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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Low-cost Ti alloys: Assessment of their microstructure, mechanical properties, corrosion behaviour, and biological response
(Elsevier, 2026) Bolzoni, Leandro; Nishio, W; Appadan, AM; Manogar, Balakrishnan
Orthopaedic and dental implants, the majority of which are made from titanium alloys, face the crucial challenge of both inducing osteogenesis whilst inhibiting bacterial biofilm formation in an economical manner over the life of the implant. This study introduces an innovative strategy combining cost-effective alloying elements, selected due to their reported biological benefits, for developing new titanium alloys that achieve a tailorable mechanical, corrosion, and biological response. The combination of alloying and manufacturing results in homogeneous materials characterised by a lamellar microstructure. The developed low-cost Ti alloys have a maximum ultimate compression strength of 659 MPa, maximum tensile yield stress of 606 MPa, and maximum elongation of 8.3% without failing catastrophically. The alloys do not degrade as abiotic corrosion is significantly hampered by their intrinsic passivation behaviour (maximum corrosion rate of 8.9 μm/year), and have adjustable surface wettability with contact angles in the 60-81° range. Consequently, stomal cell attachment, cytotoxicity and cytokine production (IL-6 and TGF-β1), and antibacterial rate on S. aureus are consistent and comparable to those of current implnat materials. Based on these characteristics, the low-cost Ti alloys are promising materials for load-bearing biomedical devices.
On a Neural Phonon Model of EEG Brain Dynamics
(Springer, 2026-03-16) Head, Mitchell; Batterton, Christopher; Owen, Mahonri; Konig, Jemma; Ensing, Simeon; Shepherd, Craig
Neuronal oscillations are a ubiquitous feature of brain activity, indexing functions from sensory selection to memory formation. Yet a unified framework that (i) accommodates the nonlinear, noise-driven nature of cortical dynamics and (ii) explains standard empirical measures—power, spectral entropy, coherence, Phase-Locking Value (PLV), Phase-Amplitude Coupling (PAC), and envelope correlations—remains elusive. A natural candidate is the noisy Stuart–Landau (SL) oscillator, whose deterministic form models cortical rhythms as limit cycles, while additive noise induces stochastic phase and amplitude fluctuations. Prior work has shown that networks of SL oscillators can replicate burst statistics, multistability, and cross-frequency modulation in electroencephalography/magnetoencephalography (EEG/MEG). However, an analytical framework linking these models directly to observed connectivity metrics has been lacking. Here we derive such a framework by mapping the Fokker–Planck equation (FPE) of each SL oscillator to an imaginary-time Schrödinger operator via a classical similarity transform. A second-order expansion around the limit-cycle amplitude yields a quadratic Hamiltonian whose ladder operators describe quantised fluctuations—neural phonons—in oscillatory power. Bilinear coupling terms inherited from diffusion give rise to analytically diagonalisable bosonic interactions. This construction yields closed-form expressions for spectral observables and their dynamics, including Green-function-derived coherence and PLV, perturbative PAC, and a five-parameter “personality map” linking microscopic physics to macroscopic brain states. By unifying noisy limit-cycle theory with operator methods from statistical physics, we introduce a tractable, interpretable formalism for understanding neural coherence as the dynamics of quantised phonons.
Effects of PZT Reinforcement on the Properties of Fe-Based Composites Fabricated by Powder Metallurgy
(MDPI, 2026-02-05) Alshammari, Yousef; Parol, Jafarali; Yang, Fei; Bolzoni, Leandro
Fe composites are highly valued for their unique mechanical and magnetic properties, making them essential in various industrial applications. This study represents the first reported attempt to combine PZT into an Fe matrix, aiming to develop novel Fe-PZT composites. The primary objective was to assess how the concentration of PZT influences the properties of these composites. The results show that increasing the PZT content in Fe-xPZT composites (where x = 1, 5, and 10 wt.%) reduces the relative sintered density. Microstructural analysis reveals that the composites with higher PZT levels contained numerous large, irregularly shaped pores due to a pronounced Kirkendall effect and limited densification. Furthermore, the evaporation of the volatile PbO compound was observed to affect the thermal stability of the PZT system, leading to reduced composite homogeneity. SEM analysis showed the formation of intermetallic compounds corresponding to Fe2Ti, FeTi, and FeZr2. Finally, an increase in PZT content tends to degrade the tensile and mechanical properties of the Fe-xPZT composites, though they still do not fail catastrophically. These preliminary findings prove the concept of the feasibility of producing Fe-PZT composites and set the basis for the optimization of their manufacturing process. This should eventually unlock the possibility of producing multifunctional materials.
