title: Polylactide composites reinforced with pre-impregnated natural fibre and continuous cellulose yarns for 3D printing applications

authors: Priya Muthe, Lakshmi

subjects: additive manufacturing

abstract: Achieving high-performance 3D printing composite filaments requires addressing challenges related to fibre wetting and uniform fibre/polymer distribution. This study evaluates the effectiveness of solution (solvent-based) and emulsion (water-based) impregnation techniques to enhance fibre wetting in bleached flax yarns by polylactide (PLA). For the first time, continuous viscose yarn composites were also produced using both impregnation techniques. All the composites were carefully characterised throughout each stage of production. Initially, single yarns were impregnated and consolidated to optimise formulations and processing parameters. Solution impregnation resulted in the highest tensile strength (356 MPa) for PLA/bleached flax filaments, while emulsion impregnation yielded the highest tensile strength for PLA/viscose filaments (255 MPa) due to better fibre wetting and fibre distribution. Impregnated single yarns were then combined, with additional polymer added to produce filaments compatible with standard material extrusion 3D printers. Despite a reduction in the mechanical performance of the 3D-printed composites due to additional polymer impregnation, relatively high tensile and bending strengths were achieved, and the Charpy impact strength (&gt;127 kJ/m2) for the viscose-based composite exceeded the reported values for bio-derived fibre reinforced composites. The robust mechanical performance of these filaments offers new opportunities for the large-scale additive manufacturing of structural components from bio-derived and renewable resources.

text: Polylactide composites reinforced with pre-impregnated natural fibre and continuous cellulose yarns for 3D printing applications Achieving high-performance 3D printing composite filaments requires addressing challenges related to fibre wetting and uniform fibre/polymer distribution. This study evaluates the effectiveness of solution (solvent-based) and emulsion (water-based) impregnation techniques to enhance fibre wetting in bleached flax yarns by polylactide (PLA). For the first time, continuous viscose yarn composites were also produced using both impregnation techniques. All the composites were carefully characterised throughout each stage of production. Initially, single yarns were impregnated and consolidated to optimise formulations and processing parameters. Solution impregnation resulted in the highest tensile strength (356 MPa) for PLA/bleached flax filaments, while emulsion impregnation yielded the highest tensile strength for PLA/viscose filaments (255 MPa) due to better fibre wetting and fibre distribution. Impregnated single yarns were then combined, with additional polymer added to produce filaments compatible with standard material extrusion 3D printers. Despite a reduction in the mechanical performance of the 3D-printed composites due to additional polymer impregnation, relatively high tensile and bending strengths were achieved, and the Charpy impact strength (&gt;127 kJ/m2) for the viscose-based composite exceeded the reported values for bio-derived fibre reinforced composites. The robust mechanical performance of these filaments offers new opportunities for the large-scale additive manufacturing of structural components from bio-derived and renewable resources.

year: 2024

title: Tree-structured multiclass probability estimators

authors: Leathart, Timothy Matthew

abstract: Nested dichotomies are used as a method of transforming a multiclass classification problem into a series of binary problems. A binary tree structure is constructed over the label space that recursively splits the set of classes into subsets, and a binary classification model learns to discriminate between the two subsets of classes at each node. Several distinct nested dichotomy structures can be built in an ensemble for superior performance. In this thesis, we introduce two new methods for constructing more accurate nested dichotomies. Random-pair selection is a subset selection method that aims to group similar classes together in a non-deterministic fashion to easily enable the construction of accurate ensembles. Multiple subset evaluation takes this, and other subset selection methods, further by evaluating several different splits and choosing the best performing one. Finally, we also discuss the calibration of the probability estimates produced by nested dichotomies. We observe that nested dichotomies systematically produce under-confident predictions, even if the binary classifiers are well calibrated, and especially when the number of classes is high. Furthermore, substantial performance gains can be made when probability calibration methods are also applied to the internal models.

