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Accidental Superblock: results of closing a street to through traffic?
(2024) Kingham, Simon; Banwell , Karen; Curl , Angela
Investigating the detection sensitivity of the mismatch response in normal hearing adults: a study using complex tones with high ecological validity, in the application of validation of infant hearing aid fittings
(2024) Liu, Xu
Background: Permanent congenital hearing impairment has a high prevalence and can negatively impact the development of the auditory cortex, especially during the critical first few years of life. To address this, worldwide initiatives have implemented newborn hearing screenings and early intervention programs, enabling the diagnosis and fitting of hearing aids in children as young as two months old. At such an early age, where subjective feedback is limited or unavailable, objective validation tools become crucial. Amongst current and emerging electrophysiological objective tools, most focus on assessing audibility of aided speech sounds. The Mismatch Response (MMR) on the other hand, is notable for its ability to assess both audibility and discrimination of speech sounds. MMRs can be recorded in sleeping or awake infants and exhibit a high response detection rate (>90%) based on recent data but for coarse discrimination tasks. This study aims to determine the response detection rate for of MMRs when the differences between speech-like sounds are more subtle.
Design: MMRs were measured in 13 normal hearing adults, using an optimised 4-deviant paradigm in response to complex tones (CTs) with a centre frequency representative of the first formant of five common English vowels, in the frequency range of 536 Hz to 753 Hz.
Results: Objective response detection analyses using the Hotelling’s T2 statistical method revealed that the detection rate of MMR for stimulus pairs with approximately 20 Hz spectral difference was low (40% or lower). Conversely, for most stimulus pairs with a spectral difference exceeding 80 Hz, the detection rates were notably higher, at 80% or above.
Conclusion: A spectral difference of 20 Hz between CTs is too small to elicit reliably detectable MMRs at the level of the individual listener, although some elements of natural speech are characterised by such small spectral cues. However, when the difference limen between the CTs was at least 80 Hz we found an MMR detection sensitivity that might be considered acceptably high for the clinical setting.
The carrying capcities [i.e. capacities] of huts and tracks inside Mount Cook National Park
(1995) Druce, Daniel Matthew Ishtar
The social carrying capacities of huts and tracks inside Mount Cook National Park are explored within the contexts of current approaches to the management of natural areas.
Data was collected, during March and April 1995, from 391 questionnaires, at four sites; the Blue Lakes, Hooker Valley, Mueller Hut and Hooker Hut.
Due to the physical constraints on access, each track was seen to offer different recreational opportunities.
A review of the carrying capacity literature provides the theoretical basis for this research. Theories of perceived crowding, social norms and frameworks for managing natural areas are seen to emphasise 'change' in settings rather than restrictions of use. Results indicate that perceived crowding is an appropriate method for defining social carrying capacity in recreation areas. The use of social norms did not define acceptable levels of use.
Analysis of perceived crowding found that the Hooker Valley and Mueller Hut had exceeded their social carrying capacities. Yet users still reported high levels of enjoyment from all four sites. It was suggested that this was due to coping behaviours being utilised in 'crowded' situations.
Results are applied within the Limits of Acceptable Change planning framework. This places subjective limits of acceptable change within the study sites and examines how these limits could be measured in Mount Cook National Park.
Response of micro-eukaryote and slime mould communities to land use change and pine invasion in Aotearoa
(2024) Cox, George R.
Soil micro-eukaryotes are a highly diverse group that drive key biogeochemical cycles and regulate the communities of other soil microorganisms, yet their responses to ecosystem changes in Aotearoa New Zealand are unknown. Micro-eukaryote communities are highly responsive to changes in soil conditions such as soil moisture and carbon availability, with these community level responses often differing from those of other soil biota. Human activity has changed many ecosystems in Aotearoa with the shift from native beech (Nothofagus sp.) to open shrublands, and now to exotic pine forests being one of the most notable. These large-scale changes in plant community composition have impacted animal, bacterial, and fungal communities within the soil, in addition to changing soil abiotic factors like nutrient ratios. This thesis aims to test the impacts of land use change and particularly pine invasion on soil micro-eukaryote communities in Aotearoa, to fill this research gap.
I extracted soil DNA from 33 sites in the Molesworth Recreation Reserve, with the sites being split between mountain beech (Nothofagus cliffortiodies) forest, native dominated grass-/shrublands, and invasive pine stands. A general eukaryote primer was used to generate OTUs (operational taxonomic units) via DNA metabarcoding to reveal the community level changes of micro- eukaryotes between different vegetation types. Slime moulds, a subgroup of micro-eukaryotes, were surveyed and cultured from these same sites to supplement the sequencing data.
DNA metabarcoding revealed that shrubland sites had significantly higher OTU richness and effective diversity than pine sites. Community dissimilarity (beta diversity) was also higher in shrubland sites than either beech or pine sites. The soil micro-eukaryote communities of all sites were dominated by the Cercozoa, with the Apicomplexa, Ciliophora, and Amoebozoa also identified as key soil micro-eukaryote groups in Aotearoa. The collected slime moulds did not significantly differ in diversity or community composition between vegetation types but did reveal multiple novel sequences and the detection of four species in Aotearoa for the first time. The slime mould communities of these sites were dominated by the genus Didymium, with most other slime moulds belonging to the family Physaraceae.
Land use change and pine invasion do impact the soil micro-eukaryote communities of Aotearoa, with pine invasion into shrublands leading to a reduction in micro-eukaryote diversity. However, these changes may be returning the soil micro-eukaryote community to a more natural state, as
beech and pines forests shared similar levels of diversity. The community level responses of micro-eukaryotes to anthropogenic changes differ from those seen in other soil biota where beech forest usually hosts the most diverse communities.
Further work should be done to identify the specific drivers of change in these micro-eukaryote communities. The taxonomy of the collected but unidentified slime moulds should be investigated further to either complete online sequence database or reveal novel taxa.
Ion implantation in β-Ga2O3 thin films
(2024) Sinclair, Andrew
As silicon devices are pushed to their physical limit, there is currently significant academic and commercial interest in wide band gap, and ultra wide band gap semiconductors which can operate at high power densities. One such semiconductor, β-Ga2O3, is seeing significant attention in recent years due to its high band gap (4.5 - 4.9 eV), and breakdown field (8 MV/cm) which makes it a desirable material for the manufacture of high power devices and photoelectronic devices operating in the deep ultraviolet (UV) region. n-type doping of β-Ga2O3 can be increased through the use of ion implantation with Si, Ge, and Sn substituting Ga in the crystal. Monte Carlo simulations of Si, Ge, and Sn implantation in β-Ga2O3 were undertaken to determine an implantation procedure that would result in a uniform dopant concentration of 1 × 1018 cm−3 and 1 × 1019 cm−3. This implantation procedure was used to implant Si into six thin films of Ga2O3, including two grown by Molecular Beam Epitaxy (MBE) on MgO (100) substrates, two by MBE on c-plane Al2O3 (c-Al2O3) substrates, and two grown by the sol-gel process on c-Al2O3. The implanted thin films underwent thermal annealing over a temperature range from 950 ◦C to 1100 ◦C to restore damage resulting from the implantation process. The effect of annealing on the electrical, optical, and material properties of the samples was examined using UV - Vis transmission spectroscopy, X-ray Diffraction (XRD) crystallography, Atomic force Microscopy (AFM), and Hall effect measurements. Electrical measurements indicated Si implantation failed to produce conducting thin films. Results of XRD measurements and UV-Vis transmission measurements indicate that this is likely due to the diffusion of Mg and Al in the substrates into the β-Ga2O3 films, which prevents the activation of Si by occupying Ga sites.