12,570 results for Doctoral

  • Hydrodynamics and chemistry of silica scale formation in hydrogeothermal systems.

    Kokhanenko, Pavlo (2015)

    Doctoral thesis
    University of Canterbury Library

    The extraction of geothermal heat can cause precipitation of the minerals dissolved in geothermal fluid. Their deposition on the walls of wells and above-ground plant and in pores near reinjection wells, also known as mineral scaling, is one of the main obstacles to increasing the effectiveness of utilization of the limited geothermal resources. If not controlled properly it can result in accumulation of a significant amount of scale which obstructs pipes and reinjection wells and reduces the efficacy of heat exchangers. The most abundant mineral in geothermal fluid is silica and thus its precipitation can cause the highest scaling rate. While this dissertation is devoted to the study of silica scaling the results obtained may be applicable to other minerals with similar deposition mechanism. Oversaturated silica is known to precipitate from aqueous solution either by the direct chemisorption of single silicic acid molecules (monomers) or by forming colloidal particles suspended in the solution. These particles can subsequently be transported to, and attach onto, a wall. This process of colloidal silica deposition was previously recognised to cause much faster scaling than the direct deposition of silica monomers under typical geothermal plant conditions. While the chemical kinetics of silica polymerization and colloid formation are relatively well understood, transport of these colloids and their stability, which control their aggregation and attachment rates, on the other hand are not. Previous studies of the silica scaling process have identified prominent effects of geothermal brine hydrodynamics on the scaling rate. It was found to increase with the flow rate and particle size, thus suggesting the dominance of the advective (inertial) deposition of colloidal silica. However, this conclusion contradicted the present theory of particle transport in turbulent flows which argues the dominance of the diffusive transport for the relevant range of particle sizes (<1 μm). The development and continuing improvement of the anti-scaling measures required deeper understanding of the complex combination of the phenomena involved in the process of silica scaling. This was pursued in the present study using theoretical and experimental methods. First, the rate of colloidal silica transport from a turbulent flow onto the internal surface of a circular pipe, a cylinder and a flat plate were calculated using available analytical and numerical methods. The obtained theoretical transport rate was found to be about four orders of magnitude higher than the corresponding experimental scaling rate. The latter was determined in the previous studies to be 4.2·10-8 kg/s/m2 for silica colloids of 125 nm in diameter which corresponded to the dimensionless deposition velocity (the dimensionless deposition velocity is the scaling rate normalised by the particle mass concentration and friction velocity) of 1.2·10-6 for the dimensionless particle relaxation time of 2·10-4. Next, based on the standard DLVO theory of particle interactions and in the framework of the Smoluchowski approach the probability of colloidal silica particle attachment to a wall was found to be 10-6. Therefore, the theoretical scaling rate, calculated as a product of this probability and the above-mentioned transport rate was two orders of magnitude lower than the experimental scaling rate. This suggested that the implemented theoretical approach either underestimated particle transport rate or overestimated particle stability. Both possibilities are explored in this dissertation. In addition, the silica scaling rate was measured for a range of conditions: particle size from 20 to 60 nm, particle concentration 1600-10000 ppm, friction velocity from 0.09 to 0.18 m/s (Re = 9-50·103) and ionic strength from 30 to 80 mM, pH 8.1-9.5 and temperature from 25 to 44 °C. For this, laboratory experiments were designed and progressively modified in order to improve the repeatability of the results and to study the scaling process. In these experiments colloidal silica deposition onto the walls of mild steel pipe sections was studied with a recirculating flow rig with variable (but controllable) particle size, concentration, flow rate, pH and ionic strength of the solution. In addition, a parallel plate flow test section was designed and built which will provide better capabilities for the control over the hydrodynamic and test surface conditions in future experiments. The control over the chemical conditions was achieved by the use of the synthetic colloidal solutions. Two methods of their production – hydrolysis of either sodium metasilicate or active silicic acid – were employed. The influence of the synthesis conditions, ion content and pH on the long term behaviour of these colloidal solutions was investigated. The particle size data, obtained using dynamic light scattering (DLS) and verified by electron microscopy, was analysed and compared against the predictions of the current models of nanoparticle growth and stability. The kinetic aggregation was identified to be the dominant particle growth mechanism. Experimental data collected during the long-term observations of the particle growth allowed relationships between the aggregative stability and such parameters as the particle size, ion concentration and pH of the solution to be elucidated. In particular, the aggregative stability of 10-20 nm particles was found to be 108-1010 which is 7-9 orders of magnitude higher than the corresponding DLVO stability. It was also found to decrease with the increase of the particle size. This agreed with the theory of the colloid stabilization by steric interactions. Moreover, the model of the “gel” layer was used to explain the observed “anomalies” of the colloidal silica behaviour. The deposition experiments conducted with these synthetic colloidal solutions showed that the scaling rate increased with the particle size, flow rate and ionic strength (IS) of the solution. Thus, it was measured to be 9.7·10-9 kg/s/m2 for the 45 nm particles in a solution with IS = 0.05 M, which corresponded to the dimensionless deposition velocity of 6.6·10-8 for a dimensionless particle relaxation time of 2.2·10-6. The scaling rate was calculated for these conditions by multiplying the corresponding transport rate and the actual attachment probability determined as an inverse of the experimental stability. It was found to agree with the experimental value within an order of magnitude. In addition, the observed increase of the scaling rate with the increase of particle size was explained by the compensation of the decreased rate of the particle transport by faster decrease of actual particle stability (increase in attachment probability). Therefore the contradiction between the theory and the experiment was resolved for the particles of 20 to 60 nm in diameter. Moreover, the observations of the dimensions and distribution of the scale elements formed in some of the present experiments strongly suggested the significance of the advective (inertial) mechanism of particle deposition. This and comparative analysis of other experimental and theoretical data suggested that the present theory may underestimate the convective transport of the particles onto a rough wall. Therefore, the hypothesis of the parallel-to-wall advective deposition of the nanoparticles onto the roughness/scale elements (not accounted in the current theory) was proposed. The corresponding mass transfer problem was solved analytically using experimentally found dimensions of the scale elements. The additional transport was found to decrease the above-stated discrepancy between the theoretical and experimental scaling rate for large (125 nm) particles by one order of magnitude. The remaining difference of one order of magnitude was speculated to be due to the underestimation of these particles attachment probability derived with the standard DLVO theory. The actual aggregative stability of the silica colloids larger than 60 nm in diameter and for a wider range of IS values is of interest for future experimental studies. An improved understanding of the interrelation between the chemical and hydrodynamic phenomena in the process of silica scaling and its dominant mechanisms was achieved in this dissertation. This allowed optimization of the present anti-scaling practices aimed to minimize the negative effects of mineral scaling on the operation of geothermal power stations. Besides the practical recommendations, which may ultimately help to increase the efficiency of geothermal power stations, the results of the present study may be of value in the fields of mass transfer and colloid science.

