Science and Engineering Papers

Permanent URI for this collectionhttps://researchcommons.waikato.ac.nz/handle/10289/38

This collection houses research from the School of Science and from the School of Engineering at the University of Waikato.

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Work-integrated learning in higher education
(2024) Zegwaard, Karsten E.
Seminar presented at University College Cork, Ireland, on the definition of WIL, design of quality WIL frameworks and the different models of WIL such as curricular, co-curricular and extra-curricular activities. Also international perspectives - developments from various countries including New Zealand, Australia, Canada, and Germany. Discussions included the critical role of WIL in enhancing employability outcomes for students and detailing the University of Waikato’s approach to integrating WIL into their curriculum, which includes compulsory WIL components across all disciplines.
Assessment practices in work-integrated learning
(2024) Zegwaard, Karsten E.
The purpose of this webinar is to discuss the purpose of assessment in work-integrated learning (WIL), what authentic assessments means and explore examples of high quality assessment in different modalities of WIL.
Time's scales: Working with time at Roonka
(2023) Littleton, Judith; Allen, Harry; Emmitt, Joshua; Karstens, Sarah; Petchey, Fiona; Walshe, Keryn
The site of Roonka, subject of long-term excavation by Graeme Pretty and volunteers under the aegis of the South Australian Museum, is still the most extensive excavation of a Holocene burial ground in Australia. The Roonka project between the University of Auckland and the River Murray and Mallee Aboriginal Corporation began in 2014 with the aim of re-analysing the mortuary customs and human remains through the lens of time prior to repatriation. Rather than assuming a single site function e.g. a cemetery or a history which can be divided into two phases (e.g. pre- and post-ENSO), we aim to trace changes in human health and behaviour over the Holocene as people adapted or accommodated changing conditions – the cycle of change and resilience. This means thinking through the nature of the record and the periods of time within it – the event of death, precise memories of other events, the life history of an individual, discontinuous records of site formation, long term continuities of cultural change and differential preservation. In this paper we go back to that original set of ideas and consider how the work and conversations we have had with each other have added more elements of time and different conceptions of what matters. We now have a much clearer model of site formation, taphonomic processes, long term cultural practices and short term catastrophes of individual lives. But what has been added to our sense of time? Ideas of time here in Australia versus time elsewhere, legacy archaeology, the rapidity of time’s change post 1830, COVID time, lived time, research project time… In this paper, we analyse how these different aspects of time interact or remain separate, are useful in different circumstances and provide new interpretations of Roonka and its people.
Changing the future of higher education: Integrating work and learning
(2024) Zegwaard, Karsten E.
The increasing expectation that higher education directly links to student employability outcomes has sharpened the focus on work-integrated learning (WIL) and work-based learning (WBL). This keynote will explore this topic including current challenges, and trends; and propose practical resources for educators.
Advice on the use of models to support estuarine outcomes
(Environmental Research Institute, The University of Waikato, 2025) Ellis, Joanne I.; Flowers, Georgina; Gladstone-Gallagher, Rebecca; Pilditch, Conrad A.; Hewitt, Judi ; Maradasz-Smith, Anna; Thrush, Simon; Thomas, Sam
As the interface between the land and sea, estuaries are uniquely distinctive and dynamic environments. They are highly productive and provide numerous ecosystem services (e.g., improving water quality, supporting fisheries, protecting our coastline). The diversity of habitats contained within estuaries (e.g., crab burrows, seagrass meadows, worm mats, shellfish beds) support a wide array of species that are critical for ecosystem functioning and integrity. Unfortunately, the Our Marine Environment 2019 report clearly identified continued national degradation of the marine environment, particularly for estuaries. Subsequent reports in 2022 and 2025 have not indicated any reversal of these trends.