Machine learning-based prediction of young’s modulus in Ti-Alloys
(MDPI, 2026-02-19) Dinibutun, Seza; Alshammari, Yousef; Bolzoni, Leandro
This study explores the use of machine learning to predict the experimental Young’s modulus of titanium alloys based on their mechanical and microstructural properties. Several regression models were developed and compared, including Random Forest, XGBoost, CatBoost, Multi-Layer Perceptron, and a Stacking Regressor. Among these, Random Forest, XGBoost and CatBoost achieved the most accurate results with R² values above 0.85. To improve interpretability, SHapley Additive exPlanations were applied to examine which input features most strongly influenced the predictions. The results showed that yield strength, hardness, and the molybdenum equivalent parameter (moe) were among the most influential descriptors. While yield strength and hardness were positively associated with the predicted values, higher moe values corresponded to lower predicted Young’s modulus. This study focuses on the prediction of Young’s modulus, a comparatively less explored elastic property in Ti-alloy machine learning studies and combines systematic model comparison with SHAP-based interpretability to provide physically consistent insights into feature–property relationships.
On the precipitability of binary Ti alloys bearing 4-period d-metal eutectoid stabilisers
(Elsevier, 2026-06) Bolzoni, Leandro; Yang, Fei
There is no specific, simple approach for predicting whether the addition of an eutectoid beta stabiliser to Ti leads to an ‘active’ eutectoid transformation upon primary processing (e.g., sintering). Here, we demonstrate that, among theoretical/empirical models, phase diagram features, and electronic structure parameters, the hypoeutectoid area is the best predictor, followed by the molybdenum equivalent parameter (MoE), of the precipitability for 4-period d-metals. As the area increases, which corresponds to the addition of progressively stronger β-eutectoid stabilisers, the less active the eutectoid phase transformation, changing from pearlitic to bainitic (i.e., need for an ageing heat treatment). This occurs if the MoE weighted coefficient is, respectively, lower than or higher than 1. This is because molybdenum is taken as reference, and the higher the coefficient, the larger the drop of the β transus temperature (i.e., higher stabilisation). Valid for 4-period d-metals, it remains to be proven for 5-period and 6-period d-metals.
Tephra seismites - Understanding seismic hazard of hidden faults by analyzing liquefied tephra layers in lakes
(American Association for the Advancement of Science, 2026-02) Kluger, Max O.; Melchert, Richard A.; Moratalla, José M.; Ilanko, Tehnuka; Lowe, David J.; Moon, Vicki G.; Villamor, Pilar; Chaneva, Jordanka; Ross, Nic; Orense, Rolando P.
Assessing seismic hazards in regions with hidden or poorly expressed faults is one of the major challenges in paleoseismology today. Here, we used computed tomography imaging to quantify the dimensions and distribution of liquefaction structures in ≤17.5-thousand-year-old tephra layers in 18 lakes scattered across the poorly expressed Hamilton Basin fault system in northern New Zealand. These "tephra seismites," embedded in unconsolidated, organic-bearing lake sediment, increase in occurrence and dimensions toward known faults and indicate the occurrence of a local hidden fault segment. Through incorporating peak ground acceleration modeling, we found that the spatial distribution of tephra seismites directly relates to the ground shaking induced by near-field fault ruptures. We used the variability in tephra seismites within the stratigraphic record and tephrochronology to better constrain the recurrence intervals and magnitudes of paleoearthquakes from both the Hamilton Basin and adjacent Hauraki Basin fault systems. Our methodology is globally applicable in volcanic and tectonic regions where liquefaction structures are preserved among (hidden) faults.
Student perceptions of paid and unpaid work placements: A comparative analysis
(WACE (Advancing Cooperative & Work-Integrated Education), 2024) Zegwaard, Karsten E.; Adams-Hutcheson, Gail; Zegwaard, Karsten E.; Fleming, Jenny
Work-integrated learning (WIL) is an educational approach that is highly authentic and meaningful, therefore, some of the challenges within can be complex. Student wellbeing has been a focal point within higher education for some years (Konstantinou et al., 2023), albeit the debate around unpaid work placements has only recently been given some scholarly attention (see, e.g., Hoskyn et al., 2023).
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.

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