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Item Open Access Characterisation of turbulent non-premixed hydrogen-blended flames in a scaled industrial low-swirl burner(Elsevier BV, 2024) Gee, A.J.; Smith, N.; Chinnici, A.; Medwell, P.R.The performance of a scaled industrial, non-premixed, low-swirl burner design was experimentally investigated for hydrogen addition to natural gas. Two strategies for introducing hydrogen are considered, namely, conserving (i) heat input and (ii) velocity/volumetric flow of the original fuel. This work characterises the effects on key performance metrics of the burner as hydrogen fraction is increased. Compared with natural gas, the results with hydrogen showed a 33 % reduction in the radiant fraction and up to a 380 % increase in NOx emissions. The lift-off height was reduced by a maximum of 23 % and 51 % for addition of 10 and 30 vol% hydrogen addition, respectively, with 100 % cases becoming completely attached to the burner. The influence of hydrogen-addition strategy and air adjustment was shown to be significant with respect to NOx emissions but less significant than the resulting changes in fuel composition and heat input with respect to flame appearance, stability and radiant heat transfer.Item Metadata only Review of scaling laws applied to floating offshore wind turbines(Elsevier BV, 2022) Sergiienko, N.Y.; da Silva, L.S.P.; Bachynski-Polić, E.E.; Cazzolato, B.S.; Arjomandi, M.; Ding, B.The wind energy industry is moving to offshore installations allowing for larger wind turbines to be deployed in deep-water regions with higher and steadier wind speeds. Floating offshore wind turbines consist of two main subsystems: a wind turbine itself and a floating substructure that supports it and provides stability. While the wind turbine technology is mature, the floating support structures for offshore wind turbines are still evolving and have not been deployed at a commercial scale. Due to a significant increase in the size of wind turbines over the last decade, it is important to understand how to design the floating platform to support larger wind turbines, and how the dynamics of the entire system change with increasing scale. Firstly, this article provides an overview of the trends in wind energy systems for offshore applications. Secondly, a review of existing semi-submersible platforms designed to support 5–15 MW wind turbines is provided. In addition, this article provides a comparative analysis of the techniques proposed to upscale floating support structures for larger wind energy systems with a particular focus on the system dynamics. The results demonstrate that the wind turbine mass, rated power and rotor thrust force scale with close to square rotor diameter. Towers designed for floating wind applications are usually significantly stiffer and heavier as compared to their fixed-bottom counterparts to place the tower’s natural frequencies outside the wave excitation region. The analysis of semisubmersible platforms revealed a strong correlation between the wind turbine rotor diameter and the product of the distance to the offset columns and their diameter. Also, it has been found that design practices adapted by the platform developers roughly follow the theoretical square–cube (or ‘mass’) scaling law when designing platforms for larger wind turbines.Item Metadata only Robust functional observer for stabilising uncertain fuzzy systems with time-delay(Springer, 2020) Islam, S.I.; Shi, P.; Lim, C.C.This paper presents a new technique for stabilising a Takagi-Sugeno (T-S) fuzzy system with time-delay and uncertainty. A robust fuzzy functional observer is employed to design a controller when the system states are not measurable. The model uncertainty is norm bounded, and the time delay is time varying but bounded. The parallel distributed compensation method is applied for defining the fuzzy functional observer to design this controller. The proposed procedure reduces the observer order to the dimension of the control input. Improved stability conditions are provided for the observer compared with the existing results of functional observer based stabilisation of T-S fuzzy models. Lyapunov-Krasovskii functionals are used to construct delay dependent stability conditions as linear matrix inequalities. The solution of these inequalities is used for calculating the observer