1,025 results for Doctoral, 2011

  • 'An education system characterised by equity' : a critical evaluation of educational change in Samoa, 1995-2005 : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Education at Massey University, Palmerston North, New Zealand

    Male, Alan G R (2011)

    Doctoral thesis
    Massey University

    The problem investigated in this thesis arose from my professional practice as a consultant with regard to educational reforms in a number of countries, including Samoa. This created an initial interest in why different policy options were chosen by different countries in response to similar problems. Observation of the implementation of reforms in various contexts also created questions as to why the implementation of reforms often seemed to lead to new formulations of the original arrangements, resulting in development but little change. A prior review of evaluations of educational reform programmes showed that many educational evaluations are confined to matters of technical advice inputs, resource management and the achievement of milestones. This study however, considers other factors relevant to the successful achievement of an educational reform programme situated within a particular social, political and historical context. In particular, this thesis reports on a critical evaluation of the development, between the mid-1980s and 1994, of a policy aimed at producing an education system “characterised by equity” (Department of Education, 1995) in Samoa and then on the results of the implementation of that policy between 1995-2005. The study focused first on the differences in the performance of student groups based in the national Year 8 secondary school selection examination and in their subsequent access to secondary schooling and to the achievement outcomes in Year 12 over the period between 1994 and 2008. Information was gathered through analysis of national examination results databases. Additional information was gathered through interviews and questionnaires from senior educational system managers and from the principals of a sample of four secondary schools. Questionnaires, aimed at gathering socio-economic data, were administered to 2000 students and their families from Years 9, 11, 12 and 13 at the sample schools. The evidence showed little change in the patterns of achievement between advantaged and disadvantaged groups. The system had expanded but the patterns of inequity remained unchanged. The reasons for the selection of the reform options that resulted in the maintenance of disparities through the 1995-2005 programme were found in the history, culture and political setting of Samoa. Because of the small size and ethnic and cultural homogeneity of the population, the evaluation was based on the theories of Pierre Bourdieu. Bourdieu’s concepts of field practice and habitus showed how the policy options included in the reform programme were influenced by an underlying habitus that generated the desire for change but also constrained the achievement of the stated aim of a “system characterised by equity”. The research showed how the historical background to the patterns of advantage within the system and the structure and patterns of advantage that resulted from the reforms continued beyond the reform.

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  • Advances in Visibility Modelling in Urban Environments to Support Location Based Services

    Bartie, Philip James (2011)

    Doctoral thesis
    University of Canterbury Library

    People describe and explore space with a strong emphasis on the visual senses, yet modelling the field of view has received little attention within the realm of Location Based Services (LBS), in part due to the lack of useful data. Advances in data capture, such as Light Detection and Ranging (LiDAR), provide new opportunities to build digital city models and expand the range of applications which use visibility analysis. This thesis capitalises on these advances with the development of a visibility model to support a number of innovative LBS functions in an urban region and particular focus is given to the visibility model‟s supporting role in the formation of referring expressions, the descriptive phrases used to identify objects in a scene, which are relevant when delivering spatial information to the user through a speech based interface. Speech interfaces are particularly useful to mobile users with restricted screen viewing opportunities, such as navigational support for motorists and a wider range of tasks including delivering information to urban pedestrians. As speech recognition accuracies improve so new interaction opportunities will allow users to relate to their surroundings and retrieve information on buildings in view through spoken descriptions. The papers presented in this thesis work towards this goal, by translating spatial information into a form which matches the user‟s perspective and can be delivered over a speech interface. The foundation is the development of a new visual exposure model for use in urban areas, able to calculate a number of metrics about Features of Interest (FOIs), including the façade area visible and the percentage on the skyline. The impact of urban vegetation as a semi-permeable visual barrier is also considered, and how visual exposure calculations may be adjusted to accommodate under canopy and through canopy views. The model may be used by pedestrian LBSs, or applied to vehicle navigation tasks to determine how much of a route ahead is in view for a car driver, identifying the sections with limited visibility or the best places for an overtaking manoeuvre. Delivering information via a speech interface requires FOI positions to be defined according to projective space relating to the user‟s viewpoint, rather than topological or metric space, and this is handled using a new egocentric model. Finally descriptions of the FOIs are considered, including a method to automatically collect façade colours by excluding foreground objects, and a model to determine the most appropriate description to direct the LBS user‟s attention to a FOI in view.

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  • A Traditional Institutionsurviving in a Modern Setting?The Reinterpretation of Caste in the IndianIT Industry

    Lindt, Benjamin (2011)

    Doctoral thesis
    University of Canterbury Library

    This thesis aims to explore and understand the changes to the social institution of caste that arise from the ongoing modernisation of Indian society. The research setting is the IT industry in Bangalore and Hyderabad. As the Indian IT industry is the economic sector most exposed to globalised modernisation, it has come to represent a social milieu deemed particularly modern in India. The thesis discusses the social role of the IT industry in India; the rise of the new middle classes, and the specifics of the locality of Bangalore. It is argued that caste as a social institution systematically connects three different dimensions of human existence; the economic (caste-wise division of labour); the biological (rules concerning exogamy and endogamy); and the ideational (various rationalisations for caste). While the economic dimension of caste is increasingly losing its meaning, caste endogamy remains largely intact and is rationalised in forms much more compatible with modernity. This composite model of caste is then contrasted with a model of modernity based arguments presented by the most relevant sociologists, from Max Weber to Peter Wagner. In the analysis here, the contemporary, ‘quasiethnic’ reinterpretation of caste appears still to conflict with the implications of modernity. Even though caste provides actual benefits for those who employ the concept and practise it – ranging from political to economic to private – its rationale nevertheless contrasts with the motives that are generally attributed to modernity. The empirical research, employing qualitative, semi-structured interviews, participant observation, and hermeneutic interpretation of first-hand sources, produces a complex picture. The interviews with more than 70 IT employees of various caste backgrounds (including over 40 from SC/ST categories – underrepresented in the industry) indicate that caste is seemingly irrelevant in professional settings. In support of this conclusion, additional research hints at the prevalence of widespread anonymity in the IT industry and limited understanding of caste amongst IT employees. By contrast, participant observation during seven months living amongst IT engineers suggests that caste still matters: In private, the consequences of the practise of caste are still apparent, even though ritual restrictions are waning in importance. Thus, a pronounced caste-wise compartmentalisation of Indian society remains visible even amongst young IT engineers. The thesis concludes that caste is not disappearing from Indian society; rather, it is dramatically adapting to modern circumstances.

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  • Spatial pattern and community assembly: does the configuration of stream networks influence their community structure?