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  • Development and optimization of an in vitro process for the production of Oryctes nudivirus in insect cell cultures

    Pushparajan, Charlotte (2015)

    Doctoral thesis
    University of Canterbury Library

    The coconut rhinoceros beetle, an economically important pest of coconut and oil palms, is effectively managed by application of its natural pathogen, the Oryctes nudivirus (OrNV), which act as a bioinsecticide. While this approach offers an environment-friendly alternative to chemical pesticides, the current method of production in infected larvae suffers from inconsistencies in virus productivity and purity. While the anchorage-dependent DSIR-HA-1179 insect cell line has been identified as a susceptible and permissive host for OrNV and therefore would be suitable for the in vitro mass production of the virus, no attempts have been made toward the mass production of the virus, because of the technological challenges that working with DSIR-HA-1179 cells represent. Thus, the main objective of this research was to develop processes for the in vitro production of OrNV in the DSIR-HA-1179 cell line. Knowledge of the growth kinetics and metabolic properties of the host cell line in a chosen culture medium, as well as the selection of an appropriate infection strategy, form the basis for the rational development of bioreactor-based virus production processes. However, characterization of these properties in the DSIR-HA-1179 cell line has been virtually precluded, due to its strongly adherent growth characteristics and the lack of a reliable method to accurately dissociate and count cells grown in monolayers. Using TrypLE™ Express enzyme, a technique allowing the precise counting of cells was developed. The cell line was adapted to grow in four serum-supplemented culture media: TC-100, IPL-41, Sf-900 II and Sf-900 III, which were then individually screened for cell growth and virus production in 25 cm2 attached T-flask cultures. TC-100 supplemented with 10% fetal bovine serum was chosen as a suitable culture medium, based on its capacity for achieving a high cell yield and OrNV production. The cell line metabolism was characterized with respect to nutrient consumption and metabolites production in this culture medium. Glucose, along with glutamine were found to be the nutrients that were consumed faster and to a greater extent, while other amino acids were not consumed to a significant degree. The production of metabolites was characterized by non-production of lactate and ammonia, and production of alanine, as a non-toxic alternative to ammonia. The influence of cell density (CD) at time of infection (TOI) and multiplicity of infection (MOI) on OrNV production was evaluated in T-flask cultures that were infected at different CDs at the TOI and a range of MOIs. The CD at TOI was found to significantly influence OrNV yields, while MOI influenced the dynamics of infection. The cell density effect was found to exist for the DSIR-HA-1179/OrNV system with the progressive decline in cell-specific yield beginning at low cell densities. It was found that in order to maximize OrNV volumetric yield, a combination of MOI and CD at TOI should be selected that allows to keep the maximum cell density reached by the infected culture within a range between 5.0 and 7.0 x 105 viable cells/ml. The roller bottle system was evaluated for its potential to scale-up DSIR-HA-1179 cell growth and OrNV production, and culture parameters were optimized for the improvement of cell and virus yields. An inoculum density of 3.3 x 105 cells/ml and culture volume of 60 ml resulted in the highest cell yield of 1.5 x 106 cells/ml, in 490 cm2 roller bottles. It was found that an optimal infection strategy for roller bottle cultures, which represented the most efficient use of viral inoculum, involved infecting cells at a density of 5.0 x 105 cells/ml and at a MOI of 1. The resulting OrNV volumetric yield of 2.5 x108 TCID50/ml, improved significantly the viral yields obtained in attached T-flask cultures infected under similar conditions (6.8 x 107 TCID50/ml). The microcarrier system was also evaluated for culturing DSIR-HA-1179 cells and producing OrNV in spinner flask bioreactors. Three types of microcarriers (Cytodex-1, Cytodex-3 and Cultispher-G microcarriers) were screened for their ability to support DSIR-HA-1179 growth. Cells attached to Cytodex-1 and 3, but failed to attach to Cultispher-G microcarriers. The final cell density reached in microcarrier culture was dependent on bead type and concentration, and the cell to bead ratio. At an optimal bead concentration of 1 mg/ml and cell to bead ratio of 30, cells grew to a maximum density of 1.7 x 106 cells/ml on Cytodex-1, but only to 1.3 x 106 cells/ml on Cytodex-3 microcarriers. Since it supported higher cell yields, Cytodex-1 was chosen to study the kinetics of OrNV production in this system. Microcarrier cultures infected at a cell density of 5.0 x 105 cells/ml and a MOI of 1, produced OrNV at 1.4 x 108 TCID50/ml, which was higher than the yield obtained in T-flask cultures infected under similar conditions. A framework of knowledge on the physiology, metabolism and growth kinetics of the DSIR-HA-1179 insect cell line has been developed in this thesis. In addition, the feasibility of using roller bottles and microcarrier systems for the in vitro production of the virus has been ascertained. It is envisaged that these findings will contribute to the future development of a large-scale industrial process for the production of the OrNV biopesticide.

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  • Gold-based Nanomaterials: Spectroscopy, Microscopy and Applications in Catalysis and Sensing

    Adnan, Rohul (2015)

