Faculty of Science 2

Doctor of Philosophy

ADIKARAM MUDIYANSELAGE, Janith Sajitha Weerasinghe

Thesis Title

Nanomaterial Synthesis and Surface Treatment by Atmospheric Pressure Cold Plasmas

Supervisors

• Dr Nathan Jonathan Castro (External Supervisor)
• Professor Kostyantyn Ostrikov (Principal Supervisor)
• Professor Prashant Murlidhar Sonar (Associate Supervisor)
• Associate Professor Krasimir Atanasov Vasilev (External Supervisor)

Citation

The main goal of this study was to demonstrate the potential of atmospheric pressure cold plasmas to synthesize nanoparticles and surface treatments. Silver nanoparticles and carbon quantum dots were selected for this work. The use of silver nanoparticles in bactericidal applications has been tested. In addition, carbon quantum dots are used to manufacture a low-cost metal ion sensor for the detection of copper in drinking water. The second part of the study investigated the chemical reactions that occur in plasma treated mesoporous tin oxide films. These are used to increase the efficiency of dye sensitized solar cells.

BEIGHTON, Matthew

Thesis Title

Security Analysis of Shift-Register Based Keystream Generators for Stream Ciphers

Supervisors

• Dr Harold John Gregory Bartlett (Principal Supervisor)
• Leonie Ruth Simpson (Associate Supervisor)

Citation

Society's thirst for smaller, faster and more complex technology requires highly secure cryptosystems. These systems are under constant pressure to evolve higher levels of security integrated within ever-shrinking, highly complex hardware, with minimal runtime costs. These demands have focused attention on the design of lightweight cryptographic algorithms because of their speed. The research presented in this thesis focuses on the design and security analysis of lightweight stream ciphers capable of authenticated encryption with associated data (AEAD), proposed as part of the National Institute of Standards and Technology's (NIST) lightweight cryptography competition.

BON, Joshua Joannes

Thesis Title

Advances in Sequential Monte Carlo Methods

Supervisors

• Professor Christopher Colin Drovandi (Principal Supervisor)
• Mr Anthony Rowland Lee (External Supervisor)
• Emeritus Professor Anthony Nicholas Pettitt (Associate Supervisor)

Citation

Estimating parameters of complex statistical models and their uncertainty from data is a challenging task in statistics and data science. This thesis developed novel statistical algorithms for efficiently performing statistical estimation, established the validity of these algorithms, and explored their properties with mathematical analysis. The new algorithms and their associated analysis are significant since they permit principled and robust fitting of statistical models that were previously intractable and will thus facilitate new scientific discoveries.

HERATH MUDIYANSELAGE, Dimuthu Prasad Wijethunge

Thesis Title

Theoretical Investigation of Ferroelectric Properties in 2D Materials and Their Applications

Supervisors

• Professor Aijun Du (Principal Supervisor)
• Professor Anthony Peter O'Mullane (Associate Supervisor)

Citation

This thesis examined two-dimensional ferroelectric materials and their applications using density functional theory calculations. The research has revealed several novel applications for 2D ferroelectric materials. It illustrated that ferroelectric materials can be used to modify electronic, photocatalytic and magnetic properties of two-dimensional materials. In addition to exploring applications, new two-dimensional ferroelectric material which exhibits metallic properties was discovered through high through output search. Two-dimensional ferroelectric metals are extremely rare and only handful of materials were ever discovered.

HILLY, Lynette Jay

Thesis Title

Bacillus Species as Potential Probiotics for Poultry: Role of Xylanase Production

Supervisors

• Wayne Leslie Bryden (External Supervisor)
• Dr Leigh Kirsten Gebbie (Associate Supervisor)
• Adjunct Professor Robert Edward Speight (Principal Supervisor)

Citation

Probiotics contain bacteria that are beneficial to the gut and have demonstrated to improve the health status of production animals including improved growth performance, protection against intestinal pathogens and enhanced immunity. The mechanisms of how these effects are achieved remains poorly understood. Thus, the overarching purpose of this thesis was to select and examine novel Bacillus strains for their potential as probiotics for poultry. The work showed Bacillus is a good source of probiotic bacteria and is safe to feed to poultry. These outcomes provided new insights into relationships between diet, probiotic species, and the intestinal microbiota of poultry.