Derivation and experimental analysis of Peukert’s equation in terms of fractional equivalent circuits
(Elsevier BV, 2026-02) Cree, Michael J; Wilson, Marcus; Scott, Jonathan B
Using an equivalent circuit model (ECM) of a battery that involves fractional elements we analytically derive Peukert’s empirical equation along with generalisations of the equation for the increasing capacity of the battery as the charge and discharge currents are reduced. The derived generalised Peukert’s Equations are dimensionally consistent and all parameters (including Peukert’s coefficient and the so-called ‘capacity constant’) can be calculated from the parameters of the ECM and operating voltage range of the battery. Experiments are conducted on ten batteries to demonstrate that the resistor fractional-capacitor series ECM fit to discharge times predicts well the impedance spectrum found by electrochemical impedance spectroscopy (EIS), and vice versa, on Li-CO/NCA/NMC and Na-ion batteries. This agreement is not observed on the tested LiFePO and LiTO batteries because the impedance spectrum exhibits behaviour not captured by the ECM. Peukert’s Equation predicts ever increasing capacity as both the charge and discharge currents are reduced. The experimental results confirm this behaviour for all batteries down to the lowest current measured (C/256).
Recent progress in remanufacturing technologies using metal additive manufacturing processes and surface treatment
(Springer, 2024) Kahhal, Parviz; Jo, Yeong-Kwan; Park, Sang-Hu
Remanufacturing has emerged as an effective strategy to promote sustainability, reduce waste, and enhance resource efficiency in modern manufacturing processes. However, traditional remanufacturing methods have limitations in producing complex geometries and restoring parts to their original condition, leading to reduced performance and durability. Metal additive manufacturing (AM) methods have shown significant potential in overcoming these limitations and enhancing the quality and reliability of remanufactured parts. Metal AM enables the production of replacement parts with high geometrical complexity and tight tolerances. On the other hand, surface treatment techniques, such as polishing and coating, can improve the surface properties of additively manufactured parts. Recent advancements in metal AM have led to significant progress in manufacturing technologies, including the development of hybrid methods combining metal AM with a surface treatment to achieve superior surface finish and accuracy while reducing production time and cost. Despite progress, challenges such as the need for cost-effective and scalable processing methods, the development of new materials, and the optimization of process parameters for specific applications still need to be addressed. Moreover, although surface modification techniques suitable for metal components fabricated through additive manufacturing can be employed for remanufactured parts, their adoption needs to be improved and necessitates additional advancement. This paper provides an overview of recent progress in manufacturing and remanufacturing technologies using metal additive manufacturing processes and surface treatments, highlighting their potential to significantly improve the quality and reliability of remanufactured parts. The paper concludes with a discussion of the future prospects of this field and the need for continued research and development to fully realize the potential of remanufacturing technologies.
Supplementary notes for 2024 Moana Oceania NZ soil judging handbook
(New Zealand Society of Soil Science, 2024-11-20) Lowe, David J.
These supplementary maps and tables were compiled by David J. Lowe to accompany and enhance the NZ soil judging handbook prepared for the 2024 Moana Oceania Soil Judging competition held in the Rotorua region 29 November-1 December 2024 (prior to the joint NZSSS and SSA soils conference 2-5 December 2024 in Rotorua). They include maps of volcanic centres and explosively erupted products in North Island, the general soil pattern for tephra-derived soils, the main rhyolitic tephras deposited in the Rotorua-Tarawera region over the past c. 25,400 years, and the distribution of Taupo tephra (c. 232 AD), Kaharoa tephra (c. 1314 AD) and Tarawera tephra (10 June 1886 AD). Notes on the development of the Mamaku Plateau via ignimbrite emplacement and erosion and on the nature and formation of the nanoclay, allophane, are also included.
