Science and Engineering Papers
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This collection houses research from the School of Science and from the School of Engineering at the University of Waikato.
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Item Rapid time-domain simulation of fractional capacitors with SPICE(Journal Article, Springer, 2024-01-01) Wilson, Marcus T.; Cowie, L; Farrow, Vance; Cree, Michael J.; Scott, Jonathan B.Fractional capacitors, commonly called constant-phase elements or CPEs, are used in modeling and control applications, for example, for rechargeable batteries. Unfortunately, they are not natively supported in the well-used circuit simulator SPICE. This manuscript presents and demonstrates a modeling approach that allows users to incorporate these elements in circuits and model the response in the time domain. The novelty is that we implement for the first time a particular configuration of RC elements in parallel in a Foster-type network with SPICE in order to simulate a constant-phase element across a defined frequency range. We demonstrate that the circuit produces the required impedance spectrum in the frequency domain, and shows a power-law voltage response to a step change in current in the time domain, consistent with theory, and is able to reproduce the experimental voltage response to a complicated current profile in the time domain. The error depends on the chosen frequency limits and the number of RC branches, in addition to very small SPICE numerical errors. We are able to define an optimum circuit description that minimizes error while maintaining a short computation time. The scientific value is that the work permits rapid and accurate evaluation of the response of CPEs in the time domain, faster than other methods, using open source tools.Item Joint effect of β-eutectoid content and heat treatment on the properties of binary Ti-Cu and Ti-Mn alloys(Journal Article, Elsevier BV, 2024) Bolzoni, Leandro; Yang, Fei; Alshammari, Yousef NamlanThe use of cheap alloying elements and alternative manufacturing techniques are two strategies that can be used to reduce the high cost of Ti alloys. Furthermore, heat treatments are an easy and cost effective method to tailor the mechanical behaviour by means of the modification of the microstructure. For that, this work analysed the quenching and aging heat treatment of binary Ti-Cu and Ti-Mn alloys manufactured via powder metallurgy. It is found that the post-processing solution treatment does not significantly affect the physical properties and residual porosity remains unchanged within the microstructure; however, the heat treatment changes the microconstituents. Serrated martensitic transformed β is formed in quenched Ti-Cu alloys and it is converted into a coarse lamellar or a hypoeutectoid structure as the Cu content increases with the subsequent aging treatment. Aging of the Ti-Mn alloys slightly coarsen the microstructural features where martensite or equiaxed metastable β grains are obtained after quenching. Enhancing of the mechanical behaviour is generally achieved and the solution treatment switches from improving the ductility to increasing the strength and the hardness as the amount of the alloying element increases.Item Pūtahitanga: The intersection of western science and mātauranga Māori in the context of Aotearoa New Zealand’s physical oceanography(Journal Article, Taylor & Francis Group, 2021) Stevens, Craig L.; Paul-Burke , Kura; Russell , PeterAotearoa New Zealand is a land and cultures surrounded by one of the planet’s larger marine exclusive economic zones per capita. Understanding, living within and utilising this domain requires a well-developed knowledge of the physical oceanography–fate, provenance and transfer of ocean-water, material and energy. In the Aotearoa New Zealand context, understanding and utilising the environment through science also requires that Māori have a stake in the science and a pathway to connecting with their mātauranga. The pūtahitanga (intersection) of mātauranga Māori and western science perspectives brings challenges for implementation of the Vision Mātauranga framework for physical oceanographic science. Here we discuss the drivers and key themes for the pūtahitanga and propose a mahere kaupapa/plan bound by: (i) climate, (ii) decolonisation, (iii) shared language, (iv) data sovereignty, and (v) developing a cohort who can lead the field in the coming decades.Item A porous fluoride-substituted bovine-derived hydroxyapatite scaffold constructed for applications in bone tissue regeneration(Journal Article, MDPI AG, 2024-02-28) Ratnayake, Jithendra; Gould, Maree; Ramesh, Niranjan; Mucalo, Michael R.; Dias, George J.Hydroxyapatite is widely used in bone implantation because of its similar mineral composition to natural bone, allowing it to serve as a biocompatible osteoconductive support. A bovine-derived hydroxyapatite (BHA) scaffold was developed through an array of defatting and deproteinization procedures. The BHA scaffold was substituted with fluoride ions using a modified sol-gel method to produce a bovine-derived fluorapatite (BFA) scaffold. Fourier-transform infrared spectroscopy and X-ray diffraction analysis showed that fluoride ions were successfully substituted into the BHA lattice. According to energy dispersive X-ray analysis, the main inorganic phases contained calcium and phosphorus with a fluoride ratio of ~1–2 wt%. Scanning electron microscopy presented a natural microporous architecture for the BFA scaffold with pore sizes ranging from ~200–600 μm. The BHA scaffold was chemically stable and showed sustained degradation in simulated-body fluid. Young’s modulus and yield strength were superior in the BFA scaffold to BHA. In vitro cell culture studies showed that the BFA was biocompatible, supporting the proliferative growth of Saos-2 osteoblast cells and exhibiting osteoinductive features. This unique technique of producing hydroxyapatite from bovine bone with the intent of producing high performance biomedically targeted materials could be used to improve bone repair.Item Vibration analysis of cracked structures as a roving body passes a crack using the Rayleigh-Ritz Method(Journal Article, Center of Technology (COT), 2018) Ilanko, Sinniah; Mochida, Yusuke; De Los Rois, JulianThe natural frequencies of a cracked plate with a roving mass were computed using the Rayleigh-Ritz Method for various sets of boundary condition. The obtained frequencies exhibit a sudden shift as a roving body crosses a crack. If the crack is only partial and continuity of translation is maintained, then the frequency shift occurs only when the body possesses a rotary inertia. If the crack is a complete one (through thickness) which permits differential translation to occur on either side of the crack, a particle having mass only (translatory inertia) is sufficient to cause a sudden shift. There is no need for a rotary inertia. This is potentially useful in detecting cracks in structures, as it is possible to track the changes in the natural frequencies of a structure as a test body such as a vehicle on a bridge moves and identify points where sudden frequency changes occur.