HOANG, Minh Tam

Thesis Title

Metal Halide Perovskite Nanocrystals: From Synthesis to Applications

Supervisors

• Adjunct Professor John Marcus Bell (Associate Supervisor)
• Professor Hongxia Wang (Principal Supervisor)
• Associate Professor Geoffrey David Will (Associate Supervisor)

Citation

This thesis primarily focuses on perovskite nanocrystals (NCs), addressing synthesis of the materials with tailored optical and electrical properties, morphology, stability for applications in optoelectrical devices and catalytic reactions. In particular, the methods of solvent engineering and compositional engineering were applied to tackle the toxicity and stability issues of the metal halide perovskite NCs. Advanced measurements were used to investigate the fundamental properties of the metal halide perovskite NCs. The developed perovskite NCs were successfully employed in highly efficient light emitting devices and catalytic applications.

HORCHLER, Eva Johanna

Thesis Title

Secondary Organic Aerosol Formation in a Smog Chamber Using Ambient Urban Air as a Matrix Component

Supervisors

• Associate Professor Branka Miljevic (Associate Supervisor)
• Professor Zoran Ristovski (Principal Supervisor)
• Dr Boguang Wang (External Supervisor)
• Dr Hao Wang (External Supervisor)

Citation

In urban environments, a significant portion of atmospheric aerosols are of organic composition with the secondary organic aerosol (SOA) fraction being one of the most important but least understood. This work examines SOA production in a smog chamber using a-pinene and isoprene as biogenic precursors and particle-free ambient urban air as anthropogenic emissions. The observations revealed that the SOA formation is controlled by the components present in the matrix and a-pinene or isoprene affect the reaction processes in such a way that the SOA concentration is either increased or decreased.

KALAYCI, Kubra

Thesis Title

Advanced Photochemical Systems with Bathochromic Shift for Precision Soft Materials Design

Supervisors

• Professor Yvonne Leonie Barner (Associate Supervisor)
• Distinguished Professor Christopher Winfried Barner-Kowollik (Principal Supervisor)
• Dr Hendrik Clemens Wolfgang Frisch (Associate Supervisor)

Citation

The current thesis introduces novel tools via two photochemically induced ligations; [2+2] photocycloadditions and photouncaging reactions for light-controlled Staudinger-Bertozzi ligations. New chromophores were designed to provide a bathochromic shift for the activation wavelength of both reaction types to address the challenges that prevent these systems to be available for biological applications. In-depth photoreactivity studies using action plots revealed the exact wavelength dependent reactivity of the developed systems along with the effect of solvent and pH on the photoreactivity, which contributed to a fundamental understanding of these reactions. The applicability of these systems was demonstrated by hydrogel fabrication and surface patterning.

KARIM, Rezaul

Thesis Title

Nutrient and Pesticide Dynamics Through the Vadose Zone in the Wet Tropics, Australia

Supervisors

• Professor Leslie Anthony Dawes (Associate Supervisor)
• Associate Professor Lucy Reading (Principal Supervisor)

Citation

This thesis involves the implementation of a vadose zone monitoring system (VMS), which has not previously been installed in Australia or in the Wet Tropical environments. Using this VMS, the fluctuations of water content at various layers was found correlating with the magnitude of the rain events, plant uptake and the site lithology. It also enables the characterization of pesticide migration with respect to rainwater infiltration, sugar cane growing phase and pesticide application. The possible nutrient dynamics (ammonium, nitrite, nitrate and vice versa) with respect to their application regime, local rain patterns and infiltration dynamics are also defined.

KEKULTHOTUWAGE DON, Shamika Prasadini

Thesis Title

Novel Mathematical Models and Simulation Tools for Stochastic Ecosystems

Supervisors

• Dr Pamela Marion Burrage (Principal Supervisor)
• Kate Jessica Helmstedt (Associate Supervisor)

Citation

Interacting species systems have complex dynamics that are often subject to change due to internal and external factors. Quantitative modelling approaches to capture demographic fluctuations can be insufficient in the presence of stochastic variation and uncertainty. This thesis establishes new modelling techniques to account for such demographic variations and develops novel numerical simulation tools for solving these systems. These explorations are extended for solving invasive species management problems where robust management actions and efficient use of allocated budgets are necessary.