Web crippling behaviour of cold-formed steel channel sections having elongated edge-stiffened web holes under interior-two-flange loading condition
(Elsevier, 2023-11-01) Wang, Wei; Roy, Krishanu; Fang, Zhiyuan (Arthur); Beulah Gnana Ananthi, G.; Lim, James Boon Piang
In the past decade, cold-formed steel (CFS) channel sections having circular edge-stiffened web holes have been developed in New Zealand. Such edge-stiffened holes increase the strength of the CFS channel sections, compared to an equivalent section having unstiffened holes, while still allowing full service integration. In the case of web crippling, previous research has found that use of edge-stiffened holes almost results in the same strength of an equivalent channel-section having a plain web. Such circular edge-stiffened web holes can now be extended to elongated edge-stiffened web holes. However, for such elongated holes, no experimental tests have been reported in the literature. In this paper, a numerical investigation was carried out, and non-linear finite element (FE) analyses were used to investigate the web crippling behaviour of CFS channel sections having edge-stiffened web holes under the interior-two-flange (ITF) loading condition. The cases of both flange fastened and flange unfastened were considered. The FE models were validated against test results of sections having circular edge-stiffened web holes; good agreement in terms of the load–displacement curves and deformed shapes was shown. Using the validated FE models, a parametric study was carried out on CFS channel sections having elongated un-stiffened and edge-stiffened web holes, comprising 1,227 finite element analyses (FEA) results. Compared to sections having a plain web, for the case of an elongated opening, without any edge-stiffener, having an aspect ratio of two and three, the average reduction in web crippling strength was 39% and 49%, respectively. However, for an edge-stiffened hole, the reduction in the web crippling strength was reduced to only 2% and 16%, respectively. Finally, the design equations in the form of the web crippling reduction factor (Rp) and the equations based on the direct strength method (DSM) for CFS sections with elongated web holes were proposed.
Web crippling design of cold-formed stainless steel channels under interior-two-flange loading condition using deep belief network
(Elsevier, 2023-01) Fang, Zhiyuan (Arthur); Roy, Krishanu; Padiyara, Sujith; Chen, Boshan; Raftery, Gary M.; Lim, James Boon Piang
This research presents a deep-learning framework, namely a deep belief network (DBN), for analyzing the interior-two-flange web crippling performance of cold-formed stainless steel channels with centered and offset web holes. An elastoplastic finite element (FE) model, validated using 101 experimental results which were previously reported in the literature, generates a total of 43,200 data points for training the DBN. When compared to a total of 54 experimental results published in the literature, the DBN predictions were shown to be approximately 10% more conservative. Using the same large training data, the developed DBN model outperformed the Backpropagation Neural Network (a typical shallow artificial neural network) and the PaddlePaddle-based linear regression model. A parametric analysis was then performed using the DBN predictions to explore the effect of section size, web holes and bearing length. Design equations for (reduced) web crippling strength are proposed for the cold-formed stainless steel perforated channels, and the feasibility of the proposed equations was assessed by the conducted reliability analysis.
Numerical investigation of cold-formed steel channels with edge-stiffened and unstiffened elongated web holes under shear
(Elsevier BV, 2024) Chandramohan, Dinesh Lakshmanan; Roy, Krishanu; Fang, Zhiyuan (Arthur); Beulah Gnana Ananthi, G.; Lim, James Boon Piang
Over the past decade, cold-formed steel (CFS) channel sections having edge-stiffened circular web holes have been developed in New Zealand. Such edge-stiffened holes increase the strength of the CFS channel sections, compared to an equivalent section having unstiffened web holes, while still allowing full building service integration. In the case of shear, previous research has found that the use of edge-stiffened web holes significantly improves the shear strength of such channel sections. However, no studies are available in the literature investigating the shear strength of CFS channel sections with edge-stiffened elongated web holes. The issue is addressed herein. Non-linear finite element (FE) analyses are used to investigate the shear strength of CFS channel sections with a shear span aspect ratio of 2.0. The FE models were validated against the experimental test results of sections having unstiffened elongated web holes and edge-stiffened circular web holes; good agreement in terms of the load-displacement curves and failure behaviour was shown. Using the validated FE models, a parametric study was conducted, comprising 2124 finite element analyses (FEA) results. The parametric results were then compared to the design predictions of the American Iron and Steel Institute (AISI 2016), and Australia/New Zealand Standards (AS/NZS 2018) and Wanniarchchi et al. (2017) for unstiffened elongated web holes, showing that the design predictions are unconservative in comparison results. Moreover, the direct strength method (DSM) approach of Pham et al. (2020a and 2023) provides conservative results for channels with unstiffened elongated web holes. It was also found that the design equations proposed by Chen et al. (2022) for edge-stiffened circular web holes were unconservative in predicting the shear strength of channels having edge-stiffened elongated web holes. Therefore, design equations in the form of a shear reduction factor and a modified DSM approach for CFS channel sections having unstiffened and edge-stiffened elongated web holes were proposed. Finally, a reliability analysis was carried out to ensure that the proposed equations are reliable to predict the shear strength of CFS channel sections with edge-stiffened and unstiffened web holes.
