UC Research Repository
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The UC Research Repository collects, stores and makes available original research from postgraduate students, researchers and academics based at the University of Canterbury.
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Recent Submissions
Hydrogen-Rich Syngas Production via Dry and Steam Reforming of Methane in Simulated Producer Gas over ZSM-5-Supported Trimetallic Catalysts
(MDPI AG, 2023) Iminabo JT; Iminabo M; Yip, Alex; Pang, Shusheng
This study investigated the production of hydrogen-rich syngas from renewable sources using durable and efficient catalysts. Specifically, the research focused on steam methane reforming (SRM) and dry methane reforming (DRM) of simulated producer gas from biomass steam gasification in a fluidized bed reactor. The catalysts tested are ZSM-5-supported nickel-iron-cobalt-based trimetallic catalysts in different ratios, which were prepared via the wet impregnation method. Synthesized catalysts were characterized using XRD, BET, H2-TPR, and SEM techniques. The results of the SRM with the simulated producer gas showed that the 20%Ni-20%Fe-10%Co/ZSM-5 trimetallic catalyst, at a gas hourly space velocity (GHSV) of 12 L·h−1·g−1 and reaction temperature of 800 °C, achieved the highest CH4 conversion (74.8%) and highest H2 yield (65.59%) with CO2 conversion (36.05%). Comparing the performance of the SRM and DRM of the simulated producer gas with the 20%Ni-20%Fe-10%Co/ZSM5 at a GHSV of 36 L·h−1·g−1 and 800 °C, they achieved a CH4 conversion of 67.18% and 64.43%, a CO2 conversion of 43.01% and 52.1%, and a H2 yield of 55.49% and 42.02%, respectively. This trimetallic catalyst demonstrated effective inhibition of carbon formation and sintering, with only 2.6 wt.% carbon deposition observed from the thermo-gravimetric analysis of the used catalyst from the SRM of the simulated producer gas, thus promoting the potential of the ZSM-5-supported trimetallic catalysts in methane reforming.
Mathematical aspects of phylogenetic diversity measures
(2024) Manson, Kerry
Phylogenetic diversity (PD) is a popular measure of biodiversity, with particular applications to conservation management. It brings a focus to the evolutionary relationships between species that is missing in simpler approaches, such as the use of species richness. PD attains this focus by considering species in terms of their positions on a phylogenetic tree. The mathematical properties of PD, and a suite of methods derived from it, have been studied since its introduction in the early 1990’s. In this thesis, we explore these properties further, covering three main aspects of PD-related studies.
The first strand of the thesis covers the study and comparison of the PD values of sets of a fixed size. We use combinatorial and algorithmic approaches to understand those sets of species that obtain the extreme PD scores for sets of their size. A combinatorial characterisation of maximum PD sets is provided. This leads to a polynomial-time algorithm for calculating the number of maximum PD sets of each size by applying a generating function. We then use this characterisation to maximise a linear function on the leaves of a phylogenetic tree, subject to the solution being a maximum PD set. Additionally, dynamic programming is used to find solutions to the dual problem, determining minimum PD sets of each size.
The second strand involves phylogenetic diversity indices, a type of function that partitions the PD of a set of species among its constituent members. We give a formal definition of this class of function, and investigate the properties of functions in this class. This process is aided by a description of diversity indices as points within a convex space, whose dimension and extremal points we describe. Particularly, we show that rankings derived from these measures are susceptible to being disrupted by the extinction of some of the species being measured. We introduce a number of new measures that avoid this disruption to a greater extent than existing approaches.
The third strand deals with the link between PD and feature diversity (FD), another means of measuring biodiversity. We provide models for evolution of features on phylogenetic trees that account for loss of features, such as the loss of flight in some bird species. Doing so leads to results showing that PD is an imperfect proxy for FD unless feature loss is (unrealistically) ignored. We show how our new measure, EvoHeritage, spans a continuum that connects PD and SR at the extremes, based on the rate of assumed feature loss.
The distinct parts of this thesis are linked by an aim to better understand what is meant by the concept of biodiversity and to investigate how that understanding is reflected in the way that we measure this idea. We provide a mathematical approach, complemented by a number of algorithms that enable these ideas to be put into practice.
Mana whenua engagement in Crown and Local Authority-initiated environmental planning processes: A critique based on the perspectives of Ngāi Tahu environmental kaitiaki
(Wiley, 2021) Bennett C; Matunga H; Steyl S; Borell, Phil; De Jesus Dionisio, Maria Rita ; Hāpuku A
In New Zealand, the Crown and Local Authorities are required to engage with iwi in resource management matters, yet iwi engagement is a widely recognised weakness in many resource management professionals' skillsets. Coloniality permeates many interactions with iwi, and reflects a profession where practitioners' skillsets have not kept pace with developments in resource management legislation that better recognise the rights and interests of mana whenua. This article explores the real-life impacts of this skill paucity on Ngāi Tahu environmental kaitiaki, and, through a Braided River methodological approach comprised of Kaupapa Māori research and Narrative Inquiry, offers recommendations for best practice mana whenua engagement. The article concludes by discussing the coloniality of planning, and how this impacts practitioners' ability to implement these best practice recommendations.