parameters. The sensitivity of the estimation error to the model uncertainty is reduced by minimising the L2 gain. The new design method developed is illustrated and verified using two examples.Item Open Access Brain fog in postural tachycardia syndrome: An objective cerebral blood flow and neurocognitive analysis(Wiley, 2020) Wells, R.; Paterson, F.; Bacchi, S.; Page, A.; Baumert, M.; Lau, D.H.Background: It remains unclear whether brain fog is related to impaired cerebral blood flow (CBF) in postural tachycardia syndrome (POTS) patients. Methods: We assessed CBF in the posterior cerebral artery (PCA) using transcranial Doppler with visual stimuli in 11 POTS and 8 healthy subjects in the seated position, followed by neurocognitive testing. Results: CBF parameters were similar between the two groups. POTS patients demonstrated significantly longer latency in delayed match to sample response time and greater errors in attention switching task. Conclusions: Impaired short-term memory and alertness may underlie the symptom of brain fog in POTS patients, despite normal CBF.Item Open Access Turbulent boundary layer flow over a three-dimensional sinusoidal surface(Cambridge University Press (CUP), 2023) Chan, C.I.; Chin, R.C.The sinusoidal roughness effect is investigated using a direct numerical simulation (DNS) of a spatially developing turbulent boundary layer (TBL) over three-dimensional sinusoidal roughness. The validity of Townsend’s outer-layer similarity hypothesis is assessed based on comparisons of mean and second-order flow statistics, with a DNS of smooth-wall TBL data set at a similar Reynolds number. The total, Reynolds and dispersive stress tensors are calculated using the double-averaging procedure. The mean and second-order statistical similarities in the outer layer between rough-wall and smooth-wall TBLs are generally observed. The transport between total, turbulent and dispersive kinetic energy is investigated utilising triple-decomposed kinetic energy transports equations. The transport behaviour of turbulent kinetic energy (TKE) is significantly affected by the local mean shear induced by the surface roughness. However, the TKE transport shows good collapse with the smooth-wall case in the outer region of the flow. On the other hand, the transport of dispersive kinetic energy, including local production, redistribution and dissipation, are confined within the roughness sublayer. The intercomponent transfer between TKE and dispersive kinetic energy is quantified from the triple-decomposed kinetic energy transport equations. The intercomponent energy transfer is associated with the local spatial gradients of the turbulent momentum fluxes generated near the roughness canopy.Item Metadata only Unlocking the performance of ternary metal (hydro)oxide amorphous catalysts via data-driven active-site engineering(Royal Society of Chemistry, 2023) Zhang, D.; Li, H.; Lu, H.; Yin, Z.; Fusco, Z.; Riaz, A.; Reuter, K.; Catchpole, K.; Karuturi, S.Ternary metal (hydro)oxide amorphous catalysts are attractive oxygen evolution reaction (OER) catalysts due to their high performance and cost-effectiveness, but a fundamental understanding of their structure–property relationships remains elusive. Herein, we fabricate a highly active ternary metal (hydro)- oxide (NiFeCo) OER catalyst, showing an overpotential of 146 mV at 10 mA cm2 and B300 hours of durability in 1 M KOH. Inspired by this finding, a dataset with first-principles adsorption energies of reaction intermediates at over 300 active-site structures for both oxides and hydroxides is computed and used to train a machine-learning model for screening the dominant factors and unveiling their intrinsic contributions. The computational work confirms that adding Fe and Co makes the original Ni (hydro)oxide reach ultra-low overpotentials below 200 mV through the modulation from hydroxide towards oxide and the formation of active-sites of ternary metallic components. A series of physical properties of the Fe, Co and Ni atoms in the active-sites are further included in the analysis, and it is found that the magnetic moment (mag) plays an important role in the OER activity. This work demonstrates the application of machine-learning methods in atomic-scale active-site engineering to understand the activity mechanism of ternary metal (hydro)oxide amorphous catalysts for water oxidation, and it has the potential to be extended to wider applications.Item Open Access Ultrahigh-Q Resonance in Bound States in the Continuum–Enabled Plasmonic Terahertz Metasurface(Wiley, 2023) Islam, M.S.; Upadhyay, A.; Ako, R.T.; Lawrence, N.P.; Sultana, J.; Ranjan, A.; Ng, B.W.