Editorial: The genomics of biological invasion
(Frontiers Media, 2021-12-23) McGaughran, Angela; Mori, Emiliano; Quilodrán, Claudio S.
Understanding how invasive species rapidly infiltrate and establish in new areas is critically relevant for ecological management, pest control, climate change adaptation, and evolution. Invasive species are almost always detrimental to native flora and fauna: they may out-compete natives in the race for resources, introduce parasites and diseases, and cause immense environmental damage.
Comparative phylogeography in the genomic age: Opportunities and challenges
(Wiley, 2022) McGaughran, Angela; Liggins, Libby; Marske, Katharine A.; Dawson, Michael N.; Schiebelhut, Lauren M.; Lavery, Shane D.; Knowles, L. Lacey; Moritz, Craig; Riginos, Cynthia
Aim: We consider the opportunities and challenges comparative phylogeography (CP) faces in the genomic age to determine: (1) how we can maximise the potential of big CP analyses to advance biogeographic and macroevolutionary theory; and (2) what we can, and will struggle, to achieve using CP approaches in this era of genomics. Location: World-wide. Taxon: All. Methods: We review the literature to discuss the future of CP - particularly examining CP insights enabled by genomics that may not be possible for single species and/or few molecular markers. We focus on how geography and species' natural histories interact to yield congruent and incongruent patterns of neutral and adaptive processes in the context of both historical and recent rapid evolution. We also consider how CP genomic data are being stored, accessed, and shared. Results: With the widespread availability of genomic data, the shift from a single- to a multi-locus perspective is resulting in detailed historical inferences and an improved statistical rigour in phylogeography. However, the time and effort required for collecting co-distributed species and accruing species-specific ecological knowledge continue to be limiting factors. Bioinformatic skills and user-friendly analytical tools, alongside the computational infrastructure required for big data, can also be limiting. Main conclusions: Over the last ~35 years, there has been much progress in understanding how intraspecific genetic variation is geographically distributed. The next major steps in CP will be to incorporate evolutionary processes and community perspectives to account for patterns and responses among co-distributed species and across temporal scales, including those related to anthropogenic change. However, the full potential of CP will only be realised if we employ robust study designs within a sound comparative framework. We advocate that phylogeographers adopt such consistent approaches to enhance future comparisons to present-day findings.
Adaptation to environmental temperature in divergent clades of the nematode Pristionchus pacificus
(Oxford University Press, 2022) Leaver, Mark; Moreno, Eduardo; Kayhan, Merve; McGaughran, Angela; Rödelsperger, Christian; Sommer, Ralf J.; Hyman, Anthony A.
Because of ongoing climate change, populations of organisms are being subjected to stressful temperatures more often. This is especially problematic for ectothermic organisms, which are likely to be more sensitive to changes in temperature. Therefore, we need to know if ectotherms have adapted to environmental temperature and, if so, what are the evolutionary mechanisms behind such adaptation. Here, we use the nematode Pristionchus pacificus as a case study to investigate thermal adaptation on the Indian Ocean island of La Réunion, which experiences a range of temperatures from coast to summit. We study the evolution of high-temperature tolerance by constructing a phylogenetic tree of strains collected from many different thermal niches. We show that populations of P. pacificus at low altitudes have higher fertility at warmer temperatures. Most likely, this phenotype has arisen recently and at least twice independently, consistent with parallel evolution. We also studied low-temperature tolerance and showed that populations from high altitudes have increased their fertility at cooler temperatures. Together, these data indicate that P. pacificus strains on La Réunion are subject to divergent selection, adapting to hot and cold niches at the coast and summit of the volcano. Precisely defining these thermal niches provides essential information for models that predict the impact of future climate change on these populations.
