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Digital Twin of Wire Arc Additive Manufacturing
No full textWire Arc Additive Manufacturing (WAAM) is an emerging manufacturing technology that has been used to build medium to larger-sized components. With the rise of Industry 4.0 and smart manufacturing, production automation, intelligence, and digitalization has attracted increasing scientific attention in manufacturing field. Despite the adoption of intelligent algorithms in WAAM, their application remains fragmented, targeting specific issues without a unified, intelligent optimization system. This thesis aims to bridge this gap by introducing a comprehensive Digital Twin (DT) framework that integrates monitoring, modelling, control, and simulation to enhance WAAM processes.In this study, the monitoring system of WAAM-DT framework consists of a high-frequency bead geometry measuring system and a sensor-fusion defect detection system. Utilizing electric signal sensors, the system captures welding parameters to predict bead dimensions with high accuracy, leveraging Multi-layer Perceptron (MLP) regressors and an incremental learning framework for optimized performance. Comparative studies underscore the system's efficacy, offering speed and precision superior to traditional methods.Defect detection system includes multi-scale sensing technologies: a welding electric signal sensor, a camera, and a laser profilometer are used to collect welding current and voltage data, image data, and point cloud data. The collected multi-scaled data are subsequently analysed by Multi-layer Perceptron (MLP) classifier and YOLOv5 in temporal and spatial scale, respectively, then fused in decision-level via a Variational Autoencoder (VAE). The system performance is then tested to detect defects and geometric errors in practical experiments and the results show that the overall F1 score is 0.791, including detecting, classifying, and analysing the cause of defects. Additionally, the total predicting time is within 0.5 s, which is suitable for an in-process monitoring system.The WAAM-DT framework also introduces an adaptive simulation model for predicting physical distortions during deposition, using a novel diffusion model architecture for spatial and temporal analysis. Pretrained offline with Finite Element Method (FEM) simulated distortion fields, the model successfully predicts distortion fields online using laser-scanned distortion fields during the deposition process. Experimental validation on seven thin-wall structures demonstrated its superior performance, achieving a Root Mean Square Error (RMSE) below 0.9 m, outperforming FEM by 143% and Artificial Neural Networks (ANN) based methods by 151%, marking a significant stride towards realizing an WAAM-DT.Furthermore, an innovative control system combining a linear autoregressive (ARX) model and a multi-input multi-output (MIMO) model-predictive control (MPC) algorithm optimizes geometric outcomes of WAAM processes in real-time. Through both simulation and experiments, results show that the real-time control performance is improved by increasing the complexity of implemented control algorithm: Controlled geometric fluctuations in the test component were reduced by 200% whilst maintaining fluctuations within a 3 mm limit under various welding conditions. In addition, the adaptiveness of designed control strategy is verified by accurately controlling the fabrication of a part with complex geometry.This thesis lays the groundwork for a robust WAAM-DT system, presenting a holistic approach to addressing the technology's current limitations. Future work focus on investigation and modelling of the deposition mechanism to further refining the WAAM-DT's predictive accuracy and operational efficiency.</p
Mitigation of drying shrinkage in alkali-activated reactive powder concrete through copper-coated microwire steel fibers
No full textThis study investigated the drying shrinkage in alkali-activated ground granulated blast furnace slag (GGBFS)-based reactive powder concrete (AARPC) and evaluated the efficacy of copper-coated microwire steel fibers in minimizing drying shrinkage. Three different mix designs with varying liquid ratios were developed and fibers were incorporated into each AARPC mix at different volumetric ratios. The drying shrinkage of the AARPC was investigated over a duration of 112 days under the drying at 23 ± 2°C with a relative humidity of 50 ± 2%. Drying shrinkage increased with the increase in the liquid ratio in the AARPC mixes without fibers. Incorporating fibers into the AARPC resulted in a substantial reduction in the drying shrinkage. The effectiveness of reducing drying shrinkage improved with an increase in fiber content. Fibers significantly attenuated drying shrinkage of AARPC by up to 51% when 2.4% of microwire steel fibers were used.</p
Beginner's Mind
No full textThe off-shore islands of New South Wales and their surrounding seas archive millenia of change. How can we learn from the deep human and ecological histories of these unique places?</p
Policy Briefing: Abrupt changes in the Antarctic environment