    Campbell, Rebecca Elisabeth (2011)

    Doctoral thesis
    University of Canterbury Library

    Dendritic stream networks are inherently spatially and hierarchically structured, but the effects of this structure on stream communities are largely unknown. My aim was to investigate spatial patterns in stream networks using extensive spatial sampling of both adult and benthic macroinvertebrates in four stream networks on the West Coast of the South Island, New Zealand. Using spatial modelling and analyses, I answered questions about appropriate spatial measurements to capture ecological processes in stream networks, metacommunity processes at different scales in space and time, and how local and regional processes interact to structure metacommunities in stream networks. Spatial eigenfunction analyses showed that distance measures that explained most variance in stream macroinvertebrate communities were stream distance and weighted stream distance measures. They performed better than Euclidean distance to measure spatial structure that is ecologically relevant to stream network communities. The spatial pattern of benthic stream macroinvertebrates was stable over time, whereas community composition changed significantly, as shown by space-time interactions modelled by MANOVA-like redundancy analysis. Thus, spatial processes structuring stream metacommunities remained constant, in agreement with neutral model predictions. Network-scale properties, particularly flood disturbances, influenced the relative importance of spatial and environmental variation in stream network metacommunities. Additionally, quantile regression indicated that three key variables, habitat size, isolation and local habitat conditions, jointly limited community structure in stream networks, providing empirical support for both island biogeography and metacommunity theories. My study indicated that spatial structuring has an important influence on stream macroinvertebrate communities. The results contribute to broader ecological theory and understanding of community assembly by relating empirical results to theoretical predictions. In particular, they advance understanding of spatial processes in stream networks. The research also highlights a number of new methods, which were successfully applied to stream systems to elucidate complex spatial patterns.

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  • Land-Use Intensification in Grazing Systems: Plant Trait Responses and Feedbacks to Ecosystem Functioning and Resilience

    Laliberté, Etienne (2011)

    Doctoral thesis
    University of Canterbury Library

    Land-use change is the single most important global driver of changes in biodiversity. Such changes in biodiversity, in turn, are expected to influence the functioning of ecosystems and their resilience to environmental perturbations and disturbances. It is widely recognised that the use of functional traits and functional diversity is best for understanding the causes and functional consequences of changes in biodiversity, but conceptual development has outpaced empirical applications. This thesis explores these ideas in grazing systems, which are expected to undergo rapid intensification of fertiliser use and grazing pressure to meet the growing global demand for livestock products. First, a flexible framework for measuring different facets of functional diversity is described, and a new multidimensional functional diversity index, called functional dispersion (FDis), is presented. Second, two vegetation sampling methods are compared with regard to their ability to detect changes in vegetation composition. Third, shifts in plant trait distributions following land-use changes are quantified and compared to null models, and a maximum entropy approach is used to quantify the direction and strength of selection on each trait. Fourth, it is shown that these shifts in trait distributions have cascading effects on primary production, litter decomposition, soil respiration, and ultimately soil carbon sequestration. Finally, data from 18 land-use intensity gradients are used to show that land-use intensification reduces functional redundancy and response diversity, two components of biodiversity that are thought to influence ecosystem resilience to future disturbances. This study illustrates (i) the importance of considering species functional differences to understand how plant communities react to changes in soil resource availability and grazing pressure, and (ii) how such changes directly, indirectly, and interactively control ecosystem functioning, as well as (iii) increasing the vulnerability of ecosystems to future disturbances.

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  • Analysing the Interactions between Water-induced Soil Erosion and Shallow Landslides

    Acharya, Govind (2011)

    Doctoral thesis
    University of Canterbury Library

    Water-induced soil erosion and shallow landslides interact with each other and need to be studied in an integrated approach to understand hillslope sediment yields. The principal aim of this thesis was to study and model soil erosion and shallow landslides in an integrated way. The thesis presents results from laboratory and catchment-scale studies and modelling. A laboratory flume under a rainfall simulator was used for shallow landslide and soil erosion experiments using sandy and silty loess soils. In the experiments, landslide initiation, retrogressions and slip surface depths were measured and monitored directly or by using video camera recordings. Sediment and runoff were collected from the flume outlet every minute during landslides and every 10 minutes before and after landslides. Changes in the soil slope, after landslides, were recorded. Initially, six experiments including two repetitions were conducted using sandy soils at a 30º and 10º compound slope configuration, but with different soil profile depths. The experimental results showed that total and landslide-driven sediment yields were affected by the original soil profile depth; the greater the depth, the higher the sediment yield. Later, twelve other experiments were conducted on different slopes using silty loess soils. The experimental observations were used to validate an integrated modelling approach which includes WEPP for runoff and soil erosion modelling, a slope stability model for simulating shallow landslides, and a simple soil redistribution model for runout distance prediction. The model predictions were in good alignment with the observations. In all (sandy and silty loess) experiments, peak sediment discharges were related to the landslide events, proximity to the outlet and landslide volume. The post-failure soil erosion rate decreased as a function of changes in the slope profile. The GeoWEPP-SLIP modelling approach was proposed for catchment-scale modelling. The approach simulates soil erosion using the Hillslope and Flowpath methods in WEPP, predicts shallow landslides using a slope stability model coupled with the WEPP’s hillslope hydrology and finally uses a simple rule-based soil redistribution model to predict runout distance and post-failure topography. A case study application of the model to the Bowenvale research catchment (300 ha) showed that the model predictions were in good agreement with the observed values. However, the Hillslope method over-predicted the outlet sediment yield due to the computational weighting involved in the method. The Hillslope method predicted consistent values of sediment yield and soil erosion regardless to the changes in topography and land-cover in the post-failure scenarios. The Flowpath method, on the other hand, predicted higher values of sediment yield in the post-failure vegetation removal scenario. The effects of DEM resolution on the approach were evaluated using four different resolutions. Statistical analyses for all methods and resolutions were performed by comparing the predicted versus measured runoff and sediment yield from the catchment outlet and the spatial distribution of shallow landslides. Results showed that changes in resolution did not significantly alter the sediment yield and runoff between the pre- and post-failure scenarios at the catchment outlet using the Hillslope method. However, the Flowpath method predicted higher hillslope sediment yields at a coarser resolution level. Similarly, larger landslide areas and volumes were predicted for coarser resolutions whereas deposition volume decreased with the increase in grid-cell size due to changes in slope and flowpath distributions. The research conducted in the laboratory and catchment presented in this thesis helped understand the interactions between shallow landslides and soil erosion in an integrated approach.

