title: Characterisation of hemp fibre reinforced Poly(Lactic Acid) composites

authors: Sawpan, Moyeenuddin Ahmad

subjects: fibre reinforced composites

abstract: In this work, the mechanical properties including tensile strength, flexural strength, impact strength and fracture toughness of the PLA/hemp composites were investigated over a range of fibre content (0-30 wt.%). It was observed that, the tensile strength and Young's modulus of the composites increased with increased fibre content. The flexural strength did not increase with fibre reinforcement, however, the flexural modulus of the composites increased significantly. Impact strength of the composites increased up to 20 wt. % fibre loading, however, further increased fibre loading caused a reduction of impact strength. KIc and GIc values decreased with increased fibre content.

text: Characterisation of hemp fibre reinforced Poly(Lactic Acid) composites In this work, the mechanical properties including tensile strength, flexural strength, impact strength and fracture toughness of the PLA/hemp composites were investigated over a range of fibre content (0-30 wt.%). It was observed that, the tensile strength and Young's modulus of the composites increased with increased fibre content. The flexural strength did not increase with fibre reinforcement, however, the flexural modulus of the composites increased significantly. Impact strength of the composites increased up to 20 wt. % fibre loading, however, further increased fibre loading caused a reduction of impact strength. KIc and GIc values decreased with increased fibre content.

year: 2009

title: Computational Bayesian inference using low discrepancy sequences

authors: Brown, Paul Tamataatoi

subjects: Bayesian Inference

abstract: The Integrated Nested Laplace Approximation (INLA) provides fast and accurate Bayesian inference for complex hierarchical models. For INLA, and other deterministic methods, the hyperparameter space is explored and points are laid out in a grid structure. These points are used in some numerical integration scheme for which marginal posterior distributions are computed. The main drawback is that the number of points increase exponentially with the number of hyperparameters. The grid is a type of quasi-Monte Carlo (QMC) point set. Low discrepancy sequences (LDS) are QMC point sets that are well known to have significant advantages over grids in terms of convergence and accuracy, and suffer less from the so-called curse of dimensionality.

This work makes several important contributions. We introduce a new method using LDS to compute marginal posterior distributions for hyperparameters, discuss the convergence properties of the approximations and show that they converge to the true posterior. We also show how these methods can be incorporated into the INLA inference framework, and we outline important extensions that improve the accuracy of our approximations with little extra computational effort needed. Lastly, we build a unique spatio-temporal model of residential crime in Hamilton, using INLA’s stochastic partial differential equation approach to a Log-Gaussian Cox Process, and use an LDS to approximate the latent parameters of the model.

Our results show that for a fixed number of points or computational time, LDS methods can outperform general grid-based methods, leading to better marginal posterior approximations. Modifying the method for the purposes of incorporation to INLA, we show that we can outperform INLA’s grid with respect to computational speed, and obtain accurate and flexible approximations to the model hyperparameters.

text: Computational Bayesian inference using low discrepancy sequences The Integrated Nested Laplace Approximation (INLA) provides fast and accurate Bayesian inference for complex hierarchical models. For INLA, and other deterministic methods, the hyperparameter space is explored and points are laid out in a grid structure. These points are used in some numerical integration scheme for which marginal posterior distributions are computed. The main drawback is that the number of points increase exponentially with the number of hyperparameters. The grid is a type of quasi-Monte Carlo (QMC) point set. Low discrepancy sequences (LDS) are QMC point sets that are well known to have significant advantages over grids in terms of convergence and accuracy, and suffer less from the so-called curse of dimensionality.

This work makes several important contributions. We introduce a new method using LDS to compute marginal posterior distributions for hyperparameters, discuss the convergence properties of the approximations and show that they converge to the true posterior. We also show how these methods can be incorporated into the INLA inference framework, and we outline important extensions that improve the accuracy of our approximations with little extra computational effort needed. Lastly, we build a unique spatio-temporal model of residential crime in Hamilton, using INLA’s stochastic partial differential equation approach to a Log-Gaussian Cox Process, and use an LDS to approximate the latent parameters of the model.

Our results show that for a fixed number of points or computational time, LDS methods can outperform general grid-based methods, leading to better marginal posterior approximations. Modifying the method for the purposes of incorporation to INLA, we show that we can outperform INLA’s grid with respect to computational speed, and obtain accurate and flexible approximations to the model hyperparameters.

year: 2019

title: Whānau aspirations, extracurricular activity  and positive youth development:  The leisure activity patterns and narratives of successful young Māori men and how they might inform  urban whānau raising tamatāne.