    Doctoral thesis
    University of Canterbury Library

    The birth of nanotechnology era has revolutionized materials science, catalysis and field of optoelectronics. Novel and unique phenomena emerge when material dimensions are reduced to ultra-small size regime and enter nanometre (2-100 nm) realm. Such novel materials are expected to replace bulk materials, offering lower cost of manufacturing and enabling progress in many areas such as solar cell, drug delivery, quantum communication and computing, catalysis and sensing applications. With the progress in nanomaterial synthesis and fabrication, the need for the state-of-art characterization techniques became obvious; such techniques help to establish a complete understanding of the nature and interactions of nanosized materials. In this thesis, the first part focuses on the synthesis of gold and ruthenium clusters, namely Au8, Au9, Au101, Ru3, Ru4 and AuRu3, using the well-established synthetic protocols in the literature. Apart from the standard lab-based characterization techniques such as nuclear magnetic resonance (NMR), UV-visible spectroscopy (UV-vis) and Fourier Transform Infra-red (FTIR), a less explored but useful technique far infra-red (far IR) spectroscopy, available at the Australian Synchrotron (AS), was employed to investigate the vibrational modes in these clusters. Peaks in the experimental far IR spectra were assigned unambiguously to specific vibrations by comparing with the ones generated via DFT calculations with the help of collaborators, group of Professor Gregory Metha, University of Adelaide. For the Au9 cluster, three significant gold core vibrations are observed at 157, 177 and 197 cm-1 in the experimental spectrum. In the case of the Ru3 cluster, only a single ruthenium core vibration is identified within the spectrum, at 150 cm-1 with the calculated force constant, k = 0.33 mdyne/Å. The Ru4 cluster exhibits two metal core vibrations at 153 and 170 cm-1 with force constants of 0.35 and 0.53 mdyne/Å, respectively. Substitution with a gold atom yielding a mixed metal AuRu3 cluster shifts the core transitions toward higher wavenumbers at 177 and 299 cm-1 with an increase in force constants to 0.37 and 1.65 mdyne/Å, respectively. This is attributed to the change in chemical composition and geometry of the metal cluster core. A combination of the DFT calculations and high quality synchrotron-based experimental measurements allowed the full assignment of the key transitions in these clusters. Next, these clusters were fabricated into heterogeneous catalysts by depositing on different metal oxide nanopowders. Synchrotron X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) studies were performed at the Australian Synchrotron and the Photon Factory synchrotron in Japan to investigate the electronic structure of Au8, Au9 and Au101 on TiO2 catalysts. The XPS analysis reveals that “as-deposited” Au8 and Au9 retain some un-aggregated clusters while Au101 show bulk-like gold. These findings are in line with TEM observations, where the aggregates (large particles, > 2 nm) of Au8, Au9 and Au101 are hardly seen under HRTEM. UV-visible diffuse reflectance spectroscopy (UV-vis DRS) studies show the absence of localised surface plasmon resonance (LSPR) peaks in these “as-deposited” clusters, suggesting they are below 2 nm in size. Importantly, the XAS spectrum of “as-deposited” Au9 clusters estimates that 60% of pure, un-aggregated Au9 clusters and 40% of bulk gold in the sample. Upon calcination under O2 and combined O2 and H2 (O2-H2), Au8, Au9 and Au101 clusters form larger nanoparticles (> 2 nm) with the appearance of LSPE peak in UV-vis DR spectra. In addition, majority of the phosphine ligands (that stabilise the gold core) dislodge and form phosphine oxide-like species by interacting with oxygen on the TiO2 surface. The third part focused on testing the catalytic performance of the supported Au8, Au9, Au101, Ru3, Ru4 and AuRu3 clusters on different TiO2, SiO2, ZnO and ZrO2 in benzyl alcohol oxidation. Au101-based catalysts display the highest catalytic activity with a turn-over frequency (TOF) up to 0.69 s-1. The high catalytic activity is attributed to the formation of large Au nanoparticles (> 2 nm) that coincides with the partial removal of capping ligands. Au8 and Au9 clusters which contain NO3- counter anions are found to be inactive in benzyl alcohol oxidation. Further work shows that the presence of NO3- species diminishes the catalytic activity. Monometallic ruthenium clusters, Ru3 and Ru4, are found to be inactive yet the bimetallic AuRu3 clusters are active in benzyl alcohol oxidation, suggesting the synergistic effect between ruthenium and gold metal. Investigation of catalytic testing parameters reveals that tuning selectivity of the product is possible through manipulating the reaction temperature. Finally, a joint experiment with Prof. Wojtek Wlodarski’s group at RMIT, Melbourne was undertaken to test the sensing ability of Au9 clusters for hydrogen detection. Au9 clusters were deposited onto radio-frequency (RF) sputtered WO3 films at two different concentrations; 0.01(S1) and 0.1(S2) mg/mL. It was found that the optimal temperatures for sensor S1 and S2 were 300 °C and 350 °C, respectively. The sensor with lower Au9 concentration (S1) displays a faster response and recovery time, and a higher sensitivity toward H2. HRTEM studies reveal that the sensor S1 contain a significant population of sub-5 nm Au nanoparticles which might be responsible for a faster rate of H2 adsorption and dissociation. The key finding in this study suggest that the addition of catalytic layer such as ultra-small Au9 clusters results in improved sensitivity and dynamic performance (response and recovery time) of H2 sensors. In summary, this thesis demonstrated that cluster-based nanomaterials have wide range of applications spanning from catalysis to sensing. Further improvements in material synthesis and use of multiple complimentary characterization techniques allowed better understanding of the nature of the key active species (metal nanoparticles) assisting design of catalysts and sensors with enhanced performance.

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  • Investigation and Prediction of the Sound Transmission Loss of Plywood Constructions

    Wareing, Robin Richard (2015)

    Doctoral thesis
    University of Canterbury Library

    The sound transmission loss of a range of plywood panels was measured to investigate the influence of the orthotropic stiffness of the plywood panels. The plywood panels were tested as single and also double leaf partitions, with a range of stud configurations. A new method was developed for predicting the sound transmission loss of single leaf partitions with both orthotropic and frequency dependent stiffness values. The sound transmission loss was evaluated for two significantly different sample sizes. The observed influence of the sample size on the measured sound transmission loss was profound. The construction of the partition was shown to significantly affect the influence of the sample size on the sound transmission loss. A qualitative analysis based on existing published research of the contributing factors is presented, and methods for adjusting the results for the small sample size for comparison with the large results were developed. The influence of a range of acoustic treatments of lightweight plywood partitions was investigated. The treatments involved internal viscoelastic materials and decoupled mass loaded barriers in various arrangements. The attachment between the treatment and the plywood panel was found to influence the sound transmission loss significantly. A prediction method based on published models was modified to allow the influence of the treatments to be included. Reasonable agreement was achieved between the predicted and measured results for a wide range of samples. A prediction method was developed that accounts for the influence of orthotropic, frequency dependent material parameters. This method utilised an adaptive, numerical integration method to solve an analytical formulation for the sound transmission loss. The influence of the finite sample size was accounted for using an expression for the finite panel radiation impedance. The finite panel radiation impedance was predicted analytically and an approximation was also presented. The presence of a significant source room niche was accounted for by applying an appropriate limit to the integration range of the angle of incidence. The prediction methods developed are compared with the measured transmission loss results from both the small and large test facilities. Good agreement was seen for some of the predicted results. Generally the agreement within the coincidence region was worse than for the rest of the transmission loss curve. The inclusion of orthotropic and frequency dependent stiffness values significantly improved the agreement within the coincidence region.

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  • El camino se hace caminando: Using Participatory Action Research to evaluate and develop Peace Education practice in a Secondary School in Northern Nicaragua

    Kertyzia, Heather (2015)

    Doctoral thesis
    University of Otago

    Peace education (PE) is included in the cross-curricular themes of the Nicaraguan curriculum, yet in the Secondary School in Northern Nicaragua (SSINN) where this research was conducted there was varied implementation by teachers. The SSINN was selected for this research due to particular problems with violence. Based on a critical and post-development theory perspective and using participatory action research (PAR) methodology, teachers, school psychologists and administrators were led through a facilitated process of reflection upon the culture of peace/violence in the SSINN and teacher practice. This was guided by the concepts of education about (content), for (skills and behaviours) and by peace (pedagogy). PAR is guided by a series of principles that allow for flexibility and response to participant needs. In this case SSINN educators and I engaged in a process of building trust, gathering reconnaissance data, developing action plans and taking action. This was guided by our unofficial motto ‘the path is made by walking’ (el camino se hace caminando), implying that we were learning as we worked together and the process had to be adaptable to new circumstances. Through workshops and coffee chats we evaluated staff definitions of a culture of peace, priorities in relation to peace values, behaviours and content, and teacher practice in regards to peace principles. As part of the reciprocal process, educators gave feedback and directed the research, which was designed to emphasize educator voice and minimize the neo-colonial imposition of values from outside actors. In this way I sought to balance critical theory’s need to take action for positive change with post-development theory’s prioritizing of local educator voice. The primary goals of the research were to develop an understanding of how PE was practised in the SSINN and, if the educators requested it, to provide support in taking positive action for change, while assessing the effectiveness of the PAR methodology. In the beginning the educators had differing definitions of a culture of peace, but they were very consistent in their ideas of what content, skills and values should be included in PE. Although they regularly mentioned problems that were directly relevant to students’ lives that should be addressed in the classroom, not all of the teachers were actively doing this. Due to a lack of resources, time, teacher stress and overcrowding, many teachers were unable to translate those ideas into action. Also due to those factors, many teachers fell into habits of traditional teaching practice that were inconsistent with peace pedagogy. Recognizing these issues, the teachers requested workshops on non-violent communication and conflict transformation in the hope that that knowledge would aid them to more positively manage behaviour. They also created and implemented an action plan. Although positive steps were taken, this was the first stage of a long-term process of change. Partnering with local non-governmental organizations (NGOs) has provided the possibility of the continuation of the process; nevertheless those NGOs have stated that they need continued external support. This flexible PAR methodology was effective at exploring and developing PE practice in the SSINN, and has the potential, if continued, to lead to fundamental positive change.