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  • Investigations on the use of ionic liquids for superior biomass processing

    Pinkert, Andre (2011)

    Doctoral thesis
    University of Canterbury Library

    Biocompatible composites, generated from renewable biomass feedstock, are regarded as promising materials that could replace synthetic polymers and reduce global dependence on fossil fuel sources. Wood cellulose, the most abundant biopolymer on earth, holds great potential as a renewable biomass feedstock. To unlock the entire scope of potential benefits of this feedstock, the wood components - namely cellulose, hemicellulose and lignin - need to be separated and processed individually. Current methods to separate wood components, such as Kraft pulping for example, suffer considerable drawbacks and cannot be considered environmentally benign. This thesis aims to increase our understanding of the interaction between ionic liquids (ILs) and biomass, in order to develop superior biomass processing techniques necessary to ensure a rapid transformation of our society towards full sustainability. The first part of this work deals with the particular interaction of ILs with cellulose, and aims to investigate the structural requirements of ILs in order to qualify as a cellulose solvent. The cellulose-dissolving behaviour of selected alkanolammonium ILs was studied, and, combined with the results of an extensive literature review, a novel concept for the interaction of cellulose-dissolving ILs with cellulose was developed. It was postulated that efficient cellulose solvents need to position themselves in a distinct manner - with respect to the cellulose chain - in order to offer H-bond interaction sites with enhanced stability. As a result, alternative ions for cellulose-dissolving ILs were proposed, including oxazolium, 1,3-oxaphospholium, dimethylcarbamate, phosphate, nitrate, and nitrite. The second part of the work investigated the use of food-additive based ILs for the separation of wood lignin, and studied the influence of selected process parameters, such as extraction time, extraction temperature, IL moisture content, wood particle size, wood species, IL cation species, solvent composition, and IL recyclability on the lignin extraction efficiency. The lignin extract and the wood residues were characterised via infrared spectroscopy, elemental analysis, thermogravimetric analysis, differential scanning calorimetry, X-ray diffraction, and gel permeation chromatography. An extraction efficiency of e = 0.43 of wood lignin was achieved in one gentle extraction step ( T = 373 K, t = 2 h), and it was found that the presence of a co-solvent increased the extraction efficiency to e = 0.60. Gentle conditions during IL treatment did not decrease the crystallinity of the wood sample, and the extracted lignin had both a larger molecular mass and a more uniform molecular mass distribution, compared to commercially available Kraft lignin. The outcomes of both studies were critically evaluated, addressing existing drawbacks and restrictions that need to be considered, and possibilities for future work were suggested.

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  • Microbial (Microalgal-Bacterial) Biomass Grown on Municipal Wastewater for Sustainable Biofuel Production

    Valigore, Julia Marie (2011)

    Doctoral thesis
    University of Canterbury Library

    High biomass productivity and efficient harvesting are currently recognised challenges in microbial biofuel applications that were addressed by this research using ecological engineering principles and an integrated systems approach. Microbial (microalgal-bacterial) biomass was grown in laboratory reactors using municipal wastewaters from the Christchurch Wastewater Treatment Plant (CWTP) in New Zealand. Reactors were inoculated with native microbes, fed with primary and secondary treated wastewaters, and subjected to various hydraulic and solids retention times (i.e., 1.4- to 9-d HRT and 4- to 80-d SRT, respectively) under cold, warm, and ambient climate conditions. Biomass settleability and productivity (i.e., settleable productivity) were sequentially improved over the course of experiments to optimise settleable productivity at 21 g/m2/d on average using primary treated wastewater, 2-d HRT, 12-d SRT, and warm climatic conditions. Secondary treated wastewater was a poor substrate most likely because of low C, elevated pH, and supersaturated oxygen levels limiting growth. Biomass recycling generally improved settleable productivity of primary treated wastewater cultures since productivity increased at short HRT and settleability increased at longer SRT. No overriding trends were found relating productivity or settleability to biomass ecology or biochemistry. Growth rate modelling of warm climate cultures indicated that heterotrophy was mostly C limited at long (≥ 4-d) HRT and DO limited at short (≤ 2-d) HRT of primary treated wastewater while photoautotrophy was probably always light limited. Nevertheless, almost 50% greater C fixation was achieved using these systems compared to conventional activated sludge systems. Cold climate cultures, with up to 66% less biomass than warm climate cultures, were limited by lower light and/or temperature (i.e., 13 °C mean water temperature with 410 μmol/m2/s photosynthetically active radiation [PAR] for 9.6 h/d vs. 21 °C mean water temperature with 925 μmol/m2/s PAR for 14.7 h/d). Biomass settleability was facilitated by microbial aggregation into stable, compact flocs over time and also by bioflocculation during 1-h sedimentation periods. These mechanisms were largely influenced by wastewater loading and microbial growth rate, but also to a lesser extent by monitoring methods (i.e., light, duration, and sedimentation container). Settleability of primary treated wastewater cultures was mainly greater than 70% and more consistent when operated at longer SRT and shorter HRT compared to only 22% on average for secondary treated wastewater cultures. Symbiotic growth of native microalgae and bacteria promoted efficient O2/CO2 exchange to improve productivity and enhanced natural floc formation to improve settleability while requiring low energy inputs and providing some wastewater treatment. These capabilities greatly increased the biomass’ sustainability for biofuel production compared to other feedstocks. This research demonstrated the value of biomass recycling to concurrently achieve greatest productivity and settleability to maximise harvestable yield since the overall growth rate of more total biomass was reduced at longer SRT which thereby facilitated excellent floc formation and sedimentation at shorter HRT. The resulting biomass was best suited for biofuel conversion pathways such as anaerobic digestion or thermochemical liquefaction. Potential other uses included animal feed and fertiliser since biomass was harvested without additional chemicals.

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  • Complicity in games of chase and complexity thinking: Emergence in curriculum and practice-based research

    Hussain, Hanin Binte (2011)