No full textAbrupt changes are developing across Antarctica’s ice, ocean and biological systems. These systems interact so that a change in one part can increase the risks of triggering abrupt change in other parts of Antarctica and the Southern Ocean.For Australia, abrupt changes are expected to bring:Increased vulnerability to coastal infrastructure and communities due to accelerating sea level rise;Intensified global warming through reduced carbon dioxide removal by the Southern Ocean;Amplified regional warming due to Antarctic sea-ice loss; andReduced rainfall over Southern Hemisphere continents from shifting weather patterns.Existing efforts through the Antarctic Treaty System to reduce non-climatic pressures on Antarctica’s biological systems and establish protected areas are critical for building resilience, but to be effective they must be in addition to decisive policy action that mitigates global climate changes.The only way to avoid further abrupt Antarctic changes and their impacts is to reduce CO2 emissions rapidly enough to limit global warming to as close to 1.5°C as possible.Even with transformative emission reduction actions, plausible futures including multiple abrupt changes from Antarctica should be considered by governments, businesses and communities in their planning for future climate and sea-level rise impacts.</p
Large volcanic eruptions are mostly sourced above mobile basal mantle structures
No full textMost deep mantle plumes rise from hot basal mantle structures, creating large volcanic eruptions at Earth’s surface. In previous studies, mantle plumes were the implicit process connecting volcanic eruptions to hot basal mantle structures. Here, we investigate the spatiotemporal links between volcanic eruptions, hot basal mantle structures, and explicitly modelled plume conduits from 300 million years ago. We consider three volcanic eruption databases, four tomographic models and six global mantle flow models. Through Monte Carlo significance testing we find a statistical-dependence relationship between modelled plume conduits and an eruption database containing both plume head and plume tail products. We show that these eruptions, if reconstructed above the exterior of basal mantle structures, are related to the edges of fixed basal mantle structures in one tomographic model, and to the edges of mobile basal mantle structures 1% to 1.6% denser than the surrounding mantle in mantle flow models.</p
Using oral histories and remote sensing to understand transitions of kelp gardens to urchin barrens in southern NSW
No full textCentrostephanus rodgersii is a native sea urchin to New South Wales (NSW) that consumes kelp as part of its natural diet. Kelp is a key habitat for various species, and its eradication results in long-term loss of biodiversity. Urchin barrens are a natural part of the NSW ecosystems, but they can also expand or occur in new areas when the population of sea urchins’ surges, preventing the recolonisation of kelp that may have been lost due to other stressors. This has occurred in Tasmania and elsewhere around the world, but there remains no clear evidence of this in NSW. However, existing studies have only encompassed the past 50 years, and changes in barrens and kelp over longer periods remain unknown. Through a dual approach utilising both oral Traditional Knowledge and remote sensing data, which is supported by existing knowledge from scientific literature, this study addresses critical gaps in knowledge about urchin barrens on the South Coast of New South Wales. In the first investigation of urchins and kelp relationships that braids Traditional knowledge with western science from remote sensing, this study explicitly aims to identify whether barrens in southern NSW may be increasing due to Centrostephanus rodgersii. Moreover, this research presents a new perspective to the issue of urchin barrens on the South Coast of NSW.Through analyses of oral Traditional Knowledge and from the perspective of Walbunja Traditional Owners, this study identified the decline of culturally significant species such as abalone, Marine Protected Areas/Sanctuary Zones, and commercial fishing to be potential driving factors creating urchin barrens on the South Coast of New South Wales. Object Based Image Analysis applied to aerial photography, in conjunction with ground validation, identified Lilli Pilli and Burrewarra to contain urchin barrens, while Bass Point and Bushrangers Bay are likely to contain urchin barrens. Coverage of kelp and urchin barrens fluctuated in aerial photography over time. The available aerial imagery was limited in time, and the yarning circles considered longer time periods and enhanced understandings of the urchin barren dynamics on the South Coast. This study demonstrates the benefits of applying a dual approach that braids oral Traditional Knowledge with observations of kelp and urchin extent from aerial photography. It has produced several future research opportunities, including utilising multispectral remotely piloted aircraft to improve validation of OBIA results, and further investigating the links between culturally significant species such as abalone, and the proliferation of sea urchins in New South Wales. Additionally, this study has provided recommendations to inform future fisheries management within New South Wales, regarding urchin barrens.</p
Boundary-line trade-off in bryophytes between UV photoprotection and photosynthetic capacity, but not desiccation tolerance.
