School of Engineering, Computer and Mathematical Sciences - Te Kura Mātai Pūhanga, Rorohiko, Pāngarau

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https://hdl.handle.net/10292/553
AUT is home to a number of renowned research institutes in engineering, and computer and mathematical sciences. The School of Engineering, Computer and Mathematical Sciences strong industry partnerships and the unique combination of engineering, computer and mathematical sciences within one school stimulates interdisciplinary research beyond traditional boundaries. Current research interests include:
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Browsing School of Engineering, Computer and Mathematical Sciences - Te Kura Mātai Pūhanga, Rorohiko, Pāngarau by Subject "0306 Physical Chemistry (incl. Structural)"

Now showing 1 - 9 of 9
  • Item
    A Linear Relation between the Color Stretch sBV and the Rising Color Slope s0*(B−V) of Type Ia Supernovae
    (American Astronomical Society, 2023-04-05) Chen, Ping; Dong, Subo; Ashall, Chris; Benetti, S; Bersier, D; Bose, S; Brimacombe, Joseph; Brink, Thomas G; Buckley, David AH; Cappellaro, Enrico; Christie, Grant W; Elias-Rosa, N; Filippenko, Alexei V; Gromadzki, Mariusz; Holoien, Thomas W-S; Hu, Shaoming; Kochanek, CS; Koff, Robert; Kollmeier, Juna A; Lundqvist, P; Mattila, S; Milne, Peter A; Muñoz, JA; Mutel, Robert; Natusch, Tim; Nicolas, Joel; Pastorello, A; Prentice, Simon; Prieto, JL; Roth, Tyler; Shappee, BJ; Stone, Geoffrey; Stanek, KZ; Stritzinger, MD; Thompson, Todd A; Tomasella, Lina; Villanueva, Steven
    Using data from the Complete Nearby (redshift zhost < 0.02) sample of Type Ia Supernovae (CNIa0.02), we find a linear relation between two parameters derived from the B − V color curves of Type Ia supernovae: the color stretch sBV and the rising color slope ${s}_{0}^{* }(B-V)$ after the peak, and this relation applies to the full range of sBV. The sBV parameter is known to be tightly correlated with the peak luminosity, especially for fast decliners (dim Type Ia supernovae), and the luminosity correlation with sBV is markedly better than with the classic light-curve width parameters such as Δm15(B). Thus, our new linear relation can be used to infer peak luminosity from ${s}_{0}^{* }$. Unlike sBV (or Δm15(B)), the measurement of ${s}_{0}^{* }(B-V)$ does not rely on a well-determined time of light-curve peak or color maximum, making it less demanding on the light-curve coverage than past approaches.
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    Effect of Laser Power in Laser Powder Bed Fusion on Ni Content and Structure of Nitinol
    (Elsevier BV, 2023-06-10) Sequeda Leon, EM; Singamneni, S; Guraya, T; Chen, ZW
    Laser powder bed fusion (LPBF) additive manufacturing is capable of producing Nitinol stents of complex shapes, but a slight change of Ni content during LPBF can result in the stents not being suitable. Thus, there is a need to predict how laser power (P) and thus energy (E) affects the two important outcomes of Nitinol LPBF: defect level and Ni content. In this study, how Ni content may change during LPBF has been studied under two conditions: a sufficiently low P (thus E) but close to fully dense condition and a sufficiently high P that has caused keyhole pore formation. The loss of Ni has been found to be 0.36at% and 0.56at% for the sufficiently low and sufficiently high P conditions. Thus, 0.4–0.5at%Ni loss is expected for defect-free Nitinol LPBF. The morphological features of the melt pool affecting defect formation and relating to how P affects Ni loss will be discussed. With the significant loss of Ni due to LPBF, for the starting powder, which contains 50.5at%Ni and is fully austenitic, the LPBF as-built structure has remained mainly austenitic, but the samples also contain a small amount of martensite.
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    Effects of Cell Orientation on Compressive Behaviour of Electron Beam Powder Bed Fusion Ti6Al4V Lattice Structures
    (Elsevier BV, 2023-05-08) Huang, Y; Wan, ARO; Schmidt, K; Sefont, P; Singamneni, S; Chen, ZW
    Electron beam powder bed fusion (EBPBF) is suitable for making porous (or lattice) structures for medical implant applications. However, it is challenging for a lattice structure with a high porosity level to have sufficient strength, while lattice structures with sufficient strength are required for orthopedic applications. Furthermore, strength anisotropy needs to be understood for the design of femoral stems as load direction (LD) is location dependent. The present study aims to understand the effects of cell orientation on the compressive behavior of simple cubic lattice structures built using EBPBF and Ti6Al4V alloy, with [0 0 1]//LD or [1 1 1]//LD. It has been found that the apparent yield strength (σy-L) of [0 0 1] lattices is 1.8 times higher than that of [1 1 1] lattices, by experimental determination and also by numerical simulation. Simulation has shown that, with the [0 0 1]//LD condition, σ1 in vertical load supporting struts is low when the structure yields. But locally, σ1 (>1,000 MPa) is positive and high for the [1 1 1]/LD condition when yielding of the structure occurs with the load value only 57% of the value that is required for causing yielding in the [0 0 1]//LD condition. The predictive yield strength values by simulation of both [0 0 1] and [1 1 1] lattices have been found to be slightly lower than the experimentally determined values. Explanation for this will be provided by considering the effect of the struct effective diameter with EBPBF strut irregularity on the strength of the lattice structures.