    Doctoral thesis
    University of Canterbury Library

    This thesis explores how the discourse of complexity thinking can be used to foster emergence in curriculum and practice-based research. The curriculum-related exploration focused specifically on games of chase as one facet of early childhood curriculum. It investigated using complexity thinking firstly, to occasion emergence (that is, create a new phenomenon) in children’s games of chase at an early childhood centre and secondly, to describe this emergence. The research-related exploration focused on creating an emergent methodology which is underpinned by complexity thinking. In this thesis report, I present a series of emergent curriculum-related phenomena that arose during the explorations, that is, an emergent game, a local curriculum theory for games of chase, the concepts of local curriculum theory, curriculum design and curriculum dynamics, and a curriculum vision. I also present an understanding of emergent methodology and two methodological innovations in the form of the Research Data Management System and the Visual Summary. This research involved taking the role of a volunteer teacher-researcher-curriculum designer at an early childhood centre to play games of chase with children. This role was informed by and contributed to a curriculum design that focused on designing the teaching and learning environment to occasion emergence in learning and curriculum. The games of chase curriculum contributed to children’s learning, my own learning and the general rhythm of life at the centre. The children learnt to distinguish between children who were playing and those who were not. They also learnt different ways to tag people in a game. In addition, the children and I developed a game playing routine before playing each game. This routine involved putting on tag belts, discussing what game we were playing and how we were going to play it. We played three different games of chase, starting with tag, followed by What is the time Mr(s) Wolf?, and finally the emergent game Big A, Little A. The stories of emergence are described in visual, descriptive and narrative texts organised into curriculum stories, teaching stories and children’s learning stories. Curriculum stories describe the activities that unfolded. Teaching stories present stories of teaching while learning stories are stories of children’s learning. These stories represent views of the enacted curriculum as activity, teaching and learning respectively. Taken together, the stories present a description of the curriculum dynamics that unfolded at the centre in relation to games of chase. This thesis shows that a local curriculum theory for games of chase at the centre emerged from the complex interactions of curriculum design and curriculum dynamics that unfolded at the centre. It also articulates the emergent concepts of local curriculum theory, curriculum design and curriculum dynamics using the language of complexity. This thesis also presents the local curriculum theory as a curriculum vision. This vision involves a shift in thinking about curriculum as either a set “course to be run” or the “path created in the running” (currere) to embracing curriculum as both “the space for running” and currere. It is a vision that values both children’s and teachers’ interests, focuses on teachers and children exploring depth and breadth of a curriculum domain together, enables teachers to follow, generate and sustain children’s interest in the explorations, and is generative, flexible and future-focused. This thesis conceptualises an emergent methodology as a methodology for emergence which (1) involves the researcher actively striving to foster emergence in research, (2) is brought forth in the interactions between the designed and enacted facets of methodology, (3) is local to a particular research project, and (4) emerges from the interactions of several related strategies. This thesis can be seen as an attempt to change the language game of curriculum by using the language of complexity throughout the thesis. In so doing, it not only enables the reader to talk about the discourse of complexity thinking, it also enables the reader to experience the discourse and the emergence of the curriculum-related phenomena and the methodological innovations that are the focus of this thesis. Finally, this thesis argues that using the discourse of complexity thinking in teaching and research can be enabling. It can enable the teacher and/or researcher to be creative, flexible and ethical within the constraints of his/her professional and personal life.

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  • The Decision Making Process in the Adoption of Agroforestry Technology by Smallholder Rubber Farmers in Indonesia

    Iskandar, Dudi (2011)

    Doctoral thesis
    University of Canterbury Library

    The contribution of rubber to national economic and social development is important for Indonesia. However, smallholding rubber, the dominant rubber producer, has low productivity. Various new technology programmes have been introduced by the Indonesian government with other agencies to increase the productivity of existing traditional rubber and incomes among smallholder rubber farmers in Indonesia. However, the adoption of new technology was low and the reasons for these were still unclear. This study explores how smallholder farmers in Indonesia adopt new technology. Rubber Agroforestry System (RAS) introduced mainly by International Centre for Research in Agroforestry (ICRAF) in Jambi and West Kalimantan provinces in Indonesia is used as a case study. A combination of Ethnographic Decision Tree Modeling (EDTM) proposed by Gladwin (1989a) and a logistic regression model were used as the main methodologies to determine the decision criteria of rubber farmers regarding adoption of clonal rubber. The EDTM as qualitative method helped to identify the main reasons, motivations and constraints that influenced a farmer’s decision to adopt or not adopt the new technology and also present details about the process of the farmers’ decision making. Meanwhile, logit as the quantitative method was useful to identify the significant variables involved in the decision making process. The results of this study show that the decision making process for adoption of clonal rubber is complex and influenced by various factors. The decision tree models for Jambi and West Kalimantan differed showing the importance of social context and infrastructure. The main reasons for a farmer’s decisions to adopt clonal rubber is the expectation that clonal rubber is better in growth and yield and it will increase production per ha and income. The decision to adopt is supported by evidence from demonstration plots, trust in the technology deliverers and availability of incentives. The main constraint in adoption for both areas was limitation of capital as the clonal rubber required more capital to establish. The other constraints are risk and uncertainties including pest and disease problems, the shortage of labour, lack of technical knowledge, lack of access to clonal seedlings, and observation of clonal rubber that has been of low quality or managed inadequately. The decision tree models have been tested and the results show that the models were able to predict the farmers’ decision making with good accuracy of 82% and 83%. In addition, the quantitative model shows the significant factors that determine adoption of clonal rubber in Jambi and West Kalimantan are land, incentives and income factors. The qualitative and quantitative methods contributed to increased robustness of data and give different kinds of valuable data and information to stakeholders and policy makers in Indonesia. In order to encourage rubber farmers in Jambi and West Kalimantan to adopt clonal rubber, this study suggests improving policies to ensure they are aligned with needs of the rubber farmers, improving farmers’ access to capital sources such as credit with simpler mechanisms, increasing the number and skills of extension workers, encouraging farmer to farmer learning, empowering farmers and leadership, improving infrastructure including better access to clonal seedlings and improving partnership with NGOs.

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  • Improving imaging performance in planar superlenses

    Schøler, Mikkel (2011)

    Doctoral thesis
    University of Canterbury Library

    The aim of this project was to improve the imaging performance of planar superlenses for evanescent near-field lithography. An experimental investigation of the performance of superlenses with reduced surface roughness was proposed. Such an investigation poses significant requirements in regards to process control in thin film deposition of silver onto dielectric substrates. Thin film deposition of silver films, onto silicon dioxide substrates, achieved films with root mean square surface roughness as low as 0.8 nm. While these experiments provided good understanding of the deposition process, significant variability of the surface roughness parameter remained an issue. The diffculty of achieving consistent control of surface roughness led to a finite element method simulation study where this parameter could be readily controlled. An improved understanding of how surface roughness affects superlens imaging performance was obtained from the results of this investigation. Furthermore, it was shown that in order to conduct an experimental investigation to verify the simulation results, it would be necessary to improve the imaging capability of super-resolution lithography protocols to achieve 3σ line edge roughness (LER) of <20 nm. Resist-scheme optimisation was identied as an important factor in this regard. Thus, a novel calixarene-based photoresist was formulated and characterised. The resist demonstrated superior imaging capabilities through interference lithography and evanescent near-field optical lithography, capable of resolving 250-nm period half-pitch line gratings with 3σ LER below 10 nm. The development of this novel photoresist will enable future lithographical investigations to be conducted with improved resolution and imaging fidelity.