text: Tree-structured multiclass probability estimators Nested dichotomies are used as a method of transforming a multiclass classification problem into a series of binary problems. A binary tree structure is constructed over the label space that recursively splits the set of classes into subsets, and a binary classification model learns to discriminate between the two subsets of classes at each node. Several distinct nested dichotomy structures can be built in an ensemble for superior performance. In this thesis, we introduce two new methods for constructing more accurate nested dichotomies. Random-pair selection is a subset selection method that aims to group similar classes together in a non-deterministic fashion to easily enable the construction of accurate ensembles. Multiple subset evaluation takes this, and other subset selection methods, further by evaluating several different splits and choosing the best performing one. Finally, we also discuss the calibration of the probability estimates produced by nested dichotomies. We observe that nested dichotomies systematically produce under-confident predictions, even if the binary classifiers are well calibrated, and especially when the number of classes is high. Furthermore, substantial performance gains can be made when probability calibration methods are also applied to the internal models.

year: 2019

title: Understanding the potential exposure of coastal marae and urupā in Aotearoa New Zealand to sea level rise

authors: Bailey-Winiata, Akuhata Patrick Stephen

subjects: Marae

abstract: In Aotearoa New Zealand, Māori are Indigenous and have inhabited these islands for the past 700 years. They have an intricate physical and spiritual connection to places and the environment. This is reflected in the Māori creation story, where Ranginui (sky father) and Papatūānuku (Earth mother) are the ancestral parents of Māori. Between these two gods is the marae, the Māori meeting house. Marae are where the domestic life of Māori traditionally ran its course, with marae being an overarching term to illustrate multiple buildings which each have a specific role to play within the community. Often, marae have an associated urupā (burial ground). Historically, marae and their associated urupā are positioned along the low-lying coast, providing easy access to kaimoana (sea food), transport and trade. However, coastal marae and urupā are at an increasing threat of inundation and erosion from sea level rise, and will also be impacted by other effects of climate change such as drought and other changes to weather patterns such as storms.
Many coastal marae and urupā are already experiencing the impacts of coastal flooding and erosion, however, little is known about the exposure of coastal marae and urupā to sea level rise nationally. Therefore, the main aim of this thesis is to explore the potential exposure of coastal marae nationally, with a particular focus on the Bay of Plenty coastal marae including coastal urupā. This aim was achieved by addressing three objectives. The first of which was to investigate the potential national exposure of coastal marae to a 100 year annual recurrence interval extreme sea level event, with the addition of sea level rise. Second, I conducted a nationally-focused assessment of the local coastal geomorphology surrounding coastal marae to determine the potential response of the coast to sea level rise. I also undertook a case study on the BOP which included a more detailed assessment of the geomorphology around the coastal marae and urupā in this region. Third, findings from these two objectives are brought together to consider the next steps to determine how to move forward with planning to manage coastal marae and urupā with sea level rise.
A spatial mapping approach using Arc GIS and existing datasets was used to address these aims, combining the Coastlines and Islands polygon, marae and urupā locational data and the Aotearoa New Zealand coastal hydrosystem classification system proposed by Hume in 2016. This showed that 191 marae around Aotearoa New Zealand are within 1 km of the coast and in the Bay of Plenty 41 urupā are within 1 km. I then used the bathtub modelling approach to get a national first-pass assessment of the potential exposure of these marae and urupā to a 100 year extreme sea level event at current mean sea level, with 10 cm increments of sea level rise up to 3 m. Six coastal marae were potentially exposed to a 100 year extreme sea level event at current mean sea level, with 41 coastal marae are potentially exposed to a 100 year extreme sea level event with a 3 m rise in mean sea level. The most common type of coastal geomorphology nationally and in the Bay of Plenty was shallow drowned valleys, with 72 coastal marae in this category. The response of these systems to sea level rise manifests as changes in the tidal regime and sediment transport dynamics which will affect inundation and erosion of low-lying areas, where many coastal marae and urupā are positioned.
Thus, it is clear that marae and urupā are nationally at risk to sea level rise, and their responses will be highly variable with geomorphology. But what are the next steps? There are many legislative documents such as the coastal climate change and hazards report by the Ministry for the Environment which suggests that the Dynamic Adaptive Policy Pathways strategy to address the uncertainty surrounding climate change, recommended as a method for future planning. Another is the pending reform of the Resource Management Act which will introduce a climate change adaptation act where support for managed retreat will be made available. However, any management strategies for marae, hapū and iwi will need to be cognisant of the tapū and māna that these places hold, and there will be no one size fits all approach.