Genomic signals of local adaptation across climatically heterogenous habitats in an invasive tropical fruit fly (Bactrocera tryoni)
(Springer Science and Business Media LLC, 2024) Parvizi, Elahe; Vaughan, Amy L.; Dhami, Manpreet K.; McGaughran, Angela
Local adaptation plays a key role in the successful establishment of pest populations in new environments by enabling them to tolerate novel biotic and abiotic conditions experienced outside their native range. However, the genomic underpinnings of such adaptive responses remain unclear, especially for agriculturally important pests. We investigated population genomic signatures in the tropical/subtropical Queensland fruit fly, Bactrocera tryoni, which has an expanded range encompassing temperate and arid zones in Australia, and tropical zones in the Pacific Islands. Using reduced representation sequencing data from 28 populations, we detected allele frequency shifts associated with the native/invasive status of populations and identified environmental factors that have likely driven population differentiation. We also determined that precipitation, temperature, and geographic variables explain allelic shifts across the distribution range of B. tryoni. We found spatial heterogeneity in signatures of local adaptation across various climatic conditions in invaded areas. Specifically, disjunct invasive populations in the tropical Pacific Islands and arid zones of Australia were characterised by multiple significantly differentiated single nucleotide polymorphisms (SNPs), some of which were associated with genes with well-understood function in environmental stress (e.g., heat and desiccation) response. However, invasive populations in southeast Australian temperate zones showed higher gene flow with the native range and lacked a strong local adaptive signal. These results suggest that population connectivity with the native range has differentially affected local adaptive patterns in different invasive populations. Overall, our findings provide insights into the evolutionary underpinnings of invasion success of an important horticultural pest in climatically distinct environments.
Current stewardship practices in invasion biology limit the value and secondary use of genomic data
(Wiley, 2023) Vaughan, Amy L.; Parvizi, Elahe; Matheson, Paige; McGaughran, Angela; Dhami, Manpreet K.
Invasive species threaten native biota, putting fragile ecosystems at risk and having a large-scale impact on primary industries. Growing trade networks and the popularity of personal travel make incursions a more frequent risk, one only compounded by global climate change. With increasing publication of whole-genome sequences lies an opportunity for cross-species assessment of invasive potential. However, the degree to which published sequences are accompanied by satisfactory spatiotemporal data is unclear. We assessed the metadata associated with 199 whole-genome assemblies of 89 invasive terrestrial invertebrate species and found that only 38% of these were derived from field-collected samples. Seventy-six assemblies (38%) reported an ‘undescribed’ sample origin and, while further examination of associated literature closed this gap to 23.6%, an absence of spatial data remained for 47 of the total assemblies. Of the 76 assemblies that were ultimately determined to be field-collected, associated metadata relevant for invasion studies was predominantly lacking: only 35% (27 assemblies) provided granular location data, and 33% (n = 25) lacked sufficient collection date information. Our results support recent calls for standardized metadata in genome sequencing data submissions, highlighting the impact of missing metadata on current research in invasion biology (and likely other fields). Notably, large-scale consortia tended to provide the most complete metadata submissions in our analysis—such cross-institutional collaborations can foster a culture of increased adherence to improved metadata submission standards and a standard of metadata stewardship that enables reuse of genomes in invasion science.
How might climate change affect adaptive responses of Polar Arthropods?
(MDPI, 2023) Matheson, Paige; McGaughran, Angela
Climate change is expected to impact the global distribution and diversity of arthropods, with warmer temperatures forcing species to relocate, acclimate, adapt, or go extinct. The Arctic and Antarctic regions are extremely sensitive to climate change and have displayed profound and variable changes over recent decades, including decreases in sea ice extent, greening of tundra, and changes to hydrological and biogeochemical cycles. It is unclear how polar-adapted arthropods will respond to such changes, though many are expected to be at great risk of extinction. Here, we review the adaptive mechanisms that allow polar arthropods to persist in extreme environments and discuss how the effects of climate change at the poles will likely favour non-native species or those with the ability to rapidly evolve and/or acclimate. We find that physiological, behavioural, plastic, and genetic data are limited in scope for polar arthropods and research on adaptive responses to change is scarce. This restricts our ability to predict how they may respond to a warming climate. We call for a greater investment in research that specifically targets the ecology and evolution of these taxa, including genomic and transcriptomic approaches that can evaluate the potential for plastic and evolved environmental responses.