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  • Experimental Investigations of Airflow in the Human Upper Airways During Natural and Assisted Breathing

    Spence, Callum James Thomas (2011)

    Doctoral thesis
    University of Canterbury Library

    Nasal high flow (NHF) cannulae are used to deliver heated and humidified air to patients at steady flows ranging from 5-50 l/min. Knowledge of the airflow characteristics within the nasal cavity with NHF and during natural breathing is essential to understand the treatment's efficacy. In this thesis, the distribution and velocity of the airflow in the human nasal cavity have been mapped during natural and NHF assisted breathing with planar- and stereo-PIV in both steady and oscillatory flow conditions. Anatomically accurate transparent silicone models of the human nasal cavity were constructed using CT scan data and rapid prototyping. Breathing flowrates and waveforms were measured in vivo and dimensionally scaled by Reynolds and Womersley number matching to reproduce physiological conditions in vitro. Velocities of 2.8 and 3.8 m/s occurred in the nasal valve during natural breathing at peak expiration and inspiration, respectively; however on expiration the maximum velocity of 4.2 m/s occurred in the nasopharynx. Velocity magnitudes differed appreciably between the left and right sides of the nasal cavity, which were asymmetric. NHF modifies nasal cavity flow patterns significantly, altering the proportion of inspiration and expiration through each passageway and producing jets with in vivo velocities up to 20.8 m/s for 40 l/min cannula flow. The main flow stream passed through the middle airway and along the septal wall during both natural inspiration and expiration, whereas NHF inspired and expired flows remained high through the nasal cavity. Strong recirculating features are created above and below the cannula jet. Results are presented that suggest the quasi-steady flow assumption is invalid in the nasal cavity during both natural and NHF assisted breathing. The importance of using a three-component measurement technique when investigating nasal flows has been highlighted. Cannula flow has been found to continuously flush the nasopharyngeal dead space, which may enhance carbon dioxide removal and increase oxygen fraction. Close agreement was found between numerical and experimental results performed in identical conditions and geometries.

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  • The effects of digestion resistant carbohydrates on the colon microbiota and colon tissue transcriptome of weanling rats

    Young, Wayne (2011)

    Doctoral thesis
    University of Otago

    Digestion-resistant carbohydrates (DRC) in the diet pass to the terminal ileum and large bowel where they may be fermented by resident bacteria. The bacterial communities in the bowel of young animals undergo dramatic shifts in composition following weaning. These compositional and associated biochemical changes may have long-lasting impacts on the host. However, the mechanisms by which diet induced changes in the microbiota influence host physiology requires further investigation. This study examined whether bacterial community compositions could be engineered by supplementing the diet of newly-weaned rats with different forms of DRC and the subsequent effects these altered microbial communities had on host physiology. Newly weaned conventionally raised or germ-free male 21-28 day old Sprague-Dawley rats were fed a basal diet or basal diets supplemented with DRC at concentrations up to 5% for 14 or 28 days. Colonic digesta was collected from each rat for analyses to determine short chain fatty acid (SCFA) concentrations and to compare bacterial community structure by temperature gradient gel electrophoresis (TTGE) and 454 pyrosequencing analysis of the V3 hypervariable region of the 16S rRNA gene. DRC induced alterations in the host transcriptome were assessed by microarray analysis of RNA extracted from colon tissue. Feeding DRC significantly increased concentrations of SCFA in the colon digesta of young rats. The DRC induced changes in SCFA concentrations were also accompanied by alterations in the colonic microbiota structure. Each type of DRC altered the microbiota in a distinctive manner, which could be clearly differentiated from those of rats fed the basal diet. Feeding DRC also resulted in more uniform microbiota compositions compared to the basal diet. The alterations in microbiota composition were associated with changes in host colon gene expression profiles. Each form of DRC altered colonic gene expression in a distinct manner with profiles from rats fed the same diet showing greater similarity than those fed different diets. Differentially expressed genes in the colon were involved in a number of biological functions including energy metabolism, immune function, and cellular growth and differentiation. Comparisons of the effects of DRC on host gene expression between conventionally raised and germ-free rats showed that the resident microbiota was a determining factor of the host response to DRC. Feeding DRC to conventionally raised rats resulted in the differential expression of different sets of genes compared with feeding DRC to germ-free rats. The results of this study show that the bacterial communities in the colon of newly-weaned rats can be engineered by supplementing the diet with DRC. Using this approach, unique bacterial communities with enhanced fermentative capacity, increased uniformity, and distinct effects on host gene expression were selected. The findings from this study provide support and future scope for the development of different dietary supplements that target different parameters of large bowel function.

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  • The effect of intermittent and continuous hypoxia on cerebral vascular function in humans

    Peebles, Karen Clendon (2011)

    Doctoral thesis
    University of Otago

    The extent to which systemic hypoxia may compromise cerebrovascular function is likely to depend on the intensity and duration of the hypoxic insult. This thesis presents four studies that used a range of intermittent and continuous hypoxic paradigms that examined i) whether hypoxia alters cerebrovascular reactivity during acute alterations in the partial pressure of end-tidal CO2 (PETCO2) and end-tidal O2 (PETO2); and ii) whether reductions in cerebrovascular reactivity were mediated by changes in nitric oxide (NO). As a secondary goal, the impact of alterations in peripheral chemoreceptor (PCR) activity on cerebrovascular function, and on ventilatory (VE) sensitivity were also explored. Blood flow velocity in the middle cerebral artery (MCAv) and cerebral oxygenation, provided indices of cerebrovascular function. Study one demonstrated that acute hypercapnia was associated with the net release of NO from the brain. Therefore, in subsequent studies, cerebrovascular reactivity to hypercapnia, along with complementary NO metabolites (plasma nitrite and NOx [nitrite + nitrate]), was used as a surrogate index of NO bioavailability. Study two examined the effects of chronic (years) intermittent hypoxia (CIH) on cerebrovascular function in patients with severe obstructive sleep apnoea (OSA, apnoea-hypopnoea index > 30 events/h). When compared to a group of appropriate controls, hypercapnic cerebrovascular reactivity was reduced in OSA patients. Since plasma NOx was also reduced, it would seem feasible that this compromise in reactivity was due to a reduction in NO bioavailability. Nevertheless, correlative analysis revealed that the presence of OSA was not the only factor associated with a reduction in hypercapnic cerebrovascular reactivity; a novel finding was that increased age and body mass index were linked as well. Alleviating CIH with 5-6 weeks of continuous positive airway pressure (CPAP) caused no alterations in hypercapnic cerebrovascular reactivity or NO metabolites, but caused a small (4 mmHg) reduction in mean arterial blood pressure (MABP). Study three examined the effects of short-duration intermittent hypoxia [SDIH] and short-duration continuous hypoxia [SDCH]) on cerebrovascular function in healthy participants. For SDIH, participants performed 2 h of repetitive hypoxic apnoeas to mimic OSA (20 s apnoeas; nadir peripheral oxygen saturation [SpO2] ~84%; 30 times/h). For SDCH, participants were exposed to a single hypoxic episode matched in duration (i.e., 20 min) and intensity (i.e., SpO2) to SDIH. Cerebrovascular reactivity and ventilatory sensitivity were assessed during acute PETCO2 alterations under hyperoxic and hypoxic rebreathing in order to provide insight into PCR activity. SDIH (but not SDCH) led to a selective reduction in frontal cerebral oxygenation during hypoxic rebreathing; no concomitant alterations in MCAv or in NO metabolites were observed. One interpretation of these findings is that oxygenation of the frontal lobe was compromised to ensure perfusion of more vital regions of the brain (e.g., brainstem) after SDIH. SDCH (but not SDIH) led to elevations in MABP at rest and MABP reactivity during hypoxic but not hyperoxic rebreathing, likely mediated via PCR activation. No concomitant alterations in VE sensitivity during hypoxic rebreathing were observed possibly due to different rates of recovery for MABP and VE post SDCH; there were no alterations in VE sensitivity during hyperoxic rebreathing. Lastly, in study four, the effect of ~3 weeks of continuous hypoxia on cerebrovascular function and ventilatory sensitivity was examined in healthy sea-level participants following ascent to 5050 m. The main findings were that ascent to 5050 m led to an increase in resting MCAv, and enhanced MCAv reactivity during hypoxic and hyperoxic rebreathing. Alongside a high-altitude induced increase in resting VE , these cerebrovascular responses might serve to maintain oxygen delivery to the brain in the face of hypoxia until other adaptive mechanisms (e.g., an increase in capillary density) that aid oxygen extraction become manifest. Collectively, these findings indicate that the precise effect of systemic hypoxia on cerebrovascular function was contingent on the hypoxic paradigm. Shorter durations of hypoxia (i.e., 2 h intermittent hypoxia and ~3 weeks continuous hypoxia) evoke cerebrovascular responses that may serve to preserve oxygen delivery to vital regions of the brain whereas longer durations of intermittent hypoxia (i.e., CIH, in patients with OSA), is associated with a reduction in cerebrovascular function that may compromise brain function. Furthermore, the findings of this thesis suggest that: i) a reduction in NO bioavailability may contribute to a reduction in hypercapnic cerebrovascular reactivity in patients with OSA; and ii) that alteration in PCR activity may contribute to the elevated MABP after 2 h of continuous hypoxia. Irrespective of the hypoxic paradigm, the cerebrovascular, cardiovascular and ventilatory responses to acute alterations in PETCO2 and PETO2 are complex and inter-related.