No full textBackground and aimsCoping with both UV-B radiation and desiccation was essential for early land plants. In bryophytes, UV-B screening and desiccation tolerance partially depend on the physico-chemical features of cell walls, which may also constrain photosynthesis. This study tested the relationship between the accumulation of UV absorbing compounds (UVACs) and photosynthetic capacity and desiccation tolerance.MethodsGas exchange, chlorophyll fluorescence, desiccation tolerance and UVACs were analyzed for Colombian, Antarctic, Spanish and Australian species collected from locations of contrasting UV exposure. Apparent photosynthesis, quantum efficiency and heat dissipation were measured using PAM-coupled systems. Desiccation tolerance was evaluated by recovery of Fv/Fm after long-term dry storage (14 days). Cell wall-bound and soluble UVACs were quantified through spectrophotometry after methanolic and alkali extraction. Trait relationships were assessed by correlation tests and quantile regression.Key resultsA boundary line trade-off was found between apparent photosynthesis and cell wall-bound UVACs: no species simultaneously exhibited both high photosynthetic rates and large amounts of UVACs in its cell walls. The three phyla of bryophytes were segregated across this gradient, with mosses showing the highest photosynthetic capacity, but lowest UVACs and liverworts and hornworts presenting the highest UVACs together with low photosynthetic rates. No trend was observed with chlorophyll concentration or quantum efficiency of photosystem II. Long-term desiccation tolerance was not correlated with either cell wall-bound nor soluble UVACs. On the contrary, it was associated with non-photochemical quenching, which is possibly linked to a minimum ROS scavenging capacity indispensable for recovering functionality after a long-term desiccation/rehydration cycle.ConclusionsBryophytes exhibit a boundary-line trade-off between UV protection and photosynthetic capacity, possibly driven by limitations to CO2 diffusion associated with the accumulation of cell wall-bound UVAC. In contrast, desiccation tolerance appears to rely on different physiological mechanisms, related to heat dissipation.</p
Supporting Chronic Obstructive Pulmonary Disease (COPD) Self-management Using Patient Activation and Health Literacy in Primary Care Settings in Jordan
No full textThe abstract for this item has not been populated.</p
Contributions to Special Variants of Digital Signatures
No full textDigital signatures serve as a fundamental element of security and trust within the field of cryptography, offering the critical properties of authenticity, integrity and non-repudiation. These properties play a pivotal role across a diverse range of applications, including secure communication, financial transactions and the validation of digital documents. Unlike traditional signatures, which are merely digitised representations of handwritten signatures, digital signature schemes rely on the use of a cryptographic key pair: a private (or secret) key and a corresponding public key. The signer utilises the secret key to generate a digital signature for a given message and subsequently publishes the signature. This approach enables anyone in possession of the corresponding public key to verify the signature’s validity. Such verification ensures that the process remains not only secure and accurate but also accessible to the public.Despite the considerable benefits associated with traditional digital signature schemes, they possess a significant drawback: their inherent immutability. Once a digital signature has been created and published, it cannot be retracted or invalidated by the signer, as it remains permanently valid and irrevocable. This limitation presents substantial challenges in dynamic and decentralised contexts such as electronic voting systems, blockchain-based smart contracts and escrow services, where the capability to withdraw or modify prior consents is essential.To address this fundamental limitation, the thesis seeks to introduce the concept of the withdrawable signature. This novel variant of digital signature is designed to allow signers to securely and efficiently retract previously issued signatures under specific conditions, thereby offering a more adaptable and practical framework for digital signatures in dynamic environments. It is anticipated that this innovative approach will substantially improve both the flexibility and security of digital transactions and communications.This thesis presents and examines the concept of the withdrawable signature, a cryptographic primitive that empowers signers to retract their signatures while maintaining the confidentiality of their secret keys and safeguarding the security of other signatures.• In Chapter 3, we lay the foundation of the withdrawable signature. The core idea of constructing a withdrawable signature scheme is proposed in this chapter: in a withdrawable signature scheme, instead of directly publishing a conventional digital signature, a signer first generates an unverifiable (withdrawable) signature on their public key, which can only later convert into a standard, verifiable signature by itself. If the signer intends to withdraw the signature, it simply chooses not to perform this conversion. To achieve this “unverifiability”, we utilise the property of the Designated-Verifier Signature (DVS) to construct this withdrawable signature so as to ensure the generated signature can be verified by a certain verifier chosen by the signer only. We then present two constructions, one in the pairing-based setting and the other in the Discrete Logarithm (DL) setting, each accompanied by a formal security analysis.