Exploring secondary teachers’ experiences of collaboration in open plan learning spaces
(2024) Taylor, Megan
Following shifts in education policy and ideology, school buildings in Aotearoa New Zealand have in recent years been built and refurbished in line with principles of connectedness and flexibility. Also called innovative or flexible learning environments, the new large, open learning spaces call for teachers to work collaboratively with larger cohorts of students. This represents a significant disruption to established teacher practice, particularly in the secondary school sector, where teachers have traditionally been subject specialists teaching a range of classes and year levels. This thesis sheds light into a blind spot in the literature base, by exploring the secondary teacher experience of teaching collaboratively in open, shared teaching and learning spaces.
The research approach includes both theoretical and empirical elements. A conceptual model is proposed, locating the collaborative teaching experience within a complex ecology, where socio-cultural, spatial and organisational factors have both constraining and enabling effects on collaboration. Five cases of teacher collaboration across two secondary school sites were explored through a multi-site, phenomenological, interpretative case study. Data, sourced primarily from interviews, were analysed thematically, through an iterative, largely inductive process. The intrinsic qualities of each case are described and themes across the cases are elaborated. Teachers’ social and spatial practices are discussed in relation to Lefebvre’s (1974/1991) spatial triad and Giddens’ (1984) theory of structuration, illuminating the ways in which teachers who work collaboratively in open learning spaces both shape, and are shaped by their environments.
The findings of the study show that the complexities of enacting collaborative teaching in secondary schools are not captured in the existing conceptualisations of teacher collaboration available in the literature. Neither are they well accounted for in Ministry of Education policies and support materials. While teachers enjoy working collaboratively with colleagues and perceive it to infer a number of benefits, they also face some significant tensions and challenges. Those working in multiple collaborative teams carried a relational burden associated with huge student numbers and diverse, complex working relationships with colleagues. The large learning spaces were busy social environments where teachers found it difficult to respond to and manage challenging student behaviours in ways that maintained a positive environment conducive to learning. Furthermore, findings highlight a misalignment between notions of flexibility. While building policy has focused on the physical flexibility of learning spaces, teacher participants placed more value on pedagogical flexibility.
The thesis makes a theoretical and empirical contribution to the field of research into innovative learning environments and argues that to realise the potential of collaborative teaching in secondary schools, spatial, socio-cultural and organisational factors all need to align. Drawing on the findings, a number of implications are identified which have relevance for secondary school organisation and learning space design.
Development and validation of a dose accumulation workflow for MR-guided adaptive radiotherapy.
(2024) Taylor, Megan
During radiotherapy treatment, anatomical changes and discrepancies in patient setup
between fractions may result in the planned dose and actual delivered dose differing. In
conventional radiotherapy, it is common practice to assume that over a full course of
treatment, these differences in delivered and planned dose are negligible. This is because
positioning devices, margins on target volumes, etc. define “acceptable” levels of error.
With the development of adaptive radiotherapy, images of the patient can be obtained
with every fraction, allowing visualization of how the patient anatomy differs from the reference plan setup. Along with visualizing positioning changes, the Elekta Unity MR-Linac
system allows for alterations to the treatment plan on each fraction to correct for these
positional changes. This, in theory, should reduce the discrepancy in planned dose and
delivered dose. In practice, delivered dose still differs from fraction to fraction. Without
summing delivered dose per fraction, it is a qualitative assumption that the planned dose
has been delivered. A quantitative method allows for reassurance and more robust adaptive planning. The aim of this project was to develop a workflow to accurately measure
accumulated dose inter-fractionally – considering the affects of anatomical/positioning
changes. The workflow was then to be validated and compared to planned dose.
Using data of ten patients previously treated on the MR-Linac for prostate cancer, a
deformable image registration algorithm was optimised and dose mapping methods were
assessed. The finalised components were combined in a dose accumulation workflow.
Uncertainties were estimated for the workflow and synthetic deformations used to validate the method. It was found that median uncertainties were generally below 1%. However, point dose uncertainties exceeded 40% in some cases where regions of high dose
gradients occurred. Comparison to known deformations showed a high level of agreement
in dosimetric criteria (gamma passing rates above 95%).
A comparison of planned and accumulated dose showed that there were statistically significant differences in PTV coverage suggesting dose accumulation may be a useful tool
for improving understanding of planned vs delivered dose and should be considered for
applications in adaptive radiotherapy.