KODURA, Daniel

Thesis Title

Remote Controlled Folding and Unfolding of Single-Chain Nanoparticles via Photochemistry

Supervisors

• Distinguished Professor Christopher Winfried Barner-Kowollik (Principal Supervisor)
• Dr Hendrik Clemens Wolfgang Frisch (Associate Supervisor)

Citation

One of the most powerful capabilities of nature is specific catalysis of chemical reactions by enzymes, i.e., sequence-defined biopolymers with defined three-dimensional geometry, in living organisms. The aim of introducing conformational changes with potentially similar capabilities into synthetic polymers led to the development of so-called single-chain nanoparticles (SCNP). The current thesis focuses on generating remotely and reversible foldable SCNPs using photochemistry. The development of a platform technique, paired with deep understanding of the folding process, is critical for mimicking biocatalysis.

LEO, Stephen Bradley

Thesis Title

Potential of Remote and Proximal Sensing, Publicly Available Datasets and Machine Learning for Site-Specific Management in Australian Irrigated Cotton Systems

Supervisors

• Dr Max De Antoni (External Supervisor)
• Professor Peter Robert Grace (Principal Supervisor)
• David William Rowlings (Associate Supervisor)

Citation

Agricultural fields are inherently variable across both space and time but are commonly managed uniformly. Uniform management can simultaneously lead to an under and over-application of resources (e.g. fertiliser) within the same field, resulting in poor resource efficiency and reduced profit margins. This research demonstrated the potential of publicly available datasets (i.e. remote sensing, digital soil maps, weather), machine learning techniques and crop models to inform management at a sub-paddock scale. These findings will help provide a cost-effective and efficient approach to improving farm productivity, profitability and sustainability in Australian irrigated cotton systems.

LUCAS RODRIGUES, Leona

Thesis Title

Advanced Photochemical Reactions Induced by Visible Light

Supervisors

• Distinguished Professor Christopher Winfried Barner-Kowollik (Principal Supervisor)
• Professor Timothy Dargaville (Associate Supervisor)

Citation

Nature utilizes the energy of light for chemical transformations such as photosynthesis or the visual systems in human eyes, where wavelengths from high energetic UV to harmless visible light are absorbed by the respective chromophores. The current thesis focusses on developing photoreactive molecules responsive to visible light to minimize harm in the form of photo-bleaching or degradation to molecules, polymers and soft matter materials via three major reaction pathways: Light induced ligation, bond-cleavage/rearrangement and isomerization. Here, a particular focus is placed on the development of low energy triggered advanced reactions that can serve as photochemical synthetic platforms for materials applications.

PELLOTH, Jessica Laura

Thesis Title

Wavelength-Gated Control Over Material Properties in Hydrogel Networks

Supervisors

• Distinguished Professor Christopher Winfried Barner-Kowollik (Principal Supervisor)
• Dr Anja Sabrina Goldmann (Associate Supervisor)

Citation

The present thesis focusses on stimuli-responsive small molecules and their utilisation in hydrogel networks to improve control over a change in physical properties. While recent literature shows a toughening of materials through different control mechanisms, there are very few examples of a stepwise softening of hydrogel networks. This thesis aims to investigate several molecular control mechanisms to introduce a stepwise change in macroscopic properties via different wavelengths of light, enabling a precise and direct control over disparate material properties and allowing for fine-tuning post preparation. Here, different approaches were utilised, ranging from reversible thermo-couplings, photo-degradation, to isomerisation of a photo-switch.

PETHTHA THANTHRIGE, Nipuni Dhanushika

Thesis Title

Dissecting the Molecular Mechanisms of AtBAG4-Mediated Stress Tolerance

Supervisors

• Dr Sudipta Shekhar Das Bhowmik (Associate Supervisor)
• Dr Brett James Ferguson (External Supervisor)
• Mehdi Kabbage (External Supervisor)
• Professor Sagadevan Govindasamy Mundree (Associate Supervisor)
• Dr Brett Robert Walter Williams (Principal Supervisor)

Citation

Plant biotechnology holds great promise to help meet the supply-demand gaps of agriculture to feed the future population. This thesis investigated the molecular mechanisms of stress tolerance conferred by the Arabidopsis thaliana Bcl-2 associated athanogene 4 (AtBAG4), cytoprotective protein. The research identified a role for AtBAG4 in several plant stress response pathways and further investigated the implications of expressing AtBAG4 in chickpeas. The AtBAG4-chickpea were equivalent to commercially available chickpea in non-stressed conditions but supported improved yields under drought. This knowledge will be used to develop improved chickpea varieties that tolerate stress without yield penalty.