• In Chapter 4, we address a limitation of the initial withdrawable signature definition illustrated in Chapter 3: the absence of universal verifiability on the generated withdrawable signature. To overcome this, we extend the definition and revise corresponding security notions, enabling universal verification of withdrawable signatures using the public key set of all potential signers while ensuring that the signer’s public key is included. This property of the generated withdrawable signature is then realised through signer-ambiguity, meaning that while the withdrawable signature can be verified against a group of possible signers, it does not explicitly reveal which individual within the set actually produced it. We propose two types of generic constructions aligned with this extended definition: (i) one from discrete-log-based primitives, including an instantiation using the Schnorr signature and (ii) another based on hash-then-one-way (Type-H) signatures, acknowledging the practical significance of RSA signatures, with RSA serving as a concrete instantiation. Formal security analysis then ensures that our two proposed constructions meet the extended security notions, enhancing the applicability and security of the withdrawable signature in various cryptographic contexts, i.e. digital transactions and communications.• In Chapter 5, we then aim to explore the versatility of the withdrawable signature, particularly in outsourcing systems and software ecosystems, respectively. In the first part of this chapter, we extend the withdrawable property and refine the definition of the withdrawable signature to ensure that the signer’s identity can be explicitly clear when generating the withdrawable signature. This can be achieved through message-hiding: the withdrawable signature under a certain signer’s public key can be verifiable through different messages. Unlike the previous approaches than only maintaining signer-ambiguity between the public key set of all potential signers, as was done in Chapter 3 (between the signer and a chosen verifier) and Chapter 4 (among a set of potential signers), our refined definition requires the generated withdrawable signature holds either signer-ambiguity or message-hiding. A new construction based on this definition is proposed, along with a security analysis. We then demonstrate how the withdrawable signature can enable flexible outsourcing systems that support the cancellation of existing service requests. Additionally, we show how a signer can confirm a service request using a withdrawable signature while simultaneously accepting quotes from specific providers within the outsourcing system. Performance evaluations indicate that our proposed scheme achieves acceptable efficiency and security within these systems.In the second part of this chapter, motivated by the need for greater flexibility and security in software ecosystems, we first propose the universal withdrawable signature, a variant of the withdrawable signature, which introduces the universality to the withdrawable signature in this chapter. This variant enables any holder of a withdrawable signature, along with its corresponding secret commitment from the signer, to delegate the signature to another user while holding the ability to later confirm the signature using the same commitment. This feature supports applications requiring flexible delegation and management of withdrawable signatures. We provide a detailed system model, formal definitions, security notions and a concrete construction based on one of our withdrawable signature schemes from Chapter 3 and the construction with message-hiding property. We then demonstrate that our proposed scheme is provably secure.• In Chapter 6, we aim to further generalise existing constructions of the withdrawable signature in the aforementioned chapters beyond their reliance on pairing and RSA-based assumptions only. Developing generic constructions for the withdrawable signature that are not restricted to a specific cryptographic primitive enhances their flexibility, broadens their applicability across diverse cryptographic settings and ensures compatibility with various security frameworks. This adaptability allows withdrawable signatures to be integrated into a wider range of real-world applications without being constrained by the limitations of a particular underlying assumption. We answer this by proposing two generic constructions derived from three-move-type (Type-T) signatures and pairing-based signatures. We analyse the security of these constructions and offer concrete instantiations. Notably, our generic construction based on Type-T signatures remains independent of any specific cryptographic primitive, reinforcing its versatility and potential for broader adoption.This thesis contributes to the advancement of digital signature technology by presenting the withdrawable signature and its variants, conducting comprehensive security analyses and illustrating their practical applications in enhancing both flexibility and security within digital transactions and communication contexts.</p