-H.; Tansu, N.; Bhaskaran, M.; Sriram, S.; Abbott, D.The study of optical resonators is of significant importance in terms of their ability to confine light in optical devices. A major drawback of optical resonators is the phenomenon of light emission due to their limited capacity for light confinement. Bound states in the continuum are gaining significant attention in the realization of optical devices due to their unique ability for reducing light scattering via interference mechanisms. This process can potentially suppress scattering, leading to improved optical performance. Using this concept, a metasurface having two elliptical silicon (Si) resonators nonidentically angled to create an outof-plane asymmetry is studied. Various parameters are optimized by employing a genetic algorithm (GA) to subsequently achieve a high-Q factor at terahertz frequencies. Herein, the device is fabricated using a novel method, and a thick high-index resonator is achieved. Terahertz measurements are carried out to validate the results. It is indicated in the experimental results that plasmons appear at the top surface of the metasurface and create strong sharp resonances that are sensitive to the external environment. Owing to strong field confinement ability, and high-Q factor, the metasurface is sensitive to its surrounding environment and can be essentially employed in terahertz sensing applications.Item Open Access Monolithic Photonic Integrated Circuit Based on Silicon Nitride and Lithium Niobate on Insulator Hybrid Platform(Wiley-VCH, 2022) Jiang, Y.; Han, X.; Huang, H.; Zhang, P.; Dubey, A.; Xiao, H.; Yuan, M.; Frigg, A.; Thach, G.N.; Boes, A.; Li, Y.; Ren, G.; Su, Y.; Mitchell, A.; Tian, Y.Lithium niobate on insulator (LNOI) has been demonstrated as a promising platform for photonic integrated circuits (PICs), thanks to its excellent properties such as strong electro-optic effect, low material loss, and wide transparency window. Herein, a monolithic PIC for high-speed data communication application on a lithium-niobate-etchless platform with silicon nitride (Si₃N₄) as a loading material is proposed and demonstrated. The fabricated PIC consists of four racetrack resonator modulators and a pair of four-channel mode (de)multiplexers, which shows high data modulation rate of 70 Gbps for single channel and the total data throughput reaches up to 280 Gbps. To the best of knowledge, this is the first demonstration of PIC consisting of high-speed electro-optical modulators and (de)multiplexers with such high data capacity on Si₃N₄-LNOI hybrid platform, which opens up new avenues for achieving large-scale monolithic integration on LNOI platform in future.Item Open Access Tuning-Range Extension Strategies for Varactor-Based Frequency-Reconfigurable Antennas(Institute of Electrical and Electronics Engineers (IEEE), 2023) Dang, Q.H.; Nguyen-Trong, N.; Fumeaux, C.; Chen, S.J.Tuning range extension strategies for varactor-based frequency-reconfigurable planar patch antennas are presented. The three tuning range optimization methods described in the paper include cooptimization of antenna dimensions and varactor properties, exploitation of multiple radiation modes, and reduction of parasitic capacitance. The first two strategies are emphasized by briefly reviewing two previously reported wide tuning range frequency-agile planar antennas. Importantly, the influence of parasitic capacitance on reducing the tuning range of the varactor-based frequency-reconfigurable antennas is then demonstrated by examining two antennas. The three tuning range extension methods are then combined to further expand the frequency tuning range of a reported frequency-reconfigurable antenna. The antenna has been re-designed, fabricated and experimentally characterized to demonstrate enhanced performance, which validates the proposed techniques, and their simultaneous application to reconfigurable antenna designs.Item Open Access Investigation of the mechanisms for wireless nerve stimulation without active electrodes(Wiley, 2023) Smith, L.A.; Bem, J.D.; Lv, X.; Lauto, A.; Sliow, A.; Ma, Z.; Mahns, D.A.; Berryman, C.; Hutchinson, M.R.; Fumeaux, C.; Tettamanzi, G.C.Electric‐field