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  • A multi-modal device for application in microsleep detection

    Knopp, Simon James (2015)

    Doctoral thesis
    University of Canterbury Library

    Microsleeps and other lapses of responsiveness can have severe, or even fatal, consequences for people who must maintain high levels of attention on monotonous tasks for long periods of time, e.g., commercial vehicle drivers, pilots, and air-traffic controllers. This thesis describes a head-mounted system which is the first prototype in the process of creating a system that can detect (and possibly predict) these lapses in real time. The system consists of a wearable device which captures multiple physiological signals from the wearer and an extensible software framework for imple- menting signal processing algorithms. Proof-of-concept algorithms are implemented and used to demonstrate that the system can detect simulated microsleeps in real time. The device has three sensing modalities in order to get a better estimate of the user's cognitive state than by any one alone. Firstly, it has 16 channels of EEG (8 currently in use) captured by 24-bit ADCs sampling at 250 Hz. The EEG is acquired by custom-built dry electrodes consisting of spring-loaded, gold-plated pins. Secondly, the device has a miniature video camera mounted below one eye, providing 320 x 240 px greyscale video of the eye at 60 fps. The camera module includes infrared illumination so that it can operate in the dark. Thirdly, the device has a six-axis IMU to measure the orientation and movement of the head. These sensors are connected to a Gumstix computer-on-module which transmits the captured data to a remote computer via Wi-Fi. The device has a battery life of about 7.4 h. In addition to this hardware, software to receive and analyse data from the head-mounted device was developed. The software is built around a signal processing pipeline that has been designed to encapsulate a wide variety of signal processing algorithms; feature extractors calculate salient properties of the input data and a classifier fuses these features to determine the user's cognitive state. A plug-in system is provided which allows users to write their own signal processing algorithms and to experiment with different combinations of feature extractors and classifiers. Because of this flexible modular design, the system could also be used for applications other than lapse detection‒any application which monitors EEG, eye video, and head movement can be implemented by writing appropriate signal processing plug-ins, e.g., augmented cognition or passive BCIs. The software also provides the ability to configure the device's hardware, to save data to disk, and to monitor the system in real time. Plug-ins can be implemented in C++ or Python. A series of validation tests were carried out to confirm that the system operates as intended. Most of the measured parameters were within the expected ranges: EEG amplifier noise = 0.14 μVRMS input-referred, EEG pass band = DC to 47 Hz, camera focus = 2.4 lp/mm at 40 mm, and total latency < 100 ms. Some parameters were worse than expected but still sufficient for effective operation: EEG amplifier CMRR ≥ 82 dB, EEG cross-talk = -17.4 dB, and IMU sampling rate = 10 Hz. The contact impedance of the dry electrodes, measured to be several hundred kilohms, was too high to obtain clean EEG. Three small-scale experiments were done to test the performance of the device in operation on people. The first two demonstrated that the pupil localization algorithm produces PERCLOS values close to those from a manually-rated gold standard and is robust to changes in ambient light levels, iris colour, and the presence of glasses. The final experiment demonstrated that the system is capable of capturing all three physiological signals, transmitting them to the remote computer in real time, extracting features from each signal, and classifying simulated microsleeps from the extracted features. However, this test was successful only when using conventional wet EEG electrodes instead of the dry electrodes built into the device; it will be necessary to find replacement dry electrodes for the device to be useful. The device and associated software form a platform which other researchers can use to develop algorithms for lapse detection. This platform provides data capture hardware and abstracts away the low-level software details so that other researchers are free to focus solely on developing signal processing techniques. In this way, we hope to enable progress towards a practical real-time, real-world lapse detection system.

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  • Electronic Conduction in Disordered Carbon Materials

    Cheah, Chun Yee (2015)

    Doctoral thesis
    Victoria University of Wellington

    Graphene, consisting of a single layer of carbon atoms, is being widely studied for its interesting fundamental physics and potential applications. The presence and extent of disorder play important roles in determining the electronic conduction mechanism of a conducting material. This thesis presents work on data analysis and modelling of electronic transport mechanisms in disordered carbon materials such as graphene. Based on experimental data of conductance of partially disordered graphene as measured by Gómez-Navarro et al., we propose a model of variable-range hopping (VRH) – defined as quantum tunnelling of charge carriers between localized states – consisting of a crossover from the two-dimensional (2D) electric field-assisted, temperature-driven (Pollak-Riess) VRH to 2D electric field-driven (Skhlovskii) VRH. The novelty of our model is that the temperature-dependent and field-dependent regimes of VRH are unified by a smooth crossover where the slopes of the curves equal at a given temperature. We then derive an analytical expression which allows exact numerical calculation of the crossover fields or voltages. We further extend our crossover model to apply to disordered carbon materials of dimensionalities other than two, namely to the 3D self-assembled carbon networks by Govor et al. and quasi-1D highly-doped conducting polymers by Wang et al. Thus we illustrate the wide applicability of our crossover model to disordered carbon materials of various dimensionalities. We further predict, in analogy to the work of Pollak and Riess, a temperature-assisted, field-driven VRH which aims to extend the field-driven expression of Shklovskii to cases wherein the temperatures are increased. We discover that such an expression gives a good fit to the data until certain limits wherein the temperatures are too high or the applied field too low. In such cases the electronic transport mechanism crosses over to Mott VRH, as expected and analogous to our crossover model described in the previous paragraph. The second part of this thesis details a systematic data analysis and modelling of experimental data of conductance of single-wall carbon nanotube (SWNT) networks prepared by several different chemical-vapour deposition (CVD) methods by Ansaldo et al. and Lima et al. Based on our analysis, we identify and categorize the SWNT networks based on their electronic conduction mechanisms, using various theoretical models which are temperature-dependent and field-dependent. The electronic transport mechanisms of the SWNT networks can be classed into either VRH in one- and two-dimensions or fluctuation-assisted tunnelling (FAT, i.e. interrupted metallic conduction), some with additional resistance from scattering by lattice vibrations. Most notably, for a selected network, we find further evidence for our novel VRH crossover model previously described. We further correlate the electronic transport mechanisms with the morphology of each network based on scanning electron microscopy (SEM) images. We find that SWNT networks which consist of very dense tubes show conduction behaviour consistent with the FAT model, in that they retain a finite and significant fraction of room-temperature conductance as temperatures tend toward absolute zero. On the other hand, SWNT networks which are relatively sparser show conduction behaviour consistent with the VRH model, in that conductance tends to zero as temperatures tend toward absolute zero. We complete our analysis by estimating the average hopping distance for SWNT networks exhibiting VRH conduction, and estimate an indication of the strength of barrier energies and quantum tunnelling for SWNT networks exhibiting FAT conduction.