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    Evaluating and Comparing Secondary Machining Characteristics of Wrought and Additive Manufactured 316L Stainless Steel
    (Elsevier BV, 2023-05) Polishetty, Ashwin; Nomani, Junior; Littlefair, Guy
    This paper is based on evaluating, analysing and comparing the secondary machining characteristics of wrought and additive manufactured 316L Stainless Steel. This paper is an attempt to determine the process efficiency and evaluate the machinability factors which effect the service life. Stainless steel is a historic iron carbon alloy reputed for its high corrosive resistance and extensive application base. Threading, tapping, reaming and knurling are the most common secondary machining operations after a primary machining operation to achieve a required surface finish and form. As threading plays a significant role in fastening two components together. Threading is selected as a secondary machining operation in this paper. The research methodology consists of conducting threading operation on a hollow cylinder of 50 mm diameter using a lathe. Threads are cut into the workpiece using variable cutting parameters such as spindle speed; 90 and 180 rpm and coolant condition; on/off. Thread pitch which is also the feed rate (1 mm/rev) and Depth of Cut (0.3 mm) remains constant for all the trails. Statistical data are collected and analysed by qualitative and quantitative evaluation. The outputs under consideration to evaluate the machinability includes the cutting forces, thread profile accuracy (pitch) and tool wear. It has been observed that the cutting force and the tool wear was predominantly high for SLM compared to wrought. The paper concludes to convey the point that wrought components has better machinability characteristics than additive manufactured stainless steel.
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    Experimental Evaluation of a Novel Stability Control System for Two-Wheeled Robotic Wheelchairs
    (Elsevier BV, 2023-05-26) Nikpour, Mostafa; Huang, Loulin
    A conventional robotic wheelchair containing four wheels (two active driving wheels and two passive casters) is statically stable with poor manoeuvrability. In comparison, a two-wheeled robotic wheelchair (TWRW) without the support of casters offers much better manoeuvrability but is inherently unstable and requires a stability control. Most stability controllers rely on the driving torques of the wheels which are high in magnitude and result in large energy consumption. Various disturbances in the system also affect the performance of the controller. To address these problems, this paper presents a novel control approach where the stability control is achieved through the motion of a pendulum-like movable mechanism added to the TWRW. A scaled-down TWRW is designed to evaluate the performances of the controllers based on PID control and second order sliding mode control (SOSMC). Experimental results show that under the proposed controller approach, the stability of the TWRW is achieved with much less torque, power, and energy consumption than the conventional control systems.
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    Fabrication and Characterisation of Poly(Vinyl Alcohol)/Chitosan Scaffolds for Tissue Engineering Applications
    (Elsevier BV, ) Chen, Yu; Etxabide, Alaitz; Seyfoddin, Ali; Ramezani, Maziar
    In this study, poly(vinyl alcohol)/chitosan (PVA/CS) scaffolds were fabricated by freeze-drying method and the characterisations of obtained scaffolds were carried out to analyse the suitability of the product for biomedical applications such as tissue engineering. The effect of initial PVA concentrations and their hydrolysis degrees, the addition of different molecular weights (MWs) of CS along with the blending ratio of PVA/CS were studied. Fourier transmission infrared (FTIR) spectroscopy showed the presence of chemical bonds in PVA and PAV/CS scaffolds and the energy dispersive X-ray (EDX) spectroscopy confirmed the existence of the chemical element nitrogen in PVA/CS scaffolds. The stability of scaffolds under physiological conditions was studied by swelling and degradation tests, which demonstrated the effect of initial PVA concentration and CS addition on the water resistance of scaffolds. Scanning Electron Microscopy (SEM) images showed highly porous structures which became more uniform in pore size with the addition of CS. The mechanical properties of dry and hydrated scaffolds were also investigated by an unconfined compression test and the compressive modulus and maximum stress at 20% strain were calculated through stress–strain curves. The in-depth characterisation of scaffolds showed that the initial concentration and blending ratio of PVA/CS can be adjusted to tailor the desired properties of scaffolds for different biomedical applications.