stimulation of neuronal activity can be used to improve the speed of regeneration for severed and damaged nerves. Most techniques, however, require invasive electronic circuitry which can be uncomfortable for the patient and can damage surrounding tissue. A recently suggested technique uses a graft‐antenna—a metal ring wrapped around the damaged nerve—powered by an external magnetic stimulation device. This technique requires no electrodes and internal circuitry with leads across the skin boundary or internal power, since all power is provided wirelessly. This paper examines the microscopic basic mechanisms that allow the magnetic stimulation device to cause neural activation via the graft‐antenna. A computational model of the system was created and used to find that under magnetic stimulation, diverging electric fields appear at the metal ring's edges. If the magnetic stimulation is sufficient, the gradients of these fields can trigger neural activation in the nerve. In‐vivo measurements were also performed on rat sciatic nerves to support the modeling finding that direct contact between the antenna and the nerve ensures neural activation given sufficient magnetic stimulation. Simulations also showed that the presence of a thin gap between the graft‐antenna and the nerve does not preclude neural activation but does reduce its efficacy.Item Open Access Terahertz integration platforms using substrateless all-silicon microstructures(AIP Publishing, 2023) Headland, D.; Fujita, M.; Carpintero, G.; Nagatsuma, T.; Withayachumnankul, W.The absence of a suitable standard device platform for terahertz waves is currently a major roadblock that is inhibiting the widespread adoption and exploitation of terahertz technology. As a consequence, terahertz-range devices and systems are generally an ad hoc combination of several different heterogeneous technologies and fields of study, which serves perfectly well for a once-off experimental demonstration or proof-of-concept, but is not readily adapted to real-world use case scenarios. In contrast, establishing a common platform would allow us to consolidate our design efforts, define a well-defined scope of specialization for “terahertz engineering,” and to finally move beyond the disconnected efforts that have characterized the past decades. This tutorial will present arguments that nominate substrateless all-silicon microstructures as the most promising candidate due to the low loss of high-resistivity float-zone intrinsic silicon, the compactness of high-contrast dielectric waveguides, the designability of lattice structures, such as effective medium and photonic crystal, physical rigidity, ease and low cost of manufacture using deep-reactive ion etching, and the versatility of the many diverse functional devices and systems that may be integrated. We will present an overview of the historical development of the various constituents of this technology, compare and contrast different approaches in detail, and briefly describe relevant aspects of electromagnetic theory, which we hope will be of assistance.Item Metadata only Stability analysis of time-varying neutral stochastic hybrid delay system(Institute of Electrical and Electronics Engineers, 2023) Chen, H.; Shi, P.; Lim, C.C.This note analyses the stochastic stability for time-varying neutral stochastic hybrid delay system, which includes the stability in pth (p≥2)-moment, the asymptotical stability in pth (p≥2 )-moment, the exponential stability in pth (p≥2 )-moment, and the almost surely exponential stability. One modified version of generalized delay integral inequality, the Lyapunov-Krasovskii function and the stochastic analysis are used. The proposed methodology can surmount the analytical difficulty, which stems from the coexistence of neutral term, stochastic disturbance, bounded time-varying delay and a sign-changed time-varying coefficient in the diffusion condition. An example is given to show the effectiveness of the theoretical results obtained.Item Open Access Theory of transformation-mediated twinning(Oxford University Press (OUP), 2023) Lu, S.; Sun, X.; Tian, Y.; An, X.; Li, W.; Chen, Y.; Zhang, H.; Vitos, L.; Yortsos, Y.High-density and nanosized deformation twins in face-centered cubic (fcc) materials can effectively improve the combination