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  • Investigating the mode of action of tuberculosis drugs using hypersensitive mutants of Mycobacterium smegmatis

    Campen, Richard Laurence (2015)

    Doctoral thesis
    Victoria University of Wellington

    Mycobacterium tuberculosis, the etiological agent of tuberculosis (TB), is the leading cause of death and disease by a bacterial pathogen worldwide. The growing incidence of drug resistant TB, especially multi-drug resistant TB highlights the need for new drugs with novel modes of action. Current treatment of TB involves a multi-drug regimen of four drugs including isoniazid and rifampicin, both of which were discovered over 40 years ago. Bedaquiline is one of the first novel TB drugs to enter clinical trials since the discovery of rifampicin, and has shown excellent activity against drug resistant TB. Although isoniazid and rifampicin are well established anti-TB drugs, significant gaps in knowledge regarding their modes of action exist. Furthermore, little information on the mode of action of the novel drug bedaquiline is known beyond its primary target. Characterisation of drug mode of action facilitates rational modifications of drugs to improve the treatment of TB. The aim of this study was to identify novel aspects of the modes of action of isoniazid, rifampicin, and bedaquiline by characterising drug hypersensitive mutants of M. smegmatis mc²155. A sub-saturated M. smegmatis mc²155 transposon mutant collection with 1.1-fold genome coverage (7680 mutants) was constructed, with this collection estimated to contain mutations in 73.2% of all genes capable of maintaining a transposon insertion (non-essential genes). A high-throughput assay was developed for screening the collection, and mutants related to known drug mode of action were identified for isoniazid (ahpC and eccCa₁) and bedaquiline (atpB). Additionally, known mechanisms of drug inactivation were identified for isoniazid (nudC), rifampicin (arr and lspA), and bedaquiline (mmpL5). The finding that transposon mutants of nudC are hypersensitive to isoniazid independently validated the recent discovery of the role of NudC in basal isoniazid resistance by Wang et al. (2011). The remaining genes identified in this thesis represent potentially novel aspects of the modes of action or resistance mechanisms of these drugs. Cross-sensitivity to other drugs indicated that the mechanism of sensitivity was drug specific for the mutants examined. Differential-sensitivity testing against drug analogues revealed that Arr is involved in resistance to the rifampicin analogue rifapentine as well, indicating that Arr can detoxify rifapentine similar to rifampicin. The nudC mutant showed increased sensitivity to a range of isoniazid analogues, indicating that it can detoxify these analogues similar to the parent compound. Interestingly six analogues were found to be less active against the nudC mutant than expected. A number of overexpression strains were tested against these six analogues; a nudC overexpression strain, and a strain overexpressing inhA, the primary target for isoniazid. Overexpression of nudC as well inhA increased the resistance of WT to isoniazid, but failed to increase resistance to three of the analogues, NSC27607, NSC33759, and NSC40350. Isoniazid is a prodrug and is activated by the peroxidase/catalase enzyme KatG. Overexpression of katG resulted in increased isoniazid sensitivity, as well as increased sensitivity to NSC27607, NSC33759, and NSC40350. Together these results suggest that NSC27607, NSC33759, and NSC40350 are activated by KatG, but that InhA is not the primary target. Additionally the inability of NudC overexpression to confer resistance suggests these analogues are not acting via a NAD adduct, the mechanism by which isoniazid inhibits InhA. These results suggest that there are other toxic metabolites being produced by KatG activation of these three analogues. In conclusion, characterisation of mutants identified in a high-throughput assay for drug hypersensitivity identified genes involved in the modes of action or resistance mechanisms for isoniazid, rifampicin, and bedaquiline. Additionally, a number of novel genes were identified that have no known connections to the known modes of action or resistance mechanisms for these drugs. Further testing of a nudC mutant revealed three isoniazid analogues that appear to inhibit growth of M. smegmatis mc²155 independent of InhA, the primary target of isoniazid. This study has successfully demonstrated that screening for drug hypersensitivity can generate novel information on drug mode of action and resistance mechanisms. This information can ultimately be used to help drive the development of new drugs, and improve treatment of TB.

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  • An Approach to Embedding ITSs into Existing Systems

    Amalathas, Sagaya Sabestinal (2012)

    Doctoral thesis
    University of Canterbury Library

    Intelligent Tutoring Systems (ITSs) have proven their effectiveness in many domains, but very few attempts have been made to embed them with existing systems. This area of research has a lot of potential in providing life-long learning and work place training. This PhD project makes several significant contributions. This is the first attempt to embed a Constraint-Based Tutor (CBT) with an existing system, in order to investigate the benefits of providing on-the-job training. We also propose a framework for embedded ITSs, and develop DM-Tutor (Decision-Making Tutor) embedded with the MIS for palm oil. DM-Tutor is the first ITS for the domain of oil palm plantation decision making, and was developed in the ASPIRE authoring system. Our hypothesis was that DM-Tutor embedded with the MIS for palm oil would provide effective instruction and training for oil palm plantation decision making. We also wanted to investigate the role of feedback messages in helping to provide effective training.

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  • Safe, effective, and patient-specific glycaemic control in neonatal intensive care.

    Dickson, Jennifer Launa (2015)

    Doctoral thesis
    University of Canterbury Library

    Very premature infants often experience high blood sugar levels as a result of incomplete metabolic development, illness, and stress. High blood sugar levels have been associated with a range of worsened outcomes and increased mortality, but debate exists as to whether high blood sugar levels are a cause of, or marker for, these worsened outcomes. Insulin can be used to lower blood sugar levels, but there is no standard protocol for its use in neonates, and the few clinical studies of insulin use in neonatal intensive care are relatively small and/or have resulted in high incidence of dangerously low blood sugar levels. Hence, there is a need for a safe and effective protocol for controlling blood sugar levels to a normal range in order that potential clinical benefits can be successfully studied in this clinical cohort. This thesis adapted a glucose-insulin model successfully used in adult intensive care for the unique physiology and situation of the very premature infant. The model aims to reflect known physiology. As such, sources and disposal of glucose and insulin within the body are examined using both published data and unique data sets from a study here in New Zealand. In addition, the absorption of glucose from milk feeds is examined. This glucose-insulin physiological model is then used alongside statistical forecasting to develop a protocol for selecting an appropriate insulin dose based on targeting of likely outcomes to a specified target normal range. The protocol is tested in silico using virtual trials, and then clinically implemented, with results showing improved performance over current clinical practice and other published studies. In particular, ~77% of blood glucose is observed within the specified target range across the cohort, and there has been no incidence of dangerously low blood glucose levels. This protocol is thus safe and effective, accounting for inter- and intra- patient variability, and thus enabling patient-specific care.