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  • Measurement and perceptions: Physical activity in people with low back pain

    Perry, Meredith Amy Claire (2011)

    Doctoral thesis
    University of Otago

    Physical activity (PA) is recommended for the management of low back pain (LBP). This research was undertaken to: establish the use of accelerometers as an outcome measure in studies investigating the free-living PA of people with LBP; explore the free-living PA of people receiving physiotherapy for LBP; and compare patterns of PA between people with acute low back pain (ALBP) and people with chronic low back pain (CLBP). PA was measured with the RT3 accelerometer (Stayhealthy Inc., Monrovia, California, USA) which is an objective measure of PA. In addition, perceptions of being physically active with LBP and the coherence between the lived experience of LBP and physiotherapy management were explored. A review of PA and LBP literature found that while ‘advice to stay active’ is recommended, there is a paucity of research exploring the free-living PA of people with LBP with an objective measure, such as an accelerometer. It is unknown if free-living PA is altered in people with LBP compared to healthy individuals. Likewise, the psychometric properties of many accelerometers are also unknown and this may account for some discrepancies in results. A pilot study was undertaken in healthy volunteers (N = 21) to determine the minimum number of days per week of valid RT3 data required to reliably estimate PA, and the validity and utility of the RT3. The RT3 was found to have acceptable utility and good validity, and a minimum of four days of RT3 data are required to reliably assess PA. A mixed methods (MM) study explored: the responsiveness of the RT3 to measure change in PA, compare patterns of PA between people with ALBP or CLBP (N = 111); and semi-structured interviews were conducted with a sub-group of the LBP participants to explore perceptions of PA (N = 13). The RT3 demonstrated limited responsiveness to perceived change in PA, measured with the Global Rating of Change (GROC), at week six only; perceived PA and measured PA appear to be different constructs. A significant interaction between LBP and week of PA measurement was found. Neither LBP group met the recommendation for sustained bouts of moderate intensity PA per day. Interviewees knew that PA was an important aspect in the management of their LBP. However, being active was dependent on perceived control and this was unrelated to LBP classification. The use of “trial and error” strategies when increasing PA resulted in a flare of LBP, the reinforcement of negative PA beliefs and behaviours, and poor treatment coherence. Further research into the design and psychometric properties of accelerometers is warranted. People with ALBP have different PA patterns to people with CLBP; yet both groups demonstrate an inability to endure sustained and repetitive bouts of moderate intensity PA. People with LBP are unsure how to return to habitual PA. Physiotherapists may need to consider treatment coherence, and provide more time and support for changing unhelpful perceptions and PA behaviours. To conclude, perceptions of PA are not the same construct as objectively measured PA, but both constructs are important.

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  • An Epigenetic Analysis of the Human Placenta

    Macaulay, Erin Cuffe (2011)

    Doctoral thesis
    University of Otago

    The human placenta is a highly specialized organ that is responsible for the survival of pregnancy. During its development, placental trophoblast cells invade into the uterine wall to establish a blood supply for the growing fetus. Previous studies have suggested similarities between the invasive phenotypes of trophoblasts and tumour cells; however, a key difference is that trophoblast invasion is under strict control. Given that epigenetic mechanisms have been linked with the silencing of key regulatory genes in cancer, we hypothesized that the epigenetic regulation of first-trimester placental trophoblasts may provide a mechanistic relationship between placental and cancer growth. Further, although the hypomethylated environment within the pseudo-malignant placenta is unique, its role in facilitating placental function is poorly understood. We sought to document placental-specific epigenetic modifications, taking into account that the origin of the placenta is determined during the earliest stages of embryonic development, when the inner-cell mass is first distinguished from the trophectoderm, and when the inner-cell mass further differentiates into the primitive endoderm and the epiblast. A genome-wide methylation analysis was performed using methylated DNA immunoprecipitation (MeDIP) combined with hybridisation to promoter microarrays to identify differentially methylated gene promoters between first-trimester human placenta and peripheral blood DNA. The promoter methylation of 29 candidate genes was then quantified using Sequenom MassARRAY®. Differential methylation patterns were detected in placental tissues compared to both fetal and adult somatic tissues. The relationship between promoter methylation and gene expression was then assessed using real-time PCR and immunohistochemistry. The promoter methylation of one gene, KCNH5, was found to be lineage-specific: low in all tissues derived from the extra-embryonic lineages (trophectoderm and primitive endoderm) and very high in tissues derived from the embryonic (epiblast) lineage. The dichotomous promoter methylation of KCNH5 was found to regulate the lineage-specific expression of alternative gene transcripts. Interestingly, the KCNH5 promoter that is used in tissues derived from the extra-embryonic lineages, and which shows dichotomous methylation, has recently evolved from a SINE retrotransposon that is present in only humans, old world monkeys and apes. To our knowledge, this the first example of a human transcript derived from the insertion of a SINE element. Finally, the lineage origin of the extra-embryonic mesenchyme has been a topic of longstanding debate. The combined epigenetic and expression profiles of KCNH5 in placental villous stroma provide compelling evidence that the extra-embryonic mesenchyme is derived from the primitive endoderm. Retrotransposons are normally silenced by methylation to prevent genome dysfunction. However, the placenta is becoming increasingly known as a tissue in which retrotransposons are actively transcribed. We observed that the absence of retrotransposon-silencing by methylation permitted the emergence of a placental-specific transcript by allowing the retrotransposon to serve as an alternative promoter for KCNH5. Examination of additional retrotransposon-derived genes in the placenta (INSL4 and ERVWE1) confirmed that dichotomous methylation between embryonic and extra-embryonic lineages is a feature of early development. The finding that the retro-elements in these genes have escaped the normal silencing mechanism suggests that they may have functional roles that are unique to the invasive placentas of humans and recent primates.