REYES ZULUAGA, Andres

Thesis Title

Modulation and Tuning of Spin Crossover by Encapsulation of Metal Complexes within Halogen-Bonded Architectures

Supervisors

• Professor John Cameron McMurtrie (Principal Supervisor)
• Dr Aaron Salvatore Micallef (Associate Supervisor)
• Dr Kathleen Mary Mullen (Associate Supervisor)

Citation

This project aimed to establish a way to modulate the supramolecular chemistry and spin crossover properties of metal complexes through the use of anionic supramolecular networks. This research employed crystal engineering to effectively combine several molecular building blocks within the same crystalline material. The arrangement of these components within these crystalline materials and their associated magnetic properties were regulated through the use of a variety of different molecular components, resulting in the development of a variety of novel co-crystals, with potential applications as molecular sensors, switches and data storage or memory devices.

TASNIN, Mst Shahrima

Thesis Title

Demographic Structure and Aging in Bactrocera tryoni (Diptera: Tephritidae) in Subtropical Australia

Supervisors

• Professor Anthony Robert Clarke (Principal Supervisor)
• Dr Katharina Merkel (External Supervisor)
• Dr Ranawelle Liyanage Rehan Silva (Associate Supervisor)

Citation

Queensland fruit fly is a destructive horticultural insect pest. Knowing the age-structure of fly populations, that is the relative proportion of young, middle-age, and old-age flies within a population at a given time, is critical for effective management. The thesis combined behavioural ecology with a novel mathematical analysis to identify the seasonal changes in the age of a wild Queensland fruit fly population. The study showed that the abundance and age-structure of the fly changed predictably with the season, strongly suggestive of an endogenous mechanism that helps the fly cope with seasonal changes in resource availability.

UDA GEDARALAGE, Mihiri Ekanayake

Thesis Title

Plasma Assisted Nanomaterials Synthesis from Sustainable Sources

Supervisors

• Associate Professor Jennifer May MacLeod (Associate Supervisor)
• Professor Anthony Peter O'Mullane (Associate Supervisor)
• Professor Kostyantyn Ostrikov (Principal Supervisor)

Citation

This thesis represents, Plasma assisted nanomaterial synthesis from sustainable sources, which uses plasma in atmospheric pressure to produce valuable nanomaterials. The sustainable sources such as seawater and biomass have been used together with plasma to develop novel methodologies in seawater desalination, water splitting, mung bean germination, CO2 capture and organic catalysis. This work includes alternative solutions for the major global problems such as water scarcity, clean energy production and global warming using readily available raw materials.

WU, Jinran

Thesis Title

Statistical Support Vector Machines with Optimizations

Supervisors

• Professor Kevin Burrage (Associate Supervisor)
• Professor Yuchu Tian (Associate Supervisor)
• Professor You-Gan Wang (Principal Supervisor)

Citation

This thesis combines support vector machines with statistical models for analyzing data generated by complex processes. The key contribution of the thesis is to propose five regression frameworks aiming for hyperparameter estimation, support vector selection, data modelling with unequal variances, temporal patterns, and cost benefit analysis. A new optimizer is also proposed for high-dimensional optimization.

YANG, Yang

Thesis Title

Fabrication of Cost-Effective Carbon Based Stable Planar Perovskite Solar Cells

Supervisors

• Professor Hongxia Wang (Principal Supervisor)
• Professor Huai Yong Zhu (Associate Supervisor)

Citation

This project aims to explore new methods for fabrication of low-cost and stable perovskite solar cells (PSC) by using carbon-based materials. Innovative fabrication techniques for the carbon electrode and new inorganic hole transport materials were developed for PSCs, leading to enhanced interfacial contacts and higher conductivity of the carbon electrode. Consequently, PSCs with excellent stability and significantly enhanced power conversion efficiency were achieved. Moreover, this project has also demonstrated a method for fabrication of self-charging perovskite solar capacitors by integrating a PSC with a supercapacitor, which has the potential to provide reliable off-grid power supply in the future.

VAN BEEST, Marc Robert Roderick Shane

Thesis Title

The Influence of Indoor Airflow on Particle Spread: Natural versus Mechanical Ventilation

Supervisors

• Dr Ruhi Humphries (External Supervisor)
• Distinguished Professor Lidia Morawska (Associate Supervisor)
• Professor Nunzio Motta (Principal Supervisor)

Citation

This research investigated the influence of indoor airflow on particle movement originating from a human breath and cough inside a single and multi-room enclosure – a critical issue in cruise ships and quarantined facilities. Using computational fluid dynamic (CFD) modelling numerous airflow scenarios were analysed and the results provide additional information to help identifying relevant recommendations to minimise indoor particle spread.