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  • Progesterone and the striatal 6-hydroxydopamine model of Parkinson’s disease

    Perry, James Colin (2015)

    Doctoral thesis
    University of Canterbury Library

    Parkinson’s disease (PD) is a common neurodegenerative disorder that is characterised by akinesia, muscular rigidity, and postural instability, due primarily to the loss of dopaminergic neurons in the substantia nigra and depletion of upstream dopamine in the striatum. Current dopaminergic treatments reduce motor symptoms, but have diminishing benefits as the disease progresses. Treatment with the neuroactive steroid natural progesterone (PROG) improves outcomes in many experimental models of brain injury due to its pleiotropic mechanisms of neuroprotection, many of which may also benefit PD. This thesis investigated the influence of PROG on motor impairments in the unilateral intrastriatal 6-hydroxydopamine (6-OHDA) lesion model of PD in rats. We established a PD-like impairment with a d-amphetamine induced rotation test at day 7 after large lesions and then administered PROG (4 mg/kg or 8 mg/kg) once daily for 7 days starting at day 8. Both PROG doses markedly improved the primary outcome measure, forelimb akinesia on the adjusting steps test, with improvement sustained for six weeks after treatment had stopped. In a second study the beneficial influence of PROG (8 mg/kg) on akinesia was replicated for rats with large lesions and was extended to rats with small lesions so that the latter rats were now similar to sham operated controls. We also found that PROG modestly improved postural instability of the ipsilateral forelimb on the postural instability test, and sensorimotor integration on the whisker test, but did not improve skilled reaching accuracy on a single-pellet reaching task, forelimb use asymmetry on the cylinder test, sensory neglect on the corridor test, or rotation bias after apomorphine. Furthermore, PROG did not change striatal tyrosine hydroxylase density when assessed in rats with large lesions. This study has provided the most thorough examination to date regarding PROG’s influence on motor skills in an animal model of PD. Furthermore, this study has produced novel evidence of the beneficial effects of PROG treatment on forelimb akinesia. These initial promising findings suggest that PROG is an effective therapy for akinesia and thus provides an impetus to further investigate PROG’s efficacy for the treatment of PD.

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  • Aspects of the biology of some New Zealand echinoderms : feeding, growth and reproduction in the asteroids, Patiriella regularis (Verrill, 1867) and Coscinasterias calamaria (Gray, 1840).

    Crump, Robin (1969)

    Doctoral thesis
    University of Otago

    192 leaves :illus. ; 30 cm. Bibliography: p.138-147. The author's "The flight response in Struthiolaria papulosa giges Sowerby", reprinted from the New Zealand journal of marine and freshwater research, v.2, no.3, Sept., 1968, in pocket. University of Otago department: Zoology

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  • A Transcriptomic Examination of Sexual Differentiation in Zebrafish, Danio rerio

    Lee, Stephanie Ling Jie (2015)

    Doctoral thesis
    University of Otago

    Zebrafish sex determination and sexual differentiation is complex. Neither sex chromosomes, major sex-determining genes nor universal sex-linked markers have been identified, and a variety of environmental factors can influence sex ratios. It is thus unsurprising that the molecular pathways underpinning zebrafish sexual development remain poorly understood. A few key genes such as, SRY-box containing gene 9a (sox9a), anti-Müllerian hormone (amh), cytochrome P450, family 19, subfamily A, polypeptide 1a (cyp19a1a) are known to play roles in zebrafish gonadal differentiation. However, at this time, there are many more questions than answers about sex determination and differentiation in this ubiquitious, and immensely well-studied, species. As with many other vertebrates, sex hormone treatment can induce sex reversal of gonadal phenotype and sexual behaviour in zebrafish. In this study, we take advantage of hormonal manipulation of sex in developing zebrafish and RNA-Seq to unravel the unknown genetic pathways that underlie sex determination and sexual differentiation. We conducted global transcriptomic profiling of juvenile zebrafish brains and gonads at two important developmental stages in gonadal differentiation: (1) juvenile ovary-to-testis transformation (40 days post fertilization) and (2) the completion of testicular and ovarian differentiation (60 days post fertilization). Gene expression profiles from 17α-methyltestosterone masculinised juvenile zebrafish were also compared with untreated zebrafish to improve understanding of androgenic effects on zebrafish sexual differentiation pathways. To our knowledge, this is the first study profiling transcriptome-wide sex dimorphic gene expression in teleost brains during gonadal differentiation. We identified modest sex differences in developing zebrafish brains; 33 and 185 sex dimorphic genes were identified in the brains of 40 dpf and 60 dpf zebrafish respectively. Methyltestosterone treatment significantly altered expression patterns at both timepoints. We observed a total of 1,554 genes differentially expressed between control female brains and MT-treated brains at 40 dpf. 1,379 genes were differentially expressed between 40 dpf male brains and 40 dpf MT-treated brains. At 60 dpf, 728 genes exhibited differential expression between control female brains and MT-treated brains. Interestingly, significantly fewer genes (269) were differentially expressed between control male brains and MT-treated brains at 60 dpf. In contrast, we observed extensive sex differences in zebrafish gonadal transcriptomes. A total of 5,039 genes were sexually dimorphic at 40 dpf. 2,502 and 2,537 genes were up-regulated in transforming testes and juvenile ovaries respectively. At 60 dpf, we identified 4,190 testis-biased genes and 4,267 ovary-biased genes. Many of the sex dimorphic genes identified have no previous links with gonadal differentiation. Despite accelerated testicular development in MT-treated zebrafish, the numbers of differentially expressed genes identified when control ovaries were compared to control testes or MT-treated testes were similar. We identified 5,237 differentially expressed genes between 40 dpf juvenile ovaries and 40 dpf MT-treated testes. 7,513 genes were differentially expressed between ovaries and MT-treated testes at 60 dpf. There were considerably fewer differences between control testes and MT-treated testes. While 1,222 genes were differentially expressed between control testes and MT-treated testes at 40 dpf, only 20 genes separated the transcriptomes of 60 dpf control testes and MT-treated testes. It appears that androgen-induced masculinization shares key molecular regulators with normal testicular differentiation. A pair of rec8 genes were up-regulated in control testes and MT-treated testes. Testis-biased Rec8 expression was previously reported in mammals. Rec8 is required for sister chromatid cohesion, formation of synaptonemal complexes and homologous recombination during meiosis. To elucidate the functional significance of rec8 genes in testicular development, we characterized rec8 genes in adult zebrafish. Sequence homology, synteny and phylogenetic relationships between the zebrafish rec8 genes were explored in silico. Analysis of rec8a and rec8b gene expression in adult zebrafish confirmed testis-biased expression. Our work sets up a framework for which we can explore further functional testing of zebrafish rec8 genes using morpholino knockdown and CRISPR/Cas knockout technologies.