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    Inverse MultiView. II. Microarcsecond Trigonometric Parallaxes for Southern Hemisphere 6.7GHz Methanol Masers G232.62+00.99 and G323.74–00.26
    (American Astronomical Society, 2023-07-28) Hyland, LJ; Reid, MJ; Orosz, G; Ellingsen, SP; Weston, SD; Kumar, J; Dodson, R; Rioja, MJ; Hankey, WJ; Yates-Jones, PM; Natusch, T; Gulyaev, S; Menten, KM; Brunthaler, A
    We present the first results from the Southern Hemisphere Parallax Interferometric Radio Astrometry Legacy Survey: 10 μas accurate parallaxes and proper motions for two Southern Hemisphere 6.7 GHz methanol masers obtained using the inverse MultiView calibration method. Using an array of radio telescopes in Australia and New Zealand, we measured trigonometric parallaxes and proper motions for the masers associated with the star formation region G232.62+00.99 of π = 0.610 ± 0.011 mas, μx = −2.266 ± 0.021 mas yr−1, and μy = 2.249 ± 0.049 mas yr−1, which implies its distance to be d = 1.637 ± 0.029 kpc. These measurements represent an improvement in accuracy by more than a factor of 3 over the previous measurements obtained through Very Long Baseline Array observations of the 12 GHz methanol masers associated with this region. We also measure the trigonometric parallax and proper motion for G323.74–00.26 as π = 0.364 ± 0.009 mas, μx = −3.239 ± 0.025 mas yr−1, and μy = − 3.976 ± 0.039 mas yr−1, which implies a distance of d = 2.747 ± 0.068 kpc. These are the most accurate measurements of trigonometric parallax obtained for 6.7 GHz class II methanol masers to date. We confirm that G232.62+00.99 is in the Local Arm and find that G323.74–00.26 is in the Scutum–Centaurus arm. We also investigate the structure and internal dynamics of both masers.
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    Kinetic Modelling of Esterification and Transesterification Processes for Biodiesel Production Utilising Waste-based Resource
    (MDPI AG, ) Hazrat, MA; Rasul, MG; Khan, MMK; Ashwath, N; Silitonga, AS; Fattah, IMR; Mahlia, TMI
    Process optimisation and reaction kinetic model development were carried out for two-stage esterification-transesterification reactions of waste cooking oil (WCO) biodiesel. This study focused on these traditional processes due to their techno-economic feasibility, which is an important factor before deciding on a type of feedstock for industrialisation. Four-factor and two-level face-centred central composite design (CCD) models were used to optimise the process. The kinetic parameters for the esterification and transesterification processes were determined by considering both pseudo-homogeneous irreversible and pseudo-homogeneous first-order irreversible processes. For the esterification process, the optimal conditions were found to be an 8.12:1 methanol to oil molar ratio, 1.9 wt.% of WCO for H2SO4, and 60 °C reaction temperature for a period of 90 min. The optimal process conditions for the transesterification process were a 6.1:1 methanol to esterified oil molar ratio, 1.2 wt.% of esterified oil of KOH, reaction temperature of 60 °C, and a reaction time of 110 min in a batch reactor system; the optimal yield was 99.77%. The overall process conversion efficiency was found to be 97.44%. Further research into reaction kinetics will aid in determining the precise reaction process kinetic analysis in future.
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    Reducing Instrumental Errors in Parkes Pulsar Timing Array Data
    (American Astronomical Society, 2024-09-23) Rogers, Axl F; van Straten, Willem; Gulyaev, Sergei; Parthasarathy, Aditya; Hobbs, George; Chen, Zu-Cheng; Feng, Yi; Goncharov, Boris; Kapur, Agastya; Liu, Xiaojin; Reardon, Daniel; Russell, Christopher J; Zic, Andrew
    This paper demonstrates the impact of state-of-the-art instrumental calibration techniques on the precision of arrival times obtained from 9.6 yr of observations of millisecond pulsars using the Murriyang 64 m CSIRO Parkes Radio Telescope. Our study focuses on 21 cm observations of 25 high-priority pulsars that are regularly observed as part of the Parkes Pulsar Timing Array project, including those predicted to be the most susceptible to calibration errors. We employ measurement equation template matching (METM) for instrumental calibration and matrix template matching (MTM) for arrival time estimation, resulting in significantly improved timing residuals with up to a sixfold reduction in white noise compared to arrival times estimated using scalar template matching and conventional calibration based on the ideal feed assumption. The median relative reduction in white noise is 33%, and the maximum absolute reduction is 4.5 μs. For PSR J0437−4715, METM and MTM reduce the best-fit power-law amplitude (2.7σ) and spectral index (1.7σ) of the red noise in the arrival time residuals, which can be tentatively interpreted as mitigation of 1/f noise due to otherwise unmodeled steps in polarimetric response. These findings demonstrate the potential to directly enhance the sensitivity of pulsar timing array experiments through more accurate methods of instrumental calibration and arrival time estimation.
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