Sedimentary environment controls carbon sequestration potential of unvegetated intertidal estuarine sediments
(American Geophysical Union (AGU), 2025-12) La Croix, Andrew D.
Unvegetated intertidal sediments are increasingly recognized as contributors to coastal carbon storage, yet their organic carbon burial potential remains poorly constrained. This study examines spatial and temporal patterns of carbon accumulation in unvegetated intertidal flats of Ōhiwa Harbor, New Zealand, using surface sediments and three radiocarbon-dated cores spanning up to ∼7,700 yrs. Within the harbor, five distinct sedimentary facies were identified, each displaying unique sediment characteristics and patterns of organic carbon burial. Mud-rich, low-energy facies, including rippled and bioturbated muds, consistently showed higher organic carbon density and burial rates compared to sandy, more dynamic facies. Estimated carbon stocks in the upper meter of sediment range from 44 to 120 t C ha−1, comparable to or exceeding those of many vegetated coastal habitats. Temporal changes in facies distribution driven by estuarine processes and variations in sediment supply led to significant long-term fluctuations in organic carbon burial. These results demonstrate that organic carbon storage in unvegetated intertidal flats is highly heterogeneous and controlled by the persistence of fine-grained depositional environments. A facies-based framework offers a process-driven approach to assessing and managing blue-carbon potential in estuarine systems increasingly altered by climate and land-use change.
Insights into invasive species from whole‐genome resequencing
(Wiley, 2021) North, Henry L.; McGaughran, Angela; Jiggins, Chris
Studies of invasive species can simultaneously inform management strategies and quantify rapid evolution in the wild. The role of genomics in invasion science is increasingly recognised, and the growing availability of reference genomes for invasive species is paving the way for whole-genome resequencing studies in a wide range of systems. Here, we survey the literature to assess the application of whole-genome resequencing data in invasion biology. For some applications, such as the reconstruction of invasion routes in time and space, sequencing the whole genome of many individuals can increase the accuracy of existing methods. In other cases, population genomic approaches such as haplotype analysis can permit entirely new questions to be addressed and new technologies applied. To date whole-genome resequencing has only been used in a handful of invasive systems, but these studies have confirmed the importance of processes such as balancing selection and hybridization in allowing invasive species to reuse existing adaptations and rapidly overcome the challenges of a foreign ecosystem. The use of genomic data does not constitute a paradigm shift per se, but by leveraging new theory, tools, and technologies, population genomics can provide unprecedented insight into basic and applied aspects of invasion science.
Fitness consequences of population bottlenecks in an invasive blowfly
(Wiley, 2024) Croft, Lillian; Matheson, Paige; Butterworth, Nathan J.; McGaughran, Angela
Invasive species often undergo demographic bottlenecks that cause a decrease in genetic diversity and associated reductions in population fitness. Despite this, they manage to thrive in novel environments. Investigating the effects of inbreeding and genetic bottlenecks on population fitness for invasive species is, therefore, key to understanding how they may survive in new environments. We used the blowfly Calliphora vicina (Sciences, Mathématiques et Physique, 1830, 2, 1), which is native to Europe and was introduced to Australia and New Zealand, to examine the effects of genetic diversity on population fitness. We first collected 59 samples from 15 populations across New Zealand and one in Australia, and used 20,501 biallelic SNPs to investigate population genomic diversity, structure and admixture. We then explored the impacts of repeated experimental bottlenecks on population fitness by creating inbred and outbred lines of C. vicina and measuring a variety of fitness traits. In wild-caught samples, we found low overall genetic diversity, signals of genetic admixture and limited (<3%) genetic differentiation between North and South Island populations, with genetic links between the South Island and Australia. Following experimental bottlenecks, we found significant reductions in fitness for inbred lines. However, fitness effects were not felt equally across all phenotypic traits. Moreover, they were not enough to cause population collapse in any experimental line, suggesting that C. vicina (when under relaxed selection, as in laboratory settings) may be able to compensate for population bottlenecks even when highly inbred. Our results demonstrate the value of a tractable experimental system for investigating processes that may facilitate or hamper biological invasion.

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