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  • Rubisco's chiropractor: a study of higher plant Rubisco activase

    Keown, Jeremy Russell (2015)

    Doctoral thesis
    University of Canterbury Library

    Rubisco activase operates as the chaperone responsible for maintaining the catalytic competency of Ribulose 1,5-bisphophate carboxylase oxygenase (Rubisco) in plants. Rubisco is notoriously inefficient, rapidly self-inactivating under physiological conditions. Rubisco activase uses the power released from the hydrolysis of ATP to power a conformational change in Rubisco, reactivating it. Rubisco activase has been previously shown to form a large range of species in solution; however, little has been done to relate the size of oligomeric species and physiological activity. In this thesis data is presented from a range of biophysical techniques including analytical ultracentrifugation, static light scattering, and small angle X-ray scattering combined with activity assays to show a strong relationship between oligomeric state and activity. The results suggest that small oligomers comprising 2-4 subunits are sufficient to attain full specific activity, a highly unusual property for enzymes from the AAA+ family. Studies utilising a number of Rubisco activase variants enabled the determination of how Rubisco and Rubisco activase may interact within a plant cell. A detailed characterisation of the α-, β-, and a mixture of isoforms further broadened our knowledge on the oligomerisation of Rubisco activase. Of particular importance was the discovery of a thermally stable hexameric Rubisco activase variant. It is hoped that these findings may contribute to development of more heat tolerant Rubisco activase and lead research into more drought resilient crop plants.

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  • Māori Orality and Extended Cognition: A cognitive approach to memory and oral tradition in the Pacific

    Murphy, David James (2015)

    Doctoral thesis
    Victoria University of Wellington

    Though philosophers have long held that interpretive anthropology and the cognitive science of religion (CSR) are opposed, this thesis offers an extended empirical assessment of the issues surrounding the implications of utilizing ethnographic material within a cognitive study of religious transmission. Using case studies from the Pacific, I consider a core question arising in both interpretative and cognitive disciplines, namely: how have oral cultures been able to preserve and transmit bodies of sacred knowledge cross-generationally without any external administrative tools (i.e. text)? First, I focus on the historical and ethnographic details of traditional Māori orality. I look at how orally transmitted knowledge was managed through the external cognitive resources associated with religious ritual. Here I find evidence within Pacific oral traditions that the problem of managing knowledge was overcome through tools and strategies that augmented memory and oral skill. I give special attention to the traditional Māori structuring of learning environments. Next I consider how macro-spatial tools – such as landmarks, and place names – helped support working memory and information management, and show that orientations to landscape are vital to ensuring collective memory. This thesis also demonstrates how culturally learned tools and strategies support the stability of religious cultural transmission. The use of external cognitive resources implies the complexity of managing and organizing sacred knowledge. Put simply, focusing on the historical accounts from the Pacific reveals a rich suite of culturally evolved tools and strategies for the transmission of religious knowledge. I show that tools such as ritual, myth, mnemonic techniques, and artifacts enable and stabilise such transmission. I hold, that such cultural environments constitute cognitive tools that are meaningfully described as cultural cognitive systems. Thus, combining descriptive accounts with the theoretical orientations of the cognitive sciences motivates what I call a ‘cognitive ecological’ model of mind. I argue that the cognitive ecological model is important because it orients researchers to the role that culturally evolved tools play in: (1) dramatically extending the human brain’s power to reckon with its surroundings and: (2) coordinating such knowledge across social groups and over time. The cognitive ecological model of mind I propose in this study is important for three reasons: First, it challenges the received view within the CSR – what I call the ‘Standard Internal Model’ (SiM) – which holds that the transmission of religious representations carries low cognitive demands (i.e. it is cognitively optimal). In contrast to SiM, the Pacific materials discussed here suggest that the oral transmission of sacred knowledge is cognitively demanding, culturally costly, and locally contingent. Second, my thesis demonstrates that historical and ethnographic evidence contains information that is vital for progress in the CSR since qualitative resources document how niche specific cultural practices often facilitate the acquisition and coordination of the complex knowledge resources over time. The ethnographic data supports the local optimality contention. Third, my thesis reveals that formulating tractable models for cultural transmission within the CSR is benefitted by an interdisciplinary approach. Such a prospect, I urge, is vital for intellectual progress between the humanities and the CSR. As such, and contrary to received opinion, my thesis shows how the CSR and the cultural anthropology of religion share a common intellectual fate.

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  • Age, growth and feeding ecology of five co-occurring fishes in southern New Zealand

    Jiang, Weimin (2002)

    Doctoral thesis
    University of Otago

    x, 340 leaves :ill. (some col.) ; 30 cm. Includes bibliographical references. University of Otago department: Marine Science

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  • The Commonwealth Trans-Antarctic Expedition 1955-58 - How the crossing of Antarctica moved New Zealand to recognise its Antarctic heritage and take an equal place among Antarctic nations

    Hicks, Stephen Walter (2015)

    Doctoral thesis
    University of Canterbury Library

    The thesis analyses the expedition (TAE) led by Dr.Vivian Fuchs and Sir Edmund Hillary from three vantage points: 1)the years from 1948 to 1955 leading up to the expedition 2) the interaction between the IGY and the TAE projects and 3) the role of the US Navy as the expedition unfolded. The thesis also investigates key events including the purchase of the ship Endeavour from Britain, the competition for leadership of the UK and NZ parties, the 'dash to the Pole' by Hillary, and the search for base sites and routes to the Polar Plateau. The thesis contains an overview historical introduction, a comprehensive literature review as well as a broad-based set of conclusions.

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  • Pocket beach wave processes and current systems investigated via field and numerical modelling studies: A case study of Okains Bay

    Eisazadeh Moghaddam, Arash (2015)