of strength and ductility. However, the microscopic dislocation mechanisms enabling a high twinnability remain elusive. Twinning usually occurs via continuous nucleation and gliding of twinning partial dislocations on consecutive close-packed atomic planes. Here we unveil a completely different twinning mechanism being active in metastable fcc materials. The transformation-mediated twinning (TMT) is featured by a preceding displacive transformation from the fcc phase to the hexagonal close-packed (hcp) one, followed by a second-step transformation from the hcp phase to the fcc twin. The nucleation of the intermediate hcp phase is driven by the thermodynamic instability and the negative stacking fault energy of the metastable fcc phase. The intermediate hcp structure is characterized by the easy slips of Shockley partial dislocations on the basal planes, which leads to both fcc and fcc twin platelets during deformation, creating more twin boundaries and further enhancing the prosperity of twins. The disclosed fundamental understanding of the complex dislocation mechanism of deformation twinning in metastable alloys paves the road to design novel materials with outstanding mechanical properties.Item Metadata only Design Optimisation of a High Power Density Electric Machine using Soft Magnetic Composites(IEEE, 2023) Roshandel, E.; Ertugrul, N.; Mahmoudi, A.; Kahourzade, S.; Australasian Universities Power Engineering Conference (AUPEC) (26 Sep 2022 - 28 Sep 2022 : Adelaide, South Australia)Soft magnetic composites (SMCs) are considered in electrical machines applications due to their desirable magnetic properties, such as small eddy current losses. Their thermal isotropy feature is also desirable as it can allow the construction of SMC-based pole pieces to form the stator. In addition, the embedded concentrated winding structure allows to achieve higher power density electric machines. This paper presents an optimization study to offer a high-power density, low cogging torque, and high-efficiency electrical machine that are desirable in a wide range of applications. To achieve these aims, both 2-D finite element model (FEM) and 3-D FEM are developed for a benchmark machine. Then a sensitivity analysis is carried out about the arc and thickness of the permanent magnet (PM), and on the number of turns of the windings under a constant current density both under the no-load and full-load operation of the machine. The results obtained from the sensitivity analysis are used to predict the performance of the SMC-based electric machine in a large search space by means of a surrogate model. Then, a convex optimization problem is solved to find a high torque machine with the minimum cogging torque. The optimal design is validated using the 3-D and 2-D FE analysis (FEA) results performed previously. Finally, the optimal design performance parameters are obtained in the torquespeed envelope. These results are also compared with the performance characteristics of a conventional laminated machine to demonstrate the advantages of the use of SMC in motor design.Item Open Access Unbalanced Axial Forces in Axial-Flux Machines(IEEE, 2023) Soong, W.L.; Cao, Z.; Roshandel, E.; Mahmoudi, A.; Kahourzade, S.; Australasian Universities Power Engineering Conference (AUPEC) (26 Sep 2022 - 28 Sep 2022 : Adelaide, South Australia)This paper performs an analysis of the variation of unbalanced forces with airgap length in axial-flux machines. A simple analytical approach is used to provide insights into these key parameters and the results compared with finite-element results for both axial-flux permanent magnet (PM) and induction machines. For PM and current-driven induction machines, the two most important parameters are the ratio of the effective magnet/core magnetic path length to the nominal airgap, and the ratio of the saturation flux density to the nominal airgap flux density. For voltage-driven induction machines, the key parameter is the ratio of stator leakage inductance to the nominal magnetising inductance.Item Metadata only Integrated lithium niobate optical mode (de)interleaver based on an asymmetric Y-junction(Optica Publishing Group, 2023) Yuan, M.; Ma, M.; Xiao, H.; Nguyen, T.G.; Boes, A.; Ren, G.; Cheng, L.; Mitchell, A.; Tian, Y.Lithium niobate on insulator (LNOI) platforms promise unique advantages in realizing high-speed, large-capacity, and