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  • Role of NK cells in DC-based immunotherapy of melanoma

    Bouwer, Anthea Lynne (2011)

    Doctoral thesis
    University of Otago

    Natural killer (NK) cells were first identified by their ability to kill tumour or virally infected cells without prior sensitization. In spite of this, the actual role of NK cells in tumour immunotherapy remains controversial. This study therefore set out to investigate the potential of Streptococcus salivarius K12, a gram-positive bacterium that has a history of commercial application as a probiotic in New Zealand, for use as a NK cell adjuvant, applying the therapy using B16.OVA melanoma as a model. To confirm that S. salivarius K12 was able to induce efficient activation of NK cells, I first screened a number of gram-positive and gram-negative bacteria for their ability to induce IFNγ release from NK cells. Using ELISA and fluorescence activated cell sorting (FACS) I found that gram-positive bacteria stimulated a rapid release ( through interaction with self MHC during development. Therefore having a setting where the addition of S. salivarius K12 activates NK cells, I investigated whether these NK cells were recruited to the draining lymph nodes where they could potentially influence the adaptive immune response. A range of adjuvant-activated and S. salivarius K12-activated DC were injected subcutaneously into the flanks of mice and tested their ability to recruit NK cells to the draining lymph node. The adjuvants differed markedly in their ability to recruit NK cells with S. salivarius K12 being the most effective. To determine if activated NK cells would be of benefit in tumour immunotherapy, I investigated the ability of bacterially activated DCs to elicit anti-tumour responses in a B16.OVA melanoma model. Utilizing a therapeutic tumour model where treatment was started three days following tumour inoculation, I found a significant delay of tumour growth in mice that were immunized with ovalbumin-pulsed DC that had been treated for 4 hours with S. salivarius K12 as opposed to other adjuvants tested. I also determined that in vivo depletion of NK cells completely abolished the benefit of DC immunotherapy. A therapeutic tumour experiment where DC were primed in the presence or absence of tumour antigen showed that while NK cells were critical for the antigen-dependent anti-tumour response they did not appear to exert an effector function. To investigate the role of NK cells in priming the anti-tumour response I next utilized a prophylactic setting, where mice were challenged with tumours sixty days after DC immunization. By depleting CD4+/CD8+ T cells and NK cells before time of priming or challenge, I tentatively showed that all three subsets of cells play a role in the anti-tumour response, although NK cells may play a greater role at time of challenge.

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  • Reservations to Human Rights Treaties and the Diversity Paradigm: Examining Islamic Reservations

    Sawad, Ahmed Ali (2011)

    Doctoral thesis
    University of Otago

    This research is a critique of the universalist theory of international human rights treaty law through an analysis of Islamic reservations to four major human rights treaties i.e., Convention on the Elimination of All Forms of Discrimination Against Women (CEDAW), Convention on the Rights of the Child (CRC), International Covenant on Civil and Political Rights (ICCPR) and the Convention against Torture and Other Cruel, Inhuman, Degrading Treatment or Punishment (CAT). Based on my analysis of international treaty law on reservations and State practice relating to reservations to human rights treaties, I have argued that universalist claims of human rights treaties are more of an idea than an established norm. To this effect, I have examined the concept of reservations under international law as contained in the Vienna Convention on the Law of Treaties 1969 (VCLT) and evaluated its applicability to international human rights treaties. In Chapter Two I have contended, firstly, that the VCLT provides a flexible regime for making reservations to treaties and that it does not differentiate between contractual treaties and normative human rights treaties. Secondly, I have argued that the flexible nature of the VCLT regime confirms that international treaty law supports a diversity paradigm which brings together dissimilar consent, particularly in the case of human rights treaties. In Chapter Three I have scrutinised the theoretical debate on the nature of human rights that centres on whether they are universal, relative or pluralist. I have shown that the natural law theories and other transcendentalist justifications of universality of human rights have no cross-cultural validity. I have also pointed out that a posteriori justifications such as minimalist universality, overlapping consensus and relative universality theories are impractical because they attempt to derive a lowest common denominator which diminishes the efficacy of international human rights regimes. In comparison to such universalist theories, alternative human rights theories espouse more inclusive and cross-culturally legitimate approaches. However, I have submitted that theories of cultural relativism provide inadequate explanations of the pluralist State practice in the area of international human rights treaties. In particular, the thick relativist theories fail to explain the existing level of cultural participation in the international human rights regimes. In practice, States parties from different cultural-legal systems cooperate in international and regional human rights regimes through a diversity paradigm that offers pluralist consent on the various normative standards. I have shown that the legitimacy of the diversity paradigm is evident from the State practice of making reservations to human rights treaties. My critique of the reservations made by Islamic States to CEDAW, CRC, ICCPR and CAT, identifies on the one hand, the particular normative conflicts between these regimes and Shari`ah, and on the other hand, the connection between the issues raised in these reservations and the domestic laws of the reserving Islamic States. This examination is important for two reasons: firstly, it demonstrates the extent to which the Shari`ah-based reservations are actually legitimate within the cultural-legal system of the reserving States, and secondly, it helps in understanding the level of juridical flexibility that is available in these reservations. This thesis establishes that the practice of making reservations to international human rights regimes runs counter to theories of ontological universality of human rights. In the case of Shari`ah-based reservations, it reveals that Islamic States are reluctant to forfeit or bargain on certain precepts of Islamic law that are perceived to contradict normative human rights such as absolute freedom of religion and same rights of married spouses. At the same time, it suggests that Islamic States accept the large majority of human rights norms, and make exceptions to only a few select human rights. In addition, the thesis also proposes that the flexible reservations regime of the VCLT provides an effective mechanism for the Islamic States to engage and participate in international human rights treaties, in spite of the reservations. The principal contribution of this study is that it provides a hermeneutic tool - the diversity paradigm - for understanding the plurality of human rights treaty law. I have established that international treaty law on reservations and State practice of making reservations to human rights treaties confirm the existence and validity of a diversity paradigm in the current human rights discourse. The diversity paradigm approach can play a constructive role in delineating the ontological or philosophical argument for the universality of human rights and the actual State practice of committing to and implementing human rights treaties. With the help of this hermeneutic tool I have established that a flexible, international treaty law based approach to human rights treaties is more effective in the propagation of human rights norms in diverse cultural-legal environments as noted in this case study of the reservations to human rights treaties made by Islamic States.

