportunities to address hospital sustainability now and into the future
Uniting Families Report: “It takes a village to raise a child”
No full textThe Uniting Families Report is a partnership between Uniting NSW.ACT and the Social Policy Research Centre, UNSW. This second Uniting Families Report explores the networks of support that families rely upon when raising their children. It shows that while many families form and sustain these networks, not every family has a strong village of support to rely on. Based on national data and in-depth interviews, the research shows that access and to, and sustainability of, these networks is shaped not just by individual effort or relationships, but by deeper structural factors – such as income, housing and care responsibilities