Contributions to Ring Signatures
No full textCryptography is fundamental to securing electronic communications, ensuring privacy, integrity, and authenticity. Among its core tools, digital signatures enable individuals to sign electronic documents and messages securely, verifying the signer’s identity, preserving message integrity, and ensuring non-repudiation. These properties make digital signatures indispensable for applications such as legal document authentication, software distribution, and secure email. However, in many real-world scenarios, revealing the signer’s identity is undesirable. For instance, whistleblowers may need to report sensitive information without fear of retaliation; businesses may conduct confidential transactions while protecting the identities of their participants; and electronic voting systems may require voter anonymity while ensuring election integrity. In such cases, traditional digital signatures are insufficient because they explicitly link a signature to a known individual.Ring signatures allow any member of a predefined group to sign a message anonymously. While the signature confirms the authenticity and integrity of the message, the actual signer remains untraceable within the group. By contrast, group signatures also provide anonymous group signing but enable a designated manager to trace and reveal the signer’s identity when necessary. The strong anonymity property of ring signatures makes them particularly valuable for privacy-preserving applications. Nevertheless, several challenges remain, including improving efficiency, strengthening security, and ensuring scalability in practical implementations.This thesis presents significant advancements in ring signatures, focusing on improving their functionality, efficiency, and security under practical cryptographic assumptions. The main contributions are as follows:• The first contribution proposes a novel approach to constructing Traceable Ring Signatures (TRS) that is proved secure in a strong security proof model. Originally proposed by Fujisaki and Suzuki at PKC 2007, TRS enables public traceability of a user’s identity if they sign twice on different messages with the same tag. This property has practical applications in areas such as e-coupons, e-voting, and blockchain technology. Existing schemes typically rely on the (quantum) random oracle or common reference string models, which introduce impractical or inefficient assumptions. This thesis presents the first generic construction of traceable ring signatures that avoids a trusted setup and the random oracle heuristic, relying instead on standard assumptions. It achieves a signature size that scales logarithmically with the number of ring members.• The second contribution introduces Threshold Ring Signatures with Accountability (AThRS). While traditional threshold ring signatures allow multiple signers to collaboratively sign a message without revealing individual identities, AThRS balances anonymity and accountability. Specifically, it enables a designated opener to disclose the signers’ identities when necessary, provided that the signers give their consent before signing. Additionally, AThRS supports a verifiable opening mechanism, ensuring that the opener cannot falsely attribute a signature to any signer. This thesis presents a generic construction of AThRS using standard cryptographic primitives. It is secure in the plain model and achieves logarithmic signature size.• The third contribution presents a novel generic construction of Accountable Ring Signatures (ARS) in a strong security proof model. ARS bridges the conceptual and functional gap between traditional ring signatures and group signatures. Specifically, ARS preserves signer anonymity within a predefined set (as in ring signatures) while allowing a designated opener to reveal the actual signer when necessary, ensuring accountability. Previous ARS constructions have relied on trusted models or were secure only in the random oracle model. This thesis presents the first generic construction of ARS schemes that are secure in the plain model, achieve a logarithmic signature size, and eliminate the need for heuristic or trusted setup assumptions.• Lastly, we introduce the first (Linkable) Ring Signatures based on the Lattice Isomorphism Problem (LIP). Recognized as a promising post-quantum cryptographic problem, LIP is believed to be hard to solve even with the advent of quantum computers, making it an attractive basis for secure cryptographic constructions in a future where quantum attacks are a concern. The importance of LIP lies in its connection to lattice-based cryptography, which offers strong security guarantees under widely studied hardness assumptions. By leveraging the presumed difficulty of LIP, our proposed (linkable) ring signature schemes inherit post-quantum security, ensuring that they remain robust against both classical and quantum adversaries. Our schemes feature logarithmic signature sizes relative to the number of ring users, significantly reducing the signature size compared to other schemes when the number of users is large.</p