large-scale photonic integrated circuits (PICs) by leveraging lithium niobate’s attractive material properties, which include electro-optic and nonlinear optic properties, low material loss, and a wide transparency window. Optical mode interleavers can increase the functionality of future PICs in LNOI by enabling optical mode division multiplexing (MDM) systems, allowing variable mode assignment while maintaining high channel utilization and capacity. In this Letter, we experimentally demonstrate an optical mode interleaver based on an asymmetric Y-junction on the LNOI platform, which exhibits an insertion loss of below 0.46 dB and modal cross talk of below –13.0 dB over a wavelength range of 1500–1600 nm. The demonstrated mode interleaver will be an attractive circuit component in future high-speed and large-capacity PICs due to its simple structure, scalability, and capacity for efficient and flexible mode manipulation on the LNOI platform.Item Open Access Terahertz hollow core antiresonant fiber with metamaterial cladding(MDPI AG, 2020) Sultana, J.; Islam, M.S.; Cordeiro, C.M.B.; Dinovitser, A.; Kaushik, M.; Ng, B.W.H.; Abbott, D.A hollow core antiresonant photonic crystal fiber (HC-ARPCF) with metal inclusions is numerically analyzed for transmission of terahertz (THz) waves. The propagation of fundamental and higher order modes are investigated and the results are compared with conventional dielectric antiresonant (AR) fiber designs. Simulation results show that broadband terahertz radiation can be guided with six times lower loss in such hollow core fibers with metallic inclusions, compared to tube lattice fiber, covering a single mode bandwidth (BW) of 700 GHz.Item Metadata only Evolution from Air-Cladded to Effective-Medium-Cladded Dielectric Waveguides(IEEE, 2019) Gao, W.; Yu, X.; Fujita, M.; Nagatsuma, T.; Fumeaux, C.; Withayachumnankul, W.; 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) (1 Sep 2019 - 6 Sep 2019 : Paris, France)Integrated guiding structures with low loss, low dispersion and broad bandwidth are demanded in high-performance terahertz systems. In this work, an effective-medium-cladded waveguide fabricated on a single high-resistivity silicon wafer is proposed for terahertz operation. The effective medium is realized by regularly perforating a silicon slab with a period in the subwavelength region. The simulated average attenuation coefficient is around 0.05 dB/cm over the operation frequency range from 220 GHz to 330 GHz for the E₁₁× mode.Item Open Access Characteristics of Clinically Classified Oral Lichen Planus in Optical Coherence Tomography: A Descriptive Case-Series Study(MDPI AG, 2023) Gruda, Y.; Albrecht, M.; Buckova, M.; Haim, D.; Lauer, G.; Koch, E.; Joehrens, K.; Schnabel, C.; Golde, J.; Li, J.; McLaughlin, R.A.; Walther, J.Malignant transformation of oral lichen planus (OLP) into oral squamous cell carcinoma is considered as one of the most serious complications of OLP. For the early detection of oral cancer in OLP follow-up, accurate localization of the OLP center is still difficult but often required for confirmatory biopsy with histopathological examination. Optical coherence tomography (OCT) offers the potential for more reliable biopsy sampling in the oral cavity as it is capable of non-invasively imaging the degenerated oral layer structure. In this case-series study with 15 patients, features of clinically classified forms of OLP in OCT cross-sections were registered and correlated with available histologic sections. Besides patients with reticular, atrophic, erosive and plaque-like OLP, two patients with leukoplakia were included for differentiation. The results show that OCT yields information about the epithelial surface, thickness and reflectivity, as well as the identifiability of the basement membrane and the vessel network, which could be used to complement the visual clinical appearance of OLP variants and allow a more accurate localization of the OLP center. This forms the basis for further studies on OCT-assisted non-invasive clinical classification of OLP, with the aim of enabling decision support for biopsy sampling in the future.Item Metadata only Terahertz disk resonator on a substrateless dielectric waveguide platform(Optical Society of America, 2023) Dechwechprasit, P.; Tanyi Ako, R.; Sriram, S.; Fumeaux, C.; Withayachumnankul, W.Abstract not available