    Doctoral thesis
    University of Canterbury Library

    Confined coasts in general, and pocket beach environments in particular, are under huge development pressures worldwide, not least due to their sheltered nature and perceived shoreline stability. However, understanding of their physical functioning is poor in comparison to that of open coast beaches. This study aims to improve understanding in terms of the existing gaps in knowledge of wave processes and nearshore currents, and also to examine the importance of local wind and tide factors in generating nearshore currents, in micro-tidal pocket beaches. The boundaries of embayments are generally recognized as important controls of their beach processes and responses, yet little detailed knowledge exists of how the exact embayment dimensions and characteristics influences these processes. One key embayment feature the influence of which is poorly understood is the downcoast headland. In this thesis, field observations plus Zanuttigh and Van der Meer’s (2008) approach, and the SWAN wave model were used to evaluate the downcoast headland effects on wave processes within Okains Bay, an example pocket beach environment. The results showed that incident wave heights and directions were significantly influenced by wave reflection processes from the downcoast headland inside the bay. The intensity of reflection effects on wave characteristics inside the pocket beach varied according to approaching wave direction. Reflection effects reduced when waves approached from angles close to parallel to the headlands, increasing towards headland-perpendicular wave approaches. Field observations and the XBeach model were used to examine whether or not tides can significantly influence nearshore currents within example and model pocket beach environments. Results indicated that tides can be the primary driver of nearshore currents close to the bed inside micro-tidal pocket beaches, depending on incident wave conditions. In areas of micro-tidal pocket beaches exposed to direct approaching waves, currents were wave driven, while in areas further into the bay that experienced headland filtering of their wave environment, currents were mainly tide generated. The results of this study demonstrated how the current circulation system within micro-tidal pocket beaches is related to the incoming directions of offshore waves. If high energy waves approach oblique or normal to the shoreline (with the assumption that the shoreline is at 90° to the headlands), the current system was found to consist of longshore currents influenced by headlands, plus a rip current in the center of the shoreline or a toporip in proximity to headlands. The location of the rip current or toporip was determined by the direction of approaching incident waves. This study also examined the behavior of local winds in a pocket beach environment and their consequent effects on nearshore currents. Results for Okains Bay show that local winds tended to blow in offshore and onshore directions, as the bay is located in a valley, so orographic effects channel and shift the wind directions to angles close to offshore and onshore directions inside the bay. Results also indicated that local winds influence the hydrodynamic currents of pocket beaches that are confined by elevated topography, producing semi-cross shore influences since the winds are topographically channelled to blow in predominantly offshore and onshore directions. This research significantly refines our understanding of micro-tidal pocket beach wave and current processes, including quantification of the filtering effects of headlands on their wave environments, revealing the various and variable influences of tides and winds compared to in open coast beaches; and, significantly, highlighting the role of downcoast headland wave reflection effects. With regard to the latter, this research elucidates some key process differences between pocket and embayed beaches and clarifies reasons why the application of embayed beach models that include refraction and diffraction but exclude reflection effects to the study of pocket beaches is inappropriate for studying pocket beaches. This research also provides methodological and topic suggestions for future research on pocket beach environments, including how to use the improved hydrodynamic knowledge of this study in future studies seeking to better understand pocket beach sediment systems, a topic that was beyond the scope of the current research.

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  • 'The Inside View' Investigating the use of Narrative Assessment to Support Student Identity, Wellbeing, and Participation in Learning in a New Zealand secondary school.

    Guerin, Annette Patricia (2015)

    Doctoral thesis
    University of Canterbury Library

    New Zealand education policies and documents (Ministry of Education, 2007, 2009, 2010, 2011a, 2014a) situate students at the centre of assessment processes that are underpinned by the New Zealand Curriculum. They identify building student assessment capability as crucial to achieving improvement in learning. Documents recognize the impact of quality interactions and relationships on effective assessment. However these core beliefs about assessment are not observed to guide teaching practices for all students. Disabled students remain invisible in assessment data and practices within New Zealand secondary schools. There appears to be little or no assessment data about learning outcomes for this group of students. This thesis investigates possible ways to recognize the diversity of student capability and learning through the use of narrative assessment. It challenges the absence of disabled students in assessment landscapes as educator roles and responsibilities within assessment, teaching and learning are framed within an inclusive pedagogy. This research project focuses on how a team of adults and two students labeled as disabled make sense of assessment and learning within the context of narrative assessment in the students’ regular high school. The project examines the consequences of narrative assessment on student identity, wellbeing and participation within learning. The study offers opportunities to observe how specialists from outside of the school respond to the use of narrative as they work with the two student research participants. This study undertakes a critical inquiry that recognises the principles of the Treaty of Waitangi – partnership, protection and participation – as pivotal to inclusive practice where all students are valued as learners. It investigates how narrative assessment can honour these principles in everyday teaching practice. The project aims to inform education policy and practice, with a view to enriching learning outcomes and opportunities for disabled students who are frequently marginalized by inequitable assessment processes. It is argued that narrative assessment can support the construction of student identity and wellbeing. It can support the recognition of disabled students as partners in their learning. However the value of narrative assessment can be undermined by the responses of educators and other professionals who continue to work within deficit models of assessment, teaching and learning. Within this thesis adult participants from family and education contexts have clear ideas about the value and validity of assessment practices and processes that do not respect a presumption of competence or a need to establish a relationship with a student being assessed. Their views challenge everyday practices that fulfill assessment contracts, but ignore Treaty of Waitangi and New Zealand Curriculum commitments. Their views can inform better ways of working between specialists and schools supporting disabled students.

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  • Optical probes of free charge generation in organic photovoltaics

    Barker, Alexander J. (2015)

    Doctoral thesis
    Victoria University of Wellington

    Organic photovoltaics (OPVs) show considerable promise as a source of low cost solar energy. Improving our understanding of the processes governing free charge photogeneration in OPVs may unlock the improvements in efficiency required for their widespread implementation. In particular, how do photogenerated charge pairs overcome their mutual columbic attraction, and what governs the branching between bound and free charge pairs that is observed to occur shortly after their creation? Ultrafast laser techniques such as transient absorption (TA) spectroscopy are the only tools capable of probing the time scales associated with these processes (as short as 10⁻¹⁴ seconds). Challenges include achieving sufficient sensitivity to resolve the tiny signals generated in thin films under solar-equivalent excitation densities, and distinguishing and quantifying overlapping signals due to separate phenomena. We present the development of a versatile and ultra-sensitive broadband TA spectrometer, along with a comprehensive analysis of the noise sources limiting sensitivity. Through the use of referenced shot-to-shot detection and a novel method exploiting highly chirped broadband probe pulses, we are capable of resolving changes in differential transmission < 3 × 10⁻⁶ over pump-probe delays of 10⁻¹³–10⁻⁴ seconds. By comparing the absorption due to photogenerated charges to measurements of open-circuit voltage decay in devices under transient excitation, we show that TA is able to quantify the recombination of freely extractable charge pairs over many decades of pump-probe delay. The dependence of this recombination on excitation density can reveal the relative fraction of bound and free charge pairs. We apply this technique to blends of varying efficiency and find that the measured free charge fraction is correlated with published photocharge yields for these materials. We access a regime at low temperature where thermalized charge pairs are frozen out following the primary charge separation step and recombine monomolecularly via tunneling. The dependence of tunneling rate on distance enabled us to fit recombination dynamics to distributions of recombination rates. We identified populations of charge-transfer states and well-separated charge pairs, the yield of which is strongly correlated with the yield of free charges measured via their intensity dependent recombination. We conclude that populations of free charges are established via long-range charge separation within the thermalization timescale, thus invoking early branching between free and bound charges across an energetic barrier. Subject to assumed values of the electron tunneling attenuation constant, we find critical charge separation distances of ~ 3–4nm in all materials. TA spectroscopy probes the absorption of excited states, with the signal being proportional to the product of population density and absorption cross-section of the absorbing species. We show that the dependence of signal on probe pulse intensity can decouple these parameters, and apply a numerical model to determine the time-dependent absorption cross-section of photogenerated excitons in thin films of semiconducting polymers. Collectively, this thesis presents spectroscopic tools and applications thereof that illuminate the process of free charge generation in organic photovoltaics.

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