text: Understanding the potential exposure of coastal marae and urupā in Aotearoa New Zealand to sea level rise In Aotearoa New Zealand, Māori are Indigenous and have inhabited these islands for the past 700 years. They have an intricate physical and spiritual connection to places and the environment. This is reflected in the Māori creation story, where Ranginui (sky father) and Papatūānuku (Earth mother) are the ancestral parents of Māori. Between these two gods is the marae, the Māori meeting house. Marae are where the domestic life of Māori traditionally ran its course, with marae being an overarching term to illustrate multiple buildings which each have a specific role to play within the community. Often, marae have an associated urupā (burial ground). Historically, marae and their associated urupā are positioned along the low-lying coast, providing easy access to kaimoana (sea food), transport and trade. However, coastal marae and urupā are at an increasing threat of inundation and erosion from sea level rise, and will also be impacted by other effects of climate change such as drought and other changes to weather patterns such as storms.
Many coastal marae and urupā are already experiencing the impacts of coastal flooding and erosion, however, little is known about the exposure of coastal marae and urupā to sea level rise nationally. Therefore, the main aim of this thesis is to explore the potential exposure of coastal marae nationally, with a particular focus on the Bay of Plenty coastal marae including coastal urupā. This aim was achieved by addressing three objectives. The first of which was to investigate the potential national exposure of coastal marae to a 100 year annual recurrence interval extreme sea level event, with the addition of sea level rise. Second, I conducted a nationally-focused assessment of the local coastal geomorphology surrounding coastal marae to determine the potential response of the coast to sea level rise. I also undertook a case study on the BOP which included a more detailed assessment of the geomorphology around the coastal marae and urupā in this region. Third, findings from these two objectives are brought together to consider the next steps to determine how to move forward with planning to manage coastal marae and urupā with sea level rise.
A spatial mapping approach using Arc GIS and existing datasets was used to address these aims, combining the Coastlines and Islands polygon, marae and urupā locational data and the Aotearoa New Zealand coastal hydrosystem classification system proposed by Hume in 2016. This showed that 191 marae around Aotearoa New Zealand are within 1 km of the coast and in the Bay of Plenty 41 urupā are within 1 km. I then used the bathtub modelling approach to get a national first-pass assessment of the potential exposure of these marae and urupā to a 100 year extreme sea level event at current mean sea level, with 10 cm increments of sea level rise up to 3 m. Six coastal marae were potentially exposed to a 100 year extreme sea level event at current mean sea level, with 41 coastal marae are potentially exposed to a 100 year extreme sea level event with a 3 m rise in mean sea level. The most common type of coastal geomorphology nationally and in the Bay of Plenty was shallow drowned valleys, with 72 coastal marae in this category. The response of these systems to sea level rise manifests as changes in the tidal regime and sediment transport dynamics which will affect inundation and erosion of low-lying areas, where many coastal marae and urupā are positioned.
Thus, it is clear that marae and urupā are nationally at risk to sea level rise, and their responses will be highly variable with geomorphology. But what are the next steps? There are many legislative documents such as the coastal climate change and hazards report by the Ministry for the Environment which suggests that the Dynamic Adaptive Policy Pathways strategy to address the uncertainty surrounding climate change, recommended as a method for future planning. Another is the pending reform of the Resource Management Act which will introduce a climate change adaptation act where support for managed retreat will be made available. However, any management strategies for marae, hapū and iwi will need to be cognisant of the tapū and māna that these places hold, and there will be no one size fits all approach.

year: 2021