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  • Interaction between COMMD family proteins and the epithelial sodium channel

    Liu, YongFeng (2011)

    Doctoral thesis
    University of Otago

    The epithelial sodium channel (ENaC) is located at the apical membrane of many epithelial cells throughout the body and mediates Na+ influx into epithelial cells. Classical ENaC is made up of three similar subunits, α, β and γENaC subunits. ENaC provides the rate-limiting step for Na+ reabsorption in the distal nephron and therefore controls the extracellular fluid volume and blood pressure. ENaC activity at the cell surface is tightly regulated to maintain Na+ and fluid homeostasis in the body. A number of regulators of ENaC have been identified, including COMMD1 (copper metabolism Murr1 domain containing 1). COMMD1 belongs to a ten-member COMMD (copper metabolism Murr1 domain containing) family whose members all share a C-terminal COMM domain. Previous work in our laboratory has reported that COMMD1 interacts with the α, β, and γENaC subunits via its COMM domain and down-regulates the amiloride-sensitive Na+ currents generated by αβγENaC. Thus, it was hypothesised that other COMMD family members might also interact with ENaC and down-regulate ENaC activity. Therefore, the aims of this study were (1) to study the interaction between the COMMD family proteins and the ENaC subunits. (2) To investigate the effect of COMMD3 and COMMD9 on ENaC activity and the mechanism by which COMMD3 and COMMD9 regulate ENaC activity. (3) To explore the localisation of endogenous COMMD3 and COMMD9 in cultured cell lines and rat tissues and further ask whether COMMD9 colocalises with αENaC in rat kidney. Here protein-protein interaction studies demonstrated that all COMMD family members interacted with ENaC. Functionally, COMMD3 and COMMD9 were able to down-regulate the αβγENaC current through reducing the expression of ENaC at the cell surface. Western blot studies were used to show that endogenously expressed COMMD3 and COMMD9 were detected in HEK 293 cells and some rat tissues including kidney. Here immunocytochemistry studies in HEK 293 cells were used to show that COMMD3 was endogenously expressed in a perinuclear manner, while endogenous COMMD9 was present throughout HEK 293 cells. In the rat kidney, endogenous COMMD9 was found to be mainly expressed in the cortical and medullary collecting duct cells using single label immunohistochemistry. Moreover, COMMD9 was colocalised with αENaC in the collecting duct cells in the rat kidney. In summary, this study identified the interaction between COMMDs and ENaC and discovered the inhibitory effects of COMMD3 and COMMD9 on ENaC activity. In addition, the regulatory mechanism of COMMD3 and COMMD9 on ENaC was found to be through reducing ENaC surface expression. Immunohistochemistry results provide in vivo evidence for the interaction of COMMD9 and ENaC. Therefore, these data obtained in this study suggest COMMD3 and COMMD9 might be endogenous regulators of ENaC and they may be involved in Na+ and fluid homeostasis and therefore ENaC-related disease, such as hypertension. Lastly, this study may provide an insight into a new target point to treat hypertension.

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  • Multiple-stressor effects along gradients of deposited fine sediment and dissolved nutrients in streams

    Wagenhoff, Annika (2011)

    Doctoral thesis
    University of Otago

    Ecological degradation of streams and rivers as a result of agricultural land-use intensification is a major concern in New Zealand and other parts of the world. Agriculture introduces multiple stressors to streams, presenting a challenge for freshwater managers who must understand the relative strengths of each individual stressor and their combined multiple-stressor effects if they are to implement the most effective management actions and avoid ‘ecological surprises’ that arise from complex interactions between stressors. To investigate patterns of ecological response variables across broad gradients of two major stressors, augmented levels of dissolved inorganic nutrients and deposited fine sediment, I designed a streamside mesocosm experiment with eight levels each of nutrients (36 to 6900 micrograms per litre of dissolved inorganic nitrogen plus 1.4 to 450 micrograms per litre of dissolved reactive phosphorus) and deposited fine sediment (0 to 100 % cover of the streambed), and conducted a field survey in a regional set of 43 streams ranging from 2nd to 6th order. I used multiple linear regression and an information-theoretic approach to select the best predictive models for a series of ecological response variables, including algal, invertebrate and ecosystem variables, and tested (1) the subsidy-stress hypothesis for each stressor (where at low stressor levels an ecological variable responds positively until an inflection point beyond which the effect is negative), (2) whether sediment and nutrients operated as single or multiple stressors and whether they interacted with each other, and (3) whether sediment effects were more pervasive than those of augmented nutrient concentrations. In the 21-day long experiment, subsidy-stress patterns across the nutrient gradient were frequently found for algal and invertebrate taxa and communities, but consistently negative response shapes were more prevalent across the sediment gradient. The subsidy-stress hypothesis was not supported by the response of an ecosystem variable (organic matter breakdown, measured using cotton strips and fresh mahoe leaves). Overall, nutrients and fine sediment acted predominantly as multiple stressors and sometimes in complex interactive ways. The relative strengths of fine sediment and nutrient effects were similar for algal response variables but sediment was the more pervasive stressor for invertebrates, a finding that was also supported by the field survey. My field survey further suggested that nutrients and sediment commonly interact in synergistic ways to affect invertebrate variables, with fine sediment overwhelming any subsidy effects that nutrients may have in isolation. The combined experimental and survey results indicate that augmented levels of fine sediment and dissolved inorganic nutrient concentrations need to be managed together because they mostly act as multiple stressors in their effects on algal, invertebrate and ecosystem response variables. While managers should seek to control both nutrient and fine sediment inputs to streams to achieve good ecological stream condition, measures to reduce or avoid further sedimentation are particularly likely to be effective in mitigating ecological impairment and preventing further harm. Finally, in order to best assess the likely causes of decline in stream health, it will be highly desirable for managers to routinely monitor both nutrients (as currently done) and fine sediment in the future.

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