authors: Clarke, Gloria Hinemoa

subjects: Leisure

abstract: The purpose of this research is to offer parents and whānau (extended family groups) insight about the kinds of leisure activities that might make a positive contribution to their boys’ development. Focused on the positive developmental benefits of leisure participation in relation to Māori boys, and employing a kaupapa Māori framework and qualitative methods, this study represents a foray into new territory. 
	Conducted ‘by, with, and for’ Māori (the indigenous people of Aotearoa New Zealand), and guided by the question ‘How might the leisure activity patterns and narratives of successful young Māori men inform urban whānau raising tamatāne (Māori boys/sons)?’ the three-phase research design was strengths-based, collaborative, and both retrospective and prospective. In phase one, a group of 11 parents participated in focus group hui (gatherings) in which they established the criteria for ‘successful young Māori men’ (SYMM) based on their aspirations for their primary-school aged boys. In phase two, this whānau of interest then selected six SYMM from a pool of eight volunteers, who, along with one or both of their parents participated in one-off semi-structured interviews. In these interviews, we co-constructed life and leisure maps, and discussed how their childhood leisure activities and experiences contributed to their development and who they are today. In phase three, a selection of raw data from these interviews was prepared for a group analysis, during which the whānau of interest made three key observations: (1) As children and youth, these SYMM had participated in a number and range of organised and informal leisure activities including sport, kapa haka (Māori cultural performance), music, art, and for three of them, faith-based activities; (2) they were “connected” to their parent(s) and whānau; and (3) their leisure activities had brought them into contact with positive male role models. Consequently, the whānau of interest talked about increasing the number and variety of their boys’ leisure activities; how they could further support their boys’ leisure participation; and bringing more male role models into their boys’ lives. 
	The findings of this study support the current literature regarding extracurricular activity participation in relation to positive youth development, but also highlight some methodological issues and cultural and contextual nuances. The research supports international and local studies in which high-performing students participated in a number and combination of extracurricular activities. In contrast, however, the experiences and reflections of the SYMM in this study highlight the limitations of combining all sports and all arts into broad activity categories. The research participants’ leisure activities also point to the relevance and applicability of the Te Whare Tapa Whā model of health and wellbeing. Their involvement in kapa haka contrasts with the (North American) literature in which males are a minority in the performing arts, and while some studies indicate that participation in music making declines in high school, these young men began playing musical instruments in high school. Moreover, the salience and significance of the research participants’ casual leisure activities challenges the tendency to cast informal leisure as the antithesis of extracurricular activity participation. These findings raise questions about the applicability of using international activity categories in Aotearoa New Zealand research, and consequently the need to conduct our own leisure and positive youth development studies. 
Other topics raised in this thesis include rugby and masculinity, spirituality, and the tensions involved in building and honouring our children’s rangatiratanga (independence). The short answer to the research question is that a variety and balance of leisure activities has the potential to make positive contributions to boys’ lives. Implications, limitations, and recommendations for future research are also discussed.

text: Whānau aspirations, extracurricular activity  and positive youth development:  The leisure activity patterns and narratives of successful young Māori men and how they might inform  urban whānau raising tamatāne. The purpose of this research is to offer parents and whānau (extended family groups) insight about the kinds of leisure activities that might make a positive contribution to their boys’ development. Focused on the positive developmental benefits of leisure participation in relation to Māori boys, and employing a kaupapa Māori framework and qualitative methods, this study represents a foray into new territory. 
	Conducted ‘by, with, and for’ Māori (the indigenous people of Aotearoa New Zealand), and guided by the question ‘How might the leisure activity patterns and narratives of successful young Māori men inform urban whānau raising tamatāne (Māori boys/sons)?’ the three-phase research design was strengths-based, collaborative, and both retrospective and prospective. In phase one, a group of 11 parents participated in focus group hui (gatherings) in which they established the criteria for ‘successful young Māori men’ (SYMM) based on their aspirations for their primary-school aged boys. In phase two, this whānau of interest then selected six SYMM from a pool of eight volunteers, who, along with one or both of their parents participated in one-off semi-structured interviews. In these interviews, we co-constructed life and leisure maps, and discussed how their childhood leisure activities and experiences contributed to their development and who they are today. In phase three, a selection of raw data from these interviews was prepared for a group analysis, during which the whānau of interest made three key observations: (1) As children and youth, these SYMM had participated in a number and range of organised and informal leisure activities including sport, kapa haka (Māori cultural performance), music, art, and for three of them, faith-based activities; (2) they were “connected” to their parent(s) and whānau; and (3) their leisure activities had brought them into contact with positive male role models. Consequently, the whānau of interest talked about increasing the number and variety of their boys’ leisure activities; how they could further support their boys’ leisure participation; and bringing more male role models into their boys’ lives. 
	The findings of this study support the current literature regarding extracurricular activity participation in relation to positive youth development, but also highlight some methodological issues and cultural and contextual nuances. The research supports international and local studies in which high-performing students participated in a number and combination of extracurricular activities. In contrast, however, the experiences and reflections of the SYMM in this study highlight the limitations of combining all sports and all arts into broad activity categories. The research participants’ leisure activities also point to the relevance and applicability of the Te Whare Tapa Whā model of health and wellbeing. Their involvement in kapa haka contrasts with the (North American) literature in which males are a minority in the performing arts, and while some studies indicate that participation in music making declines in high school, these young men began playing musical instruments in high school. Moreover, the salience and significance of the research participants’ casual leisure activities challenges the tendency to cast informal leisure as the antithesis of extracurricular activity participation. These findings raise questions about the applicability of using international activity categories in Aotearoa New Zealand research, and consequently the need to conduct our own leisure and positive youth development studies. 
Other topics raised in this thesis include rugby and masculinity, spirituality, and the tensions involved in building and honouring our children’s rangatiratanga (independence). The short answer to the research question is that a variety and balance of leisure activities has the potential to make positive contributions to boys’ lives. Implications, limitations, and recommendations for future research are also discussed.

year: 2020